Sliding friction at multi-asperity silicon interfaces

Sliding friction, the force resisting the relative motion of two contacting bodies, is a ubiquitous yet often overlooked concept in our daily lives, and plays a crucial role in numerous natural and industrial interfaces. Over the past centuries, significant efforts have been devoted to exploring friction through both experimental and theoretical approaches. Despite these efforts, achieving a quantitative understanding of macroscopic friction at multi-asperity interfaces remains elusive. This complexity arises from the interplay of factors such as multi-scale roughness, tribochemistry, contamination, adhesion, and possible interactions between individual asperities. Particularly, measuring adhesion in these interfaces is challenging due to elastic energy release during unloading, a phenomenon also known as the adhesion paradox. Moreover, the extended macroscopic interfaces, consisting of a myriad of single asperities, remain hidden by the bulk of the contacting bodies, further complicating the direct observation of contact phenomena. In this thesis, we aim to achieve a quantitative understanding of macroscopic friction and demonstrate how the friction at larger, application-relevant interfaces emerges from the friction at atomic, single-asperity scale interfaces. Specifically, we focus on tracing how the surface roughness-scale adhesive interaction, including capillary adhesion and electrostatic adhesion, interfacial covalent bonding, interfacial local normal pressure distribution, and sliding velocity influence the macroscopic sliding friction at silicon-on-silicon interfaces. Our study provides new insights into the fundamental understanding of multi-asperity friction, thereby opening up new avenues for predicting and controlling friction at application-relevant scales.