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We examine the structure and composition of phase-pure epitaxial α-(Fe1-xVx)2O3 thin films deposited on a-Al2O3(0001) substrates by oxygen-plasma-assisted molecular beam epitaxy for 0⩽x⩽~0.5. The films crystallize in the corundum lattice, with vanadium substituting for iron throughout. Vanadium cations exhibit the expected 3+ charge state in the bulk, but exhibit higher valences nearer to the surface, most likely because of excess oxygen in interstitial sites near the surface. The extent of vanadium oxidation beyond the 3+ state is inversely proportional to x. The gradation of vanadium valence with depth has an impact on local bonding geometries, and could be highly significant in this material's efficiency as a photocatalyst. [ABSTRACT FROM AUTHOR]

Tailored metal alloy thin film-oxide interfaces generated using molecular beam epitaxy (MBE) deposition of alloy thin films on a single crystalline oxide substrate can be used for detailed studies of irradiation damage response on the interface structure. However, the presence of nanoscale phase separation in the MBE grown alloy thin films can impact the metal-oxide interface structure. Due to nanoscale domain size of such phase separation, it is very challenging to characterize by conventional techniques. Therefore, laser assisted atom probe tomography (APT) was utilized to study the phase separation in epitaxial Cr0.61Mo0.39, Cr0.77Mo0.23, and Cr0.32V0.68 alloy thin films grown by MBE on MgO(001) single crystal substrates. Statistical analysis, namely frequency distribution analysis and Pearson coefficient analysis of experimental data was compared with similar analyses conducted on simulated APT datasets with known extent of phase separation. Thus, the presence of phase separation in Cr-Mo films, even when phase separation was not clearly observed by x-ray diffraction, and the absence of phase separation in the Cr-V film were confirmed. [ABSTRACT FROM AUTHOR]

We study planar defects in epitaxial Co:ZnO dilute magnetic semiconductor thin films deposited on c-plane sapphire (Al2O3), as well as the Co:ZnO/Al2O3 interface, using aberration-corrected transmission electron microscopy and electron energy-loss spectroscopy. Co:ZnO samples that were deposited using pulsed laser deposition and reactive magnetron sputtering are both found to contain extrinsic stacking faults, incoherent interface structures, and compositional variations within the first 3-4 Co:ZnO layers next to the Al2O3 substrate. The stacking fault density is in the range of 1017 cm-3. We also measure the local lattice distortions around the stacking faults. It is shown that despite the relatively high density of planar defects, lattice distortions, and small compositional variation, the Co:ZnO films retain paramagnetic properties. [ABSTRACT FROM AUTHOR]

We examine the crystal structure and electrical and optical properties of ZnO epitaxial films grown by pulsed laser deposition in a H2 or D2 ambient. n-type electrical conductivity is enhanced by three orders of magnitude as a result of growing in H2 (D2) compared to ZnO films grown in O2. Hall effect measurements reveal very small carrier activation energies and carrier concentrations in the mid-1018 cm-3 range. Optical absorption measurements show that the enhanced conductivity is not a result of ZnO reduction and interstitial Zn formation. Photoluminescence spectra suggest excitonic emission associated with exciton-hydrogen donor complex formation and show no evidence for midgap emission resulting from defects. We have modeled the transport properties of H (D) doped ZnO films using variable range hopping and surface layer conductivity models, but our data do not fit well with these models. Rather, it appears that growth in H2 (D2) promotes the formation of an exceedingly shallow donor state not seen in ZnO crystals annealed in H2 after growth. This new state may be associated with H (D) substitution at O sites in the lattice. [ABSTRACT FROM AUTHOR]

Pure anatase TiO2 and CoxTi1-xO2 (0.01

Decomposition and mineralization of cover crop roots needs to be understood to determine if N taken up by cover crops is mineralized during main crop growth. Two experiments were conducted in a controlled environment to measure decomposition of oat (Avena sativa L. `Ogle') and rye (Secale cereale L. `Rymin') root residues and to examine its effect on soil N mineralization. In the first, oat and rye roots were mixed with soil and in the second, roots were grown in situ. At 7, 14, 28, 56, 84, and 112 d after the start of decomposition, denitrification, soil [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII], and soil [MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII] were measured to determine net mineralized N. Soil respiration and C and N contained in roots and coarse soil organic matter were measured to determine decomposition. All treatments in both experiments showed an increase in net mineralized N during the first 56 d. After 56 d, net mineralized N in the control remained relatively constant, whereas mineral N continued to accumulate in the treatments with root residues. Net N mineralization of the rye and oat root treatments did not differ. Roots mixed with soil had high respiration rates during the first 3 d and there were no differences between oat and rye root treatments. In the roots in situ experiment, however, respiration peaked for oat roots at Day 12 and for rye roots at Day 33. The oat treatment also had less C and N remaining in roots and coarse organic matter throughout the experiment. Even though oat roots decomposed faster than the rye roots, we predict that [is less than] 55% of the N contained in the roots of a spring-killed oat or rye cover crop will become available to the following crop.