温度梯度溶液法生长的Cr掺杂的ZnTe晶体的表征

以CrTe作为掺杂源、以Te作为溶剂, 用温度梯度溶液法生长了Cr掺杂的ZnTe晶锭。晶锭头部的晶粒尺寸较大(>10 mm×10 mm), 且Te夹杂相较少。Te夹杂相的大小、形状和分布可以反映晶锭中的温场分布。晶锭的径向非对称温场导致富Te相沿径向非对称分布。Te夹杂相在温度梯度作用下的热迁移会导致其相互融合长大、变长。Te夹杂相也会在晶体中引入裂纹和空洞等缺陷。部分未被掺入ZnTe中的CrTe富集于固液界面处, 表明温度梯度溶液法生长晶体时具有一定的排杂作用。Cr掺杂的ZnTe晶体的电阻率(约1000 Ω·cm)高于未掺杂的ZnTe(约300 Ω·cm)。Cr掺杂晶体在约1750 nm处的吸收峰表明Cr²⁺离子被成功地掺入了ZnTe中。但是Cr掺杂后晶体的红外透过率降低, 表明Cr掺杂引入了较多的缺陷。     

Polyvinylpyrrolidone (PVP)-assisted hydrothermal synthesis of luminescent YVO4:Eu3+ microspheres

Spherical YVO₄:Eu³⁺ microstructures were hydrothermally synthesized by the reaction of NH₄VO₃, Y₂O₃, and Eu₂O₃ at 180 °C for 24 h with the assistance of polyvinylpyrrolidone (PVP) as a surfactant. The resulting products were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and photoluminescence (PL) spectroscopy. The experimental results showed that ball-like YVO₄:Eu³⁺ microspheres with a diameter of about 4–5 μm, corresponding to the SEM observations, formed at 180 °C for 24 h using 0.2 g PVP with the molecular weight of 20,000 g mol^?1. The amount of PVP and the reaction time of hydrothermal processing were found to play a key role in the formation of YVO₄:Eu³⁺ microspheres. It has been observed that the relative luminescence intensities of the as-synthesized samples increased with increasing hydrothermal reaction times due mainly to the increase of crystallinity.     

Preparation of nanocomposite for optical application using ZnTe nanoparticles and a zero-birefringence polymer

Surface-modified ZnTe nanoparticles were mixed in a zero-birefringence polymer matrix. Transmission electron microscopy images revealed that aggregates of ZnTe nanoparticles with a diameter of ∼20 nm were uniformly dispersed in the polymer. The transmittance of ZnTe nanocomposites rapidly decreased at wavelengths shorter than the critical wavelength corresponding to the band gap of ZnTe nanoparticles, an effect which became significant as the volume fraction of particles increased. In this way, the optical characteristic of ZnTe nanoparticles was added to the polymer. The intrinsic zero-birefringence was confirmed in the heat-drawn ZnTe nanocomposites. As the ZnTe nanocomposites were left in air, a lowering of transmittance was observed. This was due to the oxidation of Zn and the resultant deposition of Te in the ZnTe nanocomposite, as the light absorption of Te is significant. The formation of oxygen non-permeable SiO₂ films onto the ZnTe nanocomposite by the sol-gel method was useful in preventing oxidation so that the decrement of transmittance decreased from 47.2% to 14.9% at 530 nm near the ZnTe band gap.     

Synthesis of ZnTe nanowires onto TiO2 nanotubular arrays by pulse-reverse electrodeposition

Growth of ZnTe nanowires using a pulse-reverse electrodeposition technique from a non-aqueous solution is reported. ZnTe nanowires were grown on to an ordered nanotubular TiO₂ template in a propylene carbonate solution at 130 °C inside a controlled atmosphere glove box. The pulse-reverse electro deposition process consisted of a cathodic pulse at − 0.62 V and an anodic pulse at 0.75 V Vs Zn²⁺/Zn. Stoichiometry growth of crystalline ZnTe nanowires was observed in the as-deposited condition. The anodic pulse cycle of the pulse-reverse electrodeposition process presumably introduced zinc vacancies as deep level acceptors at an energy level of E_v + 0.47 eV. The resultant ZnTe nanowires showed p-type semiconductivity with a resistivity of 7.8 × 10⁴ Ω cm and a charge carrier density of 1.67 × 10¹⁴ cm^− 3. Annihilation of the defects occurred upon thermal annealing that resulted in marginal decrease in the defect density.     

Rapid synthesis of pentagonal silver nanowires with diameter-dependent tensile yield strength

We synthesize silver nanowires (NWs) with pentagonal cross sections via a facile and rapid microwave-assisted polyol method in the presence of polyvinylpyrrolidone (PVP) and sodium sulfide (Na₂S). The synthesis does not use templates and needs only 2.5 min, which is 570 times faster than solvothermal preparation at 100 °C. The pentagonal Ag NWs grow along the <110> direction and reach lengths between 10 and 30 μm. Adjusting Na₂S concentration controls the wire diameters in a wide range from 60 to 480 nm. PVP and microwave irradiation both ensure the cross sections' pentagonal shape even at large diameters. We use different microwave irradiation times to investigate the morphology's evolution and to support the discussion of growth mechanisms. The electrical conductivity was measured in situ inside a transmission electron microscope. Their resistivity is diameter dependent and comparable to that of Ag NWs with round cross sections. Ultrasound fracturing analysis determined the NWs' tensile yield strengths, which is also diameter dependent and maximal around 220 nm.     

ZnTe/Si heterostructures grown by isothermal closed space sublimation

ZnTe films with different thickness were grown onto (001) Si substrates using isothermal closed space sublimation by alternated sublimation of Zn and Te sources. As a result ZnTe polycrystalline films were obtained with a strong [111] orientation as revealed by X-ray diffraction patterns. The reason for this polycrystalline nature of the samples comes from incomplete removal of SiO₂ from the Si substrate surface. A preferential adsorption of Te in the first stages of the growth was concluded from Rutherford backscattering spectra analysis.     

Morphology and crystal quality investigation of hydrothermally synthesized ZnO micro-rods

Micro-structural and room and low temperature photoluminescence response of undoped one-dimensional ZnO were investigated. ZnO rods of different morphology and size were synthesized by controlling growth parameters through hydrothermal technique. The phase and microstructure analysis were carried out by X-ray diffraction and scanning electron microscopy. The room and low temperature photoluminescence spectra of the samples were studied. Near band edge sharp exciton emission peaks and broad defect-related peaks were observed. The ratio of band edge emission to deep level emission was controlled by tuning the initial concentration, pH and reaction time period. Optimal growth condition for growth of micro-rods with improved crystal quality was obtained with initial Zn²⁺ concentration of 0.5 M, at reaction temperature of 120 °C, pH of 9.9 and in a reaction time period of 6 h.     

Structure and optical properties of polycrystalline Cd1−xZnxTe thin films prepared by simultaneous evaporation

Cd_1–xZn_xTe films were deposited by simultaneous evaporation of CdTe and ZnTe. These Cd_1–xZn_xTe films were of cubic phase, and strongly (1 1 1) oriented as deposited. Predominant direct optical transitions were observed and the band gap varied with zinc content in a non-linear way. A structure development of CdS/CdTe/ZnTe : Cu solar cells with a Cd_1–xZn_xTe buffer layer was proposed.     

Two-step growth of Cd0.96Zn0.04Te/Si(111) epilayers by HWE

High quality Cd_1−xZn_xTe, x = 0.04 epilayers are successfully grown directly on hydrogen-terminated Si(111) substrates by hot wall epitaxy method. Growth conditions are optimized in order to grow single crystal films with desired composition. It is found that surface morphology of the epilayers is dramatically affected by the growth temperature and the growth rate at the early stage of the crystal growth. Applying limited high substrate temperature of T_sub = 440 °C and low growth rate of 0.04 μm/h, the crystallinity is significantly improved and for the first time a pseudomorphic 2D growth is observed notwithstanding of the large lattice mismatch. Designing a suitable two-step growth process makes it possible that Cd_1−xZn_xTe/Si(111), x = 0.04 epilayers are fabricated with good surface morphology, which could be used as lattice matched substrates for MCT and MCZT epitaxy.     

Structural,optical and electrical properties of ZnTe<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Se<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> thin films

ZnTe_1−x Se _x films were deposited on glass substrates kept at 200 °C by the electron beam evaporation technique. These films exhibited cubic structure and the lattice parameter increased with increase of Tellurium concentration in the films which confirmed the solid solution formation. The grain size is found to increase with Te content. The dislocation density and lattice strain show a decreasing trend with increasing of Te content. Band gap values of 2.73 eV, 2.63 eV, 2.52 eV and 2.41 eV have been calculated for the films of composition ‘x’ = 0.2, 0.4, 0.6 and 0.8, respectively, which confirmed the formation of solid solution between ZnSe and ZnTe. Refractive index of the films increased from 2.535 to 2.826 as the concentration of Te increased. All the films showed high resistivity values. Laser Raman spectral studies of ZnTe_1−x Se _x revealed LO phonon frequencies whose values are located in between the LO phonon frequencies of ZnSe and ZnTe.     

A solvothermal approach for the size-, shape- and phase-controlled synthesis and properties of CuInS2

In this work, Copper Indium disulfide (CIS) nanoparticles of size ∼ 5 nm were prepared via solvothermal approach in ethanol under the nitrogen atmosphere using copper chloride, indium chloride and thiourea (Tu) as starting materials, without any assistance through organic ligands at the reaction temperature of 150 °C. The factors which might affect the morphology, structure, phase of the product during the synthesis were discussed. It was found that the products were significantly affected by the reaction time and solvent. The morphology, structure, phase constituents and optical properties of the as prepared CIS powders were characterized by X-ray diffraction (XRD), Energy dispersive Spectroscopy (EDS), scanning electron microscopy (SEM) and ultraviolet–visible (UV–Vis) spectrometry respectively. The result shows that the CIS nanoparticles can be synthesized by solvothermal method at a reaction time of 2 h and shows that when the reaction time was increased from 2 h to 48 h, CIS porous flower like nanoparticles were obtained as we increase the reaction time. We also observed that in this process, the phase selection of WZ-CIS or CH-CIS is greatly influence by solvent. We also observed that, in this process sulfur source did not influence the phase but participated in the growth of the nanoparticles.     

Kinetic studies on water-soluble gold nanoparticles coordinated to poly(vinylpyrrolidone): isotropic to anisotropic transformation and morphology

The growth kinetics, isotropic-to-anisotropic transformation, structural properties and surface morphology of polyvinylpyrrolidone (PVP)-coordinated gold nanoparticles are reported in this work. The reduction of gold ions, kinetics, and growth mechanism of gold nanoparticles, and the coordination between PVP and gold are explored for the first time in this single report. The layer-by-layer growth mechanism (adsorption of gold ions to the nuclei and their subsequent reduction) was observed in the growth of isotropic nanoparticles during the initial stage of the reaction, whereas the Ostwald ripening mechanism (growth of larger particles at the expense of smaller particles) was observed in the growth of the anisotropic nanoparticles in the later stage of the reaction. The surface plasmon resonance band for the anisotropic nanoparticles (average size for a typical sample was ca. 9 nm) was blue-shifted (20 nm) toward that of the isotropic nanoparticles (whose average size is much smaller than that of the anisotropic nanoparticles). The increased effective electron density on the surface of anisotropic particles was the cause of this blue shift. The resultant gold colloids were very stable because the PVP molecules were coordinated through both the C–N and C=O groups, instead of the C=O group alone. The positions of the surface plasmon band and morphology of the gold products were strongly dependent on the amount of PVP.     

Magnetic-Field-Induced Level Crossing and the Spin Dynamics of Excitons in Zn1−x Mn x Te/ZnTe Quantum Wells

Magnetic-field-induced level crossing and the spin dynamics of excitons in a Zn_1?x Mn _x Te/ZnTe single quantum well are studied. The circularly-polarized photoluminescence (PL) shows that the down spin branch of the Zn_1?x Mn _x Te exciton overlaps with both the up and down spin branches of the ZnTe exciton at a crossing field (H _c) of 4 T, due to the giant Zeeman shift of Zn_1?x Mn _x Te. The PL intensities and lifetimes in each layer become gradually equal toward H _c, which shows the mixing of wavefunctions of the excitons generated in each layer. Above H _c, each branch of the spin-polarized exciton separates again. The lifetimes of the spin-polarized exciton PL reflect the spin-flip relaxation in ZnTe and the spin mixing between Zn_1?x Mn _x Te and ZnTe layers.     

A rapid route for the synthesis of submicron Se and Te rod-like crystals

Submicron Se and Te rod-like crystals were successfully synthesized via a rapid polyol process by refluxing Na₂EO₃ (ESe, Te) and (NH₃)₂S₂O₃ in ethylene glycol at 180 °C for 0.5 h under vigorous stirring. The obtained samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), and XPS procedures. Studies found that reaction time and temperature have great influences on the morphology of the final products.     

Solvothermal fabrication of uniform silver nanowires

Conventional polyol synthesis has been widely used for the preparation of silver nanostructures with different morphologies. However, there is a drawback that it is difficult to control the reaction parameters for shape-controlled synthesis of silver nanostructures, such as the rate of the addition of silver ions to the solution. In this paper, we combine polyol process and solvothermal method for easily synthesizing silver nanostructures. Importantly, the introduction of cuprous chloride (CuCl) to the reaction leads to increasing the population of twinned Ag seeds (required for wire growth) at the expense of that of single Ag seeds. Silver nanowires (Ag NWs) with uniform width (~80?nm in width) can be obtained in the presence of poly(vinyl pyrrolidone) (PVP). Some other parameters, such as the reaction temperature and molar ratios of the repeating unit of PVP to AgNO₃ (R), also have been discussed. A possible mechanism is put forward to understand the evolution of silver nanostructures.     

Synthesis and characterization of Bi2S3 nanorods by solvothermal method in polyol media

Bi₂S₃ nanorods were synthesized via a simple solvothermal process in polyol media through the reaction between Bi(NO₃)₃·5H₂O, urea and CS₂ at 150 °C for 15 h using diethylene glycol as solvent. The nanorods were characterized by XRD, TEM and SAED. The results showed that the products were well-crystallized orthorhombic phase with lattice parameters a = 11.15 Å, b = 11.3 Å and c = 3.984 Å, which are consistent with the value in standard JCPDS card No. 17-0320. DEG served as an excellent solvent and structure director. Besides, compared to water and EG as solvents, the DEG system can provide a mild and homogenous condition, which is favorable to anisotropic growth and increases the yield of high quality Bi₂S₃ nanorods. Based on the experimental results, the growth mechanism was discussed.     

Characteristics of brush plated ZnTe thin films

Zinc telluride thin films were deposited by the brush plating technique at a potential of −0.90 V (SCE) on conducting glass and titanium substrates at different temperatures in the range 30–90°C. The films were polycrystalline in nature with peaks corresponding to the cubic phase. Direct band gap of 2.30 eV was observed. XPS studiers indicated the formation of ZnTe. Depth profiling studies indicated a uniform distribution of Zn and Te throughout the entire thickness. EDAX measurements were made on the films and it was found that there was a slight excess of Te.     

A modified polyol process for growing Ag nanowires and nanoplates using 2-ethoxy ethanol

A modified polyol process was proposed to prepare Ag nanowires in this study. The typical reductant, ethylene glycol, was replaced with 2-ethoxy ethanol in the presence of polyvinylpyrrolidone (PVP) to grow Ag nanowires and nanoplates. The growth of Ag nanowires was monitored by the UV–Visible spectrum, which depends on the geometry-dependent surface plasmon resonances of the Ag nanowires. The crystal phase of the Ag nanostructures was identified by X-ray diffraction. Transmission electron microscopy showed that the average dimensions of the Ag nanowires were lengths of approximately 2–10 μm and diameter of 80 nm. The PVP molecules played a key role in directing the growth of the Ag nanostructures along the (111) crystal plane, and the reduction rate of Ag⁺ at 25 °C when 2-ethoxy ethanol was used was faster than when ethylene glycol was used, which improved the growth of the Ag nanowires. When the AgNO₃-to-PVP ratio was adjusted to 2, multiple twinned particles could be observed at an initial stage of the reaction, and a higher yield of the Ag nanowires was synthesized. When the PVP drop rate was slowed, more Ag nanowires were grown. Interestingly, when the AgNO₃ and PVP molecules were initially premixed, Ag nanoplates were generated, rather than nanowires, at a higher temperature in this reduction system.     

Fabrication and characterization of electrospun mullite nanofibers

Continuous mullite (3Al₂O₃·2SiO₂) nanofibers were fabricated by a sol-gel electrospinning technique. The detailed crystallization development and micromorphological evolution of both the as-electrospun nanofibers and the sintered mullite nanofibers were investigated. Results indicated that the spinnability and micromorphological evolution of mullite nanofibers are largely dependent on the viscosity η of the mullite sol, which can be adjusted by polyvinylprrolidone (PVP) content. Mullite nanofibers with common cylindrical morphology and diameters ranging from 400 nm to 800 nm could be obtained easily and rapidly when PVP content is ranged from 5 wt.% to 8 wt.%. High purity polycrystalline mullite nanofibers with diameters of about 200 nm were obtained after sintering at 1200 °C for 2 h. All sintered nanofibers consisted of single crystalline grains with size of approximately 100 nm.     

Hydrothermal synthesis of quasi-monodisperse AWO4 (A?=?Ca, Sr, and Ba) microspheres

In this study, quasi-monodisperse AWO₄ (A = Ca, Sr, and Ba) microspheres were fabricated by a facile hydrothermal route at 180 °C for 8 h in the presence of citric acid. The as-synthesized AWO₄ powders were characterized by X-ray powder diffraction (XRD), scanning electron microscopy, transmission electron microscopy and photoluminescence spectroscopy. The XRD results revealed that the hydrothermally formed AWO₄ powders presented a scheelite-type tetragonal structure, and the formation of a secondary phase was not observed. The SEM and TEM observations demonstrated that the AWO₄ powders with uniform sphere-like morphologies could be hydrothermally obtained at 180 °C for 8 h without the use of surfactants. The growth process of quasi-monodisperse BaWO₄ microspheres, as a representative of AWO₄, was investigated as a function of hydrothermal processing time, and a possible formation mechanism was proposed. The room temperature photoluminescence properties of AWO₄ powders were studied using an excitation wavelength of 350 nm. The positions of the PL emission peaks were not considerably altered, implying that the energy band gap relating to the blue emission was not much affected by the variation in chemical composition of AWO₄ (A = Ca, Sr, and Ba) microspheres. The obtained quasi-monodisperse AWO₄ microspheres will be potential candidates for a broad range of technological applications, as phosphors, luminescent materials, photocatalysts, etc.