Thesis defense of Marie Schmitz

This work deals with the analysis of the structural arrangement and the chemical properties of two silicon-based surface systems. The investigation is performed using X-ray Photoelectron Spectroscopy (XPS), X-Ray Photoelectron Diffraction (XPD), and Low-Energy Electron Diffraction (LEED) techniques. Before the investigation of the systems, the clean and reconstructed surfaces are investigated using XPS, XPD, and LEED. Initially, a system with sub-monolayer platinum on a p(2 × 1) reconstructed Si(100) substrate is prepared via electron beam evaporation. At 1/6 ML Pt a low-dimensional Si-Pt silicide forms after high temperature annealing at approximately T ≈ 1000 °C. High-resolution core-level XPS spectra of the Si 2p and Pt 4f signals indicate a bond between the Si and the Pt atoms. There is no significant component that could show a Pt-Pt interaction. XPD measurements are taken of the Si 2p and Pt 4f signals and subsequently simulated using different starting structures. The best structure model reveals R-factors below 0.1 for both, Si 2p and Pt 4f signals. The unit cell of the structural arrangement contains 4 platinum atoms with a periodicity of  ([3, −6]; [4, 0]). The topmost silicon layer rearranged in a cross-like structure between the Pt atoms.

As second system, silicon is deposited onto a (2 × 1) reconstructed Au(110) surface, forming a low-dimensional surface alloy. While the sample is held on a temperature of T = 400 °C, 0.2 ML silicon are deposited via physical vapor deposition. The investigation with LEED reveals a combination of two overlapping domains described by the matrices ([10, −2]; [−1, 4]) and ([10, 2]; [1, 4]). High-resolution core-level XPS measurements of the Au 4f and Si 2p signals showed two distinct components that could be assigned to Au-Si bonds. XPD pattern, recorded for Au 4f and Si 2p are simulated with different structural arrangements. R-factors below 0.1 indicate an excellent agreement with the measured data. The resulting structure model is consistent with the size of the unit cell obtained in the LEED measurement. Additionally, it agrees with the missing-row reconstruction of the substrate. In the structure model, the topmost Au atoms are arranged between the Si atoms.