Effect of alcohol sources on synthesis of single-walled carbon nanotubes

The effect of oxidant species forming an alcohol molecule for hot-filament chemical vapor deposition (HFCVD) on single-walled carbon nanotubes (SWCNTs) growth has been investigated. To use a graphite rod as a filament for HFCVD to decompose alcohol sources, contamination-free sample surface can be obtained and SWCNTs are successively and densely grown at a lower temperature than those by conventional thermal CVD. It is found that the higher the molecule number of alcohol among CH₃OH, C₂H₅OH, and 2-C₃H₇OH is, the lower the initial growth rate of SWCNTs is. As for CH₃OH, diameter distribution of SWCNTs is dynamically changed with the growth time passed, and a negative growth rate is observed at the later stage of growth. The growth kinetics depending on the alcohol sources is discussed on the basis of a capability of the oxidant species to burn away SWCNTs and deactivation of Co catalysts used for the growth.     

Surface modification of pitch-based spherical activated carbon by CVD of NH3 to improve its adsorption to uric acid

Surface chemistry of pitch-based spherical activated carbon (PSAC) was modified by chemical vapor deposition of NH₃ (NH₃-CVD) to improve the adsorption properties of uric acid. The texture and surface chemistry of PSAC were studied by N₂ adsorption, pH_PZC (point of zero charge), acid-base titration and X-ray photoelectron spectroscopy (XPS). NH₃-CVD has a limited effect on carbon textural characteristics but it significantly changed the surface chemical properties, resulting in positive effects on uric acid adsorption. After modification by NH₃-CVD, large numbers of nitrogen-containing groups (especially valley-N and center-N) are introduced on the surface of PSAC, which is responsible for the increase of pH_PZC, surface basicity and uric acid adsorption capacity. Pseudo-second-order kinetic model can be used to describe the dynamic adsorption of uric acid on PSAC, and the thermodynamic parameters show that the adsorption of uric acid on PSAC is spontaneous, endothermic and irreversible process in nature.     

红外用CVD ZnS多晶材料的研制

论述了制备红外用CVD ZnS多晶材料的化学气相沉积工艺和热等静压处理工艺。针对CVD ZnS多晶材料具备优良的光学和力学性能,采用化学气相沉积工艺和热等静压处理技术成功研制出大尺寸多晶材料,其最大尺寸达到250mm×15mm。测试了CVD ZnS样品的各项光学、力学性能指标。样品的全波段透过率均接近ZnS材料的本征水平,折射指数均匀性优于2×10^-5,在1.06μm的吸收系数为2×10^-3cm^-1,抗弯强度达到104MPa。     

Synthesis of flower-like WS2 by chemical vapor deposition

Flower-like tungsten disulfide (WS₂) with a diameter of 5-10 μm is prepared by chemical vapor deposition (CVD). Scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), Raman spectroscopy, and ultraviolet-visible (UV-vis) spectroscopy are used to characterize its morphological and optical properties, and its growth mechanism is discussed. The key factors for the formation of flower-like WS₂ are determined. Firstly, the cooling process causes the generation of nucleation dislocations, and then the "leaf" growth of flower-like WS₂ is achieved by increasing the temperature.     

Growth and characterization of two-dimensional crystals for communication and energy applications

This review article covers the growth and characterization of two-dimensional (2D) crystals of transition metal chalcogenides, h-BN, graphene, etc. The chemical vapor transport method for bulk single crystal growth is discussed in detail. Top-down methods like mechanical and liquid exfoliation and bottom-up methods like chemical vapor deposition and molecular beam epitaxy for mono/few-layer growth are described. The optimal characterization techniques such as optical, atomic force, scanning electron, and Raman spectroscopy for identification of mono/few-layer(s) of the 2D crystals are discussed. In addition, a survey was done for the application of 2D crystals for both creation and deterministic transfer of single-photon sources and photovoltaic systems. Finally, the application of plasmonic nanoantenna was proposed for enhanced solar-to-electrical energy conversion and faster/brighter quantum communication devices.     

钴掺杂MoSe2共生长中氢气的作用分析及磁电特性研究

采用原位共生长化学气相沉积法,以Co3O4、MoO3、Se粉末为前驱物,710℃下在SiO2衬底上生长掺钴MoSe2纳米薄片,分析讨论氢气含量对其生长及调节机理的影响.表面形貌分析表明,氢气的引入促进了成核所需的氧硒金属化合物以及横向生长中需要的CoMoSe化合物分子的生成;AFM(Atomic Force Microscope)结果表明氢气有利于生长单层二维超薄掺钴MoSe2.随着Co3O4前驱物用量的增加,样品的拉曼和PL(Photoluminescence)谱图分别表现出红移和蓝移现象,带隙实现从1.52—1.57 eV的调制.XPS(X-ray photoelectron spectroscopy)结果分析得到Co的元素组分比为4.4%.通过SQUID-VSM(Superconducting QUantum Interference Device)和器件电学测试分析了样品的磁电特性,结果表明Co掺入后MoSe2由抗磁性变为软磁性;背栅FETs器件的阈值电压比纯MoSe2向正向偏移5 V且关态电流更低;为超薄二维材料磁电特性研究及应用拓展提供了基础探索.     

Distinctive Performance of Terahertz Photodetection Driven by Charge‐Density‐Wave Order in CVD‐Grown Tantalum Diselenide

The quantum behavior of carriers in solid is the foundation of modern electronic and optoelectronic technology, but it is still facing huge challenges within inherited single‐particle quantum processes working at the millimeter wave/terahertz (THz) band. Here, a straightforward strategy for the direct detection of millimeter wave/THz photons in a sub‐wavelength metal‐TaSe₂‐metal structure under strong interaction with a localized field of surface plasmon is proposed. By breaking the inversion symmetry under the perturbations of electric field and atomic reconstruction from van der Waals integration, the nonequilibrium electronic states under a radiant field can be manipulated in a collective fashion, leading to a large photocurrent responsivity over 40 A W^?1 and noise equivalent power less than 1 pW Hz^?1/2 even at room temperature. A more than 40‐fold enhancement in responsivity is achieved when transitioning from the normal phase to the CDW phase. The findings shed fresh light on the understanding of the delicate balance in the charge‐ordered phase, and facilitate the exploitation of a correlated electron system for optoelectronic applications in fields of security, remote sensing, and imaging.     

Morphology Engineering in Monolayer MoS2‐WS2 Lateral Heterostructures

In recent years, heterostructures formed in transition metal dichalcogenides (TMDs) have attracted significant attention due to their unique physical properties beyond the individual components. Atomically thin TMD heterostructures, such as MoS₂‐WS₂, MoS₂‐MoSe₂, MoS₂‐WSe₂, and WSe₂‐WS₂, are synthesized so far via chemical vapor deposition (CVD) method. Engineering the morphology of domains including size and shape, however, still remains challenging. Here, a one‐step CVD strategy on the morphology engineering of MoS₂ and WS₂ domains within the monolayer MoS₂‐WS₂ lateral heterostructures through controlling the weight ratio of precursors, MoO₃ and WO₃, as well as tuning the reaction temperature is reported. Not only can the size ratio in terms of area between WS₂ and MoS₂ domains be easily controlled from less than 1 to more than 20, but also the overall heterostructure size can be tuned from several to hundreds of micrometers. Intriguingly, the quantum well structure, a WS₂ stripe embedded in the MoS₂ matrix, is also observed in the as‐synthesized heterostructures, offering opportunities to study quantum confinement effects and quantum well applications. This approach paves the way for the large‐scale fabrication of MoS₂‐WS₂ lateral heterostructures with controllable domain morphology, and shall be readily extended to morphology engineering of other TMD heterostructures.     

Fluorophenyl derivatives of elements II-VI groups

The enthalpies and temperatures of melting of RSi(CH₃)₃, R₄Si, R₃P, R₃As, R₃Sb, R₃Bi, R₂Te and R₂Hg (R=C₆F₅) were obtained by scanning calorimetry measurements. The pressure of the saturated and unsaturated vapors of RSi(CH₃)₃, R₂Si(CH₃)₂, R₄Si, R₃Ga, R₃P, R₃As, R₃Sb, R₃Bi, R₂Te and R₂Hg has been measured by the static method with a membrane-gauge manometer. It was established that all investigated substances proceeded to vapor as monomers. Equations approximating the dependences of saturated vapor pressures on temperature and the enthalpies and entropies of vaporization were obtained. Grafite films with silicon intercalated up to 25 at.% were grown by CVD using R₄Si as a precursor. These films showed semiconductor properties in the temperature interval 80–300 K.     

取向Zn1-xMgxO纳米线阵列的制备及光学特性

采用化学气相沉积(CVD)法, 以高纯ZnO、Mg和活性C混合粉末为原料, 在Si(111)衬底上制备了不同配比的取向Zn1-xMgxO纳米线阵列. 用X射线衍射仪(XRD), 扫描电镜(SEM), 能量色散X射线分析(EDAX)及光致发光(PL)光谱分析仪对样品的晶体结构、形貌、成分组成和光致发光特性进行了分析. 用霍尔效应测量系统测试了不同配比样品的载流子浓度. 实验发现, 当Zn1-xMgxO纳米线阵列中Mg原子相对Zn原子摩尔比x值较小时(x<0.29), XRD衍射谱中只有ZnO晶体标准衍射峰, 没有MgO晶体衍射峰, 说明此时制备的Zn1-xMgxO纳米线样品晶格结构以ZnO纤锌矿结构为主, Mg原子只是作为替位或填隙原子分布在ZnO晶体中. 但当样品中x>0.53时, ZnO与MgO的特征衍射峰同时出现在样品的衍射谱图中, 说明随原料中Mg原子摩尔比的增加, 制备的Zn1-xMgxO纳米阵列样品中ZnO纤锌矿结构与MgO岩盐结构同时存在, 样品呈现多晶体结构形式. 实验还对比了制备的纯ZnO与不同配比的Zn1-xMgxO纳米线阵列的光致发光光谱和载流子浓度, 发现随Mg含量的增加, Zn1-xMgxO阵列紫光发光峰出现了较明显的蓝移现象, 同时, 测试结果也表明, 随Mg含量的增加, Zn1-xMgxO阵列的紫光和绿光峰发光强度都有所减弱, 样品的载流子浓度也随之下降. 文章对实验结果进行了分析和探讨.