| Popis: |
The atomic structure of the CaF2-Si(111) interface and the repeated unit cell of MnF2-CaF2-Si(111) superlattices have been determined using surface x-ray diffraction. Specular reflectivity and non-specular rod scans were measured for a number of superlattice samples. All samples had a type-B interface. Ultra-thin layers of MnF2, below a critical thickness of 5 monolayers, adopted the fluorite structure of CaF2. These layers are likely to have different magnetic properties to bulk anti-ferromagnetic MnF2, possibly leading to novel magnetic applications. We have developed software to interface with the structure factor calculation software ROD to calculate the semi-kinematical reflectivity and non-specular rods of a superlattice. Ion bombardment and annealing were used to produce atomically clean, well ordered InSb(001)-c(4x4) and GaSb(001)-c(2x6) surface reconstructions from antimony capped and uncapped samples. Auger electron spectroscopy showed that a 1000A antimony capping layer was sufficient to prevent atmospheric oxidation of the substrate. A substantial re-ordering of the cap was observed at 180°C. Desorption of the cap was achieved by annealing the sample at 300°C under an Sb overpressure. X-ray reflectivity measurements were used to determine the out-of-plane structure of the GaSbc(2x6) reconstruction. Theoretical fits indicate that both the top and the second layer of antimony dimers lie close to their bulk positions. In-plane x-ray measurements were used to verify the symmetry of the reconstruction. The InSb anti-phase x-ray position was monitored during the growth of Tl on the InSb-c(4x4) reconstruction. Fits to the data showed that the growth mode is Stranski-Krastanow at room temperature, and revealed details about the formation of the initial wetting layer. A specular reflectivity ridge scan after deposition showed reflections produced by Tl and Tl 2O. In-plane x-ray diffraction peaks can be attributed to either Tl, TlSb, or Tl7Sb2 and indicate a preferential alignment of Tl. |
