THE Si ( lOO ) - Sb 2 x 1 AND Ge ( lOO ) - Sb 2 x 1 SURFACES : A MULTI - TECHNIQUE STUDY Matthew Richter

The electronic and geometric structures of the clean a,nd Sb terminated Si(lOO)2x1 and Ge(lOO)-2x1 surfaaces have been investigated using a multi-technique approach. Low energy electron diffraction (LEED), scanning tunneling microscopy (STM), surface extended X-ray absorption fine structure (SEXAFS) spectroscopy and angle-integrated core-level photoemission electron spectroscopy (PES) were employed to measure the surface symmetry, defect structure, relevant bond lengths, atomic coordination and electronic structure. By employing a multi-t,echnique approach, it is possible to correlate changes in the geometric structure to specific features of the core-level lineshape of the substrate. This allows for the assignment of components of the core-level lineshape to be assigned to specific surface and near-surface atoms. We find that both the Si(lOO)-Sb and Ge(lOO)-Sb surfaces are comprised of Sb dimers. On the Si(lOO)-Sb surface, the Sb dimers have a Sb-Sb bond length of 2.91f0.03 A. On the Si(100) surface each Sb a,tom is bonded to two Si atoms with a Sb-Si bond length of 2.63f0.03 A. The bond lengths are given by the sum of the atoms covalent radii, 1.45 8, for Sb and 1.18 8, for Si. T unneling microscopy observed and identified the defects present in the overlayer. These were voids and some slight second-layer occupation. STM also revealed that the size of the coherent domain is r about 40 A across. The presence of these anti-phase boundaries explains the weak intensities of second-order spots in the LEED pattern. Core-level photoemission shows a correlation between changes in the geometric and electronic structure of the surface. One of the surface peaks associated with one of atoms forming the Si dimers is eliminated upon Sb adsorption. The temperature dependence of the SEXAFS amplitude shows that the surface forms clusters if more than one monolayer is deposited. These clusters can be remove by annealing the sample at about 500°C, leaving a well ordered, dimerized surface. All Sb desorbs when the sample is annealed at a temperature of 600°C. The Ge(lOO)-Sb y t s s em behaves similarly with a, few exceptions. The Sb-Sb dimer bond length is found to be 2.91f0.06 A, while the Sb-Ge bond length is slightly shorter than the sum of covalent radii, measuring 2.584~0.06 A. While STM was not performed on the Ge(lOO)-Sb system, the similas behavior of the LEED pattern suggests that anti-phase boundaries also play a significant role in the interfacial morphology. The Ge 3d core-level lineshape undergoes similar changes as the Si 2p core-level lineshape upon Sb deposition and ordered overlayer formation, allowing for similar assignments of particular surface and near-surface atoms to the various surface contributions to the overall Ge 3d lineshape. The most significant difference in behavior between the t,wo systems is their evolution as a function of anneal temperature. While on the Si(lO0) b t t su s ra e a.11 excess Sb desorbs a temperature such that a well-ordered Sb overlayer remains, this is not the case on the Ge(100) substrate. At a temperature sufficient to desorb the excess Sb, the underlying Sb also starts to desorb, leaving a partially-covered Ge(lOO) surface. This work also contains overviews of t,he relevant theories, paying special attention to the Transfer-Hamiltonian description of the STM by Tersoff and Hamann as well as &a-edge SEXAFS theory. Our results are critically compared to other relevant literature. To my family and my friends.