1. A Study of Electrophoretic Deposition (EPD) of Carbon Nanotubes on Insulator Substrates
Jared DeSoto, Anirban Sarkar, and Theda Daniels-Race
Applied Hybrid Electronics Materials & Structures (AHEMS) Laboratory
Division of Electrical and Computer Engineering
School of Electrical Engineering and
Computer Science
Louisiana State University and A&M College, Baton Rouge, LA 70803
Bottom right corner: SESAPS 2013
SESAPS, 2013

2. Table of Contents Carbon Nanotubes: Introduction and Synthesis
Solution-Based Deposition Techniques
Electrophoretic Deposition
Fundamentals
Benefits
Research Motivation
Experimental Procedure
Process Recipes
Experimental Results
Conclusions and Future Work

3. Carbon Nanotubes (CNTs): Introduction and Synthesis
Single-walled carbon nanotubes (SWCNTs)
Synthesis:
Direct Growth
Arc Discharge
(Prof. Ijima,1991)
2. Laser Ablation
(Prof. Smalley, Rice University)
3. Chemical Vapor
Deposition (CVD)
Single sheet of graphene rolled as a cylinder
Multi-walled carbon nanotubes (MWCNTs)
Multiple sheets of graphene rolled into concentric cylinders

4. Solution-Based Deposition Techniques
Benefits:
Economical set-up
Room temperature processing
Low cost
Simple apparatus
Solution based deposition
Choice of solvents for dispersion
Deposition of purified materials
Control of deposition parameters
Fast processing time
No vacuum
Potential to scale-up for mass production
Plastic and low temperature printing technologies
State-of-the-art techniques:
Spray Coating
Inkjet Printing
Drop Casting
Spin Coating
Dip/Rod Coating
Add pictures for maybe spray coating and inkjet printing
Used with Permission

5. Electrophoretic Deposition (EPD): Fundamentals and Benefits
Two step process:
Electrophoresis:
Particle migration under electric field
Deposition:
Particle coagulation on the depositing electrode
Benefits of EPD:
Simple experimental set up/ no vacuum
Fast processing, high yield
Applicable to any powdered solid that forms a stable suspension
Better surface coverage
Control of deposition thickness
Single-step processing
Possibility to scale up for large-scale applications
Schematic of EPD

6. Challenge and Research Motivation
EPD of CNTs
Predominantly performed on conducting substrates e.g. Al, Cu, ITO and conducting polymers
CNT-based thin film transistors
Deposition necessary on gate dielectric films (SiO2, polyimide, Al2O3)
Drain metal
Source metal
Gate Dielectric
Semiconducting CNT networks
Research Objective:
Study of Electrophoretic Deposition of CNTs on insulator (glass) substrates

7. Experimental Procedure
Pre-cleaning of glass substrates by piranha treatment
Surface functionalization by organosilane 20% APTES*
Acid treatment of CNTs ( H2SO4:HNO3=3:1)
Ultrasonic dispersion of CNTs in water (H2O): EtOH=1:1
Controlled drop casting of CNTs
2nd round of APTES treatment on the drop casted CNTs
Dispersion of acid-refluxed CNTs in IPA (EPD Solution)
Electrophoretic Deposition
Applied voltage: V for 3 minutes
APTES*- 3-Amino propyl tri ethoxy silane

8. Process Recipes: Recipe A Recipe B Recipe C Piranha treatment – 1 hr.
20% APTES- 1 hr.
Drop casting
Solvent: H2O: EtOH=1:1
2% APTES- 1 hr.
EPD voltage: 150 V
Dep. Time: 3 min
EPD voltage: V
Film Thickness: ~2.0µm
Film Thickness: ~1.8µm
Film Thickness: ~3.4µm

9. Experimental Results Appreciable surface coverage
Drop casted
CNTs
EPD coated CNTs
1 cm
Optical images of the EPD coated CNTs on drop casted layer of CNTs
SEM image of the EPD coated films
Appreciable surface coverage
No microscopic voids in the film morphology

10. Experimental Results Raman Spectroscopy
Thickness and Surface Roughness
KLA Tencor Alpha Step results:
Average film thickness: ~2-2.5 µm
Average surface Roughness: ~ nm
Absence of radial breathing modes (RBM)
Disordered induced D-band (~1300 cm-1)
Tangential G-band (~1600 cm-1)

11. Conclusion and Future Work
First time study of EPD of CNTs on glass (insulator) substrates
Use of CNTs (drop casted) to deposit thick CNT films by EPD
Characterization of the deposited films ( SEM, Raman, Alfa Step data)
Future work:
Use of semiconducting CNTs
Use of competing deposition techniques e.g. spray coating, inkjet printing to obtain the initial CNT coating
CNT EPD on sputter coated silicon dioxide (SiO2), silicon nitride (SiN) films
Device Fabrication

12. Acknowledgements
This work was funded in part by the Louisiana Board of Regents (LEQSF( ) -RD-A-07), NASA (2011)-DART-44, the generous support of Dr. Kristina Johnson, and the AES Corporation. We are also grateful for the use of the Electronic Material and Device Laboratory within the Division of Electrical & Computer Engineering (LSU).