SPECTROELECTROCHEMICAL INVESTIGATION OF PASSIVE LAYERS FORMED ON

ELECTRODE SURFACES

BY

NICOLE ROCHELLE HONESTY

DISSERTATION

Submitted in partial fulfillment of the requirements

for the degree of Doctor of Philosophy in Chemistry

in the Graduate College of the

University of Illinois at Urbana-Champaign, 2012

Urbana, Illinois

Doctoral Committee:

Professor Andrew A. Gewirth, Chair, Director of Research

Professor Paul J. A. Kenis

Professor Catherine J. Murphy

Professor Kenneth S. Suslick

ii

ABSTRACT

Corrosion, broadly defined as environmental damage to materials (usually metallic), is an

important concern for maintaining infrastructure and for many manufacturing and transport

processes. Corrosion is typically prevented or controlled by formation of a passivating layer that

prevents diffusion of oxidative elements that might attack the base material, either by a passive

oxide formed by sacrificial agents in the material or by use of organic inhibitors.

Various electrochemical techniques are used to compare the relative efficacy of these

passivation layers, including linear sweep voltammetry, which gives the breakdown potentials

and corrosion currents, and AC impedance, from which film resistance and inhibition efficacy

can be determined. Although voltammetry gives an idea of whether a film successfully

passivates a metal surface, it gives little insight into the mechanism of inhibition and chemical

interactions that take place between the film and metal surface. Shell-isolated nanoparticle

enhanced Raman spectroscopy (SHINERS) allows interrogation of the electrode-electrolyte

interface where corrosion occurs.

Benzotriazole (BTA) is the prototypical inhibitor used in both plating baths and for the

chemical mechanical planarization in the microprocessor manufacturing. It forms a film that

allows uniform removal of the electrodeposited copper to result in smooth surfaces. It has face

dependent protection efficiency which has been studied by various surface sensitive techniques

including scanning tunneling microscopy (STM), surface enhanced Raman spectroscopy

(SERS), polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS), and

sum frequency generation (SFG). It is a good test for the viability of shell-isolated nanoparticle

enhanced Raman (SHINERS) particles in investigating surface film formation on single crystal

iii

Cu. SHINERS did not reproduce the face dependent behavior found in STM and SFG

experiments but did confirm difference between polycrystalline and single crystalline surfaces

noted but not previously explained in literature.

Rhodanine (RD) is common subunit in many pharmaceutical agents. It has been

demonstrated to chelate metal ions, most notably Ag(I), and Cu (I) and Cu(II).It is has been

studied as a corrosion inhibitor for Cu. In this dissertation, SERS was used to characterize the

time dependent and potential dependent interactions of RD with Cu electrode surfaces to better

elucidate the mechanism for inhibition. RD has greater corrosion inhibition than BTA at the

same concentration, and this protection increases with time. The time dependent SERS spectra

showed a marked decrease in intensity after 1 h which is attributed to formation of thick films

opaque to the laser line. Atomic force microscopy (AFM) showed that films were 100 nm thick

after 1-2 h incubation time.

Levelers are used in electrodeposition of Cu to promote bottom up fill of features created

on Si chips to connect devices. They work by passivating the surface thus promoting deposition

within features rather outside. In the best case, leveler concentration is used to tune the plating

potential. Previous work showed that pH 1 benzyldimethylhexadecyl ammonium chloride

(BDAC) best served this function of tuning potential when compared to two other candidates,

dodecyltrimethyl ammonium bromide (DTAB), and thonzonium bromide (ThonB). At pH 3,

however, ThonB is best at tuning the plating potential with concentration. Using SHINERS we

show that potential dependent behavior is observed for ThonB at low concentration whereas

there is little to no corresponding behavior of DTAB or BDAC. BDAC strongly at both low and

high concentrations whereas DTAB does not interact strongly with Cu surface at any of the three

the concentrations used.

iv

Ni superalloys are typically used in aggressive environments (high temperatures and

pressures, corrosive liquids such as those present for jet turbines, chemical processing plants, and

in ductwork and heat exchangers for nuclear plants). They form a scale in high temperature

oxidixing environment composed mostly of Cr and the other oxophilic elements in the alloy that

protects the bulk alloy from oxidative damage. Investigating how long term heat treatment

affects the electrochemical behavior and speciation has implications towards their use in nuclear

reactor components. Heat treatment positively affected the corrosion resistance which

corresponded with different product speciation, specifically with regards to the appearance of

reduced Cr species.

v

To my parents

vi

ACKNOWLEDGEMENTS

The completion of this dissertation would not have been possible without the guidance of

my advisor Professor Andrew A. Gewirth. He gave me inspiration for my projects, offered

advice when I was stuck, and allowed me to circuitously end up with my thesis research.

I thank my former labmates Karen Stewart, Scott Shaw, Andrew Campbell, Jeremy

Hatch, Matt Thorum, and Matt Thorseth (the final countdown) for showing me the ropes around

lab and being open to discussing all sorts of things during lunch. I know now for instance, that it

usually helps to press the ‘on’ button when I want the potentiostat to work.

I thank Joe Buthker for politely enduring my daily nattering about this, that and the other

thing. Without your calming influence I doubt I would have survived for long at my desk. I also

enjoyed sharing my grad school journey with Brandon Long and Dennis Butcher.

Of course I appreciate Claire Tornow for becoming my friend after that initial year of

distrust. Her cheery nature and can do attitude were critical to my maintaining a semblance of

sanity. Thanks for listening to the rant and ravings of a near lunatic. I loved being introduced to

the world of fiber arts; stitching and bitching was a definite good experience. I also felt

somewhat helpful when answering the occasional question about instrumental setup. You

definitely made me feel welcome at your desk, despite my many hours of bugging you. I

appreciate it.

Thank you Adele, Laura and Jen for upping the female-to-male ratio. It’s great to have

estrogen in lab. I hope you continue the trend. I also appreciated Professor Gulfeza Kardas who

infused joy and productivity into what otherwise would be a relatively uneventful summer.

vii

I also thank my Suslick lab compatriots Rachel, Brad, John, Sandra, Maryam, and Jin

Rui. I’ve enjoyed our many hours of witty or banal banter.

MRL staff made learning about new instrumental skills easy and enjoyable. Their

insights were invaluable for my projects.

My boyfriend Matthew Small listened to all my trials and tribulations with my research

and injected my life with a bit of rationality. He is one of my role models, and I will always be

envious of his ability to focus on research and come up with his own pet projects, all the while

doing endurance events with Jessica Klinkenberg.

My parents support provided me with the grounding I required to stay the course for grad

school and my brothers allowed me to view grad school from a different perspective.

viii

TABLE OF CONTENTS

CHAPTER 1: GENERAL INTRODUCTION……..…….……………………………….………1

CHAPTER 2: EXPERIMENTAL…………..…….………………………………….…....…..…17

CHAPTER 3: SHELL-ISOLATED NANOPARTICLE ENHANCED RAMAN

SPECTROSCOPY OF BENZOTRIAZOLE FILM FORMATION ON CU(100), CU(111) AND

CU(POLY)..…….………………………………………………………………………….....….23

CHAPTER 4: SURFACE ENHANCED RAMAN INVESTIGATION OF RHODANINE FILM

FORMATION ON COPPER ELECTRODES …..……………………………………..…..…...36

CHAPTER 5: INTERACTION OF LEVELERS WITH COPPER SURFACE IN PH 3

SULFATE SOLUTION………………………......…………...…………………….……..….…58

CHAPTER 6: EFFECT OF HEAT TREATMENT ON ELECTROCHEMICAL BEHAVIOR

AND OXIDATION PRODUCTS OF ALLOYS 617 AND 230………...………………….…...73

APPENDIX A: ACCELERATOR ON COPPER………………………………………………..94

APPENDIX B: CARBON DIOXIDE ELECTROREDUCTION ON GOLD….………..…..…100

1

CHAPTER 1: GENERAL INTRODUCTION

Techniques used to investigate corrosion

Corrosion inhibition is important for maintenance of infrastructure (primarily piping for

liquid transport and structural materials) and in the microelectronics industry. It is typically

achieved through formation of passivating films on the metallic surface that prevents oxidation

of a bulk metal, either by formation of an oxide from sacrificial agents in an alloy, or by

deposition. In the US $276 billion is spent each year controlling corrosion damage.1 Corrosion

damage generally falls under two categories: uniform or localized corrosion. In uniform

corrosion, the material does not form a passive layer in its environment and is freely oxidizing.

Localized corrosion happens when the passive layer is non-uniform and the less protected areas

are attacked.2 This initial attack can be self propagating and result in pit and crevice formation on

the surface of the material which can further propagate until the material fails.2 Stress corrosion

cracking is a synergistic affect where stresses to the material, combined with environmental

factors, initialize local corrosion forming pits or crevices.2

One way to investigate corrosion inhibition is with electrochemical measurements. These

typically involve a three-electrode setup with a working, counter and reference electrode. Linear

sweep voltammetry, wherein a linear ramp of potential is applied to the working electrode

relative to the reference electrode and the current response between the working and counter

electrode is measured, allows for determination of the electrochemical window of passivation

with anodic (oxidative) and cathodic (hydrogen evolution for aqueous solution) breakdown of

the passivation layer occurring at the end potentials.3 Dampened current densities and more

positive anodic oxidation potentials are the desired characteristics for a passive layer.4

2

AC Impedance, a sinusoidal potential wave is applied to the working electrode and the

current response measured, allows one to model the passive layer as an electrical circuit with

resistors representing the electrode polarization resistance and solution resistance and a capacitor

from the film and electric double layer.5 These values allow for determination of the resistivity

and capacitance of the film, which give an idea of surface coverage as well as film thickness.

Inhibition efficiency, shown in equation 1.1, is determined from the resistance of a passivated

electrode relative to that of an unprotected electrode. It along with, film resistance, anodic

corrosion current and potential are the typical figures of merit for passivation films.

η %

'

'

p

pp

R

RRx100 (1.1)

Where η % is the inhibition efficiency, Rp’ is the polarization resistance of a passivated electrode

and Rp is the polarization resistance of an unprotected electrode.

Figure 1.1. Equivalent circuit diagram for electrical double layer.

Although electrochemical experiments give one an idea of the protective ability of the

passivating film, it does not allow for determination of the chemical composition of the film nor

the mechanism of film formation. Surface Enhanced Raman Spectroscopy allows one to obtain

vibrational information of analytes at or near the electrode surface in aqueous solutions.

Interrogatation of film behavior, before and after cathodic or anodic breakdown potentials, is

then possible.

3

Raman spectroscopy involves exciting a sample with monochromatic light and collecting

the inelastically scattered light (typically Stokes shift).6-10

The selection rule for Raman

scattering is a change in polarizability (equation 1.2). Since the typical scattering coefficient for

molecules is very small (~10-30

-10-25

cm2/molecule), normal Raman is only useful for very

concentrated samples, not the low concentrations (ppm) typically used for corrosion inhibition.11

Also, the molecules of interest are associated at or near the electrode surface, meaning that

probing the solution will have limited significance. Therefore, enhancement of signal at or near

the electrode surface is necessary to probe the electrode electrolyte interface and thus interrogate

passivating film formation.

E

i (1.2)

Where α is polarizability of a bond, μi is the induced dipole moment, and E is the electric field.

When a coinage metal (Ag, Au, Cu) has features smaller than the wavelength of scattered

light, the localized surface plasmon can be excited which produces an enhancement of the signal

corresponding to molecular vibrations occurring at or near the feature surface (eqn 1.3 and 1.4).10

There is also a two-fold enhancement from direct chemical bonding of the molecule of interest to

the substrate.12

Since the enhancement from both contributions are confined near the surface of

the metal, probing of the electronic double layer is guaranteed.

2222

0

2)Re(2cos31 gggEEout (1.3)

Where Raman intensity is , θ is the angle between the incident field vector and that of a

molecule at the surface of a particle.

4

outin

outing

2

(1.4)

Where εin is the dielectric constant of the metal particle and εout is the dielectric constant of the

outside environment. Maximum enhancement occurs when the denominator of g approaches 0.

There are many surfaces of interest related to corrosion that are not coinage metals and

examining films on unaltered materials would give valuable information to corrosion

mechanisms at single crystal faces. Strategies commonly used to obtain enhancement from non-

enhancing substrates include: deposit surface of interest onto nanostructured SERS substrate

(difficult and there is contribution from SERS substrate due to limitation of thin deposition as

signal drops off exponentially with distance), deposition of coinage metal particles onto surface

of interest (which can give confounding signals), and tip–enhanced Raman (TERS) in which a

nanoparticle is used as the Raman probe and can simultaneously give topographical

information.6 Of these strategies, TERS is most desirable because of the dual modes; however, a

few challenges prevent wide use of the technique. One is that the signal is very small. Many

models have been used to predict the field of enhancement; however, and promise with the three-

dimensional finite difference time-domain (3D-FDTD) method in particular. 13-14

Another is that

producing tips that give reproducible signal enhancement is difficult. Once a reliable tip is

produced it is susceptible to fouling as is already a problem for STM or AFM measurements.

Taguchi et al have had moderate success coating Si tips with Al2O3 to examine crystal violet and

adenine.15

Tian developed a technique called Shell-Isolated Nanoparticle Enhanced Raman

Spectroscopy (SHINERS) which expands upon the TERS concept.7 Au

7 or Ag

14 nanoparticles

5

serve as ‘probes’ and are coated with a thin layer of metal oxide consisting of SiO2, AlO3, or

MnO2 that prevents direct contact with the electrode and analyte of interest. 6-7, 16

Using these

particles allows for investigation of atomically flat electrodes and the signal from the particles in

amplified by the number of particles. Spectra of pyridine, thiosulfate, and carbon monoxide at

various single crystal faces have been obtained using SHINERS.6-7

A scheme of SHINERS setup

is pictured in Figure 1.1. This opens up a new range of systems that can be studied with Raman

spectroscopy.

Figure 1.2. Cartoon of Shell Isolated Nanoparticle Enhanced Raman at a Cu(111) face electrode

with Benzotriazole-Cu(I) dimer adsorbed.

6

Benzotriazole

1,2,3-Benzotriazole (BTA) is a common corrosion inhibitor for Cu and Cu alloys.17

It is

used in the microelectronics industry for chemical-mechanical planarization slurries as well as in

Cu plating baths.18

Cotton first researched BTA as a viable corrosion inhibitor in the 1960’s and

expected the BTA worked as a physical barrier when complexed with Cu and Poling confirmed

the proposed structure of the film with IR (BTA-Cu(I)).19-20

BTA has a protection efficiency of

about 90% in concentrated sulfuric acid solutions; protection efficiency increases with increasing

pH.17

The general understanding gathered from FTIR,20-23

SERS,22, 24-40

X-ray photoelectron

spectroscopy (XPS),41-48

, and quartz crystal microbalance (QCM),49-52

for the mechanism of film

formation of BTA is that BTA forms a stable adlayer spontaneously when exposed to Cu

surfaces. When Cu ions are released from the surface, BTA may also form an organometillic

layer that prevents diffusion of oxidants to the Cu surface.

Calculations have shown that deprotonated BTA forms a more stable adlayer than the

neutral BTAH which correlates well with its increased inhibition efficacy at higher pH (BTA has

a pKa of 8.2), also deprotonated BTA- competes with Cl

- for surface sites.

48, 53-54 Calculations

also show that the organometallic complex of BTA with Cu forms even more stable adlayers on

the Cu than the deprotonated monomer along with forming a densely packed layer that protects

the Cu surface from chemical attack.52-55

Mayanna and Setty demonstrated that BTA also has face dependent efficiency56

in the

order 100>110>111. This trend corresponds to the relative disorder of BTA adlayers formed on

Cu(111) versus Cu(100) shown in STM57-60

and verified with sum frequency generation (SFG)

by Schultz et al.61

Although the PMIRRAS spectra show no difference between the crystal faces,

the spectra showed that the BTA films formed by anodic polarization of the Cu electrode were

7

irreversible even at potentials where hydrogen evolution occurs which physically disrupts the

film.21

This contradicted SERS studies by Chan and Weaver who observed electrochemically

reversible features in spectra.30

Rhodanine (RD)

Rhodanine (RD, 4-thiazolidinone-2-thione) is a sulfur-containing N,O-heterocycle which,

when derivatized, serves many manufacturing and pharmaceutical purposes.62-64

It chelates metal

ions65

and has been used to detect heavy metals in solution.66

RD has two thiol groups and an

amino group which are both known to interact strongly with metal surfaces. This along with its

ability to chelate metal ions makes it a great candidate as a corrosion inhibitor.

Figure 1.3. Rhodanine structure.

RD has been demonstrated to have good corrosion protection for mild steel67-68

and Cu69-

70 and was patented for use as a leveler in 1952.

71Although there have been many structural

studies for RD72-77

(due to its pharmaceutical benefits) few studies have been performed

examining the RD metal interaction 78-79

and none have investigated the influence of potential on

the vibrational modes of RD.

Levelers in the standard Cu plating acid bath

8

Electrodeposition is currently used to create Cu interconnects which connect devices on

Si chips.80-81

The standard plating bath consists of an aqueous solution of sulfuric acid which

imparts sufficient conductivity to the solution and removes oxide from the electrode surface,

CuSO4 as the Cu ion source, chloride which reduces the anode polarization and acts in

conjunction with the suppressor and accelerator systems, and organic additives.80, 82-83

There are

three types of organic additives used in plating bath solutions for optimal Cu deposition to create

interconnects that fill features on the wafer: 1) suppressors (or carriers) which are polyethylene

glycols; 2) accelerators (or brighteners) containing thiol or disulfide groups and sulfonic acid

groups; and 3) levelers generally surfactants with amine functionality.84

Accelerators are thought

to enhance deposition at the bottom of features in the presence of levelers and allow for high

aspect ratio feature filling also known as superconformal filling.85-92

Carriers and levelers

promote even plating across the field of the chip by increasing the electrodeposition

overvoltage.81

Levelers prevent overfill bumps by associating with the surface and competing

with the accelerators promoting an even deposit across the plane of the chip.80, 82-83, 93-94

This

three component system allows for the efficient void-free filling of features, and generally results

in a relatively flat coating that requires minimal processing after electrodeposition of

interconnects.

It is important to know how these different additives interact with the electrode surface in

order to engineer additives with superior plating performance. SERS and SHINERS offer a

convenient, non-intrusive way to conduct in-situ monitoring of surface specific interactions and

gives an idea of how these additives orient with respect to the electrode surface and facilitate - or

impede - Cu plating. SERS has been used to investigate interaction of additives with Cu surfaces

both with and without the presence of Cu ions.94-105

Previously, it was determined that potential

9

induced orientation of quaternary ammonium salts (referred to as “quat salts”) at low

concentration corresponded to the ability to tune the Cu plating potential with concentration of

the leveler.94

Janus Green B is a typical leveler used in the damascene process and is known to

undergo potential driven orientation.97, 106-107

Passive oxide formation on Ni based alloys

Generation IV nuclear reactors such as the Very High Temperature Reactors (VHTR)

present a materials challenge because they will utilize higher temperatures and pressures for

increased efficiency in electricity production.108-109

Reactors that run at higher temperatures will

also have the capacity for thermochemical water splitting to produce hydrogen which is

(currently) easier and cheaper to store than electricity.109-110

Electrochemical and thermochemical

water splitting can utilize the excess heat of high temperature reactors to generate H2.

Because thermochemical systems only require heat to proceed, they are the more

favorable candidates for H2 generation with nuclear generators.109

The sulfur-iodine cycle, in

which SO2 and I2 are used to spit water, is a favorable candidate because of the simplicity of

separating the H2 and O2 evolving components and recyclability of inputs.109

Stress corrosion

cracking (SCC) is a major concern for failure because of the high temperatures and pressures

required for the reactors to run.111-114

Haynes 617 (Ni-Cr-Co-Mo) and Haynes 230 (Ni-Cr-W-Mo) are solid-solution

strengthened Ni-based alloys developed as high temperature and corrosion resistant materials.115-

117 They currently under consideration for use in components of generation IV reactors such as

tubing and heat exchangers.116, 118-120

Corrosion resistance is imparted on the alloy through

10

formation of a passive oxide composed primarily of Cr2O3. The effect of high temperature on the

alloys’ electrochemical behavior has important implications for use in components for VHTRs.

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13

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85. Moffat, T. P.; Josell, D., Superconformal electrodeposition for 3-dimensional

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Desalination 1993, 93 (1–3), 537.

17

CHAPTER 2: EXPERIMENTAL

Reagents

Chemicals were reagent grade and used as received. All solutions were prepared using

ultrapure water (Milli-Q UV plus, Millipore Inc., 18.2 MΩ cm) and H2SO4 (Ultrex II, J. T.

Baker). Corrosion inhibitors were rhodanine (RD) (99%, Sigma Aldrich) and Benzotriazole

(BTA) (98%, Sigma Aldrich). Leveler solutions were made with dodecyltrimethyl ammonium

bromide (DTAB), thonzonium bromide (ThonB)

and benzyldimethylhexadecyl ammonium

chloride (BDAC), and Na2SO4 (99.999%) and CuSO4 (99.999%) from Sigma Aldrich.

Raman experiments

Raman experiments were performed using an in-situ cell described previously.1 Potential

control was maintained with a CV-27 potentiostat (BAS). The He–Ne laser (λ=632.8 nm) was

projected onto the sample at ~45° incidence. Scattered radiation was collected with F/4

focusing

lens and focused at the entrance slit of a monochromator. A 1200 grooves/mm grating dispersed

radiation onto a cooled charge-coupled device (CCD, Andor). Typical acquisition time was 30 s.

Electrodes for Surface Enhanced Raman Spectroscopy (SERS) measurements were

polycrystalline Cu disks (1 cm diameter, Monocrystals Inc.) prepared by polishing to 0.3 um grit

Al2O3 and then electrochemically roughening in 0.1 M KCl with a Au wire counter electrode and

Ag/AgCl reference electrode. After roughening, electrodes were held at -0.56 V and then rinsed

with copious amounts of ultrapure water. 2. Raman cell setup was described previously.

1

Potential was controlled with a CHI 760D potentiostat (CH Instruments). The He–Ne laser (λ =

632.8 nm) was projected onto the sample at 45 incidence. Scattered radiation was collected with

an f /4 focusing lens and focused at the entrance slit of a monochromator. A 1200 grooves/mm

18

grating dispersed the radiation onto a cooled charge coupled device (CCD, Andor). The typical

acquisition time was 30 s.

Shell-isolated nanoparticle enhanced Raman preparation

Silica-coated gold sols were synthesized as described in the literature,3-5

a brief

explanation follows. A gold sol with 18 nm diameter particles was synthesized by using sodium

citrate reduction. The particles were coated with (3-Aminopropyl)trimethoxysilane (APS) and a

1-2 nm film of silica on the gold particles was created by immersing the APS-coated particles in

an aqueous solution containing 0.54 wt% sodium silicate that left stirring for 2-3 days. Excess

reagents and side products were removed by dialysis. TEM confirms the gold particles have an

average diameter of 18 nm with 1-2 nm thick silica shell. [insert tem]

SHINERS measurements were performed at room temperature using an in-situ cell

described previously6 with a Au wire counter electrode and Ag/AgCl reference electrode.

The excitation line was a HeNe laser (632.8) impinging the surface at a 45° angle. Scattered light

was collected with an air cooled CCD. Typical acquisition time was 30 s.

Preparation of single and polycrystalline Cu disks for SHINERS experiments

The working electrodes were 1 cm diameter Cu(111) and Cu(100) single crystals

(Monocrystals Co.). Surface orientation of the crystals was verified by four-circle XRD.

Crystals were mechanically polished to a 0.25 µm grit size (Metadi Supreme diamond

suspension, Buehler) and electropolished in 50% w/v phosphoric acid at 2 V versus a Pt counter

electrode for 30 s. After electropolishing, the crystals were rinsed with Millipore water and dried

under Ar. A film of SiO2-coated gold particles was made by drop casting 50 μL of the suspended

19

particles onto the crystal and drying under Ar. Polycrystalline Cu disks were also used as

working electrodes. They were prepared as above except the elecropolishing solution was 85%

w/v phosphoric acid. For comparison, the polished disks were also electrochemically roughened

as described in Chan and Weaver.2 Alternatively, polished disks were used for shiners

experiments without the electropolishing step for leveler study.

Preparation of Inconel 617 and Haynes 230 disks

Plates of alloy 617 and alloy 230 (made by were hot working and solution treatment at

1177 oC) were supplied by Haynes International.

7 Composition of the as-received alloys are

described in Mo et al.7 Discs (2-3 mm thick) were cut from plates. Some plates were aged in

laboratory air at temperatures of 900 o

C and 1000 oC for 3000 h. The disks were used as the

working electrodes and were polished to mirror finish with 0.3 um Al2O3 and were sonicated in

ultrapure water then rinsed with copious amounts of ultrapure water before use in experiments.

Electrochemical experiment setup

Electrochemical experiments were performed using a CHI 760D potentiostat (CH

Instruments) with a two component cell, Pt gauze counter electrode, and “no leak” Ag/AgCl

reference electrode (Cypress). Working electrodes were held in place with Kel-F collets screwed

into a rotating disk shaft connect to a modulated speed rotator (Pine Research Instrumentation).

Electrochemistry was performed using a CHI760C or CHI 760D potentiostat (CH Instruments).

Electrochemistry was performed in a two-compartment glass cell with Au wire counter electrode

separated from working electrode compartment by glass frit and a Ag/AgCl “no-leak” (Cypress)

reference electrode connected to working electrode compartment by Luggin capillary.

20

Electrochemical measurements were performed in a three electrode cell using a CHI760C

or CHI 760D potentiostat (CH Instruments). A ~1 cm Cu (poly) disk (Monocrystals Inc.) was

used as the working electrode for cyclic voltammetry, impedance versus potential measurements,

and plating experiments. A carbon rod was used as the counter electrode and a Ag/AgCl

electrode connected via a salt bridge was used as the reference. Solutions were purged with Ar

before use for 1 h, and an Ar atmosphere was maintained in

the cell during all electrochemical

measurements. The electrodes were maintained in the hanging meniscus configuration. Plating

experiments were performed with the crystal attached via a collet to a rotator (Pine

Instruments

MSRX Speed Control) and performed at a rotation rate of 120 rpm.

X-ray photoelectron spectroscopy (XPS)

XPS experiments were performed with an Axis ULTRA spectrometer (Kratos

Analytical). A monochromatic Al X-ray source was used with a 150 W source power, a 1000

meV step energy, and a 100 ms dwell time for two sweeps. Data were calibrated to a C 1s peak.

Atomic force microscopy (AFM)

AFM images were obtained in acoustic mode using a PicoSPM 300 (Molecular Imaging)

device controlled by a Nanoscope E controller (Digital Instruments). Si probes with a resonant

frequency of 300 kHz and force constant of 40 N/m were used for both imaging and scraping

(Tap300Al-G, Budget Sensors). Images were collected at a scan rate of 2.98 Hz and were further

analyzed with WSxM 3.0 (Nanotec Electronica) and OriginPro 8.5 (OriginLab). For AFM film

thickness measurements, the inhibitor film was formed by immersing the Cu(111) crystals in a

solution of 10 mM rhodanine and 0.5 M H2SO4. At the desired incubation time, a Cu crystal was

21

removed from the solution and immediately placed in the AFM cell for imaging. A solution of

0.5 M H2SO4 was used for imaging to prevent the surface film from reforming. The surface was

first imaged in situ in acoustic mode to find a smooth area. Moving into a smaller area, the

surface was then scraped in contact mode for several minutes to remove the Cu-inhibitor film.8

An image of the scraped area was obtained again in acoustic mode and the depth of the film

measured directly by using available bearing analysis software.

Calculations

Optimal geometries for three oxidation states of rhodanine with water solvation were

constructed by using the Spartan 08 program (Wavefunction, Inc) using a restricted Hartree-Fock

SCF calculation with Pulay DIIS and Geometric Direct Minimization method and a 3-21G* basis

set. After energy minimization, the Spartan program was utilized to find the normal modes and

frequencies for the anion, cation and neutral rhodanine molecules.

References

1. Biggin, M. E. Ph.D., University of Illinois at Urbana-Champaign, Champaign, IL, 2001.

2. Chan, H. Y. H.; Weaver, M. J., A vibrational structural analysis of benzotriazole

adsorption and phase film formation on copper using surface-enhanced raman spectroscopy.

Langmuir 1999, 15 (9), 3348.

3. Li, J.-F.; Li, S.-B.; Anema, J. R.; Yang, Z.-L.; Huang, Y.-F.; Ding, Y.; Wu, Y.-F.; Zhou,

X.-S.; Wu, D.-Y.; Ren, B.; Wang, Z.-L.; Tian, Z.-Q., Synthesis and characterization of gold

nanoparticles coated with ultrathin and chemically inert dielectric shells for shiners applications.

Appl. Spectrosc. 2011, 65, 620.

4. Li, J. F.; Huang, Y. F.; Ding, Y.; Yang, Z. L.; Li, S. B.; Zhou, X. S.; Fan, F. R.; Zhang,

W.; Zhou, Z. Y.; WuDe, Y.; Ren, B.; Wang, Z. L.; Tian, Z. Q., Shell-isolated nanoparticle-

enhanced raman spectroscopy. Nature 2010, 464 (7287), 392.

5. Honesty, N. R.; Gewirth, A. A., Shell-isolated nanoparticle enhanced raman spectroscopy

(shiners) investigation of benzotriazole film formation on cu(100), cu(111), and cu(poly). J.

Raman. Spectrosc. 2012, 43 (1), 46.

22

6. Biggin, M. E. In situ vibrational spectroscopic and electrochemical study of

electrodeposition additives on copper surfaces. Ph.D., University of Illinois at Urbana-

Champaign, Champaign, IL, 2001.

7. Mo, K.; Lovicu, G.; Tung, H.-M.; Chen, X.; Stubbins, J. F., High temperature aging and

corrosion study on alloy 617 and alloy 230. J. Eng. Gas Turb. Power 2011, 133 (5), 052908.

8. Goss, C. A.; Brumfield, J. C.; Irene, E. A.; Murray, R. W., In situ atomic force

microscopic imaging of electrochemical formation of a thin dielectric film. Poly(phenylene

oxide). Langmuir 1992, 8 (5), 1459.

23

CHAPTER 3: SHELL-ISOLATED NANOPARTICLE ENHANCED RAMAN

SPECTROSCOPY OF BENZOTRIAZOLE FILM FORMATION ON CU(100), CU(111)

AND CU(POLY)1

Introduction

Corrosion inhibition is important in processing metals submersed in oxidizing solutions.

1,2,3-Benzotriazole (BTAH) is a common additive in polishing slurries and plating baths

because of its ability to inhibit corrosion of Cu and its alloys.1 The general understanding of the

mechanism of inhibition gathered from FTIR2-3

and SERS4-6

is that when Cu ions are released

from the surface, a coordination polymer of Cu(I) and BTA- forms that prevents further

oxidation.

Figure 3.1. 1,2,3-benzotriazole.

Benzotriazole exhibits face dependent corrosion efficiency that goes in the order

100>110>111.7 In aqueous sulfuric acid solutions, STM

8-10 studies have shown that a sulfate

layer forms on the Cu surface that serves a template for BTAH adsorption. The BTAH layer on

the Cu(100) face is highly ordered whereas the BTAH layer on Cu(111) is highly disordered.

The disorder of the BTAH film is attributed with decreased corrosion inhibition on the 111 face.

One major issue regarding the BTA film concerns the reversibility of its formation. On this

1 This chapter appeared in its entirety in the Journal of Raman Spectroscopy as Honesty, N. R.; Gewirth,

A. A. “Shell-isolated nanoparticle enhanced Raman spectroscopy (SHINERS) investigation of benzotriazole film

formation on Cu(100), Cu(111), and Cu(poly)” J. Raman Spectrosc. 2011, 43 (1), 46-50,Copyright 2011,

John Wiley & Sons, Ltd.. This article is reprinted with the permission of the publisher and is available

from http://onlinelibrary.wiley.com and using DOI: 10.1002/jrs.2989. This work was funded by the National

Science Foundation.

24

issue, SFG11

and IRRAS2 measurements, along with the QCM

12-13 all agree that the BTA film

formation is irreversible. Such is not the case with numerous SERS studies, obtained from

polycrystalline Cu, which exhibit reversible BTA film formation.

Reversible BTAH physisorption14-15

is known to occur at concentrations below 0.17 mM

which is the critical concentration for effective inhibition, however the studies mentioned above

use concentrations well above this concentration. Concentration of BTAH also affects the

corrosion mechanism. When polycrystalline Cu electrodes are anodically polarized in NaCl

solutions, intergranular corrosion occurs at low BTAH concentrations (1 mM) and pitting occurs

at greater concentrations of BTAH.16

One reason that SERS measurements might show reversible behavior while those from

IRRAS and SFG do not is that the SERS measurements are performed on polycrystalline

materials while the former use single crystals. The use of single crystals in a SERS experiment

is difficult, since the plasmon mode giving rise to the SERS single is enhanced on a roughened

surface. The roughened surface also raises issues regarding the origin of the SERS signal, as

asperities (“hot spots”) where the E field is high might behave differently from the balance of the

surface. In 2011, Tian reported an elegant way to study single crystal surfaces called Shell-

Isolated Nanoparticle Enhanced Raman Spectroscopy (SHINERS).17-18

With SHINERS the

signal enhancement comes from silica-encapsulated gold particles deposited onto the surface of

interest. The gold particles provide the enhancement, while the silica shell performs prevents

agglomeration of the particles and direct interaction of the gold with the surface of interest. This

eliminates the need for the surface to be SERS active and allows for the direct investigation of

single crystal electrodes. We revisit BTA film formation to ascertain whether this process is

reversible or irreversible in Raman measurements.

25

Results and Discussion

In voltammetry, although there are minimal differences for the onset hydrogen evolution

on different faces,2, 19

crystallographic orientation has no significant effect on kinetics of Cu

dissolution in BTAH containing H2SO4 solutions.8 Figure 3.1 shows the cyclic voltammograms

of particle coated single crystal copper surfaces. The particle coating does not appear to affect

the onset of hydrogen evolution or Cu dissolution relative to literature.8, 10, 19

-20

0

20

40

-20

0

20

40

-20

0

20

40

-0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4-20

0

20

40

Cu(100)

Cu(111)

Cu

rre

nt

de

nsity (A

cm

-2)

Cu(poly)

roughened Cu(poly)

Potential (V vs Ag/AgCl)Figure 3.2. Cyclic voltammograms of particle-coated Cu(100) , Cu(111), Cu(poly), and

roughened Cu(poly) in 75 mM BTAH, 0.1 M H2SO4 at a 50 mV s-1

scan rate.

Raman spectra from solid BTAH, an aqueous solution consisting of, 0.75 mM BTAH + 0.1 M

H2SO4, SERS of Cu(poly) and SHINERS from Cu(111), Cu(100) and Cu(poly) are displayed in

26

Figure 3.2. These spectra display a number of peaks which match those assigned by Chan and

Weaver4 (Table 3.1). Differences between the SERS obtained from the solid surfaces and

aqueous and solid BTAH are similar to those described previously.4-6, 20-23

The spectra obtained

from single crystalline Cu strongly resemble that of polycrystalline Cu, except for the relative

intensity of the modes between 1100 cm-1

and 1200 cm-1

and the breathing modes at 785 cm-1

and 1390 cm-1

.

200 400 600 800 1000 1200 1400

roughened Cu(poly)

Inte

nsity

Raman shift (cm-1)

Cu(poly)

Cu(111)

Cu(100)

aqueous BTAH

solid BTAH

Figure 3.3. Raman spectrum, of solid BTAH, 75 mM BTAH, 0.1 M H2SO4, 75 mM BTAH, 0.1

M H2SO4 on Cu (100) at -0.7 V vs. Ag/AgCl, same on Cu(111), same on polycrystalline Cu, and

the same on roughened polycrystalline Cu. Intensities are normalized to the 785 cm-1

mode.

27

Table 3.1. Peaks (cm-1

) and their assignments for spectra shown in Figure 1.

vibrational frequencies/cm-1

solid

BTAH

solution

BTAH Cu(100) Cu(111) Cu(poly)

roughened

Cu(poly)

Chan and

Weaver4

Band

Assignments4, 6

235

skeletal torsion

429

442 428 435 436 440 skeletal torsion

537

545 537 549 553 555 triazole ring

bend

628

627 626 630 635 653 triazole ring

torsion

779 796 781 779 785 788 790 benzene ring

breathing

993 978 976 982 974

SO4 symmetric

stretch

1006

1013 1014 1019

1010 benzene skeletal

and (CH) bend

1022 1030 1024

1025 1024 1020 benzene skeletal

and (CH) bend

1072

1045 1046

(NH) bend

1127

1129 1125 1128 1127

(CH) bend

1147

1148 1134 1145 1140 (NH) bend6

1171

1158

1164 1159 1160

triazole

assymmetric

stretch and

(NH) bend

1206

1189 1192 1193 1196 1190 combination

1280

1285 1297 1286 1284 1286

skeletal stretch

(NH) bend and

(CH) bend

1374

1373 1375 1377 1380 1370 F. R. with 1385

1387 1396 1388 1388 1388 1391 1385 combination

breathing

1443

1444

1440 skeletal stretch

28

Figure 3.3 shows potential dependent spectra obtained for all three of the surfaces

considered. The spectra display the same peaks for all surfaces at roughly the same energy and

respond similarly to potential changes. As the potential is swept in the anodic direction, the 1020

cm-1

mode and 1190 cm-1

mode increase in intensity relative to neighboring peaks. This

difference in intensity remains as the scan changes direction for the single crystal faces but

disappears for the polycrystalline Cu. For better comparison of the surfaces Figure 3.4 has an

overlay of spectra obtained from the three surfaces considered here at three different potentials:

the starting potential of -0.7 V, a potential where dissolution of Cu is prevalent at 0 V, and back

to -0.7 V after the cathodic sweep. The spectra from the three surfaces are similar except for

differences in relative intensity in the 1100-1200 cm-1

region where three peaks have been

assigned by Chan and Weaver: 1140 cm -1

which is a NH in-plane bending mode assigned by

Youda et al6, 1160 cm

-1 associated with a combination of the asymmetric triazole stretching and

NH bending modes, and 1190 cm -1

the combination mode associated with deprotonation of

BTAH.22

The 1140 cm-1

mode is typically associated only with surface associated BTAH, while

the 1190 cm-1

mode is associated with the BTA-Cu film arising as a consequence of anodic

oxidation of BTA on Cu.6, 23

When the potential is swept in the anodic direction, the 1190 cm -1

peak increases in intensity relative to neighboring peaks for all three surfaces. As the potential is

swept in the cathodic direction the 1190 cm -1

peak continues to increase in intensity for the 111

and 100 faces but decreases for the polycrystalline face.

29

200 400 600 800 1000 1200 1400 1600 200 400 600 800 1000 1200 1400 1600

200 400 600 800 1000 1200 1400 1600 200 400 600 800 1000 1200 1400 1600

200 400 600 800 1000 1200 1400 1600 200 400 600 800 1000 1200 1400 1600

200 400 600 800 1000 1200 1400 1600 200 400 600 800 1000 1200 1400 1600

0 V

-0.3 V

-0.5 V

-0.7 V

0 V

-0.3 V

-0.5 V

-0.7 V

0 V

-0.3 V

-0.5 V

-0.7 V

0 V

-0.3 V

-0.5 V

-0.7 V

Inte

nsity

g) roughened Cu(poly)

h) roughened Cu(poly)

Raman shift (cm-1)

a) Cu(100)

c) Cu(111)

b) Cu(100)

d) Cu(111)

f) Cu(poly) e) Cu(poly)

Figure 3.4. Potential dependent spectra for Cu(100), Cu(111), and polycrystalline Cu in 75 mM

BTAH, 0.1 M H2SO4 for the anodic sweep (a), (c), (e), and (g) and the cathodic sweep (b), (d),

(f), and (h). Spectra are offset for clarity. Arrows indicate scan direction

30

200 400 600 800 1000 1200 1400 1600

a)

b)

c)

d)

a)

b)

c)

d)

Inte

nsity

a)

b)

c)

d)

Raman shift (cm-1)

Figure 3.5. Potential dependent Raman spectra obtained on Cu(100) (a), Cu(111) (b),

polycrystalline Cu (c), and roughened polycrystalline Cu (d)in 75 mM BTAH, 0.1M H2SO4 at -

0.7 V on the cathodic sweep (top), 0 V vs. Ag/AgCl (middle) and -0.7 V vs. Ag/AgCl on the

anodic sweep (bottom) . Spectra are offset for clarity.

31

Figure 3.6 displays the relative peak intensity of the 1190 cm-1

mode versus the 1140 cm-

1 mode. The 1190 cm

-1 mode is associated with deprotonated BTA, whereas the 1140 cm

-1 mode

is assigned to the NH bending mode of adsorbed BTAH. An increase in the 1190/1140 ratio is

thus associated with growth of the BTA(CuI) film. Fig. 5 shows that this ratio increases for both

single crystals surfaces from start of potential scanning at -0.7 V to the anodic limit of the scan.

The ratio stops increasing on the Cu(100) face at about -0.2 V and remains constant as the

potential is swept in the cathodic direction. However, the ratio for Cu(111) continues increasing

as the potential is swept in the cathodic direction until -0.3V when it plateaus. The ratio for

polycrystalline surface does not start increasing until -0.3 V, grows substantially until the anodic

limit of the scan, remains stable as the potential is swept in the negative direction, and then falls

after -0.4 V to the initial ratio. Thus, all three surfaces exhibit different film growth behavior.

32

1

2

1

2

1

2

-0.8 -0.6 -0.4 -0.2 0.0 0.2

1

2

anodic

cathodic

a)

b)

Ra

tio

of 1

19

0 c

m-1/1

14

0 c

m-1

c)

d)

Potential/V vs Ag/AgCl

Figure 3.6. Potential dependent ratio of peak intensities for 1190 cm-1

/1140 cm-1

for Cu(100) (a),

Cu(111) (b), Cu(poly) (c), and roughened Cu(poly) in 75 mM BTAH, 0.1 M H2SO4.

33

The behavior displayed in the SHINERS of the BTA film formed on single crystal Cu

here matches that found in other in-situ studies using Cu single crystals. STM,8, 10

IRRAS,2 and

SFG11

all show that the BTA film persists on the cathodic sweep, while film formation on the

polycrystalline surface in sulfuric acid – as measured in SERS – is reversible.4, 6

Thus reversible

BTA film formation observed in SERS on Cu seems to be intrinsic to the polycrystalline material

used previously4, 6

.

Why should the SERS signal show reversibility of the film on polycrystalline Cu? First,

Cl- -- introduced during roughening of the Cu surface -- could change properties of the BTA

film. Many studies have shown that adding Cl-, which competes for surface sites and

coordinates to the BTA-Cu film, will promote reversibility. 2, 5, 11, 24

However, other SERS

studies on polycrystalline Cu explicitly avoid roughening in Cl- - containing solution, yet the

reversibility persists.6 Second, the large number of grain boundaries present on the

polycrystalline material might affect the BTA film. Calculations of monomeric BTA and BTA-

Cu oligomer chains show that the BTA-Cu chains adsorb more strongly to the Cu surface than

monomeric BTA, thus allowing dissolution of the film from defect sites at grain boundaries.25-27

Tian suggests that negative potentials both reduce the size of the oligomers and attract sufficient

H+ to reprotonate coordinated BTA

-5, 24. A similar mechanism is suggested to occur with BTA

films with ionic liquids as the solvent.28

Disruption at grain boundaries could allow

reprotonation to occur on BTA-Cu films formed on polycrystalline Cu.

Conclusions

34

We showed that film formation depend on the face of the Cu crystal exposed. More

generally, the SHINERS technique allows information about growth on single crystal surfaces to

be obtained.

References

1. Finsgar, M.; Milosev, I., Inhibition of copper corrosion by 1,2,3-benzotriazole: A review.

Corros. Sci. 2010, 52 (9), 2737.

2. Biggin, M. E.; Gewirth, A. A., Infrared studies of benzotriazole on copper electrode

surfaces - role of chloride in promoting reversibility. J. Electrochem. Soc. 2001, 148 (5), C339.

3. Poling, G. W., Reflection infrared studies of films formed by benzotriazole on copper.

Corros. Sci. 1970, 10 (5), 359.

4. Chan, H. Y. H.; Weaver, M. J., A vibrational structural analysis of benzotriazole

adsorption and phase film formation on copper using surface-enhanced raman spectroscopy.

Langmuir 1999, 15 (9), 3348.

5. Rubim, J.; Gutz, I. G. R.; Sala, O.; Orville-Thomas, W. J., Surface enhanced raman

spectra of benzotriazole adsorbed on a copper electrode. J. Mol. Struct. 1983, 100, 571.

6. Youda, R.; Nishihara, H.; Aramaki, K., A sers [surface-enhanced raman scattering] study

on inhibition mechanisms of benzotriazole and its derivatives for copper corrosion in sulfate

solutions. Corros. Sci. 1988, 28 (1), 87.

7. Mayanna, S. M.; Setty, T. H. V., Effect of benzotriazole on the dissolution of copper

single crystal planes in dilute sulphuric acid. Corros. Sci. 1975, 15 (6-12), 627.

8. Polewska, W.; Vogt, M. R.; Magnussen, O. M.; Behm, R. J., In situ stm study of cu(111)

surface structure and corrosion in pure and benzotriazole-containing sulfuric acid solution. J.

Phys. Chem. B 1999, 103 (47), 10440.

9. Vogt, M. R.; Lachenwitzer, A.; Magnussen, O. M.; Behm, R. J., In-situ stm study of the

initial stages of corrosion of cu(100) electrodes in sulfuric and hydrochloric acid solution. Surf.

Sci. 1998, 399 (1), 49.

10. Vogt, M. R.; Polewska, W.; Magnussen, O. M.; Behm, R. J., In situ stm study of (100) cu

electrodes in sulfuric acid solution in the presence of benzotriazole: Adsorption, cu corrosion,

and cu deposition. J. Electrochem. Soc. 1997, 144 (5), L113.

11. Schultz, Z. D.; Biggin, M. E.; White, J. O.; Gewirth, A. A., Infrared-visible sum

frequency generation investigation of cu corrosion inhibition with benzotriazole. Anal. Chem.

2004, 76 (3), 604.

12. Al Kharafi, F. M.; Abdullah, A. M.; Ateya, B. G., A quartz crystal microbalance study of

the kinetics of interaction of benzotriazole with copper. J. Appl. Electrochem. 2007, 37 (10),

1177.

13. Bayoumi, F. M.; Abdullah, A. M.; Attia, B., Kinetics of corrosion inhibition of

benzotriazole to copper in 3.5% nacl. Mater. Corros. 2008, 59 (8), 691.

14. Allam, N. K.; Hegazy, H. S.; Ashour, E. A., Adsorption-desorption kinetics of

benzotriazole on cathodically polarized copper. J. Electrochem. Soc. 2010, 157 (5), C174.

15. Jin-Hua, C., Zhi-Cheng, L., Shu, C., Li-Hua, N., Shou-Zhuo, Y., An xps and baw sensor

study of the structure and real-time growth behavior of a complex surface film on copper in

35

sodium chloride solutions (ph = 9), containing a low concentration of benzotriazole.

Electrochim. Acta 1997, 43 (3-4), 265.

16. Abdullah, A. M.; Al-Kharafi, F. M.; Ateya, B. G., Intergranular corrosion of copper in

the presence of benzotriazole. Scr. Mater. 2006, 54 (9), 1673.

17. Li, J. F.; Huang, Y. F.; Ding, Y.; Yang, Z. L.; Li, S. B.; Zhou, X. S.; Fan, F. R.; Zhang,

W.; Zhou, Z. Y.; WuDe, Y.; Ren, B.; Wang, Z. L.; Tian, Z. Q., Shell-isolated nanoparticle-

enhanced raman spectroscopy. Nature 2010, 464 (7287), 392.

18. Graham, D., The next generation of advanced spectroscopy: Surface enhanced raman

scattering from metal nanoparticles. Angew. Chem., Int. Ed. 2010, 9325.

19. Wu, Y. C. Z., P.; Pickering, H. W.; Allara, D. L., Effect of potassium iodide on

improving copper corrosion inhibition efficiency of benzotriazole in sulfuric acid electrolytes. J.

Electrochem. Soc. 1993, 140 (10), 2791.

20. Shoesmith, D. W., Lee, W., The dissolution of cupric hydroxide films from copper

surfaces. Electrochim. Acta 1977, 22, 1411.

21. Stewart, K. L.; Zhang, J.; Li, S. T.; Carter, P. W.; Gewirth, A. A., Anion effects on cu-

benzotriazole film formation - implications for cmp. J. Electrochem. Soc. 2007, 154 (1), D57.

22. Weaver, G. C.; Norrod, K., Surface-enhanced raman spectroscopy: A novel physical

chemistry experiment for the undergraduate laboratory. Journal of Chemical Education 1998, 75

(5), 621.

23. Youda, R.; Nishihara, H.; Aramaki, K., Sers and impedance study of the equilibrium

between complex formation and adsorption of benzotriazole and 4-hydroxybenzotriazole on a

copper electrode in sulfate solutions. Electrochim. Acta 1990, 35 (6), 1011.

24. Cao, P. G.; Yao, J. L.; Zheng, J. W.; Gu, R. A.; Tian, Z. Q., Comparative study of

inhibition effects of benzotriazole for metals in neutral solutions as observed with surface-

enhanced raman spectroscopy. Langmuir 2002, 18 (1), 100.

25. Kokalj, A.; Peljhan, S.; Finšgar, M.; Milošev, I., What determines the inhibition

effectiveness of ata, btah, and btaoh corrosion inhibitors on copper? J. Am. Chem. Soc. 2010.

26. Kokalj, A.; Peljhan, S., Density functional theory study of ata, btah, and btaoh as copper

corrosion inhibitors: Adsorption onto cu(111) from gas phase. Langmuir 2010, 26 (18), 14582.

27. Jiang, Y.; Adams, J. B., First principle calculations of benzotriazole adsorption onto clean

cu(111). Surf. Sci. 2003, 529 (3), 428.

28. Costa, L. A. F.; Breyer, H. S.; Rubim, J. C., Surface-enhanced raman scattering (sers) on

copper electrodes in 1-n-butyl-3-methylimidazoliun tetrafluorbarate (bmi.Bf4): The adsorption

of benzotriazole (btah). Vib. Spectrosc. 2010, 54 (2), 103.

36

CHAPTER 4: SURFACE ENHANCED RAMAN INVESTIGATION OF RHODANINE

FILM FORMATION ON COPPER ELECTRODES2

Introduction

Rhodanine (RD) is a member of the thiozolidine group which has many industrial and

pharmacological applications including dyes1, antimicrobials

2-3, and as a drug scaffold.

4 Many

RD derivatives readily forms complexes with Ag and Cu ions in solution and also forms a film

on Ag colloid surfaces.5-7

Abdallah and others have shown it to have protective capabilities for

Cu.8-9

The protection of the films is attributed to the thiol group which adsorbs strongly to metal

surfaces.9

Many structural studies of RD have been performed including single crystal x-ray

diffraction,10-11

FTIR,12-15

Raman spectroscopy5-6, 13

, and DFT calculations.5-6, 13, 16

It has 11

tautomers, 5 of which are pictured in Figure 4.1. A few SERS studies investigating the

adsorption RD on Ag colloids have been undertaken. It was found that RD can make a RD-Ag(I)

organometallic complex6 or a dimerize

5 on the Ag surface.

2Work was performed with help from Professor Gülfeza Kardaş and her group at Cukurova University

which performed the fitting and interpretation of electrochemical data in Figures 4.2-4.6 as well as the

idea for the project.

37

Figure 4.1. Tautomers of rhodanine (RD).

Although many structural studies have been undertaken with RD and RD complexes,

there are few which examine the interaction between RD and metallic surfaces. As of yet, no

spectroelectrochemical experiments for RD have been published. In this chapter, we interrogate

the electrochemical behavior of RD with roughened Cu and use Surface Enhanced Raman

Spectroscopy (SERS) to study RD film formation on the electrode surface SERS allows for

vibrational information from electrode-electrolyte interface to be gathered.

Electrochemical impedance spectroscopy (EIS) measurements

Fig. 4.2 shows Nyquist plots for copper in 0.5 M H2SO4 solution with and without 10

mM RD and 10 mM BTAH at 0 time. It is clear that the impedance response of copper has

significantly changed after immersing in RD and BTAH solutions for 0 min.

38

Figure 4.2. Anodic polarization curves of Cu electrode recorded in 0.5 M H2SO4 solution ()

and containing 10 mM BTAH (), 10.0 mM RD ().

The Nyquist plot of bare copper measured in 0.5 M H2SO4 solution displayed an obvious

two capacitive loops in high and low frequency regions. The first resistance (R1) corresponds to

the oxidation of the metal, after oxidation a copper oxide film forms. When RD and BTAH are

added the corrosive media, two capacitive loops were seen in high and low frequencies at

beginning of the immersion time. All impedance plots are analyzed in terms of the equivalent

circuits shown in Fig. 4.3. Generally these circuits fall into the classical parallel capacitor and

resistor combination with the series resistance being that of the bulk solution. Rs represents the

uncompensated solution resistance, R1 represents the oxidation of the copper and R2 corresponds

E / V (Ag/AgCl)

Lo

g I / A

cm

-2

39

to the copper oxides film resistance for copper in 0.5 M H2SO4 solution. In Fig. 5, R1: oxide (Rox)

and/or film resistance (Rf), R2: pore resistance (Rpor= Rct + Rd + Ra), Rp = R1 + R2. Rp:

polarization resistance, Rct: charge transfer resistance, Rd: diffuse layer resistance, Ra: resistance

of accumulated species, CPE1: oxide/film capacitance, CPE2: double layer capacitance. n

shows the phase shift which can be explained as the degree of surface inhomogeneity or surface

roughness.17

The value of n is between 0 and 1 (0≤n≤1). This is related to deviation from the

ideal capacitive behavior. CPE represents a constant phase element to replace a double layer

capacitance (Cdl) in order to give a more accurate fit to the experimental results. 18-19

The

impedance parameters obtained by fitting the EIS data to the equivalent circuit are listed in Table

1. In this case, the inhibition efficiency (η) can be calculated from the polarization resistance

using the following formula;

η %

'

'

p

pp

R

RRx100 (4.1)

Where and are uninhibited and inhibited polarization resistances, respectively.

Figure 4.3. The equivalent circuit model for corrosion process of the Cu absence and presence

inhibitors. Rp = R1 + R2. Rs: uncompensated solution resistance, Rp: polarization resistance, R1:

film resistance (Rf), R2: pore resistance (Rpor= Rct + Rd + Ra), Rct: charge transfer resistance, Rd:

pR '

pR

CPE1

RP=R1+R2

CPE2

R1

R2

Rs

40

diffuse layer resistance, Ra: resistance of accumulated species, CPE1: film capacitance, CPE2:

double layer capacitance.

It is clear that the corrosion of copper is inhibited by the presence of RD or BTAH. As

the inhibitor added to 0.5 M H2SO4 solution, the CPE values tend to decrease while the Rp value

and inhibition efficiency increase. This suggests that inhibitor molecules are adsorbed on the

copper surface, which protects it from corrosion. The inhibition efficiency and surface coverage

are 93.8 % and 0.93 for RD respectively.

Table 4.1. Electrochemical parameters for Cu electrode corresponding to the EIS

data in 0.5 M H2SO4 solution in the absence and presence of 10 Mm BTAH and

10.0 mM RD at 0 min.

In order to examine effect of short immersion time on the corrosion behavior of Cu in 0.5

M H2SO4 solution with the addition of 10 mM RD and 10 mM BTAH, EIS technique was used.

Therefore, more reliable results can be obtained from this technique. From short immersion

times, it is possible to characterize the surface layer modification, i.e., formation and growth of

inhibitor film 20-21

Fig. 4.4 and 4.5 show the Nyquist diagrams of Cu in inhibited solutions after

inhibitor R1 (Ω )

n1

CPEdl-1 (10-6

)

Yo / 106 s

n Ω

-1

R2 (Ω ) n2 CPEdl-2 (10

-6)

Yo / 106 s

n Ω

-1

Rp (Ω ) η%

Blank 10.2 0.76 325.3 10.8 0.58 7542.8 30.0

BTAH 100 0.72 90.0 57 0.60 2628.4 157.0 80.9

RD 117 0.73 29.4 363 0.48 652.21 480.0 93.8

41

exposure times ranging from 0 to 2 h. The insets correspond to a magnification of high

frequencies region. Impedance diagrams obtained in 0.5 M H2SO4 were fit to the electrical

equivalent circuit presented in Fig. 4.5. The related electrochemical data are collected in Table

4.2. It is apparent from Fig. 4.4, at the high frequency regions, a weak depressed semicircle and

at the low frequency regions, a large depressed semicircle is observed in the Nyquist plots of RD

or BTAH. The first loop was related to the pore resistance (Rpor), and the second one was

attributed to the film resistance (Rf).22

The film resistance becomes the dominant contribution

resistances as the formation of the protective RD and BTAH film progresses. After 100 min of

immersion in a solution of RD, the high frequency loop disappears and only one capacitive loop

is observed in the Nyquist plot. This behavior may suggest the formation of a protective inhibitor

film on the copper surface. In presence of RD or BTAH in corrosive media, after 60 min, the

polarization resistances for inhibitors were increased to 940 Ω and 1625 Ω from 480 Ω and 157

Ω for RD and BTAH, respectively. The Rp values increased significantly, which indicated the

continuous growth of the surface film with time and the approach in the perfect coverage of the

surface film on the metal at the end of the 120 min. The growth of this layer enhanced the

corrosion resistance of the metal. The values of film capacitance (CPE1) and double layer

capacitance (CPE2) decreased with increasing with immersion times for inhibitors. The decrease

in CPE1 is probably due to a decrease in local dielectric constant and/or an increase in the

thickness of a protective layer at electrode surface, enhancing therefore the corrosion resistance

of the studied copper. The thickness of the protective layer (d) is related to Cdl according to the

following equation 23

dCdl

0 (4.2)

42

where ε is the dielectric constant of the protective layer and εo is the permittivity of free space.

Figure 4.4. Nyquist plots of Cu electrode obtained in 0.5 M H2SO4 solution (+) and containing

10.0 mM RD (), 10.0

mM BTAH (∆) (solid lines show fitted results, the inset corresponds to a

magnification of high frequencies region).

0 100 200 300 400 500

-500

-400

-300

-200

-100

0

Z'

Z'' cu2 rh Ar-0h seç.txt

Cu 10mM btah 0(2)m remove.txtCu H2so4 0 min ar seç.txtcu2 rh ar-0h fit.zcu 10mm btah 0(2)m fit remove.zcu h2so4 0 min ar fit.z

0 10 20 30 40 50

-50

-40

-30

-20

-10

0

Z'Z''

cu2 rh Ar-0h seç.txtCu 10mM btah 0(2)m remove.txtCu H2so4 0 min ar seç.txtcu2 rh ar-0h fit.zcu 10mm btah 0(2)m fit remove.zcu h2so4 0 min ar fit.z

Z' / Ω

Z''

/ Ω

Z' / Ω

Z''

/ Ω

43

Figure 4.5. Nyquist plots of Cu electrodes in 0.5 M H2SO4 solution in the presence of 10.0 mM

RD after 0, 60, 80, 100 and 120 min exposure time (solid lines show fitted results, the inset

corresponds to a magnification of high frequencies region).

0 3000 6000 9000 12000

-12000

-9000

-6000

-3000

0

Z'

Z''

impedance rhodanine 120 min.txtimpedance rhodanine 100 min remove.txtimpedance rhodanine 80 min remove.txtimpedance rhodanine 60 min remove.txtimpedance rhodanine 0 min remove.txtimpedance rhodanine 120min fit remove.zimpedance rhodanine 100min fit remove.zimpedance rhodanine 80min fit remove.zimpedance rhodanine 60min fit remove.zimpedance rhodanine 0min fit remove.z

0 250 500 750 1000

-1000

-750

-500

-250

0

Z'Z''

impedance rhodanine 120 min.txtimpedance rhodanine 100 min remove.txtimpedance rhodanine 80 min remove.txtimpedance rhodanine 60 min remove.txtimpedance rhodanine 0 min remove.txtimpedance rhodanine 120min fit remove.zimpedance rhodanine 100min fit remove.zimpedance rhodanine 80min fit remove.zimpedance rhodanine 60min fit remove.zimpedance rhodanine 0min fit remove.z

Z' / Ω

Z''

/ Ω

Z' / Ω

Z''

/ Ω

44

Figure 4.6. Nyquist plots of Cu electrodes in 0.5 M H2SO4 solution in the presence of 10.0 mM

BTAH after 0, 60, 80, 100 and 120 min exposure time (solid lines show fitted results, the inset

corresponds to a magnification of high frequencies region).

0 650 1300 1950 2600 3250 3900

-4000

-3350

-2700

-2050

-1400

-750

-100

Z'

Z''

Cu 10mM btah 120m.txtCu 10mM btah 100m.txtCu 10mM btah 80m.txtCu 10mM btah 60m.txtCu 10mM btah 0m.txtcu 10mm btah 120m fit.zcu 10mm btah 100m fit.zcu 10mm btah 80m fit.zcu 10mm btah 60m fit.zcu 10mm btah 0m fit.z

0 100 200 300 400

-400

-300

-200

-100

0

Z'

Z''

Cu 10mM btah 120m.txtCu 10mM btah 100m.txtCu 10mM btah 80m.txtCu 10mM btah 60m.txtCu 10mM btah 0m.txtcu 10mm btah 120m fit.zcu 10mm btah 100m fit.zcu 10mm btah 80m fit.zcu 10mm btah 60m fit.zcu 10mm btah 0m fit.z

Z' / Ω

Z''

/ Ω

Z' / Ω

Z''

/ Ω

45

Table 4.2. Electrochemical parameters for Cu electrode corresponding to the EIS

data in 0.5 M H2SO4 solution in the presence of 10 Mm BTAH and 10.0 mM RD

after different immersion time at 25 °C.

inhibitor Time (min) R1 (Ω ) n1

CPEdl-1 (10-6

)

Yo / 106 s

n Ω

-1

R2 (Ω ) n2 CPEdl-2 (10

-6)

Yo / 106 s

n Ω

-1

Rp (Ω )

BTAH 0 100 0.72 90.0 57 0.60 2628.4 157

60 450 0.60 88.0 1175 0.69 855.54 1625

80 475 0.68 49.64 2500 0.61 798.21 2975

100 520 0.69 41.29 4554 0.52 739.21 5074

120 633 0.69 40.27 5700 0.56 622.56 6333

RD 0 117 0.73 29.35 363 0.48 652.21 480

60 207 0.98 3.14 711 0.45 598.9 942

80 234 0.98 3.10 1295 0.53 329.37 1529

100 272 0.98 2.98 5340 0.64 120.31 5612

120 11664 0.82 47.55 11664

46

It is apparent from the results that RD and BTAH inhibit the corrosion of copper in 0.5 M

H2SO4 solution at 10 mM concentration used in this study. The Rp values were seen to increase

continuously with increasing the immersion time for both inhibitors as well (Table 4.2). Better

performance is seen in the case of RD, particularly 100 and 120 min immersion times.

Surface Enhanced Raman Spectroscopy (SERS) investigation of film composition

Table 4.3 shows Raman peaks from DFT calculation in comparison to calculations done

by Jabeen et al 13

. Spartan calculations the cation, neutral, and anion forms of RD solvated by

water were performed to investigate the effect of oxidation state of the inhibitor has on the

Raman spectrum.

47

Table 4.3. Calculations for oxidation states of RD NH tautomer with peak assignments.

RD+

DFT

RB3LYP

6-31G*

RD DFT

RB3LYP

6-31G*

RD DFT

RB3LP 5

RD-

DFT

RB3LYP

6-31G* Symmetry

Other

peaks Assignments5

60 117 113 124 A" out-of-plane ring deformation

71 139 135 158 A" out-of-plane ring deformation

280 251 245 260 A' C=O, C=S out-of-plane deformation

295 Cu-S bend (citation)

450 415 408 411 A'

C-S stretch, C=S stretch out-of-plane

deformation, in-plane deformation C=O

504 482 479 496 A'

in-plane ring deformation, in-plane C=O

deformation

547 534 527 541 A'

C-N stretch C-S stretch C=S stretch in-

plane deformation

541 551 543 567 A" C=O and C=S out of plane deformation

479 564 555 602 A"

CH2 rock, C=O and C=S out-of-plane ring

deformation

897 653 662 659 A’ C-S stretch in-plane ring deformation

710 680 676 A' C=O and NH out of plane deformation

858 762 757 776 A' C-S stretch, in-plane ring deformation

827 884 853 870 A'

C-N stretch, C-C stretch, in-plane ring

deformation

1062 920 881 923 A"

CH2 rock, CH2 twist, C=O out of plane

deformation

975 A' 980

C=S stretch in-plane ring deformation,

SO4 symmetric stretch

1020 asymmetric SO3 stretch

1096 1041 1067 A'

C-N stretch and C=S stretch in-plane ring

deformation

1214 A'

CH2 wag, C-C stretch, S-C stretch, C-C

stretch (NH2 wag RD+)

1413 1158 1112 1129 A" CH2 twist, C=O out-of-plane deformation

1248 1196 1168 1220 A'

C-N stretch, C=S stretch, CH2 wag, in-

plane NH

1263 1210 1227 A' C-C stretch, CH2 wag

1280 A”

CH2 and NH2 twist out-of-plane

deformation

1424 1305 1272 A"

C-N stretch, C-C stretch, C=O in-plane

deformation

1518 1420 1398 1366 A' C-N stretch, NH in plane deformation

1586 1460 1416 1467 A' CN-stretch (NH wag)

1664 A' NH2 scissoring

2046 1717 1745 1652 A' C=O stretch

48

Table 4.4. Simulated spectra of RD tautomer A and experimental data.

RD+

DFT

RB3LYP

6-31G*

RD DFT

RB3LYP

6-31G*

RD- DFT

RB3LYP

6-31G* solid Rd

RD Ag sol

(Jabeen)

RD

Cu

ocp

in-

situ

Rd Cu

ocp after

1 hr in-

situ

RD Cu at

0.4 V in-

situ

RD Cu

ex-situ

60 117 124

168

71 139 158

181

280 251 260 257 197

285 295

304

450 415 411 424 407 423 416 426 442

504 482 496 488 517

526

547 534 541 541 541 548 553 543 553

541 551 567

551

588

479 564 602

591

897 653 659

637

639 650

680

685

704

710

735 745

728 755

858 762 776 783 787

827 884 870 878 874 888 884

896

1062 920 923 893

919

975

977 978 976 994

1096 1041

1010 1017 1003 1021

1214

1064 1050 1047 1046

1413

1106

1248

1130 1036

1119 1108

1158 1129 1174 1179 1186 1188 1196

1280 1196 1220 1195 1197 1216

1424

1227

1225

1263

1276

1518 1305

1362

1309

1586 1420 1366 1379 1378 1382 1378

1346

1460 1467 1456 1388

1461

49

Figure 4.7 displays SERS results of Cu crystals that were immersed in 0.5 M H2SO4 or 10

mM RD and 0.5 M H2SO4 for ~1-2 hrs then removed from solution. The spectra for solid RD

powder is added to the overlay for comparison. The spectra of Cu disk immersed in H2SO4 has a

sharp peak at 980 cm-1

assigned to the symmetric stretching of SO42-

some broad peaks between

200 and 600 are most likely due to Cu oxides as Cu(I) oxides peaks occur at 620, 532, and 445

cm-1

in acidic and neutral solutions 24-25

The spectra of a Cu disk immersed in a solution RD has

an intense peak 1196 cm-1

which has been assigned S=C stretch 20

, coincident with some modes

in RD. RD film formation begins immediately once Cu is introduced as evidenced by intense

spectra at time 0 hr.

400 600 800 1000 1200 1400

In

ten

sity

solid Rd

ex-situ Rd

Raman shift (cm-1)

ex-situ H2SO

4

Figure 4.7. Ex-situ Raman of Cu that were immersed in 0.5 M H2SO4 or 10 mM Rd and 0.5 M

H2SO4 for ~1-2 hrs then removed from solution and solid Rd spectra for comparison.

50

Figure 4.8 shows the SERS of Cu electrode in 10 mM Rd 0.5 M H2SO4 after 0, 1, and 2

hr. Peaks shown in Table 4.4 coincide with RD peaks found by Ag SERS measurements done by

Jabeen et al and Marzec et al. 5-6

Peaks at 295 and 1216 cm-1

indicate formation of Cu-S bonds

(Liao et al 247 Cu(II) stretch, 369 Cu(I)-S stretch, 1202 C-S stretch) 20

. The intensity of all peaks

drops dramatically after an hour and even further at 2 hours. Two possible reasons for this drop

in intensity are that a thick film develops that is opaque to laser line and thus scatttering is

unenhanced or surface restructuring removes the asperities that cause enhancement.

200 400 600 800 1000 1200 1400

Inte

nsity

Raman shift (cm-1)

0 hr (I/4)

1 hr

2 hr (I*2)

400 800 1200

Figure 4.8. SERS of Cu electrode in 10 mM Rd 0.5 M H2SO4 after 0, 1, and 2 hr. Intensity is

adjusted for comparison in the graph, inset shows unadjusted spectra.

51

Figure 4.9 shows SERS of a Cu electrode in 10 mM RD 0.5 M H2SO4 as it is anodically

polarized. Additional peaks form as surface potential goes above 0.1 V vs Ag/AgCl. In particular

an intense sharp peak at 919 cm-1

and peaks at 1122 cm-1

at 1309 cm-1

which the first two are

associated with an out-of-plane deformation of C=O, and in-plane deformation of C=O. This is

most likely due to RD molecules interacting with Cu ions. RD can chelate Cu2+

ions to form a

Cu(I)RD species. Formation of the complex is associated with a downshift in the NH and C=O

stretches (from 3080 to 2980 cm-1

and 1775 to 1765 cm-1

respectively) and the appearance of

new C=S stretches at 724 and 710 cm-1

.7 In addition, Kong and Jang found new peaks appeared

at 1560 and 1650 associated with C=N and C=C stretching respectively when RD forms a

polymer with Ag(I).3 The polarization curve displayed in Figure 4.2 shows that the RD film

breaks down around 0.25 V, a marked increase in current density occurs at this potential.

52

400 800 1200 1600 400 800 1200 1600

Inte

nsity

Raman shift (cm-1)

0.4

0.3

0.2

0.1

Potential

(V vs Ag/AgCl)Potential

(V vs Ag/AgCl)

0.4

0.3

0.2

0.1

Figure 4.9. SERS of Cu electrode in 10 mM RD 0.5 M H2SO4 that is anodically polarized with

spectral window of 300-1500 cm-.

53

1200 1600 2000 1200 1600 2000

Potential

(V vs

Ag/AgCl)

0.3

0.2

0.1

Inte

nsity

Raman shift (cm-1)

0.3

0.2

0.1

Potential

(V vs

Ag/AgCl)

Figure 4.10. SERS of Cu electrode in 10 mM RD 0.5 M H2SO4 that is anodically polarized with

spectral window of 1100 to 2300 cm-1

(bottom).

Table 4.4 shows the calculated spectra for three potential oxidation states of RD along

with peaks from RD adsorbed onto Ag for comparison. Certain peaks are lowered in energy with

relation to the neural RD molecule so it is reasonable to suggest that some RD exists in a

deprotated state and thus forms a coordination polymer on the Cu surface anagolous to that

formed on Ag colloidal suspensions. Possible film composition is of organic dimmers or

polymers5, an organometallic oligamer as forms on Ag colloids

6, or a combination of both. A

54

peak at 1600 would indicate dimer formation but it is not apparent from either the time

dependent or potential dependent spectra.

Film thickness determination with AFM

The thickness of the films on the Cu surfaces was calculated from AFM images in which

the tip was used to mechanically remove the film using contact mode. Figure 4.10 shows AFM

images taken in acoustic mode. The dark square region in the middle of the images is where the

film has been removed down to the Cu surface. The ridges at the edges of the squares are most

likely from the deposition of insoluble material removed during the scratching process. The

smooth regions beyond the ridges are considered the surface of the film. The film thickness for

the Cu crystals incubated for both 1 and 2 hours are calculated to have thicknesses near or

exceeding 200 nm. The difference between the thicknesses of the films formed for 1 and 2 hours

is not statistically significant.

Figure 4.11. Representative AFM images of Cu electrode in 10 mM Rd 0.5 M H2SO4 after 1,

and 2 hr

55

Conclusions

RD is a good corrosion inhibitor relative to BTA with film resistance and protection

efficiency that improve with time. This enhancement with time corresponds to a decay in SERS

intensity and is attributed to the thick films found to be ~100 nm by AFM.

56

References

1. Ludlow, J. W.; Guikema, J. A.; Consigli, R. A., Use of 5-(4-

dimethylaminobenzylidene)rhodanine in quantitating silver grains eluted from autoradiograms of

biological material. Anal. Biochem. 1986, 154 (1), 104.

2. Habib, N. S.; Rida, S. M.; Badawey, E. A. M.; Fahmy, H. T. Y.; Ghozlan, H. A.,

Synthesis and antimicrobial activity of rhodanine derivatives. Eur. J. Med. Chem. 1997, 32 (9),

759.

3. Kong, H.; Jang, J., Synthesis and antimicrobial properties of novel silver/polyrhodanine

nanofibers. Biomacromolecules 2008, 9 (10), 2677.

4. Tomasic, T.; Masic, L. P., Rhodanine as a privileged scaffold in drug discovery. Curr.

Med. Chem. 2009, 16 (13), 1596.

5. Jabeen, S.; Dines, T. J.; Withnall, R.; Leharne, S. A.; Chowdhry, B. Z., Surface-enhanced

raman scattering studies of rhodanines: Evidence for substrate surface-induced dimerization.

Phys. Chem. Chem. Phys. 2009, 11 (34), 7476.

6. Marzec, K. M.; Gawel, B.; Lasocha, W.; Proniewicz, L. M.; Malek, K., Interaction

between rhodanine and silver species on a nanocolloidal surface and in the solid state. J. Raman

Spectrosc. 2010, 41 (5), 543.

7. Sestili, L.; Cauletti, C.; Furlani, C., Transition metal complexes with pentatomic

heterocyclic ligands containing nitrogen, oxygen and sulphur. I. Copper complexes. Inorg. Chim.

Acta 1985, 102 (1), 55.

8. Abdallah, M., Rhodanine azosulpha drugs as corrosion inhibitors for corrosion of 304

stainless steel in hydrochloric acid solution. Corros. Sci. 2002, 44 (4), 717.

9. Solmaz, R.; Altunbaş Şahin, E.; Döner, A.; Kardaş, G., The investigation of synergistic

inhibition effect of rhodanine and iodide ion on the corrosion of copper in sulphuric acid

solution. Corros. Sci. 2011, 53 (10), 3231.

10. Jabeen, S.; Palmer, R.; Potter, B.; Helliwell, M.; Dines, T.; Chowdhry, B., Low

temperature crystal structures of two rhodanine derivatives, 3-amino rhodanine and 3-methyl

rhodanine: Geometry of the rhodanine ring. J. Chem. Crystallogr. 2009, 39 (2), 151.

11. Moers, F. G.; Smits, J. M. M.; Beurskens, P. T., Crystal structure of bis-

(rhodanine)copper(i) iodide. J. Chem. Crystallogr. 1986, 16 (1), 101.

12. Andreocci, M. V.; Cauletti, C.; Sestili, L., Electronic structure of some penta-atomic

heterocyclic molecules studied by gas-phase hei and heii photoelectron spectroscopy.

Spectrochim. Acta A-M 1984, 40 (11–12), 1087.

13. Jabeen, S.; Dines, T. J.; Leharne, S. A.; Withnall, R.; Chowdhry, B. Z., A vibrational

spectroscopic investigation of rhodanine and its derivatives in the solid state. J. Raman.

Spectrosc. 2010, 41 (10), 1306.

14. Lebedev, R. S.; Yakimenko, V. I., Calculation and investigation of infrared absorption

spectrum of rhodanine. Russ. Phys. J. 1968, 11 (10), 99.

15. Moers, F. G.; Steggerda, J. J., Copper complexes of rhodanine and its 3-alkyl derivatives.

J. Inorg. Nucl. Chem. 1968, 30 (12), 3217.

16. Baryshnikov, G.; Minaev, B.; Minaeva, V.; Podgornaya, A., Theoretical study of the

dimerization of rhodanine in various tautomeric forms. Chem. Heterocyc. Compd. 2012, 47 (10),

1268.

57

17. Benedeti, A. V.; Sumodjo, P. T. A.; Nobe, K.; Cabot, P. L.; Proud, W. G.,

Electrochemical studies of copper, copper-aluminium and copper-aluminium-silver alloys:

Impedance results in 0.5m nacl. Electrochim. Acta 1995, 40 (16), 2657.

18. Li, G.; Ma, H.; Jiao, Y.; Chen, S., An impedance investigation of corrosion protection of

copper by self-assembled monolayers of alkanethiols in aqueous solution. Serb. Chem. Soc.

2004, 69 (10), 15.

19. Khaled, K. F.; Hackerman, N., Ortho-substituted anilines to inhibit copper corrosion in

aerated 0.5 m hydrochloric acid. Electrochim. Acta 2004, 49 (3), 485.

20. Liao, Q. Q.; Yue, Z. W.; Yang, D.; Wang, Z. H.; Li, Z. H.; Ge, H. H.; Li, Y. J., Inhibition

of copper corrosion in sodium chloride solution by the self-assembled monolayer of sodium

diethyldithiocarbamate. Corros. Sci. 2011, 53 (5), 1999.

21. Solmaz, R.; Kardas, G.; Yazici, B.; Erbil, M., The rhodanine inhibition effect on the

corrosion of a mild steel in acid along the exposure time. Prot. Met. 2007, 43, 476.

22. McCluney, S. A.; Popova, S. N.; Popov, B. N.; White, R. E.; Griffin, R. B., Comparing

electrochemical impedance spectroscopy methods for estimating the degree of delamination of

organic coatings on steel. J. Electrochem. Soc. 1992, 139 (6), 1556.

23. Diggle, J. W.; Downie, T. C.; Goulding, C. W., Anodic oxide films on aluminum. Chem.

Rev. 1969, 69 (3), 365.

24. Chan, H. Y. H.; Takoudis, C. G.; Weaver, M. J., Oxide film formation and oxygen

adsorption on copper in aqueous media as probed by surface-enhanced raman spectroscopy. J.

Phys. Chem. B 1999, 103 (2), 357.

25. Stewart, K. L.; Zhang, J.; Li, S. T.; Carter, P. W.; Gewirth, A. A., Anion effects on cu-

benzotriazole film formation - implications for cmp. J. Electrochem. Soc. 2007, 154 (1), D57.

58

CHAPTER 5: INTERACTION OF LEVELERS WITH COPPER SURFACE IN PH 3

SULFATE SOLUTION3

Introduction

Electrodeposition of Cu is used to make interconnects for microelectronics because of its

lower line resistance, better electromigration characteristics, and ease of feature filling compared

to Al and Al-alloy metallization.1-3

The typical Cu plating bath is composed of H2SO4, CuSO4

and organic agents termed supressors, accelerators, and levelers which work in concert for

uniform plating and feature filling across the chip.1

Levelers are used to control overfill bumps that occur during electrodeposition and also

serve to reduce the rate Cu growth on the field (outside of features). 1, 4-6

The prototypical leveler

is a quaternary ammonium salt. Functionalization of head group and altering the chain length

counter ion can affect the plating behavior. 7 Bozzini et al. showed that Janus Green B, a leveler

used for Cu plating, undergoes potential driven orientation changes.8-9

Previously, Hatch et al.

showed that this reorientation is linked with ability to tune the plating potential with

concentration.10

A ‘low acid’ bath with high Cu concentration has many benefits with regards to

electrodeposition. It decreases the conductivity of the solution which improves uniformity of

deposit. It also decreases roughness while enhancing the Cu transport rate to the surface which

should enhance via filling.11

In this chapter, we will investigate the effect of varying the

concentration with dodecyltrimethyl ammonium bromide (DTAB), thonzonium bromide

(ThonB)

and benzyldimethylhexadecyl ammonium chloride (BDAC) has on Cu plating

potentials in pH 3 sulfate solutions. Potential dependent Shell Isolated Spectroscopy will be used

3 Experiments were performed with support provided by Novellus Systems Inc.

59

to investigate the orientation of the levelers at various potentials which may give insight into the

Cu plating behavior.

Results and Discussion

Figure 5.2 shows slow scan rate voltammetry obtained from a rotating Cu electrode in a

solution containing 10 g/L K2SO4 (0.1 M) and 40 g/L CuSO4 (0.15 M) adjusted to pH 3 with

H2SO4 with the addition of 0, 10, 25, and 50 ppm of leveler.

Figure 5.1 Chemical structures of DTAB, BDAC, and ThonB.

60

Figure 5.2. Cyclic voltammogram (10 mV/s scan rate) of rotating (200 rpm) Cu(poly) working

electrode in a solution containing 0.16 M CuSO4 and 0.1 M K2SO4 adjusted to pH 3 with H2SO4

with various concentrations of a) CTAB, b) BDAC and c) ThonB.

-0.4 -0.2 0.0 0.2-10

-8

-6

-4

-2

0B)

Cu

rren

t (m

A/c

m2)

Potential (V vs. Ag/AgCl)

10ppm

25ppm

50ppm

blank

-0.4 -0.2 0.0 0.2

-8

-6

-4

-2

0C)

Cu

rren

t (m

A/c

m2)

Potential (V vs. Ag/AgCl)

10ppm

25ppm

50ppm

blank

-0.3 -0.2 -0.1 0.0 0.1 0.2

-4

-2

0

2

Cu

rren

t (m

A/c

m2)

Potential (V vs. Ag/AgCl)

10ppm

25ppm

50ppm

blank

A)

(b)

(a)

61

Absent leveler, bulk Cu deposition begins at 10 mV vs. Ag/AgCl and the current is nearly

proportional to applied voltage as has been reported previously, both at pH 3 and at lower pH

values. 10

Addition of 10 ppm of DTAB (Fig. 5.2A) inhibits the onset of Cu deposition to

approximately -50 mV. The reverse scan shows some hysteresis, which indicates that

reformation of the inhibiting DTAB layer is slow relative to the Cu plating event. With the

addition of higher concentrations of DTAB, the Cu deposition onset potential shifts to ca. -100

mV and the deposition wave does not exhibit the hysteresis seen with the lower DTAB

concentration. This indicates that the inhibition layer remains on the surface on both the forward

and reverse voltammetric scans.

Fig. 5.2B shows the effect of addition of 10 ppm of BDAC to the blank plating solution.

BDAC at this concentration inhibits the onset of bulk Cu deposition to -200 mV. The forward

sweep shows that partial breakdown of the inhibiting BDAC layer occurs, because the deposition

current initially does not reach the level of the voltammogram of the blank. However, at the

reversal potential (-0.5 V) the current approaches that of the blank, and the reverse sweep

basically traces the inhibitor-free voltammogram.

With addition of 25 ppm of BDAC, bulk deposition is inhibited until a potential of -220

mV. The return sweep displays hysteresis but Cu deposition remains inhibited as compared to

the leveler free case. With addition of 50 ppm BDAC, there are two regions of the cathodic

sweep with negative current starting at around -40 mV which gradually increases until bulk

deposition occurring at around -250 mV. Cu deposition is impeded compared with the 25 ppm

case until about -400 mV wherein the two voltammograms overlay.

62

Adding 10 ppm of ThonBr to the plating solution inhibits the onset of deposition to -230

mV as shown in Fig. 5.2C. The current on the forward scan approaches that of the blank

solution at ca. -450 mV and the return sweep displays a large hysteresis. 25 ppm ThonB inhibits

onset further to -270 mV, but the current is not as high as that found with the lower concentration

of inhibitor. Finally, with addition of 50 ppm Thon B, Cu deposition is further inhibited to -340

mV, but again the current attained at -500 mV is substantially less than that found with the

BDAC-free case.

Figure 5.3 displays cyclic voltammograms of a Cu electrode without Cu in solution and

overlay of impedance versus potential plots for 10, 25, and 50 ppm of leveler. In the presence of

DTAB, concentration has little effect on the electrochemical behavior of the electrode. Both

cyclic voltametry and impedence vs potential plots are indistinguishable at the 10, 25, and 50

ppm. BDAC, however, does have concentration dependent behavior. As the concentration of

BDAC increases, the trench for capacitance shifts to more negative potentials. At 10 ppm,

BDAC has some adsorption phenomena occur between -0.5 V and 0.8 V that does not occur at

higher concentrations. ThonB has a much larger capacitance trench than in other cases and but

cyclic voltammetry and capacity versus potential plots show little variance will concentration

increase. An reductive peak occurs at ~-1 V vs Ag/AgCl which is where the reduction of Cu+ to

Cu0 occurs in neutral sulfate solutions.

12

63

-400

-200

0

200

40010 ppm

0

50

100

-400

-200

0

200

400

Curr

en

t D

en

sity (

A c

m-2)

25 ppm

0

50

100

Cap

acita

nce (

F c

m-2)

-1.5 -1.0 -0.5 0.0

-800

-400

0

400

800

Potential (V vs Ag/AgCl)

50 ppm

DTAB

0

50

100

-500

010 ppm

0

50

100

-500

0

500

Curr

en

t D

en

sity (

A c

m-2)

BDAC

25 ppm

0

50

100

Cap

acita

nce (

F c

m-2)

-1.4 -1.2 -1.0 -0.8 -0.6 -0.4 -0.2 0.0

-200

0

Potential (V vs Ag/AgCl)

50 ppm

0

50

100

150

200

-200

-100

0

10010 ppm

0

50

100

-200

-100

0

Curr

en

t D

en

sity (

A c

m-1)

25 ppm

0

50

100

Cap

acita

nce (

F c

m-2)

-1.5 -1.0 -0.5 0.0

-200

0

200

400

Potential (V vs Ag/AgCl)

ThonB

50 ppm

0

50

100

150

200

Figure 5.3. Cyclic voltammograms (2 mV/s scan rate) and impedance versus potential

measurements (excitation frequency ω = 25 Hz and an amplitude of 10 mV) with a Cu electrode

and levelers at 10 ppm, 25 ppm, and 50 ppm in 0.1 M K2SO4 pH adjusted to 3 with H2SO4.

64

Figures 5.4 displays the potential dependent SHINERS for pH 3 sulfate solutions with 10

ppm of DTAB, BDAC, and ThonB. DTAB has no potential dependent behavior which

corresponds well with its electrochemical behavior (it does not tune the plating potential with

concentration).

BDAC has peaks at the start of the scan (0 mV) and remain over the course of the scan.

Some peaks (Peaks I, J, and M all associated with amino deformation modes along with some

CH modes of the chain) increase with intensity reach a max at -600 mV and then decrease in

intensity. Other peaks keep a relatively constant intensity until about -1000 mV whereupon they

exhibit a small decrease in intensity associated with competition between BDAC and adsorbed

H.

ThonB exhibits potential dependent behavior different than the other two cases. At 0 mV

the spectra exhibit three peaks: B, assigned to the benzyl in plane ring deformation, CH3-O-C

rocking, C-C symmetric stretch, I assigned terminal C-C-C stretch and K assigned symmetric

SO42-

stretch. Peaks I and K are convoluted together. Then as the scan progresses in the cathodic

direction peaks O and U which are assigned to CHCH wagging modes appear at -200 mV. At -

400 mV Peak K increases in intensity. Peaks D, E, F, N, P, R, S, X, and Y associated with the

head group appear along with peaks H, Q, and V associated with the tail. At -800 and -1000 mV

peak I, L, U, X and Y have very large intensities. At -1200 mV there is a reduced intensity for all

peaks associated with completion with H evolution.

65

Figure 5.4. SHINERS spectra of 10 ppm leveler in pH 3 K2SO4. Potential versus Ag/AgCl.

400 600 800 1000 1200 1400 1600

Potential/

V vs

Ag/AgCl

O,P

QN

M

LI,J,K

0

-0.2

-0.4

-0.6

-0.8

-1.0

-1.2

25 cps

DTAB

A,B

F

G

H

400 600 800 1000 1200 1400 1600

R,S

U, V

P,Q

KO

IH

B

MD,E, F

C

G

0

-0.2

-0.4

-0.6

-0.8

-1.0

-1.2

Raman shift/cm-1

25 cps

ThonB

LX,Y

Potential/

V vs

Ag/AgCl

400 600 800 1000 1200 1400 1600

P,Q,R

N

ML

CJ

I

O

GF

EB

K0

-0.2

-0.4

-0.6

-0.8

--1.0

-1.2

25 cps

BDACPotential/

V vs

Ag/AgCl

66

Figure 5.5 displays the potential dependent SHINERS for 50 ppm of DTAB, BDAC, and

Thon B in pH 3 sulfate solution. Tables 5.1-5.3 are the peak assignments for the potential

dependent spectra shown in Figures 5.4 and 5.6.

Unlike in the 10 ppm case, DTAB displays some potential dependent behavior for peaks

E end of tail C-C stretch and F methylene chain rotation. There is also potential dependent

behavior for peaks M and N associated with the head group. For the 50 ppm BDAC peaks C, I, K

P and R at all potentials gradual increase in intensity until -600 mV then decrease in intensity at

more negative potentials. For spectra of 50 ppm, ThonB peaks are very intense until -1000 mV

when a reduction in intensity occurs due to competition with H adsorption. In particular, G and N

associated with the head group and J, O, and V associated with C-C and C-H modes of the tail

group.

67

Figure 5.5. SHINERS spectra of 50 ppm leveler in pH 3 K2SO4. Potential versus Ag/AgCl.

400 600 800 1000 1200 1400 1600

H JE,F

A

QP

OL,M,N

I

GD

0

-0.2

-0.4

-0.6

-0.8

-1.0

-1.2

DTAB

25 cps

C Potential/

V vs

Ag/AgCl

400 600 800 1000 1200 1400 1600

A

P,R

OM,N

L

K

IG,H

D 0

-0.2

-0.4

-0.6

-0.8

-1.0

-1.2

BDAC

25 cps

C Potential/

V vs

Ag/AgCl

400 600 800 1000 1200 1400 1600

Y

V,W

T,UQ,R

P

OM,N

J

HG

FDAX

B,C 0

-0.2

-0.4

-0.6

-0.8

-1.0

-1.2

Raman shift/cm-1

ThonB

25 cps

Potential/

V vs

Ag/AgCl

68

Tables 5.1 Peaks and assignments for DTAB.

Assignments Calculation10

pH 1

10 ppm10

pH 3

10 ppm

pH 3

50 ppm

A Symmetric stretch N-(CHx) + (CC)

615 624

B Symmetric stretch N-(CHx) + (CC)

641

C Symmetric stretch C-N

713

D Tail CH rocking, C-C rotation

736

E End of tail C-C stretch

760

F Methylene chain rotation 789 762 788 789

G S-O symmetric stretch

980 981 976

H C-C asymmetric stretch 1052 1048 1029 1020

I

1129

J

1198 1192

K

1301

L

1372

M

1390 1390

N Combined N-(CH) asymmetric stretch and chain

C-H wag 1444 1443 1445 1440

O

1588

P

1592

Q H2O bend

1636

69

Table 5.2. Peaks and assignments for BDAC.

Assignments Calculation10

pH 1

peaks1

0

10

ppm

50

ppm

A

531

B Benzyl ring deformation 541 542 552

Benzyl ring out of plane bend 604 620

C Benzyl ring in plane bend 689 652 631 640

Benzyl ring in plane bend 710 745

D

785 786 786

E Combined benzyl ring deformation + N-(CHx)

breathing mode 781

835

F Chain (C-C)asymmetric stretch 979 979 977 982

G Combined chain (C-C) assymmetric stretch + chain

(C-H) rotation/torsion 991 996

995

Combined chain (C-C) assymmetric stretch + chain

(C-H) rotation/torsion 1013 1009

H Chain (C-C) asymmetric stretch 1037 1036 1017 1025

I

1135

J Tail rocking, benzene out of plane deformation, N-

CH3 rocking 1199 1199 1193 1183

K Combined benzyl-H in plane bend + N (CH) rotation

+ Chain (C-H) torsion 1221 1220

1209

L

1288

M CH2 torsion, CH scissoring in plane, N-CH3 rocking 1363

N

1379

1374 1369

O Tail CH2 rocking, CH rocking, benzyl in plane

deformation 1389

1388 1390

P Combined benzyl_H in plane scissoring + N-(CHx)

asymmetric stretch + chain (C-H) rotation/torsion 1440 1443 1434 1439

Q

1491

1493

R

1516

S Combined methylene spacer (C-H) wagging + (H-C-

H) scissoring on N 1591 1590 1568 1587

70

Table 5.3. Peaks and assignments for ThonB.

Assignments Calculation10

pH 1 pH 3 pH 3

10 ppm10

10 ppm 50 ppm

A Benzyl ring deformation 518 526

526

B

benzyl in plane ring deformation, CH3-O-C

rocking, C-C symmetric stretch 581

608 612

Namino-(CH2) scissoring/pyrimidyl ring in plane

stretch 614 627

C

Namino-(CH2) scissoring/pyrimidyl ring in plane

stretch 635 633 635 634

D

Symmetric stretch (N-CH2) + (CH2-CH2-N) + N

(C-C) in plane bending (C-C) out of plane bend

711 708

E

734

F

N (C-C) in plane bend + asymmetric stretch (C-

O/C-CH2)

762 764

Nquat-CH symmetric stretch 785 782

G Benzyl ring in plane stretch 798 825 815 813

H Chain (CH) wagging 854 852 853 843

I

962

J Chain terminal C-C-C symmetric stretch 979 978

975

K sulfate symmetric stretch 981 988 978

L

1027

M

1054 1077 1073

N

Combined pyrimidyl ring deformation + benzyl

methylene (C-H) rotation 1060 1065

1081

O Chain (CH) wagging 1180 1183 1177 1171

P Pyrimidyl ring out of plane deformation 1215 1215

1203

Q Tail C-C symmetric stretch 1255

1236 1243

R N-(CH3) rocking 1273 1270 1298 1297

S Cchain-H wagging nearest Nquat 1309 1310 1303

T Nmethoxy (CH3) rocking 1347 1355 1350 1341

U

1392 1382

V Chain (CH) wagging 1440 1442 1441 1434

W

1455

X

1583 1579

Y Namino-(CH2) symmetric stretch 1588 1591 1608 1603

Z Nquat methyl (C-H) scissoring 1620 1620

1621

71

In comparison to pH 1 data, DTAB has less change in behavior with regards to

concentration and much less hysteresis with regards to plating behavior at pH 3.

For the BDAC case, the behavior is similar, increased concentration increases the

overpotential for Cu deposition; however, there is slightly less hysteresis in the pH 3 case.

For the ThonB case the plating voltammetry is completely different than in pH 1 case in

which all plots overlay. The peak in current density is much lower with increased concentration

of leveler: at 10 ppm peak is the same as leveler case where as the 25 and 50 ppm concentrations

have peak current density to about 5 mA/cm2. Since pKa of pyrimidines is fairly acidic at ~1, the

ThonB is probably deprotonated at higher pH.13-14

This deprotonation promotes reorientation of

the ThonBr head group at low concentration.

Conclusions

ThonB has optimal Cu plating characteristics that do not correspond to the leveler only

electrochemistry or differential capacity. ThonB exhibits potential dependent behavior at 10 ppm

concentrations and exhibits a strong interaction with Cu at 50 ppm in SHINERS spectra. Since

potential induced reorganization was attributed to the tuning ability of BDAC at pH 1,10

it is

reasonable to infer that this potential induced reorientation is what allows ThonBr to tune the

electroplating potential of Cu at higher pH.

72

References

1. Andricacos, P. C.; Uzoh, C.; Dukovic, J. O.; Horkans, J.; Deligianni, H., IBM J. Res.

Dev. 1998, 42, 567.

2. Kim, S. K.; Josell, D.; Moffat, T. P., Electrodeposition of cu in the pei-peg-cl-sps

additive system - reduction of overfill bump formation during superfilling. J. Electrochem. Soc.

2006, 153 (9), C616.

3. Ritzdorf, T., Challenges and opportunities for electrochemical processing in

microelectronics. ECS Trans. 2007, 6 (8), 1.

4. Dow, W.-P.; Li, C.-C.; Su, Y.-C.; Shen, S.-P.; Huang, C.-C.; Lee, C.; Hsu, B.; Hsu, S.,

Microvia filling by copper electroplating using diazine black as a leveler. Electrochim. Acta

2009, 54 (24), 5894.

5. Jonathan, R., Damascene copper electroplating. In Handbook of semiconductor

manufacturing technology, second edition, CRC Press: 2007; pp 16.

6. Moffat, T. P.; Wheeler, D.; Kim, S. K.; Josell, D., Curvature enhanced adsorbate

coverage mechanism for bottom-up superfilling and bump control in damascene processing.

Electrochim. Acta 2007, 53 (1), 145.

7. Luehn, O.; Celis, J.-P.; Van Hoof, C.; Baert, K.; Ruythooren, W., Leveling of microvias

by electroplating for wafer level packaging. ECS Trans. 2007, 6 (8), 123.

8. Bozzini, B.; D'Urzo, L.; Mele, C., A novel polymeric leveller for the electrodeposition of

copper from acidic sulphate bath: A spectroelectrochemical investigation. Electrochim. Acta

2007, 52 (14), 4767.

9. Bozzini, B.; D'Urzo, L.; Mele, C.; Romanello, V., Electrodeposition of cu from acidic

sulphate solutions in presence of bis-(3-sulphopropyl)-disulphide (sps). T. I. Met. Finish. 2006,

84 (2), 83.

10. Hatch, J. J.; Willey, M. J.; Gewirth, A. A., Influence of aromatic functionality on

quaternary ammonium levelers for cu plating. J. Electrochem. Soc. 2011, 158 (6), D323.

11. Vicenzo, A.; Cavallotti, P. L., Copper electrodeposition from a ph 3 sulfate electrolyte. J.

Appl. Electrochem. 2002, 32 (7), 743.

12. Fonseca, I. T. E.; Marin, A. C. S.; Sá, A. C., The effect of so2−

on the electrochemical

behaviour of cu in neutral medium. Electrochim. Acta 1992, 37 (13), 2541.

13. Jordan, D. O., Nucleic acids, purines, and pyrimidines. Annu. Rev. Biochem. 1952, 21 (1),

209.

14. Singh, A. K.; Mukherjee, B.; Singh, R. P.; Katyal, M., Analytical reactions of substituted

pyrimidines. Talanta 1982, 29 (2), 95.

73

CHAPTER 6: EFFECT OF HEAT TREATMENT ON ELECTROCHEMICAL

BEHAVIOR AND OXIDATION PRODUCTS OF ALLOYS 617 AND 230

Introduction

Very high temperature reactors (VHTR) with the dual capacity of electricity generation

and hydrogen production are promising candidates for future nuclear generators.1 Two routes

currently under consideration are electrochemical or thermochemical water splitting. Of these

two options, thermochemical water splitting is preferred because it only requires heat. The

sulfur-iodine cycle is a promising candidate because it is relatively efficient at H2 production at

temperatures achievable with VHTR reactors, between 900 and 1000 °C and only requires

manipulation of gaseous and liquid phases.2 Haynes 617 (Ni-Cr-Co-Mo) and Haynes 230 (Ni-Cr-

W-Mo) are solid-solution strengthened Ni-based alloys developed as high temperature and

corrosion resistance materials currently under consideration for use in components of next

generation reactors.1, 3-5

The effect of ageing at high temperature on the alloys’ electrochemical

behavior has important implications for use in components for VHTRs.

Table 6.1. Elemental composition of alloys in average weight percent from Mo et al.1

Alloy Al B C Co Cr Cu Fe La

617 1.03 <0.002 0.08 12.2 22.1 0.017 1.104 --

230 0.38 0.004 0.11 0.29 21.7 0.04 1.4 0.014

Mn Mo Ni P S Si Ti W

617 0.064 9.46 52.86 0.002 <0.002 0.05 0.39 --

230 0.46 1.75 BAL 0.005 <0.002 0.4 <0.01 13.89

74

Ni, Cr, and Ni-Cr alloys are known to undergo transpassive dissolution, electron-

mediated formation of soluble species from an oxide layer, at sufficiently anodic potentials in

aqueous solutions.6-11

Ring-disk polarization and AC impedence6-9

as well as in situ x-ray

photoelectron spectroscopy12

(XPS) and x-ray absorption near edge spectroscopy13

(XANES) of

binary (Ni-Cr) alloys show that the main product of transpassive dissolution are soluble Cr(VI)

species.

Typical corrosion failure of austenitic Ni alloys in nuclear applications has been

attributed to stress corrosion cracking in which a combination of mechanical stress and corrosive

elements in the environment cause failure of the passive layer to form pits and cracks on the

material’s surface which mechanically weaken the overall structure.12-17

Raman spectroscopy

and surface-enhanced Raman spectroscopy (SERS) have both been used to investigate the effect

of pressurized water reactors on Ni alloys (Alloy 600 and Alloy 690) in which a Cr(III) rich

phase determined to be α-Cr2O3.12-17

Devine’s group has used in situ Surface-Enhanced Raman

Spectroscopy with electrodeposited gold to investigate the passive layer that forms on austenitic

nickel samples exposed to Cl- in various pHs. In HCl solutions they found the passive layer of

alloy C22 (Ni-Cr-Mo-W) to be composed of a combination of MoO3, MoO2, and amorphous

Cr(III) oxide species at low potentials and evidence for Cr2O3 at transpassive potentials.18

Although in-situ techniques have been used to characterize the passive layer in ambient

conditions and with high temperature and pressure solutions, the effect of heat treatment has not

been fully investigated 1, 4-5, 19

Unknown is whether heat aging changes the distribution of surface

species that form during transpassive dissolution in sulfuric acid. Herein we demonstrate the use

of Shell Isolated Surface Enhanced Raman Spectroscopy (SHINERS) to interrogate the

75

speciation of surface species that form in the anodic potentials for Haynes 617 and Haynes 230

that have been aged at high temperature in air and compare to the as-received alloy.

Results and Discussion

Figure 6.1 displays both anodic and cathodic polarization curves obtained in 0.1 M

H2SO4 for the various alloy materials considered here. Transpassive dissolution of the passive

layer on Cr is sulfate anion-assisted7-9

so the electrode was rotated at 1000 rpm in order to

facilitate comparison to the literature.

76

-0.4 0.0 0.4 0.8 1.21E-6

1E-5

1E-4

1E-3

0.01

0.1

1

10

j (m

A c

m-2)

Potential (V vs Ag/AgCl)

alloy 617 as received

alloy 617 900 C

alloy 617 1000C

alloy 230 as received

alloy 230 900 C

alloy 230 1000 C

Anodic sweep

-0.4 0.0 0.4 0.8 1.21E-6

1E-5

1E-4

1E-3

0.01

0.1

1

10

Cathodic sweep

j (m

A c

m-2)

Potential (V vs Ag/AgCl)

alloy 617 as received

alloy 617 900 C

alloy 617 1000C

alloy 230 as received

alloy 230 900 C

alloy 230 1000 C

Figure 6.1. Polarization curves of alloys in 0.1 M H2SO4 with 10 mV/s scan rate and 1000 rpm

rotation.

77

The polarization curves for Alloy 617 as-received and after heat treatment are reported in

Fig. 6.1. The anodic scan shows that the passive region begins at -0.24 ± 0.04 V for all samples,

suggesting that both the as-received and heat treated materials will have similar pitting behavior

as they share the same critical pitting potential.4, 20

The current density for the samples at 1.0 V

are 1.4 ± 0.4 mA/cm2 for the as-received case, 0.70 ± 0.1 mA/cm

2 for alloy 617 heat-treated at

900 ˚C, and 0.74 ± 0.3 mA/cm2 for alloy 617 heat-treated at 1000 ˚C. Heat treatment makes the

alloy 617 more corrosion resistant as the current density is reduced. Additionally, the as-received

alloy 617 exhibits an anodic current in the transpassive region ca. 1.6 times higher than that of

heat treated samples, suggesting more easily oxidizable material forms on the surface absent the

heat treatment.

The cathodic potential sweep, also shown in Figure 6.1, displays reduced current density

relative for all three samples to the anodic sweep, likely originating from the formation of a

thicker Cr layer on the anodic sweep.21

The figure also displays an exponential rise in current at

more cathodic potentials for all samples with the as-received Alloy 617 exhibiting a higher

cathodic current than the heat treated samples.

The polarization curves for various treatments of Alloy 230 are also shown in Figure 6.1.

Onset of heat treated samples more positive than for as-received case at 0.19 V ± 0.04 V vs

Ag/AgCl. The current density for the samples at 1.0 V are 0.28 ± 0.05 mA/cm2 for the as-

received alloy 230, 0.08 ± 0.05 mA/cm2 for alloy 230 heat-treated at 900 ˚C, and 0.07 ± 0.05

mA/cm2 for alloy 230 heat-treated at 1000 ˚C. The heat treatment reduces the current density at

1.0 V versus the untreated case. The as-received sample has a higher anodic current density than

that of heat treated samples, again suggesting the presence of more easily oxidizable material on

78

the surface prior to heat treatment. Return sweep is similar to alloy 617 case with as-received

having more cathodic current than the heat treated samples.

Our observation of something with regard to the transpassive region on heat treatment

has precedence in the literature. For example, Kewther et al. showed that Alloy 617 used in gas

turbines for 37,000 h could become more corrosion resistant with heat treatment 1-2 hr at 1174

°C under inert gas; heat treatment made alloy 617 samples 100 mV more noble in a solution

containing 0.05 M H2SO4 + 0.005 M NaCl.4 Alternatively, heating in air causes carbide

precipitate to form alongside grain boundaries and a passive oxide composed of Cr2O3 to form

on top of the bulk alloy with a thinner Al2O3 layer underneath. However, heating did not affect

grain size distribution.1 Carbide deposition arising from heating also increases the rate of anodic

dissolution of Ni-Cr-Mo alloys in boiling 10% H2SO4.19, 22

Segregation of Cr in the carbide

phase also causes embrittlement of alloy.1, 4, 19

According to the Pourbaix diagram, in aqueous

solution Cr(III) should be dominant species in passivation layer and Cr(VI) species are formed at

transpassive potentials.23

With regards to electrochemical passivation, in situ XPS measurements of Ni-Cr alloys

confirm that the passive layer in the double region is composed of Cr(III) and Ni(II) and thin (1-

2 nm) whereas the transpassive region (starting at 1.0 V vs SHE) was composed of a mixture

Cr(III) and Cr(VI). Jabs et al. showed that Ni-Cr alloys with 20 weight percent Cr develop an

hydroxide layer as evidence by at peak at 577 eV in the XPS after stepping the potential above

0.4 vs SHE.21

The electrochemical behavior of Alloy 230 in 25-98% H2SO4 has been studied

with solution temperatures ranging 25 to 75 °C;5 however, the effect of heat aging of the alloy on

electrochemistry has not been examined. The delayed onset and reduced current density

observed here shows that heat treatment makes both alloys more resistant to oxidation. Overall

79

our results show that Alloy 230 is more corrosion resistant than Alloy 617, a result also found in

the literature.

In order to interrogate the species present on both the as-received and heat-treated

alloy surfaces, we performed in situ SHINERS on both the alloy 617 and alloy 230 materials in

both the anodic and cathodic directions. Figure 6.2 shows potential dependent SHINERS

obtained from as-received and heat-treated alloy 617 in aqueous 0.1 M H2SO4. Table 6.1

provides a listing of peaks and their assignments.

Table 6.2. Peaks and assignments for spectra.

cm-1

assignment Reference

A 800 adsorbed CrO42-

24-25

B 810-840 CrO42-

24-25

C 850-920 Mixed Cr(III/VI) oxide (MoO42-

and WO42-

) 26-27

D 960-980 Cr2O72- 24-25

E 980 SO42-

symmetric stretch 28

F 1020 HSO4- assymetric stretch

28

For the as-received alloy 617 as the potential is swept from -0.4 V to 0.9 V only peaks

from the electrolyte are observed. Specifically, a peak at 977 cm-1

(peak E) assigned as the

symmetric SO42-

stretch.28

At 0.95 V a group of peaks with large intensities appear at 783 cm-1

(peak A) and 943 cm-1

(peak D) which are assigned adsorbed CrO42-

and Cr2O72-

respectively.24-

25 At 1.0 V, peaks A and D increase in intensity (and shift to higher wavenumbers) with peak A

developing a shoulder at 833 cm-1

(Peak B, assigned as free CrO42-

). On the cathodic sweep

peaks A and D continue increases in intensity until 0.4 V after which the peaks decrease in

intensity. At 0 V a peak centered at 862 cm-1

(peak C) appears and is assigned a mixed oxide

Cr(III/VI).26-27

The region where peak C occurs is also where MoO42-

(876 cm-1

respectively)

80

appear when adsorbed onto a Ag colloid.24

As the potential is swept from 0 to -0.4 V, the

intensity of peak C decreases in intensity. Interestingly there is no feature observed at 898 cm-1

that could be associated with HCrO4-.26-27

For the anodic sweep with the 900 °C treated alloy 617 between -0.4 V to 0.8 V only

electrolyte peaks, peak E and broad peak centered at 1020 cm-1

(peak F) assigned to HSO4- are

observed. 28

At 0.8 V a peak at 867 cm-1

(peak C) appears. At 0.9 V an intense peak at 793 cm-1

(peak A) appears with a shoulder at 970 cm-1

(peak D). All peaks increase in intensity after

reaching the switching potential of 1.0V. On the cathodic sweep, peak A reaches maximum

intensity at about 0.9 V, the while peaks C and D reach maximum intensity at around 0 V vs

Ag/AgCl.

Similar to the other two cases, in spectra obtained from the 1000 °C treated alloy 617

only electrolyte peaks (E and F) are observed from -0.4 to 0.8 V. At 0.8 V a peak at 875 cm-1

(peak C) and at 0.95 V a peak at 800 cm-1

(peak A) appears while peak D has increased in

intensity. At 1.0 V, peak A and peak C have increased in intensity while a peak at 960 cm-1

(peak

D) has appeared. On the cathodic sweep, peak A reaches its maximum intensity at 0.8 V while

peaks C and D reach a maximum between 0.2 V and -0.2 V before decreasing in intensity.

81

Figure 6.2. Potential dependent spectra of Ni alloys in 0.1 M H2SO4. Spectra offset for clarity.

anodic sweep cathodic sweep

600 800 1000 12000

10

20

30

40 alloy 617 900 C

Potential

(V vs Ag/AgCl)

1.0

0.95

0.9

0.85

0.8

0.4

0

-0.4

Inte

nsity (

cps)

Raman shift (cm-1)

E F

A

CD

600 800 1000 12000

5

10

15

Inte

nsity (

cp

s)

Raman shift (cm-1)

alloy 617 1000

Potential

(V vs Ag/Ag/Cl)

1.0

0.95

0.9

0.85

0.8

0.4

0

-0.4

EF

A C

600 800 1000 12000

50

100

150

200alloy 617 as received

Inte

nsity (

cps)

Raman shift (cm-1)

Potential

(V vs Ag/AgCl)

1.0

0.95

0.9

0.85

0.8

0.4

0

-0.4

AD

E F

B

600 800 1000 12000

50

100

150

200

Inte

nsity (

cps)

Raman shift (cm-1)

alloy 617 as receivedPotential

(V vs Ag/AgCl)

1.0

0.95

0.85

0.8

0.4

0

-0.4

A D

C

B

600 800 1000 12000

20

40

60

80

100

Inte

nsity (

cp

s)

Raman shift (cm-1)

alloy 617 900 C Potential

(V vs Ag/AgCl)

1.0

0.95

0.9

0.85

0.8

0.4

0

-0.4

A C DF

600 800 1000 12000

10

20

Inte

nsity (

cp

s)

Raman shift (cm-1)

Potential

(V vs Ag/AgCl)

1.0

0.95

0.9

0.85

0.8

0.4

0

-0.4

alloy 617 1000 C

E FA C

82

Figure 6.3 shows the peak intensity for the Cr species on Alloy 617 samples relative to their

maximum peak intensity to better interpret the change in Cr speciation with potential. The onset

for peak A -- associated with adsorbed CrO42-

-- on the anodic sweep is similar for the three

samples. On cathodic sweep the maximum intensity for peak A is reached 0.2 V earlier for the

heat-treated Alloy 617 samples relative to the as-received sample. On the cathodic sweep, the

maximum intensity for peaks C and D are delayed for 0.2 V for the heat-treated Alloy 617

samples relative to the as-received Alloy 617. Thus heat treatment controls both the nature of the

Cr overlayer and its potential dependent development.

0.0

0.4

0.8

0.0

0.4

0.8

-0.4 0.0 0.4 0.8 1.2

0.0

0.4

0.8

alloy 617 as received

alloy 617 900 C

alloy 617 1000 C

A

C

Re

lative

Pe

ak I

nte

nsity

B

Potential (V vs Ag/AgCl)

Figure 6.3. Relative peak intensity versus potential plot for a) CrO42-

b) mixed oxide, c) Cr2O72-

.

Our observation that peaks assigned to Cr(VI) species appear at anodic potentials

suggests that Cr(VI) is the major product formed in the transpassive region, a result which has

consistent with the literature.6-7, 21

There is no clear evidence for Cr2O3 formation, which is the

major product when either Alloy 230 or Alloy 617 is heated in air;1 however, the mixed

Cr(III)/Cr(VI) species is observed on the cathodic sweep. We note that Cr(III) species have a

83

smaller scattering cross-section relative to Cr(VI) peaks for spectra produced by roughened or

colloidal samples of Ag, Au, and Cu.24-25, 29

SERS spectra of Alloy 22 a Ni-Cr-Mo alloy in HCl

display broad peaks at 430 and 490 cm-1

attributed to an amorphous Cr(III) species.18

There are

some low intensity features at that region for some of the spectra.

The other interesting aspect of the spectra reported above concerns the delayed potential

associated with the formation of peaks associated with Cr2O72-

and mixed oxide and accelerated

potential of the appearance of peak A, associated with CrO42-

in the heat treated samples. We

suggest that the heat treatment produces more fully oxidized Cr material relative to Cr2O72-

, the

consequences of which are seen spectroscopically. Interestingly, the Pourbaix diagram for Cr

shows that HCrO4- rather than chromate should be stable in the potential region interrogated (at

pH 1), so the presence of CrO42-

suggests a less acidic environment overall. Correspondingly,

we note that heat treatment leads to an increase in corrosion resistance.

Figure 6.4 and Figure 6.5 present spectra and intensity vs. potential curves, respectively,

for the three Cr species observed from heat treated and as received Alloy 230 samples.

For the as-received Alloy 230 sample, as the potential is swept from -0.4 V to 0.9 V, only

electrolyte peaks (E and F) are observed. From 0.85 to 0.9 V, a peak centered at 800 cm-1

(peak

A) appears and grows in intensity while shifting to 801 cm-1

. At 1.0 V peak A develops a

shoulder at 847 cm-1

(peak B) and a peak at 978 cm-1

appears (peak D). On the cathodic sweep,

both A and D increase in intensity down to 0.9 V then rapidly decrease in intensity by 0.8 V and

continue a gradual decrease in intensity until the end of the scan at -0.4 V.

Similar to the as received case, only electrolyte peaks (E and F) are observed on the 900

°C-treated Alloy 230 sample, as the potential is swept from -0.4 V to 0.4 V. At 0.8 V, a peak

centered at 882 cm-1

(peak C) appears. At 0.95 V two other peaks at 792 cm-1

(peak A) and 975

84

cm-1

appear (peak D). All three peaks increase in intensity and shift to higher frequencies (800,

888, and 964 cm-1

) until 1.05 V. On the cathodic sweep, peak A increases in intensity until 0.8 V

then decreases as the potential is swept to more negative values. Peaks C and D remain at the

same intensity until 0 V, where peak C shifts to 920 cm-1

and increases in intensity until -0.4 V

the end of the cathodic sweep. This region is where adsorbed MoO42-

and WO42-

(876 cm-1

and

912cm-1

respectively) would also occur.24

For the 1000 °C treated Alloy 230, as the potential is swept from -0.4 to 0.95 only the

electrolyte (E and F) are observed. At 1.0 V a peak centered a 795 cm-1

(peak A) appears and

grows in intensity at 1.05 V. On the cathodic sweep, peak A increases in intensity, reaches a

maximum at 0.8 V and slowly decreases in intensity as the potential is swept to more negative

values until 0 V. After 0 V, a peak at 911 cm-1

(peak C) appears and grows in intensity for the

rest of the cathodic sweep. This region is where adsorbed MoO42-

and WO42-

(876 cm-1

and 912

cm-1

respectively) would also occur.24

85

Figure 6.4. Potential dependent spectra of 230 alloys in 0.1 M H2SO4. Spectra offset for clarity.

anodic sweep cathodic sweep

600 800 1000 12000

10

20

30

40

Inte

nsity (

cp

s)

Raman shift (cm-1)

alloy 230 as receivedA

D

Potential

(V vs Ag/AgCl)

1.0

0.95

0.9

0.85

0.8

0.4

0

-0.4

E F

B

600 800 1000 12000

10

20

30

Inte

nsity (

cps)

Raman shift (cm-1)

A

C DPotential

(V vs Ag/AgCl)

1.05

1

0.95

0.9

0.85

0.8

0.4

0

-0.4

alloy 230 900 C

E F

600 800 1000 12000

5

10

Inte

nsity (

cps)

Raman shift (cm-1)

A Potential

(V vs Ag/AgCl)

1.05

1.0

0.95

0.9

0.85

0.8

0.4

0

-0.4

alloy 230 1000 C

FE

600 800 1000 12000

20

40

60

80

100

Inte

nsity (

cps)

Raman shift (cm-1)

alloy 230 as receivedPotential

(V vs Ag/AgCl)

1.05

1.0

0.95

0.9

-0.85

0.8

0.4

0

-0.4

A B D

600 800 1000 12000

20

40

60In

tensity (

cps)

Raman shift (cm-1)

Potential

(V vs Ag/AgCl)

1.05

1

0.95

0.9

0.85

0.8

0.4

0

-0.4

alloy 230 900 CA

C D

600 800 1000 12000

2

4

6

8

Inte

nsity (

cps)

Raman shift (cm-1)

alloy 230 1000 C Potential

(V vs Ag/AgCl)

1.05

1

0.95

0.9

0.85

0.8

0.4

0

-0.4

AC E F

86

0.0

0.4

0.8

0.0

0.4

0.8

-0.4 0.0 0.4 0.8 1.2

0.0

0.4

0.8

alloy 230 as received

alloy 230 900 C

alloy 230 1000 C

A

B

C

Re

lative

Pe

ak I

nte

nsity

Potential (V vs Ag/AgCl)

Figure 6.5. Relative peak intensity versus potential plot for a) CrO42-

b) mixed oxide, c) Cr2O72-

.

As in the Alloy 617 case, spectra for alloy 230 samples show no HCrO4-. Heat treated

samples show a delayed onset of CrO4- peak and development of a mixed oxide peak during

transpassive dissolution.

Heat treated alloy 617 and 230 have different onsets for the mixed oxide peak, alloy 617

having a greater relative peak intensity of the mixed alloy phase to the CrO4- peak on the anodic

sweep. The Cr2O72-

peak reaches a maximum intensity at 0 V on 617 whereas it reaches

maximum intensity at -0.4 V on the heat treated 230 samples. The as received 230 does not

appear to have a mixed oxide phase that develops at cathodic potential.

Ex situ XPS was performed on both alloy 230 and alloy 617 after two complete

electrochemical cycles between -0.4 and 1.0 V followed by emersion at -0.4 V. XPS obtained

from the Cr region are shown in Figure 6.6 and exhibit two peaks at 577 eV and 588 eV. These

peaks are assigned as Cr(III/VI) mixed oxide because the energies match that of the 2p peaks for

87

oxidized Cr. The peaks for Cr(III) are at 577 and 586-8 eV,30

while the peak for Cr (VI) is

578.75 eV.21

88

570 575 580 585 590 5950

200

400

600

588

CP

S

Binding Energy (eV)

alloy 617 as received

alloy 617 900 oC

alloy 617 1000 oC

578

570 575 580 585 590 5950

200

400

600

588579

CP

S

Binding Energy (eV)

alloy 230 as received

alloy 230 900 oC

alloy 230 1000 oC

Figure 6.6. Ex situ XPS of Ni alloys after potential cycling. Spectra are offset for clarity.

89

Table 6.3 is a summary of the relative amounts of the most abundant elements in the

alloys (Ni, Cr, Mo, Co, and W) before and after oxidation determined from low resolution survey

scans. Samples were oxidized by applying a potential of 1.1 V vs Ag/AgCl to the Ni sample for

60 s. The as received and heat treated alloy 617 samples exhibit the same behavior; the

percentage of Cr increases, Ni and Co decrease, and Mo remains the same after electrochemical

oxidation. For the alloy 230 sample, the percentage of Cr and W increases, while Ni and Mo

decrease. The as received 230 has a higher fraction of W compared to the heat treated samples.

Heat treatment has a minimal affect on the oxidation state and relative amount of Cr found ex

situ for the Ni samples before and after corrosion in 0.1 M H2SO4.

Table 6.3. Relative atomic % of 5 major elements: Ni, Cr, Mo, W, Co before and after oxidizing

at 1.1 V for 60 sec.

alloy 617

as received

alloy 617

900 ˚C

alloy 617

1000 ˚C

Before After Before After Before After

Ni 40 11 38 12 48 13

Cr 26 77 30 76 12 75

Mo 13 13 12 11 16 12

Co 20 0.1 20 1 23 --

alloy 230

as received

alloy 230

900 ˚C

alloy 230

1000 ˚C

Before After Before After Before After

Ni 36 -- 45 14 58 14

Cr 9 29 51 75 35 46

Mo 53 4 5 4 3 --

W 2 67 -- 7 4 40

90

Conclusion

We show there is a correlation between transpassive current density and observation of

surface Cr species in the Raman spectra. Delayed transpassive dissolution is associated with

early onset of Cr(VI) species in spectra. The difference between transpassive current densities

from 217 and 630 suggest the two alloys have different corrosion susceptibility and indeed the

230 is more corrosion resistant. In both alloys, heat treatment resulted in delayed onset of the

transpassive region, likely because the heat treatment makes more Cr available to the surface. An

increase in the relative intensity of the mixed oxide phase occurs with heat treatment.4

Finally, we examine reasons that heat treated Alloy 230 and Alloy 617 exhibit greater

corrosion resistance relative to the as-received material. The XPS measurements show that

oxidation is associated with increased Cr content at the surface and speciation of the Cr to form

protective oxides is well-known to increase the passivity of electrode surfaces. 6-11

It is also

understood that the average grain size grows and distribution of sizes increases after heating in

furnace,31

thus leading to the presence of fewer reactive grain boundaries.

There are other possible contributory factors to increased corrosion resistance with the

heat treated materials. Al2O3 is known to form as a consequence of internal oxidation; 31-32

this

Al2O3 might contribute to increased corrosion resistance. Formation of a surface layer of

MnCr2O4 (spinel) imparts 230 with better corrosion resistance than 617 (as Alloy 230 contains

twice as much Mn) at 900 C; however, both undergo spallation and volatilization of Cr2O3 layer

at 1100 C.32

A study involving surface segregation in Haynes 230 showed that while S, P, and Si

remained at the surface at 875 C, no change in Ni or Cr content was observed.33

Interestingly we found less intense Cr signals in the Raman spectra from the 1000 C

treated samples of both 230 and 617. This decrease relative to the samples heat treated at lower

91

temperatures might be due the formation of volatile CrO3 from Cr2O3 at temperatures above 950

C.31

We note, however, that a decrease in Cr content following electrochemical oxidation was

not observed in the XPS.

References

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corrosion study on alloy 617 and alloy 230. J. Eng. Gas Turb. Power 2011, 133 (5), 052908.

2. Vitart, X.; Le Duigou, A.; Carles, P., Hydrogen production using the sulfur–iodine cycle

coupled to a vhtr: An overview. Energ. Convers. Manage. 2006, 47 (17), 2740.

3. Ahmed, N.; Bakare, M. S.; McCartney, D. G.; Voisey, K. T., The effects of

microstructural features on the performance gap in corrosion resistance between bulk and hvof

sprayed inconel 625. Surf. Coat. Technol. 2010, 204 (Copyright (C) 2011 American Chemical

Society (ACS). All Rights Reserved.), 2294.

4. Kewther, A.; Hashmi, M.; Yilbas, B., Corrosion properties of inconel 617 alloy after heat

treatment at elevated temperature. J. Mater. Eng. Perform. 2001, 10 (1), 108.

5. Habib, K., Electrochemical behavior of a high strength nickel-based alloy in h2so4.

Desalination 1993, 93 (1–3), 537.

6. Bojinov, M.; Fabricius, G.; Kinnunen, P.; Laitinen, T.; Mäkelä, K.; Saario, T.; Sundholm,

G., The mechanism of transpassive dissolution of ni–cr alloys in sulphate solutions. Electrochim.

Acta 2000, 45 (17), 2791.

7. Bojinov, M.; Fabricius, G.; Kinnunen, P.; Laitinen, T.; Mäkelä, K.; Saario, T.; Sundholm,

G.; Yliniemi, K., Transpassive dissolution of ni–cr alloys in sulphate solutions—comparison

between a model alloy and two industrial alloys. Electrochim. Acta 2002, 47 (11), 1697.

8. Bojinov, M.; Galtayries, A.; Kinnunen, P.; Machet, A.; Marcus, P., Estimation of the

parameters of oxide film growth on nickel-based alloys in high-temperature water electrolytes.

Electrochim. Acta 2007, 52 (Copyright (C) 2011 American Chemical Society (ACS). All Rights

Reserved.), 7475.

9. Bojinov, M.; Tzvetkoff, T., The influence of solution anion on the mechanism of

transpassive dissolution of ferrous- and nickel-based alloys. J. Phys. Chem. B 2003, 107 (21),

5101.

10. Keddam, M.; Takenouti, H.; Yu, N., Transpassive dissolution of ni in acidic sulfate

media: A kinetic model. J. Electrochem. Soc. 1985, 132 (11), 2561.

11. Schmuki, P.; Virtanen, S.; Davenport, A. J.; Vitus, C. M., Transpassive dissolution of cr

and sputter-deposited cr oxides studied by in situ x-ray near-edge spectroscopy. J. Electrochem.

Soc. 1996, 143 (12), 3997.

12. Abdallah, M.; Megahed, H. E.; Elnager, M. M.; Mabrouk, E. M.; Radwan, D., Pitting

corrosion of nickel alloys and its inhibition by some dihydrazide derivatives. Bull. Electrochem.

2003, 19 (Copyright (C) 2011 American Chemical Society (ACS). All Rights Reserved.), 245.

13. Delichere, P.; Hugot-Le Goff, A.; Joiret, S., Study of thin corrosion films by in situ

raman spectroscopy combined with direct observation of nuclear reactions. Surf. Interface Anal.

1988, 12 (7), 419.

92

14. Kim, D.-J.; Kwon, H.-C.; Kim, H. P., Effects of the solution temperature and the ph on

the electrochemical properties of the surface oxide films formed on alloy 600. Corros. Sci. 2008,

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spectra. J. Phys. Chem. 1986, 90 (19), 4590.

25. Hurley, B. L.; McCreery, R. L., Raman spectroscopy of monolayers formed from

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93

32. Kim, D.; Jang, C.; Ryu, W., Oxidation characteristics and oxide layer evolution of alloy

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(4), 2244.

94

APPENDIX A: ACCELERATOR ON COPPER

Currently copper is used to make interconnects on microprocessors, particularly when

feature-filling is required because of its lower line resistance and better electromigration

performance as compared to Al.1 Bis(3-sulfopropyl)-disulfide (SPS) is an accelerator used to

promote bottom-up fill of features in the standard Cu acid plating bath by increasing the rate of

Cu deposition within features relative to that at the plane above the features.1-6

It consists of a

disulfide bridge and a sulfonate head group. It may bind to the Cu surface through the sulfide

group and can undergo reductive bond cleavage at the Cu surface. The sulfonate head group is

thought to repel suppressors and levelers (both work by increasing the overpotential of Cu

deposition and result in slow growth at the top plane of the chip) thus facilitating Cu deposition.

When used in conjunction with Cl-, SPS and is monomer mercaptopropane sulfonate (MPS) act

to reduce the overpotential for Cu deposition.1

There are many models under consideration to explain the accelerant effect of SPS.7-12

The curvature enhanced adsorbate coverage model (CEAC model) proposed by Moffat links the

kinetics determined from electrochemical experiments on planar electrodes to that of shape-

change simulations of feature filling correctly predicts the appearance of overfill bumps when

only a suppresser and accelerator complexes are present.13-14

Figure A.1 displays the SHINERS of a solution of 5 mM SPS, 2 mM KCl, 10 mM CuSO4

and 0.1 M H2SO4 on a Cu(111) electrode. At 0 V some peaks attributed to SPS are present,

however they are low intensity. As the potential is stepped to -0.4 V, the SPS as well as Cu-Cl

peaks increase in intensity. As the potential is stepped to -0.5 V the SPS peaks continue to grow

in intensity. At -0.6 V the SPS peaks exhibit a decrease in intensity.

95

Figure A.2 displays the SHINERS of a solution of 5 mM SPS, 2 mM KCl, 10 mM CuSO4

and 0.1 M H2SO4 on a Cu(100) electrode. At 0 V the SPS peaks are more distinguishable from

the background than in the Cu(111) case. As the potential is swept in the cathodic direction there

is a gradual increase in the intensity of all peaks, especially that of peaks A, D and K assigned to

Cu-Cl, a combination mode of CH-S stretch and S-O stretch, and a symmetric S-O stretch from

the sulfonate group respectively.

96

200 400 600 800 1000 1200 1400

O

NML

K

JI

H

GF

E

D

C

B

Raman shift/cm-1

0 V

-0.1 V

-0.2 V

-0.3 V

-0.4 V

-0.5 V

-0.6 V

Potential/

V vs

Ag/AgCl

A

Figure A.1. Potential dependent SHINERS of the cathodic sweep in an aqueous solution of 5

mM SPS, 2 mM KCl, 10 mM CuSO4 and 0.1 M H2SO4 on a Cu(111) electrode.

97

200 400 600 800 1000 1200 1400

ON

ML

K

JI

H

GF

ED

C

B

A

Raman Shift/cm-1

Potential/

V vs

Ag/AgCl

0

-0.1

-0.2

-0.3

-0.4

-0.5

-0.6

Figure A.2. Potential dependent SHINERS of the cathodic sweep in an aqueous solution of 5

mM SPS, 2 mM KCl, 10 mM CuSO4 and 0.1 M H2SO4 on a Cu(100) electrode.

98

Table A.1. Peaks and assignments for SPS near Cu.

Peak

Solid

SPS15

Cu(poly)

(0 V)15

Cu(111)

(-0.5 V)

Cu(100)

(-0.3 V) Assignments15

A

299 280 286 Cu-Cl

318

CH2 rock

353

SO3 scissor

B 461

432 436 SO3 scissor

511

S-S str

C 528 539 526 525 C-S(sulfonate) str

544

C-S(sulfonate) str

D 592

608 608 C-S(sulfide) str and S-O sr

D 644 632 619 619 Gauche C-S(sulfide) str

E 705 696 680 679

Trans C-S(sulfide) str and S=O

str

F 747 743 733 732 CH2 rock

G 799 805 792 792 C-S(sulfonate) str

H 860 859 842 843 C-C str

I 898

912 CH2 rock

J 960

953 SO3 str

1014

CH2 bend

K 1075 1030 1021 1025 S-O str

1137 1113

C-C-H bend

1175

C-C-H bend

L 1207 1241 1234 1240 Assym S=O str

1253

CH2 wag

M 1277 1272 1272 1271 CH2 scissor

1326

CH2 scissor

N 1353 1348 1343 1350 CH2 scissor

O 1430 1415 1415 1416 CH2 scissor

99

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Mechanism and quantification. IBM J. Res. Dev. 2005, 49 (1), 19.

15. Schultz, Z. D.; Feng, Z. V.; Biggin, M. E.; Gewirth, A. A., Vibrational spectroscopic and

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Electrochem. Soc. 2006, 153 (2), C97.

100

APPENDIX B: CARBON DIOXIDE ELECTROREDUCTION ON GOLD

As the end product of all combustion processes, CO2 is an abundant source of carbon. By

electrochemical reduction, it can be transformed into relevant - and lucrative - products such as

carbon monoxide, methanol and ethylene. These can be used as fuels or as feedstock materials

for pharmaceuticals and polymers1-6

. There are currently four problems impeding progress in

electrochemical CO2 reduction: (1) large overpotentials, (2) simultaneous production of

hydrogen along with CO2 reduction, (3) electrode poisoning with the concomitant decrease in

efficiency over time and (4) potentially a wide distribution of products.

The study of electrochemical CO2 reduction began with fundamental voltammatry

experiments using aqueous solutions on metals with high hydrogen overvoltages (e.g. Hg and

Zn) 7. These metals are able to reduce hydrogen at potentials much more negative than the

thermodynamic equilibrium potential and, thus, reduces the amount of hydrogen evolution.

Eyring proposed a mechanism for reduction at Hg electrodes based Tafel plots (Figure B.1)7.

The general understanding is that the reaction proceeds with two consecutive one electron

transfers. The first transfer creates a radical anion that pulls a proton from water and is then

Figure B.1. Proposed mechanism for reduction CO2 to formate.

101

further reduced with another electron to formic acid8. The multiple electron reduction products of

CO2 reduction (e,g, methanol and methane) thermodynamically favorable with equilibrium

potentials of around 0.1 V vs the reference hydrogen electrode (RHE) at pH 7 and 25 oC

3, 8-9.

Table B.1. Thermodynamic Equilibrium Values for CO2 Reduction10

.

Electrons Product Potential (pH 7, V vs RHE) ΔG (kJ mol-1

)

1 ·CO2-

-2.31 202.1

2 CO -0.104 19.9

2 HCOOH -0.018 38.4

4 HCOH -0.072 27.5

6 CH3OH 0.03 -17.3

8 CH4 0.17 -130.8

Reduction of CO2 has been attempted on most of the elements of the periodic table.

Unfortunately, there is no periodic trend for the efficiency of CO2 reduction; instead metals are

generally categorized by the products they produce8, 11

. Metals with high hydrogen evolution

overpotentials (Pb, Hg, Bi, and other heavy metals) form formic acid at relatively high faradaic

efficienty (but also high overpotentials due to the unstabilized CO2 radical anion). Metals with

moderate hydrogen overpotentials bind the CO2 and form carbon monoxide. However, since

hydrogen evolution has similar thermodynamic potentials, Faradaic efficiency (where the

product distribution contains mostly C products) is only achieved in nonprotic solvents or by

using additives which impede hydrogen evolution in protic solvents. Over time the reaction

efficiency of CO2 decreases. There are two theories of cause: continual deposition over time of

heavy metal impurities in the electrolyte12

, or the formation of a carbon layer from reduced

adsorbates that blocks catalytically active sites13-17

.

102

Spectroscopic studies have been performed to further elucidate the reduction mechanism

by identifying surface intermediates. Infrared (IRAS) and Raman (SERS) studies confirm the

presence of adsorbed CO on Cu, Ag, Pt, Pd and Ni18-31

. Oda et al. found that, in CO2 saturated

solutions of 0.1 M KCl, peaks attributed to carbon monoxide appear at around -1.4 V vs the

standard hydrogen electrode (SHE) on Cu and -1.0 V on Ag. Since chloride adsorbs strongly to

these surfaces, the CO2 only displaces the M-Cl bonds at potentials negative enough to repel the

Cl- ions. Studies have also been performed on these metals in 0.1 M KHCO3 which is a standard

electrolyte for CO2 reduction. They also had characteristic CO stretches and CO32-

stretches were

found on Cu.

In this chapter, we performed SERS of electroreduction of CO2 in basic carbonate

solutions to further elucidate the mechanism of CO2 reduction on Au. Figure B.2 displays the

potential dependent SERS spectra of 0.1 M K2CO3 sparged with CO2. At open circuit potential

there is a prominent peak at 1590 cm-1

attributed to water bending and a carbonate symmetric

stretching mode. As the potential is stepped in the cathodic direction, a peak at 2080 cm-1

attributed to CO stretch appears at -800 mV vs Ag/AgCl. The water bending mode exhibits a

slight decrease in intensity with more negative polarization of the Au electrode. When the

potential scan is reversed to the anodic direction, the CO peak decreases in intensity and

disappears by 400 mV. To further investigate the potential dependent behavior of the CO peak,

Figure B.3 displays the integrated peak height of the CO mode was plotted versus potential and

overlayed on the Au electrochemistry in CO2 saturated carbonate buffer.

Figure B.4 displays the potential dependent behavior of a D2O solution of K2CO3 sparged

with CO2. At open circuit potential, there are two prominent peaks attributed to the electrolyte,

one at 1200 cm-1

assigned to the D2O bending mode and one at 1360 cm-1

assigned to CO32-

. As

103

the potential is swept in the cathodic direction, a peak at 2080 cm-1

assigned to the CO stretch at

-1000 mV. It remains as the potential is swept to -1200 mV. On the reverse sweep the CO peak

persists until 400 mV after which it disappears. Figure B.5 overlays the CO peak intensity with

the cyclic voltammogram of Au in CO2 saturated 0.1 K2CO3 in D2O. The disappearance of the

CO peak coincides with an anodic desorption event at 0 mV in the voltammogram.

104

Figure B.2. Potential dependent SERS spectra of aqueous solution of 0.1 M K2CO3 bubbled with

CO2. Spectra offset for clarity.

1000 1500 2000 2500

Inte

nsity (

cp

s)

Raman shift (cm-1)

ocp

400

-400

-800

-900

-1000

-1100

1000 1200 1400 1600 1800 2000 2200 2400

Inte

nsity (

cp

s)

Raman shift (cm-1)

-1100

-1000

-900

-800

-400

0

400

105

-1.5 -1.0 -0.5 0.0 0.5 1.0 1.5

-700

-350

0

350

-20

0

20

40

60

Curr

ent D

ensity (

mA

cm

-2)

Potential (V vs Ag/AgCl)

Peak H

eig

ht (c

ounts

per

second)

cathodic

anodic

CO peak height

Figure B.3. Cyclic voltammagram of Au electrode in aqueous solution of K2CO3 sparged with

CO2 overlayed with peak height versus potential of CO peak.

106

1000 1200 1400 1600 1800 2000 2200 2400

Inte

nsity (

cps)

Raman shift (cm-1)

ocp

400

0

-400

-800

-900

-1000

-1000

-1100

-1200

1000 1200 1400 1600 1800 2000 2200 2400

Inte

nsity (

cp

s)

Raman shift (cm-1)

-1200

-1100

-1000

-900

-800

-400

0

400

Figure B.4. Potential controlled Raman spectra of D2O solution of 0.1 M K2CO3 sparged with

CO2. Spectra offset for clarity.

107

-1.5 -1.0 -0.5 0.0 0.5 1.0 1.5-150

-100

-50

0

50

2

4

6

8

Curr

ent D

ensity (

mA

cm

-2)

Potential (V vs Ag/AgCl)

Peak H

eig

ht (c

ps)

Cathodic

Anodic

Figure B.5. Cyclic voltammagram of Au electrode in D2O solution of K2CO3 sparged with CO2

overlayed with peak height versus potential of CO peak.

108

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