A hindered phenol type radical scavenger (Irganox 1010®) was used to improvethe resistance to photo-oxidation in PPV-type polymers. The degradation wasperformed under blue light (460 nm), and the effect of the added compoundwas investigated following the intensity variation of absorbance andphotoluminescence spectra. The results showed that the addition of thecompound brought about a significant enhancement in photodegrationresistance without interfering in the electronic properties of the polymers.These results suggest that the free radical scavenger attenuates thedecrease of the polymer conjugation length induced by the radiation. FTIRmeasurements confirm this evidence.

Refrigeration, air conditioning, and other cooling requirements in buildings, industry, and transportation sectors account for about 10 quads of U.S. primary energy consumption. Therefore, advanced technologies for space cooling in buildings and vehicles – as well as for refrigeration in residential, commercial, and industrial applications – that are more energy efficient, avoid net direct greenhouse gas emissions, reduce lifecycle costs, and can impact large markets are needed. Although current technologies are reaching their efficiency limits, thermoelectric (TE) materials can be used for cooling applications and have potential for significant improvements. Compared to traditional bulk phase TE materials, literature results suggest that nanometer-scale materials allow additional opportunities to improve the efficiency of TE materials. Aerogels are one type of nano-material that offers opportunities to increase the efficiency of TE materials by controlling particle size, particle composition and by reducing the thermal conductivity. Bismuth telluride (Bi2Te3) is the most studied TE material and our objective was to produce bismuth telluride aerogels with controlled microstructures and thermal conductivities to increase the TE figure of merit. Aspen Aerogels developed a novel synthesis method to prepare Bi2Te3 aerogels using the principles of colloidal chemistry and sol-gel chemistry. The reaction conditions were investigated and optimized so that gels could be obtained at low reaction temperatures. The gels were aged and dried using supercritical CO2. The aerogels were characterized by BET, XRD, and SEM. The best aerogels were hot pressed and Seebeck coefficients were determined. The synthetic approach developed and the properties of the aerogels will be presented and compared with Bi2Te3 aerogels and materials prepared by other methods.

In this work, we report on investigation of p-type semiconducting polymer, {poly(3,4 polyethylenedioxythiophene)-poly(styrenesulfonate)} (PEDOT:PSS) as the p-layer in NIP and PIN hydrogenated amorphous silicon (a-Si:H) solar cells. The rectification ratio of solution-casted diode is ∼ 10, it increases to 3×104 when PEDOT:PSS is deposited by Spin Coating technique. We observed additional photovoltaic effect when light is illuminated through polymer side. So far, best solar cells characteristics observed for PEDOT:PSS/a-Si:H hybrid solar cells are Voc ≈ 720 mV and Jsc ≈ 1 - 2 mA/cm2.

We report a novel method to selectively deposit materials from solution into imprinted micro-capillaries. Dewetting of the solvent just outside the capillaries is balanced to evaporation inside the capillaries. In this way conductive μ-wires can be self-assembled and self-aligned on flexible substrates opening the route to faster and cheaper plastic electronics.

Carbon nanotube turfs are collections of nanotubes in a turf or mat assembly with potential application as thermal switches, flat panel displays, hard drives, sensors, etc. The nano-topology of the turf necessarily relates to the turf properties; electrical, thermal, optical, etc. A simple method to quantitatively characterize the density, tortuosity and path connectedness of the turfs using secondary electron imaging was previously developed. The present work aims at developing the groundwork for a more realistic measure of tortuosity by using a deterministic approach to obtain the radii of semi-circular tubes as observed in projected images.

Programs in the Defense Sciences Office (DSO) at the Defense Advanced Research Projects Agency (DARPA) bridge the gap from fundamental science to applications by identifying and pursuing the most promising ideas within the science and engineering research communities and transforming these ideas into new DoD capabilities. The Department of Defense (DoD) recognizes that our dependence on fossil fuel must be reduced and is actively supporting new technical solutions to this challenge. Moreover, advancements in alternative energy generation and storage technologies will render the warfighter more efficient, capable and mobile. Energy harvesting is a central pathway to solving this critical need. This paper will highlight two DARPA DSO programs which are making significant strides in the advancement in materials to improve energy harvesting technology with a focus on rapid transition to the end user. The Nanostructured Materials for Power (NMP) program is developing high performance thermoelectric materials and devices for energy harvesting with goals of energy conversion of 30%. The Low-Cost, Lightweight Portable Photovoltaics (PoP) program is developing integrated PV technologies with high power conversion efficiency (20%) in a form factor capable of being produced at low cost on flexible substrates. The paper will review the goals of the programs, discuss their implications, and highlight some of the research strategies underway.

Controlled incorporation of dopants into semiconductors nanowires is a critical step in tailoring their physical properties and hence for their utilization in future nano electronic devices. Recently, several studies addressing this issue revealed that dopant are inhomogeneously distributed in NWs grown by the popular CVD-VLS growth technique. The majority of those studies employed indirect characterization techniques which are sensitive to the active dopants only. In order to deepen our understanding of the incorporation mechanism a direct observation of the dopant chemical concentrations is required. In addition, the comparison between direct and indirect observations can shed some light on the dopant activation mechanisms in VLS grown NWs. In this study nanoprobe scanning Auger microscopy was employed to extract the longitudinal dopant distribution along P doped SiNWs. The effect of growth conditions and post-growth annealing on this distribution was studied and compared to previous studies which used indirect measurement techniques. In addition, dopant modulated segmented NWs were studied in order to distinguish the contribution of different mechanisms to the incorporation of dopants into VLS grown NWs.

Residual impurities in manganese (Mn) are a big obstacle to obtaining high- performance CdMnTe (CMT) X-ray and gamma-ray detectors. Generally, the zone-refining method is an effective way to improve the material’s purity. In this work, we purified the MnTe compounds combining the zone-refining method with molten Te that has a very high solubility. We confirmed the improved purity of the material by glow-discharge mass spectrometry (GDMS). We also found that CMT crystals from a multiple refined MnTe source, grown by the vertical Bridgman method, yielded better performing detectors.

In this study, different dispersion techniques such as sonication at high frequency, mechanical mixing, and magnetic stirring methods were employed to infuse 0.1 to 0.4 wt.% carbon nanofiber (CNF) into polyester matrix to study the influence of CNF on mechanical and thermal properties of the polyester nanocomposites. Dispersion of CNF studied using scanning electron microscopy (SEM) micrographs revealed excellent dispersion of CNF using sonication when 0.2 wt.% CNF was mixed in polyester resulting in enhanced mechanical response. On the other hand, agglomerations were observed in samples prepared with other mixing methods. Polyester with 0.2 wt.% CNF samples prepared by sonication resulted in 88% and 16% increase in flexural strength and modulus, respectively, over neat samples. Quasi-static compression tests showed similar increasing trend with addition of 0.2 wt.% CNF. Dynamic mechanical analysis (DMA) showed 35% and 5 °C improvement in the storage modulus and glass transition temperature (Tg), respectively, in the 0.2 wt.% loaded samples. Thermal mechanical analysis (TMA) performed on neat and samples with 0.2 wt.% CNF showed lower coefficient of thermal expansion (CTE) in nanophased sample compared to neat. Fracture morphology evaluated using SEM revealed relatively rougher surface in CNF-loaded polyester compared to neat as a result of better interaction between fiber and matrix due to the presence of CNF.

Four new compounds containing vanadosilicate clusters have been synthesized by hydrothermal reactions. The clusters are derived from the [V18O42] Keggin cluster by substitution of V=O caps by Si2O(O,OH)2 species. In Cs9[(V15Si6O46(OH)2Cl)(V2O4)](H2O)6.2, 1, the [V15Si6O46(OH)2] cluster shells are covalently interconnected by VO4 tetrahedra to form an infinite layer. In ((CH3)4N)4[V15Si6O42(OH)6(H2O)](H2O)20, 2, and ((CH3)4N)4(V(H2O)6)2/3 [V15Si6O42(OH)6 (H2O)](H2O), 3, separated [V15Si6O42(OH)6] cluster shells are interlinked by hydrogen bonds to form frameworks with wide channel systems. The separated cluster shell in ((CH3)4N)4((CH3)2NH2)((CH3)2NH) [V14Si8O42(OH)8(HCO2)] (H2O)4.7, 4, has four Si2O(OH)2 species in a tetrahedral configuration. The 2D structure of 1 and 0D structures of 2-4 complement the known 1D and 3D structures formed from such vanadosilicate shells.

We present a study on the liquid/solid interface, which can be electrostatically doped to a high carrier density (n~1014 cm-2) by electric-double-layer gating. Using micro-cleavage technique on the layered materials: ZrNCl and graphene, atomically flat channel surfaces can be easily prepared. Intrinsic high carrier density transport regime is accessed at the channel interface of electric double-layer field effect transistor, where novel transport properties are unveiled as the field-induced superconductivity on the ZrNCl with high transition temperature at 15 K, and accessing a high carrier density up to 2×1014 cm-2 in graphene and its multi-layers.

The present work reports the renewable hydrogen production by an anaerobic photocatalytic reforming of formic acid over CdS sensitized Na2Ti2O4(OH)2 nanotubes. the Na2Ti2O4(OH)2 nanotube was prepared and charactered by X-ray diffraction, UV-visible absorption, transmission electron microscopy, etc. The activity of the catalyst in formic acid was investigated. The greatest photocatalytic reforming activity of formic acid occurs as the formic acid initial concentration is 20 v.%. A probable mechanism for the photocatalytic reforming process was proposed and discussed.

The titanium dioxide (TiO2) nanoparticle (NP) structure has higher surface area and dye loading value to increase photon absorption while the nanotube (NT) can suppress the random walk phenomena to enhance carrier collection. In this work, hydrothermal method was utilized to infiltrate the TiO2 nanotube array by TiO2 nanoparticles with the aim of combining the advantages of both nanostructures to improve dye sensitized solar cells (DSSCs) efficiency. Structure morphology, device performance, and electrochemical properties were investigated. SEM observation confirmed that around 10 nm TiO2 nanoparticles uniformly covered the NT wall. TiO2 NT samples at three different lengths: 8 μm, 13 μm and 20 μm, decorated with different amount of nanoparticles were studied to optimize the structure for light absorption and electron transport to achieve high solar conversion efficiency. Electrochemical impedance spectroscopy (EIS) was also employed to investigate the cells’ parameters: electron lifetime (τ), diffusion length (Ln) et al, to gain insight on the device performance. The incident photon conversion efficiency (IPCE) was also reported.

Stainless steels are among the most important engineering materials, finding their principal scope in industry, specifically in cutlery, food production, storage, architecture, medical equipment, etc. Austenitic stainless steels form the largest sub-category of stainless steels having as the main building blocks the paramagnetic substitutional disordered Fe-Cr-Ni-based alloys. Because of that, austenitic steels represent the primary choice for non-magnetic engineering materials. The presence of the chemical and magnetic disorder hindered any previous attempt to calculate the fundamental electronic, structural and mechanical properties of austenitic stainless steels from first-principles theories. Our ability to reach an ab initio atomistic level approach in this exciting field has become possible by the Exact Muffin-Tin Orbitals (EMTO) method. This method, in combination with the coherent potential approximation, has proved an accurate tool in the description of the concentrated random alloys. Using the EMTO method, we presented an insight to the electronic and magnetic structure, and micromechanical properties of austenitic stainless steel alloys. In the present contribution, we will discuss the role of magnetism on the stacking fault energies and elastic properties of paramagnetic Fe-based alloys.

A “0-0 type” multiferroic BaTiO3-NiFe2O4 (BT-NF) composite thin film was prepared on SrRuO3/(La,Sr)MnO3/CeO2/YSZ/Si(001) substrate using pulsed laser deposition (PLD). Epitaxial growth of the film was confirmed using x-ray pole figure measurements. Cross-sectional TEM observations revealed that the crystal structure and morphology of the BT-NF composite thin film depends on the oxygen pressure during deposition. The film deposited at 1.0×10-2 Torr has smaller grains than that deposited at 1.0×10-1 Torr. The magnetic and ferroelectric properties of BT-NF composite thin film were correlated with the microstructure that was controlled by oxygen pressure during deposition. The film deposited at 1.0×10-2 Torr had paramagnetic properties with less polarization than the film deposited at 1.0×10-1 Torr.

Nuclear fuel pins exhibit distortions in the UO2 lattice in response to temperature gradients, defects and the introduction of fission product (FP) gases. These distortions can have a significant influence on the activation barriers associated with fission product gas diffusion. A predictive understanding of this relationship is particularly relevant to anticipating the evolution of fission product gases during rapid temperature transients. Density Functional Theory (DFT) has the capacity to provide a relationship between lattice distortion and FP gas diffusivity by generating estimates of dilation dependent activation energies.

As a first step in this direction, the relation between lattice dilation and activation energy for isolated vacancies within an otherwise pristine block of alpha-quartz is quantified, where precise experimental data is readily available. The results lend confidence to the basic approach which is based on a one-shot transition state method, developed to lessen the computational resources required by the full transition state method. This technique is first applied to α-quartz for O vacancy hopping and diamond-Si for Si vacancy hopping. The method is subsequently extended to consider isolated uranium vacancies in UO2. This in turn is further generalized to estimate the activation volume for Kr atoms in UO2. Thus two different types of defects are considered; those of species native to the material and, in the case of UO2, FP gases introduced through the fission process.

The primary objective of this modeling investigation is to optimize a two-junction three-terminal device under the AM1.5G spectrum. Based on previous studies, AlGaAs and Si cells, because of their energy bandgaps, can be combined together to achieve high-efficiency double-junction devices. In this study, the top cell is made of Al0.3Ga0.7As (1.817 eV) while the bottom cell is made of Si (1.124 eV). In order to avoid the losses and design constraints observed in two-terminal and four-terminal devices, the tandem cell AlGaAs/Si is designed with three-terminals. In order to determine the optimal structure of the device, the top and bottom junctions were investigated and optimized with regard to the thicknesses and doping level. The optimum configuration of the device shows an efficiency of 26.27% under the AM1.5G spectrum and one sun, which is higher than the efficiency of an optimized single-junction Si cell under the same illumination conditions. We also studied the effect of the optical concentration on the performance of the device and we found that the overall efficiency reaches over 31% under 50 suns.

We present a theoretical investigation of the thermoelectric power factor enhancement in metal/semiconductor nanocomposites by the energy dependent electron scattering from ionized nanoparticles. The metal nanoparticles embedded in semiconductors can be ionized to donate electrons to the matrix, which will result in a Coulomb potential tail around the nanoparticles. Here we show the significant effect of slowly varying potential tails on thermoelectric properties of the nanocomposites. The Coulomb potential is different from that of the conventional ionized impurities due to the finite size of the ionized particles, and the fact that the nanoparticles can give multiple electrons to the matrix. Detailed calculations for scattering rates and thermoelectric coefficients are presented for ErAs semi-metallic nanoparticles in InGaAs semiconductors. The partial wave method is used to consider the exact potential profile around nanoparticles and Boltzmann transport equation is used to calculate the transport coefficients. We find that an increase by 15~30% in power factor can be achieved over a wide temperature range in these material systems in addition to the thermal conductivity reduction to further enhance ZT.

We present the ionization of decaborane (B10H14) and formation of hydrogen- and boron-contents-controlled B10-yHx + through the charge transfer from ambient gas ion to decaborane molecules in an external quadrupole static attraction ion trap. The charge transfer energy is estimated from the experimentally observed products. PBE0/6-311+G(d)//B3LYP/6-31G(d) level of DFT calculations are conducted to investigate the mechanism of charge transfer from ambient gas ion. The calculation of the difference of ionization energies and mismatch of orbital energies between decaborane and ambient gas reveals the mechanism of ionization.

Recently, high K materials play an important role in microelectronic devices such as capacitors, memory devices, and microwave devices. Now a days ferroelectric barium strontium titanate [BaxSr1-xTiO3, (BST)] thin film is being actively investigated for applications in dynamic random access memories (DRAM), field effect transistor (FET), and tunable devices because of its properties such as high dielectric constant, low leakage current, low dielectric loss, and high dielectric breakdown strength. Several approaches have been used to optimize the dielectric and electrical properties of BST thin films such as doping, graded compositions, and multilayer structures. We have found that inserting a ZrO2 layer in between two BST layers results in a significant reduction in dielectric constant, loss tangent, and leakage current in the multilayer thin films. Also it is shown that the properties of multilayer structure are found to depend strongly on the sublayer thicknesses. In this work the effect of ZrO2 layer thickness on the dielectric, ferroelectric as well as electrical properties of BST/ZrO2/BST multilayer structure is studied. The multilayer Ba0.8Sr0.2TiO3/ZrO2/Ba0.8Sr0.2TiO3 film is deposited by a sol-gel process on the platinized Si substrate. The thickness of the middle ZrO2 layer is varied while keeping the top and bottom BST layer thickness as fixed. It is observed that the dielectric constant, dielectric loss tangent, and leakage current of the multilayer films reduce with the increase of ZrO2 layer thickness and hence suitable for memory device applications. The ferroelectric properties of the multilayer film also decrease with the ZrO2 layer thickness.