bluuebunny/crossref_metadata_2025 huggingface dataset:
Native Defects in Low Temperature GaAs and the Effect of Hydrogenation
Authors: Pritchard R. E. , McQuaid S. A. , Newman R. C. , MÊkinen J. , Von Bardeleben H. J. , Missous M.
Published: April 2011

GaAs grown at low temperatures by MBE has been doped with shallow impurities to ∼1019 cm−3. A layer doped with Be acceptors was completely compensated and the simultaneous detection of AsGa0 and AsGa+ confirmed that the Fermi level was close to midgap and that compensation was partly related to AsGa defects. There was no evidence for the incorporation of VGa in this layer. For Si-doped samples, more than 80 % of the donors were compensated and the detection of SiGa-VGa pairs by infrared localized vibrational mode (LVM) spectroscopy indicated that VGa were at least partly responsible. Increasing the Si concentration suppressed the incorporation of AsGa. Exposure of the Be-doped layer to a hydrogen plasma, generated a LVM near 2000 cm−1 which may be the stretch mode of a AsGa-H-VAs defect complex. For Si-doped layers, two stretch modes at 1764 cm−1 and 1773 cm−1 and a wag mode at 779 cm−1 relating to a H-defect complex were detected and we argue that the complex could be a passivated As antisite. The detection of characteristic hydrogen-native defect LVMs may provide a new method for the identification of intrinsic defects.
Time Resolved Photoluminescence Spectroscopy on GaN Epitaxial Layers
Authors: Meyer B. K. , Volm D. , Wetzel C. , Eckey L. , Holst J.-Ch. , Maxim P. , Heitz R. , Hoffmann A. , Broser I. , Mokhov E. N. , Baranov P. G. , Qiu C. , Pankove J. I.
Published: April 2011

Free and bound exciton luminescences as well as donor-acceptor pair recombination of GaN epitaxial layers on 6H-SiC and sapphire substrates were investigated using time integrated and time resolved photoluminescence measurements at low temperatures. Lifetimes are determined for the donor bound exciton at 3.4722eV and for two acceptor bound excitons with energies of 3.4672eV and 3.459eV. Luminescences between 3.29eV and 3.37eV are identified as due to excitons deeply bound to centers located near the substrate-epilayer interface.
Contactless Evaluation of the Surface Recombination Property of Silicon with an Ion-Implanted Layer
Authors: Usami Akira , Makino Takanori , Yoshida Hideaki , Morita Etsuro
Published: April 2011

The surface properties of silicon are investigated by the noncontact laser (λ=774nm)/microwave method. The effective surface recombination velocity (Seff) at an n+n high-low junction interface is estimated by fitting the experimental decay curve for excess carriers with the theoretical decay curve. The results show that Seg decreases as the dopant concentration increases and that Seff at the n+n high-low junction formed with a dose of 1×l015 ions/cm2 has values lower than 1 cm/s. And it is shown that Scff is inversely proportional to the potential barrier height of the n+n high-low junction. Similar results are obtained using an N2 laser (λ=337.1nm) instead of a laser diode (λ=774nm, 904nm) as a carrier excitation pulse source.
Ultrasound Defect Engineering of Transition Metals Via Metal-Acceptor Pairs in Silicon
Authors: Bell Ronald E. , Ostapenko Serguei , Lagowski Jacek
Published: April 2011

Experimental evidence is provided for ultrasound stimulated dissociation of metal-acceptor pairs in silicon, and also for enhanced diffusion of metal interstitials which may lead to enhanced pairing. The first effect is found dominant in Fe-doped p-type silicon where ultrasound causes low temperature dissociation of Fe-B pairs. This is in contrast to Cr-doped p-type silicon where ultrasound enhances the formation of Cr-B pairs due to enhanced diffusivity of Cr by as much as two orders of magnitude.

In this study, the metal-acceptor reaction was monitored in situ via corresponding changes of the minority carrier diffusion length measured by non-contact surface photovoltage. Ultrasound-stimulated pair reaction can be utilized for metal diagnostics for the silicon IC industry. Thus, with ultrasound, Cr-B pairing can be reduced from months to hours, making possible the identification of Cr via pairing kinetics in a reasonable period of time.
Room Temperature Infrared Electroluminescence from Thin-Film Polycrystalline Chalcopyrite Cu(In,Ga)Se2-Based Diodes
Authors: Contreras Miguel A. , Webb John , Tennant Andrew , Noufi Rommel
Published: April 2011

Evidence of room-temperature infrared electroluminescence from thin-film polycrystalline CuInxGa1-xSe2-based diodes (0<×<0.4) has been observed by Fourier transform spectroscopy using a FT-Raman spectrophotometer that operates in the near-infrared spectral region. Electroluminescence spectra from ternary CuInSe2 and quaternary Cu(In,Ga)Se2 device structures are reported. In all electroluminescence cases we observe an approximate linear relationship of intensity to forward junction current. Film fabrication process determines to a great extent the optoelectronic properties of the emitters, and consequently, the characteristics of their luminescence spectra. Using a Gaussian multi-peak curve-fit routine to analyze electroluminescence spectra, we can deduce the position, width and relative intensity of the dominant optical transitions. Our purpose in this contribution is two-fold: (1) To report the room-temperature electroluminescence phenomena from chalcopyrite Cu(In,Ga)Se2 polycrystalline thin-films, and (2) to demonstrate electroluminescence as a viable technique to optically characterize Cu(In,Ga)Se2 materials using diode structures at RT.
Some Peculiarities During Creation and Destruction of the Native Defects with the Negative Correlation Energy in Semiconductors
Authors: Savransky Semyon D.
Published: April 2011

The creation of negative-U defects (NUD) is a spin-dependent process, that could be used for getting information about NUD themselves; and the NUD destruction is accompanied by the Coulomb’s repulsion between charge carriers.
Studies of Defects in ZnO by Positron Annihilation
Authors: Puff Werner , Brunner Sebastian , Mascher Peter , Balogh Adam G.
Published: April 2011

In order to investigate the basic properties of radiation-induced defects in ZnO crystals, positron annihilation lifetime and Doppler-broadening measurements were performed on crystals sinterd for 18 hours at 1200 °C and irradiated with 3 MeV protons at 223 K. The irradiation induced a colour change of the specimens from the original yellowish-white to dark orange or even brown. Isochronal annealing experiments showed three annealing stages, centred at about 150 °C, 500 – 550 °C, and 750 °C, respectively. These stages are related to the annealing of variously sized vacancy complexes.
Unusual Behavior in The Magnetic Anisotropy of Ultra-Thin Co Sandwiches: The Role of Au Underlayers.
Authors: Marlière Christian , Engel Brad N. , Falco Charles M.
Published: April 2011

We have used in situ polar Kerr effect measurements to study the magnetic anisotropy of X/Co/Y sandwich structures grown by MBE on Cu(111) buffers, where X and Y are variable thicknesses of Au. For fixed values of Y and in the case of an underlayer wedge, e.g. variable X value, we have found a sharp minimum in both coercive field and perpendicular anisotropy at ≈1 atomic layer of the Au underlayer. This anisotropy behavior is opposite to that of an Au overlayer deposited on a Co film, i.e. variable Y and fixed X.
Magnetic Properties of Gadolinium Silicide Thin Films for Different Heat Treatments
Authors: Pescher C. , Pierre J. , Ermolieff A. , Vannuffel C.
Published: April 2011

The magnetic properties of heavy rare earth silicide GdSi2-x thin films are investigated as a function of the annealing temperature of the films. Resistivity measurements reveal in the two films annealed at high and low temperatures, but for a short time, the existence of two transition temperatures corresponding to the presence of an ordered and a disordered structure. In the film annealed at high temperature for a long time, only one transition temperature occurs. It corresponds to a magnetic structure transformation.
Giant Magnetoresistance and Electronic Structure
Authors: Schep Kees M. , Kelly Paul J. , Bauer Gerrit E.W.
Published: April 2011

The electronic structure of magnetic multilayers is expected to play an important role in determining their transport properties. We explain how the conductance through a ballistic point contact is related to simple geometrical projections of the Fermi surface. The essential physics is first discussed for simple model systems and then realistic results for magnetic metallic multilayers based on first principles band structure calculations are presented. The electronic structure is shown to make an important contribution to the perpendicular giant magnetoresistance.
Atomic Scale Engineering of Superlattices and Magnetic Wires
Authors: Camarero J. , de la Figuera J. , Spendeler L. , Torrellas X. , Alvarez J. , Ferrer S. , de Miguel J.J. , García J.M. , Sáinchez O. , Ortega J.E. , Vázquez A.L. , Miranda R.
Published: April 2011

In the past years artificially-structured materials have been grown with an increasing degree of sophistication due to steady progress in our ability to control growth processes down to the atomic level. These materials have yielded new physical properties due to the confinement of electrons in less than three dimensions. Thus, the confinement of electrons in two-dimensional (2D) metallic superlattices has resulted in oscillatory magnetic coupling with an associated oscillatory giant magnetoresistance (GMR). New properties are expected when the electrons are further confined to one dimension (1D) of free motion in the structures known as quantum wires. In this report we briefly describe two recent examples of atomic-scale engineering of materials. In the first case a surfactant is used to purposely modify the structure of magnetic/non magnetic superlattices. The second example illustrates a further reduction in dimensionality obtained by modifying the substrate onto which the growth takes place: the fabrication of 1D magnetic quantum wires on vicinal surfaces.
Growth of Fe/ZnSe Multilayers on GaAs (001) AND (111) by Molecular Beam Epitaxy
Authors: Abad H. , Jonker B. T. , Cotell C. M. , Qadri S. B. , Krebs J. J.
Published: April 2011

The growth of Fe/ZnSe/Fe multilayers on (001) and (111) GaAs substrates is reported. The samples were characterized in-situ by reflection high energy electron diffraction (RHEED), and ex situ by vibrating sample magnetometry (VSM), ferromagnetic resonance (FMR), cross sectional transmission electron microscopy (TEM), and x-ray diffraction. On the (001) surface, the quality of the layers deteriorated significantly with the growth of the first ZnSe spacer layer. In Fe/ZnSe/Fe trilayer structures, TEM revealed a well-defined layered structure, with a high density of defects in both the ZnSe spacer layer and the subsequent Fe layer. VSM and FMR clearly showed the presence of two Fe films with distinct coercive fields, with the higher coercive field attributed to the lower crystalline quality of the second Fe layer. θ-2θ xray diffraction measurements performed on samples grown on (001) GaAs substrates indicated that the ZnSe spacer layer (grown on (001) Fe) grew in a (111) orientation. Growth on GaAs(111) substrates produced better RHEED patterns for all layers with little deterioration in film quality with continued layer growth, so that the magnetic properties of the individual Fe layer could not be distinguished.
Interface Quality and Magnetic Properties of τ MnAl/Co Superlattices On GaAs
Authors: Bruynseraede C. , Boeck J. De , Van Roy W. , Lauhoff G. , Bender H. , Van Esch A. , Mertens R. , Bland J.A.C. , Borghs G.
Published: April 2011

τ MnAl / Co superlattices are grown epitaxially on GaAs (100) substrates by molecular beam epitaxy. High angle XRD spectra are analysed and indicate that good structural quality is achieved. The behaviour of the superlattice upon annealing is described and compared with inplane and out of plane magnetization data. Extraordinary hall effect measurements show low field switching comparable to MnAl thin films. Arguments on how structural properties are affecting the magnetic properties are discussed.
The Morphology of Polytetrafluoroethylene (PTFE) Thin Films Formed by Pulsed-Laser Deposition
Authors: Norton M. Grant , Jiang Wenbiao , Dickinson J. Thomas
Published: April 2011

Thin films of polytetrafluoroethylene have been formed by the pulsed-laser deposition technique. The structure of the films was found to be dependent upon the substrate temperature during deposition. At substrate temperatures from room temperature to 200°C the films were determined, by transmission electron microscopy and X-ray diffraction techniques, to be amorphous. Films formed at higher substrate temperatures were found to contain both amorphous and crystalline components. The data for the crystalline component is consistent with it being highly ordered with the long helical molecular chains aligned parallel to the film-substrate interface plane. The maximum amount of crystalline material occurred when the substrate temperature was close to the melting temperature of the polymer.
Metal Deposition on Laser Modified Teflon Surfaces
Authors: Lätsch Stefan , Hiraoka Hiroyuki , Bargon Joachim
Published: April 2011

Cu, Ni, and Au were deposited with defined patterns and good adhesion by electroless plating, e-beam evaporation, and sputtering onto Teflon (polytetrafluoroethylene, PTFE), Teflon ET (PTFE-co-ethylene), Teflon FEP (PTFE-co-hexafluoropropylene) and Teflon PFA (PTFE-coperfluoroalkoxy vinyl ether) surfaces. The polymers had been irradiated in a tetramethyl – ammonium hydoxide solution (TMAH) by a Nd:YAG laser at 266 rim and by an excimer laser at 248 nrm prior to the metal deposition process. Both, the treated and virgin polymer surfaces were characterized by x-ray photoelectron spectroscopy (XPS), secondary ion mass spectroscopy (SIMS) and Micro-Raman spectroscopy. The increased metal to polymer adhesion at the interface was found to be due to chemical changes and is in the order Ni > Cu ≅ Au.
Photopolymerization Dynamics Studies of Acrolein on Al, Ni, and Au Substrates Using Surface Second Harmonic Generation
Authors: Chen Fang , Subrahmanyan Suchitra , Lackritz Hilary S.
Published: April 2011

The dynamics of the gas phase photopolymerization of acrolein on aluminum (Al), nickel (Ni), and gold (Au) substrates were studied in-situ and in real time using surface second harmonic generation (SSHG) and monitoring vapor pressure decay. The Al and Ni substrates had a significant effect on the apparent rate of polymerization. A dark reaction after irradiation occurred in the absence of metal (Al or Ni) substrates, but no dark reaction was observed when the metal substrates were present. The significant differences in the metal/monomer interactions during photopolymerization are indicated by SEMs of the polyacrolein, as well as evidence from FTIR-ATR spectra. The SSHG intensities from the Au, Al, and polyacrolein surfaces were obtained.
Integrating Cell Transplantation and Controlled Drug Delivery Technologies to Engineer Liver Tissue
Authors: Mooney D. J. , Sano K. , Kaufmann P. M. , McNamara K. , Vacanti J. P. , Langer R.
Published: April 2011

Engineering 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 hepatocytecontaining tissues can be engineered using cell transplantation, and that regulating the microenvironment of transplanted cells can control their engraftment.
Rie Passivation Layer Removal by Remote H-Plasma and H2/SiH4 Plasma Processing
Authors: Ying Hong , Barnak J. P. , Chen Y. L. , Nemanich R. J.
Published: April 2011

Remote H-plasma and H2/SiH4 plasma processes were studied as potential dry cleaning processes following reactive ion etching (RIE). The processes were compared to a process of UV/ozone followed by an HF dip. The native oxide from Si(100) substrates was removed with an RIE etch of CHF3/Ar. The RIE process produced ∼150Å of a continuous fluorocarbon (CFx) passivation layer on the Si surface. For the post-RIE-cleaning three approaches were studied and compared including (1) uv-ozone exposure followed by an HF dip, (2) remote H-plasma exposure, and (3) remote H2/SiH4 plasma exposure. Auger electron spectroscopy (AES) was used to investigate the surface chemical composition, and AFM was used to measure changes in surface roughness. All three processes showed substantial removal of the passivation layer. The CF× polymer was completely removed in less than 1 min for samples exposed to a 100W remote H-plasma at 15mTorr and 450°C. With the addition of ∼0.1% of SiH4, the remote H2/SiH4 plasma also showed increased removal of residual oxygen contamination. The surface roughness of the plasma processed surfaces increased slightly.
Device Quality of Hydrogen Plasma Cleaning for Silicon Molecular Beam Epitaxy
Authors: Hansch W. , Eisele I. , Kibbel H. , KÖnig U.
Published: April 2011

Different substrate cleaning procedures were used before fabrication of pin diodes by silicon molecular beam epitaxy (MBE). We investigated the quality of these diodes in order to demonstrate the superior quality of a low energy plasma cleaning in an ultra-high vacuum ( UHV). This plasma cleaning by hydrogen makes a wet-chemical cleaning or a high-temperature desorption step unnecessary. Moreover, the plasma-cleaned substrates are so strongly hydrogen passivated, that they can be transported through air and processed in another MBE chamber without any additional cleaning steps.
Determination of Rinsing Parameters using a Wafer Gap Conductivity Cell in Wet Cleaning Tools
Authors: Lindquist P. G. , Walters R. N. , Throngard J. O. , Rosato J. J.
Published: April 2011

A wafer gap conductivity cell determined which rinsing parameters control the removal of wafer cleaning and etching solutions. The first part of this study focused on set up and calibration of the conductivity cell. Sodium chloride solutions with known ionic conductivities are used as model fluids. Wafer rinsing experiments showing the concentration as a function of time are analyzed. The sensitivity of the wafer gap conductivity cell is compared to a wall mounted probe, the typical method used to measure rinsing efficiency. The conductivity results are explained using a fluid dynamics model of the wafer gap.

The second part of this study focused on using the wafer gap conductivity cell to study the removal of chemicals typically used in wafer cleaning processes. Experimental results show the effect of tank geometry and flow parameters on the time required for rinsing. Analysis shows the rinse process can be modeled by assuming convective fluid flow and ideal mixing. These results provide critical insight into the most important wafer rinsing parameters.
A New Low Temperature Thin Film Deposition Process: Energetic Cluster Impact (ECI)
Authors: Haberland H. , Leber M. , Moseler M. , Qiang Y. , Rattunde O. , Reiners T. , Thurner Y.
Published: April 2011

A beam of metal cluster ions of variable size is deposited with variable kinetic energy on a substrate. Mirror-like and strongly adhering films are produced on unheated substrates for sufficiently high cluster impact energies. Numerical simulations provide the physical insight why this novel technique gives different, and sometimes superior results compared to conventional methods. Several examples are presented.
Anion Exchange Reactions and initial Gan Epitaxial Layer Formation Under Nitrogen Plasma Exposure of a GaAs Surface
Authors: Hauenstein R. J. , Collins D. A. , O‘steen M. L. , Bandic Z. Z. , Mcgill T. C.
Published: April 2011

Initial nitridation of molecular beam epitaxially (MBE) grown GaAs surfaces by means of an electron cyclotron resonance (ECR) microwave plasma source is investigated in situ through time-resolved reflection high energy electron diffraction (RHEED), and ex situ high-resolution X-ray diffraction (HRXRD) techniques. Brief (< 8-10 s) plasma exposure of GaAs (100) surfaces results in surface N-for-As anion exchange and a new, specular, commensurate (3x3) RHEED pattern which appears to correspond to up to 1 monolayer of coherently strained GaN on GaAs. anion exchange kinetics is studied through the time-dependence of the onset and decay of the (3x3) RHEED pattern as a function of substrate temperature. For the first time, coherently strained GaNyAs1_y /GaAs heterostructures are grown and characterized. Direct evidence for thermally activated processes from both RHEED and HRXRD observations is presented, and N desorption and surface-segregation phenomena are proposed to explain the experimental results.
P-Type II-VI Compound Semiconductor Thin Films Grown by Pulsed Laser Deposition
Authors: Shen W. P. , Kwok H. S.
Published: April 2011

In this paper the results on p-type ZnS, ZnSe, CdS and CdSe thin films grown by pulsed laser deposition will be discussed. these films were deposited on GaAs substrates. Li-doping has been shown to be effective in producing p-type II-VI thin films, while in-doping is excellent for n-type CdS and CdSe thin films. No post-annealing process was used. these preliminary results suggest a possible new approach through pulsed laser deposition to solve the doping problem of II-VI compound semiconductors.
Siloxane Polymers as Low Dielectric Materials for Microelectronics
Authors: Wong C. P.
Published: April 2011

A modem VLSI device is a complicated three-dimensional structure that consists of multilayer metallization conductor lines which are separated with interlayer-dielectrics as insulation. This VLSI technology drives the IC device into sub-micron feature size that operates at ultra-fast speed (in excess of > 100 MHz). Passivation and interlayer dielectric materials are critical to the device performance due to the conductor signal propagation delay of the high dielectric constant of the material. Low dielectric constant materials are the preferred choice of materials for this reasons. These materials, such as Teflon® and siloxanes (silicones), are desirable because of their low dielectric constant (∈1) = 2.0, 2.7, respectively. This paper describes the use of a low dielectric constant siloxane polymer (silicone) as IC devices passivation layer material, its chemistry, material processes and reliability testing.
High Concentration Erbium Implantation of Epitaxially Grown Caf2 /Si Structures.
Authors: Raoux S. , Barriere A. S. , Lozykowski H. J. , Brown I. G.
Published: April 2011

Calcium fluoride thin films grown on silicon substrates by sublimation under ultra high vacuum are well known to be highly efficient hosts for rare earth luminescence properties. For this reason we incorporate erbium by ion implantation in order to form optoelectronic integrated devices. Here we describe the incorporation conditions of erbium in CaF2/Si structures and their luminescence characteristics. The properties of the material have been investigated for implantation doses varying from 4×1014 to 1×1017 at.cm−2. The role of oxygen in the charge compensation mechanisms is investigated and it is shown that the maximum emission in erbium at 1.53μm occurs for an implanted dose of 2×1016 at.cm−2. This corresponds to an Er concentration three orders of magnitude greater than for the case of classical-erbium-doped semiconductors. At this high concentration (up to 15 at.%) the light emission mechanisms are of great theoretical interest. They involve strong Er-Er coupling effects: energy transfer, cross-relaxation phenomena and high conversion efficiencies.

These properties make erbium-implanted CaF2/Si structures excellent candidates for the production of optically active waveguides. The guiding structure can be formed by high energy implantation to build a buried active region of high refractive index within the CaF2 thin film.
A Molecular Architectural Approach to Second-Order Nonlinear Optical Materials
Authors: Yang Xiaoguang , McBranch Duncan , Swanson Basil , Li Dequan
Published: April 2011

The design and synthesis of a family of calix[4]arene-based nonlinear optical (NLO) chromophores are discussed. The calixarene chromophores are macrocyclic compounds consisting of four simple D-π-A units bridged by methylene groups. These molecules were synthesized such that four D-π-A units of the calix[4]arene were aligned along the same direction with the calixarene in a cone conformation. These nonlinear optical super-chromophores were subsequently fabricated into covalently bound self-assembled monolayers on the surfaces of fused silica and silicon. Spectroscopic second harmonic generation (SHG) measurements were carried out to determine the absolute value of the dominant element of the second-order nonlinear susceptibility, d33, and the average molecular alignment, ψ. We find a value of d33 = 60 pm/V at a fundamental wavelength of 890 nm, and ψ˜ 36° with respect to the surface normal.
Optical Properties of Sol-Gel (Pb,La)TiO3 Thin Films For Waveguide Application
Authors: Bae Byeong-Soo , Lee Won-Jong , No Kwang-Soo , Yoon Dae-Sung , Kim Sung-Uk
Published: April 2011

Lead lanthanum titanate ((Pb1−x/100Lax)Ti1−x/400O3, x=10, 20, 28) sol-gel thin films were prepared on SiO2/Si and glass substrates using lanthanum nitrate as a La precursor. The effect of the processing conditions was investigated and the optical properties of the films were measured to obtain good films for waveguide applications. The perovskite crystalline phase is achieved regardless of the heating condition but the slower heating creates better quality films. La content in the film does not effect on the refractive index and transparency of the film.
Molecule-Based Approaches to High-Performance Second-Order Polymeric Nonlinear Optical Materials. Properties of Ultra-high-Tg Chromophoric Polyimides and Polyureas.
Authors: Wang Jia-Fu , Geng Lifeng , Lin Weiping , Marks Tobin J. , Wong George K.
Published: April 2011

This contribution describes the synthesis and properties of three classes of model NLO chromophore-functionalized high-Tg polymers which test current ideas about architecture-Tg- χ(2) performance relationships. Condensation of bismaleimides with diallylamino-functionalized donor-acceptor chromophores yields polable matrices with Tg values as high as 325°C and χ(2) responses as high as 0.7 × 10-7 esu (27 pm/V; λohigh as 0.7 × 10-7 esu (27 pm/V; λo = 1064 nm; 1.17 eV). Likewise, = 1064 nm; 1.17 eV). Likewise, condensation of o,o'-diallylbisphenol A with bismaleimides followed by chromophore functionalization yields an analogous series of polyimides with Tg values as high as 260°C and χ(2) response as high as 1.0 × 10-7 esu (42 pm/V at λo = 1064 nm). Polymerization of a bis(4-aminophenyl)lophine chromophore with bismaleimides or diisocyanates yields polymers with Tg values as high as 350°C and χ(2) = 0.62 × 10-7 esu (25 pm/V at λo = 1064 nm). All members of the above series exhibit minor to negligible decay in χ(2) response on aging in air at 100°C for 1000 h. The lophine-based material exhibits only ∼10% χ(2) decay on aging for 100 h at 200 °C under N2.
Evaluation of Thermal Properties and Physical Aging as Function of the Pendent Chain Length in Tyrosine-Derived Polycarbonates, a Class of New Biomaterials
Authors: Tangpasuthadol Varawut , Shefer Adi , Hooper Kimberly A. , Kohn Joachim
Published: April 2011

Tyrosine-derived polycarbonates are currently in preclinical evaluations for biomedical applications. Although physical aging can significantly alter a wide range of polymer properties, physical aging is has rarely been investigated for biomedical polymers. A series of four tyrosinederived polycarbonates was used as a model system to study the effect of polymer structure on the enthalpy relaxation kinetics.
Irradiation-Induced Changes in Hydroxypropyl Cellulose
Authors: Petrich Mark A. , Rosen Lawrence A.
Published: April 2011

Gamma irradiation is used to sterilize products intended for ophthalmic and parenteral use. Ideally, the sterilization process should not affect the chemical identity or physical properties of the product. We have investigated the effects of gamma irradiation on the structure and molecular weight of hydroxypropyl cellulose (HPC), and the subsequent effect on dissolution behavior of HPC. Hydroxypropyl cellulose is a commonly used excipient in pharmaceutical formulations and tablet coatings, and can be used to manufacture water soluble objects. We find that the moisture content of the HPC influences the extent to which scission and cross-linking reactions occur. At low moisture levels (<5 wt.%), cross-linking is relatively unimportant, while above 12 wt. % moisture cross-linking becomes extensive leading to formation of insoluble, rubber-like gels.
Production of Heart Valves from Glassy Polymeric Carbon
Authors: Jenkins G. M. , Ila D. , Maleki H.
Published: April 2011

When certain resins are pyrolized they transform into a glassy polymeric carbon (GPC) with no change in shape. Using this process we have made all-carbon heart valves by rapid molding of the component pieces out of precursor resin, assemblage in the resin stage and pyrolysis to at least 1,000°C to form an accurately articulated device. A heart valve with two occluders set in a carbon ring manufactured out of highly polished carbon has been tested with an excellent record of wear, fatigue, resistance and biocompatibility, especially in contact with blood.
A New Artificial ACL Anchor
Authors: Young F. A. , An Y. H.
Published: April 2011

An artificial ligament anchor has been designed and tested in goats. The anchor may allow direct bone anchorage of artificial anterior cruciate ligaments.
2.2 eV Luminescence in GaN
Authors: Hofinann D. M. , Kovalev D. , Steude G. , Volm D. , Meyer B. K. , Xavier C. , Monteiro T. , Pereira E. , Mokov E. N. , Amano H. , Akasaki I.
Published: April 2011

The yellow Luminescence in GaN centered at 2.2 eV has been studied in various epitaxial layers grown by MOVPE on sapphire and by the sandwich sublimation methode on 6H-SiC substrates. The photoluminescence and optically detected magnetic resonance results can be consistently explained by a recombination model involving shallow donors and deep donors.
Magnetic Resonance Studies of Recombination Processes in GaN-Based Light Emitting Diodes
Authors: Carlos W.E. , Glaser E.R. , Kennedy T.A. , Nakamura S.
Published: April 2011

Magnetic resonance techniques are used to study the recombination processes in GaN-based light emitting diodes (LEDs). Electrically-detected magnetic resonance (EDMR) and electroluminescence-detected magnetic resonance (ELDMR) results on InGaN/AlGaN double heterostructures are presented for blue and green LEDs. In either technique our signals are dominated by a broad feature that we ascribe to a deep Zn-related acceptor. Our ELDMR measurements show that this is associated with the blue or green emission. Our EDMR measurements resolve a second center that is tentatively identified as a deep donor trap.
Theoretical Study of Electron Initiated Impact Ionization Rate in Bulk GaN using a Wave Vector Dependent Numerical Transition Rate Formulation
Authors: Kolnik J. , Oguzman I.H. , Brennan K.F. , Wang R. , Ruden P.P.
Published: April 2011

In this paper, we present ensemble Monte Carlo based calculations of electron initiated impact ionization in bulk zincblende GaN using a wavevector dependent formulation of the interband impact ionization transition rate. These are the first reported estimates, either theoretical or experimental, of the impact ionization rates in GaN. The transition rate is determined from Fermi’s golden rule for a two-body screened Coulomb interaction using a numerically determined dielectric function as well as by numerically integrating over all of the possible final states. The Monte Carlo simulator includes the full details of the first four conduction bands derived from an empirical pseudopotential calculation as well as all of the relevant phonon scattering mechanisms. It is found that the ionization rate has a relatively "soft" threshold.
Effects of Reactive Ion Etching on the Electrical Properties of n-GaN Surfaces
Authors: Ping A. T. , Schmitz A. C. , Asif Khan M. , Adesida I.
Published: April 2011

Dry etch damage on n-GaN has been investigated using Pd Schottky diodes fabricated on surfaces etched by conventional reactive ion etching with SiCl4 plasma. The Schottky barrier height and ideality factor were investigated as a function of the plasma self-bias voltage. Current-voltage measurements revealed severe degradation of both the forward and reverse characteristics for plasma self-bias voltages in excess of -150 V.
Electrical Properties of Nichia AlGaN/InGaN/GaN Blue LEDs in a Wide Current/Temperature Range
Authors: Zeller Joachim , Eliseev Petr G. , Sartori Philippe , Perlin Piotr , Osiński Marek
Published: April 2011

Studies of electrical characteristics of nitride-based light emitting diodes (LEDs) are of interest as they can shed light on carrier transport across the p-n heterojunction. In addition, they provide a convenient way of investigating degradation processes associated with high electrical stress. We present electrical characteristics of Nichia NLPB500 blue LEDs based on AlGaN/InGaN/GaN material system in the temperature range of 9-340 K. Two components of current are identified. High-density current stress leads to diode degradation by shunt formation caused by metal electromigration. At 8 K, blue emission was observed at currents as small as 20 nA.
In-Situ Plume Diagnosis During Pulsed Laser Deposition of Epitaxial-Oxide Thin Films
Authors: Fenner David B. , Kung Pang-Jen , Gores Jörn , Li Qi
Published: April 2011

The visible plume, induced during pulsed-laser deposition (PLD) of epitaxial La0.5.jSr0.5 5CoO3/Ba0.4Sr0.6TiO3/La0.5Sr05CoO3/YBa2Cu3O7/YSZ heterostructures on silicon (100) wafers, was studied by optical-emission spectroscopy (OES). These films are suitable for the fabrication of ferroelectric capacitors and pyroelectric-sensor devices. A YAG laser, at 266 nm, is used for ablation. A collection lens transfers the PLD-plume emission into an optical fiber and onto a diffraction grating and a CCD array, for time-averaged spectroscopy from 410 to 640 nm. Plume emissions from ablated targets in the presence of an oxygen ambient, due to various atomic (Ba, Co, Cu, Sr, Ti, Y, Zr), ionic (Ba+, La+, Sr+, Y+), and a diatomic oxide (YO) species were identified. Emission intensity and evolution of ablated species are reported for distance away from the target surface, oxygen pressures, and laser fluences (1 to 4 J/cm2). The behavior of reactive-product species, especially YO for plumes from yttria-stabilized zirconia (YSZ) and YBCO targets, is discussed. This simple and inexpensive OES system is suitable for use as a plume-quality monitor on routine PLD film synthesis.
Pulsed Laser Deposition of Poly(Tetrafluoroethylene) Films
Authors: Kjendal D.L. , Kumar Ashok , Inturi R.B. , Barnard J. A.
Published: April 2011

Thin films of poly(tetrafluoroethylene) have been deposited on amorphous (7059 Corning Glass) and silicon(l00) substrates at various temperatures by the Pulsed Laser Deposition technique. The deposition was carried out at high vacuum (˜10-6 torr)at temperatures ranging from room temperature to 350°C. The mechanical properties of these films at the varying process temperatures have been evaluated by nano-indentation techniques and compositional properties of the films have been characterized by Fourier Transform Infrared spectroscopy. The deposition parameters have been optimized in order to produce good quality films.
Liquid-Target Pulsed Laser Deposition and Its Application to Grow Diamond and Diamond-Like Carbon Films
Authors: Xiao Rong-Fu
Published: April 2011

A liquid-target pulsed laser deposition system has been designed to grow diamond and diamond-like carbon films using an organic liquid. The system has overcome the problem of target deterioration under high power laser irradiation and has prevented splashing of large particulares on the substrate. The technique is simple and safe to operate and the cost of source materials is much lower than in chemical vapor deposition experiments. With the introduction of oxygen (O2) gas during deposition, only diamond-like carbon is produced. Crystalline diamond films can be obtained when H2O2 is added along with O2 gas. The results provide a evidence that hydroxyl ions, OH-, together with atomic oxygen can indeed promote diamond growth.
Coupled Peritectic Growth of the α- and Γ- Phases in Binary Titanium Aluminides
Authors: Meissen F. , Busse P. , Laakmann J.
Published: April 2011

Coupled growth during three phase equilibrium solidification is well known from directionally solidified eutectic systems, and was recently generated in monotectic systems. Several theories predict a stationary peritectic reaction and coupled growth of the properitectic and the peritectic phases therefore should be possible. In spite of these theories coupled growth has not been observed up to now. The TiAl system was selected for further investigation on this topic because of its technical relevance and the fact that it meets the condition mentioned for coupled growth.

In a Bridgman laboratory furnace, TiAl with 53.4 at.% Al was directionally solidified with solidification rates v between 0.025 mm/min and 0.1 mm/min and a temperature gradient up to 20 K/mm. The resulting microstructures, analyzed using optical and scanning microscopy with EDX and WDX, consist of two phases parallel to the growth direction. At v = 0.05 to 0.1 mm/min, the alloy solidifies as properitectical α, which subsequently eutectoidally transforms to a substructure of α2-Ti3Al and γ-TiAl, and peritectic γ. The lamellar α2/γ-substructure is oriented parallel to the growth direction.

The experimental results were compared with the existing theoretical models of a stationary peritectic reaction and the possibility of metastable eutectic growth was discussed.
Ion Assisted Nucleation in Amorphous Silicon: Mechanism and Theoretical Description
Authors: Spinella C. , Lombardo S. , Priolo F. , Campisano S.U.
Published: April 2011

We present new results on the ion-assisted amorphous to polycrystal transition in silicon. The grain growth velocity vg and the nucleation rate r exhibit quite different behaviours: i) ion irradiation enhances r by a factor which is several orders of magnitude larger than that observed for vg; ii) irradiation with lighter ions produces a decrease of vg and a strong increase of r; iii) the increase of dose rate produces a decrease of both vg and r, but is particulary severe for r. These results have been explained by assuming that ion irradiation produces three fundamental effects: i) generation of long living defects which increase the free energy of the amorphous phase to the value of the fully unrelaxed amorphous silicon, causing the decrease of the thermodynamic barrier to nucleation; ii) generation of defects promoting the transition kinetics at concentrations well above the thermal equilibrium value; iii) prompt amorphization of a small volume at the surface of each crystalline grain.
Low Temperature Oxidation of Silicon After Copper Ion Implantation
Authors: Jaquez E.J. , Alford T.L. , Theodore N.D. , Adams D. , Li Jian , Russell S.W. , Anders Simone
Published: April 2011

Silicon oxide films ( > 1μm ) were grown at room-temperature after low-energy copper-ion implantation of Si(100) substrates. The structural properties of the silicon oxide layer and the implanted silicon were characterized by Rutherford backscattering spectrometry and transmission-electron microscopy. During room temperature oxidation a portion of the implanted copper resided on the surface and a portion moved with the advancing Si/SiOx interface. This study revealed that the oxide growth rate was dependent on the amount of Cu present at the moving interface. The resulting oxide formed was approximately stoichiometric silicon dioxide.
Solid-State Alloying in Binary Systems with a Positive Heat of Mixing
Authors: Ma E. , He J.-H. , Schilling P.J. , Pan F. , Liu B.X.
Published: April 2011

The Extended X-ray Absorption Fine Structure (EXAFS) technique has been employed to monitor the formation of metastable alloys by mechanical alloying in two positive-heat-of-mixing systems, Cu-Fe and Ag-Fe. With its unique atom selectivity and local atomic environment sensitivity, EXAFS provides clear evidence of atomic-level alloying forming bcc (Fe80Cu20) and fee (Fe50Cu50) solid solutions in the Cu-Fe system. In contrast, such alloying appears to be absent in Ag-Fe. The possible availability of a thermodynamic driving force for alloying in certain nanostructured mixtures of immiscible elements is discussed. A preliminary study was performed on the possibility of alloying and amorphization in vacuum-deposited Cu/Ta multilayer films.
Thermal Activation of the Crystallization Kinetics of Amorphous Silicon
Authors: Mohammed-Brahim T. , Briand D. , Kis-Sion K. , Guillet D. , Salaün A.C. , Bonnaud O.
Published: April 2011

Solid Phase Crystallization of amorphous silicon films, deposited by the Low Pressure Chemical Vapor Deposition technique, is studied by in-situ monitoring the film conductance. The crystal growth rate VG, deduced from this measurement, was found to be thermally activated. The activation energy E behaviour for films with different doping varying in a great range, from undoped to 4×1019 cm−3, was then deduced. This behaviour, described for the first time in this work, shows a constant E for undoped and weak doping, then a high decrease after a doping value threshold. The undoped films show a decreasing E when the deposition rate increases i.e. when the structure of the amorphous deposited film tends to correspond to the relaxed amorphous network. All these new results are used to introduce a crystallization model based on a crystalline-amorphous double phase and on the charge of defects at the crystal-amorphous interface.
Calculation of Phase Competition and Selection in Solidification Using a Combined Nucleation and Calphad Approach
Authors: Shao G. , Tsakiropoulos P.
Published: April 2011

Thermodynamic data derived by the CALPHAD method has been extended to undercooled melts to study phase competition and the role of time dependent and steady state nucleation in rapidly solidified materials. The theoretical predictions made about phase competition between hcp α, bcc β and Ll0 γ in some Al(Ti,V) alloys are compared with experimental results. It is shown that high melt cooling rates introduce significant transient nucleation effects on phase nucleation.
Partial Reduction of NiAl2O4 - Mechanism and the Influence of Doping
Authors: Zhang Z. , Üstündag E. , Sass S.L.
Published: April 2011

Metal-ceramic microstructures were formed in situ by partial reduction of the spinel compound NiAl2O4. At 1300°C the reduction reaction passed through an intermediate stage involving the formation of Ni and metastable “defect spinel” phases, before the appearance of the equilibrium phases, Ni + α-Al2O3. At 1100°C, depending on the reduction time, the products of the reduction reaction were Ni and the metastable “defect spinel” for less than 24 hours; Ni + θ-Αl2Ο3 for 24-48 hours; and Ni + GI-AI2O3 for 144-168 hours. The effects of dopants, such as Cr2O3, MgO, TiO2 and Y2O3, on the reduction mechanism and kinetics were examined and shown, in the case of TiO2, to have a controlling influence. A reduction reaction mechanism is proposed.
High dielectric SrGeO3 perovskite prepared by high pressure synthesis
Authors: Grzechnik Andrzej , McMillan Paul F. , Petuskey William
Published: April 2011

High pressure synthesis of SrGeO3 perovskite and its properties are reported. The metastable material recovered to room pressure shows a high dielectric constant (>100), due to a “stretched” crystal lattice.
Studies of Ordering in Small Particles
Authors: Herr U. , Poilack M. , Olynick D.L. , Gibson J.M. , Averback R.S.
Published: April 2011

Disordered clusters of the intermetallic compounds Ni3Al and Cu3Au have been produced using a high pressure sputtering technique. The clusters are either embedded in a film or studied, in-situ in an UHV electron microscope. The evolution of the ordered structure upon annealing is studied. Using a scanning transmission electron microscope, electron diffraction is obtained from individual clusters. Partial ordering is observed in Cu3Au clusters which have been annealed below the bulk order-disorder transition temperature. Under the experimental conditions, only clusters with sizes of 10–15 nm or larger show ordering.
Influence of Interfacial Copper on the Ti-SiO2 Reaction During Nitridation of Cu-Ti Films
Authors: Adams Daniel , Alford T.L. , Theodore N.D. , Laursen T. , Russell S.W. , Kim M.J.
Published: April 2011

Cu(90 nm)/Ti(20 nm) bilayers and Cu(Ti 27 at.%) alloy films were deposited on SiO2 and annealed in an NH3 ambient at temperatures 400–700° C for 30 min. During annealing Ti segregated to both the free surface and the alloy/SiO2 interface. At the surface Ti reacted with NH3 to form TiN, whereas at the interface the Ti reacted with the SiO2 to form a TiO/Ti5Si3 structure. High resolution energy dispersive x-ray analysis revealed the presence of interfacial Cu between the Ti-silicide and Ti-oxide layers at temperatures greater than 450°C. Using Cu-Ti alloy films enhanced the Si02 consumption rate by a factor of 3-4 compared to that of pure Ti. It is suggested that the interfacial Cu is responsible for the increased rate. It is plausible that an interfacial Cu2O component has a catalytic effect on the Ti- SiO2 reaction.
Heteroepitaxial Si1-x-yGex Cy Layer Growth on (100)Si by Atmospheric Pressure Chemical Vapor Deposition
Authors: Atzmon Z. , Bair A. E. , Alford T. L. , Chandrasekhar D. , Smith David J. , Mayer J.W.
Published: April 2011

Thin heteroepitaxial films of Si1-x-yGexCy have been grown on (100)Si substrates using atmospheric pressure chemical vapor deposition at 550 and 700°C. The crystallinity, composition and microstructure of the SiGeC films were characterized using Rutherford backscattering spectrometry (ion channeling), secondary-ion-mass-spectrometry and cross-sectional transmission electron microscopy. SiGeC films with up to 2% C were grown at 700°C with good crystallinity and very few interracial defects, while misfit dislocations at the SiGe/Si interface were observed for SiGe films grown under the same conditions. This difference indicates that the presence of carbon in the SiGe matrix increases the critical thickness of the grown layers. SiGeC thin films (>110 nm) with up to 3.5% C were grown at 550°C with good crystallinity. The crystallinity of the films grown at lower temperature (550°C) was less sensitive to the flow rate of the C source (C2H4), which enabled growth of single crystal SiGeC films with higher C content.