Synthesis and magnetic properties of CdS/α-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> hierarchical nanostructures

CdS/α-Fe₂O₃ hierarchical nanostructures, where the CdS nanorods grow irregularly on the side surface of α-Fe₂O₃ nanorods, were synthesized via a three-step process. The diameters and lengths of CdS nanorods can be tuned by changing the ethylenediamine (EDA) and Cd ion concentrations. The magnetic investigations by superconducting quantum interference device indicate that the hierarchical nanostructures have an Morin transition at lower temperature (230 K) than that of the single bulk α-Fe₂O₃ materials (263 K). Importantly, the hierarchical nanostructures exhibit weakly ferromagnetic characteristics at 300 K. A sharp peak assigned to the surface trap induced emission are observed in room temperature PL spectra. Combining with the optoelectronic properties of CdS, the CdS/α-Fe₂O₃ hierarchical nanostructures may be used as multi-functional materials for optoelectronic and magnetic devices. Supported by the National Natural Science Foundation of China (Grant Nos. 50772025 and 50872159), the Ministry of Science and Technology of China (Grant No. 2008DFR20420), the China Postdoctoral Science Foundation (Grant Nos. 20060400042 and 200801044), the Natural Science Foundation of Heilongjiang Province, China (Grant No. F200828), the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20070217002), and the Innovation Foundation of Harbin City (Grant No. RC2006QN017016)     

Factors affecting the superconductivity in the process of depositing Nd1.85Ce0.15CuO4-δ by the pulsed electron deposition technique

On SrTiO₃ single crystal substrate, by using the pulsed electron deposition technique, the high-quality electron doped Nd_1.85Ce_0.15CuO_4−δ superconducting film was successfully fabricated. After careful study on the R-T curves of the obtained samples deposited with different substrate temperatures, thicknesses, annealing methods and pulse frequencies, the effects of them on the superconductivity of the films were found, and the reasons were also analyzed. Additionally, by using the same model of the pulsed laser deposition technique, the relation between the target-to-substrate distance and the deposition pressure was drawn out as a quantitative one. Supported by the Key Project of Zhejiang Provincial Natural Science Foundation (Grant No. Z605131), the ‘100 Talents Project’ of Chinese Academy of Sciences, the Creative Research Group of National Natural Science Foundation of China (Grant No. 60321001) and the National Natural Science Foundation of China (Grant No. 60571029)     

Investigation of thermoluminescence in Li<Subscript>2</Subscript>B<Subscript>4</Subscript>O<Subscript>7</Subscript> phosphors doped with Cu,Ag and Mg

Li2B4O7 (LBO)Cu,Ag,Mg phosphors have been prepared by the sintering technique.The roles of the Ag and Mg dopants in the phosphors have been studied using the methods of thermoluminescence (TL) glow curves and TL 3D spectra. The results indicated that proper concentrations of Ag and Mg can enhance the TL of LBOCu.It was also indicated that the intensity of TL peak at ～130℃ is reduced with the increasing Ag concentration, and enhanced with the increasing Mg concentration.From the TL 3D spectra, three emission bands (λ1 = 421 nm,λ2 = 380 nm, λ3 = 350nm) were observed the intensity of low energy emission band is reduced and that of the high energy is enhanced with the increasing dopant Ag; on the contrary, the intensity of low energy emission band is enhanced and that of the high energy one is reduced with the increasing dopant Mg.     

Synthesis and characterization of single-crystalline MnFe2O4 nanorods via a surfactant-free hydrothermal route

Uniform, high-quality, single-crystalline MnFe₂O₄ nanorods with diameter around 25 nm and length up to 500 nm, have been reproducibly synthesized via a surfactant-free hydrothermal route. The growth direction of the obtained nanowires was determined to be its [1 1 1] direction, resulting in the increase of saturation magnetization. Mn²⁺ is responsible for one-dimensional growth of the nanorods, and the effects of reaction time and solution concentration on the morphology and crystallization of the MnFe₂O₄ nanorods were investigated. Saturation magnetization of the nanorods is 74.0 emu/g, which is among the best value reported so far.     

Pd-Si binary bulk metallic glass

Pd_80+x Si_20−x (x = 0, 1, and 2) binary metallic glasses with the diameter ranging from 7 to 8 mm were prepared by a combination of fluxing and water quenching or air cooling. Thermal analysis results show that with increasing Si content, the glass transition temperature T _g, the initial crystallization temperature T _x and the onset crystallization temperature T _p of Pd-Si binary glassy alloys increase. Moreover, the supercooled liquid region reaches 61 K. It indicates that Pd-Si binary alloys possess large glass forming ability, which can be greatly improved by fluxing treatment. Supported by the National Basic Research Program of China (Grant No. 2007CB613905) and the National Natural Science Foundation of China (Grant Nos. 50671050 and 50431030)     

The size effect on transport properties of colossal magnetoresistance materials La<Subscript>0.67</Subscript>Ca<Subscript>0.33</Subscript>MnO<Subscript>3</Subscript>

High quality La_0.67Ca_0.33MnO₃ (LCMO) film was deposited via a novel pulsed electron deposition technique on SrTiO₃(100) single crystal substrate. The micro-bridge with different widths was fabricated by using electron beam lithography (EBL) technique and their transport properties were studied. For the micro-bridges with width of 2 and 1.5 μm, the insulator-to-metal transition temperature (T _P) keeps unchanged compared with the film. For the micro-bridges with width of 1 μm, the T _P shifts towards the lower temperature by 50 K. When the width decreases down to 500 nm, the insulator-to-metal transition disappears. The magnetoresistance behavior of these micro-bridges was studied, and the results show that the low field magnetoresistance (LFMR) decreases and the high field magnetoresistances (HFMR) keep almost unchanged as the width of micro-bridge is reduced. Supported by the Key Project of the Natural Science Foundation of Zhejiang Province of China (Grant No. Z605131), the National Natural Science Foundation of China (Grant No. 60571029), and W. H. Tang was supported by the Creative Research Group of National Natural Science Foundation of China (Grant No. 60321001)     

Facile hydrothermal synthesis of ultrahigh-aspect-ratio V2O5 nanowires for high-performance supercapacitors

Ultrahigh-aspect-ratio V₂O₅ nanowires were successfully prepared using [VO(O₂)₂(OH₂)]⁻ as the starting material by a template-free hydrothermal route without the addition of organic surfactant or inorganic ions. The prepared samples were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Brunauer–Emmet–Teller (BET), cyclic voltammetry (CV) and galvanostatic charge–discharge (GCD). The results revealed that the peroxovanadium (V) complexes can be easily transformed to V₂O₅ nanowires by this hydrothermal route. The uniform nanowires were with width about 50 nm and length about dozens of micron. The BET analysis showed the V₂O₅ nanowires had a high specific surface area of 25.6 m² g⁻¹. The synthesized V₂O₅ nanowires performed a high capacitance of 351 F g⁻¹ when used as supercapacitor electrode in 1 mol L⁻¹ LiNO₃.     

Threshold quantum secure direct communication without entanglement

For the first time, a threshold quantum secure direct communication (TQSDC) scheme is presented. Similar to the classical Shamir's secret sharing scheme, the sender makes n shares, S1, …, Sn of secret key K and each receiver keeps a share secretly. If the sender wants to send a secret message M to the receivers, he en-codes the information of K and M on a single photon sequence and sends it to one of the receivers. According to the secret shares, the t receivers sequentially per-form the corresponding unitary operations on the single photon sequence and ob-tain the secret message M. The shared shares may be reusable if it can be judged that there is no eavesdropper in line. We discuss that our protocol is feasible with current technology.     

Charge order and spin order in Nd0.5Sr0.5Mn1? x (Ga x , Ti x )O3 system

Magnetic properties of Nd0.5Sr0.5Mn1-x(Gax,Tix)O3 system (0.04≤x≤0.4) were investigated through magnetization and electron spin resonance (ESR) measurements. It was observed that a small amount of Ti substitution for Mn will destroy the charge-ordering (CO) phase completely and induce the cluster-spin-glass phase in the system, which displays a procedure of collapse of CO and of an enhancement of spin ordering (SO) phase. In contrast, the Ga substitution for Mn induces a melting of CO phase in the system. It was observed that with substitution the CO phase is suppressed gradually and the remanent CO phase is retained all the while, and withal, there is a co-existence of AFM CO phase and FM SO at low temperature. In addition, an abrupt rise of magnetization was observed in M-Tcurves. We attributed this abnormal phenomenon to a transition from canted AFM SO to FM SO in CO region.     

Carrier transport and luminescence properties of n-type GaN

The surface morphology, electrical properties and optical properties of Si doped n-type GaN were investigated. The intentional SiH₄ doped GaN films were grown by metal organic chemical vapor deposition with the electron concentration varying from 3×10¹⁶ cm⁻³ to 5.4×10¹⁸ cm⁻³. The surface morphology shows that the roughness and dislocation pits increase as the mass flow rate of SiH₄ increases, which indicates that the quality of GaN degrades gradually. The activation energy of Si in GaN with different n concentrations varies from 12 to 22 meV, which may originate from the interactions of donor wave functions. The carrier transport mechanism with increasing temperature from 100 to 420 K was concluded as the complex effect of both impurity scattering and phonon scattering. The position of the near band edge emission peak was determined by both renormalization of the band gap and B-M effect. The intensity variations of the yellow luminescence could be explained by the change of Ga vacancy concentration caused by Si doping. Supported by the National Basic Research Program of China (Grant No. 2006CB6049), the National Hi-Tech Research and Development Program of China (Grant No. 2006AA03A142), the National Natural Science Foundation of China (Grant Nos. 60721063, 60731160628 and 60676057), the Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20050284004) and the Natural Science Foundation of Jiangsu Province of China (Grant No. BK2005210)     

Fabrication of metal oxide nanostructures based on Atomic Force Microscopy lithography

Atomic Force Microscopy (AFM) mechanical lithography is a simple but significant method for nanofabrication. In this work, we used this method to construct nanostructures on Pt/Cu bilayer metal electrodes under ambient conditions in air. The influence of various scratch parameters, such as the applied force, scan velocity and circle times, on the lithography patterns was investigated. The Pt-Cu-Cu _x O-Cu-Pt nanostructure was constructed by choosing suitable scratch parameters and oxidation at room temperature. The properties of the scratched regions were also investigated by friction force microscopy and conductive AFM (C-AFM). The I–V curves show symmetric and linear properties, and Ohmic contacts were formed. These results indicate that AFM mechanical lithography is a powerful tool for fabricating novel metal-semiconductor nanoelectronic devices. Supported by the National Natural Science Foundation of China (Grant No. 90306010), the Program for New Century Excellent Talents in University of China (Grant No. NCET-04-0653), the National Basic Research Program of China (Grant No. 2007CB616911), and the Science and Technology Department of Henan Province (Grant No. 072300420100)     

Hydrothermal synthesis and photocatalytic properties of WO3 nanorods by using capping agent SnCl4·5H2O

Hexagonal tungsten trioxide (h-WO₃) nano-rods of different sizes are prepared via hydrothermal synthesis using a capping agent of SnCl₄·5H₂O. The size of the synthesized WO₃ nanoparticles can be controlled by changing concentration of the capping agent SnCl₄·5H₂O alone. We also investigate microstructures and optical properties of the WO₃ nanorods and propose a synthesis mechanism for the nanorods. The photocatalytic activities of the h-WO₃ nanorods are evaluated by degradation of Rhodamine-B (RhB), revealing that these nanorods exhibit excellent photocatalytic properties. The capping agent SnCl₄·5H₂O is found to be critical to governing sizes and properties of the h-WO₃ nanorods. Our results demonstrate that functional nano-crystallites with tunable size and morphology can be synthesized via a facile hydrothermal synthesis process by adjusting the concentration of capping agent alone. Such a facile hydrothermal synthesis process should be applicable to other types of nanomaterials and relevant to a wide range of applications.     

Correlation between superheated liquid fragility and potential energy landscape in Gd-and Pr-based glass-forming alloys

The kinetic viscosities of superheated liquids on the Gd-based bulk glass-forming alloys are measured by an oscillating viscometer in a high vacuum atmosphere. According to the viscosity data, the parameters of superheated liquid fragility, M, are calculated. Based on the values of M in Gd-and Pr-based (cited from the literature) glass-forming alloys, we find that there is a linear correlation between M and the absolute value of mixing enthalpy, |ΔH _mix|, in an alloy system with the same base element, and the larger M, the smaller |ΔH _mix|. The alloy with larger M exhibits the larger height of energy barriers separating the minima on the potential energy landscape. Supported by the National Basic Research Program of China (973 Program) (Grant No. 2007CB613901), the National Natural Science Foundation of China (Grant No. 50231040), the Natural Science Foundation of Shandong Province of China (Grant No. Z2004F02), and the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20050422024)     

Improvement of refrigerant capacity of La<Subscript>0.67</Subscript>Ca<Subscript>0.33</Subscript>MnO<Subscript>3</Subscript> single crystal with a few percent Fe doping

Large low-field-induced magnetic entropy changes, ΔS _M, are observed in La_0.67Ca_0.33MnO₃ and La_0.67Ca_0.33Mn_0.96Fe_0.04O₃ single crystals. The peaks of ΔS _M broadened asymmetrically to high temperatures under higher magnetic fields for two materials should be attributed to the first-order magnetic phase transition at T _c. A small amount of iron doping results in an increase in the refrigerant capacity of the material though the magnetic entropy change decreases. The discovery of excellent magnetocaloric features of these single crystals in the low magnetic field can provide some ideas for exploring novel magnetic refrigerants operating under permanent magnet rather than superconducting one as magnetic field source. Supported by the State Key Project of Fundamental Research (Grant No. 2005CB724402), and the National Natural Science Foundation of China (Grant No. 50672126) Contributed by CHENG ZhaoHua     

Synthesis, characterization and applications of nanostructural/nanodimensional metal oxides

Molybdenum oxide nanorods (MOx-NR) and vanadium oxide nanotubes (VOx-NT) have been prepared using MoO₃ and V₂O₅ powders as precursors and hexadecylamine as surfactant via hydrothermal route. Porous nanocrystalline MgO powder has been prepared by a simple and instantaneous solution combustion process using corresponding magnesium nitrate as oxidizer and glycine as fuel. The compounds are characterized by XRD, TG-DTA, SEM, TEM, surface area and porosity measurements. Because of the porous nature having large surface area (107 m²/g) with nanodimension (12-23 nm), MgO powder has been successfully employed as defluoridizing agent for the removal of fluoride (75%) in ground water     

Very high upper critical fields of F-doped Fe-based layered superconductors NdO0.88F0.12FeAs and CeO0.88F0.12FeAs

Using the solid state reaction method, we have synthesized the polycrystalline F-doped NdO_0.88F_0.12FeAs and CeO_0.88F_0.12FeAs with the superconducting transition temperatures at about 48 and 40 K, respectively. To obtain the upper critical field H _c2 of Nd(Ce)O_0.88F_0.12FeAs samples, we measured the electrical resistivity under magnetic field up to 14 T. Based on the Werthamer-Helfand-Hohenberg (WHH) relation together with the H _c2(T) curves in a relatively high field, we estimated that these superconductors have a rather high upper critical field of about 115 T for Nd-based and 107 T for Ce-based samples, indicating the similarities between these ReO_1−x F _x FeAs (Re = rare earth element) superconductors and high T _c cuprate superconductors. Recommended by Prof. Nie Yuxin, Executive Editor of Science in China Series G-Physics, Mechanics & Astronomy Supported by the National Basic Research Program of China (973 Program)(Grant No. 2006CB9213001) and the National Natural Science Foundation of China (Grant No. 10774181)     

Oxygen pressure dependent electroresistance in La0.9Sr0.1MnO3 thin films grown by laser molecular beam epitaxy

We report here studies on the influence of oxygen pressure on the electroresistance behavior of La_0.9Sr_0.1MnO₃ thin films fabricated by laser molecular beam epitaxy. It was found that the film deposited at lower oxygen pressure shows larger c-axis parameter, higher resistance, and more distinct electroresistance. These results reveal that the electroresistance of manganite thin films can be tuned by the conditions of film fabrication. Supported by the National Natural Science Foundation of China (Grant No. 10334070) and the National Key Basic Research Program of China (Grant No. 2004CB619004)     

A novel strategy to synthesize cobalt hydroxide and Co3O4 nanowires

Cobalt hydroxide ultra fine nanowires were prepared by a facile hydrothermal route using hydrogen peroxide. This method provides a simple, low cost, and large-scale route to produce β-cobalt hydroxide nanowires with an average diameter of 5 nm and a length of ca. 10 μm, which show a predominant well-crystalline hexagonal brucite-like phase. Their thermal decomposition produced highly uniform nanowires of cobalt oxide (Co₃O₄) under temperature 500 °C in the presence of oxygen gas. The produced cobalt oxide was characterized by X-ray diffraction, transmission electronic microscopy, and selected-area electron diffraction. The results indicated that cobalt oxide nanowires with an average diameter of 10 nm and a length of ca. 600 nm have been formed, which show a predominant well-crystalline cubic face-centered like phase.     

First-principles calculations on the electronic structure and optical properties of BaSi<Subscript>2</Subscript>

The electronic structure, densities of states and optical properties of the stable orthorhombic BaSi₂ have been calculated using the first-principle density function theory and pseudopotential method. The results show that BaSi₂ is an indirect semiconductor with the band gap of 1.086 eV, the valence bands of BaSi₂ are mainly composed of Si 3p, 3s and Ba 5d, and the conduction bands are mainly composed of Ba 6s, 5d as well as Si 3p. The static dielectric function ɛ ₁(0) is 11.17, the reflectivity n ₀ is 3.35, and the biggest peak of the absorption coefficient is 2.15×10₅ cm⁻¹. Supported by the National Natural Science Foundation of China (Grant Nos. 60566001 and 60766002), the Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20050657003), the Scientific Research Foundation for the Returned Overseas Chinese Scholars, Ministry of Education of China (Grant No. (2005)383), the Specialized Fund of Nomarch for Excellent Talent of Science and Technology of Guizhou Province (Grant No. Z053114), the Scientific and Technological Projects for the Returned Overseas of Guizhou Province (Grant No. (2004)03), and the Top Talent’s Scientific Research Project of Organization Department of Guizhou Province (Grant No. Z053123)     

Threshold proxy quantum signature scheme with threshold shared verification

A threshold proxy quantum signature scheme with threshold shared verification is proposed. An original signer could authorize a group as its proxy signers. Then only t or more of n persons in the proxy group can generate the proxy signature on behalf of the original signer and any t − 1 or fewer ones cannot do that. When the proxy signature needs to be verified, any t or more of n persons belonging to the verification group can verify the message and any t − 1 or fewer ones cannot verify the validity of the proxy signature. Supported by the National Basic Research Program of China (973 Program)(Grant No. 2007CB311100), the National High-Technology Research and Development Program of China (Grant Nos. 2006AA01Z419 and 20060101Z4015), the Major Research Plan of the National Natural Science Foundation of China (Grant No. 90604023), the Scientific Research Common Program of Beijing Municipal Commission of Education (Grant No. KM200810005004), the Scientific Research Foundation for the Youth of Beijing University of Technology (Grant No. 97007016200701), the Doctoral Scientific Research Activation Foundation of Beijing University of Technology (Grant No. 52007016200702), and the National Laboratory for Modern Communications Science Foundation of China (Grant No. 9140C1101010601)