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The electronic and phononic properties of [V.sub.2]A1C have been extensively studied using ab initio pseudopotential density functional theory. Our investigations revealed that the longest V-V bond and its least variations have led to the stiffer c axis. The nearly unchanged net charge of the C atom under pressure has led to nearly unchanged overlapped populations along the C-V bond. The obvious charge transfer of V → Al has induced significant variations of the overlapped populations along Al-V and V-V bonds. An anomalous variation of charge transfer between V and Al atoms and V-V bond populations at about 700 GPa has been revealed, which may relate to its structural instability at about 731 GPa. Previously calculated structural instability at about 731 GPa has been successfully confirmed by the present phonon dispersion curve. The bonding natures are also studied by the electron density difference, electron density of states, and the energy band structure. PACS Nos.: 63.20.D-, 71.20.-b, 71.15.Mb. Nous avons fait une etude en profondeur des proprietes de [V.sub.2]A1C en utilisant la theorie de la fonctionnelle de densite avec pseudo-potentiel ab initio. Notre etude revele que le plus grand lien V-V et sa petite variation sont responsables de la forte rigidite de l'axe c. La charge nette de l'atome C ne change pratiquement pas sous la pression, indiquant une constance des populations de recouvrement dans le lien C-V. L'evident transfert de charges V → Al induit des variations significatives des populations de recouvrement dans les liens V-Al et V-V. Nous notons une variation anomale de transfert de charges entre les atomes V et Al autour de 700 GPa, ce qui pourrait etre relie a l'instabilite structurelle observee a 731 GPa. Des calculs anterieurs de cette instabilite structurelle a 731 GPa ont ete confirmes avec succes par notre courbe de dispersion des phonons. Nous etudions egalement la nature des liens a l'aide de la difference dans la densite electronique, de la densite d'etats electroniques et de la structure des bandes d'energie. [Traduit par la Redaction], 1. Introduction The [M.sub.n+1]A[X.sub.n] phases, where M is an early transition metal, A is an A-group element (mostly IIIA and IVA elements), X is either C or N, and n [...]

The systematic trends of electronic structure and optical properties of Ru[O.sub.2] consisting of its four phases have been studied by using norm-conserving pseudopotential within the generalized gradient approximation for the exchange- correlation potential. The total density of states (DOS) and energy band structure investigations revealed that the fluorite phase possesses the broadest conduction bandwidth (0-30 eV) and the pyrite phase possesses the narrowest conduction bandwidth (0-5 eV). Study on partial DOS we found that O 2p electrons of the fluorite phase present a significant shift towards the Fermi level and Ru s and p electrons of the rutile phase contribute little to the orbital energy level formation. For the first time, we found that the norm-conserving pseudopotential failed to obtain the normal DOS and energy band distributions for a rutile Ru atom below about -10 eV, whereas such missing electronic distributions could be obtained successfully using an ultrasoft pseudo potential. Investigations on the optical properties further found that the rutile and Ca[Cl.sub.2]-type phases behave more similarly and the fluorite phase shows the most sensitive response in the whole radiation reaction region. The electron energy loss function revealed that the pyrite phase corresponds to the least relative intensity. PACS Nos: 63.20.dk, 71.20.-b, 78.20.Ci Nous utilisons un pseudo-potentiel a norme conservee dans l'approximation du gradient generalise pour obtenir le potentiel d'echange-correlation, afin d'etudier les tendances systematiques de la structure electronique et des proprietes optiques du Ru[O.sub.2], incluant ses quatre phases. La densite totale d'etats (DOS) et la structure de la bande d'energie revelent que la phase fluorite possede la plus grande largeur de bande de valence (0-30 eV) et que la phase pyrite possede la plus etroite (-20-0 eV). Etudiant les DOS partielles, nous trouvons que les electrons 2p de O dans la phase fluorite montrent un deplacement marque vers le niveau de Fermi, alors que les electrons s et p du Ru dans la phase rutile contribuent peu aux niveaux d'energie orbitaux. Pour la premiere fois, nous trouvons que le pseudo-potentiel a norme conservee echoue a obtenir la DOS normale et les distributions de bande d'energie pour le Ru rutile sous -10 eV, alors que de telles distributions sont obtenues avec succes a partir de pseudo-potentiels ultra mous. Etudiant les proprietes optiques, nous trouvons que les phases rutile et du type Ca[Cl.sub.2] sont plus proches et que la phase fluorite a la reponse la plus sensible sur toute la region de reaction radiative. La fonction de perte d' energie electronique revele que la phase pyrite a la plus faible intensite relative. [Traduit par la Redaction], 1. Introduction The low resistivity and reactivity of Ru[O.sub.2] has made it technologically important as a strip-line conductor in integrated circuits, as a diffusion barrier in contact metallizations, etc. [1, [...]

Research describing the electrical effects of carbon dispersed in gallium nitride is presented. In particular the formation of microcrystalline graphite is investigated by means of Raman spectroscopy.

Both Fourier transform infrared (FTIR) grazing incidence reflectivity and FTIR transmission techniques were employed to investigate GaN films grown on alpha-Al2O3 (0001) substrates by atmospheric pressure metal-organic chemical vapor deposition and low pressure metal-organic chemical vapor deposition. Findings revealed that in the frequency range of 400 to 3500/cm the signal-to-noise ratio of the FTIR grazing incidence measurement is much larger than that of the FTIR transmission measurement.

An experimental examination of the Lorentz force free c-axis magnetoresistivity as a function of temperature and field H for single-crystalline (La(sub 1-x)Sr(sub x))2CuO4 reveals that the extended Josephson coupling model considers both effective thermal energy and anisotropy. All magnetoresistivity curves obtained in H//I//c at different constant temperatures can form a single curve with no adjustable constraints in a broad transition area.

Surface magneto-optic Kerr effect, reflection high energy electron diffraction, broad-beam auger electron spectroscopy and secondary electron imaging characterize the magnetic and structural properties of ultra thin films of Fe on Cu(100) lattices. Room temperature grown films are nonmagnetic below 2.1 ML. The films are ferromagnetic between 2.3 and 5 ML beyond which they lose their ferromagnetic property.

An analysis of the combined magnetooptical surface Kerr effects in room temperature grown epitaxial Fe thin films reveals that all three effects, relative to the scattering plane, can be detected by adjusting all three optical device orientations int the SMOKE system. Combined Kerr effects are simplified by optical device orientation, while transverse Kerr effect is removed by arranging the devices properly. Longitudinal Kerr effects are minimized at normal incidence for maximum polar Kerr effect signal strength.

A study was conducted on two local vibrational modes related to defects and hydrogen in undoped GaN and their atomic structures. The samples were grown using low pressure metalorganic vapor phase epitaxy, irradiated by gamma ray and then exposed to a radio frequency hydrogen plasma. A weak infrared band, which can be enhanced by gamma-ray irradiation, appears in the process of proton implantation.

Real space measurements of initial phases of fcc Fe/Cu(100) hetero-epitaxy reveal the Fe-Cu vertical atomic site exchange at subsurface and supersurface island regions during monolayer deposition. Subsurface and supersurface islands are two-dimensional structures, characterized by electron imaging and regulated by template surface properties.

Three-axis surface magneto-optical Kerr (SMOKE) effects techniques investigating the switching behavior of Fe/Cu(100) thin films indicate the presence of canted stimulated uniaxial anisotropy in the out-of-plane complex of the film. Rotational processes of SMOKE indicate the cubic anisotropy of in-plane complexes at 45 degrees orientation in the films.

Metal-organic vapor phase epitaxy is used for growing light emitting diodes (LEDs) by using InGaN/GaN quantum wells (QWs) with thin low temperature GaN (LT-GaN) layers bounding each InGaN layer. The better performance of LEDs incorporating the LT-GaN layers is because of the suppressed polarization from piezoelectric fields.

The transmission electron microscopy technique is employed to explain the microstructures of the various [In.sub.x][Al.sub.1-x]N epilayers that are grown on the GaN templates by the metalorganic chemical vapor deposition technique. The various effects of different strains on the structures and properties of these compounds are also analyzed.

Photoluminescence and monoenergetic positron annihilation spectroscopy are used for examining the yellow luminescence (YL) in as-grown high-resistance (HR) and unintentional-doped (UID) GaN films grown by metal organic chemical vapor deposition. The studies have shown that the increased wave function overlap of electrons and holes induced by the strong space localization effect of holes deduced from the short positron diffusion length is the vital factor to increase the YL efficiency in HR-GaN.

The structural, optical, and magnetic properties of Cu-implanted GaN films are examined. The results have shown that the vacancylike defects are considered for understanding the magnetic properties of the Cu-implanted GaN films.

A combination of spectroscopic and microscopic studies is conducted to examine the morphology and microstructure of dislocation etch pits in GaN epilayers etched by molten KOH. The results revealed that the chemical stabilization of Ga-polar surface plays a significant role in the formation of various types of dislocation etch pits.

The morphology and microstructure evolution of [Al.sub.0.3][Ga.sub.0.7]N epilayers grown on GaN/sapphire templates with low-temperature (LT) AlN interlayers (IL) by using metal organic chemical vapor deposition are examined by transmission electron microscopy and atomic force microscopy. The strain in [Al.sub.x][Ga.sub.1-x]N epilayers is modified by inserting the AlN IL because of the lattice mismatch between AlN, GaN, and [Al.sub.x][Ga.sub.1-x]N, which has further changed the formation of the edge-type threading dislocations.

Analysis of the magnetoresistance of magnetically ordered icosahedral quasicrystals Al-Pd-Mn-B shows that magnetoresistance undergoes a systematic alteration with changes in boron concentration. The crystals have negative magnetoresistance for boron concentrations of 8 and 10 at low magnetic fields and at high magnetic fields, they have positive magnetoresistance. The strong and weak spin-orbit scatterings due to high and low boron concentration account for the positive and negative magnetoresistance, respectively.

Abstract: Tunneling induced electron transfer in SiN x /Al0.22Ga0.78N/GaN based metal–insulator–semiconductor (MIS) structures has been investigated by means of capacitance–voltage (C–V) measurements at various temperatures. Large clock-wise hysteresis window in C–V profiles indicates the injection of electrons from the two-dimensional electron gas (2DEG) channel to the SiN x layer. Depletion of the 2DEG at positive bias in the negative sweeping direction indicates that the charges injected have a long decay time, which was also observed in the recovery process of the capacitance after injection. The tunneling induced electron transfer effect in SiN x /Al0.22Ga0.78N/GaN based MIS structure opens up a way to design Al x Ga1−x N/GaN based variable capacitors and memory devices. [Copyright &y& Elsevier]