Poly(N-isopropylacrylamide) (PNIPAM) is a thermo-sensitive polymer that exhibits a lower critical solution temperature (LCST) around 305 K. Below the LCST, PNIPAM is soluble in water and above this temperature polymer chains collapse prior to aggregation. In the presence of methanol, electron paramagnetic resonance (EPR) spectroscopy suggests that, LCST of PNIPAM is depressed up to certain mole fraction of methanol (0.35 mole fraction) and it is speculated that addition of methanol affects the PNIPAM-water interactions. Above 0.35 mole fraction of methanol, LCST gets elevated to temperatures above ∼305 K (32°C) and cannot be detected up to 373 K (100 °C). The atomistic origin of this co-solvency effect on the LCST behavior is not completely understood. In the present study, we have used molecular dynamics (MD) simulations to investigate the effect of methanol-water mixtures on conformational transitions and the LCST of PNIPAM. We employ two different force fields i.e. polymer consistent force-field (PCFF) and CHARMM to study solvation dynamics and the PNIPAM LCST phase transition in various methanol-water mixture compositions (0.018, 0.09, 0.27, 0.5, and 0.98 mole fractions). Simulations are conducted at fully atomistic level for three different temperatures (260, 278, and 310 K) and radius of gyration (Rg) of PNIPAM chains was computed for determination of LCST behavior of PNIPAM.

The use of nano-sized silver and its alloys represents an interesting alternative to common food preservation methods, which are based on radiation, heat treatment and low temperature storage. These metal nanoparticles, embedded within a polymeric matrix for instance, would extend the shelf life of perishable foods while acting as a bactericidal agent to prevent food-borne illnesses. Common methods used in the synthesis of metal nanoparticles require toxic solvents and reagents that could be harmful to health and the food itself. In addition, several steps are required to obtain aqueous stable, i.e. dispersible, silver nanoparticles. In this work we propose the microwave-assisted aqueous synthesis of silver-based nanoparticles, (Ag Based NP) functionalized by glutathione (GSH) in a single-step using sodium sulfite (Na2SO3), as reducing agent. Ag-Based nanoparticles were synthesized at pH 6 and 1:3:1 (AgNO3/GSH/ Na2SO3) molar ratio. UV-Vis measurement clearly showed the plasmon peak attributed to silver-based nanoparticles (374 nm). Highly monodispersed water stable Ag-based nanoparticles were observed and 3.897 ± 0.167 nm particle size was determined through Transmission Electron Microscopy. FT-IR measurements suggested the actual GSH-Ag based surface interaction through –SH and –COOH groups; the functionalization by GSH explained the high stability of the nanoparticles in aqueous suspensions. These Ag-GSH nanoparticles exhibited remarkable antimicrobial activity against E. Coli.

We have electrically characterized a 300 nm-thick unintentionally-doped In0.09Ga0.91N film grown by metal-organic chemical vapor deposition on a GaN template, employing capacitance-voltage (C-V), thermal admittance spectroscopy (TAS), and steady-state photocapacitance spectroscopy (SSPC) techniques on Schottky barrier diodes. TAS measurements revealed a degenerating-like shallow-donor defect with a thermal activation energy of ∼7 meV, which most likely acts as a source of residual carriers with their concentration of ∼1017 cm-3 determined from C-V measurements. Additionally, SSPC measurements revealed two characteristic deep-level defects located at ∼2.07 and ∼3.05 eV below the conduction band, which were densely enhanced near the underlayer. These electronic defects are probably introduced by alloying InN with GaN.

We have fabricated by pulse laser deposition very thin (∼5-7 nm) and thick (∼27-408 nm) films of composition Fe66B24Nb4Ni6 on silicon and quartz substrates respectively, and studied their magnetic and magneto-optic properties at room temperature. We find that the thicker films on silicon can be tuned by appropriate thermal annealing to exploit soft magnetic characteristics with low HC, and high MS values. The magnetic hysteretic loops of the as-deposited thicker films on silicon substrates show two interesting characteristics: 1) increase in the coercivity with the film thickness and 2) the onset of a two stage process during the approach to magnetic saturation. The initial in-plane characteristic of the hysteresis loop is followed by a linear anisotropic behavior between remanence and saturation- that changes into square soft-magnetic loops on decreasing the film thickness. By suitable annealing the intrinsic strain disappears at relatively low temperatures (≤200 oC); the thicker films can be tailored to exhibit a simple soft-magnetic square loop with low HC. The ∼5-7 nm films deposited on glass are transparent and have been investigated for their magneto-optic properties using Faraday rotation (FR) measurement technique. Very high values of FR in the range 4-20 deg/µm almost linearly dependent on the wavelength of light in the range 405-611 nm are observed. The observed high values of Faraday rotation over a wide range of wavelength of light are useful for the applications as magneto-optic sensors in the UV to visible range.

Continuous fiber reinforced composites (RFC) are hierarchal and complex at multiple scales. In this work, tools are developed to automate the 3D characterization and quantification of the overall microstructure. Structure quantification enables accurate representation for material simulation and property prediction for the integrated computation materials engineering (ICME) of RFC based components. Relationships are developed to describe the key attributes of the microstructure at multiple scales including the individual fibers, tows, weave, porosity, and secondary matrix phases, which are treated as 'gestalts' of the structure. Here gestalt refers to the essence of shape or complete form of key features of the microstructure such as those of the tow architecture of the textile. Visualization tools are developed based on an artificial color scheme that allow the visual recognition of whole tows instead of just the collection of simple lines and curves representative of the fibers, which provides means whereby the gestalt of the microstructure can be visualized at the tow scale. These tools are demonstrated using a 3D dataset of the SiNC/SiC S200 ceramic matrix composite material (CMC) obtained via automated serial sectioning. Methods are then demonstrated to generate microstructure models representative of the characterized material for finite element analyses (FEA).

Ordered arrays of polymeric nanostructures with different shapes were generated using laser interference lithography and plasma etching. Surface energy anisotropy was produced in each nanostructure in the array through oblique angle deposition of a hydrophilic metal. When a water droplet was placed on such a surface, it was found to wet preferentially in the direction of the hydrophilic face. Depending on the shape of the nanostructure and the deposition direction, wetting can be made uni-, bi- or tri-directional. Insights obtained in this study contribute to the understanding of wetting on rough, chemically heterogeneous surfaces and provide new methods to engineer functional surfaces for the control of wetting directions.

The warm white light emission from the MOS capacitor containing the Zr-doped HfO2 high-k thin film on a p-type Si wafer under various post deposition annealing temperatures has been investigated. The light intensity is affected by the annealing temperature and the magnitude of the stress voltage. The annealing temperature changes the defect density and the physical thickness of the high-k stack. The high stress voltage induces the strong light emission because of the passage of a large current through the conductive path. The broad band emission spectrum covers the visible and near IR wavelength range with a large color rendering index. This new light emission device has a very long lifetime of > 1,000 hours at the atmosphere without a protection layer. The device is made of the IC compatible material and fabrication process, which favors the application over a wide range of products.

We report on the development of a plasmonic-photonic coupled platform based on a plasmonic periodic nanostructure and a host matrix for active media in the visible-near infrared range, constituted by a thin film of sol-gel glass. Here, we report on preliminary results about two main tasks of the research work. On one side, we have studied and optimized the surface that supports plasmonic resonances with tunable wavelengths. On the other side, we focused on improving the sol-gel techniques to form and deposit thin films appropriate for covering the previous surface as well as to protect it (i.e. for sensing applications), embed suitable fluorophores (for active device applications) while avoiding metal-induced radiative emission quenching. Besides structural and optical characterization of the considered structures and films, finite-difference time-domain numerical simulations have been performed, in order to give a feedback on the structure features and thereby interpret its optical response.

A radio-frequency magnetron sputtering technique and subsequent rapid thermal annealing (RTA) at 600, 700, 800, and 900 °C were implemented to grow high-quality Ga-doped MgxZn1-xO (GMZO) epi-layers. The GMZO films were deposited using a radio-frequency magnetron sputtering system and a 4 inch ZnO/MgO/Ga2O3 (75/20/5 wt %) target. The Hall results, X-ray diffraction (XRD), and transmittance were determined and are reported in this paper. The Hall results indicated that the increase in mobility was likely caused by the improved crystallization in the GMZO films after thermal annealing. The XRD results revealed that MgxZn1-xO (111) and MgO2 (200) peaks were obtained in the GMZO films. The absorption edges of the as-grown and annealed GMZO films shifted toward the short wavelength of 373 nm at a transmittance of 90%. According to these results, GMZO films are feasible for forming transparent contact layers for near-ultraviolet light-emitting diodes.

We have been studying a number of nanosystems that either have potential applications in bioimaging and/or light-activated therapies, or are bioderived. The standard Z-scan technique was routinely used for most of the measurements which were carried out in a wide wavelength range, typically from ∼550 nm to 1.6 μm. The range of nanoparticles studied has included colloidal semiconductor nanoparticles (e.g. CdS, CdSe), plasmonic nanoparticles, metal clusters, lanthanide-doped fluoride and oxide nanocrystals as well as core-shell systems. Among the bioderived systems studied especially interesting one is that of protein amyloid fibers.

Many of these materials exhibit nonlinear absorption features due not only to the typical two-photon absorption processes, but also due to multiple-photon absorption taking place, especially at longer wavelengths (e.g. three- four- and five-photon processes). On the other hand, absorption saturation processes may prevail or compete with multi-photon absorption in certain wavelength ranges in some of these materials, especially those characterized by broadband absorption due to surface plasmon excitation.

Electrical conductions in insulators such as resistance switching, conduction at interfaces, and conduction at domain boundaries and free surface of ferroelectrics are of interest. These conductions are often attributed to novel mechanism such as ferroelectric polarization. On the other hand, these interpretations appear not fully accepted, because the recent advanced theories of ferroelectric domains disregard screening indicated by these conduction phenomena. That is, these conduction phenomena are quietly regarded as the classical conduction originating from defects. In this paper, we examine these conductions in pure wide bandgap insulators in view of defects, using the direct-accessibility (tangibility) of conduction at free surfaces. Although most of these conductions in ferroelectrics may not be useful in large-scale applications, we show that they have fundamental implications on renovations of ferroelectric basics.

In this paper, we discuss several strategies to tailor magnetic properties related to the magnetic anisotropy energy, such as the blocking temperature or the low temperature coercivity, of magnetic nanoparticles or materials made with magnetic nanoparticles. We describe a first approach that consists in synthesizing and dispersing bi and tri-magnetic core-shell nanoparticles that include a core made of a material with a weak anisotropy energy density and a shell made with a material with a large anisotropy energy density. This approach is a promising route to tune the blocking temperature of low temperature coercivity of a particle without altering its magnetization and with a good control of its size. Additionally, we also explore another route for the control of the shape of the hysteresis loop of material made with magnetic nanoparticles that consists in the simple mixture of magnetically soft and hard magnetic nanoparticles to create binary mixtures. In this case, it is the mixing ratio that allows one to adjust the properties of the final material.

This paper discusses formation mechanisms and potential paths to reduce defect density in current SiC epitaxy technology. Comprehensive optimization efforts have resulted in defect density measured by laser light scattering below 0.5 cm-2 for 30 um thick epi wafers. Possible approaches to reduce basal plane dislocations and mitigate interfacial dislocations are discussed. The progress in epitaxy defect reduction has been made on the foundation of the high quality 100mm substrates. The average and median BPD density is 700 cm-2 and 500 cm-2, respectively, and a low TSD density is also achieved simultaneously with both average and median values around 350 cm-2. High quality and low stress 150mm substrates have been obtained with very low TSD density of <150 cm-2.

Cu2ZnSnSe4 films were deposited on soda lime glass substrates at room temperature by one-step radio frequency magnetron-sputtering process. The effect of sputtering power on the properties of one-step deposited Cu2ZnSnSe4 thin films has been investigated. The deposited films might be suitable for the absorber layers in the solar cells. The chemical composition and the preferred orientation of the films can be optimized by the sputtering power.

Hybrid halide perovskites represent one of the most promising solutions toward the fabrication of all solid nanostructured solar cells with improved efficiency and long-term stability. This article aims at investigating the structural properties of the iodide/chloride mixed-halide perovskites and correlating them with the photovoltaic performances of the related sensitized solar cells. We found out that, independently on the components ratio in the precursor solution, Cl incorporation, in a I-based structure, is possible only at relatively low concentration levels (below 3-4%). However, even if the material band-gap remains substantially unchanged, incorporation of Cl as a dopant dramatically improves the charge transport within the perovskite layer, explaining the outstanding performances of meso-superstructured solar cells based on this material.

The heterojunctions formed between solution phase grown Cu2ZnSn(SxSe1- x)4 (CZTS,Se) and a number of important buffer materials including CdS, ZnS, ZnO, and In2S3, were studied using femtosecond ultraviolet photoemission spectroscopy (fs-UPS) and photovoltage spectroscopy. With this approach we extract the magnitude and direction of the CZTS,Se band bending, locate the Fermi level within the band gaps of absorber and buffer and measure the absorber/buffer band offsets under flatband conditions. We will also discuss two-color pump/probe experiments in which the band bending in the buffer layer can be independently determined. Finally, studies of the bare CZTS,Se surface will be discussed including our observation of mid-gap Fermi level pinning and its relation to Voc limitations and bulk defects.