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

• Ano de defesa: 2024
• Autor(a) principal: Silva, Gustavo Diniz
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Biblioteca Digitais de Teses e Dissertações da USP
• Palavras-chave em Português: Anderson catastrophe; Catástrofe de Anderson; Coeficiente de adesão; Fenômeno fora do equilíbrio; Fotoemissão de raio-X; Grupo de renormalização numérica; Numerical renormalization group; Out-of-equilibrium phenomenon; Sticking coefficient; X-ray photoemission
• Link de acesso: https://www.teses.usp.br/teses/disponiveis/76/76134/tde-18122024-090610/

Out-of-equilibrium electron-gas systems contain rich physics. We discuss the time evolution of three such systems. Our first subject is photoemission from metals, a problem traditionally studied in the frequency domain. We find unexpected features in the time dependence of the photoemission rate. The rate oscillates at relatively high frequency as it decays, and the amplitude of the oscillations decay faster than the average current. We combine analysis with numerical data to trace the oscillatory behavior to the interference between two excitation processes, one of which decays according to the Doniach-Sunjic power law while the other decays faster, following the Nozières-De Dominicis power law. We expect XPS experiments focused on this feature to identify the corresponding peak in the frequency domain. As our second problem, with a view to quantifying adiabaticity, we consider an electron gas subject to a localized potential that ramps up from zero to a maximum at constant rate. Again on the basis of analytical and numerical results, we identify the region of the parametric space of the model in which the system behaves adiabatically. In contrast with the Quantum Adiabatic Criterion, which associates adiabaticity with small ramp-up rates, our results show that the number of energy scales participating in the screening of the localized potential determines whether non-adiabaticity emerges. The object of our final study is the collision between an initially neutral hydrogen atom and a copper surface, represented by a half-filled conduction band. As the atom approaches the surface, the overlap between the atomic and surface orbitals allows electron transfer to and negative ionization of the H atom. The ionization switches on a image-charge potential, which pulls the ion towards the surface. We define a spinless model that captures the physics of the collision and, on the basis of numerical treatment, follow the evolution of the atomic wave packet and compute the sticking coefficient, that is, the probability that the atom remain close to the surface after a long time. Plotted as function of the incident energy, the sticking coefficient has a maximum around 0.3 eV. Assisted by the experience gained with first two problems, we interpret the peak as a compromise between the contribution of non-adiabatic processes, which grows with the initial energy, and the time the atom takes to traverse the region where such processes occur. The numerical results are in semi-quantitative agreement with the available experimental data.