Quantum Hydrodynamic Study Of Interactions Of Charged Particles With Electron Gases At Surfaces/Interfaces

The interactions of charged particles with electron gases at surfaces or interfaces have been a very important research field in surface physics. In particular, it has been an interesting topic due to the applications in the structure analysis, surface modification and microelectronic device processing techniques. The energetic particles can be as a probe to detect the material component, structure and photoelectric information by interacting with the surfaces. For example, the excitation characteristics and the electron gas density of the material can be detected by measuring the electron energy loss spectrum, and the material component and structure can be obtained by ion backscattering or ion beam channelling technology. Besides, in the manufacture technology in micro- or nano-scale, the surface structure can be also obtained by modulating the interactions between the focused ion beam and the material surfaces (e.g. photonic crystals and MEMS).In this thesis, a self-consistent linearized quantum hydrodynamic (QHD) model is developed to investigate the excitations of the electron gases at different surfaces or interfaces (including single layer and double layers electron gases plane, the infinitesimally thin metal film covering on the nano-dielectric sphere and finite thin metal film covering on a semi-infinite dielectric substrate). And focus on the investigations of influences of the quantum and scale effects of the materials on the induced potential, the perturbed electron gas density and the energy loss in the excitation process of surfaces and interfaces.In chapter 2, the electronic excitations induced by a charged particle moving parallel to two-dimensional electron gases plane are studied by means of the linearized QHD theory. The calculation results show that the influence of the quantum effects on the interaction process should be taken into account. The V shape oscillatory wake-field appears apparently behind the projectile particle when the particle speed becomes higher. As for the stopping power, lateral force and self-energy, the results indicate that the particle position, the damping coefficient and the electron gas density in equilibrium have effects on the peak value and position.In chapter 3, the electronic excitation is investigated when the charged particle moving parallel to the layered electron gases system. Numerical results show that double peaks will occur in the stopping power, lateral force and self-energy curves caused by the two sheets structures, in which the electron polarization in both sheets contributes to the induced electric field. And the coupling of electric field of two sheets will gradually weaken when the distance of two surface increases. Further more, the parameter of electron gas density has effect on changes of the stopping power, lateral force and self-energy with the particle speed, and the double peaks appear obviously in the curves.In chapter 4, we present a theoretical study on the interaction of the charged particle with a nano-dielectric sphere covered with infinitesimally thin metal film. The theoretical model is formulated in terms of linearized QHD equations, cooperated with trial solution of the electric potential with appropriate boundary condition. Numerical results indicate that an oscillatory wake effect exists in the electron gases during the interactions. Because of the limitation of the spherical structure, the value of stopping power is negative when the particle approaches the spherical surface and then becomes positive as the particle moves away from the sphere. In addition, as the relative permittivity is gradually larger, the peak values of the stopping power becomes smaller and shifts toward to low speed, which indicates that the total effects of polarized electric field and induced electric field on the charged particle become weaker.In chapter 5, the interactions between charged particles and metal film covering on a semi-infinite dielectric substrate are investigated based on the linearized QHD theory under three-dimension. The calculation results show that an oscillatory wake field appears apparently behind the particle at two of the surfaces of the metal film, and the effects of the film thickness on the electron gas density cannot be neglected when film is thinner. Further more, the metal film has obvious screening effects on the coulomb potential of the projected particle. Besides, the dependence of the stopping power, lateral force and self-energy on the film thickness, particle position, density parameter and relative permittivity are analyzed. Finally, the results are compared with those based on the local frequency-dependent (LFD) dielectric approach. The comparison results indicate that the values of stopping power calculated from two models are almost in agreement with each other independent of proton speed when the charged particle moves away from the metal film. But, for the case of particle approaching the film, the results arising from two models are closer when the particle speed is higher.