bluuebunny/crossref_metadata_2025_split huggingface dataset:
Self Organized Array of Quantum Nanostructures Via a Strain Induced Morphological Instability
Authors: Montiel David , Müller Judith , Poiré Eugenia Corvera 
Published: April 2011

ABSTRACTMotivated by the work of Li et al. [1], we have studied the strain induced morphological instability at the submonolayer coverage stage of heteroepitaxial growth on a vicinal substrate with regularly spaced steps. We have performed a linear stability analysis and determined for which conditions of coverage a flat front is unstable and for which conditions it is stable. For low coverages the instability will cause the front to break in an array of islands. Assuming that the fastest growing mode of the instability determines t he properties of the array, we make an estimation of the islands sizes and aspect ratios as well as an estimation of the separation length between islands of the array formed when the dominant mechanism for transport of matter is diffusion of particles along the growing front. These estimations are given as functions of the terrace width and coverage. Since these ones are experimentally controllable parameters, our results could be used to tailor the spontaneous formation of quantum nanostructures.
Spontaneous Pattern Formation from Focused and Unfocused Ion Beam Irradiation
Authors: Cuenat Alexandre , Aziz Michael J. 
Published: April 2011

ABSTRACTWe study the formation and self-organization of “ripples” and “dots” spontaneously appearing during uniform irradiation of Si, Ge, and GaSb with energetic ion beams. Features have been produced both with sub-keV unfocused Ar+ ions and with a 30 keV Ga+ Focused Ion Beam. We follow the evolution of features from small amplitude to “nanospikes” with increasing ion dose. It appears that the edge of the sputtered region influences the patterns formed, an effect that may make it possible to guide the self-organization by the imposition of lateral boundary conditions on the sputter instability.
InP Self Assembled Quantum Dot Lasers Grown on GaAs Substrates by Metalorganic Chemical Vapor Deposition
Authors: Dupuis R. D. , Ryou J. H. , Heller R. D. , Walter G. , Kellogg D. A. , Holonyak N. , Reddy C. V. , Narayanamurti V. , Mathes D. T. , Hull R. 
Published: April 2011

ABSTRACTWe describe the operation of lasers having active regions composed of InP self-assembled quantum dots embedded in In0.5Al0.3Ga0.2P grown on GaAs (100) substrates by MOCVD. InP quantum dots grown on In0.5Al0.3Ga0.2P have a high density on the order of about 1-2x10 cm-2 with a dominant size of about 10-15 nm for 7.5 ML growth.[1] These In0.5Al0.3Ga0.2P/InP quantum dots have previously been characterized by atomic-force microscopy, high-resolution transmission electron microscopy, and photoluminescence.[2] We report here the 300K operation of optically pumped red-emitting quantum dots using both double quantum-dot active regions and quantum-dot coupled with InGaP quantum-well active regions. Optically and electrically pumped 300K lasers have been obtained using this active region design; these lasers show improved operation compared to the lasers having QD-based active regions with threshold current densities as low as Jth ∼ 0.5 KA/cm2.
Formation of GaN Self-Organized Nanotips by Nanomasking Effect
Authors: Yoshida Harumasa , Urushido Tatsuhiro , Miyake Hideto , Hiramtsu Kazumasa 
Published: April 2011

ABSTRACTWe have successfully fabricated self-organized GaN nanotips by reactive ion etching using chlorine plasma, and have revealed the formation mechanism. Nanotips with a high density and a high aspect ratio have been formed after the etching. We deduce from X-ray photoelectron spectroscopy (XPS) analysis that the nanotip formation is attributed to nanometer-scale masks of SiO2 on GaN. The structures calculated by Monte Carlo simulation of our formation mechanism are very similar to the experimental nanotip structures.
Shape Transitions of Self-Assembled Ge Islands on Si(001)
Authors: Rastelli Armando , Kummer Matthias , Känel Hans Von 
Published: April 2011

ABSTRACTCoherently strained Ge islands were grown at a substrate temperature of 550°C by magnetron sputter epitaxy on Si (001) and studied by scanning tunnelling microscopy (STM). The shape changes induced by exposure to a Si-flux at 450°C were investigated as a function of the Si-coverage. During Si-capping, multifaceted domes were found to flatten and to transform into {105}-faceted pyramids and subsequently into stepped mounds through intermediate shapes. The observed sequence of morphological changes is induced by Si-Ge intermixing and is shown to be the inverse of that occurring during Ge or Si1-xGex growth on Si (001). The results are interpreted with a model in which the stable shape of an island mainly depends on its volume and composition.
Morphology of Self-Assembled InAs Quantum Dots on GaAs(001).
Authors: Arciprete F. , Patella F. , Fanfoni M. , Nufris S. , Placidi E. , Schiumarini D. , Balzarotti A. 
Published: April 2011

ABSTRACTWe have followed by Atomic Force Microscopy (AFM) the epitaxial growth of InAs on GaAs(001) starting from the initial formation of a strained two-dimensional wetting layer up to the self-assembled nucleation and growth of 3D nanoparticles. In this work we underline many aspects of the morphology of this system, which substantiate the role either of kinetics on thermodynamics in the process of growth as well as the role of surface instabilities in controlling lateral ordering of the nanoaggregates.
Optical Characterization of Self-Assembled Ge Dots on Silicon
Authors: Marabelli F. , Rastelli A. , Valsesia A. , Känel H.von 
Published: April 2011

ABSTRACTSelf assembled quantum dots of Ge were obtained by magnetron sputter epitaxy of seven monolayers of Ge on a 33nm thick undoped Si buffer grown on top of a p-doped (100) Si substrate. The samples obtained in this manner were then capped with an increasing number of silicon layers in order to study the effect of Si deposition on the strain and the morphology of the dots. They were characterized “ex situ” by spectroscopic ellipsometry and Raman spectroscopy. The optical experiments revealed well defined differences between the capped and uncapped samples and among samples with different cap thicknesses.By monitoring the energy and the splitting of the E0', E1 and E2 interband optical transitions of Ge and the Ge-Si vibrational mode, the optical measurements evidence strain effects as well as the formation of SiGe alloy, in agreement with the “in situ” STM measurements.
Magnetic Interactions in Fe Nanoparticle Arrays
Authors: Farrell D. , Yamamuro S. , Ijiri Yumi , Majetich S. A. 
Published: April 2011

ABSTRACTThe preparation of monodisperse Fe nanoparticles and self-assembly into hcp and fcc or fcc-like arrays is described. Here dipolar interactions dominate for the interparticle spacings studied (1.4-3.4 nm). Comparison of the low temperature magnetic properties of multilayer arrays with those of dilute suspensions of the same particles show increased coercivity and slower magnetic relaxation in the arrays. Mean field calculations of magnetic interaction fields suggest the type of ordered structures formed.
Free-standing Smectic LC Elastomer Films
Authors: Tolksdorf C. , Zentel R. , Köhler R. , Dietrich U. , Lösche M. , Stannarius R. 
Published: April 2011

ABSTRACTWe probe the mesophase transitions and layer structures in thin ordered smectic liquid crystalline elastomer films by means of x-ray diffraction and optical microscopy. Oriented elastomer films of submicrometer thickness are produced by crosslinking freely suspended smectic polymer films. After crosslinking, the mesomorphism is similar to that of the precursor polymer. Smectic layers align parallel to the film plane. The layer spacing increases with temperature in the SmC* phase while it decays above the SmC*-SmA transition.
Reactive Mesogenes: Synthesis and Application in Optoelectronic Devices
Authors: Strohriegl Peter , Hanft Doris , Jandke Markus , Pfeuffer Thomas 
Published: April 2011

ABSTRACTReactive mesogenes posess polymerizable groups attached to a rigid, liquid crystalline core. From such molecules, densely crosslinked networks in which the liquid crystalline order is permanentely fixed can be formed by photopolymerization.Our major synthetic goal was the formation of glass forming reactive mesogenes. Such compounds do not crystallize upon cooling but vitrify and form supercooled LC-phases ('LC-glasses'). They exhibit broad LC-phases and enable us to carry out photopolymerization in a broad range of temperatures.We have systematically investigated how the topology of the reactive mesogenes influences the stability of the resulting glasses. Comparing twin molecules with three- and four-armed stars we found that the supercooled LC-phase in the three-armed stars has a stability superior to both twin molecules and four-armed stars. In the three-armed star Triple-4 with a suitable substituent pattern the supercooled LC-phase is stable at room temperature for at least nine months. Doped with suitable chiral molecules the glass forming nematics form cholesteric phases which were used for cholesteric polymer networks and for polarization holograms with one s-and one p-polarized writing beam.Furthermore we have extended our synthetic efforts to reactive mesogenes with three or five conjugated fluorene units as LC-core. After orientation, the mesogenes were photocrosslinked and used as active layer in OLEDs that emit highly polarized blue light.
Tuning the Surface Properties of Elastomers Using Hydrocarbon-Based Mechanically Assembled Monolayers
Authors: Efimenko Kirill , Genzer Jan 
Published: April 2011

ABSTRACTWe use static contact angle measurements and near-edge absorption fine structure to elucidate the surface structure and molecular orientation of hydrocarbon-based mechanically assembled monolayers (H-MAMs), structures formed by combination of assembly of alkyl moieties onto flexible elastomeric substrates and mechanical manipulation of the substrates. Specifically, we report that the organization of the grafted molecular array (“liquid”-like vs. solid-like) can be tailored by varying the degree of stretching of the elastomeric substrate. We also show that the H-MAM surfaces exhibit excellent stability.
Effect of Semiconductor and Dye Interfacial Properties in Dye-Sensitized Solar Cells
Authors: He Jin-An , Mosurkal Ravi , Kumar Jayant , Li Lian , Chittibabu K. G. , Samuelson Lynne A. 
Published: April 2011

ABSTRACTThe back recombination processes of electrons from the semiconductor to the oxidized dye and the oxidized redox species can dramatically reduce the efficiency of conventional dyesensitized solar cells (DSSCs). In this work, we have used the electrostatic layer-by-layer (ELBL) assembly technique to specifically manipulate and control the interface between the semiconductor and adsorbed dye layers in DSSCs to potentially minimize this recombination behavior. The interfacial modification has been achieved by applying different combinations and thicknesses of polyelectrolytes using the ELBL method and the performance of the cells has been monitored by measuring the I-V characteristics and the efficiency of the solar cells. The results indicate that an ultrathin polyelectrolyte film, on the order of a few Angstroms, between the semiconductor and the dye layer plays a crucial role on the performance of the solar cell. More specifically, the efficiencies of the DSSCs do not show any improvement after the interfacial treatment when compared to untreated samples. Surprisingly, the efficiency of the cells decreases to some degree, depending on the thickness of the polyelectrolyte films. This suggests that incorporation of a thin (several Angstroms) passive layer between the semiconductor and dye layer in these devices results in an increased resistance of the device and do not significantly reduce the back electron recombination as was originally anticipated. These results show interesting mechanistic information regarding the interfacial interactions of semiconductor/dye interfaces in DSSCs.
Synthesis of TPD-Containing Polymer Thin Films by Physical Vapor Deposition
Authors: Usui Hiroaki , Yoshioka Terufumi , Katayama Takahiro , Tanaka Kuniaki , Sato Hisaya 
Published: April 2011

ABSTRACTPolymer thin films having tetraphenyl diaminobiphenyl (TPD) side chain were prepared by evaporating its acrylate monomer by the ionization-assisted deposition (IAD) method. IR absorption and GPC analyses showed that the electron irradiation to the evaporated material works efficiently to initiate the polymerization reaction on the substrate surface, while the simple evaporation produced films mainly consisting of the monomers. The reaction was enhanced by increasing the substrate temperature. However, the surface roughness increased with increasing substrate temperature. Post annealing can be an alternative method to enhance the polymer yield. Light emitting diodes were prepared by stacking the TPD polymer layer, Alq3 emissive layer, and Al electrode on ITO-coated glass. The IAD polymerization can be a useful method for preparing polymer thin films for organic optoelectronic devices.
Wafer Bonding Using Dielectric Polymer Thin Films in 3D Integration
Authors: Kwon Y. , Lu J.-Q. , Kraft R. P. , McDonald J. F. , Gutmann R.J. , Cale T. S. 
Published: April 2011

ABSTRACTA key process in our approach to monolithic three-dimensional (3D) integration is the bonding of 200-mm wafers using dielectric polymer thin films as bonding glues. After discussing the desired properties of polymer thin films, we describe how bonding protocols are evaluated using silicon and glass wafers. After bonding, the fraction of bonded area was inspected optically and a razor blade method was used to indicate bonding strength. Thermal stability and bonding integrity were evaluated using thermal cycling and backside grinding and polishing. To date, we have studied benzocyclobutene (BCB), Flare™, and methylsilsesquioxane (MSSQ) and Parylene-N as bonding glues. Wafer pairs bonded using BCB showed a larger fraction of bonded area, and those using Flare indicated higher thermal stability. Both BCB and Flare glues provided good bonding integrity after backside grinding tests. Changes in the chemical structures of BCB and Flare glue during bonding were analyzed using FTIR in order to understand the bonding mechanism and to improve the bonding process.
Dewetting of A Complex Polymer: Perfluoro-Ionomer
Authors: Hill Teresa A. , Jiao Xuesong , Martin Charles W. , Perahia Dvora 
Published: April 2011

ABSTRACTThe stability and interfacial structure of ultra thin films of perfluoro-ion containing polymers (ionomers) have been studied using atomic force microscopy and neutron reflectometry. These complex polymers have significant technological applications from thin coatings, to fuel cells as polymer electrolyte membranes, to protective clothing. In particular we focused on the study of [(CF2CF2)n (CF2CFR)]m where R= [OCF2CF2SO3 (X)] and X=H, (800 equivalent weight), coated on silicon oxide. Neutron Reflectometry has shown that film consists of three distinct regions: a region of high density at the interface with the silicon oxide, an intermediate layer with constant density and an air-interface layer where the density decreases due to interfacial roughness. In contrast to noionic polymers, the films proven stable as a function of annealing time above the bulk glass transition, i.e the films do not dewet. This stability is attributed to electrostatic interactions.
Liquids Under Shear Explored by Neutron Scattering: A Problem in Lubrication
Authors: Wolff Max , Hock Rainer , Magerl Andreas , Frick Bernhard , Zabel Hartmut 
Published: April 2011

ABSTRACTConsidering the atomic scattering cross sections for neutrons they are an excellent tool to investigate lubrication problems. Two different shear cells have been built to investigate both the dynamics and structural properties of liquids under shear: one cell has been optimised for quasielastic and inelastic neutron scattering while another one has been designed for reflectivity and diffraction work. The dynamical aspects have been studied on the high-resolution backscattering instrument (IN16 at Institut Laue-Langevin (ILL)). Data with a commercial motor oil as a sample have been taken in contact with an aluminium boundary showing directly the developing anisotropy of diffusion under shear. Furthermore within the same set-up it has been possible to monitor the macroscopic velocity distribution including surface slip. In addition, a diffraction experiment has been carried out, demonstrating from a measurement of the position and the profile of the graphite 002 reflection that the ordering of macroscopic graphite particles in a flowing liquid can be studied with neutrons and an ordering with a tilt angle of the particles of 5° to the flow has been determined.
Effect of Stationary Particles on the Phase Separation of Binary Fluids
Authors: Suppa Domenico , Kuksenok Olga , Balazs Anna C. , Yeomans J.M. 
Published: April 2011

ABSTRACTPhase separating binary fluids with the addition of immobile particles, which act as osmotic force centres, were simulated using a Lattice Boltzmann model in two dimensions. In the hydrodynamic over-damped limit, where the flow is entirely driven by capillary effects, the presence of particles that are preferentially wetted by one of the fluid components significantly affects the kinetics of the growth of the fluid domains. The late time dynamics is governed by the wetting interactions and the final size of the domains can be tailored by varying the strength of the particles-fluid interaction as well as the particles concentration. These features are predicted within a simple theoretical model and are amenable of experimental checks.
One- and Two-Particle Microrheology in Entangled Solutions of fd Virus
Authors: Addas Karim M. , Levine Alex J. , Tang Jay X. , Schmidt Christoph F. 
Published: April 2011

ABSTRACTWe have used one- and two-particle microrheology, employing μm-sized beads and laser interferometric displacement detection, to study the rheological properties of entangled solutions of the filamentous fd virus. Thermal fluctuations of the embedded probes were measured and viscoelastic parameters of the embedding medium were derived. In two-particle microrheology the correlated motions of two identical particles separated by a varying distance in the medium are analyzed, which can avoid biased results due to surface-depletion effects near the probes.
No Need To Dry - Environmental Scanning Electron Microscopy Of Hydrated System
Authors: Donald Athene M 
Published: April 2011

ABSTRACTThe environmental scanning electron microscope (ESEM) offers a new approach for the examination of biological samples at rather high resolution. It permits samples to be imaged without extensive specimen preparation, and specifically requires neither drying nor coating. This implies that organic samples can be looked at in their native state, without the danger of artefacts being introduced. A few specific examples both of static imaging, and also images obtained during dynamic mechanical testing are given in this article to illustrate the power of the technique.
Capillary Formation In Microfabricated Polymer Scaffolds
Authors: Borenstein Jeffrey T. , King Kevin R. , Terai Hidetomi , Vacanti Joseph P. 
Published: April 2011

ABSTRACTOne of the primary challenges for engineering thick, complex tissues such as vital organs is the requirement for a vascular supply for nutrient and metabolite transfer. Earlier work has shown that Solid Freeform Fabrication techniques such as Three-Dimensional Printing (3DP) are capable of producing biodegradable scaffolds for the subsequent formation of a wide range of tissues and organs. While this approach shows great promise as a method for constructing complex tissues and organs in vitro, the resolution of the process is currently limited to length scales larger than the narrowest capillaries in the microcirculation. In this work, microfabrication technology is demonstrated as an approach for organizing endothelial cells in vitro at the size scale of the microcirculation. Standard process techniques utilized to build MEMS (MicroElectroMechanical Systems) devices include photolithography, silicon and glass micromachining, and polymer replica molding. Photolithography is used to print a model network of blood vessels on silicon wafers; the network is designed to replicate the fluid dynamics of the vasculature of a particular tissue or organ. A reverse image of the channel network is formed either by Deep Reactive Ion Etching (DRIE) of silicon or through the use of a thick negative-polarity photoresist (SU-8). Polymeric scaffolds are formed by replica molding, using the silicon wafer as a master mold. Microfluidic chambers have been constructed from PDMS and other biocompatible polymers. Initial cell seeding experiments demonstrate that rat lung endothelial cells attach in a single layer to the walls of these structures without occluding them, providing early evidence that MEMS process technology can serve as a method for organizing capillary networks.
Traction Stresses and Morphology of 3T3 Fibroblast Cells on Fibronectin-versus RGD- Modified Elastic Substrata
Authors: Rajagopalan Padmavathy , Marganski William A. , Dembo Micah , Wong Joyce 
Published: April 2011

ABSTRACTWe report a study on cellular traction forces and morphology on fibronectin (FN)- and Arg-Gly-Asp (RGD) modified substrata. We have focused on fibronectin- and RGD- modified substrata because RGD is a primary cell-binding site on fibronectin. In this study we report the traction stresses exerted by NIH (National Institutes of Health) 3T3 fibroblasts on model polyacrylamide hydrogel substrates using the elastic substrata technique. At equal values of input concentration of fibronectin and RGD we find that the values forprojected cell area are similar. However, a significant difference is observed in the traction forces exerted by fibroblasts on fibronectin- compared to RGD-modified surfaces. At equal values of input concentration, the average force exerted by NIH 3T3 fibroblasts is approximately ten fold higher on fibronectin-modified surfaces in comparison to RGD-modified surfaces.
Effect of Sulfate Content of Biomacromolecules on the Crystallization of Calcium Carbonate
Authors: Arias José I. , Jure Carolina , Wiff Juan P. , Fernández María S. , Fuenzalida Víctor , Arias José L. 
Published: April 2011

ABSTRACTNatural composite bioceramics such as bone, teeth, carapaces and shells contain organic and inorganic moieties, with the organic matrix components directly involved in the precise formation of these structures. We have previously shown that chicken eggshell contains two main sulfated polymers (proteoglycans), referred to as mammillan and ovoglycan which are involved in nucleation and growth of the eggshell calcite crystals. They differ on their anionic properties due to the carboxylate and sulfate content of their glycosaminoglycan component. Based on biological and biochemical evidences, the putative role of mammillan, a keratan sulfate proteoglycan, is in the nucleation of the first calcite crystals, while that of ovoglycan, a dermatan sulfate proteoglycan, is to regulate the growth and orientation of the later forming crystals of the chicken eggshell. In this communication, a systematic study of the influence of variable concentrations of glycosaminoglycans differing in their sulfation status on the morphology, size and number of calcium carbonate crystals after crystallization on microbridges from a calcium chloride solution under an atmosphere of ammonium carbonate at different pH is presented. Depending on the pH and concentration, the variation of sulfation status drastically changed the morphology, size and number of calcite crystals. The produced calcite particles with various morphologies are promising candidates for some novel materials with desirable shape- and texture-depending properties.