Van Chuc Nguyen

The effect of sintering temperature on the mechanical properties of a Cu/CNT nanocomposite prepared via a powder metallurgy method

Metal matrix nanocomposites have become popular in industrial applications. Carbon nanotubes (CNTs), since theirs appearance, with their unique properties such as exceptionally small diameters and high Youngs modulus, tensile strength and high chemical stability, are considered to be an attractive reinforcement material for lightweight and high-strength metallic matrix composites. The powder metallurgy method allows nanocomposite materials, notably metal–ceramic composites, to be produced by sintering a mixture of powders.In this study, we have utilized the powder metallurgy method to fabricate a Cu/CNT nanocomposite. Sintering is the important process in this method; it is the process whereby powder compacts are heated so that adjacent particles fuse together. The aim of this paper is to investigate the effect of sintering temperature on the mechanical properties of the Cu/CNT nanocomposite. The sintering temperature was in the range of 850–950 °C for 2 h. A correlation between the microstructure and mechanical properties, including the microstructure, density, hardness and compressive strength, is established. In this process, the density, and the physical and mechanical properties of the nanocomposites, can be changed, depending on the rate of sintering as well as the sintering temperature.

Synthesis of multi-layer graphene films on copper tape by atmospheric pressure chemical vapor deposition method

Graphene films were successfully synthesized by atmospheric pressure chemical vapor deposition (APCVD) method. Methane (CH4) gas and copper (Cu) tapes were used as a carbon source and a catalyst, respectively. The CVD temperature and time were in the range of 800?1000??C and 10?s to 45?min, respectively. The role of the CVD temperature and time on the growth of graphene films was investigated in detail via scanning electron microscopy (SEM) and Raman spectroscopy techniques. The results of SEM images and Raman spectra show that the quality of the graphene films was improved with increasing of CVD temperature due to the increase of catalytic activity.

Graphene patterned polyaniline-based biosensor for glucose detection

This paper describes a glucose electrochemical biosensor, layer-by-layer fabricated from graphene and polyaniline films. Graphene sheets (0.5?0.5?cm2) with the thickness of 5?nm (15 layers) were synthesized by thermal chemical vapor deposition (CVD) under ambient pressure on copper tapes. Then they were transferred into integrated Fe3O4-doped polyaniline (PANi) based microelectrodes. The properties of the nanocomposite films were thoroughly characterized by scanning electron microscopy (SEM), Raman spectroscopy, atomic force microscopy (AFM) and electrochemical methods, such as square wave voltametry (SWV) and chronoamperometry. The above graphene patterned sensor (denoted as Graphene/Fe3O4/PANi/GOx) shows much improved glucose sensitivity (as high as 47??A?mM?1?cm?2) compared to a non-graphene one (10?30??A?mM?1?cm?2, as previously reported in the literature). It can be expected that this proof-of-concept biosensor could be extended for other highly sensitive biodetection.

Development of the layer-by-layer biosensor using graphene films: application for cholesterol determination

The preparation and characterization of graphene films for cholesterol determination are described. The graphene films were synthesized by thermal chemical vapor deposition (CVD) method. Methane gas (CH4) and copper tape were used as carbon source and catalyst in the graphene growth process, respectively. The intergrated array was fabricated by using micro-electro-mechanical systems (MEMS) technology in which Fe3O4-doped polyaniline (PANi) film was electropolymerized on Pt/Gr electrodes. The properties of the Pt/Gr/PANi/Fe3O4 films were investigated by field-emission scanning electron microscopy (FE-SEM), Raman spectroscopy and electrochemical techniques. Cholesterol oxidase (ChOx) has been immobilized onto the working electrode with glutaraldehyde agent. The cholesterol electrochemical biosensor shows high sensitivity (74 μA mM−1 cm−2) and fast response time (<5 s). A linear calibration plot was obtained in the wide cholesterol concentration range from 2 to 20 mM and correlation coefficient square (R2) of 0.9986. This new layer-by-layer biosensor based on graphene films promises many practical applications.

Recent trends in preparation and application of carbon nanotube–graphene hybrid thin films

The combination of one-dimensional (1D) carbon nanotubes (CNTs) and two-dimensional (2D) graphene materials to generate three-dimensional (3D) carbon nanotube–graphene hybrid thin films (CNGHTFs) has attracted great attention owing to their intriguing properties via the synergistic effects of these two materials on their electrical, optical, and electrochemical properties in comparison with their individual components. This review aims to provide a brief introduction of recent trends in preparation methodologies and some outstanding applications of CNGHTFs. It contains two main scientific subjects. The first of these is the research on preparation techniques of CNGHTFs, including reduction agent-assisted mechanical blending of reduced graphene oxide (rGO) and CNTs, hybridization methods for layer-by-layer (LBL) assembly of CNTs and rGO sheets, multi-step methods using combinations of a solution and chemical vapor deposition (CVD) processing, one-step growth of CNGHTFs by the CVD method, and modified CVD methods via thermal deposition of carbon source on catalyst surfaces. The advantages and disadvantages of the preparation methods of CNGHTFs are presented and discussed in detail. The second scientific subject of the review is the research on some outstanding applications of CNGHTFs in various research fields, including transparent conductors, electron field emitters, field-effect transistors, biosensors and supercapacitors. In most cases, the CNGHTFs showed superior performances than those of the pristine GO/graphene or CNT materials. Therefore, the CNGHTFs exhibit as high-potential materials for various practical applications. Opportunites and challenges in the fields are also presented.

Thermal dissipation media for high power electronic devices using a carbon nanotube-based composite

Challenges in the thermal dissipation of an electronic package arise from the continuous increase in power density of higher-power devices. Carbon nanotubes (CNTs) are known as the highest thermal conductivity material (2000 W mK−1). This excellent thermal property suggests an approach in applying the CNTs in thermal dispersion materials to solve the aforementioned problems. In this work, we present an effect of thermal dissipation of the CNTs in the high-brightness light emitting diode (HB-LED) and micro-processor. For the thermal dissipation of the HB-LED, a vertically aligned carbon nanotube (VA-CNT) film on a Cu substrate was applied. Meanwhile, for the thermal dissipation of a micro-processor, the composite of commercial thermal paste/CNTs was used instead of the VA-CNTs. The experimental and simulation results have confirmed the advantages of the VA-CNT film and thermal paste/CNT composite as excellent thermal dissipation media for HB-LEDs, μ-processors and other high power electronic devices.

Fabrication of few-layer graphene film based field effect transistor and its application for trace-detection of herbicide atrazine

We describe the fabrication of highly sensitive graphene-based field effect transistor (FET) enzymatic biosensor for trace-detection of atrazine. The few-layers graphene films were prepared on polycrystalline copper foils by atmospheric pressure chemical vapor deposition method using an argon/hydrogen/methane mixture. The characteristics of graphene films were investigated by scanning electron microscopy, transmission electron microscopy and Raman spectroscopy. The results indicated low uniformity of graphene layers, which is probably induced by heterogeneous distribution of graphene nucleation sites on the Cu surface. The pesticide detection is accomplished through the measurement of the drain-source current variations of the FET sensor upon the urea enzymatic hydrolysis reaction. The obtained biosensor is able to detect atrazine with a sensitivity of 56 μA/logCATZ in range between 2 × 10−4 and 20 ppb and has a limit of detection as low as 0.05 ppt. The elaboration of such highly sensitive biosensors will provide better biosensing performances for the detection of biochemical targets.

Effects of ferrite catalyst concentration and water vapor on growth of vertically aligned carbon nanotube

In this study Fe3O4 nanoparticles were used as catalysts for the growth of vertically aligned carbon nanotubes (VA-CNTs) by chemical vapor deposition (CVD). The effect of catalyst concentration and water vapor during the CVD process on the properties of the VA-CNTs was investigated. Monodisperse Fe3O4 nanoparticles (4.5?9.0 nm diameter) prepared by thermal decomposition of iron acetylacetonate compounds were spin-coated on clean silicon substrates which served as a platform for VA-CNTs growth. The results indicated that the length, density and growth rate of CNTs were strongly affected by the catalyst concentration. CNTs grown at 0.026 g ml?1 Fe3O4 catalyst had greater length, density and growth rates than those obtained at 0.01 and 0.033 g ml?1 Fe3O4 catalyst. Addition of water during the CVD process had drastically improved CNTs growth. The length and growth rate of obtained CNTs were 40 ?m and 1.33 ?m min?1, respectively. The results provided insights into the role of Fe3O4 catalyst and water vapor during VA-CNTs growth process by CVD method and the obtained information might serve as a starting point for further optimization of VA-CNTs synthesis.

A method to obtain homogeneously dispersed carbon nanotubes in Al powders for preparing Al/CNTs nanocomposite

Recently carbon nanotubes (CNTs)-reinforced metal matrix composites (MMCs) have attracted increasing attention due to their promising properties. Most research on metallic matrix–CNTs composites (MMCs–CNTs) show that uniform dispersion of CNTs has been by far the most significant challenge in the field of CNTs-reinforced composites. In this research we will present an approach to obtain homogeneously dispersed CNTs in Al powders for preparing Al/CNTs nanocomposite. A novel polyester binder-assisted (PBA) mixing method was used for achieving uniform dispersion of CNTs, and power metallurgy (PM) technique was used for preparing Al/CNTs nanocomposite. The distribution quality of CNTs in Al matrix nanocomposites was also qualified based on image analysis technique. The morphologies, structures and mechanical properties of the Al/CNTs nanocomposite were also investigated in detail by scanning electron microscopy (SEM), energy dispersive x-ray (EDX) spectroscopy, x-ray diffraction (XRD) and mechanical measurement methods. Experimental results show that this method not only achieves good dispersion but it also avoids the damage on structure of CNTs by conventional mixing methods.

Single-walled carbon nanotubes synthesized by chemical vapor deposition of C2H2 over an Al2O3 supported mixture of Fe, Mo, Co catalysts

Single-walled carbon nanotubes (SWCNTs) have been successfully synthesized by chemical vapor deposition (CVD) using acetylene (C2H2) gas as a carbon source and a mixture of Fe/Mo/Co on an Al2O3 support as a catalyst. The effects of the weight percentage (wt%) of metals in the Fe/Mo/Co/Al2O3 catalysts, growth time, gas flow rate and growth temperature on SWCNT growth were studied in detail. The optimum growth conditions were found to be a growth time of 60?min, a growth temperature of 750??C, Ar/H2/C2H2 flow rates of 420/100/14?sccm and a catalyst composition of Fe/Mo/Co/Al2O3=5/3/1/80 (wt%). The morphologies and structures of the grown SWCNTs were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy techniques.