Ag核Au壳双金属复合纳米线的制备及其表面增强拉曼光谱研究

采用氧化铝模板结合交流电沉积技术制备纯银纳米线, 然后通过化学还原方法, 并控制加入的金盐的量, 在已制备好的银线表面包裹不同厚度的金壳层, 得到具有核壳结构的Ag_核Au_壳复合纳米线. 采用电子显微镜(SEM, TEM)和表面增强拉曼光谱对该复合结构纳米线进行相关表征, 纳米线的表面形貌与加入的金盐的量有关. 以苯硫酚(TP)和对巯基苯胺(PATP)为探针分子, 研究了此类复合纳米线的表面增强拉曼散射效应. 并以PATP在金银纳米线表面吸附的表面增强拉曼光谱的差别为探针, 表征了复合纳米线表面金的包裹程度, 结果表明一定厚度的包裹程度可制备无针孔效应的核壳结构金银复合纳米线.     

锰负载量对活性炭载锰氧化物的结构及催化分解臭氧性能的影响简

将高锰酸钾与活性炭（AC）原位氧化还原制备的活性炭载锰氧化物（MnO_x/AC）用作臭氧分解的催化剂. 采用扫描电镜、X射线光电子能谱、X射线衍射、电子自旋共振波谱、拉曼光谱以及程序升温还原研究了设计Mn负载量对负载锰氧化物性质（形貌、氧化态和晶体结构）的影响. 结果表明,Mn负载量由0.44%增至11%,负载锰氧化物在活性炭表面由疏松的地衣状变为堆叠的纳米球状体,负载层的厚度由~180 nm增加至~710 nm,结构由氧化态+2.9到+3.1的低结晶β-MnOOH生长为由氧化态+3.7到+3.8的δ-MnO₂结晶. MnO_x/AC室温催化分解低浓度臭氧的活性与负载锰氧化物的形貌及含量密切相关. Mn负载量为1.1%的MnO_x/AC具有疏松的地衣状形貌,催化分解臭氧的性能最高,Mn负载量为11%的MnO_x/AC具有紧密的堆积结构,因而表现出最低的催化臭氧分解活性.     

氢分子在ZrC(111)面解离过程的动态能带结构研究

采用密度泛函方法和平板模型对H₂在ZrC(111)面上的反应途径进行了研究, 结果表明H₂在该表面上的解离易于发生. 通过考察各中间态的能带结构, 在H₂解离的过程中, H 1s诱导态(占据)所处能量位置存在着先上升后下降的过程, 同时清洁表面中处在费米能级下方的以表面Zr原子4d_xz/d_yz为主要成分的能带消失. 上述能带结构分析结果再现了活性表面态在反应过程中的作用, 并与光电子能谱观测结果相吻合.     

MnOx/Al-SBA-15的结构性质及低温NH3选择性催化还原NOx

采用后合成法制备MnO_x/Al-SBA-15催化剂, 考察了催化剂的低温NH₃选择性催化还原(SCR)NO_x的性能. 利用傅里叶透射红外变换(FTIR)光谱、N₂吸附-脱附、X射线衍射(XRD)、扫描电镜(SEM)、拉曼光谱(Raman)、X射线光电子能谱(XPS)及NH₃程序升温脱附(NH₃-TPD)的表征手段, 对催化剂的结构性质和SCR性能进行了系统分析. 结果表明, 适量Al的掺杂能提高MnO_x/SBA-15催化剂的SCR活性, 当硅铝摩尔比为50时, 催化剂活性最佳. 表征结果显示, Al掺杂后, 催化剂仍保持良好的骨架结构, 较大比表面、孔容和孔径, 并且Mn在催化剂表面富集, 由低价态转化为高价态, MnO₂为催化剂的主要活性相. 此外, Al的掺杂使MnO_x在催化剂表面高度分散, 表面酸性增强, 从而提高了催化剂的SCR活性.     

拓扑绝缘体二维纳米结构与器件

拓扑绝缘体是一种全新的量子功能材料, 具有绝缘性体能带结构和受时间反演对称性保护的自旋分辨的金属表面态, 属于Dirac 粒子系统, 将在新原理纳电子器件、自旋器件、量子计算、表面催化和清洁能源等方面有广泛的应用前景. 理论和实验相继证实Sb₂Te₃, Bi₂Se₃和Bi₂Te₃单晶具有较大的体能隙和单一Dirac 锥表面态, 已经迅速成为了拓扑绝缘体研究中的热点材料. 然而, 利用传统的高温烧结法所制成的拓扑绝缘体单晶块体样品常存在大量本征缺陷并被严重掺杂, 拓扑表面态的新奇性质很容易被体载流子掩盖. 拓扑绝缘体二维纳米结构具有超高比表面积和能带结构的可调控性, 能显著降低体态载流子的比例和凸显拓扑表面态, 并易于制备高结晶质量的单晶样品, 各种低维异质结构以及平面器件. 近年来, 我们一直致力于发展拓扑绝缘体二维纳米结构的控制生长方法和物性研究. 我们发展了拓扑绝缘体二维纳米结构的范德华外延方法, 实现了高质量大比表面积的拓扑绝缘体二维纳米结构的可控制备, 并实现了定点与定向的表面生长. 开展拓扑绝缘体二维纳米结构的谱学研究, 利用角分辨光电子能谱直接观察到拓扑绝缘体狄拉克锥形的表面电子能带结构, 发现了拉曼强度与位移随层数的依赖关系. 设计并构建拓扑绝缘体纳米结构器件, 系统研究其新奇物性, 观测到拓扑绝缘体Bi₂Se₃表面态的Aharonov-Bohm (AB)量子干涉效应等新奇量子现象, 通过栅电压实现了拓扑绝缘体纳米薄片化学势的调控, 并将拓扑绝缘体纳米结构应用于柔性透明导电薄膜. 本文首先简单介绍拓扑绝缘体的发展现状, 然后系统介绍我们开展的拓扑绝缘体二维纳米结构的范德华外延生长、谱学、电学输运特性以及透明柔性导电薄膜应用的研究, 最后对该领域所面临的机遇和挑战进行简要的展望.     

SnO2(110)弛豫表面构型与电子结构的第一性原理研究

采用基于第一性原理的密度泛函方法对SnO₂(110)表面的构型和电子结构进行了系统研究. 结果表明, 与理想表面相比, 表面弛豫导致表层五配位Sn原子向体相方向位移, 六配位Sn原子以及表面氧原子往真空方向移动, 而桥氧原子位置基本保持不变. 当表面厚度小于3 nm时, 表面能和表层原子的弛豫大小随着层数的增加出现振荡现象. 由能带计算结果得知, 以桥氧的2p_y/2i>p_z轨道为主要成分的能带出现在体相的带隙中. 进一步考察了弛豫对表面电子结构的影响.     

黄曲霉素B2分子吸附在银团簇的表面增强拉曼散射机理

采用密度泛函理论（DFT）B3LYP方法,6-311G（d,p）（C,H,O）/LANL2DZ（Ag）基组,计算了黄曲霉素B₂（AFB₂）分子吸附在Ag₂团簇的表面增强拉曼散射（SERS）光谱和预共振拉曼光谱,并与实验结果比较. 结果显示：AFB₂分子在基态Ag₂团簇表面吸附时,增强因子最大达到10²,对应吡喃（pyrane）环C=O伸缩振动,主要是由AFB₂分子周围化学环境改变而引起的基态静极化率改变导致的化学增强. 不同激发波长下的AFB₂分子预共振拉曼光谱的增强强度不同：电荷转移态激发波长为1144 和544 nm时拉曼信号增强了10²倍,而选择电荷转移预共振波长432和410 nm作为入射光时,其拉曼信号增强了10⁴倍,增强机理为银团簇和黄曲霉素分子之间的电荷转移共振增强. 因此通过改变入射光波长,选择电荷转移共振激发波长,更有利于强致癌物AFB₂分子的痕量检测.     

乙烷在V2O5(001)表面深度氧化反应机理的周期性密度泛函理论研究

采用周期密度泛函理论研究了V₂O₅ (001)表面乙烷深度氧化过程.结果表明,乙醛是主要的副产物,且脱附态的乙醛能很容易被氧化成乙酸,但多数乙醛在从表面脱附前已被氧化成CO_x.显然,在乙烷氧化脱氢反应的最终产物CO_x主要来源于乙醛.     

四元交互体系Li+,Mg2+/Cl-,SO42--H2O25℃相平衡及物化性质研究

本文采用等温溶解平衡法研究了四元交互体系Li⁺,Mg²⁺/CI^-,SO-H₂O 25℃的机关系和平衡液相的物化性质(密度、粘度、电导率、折光率和pH).该体系25℃有七个相区Li₂SO₄·H₂O,MgSO₄·7H₂O,MgSO₄·6H₂O,MgSO₄·5H₂O,MgC1₂·6H₂O,LiCI·MgCl₂·7H₂O,LiCI·H₂O,十一条单变量线,五个共饱点。其中LiCI·H₂O+LiCI·MgCl₂·7H₂O+Li₂SO₄·H₂O为一致零变量点。与文献中的研究结果比较,我们得到两个新相区MgSO₄·6H₂O和MgSO₄·5H₂O.用经验和半经验公式计算了平衡液相的密度、折光率。由实验测定的溶解度数据求得了高锂浓度下的Pitzer参数。对该体系25℃溶解度进行了理论计算复证。     

高密度非球形和球形LiNi1/3Mn1/3Co1/3O2的合成和性能比较

利用二次干燥法和共沉淀法分别制备出了非球形的Ni_1/3Co_1/3Mn_1/3OOH前驱体和球形Ni_1/3Co_1/3Mn_1/3(OH)₂前驱体, 并分别和LiNO₃混合烧结合成高密度非球形和球形的锂离子正极材料Li(Ni_1/3Co_1/3Mn_1/3)O₂. XPS分析表明, 二次干燥法制备的非球形Ni_1/3Co_1/3Mn_1/3OOH前驱体其过渡金属Ni, Co和Mn的价态分别是＋2, ＋3和＋4, 而共沉淀法制备的球形Ni_1/3Co_1/3Mn_1/3(OH)₂前驱体其各金属价态为＋2; X射线衍射分析表明, 非球形的Ni_1/3Co_1/3Mn_1/3OOH前驱体比球形的前驱体具有较高的活性, 能够在低温下合成出Li(Ni_1/3Co_1/3Mn_1/3)O₂, 而且制备的产物结晶度高, 具有规整的层状α-NaFeO₂结构, 扫描电镜显示制备的非球形产物颗粒均匀, 颗粒间隙小, 振实密度高达2.95 g•cm^－3, 远高于球形的振实密度2.35 g•cm^－3; 充放电实验表明, 由非球形前驱体制备的Li(Ni_1/3Co_1/3Mn_1/3)O₂其充放电性能和循环性能以及体积比容量均高于球形正极材料.     

La distribution on the crater surface of W-1%La2O3 produced by a single laser pulse

The W-1%La₂O₃ alloy has been irradiated by a single laser pulse (λ = 1064 nm) to simulate transient thermal loads of high energy occurring in a tokamak under operative conditions. A zone with a diameter of ~2 mm, namely, much larger than the focal spot, results to be affected by the pulse, and a crater of about 300 μm is observed in its center. La₂O₃ particles are not present inside the crater. The change of surface morphology is accompanied by elemental redistribution. Multipoint XPS analysis evidenced that the concentration of La is very low in the crater and increases moving toward the border of the affected zone while that of W shows an opposite trend. The composition changes involve only the outmost 5 nm of the sample: through depth profiling, no differences of chemical composition were detected deeper in the alloy between the center and external border of the affected area.     

Spectroscopy of growing and evaporating water droplets: exploring the variation in equilibrium droplet size with relative humidity

We demonstrate that the thermodynamic properties of a single liquid aerosol droplet can be explored through the combination of a single-beam gradient force optical trap with Raman spectroscopy. A single aqueous droplet, 2-6 microm in radius, can be trapped in air indefinitely and the response of the particle to variations in relative humidity investigated. The Raman spectrum provides a unique fingerprint of droplet composition, temperature, and size. Spontaneous Raman scattering is shown to be consistent with that from a bulk phase sample, with the shape of the OH stretching band dependent on the concentration of sodium chloride in the aqueous phase and on the polarization of the scattered light. Stimulated Raman scattering at wavelengths commensurate with whispering gallery modes is demonstrated to provide a method for determining the size of the trapped droplet with nanometer precision and with a time resolution of 1 s. The polarization dependence of the stimulated scatter is consistent with the dependence observed for the spontaneous scatter from the droplet. By characterizing the spontaneous and stimulated Raman scattering from the droplet, we demonstrate that it is possible to measure the equilibrium size and composition of an aqueous droplet with variation in relative humidity. For this benchmark study we investigate the variation in equilibrium size with relative humidity for a simple binary sodium chloride/aqueous aerosol, a typical representative inorganic/aqueous aerosol that has been studied extensively in the literature. The measured equilibrium sizes are shown to be in excellent agreement with the predictions of K?hler theory. We suggest that this approach could provide an important new strategy for characterizing the thermodynamic properties and kinetics of transformation of aerosol particles.     

Humidity controlled calorimetric investigation of the hydration of MgSO4 hydrates

The isothermal heat of hydration of MgSO₄ hydrates was studied by humidity controlled calorimetry. Two hydrates, starkeyite (MgSO₄·4H₂O) and a mixture of MgSO₄ hydrates with summary 1.3 mol H₂O were investigated. The solid-gas reactions were initiated at 30°C and 85% relative humidity. The heat of hydration was determined in a circulation cell in the calorimeter C80 (Setaram). The crystal phases formed after the hydration process were analyzed by thermogravimetry (TG) and X-ray powder diffraction (XRD). Starkeyite reacted with the water vapour to the thermodynamic stable epsomite and the MgSO₄ hydrate mixture with 1.3 mol water to hexahydrite. The hydration heats of starkeyite and the mixture were determined to be −169±3 and −257±5 kJmol⁻¹, respectively.     

Adsorption of Water on an MgSO4(100) Surface: A First‐Principles Investigation

The adsorption properties of water molecules on an MgSO₄(100) surface were investigated by using density functional theory (DFT) and supercell models. Optimized stable geometries of one and more than one water molecules adsorbed on an ideal MgSO₄(100) surface were obtained. The configurations with water molecules adsorbed on atoms of the second and third atomic layers of the MgSO₄(100) surface are quite stable. After adsorption, the separations between both the adjacent Mg atoms (R_{Mg? Mg}) and the adjacent O atoms of the surface (R_{O? O}) increase, which indicates that the MgSO₄(100) surface starts to deliquesce. In addition, water molecules are more likely to adsorb onto a defective surface rather than an ideal surface. Mulliken population analysis suggests that fewer charges transfer to the water molecule from the Mg atom of a defective substrate. Finally, Raman spectra were calculated for 0.5, 1, and 2 ML (ML=monolayer) water adsorbed on an MgSO₄(100) surface, which is helpful for further related experiments.     

Combined time- and space-resolved Raman spectrometer for the non-invasive depth profiling of chemical hazards

A time-resolved inverse spatially offset Raman spectrometer was constructed for depth profiling of Raman-active substances under both the lab and the field environments. The system operating principles and performance are discussed along with its advantages relative to traditional continuous wave spatially offset Raman spectrometer. The developed spectrometer uses a combination of space- and time-resolved detection in order to obtain high-quality Raman spectra from substances hidden behind coloured opaque surface layers, such as plastic and garments, with a single measurement. The time-gated spatially offset Raman spectrometer was successfully used to detect concealed explosives and drug precursors under incandescent and fluorescent background light as well as under daylight. The average screening time was 50 s per measurement. The excitation energy requirements were relatively low (20 mW) which makes the probe safe for screening hazardous substances. The unit has been designed with nanosecond laser excitation and gated detection, making it of lower cost and complexity than previous picosecond-based systems, to provide a functional platform for in-line or in-field sensing of chemical substances.     

Synthesis of spherical microcapsules by photopolymerization in aerosols

 The preparation of polymer microcapsules of well defined size in the range of 10–50 μm with different shell thickness to core diameter ratios is described. An aerosol of monodisperse droplets of a homogeneous ternary liquid system which contained a hydrophobic component and a hydrophilic component dissolved in a high-volatile mutual solvent, was produced by dispersing with a vibrating-orifice aerosol generator. After the evaporation of the solvent in a nitrogen atmosphere the particles demix and form a two-phase droplet of core-shell type. These droplets were illuminated with UV light and polymerized to highly monodisperse microcapsules with a solid polymer shell and a liquid core. The properties of the resulting particles (size, size distribution, shell thickness, shape and surface characteristics) were investigated by scanning electron microscopy, Raman spectroscopy on single optically levitated particles, and confocal Raman micro spectroscopy. The microcapsules were highly monodisperse and have spherical shape. Received: 24 July 1996 Accepted: 29 August 1996     

Preparation, structure, and optical properties of nanoporous gold thin films

Thin nanoporous gold (np-Au) films, ranging in thickness from approximately 40 to 1600 nm, have been prepared by selective chemical etching of Ag from Ag/Au alloy films supported on planar substrates. A combination of scanning electron microscopy (SEM) imaging, synchrotron grazing incidence small angle X-ray scattering, and N2 adsorption surface area measurements shows the films to exhibit a porous structure with intertwined gold fibrils exhibiting a spectrum of feature sizes and spacings ranging from several to hundreds of nanometers. Spectroscopic ellipsometry measurements (300-800 nm) reveal the onset of surface plasmon types of features with increase of film thicknesses into the approximately 200 nm film thickness range. Raman scattering measurements for films functionalized with a self-assembled monolayer formed from 4-fluorobenzenethiol show significant enhancements which vary sharply with film thickness and etching times. The maximum enhancement factors reach approximately 10(4) for 632.8 nm excitation, peak sharply in the approximately 200 nm thickness range for films prepared at optimum etching times, and show high spot to spot reproducibility with approximately 1 microm laser spot sizes, an indication that these films could be useful as durable, highly reproducible surface-enhanced Raman substrates.     

On optical depth profiling using confocal Raman spectroscopy

Until 2006 the performance of confocal Raman spectroscopy depth profiling was typically described and modeled through the application of geometrical optics, including refraction at the surface, to explain the degree of resolution and the precise form of the depth profile obtained from transparent and semicrystalline materials. Consequently a range of techniques, physical and analytical, was suggested to avoid the errors thus encountered in order to improve the practice of Raman spectroscopy, if not the understanding of the underlying mechanisms. These approaches were completely unsuccessful in accounting for the precise form of the depth profile, the fact that spectra obtained from laminated samples always contain characteristic peaks from all materials present both well above and below the focal point and that spectra can be obtained when focused some 40 μm above the sample surface. This paper provides further evidence that the physical processes underlying Raman spectroscopy are better modeled and explained through the concept of an extended illuminated volume contributing to the final Raman spectrum and modeled through a photon scattering approach rather than a point focus ray optics approach. The power of this numerical model lies in its ability to incorporate, simultaneously, the effects of degree of refraction at the surface (whether using a dry or oil objective lens), the degree of attenuation due to scatter by the bulk of the material, the Raman scattering efficiency of the material, and surface roughness effects. Through this we are now able to explain why even removing surface aberration and refraction effects through the use of oil immersion objective lenses cannot reliably ensure that the material sampled is only that at or close to the point of focus of the laser. Furthermore we show that the precise form of the depth profile is affected by the degree of flatness of the surface of the sample. Perhaps surprisingly, we show that the degree of flatness of the material surface is, in fact, more important than obtaining a precise refractive index match between the immersion oil and the material when seeking a high-quality depth profile or Raman spectrum from within a transparent or semicrystalline material, contrary to accepted norms that samples for interrogation by Raman spectroscopy require little preparation.     

Hygrometric Determination of Water Activities, Osmotic and Activity Coefficients, and Excess Gibbs Energy of the System MgSO4–K2SO4–H2O

Ternary aqueous solutions of MgSO₄ and K₂SO₄ have been studied by the hygrometric method at 25°C. The relative humidity of this system is measured at total molalities from 0.35 mol-kg^–1 to about saturation for three ionic-strength fractions (y = 0.25, 0.50, and 0.80 of MgSO₄. The data allow calculation of water activities and osmotic coefficients. From these measurements, the Pitzer ionic mixing parameters are determined and used to predict the solute activity coefficients in the mixture. The results are used to calculate the excess Gibbs energy at total molalities for ionic-strength fraction y.     

Cathodoluminescence depth analysis in SiO2-Si-systems

SEM cathodoluminescence (CL) is extended to luminescence center spatial depth profiling by means of electron beam energy E₀ variation and consequently variation of CL excitation range. In this way the CL profile of SiO₂-layers on Si substrate offers a dead layer of luminescence beneath the surface (10–75) nm as well as the SiO₂ oxide thickness with an accuracy of better 10% across a small spot area of less than 1 μm.