In this work we present new experimental results about the packing fraction of a granular monolayer excited by taps in the gravity direction. The role of large amplitude of tapping is discussed. Also, the relationship between packing fraction and the number of particles in the sample is analyzed.

High performance all-polymer aerogels are not only interesting for their low thermal conductivity, but also for their mechanical strength and their conversion to porous carbons. The prevalent design rule dictates that crosslinking at the monomer level decreases solubility of the developing polymer and induces phase separation of nanoparticles with high surface to volume ratios. Hence, hyperbranched structures based on trifunctional single aromatic core monomers should have enhanced interparticle connectivity and rigidity compared to those based on either difunctional or multiple aromatic core monomers. That design rule is applied here to hyperbranched polyurethane (PU) aerogels synthesized from tris(4-isocyanatophenyl)methane (TIPM) and 1,1,1-tris(4-hydroxyphenyl)ethane (HPE) in anhydrous acetone using dibutyltin dilaurate (DBTDL) as catalyst. The resulting materials vary from highly flexible to rigid as the monomer concentration increases. FTIR and 13C solid NMR confirm formation of urethane. SEM shows that the flexible variety is macroporous with a beaded worm-like structure, while the rigid variety is mesoporous and nanoparticulate. Lower-density flexible aerogels are highly porous (92%) with surface area of 132 m2 g-1, while the rigid ones have higher surface areas, up to 256 m2 g-1. Polyurethane aerogels from other triols and diols, e.g., phloroglucinol (POL) and resorcinol (RES), respectively, have also been studied and for similar monomer concentrations shrinkage and bulk density increases.

The favorable lattice matching between Au and NiO crystals made possible the growth of unique cookie-like nanoparticles (25 nm mean diameter) inside a porous SiO2 film after annealing at 700 °C. The unusual aggregates result from the coupling of well distinguishable Au and NiO hemispheres, which respectively face each other through the (100) and (200) lattice planes. The thermal evolution of the Au and NiO nanoparticles structure has been studied by high resolution transmission electron microscopy and UV-visible absorption spectroscopy and correlated with the evolution of the Au surface plasmon resonance peak.

Optimum machining parameters are of great concern in manufacturing environments, where economy of machining operation plays a key role in competitiveness in the market. Many researchers have dealt with the optimization of machining parameters for milling operations. In this paper, optimization procedures based on particle swarm optimization algorithm are developed for find machining parameters in milling operation. It describes development and utilization of the methodology that determines optimum Pareto’s front analyzing feed, speed and depth for milling operation. The relationships between machining parameters and the performance measures of interest are obtained by using experimental data and a swarm intelligent neural network system. Results show that particle swarm optimization is an effective method for solving multi-objective optimization problems, and also, that an integrated system of neural networks and swarm intelligence can be used to solve complex machining optimization problems.

Considerable research has focused on the formation of superhydrophobic surfaces utilizing both the chemical composition of surfaces and geometric effects. In this study, a superhydrophobic polycarbonate (PC) network surface was produced from hydrophilic polycarbonate through electrospinning process. Complex surface geometries often related to material roughness is used to evaluate the wetting behavior of electrospun polycarbonate fiber network. The surface properties of electrospun polycarbonate fibers are therefore examined with the potential to exploit the fibers through enhancing hydrophobic behavior. Characterization and analysis of PC electrospun fiber and PC film surfaces were carried out to compare surface roughness with wetting contact angle. Analytical models are used to describe hydrophobicity in terms of roughness.

Commercially available bulk silicon carbide (SiC) has a high number (>2000/cm2) of screw dislocations (SD) that have been linked to degradation of high-field power device electrical performance properties. Researchers at the NASA Glenn Research Center have proposed a method to mass-produce significantly higher quality bulk SiC. In order for this bulk growth method to become reality, growth of long single crystal SiC fibers must first be achieved. Therefore, a new growth method, Solvent-Laser Heated Floating Zone (Solvent-LHFZ), has been implemented. While some of the initial Solvent-LHFZ results have recently been reported, this paper focuses on further characterization of grown crystals and their growth fronts. To this end, secondary ion mass spectroscopy (SIMS) depth profiles, cross section analysis by focused ion beam (FIB) milling and mechanical polishing, and orientation and structural characterization by X-ray transmission Laue diffraction patterns and X-ray topography were used. Results paint a picture of a chaotic growth front, with Fe incorporation dependant on C concentration.

Using waste materials as aggregate for new concrete production is a growing tendency, because of several environmental problems. Recycled coarse aggregate (RCA) obtained from crushing waste concrete has lower density and greater absorption than natural aggregate, because of the higher porosity of the mortar attached to the RCA particles. Compressive strength level achieved in recycled concrete may be similar to that of conventional concrete. On the other hand, durable performance of recycled concrete is variable, and diverse evidence can be found in literature for different durability issues. In this paper, chloride ingress in conventional and recycled concrete, made with quartzite aggregate and blended Portland cement is evaluated when immersed in NaCl solution. Two strength levels (21 and 35 MPa) and two contents of RCA (25 and 75%), as substitute of natural quartzite aggregate, were considered. The chloride diffusion coefficient and the relationship between water-soluble chloride and bound chloride are analyzed.

This paper describes proposal of ReRAM switching mechanism, development of production tool for ReRAM sputtering and improvement in TaOx-ReRAM switching characteristics. We propose that a ReRAM-cell has stack a structure in which an oxygen vacancy supply layer (TaOx) and an oxygen accumulation layer (Ta2O5) sandwiched by the top and bottom electrodes. Resistance change of the ReRAM-cell is caused by the oxygen vacancies migrating between the TaOx and the Ta2O5 layers by applied voltage. This prediction corresponded to the experimental facts. The thickness of Ta2O5 film sputtered by a mass production tool had good uniformity (±1.0%) and excellent stability (±1.0%). Also the sheet resistance uniformity (1σ) of TaOx film had 3.6%. By examining the sputtering conditions, the ReRAM-cell having a Ta2O5/TaOx bi-layer operated in less than 100μA with a forming-free and had excellent endurance property to 1010 cycles at 50nsec.

We report simultaneous measurements of thermal conductivity and Seebeck coefficient on array-scale silicon nanowires fabricated by metal assisted chemical etching. The measurements are conducted on the solid and the mesoporous nanowire arrays (NWAs) obtained from etching 1 ohm-cm and 0.002 ohm-cm Si substrates respectively. We demonstrate control on sidewall morphology and doping of the arrays that have an aspect ratio up to 20 and 30 % areal coverage. We employ differential frequency-domain measurements, separately on the array and the corresponding substrate to obtain the temperature drop and Seebeck voltage contribution of the nanowire array. The technique is validated by measurements on bulk silicon across the resistivity 0.002-1 ohm-cm. The Seebeck measurements reveal quenching of the phonon drag in the nanowires in comparison to the bulk in the measured temperature range of 300 K- 500 K. The Seebeck coefficient shows a ~18 % decrease in the solid NWAs and ~22 % increase in the mesoporous NWAs at room temperature. The thermal conductivity is close to Casimir limit for the solid wires while it drops to ~2.5 W/mK in the mesoporous nanowires.

Gallium nitride thin films were grown by pulsed laser deposition. Subsequently, post-growth annealing of the samples was performed at 400, and 600 oC in the nitrogen atmosphere. Surface morphology of the as-grown and annealed samples was performed by atomic force microscopy, surface roughness of the films improved after annealing. Chemical analysis of the samples was performed using x-ray photon spectroscopy, stoichiometric Gallium nitride thin films were obtained for the samples annealed at 600 oC. Optical measurements of the samples were performed to investigate the effect of annealing on the band gap and optical constants the films.

Catalyzing the combustion of liquid fuels offers interesting prospects for further improvement of the fuel economy and the performance of engines, in particular for jets and advanced propulsion systems. Polyoxometalates are well-known oxidation catalysts which are expected to also catalyze combustion reactions. However, their polarity makes their dispersion in fuels particularly challenging. Herein, functionalized graphene sheets were used as a support due to their high surface area as well as their compatibility with the target reaction. In order to further improve the dispersion of the catalyst in fuels, alkyl chains were grafted to the sheets’ surface. An innovative grafting technique was developed to attach alkyls at a variety of oxygen-containing functionalities already present on reduced graphene oxide, such as hydroxyl and epoxy groups. A phase transfer to the organic phase was observed when dispersing the dry powder in water:toluene mixtures. In addition, the dry alkyl chain-modified graphene sheets readily dispersed in common organic solvents without the assistance of sonication. Polyoxometalates (H3PMo12O40 and H4PMo11VO40) were dispersed on the modified sheets as discrete clusters even at a relatively high loading (20 wt.%). The catalytic activity of these nanostructured materials was demonstrated for the combustion of methylcylcohexane, tested here as a model fuel.

We report in this communication on the photoelectrochemical (PEC) performances of copper tungstate (CuWO4) material class. This study was performed on 2-micron thick samples fabricated using a low-cost co-sputtering deposition process, followed by an 8-hour long annealing at 500°C in argon. Microstructural analysis pointed out that the post-deposition treatment was critical to achieve photocatalytic activity. Subsequent characterizations revealed that polycrystalline CuWO4 photoanodes owned promising characteristics for solar-assisted water splitting, i.e (i) an optical band-gap of 2.2 eV, (ii) a flat-band potential of -0.35 V vs. SCE and (iii) conduction and valence band-edges that straddle water splitting redox potentials. CuWO4 photoanodes generated 400 μA.cm-2 at 1.6V vs. SCE under simulated AM1.5G illumination in 0.33M H3PO4 with virtually no dark current up to this potential. Impedance analysis pointed out that large charge transfer resistances (2,500 Ω.cm2) could be the main weakness of this material class. Current research activity is focused on solving this issue to achieve higher PEC performances.

As device sizes are scaled down nearly to their atomic limits, the development of economically viable methods which may continue to improve device performance in accordance with Moore’s Law becomes ever more challenging. The recently developed technique of Electroplate-and-Lift (E&L) lithography promises to be an inexpensive, widely applicable method for the reproducible, controlled fabrication of micro- and nanostructures. In this study, E&L is applied to the fabrication of patterned copper micro- and nanowires as a model system. Copper wires with diameters ranging from 10 m to 200 nm have been produced using a single ultrananocrystalline diamond (UNCD)TM template, by varying only the electroplating time.

To quantify the relationship between copper wire diameter and deposition time, wires were electroplated at -0.4 V vs. the saturated calomel electrode (SCE) for durations between 2.5 and 160 s, then imaged by optical microscopy and/or scanning electron microscopy (SEM). Images were analyzed by identifying wire segments with ImageJ and examining the statistical distribution of wire diameters using Excel. This analysis verified theoretical predictions of a linear dependence between mean wire diameter and the square root of growth time.

This work explores the influence of the post-transfer anneal temperature and the substrate on transferred graphene and its Raman properties. Graphene grown by low pressure chemical vapor deposition on copper foils was transferred to SiO2/Si, fused silica, and silicon substrates via a process that involves coating the graphene with PMMA as a protective handling layer during the wet chemical etching of the copper and then placing the PMMA/graphene onto the substrate. The PMMA layer was then removed by heating in a hydrogen/argon atmosphere at temperatures ranging from 350 to 550 °C or by exposing the PMMA to heated acetone vapor/liquid. Raman spectroscopy measurements, taken before and after PMMA removal, reveal differences in the prominent Raman features, the G and G’ peaks, upon annealing. These changes include (1) a shift in the average G and G’ peak positions when comparing Raman spectra before and after PMMA removal and (2) a decrease in the G’:G peak intensity ratio (IG’/IG ), which is typically used as a measure of the number of graphene layers. For both the as-transferred graphene and graphene removed by the heated acetone, the IG’/IG peak ratio was approximately 2, indicating single layer graphene. However, when the graphene was annealed at temperatures above 350 °C, the IG’/IG intensity ratio varied from 0.5 to 1.5. These changes in the Raman spectra are similar to those observed in exfoliated single layer graphene supported on SiO2/Si substrates and are indicative of graphene-substrate interaction effects that lead to hole doping of the graphene [1,2]. These trends were observed for graphene transferred to all three substrates, regardless of the substrate surface roughness and/or composition.

A new class of high-vacuum organic deposition chamber was developed to study the structure and growth of organic semiconductor thin films. Using the chamber in situ real-time 2-dimensional grazing incidence x-ray diffraction (2D-GIXD) was measured during thin film growth of distyryl-oligothiophenes derivatives (DS2T) on SiO2 surface. An evolution of 2D-GIXD pattern was clearly observed during the growth due to the crystallization of the molecular domains consisting of standing-up orientation. A theoretical simulation on the experimental 2D-GIXD map provided a potential use of this system to determine the unit cell parameters in thin films. Thickness dependence and influence of air exposure on the film structure were also studied.

Orientation patterned (OP)-GaAs crystals are attractive materiasl for mid-infrared and terahertz lasers sources, using non linear optics frequency conversion from shorter wavelength sources. The optical propagation losses are critical to the fabrication of these sources; among the causes of optical losses the generation of defects and the incorporation of impurities must play a relevant role. The control of the incorporation of impurities and defects is, therefore, crucial to improve the performance of the OP-GaAs crystals as non linear optical materials. We present herein a cathodoluminescence (CL) analysis of OP-GaAS crystals intentionally doped with Si, in order to understand the incorporation paths of Si in the OP-GaAs crystals.

In this work we alternate breaking-symmetry-substrates (BSS) and non-breaking-symmetry-substrates (NBSS) such as SiC and SiO2,following the Silver-Mean (MSMGS) and Period-Doubling (MPDGS) sequences. We implement the Transfer Matrix technique to calculate the transmittance and the linear-regime conductance as a function of the most relevant parameters of the multilayered graphene structures: energy and angle of incidence, widths of BSS and NBSS regions and the generation of the quasi-regular sequence. We analyze the main difference of the transmission and conductance properties between MSMGS and MPDGS.

Taxol (Paclitaxel) is a very potent anticancer drug used in chemotherapy treatments. Due to its hydrophobic nature, toxic solubilizing agents are used to administer the drug via intravenously. However, this systemic administration is associated with toxic side effects and drug limited efficacy. An alternative to these problems are polymeric micelles. The effectiveness of this drug delivery system is related to its size, modification of pharmacokinetics, drug delivery control and toxicity reduction. In this study, micelles based on methoxy Poly(ethylene glycol)-block-Poly(ε-caprolactone) (mPEG-b-PCL) copolymer loaded with Taxol were synthesized thorough an uncommon method namely powder formulation, using tert-butanol as co-solvent, to our knowledge no reported previously for these micells. Taxol was conjugated to the hydrophobic block of mPEG-b-PCL copolymer. Characterization of this system was done by means of Fourier Transform Infrared Spectroscopy (FT-IR) and Field Emission Scanning Electron Microscopy (FESEM), observing good results as compared to previous reports.