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A. M. C. Ng,
X. Y. Chen,
F. Fang,
Y. F. Hsu,
A. B. Djurišić,
C. C. Ling, H. L. Tam,
K. W. Cheah,
P. W. K. Fong,
H. F. Lui,
C. Surya,
W. K. Chan
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ABSTRACT: ZnO nanorods have been grown by two inexpensive, solution-based, low-temperature methods: hydrothermal growth and electrodeposition.
Heterojunction n-ZnO nanorods/p-GaN light-emitting diodes have been studied for different nanorod growth methods and different
preparation of the seed layer. We demonstrate that both the nanorod properties and the device performance are strongly dependent
on the growth method and seed layer. All the devices exhibit light emission under both forward and reverse bias, and the emission
spectra can be tuned by ZnO nanorod deposition conditions. Electrodeposition of rods or a seed layer results in yellow emission,
while conventional hydrothermal growth results in violet emission.
Applied Physics B 04/2012; 100(4):851-858. · 2.19 Impact Factor
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ABSTRACT: Multilayer superlens has been reported that it had advantages over the single metal layer superlens. In this work, single silver layer and Ag-SiO2 multilayer superlens devices working at wavelength of 365 nm were fabricated using standard photolithography method. Grating objects with line/space (190 nm/190 nm) resolution could be resolved through both kinds of lens structures with working distance up to 128 nm. However, Ag-SiO2 multilayer lens shows higher transmittance and image contrast than the single silver layer device, the experimental result proves the theoretical calculation.
Journal of Nanoscience and Nanotechnology 12/2011; 11(12):10725-8. · 1.56 Impact Factor
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ABSTRACT: We showed that a Ag-SiO(2)-Ag Fabry-Pérot cavity can be used in near-field imaging based on omnidirectional resonance tunneling. The omnidirectional resonance was experimentally demonstrated in the Ag-SiO(2)-Ag resonant cavity working at a wavelength of 365 nm. The resonant cavity lens with high transmittance and high image fidelity was fabricated using standard photolithography method. Grating source with 190 nm line resolution was imaged through the resonant cavity lens with a total thickness of 128 nm.
Optics Express 02/2010; 18(3):2325-31. · 3.59 Impact Factor
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J. Electrochem. Soc. 01/2010; 157(3):H308-H311.
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A M C Ng,
Y Y Xi,
Y F Hsu,
A B Djurisić,
W K Chan,
S Gwo, H L Tam,
K W Cheah,
P W K Fong,
H F Lui,
C Surya
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ABSTRACT: Light emitting diodes (LEDs) consisting of p-GaN epitaxial films and n-ZnO nanorods have been fabricated and characterized. The rectifying behavior and emission spectra were strongly dependent on the electronic properties of both GaN film and ZnO nanorods. Light emission under both forward and reverse bias was obtained in all cases, and emission spectra could be changed by annealing the ZnO nanorods. The emission spectra could be further tuned by using a GaN LED epiwafer as a substrate. Both forward and backward diode behavior has been observed and the emission spectra were significantly affected by both the properties of the GaN substrate and the annealing conditions for the ZnO nanorods.
Nanotechnology 11/2009; 20(44):445201. · 3.98 Impact Factor
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ABSTRACT: Heterojunction CrO3/ZnO light emitting diodes have been fabricated. Their performance was investigated for different annealing temperature for ZnO nanorods. Annealing in oxygen atmosphere had significant influence on carrier concentration in the nanorods, as well as on the emission spectra of the nanorods. Surprisingly, annealing conditions, which yield the lowest band edge-to-defect emission ratio in the photoluminescence spectra, result in the highest band edge-to-defect emission ratio in the electroluminescence spectra. The influence of the native defects on ZnO light emitting diode performance is discussed.
Applied Physics Letters 05/2009; 94(20):203502-203502-3. · 3.84 Impact Factor
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S W Seto,
T Y Lam, H L Tam,
A L S Au,
S W Chan,
J H Wu,
P H F Yu,
G P H Leung,
S M Ngai,
J H K Yeung,
P S Leung,
S M Y Lee,
Y W Kwan
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ABSTRACT: In this study, we evaluated the pharmacological effects of Ganoderma lucidum (G. lucidum) (water-extract) (0.003, 0.03 and 0.3g/kg, 4-week oral gavage) consumption using the lean (+db/+m) and the obese/diabetic (+db/+db) mice. Different physiological parameters (plasma glucose and insulin levels, lipoproteins-cholesterol levels, phosphoenolpyruvate carboxykinase (PEPCK), 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG CoA reductase) and isolated aorta relaxation of both species were measured and compared. G. lucidum (0.03 and 0.3g/kg) lowered the serum glucose level in +db/+db mice after the first week of treatment whereas a reduction was observed in +db/+m mice only fed with 0.3g/kg of G. lucidum at the fourth week. A higher hepatic PEPCK gene expression was found in +db/+db mice. G. lucidum (0.03 and 0.3g/kg) markedly reduced the PEPCK expression in +db/+db mice whereas the expression of PEPCK was attenuated in +db/+m mice (0.3g/kg G. lucidum). HMG CoA reductase protein expression (in both hepatic and extra-hepatic organs) and the serum insulin level were not altered by G. lucidum. These data demonstrate that G. lucidum consumption can provide beneficial effects in treating type 2 diabetes mellitus (T2DM) by lowering the serum glucose levels through the suppression of the hepatic PEPCK gene expression.
Phytomedicine: international journal of phytotherapy and phytopharmacology 01/2009; 16(5):426-36. · 2.17 Impact Factor
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ABSTRACT: In this work, we proposed a resonant half-cylindrical far field superlens by combining the strong hyperbolic dispersion relationship with the coupled Fabry–Perot cavities. The half-cylindrical far field superlens consisting of the resonant and nonresonant Ag/GaP multilayer are simulated and compared under red light illumination. The calculated results reveal that the resonant far field superlens with coupled Fabry–Perot cavities has much higher transmission efficiency than that of the nonresonant far field superlens and maintains a high resolution.
Journal of Applied Physics 12/2008; · 2.17 Impact Factor
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ABSTRACT: The optical bistability and multistability in one-dimensional photonic crystal with the periodic metal-dielectric structure is investigated theoretically. In linear transmission, a structure with N periods will support N−1 resonant modes which correspond to the transmission peaks. Strong localized effect in these resonant modes is obtained. Optical bistability and multistability can be achieved when the incident wavelength is close to a resonance, which can be seen as an effect of the dynamic shifting of the wavelength of the resonant modes. It is found that the threshold for optical bistability in the periodic resonant structure is lower than the nonresonant metal-dielectric structure.
Applied Physics Letters 05/2008; 92(21):211109-211109-3. · 3.84 Impact Factor
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ABSTRACT: Metamaterials with isotropic property have been shown to possess novel optical properties such as a negative refractive index that can be used to design a superlens. Recently, it was shown that metamaterials with anisotropic property can translate the high-frequency wave vector k values from evanescence to propagating. However, electromagnetic waves traveling in single-layer anisotropic metamaterial produce diverging waves of different spatial frequency. In this work, it is shown that, using bilayer metamaterials that have complementary anisotropic property, the diverging waves are recombined to produce a subwavelength image, i.e., a superlens device can be designed. The simulation further shows that the design can be achieved using a metal/oxide multilayer, and a resolution of 30 nm can be easily obtained in the optical frequency range.
Journal of Applied Physics 12/2007; 102(11):116101-116101-3. · 2.17 Impact Factor
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A B Djurišić,
Y H Leung,
K H Tam,
Y F Hsu,
L Ding,
W K Ge,
Y C Zhong,
K S Wong,
W K Chan, H L Tam,
K W Cheah,
W M Kwok,
D L Phillips
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ABSTRACT: Defects in three different types of ZnO nanostructures before and after annealing under different conditions were studied. The annealing atmosphere and temperature were found to strongly affect the yellow and orange-red defect emissions, while green emission was not significantly affected by annealing. The defect emissions exhibited a strong dependence on the temperature and excitation wavelength, with some defect emissions observable only at low temperatures and for certain excitation wavelengths. The yellow emission in samples prepared by a hydrothermal method is likely due to the presence of OH groups, instead of the commonly assumed interstitial oxygen defect. The green and orange-red emissions are likely due to donor acceptor transitions involving defect complexes, which likely include zinc vacancy complexes in the case of orange-red emissions.
Nanotechnology 01/2007; 18(9):095702. · 3.98 Impact Factor
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ABSTRACT: The coupling of surface plasmons to the photonic modes in hexagonal textured metallic microcavity was studied. The modified photonic modes enable efficient coupling with the luminescence source in the microcavity. Hexagonal photonic crystal lattice has higher folding symmetry providing more channels for surface plasmon coupling in different in-plane directions, i.e., more isotropic light extraction profile than one—or two-dimensional gratings. Results show that strong coupling between surface plasmon modes and the waveguide mode in the microcavity has led to angle-selective enhanced light extraction and it was as much as 12 times more light extracted compare to planar microcavity.
Applied Physics Letters 09/2006; 89(13):131123-131123-3. · 3.84 Impact Factor
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Applied Physics Letters 04/2005; 86(18):186102-186102-2. · 3.84 Impact Factor
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ABSTRACT: Microcavity organic light emitting diodes (OLEDs) have attracted great attention because they can reduce the width of emission spectra from organic materials enhance brightness and achieve multipeak emission from the same material. In this work, we have fabricated microcavity OLEDs with widely used organic materials, such as N,N'-di(naphthalene-1-yl)-N,N'-diphenylbenzidine (NPB) as a hole transport layer and tris (8-hydroxyquinoline) (Alq) as emitting and electron transporting layer. These organic materials are sandwiched either between two thick silver mirrors or one thin copper and one thick silver mirrors. The influence of total cavity length (from 164 nm to 243 nm) and the cavity Q-factor to the emission behavior has been investigated. In all cases, an OLED without bottom mirror, i.e. with the organic materials sandwiched between indium tin oxide and a thick silver mirror, has been fabricated for comparison. We have characterized the devices with photoluminescence, electroluminescence, and reflectance measurements. Multiple peaks have been observed for some devices at larger viewing angles
Optoelectronic and Microelectronic Materials and Devices, 2004 Conference on; 01/2005
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ABSTRACT: Photonic microcavity promises to be one of the photonic devices that can have immediate applications such as superbright LED and low threshold laser. Most photonic crystal structures currently used on microcavity are cubic or hexagonal, whose folding symmetry is no greater than 6. In this work, we fabricated 2-D photonic microcavity with Penrose quasicrystal pattern and measured the angular resolved transmission and photoluminescence spectra of the microcavity. From the experimental result it is found that isotropic photonic band gap exists in the photonic microcavity with the Penrose quasicrystal pattern.
Lasers and Electro-Optics, 2003. CLEO/Pacific Rim 2003. The 5th Pacific Rim Conference on; 01/2004
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ABSTRACT: Microcavity that has inherent photonic band structure within exhibits unique optical characteristics. Based on electron-beam lithography, we have successfully created a two-dimensional wavelength-scale periodic texture on one of the cavity mirrors with nanometer precision. In the microcavity, Bragg scattering is expected to provide a full continuous optical bandgap and flat dispersion of optical waveguide modes in the visible regime. When the luminescing material such as Alq<sub>3</sub> is placed inside the 2-D patterned microcavity, the coupling of the luminescing matter to the photonic eigenmodes of the metallic microcavity is observed. Careful tailoring of the photonic lattice parameters allows us to tune the emission characteristic of the microcavity. From the transmission result, we found that planar microcavity result is in good agreement with the theoretical calculation. For the laterally structured metallic microcavity samples, we found that the dispersion of optical modes inside the microcavity is significantly altered compare with the planar metallic microcavity.
Optoelectronics, Proceedings of the Sixth Chinese Symposium; 10/2003
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ABSTRACT: Plasmas was generated inside pores of porous silicon and the plasma can act as a light source, thus, forming a solid state plasma emission device. Porous silicon layer was etched from n<sup>+</sup> silicon using electrochemical method. A top layer of metal alloy was deposited as top contact, and the bottom contact is Al. By biasing the top contact positive, it was successful to generate the plasma at a voltage as low as 19 V DC. The cause of ionization of the gas is attributed to electron emission from sharp tips within the pores under the introduction of high field created inside the pores. In reduced air/nitrogen pressure, strong nitrogen plasma lines were observed. The strongest peak of the UV electroluminescence (EL) occurs at 337 nm. Although red electroluminescence from porous silicon itself can be observed, it is order of magnitude smaller than that of N<sub>2</sub> plasma emission. By replacing the air/nitrogen with argon, Ar plasma emission can be obtained (main peak at 750.5 nm). This shows that colour tunability is possible by introducing different gases into porous silicon. Although power output from the emission is estimated to be of the order of μW, there is a lot room for improvement such as replace the metal contact by transparent conducting oxide like ITO and also adopt pulse operation would potentially generate higher power output. The results show that the device has the potential in plasma display and bio-agent detection applications.
Optoelectronics, Proceedings of the Sixth Chinese Symposium; 10/2003
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ABSTRACT: A hexagonal lattice photonic crystal was fabricated inside the metallic microcavity. And a thin film of Alq3 was incorporated inside the textured cavity as an active medium. The microcavity is designed such that the modified photonic modes due to the textured structure can couple to the excited electronic states of Alq3. This leads to changes in the emission characteristics of Alq3. From the angle-resolved transmission (ARTR) results, the photonic bandgap was observed at all angles from normal incident to 60°. The presence of surface plasmon (SP) was observed in both TM and TE modes of the transmission. Compare to the bulk Alq3 photoluminescence spectrum, significant modification of the photoluminescence (PL) spectrum was observed in the angle-resolved photoluminescence (ARPL). The photoluminescence spectra showed clear suppression in luminescence intensity for the range inside the photonic bandgap. We use decouple approximation for the standing wave modes and derive the photonic waveguide characteristics for two-dimensional textured metallic microcavities. The theoretical result is in good agreement to the experimental result.
MRS Proceedings. 12/2002; 797.
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ABSTRACT: Mirage technique is proved to be powerful in measurements of thermal diffusivity. Its contactless nature makes it suitable for delicate samples such as thin films and single crystals. However, as the damping of the thermal wave profile increases progressively upon the decrease in thermal diffusivity of the medium, mirage technique becomes more difficult to be applied to low thermal diffusivity measurements. Moreover influences from substrate signals make analysis difficult when the samples are thermally thin. Recently a thermal-wave-coupling method for mirage signal analysis [P. K. Wong, P. C. W. Fung, H. L. Tam, and J. Gao, Phys. Rev. B 51, 523 (1995)] was reported for thermal diffusivity measurements of thin film down to 60 nm thick. In this article we apply the thermal-wave-coupling method to thin films of low thermal diffusivity, especially polymer films. A new lower limit of thermal diffusivity measurable by mirage technique has been reached. © 1998 American Institute of Physics.
Journal of Applied Physics. 12/1998; 84(12):6623-6627.
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ABSTRACT: The two‐beam photoacoustic phase measurement was applied to measure quantitatively the thermal diffusivity (α s ) of a ceramic bulk high‐T c superconductor. Neglecting the effects of thermal dilation, and thermoelastic bending was proved valid in accordance with our composite piston model for the chosen experimental conditions. It was found that α s shows different features at the onset and offset temperatures corresponding to the normal–superconducting (NS) transition. A dip was seen at the resistivity transition onset temperature and a cusp at the offset temperature where the electrical resistance disappears. The presence of the cusp at the offset temperature is proposed to be related to weak coupling between superconducting grains. Our studies indicate that the two‐beam phase measurement is a very sensitive method for superconductor characterization and NS transition detection. The experimental results also confirm the presence of a large energy gap and strong electron–phonon coupling mechanism in the YBCO superconductor. © 1996 American Institute of Physics.
Review of Scientific Instruments 05/1996; · 1.37 Impact Factor
