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ABSTRACT: The wide-gap semiconductor ZnO with nanostructures such as nanoparticle, nanorod, nanowire, nanobelt, nanotube has high potential for a variety of applications. This article reviews the fundamentals of one-dimensional ZnO nanostructures, including processing, structure, property, application and their processing-microstructure-property correlation. Various fabrication methods of the ZnO nanostructures including vapor-liquid-solid process, vapor-solid growth, solution growth, solvothermal growth, template-assisted growth and self-assembly are introduced. The characterization and properties of the ZnO nanostructures are described. The possible applications of these nanostructures are also discussed.
Journal of Nanoscience and Nanotechnology 06/2012; 12(6):4409-57. · 1.56 Impact Factor
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ABSTRACT: Several emerging nonvolatile memories (NVMs) such as ferroelectric memory, magnetoresistive rams and ovonic universal memory
are being developed for possible applications. Resistive random access memory (RRAM) is another interesting competitor in
the class of NVMs. The RRAM is based on a large change in electrical resistance when the memory film is exposed to voltage
or current pulses, and can keep high or low resistance states without any power. The ideal RRAM should have the superior properties
of reversible switching, long retention time, multilevel switching, simple structure, small size, and low operating voltage.
Perovskite oxides, transition metal oxides, and molecular materials were found to have resistive memory properties. This presentation
reviews the ongoing research and development activities on future resistance NVMs technologies incorporating these new memory
materials. The possible basic mechanisms for their bistable resistance switching are described. The effect of processing,
composition, and structure on the properties of resistive memory materials and consequently the devices are discussed.
Journal of Electroceramics 04/2012; 21(1):61-66. · 1.19 Impact Factor
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ABSTRACT: A series of anatase phase Fe-doped TiO2 nanoparticles are prepared by a modified sol-gel method. Spontaneous Raman spectroscopy is utilized to characterize the crystal structures of these nanoparticles and investigate their structural transformation under the exposure of a 532 nm green laser. The anatase phase of TiO2 can be effectively converted into the rutile phase with the assistance of Fe doping. It is found that the critical laser intensity for phase transformation decreases with increasing the Fe content. We ascribe this tendency to the enhanced optical absorption and the photo-induced thermal heating effect, which can be associated with the defect structure within the bandgap of Fe- TiO2 nanoparticles. Our study demonstrates an all-optical approach to pump and probe the phase transformation of metal-doped TiO2 nanoparticles.
Nanotechnology 09/2009; 20(31):315702. · 3.98 Impact Factor
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ABSTRACT: The stabilization of the resistive switching properties is necessary to realize the memory application of the SrZrO<sub>3</sub>(SZO)-based resistive switching devices. During continuous resistive switching cycle, broad variations of the resistive switching parameters of the SZO-based memory devices can be improved by a thin embedded Cr layer. The Cr metal layer is proposed to diffuse into and dope the SZO thin film to produce the space charge region, further reducing the effective resistive switching region. Hence, the good stabilization of the resistive switching properties can be obtained in the SZO films with embedded Cr layer.
IEEE Electron Device Letters 11/2008; · 2.85 Impact Factor
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ABSTRACT: Single crystalline ZnO nanowires were synthesized by hydrothermal process and then formed nano-tubes by acidic etching these nanowires in acetic solution at 85 degrees C. The nanotube diameter can be easily controlled by dividing the nanowires growth and etching process. The ZnO nanotubes remain single crystalline hexagonal structure after the etching process. The defects existed in the nanowires and the dangling bonds of the nanowires' surface play the important roles for the etching process. An etching model for forming ZnO nanotubes is proposed, which can be proved by our experimental results.
Journal of Nanoscience and Nanotechnology 10/2008; 8(9):4432-5. · 1.56 Impact Factor
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ABSTRACT: Well directionally grown Ce-doped ZnO nanowires were successfully synthesized by a simple hydrothermal method. The Ce dopant plays a key role in evolving the morphology, affecting the crystalline size, and forming the uniform nanostructure of the ZnO nanowires. The amount of Ce dopant in the ZnO nanowires also affects the regions of blue-shift in the UV and green emission peaks and the intensities of emission peaks based on the cathodoluminescence spectra of the nanowires. Moreover, the effect of Ce doping amount on the microstructure of the nanowires is also presented.
Journal of Nanoscience and Nanotechnology 10/2008; 8(9):4514-9. · 1.56 Impact Factor
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ABSTRACT: The influence of top electrode material on the resistive switching properties of ZrO<sub>2</sub>-based memory film using Pt as a bottom electrode was investigated in this letter. In comparison with Pt/ZrO<sub>2</sub>/Pt and Al/ZrO<sub>2</sub>/Pt devices, the Ti/ZrO<sub>2</sub>/Pt device exhibits different resistive switching current-voltage (I- V) curve, which can be traced and reproduced by a dc voltage more than 1000 times only showing a little decrease of resistance ratio between high and low resistance states. Furthermore, the broad dispersions of resistive switching characteristics in the Pt/ZrO<sub>2</sub>/Pt and Al/ZrO<sub>2</sub>/Pt devices are generally observed during successive resistive switching, but those dispersions are suppressed by the device using Ti as a top electrode. The reliability results, such as cycling endurance and continuous readout test, are also presented. The write-read-erase-read operations can be over 10<sup>4</sup> cycles without degradation. No data loss is found upon successive readout after performing various endurance cycles
IEEE Electron Device Letters 06/2007; · 2.85 Impact Factor
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ABSTRACT: The back-propagation network (BPN) is a popular data mining technique. Nevertheless, different problems may require different network architectures and parameters. Therefore, rule of thumb or "try and error" methods are usually used to determine them. However, these methods may lead worse network architectures and parameters. A dataset may contain many features; however, not all features are beneficial for classification in BPN. Therefore, a simulated annealing (SA) approach is proposed to select the beneficial subset of features and to obtain the better network architectures and parameters which result in a better classification. In order to verify the developed approach, three dataset, namely PIMA, IONOS, and CANCER from UCI (University of California, Irvine) machine learning database, are employed for evaluation, and the 10-fold cross-validation is applied to calculate the classification result. Compared with the MONNA (multiple ordinate neural network architecture) structure developed by Leazoray and Cardot, the classification accurate rates of the developed approach are superior to those of the MONNA. When the feature selection is taken into consideration, the classification accurate rates of three dataset are increased. Therefore, the developed approach can be utilized to find out the network architecture and parameters of BPN, and discover the useful attributes effectively.
Systems, Man and Cybernetics, 2006. SMC '06. IEEE International Conference on; 11/2006
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ABSTRACT: Support Vector Machine (SVM) is a new technique for pattern classification, and is used in many applications. Kernel parameters set in the SVM training process, along with feature selection, will significantly impact classification accuracy. The objective of this paper was to simultaneously optimize parameters while finding a subset of features without degrading SVM classification accuracy. A simulated annealing (SA) approach for feature selection and parameters optimization was developed. Several UCI datasets are tested using the SA-based approach and the grid algorithm which is a traditional method of performing parameter searching. The developed SA-based approach was also compared with other approaches proposed by Fung and Mangasarian, and Liao et al. Results showed that the proposed SA-based approach significantly improves the classification accuracy rate and requires fewer input features for the SVM.
Systems, Man and Cybernetics, 2006. SMC '06. IEEE International Conference on; 11/2006
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ABSTRACT: In order to satisfy increasing demand, Internet Content Providers (ICP) must improve the respective performances of software, hardware and network devices in order to maintain the quality of transmission service and market competitiveness. However, the costs of software, hardware and maintenance may be too high for ICP. This research proposes a mixed client/server and Peer to Peer (P2P) system which includes four modules: (1) a network traffic analysis module, (2) a service mode switching module, (3) a hash table database module, (4) a Chord P2P Module. This system makes high-quality network service available at a low cost. The system reduces network congestion by dynamically adjusting application layer service, especially the network layer's packet loss rate. The simulation results show that using a mixed client/server and P2P system can reduce the packet loss rate of the server effectively when the node approaches the loading threshold, and can enable the client to complete the required services on schedule.
Systems, Man and Cybernetics, 2006. SMC '06. IEEE International Conference on; 11/2006
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ABSTRACT: In the analytic hierarchy process (AHP), the pairwise comparisons are generally applied to determine the weights of multiple criteria at the same level or the ranks of alternatives under a specific criterion. However, when one must rate the importance of multiple criteria and each criterion uses different measurement units, or when one must determine the ranks of alternatives under a qualitative criterion, there is always an inconsistency problem. This research, based on complete transitivity of preference, develops a single stage recursive algorithm to find out outliers, and enables the pairwise comparison matrix to approximate complete transitivity. Identifying and adjusting of outliers are proven to be identical with the robust priority estimation method. Inconsistency adjustment using the complete transitivity convergence algorithm in a single stage can be applied in the multi-criteria decision problems with high calculation economy.
Systems, Man and Cybernetics, 2006. SMC '06. IEEE International Conference on; 11/2006
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ABSTRACT: The resistive switching behaviors of sputtered V-doped SrZrO<sub>3 </sub> (V:SZO) memory films were investigated in this letter. The current states of the memory films were switched between high current state (H-state) and low current state (L-state). The resistance ratio of the two current states was over 1000 at a read voltage. The switching mechanism from L- to H-state corresponds to the formation of current paths. However, this mechanism from Hto L-state is thought to be due to the fact that the defects present in the V:SZO film randomly trap electrons, and hence, the current paths are ruptured. The conduction mechanism of the H-state is dominated by ohmic conduction, whereas the L-state conduction is dominated by Frenkel-Poole emission. The polarity direction of the resistive switching is an intrinsic property of the SrZrO<sub>3</sub> oxides. The V:SZO films with high uniformity and good stability are expected to be used in nonvolatile memory
IEEE Electron Device Letters 10/2006; · 2.85 Impact Factor
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ABSTRACT: The one-dimensional (1-D) nanostructures of cadmium chalcogenides (Il-VI: CdSe, CdTe), InP and GaAs (III-V), and the ternary chalcopyrites CulnS2, CulnSe2, and CulnTe2 (I-III-VI2) are the candidate semiconductors of interest as absorber layers in solar cells. In the confinement regime (approximately 1-10 nm) of these 1-D nanostructures, the electronic energy levels are quantized so that the oscillator strength and the resultant absorption of solar energy are enhanced. Moreover, the discrete energy levels effectively separate the electrons and holes at the two electrodes or at the interfaces with a polymer in a hybrid structure, so that an oriented and 1-D nanostructured absorber layer is expected to improve the conversion efficiency of solar cells. The intrinsic anisotropy of Il-VI and l-lll-VI2 crystal lattices and the progress in various growth processes are assessed to derive suitable morphological features of these 1-D semiconductor nanostructures. The present status of research in nanorod-based solar cells is reviewed and possible routes are identified to improve the performance of nanorod-based solar cells. Finally, the characteristics of nanorod-based solar cells are compared with the dye-sensitized and organic solar cells.
Journal of Nanoscience and Nanotechnology 12/2005; 5(11):1768-84. · 1.56 Impact Factor
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ABSTRACT: We report the results of the fabrication and characterization of Pt/Bi <sub>3.35</sub> La <sub>0.85</sub> Ti <sub>3</sub> O <sub>12</sub> (BLT)/LaNiO <sub>3</sub> (LNO)/Ba <sub>0.7</sub> Sr <sub>0.3</sub> TiO <sub>3</sub> (BST)/Si metal–ferroelectric–metal–insulator–semiconductor (MFMIS) structures for ferroelectric memory field effect transistor applications. The BLT films were deposited on LNO/BST/Si using the metalorganic decomposition method and annealed by rapid thermal annealing (RTA) process at 600 ° C for 3 min. The ratio of remanent polarization to saturation polarization (P<sub>r</sub>/P<sub>s</sub>) increases with reducing area ratio, A<sub>F</sub>/A<sub>I</sub>. A large memory window of 3.1 V can be obtained for a small A<sub>F</sub>/A<sub>I</sub> ratio. By the utilization of 5 mol % MgO doped BST insulator layer, LNO bottom electrode layer for BLT, and small area ratio, A<sub>F</sub>/A<sub>I</sub>=1/12 in the MFMIS structure, large P<sub>r</sub>/P<sub>s</sub> ratio in BLT film and low leakage current and good capacitance matching of the ferroelectric and the insulator in the MFMIS structures have been achieved and, hence, long data retention time ≫10<sup>6</sup> s has been obtained in this study. Experimental results demonstrate the significant progress in increase of the retention time of these structures, which make them attractive for practical ferroelectric memory field effect transistor applications. © 2003 American Institute of Physics.
Applied Physics Letters 09/2003; · 3.84 Impact Factor
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ABSTRACT: In this letter, we present the results of the fabrication and characterization of 5 mol % MgO doped Ba <sub>0.7</sub> Sr <sub>0.3</sub> TiO <sub>3</sub> (BST) films grown on Pt / TiN / SiO <sub> 2</sub> coated on Al <sub>2</sub> O <sub>3</sub> substrates using the rf magnetron sputtering technique. The dielectric and electrical properties of Ba <sub>0.7</sub> Sr <sub>0.3</sub> TiO <sub> 3</sub> thin film were found to improve obviously by means of MgO doping. The leakage current density of BST thin film decreased about 1 order of magnitude on MgO doping, while BST film with MgO doping had a higher dielectric constant than that without MgO doping. The dielectric constant of the films increased with increasing annealing temperature due to the consistent increase in grain size and crystallinity. The 750 °C annealed, 100 nm thick film indicated a high dielectric constant of 440 at 100 kHz and the lattice constant of 3.986 Å. The improvement of the electrical properties of BST films was associated with the reduced oxygen vacancies due to improved oxygenation of BST films in the presence of MgO. The MgO doped BST films exhibited a high tunability of 25% and dc resistivity of 6×10<sup> 10</sup> Ω cm at an applied electric field of 200 kV/cm. The time-dependent dielectric breakdown studies indicated that the films had a longer lifetime of over 10 yrs on operation at the electric field of 0.4 MV/cm which is better than undoped BST film. © 2002 American Institute of Physics.
Applied Physics Letters 04/2002; · 3.84 Impact Factor
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ABSTRACT: In this letter, we present the results of the fabrication and characterization of 5 mol % MgO doped Ba0.7Sr0.3TiO3 (BST) films grown on Pt/TiN/SiO2 coated on Al2O3 substrates using the rf magnetron sputtering technique. The dielectric and electrical properties of Ba0.7Sr0.3TiO3 thin film were found to improve obviously by means of MgO doping. The leakage current density of BST thin film decreased about 1 order of magnitude on MgO doping, while BST film with MgO doping had a higher dielectric constant than that without MgO doping. The dielectric constant of the films increased with increasing annealing temperature due to the consistent increase in grain size and crystallinity. The 750 °C annealed, 100 nm thick film indicated a high dielectric constant of 440 at 100 kHz and the lattice constant of 3.986 Å. The improvement of the electrical properties of BST films was associated with the reduced oxygen vacancies due to improved oxygenation of BST films in the presence of MgO. The MgO doped BST films exhibited a high tunability of 25% and dc resistivity of 6×1010 Ω cm at an applied electric field of 200 kV/cm. The time-dependent dielectric breakdown studies indicated that the films had a longer lifetime of over 10 yrs on operation at the electric field of 0.4 MV/cm which is better than undoped BST film. © 2002 American Institute of Physics.
Applied Physics Letters 03/2002; 80(10):1797-1799. · 3.84 Impact Factor
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ABSTRACT: This paper reviews recent developments in processing, properties and applications of composite and multilayer ferroelectric thin films. Methods such as physical vapor deposition, chemical vapor deposition and sol-gel, for the processing of composite and multilayer ferroelectric films are described. Among the techniques reviewed for the fabrication of multilayer ferroelectric films, molecular beam epitaxy and atomic layer metal-organic chemical vapor deposition are the most suitable techniques for the deposition of superlattices with atomically sharp interface. As an efficient and quick way, pulsed-laser deposition has been widely used for the preparation of ferroelectric multilayers and heterostructures. Superior dielectric properties have been reported for sol-gel-derived micrometer-thick ceramic/ceramic composite ferroelectric films. Properties of multilayer ferroelectric films vary as a function of periodicity, which can be exploited for the development of various electronic devices. Enhanced characteristics of composite and multilayer films with selected examples from recent literature and the origin of enhancement are discussed and summarized. Finally, applications of the materials for the development of various electronic devices are also presented.
Journal of Materials Science Materials in Electronics 01/2002; 13(8):439-459. · 1.08 Impact Factor
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ABSTRACT: A series of Al/Ba0.5Sr0.5TiO3(BST)/sapphire multi-layered coplanar waveguide (CPW) transmission lines of different geometries and thin-film configurations was fabricated. We employed an accurate on-wafer Through-Line-Reflect (TRL) calibration technique and quasi-TEM analysis to measure the dielectric constant, loss tangent, and tunability of BST thin films using this CPW structure. Experimental results show that the overall insertion loss is less than 3 dB/cm even at frequencies as high as 20 GHz, which is the lowest obtained to date for metal/BST CPW devices. This result indicates that, with optimized impedance matching, normal conductors are also possibly suitable for fabricating low-loss tunable phase-shifter devices.
IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control 12/2001; 48(6):1640-7. · 1.69 Impact Factor
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ABSTRACT: The influence of bottom electrodes (Pt, Ir, Ru) on the degradation
of (Ba,Sr)TiO<sub>3</sub> (BST) thin films under dc stress conditions
was investigated. The current-time (I-t) and current-voltage (I-V)
measurement results indicated that the BST thin films deposited on Ru
have faster degradation than those deposited on Pt and Ir. The
degradation was considered to be caused by the deterioration of the
Schottky-barrier. Under dc stress conditions, the dielectric relaxation
current in the BST dielectric films probably enhances the deterioration.
The breakdown time was found to be approximated by an exponential
function of an electric field [t<sub>B</sub>=α exp(-βE)] for
dc stress. The value of the exponential factor β for BST deposited
on Pt and Ir was about a quarter of that for BST deposited on Ru. The
different value of β observed under dc stress indicates that the
degradation of BST on Ru would be more serious than on Pt and Ir. The
ten years lifetime of time-dependent dielectric breakdown (TDDB) studies
indicate that BST on Pt, Ir and Ru have longer lifetime over ten years
for operation at the voltage bias of 1 V
IEEE Transactions on Components and Packaging Technologies 04/2000; · 0.94 Impact Factor
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ABSTRACT: The ionic and electronic conductivity characteristics and defects in the Ba0.47Sr0.53TiO3 (BST) thin films that were rf-sputtered at 450 °C on a Pt bottom electrode at various O2/(Ar+O2) mixing ratios (OMR) were studied. The dielectric properties specific to the BST films can be explained by considering the influence of the dielectric relaxation phenomenon. Through the measurement of the dielectric dispersion as a function of frequency (100 Hz f10 MHz) and temperature (27 °C T150 °C), we studied the dielectric relaxation and obtained the defect quantity of the films, on the basis of the capacitance, admittance and impedance spectra. The defect density of BST films decreases with an increase of OMR. The majority of electrical conductivity is carried by electrons (electronic conductivity) and not the ionic defects (ionic conductivity).
Journal of Physics D Applied Physics 08/1999; 32(17):2141. · 2.54 Impact Factor
