bluuebunny/crossref_metadata_2025_split huggingface dataset:
Growth of Branched Carbon Nanostructures in Nanopatterned Surfaces Created by Focused Ion Beam
Authors: Solá Francisco , Resto Oscar , Biaggi-Labiosa Azlin , Fonseca Luis F 
Published: April 2011

ABSTRACTA method to grow arrays of multibranched carbon nanostructures is explained. We use the electron-beam-induced deposition method using a transmission electron microscope with ∼10−6 Torr vacuum where hydrocarbons are present in the chamber. Saw-tooth nano-patterns were made with a focused ion beam in porous silicon substrates. Due to the dielectric properties of the films the patterns provide the corresponding sites in which high local electric fields appear during irradiation thus allowing the hydrocarbons to become preferentially attracted to those active sites. We found that the adequate ion dose to create well defined saw-tooth nano-patterns was between 8 and 10 nC/μ2 at 30 kv. Electron energy-loss spectroscopy on the branched carbon nanostructures show a high concentration of sp2 sites suggesting that they are made of graphite-like amorphous carbon.
Fabrication of Periodic Arrays of Nano-sized Si and Ni dots on SiO2 Using Linearly Polarized Nd:YAG Pulsed Laser
Authors: Nishioka Kensuke , Horita Susumu 
Published: April 2011

ABSTRACTPeriodic arrays of nano-sized Si and Ni dots were fabricated by only irradiating a linearly polarized Nd:YAG pulsed laser beam to Si and Ni thin films deposited on silicon dioxide (SiO2) film. The interference between an incident beam and a scattered surface wave leads to the spatial periodicity of beam energy density distribution on the surface of the irradiated samples. A thin film was melted using a laser beam, and the molten film was split and condensed owing to its surface tensile according to the periodic energy density distribution. Then, the fine lines (line and space structure) were formed periodically. After the formation of fine lines, the sample was rotated by 90°, and the laser beam was irradiated. The periodic energy density distribution was generated on the fine lines, and the lines split and condensed according to the periodic energy density distribution. Eventually, the periodically aligned nano-sized dots were fabricated on the SiO2 film.
Nano-sized Taper Structure Formed by Wet Process Using Catalysis of Gold Nanoparticle
Authors: Nishioka Kensuke , Horita Susumu 
Published: April 2011

ABSTRACTThis paper describes a new technique for fabrication of nano-sized taper structure formed by simple wet chemical etching using catalysis of gold (Au) nanoparticle. Single nano-sized Au particle dispersion solution was coated onto Si(111) substrate with polished surface. Then, the samples were soaked in an aqueous etching solution of hydrofluoric acid (HF) and hydrogen peroxide (H2O2). The surface of 15-min-etched Si substrate appeared black. The reflectivity of the Si substrate was reduced to below 5% throughout the entire spectrum from 300 to 800 nm owing to nano-sized taper structure called subwavelength structure (SWS). The fractional area occupied by Si as a function of the depth across the textured layer showed a smooth increase of density up to a depth. The observed optical effects are explained by the formation of a nanoscale taper structure, representing an effective medium with a smooth transition of the refractive index from that of air to that of Si.
Optimization and Constraints in Sonolithography
Authors: Campbell Paul , Prentice Paul 
Published: April 2011

ABSTRACTThe violent interaction between pressure driven cavitation nuclei and nearby rigid substrates is usually a troublesome occurrence, giving rise to damage, and often system failure in hydraulic systems. However, the extreme nature of the phenomenon can also be exploited in situations where deliberate wear or erosion of a material is desireable, such as with the application of shock wave lithotripsy to fragment kidney stones in a medical context. The purpose of the present study was to examine whether a system can be designed so as to afford a level of control over cavitation processes, so that other useful applications might arise. Specifically, we looked at controlling single cavitation nuclei, constituted by encapsulated microbubbles, in proximity to a nearby rigid substrate and activated by ultrasound. This was achieved using a novel optical trapping arrangement, which facilitated establishment of an arbitrary, stable, initial spatial configuration for a bubble system. Critically, exercising optical control in such a way meant that a microbubble could be isolated from a resident population during insonation thus ensuring that ‘cross-talk’ with the rest of the bubble population was minimised. We observed, using high speed microphotography at circa one million frames per second that fine microjets are issued from cavitation microbubbles, and these impact the nearby surface, creating indentations of controllable size. Specific applications may arise that exploit this action, which, in the general case we refer to as ‘sonolithography’. However, scaling up the process to activate multiple bubbles at once, may lead to complications arising via the action of secondary radiation forces. We discuss the salient aspects of our preliminary findings on this subject herein.
PEG-POSS Hybrid Polyurethanes: Mechanically Robust Nanostructured Hydrogels
Authors: Wu Jian , Ge Qing , Mather Patrick T 
Published: April 2011

ABSTRACTA series of unique hybrid thermoplastic polyurethanes (TPUs) was synthesized using PEG as soft segment and incorporating an isobutyl-functionalized POSS diol (TMP POSS diol) in the hard segment. The molecular weight of PEG was systematically varied to include 10, 20, and 35 kDa, while the mole ratio of POSS diol (as chain extender) to PEG was in range from 3:1 to 8:1 with samples featuring a PEG molecular weight of 10 kDa. The diisocyanate employed for TPU polymerization was 4,4'-methylenebis(phenyl-isocyanate) (MDI). We found that the hydrophobic hard segments (POSS) can form crystalline structures driven by micro-phase separation, this being due to significant thermodynamic incompatibility between POSS and ethylene oxide units. The POSS nano-crystals thus formed serve as physical crosslinking sites within an inorganic-organic hybrid network. This affords a new hybrid organic-inorganic hydrogel in the water-swollen state. The equilibrium swelling ratio increased monotonically with PEG loading and ranged from ∼70% to ∼600%. The shear modulus, G, of the hybrid hydrogels was observed to span 0.3 < G < 4.0 MPa – C values commonly found for elastomers, not hydrogels. Indeed, the hydrogel stiffness can be finely tuned through the POSS:PEG molar ratio, as this predictably controls swelling in water.
Refractive Index Change in Nanoscale Thermosensitive Hydrogel for Optoelectronic and Biophotonic Applications
Authors: Garner Brett W , Hu Zhibing , McDaniel Floyd D. , Neogi Arup 
Published: April 2011

ABSTRACTThe familiar property responses of isopropylacrylamide hydrogel, cause the hydrogel to undergo a discontinuous volumetric phase across a critical level of stimuli. Poly(N-isopropylacrylamide) hydrogel is a recognized response to global temperature stimuli across the low critical solution temperature (LCST). The basic PNIPAM hydrogel undergoes its phase change at a LCST of 34°C, where water is expelled from the interior of the gel microsphere, as the temperature increases past LCST. The responsiveness of PNIPAM hydrogel offers the potential for controlling optical properties of a medium such as refractive index and scattering index. In the present work we present the refractive index of microsphere/microbeaded hydrogel structures necessary for optical application. The particle size of the hydrogels nanostructures at room temperature is observed to be 300-400 nm as estimated by dynamic light scattering and agree well with scanning electron microscopy measurements. The temperature dependent refractive index change of hydrogel microspheres have been measured using variable angle spectroscopic ellipsometry and shows a 10% change as the temperature changes from 33°C to 34°C.
Synthesis and Self-assembly of DMPC-conjugated Gold Nanoparticles
Authors: Chatterjee Subhasish , Krikorian Markrete , Gafney Harry D. , Gersten Bonnie 
Published: April 2011

ABSTRACTBio-conjugated nanomaterials play a promising role in the development of novelsupramolecular structures, molecular machines, and biosensing devices. In this study, lipid-capped gold nanoparticles were synthesized and allowed to form a self-assembled monolayer structure. The nanoparticles were prepared by a phase transfer method, which involved the reduction of potassium tetrachloroaurate(III) by sodium citrate in an aqueous solution and the simultaneous transfer of the reduced species to an organic medium containing DMPC (1,2-dimyristoyl-sn-glycero-3-phosphocholine). The gold nanoparticles were characterized using Uv-vis spectroscopy and dynamic light scattering (DLS) particle-size analysis. In addition, the resulting nanoparticles were examined using transmission electron microscopy (TEM). The Langmuir-Blodgett (LB) technique was used to assemble the DMPC-capped nanoparticles onto a water subphase at room temperature. The measurement of the compression isotherm confirmed the assemblage of lipid capped gold nanoparticles. This method of synthesis of ordered structures utilizing molecular interactions of lipids will be useful in developing novel metamaterials and nanocircuits.
The Mechanism of Chitosan Enhanced Lung Surfactant Adsorption at the Air-Liquid Interface in the Presence of Serum Proteins
Authors: Stenger Patrick C , Palazoglu Omer M , Zasadzinski Joseph A 
Published: April 2011

ABSTRACTPressure-area isotherms and fluorescence microscopy were used to investigate the impact of chitosan on the competitive adsorption between lung surfactant (LS) and serum proteins at the air-liquid interface. Isotherms demonstrate an optimum chitosan concentration to mediate LS adsorption; higher concentrations actually reduce the amount of LS which can adsorb. Fluorescence microscopy images show the transition from a serum protein to LS-covered interface for the optimum chitosan concentration; this transition goes through a sharply phase separated coexistence region. The results suggest that the cationic chitosan molecules mediate adsorption of the negatively charged LS aggregates by reducing the electrostatic barrier imposed by negatively charged interfacial serum proteins.
Generation of Bioactive Nanostructured Interfaces to Mimic Cellular Microenvironments
Authors: Wolfram Tobias , Belz Ferdinand , Schoen Tobias , Aydin Daniel , Spatz Joachim P 
Published: April 2011

ABSTRACTThere is currently great interest in material science to mimic cellular microenvironments with controlled bioactive features and biomolecule presentation at the nanometer length scale. Target cells exposed to those 2- or 3D-substrates are stimulated to manifest a variety of cellular functions like cell adhesion, migration and differentiation.Based on micellar nanolithography, we developed an experimental setup to present single biomolecules on a 2D-nanoarray over large areas on cell-adhesive or cell-repellent substrates. The spacing between biomolecules can be adjusted to 30-250 nm. To mimic a more complex cellular micro-environment with cell-cell contacts as well as cell-extracellular matrix (ECM) contacts, we used biomolecules from different cell adhesion molecule families, like cadherins, immunglobulin-superfamily, integrins and laminins. Via a Ni2+- nitrilo triacetic acid (NTA) system, the amount and the orientation of proteins is chemically controlled such that it resembles the native in vivo settings in the cellular microenvironment. By using poly-l-lysine-grafted-polyethylene glycol (PLL-g-PEG) molecules, we generated 2D-protein-nanoarrays with a cell repellent background matrix. After modification of this matrix we incorporated small bioactive peptides to create a microenvironment which allows cell adhesion. These approaches resulted in substrates with specific presentation of biomolecules to mimic cell-cell contacts and cell-ECM interactions simultaneously.With these substrates we investigated primary fibroblast and neuronal cell adhesion mediated by different biomolecules and with different nanometer spacing. We quantified neurite outgrowth of dorsal root ganglion (DRG) neurons as a differentiation paradigm on nanostructured substrates. Gold nanoparticles were functionalized with peptides, containing the arginine-glycine-aspartic acid (RGD) motif, an integrin activation sequence. Cell adhesion as well as differentiation showed a dependency on the nanometer length scale and on the presented biomolecules.
Patterning Cylindrical Fibers with Long-Range Electrostatic Forces
Authors: Kohlstedt Kevin L. , Vernizzi Graziano , de la Cruz Monica Olvera 
Published: April 2011

ABSTRACTWe report our findings with theoretical arguments on chiral symmetry breaking on the surface of charged cylinders. We use a model for periodic patterns of charges constrained over a cylindrical surface. In particular we focus on patterns of oriented lamellar patterns, such as, chiral helices, achiral rings or vertical lamellae, with the constraint of global electroneutrality. We study the dependence of the patterns' size and pitch angle on the radius of the cylinder and salt concentration. We obtain a phase diagram by using numerical and analytic techniques. For pure Coulomb interactions, we find a ring phase for small radii and a chiral helical phase for larger radii. We extend the findings to discrete triangular lattices wrapped over a cylindrical geometry. We find no symmetry breaking chiral helical phase in the discrete wrapping when using just an electrostatic potential and the minimum energy configuration is an achiral lattice matching the six-fold symmetry of triangular lattice. Conversely, with the addition of an elastic potential between the charges on the surface of the cylinder we find a stable chiral configuration. We discuss possible consequences and generalizations of our model.
Micromechanical Investigations on Films made of Recombinant Spider Silk Proteins and Silk Fibroin
Authors: Junghans Frauke , Conrad Udo , Heilmann Andreas , Spohn Uwe 
Published: April 2011

ABSTRACTFilms made of a recombinant spider silk protein and silk fibroin were prepared by spincoating and casting. Therefore the solubility of these substances was investigated in hexafluoroisopropa-nol, ionic liquids and concentrated salt solutions. The roughness and the thickness of the protein films were determined by the Atomic Force Microscopy (AFM) and by mechanical profilometry. The micromechanical behaviour was investigated by acoustic impedance analysis using a quartz crystal microbalance (QCMB) as well as by microindentation. Films with thickness less than 350 nm revealed an almost ideal elastic behaviour in the range of 5 to 75 MHz. At a higher film thickness the half-band-half width increases considerably and the films show a viscoelastic be-haviour with a considerable dissipation. The relative humidity significantly influences the me-chanical behaviour of protein films. Hence the micro-hardness and the ability of water adsorption were determined in dependence on the relative humidity.
Effect of Ligand Density Gradient on the Adhesion Kinetics of Biological Membranes
Authors: Sarvestani Alireza , Jabbari Esmaiel 
Published: April 2011

ABSTRACTAn analytical model is developed for the effect of surface gradient in ligand density on the adhesion kinetics of a curved elastic membrane with mobile receptors. The displacement and speed of spreading at the edge of the adhesion zone as well as the density profile of receptors along the membrane are predicted as a function of time. According to results, in the diffusion-controlled regime, the front edge displacement of adhesion zone and the rate of membrane spreading decreased with increasing ligand density in a certain direction. Furthermore, the displacement of the edge of the adhesion zone did not scale with the square root of time, as observed on substrates with uniform ligand density.
Aromatic Thermosetting Copolyester (ATSP)/UHMWPE Blends with Improved Wear Properties and Biocompatibility
Authors: Huang Yongqing , Economy James 
Published: April 2011

ABSTRACTDespite the recognized success and worldwide acceptance of ultrahigh molecular weight polyethylene (UHMWPE) for total joint arthroplasty, the generation of UHMWPE wear debris from the articulating surface is of major concern and limits the longevity of the artificial joint device. Blends of UHMWPE with an aromatic thermosetting copolyester (ATSP) at 50:50 volume ratio using poly(ethylene-co-acrylic acid) (PEA) as a compatibilizer were developed to address this problem. The amount of PEA was 0, 5, 10, 15 and 20 weight percent of the weight of ATSP, respectively. The wear properties of these blends were evaluated by a pin-on-disk wear test in which an ASTM F-75 cobalt-chromium alloy disk was chosen as a counterface and sterile filtered bovine serum diluted in deionized water to 75% (volume) was used as a lubricant. The wear tests from 0.2 to 3 million cycles showed that UHMWPE/ATSP blend with 10 wt% PEA had average weight loss smaller than UHMWPE and comparable to crosslinked UHMWPE. The wear debris study indicated that UHMWPE/ATSP blend with 10 wt% PEA created a smaller size percentage of the wear debris particles in the biologically active range than UHMWPE and crosslinked UHMWPE. The direct-contact cytotoxicity tests showed that ATSP and UHMWPE/ATSP blend with 10 wt% PEA were not toxic.
Dendrimer Nanocomposites as Multifunctional X-ray Contrast Agents
Authors: Ely Teyeb Ould , Sharma Manju , Lesniak Wojciech , Klippenstein Donald L. , Foster Barbara A. , Balogh Lajos P. 
Published: April 2011

ABSTRACTWe synthesized dendrimer composite nanoparticles and investigated their potential for traditional X-ray imaging and Computed Tomography (CT). These new X-ray contrast agents show better contrast compared to traditional iodine-based contrast agents, and are expected to clear from the blood much slower than commercial agents, permitting longer imaging times. We have also investigated their safety profile in terms of viscosity and osmotic pressure.
Novel Hydrogel and Conducting Polymer-based Skin Surface Electrode Design
Authors: Alba Nicolas Alexander , Justin Gusphyl , Wadhwa Reecha , Sun Mingui , Sclabassi Robert J , Cui Xinyan Tracy 
Published: April 2011

ABSTRACTVarious formulations of polymeric hydrogels were synthesized and evaluated with the goal of developing a novel skin-surface biopotential electrode. Materials explored within the study included poly(2-hydroxyethyl methacrylate) (polyHEMA) in pure form or impregnated with the conducting polymers polypyrrole or poly(3,4-ethylenedioxythiophene) (PEDOT), as well as polyacrylate. The drying dynamics, ionic conductivity, and impedance of the prototype materials were characterized when applied to porcine and human skin, in order to determine their utility for a minimum preparation and low specific impedance surface electrode. The addition of a fraction of PEDOT or polypyrrole within a polyHEMA gel was found to decrease hydrogel impedance when tested within PBS, as well as on non-abraded porcine skin. A polyacrylate component added to polyHEMA had no significant effect on hydrogel impedance in PBS, but significantly reduced impedance on the porcine skin surface. Although having much lower specific impedance (impedance normalized by the contact area) than the commercial skin surface electrode (3M Red Dot), polyHEMA based electrodes require skin abrasion. Pure cross-linked polyacrylate gel was found to provide the most attractive option, and yielded competitive low-impedance performance on non-abraded human skin.
Characterization of amorphous/crystalline silicon interfaces from electrical measurements
Authors: Kleider Jean-Paul , Gudovskikh A. S. 
Published: April 2011

ABSTRACTElectrical techniques based on capacitance and conductance measurements are powerful tools for interface characterization in semiconductor heterostructures. We here detail their application to the study of the heterointerface formed between hydrogenated amorphous silicon (a-Si:H) and crystalline silicon (c-Si). The main parameters governing the device applications are the conduction and valence band mismatch, and the density of interface states. The presence of a high interface states density can be revealed by capacitance versus temperature and frequency measurements. For very high quality interfaces that are required for instance to reach high conversion efficiencies in solar cells, the usual measurements performed in the dark and at zero or reverse bias are not sensitive enough. We show that the sensivity to interface states can be enhanced by using capacitance measurements under illumination and at a forward bias close or equal to the open-circuit voltage. In this case, the measured capacitance is determined by the diffusion of free carriers in c-Si and limited by recombination at the interface. Regarding the determination of band offsets, the method using a plot of the inverse square capacitance as a function of bias to determine the intercept of the extrapolated linear region is shown to lead to errors even in the absence of any interface charge. This is due to the presence of a strong inversion layer in c-Si at the interface, the effect of which has been ignored so far in the literature. The presence of this strong inversion layer is evidenced from planar conductance measurements on (n) a-Si:H/(p) c-Si structures. We emphasize that these measurements are very sensitive to details of the band structure profile. In particular, it is shown that the temperature dependence of the sheet electron density allows the determination of the conduction band offset between a-Si:H and c-Si with a good precision. We find 0.15 ± 0.04 eV.
Boron Incorporation and Its Effect on Electronic Properties of Ge:H Films Deposited by LF Plasma
Authors: Kosarev Andrey , Torres Alfonso J , Checa Nery D , Kudriavtsev Yurii , Asomoza Rene , Hernandez Salvador G 
Published: April 2011

ABSTRACTBoron (B) doping of plasma deposited silicon films have been widely studied and applied in many devices, while B-doping of germanium has been poorly reported in literature. We have reported previously about Ge:H films with low density of localized states deposited by LF plasma with optimal hydrogen dilution.This work is devoted to a study of boron incorporation and its effect on electronic properties in Ge:H films. The films were obtained by low frequency (LF) plasma deposition from GeH4+SiH4 +B2H6 mixture diluted with hydrogen. The deposition parameters were as follow: substrate temperature Ts = 300 oC, discharge frequency f= 110 kHz, pressure P= 0.6 Torr, power W= 300 W, germane flow QGeH4= 50 sccm, silane flow, hydrogen flow QH2=3500 sccm, diborane flow was varied in the range of QB2H6=0 to 20 sccm providing boron concentration in gas phase in the range of Y=0 to 4%. Composition of the films was characterized by SIMS profiling. Hydrogen bonding was studied by FTIR. Temperature dependence of conductivity measured in DC regime in vacuum thermostat was employed to study carrier transport. Optical measurements provided optical gap, sub-gap absorption and refraction index. Boron incorporation in solid film demonstrated fast increase in the range of Y = 0 to 1.4% and then increase became slower. Hydrogen concentration in the films was determined by absorption of Ge-H stretching mode at k ≈ 1870 cm−1 and it showed weak increase with change of Y from 0 to 4%. Activation energy of conductivity increased in the range of Y = 0 to 1.5% suggesting a compensation of electron conductivity, reaching maximum value Ea =0.5 eV (corresponding approximately to Eg/2) at Y= 1.5%. Then Ea reduced to minimum value Ea = 0.27 eV at Y= 3.5% showing a trend to saturation with further Y increase. This behavior is related to change of charge transport from electron to intrinsic at Y= 1.5% and further to hole transport.