Showing papers by "Solid State Physics Laboratory published in 1997"
TL;DR: Using a combination of photoelectron and inverse photo-electron spectroscopy, this paper showed that the band gap in a monolayer of C60 on a Ag surface is strongly reduced from the solid C60 surface value.
Abstract: Using a combination of photoelectron and inverse photoelectron spectroscopy, we show that the band gap in a monolayer of C60 on a Ag surface is strongly reduced from the solid C60 surface value. We argue that this is a result of the reduction of the on-site molecular Coulomb interaction due to the influence of image charges in the metal substrate. This result suggests that the physical properties of correlated insulators and semiconductors will be strongly modified if prepared in ultra thin form on metal substrates or sandwiched between metal layers.
127 citations
TL;DR: In this article, an electron spectroscopy study of the development of the electronic structure in the K-doped C60 monolayer on a Ag(1 1 1) surface is presented.
90 citations
TL;DR: In this paper, it was shown that it is possible to obtain spin-resolved valence band spectra with a very high degree of spin polarization from antiferromagnetic transition metal materials if the excitation light is circularly polarized and has an energy close to the 2p(3/2) (L(3)) white line.
Abstract: We demonstrate that it is possible to obtain spin-resolved valence band spectra with a very high degree of spin polarization from antiferromagnetic transition metal materials if the excitation light is circularly polarized and has an energy close to the cation 2p(3/2) (L(3)) white line. We are able to unravel the different spin states in the single-particle excitation spectrum of CuO and show that the top of the valence band is of pure singlet character, which provides strong support for the existence and stability of Zhang-Rice singlets in high-T-c superconductors.
63 citations
TL;DR: In this paper, the authors investigated the optical conductivity of FeSi single crystals using Fourier transform infrared spectroscopy in the frequency range from 30 to 20 000 cm-l and concluded that the transverse effective charge of the Fe and Si ions is approximately 4e.
Abstract: From an investigation of the optical conductivity of FeSi single crystals using Fourier-transform infrared spectroscopy in the frequency range from 30 to 20 000 cm-l we conclude that the transverse effective charge of the Fe and Si ions is approximately 4e. Of the five optical phonons that are allowed by symmetry we observe only four, three of which have a Fano line shape presumably resulting from an interaction of these modes with the electronic continuum. We show that the large oscillator strength of the phonons results from a relatively weak coupling (lambda approximate to 0.1) of the lattice degrees of freedom to an electronic resonance above the semiconductor gap, which is also responsible for the large electronic polarizability (epsilon(infinity)approximate to 200) of the medium.
58 citations
TL;DR: In this article, the Seebeck coefficient, the DC electrical conductivity, the optical absorption and the dynamical conductivity of pure boron-rich solids were investigated and it was shown that donor levels positioned between the conduction band and the uppermost intrinsic electron trapping level and of sufficient density to overcompensate unoccupied valence and gap states are necessary for n-type conductivity.
53 citations
TL;DR: In this paper, a new approach to investigate quantum-mechanical probability density distributions of electrons in a screened wide potential well, based on low-temperature magnetotransport measurements, is presented.
Abstract: We present a new approach to investigate quantum-mechanical probability density distributions of electrons in a screened wide potential well, based on low-temperature magnetotransport measurements. Differences of subband energy levels shifted by an inserted controlled potential perturbation are measured and used to extract the difference of the squared amplitude of the respective wave functions at the location of the potential spike. The position of the wave functions and the carrier density can be tuned independently via front- and back-gate voltages. We find excellent agreement between the measured data and self-consistently calculated wave functions.
38 citations
TL;DR: In this article, an analytical device model for the conversion of images into non-uniform distribution of the output current density in a multiple-quantum-well structure for an infrared pixelless imaging system is considered.
Abstract: The conversion of images into nonuniform distribution of the output current density in a multiple-quantum-well structure for an infrared pixelless imaging system is considered using an analytical device model. The nonuniform current, which reproduces the incident image, is converted back to a light-emitting diode emission image by the device considered here. The developed model takes into account transport processes responsible for the device operation. An explicit expression for the contrast transfer characteristic is derived as a function of the number of quantum wells (QWs) and the electron capture parameter. It is shown that the quality of the up-converted images (contrast and resolution) is improved with increasing number of QWs. The pixelless imaging devices under consideration can effectively convert long-wavelength infrared images into short-wavelength infrared or visible images with contrast transfer ratio close to unity.
37 citations
TL;DR: In this article, a unified picture for the boron-based and aluminum-based compounds constructed from icosahedral clusters is presented to get a unified view for the two types of compounds.
36 citations
TL;DR: In this paper, the dielectric function of the boron-rich solids in the FIR range is analyzed on the basis of their optical reflectivity spectra, which exhibit obviously typical, strongly increasing slopes with decreasing frequencies.
31 citations
TL;DR: In this article, a spin-resolved circularly polarized 2p (L-3) resonant photoemission technique was used to measure the local Ni 3d spin polarization, not only below but also above the Curie temperature.
Abstract: We report the measurement of the local Ni 3d spin polarization, not only below but also above the Curie temperature (T-C), using the newly developed spin-resolved circularly polarized 2p (L-3) resonant photoemission technique. The experiment identifies the presence of 3d(8) singlets at high energies and 3d(8) triplets at low energies extending all the way to the Fermi energy, both below and above T-C, showing that it is the orbital degeneracy of the 3d band and the Hund's rule splitting which is of utmost importance to understand Ni and other 3d ferromagnets.
30 citations
TL;DR: In this article, the bulk moduli of CsCl- and FeSi-type RuSi were determined as (215 ± 15) GPa and (255 ± 15 ) GPa, respectively.
TL;DR: The FT Raman spectrum of B 6 O is typical for the α -rhombohedral boron structure group and the number of phonons corresponds exactly to that predicted by group theory as discussed by the authors.
TL;DR: The complex dielectric functions of β-rhombohedral boron, of Boron carbide with compositions between B 4.23 C and B 10.37 C and YB 66, were measured between about 2.5 and 9.5 eV as discussed by the authors.
TL;DR: In this paper, the optical constants (absorption coefficient α, refractive index n and extinction coefficient k ) of unirradiated and irradiated ZnIn 2 Se 4 films were calculated.
TL;DR: In this paper, the IR spectra of boron carbide containing up to about 1.5% aluminum atoms were determined between 80 and 5000 cm −1 for temperatures between 70 and 450 K.
TL;DR: In this paper, the influence of variation in composition, thermal treatment on the nature of crystallizing phases as well as on the resulting microstructures are investigated through XRD, IR and SEM.
Abstract: Glasses in the system (65 −x) [SrO·TiO2] − (35) [2SiO2·B2O3] − (x) [Bi2O3] wherex = 1, 5, 10 (wt%) prepared by melting in alumina crucible (1375–1575 K), were subjected to different heat treatment schedules followed by DTA studies. Crystallization study showed the formation of Sr2B2O5 as major phase at low temperature (≈950°C) heat treatment. At high temperatures, TiO2 and SrTiO3 with or without Sr2B2O5 crystallize out depending on heat treatment. In this paper, the influence of variation in composition, thermal treatment on the nature of crystallizing phases as well as on the resulting microstructures are investigated through XRD, IR and SEM. Uniform crystallization was achieved by suitable addition of Bi2O3 and proper heat treatment.
TL;DR: In this article, a periodic array of potential pillars is superimposed on a two-dimensional electron gas being ballistic on the length scale of the lattice period, and the magnetoconductivity as obtained from the magnetoresistance via a tensor inversion displays maxima or minima depending on the direction of current flow with respect to a lattice orientation.
Abstract: A periodic array of potential pillars is superimposed on a two-dimensional electron gas being ballistic on the length scale of the lattice period. Pronounced maxima occur in the magnetoresistance of such systems. The magnetoconductivity as obtained from the magnetoresistance via a tensor inversion displays maxima or minima depending on the direction of current flow with respect to the lattice orientation. So-called pinned electron orbits as well as runaway trajectories coexist and specifically influence a given element of the conductivity tensor. In contrast to square lattices, both sets of trajectories show up in the experimental data simultaneously. @S0163-1829~97!02119-X#
TL;DR: In this paper, Fourier transform Raman spectra of single-crystal LaB 6 and SmB 6 were measured at room temperature using a Nd:YAG laser with about 2 W irradiation power.
TL;DR: In this article, the IR-optical reflectivity spectra of icosahedral boron-rich structures and Al-based isosahedral quasicyrstals were derived.
Journal Article•
TL;DR: The physical properties of transition metal mono-silicides with the FeSi structure (CrSi, MnSi, FeSi, CoSi, NiSi, etc) were investigated in this article.
Abstract: Published in: Physica B 244 (1998) 138-147 citations recorded in [Science Citation Index] Abstract: We review some of the relevant physical properties of the transition metal mono-silicides with the FeSi structure (CrSi, MnSi, FeSi, CoSi, NiSi, etc) and explore the relation between their structural characteristics and the electronic properties. We confirm the suggestion orginally made by Pauling, that the FeSi structure supports two quasi-atomic d-states at the transition metal atom. This shell contains from 0 to 4 electrons in the sequence CrSi to NiSi. In FeSi the two quasi-atomic d-electrons are responsible for the high temperature S=1 state, which is compensated for T=0 by two itinerant electrons associated with the Fe-Si resonance bonds.
TL;DR: Optical absorption and FT Raman spectra of polycrystalline B 12 P 2 prepared by CVD on silicon substrates are presented in this article, where the silicon content is rather high, and they assume that a ternary compound with the structure formula B 12 (P 2 ) 1− x (Si 2 ) x is formed.
TL;DR: In this article, a two-step photoionization process of Si-DX centers at different temperatures and light intensities is analyzed with the negative-U model, which establishes the negatively charged ground state (DX − ) of the Si-related ground state and existence of the metastable neutral (DX 0 ) state.
TL;DR: A Gunn diode is a simple two-terminal source of low-noise, high frequency microwave power and is most commonly used as local oscillator in critical microwave and mm-wave systems as mentioned in this paper.
Abstract: A Gunn diode is a simple two terminal source of low-noise, high frequency microwave power. It is most commonly used as local oscillator in critical microwave and mm-wave systems. The system requirement of frequency agility and temperature stability impose stringent demands on the device performance and hence on its material and fabrication technology. The present paper discusses some of the technological innovations attempted in this direction along with results obtained. Some of the issues addressed are carrier concentration ramping to check velocity degradation in the active layer, power optimisation by in-situ etching, minimisation of dead zone and thermal management. Physics, design and fabrication technology and testing of Gunn diodes is also briefly described in this article.
01 Sep 1997
TL;DR: In this article, Knight shift and nuclear spin relaxation measurements performed on the ''metallic'' Na-23 line in e(-)-irradiated NaCl single-crystals between about 4 and 390 K were presented.
Abstract: Strong irradiation of NaCl crystals results in a formation of sodium colloids which exhibit metallic properties. In consequence, besides the Na-23 line of NaCl a second well-separated Na-23 line occurs in the NMR spectrum caused by the Knight shift of the conduction electrons. We present Knight shift and nuclear spin relaxation measurements performed on the ''metallic'' Na-23 line in e(-)-irradiated NaCl single-crystals between about 4 and 390 K. Evaluation of the data leads to detailed information on the electronic properties, atomic self-diffusion, and melting behavior of the colloids. The results are discussed in view of corresponding data obtained in bulk sodium.
TL;DR: In this article, the reflectivity and absorption index spectra of β -rhombohedral boron between dc and about 250 eV are presented, put together from reliable results obtained from literature and new measurements partly with very high resolution.
TL;DR: In this article, a highly localized potential spike in the middle of a parabolic quantum well was introduced to investigate differences of quantum-mechanical probability density distributions in the presence of electron screening.
Abstract: Energy spectroscopy of electron states in parabolic quantum wells is done with low-temperature magnetotransport.Introducing a highly-localized potential spike in the middle of the well, we investigate differences of quantum-mechanical probability-density distributions in the presence of electron screening. This is achieved by measuring the spike-induced energy shift and using first-order perturbation theory. With front- and back-gate electrodes, the electron density as well as the position of the electron gas relative to the spike can be tuned. The results are in good agreement with self-consistently calculated wave functions. © 1997 Elsevier Science B.V. All rights reserved.
TL;DR: In this paper, the synthesis and characterisation of a composite of Fe-Co with copolymer of aniline formaldehyde by chemical processing is described and the resulting material was studied by XRD, X-ray microradiography, TEM, Mossbauer effect and magnetisation measurements.
Abstract: The paper describes the synthesis and characterisation of a composite of Fe-Co with copolymer of aniline formaldehyde by chemical processing. The resulting material was studied by XRD, X-ray microradiography, TEM, Mossbauer effect and magnetisation measurements. Uniform dispersion of spherical shaped nano-sized particles of spinel magnetic oxide in polymer matrix is inferred.
TL;DR: In this paper, Schottky gate annealing has been used to fabricate submicron gate length GaAs MESFETs, and the effect of gate diode ideality has been investigated.
Abstract: Rf sputtered Ti/Pt/Au Schottky contacts with varying titanium thickness have been made on (n)GaAs by the lift-off process under actual device processing conditions. The ideality factor of the Schottky barrier is dose to unity (∼ 1.07) with a barrier height of 0.80 ± 0.02 eV. The contacts with Ti films as thin as 100 A remain thermally stable with annealing up to 400°C. These contacts have been next used to fabricate submicron gate length GaAs MESFETs. The MESFET's gm increases with improved gate diode ideality but is not a strong function of it. The effect of Schottky gate annealing on the MESFET's dc characteristics shows that IDSS, gm, Vp and VR(GS) remain stable with annealing upto 350°C and degrade with 400° anneal.
TL;DR: In this paper, it was shown that the phonons involved are quenched when the traps are occupied by doping with suitable metals leading to n-type phonons, and the existence of band-type carriers is proved by a Drude-type free-carrier absorption.
TL;DR: In this article, the growth of GaxIn1 − xAs epilayers using Ga-In alloy sources by chloride vapor phase epitaxial technique was studied. And the amount of indium incorporated in the epilayer with alloy source composition ranging from 3 to 12 atomic percentage (at%) of Ga is studied.