bluuebunny/crossref_metadata_2025_split huggingface dataset:
Temperature Dependent Line-Shape of the Silicon Dangling Bond EPR-Resonance in Polycrystalline Silicon
Authors: Nickel N. H. , Schiff E. A. 
Published: April 2011

AbstractThe temperature dependence of the silicon dangling-bond resonance in polycrystalline (poly-Si) and amorphous silicon (a-Si:H) was measured. At room temperature, electron paramagnetic resonance (EPR) measurements reveal an isotropie g-value of 2.0055 and a line width of 6.5 and 6.1 G for Si dangling-bonds in a-Si:H and poly-Si, respectively. In both materials spin density and g-value are independent of temperature. While in a-Si:H the width of the resonance did not change with temperature, poly-Si exhibits a remarkable T dependence of ΔHpp. In unpassivated poly-Si a pronounced decrease of ΔHpp is observed for temperatures above 300 K. At 384 K ΔHpp reaches a minimum of 5.1 G, then increases to 6.1 G at 460 K, and eventually decreases to 4.6 G at 530 K. In hydrogenated poly-Si ΔHpp decreases monotonically above 425 K. The decrease of ΔHpp is attributed to electron hopping causing motional narrowing. An average hopping distance of 15 and 17.5 Å was estimated for unhydrogenated and H passivated poly-Si, respectively.
Annealing Studies of Visible Light Emission from Silicon Nanocrystals Produced by Implantation
Authors: Ghislotti G. , Nielsen B. , Di Mauro L. F. , Sheey B. , Mutti P. , Pifferi A. , Taroni P. , Valentini L. , Corni F. , Tonini R. 
Published: April 2011

AbstractThe annealing behavior of silicon implanted SiO2 layers is studied using continuous and time-gated photoluminescence (PL). Two PL emission bands are observed. A band centered at 560 nm is present in as implanted samples and it is still observed after 1000 °C annealing. The emission time is fast (0.2 -2 ns). A second band centered at 780 nm further increases when hydrogen annealing was performed. The emission time is long (1 μs - 0.3 ms).
Effect of Quantum-Well Structures on the Thermoelectric Figure of Merit in the Si/Si1-xGex System
Authors: Sun X. , Dresselhaus M. S. , Wang K. L. , Tanner M. O. 
Published: April 2011

AbstractThe Si/Si1-xGex quantum well system is attractive for high temperature thermoelectric applications and for demonstration of proof-of-principle for enhanced thermoelectric figure of merit Z, since the interfaces and carrier densities can be well controlled in this system. We report theoretical calculations for Z in this system, based on which Si/Si1-xGex quantum-well structures were grown by molecular-beam epitaxy. Thermoelectric and other transport measurements were made, indicating that an increase in Z over bulk values is possible through quantum confinement effects in the Si/Si1-xGex quantum-well structures.
Spectral Diffusion of Ultra-Narrow Fluorescence Spectra in Single Quantum Dots
Authors: Empedocles S. A. , Norris D. J. , Bawendi M. G. 
Published: April 2011

AbstractWe collect and spectrally resolve photoluminescence from single CdSe nanocrystallite quantum dots. By eliminating spectral inhomogeneities, we reveal resolution limited linewidths < 120μev at 10K. These lines are more than fifty times narrower than what has previously been reported using ensemble measurements. Light driven spectral diffusion is seen as a form of power broadening and may be the cause of surprisingly broad linewidths at room temperature. In addition, we see no evidence of excited state emission or coupling to acoustic phonons.
Cathodoluminescence of CdSe/ZnS Quantum Dot Composites
Authors: Rodriguez-Viejo J. , Heine J. R. , Dabbousi B. O. , Mattoussi H. , Michel J. , Bawendi M. G. , Jensen K. F. 
Published: April 2011

AbstractWe report cathodoluminescence and photoluminescence spectra originating from ZnS overcoated CdSe nanocrystals of 33 and 42 Å diameter imbedded in a ZnS matrix. The thin film quantum dot composites were synthesized by electrospray organometallic chemical vapor deposition. The cathodoluminescence intensity depends on the crystallinity of the ZnS matrix and on the voltage and current density applied. Electron beam irradiation caused a decrease of the luminescence which may be explained by electron ionization of the quantum dots. Quenching of the cathodoluminescence at low temperatures is attributed to a more efficient trapping of the ionized electrons in deep traps inside the ZnS matrix.
Optical Properties of Cuprous Oxide Nanocrystals
Authors: Rodney P. J. , Freedhoff M. I. , Marchetti A. P. , McLendon G. L. , Fauchet P. M. 
Published: April 2011

AbstractOptical properties of size restricted Cu2O obtained through aqueous and non aqueous preparations are compared with those of commercially available bulk crystals. One method of synthesis involved using polyvinyl alcohol as a restraining agent in an aqueous preparation to produce nanocrystals having diameters with a mean of 11 nm and a standard deviation of 6 nm. Low-temperature spectroscopie studies indicate size restriction effects are manifest by a decrease in exciton luminescence and a 3.0 to 9.0 meV blue shift in 0,0 transition. No noticeable changes in the dynamics were observed for the nanocrystals, indicating no alteration or relaxation of the selection rules for the direct forbidden transition.
Luminescence and Surface-State Characteristics in P-Type Porous Silicon
Authors: Ramirez Porras A. , Resto O. , Weisz S. Z. , Goldstein Y. , Many A. , Savir E. 
Published: April 2011

AbstractPulse measurements on the porous-Si/electrolyte system are employed to determine the surface effective area and the surface-state density at various stages of the anodization process used to produce the porous material. Such measurements were combined with studies of the photoluminescence spectra. These spectra were found to shift progressively to the blue as a function of anodization time. The luminescence intensity increases initially with anodization time, reaches a maximum and then decreases with further anodization. The surface state density, on the other hand, increases with anodization time from an initial value of ∼2×1012 cm−2 for the virgin surface to ∼1013 cm−2 for the anodized surface. This value is attained already after ∼2 min anodization and upon further anodization remains fairly constant. In parallel, the effective surface area increases by a factor of 10–30. This behavior is markedly different from the one observed previously for n-type porous Si.
The recombination statistics of the visible photoluminescence of silicon nanocrystals
Authors: Diener J. , Kovalev D. I. , Ganichev S. D. , Polisski G. , Koch F. 
Published: April 2011

AbstractA pulsed, high-power TEA CO2 laser with Unes in the region from 9.2 to 10.6 μm has been used to irradiate luminescent porous Si samples. The IR laser pulses heat the sample on a time scale much shorter than the PL decay time which is at 300 K for the PL at 1.65 eV in the order of tenth of μs. One IR pulse serves to increase the temperature of the luminescing particles in ∼2 μs up to 100°C. This increase of temperature leads to a efficient reduction of the photoluminescence (PL) intensity. However, the PL decay times are almost not affected by the heating pulse. Based on this measurement a picture of the recombination statistics that takes account of the granular Nature of the material is developed.
Preparation of Microcrystalline Silicon with the Layer-by-Layer Technique at Various Plasma Excitation Frequencies
Authors: Hapke P. , Carius R. , Finger F. , Lambertz A. , Vetterl O. , Wagner H. 
Published: April 2011

AbstractFor application as nucleation layer in thin film devices, microcrystalline silicon was deposited with the layer-by-layer technique using plasma excitation frequencies between 27 and 95 MHz, various hydrogen treatment times and various film thicknesses per layer. An optimum phase transformation is found at an intermediate plasma excitation frequency, i.e. at this frequency the shortest hydrogen annealing time is necessary for an effective amorphous-to-crystalline phase transformation.
Microstructures of Luminescent nc-Si by Excimer Laser Annealing of a-Si:H
Authors: Huang Xinfan , Wu Wei , Shen Honghui , Li Wei , Chen Xiaoyuan , Xu Jun , Chen Kunji 
Published: April 2011

AbstractWe have reported for the first time on visible photoluminescence (PL) in crystallized a-Si:H/a-SiNx:H multilayer structures by CW Ar ion laser annealing treatments. In this paper we present new results on visible PL from crystallized a-Si:H by using KrF excimer pulse laser (wavelength 248 nm) irradiating treatments. The transmission electron microscopy and Raman scattering studies reveal the microstructures of crystallized Si films, which depend on the pulse number and the pulse energy density of KrF laser. When the laser pulse energy density is higher than 520 mJ/cm2, the nanosized Si crystallites (nc-Si) can be formed from a-Si:H layers with a thickness of 100 nm and strong PL with a peak wavelength of 610 nm has been observed at room temperature.
Deposition of Photoluminescent Nanocrystalline Silicon Films by SiF4-SiH4-H2 Plasmas
Authors: Cicala G. , Bruno G. , Capezzuto P. , Schiavulli L. , Capozzi V. , Perna G. 
Published: April 2011

AbstractVisible photoluminescence at 1.62 eV has been observed at room temperature from fluorinated and hydrogenated nanocrystalline silicon (nc-Si:H,F) produced in a typical plasma enhanced chemical vapor deposition system. The use of SiF4-SiH4-H2 mixture, because of the H2 dilution and the presence of SiF4, favours the amorphous - crystalline transition through the etching process of the amorphous phase. The x - ray diffraction measurements give an average grain size of about 100 Å. The presence of these nanocrystals shifts the absorption edge of the films towards higher energy. An energy gap of 2.12 eV is estimated, although the hydrogen content in the material is only 4.5 at. %. The temperature dependence of the photoluminescence behaves similarly to that of porous silicon.
Nanocrystalline Ge Synthesis by Picosecond Pulsed Laser Induced Melting and Rapid Soldddtcation
Authors: Solis J. , Siegel J. , Garcia C. , Jimenez J. , Serna R. 
Published: April 2011

AbstractMelting and rapid solidification has been induced in DC-sputtered amorphous Ge (a-Ge) films on glass substrates by irradiation with picosecond laser pulses at 583 nm. The melting-solidification kinetics has been followed by means of real time reflectivity measurements with ns resolution and the structure of the rapidly solidified material has been analyzed by means of Raman spectroscopy in micro-Raman configuration. The results obtained show that for laser pulse fluences above a certain threshold recalescence occurs during solidification leading to the formation of nanocrystalline Ge embedded in an amorphous matrix. The phonon correlation length (L) obtained from the Raman spectra of the irradiated regions has been used to analyze the evolution of the crystallite size with the laser fluence. For low fluences above the recalescence threshold, the values of L are in the 8–10 nm range. However, if the fluence is sufficiently increased, the crystallite size shows a clear linear dependence on the fluence with phonon correlation lengths scaling from 6 to 13 nm.
Electrical Properties of the Multilayer Structures Based on Ultrathin Diamond-Like Carbon Films
Authors: Polyakov V. I. , Perov P. I. , Rossukanyi N. M. , Rukovishnikov A. I. , Khomich A. V. , Baranov A. M. 
Published: April 2011

AbstractThe electrical characteristics of multilayer structures based on amorphous ultrathin diamondlike carbon films were investigated including dynamic and quasi-static current-voltage characteristics, capacitance-voltage characteristics, deep level transient spectra. The effect of illumination and temperature on these characteristics was also investigated. For the multilayer structures composed of lower band gap amorphous carbon layers separated with higher band gap ones, there were observed well-defined regions of negative differential resistance and sharp 20-fold changes in capacitance at definite voltages. Activation energies, capture cross sections, and locations of trapping centers were defined. The effects observed are discussed in terms of trap-assisted tunneling and, also, in terms of resonant tunneling between energy levels in superlattices and charge filling of the quantum wells and trapping centers.
Nucleation and Growth of μc-Si:H n- and p-Type Layers in a-Si:H p-i-n AND n-i-p Solar Cells: Real Time Spectroellpsometry Studies
Authors: Koh Joohyun , Fujiwara H. , Wronskii C. R. , Collins R. W. 
Published: April 2011

AbstractWe have applied real time spectroellipsometry (RTSE) to study the growth of microcrystalline silicon n- and p-layers [μc-Si:H:(P,B)] incorporated into amorphous silicon (a-Si:H) p-i-n and n-i-p solar cells, respectively. In previous research, we have applied RTSE to characterize a-Si:H solar cells having only amorphous component layers. The μc-Si:H(P,B) component layers, however, pose a more difficult RTSE analysis problem for two reasons. First, the near-surface of the underlying i-layer is modified in the μc-Si:H:(P,B) growth process, and second, the microstructural evolution near the i/(n,p) interfaces is very complicated. From RTSE spectra (1.5 < hv < 4 eV) collected every ∼4–15 s during growth, we have extracted the time evolution of the μc-Si:H:(P,B) layer microstructure, thicknesses, and optical properties along with the modifications that the near-surface i-layer properties undergo in the formation of the i/(n,p) interfaces. We suggest that the beneficial optical properties of the microcrystalline layers may be due to size effects in the crystallites that make up the films.
Carbon Coated Nanoparticle Composites Synthesized in an RF Plasma Torch
Authors: Scott John Henry J. , Majetich Sara A. , Turgut Zafer , Mchenry Michael E. , Boulos Maher 
Published: April 2011

ABSTRACTFeCo alloy nanoparticles are synthesized in an RF plasma torch reactor and characterized using X-ray powder diffraction (XRD) and transmission electron microscopy (XRD). Bare, uncoated particles exhibit a chain-like agglomeration morphology marked by large ring- and bridge-like structures surrounding open voids. Acetylene was used to generate large numbers of carbon-coated nanoparticles similar to those produced in carbon arc reactors. Conventional TEM of this powder revealed numerous particles below 50 nm in diameter embedded in a carbonaceous matrix. These results establish RF plasma torch processing as a well-characterized, scalable alternative to carbon arc synthesis of encapsulated nanoparticles.
Synthesis of Nanocomposite thin film Ti/Al Multilayers and Ti-Aluminides
Authors: Banerjee R. , Zhang X. D. , Dregia S. A. , Fraser H. L. 
Published: April 2011

ABSTRACTNanocomposite Ti/Al multilayered thin films have been deposited by magnetron sputtering. These multilayers exhibit interesting structural transitions on reducing the layer thickness of both Ti and Al. Ti transforms from its bulk stable hep structure to fee and Al transforms from fee to hep. The effect of ratio of Ti layer thickness to Al layer thickness on the structural transitions has been investigated for a constant bilayer periodicity of 10 nm by considering three different multilayers: 7.5 nm Ti / 2.5 nm Al, 5 nm Ti / 5 nm Al and 2.5 nm Ti / 7.5 nm Al. The experimental results have been qualitatively explained on the basis of a thermodynamic model. Preliminary experimental results of interfacial reactions in Ti/Al bilayers resulting in the formation of Ti-aluminides are also presented in the paper.
Lowered Diffusivity in TiO2 with a Nanophase Dispersion of SiO2
Authors: Crosbie Gary M. 
Published: April 2011

ABSTRACTIn materials that are subject to environmental reactions, one way to increase durability is to decrease the chemical interdiffusion rate. In metal systems, mass transport by diffusion is enhanced – if any change – with finer grained microstructures, because of the greater number of high diffusion interface and boundary paths. In non-metals, increased transport is not necessarily the case, as other mechanisms may control the overall diffusivity. C. Wagner [1] showed the theoretical basis of transport in certain nanocomposite cases based on space charge layers at interfaces.In an oxide-in-oxide nanocomposite, one can use the tools of bulk analysis to study the near-interface effects on transport. The immiscible pair, TiO2-SiO2, was used as a model system. Nanophase powders (50 and 200 m2/g, respectively) from flame hydrolysis were dispersed with high shear, then freeze-dried and hot-pressed to near theoretical density. Transmission electron microscopy was used to show < 10 nm particles in the composites produced at the time of diffusivity measurement. The rate of change of four-point electrical conductivity in response to a change in oxygen partial pressure was used to estimate chemical diffusivity. The re-equilibration differences between TiO2 diffusivity for bars of about 10 times different square cross-section areas confirmed the interpretation of the conductance rate changes to be the result of bulk interdiffusion.The interdiffusion rate in the nanoscale dispersoid composites was more than 5 times lower than for same SiO2-fraction composites after coarsening which were like TiO2 with no second-phase. Results are in qualitative agreement with models for impurity segregation to interfaces and for space charge layers near the dispersed nanoparticles.
Nanocrystalline BaTiO3 from the Gas-Condensation Process
Authors: Li Shaoping , Eastman J. A. , Thompson L. J. , Bjormander Carl. , Foster C. M. 
Published: April 2011

ABSTRACTNanocrystalline BaTiO3 can be prepared by the gas condensation method at a temperature as low as 700°C, with an average particle size as small as 18nm. The stoichiometry of nanocrystalline BaTiO3 particles can be controlled precisely and reproducibly. Nanocrystalline BaTiO3 powders, fabricated by a novel e-beam evaporation method, show good sintering behavior with a high density at a temperature as low as 1200°C. These samples exhibit a relatively larger dielectric constant than that of coarse-grained BaTiO3. In addition, a thermal analysis has been also carried out to determinethe lowest temperature for forming nanostructured BaTiO3 from Ba/Ti oxidized clusters at ambient pressure.
Physical and Chemical Properties of CaCl2/H2O and LiBr/H2O Systems Confined to Nanopores of Silica Gels
Authors: Aristov Yurii I. , Tokarev Mikhail M. , Cacciola Gaetano , Restuccia Giovanni , DiMarco Gaetano , Parmon Valentin N. 
Published: April 2011

ABSTRACTHere we present physical and chemical properties of CaCl2/H2O and LiBr/H2O systems confined to nanopores of silica gels. Sorption isobars, isosters and isotherms were measured at temperature 293 – 423K and vapor partial pressure 8–133 mbar. Specific heat of the systems was found as a function of temperature (300 – 400K) and sorbed water content (0 – 53 wt.%). Solidification/melting diagrams were measured over 170 – 320K temperature range at salt concentrations 0–50 wt.%. The results obtained evidenced a significant change in the thermodynamic properties of CaCl2/H2O and LiBr/H2O systems due to confinement to the silica gel micropores.
Carbon Black-Filled Polymer Blends: A Scanning Probe Microscopy Characterization
Authors: Leclère Ph. , Lazzaroni R. , Gubbels F. , Calberg F. , Dubois Ph. , Jérôme R. , Brédas J. L. 
Published: April 2011

ABSTRACTConducting polymer composites, that consist of a conducting filler randomly distributed throughout an insulating polymer or polymer blend, attract interest in several application fields such as sensors or electromagnetic radiation shielding. The macroscopic electrical resistivity of the filled polyblend strongly depends on the localization of the filler. Here, we investigate the morphology of Carbon Black (CB)-filled polymer blends in order to determine the parameters governing the selective localization of CB in one phase of the blend components or at the interface between the components. The dispersion of the CB particles in the polymer blend is observed by means of Lateral Force Microscopy (LFM) as a function of the blend composition and the load in C.B. The selective localization of CB at the interface enables the reduction of the percolation threshold down to 0.5 wt%; as a result, the mechanical properties of the polymer blend can be fully retained. Different techniques can be used to locate the CB at the interface; we compare their efficiency experimentally.
Self-Assembly of Layered Aluminum Silsesquioxanes: Clay-Like Organic-Inorganic Nanocomposites
Authors: Ukrainczyk L. , Bellman R. A. , Smith K. A. , Boyd J. E. 
Published: April 2011

ABSTRACTA series of layered silicate-like structures with a wide range of Si/AI ratios that have an organic functionality directly bonded to the structural Si atom by Si-C bond were prepared by template sol-gel synthesis at room temperature and pressure. XRD patterns indicate that organic functionalities in the interlayers are in paraffin-like arrangement and do not interpenetrate. Structural ordering is primarily governed by the assembly of the organic functionalities into lamellar micelles. Nanocomposites were studied by solid state 29Si and 27AI NMR to determine the degree of condensation of inorganic framework. The results indicate that Si-O-Al linkages do not form in gels precipitated at low pH. Stable Si-O-Al linkages form when pH of the precipitates is raised. The highest degree of Si-O-Al bonding is obtained when Al solutions are prehydrolyzed prior to the addition of silane.
Temperature Dependence of Fracture Toughness of the Cubic (L12) Titanium Trialuminides
Authors: Varin R. A. , Zbroniec L. 
Published: April 2011

ABSTRACTFracture toughness vs. temperature of the cubic (L12), Mn- modified titanium trialuminide (based on Al3Ti) was investigated in air at the temperature range up to 1000°C. Toughness calculated from the maximum load exhibits a broad peak (KQ≈7–10 MPara0,5) at the 200- 500°C temperature range and then decreases with increasing temperature, reaching a room temperature value of ∼4.5 MPam0.5 at 1000°C. However, the work of fracture (γWOF, J/m2) and the stress intensity factor calculated from it (KIWOF) increases continuously with increasing temperature. Fracture modes exhibit a gradual transition from transgranular cleavage at room temperature to predominantly intergranular failure at the 800- 1000°C range.
The Solid-Solution Alloying Effects of Ti on the High-Temperature Deformation Behavior of NiAl Single Crystals
Authors: Kitabjian P. H. , Garg A. , Noebe R. , Nix W. D. 
Published: April 2011

ABSTRACTWe have investigated the high-temperature deformation behavior of the solid-solution strengthened alloy Ni-47.5Al-2.5Ti. Single crystals were deformed in compression in the “hard” <001> and “soft” <111> orientations, at temperatures between 900°C and 1200°C. The results show that Ti has a very powerful solute strengthening effect in NiAl. The creep rates for the solid-solution alloy were observed to be three to four orders of magnitude lower than for the stoichiometric material. We discuss our efforts to understand this solid-solution strengthening effect. We have studied high-temperature deformation transients in an effort to determine whether solute drag effects contribute to the creep resistance of this solid solution. In addition, we have examined the solute size effect of Ti as it replaces Al on the Al sub-lattice. We discuss the probable mechanism of creep of this alloy in light of TEM observations of the dislocation structures in creep-deformed crystals.