bluuebunny/crossref_metadata_2025_split huggingface dataset:
Understanding the Electro-thermal and Phase-transformation Processes in Phase-change Materials for Data Storage Applications
Authors: Wright C. D. , Armand M. , Aziz M. M. , Senkader S. , Yu W. 
Published: April 2011

ABSTRACTAttempts at the practical utilization of Sb-Te based alloys beyond optical data storage have been made recently by employing these materials in both scanning probe type memories, and in electrical memory devices - namely Phase-Change Random Access Memory (PC-RAM). We have developed models to simulate the electrical, thermal, and phase-change characteristics of this important class of material. In this paper we describe the physical basis of our models and present simulation results for different memory configurations and operating conditions.
Memory Effects In Manganese Perovskites
Authors: Noginova N. , Chelule G. , Loutts G. B. 
Published: April 2011

ABSTRACTManganese doped perovskites are promising materials for non-magnetic data storage. Systems with low doping concentration, such as Mn:YAlO3 are high-quality optical crystals, demonstrating significant photorefractive effect. Optically and electrically induced quasi-permanent change in low-field conductivity was observed in the materials with high concentration of manganese such as single crystals and films of LaGa1−xMnxO3 (x= 0.1–1). These memory effects can last for a long time at room temperature and can be easily erased by heating up to 230 C. We explain our experimental results by photoinduced or thermoinduced local phase transition with the oxidation of Mn ions.
Optical Properties and Phase Transformation Kinetics of Ge-Sb-Te-(N) Alloy Thin Films Investigated by Ellipsometry
Authors: Kim Sang Youl 
Published: April 2011

ABSTRACTThe recent research works of optical properties and crystallization kinetics of phase change Ge-Sb-Te-(N) alloy by using ellipsometry are reviewed.The complex refractive index spectra of phase-change Ge2Sb2+xTe5thin films and those of the nitrogen Ge2Sb2Te5thin films have been determined.The crystallization behavior of amorphous Ge2Sb2Te5thin films investigated by in situ ellipsometry revealed that the crystallization process of Ge2Sb2Te5near 140°C is a two-step process. The kinetic exponent of the Johnson-Mehl-Avrami equation was about 4.4 for the first stage and 1.1 for the second stage. Ex situ study confirmed the cascaded crystallization behavior of phase-change Ge2Sb2Te5films.A passive type single wavelength ellipsometer adopting a DOAP (division-of-amplitude photopolarimeter) configuration with nanosecond time resolution is developed to monitor the phase transformation of Ge2Sb2Te5caused by a high power nanosecond laser pulse in real time. The two-step process - the fast nucleation-dominant stage followed by the slow anomalous grain growth stage is confirmed.Based on the recent analysis of the ellipsometric isotherm at moderately elevated temperature, we found for the first time that the fast nucleation dominant crystallization of Ge2Sb2Te5can be better explained by a modified JMA equation that illustrates the nucleation dominated process where the creation rate of a new nucleus is proportional to the density of preexisting nuclei and growth rate is negligible.
Kinetics of Crystal Nucleation and Growth in Thin Films of Amorphous Te Alloys measured by Atomic Force Microscopy
Authors: Kalb J. , Spaepen F. , Wuttig M. 
Published: April 2011

ABSTRACTBoth the crystal nucleation rate and the crystal growth velocity of sputtered amorphous Ag0.055In0.065Sb0.59Te0.29 and Ge4Sb1Te5 thin films used for optical data storage were determined as a function of temperature. Crystals were directly observed using ex-situ atomic force microscopy, and their change in size after each anneal was measured. Between 140°C and 185°C, these materials exhibited similar crystal growth characteristics, but differed in their crystal nucleation characteristics. These observations provide an explanation for the different re-crystallization mechanisms observed upon laser-induced crystallization of amorphous marks.
Design of Holographic Recording Conditions with Optical Densities of Thick Azopolymer Films
Authors: Yasuda Shin , Kawano Katsunori , Minabe Jiro , Maruyama Tatsuya , Hayashi Kazuhiro , Ogasawara Yasuhiro 
Published: April 2011

ABSTRACTWe evaluated the relation between the degradation of the Bragg selectivity and the optical densities of the films by use of the shift-multiplexing method with a spherical reference wave. Our recording media were prepared by blending methylazobenzene-containing polymer (MAP) and cyanobiphenyl-containing polymer (CBP). We fabricated four kinds of 250μm-thick films whose optical densities were increased with MAP concentrations that ranged from 10wt% to 70wt%. As a result of the evaluation, the film with a higher optical density degraded the Bragg selectivity more significantly. The degradation of the Bragg selectivity affected the bit error rate (BER). In addition, we obtained a guide to holographic recording conditions for achieving a low BER as to the films with non-negligible optical densities.
Nuclear Glass Alteration in Clay: Assessment of the Effect of Direct Contact between the Materials through Experimental and Modeling Approach
Authors: Gin S. , Thierry F. , Minet Y. 
Published: April 2011

ABSTRACTA new approach is proposed for discussing the reliability and predictability of the models intended to evaluate the performance of glass packages under geological disposal conditions. The r(t) model developed by the CEA is used in this study to simulate original laboratory test results, and the validity of the predictions is then verified experimentally. This approach allows us to check that the key mechanisms are correctly simulated, even if they are simplified. A review of the experimental results (glass alteration kinetics and morphology of the alteration film) suggests that physically separating the glass and clay under geological disposal conditions could considerably diminish the silica pump effect attributed to reactive clays such as Boom clay or FoCa7 clay.
Incorporation of AlCl3 and As2O3 in Composite Cement Systems
Authors: Hill J , Sharp J H 
Published: April 2011

ABSTRACTAs part of an investigation into the consequences of adding inorganic metal salts to composite cements, based on blastfurnace slag (BFS) and pulverised fuel ash (PFA), the effect on the hydration behaviour of adding AlCl3 or As2O3 to the mix water of a number of cementitious systems was investigated using isothermal conduction calorimetry (ICC) and x-ray diffraction (XRD). Four cement systems were investigated; ordinary Portland cement (OPC), 3:1 BFS: OPC, 9:1 BFS:OPC and 3:1 PFA:OPC. AlCl3·7H2O and As2O3 were added to the mix water at 0.1% and 1% concentrations. Results from ICC indicated that the addition of As2O3 had very little effect on the setting and early hydration of any of the cements. AlCl3, however, inhibited the setting of the composite cements at the 1% addition level but accelerated the OPC at 0.1%. The expected hydration products were observed, with the additional observation of Friedel's salt in the presence of aluminium chloride additions and vaterite in both the aluminium and arsenic-containing systems after 180 days hydration.
Corrosion of Copper in 1 M NaCl under Strictly Anoxic Conditions
Authors: Bojinov Martin , Laitinen Timo , Mäkelä Kari , Snellman Margit , Werme Lars 
Published: April 2011

ABSTRACTThe corrosion of copper in 1 M NaCl has been investigated at room temperature and at 80°C by an on-line resistance probe, solution analysis of dissolved copper and weight loss measurements. At room temperature, corrosion of the copper as indicated by an increase of the probe resistance has been detected during the first 60–80 h of exposure. After the corrosion potential has reached the immunity region of Cu, a decrease in the resistance of the sensor is observed, probably due to redeposition of Cu from the solution. It can be concluded that the corrosion of copper at room temperature virtually stops after 60–80 h due to the anoxic conditions established in the experiments. The similarity in the trends of the corrosion and redox potential during exposure seems to indicate that Cu(II) contained in the native oxide on Cu and/or formed by homogeneous oxidation of Cu(I) during the initial oxic period of exposure acts as a redox-agent determining the chemical conditions in the closed system.
The Corrosion Rate of Copper in a Test Parcel at the Äspö Hard Rock Laboratory
Authors: Rosborg Bo , Eden David , Karnland Ola , Pan Jinshan , Werme Lars 
Published: April 2011

ABSTRACTCylindrical copper electrodes have been installed in a test parcel at the Äspö Hard Rock Laboratory and real-time corrosion monitoring was initiated in May 2001. The test parcel was emplaced on October 29, 1999, and will be retrieved in 2004. The three electrodes, each of about 100 cm2 surface area, are installed in bentonite block 36, where the temperature is about 24°C.The corrosion monitoring is performed with linear polarization resistance (LPR), harmonic distortion analysis (HDA) and electrochemical noise techniques. A value on the Stern-Geary coefficient is required to calculate the corrosion rate from the measured LPR data. A default value of 10.3 mV has been used, but an actual value can in fact be obtained from the HDA. The corrosion rate will be overestimated if the frequency of the voltage perturbation for the LPR measurements is not low enough. Electrode impedance measurements have been performed to verify this.Two and a half year after emplacement the recorded corrosion rate of copper in the above bentonite block amounts to about 2.2 μm per year (using a default value of 10.3 mV for the Stern-Geary coefficient and a 0.01 Hz voltage perturbation frequency). The actual corrosion rate is estimated to less than 0.7 μm per year (considering a measured Stern-Geary coefficient of 6.5 mV and the findings from the electrode impedance measurements).
Excavation Damage Zone in the Experimental Deposition Holes at Äspö and Comparison to Existing Data
Authors: Autio Jorma , Malmlund Hanna , Hjerpe Thomas , Kelokaski Maarit , Siitari-Kauppi Marja 
Published: April 2011

ABSTRACTDisposal in deep, stable bedrock is currently one concept for isolating high-level wastes from the environment. Repository for high-level waste in rock excavated using different drilling techniques is surrounded by an excavation damaged zone (EDZ) which properties have been changed. The micro fracturing of samples taken from the experimental deposition holes in the underground Hard Rock Laboratory at Äspö were investigated by the 14C polymethylmetha-crylate (14C-PMMA) method and scanning electron microscopy (SEM) to evaluate the impact of EDZ on migration. The porosity of the damaged rock zone is clearly higher than the porosity of undisturbed rock. The thickness of the crushed zone with significantly higher porosity is a few millimetres and the average depth of the damaged zone (i.e. a clear increase in porosity found) is from 5 to 20 mm from the hole wall. The apertures of the inter- and intragranular fractures in the crushed zone varied from 5 to 30 μm according to SEM examination. Earlier results of porosity, diffusivity and permeability measurements in granites were compiled and the results of the porosity values of Äspö diorite were compared to the porosity values measured in other types of granites. The results were compiled in permeability-diffusivity-porosity space and were found to form a plane that could be used to estimate the range of diffusivity and permeability of the Äspö diorite.
Migration Behavior of Plutonium in Compacted Bentonite under Reducing Condition by Using Electromigration
Authors: Idemitsu Kazuya , Xia Xiaobin , Kikuchi Yoshiro , Inagaki Yaohiro , Arima Tatsumi , Mitsugashira T. , Hara M. , Suzuki Y. 
Published: April 2011

ABSTRACTCarbon steel is one of the candidate overpack materials for high-level waste disposal and is expected to assure complete containment of vitrified waste glass during an initial period of 1000 years in Japan. Carbon steel overpack will be corroded by consuming oxygen introduced by repository construction after closure of repository and then will keep the reducing environment in the vicinity of repository. The reducing condition will be expected to retard the migration of redox-sensitive radionuclides by lowering their solubilities. Therefore, the presence of corrosion products of iron in buffer material is important to discuss the migration behavior of redox-sensitive radionuclides. Plutonium electromigration experiments in bentonite have been carried out with source of iron ions supplied by anode corrosion of iron coupon. Plutonium migrated from the iron anode toward cathode as deep as 1 mm of the interior of bentonite within 24 h. Thus plutonium chemical species would have positive charge and were estimated as PuOH2+or PuCl2+by the thermodynamic calculation.
Modelling of Solute Transport under Flow Conditions Varying in Time, Using the Channel Network Model
Authors: Moreno Luis , Crawford James , Neretnieks Ivars 
Published: April 2011

ABSTRACTTransport of radionuclides from a repository to the biosphere is calculated in the presence of varying boundary conditions. This may occur in Sweden, for example, during post-glacial rebound. To calculate the transport of radionuclides, the flow field has to be calculated at each time step. An alternative approach is to determine the flow field at certain time intervals; i.e., modelling the dynamic flow system as a sequence of punctuated steady states. This can be done in a rather simple way by using the Channel Network model (CNM), in which radionuclide transport is calculated by particle tracking. Intuitively one would expect such a simple procedure to be permissible and lead to small errors if the time intervals are so short that only small changes in flow rates and flow directions take place. In this paper, the technique is applied to a study case. This describes a repository located at a sub sea level location outside the coastline; where, owing to the land lift that is taking place in Scandinavia the coastline is advancing towards the repository. An important issue to be determined is the minimum number of time intervals that need to be used in order to obtain a reliable solution to radionuclide transport. It is found that the number of time intervals needed is strongly dependent on the variation in the boundary conditions. For the changing conditions used in the example tested, a number on the order of 5–9 time intervals allows a sufficiently good representation of the transport.
Corrosion of Archaeological Artefacts from the Olviya Site in Ukraine
Authors: Demchenko Larisa V. , Zlobenko Borys P. , Manichev Vyacheslav I. , Kadoshnikov Vadim V. , Spasova Ludmila V. 
Published: April 2011

ABSTRACTCopper and bronze artefacts of Olviya archaeological collection dated the first century B.C. were the objects of this study. Susceptibility to soil corrosion of archaeological artefacts from pure copper and bronze was investigated. Detailed mineralogical and metallographic investigations were performed on specially prepared samples of metallic copper, such as cut and polished sections of a cylindrical body, etc. They reveal a complex picture of metal structure and mineralogical features that can be attributed to both original technological process of manufacturing and to alteration during the burial and weathering history. Corrosion products were researched and the thickness of the corrosion layer formed for the long period of time was determined. It is shown, that the corrosion rate of artefacts produced by casting depends on composition alloys and change of metal structure after the next mechanical-thermal processing. The soil corrosion rate of copper alloys also depends on the redox conditions in the soil of Olviya site.
A Comparison of Site Characterisation Data and Modelling Results from a Radiological Assessment of the Drigg Low Level Radioactive Waste Disposal Site
Authors: Small J. S. , Abraitis P. K. , Beadle I. R. , Johnstone T. L. , Kelly P. , Pettit C. L. , Stevens G. A. 
Published: April 2011

ABSTRACTThe biogeochemical processes controlling release of radionuclides from solid low level radioactive waste (LLW) disposed at the Drigg site have been represented in a computational model in order to determine the effects of varying major element chemical parameters and solubility limits of radionuclides. The model is used to provide a source term for radiological safety assessment calculations for the groundwater pathway. Site data has been compared to the results for the initial stages of the model in order to build confidence in the conceptual and mathematical model used to derive the source term for 234U, the key dose contributor, and other radionuclides which are influenced by the biogeochemical processes. Measured aqueous concentrations of radionuclides whose release from LLW is sorption controlled are compared to the model results as a basis to discuss the uncertainty in sorption input parameters used.
Accelerated Stress Testing of a-Si:H TFTs for Amoled Displays
Authors: Sakariya Kapil , Ng Clement K.M. , Huang I-Heng , Sultana Afrin , Tao Sheng , Nathan Arokia 
Published: April 2011

ABSTRACTIn this work, we have developed a method for accelerated stress testing of TFT driver circuits for AMOLED display backplane applications. Based on high current and temperature stress measurements, acceleration factors have been retrieved, which can be used to significantly reduce the testing time required to guarantee a 20000-hour display backplane lifespan.
Statistical Modeling of Grain-Enhanced Polysilicon Thin-Film Transistor in Consideration of Grain Boundary Distribution
Authors: Cheng C. F. , Poon M. C. , Kok C. W. , Chan M. 
Published: April 2011

ABSTRACTA probabilistic model to predict the statistical distribution of grain boundaries in the thin-film transistor (TFT) with an arbitrary transistor-to-grain size ratio is proposed in this paper. Performance of the TFTs, such as carrier mobility, can be estimated and the corresponding performance variation of the fabricated devices becomes predictable when the statistical distribution of grain boundaries is known. The proposed model is still applicable even when the transistor size becomes comparable to the grain size. Reliability and accuracy of the modeling results have been extensively verified by experimental data. It is believed that the model can provide design and optimization guidelines of device variation for grain-enhanced polysilicon TFT technology.
Increase of temperature and crystallinity during electrical switching in microcrystalline silicon
Authors: Hu Jian , Stradins Paul , Branz Howard M. , Wang Qi , Weinberg-Wolf J.R. , Harley E.C.T. , Lawyer Chris , Huie Brittany , Han Daxing 
Published: April 2011

ABSTRACTWe investigate electrical stressing and switching in hydrogenated microcrystalline silicon (mc-Si:H) by thermal, and optical and electrical measurements of Cr/mc-Si:H/metal thin-film structures. Boron-doped microcrystalline Si films of 30-50 nm thick are deposited by hot-wire chemical vapor deposition (HWCVD) on Cr-coated glass at 160°C and contacted with Ag or Al. Switching in devices of size 5 to 30 mm is stimulated by a current-ramp from 10 nA to 50 mA. We find that the voltage across the mc-Si:H devices initially increases logarithmically with current, then saturates at 2∼3 V, and finally drops to a low value of 1 to 1.5 V. This drop indicates a permanent decrease of device resistance to below 1 kW. During current stressing, the surface temperature increases with the bias current, and the surface reflectivity changes. After switching, a small increase in crystalline fraction can be observed by micro-Raman scattering measurements. The observations suggest electrothermal processes which cause changes in microstructure of the mc-Si bulk during current stress.
Si Wire Light Emission Changes During Si/SiOx Interface Formation
Authors: Becerril-Espinoza F.G. , Torchynska T. V. , Rodríguez M. Morales , Khomenkova L. , Scherbina L.V. 
Published: April 2011

ABSTRACTPhotoluminescence (PL), PL excitation, Raman scattering, IR absorption spectra as well as PSi surface morphology, have been studied as a function of Si/SiOx interface formation during PSi ageing in ambient air with the aim to reveal a PL mechanism. It is shown that fresh- prepared PSi layers created at low values of the anodization current Ia is characterized by “red” emission band centered at 1.72 eV, while the samples prepared at higher values of Ia have “orange” PL band centered at 2.00 eV. During oxidation in ambient air two processes take place at the PSi ageing: the oxidation of small size Si nano-crystallites up to their disappearing and the change of silicon oxide composition at the Si/SiOx crystallite surface. These processes initiate changes in PL and PL excitation spectra. The peak position of “red” PL band shifts to the high-energy up to 1.80-1.85 eV while the “orange” band does not change essentially.
Reversible Ordering of a-Si1-xGex by the Combined Effect of Light and Temperature
Authors: Martín P. , Torres A. , Jiménez J. , Rodríguez A. , Sangrador J. , Rodríguez T. 
Published: April 2011

ABSTRACTAmorphous Si and a-Si1-xGex (0 ≤= x ≤= 0.38) films illuminated by above bandgap light, and heated between 110 and 180°C, undergoes an ordering transition, which is reversed to the amorphous phase by either heating up above 180°C or cooling down below 110°C. This structural change is investigated by Raman spectroscopy. The changes observed in the Raman spectra reveal the formation of small ordered clusters (only a few lattice parameters in diameter). The ordered state was not observed by the only effect of either light or temperature, suggesting that specific temperature and light excitation conditions are necessary to generate and support the ordered state, that appears as a nano-crystalline structure.
Performance analysis of a-Si:H detectors deposited on CMOS chips
Authors: Miazza C. , Dunand S. , Wyrsch N. , Shah A. , Blanc N. , Kaufmann R. , Cavalier L. 
Published: April 2011

ABSTRACTImage and particle sensors based on thin-film on CMOS technology are currently being developed at our laboratory. In this technology, amorphous silicon detectors are vertically integrated on top of dedicated CMOS chips. For both, vision and particle detection, this approach is expected to enhance the performances. In fact very high fill factors, increased sensitivity, and integration level, coupled with extremely low dark current density values can potentially be attained.A first optimization of the a-Si:H diodes (>1mm2) on glass substrates, with the primary focus on reducing dark current densities, gave Jdark values as low as 1 pA/cm2 (at -1 V for 1 m thick detectors). These detectors were then deposited on CMOS readout chips, but so far this step was unfortunately accompanied by an increase in Jdark to values over 10 nA/cm2.Here, the possible cause for such an increase in Jdark as well as possible “remedies” against this effect will be discussed; the principle cause is supposed to be the influence of chip topology. Possible solutions include surface treatments as well as the use of metal-i-p diode configuration. Results obtained so far with these methods are given.
Femtosecond Far-Infrared Studies of Photoconductivity in a-Si:H and a-SiGe:H
Authors: Nampoothiri A. V. V. , Dexheimer S. L. 
Published: April 2011

ABSTRACTWe present femtosecond time-resolved studies of the frequency-dependent photoconductivity in the far-infrared spectral range (∼ 1 – 10 meV) in PECVD a-SiGe:H and a-Si:H thin films. The experiments are carried out using an optical pump / terahertz (THz) probe technique, in which a femtosecond pump pulse excites carriers into the extended states and a time-delayed probe pulse measures the resulting change in the far-infrared optical properties, which are directly related to the ac photoconductivity, as the carrier distribution evolves in time. We find that the frequency-dependent conductivity measured on picosecond time scales shows a strongly non-Drude behavior, with components of the response fitting to a power-law frequency dependence, reflecting processes associated with localized states.