bluuebunny/crossref_metadata_2025 huggingface dataset:
Non-Invasive Characterization for Long-Term Preservation of Cultural Heritage
Authors: France F. G
Published: September 2011

Developments in non-invasive analytical techniques advance the preservation of cultural heritage materials by identifying and analyzing substrates and media. Spectral imaging systems have been used as a tool for non-invasive characterization of cultural heritage, allowing the collection of chemical identification information about materials without sampling. The Library of Congress has been developing the application of hyperspectral imaging to the preservation and analysis of cultural heritage materials as a powerful, non-contact technique to allow non-invasive characterization of materials, by identifying and characterizing colorants, inks and substrates through their unique spectral response, monitoring deterioration or changes due to exhibit and other environmental conditions, and capturing lost and deteriorated information. The resulting image cube creates a new “digital cultural object” that is related to, but recognized as a distinct entity from the original. The range of data thisobjectcontains encourages multidisciplinary collaboration for the integration of preservation, societal and cultural information.
Growth of Large Grain Polycrystalline Silicon Thin Film on Soda-lime Glass at Low Temperature for Solar Cell Applications
Authors: Wang K. , Wong K. H.
Published: September 2011

High quality polycrystalline silicon (poly-Si) thin film solar cell was successfully fabricated on soda-lime glass substrates by electron beam (Ebeam) evaporation at low processing temperature. The initial poly-Si seed layer (p+-type 0.5 μm thick) was grown via the aluminum induced crystallization (AIC) method at 450 °C. Prominent interdiffusion and Si crystallization have been observed. X-ray diffraction (XRD) shows that (111) is the dominating crystalline orientation. Post annealing at 450 °C for six hours has produced densely packed Si grains with dimension of more than 10 μm in the plane of the film. Non-destructive Raman spectroscopy reveals the remarkable crystalline improvement for samples after thermal treatment. After removing the top diffused Al by chemical means, an absorber layer (p-type) of 0.9 μm thick was subsequently deposited onto the seed layer by Ebeam evaporation at 500 °C. Transmission electron microscopy (TEM) confirmed good homo-epitaxial growth. Without breaking the high vacuum, an n-type amorphous Si (a-Si) layer (0.7 μm thick) was coated onto the absorber layer to form p-n junction. The corresponding I-V characteristics suggest that our low temperature processing technique is applicable for production of poly-Si thin film solar cell on low cost substrates.
Low Temperature Biomass Deconstruction by Zeolite-encapsulated Enzyme Mimics
Authors: Davis L. Shannon , Eisenhart Thomas T. , Hughes Brianna C. , Pressley Amy L.
Published: September 2011

Oxidation catalysis is a reaction necessary for the production of plastics and other materials that seem now essential to our everyday lives. Unfortunately, most oxidation processes suffer from poor selectivity or yields, creating unwanted byproducts and waste. In nature, oxidative enzymes like methane monooxygenase and the family of cytochromes provide a more selective method for oxidation of organic compounds. Of particular interest is the low temperature, selective oxidation of cellulosic biomass for the production of biofuels or other useful replacements for materials currently derived from petroleum feedstocks. An enzymatic approach could replace the high temperature pyrolysis technology in use today. A series of inorganic mimics of some oxidative enzymes, using transition metal – amino acid complexes encapsulated in large pore zeolites have been synthesized and examined as oxidation catalysts under benign conditions. Several of these demonstrate turnovers comparable to native enzymes in the reaction of model compounds for the oxidation of lignin and cellulose.
Multi-Ion Beam Lithography and Processing Studies
Authors: Appleton Bill R. , Tongay Sefaattin , Lemaitre Maxime , Gila Brent , Hays David , Scheuermann Andrew , Fridmann Joel
Published: September 2011

The University of Florida (UF) have recently collaborated with Raith Inc. to modify Raith’s ion beam lithography, nanofabrication and engineering (ionLiNE) station that utilizes only Ga ions, into a multi-ion beam system (MionLiNE) by adding the capabilities to use liquid metal alloy sources (LMAIS) to access a variety of ions and an EXB filter for mass separation. The MionLiNE modifications discussed below provide a wide range of spatial and temporal precision that can be used to investigate ion solid interactions under extended boundary conditions, as well as for ion lithography and nanofabrication. Here we demonstrate the ion beam lithographic capabilities of the MionLiNE for fabricating patterned arrays of Au and Si nanocrystals, with nanoscale dimensions, in SiO2 substrates, by direct implantation; and show that the same directwrite/maskless-implantation features can be used for in situ fabrication of nanoelectronic devices. Additionally, the spatial and temporal capabilities of the MionLiNE are used to explore the effects of dose rate on the long-standing surface morphological transformation that occurs in ion bombarded Ge.
Raman scattering study of Si nanoclusters formed in Si through a double Au implantation
Authors: Sahu Gayatri , Mahapatra D.P.
Published: September 2011

A sequential two step 32 keV Au implantation and 1.5 MeV Au irradiation technique has been used to synthesize Si nanoclusters (NCs) in Si. The low energy amorphising implantation has been carried out over a fluence range of (1 – 100) × 1015 cm−2 while the high energy recrystallizing irradiation fluence was fixed at 1 × 1015 cm−2. Samples were further annealed in air at temperatures between 500° to 950° C for a fixed annealing time of 1 hr and were characterized using Raman scattering at an excitation wavelength of 514.5 nm. Results on as-implanted and irradiated samples indicate formation of strained NCs in the top amorphised layer. Annealing around 500°C has been found to result in strain relief after which the data could be well explained using a phonon confinement model with an extremely narrow size distribution.
Broadband Antireflecting Conductive Metamaterial Films
Authors: Pishbin Nafiseh , Crouse David , Bendoym Igor , Crouse Michael
Published: September 2011

A polarization-independent, broadband, antireflecting compound aperture array is designed, fabricated and characterized. The structure is composed of an aluminum film with a periodic array of perforations (apertures) configured in a square lattice with a unit cell consisting of two apertures with different diameters, both filled with silicon oxynitride. Light-channeling waveguide cavity modes of different energies are excited within the two different apertures within each unit cell thereby transmitting different parts of the solar spectrum into the substrate. Experimental characterization shows low reflection (<10%) and low diffuse backscatter. Numerous applications of the films include light detecting and emitting structures and devices.
Development of Electrochemical Copper Deposition Screening Methodologies for Next Generation Additive Selection
Authors: Ryan Kevin , Dunn Kathleen , van Eisden Jobert
Published: September 2011

To reduce time-to-knowledge and costs associated with wafer scale processing a laboratory scale copper electrochemical deposition (ECD) system was developed for screening new organic additives which promote bottom-up fill in interconnect trenches and vias. This new setup enables working process conditions and functionality trends to be identified for open source and proprietary suppressors and levelers at leading edge feature sizes (sub 50nm). The laboratory results can then be compared to the in-line wafer scale plating tool results to ensure their compatibility. A reliable laboratory setup that can mimic the dynamic conditions found inside the wafer scale plating tool will enable the main objective of this work to be efficiently realized. The main objective is to test two previously published models describing copper fill inside the trenches by bridging the gap between fundamental electrochemical measurements and wafer scale plating results. To date this work will focus on the reliability and transferability of plating results between the laboratory setup and a wafer scale plating tool and present preliminary data using gap fill and bottom-up growth ratio as performance metrics.
Imprint resist properties for bit patterned media (BPM)
Authors: Lille J. , Karis T. , Vasquez D. , Wu T-W.
Published: September 2011

Nanoimprint lithography is a low cost method which produces trillions of nanostructures on a substrate. One application of this technology is patterned magnetic media where a single imprint on a disk can create a masking layer with more than a trillion nanostructures. Several challenges exist to imprinting bit patterned media (BPM) at a density greater than 1Tbit/in2. This technology would allow an extension of hard drive magnetic recording at densities greater than 1Tbit/in2. One such challenge is imprint resist mechanical properties where the imprinted masking layer should be free of thickness variations and resist flop-over. Herein we describe the nanoindentation mechanical properties of several imprint resist systems along with analysis of imprinted features of BPM at densities between 200-482 Gdots/in2.
Rare Earth Materials Challenge to National Defense: Material Scientist’s Perspective
Authors: Hullavarad Shiva , Hullavarad Nilima , Cook Joclyn
Published: September 2011

This article provides the key technical niche that alternative rare earth metals and oxides can offer as an alternative to the ones that are under ‘Potential China Export Embargo’. The potential areas of national interest that affected by limited rare earth and the implications of such short supplies on the US businesses are discussed. The paper discusses the technology areas where US based academic and industries have an opportunity in developing the alternate rare earth materials (REM) through innovations in recycling existing rare earth (RE) metals/oxides and develop alternate solutions. Some examples are provided on how the nanotechnology research in the alternative material technologies in the rare earth metals and oxide materials significantly affect the industry trend of rare earth dependence.
Enhanced adhesion of coating layers by Ion Beam Mixing: An application for nuclear hydrogen production
Authors: Park Jae-Won , Kim Hyung-Jin , Yeo Sunmog , Hong Seong-Duk
Published: September 2011

The bonding between two dissimilar materials has been a problem, partiularly in coating metals with non-metallic protective layer. In this work, it is demonstrated that a strong bonding between ceramics/metal can be achieved by mixing the atoms at the interface by ion-beam. Specifically, SiC coating on Hastelloy X was studied for a high temperature corrosion protection. Auger elemental mapping across the interface shows a far broader mixed region than the region expected by SRIM calculation, which is thought to be due to the thermal spike liquid state diffusion. The results showed that, although the thermal expansion coefficient of Hastelloy X is about three times higher than that of SiC, the film did not peel-off at above 900 oC confirming excellent adhesion. Instead, the SiC film was cracked along the grain boundary of the substrate above 700 oC. At above 900 oC, the film was crystallized forming islands on the substrate so that a considerable part of the substrate surface could be exposed to the corrosive environment. To cover the exposed area, it is suggested that the coating/IBM process should be repeated multiply.
Hollow ZnO Nano-cone Synthesis via Catalyst Free MOCVD
Authors: Zhang Wei , Strobl Karlheinz
Published: September 2011

Zinc oxide is a wide band gap material with excellent semiconducting, photonic and piezoelectric properties. In the past ten years zinc oxide nano-structures such as nanowires and nanorods have received great interest due to their unique dimensional and material properties in the area of photonics, electronics, mechanics, energy recovery, etc. In this paper we report the manufacturing process of a new shape, i.e. hollow hexagonal ZnO nano-cones. We grew them on different kinds of substrate using a low pressure, catalyst free, metal organic chemical vapor deposition (MOCVD) process on a FirstNano EasyTube 3000™ MOCVD system. Nitrogen was used as carrier gas to bring the reactants, DEZ and H2O, to the substrate surface. At the right balance of process temperature and carrier/precursor gas flow rate the ZnO nano-structure transitioned into a hollow hexagonal cones growth mode. The both one and two dimensional aspects of these catalyst free hollow hexagonal ZnO nano-cones, which are novel to the best of our knowledge, could lead to new applications in photonics, near field probing, chemical sensors, quantum confinement, electronic, etc.
Thin Film Power Harvesting System for Displays
Authors: Ahnood Arman , Chaji Reza , Nathan Arokia
Published: September 2011

An amorphous silicon (a-Si:H) thin film transistor (TFT) circuit designed for charging of an energy storage device using a photovoltaic (PV) array is presented. The TFT circuit is fabricated at plastic compatible temperatures (∼150°C) and as such can easily be integrated within a range of platforms including flexible displays. The circuit provides a high degree of output voltage stability over a range of light intensities and device stress.
Investigations on the Aging Effect of Supercapacitors
Authors: Parigi F. , Gao Y. , Casares M. , Gachovska T. , Zhou Y. S. , Lu Y. F. , Patterson D. , Hudgins J. L.
Published: September 2011

In this paper, the degradation processes of commercial supercapacitors aged at 2.7 V and 65 °C for 2000 h were studied. The crystallinity, thermal stability, and specific surface areas of the carbon electrodes of the supercapacitors were measured. Significant changes and degradations in the carbon electrodes were observed for the aged supercapacitors. New functional groups were also found on the surface of the electrodes. The degradation of the lattice structures and the reduction in the specific surface area were as well observed for the aged supercapacitors. It was suggested that the aging of supercapacitors significantly changed the electrode surface which affects considerably electrical properties and functionality of supercapacitors. We have also performed experiments which suggest that the aging effect on the electrode is not uniformly distributed through its length.
Bottom up Nano-particle Formation via Controlled Crystallization and Chemical Reactions
Authors: Panagiotou Thomai , Fisher Robert J.
Published: September 2011

Many manufacturing techniques to produce nano-materials via a “bottom-up” approach are currently being developed and evaluated. The PureNanoTMplatform technology developed by Microfluidics International Corporation (MFIC) has proven to be both an effective and energy efficient method to produce nano-scale entities including emulsions in addition to suspensions. This nano-manufacturing platform utilizes crystallization, precipitation and chemical reaction methods that produce nano-particles with specified size distributions and a desired morphology. The solids formed can be either amorphous or crystalline, which may exist in numerous polymorphs. In many cases the ability to obtain a specific composition (single species or mixture) is possible via careful selection and implementation of key processing conditions. The methods are based on controlling the local degree of super-saturation (SS) and/or stoichiometry during their formation and subsequent configuration and growth, when appropriate. To accomplish this, operational strategies and innovative processing techniques are coupled with qualitative insight into the basic mechanisms involved with these processes. Validation of the technology at the bench scale for crystallization, emulsions/cargo loading, and multi-phase reactions (interfacial and homogeneous) provided the justification to develop commercial scale systems. Examples are given here for crystallization of drugs for the pharmaceutical industry, a catalyst formed by deposition of metallic crystals on a carbon substrate, production of fine chemicals via emulsion formation for multi-phase reactions, and a homogeneous substitution reaction forming an insoluble product. Nano-materials with median particle size as low as 50 nm were produced. With respect to the drug particles, they were highly crystalline, of a single polymorph and pure. In all cases, results indicate both process performance enhancement and product quality/functionality improvements compared to materials produced with conventional methods, with at least 1-2 order of magnitude increases in surface/interfacial area and reduced energy needs. Furthermore, the technology is suitable for current Good Manufacturing Practices (cGMP) manufacturing.
Reversible Tuning of the Electronic Properties of Graphene via Controlled Exposure to Electron Beam Irradiation and Annealing
Authors: Teweldebrhan Desalegne , Liu Guanxiong , Balandin Alexander A.
Published: September 2011

Graphene reveals many extraordinary properties including extremely high room temperature carrier mobility and intrinsic thermal conductivity. Understanding how to controllably modify graphene’s properties is essential for its proposed applications. Here we report on a method for tuning the electrical properties of graphene via electron beam irradiation. It was observed that single-layer graphene is highly susceptible to the low-energy electron beams. We demonstrated that by controlling the irradiation dose one can change, by desired amount, the carrier mobility, shift the charge neutrality point, increase the resistance at the minimum conduction point, induce the “transport gap” and achieve current saturation in graphene. The change in graphene properties is due to defect formation on the graphene surface and in the graphene lattice. The changes are reversible by annealing until some critical irradiation dose is reached.
Data Transmission Performance of Few-Layer Graphene Ribbons
Authors: Guvenc Ali Bilge , Lin Jian , Penchev Miroslav , Ozkan Cengiz , Ozkan Mihrimah
Published: September 2011

We investigated the electrical characteristics and digital data transmission performance few-layer graphene ribbons grown by chemical vapor deposition. Graphene ribbons having a mobility of 2,180 cm2V-1s-1 can sustain data rates up to 50 megabits per second at 1.5 μm length, thus the bandwidth is inversely proportional to resistance caused by defects in the graphene layers. Improving the graphene mobility to highest measured values (∼200,000 cm2V-1s-1) and using structures with multiple coplanar transmission lines in parallel could carry the bandwidth beyond the gigabits per second level.
Performance Control of High Mobility, Printed Thin Film Transistors using Semiconducting Nanotube Ink
Authors: Rouhi N. , Jain D. , Zand K. , Burke P. J.
Published: September 2011

In this work, we present progress towards device fabrication using purified, semiconducting-enriched SWNT as the base material. Nanotubes were deposited in different densities (low, moderate, and high density) with different gate length of transistors and effect of each parameter has been studied using DC measurements. It is been shown that the nanotube network density plays a significant role in controlling the performance of such devices. By controlling the density of nanotubes in the network, we laid down a road map to predict and enhance the device performance based on their mobility and on/off ratio. From this work the DC analysis of devices characterization shows a mobility more than 90 cm2/V-s and also on/off ratios as high as, 105 have been achieved. We have demonstrated the first density-control technique over the nanotube network as a key point to modify the transistor’s mobility and on/off ratio [1]. When dense network mats of nanotubes were deposited, devices outperformed with higher mobility more than 90 cm2/V-s, enabling a faster switching speed. While relatively low-density mats yielded devices with on/off ratio of more than 105, which makes this technique feasible for low power nanoelectronics. Besides, the effect of various gate lengths have been studied which reveals an interesting trend between the channel length and the mobility.
Expression and Self Assembly of Cowpea Chlorotic Mottle Virus Capsid Proteins inPichia pastorisand Encapsulation of Fluorescent Myoglobin
Authors: Wu Yuanzheng , Yang Hetong , Shin Hyun-Jae
Published: September 2011

Cowpea chlorotic mottle virus (CCMV) has been a model system for virus studies for over 40 years and now is considered to be a perfect candidate as nanoplatform for applications in materials science and medicine. The ability of CCMV to self assemblein vitrointo virus-like particles (VLPs) or capsids makes an ideal reaction vessel for nanomaterial synthesis and entrapment. Here we report expression of codon optimized CCMV coat protein inPichia pastorisand production of self assembled CCMV VLPs by large-scale fermentation. CCMV coat protein gene (573 bp) was synthesized according to codon preference ofP. pastorisand cloned into pPICZA vector. The recombinant plasmid pPICZA-CP was transformed intoP. pastorisGS115 by electroporation. The resulting yeast colonies were screened by PCR and analyzed for protein expression by SDS-PAGE. After large-scale fermentation CCMV coat protein yields reached 4.8 g L−1. The CCMV VLPs were purified by modified PEG precipitation followed by cesium chloride density gradient ultracentrifugation, and then analyzed by size exclusion fast performance liquid chromatography (FPLC), UV spectrometry and transmission electron microscopy. Myoglobin was used as a model protein to be encapsulated in CCMV VLPs. The fluorescence spectroscopy showed that inclusion of myoglobin had occurred. The results indicated the production of CCMV capsids byP. pastorisfermentation now available for utilization in pharmacology or nanotechnology fields.
Interplay Between the Crystal and Liquid Crystalline Ordering of iPP and Carbon Nanotube Composites under Melt-Shear
Authors: Georgiev Georgi , McIntyre Michael B. , Judith Robert , Gombos Erin A. , Cebe Peggy
Published: September 2011

Carbon nanotubes (CNTs) exhibit liquid crystalline order and their nematic director couples to the one of low molecular weight liquid crystals. Here we explore the interactions between CNTs and the smectic liquid crystal phase of a polymer and the possibility for a similar coupling in this system. Isotactic Polypropylene (iPP) and iPP/CNTs nanocomposites were made in solution with varying CNT concentrations and hot pressed into 50-100μm thick films. The pure iPP and iPP/CNT films were then sheared at one rotation per second in the melt state. Shearing continued as the temperature was decreased from 200°C to 145°C to induce a smectic liquid crystal phase. The sheared samples were analyzed using polarized optical microscopy, Two Dimensional Microscopic Transmission Ellipsometry (2D-MTE) and Two Dimensional Wide Angle X-Ray Scattering (2D-WAXS). During shearing we detected a sudden increase of birefringence at 151°C in the samples, higher than the iPP crystallization temperature, indicating liquid crystalline ordering. The samples were then crystallized at 135°C for 30 minutes. We measured anisotropic 2D-WAXS patterns of the samples that contained CNTs, indicating strong ordering of the crystals. Upon reheating, we measured birefringence at temperatures higher than the melting endotherm for the iPP crystals, using polarized microscopy, which indicates that some smectic order still persists in the samples, even after crystallization and complete melting of all crystals. Our results indicate that CNTs couple to the smectic phase of iPP, improve its order upon shearing and the crystals created after the formation of the oriented smectic phase are strongly aligned parallel to the direction of shearing.
Zeeman splittings of the 5D0–7F2 transitions of Eu3+ ions implanted into GaN
Authors: Kachkanov V. , O’Donnell K.P. , Rice C. , Wolverson D. , Martin R.W. , Lorenz K. , Alves E. , Bockowski M.
Published: September 2011

We report the magnetic field splittings of emission lines assigned to the 5D0–7F2 transitions of Eu3+ centres in GaN. The application of a magnetic field in the c-axis direction (B‖c) leads to a splitting of the major lines at 621 nm, 622 nm and 622.8 nm into two components. The Zeeman splitting is linear with magnetic field up to 5 Tesla for each line. In contrast, a magnetic field applied in the growth plane (B┴c) does not influence the photoluminescence spectra. The estimated g-factors vary slightly from sample to sample with mean values of g‖ ~2.8, ~1.5 and ~2.0 for the emission lines at 621 nm, 622 nm and 622.8 nm respectively.
Experimental and Theoretical Study of the New Image Force Microscopy Principle (Invited Paper)
Authors: Wickramasinghe H. Kumar , Rajapaksa Indrajith
Published: September 2011

A new technique in microscopy is demonstrated in which the domain of Atomic Force Microscopy (AFM) is extended to optical spectroscopy at the nanometer scale. Molecular resonance of feature sizes down to the single molecular level were detected and imaged purely by mechanical detection of the force gradient between the interaction of the optically driven object molecular dipole and its mirror image in a Platinum coated scanning probe tip. We provide full experimental details including a basic theory for this new technique. The microscopy and spectroscopy technique is extendable to frequencies ranging from radio to infrared and the ultra violet.
Synthesis of Resorcinol Formaldehyde Aerogel Using UV Photo-Initiators for Inertial Confinement Fusion Experiments
Authors: Paguio R.R. , Saito K.M. , Hund J.F. , Jimenez R. M.
Published: September 2011

Resorcinol formaldehyde (R/F) aerogels have been used in a variety of laser targets for Inertial Confinement Fusion (ICF) experiments in the form of thin films, cast shapes such as cylinders and cubes, and hollow and solid microspheres. Besides ICF experiments, R/F aerogel can be used for capacitors, batteries, thermal insulation, absorption/filtration media, and chromatographic packing applications. Traditionally, R/F aerogel is synthesized using a 2-step (base/acid catalysis) polycondensation reaction. We have developed a novel process to synthesize the R/F aerogel using free radical UV initiator at room temperature in 10 minutes using a UV light source. This paper will review this process, which was developed to synthesize R/F aerogels using UV-free radical initiators. Scanning electron microscopy results will also be discussed to show that the aerogel pore structure is similar to traditional R/F aerogels. Fabrication of solid and hollow microspheres for ICF experiments using this R/F aerogel synthesis technique and the technique’s limitations will also be discussed.
Enhanced Thermoelectric Properties of Strongly Degenerate Polycrystalline Silicon upon Second Phase Segregation
Authors: Narducci Dario , Selezneva Ekaterina , Arcari Andrea , Cerofolini Gianfranco , Romano Elisabetta , Tonini Rita , Ottaviani Gianpiero
Published: September 2011

We report the study of the thermoelectric properties of degenerate, boron-doped polycrystalline silicon on insulator structures. The occurrence of a regime where both the Seebeck coefficient and the conductivity increase is confirmed. This results in a power factorPof 13 mW K-2m-1. We propose that such high values ofPmay be determined by adiabatic energy filtering occurring at grain boundaries decorated by segregated boron.
Crystal Lattice Controlled SiGe Thermoelectric Materials with High Figure of Merit
Authors: Kim Hyun Jung , Park Yeonjoon , King Glen C. , Lee Kunik , Choi Sang H.
Published: September 2011

Direct energy conversion between thermal and electrical energy, based on thermoelectric (TE) effect, has the potential to recover waste heat and convert it to provide clean electric power. The energy conversion efficiency is related to the thermoelectric figure of merit ZT expressed as ZT=S2σT/κ, T is temperature, S is the Seebeck coefficient, σ is conductance and κ is thermal conductivity. For a lower thermal conductivity κ and high power factor (S2σ), our current strategy is the development of rhombohedrally strained single crystalline SiGe materials that are highly [111]-oriented twinned. The development of a SiGe “twin lattice structure (TLS)” plays a key role in phonon scattering. The TLS increases the electrical conductivity and decreases thermal conductivity due to phonon scattering at stacking faults generated from the 60° rotated primary twin structure. To develop high performance materials, the substrate temperature, chamber working pressure, and DC sputtering power are controlled for the aligned growth production of SiGe layer and TLS on a c-plane sapphire. Additionally, a new elevated temperature thermoelectric characterization system, that measures the thermal diffusivity and Seebeck effect nondestructively, was developed. The material properties were characterized at various temperatures and optimized process conditions were experimentally determined. The present paper encompasses the technical discussions toward the development of thermoelectric materials and the measurement techniques.
Contact Resistivity of Laser Annealed SiGe for MEMS Structural Layers Deposited at 210°C
Authors: El-Rifai Joumana , Witvrouw Ann , Aziz Ahmed Abdel , Puers Robert , Van Hoof Chris , Sedky Sherif
Published: September 2011

Lowering the silicon germanium (SiGe) deposition temperature from the current 450°C to below 250°C will enable processing Micro Electro-Mechanical Systems (MEMS) on flexible polymer instead of on rigid silicon substrates or glass carriers. A major disadvantage of such a low temperature deposition is that the films are amorphous, with high hydrogen content and yield poor electrical and mechanical properties. To ensure films suitable for MEMS applications, a post-deposition laser annealing (LA) treatment is used. It is essential that the contact resistance between the SiGe MEMS structural layer and any lower electrode is minimized. In this work we investigate what beneficial effect a LA treatment can have on the contact resistivity of an initially amorphous SiGe MEMS structural layer with a bottom TiN electrode. We report a minimum contact resistivity of 2.14×10−3Ωcm2.
Film Conductivity Controlled Variation of the Amplitude Distribution of High-temperature Resonators
Authors: Schmidtchen Silja , Richter Denny , Xia Han , Fritze Holger
Published: September 2011

High-temperature measurements of the spatial distribution of the displacement characteristics of a thickness shear mode langasite (La3Ga5SiO14) resonator are obtained using a laser Doppler interferometer. Thereby, the resonator is excited in the fundamental mode and the third overtone. Further, the resonator is coated with a gas sensitive CeO2-x film which exceeds the metal electrode. In reducing atmospheres the conductivity of the film increases and induces an increase of the effective electrode area. This effect leads to a broadening of the mechanical displacement distribution. The latter depends strongly on the size of the excited part of the resonator which is determined by the effective size of the electrodes. The direct determination of the mechanical displacement at different oxygen partial pressures confirms a model as derived from the electrical impedance of resonator devices [1]. Further, information about the mass sensitivity distribution of resonators is obtained since the property is directly proportional to the amplitude.
Low-Temperature Growth of Epitaxial Semiconductor Nanostructures and Films
Authors: Findikoglu Alp T. , Perea Daniel E. , Picraux S. T.
Published: September 2011

The growth of epitaxial semiconductor nanostructures and films at low temperatures is important for semiconductor technology because it allows the possibility of monolithically integrating different high-performance single-crystalline semiconductor structures directly onto low cost technologically important substrates. At sufficiently low temperatures this can enable, for example, Si or Ge device fabrication on flexible substrates such as plastics. We have studied the reduced-temperature liquid-mediated growth of Ge nanostructures and films on crystalline template layers on non-single-crystalline substrates in a low-pressure chemical vapor deposition (LPCVD) system. The heteroepitaxial process is implemented by the Au seeded vapor-liquidsolid (VLS) catalytic growth technique with germane below 400 ºC. Crystalline template layers were prepared with ion-beam-assisted-deposition (IBAD) texturing and electron-beam evaporation on glass substrates. A thin layer of e-beam evaporated Au forms the catalyst layer, upon which we grew Ge films at 386 ºC. Scanning electron microscopy and x-ray diffraction results indicated that both Ge islands and nanowires grew heteroepitaxially on the crystalline template layers on glass substrates with good alignment over large areas.
Fostering a Conceptual Understanding in Undergraduate Materials Education: A Multivariable Animated Spreadsheet Approach
Authors: Sinex Scott A. , Halpern Joshua B.
Published: September 2011

We describe how students explore materials science concepts using animated interactive spreadsheets. An engaging pedagogy is created in the classroom using spreadsheets in a way that initially camouflages mathematical complexity, which can later be revealed and taught. Use of off-the-shelf spreadsheet software, including freeware makes these spreadsheets universally available.
Novel fabrication method of ZnO films utilizing solid-phase crystallized seed layers
Authors: Itagaki Naho , Kuwahara Kazunari
Published: September 2011

A novel fabrication method of ZnO films utilizing solid-phase crystallized seed layers has been developed. In this method, solid phase crystallization (SPC) is performed by annealing amorphous ZnON films, which are prepared by sputtering of ZnO targets in Ar/N2 mixed gases, in an oxidization atmosphere. The grain size of ZnO films deposited on the seed layers is significant larger than that of ZnO films directly deposited on glass substrates, which is considered to be due to the low grain density of seed layers. By utilizing this technique, the resistivity of ZnO:Al (AZO) films is decreased from 20 × 10-4 Ωcm to 5 × 10-4 Ωcm at the film thickness of 30nm. Furthermore, we observed that SPC seed layers are in-plane aligned when Al2O3 substrates are used, which suggests that the fabrication method proposed here is also promising for synthesizing epitaxial ZnO films.
Modeling of Polycrystalline Organic Thin-Film Transistor and Schottky Diode for the Design of Simple Functional Blocks
Authors: Raja M. , Donaghy D. , Myers R. , Eccleston W.
Published: September 2011

We present analytical models for organic thin film transistors (OTFTs) and Schottky diodes based on polycrystalline semiconductors. The OTFT model is developed using a well-established approach previously developed for polysilicon, with slight modification for organics. The model predicts voltage and temperature dependencies on the various device and circuit parameters. A good agreement is obtained with experimental data of TIPS-based OTFTs. Essential parameters such as the characteristic temperature and Meyer-Neldel Energy extracted using the model with TIPS OTFTs data were in agreement with those obtained from Schottky diode measurements.
High thermally stable hybrid materials for optical interconnects
Authors: Sato Tetsuo
Published: September 2011

Optical materials in the optical circuit board are required to overcome soldering process. In detail, the material should not have absorption and shape changes after several tens of seconds heating at around 250 °C. For such application field, we have developed a novel organic-inorganic hybrid material having a high thermal stability and low absorption at telecom wavelength.

The hybrid material was designed to solvent less resin, which is free radical curable with heating at 150 °C or UV exposure at room temperature, for the sake of device fabrication activity. We demonstrated the waveguides fabrication by photolithography, and obtained high uniformity cured materials. Transparency of the waveguide sample at telecom wavelength was 0.10 dB/cm at 850 nm, 0.12 dB/cm at 1060 nm, 0.29 dB/cm at 1310 nm, and 0.45 dB/cm at 1550 nm. These values are good low attenuation for the Near-IR optical communication in optical interconnects. Without any further treatment such as post bake, the cured materials showed a high thermal stability. The temperature of 5 % weight loss was over 400 °C, and the transparency hardly changed after 1 min heating at 300 °C.

In addition, the cured material showed a high refractive index of n=1.60 at 633 nm and a low curing shrinkage about 4.7 %. From these properties, the developed organic-inorganic material is expected to be beneficial for the optical interconnection such as micro lenses and optical packages.
First Principles Predictions of Intrinsic Defects in Aluminum Arsenide, AlAs
Authors: Schultz Peter A.
Published: September 2011

The structures, energies, and energy levels of a comprehensive set of simple intrinsic point defects in aluminum arsenide are predicted using density functional theory (DFT). The calculations incorporate explicit and rigorous treatment of charged supercell boundary conditions. The predicted defect energy levels, computed as total energy differences, do not suffer from the DFT band gap problem, spanning the experimental gap despite the Kohn-Sham eigenvalue gap being much smaller than experiment. Defects in AlAs exhibit a surprising complexity—with a greater range of charge states, bistabilities, and multiple negative-U systems—that would be impossible to resolve with experiment alone. The simulation results can be used to populate defect physics models in III-V semiconductor device simulations with reliable quantities in those cases where experimental data is lacking, as in AlAs.
Non-melt Laser Thermal Annealing of Shallow Boron Implantation for Back Surface Passivation of Backside-Illuminated CMOS Image Sensors
Authors: AIT FQIR ALI-GUERRY Zahra , HUET Karim , DUTARTRE Didier , BENEYTON Rémi , BENSAHEL Daniel , NORMANDON Philippe , LU Guo-Neng
Published: September 2011

Back surface passivation is one of the major challenges in the backside illuminated sensor technology. Ion implantation followed by non-melt pulsed Laser Thermal Annealing (LTA) has been identified as a promising candidate to address this issue. In this work, a shallow B-doped layer is implanted at the backside, further activated using LTA in the non-melt regime. LTA process effectiveness in terms of crystal damage recovery as well as dopant diffusion and activation is studied through room-temperature photoluminescence, Secondary Ion Mass Spectroscopy and four-point probe sheet resistance. These studies demonstrate that non-melt LTA with multiple pulses induces high activation without visible diffusion with an effective curing of the implantation-induced crystalline defects. This is made possible thanks to a submicrosecond process timescale coupled to a reasonable number of shots as shown by thermal simulations and simple diffusion estimations.
Light-induced Open-circuit Voltage Increase in Amorphous Silicon/Microcrystalline Silicon Tandem Solar Cells
Authors: Zhang Xiaodan , Wang Guanghong , Xu Shengzhi , Xiong Shaozhen , Geng Xinhua , Zhao Ying
Published: September 2011

Light-induced metastability of amorphous/microcrystalline (micromorph) silicon tandem solar cell, in which the microcrystalline bottom cell was deposited in a single-chamber system, has been studied under a white light for more than 1000 hours. Two different light-induced metastable behaviors were observed. The first type was the conventional light-induced degradation, where the open-circuit voltage (Voc), fill factor (FF), and short-circuit current density (Jsc) were degraded, hence the efficiency was degraded as well. This phenomenon was observed mainly in the tandem cells with a bottom cell limited current mismatch. The second type was with a light-induced increase in Voc, which sometimes resulted in an increase in efficiency. The second type of light-induced metastability was observed in the tandem cells with a top cell limited current mismatch. The possible mechanisms for these phenomena are discussed.
Primary Photonic Processes in Energy Harvesting: Quantum Dynamical Analysis of Exciton Energy Transfer over Three-Dimensional Dendrimeric Geometries
Authors: Andrews David L. , Jones Garth A.
Published: September 2011

In molecular solar energy harvesting systems, quantum mechanical features may be apparent in the physical processes involved in the acquisition and migration of photon energy. With a sharply declining distance-dependence in transfer efficiency, the excitation energy generally takes a large number of steps en route to the site of its utilization; quantum features are rapidly dissipated in an essentially stochastic process. In the case of engineered dendrimeric polymers, each such step usually takes the form of an inward hop between chromophores in neighboring generation shells. A physically intuitive, structure-determined adjacency matrix formulation of the energy flow affords insights into the key harvesting and inward funneling processes. A numerical method based on this analytic approach has now been developed and is able to deliver results on significantly larger dendrimeric polymers, with the help of large multi-processor computers. Central to this study is the interpretation of key features such as the relevance of a spectroscopic gradient and the presence of traps or irregularities due to conformational changes and folding. With the objective of fine-tune the funneling process, this model now allows the incorporation of parameters derived from quantum chemical calculations, affording new insights into the detailed operation of the harvesting process in a variety of dendrimer systems.
Memristive Switches with Two Switching Polarities in a Forming Free Device Structure
Authors: Bruchhaus Rainer , Hermes Christoph R. , Waser Rainer
Published: September 2011

In this study an electroforming free device structure based on 25nm thin TiO2 thin films is presented. The TiO2 films are deposited on CMOS compatible W plugs. The use of 5nm thick interlayers of Ti and W between the TiO2 and the Pt electrode turn out to be the key step to achieve the forming free performance. In these Pt/Ti/TiO2/W or Pt/W/TiO2/W samples the switching polarity can be repeatedly changed from “eightwise” to “counter-eightwise” in one device by a proper adjustment of the I-V measurement conditions. The most simple explanation for this observation is that the switching interface can be flipped back and forth from the bottom to the top electrode.
Switching speed in Resistive Random Access Memories (RRAMS) based on plastic semiconductor
Authors: Rocha Paulo F. , Gomes Henrique L. , Kiazadeh Asal , Chen Qian , de Leeuw Dago M. , Meskers Stefan C. J.
Published: September 2011

This work addresses non-volatile memories based on metal-oxide polymer diodes. We make a thorough investigation into the static and dynamic behavior. Current-voltage characteristics with varying voltage ramp speed demonstrate that the internal capacitive double-layer structure inhibits the switching at high ramp rates (typical 1000 V/s). This behavior is explained in terms of an equivalent circuit.

It is also reported that there is not a particular threshold voltage to induce switching. Voltages below a particular threshold can still induce switching when applied for a long period of time. The time to switch is longer the lower is the applied voltage and follows an exponential behavior. This suggests that for a switching event to occur a certain amount of charge is required.
Vapor-Liquid-Solid Growth of Cadmium Telluride Nanowires by Close-Space-Sublimation for Photovoltaic Applications
Authors: Williams B. L. , Mendis B. , Bowen L. , Halliday D. P. , Durose K.
Published: September 2011

Arrays of CdTe nanowires have been grown on conductive, flexible Mo substrates by the vapor-liquid-solid technique. A method of forming the arrays on a largely continuous CdTe film is described. For producing nanowire solar cells, this structure provides the advantage of preventing shunts. Nanowires having diameters in the range 100-500 nm and lengths up to 100 μm were generated. The influence of growth temperature, time and pressure on the morphology of deposited layers was investigated, and a mechanism for the generation of layer/nanowire combinations is postulated. Characterization by SEM, TEM and low temperature photoluminescence is presented.
Surface Photovoltage Study of Indium Phosphide Nanowire Networks
Authors: Lohn Andrew J. , Han Jin-Woo , Kobayashi Nobuhiko P.
Published: September 2011

Surface photovoltage of three-dimensional networks composed of fused indium phosphide (InP) nanowires is discussed. Particular emphasis is given to the dependence of surface photovoltage on the chopping frequency of light that excites the nanowire network as observed in regions which are laterally separated from the excitation. The nanowire network is modeled as a thin film to simplify numerical solutions to transport equations which aids in the interpretation of diffusion and drift of photo-generated carriers within the nanowire network.
Patterned Polymer Nanofibers Based Biosensors
Authors: Mertz Timothy O. , Kunduru Vindhya , Patra Prabir K. , Vattipalli Krishna , Prasad Shalini
Published: September 2011

“Label-free” biomolecule sensors for detection of inflammatory cardiovascular biomarker associated with vulnerable coronary vascular plaque were designed and fabricated using micro and nano-textured polystyrene structures that functioned as sensing elements coupled with electronic measurement equipment. We demonstrated that scaling down the surface texturing from the micro to the nanoscale enhances the amplitude of the measured signal strength. We believe that the nanoscale fiber morphology provides size matched spaces for trapping and immobilizing the protein biomolecules resulting in enhanced detection and signal strength. We selected polystyrene as the model system and demonstrated the detection of human serum C-reactive protein (hs-CRP). We employed these findings in designing a platform “lab-on-a-chip” protein sensor. Comparative studies were performed on two different polystyrene textured surfaces: a polystyrene microsphere mat, and an electrospun polystyrene nanofiber matrix.