X-Ray Investigation of Bond-Charge Density in Gallium Arsenide

1971 ◽  
Vol 3 (12) ◽  
pp. 4308-4311 ◽  
Author(s):  
R. Colella
Keyword(s):  
Gallium Arsenide ◽  
Charge Density ◽  
X Ray ◽  
Bond Charge

Static and Dynamical Valence-Charge-Density Properties of GaAs

1993 ◽  
Vol 48 (1-2) ◽  
pp. 29-37
Author(s):  
Ullrich Pietsch
Keyword(s):  
Charge Density ◽  
Transfer Model ◽  
Ionic Bond ◽  
Experimental Proof ◽  
X Ray ◽  
Valence Electron Density ◽  
Nearest Neighbours ◽  
Electronic Response ◽  
The Difference ◽  
Bond Charge

Abstract Owing to the close neighbourhood of Ga and As in Mendeleev's table, GaAs shows two fundamental classes of X-ray structure amplitudes distinguished by their extremely different scattering power. They are differently sensitive to the valence electron density (VED) redistribution caused by the chemical bond and must be measured by different experimental methods. Using such data, both the VED and the difference electron densities (DED) are calculated here. Comparison with theoret-ical densities shows that the VED is characterized by covalent, ionic and metallic contributions. The DED constructed from GaAs and Ge data demonstrates the electronic response caused by a "protonic" charge transfer between both f.c.c. sublattices as well as the transition from a purely covalent to a mixed covalent-ionic bond. Especially the charge-density accumulation between nearest neighbours (bond charge (BC)) depends on the distance between the bonding atoms and changes under the influence of any lattice deformation. This phenomenon is described by a BC-transfer model. Its direct experimental proof is given by measuring the variation of the scattering power of weak reflections under the influence of an external electric field. This experiment demonstrates that the ionicity of the bond changes in addition to the BC variation.

scholarly journals Charge Density Waves in YBa2Cu3O6.67 Probed by Resonant X-Ray Scattering under Uniaxial Compression

2021 ◽  
Vol 126 (3) ◽  
Author(s):  
H.-H. Kim ◽  
E. Lefrançois ◽  
K. Kummer ◽  
R. Fumagalli ◽  
N. B. Brookes ◽  
...  
Keyword(s):  
Charge Density ◽  
Uniaxial Compression ◽  
Charge Density Waves ◽  
Density Waves ◽  
X Ray ◽  
X Ray Scattering ◽  
Ray Scattering

A Combination Method of Charge Density Measurement in Hard Materials Using Accurate, Quantitative Electron and X-ray Diffraction: The α-Al2O3 Case

2003 ◽  
Vol 9 (5) ◽  
pp. 419-427 ◽  
Author(s):  
Victor A. Streltsov ◽  
Philip N.H. Nakashima ◽  
Andrew W.S. Johnson
Keyword(s):  
Charge Density ◽  
Multiple Scattering ◽  
Density Measurement ◽  
Bloch Wave ◽  
Combination Method ◽  
X Ray Diffraction ◽  
X Ray ◽  
Hard Materials ◽  
Structure Factors ◽  
Free Data

Current X-ray diffraction techniques intended for “ideally imperfect” specimens provide structure factors only on a relative scale and ever-present multiple scattering in strong low-angle Bragg reflections is difficult to correct. Multiple scattering is implicit in the quantitative convergent beam electron diffraction (QCBED) method, which provides absolutely scaled structure factors. Conventional single crystal X-ray diffraction has proved adequate in softer materials where crystal perfection is limited. In hard materials, the highly perfect nature of the crystals is often a difficulty, due to the inadequacy of the conventional corrections for multiple scattering (extinction corrections). The present study on α-Al2O3 exploits the complementarity of synchrotron X-ray measurements for weak and medium intensities and QCBED measurement of the strong low-angle reflections. Two-dimensional near zone axis QCBED data from different crystals at various accelerating voltages, thicknesses, and orientations have been matched using Bloch-wave and multislice methods. The reproducibility of QCBED data is better than 0.5%. The low-angle strong QCBED structure factors were combined with middle and high-angle extinction-free data from synchrotron X-ray diffraction measurements. Static deformation charge density maps for α-Al2O3 have been calculated from a multipole expansion model refined using the combined QCBED and X-ray data.

Molecular tapes in the structure of isoguaninium chloride

2017 ◽  
Vol 74 (1) ◽  
pp. 108-112 ◽  
Author(s):  
Urszula Anna Budniak ◽  
Paulina Maria Dominiak
Keyword(s):  
Crystal Structure ◽  
Single Crystal ◽  
Charge Density ◽  
Interaction Energy ◽  
Electrostatic Interaction ◽  
Electrostatic Interactions ◽  
The Other ◽  
X Ray Diffraction ◽  
X Ray ◽  
Diffraction Structure

Isoguanine, an analogue of guanine, is of intrinsic interest as a noncanonical nucleobase. The crystal structure of isoguaninium chloride (systematic name: 6-amino-2-oxo-1H,7H-purin-3-ium chloride), C5H6N5O+·Cl−, has been determined by single-crystal X-ray diffraction. Structure analysis was supported by electrostatic interaction energy (E es) calculations based on charge density reconstructed with the UBDB databank. In the structure, two kinds of molecular tapes are observed, one parallel to (010) and the other parallel to (50\overline{4}). The tapes are formed by dimers of isoguaninium cations interacting with chloride anions. E es analysis indicates that cations in one kind of tape are oriented so as to minimize repulsive electrostatic interactions.

X-ray intensity fluctuation spectroscopy measurements of the charge density wave phases of NbSe3

2002 ◽  
Vol 12 (9) ◽  
pp. 3-8
Author(s):  
M. Sutton ◽  
Y. Li ◽  
J. D. Brock ◽  
R. E. Thorne
Keyword(s):  
Charge Density ◽  
Charge Density Wave ◽  
Intensity Fluctuation ◽  
Speckle Pattern ◽  
Equations Of Motion ◽  
Density Wave ◽  
Electrical Currents ◽  
X Ray ◽  
Longitudinal Correlation ◽  
Speckle Patterns

An introduction to X-ray Intensity Fluctuation Spectroscopy (XIFS) is given by describing its relationship to speckle from coherent sources. A brief description of the relationship of XIFS measurements to the underlying equations of motion is given. Preliminary results for the charge density wave (CDW) system NbSe3 are then presented. Static speckle patterns are shown for the $\overrightarrow {Q}_1 = (0 .76$ 0) CDW peak showing that XIFS experiments are possible in this systom provided time constants are long enough. For electrical currents below threshold, a static speckle pattern is observed but for currents above threshold the speckles are smeared out showing movement of the CDW. It is also shown that above threshold, the longitudinal correlation length decreases.

Phase Transitions in Gold Contacts to Gallium Arsenide

1984 ◽  
Vol 37 ◽  
Author(s):  
Edward Beam ◽  
D. D. L. Chung
Keyword(s):  
Gallium Arsenide ◽  
Phase Transitions ◽  
Peritectic Transformation ◽  
Complete Dissolution ◽  
X Ray Diffraction ◽  
X Ray ◽  
Heating And Cooling ◽  
Similar Phase ◽  
Gold Contacts

AbstractX-ray diffraction was used in situ to study the phase transitions which occurred in 1500 Å Au/GaAs(100) upon heating and cooling. The reaction between Au and GaAs took the form Au + Ga → α Au-Ga. Upon heating, α Au-Ga completely dissolved in liquid Au-Ga. Upon subsequent cooling, β Au-Ga (or Au7Ga2) formed. In 1 atm of nitrogen, phase transitions were observed reversibly at 525 ± 25°C (due to the complete dissolution of α Au-Ga upon heating) and 415 ± 5°C (due to the peritectic transformation of β Au-Ga to α Au-Ga and liquid Au-Ga upon heating). In a vacuum of 425 μ (0.031 Kg/2m) similar phase transitions were observed at 425 ± 25°C and 387 ± 13°C, respectively.

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