Daniel H. C. Chua

International Christian University, Edo, Tōkyō, Japan

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Publications (93)172.02 Total impact

  • Yong Liu, Likun Pan, Xingtao Xu, Ting Lu, Zhuo Sun, daniel h. c. chua
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    ABSTRACT: Carbon nanorods (CNRs) were fabricated from natural based nanocrystalline cellulose through simple thermal treatment at 800, 1000 and 1200 °C. The morphology, structure and electrochemical performance of CNRs were characterized by atomic force microscopy, Raman spectroscopy, nitrogen adsorption-desorption, cyclic voltammetry and electrochemical impedance spectroscopy. Their electrosorption performance in NaCl solution was studied. The results show that CNRs treated at 1200 °C exhibit the highest specific capacitance of 264.19 F g-1 and electrosorption capacity of 15.12 mg g-1 with the initial NaCl concentration is 500 mg l-1, due to their high specific surface area and low charge transfer resistance.
    J. Mater. Chem. A. 10/2014;
  • Tamie A J Loh, Daniel H C Chua
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    ABSTRACT: Pulsed laser deposition (PLD) on metal substrates has recently been discovered to present an alternative method for producing highly crystalline few-layer MoS2. However, not every metal behaves in the same manner during film growth, and hence, it is crucial that the ability of various metals to produce crystalline MoS2 be thoroughly investigated. In this work, MoS2 was deposited on metal substrates, Al, Ag, Ni, and Cu, using a pulsed laser. Highly crystalline few-layer MoS2 was successfully grown on Ag, but is absent in Al, Ni, and Cu under specific growth conditions. This discrepancy was attributed to either excessively strong or insufficient adlayer-substrate interactions. In the case of Al, the effects of the strong interface interactions can be offset by increasing the amount of source atoms supplied, thereby producing semicrystalline few-layer MoS2. The results show that despite PLD being a physical vapor deposition technique, both physical and chemical processes play an important role in MoS2 growth on metal substrates.
    ACS Applied Materials & Interfaces 09/2014; · 5.90 Impact Factor
  • Tamie A.J. Loh, Daniel H.C. Chua
    Chemical Physics Letters 08/2014; · 2.15 Impact Factor
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    ABSTRACT: Nitrogen-doped carbon microspheres (NCSs) were fabricated via a simple, fast and energy-saving microwave-assisted method followed by thermal treatment under an ammonia atmosphere. NCSs thermally treated at different temperatures were investigated as anode materials for lithium ion batteries (LIBs). The results show that NCSs treated at 900 °C exhibit a maximum reversible capacity of 816 mA h g(-1) at a current density of 50 mA g(-1) and preserve a capacity of 660 mA h g(-1) after 50 cycles, and even at a high current density of 1000 mA g(-1), a capacity of 255 mA h g(-1) is maintained. The excellent electrochemical performance of NCSs is due to their porous structure and nitrogen-doping. The present NCSs should be promising low-cost anode materials with a high capacity and good cycle stability for LIBs.
    Dalton Transactions 06/2014; · 4.10 Impact Factor
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    ABSTRACT: Graphene has been known for its superior electronic properties ever since its discovery in 2004. The high aspect ratio and ballistic transport properties exhibited by this one-dimensional material are especially useful for electron emission applications. However, they are typically grown horizontally and excess efforts, such as the use of transfer techniques, is required to orientate them before effective electron emission from the graphene edges can occur. These transfer techniques have been shown to lead to additional defects to the as-grown graphene structure, thereby degrading its properties. Here, we present an approach to directly fabricate graphene onto metal nano-sized spindt tips (or nanocones) using the solid-state transformation of carbon deposited from a pulsed laser system at low temperature. Besides providing a layer of chemical and mechanical protection for the metal nanocones, the graphene-on-metal nanocones gave enhanced emission properties compared to bare metal nanocones. This was due to the reduction of effective field emission tunneling barrier, which was a result of graphene-metal charge transfer interactions. Controlling the metal nanocones density was also an important factor in determining the field emission performance, as electron screening from neighboring cones should be minimized.
    Advanced Materials Interfaces 05/2014;
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    ABSTRACT: Carbon aerogels (CAs) electrodes with reduced graphene oxide (RGO) additive were fabricated and used as electrosorption electrodes. The capacitive deionization (CDI) performance of the CAs electrodes with different proportions of RGO was investigated. The results show that the CAs electrodes with RGO additive exhibit better electrosorption performance compared with pure CAs electrodes and an electrode with acetylene black additive, indicating that RGO can serve as a flexible bridge to form a “plane-to-point” (RGO-to-CAs) conducting network, which can improve the electron transfer within the CAs electrode. The CAs electrode with 15 wt% RGO was further used in membrane capacitive deionization which integrates ion-exchange membranes with CDI and an extremely high desalination efficiency of 98% was obtained.
    Inorg. Chem. Front. 03/2014; 1(3).
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    ABSTRACT: A simple and scalable electrospinning process followed by thermal treatment was used to fabricate carbon nanofibers (CFs). The as-prepared CFs were investigated as anode materials for sodium ion batteries (SIBs). Remarkably, due to their weakly ordered turbostratic structure and a large interlayer spacing between graphene sheets, the CFs exhibit a dominant adsorption/insertion sodium storage mechanism that shows high reversibility. As a result, the CFs show excellent electrochemical performance, especially cycle stability (97.7% capacity retention ratio over 200 cycles). Reversible capacities of 233 and 82 mA h g−1 are obtained for the CFs at a current density of 0.05 A g−1 and even a high current density of 2 A g−1, respectively. The excellent cycle performance, high capacity and good rate capability make the CFs promising candidates for practical SIBs.
    J. Mater. Chem. A. 02/2014; 2(12).
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    ABSTRACT: We report the direct growth of a unique all-carbon hierarchical graphene-carbon nanotube (G-CNT) hybrid structure on Toray carbon paper using chemical vapor deposition methods. Morphological characterization shows that the graphene is directly grafted onto the CNT scaffold. The hybrid possesses an ultra-high density of exposed graphene edges while retaining the porous structure of CNT scaffold. Using the G-CNT hybrid in the magnetron sputtering electrocatalyst preparation technique, an integrated, polytetrafluoroethylene binder-free cathode (Pt/G-CNT) with an ultra-low Pt loading of 0.04 mg cm−2 is obtained. This cathode shows superior polarization performance compared to a commercial carbon black-supported Pt catalyst (Pt/VXC72) reference.
    ECS Electrochemistry Letters. 01/2014; 3(6):F37-F40.
  • Aditya P. Murawala, Tamie A.J. Loh, Daniel H.C. Chua
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    ABSTRACT: We report the fabrication of a three-dimensional forest of highly crystalline two-dimensional (2D) molybdenum disulfide (MoS2) nano-petals encapsulating vertically aligned carbon nanotubes (CNT) in a core-shell configuration. Growth was conducted via magnetron sputtering at room temperature and it was found that the nano-petal morphology was formed only when a critical threshold in sputter deposition time was reached. Below this threshold, an amorphous tubular structure composed of mainly molybdenum oxides dominates instead. The presence of the MoS2 nano-petals was shown to impart photoluminescence to the CNTs, in addition to significantly enhancing their electron emission properties, where the turn-on field was lowered from 2.50 Vμm−1 for pristine CNTs to 0.80 Vμm−1 for MoS2-CNT heterostructures fabricated at 30 min sputter deposition time. Photoluminescence was detected at wavelengths of approximately 684 nm and 615 nm, with the band at 684 nm gradually blue-shifting as sputter time was increased. These results demonstrate that it is possible to synthesize 2D MoS2 layers without the need for chemical routes and high growth temperatures.
    Journal of Applied Physics 01/2014; 116(11):114305-114305-8. · 2.21 Impact Factor
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    ABSTRACT: A fast microwave-assisted approach was developed to fabricate carbon microspheres (CSs) using sucrose as the precursor in a microwave system. After thermal treatment at 300, 500, 700 and 1000 °C, the CSs were used as anode materials for sodium ion batteries (SIBs). The results show that CSs treated at 500 °C exhibit a maximum capacity of 183 mA h g−1 at a current density of 30 mA g−1 after 50 cycles, and even at a high current density of 1000 mA g−1 a capacity of 83 mA h g−1 is maintained. The high capacity, good cycling stability and excellent rate performance of CSs, due to their unique spherical structure, make them a promising candidate for anode materials for SIBs.
    J. Mater. Chem. A. 12/2013; 2(5).
  • Journal of Non-Crystalline Solids 10/2013; · 1.72 Impact Factor
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    ABSTRACT: In recent years, energy security and climate change have emerged as the topmost global concern. The quest for viable renewable energy technologies has been on the rise. Proton Exchange Membrane Fuel Cells (PEMFCs) are identified as one of the most promising candidates for direct applications in transportation and portable applications. However, the commercialisation of PEMFCs is currently hindered by unsolved issues of which one is the insufficient durability, partly due to carbon support corrosion during PEMFC operations. In this work, we report the use of a Graphene nanoflakes-Carbon nanotubes (GNFs-CNTs) hybrid material as an alternative catalyst support for PEMFCs. GNFs-CNTs were grown directly onto carbon paper, using radio frequency plasma enhanced chemical vapour deposition. Scanning electron microscopy (SEM) showed that GNFs-CNTs hybrid was composed mainly of GNFs densely grafted onto CNTs. The morphology of the as-grown GNFs-CNTs hybrid possessed numerous exposed graphene edges while retaining the porous morphology of CNTs with an average diameter of 100 nm. The GNFs-CNTs hybrid was both used as the catalyst support and micro-porous layer. Platinum catalyst was directly sputtered onto the surface. The accelerated degradation test (ADT) was measured on single cell 5 cm 2 membrane electrode assembly with cathode is the working electrode. ADT was performed by oxidation potential cycling between 0.6 V (for 40 s) and 1.4 V (for 20 s) for 100 cycles. The results showed a significant improvement in the electrochemical stability of the GNFs-CNTs supported Pt catalyst over commercially available Pt/Vulcan XC72 catalyst.
    246th National Meeting of the American-Chemical-Society (ACS), Indianapolis, IN; 09/2013
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    ABSTRACT: High-sensitivity ultraviolet (UV) photodetection has been attempted by utilizing the carrier multiplication effect in amorphous selenium. The prototype photodetector presented in this Letter showed an extremely high sensitivity to UV light, so that up to 1000 carriers are generated per incident photon. This result should lead to the development of an ultrahigh-sensitivity photodetector that can be used for spectrometric applications covering the visible to UV region. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
    physica status solidi (RRL) - Rapid Research Letters 07/2013; 7(7):473-476. · 2.39 Impact Factor
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    ABSTRACT: Hybrid graphene and carbon nanotube (CNT) field emitters were fabricated with electrophoretic deposition (EPD). The combination of both materials was used to improve the turn-on field for pure carbon nanotubes emitters and the reliability of pure graphene emitters deposited by the same method. The CNT was envisioned to hold down the graphene flakes, like a safety belt or Velcro, at high voltages to prevent an early short circuit at relatively low voltages. These hybrid emitters were studied for their field emission performance in relation to the EPD deposition duration. It was observed that the emitters performed better when the EPD duration was increased due to the increase in the amount and density of graphene flakes. Possible reasons for the improvement of field emission performance were suggested. The roles of graphene and CNT in these hybrid emitters were also discussed.
    Journal of Applied Physics 05/2013; 113(17). · 2.21 Impact Factor
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    ABSTRACT: Amorphous selenium is a promising candidate for high sensitivity photodetector due to its unique carrier multiplication phenomenon. More than 10 carriers can be generated per incident photon, which leads to high photo-conversion efficiency of 1000% that allows real-time imaging in dark ambient. However, application of this effect has been limited to specific devices due to the lack in material characterization. In this article, mechanism of carrier multiplication has been clarified using time-of-flight secondary ion mass spectroscopy and Raman spectroscopy. A prototype photodetector achieved photo conversion efficiency of 4000%, which explains the signal enhancement mechanism in a-Se based photodetector.
    Applied Physics Letters 02/2013; 102(7). · 3.52 Impact Factor
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    ABSTRACT: Amorphous-selenium (a-Se) based photodetectors are promising candidates for imaging devices, due to their high spatial resolution and response speed, as well as extremely high sensitivity enhanced by an internal carrier multiplication. In addition, a-Se is reported to show sensitivity against wide variety of wavelengths, including visible, UV and X-ray, where a-Se based flat-panel X-ray detector was proposed. In order to develop an ultra high-sensitivity photodetector with a wide detectable wavelength range, a photodetector was fabricated using a-Se photoconductor and a nitrogen-doped diamond cold cathode. In the study, a prototype photodetector has been developed, and its response to visible and ultraviolet light are characterized.
    Sensors 01/2013; 13(10):13744-78. · 2.05 Impact Factor
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    ABSTRACT: In this paper, we introduce an electro-chemical doping method of amorphous selenium (a-Se) using NaClaq. Recently, an a-Se photovoltaic device fabricated using this method [1], has been announced and opened up the potential of a new impurity doping method. This study will further explore its possibilities by doping chlorine (Cl) and sodium (Na) and aim to fabricate a p-n junction by reversing the applied voltage during the electrolysis. The device is characterized through photoelectric measurements. The I-V characteristics show rectification under light illumination.
    Nanoelectronics Conference (INEC), 2013 IEEE 5th International; 01/2013
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    ABSTRACT: Amorphous-selenium (a-Se) based photodetector is a promising candidate for high sensitivity imaging device with high spatial resolution, high response speed, and a wide detection wave range. Although HARP (high-gain avalanche rushing amorphous photoconductor) is known to be the first a-Se based photodetector that reported carrier multiplication and achieved effective quantum efficiency of 10, physical and chemical properties of the material are yet poorly understood. In this study, we carefully considered the recipe of a-Se and as a result, the necessary condition for obtaining the carrier multiplication has been clarified.
    Nanoelectronics Conference (INEC), 2013 IEEE 5th International; 01/2013
  • H.Y. Wang, Daniel H.C. Chua
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    ABSTRACT: Core-shelled structures such as zinc oxide (ZnO) on carbon nanotubes (CNTs) give rise to interesting material properties. In this work, a triple-layered core–shell–shell structure is presented where the effects of fluorine (F) incorporation on the outmost shell of the ZnO-CNT structure are studied. The samples prepared ranged from a short 2 min to a 30 min immersion in carbon tetraflouride (CF4) plasma. In addition, its effects on the electron emission properties also studied and it is shown that the plasma immersions create thinner field emitters with sharp tiny wrinkles giving rise to more electron emission sites and higher enhancement factor. In addition, X-ray photoelectron spectroscopy measurements showed that F ions replace O in ZnO coatings during immersion process, thus increasing the electrical conductivity and shifts the Fermi level of ZnO upwards. Both physical and electronic effects further contribute to a lower threshold field.
    Applied Surface Science 01/2013; 265:66–70. · 2.54 Impact Factor
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    ABSTRACT: Large area graphene field emitters were fabricated using electrophoretic deposition. By varying the deposition time, we were able to fabricate emitters with varied field enhancement factors. The turn-on field increased when the deposition time increased, and it was observed that a monolayer of graphene flakes covered on the substrate gave the best results. The low emission turn-on field obtained from the graphene field emitters was attributed to the random orientation of graphene flakes which give protruded edges that acted as field enhancing spots. Graphene emitters produced by this method present a low cost cold cathode that can be mass produced.
    Applied Physics Letters 11/2012; 101(18). · 3.52 Impact Factor

Publication Stats

171 Citations
172.02 Total Impact Points

Institutions

  • 2013
    • International Christian University
      • Graduate School of Arts and Sciences
      Edo, Tōkyō, Japan
  • 2007–2013
    • National University of Singapore
      • Department of Materials Science and Engineering
      Singapore, Singapore
  • 2006
    • Nanyang Technological University
      • School of Electrical and Electronic Engineering
      Singapore, Singapore
  • 2003–2004
    • University of Cambridge
      • Department of Engineering
      Cambridge, ENG, United Kingdom