bluuebunny/crossref_metadata_2025_split huggingface dataset:
Organic Thin Film Transiators on Synthesis Paper
Authors: Cheng Hua-Chi , Peng Yu-Rung , Chung Chao-An , Hou Wei-Hsin , Pei Zing-Way 
Published: April 2011

ABSTRACTWe have demonstrated organic thin-film transistor devices on synthesis paper of polypropylene (PP). All the fabrications are in solution-based processes except electrodes. As a barrier and smoother layer, photosensitive epoxy, 5μm-thich was coated on the paper substrate by using slit die coating. Polyvinyl phenol (PVP) was mixed with poly (melamine-co-formaldehyde) methylated, filmed by spin coating and ultraviolet (UV) cross linked to provide the gate dielectric layer. Using poly (3-hexylthiophene) as an active layer, a high-performance organic transistor with field effect mobility up to 0.006 cm2/ V s and an on/off ratio of 50 can be achieved. For the applications in flexible and disposable electronics, to built organic transistors on a cheap synthesis paper substrate can extremely lower the cost.
The Electronic Structure and the Energy Level Alignment at the Interface Between Organic Molecules and Metals
Authors: Kawabe Eiji , Yamane Hiroyuki , Koizumi Kenji , Sumii Ryohei , Kanai Kaname , Ouchi Yukio , Seki Kazuhiko 
Published: April 2011

ABSTRACTWe investigated the electronic structure and the energy level alignment at the interfaces between perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) and metals (Au, Cu and Co) by ultraviolet photoelectron spectroscopy (UPS). In the case of PTCDA/Au interface, the apparent interface states and charge transfer (CT) states were not observed in its UPS spectra. In the case of PTCDA/Cu and Co interfaces, however, we found that the CT from metal to PTCDA occurred, and that the apparent CT states were observed at PTCDA/Cu interface.
Very High On/Off Ratio in Vertical-Type Metal-Base Organic Transistors
Authors: Nakayama Ken-ichi , Yokoyama Masaaki 
Published: April 2011

ABSTRACTThe on/off ratio of the vertical-type metal-base organic transistors was drastically improved by heat treatment in air. The heat treatment after deposition of the collector layer and base electrode reduced the leakage current between the base and collector, resulting in remarkable suppression of the off current. As a result, in addition to the advantage of low voltage and high current operation based on the vertical structure, very high on/off ratio exceeding 105 was achieved.
Direct Local Strain Measurement In Damascene Interconnects
Authors: Kasbari Moustafa , Rivero Christian , Blayac Sylvain , Cacho Florian , Bostrom Ola , Fortunier Roland 
Published: April 2011

ABSTRACTA new mechanical stress characterization method has been developed for Damascene copper interconnects. The micro strain gauge based on a rotating beam has been fabricatedin situon a standard industrial CMOS production line. Comparison of the beam deviation in the fabricated sensor with usual geometrical model is discussed. The saturation of the beam deviation leads to an analytical model which takes the stiffness of the anchoring points into account. This model gives a direct value of the local stress in the copper line for different annealing times. We show that this value is different from the one given by a curvature measurement method. The microstructure of the Damascene copper induces a higher stress level than full sheet deposition copper. The sensor was developed to be compatible within a CMOS process. It is suitable for in situ mechanical stress monitoring in Damascene lines and process optimization.
RRAM electronics and Switching Mechanism
Authors: Hsu Sheng Teng , Li TingKai 
Published: April 2011

AbstractThe property of PCMO RRAM memory devices have been studied in terms of electrical pulse width, Pulse polarity, voltage ramping, film thickness, resistivity distribution, and temperature dependent of resistance. The PCMO material is deposited using MOD, PVD, or PLD process. The experimental results clearly indicated the resistance increase is due to localization of valence electrons. The narrow pulse induced resistance increase near the cathode indicated the localization of valence electrons is the effect of high density of excessive non-equilibrium electrons through the well known Jahn-Teller effect. High density of non-equilibrium electrons may also be induced by any other means such as displacement current, space charge limited current, SCLC, and radiation. High field intensity collapses the localized valence electrons and returns the device to the low resistance state. This is the intrinsic property of transition metal oxides. We expect all doped and un-doped transition metal oxides to exhibit resistance switching property.
Stress and Mechanical Constants Characterizations of Phase-change SbTe-alloys: Influence of the Film Thickness and Substrate
Authors: Lisoni Judit , Gille T. , Goux L. , Delhougne R. , Jossart N. , Attenborough K. , Wouters D. J. 
Published: April 2011

AbstractWe have characterized the in-film stress and the mechanical constants of a growth-dominated phase-change SbTe-alloy, a material beneficially used in the line-cell phase change memory architecture. The influence of the thickness of the films (5-120 nm) and of the substrate used for its deposition (Si, SiO2 and SiC) was studied. The characterizations were carried out on both amorphous and crystalline films. The crystallization temperature was determined by the resistance changes as a function of the temperature. The mechanical characteristics of the films were measured by the wafer curvature method. We observed that the mechanical behavior of these films was strongly dependent on their thicknesses and on the substrate material. For the thinnest amorphous films, the in-film stress was highly compressive (with the largest compressive stress for films on SiC), while it tended to be very low (fully relaxed films) for films thicker than 20 nm. The amorphous films furthermore did not reveal any stress relaxation in time-dependent stress measurements. Therefore, it was not possible to quantify the viscosity of the SbTe-alloy. This result maybe related to a lower defect state in the very thin films used, or to a blocking of the defects by enhanced reactivity of these thin SbTe-alloy films with their surroundings, both resulting in the absence of relaxation in the amorphous state. Finally, the coefficients of thermal expansion (CTE) of the amorphous and crystalline SbTe-alloys were similar, 1–3×10−6 K−1. These values were comparable to the CTE's of the substrates, clearly indicating that for thin films the substrates dominate their thermal expansion behavior.
Temperature-dependent Degradation Modes in CdS/CdTe Devices
Authors: Albin David , Demtsu Samuel H , Duda Anna M , Metzger Wyatt K 
Published: April 2011

AbstractA set of 24 identically made CdS/CdTe devices were subjected to accelerated lifetime testing (ALT) under open-circuit bias, 1 sun illumination, and temperatures of 60, 80, 100, and 120 °C. A total of 6 identical devices were tested for statistical purposes at each temperature. Current density-voltage (JV) measurements were made on stressed cells for up to 2000+ hours. Device performance parameters were calculated as a function of temperature and stress time using discrete element circuit models. Forward current behavior was represented by two parallel diodes to simulate recombination currents in the quasi-neutral (QNR) and space-charge (SCR) regions. Backcontact behavior was studied using a parallel combination blocking diode and shunt conductance. A systematic pattern of degradation was apparent with increased stress temperature. At 60 °C, degradation associated with the CdTe/backcontact dominates. At temperatures above 80 °C, greater losses in fill factor (FF) and open-circuit voltage (Voc) were observed. Recombination current modeling of JV data attributes this to increased space-charge recombination. Calculated diffusion lengths based upon an Arrhenius-derived activation energy of 0.63 eV in this temperature-range suggests Cu diffusion into the SCR is mechanistically responsible for the observed increased recombination, and decreased Vocand FF. At lower temperatures (60 to 80 ºC), degradation was considerably slower with a measured activation energy of 2.9 eV.
Investigation of ZnO:Al Doping Level and Deposition Temperature Effects on CIGS Solar Cell Performance
Authors: Duenow Joel N. , Gessert Timothy A. , Wood David M. , Egaas Brian , Noufi Rommel , Coutts Timothy J. 
Published: April 2011

AbstractCu(In,Ga)Se2 (CIGS) photovoltaic cells require a highly conducting and transparent top electrode for optimum device performance. ZnO thin films doped with 2 wt.% Al (ZnO:Al) are commonly used to ensure sufficient conductivity while providing acceptable transparency to the active absorber layers. Deposition of transparent conducting oxide (TCO) films on CIGS cells often is performed at room temperature in the manufacturing process because of production advantages. However, material properties and reproducibility may be poorer at room temperature than at higher temperatures. Maximum mobilities of 2 wt.%-doped ZnO:Al grown at room temperature in pure Ar are typically ∼20-25 cm2V-1s-1. Relatively high carrier concentration is therefore required to achieve the desired conductivity. This high carrier concentration produces low infrared transmittance due to increased free-carrier absorption.World-record CIGS cells produced at the National Renewable Energy Laboratory (NREL) are known to tolerate photolithographic processing temperatures of ∼100Â°C, though significant changes in device performance occur beyond 200Â°C. In this study, we investigate whether ZnO:Al films with superior material properties can be produced at the elevated temperatures consistent with CIGS processing parameters. We examine undoped ZnO and ZnO:Al with doping levels of 0.5, 1, and 2 wt.% Al2O3 for growth at substrate temperatures from 25Â° to 360Â°C using radio-frequency magnetron sputtering. For films grown in a 100% Ar ambient, optimal electrical and optical properties are achieved at ∼150Â°-200Â°C. Controlled incorporation of H2 in the Ar sputtering ambient at 200Â°C increases mobility to 48 cm2V-1s-1 for undoped ZnO and 36 cm2V-1s-1 for 0.5 wt.%-doped ZnO:Al. Both values are considerably higher than the 25 cm2V-1s-1 of 2 wt.%-doped ZnO:Al deposited at 200Â°C in 100% Ar. We have explored whether these higher-mobility films can be exploited in the design of high-quality CIGS devices produced at NREL. Preliminary results show similar open-circuit voltage and only slightly lower short-circuit current compared to devices utilizing the standard 2 wt.%-doped ZnO:Al deposited at room temperature. This suggests that higher-performance devices may result once the TCO thickness is optimized for the higher mobility.
InGaAs Solar Cells Grown on Wafer-Bonded InP/Si Epitaxial Templates
Authors: Zahler James M. , Tanabe Katsuaki , Ladous Corinne , Pinnington Tom , Newman Frederick D. , Atwater Harry A. 
Published: April 2011

AbstractInP/Si engineered substrates formed by wafer bonding and layer transfer have the potential to significantly reduce the cost and weight of III-V compound semiconductor solar cells. InP/Si substrates were prepared by He implantation of InP prior to bonding to a thermally oxidized Si substrate and annealing to exfoliate an InP thin film. Following thinning to remove damage caused by the implantation and exfoliation from the surface of the InP transferred film, InGaAs solar cells lattice-matched to bulk InP were grown on those substrates using metal-organic chemical vapor deposition. The photovoltaic current-voltage characteristics of the InGaAs cells fabricated on the wafer-bonded InP/Si substrates were comparable to those synthesized on commercially available epi-ready InP substrates, thus providing an initial demonstration of wafer-bonded InP/Si substrates as an alternative to bulk InP substrates for solar cell applications.
Towards Lower Deposition Temperatures of Spray Deposited ZnO Films
Authors: Gledhill Sophie E. , Allsop Nicholas , Thier Pablo , Camus Christian , Lux-Steiner Martha , Fischer Christian Herbert 
Published: April 2011

AbstractHighly transparent, conductive ZnO:Al doped films have been deposited by a non-vacuum spray deposition method. At substrate temperatures above 400C we attain resistivites of 5x10-3Ohmcm and free charge carrier concentrations of 10-20cm-3. ZnO film growth and quality are sensitive to the precursor solution. For a non-vacuum process the properties of the films are excellent.The challenge is to lower the deposition temperature to a maximum of 250C to be useful for Cu(In, Ga)(S, Se)2 solar cells and yet maintain the ZnO film quality and conductivity. As the deposition temperature decreases the resistivity of the ZnO drastically increases yet is conducting enough to be used undoped as the intrinsic ZnO layer. This is particularly relevant as the deposition technique is readily up-scalable to roll to roll coating processes.
Electroluminescence from Cu(In,Ga)Se2 Thin-film Solar Cells
Authors: Kirchartz Thomas , Mattheis Julian , Rau Uwe 
Published: April 2011

AbstractWe compare the electroluminescence (EL) of three polycrystalline ZnO/CdS/Cu(In,Ga)Se2 heterojunction solar cells with similar bandgaps but different open circuit voltages, indicating a difference in the electronic quality of the absorber. Temperature dependent electroluminescence measurements reveal that all cells feature transitions from donor-acceptor pair recombination at lower temperatures to band to band recombination at higher temperatures. However, the less efficient cells show a longer transition range with donor-acceptor pair recombination still apparent at room temperature. The thus broadened room temperature luminescence is one effect which reduces the open circuit voltage of the devices below the Shockley-Queisser-limit. The other effect is the existence of non-radiative recombination currents, which determine the efficiency of the device as light emitting diode. To quantify the open circuit voltage losses, we use reciprocity relations between electroluminescent and photovoltaic action of solar cells, which allow us to predict the light emitting diode efficiency. Measurements support the theory and show that Cu(In,Ga)Se2 solar cells reach external LED efficiencies approaching.
Analysis of Band Gap Fluctuations in Cu(In,Ga)Se2 by Confocal Optical Transmission and Photoluminescence
Authors: Gutay Levent , Bauer Gottfried H. 
Published: April 2011

AbstractWe present new insights into inhomogeneities of Cu(In,Ga)Se2 absorbers by confocal optical transmission (OT) and spectrally resolved photoluminescence (PL) with lateral resolution in the one-micron regime. We carry out scans for both measurands at identical positions and observe explicit local variations of the PL- and OT-spectra. The PL-yield shows fluctuations in the sub- and few-µm regime. As shown in previous papers we extract local variations of the splitting of quasi-Fermi-levels of about 40-50meV, which limits the open circuit voltage of cells, and of the optical threshold of the absorber of some tens of meV related to the local optical band gap. Local transmission spectra similarly show lateral variations in the few-µm regime. From these spectra we calculate local absorption coefficients and absorbance functions which yield variations of the optical threshold of the absorber of 20-30meV, amounting to the same range as PL-results. Via Planck's generalized law we are able to compute theoretical PL-spectra from the resulting absorbance functions. The discrepancies between measured and calculated hypothetical PL-spectra are discussed with respect to diffusion of excess charge carriers and fluctuations of the band gap in the sub-µm-regime below the spatial resolution of the experiment.
The Effect of Ionizing Radiations on the Structural, Electrical and Optical Properties of AIIBVI Polycrystalline Thin Films Used as Solar Cell Materials
Authors: Ion Lucian , Antohe Vlad Andrei , Ghenescu Marian , Ghenescu Oana , Bazavan Rosemary , Danila Mihai , Gugiu Marius Marin , Antohe Stefan 
Published: April 2011

AbstractThe effects of irradiation with high-energy protons (3 MeV, up to a fluency of 1013 protons/cm2), on structural, electrical and optical properties of polycrystalline CdS and CdTe thin films have been investigated. XRD investigation has revealed that the films contain wurtzite-type CdS, (001) preferentially oriented in the growth direction, and cubic phase CdTe, respectively. The defects induced by ionizing radiations have been studied by thermally stimulated currents spectroscopy (TSC). Parameters of identified defect levels were determined and their possible origin is discussed.
Influence of Metal Impurity Defects on the Electrical and Optical Properties of ITO Films on the PEN Substrates
Authors: Han Hauk , Alford Terry L 
Published: April 2011

AbstractIndium tin oxide (ITO) has drawn a great deal of attention due to its potential use as transparent electrodes in organic light emitting diode (OLED) and photovoltaic applications. This work focuses on understanding the role of impurity defects on the electrical conduction and transmittance of ITO. Thin films of ITO with high carrier concentration have been deposited onto polyethylene napthalate (PEN) substrates by electron-beam deposition without introduction of oxygen into the chamber. The influence of air anneals on the electrical and optical properties of ITO/PEN samples can is evaluated in terms of the oxygen content and is explained in terms of changes in the free electron concentrations. Rutherford backscattering spectrometry and X-ray photoelectron spectroscopy analysis were used to determine the oxygen content in the film. A Hall effect measurement is used to determine the dependence of electrical properties on oxygen content. The electrical properties of the ITO films such as carrier concentration, electrical mobility, and resistivity abruptly changes after annealing in the air atmospheres. In addition, optical transmittance is improved from 7 to 71 % and optical band gap changes from 3.18 to 3.25 eV after heat treatment. The optical band gap narrowing behavior is because of impurity band and heavy carrier concentration. Metal impurity clusters form in the films as a result of oxygen deficiency and also generate defects and/or impurity states in the band gap and produces an optical band gap shift by merging of these impurity states and conduction band.
Study of the Electronic Properties of Matched Na-Containing and Reduced-Na CuInGaSe2 Samples Using Junction Capacitance Methods
Authors: Erslev Peter T , Halverson Adam , Shafarman William , Cohen J. David 
Published: April 2011

AbstractJunction capacitance methods were used to examine a matched pair of CuInGaSe2 (CIGS) thin film solar cells, one with Na incorporated into the absorber and the other with a diffusion barrier to inhibit the Na incorporation from the soda-lime glass. Typical cells showed a 50% increase in efficiency with the addition of Na. Forward biased admittance spectroscopy revealed a large defect density located near the CdS/CIGS heterojunction in the reduced Na samples not present in the higher Na samples. This may be responsible for the lower Voc, contributing to the loss in efficiency when Na is not added. Drive-level capacitance profiles revealed free carrier densities of 3×1014cm-3 and 1.1×1014cm-3 for the higher and reduced Na samples, respectively. Transient photocapacitance spectra indicated a slight improvement in absorber properties with the addition of Na, but not enough to account for the large loss in efficiency.
High-resolution Raman imaging by optically tweezing a dielectric microsphere
Authors: Kasim Johnson , Yu T. , You Y. M. , Liu J. P. , See A. K. H. , Shen Z. X. 
Published: April 2011

AbstractWe show a different method in doing near-field Raman imaging with sub-diffraction limit spatial resolution. A dielectric microsphere (for example polystyrene microsphere) is trapped by optical tweezers. The microsphere is used to focus the laser to the sample, and also to collect the scattered Raman signals. We show the capability of this method in imaging various types of samples, such as SiGe/Si structures, gold nanopattern and carbon nanotubes. This method is comparatively easier to perform, better repeatability, and stronger signal than the normal near-field Raman techniques.
Electrostatic Force Microscopy of Nanofibers and Carbon Nanotubes: Quantitative Analysis Using Theory and Experiment
Authors: Datta Sujit Sankar , Staii Cristian , Pinto Nicholas J. , Strachan Douglas R. , Johnson AT Charlie 
Published: April 2011

AbstractElectrostatic force microscopy (EFM) is a widely used scanning-probe technique for the characterization of electronic properties of nanoscale samples without the use of electrical contacts. Here we review the basic principles of EFM, developing a quantitative framework by which EFM measurements of extended nanostructures can be understood. We support our calculations with experimental data of EFM of carbon nanotubes and conducting or insulating electrospun polyaniline-based nanofibers. Furthermore, we explore routes towards extending EFM as a means of non-invasively probing the local electronic density of states of carbon nanotubes.
Attaching Biological Entities to AFM Cantilevers for Molecular Recognition Studies
Authors: Johnson W. Travis 
Published: April 2011

AbstractAtomic force microscopy (AFM) is an important tool for high resolution studies in biophysics and mechanical studies directed at biological materials. A strong suit of AFM is its ability to measure hardness/elasticity, nonspecific adhesion or ligand-receptor interactions at the picoNewton scale. Molecular interactions are critical factors in a variety of biological phenomenon; such as the initiation, modulation and termination of DNA replication, transcription, enzyme activity, infection, immune responses, tissue generation, wound healing, cell differentiation, apotopsis and physiological responses from drugs, hormones or toxic agents. Using AFM, scientists can probe and quantify these interactions in their native, liquid environments at physiological pH or perform dynamic experiments in situ by removing or adding ions, solutes and reagents to the sample environment. Bioconjugation chemistry and surface chemistry are crucial because a selective ligand must be immobilized on the tip of an AFM probe so that the AFM can resolve the mechanical force required to separate the ligand and its target. The resulting data can be used to calculate forces of unbinding, derive rate constants and infer structural information about the binding pocket. Biomolecular recognition experiments with AFM can be greatly enhanced through the use of relatively short (~8-10 nm), heterobifunctional, elastic, polyethylene glycol (PEG) linkers to immobilize ligands. Heterobifunctional linkers are used in order to permit their sequential immobilization and bioconjugation, while minimizing undesirable polymerizations or self-conjugation. The linkers have an N-hydroxysuccinimide ester at one end to permit their attachment to aminated silicon or silicon nitride AFM probes. Other reactive functional groups, such as a biotin, maleimide, disulfide, aldehyde, or a photoreactive group reside at the opposite end of the linker to permit the direct or indirect attachment of intact antibodies, Fab fragments, peptides, nucleic acids or other biological entities. The PEG linkers are flexible, so an attached ligand has freedom to diffuse within a defined volume of space and approach the binding site in a thermodynamically favorable manner. PicoTREC, an accessory for the Agilent AFM, uses ligand-PEG modified cantilevers to generate a topography image and a recognition image of biomolecular interactions. As the modified cantilever gently oscillates at defined amplitude, it is scanned across a sample and PicoTREC converts the information derived from ligand-receptor interactions into a high resolution, nanometer-scale map. Consequently, the locations of discrete molecular interactions can be easily determined and compared with a topography image of the sample.