scholarly journals Irreversible Structural Transformation of five fold i-AlPdMn Quasicrystals after Ion Bombardment and Annealing

2000 ◽  
Vol 643 ◽  
Author(s):  
F. Schmithüsen ◽  
G. Cappello ◽  
S. Decossas ◽  
G. Torricelli ◽  
T.-L. Lee ◽  
...  
Keyword(s):  
High Resolution ◽  
Structural Transformation ◽  
Bragg Peak ◽  
Normal Incidence ◽  
Ion Bombardment ◽  
Sample Surface ◽  
Bulk Sample ◽  
X Ray Diffraction ◽  
Energy Position ◽  
X Ray

AbstractFive fold i-AlPdMn surface prepared under UHV by ion bombardment and annealing was so far considered to be bulk terminated. This result was substantially based on a quantitative LEED analyses [1]. Analysis of the specular rod in a X ray diffraction experiment at grazing incidence supported this result [2]. We present a new study of this surface by high resolution X ray diffraction at normal incidence. In this Bragg configuration the diffraction peak 18 – 29 for instance is at a photon energy of 2.873keV, the 72 – 116 reflection at 5.725keV. This results in an analyzed thickness of the sample surface of a few micrometers.The surface was cleaned by ion bombardment. During annealing (T≅880K), we clearly observed the progressive disappearance of the initial Bragg peak characteristic of the as cast bulk sample. Conversely a new Bragg peak grows at an energy position shifted by 1eV compared to the position of the original Bragg peak. This is a clear signature for an irreversible structural transformation which takes place on at least the micron thickness. On the transformed surface, both, a LEED pattern and a RHEED pattern, characteristic for a five fold surface were easily obtained.This high resolution experiment (the relative Bragg peak shift is 3ׁ10−4) was reproduced on samples from different initial compositions. This shows that five fold i-AlPdMn surface changes after preparation by ion bombardment and annealing at 900K on a micrometer thickness. This is not consistent with the conclusion that the surface is simply terminated by a cut of the original bulk. We conclude that a reorganization process of the quasicrystalline structure during annealing proceeds in the surface vicinity (probed depth is close to a few microns).

New Algorithms for Rapid Full-Wafer Mapping by High Resolution Double Axis X-Ray Diffraction

1993 ◽  
Vol 324 ◽  
Author(s):  
N Loxley ◽  
S Cockerton ◽  
L M Cooke ◽  
T Gray ◽  
B K Tanner ◽  
...  
Keyword(s):  
High Resolution ◽  
Bragg Peak ◽  
Curve Shape ◽  
X Ray Diffraction ◽  
Rocking Curve ◽  
X Ray ◽  
Incidence Plane ◽  
Symmetric Geometry ◽  
The Mean ◽  
New Algorithms

AbstractWe describe successful algorithms for rapid alignment of the Bragg planes normal to the incidence plane in a high resolution X-ray diffraction experiment. One is appropriate to the surface symmetric geometry and uses a technique of rotation about the specimen normal.From an experimental study of the rocking curve shape as a function of tilt, we have developed a new algorithm which uses tilting about an axis formed by the intersection of the specimen and incidence planes. This has been shown to be reliable for rapid optimization of the diffraction conditions for wafers cut up to 15° off the (001) plane and for asymmetric reflections. Additionally algorithms are outlined which permit rapid location of the maximum of the Bragg peak and deduction of the mean wafer curvature from the X-ray data

Effect of ion bombardment during the low-mobility growth of metallic superlattices

1988 ◽  
Vol 3 (5) ◽  
pp. 856-861 ◽  
Author(s):  
B. Window ◽  
F. Sharples
Keyword(s):  
Crystalline Phase ◽  
Lattice Spacing ◽  
Bragg Peak ◽  
Ion Bombardment ◽  
Growth Direction ◽  
X Rays ◽  
X Ray Diffraction ◽  
X Ray ◽  
Average Lattice ◽  
Profile Change

The structure of sputtered Mo/Fe superlattices of periodicities 9 to 30 Å grown at a substrate temperature of 300 K at various pressures and levels of low-energy ion bombardment have been studied using x-ray diffraction. The samples show the growth of an amorphous phase below 17 Å periodicity and a crystalline phase above 21 Å, with mixed phases in between. Limited ion bombardment reduces the coherency in the growth direction in the crystalline phase, while heavy bombardment sufficient to promote significant mixing acts to improve the coherency, but not to the level observed in films with no bombardment. The relative intensities of the average lattice spacing reflection and its most intense satellite give the composition profile change due to the ion mixing. Some ion bombardment of the iron layer markedly improves the reflectance for x-rays at both low and high angles near the Bragg peak due to the average lattice spacing.

High-resolution X-ray diffraction analysis of the Bragg peak integrated intensity in highly mismatched III-N epilayers

2003 ◽  
Vol 250 (3-4) ◽  
pp. 354-358 ◽  
Author(s):  
G. Feng ◽  
X.M. Shen ◽  
J.J. Zhu ◽  
B.S. Zhang ◽  
D.G. Zhao ◽  
...  
Keyword(s):  
High Resolution ◽  
Diffraction Analysis ◽  
Bragg Peak ◽  
X Ray Diffraction ◽  
X Ray ◽  
Integrated Intensity

High resolution x‐ray diffraction study of the Bragg peak width in highly mismatched III–V heterostructures

1996 ◽  
Vol 69 (27) ◽  
pp. 4233-4235 ◽  
Author(s):  
C. Ferrari ◽  
L. Francesio ◽  
P. Franzosi ◽  
S. Gennari
Keyword(s):  
High Resolution ◽  
Diffraction Study ◽  
Bragg Peak ◽  
Peak Width ◽  
X Ray Diffraction ◽  
X Ray

High-resolution X-ray diffraction study of highly mismatched III–V heterostructures by analysis of the layer Bragg peak width

1997 ◽  
Vol 19 (2-4) ◽  
pp. 277-284
Author(s):  
C. Ferrari ◽  
L. Francesio ◽  
P. Franzosi ◽  
S. Gennari
Keyword(s):  
High Resolution ◽  
Diffraction Study ◽  
Bragg Peak ◽  
Peak Width ◽  
X Ray Diffraction ◽  
X Ray

A High Resolution Study of G.P. Zones in Aluminum - 4.2 at % Silver

1982 ◽  
Vol 40 ◽  
pp. 722-723 ◽  
Author(s):  
R. Gronsky
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
High Resolution ◽  
Computer Simulations ◽  
Structural Characteristics ◽  
X Ray Diffraction ◽  
X Ray ◽  
Transmission Electron ◽  
Resolution Study

The phenomenon of clustering in Al-Ag alloys has been extensively studied since the early work of Guinierl, wherein the pre-precipitation state was characterized as an assembly of spherical, ordered, silver-rich G.P. zones. Subsequent x-ray and TEM investigations yielded results in general agreement with this model. However, serious discrepancies were later revealed by the detailed x-ray diffraction - based computer simulations of Gragg and Cohen, i.e., the silver-rich clusters were instead octahedral in shape and fully disordered, atleast below 170°C. The object of the present investigation is to examine directly the structural characteristics of G.P. zones in Al-Ag by high resolution transmission electron microscopy.

Tubulin structure at intermediate resolution

1995 ◽  
Vol 53 ◽  
pp. 852-853
Author(s):  
K. H. Downing ◽  
S. G. Wolf ◽  
E. Nogales
Keyword(s):  
High Resolution ◽  
Structural Data ◽  
Therapeutic Drug ◽  
Zinc Ions ◽  
Two Dimensional ◽  
X Ray Diffraction ◽  
X Ray ◽  
Negative Stain ◽  
Functional Mechanisms ◽  
Tubulin Structure

Microtubules are involved in a host of critical cell activities, many of which involve transport of organelles through the cell. Different sets of microtubules appear to form during the cell cycle for different functions. Knowledge of the structure of tubulin will be necessary in order to understand the various functional mechanisms of microtubule assemble, disassembly, and interaction with other molecules, but tubulin has so far resisted crystallization for x-ray diffraction studies. Fortuitously, in the presence of zinc ions, tubulin also forms two-dimensional, crystalline sheets that are ideally suited for study by electron microscopy. We have refined procedures for forming the sheets and preparing them for EM, and have been able to obtain high-resolution structural data that sheds light on the formation and stabilization of microtubules, and even the interaction with a therapeutic drug.Tubulin sheets had been extensively studied in negative stain, demonstrating that the same protofilament structure was formed in the sheets and microtubules. For high resolution studies, we have found that the sheets embedded in either glucose or tannin diffract to around 3 Å.

scholarly journals Dislocation Arrangement in a Thick LEO GaN Film on Sapphire

2000 ◽  
Vol 5 (S1) ◽  
pp. 97-103
Author(s):  
Kathleen A. Dunn ◽  
Susan E. Babcock ◽  
Donald S. Stone ◽  
Richard J. Matyi ◽  
Ling Zhang ◽  
...  
Keyword(s):  
High Resolution ◽  
Electron Diffraction ◽  
Threading Dislocations ◽  
X Ray Diffraction ◽  
Burgers Vector ◽  
X Ray ◽  
The Third ◽  
Dislocation Arrangement ◽  
Image Position ◽  
Gan Film

Diffraction-contrast TEM, focused probe electron diffraction, and high-resolution X-ray diffraction were used to characterize the dislocation arrangements in a 16µm thick coalesced GaN film grown by MOVPE LEO. As is commonly observed, the threading dislocations that are duplicated from the template above the window bend toward (0001). At the coalescence plane they bend back to lie along [0001] and thread to the surface. In addition, three other sets of dislocations were observed. The first set consists of a wall of parallel dislocations lying in the coalescence plane and nearly parallel to the substrate, with Burgers vector (b) in the (0001) plane. The second set is comprised of rectangular loops with b = 1/3 [110] (perpendicular to the coalescence boundary) which originate in the coalescence boundary and extend laterally into the film on the (100). The third set of dislocations threads laterally through the film along the [100] bar axis with 1/3<110>-type Burgers vectors These sets result in a dislocation density of ∼109 cm−2. High resolution X-ray reciprocal space maps indicate wing tilt of ∼0.5º.

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