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Dive into the research topics where TakFu Hung is active.

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Featured researches published by TakFu Hung.


ACS Applied Materials & Interfaces | 2014

Carbon Dot Loading and TiO2 Nanorod Length Dependence of Photoelectrochemical Properties in Carbon Dot/TiO2 Nanorod Array Nanocomposites

Juncao Bian; Chao Huang; Lingyun Wang; TakFu Hung; Walid A. Daoud; Rui-Qin Zhang

Photoelectrochemcial (PEC) properties of TiO2 nanorod arrays (TNRA) have been extensively investigated as they are photostable and cost-effective. However, due to the wide band gap, only the UV part of solar light can be employed by TiO2. To enhance the photoresponse of TNRA in the visible range, carbon dots (C dots) were applied as green sensitizer in this work by investigating the effects of C dot loading and length of TiO2 nanorod on the PEC properties of TNRA/C dot nanocomposites. As the C dot loading increases, the photocurrent density of the nanocomposites was enhanced and reached a maximum when the concentration of the C dots was 0.4 mg/mL. A further increase in the C dot concentration decreased the photocurrent, which might be caused by the surface aggregation of C dots. A compromise existed between charge transport and charge collection as the length of TiO2 nanorod increased. The incident photon to current conversion efficiency (IPCE) of the TNRA/C dot nanocomposites in the visible range was up to 1.2-3.4%. This work can serve as guidance for fabrication of highly efficient photoanode for PEC cells based on C dots.


Journal of Materials Chemistry | 2014

Electrochemical doping of anatase TiO2 in organic electrolytes for high-performance supercapacitors and photocatalysts

Hui Li; Zhenhua Chen; Chun Kwan Tsang; Zhe Li; Xiao Ran; Chris Lee; Biao Nie; Lingxia Zheng; TakFu Hung; Jian Lu; B. C. Pan; Yang Yang Li

In this article, we report a facile electrochemical method to modify anatase TiO2 by cathodically biasing TiO2 in an ethylene glycol electrolyte. The resulting black TiO2 is highly stable with a significantly narrower bandgap and higher electrical conductivity. Furthermore, largely improved photoconversion efficiency (increased from 48% to 72% in the visible region, and from nearly 0% to 7% in the UV region), photocatalytic efficiency, and charge-storage capability (∼42 fold increase) are achieved for the treated TiO2.


ACS Nano | 2012

Synthesis and characterizations of ternary InGaAs nanowires by a two-step growth method for high-performance electronic devices.

Jared J. Hou; Ning Han; Fengyun Wang; Fei Xiu; SenPo Yip; Alvin T. Hui; TakFu Hung; Johnny C. Ho

InAs nanowires have been extensively studied for high-speed and high-frequency electronics due to the low effective electron mass and corresponding high carrier mobility. However, further applications still suffer from the significant leakage current in InAs nanowire devices arising from the small electronic band gap. Here, we demonstrate the successful synthesis of ternary InGaAs nanowires in order to tackle this leakage issue utilizing the larger band gap material but at the same time not sacrificing the high electron mobility. In this work, we adapt a two-step growth method on amorphous SiO(2)/Si substrates which significantly reduces the kinked morphology and surface coating along the nanowires. The grown nanowires exhibit excellent crystallinity and uniform stoichiometric composition along the entire length of the nanowires. More importantly, the electrical properties of those nanowires are found to be remarkably impressive with I(ON)/I(OFF) ratio >10(5), field-effect mobility of ∼2700 cm(2)/(V·s), and ON current density of ∼0.9 mA/μm. These nanowires are then employed in the contact printing and achieve large-scale assembly of nanowire parallel arrays which further illustrate the potential for utilizing these high-performance nanowires on substrates for the fabrication of future integrated circuits.


Journal of Materials Chemistry | 2011

Nanoparticle size dependent threshold voltage shifts in organic memory transistors

Su-Ting Han; Ye Zhou; Zong-Xiang Xu; V. A. L. Roy; TakFu Hung

The performance of organic field-effect transistor (OFET) memory devices with different size of gold nanoparticles (Au NPs) as charge trapping layers has been investigated. We synthesized 15 nm, 20 nm and 25 nm of Au NPs through a citrate-reduction method and 3-aminopropyltriethoxysilane (APTES) functionalized substrates were used to form a monolayer of Au NPs. In the programming/erasing operation, we observed reversible threshold voltage (Vth) shifts and reliable memory performances. A strong size-dependent effect on Vth shifts and memory effect was observed. Effect of size dependence on the mobilities (μ), on/off current ratios, subthreshold swings (S), data retention characteristics (>105 s) and endurance performances operation (>800 cycles) of memory devices are discussed. The experimental results suggest a guideline for optimizing the size and density of Au NPs and their influence on the device properties.


ACS Nano | 2012

Controllable p-n switching behaviors of GaAs nanowires via an interface effect.

Ning Han; Fengyun Wang; Jared J. Hou; Fei Xiu; SenPo Yip; Alvin T. Hui; TakFu Hung; Johnny C. Ho

Due to the extraordinary large surface-to-volume ratio, surface effects on semiconductor nanowires have been extensively investigated in recent years for various technological applications. Here, we present a facile interface trapping approach to alter electronic transport properties of GaAs nanowires as a function of diameter utilizing the acceptor-like defect states located between the intrinsic nanowire and its amorphous native oxide shell. Using a nanowire field-effect transistor (FET) device structure, p- to n-channel switching behaviors have been achieved with increasing NW diameters. Interestingly, this oxide interface is shown to induce a space-charge layer penetrating deep into the thin nanowire to deplete all electrons, leading to inversion and thus p-type conduction as compared to the thick and intrinsically n-type GaAs NWs. More generally, all of these might also be applicable to other nanowire material systems with similar interface trapping effects; therefore, careful device design considerations are required for achieving the optimal nanowire device performances.


Nature Communications | 2014

Surfactant-assisted chemical vapour deposition of high-performance small-diameter GaSb nanowires

Zai-xing Yang; Ning Han; Ming Fang; Hao Lin; Ho-Yuen Cheung; SenPo Yip; Er-Jun Wang; TakFu Hung; Chun-Yuen Wong; Johnny C. Ho

Although various device structures based on GaSb nanowires have been realized, further performance enhancement suffers from uncontrolled radial growth during the nanowire synthesis, resulting in non-uniform and tapered nanowires with diameters larger than few tens of nanometres. Here we report the use of sulfur surfactant in chemical vapour deposition to achieve very thin and uniform GaSb nanowires with diameters down to 20 nm. In contrast to surfactant effects typically employed in the liquid phase and thin-film technologies, the sulfur atoms contribute to form stable S-Sb bonds on the as-grown nanowire surface, effectively stabilizing sidewalls and minimizing unintentional radial nanowire growth. When configured into transistors, these devices exhibit impressive electrical properties with the peak hole mobility of ~200 cm(2 )V(-1 )s(-1), better than any mobility value reported for a GaSb nanowire device to date. These factors indicate the effectiveness of this surfactant-assisted growth for high-performance small-diameter GaSb nanowires.


Nanotechnology | 2013

Surface roughness induced electron mobility degradation in InAs nanowires

Fengyun Wang; SenPo Yip; Ning Han; KitWa Fok; Hao Lin; Jared J. Hou; Guofa Dong; TakFu Hung; K. S. Chan; Johnny C. Ho

In this work, we present a study of the surface roughness dependent electron mobility in InAs nanowires grown by the nickel-catalyzed chemical vapor deposition method. These nanowires have good crystallinity, well-controlled surface morphology without any surface coating or tapering and an excellent peak field-effect mobility up to 15,000 cm(2) V(-1) s(-1) when configured into back-gated field-effect nanowire transistors. Detailed electrical characterizations reveal that the electron mobility degrades monotonically with increasing surface roughness and diameter scaling, while low-temperature measurements further decouple the effects of surface/interface traps and phonon scattering, highlighting the dominant impact of surface roughness scattering on the electron mobility for miniaturized and surface disordered nanowires. All these factors suggest that careful consideration of nanowire geometries and surface condition is required for designing devices with optimal performance.


Nanotechnology | 2011

Facile synthesis and growth mechanism of Ni-catalyzed GaAs nanowires on non-crystalline substrates

Ning Han; Fengyun Wang; Alvin T. Hui; Jared J. Hou; Guangcun Shan; Fei Xiu; TakFu Hung; Johnny C. Ho

GaAs nanowires (NWs) have been extensively explored for next generation electronics, photonics and photovoltaics due to their direct bandgap and excellent carrier mobility. Typically, these NWs are grown epitaxially on crystalline substrates, which could limit potential applications requiring high growth yield to be printable or transferable on amorphous and flexible substrates. Here, utilizing Ni as a catalytic seed, we successfully demonstrate the synthesis of highly crystalline, stoichiometric and dense GaAs NWs on amorphous SiO(2) substrates. Notably, the NWs are found to grow via the vapor-solid-solid (VSS) mechanism with non-spherical NiGa catalytic tips and low defect densities while exhibiting a narrow distribution of diameter (21.0 ± 3.9 nm) uniformly along the entire length of the NW (>10 µm). The NWs are then configured into field-effect transistors showing impressive electrical characteristics with I(ON)/I(OFF) > 10(3), which further demonstrates the purity and crystal quality of NWs obtained with this simple synthesis technique, compared to the conventional MBE or MOCVD grown GaAs NWs.


Applied Physics Letters | 2012

GaAs nanowire Schottky barrier photovoltaics utilizing Au–Ga alloy catalytic tips

Ning Han; Fengyun Wang; SenPo Yip; Jared J. Hou; Fei Xiu; Xiaoling Shi; Alvin T. Hui; TakFu Hung; Johnny C. Ho

Single GaAs nanowire photovoltaic devices were fabricated utilizing rectifying junctions in the Au–Ga catalytic tip/nanowire contact interface. Current-voltage measurements were performed under simulated Air Mass 1.5 global illumination with the best performance delivering an overall energy conversion efficiency of ∼2.8% for a nanowire of 70 nm in diameter. As compared with metal contacts directly deposited on top of the nanowire, this nanoscale contact is found to alleviate the well-known Fermi-level pinning to achieve effective formation of Schottky barrier responsible for the superior photovoltaic response. All these illustrate the potency of these versatile nanoscale contact configurations for future technological device applications.


Journal of Materials Chemistry | 2013

Developing controllable anisotropic wet etching to achieve silicon nanorods, nanopencils and nanocones for efficient photon trapping

Hao Lin; Ho-Yuen Cheung; Fei Xiu; Fengyun Wang; SenPo Yip; Ning Han; TakFu Hung; Jun Zhou; Johnny C. Ho; Chun-Yuen Wong

Controllable hierarchy of highly regular, single-crystalline nanorod, nanopencil and nanocone arrays with tunable geometry and etch anisotropy has been achieved over large areas (>1.5 cm × 1.5 cm) by using an [AgNO3 + HF + HNO3/H2O2] etching system. The etching mechanism has been elucidated to originate from the site-selective deposition of Ag nanoclusters. Different etch anisotropies and aspect ratios can be accomplished by modulating the relative concentration in the [AgNO3 + HF + HNO3/H2O2] etching system. Minimized optical reflectance is also demonstrated with the fabricated nano-arrays. Overall, this work highlights the technological potency of utilizing a simple wet-chemistry-only fabrication scheme, instead of reactive dry etching, to attain three-dimensional Si nanostructures with different geometrical morphologies for applications requiring large-scale, low-cost and efficient photon trapping (e.g. photovoltaics).

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Johnny C. Ho

City University of Hong Kong

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Ning Han

Chinese Academy of Sciences

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Fengyun Wang

University of Hong Kong

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SenPo Yip

City University of Hong Kong

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Jared J. Hou

City University of Hong Kong

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Fei Xiu

City University of Hong Kong

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Alvin T. Hui

City University of Hong Kong

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Hao Lin

City University of Hong Kong

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Ming Fang

City University of Hong Kong

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