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A molecular dynamics simulation method is used to study the growth of narrow single-wall carbon nanotubes. It is found that the growth temperature and the species of small carbon clusters in the feedstock are important for the quality of the nanotubes grown. There is a temperature range of 1000-1500 K in which the narrow armchair single-wall carbon nanotubes can grow rapidly via adduction of C2 dimers, even without the existence of catalysts. The narrow zigzag tubes cannot keep open-ended growth. If the feedstock consists of various species of carbon clusters, the tubes cannot keep open-ended growth. At higher temperatures, the narrow nanotubes close rapidly in the noncatalytic environment, and the products grown are fullerene-like capsules. PACS: 61. 46. +w, 36. 40. -c

A material asymmetry Co/Cu/Fe junction structure has been prepared for studying the spin-polarized electron injection at 77K. The sample performance was demonstrated to be analogous to that of a bipolar transistor. The maximal value of the output pulse voltage between Cu and Fe layers could reach the order of several μV when the bias current between Co and Cu layers was 10μA. The interface roughness, photograph of material, magnetic loop and injection characteristic curves have been measured. Some important points on this topic have been discussed.

This paper presents a new biometrics pattern, finger-articular back texture recognition using Log Gabor wavelet. Firstly, hand back image was captured by special imaging device. Then joint texture was segmented, and located by a sliding window. The texture features were extracted based on the Log Gabor wavelet transform and were classified by the corresponding feature encoding classifier. The experiment results shown that finger-articular back texture can be used for personal authentication, Log Gabor wavelet is better than Gabor wavelet for pattern extraction, and the equal right rate was 98.21% in Finger-articular back texture recognition.

Calculations of the magnetic domain structure (domain wall energy density, domain wall thickness, domain width and critical diameter of single domain particles) in Nd 2 Fe 14 B have been made by using its intrinsic parameters (lattice constants, magnetic moments of the atoms, Curie temperature, spontaneous magnetization and magneto-crystalline anisotropy constant). The four stages of magnetization reversal processes in oriented sintered Nd-Fe-B magnet after saturation magnetization along its easy direction are studied in detail in this paper. The results show that the nucleation of the reverse-magnetization nuclei in the surface layer of the grains of hard magnetic phase Nd 2 Fe 14 B, as well as the irreversible domain wall motion from the surface to the inside of the grains are dominant factors controlling the intrinsic coercivity of the Nd-Fe-B alloy.

The influence of surface polarity on the structural properties of BiFeO3 (BFO) thin films is investigated. BFO thin films are epitaxially grown on SrTiO3 (STO) (100) and polar (111) surfaces by oxygen plasma-assisted molecular beam epitaxy. It is shown that the crystal structure, surface morphology, and defect states of BFO films grown on STO substrates with nonpolar (001) or polar (111) surfaces perform very differently. BFO/STO (001) is a fully strained tetragonal phase with orientation relationship (001)[100]BFO||(001)[100]STO, while BFO/STO (111) is a rhombohedral phase. BFO/STO (111) has rougher surface morphology and less defect states, which results in reduced leakage current and lower dielectric loss. Moreover, BFO films on both STO (001) and STO (111) are direct band oxides with similar band gaps of 2.65 eV and 2.67 eV, respectively.

We give a brief introduction to the oxide (ZnO, TiO2, In2O3, SnO2, etc.)-based magnetic semiconductors from fundamental material aspects through fascinating magnetic, transport, and optical properties, particularly at room temperature, to promising device applications. The origin of the observed ferromagnetism is also discussed, with a special focus on first-principles investigations of the exchange interactions between transition metal dopants in oxide-based magnetic semiconductors.

ZnO thin film growth prefers different orientations on the etched and unetched SrTiO3(STO)(110) substrates. Inclined ZnO and cobalt-doped ZnO (ZnCoO) thin films are grown on unetched STO(110) substrates using oxygen plasma assisted molecular beam epitaxy, with the c-axis 42? inclined from the normal STO(110) surface. The growth geometries are ZnCoO[100]//STO[11?0] and ZnCoO[11?1]//STO[001]. The low temperature photoluminescence spectra of the inclined ZnO and ZnCoO films are dominated by D0X emissions associated with A0X emissions, and the characteristic emissions for the 2E(2G)?4A2(4F) transition of Co2+ dopants and the relevant phonon-participated emissions are observed in the ZnCoO film, indicating the incorporation of Co2+ ions at the lattice positions of the Zn2+ ions. The c-axis inclined ZnCoO film shows ferromagnetic properties at room temperature.

Titanium oxide ceramics doped with niobium is synthesized in reduced atmosphere at 1200 ℃ by conventional solid-state reaction technique. From their crystal structures determined by the powder X-ray diffraction(XRD), the samples have multiple-phase with low Nb concentration, but they have single tetragonal rutile phase when Nb content is larger than 0.02. The electrical conductivities, the Seebeck coefficients and the thermal conductivities of the samples with single phase are measured at a temperature range between room temperature and 900 K. The electrical conductivity and the Seebeck coefficient show non-metallic behaviors. According to the fitting, it is found that the samples show thermal-activation mechanism at low temperatures and small-polaron hopping conduction mechanism at high temperatures. Moreover, the analyses of XRD, electrical conductivity and Seebeck coefficient show that the concentration of oxygen vacancy decreases with Nb content increasing. Thermal conductivity decreases with temperature increasing, dominating by lattice thermal conductivity. In the measurement region, the figure of merit (ZT) reaches a highest value of 0.19 at 873 K in the Ti0.98Nb0.02O2- sample.

This paper proposes a universal spin-dependent variable range hopping theoretical model to describe various experimental transport phenomena observed in wide-band-gap oxide ferromagnetic semiconductors with high transition metal concentration. The contributions of the 'hard gap' energy, Coulomb interaction, correlation energy, and exchange interaction to the electrical transport are considered in the universal variable range hopping theoretical model. By fitting the temperature and magnetic field dependence of the experimental sheet resistance to the theoretical model, the spin polarization ratio of electrical carriers near the Fermi level and interactions between electrical carriers can be obtained.

Perovskite La0.9Sr0.1FeO3 ceramics have been synthesized at 1250℃，1300℃ and 1350℃ by the conventional solid-state reaction technique. From their crystal structures determined by powder X-ray diffraction，we found that the lattice volume decreases with increasing sintering temperature. The scanning electronic microscope (SEM) images of surface microstructures of the samples show that the average grain size increases with increasing sintering temperature. The electrical resistivity and Seebeck coefficient have been measured between room temperature and 800℃. At low temperatures，the electrical resistivity shows a semiconductivity-like behavior. With further increasing of temperature，the electrical resistivity slightly increases. An adiabatic hopping conduction mechanism of small-polarons is suggested from the temperature dependence of the electrical resistivity，which has different activation energies at low and high temperatures. The Seebeck coefficient rapidly decreases with increasing temperature，and reaches a saturation value about 600℃. With further increasing of temperature，the Seebeck coefficient slightly increases. With the increase of sintering temperature，the electrical resistivity decreases，while the Seebeck coefficient increases. Therefore，the power factor increases with increasing sintering temperature. The highest power factor of 90 μW/K2m was obtained at 727℃ for sample sintered at 1350℃.

Fe-doped In2O3 films are grown epitaxially on YSZ (100) substrates by pulsed laser deposition. The in-situ reflection high-energy electron diffraction, the atomic force microscopy, and the x-ray diffraction patterns show that the films have a well defined cubic structure epitaxially oriented in the (100) direction. Room temperature ferromagnetism is observed by an alternating gradient magnetometer. Strong perpendicular magnetic anisotropy with a remnant magnetization ratio of 0.83 and a coercivity of 2.5kOe is revealed. Both the structural and the magnetic measurements suggest that this ferromagnetism is an intrinsic property deriving from the spin-orbit coupling between the diluted Fe atoms.

Zn1−xFexO inhomogeneous oxide magnetic semiconductor films with high Fe concentration are prepared by sputtering, and fast annealing is carried out at different temperatures. It is found that magnetic properties are greatly modulated by controlling the composition inhomogeneity and subsequently fast annealing. Both ferromagnetic and paramagnetic components are found to coexist in the as-deposited Zn1−xFexO magnetic semiconductor. In particular, the antiferromagnetic coupling between the neighbouring local ferromagnetic regions is found in the as-deposited Zn0.23Fe0.77 O film, and the antiferromagnetic coupling strength increases with increasing temperature from 110 K to 300 K. We believe that this unusual antiferromagnetic coupling is mediated by thermally activated hopping carriers.

The possibility of forming cascading energy levels in SrTiO3 by doping Bi and Cu as an example is analyzed by using the density-functional-theory based first principles calculations of the electronic structure. The results show that both Bi doping and Cu doping can introduce a defect level in the forbidden band，and Co-doping of Bi and Cu can introduce two defect levels in the forbidden band. Electrons at the top of valence band can transit to the bottom of conduction band through a cascade transition process. Using the nonradiative transition model，we point out that the probability of electronic transition from the valence band to the conduction band through a cascade transition is much higher than that of direct transition from the valence band to the conduction band. The cascade transitions can effectively increase the carrier concentration in the conduction band.