范德华外延生长硫化镉二维纳米片及其光致发光性能研究

二维纳米材料具有独特的结构和优异的性能,在电子学及光电子学领域有广泛的应用前景,但关于硫化镉二维纳米材料的制备及性能研究还鲜有报道。本文首次采用范德华外延生长技术,在氟金云母片衬底上制备了硫化镉二维纳米片。通过扫描电子显微镜、透射电子显微镜、原子力显微镜、X射线粉末衍射仪和拉曼光谱仪等分析手段对产物的形貌、厚度、晶体结构、成分等进行了系统的研究。结果表明,纳米片具有六方纤锌矿晶体结构,尺寸约为几个微米,厚度约为几十纳米。范德华外延生长技术在硫化镉二维单晶纳米片制备上的成功应用,为其它二维非层状材料的制备提供了新的思路,并使其在高性能电子和光电子器件上的应用成为了可能。     

花生酸单分子膜诱导PbS晶体取向生长的研究

以花生酸单分子膜为模板，诱导沉积了PbS半导体纳米粒子，粒径为30～50 nm.实验发现， 由于花生酸单分子膜的诱导作用， 使得PbS晶体在膜上发生取向生长，可以形成三角形、四边形和棒状的PbS纳米粒子.通过改变单分子膜的表面压，考察了表面压对PbS晶体取向生长的影响，结合透射电镜及电子衍射实验，对PbS晶体的生长机制进行了初步的分析和探讨.     

立方体形PbS纳米晶的制备

在60～100 ℃下，以醋酸铅为铅源，硫代乙酰胺为硫源，乙二胺为溶剂，制备了立方体形的PbS纳米晶，采用XRD、TEM、SAED、SEM等对合成的产物进行了形貌和结构的表征。结果表明得到的产物为单晶的立方体形PbS，颗粒大小均匀。并且随着反应时间的延长，反应温度的升高，硫源比例的增加，立方体变大。通过控制不同的反应条件，可以合成边长从几十个纳米到几百个纳米的立方体形PbS晶体。     

一维链状聚-L-苯丙氨酸合银(Ⅰ)单晶及纳米晶体的合成与表征

合成了[Ag(L-Phe)]_∞单晶，晶体属于单斜晶系，空间群为P2₁，a=0.723 3(9) nm，b=0.641 2(8) nm，c=1.016 4(13) nm，β= 106.098(3)°，V=0.451 5(10) nm³，Z=2，F(000)=268，R₁=0.053 1。Ag(Ⅰ)分别与2个L-苯丙氨酸分子的羧基氧原子和氨基氮原子连接形成二配位结构，并沿a轴形成无限的一维链状结构，该链状结构呈现不太明显的右螺旋构型；采用“线性反应器”合成了一系列(直径为20～60 nm，长度为200 nm～2.2 μm)纳米尺寸，结构与单晶一致的[Ag(L-Phe)]_∞一维链状物，TEM观察了该纳米晶的自组装过程。     

WO3纳米片：基于有机-无机杂化前驱物的制备及光催化性能

以商业三氧化钨粉末做为钨源,通过合成WO_x-EDA（EDA=乙二胺）有机-无机杂化纳米带为前驱物,再加盐酸酸化,迅速得到中间产物正交型钨酸单晶纳米片。再在空气气氛下,将中间产物在管式炉中煅烧2h,最终得到单斜型三氧化钨单晶纳米片。一系列对比实验的结果表明,在由杂化纳米带转变成钨酸纳米片时,反应温度、反应时间、酸化浓度等实验参数对产物的结构和形貌有着很大的影响。通过计算,制得的三氧化钨纳米片带隙为2.48eV。对比于商业三氧化钨粉末,三氧化钨纳米片在可见光降解罗丹明B（RhB）中表现出更优越的性能。     

简捷溶剂热技术制备纳米棒基PbS树枝晶

以氯化铅和硫氰酸钾为原料,乙二醇为溶剂,采用简捷溶剂热技术制备了半导体PbS纳米棒基树枝晶。粉体用XRD、XPS、FESEM、TEM和ED进行了表征。单个PbS树枝晶具有三维空间结构,由一个主干和四个相互垂直侧枝组成。主干长2～10 μm,直径150～300 μm,每组侧枝纳米棒相互平行,沿主干垂直生长,棒长0.1～1.5 μm,直径80～180 nm。并对生长过程进行了探讨。     

水热合成MoO3纳米带的生长机理研究

以离子交换法制备的氧化钼溶胶为前驱体，在水热条件下制备了单晶MoO₃纳米带，对样品进行了XRD、SEM和TEM分析。通过考察水热反应温度和时间对产物结构和形貌的影响，结合材料热力学和动力学理论，探讨了MoO₃纳米带在水热条件下的生长机理。离子交换法制备的溶胶在水热条件下首先转变为热力学亚稳相h-MoO₃六角柱，随着温度的升高和时间的延长，h-MoO₃按照溶解-重结晶过程转变为稳定相α-MoO₃纳米带。     

微乳液中球形及棒状SrTiO3纳米粒子的控制合成

以氢氧化锶和钛酸四丁酯为原料, 在水溶液/Triton X-100/环己烷/正己醇反相微乳液体系中制备了直径约为20～80 nm的钛酸锶球形纳米粒子和长约300～1200 nm、直径约为30～150 nm的钛酸锶纳米棒. 用XRD, ICP, TEM, SAED和SEM对样品的结构、成分和形貌进行了表征; 用DLS分析了样品的粒度分布. 结果显示, 水与表面活性剂的物质的量比(ω₀)、反应物浓度、陈化时间等因素都能影响钛酸锶纳米粒子的形貌和尺寸. 所得钛酸锶的锶钛物质的量比约为1.0, 粒度分布较窄, 为立方相单晶结构.     

化学气相沉积法制备InSe纳米片及其近红外光探测性能

采用化学气相沉积法在云母衬底上制备了二维In Se纳米片,研究了生长温度对二维In Se纳米片晶相、形貌、尺寸及厚度的影响.构筑了基于二维In Se纳米片的光探测器并研究了其光探测性能,结果表明,在808 nm的近红外光辐照下,其光响应度为1. 5 A/W,外量子效率为230%,可探测度为3. 1×10⁸Jones(1 Jones=1 cm·Hz^1/2·W^-1),上升和衰减时间分别为0. 5和0. 8 s.     

PbS纳米棒束的水热合成与表征

以乙酸铅和硫脲为主要原料,十二烷基磺酸钠和十六烷基三甲基溴化铵为表面活性剂.在120℃反应12 h.水热法制备了PbS纳米棒束.并利用X射线粉末衍射(XRD)、透射电子显微镜(TEM)和高分辨电子显微镜(HRTEM)等手段对产物进行了表征.实验结果表明:产物为立方结构的PbS单晶纳米棒所组成的纳米棒束.考察了乙酸铅和硫脲的摩尔比以及反应温度对合成产物的影响,发现当乙酸铅和硫脲的摩尔比为1∶1时,得到大量的PbS纳米棒束,并初步探讨了其形成机理.     

碳化硅单晶材料的溶剂热合成与表征

SiC single crystals have been prepared by the method of solvothermal synthesis with a system of SiCl4, CCl4 and metal K in an auto clave. X-ray diffraction (XRD), Raman spectra and transmission electron microscopy(TEM) were used to characterize the products. XRD reveals that the products are SiC crystals and TEM exhibits that SiC single crystal sofwires and platelets are obtained under different usages of metal K. The SiC wires have diameters of 10～20 nm and length up to 1.5μm; the platelets have lateral dimensions of 0.1～3 μm, exhibiting regular polygonal shapes and step-bunched side surface. Furthermore, the growth mechanism of the SiC single crystals is discussed and the effect of super saturation on the crystal growth and morphology is also investigated.     

Ultrathin spin-coated dioleoylphosphatidylcholine lipid layers in dry conditions: a combined atomic force microscopy and nanomechanical study

Atomic force microscopy (AFM) has been used to study the structural and mechanical properties of low concentrated spin-coated dioleoylphosphatidylcholine (DOPC) layers in dry environment (RH ≈ 0%) at the nanoscale. It is shown that for concentrations in the 0.1-1 mM range the structure of the DOPC spin-coated samples consists of an homogeneous lipid monolayer ～1.3 nm thick covering the whole substrate on top of which lipid bilayer (or multilayer) micro- and nanometric patches and rims are formed. The thickness of the bilayer structures is found to be ～4.5 nm (or multiples of this value for multilayer structures), while the lateral dimensions range from micrometers to tens of nanometer depending on the lipid concentration. The force required to break a bilayer (breakthrough force) is found to be ～0.24 nN. No dependence of the mechanical values on the lateral dimensions of the bilayer structures is evidenced. Remarkably, the thickness and breakthrough force values of the bilayers measured in dry environment are very similar to values reported in the literature for supported DOPC bilayers in pure water.     

CP/MAS ~(13)C NMR技术对木浆纤维微观结构的研究

利用交叉极化结合魔角旋转技术~(13)C核磁共振法(CP/MAS ~(13)C NMR)对桉木浆纤维的微观结构进行研究,为进一步研究木质纤维素材料开发过程中反应障碍特征奠定基础.通过对NMR光谱C1区(δ 102～108)进行洛仑兹拟合,得到桉木浆纤维中纤维素Iα的相对含量为26.92%,纤维素Iβ的相对含量为52.04%,主要以纤维素Iβ晶体形式为主.通过计算纤维素C4结晶区(δ 86～92)和非结晶区(δ 80～86)的相对含量得到桉木浆的纤维素结晶度为47%.通过洛仑兹和高斯函数的混合模型对NMR光谱C4区(δ 80～92)进行拟合得到基原纤尺寸和微原纤横向尺寸分别为4.0与17.9 nm,并通过计算不同形态的结晶纤维素的相对含量得到纤维素结晶度为51%,证实了在微原纤内部次晶纤维素的存在.     

Photonics of bis(diethylaminobenzylidene)cyclopentanone and its analogue with the bisazacrown moiety in acetonitrile

Photoprocesses in bis(diethylaminobenzylidene)cyclopentanone (D1) and its bis(aza-18-crown-6) derivative (D2) have been studied in acetonitrile. The absorption, fluorescence, and phosphorescence spectra of D1 are similar to those of D2. Laser excitation of oxygen-free solutions of D1 and D2 leads to generation of a triplet state with a lifetime of ～1 μs and two intermediate species with lifetimes of ～100 μs and longer than 1 s.     

Towards Scalable Fabrications and Applications of 2D Layered Material-based Vertical and Lateral Heterostructures

Among 108423 unique, experimentally known 3D compounds, there exist 1825 ones that are either easily or potentially exfoliable. This increasingly broad library of 2D layered materials(2DLMs) with variable physical properties as well as the unique ability to vertical stacking or lateral stitching 2DLMs into complex heterostructures enables a new dimension for materials engineering and device design, offering novel functional electronics and optoelectronics for flexible industry. In this review, we present a comprehensive summary of the state-of-the-art scalable fabrication technologies, the unique properties as well as the potential device applications of the emerging 2D heterostructures. Firstly, we depict an overall picture of the 2D vertical van der Waals heterostructures. Secondly, we focus on the 2D lateral heterostructures by CVD technique. For a quick access and full coverage, both the vertical and lateral 2D heterostructures are classified into several types according to their chemical compounds with different dimensions. In the end, both the challenges and potential applications of these 2D heterostructures are discussed.     

Size fractionation of graphene oxide sheets by pH-assisted selective sedimentation

Graphene oxide (GO) sheets prepared by Hummers' method have been separated into two portions with large (f1) or small (f2) lateral dimensions from their aqueous dispersion. This method is based on the selective precipitation of GO sheets with lateral dimensions mostly (>90%) larger than 40 μm(2) at a pH value of 4.0 because of their larger hydrophobic planes and fewer hydrophilic oxygenated groups. The hydrazine reduced Langmuir-Blodgett (LB) films of f1 showed much higher conductivities than those of f2. Furthermore, the thin film of f1 prepared by filtration exhibited a smaller d-space and much higher tensile strength and modulus than those of f2 films. The one-step size fractionation method reported here is simple, cheap, efficient, and environmentally friendly, which can be used for the size fractionation of GO sheets in large scale.     

Size Fractionation of Two‐Dimensional Sub‐Nanometer Thin Manganese Dioxide Crystals towards Superior Urea Electrocatalytic Conversion

A universal technique has been proposed to sort two‐dimensional (2D) sub‐nanometer thin crystals (manganese dioxide MnO₂ and molybdenum disulfide MoS₂) according to their lateral dimensions. This technique is based on tuning the zeta potential of their aqueous dispersions which induces the selective sedimentation of large‐sized 2D crystals and leaves the small‐sized counterparts in suspension. The electrocatalytic properties of as‐obtained 2D ultrathin crystals are strongly dependent on their lateral size. As a proof‐of‐concept study, the small‐sized MnO₂ nanocrystals were tested as the electrocatalysts for the urea‐oxidation reaction (UOR), which showed outstanding performance in both half reaction and full electrolytic cell. A mechanism study reveals the enhanced performance is associated with the remarkable structural properties of MnO₂ including ultrathin (ca. 0.95 nm), laterally small‐sized (50–200 nm), and highly exposed active centers.     

Ag-Doped Free-Standing 2D TiO2 Sheets: Electronic,Optical, Magnetic,and Self-Healing Behaviour

Beyond a critical doping level, Ag–2D TiO₂ sheets (ATO) are deemed to be a flexible transparent conductor, useful for visible-range functional photonic/optoelectronic devices/sensors, sunlight-sensitive catalysis, and light-activated resistive switching. Due to the lack of control of surface energy which often leads to the formation of structural defects and even dimensionality crossover (2D to 0D) of materials during doping reaction, it is challenging to obtain ATO with a controlled doping level. Gauging the urgency, therefore we report the surface energy-controlled synthesis of ATO employing liquid phase exfoliation of TiO₂ and subsequent hydrothermal Ag-doping in the presence of Hexamethylenetetramine (HMTA). Electron microscopy and atomic force microscopy reveal ATO sheets with large lateral dimensions. 6-fold, 4-fold, and strain-mediated crystallographic phases of 2D ATO have been revealed by high-resolution electron imaging. Successful tuning of the band gap down to ~2 eV with Ag doping up to ~10 % is obtained. Synthesized 2D ATO have been investigated for their electrical, optical, optoelectronic, photoluminescence, and ferromagnetic behaviour. Visible light-sensitive thermally/structurally robust semiconductor/conductor via tuneable doping will pave the way for their flexible as well as wearable device applications. Self-healing effect of AFM tip-generated mechanical stress has also been demonstrated.     

1, 3-双磷(膦)酰基丙烯类化合物的^1H、^3^1P NMR研究

本文报道了标题类化合物中十个化合物的^1H和^3^1PNMR的研究结果。其中分别运用了2DJ分解谱以及异核COSY谱等多种技术,解析了它们的^1H和^3^1P图谱,从而证实了合成反应的区域选择性和立体选择性。文章中,讨论了手性中心或其它因素而表现出的不等性;讨论了影响δ~P和J~p~H数值的各种因素:还报道了比较少见的^3^1P-^3^1P之间的远程偶合。其中,顺式产物的^4J~P~P数值(约9Hz)大于反式产物的^4J~P~P(约7Hz)。