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)     

Structural and photoluminescent properties of ZnO films deposited by radio frequency reactive sputtering

Zinc oxide films with c-axis preferred orientation were deposited on silicon (100) substrates by radio frequency (RF) reactive sputtering. The properties of the sam- ples were characterized by X-ray diffractometer, X-ray photoelectron spectroscopy and fluorescent-spectrophotometer. The effect of sputtering power and substrate temperature on the structural and photoluminescent (PL) properties of the ZnO films was investigated. The results indicated that when the sputtering power is 100 W and the substrate temperature is 300-400℃, it is suitable for the growth of high c-axis orientation and small strain ZnO films. A violet peak at about 380 nm and a blue band at about 430 nm were observed in the room temperature photolumines- cence spectra, and the origin of blue emission was investigated.     

Formation and photoluminescence properties of boron nanocones

This paper reports that a simple chemical vapour deposition method has been adopted to fabricate large scale, high density boron nanocones with thermal evaporation of B/B2O3 powders precursors in an Ar/H2 gas mixture at the synthesis temperature of 1000-1200℃. The lengths of boron nanocones are several micrometres, and the diameters of nanocone tops are in a range of 50-100 nm. transmission electron microscopy and selected area electron diffraction indicate that the nanocones are single crystalline α-tetragonal boron. The vapour liquid solid mechanism is the main formation mechanism of boron nanocones. One broad photolumineseence emission peak at the central wavelength of about 650 nm is observed under the 532 nm light excitation. Boron nanocones with good photoluminescence properties are promising candidates for applications in optical emitting devices.     

The growth temperatures dependence of optical and electrical properties of InN films

InN films grown on sapphire at different substrate temperatures from 550°C to 700°C by metalorganic chemical vapor deposition were investigated. The low-temperature GaN nucleation layer with high-temperature annealing (1100°C) was used as a buffer for main InN layer growth. X-ray diffraction and Raman scattering measurements reveal that the quality of InN films can be improved by increasing the growth temperature to 600°C. Further high substrate temperatures may promote the thermal decomposition of InN films and result in poor crystallinity and surface morphology. The photoluminescence and Hall measurements were employed to characterize the optical and electrical properties of InN films, which also indicates strong growth temperature dependence. The InN films grown at temperature of 600°C show not only a high mobility with low carrier concentration, but also a strong infrared emission band located around 0.7 eV. For a 600 nm thick InN film grown at 600°C, the Hall mobility achieves up to 938 cm²/Vs with electron concentration of 3.9 × 10¹⁸ cm⁻³. Supported by the National Basic Research Program of China (Grant No. 2006CB6049), the National Natural Science Foundation of China (Grant Nos. 6039072, 60476030 and 60421003), the Great Fund of the Ministry of Education of China (Grant No. 10416), the Specialized 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 Nos. BK2005210 and BK2006126)     

Solution-phase synthesis of nanomaterials at low temperature

This paper reviews the solution-phase synthesis of nanoparticles via some routes at low temperatures, such as room temperature route, wave-assisted synthesis (γ-irradiation route and sonochemical route), directly heating at low temperatures, and hydrothermal/solvothermal methods. A number of strategies were developed to control the shape, the size, as well as the dispersion of nanostructures. Using diethylamine or n-butylamine as solvent, semiconductor nanorods were yielded. By the hydrothermal treatment of amorphous colloids, Bi₂S₃ nanorods and Se nanowires were obtained. CdS nanowires were prepared in the presence of polyacrylamide. ZnS nanowires were obtained using liquid crystal. The polymer poly (vinyl acetate) tubule acted as both nanoreactor and template for the CdSe nanowire growth. Assisted by the surfactant of sodium dodecyl benzenesulfonate (SDBS), nickel nanobelts were synthesized. In addition, Ag nanowires, Te nanotubes and ZnO nanorod arrays could be prepared without adding any additives or templates. Supported by the National Basic Research Program of China (Grant No. 2005CB623601) and the National Natural Science Foundation of China (Grant No. 20431020)     

Excellent UV absorption in spin-coated thin films of oleic acid modified zinc oxide nanorods embedded in Polyvinyl alcohol

The aim of the study is to investigate the optical properties of spin-coated, highly transparent nanocomposite films of oleic acid modified ZnO (Zinc oxide) nanorods embedded in Polyvinyl alcohol (PVA) matrix. Pristine and oleic acid (OA) modified ZnO nanorods have been prepared by wet chemical synthesis and are characterized by X-ray diffraction, FESEM, TEM and FT–IR spectroscopy techniques. The optical properties of ZnO/PVA films are studied using UV–visible absorption and Photoluminescence (PL) spectroscopy. The results show that the optical absorption of the films in the UV region is quite high and more than 95% absorption is observed in films prepared from OA modified ZnO nanorods. The excellent UV absorption at around 300 nm offers prospects of applications of these films as efficient UV filters in this wavelength region. The PL spectrum of pristine ZnO nanorods shows almost white light emission whereas OA modified ZnO nanorods have a more intense peak centered in the blue region. The PL emission of OA modified ZnO/PVA film shows appreciable increase in intensity compared to the film obtained with pristine ZnO. The surface modification of ZnO by the polymer matrix removes defect states within ZnO and facilitates sharp near band edge PL emission at 364 nm.     

The Influence of the Spatial Orientation of ZnO Nanorods on the Luminescence Spectrum

Zinc oxide (ZnO) nanorods were grown on glass substrates coated with a conducting indium tin oxide film using the hydrothermal method. The nanorods are 2–2.5 μm long and 70–200 nm in diameter. Under UV irradiation the nanorods exhibit photoluminescence with a maximum at 382 nm. It is found that changes in angle between the nanorods growth direction and the emission recording direction give rise to an appearance of a violet emission band centered at ～400 nm. It is possible dependence of the luminescence spectrum on the ZnO nanorods’ spatial orientation is due to localization of the violet emission centers in the surface layer.     

两步法制备空间取向高度一致的ZnO纳米棒阵列

采用两步法,即先用磁控溅射在Si(100)表面生长一层ZnO籽晶层、再利用液相法制备空间取向高度一致的ZnO纳米棒阵列.用扫描电子显微镜、X射线衍射、高分辨透射电子显微镜和选区电子衍射对样品形貌和结构特征进行了表征.结果表明,ZnO纳米棒具有垂直于衬底沿c轴择优生长和空间取向高度一致的特性和比较大的长径比,X射线衍射的(XRD)(0002)峰半高宽只有0.06°,选区电子衍射也显示了优异的单晶特性.光致发光谱表明ZnO纳米棒具有非常强的紫外本征发光和非常弱的杂质或缺陷发光特性. 关键词： ZnO纳米棒阵列 ZnO籽晶层 两步法 液相生长     

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 optical properties of flower-like ZnO nanorods by thermal evaporation method

Flower-like ZnO nanorods have been synthesized by heating a mixture of ZnO/graphite powders using the thermal evaporation and vapor transport on Si (1 0 0) substrates without any catalyst. The structures, morphologies and optical properties of the products were characterized in detail by using X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL) and Raman spectroscopy. The synthesized products consisted of large quantities of flower-like ZnO nanostructures in the form of uniform nanorods. The flower-like ZnO nanorods had high purity and well crystallized wurtzite structure, whose high crystalline quality was proved by Raman spectroscopy. The as-synthesized flower-like ZnO nanorods showed a strong ultraviolet emission at 386 nm and a weak and broad yellow-green emission in visible spectrum in its room temperature photoluminescence (PL) spectrum. In addition, the growth mechanism of the flower-like ZnO nanorods was discussed based on the reaction conditions.     

Synthesis and optical properties of ZnO nanorods on indium tin oxide substrate

ZnO nanorods with uniform diameter and length have been synthesized on an indium-tin oxide (ITO) substrate by using a simple thermal evaporation method which is suitable to larger scale production and without any catalyst or additives. The samples were characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM), ultraviolet-vis (UV-vis) absorption spectrum, photoluminescence (PL) spectrum and Raman spectrum. The single-phase ZnO nanorods grow well-oriented along the c-axis of its wurtzite structure on ITO substrate. The ZnO nanorods shows sharp and strong UV emission located at 380 nm without notable visible light emission in the PL spectrum, which suggests the good crystallinity of the nanorods, which was also testified by their Raman spectrum. The photodegradation of methylene orange (MO) in aqueous solution reveals that the well-arranged c-axis growth of ZnO nanorods possess evidently improved photocatalytic performance and these properties enable the ZnO nanorods potential application in UV laser.     

Synchronously pumped femtosecond optical parametric oscillator at 1053 nm

A femtosecond optical parametric oscillator synchronously pumped by a Ti:Sapphire oscillator is reported. By the cavity length tuning, the signal wavelength is continuously tuned from 1000 to 1200 nm. The average output power of 32 mW is obtained at 1053 nm. The pulse width is measured to be 342 fs by intensity autocorrelation method. In addition, we observed bichromatic emission during the cavity length tuning process. Supported by the National High Technology Program Research and Development Program of China, the National Natural Science Foundation of China (Grant Nos. 60490280 and 10804128), and the National Basic Research Program of China (Grant No. 2007CB815104)     

Improvement of the relative entropy based protein folding method

The “relative entropy” has been used as a minimization function to predict the tertiary structure of a protein backbone, and good results have been obtained. However, in our previous work, the ensemble average of the contact potential was estimated by an approximate calculation. In order to improve the theoretical integrity of the relative-entropy-based method, a new theoretical calculation method of the ensemble average of the contact potential was presented in this work, which is based on the thermodynamic perturbation theory. Tests of the improved algorithm were performed on twelve small proteins. The root mean square deviations of the predicted versus the native structures from Protein Data Bank range from 0.40 to 0.60 nm. Compared with the previous approximate values, the average prediction accuracy is improved by 0.04 nm. Contributed equally to this work Supported by the National Natural Science Foundation of China (Grant No. 30670497), the Beijing Natural Science Foundation (Grant No. 5072002), and the Specialized Research Foundation for the Doctoral Program of Higher Education (Grant No. 200800050003)     

Self-organization effect in poly（3-hexylthiophene）： methanofullerenes solar cells

This paper studies the self-organization of the polymer in solar cells based on poly（3-hexylthiophene）： [6, 6]-phenyl C61-butyric acid methyl ester by controlling the growth rate of active layer. These blend films are characterized by UV-vis absorption spectroscopy, charge-transport dark J - V curve, x-ray diffraction pattern curve, and atomic force microscopy. The results indicate that slowing down the drying process of the wet films leads to an enhanced selforganization, which causes an increased hole transport. Increased incident light absorption, higher carrier mobility, and balanced carrier transport in the active layer explain the enhancement in the device performance, the power conversion efficiency of 3.43% and fill factor up to 64.6% are achieved under Air Mass 1.5, 100 mW/cm^2.     

Comparing the efficiencies of different detect strategies in the ping-pong protocol

The way to compare the efficiencies of different detect strategies (DSs) in the “ping-pong” protocol is studied. The trade-off between information gain and disturbance is calculated and compared for different DSs. The comparison result primely tallies with our intuitional analysis. It is shown that the analysis of this trade-off is a feasible way to compare the performances of different DSs in theory. Supported by the National High Technology Research and Development Program of China (Grant No. 2006AA01Z419), the National Natural Science Foundation of China (Grant Nos. 90604023 and 6087319), the National Laboratory for Modern Communications Science Foundation of China (Grant No. 9140C1101010601), the Natural Science Foundation of Beijing (Grant No. 4072020), and the ISN Open Foundation.     

Characterization and optical property of ZnO nano-, submicro- and microrods synthesized by hydrothermal method on a large-scale

In the present paper, well-dispersed ZnO nano-, submicro- and microrods with hexagonal structure were synthesized by a simple low temperature hydrothermal process from zinc nitrate hexahydrate without using any additional surfactant, organic solvent or catalytic agent. The phase and structural analysis were carried out by X-ray diffraction (XRD), the morphological analysis was carried out by field emission scanning electron microscopy (FESEM) and the optical property was characterized by room-temperature photoluminescence (PL) spectroscopy. The results revealed the high crystal quality of ZnO powder with hexagonal (wurtzite-type) crystal structure and the formation of well-dispersed ZnO nano-, submicro- and microrods with diameters of about 50, 200 and 500 nm, and lengths of 300 nm, 1 μm and 2 μm, respectively, on a large-scale just using the different temperatures. Room-temperature PL spectrum from the ZnO nanorods reveals a strong UV emission peak at about 360 nm and no green emission band at ∼530 nm. The strong UV photoluminescence indicates the good crystallization quality of the ZnO nanorods. Room-temperature PL spectra from the ZnO submicro- and microrods reveal a weak UV emission peak at ∼400 nm and a very strong visible green emission at 530 nm, that is ascribed to the transition between V_oZn_i and valence band.     

Study of Au/ZnO nanorods Schottky light-emitting diodes grown by low-temperature aqueous chemical method

High quality vertically aligned ZnO nanorods (NRs) were grown by low-temperature aqueous chemical technique on 4H-n-SiC substrates. Schottky light-emitting diodes (LEDs) were fabricated. The current-voltage (I–V) characteristics of Schottky diodes reveal good rectifying behavior. Optical properties of the ZnO nanorods (NRs) were probed by cathodoluminescence (CL) measurements at room temperature complemented with electroluminescence (EL). The room-temperature CL spectra of the ZnO NRs exhibit near band edge (NBE) emission as well as strong deep level emission (DLE) centered at 690 nm. At room temperature the CL spectra intensity of the DLE was enhanced with the increase of the electron beam penetration depth due to the increase of defect concentration at the interface and due to the conversion of self-absorbed UV emission. We observed a variation in the DLE along the nanorod depth. This indicates a relatively lower structural quality near the interface between ZnO NRs and n-SiC substrate. The room-temperature CL spectra of SiC show very weak emission, which confirms that most of the DLE is originating from the ZnO NRs, and SiC has a minute contribution to the emission.     

Aligned ZnO nanorod arrays fabricated on Si substrate by solution deposition

Aligned ZnO nanorod arrays were fabricated by chemical solution deposition based on Si substrate which was spin coated with ZnO colloid as nucleation seeds. Their microstructures were characterized by X-ray diffraction, scanning electron microscopy, and high-resolution transmission electron microscopy. The results indicated that ZnO nanorods nucleated and grew vertically on Si substrates along the [0 0 1] direction with single-crystalline structure. The diameter of ZnO nanorods was greatly affected by the grain size of ZnO seeds. Room-temperature photoluminescence of nanorods has a strong emission band at about 384 nm.     

Strong optical transmission through the ellipsoid metal-film nanohole arrays

The transmission characteristics of a metallic film with subwavelength ellipsoid nanohole arrays are investigated by using the three-dimensional finite-difference time-domain (3D-FDTD) method. The extraordinary transmission is attributed to the collaboration of localized waveguide resonance and surface plasmon resonance. The influences of the lattice constant and the hole shape on the transmission are studied. By analyzing the picture of electric field and electromagnetic energy distribution, we show the mechanisms of the two different resonances: Localized waveguide resonance mode can be confined inside the ellipsoid holes region, while electric field and electromagnetic energy are localized separately at the two ends of ellipsoid holes for the surface plasma resonance mode. Supported by the National Natural Science Foundation of China (Grant No. 60708014), the Distinguished Youth Foundation of Hunan Province (Grant No. 03JJY1008), the Science Foundation for Post-doctorate of China (Grant No. 2004035083), and the Natural Science Foundation of Hunan Province (Grant No. 06JJ20034)     

Revisiting the security of quantum dialogue and bidirectional quantum secure direct communication

From the perspective of information theory and cryptography, the security of two quantum dialogue protocols and a bidirectional quantum secure direct communication (QSDC) protocol was analyzed, and it was pointed out that the transmitted information would be partly leaked out in them. That is, any eavesdropper can elicit some information about the secrets from the public annunciations of the legal users. This phenomenon should have been strictly forbidden in a quantum secure communication. In fact, this problem exists in quite a few recent proposals and, therefore, it deserves more research attention in the following related study. Supported by the National High Technology Research and Development Program of China (Grant No. 2006AA01Z419), the National Natural Science Foundation of China (Grant Nos. 90604023 and 60373059), the National Research Foundation for the Doctoral Program of Higher Education of China (Grant No. 20040013007), the National Laboratory for Modern Communications Science Foundation of China (Grant No. 9140C1101010601), the Natural Science Foundation of Beijing (Grant No. 4072020) and the ISN Open Foundation