C. Goessens

Characterization of crystal defects in mixed tabular silver halide grains by conventional transmission electron microscopy and X-ray diffractometry

Abstract Tabular silver bromide grains with iodide uniformly mixed in the shell were investigated with conventional transmission electron microscopy. The shell region was found to contain a large number of stacking faults parallel with the { 11 1 ¯ } edges and in some cases edge dislocations with a Burgers vector of 1 2 [ 1 1 ¯ 0 ] type. An atomic model for the formation of the stacking faults during the growth is presented.

Electron microscopical investigation of AgBr needle crystals

Needle shaped AgBr crystals are investigated using electron diffraction and conventional transmission electron microscopy. It will be shown that the particular morphology and growth of the needles result from the defect structure of the crystals, which consists of three non-parallel twin planes, i.e. two (111) type and one (221) type twin planes. Unilateral growth is shown to occur in a [110] type direction, being the intersection of the two non-parallel (111) twin planes. On both ends of the needle, three self-perpetuating reentrant grooves are present, responsible for the rapid growth of the needle.

In situ HREM study of electron irradiation effects in AgCl microcrystals

Abstract Cubic silver chloride microcrystals (size between 10 and 50 nm) were investigated with high-resolution electron microscopy. The print-out effect that occurs due to reaction with the electron beam was used to investigate the orientational relationship between the AgCl crystal and the Ag particles that are formed on the AgCl crystal. The particles are found to retain the same cubic directions as the AgCl crystal with a macroscopic form of a truncated octahedron.

Transmission electron microscopy studies of (111) twinned silver halide microcrystals

The present paper covers the results of different transmission electron microscopy studies on silver halide microcrystals. Pure AgBr as well as core‐shell AgBr‐AgBrI crystals are investigated. In the former parallel and non‐parallel twinning modes yielding tabular and needle‐ or tetrahedral‐shaped microcrystals, respectively, are discussed. Also the short‐range‐order of Ag+ interstitials around the twin planes as determined from diffuse intensity in reciprocal space is described. The latter yields a technique to determine the variant in which dislocations are located in certain core‐shell microcrystals. The introduction of iodine also results in the presence of inclined stacking faults in the shell and of long‐range iodine ordering on the crystal surface. Microsc. Res. Tech. 42:85–99, 1998.

Electron microscopical investigation of tetrahedral-shaped AgBr microcrystals

Abstract Tetrahedral AgBr crystals present in emulsions precipitated at high pAg values are investigated by conventional electron microscopy and electron diffraction. The defect structure of these crystals is determined to consist of two non-parallel (111)-type twin planes enclosing an angle of 70.5°. A growth model is presented explaining the morphology of both needle crystals and tetrahedral crystals in terms of the influence of twin planes on the growth behaviour of the crystals.

Long period surface ordering of iodine ions in mixed tabular AgBrAgBrI microcrystals

Abstract The occurrence of long period fringes in mixed AgBrAgBrI core-shell-type tabular crystals is explained in terms of a periodically varying composition in iodine content in the surface layer. Changes in fringe spacing are observed for different precipitation conditions and are explained in terms of a different iodine content. The difference in fringe morphology and direction in the core and shell region is attributed to the differences in interaction between the matrix and the surface layer.

Electron Microscopy of Interfaces in New Materials

Electron microscopy and electron diffraction are shown to be most useful for the characterisation of different interfaces in new materials. High resolution microscopy provides atomic scale information on the local structure of such interfaces. These structural characteristics strongly influence the physical properties of the materials. We will study planar interfaces in the high Tc superconductor YBa2Cu3O7-δ, in silverhalogenides such as AgC1, in the luminescent Y1-x(Sr,Li)xTa04 and in semiconductor devices.