Atomic arrangement of sulfur adatoms on Mo(001) at atmospheric pressure: A scanning tunneling microscopy study

An ordered monolayer of chemisorbed sulfur adatoms on a Mo(001) surface is imaged in air, by means of scanning tunneling microscopy. The p(2\ifmmode\times\else\texttimes\fi{}1) overlayer is observed, in agreement with low-energy electron-diffraction studies. The adsorption sites of the sulfur atoms on the molybdenum substrate are clarified, based on the measured corrugation amplitudes. Atomic resolution has also been obtained in the barrier height mode, by use of an ac synchronous detection, and with a better signal-to-noise ratio than in the constant current (topographic) mode.