Nanoscale analysis of ionic liquid deposition for application in micro/nanoelectromechanical devices
Ionic Liquids, MEMS/NEMS, AFM, Thin Film, Lubrication
Two phosphorus-based Ionic Liquids (IL) were deposited onto a <111> silicon substrate via dip coating. These ILs, trihexylttetradecylphosphonium bis(2,4,4-trimethylpentyl)phosphinate and tetrabutylphosphonium methanesulfonate, are two possible candidates for the lubrication of micro/nanoelectromechanical devices (MEMS/NEMS). To evaluate this, their abilities to form a thin adsorbed film (1 to 100nm) on the silicon surface were studied. Variations were made in deposition parameters such as substrate cleanliness, different concentrations and deposition speed. The surface was followed by optical microscopy, with the aid of the atomic force microscope (AFM). As a result, it was possible to observe the topography, the variation of the friction force as a function of the applied normal load and the adhesion force between the tip and the film. In addition, a confocal Raman spectroscopy (532 nm laser and 7.2 mW power) was used to observe the presence of ionic liquid in specific regions of interest. Using these tools, it was possible to observe similar behaviour in the friction coefficient and in the surface film formation mechanism between the two lubricants, which can be attributed to the fact that both have the same phosphorus-based cation