Influence of the surface on the quantum P.E.M. effect in InP

The photoelectromagnetic effect of InP is studied in quantizing magnetic fields at 4·2 K in an energy range 1·4–1·5 eV for linearly polarized light. Depending on the sample surface condition two types of spectral oscillations may appear, those associated with interband transitions between Landau levels or the LO phonon type usually seen in photoconductivity. An analysis of the spectral oscillations gives: E₀ = 1·423±0·001 eV; Δ₀ = 0·102±0·006 eV; hω_L = 0·036 eV.     

Absorptionsmessungen an OH-dotierten NaF-Kristallen im Vakuumultraviolett

A new absorption band in NaF at 8·3 eV (149 nm) is assigned to the absorption of OH^? ions. A further band at 8·8 eV (142 nm) is developed by X-raying the crystal or illuminating it with OH light. This band is supposed to be the absorption of O₂ molecules on lattice sites. Thef-value of the OH-band is estimated to 0·2.     

Optical absorption edge in SnS

Optical absorption in single crystals of tin sulfide has been studied at many temperatures between 100 and 300 °K, in the wavelength range 2·2–0·8 μ. From the interference fringe patterns the absorption coefficient, reflection coefficient and index of refraction as a function of wavelength were determined for two light polarizations (ε∥a and ε∥b). From an analysis of the data, indirect band gaps of 1·142 and 1·095 eV were found for the two directions of polarization. Also it was found that the phonon assisted transitions required the participation of two phonons at different energy thresholds with energies 0·033 or 0·038 eV and 0·082 or 0·113 eV, with reference to the two axis. The temperature dependence of the indirect band gap for each direction of light polarization is linear with a slope ?4·05 × 10^?3eV and ?4·37 × 10^?3 eV respectively.     

First-principles investigation of armchair stanene nanoribbons

In this study, we systematically investigated the structural, electronic and optical properties of armchair stanene nanoribbons (ASNRs) by using the first-principles calculations. First, we performed full geometry optimization calculations on various finite width ASNRs where all the edge Sn atoms are saturated by hydrogen atoms. The buckled honeycomb structure of two dimensional (2D) stanene is preserved, however the bond length between the edge Sn atoms is shortened to 2.77 Å compared to the remaining bonds with 2.82 Å length. The electronic properties of these nanoribbons strongly depend on their ribbon width. In general, band gap opens and increases with decreasing nanoribbon width indicating the quantum confinement effect. Consequently, the band gap values vary from a few meV exhibiting low-gap semiconductor (quasi-metallic) behavior to ～0.4–0.5 eV showing moderate semiconductor character. Furthermore, the band gap values are categorized into three groups according to modulo 3 of integer ribbon width N which is the number of Sn atoms along the width. In order to investigate the optical properties, we calculated the complex dielectric function and absorption spectra of ASNRs, they are similar to the one of 2D stanene. For light polarized along ASNRs, in general, largest peaks appear around 0.5 eV and 4.0 eV in the imaginary part of dielectric functions, and there are several smaller peaks between them. These major peaks redshifts, slightly to the lower energies of incident light with increasing nanoribbon width. On the other hand, for light polarized perpendicular to the ribbon, there is a small peak around 1.6 eV, then, there is a band formed from several peaks from 5 eV to ～7.5 eV, and the second one from 8 eV to ～9.5 eV. Moreover, the peak positions hardly move with varying nanoribbon width, which indicates that quantum confinement effect is not playing an essential role on the optical properties of armchair stanene nanoribbons. In addition, our calculations of the optical properties indicate the anisotropy with respect to the type of light polarization. This anisotropy is due to the quasi-2D nature of the nanoribbons.     

Optical absorption and electrical conductivity of flash evaporated CuGaTe2 thin films

The optical absorption edge of CuGaTe₂ thin films in the energy range 1 to 2·3 eV was studied. The characteristic band gaps were found to be 1·23 eV and 1·28 eV whereas the acceptor ionization energy was 170 meV. Electrical conductivity measurements were carried out in the temperature range 300–550 K and two acceptor states with ionization energies 400 meV and 140 meV were found. The origin of acceptor states is explained based on covalent model.     

Indirect electronic transitions in alkali halate crystals-I (sodium and potassium chlorate crystals)

The long wavelength tail of the fundamental absorption in NaClO₃ and KClO₃ crystals has been analysed based on the theory of band to band transitions of Bardeen et al.[8] developed in the case of semi-conducting crystals. Evidence of phonon involvement in the transitions giving an indirect band gap is observed. The energies of the phonons involved in the process are the same for both the crystals, and agree well with combinations of prinicple frequencies of ClO₃^? ion, their overtones and also lattice phonons. The indirect band gap in these crystals varies with temperature more or less linearly and the rate of variation is ?3·8 × 10^?4 eV/K and ?5·0 × 10^?4 eV/K for sodium chlorate and potassium chlorate respectively.     

Über den Einfluß von Zwischengitterionen auf die Absorption von Gitterlücken in KBr-Kristallen

Detailed measurements have been made of the optical properties of α-centers (anion vacancies) in KBr: KH crystals irradiated monochromatically in the U band at 58°K. The absorption band α, normally at 6·14 eV is under these conditions shifted to shorter wavelengths. In terms ofFritz's model for the infrared absorption of U₁ centers, this shift can be interpreted as the influence of the nearby interstitial hydride ions on the a absorption. The nearest observed interstitial ion, stable to 103°K, shifts the α band to 6·31 eV; the next nearest one (stable to 150°K) to 6·19 eV; heating above 150°K leaves only the normal α absorption at 6·14 eV. Data are presented on the quantum efficiency for the recombination under uv irradiation and on the oscillator strengths for the different α centers.     

Optical anisotropy of LiNbO3 and KNbO3 in the interband transition region

The reflectivity of single domain crystals of LiNbO₃ and KNbO₃ has been measured using linearly polarized light up to 10 eV. The Kramers-Kronig analysis reveals a large anisotropy of the optical constants in the interband transition region. It is shown that the large electro-optic effects observed in these compounds are due to transitions in a relatively narrow spectral region above the band edge only.     

Die Temperaturabhängigkeit des Bandabstandes von Bleiselenid,gemessen an photoleitenden Schichten

The temperature dependence of spectral distribution of photoconductivity was measured on evaporated polycrystalline layers of lead-selenide in the range from 80 to 300 °K. The method ofBardeen, Blatt andHall was used, to calculate the band gap for direct and indirect transitions. A linear positive temperature coefficient was obtained for both transitions. The values areβ _dir=+(4.5±0.2) · 10^?4 eV/°K andβ _ind=+(3.0±0.2)· 10^?4eV/°K.     

Tunneling recombination luminescence in Na2O · 3SiO2 glass

The recombination luminescence exhibited by Na₂O · 3SiO₂ glass in the spectral region from 1.5 to 5.0 eV, after excitation by X-rays or quanta with energies ranging from 5.8 to 6.2 eV, consists of thermally stimulated and tunneling components. The tunneling luminescence band shape depends on the population of various depth traps.     

Spontaneous emission of photons and electrons during chemisorption of chlorine on sodium

Photons and electrons are emitted when Cl₂ molecules react on a Na surface prepared by UHV evaporation. The emission yield per reacting molecule is 10^?7-10^?6 for photons and approximately 10^?5 for electrons. The dominating light emission band has a maximum at hv = 2.15 eV (width 0.6 eV). A less intense u.v. band has a maximum at about 4.7 eV. A drastic decrease in the photon and electron emission at a Cl₂ exposure of about 5.10^?3 torr·sec, is attributed to the formation of a continuous NaCl film on the Na surface.     

Indirect electronic transitions in alkali halate crystals-II (sodium bromate and iodate) crystals

In the case of NaClO₃ and KClO₃ crystals, analysis of the long wavelength tail of their fundamental absorption revealed the active participation of the internal vibrations of the chlorate ion (Part I). In order to test the validity of the above interpretation the absorption spectra of two more halates with different anions namely sodium bromate and sodium iodate are analysed in a manner similar to that given in Part I. It is found that the principle internal vibrations of bromate and iodate ions are involved in the indirect transitions. The variation of indirect band gap with temperature is found to be ?2·5 × 10^?4 eV/K and ?2·9 × 10^?4 eV/K for sodium bromate and sodium iodate respectively.     

Angle-resolved photoemission of the c(2 × 2) and c(3 × 1) oxygen overlayers on Fe(110)

Angle-resolved photoemission spectroscopy utilizing synchrotron radiation has been used to study the band structure of the c(2×2) and (3×1) oxygen overlayers on Fe(110). The symmetries of the O-2p-derived states at the center of the surface Brillouin zone $\text{(}\text{Γ}\text{)}$ were identified using polarized light. At $\text{Γ}$ the p_xp_y- and p_z-derived levels are at about 5.5 and 7.0 eV below the Fermi level, respectively, for both ordered overlayers. The p-states of the c(2×2)-O structure show very little dispersion (?0.1 eV) with $\text{k}{}_{\mathrm{}}$. On the other hand, the c(3×1)-O overlayer exhibits considerable dispersion of ～1.6 eV. The essential features of the measured dispersion are reproduced well by the dispersion predicted in a qualitative way for an isolated c(3×1) oxygen monolayer.     

Giant Rashba spin splitting in Bi2Se3:Tl

First‐principles calculations are employed to demonstrate a giant Rashba spin splitting in Bi₂Se₃:Tl. Biaxial tensile and compressive strain is used to tune the splitting by modifying the potential gradient. The band gap is found to increase under compression and decreases under tension, whereas the dependence of the Rashba spin splitting on the strain is the opposite. Large values of α_R = 1.57 eV Å at the bottom of the conduction band (electrons) and α_R = 3.34 eV Å at the top of the valence band (holes) are obtained without strain. These values can be further enhanced to α_R = 1.83 eV Å and α_R = 3.64 eV Å, respectively, by 2% tensile strain. (© 2014 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Knight shift and paramagnetic susceptibility study in U3P4

The Knight shift and paramagnetic susceptibility have been measured on one sample of U₃P₄ in a rather wide temperature region. Observed deviations from the Curie-Weiss law are ascribed to the conduction electrons. The s-f coupling constantΓ=?2·4 eV has been obtained from the experimental data in the approximation of homogeneously polarized conduction electrons.     

Effect of uniaxial stress on InSbtunnel junctions

The deformation potential constants of heavily doped InSb have been determined by applying uniaxial stress to p-n tunnel junctions formed below the surface of rectangular InSb bars. Stress applied parallel to the major axes of these bars and parallel to the junction plane resulted in a linear decrease in tunnel current as a function of stress. The percentage decreases were 24·5 × 10^?3, 9·5 × 10^?3 and 4·5 × 10^?3cm²kg^?1 for stress applied parallel to [010], [11¯0], and [111] directions respectively. The observed changes in tunnel currents are attributed to a decrease in the tunnel probability produced by a shift in the conduction band edge relative to that of the valence band. Our data is consistent with a hydrostatic deformation potential of — 10 eV, and valence band deformation potentials b = ? 1·3 eV and d = ?7·4 eV.     

Optical properties of orientated (SN)x-films in the visible and near infrared region

Optical reflectance and transmittance measurements between 0.3 and 5.5 eV were performed on (SN)_x-films which showed a parallel orientation of the crystallites with respect to their polymer chain axis.The optical behaviour below 3 eV for light polarized parallel to the chain axis and in particular a strong absorption peak between 1 and 2 eV is explained to be a Maxwell-Garnett resonance of the free carriers. The influence of the free carriers is also observed for light polarized perpendicular to the chains and is analysed by the same model. From the anisotropy of the transport properties the interchain coupling is inferred.     

Renormalization of polaritons due to the formation of excitonic molecules in CuCl; an experimental aspect

The modulation of the real part of the non-linear refractive index (Δn) associated with the giant two-photon absorption (GTA) band of the excitonic molecules (EM's) has been measured in CuCl at 1.6K. This has been measured by the observation of the polarization rotation effects due to the induced optical anistropy between the right circularly polarized (σ⁺) and the left circularly polarized (σ^-) components of the linearly polarized probe team of Ω₁ under the strong irradiation of the σ^- beam of Ω₂ fixed around the GTA band at 3.1861 eV. The maximum amount of Δn has been 2.9×10^-4 at 3.1920 eV under the maximum excitation level when Ω₂ has been fixed at 3.1796 eV. The experimental results have been discussed in terms of the renormalization of the polaritons due to the real and virtual formation of EM's.     

Optical and resistivity studies of intercalated layer compounds

The optical absorption of three layered compounds has been studied at 4K between 0·1 and 3·0eV. The three compounds, TaS_1·6Se_0·4, TaS_1·6Se_0·4 (pyridine)_1/2, and TaS_1·6Se_0·4 (aniline)_3/4 have layer separations of 6·14, 12·09 and 18·07 A, respectively. Well-defined, free-carrier absorption edges exist near 1.0 eV in all three materials, from which values of the plasma frequency, the interband dielectric constant, and the optical scattering time were derived using the Drude theory. As the layer spacing increases both the plasma frequency and the dielectric constant decrease. The scattering time is short, 3 × 10^?15 sec, and almost independent of layer spacing. The calculated d.c. resistivity is consistent with the measured value in two of the three compounds.The variations of plasma frequency and dielectric constant with layer spacing are successfully interpreted in terms of a simple model which assumes the organic material acts as a dielectric separating metallic layers unchanged by its presence. Although a number of possibilities are put forward, no complete explanation is given for the short relaxation time in these compounds.     

Inductive and mesomeric effects on the π orbitals of halobenzenes

Ionization potentials for the π bands of a wide range of fluoro-, chloro-, and bromobenzenes have been measured by the technique of photoelectron spectroscopy. An empirical model incorporating inductive and mesomeric terms is discussed and its validity tested with the observed energies. Satisfactory agreement is obtained with dipole moment data. The theory accurately predicts ionization energies only for molecules having no ortho halogen atoms. Deviations from linearity are adequately explained in terms of an ortho effect which is proportional to the number of halogens situated in ortho positions. An analogous effect has previously been observed in the electronic spectra of substituted benzenes. Application of the model to 1a _2u band shifts in the fluorobenzenes leads to the conclusion that the energy of this band in benzene lies in the region of 11·5 eV.