The surface charge Q_{sc} versus the surface Fermi level position Φ_{s} for real (111) surfaces of p- and n-type Si has been studied. The values of Q_{sc} have been obtained on the basis of measurements of the surface potential V_{s} by means of the surface photo voltage method. The complementary character of Q_{sc}(Φ_{s}) dependences for the surfaces of p- and n-type Si supports the fact that the surface state distribution is not dependent on the type of bulk doping but on the surface preparation process.
Using a simple model of thin film a dependence of the current carrier concentration N on thickness L in thin bismuth films is calculated in the conditions of the quantum size effect. Applying the parametrized form of the thin film potential it is shown that the experimentally determined anomalous dependence N(L) can be obtained theoretically, assuming the standard boundary conditions in contrast to the results reported in literature. It is proved that the very structure of the hole energy spectrum is responsible for the anomalous character of the N(L) dependence.
This article provides the basics of core level photoelectron spectroscopy, together with applications in the area of semiconductors. The use of synchrotron radiation is emphasized, particularly the opportunities that are opening up at the new, third generation light sources.
We investigated the surface property change of indium tin oxide (ITO) with the various cleaning methods, using photoemission spectroscopy (PES), work function change and near-edge X-ray adsorption fine structure (NEXAFS). The detergent treatments of ITO with acetone (C₃H₆O), methanol (CH₄O), 2-propanol (C₃H₈O), and deionized (D) water yielded work function shifts as high as 0.99 eV compared to the no-treatment ITO. In contrast, work function shifts of 0.10-0.35 eV were measured after other treatments. The lowest C 1s concentration was obtained after O2 plasma treatment of ITO. There was no big change in the peak position and the shape of In 3d^{5/2}, and Sn 3d^{5/}2 after each treatment. But C 1s and O 1s spectra shows a peak shift and shape change. Presence of carbon can be minimized by NaOH treatment combined with oxygen plasma. In NEXAFS spectra of C K-edge on each sample, we found two π-binding states whose positions are 284.5 and 287.9 eV, C=C and C=O, respectively.
Electronic surface states localized on the edge of a semi-infinite square lattice are studied in the tight binding approximation. We examined the existence of surface states in the presence of magnetic field applied in the surface region of a 2D lattice. The applied field is perpendicular to the lattice and confined to a stripe near the surface. We also included a surface site perturbation caused by the presence of the surface. The magnetic field is introduced into the model by the Peierls substitution.
The numerical fitting of an analytical function representing electron density profile at a jellium surface to the one tabulated by Lang and Kohn is presented. The two sets of parameters entering the electron density profile is proposed. The first one is obtained by purely numerical fitting, and the second one is calculated under condition that electron density profile must satisfy the Budd-Vannimenus theorem. The obtained parameters are given as analytical functions of the Wigner-Seitz radius r_{s} describing mean electron density n̅ in a metal (n̅^{-1} = 4/3πr³_{s} ). The comparison of presented electron density profile with variational trial function given by Perdew is also discussed.
We discuss the surface photovoltage effect observed in photoemission experiment performed at room (300 K) and low (120 K) temperatures on Si/InP(110) heterojunctions for a thin Si coverage on n- and p-doped InP substrates. The theoretical analysis of the surface photovoltage effect has been performed on the basis of thermionic and thermionic-field emission models of transport processes in Schottky barriers.
Surface photovoltage measurements performed for the Cd_{0.85}Mn_{0.15}Te single crystal samples intrinsic and gallium doped have shown influence of gallium doping on height and sign of the surface voltage barrier. From results of the surface photovoltage spectroscopy (SPS) measurements thevalues of acceptor, donor and manganese states energies have been determined. The photoconductivity (PC) measurements confirmed the effects found on the SPS curves.
Surface photovoltage spectroscopy (SPS) measurements for Cd_{1-x}Mn_{x}Se single crystals between 80 and 300 K at the pressure of 10^{-4} Pa were performed. The Fermi level energy was calculated. From the SPS curves the energy values connected with the electron transitions have been determined. Four types of effects have been stated: energy gap, shallow states close to the conduction band and two energy states connected with the structural defects, the native ones and those related to introduction of manganese into the CdSe matrix.
The bilinear and biquadratic coupling between two metallic layers separated by a nonmagnetic metal spacer are studied. The paper contains analytical formulae for the coupling which are obtained from the energy potential of the spin-polarized electron gas. The formulae for the coupling are obtained in the framework of the Hohenberg-Kohn formalism of the density functional theory and variables of the coupling are the electron density and the spin polarization of the magnetic multilayer.
The influence of the dynamic hopping term included in the Newns-Anderson Hamiltonian on the electronic structure of the chemisorbed layer at different coverages rates is investigated. It is shown that this additional interaction can destroy the initial symmetry of the Newns-Anderson model or restore this symmetry in the initial negative asymmetric case. The coverage dependence of the adatom electron charge is also studied for the case of hydrogen chemisorption on a model transition metal surface.
Low-temperature scanning tunneling spectroscopy is used to study the Ag(111) surface state over an unprecedented range of junction resistances. The presence of the tip causes a shift of the surface state towards higher binding energies, increasingly stronger as the resistance decreases. A one-dimensional model calculation reproduces this observation and provides a connection to existing photoemission spectroscopy data. Implications of the effect on STS studies are discussed.
Optical transitions in photofield emission from barium covered tungsten were observed. The initial energies of the excited electrons obtained for different crystallographic planes range near the values of s₁ = -0.07 ± 0.02 eV and s₂ = -0.28 ± 0.04 eV with respect to the Fermi level. The energies are ascribed to electrons in the thin barium layer. The work functions of the barium covered tungsten (100), (111) and (100) planes were estimated using field emission method. In order to measure very small photocurrents a modulated laser radiation and the phase-sensitive detection were used.
Graphenes bonding forces in graphite are widely known as an example of the van der Waals forces. Well-known experimental facts relative to graphite negate this. A comparison of physical properties of graphite and molecular crystals and metals is shown. A model of dominant weak metallic bonding forces between graphenes is proposed. Brief theoretical background to the model is given.
Photoreflectance spectroscopy has been used to study optical transitions in In_{0.045}Ga_{0.955}As/GaAs double quantum well at 80 K. The derivative nature of this contactless electromodulation technique allows for the observation of excited state transitions in the low-dimensional structure including the symmetry-forbidden ones. Excitonic symmetry-forbidden transitions can be observed due to the effect of mixing of heavy and light hole excitons and/or due to some asymmetry in the structure. We have shown that the built-in electric field in the region of double quantum well is weak enough (less than 0.5 kV/cm) not to cause any significant energetic shift of features due to quantum confined Stark effect, on one hand. On the other hand, it is sufficient to change strongly the oscillator strength of forbidden transitions. To change the internal electric field, we have used photoreflectance in the three-beam mode with a third beam continuously illuminating the sample and causing changes of the built-in electric fields due to the photovoltage effect. This method works as a contactless forward bias and allows for a change of the field down to the flat band conditions. We have shown that changes of built-in electric field by amount of a few tenths of kV/cm can modify the intensity of forbidden transitions significantly. We show that, although the mixing of excitons is still important, a very weak built-in electric field can be dominant in the observation of forbidden excitonic transitions in double quantum well.
Surface differential reflectivity together with photoemission and Auger electron spectroscopies have been applied to observe and identify optical transitions among surface related states on CdTe(110) surfaces. The strongest contributions to the band of optical transitions have been revealed at the photon energies of 2.8, 3.4, and 3.9 eV. Their correspondence to excitations from the occupied S1 band to the unoccupied U1 one at the Γ, Χ and Χ' points of the surface Brillouin zone is discussed.
A variational calculation of the face-dependent work function with pseudopotential corrections employed has been performed. Critical analysis of the comparison between the calculated work function values and the experimental polycrystalline data is also given. The polycrystalline work function data may be treated as the mean low-index work function values and compared with the ones calculated. The use of the simple variational method and the Ashcroft pseudopotential for the description of metallic ions leads to good agreement between theory and experiment, and also enables to explain the increasing or decreasing tendency of work function values in different series of the simple metals.
We present a new outlook at the study of metal-semiconductor interface formation. A resonant photoemission spectroscopy tuned to the Fe 3p-3d transition (56 eV) was used to investigate the changes after sequential deposition of Fe atoms on freshly cleaved Cd_{0.86}Fe_{0.14}Se crystal surface. In the first stages (0.6-4 ML) of Fe deposition the contribution of Fe 3d electrons to the valence band grows up markedly indicating the increase in Fe content in the Cd_{0.86}Fe_{0.14}Se crystal surface region. When the amount of Fe exceed 40 ML the resonant photoemission spectra became similar to the Fe metal with some contribution of the ternary crystal substrate.
The electron-hole interaction in a thin (≈10 nm) GaAs quantum wire free-standing in vacuum is strongly enhanced by the image charge due to the abrupt permittivity drop at the wire surface. As a result, the exciton binding energies are much larger and the exciton wave functions much more localised than those of the GaAs quantum wire surrounded by the AlGaAs. The absorption spectrum of the free-standing wire shows besides the 1s exciton peak also the 3s and 5s exciton peaks, even if the peaks are 15 meV broad. The continuum absorption edge shows a large blue shift due to the renormalization of single-particle energies by the image charge.
The spin-resolved photoemission spectroscopy is utilized to study the spin dependent electronic structures of solids and solid surfaces. The spin- and angle-resolved valence band spectra of ferromagnetic Ni are investigated by comparing with an atomic model and a one-electron band calculation. The electron correlation effects which appear in the spin-resolved photoemission spectra are discussed. The spin dependent electronic structures of S atoms adsorbed on Fe(100) surface are also investigated.
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