An overview is given of non-tabular crystals with {111} surfaces occurring in emulsions of silver bromide and silver chloride tabular grains. The crystal defects are characterized by transmission electron microscopy (TEM) and their influence on the growth process is discussed. It is proven that in all cases of non-tabular growth twins on two non-parallel {111} type planes are present. Different morphologies have been observed in AgBr and AgCl emulsions. The most frequently occurring morphologies are needle and tetrahedron shaped crystals in AgBr and thick tabular crystals with an incomplete microtwin as well as crystals consisting of a tetrahedral shaped part and a flat triangular to trapezoidal part in AgCl. A comparison will be made between the silver bromide and the silver chloride crystals.

Silver bromide crystals have been precipitated by the double-jet method. The presence of polar aprotic solvents or protic solvents with a dissociation constant smaller than water increased the ratio and size of tabular crystals in the precipitate. This is explained considering that {111} surfaces are mainly composed of halide ions and therefore charged. Organic solvents reduce the solvation of the halide ions in the solution and stabilize the surface charge. A high ionic strength greatly favored the ratio of tabular crystals and enhanced tabular growth probably by helping the formation of the double electrical layer on the charged {111} faces.

Silver bromide crystals have been precipitated by the double-jet method. The presence of polar aprotic solvents or protic solvents with a dissociation constant smaller than water increased the ratio and size of tabular crystals in the precipitate. This is explained considering that (111) surfaces are mainly composed of halide ions and therefore charged. Organic solvents reduce the solvation of the halide ions in the solution and stabilize the surface charge. A high ionic strength greatly favored the ratio of tabular crystals and enhanced tabular growth probably by helping the formation of the double electrical layer on the charged (111) faces.

AgCl(I) crystals with (100) surfaces are studied with conventional transmission electron microscopy for their microstructure in relation with their growth habits. The crystals are prepared according to two different growth methods which give slightly different results. The presence of dislocations of mixed character that end at only two surfaces are in both cases responsible for the tabular growth, but the formation of these dislocations is different. In the first case, a stacking fault is formed which is eliminated by dislocations. In the second case, the incorporation of iodide impurities is at the origin of the formation of dislocations.

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. (C) 1998 Wiley-Liss, Inc.

A new method is presented to determine from top views whether a tabular silver halide crystal contains an even or an odd number of twin planes. The model is based on the occurrence of diffuse intensity contours in diffraction patterns of the crystals. This implies that this information can be correlated with simultaneous observations of the shape of the tabular crystals (hexagonal or triangular). Moreover, it will be shown that this method allows one to determine from top views in which variant of an even twinned crystal dislocations are present.

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.

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.

The results of a temperature study of AgBr-AgBrI(10%I) tabular core-shell microcrystals are presented. Stacking faults, which are present in the shell of the microcrystal, are found to disappear upon heating the microcrystals to 200 degrees C and higher. A model for the disappearance of these stacking faults, involving the movement of partial dislocations in the stacking fault plane, is presented. Stacking faults are observed to be removed most easily from parts with only one reentrant angle at the twin planes, i.e., in hexagonal microcrystals or at the long segments of triangular microcrystals.

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.

The occurrence and origin of diffuse intensity contours in electron micrographs of AgBr crystals are investigated. The observations are interpreted in terms of a model, which attributes diffuse scattering to the presence of predominant atom or vacancy clusters of a particular polyhedral type. It is shown that irrespective of the crystal morphology, interstitial Ag ions order in AgBr material in clusters of finite size along 001 type planes. A different geometry of the diffuse intensity locus observed for triangular and hexagonal tabular grains is explained in terms of the different twin plane morphology of these grains.

Microscopy Research and TechniqueVolume 25, Issue 2 p. 185-186 Article Internal calibration technique for hrem studies of nanoscale particles D. Schryvers, D. Schryvers University of Antwerp, RUCA, Groenenborgerlaan 171, B-2020 ANTWERPEN, BelgiumSearch for more papers by this authorC. Goessens, C. Goessens University of Antwerp, RUCA, Groenenborgerlaan 171, B-2020 ANTWERPEN, Belgium Agfa-Gevaert N.V., Septestraat 27, B-2640 MORTSEL, BelgiumSearch for more papers by this authorG. Safran, G. Safran Research Institute for Technical Physics, H-1326 BUDAPEST, HungariaSearch for more papers by this authorL. Toth, L. Toth Research Institute for Technical Physics, H-1326 BUDAPEST, HungariaSearch for more papers by this author D. Schryvers, D. Schryvers University of Antwerp, RUCA, Groenenborgerlaan 171, B-2020 ANTWERPEN, BelgiumSearch for more papers by this authorC. Goessens, C. Goessens University of Antwerp, RUCA, Groenenborgerlaan 171, B-2020 ANTWERPEN, Belgium Agfa-Gevaert N.V., Septestraat 27, B-2640 MORTSEL, BelgiumSearch for more papers by this authorG. Safran, G. Safran Research Institute for Technical Physics, H-1326 BUDAPEST, HungariaSearch for more papers by this authorL. Toth, L. Toth Research Institute for Technical Physics, H-1326 BUDAPEST, HungariaSearch for more papers by this author First published: 1 June 1993 https://doi.org/10.1002/jemt.1070250216Citations: 1AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article.Citing Literature Volume25, Issue21 June 1993Pages 185-186 RelatedInformation

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 {111¯} edges and in some cases edge dislocations with a Burgers vector of 12[11¯0] type. An atomic model for the formation of the stacking faults during the growth is presented.

Electronic Raman scattering of Sm2+ in KCl is performed under resonant interconfigurational excitation around 500 nm. The position of the charge-compensating cation vacancy with respect to the substitutional Sm2+ ion is derived from both the Stark splitting of the J-levels and the polarization properties of the scattered light. The influence of the different site symmetries on the optical linewidth is investigated with photon echoes, stimulated from an accumulated grating, which is built up under intraconfigurational excitation between the 7 F 0 and the 5 D 1 terms of the 4f 65 s 25 p 6 ground state configuration. The echo decay time is about 10 ps and does not change sizably when tuning the excitation frequency over the inhomogeneous distribution. This shows that for zero-phonon line excitation, the Sm2+ sites are not very different. The temperature dependence of the echo is described by vertical relaxation to the bottleneck under multi-phonon emission.

Silver halide grains (AgX, X=Cl,Br,I) are commonly recognized as important entities in photographic applications. Depending on the preparation specifications one can grow cubic, octahedral, tabular a.o. morphologies, each with its own physical and chemical characteristics. In the present study crystallographic defects introduced by the mixing of 5-20% iodide in a growing AgBr tabular grain are investigated. X-ray diffractometry reveals the existence of a homogeneous Ag(Br1-xIx) region, expected to be formed around the AgBr kernel. In fig. 1 a two-beam BF image, taken at T≈100 K to diminish radiation damage, of a triangular tabular grain is presented, clearly showing defect contrast fringes along four of the six directions; the remaining two sides show similar contrast under relevant diffraction conditions. The width of the central defect free region corresponds with the pure AgBr kernel grown before the mixing with I. The thickness of a given grain lies between 0.15 and 0.3 μm: as indicated in fig. 2 triangular (resp. hexagonal) grains exhibit an uneven (resp. even) number of twin interfaces (i.e., between + and - twin variants) parallel with the (111) surfaces. The thickness of the grains and the existence of the twin variants was confirmed from CTEM images of perpendicular cuts.