This document summarizes research on depositing electrostatic copper nanoparticle films. Key points: 1) Copper nanoparticle films can be deposited at low temperatures using an electrostatic coating process with ligandless nanoparticles and an ionic liquid charge compensator. 2) Continuous and conductive copper nanoparticle films form when the ionic liquid concentration is between 2.1-2.4 mM, as this concentration increases interparticle interactions and bulk-like behavior. 3) Ellipsometry analysis shows the films have a polydisperse nanoparticle structure with increased ultraviolet absorption and particle interactions at optimal ionic liquid concentrations.

1. Electrostatic Coating with Ligandless
Copper Nanoparticles:
Films, Surfactant Concentration, 3D Deposition
AVS-62, San José, CA
October 22, 2015
Lance Hubbard & Anthony Muscat
Department of Chemical & Environmental
Engineering
University of Arizona
Tucson, AZ 85721

2. Nanoparticles, Thin Films, Features
2
Substrate
Cu NP Film
Metallic Nanoparticles (NPs): Low
Temperature Metallization
Electroless Thin
Film Plating
Spectroscopy

3. 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 compensator
3
NP SEM Surface:
Cu NPs Bath
Coated Film:

4. Ligands and Charge Compensators
4
Ligands: Charge Compensator:
3.1±1.6 nm
Diameter

5. 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

6. TEM Bath Coated Cu Films
6
Ionic Liquid Added
Substrate
Cu NP Film
Control, No Ionic
Liquid Added
Substrate
Cu NP Film
Grain
Void

7. Light Absorbance vs. Ionic Liquid Conc.
7
Discontinuous Films
Continuous Films

8. Photoluminescence vs. IL Conc.
8

9. Bulk Conductivity
9
Electrical Conductivity of Films vs. Ionic
Liquid Concentration

10. 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 roughness 10
Si (1 mm)
SiO2 (16.8 Å)
APTMS (7.6 Å)
Cu NPs + Void EMA (Variable)
(not to scale)

11. 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

12. EMA Fractions and Depolarization:
Interparticle interactions
12

13. 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

14. 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

15. Other Work: 3D Feature Deposition
15

16. Metallized Flexible-Bendable Substrates
Paper
Only:
Paper
CuNP
Film
CuNP
Reagents:
Cu NP/Wax Paper Film Sintered:
16

17. Acknowledgements
• Armando Luna
• LAM Research
• Sandia National Labs
• UA University Spectroscopy and Imaging
Facility
• Thank You for Your Time
17

18. Backup Slides
18

19. 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

20. Cross Section SEM and Ellipsometry
20

21. Other Ellipsometry Parameters
21

22. Ellipsometry Parameters
22

23. Synthesis and Characterization
23
No I.L.
I.L.
3.5±2 nm
15±7 nm

24. UV-Vis vs. IL Conc.: Max Abs. at
2.1-2.4 mM IL Conc.
24

25. Positive Charges on Substrate Influence
Film Formation
25
0.92
0.91
0.90
0.89
0.88
0.87
cos(AverageContactAngle)
12111098
pH

26. Glass and Amine Termination is
Influenced by Initial pH of Substrate
26
Cu NPs on Glass: Cu NPs on Amine-Glass:

27. Increasing Sinter Temperature Degrades
Amine Termination but not Ionic Liquid
27

28. SEM Bath Coated Cu Films
28
a
b
c
d
• Sinter reduces film
thickness
• Same interparticle
distance

29. 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:

30. 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
2
4
6
8
10
12
14
16
18
20
22
24
Run 3 (~6min Air)
Run 2 (~3min Air)
Run 1
DLS Relative Count vs. Particle Diameter of CuNPs
Count(%)
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
DLSRelativeIntensity(%)
Diameter (nm)

31. 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 200
o
C
Cycle 1
Cycle 5
Cycle 4
Cycle 3
Cycle 2
Absorbance
Wavelength (nm)

32. 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:

33. 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: