Nanotribology of Hydrogenated Amorphous Silicon: Sliding-Dependent Friction and Implications for Nanoelectromechanical Systems

Silicon-based materials are widely applied in micro- and nanoscale devices, such as micro- and nano-electromechanical systems (MEMs and NEMs, respectively). However, the nanofriction behavior of such materials is still an issue that influences or hinders some applications. Recently, a sliding-dependent friction mechanism was accessed, by simulation of hydrogenated silicon surfaces, in which friction forces increase during sliding. The experimental evaluation of this phenomenon is still lacking, as well as the confirmation of such a behavior in ambient air conditions, related to the current application. Here, the nanotribology of hydrogenated amorphous silicon (a-Si:H) was experimentally studied under repeated scanning. As an overall analysis, friction increases during sliding, without wear. After separation and new contact, the friction force recovers an intermediate value and increases again, until reaching an intermediate steady state. The mechanism may be related to the successive creation and breaking of bonds at the interface. When the contact is ceased, the dangling bonds created at both surfaces after separation may be repassivated. Moreover, the relationship of this behavior with the photoactivity of the material was tested. If an external light source is added during the scanning, it only changes the results before the stabilization of the interface. This detailed experimental study might promote the broader nanoapplication of the material, addressing the current failures and suggesting new devices based on the anomalous behavior.