1 0 0 0 OA Cu-dependent phase transition in polycrystalline CuGaSe2 thin films grown by three-stage process
- 著者
- Islam M. M. Yamada A. Sakurai T. Kubota M. Ishizuka S. Matsubara K. Niki S. Akimoto K.
- 出版者
- American Institute of Physics
- 雑誌
- Journal of applied physics (ISSN:00218979)
- 巻号頁・発行日
- vol.110, no.1, pp.014903, 2011
- 被引用文献数
- 8 6
The Cu-dependent phase transition in polycrystalline CuGaSe2 thin films has been studied by an electron probe micro-analyzer (EPMA) and the synchrotron x-ray diffraction method. A Cu-deficiency parameter, Z, defined as (1 − Cu/Ga) was used to study the phase transition. Upon increasing the Z-value, the composition of the films on the Cu2Se-Ga2Se3 pseudo binary tie line was found to shift from the stoichiometric CuGaSe2 (1:1:2) (Z = 0) to the Ga-rich composition through the formation of several ordered defect compounds.The structural modification in the Cu-poor CuGaSe2 film has been investigated by the synchrotron x-ray diffraction method. The existence of the Cu-poor surface phase over the near-stoichiometric bulk CuGaSe2 film was confirmed by the fitting of the accelerated voltage dependent EPMA data.
- 著者
- Yanagihara H. Uwabo K. Minagawa M. Kita Eiji Hirota Noriyuki
- 出版者
- American Institute of Physics
- 雑誌
- Journal of applied physics (ISSN:00218979)
- 巻号頁・発行日
- vol.109, no.7, pp.07C122, 2011-04
- 被引用文献数
- 57 16
We report on the magnetic properties of epitaxial cobalt-ferrite films with orientations parallel to [001] and [111] grown by a reactive molecular beam epitaxy method using pure ozone gas as an oxidation agent. Both Mössbauer spectroscopy and magnetization measurement of the CoFe2O4(001) film grown on MgO(001) indicate that the film has perpendicular magnetic anisotropy (PMA) with high coercivity, whereas the film of CoFe2O4(111) grown on α-Al2O3(0001) appears to be paramagnetic. The maximum uniaxial anisotropy energy for CoFe2O4(001) estimated from the magnetization and coercivity at room temperature is ≈ 3×106 erg/cm3.
- 著者
- Fukuda Junji Nakazawa Kohji
- 出版者
- American Institute of Physics
- 雑誌
- Biomicrofluidics (ISSN:19321058)
- 巻号頁・発行日
- vol.5, no.2, pp.022205, 2011-06
- 被引用文献数
- 41
Spheroid culture is a preferable cell culture approach for some cell types, including hepatocytes, as this type of culture often allows maintenance of organ-specific functions. In this study, we describe a spheroid microarray chip (SM chip) that allows stable immobilization of hepatocyte spheroids in microwells and that can be used to evaluate drug metabolism with high efficiency. The SM chip consists of 300-μm-diameter cylindrical wells with chemically modified bottom faces that form a 100-μm-diameter cell adhesion region surrounded by a nonadhesion region. Primary hepatocytes seeded onto this chip spontaneously formed spheroids of uniform diameter on the cell adhesion region in each microwell and these could be used for cytochrome P-450 fluorescence assays. A row of microwells could also be connected to a microchannel for simultaneous detection of different cytochrome P-450 enzyme activities on a single chip. The miniaturized features of this SM chip reduce the numbers of cells and the amounts of reagents required for assays. The detection of four cytochrome P-450 enzyme activities was demonstrated following induction by 3-methylcholantlene, with a sensitivity significantly higher than that in conventional monolayer culture. This microfabricated chip could therefore serve as a novel culture platform for various cell-based assays, including those used in drug screening, basic biological studies, and tissue engineering applications.
1 0 0 0 OA Origin of the n-type transport behavior of azafullerene encapsulated single-walled carbon nanotubes
- 著者
- Cuong Nguyen Thanh Otani Minoru Iizumi Yoko Okazaki Toshiya Rotas Georgios Tagmatarchis Nikos Li Yongfeng Kaneko Toshiro Hatakeyama Rikizo Okada Susumu
- 出版者
- American Institute of Physics
- 雑誌
- Applied physics letters (ISSN:00036951)
- 巻号頁・発行日
- vol.99, no.5, pp.053105, 2011-08
- 被引用文献数
- 4 4
The transport properties of C59N encapsulated semiconducting single-walled carbon nanotubes (SWCNTs) (C59N-peapod) are investigated. Transport measurements of the peapods in field effect transistors (FETs) reveal that ∼14% of the C59N-peapod sample shows n-type behavior even though the electronic properties of the host SWCNTs are similar to those of C60-peapods that exhibit only p-type property. First-principles electronic-structure calculations reveal that the unique transport behavior originates from the monomer form of C59N encapsulated in SWCNTs. The singly occupied (SO) state of C59N lies in the energy gap of the SWCNT and the energy of this state increases substantially when electrons are injected. Because of this shift to higher energy, the SO state acts as a shallow donor state for the conduction band of the nanotube, which leads to n-type behavior in FET measurements.
- 著者
- Sato Soshi Li Wei Kakushima Kuniyuki Ohmori Kenji Natori Kenji Yamada Keisaku Iwai Hiroshi
- 出版者
- American Institute of Physics
- 雑誌
- Applied physics letters (ISSN:00036951)
- 巻号頁・発行日
- vol.98, no.23, pp.233506, 2011-06
- 被引用文献数
- 9
Interfacial states of silicon nanowire field-effect transistors with rectangular-like cross-sections (wire height of 10 nm and widths of 9 and 18 nm) have been evaluated from the transfer characteristics in the subthreshold region measured at cryogenic temperatures, where kinks in the drain current becomes prominent. It is found that the kinks can be well-explained assuming local interfacial states near the conduction band (Ec). The main extracted local states have been shown to exist at 10 and 31 meV below Ec with the densities of 1.3×1013 cm−2/eV and 5.4×1012 cm−2/eV, respectively. By comparing two field-effect transistors with different wire widths, the former states can be assigned to the states located at the corner and the side surface of the wire, and the latter to the top and the bottom surfaces.
- 著者
- Masumoto Yasuaki Hirata Yuuki Mohan Premila Motohisa Junichi Fukui Takashi
- 出版者
- American Institute of Physics
- 雑誌
- Applied physics letters (ISSN:00036951)
- 巻号頁・発行日
- vol.98, no.21, pp.211902, 2011-05
- 被引用文献数
- 9
The photoluminescence from single InP/InAs/InP core-multishell nanowires (CMNs) was highly linearly polarized in perpendicular to the nanowire long axis. Taking account of dielectric confinement of light field, we found the internal optical dipole squared perpendicular to the nanotube long axis d0x2 is larger than that parallel to the axis d0z2 by two orders of magnitude. With the increase in the thickness of InAs nanotubes, the ratio β = d0x2/d0z2 increases. This strong anisotropy in β comes from nearly perfect wurtzite structure of InP/InAs/InP CMNs and small inclusion of pz-character into the Γ7(B)-hole state.
- 著者
- Masumoto Yasuaki Yoshida Seitaro Ikezawa Michio Tomimoto Shinichi Sakuma Yoshiki
- 出版者
- American Institute of Physics
- 雑誌
- Applied physics letters (ISSN:00036951)
- 巻号頁・発行日
- vol.98, no.6, pp.061905, 2011-02
- 被引用文献数
- 5 4
We observed that the biexciton binding energy in InAs quantum rhombic disks (QRDs) is enhanced by twice compared with that for InAs quantum dots (QDs) so far reported around 1.24 μm nearby the telecommunication wavelength. The heterodyne-detected four-wave-mixing detected the exciton-biexciton quantum beat superposed on photon echo decay, giving the biexciton binding energy of 3.4 meV to 3 monolayer (ML) InAs QRDs and 4.1 meV to 4 ML InAs QRDs, respectively. The largest biexciton binding energy of 4.1 meV in InAs QDs is ascribed to increased electron-hole overlap in confined geometry with a minimized strain distribution.
- 著者
- Konabe Satoru Okada Susumu
- 出版者
- American Institute of Physics
- 雑誌
- Applied physics letters (ISSN:00036951)
- 巻号頁・発行日
- vol.98, no.7, pp.073109, 2011-02
- 被引用文献数
- 4
We propose a method for optically probing the magnetic states of metallic atoms encapsulated in single-walled carbon nanotubes. The absorption spectrum is calculated by solving the Bethe–Salpeter equation, which includes the effects of magnetic atoms, under the tight-binding approximation. Due to the exchange interaction between excitons and polarized spins in ferromagnets, triplet excitons acquire a finite oscillator strength and can thus be excited by light. This mechanism is promising for detecting magnetic ordering of materials encapsulated in carbon nanotubes.
- 著者
- Sawaki D. Kobayashi W. Moritomo Y. Terasaki I.
- 出版者
- American Institute of Physics
- 雑誌
- Applied physics letters (ISSN:00036951)
- 巻号頁・発行日
- vol.98, no.8, pp.081915, 2011-02
- 被引用文献数
- 104 26
We investigate thermal rectification in a bulk material with a pyramid shape to elucidate shape dependence of the thermal rectification, and find that rectifying coefficient R is 1.35 for this shape, which is smaller than R = 1.43 for a rectangular shape. This result is fully duplicated by our numerical calculation based on Fourier’s law. We also apply this calculation to a given shape, and show a possible way to increase R depending on the shape.
- 著者
- Ohta Ryu Zushi Junta Ariizumi Takuma Kojima Seiji
- 出版者
- American Institute of Physics
- 雑誌
- Applied physics letters (ISSN:00036951)
- 巻号頁・発行日
- vol.98, no.9, pp.092909, 2011-02
- 被引用文献数
- 36
The precursor dynamics of a cubic–tetragonal ferroelectric phase transition of potassium tantalate niobate (KTa1−xNbxO3 with x = 0.32) crystals is studied by Brillouin scattering. The appearance of the central peak (CP) and marked softening of the elastic constant c11 are clearly observed above the Curie temperature, TC–T, owing to the interaction between the LA mode and local polarization fluctuations of polar nanoregions (PNRs). The relaxation time determined by the CP width clearly shows a critical slowing down above TC–T, indicating an order–disorder feature of the ferroelectric phase transition. The size of a dynamic PNR is evaluated, and it increases toward TC–T.
1 0 0 0 OA Thermal conductivity of GeTe/Sb2Te3 superlattices measured by coherent phonon spectroscopy
- 著者
- Hase Muneaki Tominaga Junji
- 出版者
- American Institute of Physics
- 雑誌
- Applied physics letters (ISSN:00036951)
- 巻号頁・発行日
- vol.99, no.3, pp.031902, 2011
- 被引用文献数
- 11 6
We report on evaluation of lattice thermal conductivity of GeTe/Sb2Te3 superlattice (SL) by using femtosecond coherent phonon spectroscopy at various lattice temperatures. The time-resolved transient reflectivity obtained in amorphous and crystalline GeTe/Sb2Te3 SL films exhibits the coherent A1 optical modes at terahertz (THz) frequencies with picoseconds dephasing time. Based on the Debye theory, we calculate the lattice thermal conductivity, including scattering by grain boundary and point defect, umklapp process, and phonon resonant scattering. The results indicate that the thermal conductivity in amorphous SL is less temperature dependent, being attributed to dominant phonon-defect scattering.
- 著者
- Umezawa Naoto Shiraishi Kenji
- 出版者
- American Institute of Physics
- 雑誌
- Applied physics letters (ISSN:00036951)
- 巻号頁・発行日
- vol.97, no.20, pp.202906, 2010-11
- 被引用文献数
- 11 12
The solubility of silicon in high-permittivity (high-κ) oxides significantly affects the performance of field-effect transistors. Our comparative study of silicon impurities in La2O3 and HfO2 reveals that the stability of silicon at substitutional sites strongly depends on its coordination number. When substituted for lanthanum, a silicon atom fits comfortably in La2O3, thanks to the formation of a SiO4 tetrahedral structure. In addition, the substitutional silicon acts as a donor impurity in La2O3, increasing oxygen content in the oxide. This contributes to absorbing silicon and oxygen from the interface region, leading to the formation of lanthanum silicate at the La2O3/silicon interface.
- 著者
- Takakura K. Ohyama H. Takarabe K. Suemasu T. Hasegawa F.
- 出版者
- American Institute of Physics
- 雑誌
- Journal of applied physics (ISSN:00218979)
- 巻号頁・発行日
- vol.97, no.09, pp.093716, 2005-04
- 被引用文献数
- 24 13
The hole mobility of intentionally undoped p-type beta-FeSi2 thin films grown by a multilayer method was investigated. With increasing annealing temperature and time, the hole mobility increased to approximately 450 cm2/V s at room temperature (RT). The observed hole mobility was analyzed by considering various carrier scatterings such as acoustic-phonon and polar-optical-phonon scatterings, intervalley scattering, ionized impurity scattering, and grain-boundary scattering. The nice fit of the mobility to the experimental results reveals that the polar-optical-phonon scattering determines the hole mobility at RT.
- 著者
- Egorov A. Yu. Kalevich V. K. Afanasiev M. M. Shiryaev A. Yu. Ustinov V. M. Ikezawa M. Masumoto Y.
- 出版者
- American Institute of Physics
- 雑誌
- Journal of applied physics (ISSN:00218979)
- 巻号頁・発行日
- vol.98, no.1, pp.013539, 2005-07
- 被引用文献数
- 24
The paper studies the circularly polarized photoluminescence (PL) from dilute GaAsN alloys with nitrogen content of 1%–3.4%, grown on GaAs substrates. The room-temperature PL is found to consist of two bands whose splitting grows with increasing nitrogen content. The analysis of the PL circular polarization has shown that the PL bands originate from the splitting of light- and heavy-hole subbands, induced by an elastic strain in GaAsN layer. The dependence of the energy gap of unstrained GaAsN on the nitrogen content has been calculated using the measured light- and heavy-hole splittings.
- 著者
- Li Cheng Lai Hongkai Chen Songyan Suemasu T. Hasegawa F.
- 出版者
- American Institute of Physics
- 雑誌
- Journal of applied physics (ISSN:00218979)
- 巻号頁・発行日
- vol.100, no.2, pp.023506, 2006-07
- 被引用文献数
- 5 4
The temperature dependence of electroluminescence from silicon p-i-n light-emitting diodes with a layer of beta-FeSi2 particles inserted in intrinsic silicon was investigated. Anomalous blueshift of the peak energy and enhanced electroluminescence intensity of the silicon band-edge emission were observed at temperatures from 50 to 200 K. The electroluminescence intensity was enhanced due to longer diffusion paths of the injected electrons at elevated temperature, as well as thermal escape of the electrons from the beta-FeSi2 particles. The low peak energy compared to that from bulk silicon at low temperature is due to the bound electron-hole pairs induced by the strain potential at the interface between silicon and beta-FeSi2 particles. The blueshift of the peak is ascribed to the transition of bound electron-hole pairs into free excitons at elevated temperature. Room temperature electroluminescence from such a silicon light-emitting diode can be obtained at a low current density of 0.3 A/cm2.
- 著者
- Fukata N. Oshima T. Okada N. Murakami K. Kizuka T. Tsurui T. Ito S.
- 出版者
- American Institute of Physics
- 雑誌
- Journal of applied physics (ISSN:00218979)
- 巻号頁・発行日
- vol.100, no.2, pp.024311, 2006-07
- 被引用文献数
- 44 33
The phonon confinement and self-limiting oxidation effects of silicon nanowires (SiNWs) synthesized by laser ablation were investigated. The size of SiNWs was controlled by the synthesis parameters during laser ablation and the subsequent thermal oxidation. Thermal oxidation increases the thickness of the SiNWs' surface oxide layer, resulting in a decrease in their crystalline Si core diameter. This effect causes a downshift and asymmetric broadening of the Si optical phonon peak due to phonon confinement, while excess oxidation causes an upshift due to compressive stress. The compressive stress retarded the oxidation of the SiNWs by self-limiting oxidation effect. This result shows that the Si core diameter can be controlled by compressive stress.
- 著者
- Koyano T. Nomiyama T. Kanoh N. Numata H. Ohba T. Kita E. Ohtsuka H.
- 出版者
- American Institute of Physics
- 雑誌
- Journal of applied physics (ISSN:00218979)
- 巻号頁・発行日
- vol.100, no.3, pp.033906, 2006-08
- 被引用文献数
- 7
The gamma iron nitride (nitrogen austenite) was subjected to high magnetic field process in order to drive the fcc-->bct martensitic transformation. Molar fraction of martensite monotonically increased with increasing the magnetic field and reached 94% at 35 T. With a combination of magnetization and 57Fe Mössbauer spectroscopy data, magnetization of bulk processed alpha[prime] phase with 9.6 at. % N is determined to be 229 emu/g, the same as that for dc sputtered thin films.
- 著者
- Fukata N. Sato S. Morihiro H. Murakami K. Ishioka K. Kitajima M. Hishita S.
- 出版者
- American Institute of Physics
- 雑誌
- Journal of applied physics (ISSN:00218979)
- 巻号頁・発行日
- vol.101, no.4, pp.046107, 2007-02
- 被引用文献数
- 12 3
The formation of hydrogen (H)-related complexes and H effects on boron (B) and phosphorus (P) dopants was investigated in B- or P-doped silicon (Si) crystal treated with high concentration of H. The reactivation process of dopant carriers by annealing after hydrogenation was significantly different between the p-type and n-type specimens. The difference is likely to be attributable to the formation of H-related defects based on the stable sites of the H atoms, i.e., complicated H multiple trapping centers are formed by bond breaking due to H atoms in only p-type B-doped Si.
- 著者
- Uedono A. Shaoqiang C. Jongwon S. Ito K. Nakamori H. Honda N. Tomita S. Akimoto K. Kudo H. Ishibashi S.
- 出版者
- American Institute of Physics
- 雑誌
- Journal of applied physics (ISSN:00218979)
- 巻号頁・発行日
- vol.103, no.10, pp.104505, 2008-08
- 被引用文献数
- 22 27
A relationship between intra-4f transitions of Er and vacancy-type defects in Er-doped GaN was studied by using a monoenergetic positron beam. Doppler broadening spectra of the annihilation radiation were measured for Er-doped GaN grown by molecular beam epitaxy. A clear correlation between the defect concentration and the photoluminescence (PL) intensity was observed. The major defect species detected by positrons was identified as a Ga vacancy VGa, and its concentration increased with increasing Er concentration [Er]. For the sample with [Er]=3.3 at. %, the maximum integrated intensity of PL was observed. The VGa concentration was above 1018 cm−3 and additional vacancies such as divacancies started to be introduced at this Er concentration. For the sample with higher [Er], the PL intensity decreased, and the mean size of vacancies decreased due to an introduction of precipitates and/or metastable phases.
- 著者
- Yokomaku Hiroomi Satoh Wataru Fukuda Junji Suzuki Hiroaki
- 出版者
- American Institute of Physics
- 雑誌
- Journal of applied physics (ISSN:00218979)
- 巻号頁・発行日
- vol.104, no.6, pp.064910, 2008-09
- 被引用文献数
- 13 6
To improve the performance of electrowetting-based microfluidic devices, we used micropillar structures to enhance the changes in the wettability of gold electrodes. The changes in the contact angle of a sessile drop were influenced by the diameter of the micropillars and interpillar distances. For a potential change between 0 V and −1.0 V, the change of the contact angle of the KCl sessile drop was 41° on a smooth electrode, but 88° on an electrode with micropillars with a 10 µm diameter. Furthermore, the existence of the micropillars accelerated the change of the contact angle. The gold electrodes with the micropillars were used to generate the capillary force to mobilize a liquid column in a microflow channel. Compared to a device with a smooth electrode, this device showed a fourfold increase in the flow velocity at −0.9 V. The electrodes were also used as a valve. The ability to stop an intruding solution and the switching speed was improved with the micropillar structure.