Micro/nanotribological studies of lanthanum-based thin films on phosphorylated 3-Aminopropyltriethoxysilane self-assembled monolayers

Lanthanum-based phosphonate 3-Aminopropyltriethoxysilane (APTES) thin films were prepared on the hydroxylated silicon substrate by a self-assembling process from formulated solution. The tribological behaviors of APTES-SAM, phosphorylated APTES-SAM and lanthanum-based films were experimentally investigated at the nanoscale using atomic force microscope (AFM) and at the microscale using a UMT-2MT reciprocating friction and wear tester. no- and microscale tribological behaviors between the films are compared and discussed. Results showed that the adhesive forces and friction forces increased with the relative humidity. When the applied normal load increased from 0 to 70 nN, the adhesion did not change, but the friction increased linearly. Results generally showed surfaces of the more hydrophobic property revealed the lower adhesion. It was also found that lanthanum-based films that had the highest water contact angle exhibited the lowest adhesion force and friction force and the relative long wear life compared with APTES-SAM and phosphorylated APTES-SAM. The superior friction reduction and wear resistance of lanthanum-based thin films are attributed to the low work of adhesion of non-polar terminal groups and enhanced load-carrying capacity of the inorganic lanthanum particles in the lanthanum-based thin films as well as good adhesion of the films to the substrate.