Synthesis and photocatalytic property of ZnSe flowerlike hierarchical structure

Spherical flowerlike hierarchical structure of ZnSe(en)_0.5 was synthesized via a solvothermal route in the NH₃·H₂O-ethylenediamine (en)-N₂H₄·H₂O system at 180 °C for 24 h. The hierarchical structure is assembled from lots of regular nanosheets. The ZnSe(en)_0.5 was further converted into pure hexagonal ZnSe by annealing in a flowing nitrogen gas at 500 °C for 1 h with morphology preserved. The formation mechanism of ZnSe was discussed. The UV-visible absorption spectrum and PL spectrum of the ZnSe spherical flowerlike hierarchical structure were measured. In addition, photocatalytic activity of the ZnSe flowerlike structure for the degradation of methyl orange under the irradiation of the simulated sunlight was investigated. The excellent catalytic activity for the degradation of methyl orange was found and the possible mechanism of the photocatalytic activity is also proposed.     

Fabrication and magnetic behaviour of 2D ordered Fe/SiO2 nanodots array

We have demonstrated a simple and universal morphology-controlled growth of 2D ordered Fe/SiO₂ magnetic nanodots array, which was based on 2D colloidal monolayer template composed of polystyrene (PS) spheres and one-step sol-gel spin-coating technique. The Fe/SiO₂ nanodots have a well-ordered structure arranged in a hexagonal pattern. The dots have the shape of quasi-pyramidal tetrahedron, which reside in the interstitial region between three PS spheres and the substrate. Magnetic measurements reveal that the nanodots array exhibits the in-plane easy magnetization direction. Compared with the unpatterned Fe/SiO₂ thin film, the dots array has lower saturated field, higher remanence and coercivity. The present method is applicable to 2D ordered nanodots array of other magnetic materials.     

Selective growth of ZnO nanodots prepared by metalorganic chemical vapor deposition on focused-ion beam-nanopatterned substrates

Selective formation of ZnO nanodots grown by metalorganic chemical vapor deposition (MOCVD) was achieved on focused-ion beam (FIB)-nanopatterned SiO₂ and Si substrates. The selective formation characteristics, dimension, and density of ZnO nanodots on FIB-nanopatterned substrates strongly depended on the FIB-patterning and MOCVD-growth conditions. The mechanism of the selective formation of ZnO nanodots on FIB-nanopatterned SiO₂ substrates is attributed to a surfactant effect of the implanted Ga which leads to the formation of the preferred nucleation sites for the growth of ZnO nanodots, while that of ZnO nanodots on nanopatterned Si substrates is mainly considered in terms of the generation of surface atomic steps and kinks, which are created by Ga⁺ ion sputtering, on the patterned Si areas.     

Enhancement of photoluminescence intensity from Si nanodots using Al2O3 surface passivation layer grown by atomic layer deposition

Temperature-dependent photoluminescence (PL) from Si nanodots with Al₂O₃ surface passivation layers was studied. The Si nanodots were grown by low pressure chemical vapor deposition and the Al₂O₃ thin films were prepared by atomic layer deposition (ALD), respectively. The BOE (Buffer-Oxide-Etch) treatment resulted in the damaged surface of Si nanodots and thus caused dramatic reduction in the PL intensity. Significant enhancement of the PL intensity from Si nanodots after the deposition of Al₂O₃ thin films was observed over a wide temperature range, indicating the remarkable surface passivation effect to suppress the non-radiative recombination at the surface of Si nanodots. The results demonstrated that the Al₂O₃ surface passivation layers grown by ALD are effectually applicable to nanostructured silicon devices.     

Enhanced field emission from PbTiO3 nanodots prepared by phase separation approach

Uniformly distributed PbTiO₃ nanodots were successfully prepared by phase separation approach. A precursor sol film was first spin-coated on Si wafer and then spontaneously separated into two distinct phases owing to the Marangoni instability. PT nanodots with tailorable size and density were obtained after further heat treatment. X-ray diffraction analysis indicated that these nanodots showed a perovskite structure. An excellent room temperature field emission property of PbTiO₃ nanodots was observed: the minimum turn-on voltage was about 5.3 V/μm; while the emission current density reached about 270 μA cm⁻² at an applied field of about 9.25 V/μm.     

Growth and characterization of InGaN nanodots hybrid with InGaN/GaN quantum wells

Uniform InGaN nanodots were successfully grown on SiO₂ pretreated GaN surface. It was found that the InGaN nanodots were 20?nm in diameter and 5?nm in height, approximately. After the growth of two periods of InGaN/GaN quantum wells on the surface of InGaN nanodots, nanodot structure still formed in the InGaN well layer caused by the enhanced phase separation phenomenon. Dual-color emissions with different behavior were observed from photoluminescence (PL) spectrum of InGaN nanodots hybrid with InGaN/GaN quantum wells. A significant blueshift and a linewidth broadening were measured for the low-energy peak as the increase of PL excitation power, while a slight blueshift and a linewidth narrowing occurred for the high-energy peak. Accordingly, these two peaks were assigned to be from the In-rich nanodots and quantized state transition from the InGaN/GaN quantum wells with indium content, respectively.     

Lattice instability induced by 3<Emphasis Type="Italic">d</Emphasis> impurities in a zinc selenide crystal

It was experimentally shown that, in a 3d-impurity-doped ZnSe crystal with the zinc blende structure, nanosized ionic shear displacements of the trigonal (ZnSe : Ni, ZnSe : V) and tetragonal (ZnSe : Cr) types arise at temperatures of 300 and 120 K. As the temperature decreases in the range 100.0–4.2 K, the shear elastic moduli C ₄₄ (ZnSe : Ni) and (C ₁₁–C ₁₂)/2 (ZnSe : Cr) are softened owing to the 3d impurities. A new peak at a frequency of 90 cm^?1 appears in the Raman scattering spectrum of ZnSe : Ni at 5 and 20 K.     

二硫化钼纳米点中的缺陷辅助载流子俘获超快动力学

二硫化钼纳米点正在成为有潜质的半导体材料用于光电设备的应用.然而,关于对其中激子动力学的研究却很少.本文利用飞秒瞬态吸收光谱学来研究二硫化钼纳米点的载流子动力学.结果显示,缺陷辅助的载流子再复合过程与观测到的动力学相符,通过俄歇散射对光激载流子进行俘获至少存在两种不同俘获速率的缺陷.四个过程参与了载流子驰豫,在受到光激发后,立即在~0.5 ps内载流子冷却,然后大部分载流子被缺陷快速俘获,随着泵浦能量的增加,该过程对应的时间从~4.9 ps增加到~9.2 ps,这可以用缺陷态的饱和来解释.接下来,拥有相对慢的载流子俘获速率的其它类型缺陷对小部分载流子进行俘获,该过程约65 ps.最后,剩余的少量载流子通过直接带间跃迁发生电子-空穴再复合,时间约为1 ns.研究结果可以深入了解二硫化钼纳米点中的载流子动力学基本原理,引导其更多的应用.     

基于ZnSe的有机-无机异质结电致发光器件

以电子束蒸发的方法制备硒化锌(ZnSe)薄膜，研究了基于ZnSe的有机-无机异质结电致发光器件.在双层器件ITO/ZnSe(50nm)/Alq₃(12nm)/Al中看到了峰值位于578nm的ZnSe电致发光，却很难得到单层器件ITO/ZnSe(50—120nm)/Al的电致发光；在此基础上进一步引入有机空穴传输层(HTL)，通过改变器件的结构，讨论了ZnSe对有机-无机异质结器件ITO/HTL/ZnSe/Alq₃/Al电致发光特性的影响.其电致发光光谱的研究结果证实了ZnSe在器件中的作用：ZnSe既起传输电子的作用，也起到传输空穴的作用，还作为发光层.并对ZnSe的发光机理进行了讨论. 关键词： 硒化锌 有机-无机异质结 电致发光 空穴传输层     

Growth of size-tunable periodic Ni silicide nanodot arrays on silicon substrates

The fabrications of size-tunable periodic arrays of nickel metal and silicide nanodots on (0 0 1)Si substrates using polystyrene (PS) nanosphere lithography (NSL) and heat treatments have been investigated. The growth of epitaxial NiSi₂ was found to be more favorable for the Ni metal nanodot arrays. The effect becomes more pronounced with a decrease in the size of the Ni nanodots. The sizes of the epitaxial NiSi₂ nanodots were tuned from 38 to 110 nm by varying the diameter of the PS spheres and heat treatment conditions. These epitaxial NiSi₂ nanodots formed on (0 0 1)Si were found to be heavily faceted and the faceted structures were more prone to form at higher temperatures. Based on TEM, HRTEM and SAED analysis, the faceted NiSi₂ nanodots were identified to be inverse pyramids in shape. Compared with the NiSi₂ nanodot arrays formed using single-layer PS sphere masks, the epitaxial NiSi₂ nanodot arrays formed from the double-layer PS sphere templates exhibit larger interparticle spacings and smaller particle sizes. Since the nanoparticle sizes, shapes and interparticle spacings can be adjusted by tuning the diameter of the PS spheres, stacking conditions, and heat treatment conditions, the PS NSL technique promises to be an effective patterning method for growth of other nanostructures.     

Growth of high-density Ru- and RuO2-composite nanodots on atomic-layer-deposited Al2O3 film

Growth of Ru- and RuO₂-composite (ROC) nanodots on atomic-layer-deposited Al₂O₃ film has been studied for the first time using ion-beam sputtering followed by post-deposition annealing (PDA). X-ray photoelectron spectroscopy analyses reveal that RuO₂ and Ru co-exist before annealing, and around 10% RuO₂ is reduced to metallic Ru after PDA at 900 °C for 15 s. Scanning electron microscopy measurements show that well-defined spherical ROC nanodots are not formed till the PDA temperature is raised to 900 °C. The mean diameter of the nanodots enlarges with increasing PDA temperature whereas the nanodot density decreases, which is attributed to coalescence process between adjacent nanodots. It is further illustrated that the resulting nanodot size and density are weakly dependent on the annealing time, but are markedly influenced by the decomposition of RuO₂. In this article, the ROC nanodots with a high density of 1.6 × 10¹¹ cm⁻², a mean diameter of 20 nm with a standard deviation of 3.0 nm have been achieved for the PDA at 900 °C for 15 s, which is promising for flash memory application.     

Structural investigations of silicon nanostructures grown by self-organized island formation for photovoltaic applications

The self-organized growth of crystalline silicon nanodots and their structural characteristics are investigated. For the nanodot synthesis, thin amorphous silicon (a-Si) layers with different thicknesses have been deposited onto the ultrathin (2 nm) oxidized (111) surface of Si wafers by electron beam evaporation under ultrahigh vacuum conditions. The solid phase crystallization of the initial layer is induced by a subsequent in situ annealing step at 700 °C, which leads to the dewetting of the initial a-Si layer. This process results in the self-organized formation of highly crystalline Si nanodot islands. Scanning electron microscopy confirms that size, shape, and planar distribution of the nanodots depend on the thickness of the initial a-Si layer. Cross-sectional investigations reveal a single-crystalline structure of the nanodots. This characteristic is observed as long as the thickness of the initial a-Si layer remains under a certain threshold triggering coalescence. The underlying ultra-thin oxide is not structurally affected by the dewetting process. Furthermore, a method for the fabrication of close-packed stacks of nanodots is presented, in which each nanodot is covered by a 2 nm thick SiO₂ shell. The chemical composition of these ensembles exhibits an abrupt Si/SiO₂ interface with a low amount of suboxides. A minority charge carrier lifetime of 18 µs inside of the nanodots is determined.     

c-Axis correlated extended defects and critical current in YBa2Cu3Ox films grown on Au and Ag-nano dot decorated substrates

We report measurements of critical current in YBa₂Cu₃O_x films deposited on SrTiO₃ substrates decorated with silver and gold nanodots. An increase in critical current in these films, in comparison with the films deposited on non-decorated substrates, has been achieved. We argue that this increase comes from the c-axis correlated extended defects formed in the films and originated from the nanodots. Additionally to creating extended defects, the nanodots pin them and prevent their exit from the sample during the film growth, thus keeping a high density of defects and providing a lower rate of decrease of the critical current with the thickness of the films. The best pinning is achieved in the samples with silver nanodots by optimising their deposition temperature. The nanodots grown at a temperature of a few hundred °C have a small diameter of a few nanometres and a high surface density of 10¹¹–10¹² particles/cm². We give evidence of c-axis correlated extended defects in YBa₂Cu₃O_x films by planar and cross-sectional atomic force microscopy, transmission electron microscopy and angle-dependent transport measurements of critical current.     

Near-infrared intersubband absorption in (CdS/ZnSe)/BeTe type-II super-lattices grown on GaAs substrate by MBE

We study the dependence of absorption wavelength on the well width in the (CdS/ZnSe)/BeTe super-lattices(SL). With well-width reduction, the wavelength decreases from 1.795 to 1.57 μm. Structural properties, strain state and interface composition are determined via XRD measurement. A (CdS/ZnSe)/Be_xMg_1−xTe structure is prepared and XRD reveals the average lattice constant match to GaAs substrate. TEM reveals that numerous stacking faults exist in the (CdS/ZnSe)/BeTe structure, and stacking faults are completely suppressed in (CdS/ZnSe)/Be_xMg_1−xTe SLs. Intersubband transition down to 1.535–1.55 μm have been observed in SLs.     

Controlling the nanodot formation on GaAs surface during focused ion beam processing

GaAs processed using gallium-focused ion beams for the fabrication of photonic devices mostly results in gallium nanodots on the surface. These gallium nanodots may produce unwanted effects and deteriorate the optical and electrical properties of the devices. We have investigated the FIB processing of GaAs with and without exposure to an insulator-enhanced etching precursor gas (XeF₂) to explore the use of XeF₂ during GaAs processing. It is reported that without the gas, FIB processing results in nanodots on the surface that vary in size and density depending on processing parameters such as incident energy, beam current, angle and dwell time. Processing with insulator (XeF₂)-enhanced etching gas irrespective of the process parameters eliminates the nanodots and results in a smooth surface, as characterized by scanning electron microscopy and atomic force microscopy. This method will be useful for surfaces which require dry processing without exposure to any wet chemical etching.     

ZnSe/SiO2复合薄膜光学常数与荧光光谱的研究

采用溶胶-凝胶工艺与原位生长技术，制备了ZnSe/SiO₂复合薄膜.X射线衍射分 析表明薄膜中ZnSe晶体呈立方闪锌矿结构.X射线荧光分析结果显示薄膜中Zn与Se摩尔比为1 ∶1.01—1∶1.19.利用场发射扫描电子显微镜观察了复合薄膜的表面形貌，结果表明复合薄 膜表面既存在尺寸约为400nm的ZnSe晶粒，也存在尺寸小于100nm的ZnSe晶粒.利用椭偏仪测 量了薄膜椭偏角Ψ，Δ与波长λ的关系，采用Maxwell-Garnett有效介质理论对薄膜的光学 常数、厚度、气孔率、ZnS 关键词： 2复合薄膜')" href="#">ZnSe/SiO₂复合薄膜 光学性质 椭偏光度法 荧光光谱     

Determination of L-tyrosine Based on Luminescence Quenching of Mn-Doped ZnSe Quantum Dots in Enzyme Catalysis System

In this paper, we attempted to develop a novel application of Mn-doped ZnSe quantum dots (Mn: ZnSe d-dots) as probes to detect L-tyrosine (L-Tyr). The bio-conjugates of horseradish peroxidase (HRP)-conjugated Mn: ZnSe d-dots were used in the enzyme catalyzed reaction of L-Tyr with H₂O_2. Compared with traditional CdTe QDs, Mn: ZnSe d-dots have better biocompatibility and less negative impact on enzyme catalyzed system. In HRP-conjugated Mn: ZnSe-L-Tyr-H₂O₂ system, electron transfer occurred between Mn: ZnSe d-dots and HRP. It resulted in the luminescence quenching of the Mn: ZnSe d-dots., which can be used to detect L-Tyr. The coupling of efficient quenching of Mn: ZnSe d-dots photoluminescence (PL) and the effective enzyme-catalysis can afford a simple and sensitive method for L-Tyr detection. The Mn: ZnSe d-dots-enzyme catalyzed system displays great potential in the development of enzyme-based biosensing systems for various analytes.     

Investigations on structural,optical and electrical parameters of spray deposited ZnSe thin films with different substrate temperature

ZnSe thin films have been deposited on high cleaned glass substrate by spray pyrolysis technique within the glass substrate temperature range (400 ^○C to 450 ^○C). The structural properties of ZnSe thin films have been investigated by (XRD) X-ray diffraction techniques. The X-ray diffraction spectra showed that ZnSe thin films are polycrystalline and have a cubic (zinc blende) structure. The most preferential orientation is along the (111) direction for all spray deposited ZnSe films together with orientations in the (220) and (311) planes also being abundant. The film thickness was determined by an interferometric method. The lattice parameter, grain size, microstrain and dislocation densities were calculated and correlated with the substrate temperature (T_S). The optical properties of ZnSe thin films have been investigated by UV/VIS spectrometer and the direct band gap values were found to be in the region of 2.65 eV to 2.70 eV. The electrical properties of ZnSe thin films have been investigated using the Van der Pauw method and the high quality ZnSe thin films were observed to develop at 430 ^○C with a resistivity of 56,4×10⁵ ohm cm, a conductivity of 1.77×10^-7 (Ω cm)^-1 and a hall mobility of 0.53 cm²/Vsec.     

The self-activated luminescence of ZnS1−xSex

The self-activated luminescence (SA) of ZnS : I, ZnSe : Cl, ZnSe : A1, and some ZnS_1?xSe_x : Cl single crystals has been investigated at LHeT under excitation with light. The SA-luminescence band has been identified in each case by the temperature dependence and by a direct excitation band resulting in polarized emission. Symmetry C_3v in case of ZnS : I and ZnSe : Cl and symmetry C_s in case of ZnSe : A1 for the SA-centre have been unambiguously revealed from angular dependences of polarization. Thus the nearest neigbour-compensated cation-vacancy has been identified as complex responsible for SA-luminescence.     

应变超晶格(ZnS)1/(ZnSe)1的光学性质

用linear mufin tin orbital能带方法，计算Si衬底上（ZnS）_n/（ZnSe）_n（001）超晶格的能带结构，计算中采用外加调整势进行带隙修正．在得到较准确的能带结构和波函数的基础上，计算该超晶格系统的光学介电函数虚部ε₂（ω）．结果表明，该超晶格系统的光学性质结合了ZnS和ZnSe体材料光学性质的特点，在相当宽的能量范围内有较好的光谱响应．并且该超晶格系统是直接带隙材料，在光电器件应用中有很大潜力． 关键词：