Surface analysis via fast atom diffraction: pattern visibility and spot-beam contribution

TL;DR

This paper investigates how incidence conditions and projectile mass influence surface analysis patterns in grazing incidence fast atom diffraction, highlighting the roles of coherence, spot-beam effects, and focusing in pattern visibility and transition.

Contribution

It introduces a detailed analysis of the impact energy, coherence, and spot-beam effects on FAD patterns, emphasizing the importance of focusing effects for accurate theoretical modeling.

Findings

Varying impact energy controls interference mechanisms.

Spot-beam effect enables exploration of different surface zones.

Focusing effects are essential for matching experimental data.

Abstract

Grazing incidence fast atom diffraction (GIFAD or FAD) is a sensitive tool for surface analysis, which strongly relies on the quantum coherence of the incident beam. In this article the influence of the incidence conditions and the projectile mass on the visibility of the FAD patterns is addressed. Both parameters determine the transverse coherence length of the impinging particles, which governs the general features of FAD distributions. We show that by varying the impact energy, while keeping the same collimating setup and normal energy, it is possible to control the interference mechanism that prevails in FAD patterns. Furthermore, we demonstrate that the contribution coming from different positions of the focus point of the incident particles, which gives rise to the spot-beam effect, allows projectiles to explore different zones of a single crystallographic channel when a narrow surface area is coherently lighted. In this case the spot-beam effect gives also rise to a non-coherent background, which contributes to the gradual quantum-classical transition of FAD spectra. Present results are compared with available experimental data, making evident that the inclusion of focusing effects is necessary for the proper theoretical description of the experimental distributions.