bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermal Dependence of Quantum Dot Solar Cells
Authors: Cress Cory , Hubbard Seth M. , Bailey Christopher , Robinson Ross , Landi Brian J. , Raffaelle Ryne P.
Published: April 2011

Various temperature dependent optoelectronic properties were measured for GaAs-based p-type / intrinsic / n-type (pin) solar cell devices containing 5-layers of InAs quantum dots (QDs) grown with strain-compensation layers. Curve fitting of the dark diode characteristics allowed for the temperature dependence of the saturation current and the ideality parameter to be determined. The resulting parameter values indicate high material quality. Air mass zero illuminated current density vs. voltage measurements were used to determine the temperature coefficients of the open circuit voltage, short circuit current, maximum power, and fill factor. A strong correlation between the temperature dependent quantum dot electroluminescence peak emission wavelength and the sub-GaAs bandgap spectral response was observed.
Electrophoretic Deposition of CdSe Nanocrystals for Photovoltaic Applications
Authors: Smith Nathanael , Emmett Kevin J , Rosenthal Sandra J
Published: April 2011

CdSe nanocrystals chemically linked to nanocrystalline titanium dioxide substrates form a promising material for nanostructured photovoltaic devices. The usual method for attaching the nanocrystals to the titanium dioxide substrate is by means of a linking molecule (such as mercaptopropionic acid) or in-situ growth. In this paper, we report the use of an alternative technique, electrophoretic deposition (EPD), to directly deposit already formed CdSe nanocrystals onto the substrate. In EPD, a voltage is established between two electrodes that are immersed in a solution of nanocrystals. At room temperature, a fraction of the nanocrystals are thermally charged, and these charged nanocrystals migrate to the electrodes and adhere to the surface. A significant advantage of EPD over the use of linking molecules is the speed with which the nanocrystals are deposited: EPD takes only a few minutes, compared to the several hours required for the alternative techniques. Additionally, we have fabricated initial photovoltaic devices based on electrophoretically deposited CdSe nanocrystals on a planar TiO2 thin film.
Novel spin-dimer system of a microporous polyborate NaCuB7O12.nH2O
Authors: Ju Jing , Sasaki Juns , Toyota Naoki , Tanigaki Katsumi
Published: April 2011

A new microporous polyborate, NaCuB7O12.nH2O, is synthesized using boric acid as a flux. It contains a 14-membered ring framework built up by CuO6 octahedra, BO4 tetrahedra and BO3 triangles. The spin-1/2 dimers of Cu2+ ions are connected by BO3 to form an infinite ladder along the b-axis. Magnetic susceptibility data between 2 and 330 K are presented, and the data are accurately fitted by theoretical predictions of Bleaney-Bowers for the spin-1/2 dimer, with J/kB = -153.8 K, and g = 1.98, where J is the intradimer exchange interaction constant and g is the Landé g factor.
Magnetic Spin Valve Sensors with Different Geometry to Magnetic Bead Detection for Biosensor Application
Authors: Suh Jeong Dae , Chung Myung Ae
Published: April 2011

We have demonstrated the use of highly sensitive spin valve sensors for the detection of micron magnetic beads. By using a ring type, cross type, and meander line type sensors, we were able to detect the presence of 2.8 μm size magnetic beads in real time by direct measurement of magnetic dipole fields from magnetic beads. The sensitivity of the ring, cross and meander line sensors were obtained about 50 μV/Oe, 7 μV/Oe, 30 μV/Oe and sensor output signals of 50 μV , 30 μV, 90 μV were obtained in an external applied field of 10 Oe and 1 mA sense current. Our results shows that ring, cross, and meander line shape spin valve sensors are very promising candidates for the detection of biomolecules with magnetic labels.
Vertically Aligned Mn-doped Fe3O4 Nanowire Arrays: Magnetic Properties and Gas Sensing at Room Temperature
Authors: Hwang Seon Oh , Kim Chang Hyun , Myung Yoon , Park Seong-Hun , Park Jeunghee , Hahn Chang Soo , Kim Jae-Young
Published: April 2011

Vertically-aligned Mn (10%)-doped Fe3O4 (Fe2.7Mn0.3O4) nanowire arrays were produced by the reduction/substitution of pre-grown Fe2O3 nanowires. These nanowires were ferromagnetic with a Verwey temperature of 129 K. X-ray magnetic circular dichroism measurements revealed that the Mn2+ ions preferentially occupy the tetrahedral sites, substituting for the Fe3+ ions. We observed that the Mn substitution decreases the magnetization, but increases the electrical conductivity. We developed highly sensitive gas sensors using these nanowire arrays, operating at room temperature, whose sensitivity showed a correlation with their bond strength of diatomic/triatomic molecules. Based on the fact that the sensitivity was highest toward water vapor, an excellent-performance humidity sensor was fabricated.
Biomedical Engineered Ferrofluids
Authors: Fischer Birgit , Mao Leidong , Gungormus Mustafa , Tamerler-Behar Candan , Sarikaya Mehmet , Koser Hur
Published: April 2011

The characteristic of combining liquid behavior with and magnetic properties makes ferrofluids unique and it provides them a variety of applications, in particular in the medial field. For medical application ferrofluids are required to be stable at neutral pH and against high salt concentration. Here we present a new approach to stabilize water-based ferrofluids by using genetically engineered peptides for inorganics (GEPI's). Such GEPI's selected for specific and strong binding to the surface of nanoparticles not only increase colloidal stability by acting as a thin surfactant, but they also enable an efficient route for rendering the ferrofluid bio-functional and bio-compatible. The stability of a ferrofluid was characterized by the ac-susceptibility and by using it in a ferro-microfluidic device. This chip actuates the ferrofluid directly via magnetic fields alone, and the pumping spectrum as a function of frequency reveals information about the size of the magnetic nanoparticles. An ideal ferrofluid with monodisperse particles displays a single and clear pumping peak. Agglomeration can directly be observed as a broadening of the pumping spectrum.
Preparation of Lateral Organic Spin-valve Devices with La0.7Sr0.3MnO3
Authors: Ikegami Tomonori , Kawayama Iwao , Tonouchi Masayoshi , Yamashita Yoshiro , Tada Hirokazu
Published: April 2011

Spin injection and transport characteristics of low-molecular-weight organic semiconductors such as pentacene and bis(l,2,5-thiadiazolo)-p-quinobis(l,3-dithiole) (BTQBT) have been studied utilizing lateral type spin-valve devices with half metal electrodes, LaA0.67Sr0.33MnO3 (LSMO). The LSMO electrodes with a spacing of 200 nm were prepared by electron-beam lithography and dry etching of the epitaxial films grown on MgO substrates. The devices showed clear spin-valve behaviors with a magneto-resistance (MR) ratio up to 29 % at 9.1K. It was found that the MR ratio depended on the crystallinity of organic films as well as on temperature and applied bias voltages
Effect of 3d Transition Metals Addition on the Ferroelectric Properties in Bi Ferrite Thin Films
Authors: Naganuma Hiroshi , Miura Jun , Okamura Soichiro
Published: April 2011

Cr, Mn, Co, Ni and Cu of 5 at % s added BiFeO3 films were fabricated by chemical solution deposition on 111-textured Pt/Ti/SiO2/Si(100) substrates. Only the diffraction peaks attributed to BiFeO3 structure could obtain except the Ni and Cr additions. The BiFeO3 films became almost amorphous by adding Ni, and non ferroelectric Bi7CrO12.5 phase was formed by adding Cr. AFM images indicated the surface morphology of the films was drastically changed by the additives. The leakage current was reduced by adding Mn, Cu and Co, although the electric coercive field increased in the case of Co addition. Therefore, it could be concluded that Mn and Cu additives improved not only the leakage current properties but also the ferroelectric properties in the course of CSD process. It should be noted that this is the first report showing the improvement of ferroelectricity of BiFeO3 films by adding Cu.
Epitaxial Growth of Spinel Ferrite Oxide (Al,Ru,Fe)3O4 on a GaAs(001) Substrate Using a MgO Buffer Layer
Authors: Kanki Teruo , Kawahara Toshio , Asakawa Naoki , Hotta Yasushi , Terai Yoshikazu , Fujiwara Yasufumi , Tabata Hitoshi , Kawai Tomoji
Published: April 2011

Spinel ferrite oxides doping non-magnetic ions show the photo-induced magnetization (PIM) effect at high temperature [1-3]. Such a magnetization enhancement by light irradiation is a unique property in this material. In order effectively to use the PIM effect and precisely to control the magnetism, direct light-emission from light-emitting element substrates would be a useful technique. In this study, spinel ferrite Al0.2Ru0.8Fe2O4 (ARFO) thin films, with the high temperature PIM effect, were prepared on GaAs(001) substrates by a pulsed laser deposition technique to aim integration with light-emitting devices based on GaAs lattice-matched materials in the future. Results showed that (001)-oriented ARFO thin films were successfully grown by using MgO buffer layers. The magnetic properties were approximately the same as ARFO films using other substrates such as Al2O3(0001) or MgO(001).
Synthesis and Characterization of Multiferroic Composites Based on Manganate Perovskite Ceramics
Authors: Song Gonbao , Li Jian , Kholkin Andrei
Published: April 2011

In this paper, phase separation and crystal structure of (x) La0.625Sr0.375MnO3 − (1-x) LuMnO3 system (LSMO-LMO), and (1-x) La0.9Ca0.1MnO3-(x) LuMnO3 system (LCMO-LMO) were studied by XRD and SEM. The results confirm that there are solid solutions in both of these two systems. There is a solid solution of monoclinic phase of space group P1121/a for x=0.980∼1.0 in LSMO-LMO system. There is a solid solution of hexagonal phase of space group P63cm for x=0.0∼0.24 in LCMO-LMO. Selected compositions were tested in terms of their magnetization, dielectric constant and ferroelectric properties at low temperatures.
Dielectric Properties of Ba0.5Sr0.5TiO3-P(VDF-CTFE) Nanocomposites
Authors: Wu Peixuan , Shan Xiaobing , Cheng Zhong-yang
Published: April 2011

Ceramic/polymer composite made of nanosize Ba0.5Sr0.5TiO3 (BST) powders and P(VDF-CTFE) copolymers as matrix. The concentration of the composites with BST from 0% to 50% in volume was investigated. The dielectric properties and structure as well as the morphology of the composites were characterized over a broad temperature range. It is found that the wetability between the polymer and ceramic powder is not good. The approach to improve the uniformity of composites was investigated. Due to the dielectric-constant-maximum temperature of the BST is different from that of copolymer, a weak dependence of the dielectric constant on temperature was observed over temperature from 10 °C to 100 °C.
Synthesis of the Ferroelectric Solid Solution, Pb(Zr1−xTix)O3 on a Single Substrate Using a Modified Molecular Beam Epitaxy Technique
Authors: Anderson Piers , Guerin Samuel , Hayden Brian E. , Khan Mikael A. , Bell Andrew J. , Han Yisong , Pasha Ashu , Whittle Karl R , Reaney Ian M.
Published: April 2011

High-throughput synthesis of the ferroelectric solid solution Pb(Zr1−xTix)O3 (PZT) on single Pt/Ti/SiO2/Si substrates was demonstrated using a modified molecular beam epitaxy (MBE) system. The PZT films exhibited a phase transition from rhombohehdral (R) to tetragonal (T) symmetry as a function of Zr:Ti ratio, across the substrate diagonal. This was consistent with the presence of a morphotropic phase boundary (MPB) at a Zr:Ti ratio of 0.64:0.36, different from the value of 0.53:0.47 observed for bulk ceramics. All points on the films exhibited ferroelectric hysteresis loops. The results demonstrate the feasibility of high-throughput MBE for deposition of complex ferroelectric oxides, and pave the way for further materials discovery, in particular Pb-free piezoceramics.
Comparative Study of Thin PZT Sol-gel Films Deposited on Pt and GaN Substrates
Authors: Chevtchenko Serguei A. , Agra Francisco A. , Xie Jinqiao , Morkoç Hadis
Published: April 2011

We provide a comparative study of the piezoresponse in thin Pb(ZrxTi1−x)O3 (PZT) films deposited onto GaN/sapphire and Pt/Ti/SiO2/Si substrates using the sol-gel process. The effective piezoelectric coefficient was measured by Piezoresponse Force Microscopy. The resulting effective piezoelectric coefficient obtained for PZT(∼180 nm)/GaN/sapphire structure is 16.7 ± 3.4 pm/V and for PZT(∼180 nm)/Pt/Ti/SiO2/Si structure is 7.8 ± 0.8 pm/V. We also discuss the substrate clamping effect of both structures and explain the relatively stronger piezoresponse of PZT on GaN by different orientation of films formed on the two types of substrates. In this investigation, the PZT thin films crystallized with preferred (100) and (110) orientations on platinum and GaN, respectively. The phase mode of the Piezoresponse Force Microscopy was used to demonstrate remanent polarization in PZT/GaN/sapphire structure.
Growth and Evaluation of Magnetoelectric Cr2O3 Single Crystal Thin Films
Authors: Iwata Nobuyuki , Asada Takeshi , Ootsuki Shunpei , Yamamoto Hiroshi
Published: April 2011

The Cr2O3 thin films were grown on Al2O3(1102)(r-cut sapphire), Al2O3(1120)(a-cut sapphire), and Al2O3(0001)(c-cut sapphire) substrates to apply magnetoelectric oxides to oxides electronics. The Cr2O3 is a representative magnetoelectric material with antiferromagnetic insulator with the Néel temperature of 308 K. From the results of X-ray diffraction and the reflection high energy electron diffraction, epitaxial Cr2O3 thin films were obtained on all cut sapphire substrates using off-axis DC-RF magnetron sputtering method. The epitaxial relationship was Cr2O3[1120]//Al2O3[1120] and Cr2O3(1102)//Al2O3(1102) on r-cut, and Cr2O3[1100]//Al2O3[1100] and Cr2O3(1120)//Al2O3(1120) on a-cut, and Cr2O3[1120]//Al2O3[1120] and Cr2O3(0001)//Al2O3(0001) on c-cut. Optimized Cr2O3 film was obtained grown at 600°C on c-cut sapphire substrate. The surface roughness (Ra) of the film was 0.28 nm, and full width at half maximum of rocking curve for Cr2O3(0006) Bragg reflection was 0.23°. Growth difference is expected to be caused by the stacking order of atoms normal to the substrate surface and arrangement of atoms of the substrate surface.
Evidence of different conduction channels in bulk ZnO using f-MEMSA Analysis of transport properties
Authors: Tavares Chevalier Celine , Rothman J. , Feuillet G.
Published: April 2011

The characterization of transport properties in Zn0 is known to be challenging, particularly due to surface (in the case of bulk) or interface (in the case of heteroepitaxial layers) conduction channels, which puts severe limitations on the interpretation of Hall Effect measurements. In this communication, we report on the study of transport properties of n-type ZnO bulk material using Hall mobility spectrum analysis estimated through the algorithm known as full Maximum Entropy Mobility Spectrum Analysis, f-MEMSA. The electrical properties of bulk Zn0 are measured using a Hall setup for applied magnetic fields µ0H in the range 0T-9T and for temperatures between 50K and 400K. The f-MEMSA analysis highlights the existence of two types of conduction channels in the considered ZnO substrate. We also show that surface conductive channel can be suppressed using appropriate annealing conditions.
Role of Neutral Impurity Scattering in the Analysis of Hall Data from ZnO and Other II-VI Materials
Authors: Yang Xiaocheng , Xu Chunchuan , Giles N. C.
Published: April 2011

To determine donor and acceptor concentrations affecting electrical properties in ZnO crystals, the relaxation time approximation (RTA) has been used to analyze mobility and carrier concentration data measured from 80 to 400 K. Five scattering mechanisms are included: polar-optical-phonon, piezoelectric potential, deformation potential, ionized impurity, and neutral impurity scattering. Temperature dependences of intrinsic mobilities and Hall r factors are determined. Neutral impurity (ni) scattering can play an important role in limiting the total mobility in ZnO single crystals. By including ni scattering, the experimental deformation potential E1 = 3.8 eV for ZnO can be used, rather than treating E1 as a fitting parameter. This approach yields “intrinsic” mobilities for n-type and p-type ZnO, and other II-VI materials. At 300 K, the intrinsic electron Hall mobility in ZnO is predicted to be 230 cm2/Vs. The results of fitting the temperature dependences of mobility and carrier concentrations from representative ZnO and CdSe bulk samples are shown. Intrinsic results for n-type CdS and ZnS will also be discussed. The 300-K intrinsic hole Hall mobility in ZnO is predicted to be about 50 cm2/Vs.
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

The 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

The 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

Highly 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

ZnO 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

The 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

In 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

ZnO 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

Erbium-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 μm 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

Ga-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

The 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

We 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

The 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

Phosphorus 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

CVD 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

DNA 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

A 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

We 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

Experimental 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

The 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

The 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

The 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

Nanoporous 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.
Modified Carbon Cryogel-Ammonia Borane Nanocomposites for Hydrogen Storage
Authors: Sepehri Saghar , Garcia Betzaida Batalla , Zhang Qifeng , Cao Guozhong
Published: April 2011

This paper reports the synthesis and characterization of coherent Boron/Nitrogen –doped –carbon cryogels- ammonia borane nanocomposites for hydrogen storage. Resorcinol formaldehyde derived doped carbon cryogels (CC) were obtained via chemical modification.CC- ammonia-borane nanocomposites were made by incorporation of ammonia borane (AB), in CCs. Nitrogen sorption analysis, scanning electron microscopy, and X-ray photoelectron spectroscopy, are used to investigate the structure and morphology of the modified CCs. Differential scanning calorimetry is used to study the dehydrogenation of coherent doped-CC-AB nanocomposites. Modified CCs show higher mesoporosity, and more homogeneous porous structure compared to undoped CCs. Also, dehydrogenation kinetics of nanocomposites is enhanced as compared to neat AB. Possible nanoscale and catalytic effects of nanocomposites in improved dehydrogenation kinetics are discussed.
In situ high pressure XRD study on hydrogen uptake behavior of Pd-carbon systems
Authors: Bhat Vinay V , Gallego Nidia C , Contescu Cristian I , Payzant E Andrew , Rondinone Adam J , Tekinalp Halil , Edie Dan D
Published: April 2011

Efficient storage of hydrogen for use in fuel cell-powered vehicles is a challenge that is being addressed in different ways, including adsorptive, compressive, and liquid storage approaches. In this paper we report on adsorptive storage in nanoporous carbon fibers in which palladium is incorporated prior to spinning and carbonization/activation of the fibers. Nanoparticles of Pd, when dispersed in activated carbon fibers (ACF), enhance the hydrogen storage capacity of ACF. The adsorption capacity of Pd-ACF increases with increasing temperature below 0.4 bar, and the trend reverses when the pressure increases. To understand the cause for such behavior, hydrogen uptake properties of Pd with different degrees of Pd-carbon contact (Pd deposited on carbon surface and Pd embedded in carbon matrix) are compared with Pd-sponge using in situ XRD under various hydrogen partial pressures (<10 bar).

Rietveld refinement and profile analysis of diffraction patterns does not show any significant changes in carbon structure even under 10 bar H2. Pd forms β PdH0.67 under 10 bar H2, which transforms to α PdH0.02 as the hydrogen partial pressure is decreased. However, the equilibrium pressure of transition (corresponding to a 1:1 ratio of α and β phases) increases with increasing the extent of Pd-carbon contact. This pressure is higher for Pd embedded in carbon than for Pd deposited on carbon surface. Both these Pd-carbon materials have higher H2 desorption pressure than pure Pd, indicating that carbon “pumps out” hydrogen from PdHx and the pumping power depends on the extent of Pd-carbon contact. These results support the spillover mechanism (dissociative adsorption of H2 followed by surface diffusion of atomic H).
Microstuctural Characterization of the Radiation Effects in ZrC, a Potential Material for Next Generation Nuclear Plants
Authors: Baldinozzi Gianguido , Gosset Dominique , Simeone David , Dollé Mickael , Thomé Lionel , Surblé Suzy
Published: April 2011

The development of a new generation of nuclear reactors (Gen-IV), with improved thermodynamic yield and a reduction of waste production, makes necessary to consider materials able to withstand high operating temperatures. Transition metal carbides, like ZrC, are then under consideration. Despite their good thermal and neutron properties, they have unfortunately a brittle mechanical behaviour. This is the reason why it is important to investigate the properties of these systems with sub-micrometric grains and as a function of their composition. Therefore, samples having micrometric and nanometric grain sizes (and different oxygen content) were irradiated by low energy ions at room temperature to simulate their behaviour in a neutron flux. The irradiation effects in these materials were studied by grazing X-ray diffraction and transmission electron microscopy.
On Modeling the Evolution of Radiation Damage in Silicon Carbide
Authors: Weber William J , Gao Fei , Devanathan Ram , Zhang Yanwen , Jiang Weilin , Bae In-Tae
Published: April 2011

Experimental charged-particle irradiations and multi-scale computer simulations have been used to investigate the primary damage state and evolution of damage in silicon carbide as functions of temperature and charged-particle mass and energy. Atomistic simulations of energetic C and Si collision cascades, similar to those created by reactor neutrons, indicate that single interstitials, vacancies, antisite defects, and small defect clusters are produced. The point defects are dominated by close Frenkel pairs, and atomistic simulations indicate that the activation energies for recombination of most close pairs range from 0.24 to 0.38 eV, which suggest significant reduction in defect survivability at room temperature. Atomistic simulations have also determined that the activation energies for long-range diffusion of C and Si interstitials are 0.7 and 1.5 eV, respectively. Using these activation energies and ab initio results as input parameters, a kinetic Monte Carlo (MC) simulation model has been developed to study isochronal annealing of defects in SiC between cascade events. The defects are produced by a 10 keV Si cascades in a molecular dynamics (MD) simulation cell, and these defects are then accurately transferred to defect lattice sites in the Monte Carlo model to investigate defect recovery. By transferring defects states back and forth between the MD and MC environments, damage accumulation can be investigated as a function of temperature. Charged particle irradiations are often used to simulate radiation damage from neutrons and radioactive decay; however, at extreme charged-particle fluxes used in irradiation studies to simulate radiation damage in nuclear materials, the ratio of ionization rate to displacement rate can have a significant impact on observed temperature-dependent processes, which can affect both interpretation and model development. At high charged-particle fluxes, the defect recovery rates in SiC increase nearly linearly with the ratio of ionization rate to displacement rate. A fundamental understanding of these ionization effects is needed if charged particle irradiation results are to be used to develop predictive models of damage evolution in nuclear materials, such as SiC, as functions of time, temperature and dose rates.