Title:
Water-drop modification of Si surfaces prepared in an ultrahigh vacuum chamber

Speaker(s):
Tomoaki Miyagi, Akira Sasahara, and Masahiko Tomitori
Japan Advanced Institute of Science and Technology, Ishikawa, Japan

Abstract:
Water contact angle (WCA) is an easy indicator to check the chemical reactivity of solid surfaces to water. To examine the reactivity of clean, H-terminated, and thinly oxidized surfaces of Si(111)-(7×7) and Si(001)-(2×1) prepared in an ultrahigh vacuum chamber, we placed water droplets on them and measured the WCAs in a nitrogen atmosphere without exposing the surfaces to air. The WCAs on the clean Si surfaces and the thinly oxidized Si surfaces exhibited super-hydrophilicity, whereas the H-terminated Si surfaces were hydrophobic. After the WCA measurements Auger electron spectroscopy analysis showed the increase of oxygen and carbon on the surfaces, but much less on the H-terminated surfaces. After the water droplets were placed, many protrusions were found on the clean surfaces by atomic force microscopy. We discuss the chemical reaction of the Si surfaces with water, and the contribution to the interface free energy between water and the surfaces by surface termination with silanol groups (Si-OH) in regard to the number of the Si dangling bonds per unit area.