The transformation of benzoin to tetraphenylfuran catalyzed with a superacid sulfonic clay under different reaction conditions was investigated. Three products with different yields were produced under a nitrogen stream and four products were obtained under an air atmosphere.

Carbon nanotubes (CNTs) synthesized by a chemical vapor deposition (CVD) method and the 2024 aluminum alloy (Al2024) are used in the production of Al2024-CNTs composites. An homogeneous dispersion of the CNTs into the aluminum matrix is achieved by a mechanical milling processing. CNTs keet their morphology after milling and sintering processes. Formation of aluminum carbide as a function of CNTs contents is observed. Formation of equilibrium phases during sintering is observed by electron microscopy. CNTs and aluminum carbide in the composites are characterized by transmission electron microscopy. Hardness results of sintered products show an increment of up to 285% over the unreinforced alloy prepared by the same route.

The performance of the thermoelectric materials and devices is shown by a dimensionless figure of merit, ZT = S2σT/K, where S is the Seebeck coefficient, σ is the electrical conductivity, T is the absolute temperature and K is the thermal conductivity. ZT can be increased by increasing S, increasing σ, or decreasing K. We have prepared 100 alternating multi-nano layer of SiO2/SiO2+Cu superlattice films using the ion beam assisted deposition (IBAD). The 5 MeV Si ions bombardments have been performed at the different fluences using the AAMU Pelletron ion beam accelerator to make quantum clusters in the multi-layer superlattice thin films to decrease the cross plane thermal conductivity increase the cross plane Seebeck coefficient and cross plane electrical conductivity. To characterize the thermoelectric thin films before and after Si ion bombardments we have measured the cross-plane Seebeck coefficient, the cross-plane electrical conductivity, and the cross-plane thermal conductivity for different fluences.

No compositional variations of periodically poled lithium niobate (PPLN) (period of ~28 μm) are found using spatially resolved near edge X-ray adsorption fine structure (XANES) spectra taken at the Nb K-edge. The periodicity the ferroelectric domain patterns can be imaged using piezoresponse force microscopy (PFM) and atomic force microscopy (AFM) and the periodic variations in the optical properties of PPLN result in a nonlinear optical response in the IR region at a fixed scattering angle.

Localized Surface Plasmon Resonances (LSPR) in rod-shaped Gold (Au) nanoparticles patterned with Electron Beam Lithography (EBL) technique are observed via reflectance measurements. Resonance peaks corresponding to the principal axes of the nano-rods are shown to be affected by each other. Excitation of one of the peaks is found to result in a decrease in the peak intensity of the resonance through the other axis. Arrays of Au nanoparticles with constant width and thickness but increasing length are examined for further understanding of the effect. As the particle length increased from 70 nm to 300 nm, resonance peak wavelength shifted from 650 nm to 1200 nm. Total reflectance intensities of samples with varying principal axis dimensions obtained through the spectral region of interest are also examined to see the relation between contributing electrons and total amount of reflected intensity. Results corresponding to both polarized and unpolarized illumination of samples are presented together to gain better understanding of lowered reflectance peak intensities obtained from the latter case. Based on the results obtained so far, nano-sized metal rods are promising tools for optically switched intensity modulation in the visible and near-IR region.

Surface plasmon resonance (SPR) biosensors are widely used in sensitive chemical, biological and environmental sensing. Recently, the studies of nano-plasmonics in metallic structures have shown that surface plasmons can also be excited by the metallic nanostructures films which can be used for high-throughput and chip-based SPR type sensing. We developed a class of plasmonic crystal-like structures consisting of a film with arrays of periodic nanoslit geometry. Because the engineered array ensures multiple resonance modes, we use the multispectral analysis to evaluate the refractive index sensing capability. Different from the common method monitoring a single peak shift, the multispectral analysis, observing all the peak shifts and intensity changes in the multiple plasmonic resonances in the spectra, can improve the signal-to-noise ratio of the system and enhance the sensing capabilities. In this investigation, we studied the best condition for the gold nanoslit arrays by testing their ability for refractive index sensing, and a high sensitivity of up to 28586 %T nm/RIU was obtained by multispectral analysis (RIU = refreactive index unit, and T= transmission).

High energy density and power density are two important considerations in the design of a portable power source. High efficiency of energy conversion is one of the important factors in achieving high energy density. We report on the design, fabrication and characterization of a high efficiency and power density thermoelectric generator. Segmented thermoelectric elements with a high temperature-weighted average zT are used in the fabrication of the generator to achieve high energy conversion efficiency. A comprehensive model of the generator has been developed that includes temperature dependent thermoelectric properties for the segmented thermoelectric element design, and system level thermal and electrical losses. These models are used to guide the design of a high efficiency thermoelectric generator. A 14W size portable thermoelectric generator was built and its performance for converting thermal energy into electrical energy was characterized and compared to the model predictions. The magnitude of individual loss mechanisms and their effect on overall system efficiency are presented. The evolution of the device design and critical design parameters that have been incorporated or modified to minimize performance losses and improved device robustness are discussed. Important future design optimizations that can further reduce losses for improved performance were identified.

This paper discusses the accuracy of the distribution of the fatigue lifetime of polysilicon thin films predicted from their strength distribution. On the basis of the authors' previous studies, where the fatigue process determining the lifetime was formulated using the well-known fatigue crack extension Paris' law, prediction error ranges for polysilicon specimens with different levels of strength are determined. The errors of the predicted fatigue lifetime in the logarithmic scale, defined as △logN = |log10 N exp-log10 N pred| where N exp and N pred were the experimental and predicted number of cycle, were found to be less than 1 in the range of the cumulative fracture probability F between 0.1 and 0.9. Therefore, based on the measured Paris' law parameters of polysilicon, the fatigue lifetimes of different polysilicon thin film structures can be predicted from their strength distributions with errors of roughly 10% in the logarithmic scale, which was average of percentages of △logN to log10 N of experimental data.

Composite particles destined to build plasma sprayed coatings, are prepared by the mechanofusion process (MF). These particles consist of a stainless steel core particle coated by finer particles of alumina. Changes induced by the MF process are monitored by SEM, DRX, and laser granulometry, revealing that the dry particle coating process is governed by agglomeration and rolling phenomena. Simultaneously, the MF performance is controlled by the operating parameters such as the compression gap, the mass ratio of host to guest particle, and the powder input rate. The mechanical energy input leads to a nearly rounded shape of the final composite particles; however, no formation of new phases or components decomposition is detected by XRD analysis. The resulting composite powder features optimal characteristics, concerning particle shape and phases distribution, to be plasma sprayed in air.

We report dye-degradation effects of a semiconductor LiBiO3 revealed under illumination of a conventionally used white fluorescent light. Optical absorbance spectra of LiBiO3 were broadened so smoothly, with the absorption edge penetrated to around 730 nm, that the material was able to absorb a wide range of visible light. Results showed that solution of a standard dye, methylene blue, was degraded completely after 4 h illumination. Furthermore, the value of total organic carbon decreased 70% in the decolorized solution, suggesting that the molecular form of the original methylene blue was mineralized effectively to nonorganic fragments by the photoinduced oxidization effect. Moreover, the wavelength dependence of apparent photonic efficiency was evaluated using a standard Xe lamp coupled with monochromatic filters. These results were interpreted from the viewpoint of this material’s electronic structure.

This paper reviews our research progresses of hydrogenated amorphous silicon (a-Si:H) and microcrystalline (μc-Si:H) based thin film solar cells. It coves the three areas of high efficiency, low cost process, and large-area proto-type multi-chamber system design and solar module deposition. With an innovative VHF power profiling technique, we have effectively controlled the crystalline evolution and made uniform μc-Si:H materials along the growth direction, which was used as the intrinsic layers of pin solar cells. We attained a 9.36% efficiency with a μc-Si:H single-junction cell structure. We have successfully resolved the cross-contamination issue in a single-chamber system and demonstrated the feasibility of using single-chamber process for manufacturing. We designed and built a large-area multi-chamber VHF system, which is used for depositing a-Si:H/μc-Si:H micromorph tandem modules on 0.79-m2 glass substrates. Preliminary module efficiency has exceeded 8%.

We study the acousto-optic effect on the polaritonic properties of DNA nanofibers which are fabricated by embedding a DNA wire into a polaritonic material. This is a new research area and can be called nanobiopolaritonics. Polaritonic materials have energy gaps in their dispersion relation due to the coupling between optical photons and photons. The bound states of DNA wire are calculated using transfer matrix method. It is found that some of the bound states of the DNA wire lie within the band gap of the polaritonic material. These states do not decay into the polaritonic material since there are not states available for decay process to occur. This means DNA nanofibers has an extremely high Q factor. We have also studied the acousto-optic effect on the photon absorption in DNA nanofibers doped with ensemble of quantum dots. The quantum dots interact with the DNA wire via electron bound polaritons interaction. We have discovered a switching mechanism in DNA nanofibers. When the resonance energy of the quantum dots lies near bound polaritons states, the system becomes transmitting for frequency of a probe field due to the strong electron bound polaritons interaction. This is can be assigned as ‘ON’ of the switch. However, when the strain field is applied the DNA fiber can now absorb the probe beam. This is can be assigned as ‘OFF’ of the switch.

We investigate the effect of hydrogenation of grain boundaries on the performance of solar cells for hydrogenated nanocrystalline silicon (nc-Si:H) thin films. Using hydrogen effusion, we found that the amplitude of the lower temperature peak in the H-effusion spectra is strongly correlated to the open-circuit voltage in solar cells. This is attributed to the hydrogenation of grain boundaries in the nc-Si:H films.

The purpose of this paper was to describe a method of preparing Fe-TiO2 supported on sepiolite fibers with sol-gel method and to discuss the feasibility of photocatalytic degradation of paper-making waste water with chemical oxygen depletion (CODcr) (Potassium dichromate method) as evaluation criterion of catalytic activity. As-fabricated catalysts consisted of TiO2 particles impregnated with iron and dispersed on the sepiolite fibers (S.F.s). The novel Fe-TiO2-sepiolite was characterized by specific surface area and pore size distribution measurements, scanning electron microscope (SEM), high resolution transmission electron microscope (HRTEM), X-ray diffraction (XRD) and Fourier transform Infrared spectrometer (FT-IR) etc. The effects of parameters such as the amount of Ti/sepiolite fibers, initial pH, H2O2, Fe-doped, concentration of waste water, etc. were studied in detail. The results indicated that the presence of sepiolite in the support preparation and its role as a matrix over which TiO2 particles were dispersed seem to play an important effect in the migration process of oxygen species through the support vacancies. On the basis of these properties, the most promising carriers to be used in a waste water treatment process were selected.

Given the limitations of the materials available for photoelectrochemical water splitting, a multiphoton (tandem) approach is required to convert solar energy into hydrogen efficiently and durably. Here we investigate a promising system consisting of a hematite photoanode in combination with dye-sensitized solar cells with newly developed organic dyes, such as the squaraine dye, which permit new configurations of this tandem system. Three configurations were investigated: two side-by-side dye cells behind a semitransparent hematite photoanode, two semitransparent dye sensitized solar cells (DSCs) in front of the hematite, and a trilevel hematite/DSC/DSC architecture. Based on the current-voltage curves of state-of-the-art devices made in our laboratories, we found the trilevel tandem architecture (hematite/SQ1 dye/N749 dye) produces the highest operating current density and thus the highest expected solar-to-hydrogen efficiency (1.36% compared with 1.16% with the standard back DSC case and 0.76% for the front DSC case). Further investigation into the wavelength-dependent quantum efficiency of each component revealed that in each case photons lost as a result of scattering and reflection reduce the performance from the expected 3.3% based on the nanostructured hematite photoanodes. We further suggest avenues for the improvement of each configuration from both the DSC and the photoanode parts.

We have employed anodic oxidation of Ti foils to prepare self-organized TiO2 nanotube arrays which show enhanced electrochemical properties for applications as Li-ion battery electrode materials. The lengths and pore diameters of TiO2 nanotubes can be finely tuned by varying voltage, electrolyte composition, or anodization time. The as-prepared nanotubes are amorphous and can be converted into anatase nanotubes with heat treatment at 480oC and nanotubes of mixed anatase/rutile phases by heating at 580oC. The morphological features of nanotubes remain unchanged after annealing. Amorphous nanotubes with a length of 3.0 μm and an outer diameter of 125 nm delivers a capacity of 91.2 μA h cm-2 at a current density of 400 μA cm-2, while those with a length of 25 μm and an outer diameter of 158 nm display a capacity of 533 μA h cm-2. The 3-μm long anatase nanotubes and nanotubes of mixed phases show lower capacities of 53.8 μA h cm-2 and 63.1 μA h cm-2, respectively at the same current density. The amorphous TiO2 nanotubes with a length of 1.9 μm exhibit a capacity five times higher than that of TiO2 compact layer even when the nanotube array is cycled at a current density 80 times higher than that for the compact layer. The amorphous nanotubes show excellent capacity retention ability over 50 cycles. Cycled nanotubes show little change in morphology compared to the nanotubes before cycling, indicating the high structural stability of TiO2 nanotubes.

In this paper, we briefly report our recent work on multiscale modeling and simulations of soft elasticity and focal adhesion of stem cells. In particular, our work is focused on modeling and simulation of contact and adhesion of stem cells on substrates with different rigidities. In order to understand the precise mechanical influences on cell contact/adhesion and to explain the possible mechanotransduction mechanism, we have developed a three-dimensional soft-matter cell model that uses liquid-crystal gel or liquid-crystal elastomer gel to model the overall constitutive relations of the cell, and we have simulated the responses of the cell to extra-cellular stimulus. The discussion here is specifically focused on the following issues: (1) how to model the overall myosin responses at the early stage of differentiation process of the stem cell, (2) the effects of both the adhesive force due to ligand-receptor interaction or focal adhesion and the surface tension, and (3) possible cell conformation and configuration changes triggered by substrate's rigidity.

Ensembles of indium phosphide nanowires were grown on amorphous quartz substrates and their optical properties were examined at various cryogenic temperatures. Complex dynamics result from the large areal densities, random orientation, combination of both zincblende and wurtzite phases, and the geometries of the nanowires. Those complex dynamics are discussed in relation to their effect on the temperature dependence of photoluminescence and Raman spectroscopy. Five peaks are found to exist in the photoluminescence spectra at low temperatures which are attributed to radiative recombinations associated with quantum confined zinc blende, quantum confined excitons in zinc blende, quantum confined wurtzite, excitons in bulk zinc blende and impurity states. An energy transfer mechanism between two types of radiative recombinations among the five is proposed to explain intensity variations and the temperature dependence of the PL peaks is discussed. The Raman spectra is observed to have peaks created by a combination of zinc blende and wurtzite vibrational modes which is explained by folding the phonon dispersion.

By virtue of their unique electronic properties, nanometer-diameter sized single-walled carbon nanotubes represent ideal candidates to function as active parts of nanoelectronic memory storage devices. We show for the first time that GeTe, a phase change material, currently considered to be one of the most promising materials for data-storage applications, can efficiently be encapsulated within single-walled carbon nanontubes of 1.4 nm diameter. Structural investigations on the encapsulated GeTe nanowires have been carried out by high resolution transmission electron microscopy. The electronic interactions between the filling material and the host nanotube have been examined using ultraviolet photoelectron spectroscopy experiments and show that the electronic structure of the encapsulating nanotube and that of the encased filling are not perturbed by the presence of each of the other component.

The newly formed hybrids offer potential to operate as active elements in non-volatile electronic memory storage devices.

Metamorphic triple-junction solar cells can currently attain efficiencies as high as 41.1%. Using additional junctions could lead to efficiencies above 50%, but require the development of a wide bandgap (2.0-2.2eV) material to act as the top layer. In this work we demonstrate wide bandgap InyGa1-yP grown on GaAsxP1-x via solid source molecular beam epitaxy. Unoptimized tensile GaAsxP1-x buffers grown on GaAs exhibit asymmetric strain relaxation, along with formation of faceted trenches 100-300 nm deep in the [01-1] direction. Smaller grading step size and higher substrate temperatures minimizes the facet trench density and results in symmetric strain relaxation. In comparison, compressively-strained graded GaAsxP1-x buffers on GaP show nearly-complete strain relaxation of the top layers and no evidence of trenches. We subsequently grew InyGa1-yP layers on the GaAsxP1-x buffers. Photoluminescence and transmission electron microscopy measurements show no indication of phase separation or CuPt ordering. Taken in combination with the low threading dislocation densities obtained, MBE-grown InyGa1-yP layers are promising candidates for future use as the top junction of a multi-junction solar cell.