Sticking coefficient for atoms impinging on a metallic surfaces, and the x-ray photoemission by metals

TL;DR

This paper explores electron dynamics in metals, revealing oscillatory photoemission behavior, mapping adiabaticity conditions in electron gases, and calculating atomic sticking coefficients on metal surfaces, with implications for experimental detection and surface interactions.

Contribution

It introduces a detailed analysis of high-frequency photoemission oscillations, clarifies adiabaticity criteria in electron gases, and computes the sticking coefficient for atoms on metals, combining analytical, numerical, and experimental comparisons.

Findings

Photoemission oscillates at high frequencies with decay faster than current.

Adiabaticity depends on screening energy scales, not just ramp rate.

Sticking coefficient peaks at around 300 meV, matching experimental data.

Abstract

Out-of-equilibrium electron-gas systems exhibit rich physics, which we explore through three problems. First, we study photoemission from metals, traditionally analyzed in the frequency domain. Unexpectedly, the photoemission rate oscillates at high frequencies as it decays, with the oscillation amplitude decaying faster than the average current. Analytical and numerical results reveal this behavior arises from interference between two excitation processes: one decaying via the Doniach-Sunjic power law and the other following the faster Nozi\`eres-De Dominicis law. XPS experiments targeting this feature could identify its frequency-domain counterpart. Second, we examine adiabaticity in an electron gas subject to a localized potential ramping up at a constant rate. Analytical and numerical findings map the parameter space where the system behaves adiabatically. Contrary to the Quantum Adiabatic Criterion, which links adiabaticity to slow ramp-up rates, we show that the number of energy scales involved in screening the potential dictates non-adiabaticity. Lastly, we investigate the collision of a neutral hydrogen atom with a copper surface. Electron transfer ionizes the H atom, activating an image-charge potential that pulls the ion toward the surface. Using a spinless model, we numerically track the atomic wave packets evolution and compute the sticking coefficient, the probability the atom remains near the surface. The coefficient peaks near 300 meV, balancing non-adiabatic contributions, which increase with energy, and the traversal time through the interaction region. Numerical results align semi-quantitatively with experimental data.