二维GaS超薄半导体的基础研究取得新进展

正最近,中国科学院半导体研究所超晶格国家重点实验室的一个研究团队,在二维GaS超薄半导体的基础研究中取得新进展。相关成果发表在2014年2月7日英国皇家化学会主办的《纳米尺度》(Nanoscale)上,并被选为"热点论文"(Hot Article)。二维半导体材料拥有独特的物理性质,可以应用于不同的技术领域,因此成为了纳米交叉学科的研究热点。石墨烯是目前研究最为广泛的二维材料,但由     

硅纳米杆拉伸的分子动力学模拟

采用Stillinger-Weber(SW)势函数描述硅纳米杆中硅原子间的相互作用,通过分子动力学方法对几种硅纳米杆进行轴向拉伸研究,发现硅纳米杆拉伸时表现出来的特性与宏观脆性材料基本一致:拉伸曲线没有明显的直线部分和屈服变形部分;进一步研究发现硅纳米杆的杨氏模量和强度极限随着尺寸增大而增大,尺寸效应随尺寸增大而逐渐减弱.     

纳米SnO_2的制备及其气敏特性分析

半导体纳米粒子应用于气敏材料是一新兴的研究领域,综述了ＳｎＯ２ 半导体超细化处理的研究进展。对各种制备方法作了详细描述,控制材料粒径的大小及粒度的分布、保证纳米团簇的稳定存在是纳米ＳｎＯ２ 制备的关键;分析了纳米ＳｎＯ２ 半导体材料的气敏特性,由于材料的比表面积增大、活性位增多,而具有着优异的气敏性能;并对其应用前景做出了进一步的展望。     

基于一种多功能系统的二维纳米器件高效制备

原子级厚度的二维层状晶体材料具有丰富的物理特性,在新型微纳米器件领域展现出重要的发展潜力,相关的器件制备和性能研究也引起了广泛的关注.二维材料微纳米器件的制备需要经过二维材料的转移及金属电极的淀积等一系列过程.然而,在传统的制备流程中所涉及多步工艺需要用到诸多不同设备,如二维材料转移对准系统、电子束曝光系统,或是光刻系...     

狭缝高度对传热倍增及温度漂移特性的影响

为研究隔板对流装置的传热特性和温度漂移特性与系统几何尺寸的关系，采用DNS方法对不同狭缝高度和不同隔板数目的隔板对流装置进行计算，结果表明：传热通道中单向层流化的流动具有很好的二维性，二维与三维模拟计算得到相同的Nu。对多层隔板对流装置的传热倍增特性进行二维数值模拟发现：改变隔板顶端狭缝高度，传热倍增效果进一步增强；在隔板厚度相同时，不同隔板数的隔板对流装置存在一致的最优狭缝高度。定量研究传热通道的温度漂移量与狭缝高度的关系，发现二者存在标度律变化关系。     

ZrO_2-NiO陶瓷气敏元件初探

在寻找新型气敏材料的过程中,我们制备了ZrO_2-NiO陶瓷材料,对其半导体特性与气敏性进行了初步研究。先后试验了它们在不同工艺条件下的导电性,对O_2、CO、C_4H_(10)等气体和氯仿、甲苯、汽油、酒精等蒸汽的敏感性。结果发现:由于ZrO_2的加入,改变了NiO的特性,不仅降低了NiO的电导,而且使其在不同烧结温度下表现出不同类型的半导体特性。 我们将材料做成直热式元件,采用图1线路测试其导电特性,並确定其导电类型。     

纳米TiO2光催化剂降解甲基橙的动力学模拟研究

TiO₂具有很好的紫外吸收和高催化活性。作为一种廉价和环境友好的光催化剂,纳米TiO₂在废水处理、空气净化和太阳能电池等方面都具有潜在应用。为筛选出优良的催化剂,必须对纳米TiO₂构效关系进行深入研究。计算机模拟作为动力学研究的重要手段之一,对于研究光催化纳米TiO₂材料XRD参数与活性关系,具有重要意义。本文通过溶胶—凝胶法制备了纳米TiO₂光催化剂,进行了XRD测试。以难降解的偶氮染料甲基橙为探针,选取材料制备中的关键影响因素,在不同的热处理温度下测定其降解甲基橙活性。在此基础上,提出一个新的速率方程模拟煅烧温度对TiO₂光催化降解甲基橙的影响.结果表明,随着温度的升高,反应速率从指数型到S-型、V-型传变。与普通的动力学方程相比,所提出的新微分方程能对这种影响进行很好的模拟。     

溶胶—凝胶法制备纳米SnO2材料

本文介绍了一种新型分散介质在溶胶－凝胶法制备纳米ＳｎＯ２材料中的应用。通过扫描电子显微镜比表面积测试仪和Ｘ射线衍射仪等实验等手段对ＳｎＯ２材料的粒径大小进行测试和分析，结果表明，本实验方法制备的ＳｎＯ２材料粒径最小为１５ｎｍ左右，实验还发现，热处理对ＳｎＯ２材料的粒径大小有很大的影响。     

氧化锌纳米线振动问题研究

采用连续介质理论与分子动力学模拟相结合的方法,研究了氧化锌纳米线的振动问题.建立了氧化锌纳米线核壳模型,解释其等效杨氏模量及压电常数的尺寸效应.通过连续介质理论求得氧化锌纳米线振动固有频率,并与分子动力学模拟得到的结果进行对比.研究表明,氧化锌纳米线在极化方向的等效拉伸杨氏模量随着横截面尺寸的增加而逐渐增大,且通过核壳模型分别求得核、壳拉伸杨氏模量.拟合得到的等效拉伸杨氏模量与分子动力学方法获得的等效拉伸杨氏模量符合得很好.根据连续介质理论得到等效弯曲杨氏模量,发现等效弯曲杨氏模量也随着横截面尺寸的增加而增大.氧化锌纳米线极化方向的压电耦合能力比一般压电陶瓷好,压电常数随着横截面尺寸的增加逐渐减小.氧化锌纳米线在不同温度条件下的振动频率没有明显变化,在不同外电场条件下的振动频率有显著变化.分子动力学模拟得到不同横截面尺寸的氧化锌纳米线振动频率不同.根据连续介质理论,求得悬臂Timoshenko梁模型相应尺寸的振动频率,发现横截面的尺寸越大,连续介质理论与分子动力学模拟得到的振动频率越接近.     

纳米SnO2材料的电子显微镜表征

纳米二氧化锡为一种常用气敏材料,可通过不同方法制备二氧化锡纳米材料,利用电子显微镜,观察纳米材料的形貌、大小、结晶、生长、缺陷以及团聚现象,分析、总结制备工艺及方法对材料结构影响.     

Direct electrochemistry and electrocatalysis of myoglobin immobilized in zirconium phosphate nanosheets film

Myoglobin (Mb) is incorporated on a novel matrix—zirconium phosphate nanosheets (ZrPNS) and immobilized at a glassy carbon electrode surface. UV–vis spectra and electrochemical measurements show that the matrix is well biocompatible and can retain the bioactivity of immobilized Mb. The direct electron transfer between Mb and electrode exhibits a couple of well-defined redox peaks. The cathodic and anodic peaks are located at −0.340 and −0.280 V vs. Ag/AgCl, respectively. The ZrPNS can improve the electron transfer between Mb and electrode with an electron transfer constant of 5.6 s⁻¹. Meanwhile, the catalytic ability of the protein toward the reduction of H₂O₂, O₂, NaNO₂, trichloroacetic acid (TCA) is also studied and a third-generation biosensor is subsequently fabricated. The linear range of biosensor to H₂O₂ is from 8 × 10⁻⁷ to 1.28 × 10⁻⁵ M with the limit detection of 1.4 × 10⁻⁷ M. The small apparent Michaelis–Menten constant (34 μM) suggests that Mb/ZrPNS film performs good affinity with H₂O₂. The biosensor also exhibits acceptable stability and reproducibility. This work paves a way to develop other biologic active materials in this kind of nanosheets for constructing novel biosensors.     

MEMS Mechanical Fatigue: Experimental Results on Gold Microbeams

This paper proposes a new strategy for detecting material strength loss under mechanical fatigue on the basis of the pull-in voltage of the test device. Gold microbeam specimens are tested for mechanical fatigue using an electrostatically actuated dedicated device. The design of the fatigue device is discussed, providing the analysis of stress distribution inside the specimen. The finite-element method is used to simulate the electromechanical coupling. The fatigue limit is estimated through the “staircase” method, and a WÖhler curve is obtained from experiments. The surface topography evolution is monitored by scanning electron microscope images; specimen failure modes and material degradation are discussed, revealing the local yield of the material on the upper surface of the beam. The type of degradation appears to be in agreement with the established literature as a consequence of fatigue.$hfill$[2008-0313]      

Fabrication and gas-sensing properties of hierarchically porous ZnO architectures

Hierarchically three-dimensional (3D) porous ZnO architectures are synthesized by a template-free, economical aqueous solution method combined with subsequent calcination. First, the precursors of interlaced and monodisperse basic zinc nitrate (BZN) nanosheets are prepared. Then calcination of the precursors produces hierarchically 3D porous ZnO architectures composed of interlaced ZnO nanosheets with high porosity resulting from the thermal decomposition of the precursors. The products are characterized by X-ray diffraction, thermogravimetric-differential thermalgravimetric analysis, scanning electron microscopy, transmission electron microscopy, and Brunauer-Emmett-Teller N₂ adsorption-desorption analyses. The BET surface area of the hierarchically porous ZnO nanostructures was calculated to be 12.8 m² g⁻¹. Compared with ZnO rods, the as-prepared porous ZnO nanosheets exhibit a good response and reversibility to some organic gases, such as ethanol and acetone. The responses to 100 ppm ethanol and acetone are 24.3 and 31.6, respectively, at a working temperature of 320 °C. These results show that the porous ZnO architectures are highly promising for gas sensor applications, as the gas diffusion and mass transportation in sensing materials are significantly enhanced by their unique structures. Moreover, it is believed that this solution-based approach can be extended to fabricate other porous metal oxide materials with a unique morphology or shape.     

Dispersive SnO2 nanosheets: Hydrothermal synthesis and gas-sensing properties

SnO₂ nanosheets with the thickness of 10 nm were successfully synthesized by a simple hydrothermal process at 180 °C for 12 h. The samples were characterized by X-ray power diffraction, scanning electron microscopy, transmission electron microscopy, and high-resolution transmission electron microscopy. The sensor performance of the as-prepared SnO₂ nanosheets for ethanol and carbon monoxide was measured. The results indicate that the sensor exhibited high response, quick response-recovery kinetics, and good repeatability.     

Highly sensitive NO2 sensor based on square-like tungsten oxide prepared with hydrothermal treatment

The square-like WO₃ nanosheets were synthesized by hydrothermal treatment of irregular WO₃ nanosheets prepared through acidification of Na₂WO₄·2H₂O. The obtained square-like and irregular WO₃ nanosheets were characterized with field emission scanning electron microscopy, X-ray powder diffraction and transmission electron microscopy. The gas sensing properties of sensors based on as-prepared samples were investigated. The results indicated that both samples exhibited high response to NO₂. The sensor based on square-like WO₃ nanosheets exhibited remarkably enhanced response and faster response/recovery time for NO₂ compared with that based on irregular nanosheets. Especially, the sensor based on square-like WO₃ nanosheets could detect NO₂ down to 40 ppb, which covered environmental standard. A possible reason for the influence of unique structure on the sensing properties of sensors based on square-like WO₃ was proposed.     

Simple and cost-effective fabrication of two-dimensional plastic nanochannels from silica nanowire templates

Nanofluidic systems are attracting a great deal of interest due to their fundamental significance and potential applications in chemistry, biology and physics. However, high fabrication cost, expensive equipments and complicated fabrication process of most current fabrication techniques prevent lots of researchers from entering the nanofluidic field. Here we present a quick, simple and cost-effective method for fabricating two-dimensional (2D) nanochannel in polycarbonate (PC) substrates. Silica nanowires, taper-drawn from commercially available single-mode fiber were used as templates and embedded in the PC substrate by hot embossing. The nanochannels were created after removing the nanowires by hydrofluoric acid (HF) etching. Poly(dimethylsiloxane) (PDMS) was used to seal the nanochannel reversibly. Nanochannels with widths range from 100 to 900 nm and lengths up to several millimeters were obtained. Various nanostructures including integrated micro and nanochannels, nanochannel array, bent nanochannel and cross-shaped nanochannel were fabricated and characterized by fluorescent microscope, scanning electron microscope (SEM) and atomic force microscope (AFM).     

Au nanoparticles-functionalized two-dimensional patterned conducting PANI nanobowl monolayer for gas sensor

A facile route for the generation of two-dimensional (2D) ordered, large-area, liftable, and patterned polyaniline (PANI) nanobowl monolayer containing Au nanoparticles has been demonstrated with the monolayer self-assembled polystyrene (PS) spheres at the aqueous/air interface as template. Tetrachloroauric acid has been used as an oxidizing agent for the polymerization of aniline in aqueous solution. The morphologies, compositions, and structure of the obtained samples were characterized by scanning electron microscope, transmission electron microscope, Fourier transform infrared spectroscopy and X-ray diffraction. Additionally, the sensor response to NH₃ of our products has been investigated and ultra-fast response and recovery behavior have been obtained, which endows our product in practical gas detector.     

Formation and optical properties of silver superlattice using hydrazine hydrate as reducing agent

Superlattice of silver nanoparticles was prepared using a liquid–liquid two-phase method with hydrazine hydrate (N₂H₄·H₂O) as reducing agent. The ordered of silver nanoparticles were formed on carbon films coated on transmission electron microscopy (TEM) copper grids by evaporating a drop of silver colloid. The scanning electron microscope, energy dispersive X-ray spectrometer analyses, X-ray diffraction, and fluorescence spectrometer were used to characterize the superlattice. The formation process of the silver nanoparticles was investigated by UV–visible absorption spectroscopy and TEM. The TEM images show directly the results with obvious structure of superlattice. In addition, the UV–visible spectra of the silver nanoparticles colloidal phase obtained finally showed that the system is monodisperse.     

基于反射光谱的PCA及BP神经网络法预测甘蔗叶片叶绿素含量

叶绿素是植物进行光合作用的重要色素,叶绿素含量可以作为评价植物生长状况的重要参数。本研究基于甘蔗叶片的反射光谱,利用PCA及BP神经网络算法,建立了甘蔗叶片的叶绿素含量预测模型。PCA算法可以在尽可能少地丢失有用光谱信息的前提下,降低输入光谱矩阵的维数,最大限度地减少冗余信息。BP神经网络算法因其良好的非线性逼近能力可大大提高该模型的预测精度。研究发现：基于PCA和BP算法建立的叶绿素含量预测模型,其预测值与实测值之间的R2达0.8929,表明该模型具有较高的预测能力。     

Synthesis of quantum size ZnO crystals and their gas sensing properties for NO2

Quantum size ZnO crystals have been synthesized successfully by a room temperature sol-gel process. Oleic acid (OA) has been used as capping agent to control the particle size of ZnO. The crystal structure and size of the ZnO are characterized by the X-ray diffraction (XRD) and transmission electron microscope (TEM). The XRD results show the as-synthesized ZnO has hexagonal wurtzite structure and the average crystallite size is 5.7 nm which is little less than TEM result. It is testified by photoluminescence (PL) and Raman spectra that the quantum size ZnO keeps the crystal structure of the bulk ZnO and possesses more surface defects. The quantum size ZnO has the highest response of 280 to NO₂ and the highest selectivity of 31 and 49 corresponding to CO and CH₄ at operating temperature of 290 °C. The effect of calcination temperatures on sensing property and transient response of the ZnO sensor are also investigated.