石墨基底上垂直生长碳纳米管为芯的碳锥结构

采用一种改进的化学气相沉积方法，成功地在石墨基底上自组装生长出以碳锥为支撑的、碳纳米管为芯的新型功能材料.该结构的材料可以用作扫描电子显微镜探针和场发射电子显微镜的针尖.利用电子显微镜研究了不同合成条件对该碳纳米管与碳锥结构生长的影响，给出了最优生长条件，并讨论了生长机制. 关键词： 碳锥 碳纳米管 化学气相沉积 场发射     

硅纳米颗粒在碳纳米管表面生长的分子动力学模拟

采用分子动力学模拟方法研究了硅纳米颗粒在碳纳米管上的生长，并分析了这种复合材料的基本结构.研究表明，由于硅原子和碳纳米管之间的相互作用以及碳纳米管的巨大的表面曲率，硅原子在碳纳米管表面不是形成覆盖碳纳米管的二维薄膜，而是生成具有三维结构的硅纳米颗粒.小纳米颗粒的结构和无基底条件下生成的颗粒结构基本一致.对于大纳米颗粒，不同于无基底条件下形成的球状纳米晶体硅结构，硅纳米颗粒沿管轴方向伸长，其结构为类似于硅晶体的无定形网络结构. 关键词： 纳米颗粒 碳纳米管 硅 分子动力学模拟     

CVD金刚石膜的结构分析

利用x射线广角衍射和低角掠入射散射谱、正电子湮没谱、定性分析软件和Positronfit程序，研究了生长在Si（100）基底上的金刚石膜微结构.研究发现，在样品邻近基底区域为纳米 多晶结构，具有弱的［111］织构；在邻近表面区域为微米多晶结构，具有强的［220］织构 .金刚石膜样品有空位、空位团和空洞3种缺陷，其中主要缺陷是大约10个空位形成的空位团 . 关键词： 金刚石膜 化学气相沉积 x射线掠入射 正电子湮没谱     

碳纳米管的氧化铝模板法合成及其退火效应研究

结合氧化铝模板制约生长技术和高温退火处理，得到了相当统一的多壁碳纳米管.扫描电子显微镜（SEM）图像表明模板制约生长的初始碳纳米管形貌和尺寸完全受控于模板结构，透 射电子显微镜（TEM）和x射线粉末衍射（XRD）结果显示其管壁结构为无定形碳和石墨纳米 晶组成的混杂结构.为减少晶格缺陷及无定形碳，对初始碳纳米管进行系列高温（1100—240 0℃）退火处理，并初步研究了管壁在高温下的晶化行为.实验证明高温退火是提高多壁碳纳 米管质量的有效途径. 关键词： 氧化铝模板 碳纳米管 高温退火     

GaAs均匀点状结构的分子束外延图形生长

报道了在(311)A腐蚀图形衬底上，用分子束外延(MBE)生长高度规则的三种点状结构的实验研究.样品表面的原子力显微镜和剖面的扫描电子显微镜测试结果表明，在不同尺寸的方形凹面腐蚀图形区域，原凹面之间形成了沿［233］晶向不完全和完全收缩的尖角形点状外延结构；而在方形台面腐蚀图形区域，台顶面之间形成了沿［233］方向收缩的脊形点状结构.分析认为这些均匀有序的三角形点状结构的形成是由非平面(311)A衬底上生长各向异性导致的必然结果，而构成这些点结构的晶面取向与原图形的取向相关.低温阴极荧光谱测试结果清晰地表 关键词：     

Si(001)衬底上闪锌矿ZnO的制备与分析

采用分子束外延方法在室温下于Si(001)表面上生长ZnO材料。实验发现:样品为闪锌矿和六角结构的ZnO混合多晶薄膜,其表面分布着一系列具一定取向的近似长方形的纳米台柱结构。在不同参数的高温退火后,这些梯形台柱将变小,形成梯形纳米环,或分解为较小的纳米柱及其团簇结构等。分析表明:ZnO混合多晶薄膜的形成,以及表面纳米台柱的演变,与Si(001)衬底、较低温的生长温度及热效应等因素相关联。     

离子轰击控制准直碳纳米管生长的研究

用CH₄,H₂和NH₃作为反应气体，利用等离子体增强热丝化学汽相沉积制备出准直碳纳米管，并用扫描电子显微镜研究了不同负偏压对准直碳纳米管生长的影响. 结果表明，随着负偏压的增大，准直碳纳米管的平均直径减小、平均长度增大. 由于辉光放电的产生，在衬底表面附近形成阴极鞘层，并在阴极鞘层内形成大量的离子和在衬底表面附近形成很强的电场. 离子在电场的作用下对衬底表面的强烈轰击将对准直碳纳米管的生长产生影响. 结合有关理论，分析和讨论了离子的轰击对准 关键词： 准直碳纳米管 离子轰击 负偏压     

基于HRTEM和Raman分析定向多壁碳纳米管阵列的生长机理

以二茂铁、二甲苯为前驱体,石英为衬底,在850 oC的管式炉内采用化学气相沉积法制备出了定向碳纳米管阵列. 高分辨透射电子显微镜和拉曼光谱的结果表明：碳纳米管阵列具有良好的定向性和多壁管状结构,石墨化程度高,并且只在表面存在少量单壁碳纳米管.定向多壁碳纳米管阵列的生长模式为“底部”生长模式,即在生长的初期,当催化剂颗粒较小时,析出的碳原子生成了单壁碳纳米管或与其性质类似的多壁碳纳米管(一般层数小于5层);催化剂颗粒逐渐长大后,大量的碳原子析出后生成了普通的多壁碳纳米管,从而形成了单壁碳纳米管只存在于碳纳米管阵列膜表面和多层碳纳米管膜表面与界面的现象.     

工作气压对磁控溅射ZnO薄膜结晶特性及生长行为的影响

采用射频反应磁控溅射方法，在Si(001)基片上制备了具有高c轴择优取向的ZnO薄膜.利用原子力显微镜、X射线衍射、透射电子显微镜和透射光谱分析技术，对不同工作气压下合成的ZnO薄膜的表面形貌、微观结构和光学性能进行表征，研究了工作气压对ZnO薄膜的结晶性能以及生长行为的影响.研究结果显示：对于Ar/O₂流量比例接近1∶1的固定比值下，ZnO薄膜的生长行为主要取决于成膜空间中氧的密度，临界工作气压介于0.5—1.0 Pa之间.当工作气压小于临界值时，ZnO薄膜的成核密度较高，且随工作气压的变化明显，ZnO的生长行为受控于氧的密度，属于氧支配的薄膜生长；当工作气压大于临界值以后，ZnO薄膜的成核密度基本保持不变，Zn原子的数量决定薄膜的生长速率；在0.1—5.0 Pa的工作气压范围内，均可获得高度c轴取向的ZnO薄膜，但工作气压的变化改变着ZnO晶粒之间的界面特征和取向关系.随着工作气压的增加，ZnO晶粒之间的界面失配缺陷减少，但平面织构特征逐渐消失，三叉晶界的空洞逐渐扩大，薄膜的密度下降，折射率减小. 关键词： ZnO薄膜 磁控溅射 表面形貌 微观结构 光学性能     

单壁碳纳米管在石墨基底上运动的分子动力学模拟

采用分子动力学模拟方法研究单壁碳纳米管在石墨基底上的运动.首先碳纳米管在基底弛豫至平衡状态，然后对其施加一固定外力，撤去外力后，碳纳米管在基底上逐渐减速至停止.为了研究管径、手性角对运动方式的影响，本文选择了C(10,10)，C(10,9)，C(10,8)，C(10,5)，C(10,0)，C(8,8)六种单壁碳纳米管进行模拟.结果表明，碳纳米管在石墨基底上的运动方式由手性角决定，与管径无关.手性角等于30°时，碳纳米管与石墨基底之间为公度结构，碳纳米管的运动出现周期性的滑动和翻滚现象；手性角大于28.3°小于30°时，碳纳米管一边向前滑动一边滚动；手性角小于26.3°时，碳纳米管在基底上滑动.碳纳米管的手性角决定了它与石墨基底接触界面的微观构型，从而决定了碳纳米管的运动方式. 关键词： 分子动力学模拟 碳纳米管 动能 结构公度性     

Selective growth of carbon nantoubes on SiO2/Si substrate

Three-step raising temperature process was employed to fabricate carbon nanotubes by pyrolysis of ferrocene/melamine mixtures on silica and single crystalline silicon wafers respectively. Then the morphologies, structures and compositions of obtained carbon nanotubes are investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscope (EDX) and electron energy-loss spectroscopy (EELS). TEM and SEM observation shows that on silica substrate, high-oriented carbon nanotube can grow compactly to form continuous film on both frontal and cross-section surfaces, but on silicon substrate, only can form on cross-section surface. These carbon nanotubes have much irregular cup-like structure, and with outer diameter varying from 25 nm to 35 nm. At the top end of carbon nanotube there is a catalyst particle. EDX analysis reveals that the particle are iron cluster, and EELS spectrum indicates that the nanotube is composed of pure carbon. Finally, the effect of substrate surface roughness on the growth behavior of carbon nanotubes has been discussed.     

Fabrication of carbon nanotube bundles and measurement of field electron emission properties

Carbon nanotube (CNT) bundles are synthesized on rough polycrystalline ceramic wafers by pyrolyzing ferrocene/melamine mixtures through a three-step process in a single stage furnace in an Ar atmosphere. The CNTs are multi-walled and have outer diameters from 10 to 90 nm and lengths from 20 to 100 microns. These CNTs display a bamboo-like structure with open graphite layers and defects at the outer surfaces. Field electron emission (FEE) measurements show that the turn-on electrical field is 2.9 V/m and the field enhancement factor is 2700. PACS 61.46.+w; 82.30.Lp; 79.70.+q     

CVD synthesis and radial deformations of large diameter single-walled CNTs

Single-walled carbon nanotubes (CNTs) were synthesized by a chemical vapor deposition (CVD) method on transmission electron microscopy (TEM) silica coated nickel grids using carbon monoxide as carbon source and iron nanoparticles as catalyst. The produced CNTs were as large as 11 nm in diameter. Investigations on the CNT deformations based on high-resolution TEM images showed that the deformation of CNTs due to their interaction with the substrate occurs at diameters larger than 2.7 nm. Small deformation of free standing tubes was found to occur at diameters above approximately 4.5 nm.     

A novel route to aligned nanotubes and nanofibres using laser-patterned catalytic substrates

We describe the generation of aligned carbon nanotube bundles and films by pyrolysis of solid organic precursors (for example 2-amino-4,6-dichloro-s-triazine, s-triaminotriazine) at 950-1050 °C over laser-patterned thin metal (Fe, Co, Ni) films, deposited on silica substrates. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) studies reveal that surface roughness of the laser-etched catalytic substrates plays a key role in achieving control of nanotube growth. We believe that, during the etching process, the energised (ablated) metal clusters condense and recrystallise evenly, possibly as the metal oxide, within the edges or surface of the eroded regions. During pyrolysis these catalytic particles, embedded in the silica substrates, are responsible for carbon agglomeration and subsequent tube axial growth, suggesting that nanotube alignment strongly depends upon the etching conditions (for example laser power, pulse duration, and focal distance). The pyrolysed products (usually nanotubes or nanofibres) were characterised by SEM, high-resolution transmission electron microscopy (HRTEM), electron energy loss spectroscopy (EELS) and energy dispersive X-ray spectroscopy (EDX). Samples containing only small amounts of amorphous carbon and other carbonaceous particles are notably absent. We observe that the degree of graphitisation is dependent upon the catalyst and the organic precursor. Interestingly, a nitrogen content З% was detected within the nanofibres, which exhibit corrugated graphite-like morphologies. This pyrolytic method may be used to advantage in generating aligned heteroatomic nanostructures such as B_xC_yN_z systems.     

Acetic acid effects on enhancement of growth rate and reduction of amorphous carbon deposition on CNT arrays along a growth window in a floating catalyst reactor

The mm-long carbon nanotube (CNT) arrays were grown in a floating catalyst reactor, using xylene-ferrocene and a small amount of acetic acid as the feed. The CNT arrays deposited on a quartz substrate at several positions along the reactor were extensively characterized using Raman spectroscopy, scanning electron microscopy, X-ray diffraction, high-resolution transmission electron microscopy, and optical microscopy. Various characterization methods consistently reveal that the acetic acid additive to the feed alleviates deposition of amorphous carbon layer, which gradually thickens CNTs along the reactor. The acetic acid also resulted in a higher growth rate along the so-called growth window, where CNT arrays are deposited on the quartz substrate. High-performance liquid chromatography of extracted byproducts (PAHs) confirmed the presence of some polycyclic aromatic hydrocarbons. The solid weight of PAHs decreased upon addition of ferrocene as the catalyst precursor, as well as of acetic acid to xylene feed. The results suggest that primary light products of xylene pyrolysis can be competitive reactants for both catalytic and subsequent pyrolytic reactions. They may also be more efficient feeds for CNT growth than xylene itself.     

Area effect of patterned carbon nanotube bundle on field electron emission characteristics

Patterned carbon nanotube (CNT) bundles were fabricated using thermal chemical vapor deposition (CVD) method. Patterns of different diameters and distances were defined on Si(100) substrates using photolithography. CNT bundle height was controlled using different acetylene (C₂H₂) flow times. The inter-bundle distance of CNTs to CNT bundle height ratio was maintained at approximately 2, a number predicted to have a maximum field emission for CNT, and left the patterned CNT bundle area as a variable parameter. The relationship between CNT bundle area and the field electron emission characteristics was studied. The lowest threshold electric field (E_th) of 0.7 V/μm was obtained when the total area of patterned CNT bundles was approximately 46%. The result shows that there is an optimal CNT bundle area for electron field emission.     

Hydrogen-free spray pyrolysis chemical vapor deposition method for the carbon nanotube growth: Parametric studies

Spray pyrolysis chemical vapor deposition (CVD) in the absence of hydrogen at low carrier gas flow rates has been used for the growth of carbon nanotubes (CNTs). A parametric study of the carbon nanotube growth has been conducted by optimizing various parameters such as temperature, injection speed, precursor volume, and catalyst concentration. Experimental observations and characterizations reveal that the growth rate, size and quality of the carbon nanotubes are significantly dependent on the reaction parameters. Scanning electron microscopy, transmission electron microscopy, and Raman spectroscopy techniques were employed to characterize the morphology, structure and crystallinity of the carbon nanotubes. The synthesis process can be applied to both semiconducting silicon wafer and conducting substrates such as carbon microfibers and stainless steel plates. This approach promises great potential in building various nanodevices with different electron conducting requirements. In addition, the absence of hydrogen as a carrier gas and the relatively low synthesis temperature (typically 750 °C) qualify the spray pyrolysis CVD method as a safe and easy way to scale up the CNT growth, which is applicable in industrial production.     

Closed-form internal impedance model and characterization of mixed carbon nanotube bundles for three-dimensional integrated circuits

Based on the complex effective conductivity method, a closed-form expression for the internal impedance of mixed carbon nanotube(CNT) bundles, in which the number of CNTs for a given diameter follows a Gaussian distribution, is proposed in this paper. It can appropriately capture the skin effect as well as the temperature effect of mixed CNT bundles.The results of the closed-form expression and the numerical calculation are compared with various mean diameters, standard deviations, and temperatures. It is shown that the proposed model has very high accuracy in the whole frequency range considered, with maximum errors of 1% and 2.3% for the resistance and the internal inductance, respectively. Moreover,by using the proposed model, the high-frequency electrical characteristics of mixed CNT bundles are deeply analyzed to provide helpful design guidelines for their application in future high-performance three-dimensional integrated circuits.     

HRTEM and EELS investigation of functionalized carbon nanotubes

We have successfully resolved and visualized the structure of some chemically functionalized carbon nanotubes (CNTs) using high-resolution transmission electron microscopy (HRTEM) and electron energy loss spectroscopy (EELS). To represent the chemically modified CNT, we selected three systems. The first system is oxidized and surface thiolated MWCNT, the second system is Dy₃N@C₈₀ peapods prepared by depositing trimetal nitride fullerenes into SWCNT. The formed structure is the Dy₃N@C₈₀@SWCNT. The third system is the conventional C₆₀@SWCNT fullerene peapods, fluorinated by xenon difluoride (XeF₂) up to 18% of F. We achieved detection of very low amount (0.6%) of sulfur and proved covalent bonding onto MWCNT surface. We present EELS imaging of the separated metal clusters inside endohedral metallofullerene peapod bundles and in the fluorinated C₆₀ peapods we show homogeneous fluorination across the whole surface.     

Monitoring structural defects and crystallinity of carbon nanotubes in thin films

We report the influence of catalyst formulation and reaction temperature on the formation of carbon nanotube (CNT) thin films by the chemical vapour deposition (CVD) method. Thin films of CNTs were grown on Fe-Mo/Al₂O₃-coated silicon wafer by thermal decomposition of methane at different temperatures ranging from 800 to 1000°C. The electron microscopic investigations, SEM as well as HRTEM, of the as-grown CNT thin films revealed the growth of uniform multi-walled CNTs in abundance. The intensity ratio of D-band to G-band and FWHM of G-band through Raman measurements clearly indicated the dependency of structural defects and crystallinity of CNTs in thin films on the catalyst formulation and CVD growth temperature. The results suggest that thin films of multi-walled CNTs with negligible amount of defects in the nanotube structure and very high crystallinity can be obtained by thermal CVD process at 925°C.