Rasdip Singh

Analysis of a Zirconium Diboride Single Crystal, ZrB2 (0001), by XPS

X-ray photoelectron spectroscopy (XPS) was used to study the clean surface of ZrB2 (0001). The clean surface exhibits Zr 3d5/2 and Zr 3d3/2 peaks at 179.2 and 181.6 eV, respectively. However, angle resolved XPS indicated ZrO2 peaks at 183.5 and 185.7 eV at higher emission angles, indicating that further cleaning was necessary. After additional cleaning cycles, these oxide peaks were no longer observed at high emission angles. This result demonstrates the necessity to probe the near surface region with higher emission angles on very reactive surfaces, in order to completely establish the cleanliness of the surface.

Gold diffusion in mercury cadmium telluride grown by molecular beam epitaxy

The growth and characterization of Au-doped HgCdTe layers on (211)B CdTe/Si substrates grown by molecular beam epitaxy reported. The electrical properties of these layers studied for diffusion are presented. For ex-situ experiments, thin Au layers were deposited by evaporation and annealed at various temperatures and times to investigate the p-type doping properties and diffusion of Au in HgCdTe. The atomic distribution of the diffused Au was determined by secondary ion mass spectroscopy. We found clear evidence for p-type doping of HgCdTe:Au by in-situ and ex-situ methods. For in-situ doped layers, we found that, the Au cell temperature needs to be around 900°C to get p-type behavior. The diffusion coefficient of Au in HgCdTe was calculated by fitting SIMS profiles after annealing. Both complementary error functions and gaussian fittings were used, and were in full agreement. Diffusion coefficient as low as 8x10-14cm2/s observed for a sample annealed at 250°C and slow component of a diffusion coefficient as low as 2x10-15 cm2/s observed for a sample annealed at 300°C. Our preliminary results indicate no appreciable diffusion of Au in HgCdTe under the conditions used in these studies. Further work is in progress to confirm these results and to quantify our SIMS profiles.

Characterization of Hafnium Diboride, HfB2 (0001), by XPS

X-ray photoelectron spectra of a clean, well-ordered HfB2 (0001) single crystal surface are reported. A survey spectrum covering a binding energy range of 0 to 1000 eV is shown, which reveals the presence of minor amounts of oxygen and zirconium. Spectra over narrower binding energy ranges are also shown for the Hf 4f, B 1s, and Hf 4s/O 1s regions. A comparison of the Hf 4s/O 1s region before and after oxygen exposure provides for unambiguous assignment of the overlapping O 1s and Hf 4s peaks at binding energies of 531 and 534 eV, respectively.

Influence of Oxygen on the B 1s and La 3d Line Shapes of a Lanthanum Hexaboride (100) Surface

X-ray photoelectron spectroscopy was used to investigate the initial stages of adsorption on the (100) surface of a single crystal of lanthanum hexaboride. Numerous previous studies had not resolved the issue of whether oxygen adsorbs at lanthanum sites, boron sites, or both. We find that oxygen adsorption produces new peaks in the La 3d region, whereas the B 1s peak is unaffected. The La 3d3/2 peak at a binding energy of 854.8 eV on the clean surface splits into two components at 855.2 and 852.1 eV after a 10 L O2 exposure at room temperature. Annealing the surface to600 °C and then to 700 °C produces sharp c(2 × 2) and p(2 × 1) LEED patterns, respectively. The La 3d peaks still show two components for both LEED patterns indicating oxygen bonding to La in both oxygen overlayer structures whereas the B 1s region remains unaffected. Thus while the XPS data clearly reveal oxygen adsorption at La sites, there is no indication of adsorption at boron sites for low O2 exposures. More extensive oxidation at high...