Structural characterization of long ZnSe nanowires

ZnSe nanowires have been synthesized by vapor transport in an Ar atmosphere. The synthesized ZnSe nanowires have a thickness of 20 to 120 nm and a length of tens of micrometers. The nanowires are single crystals with a cubic zinc-blende structure growing along the [111] direction. The as-synthesized nanowires display rich Raman modes and one photoluminescence band peaking at around 450 nm. PACS 78.67.Bf; 81.07.Bc; 61.46.+w     

Influence of Sb on a controlled-growth of aligned ZnO nanowires in nanoparticle-assisted pulsed-laser deposition

Single-crystalline ZnO nanowires on a sapphire substrate have been synthesized by a nanoparticle-assisted pulsed-laser deposition (NAPLD) using a pure and Sb₂O₃ doped ZnO target. Low density and vertically well-aligned ZnO nanowires were grown on hexagonal cone-shape ZnO cores by introduction of a ZnO buffer layer. More than 90% of the ZnO cores of the Sb-induced ZnO nanowires are formed in the same size of 400 nm. The ZnO nanowires consist of single-crystalline wurtzite ZnO crystal and grow along [0001] direction. The room-temperature photoluminescence spectrum exhibited a strong ultraviolet emission at around 380 nm and a relatively low broad band emission in the visible region, indicating a low concentration of structural defect in the nanowires. Sb can be used as one of the effective additives to control the morphology and alignment of ZnO nanowires synthesized by NAPLD.     

Temperature-Dependent Defect-Induced New Emission in ZnSe Crystal

The temperature-dependent photoluminescence behaviour of chemical vapour transport （CVT）-grown ZnSe crystal is investigated. A new emission band appears when temperature is reduced to 155K. It is shown that the new emission band is strongly related to defect emission peaked at around 2.1 eV. The emergence of the new emission band is accompanied by decreasing emission intensity of free exciton, as well as redshiR of defect emission with temperature decreases. The activated energy of the defect state is estimated to be 60.6 meV, which is approximately equal to the energy difference between the new emission and the free exciton emission at 155K.     

高分子软模板法自组装生长ZnO纳米线及其光学性能

采用自组装技术,利用均聚极性高分子(聚丙烯酰胺、聚乙烯醇等)长分子链作为自组装模板在半导体硅衬底上自组装生长出ZnO纳米线。采用扫描电镜(FE-SEM)和透射电镜(HRTEM)对样品的表面形貌和结构分析表征的结果表明,ZnO纳米线直径约50~80nm、长度大于4μm,具有六方纤锌矿单晶结构,且沿c轴方向择优取向生长。采用室温下光致发光(PL)谱和紫外吸收(UV)光谱对制得的ZnO纳米线的光学性能研究表明,其PL光谱上有较强的紫外发射和较弱的蓝光发射,UV吸收光谱表明样品在紫外区有强的宽带吸收,且随着纳米线粒径的减小,吸收峰出现了蓝移现象。研究探讨了高分子诱导ZnO纳米线自组装定向生长机制、发光机理及其与工艺条件的内在联系。     

Synthesis of [100] Wurtzite InN Nanowires and [011] Zinc-Blende InN Nanorods

One-dimensional wurtzite InN nanowires and zincblende InN nanorods are prepared by chemical vapour deposition （CVD） method on natural cleavage plane （110） of GaAs. The growth direction of InN nanowires is [100], with wurtzite structure. The stable crystal structure of InN is wurtzite （w-InN）, zincblende structure （z-InN） is only reported for 2D InN crystals before. However, in this work, the zincblende InN nanorods [011] are synthesized and characterized. The SEM and TEM images show that every nanorod shapes a conical tip, which can be explained by the anisotropy of growth process and the theory of Ehrlich Schwoebel barrier.     

Pressure-induced phase transition and electronic properties of AlN nanowires: an ab initio study

The structural stability of AlN nanowires have been analyzed in wurtzite (B4), zincblende (B3), rocksalt (B1) and CsCl (B2) type phases using density functional theory based ab initio approach. The total energy calculations have been performed in a self-consistent manner using local density approximation as exchange correlation functional. The analysis finds the B4 type phase as most stable amongst the other phases taken into consideration and observes the structural phase transition from B4?→?B3, B4?→?B1, B4?→?B2, B3?→?B1 and B3?→?B2 at 42.7, 76.54, 142, 30.4 and 108.9?GPa respectively. Lattice parameter, bulk modulus and pressure derivatives of AlN nanowires have also been calculated for all the stable phases. The electronic band structure analysis of AlN nanowires shows a semiconducting nature in its B4, B3 and B1 type phases, whereas the B2 type phase is found to be metallic.     

Growth and characterization of large-scale uniform Zinc Sulfide nanowires by a simple chemical reaction technique

Zinc Sulfide (ZnS) nanowires were grown in the pores of anodic alumina membrane. A simple chemical reaction technique was used where pores in the anodic alumina membrane act as reactors. Uniform morphology of nanowires was found using scanning electron microscopy (SEM). X-ray diffraction (XRD) and Micro-Raman spectroscopy revealed the wurtzite nature of ZnS nanowires. UV–visible spectroscopy of nanowires exhibited no blue shift. The room temperature photoluminescence measurement observed an emission peak around 390 nm.     

Photoluminescence properties of GaAs nanowire ensembles with zincblende and wurtzite crystal structure

Self‐standing III–V nanowires (NWs) are promising building blocks for future optoelectronic devices such as LEDs, lasers, photodetectors and solar cells. In this work, we present the results of low temperature photoluminescence (PL) characterization of GaAs NWs grown by Au‐assisted molecular beam epitaxy (MBE), coupled with the transmission electron microscopy (TEM) structural analysis. PL spectra contain exci‐ ton peaks from zincblende (ZB) and wurtzite (WZ) crystal structures of GaAs. The peaks are influenced by the quantum confinement effects. PL bands corresponding to the exciton emission from ZB and WZ crystal phases are identified, relating to the PL peaks at 1.519 eV and 1.478 eV, respectively. The obtained red shift of 41 meV for WZ GaAs should persist in thin NWs as well as in bulk materials. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Hydrothermal synthesis and characterization of ZnS hierarchical microspheres

In the present work, wurtzite ZnS hierarchical microsphere nanostructures composed of nanowires were synthesized through hydrothermal method. The morphologies and microstructures of the as obtained wurtzite ZnS sample were investigated by scanning electron microscopy and transmission electron microscopy. The results show that the diameter of the nanowires is about 10 nm, the length is about 500 nm, growing along the [0 0 1] direction. UV–visible spectroscopy shows that the band gap of the as obtained ZnS hierarchical microspheres is 3.4 eV. Room temperature photoluminescence measurements reveals a strong green emission peak at around 516 nm. The N₂ adsorption–desorption isotherms experiment at 77 K exhibits that the surface area of the ZnS sample is 99.87 m² g⁻¹.     

Intrinsic piezobirefringence of several semiconducting chalcogenides

We have measured the piezobirefringence spectra of several II–VI compounds with zincblende (CdTe, ZnTe, ZnSe, ZnS) and wurtzite structure (CdS, ZnO) in the region of transparency. Similar studies have also been performed with rock-salt-type lead salts (PbS, PbTe). The results have been compared with theoretical prediction based on simplified models of the interband transitions and of the corresponding excitonic effects.     

退火对溶胶-凝胶法制备的ZnO薄膜结构和光致发光的影响

采用溶胶-凝胶法在n-Si(100)衬底上制备ZnO薄膜并从三个方面对其研究。X射线衍射结果表明,在含氧气氛中退火的ZnO薄膜为多晶六角纤锌矿结构,有明显的c轴择优结晶取向;退火时间的长短和温度的高低对结晶取向性和粒径均有较大影响,通过进一步的研究发现最佳处理温度在500℃左右。用扫描电子显微镜观察样品的表面和侧面形貌,晶体的生长比较均匀,粒径平均在70~160nm范围内,与XRD测量结果相一致。室温下ZnO胶体的光致发光谱表明,随着胶体老化时间的延长,胶体的紫外峰位发生了蓝移。室温下ZnO薄膜的光致发光谱表明,紫外部分的发光峰位在365,390nm,发光强度较强;在可见光区的发光强度相对较弱,但是还没有被氧完全抑制掉。     

The influence of growth temperatures on the characteristics of GaN nanowires

This paper presents the investigation of the properties of GaN nanowires synthesized from Ni-catalyzed chemical vapour deposition method under various growth temperatures. The influence of the growth temperatures on the morphological, structural and optical characteristics of the synthesized GaN nanowires was investigated in this work. Field-emission scanning electron microscopy images revealed that the 950 °C was the optimal growth temperature for synthesizing uniform, straight and smooth morphology of GaN nanowires. X-ray diffraction results demonstrated that the synthesized low dimensional GaN structures have the hexagonal wurtzite structure. Ultraviolet and blue emissions were detected from photoluminescence measurements. In addition, phonon replicas with the energy separation of 90 meV have been observed at the lower energy of the blue emission region in photoluminescence spectra.     

The photoluminescence properties of TiO2-sheathed ZnSe nanowires

ZnSe nanowires have been synthesized by thermal evaporation of ZnSe powders on gold-coated Al₂O₃(0 0 0 1) substrates and then sheathed with TiO₂ by sputtering. Our results show that sheathing Zn nanowires with thin TiO₂ layers can significantly enhance the photoluminescence (PL) emission intensity. XPS analysis results suggest that the PL enhancement is attributed to increases in the concentrations of deep levels such as oxygen and titanium interstitials as well as the density of interface states. The PL emission of ZnSe nanowires is also enhanced by thermal annealing. Annealing in an argon atmosphere is more efficient in enhancing the PL emission than annealing in an oxygen atmosphere.     

ZnSe:Al发光光谱的研究

本文用热扩散的方法在Zn饱和蒸气压下,把Al掺杂到高纯ZnSe单晶中,通过77K下的光致发光光谱研究了Al杂质的发光行为,讨论了施主一受主对发射强度、自激活中心发射强度随掺杂温度的变化规律以及与Zn饱和蒸气压的关系.本文首次报道了在300℃～900℃温度范围内进行Al掺杂的ZnSe的发光规律.     

Synthesis and optical spectroscopy of ZnO nanowires

Single crystal ZnO nanowires with lengths and diameters ranging from 2 to 30 μm and 100 to 300 nm, respectively, have been grown by the vapor transport method on SiO₂/Si substrates using Au as catalyst. Their Raman and emission properties under different excitation wavelengths have been studied at the nanoscale. Whereas Raman measurements on nanowires corroborate the well-known ZnO phonon characteristics, their photoluminescence spectra exhibit a very broad emission band, mainly in the visible region from 450 to 800 nm, which corresponds to different defect-related recombination processes. Spectrally resolved scanning near-field optical microscopy, SNOM, of single ZnO nanowires have also been performed for a direct imaging of the photoluminescence emission with high spatial resolution below 100 nm, establishing a relationship with the simultaneously acquired topography.     

微波法制备Mn2+掺杂ZnSe纳米材料及谱学性能研究

过渡金属掺杂的Ⅱ-Ⅳ族纳米材料有望替代CdSe类量子点作为新型的荧光标记物而受到广泛关注.利用微波加热法的体加热特点,以不同有机胺为配体溶剂,控制反应条件,制备了Mn2+掺杂的ZnSe纳米材料,并分别利用TEM、EDS、荧光光谱等手段对其形貌、结构和性能的关系进行了探索.Mn2+掺杂的纳米ZnSe粒子为200～500 nm的球形粒子,表面平整,为单晶的纤锌矿结构.掺杂后纳米粒子的发射峰显示Mn2+的跃迁发射,但不同的配体溶剂和掺杂量对产物的发光性能有明显影响.     

ZnSe相变、电子结构的第一性原理计算

基于第一性原理平面波赝势(PWP)和广义梯度近似(GGA)方法,对闪锌矿结构(ZB)和岩盐结构(RS)的ZnSe在0—20GPa高压下的几何结构、态密度、能带结构进行了计算研究,分析了闪锌矿结构ZnSe和岩盐结构ZnSe的几何结构.在此基础上,研究了ZnSe的结构相变、弹性常数、成键情况以及相变压强下电子结构的变化机理.结果发现:通过焓相等原理得到的ZB相到RS相的相变压强为15.3GPa,而由弹性常数判据得到的相变压强为11.52GPa,但在9.5GPa左右并没有发现简单立方相的出现;在结构相变过程中,sp3轨道杂化现象并未消除,Zn原子的4s电子在RS相ZnSe的导电性中起主要贡献.     

Anomalous phase transition of InN nanowires under high pressure

Uniform InN nanowires were studied under pressures up to 35.5 GPa by using in situ synchrotron radiation x-ray diffraction technique at room temperature. An anomalous phase transition behavior has been discovered. Contrary to the results in the literature, which indicated that In N undergoes a fully reversible phase transition from the wurtzite structure to the rocksalt type structure, the In N nanowires in this study unusually showed a partially irreversible phase transition. The released sample contained the metastable rocksalt phase as well as the starting wurtzite one. The experimental findings of this study also reveal the potentiality of high pressure techniques to synthesize In N nanomaterials with the metastable rocksalt type structure, in addition to the generally obtained zincblende type one.     

ZnSe晶体中Cu杂质深能级的ODLTS谱

用控制Cu杂质在ZnSe品格中占据位置的方法,成功地得到了Cu-G和Cu-R中心分别占优势的ZnSe:Cu晶体.首次用ODLTS方法测得与Cu-R和Cu-G中心相应的受主能级分别位于价带顶上0.72eV和0.30eV.     

Synthesis and field emission properties of ZnO nanoneedle arrays grown at low temperatures via a thermal evaporation method

We have developed a straightforward and simple strategy for large-scale growth of well-aligned ZnO nanoneedles via a thermal evaporation method. XRD and SAED patterns of nanoneedles can be indexed to hexagonal ZnO with wurtzite structure. Room temperature photoluminescence analysis showed a strong ultra violet emission at 365 nm and a broad deep level visible emission at 472 nm. The growth mechanism of the nanoneedles has been investigated by SEM and the lower pressure of both evaporated zinc and oxygen flux would favor the nucleation of the finer nanowires from those previously formed high coverage spots. The field emission current density of ZnO nanoneedles sharply reached ~0.048 mA/cm² at a field of 3.1 V/m.