Inter-surface diffusion in GaAs MBE on (111)-(001) and (111) B-(001) non-planar substrates was studied by μ-RHEED/SEM MBE. A local growth rate on the (001) surface was measured as a function of distance from a boundary between (111) and (001) surfaces employing the technique developed by Hata et al,. It was found that the diffusion length of Ga incorporation at the growth steps depends strongly on the arsenic pressure. On (111) A-(001) non-planar substrate, Ga diffuses always from (111) A to (001) surhces in the range of arsenic pressure employed in this experiment. On the other hand, the direction of Ga diffusion was changed on (111) B-(001) non-planar substrate depending on the arsenic pressure. When the arsenic pressure was high, Ga diffuses from (001) to (111) B surfaces while when it was low the direction of the diffusion was reversed. By solving the diffusion equation, an equation for the local growth rate was derived and the diffusion lengths on the (111) A and (111) B surfaces were calculated. It was found that the change of diffusion flow on (111) B-(001) surfaces is due to the different arsenic pressure dependence of Ga lifetime on (111) B and (001) surfaces. The reason for the long diffusion length as long as 1μm on non-planar substrate was discussed and it is suggested that the larger Ga surface flux than that of As_4 makes the incorporation efficiency of Ga at the step edge considerably low.
On the basis of our recent study of atom-sticking coefficients in molecular-beam epitaxy (MBE) of InGaAs pseudobinary alloy grown on GaAs substrate, dynamic atom-incorporation process in MBE is modeled in terms of "site-correlated adsorption probabilities". Under the homogeneous growth condition in which adsorption process is the rate determining one, atom-sticking coefficient can be described by using the site-correlated adsorption probabilities which reflect the local atomic configurations of adsorption sites. The presence of surface steps and surface atom migration have not been taken into account for the sake of simplicity. The adsorption probabilities are determined by intralayer interatomic interaction as well as interlayer interatomic interaction. Intralayer (in plane) interatomic interaction is considered to be anisotropic because of the presence of surface atomic dimer bonds. It has been found that atom-sticking coefficients in heteroepitaxial alloy semiconductor like InGaAs//GaAs(001) are well described by the present theory using site-correlated adsorption probabilities. Moreover, it has been found that the site-correlated adsorption processes cause the formation of atomic long-rage ordering in epitaxial alloy semiconductors.
The existing models of atomic layer epitaxy of GaAs using trimethylgallium that explain the self-limiting nature of the epitaxy are critically reviewed. The kinetic parameters especially the methyl radical desorption constant play critical roles in the three models; the adsorbate inhibition, the site-selective decomposition, and the flux balance models. It is shown that no single model can fully explain the wide range of the experimentally observed kinetic parameters. The direction to the unified model is discussed. The role of surface reconstruction is also discussed.
Two in situ monitoring methods are described for the growth of GaAs by halogen transport atomic layer epitaxy (ALE). First, a gravimetric method is proposed and applied to the GaAs growth. An ALE growth system with a microbalance is developed as a monitoring system. In the conventional method of measurement the growth rate of ALE is obtained as an average value, but the system can directly monitor the growth rate and the surface coverage in each cycle in actual ALE growth conditions. It is shown that the growth of the monomolecular layer unit occurs in each cycle in halogen transport GaAs ALE, and the gravimetric method makes in situ and real-time monitoring of growth rate possible on a submonolayer scale. Next, the epitaxial growth reaction that proceeds on the substrate surface during halogen transport ALE is observed directly with a surface photo-adsorption method (SPA). Based on the in situ gravimetric and optical monitorings, the reaction mechanism is discussed.
"In-situ" observation of deposition of Ag on graphite substrate was carried out by scanning electron microscope.The electron beam irradiation to the substrate befor and during the deposition enhances the nucleation of Ag. The density of the Ag crystallites for various substrate temperature was measured. Elevating the substrate temperature after the deposition at room temperature, the density of the Ag crystallites decreases. This mean that coalescence of the Ag crystallites on the substrate by their migration takes place.
Recent results on the growth of ultrafine particles due to the advanced gas evaporation method and characteristic of ultrafine particles are shown. An outline for the growth of ultrafine particles is first presented. A typical example of gas pressure effect is shown on the formation of Fe, FeO, and Fe_3O_4 particles due to evaporation of FeO powder. A new experimental method of produce oxide particle by using the heat of exothermic in gas flow is shown. The growth mechanism of tubular crystal showed the liquid state in the smoke. Oxidation and reduction process of Cu particle, and the growth process by using ultrafine particle and dilm are shown.
Nucleation induced by electric field is called the electrical nucleation. A history and a recent development of induction time for the electrical nucleation are reviewed from theoretical and experimental aspects. The induction time is one of information to compare a theory with experiments on nucleation. On the theoretical aspects, Kashchiev's theory is mainly reviewed, where a relation between electric field and free energy of a system is discussed and an equation for induction time depending on electric field is drived. On the experimental aspects, measurements of the induction time of the electrical nucleation are shown for a system of supercooled aqueous solution of a sodium acetate trihydrate. It is shown that the elctric field plays a role of a dryving force of nucleation. Some comparison of the theory with experiments are also shown.
When the pressure above 90 MPa was applied to H_2O melt, the (101^^-0) facets appeared in the periphery of (0001) flat face. The corner at which two faces intersect became sharp at 200 MPa but rounded below this value. In the mixture of H_2O and D_2O, facets appeared under atmospheric pressure. In this case, the molar ratio of H_2O to D_2O is dfferent in the melt and the crystal. The effect of pressure and mixing of two isotopes on the faceting was discussed by using tow-level model. As the introduction of present study, moreover, the relation among ΔH, T_m,ΔH/RT_m and the crystal shape was examined considering the bonding mode.
Vapor growth experiments of Mg-silicates (mainly forsterite) and its isotopic mass fractionation were reported. Vapor growth sequences at high ambient gas pressures (70 Pa He and 1.4 Pa H_2) can be explained by maximum fractionation sequences based on thermo-chemical calculations for solid-gas equilibria, while those at low pressures (1.4 Pa He and vacuum) deviate from the maximum fractionation sequences. Change in crystal morphology (euhedral to dendritic) in the experiments can be explained by nucleation delay and accompanied change in supercooling in vapor. Mg and Si isotopic mass fractionation takes place as a function of temperature, and this can be explained by Rayleigh fractionation model where solids fractionate isotopically toward the heavy mass with respect to the vapor phase. The mass fractionation is small at large ambient gas pressures (70 Pa He), while it is large at low ambient pressures (1.4 Pa He and H_2 and vacuum). The small fractionations took place near isotopic solid-gas equilibrium, while the large fractionations took place due to kinetic effect, and this is almost consistent with the vapor growth sequence-pressure relation (major elemental fractionation). Isotopic effect of crystal growth was discussed, and it is concluded that the kinetic effect on the isotopic mass fractionation in the experiments is considered to be caused by mass transportation (diffusion) processes in the vapor phase. In order to understand interface kinetics effect, isotopic sector zoning should be examined.
Recent studies on minute strain fields in as-grown silicon single crystals using synchrotron radiation are described. These have been performed by means of plane wave X-ray topography using highly collimated X-rays with an angular divergence of less than 0.01 arcsec, With this method, minute strain fields in float-zone-grown Si crystals containing A- Nd D-defects, and rapidly cooled Czochralski-grown Si crystals have been imaged. It is shown that minute strain fields in the Si crystals can be quantitatively determined from the analysis of contrast in the topographs.
Cd and Zn fine crystals were grown by VLS mechanism in a binary system such as Cd-Bi, Cd-Sn and Zn-Sn. The nucleation of them was homogeneous nucleation, which was explained by our consideration. Morphology of these crystals was pencil-shaped at a low temperature but was polyhedral at a high temperature. VLS whiskers also grew at a high temperature. The transition temperature was different between these systems. The liquid shape for VLS growth on the tip of a crystal changed from hemispherical (low-temperature type) to thin filmy (high-temperature type). At the same time, faceted to non-faceted transition occurred at the interface between the liquid and the crystal, which was explained by our roughening transition theory. The growth rate of the crystals increased with in-creasing growth temperature, but was almost independent of the temperature of the vapor source, which was explained by our hert transport theory. The VLS growth was ceased by incorporating the impurity such as Bi and Sn into the crystals. Both low- and high-temperature type morphologies changed to hexagonal prism by VS growth after the cessation of VLS growth. The surfaces of the crystals were smooth or striated (step surface), which depended on the binary systems. When these crystals were grown in helium atmosphere, cavities appeared on the smooth surface, but did not on the striated surface.
Recent studies on crystallographic structures of ice and clathrate hydrates are briefly reviewed. It is shown that precise structure analysis by single crystal X-ray diffractometry is a powerful tool to clarify the electron density distribution relating to the hydrogen bonding in ice I_h, and also the distribution of guest molecules encaged in the clathrate structure. Local ordering of proton arrangements in the disordered system of ice is discussed for better understanding of the diffuse scattering observed in ice I_h. In addition, very recent data of neutron spectroscopy and a new concept of different strength of hydrogen bonding introduced in order to interpret those data are briefly explained also.