Fundamental Study of Nano-Scale Adhesion and Friction Properties of Graphene in Ambient Air and Liquid Environments

Fundamental Study of Nano-Scale Adhesion and Friction Properties of Graphene in Ambient Air and Liquid Environments Sai Suvineeth Ramayanam The aim of this study is to understand the fundamental tribological interactions of model contacts developed between a ‘single’ asperity silicon tip and a few layer graphene surface in ambient air, ionic liquid, and lubricating oil environments. The motivation to investigate such fundamental interactions stems from the need to gain an understanding of the tribological properties, morphology and defects of few layer graphene with respect to different synthesis methods including both bottom-up and top-down approaches. In particular, the surface properties of atomically thin sheets of graphene synthesized by three methods; (i) liquid phase exfoliation of graphene, (ii) chemical reduction of exfoliated graphene oxide, on a silicon oxide substrate, and (iii) graphene synthesis by halogen based plasma etching on a silicon carbide substrate are studied using atomic force microscopy, lateral force microscopy and x-ray photoelectron spectroscopy. Friction of Si ‘single’ asperities sliding against a few layer graphene surface in ambient air, ionic liquid, and lubricating oil environments is reported. It is found that oxygen based defects play a major role in controlling the friction and adhesion properties of few layer graphene surfaces. The role of substrate and its bonding with the few layer graphene is also an important parameter. In liquids, we report a newly observed Stribeck like behavior in the nanoscale. This work can lead to important device applications with reduced friction such as contact-based microelectromechanical systems. It also sheds light on liquid-graphene interfacial characteristics which can be proved vital in applications spanning from electrochemical energy devices to nanolubricants. ACKNOWLEDGEMENTS I wish to express my sincere gratitude towards Dr. Kostas Sierros for agreeing to be my research advisor and for his relentless support in guiding me through the trials and tribulations of graduate research. His extensive knowledge in the fields of material science and tribology was of utmost help throughout my research. His knowledge, enthusiasm and pursuit for excellence have inspired me beyond measure. I am extremely grateful to him for providing me with the opportunity to work with him. My sincere appreciation and respect goes to Dr. Charter Stinespring, who provided me with the inputs on the topic of research and invaluable guidance and supervision throughout my research work. I thank him for letting me use his laboratory facilities and for other technical aspects related to my work. I thank Dr. Stephen Kukureka for being part of the committee and providing inputs with his expertise on the subject. I thank Nick Morris, Saurabh Chaudhari, Dr. Aaron Kessman and Sean Cronin for their invaluable contributions to this thesis study. I acknowledge the support of my labmates Derrick Banerjee, Maria Torres, Deji Abidakun, Mark Shoukry, Jacob Cordonier and all the undergraduates of the FEST group for their contributions and camaraderie. Finally and most importantly, I express my sincere gratitude to my parents Narayana Murthy Ramayanam, Padmaja Ramayanam and my sister Samanvitha Ramayanam for their unconditional love, support, motivation and belief in me without which this thesis would not have been possible.