Investigation of the tribological behavior of octadecyltrichlorosilane deposited on silicon

In this work, the tribological behavior of octadecyltrichlorosilane (OTS, CH3(CH2)17SiCl3), which is a self-assembled monolayer (SAM) known for its low surface energy and hydrophobic property, deposited on silicon was investigated. Since the state of OTS depends heavily on the coating time, the effect of coating time on various tribological characteristics of OTS deposited on silicon (1 0 0) was of primary interest. The macroscopic frictional force of OTS deposits was also measured using a pin-on-disk type tribotester. The OTS deposited silicon specimens were slid against a 1.6 mm diameter STB2 steel ball under a normal load of 50 mN. It was found that the macroscopic friction coefficients for coating times >1 h ranged between 0.1 and 0.2 whereas the value for shorter coating time was as high as 0.7. We also found that the frictional behaviors of OTS coated silicon surface were less sensitive to humidity changes compared with bare silicon surface. Furthermore, the stiction of OTS coated silicon was much less sensitive to apparent area of contact, applied load, and soaking time. This work demonstrates the effectiveness of OTS film in reducing sliding friction of silicon micro-systems when deposited properly.