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Dive into the research topics where Phan Hong Khoi is active.

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Featured researches published by Phan Hong Khoi.


Physics of Fluids | 2015

A modified model for thermal conductivity of carbon nanotube-nanofluids

Bui Hung Thang; Phan Hong Khoi; Phan Ngoc Minh

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.


Journal of Vacuum Science & Technology B | 2009

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

Nguyen Tuan Hong; Ken Ha Koh; Soonil Lee; Phan Ngoc Minh; Ngo Thi Thanh Tam; Phan Hong Khoi

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.


RSC Advances | 2017

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

Pham Van Trinh; Nguyen Ngoc Anh; Bui Hung Thang; Le Dinh Quang; Nguyen Tuan Hong; Nguyen Manh Hong; Phan Hong Khoi; Phan Ngoc Minh; Phan Ngoc Hong

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.


Journal of Vacuum Science & Technology B | 2008

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

Nguyen Tuan Hong; Jong Hyuk Yim; Ken Ha Koh; Soonil Lee; Phan Ngoc Minh; Phan Hong Khoi

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.


Materials Science and Engineering: C | 2001

Study on hydrogen reactivity with surface chemical species of nanocrystalline porous silicon

Le T.T. Tuyen; Ngo Thi Thanh Tam; Nguyen H. Quang; Nguyen Xuan Nghia; Dao D. Khang; Phan Hong Khoi

Abstract The nanocrystalline porous silicon was prepared by the electrochemical etching of Si in a HF solution. A semi-transparent palladium layer was thermally deposited on its surface. Micro-Raman spectra were recorded in air and in the presence of hydrogen. Different SiHX stretching and wagging vibrational modes, a SiH stretching mode modified by the presence of three oxygen atoms in the Si backbonds (O3SiH unit) and a SiOSi vibration were readily revealed. Their behavior under laser irradiation and towards the hydrogen atoms dissociated from hydrogen molecules by palladium is reported.


Journal of Physics: Conference Series | 2009

Carbon nanotube: A novel material for applications

Phan Ngoc Minh; Phan Hong Khoi

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.


Journal of Raman Spectroscopy | 1999

Investigation of vibrational and photoluminescence spectra of nanocrystalline silicon by micro‐Raman spectroscopy using various laser powers

Phan Hong Khoi; Ngo Thi Thanh Tam; Pham Hong Duong; Nguyen Xuan Nghia

The Raman spectra of silicon nanocrystals embedded in silicon oxide and in porous silicon were measured at various laser powers. It was found that the Si–Si stretching Raman peak shifts to lower wavenumbers and broadens when the laser power increases. The effect is significant and reversible, i.e. the peak returns to its former position when the laser power is decreased to the initial level. It was found that this reversible phenomenon is caused by an increase in bond length due to the heating effect of the laser. In addition, the appearance of weak bands on both sides of the main Si–Si stretching mode peak at 155, 332, 620, 940, 2087, 2114 and 2145 cm−1 was observed at high laser power. It was found that the first four bands could be attributed to one- and multi-phonon Raman scattering and the last three bands are the expected SiH2, SiH and SiH3 stretching vibration modes. The photoluminescent spectrum was measured with the use of 1.959 eV illumination from an 11 mW helium–neon laser. It was found that the photoluminescence spectrum consists of a broad line centered at 1.79 eV with a full width at half-maximum of 0.21 eV and a tail located in an energy region higher than the laser incident excitation energy. Based on the analysis of Raman scattering spectra and the assumption that the luminescence spectrum arises from the ensemble of various sized particles distributed in the material, it is suggested that the later band of photoluminescence should be excited by the Raman scattering light in silicon nanocrystals. Copyright


The Scientific World Journal | 2013

Heat Dissipation for Microprocessor Using Multiwalled Carbon Nanotubes Based Liquid

Bui Hung Thang; Pham Van Trinh; Nguyen Van Chuc; Phan Hong Khoi; Phan Ngoc Minh

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.


Journal of Vacuum Science & Technology B | 2009

Field-electron emission from flexible carbon nanotube array cathodes

Nguyen Tuan Hong; Kim Sang Yong; Ken Ha Koh; Soonil Lee; Ngo Thi Thanh Tam; Phan Ngoc Minh; Phan Hong Khoi

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.


Journal of Physics: Conference Series | 2009

Application of multiwall carbon nanotubes for thermal dissipation in a micro-processor

Bui Hung Thang; Phan Ngoc Hong; Phan Hong Khoi; Phan Ngoc Minh

One of the most valuable properties of the carbon nanotubes materials is its high thermal conductivity with 2000 W/m.K (compared to thermal conductivity of Ag 419 W/m.K). It suggested an approach in applying the CNTs in thermal dissipation media to improve the performance of computer processors and other high power electronic devices. In this research, the multiwall carbon nanotubes (MWCNTs) made by thermal chemical vapour deposition (CVD) at our laboratory was employed as the heat dissipation media in a microprocessor a Personal Computer with configuration: Intel Pentium IV 3.066 GHz, 512Mb of RAM and Windows XP Service Pack 2 Operating System. We directly measured the temperature of the microprocessor during the operation of the computer in two modes: 100% usage CPU mode and over-clocking mode. The measured results showed that when using our thermal dissipation media (a mixture of the mentioned commercial thermal compound and 2 wt.%. MWCNTs), the temperature of the microprocessor decreased 5°C, and the time for increasing the temperature of the microprocessor was three times longer than that when using commercial thermal compound. In over-clocking mode, the processor speed reached 3.8 GHz with 165 MHz of system bus clock speed; it was 1.24 times higher than that in non over-clocking mode. The results confirmed a promising way of using MWCNTs as the thermal dissipation media for microprocessor and high power electronic devices.

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Phan Ngoc Minh

Vietnam Academy of Science and Technology

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Bui Hung Thang

Vietnam Academy of Science and Technology

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Ngo Thi Thanh Tam

Vietnam Academy of Science and Technology

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Phan Ngoc Hong

Vietnam Academy of Science and Technology

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Le Dinh Quang

Vietnam Academy of Science and Technology

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Nguyen Van Chuc

Vietnam Academy of Science and Technology

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Pham Van Trinh

Vietnam Academy of Science and Technology

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