News Update on Electron Energy : May 21

[1] Electron energy-loss spectroscopy in the TEM

Electron energy-loss spectroscopy (EELS) is an analytical technique that measures the change in kinetic energy of electrons after they have interacted with a specimen. When carried out in a modern transmission electron microscope, EELS is capable of giving structural and chemical information about a solid, with a spatial resolution down to the atomic level in favourable cases. The energy resolution is typically 1 eV but can approach 0.1 eV if an electron-beam monochromator is used. This review provides an overview of EELS instrumentation and of the physics involved in the scattering of kilovolt electrons in solids. Features of the energy-loss spectrum are discussed, including plasmon peaks, inner-shell ionization edges and fine structure related to the electronic densities of states. Examples are given of the use of EELS for the measurement of local properties, including specimen thickness, mechanical and electronic properties (such as bandgap) and chemical composition. Factors that determine the spatial resolution of the analysis are outlined, including radiation damage to the specimen. Comparisons are made with related techniques, particularly x-ray absorption spectroscopy.

[2] Graph theory and molecular orbitals. Total φ-electron energy of alternant hydrocarbons

The dependence of the Hückel total φ-electron energy on the molecular topology is shown. General rules governing the structural dependence of the φ-electron energy in conjugated molecules are derived.

[3] Determination of Kilovolt Electron Energy Dissipation vs Penetration Distance in Solid Materials

A universal curve of energy‐dissipation range vs normalized electron energy is proposed, which includes the average atomic number Z of the material being bombarded in the energy normalization factor. Range‐energy expressions of the form R=kEαBR=kEBα, derived from the Bohr‐Bethe energy‐loss relation, are valid over limited energy ranges, but the exponent α differs for materials of greatly different atomic numbers over the same energy range. For the aluminum‐silicon dioxide‐silicon system used here, RG = 4.0 EB(keV)1.75 μg/cm2 has been found accurate for 5 <EB <25 keV. Using this value of range, and taking the steady‐state electron‐beam‐induced current through a thin insulating layer of SiO2 as a measure of the energy dissipation in that layer, an energy‐dissipation (depth‐dose) function has been determined which should be valid for 10 <Z <15.

[4] Electron Energy Levels for a Finite Elliptical Quantum Wire in a Transverse Magnetic Field

We investigate the electron ground state energy, the first excited energy and the electron density of probability within the effective-mass approximation for a finite strain elliptical wire. A magnetic field is applied perpendicular to the wire axis. The results are obtained by diagonalizing a Hamiltonian for a wire with elliptical edge. The electron levels are calculated as functions of the ellipse parameter of the wire with different values of the applied magnetic field. For increasing magnetic field the electron has its energy enhanced. The electron energy decreases as the elliptical wire size increases. The density of probability distribution in the wire with different size in the presence of a magnetic field has been calculated also. The smaller elliptical wire size can effectively draw electron deviation from the axis. Calculated ground state energy is compared with that one obtained in previous work.

[5] Simulation of Low Energy Neutron Shielding by GEANT4 and MCNP4C Code

In this work neutrons shielding of 252Cf source simulated with GEANT4 program and MCNP4C code. The relative neutron flux rates are calculated for different materials. Among various physics models of GEANT4 for the hadronic interaction of neutron, we have used the High Precision (HP) model, which is based on the ENDF-V1 data and is able to treat elastic scattering, inelastic scattering, fission, fusion and capture. The simulation results of GEANT4 are compared with the results of MCNP4C.

 

Reference

[1] Egerton, R.F., 2008. Electron energy-loss spectroscopy in the TEM. Reports on Progress in Physics72(1), p.016502.

[2] Gutman, I. and Trinajstić, N., 1972. Graph theory and molecular orbitals. Total φ-electron energy of alternant hydrocarbons. Chemical physics letters17(4), pp.535-538.

[3] Everhart, T.E. and Hoff, P.H., 1971. Determination of kilovolt electron energy dissipation vs penetration distance in solid materials. Journal of Applied Physics42(13), pp.5837-5846.

[4] Duan, X.Z., Wang, G.X. and Chang, C.R., 2014. Electron Energy Levels for a Finite Elliptical Quantum Wire in a Transverse Magnetic Field. Physical Science International Journal, pp.1400-1412.

[5] Forozani, G. and Ebrahimi, E., 2016. Simulation of Low Energy Neutron Shielding by GEANT4 and MCNP4C Code. Current Journal of Applied Science and Technology, pp.1-5.

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