Scale dependence of micro/nano-friction and adhesion of MEMS/NEMS materials, coatings and lubricants

Abstract

Scale dependence of micro/nanotribological properties is studied for various materials, coatings and lubricants used in micro/nanoelectromechanical systems (MEMS/NEMS). The adhesive force and friction force dependence on rest time and sliding velocity and the effect of relative humidity and temperature on the scale dependence of these properties is studied. The scale dependence of the coefficient of friction is attributable to the sample surface roughness and the scan size. For larger scan sizes the sliding interface encounters larger asperities and so friction force is higher. The adhesive force is higher on the microscale although on the nanoscale surface forces such as electrostatic attraction that are generally negligible on the microscale can become dominant. The difference in the adhesive force on the micro- and nanoscale for different rest times, relative humidities and temperatures is due to the meniscus force dependence on the sample surface roughness. The velocity dependence of the friction force shows significant scale dependence due to the scale dependent roughness and the higher contact pressures that are encountered on the nanoscale.

Nanoscale friction and wear maps

“…For studying surface interaction on the micro/nanoscale, the sharp tip of an AFM is ideally suited and has been successfully employed by a number of researchers for studying friction and wear properties of various materials, coatings and lubricants (Mate et al 1987;Koinkar & Bhushan 1996;Bennewitz et al 2001;Bhushan & Liu 2001;Liu & Bhushan 2003;Tambe & Bhushan 2004, 2005aTambe 2005;Gnecco et al 2007;Tao & Bhushan 2007). Contrary to the classical friction laws postulated by Amontons (1699) and Coulomb (1785) centuries ago, nanoscale friction force is found to be strongly dependent on the normal load and sliding velocity.…”

Nanotribology, nanomechanics and nanomaterials characterization

“…Adhesive force and coefficient of friction data obtained on the nanoscale and microscale are found to be scale dependent (Ruan & Bhushan 1994c;Liu & Bhushan 2003a;Tambe & Bhushan 2004). Adhesive force and coefficient of friction values on the nanoscale are about half to one order of magnitude lower than those on the microscale.…”

“…Many materials, coatings and lubricants that have wide applications show reversals in friction behaviour corresponding to transitions between different friction mechanisms (Tambe & Bhushan 2004, 2005a. Most of the analytical models developed for explaining nanoscale friction behaviour have remained limited in their focus and have left investigators short handed when trying to explain friction behaviour scaling multiple regimes.…”

MEMS Reliability Review

“…Experiments show that the adhered length, rest time, temperature, relative humidity, and sliding velocity of a micro-cantilever can affect the adhesion forces between two contacting surfaces, and in turn affect the adhesive wear [49], [50].…”