T. C. Lovejoy

Surface morphology and electronic structure of bulk single crystal β-Ga2O3(100)

Experimental studies of the surface morphology and electronic structure of bulk single crystals of the transparent and wide gap semiconductor gallium oxide (β-Ga2O3) have been conducted using scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), and angle-resolved photoemission spectroscopy (ARPES). Atomically resolved STM and LEED results for the β-Ga2O3(100) surface clarify that the predominant surface termination contains both gallium and oxygen, and this surface does not exhibit a reconstruction. The valence band structure was obtained with ARPES and shows good agreement with existing theoretical works at the zone center and along the a∗ and c∗ directions, except that the calculated bandwidth is ∼7% too small. There is poorer agreement along the b∗ direction, where the experimental bands disperse more strongly than the calculations.

Sputtering-induced Co0 formation in x-ray photoelectron spectroscopy of nanocrystalline Zn1-xCoxO spinodal enrichment models

Nanoscale enrichments resulting from spinodal decomposition have been proposed to contribute to the interesting magnetic properties of diluted magnetic oxides such as cobalt-doped ZnO (Zn1-xCoxO), but little is known experimentally about the electronic structures or physical properties of such enrichments. Here, x-ray photoelectron spectroscopy (XPS) is used to examine wurtzite Zn1-xCoxO crystallites over the full composition range (0.0≤x≤1.0) that serve as models of the proposed spinodal decomposition nanostructures within Zn1-xCoxO bulk materials. With increasing x, the valence band edge shifts to smaller binding energies and the cobalt 2p peaks shift to greater binding energies, providing spectroscopic signatures that may allow identification of spinodal decomposition in bulk Zn1-xCoxO. Reduction of Co2+ to Co0 by argon ion (Ar+) sputtering was also found to become markedly more facile with increasing x, suggesting that locally-enriched Zn1-xCoxO is at greater risk of yielding false-positive Co0 XPS si...

MnSe phase segregation during heteroepitaxy of Mn doped Ga2Se3 on Si(001)

Heteroepitaxial thin films of Mn-doped Ga2Se3 are grown by molecular beam epitaxy on Si(001):As. Mn-doped films are laminar for the first 1–2 nm, after which oriented islands with flat tops are observed by scanning tunneling microscopy. In contrast with the bulk phase diagram, which predicts MnGa2Se4 precipitates, the precipitates are identified by bond length measurements from extended x-ray absorption fine structure as rocksalt MnSe. This difference is attributed to superior lattice matching of MnSe to the substrate, and an epitaxial relationship between the MnSe and Si substrate is inferred.