Cross Sections for Inelastic Scattering of Electrons by Atoms - Selected Topics Related to Electron Microscopy

We begin with a resume of the Bethe theory, which provides a general framework for discussing the inelastic scattering of fast electrons and leads to powerful criteria for judging the reliability of cross-section data. The central notion of the theory is the generalized oscillator strength as a function of both the energy transfer and the momentum transfer, and is the only non-trivial factor in the inelastic-scattering cross section. Although the Bethe theory was initially conceived for free atoms, its basic ideas apply to solids, with suitable generalizations; in this respect, the notion of the dielectric response function is the most fundamental. Topics selected for discussion include the generalized oscillator strengths for the K-shell and L-shell ionization for all atoms with Z ≤ 30, evaluated by use of the Hartree-Slater potential. As a function of the energy transfer, the generalized oscillator strength most often shows a non-monotonic structure near the K-shell and L-shell thresholds, which has been interpreted as manifestations of electron-wave propagation through atomic fields. For molecules and solids, there are additional structures due to the scattering of ejected electrons by the fields of other atoms

Photoelectron angular distribution of the excited 2p^2 3p ^2S state of atomic nitrogen

Relevant data is available at: http://www.astronomy.ohio-state.edu/~nahar/nahar_radiativeatomicdata/index.htmlCalculations of the photoelectron angular distribution asymmetry parameter ß for the excited 2p^2 3p ^2S state of atomic nitrogen have been performed using Hartree-Fock discrete and continuum wave functions with relaxation. The results show reasonably good agreement with a recent measurement of ß at a single energy.The work was supported by the U.S. Army Research Office and the National Science Foundation

CyberPatriot: Exploring University-High School Partnerships

Since its inception in 2008, the CyberPatriot competition has been held annually with the goal of increasing the number of technologically skilled individuals working in the field of cybersecurity. The competition is designed to address the shortage of U.S. citizens with degrees in science, technology, engineering, and math (STEM) disciplines by encouraging talented high school students to pursue post-secondary study leading to careers in cybersecurity. This paper describes how one university successfully partnered with a large metropolitan high school district to better reach out to talented students in both traditional and underrepresented groups

Photoionization of the 7d excited state of cesium

Relevant data is available at: http://www.astronomy.ohio-state.edu/~nahar/nahar_radiativeatomicdata/index.htmlThe photoionization cross section for the excited 7d state of atomic cesium has been calculated in the Hartree-Fock approximation. The results show excellent agreement with a recent measurement.This work was supported by the U.S. Army Research Office and the National Science Foundation

Structure and magnetic properties of MnII[N(CN)2]2(pyrazine). An antiferromagnet with an interpenetrating 3-D network structure

Journal ArticleMn[N(CN)2]2(pyz) (pyz = pyrazine) orders antiferromagnetically at low temperature and possesses intralayer u-NCNCN and interlayer u-pyz ligands that form a pseudo-ReO3 interpenetrating network structure

Crystal structure and magnetic properties of [Fe{N(CN)2}2(MeOH)2] a 2-D layered network consisting of hydrogen-bonded 1-D chains

Journal ArticleA novel 2-D layered network structure [Fe{N(CN)2}2(MeOH)2] was synthesized and characterized by X-ray crystallography, vibrational, and magnetic susceptibility. The neutral 2-D stair-like framework consists of hydrogen-bonded infinite 1-D {Fe[N(CN)2]2} ribbons that pack in a staggered arrangement where nearest-neighboring chains are slipped a/2 relative to one another. Two methanol molecules are coordinated to the FeII center via the oxygen atoms in a trans configuration resulting in a compressed FeN4O2 octahedron. Hydrogen-bond interactions occur via N(2)...H(1)--O(1) where N(2) is the amide nitrogen atom of a nearby ribbon. The magnetic susceptibility was interpreted according to an S=2 expression which includes the Weiss constant and zero-field splitting giving g=2.04, 0=-2.0 K, and D=-1.7 K. Intrachain exchange interactions were determined from a fit to an S=2 antiferromagnetic chain model leading to g=2.04 and J/kB=0.23 K. Further interchain interaction via the hydrogen bond was determined by incorporation of a molecular-field correction term yielding J'/kB=-0.02 K indicating very weak antiferromagnetic coupling between chains

Photoelectron angular distributions: energy dependence for \u3ci\u3es\u3c/i\u3e subshells

An overview of the theory of photoelectron angular distributions for atoms is presented. Its features, which are embodied in a single asymmetry parameter β in the electric dipole approximation, are examined within the framework of the angular momentum transfer formulation. The β parameter is in principle always energy dependent. Within the LS coupling approximation, however, there are instances, each representing a multitude of particular photoionization processes, in which β is an analytically determined constant. The energy dependence of the β parameters in such instances is due entirely to spin-orbit and other relativistic interactions. The study of the energy dependence of the β parameter in these cases is thus of interest because it spotlights weak-interaction effects which are usually overwhelmed by stronger interactions. We illustrate the general predictions by a detailed consideration of the energy dependence of the β parameter for s-subshell photoionization processes. It is shown that the asymmetry parameters for atomic s subshells are particularly suitable for distinguishing between purely geometrical effects on the photoelectron angular distribution, resulting from physical conservation laws, and dynamical effects arising from relativistic interactions and electron exchange and correlation. In general, the β parameters for s subshells vary with energy; such variation is largest near minima in the cross sections for the corresponding photoelectron channels and in the vicinity of resonances. However, a number of atomic photoionization transitions are identified for which β would be a constant (equal to one of the three values 2, 1/5, or - 1) were it not for relativistic interactions and (in some cases) final-state interchannel coupling and/or initial-state electron correlations. Measurement or calculation of the β parameters for such transitions thus provides a sensitive measure of the strength of relativistic interactions as well as of electron correlations

Interpenetrating three-dimensional rutile-like frameworks. Crystal structure and magnetic properties of MnII[C(CN)3]2

Journal ArticleThe interpenetrating double-density rutile-like structure and magnetic properties of MnII[C(CN)3]2 are determined

Doubly Differential Cross Sections for Proton-Impact Ionization of Argon

Proton-impact-ionization cross sections for argon which are differential in the energy and angle of the ejected electron have been calculated within the framework of the Born approximation using both Hartree-Slater and Hartree-Fock wave functions for the ejected electron. Results of the two types of calculations are compared with each other and with experiment. Differential cross sections for all five sub shells of argon are examined and particular attention is given to some interesting features of the K-shell cross sections. The range of applicability of the theoretical models is discussed

MnII(N3)2(pyrazine).A 2-D layered structure consisting of ferromagnetically coupled 1-D {Mn(U-1,1-N3)2}n chains

Journal ArticleMn(N3)2(pyz) (pyz = pyrazine) consists of ferromagnetically coupled linear chains of {Mn(N3)2}n comprised of u-1,1-azido bridges together with u-pyz ligands to afford 2-D planar layers