bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of Fabrication Variables on the Performance of Zinc Oxide Metal-Semiconductor-Metal Photodetectors
Authors: Yen Tingfang , Strome Dave , Kim Sung Jin , DiNezzaa Michael , Cartwright Alexander N. , Anderson Wayne A. 
Published: April 2011

AbstractThe performance of ZnO metal-semiconductor-metal (MSM) photodetectors can be significantly influenced by modifications in the fabrication process. ZnO thin films were deposited onto silicon substrates by radio frequency magnetron sputtering and later annealed by conventional furnace, rapid thermal anneal or laser anneal. The photoluminescence (PL) analysis revealed that laser annealing at 250 mW/cm2 increased the 370 nm peak from 520 to 1700 a.u. and reduced the defect peak from 380 to 20 a.u. MSM photodetectors were fabricated using an interdigitated and parallel pattern. Values of current responsivity ranged from about 0.025 A/W to above 430 A/W depending upon fabrication conditions and design.
Structural and Physical Characterisation of Zinc Oxide Thin Films Prepared from Zinc Acetate via the Sol-gel Method
Authors: O'Brien Shane , Koh Lee H.K. , Copuroglu Mehmet , Crean Gabriel M. 
Published: April 2011

AbstractThe influence of zinc acetate concentration in the range 0.3 – 1.3M and annealing temperature in the range 450 – 550°C on the microstructure of zinc oxide films prepared by the sol-gel method was investigated. Zinc acetate concentration of the sol-gel deposited was found to be the major influence on the microstructure and in particular c-axis or (002) preferred orientation of the resulting film, due to its impact on film thickness, for a single sol-gel deposition employing fixed deposition conditions. Preferentially (002) orientated films were obtained from 0.3M zinc acetate sol-gels. However, an increase in zinc acetate concentration resulted in an increase in film thickness and a loss of preferentially (002) orientation. It was found that thick preferentially (002) oriented films could be produced by using multiple depositions of a 0.7M zinc acetate sol-gel using higher drying temperatures.
Deposition of Piezoelectric ZnO Films by RF Magnetron Sputtering and its Application to SAW Devices
Authors: Choi Seol Hee , Kang Chan Hyoung 
Published: April 2011

AbstractHighly c-axis oriented, dense, and fine-grained polycrystalline ZnO films with smooth surface and high resistivity were deposited on 4 inch silicon wafers by employing ZnO targets in a radio-frequency (RF) magnetron sputtering system. By changing applied RF power, substrate temperature and O2/Ar gas ratio, the optimum process parameters were found to be 150 W, 200 °C and 30/70, respectively. Applying the ZnO films deposited under these optimum conditions, surface acoustic wave (SAW) devices of ZnO/IDT/SiO2/Si structure were fabricated by conventional photolithography and etching processes. The interdigital transducers (IDT), made of the aluminum deposited by DC magnetron sputter, were patterned as 2.5/2.5 μm of finger width/spacing. Another type of SAW filter of IDT/ZnO/diamond/Si structure was fabricated. In this structure, high-quality nanocrystalline diamond (NCD) films were deposited on 4 inch silicon wafers by direct current (DC) plasma assisted chemical vapor deposition method using H2-CH4 mixture as precursor gas. On the top of the diamond films, ZnO films were deposited under the optimum conditions. The aluminum IDT pattern was fabricated on the ZnO/diamond layered films. The characteristics of the fabricated SAW devices were evaluated in terms of center frequency, insertion loss, and wave propagation velocity.
Microwave-assisted synthesis of c-axis oriented ZnO nanorods on a glass substrate coated with ZnO film
Authors: Ogata Ken-ichi , Koike Kazuto , Sasa Shigehiko , Inoue Masataka , Yano Mitsuaki 
Published: April 2011

AbstractZnO nanorods synthesis on a glass substrate coated with ZnO film was performed by means of microwave-assisted heating. Nanorod structure was dependent on the underlying ZnO films; slightly tilted nanorods about 800nm diameter were synthesized on an as-sputtered ZnO film while highly c-axis oriented ones about 100nm diameter were developed on the ZnO film after annealing. Photoluminescence spectra of the ZnO nanorods at 6K showed a badedge excitonic emission with comparable intensity to a visible defect related emission, suggesting the existence of many radiative defects which would be originated from insufficient quality of the underlying ZnO layer. Pattered photoresist layer can successfully be utilized for synthesis of the ZnO nanolods in selective area.
Effect of Growth Conditions on Defect-related Photoluminescence in ZnO Thin Films Grown by Plasma Assisted MBE
Authors: Avrutin Vitaliy , Reshchikov Mikhail A. , Izyumskaya Natalia , Shimada Ryoko , Morkoç Hadis 
Published: April 2011

AbstractThe effect of growth conditions on the luminescence properties of ZnO films grown on a-Al2O3/GaN(0001)/c-Al2O3 templates by plasma-assisted molecular beam epitaxy has been investigated. We observed that the deflecting of the ions produced by the RF oxygen plasma away from substrate results in improved excitonic emission and modification of the defect-related PL spectrum. The intensity of the near-band-edge lines in photoluminescence spectra from the layers grown with the ion deflector deflection was found to increase as compared to the controls grown without the ion deflector. The yellow-green spectral range was dominated by different defect bands in the films grown with and without ion deflection. The effect of RF power on peak positions of the defect band was studied for the films grown without ion deflection.
Gas Sensing Properties of Porous ZnO Nano-Platelet Films
Authors: Saluja Amandeep , Pan Jie , Kerr Lei , Cho Eunjung , Hubbard Seth 
Published: April 2011

AbstractIn this work, various ZnO nanostructures were synthesized and a detailed study on the effect of different process parameters such as temperature, carrier gas flow, inter-electrode spacing, gas concentration and material properties on gas sensitivity was conducted. Initial ZnO nanoparticles were prepared by a simple solution chemical process and characterized by Secondary Electron Microscopy (SEM) and Brunauer, Emmet and Teller (BET) Sorptometer to demonstrate the morphology and surface area respectively. Sensitivity of nano-platelets and porous films was measured for different concentrations of the analytes (H2, CO). High response was observed at room temperature for H2 gas with sensitivities in excess 80% for 60ppm and about 55% for 80ppm of H2 gas at room temperature were observed for the nano-platelets and the porous films respectively with short response and recovery times of about 200 seconds. The sensitivity of the nano-platelets to CO gas was also measured and found to be about near 90% for 80 ppm CO at operating temperatures of 200 °C.
Colloidal Synthesis and Characterization of Optically Active ZnO/ZnS Core/Shell Nanocrystals
Authors: Sankar Krishnaprasad , Akins Brian A. , Memon Tosifa A. , Withers Nathan J. , Bowers Shin T. , Gu Tingyi , Gu Jiangjiang , Greenberg Melisa R. , Smolyakov Gennady A. , Osinski Marek 
Published: April 2011

AbstractZnO colloidal nanocrystals have been synthesized using two different approaches and characterized by HRTEM, EDS, and photoluminescence spectroscopy. ZnO nanocrystals synthesized from zinc alkoxy alkyl precursors in the MeIm/H2O coordinating solvent showed only visible surface-defect related emission in their PL spectra. No band-to-band UV emission was observed after ZnS coating of those ZnO nanocrystals. In contrast, a strong band-to-band UV emission dominated PL spectra of ZnO nanocrystals synthesized through wet-chemical acid-catalyzed esterification of zinc acetate.
Erbium Environment in ZnO:Er Polycrystalline Fibers Produced by Electrospinning
Authors: Mustafa Danilo , Wu Ji , Coffer Jeffery L. , Tessler Leandro R. 
Published: April 2011

AbstractErbium-doped polycrystalline ZnO fibers were prepared by electrospinning. Organo-metallic Zn and Er (0.5, 1.0 and 2.0 % Er/Zn ratio) precursors dissolved in methanol, DI water and acetic acid were forced through a syringe needle. An electric field of 20 kV over 16 cm was used to promote the growth of fibers from the needle to a rotating drum. The resulting material consisted of entangled fibers with 0.5 to 1 &#956;m typical diameter. The as-prepared samples present faint Er3+ luminescence at 1.5 μm when excited by the 488 nm line of an Ar+ laser. This luminescence intensity increases up to 25 times when the samples are annealed for 30 min at 500 °C in air. The effect of annealing over the Er environment was determined by EXAFS measurements at the Er L3 edge. In all as-prepared samples Er is coordinated to 8 ± 0.5 oxygen atoms at up to 2.36 ± 0.02 Å interatomic separation. After annealing the coordination is reduced to 5.9 ± 0.5 and the atomic separation becomes 2.30 ± 0.02 Å. This is comparable to Er2O3 where the coordination is 6 and the first neighbor distance is 2.26 ± 0.02 Å. The overcoordination in the as-prepared samples is consistent with the Er L3 edge at 8361.7 ± 0.5 eV compared to 8360.2 ± 0.5 eV in the annealed samples and 8359.9 ± 0.5 eV in Er2O3. In conclusion, the annealing of electrospun ZnO:Er fibers makes the Er environment more similar to that of Er2O3 increasing the luminescence efficiency.
Photoluminescence and Raman spectra in Ga-doped ZnO layers on sapphire
Authors: Reshchikov Michael A. , Nagata S. , Xie J. , Hertog B. , Osinsky A. 
Published: April 2011

AbstractGa-doped ZnO layers were grown on sapphire substrates by molecular beam epitaxy (MBE). Low-temperature photoluminescence (PL) and room-temperature Raman spectra were investigated. Defect-related modes at 277 and 510 cm−1 appeared in the Raman spectrum for Ga-doped layers. The PL spectrum is dominated by a donor-bound exciton peak at 3.356 eV. A weak yellow luminescence (YL) band peaking at 2.1-2.2 eV was studied in detail. It shifted to higher photon energies (up to 0.1 eV) with increasing excitation intensity. The YL band is attributed to transitions from shallow donors to a deep acceptor. The acceptor is thought to be a Zn vacancy-related defect because the intensity of the YL band decreased dramatically with Ga doping.
Influence of Gamma-Irradiation on Dielectric Properties of Recycled Polyethylene Composites
Authors: Gafurov Ulmas , Fazilova Zekie 
Published: April 2011

AbstractThe influence of γ-irradiation on the dielectric losses (tg δ) and permittivity (ε′) of recycled high density polyethylene (HDPER) thermoplastic dynamic vulcanizates (TDV) has been investigated. The materials and composites that were studied include HDPER:EPDM, HDPER+EPDM+GTR, HDPER+EPDM+GTR/plast; EPDM (ethylene-propylene diamine).The experimental data obtained shows significant differences between dielectric properties different samples, as well as between the unirradiated and γ-irradiated samples.
Unifying Chemical Bonding Models for Boranes
Authors: Du Mao-Hua , Saito Susumu , Zhang S. B. 
Published: April 2011

AbstractWe demonstrate, based on first-principles calculations, that chemical bonding in deltahedral boron hydrides, BnHn2− also known as closo boranes, can be understood within the three-center two-electron (3c2e) bonding model in line with other families of boranes. We show that bonding in the triangular lattice of BnHn2− cages can be described by delocalized resonant 3c2e bonding. We also find that the reason for all the BnHn2− to be dianions can be attributed to the reduction of boron coordination number in the deltahedral cage structure from that of boron sheet with triangular lattice.
Energy Resolution and Non-proportionality of Scintillation Detectors
Authors: Moszynski Marek 
Published: April 2011

AbstractThe limitation of energy resolution of scintillation detectors are discussed with a special emphasis on non-proportionality response of scintillators to gamma rays and electrons, which is of crucial importance to an intrinsic energy resolution of the crystals. Examples of the study carried out with different crystals and particularly those of tests of undoped NaI and CsI at liquid nitrogen temperature with the light readout by avalanche photodiodes are presented suggesting strongly that the non-proportionality of the halide crystals are not their intrinsic property. Moreover, the influence of slow components of the light pulses on energy resolution and non-proportionality are discussed.
n-Type Diamond Growth by Phosphorus Doping
Authors: Kato Hiromitsu , Makino Toshiharu , Yamasaki Satoshi , Okushi Hideyo 
Published: April 2011

AbstractPhosphorus doping on (001)-oriented diamond is introduced and compared with results achieved on (111) diamond. Detailed procedures, conditions, doping characteristics, and recent electrical properties of (001) phosphorus-doped diamond films are described. Now the highest mobility is reached to be ∼780 cm2/Vs at room temperature. The carrier compensation ratio, which is still high around 50-80 %, is the most important issues for (001) phosphorus-doped diamond to improve its electrical property. The origin of compensators in phosphorus-doped diamond is investigated, while yet to be identified.Ultraviolet light emitting diode with p-i-n junction structure is also introduced using (001) n-type diamond. A strong UV light emission at around ∼240 nm is observed even at room temperature. High performance of diamond UV-LED is demonstrated.
Probing The Transient Response To Improve The Stability Of Diamond Devices Under Pulsed Periodic Excitation
Authors: Bergonzo Philippe , Hamrita Hassen , Tromson Dominique , Descamps Caroline , Mer Christine , Nesladek Milos 
Published: April 2011

AbstractCVD diamond combines attractive properties for the fabrication of detection devices operating in specific environments. One problem that remains critical for device stability is the presence of defect levels that alter the detection performances, and the detection characteristics often appear as they are very depending on time, temperature, and history of the preceding irradiations.One issue we have proposed is to adapt one technique that is commonly used for time of flight spectroscopy in order to maintain a uniform electric field in the probed device, and based on the synchronisation of the device bias with the period of the excitation source. This can be applied to several types of detection applications, as long as we can rely on periodical triggering in order to synchronise the device polarisation. We apply it here to a LINAC electron accelerator used for photon pulse generation at the frequency of 25Hz. The result is a remarkable improvement of the performance of a polycrystalline diamond detector that exhibits a particularly defective response when used in the steady state excitation, to reach that of a perfectly stable and reproducible device response in the pulsed mode. We claim this method to be applicable to several types of excitations and particularly to present a high interest for monitoring accelerator sources, e.g. for medical dosimetry applications.
Electrochemical-microscopy analysis of bio-functionalized diamond surfaces
Authors: Uetsuka Hiroshi , Yang Nianjun , Tokuda Norio , Nebel Christoph E. 
Published: April 2011

AbstractDNA sensors fabricated on single-crystalline B-doped diamond (SBDD) electrodes were characterized by scanning electrochemical microscopy (SECM). These experiments show that circular arranged DNA sensors of typically 2 mm diameter show some spatial variations in electrochemical response. The variation of the diamond electrode with respect to DNA bonding is electrochemically characterized and discussed in the context of ion attraction/repulsion by the negatively charged backbones of DNA and the negatively charged diamond surface. Our results show that repulsive forces affect the mediator propagation of Fe(CN)64- in the close vicinity of the DNA layer which can be used to investigate DNA density variations on sensor areas.
Performances of Epitaxial Diamond in the Field of X-ray Diagnostics
Authors: Manfredotti Claudio , Lo Giudice Alessandro , Almaviva S. , Verona-Rinati G. 
Published: April 2011

AbstractA thin epitaxial single crystal CVD (Chemical Vapour Deposited) diamond detector has been used in order to monitor the X-ray pulses coming out from a standard, portable, medical X-ray apparatus. The current pulses have been acquired and digitized in order to obtain the pulse shape, timing and dose. The obtained data were successfully compared with standard X-ray monitors like air ionization chambers and silicon detector arrays. The results strongly suggest a possible use of CVD epitaxial diamond in the field of X-ray diagnostics for energies up to 120 keV and doses up to 125 mGy and for X-ray pulse timing from 0.1 s or below and 2 s or more.
Arsenic and Antimony Doping: An Attempt to Deposit n-type CVD Diamond
Authors: May Paul William , Davey Martin , Rosser Keith N , Heard Peter J 
Published: April 2011

AbstractWe report the results of experiments that attempt to deposit n-type CVD diamond in a standard hot filament reactor using 1%CH4/H2 gas mixtures, using (i) AsH3 as a gas phase source of arsenic, and (ii) evaporated Sb or Sb(Ph)3 as a source of antimony. SIMS measurements revealed that under these conditions, neither Sb nor As is incorporated into the diamond film, and the Raman spectra, electrical conductivity and crystallite morphology remain unchanged from that of undoped diamond. These experiments confirm the predicted low incorporation efficiency for As and Sb, and we conclude that doping CVD diamond with these elements cannot readily be achieved in this manner.
Novel Organometallic Fullerene Complexes for Vehicular Hydrogen Storage
Authors: Whitney Erin , Dillon Anne C. , Curtis Calvin , Engtrakul Chaiwat , O'Neill Kevin , Davis Mark , Simpson Lin , Jones Kim , Zhao Yufeng , Kim Yong-Hyun , Zhang Shengbai , Parilla Philip 
Published: April 2011

AbstractExperimental wet chemical approaches have been demonstrated in the synthesis of a new chainlike (C60-Fe-C60-Fe)n complex. This structure has been proposed based on 13C solid-state nuclear magnetic resonance, electron paramagnetic resonance, high-resolution transmission electron microscopy, energy-dispersive spectroscopy, and X-ray diffraction. Furthermore, this structure has been shown to have unique binding sites for dihydrogen molecules with the technique of temperature-programmed desorption. The new adsorption sites have binding energies that are stronger than that observed for hydrogen physisorbed on planar graphite, but significantly weaker than a chemical C-H bond. Volumetric measurements at 77 K and 2 bar show a hydrogen adsorption capacity of 0.5 wt%. Interestingly, the BET surface area is ∼31 m2/g after degassing, which is approximately an order of magnitude less than expected given the measured experimental hydrogen capacity. Nitrogen and hydrogen isotherms performed at 75 K also show a marked selectivity for hydrogen over nitrogen for this complex, indicating hidden surface area for hydrogen adsorption.
Compaction and Cold Crucible Induction Melting of Fine Poly Silicon Powders for Economical Production of Polycrystalline Silicon Ingot
Authors: Kim Daesuk , Shin Jesik , Moon Byungmoon , Kim Kiyoung 
Published: April 2011

AbstractThe consolidation and casting processes of fine silicon powders, by-product of high purity silicon rods making process in the current method, were systematically investigated for use as economical solar-grade feedstock. Morphology, size, and contamination type of the fine silicon powders were inspected by combined analysis of SEM, particle size analyzer, and FT-IR. Silicon powder compacts were tried to fabricate by a consolidation process without a binding agent and then their density ratio and strength were evaluated. Finally, the electrical resistivity of the specimens prepared by an electromagnetic casting method was examined for purity assessment.
Standing the Test of Time: Signals and Noise From Environmental Assessments of Energy Technologies
Authors: Sandén Björn A. 
Published: April 2011

AbstractThe point of view taken here is that systems analysis is a kind of learning process, not data gathering, not decision making, but the production and effective communication of arguments relevant in a particular context. This idea, that the intended application of the result of an assessment has consequences for methodological choices, is beginning to spread in the LCA research community. One problem is that standard LCA methodology is developed to answer questions about environmental impacts of the current production and use of one unit of a product or minor product or process changes. When this methodology, unchanged, is used to provide answers to questions about strategic technology choice, i.e. not decisions that aim at improving a process within an existing technological environment, but with the long-term goal of changing large-scale technological systems, the result could be of little value or misleading. In many cases, LCAs produce more noise than knowledge. This observation seems to be of particular importance for LCAs of energy technologies and for how energy use is treated in all kinds of LCAs. Here, it is suggested that a better understanding of some critical methodological issues related to time, universality, cause-effect relationships, technical maturity and system innovation, could result in better studies that reveal fundamental environmental issues related to the objects of study and reduce the noise from irrelevant information. Examples are given from the technology fields of solar cells, fuel cells, batteries, renewable transport fuels and carbon nanoparticles.
Development of SEM Metallography for the Study of the Mg-MgH2 Phase Transformation
Authors: Vittori Antisari Marco , Montone Amelia , Abazovic Nadica , Aurora Annalisa , Drvendzija Milica , Mancini Rita , Mirabile Gattia Daniele , Pilloni Luciano 
Published: April 2011

AbstractThe study of sorption reactions of metal hydrides is the subject of numerous researches in connection with the development of a safe technology for hydrogen storage, and MgH2, in particular, is one of the most promising materials. Several efforts have been already carried out in order to understand the kinetic mechanisms involved in the MgH2 decomposition which is at the basis of H2 release. However, the role of additives and induced structural defects on the sorption cycles is not clear yet. With the purpose of supporting the reaction analysis we have developed an experimental protocol for the metallographic examination at high spatial resolution of partially desorbed MgH2 powders. In particular, this procedure allows cross-sectional analysis of powders embedded into conductive matrix, while the observation method produces a different contrast among metallic Mg, MgH2 and additive particles made of heavier materials.
Hydrogen adsorbed in ab initio computationally simulated nanoporous carbon. An energetics study
Authors: Valladares R. M. , Valladares Alexander , Calles A. G. , Valladares Ariel A. 
Published: April 2011

AbstractNanoporous carbon has been considered an interesting and potentially useful material for storing hydrogen. Using nanoporous carbon periodic supercells with 216 atoms and 50 % porosity, constructed with a novel ab initio approach devised by us, the dangling bonds of the carbon atoms were first saturated with hydrogen, then relaxed and its total energy calculated with and without hydrogen. Next the same number of hydrogen atoms, in molecular form, was randomly placed within the pore of the pure carbon supercell, then the sample relaxed, and finally its total energy calculated, also with and without hydrogens. From these results the average energy per hydrogen atom is obtained for both cases. For the molecular hydrogen sample the binding energy found per hydrogen atom is 343.89 meV, which compares favourably with values reported in the literature, 300-400 meV/molecule.