bluuebunny/crossref_metadata_2025 huggingface dataset:
Microstructure and Electrical Properties of PbTe Based Films Prepared by Pulsed Laser Deposition
Authors: Dauscher Anne , Lenoir Bertrand , Jacquot Alexandre , Bellouard Christine , Dinescu Maria
Published: April 2011

Lead telluride thin films have been grown on BaF2(111) substrates by pulsed laser deposition from a Nd:YAG laser (λ = 532 nm) at very low temperature (150°C). The chemical composition, the morphology and the crystallographic structure of the layers depend strongly on the deposition conditions. Post-annealing treatments of the films also affect their microstructure. Preliminary electrical properties, conducted in the temperature range of 5 to 350 K, revealed that all the samples were n-type with Hall mobility values greater than 104 cm2/V.s at low temperatures.
Growth of PbTe films by magnetron sputtering
Authors: Jdanov A. , Pelleg J. , Dashevsky Z. , Shneck R.
Published: April 2011

Thin films of PbTe were deposited on Si (111) wafers and glass substrates at a constant power for different times and at a constant time at various power levels. In some cases substrate heating to a temperature of ∼673K was performed during sputtering. Structural analysis by Xray diffraction (XRD) and high-resolution electron microscopy (HRTEM) were performed. The composition of the PbTe film was evaluated by Auger depth profile. At an appropriate combination of power and deposition time only (200) and its higher order peaks were observed in the PbTe film. It is expected that it is feasible to obtain epitaxial PbTe film by RF magnetron sputtering.
Characteristics of Polycrystalline Silicon thin Films Prepared by Pulsed Ion-Beam Evaporation
Authors: Yang Sung-Chae , Fazlat Ali , Suematsu Hisayuki , Jiang Weihua , Yatsui Kiyoshi
Published: April 2011

Using intense pulsed ion-beam evaporation technique, we have succeeded in the preparation of polycrystalline silicon thin films on silicon substrate without impurities. Good crystallinity and high deposition rate have been achieved without heating the substrate. The crystallinity of poly-Si film has been improved with increasing the density of the ablation plasma. The intense diffraction peaks of poly-Si thin films can be obtained by using the substrate bias system. The crystallinity and the deposition rate of poly-Si thin films are increased by negative bias voltage for the substrate.
Diamond Coated WC Tools for Machining Wood and Particle Board
Authors: Makala Raghuveer S. , Yoganand S.N. , Jagannadham K. , Lemaster R.L. , Bailey J.
Published: April 2011

Diamond coating was provided to improve the performance of WC-Co tools used in machining wood and particle board. Microwave plasma chemical vapor deposition was used to deposit diamond using a gas mixture with CH4: H2 in the ratio 0.5: 100 at a temperature of 900°C. The microwave energy was set at 900W and a pressure of 35Torr was maintained in the chamber. An essential factor that determines the life of polycrystalline diamond coated tools is poor film adhesion. To counter this problem, we have developed a process that includes etching away cobalt from surface regions, treatment with H2 plasma and use of TiN/ TiC intermediate and embedding layers. The TiN/ TiC layers were deposited by reactive magnetron sputtering. These layers embed diamond crystallites and improve adhesion, and in addition act as good diffusion barriers for Co. The diamond coated and uncoated tools have been characterized in the as deposited conditions and after prescribed wear by machining particle board using SEM and X-ray mapping. It was also found that the limited contact area with diamond on the cutting edge affects the adhesion of the coating. Improvement in contact area by providing a larger radius to the cutting edge is discussed.
Phase Analysis for Single Crystalline Silicon Scratched by Spherical Diamond TIP
Authors: Jeong Seong-Min , Oh Han-Seog , Park Sung-Eun , Kim Hyun-Ho , Lee Hong-Lim
Published: April 2011

The mechanical properties of silicon crystals are important from the viewpoint of wafer and device fabrication processes. It is now widely recognized that silicon undergoes a series of phase transformations when subjected to high pressures, using conventional high pressure devices, such as diamond anvils or hydrostatic pressure cells, or under indentation. Scratching on a silicon surface in the various conditions introduces various kinds of mechanical damage and stressed states. Micro-Raman spectroscopy was used to observe the phase transition of single crystal silicon. Several different phases were observed depending on scratching speed and scratched locations.
Plasma deposition of amorphous carbon films from methane atmospheres highly diluted in argon
Authors: Jacobsohn L. G. , Freire F. L.
Published: April 2011

We investigated the deposition, structure and mechanical properties of a-C:H films grown in Ar-CH4 mixtures with the Ar partial pressure ranging from 0 to 99 %. The deposition rate strongly decreased with progressive Ar dilution of the CH4 atmosphere. Films deposited in pure CH4 atmospheres have a hydrogen content of 20 at.% that showed a trend to decrease for lower CH4 partial pressures, while the density remained nearly constant at around 1.4x1023 at./cm3. Raman spectroscopy and x-ray diffraction revealed the amorphous character of the films. The compressive internal stress remained constant around 2.5 GPa and the hardness decreases for Ar rich precursor atmospheres.
Ionizing Radiation Effects on Interfaces in Carbon Nanotube-Polymer Composites
Authors: Harmon Julie P. , Muisener Patricia Anne O. , Clayton LaNetra , D'Angelo John , Sikder Arun K. , Kumar Ashok , Meyyappan Meyya , Cassell Alan M.
Published: April 2011

The purpose of this research was to probe nanotube-polymer composites for evidences of radiation induced chemistry at the interface of the host polymer and the nanotube structures. Single wall carbon nanotube (SWNT) / poly (methyl methacrylate) (PMMA) composites were fabricated and exposed to gamma radiation with a Co60 source at a dose rate of 1.28 X 106 rad/hour in an air environment for a total dose of 5.9 Mrads. Neat nanotube paper and neat PMMA were also exposed. Spun coat films of SWNT/PMMA were exposed to gamma radiation with a Ce157at a dose rate of 4.46 x 103 rad/hr for a total dose of 3.86 Mrads. Both irradiated and non-irradiated samples were compared. Glass transition temperatures were characterized by differential scanning calorimetry. Dynamic mechanical analysis and dielectric analysis evidenced changes in relaxations induced by irradiation. Irradiated composites exhibited radiation induced chemistry distinct from degradation effects noted in the pure polymer. Scanning electron microscopy provided images of the SWNTs and SWNT/PMMA interface before and after irradiation. This investigation imparts insight into the nature of radiation induced events in nanotubes and nanocomposites.
Self-Assembled Structures of Gas-Phase Prepared FePt Nanoparticles
Authors: Rellinghaus Bernd , Stappert Sonja , Acet Mehmet , Wassermann Eberhard F.
Published: April 2011

We report on a non-lithographic method for the preparation of self-assembled FePt nanoparticles via inert-gas condensation. Prior to deposition the particles can be sintered in flight at temperatures as high as TS = 1273 K. Whereas un-sintered particles have irregular shapes, particles sintered at elevated temperatures TS ≥ 793 K show a regular faceting. (High resolution) transmission electron microscopy ((HR)TEM) shows that these regularly faceted particles are of icosahedral structure. When being deposited onto amorphous carbon films, the gas-phase sintered particles are found to have a high mobility. In particular, for the high-temperature sintered FePt nanoparticles, we observe that this mobility leads to the formation of particle arrays with hexagonal close-packed arrangements. Within these ordered patches, the particles are separated from one another. Analytical investigations using energy filtered TEM (EFTEM) show that a carbon layer is formed between the particles. Magnetization analyses give results showing that the gas-phase sintered particles are superparamagnetic at room temperature with a blocking temperature of TB = 49K.
Nanofabrication at Biologically Important Length Scale: Etching of Dislocation Array in Twist-bonded Bicrystals
Authors: Mei Fang , Murtagh Martin J. , Sass Stephen L. , Wind Rikard A. , Wang Yu , Hines Melissa A.
Published: April 2011

A process to fabricate a periodic surface structure at biologically important length scale is developed and nanostructured silicon surface with a periodicity of 38 nm has been obtained. The technique relies on controlled etching of a dislocation array in the twist boundaries formed by silicon bicrystals. The deviation from a perfect periodic structure and the method to improve the perfection have been investigated.
A photoemission spectroscopic study of the interface formation in organic thin film transistors
Authors: Watkins Neil J. , Zorba Serkan , Yan Li , Gao Yongli
Published: April 2011

Pentacene is widely used in organic thin film transistors due to relatively large mobilities. It has been suggested that the functional behavior in these organic thin film transistors occurs within the first few molecular layers of the device at the interfaces between the organic and the metals and dielectrics used in fabrication of the thin film transistors. This makes understanding the electronic behavior of the interfaces involved in these devices critical. In order to better understand these interfaces we investigated the interface formation using photoemission spectroscopy to examine layer by layer growth of pentacene on Au and Ag and vice versa. We observed indications of dipole formation at the interfaces between the metals and organics for organic on metal deposition. On the other hand, more complex material intermixing takes place during metal on organic deposition and as a result, the electronic structure of the interface differs from that of organic on metal deposition.
Near-field photoconductivity imaging of a conjugated polymer blend
Authors: Riehn R. , Stevenson R. , Halls J.J.M. , Richards D.R. , Kang D.-J. , Blamire M. , Cacialli F.
Published: April 2011

We report combined scanning near-field optical microscopy (SNOM) and near-field photocurrent (NPC) imaging of a binary conjugated polymer blend. We find phase separation on a scale of about 5 μm, with a good correspondence between topographic, fluorescence, and photocurrent images. We excited at 488 nm, a wavelength at which only one of the two polymers absorbs light. Under this illumination regions that are high in the topography image show high luminescence and photocurrent.

The photoluminescence (PL) efficiencies in the different regions of the sample were determined by calculating the absorbed energy using the Bethe-Bouwkamp model, and knowledge about the chemical composition of the different phases of the polymer blend. The calculation also allowed us to conclude that the photocurrent generation efficiency (current/absorbed photons) of the different polymer phases is comparable within the limit of confidence of this experiment (±10 %).
Luminescent Polystyrene Composition Characteristics Stability Forecasting
Authors: Borisenko Artem Yu. , Senchishin Vitalij G.
Published: April 2011

The stability of properties of luminescent polystyrene compositions depending on their material structure has been studied. The samples obtained by the methods of bulk polymerization and injection molding were used for the experiment. The influence of molecular mass distribution, supramolecular structure, plasticizer concentration and geometrical size of samples on the stability of their properties in severe conditions of natural and radiation aging has been investigated.
Evolution of Solution Chemistry through Interactions with Waste Package Internal Structural Components
Authors: Pan Y.-M. , Brossia C.S. , Cragnolino G.A. , Dunn D.S. , Jain V. , Sridhar N.
Published: April 2011

The chemistry of the aqueous environment inside any breached waste packages is critical to the release of radionuclides from the waste packages for high-level waste disposal. A corrosion test cell that simulates some aspects of the internal geometry of the waste packages has been designed to investigate changes in the in-package solution chemistry. A series of tests was conducted to evaluate solution chemistry variations as a function of applied potential and temperature using a specimen of Type 316L stainless steel with a predrilled hole as a simulated pit. A micro-syringe was used to extract solutions from inside and outside the pit. The solutions were analyzed for cation concentrations using capillary electrophoresis, and the pH was measured using a micro-electrode. Preliminary measurements showed substantially high cation concentrations inside the pit due to anodic dissolution of Type 316L stainless steel. The solution pH became considerably acidic, reaching a value of 2.6. These results suggest that interactions of waste package internal structural components with incoming water may have significant influence on the evolution of water chemistry and the subsequent corrosion of waste forms such as spent nuclear fuel.
Localized Corrosion Susceptibility of Alloy 22 as a Waste Package Container Material
Authors: Cragnolino Gustavo A. , Dunn Darrell S. , Pan Yi-Ming
Published: April 2011

Alloy 22 is the material preferred by the U.S. Department of Energy for the waste package outer container for geological disposal of high-level radioactive waste at the proposed repository site in Yucca Mountain, Nevada. The susceptibility of Alloy 22 to localized corrosion is an important consideration in the evaluation of the waste package behavior and the assessment of the overall performance of the proposed repository. The effects of the environment chemical composition and temperature on localized corrosion susceptibility were examined by measuring the repassivation potential for crevice corrosion in chloride-containing solutions at temperatures ranging from 80 to 150°C. The effect of potentially inhibiting anionic species, such as nitrate, was also determined. In addition to the mill annealed material, tests were conducted on both welded and thermally aged material to evaluate microstructural effects related to container fabrication processes. The resistance of Alloy 22 to localized corrosion decreased with increasing temperature and chloride concentration. Welding and thermal aging also decreased the localized corrosion resistance of the alloy.
Effects of Lead, Mercury, and Reduced Sulfur Species on the Corrosion of Alloy 22 in Concentrated Groundwaters as a Function of pH and Temperature
Authors: Pulvirenti April L. , Needhama Karen M. , Adel-Hadadi Mohamad A. , Marks Charles R. , Gorman Jeffrey A. , Barkatt Aaron
Published: April 2011

The effect of Pb, Hg, thiosulfate and sulfide on the corrosion of Alloy 22 was studied. In solutions of 1000xJ13 groundwater doped with these contaminants, disks and U-bend specimens exhibited general corrosion and pitting at pH 1, and some dissolution at pH 13. One specimen exposed to the presence of Pb cracked catastrophically. In basic media thiosulfate and sulfide caused both oxide spalling and enhanced general corrosion.
Radiation Damage in Titanate Ceramics for Plutonium Immobilization
Authors: Strachan Denis M. , Scheele Randall D. , Kozelisky Anne E. , Sell Richard L. , Schaef H. Todd , O'Hara Matthew J. , Brown Christopher F. , Buchmiller and William C.
Published: April 2011

Radiation damage experiments are being performed with pyrochlore and zirconolite in support of the disposition of surplus weapons-ready Pu. Pyrochlore becomes amorphous in approximately 1 year from the alpha recoil damage of ∼ 1018 alphas/g from the decay of 238Pu. The dissolution rate of 238Pu-bearing ceramics increases with increasing radiation damage as measured in a 3 d MCC-1 test at 90°C. Over the same period, zirconolite retains substantial crystallinity albeit with broadened diffraction peaks. The dissolution rate also increases with increasing radiation damage.
Corrosion of Glass-Bonded Sodalite and its Components as a Function of ph and Temperature
Authors: Jeong Seung-Young , Morss Lester R. , Ebert William L.
Published: April 2011

A glass-bonded sodalite ceramic waste form (CWF) has been developed to immobilize electrorefiner salt wastes from electrometallurgical treatment of spent sodium-bonded reactor fuel for disposal. A degradation model is being developed to support qualification of the CWF for disposal in the federal high-level waste disposal system. The parameter values in the waste form degradation model were previously determined from the dissolution rates measured in MCC-1 tests conducted at 40, 70, and 90°C. The results of several series of tests that were conducted to confirm the applicability of the dissolution rate model and model parameters are presented in this paper: (1) Series of MCC-1 tests were conducted in five dilute buffer solutions in the pH range of 4.8 – 9.8 at 20°C with hot isostatic pressing (HIP) sodalite, HIP glass, and HIP CWF. The results show that the model adequately predicts the dissolution rate of these materials at 20°C. (2) Tests at 20 and 70°C with CWF made by pressureless-consolidation (PC) indicate that the model parameters extracted from the results of tests with HIP CWF can be applied to PC CWF. (3) The dissolution rates of a glass made with a composition corresponding to 80 wt. % glass and 20 wt. % sodalite were measured at 70°C to evaluate the sensitivity of the rate to the composition of binder glass in the CWF. The dissolution rates of the modified binder glass were indistinguishable from the rates of the binder glass.
Development of a Preliminary Performance Assessment Methodology for Design and Siting of a LLW Repository in Italy
Authors: Risoluti Piero , Ventura Giancarlo , Ciabatti Piercarlo
Published: April 2011

A preliminary performance assessment (PA) analysis for the LLW Repository in Italy is described in this paper. In particular, the PA analysis of the so called SA site is reported. The AMBER code has been used for the setting up of radionuclides transport simulation model both in the near-field and geosphere. The performance assessment analysis preliminarily showed that the SA site was likely to be suitable, in geological and hydrogeological terms, for hosting a LLW Repository. Total dose to the critical group for both a normal evolution scenario and cover degradation scenario was 4.2 × 10−3 mSv/year, approximately one order of magnitude lower than the 10−2 mSv/year dose constraint adopted in this study.
A Stochastic Assessment of Nuclear Waste Management Practices at the Hanford Site, Washington
Authors: Kincaid Charles T. , Eslinger Paul W. , Engel Dave W. , Nichols William E. , Bryce Robert W. , Bunn Amoret L.
Published: April 2011

Waste management and disposal decisions at the Hanford Site, Washington, depend in part on an understanding of the risks and impacts associated with alternate disposal and remedial actions. A proof-of-principle site-wide assessment of the risks and impacts associated with all wastes that will remain at the Hanford Site following cleanup has been performed for the first time. It simulates contaminant release, migration, and fate from the initiation of site operations in 1944 forward, and, thus, illustrates historical and near-term influences on long-term risk and impact.

A stochastic simulation tool capable of addressing 1000 waste discharge and disposal sites and 10 contaminants for a period of 1000 years has been created and applied. Human health and ecological risks as well as impacts to the regional economy and local cultures are estimated. The methodology developed is known as the System Assessment Capability (SAC). It is currently in a Revision 0 state corresponding to a proof-of-principle demonstration.

An initial assessment based on the planning baseline of the U.S. Department of Energy (Richland Operations office and office of River Protection) has been undertaken. Preliminary results of the assessment indicate variability in predictions is most influenced by uncertainty in:

- geochemical adsorption (i.e., distribution coefficients, Kd) for contaminant release, vadose zone, and groundwater models; especially for uranium and iodine which are somewhat but not greatly adsorbed,

- solid waste burial ground inventories of iodine-129, and

- liquid discharge site inventories of technetium-99.

It is apparent that variables governing change in performance are a function of space and time. Initially, these results point to the need for related models and data to be examined, and, if necessary, augmented through future laboratory and field studies to better quantify or reduce uncertainty.
Self-Assembly of Glass-Ceramic / CdSe / Protein Aggregations in the Optical Trap
Authors: Zavalin Andrey , Eugene Collins W. , Morgan Steven
Published: April 2011

Aggregations, created in 2-component suspension inside the optical trap zone were studied. Particles of porous glass-ceramic of CaO-TiO2-P2O5 composition and 1–50 um size were mixed with BSA molecules in water or with CdSe-TOPO 20 nm particles in toluene. Dynamic aggregations up to 300 um size were created inside the optical trap. These aggregations in comparison with one-component aggregations have a 30% higher growth rate. This effect could be explained by the stronger bonding of the protein molecules and CdSe-TOPO particles inside the glass-ceramic particle aggregations. Micro-Raman spectra, taken from dynamic and stable permanent aggregations show several new peaks, possibly associated with creation of chemical bonds.
Nanoparticulate Hydroxyapatite Enhances the Bioactivity of a Resorbable Bone Graft
Authors: Doherty Stephen A. , Hile David D. , Wise Donald L. , Ying Jackie Y. , Sonis Stephen T. , Trantolo Debra J.
Published: April 2011

A nanoparticulate-hydroxyapatite filler augmented osteointegration within a resorbable polymer based bone graft substitute designed for orthopaedic and periodontal applications. The unsaturated polyester poly(propylene glycol-co-fumaric acid) (PPF), was used to prepare the bone graft substitute. The nanoparticulate-hydroxyapatite filler was examined in terms of biocompatibility, bony ingrowth and mechanical stability in a rat calvarial defect model. The nano-hydroxyapatite fillerwas compared against a commercially available micrometer-sized hydroxyapatite(HA) filler. Histological analysis indicated that remodeling of the newly formed bone was more advanced in the defect filled with the nano-hydroxyapatite augmented PPF. Mechanical evaluation showed a more rapid increase in stiffness of the nano-hydroxyapatite PPF. Implants of the nano-HA augmented PPF showed more advanced bone formation and recovery of mechanical properties, suggesting an improved biological response to the nano-sized particles.
Development of Woven Fabric-based Electrical Circuits
Authors: Dhawan Anuj , Ghosh Tushar K. , Seyam Abdelfattah M. , Muth John
Published: April 2011

This paper describes the development of woven electrical circuits, which are formed by interlacing conducting and non-conducting threads into a woven fabric. Conductive threads in these electrical networks are arranged and woven such that they follow desired electrical circuit designs. Electronic devices can be attached to these electrical networks, which can serve as flexible circuit boards. In these woven circuits, an efficient transfer of current from one conductive yarn to an orthogonal one is achieved by the formation of an effective electrical interconnect at the point of intersection of these yarns. Formation of woven conductive networks also involves disconnect formation or cutting of conductive yarns at certain specified points. Different methods and processes were identified and applied in order to form interconnects and disconnects at specified points of these fabrics. Efficacy of these interconnects was evaluated by DC resistance and AC Signal measurements. The results of these evaluations are reported. The conductive threads woven into these fabric-based circuits were also evaluated for signal integrity issues.
Textile Based Antennas
Authors: Slade J. , Teverovsky J. , Farrell B. , Bowman J. , Agpaoa-Kraus M. , Wilson P. , Pederson J. , Merenda J. , Horowitz W. , Tierney E. , Winterhalter Carole
Published: April 2011

The increasing desire to internet the soldier on the battlefield requires a new approach to outfit the soldier with communications systems capable of operating in multiple frequency domains as shown in Table 1. Outfitting the soldier with multiple unwieldy antennas often results in the equipment being left behind, used improperly or broken. The ultimate in unobtrusive antennas is one that conforms to the body and does not interfere with the normal degrees of freedom of the soldier's uniform. Conformal antennas mounted on the body must take into account the electrical properties of the body, particularly at frequencies above 30 MHz. In addition, integration into the textile structure requires that the antenna be isolated from effects of clothing usage including clothing movement, wet operation, washing, and mechanical abrasion.
Fluorescent fibers coupled to monolithic photovoltaic arrays for sunlight conversion
Authors: Sulima Oleg V. , Cox Jeffrey A. , Sims Paul E. , Mauk Michael G.
Published: April 2011

Thin fluorescent organic fibers are used to collect short wavelength sunlight, convert it to longer wavelengths and illuminate photovoltaic (PV) arrays. Using this approach, miniature and lightweight PV arrays have been fabricated. The incoming light is collected by many fibers and mixed before reaching the PV array. Thus homogenous illumination is provided even with partially shadowed fibers, which can cover a large area and can be arranged in a form of a fabric. The PV array itself can be located in any (even dark) place.

In this work we developed and tested high-performance miniature 21 mm2 AlGaAs/GaAs monolithic arrays consisting of 6 cells connected in series. Output electric power density of 75 mW/cm2 and an open-circuit voltage about 6 V was measured outdoors for the arrays integrated with a bundle of 0.25 – 1.00 mm thick polystyrene fibers. The influence of PV array output parameters on the fluorescent fiber diameter, length, as well as on bandgap and design of solar cells is discussed.
Organic Electrochemical Smart Pixels
Authors: Andersson Peter , Nilsson David , Svensson Per-Olof , Chen Miaoxiang , Malmström Anna , Remonen Tommi , Kugler Thomas , Berggren Magnus
Published: April 2011

An all-printed organic smart pixel is achieved through the combination of an electrochemical transistor and an electrochromic display cell. Smart pixels of this kind are arranged into a cross-point matrix resulting in an active-addressed display. This type of display has been realized on coated fine paper, operates at voltages less than 2 Volts and exhibits good bistability properties. Here we report on the operation characteristics of electrochemical smart pixels in which the ion concentration of the electrolyte has been varied.
Vt-Shift Compensating Amorphous Silicon Pixel Circuits for Flexible OLED Displays
Authors: Sakariya Kapil , Servati Peyman , Striakhilev Denis , Nathan Arokia
Published: April 2011

In this paper, we present design considerations pertinent to amorphous silicon pixel circuits for mechanically flexible active matrix display applications. We describe both circuit topologies and pixel architectures that are amenable to surface emissive pixels in a-Si:H technology. Metastable shifts in the a-Si:H material characteristics after prolonged gate bias or mechanical stress are manifested in the form of increasing TFT threshold voltages and varying mobilities. As a result, the TFT drive current and consequently the OLED brightness decrease, and the pixel eventually turns off. The circuits presented here compensate for this decrease in current through the use of current programming and feedback, and allow for stable OLED brightness over longer time periods. They also enable the implementation of high aperture ratio (close to 100%), low leakage current, surface emissive OLED pixels. Results show that the circuits provide higher linearity and dynamic range than currently available pixel circuits while minimizing the pixel area. Charge injection effects at the gate of the drive TFT have been reduced by using smaller switching TFTs, along with circuit topologies that provide in-pixel current gain. All circuits meet the speed requirements of a QVGA 60 Hz refresh rate display, and occupy less than 300um x 300um area.
Up-Conversion Luminescence in Colloidal CdTe Nanocrystals
Authors: Filonovich S. A. , Gomes M. J. M. , Rakovich Yu. P. , Donegan J. F. , Talapin D. V. , Gaponik N. P. , Rogach A. L. , Eychmüller A.
Published: April 2011

We report on the efficient photoluminescence up-conversion in colloidally synthesized CdTe nanocrystals. We demonstrate that the efficiency of photon energy up-conversion and magnitude of spectral shift can be controlled: (i) by the size of the nanocrystals; (ii) by the temperature dependence of the excited state absorption coefficient; (iii) by the dependence on excitation intensity. From the analysis of the experimental data we can suggest that intrinsic gap states are involved as intermediate states in the photoluminescence up-conversion rather than nonlinear two-photon absorption or Auger processes.
GaSb-based Nanocomposites as IR-Emitters
Authors: Bakueva Ludmila , Musikhin Sergei , Sargent Edward H. , Schulz Stephan
Published: April 2011

Nanocomposites consisting of GaSb nanocrystals in a conducting polymer matrix were fabricated and investigated. The current-voltage characteristics of the nanocomposite-based diode structures have a symmetric but strongly nonlinear character. Capacitance-voltage characteristics of the structures were investigated both in the dark and under illumination and compared with those of a pure polymer. At applied voltages exceeding 7–10 V (for different samples) electroluminescence begins and steeply increases. The position of the maximum of the measured electroluminescence spectra can be made to vary in the 1.3 – 1.6 μm wavelengths region by changing nanocrystal size. Photoluminescence spectra have a maximum nearly coinciding with that of electroluminescence but of considerably larger width. The results demonstrate the promise of GaSb-based nanocomposites for infrared light-emitting devices operating in the 1.3–1.6 μm spectral region used in optical communication systems.
Spectroscopic Study of Rare Earth Doped Nano-Crystalline Silicon in Sio2Films
Authors: Rozo C. , Fonseca L. F. , Resto O. , Weisz S. Z.
Published: April 2011

Si-rich SiO2, Nd-doped Si-rich SiO2and Nd-doped SiO2thin films were prepared. Photoluminescence (PL) spectra for visible and infrared were obtained for each as-deposited film. The samples were annealed by steps to different temperatures within the range 600°C-1100°C for 30 minutes at each annealing temperature. PL spectra were obtained at each step and their characteristics were studied. The best annealing temperature for the PL of the rare earth (RE) ions was obtained. The PL spectra of the films were compared with one another. Energy transfer from the silicon nanocrystals (Si nc) to the RE ions is verified using excitation wavelength and excitation power spectra.
Tunable Porous Silicon Mirrors for Optoelectronic Applications
Authors: Weiss Sharon M. , Haurylau Mikhail , Fauchet Philippe M.
Published: April 2011

Tunable porous silicon mirrors were fabricated as building blocks for optical interconnects and as a first step towards efficient routing of information on a small size scale. The basic structures for the tunable mirrors are porous silicon microcavities infiltrated with liquid crystals. The optical properties of the mirrors are influenced by thermal or electric field modulation. When the device is heated or a voltage is applied, the orientation of the liquid crystals changes, causing a change in the effective refractive index of the liquid crystals within the mirror. The position of the reflectance resonance of the porous silicon microcavity is particularly sensitive to such changes in the refractive index. A reversible 10nm shift of the reflectance resonance of the mirror, leading to a 30% change in the amplitude of reflectance, has been observed due to thermal effects. Not only do these results show potential for future devices, but they also confirm that the liquid crystals are able to rotate in the constricted geometry of the porous silicon microcavities. For voltage driven devices, careful attention needs to be given to the configuration of the electrical contacts. The effectiveness of various device geometries has been investigated. Using standard lithographic techniques, aluminum contacts with minimum feature sizes of 10 microns were patterned directly on the porous silicon surface. A study on the use of free-standing porous silicon films was also performed.
Effective Medium Calculations of the Electromagnetic Behavior of Single Walled Carbon Nanotube Composites
Authors: Schultz John W. , Moore Rick L.
Published: April 2011

Dielectric properties of single walled carbon nanotube assemblies were calculated with an effective medium approximation at frequencies from 200 MHz to 200 GHz. The model treats the carbon nanotubes as layered cylinders, each with a core, a graphene layer and an outer layer, to investigate the dielectric properties of coated and filled nanotubes. The graphene and metal layer properties were modeled with a Drude approximation based on literature data. A generalized Bruggeman model was then used to determine the macroscopic behavior of the modified carbon nanotubes in a composite structure as a function of volume fraction, frequency, and aspect ratio. The depolarization factors in this model were scaled by the normalized effective permittivity to better account for percolation behavior. The model showed a wide variety of frequency dependent dielectric properties. Uncoated tubes were calculated to form highly conductive materials at volume fractions of just a few percent and metal-coated tubes enhanced the conductivity by an order of magnitude. Calculations of nanotubes with insulating coatings showed that high dielectric constants with moderate to low dielectric loss were possible.
Formation of 3-Dimensionally Orientated Nano-sized Crystals in an Amorphous Alloy under Ion Beam Irradiation
Authors: Kamikawa Takuya , Tarumi Ryuichi , Takashima Kazuki , Higo Yakichi
Published: April 2011

We have succeeded to form three-dimensionally orientated nano-sized crystals in a Ni-P amorphous alloy under focused ion beam (FIB) irradiation. The FIB micro-fabrication was performed on an electroless deposited Ni-P amorphous alloy and thin films with a thickness of 100 nm were prepared. Transmission electron microscopy (TEM) observation for irradiated areas revealed the formation of crystallographically orientated nano-sized crystals (NCs) in the irradiated region. The grain size of NCs was less than 10 nm in diameter. Electron diffraction analysis showed that the formed NCs have a face-centered-cubic (f.c.c.) structure and the following orientation relationships among the specimen, the NCs and the FIB direction: irradiated plane // {111}f.c.c. and ion beam direction // <110>f.c.c..
Nanometer-scale Pattern Transfer Using Ion Implantation
Authors: Matsuura Naomi , Simpson Todd W. , McNorgan Chris P. , Mitchell Ian V. , Mei Xiang-Yang , Morales Patrick , Ruda Harry E.
Published: April 2011

Conventional, broad-area, ion implantation has been combined with unconventional masking to create 2-D geometrical patterns of amorphization in single crystals, with selectable motifs. The patterns are fully developed by use of selective etching. Two examples are discussed. In the first example, a self-assembled array (with lattice spacing ∼1 μm) of silica spheres is used as an implant mask over InP. The variation of the mask thickness created by the sphere geometry modulates the implantation depth in a periodic fashion, which is subsequently revealed after selective etching of the associated amorphized volumes. In the second example, nanochannel arrays in an alumina film are used as an implant mask to produce a hexagonal closed packed array of amorphized cylinders in InP and SrTiO3 substrates. The ion beam-amorphized regions of the substrate are then removed by selective chemical etching to achieve the full 3-D patterning of 55 nm diameter holes on a 100 nm lattice spacing.
New Ge-Sn materials with adjustable bandgaps and lattice constants
Authors: Bauer Matthew R. , Tolle John , Chizmeshya A. V. G. , Zollner S. , Menendez J. , Kouvetakis J.
Published: April 2011

The synthesis and optical properties of a new class of Si-based infrared semiconductors in the Ge1-x Snx system are described. Chemical methods based on deuterium-stabilized Sn hydrides and UHV-CVD were used to prepare a wide range of metastable compositions and structures directly on silicon. These materials exhibit high thermal stability, superior crystallinity, and unique crystallographic and optical properties, such as adjustable band gaps and lattice constants. These properties are characterized by Rutherford backscattering, low-energy secondary ion mass spectrometry, high-resolution transmission electron microscopy, x-ray diffraction as well as infrared and Raman spectroscopies and spectroscopic ellipsometry. The films grow essentially strain free and display a strong compositional dependence of the band structure.
Lattice Site Location Studies of Rare-Earths Implanted in ZnO Single-Crystals
Authors: Rita Elisabete M.C. , Wahl Ulrich , Lopes Armandina L. , Araújo João P. , Correia João G. , Alves Eduardo , Soares José C. , Collaboration Isolde
Published: April 2011

In this work we report on the lattice site location of rare earths in single-crystalline ZnO by means of the emission channeling (EC) technique. Following low dose (3×1013at/cm2) 60 keV ion implantation of the precursor isotope 169Yb, a position-sensitive electron detector was used to monitor the angular distribution of the conversion electrons emitted from 169Tm* as a function of the annealing temperature up to 600°C in vacuum. An additional annealing at 800°C in flowing O2 was performed. The EC measurements revealed that around 95–100% of the rare earth atoms occupy substitutional Zn sites up to an annealing temperature of 600°C/vacuum. After the 800°C/O2 annealing, the emission channeling effects decreased considerably.
Deposition of II/VI thin films from Novel Single-Source Precursors
Authors: Afzaal Mohammad , Malik Mohammad Azad , O'Brien Paul , Park Jin-Ho
Published: April 2011

The compound [MeCd(SePiPr2)2N]2 is used as a single-source precursor to cadmium selenide films in a low-pressure chemical vapour deposition process. Thermogravimetric analysis (TGA) shows that the precursor is reasonably volatile, making it suitable for the deposition of thin films. As-deposited films were identified as CdSe confirmed by X-ray powder diffraction (XRPD) and their morphologies were studied by scanning electron microscope (SEM).
DLTS studies of defects produced in n-type silicon by hydrogen implantation at low temperature
Authors: Sugiyama Takahide , Ishiko Masayasu , Kanazawa Shigeki , Tokuda Yutaka
Published: April 2011

Metastable defects are discovered in hydrogen-implanted n-type silicon. Hydrogen implantation was performed with the energy of 80 keV to a dose of 2×10 cm- at 109 K. After implantation, the sample temperature was raised to room temperature. DLTS measurements were carried out in the temperature range 80–290 K for fabricated diodes. When the sample is reverse-biased at 10V for 10 min at room temperature and then is cooled down to 80 K, three new peaks labeled EM1, EM2 and EM3 appear around 150, 190 and 240 K, respectively. The introduction of metastable defects is found to be characteristic of low temperature implantation. We have evaluated properties of EM1 in detail. EM1 with thermal emission activation energy of 0.29 eV has a peak in concentration around the depth of 0.64 μ m, which corresponds to the projected range of 80 keV hydrogen. EM1 is regenerated with the reverse bias applied around 270 K and is removed with the zero bias around 220 K.
Mesoscopic study of the electronic properties of thin polymer films
Authors: Ribeiro Ricardo M. , Ramos Marta M. D. , Almeida A. M. , Correia Helena M. G. , A Jaime Silva , Stoneham M.
Published: April 2011

Conjugated polymers are very interesting for light emitting diodes. Further improvement in device performance requires a better understanding on the correlation between the polymer structure and device characteristics. A mesoscopic study using a generalised Monte Carlo method of bipolar charge transport in thin poly(p-phenylene-vinylene) (PPV) films is presented in this paper. We show that energy and spatial molecular disorder have a serious influence on migration of charge carriers within the polymer layer. The transfer of carriers between two polymer chains is made dependent on the chemical potential difference as well as on other features such as the distance between both molecules involved and the direction of the electric field. The purpose of the present work is to clarify the effects of local energy and polymer structural disorder on current flow, trapping and recombination on polymer based devices.
Ti/Ni/Au/Diamond MIS Field Effect Transistors With TiO2 Gate Dielectric
Authors: Cai Yuhong , Christou Aris
Published: April 2011

Ti/Ni/Au/diamond metal-insulator-semiconductor field effect transistors with TiO2 gate dielectric have been successfully fabricated. In this work, multi-layer metallization on the semiconducting diamond surface was investigated. Post-metallization annealing was performed and EDS analysis was conducted both before annealing and after annealing. Elevated temperature annealing accelerates the diffusion between multi-layer metal and lowers the ohmic contact resistance of the interface. Current-voltage characteristics of the transistor are reported.
Far Infrared Spectroscopy of In0.53Ga0.47As Quantum Wells on InP(100)
Authors: Rowell N. L. , Lockwood D. J. , Poole P. J. , Yu G.
Published: April 2011

Polarized far infrared reflectance was measured at oblique incidence for In0.53Ga0.47As / InP multiple quantum wells grown by chemical beam epitaxy on InP(100) wafers. Both the well thickness (0.25 - 20 nm) and number of periods (10 - 40) were varied. The reflectance spectra contained sharp Berreman modes at the frequencies of the transverse (TO) and longitudinal (LO) optical phonons. The contributions of the individual phonons were resolved with the model fits. Interface layer phonon modes were observed with intensity increasing with number of wells. The interface layers were 0.6 nm thick and of different composition to adjoining wells consistent with cross-sectional scanning tunneling microscope results on the same samples. The variation due to phonon confinement of the InAs- and GaAs-like LO and TO phonon frequencies was obtained.
Precessional strategies for the ultrafast switching of soft and hard magnetic nanostructures
Authors: Devolder T. , Belmeguenai M. , Schumacher H. W. , Chappert C. , Suzuki Y.
Published: April 2011

We discuss the precessional, quasi-ballistic switching of magnetization in magnetic nanostructures. In soft spin-valve cells, fast and energy-cost effective magnetization switching can be triggered by a transverse field pulse of moderate amplitude, below the in plane anisotropy field, because of an amplification effect brought by the demagnetizing field at the early stage of the reversal. The same effect is no more possible in hard nanomagnets with perpendicular easy magnetization axis. We propose a new type of nanostructured magnetic device, designed to overcome this limitation. The speed is obtained through the use of a very high effective magnetic field, obtained by incorporating a significant exchange field which stores the energy in the form of a constrained domain wall surrounding a region of high magnetic anisotropy. This stored energy is partially available to accelerate the magnetization reversal in a precessional scenario. We illustrate the concept by studying numerically a model system. The key parameter for the reversal is the ratio of the domain wall width to the structure lateral dimension. Possible routes for device preparation are discussed. Promising application to magnetic storage are anticipated.
Nanoscale analysis of a Co-SrTiO3 interface in a Magnetic tunnel junction
Authors: Maurice J.-L. , Pailloux F. , Imhoff D. , Contour J.-P. , Barthélémy A. , Bowen M. , Colliex C. , Fert A.
Published: April 2011

We use High Resolution Electron Microscopy together with Electron Energy Loss Spectroscopy to analyze the crystallography and the chemical configuration of a Co/SrTiO3 interface in a Co/SrTiO3/La2/3Sr1/3MnO3 magnetic tunnel junction.

PACS: 75.47.-m, 75.70.Cn, 68.37.Lp, 79.20.Uv
Sm Doping Effects on Electrical Properties of Sol-Gel Derived SrBi2Ta 2O9 Films
Authors: Tokumitsu Eisuke , Kishi Masahito
Published: April 2011

We have characterized (Sr,Sm)Bi2Ta 2O9 (SSBT) films fabricated by the sol-gel technique on Pt/Ti/SiO2/Si substrates. For ferroelectric-gate FET applications, a ferroelectric film which has a small remanent polarization and a relatively large coercive field is required. It is demonstrated that Sm doping in ferroelectric SBT films is effective to reduce the remanent polarization and enhance the coercive field. Sr0.5Sm0.2Bi2.2Ta2O9 films (150nm) crystallized at 850°C exhibits good electrical properties with a remanent polarization of 1.7 μC/cm2 and a coercive fields of 85 kV/cm. These values are suitable for ferroelectric-gate FET applications.
Thin-Film Indium Oxide Doped with Refractory Metals
Authors: Yoshida Yuki , Warmsingh Chollada , Gessert Timothy A. , Perkins John D. , Ginley David S. , Coutts Timothy J.
Published: April 2011

The electrical and structural properties of sputtered indium oxide (In2O3) thin films doped with Mo, Zr, and Ti were studied. Properties of these films are compared to undoped In2O3 and tin-doped In2O3 (ITO). The as-sputtered films, doped with Mo (IO:Mo), exhibited high mobility (45 cm2V-1s-1). Pulsed laser deposition (PLD) was also used to deposit IO:Mo films. The highest mobility achieved for an as-deposited PLD IO:Mo film deposited onto a glass substrate was 42.7 cm2V-1s-1. However, PLD IO:Mo films deposited on single-crystal yttria-stabilized zirconia (YSZ) substrates exhibited a higher mobility of 53.6 cm2V-1s-1 and a greater degree of structural orientation than the sputtered films. Following post-deposition annealing, both the sputtered films on glass, and the PLD films on YSZ, exhibited improved mobilities of 47 and 66 cm2V-1s-1, respectively.
Experimental and Theoretical Studies of the Si(100)/SiO2 Interface Formed by Wet and Dry Oxidation
Authors: Chowdhuri A. Roy , Jin Dong-Un , Takoudis C. G.
Published: April 2011

Interfacial strain and substoichiometric silicon oxides are the two principal causes that result in the redshift of the transverse and longitudinal optical phonons of the asymmetric stretch of O in the Si-O-Si bridging bond of thermal SiO2 with decreasing oxide thickness. Analyses to comprehend these effects, therefore, require consideration of both strain and interfacial substoichiometry. A method to isolate the contributions of strain and suboxide content towards the observed shifts is proposed. The procedure, which utilizes simple optical model and effective medium approximation, allows estimation of the average strain and suboxide concentration in films of different thickness. Analyses of oxides formed at two different temperatures (550 and 700°C) with dry and wet oxygen reveal how process conditions affect the interface properties.