Positron re-emission, reflection, and diffraction from W(100) surface at very low energies

Area of Science:

• Materials Science
• Surface Science
• Atomic and Molecular Physics

Background:

• Tungsten (W) exhibits a negative positron work function (~ -3 eV).
• Low-energy positrons (< 25 eV) interacting with surfaces can be reflected, absorbed, or undergo diffraction.
• Understanding positron interactions is crucial for surface characterization and materials analysis.

Purpose of the Study:

• To experimentally investigate the energy distributions of scattered and re-emitted low-energy positrons from a W(100) surface.
• To analyze three distinct scattering scenarios: reflection, re-emission, and coherent diffraction.
• To determine the sensitivity of positron scattering spectra to surface conditions.

Main Methods:

• Measurement of energy distributions for scattered and re-emitted positrons.
• Varying incident positron energy from 0 to 25 eV.
• Experimental study of positron-surface interactions under varying surface conditions (e.g., oxidation, thin film deposition).

Main Results:

• Observed distinct energy spectra for reflected and re-emitted positrons.
• Demonstrated that positron reflectivity decreases as incident energy approaches the positron work function.
• Confirmed that surface conditions like oxidation and thin film deposition drastically alter measured positron spectra.

Conclusions:

• The study experimentally validates three key low-energy positron scattering mechanisms at a W(100) surface.
• Positron scattering and re-emission are highly sensitive to surface states, making them valuable probes.
• These findings contribute to the understanding of positron-surface interactions and their application in surface science.