bluuebunny/crossref_metadata_2025 huggingface dataset:
Structural, Optical and Electrical Properties of InGaN Sputtered Thin Films
Authors: Ebdah Mohammad Ahmad , Hoy Daniel R. , Kordesch Martin E.
Published: August 2010

InGaN films were successfully fabricated using radio frequency (RF) magnetron sputtering technique with a sputtering target of pure In and Ga metal alloys under a flow of nitrogen. Films were deposited on quartz substrates, with the ratio of In to Ga varied from 0.46 to 0.85 in the alloys. The structures and compositions have been studied using X-ray diffraction (XRD) and energy dispersive x-ray spectroscopy (EDX), respectively. Multiple crystallographic phases have been observed indicating phase segregation and inhomogeneous distribution of the metal compositions in the films. The existence of wurtzite structures has been observed in all samples, with the In percentage (y) in a crystalline phase calculated from the XRD being less than the total In percentage (x) in each film as determined by the EDX spectroscopy. The (0002) orientation has been observed in all films, and the (10-11) orientation has been observed for x = 0.46 and 0.70 only. The optical transmission and absorbance of the films were studied by the spectrophotometry technique, which indicate that the dominant phases in all samples are amorphous. Consequently, the corresponding optical bandgaps have been characterized. Hall Effect measurements were made in 0.55 T magnetic field at room temperature to characterize the electrical conductivity, free carrier concentration, and mobility.
High-temperature Fiber Matrix Composites for Reduction of Radiation Heat Transfer
Authors: Shklover Valery , Braginsky Leonid , Mishrikey Matthew , Hafner Christian
Published: August 2010

Recent progress in fabrication technology allows for the efficient control of electromagnetic waves by means of photonic devices. This could be attractive and promising also for high-temperature photonic structures to control electromagnetic heat transfer at temperatures above 1000 oC. We discuss the literature and present our own results on Fiber Matrix Composites (FMC), which could be superior to high-temperature metals or monolithic ceramics and can be designed for photonic applications. Possible applications include the protection of non-rotating components in high-temperature engines and turbines such as combustors and liners, coatings and parts for aerospace vehicles. Our discussion includes the material aspect and some relevant structure features. The use of woven fabrics to design new photonic band gap structures is discussed. An example of the use of the plane-wave expansion method for FMC design is given.
Chemically and Electrochemically Deposited Thin Films of Tin Sulfide for Photovoltaic Structures
Authors: Mathews Nini Rose
Published: August 2010

Thin films of tin sulfide (SnS) were deposited on TCO-coated glass substrates by pulse electrodeposition. Cyclic voltammetry showed that SnS deposition occurs in the -0.8 V to −1 V range. The films deposited using the potential pulses of -0.95V (Von) and +0.1V (Voff) are of orthorhombic crystal structure with lattice parameters and grain size similar to those of the thin films of orthorhombic structure obtained by chemical deposition. The optical band gap of the films was 1.3 eV. In CdS/SnS heterojunctions an open circuit voltage110 mV, short circuit current density 0.72 mA/cm2 and fill factor of 0.32 are reported here.
RF Sputter Deposition of Indium Oxide / Indium Iron Oxide Thin Films for Photoelectrochemical Hydrogen Production
Authors: Ingler William B , Naseem Abbasali
Published: August 2010

This project focuses on using indium oxide and indium iron oxide as an alloy to make a protective thin film (transparent, conductive, and corrosion resistant or TCCR) for amorphous silicon based solar cells, which are used in immersion-type photoelectrochemical cells for hydrogen production. From the work completed, the results indicate that samples made at 250 °C with 30 Watt of indium and 100 Watt of indium iron oxide, and a sputter deposition time of ninety minutes produced optimal results when deposited directly on single junction amorphous silicon solar cells. At 0.65 Volts, the best sample displays a maximum current density of 21.4 mA/cm2.
Effective Excitation of Superfocusing Surface Plasmons using Phase Controlled Waveguide Modes
Authors: Yamamoto Kazuhiro , Kurihara Kazuyoshi , Takahara Junichi , Otomo Akira
Published: August 2010

We propose more practical method to realize the superfocusing modes based on waveguide structures, and present a numerical analysis these structures using the finite-difference time-domain (FDTD) simulations. For metallic wedged structure coupled to dielectric waveguides, we investigate a method of controlling superfocusing by changing the phase of waveguide modes.
UV Raman Spectroscopy Study of Strain Induced by Buried Silicon Nitride Layer in the BOX of Silicon On Insulator Substrates
Authors: Paillard Vincent , Groenen Jesse , Puech Pascal , Lamrani Younes , Kostrzewa Marek , Widiez Julie , Barbé Jean-Charles , Deguet Chrystel , Clavelier Laurent , Ghyselen Bruno
Published: August 2010

Compressive strained Silicon from a Silicon on Insulator (SOI) substrate is obtained by replacing the buried oxide layer by a strained silicon nitride layer. The silicon overlayer and the buried dielectric are etched down to the substrate to form narrow wires (down to 300 nm wide). The Si overlayer is then expected to acquire compressive strain thanks to the relaxation of the SiN layer. The goal is to obtain a high uniaxial stress perpendicular to the wires. The structures and the strain are modeled using finite element simulations. The strain elements are used to calculate Raman spectra. Theoretical results are compared to experimental profiles deduced from resonant (UV) micro Raman experiments.
Measuring the glass-transition temperature in electrospun polyvinyl alcohol fibers using AFM nanomechanical bending tests
Authors: Wang Wei , Barber Asa H.
Published: August 2010

The glass transition of individual electrospun PVA fibers was found using an AFM fiber bending technique within a heated chamber. A considerably loss in the measured elastic modulus was observed with temperature when the glass transition temperature was reached. The glass transition temperature was observed to decrease as the electrospun PVA fiber diameter decreased, indicating diameter dependent enhanced polymer chain mobility.
Mechanical Principles of a Self-Similar Hierarchical Structure
Authors: Gao Huajian
Published: August 2010

Natural materials such as bone, shell, tendon and the attachment system of gecko exhibit multi-scale hierarchical structures. Here we summarize some recent studies on an idealized self-similar hierarchical model of bone and bone-like materials, and discuss mechanical principles of self-similar hierarchy, in particular to show how the characteristic length, aspect ratio and density at each hierarchical level can be selected to achieve flaw tolerance and superior stiffness and toughness across scale.
Tel.: (401) 863-2626; Email address:
Architectured Structural Materials: A Parallel Between Nature and Engineering
Authors: Dunlop John W.C. , Brechet Yves J.M.
Published: August 2010

Nature builds materials like an architect to obtain a variety of properties with a limited number of building blocks. In contrast, engineers have access to a wide range of constituent materials to fulfil a variety of requirements. The classical degrees of freedom for controlling the properties of man-made materials are the microstructure, or the macroscopic shape. Only recently, the architecture at the millimetre scale was perceived as an efficient way of expanding the range of properties offered by bulk materials. The aim of this paper is to compare the different strategies and to outline some observations on natural materials which may serve as inspiration to develop engineering architectured materials.
Channel Strain Analysis in Damascene-gate pMOSFETs on Si (100) and (110) Substrate by Conventional and Cross-sectional Raman Spectroscopy
Authors: Takei Munehisa , Kosemura Daisuke , Nagata Kohki , Akamatsu Hiroaki , Mayuzumi Satoru , Yamakawa Shinya , Wakabayashi Hitoshi , Ogura Atsushi
Published: August 2010

Channel strain in damascene gate pMOSFETs with compressive stress liner (c-SL) and embedded SiGe (eSiGe) were studied by micro-Raman spectroscopy with a quasi-line-shape UV excitation (λ=363.8nm). The channel strain profiles were obtained by the conventional mea-surement from the surface after dummy gate removal. The compressive strains at the channel edges were larger than that at the channel center for the relatively long gate length (Lgate). As the Lgate became smaller, although it became hard to recognize the strain profile, the compres-sive strain at the channel center increased by the superposition of the strain at the channel edges. However, channel strain disappeared in the measurement data for the channel length less than 160 nm. Thus, we extended the laser exposure time from 10 to 40 minutes to extract the channel strain component from obtained Raman spectra. The Raman peaks consisted of two or three peaks for the Lgate less than 160 nm. By multi peak fitting, we have succeeded in measuring the extremely large stress of - 2.4 GPa in the channel of Lgate = 30 nm pMOSFET. We also per-formed the cross-sectional measurements for the samples before and after metal-gate/high-k gate stack formation. Channel strain profiles were obtained similar to those by the conventional mea-surement. Extremely high device performance can be clearly explained by the compressive stress derived from the Raman measurements both in the Lgate dependence and eSiGe effect. We also demonstrated that Raman spectroscopy using cross-sectional measurement can evaluate the channel strain even in the MOSFETs after gate stack formation.
Relationships between Interface Structures and Electrical Properties in the High-k/III–V System
Authors: Yasuda Tetsuji , Miyata Noriyuki , Urabe Yuji , Ishii Hiroyuki , Itatani Taro , Takagi Hideki , Yamada Hisashi , Fukuhara Noboru , Hata Masahiko , Ohtake Akihiro , Yokoyama Masafumi , Hoshii Takuya , Haimoto Takashi , Deura Momoko , Sugiyama Masakazu , Takenaka Mitsuru , Takagi Shinichi
Published: August 2010

Integration of the III–V channel MISFETs on the Si platform is a potential solution to realize performance improvement and power reduction in the sub-22 nm node and beyond. To take advantage of the high electron mobility of III-Vs, the MIS interfaces of high integrity should be developed. This paper reports how the MIS characteristics vary in response to the changes in the interface composition and structures, and discusses the physics and chemistry behind these observations. We fabricated a wide variety of the high-k/III–V interface structures by employing the state-of-the-art technologies of the epitaxial wafers by MOCVD, surface reconstruction control in the MBE environment, wet/dry surface treatments optimized by utilizing XPS/AES analyses, and deposition of quality dielectrics (Al2O3, HfO2) by ALD and EB evaporation. The MIS characteristics were evaluated in the capacitor and FET structures. The talk will include the following topics: the effects of the cation composition (Al, Ga, In) of the III-V bulk on the MIS characteristics [1], the importance of the anion control (N, S) at the interface to improve the MIS characteristics, and the surface orientation ((100) vs. (111)) as a new parameter in the III-V MIS device design [1]. This work was carried out in the Nanoelectronics Project supported by NEDO/METI. [1] T. Yasuda et al., as discussed at 39th IEEE SISC (San Diego, Dec. 2008).
Stretchable Silicon Electronics and Their Integration with Rubber, Plastic, Paper, Vinyl, Leather and Fabric Substrates
Authors: Kim Dae-Hyeong , Kim Yun-Soung , Liu Zhuangjian , Song Jizhou , Kim Hoon-Sik , Huang Yonggang , Rogers John
Published: August 2010

Electronic systems that offer elastic mechanical responses to high strain deformations are of growing interest, due to their ability to enable new electrical, optical and biomedical devices and other applications whose requirements are impossible to satisfy with conventional wafer-based technologies or even with those that offer simple bendability. This talk describes materials and mechanical design strategies for classes of electronic circuits that offer extremely high flexibility and stretchability over large area, enabling them to accommodate even demanding deformation modes, such as twisting and linear stretching to ‘rubber-band’ levels of strain over 100%. The use of printed single crystalline silicon nanomaterials for the semiconductor provides performance in flexible and stretchable complementary metal-oxide-semiconductor (CMOS) integrated circuits approaching that of conventional devices with comparable feature sizes formed on silicon wafers. Comprehensive theoretical studies of the mechanics reveal the way in which the structural designs enable these extreme mechanical properties without fracturing the intrinsically brittle active materials or even inducing significant changes in their electrical properties. The results, as demonstrated through electrical measurements of arrays of transistors, CMOS inverters, ring oscillators and differential amplifiers, suggest a valuable route to high performance stretchable electronics that can be integrated with nearly arbitrary substrates. We show examples ranging from plastic and rubber, to vinyl, leather and paper, with capability for large area coverage.
Hybrid Inorganic/Organic Self-Assembled Clays Nanocomposites for Roll to Roll Fabrication in Photovoltaics
Authors: Kariuki Peter Njagwa , Gendron Jessica , Madl Christopher Matthew , Chiguma Jasper , Hagerman Michael E , Borgesen Peter , Jones Wayne E
Published: August 2010

We have been developing a new approach to layered hybrid (inorganic/organic) photovoltaic materials for fabrication by Roll-to-Roll (R2R) manufacturing. In this report, we combine the low cost and processability of organic electrically conducting polymers with the efficiency of dye sensitized titanium dioxide, semi-conductor quantum dots (CdSe) self-assembled on layered clay materials (Laponite) onto indium tin oxide coated flexible substrate polyethylene terephthalate (PET) substrates. We have shown electron transfer, guest-guest and host-guest interactions, charge separation, spectral line broadening, and quenching of fluorescence signals which indicate electronic coupling of the dye [Ru(bpy)3]2+ on a CdSe nanocrystal and titanium dioxide nanoparticles. Scanning electron microscopy and atomic force microscopy demonstrate successful nanoparticle formation and thin film self-assembly, as well as surface morphology and polymer thickness.
Light Effective Mass in the Widely-Dispersed Valence Band of Single Crystalline Rubrene Observed by High-Resolution Angle-Resolved Ultraviolet Photoelectron Spectroscopy
Authors: Nakayama Yasuo , Machida Shin-ichi , Duhm Steffen , Xin Qian , Funakoshi Akihiro , Ogawa Naoki , Kera Satoshi , Ueno Nobuo , Noguchi Yutaka , Ishii Hisao
Published: August 2010

High-resolution angle resolved ultraviolet photoelectron spectroscopy measurements were conducted on rubrene single crystals successfully through relief of the sample charging assisted by a laser illumination. Significant dispersion of the valence band was clearly resolved. The band width W and the hole effective mass mh* were estimated to be 0.4 eV and 0.7m0, respectively, along the most conductive direction. The present results strongly suggest that the transport nature in rubrene single crystals should be described in the band transport framework of a delocalized charge carrier.
Effects of LSCO Buffer Layer on the Microstructure and Dielectric Properties of Ba0.6Sr0.4TiO3 Films Prepared by Sol-gel Methods
Authors: Han Songwei , Yu Shengwen , Cheng Jinrong
Published: August 2010

In this work, Ba0.6Sr0.4TiO3(BST) thin films were deposited on Ti substrates using conductive La0.5Sr0.5CoO3 (LCSO) as buffer layers. Both BST and LSCO films were prepared by sol-gel methods. The structure and morphology of BST and LSCO films were analyzed by X-ray diffraction (XRD). XRD results show that both BST and LSCO films have perovskite structure with random orientation. The dielectric properties of BST films were dependent on the thickness of LSCO buffer layers. Upon using LSCO buffer layers, the dielectric properties of BST films were significantly improved. The dielectric constant, tunability, and dielectric loss of BST thin films for LSCO of 150 nm achieved about 453, 0.032 and 31.26% respectively.
Investigation of the Pb Depletion in Single and Dual Pulsed Laser Deposited Epitaxial PZT Thin Films and Their Structural Characterization
Authors: Mukherjee Devajyoti , Hyde Robert H , Dhakal Tara , Srikanth Hariharan , Mukherjee Pritish , Witanachchi Sarath
Published: August 2010

We have investigated the Pb depletion in laser ablated PZT (PbZr0.52Ti0.48O3) films through a systematic study of PZT target-laser interactions for both single laser and dual-laser ablation methods. The study includes films deposited from a stoichiometric and an excess PbO PZT targets. The films were deposited on single crystal SrTiO3[100] substrates at 550˚C with a background oxygen pressure of 500 mT. Single laser deposited films at a laser fluence of 5J/cm2 produced the highest Pb content while dual-laser ablated films where an excimer and a CO2 pulsed lasers were synchronized for ablation produced high Pb content for an excimer laser fluence of less than 2J/cm2. This enabled the growth of particulate-free PZT films with high Pb content. ICCD imaging of the plasma plumes showed variations in the expansion profiles at different laser fluencies that correlated well with the Pb content observed in the deposited films.
Enhancement in Ferroelectricity in V-Doped ZnO Thin Film Grown using Laser Ablation
Authors: Dhakal Tara , Mukherjee Devajyoti , Hyde Robert H , Srikanth Hariharan , Mukherjee Pritish , Witanachchi Sarath
Published: August 2010

We report evidence of enhancement in ferroelectricity in thin films of vanadium (V) doped ZnO grown at higher oxygen pressure. This process reduces oxygen deficiency and the material becomes very insulating, which in turn lowers the leakage current through the ferroelectric capacitor. 2 at. % V doped ZnO films, with thickness of approximately 1 μm were grown epitaxially on c-cut sapphire (Al2O3) (0001) at a growth temperature of 600°C. X-ray analysis showed the layers to be epitaxial where the (0002) diffraction peak had a rocking curve FWHM below 1°. The films with higher oxygen pressure were more insulating than the one grown with lower oxygen pressure. The saturation polarization doubled when the growth pressure increased from 300 mT to 500 mT. Time gated ICCD imaging of the ablated plasma during various O2 pressures and how it translated to the film quality are presented.
Low Temperature Fabrication of Sol-Gel Derived Dielectric (Ba,Sr)TiO3 Thin Films
Authors: Sakurai Hideaki , Watanabe Toshiaki , Soyama Nobuyuki
Published: August 2010

We studied the nucleation and crystallization of sol-gel derived (Ba0.7Sr0.3)TiO3 [BST(70/30)] thin films at low temperatures between 500 to 600°C on Pt(111)/TiO2/SiO2/Si substrates by a process using a combination of 2-ethyl-hexanoate based solutions and modified film preparation. We found that BST films could be crystallized at 500°C and that the films obtained had a columnar-like grainy microstructure with favorable electrical characteristic such as high relative permittivity (ɛr) of 310 at 10 kHz and high tunability of 51% at a bias electric field of 250 kV/cm. Moreover, we investigated annealing temperature dependence of BST(70/30) thin films. The results indicated er and tunability increased with annealing temperature up to 450 and 58%, respectively.
Towards a High Quality Factor DC Electric Field Switchable Barium Strontium Titanate Solidly Mounted Resonator
Authors: Saddik George N. , Son Junwoo , Stemmer Susanne , York Robert A.
Published: August 2010

Barium strontium titanate solidly mounted resonators (SMR) were fabricated with three different acoustic Bragg reflectors (ABR) on a sapphire substrate. The three devices had ABR structures consisting of W/SiO2/W/SiO2, Mo/SiO2/Mo/SiO2, and Pt/SiO2/Pt/SiO2respectively. The s-parameters of all three devices were measured. The results showed that the quality factor increased as a function of the material in the ABR structure. The quality factor for the devices with tungsten, molybdenum and platinum in the ABR structures are 101, 88, and 31, respectively. This investigation showed how the material in the ABR structure can contribute to the acoustic loss in the device.
Field-induced phase transition and its impact on the magnetoelectric effect in P(VDF-HFP)/Metglas laminates
Authors: Lu David Sheng-Guo , Zhou Xin , Fang Zhao , Zhang Qiming
Published: August 2010

The field-induced phase transition driven by electric field was observed in poly(vinylidene fluoride – hexafluoropropylene) (P(VDF-HFP)) 90/10 wt% copolymers. Experimental results indicated that the electric field may remarkably affect the remanent polarization in terms of changing the D-E loop forms from double loops to single loop, starting from 68 MV/m, and completing at 216 MV/m. It was found that the remanent polarization as well as the piezoelectric constant d31 had a linear relationship with the poling electric field in above electric field range. Thus the magnetoelectric (ME) coupling coefficient ME in P(VDF-HFP)/Metglas laminates increased with the poling electric field. Moreover, the cyclic poled ME device demonstrated different peak d.c. magnetic bias field HDC on the ME - HDC curves from conventional room temperature poled ones. The peak ME coefficient obtained was 4 V/cm Oe.
Finite-Electric Field Study of Pressure Effects on Polarization Rotation in PbTiO3
Authors: Ganesh Panchapakesan , Cohen Ronald
Published: August 2010

We perform first-principles finite-electric field simulations of PbTiO3 both at zero and high pressures to investigate the effect of pressure on polarization rotation. We find that whereas a large electric field is required at zero pressure to induce a phase transition from the tetragonal (P4mm) phase to the rhombohedral (R3m) phase, at 8GPa a relatively small electric field is required indicating the greater ease of polarization rotation at high pressure. Pressure reduces the relative well depth between the two phases leading to a softer free-energy surface. This explains the increased electro-mechanical coupling obtained in PbTiO3 with pressure.
Finite-temperature Anisotropic Elastic Properties of Ni-Mn-In Magnetic Shape Memory Alloy
Authors: Williams Kristen Smith , Cagin Tahir
Published: August 2010

Designing magnetic shape memory materials with practicable engineering applications requires a thorough understanding of their electronic, magnetic, and mechanical properties. Experimental and computational studies on such materials provide differing perspectives on the same problems, with theoretical approaches offering fundamental insight into complex experimental phenomena. Many recent computational approaches have focused on first-principles calculations, all of which have been successful in reproducing ground-state structures and properties such as lattice parameters, magnetic moments, electronic density of states, and phonon dispersion curves. With all of these successes, however, such methods fail to include the effects of finite temperatures, effects which are critical in understanding how these properties couple to the experimentally-observed martensitic transformation. To this end, we apply the quasi-harmonic theory of lattice dynamics to predict the finite-temperature mechanical properties of Ni-Mn-In magnetic shape memory alloy. We employ first-principles calculations in which we include vibrational contributions to the free energy. By constructing a free energy surface in volume/temperature space, we are able to evaluate key thermodynamic properties such as entropy, enthalpy, and specific heat. We further report the elastic constants for the austenite and martensite phases and evaluate their role as a driving force for martensitic transformation.
Hydrogen Passivation of Defects in Crystalline Silicon Solar Cells
Authors: Stavola Michael , Jiang Fan , Kleekajai Suppawan , Wen Lanlin , Peng Chao , Yelundur Vijay , Rohatgi Ajeet , Hahn Giso , Carnel Lode , Kalejs Juris
Published: August 2010

Hydrogen is commonly introduced into silicon solar cells to reduce the deleterious effects of defects and to increase cell efficiency. We have developed strategies by which hydrogen in silicon can be detected by IR spectroscopy with high sensitivity. The introduction of hydrogen into Si by the post-deposition annealing of a hydrogen-rich, SiNx coating has been investigated to determine hydrogen's concentration and penetration depth. Different hydrogenation processes were studied so that their effectiveness for the passivation of bulk defects could be compared. The best conditions investigated in our experiments yielded a hydrogen concentration near 1015 cm-3 and a diffusion depth consistent with the diffusivity of H found by Van Wieringen and Warmoltz.
Incorporation of Na in Low-Temperature Deposition of CIGS Flexible Solar Cells
Authors: Zachmann Hendrik , Puttnins Stefan , Daume Felix , Rahm Andreas , Otte Karsten , Caballero Raquel , Kaufmann Christian A. , Eisenbarth Tobias , Schock H.W.
Published: August 2010

Different methods for Na incorporation are known for the use of Na-free substrates like stainless steel or polyimide foil. In this work Cu(In,Ga)Se2 (CIGS) absorber layers with different amounts of Na are investigated. The CIGS samples were prepared via a roll-to-roll deposition process with ion beam assistance (Solarion) and by a multi-stage low temperature co-evaporation process (HZB). Na was either incorporated via in-situ co-evaporation of NaF (for roll-to-roll deposition) or by a Na-containing precursor (for multi-stage deposition).
With increasing amounts of Na an increase of VOC is observed for both deposition tech-niques. In contrast, within the deposition parameters used, jSC decreases with increasing Na amount for co-evaporation of NaF while it seems unaffected when using a NaF precursor layer. The elemental depth profiles of the different CIGS thin films were studied via secondary ion mass spectroscopy and were found to depend strongly on the deposition technique.
It seems that beneficial effects of the addition of Na are independent of the method of in-corporation, even if the distribution of Na in the CIGS layer is different due to different methods of incorporation and CIGS deposition processes.
High Efficiency Copper Indium Gallium DiSelenide (CIGS) by High Power Impulse Magnetron Sputtering (HIPIMS): A Promising and Scalable Application in Thin-film Photovoltaics
Authors: Halbe Ankush , Johnson Paul , Jackson Shen , Weiss Robert , Avachat Upendra , Welsh Alex , Ehiasarian Arutiun P.
Published: August 2010

A novel method to deposit Copper Indium Gallium Diselenide (CIGS) using High Power Impulse Magnetron Sputtering (HIPIMS) was demonstrated and compared to the existing DC magnetron sputtering process. The metal-ion assisted thin-film growth inherent to a HIPIMS deposition process was used to advantage in depositing CIGS films. The HIPIMS plasma was characterized by measuring ion currents on a Langmuir probe placed into the plasma sufficiently close to the substrate. The high density plasma consisting of both metal and metal ions resulted in CIGS thin-film solar cells of superior conversion efficiencies (˜13%) as compared to conventional DC magnetron sputtering (˜10%). The efficiency enhancement was attributed to the improvement in the shunt resistance of the solar cell which corresponds to the increase in the density of the CIGS layer. Furthermore, it was also possible to grow large grained CIGS (˜1 micron) with high mobility metal-ions from the HIPIMS process.
The scalability potential of the HIPIMS CIGS process was also demonstrated by running a 1.5 m long Copper-Indium-Gallium rotatable in a selenium environment using a HIPIMS power supply. The cylindrical magnetron was run at an average power of 7.8 KW and peak powers of as much as 300 KW with controlled arcing. The existence of a HIPIMS plasma was confirmed by the ion currents on the Langmuir probe and the metal signals from a Plasma Emission Monitor (PEM).
Intrinsic Degradation in Alq3-Based OLEDs Probed by Deep-Level Optical Spectroscopy
Authors: Nakano Yoshitaka
Published: August 2010

We have successfully investigated degradation-induced variations in electronic band-gap states in the emissive region of the Alq3-based OLEDs by a deep-level optical spectroscopy technique. Through the intrinsic degradation, both deep-level traps and near-band-edge transitions in the Alq3 emissive zone are found to be red-shifted significantly towards their corresponding bulk levels of the Alq3 single layer. These variations in the interfacial electronic states are probably induced by the intrinsic degradation and indicate that initial molecular structures characteristic of the Alq3 emissive zone are transformed into the bulk-like relaxed ones through the degradation.
Direct Study of the Thermal Conductivity in Aluminum Nanowires
Authors: Stojanovic Nenad , Maithripala D.H.S. , Berg Jordan M. , Holtz Mark
Published: August 2010

Thermal conductivity and electrical resistivity of 1 μm long aluminum nanowires, 75, 100, and 150nm in width and 100nm thick, were measured at room temperature. The method consists of microfabricated electrothermal test devices and a model-based data processing approach using finite-element analysis (FEA). The electrical and thermal properties of the nanowires differ significantly from bulk values while electrical resistivity agrees well with theoretical prediction. Electron transport equation models, which adequately describe the resistivity data, consistently underestimate the thermal conductivity. Incorporating a phonon contribution of ˜ 21 W/m·K to the total thermal conductivity is found to accurately describe the measured values.
Temperature Dependence of Nanoscale Friction Investigated with Thermal AFM Probes
Authors: Greiner Christian , Felts Jonathan R. , Dai Zhenting , King William P. , Carpick Robert W.
Published: August 2010

Measurements of nanoscale friction between silicon AFM tips featuring an in-situ solid state heater and silicon substrates (both with native oxide) were performed. The temperature of the heater was varied between room temperature and approximately 650 °C. For these temperatures and the silicon substrate, the temperatures at the point of contact are estimated to range from room temperature to approximately 120±20 °C. Experiments were carried out in ambient atmosphere (˜30% relative humidity) and under dry nitrogen. Tests under constant load revealed that in the presence of ambient, friction increased with heater temperature whereas it did not change in dry nitrogen. For experiments carried out for different tip velocities (40 to 7800 nm/s), friction decreased with velocity in ambient and did not change in dry nitrogen. Both trends can be explained by thermally-assisted formation of capillary bridges between tip and substrate and the kinetics of capillary condensation under ambient conditions.
Ultrafast Defect Manipulation with Optical Anisotropy in Fused Silica
Authors: Shimotsuma Yasuhiko , Sakakura Masaaki , Kazansky Peter G. , Miura Kiyotaka , Hirao Kazuyuki
Published: August 2010

We report the evidence that the oxygen defects induced by focusing an intense infrared femtosecond laser pulse in fused silica can be self-organized by the interference pattern between photon and electron plasma wave. Self-organized nanostructure with a sub-wavelength modulation in refractive index exhibits form birefringence which is rewritable and directionally-controllable. Intriguingly, such optical anisotropy, which indicates a remarkable non-reciprocity, has initially evolved from residual birefringence originated from internal stress distribution due to local heating followed by structural change, regardless of interpulse time. This anisotropic light-matter interaction could be interpreted in terms of an asymmetric relation between light polarization and pulse front tilt. Apart from fundamental understanding of self-organization mechanism, the direction of encoded birefringence can introduce an entirely new concept for rewritable optical storage beyond the diffraction limit of light.
Osteoconductive HAp and TiO2Coatings on Titanium using Hydro-process
Authors: Yamamoto Dai , Kuroda Kensuke , Ichino Ryoichi , Okido Masazumi
Published: August 2010

Hydroxyapatite (Ca10(PO4)6(OH)2, HAp) and titanium dioxide (TiO2, titania) are of interest for bone-interfacing implant applications, because of their demonstrated osteoconductive properties. They were coated on the titanium implants using hydro-processes and investigated thein vivoperformance. HAp coatings were formed on cp-titanium plates or rods by the thermal substrate method in an aqueous solution included 0.3 mM Ca(H2PO4)2and 0.7 mM CaCl2. In the formation of carbonate apatite coating, CaHCO3was added to the solution, and in HAp/gelatin and HAp/collagen composite coatings, acid-soluble collagen (Type I) was added. The coating experiments were conducted at 313-433 K and pH = 8 for 15 or 30 min. Titania films were formed on the titanium implants by anodizing at < 100 V in 0.1 M H2SO4, H3PO4, and NaOH aqueous solutions at 298 K. The properties for the coated samples were studied using XRD, EDX, FT-IR, and SEM. And the surface roughness of titania coatings was measured. In in vivo evaluations, the coated rod specimens were implanted in rats femoral for 2 weeks, the osteoconduction on them was evaluated. Two weeks postimplantation, new bone formed on the coated and non-coated titanium rods in the cancellous bone and cortical bone, respectively. Bone-implant contact ratio, RB-I, which was used for the evaluation of new bone formation, was significantly depended on the compound formed on titanium implants, and also the coating processes.
Modified Nanodiamonds for Adsorption of Propidium Iodide and Aflatoxin
Authors: Gibson Natalie , Luo Tizy-Jiun Mark , Shenderova Olga , Choi Yong-Jae , Brenner Donald W
Published: August 2010

Nanodiamonds (NDs) have desirable chemical, physical and biological properties that lend them to a wide range of applications. ND’s facile surface chemistry, for example, can be used to create a high affinity for adsorbing various biological molecules. However, NDs, which are commercially available from multiple vendors, show inconsistencies with surface groups, aggregate sizes and impurity contents that may limit adsorption. We explore adsorption mechanisms of molecules to NDs in efforts to expand ND applications to drug delivery agents, bio-labels and enterosorbents. In doing so, several types of NDs and modification methods are evaluated to increase adsorption capacity and selectivity of propidium iodide and aflatoxin B1. Capacities and binding strengths of target molecules are assessed by Langmuir isotherms and transform calculations. UV-Vis spectroscopy shows our modification treatments are successful in increasing ND adsorption capacities. Additionally, cyclic voltammetry measurements, used to monitor in-situ adsorption, show electrochemical detection even after binding.
Microscale Structural Model of Alzheimer's Aβ(1-40) Amyloid Fibril: Comparative Study of 2- and 3-fold Morphologies
Authors: Paparcone Raffaella , Buehler Markus J
Published: August 2010

Amyloid fibrils aggregation is a key pathological feature of many severe degenerative disorders including Alzheimer’s disease and clinical dementia. Moreover, amyloids have been classified as intriguing molecules due to their exceptional strength, sturdiness and elasticity. However, physical models that explain the structural basis of these properties remain largely elusive, preventing the description of the link between their hierarchical structure and physical properties. Here we present an atomistic-based multiscale analysis based on computational materiomics, utilized to predict the structure of the two known polymorphous Alzheimer’s Aβ(1–40) amyloid fibers. We report an analysis of the energies, structural changes and H-bonding for varying amyloid fibril lengths, elucidating their size dependent properties. We also propose an explanation for the different stability of the two morphologies. A structural model of amyloid fibers with lengths of hundreds of nanometers at atomistic resolution is obtained. It predicts the formation of twisted amyloid microfibers in close agreement with experimental results. The approach used here provides a link between the fibril geometry, the chemical interactions and the most stable configuration, and resolves the issue of missing atomistic structures for long amyloid fibers.
Fabrication and Characterization of High Aspect Ratio Conducting Polymer Fibers
Authors: Saez Miguel A. , Montemayor Lauren , Pillai Priam Vasudevan , Hunter Ian W
Published: August 2010

Electroactive conducting polymers are currently studied for use in smart textiles that incorporate sensing, actuation, control, and data transmission. The development of intelligent garments that integrate these various functionalities over wide areas (i.e. the human body) requires the production of long, highly conductive, and mechanically robust fibers. This study focuses on the electrical, mechanical and electrochemical characterization of high aspect ratio polypyrrole fibers produced using a novel, custom-built fiber slicing instrument. In order to ensure high conductivity and mechanical robustness, the fibers are sliced from tetra-ethylammonium hexafluorophosphate-doped polypyrrole thin films electrodeposited onto a glassy carbon crucible. The computer-controlled, four-axis slicing instrument precisely cuts the film into thin, long fibers by running a sharp blade over the crucible in a continuous helical pattern. This versatile fabrication process has been used to produce free-standing fibers with square cross-sections of 2 μm × 3 μm, 20 μm × 20 μm, and 100 μm × 20 μm with lengths of 15 mm, 460 mm, and 1,200 mm, respectively. An electrochemical dynamic mechanical analyzer built in-house for nano- and microfiber testing was used to perform stress-strain and conductivity measurements in air. The fibers were found to, on average, have an elastic modulus of 1.7 GPa, yield strength of 37 MPa, ultimate tensile strength of 80 MPa, elongation at break of 49%, and an electrical conductivity of 12,700 S/m. SEM micrographs show that the fibers are free of defects and have cleanly cut edges. Preliminary measurements of the fibers’ strain-resistance relationship have resulted in gage factors suitable for strain sensing applications. Initial tests of the actuation performance of fibers in neat 1-butyl-3-methylimidazolium hexaflourophosphate have shown promising results. These monofilament fibers may be spun into yarns or braided into 2- and 3-dimensional structures for use as actuators, sensors, antennae, and electrical interconnects in smart fabrics.
Nb2O5-based solar fabrics
Authors: Le Viet Anh , Jose Rajan , Ramakrishna Seeram
Published: August 2010

Photo active fibers containing dye anchored Nb2O5 nanorods, hole conduction and electron conduction materials were synthesized by the electrospinning technique. A 1.92 cm2 piece of fabric, composed of randomly aligned nanorods, was tested as a photovoltaic device under standard illumination conditions. The solar fabric exhibited an open circuit voltage (Voc) of ˜0.67 V, a short current density (JSC) of 4.77×10-4 mA/cm2, a fill factor (FF) of ˜15%, and an overall photovoltaic conversion efficiency (η) of 4.5×10-7%. This article presents for the first time the application of Nb2O5 in solar fabric.
Chemical Transport Deposition of Purified Poly-Si Films from Metallurgical-grade Si Using Subatmospheric-pressure H2 Plasma
Authors: Yasutake Kiyoshi , Ohmi Hiromasa , Kakiuchi Hiroaki
Published: August 2010

Purified Si film is prepared directly from metallurgical-grade Si (MG-Si) by chemical transport using subatmospheric-pressure H2 plasma. The purification mechanism is based on the selective etching of Si by atomic H. Since most metals are not etched by H, this process is efficient to reduce metal impurities in Si films. It is demonstrated that the concentrations of most metal impurities (Fe, Mn, Ti, Co, Cr, Ni, etc.) in the prepared Si film are in the acceptable range for applying it to solar-grade Si (SOG-Si) material, or below the determination limit of the present measurements. On the other hand B and P atoms, which make volatile hydrogen compounds such as B2H6 and PH3, are difficult to eliminate by the present principle. From the infrared absorption measurements of the etching product produced by the reaction between H2 plasma and MG-Si, it is found that the main etching product is SiH4. Therefore, a remote-type chemical transport process is possible to produce SiH4 gas directly from MG-Si. Combining other purifying principle (such as a pyrolysis filter), this process may have an advantage to eliminate B2H6 and PH3 from the produced SiH4 gas.
A SAXS Study of Hydrogenated Nanocrystalline Silicon Thin Films
Authors: Kiriluk Kristin , Williamson Don , Bobela David , Taylor Craig , Yan Baojie , Yang Jeff , Guha Subhendu , Madan Arun , Zhu Feng
Published: August 2010

We have used small-angle x-ray scattering (SAXS) in conjunction with X-ray diffraction (XRD) to study the nanostructure of hydrogenated nanocrystalline silicon (nc-Si:H). The crystallite size in the growth direction, as deduced from XRD data, is 24 nm with a preferred [220] orientation in the growth direction of the film. Fitting the SAXS intensity shows that the scattering derives from electron density fluctuations of both voids in the amorphous phase and H-rich clusters in the film, probably at the crystallite interfaces. The SAXS results indicate ellipsoidal shaped crystallites about 6 nm in size perpendicular to the growth direction. We annealed the samples, stepwise, and then measured the SAXS and ESR. At temperatures below 350◦C, we observe an overall increase in the size of the scattering centers on annealing but only a small change in the spin density, which suggests that bond reconstruction on the crystallite surfaces takes place with high efficacy.
The Grain Size Distribution in Crystallization Processes With Anisotropic Growth Rate
Authors: Lokovic Kimberly S. , Bergmann Ralf B. , Bill Andreas
Published: August 2010

The grain size distribution allows characterizing quantitatively the microstructure at different stages of crystallization of an amorphous solid. We propose a generalization of the theory we established for spherical grains, to the case of grains with ellipsoidal shape. We discuss different anisotropic growth mechanisms of the grains in thin films. An analytical expression of the grain size distribution is obtained for the case where grains grow through a change of volume while keeping their shape invariant. The resulting normalized grain size distribution is shown to be affected by anisotropy through the time-decay of the effective growth rate.
Sub-gap Photoconductivity in Germanium-silicon Films Deposited by Low Frequency Plasma
Authors: Kosarev Andrey , Avila Francisco
Published: August 2010

(GexSi1-x:H) films are of much interest for many device applications because of narrow band gap and compatibility with films deposited by plasma. However, electronic properties of GexSi1-x:H films for high Ge content x > 0.5 have been studied less than those of Si films. In this work, we present a study of sub-gap photoconductivity (σpc) in GexSi1-x:H films for x = 1 and x = 0.97 deposited by low frequency plasma enhanced chemical vapor deposition (LF PECVD) with both various H-dilution (RH) during growth (non-doped films) and boron (B) incorporation in the films. Spectra of sub-gap photoconductivity σpc(hν) were measured in the photon energy range of hν = 0.6 to 1.8 eV. σpc(hν) spectra were normalized to constant intensity. For hν < Eg two regions in σpc(hν) can be distinguished: “A”, where σpc is related to transitions between tail and extended states, and “B”, where photoconductivity is due to defect states. σpc(hν) in ”A” region showed exponential behavior that could be described by some characteristic energy EUPC similar to Urbach energy EU in spectral dependence of optical absorption. EUPC > EU was observed in all the films studied. This together with higher relative values (i.e. normalized by the maximum value at hν = Eg) for photoconductivity comparing with those for α means that mobility-lifetime product (μτ) depends on photon energy μτ = f(hν) that was determined from α(hν)and σpc(hν). μτ(hν) increases by factor of 20 to 40 depending on the sample with reducing hν from 1.1 to 0.7 eV. In some samples, this dependence was monotonous, while in others demonstrated maxima related to both interference and density of states. Effects of both RH and boron incorporation have been found and are discussed.
Thermoelectric properties of doped and undoped mixed phase hydrogenated amorphous/nanocrystalline silicon thin films
Authors: Kakalios James , Adjallah Yves , Blackwell Charlie
Published: August 2010

The Seebeck coefficient and dark conductivity for undoped, and n-type doped thin film hydrogenated amorphous silicon (a-Si:H), and mixed-phase films with silicon nanocrystalline inclusions (a/nc-Si:H) are reported. For both undoped a-Si:H and undoped a/nc-Si:H films, the dark conductivity is enhanced by the addition of silicon nanocrystals. The thermopower of the undoped a/nc-Si:H has a lower Seebeck coefficient, and similar temperature dependence, to that observed for undoped a-Si:H. In contrast, the addition of nanoparticles in doped a/nc-Si:H thin films leads to a negative Seebeck coefficient (consistent with n-type doping) with a positive temperature dependence, that is, the Seebeck coefficient becomes larger at higher temperatures. The temperature dependence of the thermopower of the doped a/nc-Si:H is similar to that observed in unhydrogenated a-Si grown by sputtering or following high-temperature annealing of a-Si:H, suggesting that charge transport may occur via hopping in these materials.
Mechanism for Improved Quality B12As2 Epitaxial Films on (0001) 4H-SiC Substrates by Tilting toward [1-100] Direction
Authors: Zhang Yu , Chen Hui , Dudley Michael , Zhang Yi , Edgar James , Gong Yinyan , Bakalova Silvia , Kuball Martin , Zhang Lihua , Su Dong , Kisslinger Kim , Zhu Yimei
Published: August 2010

In this work, 4H-SiC substrates intentionally misoriented from the (0001) plane toward [1-100] direction are shown to eliminate rotational twinning in icosahedral boron arsenide (B12As2, abbreviated here as IBA) epitaxial films. Previous studies of IBA on other substrates, including (100), (110), (111) Si and (0001) 6H-SiC, produced polycrystalline and twinned epilayers. Comparisons of IBA on on-axis and off-axis c-plane 4H-SiC by synchrotron white beam x-ray topography (SWBXT), and high resolution transmission electron microscopy (HRTEM) confirm the single crystalline and much higher quality of the films on the latter substrates. Furthermore, no intermediate layer between the epilayer and substrate was observed for IBA on off-axis 4H-SiC. Steps formed on the off-axis 4H-SiC substrate surface before deposition cause the film to adopt a single orientation, a process that is not seen with substrates with either no misorientation, or those tilted toward the [11-20] direction. This work demonstrates that c-plane 4H-SiC with 7° offcut toward (1-100) is potentially a good substrate choice for the growth of high-quality, untwinned B12As2 epilayers for future device applications.