Electrostatic Coating with Ligandless Copper Nanoparticles:

Films, Surfactant Concentration, 3D Deposition

AVS-62, San José, CAOctober 22, 2015

Lance Hubbard & Anthony MuscatDepartment of Chemical & Environmental

EngineeringUniversity of Arizona

Tucson, AZ 85721

Nanoparticles, Thin Films, Features

2

Substrate

Cu NP Film

Metallic Nanoparticles (NPs): Low

Temperature Metallization

Electroless Thin

Film Plating

Spectroscopy

Conductive Copper Nanoparticles • Cu NP film

• Electroplating seed layer

• Atmospheric pressure and lower temperatures

• Nanophase reduces sinter temp. by ↑ surface energy

• Suspended Cu metal

• Cu NPs oxidize quickly = not conductive

• Ligands (mol. bound to surface)

• Lowers conductivity

• Ionic liquid charge compensator3

NP SEM Surface:

Cu NPs Bath

Coated Film:

Ligands and Charge Compensators

4

Ligands: Charge Compensator:

3.1±1.6 nm

Diameter

5

Approach to Deposit Blanket Films

SiO2

Pt Pt PtPt PtPt

Example Conventional Process:

(not to scale)

Electroless Coating Process:

SiO2

Diffusion Barrier

7 Å Amine

Terminated

Layer

TEM Bath Coated Cu Films

6

Ionic Liquid Added

Substrate

Cu NP Film

Control, No Ionic

Liquid Added

Substrate

Cu NP Film

Grain

Void

Light Absorbance vs. Ionic Liquid Conc.

7

Discontinuous FilmsContinuous Films

Photoluminescence vs. IL Conc.

8

Bulk Conductivity

9

Electrical Conductivity of Films vs. Ionic Liquid Concentration

Ellipsometry Model: Oscillators• Woollam’s copper Palik layer

• Infrared: Lorentz

• Visible: Tauc-Lorentz

• Ultra Violet: Tauc-Lorentz

• Ultra Violet: Gauss

• Nanophase Cu response

• Alter strength/width oscillators

• Nanophase/polydisperse

• Effective medium Approximation

• Voids/ion shell

• Surface roughness10

Si (1 mm)

SiO2 (16.8 Å)

APTMS (7.6 Å)

Cu NPs + Void EMA (Variable)

(not to scale)

X-Section High Angle SEM: Void Increase vs. IL Conc.

11

0.5 mM

2.1 mM

4.3 mM

5 µm

5 µm

5 µm

EMA Fractions and Depolarization: Interparticle interactions

12

Ellipsometry: Polydisperse NPs and Increased Particle Interactions

13

• 2.1-2.5 mM:

• Increased

• Light absorbance

• Photoluminescence

• Conductivity

• Ellipsometry

• Polydisperse NPs

• Increased UV intensity

• Particle interactions

• Bulk like behavior

Conclusion• Thin blanket Cu NP

films

• Smooth layers

• Electroplating seed

• Ionic Liquid Conc.

• 2.1-2.4 mM

• Interparticle Interactions

• Increased Abs, PL, conductivity

14

Substrate

Cu NP Film

Other Work: 3D Feature Deposition

15

Metallized Flexible-Bendable SubstratesPaper

Only:

PaperCuNP

Film

CuNP

Reagents: Cu NP/Wax Paper Film Sintered:

16

Acknowledgements

• Armando Luna

• LAM Research

• Sandia National Labs

• UA University Spectroscopy and Imaging Facility

• Thank You for Your Time

17

Backup Slides

18

X-TEM: ≤3 nm Dia. Nanoparticles

19

1.9 mM

2.4 mM 4.3 mM

20 nm

20 nm 20 nm

≥ 3 nm Dia.

2.1 mM20 nm

≤ 3 nm Dia.

Cu NPs

SiO2/APTMS

Si

Cross Section SEM and Ellipsometry

20

Other Ellipsometry Parameters

21

Ellipsometry Parameters

22

Synthesis and Characterization

23

No I.L.

I.L.3.5±2 nm

15±7 nm

UV-Vis vs. IL Conc.: Max Abs. at 2.1-2.4 mM IL Conc.

24

Positive Charges on Substrate Influence Film Formation

25

0.92

0.91

0.90

0.89

0.88

0.87co

s(A

ve

rag

e C

on

tact

Ang

le)

12111098

pH

Glass and Amine Termination is Influenced by Initial pH of Substrate

26

Cu NPs on Glass: Cu NPs on Amine-Glass:

Increasing Sinter Temperature Degrades Amine Termination but not Ionic Liquid

27

SEM Bath Coated Cu Films

28

a

b

c

d

• Sinter reduces film thickness

• Same interparticle distance

SEM of Bath Coated Cu Films

• Sinter reduces irregularities in the Cu NP film

• Regularities do not expose underlying silica substrate

• Partial explanation to the decrease in film thickness seen in SEM

29

Substrate Void

ELD film 20oC N2 1hr: ELD film 200oC N2 1hr:

Copper Nanoparticles: Oxidation

• Improved particle oxidation from minutes to months

• Changed solvent from diphenyl ether to ethylene glycol

• Added µL amounts of ionic liquid as a charge compensator

• Enabled Cu NPs stable in ambient instead of nitrogen

30

0 100 200 300 400 500 600

2468

1012141618202224

Run 3 (~6min Air)

Run 2 (~3min Air)

Run 1

DLS Relative Count vs. Particle Diameter of CuNPs

Co

un

t (%

)

Diameter (nm)

0 5 10 15 20 25 30

0

5

10

15

20 Diameter Increase

Oxidation Initial DLS

After 1 Wk Air

After 2 Wks Air

After 3 Wks Air

DLS Count vs. Particle Diameter for CuNPs

in Ethylene Glycol Over 3 weeks

DLS

Rela

tive Inte

nsity (

%)

Diameter (nm)

Solution Cycle Coating of Cu NPs• Copper particles concentrate

• Mix with ethanol (EtOH), centrifuge 30min; repeated 3X

• Silica substrates prepared with MPTMS

• Increasing Cu NP SPR response

• 1st 4 cycles

• Cycle 5 response decreases

• Substrates dipped for 1 hr in Cu NP/EtOH solution

• Cleaned with EtOH between steps

• Dipped in ethane dithiol for 1 hr

• Repeated 5X

31

500 550 600 650 700

0.00

0.01

0.02

0.03

0.04

CuNP Film Response Increasing with Cycles

Up to Cycle 4, Decrease in Response at Cycle 5

CuNPs

UV-Vis Absorbance vs. Wavelength for CuNP Cycle Coat

on Glass 1mol% EDT 0.17mg/mL CuNPs in EtOH each

1hr Each EtOH wash Between, 10min Sinter FG 200oC

Cycle 1Cycle 5

Cycle 4

Cycle 3

Cycle 2

Ab

so

rba

nce

Wavelength (nm)

Reaction Coating: Alternate Substrates

• Reaction Coating

• Films form on positively charged substrate surfaces

• Metals

• Polymers

• Molybdenum

• ~80% conductivity of bulk Cu

• Steel

• ~20% conductivity of bulk Cu

• Reaction coating is applicable to multiple materials

32

Cu NPs on Moly:Molybdenum:

Cu NPs on

Steel:

Cu NP Film on

Biopolymer:

Reaction Coat Cu NPs on Biopolymers: Polysaccharide (i.e. Copy Paper)

• Paper reaction coated with Cu NPs

• Formed ~micron scale film

• Appears uniform on outer surface

• Little island growth seen upon sintering

33

Paper:160oC

EG Only:

Paper

Paper:160oC

Cu NP Reagents:

Cu

NP

Film

Cu NP/Paper Film Sintered

200oC ,N2, 30min: