Ji Hwan Hong

Highly stable carbon nanotube cathode for electron beam application

The authors fabricated an optimized electron beam (e-beam) with a carbon nanotube (CNT) cathode and triode configuration. CNT emitters grown with a resist-assisted patterning process were used as an electron source. The gate mesh was aligned with the CNT emitter islands for a lower leakage current, resulting in a higher electron emission current and transmission ratio. Additionally, the width between CNT islands and the pitch between CNTs were optimized to enhance the electric field at the tip of the CNT emitters. With the optimized e-beam module, consisting of a CNT cathode and gate mesh, CNT pitch of 30 μm, dot size of 3 μm, line width of 210 μm, and gate mesh width of 75 μm, the emission current showed an increase of 165 times and operated for more than 500 h with DC driving. The optimized e-beam can be a building block for vacuum nanoelectronic devices.

Fabrication of miniature carbon nanotube electron beam module for x-ray tube application

We fabricated miniature electron beam module by using carbon nanotube electron emitters for x-ray tube application. The x-ray tubes with the beam module were fabricated with glass envelop and vacuum sealed. The miniature electron beam module was designed to achieve more than 90 % of electron transmission ratio through gate electrode with higher than 3 mA of anode current. The x-ray tube shows micro focused focal spot size and enough flux for dental imaging.

High-performance carbon-nanotube-based cold cathode electron beam with low-thermal-expansion gate electrode

The emission of a high-performance electron beam via a carbon nanotube cold cathode requires a higher electron transmission through the gate electrode. The transmittance of electrons through the gate mesh electrode strongly depends on the gate electrode structure and material properties. Therefore, thermal expansion of the gate electrode induced by the thermal load owing to the gate leakage current is a significant hurdle to be overcome. Using a high-thermal-expansion gate electrode comprised of SUS304 grid mesh, electron emission was brought to saturation when the mesh was bent upward, which was the result of a reduction of the effective electric field under the grid mesh. To mitigate the effect of this bending, a Mo grid mesh material possessing low thermal expansion introduced. The Mo grid material properties of low linear temperature expansion coefficient, high tensile strength, and low resistivity are necessary. With this grid mesh improvement, the electron emission current increased to ten times that of the SUS304 mesh grid.The emission of a high-performance electron beam via a carbon nanotube cold cathode requires a higher electron transmission through the gate electrode. The transmittance of electrons through the gate mesh electrode strongly depends on the gate electrode structure and material properties. Therefore, thermal expansion of the gate electrode induced by the thermal load owing to the gate leakage current is a significant hurdle to be overcome. Using a high-thermal-expansion gate electrode comprised of SUS304 grid mesh, electron emission was brought to saturation when the mesh was bent upward, which was the result of a reduction of the effective electric field under the grid mesh. To mitigate the effect of this bending, a Mo grid mesh material possessing low thermal expansion introduced. The Mo grid material properties of low linear temperature expansion coefficient, high tensile strength, and low resistivity are necessary. With this grid mesh improvement, the electron emission current increased to ten times tha...

Deep-ultraviolet light source with a carbon nanotube cold-cathode electron beam

Deep-ultraviolet (UV) light is widely used in many industries including medicine because it has sufficient energy to kill viruses and bacteria. However, deep UV with a wavelength of 254 nm can damage human cells, so it is necessary to develop a deep-UV light source with a shorter wavelength to minimize the damage to human cells while still killing viruses. The authors used a carbon nanotube-based cold-cathode electron beam (C-beam) and wide-bandgap anode to fabricate a deep-UV light source with an emission wavelength below 250 nm. The anode was fabricated by annealing ZnO ink on a Si wafer; deep UV with a wavelength of 247 nm and full width at half maximum of 23 nm was obtained. In the case of C-beam irradiation of an anode fabricated on a quartz substrate, deep UV with wavelengths of 208, 226, and 244 nm was generated through excitation with a beam energy of 7 kV and beam currents of 0.3 and 0.5 mA.Deep-ultraviolet (UV) light is widely used in many industries including medicine because it has sufficient energy to kill viruses and bacteria. However, deep UV with a wavelength of 254 nm can damage human cells, so it is necessary to develop a deep-UV light source with a shorter wavelength to minimize the damage to human cells while still killing viruses. The authors used a carbon nanotube-based cold-cathode electron beam (C-beam) and wide-bandgap anode to fabricate a deep-UV light source with an emission wavelength below 250 nm. The anode was fabricated by annealing ZnO ink on a Si wafer; deep UV with a wavelength of 247 nm and full width at half maximum of 23 nm was obtained. In the case of C-beam irradiation of an anode fabricated on a quartz substrate, deep UV with wavelengths of 208, 226, and 244 nm was generated through excitation with a beam energy of 7 kV and beam currents of 0.3 and 0.5 mA.

Fabrication of a compact glass-sealed x-ray tube with carbon nanotube cold cathode for high-resolution imaging

A glass-sealed x-ray tube with field emission electron sources has been fabricated using carbon nanotubes (CNTs) grown on a silicon substrate by direct current plasma-enhanced chemical vapor deposition. Here, the authors report on the fabrication of CNT-based emitters, the field emission characteristics of these emitters, and the properties of the glass-sealed x-ray tube. The field emission produced a current of 5 mA with an electron transmission rate of 91.1% in a high-vacuum chamber. The glass-sealed x-ray tube had a conventional design and comprised a reflection anode, an evaporation getter, and a vacuum-sealed glass tube without additional focusing electrode requirements for ease of commercialization. Using this x-ray tube, the authors obtained x-ray images of objects, including a human finger and a commercial universal serial bus (USB) flash drive. The x-ray image allowed a 100 μm metal wire to be distinguished in the USB flash drive. The x-ray images were obtained at a dose rate of 1944 mrad/h, whic...

High performance glass sealed x-ray tube with CNT cold cathode electron beam (C-beam)

We fabricated field emission electron sources and applied for the glass sealed x-ray tube for medical imaging devices. The x-ray tube consists of an electron beam with a patterned grown CNT emitters with RAP process. Those electron beam shows higher electron emission current and transmittance after glass seal. With the x-ray tube, we success to measure medical image with finger and high resolution PCBs. The fabricated x-ray tube shows electron transmission ratio (>90%) and current (>3 mA).

Fabrication of highly stable carbon nanotube electron beams(C-beam)

We optimized the triode structure for carbon nanotube electron beam(C-beam) application with carbon nanotube emitters grown with resist-assisted pattering process. The CNT emitters grown through the RAP process have a structure in which a number of CNTs are congregated, and the graphitization post-treatment process proceeded in order to enhance their adhesive strength and stability. The gate mesh was self-aligned with the carbon nanotube island for lower leakage current, resulting higher electron emission current and transmission ratio. With the optimized triode structure, the emission current show high performance with less than 1 cm2 area and C-beams operated more than 500 hours with constant current mode and DC driving.

Enhanced field emssion properties of paste CNT emitters with nickel buffer layer

Stable field emitters were developed using carbon nanotubes (CNTs) composite pastes with nickel (Ni) buffer layer. The paste CNT emitters showed lower threshold for field emission but which have short lifetime and unstable emission current in high emission current. In this paper, we developed the simple process of inserting Ni buffer layer between the CNT emitters and substrate. The paste CNT emitters with Ni buffer layer showed enhanced field emission properties than bare one. The lifetime of paste CNT emitters with Ni buffer layer were 9 hours 40 min. Its 22 times longer than without buffer layered one.

Cathodoluminescence properties of ZnO thin films with the carbon nanotube emitters beam (C-beam) exposure

In this study, we optimized vertically aligned carbon nanotube electron beam (C-beam) with triode structure for cathodoluminescence of Zinc Oxide (ZnO) thin films, which solution process fabricated. Efficient cathodoluminescences were observed with C-beam exposed ZnO thin films. The origin of the luminescence were confirmed by SEM measurement. The luminescence appeared to the structural modification of thin ZnO films after C-beam exposure, resulting nano-crystalline film formation.