Koichi Kanaya

Secondary electron emission from insulators

The high yield of secondary electron emission from insulators due to electron bombardment may be the result of an increase of the depth of escape. The free-electron scattering theory is applied to the high energy of the primary beam, but it cannot be applied to the low energy of the secondary escaping beam because of the large energy gap of insulators. Then the plasmon loss with the valence electron is considered when the secondary electrons escape. Secondary electron emissions from insulators are calculated from the assumptions that the distribution of the secondary electrons due to both incident and back-scattered electrons within the target is isotropic and that it follows the absorption law of Lenard type. The universal yield-energy curve of secondary electron emission is derived.

Consistent Theory of Sputtering of Solid Targets by Ion Bombardment Using Power Potential Law

Starting from a simple atomic model by Lindhard giving a power potential between ions and atoms as V(r)=z1z2e2an-1/nrn, we assumed that the first collision with a metal atom is of the weakly screened type (n=2) or Rutherford type (n=1) and that subsequent collisions of displaced atoms are similar to collisions of hard spheres (n=5). On this basis, consistent expressions were obtained for the maximum yield Smax with the corresponding energy Em for n=2, and the universal curve of yield-energy, which on the number of atms in the target materials per unit volume N, the effective atomic radius a and the displacement energy Ed. The results were in good agreement with experiments over the energy range from 50 eV to 500 keV.

The energy dependence of secondary emission based on the range-energy retardation power formula

Based on the energy retardation power formula concerning the penetration and the energy loss of an electron probe into solid targets, the secondary electron emission yield delta due both to primary and back-scattered electrons is derived as functions of three parameters such as atomic number Z, first ionisation energy I and back-scattering coefficient r, which are found to be in good accordance with the results obtained experimentally. Notable in such theoretical procedures are the maximum yield delta m and the primary energy Em, giving delta m=0.12Z1/15I4/5(1+1.26r) for Em=57.9Z115/I4/5(1+5r2)4/5 (eV) which substantially agree with the miscellaneous experiments of many authors. The energy dependence of the yield-energy distributions, the yield of thin films and the lateral distribution of secondary yield at the distance from the centre of the beam are given as functions of the back-scattering coefficient and the primary energy.

Lattice imaging analysis of Σ3 coincidence-site-lattice boundaries in gold

Abstract High-resolution transmission electron microscope images of Σ3 coincidence-site-lattice boundaries in gold have been observed, and analysed in terms of structure models. In particular (112) A/B and (111) A/B boundaries, having different degrees of misorientation and amounts of relaxation, have been observed. The maximum amount of misorientation correlates well with Brandons θ=15/Σ1/2 criterion. Relaxation of the atoms near the boundary is explained in terms of simple atomic repulsions.

The energy dependence of a diffusion model of an electron probe into solid targets

The penetration and energy loss characteristics of an electron probe with energies 1 and 103 keV in solid targets are analysed by using the potential function of the power and exponential forms of the potential function with a screened atomic radius for scatterings. Then, the diffusion effect due to multiple collisions is combined with the energy retardation in accordance with a modified Thomson-Whiddington law, with the scattering cross-section in the Lenard absorption law, to give consistent expressions for the variation of the transmission fraction eta T and back-scattering fraction eta B with depth y=x/R together with the diffusion depth yD and the maximum energy loss depth yE normalised by the penetration range R as a function of the parameter gamma (which is a function of the incident energy and the atomic number). Diffusion is considered to take place through a hemisphere with a centre located at the most probable energy dissipation depth yC, related to the diffusion depth YD.

Ion bombardment of suitable targets for atomic shadowing for high resolution electron microscopy

Abstract The use of ion beam bombardment of suitable targets for the atomic shadowing of specimens for high resolution electron microscopy has been investigated. An apparatus is described consisting of a modified duoplasmatron source in which the ion beam is collimated and focused by an electrostatic lens and emerging atomic beam from the target is collimated by an aperture in a shield placed close to the specimen. The shadowing angle can be varied from about 10° to 75°. The thickness of the deposit or film and the rate of deposition have been studied in relation to the sputtering yield, flux of the primary ion beam and shadowing characteristics (contrast, grain size, nucleation and growth). Ion bombardment of tungsten yielded thin films with good contrast characteristics and with a barely resolvable (less than 0.4nm) grain size which, with other advantages of the technique as compared with evaporation (lower substrate temperatures and vaccum pressures) render this procedure valuable for high resolution studies. Films of tungsten prepared in this way, and up to 25nm thick, do not interfere with the phase changes of transmitted electrons at 60kV and thus have characteristics which also make them useful for serving as specimen supports. Investigations on the deposition of gold by ion bombardment revealed both the characteristics single crystall structure (1–3nm) and abnormal growth crystals up to about 0.2μm across.

The structure analysis of Hirano bodies by digital processing on electron micrographs

SummaryTo clarify the structure of Hirano bodies, electron micrographs of Hirano bodies taken at various tilting angles have been studied by digital image analysis. On the electron micrographs, the beaded filaments of Hirano bodies were turned into a pattern of lattice-like arrays by changing the tilting angles. Based on computer-procesed diffraction patterns and filtered images, it is proposed that the filaments of Hirano bodies are helical strands with a pitch of 185 Å. A model for the helical strand drawn by microcomputer at various angles of rotation is in accordance with the filtered images of the tilted filaments. Computer simulation also reveals that the helical strands appear to be lattice-like when they are arranged in parallel.

A digital fourier harmonic superposition method for the structural analysis of human tooth enamel obtained by electron microscopy

Abstract A digital processing method with the aid of a scanning densitometer system for image analysis of electron micrographs was successfully applied to human tooth enamel which has been recognized to be composed of hydroxyapatite [Ca 10 (PO 4 ) 6 (OH) 2 ]. Based on Fourier techniques for structural analysis from a computer-generated diffractogram, it was confirmed that specimens from thin sections of the material contained a hexagonal crystal structure which was basically similar to a prototype crystal of hydroxyapatite previously determined by neutron and X-ray diffraction. Some of the known structural features were confirmed but other unknown details were established from a superposition of individual harmonic images formed by the enhanced scattering amplitude and corrected phase which are inversely transformed from the selected diffraction patterns. A model is proposed for the tetragonal pyramids of PO 4 whose hexagonal co-ordinates ( u, v, w ) in the unit cell were analytically determined. According to the digital processed data, an equi-contour map representing the precise location and subsequent three-dimensional arrangement of the atoms in human tooth enamel are derived and graphically demonstrated.

Digital processing of lattice images from a diffraction spot selected in diffractograms of electron micrographs

Abstract A digital scanning-densitometer system has been assembled in the laboratory for the purpose of processing of diffractograms and image reconstruction from the original micrographs, in place of the conventional electron and light diffractograms. It is demonstrated that computer-processed diffractograms of any selected diffraction spots and their reconstructed images can be processed by the instrument. For example, specimens of gold, graphitized carbon, and LaB6 have shown that the lattice images of a pair of (hkl)-reflections can be processed more clearly than the original micrographs. A resolution of 0.1 nm at 200kV has been achieved with the aid of this process.

A digital processing method for the structural analysis of lattice images of crystalloids obtained by electron microscopy

Abstract A digital processing method with the aid of a scanning densitometer system for image analysis of electron micrographs, has been applied to a microbody crystalloid containing enzymes. Some known structural features were confirmed, but the presence of unknown components were established from the subsequent diffraction patterns and reconstructed images. A model is proposed for the crystalloid possessing two face-centred lattices with a large alcohol oxidase composed of eight subunits and a small catalase component of four subunits, two of which are paired and stacked at right angles.