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1.
J. G. Korobova D. I. Bazhanov V. V. Khvostov M. B. Guseva 《Moscow University Physics Bulletin》2013,68(1):38-44
An ab initio DFT study of atomic and electronic structure of carbyne crystals was carried out. The influence of hydrogen impurities on carbyne structure was investigated. Calculations with atomic relaxations showed that carbon chains in the carbyne crystal structure are bow-like curved; free-energy calculations showed that the most probable lengths of those chains are four and six atoms, which is in a good agreement with experiments. Carbyne-crystal electronic-structure analysis showed that there is a small gap of 0.09 eV near the Fermi level in four-atomic carbyne, while there is no such gap in six-atomic carbyne. In studying of the hydrogen impurity influence on the atomic and electronic structure of carbyne crystals, hydrogen atoms were embedded in two directions: across and along carbon chains in the crystal. As a result we found that the crystal structure is not distorted in the case of hydrogen embedded across the chains, while the type of bonding between carbon atoms in carbon chains in the carbyne crystal structure depended on the impurity concentration. The crystal structure was distorted when hydrogen was embedded along the chains. The concentration of impurities influences the conductivity of a carbyne crystal. 相似文献
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T. L. Estle 《Hyperfine Interactions》1991,64(1-4):525-533
As impurities in semiconductors muonium and hydrogen should have many similarities. In principle properties such as structures
which depend primarily on their identical adiabatic potential energies should be much the same while dynamic characteristic
such as diffusion would be quite different. The experimental results are in fact quite different for the two but for other
reasons. This paper indicates something of the current interest in hydrogen impurities, which is mostly focussed on passivation
and hydrogen pairs with other impurities or intrinsic defects, and then discusses muonium in semiconductors, where the abundant
information has to do with the isolated impurity. Consequently a complete picture of hydrogen/muonium at the moment requires
the study of both. 相似文献
5.
The behavior of impurities (Si, Zr, Mg, Zn) in titanium dioxide with an anatase structure is investigated using the electron-density functional method (with due regard for the spin polarization). The influence of these impurities on the formation of oxygen vacancies and the specific features of the electronic structure is studied. It is demonstrated that the impurities can both improve and deteriorate the optical characteristics of titanium dioxide. 相似文献
6.
This paper brings together some current concepts concerning hydrogen states in semiconductors (illustrated with reference
to silicon but quite generally applicable) and highlight certain findings of recent quantum electronic structure calculations
for defect centres involving hydrogen and its isotopes. As regards muonium, the situation which held in the early μSR literature
[1] is entirely reversed: the location and structure of Mu* are now well established [2], whereas the precise location and the nature of the metastability of Mu′ have become open questions!
In fact, neither state is stable in the presence of other electrically active impurities, which undoubtedly accounts for the
difficulty in detecting paramagnetic protium. The implications for the interpretation of existing data, and for various possible
future experiments, are examined. 相似文献
7.
The electronic structure of II–VI and III–V compound-based diluted magnetic semiconductors is calculated based on the local
density approximation (LDA) using the Korringa–Kohn–Rostoker method combined with the coherent potential approximation. The
magnetism of 3d transition-metal-atom-doped ZnO, ZnS, ZnSe, ZnTe, GaN, GaAs is investigated from first-principles. It is suggested
that the double exchange mechanism stabilizes the ferromagnetism in these DMSs. In order to obtain microscopic information
on the electronic structure of transition-metal-impurities in semiconductors, the hyperfine field of respective impurities
in each host material is calculated. It is found that the agreement with the experimental values is not good, probably because
the LDA is not sufficient to describe the core states of transition metals. However, it is suggested that the hyperfine fields
clearly reflect the local magnetic moments for 3d impurities.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
8.
The low-temperature behavior of the specific heat in disordered nanotubes strongly depends on structure changes and is not explained by the phonon contribution. Expression for electronic specific heat is carried out taking into account the multiple elastic electron scattering on impurities and structural inhomogeneities of short-range order type. The calculated electronic specific heat depends on diameter of nanotube, concentration of impurities, parameters of short-range order (structural heterogeneity) and describes the peculiarities of low-temperature behavior of specific heat observed in disordered CNT. 相似文献
9.
Ernesto Lpez-Chvez J. M. Martínez Magadn Fray de Landa Castillo-Alvarado 《Journal of magnetism and magnetic materials》2004,280(2-3):293-303
A theory of disordered binary alloys AxB1−x (A=Ni, Co; B=Fe; x0.06) is used to determine the changes in the electronic structure and magnetic properties of body centered cubic (BCC) iron induced by doping with nickel and cobalt impurities. This approximation is an extension of the cluster-Bethe lattice method, in which we incorporate electronic correlations, itinerant and localized nature of electrons 3d, and both long-range and short-range chemical correlations. The magnetism is described by means of a Hubbard Hamiltonian that in conjunction with Green's functions techniques is used to calculate local densities of electronic states. For it we take an atom in the real lattice and it is joined to a Bethe's lattice with like coordination number. The magnetic moments on sites occupied for A and B atoms are obtained self-consistently. Nickel and cobalt impurities in BCC iron can provide crucial information on the modification of the electronic band structure and magnetic moments from pure Fe. The results obtained are compared with those of both pure Fe and binary alloys of Co–Fe and Ni–Fe, which have been obtained by other authors using methods such as: first-principles electronic structure calculations using the layer Korringa–Kohn–Rostoker (KKR), the full-potential linearized augmented plane wave method, the KKR coherent potential approximation combined with the local-density functional method and by the tight-binding linear-muffin-tin orbitals method, obtained good agree. These results and other that recently we have published indicate to us that our methodology can be a new alternative for calculations of the electronic structure and magnetic properties of impurities and alloys of ferromagnetic transition metals. 相似文献
10.
M. Deicher R. Keller W. Pfeiffer H. Skudlik Th. Wichert 《Physica B: Condensed Matter》1991,170(1-4):335-350
The interaction of hydrogen with shallow and deep level impurities in crystalline semiconductors results in a passivation of their electrical activity by the formation of complexes. Nuclear techniques, like the perturbed γγ angular correlation (PAC) and the channeling of charged particles, have contributed to the understanding of the behaviour and microscopic structure of these complexes. A brief introduction to these techniques will be given.
The results on the behaviour of hydrogen, in both elemental and compound semi-conductors, will be reviewed. For the case of Si, the information obtained on the formation, geometry and stability of acceptor-hydrogen complexes will be discussed more extensively. 相似文献
11.
Recent Mössbauer isomer shift (IS) measurements on119Sn impurities substitutionally implanted in several AIIIBV compounds are interpreted in terms of their electronic structure. Since tin can replace both the A and the B atoms, two different IS lines arise corresponding to the donor and acceptor Sn impurities. To calculate the electronic configuration of ionized tin donors and acceptors and the relevant electron contact densities, a Green-function procedure is used based on the parametrized tight-binding approximation including relativistic wave functions. It turns out that with ionized Sn acceptors, the impurity is formed by a small cluster containing the tin atom in its neutral configuration rather than by a single negative Sn ion as might be anticipated at first sight. On the other hand, in the donor case the positive Sn ion plays the dominant role. 相似文献
12.
N. V. Belugina R. V. Gainutdinov E. S. Ivanova A. L. Tolstikhina 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2013,7(5):819-824
The domain structure of triglycine sulfate (TGS) crystals, specifically nominally pure crystals and those with impurities (LADTGS+ADP, DTSG, and TGS:Cr), is studied by piezoresponse force microscopy (PFM). The measured macroscopic dielectric characteristics are compared with microscopic data on the domain structure of these crystals. The values of the spontaneous polarization, bias voltage, and dielectric permeability as a function of temperature ?(T) are shown to be in agreement with the PFM data. The anomalous behavior of the dependence ?(T) was observed for LADTGS+ADP crystals. 相似文献
13.
A framework for studying impurity scattering in dilute, non-magnetic, metal alloys can be developed from a knowledge of the exact electronic eigenstates of a single impurity in an otherwise perfect lattice of muffin tin potentials. Such an approach has been developed for systems in which the impurity occupies a substitutional site of the lattice, as will be discussed by Coleridge, Lee, Harris, and other speakers of this conference. In this paper, motivated by recent experimental studies of Dingle temperature anisotropies induced by hydrogen impurities in copper, we will discuss the analogous treatment of scattering by interstitial impurities. In contrast to a substitutional impurity, an interstitial impurity introduces an additional scattering site into the lattice. Whereas the substitutional impurity wavefunctions can be described in terms of the same structure factors as can the Bloch wavefunctions for the pure host lattice, the interstitial impurity wavefunctions depend upon additional structure factors appropriate to the new scattering geometry. These additional structure factors appear in the transition matrix for impurity-induced scattering between Bloch states of the host lattice, and consequently in the weight factors involved in a partial wave analysis of the Dingle temperature anisotropies. 相似文献
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We investigate the electronic and atomic structure of interstitial hydrogen impurities in PbTiO3 and investigate their effect on ferroelectric polarization through first-principles total-energy calculations. Interstitial H in PbTiO3 is found to bond to oxygen and to act as a shallow donor impurity. At equilibrium, H does not much affect nearby Ti-O bonds and the H-O dipole increases the polarization. The barrier for reversing the defect dipole can give rise to imprint (extra stabilization of one of the two polarization modes). 相似文献
16.
A framework for studying impurity scattering in dilute, non-magnetic, metal alloys can be developed from a knowledge of the exact electronic eigenstates of a single impurity in an otherwise perfect lattice of muffin tin potentials. Such an approach has been developed for systems in which the impurity occupies a substitutional site of the lattice, as will be discussed by Coleridge, Lee, Harris, and other speakers of this conference. In this paper, motivated by recent experimental studies of Dingle temperature anisotropies induced by hydrogen impurities in copper, we will discuss the analogous treatment of scattering by interstitial impurities. In contrast to a substitutional impurity, an interstitial impurity introduces an additional scattering site into the lattice. Whereas the substitutional impurity wavefunctions can be described in terms of the same structure factors as can the Bloch wavefunctions for the pure host lattice, the interstitial impurity wavefunctions depend upon additional structure factors appropriate to the new scattering geometry. These additional structure factors appear in the transition matrix for impurity-induced scattering between Bloch states of the host lattice, and consequently in the weight factors involved in a partial wave analysis of the Dingle temperature anisotropies.This work was supported by the National Science Foundation through the Materials Research Laboratory at the University of Chicago. 相似文献
17.
Morr DK 《Physical review letters》2002,89(10):106401
We study the electronic structure near impurities in the d-density-wave (DDW) state, a possible candidate phase for the pseudogap region of the high-temperature superconductors. We show that the density of states near a nonmagnetic impurity in the DDW state is qualitatively different from that in a superconductor with dx(2)(-y(2)) symmetry. Thus, the electronic structure near impurities can provide insight into the nature of the two phases recently observed by scanning tunneling microscopy experiments in the superconducting state of underdoped Bi-2212 compounds. 相似文献
18.
Density-functional theory in combination with the nonequilibrium Green's function formalism is used to study the effect of substitutional doping on the electronic transport properties of hydrogen passivated zig-zag graphene nanoribbon devices. B, N and Si atoms are used to substitute carbon atoms located at the center or at the edge of the sample. We found that Si-doping results in better electronic transport as compared to the other substitutions. The transmission spectrum also depends on the location of the substitutional dopants: for single atom doping the largest transmission is obtained for edge substitutions, whereas substitutions in the middle of the sample give larger transmission for double carbon substitutions. The obtained results are explained in terms of electron localization in the system due to the presence of impurities. 相似文献
19.
Motivated by the observation of a so-called non-monotonic gap in recent angle-resolved photoemission spectroscopy measurement, we study the local electronic structure near impurities in electron-doped cuprates by considering the influence of antiferromagnetic (AF) spin-density-wave (SDW) order. We find that the evolution of density of states (DOS) with AF SDW order clearly indicates the non-monotonic d-wave gap behavior. More interestingly, the local DOS for spin-up is much different from that for spin-down with increasing AF SDW order. As a result, the impurity induced resonance state near the Fermi energy exhibits a spin-polarized feature. These features can be detected by spin-polarized scanning tunneling microscopy experiments. 相似文献
20.
H. Akai 《Hyperfine Interactions》1988,43(1-4):253-270
Due to the development of Green's function method the calculation of the nuclear spin-lattice relaxation time of impurities
in ferromagnets has become feasible in the last years. We present the result of calculations for allsp andd impurities in ferromagnetic iron. The calculations are based on the density functional formalism. They well, reproduce the
experimental trend of the relaxation timeT
1 for bothsp andd impurities. By decomposing the relaxation rate into various contributions, we explain the observed systematic behavior ofT
1
T in terms of the local electronic structure. 相似文献