Liu Wei Wen
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Preferred name
Liu Wei Wen
Official Name
Wen, Liu Wei
Alternative Name
Liu, Wei Wen
Wei-Wen, Liu
Liu W., -W.
Main Affiliation
Scopus Author ID
57194266103
Researcher ID
D-2098-2015

Research Output

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  • Publication
    Thickness dependent nanostructural, morphological, optical and impedometric analyses of Zinc Oxide-Gold hybrids : Nanoparticle to thin film
    ( 2015)
    Veeradasan Perumal
    ;
    Uda Hashim
    ;
    Subash Chandra Bose Gopinath
    ;
    R. Haarindraprasad
    ;
    Liu Wei Wen
    ;
    Prabakaran A/L Poopalan
    ;
    S. R. Balakrishnan
    ;
    V. Thivina
    ;
    Ruslinda A. Rahim
    ;
    Yogendra Kumar Mishra
    The creation of an appropriate thin film is important for the development of novel sensing surfaces, which will ultimately enhance the properties and output of high-performance sensors. In this study, we have fabricated and characterized zinc oxide (ZnO) thin films on silicon substrates, which were hybridized with gold nanoparticles (AuNPs) to obtain ZnO-Au x (x = 10, 20, 30, 40 and 50 nm) hybrid structures with different thicknesses. Nanoscale imaging by field emission scanning electron microscopy revealed increasing film uniformity and coverage with the Au deposition thickness. Transmission electron microscopy analysis indicated that the AuNPs exhibit an increasing average diameter (5–10 nm). The face center cubic Au were found to co-exist with wurtzite ZnO nanostructure. Atomic force microscopy observations revealed that as the Au content increased, the overall crystallite size increased, which was supported by X-ray diffraction measurements. The structural characterizations indicated that the Au on the ZnO crystal lattice exists without any impurities in a preferred orientation (002). When the ZnO thickness increased from 10 to 40 nm, transmittance and an optical bandgap value decreased. Interestingly, with 50 nm thickness, the band gap value was increased, which might be due to the Burstein-Moss effect. Photoluminescence studies revealed that the overall structural defect (green emission) improved significantly as the Au deposition increased. The impedance measurements shows an increasing value of impedance arc with increasing Au thicknesses (0 to 40 nm). In contrast, the 50 nm AuNP impedance arc shows an increased value compared to lower sputtering thicknesses, which indicated the presence of larger sized AuNPs that form a continuous film, and its ohmic characteristics changed to rectifying characteristics. This improved hybrid thin film (ZnO/Au) is suitable for a wide range of sensing applications.
  • Publication
    Fabrication of silicon nitride ion sensitive field-effect transistor for pH measurement and DNA Immobilization/Hybridization
    ( 2013)
    Uda Hashim
    ;
    Soon Weng Chong
    ;
    Liu Wei Wen
    The fabrication of ion sensitive field-effect transistor (ISFET) using silicon nitride (Si3N4) as the sensing membrane for pH measurement and DNA is reported. For the pH measurement, the Ag/AgCl electrode was used as the reference electrode, and different pH values of buffer solution were used in the ISFET analysis. The ISFET device was tested with pH buffer solutions of pH2, pH3, pH7, pH8, and pH9. The results show that the IV characteristic of ISFET devices is directly proportional and the device’s sensitivity was 43.13 mV/pH. The ISFET is modified chemically to allow the integration with biological element to form a biologically active field-effect transistor (BIOFET). It was found that the DNA immobilization activities which occurred on the sensing membrane caused the drain current to drop due to the negatively charged backbones of the DNA probes repelled electrons from accumulating at the conducting channel. The drain current was further decreased when the DNA hybridization took place.
  • Publication
    Synthesis of single-walled carbon nanotubes: effects of active metals, catalyst supports, and metal loading percentage
    ( 2013-06-27)
    Liu Wei Wen
    ;
    Siang-Piao Chai
    ;
    Abdul Rahman Mohamed
    ;
    Uda Hashim
    ;
    Azizan Aziz
    The effects of active metals, catalyst supports, and metal loading percentage on the formation of single-walled carbon nanotubes (SWNTs) were studied. In particular, iron, cobalt, and nickel were investigated for SWNTs synthesis. Iron was found to grow better-quality SWNTs compared to cobalt and nickel. To study the effect of catalyst supports, magnesium oxide, silicon oxide, and aluminium oxide were chosen for iron. Among the studied supports, MgO was identified to be a suitable support for iron as it produced SWNTs with better graphitisation determined by Raman analysis. Increasing the iron loading decreased the quality of SWNTs due to extensive agglomeration of the iron particles. Thus, lower metal loading percentage is preferred to grow better-quality SWNTs with uniform diameters.
  • Publication
    Precise alignment of individual single-walled carbon nanotube using dielectrophoresis method for development and fabrication of pH sensor
    ( 2013)
    Uda Hashim
    ;
    Foo Wah Low
    ;
    Liu Wei Wen
    Development and fabrication of single-walled carbon nanotube (SWNT) based pH sensor were reported. The precise alignment of individual SWNT using dielectrophoresis method between the two microgap electrodes was conducted, and the effects of precise alignment of individual SWNT on impedance, long term stability, and capacitance of the sensor were studied. The pH sensor was fabricated using conventional photolithography and wet etching process. The impedance values were found to decrease in the order of distilled water > pH 10 > pH 5 > pH 3 > air. Without the alignment of SWNT, the capacitances values decreased with increasing of pH values at low frequency. All the impedance and capacitance results were highly repeatable.
  • Publication
    Thickness dependent nanostructural, morphological, optical and impedometric analyses of Zinc Oxide-Gold Hybrids: Nanoparticle to thin film
    ( 2015)
    Veeradasan Perumal
    ;
    Uda Hashim
    ;
    Subash Chandra Bose Gopinath
    ;
    R. Haarindraprasad
    ;
    Liu Wei Wen
    ;
    Prabakaran A/L Poopalan
    ;
    S. R. Balakrishnan
    ;
    V. Thivina
    ;
    Ruslinda A. Rahim
    The creation of an appropriate thin film is important for the development of novel sensing surfaces, which will ultimately enhance the properties and output of high-performance sensors. In this study, we have fabricated and characterized zinc oxide (ZnO) thin films on silicon substrates, which were hybridized with gold nanoparticles (AuNPs) to obtain ZnO-Aux (x = 10, 20, 30, 40 and 50 nm) hybrid structures with different thicknesses. Nanoscale imaging by field emission scanning electron microscopy revealed increasing film uniformity and coverage with the Au deposition thickness. Transmission electron microscopy analysis indicated that the AuNPs exhibit an increasing average diameter (5–10 nm). The face center cubic Au were found to co-exist with wurtzite ZnO nanostructure. Atomic force microscopy observations revealed that as the Au content increased, the overall crystallite size increased, which was supported by X-ray diffraction measurements. The structural characterizations indicated that the Au on the ZnO crystal lattice exists without any impurities in a preferred orientation (002). When the ZnO thickness increased from 10 to 40 nm, transmittance and an optical bandgap value decreased. Interestingly, with 50 nm thickness, the band gap value was increased, which might be due to the Burstein-Moss effect. Photoluminescence studies revealed that the overall structural defect (green emission) improved significantly as the Au deposition increased. The impedance measurements shows a decreasing value of impedance arc with increasing Au thicknesses (0 to 40 nm). In contrast, the 50 nm AuNP impedance arc shows an increased value compared to lower sputtering thicknesses, which indicated the presence of larger sized AuNPs that form a continuous film, and its ohmic characteristics changed to rectifying characteristics. This improved hybrid thin film (ZnO/Au) is suitable for a wide range of sensing applications.
  • Publication
    A review of the effect of different electrolytes on the synthesis of graphene sheets by electrochemical exfoliation
    ( 2024-04)
    S. S. Bhullar
    ;
    Liu Wei Wen
    Graphene oxide (GO) possess some excellent properties that fulfil various applications. Hummers’ method has been used in GO synthesis for years but some issues such as high-cost GO synthesis, the use of toxic chemicals and low yield of GO are still remains and concerned. In addition, this method spends very long time to be completed and subjected to thorough cleaning process to remove toxic chemicals. On the other hand, the electrochemical method saves time, has no explosion risk, releases no toxic gases, and keep safe environmental. The demand of GO supply is crucial particularly important in applications such as energy storage in automobiles thus, a large scale and cheap production of GO is needed. It is reported that the electrochemical synthesis of GO has more benefits such as rapid synthesis, low cost and environmentally friendly than Hummers’ method, therefore, the impact of different electrolytes is important to be studied. Herein, various research works about the electrochemical synthesis of GO are reviewed, precisely involving the anodic exfoliation of graphite, exfoliation mechanism and effects of exfoliation parameters.
  • Publication
    Graphene synthesis by electrochemical reduction of graphene oxide and its characterizations
    ( 2023-07)
    Nur Syahirah Kholib
    ;
    Liu Wei Wen
    Graphene is one of the nanoscale materials that has attracted many researchers to continue in-depth study on its unique properties where both the graphene oxide (GO) and electrochemical reduced graphene oxide (ERGO) are the derivatives of graphene. GO and ERGO can be further modified chemically for many types of application such as sensor and water filter membrane. However, to restore the electrical property of graphene, GO should be reduced to ERGO. There are several types of reduction methods which are fast to produce good quality and high yield of graphene material. However, those methods use toxic chemicals to reduce GO which can bring negative impact to both human and environment. Therefore, an electrochemical approach can be carried out to solve this issue. This study presents the electrochemical synthesis of GO and electrochemical reduction of ERGO. All characterizations were conducted by using Fourier transform infrared (FTIR) spectroscopy, X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM).
  • Publication
    Synthesis of few layers graphene sheets from graphite rod via electrochemical exfoliation
    ( 2023-07)
    Siti Nur Adlina Norazman
    ;
    Liu Wei Wen
    Graphene has many excellent properties in mechanical strength, electrical conductivity, optical transparency and thermal conductivity. The basic unit of graphene is made of hexagonal ring of carbon shape. The production of graphene in large amounts can be done using conventional ways such as chemical vapour deposition (CVD). However, the cost production is very high due to high reaction temperature. Therefore, electrochemical exfoliation could become a promising method in future because of its simple, low cost and large-scale production. Electrochemical method is performed in the manner by connecting the graphite rod to the positive terminal (anode) while the copper sheet is connected to the negative terminal (cathode) and both of were immersed into electrolyte with a distance between them. Then, due to the potential difference, the exfoliation of graphite into graphene sheets occurs. X-Ray Diffraction revealed that high amount of exfoliated graphene sheets was synthesized successfully where the peak was seen at approximately 26.60°. Fourier Transform Infrared confirmed the synthesized of graphene oxide (GO) sheets (by using H2SO4 as electrolyte) shows the higher intensity of O-H band because of strongest oxidation behaviour of H2SO4 acid among all electrolytes used in experiment. Besides. SEM images show that the morphologies of the exfoliated graphene sheets have stacked, flaky-like, wrinkled and crumpled structures.
  • Publication
    Improvement synthesis of graphene oxide yield in two steps of intercalation and oxidation of flexible graphite foil by electrochemical exfoliation
    ( 2024-04)
    M. O. Ariffa
    ;
    Liu Wei Wen
    ;
    Foo Kai Loong
    Synthesis of high quality and quantity of graphene by cost-effective methods are highly desirable for various application. In electrochemical exfoliation, graphite foil has been used as carbon source for the synthesis of high yield of graphene flakes. Electrochemical exfoliation is one of the faster and cheaper method to synthesize graphene sheets. In this work, five different types of concentration of sulphuric acid were used for electrochemical exfoliation. The electrochemical cell design where graphite foil as anode and copper foil as cathode which were connected to DC power supply of 5V. To examine the morphology scanning electron microscope (SEM) was employed in which the sheet structures with large lateral dimension and thin graphene flakes. Furthermore, X-ray diffraction (XRD) revealed that exfoliated graphene samples showed a significant peak at about 2θ = 26º corresponded to graphite.
  • Publication
    Extraction of bioactive secondary metabolites from Citrus Axima peel via pressurized hot water extractor for the synthesis of iron oxide nanoparticles
    ( 2024-06)
    Yi-Peng Teoh
    ;
    Nurdalilah Othman
    ;
    Sam Sung Ting
    ;
    Zhong-Xian Ooi
    ;
    Liu Wei Wen
    ;
    Saparu Walli
    ;
    Lian-See Tan
    ;
    Lee Boon Beng
    Using bioactive secondary metabolites (BSM) from Citrus maxima peel extract, this work investigated a green method of synthesizing magnetite iron oxide (Fe3O4) nanoparticles (NPs). The BSM acts as a reducing cum stabilizing agent in the process. The optimization of the BSM parameters were conducted through response surface methodology (RSM). The optimal condition obtained in this study for pressurized hot water extractor (PHWE) extraction was temperature of 94.96 °C, solvent-to-solid ratio of 29.7 ml/g and extraction time of 27.6 min. BSM Yield of 49.31 % could be obtained based on this condition. The formation of Fe3O4 NPs were detected using the FTIR analysis with the absorption peaks observed at around 590 and 580 cm−1. X-ray diffraction results matched standard magnetite Fe3O4 patterns with planes at (220), (311), (400), (511) and (440). Field emission scanning electron microscopy (FESEM) results showed that the magnetite Fe3O4 NPs synthesized in this study predominantly appeared in spherical shape. The extraction process's kinetics were examined using various empirical models, including the Elovich’s model, Peleg’s model, Power law and parabolic diffusion model. All applied models were found to be well fitted with the measured data from experiment, with R2 values exceeding 0.9. Notably, the Peleg’s model exhibited the highest R2, the smallest RMSD, and the least significant p-values, indicating its superior performance.