Temperature Activates Contact Aging in Silica Nano­contacts​​

Understanding the time evolution of contact strength in silica nano­contacts is of great funda­mental and practical relevance in diverse areas like earth­quake dynamics, wafer bonding mecha­nisms, as well as MEMS applications. The loga­rithmic increase of contact strength with hold time, termed contact aging, can be "quanti­tative" due to defor­mation creep in plastic contacts. An alternative mechanism, termed "quali­tative aging," is the gradual change in inter­facial chemistry, which so far was only observed in the presence of humidity. Here we present nano­scale friction experi­ments of dry silica contacts in ultrahigh vacuum that show a doubling of shear strength with time following a loga­rithmic law. We find that the aging rate scales linearly with tempe­rature, and that shear stress shifts the relevant energy barriers. All-atom MD simu­lations provide a live picture of the bond formation dynamics occurring at the interface. Our experi­ments link contact aging to thermally activated bond formation, show that it exists even in the absence of water molecules, and demon­strate that this atomic aging mecha­nism can stretch over time­scales up to several seconds. Qualitative contact aging is thus highly relevant for a broad variety of material combi­nations and con­ditions.

Publication

Matthias Vorholzer, J. G. Vilhena, Ruben Perez, Enrico Gnecco, Dirk Dietzel, André Schirmeisen: "Temperature Activates Contact Aging in Silica Nanocontacts", Phys. Rev. X 9 (2019) 041045, DOI: 10.1103/PhysRevX.9.041045External link