High-resolution coherent imaging in STEM

1993 ◽  
Vol 51 ◽  
pp. 1082-1083
Author(s):  
J.M. Cowley ◽  
M.A. Gribelyuk
Keyword(s):  
High Resolution ◽  
Accurate Determination ◽  
High Resolution Electron Microscopy ◽  
Image Resolution ◽  
Coherent Imaging ◽  
Reconstruction Process ◽  
Original Proposal ◽  
Resolution Electron ◽  
Imaging Theory

The ultimate aim of high resolution electron microscopy is the accurate determination of the positions and types of the atoms in a specimen. The coherent imaging theory for STEM is reviewed with the emphasis on its potential for achieving this aim by holographic methods. The STEM modes of holography are in many respects equivalent to the corresponding TEM modes, but have the advantage that, because with a FEG electron source the focussed probes have sub-nanometer diameter, a strong signal is obtained from the illuminated region and the problem of shot-noise is much less important.The original proposal for holography by Gabor envisaged the use of a reconstruction process on the recorded hologram to correct for the lens aberrations and hence improve the image resolution. The more general and more challenging problem is to reconstruct the aberration-free wave function at the exit face of the specimen (with its real and imaginary, or amplitude and phase, components) and then to invert the dynamical diffraction process and derive the projected potential distribution of the object.

Combined Experimentaland Theoretical Determination of the Atomic Structure of the (310) Twin in NB

1991 ◽  
Vol 238 ◽  
Author(s):  
Geoffrey H. Campbells ◽  
Wayne E. King ◽  
Stephen M. Foiles ◽  
Peter Gumbsch ◽  
Manfred Rühle
Keyword(s):  
High Resolution ◽  
Theoretical Models ◽  
High Resolution Electron Microscopy ◽  
Interatomic Potentials ◽  
Image Simulation ◽  
Theoretical Determination ◽  
Atomic Structures ◽  
Resolution Electron ◽  
High Resolution Images

ABSTRACTA (310) twin boundary in Nb has been fabricated by diffusion bonding oriented single crystals and characterized using high resolution electron microscopy. Atomic structures for the boundary have been predicted using different interatomic potentials. Comparison of the theoretical models to the high resolution images has been performed through image simulation. On the basis of this comparison, one of the low energy structures predicted by theory can be ruled out.

Microstructural determination of a metastable phase during rhodium oxidation

1989 ◽  
Vol 47 ◽  
pp. 262-263
Author(s):  
A. David Logan
Keyword(s):  
Electron Microscopy ◽  
High Resolution ◽  
Volume Expansion ◽  
Lattice Structure ◽  
Metastable Phase ◽  
Active Surface ◽  
High Resolution Electron Microscopy ◽  
Silica Spheres ◽  
Resolution Electron

In heterogeneous catalysis, oxidation of the catalyst is frequently used as a means of removing impurities from the active surface. However, bulk oxidation severely alters the microstructure of the metal due to atom repositioning and valence changes. Transformation of Rh to Rh2O3 causes the lattice structure to change from fcc to hexagonal with a resulting volume expansion of 90% due to density changes. This is the reported cause for fracturing of crystallites and variations in reactivity. In this study, microstructural changes during progressive oxidation of 5 nm metal Rh particles have been examined.A 2 wt% Rh/Silica catalyst was prepared using Rh(III)-2,4 pentanedionate as a precursor and nonporous silica spheres as a support. The catalyst was then reduced in flowing H2 at 473 K. High resolution electron microscopy (HREM) was performed on a JEM-4000EX having a point resolution of 0.17 nm. The catalyst was oxidized in research purity O2 (Matheson 99.99%) using an all glass volumetric chemisorption system.

Image Deconvolution - An Effective Tool of Crystal Structure and Defect Determination in High-Resolution Electron Microscopy

2009 ◽  
Vol 1184 ◽  
Author(s):  
Fanghua Li ◽  
Chunyan Tang
Keyword(s):  
Crystal Structure ◽  
Electron Microscopy ◽  
High Resolution ◽  
High Resolution Electron Microscopy ◽  
Image Deconvolution ◽  
One Dimensional ◽  
Modulated Structures ◽  
Resolution Electron ◽  
Different Types

AbstractImage deconvolution is introduced as an effective tool to enhance the determination of crystal structures and defects in high-resolution electron microscopy. The essence is to transform a single image that does not intuitively represent the examined crystal structure into the structure image. The principle and method of image deconvolution together with the related image contrast theory, the pseudo weak phase object approximation (pseudo WPOA), are briefly described. The method has been applied to different types of dislocations, twin boundaries, stacking faults, and one-dimensional incommensurate modulated structures. Results on the semiconducting epilayers Si0.76Ge0.24/Si and 3C-SiC/Si are given in some detail. The results on other compounds including AlSb/GaAs, GaN, Y0.6Na0.4Ba2Cu2.7Zn0.3O7-δ, Ca0.28Ba0.72Nb2O6 and Bi2.31Sr1.69CuO6+δ are briefly summarized. It is also shown how to recognize atoms of Si from C based on the pseudo WPOA, when the defect structures in SiC was determined at the atomic level with a 200 kV LaB6 microscope.

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