In the development of novel materials for enhanced photovoltaic (PV) performance, it is critical to have quantitative knowledge of the initial performance, as well as the performance of these materials over the required 25-year lifetime of the PV system. Lifetime and degradation science (L&DS) allows for the development of new metrology and metrics, coupled to degradation mechanisms and rates. Induced absorbance to dose (IAD), a new metric being developed for solar radiation durability studies of solar and environmentally exposed photovoltaic materials, is defined as the rate of photodarkening or photobleaching of a material as a function of total absorbed solar radiation dose. In a reliability engineering framework, these quantitative degradation rates can be determined at various solar irradiances making possible real time and accelerated testing. The potential to predict power losses in a photovoltaic system over time caused by the accumulation of this kind of degradation can be calculated for real time applications or extrapolated for accelerated exposure conditions. Three formulations of poly (methyl methacrylate) (PMMA) used for mirror augmented PV systems were analyzed for the changes in IAD after accelerated testing.

Three-dimensional (3-D) optical modeling based on Finite Element Method of single, double, and triple junction thin-film silicon solar cells is presented. The combination of front periodic gratings with optimal geometrical parameters and rear ZnO/Ag reflector constitutes an efficient light trapping scheme for solar cells in superstrate (pin) configuration. The application of optimized trapezoidal 1-D and 2-D gratings resulted in 25.5% (1-D case) and 32.5% (2-D case) increase in photo-current density with respect to the flat solar cell. The application of inverted pyramidal 2-D gratings in double and triple junction silicon solar cells with very thin absorber layers resulted in a photo-current density > 11 mA/cm2 and > 9 mA/cm2, respectively.

This article applies a recently discovered gas phase nanocluster electrodeposition process to the formation and combinatorial improvement of 3D bulk heterojunction photovoltaic cells. The gas phase deposition process used here is a single reactor system that forms charged nanoclusters (gold, silver, tungsten, and platinum) at atmospheric pressure. The clusters deposit onto selected surface areas with sub 100 nm lateral resolution using a programmable concept similar to liquid phase electrodeposition such that biased electrodes turn ON or OFF deposition in selected areas. Continued deposition of the nanoparticles results in a tower array with different lengths and density on a single substrate which is used as contacts to the active organic layer of 3D bulk heterojunction photovoltaic cells. Applying a combinatorial approach identifies in a massively parallel way electrode designs and topologies that improve light scattering, absorption, and minority carrier extraction. We report photovoltaic cells with higher and denser nanocluster tower arrays that improve the power conversion efficiency of bulk heterojunction photovoltaic cells by approximately 47.7%.

Spinel cobalt ferrite nanotubes and nanowires of about five micrometers in length were fabricated using anodic aluminum oxide (AAO) templates of 20 – 200 nm pore diameters and sol-gel processing. A cobalt ferrite sol was prepared by mixing the acetic acid solution of cobalt (II) acetate and ethanol solution of iron (III) acetylacetonate. The templates filled with precursor were obtained after they were dipped into the sol and dried in air. The template/precursor composites were sintered in air at 500 ºC to form cobalt ferrite phase, which was verified by XRD. The morphology of the nanostructures determined by SEM revealed that the cobalt ferrite nanotubes were formed in the channels of 100 nm and 200 nm diameters in the templates, whereas the nanowires were formed in the 20 nm channels of the templates. The magnetic measurement of cobalt ferrite nanowires by a SQUID magnetometer showed that the nanowires are superparamagnetic at room temperature. The room temperature measurement of magnetization versus the applied field on the nanowire arrays in 20 nm channels of templates showed that the coercivity is 1.57 kOe and 1.47 kOe for the nanowire axis parallel and perpendicular to the applied field, respectively, indicating that the nanowire arrays are nearly magnetically isotropic. However, the coercivity of cobalt ferrite nanowires fabricated in this work is much larger than those in the similar systems reported in the literatures.

This paper demonstrates that electrostatic spray deposition (ESD) method is a promising solution process to fabricate highly-crystalline organic films (6,13-bis(triisopropylsilylethynyl) pentacene; TIPS pentacene) for the use in bottom-contact organic field-effect transistors (OFETs). We obtained large crystalline domains (i.e., molecularly-oriented domains) by using an o-DCB:acetone mixed solvent (1:1), and observed good transistor behavior in an OFET having the channel length of 20 μm.

Porous Si/hydrogel thin films combine a porous Si optical nanostructure and a functional hydrogel. These hybrids show great promise as versatile platforms for the fabrication of miniaturized sensors with various transduction mechanisms, cell culture supports, autonomous drug delivery systems, and many other functional systems. The basic considerations in designing functional PSi/hydrogel hybrids, synthesis routes, and novel characterization methods are discussed. New exciting applications of these nanomaterials as label-free optical biosensing platforms for bacteria and organophosphates detection are described.

This paper deals with several concrete properties and to what extent they are influenced by slag and limestone filler, either one or both of them are included. Concrete was designed for low paste content, this is, a water reducing admixture (WR) was used to limit mixing water content. The results are compared with concrete made with commercial composite cement, blended during milling. Concrete was tested for compressive strength, sorptivity, resistivity, and water penetration under pressure. The volume of paste in all concrete mixes was the same.

Results showed the effect of slag on concrete transport properties. The effect of limestone filler was minimal either admixed solely or in conjunction with slag. On the other hand, blended cement appeared to be less effective on improving concrete transport properties. Compressive strength was less affected than transport properties by slag inclusion.

Resonant coupling of an optical mode confined within a microcavity and an emitter is the basic prerequisite for the observation of Bose-Einstein condensation phenomena and the development of novel optical devices based on cavity polaritons.

We demonstrate highly spatially resolved 2” wafer characterization of the reflectivity and emission properties of a nitride based multi quantum well semi microcavity (i.e. structure without top Bragg reflector) to verify resonant regions. Photoluminescence and reflectivity spectra recorded at the same positions on the wafer exhibit a strong spatial dependence of the multi quantum well emission and the center wavelength of the stop band of the bottom Bragg reflector across the sample. Resonance, i.e., matching of the emission and the center wavelength of the stop band, is found in a region 8 mm off the center of the wafer.

The thickness profile across the AlInN/GaN Bragg reflector and multi quantum well layers was obtained by x-ray mappings over the full wafer. A perfect correlation between the local optical properties and the x-ray thickness distribution is found. Additional transmission electron microscopy investigations indicate a complete crack free structure and smooth interfaces between the layers within the Bragg reflector making the structure appropriate for strong coupling applications.

Enhanced thermal conductivity oxide fuels offer increases in both safety and efficiency of commercial light water reactors. Low-temperature oxidative sintering and Spark Plasma Sintering (SPS) techniques have been used to produce UO2-SiC composite pellets. Oxidative sintering performed for 4 hours at 1200∼1600oC and SPS was employed only for 5 mins at the same temperature. While oxidative sintering failed to achieve enhanced thermal conductivity, the SPS sintered pellet obtained promising features such as higher density, better interfacial contact, and reduced chemical reaction. Thermal conductivity measurement at 100oC, 500oC, and 900oC revealed maximum 62% higher thermal conductivity value, when compared to UO2 pellets, in SPS sintered UO2-10vol% SiC composite pellet. The result shows that the SPS technique is required to sinter UO2-SiC nuclear fuel pellets with a high value of thermal conductivity.

The presence of elongation, streak and blurring artifacts in tomograms recorded under a missing wedge of rotation angles presents a major challenge for the quantitative analysis of tomographic image data. We show that the missing wedge artifacts of standard reconstruction algorithms may be reduced by the innovative reconstruction technique DIRECTT. For the comparison of missing wedge artifacts we apply techniques from spatial statistics, which have been specifically designed to investigate the shape of phase boundaries in tomograms.

The use of non-standard materials (e.g. specific substrates shapes and dimensions or polymer materials) for MEMS applications imposed a requirement for the development of new techniques for even well-established processes. Acoustic energy in the MHz frequency range has been used in the semiconductor industry for various processes such as photoresist development, substrate cleaning and electro-plating enhancement. The work presented here is focusing on single wafer cleaning and on photoresist development.

The cleaning process developed addresses mainly wafer cleaning prior to wafer bonding processes, in which particle contamination is of crucial importance.

The photoresist development process was developed mainly for thick resist layers development (few hundreds of μm) in order to improve definition of high aspect ratio features but was used as well as a significant process time reduction factor for development of regular thickness resists (few μm).

We have investigated an InAs channel Hall-bar structure with ferromagnetic spin injector in one of the current terminals. After magnetizing the Fe electrode, spin polarized electrons are injected through the edge of the isolation mesa structure and the anomalous Hall voltage is observed, when electrons are injected from the ferromagnetic terminal. However, when electrons are injected from the non-magnetic metal (Ti/Au) of opposite terminal, the Hall voltage disappeared to the variation error level due to the fabrication imperfections. This result suggests the possibility that out-of-plane spin injection from the channel edge lead to perpendicular nuclear magnetic field. It is presumably caused by nuclear spin polarization in InAs channel near the spin source edge through Overhauser effect. The estimated internal magnetic field was 2000 Gauss.

Amorphous (a-Si) and polycrystalline silicon(c-Si) films have been obtained by low pressure chemical vapor deposition (LPCVD) in fixed silane flow at low pressure (200 mtorr) with variable growth temperature. Measurement of residual stress of polysilicon films growth between 570°C to 620°C was reported. Residual stress of polycrystalline silicon depends on film microstructure. The poly-silicon microstructure is a strong function of LPCVD growth temperature and pressure. In this work, Raman Scattering and X-ray diffraction (XRD) were used to study the film structure and composition. The multilayer optical model of Spectroscopic ellipsometry (SE) was used to crosscheck the crystallinity fraction. The surface roughness was identified by Atomic force microscopy (AFM) and SE. The residual stress changed from compressive to tensile and back to compressive for deposition temperature between 570°C and 620°C. Film’s c-Si fraction increased as a function of deposition temperature. The roughness surface was found at deposition temperature of 580°C. For deposition temperature larger then 580°C, all films shown (200) texture. The (220) grain size increased from 18.6 nm to 25 nm when deposition temperature increased from 580°C to 620°C. The film residual stress change can be explained by grain structure, surface stress and volume stress. At deposition temperature from 580°C to 587°C, grain is equi-axes type and volume stress dominate which cause the tensile stress. For temperature higher then 587°C inverse conical grain formed from oxide interface to surface and surface stress dominate cause the stress back to compressive. The columnar structure formed when deposition temperature > 600°C, grain growth push the compressive stress decrease again.

The influence of surface segregation on the elastic properties of Pt-M (M = Ni, Co, or Fe) nanowires (NWs) are examined by comparing the predicted Young’s moduli of the segregated and non-segregated nanowires using density functional theory (DFT) calculations and the computed stress-strain curves under tensile loading using molecular dynamics (MD) simulation method. The moduli of the segregated NWs were found to be higher than that of the non-segregated ones. It is believed that the surface segregation increases the number of Pt-M bonds across the outermost and second surface layers, and thus enhances the Young’s modulus of the segregated Pt-M nanowires. MD results confirm our DFT results and it is found that onset of plastic deformation could be altered by the surface segregation process, as well.

The interactions and ordering of oxygen vacancies in rutile TiO2 were thoroughly investigated by density functional calculations to search for atomic configurations of the conductive filament. As random isolated vacancies could not support the low-resistance state conduction in TiO2 ReRAM, vacancy ordering was introduced in [110] and [001] directions of the lattice to study the electronic structures. The calculation results revealed that a di-vacancy chain in [001] direction makes the electrons delocalized in that direction, which is identified as a possible configuration of the conductive filament. This low-resistance state can be effectively disrupted by moving oxygen vacancies out of the filament to reach high-resistance states.

Four Celsian (Ba0.75Sr0.25Al2Si2O8)/Mullite (Al6Si2O13) composites, with potential structural applications at high temperatures, are synthesized from coal fly ash (byproduct of a Mexican coal-burning power plant, constituted mainly by SiO2 and Al2O3). Nominal Celsian/Mullite weight ratios studied are 80/20, 60/40, 40/60 and 20/80. Mullite is synthesized separately at 1600ºC/2h and then mixed with a Celsian precursor mixture previously calcined at 900°C/5h. During this process the Celsian phase is formed by a solid state reaction at 1100-1400ºC/5h. Prior to this, the reacting mixture is milled in a planetary mill during 1 or 2h and then compacted by uniaxial and cold isostatic pressing. The microstructure and phase composition of the synthesized composites are characterized by X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM/EDS). Their dynamic Young’s modulus is measured by an ultrasonic technique, and their mechanical strength is evaluated from flexural tests carried out at room temperature. The expected phases are obtained in all cases, although with some differences with respect to their expected relative proportions, according to the studied nominal compositions. In general, the longest milling time employed produced samples with the largest degree of crystallinity and density, as well as with the best microstructural characteristics and mechanical properties.

Block copolymers are considered to be highly attractive materials with regards to future applications of nanomaterials and nanostructures owing to their self-assembling nature. Block copolymers, when supplied with sufficient energy, phase separate at the nanoscales to form periodically ordered structures in the nanometer-scale range. A diversity of architectures can be accessed via composition control of individual block components. An exciting area of application for block copolymer self assembly is organic photovoltaic devices (OPV‟s) where it is expected that the very high interfacial area of the blocks with ∼10-20 nm domain spacing would be highly advantageous for exciton diffusion and separation. For this purpose BCPs composed of amorphous (non-conjugated) polymers can also serve as a template for directed assembly of nanoparticles. Zone annealing is a well established method predominantly utilized for metallurgical and semi-conductor purification processes, where recrystallization and oriented grain growth occur on the planar front formed by the cooling-edge of the zone. We have previously applied this process to create highly ordered BCP cylinders that are parallel to the substrate with orientational control, long range order and faster ordering kinetics than conventional thermal annealing. In the present paper, we extend this idea to block copolymer - [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) blend system and report how the presence of PCBM nanoparticles influence the micro-phase separation behavior of cylinder forming poly(styrene-b-2-vinyl pyridine) under a dynamic thermal gradient field. A range of scattering techniques have been on the BCP:PCBM blend system, including grazing incidence small angle x-ray scattering (GISAXS) experiments to characterize in-plane and lateral ordering of BCP-PCBM blend system.

Two strains of E-Coli K-12, viz, RP437, MG1655 and B/r (E. coli B derivative, not a K-12 strain) were grown on various surfaces to study bacterial adhesion and subsequent biofilm formation. We observed biofilm and large colonies on cover slides, beads made of soda lime or borosilicate glasses, on plasma treated PDMS (Polydimethylsiloxane), on Tissue Culture (TC) polystyrene, and observed some clusters on plasma treated ZnTi cover slide; but no evidence of biofilm on untreated-PDMS and ZnTi glass cover slides. From contact angle measurements, we conclude that the hydrophobic nature of untreated PDMS prevent bacterial adhesion for these three strains.

Single-phase samples of YCrx Fe1−x O3 were synthesized by a mechanochemical method. X-ray diffraction data show linear reduction in the lattice parameters of YCrxFe1−x O3 perovskites with the Cr content, indicating that Cr ions substitute for Fe ions to form a solid solution. Magnetic measurements show hysteresis loops at 5K. The substitution of Cr for Fe enhances the magnetization for up to x=0.33 Cr doping level. For higher doping levels, 0.33<x<1, the system behaves as a frustrated system. At x=1, YCrO3 behaves as a week ferromagnet with TN ~140 K. The chloride salt based machenochemical method offers simple synthesis route for the synthesis of pure multiferroic compounds.

The stress corrosion cracking (SCC) of the commercial austenitic stainless steel type 304 was investigated as function of test temperature, microstructure and mechanical properties in acidic chloride solution (25 wt.%-MgCl2) using slow strain rate tests (SSRT). Susceptibility and mechanism of SCC was investigated using SSRT performed at strain rate of 1 x 10-6 in/s in a glass autoclave containing a magnesium chloride solution at 20, 50 and 80°C. The SCC assessment was carried out in function of the results of time to failure ratio (TFR), elongation ratio (ELR), ultimate tensile strength ratio (UTS-R), strain ratio(eR), yielding strength ratio (YS-R) and stress rupture ratio (SR-R). This assessment was complemented by some scanning electron microscopy (SEM) observations, in order to determine the type of fracture and its features. SSRT results indicate that 304 stainless steel was susceptible to SCC at 50 and 80°C. SCC susceptibility increases as the temperature increase. By the contrary, the mechanical properties decreases with temperature increase. SEM observations showed a ductile type of fracture, indicating that cracks appear to be originated from the pits, increasing the number of cracks as the temperature increases. Corrosion pits are one of the main potential sites for surface crack initiation. The stress concentration in the pits will be the nucleation site for cracks.