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

Area of Science:

• Surface Science
• Materials Science
• Condensed Matter Physics

Background:

• Low Energy Electron Microscopy (LEEM) is a powerful surface-sensitive technique.
• Understanding surface phenomena during thin film deposition is crucial for materials development.
• Tungsten (W) and Lead (Pb) systems are relevant in various technological applications.

Purpose of the Study:

• To investigate the anomalous step contrast observed during Pb deposition on a W(110) surface using LEEM.
• To correlate the observed contrast changes with the surface atomic density and phase transitions of Pb.
• To elucidate the mechanisms behind contrast reversal and anomalous intensity profiles.

Main Methods:

• Low Energy Electron Microscopy (LEEM) was employed to image the W(110) surface during Pb deposition.
• In-situ observation of surface morphology and step contrast changes at approximately 200°C.
• Analysis of the relationship between Pb coverage, surface atomic density, and step contrast.

Main Results:

• Anomalous step contrast was observed, changing from dark to bright upon initial Pb deposition.
• The bright contrast was attributed to the presence of a two-dimensional (2D) Pb gas with a specific atomic density distribution.
• Further Pb deposition led to a reversal of contrast (steps becoming dark) with an anomalous intensity profile, indicating 2D crystallization.

Conclusions:

• The observed anomalous step contrast in LEEM is directly related to the dynamic processes of Pb adsorption and phase transitions on the W(110) surface.
• The study highlights the sensitivity of LEEM to surface atomic density variations and 2D gas formation.
• The findings provide insights into the initial stages of thin film growth and surface restructuring.