As a preliminary study aiming to possible applications, novel polythiophenes (PTs) derivatives of 3-hexylthiophene and a thiophene functionalized with pyrene chromophore were synthesized. Homopolymer and copolymers of these monomers were obtained in different stoichiometric ratios which allow obtaining structure-property relation of each of the polymers. PTs were characterized by FT-IR, 1H NMR, UV-vis, DSC-TGA, GPC and fluorescence experiments. Polymers have λmax between 345 to 450 nm and an emission band at 485 and 542 nm. Low molecular weights distribution (Mn = 875 to 1600 g/mol) and thermostable products (Td = 336 to 474°C) were obtained. These PTs functionalized with aromatic molecules and π-conjugated systems could offer interesting applications such as optical sensors, nonlinear optics and photovoltaic cells.

Atomic force microscopy (AFM) suffers from an important limitation: it does not provide quantitative information about the scanned sample. This is because too many unknowns come into play in AFM measurements. The shape of the tip is probably the most important. A technique able to characterize in situ the shape of the tip apex would represent an important step ahead to turn the AFM into a quantitative tool.

Standard methods can be destructive to the tip and are time consuming. Two main methods are currently used to characterize the tip radius in situ without affecting its shape. The first consists of characterizing the tip radius by monitoring the dynamics of the cantilever. The value of free amplitude, for which transitions from the attractive to repulsive force regimes are observed, strongly depends on the curvature of the tip. The second method to characterize the tip radius consists instead on fitting the capacitance curve of the tip-sample system with an analytical function.

In this work we compare the two methods to characterize in situ the tip radius and results are verified with SEM images. The value of the free amplitude is correlated with the value of R while the capacitance curve is derived with a method we proposed. Tips with different tip radii are used. The investigation is conducted with the aim of determining the most reliable technique for characterizing the tip radius for both sharp and blunt tips.

A model is presented for computing the temperature increase associated with the formation of an adiabatic shear band. The hypothesis is that the heating is supplied by the difference in energy of a pile-up of n dislocations and the energy of n individual dislocations. The heating is assumed to occur within a volume determined by the grain size (i.e. slip band length) and an effective thermal length determined by the dislocation velocity. The model predicts increases in temperature with increasing shear modulus (G), increasing numbers of piled up dislocations (n), increasing Burgers vector (b), increased grain size (d), and increased dislocation velocity (v d ). Increasing temperature is also predicted with decreasing heat capacity (c*) and thermal diffusivity (α) as would be expected. The model was applied to low carbon steel for which considerable data are available. Application to low carbon steel gives a temperature increase of about 1400K. The implied result that untempered martensite should be observed after adiabatic shear banding is in agreement with examples cited in the literature. Further investigation into the dynamics of pile-up release and the associated heat transfer mechanisms is discussed.

High performance and cost effective multi-junction III-V solar cells are attractive for satellite applications. High performance multi-junction solar cells are based on a triple-junction design that employs an InGaP top-junction, a GaAs middle-junction, and a bottom-junction consisting of a 1.0 – 1.25 eV-material. The most attractive 1.0 – 1.25 eV-material is the lattice-matched dilute nitride such as InGaAsN(Sb). A record efficiency of 43.5% was achieved from multi-junction solar cells including dilute nitride materials [1]. In addition, cost effective manufacturing of III-V triple-junction solar cells can be achieved by employing full-wafer epitaxial lift-off (ELO) technology, which enables multiple substrate re-usages. We employed time-resolved photoluminescence (TR-PL) techniques to study carrier dynamics in both pre- and post-ELO processed GaAs double heterostructures (DHs) as well as in MOVPE-grown bulk dilute nitride layers lattice matched to GaAs substrates.

Three types of 316L stainless steel surface with different topography were prepared by a Fine Particle Peening (FPP) treatment using titania, silica and alumina shot particles and analyzed the cell proliferation and cell-scaffold interaction. FPP-treated surface with titania and silica particles had micro asperities at low frequency. On the other hand, the alumina treated surface had micro asperities at high frequency. L929 fibroblasts were seeded on these specimens and then the number of cells was counted after 72 hours of culturing. The FPP-treated surfaces showed good cell proliferation comparing to polished surface. This indicates that micro asperities formed on the surface encourage cell adhesion. Cell adhesion behavior was evaluated by a scanning electron microscope (SEM) and a fluorescence microscope. Dense filopodia were observed when cells cultured on the FPP-treated surface. This means that FPP treatment enhances cell adhesion and proliferation. The number of cells observed on the FPP-treated surface depended on the shape of asperities formed by FPP treatment; the highest cell counts were obtained on alumina treated surface. This is because cell migration was not inhibited by the shape of alumina treated surface asperities.

In this work we report the fractographic study of polymer matrix composites specimens reinforced with glass and carbon fibers. Specimens of a polyester matrix composite with 30% of E-glass fibers are prepared and fractured in flexure mode. We also test an epoxy matrix composite with 30% carbon fibers, which is fractured in flexure mode. All specimens are manufactured based on the D790 ASTM standard for bending mode at room temperature. As an exception, the composites with epoxy matrix and reinforced with carbon fiber are cured in an autoclave. The most commonly observed fracture mechanisms are debonding in the interphase, delamination, Chevron lines, microbuckling, river patterns and radial fracture on the fibers.

This work presents two multifunctional magnetic hybrid materials with potential applications as micro-actuators. The first one consists of iron oxide (Fe2O3) nanoparticles embedded in polyvinyl butyral (PVB). For the second one, Fe2O3 nanoparticles, coated with carboxymethyl cellulose (CMC), were embedded in PVB. The main objective is to describe their synthesis and morphological and magnetic characterizations, and to evaluate their displacement against a variable magnetic field. The maximal displacement is obtained by the (Fe2O3-CMC)/PVB beam-shaped structure (28.37 x 2.6 x 0.183 mm3) with 843 μm; the maximal electric power being 1.14 W. The levels of displacement induced in both hybrid materials as a response of the external magnetic field, besides the low electric power required, let us conclude that the studied materials could be considered as good candidates to micro-actuators applications.

We have previously reported, based on fluctuation electron microscopy (FEM) data, that Zr50Cu45Al5 bulk metallic glass (BMG) contains significant icosahedral and crystal-like medium-range order. Here, we report similar finding for Zr54Cu38Al8 BMG, which is a poorer glass former. Like Zr50Cu45Al5, Zr54Cu38Al8 contains icosahedral and crystal-like structures. In the as-cast state, the crystal-like peak in the FEM data is stronger than icosahedral-like peak. After annealing at 0.83T g (573 K), the icosahedral-like peak increases, but, unlike Zr50Cu45Al5, the crystal-like peak does not decrease. This tendency toward stronger, more thermally stable crystal-like order may be associated with the poorer glass forming ability of Zr54Cu38Al8.

ITO samples were sputtered at room temperature by ion assisted dual ion beam sputtering using atomic or molecular oxygen. The electrical properties appear to depend on the oxygen flow rate during deposition and the resistivity decreases for samples sputtered at a higher oxygen flow rate (1-5 sccm). The resistivity is lowest at an oxygen flow rate of 4 sccm. The average absorption in the visible part of the spectrum also decreases as a function of the oxygen flow rate and is lower for samples sputtered with atomic oxygen. The figure of merit, i.e. the ratio of the conductivity versus the average absorption in the visible range, increases for higher oxygen flow rates and is typically 20-60% higher for samples sputtered using an atomic oxygen assist beam.

One of the main problems encountered by curators and conservators in charge of metallic collections from Historical Heritage is related to their long-term conservation, since metallic artifacts undergo corrosion phenomena, which are the result of the interaction between the metal and its environment. The use of rust converters and microcrystalline waxes can be an ecological alternative to the traditional and more aggressive conservation techniques. Although the mechanism of action of these compounds is not clear, it is assumed that they react with iron oxides and generate new compounds that may have a passivation effect on the metallic surface. This paper proposes to show how simple electrochemical techniques can be used as an efficient tool to contribute to the diagnosis of the conservation state of cannon balls and to monitor the restoration treatment. The objective of the present work is to evaluate the effectiveness of a rust converter based on tannins and phosphoric acid, and one microcrystalline wax applied on cannon balls samples exposed to a marine atmosphere. The protection properties of the oxide or conversion layer are evaluated by electrochemical impedance spectroscopy (EIS) technique. The results obtained suggest that the use of the rust converter and microcrystalline wax protects the cannon balls, even though its effect is less evident when the deterioration degree is larger.

Nanoisland films have been grown via incongruent evaporation films. The basis of incongruent evaporation growth method was worked out. Samples surface morphology has been studied by atomic force microscopy. The surface density and characteristic dimensions of the islands have been shown.

Although 3C-SiC has a narrower bandgap than 4H-SiC, it is the only SiC polytype that can be grown directly over large area silicon substrates. It has the potential to provide a more economical choice than 4H-SiC for intermediate power devices, such as inverters for electric vehicles. To fabricate a vertical device on 3C-SiC, the Si substrate is usually removed either by etching or polishing. Neither of these processes is economical nor efficient. In this paper we propose a lateral Schottky diode design for 3C-SiC on Si structure. 2D finite element simulations using ATLAS showed that a breakdown voltage beyond 1200 V can be achieved with a 4 μm thick epilayer. Physical models used for 3C-SiC/Si power devices simulations are introduced. Advantages of lateral 3C-SiC/Si diodes over free standing 3C-SiC are also discussed.

Stress control using AlN/GaN superlattices (SLs) for epitaxy of GaN on 200 mm Si (111) substrates is reported. Crack-free 2 μm GaN layers were grown over structures containing 50 to 100 pairs of 3-5 nm AlN/10-30 nm GaN SLs. Compressive and tensile stress can be precisely adjusted by changing the thickness of the AlN and GaN layers in the SLs. For a constant period thickness, the effects of growth conditions, such as growth rate of GaN, V/III ratio during AlN growth, and growth temperature, on wafer stress were investigated.

This investigation is a comprehensive study of the effect of ammonium acetate on the electrical, optical, morphology and microstructure of CdS thin films grown by Chemical Bath Deposition method (CBD). Two sets of CdS thin films (A and B) were deposited on glass substrates at 60°C for 60 min. The films were deposited using chemical bath solution that consists of cadmium acetate, ammonium hydroxide, and thiourea. However, ammonium acetate was added into the chemical bath used to deposit set (B), where ammonium acetate was eliminated from bath solution used to deposit set (A). The films’ morphology was examined by Field Emission Scanning Electron Microscopy (FE-SEM), whereas, the chemical composition was investigated by Electron Probe Micro-Analyzer (EPMA). The X-Ray Diffraction (XRD) θ/2θ technique was applied to study the structure of the films. Atomic Force Microscopy (AFM) was used to measure the average surface roughness of the films, and Dektak Profilometer was used to determine the CdS films thickness. The optical and electrical properties for the films were determined using UV-Vis-NIR Spectrometer, and the Hall Effect technique, respectively. The highest carrier mobility was obtained for the films deposited in an ammonium acetate free bath. However, both films were polycrystalline with hexagonal structure exhibiting a tendency toward <002> texture, that increase with increasing the pH value of the chemical bath.

Charge generation and transport in CH3NH3PbI3-xClx based mesostructured solar cells are investigated. Time correlated single photon counting analysis proves highly efficient charge generation and provides insights on the structural properties of perovskite films. Photoinduced absorption and transient photovoltage analyses depict a double charge recombination dynamics suggesting the existence of two complementary paths for electron transport, involving either TiO2 and perovskite matrixes. Stark spectroscopy, a powerful tool allowing interface-sensitive analysis, is employed to prove the existence of oriented permanent dipoles, consistent with the hypothesis of an ordered perovskite layer close to the oxide surface. This evidence is also confirmed by first principle DFT calculations. The existence of a structural order, promoted by specific local interactions, could be one of the decisive reasons for highly efficient carriers transport within perovskite films.

An excellent candidate for an earth abundant absorber material is WSe2 which can be directly grown as a p-type semiconductor with a band gap near 1.4 eV. In this work we present the structural, optical, and electrical properties of thin film WSe2 grown via the selenization of sputter deposited tungsten films. We will show that highly textured films with an optical band gap in range of 1.4 eV, and absorption coefficients greater than 105/cm across the visible spectrum can be easily achieved. In addition we will present Hall Effect and carrier density measurements as well, where will show densities in the 1017cm-3 range and p-type Hall mobilities greater than 10 cm2/V-s range can be obtained. We employ these results to numerically simulate solar cells based on this material, where we will show efficiencies greater than 20% are possible.

Bacteriophytochromes (BphPs) are red-light photoreceptors found in photosynthetic and nonphotosynthetic bacteria that have been recently engineered as infrared fluorescent tissue markers. Light-induced, global structural changes are proposed to originate within their covalently bound biliverdin chromophore and propagate through the protein. Classical BphPs undergo reversible photoconversion between spectrally distinct light absorbing states, red (Pr) and far-red (Pfr), respectively. RpBph3 (P3), from Rhodopseudomonas palustris, photoconverts between a Pr and a unique near-red (Pnr) light-absorbing state. Due to size and photosensitivity of BphPs, structures of the intact proteins have not been resolved by nuclear magnetic resonance and/or X-ray crystallography. Therefore, structural details about the light and dark-adapted structures of the intact BphPs are not well understood at the molecular level. We have utilized fluid cell atomic force microscopy (AFM) to investigate the domain structure of intact P3 in its light-adapted state (Pnr). By varying the concentration of the protein, deposition time, and the ionic strength of the buffer, the aggregation of P3 on a mica surface can be controlled and single dimers may be observed in a biologically relevant media. Domain resolution has been achieved for several orientations of the dimer on the surface. The structural dimensions of the dimer have been compared to a modeled BphP in its intact form generated using PyMOL software. AFM experiments are currently underway to analyze the dark-adapted state (Pr) of P3 in order to observe the anticipated structural changes. Ultimately, the goal is to use AFM and other surface analytical methods such as scanning tunneling microscopy and electron microscopy to gain new insight into the unique photochemistry of P3.

The electromigration lifetimes of a very large quantity of passivated electroplated Au interconnects were measured utilizing high-resolution in-situ resistance monitoring equipment. Application of moderate accelerated stress conditions with current density limited to 2 MA/cm2 and oven temperatures in the range of 300°C to 375°C prevented large Joule-heated temperature gradients and electrical overstress failures. A Joule-heated Au film temperature increase of 10°C on average was determined from measured temperature coefficients of resistance (TCRs). A failure criterion of 50% resistance degradation was selected to avoid thermal runaway and catastrophic open circuit failures. All Au lifetime distributions followed log-normal statistics. An activation energy of 0.80 ± 0.05 eV was measured from constant-current electromigration tests at multiple temperatures. A current density exponent of 1.91 ± 0.03 was extracted from multiple current densities at a single constant temperature.

Millions of medical implants and devices (e.g., screws, plates, and pins) are used each year worldwide in surgery, and traditionally the components have been limited to permanent metals (e.g., stainless steel, titanium alloys) and polyester-based absorbable polymers. Because of clinical problems associated with these traditional materials, a novel class of biodegradable metallic materials, i.e., magnesium-based alloys, attracted great attention and clinical interests. Magnesium (Mg) is particularly attractive for load-bearing orthopedic applications because it has comparable modulus and strength to cortical bone. Controlling the interface of Mg with the biological environment, however, is the key challenge that currently limits this biodegradable metal for broad applications in medical devices and implants. This paper will particularly focus on creating nanostructured interface between the biodegradable metallic implant and surrounding tissue for the dual purposes of (1) mediating the degradation of the metallic implants and (2) simultaneously enhancing bone tissue regeneration and integration. Nanophase hydroxyapatite (nHA) is an excellent candidate as a coating material due to its osteoconductivity that has been widely reported. Applying nHA coatings or nHA containing composite coatings on Mg alloys is therefore promising in serving the needed dual functions. The composite of nHA and poly(lactic-co-glycolic acid) (PLGA) as a dual functional interface provides additional benefits for medical implant applications. Specifically, the polymer phase promotes interfacial adhesion between the nHA and Mg, and the degradation products of PLGA and Mg neutralize each other. Our results indicate that nHA and nHA/PLGA coatings slow down Mg degradation rate and enhance adhesion of bone marrow stromal cells, thus promising as the next-generation multifunctional implant materials. Further optimization of the coatings and their interfacial properties are still needed to bring them into clinical applications.