Friction behaviour of chemical vapor deposited self-assembled monolayers on silicon wafer

摘要

Friction characteristics of self-assembled monolayers (SAMs) coated on Si-wafer (100) by chemical vapor deposition technique were studied experimentally at nano and micro-scales. Four self-assembled monolayers, such as dimethyldichlorosilane (DMDC), diphenyldichlorosilane (DPDC), perfluorooctyltrichlorosilane (PFOTS) and perfluorodecanoicacid (PFDA) coated on Si-wafer (100) were used as test materials. Nano-scale friction was measured using atomic force microscopy (AFM) in the range of 0-40 nN normal loads, in LFM (lateral force microscopy) mode, using a contact mode type Si{sub}3N{sub}4 tip. Results showed that the friction of SAMs at this scale was influenced by their physical/chemical properties, while that of Si-wafer by its inherent adhesion. Further, micro-scale friction tests were also performed with a ball-on-flat type micro-tribotester under reciprocating motion. Friction was measured in the range of 1500-4800 μN applied normal loads using glass balls of varying radii, viz., 0.25, 0.5 and 1 mm. It was observed that the performance of SAMs was more superior to Si-wafer even at micro-scale, except for PFDA. Evidences obtained using scanning electron microscope showed that Si-wafer and PFDA exhibited wear at this scale. Wear in the case of Si-wafer was due to solid-solid adhesion and that in the case of PFDA due to the influence of humidity (moisture), The micro-scale friction in both these materials was severely influenced by their wear.