光折变晶体与应用

一光折变晶体是指具有光致折射率变化效应的一类晶体,它是一种新型光学非线性材料。它的光学非线性是由晶体在激光作用下产生的光生自由载流子,经扩散、漂移,被陷     

碳纳米管/P25复合光催化剂的制备与光催化性能研究

采用水热法制备了碳纳米管与P25复合的光催化材料,运用XRD、FESEM、UVPC、Laser Raman spec-troscopy及PL测试手段表征了样品的晶相组成、显微结构、光谱吸收及光生载流子。结果表明,复合碳纳米管的P25的禁带宽度变窄,光谱吸收能力增强,光生载流子效率提高,光催化活性比纯P25高。     

碳纳米管场发射烧毁机理研究

在碳纳米管场发射过程中,碳纳米管烧毁现象一直是影响碳纳米管场发射能力及稳定性的重要因素。目前,对碳纳米管烧毁机理研究较少。本文采用化学气相沉积原位生长技术制备了不同形貌的碳纳米管阵列。通过对不同形貌的碳纳米管场发射测试过程及碳纳米管烧毁前后形貌的研究,得出碳纳米管烧毁机理主要有三种。一是碳纳米管高度不均匀和碳纳米管本身的缺陷等原因引起了电场局域现象,这种局域场强使得碳纳米管局域温度过高而引起碳纳米管烧毁;二是碳纳米管吸附和脱附造成碳纳米管烧毁;三是碳纳米管与基片间存在较高的接触电阻而产生较高的焦耳热,使得碳纳米管烧毁。本文不仅给出了碳纳米管烧毁机理,还给出了相应的解决方案。这对碳纳米管场发射阴极的研究具有一定的意义。     

碳纳米管阵列耦合对其介电常数及光吸收系数影响研究

通过密度泛函方法对手性矢量为(12,0),排列间距分别为3nm、6nm、9nm和12nm的碳纳米管阵列在沿轴方向和垂轴方向的介电常数和电磁波吸收系数进行理论计算。结果表明:碳纳米管阵列在近红外、可见光和近紫外频段有很高的介电常数和光学吸收系数,随着碳纳米管阵列排列间距的减小,其介电常数和光学吸收系数都有大幅度的提高。就其方向来讲,碳纳米管阵列的在沿轴方向和垂轴方向差异比较大,一般情况下沿轴方向的介电常数和吸收系数大于垂轴方向,体现了碳纳米管的各向异性特点。从几何结构和电子结构入手分析了碳纳米管高介电常数的原因以及影响其介电常数的因素。从量子论分析碳纳米管的光学吸收性,可以得出碳纳米管阵列就其手性矢量的不同,存在着本征吸收、激子吸收、自由载流子吸收等多种吸收形式。宏观的介电常数和光学吸收系数,实际是多种复杂吸收过程的综合作用结果。     

卟啉修饰多壁碳纳米管及其电荷传输性能研究

采用湿化学方法合成四(对羟基苯基)卟啉(THPP),通过羟基官能团与碳纳米管表面的酰氯反应而将卟啉分子修饰到碳纳米管的表面,并研究复合材料内部的电荷传输性能。结果表明:THPP和碳纳米管两个共轭结构之间存在明显的光致电荷传输。所得材料有望在有机太阳能电池,光致能量和电荷转移方面有很好的应用。     

CVD法和丝印法制作的碳纳米管场致发射冷阴极的研究

本文研究了丝网印刷法和CVD生长法制备的碳纳米管冷阴极的场致发射性能.结果表明,在没有模板的情况下,通过CVD生长的碳纳米管的直径与催化剂颗粒的直径有关,随催化剂颗粒的直径变化而变化,生长方向是随机的,但大电流发射稳定性较差;用丝网印刷方法制作的碳纳米管致发射冷阴极,场发射电流发射较稳定.     

碳源对碳纳米管形态的影响

以苯和甲苯为碳源,二茂铁为催化剂,含硫化合物为助催化剂,采用浮游催化裂解法制备了碳纳米管,并采用TEM对不同条件下所得碳纳米管进行了形态分析。结果发现,碳源中苯和甲苯的配比对碳纳米管的形态有着重要的影响。以纯苯为碳源时,产物主要为直线型碳纳米管,并存在极少量短的弯曲型碳纳米管。随着碳源中甲苯比例的增加,产物中折线型碳纳米管增加。以纯甲苯为碳源,产物中仍有少量直线型碳纳米管,而不完全是折线型碳纳米管;此外,产物中还发现了极少量分支型碳纳米管。根据所得结果讨论分析了甲苯的加入对碳纳米管形态的影响以及各种碳纳米管的形成机理,认为可能是由于甲苯在催化热解过程中产生的碳种不同于苯催化热解所产生的碳种,造成碳在催化剂颗粒各处浓度不同,从而在碳纳米管的不同部位引入五元环和七元环而形成各种形态的碳纳米管。     

La掺杂对TiO_2薄膜性能的影响

用溶胶-凝胶法制备TiO2以及La掺杂TiO2的前驱体凝胶,将其均匀旋涂不同层数制备出不同厚度的薄膜,研究了La掺杂对TiO2薄膜结晶性能,表面形貌,光学特性和亲水性能的影响.结果表明:在500℃可以获得结晶性良好的锐钛矿相TiO2薄膜;随着La掺杂量的增加,薄膜中TiO2晶粒会变大,同时引起紫外可见光谱中吸收边的蓝移.掺La的TiO2薄膜经紫外照射后其接触角明显高于未掺杂样品,主要原因是到达表面的活性载流子相对减少.一方面,大的TiO2晶粒使得光生载流子到达光催化表面的路程变长,电子一空穴对的复合几率也随之变大;另一方面,未完全替代Ti的La可能成为光生电子一空穴对的复合中,因此,通过La的掺杂可以有效调节TiO2晶粒尺寸和光致接触角. 能,表面形貌,光学特性和亲水性能的影响.结果表明:在500℃可以获得结晶性良好的锐钛矿相TiO2薄膜;随着La掺杂量的增加,薄膜中TiO2晶粒会变大,同时引起紫外可见光谱中吸收边的蓝移.掺La的TiO2薄膜经紫外照射后其接触角明显高于未掺杂样品,主要原因是到达表面的活性载流子相对减少.一方面,大的TiO2晶粒使得光生载流子到达光催化表面的路程变长,电子一空穴对的复合几率也随 变大;另一方面,未完全替代Ti的La可能成为光生电子一空穴对的复合中,因此,通过La的掺杂可以有效调节TiO2晶粒尺寸和光致接触角     

在涂覆镍盐的基板上火焰法制备碳纳米管

本文利用在基板材料上涂敷镍盐作为催化剂前驱体,在火焰中成功制备出了碳纳米管材料。与前期的抛光和腐蚀法相比,该方法简化了催化剂的制备过程,碳纳米管合成的重复性和稳定性好,适合于大批量合成碳纳米管;采用场发射枪高分辨扫描电镜(SEM)、透射电镜(TEM)和激光拉曼光谱对碳纳米管的形貌进行了表征;研究了不同基板材料和燃料对碳纳米管形态的影响;讨论了碳纳米管的形成机理。认为涂敷镍盐而产生的高活性Ni催化剂是制备碳纳米管的主要因素。     

基于热刺激电流的空间电介质载流子迁移率测量方法

为了研究空间用聚酰亚胺材料在不同温度下的载流子迁移率,提出了基于热刺激电流(TSC)测量载流子迁移率的模型。对试样施加一段时间的电压,会有电荷注入到材料中。当试样温度降低到液氮温度时,注入电荷被保持在材料的陷阱中。假设入陷的电荷服从玻尔兹曼分布,陷阱中电荷会随着材料温度的上升而出陷,然后在自建电场的作用下向电极传输。在这个物理模型的基础上,推导出了载流子迁移率的解析公式。通过计算,得到了聚酰亚胺在不同温度下的载流子迁移率。同时,采用空间电荷限制电流方法测量了聚酰亚胺材料的迁移率。通过比较2种方法得到的迁移率表明,提出的迁移率计算模型可以比较精确地得到在强场下较大温度范围内的载流子迁移率。该方法为空间介质电荷输运规律和机理的研究提供了基础。     

Microwave impedance spectroscopy of dense carbon nanotube bundles

We have performed impedance spectroscopy of dense carbon nanotube (CNT) bundles in the broad frequency range from 10 MHz to 67 GHz. Dense CNT bundles were formed on sharp tips from aqueous suspension by ac dielectrophoresis and incorporated into on-wafer test structures. The frequency response of the bundles can be fit to a model with frequency-independent elements in the entire frequency range up to 67 GHz strongly suggesting that CNT properties do not depend on the frequency throughout the whole frequency range. The measurements at microwave frequencies allowed separate characterization of the bundle/metal electrode contacts and the bundle bulk. Effects of different CNT fabrication and suspension processing routes on bundle characteristics were identified. We have also made a preliminary estimation of the average inductance per current carrying shell in the bundles. For good quality nanotube bundles, the inductance has been found to fall within the range from approximately 3.5 to 40 nH/microm. With decreasing nanotube quality, the implemented estimation procedure yields higher values with a large uncertainty. Systematic measurements of devices with individual nanotubes are required to provide more accurate data.     

Nanomechanics of imperfectly straight single walled carbon nanotubes under axial compression by using molecular dynamics simulation

The buckling characteristics of several curved forms of single walled carbon nanotubes (SWCNTs) were studied in this work via molecular dynamics simulation method. The structural morphology of the CNT was modified to induce curvature along the tube axis. The nature of mechanical properties of these classes of CNTs under compression deviates from the ideal ‘perfectly straight’ CNTs. We found that the inclusion of curvature along the tube axis can significantly impact the performance of the carbon nanotube under compression. These curvilinear CNTs, when combined with other CNTs to form a bundle, will have a greater weakening effect on the mechanical performance of the CNT bundle.     

Design, Manufacturing, and Testing of Single-Carbon-Nanotube-Based Infrared Sensors

As a 1-D nanostructural material, carbon nanotube (CNT) has attracted lot of attention and has been used to build various nanoelectronic devices due to its unique electronic properties. In this paper, a reliable and efficient nanomanufacturing process was developed for building single-CNT-based nanodevices by depositing the CNTs on the substrate surface and then aligning them to bridge the electrode gap using the atomic force microscopy (AFM) based nanomanipulation. With this technology, single CNT-based IR sensors have been fabricated for investigating CNT's electronic and photonic properties. The fabrication of single-CNT-based IR sensors demonstrated the reliability and efficiency of the nanomanufacturing process. Experimental tests on single-multiwalled-CNT-based IR sensors have shown much larger photocurrent and quantum efficiency than other reported studies. It has also been shown that a high signal to dark current ratio can be accomplished by single-walled-CNT (SWNT) based IR sensors. Moreover, the testing of SWNT-bundle-based IR sensors verified that the performance of CNT bundle/film-based nanoelectronic devices was limited by the mixing of semiconducting CNTs and metallic CNTs, as well as the unstable CNT–CNT junctions in a CNT bundle or network.      

On the Applicability of Single-Walled Carbon Nanotubes as VLSI Interconnects

This paper presents a comprehensive study of the applicability of single-walled carbon nanotubes (SWCNTs) as interconnects in nanoscale integrated circuits. A detailed analysis of SWCNT interconnect resistance (considering its dependence on all physical parameters, as well as factors affecting the contact resistance), the first full 3-D capacitance simulations of SWCNT bundles for realistic very large scale integration (VLSI) interconnect dimensions, and a quantitative evaluation of the importance of inductive effects in SWCNT interconnects are presented. The applicability of carbon nanotube (CNT) based vias (vertical interconnects)-the most realizable CNT interconnects in the current state of the art-is addressed for the first time. It is shown that CNT interconnects can provide 30%-40% improvement in the delay of millimeter-long global interconnects. The applicability of CNT monolayers as local interconnects is found to be much more limited than that reported in the prior literature. Dense CNT bundle global interconnects are shown to offer a 4times reduction in power dissipation while achieving the same delay as optimally buffered Cu interconnects at the 22 nm node. This power saving increases to 8times at the 14 nm node. Furthermore, 3-D finite-element electrothermal simulations show that CNT bundles used as vias in between Cu metal layers can provide large improvement in metal interconnect lifetime by lowering the temperature of the hottest interconnects.     

Linear increases in carbon nanotube density through multiple transfer technique

We present a technique to increase carbon nanotube (CNT) density beyond the as-grown CNT density. We perform multiple transfers, whereby we transfer CNTs from several growth wafers onto the same target surface, thereby linearly increasing CNT density on the target substrate. This process, called transfer of nanotubes through multiple sacrificial layers, is highly scalable, and we demonstrate linear CNT density scaling up to 5 transfers. We also demonstrate that this linear CNT density increase results in an ideal linear increase in drain-source currents of carbon nanotube field effect transistors (CNFETs). Experimental results demonstrate that CNT density can be improved from 2 to 8 CNTs/μm, accompanied by an increase in drain-source CNFET current from 4.3 to 17.4 μA/μm.     

Ultrahigh Frequency Carbon Nanotube Transistor Based on a Single Nanotube

Single-walled carbon nanotube field-effect transistors (CNT FETs) are predicted to have intrinsic cutoff frequencies approaching the THz range. Here ldquointrinsicrdquo means that the parasitic capacitance due to fringing fields is negligible compared to the gate-source capacitance required to modulate the conductance. In practice, although there are strategies proposed to mitigate this based on parallel arrays of CNT FETs, this parasitic capacitance dominates most geometries (even aligned arrays to date). In this work we show nanotube transistor performance with maximum stable gain above 1 GHz (even including the parasitics) by combining ldquoon-chiprdquo the electrical properties of 100 CNT FETs fabricated on one long nanotube. This also solves the problem of impedance matching by boosting the on current to a large (mA) value, and at the same time allows one to extract properties of each individual CNT FET, since they are identical in electrical characteristics as they are made out of the same CNT. This strategy opens the door to applications of carbon nanotube devices in the RF and microwave frequency range, a technologically relevant portion of the spectrum for both wired and wireless electronics, that has been (until now) incompatible with nanotube device technology.     

Role of Doping in Carbon Nanotube Transistors With Source/Drain Underlaps

The effects of doping on the performance of coaxially gated carbon nanotube (CNT) field-effect transistors for both zero Schottky-barrier (SB) and doped carbon nanotube contacts are theoretically investigated. For ultrascaled CNTFETs in which the source/drain metal contacts lie 50 nm apart, there is no MOSFET-like contact CNTFET (C-CNTFET) with an acceptable on/off current ratio using a CNT of diameter ges1.5 nm and a source/drain voltage ges0.4 V. For CNTFETs with source/drain metal contacts either 50 nm or 100 nm apart, there is an optimal doping concentration of 10^-3 dopants per atom. The maximum on/off current ratios for the 50 nm CNT/5 nm gate and the 100 nm CNT/10 nm gate SB-CNTFETs are 5 times 10⁴ and 6 times 10⁵, respectively. Performance metrics of delay time, cutoff frequency, and LC frequency are presented and compared.     

碳纳米管工具电极的制备

纳米工具电极是进行纳米电解加工的必备条件,其特征尺寸直接影响纳米结构的最终尺寸.提出了利用电弧放电将碳纳米管束焊接在钨针尖上的纳米工具电极制备方法,并通过试验研究了钨针的针尖圆弧半径和放电电压对制备碳纳米管工具电极的影响.试验结果表明,不同尖端圆弧半径的钨针,所需有效放电电压不同,圆弧半径越小,有效放电电压越小,强电场分布越集中,越容易将碳纳米管束焊接在针尖的顶端;圆弧半径越大,强电场分布区域越大,越不容易控制碳纳米管束焊接的方向性.在针尖圆弧半径约为100 nm和300 nm的钨针上,放电电压分别为25 V和35 V时,成功制备出碳纳米管工具电极.     

Wafer-Scale Growth and Transfer of Aligned Single-Walled Carbon Nanotubes

Experimental demonstration of wafer-scale growth of well-aligned, dense, single-walled carbon nanotubes on 4" ST-cut quartz wafers is presented. We developed a new carbon nanotube (CNT) wafer-scale growth process. This process allows quartz wafers to be heated to the CNT growth temperature of 865degC through the alpha-beta phase transformation temperature of quartz (573degC) without wafer fracture. We also demonstrate wafer-scale CNT transfer to transfer these aligned CNTs from quartz wafers to silicon wafers. The CNT transfer process preserves CNT density and alignment. Carbon nanotube FETs fabricated using these transferred CNTs exhibit high yield. Wafer-scale growth and wafer-scale transfer of aligned CNTs enable carbon nanotube very large-scale integration circuits and their large-scale integration with silicon CMOS.     

Manufacturing polymer/carbon nanotube composite using a novel direct process

A direct process for manufacturing polymer carbon nanotube (CNT)-based composite yarns is reported. The new approach is based on a modified dry spinning method of CNT yarn and gives a high alignment of the CNT bundle structure in yarns. The aligned CNT structure was combined with a polymer resin and, after being stressed through the spinning process, the resin was cured and polymerized, with the CNT structure acting as reinforcement in the composite. Thus the present method obviates the need for special and complex treatments to align and disperse CNTs in a polymer matrix. The new process allows us to produce a polymer/CNT composite with properties that may satisfy various engineering specifications. The structure of the yarn was investigated using scanning electron microscopy coupled with a focused-ion-beam system. The tensile behavior was characterized using a dynamic mechanical analyzer. Fourier transform infrared spectrometry was also used to chemically analyze the presence of polymer on the composites. The process allows development of polymer/CNT-based composites with different mechanical properties suitable for a range of applications by using various resins.