Electronic and optical surface properties of noble metals studied by reflection anisotropy spectroscopy

Abstract

The thesis demonstrates some of the possibilities of using light to measure and understand microscopic properties of noble metal and nickel surfaces. The work consist mainly of three parts:

1. The design and construction of a complete reflection anisotropy spectroscopy (RAS) system, connected to a ultra-high vacuum (UHV) chamber where samples can be cleaned and measured at pressure levels less than 1∙10-10mbar.

2. Theoretical progress in classical local field effect calculations of resonat dipoles at (110) surfaces of noble metals. Methods to solve the plane-wise dipole-interaction coefficients are developed. It is investigated how variations in local-field effect model parameters inclluding effective surface hieght and plasma-frequency, change the shape of the calculated spectra. In addition, it is discussed how imperfections in the surface, such as steps and vacancies, can be inlcuded in the model.

3. RAS measurements of clean and reconstructed surfaces Ag(110), Cu(110), Au(110), Au (100), Pt(100) and Ni(110) surfaces. The spectra for each of these surfaces are compared to theoretical model spectra. Using expressions for the screened dipole-dipole interaction we have found that the surface local-field effect contribute to the reflection anistropy of all the above surfaces except for Pt(100). Transitions between surface states at the Y point of the surface Brillouin zone are responsible for features in the spectra of Ag(110), Cu(110). Many of the above surfaces have a reflection anisotropy that can be described by a phenomenological shift or broadening of the permittivity near a critical-point energy.