The atomic form factor and the X-ray dispersion corrections as tensor quantities: comparisons between theory and experiment

1999 ◽  
Vol 56 (1-2) ◽  
pp. 61-83
Author(s):  
D.C. Creagh
1984 ◽  
Vol 37 (6) ◽  
pp. 651 ◽  
Author(s):  
JK Mackenzie ◽  
A McL Mathieson

The value of the atomic form factor, /(220), for copper has been determined in recent years by a variety of methods. All the dynamical methods agree on a value in the region of 16'70-16�75. These methods include two X-ray methods, one involving measurement of intensity profiles and the other of Pendellosung beats, and also an electron diffraction measurement using a critical voltage procedure. By contrast, two recent kinematical measurements using y rays both report a distinctly different value of about 16�45. One of these determinations has already been re-examined by the present authors and the iscrepancy removed by an appropriate extrapolation to zero extinction.


2010 ◽  
Vol 81 (2) ◽  
Author(s):  
Nicholas A. Rae ◽  
Christopher T. Chantler ◽  
Zwi Barnea ◽  
Martin D. de Jonge ◽  
Chanh Q. Tran ◽  
...  

2000 ◽  
Vol 89 (1) ◽  
pp. 6-8
Author(s):  
A. N. Khoperskiĭ ◽  
V. F. Demekhin ◽  
S. A. Novikov ◽  
V. V. Timoshevskaya

Author(s):  
F. Stanglmeier ◽  
B. Lengeler ◽  
W. Weber ◽  
H. Göbel ◽  
M. Schuster
Keyword(s):  
X Ray ◽  

Author(s):  
T. Geipel ◽  
W. Mader ◽  
P. Pirouz

Temperature affects both elastic and inelastic scattering of electrons in a crystal. The Debye-Waller factor, B, describes the influence of temperature on the elastic scattering of electrons, whereas the imaginary part of the (complex) atomic form factor, fc = fr + ifi, describes the influence of temperature on the inelastic scattering of electrons (i.e. absorption). In HRTEM simulations, two possible ways to include absorption are: (i) an approximate method in which absorption is described by a phenomenological constant, μ, i.e. fi; - μfr, with the real part of the atomic form factor, fr, obtained from Hartree-Fock calculations, (ii) a more accurate method in which the absorptive components, fi of the atomic form factor are explicitly calculated. In this contribution, the inclusion of both the Debye-Waller factor and absorption on HRTEM images of a (Oll)-oriented GaAs crystal are presented (using the EMS software.Fig. 1 shows the the amplitudes and phases of the dominant 111 beams as a function of the specimen thickness, t, for the cases when μ = 0 (i.e. no absorption, solid line) and μ = 0.1 (with absorption, dashed line).


2014 ◽  
Vol 47 (1) ◽  
pp. 35-40 ◽  
Author(s):  
Zoltán Varga ◽  
András Wacha ◽  
Attila Bóta

Time-resolved synchrotron small-angle X-ray scattering (SAXS) was used to study the structural changes during the osmotic shrinkage of a pharmacologically relevant liposomal drug delivery system. Sterically stabilized liposomes (SSLs) with a diameter of 100 nm and composed of hydrogenated soy phosphocholine, cholesterol and distearoyl-phosphoethanolamine-PEG 2000 prepared in a salt-free buffer were mixed with a buffered 0.3 MNaCl solution using a stopped flow apparatus. The changes in the liposome size and the bilayer structure were followed by using SAXS with a time resolution of 20 ms. A linear decrease in liposome size is observed during the first ∼4 s of the osmotic shrinkage, which reveals a water permeability value of 0.215 (15) µm s−1. The change in the size of the liposomes upon the osmotic shrinkage is also confirmed by dynamic light scattering. After this initial step, broad correlation peaks appear on the SAXS curves in theqrange of the bilayer form factor, which indicates the formation of bi- or oligolamellar structures. Freeze-fracture combined with transmission electron microscopy revealed that lens-shaped liposomes are formed during the shrinkage, which account for the appearance of the quasi-Bragg peaks superimposed on the bilayer form factor. On the basis of these observations, it is proposed that the osmotic shrinkage of SSLs is a two-step process: in the initial step, the liposome shrinks in size, while the area/lipid adapts to the decreased surface area, which is then followed by the deformation of the spherical liposomes into lens-shaped vesicles.


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