Nguyen Van Chuc

Synthesis of magnetic cobalt ferrite nanoparticles with controlled morphology, monodispersity and composition: the influence of solvent, surfactant, reductant and synthetic conditions.

In our present work, magnetic cobalt ferrite (CoFe2O4) nanoparticles have been successfully synthesised by thermal decomposition of Fe(III) and Co(II) acetylacetonate compounds in organic solvents in the presence of oleic acid (OA)/ oleylamine (OLA) as surfactants and 1,2-hexadecanediol (HDD) or octadecanol (OCD-ol) as an accelerating agent. As a result, CoFe2O4 nanoparticles of different shapes were tightly controlled in size (range of 4-30 nm) and monodispersity (standard deviation only at ca. 5%). Experimental parameters, such as reaction time, temperature, surfactant concentration, solvent, precursor ratio, and accelerating agent, in particular, the role of HDD, OCD-ol, and OA/OLA have been intensively investigated in detail to discover the best conditions for the synthesis of the above magnetic nanoparticles. The obtained nanoparticles have been successfully applied for producing oriented carbon nanotubes (CNTs), and they have potential to be used in biomedical applications.

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.

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.

Effect of Surface Morphology and Dispersion Media on the Properties of PEDOT:PSS/n-Si Hybrid Solar Cell Containing Functionalized Graphene

We present the results on the effect of surface morphology and dispersion media on the properties of PEDOT:PSS/n-Si hybrid solar cell containing functionalized graphene (Gr). The hybrid solar cells based on SiNWs showed higher power conversion efficiency (PCE) compared to the planar based cells due to suppressing the carrier recombination and improving carrier transport efficiency. The PCE of hybrid solar cells could be improved by adding Gr into PEDOT:PSS. Different solvents including deionized (DI) water, ethylene glycol (EG), and isopropyl alcohol (IPA) were used as media for Gr dispersion. The best performance was obtained for the cell containing Gr dispersed in EG with a measured PCE of 7.33% and nearly 13% and 16% enhancement in comparison with the cells using Gr dispersed in IPA and DI water, respectively. The increase in PCE is attributed to improving the carrier-mobility, electrical conductivity, PEDOT crystallinity, and ordering.

Synthesis of vertically aligned carbon nanotubes and diamond films on Cu substrates for use in high-power electronic devices

Currently, most of the vertically aligned carbon nanotubes (VA-CNTs) and diamond films are mainly synthesised on flat silicon (Si) substrate. However, to achieve thermal dissipation in high-power electronic devices (HPEDs), the VA-CNTs and diamond films need to be attached to thermal dissipation metal substrates (like Cu, Ag, Al, etc.). In this paper, the fabrication process of the VA-CNTs and diamond films on Cu substrate is reported in detail. The VA-CNTs were synthesised by the thermal chemical vapour deposition (CVD) method. The VA-CNTs on Cu substrates were fabricated by two different methods: directly growing the VA-CNTs using thin catalytic metal layers such as Fe/Al or Cr/Al as a catalyst; transferring the VA-CNTs film that was pre-grown on Si substrate to Cu substrate. The diamond films were also directly grown on the Cu substrate by microwave plasma chemical vapour deposition (MPCVD). The grown VA-CNTs and diamond films were tested as the thermal dissipation media on a 0.5W InGaN LED chip. The VA-CNTs and diamond films greatly increased input current of the LED by more than 500 mA and 350 mA without reaching saturation. This is higher compared with that of the device packaged using normal commercial silver thermal paste. Initial experiment results on the LED demonstrated that the VA-CNTs and diamond films greatly improve the lights output power and that they are optimal choices for the thermal dissipation of HPED.

Thermal Dissipation Efficiency in a Micro‐Processor Using Carbon Nanotubes Based Composite

Modern electronic and optoelectronic devices such as μ‐processor, light emitting diode, semiconductor laser issued a challenge in the thermal dissipation problem. Finding an effective way for thermal dissipation therefore becomes a very important issue. It is known that carbon nanotubes (CNTs) is one of the most valuable materials with high thermal conductivity (2000 W/m.K compared to thermal conductivity of Ag 419 W/m.K). This suggested an approach in applying the CNTs as an essential component for thermal dissipation media to improve the performance of computer processor and other high power electronic devices. In this work multi walled carbon nanotubes (MWCNTs) based composites were utilized as the thermal dissipation media in a micro processor of a personal computer. The MWCNTs of different concentrations were added into polyaniline, commercial silicon thermal paste and commercial silver thermal paste by mechanical methods. A personal computer with configuration: Intel Pentium IV 3.066 GHz, 512 MB of ...

Effect of Annealing Time on the Power Conversion Efficiency of Silicon Nanowire Based Solar Cell Prepared by Wet Diffusion Technique

1 Institute of Materials Science, Vietnam Academy of Science and Technology, 18, Hoang Quoc Viet Str., Cau Giay Distr., Hanoi, Vietnam 2 Graduate University of Science and Technology, Vietnam Academy of Science and Technology, 18, Hoang Quoc Viet Str., Cau Giay Distr., Hanoi, Vietnam 3 Center for High Technology Development, Vietnam Academy of Science and Technology, 18, Hoang Quoc Viet Str., Cau Giay Distr., Hanoi, Vietnam

Hydrothermal Synthesis and Enhanced Photocatalytic Activity of TiO\(_{2}\)-Fe@CNTs Nanocomposite for Methylene Blue Degradation under Visible Light Irradiation

TiO2 is one of the most attractive metal oxides because of the excellent chemical and photocatalytic properties. However, a problem in the application of TiO2 is the large band gap energy of 3.2 eV, corresponding to its photocatalytic activity under UV-light irradiation of wavelengths < 387 nm. In this work, TiO2 nanoparticles doped with iron were grown on the surface of functionalized carbon nanotubes (TiO2-Fe@CNTs) to expand the photoabsorbance of the nanocomposite materials in the visible light region and improve their photocatalytic activity. TiO2-Fe@CNTs nanocomposite materials were synthesized by hydrothermal route in Teflon-sealed autoclave at 180 ̊C for 10h. The FESEM and X-Ray diffraction measurements were taken for morphology and structural analysis of TiO2 nanoparticles doped with Fe coating on CNTs. The effects of the iron and CNTs on the enhanced photocatalytic activity for methylene blue degradation under AM 1.5 illumination of 100 mW.cm−2were investigated.

Fe nanodot system fabricated by non-lithographic method and its structural properties

In this work, we study the magnetic structure and morphology of the Fe nanodot system fabricated by the non-lithographic method, using anodic aluminum oxide (AAO) membrane as a template. By the two-steps aluminum anodization, the AAO patterns with the hexagonal pore arrangement have been achieved. Using AAO pattern as a template, under suitable conditions we successfully deposited the iron metal in the pores by the thermal vacuum evaporation. By the exposure of the deposited system from the bottom of the AAO membrane, the hexagonal ordered Fe nanodot system has been obtained. The morphologies of the nanodot system were imaged by the Atomic Force Microscopy (AFM) and Field Emission Scanning Microscopy (FESEM) methods. The magnetic structures were investigated by the Energy Dispersive X-Ray Fluorescence Spectroscopy (EDS) and Magnetic Force Microscopy (MFM) methods. Experimental results confirmed that the MFM image of the fabricated Fe nanodot system is similar to their AFM image.