化学气相沉积法制备螺旋状纳米碳纤维研究

采用化学气相沉积方法在基体上生长螺旋状纳米碳纤维,以Ni为催化剂热解乙炔可制备出纯净、规则的单、双螺旋形碳纤维,单螺旋纤维的直径约为1—2μm,双螺旋的直径约为2—5wm;同时伴有少量的不规则螺旋形碳纤维的生成。拉曼光谱和X射线衍射分析证明螺旋形碳纤维是由小石墨微晶组成。根据机体法制备螺旋形的形貌、结构和生长过程,提出了螺旋形碳纤维的生长机制。     

激光诱导化学气相沉积法制备纳米氮化硅及粉体光谱特性研究

氮化硅是优良的陶瓷材料,应用广泛.本文研究了激光诱导化学气相沉积法制备纳米氮化硅的工作原理,提出了减少游离硅的措施,利用双光束激发制备了超微的、非晶纳米氮化硅粉体.实验证明,纳米氮化硅粉体具有一些特殊的物理性能和光谱特性.     

纳米微粒的化学制备法

综述了近年来制备纳米微粒的化学方法的最近研究进展,包括沉淀法、水热法、喷雾法、溶胶－ 凝胶法、有机树脂法等。这些方法是合成粒径＜100m超微粉末的有效方法。     

化学气相沉积法制备富勒烯结构二硫化钼纳米粒子

以MoO3和S粉为原料,高纯氩气为载气和反应气氛,在石英管反应器中,用化学气相沉积法制备富勒烯结构MoS2纳米粒子,用XRD对产品的成分进行测量,SEM观察产品的整体微观形貌。结果表明,在900℃下,通氩气1 cm3/min,保温8 h,制备了平均粒径在250 nm左右的高纯富勒烯结构MoS2纳米粒子。     

负载型纳米二氧化钛的液相沉积法制备及性能研究

以硫酸钛作为前驱体,采用液相沉积法在自制硅酸盐微球上负载纳米二氧化钛。实验发现：在硅酸盐微球上负载的二氧化钛粒子晶型为锐钛矿相,粒径分布均匀,大小约为400nm,并结合紧密,纳米二氧化钛粒子没有出现量子尺寸效应。对于二氧化钛粒子在硅酸盐微球上的负载机理进行了讨论,并以甲基橙作为目标分子研究样品的光催化活性。     

化学气相沉积法碳纳米管的制备及性能研究

开发以煤气为碳源采用化学气相沉积法制备单壁碳纳米管，并对其作为超级电容器电极的电化学性能进行研究。通过电子扫描电镜、电子透射电镜、拉曼光谱以及X射线衍射等手段对产品的形态、结构及性质进行表征分析，并对单壁碳纳米管的生长机理进行讨论；分别通过循环伏安、恒压充放电实验对单壁碳纳米管电极进行电化学性能分析。     

气相法合成纳米颗粒的制备技术进展

本文综述了气相法合成纳米颗粒材料的主要制备技术，并介绍了制备方法的最新进展－化学气相冷凝技术制备纳米颗粒材料，提出了制备纳米颗粒技术研究中面临的问题及今后的发展方向。     

化学气相沉积法合成纳米碳管阵列研究

研究以环己烷为前驱体采用化学气相沉积法制备纳米碳管阵列。将催化剂二茂铁定量溶解在环己烷中，通过载气夹带进入反应器中，采用化学气相沉积方法定向生长出炭纳米管阵列，此法有效地控制反应体系中的催化剂含量，使生产稳定性及重现性较好。并通过透射电子显微镜、扫描电子显微镜、拉曼光谱及X射线衍射对产品形态和结构进行分析和表征，所制备出的纳米碳管阵列形态比较规整，纯度较高，具有较好的石墨微晶结构；并对纳米碳管的生长机理进行了详细讨论。     

化学气相沉积法制备碳化硅纤维

一、前言 现代宇航、航空等尖端科学技术的迅速发展,对高比强、高比模、耐高温、抗氧化及易加工的新型材料要求越来越迫切。碳纤维增强金属基复合材料固然有很优异的性能,但需在接近或高于金属熔点的高温下制造,金属与碳纤维之间会发生界面反应,从而产生浸润性差、粘结强度不高及高温抗氧化性能差等问题,导致复合材料性能下降,难以满足高温氧化等苛刻条件的使用要求。     

TiO_2纳米管的制备与表征

用化学处理法制备TiO2纳米管时,溶液的温度应大于80℃,碱液浓度应控制在8～12mol/L,反应时间为8～24h。通过TEM、XRD、FT-IR、Raman光谱和BET、GT-DTA等技术对TiO2纳米管进行了表征,结果发现:TiO2纳米管都是长约300～500nm的直管,有的是双层管,有的是多层管。TiO2纳米管为无定型结构。400℃煅烧后,TiO2纳米管的管状结构被破坏,变为锐钛矿型的实心结构。当TiO2由粉体形成TiO2纳米管后,TiO2的Ti—O键的振动特性发生改变。合成的TiO2纳米管具有很大的比表面积(403 7900m2/g)和孔体积(0 6740cm3/g)。     

Synthesis and field emission studies of tower-like GaN nanowires

Tower-like GaN nanowires were successfully fabricated on Au-coated Si substrates by chemical vapor deposition. The tower-like nanowire consisted of a nanowire at the center and microcrystal layers stacked one by one around the nanowire. The tower-like nanowires grew along the [0001] direction, and the exposed surfaces of the microcrystal layers are 101¯1 and 101¯1¯ facets. The growth mechanism of the tower-like GaN nanowires was proposed. The field emission property of tower-like GaN nanowires was tested. Due to the sharp tips, nearly vertical alignment and rough surfaces caused by the microcrystal layers, the tower-like GaN nanowires show excellent performance in field emission with a turn-on field of 2.44 V/μm which is lower than those of other GaN one-dimensional (1D) nanomaterials.

PACS

81.15.Gh; 68.37.Lp; 68.37.Vj     

Synthesis of oriented nanotube films by chemical vapor deposition

Oriented nanotube films (20-35 μm thick) were synthesised on flat silicon substrates by chemical vapor deposition (CVD) of a gas mixture of acetylene and nitrogen. For the CVD we used metal oxide clusters formed by spin coating an iron(III) nitrate ethanol solution onto a silicon substrate and subsequent heating. The cluster density and its effects on the nanotube density were investigated as a function of the iron(III) nitrate concentration and the synthesis temperature. A high nanotube density was achieved with a high density of iron oxide clusters as nucleation centres for the growth of nanotubes. The cluster density was controlled by the iron(III) concentration of the ethanolic coating solution and by the synthesis temperature. The perpendicular orientation of the nanotubes with respect to the substrate surface is attributed to a high density of nanotubes.     

Field emission from patterned carbon nanotube emitters produced by microwave plasma chemical vapor deposition

Large area carbon nanotube patterns were fabricated by microwave plasma chemical vapor deposition. The carbon nanotubes were grown on pre-patterned catalyst films. Scanning electron microscopy and Raman spectroscopy were used to characterize the structure of the carbon nanotubes. The carbon nanotubes were very uniform and approximately 100 nm in diameter. The Raman spectrum shows a good graphitization for the carbon nanotubes. Aligned growth was found on the pattern line area. Field emission characteristics of the patterns were characterized. A threshold field of 2.0 V/μm and emission current density of 1.1 mA/cm² at 3.6 V/μm were achieved. A clear and stable image showing the patterns were obtained.     

Field emission properties of carbon nanotubes synthesized by capillary type atmospheric pressure plasma enhanced chemical vapor deposition at low temperature

Carbon nanotubes (CNTs) were grown using a modified atmospheric pressure plasma with NH₃(210 sccm)/N₂(100 sccm)/C₂H₂(150 sccm)/He(8 slm) at low substrate temperatures (?500 °C) and their physical and electrical characteristics were investigated as the application to field emission devices. The grown CNTs were multi-wall CNTs (at 450 °C, 15-25 layers of carbon sheets, inner diameter: 10-15 nm, outer diameter: 30-50 nm) and the increase of substrate temperature increased the CNT length and decreased the CNT diameter. The length and diameter of the CNTs grown for 8 min at 500 °C were 8 μm and 40 ± 5 nm, respectively. Also, the defects in the grown CNTs were also decreased with increasing the substrate temperature (The ratio of defect to graphite (I_D/I_G) measured by FT-Raman at 500 °C was 0.882). The turn-on electric field of the CNTs grown at 450 °C was 2.6 V/μm and the electric field at 1 mA/cm² was 3.5 V/μm.     

Laser assisted chemical vapor deposition synthesis of carbon nanotubes and their characterization

The deposition of carbon nanotubes using the laser assisted chemical vapor deposition process was studied to determine the effects of processing conditions on the quantity and quality of the tubes. A structured experimental design was utilized to test the effects of laser power, and concentration of the two precursors, acetylene and iron pentacarbonyl. Processing conditions were optimized with the assistance of heat and mass transport modeling. The synthesis of lines of carbon nanotubes as well as deposits formed under the influence of an electric field were also investigated.     

化学气相沉积工艺制备绳状纳米碳管的研究

用硝酸铁作催化剂,乙炔作碳源气体,高纯氮气作稀释气体,在750℃下化学气相沉积生长了绳状纳米碳管,用高分辨扫描电镜观察了所得绳状纳米碳管的形貌.纳米碳管的直径为100～200nm,长度为10～20 μm.文中还提出了绳状纳米碳管的生长机理.     

Synthesis of gallium-catalyzed silicon nanowires by hydrogen radical-assisted deposition method

Gallium-catalyzed silicon nanowires (SiNWs) were synthesized by the hydrogen radical-assisted deposition method. The voluminous quantities of SiNWs with various crystal growth directions were synthesized and their characteristics were estimated by using XRD, FE-SEM, TEM and EDX analyses. Most of the Ga-capped SiNWs were directly grown with some smoothly curved SiNWs. Large quantities of small-SiNWs with diameters of 20–80 nm were tree-likely grown on the large-SiNWs surface. The diameters of large-SiNWs were approximately 200 nm–2 μm. Furthermore, a simple model of growth mechanism for sub-grown silicon nanowires by the hydrogen radical-assisted deposition method was proposed.     

Synthesis of boron nitride nanotubes by combining citrate-nitrate combustion reaction and catalytic chemical vapor deposition

High-quality boron nitride nanotubes were successfully synthesized via a novel two-step method, including citrate-nitrate combustion reaction and catalytic chemical vapor deposition. The composition, bonding features and microstructures of as-synthesized sample were investigated by X-ray diffraction, Fourier transform infrared spectroscopy, Raman microscopy, X-ray photoelectron spectroscopy, scanning electron microscopy coupled with energy dispersive X-ray spectroscopy, transmission electron microscopy and selected area electron diffraction techniques. The results show that the as-synthesized boron nitride nanotubes with smooth surface are relatively pure. The diameter ranges between 20 and 80?nm, while the length is about dozens of micrometers. During the synthesis process of boron nitride nanotubes, citric acid chelates the cobalt ions and reacts with nitrate to form the cobalt oxide, depositing on the surface of boron powder homogeneously. The catalyst content and annealing temperature have a significant impact on the composition and microstructures of the final products. Based on the experimental results and thermodynamic analysis, the possible chemical reactions are listed, and vapor-liquid-solid mechanism is proposed to be dominant for the formation of boron nitride nanotubes.