Atomistic Simulations of Tribological Properties of Ultra-Thin Carbon Nanotube Films on Silicon

Molecular dynamics simulations are used to study relationships between material morphology, adhesion, and sliding friction in carbon nanotube (CNT) coatings at the nanoscale. Two controlled quantities, CNT chirality and vacancy defects, are found to have significant effects on CNT coating adhesion to Si surfaces and sliding friction in turn. For example, using free energy calculations, a CNT of chirality (10,0) with a corresponding diameter of 7.777 Å was observed to have an adhesion energy-per-unit-length of approximately three-times that of a CNT with (5,5) chirality and corresponding diameter of 6.732 Å. Simulations of aligned carbon nanotube arrays containing various vacancy defect densities in sliding contact with Si substrates were also performed. Friction and wear were shown to increase with defect density. Similar studies are underway to investigate how other characteristics of CNTs in addition to chirality, such as CNT length distribution and defect concentration, affect adhesion and friction in CNT-Si coatings. Outcomes may shed light on fundamental principles governing, for example, sliding interfaces in micro- and nano-electro-mechanical and other tribological systems.