Load dependence and lifetime studies of self-assembled monolayers

A comparative study of the microtribological properties of native oxide on Si (100), Si (100) coated with octadecyltrichlorosilane (OTS) and perfluorode‐cyltrichlorosilane (FDTS) self‐assembling monolayers (SAMs) is presented. The frictional properties between these samples and a bare silicon sphere were examined using a microtribometer. Microfriction was investigated as a function of the normal load and relative humidity. Also, the microfriction of OTS‐ and FDTS‐coated surfaces was studied as a function of sliding time and normal load to examine the lifetime of these monolayers. Confirming the results of earlier studies, in the microtribological regime OTS and FDTS significantly reduce the friction force in comparison to the bare, native oxide covered (hydrophilic) silicon surface. The friction vs. normal load curve of oxide‐covered surfaces as well as the SAMs can be described by contact mechanics. Lifetime measurements of the SAMs, examined as a function of the normal load and relative humidity, indicate that the OTS monolayers wear quickly in both dry and moist environments, while the lifetime of FDTS monolayers appears to increase in moist environments. Copyright © 2006 John Wiley & Sons, Ltd.