bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermochromism of VO2 Nanoparticles: Calculated Optical Properties and Applications to Energy Efficient Windows
Authors: Li S.-Y. , Niklasson G. A. , Granqvist C. G.
Published: September 2011

Thermochromic materials have temperature-dependent optical properties. This paper discusses the limitations of thermochromic VO2 films for energy efficient fenestration and shows from calculations that nanocomposites containing VO2 can have superior properties and display high luminous transmittance and large temperature-dependent solar transmittance modulation. Even better results may be found for nanoparticles of VO2:Mg.
ZnO Thin Films of High Crystalline Quality Deposited on Sapphire and GaN Substrates by High Temperature Sputtering
Authors: Borysiewicz Michał A. , Pasternak Iwona , Dynowska Elżbieta , Jakieła Rafał , Wzorek Marek , Kolkovski Valery , Dużyńska Anna , Kamińska Eliana , Piotrowska Anna
Published: September 2011

Single orientation ZnO (00.2) films were deposited by means of high temperature high vacuum reactive magnetron sputtering onto Al2O3 (0001) and GaN (0001) substrates. In order to obtain films of high crystalline quality a novel approach to ZnO sputter deposition was employed, adapting the practice used in MBE technology, of using a MgO buffer layer deposited on sapphire at a high-temperature followed by a ZnO nucleation layer deposited at low temperature. ZnO films were also grown on epitaxial GaN/Al2O3 substrates where the GaN layer was treated as the buffer layer. Following the deposition, all samples were annealed ex-situ in an O2 flow at 800°C. The obtained ZnO films have a lattice constant c equal to 5.2036 Å and 5.214 Å for the films deposited on Al2O3 and GaN substrates, respectively. Secondary ion mass spectroscopy depth profiles, scanning and transmission electron microscopy cross sectional images and atomic force microscope were used to characterize the structural properties of the films. Electrical properties were assessed using Hall effect measurement. Photoluminescence spectra were also taken.
Microstructure and Its Physicochemical Basis for the White Porcelain from Gongyi Kiln of Henan Province in China
Authors: Li Weidong , Luo Hongjie , Sun Xinmin , Liu Lanhua , Lu Xiaoke , Zhao Zhiwen , Guo Musen
Published: September 2011

Gongyi is the birthplace and one of the most famous production areas of white porcelain in China. In this study, white porcelain samples from the Northern Wei to Tang Dynasties excavated from Baihe and Huangye kiln sites were analyzed to investigate microstructure and its physicochemical basis. The result demonstrates that the formation of an interaction layer of Anorthite crystals and the accompanied phase-separation structure at glaze-body boundary is a common character of microstructure. And there is little probability for crystal precipitation within the glaze layer.
A study on the importance of isolation of the active regions for high performance organic circuits
Authors: Myers R. , Donaghy D. , Raja M.
Published: September 2011

The authors present electrical comparisons on an array of test structures including organic lateral diodes and thin film transistors (OTFT), fabricated with a range of disordered and polycrystalline organic semiconductors, to examine the increasing need for effective isolation for organic-based circuits. As the minimum feature size decreases, circuit components become closely positioned, which leads to increased electrical crosstalk. The organic semiconductors utilised for this work include solution-processable organic semiconductors such as disordered polymers P3HT and PTAA, and a polycrystalline material TIPS-pentacene. In order to predict the magnitude required for isolation for the different semiconductors, simple test structures have been designed consisting of two gold electrodes separated by a distance ranging from 4 μm up to 2000 μm. The bulk conductivity from such test structures provides the limits at which circuit components may be placed for crosstalk free operation. The work presented culminates in the development of an isolation layer to help reduce the off-currents and gate leakages of the OTFTs.
Comparison between the optical and surface properties of TiO2 and Ag/TiO2 thin films prepared by sol-gel process
Authors: Viana Marcelo M. , Mohallem Nelcy D. S.
Published: September 2011

Colloidal precursor solutions, obtained from a mixture of titanium isopropoxide, isopropyl alcohol and silver nitrate, were used to fabricate amorphous TiO2 and Ag/TiO2 thin films by sol-gel process. The films were deposited on borosilicate substrates, which were heated at 400 °C for 30 minutes and cooled rapidly to the formation of amorphous coatings. The films were investigated by X-ray diffraction, scanning electron microscopy, atomic force microscopy and UV-vis spectroscopy. The thickness, roughness, refraction index, and particle size of the TiO2 and Ag/TiO2 films were determined and compared. Finally, hydrophobic-hydrophilic property was evaluated to the thin films produced.
(Green) Photocatalytic Synthesis Employing Nitroaromatic Compounds
Authors: Dillert Ralf , Hakki Amer , Bahnemann Detlef W.
Published: September 2011

The combination of a solid photocatalyst (TiO2) and a co-catalyst (p-toluenesulfonic acid) has been successfully applied for the light-induced conversion of nitroarenes in O2-free ethanolic suspensions yielding substituted quinolines and tetrahydroquinolines, while in the presence of TiO2 loaded with a noble metal (Pt, Pd) N-alkylarylamines and N,N-dialkylarylamines were formed. Depending on the compounds that have been detected by GC–MS the reaction mecha-nism is discussed comprising the formation of anilines and ethanal by a photocatalytic reaction step and their subsequent thermal reactions to quinolines, tetrahydroquinolines, and N-alkylated anilines via a Schiff base as an intermediate product.
Structural, Electronic and Defect Properties of Cu2ZnSn(S,Se)4 Alloys
Authors: Chen Shiyou , Gong Xin-Gao , Walsh Aron , Wei Su-Huai
Published: September 2011

Kesterite Cu2ZnSnS4 (CZTS) and Cu2ZnSnSe4 (CZTSe) compounds are candidate low-cost absorber materials for thin-film solar cells, and a light-to-electricity efficiency as high as ~10% has been achieved in the solar cell based on their alloys, Cu2ZnSn(S,Se)4 (CZTSSe). In this paper, we discuss the crystal and electronic structure of CZTSSe alloys with different composition, showing that the mixed-anion alloys keep the kesterite cation ordering, and are highly miscible with a small band gap bowing parameter. The phase stability of CZTS and CZTSe relative to secondary compounds such as ZnS and Cu2SnS3 has also been studied, showing that chemical potential control is important for growing high-quality crystals, and the coexistence of these secondary compounds is difficult to be excluded using X-ray diffraction technique. Both CZTS and CZTSe are self-doped to p-type by their intrinsic defects, and the acceptor level of the dominant CuZn antisite is deeper than Cu vacancy. Relatively speaking, CZTSe has shallower acceptor level and easier n-type doping than CZTS, which gives an explanation to the high efficiency of CZTSSe based solar cells.
Towards a Room Temperature Organic Spin Valve: Structural, Magnetic and Transport Properties of Fe3O4/PTCTE/Co Devices
Authors: Palosse Mathieu , Bedel-Pereira Elena , Olivié François , Séguy Isabelle , Villeneuve Christina , Blon Thomas , Gatel Christophe , Warot-Fonrose Bénédicte , Bobo Jean-François
Published: September 2011

This paper describes first steps in preparation of an organic spin valve based on a perylene derivative (PTCTE) sandwiched between magnetite (Fe3O4) and cobalt (Co) ferromagnetic electrodes. MgO(001)/Fe3O4/PTCTE (450 nm)/Co devices were prepared with different Co soft deposition methods: off-axis dc-sputtering or Joule evaporation. Vibrating Sample Magnetometer (VSM) studies of the Fe3O4/PTCTE/Co stacks evidence spin valve behavior with magnetically uncoupled electrodes. These results are correlated with a morphological study by atomic force microscopy (AFM) of each layer and tunneling AFM (TUNA) for the investigation of inhomogeneity of current distribution in the devices. Finally, macroscopic I-V characteristics performed on the same devices will be presented and compared with TUNA results.
Growth and characterization of orientation patterned GaAs crystals for non-linear optical frequency conversion
Authors: Martínez O. , Avella M. , Hortelano V. , Jiménez J. , Snure M. , Lynch C. , Bliss D.
Published: September 2011

Orientation patterned (OP)-GaAs crystals have high potential as non linear optical systems. Mid-infrared and terahertz lasers sources can be fabricated with these crystals by frequency conversion from shorter wavelength sources. The optical propagation losses are critical; therefore, the OP-GaAs crystals must have high quality with low incorporation of defects and high homogeneity to reduce the refractive index fluctuations. Defects with electro-optic signature must be characterized in order to reduce their presence. Cathodoluminescence studies of these crystals permit the distribution of the main defects to be established, both extended and point defects. Special attention is paid to the role of the walls between the two domain orientations, and to the incorporation of impurities in Si-doped samples.
Preparation of luminescent inorganic core/shell-structured nanoparticles
Authors: Milde Moritz , Dembski Sofia , Rupp Sabine , Gellermann Carsten , Sextl Gerhard , Batentschuk Miroslaw , Osvet Andres , Winnacker Albrecht
Published: September 2011

SiO2 nanoparticles (NPs) were coated with Eu3+-doped calcium phosphate (CP) and Mn2+-doped ZnO to give Zn2SiO4 via a modified Pechini sol-gel process. Annealing at high temperatures resulted in NPs with an amorphous core and a crystalline luminescent shell. It was shown that this procedure can be applied to silica cores with diameters below 300 nm. By transmission electron microscopy, elemental analysis and from X-ray diffraction patterns it was determined that shell composition and structure are influenced by the annealing temperature and pH of the coating solution. Measurements of photoluminescence intensities displayed their dependency on the concentration of dopant in the resulting core/shell NPs.
Size-dependent Reactivity in the Functionalization of Nanostructured Silicon Surfaces
Authors: Kelly Joel A. , Shukaliak Amber M. , Fleischauer Michael D. , Veinot Jonathan G.C.
Published: September 2011

The reactivity of silicon nanocrystals (Si-NCs) in near-UV photochemical hydrosilylation was evaluated as a function of size. Results show that Si-NCs with photoluminescence (PL) in the visible spectral region react faster than Si-NCs with near-IR PL. Fourier-transform infrared (FTIR) spectroscopy suggests this difference in reactivity is due to quantum size effects in the exciton-mediated mechanism proposed for this reaction. We have carried out a detailed comparison of Si-NC reactivity in photochemical and thermal hydrosilylation and determined the conditions under which Si-NCs may be size-selected based on their reactivity.
Non-lithographic Patterning of Oxide-Embedded Silicon Nanoparticles
Authors: Rodríguez Núñez José R. , Johnson Melanie , Veinot Jonathan G. C.
Published: September 2011

Oxide-embedded Silicon nanoparticles (OE-Si-NPs) are of great interest for many applications due to unique size effects observed when their size drops below 5 nm (Silicon’s Bohr exciton radius). Some of the suggested applications require patterning of the nanoparticles in an ordered array. Lithographic methods to pattern Si-NPs are common in the literature, however these methods can be costly, and are not time-efficient. Recently, non-lithographic patterning techniques have become very attractive because they are cost-effective and straightforward. In this proceeding we will demonstrate non-lithographic patterning of OE-Si-NPs characterized via AFM and XPS.
An Evaluation of Decorative Techniques on a Red-Figure Attic Vase from the Worcester Art Museum using Reflectance Transformation Imaging (RTI) and Confocal Microscopy with a Special Focus on the “Relief Line”
Authors: Artal-Isbrand Paula , Klausmeyer Philip , Murray Winifred
Published: September 2011

Decorative features on a Greek red-figure stamnos in the collection of the Worcester Art Museum were examined using Reflectance Transformation Imaging (RTI) and scanning laser confocal microscopy. These two surface examination tools helped to answer questions relating to the decorative process, particularly the tools and techniques that Attic painters used to create the so-called glossy black “relief lines” and “relief dots.” This research also incorporated fabricated mock-ups to help understand the ancient technology. It was determined that the relief line was not produced by an extruded method, but with a brush made of one or very few hairs, an idea first proposed by Gérard Seiterle in 1976 and termed Linierhaar. It was observed that not one but two distinct types of relief lines exist: the “laid” line (proposed by Seiterle) characterized by a ridge running through the middle of the line and the “pulled” line (proposed in this paper) which has a furrowed profile. Both line types were reproduced with a Linierhaar. Additionally, relief dots were replicated using a conventional brush. Surface examinations of other red-figure vessels using RTI and the confocal microscope suggest these conclusions apply to vessels of this genre as a whole.
Structural Degradation of Third Millennium B.C.E. Archaeological Wood from Shahr-i Sukhta, Iran
Authors: Mohammadi Achachluei Mohsen , Vatankhah Gholamreza
Published: September 2011

Detection of structural changes has a great importance in conservation and treatment of wooden artifacts found in burial environments. In this study, two wooden samples excavated in Shahr-i Sukhta, an important prehistoric site in eastern Persia, were tested by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). FTIR results showed that decay of lignin occurred. This was accompanied by cellulose degradation. SEM images showed detachment of wood fibers in cross sections and cell wall breakage in tangential sections of the wood samples. These results indicated that the structural change in cellulose and lignin has caused detachment of wood fibers and cell wall breaking. This is the sign of low physical characteristics of wood which has direct relevance to cellulose decay and lignin degradation in middle lamella of wood cells. Cellulose chain breaking over time, has produced stresses in the compound middle lamella layer of the cell wall, that became accelerated in the middle of the lamella layer. Consequently, wood fibers were detached, and disintegration and powdering of wood surfaces occurred.
New Dynamic Air-Brush Technique for SWCNTs Deposition: Application to Fabrication of CNTFETs for Electronics and Gas Sensing
Authors: Bondavalli P. , Gorintin L. , Legagneux P. , Simonato J.P. , Cailler L.
Published: September 2011

This contribution deals with Carbon Nanotubes Field Effect transistors (CNTFETs) based gas sensors fabricated using a completely new dynamic spray based technique (patented) for SWCNTs deposition. The extreme novelty is that our technique is compatible with large surfaces, flexible substrates and allows to fabricate high performances transistors exploiting the percolation effect of the SWCNTs networks achieved with extremely reproducible characteristics. Recently, we have been able to achieve extremely selective measurement of NO2, NH3 and CO using four CNTFETS fabricated using different metals as electrodes, exploiting the specific interaction between gas and metal/SWCNT junctions. In this way we have identify an electronic fingerprinting of the gas detected. The response time is evaluated at less than 30sec.
Fracture mechanism of copper micro-crystals by diamond single crystal
Authors: Kano Seisuke , Korenaga Atsushi
Published: September 2011

Copper micro-crystal fracture mechanisms were discussed with the machining precisions under the several cutting conditions, such as cutting speed, cutting depth and width of grove formation by the diamond single crystal cutting tool which the scoop face of (100) crystal face. For the cutting test, the copper single at the size of 10 mm in diameter and 5 mm in height as the test piece which cut by single crystal diamond cutting tool with silicon oil on the shaper type ultra-precision cutting machine. Before groves cutting, the specimen surface was cut as flat by cutting-off tool (corner diameter; 50 mm, cutting width; 3.0 mm, scooping angle; 0 degree, and escape angle; 7.0 degree) at the work speed as 4000 mm/min and cutting depth of 5 μm. For the V-shape grove cutting, the flat copper surface was cut with the diamond-point cutting tool (V angle = 90 degree, scooping angle = 0 degree, and escape angle = 7.0 degree) at the work speed as 4-4000 m m/min and cutting depth of 0.1-10 μm for finishing machining. The cut machined surface was observed by optical microscope comparing the grove shapes. The diamond-point tool was also observed by optical microscope. As results of the cutting test of copper single crystal, the machining precision was better for the crystallographic direction of $[01\bar 1]$ than the direction of $[00\bar 1]$ under the deeper cutting profiles. The mechanisms of this fracture results considered that the slip plane of (111). On the other hand, shallow grove under 1.0 μm was better tracks scratched for the crystallographic direction of $[00\bar 1]$ than the direction of $[01\bar 1]$. This result was also considered that the slip plane related to the fracture behavior. For copper crystal cutting in nanometric scale, the crystallographic direction was quite important.
Impact of a Finite Shunt Resistance on the Dark Spectral Response of a-Si:H/μc-Si Thin-film Multi-junction Photovoltaic Devices
Authors: Pravettoni Mauro , Virtuani Alessandro
Published: September 2011

Hydrogenated amorphous silicon (a-Si:H) multi-junction devices have demonstrated a way to increase the efficiency of a-Si:H thin-film photovoltaic (PV) modules, which is now well above 10%. Since the current–matching behaviour of all sub-cells is a critical aspect, the measurement of the spectral response (SR) of all junctions provides valuable information to optimize the device performance under a given spectral distribution. In this work the authors investigate the impact of low shunt resistances on the SR of a double-junction a-Si:H/μc-Si PV module. The origin of a low shunt resistance in a-Si:H multi-junction devices is revised. A simple theoretical approach is then used to describe the anomalous dark SR observed experimentally as a consequence of the presence of low shunt resistances. The dark SR allows therefore to detect the presence of shunts and discriminate the defective sub-cell.
Characterization of Green Laser Crystallized GeSi Thin Films
Authors: Rangarajan Balaji , Brunets Ihor , Oesterlin Peter , Kovalgin Alexey Y. , Schmitz Jurriaan
Published: September 2011

Green laser crystallization of a-Ge0.85Si0.15 films deposited using Low Pressure Chemical Vapour Deposition is studied. Large grains of 8x2 μm2 size were formed using a location-controlled approach. Characterization is done using Scanning Electron Microscopy, Atomic Force Microscopy, X-Ray Photoelectron Spectroscopy and X-Ray Diffraction.
Hopping transport in doped co-deposited mixed-phase hydrogenated amorphous/nanocrystalline silicon thin films
Authors: Wienkes L. R. , Blackwell C. , Kakalios J.
Published: September 2011

Studies of the electronic transport properties of n-type doped hydrogenated amorphous/nanocrystalline silicon (a/nc-Si:H) films deposited in a dual-plasma co-deposition reactor are described. For these doped a/nc-Si:H, the conductivity increases monotonically for increasing crystal fractions up to 60% and displays marked deviations from a simple thermally activated temperature dependence. Analysis of the temperature dependence of the activation energy for these films finds that the dark conductivity is best described by a power-law temperature dependence, σ = σo (T/To)n where n = 1 – 4, suggesting multiphonon hopping as the main transport mechanism. These results suggest that electronic transport in mixed-phase films occurs through the a-Si:H matrix at lower nanocrystal concentrations and shifts to hopping conduction between clusters of nanocrystals at higher nanocrystal densities.
Reflectance Improvement by Thermal Annealing of Sputtered Ag/ZnO Back Reflectors in a-Si:H Thin Film Silicon Solar Cells
Authors: Söderström Karin , Haug Franz-Josef , Pahud Céline , Biron Rémi , Escarré Jordi , Duchamp Martial , Dunin-Borkowski Rafal , Ballif Christophe
Published: September 2011

Silver can be used as the back contact and reflector in thin film silicon solar cells. When deposited on textured substrates, silver films often exhibit reduced reflectance due to absorption losses by the excitation of surface plasmon resonances. We show that thermal annealing of the silver back reflector increases its reflectance drastically. The process is performed at low temperature (150°C) to allow the use of plastic sheets such as polyethylene naphthalate and increases the efficiency of single junction amorphous solar cells dramatically. We present the best result obtained on a flexible substrate: a cell with 9.9% initial efficiency and 15.82 mA/cm2 in short circuit current is realized in n-i-p configuration.
Optical bias controlled amplification in tandem Si-C pinpin devices
Authors: Vieira M. , Vieira M. A , Louro P. , Fernandes M. , Fantoni A. , Barata M.
Published: September 2011

A monolithic double pi’n/pin a-SiC:H device that combines the demultiplexing operation with the simultaneous photodetection and self amplification of the signal is analyzed under different electrical and optical bias conditions at low and high excitation frequencies. Results show that the transducer is a bias wavelength current-controlled device that make use of changes in the wavelength of the background to control the power delivered to the load. Self optical bias amplification or quenching under uniform irradiation and transient conditions is achieved. The device acts as an optical amplifier whose gain depends on the background wavelength and frequency. An optoelectronic model supported by an electrical simulation explains the operation of the optical system.
Self optical gain in multilayered silicon-carbon heterostructures: A capacitive active band-pass filter model
Authors: Vieira M. A. , Vieira M. , Louro P. , Fernandes M. , Costa J. , Garção A. S.
Published: September 2011

This paper reports results on the use of a pi’n/pin a-SiC:H heterostructure as an active band-pass filter transfer function whose operation depends on the wavelength of the trigger light, on the applied voltage and on the wavelength of the additional optical bias.

Results show that the device combines the demultiplexing operation with the simultaneous photodetection and self amplification of the signal. Experimental and simulated results show that the output signal has a strong nonlinear dependence on the light absorption profile. The device, modeled by a simple circuit with variable capacitors and interconnected phototransistors through a resistor, is a current-controlled device. It uses a changing capacitance to control the power delivered to the load acting as a state variable filter circuit. It combines the properties of active high-pass and low-pass filter sections into a capacitive active band-pass filter.
OPTICAL LAYERS AND MATERIALS FOR NEXT GENERATION SOLAR CELLS
Authors: Lee Ping , Shank Jason , Magsi Komal , Kang Yeona , Fortmann C.M.
Published: September 2011

Layers that enhance light scattering and Raman-scattering-based spectral modification for solar cell applications were investigated. Titanium-oxide based rear diffuse reflector were found to increase the long wavelength response of crystalline solar cells. Also particle within the Titanium-oxide produce a far greater Stokes and anti-Stokes shift when compared to bulk crystal counterparts. The anti-Stokes to Stokes shift ratio in these particle systems is also greater and increased with increasing probe or bias light intensity. When applied to solar cells these layers extend the red response and thereby increase the overall performance.
Rapid Plasma-Assisted, Ambient-Pressure Deposition of Conformal Nanocrystalline Zinc Oxide Thin Films for Solar Cell Applications
Authors: Pedersen Joachim D. , Teh Kwok Siong
Published: September 2011

This paper reports a plasma-assisted, rapid, ambient-pressure, low-temperature one-step process for depositing conformal, non-porous nanocrystalline ZnO thin film on various substrates ranging from Si (100), fused quartz, glass, muscovite, c- and a-plane sapphire (Al2O3), to the common polymer polyimide (KaptonTM). The as-synthesized polycrystalline films range in thickness from 20nm to 200nm, deposited at a growth rate ranging from 2 nm/min to 50 nm/min. The lowest deposition temperature achieved with this method is 180°C and progress is being made in further lowering this temperature. The as-deposited films are highly oriented in the caxis, with (002) being the dominant planes.
Pore-opening Process in Nanoporous AAO Membranes for Electrodeposition of Semiconducting Nanowires
Authors: Phok Sovannary , Rajaputra Suresh S. , Singh Vijay P. , Al-Thani Hamda A. , Hasoon Falah
Published: September 2011

The fabrication of nanoporous aluminum oxide (Al2O3) membranes for large scale production of nanowires is performed at room temperature by a two-step anodization of commercially available aluminum foil tapes. During the anodization process, an oxide barrier layer is formed at the interface with aluminum. In the present work, the removal of the barrier is performed by (i) ramping down the voltage with a rate in the range of 0.5 V per 60s to 2 V per 60s and (ii) immersing the substrate in 50% phosphoric acid for up to 5 minutes. Depending on the removal conditions, several morphologies at the oxide-aluminum interface are observed by Scanning Electron Microscopy (SEM). Ramping down the voltage at less than 0.3 V per 15s combined by immersion in 50% phosphoric acid for less than 3 minutes is found to open the barrier layer of the nanopores. The pores have root-like structure with branches as small as few nanometers due to the slow voltage ramping. Several amorphous anodized Al2O3 (AAO) templates with pore diameter ranging from 30 to 40 nm and with length up to 25 μm were prepared by two-step anodization for the cathodic electrodeposition of photoactive nanowire semiconductors such as copper indium diselenide and cadmium sulfide.
Structural Study of CIGS2 Thin Film Absorbers using EBSD Technique
Authors: Kaul Ashwani , Pethe Shirish A. , Dhere Neelkanth G. , Moutinho Helio R.
Published: September 2011

In this study electron backscatter diffraction (EBSD) investigation is carried out for CuIn1-xGaXS2 (CIGS2) samples that were prepared by two stage process in which the initial precursor was deposited by DC magnetron sputtering followed by sulfurization in conventional furnace. Due to high surface roughness, low quality EBSD signal was obtained in the samples that were initially polished with ion milling. Polishing with dimpler grinder followed by chemical treatment with bromine/methanol solution improved the quality of EBSD patterns. Efforts are being made to build the database for CIGS2 in the system using high quality EBSD patterns and finally to obtain grain orientation maps.
Electrospun Composite Nanofiber Transparent Conductor Layer for Solar Cells
Authors: Ritchie Justin , Mertens Joël , Yang Heejae , Servati Peyman , Ko Frank K.
Published: September 2011

Developing a durable and scalable transparent conductor (TC) as an electrode with high optical transmission and low sheet resistance is a significant opportunity for enabling next generation solar cell devices. High performance fibrous composite materials based on a carrier polymer with embedded functional nanostructures have the potential to serve as a TC with high surface area that can be deposited by the novel and scalable process of electrospinning. This work presents the development of a fibrous TC, where polyacrylonitrile (PAN) is used as a carrier polymer for multi-walled carbon nanotubes (MWCNT) to create electroactive nanofibers 200-500nm in diameter. Once carbonized, thin layers of this material have a low sheet resistance and high optical transmission. It is shown that in a two stage carbonization process, the second stage temperature of above 700C is the primary factor in establishing a highly conductive material and single layers of nanofibers are typically destabilized at high temperatures. A high performance TC has been developed through optimizing carbonization rates and temperatures to allow for single nanofiber layers fabricated by electrospinning MWCNT/PAN solutions onto quartz. These TCs have been optimized for concentrations of MWCNTs less than 20% volume fraction with well above 90% transmissivity and sheet resistances of between .5-1kohm/square. The required MWCNT loading is well below that for TCs based on random networks of MWCNTs.
Comparative Study on Manufacturability of Selective Emitter and Double Printing on Mono-Si PV Cells
Authors: Liu Y. , Jiang F.D. , Wang S. , Zeng Y. , Shan W.
Published: September 2011

Selective emitter structure has long been regarded as a good and relatively simple approach to improve the energy conversion efficiency of Si wafer-based single-junction photovoltaic (PV) cells. Recently emerged double printing method, on the other hand, potentially has the capability of improving the efficiency with no requirement for device structure modification. The manufacturability of these two approaches has been studied on a mass-production platform at JA Solar recently with large scale sampling. The experimental results collected from over two hundred thousand cells demonstrated that both approaches are capable of achieving significant conversion-efficiency gain in a cost-effective way with high yield rate on the PV industry commonly used mass production platform currently adopted by the vast majority of cell manufacturers
Roll-to-Roll Front Contact Patterning by Wire Shading
Authors: Merz R. , Schubert M. B. , Werner J. H.
Published: September 2011

Wire shading during thin film deposition is a promising approach to low-cost, high volume manufacturing of flexible thin film photovoltaic modules. This contribution demonstrates successful patterning of a transparent conducting oxide layer by wire shading during dynamic web coating. Continuous sputter deposition of Al-doped ZnO on a 30 cm wide polymer foil and simultaneous wire shading form 1 cm wide and 300 cm long front contact stripes for thin film photovoltaic modules. Analysing the distribution of lateral shunt resistances after separating the initial 28 stripes into 1323 pieces, yields a patterning success of 97.3 %. Thus the technique seems well suited for flexible modules from organic solar cells.
Characterization of Thin Film CdTe photovoltaic materials deposited by high plasma density magnetron sputtering
Authors: Abbas A. , Bowers J.W. , Maniscalco B. , Moh S. , West G.D , Rowley P.N. , Upadhyaya H.M , Walls J. M.
Published: September 2011

A new magnetron sputtering strategy is introduced that utilizes high plasma density (~5mA.cm-2) to avoid or reduce high temperature processing. The technique uses magnetrons of opposing magnetic polarity to create a “closed field” in which the plasma density is enhanced without the need for high applied Voltages. A batch system has been used which employs a rotating vertical drum as the substrate carrier and a symmetrical array of linear magnetrons. The magnetrons are fitted with target materials for each of the thin films required in the photovoltaic (PV) stack including the CdTe absorber layer, CdS window layer, metal contact using the conventional superstrate configuration. The “closed field” sputtering technology allows scale up not only for larger batch system designs but it is also configurable for “in-line” or “roll to roll” formats for large scale production. The morphology of each of the layers is characterized using a variety of structural and optical techniques including Field Emission Gun SEM and X-ray diffraction (XRD).
Large-Scale Deposition of Transparent Conducting Oxides by Hollow Cathode Sputtering
Authors: Delahoy Alan E. , Jansen Kai , Robinson Chris , Varvar Anthony , Fabiano Paul , Kappera Rajesh , Guo Sheyu , Li Hongmei , Yang Shaohua
Published: September 2011

This paper reviews the status of hollow cathode sputtering as an evolving technology for production of thin-film transparent conducting oxides for PV applications. A large market segment for PV TCOs is represented by thin-film a-Si:H and tandem a-Si:H/nc-Si:H modules. For superstrate devices, textured SnO2:F produced on-line by APCVD is currently the market leader, although alternative off-line methods and materials are now emerging. In particular, zinc oxide can be produced by LPCVD, APCVD, magnetron sputtering, and hollow cathode sputtering (HCS). HCS is a stable process featuring low-cost metal targets and a soft deposition process. We discuss the deposition principles and the film results obtained using linear hollow cathodes 0.5 m and 1.0 m in length. We report the direct deposition of highly textured doped ZnO having an electron mobility in excess of 50 cm2/Vs. The production cost of textured ZnO is estimated for several competing techniques.
Comparison of Aluminum Nitride Nanowire Growth with and without Catalysts via Chemical Vapor Deposition
Authors: Teker Kasif , Oxenham Joseph A.
Published: September 2011

This paper presents a systematic investigation of AlN nanowire synthesis by chemical vapor deposition using Al and NH3 on SiO2/Si substrate and direct nitridation of mixture of Al-Al2O3 by NH3. A wide variety of catalyst materials, in both discrete nanoparticle and thin film forms, have been used (Co, Au, Ni, and Fe). The growth runs have been carried out at temperatures between 800 and 1100oC mainly under H2 as carrier gas. It was found that the most efficient catalyst in terms of nanowire formation yield was 20-nm Ni film. The AlN nanowire diameters are about 20-30 nm, about the same thickness as the Ni-film. Further studies of direct nitridation of mixture of Al-Al2O3 by NH3 have resulted in high density one-dimensional nanostructure networks at 1100oC. It was observed that catalyst-free nanostructures resulted from the direct nitridation were significantly longer than that with catalysts. The analysis of the grown nanowires has been carried out by scanning electron microscopy, transmission electron microscopy, atomic force microscopy, and x-ray diffraction.
Dependence of the Elastic Moduli of Skutterudites on Density and Temperature
Authors: Rogl G. , Puchegger S. , Zehetbauer M. , Grytsiv A. , Rogl P.
Published: September 2011

The dependency of Young’s and shear modulus on relative density and temperature was determined for three series of skutterudites: p-type MmyFe3CoSb12 (y = 0.70, 0.80), p-type DDyFe3CoSb12 (y = 0.65, 0.68) and n-type Sr0.07Ba0.07Yb0.07Co4Sb12. For all three groups of materials the dependency of Young’s modulus, E, on the density and temperature is linear: E(d) = 4.1(1)×d – 268(3) GPa (d is the relative density in %), ΔE/ΔT = 0.20(1) GPa/K, thus allowing extrapolation of E as a function of temperature and towards 100% density.
Thermoelectric Properties of Er-doped InGaN Alloys for High Temperature Applications
Authors: Aryal K. , Feng I. W. , Pantha B. N. , Li J. , Lin J. Y. , Jiang H. X.
Published: September 2011

Thermoelectric (TE) properties of erbium-silicon co-doped InxGa1-xN alloys (InxGa1-xN: Er + Si, 0≤x≤0.14), grown by metal organic chemical vapor deposition, have been investigated. It was found that doping of InGaN alloys with Er atoms of concentration, N[Er] larger than 5x1019 cm-3, has substantially reduced the thermal conductivity, κ, in low In content InGaN alloys. It was observed that κ decreases as N[Er] increases in Si co-doped In0.10Ga0.90N alloys. A room temperature ZT value of ~0.05 was obtained in In0.14Ga0.86N: Er + Si, which is much higher than that obtained in un-doped InGaN with similar In content. Since low In content InGaN is stable at high temperatures, these Er+Si co-doped InGaN alloys could be promising TE materials for high temperature applications.
Nano-Structured Materials for Next Generation Fuel Cells and Photoelectrochemical Devices
Authors: Tuller Harry L. , Engel Johanna , Litzelman Scott J. , Bishop Sean R.
Published: September 2011

Progress in achieving improved performance in the generation and utilization of hydrogen depends on our ability to identify materials with optimized electrical and (photo)- electrochemical performance. Given their high volume fraction of interfaces, high chemical stability and versatility (ionic, electronic, optical property control), nanocrystalline electroceramic materials are of growing interest for advanced energy conversion and storage technologies. As grain size decreases towards the Debye length and grain boundaries come in closer proximity, space charge properties begin to dominate, resulting in modified charge transport. Through systematic variation of grain boundary properties by heterogeneous indiffusion of cations, the electronic and ionic carrier profiles in the space charge region may be altered. The relationships between space charge potential and defect profiles in the space charge regions are quantitatively analyzed, and implications for nano-ionic materials in thin film solid oxide fuel cells are discussed. From the standpoint of photoelectrochemical water splitting for hydrogen generation, optimizing the band gap, band alignments, and transport properties while retaining stability has remained a challenging objective. Novel nanocrystalline composite structures are discussed which exhibit features amenable to optimization of required properties and electrical measurements to determine key transport properties of titanium dioxide nanopowder, a photoanode material are introduced.
Influence of Copper on the Switching Properties of Hafnium Oxide-Based Resistive Memory
Authors: Briggs B.D. , Bishop S.M. , Leedy K.D. , Butcher B. , Moore R. L. , Novak S. W. , Cady N.C.
Published: September 2011

Hafnium oxide-based resistive memory devices have been fabricated on copper bottom electrodes. The HfOx active layers in these devices were deposited by atomic layer deposition at 250 °C with tetrakis(dimethylamido)hafnium(IV) as the metal precursor and an O2 plasma as the reactant. Depth profiles of the HfOx by x-ray photoelectron spectroscopy and secondary ion mass spectroscopy revealed a copper concentration on the order of five atomic percent throughout the HfOx film. This phenomenon has not been previously reported in resistive switching literature and therefore may have gone unnoticed by other investigators. The MIM structures fabricated from the HfOx exhibited non-polar behavior, independent of the top metal electrode (Ni, Pt, Al, Au). These results are analogous to the non-polar switching behavior observed by Yang et al. [2] for intentionally Cu-doped HfOx resistive memory devices. The distinguishing characteristic of the material structure produced in this research is that the copper concentration increases to 60 % in a conducting surface copper oxide layer ~20 nm thick. Lastly, the results from both sweep- and pulse-mode current-voltage measurements are presented and preliminary work on fabricating sub-100 nm devices is summarized.
Red-emitting Ca1-xSrxS:Eu2+ Phosphors as Light Converters for Plant-growth Applications
Authors: Xia Qi , Batentschuk Miroslaw , Osvet Andres , Richter Peter , Häder Donat P. , Schneider Jürgen , Wondraczek Lothar , Winnacker Albrecht , Brabec Christoph J.
Published: September 2011

A series of Ca1-xSrxS:Eu2+y mol% phosphors were synthesized with solid state reactions and with various Ca/Sr ratio and Eu2+ doping concentrations. The influences of the lattice composition and the Eu2+ doping level on photoluminescent properties were analyzed. With doping concentrations between 0.1 to 3 mol%, concentration quenching takes place leading to the decrease of luminance; the emission maxima are also red-shifted. Further, this work reports enhanced photosynthetic activities of intact spinach leaves due to spectral modification of simulated solar irradiation by one synthesized phosphor (Ca0.4Sr0.6S:Eu1 mol%). The CO2 assimilation rates of intact spinach leaves were monitored with an effective homemade photosynthesis measurement system with controlled light conditions. The phosphor could efficiently convert the photosynthetically less active green part of the solar spectrum into the red, with a broad-band red emission centered at 650 nm and a halfband-width of 68 nm, giving an excellent match with the absorption spectrum of spinach chloroplasts. By careful referencing the photon flux, we found an enhanced photosynthetic activities by about 30 % due to the emission of the phosphor.
Single-Molecule Rapid Imaging of Linear Genomes in Nanochannel Array
Authors: Austin M. D. , Deshpande P. , Requa M. , Kunkel M. , Sadowski H. , Bozinov D. , Sibert J. , Gallagher S. , Stedman W. , Fernandes N. , Thomas A. , Das S. , Hastie A. , Finklestein J. , Marlin A. , Xiao M. , Cao H.
Published: September 2011

Human genomic structural variation (SV) is significant factor in genome complexity, and thus has substantial implications to the cause, development and progression of genetic diseases. These SVs, ranging in size of 1kbp-1Mbp, are challenging to assess with current technologies. As such, we have developed a commercial system (nanoAnalyzer® 1000) for the rapid linear analysis of genomes at single-molecule level.

The core of our system is a nanofluidic chip consisting of an array of channels with a diameter less than 100 nm, nanofabricated on the surface of a silicon substrate. Thousands of unamplified genomic DNA molecules of 100’s kbps to several Mbps can be isolated and linearly streamed into the array for analysis in a parallel fashion. Fluorescently labeled sequence-specific signatures can then be identified and aligned to reference patterns at high resolution with custom software. This automated, multi-color imaging platform will enable a wide range of applications, such as accurate sequencing assembly, discovering genome structural variations, and uncovering epigenomic content. Nanochannel arrays promise to substantially lower the barriers of entry for single-molecule DNA analysis for scientists and clinicians, greatly impacting the advancement of molecular diagnostics, personalized medicine, and biomedical research.
The Invariance of Electrowetting Contact Angle Saturation to Polymer, Fluid, and Interfacial Materials Properties
Authors: Chevalliot Stéphanie , Heikenfeld Jason
Published: September 2011

The electrowetting equation predicts contact angle modulation to zero degrees as voltage is continually increased. However, in practice contact angle appears to saturate around 60 to 70°. Although several hypotheses have been advanced to explain the physical mechanisms of contact angle saturation, none satisfactorily and unequivocally holds for the large body of electrowetting data. Herein we experimentally demonstrate that under DC voltage electrowetting contact angle saturation is invariant to polymer, fluid, and interfacial materials properties. We furthermore reveal that saturation is also a time-dependant phenomenon.
Single-Carrier Devices for the Understanding of the Voltage Drift in Organic Light Emitting Diodes
Authors: Boizot J. , Gohri V. , Doyeux H.
Published: September 2011

The aim of this study is to analyze and mitigate the voltage drift phenomenon observed in top-emitting organic light emitting diodes (OLED) when driven at constant current. An operating device may experience voltage increase over time due to factors such as interface or bulk material degradation, charge accumulation and formation of trap states. Single-carrier devices were fabricated to understand the contribution to voltage drift from each of these causes. Doping in electron injection layer (4, 7-diphenyl-1,10-phenanthroline or Bphen) and hole injection layer (2,2’,7,7’-tetra(N,N-di-tolyl)amino-spiro-bifluorene or Spiro-TTB) were optimized to obtain ohmic injection contacts. Devices with tris(8-hydroxy-quinoline) aluminium (Alq3) degrade significantly with holes injection and undergo high voltage increase in lifetime test measurements. On the contrary, devices with N,N’-di(naphtalen-1-y1)-N,N’-diphenyl-benzidine (NPB) exhibit an ambipolar charge transport behavior and low voltage drift under both hole and electron injection.
Hybrid gold nanofinger SERS structure for sensing applications
Authors: Kim Ansoon , Li Zhiyong
Published: September 2011

We 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

Fabrication 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

Single 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.