Electron Refraction of Amorphous Nanospheres

1997 ◽  
Vol 3 (S2) ◽  
pp. 1055-1056
Author(s):  
Y.C. Wang ◽  
T.M. Chou ◽  
M. Libera
Keyword(s):  
Refractive Index ◽  
Electron Scattering ◽  
Unit Volume ◽  
High Energy ◽  
Covalent Bonding ◽  
Electron Holography ◽  
High Energy Electron ◽  
Electron Wave ◽  
Transmission Electron ◽  
The Mean

The phase shift imparted to an incident high-energy electron wave in a TEM is related to the specimen’s electron-refractive properties. These, in turn, are related to the electrostatic potential and, by Fourier transform (1), to the electron scattering factors fei(s) for the various atom species i in the specimen and scattering vectors s. The average refractive index is determined by the mean electrostatic (inner) potential, Φo, and can be modelled as Φo = (C/Ω) Σfei(s0) [equation 1] where C = 47.878 (V-Å2) and the summation runs over all of the atoms in the unit volume Ω (2). Calculated fei(s) data are available from the literature (e.g. 3). These calculations have only been done for neutral atoms and some fully ionized cations and anions. They do not account for electron redistribution due to covalent bonding to which Φo is quite sensitive (4).This research is making Φo measurements using transmission electron holography. Holograms were collected using a 200keV Philips CM20 FEG TEM equipped with a non-rotatable biprism (5) and a Gatan 794 Multiscan camera.

Mean inner potential measurements of polymer latexes by transmission electron holography

1996 ◽  
Vol 54 ◽  
pp. 168-169
Author(s):  
Young-Chung Wang ◽  
Matthew Libera
Keyword(s):  
Refractive Index ◽  
Polymeric Materials ◽  
High Energy ◽  
Electron Holography ◽  
Specimen Thickness ◽  
Phase Imaging ◽  
Rest Energy ◽  
Polymer Microstructure ◽  
Transmission Electron ◽  
Energy Dependent

Because polymeric materials consist primarily of light elements, weak contrast is often observed when imaging polymer microstructure in a transmission electron microscope. Preferential staining of microstructural features by heavy elements such as osmium, ruthenium, or uranium is commonly used to induce amplitude contrast. Because of its ability to recover the entire exit-face electron wavefunction, transmission electron holography raises the possibility of using phase contrast to measure polymer microstructure without the need for heavy-element stains. Under kinematic scattering conditions, the phase shift, ΔΦ, imposed on an incident high-energy electron wave is given by the product of the electron-optical refractive index, neo, and the specimen thickness, t: Δφ=(2π/λ)(neo−1)t. The refractive index is related to the specimen’s mean coulombic (inner) potential Φ0: neo−1 = (e |Φ0|/E) [(E0+E)/(2E0+E)] = CEΦ0 where e is the electron charge, E is the kinetic energy of the incident electrons, E0 is the rest energy, and CE is an energy-dependent constant. Quantitative measurements of Φ0 and neo can be made using holographic phase imaging to determine from specimens of known thickness.

Temperature Dependent Quasi-Periodic Facetting of AlAs Grown by MBE on (100) GaAs Substrates

1993 ◽  
Vol 312 ◽  
Author(s):  
Richard Mirin ◽  
Mohan Krishnamurthy ◽  
James Ibbetson ◽  
Arthur Gossard ◽  
John English ◽  
...  
Keyword(s):  
Growth Conditions ◽  
High Energy ◽  
High Energy Electron ◽  
Temperature Dependent ◽  
Cross Sectional ◽  
Mbe Growth ◽  
Atomic Force ◽  
Gaas Substrates ◽  
Transmission Electron ◽  
Facet Formation

AbstractHigh temperature (≥ 650°C) MBE growth of AlAs and AlAs/GaAs superlattices on (100) GaAs is shown to lead to quasi-periodic facetting. We demonstrate that the facetting is only due to the AlAs layers, and growth of GaAs on top of the facets replanarizes the surface. We show that the roughness between the AlAs and GaAs layers increases with increasing number of periods in the superlattice. The roughness increases to form distinct facets, which rapidly grow at the expense of the (100) surface. Within a few periods of the initial facet formation, the (100) surface has disappeared and only the facet planes are visible in cross-sectional transmission electron micrographs. At this point, the reflection high-energy electron diffraction pattern is spotty, and the specular spot is a distinct chevron. We also show that the facetting becomes more pronounced as the substrate temperature is increased from 620°C to 710°C. Atomic force micrographs show that the valleys enclosed by the facets can be several microns long, but they may also be only several nanometers long, depending on the growth conditions.

High-energy electron scattering study of molecular hydrogen

1991 ◽  
Vol 43 (7) ◽  
pp. 3548-3552 ◽  
Author(s):  
Yuheng Zhang ◽  
Andrew W. Ross ◽  
Manfred Fink
Keyword(s):  
Electron Scattering ◽  
Molecular Hydrogen ◽  
High Energy ◽  
Energy Electron ◽  
High Energy Electron ◽  
Scattering Study

scholarly journals A CHARGE FORM FACTOR (CFF) OF 5He NUCLEUS

2019 ◽  
Vol 14 (2) ◽  
Author(s):  
Piyush Sinha ◽  
Neelam Sinha
Keyword(s):  
Electron Scattering ◽  
Fourier Transforms ◽  
Form Factors ◽  
High Energy ◽  
Energy Electron ◽  
High Energy Electron ◽  
Structure Factors ◽  
Transition Matrix Elements ◽  
Current Densities ◽  
A Charge

High energy electron scattering is a very powerful tool for studying geometrical details of nuclear structure. The studies provide information on static distribution of charge and magnetization in nuclei. As the interaction is relatively weak so that in the scattering process the internal structure of the target nucleus is not significantly disturbed. Using electrons as projectile, we can study how transition matrix elements vary with q2 and map out the Fourier transforms of the transition charge and current densities called Form Factors or Structure factors. In the high energy electron scattering we can know the details of the spatial distribution of transition charge and current density. In this paper we have formulated CFF for 5He nucleus

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