Study of Ion Beam Mixing by x ray reflectometry

2011 ◽  
Vol 1298 ◽  
Author(s):  
D Simeone ◽  
D Gosset ◽  
L. Luneville ◽  
G Baldinozzi ◽  
N Moncoffre ◽  
...  
Keyword(s):  
Density Gradient ◽  
Electron Density ◽  
Functional Dependence ◽  
Ion Beam ◽  
X Ray Diffraction ◽  
X Ray ◽  
Electron Density Gradient ◽  
Auto Correlation Function ◽  
Atomic Mixing

ABSTRACTWe present in this text a new experimental tool to study the mixing of atoms under irradiation. Based on physics of x ray diffraction, the specular reflectivy of x ray was used to estimate the Auto Correlation Function associated with the electron density gradient. The accuracy of the ACF is around 1 nanometer and does not evolve with the thickness of the probed layer. Thus, this point allows accurately measuring the broadening of the electron density gradient spreading induced by irradiation. Such an accurate profile extracted over a large range of fluences (about 3 decades) would lead to the determination of the functional dependence of this spreading with the fluence. This could allow pointing out the main mechanisms triggering the atomic mixing over large distances when atomic mixing occurring in thermal spikes is washed out.

Unambiguous determination of H-atom positions: comparing results from neutron and high-resolution X-ray crystallography

2010 ◽  
Vol 66 (5) ◽  
pp. 558-567 ◽  
Author(s):  
Anna S. Gardberg ◽  
Alexis Rae Del Castillo ◽  
Kevin L. Weiss ◽  
Flora Meilleur ◽  
Matthew P. Blakeley ◽  
...  
Keyword(s):  
Neutron Diffraction ◽  
Electron Density ◽  
Pyrococcus Furiosus ◽  
X Ray Diffraction ◽  
Neutron Data ◽  
X Ray ◽  
X Ray Crystallography ◽  
Density Maps ◽  
Improved Model

The locations of H atoms in biological structures can be difficult to determine using X-ray diffraction methods. Neutron diffraction offers a relatively greater scattering magnitude from H and D atoms. Here, 1.65 Å resolution neutron diffraction studies of fully perdeuterated and selectively CH3-protonated perdeuterated crystals ofPyrococcus furiosusrubredoxin (D-rubredoxin and HD-rubredoxin, respectively) at room temperature (RT) are described, as well as 1.1 Å resolution X-ray diffraction studies of the same protein at both RT and 100 K. The two techniques are quantitatively compared in terms of their power to directly provide atomic positions for D atoms and analyze the role played by atomic thermal motion by computing the σ level at the D-atom coordinate in simulated-annealing composite D-OMIT maps. It is shown that 1.65 Å resolution RT neutron data for perdeuterated rubredoxin are ∼8 times more likely overall to provide high-confidence positions for D atoms than 1.1 Å resolution X-ray data at 100 K or RT. At or above the 1.0σ level, the joint X-ray/neutron (XN) structures define 342/378 (90%) and 291/365 (80%) of the D-atom positions for D-rubredoxin and HD-rubredoxin, respectively. The X-ray-only 1.1 Å resolution 100 K structures determine only 19/388 (5%) and 8/388 (2%) of the D-atom positions above the 1.0σ level for D-rubredoxin and HD-rubredoxin, respectively. Furthermore, the improved model obtained from joint XN refinement yielded improved electron-density maps, permitting the location of more D atoms than electron-density maps from models refined against X-ray data only.

Superconducting Mbtallic Supkrlattices

1986 ◽  
Vol 77 ◽  
Author(s):  
Charles M. Falco ◽  
Ruggero Vaglio ◽  
Annamaria Cucolo
Keyword(s):  
Thin Films ◽  
Ion Beam ◽  
London Penetration Depth ◽  
X Ray Diffraction ◽  
Josephson Tunneling ◽  
X Ray ◽  
Analysis Techniques ◽  
Beam Analysis ◽  
Superlattice Layer

ABSTRACTSince the coherence length is of order 50 Å to 1 μm, it is possible to alternately layer thin films of a superconductor with another material to affect the physical properties of the resulting superlattice. A brief description of our sputtering technique used to prepare superlat t ices consisting of Nb/Cu and Ta/Mo is given. Optical interferometry, x-ray diffraction and ion beam analysis techniques independently confirm that control of ±0.3% is achieved over the amount of material deposited in each layer. Results of a study of Josephson tunneling to Nb/Cu metallic super lattices are reviewed. These measurements enable a determination of the London penetration depth to be made as a function of superlattice layer thickness.

scholarly journals High-resolution X-ray diffraction determination of the electron density of 1-(8-PhSC10H6)SS(C10H6SPh-8′)-1′ with the QTAIM approach: evidence for S4 σ(4c–6e) at the naphthalene peri-positions

RSC Advances ◽  
2018 ◽  
Vol 8 (18) ◽  
pp. 9651-9660 ◽  
Author(s):  
Yutaka Tsubomoto ◽  
Satoko Hayashi ◽  
Waro Nakanishi ◽  
Lucy K. Mapp ◽  
Simon J. Coles
Keyword(s):  
High Resolution ◽  
Electron Density ◽  
X Ray Diffraction ◽  
Ray Method ◽  
X Ray ◽  
Diffraction Determination

The nature of S4 σ(4c–6e) at the 1,8-positions of naphthalene is elucidated via a high-resolution X-ray method with the QTAIM approach.

On the transferability of QTAIMC descriptors derived from X-ray diffraction data and DFT calculations: substituted hydropyrimidine derivatives

2011 ◽  
Vol 67 (5) ◽  
pp. 425-436 ◽  
Author(s):  
A. A. Rykounov ◽  
A. I. Stash ◽  
V. V. Zhurov ◽  
E. A. Zhurova ◽  
A. A. Pinkerton ◽  
...  
Keyword(s):  
Electron Density ◽  
Density Functional ◽  
Molecular Structures ◽  
X Ray Diffraction ◽  
Covalent Bonds ◽  
Functional Theory ◽  
X Ray ◽  
Biginelli Compounds ◽  
Empirical Corrections

The combined study of electron-density features in three substituted hydropyrimidines of the Biginelli compound family has been fulfilled. Results of the low-temperature X-ray diffraction measurements and density functional theory (DFT) B3LYP/6-311++G** calculations of these compounds are described. The experimentally derived atomic and bonding characteristics determined within the quantum-topological theory of atoms in molecules and crystals (QTAIMC) were demonstrated to be fully transferable within chemically similar structures such as the Biginelli compounds. However, for certain covalent bonds they differ significantly from the theoretical results because of insufficient flexibility of the atom-centered multipole electron density model. It was concluded that currently analysis of the theoretical electron density provides a more reliable basis for the determination of the transferability of QTAIMC descriptors for molecular structures. Empirical corrections making the experimentally derived QTAIMC bond descriptors more transferable are proposed.

scholarly journals On avoiding negative electron density in Gram-Charlier refinements of anharmonic motion: the example of glutathione

2018 ◽  
Vol 233 (9-10) ◽  
pp. 695-706 ◽  
Author(s):  
Christian B. Hübschle ◽  
Charlotte Ruhmlieb ◽  
Anja Burkhardt ◽  
Sander van Smaalen ◽  
Birger Dittrich
Keyword(s):  
Electron Density ◽  
Maximum Entropy Method ◽  
Entropy Method ◽  
Free Lunch ◽  
X Ray Diffraction ◽  
Third Order ◽  
X Ray ◽  
Density Maps ◽  
Anisotropic Displacement Parameters

Abstract The structure of glutathione, γ-l-Glutamyl-l-cysteinyl-glycine (C10H17N3O6S), was studied by multi-temperature single-crystal X-ray diffraction. Residual density maps from conventional independent atom model refinement gave indication of anharmonic motion in the molecule. This was further investigated by invariom refinement with anisotropic displacement parameters for all atoms, which described asphericity due to chemical bonding and lone pairs; afterwards only the residual-density signal of anharmonic motion remained. Treating anharmonicity with third-order Gram-Charlier displacement parameters led to regions with unphysical negative electron density. In contrast, a maximum entropy method (MEM) determination of the electron density successfully takes the features into account. Respective difference electron density plots (MEM minus prior and [Invariom+GC] minus invariom) agree well with each other. Challenges in treating and understanding the phenomenon are discussed. A procedure is proposed how unphysical negative electron density can be avoided. It is closely related to the free lunch algorithm.

Sem and X-Ray Analysis of Renal and Biliary Calculi

1976 ◽  
Vol 34 ◽  
pp. 306-307
Author(s):  
R. J. Narconis ◽  
G. L. Johnson
Keyword(s):  
Chemical Constituents ◽  
Natural State ◽  
X Ray Diffraction ◽  
Chemical Methods ◽  
X Ray ◽  
Additional Dimension ◽  
Biliary Calculi ◽  
Calculus Formation ◽  
Scanning Electron

Analysis of the constituents of renal and biliary calculi may be of help in the management of patients with calculous disease. Several methods of analysis are available for identifying these constituents. Most common are chemical methods, optical crystallography, x-ray diffraction, and infrared spectroscopy. The application of a SEM with x-ray analysis capabilities should be considered as an additional alternative.A scanning electron microscope equipped with an x-ray “mapping” attachment offers an additional dimension in its ability to locate elemental constituents geographically, and thus, provide a clue in determination of possible metabolic etiology in calculus formation. The ability of this method to give an undisturbed view of adjacent layers of elements in their natural state is of advantage in determining the sequence of formation of subsequent layers of chemical constituents.

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