Two‐dimensional versus three‐dimensional excitons in wide GaAs quantum wells

1994 ◽  
Vol 75 (1) ◽  
pp. 289-296 ◽  
Author(s):  
Jun‐ichi Kusano ◽  
Gerrit E. W. Bauer ◽  
Yoshinobu Aoyagi
Keyword(s):  
Quantum Wells ◽  
Three Dimensional ◽  
Two Dimensional

Electric-field-dependent absorption of ZnSe-based quantum wells: The transition from two-dimensional to three-dimensional behavior

1998 ◽  
Vol 58 (16) ◽  
pp. 10709-10720 ◽  
Author(s):  
D. Merbach ◽  
E. Schöll ◽  
W. Ebeling ◽  
P. Michler ◽  
J. Gutowski
Keyword(s):  
Electric Field ◽  
Quantum Wells ◽  
Three Dimensional ◽  
Two Dimensional ◽  
Field Dependent ◽  
Dependent Absorption

EXCITON CONFINEMENT IN SEMICONDUCTOR MULTIPLE QUANTUM WELLS

1990 ◽  
Vol 04 (15n16) ◽  
pp. 2345-2356
Author(s):  
Y. FU ◽  
K. A. CHAO
Keyword(s):  
Wave Function ◽  
Perturbation Theory ◽  
Binding Energy ◽  
Quantum Wells ◽  
Multiple Quantum Well ◽  
Three Dimensional ◽  
Exciton Binding Energy ◽  
Multiple Quantum ◽  
Two Dimensional ◽  
Barrier Width

Exciton binding energy in semiconductor multiple quantum well (MQW) systems is analyzed with both the variational method and the perturbation theory. The intrinsic deficiency of the use of the two-dimensional exciton envelop wave function is clearly demonstrated. Using a GaAs/Al x Ga 1−xAs MQW as an example to calculate the exciton binding energy with a variational three-dimensional trial envelop function, we found that in many realistic samples the spatial extension of an exciton covers a region of several lattice constant dA + dB, where dA is the barrier width and dB is the well width.

High Resolution Microscopy of Multi-Layered Biological Crystals

1982 ◽  
Vol 40 ◽  
pp. 80-83
Author(s):  
H.A. Cohen ◽  
T.W. Jeng ◽  
W. Chiu
Keyword(s):  
High Resolution ◽  
Low Dose ◽  
Three Dimensional ◽  
Data Interpretation ◽  
Two Dimensional ◽  
Biological Objects ◽  
Density Maps ◽  
Density Map ◽  
Complex Crystal ◽  
High Resolution Microscopy

This tutorial will discuss the methodology of low dose electron diffraction and imaging of crystalline biological objects, the problems of data interpretation for two-dimensional projected density maps of glucose embedded protein crystals, the factors to be considered in combining tilt data from three-dimensional crystals, and finally, the prospects of achieving a high resolution three-dimensional density map of a biological crystal. This methodology will be illustrated using two proteins under investigation in our laboratory, the T4 DNA helix destabilizing protein gp32*I and the crotoxin complex crystal.

Instrumentation For Quantitative Microscopy

1977 ◽  
Vol 35 ◽  
pp. 206-209
Author(s):  
B. Ralph ◽  
A.R. Jones
Keyword(s):  
Volume Fraction ◽  
Three Dimensional ◽  
Two Dimensional ◽  
Automatic Data ◽  
Phase Volume Fraction ◽  
Statistical Confidence ◽  
Resultant Data ◽  
Automatic Data Collection ◽  
Third Dimension ◽  
Evolution Of Microstructure

In all fields of microscopy there is an increasing interest in the quantification of microstructure. This interest may stem from a desire to establish quality control parameters or may have a more fundamental requirement involving the derivation of parameters which partially or completely define the three dimensional nature of the microstructure. This latter categorey of study may arise from an interest in the evolution of microstructure or from a desire to generate detailed property/microstructure relationships. In the more fundamental studies some convolution of two-dimensional data into the third dimension (stereological analysis) will be necessary.In some cases the two-dimensional data may be acquired relatively easily without recourse to automatic data collection and further, it may prove possible to perform the data reduction and analysis relatively easily. In such cases the only recourse to machines may well be in establishing the statistical confidence of the resultant data. Such relatively straightforward studies tend to result from acquiring data on the whole assemblage of features making up the microstructure. In this field data mode, when parameters such as phase volume fraction, mean size etc. are sought, the main case for resorting to automation is in order to perform repetitive analyses since each analysis is relatively easily performed.

A linearity test for thick specimens imaged by HVEM over a 180° angular range

1991 ◽  
Vol 49 ◽  
pp. 552-553
Author(s):  
Yu Liu
Keyword(s):  
Phase Contrast ◽  
Three Dimensional ◽  
Angular Range ◽  
Two Dimensional ◽  
Back Projection ◽  
Line Integral ◽  
Exponential Law ◽  
Transmission Electron ◽  
Absorption Law ◽  
Linearity Test

The image obtained in a transmission electron microscope is the two-dimensional projection of a three-dimensional (3D) object. The 3D reconstruction of the object can be calculated from a series of projections by back-projection, but this algorithm assumes that the image is linearly related to a line integral of the object function. However, there are two kinds of contrast in electron microscopy, scattering and phase contrast, of which only the latter is linear with the optical density (OD) in the micrograph. Therefore the OD can be used as a measure of the projection only for thin specimens where phase contrast dominates the image. For thick specimens, where scattering contrast predominates, an exponential absorption law holds, and a logarithm of OD must be used. However, for large thicknesses, the simple exponential law might break down due to multiple and inelastic scattering.

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