X-Ray Studies of Solid State Layers and Interfaces.

Available from UMI in association with The British Library. The structure of the (sqrt{3 }timessqrt{3})R30 ^circ reconstruction induced by adsorption of 1/3 of a monolayer of Sn on the Si(111) surface has been determined using surface X-ray diffraction. The Sn adatoms occupy sites above second layer Si atoms and there are substantial lateral displacements of the Si atoms. A model allowing perpendicular relaxations in the topmost four layers of Si atoms indicated severely overstretched bonds in these layers. Incorporation of elastic strain minimization into the structure factor analysis enabled the identification of relaxations extending six layers into the bulk. An analysis of structure factors measured from the Ge(111)-(sqrt{3}times sqrt{3})R30^circ -Sn reconstruction was also consistent with a six layer model. A multipurpose high resolution X-ray diffraction instrument has been designed and constructed around a double crystal diffractometer. The structural quality of CdTe/InSb superlattice samples has been assessed using double crystal X-ray diffraction. The crystalline quality of samples with layer thicknesses less than 200 A was very poor whereas samples with layer thicknesses greater than 200 A were generally monocrystalline. The double crystal profile from a sample with a period thickness of 1249 +/- 26 A showed a strong asymmetric modulation in the satellite intensity pattern, indicating that the periods contained strained layers. An attempt has been made to simulate the satellite intensity modulation using a one-dimensional kinematical step model. Extended X-ray absorption fine structure spectroscopy (EXAFS) has been used to study the environment of Mn-dopant atoms in both annealed (450^circC) and untreated ZnS:0.5% Mn thin film samples. It has been found that the majority of Mn atoms occupy substitutional Zn sites in both samples. In the untreated sample, however, there are probably some Mn atoms on interstitial sites and the environment around the Mn atoms is less ordered than in the annealed sample.