The valence band (VB) structures of face-centered-cubic Ag-Rh alloy nanoparticles (NPs), which are known to have excellent hydrogen-storage properties, were investigated using bulk-sensitive hard x-ray photoelectron spectroscopy. The observed VB spectra profiles of the Ag-Rh alloy NPs do not resemble simple linear combinations of the VB spectra of Ag and Rh NPs. The observed VB hybridization was qualitatively reproduced via a first-principles calculation. The electronic structure of the Ag0.5Rh0.5 alloy NPs near the Fermi edge was strikingly similar to that of Pd NPs, whose superior hydrogen-storage properties are well known.
In this work, we developed a solution growth method that uses Li–Al–N solution to epitaxially grow AlN on a self-nucleated, columnar AlN seed crystal. The seed crystal was grown by physical vapor transport, and the solution was obtained by annealing a Li3N–Al mixture. The epitaxial AlN grew ∼5 µm in 10 h. Scanning electron microscopy analyses showed that the grown layer had many voids near the epilayer/seed interface, but no evidence of cracks. Using transmission electron microscopy analyses, we found that the growth direction of the AlN was [1100] and the layer had threading dislocation propagating along [1100] with a density of ∼4×108 cm-2.
The effect of growth orientation on In incorporation efficiency in InGaN films grown by metal–organic vapor phase epitaxy (MOVPE) is theoretically investigated. We propose a new theoretical model that explains the role of the surface N–H layer in In incorporation based on first-principles calculations. During III–nitride MOVPE, N-terminated reconstruction with N dangling bonds passivated by H is stable. A surface N–H layer that covers a group-III (In, Ga) atomic layer prevents In atoms from desorbing and being replaced by Ga atoms. In incorporation is therefore more efficient for higher N–H layer coverage and stability. To investigate this relationship, the enthalpy change for the decomposition of a N–H layer was calculated. This enthalpy change which depends on growth orientations is in good agreement with the experimental In content.
Using the density functional theory, we study the geometric and electronic structures of a GaN sheet possessing a honeycomb network. The sheet preserves the planar conformation under an equilibrium lattice constant of 3.2 Å, possessing a semiconducting electronic structure with an indirect band gap of 2.28 eV. The biaxial compressive strain causes structural buckling, leading to polarization normal to the atomic layer. An external electric field normal to the layer also induces structural buckling whose height is proportional to the field strength. The polarity of the buckled GaN sheet is tunable by attaching H atoms on Ga and N atoms.
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