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The optical Stark effect in the Q(1) and R(0) lines of the [15.1]1-X 1Σ+ (1,0) band of rhodium mononitride (RhN) were recorded and analyzed to determine the permanent electric dipole moments μ for the X 1Σ+(υ=0) and [15.1]1(υ=1) states to be 2.43(5) and 1.75(1) D, respectively. The determined dipole moments are compared to predicted values obtained from density functional theory [Stevens et al., Chem. Phys. Lett. 421, 281 (2006)] and an all-electron ab initio calculation [Shim et al., J. Mol. Struct. THEOCHEM 393, 127 (1997)]. A simple single configuration molecular orbital correlation diagram is used to rationalize the relative values of μ for the 4d mononitrides and RhO. An electronic configuration for the [15.1]1 state is proposed based on the interpretation of the 103Rh and 14N magnetic hyperfine interactions. [ABSTRACT FROM AUTHOR]

We have studied Al/Nb interface with help of spectroscopy of reflected electrons. Ion sputtering combined with monitoring of Auger peaks has been used to approach the interface. The developed method of quantitative interpretation of spectra allowed us to characterize the distribution of Al and Nb in the interface region with a nanometer depth resolution. The Al/Nb interface was found to have an intermediate layer of about 10 nm thickness, which is more likely due to the interface roughness, rather than diffusion smearing. We discuss the possibility to distinguish by means of spectroscopy of reflected electrons either material under analysis is a single phase or a mixture of two phases. [ABSTRACT FROM AUTHOR]

We present a direct observation of time-resolved intervalley transitions of electrons between the conduction band Γ and L valleys in GaN single crystals using a two-color (ultraviolet and near-infrared), femtosecond, pump-probe spectroscopic technique. We have found that the threshold for the Γ↔L transition appears at the energy of 4.51±0.05 eV and the electron scattering time from the Γ to L valley is comparable to the 170 fs width of our pump pulses, while the return process of electrons from L to Γ is measurably slower. The L to Γ scattering time is 1.02 ps, while the total depopulation time of the L valley is estimated to be ∼20 ps. Our physical model, based on the three-state rate equations, fitted our experimental data very well and allowed us to calculate the optical phonon emission time of 290 fs. The deformation potential between the two valleys was also obtained from the intervalley scattering modeling and the value was 0.92×109 eV/cm. [ABSTRACT FROM AUTHOR]

The solvation of electrons in polar liquids is analyzed on the basis of an extended continuum model. In addition to the long-range electron-dipole interaction two short-range interactions are introduced. Among others one accounts for interactions with groups capable of forming hydrogen bonds and the second for quadrupolar characteristics of the liquid molecules. Both are induced by the orientation of the molecular dipole. Applying the scaling method a proper reaction coordinate is introduced and the solvation dynamics are discussed for the electron in the electronic ground state and after excitation to the p-type excited state. The observed spectral evolution of the transient absorption spectra, after two photon excitations for electrons in water and in methanol, is well described by this theory. An analytic estimate for the nonradiative deactivation from the electronically excited solvated electron is found to be consistent with an observed lifetime of 50 fs for the electron in water. The theory predicts an about three times slower internal conversion in methanol as solvent in comparison with water. [ABSTRACT FROM AUTHOR]

We report the bipolar transport properties of the LUMATION™ (Sumitomo Chemical) 1300 Series green-emitting polymer investigated by means of admittance spectroscopy. Analysis of the inductive response in single-carrier polymer diodes yields electron and hole mobilities which are in excellent agreement with the results of independent measurements. Admittance measurements in dual injection diodes, in combination with the analysis of current-voltage characteristics, provide evidence that the dual injection diodes operate in space-charge-limited regime, indicative of strong recombination within the material. Our results provide strong evidence that the space-charge-related admittance response of dual-carrier diodes is dominated by combined electron-hole response, which corresponds to the sum of electron and hole mobilities. This implies that electron and hole mobilities cannot be obtained separately from admittance measurements in space-charge-limited dual-carrier devices. [ABSTRACT FROM AUTHOR]

As-supplied polycrystalline ZnO samples (purity 99.9% from Sigma-Aldrich, Germany) have been annealed at different temperatures and subsequently characterized by positron annihilation spectroscopy, x-ray-diffraction (XRD) analysis, thermogravimetric analysis (TGA), and resistivity measurements. Positron annihilation lifetime analysis and coincidence Doppler-broadened electron-positron annihilation γ-radiation (CDBEPAR) line-shape measurements have been employed at a time to identify the nature of defects in differently annealed ZnO materials. Annealing up to 300 °C, an increase of defect lifetime (τ2) as well as shape parameter (S parameter) has been observed. Further annealing causes a large decrease of τ2 and S parameter. TGA study shows considerable mass loss from ZnO as the annealing temperature is increased above 300 °C. This is possibly due to oxygen evaporation from the sample. The c-axis lattice parameter, extracted from the XRD spectra, shows an increase due to annealing above 600 °C, which is a signature of the presence of a huge number of oxygen vacancies. Resistivity variations of the annealed samples are also consistent with the TG and XRD analyses. The ratio curve analysis of the CDBEPAR spectra successfully probes the change in zinc-related vacancy defects in annealed ZnO. [ABSTRACT FROM AUTHOR]

Accelerator-based γ-ray-induced positron annihilation spectroscopy performs positron annihilation spectroscopy by utilizing MeV bremsstrahlung radiation generated from an accelerator (We have named the technique “accelerator-based γ-ray-induced PAS,” even though “bremsstrahlung” is more correct here than “γ rays”. The reason for that is to make the name of the technique more general, since PAS may be performed by utilizing MeV γ rays emitted from nuclei through the use of accelerators as described later in this article and as in the case of positron lifetime spectroscopy [F.A. Selim, D.P. Wells, and J.F. Harmon, Rev. Sci. Instrum. 76, 033905 (2005)].) instead of using positrons from radioactive sources or positron beams. MeV γ rays create positrons inside the materials by pair production. The induced positrons annihilate with the material electrons emitting a 511-keV annihilation radiation. Doppler broadening spectroscopy of the 511-keV radiation provides information about open-volume defects and plastic deformation in solids. The high penetration of MeV γ rays allows probing of defects at high depths in thick materials up to several centimeters, which is not possible with most of the current nondestructive techniques. In this article, a detailed description of the technique will be presented, including its benefits and limitations relative to the other nondestructive methods. Its application on the investigation of plastic deformation in thick steel alloys will be shown. [ABSTRACT FROM AUTHOR]

Ab initio calculations were carried out to study the structures of the photoelectron spectra of the O2 molecule using complete active space self-consistent field and multireference single and double excitation configuration interaction methods. We focused our attention primarily on the inner-valence ionized states lying below 26 eV. Vibrational levels were calculated using adiabatic potential curves and vibrational wave functions were used to obtain Franck–Condon factors. We show that not only discrete vibrational levels of (3) 2Πu, but also the continuum of nuclear motion in (1) 2Σu- contribute to the bands of vibrational progression and the broad peak of the continuum between 22.5 and 26 eV. Other states with weak intensity lying between 19 and 26 eV are also discussed. © 2005 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Electron-bound water clusters [e-(H2O)n] show very strong peaks in mass spectra for n=2, 6, 7, and (11), which are called magic numbers. The origin of the magic numbers has been an enigma for the last two decades. Although the magic numbers have often been conjectured to arise from the intrinsic properties of electron-bound water clusters, we attributed them not to their intrinsic properties but to the particularly weak stability of the corresponding neutral water clusters (H2O)n=2,6,7, and (11). As the cluster size increases; this nonsmooth characteristic feature in stability of neutral water clusters is contrasted to the smooth increase in stability of e--water clusters. As the magic number clusters have significant positive adiabatic electron affinities, their abundant distributions in atmosphere could play a significant role in atmospheric thermodynamics. © 2005 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The Zeeman effect in the excited A 2Π3/2 state of CaF is measured and analyzed over a wide range of magnetic fields. It is found that the splitting of the Zeeman levels is largely determined by the coupling between different rotational states and there are no low-field seeking states in the J=3/2 manifold of Zeeman levels at high magnetic fields. A model of the Zeeman spectrum based on the ligand-field theory of CaF is shown to be accurate in the interval of magnetic fields 0–5 Tesla. This demonstrates that the magnetic moment of the CaF(A 2Π3/2) molecule is effectively determined by the spin angular momentum of a single electron and the orbital motion of the valence electron around the Ca2+ core. An analysis of the Zeeman spectrum as a function of the molecular rotational constant indicates that 2Π3/2 molecules should have significant rotational constants (at least as large as twice the rotational constant of CaF) to be amenable to magnetic trapping in high fields.© 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We study inelastic electron tunneling through a molecular junction using the nonequilibrium Green’s function formalism. The effect of the mutual influence between the phonon and the electron subsystems on the electron tunneling process is considered within a general self-consistent scheme. Results of this calculation are compared to those obtained from the simpler Born approximation and the simplest perturbation theory approaches, and some shortcomings of the latter are pointed out. The self-consistent calculation allows also for evaluating other related quantities such as the power loss during electron conduction. Regarding the inelastic spectrum, two types of inelastic contributions are discussed. Features associated with real and virtual energy transfer to phonons are usually observed in the second derivative of the current I with respect to the voltage [uppercase_phi_synonym] when plotted against [uppercase_phi_synonym]. Signatures of resonant tunneling driven by an intermediate molecular ion appear as peaks in the first derivative dI/d[uppercase_phi_synonym] and may show phonon sidebands. The dependence of the observed vibrationally induced lineshapes on the junction characteristics, and the linewidth associated with these features are also discussed. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The Zeeman effect in the excited A 2Π3/2 state of CaF is measured and analyzed over a wide range of magnetic fields. It is found that the splitting of the Zeeman levels is largely determined by the coupling between different rotational states and there are no low-field seeking states in the J=3/2 manifold of Zeeman levels at high magnetic fields. A model of the Zeeman spectrum based on the ligand-field theory of CaF is shown to be accurate in the interval of magnetic fields 0–5 Tesla. This demonstrates that the magnetic moment of the CaF(A 2Π3/2) molecule is effectively determined by the spin angular momentum of a single electron and the orbital motion of the valence electron around the Ca2+ core. An analysis of the Zeeman spectrum as a function of the molecular rotational constant indicates that 2Π3/2 molecules should have significant rotational constants (at least as large as twice the rotational constant of CaF) to be amenable to magnetic trapping in high fields.© 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In this work, the decay of secondary-electron emission (SEE) intensity and charging of hydrogenated and hydrogen-free diamond film surfaces subjected to incident electron irradiation at energies between 5 and 20 eV are investigated. Electron emission curves as a function of incident electron energy were measured. For the hydrogenated films, it was found that the SEE intensity decays in intensity under continuous electron irradiation, albeit maintains a nearly constant onset. The decay in time of the SEE intensity was measured for various incident electron energies. From these measurements, the SEE intensity decay rate from the hydrogenated diamond surface was calculated as a function of incident electron energy and found to display a broad peak at ∼9 eV. The decay of the SEE intensity is explained as due to electron trapping in the near-surface region of the hydrogenated diamond films resulting in the formation of a depletion layer and upward surface band bending while overall charge neutrality is maintained. It is suggested that the mechanism of charge trapping is by resonant electron attachment of incident electrons into C-H (ads) bonds present within the near-surface region of the hydrogenated diamond films which displays a similar dependence on incident electron energy. Upward band bending results in a surface potential barrier to secondary electrons created within the solid. For the hydrogen-free diamond surface, decay in intensity and a positive shift in the onset of the SEE were observed for all incident electron energies and currents used. It was found that surface charging increases monotonically with incident electron energy. In this case, charging is associated with electron trapping into localized surface states of π[sup *] symmetry. These electronic states are associated with surface reconstruction resulting from hydrogen desorption. [ABSTRACT FROM AUTHOR]

To make a uniform AlOx barrier layer in tunnel junctions, a thin layer of Al is often sputtered first and then oxidized. In this study, we sputtered a thick layer of Al onto Fe3O4 and then employed high resolution transmission electron microscopy and x-ray energy dispersive spectroscopy to investigate the interfacial microstructures. Two new layers have been found and investigated at the Al/Fe3O4 interface. The interfacial reaction has been determined to be: Fe3O4+Al⇒Fe+(a)AlOx, where a denotes the amorphous state. The consequence of the interfacial reaction to transport properties is also discussed.© 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We have investigated the effect of a metallic gate on the bound states of a shallow donor located near the gate. We calculate the energy spectrum as a function of the distance between the metallic gate and the donor and find an anticrossing behavior in the energy levels for certain distances. We show how a transverse electric field can tune the average position of the electron with respect to the metallic gate and the impurity. [ABSTRACT FROM AUTHOR]

The authors have used positron annihilation spectroscopy and photoluminescence measurements to study the influence of silicon doping on vacancy formation in AlGaN:Si structures. The results show a correlation between the Doppler broadening measurements and the intensity from 510 nm photoluminescence transition. The reduction in the W parameter when the [Si]/[Al+Ga] fraction in the gas phase is above 3×10-4 indicates that the positrons annihilate in an environment where less Ga 3d electrons are present, i.e., they are trapped in group-III vacancies. The observation of vacancies at these silicon concentrations coincides with the onset of the photoluminescence transition at 510 nm. [ABSTRACT FROM AUTHOR]

Optically detected magnetic resonance and positron annihilation spectroscopy experiments have been employed to study magnesium-doped GaN layers grown by metal-organic vapor phase epitaxy. As the Mg doping level is changed, the combined experiments reveal a strong correlation between the vacancy concentrations and the intensity of the red photoluminescence band at 1.8 eV. The analysis provides strong evidence that the emission is due to recombination in which electrons both from effective-mass donors and from deeper donors recombine with deep centers, the deep centers being vacancy-related defects. [ABSTRACT FROM AUTHOR]

The terminations of buried surfaces of two different cavity types (nano- and microcavities) produced in the same He+–H+ co-implanted p-type Si (100) sample annealed at 900 °C, are studied and characterized by positron annihilation spectroscopy. The characterization was carried out by means of three complementary positron techniques: Doppler broadening and coincidence-Doppler broadening spectroscopy with a continuous slow positron beam, and lifetime spectroscopy with a pulsed slow positron beam. It was found that the nanocavities have a pristine surface of Si, while the surfaces of the microcavities, formed below protruding blisters, are oxygen decorated. This case study opens the interesting use of the positron spectroscopy tool in the topical subject of empty space for microelectronics applications. [ABSTRACT FROM AUTHOR]

An analytical approach was proposed for simultaneously determining an inelastic mean-free path (IMFP) and a surface excitation parameter (SEP) with absolute units by the analysis of an absolute experimental reflection electron energy loss spectrum. The IMFPs and SEPs in Ni were deduced for electrons of 300 to 3000 eV. The obtained IMFPs were in good agreement with those calculated using the TPP-2M equation. The Chen-type empirical formula was proposed for determining the SEP. The results confirmed the applicability of the present approach for determining the IMFP and SEP for medium-energy electrons. [ABSTRACT FROM AUTHOR]

Electron transfer from sol–gel–prepared TiO2 into adsorbed benzene diazonium compounds has been investigated using cyclic voltammetry, x-ray photoelectron spectroscopy, contact potential difference, and surface photovoltage spectroscopy. The results show that the potential of maximum electron transfer depends strongly on the dipole moment of the benzene compound. Two reactive surface sites at which electron transfer occurs have been identified. [ABSTRACT FROM AUTHOR]