bluuebunny/crossref_metadata_2025_split huggingface dataset:
Computational Models for Crystal Growth of Radiation Detector Materials: Growth of CZT by the EDG Method
Authors: Derby Jeffrey J. , Gasperino David 
Published: April 2011

AbstractCrystals are the central materials element of most gamma radiation detection systems, yet there remains surprisingly little fundamental understanding about how these crystals grow, how growth conditions affect crystal properties, and, ultimately, how detector performance is affected. Without this understanding, the prospect for significant materials improvement, i.e., growing larger crystals with superior quality and at a lower cost, remains a difficult and expensive exercise involving exhaustive trial-and-error experimentation in the laboratory. Thus, the overall goal of this research is to develop and apply computational modeling to better understand the processes used to grow bulk crystals employed in radiation detectors. Specifically, the work discussed here aims at understanding the growth of cadmium zinc telluride (CZT), a material of long interest to the detector community. We consider the growth of CZT via gradient freeze processes in electrodynamic multizone furnaces and show how crucible mounting and design are predicted to affect conditions for crystal growth.
Recent Advances in Ceramic Scintillators
Authors: Van Loef Edgar , Wang Yimin , Glodo Jarek , Brecher Charles , Lempicki Alex , Shah Kanai S 
Published: April 2011

AbstractA review is presented of recent ceramic scintillator R&D. Attention is focussed on Ce doped gamma-ray scintillators for medical imaging applications. Ceramic scintillators discussed in detail include SrHfO3:Ce and Lu2Hf2O7:Ce. These materials combine a high density and high atomic number with fast emission and a good light yield and may find practical application in medical imaging modalities such as Positron Emission Tomography and Computed Tomography.
Passivation of Semiconductor Surfaces for Improved Radiation Detectors: X-Ray Photoemission Analysis
Authors: Nelson Art J , Conway A M , Reinhardt C E , Ferreira J L , Nikolic R J , Payne S A 
Published: April 2011

AbstractSurface passivation of device-grade radiation detector materials was investigated using x-ray photoelectron spectroscopy in combination with transport property measurements before and after various chemical treatments. Specifically Br-MeOH (2% Br), KOH with NH4F/H2O2 and NH4OH solutions were used to etch, reduce and oxidize the surface of Cd(1-x)ZnxTe semiconductor crystals. Scanning electron microscopy was used to evaluate the resultant microscopic surface morphology. Angle-resolved high-resolution photoemission measurements on the valence band electronic structure and core lines were used to evaluate the surface chemistry of the chemically treated surfaces. Metal overlayers were then deposited on these chemically treated surfaces and the I-V characteristics measured. The measurements were correlated to understand the effect of interface chemistry on the electronic structure at these interfaces with the goal of optimizing the Schottky barrier height for improved radiation detector devices.
Surface behavior of heterosubstrates during BEN-MPCVD: a key for diamond heteroepitaxy
Authors: Arnault Jean-Charles , SAADA Samuel , DELCLOS Sophie , INTISO Luciana , PECORARO Stéphane , BERGONZO Philippe 
Published: April 2011

AbstractThe chemical stability of three heterosubstrates (Si, 3C-SiC and iridium) has been studied using the same MPCVD reactor during the successive steps of BEN process. An in situ sequential approach allows a monitoring of the chemical modifications induced by interactions between plasma and surfaces. Contrary to silicon, 3C-SiC and iridium underwent weak surface evolutions during BEN. This leads to favourable conditions for the interface formation in agreement with the better Highly Oriented Diamond films reported in the literature. A short description of the nucleation pathways identified for each heterosubstrate is also presented.
Diamond Amplified Photocathodes
Authors: Smedley John , Ben-Zvi Ilan , Bohon Jen , Chang Xiangyun , Grover Ranjan , Isakovic Abdel , Rao Triveni , Wu Qiong 
Published: April 2011

AbstractHigh-average-current linear electron accelerators require photoinjectors capable of delivering tens to hundreds of mA average current, with peak currents of hundreds of amps. Standard photocathodes face significant challenges in meeting these requirements, and often have short operational lifetimes in an accelerator environment. We report on recent progress toward development of secondary emission amplifiers for photocathodes, which are intended to increase the achievable average current while protecting the cathode from the accelerator.The amplifier is a thin diamond wafer which converts energetic (few keV) primary electrons into hundreds of electron-hole pairs via secondary electron emission. The electrons drift through the diamond under an external bias and are emitted into vacuum via a hydrogen-terminated surface with negative electron affinity (NEA). Secondary emission gain of over 200 has been achieved. Two methods of patterning diamond, laser ablation and reactive-ion etching (RIE), are being developed to produce the required geometry. A variety of diagnostic techniques, including FTIR, SEM and AFM, have been used to characterize the diamonds.
Phosphorus Doped Diamond Electron Emitter Devices
Authors: Tatsumi Natsuo , Ueda Akihiko , Tanizaki Keisuke , Nishibayashi Yoshiki , Imai Takahiro 
Published: April 2011

AbstractThe n-type diamond is known to have high electron emission properties. However, device fabrication on n-type phosphorus doped diamond had 2 difficulties. First, because highly phosphorus doped n-type diamond layer can be grown only on very small (111) diamond substrate, fabrication of highly homogeneous 3 dimensional device such as gate electrode was very difficult. Second problem was that the resistivity of n-type diamond was still over 100 Ω cm and too high for high current electron emission devices. To solve these problems, we developed a new large size composite wafer in which (111) single crystal diamond was buried in polycrystal diamond and a new electrode coated emitter tip structure for conduction support only whose apex was exposed from the electrode. N-type phosphorus doped diamond was grown on the 15 mm composite diamond wafer with high PH3/CH4 concentration of 20% and highly doped active layer was grown on the embedded (111) single crystal. Sharp emitter tip arrays were fabricated by etching the n-type diamond. Electrodes were coated on these tips and exposed area of diamond was less than 200 nm from the apex of the tip. Gate electrodes were fabricated for each emitter tips. Electron emission of these devices were measured in the vacuum of 10−7 Pa. The threshold voltage of the n-type diamond device was 60 V which was lower than 100 V of the p-type diamond device. The threshold voltage of n-type diamond with and without electrode coatings did not changed. This means that electrode coating did not affect the emission properties and electrons were emitted from the diamond surface. The emission current was enhanced by 2 orders by the electrode coatings and total emission current from 1 mm2 reached 1103 mA. This high emission current electron source enables applications to microwave tubes, electron beam processing and integrated micro vacuum devices.
CVD Diamond Applications as TL Radiation Dosimeters
Authors: Pedroza-Montero M. , Melendrez R , Chernov V , Pedroza-Montero M. , Gastelum S , Cruz-Zaragoza E 
Published: April 2011

AbstractThe extraordinary characteristics of chemically vapor deposited (CVD) diamond such as tissue equivalence, radiation hardness, and lack of solubility in water; makes CVD diamond a very promising material for radiation dosimetry applications. Recent investigations have shown that CVD techniques allowed the growing of good quality diamond films in a diversity of substrates to be used in the form of ionization chambers, thermoluminescence (TL) detectors and dosimeters. In the present work, we report on the TL properties of MWCVD diamond exposed to gamma radiation in the 0.05 -1.0 kGy dose range and 43.5 and 81.11 Gy min−1 dose rates. The CVD diamond displays a linear dose behavior and 5% TL cycle reproducibility, without requiring any annealing or thermal treatment before using it as TL dosimeter. In spite of the significant results, some problems remain and a lot of research work is necessary to improve the synthetic material characteristics to optimize the TL/OSL radiation dosimeter properties.
HIGH-SURFACE-AREA BIOCARBONS FOR REVERSIBLE ON-BOARD STORAGE OF NATURAL GAS AND HYDROGEN
Authors: Pfeifer Peter , Burress Jacob W. , Wood Mikael B. , Lapilli Cintia M. , Barker Sarah A. , Pobst Jeffrey S. , Cepel Raina J. , Wexler Carlos , Shah Parag S. , Gordon Michael J. , Suppes Galen J. , Buckley S. Philip , Radke Darren J. , Ilavsky Jan , Dillon Anne C. , Parilla Philip A. , Benham Michael , Roth Michael W. 
Published: April 2011

AbstractAn overview is given of the development of advanced nanoporous carbons as storage ma-terials for natural gas (methane) and molecular hydrogen in on-board fuel tanks for next-generation clean automobiles. The carbons are produced in a multi-step process from corncob, have surface areas of up to 3500 m2/g, porosities of up to 0.8, and reversibly store, by physisorp-tion, record amounts of methane and hydrogen. Current best gravimetric and volumetric storage capacities are: 250 g CH4/kg carbon and 130 g CH4/liter carbon (199 V/V) at 35 bar and 293 K; and 80 g H2/kg carbon and 47 g H2/liter carbon at 47 bar and 77 K. This is the first time the DOE methane storage target of 180 V/V at 35 bar and ambient temperature has been reached and exceeded. The hydrogen values compare favorably with the 2010 DOE gravimetric and volu-metric targets for hydrogen. A prototype adsorbed natural gas (ANG) tank, loaded with carbon monoliths produced accordingly and currently undergoing a road test in Kansas City, is de-scribed. A preliminary analysis of the surface and pore structure is given that may shed light on the mechanisms leading to the extraordinary storage capacities of these materials. The analysis includes pore-size distributions from nitrogen adsorption isotherms; spatial organization of pores across the entire solid from small-angle x-ray scattering (SAXS); pore entrances from scanning electron microscopy (SEM) and transmission electron microscopy (TEM); H2 binding energies from temperature-programmed desorption (TPD); and analysis of surface defects from Raman spectra. For future materials, expected to have higher H2 binding energies via appropriate sur-face functionalization, preliminary projections of H2 storage capacities based on molecular dy-namics simulations of adsorption of H2 on graphite, are reported.
Hydrogen Adsorption in MOF-74 Studied by Inelastic Neutron Scattering
Authors: Liu Yun , Brown Craig M. , Neumann Dan A. , Kabbour Houria , Ahn Channing C. 
Published: April 2011

AbstractAdsorption of hydrogen and the occupancy of different binding sites as a function of hydrogen loading in MOF-74 are studied using inelastic neutron scattering (INS). Hydrogen molecules are observed to fully occupy the strongest binding site before populating other adsorption sites. The comparison of the INS spectra at 4 K and 60 K indicates that hydrogen adsorbed at the strongest binding site is strongly bound and localized. We also show that when two hydrogen molecules are adsorbed into a single, attractive potential well, the shortest inter-H2 distance is about 3 Å, consistent with our previous observation of inter-H2 distance when adsorbed in two neighboring potential wells.
Evolution of Crystal Orientation in Obliquely Deposited Magnesium Nanostructures for Hydrogen Storage Applications
Authors: Cansizoglu Mehmet F. , Watanabe Fumiya , Wang Pei-I , Karabacak Tansel 
Published: April 2011

AbstractCrystal orientation (texture) is an important parameter in the hydrogen absorption and desorption properties of various materials. In this study, we investigate the formation of magnesium nanorod arrays with crystal orientations that are not normally observed in conventional Mg thin films. Mg nanorods are produced using an oblique angle deposition technique through a physical self-assembly process. In this study sputtering and thermal evaporation systems are utilized for the growth of Mg nanorods and thin films on silicon wafer pieces. We present a detailed X-ray diffraction and scanning electron microscopy analysis. It is discussed that under oblique incidence, evolution of crystal orientations with lower adatom mobility are promoted due to the shadowing effect.
Mechanisms for the Variation of Electrical Resistivity of Palladium Films in Hydridation-dehydridation Processes
Authors: Tang Yu Ming , Chan Yiu Bun , Ong Chung Wo 
Published: April 2011

AbstractHydridation of palladium (Pd) is accompanied by a substantial volume expansion. The electrical resistivity (ρ) would rise because the volume fraction of the hydride phase increases. However, if the material structure is porous/defective, hydridation induced volume expansion may lead to the closing of some pores/defects to result in a drop of ρ. We verified that a magnetron sputtered Pd film deposited at a higher argon ambient pressure (ϕ) was more defective, such that the contribution from the latter mechanism was stronger with increasing ϕ, and reached a maximum level for a film deposited at a ϕ of 6 mTorr. However, the film structure was weaker and unstable during the switching cycles, such that the magnitude of the change of ρ was found to increase successively with increasing number of switching cycles. The performances of ρ during initial soaking in H2 and subsequent hydridation and dehydridation switching cycles were different. The observed results are presented and discussed in this paper.
Study on Effects of Heavy Ion Irradiation on CeO2 by Using Synchrotron Radiation X-Ray Absorption Spectroscopy -as a Simulation Study for Radiation Damage in High-Burnup Light Water Reactor Fuels-
Authors: Ohno Hirotaka , Matsumura Daiju , Nishihata Yasuo , Mizuki Jun'ichiro , Ishikawa Norito , Sonoda Takeshi , Kinoshita Motoyasu , Iwase Akihiro 
Published: April 2011

AbstractCeO2 thin films were irradiated with 200MeV Xe ions. Effects of the irradiation were studied by using Extended X-ray Absorption Fine Structure (EXAFS) measurement at SPring8 synchrotron radiation facility. EXAFS spectra for the irradiated thin films near the Ce K-edge show that the coordination number for oxygen atoms around Ce atom decreases and that the Ce-O Debye-Waller factor increases by the irradiation. The atomic distance between oxygen atom and Ce atom does not vary within the accuracy of EXAFS measurement. The effect of high density electronic excitation on the structure of CeO2 is discussed.
Evaluation of Mechanical Properties of Stabilized Zirconia and Zirconate Pyrochlore
Authors: Matsuo Takuya , Shimamura Keiichi , Arima Tatsumi , Idemitsu Kazuya , Inagaki Yaohiro 
Published: April 2011

AbstractMechanical properties of stabilized zirconia and zirconate pyrochlore were evaluated by experiment, MD simulation and ab initio calculation.
Progress in Out-Of-Pile Study of Low Enriched UMo/AlSi Fuel
Authors: Cornen Marilyne , Iltis Xavière , Mazaudier Fabrice , Dubois Sylvie , Lemoine Patrick 
Published: April 2011

AbstractThe main problem we have to face in order to improve the in-pile behaviour of the UMo/Al dispersed fuel, is the instability of the interaction zone, that is formed between the UMo particles and their surrounding Al matrix during irradiation. As the latest irradiations (e.g. IRIS 3 or RERTR 6) tend to prove, addition of Si into the Al matrix seems to be beneficial for the interaction rate decrease. To further understand the role of silicon, a wide out-of-pile interdiffusion study has been launched in CEA-France in 2006 and is still under progress. It has given promising preliminary results by showing a real effect of Si addition upon the interaction zone. The first results related to the physico-chemical aspects of the modified UMo/Al interaction as well as the kinetics aspects of the interaction layer (IL) formation are described in this paper. On a wide range of annealed couples made of UMo7 or UMo10 and Al-Si matrix (Si content ranging from 0.11 wt % to 12 wt %), the IL thicknesses have been systematically measured. Microstructures have been fully characterized by means of optical and scanning electron microscopy and the elementary compositions have been evaluated through EDX analyses. Finally, XRD characterizations and micro-hardness tests have also been performed on a few samples. On the basis of these different results, we discuss first clues about the role played by silicon on slowing down the UMo/Al interaction process.
Light Water Reactor Fuel Degradation Mechanisms at High Burnup: Implications to Generation IV Materials
Authors: Motta Arthur Thompson 
Published: April 2011

AbstractThe proposed designs of GenIV reactors call for high operating temperatures and long exposure times, aimed at increasing thermal efficiency, enabling hydrogen production, decreasing waste and increasing safety, among other goals. These requirements will require imply the materials will be subjected to higher radiation damage doses than seen in light water reactors, requiring an even higher degree of alloys stability. In addition the higher temperatures and exposure times in corrosive environments will require much higher corrosion resistance than current materials. One of the main challenges of designing these materials is that our ability to predict material response in the face of the synergistic effects of temperature, radiation damage and a corrosive environment is limited. However, efforts are underway to understand mechanistically the degradation processes so that they can be extrapolated to conditions beyond the experimental database.In this context, it is interesting to consider the effort made by the nuclear power industry to qualify nuclear fuel for operation at higher burnup in existing light water reactors. In the last two decades, the average discharge burnup of nuclear fuel in light water reactors has increased almost two fold, thereby increasing the reactor exposure time and the amount of radiation damage withstood by the cladding. Experience has shown that the material degradation rates can increase at high burnup, sometimes through the synergistic operation of various processes. Two examples will be given to illustrate the complexity of the problem:(i) The rate of irradiation growth of zirconium alloys increases significantly at high burnup. The mechanism has been shown to depend on the amorphization of intermetallic ZrCrFe precipitates with consequent release of Fe into the Zr matrix. This has been shown to help nucleate component dislocation loops which preferentially absorb vacancies, thereby increasing the net rate of growth. This causes the interstitial and vacancy fluxes both to contribute towards irradiation growth, thus increasing the rate.(ii) One of the most significant obstacles to approval of cladding operation at high burnup is difficulty in the evaluation of the behavior of the fuel during a reactivity initiated accident (RIA). The degradation of the mechanical properties of the zirconium cladding with increasing corrosion and consequent hydrogen ingress, the radiation damage and the microstructure evolution in the fuel all have to be taken into account in evaluating the likelihood of severe fuel failure at high burnup. This problem is still being addressed in various research programs.Such mechanisms and the efforts to qualify nuclear fuel for higher burnup in light water reactors will be reviewed as a means of illustrating the challenges (known and unknown) faced by GenIV reactor materials.
Thermopower Measurements of Arrays of Small Diameter (18-60 nm) Bi Nanowires
Authors: Huber Tito , Adeyeye A. , Odunfa T. , Nikolaeva A. , Konopko L. , Johnson R. , Graf M.J. 
Published: April 2011

AbstractTheoretical work based on one-dimensional (1D) models indicates that Bi wires with diameter smaller than 50 nm can exhibit superior thermoelectric properties since the density of states at the Fermi level of a 1D system can be tuned to very high values. Recently, angle-resolved photoemission spectroscopy (ARPES) studies of Bi surfaces have shown that Bi nanowires support Rashba spin-orbit surface states, with high carrier densities of around 5×1012/cm−2, that have not been considered in current models of Bi nanowires. According to our estimates, the sheath of surface charge on Bi nanowires should contribute substantially to the thermopower of Bi nanowires. We carried out an experimental study of the transport properties and thermopower of bismuth nanowire arrays (NWA) with wire diameters ranging between 60 nm and 13 nm to investigate these phenomena. The Rashba interaction is a spin orbit interaction that is important for surfaces of materials consisting of heavy ion elements; thermoelectric materials frequently consist of these elements (i.e.PbTe) because they scatter phonons and form low thermal conductivity materials.
Synthesis and Optical Properties of 1D Bismuth Nanorods
Authors: Reppert Jason , Krishnan Sivaram , He Jian , Rao Rahul , Tritt Terry , Rao Apparao 
Published: April 2011

AbstractThe presence of a high electron density of states in low-dimensional systems such as, nanowires and nanotubes, suggests that these 1D structures can be useful thermoelectric materials. Theoretical calculations predict that: (i) Semimetallic Bi nanowires exhibit semiconducting nature when their nanowire diameter is below 50 nm, and (ii) Semiconducting Bi nanowires with diameter < 10 nm are expected to have an enhanced figure of merit (ZT > 2), when Z=S2σ/κ (S: Seebeck coefficient, σ: electrical conductivity, and κ is the thermal conductivity). We report the synthesis of ∼10 nm diameter Bi nanorods using a pulsed laser vaporization method. The high resolution transmission electron microscopy images of our Bi nanorods show (i) crystalline <012> planes in the core of the nanorods, and (ii) coated with a thin amorphous Bi2O3 layer. The infrared absorption and the surface plasmon peaks in our Bi nanorods are blue-shifted in energy when compared to the corresponding spectra in bulk Bi.
Thermoelectric properties of nanostructured (Pb1-mSnmTe)1-x(PbS)x with Pb and Sb precipitates
Authors: Girard Steven N , Sootsman Joseph R. , Lin Chia-Her , Androulakis John , Kanatzidis Mercouri G. 
Published: April 2011

AbstractWe report the physical characterization and thermoelectric properties of (Pb0.95Sn0.05Te)0.92(PbS)0.08 containing excess Pb and Sb prepared using the matrix encapsulation technique. Samples of (Pb0.95Sn0.05Te)0.92(PbS)0.08 : Pb 0.5 - 4 at. % rapidly quenched from the melt show microscale Pb inclusions that increase the thermal conductivity while slightly increasing the power factor, compared to (Pb0.95Sn0.05Te)0.92(PbS)0.08. Samples of (Pb0.95Sn0.05Te)0.92(PbS)0.08 : Pb 0.5%, Sb 2% prepared using the same technique show microscale Sb and Pb inclusions that upon heating cause rapid PbS and Sb segregation from the PbTe matrix. This behavior significantly alters the microstructure and degrades the transport properties of the material.