Twin Plane Re-entrant Edge Research Articles

The crystal morphology of fibrous silicon in strontium-modified Al-Si eutectic

Abstract The crystallography of silicon in strontium-modified Al-Si eutectic has been studied by transmission electron microscopy. Strontium addition results in a massive increase in twin density in the silicon phase, and the twin density increases with cooling rate for fixed strontium content Growth of the fibrous eutectic silicon is shown to be compatible with the twin-plane reentrant edge growth mechanism. Branching mechanisms are described. No consistent orientation relationships between the eutectic phases were observed, but the aluminium phase exhibited a 〈110〉 texture.

Growth Mechanisms of Silicon Crystallites Grown on Top of a Metal‐Coated Graphite Substrate

Microscopic in situ observations and a posteriori surface topography by means of optical and scanning electron microscopy have been carried out in order to study the growth of large‐grain polycrystalline silicon films from the gas phase onto a graphite substrate coated with a liquid layer of tin or aluminum. In the present study, only the initial stages of the process, where crystal growth is governed by vapor‐liquid‐solid mechanisms, are considered. For the growth of the crystallites in the polycrystalline layers, which occur in two morphological forms, viz., needles and platelets, two different mechanisms could be identified: (i) a twin plane reentrant edge (TPRE) mechanism, leading to a fast lengthwise growth of needles and a fast sidewise growth of platelets; and (ii) a nucleation mechanism, accounting for a slow thickness growth of the needles and a slow expansion of the platelike crystals. On the upper surfaces of some needles and platelets a capricious surface pattern (always in conjunction with the occurrence of some solidified metal droplets) could be identified, which could be interpreted in terms of a two‐dimensional VLS growth mechanism.

Crystallography of the Al-Al 3 Fe eutectic

Crystallographic characteristics and limits of stability of the Al–Al 2Fe abnormal eutectic microstructure have been observed. When the G R ratio is low, Al 3Fe grows as frequently branched, narrow platelets in a dendritic aluminium matrix. When G R > 1000°C sec/mm 2 branching is largely eliminated and [010]Al 3Fe ∥ [100]Al ∥ growth direction. The Al 3Fe platelets grow in the [010] direction by a twin plane re-entrant edge mechanism in which grooves between faceting {111} planes are formed between multiple (001) twins. (001) twins were observed at 50–200 Å intervals for all freezing conditions, and (100) twins were also observed at higher values of G R .

Effect of growth parameters on habit and morphology of electrodeposited lead dendrites

Changes in habit and morphology of lead dendrites grown by electrodeposition from aqueous solutions were studied as a function of various growth parameters. Changes resulting from current density and concentration of the electrolyte are given in chart form. The following changes in morphology were observed in order of increasing current density, (a) polyhedral growth, (b) dendrites growing in the 〈110〉 directions, (c) acicular dendrites growing in the 〈110〉 directions, (d) dendrites growing in the 〈211〉 directions, (e) dendrites growing in the 〈100〉 directions, and (f) spongy growth. Not all of these morphologies were found, however, at each concentration. Dendrites were faceted in all cases by {111} planes. (a), (e), and (f) did not contain twin planes. Dendrites in (b) and (d) contained twin planes parallel to the main faces, while those in (c) had twin planes radiating from a common line. Evidence suggests that the dendrites containing twin planes grow by the twin plane re-entrant edge mechanism.

Crystallographic and morphological studies of electrolytic zinc dendrites grown from alkaline zincate solutions

Electrolytic zinc dendrites grown potentiostatically from a range of alkaline zincate solutions were studied using X-ray diffraction and scanning electron microscopy (SEM) to reveal structural and morphological characteristics as a function of their growth rate. Conclusions from this work were as follows: Dendrites grown at a rate of 3 μm min−1 were identified as twinned monocrystalline “swords” with a noticeable absence of regular branching. Dendrites grown at a rate of 24 μm min−1 were basically twinned monocrystals with some polycrystalline character. As for the slowest growing dendrites, the morphological character was of a sword-like nature. Morphologically these first two types of dendrites show great similarity to the butterfly dendrites of DeVries. Dendrites grown at 67 μm min−1 were of the fern-like morphological type with a large degree of polycrystalline character. These dendrites are suggested as being composites of very small slow growth rate dendrites in a roof tile arrangement. The results for the ideal fern-like dendrites seemingly disagree with the earlier hcp dendrite work of Wranglen who identified this type of dendrite as a monocrystal. An explanation for this discrepancy is offered. The work presented here appears to be consistent with the twin plane re-entrant edge (TPRE) growth mechanism.

The dendritic growth of lead from gels

Lead dendrites were grown from gels, and their habit, morphology, and internal structure were studied. Growth was found to proceed in three stages. The first stage showed mainly single crystal dendrites growing in the 〈100〉 direction while the second and third stages gave dendrites growing in the 〈211〉 direction. All dendrites were faceted by {111} planes. The dendrites from the second and third stages were shown to grow by the twin plane re-entrant edge mechanism

The growth of semiconductor crystals from solution using the twin-plane reentrant-edge mechanism

Experimental conditions are described for growing crystals of diamond lattice and zinc blende semiconductors from metal solutions using the twin plane reentrant edge mechanism. In addition to the expected < 211 > type twinned platelets, some unusual < 110 > extended forms with intersecting twin configurations were obtained. Etch techniques were used to study microresistivity striations and to determine the growth history of the platelets. The relative number of nucleation events at different sites and the possible effect of polarity on the growth of III-V compound platelets are discussed. Electrical measurements are reported on some of the platelets.