Step contrast reversal in LEEM during Pb deposition on W(110)

Abstract

Anomalous step contrast in low energy electron microscopy (LEEM) imagesobserved during Pb deposition on a W(110) surface is discussed. The stepsare dark on the clean surface, and become bright by Pb deposition at about200 °C. The contrast reversal is related to the presence of a two-dimensional (2D) Pb gas on thesurface and its atomic density distribution. Upon further deposition the steps become darkagain and show an anomalous intensity profile. This change is attributed to the 2Dcrystallization process.