Mami Kurumada

Structure and thickness of natural oxide layer on ultrafine particle

Ultrafine particles of various metals [Cr, Mn, Fe, Al, Ni, Cu, In, Si, Ge, Zn, Mg and Sn], produced by the gas evaporation method were covered with the oxide layer of thickness less than 10 nm by exposure to air. In order to clarify the structure and thickness of the surface oxide layer on various metal ultrafine particles, high-resolution electron microscopy and infrared spectroscopy have been extensively used.

Growth process of TiC clusters from Ti nanoparticles with evaporated carbon layer

Abstract Titanium carbide formation by the solid–solid reaction on the surface of Ti nanoparticles was studied in situ using a high-resolution transmission electron microscope with a heating stage. The cross-sectional image of the Ti surface was clearly observed. Vacuum-deposited carbon covered the whole the surface of Ti nanoparticles in spite of the partly evaporation on the nanoparticle surface. The diffusion of the carbon atoms inside the Ti nanoparticles depended on the size of the nanoparticles. When the Ti nanoparticle diameter was less than 30 nm, carbon atoms diffused into the Ti nanoparticle and formed TiC. The superstructure of the Ti nanoparticles was observed, which revealed the growth process of TiC to be the diffusion of carbon atoms. For Ti nanoparticles with diameter larger than 30 nm it was observed that diffusion of Ti atoms into the carbon layer was dominant, which resulted in formation of TiC in the carbon layer at the surface of Ti nanoparticles.

Laboratory production of magnesium sulfide grains and their characteristic infrared spectra due to shape

Nanosized MgS grains, which have been considered the origin of the 30 µm emission feature of carbon-rich evolved objects, were produced from the gas phase using an advanced gas evaporation method. The far-infrared spectrum of cubic MgS grains showed a characteristic absorption peak at 311 cm −1 (32.1 µm) with three shoulders at 460, 400 and 262 cm −1 (21.7, 25.0 and 38.2 µm). On the other hand, when the grains were roundish or network-like, the absorption peak at 250 cm −1 became predominant. The cubic MgS grains were produced by direct nucleation from the gas phase. In the case of production via a gas-solid reaction, the MgS grains were network-like. Therefore, the formation environments of MgS grains around carbon-rich evolved objects may be predicted from the intensity of 310 and 250 cm −1 bands. We suggest that the origins of the absorption band at 310 and 250 cm −1 are (100), (110) and/or (111) surfaces of MgS grains, respectively.

Phase transition temperature of γ-Fe2O3 ultrafine particle

The iron oxide ultrafine particles prepared by the gas evaporation method, in which commercial α-Fe 2 O 3 powder is evaporated, are composed of α-Fe 2 O 3 particles covered with a γ-Fe 2 O 3 mantle layer. To study the phase transition temperature of the γ-Fe 2 O 3 mantle layer, the particles were heated and observed in a transmission electron microscope. The present specimen of γ-Fe 2 O 3 transformed completely to α-Fe 2 O 3 at above 700°C, and this phase transition was irreversible. The phase transition temperature was 1.4 times higher than the bulk value. The growth mechanism of the present specimen of α-Fe 2 O 3 particles covered with the γ-Fe 2 O 3 mantle layer has been discussed in terms of the difference in the cooling rates between the inside and the surface of the particle at around the evaporation source.

Change in IR Spectra of Molybdenum Oxide Nanoparticles Due to Particles Size or Phase Change

Various molybdenum oxide particles such as MoO 3 , Mo 4 O 11 , Mo 4 O 11 (60M) were produced from vapor phase by controlling the total pressure of Ar–O 2 mixed gas or oxygen partial pressure. The c...

Dynamic process of crystallization of Sb2Se3 from Sb50Se50 amorphous film

Abstract Dynamics of crystallization of amorphous antimony-selenium film deposited on carbon substrate have been studied by the high-resolution transmission electron microscopy. The amorphous film was suddenly crystallized at 200°C by heating in vacuum. By the electron beam irradiation crystallization occurred at the focused electron beam region in the amorphous film. The growth process of crystallization by electron beam irradiation was recorded on a video image at the atomic resolution mode. The growth front of crystallization showed nano-concave and -convex shapes. The recrystallization with the different orientation at the first grown crystal have been found, and discussed as the influence of remaining antimony crystallites at the first crystallized film region.

Size Control and Characteristic Growth of CdS and CdTe Ultrafine Particles in Electric Field

By applying an electric field just above the evaporation source of CdS and CdTe, the smoke produced in Ar gas at 10 kPa curved towards the negative plate. The size of collected particles became smaller by about 30% than that of particles without the electric field. The dispersion of particles became good. By applying the electric field, multiply twinned particle growth occurred on these polarity crystals.

Pentagonal Configuration in GaP Ultrafine Particle

Phosphorous-based III–V compound semiconductors are an essential component in the optoelectronics industry. Gallium phosphide (GaP) is also one of the basic materials of light emission upon doping with ZnO or nitrogen. GaP is a nearly ideal material for investigating the salient features of the heteroepitaxy of group III–V materials on silicon, because the mismatch is relatively small. A number of studies indicate that GaP growth nucleates in the form of islands. Particles with the icosahedral configuration exhibiting polarity, such as II–VI and III–V crystals, are rarely produced because of mismatch of the antiphase boundary. The growth of icosahedra and decahedra of FCC metals was studied in detail by Ogawa and Ino in the initial stage of film growth. They were composed of multiply twinned particles. Among smoke particles of FCC metals, pentagonal decahedra of perfect symmetry are found. In the growth of II–VI compounds, the tetrapod crystal was produced. The multiply twinned particles were only observed on the FCC basic structure. GaP ultrafine particles were prepared by evaporating GaP powder (99.999%) from a V-shaped tungsten boat heated at 1200 C in Ar gas at 10 kPa. Typical GaP particles and corresponding electron diffraction patterns are shown in Fig. 1. The particles were composed of spheres and rods. As was elucidated in a previous study, the round (complicated polyhedron) particles indicated by arrows A had the zinc-blende structure with a truncated octahedral shape. The rod particles indicated by arrows B comprised wurtzite particles with the ð0001Þ surface and zinc-blende particles with the ð110Þ surface. The zinc-blende particles with the ð110Þ surfaces sometimes contained growth faults, which is evidence of coalescence growth. The electron diffraction patterns can be indexed as a mixture of both structures of GaP. The spindle-shaped particles, as indicated by arrows C in Fig. 1(a), were often produced. Similar particles were also seen in a previous study. A HRTEM image of a spindleshaped particle is shown in Fig. 2. The particle was multiply twinned and composed of 5 crystals, i.e., it had the pentagonal decahedral configuration of GaP. The lattice image corresponds to a projection along the 1⁄2110 direction. Therefore two {111g planes with the crossed angle of 70 can be seen for A, B, C, D and E crystals. Therefore all 5 crystals had the zinc-blende structure. A and E crystals contained growth faults, as described in a previous paper. Figure 3 shows a model of the zinc-blende crystal viewed along the 1⁄2110 direction. Black and white spheres represent Ga and P atoms, respectively. In the HRTEM

Correlations between Crystallite Size, Shape, Surface, and Infrared Spectra Using the Ti-C System

TiC crystallites less than 10 nm in size showed an absorption feature at 14.3 μm. This 14.3 μm absorption was rarely seen in specimens ranging from bulk material to grains of 50 nm in size. The 14.3 μm feature was weakened as a result of the growth of TiC crystallites by heat treatment. When the carbide grains were covered with a carbon layer, the absorption peaks were considerably weakened, i.e., the absorption intensity depended on the grain surface state. A possible explanation is that the effects of size and shape on the spectra depend on the surface anisotropy.

Direct observation of the formation of alumina phase by metallic Al solid-SiO2 solid reaction

The formation of Al2O3 phases by the solid-solid reaction of a metallic Al layer evaporated on a SiO2 amorphous grain has been induced by heating above 600°C in vacuum (1×10−6 Pa). The distortion process of the amorphous SiO2 grains by the formation of Al2O3 have been directly imaged by in-situ TEM observation. A partly deposited Al layer covered the SiO2 grains after heating at 750?C, and ψ -Al2O3 grains of about 25 nm diameters were formed on the SiO2 surface. Upon the growth of Al2O3, the SiO2 grain decomposed into a mixture of metallic Si and SiO2 and disappeared as a result of sublimation due to the formation of SiOx at high temperatures. The present result on dust surface dynamics will become an important field with respect to the metamorphism of grains from the astromineralogical viewpoint.