scholarly journals Observations of Local Electronic States in Al-based quasicrystals by STEM-EELS

2014 ◽  
Vol 70 (a1) ◽  
pp. C83-C83
Author(s):  
Takehito Seki ◽  
Eiji Abe
Keyword(s):  
Electronic Structures ◽  
Wave Length ◽  
Density Wave ◽  
Core Loss ◽  
Electronic States ◽  
Electron Model ◽  
Brillouin Zone Boundary ◽  
Sports Science ◽  
Valence Electron Density ◽  
Scanning Transmission

Most quasicrystals (QCs) reveal pseudogaps in their density of states around Fermi level, and hence the stability of QCs have been discussed in terms of energetic gains in electron systems. In fact, many QCs have been discovered by tuning valence electron density based on Hume-Rothery rule. Therefore, understanding electronic structures in QCs may provide an important clue for their stabilization mechanism. Generally, it has been frequently discussed based on an interaction between Fermi surface and Brillouin zone boundary within the framework of nearly free electron model, which is believed to be an underlying physics of a Hume-Rothery's empirical criteria. However, the electronic structures of QCs have not yet been fully understood, particularly being in microscopic-macroscopic relations. In the present work, we investigate local electronic states in Al-based QCs using electron energy loss spectroscopy (EELS) combined with scanning transmission electron microscopy (STEM), by which EELS spectra with sub-Å probe and atomic structure can be obtained simultaneously. We report STEM-EELS results on AlCuIr decagonal phases [1]. Principal components analysis clearly shows up the atomic-site dependence of plasmon loss spectra in a two-dimensional map. Qualitatively, there seems to be certain correlations between the plasmon peaks and the core-loss edges, Al L1, Ir O23, Ir N67and Cu L23, all of which reveal different behaviours at the cluster centers and the edges. All results indicate the cluster centers have metallic states and the cluster edges have covalent states in comparison. First-principles calculations confirm the unusual electronic state. We analyse a distribution of covalent electrons by Fourier transformation of electron localization function. The distribution seems like a 10-fold charge density wave with Fermi wave length. It suggests that the Hume-Rothery mechanism is important even when hybridization effect mainly contributes to pseudogap formation. The cluster centers can be regarded as the regions which are unable to contribute to the Hume-Rothery mechanism. It may be origin of the unusual electronic states. This work was conducted in Research Hub for Advanced Nano Characterization, The University of Tokyo, supported by the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan. It is acknowledged that T. Seki is a research fellow of Japan Society for the Promotion of Science.

Probing vacancies and structural distortions at individual defects in ceramics using EELS

1996 ◽  
Vol 54 ◽  
pp. 678-679
Author(s):  
D. J. Wallis ◽  
N. D. Browning
Keyword(s):  
Structural Information ◽  
Core Loss ◽  
Nearest Neighbors ◽  
Ceramic Materials ◽  
Scanning Transmission Electron Microscope ◽  
Real Space ◽  
Atomic Scale ◽  
Structure Property ◽  
Scanning Transmission ◽  
Key Issues

In electron energy loss spectroscopy (EELS), the near-edge region of a core-loss edge contains information on high-order atomic correlations. These correlations give details of the 3-D atomic structure which can be elucidated using multiple-scattering (MS) theory. MS calculations use real space clusters making them ideal for use in low-symmetry systems such as defects and interfaces. When coupled with the atomic spatial resolution capabilities of the scanning transmission electron microscope (STEM), there therefore exists the ability to obtain 3-D structural information from individual atomic scale structures. For ceramic materials where the structure-property relationships are dominated by defects and interfaces, this methodology can provide unique information on key issues such as like-ion repulsion and the presence of vacancies, impurities and structural distortion.An example of the use of MS-theory is shown in fig 1, where an experimental oxygen K-edge from SrTiO3 is compared to full MS-calculations for successive shells (a shell consists of neighboring atoms, so that 1 shell includes only nearest neighbors, 2 shells includes first and second-nearest neighbors, and so on).

History and Cross-Disciplinary Perspective of Compositional Imaging and Mapping With Nexafs Microscopy

1998 ◽  
Vol 4 (S2) ◽  
pp. 154-155
Author(s):  
H. Ade
Keyword(s):  
Electronic Structures ◽  
Chemical Shifts ◽  
Electronic States ◽  
Inorganic Materials ◽  
Chemical Bonds ◽  
Fundamental Physics ◽  
X Ray ◽  
Disciplinary Perspective ◽  
Core Electrons ◽  
X Ray Absorption

In Near Edge X-ray Absorption Fine Structure (NEXAFS) microscopy, excitations of core electrons into unoccupied molecular orbitals or electronic states provide sensitivity to a wide variety of chemical functionalities in molecules and solids. This sensitivity complements infrared (IR) spectroscopy, although the NEXAFS spectra are not quite as specific and “rich” as IR spectra. The sensitivity of NEXAFS to distinguish chemical bonds and electronic structures covers a wide variety of samples: from metals to inorganics and organics. (There is a tendency in the community to use the term NEXAFS for soft x-ray spectroscopy of organic materials, while for inorganic materials or at higher energies X-ray Absorption Near Edge Spectroscopy (XANES) is utilized, even though the fundamental physics is the same.) The sensitivity of NEXAFS is particularly high to distinguish saturated from unsaturated bonds. NEXAFS can also detect conjugation in a molecule, as well as chemical shifts due to heteroatoms.

Electronic structure of the thermoelectric materials PbTe and AgPb18SbTe20 from first-principles calculations

2010 ◽  
Vol 25 (6) ◽  
pp. 1030-1036 ◽  
Author(s):  
Pengxian Lu ◽  
Zigang Shen ◽  
Xing Hu
Keyword(s):  
Band Structure ◽  
Thermoelectric Properties ◽  
First Principles ◽  
Electronic Structures ◽  
Density Functional ◽  
Partial Density ◽  
Functional Theory ◽  
The Density Functional Theory ◽  
Scanning Transmission ◽  
Linearized Augmented Plane Wave

To investigate the effects of substituting Ag and Sb for Pb on the thermoelectric properties of PbTe, the electronic structures of PbTe and AgPb18SbTe20 were calculated by using the linearized augmented plane wave based on the density-functional theory of the first principles. By comparing the differences in the band structure, the partial density of states (PDOS), the scanning transmission microscope, and the electron density difference for PbTe and AgPb18SbTe20, we explained the reason from the aspect of electronic structures why the thermoelectric properties of AgPb18SbTe20 could be improved significantly. Our results suggest that the excellent thermoelectric properties of AgPb18SbTe20 should be attributed in part to the narrowing of its band gap, band structure anisotropy, the much extrema and large DOS near Fermi energy, as well as the large effective mass of electrons. Moreover, the complex bonding behaviors for which the strong bonds and the weak bonds are coexisted, and the electrovalence and covalence of Pb–Te bond are mixed should also play an important role in the enhancement of the thermoelectric properties of the AgPb18SbTe20.

scholarly journals Multiorbital charge-density wave excitations and concomitant phonon anomalies in Bi2Sr2LaCuO6+δ

2020 ◽  
Vol 117 (28) ◽  
pp. 16219-16225 ◽  
Author(s):  
Jiemin Li ◽  
Abhishek Nag ◽  
Jonathan Pelliciari ◽  
Hannah Robarts ◽  
Andrew Walters ◽  
...  
Keyword(s):  
Charge Density ◽  
Cuprate Superconductors ◽  
Density Wave ◽  
Charge Density Waves ◽  
Valence Electron Density ◽  
X Ray Scattering ◽  
Bond Stretching ◽  
Comprehensive Picture ◽  
Strong Hybridization ◽  
Orbital Character

Charge-density waves (CDWs) are ubiquitous in underdoped cuprate superconductors. As a modulation of the valence electron density, CDWs in hole-doped cuprates possess both Cu-3dand O-2porbital character owing to the strong hybridization of these orbitals near the Fermi level. Here, we investigate underdoped Bi2Sr1.4La0.6CuO6+δusing resonant inelastic X-ray scattering (RIXS) and find that a short-range CDW exists at both Cu and O sublattices in the copper-oxide (CuO2) planes with a comparable periodicity and correlation length. Furthermore, we uncover bond-stretching and bond-buckling phonon anomalies concomitant to the CDWs. Comparing to slightly overdoped Bi2Sr1.8La0.2CuO6+δ, where neither CDWs nor phonon anomalies appear, we highlight that a sharp intensity anomaly is induced in the proximity of the CDW wavevector (QCDW) for the bond-buckling phonon, in concert with the diffused intensity enhancement of the bond-stretching phonon at wavevectors much greater than QCDW. Our results provide a comprehensive picture of the quasistatic CDWs, their dispersive excitations, and associated electron-phonon anomalies, which are key for understanding the competing electronic instabilities in cuprates.

Relation between oxygen stoichiometry and thermodynamic properties and the electronic structure of nonstoichiometric perovskite La0.6Sr0.4CoO3−δ

2016 ◽  
Vol 18 (42) ◽  
pp. 29543-29548 ◽  
Author(s):  
S. F. Bychkov ◽  
A. G. Sokolov ◽  
M. P. Popov ◽  
A. P. Nemudry
Keyword(s):  
Electronic Structure ◽  
Thermodynamic Properties ◽  
Fermi Level ◽  
Electronic States ◽  
Oxygen Activity ◽  
Oxygen Stoichiometry ◽  
Itinerant Electron ◽  
Electron Model ◽  
Density Of Electronic States

Within the framework of the itinerant electron model, the dependence of the oxide nonstoichiometry on the oxygen activity was related to the density of electronic states near the Fermi level.

scholarly journals Atomic lattice disorder in charge-density-wave phases of exfoliated dichalcogenides (1T-TaS2)

2016 ◽  
Vol 113 (41) ◽  
pp. 11420-11424 ◽  
Author(s):  
Robert Hovden ◽  
Adam W. Tsen ◽  
Pengzi Liu ◽  
Benjamin H. Savitzky ◽  
Ismail El Baggari ◽  
...  
Keyword(s):  
Charge Density ◽  
Density Wave ◽  
Transition Metal Dichalcogenides ◽  
Charge Density Waves ◽  
Periodic Lattice ◽  
Atomic Lattice ◽  
Scanning Transmission ◽  
Out Of Plane ◽  
Metal Dichalcogenides ◽  
Layered Transition Metal

Charge-density waves (CDWs) and their concomitant periodic lattice distortions (PLDs) govern the electronic properties in several layered transition-metal dichalcogenides. In particular, 1T-TaS2 undergoes a metal-to-insulator phase transition as the PLD becomes commensurate with the crystal lattice. Here we directly image PLDs of the nearly commensurate (NC) and commensurate (C) phases in thin, exfoliated 1T-TaS2 using atomic resolution scanning transmission electron microscopy at room and cryogenic temperature. At low temperatures, we observe commensurate PLD superstructures, suggesting ordering of the CDWs both in- and out-of-plane. In addition, we discover stacking transitions in the atomic lattice that occur via one-bond-length shifts. Interestingly, the NC PLDs exist inside both the stacking domains and their boundaries. Transitions in stacking order are expected to create fractional shifts in the CDW between layers and may be another route to manipulate electronic phases in layered dichalcogenides.

Studies of the ionization of molecules by electron impact - II. Excited states of the molecular ions of methane and the methyl halides

1957 ◽  
Vol 241 (1225) ◽  
pp. 194-207 ◽  
Keyword(s):  
Excited States ◽  
Electronic Structures ◽  
Mass Spectra ◽  
Electronic States ◽  
Molecular Ions ◽  
Methyl Halides ◽  
Spin Orbital ◽  
Orbital Interactions ◽  
Electronic Excited States ◽  
First Time

The ionization of methane and the methyl halide molecules by essentially mono-energetic electrons, produced by pulse techniques, has been studied in detail in a mass spectrometer. It has been possible to detect for the first time the production of the molecular ions of these compounds in most of their excited electronic states. In the cases of the ions of methyl bromide and iodide we have been able to resolve the components of the doublets of the ground 2 E states which arise from spin-orbital interactions in these molecular ions. The several ionization potentials of each of the molecules which refer to the formation of the ions in their different electronic excited states have been measured. These new results are of interest in that they enable the molecular-orbital theories of the electronic structures of methane and the methyl halides to be assessed. They also provide support for recent theories of the origin of the ions in the mass spectra of organic compounds. It has been demonstrated that there is a monotonic relationship between the ionization potential of electrons in the [ σα 1 ] bonding orbital localized in the C— X bond of these molecules and the corresponding bond dissociation energy.

The absorption spectrum of liquid bromine

1937 ◽  
Vol 162 (910) ◽  
pp. 414-419 ◽  
Author(s):  
D. Porret ◽  
Frederick George Donnan
Keyword(s):  
Absorption Spectrum ◽  
Absorption Spectra ◽  
Ground State ◽  
Wave Length ◽  
Electronic States ◽  
Excited Electronic States ◽  
Long Wave ◽  
Liquid Bromine ◽  
Continuous Absorption ◽  
The Continuum

The continuous absorption spectra of gaseous bromine (Peskow 1917; Ribaud 1919; Gray and Style 1929; Acton, Aikin and Bayliss 1936) and of dissolved bromine (Bovis 1929; Gillam and Morton 1929) have been studied many times. They present a wide continuum (from about 30, 000 to 17, 000 cm. -1 .) with a maximum at 24, 000 cm. -1 . For the gas the continuum is preceded by two band systems on the long wave-length side. These systems converge at 19, 585 and 15, 896 cm. -1 . respectively. Acton, Aikin and Bayliss (1936) have shown that the continuum is not simple, and Mulliken (1936) and Darbyshire (1937) have pointed out that there are three overlapping continua corresponding to transitions from the ground state to three different excited electronic states. There are 3 II 0 + ← 1 Σ g , 3 II 1 ← 1 Σ g and 1 II ← 1 Σ g . The absorption spectrum of liquid bromine has been studied by Bovis (1929) form 18, 525 to 31, 750c cm. -1 . and by Camichel (1893) for two frequencies only (16, 978 and 18, 691 cm. -1 ).

The Control of Electronic States Spreading Outside the Conjugated Polymer Surface

2006 ◽  
Vol 965 ◽  
Author(s):  
Xiao Tao Hao ◽  
Takuya Hosokai ◽  
Noritaka Mitsuo ◽  
Satoshi Kera ◽  
Kazuyuki Sakamoto ◽  
...  
Keyword(s):  
Thin Films ◽  
Photoelectron Spectroscopy ◽  
Electronic Structures ◽  
Conjugated Polymer ◽  
Polymer Surface ◽  
Electronic States ◽  
Penning Ionization ◽  
X Ray ◽  
Molecular Ordering ◽  
X Ray Absorption

ABSTRACTThe surface electronic structures of conjugated regio regular and regio random poly (3- hexylthiophene) (rr-P3HT and rra-P3HT) thin films were studied by near edge X-ray absorption fine structure spectroscopy, ultraviolet photoelectron spectroscopy and Penning ionization electron spectroscopy (PIES). The distribution of the surface electronic states was controlled on rr-P3HT and rra-P3HT thin films with different molecular ordering by varying the coating process and PIES was adopted to observe the electronic states existing outside the surface.

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