Ultralow nanoscale wear through atom-by-atom attrition in silicon-containing diamond-like carbon

Abstract

Understanding friction1-4 and wear5-11 at the nanoscale is important for many applications that involve nanoscale components sliding on a surface, such as nanolithography, nanometrology and nanomanufacturing. Defects, cracks and other phenomena that influence material strength and wear at macroscopic scales are less important at the nanoscale, which is why nanowires can, for example, show higher strengths than bulk samples12. The contact area between the materials must also be described differently at the nanoscale13. Diamond-like carbon is routinely used as a surface coating in applications that require low friction and wear because it is resistant to wear at the macroscale14-20, but there has been considerable debate about the wear mechanisms of diamond-like carbon at the nanoscale because it is difficult to fabricate diamond-like carbon structures with nanoscale fidelity. Here, we demonstrate the batch fabrication of ultrasharp diamond-like carbon tips that contain significant amounts of silicon on silicon microcantilevers for use in atomic force microscopy. This material is known to possess low friction in humid conditions, and we find that, at the nanoscale, it is three orders of magnitude more wear-resistant than silicon under ambient conditions. A wear rate of one atom per micrometre of sliding on SiO2 is demonstrated. We find that the classical wear law of Archard21 does not hold at the nanoscale; instead, atom-by-atom attrition7,8 dominates the wear mechanisms at these length scales. We estimate that the effective energy barrier for the removal of a single atom is ∼ 1eV, with an effective activation volume of ∼ 1×10 28 m. © 2010 Macmillan Publishers Limited. All rights reserved.