Effect of micro-dimple patterns on capillary pull-off force and friction force of silicon surface

A microtribometer is used to measure and compare pull-off forces andfriction forces exerted on (a) micro-dimpled silicon surfaces, (b)bare silicon surfaces, and (c) octadecyltrichlorosilane (OTS)treated silicon surfaces at different relative humidity (RH) levelsseparately. It is found that above a critical RH level, thecapillary pull-off force increases abruptly and that themicro-dimple textured surface has a lower critical RH value as wellas a higher pull-off force value than the other two surfaces. Amicro topography parameter, namely sidewall area ratio, is found toplay a major role in controlling the capillary pull-off force.Furthermore, micro-dimpled silicon surface is also proved to be notsensitive to variation in RH level, and can realize a stable anddecreased friction coefficient compared with un-textured siliconsurfaces. The reservoir-like function of micro dimples is consideredto weaken or avoid the breakage effect of liquid bridges atdifferent RH levels, thereby maintaining a stable frictionalbehaviour.