Cameron Keenan

Molecular beam epitaxy and characterization of thin Bi2Se3 films on Al2O3 (110)

The structural and electronic properties of thin Bi2Se3 films grown on Al2O3 (110) by molecular beam epitaxy are investigated. The epitaxial films grow in the Frank-van der Merwe mode and are c-axis oriented. They exhibit the highest crystallinity, the lowest carrier concentration, and optimal stoichiometry at a substrate temperature of 200 °C determined by the balance between surface kinetics and desorption of Se. The crystallinity of the films improves with increasing Se/Bi flux ratio. Our results enable studies of thin topological insulator films on inert, non-conducting substrates that allow optical access to both film surfaces.

Molecular beam epitaxy and characterization of thin Bi{sub 2}Se{sub 3} films on Al{sub 2}O{sub 3} (110)

The structural and electronic properties of thin Bi2Se3 films grown on Al2O3 (110) by molecular beam epitaxy are investigated. The epitaxial films grow in the Frank-van der Merwe mode and are c-axis oriented. They exhibit the highest crystallinity, the lowest carrier concentration, and optimal stoichiometry at a substrate temperature of 200 °C determined by the balance between surface kinetics and desorption of Se. The crystallinity of the films improves with increasing Se/Bi flux ratio. Our results enable studies of thin topological insulator films on inert, non-conducting substrates that allow optical access to both film surfaces.

In situ thin film and multilayer structural characterization using x-ray fluorescence induced by reflection high energy electron diffraction

The angular dependence of the x-ray fluorescence from Y and Mn inner K shell ionization induced by a grazing angle incident electron beam in several multilayered Y/Mn structures was analyzed using the distorted-wave approximation. Estimates of structural parameters, thickness, and interfacial roughness were obtained from the x-ray fluorescence measured in the total reflection regime and compared with ex situ x-ray reflectivity results. Although the sensitivity to the surface and interface roughness was relatively low, the thickness values for both single and buried layers were in good agreement with the x-ray reflectivity measurements.

Properties of YMnO3 self-assembled nanocrystalline prisms on GaN

Growth of YMnO3 on GaN (0001) using molecular beam epitaxy at temperatures greater than 850°C resulted in the spontaneous formation of crystalline prisms, ranging from 20to60nm in height and 50to500nm in lateral size, surrounded by a 6nm thick continuous YMnO3 film. The local dielectric properties were measured using scanning surface probe microscopy. The prisms were ferroelectric at room temperature and their ferroelectric properties were enhanced for taller prisms. This is consistent with these structures being less constrained than the continuous layer, which is clamped by the surrounding unpolarized film.

In-situ stoichiometry determination using x-ray fluorescence generated by reflection-high-energy-electron-diffraction

A major challenge in the stoichiometric growth of complex oxide compounds is the control of the relative compositions of the constituent materials. A potential avenue for compositional analysis during growth is the use of x-ray fluorescence generated during reflection high energy electron diffraction measurements. Using this technique, relative compositions of Y and Mn in molecular beam epitaxy grown YMnO3 samples were studied. Comparing the results with Rutherford back scattering spectroscopy suggests that the technique has the potential for real-time analysis of elemental fluxes and stoichiometry control during sample growth.