Physisorption of an electron in deep surface potentials off a dielectric surface

TL;DR

This paper investigates phonon-mediated electron adsorption and desorption on dielectric surfaces with deep potentials, focusing on multi-phonon processes and their impact on electron kinetics and surface interactions.

Contribution

It provides a detailed quantum-mechanical analysis of multi-phonon transitions affecting electron physisorption on various dielectric materials, including calculations of desorption times and sticking coefficients.

Findings

Identifies two generic adsorption/desorption scenarios depending on potential depth and temperature.

Calculates electron desorption times for graphite, MgO, CaO, Al₂O₃, and SiO₂.

Determines electron sticking coefficients for Al₂O₃, CaO, and SiO₂.

Abstract

We study phonon-mediated adsorption and desorption of an electron at dielectric surfaces with deep polarization-induced surface potentials where multi-phonon transitions are responsible for electron energy relaxation. Focusing on multi-phonon processes due to the nonlinearity of the coupling between the external electron and the acoustic bulk phonon triggering the transitions between surface states, we calculate electron desorption times for graphite, MgO, CaO, (\text{Al}_2\text{O}_3), and (\text{SiO}_2) and electron sticking coefficients for (\text{Al}_2\text{O}_3), CaO, and (\text{SiO}_2). To reveal the kinetic stages of electron physisorption, we moreover study the time evolution of the image state occupancy and the energy-resolved desorption flux. Depending on the potential depth and the surface temperature we identify two generic scenarios: (i)adsorption via trapping in shallow image states followed by relaxation to the lowest image state and desorption from that state via a cascade through the second strongly bound image state in not too deep potentials and (ii)adsorption via trapping in shallow image states but followed by a relaxation bottleneck retarding the transition to the lowest image state and desorption from that state via a one step process to the continuum in deep potentials.