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Scanning Electrochemical Microscopy (SECM) Informational Meeting

June 6th 2018 SEAS Research Equipment Assistance Program (REAP)

“Host” PI’s: D. Esposito and Y. Yang

Superuser: Anna Dorfi

Meeting Outline

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I. What is SECM, and what can it be used for?

II. Imaging Modes with 3 Examples

III. CHI 920D – Capabilities and limitations

IV. Training, Fees, & other logistics

What is SECM?

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SECM: a scanning probe microscopy (SPM) technique that utilizes an electrochemical probe (“ultramicroelectrode” (UME) or tip ) to measure the physical and/or chemical properties of an interface.

• Largely credited to Bard and coworkers in 1989.

• Can generate images with quantitative information about spatial variation in:

-chemical reaction rates -topology -conductivity -surface coverages in addition to being used for.. -surface patterning -measuring rxn rate constants -High-throughput screening -much more….. Solid sample

or substrate

d= tip/substrate separation distance

a= tip radius

2a

O R

e-

e- active metal

insulating sheath

Common SECM Imaging Mode: “Feedback Mode”

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Psuedo steady state diffusion limiting current:

“negative feedback” “positive feedback” Tip current at infinite distance from sample

d d

d= Tip/substrate separation distance

a= probe radius D=diffusion coef. of O c=concentration of O

(-) (-)

(+)

Example #1: Imaging a catalytic disc electrode

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Optical Image of 150 μm Pt disc.

150 μm

Imaging Conditions: Electrolyte: 1 mM H2SO4 in 0.1 M Na2SO4 , UME Radius: ≈1.5 µm, Scan Height = ≈ 3 µm. Tip potential: 0.6 V vs Ag|AgCl, Substrate Potential: -0.7 V vs Ag|AgCl.

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Inert Si++ substrate

1 mM H2SO4 electrolyte 2H+ H2

e-

e-

SECM image of Pt disc electrode at right.

inert substrate

catalytic Pt disc

Side-view of constant-height SECM imaging in feedback mode using the H+/H2 redox couple.

catalytic disc

probe scan path

EUME=+0.6 V Ag|AgCl

ESubstrate=-0.7 V Ag|AgCl (-)

(+)

SECM Approach Curve

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SECM Approach curves can be used for quantitative determination of local reaction kinetics.

Normalized rate constant

k=heterogeneous electron transfer rate constant.

Approach curves for different normalized reaction rate constants.[1]

Ref.: N. Ritzert, H. Abruna, Langmuir, 29 (2013), 1683-1693.

7 [1] Polcari et. al. Chem. Rev. 2016, 116, 13234−13278

What is SECM used for?

List of fields and applications of SECM.[1]

Key Advantages • High resolution imaging

technique. • Quantitative information

about local reaction kinetics.

• Unique chemical imaging modalities.

• Capable of In situ imaging in the liquid environment.

Generic SECM Instrument

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Schematic of an SECM setup

Polcari et. al. Chem. Rev. 2016, 116, 13234−13278

Cell

SECM: Probes

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• SECM spatial resolution is strongly dependent on probe dimensions.

• Many studies use “ultra-microelectrodes” (UMEs) with probe diameter <25 μm

• Nanoelectrodes are also possible, with nanoprobes down to ~ 3 nm used for high resolution SECM imaging.

• Materials for electroactive metal:

• Platinum (74%), carbon (10.8%), gold (9.5%), mercury (2.1%), and silver (1.7%)

Polcari et. al. Chem. Rev. 2016, 116, 13234−13278

~ 4 cm

CH Instruments 10 um diam. Pt UME for SECM imaging.

Two Common Amperometric Imaging Modes

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I. Tip Generation, Substrate Collection

(TG/SC mode)

II. Substrate Generation, Tip Collection

(SG/TC mode)

Ref.: P. Sun, M. Mirkin, “SECM in the 21st Century”, Phys. Chem. Chem. Phys., 2007, 9, 802–823.

CO,b CR,b

11 http://www.chinstruments.com/chi900.shtml

Lots of possibilities!!

Example #2: Monitoring Biochemical Processes

12 Ref.: Takahashi, Y.; Miyamoto, T.; Shiku, H.; Asano, R.; Yasukawa, T.; Kumagai, I.; Matsue, T. Electrochemical Detection of Epidermal Growth Factor Receptors on a Single Living Cell Surface by Scanning Electrochemical Microscopy. Anal. Chem. 2009, 81, 2785−2790

SECM is also used in imaging and studying the uptake or release of chemical species from a surface, including processes in biological cells.

epidermal growth factor receptor

Microelectrode

SGTC mode

SECM imaging of EGF-triggered endocytosis, in which EGF induces entrapment of EGFR in the cell membrane.

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Example #3: Measuring local Ion Transport through membranes

Ref: M. Shen, S. Amemiya, et al., “Quantitative Imaging of Ion Transport through Single Nanopores by High Resolution SECM”, JACS, 134 (2012), 9856-9859.

TEM image of porous nanocrystalline (pnc) silicon membrane.

SECM image of ion flux through pnc Si membrane. The electroactive species was tetrabutyl-ammonium (TBA), which diffused through the nanopores and was detected at a Pt electrode within a nanopipette probe.

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Example #4: Charge transfer kinetics at vdW materials

[1] A. Guell, P. Unwin, et al. ACS Nano 2015, 9, 3558-3571

AFM image of exfoliated graphene on Si /SiO2 substrate[1]

SECCM image measured with 5 mM Ru(NH3)6

3+ at E=-0.46 V Ag|AgCl[1]

SECM Resources

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1. Good introduction: Bard & Faulkner. “Scanning Probe Techniques”, in Electrochemical Methods. 2nd Ed., Section 16.4, pp. 669-677.

2. More detailed overview: F. Fan, J. Mauzeroll, et al. “Chapter 12: Scanning Electrochemical Microscopy”, in Handbook of Electrochemistry, Elsevier, 2007, 471-540, XII-XIII.

3. SECM Review Articles: • P. Sun, M. Mirkin, “SECM in the 21st Century”, Phys. Chem. Chem. Phys., 2007, 9, 802–823.

• C. Zoski, “Advances in SECM”, J. Electrochem. Soc., 163 (4) H3088-H3100 (2016)

• SECM for energy applications: P. Bertoncello, Energy & Environ. Sci., 3 (2010), 1620-1633.

• SECM for Biological applications: S. Amemiya, et al., Analytical and Bioanalytical Chemistry 386 (2006), 458–471.

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Reference Electrode

Probe (tip)

Counter Electrode

Sample connection

[1] http://www.chinstruments.com/chi900.shtml

CHI 9200 SECM

Cell

Z-positioner

Optical (air) table

SECM sample cells

CHI 9200 SECM- Specifications & Limitations

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• Scanning capabilities w/ closed loop positioners:

• Minimum X,Y,Z step size: 1.5 nm

• Maximum X,Y,Z scan lengths: 50 mm

• CHI bipotentiostat (2 working electrodes)

• Measured current accuracy down to 0.1 pA (min. res. 0.3 fA)

• Impedance analyzer for EIS and impedance mapping.

• Compliance voltage: ±13 V

• Sample, electrolyte, & scanning restrictions:

• Roughness >> desired resolution is very challenging

• Samples must be stable in electrolyte (unless studying corrosion!)

• Electrolytes must be air-stable & safe for use in open lab

• Max scan speed is typically a couple probe radii per second

Logistics Training

• Users: Ph.D. and postdocs. Exceptional UG or MS may be considered. • Attend general demo / overview of instrument (email

columbiasecm@gmail.com ) • Read through SOP/manual and take short quiz. • 1-on-1 training with certified user. • Final certification by super user (use instrument to generate an image), who

will email Ariel Sanchez (aes2307@columbia.edu ) to grant lab access. • Submit SECM new user form to rb3230@columbia.edu before independent

use.

Usage / Reservation • Instrument must be reserved through a google calendar. • Manual sign-in on notebook next to instrument. • SOPs, forms, analysis files, etc. available on shared google drive folder.

User fees • Initial user fee rate of 30 $/hr. (Based on recovering SECM cost over 10 yrs) • Pi’s will be emailed by ChemE admin. staff once every 3 mo.’s to ask for

approval of a list of charges incurred by group members.

Logistics : Supplies

• Probes / electrodes • Miniature Ag|AgCl reference electrodes & Pt counterelectrodes provided. • 10 um diam. Pt UMEs: supplied for training & general use. (~$120 /ea.) • 1 um or 5 um diam. Pt UMEs: Available through Sensolytics. (~ $215/ea.) • 12 um, 25 um diam. Au UMEs: available through CH Instruments. • Nanoscale probes: You can use our pipette puller (no fee).

• Chemicals • Two standard redox couples will be kept in stock (FFC, Ferrocenemethanol),

with 18 MΩ DI water available in the lab. • Any other chemicals must be approved by the super user; no chemical

storage is available within the lab (take-in / take-out policy). • Access to fume hood will be available.

• Test cells • Standard teflon test cell is freely available • Custom cell may be necessary (different sample size, etc.)

[1] https://www.sensolytics.de/en/products/microelectrodes/58-ultramicroelectrodes-platinum.html [2] http://www.chinstruments.com/accessories.shtml

Probes for SECM

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• Fabrication of UMEs or nanoelectrodes.

Laser heated pipette during UME fabrication.

Source: Sutter Instruments

Laser pipette puller (Sutter P-2000) located in the Esposito Lab.

• Nanoelectrodes made with a laser pipette puller have been demonstrated with probe diameter down to ≈6 nm.[1] (not easy!)

• See review article on nanoelectrodes.[2]

[1] Sun, Mirkin, et al., Angew. Chemie Int. Ed., 53, (2014), 14120-14123. [2] Cox, Zhang, et al., Annual Review of Analytical Chemistry, 5 (2012), 253-272.

Closing Thoughts…….

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• SECM has a lot of powerful / unique capabilities that are of interest to a wide range of scientific fields and applications

• but……there is a learning curve (have patience!)

• Knowledge of electrochemistry helps (but not required).

• Plan 1-2 session to understand basic e-chem properties.

• Not all projects/samples are equal…

• Smooth sample, microscopic features, simple chemistry…

• Sample roughness, nanoscopic features, exotic chemistry, advanced imaging modes….. have patience!

• Keep in mind for future proposals

•Spread the word to others!

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Questions? Suggestions?

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•Extra Slides

Background:

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Scanning Electrochemical Microscopy:

• A scanning probe technique that examines:

- Surface Reactivity, processes at solid/liquid or liquid/liquid interfaces, Redox reactions and kinetics involving active species, etc.

Polcari et. al. Chem. Rev. 2016, 116, 13234−13278

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SECM: Procedures

1. Characterize the reaction of interest in your system and mode of operation (i.e. determination of applied potentials, etc.) 2. Perform an approach curve - Sets distance for scanning measurements 3. Set 2D area for measurement of sample - Set scan step size, etc. 4. Analyze signal

Inert

Electroactive features

High Low