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

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.