The earliest colonisation of oceanic islands by Homo sapiens occurred ~50 000–30 000 years ago in the Western Pacific, yet how this was achieved remains a matter of debate. With a focus on East Asia, the research presented here tests the hypothesis that bamboo rafts were used for these early maritime migrations. The authors review the evidence for Palaeolithic seafaring in East Asia as the context for an experimental archaeology project to build two bamboo watercraft. Sea trials demonstrate the unsuitability of bamboo, at least in East Asia, indicating that more sophisticated and durable vessels would have been required to traverse the Kuroshio Current.

DNA-immobilized Fe3O4 particles (DNA–Fe-particles) were prepared by mixing DNA, magnetic Fe3O4 particles, and the silane coupling reagent, bis[3-(trimethoxysilyl)propyl]amine. The DNA–inorganic hybrid material was uniformly immobilized onto magnetic Fe3O4 particles with the diameters of approximately 450 nm. These DNA–Fe-particles were stable in water. Additionally, we could simply collect the DNA–Fe-particles by a magnet from an aqueous solution. Therefore, we demonstrated the accumulation of various metal ions, such as heavy and rare-earth metal ions, by the DNA–Fe-particles. As a result, although these DNA–Fe-particles could selectively accumulate heavy and rare-earth metal ions, these materials could not accumulate the light metal ions, such as Mg(II) and Ca(II) ions. Furthermore, the metal ion-accumulated DNA–Fe-particles could be recycled by washing them with an aqueous ethylenediaminetetraacetic acid solution.

We carried out theoretical calculation for Cu(In,Ga)Se2 (CIGS) solar cells with energy bandgap of 1.4 eV assuming formation of a Cu-poor layer on the surface of CIGS films. This calculation result revealed that formation of a thinner Cu-poor layer such as a few nanometers leads to improvement of the solar cells performance. This is because interfacial recombination was suppressed due to repelling holes from the interface by valence band offset (ΔEV). Next, we investigated composition distribution in the cross section of CIGS solar cells with Ga contents of 30% and 70% by transmission electron microscopy (TEM) and energy dispersive X-ray analysis (EDX). It was revealed that the Cu-poor layer was formed on the surface and at the grain boundary (GB) in the case of conversion efficiency (η) of 17.3%, although it was not formed in the case of lower η of 13.8% for a Ga content of 30%. These results indicate that formation of the Cu-poor layer contributed to improvement of cell performance by suppression of carrier recombination. Moreover, it was also confirmed that although the Cu-poor layer was observed on the surface, it was not observed at the GB in the case of CIGS solar cells with a Ga content of 70% which had η of 12.7%. It is thought that the effect of repelling holes by ΔEV is not obtained at the GB and the solar cell performance in the Ga content of 70% is lower than that in the Ga content of 30%. Thus, we suggest importance of the Cu-poor layer at the GB for high efficiency of CIGS solar cells with high Ga contents.

Al2O3 was deposited on silicon nanowire (SiNW) arrays by atomic layer deposition (ALD) as a passivation layer to reduce surface recombination velocity. As a result, effective minority carrier lifetime was improved from 1.82 to 26.2 μs. From this result, the relative low-surface recombination rate of 2.73 cm/s was obtained from a calculation using one-dimensional device simulation (PC1D). The performance of SiNW solar cells was also simulated by considering the surface recombination velocity on the side of SiNWs using two-dimensional device simulation. It was found that Al2O3 deposited by ALD can improve open-circuit voltage of SiNW solar cells even if the structure has a high-aspect ratio and large surface area. Therefore, improvement in the performance of SiNW solar cells can be expected.

The electrical characteristics of silicon nanowire (SiNW) solar cells with p-type hydrogenated amorphous silicon oxide (Eg=1.9 eV)/n-type SiNWs embedded in SiO2/n-type hydrogenated amorphous silicon (Eg=1.7 eV) structure have been investigated using a two-dimensional device simulator with taking the quantum size effects into account. The average bandgap of a SiNW embedded in SiO2 increased from 1.15 eV to 2.71 eV with decreasing the diameter from 10 nm to 1 nm due to the quantum size effect. It should be noted that under the sunlight with AM1.5G the open-circuit voltage (Voc) of SiNW solar cells also increased to 1.54 V with decreasing the diameter of the SiNWs to 1 nm. This result suggests that it is possible to enhance the Voc by the quantum size effect and a SiNW is a promising material for the all silicon tandem solar cells.

We prepared fine Cu(In,Ga)Se2 (CIGS) powder suitable for screen printing using a mechanochemical synthesis and wet bead milling. Particulate precursors were deposited in a layer by a screen-printing technique, and the porous precursor layer was sintered into a dense polycrystalline film by atmospheric-pressure firing in an N2 gas atmosphere. The microstructure of CIGS powder and fired CIGS film were observed in an SEM. The wet bead milling was effective for the reduction and homogenization of the average grain size of CIGS powder. The CIGS grains in the film were well sintered and the size of CIGS grains was as large as about 2 μm. The CIGS solar cell showed an efficiency of 3.1%, with Voc of 0.279 V, Jsc of 28.8 mA/cm2 and FF of 0.386.

We prepared size-controlled silicon quantum dots superlattices (Si-QDSLs) by thermal annealing of stoichiometric hydrogenated amorphous silicon carbide (a-SiC:H)/silicon rich hydrogenated amorphous silicon carbide (a-Si1+xC:H) multilayers for thin-film solar cell applications. Transmission electron microscope (TEM) observation revealed that the size of silicon quantum dots can be controlled by the thickness of the a-Si1+xC:H layers. It was found that hydrogen plasma treatment (HPT) significantly enhanced the photoluminescence (PL) of the Si-QDSLs. From the results of the PL measurement, the bandgap of the Si-QDSLs can be controlled from 1.1 eV to 1.6 eV by varying the diameter of silicon quantum dots. ESR measurement indicated that HPT reduced the defect density in a Si-QDSL from 1.83 ×1019 to 1.67 sup1018 cm-3.

ZnMgO was fabricated by MOCVD and the films were applied to a buffer layer of Cu(InGa)Se2 solar cells.

A nove growth method for Cu(InGa)Se2 was described in which cracked Se was utilized.

The temperature dependence of Si-based thin-film single junction solar cells on the phase of the intrinsic absorber is investigated in order to find the optimal absorber at high operating temperatures. For comparison, hydrogenated amorphous, protocrystalline, and microcrystalline silicon solar cells are fabricated by plasma-enhanced chemical vapor deposition and hot-wired CVD techniques. Photo J-V characteristics are measured using a solar simulator at the ambient temperature range of 25-85°C. It is found that the cells with a higher open-circuit voltage usually show lower temperature-dependent behaviors; the protocrystalline silicon solar cells provide the lowest temperature coefficient of efficiency, while the microcrystalline silicon solar cells are highly sensitive to the temperature. Therefore, protocrystalline silicon solar cells are promising for use in high temperature regions.

Effects of boron doping on microcrystalline germanium carbon alloy (μc-Ge1-xCx:H) thin films have been investigated. We deposited boron-doped p-type μc-Ge1-xCx:H thin films by hot-wire chemical vapor deposition technique using hydrogen diluted monomethylgermane (MMG) and diborane (B2H6). A dark conductivity of 1.3 S/cm and carrier concentration of 1.7 x 1020 cm-3 were achieved with B2H6/MMG ratio of 0.1. Furthermore, the activation energy decreased from 0.37 to 0.037 eV with increasing B2H6/MMG ratio from 0 to 0.1. We also fabricated p-type μc-Ge1-xCx:H/n-type c-Si heterojunction diodes. The diodes showed rectifying characteristics. The typical ideality factor and rectifying ratio were 1.4 and 3.7 x 103 at ¡Ó 0.5 V, respectively.

We deposited a-SiCN:H films by HWCVD using a gas mixture of hexamethyldisilazane, H2 and N2, and fabricated cast polycrystalline silicon solar cells with the a-SiCN:H passivation and anti-reflection layer. N2 addition led to the reduction of the refractive index of the a-SiCN:H films due to the increase in nitrogen concentration of the films. This improved performance of the antireflection layer. The advantage of adding N2 to the process was demonstrated by the improvement in short circuit current (JSC) and efficiency of cast polycrystalline silicon solar cells. At present, the efficiency of cast polycrystalline silicon solar cell using a-SiCN:H film as a passivation layer reached 14.2%.

We have investigated the thickness dependence of critical current for YBa2Cu3O7-x (YBCO) film with artificial pinning centers on metallic substrate. Artificial pinning centers were introduced by the pulsed laser deposition (PLD) using YBCO target including YSZ particles. The film over 1 μm in thickness exhibited with high critical current (Ic) of 40.7A in applied magnetic field of 3T parallel to the c-axis at 77K. This value was 5 times as high as the normal YBCO film without artificial pinning centers. The large Ic enabled us to approach to a practical application in the near future. Furthermore, it was clarified that the columnar nano-structure formed in the film, we call “the bamboo structure”, was a dominant pinning center because each Jc-θ curve of all thick films formed a universal line by the normalization of Jc. In addition, it was also found that YSZ addition has an optimal concentration for pinning by the study of YSZ concentration in the film.

We have investigated properties of nanocrystalline hydrogenated cubic silicon carbide (nc-3C-SiC:H) and silicon carbide: germanium alloy (nc-SiC:Ge:H) films deposited by hot-wire chemical vapor deposition (HWCVD) at low temperatures of about 300°C. we found that the density of charged defects was strongly influenced by grain size of the films. In-situ doping into nc-3C-SiC:H films was also carried out. N-type nc-3C-SiC:H films were successfully deposited by using phosphine (PH3) and hexamethyldisilazane (HMDS) as dopants. We found that HMDS is an effective n-type dopant for low temperature deposition of nc-3C-SiC:H films by HWCVD. For the deposition of p-type nc-3C-SiC:H with trimethylaluminum (TMA), it was found that the substrate temperature of above 300°C is required to activate the acceptors. We added dimethylgermane (DMG) into mixture of MMS and H2 to prepare nc-SiC:Ge:H films. The nc-SiC:Ge:H films with Ge mole fraction of 1.9% were successfully deposited.

Our multi-plume and multi-turn (MPT) pulsed-laser deposition (PLD) has been improved to accelerate reliable and fast deposition technique of high Ic (critical current) YBCO (YBa2Cu3O7-x) layer for a long coated conductor fabrication, for we increased the number of multi-turn, from three to four, in our multi-plume and multi-turn (MPT) PLD system. This increase of the number of depositing turns achieved high deposition rate corresponded to 75 mm3/h (=1 μm-thick × 10 mm-wide × 7.5 m/h, throughout all 4 turns) for YBCO layer. This four turn (4t)-MPT-PLD also indicated a capability to combine high deposition rate and high Ic. We attained the highest Ic's of 321 A at the tape speed of 3 m/h and 340 A at tape speed of 2 m/h by 4t-MPT-PLD in 10 mm-wide and 10 cm-long samples.

Based on these results, we successfully deposited a 100 m long YBCO layer by 4t-MPT-PLD. This coated conductor had high Ic as high as 159 A, therefore, the multiplication of Ic and length exhibited high value of 15.9 kA·m.

For further improvements in AlGaN/GaN heterojunction field-effect transistor performance (HFET), it is necessary to reduce the leakage current of the GaN buffer layer. We found a correlation between the leakage current and the intensity of the yellow luminescence of GaN layers taken by UV lamp excitation. The GaN layers were grown by metal organic chemical vapor deposition on SiC substrates. When the samples were excited by a UV (365 nm) lamp, visible yellow luminescence was observed. The leakage current of the GaN buffer layer was measured after deposition of ohmic metal contact. We confirmed clear correlation between the leakage current and the luminescence intensity based from result that the samples with the larger leakage current showed the stronger luminescence intensity. This correlation gives us useful information to understand the drain-source leakage current of AlGaN/GaN HFET.

Current-voltage (IV) measurements and capacitance-voltage (CV) measurements have been carried out to investigate electrical properties of AlGaN/GaN-HEMT structures. By CV measurements of Schottky barrier diodes (SBDs) with large leak currents, we observed a distinct peak in CV profiling at low frequencies. The integral of this peak was found to have a correlation with a leak current. The behavior of this peak might be described by the Shockley-Read-Hall (SRH) model if we assume this peak is due to a phenomenon of an electron emission and capture by deep levels. Then Quasi-Fermi Level (Imref) at the bias point where this peak appears in CV profiling corresponds to energy depth of deep levels. That energy level can be approximated by Imref of two-dimensional (2D) electron gas. The result of our samples showed that the energy depth of deep levels from the conduction band is distributed from 320meV to 470meV for Al mole fraction from 0.19 to 0.30, respectively.

We prepared REBa2Cu3O7- δ (RE= Gd, Sm, Dy, Er, Y) coated conductors on pulsed laser deposition (PLD) -CeO2/ion-beam assisted deposition (IBAD) – Gd2Zr2O7 (GZO) / metal tapes by the PLD method and measured the characteristics in magnetic fields. The GdBa2Cu3O7- σ (Gd-123) films showed superior characteristics than others in magnetic fields and showed weak anisotropy. Critical current density (Jc) value of the Gd-123 film was 3.87MA/cm2 at self-field and 0.19MA/cm2 at 3 T of perpendicular field to the tape surface in liquid nitrogen (77 K). Angular dependences in magnetic fields (Jc -Θ) of the Gd-123 and the SmBa2Cu3O7- σ (Sm-123) were superior to others and peaks in Jc -Θ were found also at 0 degree. The reduction ratios of Jc in Jc -Θ for the Gd-123 film and the Sm-123 film were smaller than other films. Transmission electron microscopy showed that the Gd-123 film had many stacking faults. It may be considered that this stacking faults naturally introduced by the PLD method contribute to improvement of anisotropy of Jc -Θ in the Gd-123 film.

Extended abstract of a paper presented at Microscopy and Microanalysis 2004 in Savannah, Georgia, USA, August 1–5, 2004.

Thin HfAlOx films grown on SiON(0.9 nm)/Si by atomic layer deposition technique were characterized by using monoenergetic positron beams. The lifetimes of positrons in the HfAlOx film after post-deposition annealing (PDA) ranged between 412–403 ps. Since these lifetimes were longer than the lifetime of positrons trapped by point defects in metal oxides, such as LaCoO3, PbTiO3, and BaTiO3, the positrons in HfAlOx films were considered to annihilate from the trapped state by open spaces which exist intrinsically in their amorphous structure. The line-shape parameter S of the Doppler broadening spectrum corresponding to the annihilation of positrons in HfAlOx films decreased by PDA, and the S value decreased with increasing an O2-content in an atmosphere during PDA (0.004–1%). The observed behavior of the S value was attributed to the shrinkage of the open spaces due to the change in the matrix structure of HfAlOx. After P+- and B+-implantation into poly-Si films grown on the HfAlOx films, the diffusion of positrons in the Si substrates toward the HfAlOx film was suppressed. This fact was attributed to positive charges introduced near the HfAlOx films.