bluuebunny/crossref_metadata_2025_split huggingface dataset:
X-ray Absorption and Reflection as Probes of the GaN Conduction Bands: Theory and Experiment of the N-K-Edge and Ga M2,3, Edges
Authors: Lambrecht W. R. L. , Rashkeev S. N. , Segall B. , Lawniczak-Jablonska K. , Suski T. , Gullikson E. M. , Underwood J. H. , Perera R. C. C. , Rife J. C. 
Published: April 2011

ABSTRACTX-ray absorption and glancing angle reflectivity measurements in the energy range of the Nitrogen K-edge and Gallium M2,3 edges are reported. Linear muffin-tin orbital band-structure and spectral function calculations are used to interpret the data. Polarization effects are evidenced for the N-K-edge spectra by comparing X-ray reflectivity in s- and p-polarized light.
Offsets and Polarization at Strained AlN/GaN Polar Interfaces
Authors: Bernardini Fabio , Fiorentini Vincenzo , Vanderbilt David 
Published: April 2011

ABSTRACTThe strain induced by lattice mismatch at the interface is responsible for the different value of the band discontinuities observed recently for the AlN/GaN (AlN on GaN) and the GaN/AlN (GaN on AlN) polar (0001) interface. We present a first-principles calculation of valence band offsets, interface dipoles, strain-induced piezoelectric fields, relaxed geometric structure, and formation energies. Our results confirm the existence of a large forward-backward asymmetry for this interface.
Ferromagnetic Properties of Spark-Processed Photoluminescing Silicon
Authors: Hack J. , Ludwig M. H. , Geerts W. , Hummel R. E. 
Published: April 2011

AbstractMagnetic properties of photoluminescing spark-processed silicon (sp-Si) have been investigated for the first time. Contrary to the diamagnetic signal known for bulk silicon, sp-Si displays a paramagnetic resonance as well as a ferromagnetic hysterisis loop. The paramagnetic resonance was studied using an EPR system and showed a high concentration of at least two distinct paramagnetic centers. One center can be eliminated by annealing in Ultra-High Purity nitrogen for 30 minutes at 600 °C. Measurements utilizing a SQUID magnetometer revealed that sp-Si displays ferromagnetic ordering with a saturization magnetization occuring at low fields. This is attributed to the high density of paramagnetic centers. Temperature dependent measurements were performed to establish possible links between magnetic properties and the luminescence of sp-Si.
Multicolor-Effects of Luminescing, Nanostructured Silicon After Spark-Processing in Pure and Composite Gases
Authors: Ludwig M. H. , Augustin A. , Hummel R. E. 
Published: April 2011

AbstractSpark-processing has been shown recently to generate a silicon-based substance which intensely photoluminesces in the UV/blue or green spectral range, depending on whether the preparation was performed in flowing or stagnant air, respectively. This study reports about significant differences for the radiative properties of spark-processed silicon after preparations in oxygen, nitrogen, and mixtures of both gases. Whereas there is essentially no photoluminescence (PL) after processing in pure nitrogen, an orange PL band at 1.89 eV occurs after preparation in pure oxygen. The orange PL degrades with time and when exposed to laser light. Furthermore, it switches immediately to a more intense blue emission centered at 2.61 eV when the sample is subjected to lower gas pressures. A similar 2.6 eV PL is observed after heat treatments up to 350°C. If, however, spark-processing of Si is carried out in nitrogen and oxygen is added, a green PL arises, centered at 2.35 eV. Moreover, for a volume ratio of about 1:1 N2/O2 a PL band at 3.22 eV emerges, superimposing the green emission. Both bands are about two orders of magnitude more intense than the orange PL, when prepared under otherwise identical processing conditions.
Porous Semiconductors: A Tutorial Review
Authors: Canham L T 
Published: April 2011

AbstractPorous semiconductors constitute a class of material that exhibit surprising properties, are quite easy to fabricate, but are however fragile, complex, and difficult to characterise. This tutorial review extracts specific topics from the large knowledge base now available on porous Si that are deemed relevant to other porous semiconductors beginning to receive study. It also highlights topics where controversy is now resolved, where problems remain, and where further effort could be focused.
Effects of Mn2+ Distribution Controlled by Carboxylic Acids on Photoluminescence Intensity of Nanosized ZnS:Mn Particles
Authors: Isobe T. , Igarashi T. , Senna M. 
Published: April 2011

AbstractAddition of methacrylic acid (MA) during preparation of ZnS doped with Mn2+ (ZnS:Mn) increased the photoluminescence (PL) due to 4T1-6A1 transition of Mn2+. According to X-ray fluorescence analysis and electron paramagnetic resonance spectroscopy, ion exchange between Zn2+ and Mn2+ through a preferential dissolution of Mn2+ was promoted by acidic additives. This caused that Mn ions were isolatedly incorporated into ZnS. The X-ray photoelectron spectra show that the intensity of S 2p3/2 peak due to S6+ increased relative to that of S2- by virtue of carboxylic groups. The intensities of PL peaks at 450 and 580 nm, corresponding to polymethacrylic acid and Mn2+, respectively, increased after heating at 80°C for 1 week. We conclude that MA plays important roles on selective leaching to increase the amount of isolated Mn2+ ions, chemical interaction between ZnS:Mn and MA and energy transfer to Mn2+, leading to the increase in PL intensity.
Electron and Hole Trapping Dynamics in Semiconductor Nanocrystals: Femtosecond Nonlinear Transmission and Photoluminescence Study
Authors: Klimov V. , McBranch D. 
Published: April 2011

AbstractApplication of two complementary femtosecond techniques (time-resolved nonlinear transmission and photoluminescence up-conversion) allows us to observe separately the electron and the hole relaxation paths in CdS nanocrystals. The obtained data indicate that hole relaxation channels are different at low and high pump fluences which is attributed to an Auger-process-assisted hole trapping at surface/interface states activated at high excitation intensities.
Synthesis and Characterization of Highly Luminescent (CdSe)ZnS Quantum Dots
Authors: Mikulec F. V. , Dabbousi B. O. , Rodriguez-Viejo J. , Heine J. R. , Mattoussi H. , Jensen K. F. , Bawendi M. G. 
Published: April 2011

AbstractWe report the synthesis of a series of nearly monodisperse ZnS-overcoated CdSe quantum dots whose room temperature photoluminescence quantum yield approaches 50%. This spectrally narrow (FWHM < 40nm) band edge luminescence spans the visible region from blue to red light. We use a two-step synthesis based on the high temperature decomposition of organometallic precursors in a coordinating solvent. We characterize our composite quantum dots using optical spectroscopies, wavelength dispersive x-ray spectroscopy, x-ray photoelectron spectroscopy, high resolution transmission electron microscopy, small angle x-ray scattering, and wide angle x-ray diffraction. The data indicate that samples displaying the highest quantum yield are those which have just achieved a closed shell of ZnS encapsulating the CdSe core. As more ZnS is added, the quantum yield decreases somewhat, possibly due to the many defects present in larger ZnS shells.
Porous Silicon from Hydrogenated Amorphous Silicon: Comparison with Crystalline Porous Silicon
Authors: Chazalviel J.-N. , Wehrspohn R. B. , Solomon I. , Ozanam F. 
Published: April 2011

AbstractDevice-grade, boron-doped amorphous hydrogenated silicon can be made microporous by anodization in ethanoic HF. The thickness of the porous layer is limited by an instability due to the high resistivity of the material. Amorphous porous silicon exhibits strong room-temperature photoluminescence around 1.5 eV even in samples containing a high density of non-radiative recombination centers. This demonstrates the presence of a spatial confinement effect, as opposed to quantum confinement effect for crystalline porous silicon. The temperature dependence of the luminescence intensity is also accounted for on the same grounds.
Local Structure of Indium-Plated Porous Silicon
Authors: Ito Toshimichi , Ooiwa Takashi , Nagao Takanobu , Hatta Akimitsu 
Published: April 2011

AbstractThe fine structure of porous silicon (PS) plated electro-chemically with indium at a low plating charge of 0.03 C/cm2 has been studied mainly using Rutherford backscattering spectrometry and a transmission electron microscope. The results obtained here show (1) that the amount of plated In atoms strongly depends on the oxidation states of the pore surfaces, (2) that the average In densities, the maximum of which is usually located near the PS - Si substrate interface, are typically larger than 1 % of the Si densities in the PS layers, and (3) that the plated In atoms are concentrated locally in pores larger in size. Two-step thermal oxidation of an In-plated PS specimen results in a structure of nm-sized Si crystallites surrounded mainly by Si oxide and In oxide.
Comparative Theoretical Study of Amorphous and Crystalline Silicon Clusters
Authors: Lannoo M. , Delerue C. , Allan G. 
Published: April 2011

AbstractThe occurence of confinement effects for amorphous Si and Si:H clusters is investigated theoretically in an empirical tight binding treatment. The results show that one must consider three categories of states: strongly localized, weakly localized and delocalized. In all cases a substantial blue shift with reduction in size is obtained, of comparable magnitude for amorphous a-Si:H and crystalline clusters. These results are compared with available experimental data
«Holographie grating in Porous Silicon»
Authors: Lérondel G. , Thönissen M. , Setzu S. , Romestain R. , Vial J. C. 
Published: April 2011

AbstractWe have produced lateral porosity modulation in porous silicon layers on a micron scale. Using the photosensitivity of the etching process and optical interferences, stripes are formed periodically on the top but also in the depth of the layer depending on the illumination wavelength. The periodicity of the structure is easily modified by changing the wavelength or the incident angles of the two laser beams used to create the modulated illumination. By rotating the sample, two dimensional structures have also been obtained. The samples formed by this procedure are characterised by light diffraction and photoluminescence both of which show the alternance of high and low porosity ranges. With this kind of in-depth lithography, easy and very cheap fabrication of porous silicon gratings promises a large potential range of applications of this material to integrated optics and photonics.
Structural Analysis of Nanocrystals Embedded in Amorphous Si Films
Authors: Garrido B. , Achiq A. , Macía J. , Morante J. R. , Pérez-Rodríguez A. , Ruterana P. , Rizk R. 
Published: April 2011

AbstractSilicon nanocrystals embedded in amorphous silicon films have been obtained by RF sputtering using two approaches : i) with a pure H2 plasma at different substrate temperatures (between 50° and 250°C) and ii) with the substrate at 250°C, from a mixture of Ar and a variable partial pressure of H2, and annealing at 750°C. In the first case (i) Raman spectra show strong phonon confinement effects and an increase in the crystalline fraction as temperature increases. In the second case (ii), a higher compressive stress is estimated and a close correlation is found between the optical band gap E0 and the hydrogen content in the basic amorphous layer a-Si:H (i.e. before annealing). These results correlate with the TEM data, which corroborate an enhancement of the crystallinity of the layers and an increase in the particle size when the substrate temperature increases. Furthermore, the crystalline fraction remains nearly constant with the H2 partial pressure. The role of hydrogen and voids in the structure of the films is presented and discussed.
Crystalline and Electrical Properties of ITO Semiconductive Films deposited by Atmospheric RF Plasma Technique
Authors: Moss R. W. , Misture S. , Lee D. H. , Condrate R. A. , Wang X. W. 
Published: April 2011

AbstractIndium tin oxide (ITO) semiconductive films were deposited by an atmospheric RF plasma technique. Indium-to-tin (In:Sn) ratios varied from 10:0 to 0:10. A small amount of antimony was doped into some ITO samples for comparative studies. Substrate materials were soda-lime-silicate (SLS) float glass and fused silica glass. Structural, electrical, and optical properties were dependent on the In:Sn ratio, precursor material feeding rate, oxygen feeding rate, and other deposition conditions.
Morphotropic Phase Boundary in the Nanocrystalline PbZrxTi1-xO3 System
Authors: Katiyar R. S. , Meng J. F. 
Published: April 2011

AbstractMicro Raman spectra for PbZrxTi1-xO3 (PZT) with a grain size of 60 nm have been recorded. The results show that the lowest E(TO) phonon mode of PbTiO3 (soft mode) displays a decrease in frequency and increase in linewidth with increasing Zr concentration. A discontinuous behavior of the phonon energy of the soft mode occurs at x=0.4 and it can be attributed to a phase transformation from the tetragonal ferroelectric to rhombohedral ferroelectric phase in PZT. The coupling between the soft mode and an additional impurity mode, has been observed, which plays an important role in the phase transformation. A lowest phonon mode at 10 cm−1 is detected and it is found to exhibit an increase in intensity for x above 0.2. The grain size dependence of the mode seems to be associated with the effect of grain size on the microstructure in PZT. The mechanism of grain size - induced new morphotropic phase boundary, which is lower than that of the corresponding bulk materials, is discussed.
N-I-P Micromorph Solar Cells on Aluminium Substrates
Authors: Goetz M. , Torres P. , Pernet P. , Meier J. , Fischer D. , Keppner H. , Shah A. 
Published: April 2011

AbstractThe first successful deposition of ‘micromorph’ silicon tandem solar cells of the n-i-p-n-i-p configuration is reported. In order to implement the ‘micromorph’ solar cell concept, four key elements had to be prepared: First, the deposition of mid-gap, intrinsic microcrystalline silicon (μc-Si:H) by the 'gas purifier method', second, the amorphous silicon (a-Si:H) n-i-p single junction solar cell, third, the microcrystalline silicon n-i-p single junction solar cell and fourth, the ability of depositing on aluminium sheet substrates.All the solar cells presented have been deposited on flat aluminium sheets, using a single layer antireflection coating to couple the light into the cell. It is shown, that this antireflection concept- together with a flat substrate- holds for amorphous single junction solar cells, but it reaches its limit with the extended range of spectral response of the ‘micromorph’ cell.The best initial efficiencies for each category of n-i-p cells on flat substrates were: 8.7% for the amorphous silicon single junction cell, 4.9% for the microcrystalline silicon single junction cell and 9.25% for the ‘micromorph’ tandem cell.
Synthesis of Nanophase Noble Metal Systems Utilizing Porous Silicon
Authors: Coulthard I. , Sham T. K. 
Published: April 2011

ABSTRACTApart from its well known ability to luminesce very intensely at room temperature in the visible range, porous silicon is also an effective reducing agent. We report the formation of several noble metal (Pd, Ag, Au, Pt) nanostructures by reductive dispersion of metal ions from aqueous solutions onto the surface of porous silicon. The nanophase systems produced by reductive deposition vary with the element deposited and the metallic salt utilized in the process. The resulting nanophase systems were studied using a variety of techniques including: scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and spectroscopie methods using synchrotron radiation.
Ferromagnetic Nanocomposite Films from Thermally Labile Nitride Precursors
Authors: Maya L. , Paranthaman M. , Thompson J. R. , Thundat T. , Stevenson R. J. 
Published: April 2011

ABSTRACTA series of nanocomposite films containing nickel or cobalt nitride dispersed in a ceramic matrix of aluminum nitride, boron nitride or silicon nitride, were prepared by reactive sputtering of selected alloys or compounds such as nickel aluminide or cobalt suicide. Thermal treatment of the nitride composites in vacuum at ≤ 500 °C leads to selective loss of nitrogen from CoN or Ni3N to generate dispersions of the metal in the ceramic matrix. This treatment may be performed in a localized manner by means of a focused laser beam to generate microscopic features that are imaged by magnetic force microscopy. The films are potentially useful for data storage with superior chemical and mechanical stability provided by the ceramic matrix and high encoding density made possible because of the size of the magnetic particles of less than 10 nm generated in the thermal treatment. The films were characterized by chemical and physical means including FTIR, TEM, MFM and magnetic measurements. Preliminary results on similar iron composites are also described.
Microstructural Valuation of Iron-Based Composite Materials as an Ecomaterial
Authors: Itsubo Norihiro , Halada Koumei , Minagawa Kazumi , Yamamoto Ryoichi 
Published: April 2011

ABSTRACTOne of an important method to realize is said that we should take recycle processes into consideration and select the material without the mixture of particular elements that make it difficult to recycle. Therefore, it is useful to control of microstructure for improvement.From this point of view, we paid attention to “SCIFER (that is made from Kobe Steel Ltd.)” that has a recyclable formation (Fe-C-Si-Mn) and superior characteristic (tensile strength is 5000MPa). The grain size of this fiber is nano-size. In this study, we used this material and compounded it together with iron-matrix to make an iron-based composite for recycle and investigated the possibilities of realization. The difficulty of this study is to make this composite without injuring the fiber's microstructure. Therefore, we have adopted powder metallurgy which could fabricate composite at low temperature comparatively. Especially, Ultra Fine Particles (UFP) that would sinter at low temperature to bond the interface between fiber and matrix with keeping fiber's capacity. This method is useful to ascend the density of the matrix. Results are as follows. (1) Utilization of UFP slurry made it possible to adhere UFP to the surface of fiber and seed powder. Still more, this procedure enabled it to make a thin film uniformly by selecting the condition of slurry density and procedure of dryness. (2) Applying UFP to the surface of fiber and seed powder make it possible to get the bond between fiber and matrix. By the bond of interface, both fracture strength and energies have ascended remarkably due to pull out of fiber.
Synthesis, Characterization and Mechanical Properties of Nanocrystalline NiAl
Authors: Choudry M. S. , Eastman J. A. , DiMelfi R. J. , Dollar M. 
Published: April 2011

ABSTRACTNanocrystalline NiAl has been produced from pre-cast alloys using an electron beam inert gas condensation system. In-situ compaction was carried out at 100 to 300°C under vacuum conditions. Energy dispersive spectroscopy was used to determine chemical composition and homogeneity. Average grain sizes in the range of 4 to 10 nm were found from TEM dark field analyses. A compression-cage fixture was designed to perform disk bend tests. These tests revealed substantial room temperature ductility in nanocrystalline NiAl, while coarse grained NiAl showed no measurable room temperature ductility.
Structural Evolution of Fe Rich Fe-Al Alloys During Ball Milling and Subsequent Heat Treatment
Authors: Jiang H. G. , Perez R. J. , Lau M. L. , Lavernia E. J. 
Published: April 2011

ABSTRACTX-ray diffraction (XRD) and differential scanning calorimetry (DSC) have been utilized to investigate the structural evolution of Fe rich Fe-Al alloys during ball milling. It is found that b.c.c. solid solutions can be formed either through ball milling alone or through ball milling together with heat treatment. Thermal diagrams of the milled Fe-Al powders reveal exothermic peaks corresponding to the formation of cc-Fe(Al) solid solution (in both Fe-4wt.%Al and Fe-10wt.%Al) and the formation of FeAl intermetallic compound (in Fe-10wt.%Al). The transformation kinetics of cc-Fe(Al) solid solution in Fe-4wt.%Al were found to follow the Johnson-Mehl-Avrami equation.
Rapid Consolidation of Nanophase Al2O3 and an Al2O3/Al2TiO5 Composite
Authors: West David A. , Mishra Rajiv S. , Mukherjee Amiya K. 
Published: April 2011

ABSTRACTA rapid consolidation technique has been utilized in producing single phase AI2O3 in less than 10 minutes at 1400°C resulting in a grain size less than 500 nm. TiO2 has been added in hopes of obtaining Al2O3/Al2TiO5 nanocomposites in sintering times less than 30 minutes. The sintering process involves resistance heating of a graphite die containing the powder at heating rates of about 10 °C/s. The resistance heating step is preceded by a preparatory step consisting of DC voltage pulses applied across a prepressed powder compact. The retention of the nanostructure is attributed to the rapid heating rate although the possible effect of the DC pulses are also discussed. An Al2O3/Al2TiO5 composite has been produced during a short anneal immediately following sintering of an Al2O3/TiO2 nanocomposite. Substantial grain growth has been observed to occur during the transformation taking the composite to the microcrystalline regime.
Percolation Threshold in Superhard Nanocrystalline Transition Metal-Amorphous Silicon Nitride Composites: The Control and Understanding of the Superhardness
Authors: Vepřek Stan , Christiansen S. , Albrecht M. , Strunk H. P. 
Published: April 2011

ABSTRACTThe hardness of the recently developed novel superhard nanocrystalline composites exceeds 5000 kg/mm2 (50 GPa) and the elastic modulus 550 GPa. This is due to a special microstructure which is formed when the fraction of the amorphous component reaches the percolation threshold. Experimental data are presented and discussed.
Nano-Sized Fine Droplets of Liquid Crystals for Optical Application
Authors: Matsumoto Shiro , Houlbert Marthe , Hayashi Takayoshi , Kubodera Ken-ichi 
Published: April 2011

ABSTRACTNano-sized fine droplets of liquid crystal (LC) were obtained by phase separation of nematic LC in UV curing polymer. The polymer composite had a high transparency in the infrared region. The fine droplets responded to an electric field causing a change in birefringence. Output power change was brought about by the generated retardation between two polarizations, parallel and perpendicular to the applied electric field. This differs from the composite containing much larger droplets, where output depends on the degree of scattering. The birefringence changed by 0.001 at the applied voltage of 7.5 V/μm.
A New Tetragonal Boride Phase in FeAl+B Type Alloys
Authors: Pierron Xavier , Baker Ian 
Published: April 2011

ABSTRACTThe structure and composition of a previously unreported second phase were investigated in both Fe-43A1–0.12B and Fe-48Al-0.12B alloys. Energy dispersive x-ray and electron energy loss spectroscopy showed that the precipitates contained boron and were enriched in iron. This new boride phase had a tetragonal symmetry, with at = 4aB2 and ct = aB2, where aB2 is the matrix lattice parameter. The effect of iron content and heat treatments on the microstructure of those two boron-doped FeAl alloys are discussed.