bluuebunny/crossref_metadata_2025 huggingface dataset:
Figures of Merit for Electrically Conductive Polymer Composites
Authors: Grunlan Jaime C. , Gerberich William W. , Francis Lorraine F.
Published: April 2011

In an effort to determine the optimal balance of electrical and mechanical performance for electrically conductive polymer composites, three figures of merit were evaluated. All three figures of merit displayed peaks and/or discontinuities at a particular filler loading. These loadings appear to correspond to the critical pigment volume concentration for a given system. Composite systems based upon latex as the matrix starting material showed peaks in the figures of merit at very low carbon black concentrations (10 vol%), while composites prepared with polymer solutions or melts had peaks above 20 vol% carbon black. These differences in behavior are attributed to differences in microstructural evolution that occur with filler loading.
Electrospinning of Polymeric Nanofibers: Analysis of Jet Formation
Authors: Senador Antonio E. , Shaw Montgomery T. , Mather Patrick T.
Published: April 2011

Producing nanofiber-diameter polymeric fibers presents an attractive and robust approach toward the processing of nanocomposites, with applications ranging from clear optical components to toughened structural materials. In this work, we are examining the electrospinning process for the production of nanometer-diameter polymer fibers, giving particular attention to the following key features: jet-initiation, fiber architecture, and fiber distribution. A wide range of polymer systems and polymer-solvent combinations were studied in order to broaden the applicability of our conclusions to other systems. Specifically, a dimensional analysis was applied to jet-formation data obtained by quantifying the conditions required for the expulsion of fibers from a charged capillary to a grounded collection plate. The relationships between various dimensionless groups were compared with the expressions for the critical voltage that have been proposed for electrospinning of polymer solutions.
The Influence of Block Copolymers on Silica-Filled Polyisoprene
Authors: Gurovich Daniel , Macosko Christopher W. , Tirrell Matthew
Published: April 2011

The influence of PDMS-polyisoprene diblock copolymers on the dynamic rheological properties of silica-filled uncured polyisoprene was investigated. Unlike binary silica-polyisoprene systems, the ternary systems in our study showed a decrease in low-amplitude dynamic storage modulus (G') with room-temperature storage time. This aging behaviour is accompanied by an increase in the concentration PDMS segments at the filler-polymer interface, as measured by solid-state 1H NMR. The decrease in G' is thus attributed to a progressive disruption of a filler-filler network by selective block copolymer adsorption onto the filler surface.
Role of fractal features in the structure-property relationships of carbon black filled polymers
Authors: Ehrburger-Dolle Françoise , Hindermann-Bischoff Manuela , Geissler Erik , Rochas Cyrille , Bley Françoise , Livet Frédéric
Published: April 2011

Carbon black is widely used as a filler in order to modify the mechanical or the electrical properties of polymers. Such composites display significant non-linear effects. Moreover, examination of the large number of papers devoted to the physical properties of carbon black filled polymers indicates that each composite, even composites apparently consisting of similar matrixes and similar carbon blacks, may behave differently when prepared by different mixing methods. The present work aims to show that these particular behaviors can be related to the fact that carbon blacks used for composites are mass fractals of low dimensionality (Df ˂2) that are able to interpenetrate each other to an extent that depends on the filler-matrix surface interaction and on the volume fraction of filler.

Small-angle X-ray scattering (SAXS) is a convenient method for studying disordered systems at length scales ranging between a few tenths and a few hundred nm. SAXS is therefore particularly advantageous for exploring the morphology of carbon black aggregates and their degree of interpenetration when dispersed in a matrix. Furthermore, the use of an area detector yields two-dimensional images and hence information about anisotropy of the arrangement of scatterers. It is shown that this arrangement profoundly influences the physical properties of the composites.

Analysis of SAXS curves obtained for a rubber grade carbon black (N330) and for composites prepared by dispersing it into polyethylene or EPR will be presented. As an example, the temperature and frequency dependence of the electrical conductivity will be discussed and compared to theoretical models. Finally, the mutual consistency of the electrical and mechanical behavior, theoretical models and information deduced from the scattering curves will be shown.
Organoclay Nanoplatelets at the Air/water Interface
Authors: Shin Kwanwoo , Zhang Yimin , White Henry , Rafailovich Miriam H. , Sokolov Jonathan , Peiffer Dennis
Published: April 2011

We have demonstrated that films of single clay platelets can be produced by the Langmuir technique where a solution of organoclay particles dissolved in xylene was spread at the air water interface. The total thickness of the layer was found to be 21 ± 3Å which is in good agreement with previous X-ray diffraction data. Scanning probe microscopy showed the individual platelets to be rectangular in shape with an aspect ratio in excess of 100 to 1 and of uniform organic surfactant coverage.
State of Dispersion of Reinforcing Silica in a Silicone Elastomer, as Investigated by Transmission Electron Microscopy
Authors: Field Rex J , Cambray Jeanne , Floess Joachim , Rouanet Stephane
Published: April 2011

Commercial silicone rubbers typically contain submicron particles dispersed within them, the particles being responsible for the mechanical properties required for commercial success. Fumed silica has long been used for the reinforcement of higher-perfomance silicone rubber compositions, but high-porosity aerogels can function as well. The object of the work here was to compare the state of dispersion of some high-porosity aerogels with that of a fumed silica.

Model silicone HCR (“heat-cured rubber”) compositions were prepared, and their mechanical properties characterized. Thin sections of the rubbers were then examined by TEM.

Much of the fumed silica had been dispersed to give sub-micron sized features, although a number of larger features were present. The hydrophobic aerogel, in contrast, had been dispersed to give even finer features in the rubber, with very few super-micron fragments. The state of dispersion of the hydrophilic aerogel was quite different, showing many poorly-broken down large fragments up to 5 µm or more in diameter. The visual appearance of the compound reflected this poorer state of dispersion.
Biological Reaction to Electrically Polarized Hydroxyapatite
Authors: Sakai Tomoko , Ueshima Masato , Morita Sadao , Nakamura Satoshi , Yamashita Kimihiro
Published: April 2011

We have studied the polarized hydroxyapatite (HAp) whose surface was negatively or positively charged. In this study, we assessed the interfaces in vitro and in vivo periodically. As in vitro experiment, samples were immersed in simulated body fluid for 7 days and the surface was examined by scanning electron microscope (SEM). As in vivo experiments, cortical bone defects were created on the femoral trochanters and the condyles of the six Japanese white rabbits and the samples were implanted. The rabbits were sacrificed at 1, 2 and 4 W after the operation to analyze the surfaces by the SEM and the optical microscopy. In this study, a new thick apatite layer was formed on the negatively charged surface (N-surface) after 1week immersion in SBF in vitro. Besides, significant new bone formation was found at 2 weeks after the operation on N-surface in vivo, which was earlier than positively charged or non-polarized HAp surface. From this study negatively charged HAp surface by polarization accelerated the HAp crystal growth or the new bone formation. Thus, this N-surface will be promising for earlier fixation of the prosthesis or better recovery of the bone defect.
Using Indentation and Intra-Vascular Ultrasound to Measure Arterial Response
Authors: Anderson P.M. , Glaser E.N. , Veress A.I. , Pharr G.M. , Vince D.G. , Cornhill J.F. , Herderick E.E.
Published: April 2011

Two alternatives to standard tensile testing of arteries are discussed. The first involves inflation of arteries and simultaneous measurement of radial displacement with intra-vascular ultrasound (IVUS). The second involves the measurement of load versus displacement during micro-indentation of the intimal surface. The IVUS technique is used to study the nonlinear stiffening of porcine coronaries during inflation and, ultimately, it may provide a method to determine mechanical properties in vivo. Processing of the IVUS data relies on accurate determination of the luminal/intimal and medial/advential boundaries during inflation. The microindentation technique is used to study the effect of loading rate on tissue stiffness, recovery, and internal dissipation. Ultimately, this technique may provide a method to measure local mechanical properties in the vicinity of an atherosclerotic plaque, for example. Accurate determination of the initial contact point between the indenter and intima is required, however. The techniques appear to successfully capture significant, nonlinear, time-dependent properties of arterial tissue.
Controlled Release of Bone Growth Factors from Injectable, Biodegradable Polymer Scaffolds for Bone Tissue Engineering
Authors: Hedberg Elizabeth L. , Mikos Antonios G.
Published: April 2011

The objective of this research is to fabricate injectable, polymeric composites that will act as scaffolds for bone ingrowth as well as carriers for the controlled release of bone growth factors. To that end, the injectable polyester poly(propylene fumarate) (PPF) was loaded with poly(DLlactic-co-glycolic acid) (PLGA) microparticles carrying the model drug FITC-dextran. This preparation was then crosslinked with N-vinyl pyrrolidinone in the presence of benzoyl peroxide as initiator and sodium chloride (NaCl) as leachable porogen. The encapsulation of growth factors in microparticles is necessary to minimize their denaturation during scaffold crosslinking. PLGA microparticles (0.04 g microparticles/g PPF) were incorporated into PPF composites having variable NaCl weight percents (50 and 70 wt% NaCl) and the effect on FITC-dextran release kinetics was determined in vitro for cylinders of diameter 6.5 mm and height 13.0 mm. The FITC-dextran loaded microparticles alone exhibited a large initial burst effect, while the composite materials displayed a smaller burst effect and a longer linear region of release. At day 3, 54.6±2.1%, 5.1±0.9%, and 12.5±0.3% of loaded FITC-dextran was released into pH 7.4 phosphate buffered saline from the microparticles, the 50 wt% NaCl, and the 70 wt% NaCl composites, respectively. By day 28, 90.9±6.9%, 12.7±1.7%, and 34.4±0.4% of loaded FITC-dextran was released. Our results demonstrate that PLGA microparticles can be incorporated into PPF composites and that the release kinetics of FITC-dextran can be systematically manipulated through alteration of the composite initial salt content.
Admittance Spectroscopy on Polymer Light-Emitting Diodes
Authors: Blom P.W.M. , Martens H.C.F. , Brom H.B. , Huiberts J.N.
Published: April 2011

From admittance spectroscopy measurements on poly(p-phenylene vinylene) based light-emitting diodes various relaxation processes can be observed. At low bias inductive contributions due to the transit of charge carriers dominate, at high bias capacitive contributions as a result of charge redistribution appears. These processes reveal a transition from space-charge limited to recombination limited behavior, as is also indicated by the current-voltage characteristics.
Metal-to-Ligand Charge Transfer Excited States in π-Conjugated Systems
Authors: Li Yiting , Whittle C. Ed , Walters Keith A. , Ley Kevin D. , Schanze Kirk S.
Published: April 2011

This paper overviews recent work that examined the optical properties of mono-disperse, PPE-based π-conjugated oligomers that contain a 2,2-bipyridine-5,5'-diyl metal coordinating unit. The photophysical properties of the free oligomers and metallated oligomers that contain the -Ru(bpy)22+ and -Re(CO)3Cl transition metal complexes coordinated to the bpy-diyl unit have been characterized by absorption, photoluminescence and transient absorption spectroscopy. In addition, we report the photophysics of a novel organometallic “square” that features “sides” consisting of a PPE-type π-conjugated oligomer and “corners” that consist of (dbubpy)PtII(acetylide)2 units (where dbubpy = 4,4'-di-tert-butyl-2,2'-bipyridine).
Approaches to Advanced Organic Light Emitting Diodes: Materials and Devices
Authors: Ikai Masamichi , Taga Yasunori
Published: April 2011

We present our recent findings on the development of organic light emitting diodes (OLEDs). One of the keys to highly efficient phosphorescent emission in organic light-emitting diodes is to confine triplet excitons generated within the emitting layer. To confine triplet excitons, we employ perfluorinated phenylene dendrimers (C60F42) as a both hole- and exciton-block layer, and a hole-transport material (4,4',4”-tris(N-carbazolyl) triphenylamine [TCTA]) as a host for the phosphorescent dopant, Ir(ppy)3, in the emitting layer. The maximum external quantum efficiency reaches to 19.2%, and is over 15% even at high injection current densities of 10 to 20 mA/cm2, where the brightness of the device reaches to approximately 10,000 cd/m2.
A Mercury Selective Electrode
Authors: Scaggs Jon , Russell Dale D. , Duttagupta S. P. , Hill Michael W.
Published: April 2011

A novel mercury ion selective electrode has been constructed to have strongly coordinating macrocyclic ligand binding site covalently attached to polythiophene film using 1-1,4,10-trioxa-7,13-diazacyclopentadecane-1-thiophenylmethane (TDCD-thiophenylmethane) as a specific chelator. In amperometric mode, the current is proportional to mercury (II) concentrations down to 2 ppb. Reversible cyclic voltammetric waves show that both mercury (I) and mercury (II) are stabilized by the ligand. Monomethyl mercury and vapor phase elemental mercury are also electrochemically determined. Dissolved oxygen and heavy metal cations show no significant interference even at ten times the mercury concentration. The polymer surface shows robust performance for two years or longer. Fabrication strategies are being developed to optimize the probe performance. The variables under investigation include substrate surface roughness, the ratio of derivitized thiophene (TDCD-thiophenylmethane) to underivatized thiophene in the surface polymer, ratio of thiophene with two chelating rings to thiophene with only one, number and thickness of electrodeposited polymer layers, composition of polymer layers, and number of -CH2- units separating the chelating ring from the thiophene monomer units. The probe exhibits linear response to mercury concentration, and detects mercury in several forms.
The Relationship Between Molecular Structure and Spectroscopic Properties of a Series of Transition Metal-Containing Phenylacetylene Oligomers and Polymers
Authors: Cooper Thomas M. , McLean Daniel G , Rogers Joy E.
Published: April 2011

To develop novel nonlinear dyes for photonic applications, we synthesized a series of transition metal-containing phenylacetylene oligomers and polymers. The optical properties of these compounds were measured by UV/Vis, fluorescence, and flash photolysis experiments. As the number of oligomer units increased, the transition energies decreased. A solvatochromism experiment suggested the fluorescing state was different from the absorbing state. As a group, the spectra of the polymeric versions of these complexes were red shifted from the spectra of the oligomers. The polymeric complexes had less clear trends relating the number of oligomer units to transition energies. A comparison of a low molecular weight and a high molecular weight polymer showed the degree of polymerization caused spectroscopic shifts comparable to the number of phenylacetylene units in the monomer unit.
Investigation of Morphology and Interface in Polymer Composite Thin Films
Authors: Chiang C. K. , Sung L. P. , Popielarz R.
Published: April 2011

Laser scanning confocal microscopy (LSCM) has been applied to examine the filler particles and their distribution in BaTiO3-polymer composite films. We have measured thin-slice images of the composite films at various depths from the film surface and visualized the submicron size particles and the polymer between them nondestructively. We have found that, although BaTiO3 particles appear to be uniformly dispersed in the composite films when observed under conventional microscope, the particles form clusters at low BaTiO3 concentrations. The lower the concentration the larger the cluster size. The particles appear to be better dispersed in the high concentration composites than at low concentrations.
Charge Transport in Pentacene Thin Film Transistors
Authors: Schön J. H. , Buchholz L. D. , Kloc Ch. , Batlogg B.
Published: April 2011

The charge transport properties in polycrystalline pentacene thin film transistors is investigated. A potential barrier is formed at grain boundaries due charged trapping states. The influence of such grain boundaries on the hole mobility of the devices is analyzed for different grain sizes, trap concentrations, and carrier densities. The results reveal that room temperature mobilities exceeding 0.5 cm2/Vs can be obtained in thin films with large grains as well as in nanocrystalline material. Consequently, single crystal device limits can be reached also by polycrystalline pentacene thin film transistors.
A Comparative Study of the Photophysics in Polyfluorenes and Polyfluorenes with Polyphenylene Dendron Sidechains
Authors: List E. J. W. , Pogantsch A. , Wenzl F.P. , Kim C.-H. , Shinar J. , Loi M. A. , Bongiovanni G. , Mura A. , Setayesh S. , Grimsdale A. C. , Nothofer H.G. , Müllen K. , Scherf U. , Leising G.
Published: April 2011

The cw absorption, steady state photoluminescence (PL), photoinduced absorption (PA), PL-detected magnetic resonance (PLDMR), and the time resolved PL of a novel polyfluorene (PF) prepared with bulky polyphenylene dendrimer substituents are compared with those of (PF) with ethyl-hexyl substituents. We show that the dendronic sidechains suppress the contribution from unwanted low energetic emission, yielding a polymer with pure blue emission. The sidechains also strongly alter the dynamics of the excited entities. In particular, the time-resolved PL and temperature-dependence of the cw PL from 20-320 K reveal distinct singlet exciton (SE) dynamics in the polymer films, while the behavior in solution is essentially the same. However, the PA results show that the dynamics of polarons and triplet excitons (TEs) are similar, and the PLDMR shows that the interaction between the SEs and polarons are also similar.
Structural Properties of Conjugated Molecular Crystals Under high Pressure
Authors: Heimel Georg , Zojer Egbert , Resel Roland , Pushning Peter , Weinmeier Kerstin , Ambrosch-Draxl Claudia
Published: April 2011

Electro-active organic materials based on conjugated molecules, showing promising optical features in the UV/Vis region combined with high electron mobility and fluorescence quantum yield, are of great interest for both, scientific and commercial use. Since the electro-optical properties of these materials are critically influenced by their the crystal and molecular structures, the goal of our work is to study the nature of the intermolecular interactions by applying hydrostatic pressure. X-Ray powder diffraction experimets were carried out to determine the lattice parameters. These experimental data then served as an input for an optimization of the atomic positions and molecular orientation based on total -energy and atomic-force computations within density functional theory.
High Pressure Studies of Polyaromatic Molecilar Crystals: Optical and Electronic Properties from first Principles
Authors: Weinmeier Kerstom , Puschning Peter , Ambrosch-Drax Claudia , Heimel Georg , Zojer Egbert , Resel Roland
Published: April 2011

Molecular crystals based on conjugated aromatic molecules have attracted a lot of interest, since their combined electrical and optical properties enable them many technical applicatins. The optical features and the anisotropic electron mobility strongly depend on the crystalline structure of such materials, which itself is determined by the inter-and intramolecular interactions. We investigate those interactions by performing full potential linearized augmented plane wave (FP-LAPW) band structure calculcations accompanied by X-ray [powder diffraction experiments imder hydrpstatoc [ressure up to 50 κbar. In this work we focus on the compounds anthracene and para-terphenyl and report their internal geometry, electronic structure and optical spectra as a functionof pressure.
Esr Investigations On Polyaniline-Polyvinylchloride Blends
Authors: Chipara M. , Goovaerts E. , Chipara Magdalena , Munteanu I.
Published: April 2011

Electron spin resonance (ESR) investigations on blends of polyaniline (PANI) and polyvinylchloride (PVC), containing different amounts of PANI, ranging from 0 to 40% (in weight), are reported. The temperature dependence of resonance line parameters, in the temperature range 150 K to 500K is analyzed. It is proved that the high spins bipolarons are not contributed to the ESR spectrum and that the resonance spectrum does not contain contributions due to extremely high conducting islands, with lengths of the order of at least 1micron. From the temperature dependence of the double integral of the resonance line, it is concluded that, the blends exhibit an almost pure paramagnetic behavior and that at short times physical processes control the behavior of these blends. At long times (102 to103 hours), the resonance spectrum is drastically reduced due to the consumption of free electrons in the chemical reactions involved by the degradation processes occurring mainly in PVC. A stationary value is reached for storage times of about 2500 hours, in air, at room temperature.
Solvent-enhanced Dye Diffusion in Polymer This-Films for OLED Application
Authors: Pschenitzka F. , Long K. , Sturm J. C.
Published: April 2011

A method of solvent-enhanced dye diffusion in polymer films for organic light-emitting diode (OLED) application is introduced. After an initial dye transfer from a dye source substrate into the top of the electractive polymer film, the device substrate is then exposed to solvent vapor. Due to solvent absorption by the polymer film, the glass transition temperature of the polymer is significantly decreased, which leads to greatly enhanced diffusion of the dye in the polymer film. Secondary ion mass spectroscopy shows that the temperature for dye diffusion can be decreased by 150 °C. OLEDs with 0.4% external quantum efficiency were demonstrated. The materials used are the polymer poly(9-vinylcarbazole) (PVK) combined with electron transport molecules (PBD), and the dyes coumarin 47, coumarin 6 and Nile red.
Transparent Conductive Oxide Semiconductor ZnO:Al Films Produced by Magnetron Reactive Sputtering
Authors: Meng Chen , Zhiliang Pei , Xi Wang , Cao Sun , Lishi Wen
Published: April 2011

ZnO:Al (ZAO) films were deposited on quartz substrates by dc magnetron reactive sputtering from a Zn target mixed with Al. The effect of substrate temperature and Al doping content on the structural, electrical and optical properties of ZAO films were investigated. It was observed that the (002) peak position of all films shifts to lower angle comparable to that of bulk ZnO due to the residual stress change with deposition parameters. The dependences of electrical properties such as resistivity, carrier concentration and Hall mobility on substrate temperature and Al doping content were measured. The minimum resistivity is 4.23×10−4 ω.cm with the carrier concentration of 9.21×1020 cm−3 and Hall mobility of 16.0 cm2v−1s−1. The visible transmittance of above 80% was obtained. The optical band gap was observed to increase with increasing carrier concentration. The possible mechanisms are discussed.
Transparent Conductive Tin Doped Indium Oxide Thin Films with Silver Additive
Authors: Hultåker Annette , Lu Jun , Olsson Eva , Niklasson Gunnar A. , Granqvist Claes-Göran
Published: April 2011

Thin films of intermixed layers of In2O3:Sn (denoted ITO) and silver were made by reactive dc magnetron sputtering. The silver to indium atomic ratio was 0 ≤ x ≥ 0.09 Films with x = 0.01 showed increased luminous transmittance Tlum after annealing at 100 or 200°C, whereas x > 0.01 yielded lowered Tlum. The optical properties could be reconciled with the Maxwell-Garnett effective medium theory assuming that a well-defined portion of the silver was occluded as spheroidal particles. Films with x ≤ 0.06 had enhanced electrical conductivity after annealing at 200 or 300°C. Transmission electron microscopy displayed columnar features whose character depended on x.
Doping Experiments in ZNO
Authors: Stauber R.E. , Parilla P.A. , Perkins J.D. , Cueto J.A. Del , Ginley D.S.
Published: April 2011

This paper reports on attempts to fabricate transparent electrically conductive p-type ZnO by pulsed laser deposition (PLD) and sputtering using N2, N2O and NO gases. Expanding on the work of Kawai and coworkers [1,2], we used an ion source, rather than an ECR source in the PLD chamber to dissociate N2O gas, and explored the use of aluminum in addition to gallium as potential co-dopants. The most promising results have been obtained with DC reactive sputtering of gallium-doped zinc metal targets. A three to six order of magnitude reduction in n-type carrier density was observed when 2% of the argon sputtering gas was replaced with NO.
Thin Film Growth of Zinc Oxide by Vapor Phase Epitaxy
Authors: Ellis James A. , Seng William F. , Barnes Peter A.
Published: April 2011

Zinc Oxide is a potentially valuable semiconductor with photoconducting, piezoelectric, optoelectronic, and optical waveguide applications. A technique for the growth of ZnO epitaxial layers is necessary for improved device fabrication. Previously, attempts at ZnO epitaxial growth were constrained to sapphire substrates using sputtering as the preferred preparation technique. However, with the present availability of single crystal ZnO substrates the hope of high quality epitaxial layers exists. The authors will discuss several possibilities for growth precursors, and the resulting chemical reactions required for the formation of ZnO. This presentation discusses the growth of ZnO epitaxial layers by chemical vapor deposition without using metal-organic compounds. The thermodynamics and predicted growth rates for several reactions are presented as well as the preliminary growth results. The preliminary growths are characterized with the aid of Hall Effect measurements, providing information on resistivity, Hall mobility, and carrier concentration.
Transparent p-n Heterojunction Thin Film Diodes
Authors: Jayaraj M. K. , Draeseke A. D. , Tate J. , Hoffman R. L. , Wager J. F.
Published: April 2011

Transparent p-n heterojunction diodes are fabricated using p-type CuYO2:Ca and n-type ZnO:Al thin films on a glass substrate coated with indium-tin oxide (ITO). The contact between the n-ZnO:Al / p-CuYO2:Ca heterojunction is found to be rectifying, while the ITO / ZnO:Al contact is ohmic. The typical ratio of forward to reverse current is 15 in the range -3 to 3V. The diode current-voltage characteristics are dominated by the flow of space charge limited current, which is ascribed to the existence of an insulating ZnO interfacial layer. The diode structure has a total thickness of 0.85 μm and an optical transmission of 40%-50% in the visible region.
Prospects for the Mott Transition Field Effect Transistor
Authors: Misewich J.A. , Schrott A.G.
Published: April 2011

We have been investigating the potential for a channel transistor which utilizes a perovskite oxide capable of undergoing the Mott metal-insulator transition as the channel material. Our experiments have identified three limitations to the performance of the oxide devices: contact resistance to the channel, mobility limitations due to polycrystalline channels, and inadequate field induced surface charge density. In this paper we review progress we have made in oxide electrodes and in improving channel growth conditions which have mitigated the limitations due to contact resistance and polycrystalline channels. We conclude with an outline of our approach to improving the field induced surface charge density.
Structural and Electrical Properties of Y2O3 Buffer Layer Prepared by Two Step Process
Authors: Lim Dong-Gun , Jang Bum-Sik , Moon Sang-Il , Jang Dong-Min , Heo Jinhee , Yi Junsin
Published: April 2011

In this paper we investigated a feasibility of Y2O3 films as a buffer layer of MFIS (metal ferroelectric insulator semiconductor) type capacitor. Buffer layers were prepared by two-step process of a low temperature film growth and subsequent RTA treatment. Investigated parameters are given as substrate temperature, O2 partial pressure, post-annealing temperature, and suppression method of interfacial SiO2layer generation. By employing an ultra thin Y pre-metal layer, unwanted SiO2 layer generation was successfully suppressed at an interface between the buffer layer and Si substrate. By using two-step process, we improved the leakage current density of Y2O3 films by 2 orders and the Dit as low as 8.72×1010 cm−2eV−1. For a substrate temperature above 400°C and O2 partial pressure of 20%, we observed cubic Y2O3 phase domination in XRD spectra. We achieved 1.75% lattice mismatch between Y2O3 film and silicon substrate. Y2O3 buffer layer for a single transistor FRAM exhibited optimal properties when it was grown at 400°C with 20% O2 partial pressure then RTA treatment at 900°C in oxygen ambient.
Application of ultraviolet radiation to minimize interfacial layer formation during the growth of alternate high-k gate dielectrics on Si
Authors: Craciun V. , Bassim N. D. , Howard J. M. , Spear J. , Bates S. , Singh R. K.
Published: April 2011

Yttrium oxide and barium strontium titanate (BST) thin films were grown directly on Si substrates by the pulsed laser deposition (PLD) technique. Because the optimum oxygen pressure during PLD process is of the order of 10 mTorr, some of the oxygen atoms are trapped inside the grown films and contribute to the growth of a silicon oxide interfacial layer. The use of an UV source during the growth resulted in the reduction of the optimum oxygen pressure and, as a consequence, the amount of trapped oxygen and thickness of the interfacial layer. In addition to that, UV radiation influenced the film morphologies and electrical properties. A further reduction of the interfacial layer was obtained on substrates that were exposed prior to deposition to NH3 for short periods of time under UV radiation.
Development of an organic dye solution for laser cooling by anti-Stokes fluorescence
Authors: Bartholomew Jarett L. , DeBarber Peter A. , Heeg Bauke , Rumbles Garry
Published: April 2011

Several independent groups have observed optical cooling by means of anti-Stokes luminescence in condensed media. The most promising materials are grouped into two categories: ion-doped glasses and organic dye solutions. It is this latter group that we focus our efforts on. Recent studies by our group show that irradiating a solution of rhodamine 101 in the long wavelength wing of the absorption spectrum results in the observation of optical cooling. To improve upon the initial observation of a few degree drop in temperature requires a better understanding of the conditions and phenomena leading to anti-Stokes luminescence in dye solutions. We develop a thermal lensing experiment to obtain fluorescence quantum yields of various dye solutions. The importance of concentration, choice of solvent, deuteration, and acidification are discussed.
Electrical and Optical Studies of the Organic Thin Film Devices Produced by Cluster Beam Deposition Methods
Authors: Kim J.Y. , Kim E.S. , Choi J.-H.
Published: April 2011

The neutral and ionized cluster beam deposition (NCBD and ICBD) methods have been applied to fabricate the new double-layer organic light emitting devices (OLEDs) with the structure of indium-tin-oxide (ITO)-coated glass/spin-coated poly[2-(N-carbazolyl)-5-(2-ethyl-hexyloxy)-1,4-phenylenevinylene] (CzEH-PPV)/8-hydroxyquinoline aluminum (Alq3)/Li:Al. The surface morphology profiles measured by atomic force microscopy (AFM) showed that the cluster beam deposition methods are efficient in producing uniform and smooth film surfaces. Photo- and electro-luminescence (PL, EL) spectroscopies demonstrated that while the new hole transporting medium CzEH-PPV is susceptible to the bombardment of energetic ionized beam, the introduction of the neutral buffer layer significantly improves the device characteristics, i.e., lower threshold and turn-on voltages and higher external quantum efficiency (EQE). In addition, the effect of doping of highly fluorescent dye (DCM) into Alq3 layer showed a complete energy transfer, color-tuning capability and higher EQE compared to the undoped devices.
Polygermyne: Germanium sheet polymers with efficient near-infrared luminescence
Authors: Vogg Günther , Brandt Martin S. , Meyer Lex J.-P. , Stutzmann Martin , Hajnal Zoltán , Szücs Bernadett , Rauenheim Thomas
Published: April 2011

The structural, optical and electronic properties of the Ge sheet polymer poylgermyne are summarized. Prepared via topotactic transformation of Zintl-phase CaGe2, (GeH)n forms a layered crystal in a tr6 stacking sequence with a distance of 5.65 Å between adjacent layers. The photoluminescence at 1.3 eV is excited nearly resonantly with a Stokes shift of 0.2 eV. Together with band structure calculations this shows that polygermyne has a direct band gap.
Photoluminescence and Raman Spectroscopy Studies of H+ Ion Implanted SOI Structures Formed by Hydrogen Ion Slicing
Authors: Popov Vladimir P. , Tyschenko Ida E. , Zhuravlev Konstantin S. , Morosov Ivan I.
Published: April 2011

H+ ion implanted SOI structures formed by hydrogen ion slicing have been investigated by Raman spectroscopy and photoluminescence (PL). After implantation the wafers have been heat-treated by either furnace annealing (FA) or rapid thermal annealing (RTA). It has been found that implantation of 3 × 1017 H+/cm2 results in the formation of the amorphous Si layer (a-Si) inside silicon film on insulator. Structural transformations in a-Si depended on the annealing conditions. FA led to crystallization of a-Si and to the formation of monocrystalline silicon films. RTA results in the formation of the layers containing a high density of Si nanocrystals. A comparison of the Raman measurements with the PL data allows to conclude that PL bands obtained near 420 and 500 nm are not associated with the radiative recombination in Si nanocrystals.
Luminescence of Lu2O3:Tm3+ nanoparticles
Authors: Donegá Celso de Mello , Zych Eugeniusz , Meijerink Andries
Published: April 2011

This paper presents for the first time a comparison between the luminescence properties (viz. emission and excitation spectra, lifetimes, and concentration quenching) of nanocrystalline and microcrystalline Lu2O3:xTm3+ (x= 0.1– 5 mol%). The results show that the most important difference between the two size regimes is the higher defect concentration in the nanoparticles. These defects give rise to a broadband emission (λmax = 430 nm), and to partial quenching of the Tm3+ emission, in addition to the expected concentration quenching by cross-relaxation between Tm3+ ions. The defect concentration seems to be similar in all nanocrystalline samples, so that those with the lowest Tm3+ concentrations experience the most pronounced quenching. The nature of these defects is as yet unknown. The local structure around the Tm3+ ions is not noticeably different in the two size regimes. No evidence of phonon confinement or quantum size effects was observed in the Tm3+luminescence.
Red Emitting Electroluminescent Devices Using Ga2O3 Phosphor Thin Films Prepared by Sol-Gel Process
Authors: Minami Tadatsugu , Shirai Tetsuya , Miyata Toshihiro
Published: April 2011

High-luminance red-emitting thin-film electroluminescent (TFEL) devices have been developed using Ga2O3 phosphor thin films prepared by a sol-gel deposition method. Single-insulating-layer-type TFEL devices were fabricated by depositing a Cr- or a Eu-activated Ga2O3 phosphor thin film onto a thick BaTiO3 ceramic sheet insulator. The Ga2O3:Cr or Ga2O3:Eu thin-film emitting layer was prepared by a sol-gel process using gallium acethylacetonate (Ga(C5H7O2)3) as the Ga source with Cr(C5H7O2)3 or EuC13 as the dopant source, respectively. A high red luminance of 622 cd/m2 was obtained for a Ga2O3:Cr TFEL device driven by a sinusoidal wave voltage at 1 kHz.
Novel Fluorescent Labels Prepared by Layer-by-Layer Assembly on Colloids for Biodetection Systems
Authors: Yang Wenjun , Trau Dieter , Renneberg Reinhard , Yu Nai-Teng , Caruso Frank
Published: April 2011

Fluorescent polystyrene microparticles with different sizes were produced by the consecutive assembly of fluorescently labeled polyelectrolytes using the layer-by-layer self-assembly method. Film growth was characterized by microelectrophoresis and fluorescence microscopic image (FMI) analysis. Alternating negative and positive ζ-potentials with deposition of each successive polyelectrolyte layer demonstrated that the alternate adsorption of polyelectrolytes was achieved. FMI analysis provided direct measurement of the fluorescence intensity of single microparticles. The subsequent deposition of a protein (immunoglobulin G, IgG) layer onto the fluorescent microparticles was confirmed by a sandwich immunoassay.
Color Centers in Magnesium Doped Polycrystalline Alumina
Authors: Brock L. R. , Mishra K. C. , Raukas Madis , Lapatovich Walter P. , Wei George C.
Published: April 2011

We have investigated color centers in MgO-doped polycrystalline alumina (PCA) using absorption, excitation, and emission spectroscopy. Most of the color centers that were reported in earlier studies of the crystalline material have been observed to be present in the polycrystalline material. The absorption spectral features observed in the PCA are attributed to various color centers; however, they are not sufficiently resolved to make unique assignments. Suitable combinations of excitation and emission spectroscopy and also measurements at low temperature were therefore used to identify most of the color centers in this material.

Among the numerous color centers that we have identified in PCA are variations of electron centers including F, F+, F2+, F22+ and F+-Mg ((Vo•-MgAl')x). The most prominent oxygen vacancy related defect observed at room temperature was the F+-Mg center, with absorption bands located at 217 and 249 nm, and an emission band at 303 nm. This center can be thought of as being formed by association of an F+ center with a Mg defect. The single crystal sapphire samples containing no Mg show only F+ (Vo•) centers with 230 and 257 nm absorption bands, and a 328 nm emission band.

Low temperature (22 K) fluorescence excitation measurements of PCA led to emission from F22+center at 467 nm. Additionally, there is evidence that the observed 368 nm emission band could be attributed to the zero-phonon line associated with the F2+center.
Advanced Ion Implantation Technology for High Performance Transistors
Authors: Suguro Kyoichi , Murakoshi Atsushi , Iinuma Toshihiko , Akutsu Haruko , Shibata Takeshi , Sugihara Yoshikazu , Okumura Katsuya
Published: April 2011

Cryo-implantation technology is proposed for reducing crystal defects in Si substrates. The substrate temperature was controlled to be below at -160°C during ion implantation. No dislocation was observed in the implanted layer after rapid thermal annealing. Pn junction leakage was successfully reduced by one order of magnitude as compared with room temperature implantation. Precise dose control is indispensable in channel region of high performance MOSFETs. In order to improve the precision of implanted dose, chip size implantation technology without photoresist mask was developed. In this technology, chip-by-chip implantation can be carried out by step-and-repeat wafer stage, and different implantation conditions are available in the same wafer independent of wafer size.
Computer Simulation of Decaborane Implantation into Silicon, Annealing and Re-crystallization of Silicon
Authors: Insepov Zinetulla , Yamada Isao
Published: April 2011

Molecular Dynamics (MD) and Activation-Relaxation Technique (ART) models of decaborane ion implantation into Si and following rapid thermal annealing (RTA) processes have been developed. The B and Si atomic positions for implantation of accelerated decaborane ions, with total energy 3.5- 15 KeV, into Si substrate were obtained by MD simulation. The main difference between monomer and decaborane ion implantation with the same doses is the formation of a large amorphized area in a subsurface region for the decaborane case. The number of displaced Si atoms shows non-linear energy dependence at low impact energies. At higher energies ofthe investigated range of the decaborane energy range, however, a linear dependence is observed in accordancewith the prediction of the Kinchin-Pease formula. A new method that incorporates Activation-Relaxation Technique (ART) with MD has been developed and used to study re-crystallization of Si amorphized in the implantation process.
Effect of Arsenic on Extended Defect Evolution in Silicon
Authors: Brindos R. , Jones K. S. , Law M. E.
Published: April 2011

The effect of arsenic on {311} defect formation was determined for temperatures ranging from 700°C to 800°C. Arsenic well structures were formed at arsenic concentrations of 3×1017, 3×1018, and 3×1019 cm−3. A 40 keV 1×1014 cm−2 silicon implant, that is known to form {311} defects, was then incorporated into the structures. Extended defect evolution and dissolution was then studied after furnace annealing at 700°C, 750°C and 800°C for various times. It was determined that arsenic has a strong affect on the nucleation of extended defects. However, once the defects were formed, the dissolution time constant was the same for all concentrations considered. The activation energy for defect dissolution was found to be 3.4eV and was also independent of arsenic concentration. Using a newly developed {311} model in the FLOOPS process simulation software, the effect of the arsenic on {311} formation and dissolution was simulated. It was found that by using a pair model with an arsenic-interstitial binding energy of 0.95eV, the experimental results were able to be simulated.
Influence of Arsenic Clustering and Precipitation on the Interstitial and Vacancy Concentration in Silicon
Authors: Brindos R. , Clark M. H. , Jones K. S. , Griglione M. , Gossmann Hans-J. , Agarwal A. , Murto B. , Andideh E.
Published: April 2011

The point defect injection from arsenic precipitation was studied using boron marker layers and antimony doped superlattices. Comparisons of arsenic and germanium amorphizing implants showed similar boron marker layer diffusion enhancements after spike annealing. The results indicate that the end of range damage caused by the implants was the source of the diffusion enhancement. Additional annealing cycles showed that there was retardation in the diffusion enhancement of the boron marker layers for precipitation range arsenic implants. Antimony marker layers showed no diffusion enhancement due to vacancy injection. The results of the experiments indicate that arsenic-interstitial complexes are the cause of the decrease flux of interstitials to the bulk.
A Study of the Deactivation of High Concentration, Laser Annealed Dopant Profiles in Silicon
Authors: Takamura Yayoi , Jain Sameer , Griffin Peter B. , Plummer James D.
Published: April 2011

As semiconductor device dimensions continue to decrease, the main challenge in the area of junction formation involves decreasing the junction depth while simultaneously increasing the active dopant concentration. Laser annealing is being investigated as an alternative to rapid thermal annealing (RTA) to repair the damage from ion implantation and to activate the dopants. With this technique, uniform, box-shaped profiles are obtained, with dopant concentrations that can exceed equilibrium solubility limits. Unfortunately, these super-saturated dopant concentrations exist in a metastable state and deactivate upon further thermal processing. In this work, a comprehensive study of the deactivation kinetics of common dopants (P, B, and Sb) was performed across a range of annealing conditions. For comparison, As deactivation data from the work of Rousseau et al.1 is also presented. Each dopant exhibits different deactivation behavior, however, As and P can be classified as unstable species while B and Sb are stable against deactivation until higher temperatures of 700-800°C. In addition, a means of maintaining these metastably doped layers is being investigated with the goal of meeting the International Technology Roadmap for Semiconductors (ITRS) requirements for ultrashallow junctions.
Antimony and Boron Diffusion in Silicon and Silicon Germanium under the Influence of Point Defects Injection by Rapid Thermal Anneal
Authors: Dan Aihua , Willoughby Arthur F. W. , Bonar Janet M. , McGregor Barry M. , Dowsett Mark G. , Ormsby Terry J.
Published: April 2011

The effect of point defect injection on the diffusion of antimony and boron in silicon and silicon-germanium alloys has been studied by comparison of inert with injection diffusions. In this work, Sb and B in Si were used as control wafers to investigate Sb and B diffusion behavior in Si0.9Ge0.1. The point defect injection technique was carried out by rapid thermal annealing (RTA) Sb and B in Si and Si0.9Ge0.1 samples with the various surface coatings in either oxygen or ammonia atmospheres to inject either interstitial or vacancy defects. The diffusion profiles for as-grown and RTA annealed samples were measured by Secondary Ion Mass Spectrometry (SIMS). Diffusivities for B in Si and Si0.9Ge0.1 were obtained using computer simulations of the measured boron profiles for their annealed samples. Sb diffusion in Si and Si0.9Ge0.1 was found enhanced by vacancy injection and retarded by interstitial injection. The enhanced B diffusion in Si and Si0.9Ge0.1 was found by interstitial injection. These results confirm that Sb diffusion in Si0.9Ge0.1 is primarily dominated by vacancy-mediated mechanism, while B diffuses in Si0.9Ge0.1 by an interstitially mediated mechanism. The effect of the RTA diffusion time on the B diffusion in Si and Si0.9Ge0.1 has also been investigated. The diffusivity versus diffusion time of B in Si and Si0.9Ge0.1 for inert and injection samples is presented. It was found that the shorter annealing time had the faster diffusion. This suggested that it caused by transient diffusion effect arising from point defects.
Atomistic Modeling of Amorphization in Silicon
Authors: Pelaz Lourdes , Marqués Luis A. , Gilmer George H. , Barbolla Juan
Published: April 2011

We discuss atomistic simulations of ion implantation and annealing of Si over a wide range of ion dose and substrate temperatures. The DADOS Monte Carlo model has been extended to include the formation of amorphous regions, and this allows simulations of dopant diffusion at high doses. As the dose of ions increases, a continuous amorphous layer may be formed. In that case, most of the excess interstitials generated by the implantation may be swept to the surface as the amorphous layer regrows, instead of diffusing through the crystalline region. This process reduces the amount of transient enhanced diffusion during annealing. This model also reproduces the dynamic annealing during high temperature implants.