Phan Ngoc Minh

Microelectron field emitter array with focus lenses for multielectron beam lithography based on silicon on insulator wafer

We report on a device concept, results of fabrication, and characterization of a monolithic electron field emitter array with focus lenses for multielectron beam lithography and high-density nano data storage. An array of individually addressable emitters of various materials was patterned on oxidized etch pits of a silicon on insulator (SOI) wafer. Si active layer of the SOI with gate hole array that self-aligned with the emitters was used as a common gate electrode. An array of cylindrical holes formed at the Si base of the SOI was used as a common lens electrode. For a single Pt emitter with gate hole of 2 μm diameter, the emission current started at a gate voltage Vgate=90 V and reached to 1.2 μA current and 0.84 mW beam power at Vgate=300 V and anode voltage Vanod=0.7 kV. The emission current was found to be stable with a fluctuation smaller than 10%/h. The emitter-gate and emitter-lens leak currents were found to be less then 1% compared with the emission current. The focusing characteristic of the ...

A modified model for thermal conductivity of carbon nanotube-nanofluids

Carbon nanotubes (CNTs) are one of the most valuable materials with high thermal conductivity (above 1750 W/m K compared to thermal conductivity of Ag 419 W/m K). Owing to their very high thermal conductivity, CNTs are one of the most suitable nanoadditives in fabricating the nanofluid with thermal conductivities that are significantly higher than those of the parent liquids even when the CNTs’ concentrations are negligible. This work presents a modified model for predicting the thermal conductivity of carbon nanotube-nanofluids (CNT-nanofluids), which take into consideration the effects of size, volume fraction, and thermal conductivity of CNTs as well as the properties of base liquid. The modified model is found to correctly predict the trends observed in experimental data for different combinations of CNT-nanofluids with varying concentrations.

Comparison of field-electron emission from different carbon nanotube array structures

The effect of macroscopic cathode structures, which consisted of an array of the identical vertically aligned carbon nanotube (VACNT) columns in a particular arrangement, on the field emission was investigated. The electric field simulation based on the FEMLAB code showed characteristics of edge-induced U-shaped field distribution on CNT column. It was found that the degree of the field screening was dependent on VACNT-column array patterns, and that the overall field distribution depended on a number of VACNT columns at the periphery for the finite array size. Three different types of VACNT-column array cathodes were fabricated and tested for the field-electron emission: square, hexagonal, and triangular pattern arrays. All these VACNT-column array cathodes showed excellent electron-emission characteristics and a general trend consistent with field distribution simulations.

Enhanced thermal conductivity of nanofluid-based ethylene glycol containing Cu nanoparticles decorated on a Gr–MWCNT hybrid material

In this study, nanofluid based ethylene glycol (EG) containing Cu nanoparticles decorated on a Gr–MWCNT hybrid material (Gr–MWCNT/Cu) was synthesized successfully for the first time via a chemical reduction method. The SEM, HRTEM, FTIR and XRD studies revealed that Cu nanoparticles with an average diameter of 18 nm were well decorated on the surface of both MWCNTs and graphene sheets. The nanofluids containing Gr–MWCNT/Cu material showed good stability and a maximum thermal conductivity enhancement of 41% at 60 °C for the nanofluid containing 0.035 vol% material compared to EG alone. The enhancement is due to the combination of the high thermal conductivity of graphene, CNT and Cu nanoparticles as well as the higher surface area of the Gr–MWCNT/Cu hybrid structure. Experimental results of thermal conductivity were evaluated using different theoretical models, amongst which the Hamilton–Crosser model was found suitable for predicting the thermal conductivity of the nanofluid.

Synthesis of individual ultra-long carbon nanotubes and transfer to other substrates

In this article, we report the synthesis of ultra-long carbon nanotubes (CNTs) by thermal chemical vapour deposition method. Ultra-long, individual and aligned CNTs were directly grown on a flat silicon substrate. The orientation of the nanotubes was found parallel to the gas flow direction. The ultra-long CNTs were grown with different transition metallic salts, such as nickel chloride, iron (III) chloride, cobalt acetate and ruthenium acetate, as the catalysts. The influence of the growth conditions, such as growth temperature, reactive gas flow on the length and alignment of the CNTs was studied in detail. By using different catalysts, ultra-long single-walled carbon nanotubes (SWCNTs) or multi-walled carbon nanotubes (MWCNTs) were successfully grown. These ultra-long CNTs were transferred to other substrates by two methods. (1) The first method is to use polydimethylsiloxane as a stamp. (2) The second method is to use KOH as an etching agent. The diameter and length of the CNTs were characterised by transmission electron microscope, scanning electron microscope, atomic force microscope and Raman spectroscopy. The results indicate that the length of the CNTs can reach up to 4 mm. The diameter of the SWCNTs is in the range of 0.7–2.1 nm and the diameter of the MWCNTs is approximately 150 nm.

Field electron emission from free-standing flexible PDMS-supported carbon-nanotube-array films

Fabrication of free-standing carbon-nanotube- (CNT) array films supported by PDMS (poly-dimethylsiloxane) matrix, which opens up the possibility to transform deliberate CNT-array architecture into flexible electronic and photonic components, is reported. Low viscosity and good wetting characteristics of uncured PDMS prepolymer solution are important for thorough infiltration, and robustness and elasticity of cured PDMS are important for realization of deformable free-standing films detachable from substrates. Field-emission characterization of a series of CNT column arrays in diode configuration shows that fabrication of a flexible electron emitter is feasible, but the excellent emission characteristics of as-grown CNT column arrays is compromised after PDMS infiltration. In particular, emission current level and stability of a free-standing PDMS-supported CNT array is inferior to those of as-grown or PDMS-infiltrated CNT arrays on silicon substrates.

Carbon nanotube: A novel material for applications

In this paper, current state of research and development on carbon nanotube material is overviewed. A brief description on the authors current results of synthesis and purification technologies, characterization and application potentials of multiwall carbon nanotubes in advanced composite materials, thermal dissipation media, electro-magnetic wave absorption, scanning probe and electron field emitters are presented. Future trends and potential breakthrough in applications using the materials will be discussed.

Heat Dissipation for Microprocessor Using Multiwalled Carbon Nanotubes Based Liquid

Carbon nanotubes (CNTs) are one of the most valuable materials with high thermal conductivity (2000 W/m · K compared with thermal conductivity of Ag 419 W/m · K). This suggested an approach in applying the CNTs in thermal dissipation system for high power electronic devices, such as computer processor and high brightness light emitting diode (HB-LED). In this work, multiwalled carbon nanotubes (MWCNTs) based liquid was made by COOH functionalized MWCNTs dispersed in distilled water with concentration in the range between 0.2 and 1.2 gram/liter. MWCNT based liquid was used in liquid cooling system to enhance thermal dissipation for computer processor. By using distilled water in liquid cooling system, CPUs temperature decreases by about 10°C compared with using fan cooling system. By using MWCNT liquid with concentration of 1 gram/liter MWCNTs, the CPUs temperature decreases by 7°C compared with using distilled water in cooling system. Theoretically, we also showed that the presence of MWCNTs reduced thermal resistance and increased the thermal conductivity of liquid cooling system. The results have confirmed the advantages of the MWCNTs for thermal dissipation systems for the μ-processor and other high power electronic devices.

Field-electron emission from flexible carbon nanotube array cathodes

The authors report two approaches to fabricate flexible cold cathodes having vertically aligned carbon nanotubes (VACNTs) as active electron-emitting material. In the first approach, VACNT arrays were removed from substrates, transferred to flexible metal foils or plastic films, and secured by conductive epoxy. In the other approach, polydimethylsiloxane (PDMS) was used as a supporting matrix to fabricate more sturdy freestanding flexible cathodes. Controlled infiltration of PDMS to keep the top surfaces of VACNT columns from being buried underneath PDMS was the key of this approach. Both of these methods allowed fabrication of flexible cold cathode, and preliminary test results of fabricated flexible cold cathodes showed good field-emission characteristics.

Schottky emitter using boron-doped diamond

In this paper, we demonstrate fabrication of a diamond Schottky emitter with integrated heating element by hot filament chemical vapor deposition on silicon substrate and characterisation by SEM. The diamond emitter provided an emission current of 800nA in the electric field.