Epitaxial relationships during the formation of three-dimensional snow dendrites

Investigations of natural polycrystalline snow crystals, especially of plane assemblage of crystals of spatial type, have disclosed a predominant misorientation of 70° in the c-axes between the main branch and the secondary branch. As the result of application of the Coincidence Site Lattice (CSL) theory to the interpretation of this misorientation, {30$\text{3}$2}/{0001}, {30$\text{3}$4}/{30$\text{3}$4} and {30$\text{3}$8}/{30$\text{3}$8} are proposed as probable boundaries having a good atomic fit and low energies. It follows from this proposition that, once an m-c-c-m type of stacking fault is induced, CSL boundaries will extend beyond the junction, giving the 70° misorientation between a deposit and a substrate.     

Stacking faults in deformed zinc and magnesium single crystals

Using the transmission electron microscopy dissociated dislocations containing stacking faults were observed in Mg single crystals, deformed in (0001) <1120> slip system, and in Zn single crystals deformed in {1122} <1123> slip system. The overlapping flat stacking faults lying in {1102} planes and dissociated triple nodes in (0001) planes are observed in Mg. In Zn flat stacking faults are found in {112 2} planes. The value of stacking fault energy γ has been determined in Mg crystals (γ ⋍ 10 erg/cm²). Such a low value of γ is attributed to the segregation of impurities on dislocations.     

TEM-Untersuchungen von Gitterfehlern in ZnSiP2-Einkristallen

Results are dealt with concerning TEM investigations of lattice defects in ZnSiP₂ single crystals. After the crystal growth dislocations or stacking faults were found in a few cases only. More frequently twins were present in the microstructure. The crystallographic elements of twinning are {112} 〈111〉. After plastic deformation by bending at 900 °C local dislocation arrangements with high defect density (N_v ≈ 10⁶…︁ 10⁷ cm⁻²) were observed. By means of the diffraction contrast one Burgers vector b = 1/2 〈111〉 could be identified. In some cases the crystals also contained wide deformation stacking faults, which were limited by partial dislocations. The density of twins was not increased under the conditions of deformation reported here. As it can be concluded from investigations of Oettel et al. and from the results of the twin analysis, slip and generation of stacking faults take place on {112}-planes in ZnSiP₂ crystals. Crystallographic considerations on both processes are dealt with.     

Controls on Morphology of Analcime-Pollucite in Natural Minerals,Synthetic Phases,and Nuclear Waste Products

Crystals of the analcime-pollucite series (NaAlSi₂O₆ · H₂O CsAlSi₂O₆) exhibit tetragon-trioctahedral {211} and hexahedral {100} morphology, with rare modification by tetrahexahedral {210} or rhombic dodecahedral {110} forms. Under weakly acidic to weakly basic conditions {100} is dominant; with increasing alkalinity (cation concentration), basicity (pH), and temperature {211} is dominant over {100}, with minor development of {210}. The morphology does not appear to be influenced by broad ranges in Si/Al (from 2.0 to 2.6 in the natural minerals) and Na-Cs contents between analcime and pollucite, by substitutions of univalent cations Li, K, Rb, and Tl, or by small amounts of divalent cations Mg, Mn, Ni, Zn, Fe. Larger amounts of Ca, however, and possible substitutions for framework Al and Si seem to produce a more complex morphology.     

The Epitaxial Orientation of Al on Si

It is shown that the epitaxial growth of Al on Si {111} favours the epitaxial relation {111} Si ‖ {100} Al; 〈110〉 Si ‖ 〈110〉 Al instead of the more expected relation {111} Si ‖ {111} Al; 〈110〉 Si ‖ 〈110〉 Al. The elastic energy density of the epitaxial layer in the first case mounts to about 40% of that belonging to the second relation. The calculation of the elastic energy density in both cases is based on the assumption of pseudomorphical epitaxial film overgrowth between deposit and substrate supercells.     

Defects in implanted and Czochralski silicon

Rod-like defects, a6〈114〉 and a/3〈111〉 faults, and a/2〈110〉 loops may all be generated by self-interstitial aggregation during the annealing of implanted or Czochralski silicon, and several models, intended to account for one or more of these, are compared. It is concluded that the rod-like defects are {113} faults, and that the three faulted defects form independently (i.e. they are not related in an „evolutionary”︁ sequence). The dipolelike a/2〈110〉 loops probably result from the unfaulting of {113} faults, while other perfect loops are generated by the shear of a/6〈114〉 defects. At a given temperature, the latter appear considerably more likely to unfault than the a3〈111〉 faults. The structure of the {113} fault remains uncertain.     

Study on the Growth of Triglycinsulphate Single Crystals

Crystallization of TGS at 52.0°C - above the transition point - has been studied in a wide range of supersaturation of the solution (σ = 0 to 10⁻²). The rates of growth of {110} and {001} faces were measured as a function of supersaturation at constant hydrodynamical conditions (Re = 3.4 · 10⁻³). Further, the influence of hydrodynamical conditions on the growth of {110} faces at constant supersaturation (σ = 4.2 · 10⁻³) was established. The parameters of the experimentally found dependences are determined on the basis of the surface-diffusion model of BURTON . CABRERA and FRANK . From these dependences follows that the growth rate of the {110} faces is already almost limited by the volume diffusion of TGS molecules towards the crystal surface, while in the case of {001} faces the surface diffusion mechanism of crystallization is clearly manifested. Dislocation densities in the crystals have been determined by means of etching technique. The number of dislocations increases with increasing supersaturation; hence, supersaturation of the solution together with the processes taking place in the regeneration zone surrounding the seed determine the number of dislocations in the crystal volume and thus the resulting structural perfection of single crystals. Investigation of the spontaneous redistribution of domains showed that the growth rate of TGS crystals influences the dielectric properties to much smaller extent than does chemical purity.     

Formation of microtwins in TmP/GaAs heterostructures

Microtwins in semi-metal thulium phosphide (TmP) epilayers grown on (0 0 1) GaAs substrates by molecular beam epitaxy have been studied by transmission electron microscopy. Selected area diffraction patterns show extra spots along 〈1 1 1〉 and 〈2 2 4〉 corresponding to three times the normal rock-salt periodicity. Only one or two twin variants are found in the crystal. The occurrence of the observed microtwins in the TmP-GaAs heterostructure can be accounted for by the growth-accident mechanism, i.e., the formation of microtwins is via growth accidents in the stacking sequence on {1 1 1} and {1 1 2} planes. The growth accidents appear to occur due to rapid growth rates and/or contamination.     

CBr4 as precursor for VPE growth of cubic silicon carbide

This work presents a study of carbon tetrabromide (CBr₄) as precursor to deposit 3C‐SiC on (001) and (111) Si by VPE technique at temperatures ranging between 1000 °C and 1250 °C. TEM, AFM and SEM results indicate that the epitaxy proceeds as a 3D growth of uncoalesced islands at low temperature, whereas a continuous crystalline layer with hillocks on top is obtained above 1200 °C. The hillocks observed at high temperature appear well faceted and their shape and orientation are analyzed in detail by AFM, showing a {311} preferred orientation. 3D island growth was suppressed by adding C₃H₈ to the precursor gases. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Atomic and electronic structures of nanometer sized silica particles

The Austin Model 1 semi-empirical method combined with geometry optimization procedure was used to study atomic and electronic structures of nanoscale silica particles containing up to 192 atoms (64 Si and 128 O). Twofold Si–O rings were found to dominate in nanometer sized particles. The fraction of larger rings increases with increasing particle sizes. Bond length and bond angle distributions were calculated. The shortest Si–O, O–O and Si–Si interatomic distances are approximately 1.7, 3.0 and 3.3 Å, respectively. Average O–Si–O and Si–O–Si bond angles are approximately 110^∘ and 130^∘. Average electronic energy band gap is 6.9 eV.     

Reflection Splitting in RHEED Investigations of Vacuum Evaporated GaAs Layers

RHEED-diagrams of vacuum deposited GaAs-films with high density of structural defects often show splitting of matrix reflections into satellites. It can be shown by simple models, for example of {111}-oriented films, that this phenomenon is originated by formation of stacking faults perpendicular to 〈ĪĪĪ〉-B growth directions of the films. The conditions for 〈110〉 and 〈211〉 azimuths are discussed.     

The Morphology of Hydrothermally Grown Plagioclase

Plagioclase crystals Ab₂₀An₀₀ and nearly pure anorthite were grown on the surface of artificial melts by hydrothermal treatment at 2 kb. The average crystal size was 0.002 to 0.008 mm. In the temperature range of 400° to 600°C a pseudohexagonal habit was observed for anorthite while a lath-like habit due to the prevalence of {010} was found for the Ab₂₀An₈₀ composition. Dominating faces are {010} {130} {110} {100} {110} {130} in the zone [001] and {021} {111} {111} {021} {111} {111} together with {001}.     

Vapor phase epitaxy of CdTe on sapphire substrates in dependence on the vapor-flow orientation

The growth of cadmium telluride films on a structured (0001) sapphire surface oriented at an angle of 44° to the vapor-flow direction and normal to the steps formed along the \(11\overline 2 0\) direction is studied. It is found that this geometry of the vapor source and a substrate (heated to a temperature of 300°С) provides the growth of single-crystal CdTe films if a step height on the substrate surface is more than 1 nm. The results are explained by the occurrence of a longitudinal component of the diffusion flux of СdTe molecules and atoms toward the steps from the inner side and their high density at the step edge from the outer side due to the presence of the Ehrlich–Schwoebel barrier, which ensures the efficient supply of material and minimum supersaturation necessary for the nucleation at the step edge and growth of oriented CdTe islands. The cadmium telluride films that are grown have the \(\left( {110} \right)\left[ {1\overline 1 0} \right]CdTe\left\| {\left( {0001} \right)} \right.\left[ {11\overline 2 0} \right]A{l_2}{O_3}\) orientation and a composition similar to stoichiometric CdTe.     

Growth Mechanism and Twinning of Sucrose Effected by Surface Adsorption Processes

Growth experiments with sucrose dependent on temperature and supersaturation of solutions were carried out to find the conditions for appearance of the three different growth types. Measurements of growth rates of {110} and {1 1 0} faces at 50°C and supersaturation c_s = 10% resulted in the known feature that in pure solutions a crystal grows faster in positive b-direction than in the negative one. Addition of raffinose stopped growth of {110}. In an electric field generated by 20 kV direct voltage (crystal orientation: negative pole of b-axis pointed towards the negative electric pole) the crystal grew in negative b-direction three times faster than in the positive one. In the presence of raffinose the growth rates in both directions become equal. If the crystal is turned by 180° in the solution (pure solution and in the presence of raffinose) the growth behaviour is the same as without an electric field. These results can be interpreted in such way that in pure solutions sucrose molecules adsorb to {1 1 0} (bonds exist between the fructose rings of molecules in liquid and solid phases) and that in presence of raffinose these molecules adsorb to {110} (bonds exist between glucose (solid) and galactose rings (liquid phases)). By the electric field the adsorption is hindered. The theory is in accordance with the fact that crystals situated in a suspension of the solution can intergrow with a host crystal in twin positions (in pure solutions on {1 1 0} and in the presence of raffinose on {110}).     

The change of the lattice constant in heteroepitaxial silver films with increase of thickness

Deposition of silver on NaCl, KCl, and LiF with 20 Å · s⁻¹ in vacuum (5 · 10⁻⁶ torr) and electronographical determination of changes of lattice constant. Precision of measurement better than ± 0.004 Å (reflections {400} and {220}). Thickness of films from 50 to 500 Å with intervals of 10 Å. The lattice parameter of films till to 115 Å in thickness did'nt differ from the parameter of bulk silver (4.086 Å). At about 175 Å the parameter reached minimum (about 4.00 Å) and took again the parameter of bulk material with the film thickness of 215 Å. With polycrystals no changes of lattice parameters occurred. – The phenomenon is connected to growth mechanism, two-dimensional and three-dimensional nucleation and to the differences in lattice parameters of substrate and deposit.     

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

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 } edges and in some cases edge dislocations with a Burgers vector of type. An atomic model for the formation of the stacking faults during the growth is presented.     

The structure analysis liquid Sb2Se3 by neutron diffraction

The radial distribution analysis of liquid Sb₂Se₃ at 670, 720 and 770°C is carried out by the neutron diffraction method. A small but apparent maximum is found at $\text{K = 1.2}\text{A}\text{?}{}^{\mathrm{?1}}$ in the structure factor. The interatomic distance and the coordination number are 2.74 Å and 2.84 respectively, at 670°C. These results suggest that intramolecular bonds in the crystalline Sb₂Se₃ remain unbroken in the liquid state. The general feature of the structure factor and the distribution function for liquid Sb₂Se₃ is similar to that for the amorphous state. However, it is clear that the liquid phase tends to have a similar atomic arrangement to that of liquid tellurium.     

Neutron diffraction study of the formation of ordered antiphase domains in cubic titanium carbide TiC0.60

A series of superstructural reflections (described within the sp. gr. Fd3m) are found to be split into three symmetric parts in the neutron powder diffraction pattern of titanium carbide TiC_0.60 annealed at a temperature of 600°C. No splitting of superstructural reflections is observed in the neutron diffraction pattern of TiC_0.60 annealed at relatively high temperatures (780°C). This phenomenon can be explained by that fact that the ordering of carbon atoms at relatively high temperatures (780°C) is accompanied by the formation of randomly oriented rather large antiphase domains (APDs) (450 Å). At relatively low temperatures (600°C), stacking faults arise in the arrangement of partially ordered carbon atoms. In this case, relatively small ordered APDs (290 Å) are formed, along with disordered ones.     

Electrical,structural and optical properties of amorphous carbon

The planar and transverse electrical resistivity of amorphous carbon (a-C) films getter-sputtered at low temperature (77–95 K) is well-fitted by the expression $\text{? = ?}{}_0\text{exp}\text{(T}{}_0\text{/T)}{}^{\mathrm{<mtext>1</mtext><mtext>4</mtext>}}$ The exponent T₀ being approximately the same in both cases (≈ 7 × 10⁷ K) suggests that the amorphous films are isotropic. Films thinner than 600 Å display a two-dimensional hopping conductivity from which one deduces a density of states N(E_F) at the Fermi level of 10¹⁸ eV^?1 cm^?3 and a radius of the localized wave functions (a) of 12 Å. Tunneling experiments and optical absorption measurements are consistent with a pseudogap of approximately 0.8 eV. Electron diffraction experiments indicate that a-C films consist of a mixture of diamond and graphite bonds; this fact taken in the light of the other experiments would suggest that the graphite bonds act as the localized conduction states.