bluuebunny/crossref_metadata_2025_split huggingface dataset:
Characterization of Carbon Nitride Films Produced by Pulsed Laser Deposition
Authors: Friedmann T. A. , Tallant D. R. , Barbour J. C. , Sullivan J. P. , Siegal M. P. , Simpson R. L. , Mikkalson J. , McCarty K. F. 
Published: April 2011

AbstractCarbon Nitride (CNX) films have been grown by ion-assisted pulsed-laser deposition (IAPLD). Graphite targets were laser ablated while bombarding the substrate with ions from a broad-beam Kaufman-type ion source. the ion voltage, current density, substrate temperature, and feed gas composition (N2 in ar) have been varied. the resultant films were characterized by Raman, Fourier transform infrared (FTIR), and Rutherford back scattering (RBS) spectroscopy.Samples with -30% N/C ratio have been fabricated. the corresponding Raman and FTIR spectra indicate that nitrogen is incorporated into the samples by insertion into sp2-bonded structures. a low level of C=N triple bonds is also found. as the ion current and voltage are increased with a pure ar ion beam, Raman peaks associated with nanocrystalline graphite appear in the spectr A. adding low levels of nitrogen to the ion beam first reduces the Raman intensity in the vicinity of the graphite disorder peak without adding detectable amounts of nitrogen to the films (as measured by RBS). at higher nitrogen levels in the ion beam, significant amounts of nitrogen are incorporated into the samples, and the magnitude of the "disorder" peak increases. by increasing the temperature of the substrate during deposition, the broad peak due mainly to sp2-bonded C-N in the FTIR spectra is shifted to lower wavenumber. This could be interpreted as evidence of single-bonded C-N; however, it is more likely that the character of the sp2 bonding is changing.
Observations on the Growth of YBa2Cu3O7 Thin Films at Very High Laser Fluences
Authors: Biggers. Rand R. , Grant Norton M. , Maartense I. , Peterson T.L. , Moser E. K. , Dempsey D. , Brown Jeff L. 
Published: April 2011

AbstractThe pulsed-laser deposition (PLD) technique utilizes one of the most energetic beams available to form thin films of the superconducting oxide YBa2Cu3O7 (YBCO). IN this study we examine the growth of YBCO at very high laser fluences (25 to 40 J/cm2); a more typical fluence for PLD would be nearer to 3 J/cm2. the use of high fluences leads to unique film microstructures which, in some cases, appear to be related to the correspondingly higher moveabilities of the adatoms. Films grown on vicinal substrates, using high laser fluences, exhibited well-defined elongated granular morphologies (with excellent transition temperature, Tc, and critical current density, Jc). Films grown on vicinal substrates using off-axis magnetron sputtering, plasma-enhanced metal organic chemical vapor deposition (PE-MOCVD), or PLD at more typical laser fluences showed some similar morphologies, but less well-defined. Under certain growth conditions, using high laser fluences with (001) oriented substrates, the YBCO films can exhibit a mixture of a- and c-axis growth where both crystallographic orientations nucleate on the substrate surface at the same time, and grow in concert. the ratio of a-axis oriented to c-axis oriented grains is strongly affected by the pulse repetition rate of the laser.
Growth of Highly Doped P-Type Znte Films by Pulsed Laser ablation in Molecular Nitrogen
Authors: Lowndes Douglas H. , Rouleau C. M. , Mccamy J. W. , Budai J. D. , Poker D. B. , Geohegan D. B. , Puretzky A. , Zhu Shen 
Published: April 2011

AbstractHighly p-doped ZnTe films have been grown on semi-insulating GaAs (001) substrates by pulsed-laser ablation (PLA) of a stoichiometric ZnTe target in a high-purity N2 ambient without the use of any assisting (DC or aC) plasma source. Free hole concentrations in the mid-1019 cm-3 to 1020 cm-3 range were obtained for a range of nitrogen pressures the maximum hole concentration equals the highest hole doping reported to date for any wide band gap II-VI compound. the highest hole mobilities were attained for nitrogen pressures of 50–100 mTorr (~6.5–13 Pa). Unlike recent experiments in which atomic nitrogen beams, extracted from RF and DC plasma sources, were used to produce p-type doping during molecular beam epitaxy deposition, spectroscopic measurements carried out during PLA of ZnTe in N2 do not reveal the presence of atomic nitrogen. This suggests that the high hole concentrations in laser ablated ZnTe are produced by a new and different mechanism, possibly energetic beam-induced reactions with excited molecular nitrogen adsorbed on the growing film surface, or transient formation of Zn-N complexes in the energetic ablation plume. This appears to be the first time that any wide band gap (Eg 2 eV) II-VI compound (or other) semiconductor has been impurity-doped from the gas phase by laser ablation. In combination with the recent discovery that epitaxial ZnSe1-xSx films and heterostructures with continuously variable composition can be grown by ablation from a single target of fixed composition, these results appear to open the way to explore PLA growth and doping of compound semiconductors as a possible alternative to molecular beam epitaxy.
Inhibited SN Surface Segregation in Epitaxial SNxGE1-x Alloy Films Grown by Pulsed Laser Deposition
Authors: Taylor M.E. , He G. , Saipetch C. , Atwater H.A. , Watson Thomas J. 
Published: April 2011

AbstractEpitaxial and compositionally homogeneous SnxGe1-x alloy films have been grown on Si (001) by pulsed laser deposition using elemental Sn and Ge targets. these results demonstrate that pulsed laser deposition can be used to grow alloys by overcoming the strong tendency for Sn surface segregation seen in growth by other methods such as molecular beam epitaxy.
Deposition of Molten Eutectic Solder using Jet Printing Techniques
Authors: Snyder Michael D. , Lasky Ronald 
Published: April 2011

ABSTRACTThis paper discusses the use of Ink Jet printing techniques to dispense small (50 to 75 micrometer diameter) particles of molten eutectic solder individually at programmable dispense rates from drop on demand to several thousand per second. Alternative jet dispensing techniques are discussed. The technology could allow the selective application of programmable amounts of solder on precision circuit boards and wafer substrates, while avoiding the high cost and flexibility limits associated with hard tooling. Large solder features can be constructed by dispensing individual droplets and relying on surface tension to draw them together to form a large single feature. Alternatively, columnar features can be created by successively dispensing solder droplets at the same site, allowing time between successive droplets to avoid forming a single large spherical feature.Several potential application areas in industry are discussed along with some of the issues associated with the projected performance of the method in the accuracy and speed domains.
Laser Machining and Metallization of VIAS in Aluminum Nitride
Authors: Raman Sudhakar , Lumpp Janet K. 
Published: April 2011

ABSTRACTA via metallization technique involving excimer laser ablation of aluminum nitride substrate with a metal backing, attached with cyanoacrylate adhesive was investigated. The objective was to develop a procedure to ensure good electrical interconnection between the thick film conductor pads and the walls of the via. An aluminum nitride compatible Ag-Pd thick film paste was used in this experiment. Two different sequences were tested: In the first sequence both sides of the aluminum nitride substrate were printed and fired and then the vias were laser drilled. In the second sequence, one side of the substrate was printed and fired first, then the vias were laser drilled and the second side was printed and fired. In both of the above sequences, laser ablation of the printed conductor and redeposition of the ablated metal backing are necessary for making a proper contact with the thick film conductor pads.
Deposition of Potassium Niobate Thin Films by Metalorganic Chemical Vapor Deposition and their Nonlinear Optical Properties
Authors: Nystrom M. J. , Wessels B. W. , Chen J. , Studebaker D. , Marks T. J. , Lin W. P. , Wong G. K. 
Published: April 2011

AbstractFerroelectric potassium niobate thin films have been deposited by conventional, low pressure metalorganic chemical vapor deposition on several types of oxide substrates. The films were epitaxial with a c-axis orientation normal to the substrate. Atomic force microscopy revealed a surface roughness of 1 - 4 nm. Transmission electron microscopy showed the film/substrate interface to be semi-coherent with lattice misfit accommodated by misfit dislocations. The nonlinear optical properties of the KNbO3 films were measured by a transmission technique. The room temperature, effective second order nonlinear coefficient was 13 pm/V.
Highly Active and Thermally Stable Ctlromophores and Polymers for Electro-Optic Applications
Authors: Jen Alex K-Y. , Chen Tian-An , Rao Varanasi Pushkara , Cai Yong-Ming , Liu Yue-Jin , Drost Kevin J. , Mininni Robert M. , Dalton Larry R. , Bedworth Peter , Marder Seth R. 
Published: April 2011

AbstractWe have developed two new classes of highly active and thermally stable nonlinear optical (NLO) chromophores based on the use of efficient thiophene conjugating units, a N,N-diphenylamino electron-donating group, and a 1,1′-dicyanovinyl substituted electron-accepting group. We have also developed a facile and generally applicable method to functionalize NLO chromophores onto high temperature polymers to demonstrate both high electro-optic (E-O) coefficients and long-term alignment stability at 100 °C.
Dynamic Mechanical Analysis and Dielectric Relaxation for Second Order Nonlinear Optical Applications
Authors: Sullivan Leah A. , Lackritz Hilary S. 
Published: April 2011

AbstractRelaxation dynamics of poly(methyl methacrylate) (PMMA) and doped PMMA systems are investigated as a function of processing temperature and frequency. Polymer relaxations and changes in local mobility are responsible for chromophore reorientation and lead to a loss in second-order nonlinear optical (NLO) properties. Studying polymer relaxations enables the temporal and thermal stability of the NLO polymer systems to be more accurately and readily predicted. The polymer dynamics are studied by correlating mechanical and dielectric relaxations to polymer and chromophore relaxations that occur during chromophore reorientation in second harmonic generation experiments. Dielectric and mechanical relaxation techniques enable polymer relaxation dynamics to be observed over a broad frequency range. The plasticization effect of the NLO chromophores on the polymer relaxation dynamics is also investigated.
Integrating cell Transplantation and Controlled Drug Delivery Technologies to Engineer Liver Tissue
Authors: Mooney D. J. , Sanog K. , Kaufmann P.M. , Mcnamara K. , Vacanti J.P. , Langer R. 
Published: April 2011

AbstractEngineering liver tissue using hepatocyte transplantation may provide a new approach for treating a variety of liver diseases. However, techniques to transplant hepatocytes and promote their survival must be developed. We have developed systems to transplant hepatocytes on highly porous (95%), biodegradable sponges, and to regulate the survival of cultured hepatocytes by releasing specific growth factors in the cellular environment. Sponges were fabricated from poly (L, lactic acid) (PLLA) and polyvinyl alcohol using a particulate leaching technique. Epidermal growth factor and insulin, critical factors for hepatocyte growth and survival in culture, were incorporated into microspheres fabricated from poly (lactic-co-glycolic acid) (PLGA) utilizing a double emulsion technique. The incorporated factors were released in a controlled manner over one month in vitro, and the released factors maintained their biological activity, as measured by their ability to promote hepatocyte growth and survival in culture. The growth factor-containing microspheres could be transplanted with hepatocytes using the porous sponges, and the localized, sustained release of these factors improved hepatocyte engraftment 2-fold. These studies suggest that hepatocyte containing tissues can be engineered using cell transplantation, and that regulating the microenvironment of transplanted cells can control their engraftment.
Enzyme-Mediated Oscillatory Drug Release through Hydrogel Membranes
Authors: Baker John P. , Siegel Ronald S. 
Published: April 2011

AbstractImplantable polymeric drug-delivery devices have been constructed to deliver drugs at welldefined rates. Typically, these devices have been designed to deliver drugs at a constant rate, or in response to the concentration of a certain body metabolite. For some drugs, pulsatile delivery is sought. For example, under normal conditions, human growth hormone is released in the body in periodic bursts. Current treatments for HGH deficiency often fail because HGH is not administered following the endogenous pattern. Thus, pulsatile hormone-replacement therapy should be considered. Also, it may be useful to deliver in a periodic, pulsatile manner drugs that exhibit significant acute tolerance.Currently, an oscillator is under development that is fueled by endogenous compounds and contains a variable-permeability membrane. The membrane's permeability to the substrate of an enzymatic reaction is assumed to be dependent on the concentration of the product of the reaction in a manner that displays product inhibition. Under certain conditions, this negative-feedback control can lead to oscillations in the membrane's permeability to substrate. If the membrane's permeability to a drug is simultaneously affected, then this will lead to oscillatory drug release.We report encouraging initial studies. A simple theoretical model has been developed for the membrane oscillator, and results of simulations based on the model are discussed.Diffusion-cell studies have been performed with a variable-permeability poly(N-isopropylacrylamide- co-methacrylic acid) hydrogel membrane. Using glucose as a probe solute, the results show that lowering the pH induces hydrogel volume collapse and cessation of glucose permeation across the membrane.
Tailored Viscosity Reduction in Aqueous Hydroxypropylcellulose Solutions
Authors: Prevysh Victoria A. , Spontak Richard J. , Khan Saad A. 
Published: April 2011

AbstractPolysaccharides, including cellulosic derivatives such as hydroxypropylcellulose (HPC), are used extensively in the pharmaceutical industry due to their biocompatibility and self-organization properties. While drug delivery vehicles employing, for instance, aqueous polysaccharide gels are desirable, production of such gels can be hindered by tremendously high solution viscosity. In this work, we describe a novel means by which to reduce the viscosity and enhance the solubility of aqueous HPC. Here, the efficacy of several additives which promote HPC viscosity reduction through molecular salting-in is examined by dynamic rheology and light/electron microscopy.
ECR-MBE and GSMBE of Gallium nitride on Si(111)
Authors: Rossner U. , Rouviere J.-L. , Bourret A. , Barski A. 
Published: April 2011

ABSTRACTElectron Cyclotron Resonance Plasma Assisted Molecular Beam Epitaxy (ECR-MBE) and Gas Source Molecular Beam Epitaxy (GSMBE) have been used to grow hexagonal GaN on Si (111). In the ECR-MBE configuration high purity nitrogen has been used as nitrogen source. In GSMBE ammonia was supplied directly to the substrate to be thermally cracked in the presence of gallium.By a combined application of in-situ reflection high-energy electron-diffraction (RHEED) and cross-sectional transmission electron microscopy (TEM) the growth mode and structure of GaN were determined. The growth mode strongly depends on growth conditions. Quasi two dimensional growth was observed in ECR-MBE configuration for a substrate temperature of 640°C while three dimensional growth occured in GSMBE configuration in the temperature range from 640 to 800°C.Low temperature (9 K) photoluminescence spectra show that for samples grown by ECR-MBE and GSMBE a strong near band gap emission peak dominates while transitions due to deep level states are hardly detectable. The best optical results (the highest near band gap emission peak intensity) have been observed for samples grown by GSMBE at high temperature (800°C). This could be explained by the increase of grain dimensions (up to 0,3 – 0,5 μm) observed in samples grown by GSMBE at 800°C.
Growth of High Quality InGaN Films by Metalorganic Chemical Vapor Deposition
Authors: Roberts J. C. , McIntosh F. G. , Boutros K. S. , Bedair S. M. , Moussa M. , Piner E. L. , He Y. , El-Masry N. A. 
Published: April 2011

ABSTRACTInGaN based optical devices can cover from the violet through orange regions of the visible spectrum. Difficulties in the growth of this alloy, which have impeded its applications, include problems such as the high vapor pressure of In, weak In-N bonds and lack of sufficient nitrogen during growth. We report on the MOCVD growth of InxGa1−xN (0 < x < 0.4) on sapphire substrates in the 750 - 800 °C temperature range. X-ray diffraction data show full width at half maximum line widths as narrow as 250 arcsec for low values of x, while films with higher lnN% exhibit broader line widths. Room temperature photoluminescence spectra exhibit band edge emission, with emission from deep levels increasing with x. Preliminary investigations of AlGaN/lnGaN/AlGaN double heterostructures have been conducted.
GaAsN Alloys and GaN/GaAs Double-Hetero Structures
Authors: Sato Michio 
Published: April 2011

ABSTRACTTernary alloys; GaAsN (N<3%) were grown by plasma-assisted metalorganic chemical vapor deposition using triethylgallium, AsH3, and plasma-cracked NH3 or N2 as the precursors. More N atoms were incorporated into the alloys from N2 than NH3 at constant N/As ratios. Both photoluminescence peaks and optical absorption edges were redshifted from GaAs bandgap with increasing the N content, indicating the GaAsN alloys have narrower bandgaps than GaAs.GaN/GaAs double-hetero structures were grown by exposing GaAs surfaces to N-radical flux to replace surface As atoms by N atoms, and by growing GaAs on the thin GaN layers. When the GaN thickness exceeded one-monolayer, the GaN/GaAs interfaces and the GaAs cap layers deteriorated drastically. The one-monolayer-thick GaN embedded in GaAs attracts electrons and shows intense photoluminescence, whereas the GaN cluster is non-radiative, probably because of the defects caused by the large lattice-mismatch between GaN and GaAs.
Single Crystal Wurtzitic Aluminum Nitride Growth on Silicon Using Supersonic Gas Jets
Authors: Ustin S. A. , Lauhon L. , Brown K. A. , Hu D. Q. , Ho W. 
Published: April 2011

ABSTRACTHighly oriented aluminum nitride (0001) films have been grown on Si(001) and Si (111) substrates at temperatures between 550° C and 775° C with dual supersonic molecular beam sources. Triethylaluminum (TEA;[(C2H5)3Al]) and ammonia (NH3) were used as precursors. Hydrogen, helium, and nitrogen were used as seeding gases for the precursors, providing a wide range of possible kinetic energies for the supersonic beams due to the disparate masses of the seed gases. Growth rates of AIN were found to depend strongly on the substrate orientation and the kinetic energy of the incident precursor; a significant increase in growth rate is seen when seeding in hydrogen or helium as opposed to nitrogen. Growth rates were 2–3 times greater on Si(001) than on Si(111). Structural characterization of the films was done by reflection high energy electron diffraction (RHEED) and x-ray diffraction (XRD). X-ray rocking curve (XRC) full-width half-maxima (FWHM) were seen as small as 2.5°. Rutherford back scattering (RBS) was used to determine the thickness of the films and their chemical composition. Films were shown to be nitrogen rich, deviating from perfect stoichiometry by 10%–20%. Surface analysis was performed by Auger electron spectroscopy (AES).
Analysis of Strain in GaN on Al2O3 and 6H-SiC: Near-Bandedge Phenomena
Authors: Edwards N. V. , Bremser M. D. , Weeks T. W. , Kern R. S. , Liu H. , Stall R. A. , Wickenden A. E. , Doverspike K. , Gaskill D. K. , Freitas J. A. , Rossow U. , Davis R. F. , Aspnes D. E. 
Published: April 2011

ABSTRACTWe report the dielectric functions of various GaN samples as measured by spectroscopic ellipsometry. Structure related to the A and B excitons is resolved at room temperature, in principle allowing strain to be assessed. However, the data indicate that dead-layer and dispersion effects are present, preventing a simple interpretation. We discuss various complications including the Edn/dE contribution to dispersion, which is important for laser action. Our data appear to indicate that the spin-orbit splitting of GaN is about 15 meV, somewhat larger than the currently accepted value of about 11 meV.
Transition Metal Luminescence in AlN Crystals
Authors: Pressel K. , Heitz R. , Nilsson S. , Thurian P. , Hoffmann A. , Meyer B.K. 
Published: April 2011

ABSTRACTWe study deep defects in AIN crystals in the near infrared by photoluminescence and compare the observed emissions with those in GaN. By below bandgap excitation with an Ar ion laser three no-phonon lines at 1.043 eV, 0.943 eV, and 0.797 eV were detected, which are caused by different residual transition metal contaminants. The weak emission at 1.043 eV and the intensive emission at 0.797 eV show A1N related phonon sidebands, whereas the emission at 0.943 eV has practically no phonon sideband. No hot lines could be detected for the emissions at 0.943 and 0.797 eV in temperature dependent measurements. We discuss possible identifications of the luminescence centers and the similarity between GaN and AIN in view of transition metals.
Dry Etching of III-V Nitrides
Authors: Pearton S. J. , Shul R. J. , McLane G. F. , Constantine C. 
Published: April 2011

ABSTRACTThe chemical inertness and high bond strengths of the III-V nitrides lead to slower plasma etching rates than for more conventional III-V semiconductors under the same conditions. High ion density conditions (>3×1011cm−3) such as those obtained in ECR or magnetron reactors produce etch rates up to an order of magnitude higher than for RIE, where the ion densities are in the 109 cm−3 range. We have developed smooth anisotropic dry etches for GaN, InN, AlN and their alloys based on Cl2/CH4/H2/Ar, BCl3/Ar, Cl2/H2, C12/SF6, HBr/H2 and HI/H2 plasma chemistries achieving etch rates up to ∼4,000Å/min at moderate dc bias voltages (≤-150V). Ion-induced damage in the nitrides appears to be less apparent than in other III-V’s. One of the key remaining issues is the achievement of high selectivities for removal of one layer from another.
(Negative) Electron Affinity of AlN and AlGaN Alloys
Authors: Nemanich R.J. , Benjamin M.C. , Bozeman S.P. , Bremser M.D. , King S.W. , Ward B.L. , Davis R.F. , Chen B. , Zhang Z. , Bernholc J. 
Published: April 2011

ABSTRACTThe electron affinity of a semiconductor defines the relationship of the vacuum level and the semiconductor band structure. It is dependent on the atomic orbitals of the material and the surface termination. We report experimental and theoretical results that support the presence of a negative electron affinity on AlN and the Al rich AlGaN alloys. The GaN surface is found to exhibit a (positive) electron affinity of 3.3eV. The experimental measurements employ UV-photoemission spectroscopy on in situ gas-source MBE samples and on CVD samples. Theoretical results indicate that the (negative) electron affinity of AlN depends sensitively on the surface reconstruction and adatom termination. The experimental dependence of the electron affinity on alloy concentration is presented. The results indicate that AlGaN alloys with band gap similar or greater than that of diamond will exhibit a negative electron affinity. Field emission results are reported, and the characteristics are similar to those obtained from a diamond film. Issues related to cold cathode electronic devices based on NEA surfaces are noted.