Vertically aligned carbon nanotube field-effect transistors

Vertically aligned carbon nanotube field-effect transistors (CNTFETs) have been developed using pure semiconducting carbon nanotubes. The source and drain were vertically stacked, separated by a dielectric, and the carbon nanotubes were placed on the sidewall of the stack to bridge the source and drain. Both the effective gate dielectric and gate electrode were normal to the substrate surface. The channel length is determined by the dielectric thickness between source and drain electrodes, making it easier to fabricate sub-micrometer transistors without using time-consuming electron beam lithography. The transistor area is much smaller than the planar CNTFET due to the vertical arrangement of source and drain and the reduced channel area.     

Growth of self-aligned carbon nanotube for use as a field-effect transistor using cobalt silicide as a catalyst

The growth of carbon nanotube (CNT) using cobalt silicide as a catalyst and source/drain electrode is proposed to explore its feasibility for fabricating integrated-circuit process compatible, self-aligned CNT field-effect transistors (CNTFET). The silicide nanoparticles formed in the Ti/Co/poly-Si source/drain stack were used as a catalyst for CNT growth. Results show that single-walled CNTs have been synthesized between pre-defined catalytic cobalt silicide source/drain pairs by chemical vapor deposition at 800-900 °C. Preliminary transistor characteristics of the CNTFETs have also been achieved.     

Field emission characteristics of a single free standing carbon nanotube with gate electrode

In this paper, we have constructed and analyzed the field emission behavior of a single vertically aligned free standing carbon nanotube (CNT) with a gate electrode in order to verify the feasibility of using a single CNT as the low-voltage field emission electron source. The single vertically aligned CNT with gate electrode was fabricated by combining optical lithography, electron beam lithography (EBL) and inductively coupled plasma chemical vapor deposition (ICP-CVD) processes. A self-aligned process with a single mask was utilized to define the gated structure and the nano-size catalyst for CNT growth. A single vertically aligned CNT was then grown within the gate hole by ICP-CVD. The length-to-diameter ratio of CNT could be varied by adjusting the e-beam exposure time, and the CNT height was controlled to equal to the gate-to-cathode spacing (800) nm in one gated device and less than the spacing (530 nm) in another device. The field emission characteristics of the integrated gate electrode devices were then measured under a scanning electron microscopy (SEM) with a three-axis nano-positioning device. The turn-on field of the gated devices with 800 and 530 nm height CNT were 2.77 and 3.57 V/μm, respectively, with applying − 10 V gate voltage, and 0 V anode voltage.     

Carbon nanotube counter electrode for high-efficient fibrous dye-sensitized solar cells

ABSTRACT: High-efficient fibrous dye-sensitized solar cell with carbon nanotube (CNT) thin films as counter electrodes has been reported. The CNT films were fabricated by coating CNT paste or spraying CNT suspension solution on Ti wires. A fluorine tin oxide-coated CNT underlayer was used to improve the adherence of the CNT layer on Ti substrate for sprayed samples. The charge transfer catalytic behavior of fibrous CNT/Ti counter electrodes to the iodide/triiodide redox pair was carefully studied by electrochemical impedance and current-voltage measurement. The catalytic activity can be enhanced by increasing the amount of CNT loading on substrate. Both the efficiencies of fibrous dye-sensitized solar cells using paste coated and sprayed CNT films as counter electrodes are comparative to that using Pt wires, indicating the feasibility of CNT/Ti wires as fibrous counter electrode for superseding Pt wires.     

光刻法制作源漏电极的薄膜晶体管

采用光刻法制备了薄膜晶体管的银源漏电极,实验中变换不同的刻蚀剂以减少对SiO2栅绝缘层的损害。底接触法蒸镀的酞菁铜作为晶体管器件的有源层,制得的晶体管器件的输出特性曲线显示该器件的输出电流具有趋于饱和的倾向。     

Fabrication and electrochemical properties of carbon nanotube film electrodes

Carbon nanotube (CNT) film electrodes were fabricated by a novel process involving the electrostatic spray deposition (ESD) of a CNT solution. Acid treated CNTs were dispersed in an aqueous solvent through sonication and then the CNT solution was electrostatically sprayed onto a metallic substrate by the ESD method. The CNT film electrodes showed well-entangled and interconnected porous structures with good adherence to the substrate. A specific capacitance of 108 F/g was achieved for the electrodes in 1 M H₂SO₄. In addition, the CNT film electrode showed good high rate capability.     

Simple fabrication process of a screen-printed triode-CNT field emitter array

We introduced a simple fabrication process for field emission devices based on carbon nanotubes (CNTs) emitters. Instead of using the ITO material as a transparent electrode, a metal (Au) with thickness of 5–20 nm was used. Moreover, the ITO patterning process was eliminated by depositing metal layer, before the CNT printing process. In addition, the thin metal layer on a photoresist (PR) layer was used as UV block. We fabricated the CNT field emission arrays of triode structure with a simple process. And I–V characteristics of field emission arrays were measured. The maximum current density of 254 μA/cm² was achieved when the gate and the anode voltages were kept 150 and 3000 V, respectively. The distance between anode and cathode was kept constant.     

An under-gate triode structure field emission display with carbon nanotube emitters

A new triode structure for field emission displays based on carbon nanotube emitters is demonstrated. In this structure, gate electrodes are located underneath the cathode electrodes with an in-between insulating layer, a so-called under-gate type triode structure. Although the gate is on the opposite side of the anode with respect to the cathode electrodes, modulation of electron emission from the carbon nanotube emitters by the gate voltage is confirmed. The simple structure and fabrication process may lead to practical applications for the under-gate triode type structure.     

Development of triode type RF plasma enhanced CVD equipment for low temperature growth of carbon nanotube

Triode-type radio frequency plasma enhanced chemical vapor deposition (RF-PECVD) equipment has been developed in order to grow well-aligned carbon nanotubes on Si and glass substrates at 550 °C. The CVD equipment employs a grid electrode in addition to the cathode and anode electrodes. The grid electrode allows the growth of a well-aligned carbon nanotube with an inside and an outside diameter of 7 and 17 nm, respectively. Moreover, the patterning growth of the well-aligned CNT on a glass substrate was also demonstrated.     

Secondary electron emission in a triode carbon nanotube field emission display and its influence on the image quality

The secondary electron (SE) emission (SEE) in a triode carbon nanotube (CNT) field emission display (FED) and its influence on the image quality have been studied with a 3.5 in. vacuum-sealed FED prototype fabricated by using screen printing and frit sealing techniques. By analyzing the emission property difference of the device under two different kinds of work modes, we have found that it is the SEE from the insulator above the gate that induced the anode image distortion of FED under normal work mode. Two improved structures, by decreasing the size of insulator layer and by coating a conductive layer to stabilize the potential of the insulators, are provided to eliminate SEE influence and achieved a uniform anode image. It is expected that our results will benefit the research and design of CNT FED with high performance.     

A novel sensor platform based on aptamer-conjugated polypyrrole nanotubes for label-free electrochemical protein detection

We first present a simple yet versatile strategy for the functionalization of polymer nanotubes in a controlled fashion. Carboxylic-acid-functionalized polypyrrole (CPPy) nanotubes were fabricated by using cylindrical micelle templates in a water-in-oil emulsion system, and the functional carboxyl groups were effectively incorporated into the polymer backbone during the polymerization by using pyrrole-3-carboxylic acid (P3CA) as a co-monomer without a sophisticated functionalization process. It was noteworthy that the chemical functionality of CPPy nanotubes was readily controlled in both qualitative and quantitative aspects. On the basis of the controlled functionality of CPPy nanotubes, a field-effect transistor (FET) sensor platform was constructed to detect specific biological entities by using a buffer solution as a liquid-ion gate. The CPPy nanotubes were covalently immobilized onto the microelectrode substrate to make a good electrical contact with the metal electrodes, and thrombin aptamers were bonded to the nanotube surface via covalent linkages as the molecular recognition element. The selective recognition ability of thrombin aptamers combined with the charge transport property of CPPy nanotubes enabled the direct and label-free electrical detection of thrombin proteins. Upon exposure to thrombin, the CPPy nanotube FET sensors showed a decrease in current flow, which was probably attributed to the dipole-dipole or dipole-charge interaction between thrombin proteins and the aptamer-conjugated polymer chains. Importantly, the sensor response was tuned by adjusting the chemical functionality of CPPy nanotubes. The efficacy of CPPy nanotube FET sensors was also demonstrated in human blood serum; this suggests that they may be used for practical diagnosis applications after further optimization.     

Effect of Purity and Substrate on Field Emission Properties of Multi-walled Carbon Nanotubes

Multi-walled carbon nanotubes (MWNT) have been synthesized by chemical vapour decomposition (CVD) of acetylene over Rare Earth (RE) based AB₂ (DyNi₂) alloy hydride catalyst. The as-grown carbon nanotubes were purified by acid and heat treatments and characterized using powder X-ray diffraction, Scanning Electron Microscopy, Transmission Electron Microscopy, Thermo Gravimetric Analysis and Raman Spectroscopy. Fully carbon based field emitters have been fabricated by spin coating a solutions of both as-grown and purified MWNT and dichloro ethane (DCE) over carbon paper with and without graphitized layer. The use of graphitized carbon paper as substrate opens several new possibilities for carbon nanotube (CNT) field emitters, as the presence of the graphitic layer provides strong adhesion between the nanotubes and carbon paper and reduces contact resistance. The field emission characteristics have been studied using an indigenously fabricated set up and the results are discussed. CNT field emitter prepared by spin coating of the purified MWNT–DCE solution over graphitized carbon paper shows excellent emission properties with a fairly stable emission current over a period of 4 h. Analysis of the field emission characteristics based on the Fowler–Nordheim (FN) theory reveals current saturation effects at high applied fields for all the samples.     

Optimization of methane cold wall chemical vapor deposition for the production of single walled carbon nanotubes and devices

Carbon nanotubes are synthesized by cold wall chemical vapor deposition (CVD) using methane as the carbon source and iron thin film catalyst. The yield of thin nanotubes as determined by scanning electron microscopy (SEM) is strongly dependent on the precise CVD process and the preparation of the substrate. The effects of pressure (5–80 kPa), temperature (700–950 °C), substrate conditioning (air preheat) and metallization (Fe, Al, Mo) on thin nanotube yield are reported. High yields of thin nanotubes are obtained under optimum conditions. These thin nanotubes are candidates to be single walled carbon nanotubes (SWNTs) and Raman spectroscopy, photoluminescence spectroscopy and electrical transport provide evidence that, at least at optimum conditions, many, and perhaps all of the thin nanotubes are single walled. Single nanotube field effect transistors are fabricated and factors affecting device yield are reported. Optimum single nanotube device yield does not necessarily coincide with the optimum nanotube yield.     

A pH sensor based on the TiO2 nanotube array modified Ti electrode

In this paper, a novel solid state pH sensor was fabricated by anodization of titanium substrate electrode. The relationship between pH sensitivity and hydrophilicity or surface morphology of TiO₂ film was investigated. Amorphous TiO₂ nanotube has better pH response than anatase TiO₂ nanotube. After being irradiated by ultraviolet light (UV), the potential response of the electrode modified by amorphous TiO₂ nanotube was close to Nernst equation (59 mV/pH). SEM, XRD, and XPS were used to characterize electrodes. Possible mechanism was discussed by analyzing surface hydroxyl groups, crystal structure and hydrophilicity of the electrodes. The electrode has been used to detect some kinds of soft drinks and shows good response.     

Highly flexible and stretchable carbon nanotube network electrodes prepared by simple brush painting for cost-effective flexible organic solar cells

We developed highly flexible and transparent carbon nanotube (CNT) network electrodes prepared by a simple brush-painting method for the production of cost-effective flexible organic solar cells (FOSCs). By direct, rapid brush-painting of CNTs on a polyethylene terephthalate (PET) substrate using a conventional paintbrush made of nylon fibrils, we achieved percolated CNT network electrodes with a low sheet resistance of 286 Ω/square, a high diffusive transmittance of 78.45%, and superior mechanical flexibility at room temperature. The electrical, optical, and mechanical properties of the brush-painted CNT electrodes were investigated as a function of the number of repeated brush-painting cycles. In particular, brush-painted CNT electrodes showed outstanding flexibility in several test modes, including outer bending, inner bending, twisting and stretching, which are critical requirements in flexible electrodes. Notably, the brush-painted CNT network electrodes had a constant resistance change (ΔR/R₀) within outer and inner bending radii of 5 mm during dynamic fatigue testing. FOSCs fabricated on the brush-painted CNT electrode showed a power conversion efficiency of 1.632%, indicating the possibility of using brush-painted CNT electrodes as cost-effective flexible and transparent electrodes for printing-based low cost FOSCs.     

Synthesis and electro-catalytic activity of methanol oxidation on nitrogen containing carbon nanotubes supported Pt electrodes

Template synthesis of various nitrogen containing carbon nanotubes using different nitrogen containing polymers and the variation of nitrogen content in carbon nanotube (CNT) on the behaviour of supported Pt electrodes in the anodic oxidation of methanol in direct methanol fuel cells was investigated. Characterizations of the as-prepared catalysts are investigated by electron microscopy and electrochemical analysis. The catalyst with N-containing CNT as a support exhibits a higher catalytic activity than that carbon supported platinum electrode and CNT supported electrodes. The N-containing CNT supported electrodes with 10.5% nitrogen content show a higher catalytic activity compared to other N-CNT supported electrodes. This could be due to the existence of additional active sites on the surface of the N-containing CNT supported electrodes, which favours better dispersion of Pt particles. Also, the strong metal-support interaction plays a major role in enhancing the catalytic activity for methanol oxidation.     

One-pot facile synthesis and electrochemical evaluation of selenium enriched cobalt selenide nanotube for supercapacitor application

The present study emulates a one-pot facile synthesis of selenium-enriched CoSe nanotube using a chemical bath deposition (CBD) procedure. Schematic incorporation of 3D Ni foam current collectors as substrates for the growth of CoSe–Se nanotubes helped us achieve a binder-less thin film coating. The controlled synthesis of CoSe–Se nanotube was carried out by optimizing the temperature and time of the deposition. CoSe–Se nanotubes were grown on a porous Ni foam substrate using lithium chloride as a shape directing agent. The study found that the one dimensional structure of the nanotubes with porous nature results in an uninterrupted network of electroactive sites. Due to the superior conductivity, the as-fabricated material exhibited excellent rate capability and a higher degree of electrolyte ion diffusion across the CoSe–Se crystal structure. The CoSe–Se@Ni foam electrodes exhibited a specific capacitance of 1750.81 F g^?1 at 1 A g^?1. The electrode exhibited excellent cycling stability and showed a capacitance retention of 95% after 4000 charge-discharge cycles. Finally, an asymmetric supercapacitor (ASC) device was fabricated with the as-synthesized CoSe–Se@Ni foam electrode as the cathode, activated carbon@Ni foam electrode as the anode, and a thin filter paper separator soaked in 1 M aqueous KOH electrolyte solution. The ASC device showed a specific capacitance value of 106.73 F g^?1 at 0.5 A g^?1, and achieved an energy density of 37.94 Wh kg^?1 at a power density of 475.30 W kg^?1. The ASC device was utilized in an extended potential window of 1.6 V. The fabricated device displayed exceptional cycling stability with a capacitance retention of 93% after 5000 charge-discharge cycles.     

Towards molecular spintronics: magnetotransport and magnetism in carbon nanotube-based systems

We describe first approaches towards a carbon nanotube (CNT) based spintronics. The building blocks consist of pristine multi-wall CNTs and metallic ferromagnetic electrodes. The devices exhibit magnetoresistive effects up to several 10% at 4.2 K the origin of which is tentatively attributed to spin-dependent tunneling through an insulating barrier between the CNT and the electrode. We also show results of filling multi-wall CNTs with ferromagnetic materials. These magnetic quantum wires are fascinating objects in itself, revealing unusual magnetic properties. They may also be used, however, as magnetic electrodes to contact to the innermost shell of the nanotube in future molecular spintronics devices.     

Fabrication and properties of under-gated triode with CNT emitter for flat lamp

We investigated under-gate type carbon nanotube field emitter arrays (FEAs) for back light unit (BLU) in liquid crystal display (LCD). Gate oxide was formed by wet etching of ITO coated glass substrate instead of depositing SiO₂ on the glass substrate. Wet etching is easier and simpler than depositing and etching thick gate oxide to isolate the gate metal from cathode electrode in triode. To optimize the triode, we simulated the electric field distribution and electron trajectory in triode structures by the SIMION simulator. CNT emitters were formed using screen printing of photosensitive CNT paste. Field-emission characteristics of triode structure were measured. The maximum current density of 92.5 μA/cm² was when the gate and anode voltage was 95 and 2500 V, respectively, at the anode–cathode spacing of 1500 μm.     

Hydrothermally Grown ZnO Micro/Nanotube Arrays and Their Properties

We reported the optical and wettability properties of aligned zinc oxide micro/nanotube arrays, which were synthesized on zinc foil via a simple hydrothermal method. As-synthesized ZnO micro/nanotubes have uniform growth directions along the [0001] orientations with diameters in the range of 100–700 nm. These micro/nanotubes showed a strong emission peak at 387 nm and two weak emission peaks at 422 and 485 nm, respectively, and have the hydrophobic properties with a contact angle of 121°. Single ZnO micro/nanotube-based field-effect transistor was also fabricated, which shows typical n-type semiconducting behavior.