bluuebunny/crossref_metadata_2025 huggingface dataset:
Reactive Ion Etching of GaN Thin Films
Authors: Manfra Michael , Berkowitz Stuart , Molnar Richard , Clark Anna , Moustakas T.D. , Skocpol W.J.
Published: March 2011

Reactive ion etching of GaN grown by electron-cyclotron-resonance, microwave plasma-assisted molecular beam epitaxy on (0001) sapphire substrates was investigated. A variety of reactive and inert gases such as CC12F2, SF6, CF4, H2/CH4 mixtures, CF3Br, CF3Br/Argon mixtures and Ar were investigated. From these studies we conclude that of the halogen radicals investigated, Cl and Br etch GaN more effectively than F. The etching rate was found to increase with decreasing pressure at a constant cathode voltage, a result attributed to larger mean free path of the reactive species.
Reactive-Ion-Etching of 100nm Linewidth Tungsten Features Using SF6:H2 and a Cr-Liftoff Mask
Authors: Shirey Loretita M. , Foster Kelly W. , Chu William , Kosakowski John , Rhee Kee Woo , Eddy Charles , Park Doewon , Isaacson I. Peter , Mccarthy Daniel , Marrian Christie R. K. , Peckerar Martin C. , Dobisz Elizabeth A.
Published: March 2011

Reactive ion etching of features down to 100 nm in linewidth in tungsten has been studied using an SF6 based chemistry. The studies were carried out in a PlasmaTherm 500 etcher operated at low pressure (2 mTorr) and power (100 mWatts/cm2). Key processing parameters have been identified to achieve the resolution and aspect ratio required for high contrast x-ray masks. The critical parameters include sample temperature, gas dilution and end point detection. However, even with all of these parameters optimized, additional sidewall passivation is required to obtain the necessary 6.5:1 aspect ratio. A novel method of achieving such passivation based on an intermittent etching process is described.
Spectral Reflectance as an in Situ Monitor for Mocvd
Authors: Breiland W G. , Killeen K. P.
Published: March 2011

Near normal-incidence spectral reflectance has been used to monitor the growth of AlAs, GaAs, and AlGaAs thin films by MOCVD in real time. The method has been used in a research rotating disk CVD reactor and in a modified commercial horizontal channel reactor. Reflectance is simple, robust, and is insensitive to perturbations such as mechanical strains, wafer rotation, and imperfect windows commonly encountered in an actual MOCVD system. Data may be collected over a wide spectral range, 390 to 950 nm, in less than one second using a multichannel detector and broad-band light source. This wide bandwidth provides detailed compositional discrimination and greater thickness sensitivity than single-wavelength measurements. The technique may be used to extract wavelength-dependent optical constant data under growth temperature conditions. Examples from the growth of multi-layered structures used in the fabrication of Vertical Cavity Surface Emitting Lasers is presented. The method shows promise as a valuable tool in process modeling, optimization, and control.
Photoluminescence of Sige Alloys Implanted with Erbium
Authors: Erzgräber H.B. , Gaworzewski P. , Schmalz K. , Krôger D. , Morgenstern T. , Osinsky A. , Vatnik M.
Published: March 2011

The 1.54μm emission of erbium implanted SiGe alloys was investigated as a function of oxygen and germanium concentrations as well as defect densities. Samples of SiGe layers grown by atmospheric pressure chemical vapor deposition technique which contain high concentrations of grown-in oxygen in the 10 19 - 1020 cm−3 range and 2 - 24 % Ge were chosen for the experiments. By using rapid thermal annealing in nitrogen atmosphere, a high optical activation of Er was found by photoluminescence. In samples with low defect densities nearly one third of the implanted Er ion dose could be detected in form of electrically active donors by spreading resistance measurements. The behavior of different SiGe : Er layers, based on sample property and annealing condition, suggests that more than only one type of luminescent Er-complex is present.
Oriented Carbon Pair Defects Stabilized by Hydrogen in as-Grown GaAs Epitaxial Layers
Authors: Cheng Y.M. , Stavola M. , Abernathy C.R. , Pearton S.J.
Published: March 2011

We have studied the IR absorption of heavily carbon doped GaAs grown by metalorganic molecular beam epitaxy. A striking observation is that the hydrogen-stretching vibration of a Crelated complex at 2688 cm−1 is strongly polarized along just one of the <110> directions in the (001) growth plane. This polarized C-H vibration is assigned to a defect complex that is aligned at the growth surface and then maintains its alignment as it is incorporated into the growing crystal. In a series of experiments, we have studied the annealing of the 2688 cm−1 band and its alignment and suggest that the defect complex consists of a CAs-CAs pair stabilized by hydrogen.
Metastable Defects and Stretched Exponentials
Authors: Redfield David , Bube Richard
Published: March 2011

Metastability of defects in semiconductors provides the basis for (1)An integrated picture of defects that includes the DX center in crystalline HI-V compounds, the dangling-bond defect in amorphous Si, and ‘self-compensation’ effects in I1-VI compounds. The unifying physical property is the ability of many foreign atoms to have two nearly equal-energy sites, one with a shallow electronic level and the other with a deep level. (2)Elucidation of stretched-exponential kinetics in these materials, including the first demonstrable microscopic model for them. This stretched-exponential model is a distribution of independent response times.
Characterization of Defects in N-Type 6H-SiC Single Crystals by Optical Admittance Spectroscopy
Authors: Evwaraye A.O. , Smith S.R. , Mitchel W.C.
Published: March 2011

Optical admittance spectroscopy is a technique for measuring the conductance and capacitance of a junction under illumination as a function of the wavelength of the light and the frequency of the measuring AC signal. For the first time, this technique is applied to characterize deep defect levels in 6H-SiC:N. Nitrogen is a donor atom in 6H-SiC which substitutes for carbon in three inequivalent sites (h, kl, k2). giving rise to n-type conduction. Deep defect levels attributible to transition metal impurities have been identified in 6H-SiC:N by optical admittance spectroscopy.
Tuning of Energy Levels in a Superlattice
Authors: Peeters Francois M.
Published: March 2011

The gap between the minibands of a conventional superlattice (or between the subbands of a quantum well) can be controlled by introducing potential barriers in its wells. An appropriate choice of the position, the width d, and the height Vd of these barriers, achieved by standard methods, can reduce the energy minibands to the desired values. When these barriers are introduced at the center of the wells of the original structure, the position of the second miniband in energy space changes very little with d and/or Vd whereas that of the first miniband can change by one to two orders of magnitude. This leads to a tuning of the first miniband and of the energy gap between the first two minibands. Similar results are obtained for the case of wells in the barriers and for the tuning of impurity states in a superlattice. Possible applications include infrared photodetectors and tuning of the tunneling current.
Optical Properties and Electroluminescence of Ordered and Disordered ALAS/GAAS Superlattices
Authors: Arent D. J. , Alonso R. G. , Horner G. S. , Kibbler A. E. , Olson J. M. , Yin X. , Delong M. C. , Springthorpe A. J. , Majeed A. , Mowbray D. J. , Skolnick M. S.
Published: March 2011

In this study, we report the optical properties of a variety of compositionally equivalent disordered superlattices in the AlAs/GaAs system. Markedly different signatures are seen in the steady-state optical signatures of a random pseudobinary A10.5Ga0.5As alloy and (AlAs)n(GaAs)4-n superlattices (SLs) where n = 2 (ordered) or n is randomly chosen (disordered). Relative to the properties of the pseudobinary alloy or ordered SL, intense, redshifted, photoluminescence (PL) peaks and broad non-excitonic absorption are observed from disordered (AlAs)n(GaAs)4-n SLs where n is randomly chosen from the sets [0, 1, 2, 3, 4] or [1, 2, 3]. Our observations suggest that a large density of states at energies lower than the compositionally equivalent pseudobinary band gap exist, and including wider wells and barriers may lead strongly localized regions and the onset of quantum effects. Room temperature electroluminescence is also observed from disordered SL pn samples, and the energy, intensity, and efficiency are shown to vary with deposition sequence.
Performance of CVD and CVR Coated Carbon-Carbon in High Temperature Hydrogen
Authors: Adams J. W. , Barlettia R. E. , Svandrlik J. , Vanier P. E.
Published: March 2011

As a part of the component development process for the particle bed reactor (PBR), it is necessary to develop coatings which will be time and temperature stable at extremely high temperatures in flowing hydrogen. These coatings must protect the underlying carbon structure from attack by the hydrogen coolant. Degradation which causes small changes in the reactor component, e.g. hole diameter in the hot frit, can have a profound effect on operation. The ability of a component to withstand repeated temperature cycles is also a coating development issue. Coatings which crack or spall under these conditions would be unacceptable. While refractory carbides appear to be the coating material of choice for carbon substrates being used in PBR components, the method of applying these coatings can have a large effect on their performance. Two deposition processes for these refractory carbides, chemical vapor deposition (CVD) and chemical vapor reaction (CVR) have been evaluated.

Screening tests for these coatings consisted of testing of coated 2-D and 3-D weave carbon-carbon in flowing hot hydrogen at one atmosphere. Carbon loss from these samples was measured as a function of time. Exposure temperatures up to 3000 K were used and samples were exposed in a cyclical fashion, cooling to room temperature between exposures. The results of these measurements are presented along with an evaluation of the relative merits of CVR and CVD coatings for this application.
Processing of Silicon Carbide Fiber with Controlled Stoichiometry Using Polymethylsilane, -[MeSiH]x-
Authors: Zhang Zhi-Fan , Scotto Cathy S. , Laine Richard M.
Published: March 2011

Polymethylsilane (-[MeSiH]x-) synthesized from a single step catalytic polymerization of methylsilane (MeSiH3), provides a new route to near stoichiometric, microcrystalline silicon carbide fibers. The final composition is controlled by selected additives. The entire process simply contains 3 simple steps: (1) a single step synthesis of polymer precursor, (2) precursor fiber spinning, and (3) a single step pyrolytic conversion to target ceramic fibers.
Rapid Solid-State Precursor Synthesis of Non-Oxide Ceramics
Authors: Rao Lin
Published: March 2011

Rapid self-sustaining solid-state precursor methods have proven to be an effective route to non-oxide ceramics. With the appropriate choice of precursors, fine powders of crystalline BN, AIN as well as composites such as TiB2-TiN-BN can be formed easily within seconds. These materials are characterized by X-ray diffraction, scanning electron microscopy and elemental analysis (XPS, EDS, and conventional chemical methods). The synthetic techniques will be discussed along with characterization and numerical simulation results. Further applications of this technique will be proposed.
Microstructure and Densification of Sintered (B+C)-Doped β-Silicon Carbide
Authors: Braue Wolfgang , Kleebe Hans-J. , Wehling Carsten
Published: March 2011

The role of boron and carbon during densification of sintered β-SiC was investigated through the combined approach of in-situ dilatometry and CTEM/AEM inspection of TEM-foils referring to well-defined densification events. Preliminary data obtained indicate that in the early stages of densification, boron is not enriched in the continuous carbon-rich surface layer covering the β-SiC powder particles nor does it segregate to internal interfaces in high quantities. Small boron quantities are dissolved in the SiC grains- Simultaneously with the β- to α- phase transformation, decomposition of foam-like B4C aggregates releases small B4C particles, which are bound intragranularly to α-SiC.
Atomic Defects in Transition Metal Carbides and SiC Studied by Positron Annihilation
Authors: Rempel A. A. , Schaefer H. -E. , Forster M. , Girka A.I.
Published: March 2011

Nonstoichiometric defects in carbides of the Group IV and V transition metals and radiation-induced atomic defects in SiC were studied by positron lifetime measurements before and after low-temperature (80 K) electron irradiation and subsequent thermal annealing up to 1900 K. Agglomeration of radiation-induced atomic defects which strongly depends on the energy of the irradiation electrons and subsequent decay of the agglomerates in SiC is observed.
Gaseous Alkali Corrosion Kinetics of Silicon Carbide
Authors: Sun Tawei , Pickrell Gary R. , Brown Jesse J.
Published: March 2011

The gaseous alkali corrosion kinetics of α-SiC were systematically investigated from 950°C to 1100°C in an atmosphere containing 0.98 vol% sodium nitrate vapors. The reaction of the SiC in the alkali-containing atmosphere follows a linear rate law with an activation energy of 104 kJ/mol. The alkali corrosion is composed of dissolution of SiO2 in the sodium silicate liquid, oxidation of SiC, and adsorption of Na2O from the vapor phase. The overall reaction appears to be controlled by the oxidation at the SiC substrate/sodium silicate liquid interface.
Study on the Heat–Treatment Reinforcement of Aluminum Nitride–Silicon Carbide Composites
Authors: Ningfang Li , Hongquan Zhang , Guomei Wang
Published: March 2011

The effects of heat – treatment on the mechanical properties of AIN – SiC whisker composites with Y2O3 and SiO2 additives has been studied. When the sample containing 10 wt% Y2O3 +SiO2 (Y2O3/SiO2= 1/0. 66) was treated at 1300°C in air for 140 hours the strength of compositqs was raised from 481 MPa to 784 MPa.

The phase composition, microstructure and grain boundary phase structure have been characterized by combining XRD, SEM, TEM/EDXA and HREM techniques. The reinforcement mechanism of the composites results from crystallization of the glass phase in the grain boundary at the high temperature oxidizing atmosphere to form the crossing structure of 2Hδ Sialon fibrous phase and SiC whisker.
Preparation and Characterization of Group 14 Element BIS(Thiolate) Compounds and Evaluation of Their Potential as Molecular Precursors in the Low Temperature Syntheses of Binary Metal Sulfides
Authors: KrÄuter Gertrud , Favreau Philippe , Nunnally Brian K. , Rees W. S.
Published: March 2011

Three isomeric lead bis(butylthiolate) and tin bis(butylthiolate) compounds have been prepared and characterized. Their solid state decomposition, and in the case of the lead bis(thiolate) compounds, their thermolyses in suspension in a high boiling hydrocarbon, have been studied. X-ray powder diffraction patterns and scanning electron micrographs of the obtained solid state material are discussed. Volatile co-products of the decomposition have been isolated and characterized.
Electrical Properties of Alkyl-Trichlorosilane Monolayers Grafted on Silicon Substrate
Authors: Vuillaume Dominique , Rondelez Francis
Published: March 2011

We demonstrate that a single monolayer of alkyl-trichlorosilane Molecules, covalently grafted to the native oxide of a silicon substrate, allows to fabricate silicon based MIS (Metal-Insulator-Semiconductor) devices with excellent electrical properties. The thickness of the organic monolayer is in the range 1.5–2.8 nm, corresponding to long alkyl chains with 8 to 18 carbon atoms. We have fabricated MIS capacitors with a leakage current density as low as 10-8 A/cm2 at 6 MV/cm, high dielectric breakdown field (12 MV/cm), electrically active defect density lower than 1011 cm-2, and low field dc conductivity as low as 10-16–10-15 Scm-1. Thermal stability has been demonstrated up to 450 °C.
Sulfur Containing Conjugated Polymers with Interesting Electronic Properties.
Authors: Elsenbaumer R. L. , Marynick D. S. , Seong S. , Meline R. L.
Published: March 2011

The electronic properties of the isomerie (C2S2)n conjugated sulfur containing polymers 1, 2, and 3 were characterized using ab initio and PRDDO Molecular orbital calculations, as well as EH band structure calculations. It is anticipated that such structures might exhibit enhanced electrical conductivities when doped owing to the possibility of the peripheral sulfur atoms extending orbital interactions transverse to the chain axis direction. Such increased dimensionality is demonstrated for the structurally similar superconductive Molecular TTF and ET charge-transfer salts. Of the three polymeric structures, indications are that polymer 2 is highest in energy. Polymer 3 can exist in both “chair” and “boat” conformations, with the chair form slightly more stable. Both the chair and boat forms of 3 were found to be of lower energy than 1. Calculated band gaps and band widths are reported along with preliminary synthetic attempts to prepare these polymers and observed properties.
Tetrazine-Bridged Phthalocyaninato Metal Complexes: A New Class Of Intrinsic Semiconductors
Authors: Hanack Michael , Barcina Jose Osio , Pohmer JöRg , Witke Elisabeth
Published: March 2011

Stacked transition Metal Macrocycles [Macm (L)]n with M e.g. Fe, Ru, Os, Co, Rh and Mac = phthalocyanine (Pc) 1,2- or 2,3-naphthalocyanine (1,2-, 2,3-Nc) have been synthesized by us. The bridging ligands (L) are e.g. pyrazine (pyz) or s-tetrazine (tz). In general, these complexes [Macm (L)]n are insoluble in organic solvents, however, soluble oligomers [R4Pcm (L)]n can be prepared using Metallomacrocycles RnPcm, R = t-bu, et, OR, M = Fe, Ru, which are substituted in the périphérie positions.

A systematic investigation of the influence of the bridging ligánds on the semiconducting properties in [Macm (L)]n reveal, that changing L, e.g from dabco over pyz to tz leads to a steady increase of the semiconducting properties without external oxidative doping. Powder conductivities in the order of 0.1 S/cm can be reached by using s-tetrazine, 3,6-dimethyl-j-tetrazine (Me2tz) and others, e.g. fu marodini tri le as the bridging ligands. The intrinsic conductivities are a result of the low oxidation potential of tz and Me2tz and due to the low lying LUMO in the corresponding bridged systems [Macm (tz)]n.

The electrical and physical properties, especially the UV and the Möβbauer spectra for the tetrazine-bridged Macrocyclic Metal complexes are discussed in respect to intrinsic semiconducting properties of these compounds.
High Electrical Conductivity in Organic Single-Component Systems Based on 2,5-Dimethylthio-TCNQ
Authors: Zambounis J. S. , Mizuguchi J. , Hediger H. , Pfeiffer J. , Schmidhalter B. , Rihs G. , Chauvet O. , Zuppiroli L.
Published: March 2011

2,5-dimethylthio-TCNQ has been newly synthesized, and its optical and electrical properties have been investigated in evaporated films. A high electrical conductivity of σ=2× 10−5 Scm−l has been measured at room temperature. The present single-component system is found to contain 2×1017 spins/cm3. The charge carriers are presumably due to incorporated impurities which give the ESR signals. Carrier hopping is considerably facilitated by close intermolecular S-N contacts between the S atom of the -SCH3 group of one molecule and the N atom of -C≡N group of the neighboring Molecule.
Infrared And Raman Spectroscopy Of Organic Electron Conductors
Authors: Ridaura R. , GóMez R. , Marquina V. , Aburto S. , Marquina M. L. , Jiménez M. , Robles-Martínez J. G. , Salmerón-Valverde A.
Published: March 2011

FT-Raman and infrared (IR) spectra of a series of TTF-fluorene derivative family were obtained using a conventional IR spectrometer and a FT-Raman spectrometer. The Raman shifts of the observed band (ν3 stretching band) changes from sample to sample and we correlate these changes with the degree of charge transfer between the donor (TTF) and the acceptor (fluorene derivative) Molecules. These results are compared with those obtained from changes in the IR absorption frequencies of the C≡N stretching mode in the acceptor Molecule.
Poly (L,4-Naphthylene Sulfide) Oligomers: Electronic And Vibrational Spectra Of The Pristine And Oxidized Forms
Authors: Piaggio P. , Petrillo G. , Novi M. , Dell'Erba C.
Published: March 2011

New naphthalene-sulfur compounds, oligomers of poly (l,4-naphthylene sulfide), have been synthesized and studied by electronic and vibrational spectroscopy in both pristine and oxidized forms. It has been found that the charged defects induced on these molecules are Much More stable than in the corresponding 1,4-phenylene derivatives. Nevertheless their physical properties are strongly affected by steric effects which hinder a regular arrangement of the repeating units.
Investigation Of Luminescence And Absorption Spectra Of Bedt-Ttf And Its Ion Radical Salt
Authors: Kozlov M. E. , Tanaka Y , Tokumotot M. , Tani T.
Published: March 2011

Luminescence with maximum near 1.96 eV of organic donor compound bis (ethylenedi-thio) tetrathiafulvalene (BEDT-TTF) was observed in crystals and frozen at low temperature solution. It was found that solid state effects sharply reveal themselves in excitation spectra of the substance and have almost no influence on the shape of the emission. Intensity of the emission is strong at liquid He temperature but rapidly decreases with heating of the sample as well as after modification of charged state of molecules forming the crystal and is very weak in case of Monovalent (BEDT-TTF) Br salt. Shape of the luminescence spectra correlates with the absorption of the investigated compounds. The data obtained can be interpreted assuming dimer-like arrangement of molecules in the crystal structure.
Molecularly Engineered Polymer Leds
Authors: Moratti Stephen C. , Bradley Donald C. , Friend Richard H. , Greenham Neil C. , Holmes Andrew B.
Published: March 2011

Polymeric light emitting devices may be fabricated from a simple structure consisting of a low work function cathode (typically calcium or Magnesium), a conjugated semiconducting polymer and a transparent anode (typically indium-tin oxide). Optimum device efficiencies require the balanced injection of electrons and holes. This paper describes the application of molecular engineering in the design of a family of poly (cyanoterephthalylidenene) s which show increased electron affinity over the unsubstituted analogue [poly (p-phenylenevinylene) PPV]. In particular these polymers as the emissive layer in a bilayer device with indium tin oxide (ITO, positive transparent contact) and aluminum (stable negative contact) and PPV as a hole transporting layer exhibit internal efficiencies up to 4%.
Issues in Organics For Nonlinear Optics
Authors: Stegeman George I. , Torruellas William
Published: March 2011

The potential of organic materials for nonlinear optics was recognized early with the identification of charge transfer concepts for second order Materials, and π-electron delocalization in conjugated polymers for third order effects.[l,2] Nevertheless, they have not been seriously considered for applications until the past five years over which applications to electro-optics have been vigorously pursued. At this point many of the relevant technological problems for electro-optics have been faced and solved. This progress has been driven by imminent applications in information processing and communications. Frequency conversion, specifically doubling of near infrared lasers into the blue for data storage etc., also relies on the second order nonlinearities. But progress towards efficient doublers has been dominated by other well-established Materials such as KTP and LiNbO3 because of the short time window perceived for applications.[3,4] However, because of the inherently large nonlinearities associated with organic Materials, one would expect that ultimately the most efficient doubling devices could be made from organic Materials.
High Glass Transition TemperatÜRe Electro-Optic Polymers
Authors: Wu Chengjiu , Beeson Karl , Ferm Paul , Knapp Charles , Mcfarland Michael J. , Nahata Ajay , Shan Jianhui , Yardley James T.
Published: March 2011

Disperse Red-1 type chromophores were attached to the backbones of PMMA, polyvinyl-phenol as well as the styrene-Maleimide alternative copolymer and glass transition temperatures of these three polymer derivatives were in the range of 125, 165, and 245°C, respectively. We have also, for the first time, attached EO chromophores to some thermostable cardo-polymers. Fluorene derivatives in which the 2- and 7-positions were substituted with an electron accepting and an electron donating substitutem, respectively, were made polymerizable through their reactive functional groups at the 9,9′-positions. Various condensation polymers were prepared. These polymers are amorphous, film-forming, thermostable, and having Tg ranging from 150 to 300°C. These polymers exhibit strong electro-optic properties after electrode poling. Thermal stabilities of these polymers were compared by following the spectral decay of the chromophore and the decay of the electro-optic coefficient. The loss of EO activity at elevated temperature can be realized as a combination of chromophore reorientation and chemical degradation.
Channel Waveguides and Modulators Fabricated From High Temperature Second Order Nonlinear Optical Polymers
Authors: Kenney J. T. , Binkley E. S. , Jen A. K-Y. , Wong K.
Published: March 2011

Buried channel wave guides have been fabricated from thermally stable non linear optical polyimides. The Material system consists of a polyimide cladding and a polyimide based active Material. The buried channel wave guides are fabricated by a trench and fill process. This process was used for the fabrication of active wave guides at process temperatures above 300 °C. Single Mode wave guides, and Mach-Zenhder interferometers, were fabricated with attenuation < 2 dB/cm. Active Mach-Zehnder interferometers with a Vπ phase shift of 50 volts and the low attenuation were fabricated. Thermal aging of the poled active device demonstrated no change in activity after 30 Minutes at 230°C.
A Synthetic Approach for the Incorporation of Highly Efficient, Thermally Stable Second Order Nonlinear Optical Chromophores Into Side-Chain Polymers
Authors: Drost Kevin J. , Jen Alex K-Y. , Pushkara Rao V. , Mininni R. M.
Published: March 2011

A new synthetic method is developed to incorporate efficient nonlinear optical chromophores containing thiophene conjugating units and tricyanovinyl acceptors into side-chain polymers. This approach emphasizes the incorporation of the tricyanovinyl groups into the pendant side chains after the desired polymer is formed.
Hyper-Rayleigh Scattering (Hrs) In Isotropic Media
Authors: Hendrickx Eric , Verbiest Thierry , Clays Koen , Samyn Celest , Persoons Andre
Published: March 2011

In this paper some of the more important Hyper Rayleigh Scattering (HRS) Measurements performed in our laboratory are reviewed. The results of experiments conducted on polymers, the protein Bacteriorhodopsin, retinal derivatives and octopoles are presented. Basic HRS theory, along with a brief description of the HRS set-up, is also included.

We demonstrate that the experimental simplicity of HRS allows for an accurate determination of the first hyperpolarizability of molecules that could not have been measured by the more traditional Electric Field Induced Second Harmonic Generation (EFISHG) technique.
Optical Properties and Photoexcitations in Regularly Alternating Conjugated Copolymers
Authors: Tubino R. , Botta C. , Destri S. , Porzio W. , Rossi L.
Published: March 2011

We report in this short paper a preliminary account on the design, preparation, optical characterization and photoexcitation of a class of novel conjugated polymers consisting of regularly alternating thiophene and benzene sequences, which Might represent Models for one-dimensional superlattices. Optical absorption and emission spectra suggest that the barriers produced by the phenylene Moieties do not interrupt the conjugation but can produce localization effects. Resonant Raman spectra indicate that a selective response of the thiophene Moiety occurs upon excitation with visible light. Moreover these Measurements confirm the presence of a confinement on the thiophene blocks, while the biphenil Moiety does not appear to feel the energy barrier and behaves as the corresponding polymer poly (paraphenylene) (PPP). CW photomodulation spectra show that the formation of long-lived bipolarons takes place only if the thienylenic Moiety is long enough to accomodate the lattice distortion.
Broad Temperature Range Of Chiral Smectic C Phase In Some Ferroelectric Side-Chain Liquid Crystalline Polysiloxanes Containing Oligooxyethylene Spacers
Authors: Hsiue G. H. , Chen J. H. , Hsu C. S.
Published: March 2011

The Mesomorphic behaviors of some ferroelectric liquid crystalline monomers and side-chain polysiloxanes studied by X-ray diffraction Measurement, differential scanning calorimeter and polarizing Microscope. All obtained polymers exhibit wide temperature range of chiral smectic C phase including room temperature.

These Mesogenic structures contain oligooxyethylene spacers and (S)-2-Methyl-l -butyl chiral tail via a three phenyl ester linkage (i.e. -Ph-COO-Ph-Ph- or -Ph-Ph-COO-Ph-). Two series of monomers with different biphenyl group linkage position were compared. One shows a novel twisted smectic A phase, in addition to the liquid crystalline sequence (Ch→SA→Sc*) obtained between cholesteric phase and smectic A phase. It also presents an unusual smectic A and chiral smectic C phase.

All the prepared polymers present smectic Mesomorphism. As the unit of flexible oligooxyethylene spacers increases, the clearing temperature decreases and the stability of the smectic phase also increases.
Domains In Nematic Elastomers
Authors: Ten Bosch A. , Varichon L.
Published: March 2011

A theory based on an elastic model and including coupling between elastic deformation and nematic order parameter as well as an interaction between crosslinks and orientation is given. The nematic order parameter and the stress tensor have been determined on elongation and as a function of temperature as well as he anisotropy of the conformation of a side chain liquid crystal elastomer on application of a mechanical stress. A transition from a turbid, low ordered polydomain phase to a transparent, Monodomain is shown to occur.
Long-Lived Defects In Polycarbazolyld1 Acetylenes. Photoinduced Vis And Infrared Spectra
Authors: Dellepiane G. , Cuniberti C. , Comoretto D. , Musso G. F. , Piaggio P. , Speroni F. , Botta C. , Luzzati S.
Published: March 2011

Photoinduced absorption spectra of different polycarbazolyldiacetylenes in the visible and infrared regions are reported. Long-lived bipolaronic defects, photogenerated by excitation above the band-gap (2.54 eV), are found responsible for the observed signals. Associated with these defects, photogenerated infrared active vibrations (IRAV) are observed as absorption bands or apparent bleachings arising from Fano-type interference. This different behaviour originates from the different degree of overlap of the IRAV Modes with the associated low-energy bipolaronic absorption.
Fabrication Of Organic Dye-Coated High-Tc Superconductor Optical Devices: Interface Chemistry And Properties
Authors: Jurbergs David , Zhao Jianai , Haupt Steven G. , Mcdevitt John T.
Published: March 2011

The preparation and characterization of a new generation of optical sensors fabricated from high-temperature superconductor (HTSC) thin films is reported herein. These new hybrid devices are prepared using HTSC thin films which are coated with organic dye overlayers. These systems have been shown to respond selectively to those wavelengths which are absorbed strongly by the molecular dye. Methods for fabricating the superconductor element and depositing the dye layer are discussed. Moreover, scanning electron microscopy and resistivity versus temperature measurements are utilized to characterize these hybrid structures.
Conductive Polymer Switch For Controlling Superconductivity
Authors: Haupt Steven G. , Lo Rung-Kuang , Riley David R. , Zhao Jianai , McDevitt John T.
Published: March 2011

Electrochemical techniques are exploited to fabricate conductive polymer/high-Tcsuperconductor sandwich structures. In such hybrid polymer/superconductor systems, it is found that when the polymer is oxidized to its conductive state, the transition temperature (Tc) and critical current (Jc) of the underlying superconductor film are suppressed. Reversible Modulations in the values of the transition temperatures up to 50 K are noted for these structures. Upon reduction of the conductive polymer layer back to its non-conductive form, Tc is found to return to values close to those acquired for the underivatized YBa2Cu3O7-δ film. Thus, the principle of a Molecular/superconductor switch for controlling superconductivity is demonstrated.
Poly (SNS) Quantitative Electrosynthesis and Electrodissolution
Authors: Otero T. F. , Brillas E. , Carrasco J. , Figueras A.
Published: March 2011

The electrogeneration and electrodissolution of poly (SNS) have been improved by using aqueous acetonitrile solutions having a 1% (ν/ν) of water constant. Compact, adherent and thick films (until 0.4 Mg cm-2) were galvanostatically electrogenerated. The electrodeposited (oxidized) polymer is insoluble in 0.1 M L?CIO4 aqueous acetonitrile solution and solubilizes by cathodic reduction. Both, electrogeneration and electrodissolution, are faradaic processes. Those facts mimic electrodeposition and electroerosion of metals and their concomitant industrial applications. New technological possibilities using polymers in electrophotography, electroreprography, electropolishing, electro-erosion and electromachining are open through polymeric electrodissolution altogether to a new processible way, through the obtained solution, for the conducting polymers.
Synthesis and Crystal Structure of C60 Complex with a Symmetrical Donor of 2,3,6,7,10,11- Hexamethoxytriphenylene (HMT)
Authors: Chiang Long Y. , Swirczewski John W. , Liang Keng S.
Published: March 2011

We have successfully synthesized single crystals of C60 fullerene complex with a symmetrical triplet donor of 2,3,6,7,10,11-hexamethoxytriphenylene (HMT). All spectroscopie data and analyses support the chemical composition of this complex as C60(HMT)2. Single crystals of C60(HMT)2 are, at 20±1 °C, cubic, space group Fd3c-Oh8 (No. 228) with a = 30.251(9) Å, α = 90.00°, V = 27682(30) Å3, Z = 16 (dcalcd = 1.476 gcm-3), and Ru (unweighted) = 0.098.
Vertical, Dual Gate CMOS Structure in Two Laser-Recrystallized Silicon Layers over Oxidized Silicon Substrate
Authors: Kenyon P. , Dressel H. , Negri A.
Published: March 2011

A seven mask CMOS process that provides vertically integrated structures with joint gates is described. The structures have been characterized as individual NMOS and PMOS transistors. An implant technique will be described which may permit the fabrication of fully self-aligned CMOS structures.
Modeling of Polysilicon Resistors, P-N Junction Diodes and Mosfet's
Authors: Khondker A. N. , Ahmed S. S. , Liou T. , Kim D. M.
Published: March 2011

Conductivity in bulk polysilicon is discussed, applicable over a wide range of dopant concentration, temperature, grain size and trap density. The I-V behavior in a lateral poly p-n junction is analytically modeled, incorporating the effects of carrier lifetime operative in crystalline grain and amorphous conducting boundary. In particular, the extremely short carrier lifetime within the grain boundary is shown to provide an ohmic conduction channel in a direction parallel to current flow. This ohmic current can account for the unusually high current levels observed at small applied voltages. Also, the shift of the threshold voltage of MOS devices, as influenced by grain traps near the channel region, is analysed.
Liqiuid Crystal Display Fabricated from Laser Recrystallized Silicon on Bulk Fused Silica
Authors: Hawkins W. G. , Drake D. J. , Goodman N. B. , Hartman P. J.
Published: March 2011

This paper discusses four aspects of fabrication of an active address liquid crystal array from laser recrystallized polycrystalline silicon: recrystallization, processing, device performance and array fabrication. The recrystallization process produces material which is imperfect by silicon wafer standards, but which contains few incoherent defects. The material was used to fabricate discrete n-channel MOS devices which had consistent off currents of 10−11 amps (0.4pA/μm of channel width) and on currents of 10−4 amps. Device threshold is controlled to + 200 mV and channel mobility is 500 to 600 cm2 /V-sec. The crossovers between Al/1% Si source and degenerately doped polycrystalline silicon gate lines were fabricated by use of high temperature reflowed, phosphorus doped chemical vapor deposited SiO2. Completed arrays had very few defects (no crossover defects and 0.3% bad devices).
Semitransparent Silicide Electrode Formed on the Surface of a-Si:H
Authors: Tsukada T. , Seki K. , Yamamoto H. , Sasano A.
Published: March 2011

Thin silicide layers are found to be formed through solid state reaction between hydrogenated amorphous silicon(a-Si:H) and metals. The method of formation of the silicide layer is very simple: deposition of metal on top of amorphous silicon layer and annealing and etching of the residual metal layer. The reaction kinetics and properties of this layer are described. The thickness of this silicide layer is estimated to be 5 nm. Accordingly, it can be used as a transparent electrode in a-Si:H photodiodes. Photodiodes using this semitransparent electrode have as good optical and electrical properties as conventional a-Si:H photodiodes using ITO(indium tin oxide). Schottky barrier characteristics are also de-scribed.
Biogenic Hydroxylated Carboxylate Monomers Serve as Dispersants for Ceramic Particles
Authors: Ren Tao , Aksay I. A. , Yasrebi M. , Pellerin N. B. , Staley J. T.
Published: March 2011

A total of 20 biogenic carboxylic acids, which contain one to three negatively charged -COO−group(s), were investigated as dispersion additives in the processing of ceramic particles. Only carboxylic acids containing one or more hydroxyl groups were able to disperse α-A12O3particles in aqueous suspensions. Detailed studies of two carboxylic acids, citric acid and tricarballylic acid were undertaken: measurements of zeta potential, particle packing, and dispersant adsorption characeristics indicated that carboxylic acid groups and hydroxyl groups are both important for dispersion of the ceramic particles. Hydroxyl groups increased the adsorption of the molecules to the particles.
Supramolecular Engineering at Functionalized Surfaces
Authors: Knoll Wolfgang , Angermaier L. , Batz G. , Fritz T. , Furuno T. , Guder H.-J. , Hara M. , Liley M. , Niki K. , Spinke J.
Published: March 2011

This contribution summarizes some strategies that we followed for the optimization of supramolecular architectures aiming at controlling the binding and organization of biopolymers at solid/solution-interfaces in a membrane-mimetic approach. The examples given concern mostly self-assembly processes and the biorecognition between biotin and streptavidin.
Chemoenzymatic Preparation of Sugar-Based Hydrogels
Authors: Rethwisch D. G. , Chen X. , Martin B. D. , Dordick J. S.
Published: March 2011

We have prepared sugar-based hydrogels using a chemoenzymatic synthetic approach. Specifically, the regioselectivity of enzymes was used to prepare sugar acrylate monomers. These monomers were polymerized with a crosslinker in a standard free radical polymerization. The polymers consist of a polyacrylate backbone with sucrose, (α-methyl glucoside, or β-methyl galactoside pendant groups. These materials are highly water absorbent swelling to more than 100 times their initial weight when placed in water. The degree of swelling for poly(β-methyl galactoside 6-acrylate) hydrogel was relatively insensitive to pH (from pH 4.5-9) and ionic strength (0.15-3 M NaCl). Potential applications of these materials include waterabsorbents and drug delivery systems.
Second Harmonic Generation of Bacteriorhodopsin and its Application for Three-Dimensional Optical Memory
Authors: Chen Zhongping , Lewis A. , Kumart J. , Tripathy S. , Marxt K. , Akkarat J. , Kaplan D.
Published: March 2011

A novel three-dimensional optical memory system based on a light transducing protein, bacteriorhodopsin, is investigated. The system uses the nonlinear optical properties of bacteriorhodopsin to accomplish reading and writing operations. A nondestructive method of reading information in three-dimensional optical memory that uses second harmonic generation is demonstrated. This method has the advantage of fast speed, is nondestructive, and has the potential for parallel access.
Genetic Modified Bacteriorhodopsin for Holographic Interferometry
Authors: Hampp N. , Schmid R. , Zeisel D.
Published: March 2011

Controlled modification of bacteriorhodopsin (BR) by means of genetic engineering is a powerful tool to create BR-variants with photophysical properties significantly different from the wildtype molecule and, in addition, adapted to the physical demands of various optical information processing techniques. The application of BR-films containing the variant D96N in real-time interferometry is described.
Bacterial Macrofibers and Bionites: Materials of Natural and Synthetic Design
Authors: Mendelson Neil H.
Published: March 2011

Two fiber forms can be obtained from cells of the rod-shaped bacterium,Bacillus subtilis, one called macrofibers, the other bacterial thread. Macrofibers are highly organized, multicellular structures, millimeters in length that selfassemble in a unique way. Each fiber is essentially a single chain of cells linked end-to-end that has repeatedly folded upon itself and twisted into helical form. The growth of individual cells yields both the material of the macrofiber and the forces required for its assembly. The forces involved stem from twisting motions caused by cell growth geometry. The folding process is akin to negative supercoiling. New approaches have been used to estimate the magnitude of forces. Torque generated by single filaments has been estimated from snapopening motions resulting from aborted attempts at folding to be in the range of 10−10to10−8dyne-cm. In contrast, multifilament fibers carrying small wires in their loops must have generated a torque of at least 10−5dyne-cm and a supercoiling force of at least 10−5dyne in order to have moved the wires in viscous solutions at the rates observed. The second bacterial fiber form, bacterial thread, and its mineralized derivatives, called bionites, are man-made materials. They are produced by the drawing and drying of bacterial cell filaments from cultures grown in the form of a textile-like web. The material properties of bacterial thread reflect primarily those of the strength-bearing cell wall polymer, peptidoglycan. A variety of new fiber-like materials have been produced by mineralizing the cell walls in situ in web cultures and drawing the products. Iron, copper, calcium, and potassium phosphate-containing bionites have been obtained in this manner. We are currently searching for order in the bionite crystal forms that may reflect the electrostatic nature of the wall polymer structural templates.
Synthesis, Surface and Cell-Adhesion Properties of Polyurethanes Containing Covalently Grafted RGD-Peptides
Authors: Lin Horng-Ban , Cooper Stuart L.
Published: March 2011

In an attempt to improve endothelial cell adhesion and growth on a polyurethane copolymer, cell adhesive RGD-containing peptides were grafted to the polymer backbone. Two peptide grafting reaction schemes, including one-step and two-step approaches, were developed. Amino acid analysis confirmed that the two-step approach had a higher peptide coupling efficiency. The two-step reaction scheme was utilized to prepare GRGDSY, GRGDVY and GRGESY (inactive control) peptide grafted polyurethanes with two different peptide densities (100 and 250 μmol/g polymer). Dynamic contact angle measurements indicated that the surfaces of the peptide grafted polyurethanes were more hydrophilic than the starting and carboxylated versions of the precursor polyurethane. In-vitro endothelial cell adhesion experiments showed that, without the presence of serum in culture medium, the GRGDSY- and GRGDVY-grafted polyurethanes dramatically enhanced cell attachment and spreading. Increasing the peptide density from 100 to 250 μmol/g polymer for the GRGDSYand GRGDVY-grafted polyurethanes resulted in an increase in cell attachment. With approximately the same peptide density (100 or 250 μmol/g polymer), the GRGDVY-grafted polymers supported more adherent cells than the GRGDSY-grafted polymers. Similar trends were observed in the in-vitro endothelial cell growth studies using culture medium containing serum and endothelial cell growth supplement. These RGD-peptide grafted polyurethanes may be useful in providing an easily prepared cell-adhesive substrate for various implantable devices and hybrid organs.
Human Osteoblast Expression of Osteonectin on Different Charged Substrata
Authors: Russell M. , Zou L. , Keeping H. , Ehrlich M. G. , Walsh W. R.
Published: March 2011

Cellular interactions at the interface between bone and a prosthetic device plays an important role in total joint reconstruction success or failure. Aseptic loosening is a typical long-term complication encountered due to a failure at this interface. A number of factors have been shown to influence cell mitogenic and morphological behavior including load and stability [1] surface topography and surface chemistry [2]. The selection of suitable surface coatings on a prosthetic device would be facilitated if the nature of the interaction of bone cells to surface could be predicted from appropriate behavior of cells in tissue culture [3]. Molecular biology techniques now enable investigators to study cell-substrate interactions and gene expression at the mRNA level.
Integrin-Mediated Fibroblast Adhesion Strength: Role of the β1 Subunit
Authors: Ward Kelly A. , Guan Jun-Lin , Hammer Daniel A.
Published: March 2011

Cell-substratum adhesion is important in wound healing [4], embryogenic development [11], tissue architecture [6], and metastasis [7]. Integrins constitute a major class of heterodimeric cell-surface glycoproteins involved in receptor-mediated adhesion to the extracellular matrix (ECM). Focal contacts are regions of the cell-substratum adhesion in which clusters of integrin receptors connect the cytoskeleton to extracellular matrix molecules such as fibronectin. Focal contacts strengthen cell-substrate adhesion, and are sites of biochemical activity. Since cell adhesion strength in part depends on the cell's ability to cluster receptors and cytoskeleton into focal contacts, the integrity of the focal contact, and hence a cell's adhesive strength, will depend both on integrin-cytoskeletal binding as well as integrin-ligand binding.

Using a centrifugation assay, we have quantified cell-substratum adhesion strength of mouse 3T3 cells transfected with the avian β1 integrin receptor (wild type), including various deletion mutants of its cytoplasmic domain, to surfaces containing varying concentrations of CSAT, a monoclonal antibody against the extracellular domain of the avian β1 subunit. For all the transfectants, adhesion strength decreases with decreasing CSAT concentration and increasing centrifugal strength. Different truncations of the cytoplasmic domain lead to different levels of adhesion. There is no simple correlation between the length of the cytoplasmic domain and the strength of adhesion.