An XPS and atomic force microscopy study of the micro-wetting behavior of water on pure chromium

Abstract

The surface compositions and morphologies of pure chromium after wet polishing, air oxidation and further micro-wetting by distilled water, were investigated with X-ray photoelectron spectroscopy (XPS) and the AC non-contact mode of atomic force microscope (AFM). An organic contaminants/water layer on the chromium oxide/hydroxide layer, was detected by XPS analysis for each surface. The oxide/hydroxide layer became thicker, and the oxide: hydroxide ratio increased, after air oxidation. In ambient air, the AFM showed a thin liquid layer on each surface, which was easily moved by the cantilever of the AFM and can be condensed or evaporated. The inner part of the liquid might be adsorbed water, and the outer part is thought to be organic contaminants since the liquid did not combine with distilled water applied by post-wetting. Micro-droplets of distilled water deposited by post-wetting always occupied positions without or with little of this liquid, which might explain the obtained higher micro- than macro-wettability.