Browsing by Author "Kuo, C. C."

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Bipolar resistive switching characteristics of Gd2O3 thin film structure
(2011)
Chang, K. M.
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Tzeng, W. H.
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Liu, K. C.
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Chan, Y. C.
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Kuo, C. C.
The resistive switching (RS) behavior of the Ti/Gd2O3/Pt capacitor structure is fabricated and discussed in this paper. The switching characteristics operated under positive bias exhibits stable switching properties with a condensed voltage and resistance values dispersion, while the switching characteristics becomes unstable and large fluctuation on switching parameters under the negative bias operation. We suggest that the anode electrode plays an important role to the switching characteristics, and might be the causes of the asymmetry of the I-V curves between positive and negative operation. Constant voltage stress measurement is also tested to reveal the switching mechanism of the Gd2O3 film, and the switching mechanism is mainly based on the applied voltage and thermal Joule heat.
Crystal symmetry breaking of wurtzite to orthorhombic in nonpolar a-ZnO epi-films
(2009)
Kuo, C. C.
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Liu, W. -R.
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Hsieh, W. F.
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Hsu, C. -H.
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Hsu, H. C.
Crystal symmetry breaking of wurtzite C(6V) to orthorhombic C(2V) due to in-plane anisotropic strain was investigated for nonpolar a-ZnO epi-films grown on R-sapphire.
Crystal symmetry breaking of wurtzite to orthorhombic in nonpolar a-ZnO epifilms
(2009-07-06)
Kuo, C. C.
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Liu, W. -R.
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Hsieh, W. F.
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Hsu, C. -H.
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Hsu, H. C.
Crystal symmetry breaking of wurtzite C-6V to orthorhombic C-2V due to in-plane anisotropic strain was investigated for nonpolar (11 (2) over bar0) ZnO epifilms grown on the R-sapphire. X-ray diffraction results reveal the epilayer is subjected to a compressive strain along the polar c-axis and tensile strains along both a-[11 (2) over bar0] surface normal and in-plane p-[1 (1) over bar 00] axis. The polarized Raman spectra of E-2 modes reveal violation of the C-6V selection rules. Oppositely, the C-2V configuration satisfies the selection rules for the Raman modes. The observed E-1 and E-2 bands in polarized optical reflection and photoluminescence spectra confirm the anisotropic strain causes the structure change to the orthorhombic one. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3159470]
Electrochemical Degradation of Nafion Ionomer to Functionalize Graphene As a Support for Core-Shell Palladium-Ruthenium Alloy @ Platinum Electrocatalysts
(2016-01-01)
Kuo, C. C.
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Chang, Y. C.
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Chou, C. L.
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Chou, S. C.
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Wu, P. W.
A simple but effective electrochemical route to functionalize graphene is demonstrated. Cyclic voltammetric sweeps are performed in H2SO4 aqueous solution on electrodes containing carbon cloth, graphene, and Nafion ionomer. With supply of ambient oxygen, the formation of hydroxyl radicals from the oxygen reduction reaction during CV cycles initiates the decomposition of Nafion ionomer that engenders oxygenated functional groups on the graphene surface. Raman analysis suggests a minor change for the graphene structure. Exploring various amounts of Nafion ionomer, we determine the optimized conditions for graphene functionalization. Contact angle is used to evaluate the effect of Nafion ionomer decomposition. X-ray photoelectron spectroscopy is employed to study relevant functional groups. Afterwards, nanoparticles of Pd9Ru are synthesized and impregnated on those functionalized graphene (FGN) via a wet chemical reflux process. X-ray diffraction patterns of the as-synthesized samples suggest successful formation of alloy. Images from transmission electron microscope confirm the average size of 3-4 nm. As expected, the Pd9Ru alloy are much more dispersive in FGN rather than in the one without functionalization.
Improvement of Crystalline and Photoluminescence of Atomic Layer Deposited m-Plane ZnO Epitaxial Films by Annealing Treatment
(2012-10-01)
Yang, S.
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Lin, B. H.
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Kuo, C. C.
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Hsu, H. C.
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Liu, W-R
Monocrystalline m-plane ZnO epitaxial films with flat surface morphology were grown on m-plane sapphire by using atomic layer deposition. X-ray diffraction and transmission electron microscopy measurements verify not only the in-plane epitaxial relationship of the as-grown films as (10 (1) over bar0)< 0001 >(ZnO)parallel to(10 (1) over bar0)<(1) over bar2 (1) over bar0 > Al2O3 but also the absence of domains with undesirable orientations, which are generally obtained in the m-plane ZnO films grown by other methods. Experimental results indicate that the basal plane stacking fault (BSF) is the dominant structural defects that contribute to the emission at 3.31 eV in m-plane ZnO films. Exactly how thermal annealing affects the structural and optical properties of ZnO epi-films was also investigated. Additionally, based on time-resolved photoluminescence at 5 K, the decay time of BSF related emission and near-band-edge (NBE) emission were determined. Results of this work further demonstrated that the decay time of NBE emission increases with a higher annealing temperature, accompanied by an improvement in crystal structure.
Optical properties of one- and two-dimensional excitons in m-plane ZnO/MgZnO multiple quantum wells
(2016-03-09)
Chen, H. R.
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Tsai, C. Y.
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Huang, Y. C.
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Kuo, C. C.
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Hsu, H. C.
Five pairs of ZnO/Zn0.9Mg0.1O multiple quantum wells (MQWs) with fixed barrier thickness of 55 nm and three well widths of 4, 8 and 16 nm have been grown on m-plane sapphires by pulsed laser deposition. Due to 2D quantum confinement with decreasing well width, the emission of excitons bound to the basal-plane stacking faults, which are one-dimensionally confined in MQWs, encounters larger blue shift than that of the near-band edge excitons. Furthermore, remarkably reducing coupling of free excitons with A1 longitudinal optical phonons is closely correlated with increasing exciton binding energy but enhanced coupling of E-2-low phonons is a result of increasing interaction with the interface phonons with decreasing well width.
Photoluminescence associated with basal stacking faults in c-plane ZnO epitaxial film grown by atomic layer deposition
(2012-03-05)
Yang, S.
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Kuo, C. C.
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Liu, W. -R.
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Lin, B. H.
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Hsu, H. -C.
Basal plane stacking faults (BSFs) with density of similar to 1 x 10(6) cm(-1) are identified as the dominant defect in the annealed ZnO thin films grown on c-plane sapphire by atomic layer deposition. The dominant peak centered at 3.321 eV in low-temperature photoluminescence measurements is attributed to the emission from the BSFs. The emission mechanism is considered to be the confined indirect excitons in the region of quantum-well-like structure formed by the BSFs. The observed energy shift of 19 meV with respect to the BSF-bounded exciton at low temperature may be caused by the localization effect associated with the coupling between BSF quantum wells. (C) 2012 American Institute of Physics. [http://dx.doi. org/10.1063/1.3692730]
Recombination dynamics of a localized exciton bound at basal stacking faults within the m-(p)lane ZnO film
(2014-07-07)
Yang, S.
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Hsu, H. C.
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Liu, W-R.
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Lin, B. H.
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Kuo, C. C.
We investigated the carrier dynamics near basal stacking faults (BSFs) in m-plane ZnO epitaxial film. The behaviors of the type-II quantum wells related to the BSFs are verified through time-resolved and time-integrated photoluminescence. The decay time of the emission of BSFs is observed to have a higher power law value and longer decay time than the emission of the donor-bound excitons. The spectral-dependent decay times reveal a phenomenon of carriers migrating among band tail states, which are related to the spatial distribution of the type-II quantum wells formed by the BSFs. A high density of excited carriers leads to a band bending effect, which in turn causes a blue-shift of the emission peak of BSFs with a broadened distribution of band tail states. (C) 2014 AIP Publishing LLC.
Single Domain m-Plane ZnO Grown on m-Plane Sapphire by Radio Frequency Magnetron Sputtering
(2012-10-01)
Lin, B. H.
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Liu, W. -R
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Lin, C. Y.
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Hsu, S. T.
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Yang, S.
High-quality m-plane orientated ZnO films have been successfully grown on m-plane sapphire by using radio frequency magnetron sputtering deposition. The introduction of a nanometer-thick, low-temperature-grown ZnO buffer layer effectively eliminates inclusions of other undesirable orientations. The structure characteristics of the ZnO epi-layers were thoroughly studied by synchrotron X-ray scattering and transmission electron microscopy (TEM). The in-plane epitaxial relationship between ZnO and sapphire follows (0002)(ZnO) parallel to (11 (2) over bar0)(sapphire) and (11 (2) over bar0)(ZnO) parallel to (0006)(sapphire) and the ZnO/sapphire interface structure can be described by the domain matching epitaxy along the [11 (2) over bar0](ZnO) direction. The vibrational properties of the films were investigated by polarization dependent micro-Raman spectroscopy. Both XRD and micro-Raman results reveal that the obtained m-ZnO layers are tinder an anisotropic biaxial strain but still retains a hexagonal lattice.
Surface-bound-exciton emission associated with domain interfaces in m-plane ZnO films
(1970-01-01)
Kuo, C. C.
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Lin, B. H.
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Yang, Song
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Liu, W. R.
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Hsieh, W. F.
"Small amount of (10 (1) over bar3)(ZnO) domains were found in the m-plane ZnO films grown on m-sapphire by pulsed laser deposition, which provide strain relaxation of the m-ZnO matrix behaving as a low strain layer. Through carefully correlating low-temperature polarized photoluminescence spectra with the x-ray diffraction peak intensity ratio of (10 (1) over bar3)(ZnO)/(10 (1) over bar0)(ZnO) of the samples grown at different temperature and after thermal treatment, we found that the broad-band emission around 3.17 eV may result from the interface defects trapped excitons at the boundaries between the (10 (1) over bar3)(ZnO) domains and the m-ZnO matrix. The more (10 (1) over bar3)(ZnO) domains in the m-ZnO layer cause the more surface boundary that makes the stronger surface-bound-exciton emission. And the a-axes of both the (10 (1) over bar3)(ZnO) domains and the m-ZnO matrix are aligned with the c-axis of the sapphire (alpha-Al2O3) substrate. The c-axis of the (10 (1) over bar3)(ZnO) domains rotates by about +/- 59 degrees against the common a-axis of the m-ZnO. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4732140]"
The Growth of an Epitaxial ZnO Film on Si(111) with a Gd(2)O(3)(Ga(2)O(3)) Buffer Layer
(2011-07-01)
Lin, B. H.
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Liu, W. R.
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Yang, S.
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Kuo, C. C.
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Hsu, C. -H.
High-quality (0001)-oriented ZnO epitaxial films have been grown by pulsed laser deposition on Si(111) buffered with a nanometer-thick Gd(2)O(3)(Ga(2)O(3)), GGO, layer. The structural characteristics of the ZnO epi-layers were studied by X-ray diffraction and transmission electron microscopy (TEM). The in-plane epitaxial relationship between the wurtzite ZnO, cubic GGO, and cubic Si follows {10 (1) over bar0}(ZNO)parallel to{4 (22) over bar}(Gd2O3)parallel to{(4) over bar 22}(Si) and the ZnO/GGO interface can be described by the domain matching epitaxy. TEM contrast analysis reveals that the major defect structures in the ZnO films are edge-type threading dislocations and intrinsic basal plane stacking faults. All the ZnO epi-films studied are under a tensile biaxial strain, but no cracks were found. Temperature-dependent photoluminescence results show the excellent optical properties of the obtained ZnO layers, and the origins of the spectral features are discussed.
The Growth of an Epitaxial ZnO Film on Si(111) with a Gd2O3(Ga2O3) Buffer Layer
(2011-07-01)
Lin, B. H.
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Liu, W. R.
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Yang, S.
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Kuo, C. C.
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Hsu, C. -H.
High-quality (0001)-oriented ZnO epitaxial films have been grown by pulsed laser deposition on Si(111) buffered with a nanometer-thick Gd2O3(Ga2O3), GGO, layer. The structural characteristics of the ZnO epi-layers were studied by X-ray diffraction and transmission electron microscopy (TEM). The in-plane epitaxial relationship between the wurtzite ZnO, cubic GGO, and cubic Si follows {10 (1) over bar0}(ZNO)parallel to{4 (22) over bar}(Gd2O3)parallel to{(4) over bar 22}(Si) and the ZnO/GGO interface can be described by the domain matching epitaxy. TEM contrast analysis reveals that the major defect structures in the ZnO films are edge-type threading dislocations and intrinsic basal plane stacking faults. All the ZnO epi-films studied are under a tensile biaxial strain, but no cracks were found. Temperature-dependent photoluminescence results show the excellent optical properties of the obtained ZnO layers, and the origins of the spectral features are discussed.
The influence of dislocations on optical and electrical properties of epitaxial ZnO on Si (111) using a gamma-Al2O3 buffer layer
(2012)
Liu, W. -R.
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Lin, B. H.
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Yang, S.
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Kuo, C. C.
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Li, Y. -H.
The structural, optical and electrical properties of the c-plane ZnO epitaxial films grown by pulsed laser deposition on a Si(111) substrate buffered with a thin layer of gamma-Al2O3 were investigated by X-ray diffraction, transmission electron microscopy, photoluminescence (PL) and Hall measurements. Detailed structural investigation showed that the dominant structural defects in the ZnO films are threading dislocations (TDs). Experimental results manifest the edge-and screw-type of TDs influence the optical and electric properties differently; the intensity ratio between the PL yellow-green band to near band edge emission and the carrier concentration are affected mainly by the edge TD, and the FWHM of the near band edge emission is dominantly influenced by the screw TD.
Thickness-dependent lattice relaxation and the associated optical properties of ZnO epitaxial films grown on Si (111)
(2012)
Liu, W. -R.
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Lin, B. H.
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Kuo, C. C.
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Lee, W. C.
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Hong, M.
The evolution of the strain state as a function of layer thickness of (0001) oriented ZnO epitaxial films grown by pulsed-laser deposition on Si (111) substrates with a thin oxide Y2O3 buffer layer was investigated by high resolution X-ray diffraction (XRD). The ZnO layers experience a tensile strain, which gradually diminishes with increasing layer thickness. Regions with a nearly strain-free lattice develop as the layer thickness exceeds a critical value and are correlated with the emergence of the < 11 (2) over bar0 > oriented crack channels. The influence of the biaxial strain to the vibrational and optical properties of the ZnO layers were also studied by micro-Raman, optical reflectance, and photoluminescence. The deformation-potential parameters, a(lambda) and b(lambda), of the E-2(high) phonon mode are determined to be -740.8 +/- 8.4 and -818.5 +/- 14.8 cm(-1), respectively. The excitonic transitions associated with the FXA, FXB, and D degrees X-A emissions and the A-exciton binding energy all show linear dependence on the in-plane strain with a negative slope.
Vertical-cavity and randomly scattered lasing from different thicknesses of epitaxial ZnO films grown on Y2O3-buffered Si (111)
(2013-01-28)
Kuo, C. C.
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Liu, W. -R.
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Lin, B. H.
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Hsieh, W. F.
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Hsu, C. -H.
Two different types of lasing modes, vertical Fabry-Perot cavity and random lasing, were observed in ZnO epi-films of different thicknesses grown on Si (111) substrates. Under optical excitation at room temperature by a frequency tripled Nd:YVO4 laser with wavelength of 355 nm, the lasing thresholds are low due to high crystalline quality of the ZnO epitaxial films, which act as microresonators. For the thick ZnO layer (1,200 nm), its lasing action is originated from the random scattering due to the high density of crack networks developed in the thick ZnO film. However, the low crack density of the thin film (555 nm) fails to provide feedback loops essential for random scattering. Nevertheless, even the lower threshold lasing is achieved by the Fabry-Perot cavity formed by two interfaces of the thin ZnO film. The associated lasing modes of the thin ZnO film can be characterized as the transverse Gaussian modes attributed to the smooth curved surfaces. (C) 2013 Optical Society of America