On the growth mechanism of polycrystalline snow crystals with a specific grain boundary

Observed frequently in a natural snowfall at temperatures lower than -20°C, the crossed-plate crystal is an assemblage of two to four thin basal plates, each plate extending along a CSL grain boundary with a relation of 70.3°/[11$\text{2}$0]. A possible growth mechanism is proposed to account for the characteristics growth in the direction of the axis [11$\text{2}$0]. If two or more grain boundary dislocation (GBD) structures are contained at a CSL grain boundary, growth layers will overflow alternately on the (10$\text{1}$0) planes of each component crystal at the intersection of these planes. Thus, the distinctive structure of the CSL grain boundary, like the feature of a screw dislocation step, will induce the preferential growth in this direction.     

Electron microscope study of intrinsic and extrinsic stacking faults,and twins in SOS at the early stage of epitaxial growth

Fine structures of the Si films on (1$\text{1}$02) sapphire have been studied by a lattice resolution TEM. The Si was deposited by the pyrolysis of silane in H₂ at 1000°C at a growth rate of 0.1μm/min. The samples for TEM were prepared by peeling off the Si films from the substrates after HF treatment. A film having a mean thickness of 500 Å was composed of (100) and {110} domains. The volume fraction of the {110} domains was more than 50% and about constant as a function of growth time. The {110} domains contained much higher density of microtwins than the (100) domains. These microtwins had various thicknesses including one atomic layer (intrinsic stacking faults) and two atomic layers (extrinsic stacking faults). The density of the intrinsic stacking faults was higher than those of extrinsic stacking faults and other twins. The {110} and (100) islands were nucleated independently and the microtwins were also present in the islands smaller than 500 Å in diameter.     

Growth parameters for large diameter float zone silicon crystals

Factors that directly affect the ability to grow dislocation free float zone silicon crystals up to 80 mm in diameter have been experimentally determined. The highest yield is obtained for 80 mm diameter crystals by starting with 68 mm to 74 mm diameter poly crystal rod stock. Lower transport speeds for crystal growth of (111) orientation crystals were 3 to 4 mm/min and for (100), 2 to 3 mm/min. Rotation rates of both upper and lower shafts were found to have an effect on growth at the solid-liquid interface. Rates established for lower shaft were 6 to 8 rpm for the (111) crystals and 3 to 4 rpm for (100), counter-clock-wise. Upper rotation rates were 2 rpm on (111) crystals and 3 to 5 rpm on (100), clockwise. Seed orientation, which is critical, was held to within plus or minus $\text{1}\text{2}\text{°}$ of perfect orientation. The minimum seed growth length was 50 to 70 mm. To assist in reducing the side lobes on (111) dislocation free crystals, a cooling ring with a flow or argon was used. For best (100) growth the shape of the lower side of a one turn copper rf work coil was made conical. Six to ten dislocation free crystals in each orientation group were produced using these parameters.     

Single crystal synthesis and properties of lithium-gallium-, lithium-aluminium-oxide and mixed compounds (I) growing of LiGaO2-, LiAlO2- and LiAlxGa1−x crystals from fluxes

LiGaO₂ forms a single eutectic with PbO/B₂O₃ (molar ratio 9:4). A nearly linear slope of the liquidus curve is followed by a steep rise of the temperature coefficient of solubility. The solvent power at 1300°C is 0.35 g LiGaO₂/g PbO, B₂O₃; from 1000 to 1300°C there exist only poor differences in solubility of LiGaO₂ and LiAlO₂ in PbO/B₂O₃. LiGaO₂ crystals up to 1 p in weight grew spontaneously by slow cooling from fluxes or by evaporation of the solvent, those of about 1–1.5 p from seeds by cooling stirred fluxes. LiAlO₂ crystals are essentially smaller (6 mm). – By partial substitution of Ga₂O₃ by Al₂O₃ mixed crystals LiAl_xGa_1−xO₂ result. In the case of x ≦ 0.5 the coefficient of segregation remains ≦1. The al concentrations along the polar axis decrease by more than 25 p.c., perpendicular to [001] they keep constant till to the crystal surface. – Crystals show hypermorphism from mm2 to mmm. With high initial exceedings only {110} and {011}, with lower ones also {120}, {130}, {210} and {310} as well as the reduced {100}, {010} combinations are observed. – LiGaO₂ crystals grow by nucleous, sceletal or faceted growth resp. during the cooling period. – Primarily at 1270°C formed nuclei up to 1150°C grow to critical dimensions (≈0.5 mm) and develop to the main branch along [001]. Primary branches deflect to [010]. The convex secondary branches intergrow along (110), often including flux. With decreasing temperature a new crystallisation front is formed at the periphery leading to a stable faceted growth at about 1000°C.     

Melt Growth of CdTe Crystals and Transmission Electron Microscopic Investigations of their Grain Boundaries

Transmission electron microscopy investigations are carried out on CdTe crystals grown in quartz ampoules in a temperature region (1020–1091 °C) near to the melting point of 1092 °C, by travelling heater method in quasi-closed and in sealed (at 0.135 Pa) volume, and by the Bridgman method from nearly stoichiometric melts. An original method for preparation of CdTe thin foil is reported. Two types of grain boundaries are observed: high-angle misoriented grain boundaries (more than ten degrees misorientation between adjacent grains) and low-angle misoriented grain boundaries (less than one degree misorientation between adjacent sub-grain). Both dislocations with Burgers vector b = a/6 〈112〉 and b = a/2 〈110〉 are present.     

Growth and morphology of 6H-SiC epitaxial layers by CVD

Single crystals of 6H-SiC were epitaxially grown on 6H-SiC substrates in the temperature range of 1500 to 1750°C with gas composition: H₂ ≈ 1 l/min, SiCl₄ ≈ 1 ml/min, C₃H₈ ≈ 0.05 ml/min. The grown layers were transparent and mirror-like. The morphology of the grown layer was strongly influenced by the polarity of the substrate surface. Aggregates of trapezoidal crystals were observed on the (000$\text{1}$)C surface and a mosaic pattern was observed on the (0001)Si surface. By observing the initial stage of the crystal growth, the growth mechanism of 6H-SiC is discussed. On (000$\text{1}$)C surfaces the vertical growth dominates, while on (0001)Si surfaces the lateral growth dominates.     

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}.     

Change of short-range order with temperature and composition in liquid GexSe1−x as shown by density measurements

Density measurements were performed on melts of the binary chalcogenide system Ge_xSe_1?x (0 ? x ? 0.5) up to 1000°C. The isotherm of molar volumes V_m at 750°C shows a relative maximum near GeSe₂. Molar volumes of the system behave linearly between GeSe and Se at 1000°C. V_m's of melts between x = 0.30 and x = 0.35 decrease at high temperatures on heating. The anomalous density behaviour of the melts clearly shows a change of short-range order from a less to a more densely packed structure, caused by the development of a pσ-bonding system. Within the composition range $\text{0 ? x ?}\text{1}\text{3}$ the short-range order at lower temperatures is determined mainly by $\text{GeSe}{}_{\mathrm{<mtext>4</mtext><mtext>2</mtext>}}$ tetrahedra linked directly corner-to-corner or via Se atoms. At higher temperatures pσ bonds arise more and more, even in melts rich in selenium. Within the composition range $\text{1}\text{3}\text{? x ? 0.5}$ the short-range order is mainly determined by a distorted octahedral configuration, even at lower temperatures. From the short-range orders of melts and from crystalline structures of GeSe₂ and GeSe, the tendency of glass formation from the melt is discussed in detail.     

Domain structure of Na1 − x LixNbO3 crystals

The domain structure of single-crystal and ceramic samples of Na_{1 ? x} Li_xNbO₃ solid solutions (at x ≤ 0.14) in the orthorhombic ferroelectric and antiferroelectric phases at room temperature is investigated by optical and electron microscopies and X-ray diffraction. The characteristic feature of the domain structure is the formation of 90° complexes consisting of laminar domains with a specific orientation relative to the lattice of the initial cubic phase. Consideration is given to the specific features in packing of these complexes and typical configurations of domains in the crystals. Observations revealed that the domain structure can involve 90°, 60°, 120°, and 180° boundaries, as well as (hhl) boundaries of the S type whose orientation depends on the cell distortion and changes with a variation in _x. The indices of these boundaries are determined. The density of 180° boundaries in the ferroelectric phase is very low compared to that of non-90° boundaries.     

The effects of oxygen,hydrogen and fluorine on the conductivity of high purity evaporated amorphous silicon films

Electron bombardment evaporation was used to deposit amorphous silicon (α-Si) films in an evaporator with a base pressure of 2 × 10^?10 Torr. Rutherford backscattering analysis was used to establish the conditions necessary for deposition of pure films.The DC conductivity was measured as a function of temperature (? 150°C to + 140°C). Pure films, which were deposited between room temperature and 400°C, were found to have a room temperature conductivity (σ_RT) in the region of 10^?3μ^?1cm^?1 and a log $\text{σα}\text{T}{}^{\mathrm{<mtext>1</mtext><mtext>4</mtext>}}$ dependence. The value of σ_RT could be reduced by annealing reaching a minimum of 2 × 10^?7μ^?1 cm^?1 for an anneal temperature (T_A) of 520°C, but activated conduction was not observed.The implantation of hydrogen or fluorine (or contamination with oxygen) had the effect of reducing σ_RT, with a minimum value of less than 10^?8μ^?1cm^?1 (T_A = 400°C) for fluorine implantation to a dose of ≈ 10¹⁶ cm² (≈ 0.4 at% concentration). These films had high temperature (50°C) activation energies typical of activated conduction in extended states on the edge of the mobility gap. Implantation of fluorine to a dose of 1.5 × 10¹⁷ resulted in a rise of σ_RT (T_A = 400°C) to nearly 10⁴μ^?1 cm^?1 and log $\text{σα}\text{T}{}^{\mathrm{<mtext>?1</mtext><mtext>4</mtext>}}$ behaviour.X-ray analysis revealed that some crystallization occurred in films annealed at 600°C. This is correlated with a rise in σ_RT of the pure films and the disappearance of the effects of the introduced impurities.     

H3PO4 — etching of {001}-faces of InP, (GaIn)P,GaP, and Ga(AsP)

This paper shows that hot H₃PO₄ is a suitable etchant for the production of dislocation etch pits on {001}-InP, (InGa)P, GaP, Ga(AsP), and {111}-GaP. The effects upon etch pit morphology of the misorientation of samples and the type of dislocations are investigated in detail.     

Growth and morphological study of copper oxide single crystals

Experiments on the growth of CuO single crystals by crystallization from flux in the CuO-Bi₂O₃-PbO-PbF₂, CuO-Bi₂O₃-Li₂O, CuO-Bi₂O₃-B₂O₃, CuO-BaO-Y₂O₃, and CuO-MO_x systems (M = P, V, or Mo) have been performed. The best results were obtained in crystallization in the CuO-Bi₂O₃-PbF₂ system: prismatic single crystals of platelet-and needlelike or isometric habit with dimensions up to 1 × 10 × 10, 1 × 1 × 20, or 6 × 6 × 8 mm, respectively, have been grown. The CuO crystals show polysynthetic twinning in the form of numerous alternating light and dark bands bound by systems of parallel straight lines on the {110} and {111} faces. A possible model of twinning associated with the Cu₂O → CuO transformation is considered.     

Zur Epitaxie von Galliumnitrid auf Korund im System GaCl/NH3/Ar

The vapour growth of single crystalline layers of GaN on {0001} oriented sapphire substrates in the temperature range of 500–1100°C is described for the system GaCl/NH₃/Ar. The RHEED micrographes of samples grown in the high temperature range of 1000–1050°C show KIKUCHI pattern, thus indicating a good crystalline perfection of the layers. The large free electron concentration of about 10²⁰ cm⁻³ decreases below 700°C rapidly with decreasing growth temperature. Simultaneously the crystalline perfection is remarcably lowered due to increasing misorientation of the subgrains, but no arcing of the RHEED spots due to polycrystalline behaviour is observed. The layers grown at 500°C are contaminated by chloride. Sometimes a dendritic overgrowth of the layers by the GaN sphalerite polytype takes place.     

Defect Structure of Strained Heteroepitaxial In(1—x)Al(x)P Layers Deposited by MOVPE on (001) GaAs Substrates

Weak-beam, large angle convergent beam electron diffraction and high resolution transmission electron microscope experiments have revealed, that after strain relaxation due to plastic deformation dislocation networks can be observed in In_(1—x)Al_(x)P heteroepitaxial layers grown on (001) GaAs substrates under compressive stress. The 60° slip dislocations are mostly dissociated into partials of Shockley type whereas in the particular case of layers grown under tension twins are predominantly formed by successive nucleation and slip of 90° Shockley partials on adjacent {111} glide planes lying inclined to the (001) surface. When a few 90° Shockley partials pile up during extension of twins, then planar incoherent twin boundaries with {112} coincidence planes have been formed during strain relaxation. Due to the space group symmetry ((InAl)P belongs to the space group F4-3m) there is a striking asymmetry in defect formation, i.e. defect nucleation and slip on the planes (111) and (1-1-1) slip of the [1-10] zone are preferred to nucleation and slip on the {111} planes of the [110] zone. Apparently, the occupacy of the atomic sites in the dislocation core with either group-III or group-V atoms is responsible for this behaviour. The nature of the defects implies that their spontaneous nucleation should have taken place at the growing surface. Under tensile strain the 90° Shockley partial is nucleated first and the 30° one trails. Under compressive strain this sequence is reversed. It is evident, for dissociated dislocations lying at the interface always the 30° partial, i.e. the partial with less mobility or with higher friction force, is detained near or directly in the interface. Thus, in layers grown under tension the stacking fault associated with the dissociated 60° dislocation lies inside the GaAs substrate. For layers grown under compression it is located inside the ternary layer.     

Structures of vapour-deposited amorphous films of arsenic chalcogenides

The structures of vapour-deposited amorphous films of composition As_xSe_1?x′, with x between 0 and 1, have been investigated by X-ray diffraction. In all cases the structure of the freshly deposited film differs very considerably from that of the corresponding bulk glass. For the elemental amorphous films the structure is highly disordered and contains voids which for Se cannot be annealed out below the crystallization temperature of 70°C or, for As, below the temperature ($\text{?130°}\text{C}$) where the As film re-evaporated. Annealing of the arsenic selenide films at temperatures below T_g causes the structures to relax towards those of the bulk, with a distribution of activation energies around 25 kJ mol^?1. The composition of the vapour has been examined by mass spectroscopy and it is concluded that even if some molecular identity is retained on condensation there must be considerable cross-linking to give the observed structural behaviour.     

Small angle X-ray scattering study of spinodal decomposition in B2O3---PbO---Al2O3 glass

SAXS measurement for 80B₂O₃·15PbO·5Al₂O₃ (wt%) glass can be performed with high accuracy. SAXS spectra were obtained for glasses which had been heat-treated for different lengths of time at 380°C and 400°C. A converging point k′_c and a common curve for k >k′_c were observed in the SAXS spectra of glasses subjected to appropriate aging. This suggests the validity of Cook's modification of Cahn's theory. At the very early stage of the decomposition a relaxation takes place of $\text{?″}\text{and}\text{D}\text{?}$ and the spectra of Cahn-Cook's amplification factor show a typical aspect of the early stage of decomposition after the relaxation. Plots of k³I(k) versus k³ suggest that the interface between the two phases is diffuse and the demixing process is in the early stage of the spinodal decomposition.     

Polyhedral to nearly spherical morphology transformation of silver microcrystals grown from vapor phase

Silver microcrystals of various shapes were grown from co-evaporation of Ag₂O and SiO powders in the nominal evaporating temperature range (heat source temperature) from 800 to 1200 °C under a reductive atmosphere. Pathways for the polyhedral to nearly spherical morphology transformation were established. At evaporating temperatures below 900 °C, the polyhedral crystals are generally bounded by {1 1 1}-facets and {1 0 0}-facets. With increase in evaporation temperature facets of the {1 1 0}-, {2 1 0}- and {3 1 0}-families come forth successively, that make the Ag polyhedron microcrystals transform into nearly spherical microcrystals. A mechanism based on the recession of {1 0 0} or {1 1 0} steps induced by the solvent SiO_x (x～2.0), which modifies the growth kinetics, is proposed to explain the emergence of {2 1 0}- and {3 1 0}-facets at high temperatures. By evaporating at 1200 °C, smooth-looking spherical Ag crystals with 6 nm multi-layered steps on the {1 1 1} facets were obtained. These results are also of significant industry relevance when preparation of noble metal particles with high-index facets is of concern.     

Investigation of recombination and trapping processes in 3As2Se32Sb2Se3 amorphous films by photoconductivity method

Photoconductivity experiment has been performed on high resistivity ($\text{π ? 10}{}^9\text{Ω-}\text{cm}$) 3As₂Se₃2Sb₂Se₃ amorphous films in the temperature range from 278°K to 308°K, as a function of light intensity, I₀. The results are that at intermediate light levels the photocurrent varies as I₀^0.7 and at high light levels the photocurrent is directly proportional to I₀. A simple recombination and trapping model is developed to interpret the observed photoconductivity data. From the temperature dependence of the photocurrent, an effective trap level located 0.3 eV below the band edge is deduced.     

Crystal growth of SnO2 by chemical transport method

Single crystals of SnO₂ were grown by the chemical transport method from the powder prepared by heating hydrous stannic oxide. The transport reactions were carried out when iodine and sulfur were simultaneously used as transporting agent, and fine crystals of a few millimeters in dimensions were grown after a ten-day transport; the transport proceeded from 1100°C (charge) to 900°C part in a silica ampoule. The crystals were identified as SnO₂ (cassiterite) by the Weissenberg method. Thermodynamic calculations led to the equilibrium $\text{SnO}{}_2\text{(s) + I}{}_2\text{(g)}\text{+}\text{1}\text{2}\text{S}{}_2\text{(g)}\text{?}\text{SnI}{}_2\text{(g) + SO}{}_2\text{(g)}$ for this transport reaction.