During two winter seasons, we observed avalanche winds and the air movement in the snow dust region. The wind velocity near the avalanche front was comparable to the averaged internal velocity of the front region. The avalanche wind blew down the valley. However, there was a rising air current just before the avalanche front. The wind velocity and direction showed a periodic change in the snow cloud region, from which the size of the ordered structure (vortex) was estimated to be 35–70 m. The density of the frontal part of one avalanche was estimated to be 1.9–3.8 kg m−3.

In 1987 an ice core to the bedrock at a depth of 85.6 m was drilled at the top of Høghetta ice dome in northern Spitsbergen. Chronology of the ice core was examined by tritium and 14C methods showing time gap at about 50 m depth. The age of three bottom ice samples was determined as 4150–5670 year B.P. by 14C method done for frozen bacteria colonies and a frozen petal. This chronology and negative bottom temperature of −9.4°C suggest that glaciers in Spitsbergen shrank considerably during the hypsithermal. The pH of melt-water samples lower than 5.0 corresponds well to large northern hemispheric volcanic eruptions during the last 300 years. Increase of acidity from 30 m depth to the surface may reflect the spread of air pollution to the Arctic during the past 200 years. On the basis of ice-core analyses on electrical conductivity, pH, chemical composition and air bubble pattern, climate and environment in Spitsbergen during the last 6000 years are discussed.

In 1986, a large avalanche destroyed 11 houses and killed 13 people at Maseguchi, Japan. Previous attempts to model the avalanche were based on the assumption that it was a powder avalanche consisting of snow particles suspended by air turbulence. In this paper, the avalanche is modelled as a dry flowing avalanche with a dense core of flowing material at the base. It is suggested that for a comprehensive explanation of the observed damage and the characteristics of the avalanche deposit, the assumption that the avalanche was a flowing avalanche is more appropriate. The comparison of model results from a flowing versus a powder avalanche is of general interest for avalanche zoning and design of structures in avalanche-threatened areas.

Over 30 funerary bundles were excavated in 2005 from a large chamber tomb at the prehispanic religious center of Pachacamac on the central coast of Peru. The largest and most elaborate bundle was found in the innermost part of the tomb, tightly surrounded by other bundles. We hypothesized that this bundle contained the deceased leader of a social group whose members collectively cared for their ancestor's bundle (for example, by rewrapping it) and continued to use the tomb to inter deceased individuals from subsequent generations. We tested this hypothesis by dating samples from different layers of the wrapping materials and soft tissue from the bodies and conducting a Bayesian analysis of the resultant dates. We determined carbon and nitrogen isotope ratios in the diet of the interred individuals to correct for marine reservoir effects. Our findings suggest that (1) rewrapping did not occur; (2) the tomb was used for over 500 years starting at cal A.D. 1000; and (3) existing bundles were reshuffled each time new bundles were introduced. Overall, diverse lines of evidence indicate that the tomb had a complex use history and contained individuals with diverse geographical and social origins. This challenges conventional thinking about the social and chronological significance of coexisting bundles in large tombs.

Microstructure evolution of YBa2Cu3O7−y (YBCO) films during the two heat-treatments in the advanced trifluoroacetates metalorganic deposition (TFA-MOD) process has been investigated by means of transmission electron microscopy. In the calcination process, precursor films including nanopores were formed through the shrinkage of the film after a remarkable increase of the thickness due to the thermal decomposition of metalorganic salts in the starting solution. During the crystallization process, the densification and shrinkage of the film occurred after agglomeration of nanopores and coarsening of unreacted phase particles such as Y2Cu2O5, CuO, and Ba–O–F in the precursor films. The YBCO films were then epitaxially grown with the remaining unreacted phase particles in the film, finally pores were generated again by a reaction of these unreacted particles to form YBCO accompanied by the volume reduction. It is important to control the densification of precursor films and coarsening of the unreacted phase particles in the crystallization process, to fabricate YBCO final films with fine crystallinity and high critical current values.

Extended abstract of a paper presented at Microscopy and Microanalysis 2006 in Chicago, Illinois, USA, July 30 – August 3, 2006

Separation by implemented oxygen (SIMOX)(111) substrates have been formed by oxygen-ion (16O+) implantation into Si(111), showing that a so-called “dose-window” at 16O+-implantation into Si differs from Si(100) to Si(111). In SIMOX(100), an oxygen dose of 4 × 1017/cm2 into Si(100) is widely recognized as the dose-window when the acceleration energy is 180 keV. For the first time, our work shows that an oxygen dose of 5 × 1017/cm2 into Si(111) is the dose-window for the formation of SIMOX(111) substrates when the acceleration energy is 180 keV. The difference between dose-windows is caused by anisotropy of the crystal orientation during growth of the faceted buried SiO2. We also numerically analyzed the data at different oxidation velocities for each facet of the polyhedral SiO2 islands. Numerical analysis results show good agreement with the experimental data.

Interfacial structures of c-axis-oriented YBa2Cu3O7–y (Y123) and Nd1+xBa2–xCu3O7–y (Nd123) films were investigated by high-resolution transmission electron microscopy (HRTEM) in conjunction with geometrical lattice matching and molecular orbital calculations. These films were formed on MgO(001) substrates by liquid-phase epitaxy. Despite the similarity in lattice constants between Y123 and Nd123, the in-plane orientation relationship (OR) to the substrates is different: [100]film//[100]substrate(I) for Y123 and [110]film//[100]substrate(II) for Nd123. From the results of HRTEM observations and image simulations, it was found that the Y123 and Nd123 films are terminated by BaO and CuO-chain layers at the interfaces, respectively. For both the Y123/MgO and Nd123/MgO systems, the OR(I) is assessed to be the most favorable in point of geometrical matching and the OR(II) is the second among the rotational misorientations on the [001]film and [001]MgO. The molecular orbital calculations reveal that the interface with the OR(II) and the CuO-chain layer termination is preferable in terms of covalent bonding for both the systems. Consequently, we suggest that the preferential interfacial structures are delicately determined by a balance of the geometrical and chemical factors at the interfaces, resulting in making the lowest interfacial free energies.

We have investigated direct current (DC) operating voltage and luminescence properties of electroluminescent (EL) devices with and/or without a silicon dioxide (SiO2) layer in nanocrystalline Si (nc-Si) region/Si substrate interface. The device with the SiO2 layer showed red luminescence with a peak at 670 nm by applying the DC operating voltage above 4.0 V. When the SiO2 layer in the device was completely removed by the hydrofluoric acid (HF) treatment, the red luminescence from the device was observed at the DC operating voltage of 2.0 V. Moreover, the luminescent intensity was also increased more than one order of magnitude, because carriers were efficiently and easily injected into the nc-Si region by the removal of SiO2 layer. The red luminescence from the device could be clearly seen with the naked eye under the DC operating voltage above 3.0 V. These results indicate that the removal of SiO2 layer leads to the lowering of DC operating voltage and increase of luminance for the nc-Si based EL device.

Growth technique for thick SiC epilayers with a reduced micropipe density has been developed in a vertical hot-wall CVD reactor. Micropipe closing by growing an epilayer is possible with a nearly 100% probability for 4H-SiC substrates oriented (0001) and (000-1) off-cut towards either [11-20] or [1-100]. By applying the micropipe closing technique, a high-performance Schottky barrier diode (SBD) was demonstrated on a substrate including micropipes. Growth of low-doped and thick SiC epilayers is also possible with a good morphology at a high growth rate, and 14.4 kV blocking performance was demonstrated using a 210 μm-thick epilayer. Epitaxial growth on (000-1) substrates with low doping and a low epi-induced defect density was also demonstrated. Deep centers and impurities were investigated to determine the effective lifetime killer of the epilayers. Dislocations and stacking faults in epilayers grown on 4H-SiC substrates off-cut towards different directions were also investigated.

This paper reports about the interface of silicon nitride (SiNx) formed on Si(100) prepared by combination of catalytic-nitridation and catalytic-vapor deposition method in a catalytic chemical vapor deposition system. It is found that flat interface of SiNx/Si(100) is formed by inserting nitridation layer before growing the SiNx films.

We fabricated the multi-color electroluminescent (EL) device using hydrofluoric (HF) acid solution treated and oxidized silicon (Si) nanoparticles. Strong red luminescence was obtained from the HF treated Si nanoparticles based EL device under a low forward bias of 4.0 V. On the other hand, green and blue luminescence, which could be seen with naked eye under room illumination, was observed for the oxidized Si nanoparitcles based EL device at the forward bias below 9.5 V, because of reduction of size due to oxidation onto the Si nanoparticle surface. Furthermore, the red/green/blue lights showed good stability for aging of a long period of time in air by the formation of oxidized layer on the surface. These results indicate that the EL devices developed in this study can realize as application to future flat panel display.

NdBa2Cu3O7-x (NdBCO) superconducting films were successfully grown on MgO substrates by liquid-phase epitaxy (LPE) using YBa2Cu3O7-x (YBCO) seed films which have lower peritectic temperatures. Microstructural characterizations using optical and electron microscopes revealed that most of the seed grains decomposed at the high processing temperature and dissolved when they touched the solution. The NdBCO grains were formed first by the quasi-homoepitaxial growth of NdBCO units on the few surviving YBCO seed grains and then grew pendently to cover the large bare surface areas of the MgO substrates quickly by lateral overgrowth. A micrometer-thick melt layer was entrapped between the film and the substrate. Through the few links provided by the surviving seed grains, a stable film/substrate orientation relationship could still be maintained. A semiquantitative analysis was done for the lateral overgrowth process, and two different lateral overgrowth stages were observed with about 50 times difference in the lateral overgrowth rate. Then, a semiquantitative understanding for the entire YBCO-seeded NdBCO LPE growth process was finally reached.

Non-steady-state solidification of YBa2Cu3O6+δ (Y-123) superconducting oxides was observed by the isothermal undercooling experiment. A sudden decrease in crystal growth rate was found for all the Y-123 samples processed at the different temperatures and from the different Y2BaCuO5 (Y-211) contents in the initial composition. Quantitative analysis revealed that the Y-211 particles are pushed by the Y-123 crystal and accumulate in the liquid during solidification. It is also found that the particle volume fraction increased and reached a constant value of about 0.6, when the growth rate decreased abruptly, regardless of a variety of growth conditions. A simple solidification model is developed to interpret the experimental observation. This model shows that particle accumulation, as a result of the particle-pushing behavior, causes less connectivity of the liquid and thereby decreases the liquid diffusion flux, which is responsible for the non-steady-state solidification of Y-123.

Growth of very thick 4H-SiC epilayers up to 215 μm has been demonstrated in a vertical radiant-heating reactor. Surface roughness is maintained as small as ˜0.2 nm even for epilayers over 150 μm in thickness, and a regular step structure without macro step bunching is observed from the very thick epilayers indicating a stable step-flow growth. Photoluminescence and secondary ion mass spectroscopy (SIMS) were performed for a 150 μm-thick epilayer. The Photoluminescence showed strong free excitons and comparatively small nitrogen bound excitons, while aluminum-, boron- and titanium-related lines were almost negligible. The SIMS analysis found no impurities exceeding 1 × 1014 cm−3. The influence of growth parameters on thickness uniformity will also be shown.

Growth of YBa2Cu3Oy (YBCO) crystals both on the MgO and the YBCO substrates has been investigated in order to clarify the growth mechanism of the liquid phase epitaxy (LPE) process for the coated conductor. It was found that the slope angle of the growth grain varied with growing in the initial stage of the LPE growth. In the case of the MgO substrate, the slope angle increased with laterally growing the crystal. On the other hand, the slope angle decreased with growing the crystal in the case of the YBCO substrate. This phenomenon with the opposite tendency could be explained by considering the difference in the step-advancing rates between on the MgO and the YBCO surfaces. It was found that the deep and steep valley of the LPE grains due to the slow step-advancing rate on the MgO is the origin of the flux trapping inclusions. It is necessary that the seed films should cover the entire MgO surface without undesired orientation grains and impurity particles in order to obtain the high quality LPE layer.

We have fabricated the electroluminescence (EL) device using silicon (Si) nanocrystals, which were formed on Si substrate by co-sputtering of Si and silicon dioxide (SiO2). By treating with the Si nanocrystals in the hydrofluoric (HF) acid solution, the SiO2 region of the luminous layer reduced, and then, the electrons were efficiently injected in the Si nanocrystals. At the same time, Pb-center (non-radiative recombination center) was decreased by hydrogen termination to the Si-dangling bond in the interface between the Si nanocrystals and the SiO2 layer From these effects of the HF treatment, the high efficiency red light emission with the external quantum efficiency (EQE) of 0.35 % was obtained from the HF treated EL device under the operating voltage of +4.5 V.

Correlation between defect structures and light emission from Si-nanocrystal doped SiO2 films has been studied using electron spin resonance ( ESR ) and photoluminescence ( PL ) methods. The ESR analysis revealed the presence of three kinds of ESR centers in the film after annealing at above 900 °C in argon ( Ar ) atmosphere, i.e. Si dangling bond in amorphous Si cluster ( a-center: g=2.006 ), Si dangling bond at Si-nanocrystal/SiO2 interface ( Pb-center: g=2.003 ) and conduction electrons in Si-nanocrystal ( Pce-center: g=1.998 ). Moreover, visible light emission was observed in the annealed sample from the PL measurement. Both the PL intensity and the ESR signal intensity of the Pce-center were increased with an increase of annealing temperature. These results indicate that the Pce-center is strongly associated with the emission center.

We have investigated radiation hardening in alumina (A1203), stoichiometric and nonstoichiometric spinel (MgO·nA1203: n= 1, 2.4) crystals at 300 K irradiated with 100 keV He+ ions by using a ultra-microhardness technique. Al203 shows a remarkable radiation hardening (35% increase in hardness) at a fluence of 5×1019 He+/m2 and saturates at 60 % of the maximum value at fluences higher than 8×1019 He+/m2. In spinel crystals, hardness increases monotonically with fluence, reaching to a saturation at a fluence of 1×1020He+/m2. Analyses of load- displacement curves indicate that both plastic and elastic hardening are responsible for the radiation hardening in A1203, and that plastic hardening is the main cause in MgO'nAl2O3. Microstructure observations and lattice constant measurements showed that point defects are mainly responsible for the radiation hardening in both A1203 and MgO·nAl2O3. The difference in the radiation hardening response is discussed in terms of the difference in recombination rate of point defects among the MgO-A1203 system ceramics.