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Auswahl der wissenschaftlichen Literatur zum Thema „Surface states, band structure, electron density of states“
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Zeitschriftenartikel zum Thema "Surface states, band structure, electron density of states"
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MUN, B. S., M. WATANABE, M. ROSSI, V. STAMENKOVIC, N. M. MARKOVIC und P. N. ROSS. „THE STUDY OF SURFACE SEGREGATION, STRUCTURE, AND VALENCE BAND DENSITY OF STATES OF Pt3Ni(100), (110), AND (111) CRYSTALS“. Surface Review and Letters 13, Nr. 05 (Oktober 2006): 697–702. http://dx.doi.org/10.1142/s0218625x06008682.
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The surface segregation, structure, and valence band density of states of Pt 3 Ni (100), (110), and (111) single crystals are characterized with low energy ion scattering (LEIS), low energy electron diffraction (LEED), and ultraviolet photoemission spectroscopy (UPS). The results of LEIS clearly reveal the complete surface segregation of Pt to the top layer on all crystal alloys. LEED indicates the (5 × 1) surface reconstruction on the Pt 3 Ni (100), while (110) and (111) surfaces show (2 × 1) and (1 × 1) patterns, respectively, identical to Pt single crystals. The valence bands density of states on Pt 3 Ni alloys are compared to those of Pt single crystals via UPS measurements.
2
PENG, J. L., SHAUN BULCOCK, PETER I. BELOBROV und L. A. BURSILL. „SURFACE BONDING STATES OF NANO-CRYSTALLINE DIAMOND BALLS“. International Journal of Modern Physics B 15, Nr. 31 (20.12.2001): 4071–85. http://dx.doi.org/10.1142/s0217979201007865.
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The rough surface of nano-crystalline diamond spheres induces surface electronic states which appear as a broadened pre-peak over approx. 15 eV at the C K-edge energy threshold for carbon in the parallel electron energy loss spectrum (PEELS). This appears to be at least partially due to 1s-π* transitions, although typically the latter occupy a range of only 4 eV for the sp2 edge of highly-oriented pyrollytic graphite (HOPG). No π* electrons appear in the conduction band inside the diamond particles, where all electrons are sp3 hybridized. PEELS data were also obtained from a chemical vapour deposited diamond film (CVDF) and gem-quality diamond for comparison with the spectra of nano-diamonds. The density of sp2 and sp3 states on the surface of diamond nano-crystals is calculated for simple structural models of the diamond balls, including some conjecture about surface structures. The results are used to interpret the sp2/sp3 ratios measured from the PEELS spectra recorded as scans across the particles. Surface roughness at the atomic scale was also examined using high-resolution transmission electron microscopy (HRTEM) and electron nano-diffraction patterns were used to confirm the crystal structures.
3
Liu, Xiao Qing, Rui Fang Zhang, Yi Guo Su und Xiao Jing Wang. „Study on the Energy Band Structure of La Doped ZnO“. Advanced Materials Research 233-235 (Mai 2011): 2119–24. http://dx.doi.org/10.4028/www.scientific.net/amr.233-235.2119.
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The energy bands of La -doped ZnO were studied systematically by the density functional theory (DFT). Based on the data of the band structure, DOS (Density of State) and PDOS( Partial Density of States), atomic populations and net charge, the influence on the energy band structure of the macrostructure of ZnO and La-doped ZnO was investigated. The results showed that the free electrons were produced by the doping of La on (or in) ZnO crystal. The Fermi energy was shifted up to the conduction band, making the ZnO particles having the characters of degenerated semiconductor. The excitation from impurity states to the conduction band may account for the blue shift of the absorption edge in the model of La-doped ZnO. Comparison with the different models of the La doped/loaded on the ZnO surface, La atoms loaded on the surface of ZnO and La atoms replaced of Zn atoms on the ZnO surface, the shift to the lower energy location were found after La doping/loading. The more shift and the large band gap was found for the model of La doped on the Zn position in the ZnO crystal.
4
Donath, Markus. „Spin-polarised Electron Studies of Low-dimensional Magnetic Systems“. Australian Journal of Physics 52, Nr. 3 (1999): 579. http://dx.doi.org/10.1071/ph99006.
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Spin-polarised electrons provide unique experimental access to magnetic properties of surfaces and layered structures. The combined use of different techniques allows us to develop a microscopic picture of the physics underlying the macroscopic magnetic properties, e.g. magnetic phase transitions, magnetic coupling phenomena, exceptional surface magnetic properties. In this paper, two techniques are described together with the kind of questions addressed by them. Spin-resolved appearance potential spectroscopy gives local magnetic information about multi-component systems by probing the spin-dependent local density of unoccupied states. Spin-resolved inverse photo-emission measures specific electron states above the Fermi level. In particular, two-dimensional states serve as magnetic sensors at surfaces. Examples from surfaces as well as thin-film structures of band and local-moment ferromagnets are presented.
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Ahuja, Babu Lal, Ashish Rathor, Vinit Sharma, Yamini Sharma, Ashvin Ramniklal Jani und Balkrishna Sharma. „Electronic Structure and Compton Profiles of Tungsten“. Zeitschrift für Naturforschung A 63, Nr. 10-11 (01.11.2008): 703–11. http://dx.doi.org/10.1515/zna-2008-10-1114.
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The energy bands, density of states and Compton profiles of tungsten have been computed using band structure methods, namely the spin-polarized relativistic Korringa-Kohn-Rostoker (SPR-KKR) approach as well as the linear combination of atomic orbitals with Hartree-Fock scheme and density functional theory. The full potential linearized augmented plane wave scheme to calculate these properties and the Fermi surface topology (except the momentum densities) have also been used to analyze the theoretical data on the electron momentum densities. The directional Compton profiles have been measured using a 100 mCi 241Am Compton spectrometer. From the comparison, the measured anisotropies are found to be in good agreement with the SPR-KKR calculations. The band structure calculations are also compared with the available data.
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HONG, SOON C., und JAE IL LEE. „ELECTRONIC STRUCTURE OF THE Mo(001) SURFACE: LOCAL DENSITY STUDY“. International Journal of Modern Physics B 07, Nr. 01n03 (Januar 1993): 524–27. http://dx.doi.org/10.1142/s0217979293001104.
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LEED observed an incommensurate surface reconstruction for the Mo(001) surface and a recent photoemission experiment measured electronic structure of the Mo(001) surface at room and low temperature (52 K). Employing the all-electron local density full potential linearized augmented plane wave (FLAPW) method, we calculated the electronic structure of the Mo(001) surface. Two prominent LDOS peaks at the surface are found just below Fermi level and E b = 0.50 eV and they are confirmed to come from surface states along [Formula: see text] symmetry line. The surface states (just below Fermi level) with even symmetry show no energy dispersion while the surface states ( E b = 0.50 eV ) with odd symmetry have upward energy dispersion from [Formula: see text] to [Formula: see text]. The two bands of surface states fade off at [Formula: see text], which is very consistent with experiments. The work function is calculated to be 4.20 eV. We will present the character of charge densities of the surface states and compare to experiments.
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REFOLIO, M. C., J. M. LÓPEZ SANCHO, M. P. LÓPEZ SANCHO und J. RUBIO. „CORRELATION EFFECTS IN PHOTOEMISSION SPECTROSCOPY: Cl/Si(100)-(2 × 1)“. Surface Review and Letters 04, Nr. 05 (Oktober 1997): 923–27. http://dx.doi.org/10.1142/s0218625x9700105x.
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Different calculations of the electronic structure of this system have been unable to explain satisfactorily some puzzling features of the experimental surface band structure measured by angle-resolved photoemission (namely, the absence of any adsorbate structure near the Fermi level and the extremely small dispersion of all the adsorbate bands). Here we present a new calculation based on the lattice Anderson model in the (adsorbate) low-density regime. The one-electron Green function is computed directly from its Lehmann representation in terms of N-1 and N+1 electron states. These are obtained approximately with a new configuration interaction approach supplemented by renormalization group techniques in order to include iteratively states with an increasing number of electron–hole pairs. The resulting spectral function is in quantitative agreement with the photoemission spectrum: (1) all the adsorbate features lie between 5 and 10 eV below the Fermi level and (2) the adsorbate band dispersion is small (less than 0.5 eV). We also compare with the random phase approximation.
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Ushio, Hideki, und Hiroshi Kamimura. „III. Energy Bands, Fermi Surfaces and Density of States of the Hole Carriers in the Presence of the Local Antiferromagnetic Ordering“. International Journal of Modern Physics B 11, Nr. 32 (30.12.1997): 3759–96. http://dx.doi.org/10.1142/s0217979297001933.
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We have separated a hole carrier and a localized spin, by treating the exchange interaction between the spins of a carrier hole and a localized spin in a mean field sense. Then we have constructed the effective one-electron-type band structure for the hole carriers in the presence of the antiferromagnetic (AF) ordering of the localized spins. In the case of the undoped La2CuO4 all the energy bands are fully occupied by electrons so that La2CuO4 is an insulator. In this sense the present energy bands which include the many body effect fully is completely different from the ordinary energy band in the local density functional method. The top of the highest valence band is at (π/a, π/a, 0)-point, and the calculated Fermi surface is small as far as the spin correlation length of the AF order is larger than the mean free path. Based on this energy band and Fermi surfaces we have calculated various normal state properties and explained their anomalous features, such as the x-dependence of the electronic specific heat, the linear temperature dependence of the resistivity down to T c , the x-dependence of the Hall coefficient with the sign change, the large T dependence of R H , the incommensurate peak of the neutron scattering and the instability at x=0.125.
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Su, Hong Bin, Ping Yang, Jin Biao Wang und Nan Huang. „First-Principles Calculations on the Geometry and Electronic Structure of Rutile TiO2 (110) Surface“. Advanced Materials Research 79-82 (August 2009): 1201–4. http://dx.doi.org/10.4028/www.scientific.net/amr.79-82.1201.
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In this paper, both geometrical and electronic properties of rutile TiO2 (110) surfaces have been investigated using First-Principles Density-Functional calculations with CASTEP code, the model of stoichiometric surface is a (2x1) super-cell which has 12 atomic-layer slabs with the bottom 6 held fixed, the bridging-oxygen vacancy surface has been constructed by removing a neutral bridging oxygen atom from this surface. For the stoichiometric surface, the atom relaxations are: Ti6f (+0.2865Å), Ti5f (-0.1039Å), O3f (+0.2433Å) and Ob (+0.0075Å), we find no reconstruction and no surface states in the band gap, the density of states (DOS) is similar to the bulk except the lower conduction band intensity, in accord with recent experiments. Whereas, as a result of bridging-oxygen vacancy, the atom relaxations exchanged and reconstruction occur. The 2 excess electrons left behind removal of one bridge O atom are localized on the Ti-t2g conduction band orbitals, convert some of the Ti4+ ions into Ti3+ ions and result a compensatory shift in the Fermi level. The band gaps we calculated for stoichiometric surface is similar to the bulk, but its increase can be found for Ob vacancy surface.
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Бекенев, В. Л., und С. М. Зубкова. „Атомная и электронная структура реконструкций поверхности (111) в кристаллах ZnSe и CdSe“. Физика твердого тела 60, Nr. 1 (2018): 187. http://dx.doi.org/10.21883/ftt.2018.01.45308.136.
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AbstractThe atomic and electron structure of four variants of polar (111)-(2 × 2) surfaces in ZnSe and CdSe terminated by a cation, namely, the ideal, relaxed, reconstructed, and relaxed after reconstruction surfaces, are calculated for the first time from the first principles. The surface is simulated by a film with a thickness of 12 atomic layers and a vacuum gap of ~16 Å in the layered superlattice approximation. Four fictitious hydrogen atoms with a charge of 0.5 electrons each are added for closing dangling Se bonds on the opposite side of the film. Ab initio calculations are performed using the QUANTUM ESPRESSO software based on the density functional theory. It is shown that relaxation results in splitting of atomic layers. We calculate and analyze the band structures and total and layer-wise densities of electron states for four variants of the surface.
Dissertationen zum Thema "Surface states, band structure, electron density of states"
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Zu, Fengshuo. „Electronic properties of organic-inorganic halide perovskites and their interfaces“. Doctoral thesis, Humboldt-Universität zu Berlin, 2019. http://dx.doi.org/10.18452/20396.
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Über die besonders hohe Effizienz von Halid-Perowskit (HaP)-basierten optoelektronischen Bauteilen wurde bereits in der Literatur berichtet. Um die Entwicklung dieser Bauteile voranzutreiben, ist ein umfassendes und verlässliches Verständnis derer elektronischen Struktur, sowie der Energielevelanordnung (ELA) an HaP Grenzflächen von größter Bedeutung. Demzufolge beschäftigt sich die vorliegende Arbeit mit der Untersuchung i) der Bandstruktur von Perowskit-Einkristallen, um ein solides Fundament für die Darlegung der elektronischen Eigenschaften von polykristallinen Dünnschichten zu erarbeiten, und mit ii) den Einflüssen von Oberflächenzuständen auf die elektronische Struktur der Oberfläche, sowie deren Rolle bei der Kontrolle von ELA an HaP Grenzflächen. Die Charakterisierung erfolgt überwiegend mithilfe von Photoelektronenspektroskopie (PES) und ergänzenden Messmethoden wie Beugung niederenergetischer Elektronen an Oberflächen, UV-VIS-Spektroskopie, Rasterkraftmikroskopie und Kelvin-Sonde.
Erstens weist die Banddispersion von zwei prototypischen Perowskit-Einkristallen eine starke Dispersion des jeweiligen oberen Valenzbandes (VB) auf, dessen globales Maximum in beiden Fällen am R-Punkt in der Brillouin-Zone liegt. Dabei wird eine effektive Lochmasse von 0.25 m0 für CH3NH3PbBr3, bzw. von ~0.50 m0 für CH3NH3PbI3 bestimmt. Basierend auf diesen Ergebnissen werden die elektronischen Spektren von polykristallinen Dünnschichten konstruiert und es wird dadurch aufgezeigt, dass eine Bestimmung der Valenzbandkantenposition ausgehend von einer logarithmischen Intensitätsskala aufgrund von geringer Zustandsdichte am VB Maximum vorzuziehen ist.
Zweitens stellt sich bei der Untersuchung der elektronischen Struktur von frisch präparierten Perowskit-Oberflächen heraus, dass die n-Typ Eigenschaft eine Folge der Bandverbiegung ist, welche durch donatorartige Oberflächenzustände hervorgerufen wird. Des Weiteren weisen die PES-Messungen an Perowskiten mit unterschiedlichen Zusammensetzungen aufgrund von Oberflächenphotospannung eine Anregungslichtintensitätsabhängigkeit der Energieniveaus von bis zu 0.7 eV auf. Darüber hinaus wird die Kontrolle von ELA durch gezielte Variation der Oberflächenzustandsdichte gezeigt, wodurch sich unterschiedliche ELA-Lagen (mit Abweichungen von über 0.5 eV) an den Grenzflächen mit organischen Akzeptormolekülen erklären lassen. Die vorliegenden Ergebnisse verhelfen dazu, die starke Abweichung der in der Literatur berichteten Energieniveaus zu erklären und somit ein verfeinertes Verständnis des Funktionsprinzips von perowskit-basierten Bauteilen zu erlangen.Optoelectronic devices based on halide perovskites (HaPs) and possessing remarkably high performance have been reported. To push the development of such devices even further, a comprehensive and reliable understanding of their electronic structure, including the energy level alignment (ELA) at HaPs interfaces, is essential but presently not available. In an attempt to get a deep insight into the electronic properties of HaPs and the related interfaces, the work presented in this thesis investigates i) the fundamental band structure of perovskite single crystals, in order to establish solid foundations for a better understanding the electronic properties of polycrystalline thin films and ii) the effects of surface states on the surface electronic structure and their role in controlling the ELA at HaPs interfaces. The characterization is mostly performed using photoelectron spectroscopy, together with complementary techniques including low-energy electron diffraction, UV-vis absorption spectroscopy, atomic force microscopy and Kelvin probe measurements. Firstly, the band structure of two prototypical perovskite single crystals is unraveled, featuring widely dispersing top valence bands (VB) with the global valence band maximum at R point of the Brillouin zone. The hole effective masses there are determined to be ~0.25 m0 for CH3NH3PbBr3 and ~0.50 m0 for CH3NH3PbI3. Based on these results, the energy distribution curves of polycrystalline thin films are constructed, revealing the fact that using a logarithmic intensity scale to determine the VB onset is preferable due to the low density of states at the VB maximum. Secondly, investigations on the surface electronic structure of pristine perovskite surfaces conclude that the n-type behavior is a result of surface band bending due to the presence of donor-type surface states. Furthermore, due to surface photovoltage effect, photoemission measurements on different perovskite compositions exhibit excitation-intensity dependent energy levels with a shift of up to 0.7 eV. Eventually, control over the ELA by manipulating the density of surface states is demonstrated, from which very different ELA situations (variation over 0.5 eV) at interfaces with organic electron acceptor molecules are rationalized. Our findings further help to explain the rather dissimilar reported energy levels at perovskite surfaces and interfaces, refining our understanding of the operational principles in perovskite related devices.
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Woodley, Scott Marcus. „A real-space approach to surface and defect states“. Thesis, University of Bath, 1997. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.338412.
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Alves, Arilson Costa [UNESP]. „Propriedades estruturais e eletrônicas de filmes finos de β-PbO2“. Universidade Estadual Paulista (UNESP), 2016. http://hdl.handle.net/11449/145028.
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O chumbo, em função de sua alta resistividade é mau condutor de eletricidade, sendo classificado como um metal semicondutor. Já os seus óxidos são muito utilizados na confecção de baterias automotivas, pelo seu comportamento condutor. Dos vários óxidos de chumbo que existem, o dióxido de chumbo (PbO2) é um dos que mais se destacam devido a suas aplicações. O β-PbO2 é um semicondutor com band gap estreito, que recebeu uma grande atenção ultimamente devido à sua potencial utilização como óxidos condutores transparentes (TCO). Os TCO são compostos que combinam as propriedades normalmente mutuamente excludentes da transparência e da condutividade. O desempenho óptico e elétrico dos TCO está intimamente ligado à estrutura de bandas e, desta forma, a distribuição periódica de potencial em um cristal. Neste trabalho procura-se compreender os fundamentos das propriedades elétricas macroscópicas do material β-PbO2 na forma de filmes finos. Para tanto, adotou-se abordagem da mecânica quântica baseada na Teoria do Funcional Densidade (DFT), com potencial híbrido B3LYP, implementada no código CRYSTAL09. Cálculos de estrutura de bandas e densidade de estados mostram que o band gap de filmes de β-PbO2 tendem para o gap do material na forma de bulk e cálculos de energia de superfície permitem concluir que sua face mais estável é a (110).
Lead, due to its high resistivity, is a poor conductor of electricity and is classified as a semiconductor. On the other hand their oxides are widely used in the manufacture of automotive batteries, because of its conductivity. β-PbO2 is a narrow band gap semiconductor which received great attention lately due to their potential use as a transparent conducting oxide (TCO). The TCO are compounds which combine transparency and conductivity, properties that normally do not coexist. The optical and electrical performance of the TCO are intimately connected to the band structure and thus the potential distribution in a periodic crystal. This work, seeks to contribute for understanding the fundamentals of macroscopic electrical properties of β-PbO2 material in the form of thin films. Therefore, it was adopted the quantum mechanics approach based on Density Functional Theory (DFT), with B3LYP hybrid potential, implemented in the CRYSTAL09 code. Band structure and density of states calculation show that the band gap of β-PbO2 films tend to the bulk band gapsurface energy calculations permit conclude that its most stable face is the (110).
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Alves, Arilson Costa. „Propriedades estruturais e eletrônicas de filmes finos de β-PbO2 /“. Ilha Solteira, 2016. http://hdl.handle.net/11449/145028.
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Orientador: João Manuel Marques CordeiroResumo: O chumbo, em função de sua alta resistividade é mau condutor de eletricidade, sendo classificado como um metal semicondutor. Já os seus óxidos são muito utilizados na confecção de baterias automotivas, pelo seu comportamento condutor. Dos vários óxidos de chumbo que existem, o dióxido de chumbo (PbO2) é um dos que mais se destacam devido a suas aplicações. O β-PbO2 é um semicondutor com band gap estreito, que recebeu uma grande atenção ultimamente devido à sua potencial utilização como óxidos condutores transparentes (TCO). Os TCO são compostos que combinam as propriedades normalmente mutuamente excludentes da transparência e da condutividade. O desempenho óptico e elétrico dos TCO está intimamente ligado à estrutura de bandas e, desta forma, a distribuição periódica de potencial em um cristal. Neste trabalho procura-se compreender os fundamentos das propriedades elétricas macroscópicas do material β-PbO2 na forma de filmes finos. Para tanto, adotou-se abordagem da mecânica quântica baseada na Teoria do Funcional Densidade (DFT), com potencial híbrido B3LYP, implementada no código CRYSTAL09. Cálculos de estrutura de bandas e densidade de estados mostram que o band gap de filmes de β-PbO2 tendem para o gap do material na forma de bulk e cálculos de energia de superfície permitem concluir que sua face mais estável é a (110).
Mestre
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GIGNOUX, CLAIRE. „Etude des proprietes electroniques de l'alliage quasicristallin alpdre“. Université Joseph Fourier (Grenoble), 1996. http://www.theses.fr/1996GRE10233.
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Ce travail de these est consacre a l'elaboration et l'etude des proprietes electroniques de la phase quasicristalline alpdre. La recherche d'une procedure d'elaboration nous a permis d'obtenir des echantillons de phase icosaedrique pure de tres grande qualite structurale. L'alliage quasicristallin alpdre presente des proprietes de transport exceptionnelles pour un alliage constitue uniquement de metaux. En particulier, nous avons confirme que la valeur de resistivite de certains echantillons de i-alpdre peut atteindre #4#37 1 cm, ce qui est 10#6 fois superieure a celle des metaux standards, et 10#3 fois superieure a celles des amorphes metalliques. Les valeurs de resistivite de ces echantillons et leur dependance en temperature semblent s'approcher de celles des systemes ayant franchi la transition metal-isolant. Toutefois, il existe de fortes variations des proprietes de transport entre differents echantillons de la phase i-alpdre. D'autres echantillons ont montre des proprietes electroniques semblables a celles des phases icosaedriques bien connues i-alpdmn et i-alcufe qui se trouvent du cote metallique d'une transition metal-isolant. Nous avons etabli que ces disparites de proprietes de transport sont liees a des variations de composition et de qualite structurale. A l'inverse des metaux, meilleure est la qualite structurale plus la resistivite des echantillons est elevee ce qui exclu la possibilite d'une transition metal-isolant par le desordre (anderson) dans cette phase. D'autre part, nos mesures de densite d'etats electroniques permettent d'etablir la presence d'un pseudogap au niveau de fermi mais pas de gap reel comme dans les semi-conducteurs. On a donc affaire a un type de transport nouveau qui n'obeit pas aux lois connues dans les materiaux classiques (amorphes, semi-conducteurs, metaux). Un modele de transport par sauts entre etats critiques pourrait expliquer une transition metal-isolant dans ces structures ordonnees sans gap. Nous avons entrepris, par ailleurs, des mesures d'energie de surface de couches minces quasicristallines en collaboration avec l'industrie de revetements aps. Ces mesures, nous ont permis d'etablir que les couches minces quasicristallines ont une faible mouillabilite
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Houwaart, Torsten. „Cobalt porphyrins on coinage metal surfaces - adsorption and template properties“. Thesis, Lyon, École normale supérieure, 2014. http://www.theses.fr/2014ENSL0927.
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Cette thèse est une étude théorique sur la interface de porphyrine de cobalt avec des surfaces métalliques avec le code VASP DFT. Le cadre DFT nécessaire a été introduit dans le chapitre 1. La structure de la jBardeen, une programme ecrit en Java, pour la simulation de la STM est expliqué dans le chapitre 2 et le code source est jointe en annexe. Une étude de l'adsorption de CoTPP sur les surfaces métalliques a été entrepris dans le chapitre 3. Différents paramètres de calcul ont été évalués: Le site d'adsorption et de la géométrie à la fois la molécule et la surface ont été étudiés par rapport à la xc-fonctionnel et correction de la dispersion utilisée. Une adsorption site le plus stable est identifié. Par conséquent, ce site plus stable a été étudiée pour sa structure électronique. Calculés images STM avec le code jBardeen ont été comparés avec une experimentation de CoTPP Cu sur une surface (111) avec une couverture sous monocouche. Dans le chapitre 4, un adatome Fe a été présenté à la CoTPP sur Ag système (111). Trois sites de liaison symétrique différentes pour l'atome Fe ont été identifiés sur le macrocycle, marqué les , bi-, brd- et bru-positions. Un moment magnétique pouvait être attestée qui a été principalement situé sur l'atome Fe. Voies possibles entre les quatre, symétriquement équivalentes, sites bi- ont été étudiées avec des méthodes différentes. Simples calculs dans le vacuum et calculs de la “Nudged Elastic Band” (NEB) de l'ensemble du système a révélé une hauteur de barrière légèrement au-dessus de 0,2 eV allant de position bi à la posititon brd. Une analyse de vibration a montré que la commutation de l'atome Fe est susceptible, lorsqu'il est perturbé hors d'équilibre dans les positions brd et bruThis thesis is a theoretical study on the cobalt porphyrin - coinage metal surface interface with the DFT code VASP. The necessary DFT framework has been introduced in chapter 1. The structure of the Java program jBardeen for STM simulation is explained in chapter 2 and the source code is attached as Appendix. A study of the adsorption of CoTPP on coinage metal surfaces has been undertaken in chapter 3. Different parameters of the calculation have been evaluated: the adsorption site and the geometry of both the molecule and surface have been investigated with respect to the xc-functional and dispersion correction used. A most stable adsorption site -bridge down- is identified. Consequently, this most stable site was investigated for its electronic structure. Calculated STM images with the jBardeen code were compared with an experiment of CoTPP on a Cu(111) surface with sub monolayer coverage. In chapter 4 an Fe adatom was introduced to the CoTPP on Ag(111) system. Three symmetrically different binding sites for the Fe atom were identified on the macrocycle, labelled the bi-, brd- and bru-positions for bisector, bridge down and bridge up respectively. A magnetic moment could be evidenced which was mainly located on the Fe atom. Possible pathways between the four symmetrically equivalent bisector sites were investigated with different methods. Single point calculations in vacuum and Nudged Elastic Band (NEB) of the whole system revealed a barrier height of slightly above 0.2 eV going from bi- to the brd-position. A vibrational analysis showed that switching of the Fe atom is likely, when perturbed out of equilibrium in the brd- and bru- positions
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Ruderman, Andrés. „Electrocatálisis en electrodos nano estructurados de plata“. Doctoral thesis, 2016. http://hdl.handle.net/11086/5468.
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Tesis (Doctor en Física)--Universidad Nacional de Córdoba, Facultad de Matemática, Astronomía, Física y Computación, 2016.Los estudios realizados en este trabajo abarcan diferentes aspectos de la cinética de la reacción de desprendimiento de hidrógeno (her). Esto tiene como finalidad la obtención de nuevos conocimientos que permitan comprender la actividad electrocatalítica en diversas superficies monocristalinas de plata. De esta manera, las investigaciones realizadas se enmarcan en la búsqueda de un catalizador eficiente y a un costo razonable para la her. El trabajo desarrollado se divide en dos áreas: comprender la cinética de la her en diferentes superficies monocristalinas escalonadas de Ag(11n) y estudiar el mecanismo de deposición de Rh sobre Ag, el cuál puede ser un electrocatalizador bimetálico eficiente para la her.
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Pérez, Piskunow Pablo Matías. „Efectos de la radiación en las propiedades eléctricas del grafeno : estados topológicos de Floquet inducidos por láser“. Doctoral thesis, 2015. http://hdl.handle.net/11086/3563.
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Tesis (Doctor en Física)--Universidad Nacional de Córdoba, Facultad de Matemática, Astronomía, Física y Computación, 2015.Esta tesis está dedicada al estudio teórico del grafeno iluminado por un láser intenso. Nos enfocamos en efectos no perturbativos de la luz sobre el material, utilizando la teoría de Floquet. Mostramos cómo un láser puede modificar la estructura electrónica del grafeno, alterando sus propiedades de conducción, y generando también características topológicas de otra manera ausentes en el material no iluminado. Verificamos la existencia de estados topológicos de Floquet con cálculos espectrales y de los invariantes topológicos, dándole especial importancia al caso más realista y más complejo de radiación bajas frecuencias.
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Yi, Zhijun. „Ab-initio Study of Semi-conductor and Metallic Systems: from Density Functional Theory to Many Body Perturbation Theory“. Doctoral thesis, 2010. https://repositorium.ub.uni-osnabrueck.de/handle/urn:nbn:de:gbv:700-201002115394.
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Substitutional dopants in III-V semi-conductors, such as Si atoms in GaAs, are of great interest for the applications in transistors, Schottky diodes, and doping super-lattices which have been widely employed to control the electrical properties of semi-conductors. Although Si doped GaAs systems have been intensively investigated theoretically and experimentally in the last
several decades, some properties are still debated. In order to give a further explanation of Si
doped GaAs systems, we systematically studied DX center in bulk GaAs and in GaAs(110), as
well as the relative stabilities of different charged systems for Si atom replacing Ga atom at the substitutional site near GaAs(110) surface from first principles ground state
method. We show that DX centre is a metastable state in bulk GaAs and completely unstable in
the top few layers of GaAs(110). When Si atom replaces Ga atom at the surface, Charge states have an important influence on the stability of the system, and the additional charge is mainly concentrated on the Si atom for charged system. In addition, we studied the STM images of clean GaAs(110) and
charged Si:GaAs(110) by employing Tersoff-Hamann approximation. The calculated STM
images are in good agreement with experimental results. We show that at the positive bias
voltage the positively charged Si atom presents a bright feature while the negatively charged Si
atom shows a dark feature. In a semi-conductor, all bands are either completely full or completely empty. It is well known that DFT underestimates the band gaps of semi-conductors, a simple rigid shift can be used to
correct the band energies of semi-conductors. Unlike semi-conductor, the fermi energies of
metals lie in some bands. Furthermore, it turned out that some noble metals such as Cu and Ag
depend on the considered band and k point , therefore, the so-called scissors operator can not be
used for the metallic systems. The most successful approach within theoretical method for these
metals is the many body perturbation theory. On the other hand, an interesting study for metals is quasi-particle excitations, which play an important role in a rich variety of physical and
chemical phenomena such as energy transfer in photochemical reaction, desorption and
oxidation of molecules at surfaces, spin transport within bulk metals, across interfaces, and at
surfaces. One of the crucial properties of quasi-particle excitation is their lifetimes which
determine the duration of these excitations. We carried out the calculations of quasi-particle
band-structures and lifetimes for noble metals Cu and Ag within the GW approximation. For
Cu, both the calculated positions of the d bands and the width of the d bands is within 0.1 eV
compared to the experimental results. For Ag, partial core correction should be included in the
pseudo-potential to get reliable positions of the d bands. The calculated lifetime agree with the
experiment in the energy region away from the Fermi level, but deviates from the experimental
results near the Fermi level where short range interactions which GW approach fails to describe
play an important role. For a better description of the lifetime near the Fermi level, higher terms
beyond the GW approximation in the many body perturbation theory need to be considered. In
addition, the image potential state lifetimes in Cu(100) have been calculated using GW
approximation based on the localized Gaussian basis set, and the calculated n=1, 2 imagepotential
state lifetimes are in good agreement with experimental results.
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Dal, Lago Virginia. „Dirección y manipulación de estados topológicos de la materia. Efectos en grafeno y otros materiales de baja dimensión“. Bachelor's thesis, 2017. http://hdl.handle.net/11086/5979.
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Tesis (Doctor en Física)--Universidad Nacional de Córdoba, Facultad de Matemática, Astronomía, Física y Computación, 2017.Los descubrimientos experimentales del grafeno y de los materiales aislantes topológicos han suscitado un gran interés en la comunidad científica. El objetivo de la presente tesis es estudiar los estados topológicos de borde del grafeno y otros materiales de baja dimensión, y analizar diferentes formas de manipulación y dirección de los mismos para obtener sistemas con nuevas propiedades. Para ello, empleamos como base el modelo SSH para polímeros conductores (presenta carácter topológico nativo), y el grafeno. A este último se le inducen propiedades topológicas a partir de perturbaciones externas como ser campos magnéticos, términos de acoplamiento de tipo Haldane o irradiación con luz láser (teoría de Floquet). Entre los resultados encontrados podemos destacar la posibilidad de destruir y crear selectivamente estados de borde topológicos, y de dirigir la corriente eléctrica a través de los mismos. Estos efectos resultan atractivos para el diseño de futuros nanodispositivos y sus posteriores aplicaciones.
The experimental discoveries of graphene and topological insulator materials have aroused great interest in the scientific community. The aim of this thesis is to study the topological edge states of graphene and others low dimensional materials, and to analyze different ways of manipulating and directing them to achieve systems with new properties. In order to do this, we employ the SSH model for conducting polymers (it has a native topological character) and graphene as a base. Topological properties are induced to the latter through external perturbations such as magnetic fields, Haldane coupling terms or irradiation with laser light (Floquet theory). Among the results found we can highlight the possibility of selectively destroying and creating topological edge states, and of directing the electrical current through them. These effects are attractive for the design of future nanodevices and their subsequent applications.
Bücher zum Thema "Surface states, band structure, electron density of states"
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van Houselt, Arie, und Harold J. W. Zandvliet. Self-organizing atom chains. Herausgegeben von A. V. Narlikar und Y. Y. Fu. Oxford University Press, 2017. http://dx.doi.org/10.1093/oxfordhb/9780199533046.013.9.
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This article examines the intriguing physical properties of nanowires, with particular emphasis on self-organizing atom chains. It begins with an overview of the one-dimensional free electron model and some interesting phenomena of one-dimensional electron systems. It derives an expression for the 1D density of states, which exhibits a singularity at the bottom of the band and extends the free-electron model, taking into consideration a weak periodic potential that is induced by the lattice. It also describes the electrostatic interactions between the electrons and goes on to discuss two interesting features of 1D systems: the quantization of conductance and Peierls instability. Finally, the article presents the experimental results of a nearly ideal one-dimensional system, namely self-organizing platinum atom chains on a Ge(001) surface, focusing on their formation, quantum confinement between the Pt chains and the occurrence of a Peierls transition within the chains.
Buchteile zum Thema "Surface states, band structure, electron density of states"
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Chu, J. „HgSe: band structure, electron density of states“. In New Data and Updates for III-V, II-VI and I-VII Compounds, 396–99. Berlin, Heidelberg: Springer Berlin Heidelberg, 2010. http://dx.doi.org/10.1007/978-3-540-92140-0_291.
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Hönerlage, B. „AgCl: band structure, electron density of states“. In New Data and Updates for III-V, II-VI and I-VII Compounds, 23. Berlin, Heidelberg: Springer Berlin Heidelberg, 2010. http://dx.doi.org/10.1007/978-3-540-92140-0_18.
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Autschbach, Jochen. „Band Structure Theory for Extended Systems“. In Quantum Theory for Chemical Applications, 246–78. Oxford University Press, 2020. http://dx.doi.org/10.1093/oso/9780190920807.003.0013.
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The electronic structure of infinite periodic systems (crystals) is treated with band structure theory, replacing molecular orbitals by crystal orbitals. The chapter starts out by introducing the electron gas and definitions of the Fermi momentum, the Fermi energy, and the density of states (DOS). A periodic linear combination of atomic orbitals (LCAO) type treatment of an infinite periodic system is facilitated by the construction of Bloch functions. The notions of energy band and band gap are discussed with band structure concepts, using the approximations made in Huckel theory (chapter 12). One, two, and three-dimensional crystal lattices and the associated reciprocal lattices are introduced. The band structures of sodium metal, boron nitride, silicon, and graphite, are discussed as examples of metals, insulators, semi-conductors, and semi-metals, respectively. The chapter concludes with a brief discussion of the projected DOS and measures to determine bonding or antibonding interactions between atoms in a crystal.
Konferenzberichte zum Thema "Surface states, band structure, electron density of states"
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Li, Rusong, Bin He, Quanhu Zhang und Qianwei Du. „Density Functional Calculation of Property of the (1 0 0) Surface of γ-Pu“. In 18th International Conference on Nuclear Engineering. ASMEDC, 2010. http://dx.doi.org/10.1115/icone18-29071.
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Pu material can generate surface corrosion and self-radiation effect during storage, leading to the creation and recoil of uranium and helium ions, which produce defects through displacement cascades, these self-irradiation defects tend to change plutonium properties. To study these aging behavior, calculations at the spin unrestricted generalized gradient approximation (GGA) level of density functional theory (DFT) have been performed using the DMol3 programs. Relativistic effects, such as mass-velocity, Darwin term, are considered in this code. Some conclusions are draw as follows: 1) Band structure of the (100) surface of γ-Pu is very narrow around the Fermi level, showing that the eigenstate of this level is mainly composed of local atomic orbital, the local property of electrons in this band is very strong, while the band around the Fermi level is mainly constituted by 5f narrow band; 2) DOS of the (100) surface of γ-Pu are mainly composed of the density of states in −48–41eV, −23–16eV, −3–2eV; 3) Contribution of s shell to the total DOS is mainly distributed in the first interval, and p shell is mainly in the second interval, while d and f shells are mainly in the third interval.
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Lin, Zhibin, und Leonid V. Zhigilei. „The Role of Thermal Excitation of D Band Electrons in Ultrafast Laser Interaction With Noble (Cu) and Transition (Pt) Metals“. In 2007 First International Conference on Integration and Commercialization of Micro and Nanosystems. ASMEDC, 2007. http://dx.doi.org/10.1115/mnc2007-21076.
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The temperature dependences of the electron heat capacity and electron-phonon coupling factor for noble (Cu) and transition (Pt) metals are investigated based on the electron density of states (DOS) obtained from ab initio electronic structure calculations. For Cu, d band electrons could be thermally excited when the electron temperature exceeds ∼3000 K, leading to a significant increase, up to an order of magnitude, in the electron-phonon coupling factor and strong enhancement of the electron heat capacity away from the linear dependence on the electron temperature, which is commonly used in most of the current computational and theoretical investigations of ultrafast laser interactions with metals. Opposite to the case in Cu, the thermal excitation of d band electrons in Pt leads to a monotonic decrease of the electron-phonon coupling factor and contributes to significant negative deviations of the electron heat capacity from the linear dependence in the range of electron temperatures that are typically realized in ultrafast laser material processing applications. Strong and drastically different temperature dependences of the thermophysical properties predicted for Cu and Pt point to the importance of the electron DOS effects and the necessity of full consideration of thermal excitation of d band electrons for realistic modeling of short pulse laser interaction with noble and transition metals.