bluuebunny/crossref_metadata_2025_split huggingface dataset:
Hybrid gold nanofinger SERS structure for sensing applications
Authors: Kim Ansoon , Li Zhiyong 
Published: September 2011

ABSTRACTWe report here a novel hybrid nanostructure for ultra-sensitive sensing applications based on surface-enhanced Raman spectroscopy (SERS). We rationally engineered gold-coated polymer pillar structures, named as gold nanofingers, in analogy to the tweezers at nanoscale, for active molecule capture and detection using SERS technique. Using nanoimprint lithography, we have demonstrated a cost effective manufacturing method of making such hybrid structures over large scale and achieve reliable enhancement factor. In particular, we have demonstrated the sensing application of the nanofinger structures for melamine and chlropyrifos. The limit of detection (LOD) of melamine in water is found to be 10 nM (1.3 ppb), and LOD of chlropyrifos (a pesticide) is found to be 1 nM (0.35 ppb), which is below the EPA tolerance level of 0.1 ppm for chlropyrifos on citrus fruits.
Electrospun TiO2 Nanofibers for Organic-Inorganic Hybrid Photovoltaic Cells
Authors: Chuangchote Surawut , Sagawa Takashi , Yoshikawa Susumu 
Published: September 2011

ABSTRACTFabrication of TiO2 nanofibers and their applications as the electron transporting layer for hybrid photovoltaic cells were studied. TiO2 nanofibers were electrospun onto an indium tin oxide (ITO) on glass substrate with a thin TiO2 blocking layer from a precursor solution [polyvinylpyrrolidone (PVP), titanium(IV) butoxide (TiBu), and acetylacetone (ACA)] in methanol. Many sources of precursor for fabrication of the thin TiO2 blocking layer, i.e. sintered TiO2 nanoparticle paste, sintered TiO2 nanoparticle-dispersed solution, TiBu solution with ACS in methanol, and titanium isopropoxide solution in ethanol were studied. The thin TiO2 blocking layer/nanofiber electrode was subjected to calcination at 450 °C for 3 h. The nanofiber electron transporting matrix was penetrated by blended poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). Thermal annealing and deposition of Au electrode were then carried out. After photovoltaic characterizations, it was found that hybrid organic-inorganic photovoltaic cells made of TiO2 nanofibers exhibited remarkable improvement of the cell efficiencies as compared with that of TiO2 flat film. Maximum power conversion efficiency (PCE) of hybrid organic-inorganic photovoltaic cells made of TiO2 nanofibers of 1.11% could be obtained (efficiency of flat TiO2 device = 0.28%).
Cellulose Nanocrystals Mediated Dispersion of Single Walled Carbon Nanotubes (SWNTs) and Elaboration of SWNTs /Cellulose Nanocrystals multilayered Thin Films.
Authors: Olivier Christophe , Moreau Céline , Bizot Hervé , Cathala Bernard , Chauvet Olivier 
Published: September 2011

ABSTRACTSingle Walled Carbon Nanotubes (SWNTs) dispersions are obtained after ultrasonication in Cellulose Nanocrystals (CNs) colloidal suspensions and they are found to be stable during several months. Similarly to CNs suspensions, SWNTs/CNs dispersions are used to elaborate multilayered thin films by the layer by layer method. Characterizations of the growth pattern, Raman and optical properties of the films are investigated. The presence of isolated SWNTs in each bi-layer is attested by characteristic Raman and luminescence signals. These films may be interesting for sensing applications.
Mechanical Properties of Single Crystal Diamond Estimated by Molecular Dynamics Simulation with the Second-Generation REBO Potential
Authors: Okamoto Shingo , Ito Akihiko 
Published: September 2011

ABSTRACTWe investigated the effects of tensile direction and periodic boundary condition (PBC) on the mechanical properties of single crystal diamond (SCD) under tensile loading, using MD simulations with the second-generation reactive empirical bond order (REBO) potential. We found that when the Poisson’s ratio is assumed to be constant under the canonical (NVT) ensemble and the PBC is applied to all directions of X, Y, and Z, each qualitative relation between a mechanical property such as tensile strength or Young’s modulus and the tensile direction is in agreement with both the results calculated by the first principle and by the cleavage energy method. In addition, we found that when the PBC is applied only to the Y direction under the NVT ensemble, each qualitative relation between a mechanical property and the tensile directions is in agreement with the MD results using the Tersoff potential.Our results indicate that the second-generation REBO potential is also useful for MD simulations on the tension of diamond.
ZrO2 Layer Thickness Dependent Electrical and Dielectric Properties of BST/ZrO2/BST Multilayer Thin Films
Authors: Sahoo Santosh K. , Misra D. , Agrawal D. C. , Mohapatra Y. N. 
Published: September 2011

ABSTRACTRecently, 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.
Electronic Structure and Optical Absorption of Fluorographene
Authors: Liang Yufeng , Yang Li 
Published: September 2011

ABSTRACTA first-principles study on the quasiparticles energy and optical absorption spectrum of fluorographene is presented by employing the GW + Bethe-Salpeter Equation (BSE) method with many-electron effects included. The calculated band gap is increased from 3.0 eV to 7.3 eV by the GW approximation. Moreover, the optical absorption spectrum of fluorographene is dominated by enhanced excitonic effects. The prominent absorption peak is dictated by bright resonant excitons around 9.0 eV that exhibit a strong charge transfer character, shedding light on the exciton condensation and relevant optoelectronic applications. At the same time, the lowest-lying exciton at 3.8 eV with a binding energy of 3.5 eV is identified, which gives rise to explanation of the recent ultraviolet photoluminescence experiment.
Ionizing Radiation Total Dose Detectors Using Oligomer Organic Semiconductor Material and Devices
Authors: Raval Harshil N. , Rao V. Ramgopal 
Published: September 2011

ABSTRACTOrganic semiconducting oligomer – Pentacene, as a material and organic electronic devices based on it, are proposed here as total dose detectors for ionizing radiation. Pentacene, when exposed to ionizing radiation of γ – rays using Cobalt – 60 (60Co) radiation source, shows increase in the conductivity of the material which can be used as a sensing phenomenon for determining the dose of ionizing radiation. The change in material property was also verified using UV-visible (UV-VIS) spectrum for pentacene thin-films with rising absorption peaks at the oxidized positions in the wavelength. A pentacene resistor can be used as a detector, as the change in the conductivity of the pentacene film can be easily quantified by measuring the change in resistance of the pentacene resistor after different total radiation dose exposures. The experiments resulted in a sensitivity of 340 kΩ/Gy for a total 100 Gy radiation dose for the pentacene resistor. Furthermore, employing this simple electrical measurement technique for determining the dose of ionizing radiation and to improve the sensitivity of the sensor by transistor action, a pentacene based organic field effect transistor (OFET) was exposed to ionizing radiation. Change in OFF current (IOFF) of the OFET sensor with W/L = 19350 μm/100 μm, suggests a sensitivity of 21 nA/Gy for 100 Gy dose. Also, changes in various other parameters like threshold voltage, subthreshold swing, field effect mobility, number of interface states etc. can be extracted from the electrical characterizations which prove their usefulness as a detector for ionizing radiation.
Multi-layered PVDF Systems for Enhanced Energy Harvesting and Sensing
Authors: Jones Jennifer , Aga Roberto S. , Mu Richard 
Published: September 2011

ABSTRACTThe peak output voltage (VL) of polyvinylidene fluoride (PVDF) piezoelectric devices has been investigated as a function of load resistance (RL). Two identical piezoelectric devices were mounted, back to back, on a vibrating cantilever giving almost similar VL. Using RL values in the range of 4.6 KΩ to 1 MΩ, it was observed that VL was doubled when the devices were connected in parallel but it did not change when the devices were connected in series. For single, parallel and series configurations, VL increases linearly with increasing RL. These results are explained well by modeling the device as a discharging capacitor with internal source of charge generation.
Investigation of Inherently Conductive Polymer as Structure Health Monitoring Sensor for Composite
Authors: Yang Huaxiang , Kim Dongsik , Singh Abhishek K. , Pitts Brady W. , Tregre Gregory J. , Kinlen Patrick J. 
Published: September 2011

ABSTRACTA soluble polyaniline was synthesized through emulsion polymerization and characterized using differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), gel permeation chromatography (GPC), viscosity analysis, and coefficient of linear thermal expansion (CLTE) determination. The electrical conductivity is found to reach 1000 S/cm with specific post doping treatments. Multiple printing processes, such as inkjet printing, screen printing and aerosol jet printing etc, make it feasible to print a variety of sensor patterns. The electromechanical response of these sensors was used to measure strain/stress or damage of composite structures under various load conditions expected to be experienced by aircraft. These unique conductive polymer sensors provide a feasible, near real time monitoring system for composites without adding significant additional weight to the structure.
Stability Improvement of Polymer Based Solar Cells by Thermally Evaporated Cr2O3 Interfacial Layer
Authors: Wang Mingdong , Xie Fangyan , Zheng Shizhao , Xu Jianbin. 
Published: September 2011

ABSTRACTWe report on Cr2O3 layer by thermal evaporation of Cr2O3 powder as cathode interfacial layer to improve the stability in air for the bulk heterojunction solar cells of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61 butyric acid methyl ester (PCBM). Devices with Cr2O3 interfacial layers show higher power conversion efficiency (PCE) and stability than those without interfacial layer. Devices with Cr2O3 show improved stability approximately 100 times than that of devices without interfacial layer or with LiF interfacial layer.
Poly(vinylidene fluoride-trifluoroethylene) (72/28) interconnected porous membranes obtained by crystallization from solution
Authors: Ferreira Armando , Silva Jaime , Sencadas Vitor , Gómez-Ribelles José Luís , Lanceros-Méndez Senentxu 
Published: September 2011

ABSTRACTElectroactive macroporous poly[(vinylidene fluoride)-co-trifluoroethylene] membranes have been processed by solvent evaporation at room temperature with different polymer/solvent concentrations. The pore architecture consists on interconnected spherical pores and this morphology is independent of the membrane thickness. The porosity of the produced membranes increases from 72% for the higher polymer concentration in the polymer/solvent solution (15/85), up to 80% for the lowest polymer concentration in the polymer/solvent solution.Fourier transform infrared spectroscopy and differential scanning calorimetry measurements reveal that the polymer crystallizes in the ferroelectric phase and the polymer/solvent ratio does not influences the Curie transition and the melting temperature of the polymer.
In situ Imaging at the NIST Neutron Imaging Facility
Authors: Jacobson David L. , Hussey Daniel S. , Baltic Eli 
Published: September 2011

ABSTRACTNeutron imaging as a method to perform in situ studies of hydrogen fuel cells, hydrogen storage devices, heat pipes, and batteries has made tremendous progress in recent years. Neutrons are useful to study light elements mixed with heavy Z elements where penetration by other forms of radiation is either impossible or incapable of contrasting the light elements. Useful spatial resolution available at neutron imaging facilities is now approaching 10 micrometers. Complimentary time resolution of 30 fps or greater is also possible with a spatial resolution approaching 300 micrometers. Here we will provide an overview of the technique of neutron imaging and experimental studies with neutrons at the National Institute of Standards and Technology. Examples of in situ studies of fuel cells, hydrogen storage devices, heat pipes and batteries will be discussed.
Magnetic Nanocomposite Aerogels
Authors: Corrias Anna , Loche Danilo , Casula Maria F. 
Published: September 2011

ABSTRACTAerogels are regarded as ideal candidates for the design of functional nanocomposites containing supported metal or metal oxide nanoparticles. The large specific surface area together with the open pore structure enables aerogels to effectively host finely dispersed nanoparticles up to the desired loading, to provide nanoparticle accessibility and/or to prevent nanoparticle agglomeration, as required to supply their specific functionalities.The preparation of highly porous nanocomposite aerogels containing magnetic metal, alloy or metal oxide nanoparticles dispersed into amorphous silica, with high purity and homogeneity, was successfully achieved by a novel sol-gel procedure involving urea-assisted co-gelation of the precursor phases. This method allows fast gelation, giving rise to aerogels with 97% porosity, and it is very versatile allowing to vary composition, loading and average size of the nanoparticles.The characterization of the morphological and structural features of the nanocomposite aerogels is carried out using different techniques, such as X-ray diffraction, Transmission Electron Microscopy and X-ray Absorption Spectroscopy. The characterization of the magnetic properties is carried out by SQUID magnetometry.
Automated Crystallite Orientation and Phase Mapping in a Transmission Electron Microscope
Authors: Rouvimov Sergei , Moeck Peter , Häusler Ines , Neumann Wolfgang , Nicolopoulos Stavros 
Published: September 2011

ABSTRACTAn automated technique for the mapping of nanocrystal phases and orientations in a transmission electron microscope (TEM) is briefly described. It is primarily based on the projected reciprocal lattice geometry that is extracted automatically from precession electron diffraction (PED) enhanced spot patterns. The required hardware allows for a scanning-precession movement of the primary electron beam on the crystalline sample and can be interfaced to any newer or older mid-voltage TEM. Comprehensive open-access crystallographic databases that may be used in support of this technique are mentioned.
Improvement of Single-Junction a-Si:H Thin-Film Solar Cells Toward 10% Efficiency
Authors: Cheng P. H. , Liang S. W. , Lin Y. P. , Hsu H. J. , Hsu C. H. , Tsai C. C. 
Published: September 2011

ABSTRACTThe hydrogenated amorphous silicon (a-Si:H) single-junction thin-film solar cells were fabricated on SnO2:F-coated glasses by plasma-enhanced chemical vapor deposition (PECVD) system. The boron-doped amorphous silicon carbide (a-SiC:H) was served as the window layer (p-layer) and the undoped a-SiC:H was used as a buffer layer (b-layer). The optimization of the p/b/i/n thin-films in a-Si:H solar cells have been carried out and discussed. Considering the effects of light absorption, electron-hole extraction and light-induced degradation, the thicknesses of p, b, n and i layers have been optimized. The optimal a-Si:H thin-film solar cell having an efficiency of 9.46% was achieved, with VOC=906 mV, JSC=14.42 mA/cm2 and FF=72.36%.
Numerical 3D-Simulation of Micromorph Silicon Thin Film Solar Cells
Authors: Geißendörfer Stefan , von Maydell Karsten , Agert Carsten 
Published: September 2011

ABSTRACTIn this contribution 1, 2 and 3-dimensional simulations of micromorph silicon solar cells are presented. In order to simulate solar cells with rough interfaces, the surface topographies were measured via atomic force microscopy (AFM) and transferred into the commercial software Sentaurus TCAD (Synopsys). The model of the structure includes layer thicknesses and optoelectronic parameters like complex refractive index and defect structure. Results of the space resolved optical generation rates by using of the optical solver Raytracer are presented. The space resolved optical generation rate inside the semiconductor layers depends on the structure of the transparent conductive oxides (TCO) interface. In this contribution the influence of different optical generation rates on the electrical characteristics of the solar cell device are investigated. Furthermore, the optical and electrical results of the 1D, 2D and 3D structures, which have equal layer thicknesses and optoelectronic parameters, are compared.
Opto-electronic properties of co-deposited mixed-phase hydrogenated amorphous/nanocrystalline silicon thin films
Authors: Kakalios James , Kortshagen U. , Blackwell C. , Anderson C. , Adjallah Y. , Wienkes L. R. , Bodurtha K. , Trask J. 
Published: September 2011

ABSTRACTMixed-phase thin film materials, consisting of nanocrystalline semiconductors embedded within a bulk semiconductor or insulator, have been synthesized in a dual-chamber co-deposition system. A flow-through plasma reactor is employed to generate nanocrystalline particles, that are then injected into a second, capacitively-coupled plasma deposition system in which the surrounding semiconductor or insulating material is deposited. Raman spectroscopy, X-ray diffraction and high resolution TEM confirm the presence of nanocrystals homogenously embedded throughout the a-Si:H matrix. In undoped nc-Si within a-Si:H (a/nc-Si:H), the dark conductivity increases with crystal fraction, with the largest enhancement of several orders of magnitude observed when the nanocrystalline density corresponds to a crystalline fraction of 2 – 4%. These results are consistent with the nc donating electrons to the surrounding a-Si:H matrix without a corresponding increase in dangling bond density for these films. In contrast, charge transport in n-type doped a/nc-Si:H films is consistent with multi-phonon hopping, possibly through extended nanocrystallite clusters with weak electron-phonon coupling. The flexibility of the dual-chamber co-deposition process is demonstrated by the synthesis of mixed-phase thin films comprised of two distinct chemical species, such as germanium nanocrystallites embedded in a-Si:H and Si nanocrystallites embedded within an insulating a-SiNx:H film.
Calibration of multi-junction (tandem) thin film photovoltaic modules under natural sunlight
Authors: Tzamalis Georgios , Müllejans Harald 
Published: September 2011

ABSTRACTWe present a procedure for calibrating tandem thin film photovoltaic modules under natural sunlight. The distinct steps involve pre-conditioning via light soaking, spectral response measurements and I-V measurements under natural sunlight. The measurements were done using a crystalline silicon reference cell as well as two filtered reference cells designed to spectrally match the top and bottom junctions in the tandem module.
PERFORMANCE of HYDROGENATED a-Si:H SOLAR CELLS with DOWNSHIFTING COATING
Authors: Nemeth Bill , Xu Yueqin , Wang Haorong , Sun Ted , Lee Benjamin G. , Duda Anna , Wang Qi 
Published: September 2011

ABSTRACTWe apply a thin luminescent downshifting (LDS) coating to a hydrogenated amorphous Si (a-Si:H) solar cell and study the mechanism of possible current enhancement. The conversion material used in this study converts wavelengths below 400 nm to a narrow line around 615 nm. This material is coated on the front of the glass of the a-Si:H solar cell with a glass/TCO/p/i/n/Ag superstrate configuration. The initial efficiency of the solar cell without the LDS coating is above 9.0 % with open circuit voltage of 0.84 V. Typically, the spectral response below 400 nm of an a-Si:H solar cell is weaker than that at 615 nm. By converting ultraviolet (UV) light to red light, the solar cell will receive more red photons; therefore, solar cell performance is expected to improve. We observe evidence of downshifting in reflectance spectra. The cell Jsc decreases by 0.13 mA/cm2, and loss mechanisms are identified.
Modulated surface-textured substrates with high haze for thin-film silicon solar cells
Authors: Isabella O. , Liu P. , Bolman B. , Krč J. , Zeman M. 
Published: September 2011

ABSTRACTModulated surface-textured substrates for thin-film silicon solar cells exhibiting high haze in a broad range of wavelengths were fabricated. Glass substrates coated with different thicknesses of a sacrificial layer were wet-etched allowing the manipulation of the surface morphology with surface roughness ranging from 200 nm up to 1000 nm. Subsequently, zinc-oxide layers were sputtered and then wet-etched constituting the final modulated textures. The morphological analysis of the substrates demonstrated the surface modulation, and the optical analysis revealed broad angle intensity distributions and high hazes. A small anti-reflective effect with respect to untreated glass was found for etched glass samples. The performance of solar cells on high-haze substrates was evaluated. The solar cells outperformed the reference cell fabricated on a randomly-textured zinc-oxide-coated flat glass. The trend in the efficiency resembled the increased surface roughness and the anti-reflective effect was confirmed also in solar cell devices.