Defect Surface States Research Articles

Reactions of NO and H2O on the PuO2 {111} surface: A DFT study

The effect of the Hubbard U parameter is explored in periodic boundary condition PBE+U calculations of a variety of properties of bulk PuO2 and its {111} surface. Comparison is made with experimentally-determined bulk and surface properties, including band gap and lattice parameter, hybridization of the Pu 5f and O 2p states at the top of the valence band, peak separation in the valence band, and the {111} surface work function. Comparative PBE0 calculations, and the Bader charges of the atoms in the {111} surface, are also assessed. A U value of 3 eV is recommended, and is used in PBE+U study of H2O and NO reacting both individually and sequentially on PuO2 {111}. For NO interacting individually, approach to the surface is orientation-dependent, and surface-bound NO forms defect surface states between the valence and conduction bands. For water reactions with and without NO present on the surface, the Pu 5f band centre plays a major role in the reactions. When NO is present, a linear relation emerges between water adsorption energy and 5f band centre relative to the Fermi level. Both Pu 5f band centre relative to the Fermi level and the energetic gap between the 5f band centre and 2p band centre of the water O govern the barrier to water splitting.

Energy Spectra and Electric and Magnetic Properties of One-Dimensional Stacks of Conjugated π-Electron Systems with Defect Surface States. II. π-Systems with Schottky and Chemisorption Surface States

The energy spectra and magnetic properties of one-dimensional stacks consisting of polycyclic aromatic hydrocarbons with Schottky, chemisorption, and Tamm-chemisorption-type surface defects are inv...

Surface defects in semiconductor lasers studied with cross-sectional scanning tunneling microscopy

Cross-sectional scanning tunneling microscopy is used to study defects on the surface of semiconductor laser devices. Step defects across the active region caused by the cleave process are identified. Curved blocking layers used in buried heterostructure lasers are shown to induce strain in the layers above them. Devices are also studied whilst powered to look at how the devices change during operation, with a numerical model that confirms the observed behavior. Whilst powered, low-doped blocking layers adjacent to the active region are found to change in real time, with dopant diffusion and the formation of surface states. A tunneling model which allows the inclusion of surface states and tip-induced band bending is applied to analyze the effects on the tunneling current, confirming that the doping concentration is reducing and defect surface states are being formed.

Energy Spectra and Electric and Magnetic Properties of 1D Stacks of Conjugated π-Electron Systems with Defect Surface States. I. π Systems with Tamm Surface States

The energy spectra and the electric and magnetic properties of one-dimensional (1D) stacks consisting of conjugated π-electron systems (polycyclic aromatic hydrocarbons and polymethines) with Tamm defects are investigated theoretically by means of the many-electron band theory. The conditions for the relative arrangement of the stacks in terms of the slip parameters for yielding different magnetic and electric ground-state properties are studied.

Analysis of the low-frequency dispersion of the dielectric parameters in AsxSe1-x amorphous layers

This paper reports on the results of the investigation into the dispersion of the permittivity e’ and the dielectric loss tangent tanδ for amorphous layers in the AsxSe1-x system (x = 0.4, 0.5) in the frequency range from 10−3 to 10−1 Hz. It is found that the permittivity increases with a decrease in the frequency of the polarizing field due to the possible effect exerted by defect surface states on the polarization processes occurring in the layers of this system. The shape of the Cole-Cole plots indicates the existence of several groups of relaxation oscillators that are responsible for the relaxation processes observed in this frequency range.

Efficient Luminescence from Rare‐Earth Fluoride Nanoparticles with Optically Functional Shells

AbstractRare‐earth fluorides are a class of materials with considerable potential in optical applications. Fluoride lattices typically permit high coordination numbers for the hosted rare‐earth ions, and the high ionicity of the rare‐earth‐to‐fluorine bond leads to a wide bandgap and very low vibrational energies. These factors make rare‐earth fluorides very useful in optical applications employing vacuum ultraviolet and near‐infrared excitation. The preparation of nanometer‐sized particles has opened the door for new properties and devices if the performance of their macroscopic counterparts can be conserved in the nanometer regime. However, at small particle sizes, defect surface states and adhering water reduce the optical efficiency. These shortcomings can be reduced by applying protective shells around the luminescent cores, which can also be involved in the luminescent process.

5218. Intrinsic and defect surface states on single-crystal metal oxides: Victor E Henrich and Richard L Kurtz,J Vac Sci Technol,18 (2), 1981, 416–419

5218. Intrinsic and defect surface states on single-crystal metal oxides: Victor E Henrich and Richard L Kurtz,J Vac Sci Technol,18 (2), 1981, 416–419

Intrinsic and defect surface states on single‐crystal metal oxides

The electronic properties of the surfaces of several single‐crystal metal oxides have been studied by electron spectroscopic techniques, yielding information on both intrinsic and extrinsic (defect) surface states. SrTiO3 and TiO2 have no intrinsic band‐gap surface states, while nearly perfect MgO(100) surfaces exhibit a cation‐derived empty surface state about 2 eV below the bulk conduction band edge. Defect surface states generally involve 0 vacancies, with attendant charge transfer to surface cations that results in occupied states in the band‐gap region.

Surface defects and the electronic structure of SrTiO3surfaces

The electronic properties of various types of SrTi${\mathrm{O}}_{3}$ surfaces have been studied by using ultraviolet-photoemission and electron-energy-loss spectroscopy, low-energy electron diffraction and Auger spectroscopy. Vacuum-fractured surfaces exhibit weak photoemission in the region of the bulk band gap, which is probably due to residual surface defects. When surface defects are produced by Ar-ion bombardment, a much stronger band of surface states appears in the band-gap region. These states arise from the creation of ${\mathrm{Ti}}^{3+}$-O-vacancy complexes and are predominantly of $d$-electron character. Two surface defect phases are seen, one due to surface disorder and the other to changes in surface composition. The latter phase is stable under annealing to at least 1100 K. Exposure to ${\mathrm{O}}_{2}$, however, depopulates the band-gap surface states on both vacuum-fractured and ion-bombarded surfaces. Models for the detailed structure of the defect surface states are discussed.