利用场发射显微镜研究单壁碳纳米管的场发射特性

利用场发射显微镜研究了单壁碳纳米管（SWCNTs)的场发射特性。由于实验中所用的SWCNTs的长度基本一致，因此能同时观察到多根SWCNTs的场发射像。SWCNTs的场发射像随着热处理温度的升高而变化，直至热处理温度过高而塌缩。在一定的实验条件下，观察到了具有精细结构的单根碳纳米管顶端“帽子”的场发射像。电流－电压（I－U）曲线分析表明，SWCNTs的电流来源于场发射。     

热处理对氧化锌纳米线场发射特性的影响

用场发射显微镜研究了在钨针尖上生长的氧化锌纳米线的场发射性能,得到了氧化锌纳米线的场发射像及场发射电流与电压关系,并讨论了氧化锌纳米线场发射像的形成原因和不同热处理条件对其场发射性能的影响,给出了氧化锌纳米线比较合适的热处理温度.     

场离子显微镜观测单壁碳纳米管

场离子显微镜是具有原子级分辨能力的尖端表面分析工具.它适用于纳米尺度的单壁碳纳米管(SWCNTs)末端表面原子排列的观测.利用范氏力将SWCNTs组装到钨针尖上,用场离子显微镜观察了这种针尖样品.在观察过程中对针尖样品进行了加热处理,既除掉非晶的C原子,也破坏了由于碳纳米管切割制造过程使用表面活化剂引起的高电阻层,得到了开口SWCNTs的场离子显微镜像,由此推断出SWCNTs束的顶端原子结构,估算出观察到的SWCNTs的直径,并且模拟了其中一个图像所代表的SWCNTs顶端开口的原子排列,推断出产生这个图像的SWCNTs是(7,7)型结构.     

热处理对单壁碳纳米管场发射的影响

将单壁碳纳米管组装于W针尖 ,对它进行热处理 ,得到单壁碳纳米管在不同温度去气时的残气质谱图和热处理后的场发射特性曲线。通过对不同温度去气后的I U特性曲线的Fowler Nordheim直线斜率的变化 ,结合残气质谱图的分析 ,研究热处理对单壁碳纳米管场发射特性的影响 ,并对其机理进行了初步讨论     

MWCNT/ZnO纳米线复合阴极薄膜的场发射特性

实验提出以多壁碳纳米管(MWCNT)/ZnO纳米线复合材料作为场发射阴极薄膜,研究其图形化制备工艺以及其场发射特性.用丝网印刷工艺制备图形化MWCNT/ZnO纳米线复合阴极薄膜,实验获得合适的浆料配比以及适合的烘烤和烧结温度.对MWCNT/ZnO纳米线样品进行SEM分析和场发射特性测试,发现图形化阴极设计提高了场发射电流,并且改善场发射发光均匀度;材料组分的低维化明显降低场发射开启电压;加电老练处理有效改善场发射特性.     

碳纳米管与聚苯胺混合物的场发射

本文研究碳纳米管和聚苯胺混合物的场发射.用N-甲基吡咯烷酮溶解的聚苯胺和单壁碳纳米管混合溶液滴在硅片上,在垂直于样品平面的稳恒静电场的作用下,制成了不连续的薄膜.薄膜由尺寸在(2～5)μm的岛组成,分布比较均匀.测试其场发射特性,开启电场(10μA/cm2)为8.06 V/μm.经过计算,得到升压过程和降压过程的场增强因子β分别为8.3×102和1.1×103.用透明阳极技术观测其场发射中心分布,荧光屏上的像点比较均匀,没有观察到明显的屏蔽效应.     

热处理对单壁碳纳米管场发射的影响

将单壁碳纳米管组装于W针尖，对它进行热处理，得到单壁碳纳米管在不同温度去气时的残气质谱图和热处理后的场发射特性曲线。通过对不同温度去气后的I－U特性曲线的Fowler-Nordheim直线斜率的变化，结合残气质谱图的分析，研究热处理对单壁碳纳米管场发射特性的影响，并对其机理进行了初步讨论。     

碳纳米管表面化学镀银及场发射性能研究

利用化学镀方法对碳纳米管(carbon nano-tubes,CNTs)表面金属化镀银,研究表面化学镀银碳纳米管的场发射性能。碳纳米管经氧化处理后,表面存在一些羰基(CO)、羧基(—COOH)和羟基(—OH)等活性基团,经敏化、活化处理后,形成金属钯活化中心,进而还原金属银离子,从而获得表面化学镀银的碳纳米管。表面化学镀银碳纳米管阴极的开启电场约为0.19V/μm,当电场强度为0.37V/μm时,最大发射电流达6mA/cm2,场增强因子约为25565。实验结果表明,化学镀银层可以提高碳纳米管的电子传输和热传输能力,提高碳纳米管的场发射电流和发射稳定性,有利于碳纳米管在场发射平板显示领域的应用。     

铬酸溶液后处理增强碳纳米管的场发射特性

采用铬酸溶液对碳纳米管进行后处理,旨在修饰碳纳米管的表面形态及改变碳纳米管的表面结构,进一步增强碳纳米管的场发射特性.铬酸溶液后处理与传统以硝酸后处理的厅法不同之处在于,铬酸溶液可以更有效率地与非品质碳及碳纳米管发生化学反应.可以预期碳纳米管经过铬酸溶液处理后,碳纳米管的表而形态、化学组成及场发射特性会产生很大的变化.场发射的数据显示,经铬酸溶液处理20 min的碳纳米管场发射电流比未经过铬酸溶液处理的场发射电流有明显的增加.然而,长时间的铬酸溶液处理也会降低碳纳米管场发射特性.经铬酸溶液处理20min的碳纳米管场发射电流增强原因主要为适度的铬酸溶液处理可以改变碳纳米管的表面形态,使碳管的表面密度增大、场发射功函数降低.但过长时间的铬酸溶液后处理,又会造成碳纳米管数目减少及表面结构受到损害,导致碳纳米管场发射特性变差.     

表面态对碳纳米管场发射的影响

采用CVD法在Ni丝上直接沉积碳纳米管,并应用二极管结构测试表面态(突出尖端和吸附)对碳纳米管场发射的影响。测试表明,突出尖端主要影响碳纳米管场发射的开启电场以及场发射电流稳定性;吸附作用的影响表现在改变碳纳米管能带结构进而改变其场发射性能。     

用FEM/FIM研究单壁碳纳米管束

利用范氏力将单壁碳纳米管样品组装到钨针尖上 ,用FEM/FIM对同一碳纳米管样品用热处理方法和场脱附方法进行了研究。场离子显微镜是具有原子级分辨能力的尖端表面分析工具 ,由场离子像推测这次组装的样品是由三根单壁碳纳米管突起组成的碳纳米管束。清洁碳纳米管束样品的场发射像和场离子像有极好的对应关系。场脱附后的碳纳米管束的场发射特性较好地符合Fowler Nordheim场发射模型。通过比较碳纳米管束吸附态和热处理后以及场脱附后的Fowler Nordheim曲线的斜率变化 ,得出碳纳米管束样品逸出功的变化 ,再结合场发射像的变化推断出场脱附与热处理结合是一种较理想的获得清洁碳纳米管表面的方法     

Single- and few-walled carbon nanotubes grown at temperatures as low as 450 degrees c: electrical and field emission characterization

Single-wall (SW-) and few-walled (FW-) carbon nanotubes (CNTs) were synthesized on aluminum/ cobalt coated silicon at temperatures as low as 450 degrees C by plasma enhanced chemical vapor deposition technique (PECVD). The SWCNTs and FWCNTs grow vertically oriented and well separated from each other. The cold field emission studies of as-grown SWCNTs and FWCNTs showed low turn-on field emission threshold voltages, strongly dependent of the nanotubes morphology. Current-voltage curves of individual CNTs, measured by conductive atomic force microscopy (CAFM), showed an electrical resistance of about 90 Komega, that is attributed mainly to the resistance of the contact between the CNTs and the conductive CAFM tip (Au and Pt).     

Polydiacetylene single-walled carbon nanotubes nano-hybrid for cellular imaging applications

The functionalization of single-walled carbon nanotubes (SWCNTs) by forming self-assembled supramolecular structure of 10,12-pentacosadiynoic acid (PCDA) on the carbon nanotube wall is reported. PCDA assemblies on SWCNTs (PCDA/SWCNTs) were polymerized by UV irradiation to extensively conjugated polydiacetylene (PDA). PDA/SWCNT was identified by absorption and emission spectroscopy, scanning and transmission electron microscopies (SEM and TEM) and atomic force microscopy (AFM). PDA/SCWNTs showed strong near-infrared (NIR) fluorescence caused by fluorescence resonance energy transfer (FRET) between PDA network and semiconducting SWCNT core. The micro-patterning of biotinylated PDA/SWCNT with FITC-avidin on biotinylated glass surface demonstrated the potential application for a bio-sensing device. Furthermore, the biocompatibility for mammalian cancer cells was tested by viability experiments, which revealed that the PDA/SWCNTs had very low toxicity below 31.3 mg/L in terms of pristine SWCNTs concentration. Also, PDA/SWCNTs inside the cells can be observed by NIR microscopy. This unique modular method of preparation can contribute to diverse functionalities for practical applications in various non-invasive cellular imaging.     

Field Electron Emission from Layers with Very Long and Sparse Carbon Nanotubes

For carbon layers with very long and sparse nanotubes (nanofilaments) field electron emission at very low average electric field was observed. Field emission current of 10 µA was obtained at the average electric field E_av=0.16 V/µm and the value of the field amplification coefficient β reached 45,000. At high emission currents (exceeding 30-50 µA) one or several luminous nanotubes (nanofilaments) heated by the emission cuurent have been observed in the gap between the sample and the anode.     

Quantum light signatures and nanosecond spectral diffusion from cavity-embedded carbon nanotubes

Single-walled carbon nanotubes (SWCNTs) are considered for novel optoelectronic and quantum photonic devices, such as single photon sources, but methods must be developed to enhance the light extraction and spectral purity, while simultaneously preventing multiphoton emission as well as spectral diffusion and blinking in dielectric environments of a cavity. Here we demonstrate that utilization of nonpolar polystyrene as a cavity dielectric completely removes spectral diffusion and blinking in individual SWCNTs on the millisecond to multisecond time scale, despite the presence of surfactants. With these cavity-embedded SWCNT samples, providing a 50-fold enhanced exciton emission into the far field, we have been able to carry out photophysical studies for the first time with nanosecond timing resolution. We uncovered that fast spectral diffusion processes (1-3 ns) remain that make significant contributions to the spectral purity, thereby limiting the use of SWCNTs in quantum optical applications requiring indistinguishable photons. Measured quantum light signatures reveal pronounced photon antibunching (g(2)(0) = 0.15) accompanied by side-peak bunching signatures indicative of residual blinking on the submicrosecond time scale. The demonstrated enhanced single photon emission from cavity-embedded SWCNTs is promising for applications in quantum key distribution, while the demonstrated passivation effect of polystyrene with respect to the stability of the optical emission opens a novel pathway toward optoelectronic devices with enhanced performance.     

电泳沉积制备平行栅碳纳米管场发射阴极的研究

利用磁控溅射、光刻、湿法刻蚀和电泳技术在玻璃基片上成功制备平行栅场发射阴极阵列,用光学显微镜、场发射扫描电镜和拉曼光谱观察了碳纳米管的形貌和结构,并测试所制备的平行栅碳纳米管阴极的场发射性能.光学显微镜和场发射电子显微镜测试表明,平行栅结构阴极和栅极交替地分布,同一个平面内,CNTs有选择性地沉积在平行栅结构中的阴极表...     

Emission properties of DLC films on Si substrates

DLC films were deposited on polished both n-type and p-type silicon substrates. The silicon resistivity was ～0.02 Θ cm. Some of the DLC films 20 nm thick were deposited on the n-type Si surface with the submicron cones. SEM and Raman spectroscopy were used for structural investigations. Field electron emission occurs after dielectric breakdown, except for the samples with Si cones for which the emission seems to originate from SiC formed during the first stage of electron emission. It seems that too much sp² graphite phase may give rise to the observed increase in the turn-on field from 50 V/μm up to 150 V/μm.     

应用于场致发射的掺杂纳米金刚石膜的研究

场致发射是一种新型显示技术,具有良好应用前景,场发射显示器的核心内容是场发射阴极材料,纳米金刚石由于低表面粗糙度、低场发射强度、高发射电流密度、大比表面积、网状结构以及高密度悬挂键等优秀电化学性能成为场发射的理想阴极材料.本文阐述了化学气相沉积法制备纳米金刚石薄膜的沉积装置、预处理和工艺参数,并介绍了金刚石掺杂机理和掺入元素的研究现状.     

Electronic structure, electron field emission and magnetic behaviors of carbon nanotubes fabricated on La0.66Sr0.33MnO3 (LSMO) for spintronics application

This work elucidates the electronic structure, electron field emission and magnetic anisotropic behaviors of single wall carbon nanotubes (SWCNTs) for the spin-electronics device application grown on the La0.66Sr0.33MnO3 (LSMO)/SrTiO3 (STO) substrate. Micro-Raman spectroscopy, X-ray absorption near-edge structure (XANES) and valence-band photoemission spectroscopy (VBPES) were used for the study of electronics structure. The field emission characteristics were studied from the electron field emission current density (J) versus applied electric field (E(A)) from which the turn-on electric field (E(TOE)) was evaluated. The magnetization behaviors are also presented by the M-H hysteresis loop and were obtained by applying the magnetic field in the parallel and perpendicular direction of the CNTs at 305 K and 5 K temperatures. A magnetic measurement shows that the coercivity of the CNTs/LSMO/STO is higher and has hig anisotropic-nature than the composite LSMO/STO that could be the good material for the future possible spin-electronics device applications.     

p-n homo-junction arrays of aligned single walled carbon nanotubes fabricated by selective patterning of polyethyleneimine film

We describe the fabrication and electrical performance of p-n homo-junction diode arrays of horizontally aligned single walled carbon nanotubes (SWCNTs). Horizontally aligned SWCNTs grown on stable temperature-cut quartz with a density of ～ 6 SWCNTs μm(-1) were transferred onto a SiO(2)/Si substrate. After the electrical breakdown, aligned SWCNT field effect transistors (FETs) showed unipolar p-type characteristics with a large current on/off ratio of 10(6) at 1 V and a hole mobility per tube of 1500 cm(2) V(-1) s(-1). Spin-coating of polyethyleneimine (PEI) onto p-type SWCNT FETs showed the n-type transfer characteristics. Patterning of spin-coated PEI film enabled the fabrication of p-n homo-junction arrays of aligned SWCNTs in an easy way, where the rectifying behavior was observed with a rectification ratio of ～ 10(4) at ± 2 V. A comparative study with a p-n homo-junction of random networks of SWCNTs confirmed the advantage of aligned SWCNTs for applications in high performance electronic devices.