Papers by Author: Wei Wen Liu

Abstract: This paper aims to present an effective electromagnetic (EM) modelling approach for rectangular bundle of single-walled carbon nanotubes (RB-SWCNTs), based on the electrical conductivity, relative complex permittivity and linear distribution impedance by applying General Ohm’s law for this bundle. The equivalent single conductor material (ESCM) model for personification the RB-SWCNTs is present in this paper. The main target of this modeling approach is to estimate and investigate the EM properties of RB-SWCNTs using common EM engineering tool solver CST (MWS). For this purpose, the RB-SWCNTs and ESCM dipole antennas will be designed and implemented using CST (MWS). The equivalent conductivity model, relative complex permittivity and other parameters of the RB-SWCNTs will be derived in this paper and considered as an equivalent material parameters for the ESCM. This modeling technique is expected to provide new avenues for designing different antenna structures.

Abstract: Silicon carbide is an attractive material for engineering and industrial applications in harsh conditions. In manufacturing process, conventional heating process is commonly used to synthesis the silicon carbide. In this study, SiC nanowhiskers were synthesized from microwave heating of mixture of graphite and silica in the ratio of 3: 1. The mixture was heated by using laboratory microwaves oven to 1400°C at heating rate of 20 °C/min and temperature was hold for 30 minutes. Photoluminescence spectroscopy and Fourier transform infrared spectroscopy were used to characterize the SiC nanowhiskers. Photoluminescence spectrum of SiC nanowhiskers showed a sharp peak at 420 nm corresponding to band gap of SiC (2.39 ev). FTIR absorption spectra of SiCNWs recorded a band at 805.22 cm^-1 corresponding to Si-C bond.

Abstract: In this paper, the effect of ratio of silicon dioxide and graphite for the synthesis of silicon carbide nanowhiskers by microwaves heating was reported. The mixtures of SiO₂ and graphite with different ratio were prepared by ultrasonic mixing using ethanol as medium. The mixtures were dried on hotplate and cold pressed by using hydraulic hand press uniaxially into a pellet die. The mixture in the form of pellet were heated up to 1400 °C at heating rate of 20 °C/min and soaked for 30 minutes. Scanning electron microscopy was used to study the morphology of sample of each different ratio of mixture. It was found that almost complete conversion of graphite and silica to silicon carbide nanowhiskers was observed for sample of mixture SiO₂ and graphite in the ratio of 1:3. Result from x-ray diffraction analysis also indicated that single β-SiC phase was present in the diffractogram of silicon carbide nanowhiskers synthesized from mixture SiO₂ and graphite in the ratio of 1:3.

Abstract: Mass production of GO has always been an issue. Generally, there are 3 general methods available, namely Brodie’s, Staudenmaier’s and Hummer’s Method. These three methods differ in the type of oxidation agents used. There are plenty of developed methods to produce GO were reported in the literature including the improved Hummer’s method. This method is associated with the use of mixture of sulphuric acid/phosphoric acid (H2SO4/H3PO4) in 9:1 ratio without the presence of sodium nitrate (NaNO3).The amount of potassium permanganate (KMnO4) was set at 9.0g. This method allows high yield and ease of control. In this reaction, one of the important indicators was the colour changes during the addition of hydrogen peroxide (H2O2) into the mixture. However, with the large amount of KMnO4 added, the colour change was hardly observed. Therefore, one possible way to cope with that was to vary the amount of added KMnO4. Subsequently, the produced GO were characterized by X-Ray diffraction (XRD) and scanning electron microscope (SEM).

Abstract: This paper is to study the dielectric properties, magnetic properties, and dielectric conductivity of Multi-walled carbon nanotubes (MWCNTs) and polyester (PE) composites. The composites with different amount of MWCNTs (5-15%) have been studied in the Ku-Band range (12.4-18 GHz). The rectangular waveguide (WR-62) was used to measure the dielectric properties and magnetic properties of the samples. The results show the dielectric properties and conductivity of MWCNTs/PE composites is increasing with the MWCNTs filler increases. The real part of dielectric properties values increase from 5.5 to 26.6 with increasing the MWCNTs loading from 5 % to 15 %. The increasing of MWCNTs filler in the MWCNTs/PE composites does not effects on magnetic properties, the real part and imaginary part of magnetic properties are approximate to 1 and 0. The highest conductivity of 15 % MWCNTs loading is reach to 11.02 (S/m) at 18 GHz. Keywords: composites, dielectric properties, magnetic properties, conductivity

Abstract: Today, research on graphene and other two-dimensional sp²-hybridized carbon nanomaterials has tremendously impacted the areas of modern chemistry, physics, and materials science and engineering. The significant attraction of these materials can be attributed to the outstanding electrical, optical, electrochemical, and mechanical properties of graphene-like materials, especially in comparison to other carbon materials. In this manner, graphene oxide as a substrate for graphene-like materials reduction process is getting more and more interesting. Although early routes to these materials were challenging, significant advances in synthetic and processing methods have enabled access to high-quality exfoliated graphene oxide sheets in appreciable quantities. Herein, we introduced a simple and efficient method for the high-conversion preparation of graphene oxide using a simplified hummer’s method from large graphite flakes (an average flake size of 100 μm). One-pot chemical oxidation of graphite was carried out at room temperature for the preparation purpose. It was found that different degree of oxidation of graphite flakes could be realized by stirring graphite in a mixture of sulphuric acid and potassium permanganate under different oxidation durations, resulting in exfoliated graphene oxide sheets with large lateral dimension and area. The simplified Hummer’s method provides a facile approach for the preparation of large-area exfoliated graphene oxide sheets.

Abstract: Nowadays, graphene (Gr) is one of the most promising materials in the field of nanoscience and nanotechnology and has attracted extensive attention in variety of applications, such as solar energy, environmental management, sensor, electronic device as well as energy storage and conversion. From a theoretical point of view, Gr provides the ultimate two-dimensional (2D) model of a catalytic support with sp² hybridized carbon atoms. Its unique physical, chemical and mechanical properties are outstanding, and could allow the preparation of this composite material with unprecedented characteristics, such as superior electron mobility, good conductivity, excellent transparent property and high chemical stability. These unique characteristics inherent to well-defined 2D Gr are suitable for facilitating a wide range of transformations and may offer extraordinary potential in the design of novel catalytic systems. Herein, a simple and well-controllable Improved Hummer’s method was presented for the first time by controlling it’s stirring duration for high yield production of GO (62.50%). Based on our preliminary results, it was found that large amount of oxygen functional groups appeared after the conversions of graphite into graphene oxide (GO) by applying the vigorous stirring speed for 72 hours continuously. The main reason mainly attributed to the improvement of the mass transfer rate of oxygen molecules during the oxidation reactions; thus, high yield of GO could be achieved under this experimental condition. In addition, the resultants GO exhibited higher short-circuit currents with 290 μA compare to short circuit of Gr with 70 μA under light simulation condition.

Abstract: Surface acoustic wave can be generated at the free surface of an elastic solid. Interdigital transducers (IDTs) are fabricated on the piezoelectric substrate surface that will act as electrical input and output port. When appropriate AC voltage stimulus is applied to the input transducer, surface acoustic wave will be produced. The output or receiving port will detect the incident surface acoustic wave and convert it back to a suitably filtered electrical once. For this property, surface acoustic based devices were initially developed for the telecommunication purpose such as signal filters and resonators. SAW based devices have been modified to be sensors later on from for gas detections and have been moving towards biological detections recently for its ultra-sensitivity to surface perturbation. The main component of this device is the IDTs. Recently, there are several methods to produce IDTs; Ultra-Violet (UV), deep UV lithography, Electron beam (e-beam) lithography and X-ray lithography. Although, these methods can produce very fine and accurate electrodes in term of submicron size but the costs are extremely expensive. Thus, this paper will discuss the conventional CMOS method which is much more economical to produce the applicable IDTs for the bacterial pathogens sensing purpose. Shear horizontal surface acoustic wave (SHSAW), one of the SAW based types is used in this paper as it is most suitable for the liquid based application as it has the advantage of acoustic energy is not being radiated into liquid.

Abstract: The effect of chemical solutions on the dispersion of single-walled carbon nantubes (SWCNTs) was studied. The SWCNTs were dispersed using several chemical solutions such as isopropyl alcohol (IPA), dichloromethane (DCM), acetone and triton X-100 (Triton-X) under ultrasonically process. The results show that the types of chemical solutions greatly affect the dispersion of SWCNTs. The IPA solution is found to be the best solution to disperse SWCNTs using ultrasonication process due to the difficultly of evaporation in room temperature to get a transparent solution.

Abstract: Magnetite (Fe₃O₄) nanoparticles were synthesized in aqueous solutions without any surfactants. The Fe₃O₄ nanoparticles are nearly spherical and have an average diameter of 10.33nm and a narrow size distribution. Bundles of single-walled carbon nanotube (SWCNT) were synthesized using these Fe₃O₄ nanoparticles supported by MgO. Transmission electron microscopy (TEM) images show that tremendous amount of bundles SWCNT with uniform diameters were produced. The average diameter of bundles SWCNT is 1.22nm. Raman spectrum shows that well graphitized SWCNTs were formed based on the low ratio of I_D/I_G. Fe₃O₄ nanoparticles could be an effective active metal to synthesize large quantity bundles of SWCNT.