scholarly journals Direct Determination of the Stacking Order in Gd2O3 Epi-Layers on GaAs

2002 ◽  
Vol 751 ◽  
Author(s):  
Yizhak Yacoby ◽  
Mukhles Sowwan ◽  
Ron Pindak ◽  
Julie Cross ◽  
Don Walko ◽  
...  
Keyword(s):  
Electron Density ◽  
Atomic Structure ◽  
Gaas Substrate ◽  
Direct Determination ◽  
Real Space ◽  
Two Dimensions ◽  
Stacking Order

ABSTRACTWe have used Coherent Bragg Rod Analysis (COBRA) to investigate the atomic structure of a 5.6 nm thick Gd2O3 film epitaxially grown on a (100) GaAs substrate. COBRA is a method to directly obtain the structure of systems periodic in two-dimensions by determining the complex scattering factors along the substrate Bragg rods. The system electron density and atomic structure are obtained by Fourier transforming the complex scattering factors into real space. The results show that the stacking order of the first seven Gd2O3 film layers resembles the stacking order of Ga and As layers in GaAs then changes to the stacking order of cubic bulk Gd2O3. This behavior is distinctly different from the measured stacking order in a 2.7 nm thick Gd2O3 in which the GaAs stacking order persists throughout the entire film.

Direct Determination of Grain Boundary Atomic Structure in SrTiO3

Science ◽  
1994 ◽  
Vol 266 (5182) ◽  
pp. 102-104 ◽  
Author(s):  
M. M. McGibbon ◽  
N. D. Browning ◽  
M. F. Chisholm ◽  
A. J. McGibbon ◽  
S. J. Pennycook ◽  
...  
Keyword(s):  
Grain Boundary ◽  
Atomic Structure ◽  
Direct Determination

Direct determination of the absolute electron density of nanostructured and disordered materials at sub-10-nm resolution

2003 ◽  
Vol 68 (1) ◽  
Author(s):  
Jianwei Miao ◽  
James E. Amonette ◽  
Yoshinori Nishino ◽  
Tetsuya Ishikawa ◽  
Keith O. Hodgson
Keyword(s):  
Electron Density ◽  
Direct Determination ◽  
Disordered Materials ◽  
The Absolute

Determination of the Relative Precision of Atoms in a Macromolecular Structure

1998 ◽  
Vol 54 (3) ◽  
pp. 391-399 ◽  
Author(s):  
Genfa Zhou ◽  
Junfeng Wang ◽  
Eric Blanc ◽  
Michael S. Chapman
Keyword(s):  
Electron Density ◽  
Grid Point ◽  
Real Space ◽  
Positional Error ◽  
Electron Densities ◽  
Isomorphous Replacement ◽  
Temperature Factors ◽  
Improved Methods

Several real-space indices and temperature factors are compared with respect to their correlation with atomic positional error and their ability to indicate atoms and residues with the worst of subtle errors. The best index, r ED, is a correlation coefficient between model and map electron densities, similar to one proposed earlier, but incorporating two improvements. Firstly, resolution is accounted for explicitly by calculating the model electron density by Fourier transformation of resolution-truncated scattering factors. Secondly, the deviation between model and map electron densities is assigned to neighboring atoms according to their contribution to the electron density of each grid point. With maps of various qualities, r ED is the single index with best correlation to atomic error with grouped or individual atoms, and it is the most reliable indicator of poor residues. With poorer omit maps, imprecision of individual atoms is best diagnosed by a combination of low r ED or high B factor. With the improved methods, 60–70% of the least precise atoms can detected in a fully refined structure. Similarly, 40–80% of the least precise atoms of an unrefined model can be detected by comparison with an isomorphous replacement map. This is useful in assessing and improving the quality of a model, but not sufficient to confidently validate all atoms of a structure at sub-atomic resolution.

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