The Valence Electronic Structure of Co3O4: Is It a Charge-Transfer Insulator?

1998 ◽  
Vol 547 ◽  
Author(s):  
M.A. Langell ◽  
G.A. Carson ◽  
S. Smith ◽  
L. Peng ◽  
M.H. Nassir
Keyword(s):  
Electronic Structure ◽  
Charge Transfer ◽  
Band Structure ◽  
Valence Band ◽  
Transition Metal Oxides ◽  
Resolution Electron ◽  
Bonding Properties ◽  
Low Energy Electron ◽  
A Charge ◽  
Electron Energy Loss

AbstractDespite the relevance to a variety of materials applications, the electronic and bonding properties of spinel transition metal oxides are not well established. We report here the slow oxidation of CoO(100) to Co3O4, studied by photoemission (UPS and XPS), low energy electron diffraction (LEED) and high resolution electron energy loss spectroscopy (HREELS) with the aim of elucidating the valence band electronic structure of the Co3O4 spinel. The original Mott insulator picture of the parent CoO substrate has been revised in recent times, after careful analyses and extensive debate, to the more detailed charge-transfer insulator model which includes some admixture of oxygen 2p levels in the 3d-derived valence band. No equivalent band structure analysis has been performed on the spinel oxides, perhaps in part because of the greater complexity of the 56-atom unit cell with two different cation lattice sites and oxidation states. In this study, we determine the valence band structure of the spinel oxide and address the question of whether Co3O4 can be modeled as a charge-transfer insulator in analogy with its closely related rocksalt substrate.

Band structure investigation of chalcopyrite CuInSe2(001) by angle-resolved photoelectron spectroscopy

2005 ◽  
Vol 865 ◽  
Author(s):  
Ralf Hunger ◽  
Christian Pettenkofer
Keyword(s):  
Electronic Structure ◽  
Band Structure ◽  
Valence Band ◽  
Photoelectron Spectroscopy ◽  
Bulk Composition ◽  
Synchrotron Source ◽  
Band Dispersion ◽  
Low Energy Electron ◽  
Copper Chalcopyrite ◽  
Valence Bands

AbstractClean and ordered chalcopyrite CuInSe2 surfaces are a precondition for the study of the electronic structure by angle-resolved photoelectron spectroscopy. The preparation of welldefined CuInSe2(001) surfaces by the combination of molecular beam epitaxy and a selenium capping and decapping process is described. The surface structure of CuInSe2 epilayers with different bulk composition is compared and analysed by low-energy electron diffraction.Employing near-stoichiometric surfaces, the valence electronic structure of CuInSe2 was investigated by angle-resolved photoelectron spectroscopy at the synchrotron source BESSY 2. This is the first study of the valence band structure of a copper chalcopyrite semiconductor material by photoelectron spectroscopy. The valence band dispersion along τT, i.e. the [001] direction, was investigated by a variation of the excitation energy from 10 to 35 eV under normal emission, and the band dispersion along τT, i.e. the [110] direction, was analysed by angular scans with hv = 13 eV.The valence bands derived from antibonding and bonding Se4p-Cu3d hybrid orbitals, nonbonding Cu3d states and In-Se hybrid states are clearly indentified. The strongest dispersion is found for the topmost valence band with a bandwidth of ∼0.7 eV from τ to T. From τ to N, the observed dispersion was 0.5 eV. The experimental valence bands are discussed in relation to calculated band structures in the literature.

scholarly journals Controlling magnetoresistance by tuning semimetallicity through dimensional confinement and heteroepitaxy

2021 ◽  
Vol 7 (16) ◽  
pp. eabe8971
Author(s):  
Shouvik Chatterjee ◽  
Shoaib Khalid ◽  
Hadass S. Inbar ◽  
Aranya Goswami ◽  
Taozhi Guo ◽  
...  
Keyword(s):  
Thin Film ◽  
Electronic Structure ◽  
Charge Transfer ◽  
Band Structure ◽  
Quantum Confinement ◽  
Model System ◽  
General Strategy ◽  
Two Dimensional ◽  
A Charge ◽  
Structure Engineering

Controlling electronic properties via band structure engineering is at the heart of modern semiconductor devices. Here, we extend this concept to semimetals where, using LuSb as a model system, we show that quantum confinement lifts carrier compensation and differentially affects the mobility of the electron and hole-like carriers resulting in a strong modification in its large, nonsaturating magnetoresistance behavior. Bonding mismatch at the heteroepitaxial interface of a semimetal (LuSb) and a semiconductor (GaSb) leads to the emergence of a two-dimensional, interfacial hole gas. This is accompanied by a charge transfer across the interface that provides another avenue to modify the electronic structure and magnetotransport properties in the ultrathin limit. Our work lays out a general strategy of using confined thin-film geometries and heteroepitaxial interfaces to engineer electronic structure in semimetallic systems, which allows control over their magnetoresistance behavior and simultaneously provides insights into its origin.

Electronic Structure of Cr2O3 Studied by Photoemission Spectroscopies

1993 ◽  
Vol 307 ◽  
Author(s):  
Xiaomei Li ◽  
Victor E. Henrich ◽  
Tomohiko Saitoh ◽  
Atsushi Fujimori
Keyword(s):  
Electronic Structure ◽  
Charge Transfer ◽  
Valence Band ◽  
Correlation Energy ◽  
Interaction Analysis ◽  
Experimental Spectrum ◽  
Core Level ◽  
Photoemission Spectrum ◽  
Transfer Energy ◽  
A Charge

ABSTRACTThe electronic structure of single-crystal Cr2O3 has been studied by Cr 2p core-level XPS and valence-band UPS spectroscopies. A cluster configuration-interaction analysis was applied to investigate the nature of the satellite in the Cr 2p core-level photoemission spectrum. It is argued that the satellite can be understood as a charge-transfer satellite, and Cr2O3 is found to be situated at the boundary between the Mott-Hubbard and the charge-transfer regimes. The values of the charge-transfer energy, Δ, the Coulomb correlation energy, U, and the ligand 2p-cation 3d hybridization energy, T, found from fitting the Cr 2p XPS spectrum were also used to analyze the valence-band UPS spectrum. The comparison between the experimental spectrum and the spectrum from theoretical fitting is fair.

Core Level Shifts and Grain Boundary Cohesion

1998 ◽  
Vol 4 (S2) ◽  
pp. 766-767
Author(s):  
D. A. Muller
Keyword(s):  
Charge Transfer ◽  
Valence Band ◽  
Core Level ◽  
Level Shift ◽  
The Core ◽  
Metallic Interfaces ◽  
Level Shifts ◽  
Electron Energy Loss ◽  
Valence Band Width

The role of core level shifts at metallic interfaces has often been ignored in electron energy loss spectroscopy (EELS) even though very small changes in bond length can lead to large core level shifts. However, the popular interpretation of core level shifts as measures of charge transfer is highly problematic. For instance, in binary alloys systems, the core level shifts can be the same sign for both atomic constituents[l]. The simple interpretation would require that both atomic species had lost or gained charge. Further, the signs of the core level shifts can be opposite to those expected from electronegativity arguments[2]. A core level shift (CLS) is still possible, even when no charge transfer occurs. As illustrated in Fig. 1, if the valence band width is increased, the position of the center of the valence band with respect to the Fermi energy will change (as the number of electrons remains unchanged).

A STUDY ON STRAIN AFFECTING ELECTRONIC STRUCTURE OF WURTZITE ZnO BY FIRST PRINCIPLES

2009 ◽  
Vol 23 (19) ◽  
pp. 2339-2352 ◽  
Author(s):  
LI BIN SHI ◽  
SHUANG CHENG ◽  
RONG BING LI ◽  
LI KANG ◽  
JIAN WEI JIN ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Electronic Structure ◽  
Band Structure ◽  
Valence Band ◽  
Density Of States ◽  
First Principles ◽  
Density Functional ◽  
Functional Theory ◽  
Electron Density Difference ◽  
Different Strains

Density of states and band structure of wurtzite ZnO are calculated by the CASTEP program based on density functional theory and plane-wave pseudopotential method. The calculations are carried out in axial and unaxial strains, respectively. The results of density of states in different strains show that the bottom of the conduction band is always dominated by Zn 4s, and the top of valence band is always dominated by O 2p. The variation of the band gap calculated from band structure is also discussed. In addition, p-d repulsion is used in investigating the variation of the top of the valence band in different strains and the results can be verified by electron density difference.

Atomic and Electronic Structure Analysis of Σ=3, 9 and 27 Boundary, and Multiple Junction in β-SiC

1999 ◽  
Vol 589 ◽  
Author(s):  
K. Tanaka ◽  
M. Kohyama
Keyword(s):  
Electronic Structure ◽  
Energy Loss ◽  
Twin Boundary ◽  
Structural Unit ◽  
High Resolution Electron Microscopy ◽  
Coherent Twin Boundary ◽  
Atomic Structures ◽  
Resolution Electron ◽  
Electron Energy Loss ◽  
Atomic And Electronic Structure

AbstractThe atomic structures of σ=3, 9 and 27 boundaries, and multiple junctions in β-SiC were studied by high-resolution electron microscopy (HREM). Especially, the existence of the variety of structures of σ=3 incoherent twin boundaries and σ=27 boundary was shown by HREM. The structures of σ=3, 9 and 27 boundary were explained by structural unit models. Electron energy-loss spectroscopy (EELS) was used to investigate the electronic structure of grain boundaries. The spectra recorded from bulk, {111}σ=3 coherent twin boundary (CTB) and {1211}σ=3 incoherent twin boundary (ITB) did not show significant differences. Especially, the energy-loss corresponding to carbon 1s-to Φ* transition was not found. It indicates that C atoms exist at grain boundary on the similar condition of bulk

Chemisorption Geometry, Vibrational Spectra, and Thermal Desorption of Formic Acid on TiO2(110)

1998 ◽  
Vol 05 (01) ◽  
pp. 381-385 ◽  
Author(s):  
S. A. Chambers ◽  
M. A. Henderson ◽  
Y. J. Kim ◽  
S. Thevuthasan
Keyword(s):  
Formic Acid ◽  
Photoelectron Spectroscopy ◽  
High Energy ◽  
Decomposition Products ◽  
X Ray ◽  
Low Energy Electron Diffraction ◽  
Resolution Electron ◽  
Low Energy Electron ◽  
Temperature Programmed ◽  
Electron Energy Loss

We have used high-energy X-ray photoelectron spectroscopy and diffraction (XPS/XPD), low-energy electron diffraction (LEED), high-resolution electron energy loss spectroscopy (HREELS) and temperature-programmed desorption (TPD) to determine the molecular orientation, long-range order, vibrational frequencies, and desorption temperatures for formic acid and its decomposition products on TiO 2(110). Molecular adsorption occurs at coverages approaching one monolayer, producing a weakly ordered (2 × 1) surface structure. High-energy XPD reveals that the formate binds rigidly in a bidentate fashion through the oxygens to Ti cation rows along the [001] direction with an O–C–O bond angle of 126 ± 4°. During TPD some surface protons and formate anions recombine and desorb as formic acid above 250 K. However, most of the decomposition products follow reaction pathways leading to H 2 O , CO and H 2 CO desorption. Water is formed in TPD below 500 K via the abstraction of lattice oxygen by deposited acid protons.

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