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Doping ${\mathrm{V}}_{2}{\mathrm{O}}_{3}$ with Ti stabilizes the corundum paramagnetic metallic phase and restricts the transition to the monoclinic antiferromagnetic insulating phase at lower temperatures. In this study, we investigated the dependence of phase stability on Ti concentration for ${\mathrm{V}}_{2}{\mathrm{O}}_{3}$ nanocrystals as small as 20 nm. Ti doping of several percent induces a high-temperature insulating phase preserving the magnetic transition without the crystal symmetry change. The emergence of the insulating phases, which are peculiar to this crystal size, can be attributed to the enhancement of the on-site Coulomb interaction $U$ and increased mixing between ${a}_{1g}$ and ${e}_{g}^{\ensuremath{\pi}}$ states accompanied by characteristic lattice parameter changes in the high Ti doping region.

Nanocrystalline Ni can adopt a hexagonal close-packed (hcp) structure,which does not appear in a bulk form under any conditions.Structural studies found its $>$ 20% expansion of volume per atom compared with face-centered cubic (fcc) Ni.Hard x-ray photoemission spectroscopy of the hcp phase revealed a $>$ 0.14 valence electron transfer from 3$d$ to 4$s$ and 4$p$ orbitals and a 0.25 eV reduction in band energy per electron compared with the fcc phase.Its nonmagnetic nature was attributed to a low density of states at the Fermi level.Thermodynamic stability of the hcp phase can be explained by the band energy gain and the electrostatic potential energy loss as related to the large lattice expansion., 6 pages, 5 figures

ZnO nanocrystals (NCs) were synthesized by heating Zn (II) acetylacetonate in oleic acid/oleylamine in the presence of 1,2-hexadecanediol at 220°C. Transmission electron microscopy (TEM) and dynamic light scattering (DLS) measurements revealed the formation of monodispersed ZnO NCs of ca. 7nm. ZnO NC assembled films were fabricated on a glass substrate by deposition with the colloidal ZnO NCs dispersed in toluene. The film composed of the NCs showed good optical transparency in the visible to near-infrared region. A device coupling the ZnO NC film with a p-type Cu2ZnSnS4 (CZTS) NC film exhibited an obvious diode-like current–voltage behavior. The results suggest that the transparent ZnO film has a potentiality to be used for an n-type window layer in some optoelectronic applications.

Quaternary Cu2ZnSnS4 is a promising solar cell material because of its narrow band gap, high light absorption coefficient, and low cost. It is known that the composition of Cu2ZnSnS4 largely influences the solar cell performance. Here, to study the composition dependent properties of Cu2ZnSnS4 NCs as a solar cell material, we synthesized oleylamine-capped Cu2ZnSnS4 NCs with different compositions by a one-pot solution process, and fabricated solar cells with a ITO/ZnO/CdS/Cu2ZnSnS4/Au structure, and photoelectrochemical cells. A photovoltaic device using Cu2ZnSnS4 NCs with Cu/ (Zn + Sn)=0.87 showed the best performance among the devices tested. To improve the performance, the NC film fabrication processes were modified. We found that ligand stripping with BF3:OEt2 and the subsequent annealing at 250 °C in N2 improved the power conversion efficiency from 0.06 to 0.14 %, most likely due to efficient stripping of surface insulating organic layers. The photocurrent response of a photoelectrochemical cell using the Cu2ZnSnS4 NCs deposited on a ITO substrate was also improved by the modified NC film fabrication processes.

Colloidal suspensions of copper oxide (CuO) nanoparticles were prepared by an alcothermal method, in which copper acetate was reacted with sodium hydroxide in the presence of acetic acid in ethanol at 78°C. The prepared suspension was stable for up to 1 month without stabilizers such as surfactants. Transmission electron microscopy analyses revealed that the suspension contained nanosized CuO particles of 5–10 nm size with a narrow size distribution. Nanoparticulate CuO films packed with grains smaller than 60 nm were fabricated on Si substrates by spin coating a suspension of CuO nanoparticles and subsequent heat treatment at 500°C.

The p-type nanocrystals (NCs) of copper-based chalcogenides, such as CuInSe2 and Cu2ZnSnS4, have attracted increasing attention in photovoltaic applications due to their potential to produce cheap solution-processed solar cells. Herein, we report the synthesis of copper-antimony-sulfide (CAS) NCs with different crystal phases including CuSbS2, Cu3SbS4, and Cu12Sb4S13. In addition, their morphology, crystal phase, and optical properties were characterized using transmission electron microscopy, X-ray diffractometry, UV-vis-near-IR spectroscopy, and photoemission yield spectroscopy. The morphology, crystal phase, and electronic structure were significantly dependent on the chemical composition in the CAS system. Devices were fabricated using particulate films consisting of CAS NCs prepared by spin coating without a high-temperature treatment. The CAS NC-based devices exhibited a diode-like current-voltage characteristic when coupled with an n-type CdS layer. In particular, the CuSbS2 NC devices exhibited photovoltaic responses under simulated sunlight, demonstrating its applicability for use in solution-processed solar cells.

We have investigated spin-dependent transport through CoFe-contacted single- and multi-walled carbon nanotubes (SWNT and MWNT) with the contact separation of 200–300 nm. At low temperature, the devices exhibit very high magnetoresistance (MR) ratios, which reach to ∼1200% for the SWNT-based system and ∼150% for the MWNT-based system. In addition, the MR characteristics show coercivity enhancement or exchange bias, depending on the properties of contacts. Another MWNT device widely shows the MR oscillation overlapped on the hysteretic change near 0 T. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We study the electronic structure of NiO using resonant soft X-ray emission spectroscopy across the Ni L 2,3 thresholds. We observe inelastic (Raman) features within 10 eV of the elastic peak energ...

The hole-state and defect structure of proton conductor SrTi 1-x Sc x O 3 have been studied by high-resolution X-ray absorption spectroscopy. The proton-induced level is observed in proton-doped SrTi 1-x Sc x O 3 . The energy separation between the top of the valence band and the bottom of the acceptor or proton level is considered to be the activation energy determined by electronic or proton conductivity.

We propose a new method of photoluminescence (PL) measurements, that is, exciting core levels using synchrotron radiation. This method has been applied to characterize CdSe quantum dot (QD) structures in this study. PL spectra of the CdSe QD sample under Zn 2p core-level excitation are slightly different from conventional PL. PL core-level excitation (PLCLE) spectra have sharp Zn 2p3/2 and Zn 2p1/2 absorption edges and core-exciton peaks for CdSe QDs. Moreover, the PLCLE spectra reveal interfacial states between ZnSe barrier layers and CdSe QDs. This result indicates that PLCLE is useful as a local probe for the thin films and semiconductor nanostructures.

We introduce a photoluminescence inner core excitation (PLICE) for the studies of semiconductor quantum structures. This novel method, in which we use synchrotron radiation as tunable excitation source, is expected to facilitate us to obtain electronic and compositional information about buried quantum structures. Here we report experimental results on quantum dots (QDs) and quantum wires (QWRs), in order to demonstrate potential applicability of the method to the semiconductor nanostructure studies.

(2000). Characteristics of obstacle avoidance behavior in a linear cluster robotic system. Advanced Robotics: Vol. 14, No. 5, pp. 399-402.

Mn L 2,3 X-ray absorption spectra of various manganese compounds were measured using a synchrotron radiation facility. Very high-resolution spectra were obtained. Sharp lines, which were not found before, were observed, and reproducibility was checked using a different beam line in the synchrotron radiation facility. Difference in spectral line shape was observed as the difference of quantum yield method. An unknown sample was measured and the specimen was concluded to be a mixture of two different oxidation states of Mn. The effects on the change of spectral profiles are discussed.

We present a systematic investigation of the crystal and electronic structure and the magnetic properties above and below the metal-insulator transition of ball-milled VO$_2$ nanoparticles and VO$_2$ microparticles. For this research, we performed a Rietveld analysis of synchrotron radiation x-ray diffraction data, O $K$ x-ray absorption spectroscopy, V $L_3$ resonant inelastic x-ray scattering, and magnetic susceptibility measurements. This study reveals an unusual low-temperature phase that involves the formation of an elongated and less-tilted V-V pair, a narrowed energy gap, and an induced paramagnetic contribution from the nanoparticles. We show that the change in the crystal structure is consistent with the change in the electronic states around the Fermi level, which leads us to suggest that the Peierls mechanism contributes to the energy splitting of the $a_{1g}$ state. Furthermore, we find that the high-temperature rutile structure of the nanoparticles is almost identical to that of the microparticles., 7 pages, 8 figures, 2 tables

Most solids expand when they are heated, but a property known as negative thermal expansion has been observed in a number of materials, including the oxide ZrW2O8 (ref. 1) and the framework material ZnxCd1-x(CN)2 (refs 2,3). This unusual behaviour can be understood in terms of low-energy phonons, while the colossal values of both positive and negative thermal expansion recently observed in another framework material, Ag3[Co(CN)6], have been explained in terms of the geometric flexibility of its metal-cyanide-metal linkages. Thermal expansion can also be stopped in some magnetic transition metal alloys below their magnetic ordering temperature, a phenomenon known as the Invar effect, and the possibility of exploiting materials with tuneable positive or negative thermal expansion in industrial applications has led to intense interest in both the Invar effect and negative thermal expansion. Here we report the results of thermal expansion experiments on three magnetic nanocrystals-CuO, MnF2 and NiO-and find evidence for negative thermal expansion in both CuO and MnF2 below their magnetic ordering temperatures, but not in NiO. Larger particles of CuO and MnF2 also show prominent magnetostriction (that is, they change shape in response to an applied magnetic field), which results in significantly reduced thermal expansion below their magnetic ordering temperatures; this behaviour is not observed in NiO. We propose that the negative thermal expansion effect in CuO (which is four times larger than that observed in ZrW2O8) and MnF2 is a general property of nanoparticles in which there is strong coupling between magnetism and the crystal lattice.

A first-order phase transition in a bulk material is generally considered to arise at extended defects such as grain boundaries or dislocations, where the energetic barrier between the two phases is reduced. Downsizing a crystal to the nanoscale can exclude the number of defects, leading to enhanced kinetic stabilization of the metastable phase. Here, the disappearance of the first-order metal–insulator transition in defect-free V2O3 nanocrystals and the revival of the transition by introducing a certain Cr or Ti impurity content are investigated. The hysteresis width of the transition corresponding to the barrier height decreases with the impurity content. It is proposed that homogeneous impurity doping is a universal method that can control the occurrence of a first-order phase transition in nanoscale materials.

In this paper we realize a real-time communication on Ethernet and develop an onbody distributed control system for a humanoid robot, HRP-3P. Real-time communication on Ethernet is realized by (1) a communication method using the data link layer directly and (2) timing control using a real-time operating system ARTLinux. This enables us to reduce the cost of embedded systems and improve developmental efficiency. A CORBA implementation which works on this communication layer is also developed to increase compatibility with existing software. Finally a small-size distributed robot controller is developed for the onbody network of HRP-3P and a distributed I/O system is developed on top of this.

Quantum dots have been fabricated in an individual single-wall carbon nanotube, and their single electron transport has been measured at low temperatures with magnetic field up to 5T. The Coulomb diamonds have shown two and four electron periodicities in different gate voltage ranges. The results can be understood by the two- or four-electron shell filling model. In magnetic fields, the Zeeman splitting of single particle levels has been observed. This means that the single spin polarization is realized when an odd number of electrons are in the dot. The experimental observation suggests an important step for realization of the spin qubit.

We have studied spin‐dependent transport through a single‐wall carbon nanotube, contacted by two CoFe electrodes with a gap of about 300 nm. At 1.8 K, the junction exhibits extraordinarily high magnetoresistance ratio over 1000 %.

We have been developing prototypes of teleoperation systems via a standard protocol with a standard human interface, where VRML2.0 is employed as the protocol and a Web browser as the human interface. Using a Web browser, an operator can plan motions of objects interactively on a manipulation simulator with a world model which was sent from a remote site via VRML. The employment of a standard protocol and human interface enables our teleoperation system to be used by non-specialists from any Internet site, or by anyone from anywhere, without installing any specific software on the client side a priori.

We have obtained monodisperse (V1−xCrx)2O3 nanocrystals with crystal sizes of 21.0 ± 4.1 nm using organic-phase synthesis. The (V1−xCrx)2O3 nanocrystals clearly show the transition from a corundum structured paramagnetic metal to a monoclinic structured antiferromagnetic insulator in contrast to non-doped V2O3 nanocrystals, in which the disappearance of the metal-insulator transition has been observed. We have found that Cr doping works effectively in narrowing the a1g band, which tends to be broadened by nanocrystallization. This result suggests that chemical doping is useful for control of material phase transitions at the nanoscale.

A bulk-sensitive measurement is required in order to observe changes in the electronic states across metal–insulator transition (MIT). We have measured unoccupied and occupied electronic states for V 2 O 3 powder above and below the MIT by O K partial fluorescence yield (PFY) and soft x-ray emission spectroscopy (SXES) using a soft x-ray emission spectrometer. The PFY spectra for the metallic and insulating phases show an O K edge shift of ∼0.5 eV and a change in intensity near the edge. The SXES spectra excited by the incident photon energy near the O K threshold also show a spectral change above and below the MIT. This study shows that the soft x-ray spectrometer allows us to measure the bulk electronic states of powder samples where surface cleaning is difficult.

Electronic transport properties of weakly and strongly coupled carbon nanotube quantum dots are investigated using one device. After transition from a weakly coupled dot to a strongly coupled dot, both height increases and broadening of Coulomb peaks are observed due to increasing tunneling rate. From the measurements of Coulomb diamonds, twofold degeneracy is observed for a weakly coupled dot, and twofold and fourfold degeneracy is observed for a strongly coupled dot. The excitation lines due to the confined levels disappear after the transition to strong coupling.