花状TiO2的制备及光催化性能研究

采用溶剂热法合成了花状TiO2,运用SEM、XRD和N2物理吸附-脱附等对其形貌、结构、比表面积和孔径进行了表征,并以甲基橙为模拟污染物研究了它们的光催化性能.结果表明,花状TiO2结构为锐钛矿相,是由纳米晶定向聚集形成纳米棒组成的3D花状结构,花状结构的直径在0.7～1.5 μm,平均直径在1.1μm,细小纳米晶聚集形成的纳米棒的直径在20～25 nm,长度100～ 150 nm.该样品具有较高的比表面积,表现出良好的光催化活性.     

CdSe纳米晶薄膜的光敏特性研究

硒化镉(CdSe)是一种光电性能优异的II-VI族化合物半导体.采用真空热蒸发技术在Si(100)衬底上制备出高质量的CdSe纳米晶薄膜,并利用X射线衍射仪(XRD)、Raman光谱仪、膜厚测试仪、扫描电镜(SEM)和数字源表对其结晶性能、晶体结构、表面形貌及光敏特性进行了表征.结果显示,CdSe纳米晶薄膜呈六方纤锌矿结构,纯度较高,结晶性能较好,沿c轴择优生长的优势明显;同时,薄膜具有典型的光敏电阻特性,且电阻值受光照强度、退火温度影响明显.     

ZnO纳米颗粒团聚微球的生长机理研究

采用化学浴沉积法,以Zn(CH3COO)2和TEA为反应体系,制备了ZnO纳米颗粒团聚微球,并对不同陈化时间阶段下的产物分别进行了物相、形貌、热重以及傅里叶红外吸收光谱表征,同时研究了不同TEA含量对最终产物的影响.结果表明:在恒温陈化过程中,首先会生成纳米片状的Zn5(OH)8Ac2·2H2O,同时它们之间相互连接为花状结构.其次随着陈化时间的增加,花状的Zn5(OH)8Ac2·2H2O不断分解为ZnO纳米颗粒,最后ZnO纳米颗粒会进一步自组装为一定尺寸的微米球.     

三硒化二铋微/纳米晶的可控合成

采用溶剂热法,在N,N-二甲基甲酰胺和乙二醇的混合溶剂中,无碱条件下,通过添加适量聚乙烯吡咯烷酮(PVP),成功制备出硒化铋微/纳米晶.采用X射线衍射(XRD)、扫描电子显微术(SEM)、透射电子显微术(TEM)、选区电子衍射(SAED)、高分辨透射电镜(HRTEM)和X射线光电子能谱(XPS)对产物进行了表征,结果表明获得了Bi2Se3单晶纳米片结构,边长约为300～1100 nm,厚度约为200～500 nm,讨论了PVP添加量对产物形貌的影响,并研究了六方片状硒化铋产物的产生机理.     

水热法制备类花状MoS2纳米纸微球

采用水热合成技术,以钼酸钠、硫脲为反应剂,草酸为助还原剂,去离子水为溶剂,合成了类花状结构的MoS2纳米纸微球,采用X射线衍射仪(XRD)、拉曼光谱、透射电镜(HRTEM)、扫描电子显微镜(SEM)和X射线能量色散谱(EDS)对样品的结构、形貌和成分进行分析,重点研究了草酸浓度对MoS2纳米纸微球的形貌和结构的影响规律.结果表明:在适当的反应剂浓度下,合成的MoS2是由大量厚度约30 nm左右的纳米纸花瓣聚集在一起形成的类花状微球组成的.MoS2微球具有2H型六方晶系结构,而每片纳米纸花瓣是单晶结构的层状MoS2.反应前驱液中草酸的浓度对微球的大小、形貌和结晶度有显著的影响.最后讨论了类花状结构的MoS2纳米纸微球的生长机理.     

单层MoSe2-WSe2平面异质结的可控生长及表征

二维(2D)材料由于其独特的性质和原子级厚度而受到了广泛的关注.尽管目前学术界与工业界已经成功地制备了具有不同光学和电学性质的单种2D材料,但是为了构建用于实际应用的更复杂的器件,必须开发用于制造2D异质结构的策略.在这里主要研究了单层二硒化钼(MoSe2)与二硒化钨(WSe2)平面异质结的生长,以水溶性钼酸铵((NH4)6Mo7O24·4H2O)与钨酸铵((NH4)10W12O41)分别作为钼源与钨源,通过改进的一步生长法,并调控前驱体反应位置、含量与生长时间、温度等关键生长参数,采用化学气相沉积(CVD)法在SiO2/Si衬底上制备出平面异质结,并使用光学显微镜,拉曼光谱(RAMAN),光致发光光谱(PL),原子力显微镜(AFM),扫描电子显微镜(SEM)等,对异质结的样貌、物质组分、表面形貌、表面形态等进行表征.分析可见制备的异质结由单层硒化钼与硒化钨组成,且高度为0.8 nm.这种连续可控的方法具有很强的普适性,为其他多结异质结的制备开辟了道路.     

分等级结构氧化镍花状微球的制备及其机理研究

以六水合硝酸镍为原料,采用简易溶剂热法制备了具有分等级结构的氧化镍纳米片-花状微球.采用X-射线衍射(XRD)、扫描电镜(SEM)和高分辨率透射电镜(HR-TEM)、傅立叶变换红外光谱(FT-IR)等测试技术对其物相形貌进行分析表征.结果表明:在脲素存在条件下,利用醇热法可以合成花状碱式硝酸镍前驱体,在经400℃热处理2h后,形成了由薄片组成的花状微球,并且由于二次结晶过程,在原来的球体表面形成了扇面状平滑单晶薄片,厚度约为几十纳米.整个晶体生长过程,出现了溶解-再结晶的现象,即可以通过溶解-再结晶的过程来实现对氧化镍微观形貌的调控;并初步探讨了这种具有分等级结构的纳米片-花球结构的形成机理.     

介孔Co3S4纳米棒的制备及电催化产氧性能的研究

以六水合硝酸钴(Co(NO3)2· 6H2O)为钴源,硫脲(CS(NH2)2)为硫源,采用溶剂热法和低温固相硫化的方法制备出了介孔Co3S4纳米棒.采用X射线衍射(XRD),扫描电镜(SEM)和透射电镜(TEM)等手段对于介孔Co3S4纳米棒进行表征,同时对介孔Co3S4纳米棒进行了电催化产氧性能测试.结果表明:介孔Co3S4纳米棒的起始过电位为0.37 V,塔菲尔斜率为76.95 mV/dec,具有高的电催化产氧性能.     

水热法制备纳米Co0.5Zn0.5Fe2O4工艺条件试验研究

采用水热法合成纳米Co0.5Zn0.5Fe2O4粉体,并借助X射线衍射仪(XRD)、透射电子显微镜(TEM)、矢量网络分析仪(VNA)研究工艺条件(晶化温度、晶化时间)对Co0.5Zn0.5Fe2O4物相、形貌及吸波性能的影响.结果表明,当晶化时间为8 h、晶化温度为180℃时制备出纯相的尖晶石结构的纳米Co0.5Zn0.5Fe2O4,样品形貌为类球形,平均粒径为10～15 nm.在1～18 GHz频段内,样品在16.47 GHz处的反射率达到-33.9 dB,吸波性能最好.     

NiTiO3纳米晶的溶胶-凝胶制备工艺研究

以无机镍盐和钛酸四丁酯为起始原料,采用溶胶-凝胶法制备了NiTiO3纳米晶.采用X射线衍射(XRD)、综合热分析仪(DSC/TG)以及透射电镜(TEM)对制备的纳米晶进行了测试和表征.研究了不同镍源、后处理温度对钛酸镍纳米晶相组成以及显微结构的影响.结果表明:以硝酸镍为起始原料更易获得单一物相的NiTiO3纳米晶;以硝酸镍为原料,乙醇为溶剂,n(柠檬酸):n(Ni2++Ti4+)=1:1,后处理温度为700 ℃为制备NiTiO3纳米晶的最佳工艺条件.由谢乐公式推算得出NiTiO3晶粒生长符合Brook关系式,计算得到晶粒生长活化能为Ea=43.07 kJ/mol.     

CsI-LiCl共晶材料的坩埚下降法生长与闪烁性能研究

本文采用坩埚下降法,在真空密封的石英坩埚中成功生长出CsI-LiCl与CsI-LiCl:Na共晶闪烁体。通过扫描电子显微镜(SEM)观察晶体微结构表明该共晶中LiCl相与CsI相存在周期性的层状排列,CsI相的厚度在5 μm左右。共晶样品的X射线激发发射谱显示在CsI-LiCl和CsI-LiCl:Na共晶样品存在缺陷发光,在CsI-LiCl样品中还观察到了纯CsI的自陷激子(STE)发光。CsI-LiCl样品在α粒子激发下的多道能谱中观察到明显的全能峰,这一结果证明CsI-LiCl共晶可用于热中子探测的潜力。     

静电纺丝法制备CeO2微纳米纤维及其除氟性能

以聚丙烯腈(PAN)为载体,六水合硝酸铈[Ce(NO₃)₃·6H₂O]为原料,采用静电纺丝法制备了Ce(NO₃)₃/PAN纤维,在空气中热处理得到CeO₂微纳米纤维,通过XRD、BET和SEM对CeO₂微纳米纤维进行表征。采用静态吸附实验探讨了CeO₂微纳米纤维去除水溶液中氟离子的性能,考察了溶液pH值、初始氟离子浓度及共存阴离子等对吸附性能的影响。结果表明,pH=3时,CeO₂微纳米纤维对F^-的吸附性能最佳,CeO₂吸附量随着F^-浓度的增大呈上升趋势。CeO₂微纳米纤维对F^-的吸附等温线遵循Langmuir模型,二级动力学模型能很好地描述CeO₂微纳米纤维对F^-的吸附过程。CeO₂微纳米纤维的除氟性能优良,可为其实际应用提供理论参考。     

First-principles coexistence simulations of supercooled liquid silicon

We perform first-principles coexistence simulations of the low-density and the high-density phases of supercooled liquid silicon and find a negative slope for the coexisting line in the temperature-pressure plane. Electron density maps and electron-localization function plots of the two phases of silicon show marked differences. The calculated differences suggest more localized electrons in the low-density liquid compared to the high-density liquid, coming from an increased population of covalent bonds, which further explain the calculated negative slope in the two phase coexistence regime. This is consistent with the presence of a pseudo-gap in low-density liquid silicon, absent in the high-density liquid which shows a metallic behavior.     

Crystal structures of thecis andtrans isomers of dithiahexahydro[3.3]metacyclophane

Structures of both thecis andtrans isomers of dithiahexahydro[3.3]metacyclophane, ?C₆H₄?CH₂SCH₂?C₆H₁₀?CH₂SCH₂?, have been determined, wherecis andtrans refer to the attachments to the cyclohexane ring. Thecis form crystallizes in the monoclinic space groupP2₁/c witha=8.4299(11)Å,b=21.772(2)Å,c=8.9724(13)Å, β=116.574(11)^o, andZ=4. Thetrans isomer packs into the monoclinic space groupP2₁ witha=8.159(16)Å,b=10.185(5)Å,c=9.558(2)Å, β=112.435(18)^o, andZ=2. The cyclohexane ring of thecis isomer is in the chair conformation, while the cyclohexane of thetrans isomer is found in a twisted boat conformation.     

CTAB与SDBS对碳酸锶粒子生长形态调控及机理研究

以表面活性剂CTAB和SDBS为化学添加剂,采用化学共沉淀法对碳酸锶晶体的生长形态进行调控,成功地制备出了实心的树枝状和花瓣为空心的花状碳酸锶粉体,并用X射线衍射(XRD)、扫描电子显微镜(SEM)和傅里叶变换红外光谱(FT-IR)等分析手段对样品进行了表征;最后重点对化学添加剂可能产生的影响机理进行了初步的探讨.结果表明,CTAB和SDBS在晶体生长的过程中能起到显著的影响作用,两者对粒子分散性能的作用效果相反,而且后者对晶体(013)和(213)晶面表面能降低的贡献明显大于前者.     

Triethyl ammonium salt of O,O′-bis(p-tolyl)dithiophosphate, [Et3NH]+[(4-MeC6H4O)2PS2]−

Triethyl ammonium Salt of O,O′-bis(p-tolyl)dithiophosphate and O,O′-bis(m-tolyl)dithiophosphate have been obtained by reaction of p- and m-cresol, respectively with P₂S₅ in toluene and have been characterized by elemental analysis, IR, ¹H and ³¹P NMR spectroscopy. The molecular structure of O,O′-bis(p-tolyl)dithiophosphate has been determined. Crystal data: [Et₃NH]⁺[(4-MeC₆H₄O)₂PS₂]⁻: Monoclinic, P2₁/c, a=15.2441(9) ?, b=10.415(2) ?, c=3.9726(9) ?, β=91.709(7)°, V=2217.5(1) ?⁻³, Z=4.Supplementary materials Additional material available from the Cambridge Crystallographic Data Centre (CCDC no. 600927 for [Et₃NH]⁺[(4-MeC₆H₄O)₂PS₂]⁻ comprises the final atomic coordinates for all atoms, thermal parameters, and a complete listing of bond distances and angles. Copies of this information may be obtained free of charge on application to The Director, 12 Union Road, Cambridge CB2 2EZ, UK (fax: +44-1223-336033; email: deposit@ccdc.cam.ac.uk or www:http://www.ccdc.cam.ac.uk).     

Crystal structure of Zn4Na(OH)6SO4Cl·6H2O

The structure of Zn₄Na(OH)₆SO₄Cl·6H₂O, a secondary mineral from Hettstedt, Germany, was determined by single-crystal X-ray diffraction. The crystals are hexagonal,a=8.413(8),c=13.095(24) Å, space group $P\bar 3$ , Z=2. The structure was refined to R=0.0554 and R_w=0.0903 for 970 reflections with I≥3σ(I). The structure can be described as zinc hydroxide layers perpendicular toc, from which sulfates and chlorides extend. The layers are held together by a system of hydrogen bonds involving hexaaquo Na⁺ ions which occupy the interlayer space.     

X-ray analysis of sideroxol from <Emphasis Type="Italic">Sideritis leptoclada</Emphasis>

Sideroxol (1), a kaurane diterpene which has the ent-7α,18-dihydroxy-15β,16β-epoxykaurane structure (MW = 320.47, C₂₀H₃₂O₃) was obtained from the acetone extract of Sideritis leptoclada plant as well as from some other Sideritis species. It crystallizes in the orthorhombic space group P2₁, 2₁, 2₁ with a = 10.967(3), b = 24.555(5), c = 6.372(4) Å, Dc = 1.240 g cm⁻³, Z = 4, and refines to R = 0.065 for 721 independent reflections. The skeleton consists of three fused six-membered rings and a five-membered ring with fused epoxide. The six membered rings exhibited slightly distorted chair conformation. In addition to sideroxol, two kaurane and five kaurene diterpenes were isolated from the hexane and acetone extracts of the studied plant.     

Photoluminescence characteristics of Mg- and Si-doped GaN thin films grown by MOCVD technique

We have studied the optical, structural and surface morphology of doped and undoped GaN thin films. The p- and n-type thin films have been successfully prepared by low-pressure MOCVD technique by doping with Mg and Si, respectively. The different carrier concentrations were obtained in the GaN thin films by varying dopant concentrations. Photoluminescence (PL) studies were carried to find the defect levels in the doped and undoped GaN thin films at low temperature. In the undoped GaN thin films, a low intensity and broad yellow band peak was observed. The donor–acceptor pair (DAP) emission and its phonon replicas were observed in both the Si or Mg lightly doped GaN thin films. The dominance of the blue and the yellow emissions increased in the PL spectra, as the carrier concentration was increased. The XRD and SEM analyses were employed to study the structural and surface morphology of the films, respectively. Both the doped and the undoped films exhibited hexagonal structure and polycrystalline nature. Mg-doped GaN thin films showed columnar structure whereas Si-doped films exhibited spherical shape grains.