A saddle-field gauge with carbon nanotube field emitters

A saddle-field ionization vacuum gauge with a carbon nanotube field emission cathode is described in this paper, and its primary results are reported. The gauge's cathode was prepared by adhering the as-grown carbon nanotube array to one end of a nickel rod. This nanotube-cathode saddle-field gauge has the advantages of small electrode sizes, high sensitivity and low power consumption. The dependences of the sensitivity factor of the gauge on electrical parameters were measured. A gauge sensitivity factor of 1.7 Pa^− 1 under an anode current of 3 μA was achieved for air. The power consumption of the gauge was less than 8 mW.     

Multi-walled carbon nanotube/Co composite field emitters fabricated by in situ spray coating

Multi-walled carbon nanotube(MWCNT)/Co composite powders, in which MWCNTs are homogeneously implanted in Co nanoparticles, were fabricated by polyol method. Homogeneous field emitters were fabricated by in situ spray coating of MWCNT/Co composite powders without using polymer binder and followed by sintering MWCNT/Co composite powders to form powder-powder bonding and powder-substrate bonding. Field emission properties of MWCNT/Co composite field emitters made by in situ spray coating were enhanced compared to those of MWCNT/Co composite field emitters made by screen printing due to self-activation of MWCNTs and minimization of contamination and structural defects of MWCNTs.     

Fabrication of efficient field emitters with thin multiwalled carbon nanotubes using spray method

Thin multiwalled carbon nanotube (t-MWCNTs)-based field emitters are made by use of a spray method. The number of tube walls is between 2 and 6, with the corresponding outer diameters between 3 and 6 nm. They were dispersed in dichloroethane and sprayed onto metal-deposited indium tin oxide glass. After heat treatment, they were found to be tightly adhered to metal electrode. Excellent field emission characteristics were exhibited, with a large field enhancement factor and low turn-on voltage, comparable to those of singlewalled CNTs. However, the t-MWCNTs demonstrated a significantly lower degradation rate than SWCNTs in the emission current. This high emission stability was attributed to their stable edge structures, similar to conventional large-diameter MWCNTs. Therefore, t-MWCNTs could be utilized as an alternative material for field emitters.     

A multi-wall carbon nanotube/polymethyl methacrylate composite for use in field emitters on flexible substrates

A polymer-based multi-walled carbon nanotube (MWCNT) field emission device was fabricated from a mixture of dispersed MWCNTs and an aqueous solution of polymethyl methacrylate (PMMA). When the mixture was applied to a substrate, the PMMA formed a strong composite with the MWCNTs, while strongly binding to the substrate. Process optimization was carried out to obtain high field emission performance by controlling the density of the MWCNT emitter tips under good adhesion conditions. The polymer concentration in the MWCNT dispersion and the number of spray coatings of the solution on the substrate served as the variables. The optimized polymer-based MWCNT field emission device showed a low turn-on field of 1.07 V/μm, a high electric field enhancement factor of 2450, highly uniform emission, and long-term stability. The successful application of the developed emitters to a flexible polymer polyethylene terephthalate (PET) substrate was accomplished with good emission uniformity and long stability.     

Horizontally aligned single-walled carbon nanotube field emitters fabricated on vertically aligned multi-walled carbon nanotube electrode arrays

Vertically aligned multi-walled carbon nanotube (MWCNT) arrays were fabricated on an anodic aluminum oxide membrane bonded to a Si wafer. After obtaining a protruding tip for the MWCNTs by etching away some oxide, they were used as electrodes in the fabrication of carbon nanotube field emitters. Long single-walled carbon nanotubes (SWCNTs) were spin coated on the MWCNT arrays of uniform height. Clean SWCNTs were suspended by attaching them to the tips of the vertically aligned MWCNT arrays. The spin coated SWCNTs function as emitters, while the MWCNT arrays function as electrodes. The field emission was greatly improved by coating gold on the MWCNT arrays and annealing at 400 °C. Our field emitter exhibits good field emission properties such as a low turn-on field (1.4 V/μm), high current density (122 mA/cm²), and good stability (55 h for 10% degradation of current density from 400 μA/cm²).     

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.     

A vacuum-sealed miniature X-ray tube based on carbon nanotube field emitters

ABSTRACT: A vacuum-sealed miniature X-ray tube based on a carbon nanotube field-emission electron source has been demonstrated. The diameter of the X-ray tube is 10 mm; the total length of the tube is 50 mm, and no external vacuum pump is required for the operation. The maximum tube voltage reaches up to 70 kV, and the X-ray tube generates intense X-rays with the air kerma strength of 108 Gy * cm2 min1. In addition, X-rays produced from the miniature X-ray tube have a comparatively uniform spatial dose distribution.     

Horizontally aligned carbon nanotube field emitters having a long term stability

Horizontally aligned carbon nanotube (CNT) field emitters fabricated by electrophoresis deposition and fissure formation techniques show good field emission properties such as high current density, low turn-on voltage and long-term stability. Horizontally aligned multi-walled carbon nanotube (MWCNT) field emitters show an unusual very long-term stability, much better stability than the single-walled carbon nanotube (SWCNT) ones. The cause of the degradation is due to the heat generated by the resistance of CNTs. We were able to prevent effectively the degradation of the horizontally aligned field emitters by using MWCNTs and an additional deposition of aluminum on the CNT films, and the required time for 10% degradation is very long, 121 h.     

Horizontally aligned carbon nanotube field emitters fabricated on ITO glass substrates

Horizontally aligned carbon nanotube (CNT) field emitters, in which electrons are emitted from the side of CNTs, are fabricated on indium tin oxide (ITO) glass substrates by electrophoretic deposition and fissure formation techniques. A thin film of CNTs is deposited onto an ITO glass plate using an aqueous mixture of CNTs and the cationic detergent cetyltrimethylammonium bromide by applying a negative voltage to the ITO glass plate. Then, an additional layer of sodium dodecyl sulfate (SDS), an anionic detergent, is deposited on the CNT film. This is done using an aqueous solution of SDS by applying a positive voltage. Through the process of firing, CNTs with a clean surface are exposed in the fissures produced. No further treatment is needed to initiate or augment field emission. The CNT field emitters show relatively good field-emission properties such as high current density (11 mA/cm² at an applied electric field of 4.3 V/μm), low turn-on field (2.2 V/μm), and good stability (98 h for 10% degradation of current density from 400 μA/cm²).     

High-current field emission of point-type carbon nanotube emitters on Ni-coated metal wires

The fabrication and field emission characteristics are reported for point-type carbon nanotube (CNT) emitters formed by transferring a CNT film onto a Ni-coated Cu wire with a diameter of 1.24 mm. A Ni layer plays a role in enhancing the adhesion of CNTs to the substrate and improving their field emission characteristics. On firing at 400 °C, CNTs appear to directly bonded to a Ni layer. With a Ni layer introduced, a turn-on electric field of CNT emitters decreases from 1.73 to 0.81 V/μm by firing. The CNT film on the Ni-coated wire produces a high emission current density of 667 mA/cm² at quite a low electric field of 2.87 V/μm. This CNT film shows no degradation of emission current over 40 h for a current density of 60 mA/cm² at electric field of 6.7 V/μm. X-ray imaging of a printed circuit board with fine features is demonstrated by using our point-type CNT emitters.     

High performance field emission of carbon nanotube film emitters with a triangular shape

We report novel two-dimensional (2D) shaped carbon nanotube (CNT) field emitters using triangular-shaped CNT films and their field emission properties. Using the 2D shaped CNT field emitters, we achieved remarkable field emission performance with a high emission current of 22 mA (equivalent to an emission current density >10⁵ A/cm²) and long-term emission stability at 1 mA for 20 h. We also discuss the field emission behavior of the 2D shaped CNT field emitter in detail.     

Carbon nanotube films as electron field emitters

Carbon nanotubes have been recognized as one of the most promising electron field emitters currently available. We review the state of the art of current research on the electron field emission properties of carbon nanotube films and present recent results outlining their potential as field emitters as well as illustrating some current concerns in the research field.     

New approach to enhance adhesions between carbon nanotube emitters and substrate by the combination of electrophoresis and successive electroplating

Complementary electroplating combined with electrophoresis enhanced the field emission characteristics of emitters by improving the adhesions between CNT emitters and substrate. The emitting current of the CNT emitters prepared by our combined method increased nine times higher than that of CNT emitters prepared by electrophoresis only, since electroplating improved the adhesion of CNT emitters. During the life-time measurement for 10 h, the emitting current of CNT emitters fabricated by electrophoresis only was drastically decreased to 13% of the initial current, while that prepared by the combination of electrophoresis and successive electroplating decreased to 64% of the initial current. We suggest that our method is a promising approach for the efficient fabrication of reliable CNT emitters.     

Highly stable carbon nanotube field emitters on small metal tips against electrical arcing

Carbon nanotube (CNT) field emitters that exhibit extremely high stability against high-voltage arcing have been demonstrated. The CNT emitters were fabricated on a sharp copper tip substrate that produces a high electric field. A metal mixture composed of silver, copper, and indium micro- and nanoparticles was used as a binder to attach CNTs to the substrate. Due to the strong adhesion of the metal mixture, CNTs were not detached from the substrate even after many intense arcing events. Through electrical conditioning of the as-prepared CNT emitters, vertically standing CNTs with almost the same heights were formed on the substrate surface and most of loosely bound impurities were removed from the substrate. Consequently, no arcing was observed during the normal operation of the CNT emitters and the emission current remained constant even after intentionally inducing arcing at current densities up to 70 mA/cm².     

Multi-walled carbon nanotube/ribonucleic acid hybrid field emitters fabricated by spray deposition

Multi-walled carbon nanotubes (MWCNTs) are shown to disperse in water, and be functionalized using RNA so that MWCNT/RNA hybrids can be fabricated on substrates by spray method. The material has strong adhesion on glass substrates or metal wires. A liquid elastomer surface treatment is used to make the field emitter tips protrude from the cathode. Possible methods of realizing field emitter sources, including X-ray sources, are discussed. The MWCNT/RNA hybrids have a higher emission current density and more uniform emission image than the MWCNTs on their own, since the RNA coated MWCNTs attach more strongly to the substrate. A diode configuration field emission X-ray source using the MWCNT/RNA hybrids on tungsten wire tip was tested and found to provide clear X-ray images.     

Dynamic behavior of carbon nanotube field emitters observed by in situ transmission electron microscopy

We examined dynamic behavior of field-emitting carbon nanotubes (CNTs) by in situ transmission electron microscopy (TEM). CNTs employed in the present study were multi-wall CNTs prepared by chemical vapor deposition, double-wall and single-wall CNTs produced by arc discharge. Orientation of CNTs, being random when no electric field was applied, were aligned parallel to the electric field and returned reversibly to their original direction when the field was turned off. In addition to this reversible behavior without serious structural damage in CNTs, sublimation and violent oscillation of CNTs were observed. When CNTs were bundled, branching of the bundle by electric static force was also observed.     

Fabrication of carbon nanotube field effect transistors by AC dielectrophoresis method

Single wall carbon nanotubes (SWNTs) suspended in isopropyl alcohol have been placed between two electrodes by AC dielectrophoresis method. The number of SWNTs bridging the two electrodes is controlled by SWNT concentration of the suspension and deposition time. Through selectively burning off the metallic SWNTs by current induced oxidation, the back-gate carbon nanotube field effect transistors (CNTFETs) with a channel current on-off ratio of up to 7 × 10⁵ have been successfully fabricated. The success rate of the CNTFETs in 20 samples is 60%. These results suggest that AC dielectrophoresis placement method is an efficient technique to fabricate CNTFETs with some flexibilities of controlling CNT reconnection, length and orientation.     

聚砜/改性碳纳米管复合膜的制备及亲水性能

利用浸没沉淀相转化法,以聚砜(PSF)为膜材料,羧基化碳纳米管(MWCNTs-COOH)为添加剂,聚乙烯吡咯烷酮(PVP)为致孔剂,N,N-二甲基乙酰胺(DMAc)为溶剂,制备了聚砜/多壁碳纳米管复合膜,系统研究了制备复合膜时碳纳米管的添加量、预挥发时间以及凝固浴组成对其结构和性能的影响。实验结果表明,添加MWCNTs-COOH后,复合膜的亲水性能和抗污性能显著提高,同时复合膜的力学性能也明显增强。复合膜的 SEM 照片显示,随预挥发时间的延长和凝固浴中DMAc 质量分数的增加,复合膜断面由指状孔结构向海绵状孔结构过渡;复合膜的水通量下降,截留率上升。     

Fabrication and characterization of carbon nanotube arrays using sandwich catalyst stacks

A novel synthesis of carbon nanotubes for field-emitter arrays with a uniform field emission current is reported. Microwave plasma chemical vapor deposition and a unique structure of a sandwich catalyst stack are used to grow vertically aligned carbon nanotubes with a high density, uniform length and diameter. After being etched in a H₂/N₂-microwave plasma, the overall field emission current density from the prepared emitter arrays is 1.2 A/cm² at an electric field of 6.5 V/μm with stable and uniform emission characteristics. The threshold field is 3.2 V/cm, defined at an emission current density of 10⁻⁶ A/cm².     

Great improvement in adhesion and uniformity of carbon nanotube field emitters through reactive nanometer-scale SiC fillers

We developed highly adhesive uniform field emitters (FEs) from carbon nanotube (CNT) pastes by reacting nanometer-scale silicon carbide (SiC) fillers on a Kovar substrate at a high temperature in vacuum. The reaction of SiC on Kovar results in significant morphological changes at the substrate–composite interface along with moderate Si diffusion into the substrate, enhancing adhesion of CNT FEs to the substrate greatly. Furthermore, a post surface-treatment after the reaction of SiC fillers results in very uniform CNT FEs over an entire emitter pattern of several hundred micrometers. The strongly enhanced adhesion and uniformity of the CNT FEs, in turn, give stable and reliable field emission even at a high current density. The applicability of the SiC/CNT FEs was evaluated in super-miniature X-ray tubes where any detachment of materials including outgassing from the inner side of the tubes should be avoided. The smallest super-miniature CNT X-ray tube to date, with an outer diameter of 2.0 mm, shows good operation with X-ray imaging at an anode voltage of above 25 kV, confirming almost no outgassing and strong substrate adhesion of the CNT FEs.