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。     

Synthesis of europium-doped zinc oxide micro- and nanowires

Single crystalline Eu³⁺-doped wurtzite ZnO micro- and nanowires were synthesized by a chemical vapor deposition method (CVD). The nanostructures were grown by autocatalytic mechanism at walls of an alumina boat. The structure and properties of the doped ZnO is fully characterized by X-ray diffraction (XRD), energy-dispersive X-ray spectrometry (EDX), scanning and transmission electron microscopy (SEM and TEM), and photoluminescence (PL) methods. The synthesis was carried out for 10 min giving vertically aligned nanowires with mean diameter of 50–400 nm and with length of up to several microns. The nanowires were grown along ±[0001] direction. The concentration of Eu³⁺ dopant in the synthesized nanowires was varied from 0.7 to 0.9 at %. The crystal structure and microstructures of the doped nanomaterials were discussed and compared with undoped ZnO. The photoluminescence spectra show that emission of doped samples were shifted towards orange-red region (2.02 eV) relative to undoped zinc oxide nanostructures (2.37 eV) due to Eu³⁺ intraionic transitions from ZnO/Eu.     

Synthesis and optical properties of S-doped ZnO nanostructures: nanonails and nanowires

S-doped ZnO nanostructures such as nanonails and nanowires have been synthesized via a simple one-step catalyst-free thermal evaporation process on a large scale. The doping concentration of sulfur into ZnO nanonails and nanowire were 2 atm % and 7.5 atm %, respectively. Studies found that the S-doped ZnO nanonails and nanowires were single-crystalline wurtzite structure and grew along the (001) direction. The average diameters of the nanonails and nanowires were 70 and 50 nm, respectively. Low-temperature photoluminescence spectra of ZnO samples showed two luminescence peaks in the UV and green emission region, respectively. As the concentration of sulfur in the ZnO nanostructures increased, the intensity of the UV emission peak decreased dramatically, and it showed a little blue-shift while the intensity of the green emission increased greatly.     

Property–Performance Control of Multidimensional,Hierarchical, Single‐Crystalline ZnO Nanoarchitectures

Diverse morphologies of multidimensional hierarchical single‐crystalline ZnO nanoarchitectures including nanoflowers, nanobelts, and nanowires are obtained by use of a simple thermal evaporation and vapour‐phase transport deposition technique by placing Au‐coated silicon substrates in different positions inside a furnace at process temperatures as low as 550 °C. The nucleation and growth of ZnO nanostructures are governed by the vapour–solid mechanism, as opposed to the commonly reported vapour–liquid–solid mechanism, when gold is used in the process. The morphological, structural, compositional and optical properties of the synthesized ZnO nanostructures can be effectively tailored by means of the experimental parameters, and these properties are closely related to the local growth temperature and gas‐phase supersaturation at the sample position. In particular, room‐temperature photoluminescence measurements reveal an intense near‐band‐edge ultraviolet emission at about 386 nm for nanobelts and nanoflowers, which suggests that these nanostructures are of sufficient quality for applications in, for example, optoelectronic devices.     

Large-scale growth of millimeter-long single-crystalline ZnS nanobelts

Millimeter-long single-crystalline hexagonal ZnS nanobelts were grown on specific locations on a wafer scale. This is the first time that the millimeter-scale ZnS nanobelt has been synthesized. The longest nanobelts are about 3 mm. The as-grown nanobelts were characterized by means of field emission scanning electron microscopy, X-ray powder diffraction, high-resolution transmission electron microscopy, and selected area electron diffraction. The results indicate that the ultra-long nanobelts are pure single-crystalline hexagonal ZnS. There are two kinds of ZnS nanobelts existing in the products. One is the nanobelts that have two smooth sides and grow along the [0 0 1] longitudinal direction, and the other is the nanobelts that have one smooth side and one saw-teeth-like side, namely nanosaws, and grow along the [2 1 0] longitudinal direction. A vapor-liquid-solid mechanism is suggested for the lengthwise growth of the ZnS nanobelts (nanosaws) and a vapor-solid mechanism for the side direction growth of the saw-teeth of the nanosaws.     

Enhanced ultraviolet emission from ZnS-coated ZnO nanowires fabricated by self-assembling method

A simple chemical route for ZnS-coated ZnO nanowires with preferential (002) orientation is reported. Sodium sulfide and zinc nitrate were employed to supply S and Zn atoms at 60 degrees C to form ZnS-coated ZnO nanowires structures. Electron diffraction measurement shows that the ZnO/ZnS core-shell nanostructure is single crystalline. Interesting features are found in the photoluminescence (PL) spectra of ZnS-coated ZnO nanostructures. After coating, the UV emission of nanorods is dramatically enhanced at the expense of the green emission. The core/shell structure with higher band gap shell material and reduced surface states should be responsible for this PL enhancement.     

ZnO Nanobelts and Hollow Microspheres Grown on Cu Foil

ZnO nanobelts, hollow microspheres, and urchins have been prepared on copper foil via a simply low temperature evaporation route. The microstructure, morphologies, and photolu-minescence of the ZnO nanostructures were studied with X-ray diffraction, Raman spectra, scanning electron microscopy and photoluminescence spectra. The width of the nanobelts was about 500 nm and the length was longer than 10μm. The diameter of the hollow microspheres was between 5 and 10μm. A possible growth mechanism of the nanobelts, microspheres and urchins was proposed. The photoluminescence spectrum exhibited strong deep level energy emissions and a weak near band edge emission. These ZnO nanostructures on a copper substrate have the advantages of naturally good adhesion and electrical connection between the ZnO nanostructures and the conductive substrate.     

Growth mechanism and optical properties of aligned hexagonal ZnO nanoprisms synthesized by noncatalytic thermal evaporation

Vertically aligned perfectly hexagonal-shaped ZnO nanoprisms have been grown on a Si(100) substrate via a noncatalytic thermal evaporation process by using metallic zinc powder in the presence of oxygen gas. The as-grown nanoprisms consist of ultra smooth Zn-terminated (0001) facets bounded with the {0110} surfaces. The as-synthesized products are single-crystalline with the wurtzite hexagonal phase and grown along the [0001] direction, as confirmed from the detailed structural investigations. The presence of a sharp and strong nonpolar optical phonon high-E2 mode at 437 cm(-1) in the Raman scattering spectrum further confirms good crystallinity and wurtzite hexagonal phase for the as-grown products. The as-grown nanoprisms exhibit a strong near-band-edge emission with a very weak deep-level emission in the room-temperature and low-temperature photoluminescence measurements, confirming good optical properties for the deposited products. Moreover, systematic time-dependent experiments were also performed to determine the growth process of the grown vertically aligned nanoprisms.     

ZnO/ZnS大面积单晶异质结及其光电性能研究

ZnO和ZnS是重要的Ⅱ-Ⅵ族宽禁带半导体材料,二者之间形成的异质结具有Ⅱ型能带结构,可以促使受激载流子实现空间分离,延长受激载流子的寿命,从而提高材料的光催化和光电探测性能。本文利用物理气相沉积方法,首次在ZnO块状单晶衬底上生长了一层ZnS单晶薄膜,薄膜由厚约4nm、边长几百纳米,取向一致的等边三角形纳米片组成。X射线衍射和透射电子显微镜的表征结果显示,ZnS薄膜与ZnO衬底具有单一外延取向关系。阴极射线荧光光谱表明ZnS薄膜的制备显著提高了ZnO单晶片可见光荧光发光峰的强度。此外,对ZnO/ZnS异质结的紫外光电探测性能的研究结果显示,异质结对不同波长的紫外光均有响应,光响应的上升弛豫时间和下降弛豫时间分别为200ms和1050ms,展示了较好的光电应用潜力。     

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."     

Formation of well-aligned ZnGa(2)O(4) nanowires from Ga(2)O(3)/ZnO core-shell nanowires via a Ga(2)O(3)/ZnGa(2)O(4) epitaxial relationship

Formation of well-aligned and single-crystalline ZnGa(2)O(4) nanowires on sapphire (0001) substrates has been achieved via annealing of the Ga(2)O(3)/ZnO core-shell nanowires. Ga(2)O(3)/ZnO core-shell nanowires were prepared using a two-step method. The thickness of the original ZnO shell and the thermal budget of the annealing process play crucial roles for preparing single-crystalline ZnGa(2)O(4) nanowires. Structural analyses of the annealed nanowires reveal the existence of an epitaxial relationship between ZnGa(2)O(4) and Ga(2)O(3) phases during the solid-state reaction. A strong CL emission band centered at 360 nm and a small tail at 680 nm are obtained at room temperature from the single-crystalline ZnGa(2)O(4) nanowires.     

Unconventional zigzag indium phosphide single-crystalline and twinned nanowires

Unconventional zigzag indium phosphide (InP) single-crystalline and twinned nanowires were produced via thermal evaporation of indium phosphide in the presence of zinc selenide. The structure and morphology of the as-synthesized products were characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Studies found that two type of nanowires exist in the products, namely, the periodic-rhombus-decorated single-crystalline InP (type I) nanowires and jagged twinned InP (type II) nanowires. Both of them have preferential 111 growth directions. The optical properties were also investigated at room temperature, and they show that the nanowires display a strong emission at approximately 750 nm, which is quite different from that observed in all previous reports related to the InP nanostructures.     

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.     

Synthesis and characterization of bismuth single-crystalline nanowires and nanospheres

A facile solution-phase process has been demonstrated for the selective preparation of single-crystalline bismuth nanowires and nanospheres by reducing sodium bismuthate with ethylene glycol in the presence of poly(vinyl pyrrolidone) (PVP) or acetone. Bismuth nanobelts and Bi/Bi(2)O(3) nanocables could be also obtained by changing some reaction parameters. Various techniques such as XRD, EDXA, SEM, TEM, HRTEM, and FT-IR have been used to investigate the physical characteristics of these low-dimensional bismuth nanostructures.     

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.     

Surface-enhanced Raman scattering and polarized photoluminescence from catalytically grown CdSe nanobelts and sheets

We have successfully fabricated single-crystalline CdSe nanowires, nanobelts, and sheets by a chemical vapor deposition (CVD) method assisted with laser ablation. The synthesized CdSe nanostructures have hexagonal wurtzite phase as characterized by X-ray diffraction (XRD). CdSe nanobelts can range in length from several tens to a hundred micrometers, in thickness from 40 to 70 nm, and a tapered width which is approximately 3 microm at one end and tapers off to approximately 100 nm at a catalytic gold particle. Both selected area electron diffraction (SAED) and high-resolution transmission electron microscopic (HRTEM) measurements show that the single-crystalline hexagonal belts and sheets grew along the [0.1-1.0] direction with side surface of +/-(0 0 0 1) and top surface of +/-(2 -1 -1 0). While the growth mechanism of nanobelts complies with a combination of vapor-liquid-solid (VLS) and vapor-solid (VS) processes, the formation of sheets is primarily based on the VS mechanism. For comparison, the phonon modes of CdSe nanobelts and bulk powder have been measured by surface-enhanced Raman scattering (SERS) and normal Raman scattering (NRS) spectroscopies with off- and near-resonant excitations. A blue-shift of 2.4 cm(-1) for the longitudinal optical (LO) phonon of CdSe nanobelts, relative to bulk CdSe, is attributed to a lattice contraction in the belt structure, which is confirmed by the XRD measurement. Room-temperature microphotoluminescence (PL) at approximately 1.74 eV from single CdSe nanobelts shows a 3-fold enhancement compared to that from bulk CdSe powder and displays a partial polarization dependence of emission angles.     

氧化锌纳米带的低温无催化热蒸发制备及其表征

通过纯锌粉蒸发，在600 ℃无催化条件下成功制备了高质量的不同形貌的ZnO纳米带.该制备方法中控制产物形貌和尺寸的关键是氧、氩及锌蒸气的流速及分压.扫描电镜及高分辩透射电镜观察显示，氧化锌纳米带具有规整光滑及齿状等不同形貌，且皆为单晶，其生长由固-气机理控制.室温光致发光谱表明，齿状氧化锌纳米带在390 nm附近形成紫外发射峰；在455～495 nm时，形成绿光发射峰，该处由4个次级发射峰组成.     

Fabrication of 3D rotor-like ZnO nanostructure from 1D ZnO nanorods and their morphology dependent photoluminescence property

A facile and eco-friendly sonochemical route to fabricate well-defined dentritic (rotor-like) ZnO nanostructures from 1D ZnO nanorods without alloying elements, templates and surfactants has been reported. Phase and structural analysis has been carried out by X-ray diffraction (XRD) and Fourier Transform Infra-Red (FTIR) spectroscopy, showed the formation of hexagonal wurtzite structure of ZnO. Scanning electron microscopic (SEM) study showed the formation of rotor-like ZnO nanostructure having a central core which is surrounded by side branches nanocones. Transmission electron microscopic (TEM) study showed that these nanocones grow along [0001] direction on the six {01–10} planes of central core ZnO nanorods. A plausible formation mechanism of rotor-like ZnO nanostructures was studied by SEM which indicates that the size and morphology of side branches can be controlled by adjusting the concentration of OH^? ions and time duration of growth. The photoluminescence (PL) spectrum of the synthesized rotor-like ZnO nanostructures exhibited a weak ultraviolet emission at 400 nm and a strong green emission at 532 nm recorded at room temperature. The influence of morphology on the origin of green emission was discussed in detail. The results suggested a positive relationship among polar plane, oxygen vacancy and green emission.     

Catalyst-nanostructure interfacial lattice mismatch in determining the shape of VLS grown nanowires and nanobelts: a case of Sn/ZnO

Vapor-liquid-solid (VLS) is a well-established process in catalyst-guided growth of nanowires. The catalyst particle is generally believed to be in liquid state during growth, and it is the site for adsorbing incoming molecules; the crystalline structure of the catalyst may not have any influence on the structure of the grown one-dimensional nanostructures. In this paper, using tin particle guided growth of ZnO nanostructures as a model system, we show that the interfacial region of the tin particle with the ZnO nanowire/nanobelt could be ordered (or partially crystalline) during the VLS growth, although the local growth temperature is much higher than the melting point of tin, and the crystallographic lattice structure at the interface is important in defining the structural characteristics of the grown nanowires and nanobelts. The interface prefers to take the least lattice mismatch; thus, the crystalline orientation of the tin particle may determine the growth direction and the side surfaces of the nanowires and nanobelts. This result may have important impact on the understanding of the physical chemical process in the VLS growth.     

Self-assembly and hierarchical organization of Ga2O3/In2O3 nanostructures

We report on the realization of novel 3-D hierarchical heterostructures with 6-and 4-fold symmetries by a transport and condensation technique. It was found that the major core nanowires or nanobelts are single-crystalline In2O3, and the secondary nanorods are single-crystalline monoclinic beta-Ga2O3 and grow either perpendicular on or slanted to all the facets of the core In2O3 nanobelts. Depending on the diameter of the core In2O3 nanostructures, the secondary Ga2O3 nanorods grow either as a single row or multiple rows. The one-step growth of the unique Ga2O3/In2O3 heteronanostructures is a spontaneous and self-organized process. The simultaneous control of nanocrystal size and shape together with the possibility of growing heterostructures on certain nanocrystal facets opens up novel routes to the synthesis of more sophisticated heterostructures as building blocks for opto- and nanoelectronics.