Clear Facets Research Articles

Growth behavior and surface feature of quasi-one-dimensional anisotropic antiferromagnet BaCo 2V 2O 8 crystal

We report on the growth behavior and surface feature of quasi-one-dimensional anisotropic antiferromagnet BaCo 2V 2O 8 crystal grown from its stoichiometrical melt in air by spontaneous nucleation method. The grown crystals are found to have a characteristic morphology with clear facets, growth lines and veins. Clear steps on the crystal surface show layer-by-layer growth process from a nucleus at the center. Also large defect (vacancies) are clearly seen on the step edges.

Influence of oxygen and nitrogen addition during growth of CVD diamond on pure cobalt substrates

It was shown that in MPCVD reactors the use of common H and CH 4 flows, can lead to the formation of free-standing diamond films directly on pure cobalt substrates. The characteristic low adhesion of these films can be explained by the formation of a graphitic layer between the substrate and the film. Scanning electron microscopy analysis shows special areas at the film grain boundaries that were subsequently identified as cobalt inclusions by EDS. In this work we have studied the influence of oxygen and nitrogen addition on the film's growth morphology. Once again SEM and EDS were used to access respectively the films growth morphology and cobalt content. Our results clearly indicate that the addition of oxygen during the initial stages of diamond nucleation prevents diffusion of cobalt into the film. Further, we believed that this effect is likely due to the formation of a cobalt-oxide layer between the film and the substrate. Also, the addition of nitrogen and oxygen the later during nucleation or during growth leads to an increase in the film's growth rate. A preferential (111) surface morphology with clear octahedron facets and films with dominant (100) crystallographic planes are detected. A model is presented for the growth of CVD diamond on cobalt substrates with the addition of oxygen and nitrogen.

Growth of gallium nitride via fluid transport in supercritical ammonia

Ammonothermal growth of GaN was studied through three types of experiments: synthesis of powder GaN from metallic Ga with various kinds of mineralizers, a weight loss measurement of polycrystalline GaN, and growth of GaN via fluid transport. Hexagonal (wurtzite) GaN was exclusively synthesized with basic mineralizers, whereas neutral and acidic mineralizers resulted in a mixture of hexagonal and cubic (zinc blende) phases, confirming that basic mineralizers are suitable for growing hexagonal GaN. Through a dissolution study of GaN in basic supercritical ammonia, it was discovered that the solubility of GaN has negative temperature dependence. Based on these results, the Ga nutrient was placed in a lower temperature zone and GaN was precipitated on single crystalline GaN seeds. Seeds placed in a higher-temperature zone showed more weight gain than those in a lower-temperature zone. Spontaneously nucleated precipitates on the GaN seeds showed clear crystallographic facets. The maximum size obtained in 24-h growth was about 10 μ m. Deposition of planar GaN on seed surfaces was also confirmed.

Photosensitivity of surface barrier structures based on Cu(In,Ga)Se2 films grown by codeposition in vacuum

Polycrystalline Cu(In,Ga)Se2 (CIGS) films with various ratios of Cu, In, and Ga were grown by codeposition of all elements in vacuum. The X-ray diffraction study showed that the films are single-phase and possess a chalcopyrite structure with predominant [112] orientation. The films exhibited a mirror smooth surface and had a close-packed structure composed of crystallites with clear faceting and a transverse size of 0.1–0.3 μm. Related surface barrier structures of the (In,Ag)/Cu(In,Ga)Se2 type were obtained and their spectra of the quantum efficiency of photoconversion were studied. The obtained structures can be used for optimization of the CIGS film technology.

Size- and shape-tailored hydrothermal synthesis of YVO4 crystals in ultra-wide pH range conditions

Yttrium orthovanadate (YVO4) crystals have been prepared hydrothermally in both strongly acidic and basic media. The effects of vanadium source, acid, addition of sodium hydroxide, chelating reagent, and even solvent on the crystalline size and shape were explored using X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Models for the generation of YVO4 crystals in both acidic and basic media are proposed from the experimental results. The influence of alkaline concentration on the sizes and shapes of YVO4 crystals has been investigated, and it has been found that the addition of sodium hydroxide can reduce the crystal sizes of YVO4. Well-defined YVO4 microcrystals with clear facets have been prepared, and dispersed YVO4 nanograins and nanoflakes with dimensions of 5–50 nm have been obtained. Both the size and shape of YVO4 crystals can be tailored by changing the reaction conditions even though YVO4 crystals generally show a tetragonal growth habit due to its tetragonal crystallographic symmetry.

Growth Behavior of Cubic Boron Nitride Films in a Two-Step Process: Changing Bias Voltage, Gas Composition, and Substrate Temperature

In the deposition of cubic boron nitride (cBN) films by DC-bias-assisted DC jet chemical vapor deposition in an Ar–N2–BF3–H2 gas system, the balance between growth and etching and its relation to the deposition conditions were investigated. A two-step process was designed to optimize the nucleation and growth separately, and a critical bias voltage for the growth of cBN after nucleation was observed. It was found that etching occurred when the bias voltage was below this critical value. Under optimized conditions, the crystallinity and crystal size of the cBN films were improved during the second step. Furthermore, cBN films showing clear crystal facets were obtained.

High-quality, faceted cubic boron nitride films grown by chemical vapor deposition

Thick cubic boron nitride (cBN) films showing clear crystal facets were achieved by chemical vapor deposition. The films show the highest crystallinity of cBN films ever achieved from gas phase. Clear evidence for the growth via a chemical route is obtained. A growth mechanism is suggested, in which fluorine preferentially etches hBN and stabilizes the cBN surface. Ion bombardment of proper energy activates the cBN surface bonded with fluorine so as to enhance the bonding probability of nitrogen-containing species on the F-stabilized B (111) surface.

Crystal growth of β-FeSi 2 by temperature gradient solution growth method using Zn solvent

Single crystalline β-FeSi 2 with a low carrier density has been grown by a temperature gradient solution growth method using Zn solvent. The crystals were polyhedral with clear growth facets. Hall measurements revealed that the crystals showed p-type conductivity. The hole concentration and Hall mobility at room temperature were about 4×10 17 cm −3 and about 19 cm 2 /V s, respectively.

Synthesis and properties of boron carbon nitride (BN:C) films by pulsed-DC magnetron sputtering

The ion-assisted, high-rate, reactive and pulsed-DC magnetron sputtering technique was used to deposit boron carbon nitride (BN:C) films by sputtering a boron carbide (B 4C) target in argon and nitrogen plasma. Various processing parameters were explored to grow BN:C films with high cubic boron nitride (c-BN) content. FTIR, SEM, TEM, AES, and Raman spectroscopy were used to characterize the phases, composition and surface morphology of the films. Significant influence of substrate bias voltage and temperature on phase composition of the films was found. The deposited BN:C films exhibit h-BN, wurtzite-BN (w-BN), c-BN phases and their mixed phases with the variation in substrate bias and temperature. A multi-stage deposition technique with variable substrate bias was exploited to obtain 90% c-BN film with clear grains and facets.

Growth of a 3″ langasite crystal with clear faceting

A macrodefect-free langasite (La 3Ga 5SiO 14) crystal 3" in diameter was grown along its Z-axis by the Czochralski technique. The grown crystal showed clear faceting on (0 0 0 1) and (0 1 1̄ 0) faces, forming a hexagonal column shape, and it had minor faceting on (0 1 1̄ 1) in the conical part, making a stepped hexagonal pyramid. Thermal treatment of the melt and uniform interface shape are important to the growth of langasite with stable facet development. Interface instability occurred during the formation of the conical portion of the crystal under a high crystal rotation rate. The homogeneity in composition was investigated two dimensionally by the X-ray Bond diffraction method. The congruent melt composition for langasite is also discussed relative to the stoichiometric composition.

Effect of growth interruption time and growth temperature on the natural formation of InGaAs/AlGaAs quantum disk structures on GaAs (311)B substrates

We studied the effect of growth interruption time and growth temperature on the natural formation of InGaAs/AlGaAs quantum disk structures grown on high-index GaAs (311)B substrates by metalorganic vapor phase epitaxy at about 800 °C. The InGaAs/AlGaAs quantum disks were uniformly grown only with growth interruption time of 0 s. With increasing growth interruption time, the self-organized growth mode disappeared with the growth interruption time of 20 s. During growth interruption, strain for the natural formation of quantum disks was released by intermixing between In and Al. With decreasing growth temperature, the quantum disk did not show a hexagonal shape with clear facets. The quantum disks were formed at temperature range between 700 and 830 °C. The self-organization appeared through strain-driven mass transport. The strain-driven mass transport seems to have two characteristic lengths such as the amplitude and the periodicity determined by In composition and the InGaAs layer thickness from electron-beam induced mass transport phenomena.

Epitaxial film growth of the charge-density-wave conductorRb0.30MoO3onSrTiO3(001)

Thin films of the charge-density-wave compound Rb 0.30MoO 3 ~blue bronze! have been grown on SrTiO 3~001! substrates. The films have been analyzed with atomic force microscopy and x-ray diffraction. The growth initially proceeds in the three-dimensional island growth mode ~Volmer-Weber mode! with dropletlike islands that are highly uniform and fully relaxed. Epitaxial growth is observed: the fourfold symmetry of the SrTiO 3~001! surface results in four crystallographic orientations. Thick films show cluster formations that differ in size and form from the islands that appear at the initial stage of growth. They are larger and have an asymmetric shape with clear facets. X-ray diffraction on thick films shows a decrease of both the in-plane and out-of-plane texture. The data are explained with a simple model that involves blue bronze layer growth over the facets of the clusters. The model indicates that the crystalline correlation length perpendicular to the charge-density-wave axis is smaller than the dimensions of the grains. The implications of the model on the electrical transport are discussed. @S0163-1829~98!06916-1#

Formation of InAs islands on InP (001) by droplet hetero-epitaxy

We have successfully obtained InAs islands on InP (001) by a novel droplet hetero-epitaxy using low-pressure organometallic vapor phase epitaxy (LP-OMVPE). The island growth sequence was initiated by trimethylindium (TMIn) supply in H 2 atmosphere which was intended to form In droplets and followed by tertiarybutylarsine (TBAs) supply after the TMIn supply was stopped at a growth temperature. By this process, large islands of which height was above 100 nm with clear facets were observed under atomic force microscope (AFM). Using a modified sequence in which the TMIn supply was stopped and the substrate temperature was lowered before the TBAs supply, the appearance of the islands was drastically changed. In the specimen prepared by this sequence at the same substrate temperature, small islands of about 10 nm in height were observed together with the large islands. In order to form smaller islands and to suppress formation of the large islands, the substrate temperature dependence of the islands from 530 to 610°C were investigated. The smallest islands with the height of 5 nm were obtained at the substrate temperature of 565°C.

BaFe12−2xCoxTixO19 (x=0, 0.6, 0.9) Films Synthesized by the Spray-ICP Technique

Barium ferrite films (BaFe 12 - 2 xCo x Ti x O 19 ; x=0, 0.6, 0.9) were synthesized on (001)-oriented sapphire substrates by introducing atomized aqueous metal nitrate solutions into a high temperature inductively coupled plasma (ICP) generated under atmospheric pressure (the spray-ICP technique). All the films exhibited a c-axis orientation. The a-axes of the film and the substrate crossed at 30°. They were about 0.2 μm thick after 10 min of running, composed of crystallites with sizes of 300-500 nm. At x=0, the films were of single phase barium ferrite, consisting of crystallites with clear facets. Doping Co and Ti induced the formation of a small amount of (001)-oriented α-Fe 2 O 3 and degraded the crystallinity and facet of the crystallites. The films exhibited perpendicular magnetic anisotropy. Their saturation magnetizations and coercive forces almost agreed with those of films prepared by sputtering.

Characterization of MOCVD-grown InP on [formula omitted

Atomic force microscopy and transmission electron microscopy have been used to investigate the metalorganic chemical vapor deposition of InP on nominally flat InGaP GaAs(001) substrates. From a detailed structural analysis of the deposited InP, we observe coherent Stranski-Krastanov growth, i.e., after the initial formation of a two-dimensional layer, two types of coherently strained islands appear above a defined thickness. At higher coverages a third type of larger, incoherent and defected island is observed. The two types of coherently strained islands can be characterized by their distinct sizes. For low coverages the coherently strained islands possess irregular dimensions in the plane of the substrate and have a maximum height of 6 nm. At higher coverages the second type of coherently strained islands appears. These are cap-shaped and have a rather narrow distribution of base diameter (120 ± 10 nm) and height (22.5 ± 2.5 nm). An appreciable density of incoherent and defected relaxed islands also becomes evident at increased coverages. These have a hexagonal shape exposing clear facets and are elongated along the [110] crystallographic direction of the substrate.

7217. Plasma deposited silicon nitride encapsulant for rapid thermal annealing of Si-implanted GaAs: S Lee and A Gopinath,J Vac Sci Technol, A8, 1990, 402–406

The ion-assisted, high-rate, reactive and pulsed-DC magnetron sputtering technique was used to deposit boron carbon nitride (BN:C) films by sputtering a boron carbide (B4C) target in argon and nitrogen plasma. Various processing parameters were explored to grow BN:C films with high cubic boron nitride (c-BN) content. FTIR, SEM, TEM, AES, and Raman spectroscopy were used to characterize the phases, composition and surface morphology of the films. Significant influence of substrate bias voltage and temperature on phase composition of the films was found. The deposited BN:C films exhibit h-BN, wurtzite-BN (w-BN), c-BN phases and their mixed phases with the variation in substrate bias and temperature. A multi-stage deposition technique with variable substrate bias was exploited to obtain 90% c-BN film with clear grains and facets.

An observation of 650 °C deformation of Si surface under ultra high vacuum

Significant deformation of a grooved Si surface is discovered during low temperature processing (650–900 °C) in a ultra high vacuum. The lowest temperature at which deformation results is determined to be 650 °C for a (111)Si substrate. In addition, clear facets are formed after high temperature processing (850–900 °C). These new findings are tentatively considered to originate from the surface migration of Si atoms on atomically clean surfaces.

ＳｎＯ２：Ｅｕ粉末けい光体の合成と物理化学的および発光特性

SnO2:Eu powder phosphor was examined concerning to its synthesis, physcochemical properties and luminescent characteristics for the purpose of practical use in low-energy-election excitation. The oxalate coprecipitate of Sn and Eu composed of large particles with clear crystal facets was found to give bright SnO2:Eu powder phosphor. The solubility limit of Eu into SnO2 was 0.05∼0.06 at.%, and smaller mean diameter, higher resistivity (order of 106Ω·cm) and more intensive diffused reflectance were observed with increasing Eu addition.Although the same emission spectra by f-f transition (5D0-7F1 main emission) were observed in UV, high and low-energy-electron excitation, the intrinsic emission from SnO2 matrix was different in each excitation method. The Optimum addition of 0.1 at.% Eu, 5.9msec decay (1/10), and the efficiency of 2lm/W at 9-10V were obtained at low-energy-electron excitation. Efficiency increased at lower voltage and current excitation due to sublinearities of brightness-voltage and current dependences.

ON THE CRANIAL MORPHOLOGY OF ICHTHYOSAURS

One of the difficulties in the study of ichthyosaurs has been the lack of ossification, said to be a common characteristic of aquatic groups. This difficulty has been partially removed by the discovery of a specimen of Ophthalmosaurus which is particularly well ossified, revealing clear facets which are not usually present. This specimen, together with well preserved skulls of Ichthyosaurus, Leptopterygius and Stenopterygius and many other isolated elements and fragments of Ichthyosaurus s.l. formed a basis for the interpretation of the ichthyosaur skull which, with literature of Triassic forms, has led to the recognition of a large number of ancestral ichthyosaurian features. The principal theories of the origin of ichthyosaurs have been examined in the light of this new evidence and shown to be untenable. In particular, von Huene's and Nielsen's theories of direct descent from amphibia are criticised and it is shown that Romer's suggestions of pelycosaur affinities of the ichthyosaurs are mistaken. The relationships of ichthyosaurs are then discussed in terms of the fuller knowledge of ichthyosaur anatomy and of recent literature on primitive reptiles and amphibia. Ichthyosaurs are shown to have common ancestry with chelonians and the ichthyosaur‐chelonian stock is considered to be derived from a more primitive stock evolving towards procolophonids or towards procolophonids and pareiasaurs. It is shown that otic conditions superficially similar to those of captorhinomorphs and pelycosaurs but which are, in fact, “sauropsid” may occur in several groups, including ichthyosaurs. The evolution of the temporal region is discussed and used to suggest that ichthyosaurs and chelonians had their origins in Deuterosaurus (Permian) times or later but probably not later than the close of the Permian.