Self-organized hierarchical ZnS/SiO(2) nanowire heterostructures

Novel hierarchical heterostructures formed by wrapping ZnS nanowires with highly dense SiO(2) nanowires were successfully synthesized by a vapor-liquid-solid process. The as-synthesized products were characterized using X-ray diffraction, scanning electron microscopy and transmission electron microscopy equipped with an energy-dispersive X-ray spectrometer. Studies indicate that a typical hierarchical ZnS/SiO(2) heterostructure consists of a single-crystalline ZnS nanowire (core) with diameter gradually decreasing from several hundred nanometers to 20 nm and adjacent amorphous SiO(2) nanowires (branches) with diameters of about 20 nm. A possible growth mechanism was also proposed for the growth of the hierarchical heterostructures.     

硫化锌与硫化锌/氧化锌异质结纳米线的化学气相沉积法制备与表征

介绍一种利用石墨还原快速制备大量硫化锌纳米线的方法,并分别合成了超晶格型、双轴型、核/壳型的硫化锌/氧化锌异质结纳米线。所合成的硫化锌纳米线存在六方纤锌矿和立方闪锌矿两种晶型,纳米线长度达几十微米,直径在20-50 nm,直径均匀且产量很高。在具有双轴型的硫化锌/氧化锌异质结中,首次发现具有超结构特征的氧化锌。HRTEM分析表明,硫化锌/氧化锌超晶格异质结界面为ZB-ZnS(111)∥ZnO(0001),而核/壳型异质结界面为W-ZnS(0001)∥ZnO(0001),这三个晶面分别为各自晶体的极性面,即所合成的硫化锌/氧化锌异质结中极性面相互平行。对ZnS 和ZnS/ZnO 异质结的生长机制进行了探讨,并对硫化锌纳米线与硫化锌/氧化锌异质结的光学性质进行了分析。     

Solvothermal synthesis and photoluminescent properties of ZnS/cyclohexylamine: inorganic-organic hybrid semiconductor nanowires

An inorganic-organic hybrid semiconductor, ZnS/CHA (CHA = cyclohexylamine) nanocomposites was successfully synthesized via a solvothermal method using CHA as solvent, which yielded uniform and ultralong nanowires with widths of 100-1000 nm and lengths of 5-20 microm. Changing the reaction conditions could alter the morphology and optical properties of the nanocomposites. The periodic layer subnanometer structures were identified by high-resolution transmission electron microscopy (HR-TEM) images, with thickness of approximately 2 nm. The composites exhibited a very large blue-shift in their optical absorption edge as well as an exciton excitation band due to a strong quantum confinement effect caused by the internal subnanometer-scale structures. The pure hexagonal wurtzite ZnS nanowires were also obtained by extracting the ZnS/CHA nanocomposites with dimethyl formamide (DMF). In addition, the luminescent properties of exciton and defect-related transitions in different samples of ZnS/CHA were discussed in detail.     

化学气相沉积法合成高结晶度的三元系Cd1-xZnxS纳米线

以硫化锌、硫化镉和活性碳粉作为反应物, 利用化学气相沉积方法成功合成了单晶Cd1-xZnxS纳米线. 为了解产物的结构、形貌、组分、微结构以及声子振动模式, 对样品进行了扫描电镜、透射电镜、X射线衍射、能谱分析以及拉曼光谱分析. 分析显示合成的纳米线为六方铅锌矿结构, 生长方向沿着[210]方向, 长度均为10 μm, 直径在80-100 nm之间, x的值约为0.2. 拉曼光谱分析显示产物的拉曼峰位与纯CdS相比发生了蓝移.     

化学气相沉积法合成高结晶度的三元系Cd1-xZnxS纳米线

以硫化锌、硫化镉和活性碳粉作为反应物,利用化学气相沉积方法成功合成了单晶Cd1-xZnxS纳米线.为了解产物的结构、形貌、组分、微结构以及声子振动模式,对样品进行了扫描电镜、透射电镜、X射线衍射、能谱分析以及拉曼光谱分析.分析显示合成的纳米线为六方铅锌矿结构,生长方向沿着[210]方向,长度均为10μm,直径在80-100 nm之间,x的值约为0.2.拉曼光谱分析显示产物的拉曼峰位与纯CdS相比发生了蓝移.     

ZnS nanosheets: Egg albumin and microwave-assisted synthesis and optical properties

ZnS nanosheets were prepared via egg albumin and microwave-assisted method. The phases, crystalline lattice structures, morphologies, chemical and optical properties were characterized by X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), field-emission scanning electron microscope(FE-SEM), selected area electron diffraction (SAED), Fourier transform infrared (FTIR) spectroscopy, ultraviolet–visible (UV–Vis) spectroscopy and fluorescence(FL) spectrometer and growth mechanism of ZnS nanosheets was investigated. The results showed that all samples were pure cubic zinc blende with polycrystalline structure. The width of ZnS nanosheets with a rectangular nanostructure was in the range of 450–750 nm. The chemical interaction existed between egg albumin molecules and ZnS nanoparticles via the amide/carboxylate group. The band gap value calculated was 3.72 eV. The band at around 440 nm was attributed to the sulfur vacancies of the ZnS nanosheets. With increasing volumes of egg albumin, the photoluminescence (PL) intensity of ZnS samples firstly increased and then decreased, attributed to concentration quenching.     

Low-temperature growth and photoluminescence property of ZnS nanoribbons

At a low temperature of 450 degrees C, ZnS nanoribbons have been synthesized on Si and KCl substrates by a simple chemical vapor deposition (CVD) method with a two-temperature-zone furnace. Zinc and sulfur powders are used as sources in the different temperature zones. X-ray diffraction (XRD), selected area electron diffraction (SEAD), and transmission electron microscopy (TEM) analysis show that the ZnS nanoribbons are the wurtzite structure, and there are two types-single-crystal and bicrystal nanoribbons. Photoluminescence (PL) spectrum shows that the spectrum mainly includes two parts: a purple emission band centering at about 390 nm and a blue emission band centering at about 445 nm with a weak green shoulder around 510 nm.     

Laser Assisted Catalytic Growth of ZnS/CdSe Core‐Shell and Wire‐Coil Nanowire Heterostructures

ZnS/CdSe core‐shell and wire‐coil nanowire heterostructures have been synthesized by chemical vapor deposition assisted with pulsed laser ablation. Measurements from high‐resolution transmission electron microscopy and selected area electron diffraction have revealed that both ZnS/CdSe core‐shell and wire‐coil nanowires are of single‐crystalline hexagonal wurtzite structures and grow along the [0001] direction. While the lattice parameters of ZnS and CdSe in the core‐shell nanowires are nearly equal to those of bulk ZnS and CdSe, change of the lattice parameters in the CdSe‐coil is attributed to the doping of Zn into CdSe, resulting in the relaxation of compressive strain at the interface between CdSe‐coil and ZnS‐wire. Composition variation across the interfacial regions in the ZnS/CdSe nanowire heterostructures ranges only 10–15 nm despite the pronounced lattice mismatch between ZnS and CdSe by ?11%. Growth mechanisms of the ZnS/CdSe nanowire heterostructures are discussed.     

Preparation and characterization of ZnS nanoparticles deposited on montmorillonite

ZnS nanoparticles were prepared and deposited on montmorillonite (MMT) in the presence of cetyltrimethylammonium (CTA). UV spectrometry and transmission electron microscopy (TEM) proved the formation of nanoparticles with diameters ranging from 3 nm to 5 nm. Selected-area electron diffraction (SAED) patterns revealed the presence of romboedric ZnS. The band gap energy of nanosize ZnS was estimated at 3.89 ± 0.03 eV. Photoluminescence spectra exhibited a strong emission band between 300 nm and 600 nm explained by the vacant ZnS nanostructure. The prepared ZnS-montmorillonite nanocomposite (ZnS-MMT) was used for the photocatalytic reduction of CO(2) providing a considerably high efficiency that exceeded 5-6-fold the results of commercial TiO(2) Degussa P25. The main reaction products were hydrogen and methane. Methanol and carbon oxide were also observed in about 7-fold lower amounts. The stability of ZnS against oxidation was confirmed by the determination of sulphate using capillary isotachophoresis.     

核壳结构CdS/ZnS纳米微粒的制备与光学特性

CdS and CdS/ZnS core-shell structure nano particles were synthesized in micro emulsion, and characterized by X-ray diffraction(XRD), transmission electron microscopy (TEM), UV absorption spectra and PL. The average diameter of CdS was about 3.3 nm, and CdS/ZnS core-shell structure was confirmed by XRD and UV. Considering the optical properties of CdS/ZnS core-shell structure nanoparticles which have different ZnS shell thickness, the UV absorption edge of CdS/ZnS becomes as lightred-shift with the thickness of ZnS layer increasing, and the absorption of shortwave band is strongly enhanced at the same time. The PL spectra indicate that ZnS shell layer can greatly eliminate surface defects of CdS nanoparticles and make its band-edge directed recombination increased, and the luminous efficiency of CdS is improved greatly when it has appropriate shell thickness.     

Synthesis and photoluminescence of ZnS macrolattice

ZnS macrolattice has been synthesized by an ultrasonication-assisted method. It is a face-centred cubic stucture with a lattice constant of about 5.4 nm. Each basis in one unit cell composes of about 1,400 atoms. The d-spacing of the macrolattice is about 10 times to that of ordinary sphalerite crystalline. The new structure can be confirmed by small angle X-ray diffraction, high-resolve TEM and selected area electron diffraction. The emission spectrum of the ZnS macrolattice consists of two main peaks at about 333 and 349 nm, respectively under 236 nm excitation. However, it consists of only one main peak at about 438 nm under 370 nm excitation and only one main peak at about 530 nm under 473 nm excitation. The near band transition about 349 nm demonstrates that the valence band composed of P-type function on the S atom splits to two bands. The conduct band has also split because of many peaks in the excitation spectra. In addition, some defect energy levels must appear in the band gap because blue and green emissions are observed.     

ZnO纳米线形态对其光致发光性能的影响

以多孔氧化铝膜为模板,电化学沉积出Zn纳米线,再通过高温氧化得到ZnO纳米线阵列。通过改变制备多孔氧化铝模板的工艺参数来改变模板纳米孔径,进而改变ZnO纳米线的直径,得到不同形态的ZnO纳米线阵列。应用X射线衍射仪、透射电子显微镜测试技术表征了ZnO纳米线的结构与形貌。结果发现,X射线衍射时会出现随ZnO纳米线直径增大衍射峰增多和增强的现象。采用荧光光谱仪测试样品的光致发光性能,通过Gaussian原理对谱峰的拟合分析了ZnO纳米线形态对其光致发光光谱的影响。结果表明,随着纳米线直径从30nm至60nm依次增大,其结晶性和化学计量比逐渐变好。近紫外区和蓝光区的发射峰随着纳米线直径的增大而蓝移,而纳米线直径为60nm的样品则出现随直径增大而红移的现象。结果可见,直径在55~60nm间的某点将是ZnO纳米线的结构和光致发光性能变化的临界点。     

Preparation of cellulose-based fluorescent materials using Zinc sulphide quantum dot-decorated graphene by a one-step hydrothermal method

Cellulose-based fluorescent materials using Zinc sulphide (ZnS) quantum dot-decorated graphene were prepared by a one-step hydrothermal method. X-ray photoelectron spectroscopy analysis identified the chemical states of Zn, S, C, O, and N in the composite paper. Transmission electron microscopy showed that the graphite oxide was reduced to graphene sheets, and ZnS nanoparticles (<10 nm) were deposited on the surface of these sheets. Scanning electron microscopy indicated that graphene sheets were attached to the surface of paper fibers, and the paper structure and morphology of the fibers were not observably damaged during the hydrothermal reaction. The cellulose-based composite had strong ultraviolet absorption in the range of 200–340 nm, and its main absorption peak was at approximately 296 nm. The band edge emission of photoluminescence spectrum of the composite occurred at 466 nm with an excitation wavelength of 320 nm. The laser scanning confocal microscope image of the composite exhibited an intense blue fluorescence under UV light at 405 nm.     

ZnS:Mn2+/聚苯乙烯核壳及ZnS:Mn2+中空球的制备和光谱性质

ZnS:Mn2+ polystyrene (PS) core-shell structures and ZnS:Mn2+ hollow spheres were prepared by a sonoehemical deposition approach. Transmission electron micrograph (TEM) studies show that the PS surface is covered by a thin shell consisted of ZnS: Mn2+ nanoparticles with an average size of 9 nm. ZnS: Mn2+ hollow spheres were obtained by heating the core-shell particles in air at 500 ℃ to drive off PS. The photoluminescence spectrum for the emission band of Mn2+ peaked at 540 nm, and a 45 nm blue shift compared to that of corresponding bulk sample, was discussed based on the Mn-O octahedral distortion induced by shell structure.     

Template-directed synthesis of ordered iron pyrite (FeS2) nanowires and nanotubes arrays

Highly ordered iron pyrite (FeS₂) nanowires and nanotubes arrays have been fabricated by using sol–gel method with AAO templates. The prepared nanowires and nanotubes have uniform lengths and 200 nm diameters. Their crystal phase was identified as cubic FeS₂ by using X-ray diffraction, Raman spectroscopy, high-resolution transmission electron microscopy and selected-area electron diffraction pattern. The direct optical band gaps of the as-prepared FeS₂ nanowires were 0.98 and 1.23 eV, respectively, indicating their suitability for photovoltaic application.     

Luminescence Property and Synthesis of Sulfur-doped ZnO Nanowires by Electrochemical Deposition

"Sulfur-doped zinc oxide (ZnO) nanowires were successfully synthesized by an electric field-assisted electrochemical deposition in porous anodized aluminum oxide template at room temperature. The structure, morphology, chemical composition and photoluminescence properties of the as-synthesized ZnO:S nanostructures were investigated. X-ray diffraction and the selected area electron diffraction results reveal that the as-ynthesized products are single phase with hexagonal wurtzite structure with a highly preferential orientation in the (101) direction. Transmission electron microscopy observations indicate that the nanowires are niform with an average diameter of 70 nm and length up to several tens of micrometers. X-ray photoelectron pectroscopy further reveals the presence of S in the ZnO nanowires. Room-temperature photoluminescences observed in the sulfur-doped ZnO nanowires which exhibits strong near-band-edge ultraviolet peaks at 378 and 392 nm and weak green emissions at 533 and 507 nm. A blue emission at 456 nm and violet emissions at around 406, 420, and 434 nm were also observed in the PL spectrum for the as-synthesized ZnO:S nanowires. The PL spectrum shows that S-doping had an obvious effect on the luminescence property of typical ZnO nanowires."     

Ultrathin ZnS single crystal nanowires: controlled synthesis and room-temperature ferromagnetism properties

Highly uniform single crystal ultrathin ZnS nanowires (NWs) with 2 nm diameter and up to 10 μm length were fabricated using a catalyst-free colloidal chemistry strategy. The nanowires crystallized in hexagonal phase structure with preferential growth along the direction of the (001) basal plane. The strong polarity of the (001) plane composed of Zn cations or S anions drives the oriented attachment of ZnS nanocrystals (NCs) along this direction via electrostatic (or dipole) interaction. The ultrathin ZnS nanowires show intrinsic ferromagnetism at room temperature and other unusual properties related to its unique nature, such as large anisotropic lattice expansion, large blue-shift of UV-vis absorption band of the excition, and photoluminescence spectrum of the exciton band edge. First-principles DFT computation results show that Zn vacancies can induce intrinsic ferromagnetism in these undoped ZnS NWs. The main source of the magnetic moment arises from the unpaired 3p electrons at S sites surrounding the Zn vacancies carrying the magnetic moment ranging from 0.26 to 0.66 μ(B). Calculated results indicate that the magnetic moment of the ultrathin ZnS NWs can be increased by increasing the Zn vacancy concentration without significant energy cost. The calculated magnetization value (1.96 or 0.40 emu/g for Zn vacancies on the surface of NWs or inside, respectively) by Zn(53)S(54) supercell model is larger than our experimental value (0.12 emu/g at 1.8 K and 0.05 emu/g at 300 K), but the ferromagnetic result is qualitatively in agreement.     

Controlled synthesis and photoluminescence properties of ZnS nanowires and nanoribbons

Rapid synthesis of wurtzite ZnS nanowires and nanoribbons has been achieved by a simple thermal evaporation of ZnS powder onto Si substrate in the presence of Au catalyst. A vapor-liquid-solid process is proposed for the formation of the ZnS nanostructures. The flow rate of the inert carrier Ar gas along with the temperature play an important role in defining the morphology of the ZnS nanostructures. The morphological change of the ZnS nanostructures and their growth sequence were studied through scanning electron microscopy. Room-temperature photoluminescence measurements showed intense blue emission at approximately 398 nm from both the nanowires and the nanoribbons.     

Bi3.25La0.75Ti3O12纳米线的可见光催化性能

研究了用一步水热法制备的掺镧钛酸铋(Bi_3.25La_0.75Ti₃O₁₂, BLT)纳米线的光学和可见光催化性能, 并对其晶体结构和微观结构用X射线衍射(XRD)、透射电子显微镜(TEM)和高分辨透射电子显微镜(HRTEM)等手段进行了表征. 结果表明, 制备的纳米线为纯相的Bi_3.25La_0.75Ti₃O₁₂, 平均直径约为25 nm. 室温光致发光谱(PL)显示BLT纳米线在433和565 nm附近有较强的发射峰, 分别对应激子发射和表面缺陷发光. 紫外-可见漫反射光谱(UV-Vis DRS)表明BLT样品的带隙能约为2.07 eV. 利用可见光(λ>420 nm)照射下的甲基橙降解实验评价了BLT样品的光催化性能. 结果表明, BLT的光催化活性比商用TiO₂催化剂P25、掺氮TiO₂和纯相钛酸铋(Bi₄Ti₃O₁₂, BIT)高得多. BLT光催化剂具有更高催化活性的原因是La³⁺离子掺杂拓展了BIT对可见光的吸收范围, 同时抑制了BIT的光生电子-空穴的复合.     

Photoluminescence resulting from semiconductor-metal solid solution observed in one-dimensional semiconductor nanostructures

A narrow band photoluminescence (PL) emission peak resulting from CdS-Au solid solution was observed when growing one-dimensional nanostructures of CdS via the vapor-liquid-solid mechanism by using Au as the catalyst. This emission peak was located at 680 nm, a wavelength longer than the near band edge emission of CdS at 520 nm, and was shown not to be caused by the usual trap states of CdS which lead to a broad band emission. Here, the one-dimensional nanostructures of CdS were grown in a simple, low-temperature (360 degrees C) metal-organic chemical vapor deposition process with a single source precursor of CdS. Straight nanowires of diameter 50-70 nm and wormlike nanorods of diameter 100-200 nm were obtained. Both the upper and lower portions of the nanorods/nanowires possessed single crystallinity as judged from the corresponding high-resolution transmission electron microscopy images and selected area electron diffraction data. This work demonstrates the feasibility of adjusting PL emission peaks of optoelectronic semiconductors through alloying with metals.