Scanning force microscopy of plasma polymerised hexane: information on the mechanical properties of thin films from tip-induced wear

Abstract

Scanning force microscopy has been used in contact mode to induce wear of thin plasma polymerised hexane (ppHex) films. The extent of wear observed can be used to qualitatively assess the mechanical properties of such thin films. The wear-resistance of the ppHex films varies greatly with the deposition power. They are harder than conventional polymers when deposited at high power and considerably softer when deposited at low power. On continued scanning, the morphology of the ppHex films is modified, leading to the formation of two parallel ridges that gradually merge into one larger central ridge. This behaviour differs significantly from that observed on tip-induced wear of conventional polymer films where patterns of many ridges and troughs often form. Tip-induced wear was more extensive at higher applied load, lower scan rate and at higher scan line densities. The scan speed dependence is different from that observed for conventional polymers, and may be explained in terms of the viscoelastic behaviour of the materials.