A Study of Electrophoretic Deposition (EPD) of Carbon Nanotubes on Insulator Substrates

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 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 Synthesis: Direct Growth Arc Discharge (Prof. Ijima,1991) 2. Laser Ablation (Prof. Smalley, Rice University) 3. Chemical Vapor Deposition (CVD) Single-walled carbon nanotubes (SWCNTs) • Single sheet of graphene rolled as a cylinder Multi-walled carbon nanotubes (MWCNTs) • Multiple sheets of graphene rolled into concentric cylinders http://www.futuretimeline.net/21stcentury/images/carbon-nanotube-2040.jpg http://jnm.snmjournals.org/content/48/7/1039/F1.large.jpg

4. Solution-Based Deposition Techniques • State-of-the-art techniques: • Spray Coating • Inkjet Printing • Drop Casting • Spin Coating • Dip/Rod Coating • 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 Used with Permission http://spie.org/Images/Graphics/Newsroom/Imported/0969/0969_fig1.jpg

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 Gate Dielectric Source metal 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 • 2ndround of APTES treatment on the drop casted CNTs • Dispersion of acid-refluxed CNTs in IPA (EPD Solution) • Electrophoretic Deposition • Applied voltage: 100-150 V for 3 minutes APTES*- 3-Amino propyl tri ethoxy silane

8. Process Recipes:

9. Experimental Results 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: ~500-600 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(2011-14) -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).