bluuebunny/crossref_metadata_2025 huggingface dataset:
The Effects of Sintering on the Microstructure and the Luminescent Characteristics of Polycrystalline ZnS
Authors: Adams R. Matthew , Mascher Peter , Kitai Adrian H.
Published: April 2011

Positron annihilation spectroscopy and cathodoluminescence were employed to study changes in the microstructural and luminescent properties of pure and doped polycrystalline ZnS. All samples show evidence of defect clustering, when sintered at temperatures up to 400 °C, indicated by an increase in the average positron lifetime. The average lifetime of the undoped material is constant (at about 290 ps) from 300 to 700 °C, and then decreases beyond this temperature, due to the out diffusion of vacancy clusters. In comparison, the average lifetime for MnS doped material decreases beyond 600 °C. This decrease in the average lifetime is correlated with an increase in the luminescent intensity of the 585 nm Mn band, indicating that Mn compensation of zinc vacancies contributes to the decrease in the average lifetime. At sintering temperatures above 400 °C, the average lifetime of TbF3 doped material decreases by ∼3 ps / 100 °C, from a peak value of 285 ps, and then at 700 °C drops an additional 15 ps to 260 ps. At 650 °C a change from the distinct Tb spectrum to a broad band emission is observed It is believed that these effects can be linked to the incorporation of Tb3+ ions on Zn2+ lattice sites.
The Influence of Non-Stoichiometry on the Electrical Activation of n-Type Dopants in InP
Authors: Ridgway M. C. , Johnson C. M. , KringhØj P.
Published: April 2011

The influence of implantation-induced non-stoichiometry on the electrical activation and depth distribution of Group IV (Ge and Sn) and VI (Se and Te) elements in InP has been investigated with a variety of analytical techniques. Electrical measurements indicate that P co-implantation can increase the electrical activation of the Group IV elements through reductions in amphoteric behaviour and dopant-defect complexes for Ge and Sn, respectively. The relative influence of P co-implantation increases as the dopant ion dose increases. Though others have demonstrated that co-implantation increases the electrical activation of Group II elements, similar observations were not apparent for Group VI elements, the latter attributed to the lack of Group VI element interstitial character.
Improvement of Pin Photodiodes on the Soi Layer by Rapid Thermal Annealing
Authors: Fujii Yoshimaro , Usami Akira , Fujiyoshi Katsuhiro , Yoshida Hideaki , Ichimura Masaya
Published: April 2011

Electrical properties of PIN photodiodes fabricated on the bonded silicon on insulator (SOI) wafers annealed at 900°C for 5 seconds were evaluated in order to investigate the effect of rapid thermal annealing (RTA) on SOI wafers. Traps in the SOI layers with different thicknesses (10,30,100 μm) were investigated using the deep level transient spectroscopy (DLTS) method. In the SOI layer with a thickness of 100 μm, a trap with deep energy level (about Ec-Et=0.55 eV) was observed and the concentration of the trap decreased from 5.0 × 1011 cm−3 to 1.5 × 1011 cm−3 by RTA. For PIN photodiodes on the 100 μm-thick SOI layer, the dark current decreased from 2 × 10−9 A to 6 × 10−10 A, and sensitivity uniformity for a 35 μmφ light spot and spectral responses were both improved by RTA. Lifetimes were obtained from open-circuit voltage (Voc) decay curves for 940 nm and 655 nm light, and they increased from 37 μs to 57 μs and from 47 μs to 62 μs, respectively, by RTA. For thinner SOI layers (thickness=10, 30 μm), PIN photodiodes have good uniformity and low dark current, and their characteristics were not changed by RTA.
Magnetic Phase Transitions in Epitaxial Fe/Cr Superlattices
Authors: Fullerton Eric E. , Riggs K. T. , Sowers C. H. , Berger A. , Bader S. D.
Published: April 2011

The surface spin-flop and Néel transitions are examined in Fe/Cr superlattices. The surface spin-flop, originally predicted by Mills [Phys. Rev. Lett. 20, 18 (1968)], is observed in Fe/Cr(211) superlattices with antiferromagnetic interlayer coupling and uniaxial in-plane anisotropy. The Néel transition (TN) of Cr is observed in Fe/Cr(001) superlattices, for which the onset of antiferromagnetism is at a thickness tCr of 42Å. The bulk value of TN is approached asymptotically as tCr increases and is characterized by a three-dimensional shift exponent. These TN results are attributed to finite-size effects and spin-frustration near rough Fe-Cr interfaces.
Different Temperature Dependencies of Magnetic Interface and Volume Anisotropies in Gd / W(110)
Authors: Farle M. , Schulz B. , Aspelmeier A. , Andre G. , Baberschke K.
Published: April 2011

The magnetic anisotropy of epitaxial Gd(0001) films on W(110) is determined as a function of temperature (150 to 350 K) and film thickness (9 to 30 monolayers) by in situ ferromagnetic resonance. It is found that the usual analysis in terms of a thickness independent part KV and a thickness dependent contribution 2KS/d must be performed at the same reduced temperature t = T/Tc(d). Kv shows qualitatively the same temperature dependence as the magnetocrystalline anisotropy of bulk Gd. It changes in sign near 0.7 Tc and does not vanish at Tc. KS on the other hand decreases linearly from 1.2 meV/atom at 0.6.Tc to zero at Tc. It appears that the intrinsic origin for Kv and KS is fundamentally different. The vanishing of KS at Tc indicates that two-ion anisotropy (spin-spin interaction) is dominating the interface anisotropy. The non- zero KV(T≥Tc) is likely due to a single ion magnetic anisotropy which is known for bulk Gd.
Perpendicular Resistance of Co/Cu Multilayers Prepared by Molecular Beam Epitaxy
Authors: List N.J. , Pratt W.P. , Howson M.A. , Xu J. , Walker M.J. , Hickey B.J. , Greig D.
Published: April 2011

Results are presented of the magnetoresistance of MBE-grown (111) Co/Cu multilayers measured with the current perpendicular to the plane of the layers (CPP). Although for measurements made with the more common geometry of current in the plane of the layers (CIP) there are large differences between the results on samples made by sputtering and those prepared by MBE, for these new CPP data the results on samples made by the two techniques are very much alike. For copper layers with thicknesses between 0.9nm to 6nm the magnetoresistance shows oscillations with copper thickness that were almost non-existent in the earlier CIP data. At the second peak the magnetoresistance in the CPP geometry is an order of magnitude greater than that in the CIP configuration. Although the interfaces in these samples have been shown to be very sharp, they appear to form a mosaic structure with the antiferromagnetic regions embedded in a ferromagnetic structure. It is argued that for CIP measurements the GMR is greatly reduced by these ferromagnetic correlations over lengthscales long compared to the electron mean free path. For CPP measurements, on the other hand, it is the spin diffusion length that is the determining factor with the mean free path no longer a key parameter and with values of the GMR virtually independent of the growth process.
Gmr Multihayer Patterned Structures
Authors: Melo L.V. , Rodrigues L.M. , Sousa A.T. , Freitas P.P.
Published: April 2011

Co-Cu-NiFe-Cu weakly coupled multilayers, were patterned into stripes with dimensions from 1×6μm2 to 2×20μm2. After proper biasing using a DC field created by an adjacent bias conductor, these structures show large linear field spans (±1500e), with MR values up to 6%. These can be used for current or position sensor applications. Sensor response to AC fields was studied up to 1Mhz, using the bias conductors as sources of the AC field. We find that the signal output is reduced above 10 to 100kHz. For comparison, sensors were also fabricated out Co-Cu AF-coupled multilayer (3×100μm2 structures) needed for field detection up to several kOe.
Giant Magnetoresistance and Oscillation in Epitaxial Fe/Cr(111) Multilayers
Authors: Chiang Wen-C. , Baxter David V. , Cheng Yang-Tse
Published: April 2011

We report on the first studies of the giant magnetoresistance and oscillatory coupling in epitaxial Fe/Cr(111) multilayers. A series of samples were grown on hydrogen terminated Si(111) substrates at room temperature by UHV electron beam evaporation; with the thickness of Fe layer fixed at 30 Å, and the thickness of Cr layer varied from 10–47 Å. Giant magnetoresistance (GMR) is observed at 4.2 Å in these samples, with a maximum value of 13% for a Cr layer thickness of 13 Å. The associated oscillatory coupling is comparable to that reported in other crystallographic orientations in terms of both its period and phase.
Microstructure and Gmr in (111) Sputter-Deposited Co/Cu Multilayers
Authors: Pollard R.J. , Wilson M.J. , Grundy P.J.
Published: April 2011

This paper presents the results of giant magnetoresistance (GMR), magnetic and microstructural investigations of sputter-deposited Co/Cu multilayers. The multilayers were designed to be at the second maximum of the oscillatory exchange coupling and were deposited onto a range of ion beam irradiated (111) Si substrates giving a transition from a random orientation to a highly oriented (111) texture. The randomly oriented multilayers exhibited mixed coupling and ∼20% GMR, which had components arising from irreversible and reversible magnetization changes, whereas the highly oriented (111) multilayers were almost completely ferromagnetically coupled and showed very little GMR.
Giant Magnetoresistance in Hybrid Magnetic Nanostructures Including Both Layers and Clusters
Authors: Schroeder P.A. , Holody P. , Loloee R. , Duvail J. L. , BarthÉlemy A. , Steren L.B. , Morel R. , Fert A.
Published: April 2011

Early experiments to define oscillations in the CIP magnetoresistance (CIP-MR) of Ag/Co analogous to those for tcu < 5nm in Cu/Co were unsuccessful. The MR in this region was very small. Later experiments by Araki using thin (0.6nm ) Co layers produced much larger MRs and lead us to look at the MRs of similar samples more closely. We conclude that the large MR of such samples is associated with the discontinuous nature of the Co layers. The object of the present paper is to combine the high MR associated with the thin Co layers with the field dependence governed by the magnetization reversal in thick, and magnetically soft permalloy (Py) layers. We have measured the CIP-MR of sputtered samples of the [Co(O.4 nm)/Ag(tAg)/Py(tpy)/Ag(tAg)]×15 system with tAg ranging from 1.05 to 4nm and with tpy = 2 or 4nm. We obtain MRs at 4.2K as large as 35% in less than 100e with slopes as high as 5%/Oe. With CPP measurements slopes as high as 10%/Oe have been obtained. Squid magnetometer measurements indicate that, as the temperature increases, there is a crossover to superparamagnetic behaviour and a resulting gross deterioration of the MR slopes at room temperature. Efforts to increase the room temperature sensitivity are described. Detailed measurements of the CPP-MR of the [Co(0.4nm)/Ag(4nm)/Py(tpy)/Ag(4nm)]x20 series of multilayers are consistent with a two spin band model modified to take account of the granular nature of the Co.
Giant Magnetoresistance Behavior in Epitaxial Nd0.7Sr0.3MnO3−δ and La0.67Ba0.33MnO3−δ Thin Films
Authors: Xiong G.C. , Li Q. , Ju H.L. , Wu J. , Senapati L. , Greene R.L. , Venkatesan T.
Published: April 2011

Epitaxial Nd0.7Sr0.3MnO3-δ and La0.67Ba0.33MnO3-δ thin films with large magnetoresistance ratios have been prepared by pulsed laser deposition. Huge negative magnetoresistance ratios of -ΔR/RH > 1×106 % were obtained at 60 K and a magnetic field of 8 T in a Nd0.7Sr0.3MnO3-δ film. The influence of sample preparation conditions on the resistivity behavior of these films has been studied. Results suggest that oxygen stoichiometry and diffusion are important factors in causing the behavior observed in doped manganese oxide films.
Atom Specific Surface Magnetometry with Linear Magnetic Dichroism in Directional Photoemission
Authors: Rossi Giorgio , Sirotti Fausto , Panaccione Giancarlo
Published: April 2011

A practical atom specific surface magnetometry can be based on the measure of magnetic dichroism in the angular distribution of core photoelectrons using linearly polarized synchrotron radiation. The magnetic dichroism effect on the photoemission intensity of 3p core levels of the ferromagnetic transition elements is as large as 46% in the case of Fe(100). The most efficient scheme for measuring the magnetic dichroism in photoemission requires two mirror experiments in chiral geometry, i.e. only two times more experiments than standard core level photoemission for surface chemical analysis. We describe the dichroism magnetometry and show examples for Fe, Co, Ni and Cr surfaces and interfaces, including the measurement of the temperature dependence of the Fe(100) surface magnetization and of the effect of S-segregation on the surface magnetic moment of iron.
Soft X-Ray Optical Rotation as Element-Specific Magneto-Optical Probe
Authors: Kortright J.B. , Rice M.
Published: April 2011

Continuously tunable multilayer linear polarizers extend magneto-optical rotation techniques into the extreme ultraviolet and soft x-ray regions. Resonant magneto-optical rotation is large at the Fe L2,3 edges. Magneto-optical Kerr rotation can be either bulk or surface sensitive depending on incidence angle. A SMOKE hysteresis loop measured from the Fe in an Fe/Cr multilayer reveals high sensitivity and a complex magnetic response of Fe.
Ferromagnetic Behaviour in Nanoscale Cobalt Particles Dispersed by Zeolite Na-X.
Authors: Hussain I. , Gameson I. , Anderson P.A. , Edwards P. P.
Published: April 2011

This investigation has looked at the preparation of nanoscale cobalt particles by a simple solid state reaction involving cobalt (II) nitrate and zeolite Na-X under vacuum conditions followed by reduction in an hydrogen atmosphere. Samples were characterised by powder x-ray diffraction and scanning/transmission electron microscopy (TEM). Magnetic measurements were performed on the samples below 300 K using a SQUID magnetometer.
Synthesis and Characterization of Organic/Inorganic Interpenetrating Polymer Networks
Authors: Bauer Barry J. , Jackson Catheryn L. , Liu Da-Wei
Published: April 2011

Interpenetrating polymer networks have been synthesized by performing sol-gel chemistry and conventional organic polymerizations in mixtures of the monomers. The organic polymers were acrylates, and the inorganic phase was SiO2 formed by hydrolysis of orthosilicates. Polymerizations were conducted at a variety of relative rates, and the chemistry was designed to allow different amounts of grafting between the components. The morphology was characterized by transmission electron microscopy and small angle neutron and x-ray scattering. Wide variations in morphology were observed depending on the polymerization conditions, ranging from grossly phase separated to dendritic to finely divided structures (at a 100Å size scale). The phases ranged from mixtures of the two components to relatively pure phases. The interface between the phases ranged from very narrow to relatively broad.
Removal of SiO2 From Si (100) by Remote H2/SiH4 Plasma Prior to Epitaxial Growth
Authors: Barnak J. P. , Ying H. , Chen Y. L. , Montgomery J. , Nemanich R. J.
Published: April 2011

This study demonstrates the cleaning of Si(100) surfaces with a remote H2/SiH4 plasma. The surfaces were prepared with a chemical oxide the remains after an RCA clean. The plasma cleaning process was designed to remove contaminants such as C, F, and SiO2. The key to successful removal of the oxide is to have the plasma chemistry in a neutral deposition regime. The neutral deposition process regime is a balance between the deposition of Si by SiH4 and the etching of the deposited Si by atomic H. During the neutral deposition mode the SiO2 was removed without deposition of Si on the SiO2 surface. Once the SiO2 layer is removed, theunderlying Si surface is exposed to the H2/SiH4 plasma and a thin epitaxial film may be deposited. The final Si surface configuration after plasma cleaning is a 2×1 hydrogen terminated surface. The characterization of the interface and epitaxial film were investigated using Auger electron spectroscopy (AES) and transmission electron microscopy (TEM).
Deposition of Gan Films Using Seeded Supersonic Jets
Authors: Henry Lamb H. , Lai Ken K. , Torres Victor , Davis Robert F.
Published: April 2011

GaN films were deposited on sapphire (0001) from triethylgallium (TEG) and NH3 seeded in separate He free jets. as the dissociative chemisorption of NH3 is expected to be rate-limiting in GaN growth, the NH3/He nozzle temperature was varied to control the incident kinetic energy of the NH3 molecules. Using an NH3/TEG flow ratio of 205 and an NH3/He nozzle temperature of 400°C, stoichiometric films were deposited at substrate temperatures ≥530°C. Scanning electron microscopy revealed that films deposited at 580°C are polycrystalline α-GaN with randomly oriented 0.5-μm grains. Films with a closely similar morphology are deposited by using an NH3/He nozzle temperature of 90°C. IN contrast, films deposited at 580°C using an NH3/He nozzle temperature of 510°C consist of whiskers (aspect ratio = c A. 4) which exhibit a-GaN (0001)/sapphire (0001) heteroepitaxy, as evidenced by X-ray diffraction and reflection high-energy electron diffraction.
Nitrogen Plasma Ion Implantation into Carbon Films Deposited by the Anodic Vacuum ARc
Authors: Husein Imad F. , Li Fan , Zhou Yuanzhong , Allen Ryne C. , Chan Chung
Published: April 2011

Amorphous carbon films (a-C) deposited by the anodic vacuum arc on Si substrates were implanted with nitrogen using the Plasma Immersion Ion Implantation (PIII) technique to form carbon nitride films (CNX). Scanning Electron Microscopy (SEM) of the a-C films show a surface morphology with maximum grain size in the order of a few nanometers and the exclusion of macroparticles. INcreasing the nitrogen content of the CNX films increased the intensity of the X-ray Photoelecton Spectroscopy (XPS) C Is peak at 286.6 eV and formed a new peak at 285.6 eV which both can be associated with the carbon-nitrogen bond formation. Nanoindentaiton measurements showed that the hardness of the a-C films increased after implanting nitrogen into them. these CNX films exhibited a hardness of 19 GP A.
Dynamical Modeling of Laser ablation Processes
Authors: Leboeuf J. N. , Chen K. R. , Donato J. M. , Geohegan‡ D. B. , Liu C. L. , Puretzky A. A. , Wood ‡ R. F.
Published: April 2011

Several physics and computational approaches have been developed to globally characterize phenomena important for film growth by pulsed laser deposition of materials. these include thermal models of laser-solid target interactions that initiate the vapor plume; plume ionization and heating through laser absorption beyond local thermodynamic equilibrium mechanisms; gas dynamic, hydrodynamic, and collisional descriptions of plume transport; and molecular dynamics models of the interaction of plume particles with the deposition substrate. the complexity of the phenomena involved in the laser ablation process is matched by the diversity of the modeling task, which combines materials science, atomic physics, and plasma physics.
Study of annealed Indium Tin Oxide Films Prepared by RF Reactive Magnetron Sputtering
Authors: Meng Li-Jian , Maçarico A. , Martins R.
Published: April 2011

Tin doped indium oxide (ITO) films were deposited on glass substrates by rf reactive magnetron sputtering using a metallic alloy target (In-Sn, 90-10). the post-deposition annealing has been done for ITO films in air and the effect of annealing temperature on the electrical, optical and structural properties of ITO films was studied. It has been found that the increase of the annealing temperature will improve the film electrical properties. the resistivity of as-deposited film is about 1.3 х 10-1 Ω*cm and decreases down to 6.9 х 10-3Ω*cm as the annealing temperature is increased up to 500 °C. IN addition, the annealing will also increase the film surface roughness which can improve the efficiency of amorphous silicon solar cells by increasing the amount of light trapping.
Surface and Interface Microstructure of Epitaxial Ferroelectric (Ba, Sr)Tio3 Thin Films
Authors: Alyoshin V. A. , Sviridov E. V. , Mukhortov Vi. M. , Zakharchenko I. N. , Dudkevich V. P.
Published: April 2011

Surface and cross-section relief evolution of ferroelectric epitaxial (Ba,Sr)Ti03 films rf-sputtered on (001) MgO crystal cleavage surfaces versus the oxygen worKing gas pressure P and substrate temperature T were studied. Specific features of both three-dimensional and two-dimensional epitaxy mechanisms corresponding to various deposition conditions were revealed. Difference between low and high P-T-value 3D epitaxy was established. the deposition of films with mirror-smooth surfaces and perfect interfaces is shown to be possible.
Fatigue Crack Growth Behavior of Small Sn-Bi-Ag Solder Joints
Authors: Liu Tao , Korhonen M. A. , Ting S. , Kim D. , Li C.-Y.
Published: April 2011

Reliability of solder interconnects is normally characterized by extrapolation of bulk solder reliability data, such as crack growth measurements of solder materials in the bulk form. In the present study, experimental evidence will be presented to show that crack growth, which is the most commonly observed failure mode in small solder joints strongly depends on the size and shape of the joint cross-section. Furthermore, the crack growth rate can be appropriately correlated to the size of the intense plastic yielding zone at the crack tip using a plastic decohesion argument.
Electronics Packaging Materials Research at NIST
Authors: Schen Michael A. , Davis G. T. , Mopsik F. I. , Wu W. L. , Wallace W. E. , Manning Jr. , Handwerker C. A. , Read D. T.
Published: April 2011

The Materials Science and Engineering Laboratory at NIST has augmented its laboratory-based research in support of the U.S. commercial microelectronics industry by expanding its efforts in electronics packaging, interconnection and assembly (P/I/A) materials technologies. In conjunction with industry, university and other government agency partners, these new NIST efforts target materials technology issues that underlie the priorities contained within the various electronics industry technology roadmaps. A dominant aspect of the laboratory P/I/A program focuses on the in-situ metrology and data needs associated with the materials and complex material assemblies which comprise today's microelectronic components and circuits.
Ferroelectric Liquid Crystals for Nonlinear Optics: can we Really do It?
Authors: Walba David M. , Dyer Daniel J. , Cobben Peter L. , Sierra Teresa , Rego James A. , Liberko Charles A. , Shao Renfan , Clark Noel A.
Published: April 2011

Ferroelectric liquid crystals (FLCs) are true liquids with a thermodynamically stable polar structure. Furthermore, in some systems excellent polar stereocontrol has been demonstrated (> 80% of the molecular dipole oriented along the polar axis with infinite “thermal stability”). These properties make FLCs an interesting candidate for second order NLO applications. However, until now the orientation of organic functional arrays with “large β”, typified by the disperse red 1 (DRI) chromophore, has not been demonstrated.

Herein we report the initial results of a study directed towards providing a solution to this problem. Specifically, a new FLC dopant wherein the DRI chromophore (p-nitro-p'-dialkyl-aminoazobenzene unit) is oriented along the polar axis in FLC mixtures up to 30% by weight is described. These results suggest that it will be possible to obtain FLCs with good stereocontrolled orientation of large β functional arrays. Given that hybrid VLSI silicon/FLC optical chips are under intense investigation as micro-displays, and manufacturing issues for this class of devices are being addressed in the display context, the materials presented here suggest VLSI/FLC chips may be useful as high speed electro-optic modulators as well.
Heteroepitaxy and Waveguide Formation for Solution Deposited LiNbO3 Thin Layers
Authors: Clem P. G. , Payne D. A.
Published: April 2011

Lithium niobate thin layers have potential applications in integrated, high efficiency signal modulators, and in second harmonic generation devices. We report the solution deposition of heteroepitaxial LiNbO3 thin layers on (006), (110) and (012) sapphire. Factors affecting surface roughness were investigated by atomic force microscopy. The best results for optical losses occurred after fresh, 0.1M unhydrolyzed solutions were used. Channel waveguides were developed by lithography and proton exchange. Waveguides were formed in Nd3+- and Er3+-doped thin layers to confine light and assess the possibility of integrated waveguide lasers.
Plasma Synthesis of Rare Earth Doped Integrated Optical Waveguides
Authors: Raoux S. , Anders S. , Yu K. M. , Ivanov I. C. , Brown I. G.
Published: April 2011

We describe a novel means for the production of optically active planar waveguides. The technique makes use of a low energy plasma deposition. Cathodic-arc-produced metal plasmas are used for the metallic components of the films and gases are added to form compound films. Here we discuss the synthesis of A12-xErxO3 thin films. The erbium concentration (x) can vary from 0 to 100% and the thickness of the film can be from Angstroms to microns. In such material, at high active center concentration (x=l% to 20%), erbium ions give rise to room temperature 1.53μm emission which has minimum loss in silica-based optical fibers. With this technique, multilayer integrated planar waveguide structures can be grown, such as Al2O3/Al2-xErO3/A12O3/Si, for example.
Time-Dependent SHG in Thin Film Germanium-Doped Silica Waveguides
Authors: Dajani I. , Kester J. J. , Ranon P. M. , Brauer M. L. , Mcgillen D. J.
Published: April 2011

The evolution of second harmonic generation (SHG) in germanium doped silica planar waveguides is simulated numerically. Based on the asymmetric photoionization model, the total current in the waveguide is taken to be the sum of an asymmetric current and a current due to the resulting dc field. The interplay between these two currents causes the SHG to saturate in time. The saturation of SHG in length is due to diffraction.
New Nonlinear Optically Active Polymers Containing Hydrazone Chromophores
Authors: Mang M. N. , Bales S. E. , Brennan D. J. , Chartier M. A. , Gulotty R. J. , Haag A. P. , Inbasekaran M. N. , Langhoff C. A. , Newsham M. D.
Published: April 2011

A family of new polymeric nonlinear optical materials with high second order non-linearities, good thermo-oxidative and reorientational stability, and low waveguide losses have been prepared from a series of chromophores containing hydrazone moieties. These new polymerizable chromophores can be readily prepared by the acid-catalyzed condensation of substituted arylhydrazines with functionalized ketones or aldehydes to give molecules that have μ3 values up to 2440 × 10−48 esu (1579 nm) in solution. Thermoplastic polycarbonates and poly(hydroxy ethers) containing hydrazone chromophores have been prepared with Tg's ranging from 135 °C to 285 °C. Epoxy systems crosslinked with amino-functional arylhydrazones, have high d33 values and high glass transition temperatures, albeit with lower relative thermo-oxidative stability. Simple Mach-Zehnder modulators and registered multi-level structures based on these polymers have been reported previously. One device, prepared from a hydrazone-containing poly(hydroxy ether), has an r33 value of 10 pm/V (1320 nm), and retains most of that activity to 140 °C.
Biocompatibility of Hylan Polymers in Various Tissue Compartments
Authors: Larsen N.E. , Leshchiner E. , Balazs E.A. , Belmonte C.
Published: April 2011

Hylans (hyaluronan derivatives) retain the biological compatibility of the natural hyaluronan and have enhanced rheological properties which expands their utility in medical applications. Hylan materials (hylan A fluid, hylan B gel) were evaluated in a variety of tissue compartments for local and systemic tissue reaction (gross and microscopic), residence time and overall behavior in vivo. Hylan material was implanted into the subcutaneous, intradermal, submucosal, intramuscular, eye (vitreus, anterior chamber, trabecular meshwork), and neural (sciatic nerve) tissues at volumes ranging from 0.50 ml/kg to 20 ml/kg (2.5 mg/kg to 100 mg/kg). There was no difference in tissue response to hylan implants at the various ‘doses’ evaluated; all samples tested were observed to be biocompatible and did not elicit significant tissue response. Therefore, tissue reaction of hylan implants was not dependent on dose or concentration of hylan administered, since implantation of small amounts resulted in the same response as implantation of large amounts of material. In one of the most sensitive tests of biocompatibility, hylan was found to have no adverse effect on nerve regeneration (severed sciatic nerves in rat), and the results indicated that hylan materials “regeneration-friendly” environment for peripheral nerve growth as commatpearriaelds tpor othveid BedS Sa controls.

Hylan materials provide biologically and physically compatible intercellular matrices which are useful in a variety of medical applications, including use as viscosurgical and viscoprotective tools (to maintain space, separate and protect tissues) and as viscosupplementation devices and implants.
Polymers for Forming Drug-Loaded Microspheres: Natural Versus Synthetic
Authors: Thies Curt
Published: April 2011

Numerous research groups currently are working to develop microcapsules, microspheres, and nanoparticles able to function as effective drug carriers. Much effort is focused on forming biodegradable particles from iactide-glycolide copolymers (PLGA)1−3. Although microparticles prepared from PLGA copolymers have had many successes, PLGA copolymers are not ideal drug carriers. Many other materials conceptually could be formed into suitable particulate drug carriers: synthetic polymers other than PLGA, natural polymers, chemical derivatives of natural polymers, selected inorganics, and nonpolymeric lipids. The purpose of this paper is not to discuss the advantages and limitations of each of these classes of carrier materials, but to contrast the features of PLGA copolymers with those of potentially competitive natural polymers. PLGA copolymers are used as the reference standard, because they are an approved family of biodegradable drug carrier polymers utilized by many research groups globally.
Engineered Bone from Polyglycolic Acid Polymer Scaffold and Periosteum
Authors: Kim Tae Ho , Jannetta Carol , Vacanti Joseph P. , Upton Joseph , Vacanti Charles A.
Published: April 2011

The ability to create bone from periosteum and biodegradable polymer may have significant utility in reconstructive orthopedic and plastic surgery. Polyglycolic acid (PGA) serves as a biodegradable matrix which can be configured to a desirable shape and structure. This study was conducted to generate new bone tissue from periosteum and PGA polymer and to compare the tissue to the bone tissue generated from periosteal cells seeded onto PGA polymer. Bovine periosteum, harvested from fresh calf limbs, was placed either directly onto PGA polymer (1 cm2) or onto tissue culture dishes for periosteal cell isolation. In Medium 199 media with antibiotics and ascorbic acid, the periosteum/PGA construct was cultured for one week, then implanted into the dorsal subcutaneous space of nude mice. Periosteal cells, cultured from pieces of periosteum for two weeks, were isolated into cell suspension and seeded (˜l-3× 107cells) onto PGA polymer (1 cm2); after one week in culture, the periosteal cell-seeded polymer was implanted into the subcutaneous space of athymic mice. Specimens, harvested at 4, 8, and 14 week intervals, were evaluated grossly and histologically. The periosteum/PGA constructs showed an organized cartilage matrix with early evidence of bone formation at 4 weeks, a mixture of bone and cartilage at 8 weeks, and a complete bone matrix at 14 weeks. Constructs created from periosteal cells seeded onto polymer showed presence of disorganized cartilage at 4 and 8 weeks, and a mixture of bone and cartilage at 14 weeks. Periosteum placed directly onto polymer will form an organized cartilage and bone matrix earlier than constructs formed from periosteal cell-seeded polymer. This data suggests that PGA is an effective scaffold for periosteal cell attachment and migration to produce bone which may offer new approaches to reconstructive surgery.
Growth and Doping of GaN Directly on 6H-SiC by MBE
Authors: Korakakis D. , Sampath A. , NG H.M. , Morales G. , Goepfert I.D. , Moustakas T.D.
Published: April 2011

We report on methods for the growth of GaN by MBE directly on 6H-SiC substrates. The films were doped p-type by the incorporation of Mg and the samples were characterized by studying their structure and morphology by RHEED, XRD and SEM and their recombination properties by photoluminescence measurements. The undoped films were found to be atomically smooth with 2×2 surface reconstruction and have an x-ray rocking curve with a FWHM of 3.5 arcmin. The photoluminescence spectra indicate that recombination is dominated by transition across the gap. The p-type doped films have a rocking curve with FWHM of 6.5 arcmin. and the majority of recombination occurs through D-A transitions at 3.26 eV.
P-type Mg-doped GaN grown by molecular beam epitaxy using ammonia as the nitrogen source
Authors: Yang Z. , Li L.K. , Wang W.I.
Published: April 2011

The electrical and luminescent properties of Mg-doped GaN films grown by molecular beam epitaxy (MBE) using ammonia as the nitrogen source have been investigated. Due to their different growth environments, the Mg-doped GaN films grown by MBE using ammonia exhibited properties that were different from similar films grown by metal-organic chemical vapor deposition (MOCVD). It has been found that the introduction of positive charges during growth is important in the achievement of p-type Mg-doped GaN grown by MBE using ammonia. With the introduction of a moderate nitrogen plasma, we have achieved p-type Mg-doped GaN films with a hole density of 4×1017 cm−3 and a mobility of 15 cm2/V-s at room temperature.
Conductivity Measurements on GaN Grown by OMVPE and HVPE
Authors: Ben-Chorin M. , Diener J. , Meyer B.K. , Drechsler M. , Volm D. , Amano H. , Akasaki I. , Detchprohm T. , Hiramatsu K.
Published: April 2011

We report on conductance and cyclotron resonance (CR) experiments on GaN epitaxial films grown by the OMVPE and HVPE techniques. From a precise determination of the electron effective mass the donor binding energy in the effective mass approximation (EMT) is calculated. We obtain 31.7 meV. The transport experiments on the HVPE films show that the conductance is thermally activated with an activation energy of 15 meV in contrast to the OMVPE films which showed temperature independent conductivity for temperatures between 4 and 100 K.
Exciton Luminescence of Single-Crystal GaN
Authors: Müllhaüser J.R. , Brandt O. , Yang H. , Ploog K.H.
Published: April 2011

Detailed photoluminescence (PL) studies of high-quality MBE-grown single-crystal cubic and hexagonal GaN are presented. We identify free and bound exciton recombination. By means of a line-shape analysis, we quantitatively analyze our spectra, which were taken as a function of temperature (T = 4 - 300 K) and excitation density (Pex = 0.3 - 200W/cm2). We show the dominant recombination channel at 300 K to be free-excitonic in nature with an internal small-signal quantum efficiency of 6 · 10−3 for both cubic and hexagonal material. Based on a three-level model, activation energies for exciton dissociation are evaluated. Radiative (τrad ≈ 2 ns) and nonradiative lifetimes (τe ≈ 1μs, τh ≈ 20 ps) are determined, where in the latter case, electron and hole trapping are considered separately. Furthermore, we show that the dominant nonradiative recombination center, being a hole trap, saturates at Pex ≥ 20 W/cm2.
Room-Temperature Life Test of Nichia AlGaN/InGaN/GaN Blue Light Emitting Diodes
Authors: Osiński Marek , Helms Christopher J. , Berg Niel , Barton Daniel L. , Scott Phillips B.
Published: April 2011

We report on the current status of room-temperature life testing of Nichia NLPB-500 blue light emitting diodes. So far, two tests have been completed. During the first 1000-h test, a constant current of 20 mA was maintained in all devices. During the second 1650 h test, groups of 3 or 4 devices were driven at currents ranging from 20 mA to 70 mA. Very little degradation has been observed in devices driven at normal conditions (20-30 mA), with a noticeable increase in degradation rate above 60 mA.
Directed Light Fabrication of Iron-Based Materials
Authors: Thoma D.J. , Charbon C. , Lewis G.K. , Nemec R.B.
Published: April 2011

Directed light fabrication (DLP) is a rapid fabrication process that fuses gas delivered metal powders within a focal zone of a laser beam to produce fully dense, near-net shape, 3-dimensional metal components from a computer generated solid model. This study used iron-based alloys to evaluate the microstructural development in the DLF process. Continuous microstructural features are evident, implying a continuous liquid/solid interface during processing. In addition, solidification cooling rates have been determined based upon secondary dendrite arm spacings in Fe-25wt.%Ni and 316 stainless steel. Cooling rates vary from 101-105 K s-1, and the solidification behavior has been simulated using macroscopic heat transfer analyses.
Synthesis of Magnetite Particles by Pulsed Alexandrite Laser Processing of Metallic Glass Precursors
Authors: Sorescu Monica , Schafer S.A. , Knobbe E.T.
Published: April 2011

Samples of Fe78B13Si9 and Fe81B13.5Si3.5C2 metallic glasses were irradiated with a pulsed alexandrite laser (λ=750 nm, τ=60 μs) using different laser fluences. Kinetics of laser-induced phase transformations and fluence dependence of magnetic properties were studied by scanning electron microscopy (SEM) and Mössbauer spectroscopy. Low laser fluences were found to induce changes in magnetic texture and onset of crystallization. High laser fluences, however, correlated with additional oxidation effects and the formation of stoichiometric Fe3O4 particles in the irradiated alloy system. An activation energy of 11.9 eV was estimated for the laser-driven synthesis of magnetite nanoparticles. Pulsed alexandrite laser processing is an intriguing alternative technique for the controlled synthesis of iron oxide phases from ferromagnetic glass precursors.
Melting Evaporation and Recrystallization of A-Sic:H Films by Excimer Laser
Authors: Wickramanayaka S. , Kitamura K. , Nakanishi Y. , Hatanaka Y.
Published: April 2011

A study of laser annealing of a-SiC:H films was carried out in order to obtain poly-SiC films. First, a-SiC:H films were fabricated at temperatures ranging from 30 to 400 °C. All these films show amorphous structure before the annealing process. After annealing by a single pulse of 248 nm laser, films show poly-SiC structure. The pulse energies used for these anneals varied from 30 to 300 mJ/pulse. After exposing to a laser pulse, the a-SiC:H films melt and recrystallize forming poly-SiC structure. In addition to this process, a fraction of the film is observed to be vaporized. This vaporized fraction depends on the original film composition, hardness and the laser pulse-energy. Electrical resistivity of the films before the annealing process lies in the region of 1015 Ωcm. This resistivity drops drastically after the annealing process.
Crystallization of Amorphous Titanium Oxide Thin Films by Pulsed UV-Laser Irradiation
Authors: Ichikawa Yo , Chi Hideaki Ada , Setsune Kentaro , Kawashima Syun-Ichiro , Kugimiya Koichi
Published: April 2011

Effects of ultraviolet (UV) laser irradiation on the local crystal structure have been investigated for amorphous Ti-O thin films sputtered on ST-cut quartz substrates. The irradiation was conducted with a pulsed KrF excimer laser of 248nm in wavelength. There were few changes in the optical transmission spectra of the films before and after the irradiation. The crystal structure of the films was characterized by electron diffraction, XPS and EXAFS analyses. The results obtained from these analyses suggest the films gradually crystallize to a TiO2 crystal with the rutile type structure by the increasing of the laser pulses.
Non-Equilibrium Two-Dimensional Model of Excimer-Laser Melting and Solidification of Thin Si Films on SiO2
Authors: Gupta Vikas V. , Song H. Jin , Im James S.
Published: April 2011

We have developed a two-dimensional numerical model of excimer-laser melting and solidification that properly takes into account the non-equilibrium and transient nature of the process. The model incorporates a novel explicit finite difference scheme for efficiently solving the heat conduction equation and an algorithm that incorporates the interface response function for properly simulating the evolution of phase domains. The model provides space- and time-resolved information regarding the thermal profile and phase domains from which nearly all of the important solidification details can be extracted (e.g., interface location, solidification velocity, interfacial undercooling, etc.). For the simple partial-melting-and-vertical-regrowth scenario, results from the model converge with the results from the well-established one-dimensional model. As a result of its two-dimensional and non-equilibrium formulation, which also respects the amorphous and inert nature of the underlying oxide surface, the model is unique in its capability for properly simulating those solidification scenarios that involve extensive lateral growth of solids, as for example those behind the super-lateral growth phenomenon and various artificially controlled super-lateral growth processes.
Photo-Chemical Etching on Silicon-Carbide by Using Krf Excimer Laser and Xe2* Excimer Lamp
Authors: Hasegawa K. , Murahara M.
Published: April 2011

Silicon-carbide (SiC) has excellent refractivity in the range of soft X-ray and is well-used as a diffraction grating for Synchrotron-radiation (SR) light. This material has a high melting point, hardness and chemical stability. Therefore, etching of the material by chemical or physical methods is very difficult. We reported a photo-chemical etching method in which a SiC surface is placed in NF3 gas atmosphere and irradiated by the Xe2* excimer lamp light parallelly and the grating patterned KrF laser light of 248nm perpendicularly on the sample surface. The Xe2* excimer lamp light are employed for NF3 gas decomposition, and KrF laser light used for excitation on the sample surface. This photochemical etching reaction are detected by XPS, QMS and FTIR measurements. This method achieved 0.18 Å/shot in etching efficiency, and became maximum approximately 7 times as high as ArF laser light for photodecomposition.
Optical Detection of Slow Excited Neutrals in Plasma-Assisted Excimer Laser Ablation
Authors: Mukherjee P. , Sakthivel P. , Witanachchi S.
Published: April 2011

The observation of a slow optically excited component in the excimer laser-ablated YBCO plume due to the presence of a biased ring electrode is reported. The temporal dynamics of the plume were investigated by using time-of-flight (TOF) optical emission spectroscopy (OES). Time-resolved emission signals reveal excitation and resultant fluorescence from slow-moving plume species in the presence of the discharge.
Time Resolved Vacuum Ultraviolet Observations of Excimer Laser-Produced Yba2cu3O7 Plasmas
Authors: Chrisey D.B. , Horwitz J.S. , Mehlman G. , Auyeung R.C.Y. , Dorsey P.C.
Published: April 2011

Simultaneous temporal and spatial resolution of the monochromatic vacuum ultraviolet emission from an excimer laser ablated YBa2Cu3O7 plasma has yielded quantitative information on the plasma generation and velocity. From the time resolved spectral data, plasma velocities were measured and found to be ∼2.3x106 cm/s. It was observed that vacuum ultraviolet emission from above the YBa2Cu3O7 surface does not occur until ˜20 ns after the beginning of the laser pulse. Energetic material continues to be ejected from the target for more than 100 ns after the end of the laser pulse.
Amorphous and Crystalline Phase Formation in Ni/Al Multilayer Thin Films
Authors: Lucadamo G. , Barmak K. , Michaelsen C.
Published: April 2011

We have investigated reactive phase formation in magnetron sputter-deposited Ni/Al multilayer films with a 1:3 molar ratio and various periodicities ranging from 320 nm to a codeposited film with an effective periodicity of zero. The films were studied by x-ray diffraction, differential scanning calorimetry, electrical resistance measurements, and transmission electron microscopy. We find that a reaction which results in the formation of an amorphous phase has taken place during the multilayer deposition process. This reaction substantially reduces the driving force for subsequent reactions and explains why nucleation kinetics become important for these reactions. The mode of transformation for a film with 10 nm periodicity was investigated, in detail, by applying the Johnson-Mehl-Avrami analysis to data obtained from isothermal and constant heating rate differential scanning calorimetry, in combination with electron microscopy studies of the transformation microstructure.
Free Energy Calculations of Cu-Sn Interfaces
Authors: Ravelo R. , Baskes M.
Published: April 2011

Excess free energies of solid Cu - Solid Sn and Solid Cu - liquid Sn have been calculated employing an adiabatic switching formalism in a Molecular Dynamics (MD) framework. The atomic interactions are described by modified embedded atom method (MEAM) potentials which includes the angular dependence of the electron density to describe bond bending forces necessary to model covalent materials.
Crystallization of Amorphous Sputtered NiTi Shape-Memory Alloy Films
Authors: Gong F.F. , Shen H.M. , Wang Y.N.
Published: April 2011

The crystallization of amorphous sputtered NiTi films was investigated for selected heat treatments. From x-ray diffraction patterns, when the films were annealed below the crystallization temperature, the intensity of the broad maximum centered at 2θ = 43.5° increased with increasing the annealing temperature and time. When the films were annealed at 550°C for 0.5hr, parent B2 phase and Ni4Ti3 precipitates appeared. For annealing temperature above 700°C, the films showed embrittlement and volatilization. Therefore the optimum heat treatment for the optimum shape memory effect is found. The average grain size increased slowly in the initial stage of annealing but remained almost unchanged when the films were annealed for more than 1hr. This is because the grain boundary grooving caused by the titanium at a certain temperature volatilization seriously hinder the grain growth.
An Ultrafast Thin-Film Microcalorimeter with Monola Yer Sensitivity (J/m2)
Authors: Lai S.L. , Infante P. , Ramanath G. , Allen L.H.
Published: April 2011

We introduce a high-sensitivity (∼1 J/m2) scanning microcalorimeter that can be used to perform direct calorimetric measurements on thin film samples at ultrafast heating rate (∼104 °C/s). This novel microcalorimeter is fabricated by utilizing SiN thin-film membrane technology, resulting in dramatically reduced thermal mass of the system. Calorimetric measurements are accomplished by applying a dc-current pulse to the thin-film metal (Ni) heater which also serves as a thermometer, and monitoring the real-time voltage and current of the heater. The temperature of the system and the energy delivered to the system are then determined. This calorimetric technique has been demonstrated by measuring the melting process of thin Sn films with thickness ranging from 13 to 1000 Å, and shows potential for calorimetric probing of irreversible reactions at interfaces and surfaces, as well as transformations in nanostructured materials.