bluuebunny/crossref_metadata_2025_split huggingface dataset:
Location of Er atoms with respect to Si nanoclusters in luminescent Er and Si co-implanted silicates
Authors: Pellegrino P. , Garrido B. , Arbiol J. , Garcia C. , Lebour Y. , Morante J.R. 
Published: April 2011

ABSTRACTIn this contribution we explore the structural properties of different silicate glasses c o-implanted with Si and Er ions to various doses, and see how they affect the emission properties around 1540 nm. We have used silica, soda-lime and aluminium silicates as substrates. A multiimplantation scheme provided an uniform Si excess (5 or 15%) background to the subsequently implanted Er atoms. Er peak concentration has been varied between 2×1019 cm−3 to 6×1020 cm−3. The structural analysis of the resulting structures have been performed by means of SIMS, XPS, Raman, and EFTEM.It was found that the best photoluminescence (PL) emission properties are the ones for which a phase separation between the implanted Si and the matrix occurs, even without the formation of nanocrystalline aggregates. Amorphous Si nanoclusters with average size around 3 nm (for high Si content) or below 1nm (for low Si content) have been revealed after the EFTEM analysis. By analysing the layers by EELS and HAADF we have been able to determine the location of Er atoms relative to the Si nanoclusters for the first time to our knowledge. In samples with Er concentration higher than 1020 cm−3, the Er atoms are not randomly dispersed in the matrix. On the contrary, they tend to aggregate, forming large agglomerations mostly in the regions of lower density of Si precipitates. This observation correlates with the appearance of PL quenching at concentrations around 2×1020 cm−3. A suitable tuning of the annealing temperature has been found to drastically reduce this deleterious effect.
Possible Operation of Periodically Layered Nanocrystalline Porous Silicon as an Acoustic Band Crystal Device
Authors: Kiuchi Akira , Gelloz Bernard , Kojima Akira , Koshida Nobuyoshi 
Published: April 2011

ABSTRACTIt is shown that the periodic stacked structures of nanocrystalline porous silicon (nc-PS) layers with controlled densities and elastic properties act as an acoustic band crystal (ABC) device. Supposing that the periodic nc-PS layers are formed by conventional modulated anodization technique to fabricate the multi-layered distributed Brag reflection mirror, the acoustic wave propagation modes are investigated theoretically for various structural parameters. According to the calculation results, a significant acoustic band gaps are generated in the ultrasonic regions due to a big contrast in the elastic constant produced between low-porosity and compact nc-PS layers. The propagation of acoustic wave can be completely suppressed in the characteristic band determined from designed parameters. The present result suggests further possibility of the nc-PS layer as a key component of ABC devices.
Towards a Si/SiGe Quantum Cascade Laser for Terahertz Applications
Authors: Paul D.J. , Lynch S.A. , Townsend P. , Ikonic Z. , Kelsall R.W. , Harrison P. , Liew S.L. , Norris D.J. , Cullis A.G. , Zhang J. , Bain M. , Gamble H.S. , Tribe W.R. , Arnone D.D. 
Published: April 2011

ABSTRACTWhile electroluminescence has been demonstrated at terahertz frequencies from Si/SiGe quantum cascade emitters, to date no laser has been achieved due to poor vertical confinement of the optical mode. A method of increasing the vertical confinement of the optical mode for a Si/SiGe quantum cascade laser is demonstrated using silicon-on-silicide technology. Such technology is used with epitaxial growth to demonstrate a strain-symmetrised 600 period Si/SiGe quantum cascade interwell emission and the polarisation is used to demonstrate the optical confinement. Electroluminescence is demonstrated at ∼3 THz (∼100 μm) from an interwell quantum cascade emitter structure. Calculated model overlap and waveguide losses for ridge waveguides are comparable to values from GaAs quantum cascade lasers demonstrated at terahertz frequencies. The effects of high doping levels in Si/SiGe quantum cascade structures is also investigated with impurity emission demonstrated rather than intersubband emission for the highest doping levels used in the cascade active regions.
C, Si and Sn Implantation of CVD Diamond as a means of Enhancing Subsequent Etch Rate
Authors: Leech P. W. , Perova T. , Moore R. A. , Reeves G. K. , Holland A. S. , Ridgway M. 
Published: April 2011

ABSTRACTDiamond films were implanted with C+, Si+ or Sn+ ions at multiple energies in order to generate a uniform region of implantation-induced disorder. Analysis of the C+ implanted surfaces by micro-Raman spectroscopy has shown only minor increase in the proportion of nondiamond or sp2-bonded carbon at doses of 5 × 1013 - 5 × 1015 ions/cm2. In comparison, an amorphization of the structure was evident after implantation with either Si+ ions at a dose of 5 × 1015 ions/cm2 or with Sn+ ions at >5 × 1014 ions/cm2. At a given implantation dose, the etch rate of the diamond film in a CF4/O2 plasma increased with the mass of the implanted species in the order of C+, Si+ and Sn+. For a given implant species, the etch rate was directly proportional to vacancy concentration as controlled by the dose or the implantation-induced disorder.
Photochemical Moisture Proof Coating on Nonlinear Optical Crystal by ArF Excimer Laser
Authors: Kojima M. , Murahara M. 
Published: April 2011

ABSTRACTSilicone oil was photo-chemically oxidized to change into SiO2 on the crystal by using an ArF excimer laser; the protective moistureproof film has been developed for a nonlinear optical crystal that is deliquescent.The nonlinear optical crystals such as CsLiB6O10 (CLBO) and KH2PO4 (KDP) are deliquescent, which causes their surfaces to be cloudy by absorbing moisture in the air. We, therefore, demonstrated the growth of the SiO 2 film directly on the crystal so as to be moistureproof.Firstly, dimethylsiloxane silicone oil (-O-Si(CH3)2-O-)n was poured on the substrate and coated by a spinner for making the silicone oil thin layer. Then, the ArF excimer laser was vertically irradiated on the sample in oxygen atmosphere. The O atom on the substrate surface was photo-excited by the laser to generate a high active O atom. At the same time, the Si-CH3 bond of the silicone oil was photo-dissociated and the dangling bond of Si was linked with the active O atom to form a SiO 2 film on the crystal surface.In short, the film formed by the new technology can be used as a protective coating, which has the moisture resistance and the UV permeability, for a nonlinear optical crystal.
Pseudomorphic stabilization on crystal structure and mechanical properties of nanocomposite Ti-Al-N thin films
Authors: Karimi A. , Vasco Th. , Santana A. 
Published: April 2011

ABSTRACTAs the dimensions of materials are reduced to the nanometer scale, the stabilization of pseudomorphic crystal structures that differ from their bulk equilibrium phases can occur. The pseudomorphic growth could provide a substantially larger bulk modulus and greater hardness than the average of the constituent materials in nanolayered and nanocomposite thin films. To evaluate this effect in Ti1-xAlxN system, a series of nanostructured films with × up to 0.7 were deposited onto WC-Co substrates using arc PVD, and characterised in terms of structure-property relations. Chemical composition by RBS together with HRTEM and XRD analysis showed that for the Al content below × = 0.4 a solid solution single-phase film is formed, while for × values beyond 0.5 mixed structures made of fcc-TiN and hcp-AlN, or nanocomposite films made of fcc-TiN, hcp-AlN, and fcc-AlN appeared depending on deposition conditions. Hardness of solid solution films was found to increase almost linearly with the Al content, while two opposite behaviours were distinguished for composite structures. Hardness rapidly decreased according to the rule of mixture as soon as solid solution phase began to separate into TiN and AlN growing in their natural structures with misfit dislocation at the interface. In contrast, further hardness enhancement was measured when nanocomposites with coherent interfaces were formed due to pseudomorphic stabilization of fcc-AlN on fcc-TiN crystallites.
Competitive Guidance Cues Affect Fibroblast Cell Alignment: Electric Fields vs. Contact Guidance
Authors: Gibson Iain R. , McCaig Colin D. 
Published: April 2011

ABSTRACTWhen bovine ligament fibroblast cells were cultured on parallel micro-grooved surfaces, they aligned their long axes parallel to the groove direction. This alignment was dependent on the groove depth, with increasing groove depth increasing guided cell alignment. When cells were cultured in a physiological dc electric field (EF) on non-grooved, flat surfaces, the cells aligned in response to the EF, with their long axes perpendicular to the EF vector. This response was EF strength dependent, increasing EF strength (from 20 to 200mV/mm) increased cell alignment, perpendicular to the EF vector. These two guidance cues were applied simultaneously, so that the EF vector was parallel to the groove direction. At high but still physiological EF strengths (200mV/mm) cells ignored the topography and were guided by the EF alone, aligning perpendicular to the EF vector, as on non-grooved surfaces. At low field strengths (20mV/mm) cells responded only to the topographic guidance cue, with cells aligning parallel to the grooves and therefore also to the EF vector. Intermediate field strengths (50 to 100mV/mm) produced a mixed response, with cells responding to both guidance cues. The effect of removing serum from the culture medium on the EF and topographical guidance of fibroblast cells was studied and the results were compared to cells on non-grooved surfaces. Removal of serum produced a small but significant decrease in the angle of cell alignment for cells on non-grooved surfaces, from 78 to 63 degrees, relative to the EF vector, but did not completely suppress the EF guidance cue. In contrast, the EF guidance of cells on grooved substrates was suppressed almost completely by the absence of serum, with cells responding only to the grooved topography, aligning their long axis parallel to the grooves and the EF vector. These results imply that alignment of fibroblasts by topography is serum-independent, but alignment by EFs is serum-dependent. In addition they demonstrate that the alignment of fibroblast cells can be tailored by the dual guidance cues of topography and electric fields.
Controlled Macrophage Adhesion on Micropatterned Hydrogel Surfaces
Authors: Krsko P. , Vartanian K. , Geller H. , Libera M. 
Published: April 2011

ABSTRACTWe studied the protein adsorption and subsequent macrophage adhesion on poly(ethylene glycol) [PEG] hydrogels crosslinked using a focused electron beam. Thin-film gels were patterned on silicon substrates and could be formed with swell ratios (hydrated height/ dry height) anywhere between fifteen and unity. We have shown that laminin does not adsorb onto highly swelling gels but that it does adsorb on heavily-crosslinked low-swelling gels. As part of ongoing research on patterning surfaces to control neurite growth in the context of the inflammatory environment of a spinal cord injury, we are interested in how these gel surfaces interact with macrophages. We show that the high-swelling PEG gels resist macrophage adhesion, but the macrophages adhere to low-swelling gels pre-exposed to laminin. By spatially patterning combinations of low and high swelling gels, we show that macrophage adhesion can be confined to specific locations on a surface.
A Molecular Route to Dip-coated Transition Metal Nitride Thin Films.
Authors: Jackson Andrew W. , Hector Andrew L. 
Published: April 2011

ABSTRACTThere is an increasing interest in sol-gel synthesis of nitrides. The ability to deposit films of these materials by dip- or spin-coating will increase the range of applications in which they are viable and is an important step toward general sol-gel processing of nitride materials.With transition metals, the ammono based analogue of the well established alkoxy route to gels is inherently difficult to control. Due to the basicity of the system, the overwhelming tendency is of the starting materials to favour particle growth which results in a precipitate rather than a stable emulsion, unless both environment and synthetic pathway are carefully controlled. Hence reports to date of sol-gel routes to nitrides describe production of powders. We report work on a sol-gel route to titanium nitride with the ammonolysis of titanium amides controlled by temperature and chemical moderators, resulting in stable emulsions useful for dip-coating.
Synthesis, Structure and Magnetism of ErCoIn5
Authors: Thomas Evan Lyle , Erickson Erin E. , Moldovan Monica , Young David P. , Chan Julia Y. 
Published: April 2011

AbstractA new member of theLnMIn5family, ErCoIn5, has been synthesized by a flux-growth method. The structure of ErCoIn5was determined by single crystal X-ray diffraction. It crystallizes in the tetragonal space groupP4/mmm,Z= 1, with lattice parametersa= 4.5400(4) andc= 7.3970(7) Å, andV= 152.46(2) Å3. Electrical resistivity data show metallic behavior. Magnetic susceptibility measurements show this compound to be antiferromagnetic withTN= 5.1 K. We compare these experimental results with those of LaCoIn5in an effort to better understand the effect of the structural trends observed on the transport and magnetic properties.
Ferroelectric Properties of SBT doped with Pr
Authors: Mata J. , Durán A. , Martínez E. , Siqueiros J. M. , Heiras J. 
Published: April 2011

ABSTRACTThe Sr1-xPrxBi2Ta2O9 (SBT-Pr) ferroelectric ceramic doped with Praseodymium in the range of concentration between 0 and 0.20 was studied. X-ray diffraction patterns show that the Pr-ion substitutes the Sr-ion in the main structure (A21am space group) and, as a consequence of this substitution the unit cell decreases monotonically. Thermoelectric Analysis (ε vs T) and ferroelectric hysteresis measurements were performed. From the ε-T curves it was observed that the transition temperature depends almost linearly on Pr content. Broad phase transitions were also observed, a typical behavior of ferroelectric materials with diffuse phase transition (DPT). An increase in the diffuseness coefficient is obtained by increasing Pr content according to the Isupov model, due to the higher cationic disorder in the structure, resulting in the loss of the long-range ferroelectric ordering. The hysteresis loop indicates that the substitution of Sr2+ by Pr3+,4+ lowers the polarization due possible to strong pinning domain mechanisms that obstruct long range ferroelectric ordering.
Mercury and C2B10 Icosahedra Interaction
Authors: Ilie Carolina C. , Lunca-Popa Petru , Zhang Jiandi , Doudin Bernard , Dowben Peter A. 
Published: April 2011

ABSTRACTWe contrast the interaction of mercury with adsorbed orthocarborane films and semiconducting (dehydrogenated) boron carbide. Photoemission spectra reveal small shifts in orthocarborane (C2B10H12) molecular orbital binding energies as well as the shift in mercury 5d5/2 shallow core level binding energies, suggesting only small interaction between mercury and the molecular film. Mercury does, however, interact with decomposed orthocarboranes i.e. semiconducting boron carbide.
From configuration space to thermodynamic space: Predicting new inorganic solids via global exploration of their energy landscapes
Authors: Schön J. C. , Jansen M. 
Published: April 2011

ABSTRACTWe present a general approach to predict new inorganic solid compounds as a function of pressure, composition and temperature. Our method is based on the global exploration of the energy and enthalpy landscapes of the chemical system, followed by the construction of the corresponding free energy/enthalpy landcsapes.
Solution Phase Synthesis of Semiconductor Nanowires
Authors: Hull Katherine L. , Grebinski James W. , Zhang Jing , Kosel Thomas H. , Kuno Masaru 
Published: April 2011

ABSTRACTThe solution phase synthesis of narrow diameter CdSe and PbSe nanowires (NWs) is described. Crystalline NWs with lengths between 1–10 μm are obtained using a seeded solution approach, whereby NW growth is catalyzed by Au/Bi core/shell nanoparticles (NPs). A gold biphasic reduction step results in 1.5 (3) nm diameter Au NPs and is followed by the thermolysis of trialkylbismuthines to yield low melting, bimetallic particles with diameters less than 3 nm. These Au/Bi NPs are catalytically active towards the growth of similar diameter CdSe NWs (∼7 nm) that exhibit quantum confinement effects. By varying the ratio of Cd (or Pb) to Se, both straight and branched NWs can be obtained, with branched structures including v-shapes, tripods, and y-shapes in the case of CdSe and t-shapes in the case of PbSe. Structural characterization shows that both straight and branched CdSe NWs grow along either the <111> zinc blende (ZB) or <0001> wurtzite (W) directions. Conversely, PbSe has a rocksalt crystal structure, and both straight and branched NWs grow along <100> directions.
Amorphous Nanowires and Crystalline Thin Films of SiO2-Li2O Compounds obtained by Combustion Chemical Vapor Deposition
Authors: Lima M. D. , Stein S.S. , de Andrade M.J. , Bergmann C.P. 
Published: April 2011

ABSTRACTAmorphous silica films deposited by Combustion Chemical Vapor Deposition (CCVD) were modified by lithium addition in the precursor solution. The modified films were characterized by X-ray diffraction and scanning and transmission electron microscopy. The addition of lithium promoted the crystallization of Li2O-SiO2 compounds, mainly crystalline phases like Li2SiO3, Li2Si2O5, quartz and cristobalite. Besides that, the morphology of the film was modified, leading to the formation of acicular structures and nanowires. The acicular structures were identified through TEM associated with SAED as crystalline phases, mainly constituted by Li2SiO3 and Li2SiO5. TEM and SEM analysis indicated that the nanowire diameter is between 20 and 80nm. In addition to this, SAED and microprobe EDS analysis indicated that these nanowires are constituted by amorphous silica. The probable growth mechanism of these nanowires is the vapor-liquid-solid (VLS) catalyzed by a liquid particulate composed by Li2O-SiO2.
Polaritonic materials fabricated and tested with ultrashort-pulse lasers
Authors: Ward David W. , Statz Eric , Feurer Thomas , Nelson Keith A. 
Published: April 2011

ABSTRACTUsing femtosecond laser machining, we have fabricated photonic bandgap materials that influence propagation of phonon-polaritons in ferroelectric crystals. Broadband polaritons were generated with impulsive stimulated Raman scattering (ISRS) using an ultrashort laser pulse, and the spatial and temporal evolution of the polaritons were imaged as they propagated through the fabricated structures with polariton real-space imaging. These techniques offer a new approach to optical materials design.
Femtosecond Laser-Induced Micro-Structuring of Thin a-Si:H Films
Authors: Nayak Barada K. , Gupta Mool C. 
Published: April 2011

ABSTRACTIn a-Si:H solar cells, light trapping has been sought as a method to enhance absorption and improve the efficiencies of these devices. Here we present results for surface texturing of 2μm thick a-Si:H films by 800 nm wavelength femtosecond laser. The texture led to a significant enhancement in optical absorption (80%) in visible through near IR (60%). The textured surface was examined by a scanning electron microscope (SEM) and atomic force microscope (AFM). The results indicated the formation of dense spikes with height of 65–75 nm. The samples were completely black after femtosecond laser treatment.
Ultrafast Laser Deposition of Semiconductor Nanowires
Authors: Mao Samuel S. 
Published: April 2011

ABSTRACTPulsed laser deposition (PLD) has been applied to fabricate thin films of a variety of materials. However, formation of micron-sized particulates during conventional nanosecond laser-based deposition process makes it unsuitable for growing high quality nanoscale materials. Owing to a nonequilibrium non-thermal ablation mechanism and characterized by their short pulse duration compared to thermal diffusion time (tens of picoseconds), ultrafast laser pulses are able to produce particulate-free precursor vapor for nanoscale material deposition. In this article, the foundation of non-thermal ultrafast laser ablation will be examined by both experimental and theoretical investigations. Ultrafast laser-induced high-density electron ejection and subsequent build -up of a strong electric field above the target material were observed. Mass spectrometry and electron microscopy measurements confirmed the particulate-free nature of ultrafast laser ablation. Using ultrafast laser-based particulate-free PLD approach, high quality ZnO nanowires were grown on sapphire and silicon substrates. The optical properties of ZnO nanowires, including the external and internal quantum efficiency of nanowire nanolasers, were experimentally determined. In addition, a nanowire UV photodiode based on p−Si/n−ZnO nanowires was successfully fabricated. This first nanowire photodiode device shows good photocurrent characteristics when operated under reverse bias.
Investigation of Femtosecond Laser Irradiation on Fused Silica Etching Selectivity
Authors: Bellouard Yves , Said Ali A. , Dugan Mark , Bado Philippe 
Published: April 2011

ABSTRACTFemtosecond laser irradiation has various noticeable effects on fused silica. It can locally increase the index of refraction or modify the material chemical selectivity. Regions that have been exposed to the laser are etched several times faster than unexposed regions. Various observations reported in the literature seem to show that these effects are possibly related to a combination of structural changes and the presence of internal stress. However, a detailed analysis of the contribution of both effects is still lacking.In this paper, we present systematic SEM-based investigations performed on fused silica (a-SiO2). Line-patterns were first scanned on the substrate using a femtosecond laser and then etched in a low-concentration HF solution. The effects of various laser parameters like power and scanning speed are analyzed and we show further evidence of an interface between two different etching regimes.
Rich Dynamics in Diblock Copolymers
Authors: Fytas G. 
Published: April 2011

ABSTRACTThe dynamic structure factor S(q, t) of ultra-high molecular mass diblock copolymers BC in a common solvent was systematically investigated by photon correlation spectroscopy in different regimes of the phase diagram. Through proper probing of the composition fluctuations in symmetric and asymmetric BC the different relaxation mechanisms were identified and the influence of the disorder to order (ODT) transition was assessed. In the disordered regime, S(q, t) sensitively depends on the composition polydispersity of BC and the proximity to ODT complementing the real phase morphology of BC. The dynamic response of BC is therefore predictable.
TiCp2Cl-Catalyzed Living Radical and Ring Opening Polymerizations Initiated from Epoxides and Aldehydes in the Synthesis of Linear, Graft and Branched Polymers
Authors: Asandei Alexandru D. , Moran Isaac W. , Saha Gobinda , Chen Yanhui 
Published: April 2011

ABSTRACTTi(III)Cp2Cl-catalyzed radical ring opening (RRO) of epoxides or single electron transfer (SET) reduction of aldehydes generates Ti alkoxides and carbon centered radicals which add to styrene, initiating a radical polymerization. This polymerization is mediate in a living fashion by the reversible termination of growing chains with the TiCp2Cl metalloradical. In addition, polymers or monomers containing pendant epoxide groups (glycidyl methacrylate) can be used as substrates for radical grafting or branching reactions by self condensing vinyl polymerization. In addition, Ti alkoxides generated in situ by both epoxide RRO and aldehyde SET initiate the living ring opening polymerization of ε-caprolactone. Thus, new initiators and catalysts are introduced for the synthesis of complex polymer architectures.