Fabrication of a carbon-nanotube-based field-effect transistor by microcontact printing

The fabrication of a field-effect transistor with both channel material and source and drain electrodes made from carbon nanotubes (CNTs) through patterned deposition of CNT films by microcontact printing is described. Surfactant-dispersed single-walled CNTs are first separated into semiconducting and metallic fractions by gel filtration. The semiconducting and metallic CNTs are then sequentially transferred by dendrimer-coated polydimethylsiloxane stamps onto dendrimer-coated silicon wafers following a printing protocol optimized for this purpose. The resulting CNT micropatterns are visualized by atomic force microscopy. Semiconducting as well as metallic CNTs preserve their characteristic electronic properties within the transferred films. A device composed of a rather thick (ca. 5 nm) and densely patterned film of metallic CNTs cross-printed on top of a thinner (ca. 1.5 nm) and less dense film of semiconducting CNTs shows the typical properties of a field-effect transistor with the metallic CNT stripes as electrodes, the semiconductive CNT stripes as channel material, and the silicon substrate as gate electrode.     

Growth of carbon nanotubes on aluminium foil for supercapacitors electrodes

A new approach for the preparation of carbon nanotubes (CNTs) electrode is proposed in the present work. Multi-walled carbon nanotubes (MWCNTs) were grown by chemical vapour deposition on aluminium strips pre-plated with a nickel thin film as the catalyst. The CNTs were characterized by scanning and transmission electron microscopy, Brunauer–Emmett–Teller surface area measurement and thermogravimetric analysis. The nickel-plated aluminium foil with a layer of CNTs was further characterized for an assessment of its electrochemical behaviour as electrode for supercapacitors. The specific capacitances of the electrode, as derived from cyclic voltammetry measurement at 0.1 V s⁻¹ scan rate, was found to be 54 and 79 F g⁻¹ in aqueous and organic electrolytes, respectively, in line with the highest reported values for either activated carbon or MWCNTs electrodes. Further evidence in support of the viability of the present approach for the preparation of a CNTs electrode was obtained from electrochemical impedance spectroscopy.     

The influence of Ni catalyst on the growth of carbon nanotubes on Si substrates

This article treats the influence of the treatment of a Ni catalyst upon the growth of carbon nanotubes in alcohol catalytic chemical vapour deposition (AC CVD) equipment. Prior to the growth of diamond, a thin film of Ni was deposited on a silicon substrate by magnetron sputtering. We observed that a combination of annealing of the Ni catalyst in vacuum and NH₃ had a positive effect upon the growth of carbon nanotubes (CNTs). The prepared CNTs were analysed by scanning electron microscopy and Raman spectroscopy.     

Growth and characterization of bamboo-shaped carbon nanotubes using nanocluster-assembled ZnO:Co thin films as catalyst

Bamboo-shaped carbon nanotubes (CNTs) had been successfully fabricated by a plasma enhanced chemical vapor deposition method, in which nanocluster-assembled ZnO:Co thin film was used as catalyst. It was found that bamboo-shaped CNTs were generally grown in a direction perpendicularly to the substrate surface with the tops of CNTs dominated by the droplet-like catalyst covered by the carbon layer. The diameter of CNTs was ranged from 20-50 nm. High resolution of TEM image showed that the typical CNT had a multi-walled structure with an inner core presented. The ordered graphite layers were inclined to an axis of CNT about 18 degrees and the interlayer space of a CNT was about 0.35 nm. Two peaks in Raman spectrum at 1586 cm(-1) and 1372 cm(-1) were identified as G-band and D-band for graphite, respectively. The results showed that catalyst based on ZnO:Co thin films could be used for the growth of CNTs with bamboo-shaped structure.     

Preconcentration of volatile organics on self-assembled, carbon nanotubes in a microtrap

This paper reports the self-assembly of carbon nanotubes (CNTs) on the inside wall of a steel capillary to fabricate a microtrap for the adsorption/desorption of trace organics. The microtrap functioned as a nanoconcentrator and an injector for gas chromatography (GC). The CNTs were deposited as a thin film by catalytic chemical vapor deposition from either CO or C2H4 as the precursor. The sorbent film synthesized from C2H4-CVD (CVD = chemical vapor deposition) had higher CNT density and thus was a stronger sorbent. In general, the CNT microtraps showed high-capacity adsorption and fast quantitative desorption, and the process showed excellent precision. This study demonstrates that CNT films can be deposited quite easily in a steel capillary for use in different analytical applications, and CNT films can perform as efficiently as packed-bed carbon sorbents.     

Clean carbon nanotube field emitters aligned horizontally

Horizontally aligned carbon nanotube (CNT) field emitters, which strongly adhere to the substrate and show good field emission properties, were fabricated by electrophoresis deposition and fissure formation techniques. A thin film of CNTs was deposited on a substrate, by electrophoresis, from an aqueous mixture of CNT and detergent, and then the detergent was deposited also by electropholysis. CNTs with a clean surface were exposed in the fissures produced by firing. The field emission was increased significantly due to the additional deposition of the detergent. When the CNTs were cut by increasing the firing time, the field emission increased significantly, while their stability decreased considerably. Our method does not require any further treatment for field emission.     

Templated growth of carbon nanotubes with controlled diameters using organic-organometallic block copolymers with tailored block lengths

Block copolymer thin films fabricated from polystyrene-polyferrocenylsilane (PS-b-PFS) block copolymers on silicon substrates were used as precursors of well-ordered, nanosized growth catalysts for carbon nanotubes (CNTs). The size of the catalytic domains was tuned by changing the molecular weight of the block copolymer, enabling control of the diameter of the CNTs grown from these substrates. CNT growth on catalytic substrates with larger organometallic domain sizes, using acetylene as a carbon source, resulted in enhanced amounts of CNT deposition compared to smaller PFS domains, which exhibited low catalytic activity. The inner and outer diameters of the multi-walled CNTs obtained were typically 8 and 16 nm, respectively, and were not influenced by the catalytic domain sizes. Various annealing strategies in inert or in hydrogen atmosphere were investigated. The use acetylene with an additional hydrogen flow as gas feed resulted in a significant increase in deposition on all PS-b-PFS decorated substrates. Under these conditions, the CNT diameters could be controlled by the catalyst domain sizes, resulting in decreasing diameters with decreasing domain sizes. Multiwalled CNTs with inner and outer diameters of 4 and 7 nm, respectively, and a narrow diameter distribution were obtained.     

Influence of co-catalyst on growth of carbon nanotubes using alcohol catalytic CVD method

This paper describes the influence of a co-catalyst on growth of carbon nanotubes (CNTs) by alcohol catalytic chemical vapour deposition (ACCVD) method. Silicon wafers covered with thermal oxide or polycrystalline diamond thin film were used as substrates. Ni thin film supported with Al, Cu or Ti was used as a catalyst. The films were deposited by pulsed laser deposition technique. Comparison of the various types of the co-catalyst (Al, Cu, Ti) leads to the conclusion that Cu co-catalyst is suitable for producing very thin single wall carbon nanotubes (SWCNTs) and combination of Al and Ni provide a good condition to the catalytic growth of CNTs. In addition, we observed also the influence of the various diffusion barriers (thermal oxide and polycrystalline diamond) on growth of CNTs. Prepared samples were analysed by Raman spectroscopy (RS) and scanning electron microscopy (SEM).     

Investigation of the effective parameters in the growth of carbon nanotubes by thermal chemical vapour deposition method

Synthesis and growth of carbon nanotubes (CNTs) from C₂H₂ by thermal chemical vapour deposition (TCVD) using a mixture of different gases were investigated. A thin film of nickel was coated as catalyst on silicon substrates by ion beam sputtering technique. Various parameters such as thickness of oxide layer and time, as well as reduction temperature were investigated in view of obtaining the best conditions for CNTs growth. C₂H₂ was very effective as carbon feedstock and NH₃ pretreatments were crucial steps towards obtaining a high density of nucleation sites for CNTs growth by inhibiting amorphous carbon generation in the initial stage of the synthesis. The substrate oxide layer was analysed by secondary ion mass spectrometry. The prepared CNTs were confirmed by Raman spectroscopy and were further characterised using scanning electron microscopy and transmission electron microscopy.     

Confined palladium colloids in mesoporous frameworks for carbon nanotube growth

Palladium colloidal nanoparticles with an average size of approximately 2.4 nm have been incorporated into mesoporous inorganic thin films following a multistep approach. This involves the deposition of mesoporous titania thin films with a thickness of 200 nm by spin-coating on titanium plates with a superhydrophilic titania outer layer and activation by calcination in a vacuum furnace at 573 K. Nanoparticles have been confined within the porous titania network by dip-coating noble metal suspensions onto these mesoporous thin films. Finally, the resulting nanoconfined systems were used as substrates for the growth of oriented carbon nanotubes (CNTs) using plasma-enhanced chemical vapour deposition at 923 K in order to enhance their surface area. These CNTs were tested in the hydrogenation of phenylacetylene by hydrogen in a batch reactor. The initial reaction rate observed on a CNT/TiO₂ structured catalyst was considerably higher than that on 1 wt% Pd/TiO₂ thin films.     

Coating of carbon nanotubes with amorphous carbon nitride thin films and characterization of long-term emission stability

The effects of amorphous carbon nitride (CN) thin films that were coated on carbon nanotubes (CNTs) and their thermal treatment were investigated, in terms of the chemical bonding and morphologies of the CNTs and their field emission properties. CNTs were directly grown on conical tip-type tungsten substrates via the inductively coupled plasma-chemical vapor deposition (ICP-CVD) system, and the CNTs were coated with CN films using the RF magnetron sputtering system. The CN-coated CNTs were thermally treated using the rapid thermal annealing (RTA) system by varying the temperature (300-700 °C). The morphologies, microstructures, and chemical compositions of the CN-coated CNTs were analyzed as a function of the thickness of the CN layers and the RTA temperatures. The field emission properties of the CN/CNT hetero-structured emitters, and the fluctuation and long-term stability of the emission currents were measured and compared with those of the conventional non-coated CNT-emitter. The results showed that the electron emission capability of CNT was noticeably improved by coating a thin CN layer on the surface of the CNT. This was attributed to the low work function and negative electron affinity nature of the CN film. The CN-coated CNT-emitter had a more stable emission characteristic than that of the non-coated one. In addition, the long-term emission stability of the CN-coated emitter was further enhanced by thermal treatment, which was verified by x-ray photoelectron spectroscopy (XPS) analysis.     

Synthesis of regular nano-pitched carbon nanotube array by using nanosphere lithography for interconnect applications

In this paper, we report a method based on nanosphere lithography technology for the synthesis of nano-pitched vertically aligned multi-walled carbon nanotube array. A monolayer of polystyrene nanospheres with diameter of 650 nm was coated on silicon oxide layer to create hexagonally arranged patterns. A metal layer, which acted as a catalyst for carbon nanotube growth, was deposited on the patterns by e-beam evaporation method. Nano-sized metallic patterns were formed by removing the polystyrene nanospheres. Uniform CNT arrays with pitch of 800 nm were successfully synthesized from the metallic patterns by plasma enhanced chemical vapor deposition. Using nanosphere lithography, the pitch of the single CNT array can be well-controlled. Therefore, the as-grown CNTs have potential applications in advanced interconnects technology and other nano applications.     

Electrochemical characterization of carbon nanotube forests grown on copper foil using transition metal catalysts

Growth of vertical, multiwalled carbon nanotubes (CNTs) on bulk copper foil substrates can be achieved by sputtering either Ni or Inconel thin films on Cu substrates followed by thermal chemical vapor deposition using a xylene and ferrocene mixture. During CVD growth, Fe nanoparticles from the ferrocene act as a vapor phase delivered catalyst in addition to the transition metal thin film, which breaks up into islands. Both the thin film and iron are needed for dense and uniform growth of CNTs on the copper substrates. The benefits of this relatively simple and cost effective method of directly integrating CNTs with highly conductive copper substrates are the resulting high density of nanotubes that do not require the use of additional binders and the potential for low contact resistance between the nanotubes and the substrate. This method is therefore of interest for charge storage applications such as double layer capacitors. Inconel thin films in conjunction with Fe from ferrocene appear to work better in comparison to Ni thin films in terms of CNT density and charge storage capability. We report here the power density and specific capacitance values of the double layer capacitors developed from the CNTs grown directly on copper substrates.     

Photolithographic fabrication of gated self-aligned parallel electron beam emitters with a single-stranded carbon nanotube

In this paper we report on the development of a photolithographic process to fabricate a gated-emitter array with single-stranded carbon nanotubes (CNTs) self-aligned to the center of the emitter gate using plasma-enhanced chemical vapor deposition (PECVD). Si tips are formed on a silicon wafer by anisotropic etching of Si using SiO(2) as a mask. Deposition of a SiO(2) insulating layer and Cr-W electrode layers creates protrusions above the Si tips. This wafer is polished, and the Cr-W on the tips is removed. Etching of the SiO(2) using hydrofluoric acid is performed to expose the gated Si tip. Incorporation of a novel diffusion process produces single-stranded CNTs by depositing a thin Ni layer on the Si tips and thermally diffusing the Ni layer to yield a catalyst particle for single-stranded CNT growth. The large surface to volume ratio at the apex of the Si tip allows a Ni particle to remain to act as a catalyst to grow a single-stranded CNT for fabricating the CNT based emitter structure. Diffusion of the Ni is carried out in situ during the heating phase of the PECVD CNT growth process at 600?°C. The diameters of the observed CNTs are on the order of 20?nm. The field emission characteristics of the gated field emitters are evaluated. The measured turn-on voltage of the gated emitter is 5?V.     

Improved field emission properties of carbon nanotubes by dual layer deposition

In this paper, we tried to increase the current density of carbon nanotubes (CNTs) by depositing double layer of CNTs instead of single layer. Both the layers of CNTs are deposited by the low pressure chemical vapour deposition technique on silicon substrate with Fe catalyst. Scanning electron microscopic images show the surface morphology of single and double layer of CNTs. Dual layer deposition of CNTs is a very simple and easy method to increase the current density of CNTs based field emitters than other conventional methods. Excellent field emission properties of double layer of CNTs are exhibited with large field enhancement factor and low turn-on voltage as compared to those for single layer of CNTs. High current density of CNTs is required for field-emission-based display devices associated with field enhancement factor and number of emitting electrons. Therefore, we may say that dual layer deposition of CNTs can be utilised as an alternative approach to improve the current density for field emitters. Stability measurement of the samples was also performed for 3 h (180 min) with current at constant applied voltage, and it was found that the stability of dual layer of CNTs is remarkable than that of single layer of CNTs.     

The effect of temperature on the growth of carbon nanotubes on copper foil using a nickel thin film as catalyst

Growth of carbon nanotubes (CNTs) on bulk copper foil substrates has been achieved by sputtering a nickel thin film on Cu substrates followed by thermal chemical vapor deposition. The characteristics of the nanotubes are strongly dependent on the Ni film thickness and reaction temperature. Specifically, a correlation between the thin film nickel catalyst thickness and the CNT diameter was found. Two hydrocarbon sources investigated were methane and acetylene to determine the best conditions for growth of CNTs on copper. These results demonstrate the effectiveness of this simple method of directly integrating CNTs with highly conductive substrates for use in applications where a conductive CNT network is desirable.     

Horizontally oriented carbon nanotubes coated with nanocrystalline carbon

Single-walled carbon nanotubes (CNTs) and multi-walled CNTs of length 2-5 mm were grown from Fe/Mo nanoparticles and Fe thin film catalyst, respectively, by thermal chemical vapor deposition. Following CNT growth, the CNTs were in-situ coated with nanocrystalline carbon shells of thickness 100-1500 nm. Horizontally oriented CNTs with carbon shells in the direction of the feeding gas were visible under a regular optical microscope. They were easily manipulated by optical manipulators, and CNT probes can thus be fabricated.     

改善沉积氮化硅薄膜对FFS-TFT透明电极ITO影响的研究

研究了在FFS-TFT制作工艺中,沉积非晶氮化硅薄膜对透明金属ITO的影响。结果表明沉积氮化硅薄膜的硅烷流量对ITO的透过率有着很大影响,降低硅烷的流量可以阻止薄雾状姆拉的产生。通过优化氮化硅薄膜沉积条件,先在透明导电金属ITO薄膜上面使用低流量硅烷沉积一薄层氮化硅作为缓冲层,然后使用高流量的硅烷在其上再沉积氮化硅薄膜,这样不仅解决了薄雾状姆拉,同时还以提高氮化硅的沉积速率,满足生产需求。     

Preparation, characterization and anion exchange properties of polypyrrole/carbon nanotube nanocomposites

In this study, polypyrrole (PPy) thin films were electrodeposited on carbon nanotube (CNT) backbones by applying a constant deposition potential in 0.1 M pyrrole solution with different electrolytes, such as NaCl, NaNO3, or NaClO4. The hybrid films were characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy, and cyclic voltammetry. SEM images revealed the nanostructrure of PPy films generated on CNT surface. The electrochemical and anion exchange properties of the PPy-CNT composite films have been investigated. Nanostructured composite thin films of PPy-CNTs were studied by cyclic voltammetry between 0.4 and -0.8 V in aqueous solution to evaluate their cycling stability and capacity for electrically switched anion exchange. The presence of the CNT backbone greatly improved the anion exchange capacity and stability of the PPy-CNT composite film, which may be attributed to the high surface area of CNT matrix, nanostructure of the PPy film, and the interaction between CNTs and PPy.     

Growth control of carbon nanotubes by plasma enhanced chemical vapor deposition

Plasma enhanced chemical vapor deposition (PECVD), which enables growth of vertically aligned carbon nanotubes (CNTs) directly onto a solid substrate, is considered to be a suitable method for preparing CNTs for nanoelectronics applications such as electron sources for field emission displays (FEDs). For these purposes, establishment of an efficient CNT growth process has been required. We have examined growth characteristics of CNTs using a radio frequency PECVD (RF-PECVD) method with the intention to develop a high efficiency process for CNT growth at a low enough temperature suitable for nanoelectronics applications. Here we report an effect of pretreatment of the catalyst thin film that plays an important role in CNT growth using RF-PECVD. Results of this study show that uniform formation of fine catalyst nanoparticles on the substrate is important for the efficient CNT growth.