Diffraction and imaging theory of inelastically scattered electrons: A new approach

Conference · Tue Jan 01 00:00:00 EST 1991

OSTI ID:6381243

Wang, Z L ^[1]; Bentley, J ^[2]

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1. Oak Ridge National Lab., TN (United States) Tennessee Univ., Knoxville, TN (United States). Dept. of Materials Science and Engineering
2. Oak Ridge National Lab., TN (United States)

A new dynamical theory is developed for describing inelastic electron scattering in thin crystals. Compared to existing theories, the first advantage of this new theory is that the incoherent summation of the diffracted intensities contributed by electrons after exciting vast numbers of different excited states has been evaluated before any numerical calculation. The second advantage is that only the modulus squared of the transition matrix elements are needed in the final computation. This greatly reduces the effort in searching for phase shifts'' in inelastic scattering matrix calculations. By iterative operation of this single-inelastic scattering theory, multiple-inelastic electron scattering of phonons, single-electrons and valence (or plasmon) excitations can be included in diffraction pattern calculations. High resolution images formed by valence excited electrons can also be calculated in this theoretical scheme for relatively thick crystals. The sharpness of thermal diffuse scattering (TDS) streaks is determined by the phonon dispersion relationships of the acoustic branches; optical branches contribute only a diffuse background. Dynamical scattering effects can change the intensity distribution of TDS electrons but have almost no effect on the sharpness of TDS streaks. To a good approximation, the TDS streaks are defined by the q{sub x}{minus}q{sub y} curves which satisfy {omega}{sub j}(q) = 0, where {omega}{sub j}(q) is the phonon dispersion relationship determined by the 2-D atomic vibrations in the (hkl) plane perpendicular to the incident beam direction B = (hkl). This is a simplified 2-D vibration model. The directions of TDS streaks can be predicted according to a simple q{center dot}(r({iota})-r({iota}{sub 1})) = 0 rule, where the summation of {iota}{sub 1} is restricted to the first nearest neighbors of the {iota}{sup th} atom that are located in the same atomic plane as the {iota}{sup th} atom perpendicular to the incident beam direction.

• Research Organization: Oak Ridge National Lab., TN (United States)
• Sponsoring Organization: USDOE; USDOE, Washington, DC (United States)
• DOE Contract Number: AC05-84OR21400
• OSTI ID: 6381243
• Report Number(s): CONF-9109256-1; ON: DE91018248
• Resource Relation: Conference: 10. Pfefferkorn conference on signal and image processing in microscopy and microanalysis, Cambridge (United Kingdom), 16-19 Sep 1991
• Country of Publication: United States
• Language: English

Related Subjects

75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
Ta
CRYSTALS
ELECTRON DIFFRACTION
ELECTRON BEAMS
INELASTIC SCATTERING
IMAGES
CRYSTAL LATTICES
MATRIX ELEMENTS
PHASE SHIFT
PHONONS
WAVE FUNCTIONS
BEAMS
COHERENT SCATTERING
CRYSTAL STRUCTURE
DIFFRACTION
FUNCTIONS
LEPTON BEAMS
PARTICLE BEAMS
QUASI PARTICLES
SCATTERING
665300* - Interactions Between Beams & Condensed Matter- (1992-)
661220 - Particle Beam Production & Handling
Targets- (1992-)