Improving the Lubrication of Silicon Surfaces Using Ionic Liquids as Oil Additives: The Effect of Sulfur-Based Functional Groups

The performance of micro/nanoelectromechanical systems (MEMS/NEMS) relies on efficient lubrication. In the present work, new sulfur-based organic salts were tested as additives in a polyethylene glycol to lubricate silicon surfaces used in the manufacture of MEMS/NEMS. Seven salts were tested: 1-butylsulfonic-3-methylimidazolium triflate [(C 4 SO 3 H)MIM][TfO], thiamine triflate [Thiamine][TfO] 2 , 1-ethyl-3-methylimidazolium camphorsulfonate [C 2 MIM][CSA] [isomers (R) and (S)], 1,3-dimethylpiridinium methylsulfate [C 1 -3pic][MeSO 4 ], methylimidazolium methanesulfonate [HMIM][MeSO 3 ], and tetramethylguanidine methanesulfonate [TMG][MeSO 3 ]. A nanotribometer was used to determine the friction coefficients using steel spheres as counter bodies. Excellent tribological properties were achieved with the additives containing the anions [MeSO 4 ] − and [MeSO 3 ] − . The films formed on the Si substrates were studied by FTIR, ellipsometry and AFM. A mixed lubrication mechanism was proposed where additive adsorption avoids contact between sliding surfaces. Graphical Abstract Sulfur-based organic salts as additives in the base oil PEG200 significantly improve the lubrication of silicon surfaces used in MEMS/NEMS