过渡金属轻元素化合物的高温高压制备

过渡金属轻元素化合物（TMLEs）由于具备高硬度,高熔点,优异电学、磁学、超导等性质受到广泛关注,是一类 具有优异力学性能的功能性材料。优异力学性能与功能性的结合使TMLEs成为极端环境下使用的特种材料。然而, TMLEs的制备往往需要高温高压（HPHT）极端实验条件来克服能垒。目前,已经有了大量HPHT制备TMLEs的报道, 然而,多数只关注产物的性质,对在HPHT下TMLEs的生长机制报道较少。因此,总结HPHT制备的TMLEs,分析TMLEs的晶体生长过程,对理解TMLEs的晶体生长机理、探究新型 TMLEs的制备具有重要意义。结合本课题组研究 经验及其他相关文献,总结了HPHT方法制备的过渡金属硼化物（TMBs）、碳化物（TMCs）和氮化物（TMNs）的晶体生 长情况,分别从起始原料、温压条件、晶体形貌等方面分析了TMLEs的生长机制。总结如下：通过原料配比和温度控 制是制备TMBs单一相的关键,提出硼亚结构单元是使TMBs形成台阶式生长模式的本质因素,碳源和氮源的选择决 定了 TMCs和TMNs的生长机制。同时提出,缺少利用HPHT制备TMLEs毫米级单晶的报道,限制了TMLEs部分本 征的性质探究;并且,新型高轻元素含量的TMLEs结构依然有待开发。随着人类对材料的要求越来越苛刻,以及TMLEs的不断发展,TMLEs将在未来特种材料领域具有不可替代的地位。     

化学气相沉积单层VIB族过渡金属硫化物的研究进展

2004年以来,石墨烯因其优异的光学、电学性质而被广泛地研究,但由于其零带隙的特性极大地限制了它的应用前景.单层的VIB族过渡金属硫化物(TMDs)拥有类似石墨烯的晶体结构及可控的能带结构,是一类理想的二维直接带隙半导体材料,不仅可用于探索如谷极化等一些基础和前沿的物理问题,也可以广泛应用于纳米器件、光电子学和光催化的研究.近年来,化学气相沉积(CVD)技术作为一种相较于传统化学合成或物理剥离更加有效的制备方法被引入此类材料的生长,能够合成出拥有大面积连续的、厚薄均匀和较高晶体质量的单层TMDs.基于此,重点介绍了利用CVD技术生长单层TMDs所取得的进展,讨论了各工艺条件(如反应温度、载流气体、衬底、前驱物与衬底之间的距离等)对单层TMDs的生长及性质的影响.最后,探讨了利用CVD技术实现调控单层TMDs的尺寸、覆盖度和层厚均匀性的途径和方法.     

Electrical Conductivity in TCNQ Salts of Bis(4-dimethylaminophenylimino) sulfur and its Structural Analogues

Four compounds, N,N,N',N'-tetramethyl-p-phenylene diamine, N,N,N',N'-tetramethyl-benzidine, 4,4'-bis(dimethylamino)azobenzene and bis(4-dimethylaminophenylimino)sulfur (BAPIS) were examined electrochemically and spectroscopically. Each was shown to be a fairly good donor forming in its first oxidation state a radical-cation. The latter two materials surprisingly exhibited only single one-electron oxidations. Conformational flexibility about the -NSN- unit was studied by NMR spectroscopy and ab initio molecular orbital theory. The experimental ΔG* for a cis-trans to trans-cis interconversion in BAPIS was found to be 11.9 kcal/mole.

The four donors all form 1:1 adducts with TCNQ. The compaction resistances of the complexes have been measured as a function of temperature. Of the four, (BAPIS)(TCNQ) appears to be a one-dimensional material. The other three complexes behave as typical mixed stack organic semiconductors.     

化学气相沉积法制备二维过渡金属硫族化合物研究进展

二维过渡金属硫族化合物(TMDs)是继石墨烯之后的新型二维材料,由于其自身的独特物理化学性质在半导体、光电材料、能源储存和催化制氢等方面备受瞩目。化学气相沉积(CVD)是目前适合实现大规模制备二维材料的工艺之一,制备过程中参数的高度可控性使其具有很大优势。本文综述了近期通过CVD制备TMDs的研究进展,探讨了在CVD制备工艺中各种参数对产物生长和最终形貌的影响,包括前驱体、温度、衬底、辅助剂、压力和载气流量等。列举了一些改进的CVD制备工艺,并对其特点进行了总结。最后讨论了目前CVD制备TMDs所面临的挑战并对其发展前景进行展望。     

掺杂VO2薄膜的相变机理和研究进展

掺杂VO2薄膜是一种具有相变特性的功能材料,具有广阔的应用前景.本文综述了掺杂VO2薄膜的相变机理、制备方法和应用前景,并指出掺杂VO2薄膜的发展趋势,以期更好地探讨掺杂VO2薄膜的应用研究.     

4d过渡金属掺杂石墨烯体系对NO2分子的吸附

基于第一性原理的密度泛函理论对NO2分子吸附在4d过渡金属掺杂的石墨烯体系进行了研究.发现Cd原子价电子构型为4d105s2,形成饱和结构,不容易掺入石墨烯体系.调查了三种NO2分子的吸附情况,分别是N原子、一个O原子、两个O原子靠近石墨烯体系吸附点.通过能量优化获得最稳定的吸附构型.通过吸附能、电荷转移等数据研究了各吸附构型对NO2的吸附情况.纯的石墨烯体系对NO2分子的吸附较弱,吸附能小于0.2 eV,而4d掺杂可以明显提高吸附体系的吸附性能,多数吸附能超过了2 eV.其中掺Nb原子对NO2吸附效果最好,且吸附构型较稳定,吸附能为3.686 eV.此外,通过比较吸附前后带隙的变化,可发现掺Zr原子,石墨烯体系由半导体转变为金属,而掺Nb原子,石墨烯体系由金属转变为半导体.     

Low Dimensional Triangular Magnetic Systems in Transition Metal Intercalates of Misfit Layer Compounds

Abstract

Low dimensional triangle magnetism was studied for transition metal intercalates of incommensurate misfit layer compounds (RS)^x[M^0.33(NbS²)²] (R = La, Ce, M = Fe, Mn). Magnetization measurements for the single crystals of the Fe intercalated compounds (RS)^x[Fe^0.33(NbS²)²] show the successive magnetic transition at 14 K and 22 K. The strong frustration appears between two transition temperatures as quasi two-dimensional antiferro-magnetic triangular Ising spin system. In contrast, the Mn compounds (RS)^x[Mn^0.33(NbS²)²] has very low transition temperature of 3.0 K due to the nature of quasi two-dimensional Heisenberg spin system.     

Structural and Electrical Properties of Cd Doped InSe Thin Films

Polycrystalline Cd doped InSe thin films were obtained by thermal co‐evaporation of alpha‐In₂Se₃ lumps and Cd onto glass substrates at a temperature of 150°C. The films were annealed at 150°C and 200°C. The films were found to contain around 46% In, 47% Se and 7% Cd in weight. The films exhibited p‐type conductivity. The results of conductivity measurements have revealed that thermionic emission and variable range hopping are the two dominant conduction mechanisms, in the temperature ranges of 320‐160 K and 150‐40 K respectively. It was observed that above 240 K mobility is limited by the scattering at the grain boundaries. As the temperature decreases, thermal lattice scattering followed by the ionized impurity scattering dominate as the two main mechanisms controlling the mobility. Acceptor to donor concentration ratio was found to be slightly increasing due to annealing.     

Electrical and Photoelectrical Properties of Vacuum Deposited SnSe Thin Films

Polycrystalline thin films of tin selenide have been prepared by vacuum deposition at a substrate temperature of 150°C and reported. X‐ray diffraction, optical transmission, electrical conductivity and photoconductivity studies have been carried out on these films. Annealing the films at 300°C for 2 hours improves the crystallinity and a preferred orientation along the (111) plane develops. The optical transmission measurement reveals that the SnSe thin films have a direct allowed band gap of 1.26 eV. Electrical conductivity study shows that the conductivity increases with increasing temperature. The observed electrical conductivity at low temperature is explained based on hopping conduction mechanism. The photoconductivity measurement indicates the presence of continuously distributed deep localised gap states in this material.     

Thermodynamic feasibility study for chemical vapour deposition of some ternary crystals using iodine and hydrogen iodide

Thermodynamic feasibility of transition metal dichalcogenide (TMDC) single crystals of Cu Al S₂, Cu Al Se₂, Cu Al Te₂, Cu Ga S₂, Cu Ga Se₂, Cu Ga Te₂, Cu In S₂, Cu In Se₂, Cu In Te₂, Ag Ga S₂, Ag Ga Se₂, Ag Ga Te₂, Ag In Se₂, Ag In Te₂, using iodine and hydrogen iodide as transporting agents has been reported in this paper. Results give range of temperature for the iodide transport and prevention of starting material formation (elemental transport) in the growth zone. From the range of temperature for the growth of crystals, selected source zone and growth zone temperatures with a differential of 100 °C are also listed. Referring the data listed in the tables can grow good quality crystals. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Nb掺杂ZnO透明导电薄膜的结构以及光电性能研究

采用直流磁控溅射法在玻璃衬底上制备了高质量的Nb掺杂ZnO( NZO)透明导电薄膜.为了研究薄膜厚度对薄膜性质的影响,制备了五个厚度分别为239 nm,355 nm,489 nm,575 nm和679 nm的样品.XRD结果表明,ZnO∶ Nb薄膜是具有六角纤锌矿结构的多晶薄膜,并且具有垂直于衬底的c轴择优取向.随着膜厚的增加,薄膜的结晶质量明显提高.当厚度从239 nm增加到489 nm时,平均晶粒尺寸从19.7 nm增加到24.7 nm,薄膜的电阻率持续减小;当厚度进一步增加时,晶粒尺寸略有减小,电阻率有所增加.本实验获得的最低电阻率为4.896×10-4Ω·cm.随膜厚的增加,光学带隙先增大后减小.所有薄膜在可见光区域的平均透过率均超过88.3;.     

Electrical conductivity and dielectric properties of potassium sulfamate single crystals

Single crystals of potassium sulfamate are grown by the method of slow evaporation at constant temperature. AC electrical conductivity of potassium sulfamate is measured in the temperature range 300–430 K and in the frequency region between 100 Hz and 3 MHz along the a, b and c‐axes. Complex impedance spectroscopy is used to investigate the frequency response of the electrical properties of the potassium sulfamate single crystal. Temperature variation of AC conductivity and dielectric measurements show a slope change around 345 K for both heating and cooling run and this anomaly is attributed as phase transition, which is well supported by the DSC measurements. Value of loss tangent in the temperature region 330–400 K is found to be very low. Activation energies for the conduction process are calculated along the a, b and c‐axes. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

退火升温速率对LaNiO3薄膜结构和电学性能的影响

采用溶胶-凝胶法在SiO2/Si(100)衬底上制备了镍酸镧(LaNiO3,LNO)薄膜,并利用XRD、SEM、AFM和半导体参数分析仪等研究了退火升温速率对LNO薄膜结构和电学性能的影响.结果表明,溶胶-凝胶法制备的LNO薄膜呈现赝立方钙钛矿型多晶结构,呈(110)择优取向生长;薄膜表面平整、均匀、无裂纹.随着退火升温速率的增加,LNO薄膜的晶粒尺寸先增大后减小;其电阻率先减小后增大.在退火升温速率为20℃/min时,LNO薄膜晶粒尺寸达到最大值94 nm,电阻率达到最小值9.5 x10-4 Ω·m.     

电子束蒸发制备ZnO:Al透明导电膜及其性能研究

在本实验中我们利用电子束蒸发方法在玻璃衬底上制备了ZnO:A l透明导电膜,并对所得样品在400℃下进行了退火处理。利用扫描电子显微镜观察了样品的表面形貌,利用分光光度计分析了样品的光学性质,结果表明所得样品在可见光范围具有较好的透光性。利用四探针对其进行了电学性质的测量,表明衬底温度为200℃时制备的样品电阻率可达6×10-3Ω.cm。     

Conductivity and temperature coefficient of resistance of multilayered polycrystalline films

We calculate the electric conductivity and the temperature coefficient of resistance (TCR) of a multilayered film consisting of the alternating polycrystalline metal layers of different thickness and purity within the relaxation time formalism. In the case of Cr, Cu and Co‐based multilayered films we perform verification of our analytical formulas and demonstrate a qualitative agreement between the theoretically calculated values of the TCR and experiment. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Electrical and dielectric properties of Sb2O3–V2O5–K2O glasses

Electric measurements, including temperature dependencies of direct electrical conductivity and temperature dependencies of complex electrical modulus, have been implemented using Sb₂O₃–V₂O₅–K₂O glass samples. These glasses absorb ambient humidity but their resistance to water attack depends on composition. The significant decrease of conductivity up to 100 °C can arise from water desorption. Cycling measurements of direct electrical conductivity versus temperature were also implemented. They show that the 30Sb₂O₃–30V₂O₅–40K₂O and 70Sb₂O₃–30K₂O glasses are irreversibly damaged with the formation of the hydrated layer. In addition, it was observed that the evolution of DC conductivity is ruled by Arrhenius relation, while activation energy decreases as Sb₂O₃ concentration increases.     

等离子体增强分子束外延生长ZnO薄膜及光电特性的研究

利用等离子体辅助分子束外延设备(P-MBE)在蓝宝石(Al2O3)衬底上外延生长ZnO薄膜,研究了不同生长温度对结晶质量的影响.随着生长温度的升高,X射线摇摆曲线(XRC)半高宽从0.88°变窄至 0.29°,从原子力显微镜(AFM)图像中发现薄膜中晶粒从20nm左右增大至200nm,室温光致发光(PL)谱中显示了一个近带边的紫外光发射(UVE)和一个与深中心有关的可见光发射.随着生长温度升高,可见光发射逐渐变弱,薄膜的室温载流子浓度由1.06×1019/cm3减少到7.66×1016/cm3,表明在高温下生长的薄膜中锌氧化学计量比趋于平衡,高质量的ZnO薄膜被获得.通过测量变温光谱,证实所有样品在室温下PL谱中紫外发光都来自于自由激子发射;随着生长温度的变化UVE峰位蓝移与晶粒尺寸不同引起的量子限域效应相关.     

单层MXene纳米片Ti2N电磁特性的过渡金属(Sc、V、Zr)掺杂效应

二维材料MXene纳米片由于具有较大的比表面积和较高的电子迁移率而受到广泛的关注。本文采用基于密度泛函理论的第一性原理计算,对单层MXene纳米片Ti₂N电磁特性的过渡金属(Sc、V、Zr)掺杂效应进行了系统研究。结果表明,所有过渡金属掺杂体系结合能均为负值,结构均稳定;其中Ti₂N-Sc体系的形成能为-2.242 eV,结构更易形成,且保持稳定;掺杂后Ti₂N-Sc、Ti₂N-Zr体系磁矩增大;此外,Ti₂N-Sc体系中保留了较高的自旋极化率,达到84.9%,可预测该体系在自旋电子学中具有潜在的应用价值。     

Studying of optical and morphological properties of SiO2-MOx (M: Co/Cu) glasses prepared by the sol-gel method

The cobalt oxide-silica and copper oxide-silica glasses are prepared by the sol-gel method. Tetra-Ethyl-Ortho-Silicate (TEOS) is used as source of the silica and transition metal nitrate is used as the dopant. The morphological, structural and optical properties of the samples are investigated by Scanning Electron Microscope (SEM), Energy Dispersion Analysis by X-ray (EDAX), X-ray diffraction (XRD) and Ultra-Violet/Visible (UV/Vis) spectrophotometer. The influences of heat treatment temperature and withdrawal rate on absorption/transmission spectra are investigated in the range 400-800 nm. In the cobalt oxide-silica, the intensity and position of absorption bands (λ_max) are changed by heat treatment. These behaviors are explained through the Bathochromic and the Hyperochromic effects. In addition, the effect of the withdrawal rate on transmission curves is explained in terms of the Levich equation and Beer-Lambert law.