H. Shimoda

Generation of continuous and pulsed diagnostic imaging x-ray radiation using a carbon-nanotube-based field-emission cathode

X-ray radiation is widely used in medical and industrial applications. The basic design of the x-ray tube has not changed significantly in the last century. In this paper, we demonstrate that medical diagnostic x-ray radiation can be generated using a carbon nanotube (CNT)-based field-emission cathode. The device can readily produce both continuous and pulsed x-rays with a programmable wave form and repetition rate. A total emission current of 28 mA was obtained from a 0.2 cm2 area CNT cathode. The x-ray intensity is sufficient to image a human extremity at 14 kVp and 180 mAs. Pulsed x-ray with a repetition rate greater than 100 kHz was readily achieved by programming the gate voltage. The CNT-based cold-cathode x-ray technology can potentially lead to portable and miniature x-ray sources for industrial and medical applications.

Fabrication and properties of composites of poly(ethylene oxide) and functionalized carbon nanotubes

Abstract : We show that composites with improved uniformity and dispersion can be formed using chemically functionalized carbon nanotubes. A significant enhancement of the mechanical properties was obtained at low nanotube loading. In contrary to previous results from pristine nanotubes, the composites show efficient load transfer between the fillers and matrix.

Application of carbon nanotubes as electrodes in gas discharge tubes

turn-on fields. Recent experiments have reported turn-on electric fields in the range of 1.5‐3 V/mm. 3‐5 The nanotubes emitters, especially the SWNTs, are capable of producing stable electron emission with a current density exceeding 4 A/cm 2 ~Ref. 5! which make them attractive cold-cathode materials for microvacuum electronic applications. Assynthesized SWNTs are in the form of either free-standing mat or powder, unsuitable for device applications. We have processed the raw materials to uniform films by a spray method. 6 Adhesion between the substrates and the films is enhanced by introducing either a carbon-dissolving or a carbide-forming metal interlayer. In this letter, we report the effects of carbon nanotube coating on the performance of the gas discharge tubes. The direct current ~dc! breakdown voltages of GDTs fabricated using SWNT-coated electrodes were measured and compared with commercial GDTs. A significant reduction in the breakdown voltage and voltage fluctuation ~over 1000 surges! was observed for the nanotubebased GDTs as compared to typical commercial devices.

Liquid-phase fabrication of patterned carbon nanotube field emission cathodes

High-resolution electron field emission cathodes were fabricated at room temperature by a high throughput electrophoresis process using functionalized carbon nanotubes (CNTs). Well-defined and adherent CNT patterns with 20 μm feature size were achieved on a variety of substrates with fine control of the CNT morphology. The cathodes show uniform emission pattern across the entire surfaces and emission current with long-term stability. This room-temperature liquid-phase process is efficient and has no intrinsic limit on the deposition area. The emission characteristics of these cathodes compare favorably to those from other fabrication methods for CNT based field emission display applications.

Room-temperature fabrication of high-resolution carbon nanotube field-emission cathodes by self-assembly

In this letter, we report a process for room-temperature assembly of patterned and periodic structures of carbon nanotubes (CNTs). Well-defined patterns with less than a 10-μm linewidth and variable thickness were readily deposited. The CNTs show long-range in-plane orientation ordering and adhere strongly to the substrates. The self-assembled macroscopic structures emit electrons under applied electrical field with the emission characteristics comparable to those from the high-temperature or/and low-resolution deposition processes. This room-temperature self-assembly method can be utilized for assembly and integration of nanostructured materials for a variety of devices, including the field-emission displays.

Lithium intercalation into etched single-wall carbon nanotubes

Abstract The effects of structure and morphology on lithium storage in single-wall carbon nanotubes (SWNTs) were studied by electrochemistry. SWNTs were chemically etched and were intercalated with Li. The reversible Li storage capacity increased from LiC6 in close-end SWNTs to LiC3 after etching, which is twice the value observed in Li intercalated graphite. The enhanced capacity is attributed to Li diffusion into the interior of the SWNTs through the opened ends and sidewall defects.

Formation of macroscopically ordered carbon nanotube membranes by self-assembly

Abstract In this paper, we report the formation membranes of the aligned single-wall carbon nanotube (SWNT) bundles on a substrate by self-assembly. SWNTs produced by the laser ablation method and purified by reflux and filtration were chemically etched to short bundles by ultrasonic-assisted oxidation. After removing the acid by filtration, the processed SWNTs were dispersed in de-ionized water. Thin film appears on the surface of a soaked glass substrate in the SWNTs/water dispersion with natural vaporization of water. Transmission electron microscopy measurements show that the SWNT bundles are uniaxially aligned.

Structure and Electrochemical Properties of Carbon Nanotube Intercalation Compounds

Abstract This article summarizes the current status of carbon nanotube intercalation compounds. It focuses on the structure and electrochemical properties of intercalated single-walled carbon nanotubes (SWNTs). Materials synthesis, purification and characterization methods are also discussed. This article draws mostly from works performed at UNC.

Lithium storage in single wall carbon nanotubes

The effects of structure and morphology on lithium storage in single wall carbon nanotubes (SWNTs) were studied by electrochemistry, x-ray diffraction and nuclear magnetic resonance (NMR) techniques. Purified SWNT bundles were chemically etched to variable lengths and were reacted with Li via the electrochemical and solid state routes. The reversible Li storage capacity increased from LiC6 in close-end SWNTs to LiC3 after etching. The increase is attributed to diffusion of the Li ions into the interior space of the individual SWNTs through the open ends and defects on the sidewalls.

Room‐Temperature Fabrication of High‐Resolution Carbon Nanotube Field‐Emission Cathodes by Self‐Assembly

We report a process to assemble carbon nanotubes (CNTs) into patterned and periodic structures by self‐assembly at room temperature. Patterns of 10 μm or smaller can be readily deposited on various types of substrates using functionalized CNTs. The self‐assembled CNTs have in‐plane orientational order, and adhere strongly to the substrates. Under applied electric field they emit electrons with emission characteristics comparable to the CNT cathodes made by other techniques. This room temperature process can be utilized for assembly and integration of nano‐structured materials for a variety of devices including field emission displays.