Tip in situ chemical modification and its effects on tribological measurements

In this paper, we present our experimental results on the process of the in situ chemical modification of the silicon nitride atomic force microscopy/ frictional force micros copy tip by n-octadecyltrimethoxysilane (OTE)/mica, OTE/SiO2, and SiO2. The modified tips have different friction and adhesion properties against mica reference samples compared to those before modific ation. The resultant tip modification depends not only on OTE self-assemble d monolayer (SAM) but also on the substrates the OTE SAM is prepared on. In the case of OTE/mica, the friction of the modified tip against mica refere nce is greatly reduced; in the case of OTE/SiO2, the friction of the modifi ed tip against mica reference is greatly increased. It is surprising that b are SiO2 can also chemically modify the Si3N4 tip to increase the friction against mica reference. In the case of OTE modification, it was found that the tips could be cleaned by repetitive friction scans on mica. However, a tip modified by SiO2 cannot be mechanically cleaned. Moreover, it was found that humidity and load could also affect the tip chemical modification. Ou r results are important for interpreting tribological data since the actual contact chemistry was often overlooked in the atomic force microscopy expe riments in the past.