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Sample records for 6h-sic homoepitaxial layers

  1. Extended defects in 4H-silicon carbide homoepitaxial layers

    NASA Astrophysics Data System (ADS)

    Zhang, Xuan

    The purpose of this thesis is to study the structure of extended defects in 4H-SIC homoepitaxial layers, and to identify their nucleation mechanisms. Characteristics of basal plane dislocations in 4H-SiC epilayers were investigated in a comprehensive manner, including their morphologies, Burgers' vectors, positions, and correlation with the extended defects propagating from the substrate. Plan-view transmission x-ray topography was the major characterization technique used in this study. Complementary data was obtained by KOH etching and optical microscopy. Trace of glide was detected on every basal plane dislocation in the entire 3-inch epilayer. In the center area of the epi-wafer, the glide can extend to macroscopic distance and form edge-type dislocations at the epilayer/surface interface. During the motion, dislocation half loop arrays were found to nucleate at the growth front. The magnitude of the resolved shear stress was estimated based on the radius of curvature of the dislocation lines. It surpassed the critical resolved shear stress at the epitaxial growth temperature. The stress was identified to be compressive in the epilayer. Its origin was studied. Nitrogen-doping-difference-induced misfit strain was excluded as the source of the stress. The structures of two morphological defects, 'carrots' and 'arrows', were studied. Cross-section x-ray topography was used to image the structure of carrot defect in whole. The defect was found to nucleate at the epilayer/substrate interface on a threading screw dislocation propagating from the substrate. Its structure was mainly composed of a prismatic stacking fault and a Frank-type basal plane stacking fault. The arrow defect was found to be produced by a spheroid shape inclusion in the volume of the epilayer. Zone axis diffraction pattern under transmission electron microscope identified the nature of the inclusion as 3C-SIC. It was determined to nucleate at the substrate surface contaminations.

  2. Growth and optical properties of AlN homoepitaxial layers grown by ammonia-source molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Iwata, Shiro; Nanjo, Yoshiyuki; Okuno, Toshihiro; Kurai, Satoshi; Taguchi, Tsunemasa

    2007-04-01

    We have performed the homoepitaxial growth of high-crystalline quality Aluminium nitride (AlN) epilayers by the ammonia-gas source (GS) molecular-beam epitaxy method using the hydride vapor-phase epitaxy (HVPE) grown AlN thin layers as substrates. Surface morphologies and step-bunching structures of the homoepitaxially grown AlN epilayers were evaluated using in situ reflection high-energy electron diffraction (RHEED) patterns and scanning probe microscopy. It is noted that the step height of several monolayers was achieved on the surface of homoepitaxial layers. The homoepitaxial AlN thin films had the same or improved crystalline quality compared with the HVPE-grown AlN layers from X-ray rocking curve measurements, and its optical properties were investigated using cathodoluminescence measurements. Excitonic emission, which originates from the A free-exciton transition, was clearly observed in the present high-quality homoepitaxial AlN epilayers.

  3. Cathodoluminescence Study of the Properties of Stacking Faults in 4H-SiC Homoepitaxial Layers

    DTIC Science & Technology

    2009-01-01

    Cathodoluminescence study of the properties of stacking faults in 4H- SiC homoepitaxial layers Serguei I. Maximenko,1,a Jaime A. Freitas, Jr.,1 Paul...2009 In-grown stacking faults in n-type 4H- SiC epitaxial layers have been investigated by real-color cathodoluminescence imaging and spectroscopy...carried out at room and liquid helium temperatures. Stacking faults with 8H stacking order were observed, as well as double layer and multilayer 3C- SiC

  4. Atomic force microscopy studies of homoepitaxial GaN layers grown on GaN template by laser MBE

    SciTech Connect

    Choudhary, B. S.; Singh, A.; Tyagi, P. K.; Tanwar, S.; Kumar, M. Senthil; Kushvaha, S. S.

    2016-04-13

    We have grown homoepitaxial GaN films on metal organic chemical vapor deposition (MOCVD) grown 3.5 µm thick GaN on sapphire (0001) substrate (GaN template) using an ultra-high vacuum (UHV) laser assisted molecular beam epitaxy (LMBE) system. The GaN films were grown by laser ablating a polycrystalline solid GaN target in the presence of active r.f. nitrogen plasma. The influence of laser repetition rates (10-30 Hz) on the surface morphology of homoepitaxial GaN layers have been studied using atomic force microscopy. It was found that GaN layer grown at 10 Hz shows a smooth surface with uniform grain size compared to the rough surface with irregular shape grains obtained at 30 Hz. The variation of surface roughness of the homoepitaxial GaN layer with and without wet chemical etching has been also studied and it was observed that the roughness of the film decreased after wet etching due to the curved structure/rough surface.

  5. Characterization of V-shaped defects in 4H-SiC homoepitaxial layers

    SciTech Connect

    Zhang, Lihua; Su, Dong; Kisslinger, Kim; Stach, Eric; Chung, Gil; Zhang, Jie; Thomas, Bernd; Sanchez, Edward K; Mueller, Stephan G.; Hansen, Darren; Loboda, Mark J.; Wu, Fangzhen; Wang, Huanhuan; Raghothamachar, Balaji; Dudley, Michael

    2014-12-04

    Synchrotron white beam x-ray topography images show that faint needle-like surface morphological features observed on the Si-face of 4H-SiC homoepitaxial layers using Nomarski optical microscopy are associated with V shaped stacking faults in the epilayer. KOH etching of the V shaped defect reveals small oval pits connected by a shallow line which corresponding to the surface intersections of two partial dislocations and the stacking fault connecting them. Transmission electron microscopy (TEM) specimens from regions containing the V shaped defects were prepared using focused ion beam milling, and stacking sequences of (85), (50) and (63) are observed at the faulted region with high resolution TEM. In order to study the formation mechanism of V shaped defect, low dislocation density 4H-SiC substrates were chosen for epitaxial growth, and the corresponding regions before and after epitaxy growth are compared in SWBXT images. It is found that no defects in the substrate are directly associated with the formation of the V shaped defect. Simulation results of the contrast from the two partial dislocations associated with V shaped defect in synchrotron monochromatic beam x-ray topography reveals the opposite sign nature of their Burgers vectors. Therefore, a mechanism of 2D nucleation during epitaxy growth is postulated for the formation of the V shaped defect, which requires elimination of non-sequential 1/4[0001] bilayers from the original structure to create the observed faulted stacking sequence.

  6. Characterization of V-shaped defects in 4H-SiC homoepitaxial layers

    DOE PAGES

    Zhang, Lihua; Su, Dong; Kisslinger, Kim; ...

    2014-12-04

    Synchrotron white beam x-ray topography images show that faint needle-like surface morphological features observed on the Si-face of 4H-SiC homoepitaxial layers using Nomarski optical microscopy are associated with V shaped stacking faults in the epilayer. KOH etching of the V shaped defect reveals small oval pits connected by a shallow line which corresponding to the surface intersections of two partial dislocations and the stacking fault connecting them. Transmission electron microscopy (TEM) specimens from regions containing the V shaped defects were prepared using focused ion beam milling, and stacking sequences of (85), (50) and (63) are observed at the faulted regionmore » with high resolution TEM. In order to study the formation mechanism of V shaped defect, low dislocation density 4H-SiC substrates were chosen for epitaxial growth, and the corresponding regions before and after epitaxy growth are compared in SWBXT images. It is found that no defects in the substrate are directly associated with the formation of the V shaped defect. Simulation results of the contrast from the two partial dislocations associated with V shaped defect in synchrotron monochromatic beam x-ray topography reveals the opposite sign nature of their Burgers vectors. Therefore, a mechanism of 2D nucleation during epitaxy growth is postulated for the formation of the V shaped defect, which requires elimination of non-sequential 1/4[0001] bilayers from the original structure to create the observed faulted stacking sequence.« less

  7. DEFECT SELECTIVE ETCHING OF THICK ALN LAYERS GROWN ON 6H-SIC SEEDS - A TRANSMISSION ELECTRON MICROSCOPY STUDY

    SciTech Connect

    Nyakiti, Luke; Chaudhari, Jharna; Kenik, Edward A; Lu, Peng; Edgar, J H

    2008-01-01

    In the present study, the type and densities of defects in AlN crystals grown on 6H-SiC seeds by the sublimation-recombination method were assessed. The positions of the defects in AlN were first identified by defect selective etching (DSE) in molten NaOH-KOH at 400 C for 2 minutes. Etching produced pits of three different sizes: 1.77 m, 2.35 m , and 2.86 m. The etch pits were either aligned together forming a sub-grain boundary or randomly distributed. The smaller etch pits were either isolated or associated with larger etch pits. After preparing crosssections of the pits by the focused ion beam (FIB) technique, transmission electron microscopy (TEM) was performed to determine which dislocation type (edge, mixed or screw) produced a specific etch pit sizes. Preliminary TEM bright field and dark field study using different zone axes and diffraction vectors indicates an edge dislocation with a Burgers vector 1/3[1120] is associated with the smallest etch pit size.

  8. Nucleation mechanism of dislocation half-loop arrays in 4H-silicon carbide homoepitaxial layers

    NASA Astrophysics Data System (ADS)

    Zhang, N.; Chen, Y.; Zhang, Y.; Dudley, M.; Stahlbush, R. E.

    2009-03-01

    A model is presented for the formation mechanism of dislocation half-loop arrays formed during the homoepitaxial growth of 4H-SiC. The reorientation during glide of originally screw oriented threading segments of basal plane dislocation (BPD) renders them susceptible to conversion into sessile threading edge dislocations (TEDs), which subsequently pin the motion of the BPD. Continued glide during further growth enables parts of the mobile BPD to escape through the surface leaving arrays of half loops comprising two TEDs and a short BPD segment with significant edge component. The faulting behavior of the arrays under UV excitation is consistent with this model.

  9. [Calculation of dislocation destiny using X-ray diffraction for 4H-SiC homoepitaxial layers].

    PubMed

    Jia, Ren-xu; Zhang, Yu-ming; Zhang, Yi-men; Guo, Hui

    2010-07-01

    A theoretical and experimental study on calculating dislocation destiny for 4H-SiC homoepitaxial layers has been carried out. There is some difficulty in measuring dislocation density if it is more than 10(6) * cm(-2). In the paper, a theoretical analysis is made about the effects of dislocation density on the results of X-ray diffraction, and the relationship of dislocation density and FWHM spread is obtained. Then the X-ray diffraction curves of 4H-SiC in omego2theta with two different crystal faces are presented from which the density of dislocation is calculated. According to the result, the cause of dislocation origin is analyzed and the methods of decreasing dislocation density are proposed.

  10. A theoretical study of surfactant action in the layer-by-layer homoepitaxial growth of metals: the case of In on Cu(111)

    NASA Astrophysics Data System (ADS)

    Jiang, Ming; Qiu, Min; Zhao, Yu-Jun; Cao, Pei-Lin

    1998-02-01

    A surfactant-mediated homoepitaxial metal system, Cu/In/Cu(111), is studied by using first-principles calculations and the kinetic Monte Carlo method. A new repulsion model is proposed for the Cu/In/Cu(111) system where surface-substitutional In atoms repel diffusing Cu adatoms and build a repulsion network. This repulsion network results in an average increase of terrace barriers for adatoms Cu and enhanced island density. The layer-by-layer growth for the Cu/In/Cu(111) system is achieved with a repulsion model in a kinetic Monte Carlo simulation. The importance of the additional barrier ΔE is confirmed in determining film morphology.

  11. Surfactant-mediated layer-by-layer homoepitaxial growth of Cu/In/Cu(100) and Ag/Sb/Ag(111) systems: A theoretical study

    NASA Astrophysics Data System (ADS)

    Jiang, Ming; Zhao, Yu-Jun; Cao, Pei-Lin

    1998-04-01

    Two typical surfactant-mediated homoepitaxial metal systems, Cu/In/Cu(100) and Ag/Sb/Ag(111), are studied by using first-principles calculations and a kinetic Monte Carlo method. Our results confirm the validity of the model that Zhang and Lagally suggested for Cu/In/Cu(100) system. A repulsion model is proposed for the Ag/Sb/Ag(111) system where surface-substitutional Sb atoms repel diffusing Ag adatoms. The layer-by-layer growth for Ag/Sb/Ag(111) system is achieved with a repulsion model in kinetic Monte Carlo simulation. By comparing the two different growth models, the importance of the additional barrier ΔE and effectiveness of two ways of reducing ΔE are confirmed in determining film morphology.

  12. Complex Pattern Formation from Current-Driven Dynamics of Single-Layer Homoepitaxial Islands on Crystalline Conducting Substrates

    NASA Astrophysics Data System (ADS)

    Kumar, Ashish; Dasgupta, Dwaipayan; Maroudas, Dimitrios

    2017-07-01

    We report a systematic study of complex pattern formation resulting from the driven dynamics of single-layer homoepitaxial islands on surfaces of face-centered-cubic (fcc) crystalline conducting substrates under the action of an externally applied electric field. The analysis is based on an experimentally validated nonlinear model of mass transport via island edge atomic diffusion, which also accounts for edge diffusional anisotropy. We analyze the morphological stability and simulate the field-driven evolution of rounded islands for an electric field oriented along the fast edge diffusion direction. For larger-than-critical island sizes on {110 } and {100 } fcc substrates, we show that multiple necking instabilities generate complex island patterns, including not-simply-connected void-containing islands mediated by sequences of breakup and coalescence events and distributed symmetrically with respect to the electric field direction. We analyze the dependence of the formed patterns on the original island size and on the duration of application of the external field. Starting from a single large rounded island, we characterize the evolution of the number of daughter islands and their average size and uniformity. The evolution of the average island size follows a universal power-law scaling relation, and the evolution of the total edge length of the islands in the complex pattern follows Kolmogorov-Johnson-Mehl-Avrami kinetics. Our study makes a strong case for the use of electric fields, as precisely controlled macroscopic forcing, toward surface patterning involving complex nanoscale features.

  13. Studies of the Origins of Half-Loop Arrays and Interfacial Dislocations Observed in Homoepitaxial Layers of 4H-SiC

    NASA Astrophysics Data System (ADS)

    Wang, H.; Dudley, M.; Wu, F.; Yang, Y.; Raghothamachar, B.; Zhang, J.; Chung, G.; Thomas, B.; Sanchez, E. K.; Mueller, S. G.; Hansen, D.; Loboda, M. J.

    2015-05-01

    Synchrotron x-ray topography and KOH etching studies have been carried out on n-type 4H-SiC offcut substrates before and after homoepitaxial growth to study defect replication and strain relaxation processes and identify the nucleation sources of both interfacial dislocations (IDs) and half-loop arrays (HLAs), which are known to have a deleterious effect on device performance. Two cases are reported. In one, they nucleate from short segments of edge-oriented basal plane dislocations (BPDs) in the substrate which are drawn into the epilayer. In the other, they form from segments of half-loops of BPD that are attached to the substrate surface prior to growth which glide into the epilayer. The significance of these findings is: (1) It is demonstrated that it is not necessary for a BPD to intersect the substrate surface in order for it to be replicated into the homoepitaxial layer and take part in nucleation of IDs and HLAs; (2) The conversion of the surface intersections of a substrate BPD half-loop into threading edge dislocations (TEDs) does not prevent it from also becoming involved in nucleation of IDs and HLAs. This means that, while BPD to TED conversion can eliminate most of the BPD transfer into the epilayer, further mitigation may only be possible by continued efforts to reduce the BPD density in substrates by control of temperature-gradient- induced stresses during their physical vapor transport (PVT) growth.

  14. Surface Evolution of Nano-Textured 4H–SiC Homoepitaxial Layers after High Temperature Treatments: Morphology Characterization and Graphene Growth

    PubMed Central

    Liu, Xingfang; Chen, Yu; Sun, Changzheng; Guan, Min; Zhang, Yang; Zhang, Feng; Sun, Guosheng; Zeng, Yiping

    2015-01-01

    Nano-textured 4H–SiC homoepitaxial layers (NSiCLs) were grown on 4H–SiC(0001) substrates using a low pressure chemical vapor deposition technique (LPCVD), and subsequently were subjected to high temperature treatments (HTTs) for investigation of their surface morphology evolution and graphene growth. It was found that continuously distributed nano-scale patterns formed on NSiCLs which were about submicrons in-plane and about 100 nanometers out-of-plane in size. After HTTs under vacuum, pattern sizes reduced, and the sizes of the remains were inversely proportional to the treatment time. Referring to Raman spectra, the establishment of multi-layer graphene (MLG) on NSiCL surfaces was observed. MLG with sp2 disorders was obtained from NSiCLs after a high temperature treatment under vacuum at 1700 K for two hours, while MLG without sp2 disorders was obtained under Ar atmosphere at 1900 K.

  15. Nucleation Mechanism of Dislocation Half-Loop Arrays in 4H-Silicon Carbide Homo-Epitaxial Layers

    SciTech Connect

    Zhang, N.; Chen, Y; Zhang, Y; Dudley, M

    2009-01-01

    A model is presented for the formation mechanism of dislocation half-loop arrays formed during the homoepitaxial growth of 4H-SiC. The reorientation during glide of originally screw oriented threading segments of basal plane dislocation (BPD) renders them susceptible to conversion into sessile threading edge dislocations (TEDs), which subsequently pin the motion of the BPD. Continued glide during further growth enables parts of the mobile BPD to escape through the surface leaving arrays of half loops comprising two TEDs and a short BPD segment with significant edge component. The faulting behavior of the arrays under UV excitation is consistent with this model.

  16. Properties of YBCO on LaMnO3-capped IBAD MgO-templates without Homo-epitaxial MgO layer.

    SciTech Connect

    Aytug, Tolga; Paranthaman, Mariappan Parans; Kim, Kyunghoon; Zhang, Yifei; Cantoni, Claudia; Zuev, Yuri L; Goyal, Amit; Thompson, James R; Christen, David K

    2009-01-01

    Previously, it has been well established that in an IBAD architecture for coated conductors, (1) LaMnO3 (LMO) buffer layers are structurally and chemically compatible with an underlying homo-epitaxial MgO layer and (2) high current density YBCO films can be grown on these LMO templates. In the present work, the homo-epi MgO layer has been successfully eliminated and a LMO cap layer was grown directly on the IBAD (MgO) template. The performance of the LMO/IBAD (MgO) samples has been qualified by depositing 1 m-thick YBCO coatings by pulsed laser deposition. Electrical transport measurements of YBCO films on the standard (with homo-epi MgO) and simplified (without homo-epi MgO) IBAD architectures were carried out. The angular dependencies of critical current density (Jc) are similar for both IBAD architectures. XRD measurements indicate good, c-axis aligned YBCO films. Transmission electron microscopy (TEM) images reveal that microstructures of YBCO/LMO/IBAD (MgO) and YBCO/LMO/homo-epi MgO/IBAD (MgO) templates are similar. These results demonstrate the strong potential of using LMO as a single cap layer directly on IBAD (MgO) for the development of a simplified IBAD architecture.

  17. Evolution of planar defects during homoepitaxial growth of β-Ga2O3 layers on (100) substrates—A quantitative model

    NASA Astrophysics Data System (ADS)

    Schewski, R.; Baldini, M.; Irmscher, K.; Fiedler, A.; Markurt, T.; Neuschulz, B.; Remmele, T.; Schulz, T.; Wagner, G.; Galazka, Z.; Albrecht, M.

    2016-12-01

    We study the homoepitaxial growth of β-Ga2O3 (100) grown by metal-organic vapour phase as dependent on miscut-angle vs. the c direction. Atomic force microscopy of layers grown on substrates with miscut-angles smaller than 2° reveals the growth proceeding through nucleation and growth of two-dimensional islands. With increasing miscut-angle, step meandering and finally step flow growth take place. While step-flow growth results in layers with high crystalline perfection, independent nucleation of two-dimensional islands causes double positioning on the (100) plane, resulting in twin lamellae and stacking mismatch boundaries. Applying nucleation theory in the mean field approach for vicinal surfaces, we can fit experimentally found values for the density of twin lamellae in epitaxial layers as dependent on the miscut-angle. The model yields a diffusion coefficient for Ga adatoms of D = 7 × 10-9 cm2 s-1 at a growth temperature of 850 °C, two orders of magnitude lower than the values published for GaAs.

  18. Effect of V/III ratio on the surface morphology and electrical properties of m-plane (10 1 bar 0) GaN homoepitaxial layers

    NASA Astrophysics Data System (ADS)

    Barry, Ousmane I.; Tanaka, Atsushi; Nagamatsu, Kentaro; Bae, Si-Young; Lekhal, Kaddour; Matsushita, Junya; Deki, Manato; Nitta, Shugo; Honda, Yoshio; Amano, Hiroshi

    2017-06-01

    We have investigated the effect of V/III ratio on the surface morphology, impurity concentration and electrical properties of m-plane (10 1 bar 0) Gallium Nitride (GaN) homoepitaxial layers. Four-sided pyramidal hillocks are observed on the nominally on-axis m-plane GaN films. Hillocks sizes relatively increase by increasing the V/III ratio. All facets of pyramidal hillocks exhibit well-defined step-terrace features. Secondary ion mass spectrometry depth profiles reveal that carbon impurities decrease by increasing the V/III ratio while the lowest oxygen content is found at an optimized V/III ratio of 900. Vertical Schottky barrier diodes fabricated on the m-GaN samples were characterized. Low leakage current densities of the order of 10-10 A/cm2 at -5 V are obtained at the optimum V/III ratio. Oxygen impurities and screw-component dislocations around hillocks are found to have more detrimental impact on the leakage current mechanism.

  19. Effect of Threading Screw and Edge Dislocations on Transport Properties of 4H-SiC Homoepitaxial Layers

    DTIC Science & Technology

    2010-01-01

    across the sample and measuring the collected current as a function of e-beam position using a Keithley model 617 Electrometer. The experimental data were...electron-hole pairs excited by the e-beam, q is the electron charge, and w is the deple- tion layer width. The Wittry model assumes that recombina- tion...height. Their degree of magni- FIG. 1. !Color online" Schematic of the EBIC model used in this work for diffusion length measurements. 013708-2

  20. Strain-compensated AlGaN /GaN/InGaN cladding layers in homoepitaxial nitride devices

    NASA Astrophysics Data System (ADS)

    Czernecki, R.; Krukowski, S.; Targowski, G.; Prystawko, P.; Sarzynski, M.; Krysko, M.; Kamler, G.; Grzegory, I.; Leszczynski, M.; Porowski, S.

    2007-12-01

    One of the most important problems in III-nitride violet laser diode technology is the lattice mismatch between the AlGaN cladding layers and the rest of the epitaxial structure. For efficiently working devices, it is necessary to have both a high Al content and thick claddings. This leads, however, to severe sample bowing and even cracking of the upper layer. In this work, we propose a cladding structure of strain-compensated AlGaN /GaN/InGaN superlattice grown by metal-organic vapor phase epitaxy on bulk GaN substrates. Various thicknesses and compositions of the layers were employed. We measured the radius of bowing, lattice mismatches, aluminum and indium contents, and densities of threading dislocations. The proposed cladding structures suppress bowing and cracking, which are the two parasitic effects commonly experienced in laser diodes with bulk AlGaN claddings. The suppression of cracking and bowing is shown to occur due to modified strain energy distribution of the superlattices structure.

  1. Ultraviolet light-absorbing and emitting diodes consisting of a p-type transparent-semiconducting NiO film deposited on an n-type GaN homoepitaxial layer

    NASA Astrophysics Data System (ADS)

    Nakai, Hiroshi; Sugiyama, Mutsumi; Chichibu, Shigefusa F.

    2017-05-01

    Gallium nitride (GaN) and related (Al,Ga,In)N alloys provide practical benefits in the production of light-emitting diodes (LEDs) and laser diodes operating in ultraviolet (UV) to green wavelength regions. However, obtaining low resistivity p-type AlN or AlGaN of large bandgap energies (Eg) is a critical issue in fabricating UV and deep UV-LEDs. NiO is a promising candidate for useful p-type transparent-semiconducting films because its Eg is 4.0 eV and it can be doped into p-type conductivity of sufficiently low resistivity. By using these technologies, heterogeneous junction diodes consisting of a p-type transparent-semiconducting polycrystalline NiO film on an n-type single crystalline GaN epilayer on a low threading-dislocation density, free-standing GaN substrate were fabricated. The NiO film was deposited by using the conventional RF-sputtering method, and the GaN homoepitaxial layer was grown by metalorganic vapor phase epitaxy. They exhibited a significant photovoltaic effect under UV light and also exhibited an electroluminescence peak at 3.26 eV under forward-biased conditions. From the conduction and valence band (EV) discontinuities, the NiO/GaN heterointerface is assigned to form a staggered-type (TYPE-II) band alignment with the EV of NiO higher by 2.0 eV than that of GaN. A rectifying property that is consistent with the proposed band diagram was observed in the current-voltage characteristics. These results indicate that polycrystalline NiO functions as a hole-extracting and injecting layer of UV optoelectronic devices.

  2. Suppression of 3C-Inclusion Formation during Growth of 4H-SiC Si-Face Homoepitaxial Layers with a 1° Off-Angle

    PubMed Central

    Masumoto, Keiko; Asamizu, Hirokuni; Tamura, Kentaro; Kudou, Chiaki; Nishio, Johji; Kojima, Kazutoshi; Ohno, Toshiyuki; Okumura, Hajime

    2014-01-01

    We grew epitaxial layers on 4H-silicon carbide (SiC) Si-face substrates with a 1° off-angle. The suppression of 3C-inclusion formation during growth at a high C/Si ratio was investigated, because a growth technique with a high C/Si ratio is needed to decrease residual nitrogen incorporation. 3C inclusions were generated both at the interface between the substrate and epitaxial layer, and during epitaxial growth. 3C-SiC nucleation is proposed to trigger the formation of 3C inclusions. We suppressed 3C-inclusion formation by performing deep in situ etching and using a high C/Si ratio, which removed substrate surface damage and improved the 4H-SiC stability, respectively. The as-grown epitaxial layers had rough surfaces because of step bunching due to the deep in situ etching, but the rough surface became smooth after chemical mechanical polishing treatment. These techniques allow the growth of epitaxial layers with 1° off-angles for a wide range of doping concentrations. PMID:28788228

  3. Critical impact of Ehrlich-Schwöbel barrier on GaN surface morphology during homoepitaxial growth

    NASA Astrophysics Data System (ADS)

    Kaufmann, Nils. A. K.; Lahourcade, L.; Hourahine, B.; Martin, D.; Grandjean, N.

    2016-01-01

    We discuss the impact of kinetics, and in particular the effect of the Ehrlich-Schwöbel barrier (ESB), on the growth and surface morphology of homoepitaxial GaN layers. The presence of an ESB can lead to various self-assembled surface features, which strongly affect the surface roughness. We present an in-depth study of this phenomenon on GaN homoepitaxial layers grown by metal organic vapor phase epitaxy and molecular beam epitaxy. We show how a proper tuning of the growth parameters allows for the control of the surface morphology, independent of the growth technique.

  4. Lateral Movement of Screw Dislocations During Homoepitaxial Growth and Devices Yielded Therefrom Free of the Detrimental Effects of Screw Dislocations

    NASA Technical Reports Server (NTRS)

    Neudeck, Philip G. (Inventor); Powell, J. Anthony (Inventor)

    2004-01-01

    The present invention is related to a method that enables and improves wide bandgap homoepitaxial layers to be grown on axis single crystal substrates, particularly SiC. The lateral positions of the screw dislocations in epitaxial layers are predetermined instead of random, which allows devices to be reproducibly patterned to avoid performance degrading crystal defects normally created by screw dislocations.

  5. Optical functions of silicon from reflectance and ellipsometry on silicon-on-insulator and homoepitaxial samples

    SciTech Connect

    Humlíček, J.

    2015-11-21

    The optical properties of silicon have been determined from 0.2 to 6.5 eV at room temperature, using reflectance spectra of silicon-on-insulator (SOI) and ellipsometric spectra of homoepitaxial samples. Optimized Fabry-Perot-type SOI resonators exhibit high finesse even in near ultraviolet. Very high precision values of the real part of the refractive index are obtained in infrared up to a photon energy of 1.3 eV. The spectra of the extinction coefficient, based on observations of light attenuation, extend to 3.2 eV due to measurements on SOI layers as thin as 87 nm. These results allowed us to correct spectroellipsometric data on homoepitaxial samples for the presence of reduced and stabilized surface layers.

  6. Evolution of pyramid morphology during InAs(001) homoepitaxy

    SciTech Connect

    Babu, J. Bubesh; Yoh, Kanji

    2010-08-16

    Growth of InAs(001) homoepitaxial layer has been carried out especially at the bistable region, where the coexistence of both In-stabilized (4x2) and As-stabilized (2x4) surface reconstruction are found to be predominant. The observation of pyramid morphology in this bistable region is reported here. Atomic force microscopy studies have been performed on such pyramids. The heights of the observed pyramids vary from 12 to 26 nm with their bases from 3.6x1.2 to 18x6.3 {mu}m{sup 2}. Formation of such pyramids in the bistable region is attributed to the unique anomalous As-desorption observed during the surface reconstruction.

  7. The homoepitaxial growth of Pt on Pt(111) studied with STM

    NASA Astrophysics Data System (ADS)

    Bott, Michael; Michely, Thomas; Comsa, George

    The homoepitaxial growth of Pt on Pt(111) has been investigated by STM and the results have been compared to recent thermal He scattering (TEAS) data obtained on the same system. Additional information on the growth modes is obtained and the real space aspect of the growing surface, which results in TEAS and RHEED oscillations is evidenced. The three different growth modes, including the reentrant layer-by-layer growth at low temperatures, are confirmed. The limited diffusion along the adatom island edges, which causes their fractal aspect with dendritic structures, appears to play a significant role in the appearance of the low temperature layer-by-layer growth.

  8. Homoepitaxial ZnO Film Growth

    NASA Technical Reports Server (NTRS)

    Zhu, Shen; Su, C-H; Lehoczky, S. L.; Harris, M. T.; Callahan, M. J.; McCarty, P.; George, M. A.; Rose, M. Franklin (Technical Monitor)

    2000-01-01

    ZnO films have high potential for many applications, such as surface acoustic wave filters, UV detectors, and light emitting devices due to its structural, electrical, and optical properties. High quality epitaxial films are required for these applications. The Al2O3 substrate is commonly used for ZnO heteroepitaxial growth. Recently, high quality ZnO single crystals are available for grow homoepitaxial films. Epitaxial ZnO films were grown on the two polar surfaces (O-face and Zn-face) of (0001) ZnO single crystal substrates using off-axis magnetron sputtering deposition. As a comparison, films were also deposited on (0001) Al2O3 substrates. It was found that the two polar ZnO surfaces have different photoluminescence (PL) spectrum, surface structure and morphology, which strongly influence the epitaxial film growth. The morphology and structure of homoepitaxial films grown on the ZnO substrates were different from heteroepitaxial films grown on the Al2O3. An interesting result shows that high temperature annealing of ZnO single crystals will improve the surface structure on the O-face surface rather than the opposite surface. The measurements of PL, low-angle incident x-ray diffraction, and atomic force microscopy of ZnO films indicate that the O-terminated surface is better for ZnO epitaxial film growth.

  9. Homoepitaxial ZnO Film Growth

    NASA Technical Reports Server (NTRS)

    Zhu, Shen; Su, C-H; Lehoczky, S. L.; Harris, M. T.; Callahan, M. J.; McCarty, P.; George, M. A.; Rose, M. Franklin (Technical Monitor)

    2000-01-01

    ZnO films have high potential for many applications, such as surface acoustic wave filters, UV detectors, and light emitting devices due to its structural, electrical, and optical properties. High quality epitaxial films are required for these applications. The Al2O3 substrate is commonly used for ZnO heteroepitaxial growth. Recently, high quality ZnO single crystals are available for grow homoepitaxial films. Epitaxial ZnO films were grown on the two polar surfaces (O-face and Zn-face) of (0001) ZnO single crystal substrates using off-axis magnetron sputtering deposition. As a comparison, films were also deposited on (0001) Al2O3 substrates. It was found that the two polar ZnO surfaces have different photoluminescence (PL) spectrum, surface structure and morphology, which strongly influence the epitaxial film growth. The morphology and structure of homoepitaxial films grown on the ZnO substrates were different from heteroepitaxial films grown on the Al2O3. An interesting result shows that high temperature annealing of ZnO single crystals will improve the surface structure on the O-face surface rather than the opposite surface. The measurements of PL, low-angle incident x-ray diffraction, and atomic force microscopy of ZnO films indicate that the O-terminated surface is better for ZnO epitaxial film growth.

  10. Nearly stress-free substrates for GaN homoepitaxy

    NASA Astrophysics Data System (ADS)

    Hermann, M.; Gogova, D.; Siche, D.; Schmidbauer, M.; Monemar, B.; Stutzmann, M.; Eickhoff, M.

    2006-08-01

    High-quality 300 μm thick GaN crack-free layers grown by hydride vapor phase epitaxy (HVPE) on c-plane sapphire without buffer layers and separated from the substrate by laser lift-off were investigated by high resolution X-ray diffraction (XRD), low-temperature photoluminescence and cathodoluminescence. All these characterization techniques confirm the high structural quality of the resulting material. Lateral X-ray mapping of the free-standing bulk-like GaN shows a homogeneous compressive stress of less than 40 MPa and a heterogeneous stress of about 80 MPa. The formation of twin grains (domains) were observed both in the reciprocal space mapping of the (2 0 .5) reflection and in rocking curve measurements. The latter ones revealed an estimated lateral coherence length of about 1.2 μm. The crystallite size along the c-axis is estimated to be larger than 20 μm. An upper limit of the density of dislocations with a component of the Burgers vector along the c-axis (screw and mixed type) of 1.3×10 7 cm -2 was extracted from the XRD data, while transmission electron microscopy measurements revealed a dislocation density of 1.7×10 7 cm -2. Thus, these layers are suitable as lattice-parameter and thermal-expansion matched substrates for strain-free homoepitaxy of GaN-based device heterostructures.

  11. High quality (In)GaN films on homoepitaxial substrates

    NASA Astrophysics Data System (ADS)

    Liu, Li; Zhang, Yong; Yin, Yian

    2017-02-01

    High quality GaN and InGaN epitaxial thin films were deposited by metal organic chemical vapor deposition (MOCVD). Two sets of thin film samples were prepared by varying the substrates and temperatures under a proper condition for achieving better optical properties. The morphological, crystalline quality and optical property of epitaxial layers were characterized by atomic force microscope (AFM), X-ray diffraction (XRD), photoluminescence (PL) and Raman spectra, respectively. It was found that the epitaxial layers grown on GaN homoepitaxial substrate have higher quality than those grown on sapphire substrate. The root mean square (RMS) of GaN film and InGaN film in AFM morphological were 0.5 nm, 2.7 nm respectively. The full width at half maximum (FWHM) of (102) in GaN film on GaN substrate was 33arcsec and the FWHM of (002) in InGaN film on GaN substrate was 50.58arcsec by XRD. The PL peaks of GaN film and InGaN film were 361 nm, 458 nm respectively. The E2 (high) of GaN film and InGaN film in Raman were both 567.08 cm-1.

  12. InAs homoepitaxy and InAs/AlSb/GaSb resonant interband tunneling diodes on InAs substrate

    NASA Astrophysics Data System (ADS)

    Xiang, Wei; Wang, Guowei; Hao, Hongyue; Liao, Yongping; Han, Xi; Zhang, Lichun; Xu, Yingqiang; Ren, Zhengwei; Ni, Haiqiao; He, Zhenhong; Niu, Zhichuan

    2016-06-01

    In this paper, the optimal conditions for growth of homoepitaxial InAs layer on InAs (001) substrate by molecular beam epitaxy were investigated over wide growth temperatures and As/In flux ratios. The oxide remove process is important and both the As/In flux ratio and growth temperature is in narrow range for InAs homoepitaxy. The high quality homoepitaxy has an RMS surface roughness of 0.26 nm measured by atomic force microscopy. High quality lattice matched InAs/AlSb/GaSb/InAs/AlSb/InAs double barrier resonant interband tunneling diodes was grown on InAs (001) substrate on the optimal condition. It shows high peak-valley current ratios of 105 at 77 K and 15 at room temperature.

  13. Critical issues for homoepitaxial GaN growth by molecular beam epitaxy on hydride vapor-phase epitaxy-grown GaN substrates

    NASA Astrophysics Data System (ADS)

    Storm, D. F.; Hardy, M. T.; Katzer, D. S.; Nepal, N.; Downey, B. P.; Meyer, D. J.; McConkie, Thomas O.; Zhou, Lin; Smith, David J.

    2016-12-01

    While the heteroepitaxial growth of gallium nitride-based materials and devices on substrates such as SiC, sapphire, and Si has been well-documented, the lack of a cost-effective source of bulk GaN crystals has hindered similar progress on homoepitaxy. Nevertheless, freestanding GaN wafers are becoming more widely available, and there is great interest in growing GaN films and devices on bulk GaN substrates, in order to take advantage of the greatly reduced density of threading dislocations, particularly for vertical devices. However, homoepitaxial GaN growth is far from a trivial task due to the reactivity and different chemical sensitivities of N-polar (000_1) and Ga-polar (0001) GaN surfaces, which can affect the microstructure and concentrations of impurities in homoepitaxial GaN layers. In order to achieve high quality, high purity homoepitaxial GaN, it is necessary to investigate the effect of the ex situ wet chemical clean, the use of in situ cleaning procedures, the sensitivity of the GaN surface to thermal decomposition, and the effect of growth temperature. We review the current understanding of these issues with a focus on homoepitaxial growth of GaN by molecular beam epitaxy (MBE) on c-plane surfaces of freestanding GaN substrates grown by hydride vapor phase epitaxy (HVPE), as HVPE-grown substrates are most widely available. We demonstrate methods for obtaining homoepitaxial GaN layers by plasma-assisted MBE in which no additional threading dislocations are generated from the regrowth interface and impurity concentrations are greatly reduced.

  14. Lattice strains and polarized luminescence in homoepitaxial growth of a-plane ZnO

    NASA Astrophysics Data System (ADS)

    Matsui, Hiroaki; Tabata, Hitoshi

    2012-12-01

    In-plane lattice strains in a-plane zinc oxide (ZnO) homoepitaxial layers were selectively introduced by changing substrate type and growth conditions. Strain-free layers were observed when using a Crystec ZnO substrate, which resulted in atomically flat surfaces with nano-facets consisting of the m-plane (10-10) at atomic scale. In contrast, ZnO layers on Goodwill ZnO substrates possessed in-plane lattice strains due to generation of basal-plane stacking faults. The degree of lattice strains was systematically changed by the oxygen pressure, which clarified the close correlation between photoluminescence (PL) polarization and lattice strains. The polarization ratio of PL enhanced with the lattice strains.

  15. Homoepitaxial tunnel barriers with functionalized graphene-on-graphene for charge and spin transport.

    PubMed

    Friedman, Adam L; van 't Erve, Olaf M J; Li, Connie H; Robinson, Jeremy T; Jonker, Berend T

    2014-01-01

    The coupled imperatives for reduced heat dissipation and power consumption in high-density electronics have rekindled interest in devices based on tunnelling. Such devices require mating dissimilar materials, raising issues of heteroepitaxy, layer uniformity, interface stability and electronic states that severely complicate fabrication and compromise performance. Two-dimensional materials such as graphene obviate these issues and offer a new paradigm for tunnel barriers. Here we demonstrate a homoepitaxial tunnel barrier structure in which graphene serves as both the tunnel barrier and the high-mobility transport channel. We fluorinate the top layer of a graphene bilayer to decouple it from the bottom layer, so that it serves as a single-monolayer tunnel barrier for both charge and spin injection into the lower graphene channel. We demonstrate high spin injection efficiency with a tunnelling spin polarization >60%, lateral transport of spin currents in non-local spin-valve structures and determine spin lifetimes with the Hanle effect.

  16. Multi-scale simulation of quantum dot formation in Al/Al (110) homoepitaxy

    NASA Astrophysics Data System (ADS)

    Tiwary, Yogesh; Fichthorn, Kristen

    2007-03-01

    In experimental studies of Al(110) homoepitaxy, it is observed that over a certain temperature window (330-500K), 3D huts, up to 50 nm high with well defined and smooth (111) and (100) facets, form and self-organize over the micron scale [1]. The factors leading to this kinetic self-organization are currently unclear. To understand how these structures form and evolve, we simulated multi-layer, homoepitaxial growth on Al(110) using ab initio kinetic Monte Carlo (KMC). At the high temperatures, where nano-huts form, the KMC simulations are slow. To tackle this problem, we use a technique developed by Devita & Sander [2], in which isolated adatoms make multiple moves in one step. We achieve high efficiency with this algorithm and we explore very high temperatures on large simulation lattices. We uncover a variety of interesting morphologies (Ripples, mounds, smooth surface, huts) that depend on the growth temperature. By varying the barriers for various rate processes, we discern the factors that determine hut sizes, aspect ratios, and self-organization. [1] F. Buatier de Mongeot, W. Zhu, A. Molle, R. Buzio, C. Boragno, U. Valbusa, E. Wang, and Z. Zhang, Phys. Rev. Lett. 91, 016102 (2003). [2] J.P. Devita & L.M. Sander, Phys. Rev. B 72, 205421 (2005).

  17. Ultra-Low-Temperature Homoepitaxial Growth of Sb-Doped Silicon

    NASA Technical Reports Server (NTRS)

    Blacksberg, Jordana; Hoenk, Michael E.; Nikzad, Shouleh

    2005-01-01

    An ultra-low-temperature process for homoepitaxial growth of high-quality, surface-confined, Sb-doped silicon layers is presented. Non-equilibrium growth by molecular beam epitaxy (MBE) is used to achieve dopant incorporation in excess of 2x10(exp 14) per sq cm in a thin, surface-confined layer. Sb surface segregation larger than expected from theoretical models was observed, in agreement with other experimental works. Furthermore, this work details an entirely low-temperature process (less than 450 degree C) that can be applied to fully processed and aluminum-metallized silicon devices. One application of this process is the formation of a back-surface electrode for back-illuminated high-purity silicon imaging arrays.

  18. Homoepitaxial HVPE-GaN growth on non-polar and semi-polar seeds

    NASA Astrophysics Data System (ADS)

    Amilusik, M.; Sochacki, T.; Lucznik, B.; Fijalkowski, M.; Smalc-Koziorowska, J.; Weyher, J. L.; Teisseyre, H.; Sadovyi, B.; Bockowski, M.; Grzegory, I.

    2014-10-01

    In this work homoepitaxial HVPE-GaN growth on non-polar and semi-polar GaN seeds was described. Two crystallization processes, in the same experimental conditions but using different carrier gases: N2 and H2, were performed. An influence of growth directions and growth conditions on the growth rate and properties (morphology, structural quality and oxygen and silicon contaminations) of obtained crystals were investigated and discussed. It was shown that the growth rate strongly depends on the growth direction and the carrier gas. It was demonstrated that for the semi-polar [20-21] direction it was possible to obtain high quality and highly conductive (without intentional doping) gallium nitride layers.

  19. Homoepitaxial growth of MOD-YBCO thick films on evaporated and MOD templates

    NASA Astrophysics Data System (ADS)

    Tanabe, D.; Yamaguchi, I.; Sohma, M.; Tsukada, K.; Matsui, M.; Kumagai, T.; Manabe, T.

    2011-11-01

    We have prepared metal organic deposition (MOD)-YBCO thick films by repeating the coating-pyrolysis-crystallization procedure onto ∼100-nm-thick evaporated and MOD templates. Surface morphology of the template was found to strongly affect the homoepitaxial growth of MOD-YBCO layers on the template; namely, the epitaxial growth of MOD-YBCO on the evaporated template was much easier than that on the MOD template. A 220-nm-thick epitaxial MOD-YBCO film was successfully prepared on the 100-nm-thick evaporated-YBCO template to obtain a 320-nm-thick YBCO film, which exhibited Jc = 2.44 MA/cm2 and Ic = 78 A/cm. The Ic value has significantly increased from 37 A/cm for the evaporated-template.

  20. Homoepitaxial growth of HVPE-GaN doped with Si

    NASA Astrophysics Data System (ADS)

    Iwinska, M.; Sochacki, T.; Amilusik, M.; Kempisty, P.; Lucznik, B.; Fijalkowski, M.; Litwin-Staszewska, E.; Smalc-Koziorowska, J.; Khapuridze, A.; Staszczak, G.; Grzegory, I.; Bockowski, M.

    2016-12-01

    Results of growth of high structural quality gallium nitride single crystals doped with silicon are described in this paper. Dichlorosilane was used as precursor of silicon in the hydride vapor phase epitaxy method. Crystallization runs with different flows of dichlorosilane were performed and compared. One-inch free-standing HVPE-GaN crystals of high structural quality and high purity, previously grown on ammonothermal GaN substrates, were used as seeds. Structural, electrical, and optical properties of HVPE-GaN doped with silicon are presented and discussed in detail. A laser diode built on the homoepitaxially grown GaN is demonstrated.

  1. Homoepitaxial growth of metal halide crystals investigated by reflection high-energy electron diffraction

    DOE PAGES

    Chen, Pei; Kuttipillai, Padmanaban S.; Wang, Lili; ...

    2017-01-10

    Here, we report the homoepitaxial growth of a metal halide on single crystals investigated with in situ reflection high-energy electron diffraction (RHEED) and ex situ atomic force microscopy (AFM). Epitaxial growth of NaCl on NaCl (001) is explored as a function of temperature and growth rate which provides the first detailed report of RHEED oscillations for metal halide growth. Layer-by-layer growth is observed at room temperature accompanied by clear RHEED oscillations while the growth mode transitions to an island (3D) mode at low temperature. At higher temperatures (>100 °C), RHEED oscillations and AFM data indicate a transition to a step-flowmore » growth mode. To show the importance of such metal halide growth, green organic light-emitting diodes (OLEDs) are demonstrated using a doped NaCl film with a phosphorescent emitter as the emissive layer. This study demonstrates the ability to perform in situ and non-destructive RHEED monitoring even on insulating substrates and could enable doped single crystals and crystalline substrates for a range of optoelectronic applications.« less

  2. Homoepitaxial Growth of Metal Halide Crystals Investigated by Reflection High-Energy Electron Diffraction

    NASA Astrophysics Data System (ADS)

    Chen, Pei; Kuttipillai, Padmanaban S.; Wang, Lili; Lunt, Richard R.

    2017-01-01

    We report the homoepitaxial growth of a metal halide on single crystals investigated with in situ reflection high-energy electron diffraction (RHEED) and ex situ atomic force microscopy (AFM). Epitaxial growth of NaCl on NaCl (001) is explored as a function of temperature and growth rate which provides the first detailed report of RHEED oscillations for metal halide growth. Layer-by-layer growth is observed at room temperature accompanied by clear RHEED oscillations while the growth mode transitions to an island (3D) mode at low temperature. At higher temperatures (>100 °C), RHEED oscillations and AFM data indicate a transition to a step-flow growth mode. To show the importance of such metal halide growth, green organic light-emitting diodes (OLEDs) are demonstrated using a doped NaCl film with a phosphorescent emitter as the emissive layer. This study demonstrates the ability to perform in situ and non-destructive RHEED monitoring even on insulating substrates and could enable doped single crystals and crystalline substrates for a range of optoelectronic applications.

  3. Homoepitaxial Growth of Metal Halide Crystals Investigated by Reflection High-Energy Electron Diffraction

    PubMed Central

    Chen, Pei; Kuttipillai, Padmanaban S.; Wang, Lili; Lunt, Richard R.

    2017-01-01

    We report the homoepitaxial growth of a metal halide on single crystals investigated with in situ reflection high-energy electron diffraction (RHEED) and ex situ atomic force microscopy (AFM). Epitaxial growth of NaCl on NaCl (001) is explored as a function of temperature and growth rate which provides the first detailed report of RHEED oscillations for metal halide growth. Layer-by-layer growth is observed at room temperature accompanied by clear RHEED oscillations while the growth mode transitions to an island (3D) mode at low temperature. At higher temperatures (>100 °C), RHEED oscillations and AFM data indicate a transition to a step-flow growth mode. To show the importance of such metal halide growth, green organic light-emitting diodes (OLEDs) are demonstrated using a doped NaCl film with a phosphorescent emitter as the emissive layer. This study demonstrates the ability to perform in situ and non-destructive RHEED monitoring even on insulating substrates and could enable doped single crystals and crystalline substrates for a range of optoelectronic applications. PMID:28071732

  4. Experimental verification of the model by Klapper for 4H-SiC homoepitaxy on vicinal substrates

    NASA Astrophysics Data System (ADS)

    Kallinger, Birgit; Polster, Sebastian; Berwian, Patrick; Friedrich, Jochen; Danilewsky, Andreas N.

    2013-11-01

    4H-SiC homoepitaxial layers free of basal plane dislocations (BPDs) are urgently needed to overcome the so-called bipolar degradation of high-voltage devices. BPDs being present in substrates are able to either propagate to the epilayer or convert to harmless threading edge dislocations (TEDs) in the epilayer. The model by Klapper predicts the conversion of BPDs to TEDs to be more efficient for growth on vicinal substrates with low off-cut angle. This paper aims to verify the model by Klapper by an extensive variation of epitaxial growth parameters and the substrates' off-cut. It is shown that the off-cut angle is the key parameter for growth of BPD-free epilayers. Furthermore, it is shown that the model also describes adequately the behavior of different types of TEDs, i.e., TED II and TED III dislocations, during epitaxial growth. Therefore, the model by Klapper is verified successfully for 4H-SiC homoepitaxial growth on vicinal substrates.

  5. Imaging pulsed laser deposition growth of homo-epitaxial SrTiO3 by low-energy electron microscopy

    NASA Astrophysics Data System (ADS)

    van der Torren, A. J. H.; van der Molen, S. J.; Aarts, J.

    2016-12-01

    By combining low-energy electron microscopy with in situ pulsed laser deposition we have developed a new technique for film growth analysis, making use of both diffraction and real-space information. Working at the growth temperature, we can use: the intensity and profile variations of the specular beam to follow the coverage in a layer-by-layer fashion; real-space microscopy to follow e.g. atomic steps at the surface; and electron reflectivity to probe the unoccupied band structure of the grown material. Here, we demonstrate our methodology for homo-epitaxial growth of SrTiO3. Interestingly, the same combination of techniques will also be applicable to hetero-epitaxial oxide growth, largely extending the scope of research possibilities.

  6. Cathodoluminescence measurements on heavily boron doped homoepitaxial diamond films and their interfaces with their Ib substrates

    NASA Astrophysics Data System (ADS)

    Baron, C.; Deneuville, A.; Wade, M.; Jomard, F.; Chevallier, J.

    2006-02-01

    Heavily boron doped 1.8 to 2.4 μm thick homoepitaxial diamond films with 1.5 × 1021 cm-3 [B] 1.75 × 1021 cm-3 have been deposited directly on their (100) Ib substrates at 830 °C. Their cathodoluminescence spectra probe the controlled thicknesses from 0.28 to 2.8 μm, therefore the bulk of the films as well as their interfaces with their substrates. The bulk of these films exhibit a band with shoulders ascribed to BETO (5.036 eV), FETO (5.094 eV) and BENP (5.184 eV) excitons whose energies are downward shifted by about 180 meV in comparison with monocrystalline diamond with low [B] < 5 × 1018 cm-3. This large shift allows the appearance of narrow peaks around 5.216, 5.271 and 5.357 eV ascribed to BETO, FETO and BENP from interfacial layers with low [B]. From their BETO to FETO ratio, their concentration of boron on isolated substitutional sites is significantly lower than their total low [B] content measured by SIMS. A tentative model is proposed to explain the characteristics of these 40 to 160 quasihomogeneous interfacial layers.

  7. Evolution of Mound Morphology in Reversible Homoepitaxy on Cu(100)

    SciTech Connect

    Zuo, J.; Wendelken, J.

    1997-04-01

    Evolution of mound morphology in reversible homoepitaxy on Cu(100) was studied via spot-profile-analysis (SPA) LEED and scanning tunneling microscopy. The mound separation shows coarsening vs growth time with L(t){approximately}t{sup 1/4}, in support of theory based on capillarity between mounds. The growth ultimately reaches a steady state characterized by a selected mound angle of {approximately}5.6{degree}. We suggest that this results from a downhill current driven by step edge line tension in balance with an uphill current due to the Schwoebel barrier effect. Also, we have clarified the interpretation for the evolution of the SPA-LEED profile from a ring structure to a single time-invariant peak. {copyright} {ital 1997} {ital The American Physical Society}

  8. Slope selection of mounds with permeable steps in homoepitaxy

    NASA Astrophysics Data System (ADS)

    Korutcheva, Elka; Koroutchev, Kostadin; Markov, Ivan

    2013-02-01

    We study the growth of mounds representing stacks of monolayer islands in homoepitaxy assuming terrace-edge-kink mechanism of attachment of atoms to kink sites and allowing a permeability of the single steps. We show that the latter can result in slope selection of the growing mounds at comparatively small values of the Ehrlich-Schwoebel barrier to down-step diffusion. The value of the permeability coefficient at which a slope selection occurs is always very close to the upper limit for complete step permeability. The latter is in agreement with the row-by-row mechanism of step propagation at which the steps are kink-free for most of the time.

  9. Growth of Homoepitaxial ZnO Semiconducting Films

    NASA Technical Reports Server (NTRS)

    Zhu, Shen; Su, C.-H.; Lehoczky, S. L.; Harris, M. T.; George, M. A.; McCarty, P.

    1999-01-01

    As a high temperature wide-band-gap (3.3 eV at room temperature) semiconductor, ZnO has been used for many applications such as wave-guides, solar cells, and surface acoustic wave devices, Since ZnO has a 60 meV excitonic binding energy that makes it possible to produce excitonic lasing at room temperature, a recent surge of interest is to synthesize ZnO films for UV/blue/green laser diodes. These applications require films with a smooth surface, good crystal quality, and low defect density. Thus, homoepitaxial film growth is the best choice. Homoepitaxial films have been studied in terms of morphology, crystal structure, and electrical and optical properties. ZnO single crystal substrates grown by the hydrothermal method are mechanically polished and annealed in air for four hours before the films are deposited. The annealing temperature-dependence on ZnO substrate morphology and electrical properties is investigated. Films are synthesized by off-axis reactive sputtering deposition. This produces films that have very smooth surfaces with roughness less than or equal to 5 nm on a 5 microns x 5 microns area. The full width at half maximum of film theta rocking curves measured by the x-ray diffraction is slightly larger than that of the crystal substrate. Films are also characterized by measuring resistivity, optical transmittance, and photoluminescence. The properties of ZnO films grown on (0001) ZnO and (0001) sapphire substrates will also be compared and discussed.

  10. Self-organized homo-epitaxial growth of (001) vanadium assisted by oxygen surface reconstruction

    NASA Astrophysics Data System (ADS)

    Andrieu, S.; Turban, P.; Kierren, B.

    2016-09-01

    In this paper the effect of oxygen on the vanadium homoepitaxial growth process is analyzed by using Auger spectroscopy, electron diffraction and scanning tunneling microscopy. As the oxygen induced 1 × 5 surface structure got a lattice spacing 6% different from the pure V lattice, relaxation is observed by electron diffraction during the growth. The average in-plane lattice spacing is thus shown to be proportional to the oxygen surface concentration. The surface lattice relaxation is observed to exponentially vary with the number of deposited atomic planes. A kinetic model is proposed and allows us to explain these observations. Furthermore, it helps us to distinguish two regimes depending on growth temperature. At high temperature, the oxygen surface concentration during growth is due to oxygen upward diffusion from the underneath V layer. For lower temperature however, this upward diffusion is not efficient and another source of oxygen contamination is evidenced. When the oxygen surface concentration is sufficient, a spectacular self-organization is observed at the surface by surface microscopy. Ribbons shape islands are observed and are tentatively explained as a consequence of oxygen surface concentration and stress induced by the surface reconstruction.

  11. Homoepitaxial Boron Doped Diamond Anvils as Heating Elements in a Diamond Anvil Cell

    NASA Astrophysics Data System (ADS)

    Montgomery, Jeffrey; Samudrala, Gopi; Smith, Spencer; Tsoi, Georgiy; Vohra, Yogesh; Weir, Samuel

    2013-03-01

    Recent advances in designer-diamond technology have allowed for the use of electrically and thermally conducting homoepitaxially-grown layers of boron-doped diamond (grown at 1200 °C with a 2% mixture of CH4 in H, resulting in extremely high doping levels ~ 1020/cm3) to be used as heating elements in a diamond anvil cell (DAC). These diamonds allow for precise control of the temperature inside of the diamond anvil itself, particularly when coupled with a cryostat. Furthermore, the unmatched thermally conducting nature of diamond ensures that no significant lateral gradient in temperature occurs across the culet area. Since a thermocouple can easily be attached anywhere on the diamond surface, we can also measure diamond temperatures directly. With two such heaters, one can raise sample temperatures uniformly, or with any desired gradient along the pressure axis while preserving optical access. In our continuing set of benchmark experiments, we use two newly created matching heater anvils with 500 μm culets to analyze the various fluorescence emission lines of ruby microspheres, which show more complicated behavior than traditional ruby chips. We also report on the temperature dependence of the high-pressure Raman modes of paracetamol (C8H9NO2) up to 20 GPa.

  12. Homoepitaxial Boron Doped Diamond Anvil as Heating Element in a Diamond Anvil Cell

    NASA Astrophysics Data System (ADS)

    Montgomery, Jeffrey; Samudrala, Gopi; Vohra, Yogesh

    2012-02-01

    Recent advances in designer-diamond technology have allowed for the use of electrically and thermally conducting homoepitaxially-grown layers of boron-doped diamond (grown at 1200 C with a 2% mixture of CH4 in H, resulting in extremely high doping levels ˜ 10^20/cm^3) to be used as heating elements in a diamond anvil cell (DAC). These diamonds allow for precise control of the temperature inside of the diamond anvil itself, particularly when coupled with a cryostat. Furthermore, the unmatched thermally conducting nature of diamond ensures that no significant spatial gradient in temperature occurs across the culet area. Since a thermocouple can easily be attached anywhere on the diamond surface, we can also measure diamond temperatures directly. With two such heaters, one can raise sample temperatures uniformly, or with any desired gradient along the pressure axis while preserving optical access. In our initial experiments with these diamond anvils we report on the measurement of the thermal conductivity of copper-beryllium using a single diamond heater and two thermocouples. We augment these measurements with measurements of sample pressure via ruby fluorescence and electrical resistance of the sample and diamond heater.

  13. Donor and acceptor levels in ZnO homoepitaxial thin films grown by molecular beam epitaxy and doped with plasma-activated nitrogen

    SciTech Connect

    Muret, Pierre; Tainoff, Dimitri; Morhain, Christian; Chauveau, Jean-Michel

    2012-09-17

    Deep level transient spectroscopy of both majority and minority carrier traps is performed in a n-type, nitrogen doped homoepitaxial ZnO layer grown on a m-plane by molecular beam epitaxy. Deep levels, most of them being not detected in undoped ZnO, lie close to the band edges with ionization energies in the range 0.12-0.60 eV. The two hole traps with largest capture cross sections are likely acceptors, 0.19 and 0.48 eV from the valence band edge, able to be ionized below room temperature. These results are compared with theoretical predictions and other experimental data.

  14. Growth of Homoepitaxial ZnO Semiconducting Films

    NASA Technical Reports Server (NTRS)

    Zhu, Shen; Su, Ching-Hua; Lehoczky, S. L.; Harris, M. T.; George, Michael A.; McCarty, P.

    1999-01-01

    As a high temperature semiconductor, ZnO has been used for many applications such as wave-guide, solar cells, and surface acoustic wave devices. Since the ZnO material has an energy gap of 3.3 eV at room temperature and an excitonic binding energy (60 meV) that is possible to make excitonic lasering at room temperature a recent surge of interest is to synthesize ZnO films for electro-optical devices. These applications require films with a smooth surface, good crystal quality, and low defect density. Homoepitaxial films have been studied in terms of morphology, crystal structure, and electrical and optical properties. ZnO single crystals are grown by the hydrothermal method. Substrates are mechanically polished and annealed in air for four hours before deposited films. The annealing temperature-dependence of ZnO substrates is studied. Films are synthesized by the off-axis reactive sputtering deposition. The films have very smooth surface with a roughness

  15. Chloride-based fast homoepitaxial growth of 4H-SiC films in a vertical hot-wall CVD

    NASA Astrophysics Data System (ADS)

    Guoguo, Yan; Feng, Zhang; Yingxi, Niu; Fei, Yang; Xingfang, Liu; Lei, Wang; Wanshun, Zhao; Guosheng, Sun; Yiping, Zeng

    2016-06-01

    Chloride-based fast homoepitaxial growth of 4H-SiC epilayers was performed on 4° off-axis 4H-SiC substrates in a home-made vertical hot-wall chemical vapor deposition (CVD) system using H2-SiH4-C2H4-HCl. The effect of the SiH4/H2 ratio and reactor pressure on the growth rate of 4H-SiC epilayers has been studied successively. The growth rate increase in proportion to the SiH4/H2 ratio and the influence mechanism of chlorine has been investigated. With the reactor pressure increasing from 40 to 100 Torr, the growth rate increased to 52 μm/hand then decreased to 47 μm/h, which is due to the joint effect of H2 and HCl etching as well as the formation of Si clusters at higher reactor pressure. The surface root mean square (RMS) roughness keeps around 1 nm with the growth rate increasing to 49 μm/h. The scanning electron microscope (SEM), Raman spectroscopy and X-ray diffraction (XRD) demonstrate that 96.7 μm thick 4H-SiC layers of good uniformity in thickness and doping with high crystal quality can be achieved. These results prove that chloride-based fast epitaxy is an advanced growth technique for 4H-SiC homoepitaxy. Project supported by the National High Technology R&D Program of China (No. 2014AA041402), the National Natural Science Foundation of China (Nos. 61474113, 61274007, 61574140), the Beijing Natural Science Foundation of China (Nos. 4132076, 4132074), the Program of State Grid Smart Grid Research Institute (No. SGRI-WD-71-14-004), and the Youth Innovation Promotion Association of CAS.

  16. Kinetic Monte Carlo simulations of GaN homoepitaxy on c- and m-plane surfaces.

    PubMed

    Xu, Dongwei; Zapol, Peter; Stephenson, G Brian; Thompson, Carol

    2017-04-14

    The surface orientation can have profound effects on the atomic-scale processes of crystal growth and is essential to such technologies as GaN-based light-emitting diodes and high-power electronics. We investigate the dependence of homoepitaxial growth mechanisms on the surface orientation of a hexagonal crystal using kinetic Monte Carlo simulations. To model GaN metal-organic vapor phase epitaxy, in which N species are supplied in excess, only Ga atoms on a hexagonal close-packed (HCP) lattice are considered. The results are thus potentially applicable to any HCP material. Growth behaviors on c-plane (0001) and m-plane (011¯0) surfaces are compared. We present a reciprocal space analysis of the surface morphology, which allows extraction of growth mode boundaries and direct comparison with surface X-ray diffraction experiments. For each orientation, we map the boundaries between 3-dimensional, layer-by-layer, and step flow growth modes as a function of temperature and growth rate. Two models for surface diffusion are used, which produce different effective Ehrlich-Schwoebel step-edge barriers and different adatom diffusion anisotropies on m-plane surfaces. Simulation results in agreement with observed GaN island morphologies and growth mode boundaries are obtained. These indicate that anisotropy of step edge energy, rather than adatom diffusion, is responsible for the elongated islands observed on m-plane surfaces. Island nucleation spacing obeys a power-law dependence on growth rate, with exponents of -0.24 and -0.29 for the m- and c-plane, respectively.

  17. Kinetic Monte Carlo simulations of GaN homoepitaxy on c- and m-plane surfaces

    NASA Astrophysics Data System (ADS)

    Xu, Dongwei; Zapol, Peter; Stephenson, G. Brian; Thompson, Carol

    2017-04-01

    The surface orientation can have profound effects on the atomic-scale processes of crystal growth and is essential to such technologies as GaN-based light-emitting diodes and high-power electronics. We investigate the dependence of homoepitaxial growth mechanisms on the surface orientation of a hexagonal crystal using kinetic Monte Carlo simulations. To model GaN metal-organic vapor phase epitaxy, in which N species are supplied in excess, only Ga atoms on a hexagonal close-packed (HCP) lattice are considered. The results are thus potentially applicable to any HCP material. Growth behaviors on c-plane (0001) and m-plane (01 1 ¯ 0 ) surfaces are compared. We present a reciprocal space analysis of the surface morphology, which allows extraction of growth mode boundaries and direct comparison with surface X-ray diffraction experiments. For each orientation, we map the boundaries between 3-dimensional, layer-by-layer, and step flow growth modes as a function of temperature and growth rate. Two models for surface diffusion are used, which produce different effective Ehrlich-Schwoebel step-edge barriers and different adatom diffusion anisotropies on m-plane surfaces. Simulation results in agreement with observed GaN island morphologies and growth mode boundaries are obtained. These indicate that anisotropy of step edge energy, rather than adatom diffusion, is responsible for the elongated islands observed on m-plane surfaces. Island nucleation spacing obeys a power-law dependence on growth rate, with exponents of -0.24 and -0.29 for the m- and c-plane, respectively.

  18. Kinetic Monte Carlo simulations of GaN homoepitaxy on c- and m-plane surfaces

    DOE PAGES

    Xu, Dongwei; Zapol, Peter; Stephenson, G. Brian; ...

    2017-04-12

    The surface orientation can have profound effects on the atomic-scale processes of crystal growth and is essential to such technologies as GaN-based light-emitting diodes and high-power electronics. We investigate the dependence of homoepitaxial growth mechanisms on the surface orientation of a hexagonal crystal using kinetic Monte Carlo simulations. To model GaN metal-organic vapor phase epitaxy, in which N species are supplied in excess, only Ga atoms on a hexagonal close-packed (HCP) lattice are considered. The results are thus potentially applicable to any HCP material. Growth behaviors on c-plane (0001) and m-plane (011¯0) surfaces are compared. We present a reciprocal spacemore » analysis of the surface morphology, which allows extraction of growth mode boundaries and direct comparison with surface X-ray diffraction experiments. For each orientation, we map the boundaries between 3-dimensional, layer-by-layer, and step flow growth modes as a function of temperature and growth rate. Two models for surface diffusion are used, which produce different effective Ehrlich-Schwoebel step-edge barriers and different adatom diffusion anisotropies on m-plane surfaces. Simulation results in agreement with observed GaN island morphologies and growth mode boundaries are obtained. These indicate that anisotropy of step edge energy, rather than adatom diffusion, is responsible for the elongated islands observed on m-plane surfaces. As a result, island nucleation spacing obeys a power-law dependence on growth rate, with exponents of –0.24 and –0.29 for the m- and c-plane, respectively.« less

  19. Tuning thermal conductivity in homoepitaxial SrTiO{sub 3} films via defects

    SciTech Connect

    Brooks, Charles M.; Wilson, Richard B.; Cahill, David G.; Schäfer, Anna; Schubert, Jürgen; Mundy, Julia A.; Holtz, Megan E.; Muller, David A.; Schlom, Darrell G.

    2015-08-03

    We demonstrate the ability to tune the thermal conductivity of homoepitaxial SrTiO{sub 3} films deposited by reactive molecular-beam epitaxy by varying growth temperature, oxidation environment, and cation stoichiometry. Both point defects and planar defects decrease the longitudinal thermal conductivity (k{sub 33}), with the greatest decrease in films of the same composition observed for films containing planar defects oriented perpendicular to the direction of heat flow. The longitudinal thermal conductivity can be modified by as much as 80%—from 11.5 W m{sup −1}K{sup −1} for stoichiometric homoepitaxial SrTiO{sub 3} to 2 W m{sup −1}K{sup −1} for strontium-rich homoepitaxial Sr{sub 1+δ}TiO{sub x} films—by incorporating (SrO){sub 2} Ruddlesden-Popper planar defects.

  20. Electrical mechanisms for carrier compensation in homoepitaxial nonpolar m-ZnO doped with nitrogen

    NASA Astrophysics Data System (ADS)

    Kurtz, A.; Hierro, A.; Lopez-Ponce, M.; Tabares, G.; Chauveau, J. M.

    2016-03-01

    By combining photoluminescence, capacitance-voltage profiling and deep level optical spectroscopy, the optical and electrical signatures of the deep levels induced by N in MBE-grown homoepitaxial m-ZnO layers are identified and correlated to different physical origins. The films are electrically compensated, with carrier concentrations that decrease from ˜1 · 1016 cm-3 to ˜2 · 1015 cm-3 as a result of increasing N incorporation. Regardless of the presence of N, an intrinsic trap is found in all films at EV + 0.25 eV, most likely related to VZn defects. More interestingly, N induces three new deep levels close to the valence band whose bandgap position is electrically observed to be at EV + 0.48 eV, EV + 0.17 eV and EV + 0.12 eV. The deepest trap at EV + 0.48 eV correlates well with a N-induced level observed in previous studies on both ZnMgO and ZnO films. The EV + 0.17 eV trap behaves as a minority (hole) carrier trap, and can be uniquely correlated with the acceptor level involved in the N-induced DAP emission observed in the photoluminescence spectra. Finally, the shallowest level at EV + 0.12 eV shows an electrical signature completely distinguishable from the EV + 0.17 eV level, and dominates the deep level spectra after N-incorporation with a trap concentration of ˜1.2 · 1015 cm-3.

  1. Homoepitaxial SrTiO3(111) Film with High Dielectric Performance and Atomically Well-Defined Surface

    PubMed Central

    Liang, Yan; Li, Wentao; Zhang, Shuyuan; Lin, Chaojing; Li, Chao; Yao, Yuan; Li, Yongqing; Yang, Hao; Guo, Jiandong

    2015-01-01

    The six-fold symmetry possessed by the (111) surfaces of perovskite oxides allows the epitaxial growth of novel quantum materials such as topological insulators. The dielectric SrTiO3(111) thin film is an ideal buffer layer, providing the readily tunability of charge density in gate-controlled structures. But the high-quality film growth is challenging due to its strong surface polarity as well as the difficulty of obtaining the chemical stoichiometry. Here we show that the layer-by-layer growth of homoepitaxial SrTiO3(111) thin films can be achieved in molecular beam epitaxy method by keeping the growing surface reconstructed. And the cation stoichiometry is optimized precisely with the reflective high energy electron diffraction as the feedback signal that changes sensitively to the variation of metal concentration during growth. With atomically well-defined surfaces, the SrTiO3(111) films show high dielectric performance with the charge density modulated in the range of 2 × 1013/cm2 with the back gate voltage lower than 0.2 V. Methods of further broadening the range are also discussed. PMID:26073468

  2. Transient Evolution of Surface Roughness on Patterned GaAs(001) during Homoepitaxial Growth

    NASA Astrophysics Data System (ADS)

    Kan, H.-C.; Shah, S.; Tadyyon-Eslami, T.; Phaneuf, R. J.

    2004-04-01

    We have investigated the length scale dependence of the transient evolution of surface roughness during homoepitaxial growth on GaAs(100), patterning the surface lithographically with an array of cylindrical pits of systematically varied sizes and spacings. Our atomic force microscopy measurements show that the amplitude of the surface corrugation has nonmonotonic behavior in both the length scale dependence and time evolution. This behavior allows us to rule out a number of existing continuum models of growth.

  3. Homoepitaxial growth of β-Ga2O3 thin films by low pressure chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Rafique, Subrina; Han, Lu; Tadjer, Marko J.; Freitas, Jaime A.; Mahadik, Nadeemullah A.; Zhao, Hongping

    2016-05-01

    This paper presents the homoepitaxial growth of phase pure (010) β-Ga2O3 thin films on (010) β-Ga2O3 substrate by low pressure chemical vapor deposition. The effects of growth temperature on the surface morphology and crystal quality of the thin films were systematically investigated. The thin films were synthesized using high purity metallic gallium (Ga) and oxygen (O2) as precursors for gallium and oxygen, respectively. The surface morphology and structural properties of the thin films were characterized by atomic force microscopy, X-ray diffraction, and high resolution transmission electron microscopy. Material characterization indicates the growth temperature played an important role in controlling both surface morphology and crystal quality of the β-Ga2O3 thin films. The smallest root-mean-square surface roughness of ˜7 nm was for thin films grown at a temperature of 950 °C, whereas the highest growth rate (˜1.3 μm/h) with a fixed oxygen flow rate was obtained for the epitaxial layers grown at 850 °C.

  4. Homoepitaxial growth of β-Ga{sub 2}O{sub 3} thin films by low pressure chemical vapor deposition

    SciTech Connect

    Rafique, Subrina; Han, Lu; Zhao, Hongping; Tadjer, Marko J.; Freitas, Jaime A.; Mahadik, Nadeemullah A.

    2016-05-02

    This paper presents the homoepitaxial growth of phase pure (010) β-Ga{sub 2}O{sub 3} thin films on (010) β-Ga{sub 2}O{sub 3} substrate by low pressure chemical vapor deposition. The effects of growth temperature on the surface morphology and crystal quality of the thin films were systematically investigated. The thin films were synthesized using high purity metallic gallium (Ga) and oxygen (O{sub 2}) as precursors for gallium and oxygen, respectively. The surface morphology and structural properties of the thin films were characterized by atomic force microscopy, X-ray diffraction, and high resolution transmission electron microscopy. Material characterization indicates the growth temperature played an important role in controlling both surface morphology and crystal quality of the β-Ga{sub 2}O{sub 3} thin films. The smallest root-mean-square surface roughness of ∼7 nm was for thin films grown at a temperature of 950 °C, whereas the highest growth rate (∼1.3 μm/h) with a fixed oxygen flow rate was obtained for the epitaxial layers grown at 850 °C.

  5. Using the graphene Moiré pattern for the trapping of C60 and homoepitaxy of graphene.

    PubMed

    Lu, Jiong; Yeo, Pei Shan Emmeline; Zheng, Yi; Yang, Zhiyong; Bao, Qiaoliang; Gan, Chee Kwan; Loh, Kian Ping

    2012-01-24

    The graphene Moiré superstructure offers a complex landscape of humps and valleys to molecules adsorbing and diffusing on it. Using C(60) molecules as the classic hard sphere analogue, we examine its assembly and layered growth on this corrugated landscape. At the monolayer level, the cohesive interactions of C(60) molecules adsorbing on the Moiré lattice freeze the molecular rotation of C(60) trapped in the valley sites, resulting in molecular alignment of all similarly trapped C(60) molecules at room temperature. The hierarchy of adsorption potential well on the Moiré lattice causes diffusion-limited dendritic growth of C(60) films, as opposed to isotropic growth observed on a smooth surface like graphite. Due to the strong binding energy of the C(60) film, part of the dentritic C(60) films polymerize at 850 K and act as solid carbon sources for graphene homoepitaxy. Our findings point to the possibility of using periodically corrugated graphene in molecular spintronics due to its ability to trap and align organic molecules at room temperature.

  6. Modeling RHEED intensity oscillations in multilayer epitaxy: Determination of the Ehrlich-Schwoebel barrier in Ge(001) homoepitaxy

    SciTech Connect

    Shin, Byungha; Aziz, Michael J.

    2007-10-15

    We report the study of submonolayer growth of Ge(001) homoepitaxy by molecular beam epitaxy at low temperatures, 100-150 deg. C, using reflection high energy electron diffraction (RHEED) intensity oscillations obtained for a range of low incidence angles, where the influence of the dynamical nature of electron scattering such as the Kikuchi features is minimized. We develop a model for the RHEED specular intensity in multilayer growth that includes the diffuse scattering off surface steps and the layer interference between terraces of different heights using the kinematic approximation. The model describes the measured RHEED intensity oscillations very well for the entire range of incidence angles studied. We show that the first intensity minimum occurs well above 0.5 ML (monolayer) of the total deposited coverage, which contradicts the common practice of assigning the intensity minimum to 0.5 ML. By using the model to interpret the measured RHEED intensity, we find the evolution of the coverage of the first 1-2 ML. We find that second-layer nucleation takes place at low coverage, 0.3 ML, implying a substantial Ehrlich-Schwoebel (ES) barrier. The value inferred for the ES barrier height, 0.084{+-}0.019 eV, includes an analysis of the beam steering effect by step edges. Comparison is made with the value of the barrier height inferred from other measurements. The model for RHEED intensity and the method of inferring the ES barrier height can be applied to any system for which RHEED measurements can be obtained without interference from Kikuchi features.

  7. Potential energy barriers for interlayer mass transport in homoepitaxial growth on fcc(111) surfaces: Pt and Ag

    NASA Astrophysics Data System (ADS)

    Li, Yinggang; DePristo, Andrew E.

    1994-11-01

    The efficiency of interlayer mass transport determines the growth mode and film quality in molecular beam epitaxy. In this paper we report potential energy barriers (PEB) to interlayer diffusion for Pt and Ag homoepitaxial growth on fcc (111) surfaces, as calculated using the corrected effective medium theory. Various island structures were considered. The island sizes ranged from 3- to about 60-atom islands and to various steps ("infinite" large islands). We found that jumping directly over the island edge has a much higher PEB than does the so-called displacement-exchange mechanism. Exchange at edges with kink sites also had a higher or comparable PEB to those at the straight (perfect) edges, contrary to previous speculations [M. Henzler, T. Schmidt and E.Z. Luo, in: The Structure of Surfaces IV (World Scientific, Signapore, 1994)]. The PEB depended strongly on the local atomic arrangement but was insensitive to the global island size and shape as long as the island edges were at least five atoms long. For the displacement-exchange process, the PEB did not decrease monotonically with decreasing island size over the entire island size range. For very small islands of less than ten atoms the PEB increased abruptly by an order of magnitude. This qualitative behavior was exhibited by both Pt and Ag systems but the two differed quantitatively for island sizes above ten atoms. We discuss the relevance of these results to the experimental observations, i.e., the reentrant growth in Pt [R. Kunkel, B. Poelsema, L.K. Verheij and G. Comsa, Phys. Rev. Lett. 65 (1990) 733], layer-by-layer growth in Ag induced by surfactant [H.A. van der Vegt, H.M. van Pinxteren, M. Lohmerier and E. Vlieg, Phys. Rev. Lett. 68 (1992) 3335] or by high-density of islands [G. Rosenfeld, R. Servaty, C. Teichert, B. Poelsema and G. Comsa, Phys. Rev. Lett. 71 (1993) 895 ], as well as the different growth behaviors found in the two systems.

  8. High-quality and high-purity homoepitaxial diamond (100) film growth under high oxygen concentration condition

    SciTech Connect

    Teraji, Tokuyuki

    2015-09-21

    Defect formation during diamond homoepitaxial growth was sufficiently inhibited by adding oxygen simultaneously in the growth ambient with high concentration of 2%. A 30-μm thick diamond films with surface roughness of <2 nm were homoepitaxially deposited on the (100) diamond single crystal substrates with reasonable growth rate of approximately 3 μm h{sup −1} under the conditions of higher methane concentration of 10%, higher substrate temperature of ∼1000 °C, and higher microwave power density condition of >100 W cm{sup −3}. Surface characteristic patterns moved to an identical direction with growth thickness, indicating that lateral growth was dominant growth mode. High chemical purity represented by low nitrogen concentration of less than 1 ppb and the highest {sup 12}C isotopic ratio of 99.998% of the obtained homoepitaxial diamond (100) films suggest that the proposed growth condition has high ability of impurity control.

  9. Submonolayer nucleation and growth and the initial stage of multilayer kinetic roughening during Ag/Ag (100) homoepitaxy

    SciTech Connect

    Zhang, C.

    1996-08-01

    A comprehensive Scanning Tunneling Microscopy (STM) study of submonolayer nucleation and growth of 2D islands in Ag/Ag(100) homoepitaxy for temperature between 295K and 370K is presented. The initial stages of multilayer kinetic roughening is also studied. Analysis of an appropriate model for metal (100) homoepitaxy, produces estimates of 350 meV for the terrace diffusion barrier, 400 meV for the adatom bond energy, and 25 meV for the additional Ehrlich-Schwoebel step-edge barrier.

  10. Homoepitaxial growth of catalyst-free GaN wires on N-polar substrates

    NASA Astrophysics Data System (ADS)

    Chen, X. J.; Perillat-Merceroz, G.; Sam-Giao, D.; Durand, C.; Eymery, J.

    2010-10-01

    The shape of c-oriented GaN nanostructures is found to be directly related to the crystal polarity. As evidenced by convergent beam electron diffraction applied to GaN nanostructures grown by metal-organic vapor phase epitaxy on c-sapphire substrates: wires grown on nitridated sapphire have the N-polarity ([0001¯]) whereas pyramidal crystals have Ga-polarity ([0001]). In the case of homoepitaxy, the GaN wires can be directly selected using N-polar GaN freestanding substrates and exhibit good optical properties. A schematic representation of the kinetic Wulff's plot points out the effect of surface polarity.

  11. Hydrogenated Graphene as a Homoepitaxial Tunnel Barrier for Spin and Charge Transport in Graphene.

    PubMed

    Friedman, Adam L; van 't Erve, Olaf M J; Robinson, Jeremy T; Whitener, Keith E; Jonker, Berend T

    2015-07-28

    We demonstrate that hydrogenated graphene performs as a homoepitaxial tunnel barrier on a graphene charge/spin channel. We examine the tunneling behavior through measuring the IV curves and zero bias resistance. We also fabricate hydrogenated graphene/graphene nonlocal spin valves and measure the spin lifetimes using the Hanle effect, with spintronic nonlocal spin valve operation demonstrated up to room temperature. We show that while hydrogenated graphene indeed allows for spin transport in graphene and has many advantages over oxide tunnel barriers, it does not perform as well as similar fluorinated graphene/graphene devices, possibly due to the presence of magnetic moments in the hydrogenated graphene that act as spin scatterers.

  12. Growth rate and quality variation of homoepitaxial diamond grown at elevated temperatures

    NASA Astrophysics Data System (ADS)

    Weimer, R. A.; Thorpe, T. P.; Snail, K. A.

    1995-01-01

    Homoepitaxial diamond films were grown at temperatures between 1000 and 1400 C with an oxy-acetylene torch. The growth rates of the (100) and (111) faces were observed to increase through 1400 C, while the (110) face did not grow above 1400 C. The quality of all faces deteriorated significantly between 1300 and 1400 C, as shown by scanning electron microscopy and Raman spectroscopy. The transparency of a film as measured by Fourier-transform infrared spectroscopy was type-IIa quality with very little C-H absorption.

  13. Homoepitaxial meso- and microscale crystal co-orientation and organic matrix network structure in Mytilus edulis nacre and calcite.

    PubMed

    Griesshaber, Erika; Schmahl, Wolfgang W; Ubhi, Harbinder Singh; Huber, Julia; Nindiyasari, Fitriana; Maier, Bernd; Ziegler, Andreas

    2013-12-01

    New developments in high-resolution, low accelaration voltage electron backscatter diffraction (EBSD) enable us to resolve and quantify the co-orientation of nanocrystals constituting biological carbonate crystals with a scan step resolution of 125 nm. This allows the investigation of internal structures in carbonate tablets and tower biocrystals in the nacre of mollusc shells, and it provides details on the calcite-aragonite polymorph interface in bivalves. Within the aragonite tablets of Mytilus edulis nacre we find a mesoscale crystallographic mosaic structure with a misorientation distribution of 2° full width at half maximum. Selective etching techniques with critical point drying reveal an organic matrix network inside the nacre tablets. The size scales of the visible aragonite tablet subunits and nanoparticles correspond to those of the open pore system in the organic matrix network. We further observe by EBSD that crystal co-orientation spans over tablet boundaries and forms composite crystal units of up to 20 stacked co-oriented tablets (tower crystals). Statistical evaluation of the misorientation data gives a probability distribution of grain boundary misorientations with two maxima: a dominant peak for very-small-angle grain boundaries and a small maximum near 64°, the latter corresponding to {110} twinning orientations. However, the related twin boundaries are typically the membrane-lined {001} flat faces of the tablets and not {110} twin walls within tablets. We attribute this specific pattern of misorientation distribution to growth by particle accretion and subsequent semicoherent homoepitaxial crystallization. The semicoherent crystallization percolates between the tablets through mineral bridges and across matrix membranes surrounding the tablets. In the "prismatic" calcite layer crystallographic co-orientation of the prisms reaches over more than 50 micrometers.

  14. Nitrogen and silicon defect incorporation during homoepitaxial CVD diamond growth on (111) surfaces

    SciTech Connect

    Moore, Samuel L.; Vohra, Yogesh K.

    2015-01-01

    Chemical Vapor Deposited (CVD) diamond growth on (111)-diamond surfaces has received increased attention lately because of the use of N-V related centers in quantum computing as well as application of these defect centers in sensing nano-Tesla strength magnetic fields. We have carried out a detailed study of homoepitaxial diamond deposition on (111)-single crystal diamond (SCD) surfaces using a 1.2 kW microwave plasma CVD (MPCVD) system employing methane/hydrogen/nitrogen/oxygen gas phase chemistry. We have utilized Type Ib (111)-oriented single crystal diamonds as seed crystals in our study. The homoepitaxially grown diamond films were analyzed by Raman spectroscopy, Photoluminescence Spectroscopy (PL), X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). The nitrogen concentration in the plasma was carefully varied between 0 and 1500 ppm while a ppm level of silicon impurity is present in the plasma from the quartz bell jar. The concentration of N-V defect centers with PL zero phonon lines (ZPL) at 575nm and 637nm and the Si-defect center with a ZPL at 737nm were experimentally detected from a variation in CVD growth conditions and were quantitatively studied. As a result, altering nitrogen and oxygen concentration in the plasma was observed to directly affect N-V and Si-defect incorporation into the (111)-oriented diamond lattice and these findings are presented.

  15. Nitrogen and silicon defect incorporation during homoepitaxial CVD diamond growth on (111) surfaces

    DOE PAGES

    Moore, Samuel L.; Vohra, Yogesh K.

    2015-01-01

    Chemical Vapor Deposited (CVD) diamond growth on (111)-diamond surfaces has received increased attention lately because of the use of N-V related centers in quantum computing as well as application of these defect centers in sensing nano-Tesla strength magnetic fields. We have carried out a detailed study of homoepitaxial diamond deposition on (111)-single crystal diamond (SCD) surfaces using a 1.2 kW microwave plasma CVD (MPCVD) system employing methane/hydrogen/nitrogen/oxygen gas phase chemistry. We have utilized Type Ib (111)-oriented single crystal diamonds as seed crystals in our study. The homoepitaxially grown diamond films were analyzed by Raman spectroscopy, Photoluminescence Spectroscopy (PL), X-ray Photoelectronmore » Spectroscopy (XPS), Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). The nitrogen concentration in the plasma was carefully varied between 0 and 1500 ppm while a ppm level of silicon impurity is present in the plasma from the quartz bell jar. The concentration of N-V defect centers with PL zero phonon lines (ZPL) at 575nm and 637nm and the Si-defect center with a ZPL at 737nm were experimentally detected from a variation in CVD growth conditions and were quantitatively studied. As a result, altering nitrogen and oxygen concentration in the plasma was observed to directly affect N-V and Si-defect incorporation into the (111)-oriented diamond lattice and these findings are presented.« less

  16. Effect of substrate orientation on CdS homoepitaxy by molecular dynamics

    DOE PAGES

    Almeida, S.; Chavez, J. J.; Zhou, X. W.; ...

    2016-02-10

    CdS homoepitaxy growth was performed by molecular dynamics using different substrate orientations and structures in order to analyze the CdS crystallinity. As anticipated from thermodynamics of homoepitaxy, highly crystalline films with only point defects were obtained on substrates with rectangular surface geometries, including View the MathML source[112¯] zinc blende (ZB), [101¯0] wurtzite (WZ), [112¯0] WZ, [110][110] ZB, [010][010] ZB, and View the MathML source[1101110] ZB. In contrast, films grown on substrates with hexagonal surface geometries, corresponding to the [0001][0001] WZ and [111][111] ZB growth directions, showed structures with a large number of defects including; anti-sites, vacancies, stacking faults, twinning, andmore » polytypism. WZ and ZB transitions and grain boundaries are identified using a lattice identification algorithm and represented graphically in a structural map. A dislocation analysis was performed to detect, identify, and quantify linear defects within the atomistic data. Systematic simulations using different temperatures, deposition rates, and substrate polarities were perform to analyze the trends of dislocation densities on [0001][0001] WZ direction and showed persistent polytypism. As a result, the polytypism observed in the films grown on the substrates with hexagonal surface geometry is attributed to the similar formation energies of the WZ and ZB phases.« less

  17. Effect of substrate orientation on CdS homoepitaxy by molecular dynamics

    NASA Astrophysics Data System (ADS)

    Almeida, S.; Chavez, J. J.; Zhou, X. W.; Zubia, D.

    2016-05-01

    CdS homoepitaxy growth was performed by molecular dynamics using different substrate orientations and structures in order to analyze the CdS crystallinity. As anticipated from thermodynamics of homoepitaxy, highly crystalline films with only point defects were obtained on substrates with rectangular surface geometries, including [ 11 2 bar ] zinc blende (ZB), [ 10 1 bar 0 ] wurtzite (WZ), [ 11 2 bar 0 ] WZ, [ 110 ] ZB, [ 010 ] ZB, and [1/10 1 1/10] ZB. In contrast, films grown on substrates with hexagonal surface geometries, corresponding to the [ 0001 ] WZ and [ 111 ] ZB growth directions, showed structures with a large number of defects including; anti-sites, vacancies, stacking faults, twinning, and polytypism. WZ and ZB transitions and grain boundaries are identified using a lattice identification algorithm and represented graphically in a structural map. A dislocation analysis was performed to detect, identify, and quantify linear defects within the atomistic data. Systematic simulations using different temperatures, deposition rates, and substrate polarities were perform to analyze the trends of dislocation densities on [ 0001 ] WZ direction and showed persistent polytypism. The polytypism observed in the films grown on the substrates with hexagonal surface geometry is attributed to the similar formation energies of the WZ and ZB phases.

  18. Effect of substrate orientation on CdS homoepitaxy by molecular dynamics

    SciTech Connect

    Almeida, S.; Chavez, J. J.; Zhou, X. W.; Zubia, D.

    2016-02-10

    CdS homoepitaxy growth was performed by molecular dynamics using different substrate orientations and structures in order to analyze the CdS crystallinity. As anticipated from thermodynamics of homoepitaxy, highly crystalline films with only point defects were obtained on substrates with rectangular surface geometries, including View the MathML source[112¯] zinc blende (ZB), [101¯0] wurtzite (WZ), [112¯0] WZ, [110][110] ZB, [010][010] ZB, and View the MathML source[1101110] ZB. In contrast, films grown on substrates with hexagonal surface geometries, corresponding to the [0001][0001] WZ and [111][111] ZB growth directions, showed structures with a large number of defects including; anti-sites, vacancies, stacking faults, twinning, and polytypism. WZ and ZB transitions and grain boundaries are identified using a lattice identification algorithm and represented graphically in a structural map. A dislocation analysis was performed to detect, identify, and quantify linear defects within the atomistic data. Systematic simulations using different temperatures, deposition rates, and substrate polarities were perform to analyze the trends of dislocation densities on [0001][0001] WZ direction and showed persistent polytypism. As a result, the polytypism observed in the films grown on the substrates with hexagonal surface geometry is attributed to the similar formation energies of the WZ and ZB phases.

  19. In situ growth and density-functional-theory study of polarity-dependent homo-epitaxial ZnO microwires

    SciTech Connect

    Zhu, Rui; Xu, Jun; Gao, Jingyun; Zhang, Jingmin; Zhu, Wenguang; Xu, Hongjun; Sun, Yanghui; Fu, Qiang; Chen, Li; Du, Dapeng

    2012-01-01

    Polarity-dependent homo-epitaxy on (0001)-Zn and (0001)-O surfaces of cleaved ZnO microwires was investigated by in situ growth in ESEMand DFT simulations. ZnO monomers adsorption, adatoms desorption and chemisorption were simulated to understand the explicit mechanism.

  20. Performances of homoepitaxial single crystal diamond in diagnostic x-ray dosimetry

    SciTech Connect

    Garino, Y.; Lo Giudice, A.; Manfredotti, C.; Marinelli, Marco; Milani, E.; Tucciarone, A.; Verona-Rinati, G.

    2006-04-10

    Pulsed x-ray dose measurements have been carried at maximum x-ray energies from 40 to 120 KeV out by using a single crystal epitaxial diamond sample grown by chemical vapor deposition (CVD). Delivered doses were between 0.1 and 10 mGy and pulse duration times between 0.01 and 0.5 s. Values of dose linearity index very close to 1 (between 1.02 and 1.07) at increasing x-ray energies and pulse decay times between 15 and 20 ms were obtained. The reproducibility was very good with no memory effects. CVD homoepitaxial diamond results to be very promising for x-ray diagnostic applications.

  1. Thick homoepitaxial (110)-oriented phosphorus-doped n-type diamond

    SciTech Connect

    Balasubramaniam, Y.; Pobedinskas, P. Janssens, S. D.; Nesládek, M.; Haenen, K.; Sakr, G.; Jomard, F.; Barjon, J.; Turner, S.; Lu, Y.-G.; Verbeeck, J.; Dexters, W.; Soltani, A.

    2016-08-08

    The fabrication of n-type diamond is essential for the realization of electronic components for extreme environments. We report on the growth of a 66 μm thick homoepitaxial phosphorus-doped diamond on a (110)-oriented diamond substrate, grown at a very high deposition rate of 33 μm h{sup −1}. A pristine diamond lattice is observed by high resolution transmission electron microscopy, which indicates the growth of high quality diamond. About 2.9 × 10{sup 16} cm{sup −3} phosphorus atoms are electrically active as substitutional donors, which is 60% of all incorporated dopant atoms. These results indicate that P-doped (110)-oriented diamond films deposited at high growth rates are promising candidates for future use in high-power electronic applications.

  2. Thick homoepitaxial (110)-oriented phosphorus-doped n-type diamond

    NASA Astrophysics Data System (ADS)

    Balasubramaniam, Y.; Pobedinskas, P.; Janssens, S. D.; Sakr, G.; Jomard, F.; Turner, S.; Lu, Y.-G.; Dexters, W.; Soltani, A.; Verbeeck, J.; Barjon, J.; Nesládek, M.; Haenen, K.

    2016-08-01

    The fabrication of n-type diamond is essential for the realization of electronic components for extreme environments. We report on the growth of a 66 μm thick homoepitaxial phosphorus-doped diamond on a (110)-oriented diamond substrate, grown at a very high deposition rate of 33 μm h-1. A pristine diamond lattice is observed by high resolution transmission electron microscopy, which indicates the growth of high quality diamond. About 2.9 × 1016 cm-3 phosphorus atoms are electrically active as substitutional donors, which is 60% of all incorporated dopant atoms. These results indicate that P-doped (110)-oriented diamond films deposited at high growth rates are promising candidates for future use in high-power electronic applications.

  3. Evolution of patterned GaAs(001) during homoepitaxial growth: Size versus spacing

    NASA Astrophysics Data System (ADS)

    Kan, H.-C.; Ankam, R.; Shah, S.; Micholsky, K. M.; Tadayyon-Eslami, T.; Calhoun, L.; Phaneuf, R. J.

    2006-05-01

    We report an extended experimental characterization of the transient evolution of the surface morphology of patterned GaAs(001) surfaces during homoepitaxial growth [Phys. Rev. Lett. 92, 146101 (2004)]. The size and the periodicity in the patterned structures are varied independently. Our results indicate different, nonmonotonic dependences of the evolution on these two characteristic distances. Numerical simulations of the growth based upon the conserved KPZ equation [Phys. Rev. A 40, 6763 (1989)] reproduce qualitatively the very different size and spacing dependences we observe during growth. We speculate on a physically based scenario in which a reduced collection efficiency on narrow terraces during growth breaks the up-down symmetry in the evolution of the surface topography.

  4. Homoepitaxial n-core: p-shell gallium nitride nanowires: HVPE overgrowth on MBE nanowires.

    PubMed

    Sanders, Aric; Blanchard, Paul; Bertness, Kris; Brubaker, Matthew; Dodson, Christopher; Harvey, Todd; Herrero, Andrew; Rourke, Devin; Schlager, John; Sanford, Norman; Chiaramonti, Ann N; Davydov, Albert; Motayed, Abhishek; Tsvetkov, Denis

    2011-11-18

    We present the homoepitaxial growth of p-type, magnesium doped gallium nitride shells by use of halide vapor phase epitaxy (HVPE) on n-type gallium nitride nanowires grown by plasma-assisted molecular beam epitaxy (MBE). Scanning electron microscopy shows clear dopant contrast between the core and shell of the nanowire. The growth of magnesium doped nanowire shells shows little or no effect on the lattice parameters of the underlying nanowires, as measured by x-ray diffraction (XRD). Photoluminescence measurements of the nanowires show the appearance of sub-bandgap features in the blue and the ultraviolet, indicating the presence of acceptors. Finally, electrical measurements confirm the presence of electrically active holes in the nanowires.

  5. Electric field breakdown of lateral-type Schottky diodes formed on lightly doped homoepitaxial diamond

    NASA Astrophysics Data System (ADS)

    Teraji, Tokuyuki; Koizumi, Satoshi; Koide, Yasuo; Ito, Toshimichi

    2008-07-01

    The reverse current of lateral-type Schottky diodes fabricated on p-type homoepitaxial diamond was analyzed by changing the distance between Schottky and Ohmic electrodes and the metal materials in the Schottky electrodes. The maximum electric field at breakdown was 0.56 MV cm -1 for the Au Schottky contact and less than 0.26 MV cm -1 for the Al Schottky contact. The breakdown voltage depended on the electrode distance when the diamond surface was revealed in vacuum, whereas the Schottky diodes sustained the applied voltage of 500 V, corresponding to 0.69 MV cm -1, after covering of the diamond surface with an insulating liquid. Diamond surface protection is an indispensable technique for fabrication of high-voltage Schottky diodes based on diamond.

  6. Surface preparation and homoepitaxial deposition of AlN on (0001)-oriented AlN substrates by metalorganic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Rice, A.; Collazo, R.; Tweedie, J.; Dalmau, R.; Mita, S.; Xie, J.; Sitar, Z.

    2010-08-01

    Chemical surface treatments were conducted on mechanically polished (MP) and chemomechanically polished (CMP) (0001)-oriented single crystalline aluminum nitride (AlN) substrates to determine a surface preparation procedure for the homoepitaxial deposition of AlN epitaxial layers by metalorganic chemical vapor deposition. MP AlN substrates characterized by atomic force microscopy exhibited 0.5 nm rms roughness and polishing scratches, while CMP AlN substrates exhibited 0.1 nm rms roughness and were scratch-free. X-ray photoelectron spectroscopy analysis of MP and CMP AlN substrates indicated the presence of a surface hydroxide layer composed of mixed aluminum oxide hydroxide and aluminum trihydroxide. Wet etching with sulfuric and phosphoric acid mixtures reduced the amount of surface hydroxide. Ammonia annealing at 1250 °C converted the substrate hydroxide layer to AlN and increased the rms roughness of MP and CMP AlN substrates to 2.2 nm and 0.2 nm, respectively. AlN epitaxial layers were deposited at 1100-1250 °C under 20 Torr total pressure with a V/III ratio of 180-300 in either N2 or H2 diluent. High-resolution x-ray diffraction measurements revealed that AlN epitaxial layers deposited on MP substrates were strained due to nucleation and coalescence of AlN grains on the mechanically damaged surfaces. AlN deposited on CMP substrates was epitaxial and strain-free. Thermodynamic models for nitridation and AlN deposition were also proposed and evaluated.

  7. Precise control of photoluminescence of silicon-vacancy color centers in homoepitaxial single-crystal diamond: evaluation of efficiency of Si doping from gas phase

    NASA Astrophysics Data System (ADS)

    Ralchenko, Victor; Sedov, Vadim; Saraykin, Vladimir; Bolshakov, Andrey; Zavedeev, Evgeny; Ashkinazi, Evgeny; Khomich, Andrew

    2016-09-01

    Ability to precisely control the Si-related color center abundance in diamond is important for the use of silicon-vacancy (SiV) defects with bright photoluminescence (PL) in quantum information technologies and optical biomarkers. Here, we evaluated the efficiency of Si incorporation in (100) plane of homoepitaxial diamond layers upon in situ doping by adding silane SiH4 in the course of diamond chemical vapor deposition in microwave plasma using CH4-H2 mixtures. Both the Si concentration in the doped samples, as determined by secondary ion mass spectrometry, and PL intensity of SiV centers at 738 nm wavelength, measured at excitation wavelength of 473 nm, demonstrate a linear increase with silane content in feed gas in the range. The incorporation efficiency f, defined as the ratio of Si concentration in diamond to that in gas, f = [Si/C]dia/[Si/C]gas is found to be (1.1 ± 0.5) × 10-3 for the silane concentrations explored, [SiH4/CH4] < 0.7 %; thus, the Si atoms are accommodated in (100) diamond face easier than nitrogen and phosphorus, but more difficult than boron. This finding allows a tailoring of the Si content and photoluminescence intensity of SiV centers in in situ doped CVD diamond.

  8. Highly conductive homoepitaxial Si-doped Ga2O3 films on (010) β-Ga2O3 by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Leedy, Kevin D.; Chabak, Kelson D.; Vasilyev, Vladimir; Look, David C.; Boeckl, John J.; Brown, Jeff L.; Tetlak, Stephen E.; Green, Andrew J.; Moser, Neil A.; Crespo, Antonio; Thomson, Darren B.; Fitch, Robert C.; McCandless, Jonathan P.; Jessen, Gregg H.

    2017-07-01

    Si-doped Ga2O3 thin films were fabricated by pulsed laser deposition on semi-insulating (010) β-Ga2O3 and (0001) Al2O3 substrates. Films deposited on β-Ga2O3 showed single crystal, homoepitaxial growth as determined by high resolution transmission electron microscopy and x-ray diffraction. Corresponding films deposited on Al2O3 were mostly single phase, polycrystalline β-Ga2O3 with a preferred (20 1 ¯ ) orientation. An average conductivity of 732 S cm-1 with a mobility of 26.5 cm2 V-1 s-1 and a carrier concentration of 1.74 × 1020 cm-3 was achieved for films deposited at 550 °C on β-Ga2O3 substrates as determined by Hall-Effect measurements. Two orders of magnitude improvement in conductivity were measured using native substrates versus Al2O3. A high activation efficiency was obtained in the as-deposited condition. The high carrier concentration Ga2O3 thin films achieved by pulsed laser deposition enable application as a low resistance ohmic contact layer in β-Ga2O3 devices.

  9. Layering

    NASA Image and Video Library

    2011-04-01

    At the bottom of this image from NASA Mars Odyssey is the cliff-face that is the sidewall of Ophir Chasma. Layering is easily visible in the upper cliff wall, with the thickness of the surface clearly visible.

  10. Nanoscale conductive pattern of the homoepitaxial AlGaN/GaN transistor

    NASA Astrophysics Data System (ADS)

    Pérez-Tomás, A.; Catalàn, G.; Fontserè, A.; Iglesias, V.; Chen, H.; Gammon, P. M.; Jennings, M. R.; Thomas, M.; Fisher, C. A.; Sharma, Y. K.; Placidi, M.; Chmielowska, M.; Chenot, S.; Porti, M.; Nafría, M.; Cordier, Y.

    2015-03-01

    The gallium nitride (GaN)-based buffer/barrier mode of growth and morphology, the transistor electrical response (25-310 °C) and the nanoscale pattern of a homoepitaxial AlGaN/GaN high electron mobility transistor (HEMT) have been investigated at the micro and nanoscale. The low channel sheet resistance and the enhanced heat dissipation allow a highly conductive HEMT transistor (Ids > 1 A mm-1) to be defined (0.5 A mm-1 at 300 °C). The vertical breakdown voltage has been determined to be ˜850 V with the vertical drain-bulk (or gate-bulk) current following the hopping mechanism, with an activation energy of 350 meV. The conductive atomic force microscopy nanoscale current pattern does not unequivocally follow the molecular beam epitaxy AlGaN/GaN morphology but it suggests that the FS-GaN substrate presents a series of preferential conductive spots (conductive patches). Both the estimated patches density and the apparent random distribution appear to correlate with the edge-pit dislocations observed via cathodoluminescence. The sub-surface edge-pit dislocations originating in the FS-GaN substrate result in barrier height inhomogeneity within the HEMT Schottky gate producing a subthreshold current.

  11. Low temperature homoepitaxy of GaN structures by Vapor Liquid Solid transport

    NASA Astrophysics Data System (ADS)

    Jaud, Alexandre; Auvray, Laurent; Kahouli, Abdelkarim; Abi-Tannous, Tony; Linas, Sébastien; Ferro, Gabriel; Brylinski, Christian

    2017-06-01

    Low temperature (500-800 °C) homoepitaxy of not intentionally doped GaN structures on GaN(0 0 0 1)/Si(1 1 1) seed has been investigated by Vapor-Liquid-Solid (VLS) approach. The growth sequence consists in the metalorganic chemical vapor deposition of a network of submicrometric liquid Ga droplets, followed by their nitridation under flowing ammonia diluted either in H2 or Ar. When nitridation is performed under Ar carrier gas, GaN growth is very difficult to control due to too high N supersaturation within the droplets, despite very low NH3 flows. Nucleation and growth at the droplets periphery are always favored and, in most cases, high growth rates induce a crust-like growth, forming hollow GaN gangues. The use of H2 as carrier gas is detrimental to GaN (seed and grown material) stability, for nitridation temperatures ≥700 °C. But, compared to Ar atmosphere, a pronounced decrease of N supersaturation is demonstrated, allowing a better control of the growth mode. This is probably a consequence of a lower thermal decomposition efficiency of NH3 at the droplets surface. Optimal growth conditions are found at relatively low temperature (600 °C) and NH3 flow (20 sccm) for which a network of well-separated and faceted epitaxial GaN dots or rings is obtained. The growth mechanisms allowing these results are discussed.

  12. Nanoscale conductive pattern of the homoepitaxial AlGaN/GaN transistor.

    PubMed

    Pérez-Tomás, A; Catalàn, G; Fontserè, A; Iglesias, V; Chen, H; Gammon, P M; Jennings, M R; Thomas, M; Fisher, C A; Sharma, Y K; Placidi, M; Chmielowska, M; Chenot, S; Porti, M; Nafría, M; Cordier, Y

    2015-03-20

    The gallium nitride (GaN)-based buffer/barrier mode of growth and morphology, the transistor electrical response (25-310 °C) and the nanoscale pattern of a homoepitaxial AlGaN/GaN high electron mobility transistor (HEMT) have been investigated at the micro and nanoscale. The low channel sheet resistance and the enhanced heat dissipation allow a highly conductive HEMT transistor (Ids > 1 A mm(-1)) to be defined (0.5 A mm(-1) at 300 °C). The vertical breakdown voltage has been determined to be ∼850 V with the vertical drain-bulk (or gate-bulk) current following the hopping mechanism, with an activation energy of 350 meV. The conductive atomic force microscopy nanoscale current pattern does not unequivocally follow the molecular beam epitaxy AlGaN/GaN morphology but it suggests that the FS-GaN substrate presents a series of preferential conductive spots (conductive patches). Both the estimated patches density and the apparent random distribution appear to correlate with the edge-pit dislocations observed via cathodoluminescence. The sub-surface edge-pit dislocations originating in the FS-GaN substrate result in barrier height inhomogeneity within the HEMT Schottky gate producing a subthreshold current.

  13. Sequential pulsed laser deposition of homoepitaxial SrTiO3 thin films

    NASA Astrophysics Data System (ADS)

    Groenendijk, D. J.; Gariglio, S.

    2016-12-01

    The control of thin film stoichiometry is of primary relevance to achieve desired functionality. Pulsed laser deposition ablating from binary-oxide targets (sequential deposition) can be applied to precisely control the film composition, offsetting the importance of growth conditions on the film stoichiometry. In this work, we demonstrate that the cation stoichiometry of SrTiO3 thin films can be finely tuned by sequential deposition from SrO and TiO2 targets. Homoepitaxial SrTiO3 films were deposited at different substrate temperatures and Ti/Sr pulse ratios, allowing the establishment of a growth window for stoichiometric SrTiO3. The growth kinetics and nucleation processes were studied by reflection high-energy electron diffraction and atomic force microscopy, providing information about the growth mode and the degree of off-stoichiometry. At the optimal (stoichiometric) growth conditions, films exhibit atomically flat surfaces, whereas off-stoichiometry is accommodated by crystal defects, 3D islands, and/or surface precipitates depending on the substrate temperature and the excess cation. This technique opens the way to precisely control stoichiometry and doping of oxide thin films.

  14. Hetero- and homo-epitaxial growth of III-nitride based junctions and devices by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Sampath, Anand Venktesh

    2002-01-01

    nucleation conditions, while Ga-polar films are deposited directly on the latter without the use of buffer layers. GaN films of both polarities were doped p-type using Mg, but Ga-polar material is observed to dope more efficiently than N-polar material under Ga-rich conditions. The n-type doping of AlxGa1-xN alloys containing up to 50% AlN mole fraction has been explored and it is found that up to 50% AlGaN alloys can be doped degenerately to ˜1019 cm -3. A number photodetectors and power electronic devices have been fabricated based on these materials. Schottky diodes have been fabricated based on homoepitaxial growth of GaN by MBE on GaN templates grown by hydride vapor phase epitaxy (HVPE) on c-plane sapphire substrates. Photodetectors based on these materials have high quantum efficiency, 70%. GaN pn junctions fabricated by depositing a p-GaN layer on similar GaN templates show reduced leakage current in comparison to heteroepitaxially grown devices. A number of high power rectifiers have been fabricated by depositing n-GaN films on p-type epitaxial SiC. These heterojunctions have a very large breakdown (>830 V) and good ideality. A number of pnpn thyristor structures have been fabricated for application as optically gated switches. These devices show forward breakover voltage of 14V without requiring any rapid thermal annealing. The holding current and voltage for these devices was found to be 11 mA and 2 V.

  15. Silicon surface passivation by metal layers for low-temperature epitaxy

    NASA Astrophysics Data System (ADS)

    Kühnle, Jürgen; Bergmann, Ralf; Werner, Jürgen H.; Albrecht, Martin

    1996-06-01

    A novel surface passivation technique permits low-temperature homoepitaxy of Si above the stability limit (450°C) of a conventional hydrogen passivation. An evaporated metal film replaces the hydrogen passivation by a more stable metal layer and thus allows for epitaxial growth up to 570°C. Our passivation by a metal layer (PAMELA) technique is particularly suitable for liquid phase epitaxy.

  16. Homoepitaxial "Web Growth" of SiC to Terminate C-Axis Screw Dislocations and Enlarge Step-Free Surfaces

    NASA Technical Reports Server (NTRS)

    Neudeck, Philip G.; Powell, J. Anthony; Trunek, Andrew; Spry, David; Beheim, Glenn M.; Benavage, Emye; Abel, Phillip; Vetter, William M.; Dudley, Michael

    2001-01-01

    Homoepitaxial CVD growth of thin lateral cantilevers emanating from the edges of mesa patterns dry-etched into on-axis commercial 4H-SiC substrates prior to growth is reported. Cantilevers on the order of a micrometer thick extending tens of micrometers from the edge of a mesa have been grown. The termination of vertically propagating screw dislocations, including a micropipe, that are overgrown by the cantilevers has been demonstrated, in large part because the crystal structure of the cantilevers is established laterally from the mesa sidewalls. This technique could help reduce performance-degrading dislocations in SiC electrical devices.

  17. Improving optical performance of GaN nanowires grown by selective area growth homoepitaxy: Influence of substrate and nanowire dimensions

    NASA Astrophysics Data System (ADS)

    Aseev, P.; Gačević, Ž.; Torres-Pardo, A.; González-Calbet, J. M.; Calleja, E.

    2016-06-01

    Series of GaN nanowires (NW) with controlled diameters (160-500 nm) and heights (420-1100 nm) were homoepitaxially grown on three different templates: GaN/Si(111), GaN/AlN/Si(111), and GaN/sapphire(0001). Transmission electron microscopy reveals a strong influence of the NW diameter on dislocation filtering effect, whereas photoluminescence measurements further relate this effect to the GaN NWs near-bandgap emission efficiency. Although the templates' quality has some effects on the GaN NWs optical and structural properties, the NW diameter reduction drives the dislocation filtering effect to the point where a poor GaN template quality becomes negligible. Thus, by a proper optimization of the homoepitaxial GaN NWs growth, the propagation of dislocations into the NWs can be greatly prevented, leading to an exceptional crystal quality and a total dominance of the near-bandgap emission over sub-bandgap, defect-related lines, such as basal stacking faults and so called unknown exciton (UX) emission. In addition, a correlation between the presence of polarity inversion domain boundaries and the UX emission lines around 3.45 eV is established.

  18. Improving optical performance of GaN nanowires grown by selective area growth homoepitaxy: Influence of substrate and nanowire dimensions

    SciTech Connect

    Aseev, P. E-mail: gacevic@isom.upm.es; Gačević, Ž. E-mail: gacevic@isom.upm.es; Calleja, E.

    2016-06-20

    Series of GaN nanowires (NW) with controlled diameters (160–500 nm) and heights (420–1100 nm) were homoepitaxially grown on three different templates: GaN/Si(111), GaN/AlN/Si(111), and GaN/sapphire(0001). Transmission electron microscopy reveals a strong influence of the NW diameter on dislocation filtering effect, whereas photoluminescence measurements further relate this effect to the GaN NWs near-bandgap emission efficiency. Although the templates' quality has some effects on the GaN NWs optical and structural properties, the NW diameter reduction drives the dislocation filtering effect to the point where a poor GaN template quality becomes negligible. Thus, by a proper optimization of the homoepitaxial GaN NWs growth, the propagation of dislocations into the NWs can be greatly prevented, leading to an exceptional crystal quality and a total dominance of the near-bandgap emission over sub-bandgap, defect-related lines, such as basal stacking faults and so called unknown exciton (UX) emission. In addition, a correlation between the presence of polarity inversion domain boundaries and the UX emission lines around 3.45 eV is established.

  19. LETTER TO THE EDITOR: Homoepitaxial diamond films on diamond anvils with metallic probes: the diamond/metal interface up to 74 GPa

    NASA Astrophysics Data System (ADS)

    Catledge, Shane A.; Vohra, Yogesh K.; Weir, Samuel T.; Akella, Jagan

    1997-02-01

    A (100)-oriented natural type-Ia brilliant-cut diamond anvil with thin zirconium electrical probes sputtered onto the culet was coated with an insulating film of diamond using microwave-plasma-enhanced chemical vapour deposition (MPCVD). The critical issue in this high-pressure study is the quality of the homoepitaxial diamond film and its correlation with the mechanical strength of the diamond film/metallic probe interface. We report the first high-pressure study on a homoepitaxial diamond film and underlying zirconium probes to a pressure of 74 GPa. The metallic probes were observed through a transparent lithium fluoride sample with ruby serving as a pressure sensor. After decompression, Raman spectroscopy revealed that the homoepitaxial film was free from deformation and delamination despite the presence of some 0953-8984/9/7/001/img7-bonded carbon at the Zr/diamond interface and within the bulk of the film itself. The present study demonstrates that the presence of residual defects and graphitic impurities has no significant effect on high-pressure applications of homoepitaxial diamond films. This opens up new areas of research with diamond anvil cell devices including those of ohmic heating and electrical transport measurements at ultra-high pressures.

  20. Low-temperature halo-carbon homoepitaxial growth of 4H-silicon carbide

    NASA Astrophysics Data System (ADS)

    Lin, Huang-De

    New halo-carbon precursor, CH3Cl, is used in this work to replace the traditional C3H8 gas as a carbon precursor for the homoepitaxial growth of 4H-SiC. The traditional SiH4-C 3H8-H2 systems require high growth temperatures to enable the desirable step-flow growth for high-quality epilayers. A well known problem of the regular-temperature growth is the homogeneous gas-phase nucleation caused by SiH4 decomposition. However, the degree of Si cluster formation in the gas phase and its influence on our low-temperature epitaxial growth was unknown prior to this work. Growth at temperatures below 1400°C was demonstrated previously only for a limited range of substrate surface orientations and with poor quality. Mirror-like epilayer surface without foreign polytype inclusions and with rare surface defects was demonstrated at temperatures down to 1280-1300°C for our halo-carbon growth. Quantitatively different growth-rate dependences on the carbon-precursor flow rate suggested different precursor decomposition kinetics and different surface reactions in CH3Cl and C3H 8 systems. Photoluminescence measurement indicated the high quality of the epilayers grown at 1300°C. A mirror-like surface morphology with rare surface defects was demonstrated for the growth on low off-axis substrates at 1380°C. The most critical growth-rate limiting mechanism during the low-temperature epitaxial growth is the formation of Si clusters, which depleted the Si supply to the growth surface, in the gas phase. Presence of chlorine in the CH 3Cl precursor significantly reduces but does not completely eliminate this problem. The addition of HCl during growths improved the growth rate and surface morphology drastically but also brought up some complex results, suggesting more complex mechanisms of HCl interaction with the gas-phase clusters. These complicated results were explained partly by an additional mechanism of precursor depletion enhanced in presence of HCl. Complex changes in the

  1. Homoepitaxial and Heteroepitaxial Growth on Step-Free SiC Mesas

    NASA Technical Reports Server (NTRS)

    Neudeck, Philip G.; Powell, J. Anthony

    2004-01-01

    This article describes the initial discovery and development of new approaches to SiC homoepitaxial and heteroepitaxial growth. These approaches are based upon the previously unanticipated ability to effectively supress two-dimensional nucleation of 3C-SiC on large basal plane terraces that form between growth steps when epitaxy is carried out on 4H- and 6H-SiC nearly on-axis substrates. After subdividing the growth surface into mesa regions, pure stepflow homoeptixay with no terrace nucleation was then used to grow all existing surface steps off the edges of screw-dislocation-free mesas, leaving behind perfectly on-axis (0001) basal plane mesa surfaces completely free of atomic-scale steps. Step-free mesa surfaces as large as 0.4 mm x 0.4 mm were experimentally realized, with the yield and size of step-free mesas being initally limited by substrate screw dislocations. Continued epitaxial growth following step-free surface formation leads to the formation of thin lateral cantilevers that extend the step-free surface area from the top edge of the mesa sidewalls. By selecting a proper pre-growth mesa shape and crystallographic orientation, the rate of cantilever growth can be greatly enhanced in a web growth process that has been used to (1) enlarge step-free surface areas and (2) overgrow and laterally relocate micropipes and screw dislocations. A new growth process, named step-free surface heteroepitaxy, has been developed to achieve 3C-SiC films on 4H- and 6H-SiC substrate mesas completely free of double positioning boundary and stacking fault defects. The process is based upon the controlled terrace nucleation and lateral expansion of a single island of 3C-SiC across a step-free mesa surface. Experimental results indicate that substrateepilayer lattice mismatch is at least partially relieved parallel to the interface without dislocations that undesirably thread through the thickness of the epilayer. These results should enable realization of improved Si

  2. Photo Electron Paramagnetic Resonance (Photo EPR) Study of Trapping and Recombination Processes in Semi-Insulating 4H, 6H Sic Crystals Over a Wide Temperature Interval

    DTIC Science & Technology

    2004-07-02

    Proceedings of the ICDS22 (Physica B) accepted. 12. J.S. Blakemore , " Semiconductor Statistics " (Dover Publications, Inc. New York, 1987). STCU...electronic and optical devices. The Institute for Semiconductor Physics, with more than 15 years of experience in semiconductor material analysis, is...levels are among the most important processes in semiconductor physics and technology. An understanding of these processes is essential for device

  3. On the phase shift of reflection high energy electron diffraction intensity oscillations during Ge(001) homoepitaxy by molecular beam epitaxy

    SciTech Connect

    Shin Byungha; Leonard, John P.; McCamy, James W.; Aziz, Michael J.

    2007-03-15

    The authors have conducted a systematic investigation of the phase shift of the reflection high energy electron diffraction (RHEED) intensity oscillations during homoepitaxy of Ge(001) by molecular beam epitaxy for a wide range of diffraction conditions. Their results show that for small incidence angles with a beam azimuth several degrees away from the <110> crystallographic symmetry direction, the phase is independent of incidence angle; however, it starts to shift once the incidence angle is high enough that the (004) Kikuchi line appears in the RHEED pattern. Moreover, under some conditions they observe the oscillations from only the Kikuchi feature and not from the specular spot, and the oscillatory behavior of the Kikuchi feature is almost out of phase with that of the specular spot. They conclude that the phase shift is caused by the overlap of the specular spot and the Kikuchi features, in contrast to models involving dynamical scattering theory for the phase shift. They discuss necessary conditions for avoiding interference.

  4. Interplay of point defects, biaxial strain, and thermal conductivity in homoepitaxial SrTiO{sub 3} thin films

    SciTech Connect

    Wiedigen, S.; Kramer, T.; Knorr, I.; Nee, N.; Hoffmann, J.; Volkert, C. A.; Jooss, Ch.; Feuchter, M.; Kamlah, M.

    2012-02-06

    Separating out effects of point defects and lattice strain on thermal conductivity is essential for improvement of thermoelectric properties of SrTiO{sub 3}. We study relations between defects generated during deposition, induced lattice strain, and their impact on thermal conductivity {kappa} in homoepitaxial SrTiO{sub 3} films prepared by ion-beam sputtering. Lowering the deposition temperature gives rise to lattice expansion by enhancement of point defect density which increases the hardness of the films. Due to a fully coherent substrate-film interface, the lattice misfit induces a large biaxial strain. However, we can show that the temperature dependence of {kappa} is mainly sensitive on the defect concentration.

  5. Effects of hydrogen addition and growth-etch cycling on the oxy-acetylene torch deposition of homoepitaxial diamond

    NASA Astrophysics Data System (ADS)

    Weimer, R. A.; Thorpe, T. P.; Snail, K. A.; Merzbacher, C. E.

    1995-09-01

    Homoepitaxial diamond films were deposited onto (110) single crystal substrates using oxy-acetylene torch deposition at a constant substrate temperature of 1150 °C. Growth-etch cycling of the deposition increased the linear growth rates of the (100) and (111) faces by a factor of 2. The growth-etch films were shown to be less transparent in the infrared than the reference depositions as determined by microfocus Fourier transform infrared spectroscopy. Using the growth-etch technique, the growth rates of the (100), (111), and (110) faces decreased with increasing hydrogen addition to the combustion flame for hydrogen flow rates up to 50% of the acetylene flow rate. The additional hydrogen did not improve the growth-etch films' transparency.

  6. As-pressure influence on the surface corrugation in the homoepitaxial growth of GaAs (6 3 1)A

    NASA Astrophysics Data System (ADS)

    Cruz-Hernández, E.; Shimomura, S.; López-López, M.; Vázquez-Cortes, D.; Méndez-García, V. H.

    2011-02-01

    The achievement of defect-free and highly uniform semiconductor quantum wires is a projected goal with many potential applications. In this article, we report on the homoepitaxy of GaAs on (6 3 1)A-oriented substrates grown by molecular beam epitaxy (MBE) as a function of the As 4 pressure ( PAs). By finding the optimal growth conditions that allow the minimization of intrinsic surface free energy on the substrate and the PAs value, which results in the optimal adatoms diffusion, we were able to realize the outstanding formation of a periodic array of parallel straight nano facets. An analysis of the autocorrelation function is presented, which can be used to quantitatively describe the periodic surface corrugation, and to investigate the optimal growth conditions. We review the thermodynamic and kinetic factors that contribute to the faceting process and discuss how, by reducing the kinetic influence in the growth process, we can promote homogeneous faceting on high-index substrates.

  7. Lattice location of phosphorus in n-type homoepitaxial diamond films grown by chemical-vapor deposition

    NASA Astrophysics Data System (ADS)

    Hasegawa, Masataka; Teraji, Tokuyuki; Koizumi, Satoshi

    2001-11-01

    The lattice location of phosphorus dopant atoms in n-type homoepitaxial diamond {111} films grown by chemical-vapor deposition has been investigated by Rutherford backscattering spectrometry and particle-induced x-ray emission under ion-channeling conditions. It is found that phosphorus dopant atoms occupy the substitutional sites almost completely in the host diamond lattice. The substitutional fraction of phosphorus was more than 0.9 for <011> and <111> directions. Present observation implies that the deep ground-state energy level of phosphorus in diamond, which is at 0.6 eV below the bottom of the conduction band, is attributed to the relaxation of surrounding carbon atoms.

  8. In-situ x-ray scattering investigation of strain in thin-film morphological evolution of homoepitaxial Ag(001)

    NASA Astrophysics Data System (ADS)

    Hayden, S. T.; Kim, C.; Conrad, E. H.; Gramlich, M. W.; Miceli, P. F.

    2010-03-01

    Because it escapes detection in most experimental probes of surfaces, the role of strain during film growth has not been widely investigated. However, large strain fields arise from vacancy nano-clusters [C. Kim et al., APL 91, 093131 (2007)] that can be incorporated during film growth at lower temperatures. It has also been suggested that extreme surface morphologies, resulting from a deposition flux at grazing angles, might lead to significant strain [Y. Shim et. al., PRL 101, 11601 (2008)]. Because of its simultaneous sensitivity to both the surface and the subsurface, x-ray scattering is a particularly valuable technique for exploring the role of strain in epitaxial crystal growth. This talk will discuss our recent in-situ x-ray diffuse scattering and reflectivity measurements, performed at the Advanced Photon Source, which investigate the low temperature homoepitaxial growth of Ag(001).

  9. Confinement of Screw Dislocations to Predetermined Lateral Positions in (0001) 4H-SiC Epilayers Using Homoepitaxial Web Growth

    NASA Technical Reports Server (NTRS)

    Neudeck, Philip G.; Spry, Andrew J.; Trunek, Andrew J.; Powell, J. Anthony; Beheim, Glenn M.

    2002-01-01

    This paper reports initial demonstration of a cantilevered homoepitaxial growth process that places screw dislocations at predetermined lateral positions in on-axis 4H-SiC mesa epilayers. Thin cantilevers were grown extending toward the interior of hollow pre-growth mesa shapes etched into an on-axis 4H-SiC wafer, eventually completely coalescing to form roofed cavities. Each completely coalesced cavity exhibited either: 1) a screw dislocation growth spiral located exactly where final cantilever coalescence occurred, or 2) no growth spiral. The fact that growth spirals are not observed at any other position except the central coalescence point suggests that substrate screw dislocations, initially surrounded by the hollow portion of the pre-growth mesa shape, are relocated to the final coalescence point of the webbed epilayer roof. Molten potassium hydroxide etch studies revealed that properly grown webbed cantilevers exhibited no etch pits, confirming the superior crystal quality of the cantilevers.

  10. Properties of the State of the Art of Bulk III-V Nitride Substrates and Homoepitaxial Layers

    DTIC Science & Technology

    2010-01-01

    Schwalter L J, Susterman Y, Wang R, Bhat I, Arunmozhi G and Slack G A 2000 Appl. Phys. Lett. 76 985 [25] Schwalter L J, Rojo J C, Slack G A, Susterman Y...Wang R, Bhat I and Arunmozhi G 2000 J. Cryst. Growth 211 78 [26] Rojo J C, Slack G A, Morgan K, Raghothamachar B, Dudley M and Schwalter L J 2000 J

  11. Seed layer technique for high quality epitaxial manganite films.

    PubMed

    Graziosi, P; Gambardella, A; Calbucci, M; O'Shea, K; MacLaren, D A; Riminucci, A; Bergenti, I; Fugattini, S; Prezioso, M; Homonnay, N; Schmidt, G; Pullini, D; Busquets-Mataix, D; Dediu, V

    2016-08-01

    We introduce an innovative approach to the simultaneous control of growth mode and magnetotransport properties of manganite thin films, based on an easy-to-implement film/substrate interface engineering. The deposition of a manganite seed layer and the optimization of the substrate temperature allows a persistent bi-dimensional epitaxy and robust ferromagnetic properties at the same time. Structural measurements confirm that in such interface-engineered films, the optimal properties are related to improved epitaxy. A new growth scenario is envisaged, compatible with a shift from heteroepitaxy towards pseudo-homoepitaxy. Relevant growth parameters such as formation energy, roughening temperature, strain profile and chemical states are derived.

  12. Seed layer technique for high quality epitaxial manganite films

    NASA Astrophysics Data System (ADS)

    Graziosi, P.; Gambardella, A.; Calbucci, M.; O'Shea, K.; MacLaren, D. A.; Riminucci, A.; Bergenti, I.; Fugattini, S.; Prezioso, M.; Homonnay, N.; Schmidt, G.; Pullini, D.; Busquets-Mataix, D.; Dediu, V.

    2016-08-01

    We introduce an innovative approach to the simultaneous control of growth mode and magnetotransport properties of manganite thin films, based on an easy-to-implement film/substrate interface engineering. The deposition of a manganite seed layer and the optimization of the substrate temperature allows a persistent bi-dimensional epitaxy and robust ferromagnetic properties at the same time. Structural measurements confirm that in such interface-engineered films, the optimal properties are related to improved epitaxy. A new growth scenario is envisaged, compatible with a shift from heteroepitaxy towards pseudo-homoepitaxy. Relevant growth parameters such as formation energy, roughening temperature, strain profile and chemical states are derived.

  13. Seed layer technique for high quality epitaxial manganite films

    PubMed Central

    Graziosi, P.; Gambardella, A.; Calbucci, M.; O’Shea, K.; MacLaren, D. A.; Bergenti, I.; Homonnay, N.; Schmidt, G.; Pullini, D.; Busquets-Mataix, D.; Dediu, V.

    2016-01-01

    We introduce an innovative approach to the simultaneous control of growth mode and magnetotransport properties of manganite thin films, based on an easy-to-implement film/substrate interface engineering. The deposition of a manganite seed layer and the optimization of the substrate temperature allows a persistent bi-dimensional epitaxy and robust ferromagnetic properties at the same time. Structural measurements confirm that in such interface-engineered films, the optimal properties are related to improved epitaxy. A new growth scenario is envisaged, compatible with a shift from heteroepitaxy towards pseudo-homoepitaxy. Relevant growth parameters such as formation energy, roughening temperature, strain profile and chemical states are derived. PMID:27648371

  14. Comparison of morphology evolution of Ge(001) homoepitaxial films grown by pulsed laser deposition and molecular-beam epitaxy

    SciTech Connect

    Shin Byungha; Leonard, John P.; McCamy, James W.; Aziz, Michael J.

    2005-10-31

    Using a dual molecular-beam epitaxy (MBE)-pulsed laser deposition (PLD) ultrahigh vacuum chamber, we have conducted the first experiments under identical thermal, background, and surface preparation conditions to compare Ge(001) homoepitaxial growth morphology in PLD and MBE. We find that in PLD with low kinetic energy and in MBE the film morphology evolves in a similar fashion: initially irregularly shaped mounds form, followed by pyramidal mounds with edges of the square-base along the <100> directions; the film roughness and mound separation increase with film thickness. In PLD with high kinetic energy, well-defined pyramidal mounds are not observed and the morphology rather resembles that of an ion-etched Ge(001) surface. The areal feature density is higher for PLD films than for MBE films grown at the same average growth rate and temperature. Furthermore, the dependence upon film thickness of roughness and feature separation differ for PLD and MBE. We attribute these differences to the higher yield of defect generation by energetic species in PLD.

  15. Growth control of oxygen stoichiometry in homoepitaxial SrTiO3 films by pulsed laser epitaxy in high vacuum.

    PubMed

    Lee, Ho Nyung; Ambrose Seo, Sung S; Choi, Woo Seok; Rouleau, Christopher M

    2016-01-29

    In many transition metal oxides, oxygen stoichiometry is one of the most critical parameters that plays a key role in determining the structural, physical, optical, and electrochemical properties of the material. However, controlling the growth to obtain high quality single crystal films having the right oxygen stoichiometry, especially in a high vacuum environment, has been viewed as a challenge. In this work, we show that, through proper control of the plume kinetic energy, stoichiometric crystalline films can be synthesized without generating oxygen defects even in high vacuum. We use a model homoepitaxial system of SrTiO3 (STO) thin films on single crystal STO substrates. Physical property measurements indicate that oxygen vacancy generation in high vacuum is strongly influenced by the energetics of the laser plume, and it can be controlled by proper laser beam delivery. Therefore, our finding not only provides essential insight into oxygen stoichiometry control in high vacuum for understanding the fundamental properties of STO-based thin films and heterostructures, but expands the utility of pulsed laser epitaxy of other materials as well.

  16. Growth control of oxygen stoichiometry in homoepitaxial SrTiO3 films by pulsed laser epitaxy in high vacuum

    DOE PAGES

    Lee, Ho Nyung; Ambrose Seo, Sung S.; Choi, Woo Seok; ...

    2016-01-29

    In many transition metal oxides, oxygen stoichiometry is one of the most critical parameters that plays a key role in determining the structural, physical, optical, and electrochemical properties of the material. However, controlling the growth to obtain high quality single crystal films having the right oxygen stoichiometry, especially in a high vacuum environment, has been viewed as a challenge. In this work, we show that, through proper control of the plume kinetic energy, stoichiometric crystalline films can be synthesized without generating oxygen defects even in high vacuum. We use a model homoepitaxial system of SrTiO3 (STO) thin films on singlemore » crystal STO substrates. Physical property measurements indicate that oxygen vacancy generation in high vacuum is strongly influenced by the energetics of the laser plume, and it can be controlled by proper laser beam delivery. Thus, our finding not only provides essential insight into oxygen stoichiometry control in high vacuum for understanding the fundamental properties of STO-based thin films and heterostructures, but it expands the utility of pulsed laser epitaxy of other materials as well.₃« less

  17. Analytic formulations for one-dimensional decay of rectangular homoepitaxial islands during coarsening on anisotropic fcc (110) surfaces

    SciTech Connect

    Wang, Chi-Jen; Han, Yong; Walen, Holly; Russell, Selena M.; Thiel, Patricia A.; Evans, James W.

    2013-10-01

    Submonolayer homoepitaxial fcc (110) systems display behavior reflecting strong anisotropy at lower temperatures, including one-dimensional decay during Ostwald ripening of rectangular islands maintaining constant width in the (001) direction. To appropriately describe this behavior, we first develop a refined continuum Burton-Cabrera-Frank formalism, which accounts for a lack of equilibration of island shape and importantly also for inhibited incorporation of adatoms at almost-faceted (1¯10) island edges through effective kinetic coefficients. This formalism is shown to describe accurately the adatom diffusion fluxes between islands and thus island evolution for a complex experimental island configuration, as confirmed by matching results from realistic atomistic simulations for this configuration. This approach also elucidates basic dependencies of flux on island geometry and temperature. Second, a further refinement is presented incorporating separate terrace and edge adatom density fields either in a continuum setting or alternatively in a spatially discrete diffusion equation setting. The second approach allows more flexibility and accuracy in accounting for edge-diffusion kinetics including corner rounding, a lack of equilibration of the edge adatom density at (1¯10) island edges, and the effect of rare kinks on (1¯10) island edges. Finally and significantly, it suggests facile two-way corner rounding at the island periphery during island decay, contrasting the previous picture.

  18. Growth control of oxygen stoichiometry in homoepitaxial SrTiO3 films by pulsed laser epitaxy in high vacuum

    PubMed Central

    Lee, Ho Nyung; Ambrose Seo, Sung S.; Choi, Woo Seok; Rouleau, Christopher M.

    2016-01-01

    In many transition metal oxides, oxygen stoichiometry is one of the most critical parameters that plays a key role in determining the structural, physical, optical, and electrochemical properties of the material. However, controlling the growth to obtain high quality single crystal films having the right oxygen stoichiometry, especially in a high vacuum environment, has been viewed as a challenge. In this work, we show that, through proper control of the plume kinetic energy, stoichiometric crystalline films can be synthesized without generating oxygen defects even in high vacuum. We use a model homoepitaxial system of SrTiO3 (STO) thin films on single crystal STO substrates. Physical property measurements indicate that oxygen vacancy generation in high vacuum is strongly influenced by the energetics of the laser plume, and it can be controlled by proper laser beam delivery. Therefore, our finding not only provides essential insight into oxygen stoichiometry control in high vacuum for understanding the fundamental properties of STO-based thin films and heterostructures, but expands the utility of pulsed laser epitaxy of other materials as well. PMID:26823119

  19. Growth regimes during homoepitaxial growth of GaN by ammonia molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Corrion, A. L.; Wu, F.; Speck, J. S.

    2012-09-01

    c-plane GaN films were grown by ammonia molecular beam epitaxy on metal-organic chemical vapor deposition templates for a wide range of NH3:Ga flux ratios and growth temperatures, and the resulting films were characterized using atomic force microscopy, reflection high-energy electron diffraction, and transmission electron microscopy. Three distinct nitrogen-rich growth regimes—unstable layer-by-layer, quasi-stable step flow, and dislocation-mediated pitting—were identified based on the growth mode and film properties. In addition, step flow growth was observed under conditions of gallium droplet accumulation. The results indicate the existence of two regimes for step-flow growth of GaN by ammonia MBE—both gallium-rich and nitrogen-rich. Growth mode instabilities and mound formation were observed and are discussed in the context of a step-edge energy barrier to adatom diffusion over a terrace.

  20. Growth regimes during homoepitaxial growth of GaN by ammonia molecular beam epitaxy

    SciTech Connect

    Corrion, A. L.; Wu, F.; Speck, J. S.

    2012-09-01

    c-plane GaN films were grown by ammonia molecular beam epitaxy on metal-organic chemical vapor deposition templates for a wide range of NH{sub 3}:Ga flux ratios and growth temperatures, and the resulting films were characterized using atomic force microscopy, reflection high-energy electron diffraction, and transmission electron microscopy. Three distinct nitrogen-rich growth regimes - unstable layer-by-layer, quasi-stable step flow, and dislocation-mediated pitting - were identified based on the growth mode and film properties. In addition, step flow growth was observed under conditions of gallium droplet accumulation. The results indicate the existence of two regimes for step-flow growth of GaN by ammonia MBE - both gallium-rich and nitrogen-rich. Growth mode instabilities and mound formation were observed and are discussed in the context of a step-edge energy barrier to adatom diffusion over a terrace.

  1. Sintering of two-dimensional nanoclusters in metal(100) homoepitaxial systems: Deviations from predictions of Mullins continuum theory

    NASA Astrophysics Data System (ADS)

    Liu, Da-Jiang; Evans, J. W.

    2002-10-01

    We present a comparison of the predictions of atomistic and continuum models for the sintering of pairs of near-square two-dimensional nanoclusters adsorbed on the (100) surface in fcc metal homoepitaxial systems. Mass transport underlying these processes is dominated by periphery diffusion (PD) of adatoms along the edge of the clusters. A Mullins-type continuum model for cluster evolution incorporates anisotropy in the step edge stiffness (reflecting the energetics and adsorption site lattice structure in the atomistic model), and can also account for anisotropy in the step edge mobility (reflecting details of the kinetics). In such continuum treatments, the characteristic time τeq for relaxation of clusters with linear size of order L satisfies τeq~L4. Deviations may generally be expected for small sizes L or low temperatures T. However, for the relaxation of dumbbell-shaped clusters (formed by corner-to-corner coalescence of square clusters), atomistic simulations for PD with no kink rounding barrier (δ=0) reveal that τeq~L4 always applies. In contrast, atomistic simulations with a large kink rounding barrier (δ>0) reveal distinct scaling with τeq~L3, for low T or small L, thus providing an effective way to test for δ>0. For the relaxation of faceted rectangular clusters (formed by side-to-side coalescence of square clusters), atomistic simulations for PD with δ=0 reveal that τeq~L2, for low T or small L. This is consistent with a recent proposal by Combe and Larralde. For large δ>0, τeq has an even weaker dependence on L. We elucidate scaling behavior and the effective activation barrier for relaxation in terms of the individual atomistic PD processes and their barriers.

  2. Enlargement of Step-Free SiC Surfaces by Homoepitaxial Web-Growth of Thin SiC Cantilevers

    NASA Technical Reports Server (NTRS)

    Neudeck, Philip G.; Powell, J. Anthony; Beheim, Glenn M.; Benavage, Emye L.; Abel, Phillip B.; Trunek, Andrew J.; Spry, David J.; Dudley, Michael; Vetter, William M.

    2002-01-01

    Lateral homoepitaxial growth of thin cantilevers emanating from mesa patterns that were reactive ion etched into on-axis commercial SiC substrates prior to growth is reported. The thin cantilevers form after pure stepflow growth removes almost all atomic steps from the top surface of a mesa, after which additional adatoms collected by the large step-free surface migrate to the mesa sidewall where they rapidly incorporate into the crystal near the top of the mesa sidewall. The lateral propagation of the step-free cantilevered surface is significantly affected by pregrowth mesa shape and orientation, with the highest lateral expansion rates observed at the inside concave comers of V-shaped pregrowth mesas with arms lengthwise oriented along the {1100} direction. Complete spanning of the interiors of V's and other mesa shapes with concave comers by webbed cantilevers was accomplished. Optical microscopy, synchrotron white beam x-ray topography and atomic force microscopy analysis of webbed regions formed over a micropipe and closed-core screw dislocations show that c-axis propagation of these defects is terminated by the webbing. Despite the nonoptimized process employed in this initial study, webbed surfaces as large as 1.4 x 10(exp -3) square centimeters, more than four times the pregrowth mesa area, were grown. However, the largest webbed surfaces were not completely free of bilayer steps, due to unintentional growth of 3C-SiC that occurred in the nonoptimized process. Further process optimization should enable larger step-free webs to be realized.

  3. Electron beam induced current study of minority carrier diffusion length in homoepitaxial GaN (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Talin, A. Alec; Collins, Kimberlee C.; Armstrong, Andrew M.; Allerman, Andrew A.; Léonard, François

    2016-09-01

    GaN is a promising material for a range of high power, high frequency, and high temperature device applications. The wide bandgap of GaN leads to high breakdown voltages and low switching losses. Recently, large HVPE grown GaN substrates have become available for homoepitaxial growth leading to 103 reduction in dislocation density compared to similarly grown heteroepitaxial films. Device performance, however, is ultimately limited by the transport properties of minority carriers. Measured values for minority carrier diffusion lengths and lifetimes in GaN vary widely1-3, and a recent report suggests flaws in the commonly adopted electron beam induced current (EBIC) method in the planar-collection geometry.1 Here we report on EBIC measurements performed on 8 micrometer thick GaN grown by MOCVD on 2 inch GaN substrates with a n-type dopant density of 5×1016 cm-3. We determine the carrier diffusion length using both the conventional EBIC method by varying the electron beam-to-contact lateral distance as well as by varying the electron beam penetration depth and find the extracted values differ by 10×, with the latter technique yielding the lower diffusion length. We rationalize these results in light of other materials characteristics including Raman and photoluminescence. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

  4. Enlargement of Step-Free SiC Surfaces by Homoepitaxial Web-Growth of Thin SiC Cantilevers

    NASA Technical Reports Server (NTRS)

    Neudeck, Philip G.; Powell, J. Anthony; Beheim, Glenn M.; Benavage, Emye L.; Abel, Phillip B.; Trunek, Andrew J.; Spry, David J.; Dudley, Michael; Vetter, William M.

    2002-01-01

    Lateral homoepitaxial growth of thin cantilevers emanating from mesa patterns that were reactive ion etched into on-axis commercial SiC substrates prior to growth is reported. The thin cantilevers form after pure stepflow growth removes almost all atomic steps from the top surface of a mesa, after which additional adatoms collected by the large step-free surface migrate to the mesa sidewall where they rapidly incorporate into the crystal near the top of the mesa sidewall. The lateral propagation of the step-free cantilevered surface is significantly affected by pregrowth mesa shape and orientation, with the highest lateral expansion rates observed at the inside concave comers of V-shaped pregrowth mesas with arms lengthwise oriented along the {1100} direction. Complete spanning of the interiors of V's and other mesa shapes with concave comers by webbed cantilevers was accomplished. Optical microscopy, synchrotron white beam x-ray topography and atomic force microscopy analysis of webbed regions formed over a micropipe and closed-core screw dislocations show that c-axis propagation of these defects is terminated by the webbing. Despite the nonoptimized process employed in this initial study, webbed surfaces as large as 1.4 x 10(exp -3) square centimeters, more than four times the pregrowth mesa area, were grown. However, the largest webbed surfaces were not completely free of bilayer steps, due to unintentional growth of 3C-SiC that occurred in the nonoptimized process. Further process optimization should enable larger step-free webs to be realized.

  5. Defects and Impurities in 4H- and 6H-SiC Homoepitaxial Layers: Identification, Origin, Effect on Properties of Ohmic Contacts and Insulating Layers and Reduction.

    DTIC Science & Technology

    1997-03-01

    495 (1993). 6. M. Diani, D. Aubel, J.L. Bischoff, L. Kubier, and D. Bolmont, Surface Science 29, 110(1993). 7. G. R. Harp, D. K. Saldin , and B. P...Tonner, Phys. Rev. Lett. 65, 1012 (1990). 8. B. P. Tonner, Z. L. Han, G. R. Harp, and D. K. Saldin , Phys. Rev. B 43, 14423 (1991). 9. G. R. Harp, D...K. Saldin , and B. P. Tonner, Phys. Rev. B 42, 9199 (1990). 10. A. Stuck, D. Naumovic, H. A. Aebischer, T. Greber, J. Osterwalder, and L

  6. Atomic self-diffusion behaviors relevant to 2D homoepitaxy growth on stepped Pd(001) surface

    NASA Astrophysics Data System (ADS)

    Liu, Fusheng; Hu, Wangyu; Chen, Yifeng; Deng, Huiqiu; Chen, Han; Yang, Xiyuan; Luo, Wenhua

    2014-06-01

    Using molecular dynamics, nudged elastic band and modified analytic embedded atom methods, the diffusion behaviors of Pd adatom on stepped Pd(001) surface have been investigated. Lower than 975 K, Pd adatom just hops along the perfect [110]-direction step. The diffusion dynamics equation is derived from the Arrhenius law between 875 and 975 K, and the corresponding migration energy and prefactor are 0.76 eV and 5.2 × 10- 2 cm2/s respectively, which shows that they adhere to the step in case of adatom moving to the step. The adatom diffuses across the perfect step with an Ehrlich-Schwoebel barrier of 0.09 eV by exchange mechanism. Our calculations show the kink at step can markedly decrease the static energy barrier across the step with a negative Ehrlich-Schwoebel barrier, and it contributes to form layer-by-layer growth model in the epitaxial experiment. Our calculations show that the kink can also markedly improve the adatom's mass transport of interlayer, contributing to the formation of the compact film. Lastly, a quantitative result at 300 K shows that the kink affects tremendously the diffusion mobility of adatom near it, which indicates that the kink plays a key role in the formation of the compact and uniform film on Pd(001) surface in an epitaxial growth experiment.

  7. Mutual relation among lattice distortion, Hall effect property and band edge cathodoluminescence of heavily-boron-doped microwave-plasma CVD diamond films homoepitaxially grown on vicinal (001) high-pressure/high-temperature-synthesized Ib substrates

    NASA Astrophysics Data System (ADS)

    Mori, Reona; Maida, Osamu; Ito, Toshimichi

    2015-04-01

    We have investigated properties of heavily-B-doped diamond (HBD) films homoepitaxially grown with boron-to-carbon (B/C) mole ratios ranging from 1000 to 5000 ppm in the source gas mainly by using X-Ray diffraction (XRD), cathodoluminescence (CL), and Hall effect measurements. Each HBD layer was deposited on a vicinal (001) substrate of high-pressure/high-temperature synthesized Ib-type diamond with 5° misorientation angle by means of high-power-density microwave-plasma chemical-vapor-deposition method with a source gas composed of 4% CH4 in H2 and H2-diluted B(CH3)3. XRD data indicated that the lattice constant of the B-doped layer slightly decreased for the B/C ratios≤3000 ppm while slightly increasing for that of 5000 ppm, suggesting that for the latter HBD sample a part of the incorporated B atoms behaved differently from the remaining other B atoms. By contrast the Hall data indicated that all the HBD samples had a degenerate feature only at temperatures well below room temperature (RT), above which a semiconducting feature was evident, and that the density of the degenerate holes steeply increased from 1.3×1019 to 1.2×1021 cm-3 with increases in the incorporated B density, [B], from 1.2×1020 to 5.9×1020 cm-3. This drastic change in the hole density strongly suggested the presence of a [B]-dependent impurity band. Their evident near-band-edge CL spectra taken at RT and 85 K demonstrated that radiative transition features in the HBD layers considerably varied for the B/C ratios studied. The CL peaks were consistently assigned by assuming both the presence of an impurity band and a slight bandgap shrinkage. These observed features are discussed in relation to the energy separation between the low-mobility impurity band assumed and the valence band in the high-quality HBD layer which are not merged in energy.

  8. Homoepitaxial seeding and growth of bulk AlN by sublimation

    NASA Astrophysics Data System (ADS)

    Hartmann, Carsten; Wollweber, Jürgen; Seitz, Christoph; Albrecht, Martin; Fornari, Roberto

    2008-03-01

    AlN boules, 35 mm in diameter and up to 25-mm long, were grown on TaC crucible lid in an inductively heated reactor. The growth rates range between 100 and 300 μm/h. The boules grown on TaC show a columnar structure mostly composed of <0 0 0 1> grains. The largest grains (4-5 mm in diameter) were sliced and used for subsequent growth runs. Successful epitaxial seeding and growth on the starting AlN wafer was demonstrated and confirmed by electron back-scatter diffraction (EBSD) measurements. Crystals were grown on both Al and N surfaces of the seeds up to a maximum diameter of about 9 mm so far. Formation of oxy-nitride layers, very detrimental to the further AlN deposition, could be avoided when starting from pre-sintered source powder. Secondary ion mass spectroscopy (SIMS) measurements on axial cuts revealed a relatively low oxygen content, with variable distribution along the growth direction (290 ppm near seed, 100 ppm near external surface).

  9. Observations of Screw Dislocation Driven Growth and Faceting During CVD Homoepitaxy on 4H-SiC On-Axis Mesa Arrays

    NASA Technical Reports Server (NTRS)

    Neudeck, Philip G.; Trunek, Andrew J.; Powell, J. Anthony; Picard, Yoosuf N.; Twigg, Mark E.

    2009-01-01

    Previous studies of (0001) homoepitaxial growth carried out on arrays of small-area mesas etched into on-axis silicon-face 4H-SiC wafers have demonstrated that spiral growth emanating from at least one screw dislocation threading the mesa is necessary in order for a mesa to grow taller in the <0001> (c-axis vertical) direction while maintaining 4H stacking sequence [1]. However, even amongst mesas containing the screw dislocation step source necessary for vertical c-axis growth, we have observed striking differences in the height and faceting that evolve during prolonged homoepitaxial growths. This paper summarizes Atomic Force Microscopy (AFM), Electron Channeling Contrast Imaging (ECCI), Scanning Electron Microscopy (SEM), and optical microscopy observations of this phenomenon. These observations support our initially proposed model [2] that the observed large variation (for mesas where 3C-SiC nucleation has not occurred) is related to the lateral positioning of a screw dislocation step source within each etched mesa. When the screw dislocation step source is located close enough to the developing edge/sidewall facet of a mesa, the c-axis growth rate and facet angle are affected by the resulting interaction. In particular, the intersection (or near intersection) of the inward-sloping mesa sidewall facet with the screw dislocation appears to impede the rate at which the spiral provides new steps required for c-axis growth. Also, the inward slope of the sidewall facet during growth (relative to other sidewalls of the same mesa not near the screw dislocation) seems to be impeded by the screw dislocation. In contrast, mesas whose screw dislocations are centrally located grow vertically, but inward sloping sidewall facets shrink the area of the top (0001) growth surface almost to the point of vanishing.

  10. Step-structure dependent step-flow: models for the homoepitaxial growth at the atomic steps on Si(111)7 × 7

    NASA Astrophysics Data System (ADS)

    Shimada, Wataru; Tochihara, Hiroshi

    1994-05-01

    Step-flow models of homoepitaxial growth at atomic steps on Si(111)7 × 7 are considered within the framework of the dimer-adatom-stacking-fault (DAS) model with the aid of a scanning tunneling microscopy (STM) image published by Köhler, Demuth and Hamers [J. Vac. Sci. Technol. A 7 (1989) 2860]. The image was taken at room temperature for a surface epitaxially grown at 330°C. From the image around the growing step, we find that the step flow is separated into two processes; the initial growth on the end zone of the lower terrace where the (7 × 7) DAS reconstruction is not formed due to its insufficient space, and the subsequent growth where the (7 × 7) DAS reconstruction at the lower step-edge has to be canceled to grow epitaxially. For the initial growth we propose step-structure dependent step-flow models, according to our classification of the atomic steps. For the subsequent growth, in addition to our previously proposed model for the cancelation of the (7 × 7) DAS structure during homoepitaxial growth on terraces (termed as the coalescent destruction model), we postulate the following four guidelines to construct models. (i) The destruction of the faulted halves and dimers at lower step-edge is the rate-determining step for step-flow, (ii) The epitaxial growth on the unfaulted halves at the lower step-edge is rapid, (iii) The faulted half at the "macrokink" is much easier to be broken than that at the straight step. (iv) The advanced step grows faster than the receded step does. By using the guidelines and the coalescent destruction model, we propose models for the subsequent growth at the U and F steps whose outward normal of the risers are the [1¯1¯2] and [112¯] directions, respectively. As the step-flows proceed with increasing Si deposition, the proposed model naturally leads to the following change of macroscopic shapes of the atomic steps: The straight F step converts to a zigzag step consisting of the U steps, while the straight U step maintains

  11. Boron concentration profiling by high angle annular dark field-scanning transmission electron microscopy in homoepitaxial δ-doped diamond layers

    SciTech Connect

    Araújo, D.; Alegre, M. P.; Piñero, J. C.; Fiori, A.; Bustarret, E.; Jomard, F.

    2013-07-22

    To develop further diamond related devices, the concentration and spatial location of dopants should be controlled down to the nanometer scale. Scanning transmission electron microscopy using the high angle annular dark field mode is shown to be sensitive to boron doping in diamond epilayers. An analytical procedure is described, whereby local boron concentrations above 10{sup 20} cm{sup −3} were quantitatively derived down to nanometer resolution from the signal dependence on thickness and boron content. Experimental boron local doping profiles measured on diamond p{sup −}/p{sup ++}/p{sup −} multilayers are compared to macroscopic profiles obtained by secondary ion mass spectrometry, avoiding reported artefacts.

  12. Growth control of oxygen stoichiometry in homoepitaxial SrTiO3 films by pulsed laser epitaxy in high vacuum

    SciTech Connect

    Lee, Ho Nyung; Ambrose Seo, Sung S.; Choi, Woo Seok; Rouleau, Christopher M.

    2016-01-29

    In many transition metal oxides, oxygen stoichiometry is one of the most critical parameters that plays a key role in determining the structural, physical, optical, and electrochemical properties of the material. However, controlling the growth to obtain high quality single crystal films having the right oxygen stoichiometry, especially in a high vacuum environment, has been viewed as a challenge. In this work, we show that, through proper control of the plume kinetic energy, stoichiometric crystalline films can be synthesized without generating oxygen defects even in high vacuum. We use a model homoepitaxial system of SrTiO3 (STO) thin films on single crystal STO substrates. Physical property measurements indicate that oxygen vacancy generation in high vacuum is strongly influenced by the energetics of the laser plume, and it can be controlled by proper laser beam delivery. Thus, our finding not only provides essential insight into oxygen stoichiometry control in high vacuum for understanding the fundamental properties of STO-based thin films and heterostructures, but it expands the utility of pulsed laser epitaxy of other materials as well.₃

  13. Self-organized homo-epitaxial growth in nonlinear optical BaAlBO3F2 crystal crossing lines patterned by laser in glass

    NASA Astrophysics Data System (ADS)

    Shinozaki, K.; Abe, S.; Honma, T.; Komatsu, T.

    2015-11-01

    Crystallization processing of glasses is important as a novel technique for the development of new optical materials, and laser-induced crystallization provides a new challenge in science and technology of materials. Nonlinear optical BaAlBO3F2 crystal lines with crossing, bending, and spiral shapes were patterned at the surface of 2NiO-49BaF2-24.5Al2O3-24.5B2O3 (mol%) and 2.9NiO-48.5BaF2-24.3Al2O3-24.3B2O3 (mol%) glasses by laser irradiation (Yb:YVO4 laser with a wavelength of 1080 nm) and the orientation state of BaAlBO3F2 crystals was examined from birefringence image observations. The birefringence images indicate that the growth of highly c-axis oriented BaAlBO3F2 crystals follows along the laser scanning direction even if the laser scanning direction changes, and in particular the direction of the c-axis of BaAlBO3F2 crystals changes gradually at the crossing and bending points. The model of "self-organized homo-epitaxial growth" is proposed for the crystal orientation at the crossing and bending points, as a new crystal growth science and engineering beyond the wise providence of nature.

  14. Configuration of a single grown-in dislocation corresponding to one etch pit formed on the surface of CVD homoepitaxial diamond

    NASA Astrophysics Data System (ADS)

    Tsubouchi, Nobuteru; Mokuno, Yoshiaki

    2016-12-01

    We present a detailed crystalline structure around one etch pit formed on the as-grown surface of a (001)-oriented chemical vapor deposition (CVD) homoepitaxial single crystal diamond film investigated using cross-sectional transmission electron microscopy (TEM). One threading dislocation corresponding to one pit is found, and it is shown that this dislocation line continuously runs from the apex of the pit to the deeper region in the film toward the substrate. The observed threading dislocation directs parallel to the approximate [001] film-growth direction, but is not a perfect straight line and propagates in a zig-zag manner. The contrast analysis of the dislocation in TEM micrographs is performed under several major two-beam reflections. These results suggest that the dislocation is composed of short segments of undissociated perfect dislocations with Burgers vectors b=1/2[110], 1/2[011] and 1/2[101] lying on the {111} glide plane and, as a whole, travels approximately parallel to the [001] direction.

  15. Excitonic emission and N- and B-incorporation in homoepitaxial CVD-grown diamond investigated by cathodoluminescence

    NASA Astrophysics Data System (ADS)

    Araujo, D.; Kadri, M.; Wade, M.; Bustarret, E.; Deneuville, A.

    2005-03-01

    Diamond is a very large bandgap material arising high expectations either for optoelectronic applications or for active semiconducting layers in specific electronic devices to be used under extreme conditions of pressure, temperature, wear or radiation, as well as in chemically aggressive environments. Unintentionally boron-doped diamond layers were grown by microwave plasma-assisted chemical vapour deposition (CVD) on {001}-oriented undoped Ib substrates with the addition of oxygen gas during growth. The relative quantities of nitrogen and boron incorporated in the diamond lattice are evaluated by cathodoluminescence (CL) spectra recorded at 5 K. Two different effects are shown to limit nitrogen incorporation: the substrate crystalline quality and the addition of oxygen into the precursor during the growth. First, the CL spectra are shown to change strongly near the edges of the substrate in the regions corresponding to different bulk crystal growth modes. Some regions show a luminescence governed by UV emission while in other regions, where the H3 defect-related luminescence of the substrate is much stronger, the film UV emission is reduced. Second, the relative importance of the free exciton emission with respect to those from the nitrogen-related H3 centre and from the boron-bound exciton is shown to increase with the addition of oxygen during growth. Such observations are of first importance to improve the spectral emission and absorption threshold of the diamond material in the deep UV range.

  16. Efficiency enhancement of homoepitaxial InGaN/GaN light-emitting diodes on free-standing GaN substrate with double embedded SiO2 photonic crystals.

    PubMed

    Wei, Tongbo; Huo, Ziqiang; Zhang, Yonghui; Zheng, Haiyang; Chen, Yu; Yang, Jiankun; Hu, Qiang; Duan, Ruifei; Wang, Junxi; Zeng, Yiping; Li, Jinmin

    2014-06-30

    Homoepitaxially grown InGaN/GaN light emitting diodes (LEDs) with SiO2 nanodisks embedded in n-GaN and p-GaN as photonic crystal (PhC) structures by nanospherical-lens photolithography are presented and investigated. The introduction of SiO2 nanodisks doesn't produce the new dislocations and doesn't also result in the electrical deterioration of PhC LEDs. The light output power of homoepitaxial LEDs with embedded PhC and double PhC at 350 mA current is increased by 29.9% and 47.2%, respectively, compared to that without PhC. The corresponding light radiation patterns in PhC LEDs on GaN substrate show a narrow beam shape due to strong guided light extraction, with a view angle reduction of about 30°. The PhC LEDs are also analyzed in detail by finite-difference time-domain simulation (FDTD) to further reveal the emission characteristics.

  17. Homoepitaxial nonpolar (10-10) ZnO/ZnMgO monolithic microcavities: Towards reduced photonic disorder

    SciTech Connect

    Zuniga-Perez, J. Kappei, L.; Deparis, C.; Chenot, S.; Leroux, M.; Reveret, F.; Jamadi, O.; Leymarie, J.; Grundmann, M.; Prado, E. de

    2016-06-20

    Nonpolar ZnO/ZnMgO-based optical microcavities have been grown on (10-10) m-plane ZnO substrates by plasma-assisted molecular beam epitaxy. Reflectivity measurements indicate an exponential increase of the cavity quality factor with the number of layers in the distributed Bragg reflectors. Most importantly, microreflectivity spectra recorded with a spot size in the order of 2 μm show a negligible photonic disorder (well below 1 meV), leading to local quality factors equivalent to those obtained by macroreflectivity. The anisotropic character of the nonpolar heterostructures manifests itself both in the surface features, elongated parallel to the in-plane c direction, and in the optical spectra, with two cavity modes being observed at different energies for orthogonal polarizations.

  18. Influence of silicon dioxide capping layers on pore characteristics in nanocrystalline silicon membranes.

    PubMed

    Qi, Chengzhu; Striemer, Christopher C; Gaborski, Thomas R; McGrath, James L; Fauchet, Philippe M

    2015-02-06

    Porous nanocrystalline silicon (pnc-Si) membranes are a new class of membrane material with promising applications in biological separations. Pores are formed in a silicon film sandwiched between nm thick silicon dioxide layers during rapid thermal annealing. Controlling pore size is critical in the size-dependent separation applications. In this work, we systematically studied the influence of the silicon dioxide capping layers on pnc-Si membranes. Even a single nm thick top oxide layer is enough to switch from agglomeration to pore formation after annealing. Both the pore size and porosity increase with the thickness of the top oxide, but quickly reach a plateau after 10 nm of oxide. The bottom oxide layer acts as a barrier layer to prevent the a-Si film from undergoing homo-epitaxial growth during annealing. Both the pore size and porosity decrease as the thickness of the bottom oxide layer increases to 100 nm. The decrease of the pore size and porosity is correlated with the increased roughness of the bottom oxide layer, which hinders nanocrystal nucleation and nanopore formation.

  19. South Layers

    NASA Image and Video Library

    2006-05-20

    This MOC image shows remnants of layered materials near the west rim of South Crater, Mars. The composition of these layered rocks is unknown -- are they the remains of sedimentary rocks or accumulations of dust and ice?

  20. Calibration of an isotopically enriched carbon-13 layer pressure sensor to 156 GPa in a diamond anvil cell

    SciTech Connect

    Qiu,W.; Baker, P.; Velisavljevic, N.; Vohra, Y.; Weir, S.

    2006-01-01

    An isotopically enriched {sup 13}C homoepitaxial diamond layer of 6{+-}1 {mu}m thickness was grown on top of a brilliant cut diamond anvil by a microwave plasma chemical vapor deposition process for application as a pressure sensor. This isotopically enriched diamond tip was then used in conjunction with a natural isotopic abundance diamond anvil to generate high pressure on the sample. We provide a calibration for the {sup 13}C Raman mode of this extremely thin epitaxial layer to 156 GPa using ruby fluorescence and the equation of state of copper as secondary pressure standards. The nonlinear calibration of the {sup 13}C Raman mode pressure sensor is compared with similar calibrations of {sup 12}C Raman edge and a good agreement is obtained. The Raman signal from the {sup 13}C epitaxial layer remained a distinct singlet to 156 GPa, and pressure calibration is independent of sample mechanical strength or the diamond anvil geometry. The use of even thinner layer would allow calibration further into ultrahigh pressure regime where the use of other optical sensors has proven to be difficult.

  1. Boundary Layer

    NASA Technical Reports Server (NTRS)

    Loitsianskii. L. G.

    1956-01-01

    The fundamental, practically the most important branch of the modern mechanics of a viscous fluid or a gas, is that branch which concerns itself with the study of the boundary layer. The presence of a boundary layer accounts for the origin of the resistance and lift force, the breakdown of the smooth flow about bodies, and other phenomena that are associated with the motion of a body in a real fluid. The concept of boundary layer was clearly formulated by the founder of aerodynamics, N. E. Joukowsky, in his well-known work "On the Form of Ships" published as early as 1890. In his book "Theoretical Foundations of Air Navigation," Joukowsky gave an account of the most important properties of the boundary layer and pointed out the part played by it in the production of the resistance of bodies to motion. The fundamental differential equations of the motion of a fluid in a laminar boundary layer were given by Prandtl in 1904; the first solutions of these equations date from 1907 to 1910. As regards the turbulent boundary layer, there does not exist even to this day any rigorous formulation of this problem because there is no closed system of equations for the turbulent motion of a fluid. Soviet scientists have done much toward developing a general theory of the boundary layer, and in that branch of the theory which is of greatest practical importance at the present time, namely the study of the boundary layer at large velocities of the body in a compressed gas, the efforts of the scientists of our country have borne fruit in the creation of a new theory which leaves far behind all that has been done previously in this direction. We shall herein enumerate the most important results by Soviet scientists in the development of the theory of the boundary layer.

  2. Nonmixing layers

    NASA Astrophysics Data System (ADS)

    Gaillard, Pierre; Giovangigli, Vincent; Matuszewski, Lionel

    2016-12-01

    We investigate the impact of nonideal diffusion on the structure of supercritical cryogenic binary mixing layers. This situation is typical of liquid fuel injection in high-pressure rocket engines. Nonideal diffusion has a dramatic impact in the neighborhood of chemical thermodynamic stability limits where the components become quasi-immiscible and ultimately form a nonmixing layer. Numerical simulations are performed for mixing layers of H2 and N2 at a pressure of 100 atm and temperature around 120-150 K near chemical thermodynamic stability limits.

  3. Spallanzani Layers

    NASA Technical Reports Server (NTRS)

    2006-01-01

    31 March 2006 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a layered, light-toned mesa among other layered materials exposed in a mound that covers much of the floor of Spallanzani Crater.

    Location near: 58.3oS, 273.9oW Image width: 3 km (1.9 mi) Illumination from: upper left Season: Southern Summer

  4. Reduction of epitaxial defects on 4°-off 4Hsbnd SiC homo-epitaxial growth by optimizing in-situ etching process

    NASA Astrophysics Data System (ADS)

    Sun, Yongqiang; Feng, Gan; Zhang, Jianhui; Qian, Weining; Kang, Junyong

    2016-11-01

    The investigations of in-situ etching of 4Hsbnd SiC epi-growth on 4° off-axis 100 mm diameter substrates under different conditions have been carried out in a commercial warm-wall multi-wafer planetary reactor. The surface morphologies of the as-etched substrates have been characterized by atomic force microscopy on 20 × 20 μm2. Based on the step height and roughness mean square, the best etching condition for 4Hsbnd SiC 4° off-axis substrates was determined to be H2 + HCl at 1500 °C for 10 min. With the optimized in-situ etching process, high quality 4Hsbnd SiC epitaxial layers with excellent surface morphology have been obtained, and the defect density is lowered to 0.45 cm-2 resulting in a projected 2 × 2 mm die yield of ∼98%.

  5. Real-time ellipsometric modeling and characterization of the evolution of nanometer-scale Ge islands and pits in Ge homoepitaxy

    NASA Astrophysics Data System (ADS)

    Akazawa, Housei

    2009-11-01

    Nanometer-scale Ge islands and pits are self-organized during GeH4 vacuum-ultraviolet-excited chemical vapor deposition on a Ge(001) substrate. We carried out simulation and fitting on real-time ellipsometric Ψ -Δ trajectories that reflect undergoing changes in the surface morphology. The islanded Ge epitaxial layer was optically represented by multiple stacked slabs with linearly varying graded indices from the bottom to the top of the islands. The dielectric function of each slab was calculated by mixing the dielectric functions of Ge with that of voids under Bruggeman effective medium approximation. The only model that could reproduce the roughening Ψ -Δ trajectory was preferential nucleation of Ge on the top surface of truncated pyramidal islands after almost 100% of the initial surface had been wet. The smoothing section was consistent with the model assuming nucleation on the sidewalls of islands as well as on the top surface, which led to simultaneous deepening and narrowing of the valleys or pits between the islands. This smoothing model was supported by atomic force microscopy images.

  6. Layered materials

    NASA Astrophysics Data System (ADS)

    Johnson, David; Clarke, Simon; Wiley, John; Koumoto, Kunihito

    2014-06-01

    Layered compounds, materials with a large anisotropy to their bonding, electrical and/or magnetic properties, have been important in the development of solid state chemistry, physics and engineering applications. Layered materials were the initial test bed where chemists developed intercalation chemistry that evolved into the field of topochemical reactions where researchers are able to perform sequential steps to arrive at kinetically stable products that cannot be directly prepared by other approaches. Physicists have used layered compounds to discover and understand novel phenomena made more apparent through reduced dimensionality. The discovery of charge and spin density waves and more recently the remarkable discovery in condensed matter physics of the two-dimensional topological insulating state were discovered in two-dimensional materials. The understanding developed in two-dimensional materials enabled subsequent extension of these and other phenomena into three-dimensional materials. Layered compounds have also been used in many technologies as engineers and scientists used their unique properties to solve challenging technical problems (low temperature ion conduction for batteries, easy shear planes for lubrication in vacuum, edge decorated catalyst sites for catalytic removal of sulfur from oil, etc). The articles that are published in this issue provide an excellent overview of the spectrum of activities that are being pursued, as well as an introduction to some of the most established achievements in the field. Clusters of papers discussing thermoelectric properties, electronic structure and transport properties, growth of single two-dimensional layers, intercalation and more extensive topochemical reactions and the interleaving of two structures to form new materials highlight the breadth of current research in this area. These papers will hopefully serve as a useful guideline for the interested reader to different important aspects in this field and

  7. Growing 3C-SiC heteroepitaxial layers on α-SiC substrate by vapour-liquid-solid mechanism from the Al-Ge-Si ternary system

    NASA Astrophysics Data System (ADS)

    Lorenzzi, Jean; Ferro, Gabriel; Cauwet, François; Souliere, Véronique; Carole, Davy

    2011-03-01

    In this work, we present and compare the results obtained from different Si-based melts (Ge-Si, Al-Si and Al-Ge-Si) for growing SiC layers on α-SiC substrate by vapour-liquid-solid (VLS) mechanism. It was found that, depending on melt composition, the deposit could be either a complete 3C or α-SiC layer or even a mixture of these polytypes. The binary Al-Si melt leads systematically to a highly p-type homoepitaxial α-SiC deposit while Ge-Si melt gives a non-intentional n-type doped layers of either 3C or 6H polytypes depending on growth conditions. However, highly p-type doped 3C heteroepitaxial deposit can be obtained if a small amount of Al is added to the Ge-Si binary liquid phase. This means that the VLS mechanism is very flexible and allows growing either n- or p-type SiC layers of 3C or 6H polytypes.

  8. Fabrication of CeO 2 buffer layer with high deposition rate on biaxially textured Ni-3%W substrate by electron beam evaporation

    NASA Astrophysics Data System (ADS)

    Lee, J. B.; Park, S. K.; Kim, B. J.; Lee, H. J.; Kim, S. S.; Moon, S. H.; Lee, H. G.; Hong, G. W.

    2011-11-01

    CeO2 has been used as a buffer layer of a coated conductor because of good chemical and structural compatibility with YBCO. But cracks were often observed at the surface for films thicker than 100 nm deposited at a high temperature because of a large difference in a thermal expansion coefficient between metal and CeO2. The deposition rate was limited to be slow for getting good epitaxy. In order to increase the film deposition rate, while maintaining the epitaxy till a final thickness, two-step deposition process was tested. The thin seed layer with a thickness less than 10 nm was deposited with a deposition rate of 3 Å/s, and the homo-epitaxial layer at a thickness more than 240 nm was deposited at a deposition rate of 30 Å/s. The resulting CeO2 films deposited at 600 °C showed a good texture with a Δφ of 5.3°, Δω of 4.2° and Ra of 2.2 nm. The two-step process may be option for a low cost buffer layer for Ni-3%W metal substrates for the coated conductor.

  9. Tuning of strain and surface roughness of porous silicon layers for higher-quality seeds for epitaxial growth.

    PubMed

    Karim, Marwa; Martini, Roberto; Radhakrishnan, Hariharsudan Sivaramakrishnan; van Nieuwenhuysen, Kris; Depauw, Valerie; Ramadan, Wedgan; Gordon, Ivan; Poortmans, Jef

    2014-01-01

    Sintered porous silicon is a well-known seed for homo-epitaxy that enables fabricating transferrable monocrystalline foils. The crystalline quality of these foils depends on the surface roughness and the strain of this porous seed, which should both be minimized. In order to provide guidelines for an optimum foil growth, we present a systematic investigation of the impact of the thickness of this seed and of its sintering time prior to epitaxial growth on strain and surface roughness. Strain and surface roughness were monitored in monolayers and double layers with different porosities as a function of seed thickness and of sintering time by high-resolution X-ray diffraction and profilometry, respectively. Unexpectedly, we found that strain in double and monolayers evolves in opposite ways with respect to layer thickness. This suggests that an interaction between layers in multiple stacks is to be considered. We also found that if higher seed thickness and longer annealing time are to be preferred to minimize the strain in double layers, the opposite is required to achieve smoother layers. The impact of these two parameters may be explained by considering the morphological evolution of the pores upon sintering and, in particular, the disappearance of interconnections between the porous seed and the bulk as well as the enlargement of pores near the surface. An optimum epitaxial growth hence calls for a trade-off in seed thickness and annealing time, between minimum-strained layers and rougher surfaces. 81.40.-z Treatment of materials and its effects on microstructure, nanostructure, and properties; 81.05.Rm Porous materials; granular materials; 82.80.Ej X-ray, Mössbauer and other γ-ray spectroscopic analysis methods.

  10. Tuning of strain and surface roughness of porous silicon layers for higher-quality seeds for epitaxial growth

    PubMed Central

    2014-01-01

    Sintered porous silicon is a well-known seed for homo-epitaxy that enables fabricating transferrable monocrystalline foils. The crystalline quality of these foils depends on the surface roughness and the strain of this porous seed, which should both be minimized. In order to provide guidelines for an optimum foil growth, we present a systematic investigation of the impact of the thickness of this seed and of its sintering time prior to epitaxial growth on strain and surface roughness. Strain and surface roughness were monitored in monolayers and double layers with different porosities as a function of seed thickness and of sintering time by high-resolution X-ray diffraction and profilometry, respectively. Unexpectedly, we found that strain in double and monolayers evolves in opposite ways with respect to layer thickness. This suggests that an interaction between layers in multiple stacks is to be considered. We also found that if higher seed thickness and longer annealing time are to be preferred to minimize the strain in double layers, the opposite is required to achieve smoother layers. The impact of these two parameters may be explained by considering the morphological evolution of the pores upon sintering and, in particular, the disappearance of interconnections between the porous seed and the bulk as well as the enlargement of pores near the surface. An optimum epitaxial growth hence calls for a trade-off in seed thickness and annealing time, between minimum-strained layers and rougher surfaces. PACS codes 81.40.-z Treatment of materials and its effects on microstructure, nanostructure, and properties; 81.05.Rm Porous materials; granular materials; 82.80.Ej X-ray, Mössbauer and other γ-ray spectroscopic analysis methods PMID:25136277

  11. Layered Slope

    NASA Technical Reports Server (NTRS)

    2005-01-01

    28 August 2005 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a frost-covered slope in the south polar region of Mars. The layered nature of the terrain in the south polar region is evident in a series of irregular, somewhat stair-stepped bands that run across the image.

    Location near: 84.3oS, 27.2oW Image width: width: 3 km (1.9 mi) Illumination from: upper left Season: Southern Spring

  12. Double Layers in Astrophysics

    NASA Technical Reports Server (NTRS)

    Williams, Alton C. (Editor); Moorehead, Tauna W. (Editor)

    1987-01-01

    Topics addressed include: laboratory double layers; ion-acoustic double layers; pumping potential wells; ion phase-space vortices; weak double layers; electric fields and double layers in plasmas; auroral double layers; double layer formation in a plasma; beamed emission from gamma-ray burst source; double layers and extragalactic jets; and electric potential between plasma sheet clouds.

  13. Becquerel Layers

    NASA Technical Reports Server (NTRS)

    2003-01-01

    MGS MOC Release No. MOC2-350, 4 May 2003

    This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows layered sedimentary rock outcrops in Becquerel Crater of western Arabia Terra. These materials were deposited in the crater some time in the distant past, and later eroded to their present form. They probably consist of fine-grained sediments; they could have been deposited directly from dust and/or volcanic ash settling out of the martian atmosphere, or silt and sand settling to the floor of an ancient lake. The image does not provide enough information to distinguish between the two possibilities. The picture is located near 21.5oN, 8.1oW. Sunlight illuminates the scene from the lower left.

  14. Polar Layers

    NASA Technical Reports Server (NTRS)

    2005-01-01

    [figure removed for brevity, see original site] Context image for PIA03581 Polar Layers

    This image shows just one example of the bright and dark markings that appear during summer time. The marks are related to the polar layers. If you happen to see a wild-eyed guy sticking his tongue out at you, you'll know why this image qualifies for the old 'art' category of THEMIS releases.

    Image information: VIS instrument. Latitude 80.6S, Longitude 34.1E. 17 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  15. Ozone Layer Protection

    MedlinePlus

    ... EPA United States Environmental Protection Agency Search Search Ozone Layer Protection Share Facebook Twitter Google+ Pinterest Contact Us Ozone Layer Protection Welcome to EPA's ozone layer protection web ...

  16. Diamond Homoepitaxy by Chemical Vapor Deposition

    DTIC Science & Technology

    1993-02-01

    with crystal lattice twinning. In the < I I I growth processes favor the cubic structure . CVD growth growth sector, a high density of stacking faults...birefringence indicating non- cubic structure of the crystal lattice. Ca) Attempts to generate a second harmonic were not - successful. Second...Scaic and M. Seal, Surf. Coat. Technol., 47 (1991)i113. Assumption of cubic structure distorted by defects was 8 K. A. Snail and L M. Hanssen J. Cryst

  17. High Performance Green LEDs by Homoepitaxial

    SciTech Connect

    Wetzel, Christian; Schubert, E Fred

    2009-11-22

    This work's objective was the development of processes to double or triple the light output power from green and deep green (525 - 555 nm) AlGaInN light emitting diode (LED) dies within 3 years in reference to the Lumileds Luxeon II. The project paid particular effort to all aspects of the internal generation efficiency of light. LEDs in this spectral region show the highest potential for significant performance boosts and enable the realization of phosphor-free white LEDs comprised by red-green-blue LED modules. Such modules will perform at and outperform the efficacy target projections for white-light LED systems in the Department of Energy's accelerated roadmap of the SSL initiative.

  18. Core layering

    NASA Astrophysics Data System (ADS)

    Jacobson, S. A.; Rubie, D. C.; Hernlund, J. W.; Morbidelli, A.

    2015-12-01

    We have created a planetary accretion and differentiation model that self-consistently builds and evolves Earth's core. From this model, we show that the core grows stably stratified as the result of rising metal-silicate equilibration temperatures and pressures, which increases the concentrations of light element impurities into each newer core addition. This stable stratification would naturally resist convection and frustrate the onset of a geodynamo, however, late giant impacts could mechanically mix the distinct accreted core layers creating large homogenous regions. Within these regions, a geodynamo may operate. From this model, we interpret the difference between the planetary magnetic fields of Earth and Venus as a difference in giant impact histories. Our planetary accretion model is a numerical N-body integration of the Grand Tack scenario [1]—the most successful terrestrial planet formation model to date [2,3]. Then, we take the accretion histories of Earth-like and Venus-like planets from this model and post-process the growth of each terrestrial planet according to a well-tested planetary differentiation model [4,5]. This model fits Earth's mantle by modifying the oxygen content of the pre-cursor planetesimals and embryos as well as the conditions of metal-silicate equilibration. Other non-volatile major, minor and trace elements included in the model are assumed to be in CI chondrite proportions. The results from this model across many simulated terrestrial planet growth histories are robust. If the kinetic energy delivered by larger impacts is neglected, the core of each planet grows with a strong stable stratification that would significantly impede convection. However, if giant impact mixing is very efficient or if the impact history delivers large impacts late, than the stable stratification can be removed. [1] Walsh et al. Nature 475 (2011) [2] O'Brien et al. Icarus 223 (2014) [3] Jacobson & Morbidelli PTRSA 372 (2014) [4] Rubie et al. EPSL 301

  19. Epitaxy of layered semiconductor thin films

    NASA Astrophysics Data System (ADS)

    Brahim Otsmane, L.; Emery, J. Y.; Jouanne, M.; Balkanski, M.

    1993-03-01

    Epilayers of InSe on InSe(00.1) and GaSe(00.1) have been grown by the molecular beam epitaxy (MBE) technique. Raman spectroscopy was used for a characterization of the structure and crystallinity in InSe/InSe(00.1) (homoepitaxy) and InSe/GaSe(00.1) (heteroepitaxy). The Raman spectra of the InSe thin films are identical to those of polytype γ-InSe. An activation of the E(LO) mode at 211 cm -1 is observed in these films here. Scanning electron microscopy (SEM) is also used to investigate surfaces of these films.

  20. Tailoring graphene layer-to-layer growth

    NASA Astrophysics Data System (ADS)

    Li, Yongtao; Wu, Bin; Guo, Wei; Wang, Lifeng; Li, Jingbo; Liu, Yunqi

    2017-06-01

    A layered material grown between a substrate and the upper layer involves complex interactions and a confined reaction space, representing an unusual growth mode. Here, we show multi-layer graphene domains grown on liquid or solid Cu by the chemical vapor deposition method via this ‘double-substrate’ mode. We demonstrate the interlayer-induced coupling effect on the twist angle in bi- and multi-layer graphene. We discover dramatic growth disunity for different graphene layers, which is explained by the ideas of a chemical ‘gate’ and a material transport process within a confined space. These key results lead to a consistent framework for understanding the dynamic evolution of multi-layered graphene flakes and tailoring the layer-to-layer growth for practical applications.

  1. Innovation in Layer-by-Layer Assembly.

    PubMed

    Richardson, Joseph J; Cui, Jiwei; Björnmalm, Mattias; Braunger, Julia A; Ejima, Hirotaka; Caruso, Frank

    2016-12-14

    Methods for depositing thin films are important in generating functional materials for diverse applications in a wide variety of fields. Over the last half-century, the layer-by-layer assembly of nanoscale films has received intense and growing interest. This has been fueled by innovation in the available materials and assembly technologies, as well as the film-characterization techniques. In this Review, we explore, discuss, and detail innovation in layer-by-layer assembly in terms of past and present developments, and we highlight how these might guide future advances. A particular focus is on conventional and early developments that have only recently regained interest in the layer-by-layer assembly field. We then review unconventional assemblies and approaches that have been gaining popularity, which include inorganic/organic hybrid materials, cells and tissues, and the use of stereocomplexation, patterning, and dip-pen lithography, to name a few. A relatively recent development is the use of layer-by-layer assembly materials and techniques to assemble films in a single continuous step. We name this "quasi"-layer-by-layer assembly and discuss the impacts and innovations surrounding this approach. Finally, the application of characterization methods to monitor and evaluate layer-by-layer assembly is discussed, as innovation in this area is often overlooked but is essential for development of the field. While we intend for this Review to be easily accessible and act as a guide to researchers new to layer-by-layer assembly, we also believe it will provide insight to current researchers in the field and help guide future developments and innovation.

  2. Link Layer Modeling

    NASA Astrophysics Data System (ADS)

    Mühleisen, M.; Bültmann, D.; Klagges, K.; Schinnenburg, M.

    The Data Link Layer (DLL) is located above the PHY layer described in the previous chapter and below the network layer described in Chapter 16. All data received from these layers is digital. Today most parts of the DLL are implemented in software, either as device drivers running on general purpose Central Processing Units (CPUs) or as firmware running on dedicated network interface hardware.

  3. Stable Layers in the Atmospheric Boundary Layer

    NASA Astrophysics Data System (ADS)

    Mahalov, A.; Berman, N. S.; Fernando, H. J. S.; Yu, F.; Pardyjak, E.

    1998-11-01

    Field experimental studies on the establishment and growth of the nocturnal stable layer near the ground were made in January, 1998 using a tethered balloon at a site in Phoenix, Arizona. Days and nights with clear skies and light surface winds were of particular interest because small particle and carbon monoxide concentrations can be high during such times. Closest to the ground a shallow stable layer 20 meters deep with a buoyancy frequency (N) of 0.05 1/s rapidly developed before sundown. The height of this layer and N remained constant throughout the night. Above the 20-meter level, there was a transition layer which was also stable with N = 0.025 1/s. This transition layer grew throughout the night and reached 120 meters by dawn. Above the transition layer was a neutrally stable (residual) layer left over from the previous day. An unsteady layer 10 to 100 m thick with N = 0.025 1/s was also found at the top of the troposphere with the neutrally stable troposphere below and the stable stratosphere above. The growth and/or decay of turbulence in such stable layers will be discussed in light of recent theoretical developments.

  4. Large-roll growth of 25-inch hexagonal BN monolayer film for self-release buffer layer of free-standing GaN wafer

    NASA Astrophysics Data System (ADS)

    Wu, Chenping; Soomro, Abdul Majid; Sun, Feipeng; Wang, Huachun; Huang, Youyang; Wu, Jiejun; Liu, Chuan; Yang, Xiaodong; Gao, Na; Chen, Xiaohong; Kang, Junyong; Cai, Duanjun

    2016-10-01

    Hexagonal boron nitride (h-BN) is known as promising 2D material with a wide band-gap (~6 eV). However, the growth size of h-BN film is strongly limited by the size of reaction chamber. Here, we demonstrate the large-roll synthesis of monolayer and controllable sub-monolayer h-BN film on wound Cu foil by low pressure chemical vapor deposition (LPCVD) method. By winding the Cu foil substrate into mainspring shape supported by a multi-prong quartz fork, the reactor size limit could be overcome by extending the substrate area to a continuous 2D curl of plane inward. An extremely large-size monolayer h-BN film has been achieved over 25 inches in a 1.2” tube. The optical band gap of h-BN monolayer was determined to be 6.0 eV. The h-BN film was uniformly transferred onto 2” GaN or 4” Si wafer surfaces as a release buffer layer. By HVPE method, overgrowth of thick GaN wafer over 200 μm has been achieved free of residual strain, which could provide high quality homo-epitaxial substrate.

  5. Large-roll growth of 25-inch hexagonal BN monolayer film for self-release buffer layer of free-standing GaN wafer.

    PubMed

    Wu, Chenping; Soomro, Abdul Majid; Sun, Feipeng; Wang, Huachun; Huang, Youyang; Wu, Jiejun; Liu, Chuan; Yang, Xiaodong; Gao, Na; Chen, Xiaohong; Kang, Junyong; Cai, Duanjun

    2016-10-19

    Hexagonal boron nitride (h-BN) is known as promising 2D material with a wide band-gap (~6 eV). However, the growth size of h-BN film is strongly limited by the size of reaction chamber. Here, we demonstrate the large-roll synthesis of monolayer and controllable sub-monolayer h-BN film on wound Cu foil by low pressure chemical vapor deposition (LPCVD) method. By winding the Cu foil substrate into mainspring shape supported by a multi-prong quartz fork, the reactor size limit could be overcome by extending the substrate area to a continuous 2D curl of plane inward. An extremely large-size monolayer h-BN film has been achieved over 25 inches in a 1.2" tube. The optical band gap of h-BN monolayer was determined to be 6.0 eV. The h-BN film was uniformly transferred onto 2" GaN or 4" Si wafer surfaces as a release buffer layer. By HVPE method, overgrowth of thick GaN wafer over 200 μm has been achieved free of residual strain, which could provide high quality homo-epitaxial substrate.

  6. Large-roll growth of 25-inch hexagonal BN monolayer film for self-release buffer layer of free-standing GaN wafer

    PubMed Central

    Wu, Chenping; Soomro, Abdul Majid; Sun, Feipeng; Wang, Huachun; Huang, Youyang; Wu, Jiejun; Liu, Chuan; Yang, Xiaodong; Gao, Na; Chen, Xiaohong; Kang, Junyong; Cai, Duanjun

    2016-01-01

    Hexagonal boron nitride (h-BN) is known as promising 2D material with a wide band-gap (~6 eV). However, the growth size of h-BN film is strongly limited by the size of reaction chamber. Here, we demonstrate the large-roll synthesis of monolayer and controllable sub-monolayer h-BN film on wound Cu foil by low pressure chemical vapor deposition (LPCVD) method. By winding the Cu foil substrate into mainspring shape supported by a multi-prong quartz fork, the reactor size limit could be overcome by extending the substrate area to a continuous 2D curl of plane inward. An extremely large-size monolayer h-BN film has been achieved over 25 inches in a 1.2” tube. The optical band gap of h-BN monolayer was determined to be 6.0 eV. The h-BN film was uniformly transferred onto 2” GaN or 4” Si wafer surfaces as a release buffer layer. By HVPE method, overgrowth of thick GaN wafer over 200 μm has been achieved free of residual strain, which could provide high quality homo-epitaxial substrate. PMID:27756906

  7. Investigation of Electron-Hole Recombination-Activated Partial Dislocations and Their Behavior in 4H-SiC Epitaxial Layers

    SciTech Connect

    Chen,Y.; Zhang, N.; Dudley, M.; Caldwell, J.; Liu, K.; Stahlbush, R.; Huang, X.; Macrander, A.; Black, D.

    2008-01-01

    Electron-hole recombination-activated partial dislocations in 4H silicon carbide homoepitaxial layers and their behavior have been studied using synchrotron X-ray topography and electroluminescence. Stacking faults whose expansion was activated by electron-hole recombination enhanced dislocation glide were observed to be bounded by partial dislocations, which appear as white stripes or narrow dark lines in back-reflection X-ray topographs recorded using the basal plane reflections. Such contrast variations are attributable to the defocusing/focusing of the diffracted X-rays due to the edge component of the partial dislocations, which creates a convex/concave distortion of the basal planes. Simulation results based on the ray-tracing principle confirm our argument. Observations also indicate that, when an advancing partial dislocation interacts with a threading screw dislocation, a partial dislocation dipole is dragged behind in its wake. This partial dislocation dipole is able to advance regardless of the immobility of the C-core segment. A kink pushing mechanism is introduced to interpret the advancement of this partial dislocation dipole.

  8. Investigation of electron-hole recombination-activated partial dislocations and their behavior in 4H-SiC epitaxial layers.

    SciTech Connect

    Chen, Y.; Zhang, N.; Dudley, M.; Caldwell, J.D.; Liu, K.X.; Stahlbush, R.E.; Huang, X.; Macrander, A.T.; Black, D.R.; X-Ray Science Division; Stony Brook Univ.; Naval Research Lab.; NIST

    2008-05-01

    Electron-hole recombination-activated partial dislocations in 4H silicon carbide homoepitaxial layers and their behavior have been studied using synchrotron X-ray topography and electroluminescence. Stacking faults whose expansion was activated by electron-hole recombination enhanced dislocation glide were observed to be bounded by partial dislocations, which appear as white stripes or narrow dark lines in back-reflection X-ray topographs recorded using the basal plane reflections. Such contrast variations are attributable to the defocusing/focusing of the diffracted X-rays due to the edge component of the partial dislocations, which creates a convex/concave distortion of the basal planes. Simulation results based on the ray-tracing principle confirm our argument. Observations also indicate that, when an advancing partial dislocation interacts with a threading screw dislocation, a partial dislocation dipole is dragged behind in its wake. This partial dislocation dipole is able to advance regardless of the immobility of the C-core segment. A kink pushing mechanism is introduced to interpret the advancement of this partial dislocation dipole.

  9. Burning Graphene Layer-by-Layer

    NASA Astrophysics Data System (ADS)

    Ermakov, Victor A.; Alaferdov, Andrei V.; Vaz, Alfredo R.; Perim, Eric; Autreto, Pedro A. S.; Paupitz, Ricardo; Galvao, Douglas S.; Moshkalev, Stanislav A.

    2015-06-01

    Graphene, in single layer or multi-layer forms, holds great promise for future electronics and high-temperature applications. Resistance to oxidation, an important property for high-temperature applications, has not yet been extensively investigated. Controlled thinning of multi-layer graphene (MLG), e.g., by plasma or laser processing is another challenge, since the existing methods produce non-uniform thinning or introduce undesirable defects in the basal plane. We report here that heating to extremely high temperatures (exceeding 2000 K) and controllable layer-by-layer burning (thinning) can be achieved by low-power laser processing of suspended high-quality MLG in air in “cold-wall” reactor configuration. In contrast, localized laser heating of supported samples results in non-uniform graphene burning at much higher rates. Fully atomistic molecular dynamics simulations were also performed to reveal details of oxidation mechanisms leading to uniform layer-by-layer graphene gasification. The extraordinary resistance of MLG to oxidation paves the way to novel high-temperature applications as continuum light source or scaffolding material.

  10. Burning Graphene Layer-by-Layer

    PubMed Central

    Ermakov, Victor A.; Alaferdov, Andrei V.; Vaz, Alfredo R.; Perim, Eric; Autreto, Pedro A. S.; Paupitz, Ricardo; Galvao, Douglas S.; Moshkalev, Stanislav A.

    2015-01-01

    Graphene, in single layer or multi-layer forms, holds great promise for future electronics and high-temperature applications. Resistance to oxidation, an important property for high-temperature applications, has not yet been extensively investigated. Controlled thinning of multi-layer graphene (MLG), e.g., by plasma or laser processing is another challenge, since the existing methods produce non-uniform thinning or introduce undesirable defects in the basal plane. We report here that heating to extremely high temperatures (exceeding 2000 K) and controllable layer-by-layer burning (thinning) can be achieved by low-power laser processing of suspended high-quality MLG in air in “cold-wall” reactor configuration. In contrast, localized laser heating of supported samples results in non-uniform graphene burning at much higher rates. Fully atomistic molecular dynamics simulations were also performed to reveal details of oxidation mechanisms leading to uniform layer-by-layer graphene gasification. The extraordinary resistance of MLG to oxidation paves the way to novel high-temperature applications as continuum light source or scaffolding material. PMID:26100466

  11. Basic Ozone Layer Science

    EPA Pesticide Factsheets

    Learn about the ozone layer and how human activities deplete it. This page provides information on the chemical processes that lead to ozone layer depletion, and scientists' efforts to understand them.

  12. Many-Layered Rock

    NASA Image and Video Library

    2006-08-23

    This MOC image shows light-toned, layered, sedimentary rocks in a crater in the northwestern part of Schiaparelli basin. The repetition of these horizontal layers suggests the sediments could have been deposited in an ancient crater lake

  13. Colorful Polar Layered Deposits

    NASA Image and Video Library

    2016-03-23

    The North Polar layered deposits provide a record of recent climate changes on Mars as seen by NASA Mars Reconnaissance Orbiter spacecraft. Color variations between layers are due to differences in composition of the dust.

  14. Modelling Layer parallel stylolites

    NASA Astrophysics Data System (ADS)

    Koehn, Daniel; Pataki Rood, Daisy; Beaudoin, Nicolas

    2016-04-01

    We modeled the geometrical roughening of mainly layer-dominated stylolites in order to understand their structural evolution, to present an advanced classification of stylolite shapes and to relate this classification to chemical compaction and stylolite sealing capabilities. Our simulations show that layer-dominated stylolites can grow in three distinct stages, an initial slow nucleation, a fast layer-pinning phase and a final freezing stage if the layer dissolves completely during growth. Dissolution of the pinning layer and thus destruction of the compaction tracking capabilities is a function of the background noise in the rock and the dissolution rate of the layer itself. Low background noise needs a slower dissolving layer for pinning to be successful but produces flatter teeth than higher background noise. We present an advanced classification based on our simulations and separate stylolites into four classes: rectangular layer type, seismogram pinning type, suture/sharp peak type and simple wave-like type.

  15. Layer-by-layer cell membrane assembly

    NASA Astrophysics Data System (ADS)

    Matosevic, Sandro; Paegel, Brian M.

    2013-11-01

    Eukaryotic subcellular membrane systems, such as the nuclear envelope or endoplasmic reticulum, present a rich array of architecturally and compositionally complex supramolecular targets that are as yet inaccessible. Here we describe layer-by-layer phospholipid membrane assembly on microfluidic droplets, a route to structures with defined compositional asymmetry and lamellarity. Starting with phospholipid-stabilized water-in-oil droplets trapped in a static droplet array, lipid monolayer deposition proceeds as oil/water-phase boundaries pass over the droplets. Unilamellar vesicles assembled layer-by-layer support functional insertion both of purified and of in situ expressed membrane proteins. Synthesis and chemical probing of asymmetric unilamellar and double-bilayer vesicles demonstrate the programmability of both membrane lamellarity and lipid-leaflet composition during assembly. The immobilized vesicle arrays are a pragmatic experimental platform for biophysical studies of membranes and their associated proteins, particularly complexes that assemble and function in multilamellar contexts in vivo.

  16. Photonic layered media

    DOEpatents

    Fleming, James G.; Lin, Shawn-Yu

    2002-01-01

    A new class of structured dielectric media which exhibit significant photonic bandstructure has been invented. The new structures, called photonic layered media, are easy to fabricate using existing layer-by-layer growth techniques, and offer the ability to significantly extend our practical ability to tailor the properties of such optical materials.

  17. The ozone layer.

    PubMed

    van der Leun, Jan C

    2004-08-01

    The intention of this paper is to stimulate the interest for the ozone layer, especially among young colleagues in photobiology; the "layer" is not only important, but also fascinating. In spite of remarkably effective action, the recovery of the ozone layer will be a long-term process. It will need the attention, also of scientists, for decades to come.

  18. Scintillator reflective layer coextrusion

    DOEpatents

    Yun, Jae-Chul; Para, Adam

    2001-01-01

    A polymeric scintillator has a reflective layer adhered to the exterior surface thereof. The reflective layer comprises a reflective pigment and an adhesive binder. The adhesive binder includes polymeric material from which the scintillator is formed. A method of forming the polymeric scintillator having a reflective layer adhered to the exterior surface thereof is also provided. The method includes the steps of (a) extruding an inner core member from a first amount of polymeric scintillator material, and (b) coextruding an outer reflective layer on the exterior surface of the inner core member. The outer reflective layer comprises a reflective pigment and a second amount of the polymeric scintillator material.

  19. Piezoelectric Resonator with Two Layers

    NASA Technical Reports Server (NTRS)

    Stephanou, Philip J. (Inventor); Black, Justin P. (Inventor)

    2013-01-01

    A piezoelectric resonator device includes: a top electrode layer with a patterned structure, a top piezoelectric layer adjacent to the top layer, a middle metal layer adjacent to the top piezoelectric layer opposite the top layer, a bottom piezoelectric layer adjacent to the middle layer opposite the top piezoelectric layer, and a bottom electrode layer with a patterned structure and adjacent to the bottom piezoelectric layer opposite the middle layer. The top layer includes a first plurality of electrodes inter-digitated with a second plurality of electrodes. A first one of the electrodes in the top layer and a first one of the electrodes in the bottom layer are coupled to a first contact, and a second one of the electrodes in the top layer and a second one of the electrodes in the bottom layer are coupled to a second contact.

  20. Modeling Transport Layer Protocols

    NASA Astrophysics Data System (ADS)

    Sasnauskas, Raimondas; Weingaertner, Elias

    In a layered communication architecture, transport layer protocols handle the data exchange between processes on different hosts over potentially lossy communication channels. Typically, transport layer protocols are either connection-oriented or are based on the transmission of individual datagrams. Well known transport protocols are the connection-oriented Transmission Control Protocol (TCP) [372] and the User Datagram Protocol (UDP) [370] as well as the Stream Control Transmission Protocol (SCTP) [340] and DCCP, the Datagram Congestion Control Protocol [259]. In this chapter, we focus on the modeling process of the transport layer. While we mostly use TCP and UDP as a base of comparison from this point, we emphasize that the methodologies discussed further on are conferrable to virtually any transport layer in any layered communication architecture.

  1. Electrochemical Atomic Layer Processing

    DTIC Science & Technology

    1994-06-25

    where an atomic layer of an element is deposited , or removed, in a surface limited reaction. The potentials used are referred to as underpotentials in...the electrochemical literature. The atomic layer deposition process is referred to as underpotential deposition (UPD). 14. SUBJECT TERMS 15, NUMBER OF...reaction. The potentials used are referred to as underpotentials in the electrochemical literature. The atomic layer deposition process is referred to as

  2. Layered plasma polymer composite membranes

    DOEpatents

    Babcock, W.C.

    1994-10-11

    Layered plasma polymer composite fluid separation membranes are disclosed, which comprise alternating selective and permeable layers for a total of at least 2n layers, where n is [>=]2 and is the number of selective layers. 2 figs.

  3. Layers and Erosion and more Layers

    NASA Technical Reports Server (NTRS)

    2003-01-01

    [figure removed for brevity, see original site]

    Released 4 November 2003

    This image is located within a set of eroded layered rocks known as the Medusae Fossae Formation. Careful inspection of this image reveals four separate layers. Starting at the bottom of the image, as well as the bottom of the sequence of layers, is a somewhat hilly, cratered plain. Above that is a mud or lava flow with a lobate edge that is characteristic of fluid flow. Above that is a layer with a spectacular rayed crater. This layer shows linear erosional patterns that are probably caused by persistent wind abrasion, typical of rocks in this area. And finally, a more blocky unit lies on top, mostly eroded away.

    Image information: VIS instrument. Latitude 3.6, Longitude 218.6 East (141.4 West). 19 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  4. The Atmospheric Boundary Layer

    ERIC Educational Resources Information Center

    Tennekes, Hendrik

    1974-01-01

    Discusses some important parameters of the boundary layer and effects of turbulence on the circulation and energy dissipation of the atmosphere. Indicates that boundary-layer research plays an important role in long-term forecasting and the study of air-pollution meteorology. (CC)

  5. Multiple density layered insulator

    DOEpatents

    Alger, T.W.

    1994-09-06

    A multiple density layered insulator for use with a laser is disclosed which provides at least two different insulation materials for a laser discharge tube, where the two insulation materials have different thermoconductivities. The multiple layer insulation materials provide for improved thermoconductivity capability for improved laser operation. 4 figs.

  6. Multiple density layered insulator

    DOEpatents

    Alger, Terry W.

    1994-01-01

    A multiple density layered insulator for use with a laser is disclosed wh provides at least two different insulation materials for a laser discharge tube, where the two insulation materials have different thermoconductivities. The multiple layer insulation materials provide for improved thermoconductivity capability for improved laser operation.

  7. North Polar Layers

    NASA Image and Video Library

    2017-02-28

    The North Polar layered deposits are a 3-kilometer thick stack of dusty water ice layers that are about 1000 kilometers across. The layers record information about climate stretching back a few million years into Martian history. In many locations erosion has created scarps and troughs that expose this layering. The tan colored layers are the dusty water ice of the polar layered deposits; however a section of bluish layers are is visible below them. These bluish layers contain sand-sized rock fragments that likely formed a large polar dunefield before the overlying dusty ice was deposited. The lack of a polar ice cap in this past epoch attests to the variability of the Martian climate, which undergoes larger changes over time than that of the Earth. The map is projected here at a scale of 50 centimeters (19.6 inches) per pixel. [The original image scale is 63.6 centimeters (25 inches) per pixel (with 2 x 2 binning); objects on the order of 191 centimeters (75.2 inches) across are resolved.] North is up. http://photojournal.jpl.nasa.gov/catalog/PIA21465

  8. The Atmospheric Boundary Layer

    ERIC Educational Resources Information Center

    Tennekes, Hendrik

    1974-01-01

    Discusses some important parameters of the boundary layer and effects of turbulence on the circulation and energy dissipation of the atmosphere. Indicates that boundary-layer research plays an important role in long-term forecasting and the study of air-pollution meteorology. (CC)

  9. Multiple layer insulation cover

    DOEpatents

    Farrell, James J.; Donohoe, Anthony J.

    1981-11-03

    A multiple layer insulation cover for preventing heat loss in, for example, a greenhouse, is disclosed. The cover is comprised of spaced layers of thin foil covered fabric separated from each other by air spaces. The spacing is accomplished by the inflation of spaced air bladders which are integrally formed in the cover and to which the layers of the cover are secured. The bladders are inflated after the cover has been deployed in its intended use to separate the layers of the foil material. The sizes of the material layers are selected to compensate for sagging across the width of the cover so that the desired spacing is uniformly maintained when the cover has been deployed. The bladders are deflated as the cover is stored thereby expediting the storage process and reducing the amount of storage space required.

  10. Layering in Spallanzani Crater

    NASA Image and Video Library

    2015-04-22

    In this image from NASA Mars Mars Reconnaissance Orbiter, we can see quite a spectacular layering pattern inside an impact crater called Spallanzani. Seeing layering is always exciting to geologists because it implies that the region has experienced multiple climatic conditions or geologic processes through time. The study of layering is so important in geology that it has its own dedicated branch of study: stratigraphy! Commonly, layering implies different lithologies (i.e., rock types). However, sometimes the layers could be of very similar composition but formed in different periods of time. This could happen for example in the case of annual flood deposits from rivers, multiple volcanic eruptions, or annual or periodic deposition of ice-rich material. We can also see in this image another feature called terracing, which happens when the layers form distinctive planes on top of one another like terraces. This could imply that the layers are being eroded with time but some of the layers are being eroded quicker than others because they are less resistant to erosion. So what is the composition of these layers? Spallanzani Crater lies in the high latitudes of the Southern hemisphere (around 60 degrees in latitude) so there is a good possibility that the deposits are ice-rich. If we look more closely we will notice fractured mounds, which sometimes indicate the presence of subsurface ice. Another interesting observation is the presence of grooves in the shaded slopes of some of the layers. Perhaps these grooves formed because of the sublimation (the direct transfer of solid ice to water vapor) of ice from these slopes since slopes tend to get warmer than the surrounding terrains. A close inspection of this image may help answer this question and investigate the multiple cycles in which these deposits were laid down as well as the duration of these individual cycles. http://photojournal.jpl.nasa.gov/catalog/PIA19367

  11. Characterization of triple layers

    NASA Astrophysics Data System (ADS)

    Otero, Toribio F.; Cortes, M. Teresa

    2001-07-01

    We reported the characterization of a macroscopic electrochemomechanical actuator like triple layer (3x1 cm) formed by polypyrrole)/double- sided, non-conducting and flexible tape/ polypyrrole that works in liquid electrolytes under electrochemical control. This triple layer has characteristics of artificial muscle. The influence of variables that control the volume change in the polymer as electrolyte concentration, or temperature has been studied. Variations of time, energy and charge under different conditions are described. We have found that the triple layer acts, at the same time, as sensor and actuator. Therefore, physical magnitudes like the electrolyte concentration or the temperature in the cell can be obtained from electrical energy consumed by a muscle. We have evaluated the influence of variables as area of the triple layer or the trailing weight, which don't participate in the electrochemical reaction. We propose an explication to the results, which show a correlation between the trailed mass and the consumed charge required to move a constant angle those masses by the triple layer. When different surface areas of the triple layer has been evaluated we found that the consumed electrical charge is proportional to area (the mass) of the triple layer. The triple layer can make macroscopical movements in short times, their position is absolutely controlled with the electrical charge, and it has capacity to lift masses. These characteristics allow their use in the design of tools. So, we present a macroscopic tool constituted by two triple layers, which allows catch and translate objects in liquid medium (nipper).

  12. The Application of Layer Theory to Design: The Control Layer

    ERIC Educational Resources Information Center

    Gibbons, Andrew S.; Langton, Matthew B.

    2016-01-01

    A theory of design layers proposed by Gibbons ("An Architectural Approach to Instructional Design." Routledge, New York, 2014) asserts that each layer of an instructional design is related to a body of theory closely associated with the concerns of that particular layer. This study focuses on one layer, the control layer, examining…

  13. The Application of Layer Theory to Design: The Control Layer

    ERIC Educational Resources Information Center

    Gibbons, Andrew S.; Langton, Matthew B.

    2016-01-01

    A theory of design layers proposed by Gibbons ("An Architectural Approach to Instructional Design." Routledge, New York, 2014) asserts that each layer of an instructional design is related to a body of theory closely associated with the concerns of that particular layer. This study focuses on one layer, the control layer, examining…

  14. Ventilated Oscillatory Boundary Layers

    DTIC Science & Technology

    1993-02-01

    AD-A266 226IllII !i III ll11111 II •" Ventilated Oscillatory Boundary Layers 0 Daniel -. Conley Douglas L. I nman C 0 UM U U U U till 1% w 1% W" Z t...A SIGNIFICANT NUMBER OF PAGES WHICH DO NOT REPRODUCE LEGIBLY. VENlTILATiD SCIILLAORY BOUNDARY LAYERS Daniel C. C7onley DoL’laN L. . ... La olDla...Wave Crest ........ 5. Boundary Layer Development Under the Wave Trough W 6 . Laboratory Observations .................. ................ 7

  15. Compliant layer chucking surface

    DOEpatents

    Blaedel, Kenneth L.; Spence, Paul A.; Thompson, Samuel L.

    2004-12-28

    A method and apparatus are described wherein a thin layer of complaint material is deposited on the surface of a chuck to mitigate the deformation that an entrapped particle might cause in the part, such as a mask or a wafer, that is clamped to the chuck. The harder particle will embed into the softer layer as the clamping pressure is applied. The material composing the thin layer could be a metal or a polymer for vacuum or electrostatic chucks. It may be deposited in various patterns to affect an interrupted surface, such as that of a "pin" chuck, thereby reducing the probability of entrapping a particle.

  16. Layered South Polar Slope

    NASA Technical Reports Server (NTRS)

    2004-01-01

    28 March 2004 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows layers exposed in the walls of a crater-like form (only partially seen here) in the south polar region. These layers record some of the history of the martian south pole, although deciphering this record will require human or robotic explorers to get a closer view. The layered outcrop is located near 84.6oS, 359.6oW. The image covers an area about 3 km (1.9 mi) across. Sunlight illuminates the scene from the upper left.

  17. Concentric layer ramjet fuel

    SciTech Connect

    Burdette, G.W.; Francis, J.P.

    1988-03-08

    This patent describes a solid fuel ramjet grain comprising concentric layers of solid ramjet fuel having a perforation therethrough along the center axis of the grain. The performation is connected to a combustion after-chamber. The solid ramjet fuel layers comprises a pure hydroxyl-terminated polybutadiene hydrocarbon fuel or a mixture of a hydroxyl-terminated polybutadiene hydrocarbon fuel and from about 5 to about 60 percent by weight of an additive to increase the fuel regression rate selected from the group consisting of magnesium, boron carbide, aluminum, and zirconium such that, when buried in the operation of the ramjet, each fuel layer produces a different level of thrust.

  18. Multi-layer coatings

    DOEpatents

    Maghsoodi, Sina; Brophy, Brenor L.; Abrams, Ze'ev R.; Gonsalves, Peter R.

    2016-06-28

    Disclosed herein are coating materials and methods for applying a top-layer coating that is durable, abrasion resistant, highly transparent, hydrophobic, low-friction, moisture-sealing, anti-soiling, and self-cleaning to an existing conventional high temperature anti-reflective coating. The top coat imparts superior durability performance and new properties to the under-laying conventional high temperature anti-reflective coating without reducing the anti-reflectiveness of the coating. Methods and data for optimizing the relative thickness of the under-layer high temperature anti-reflective coating and the top-layer thickness for optimizing optical performance are also disclosed.

  19. Addressing Ozone Layer Depletion

    EPA Pesticide Factsheets

    Access information on EPA's efforts to address ozone layer depletion through regulations, collaborations with stakeholders, international treaties, partnerships with the private sector, and enforcement actions under Title VI of the Clean Air Act.

  20. Development of retinal layers.

    PubMed

    Nguyen-Ba-Charvet, Kim Tuyen; Chédotal, Alain

    2014-03-01

    A noticeable characteristic of nervous systems is the arrangement of synapses into distinct layers. Such laminae are fundamental for the spatial organisation of synaptic connections transmitting different kinds of information. A major example of this is the inner plexiform layer (IPL) of the vertebrate retina, which is subdivided into at least ten sublayers. Another noticeable characteristic of these retina layers is that neurons are displayed in the horizontal plane in a non-random array termed as mosaic patterning. Recent studies of vertebrate and invertebrate systems have identified molecules that mediate these interactions. Here, we review the last mechanisms and molecules mediating retinal layering. Copyright © 2013 Académie des sciences. Published by Elsevier SAS. All rights reserved.

  1. Terby's Layered Rocks

    NASA Technical Reports Server (NTRS)

    2004-01-01

    14 March 2004 Layered rock outcrops are common all across Mars, and the Mars rover, Opportunity, has recently investigated some layered rocks in Meridiani Planum. This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows layered sedimentary rocks in northern Terby Crater, located just north of the giant Hellas Basin near 27.5oS, 285.8oW. Hundreds of layers are exposed in a deposit several kilometers thick within Terby. A history of events that shaped the northern Hellas region is recorded in these rocks, just waiting for a person or robot to investigate. The picture covers an area 3 km (1.9 mi) across. Sunlight illuminates the scene from the left.

  2. Terby's Layered Rocks

    NASA Technical Reports Server (NTRS)

    2004-01-01

    14 March 2004 Layered rock outcrops are common all across Mars, and the Mars rover, Opportunity, has recently investigated some layered rocks in Meridiani Planum. This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows layered sedimentary rocks in northern Terby Crater, located just north of the giant Hellas Basin near 27.5oS, 285.8oW. Hundreds of layers are exposed in a deposit several kilometers thick within Terby. A history of events that shaped the northern Hellas region is recorded in these rocks, just waiting for a person or robot to investigate. The picture covers an area 3 km (1.9 mi) across. Sunlight illuminates the scene from the left.

  3. Structured luminescence conversion layer

    DOEpatents

    Berben, Dirk; Antoniadis, Homer; Jermann, Frank; Krummacher, Benjamin Claus; Von Malm, Norwin; Zachau, Martin

    2012-12-11

    An apparatus device such as a light source is disclosed which has an OLED device and a structured luminescence conversion layer deposited on the substrate or transparent electrode of said OLED device and on the exterior of said OLED device. The structured luminescence conversion layer contains regions such as color-changing and non-color-changing regions with particular shapes arranged in a particular pattern.

  4. Tests on Double Layer Metalization

    NASA Technical Reports Server (NTRS)

    Woo, D. S.

    1983-01-01

    28 page report describes experiments in fabrication of integrated circuits with double-layer metalization. Double-layer metalization requires much less silicon "real estate" and allows more flexibility in placement of circuit elements than does single-layer metalization.

  5. EDITORIAL: Atomic layer deposition Atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Godlewski, Marek

    2012-07-01

    The growth method of atomic layer deposition (ALD) was introduced in Finland by Suntola under the name of atomic layer epitaxy (ALE). The method was originally used for deposition of thin films of sulphides (ZnS, CaS, SrS) activated with manganese or rare-earth ions. Such films were grown for applications in thin-film electroluminescence (TFEL) displays. The ALE mode of growth was also tested in the case of molecular beam epitaxy. Films grown by ALD are commonly polycrystalline or even amorphous. Thus, the name ALE has been replaced by ALD. In the 80s ALD was developed mostly in Finland and neighboring Baltic countries. Deposition of a range of different materials was demonstrated at that time, including II-VI semiconductors (e.g. CdTe, CdS) and III-V (e.g. GaAs, GaN), with possible applications in e.g. photovoltaics. The number of publications on ALD was slowly increasing, approaching about 100 each year. A real boom in interest came with the development of deposition methods of thin films of high-k dielectrics. This research was motivated by a high leakage current in field-effect transistors with SiO2-based gate dielectrics. In 2007 Intel introduced a new generation of integrated circuits (ICs) with thin films of HfO2 used as gate isolating layers. In these and subsequent ICs, films of HfO2 are deposited by the ALD method. This is due to their unique properties. The introduction of ALD to the electronics industry led to a booming interest in the ALD growth method, with the number of publications increasing rapidly to well above 1000 each year. A number of new applications were proposed, as reflected in this special issue of Semiconductor Science and Technology. The included articles cover a wide range of possible applications—in microelectronics, transparent electronics, optoelectronics, photovoltaics and spintronics. Research papers and reviews on the basics of ALD growth are also included, reflecting a growing interest in precursor chemistry and growth

  6. Layered electrode for electrochemical cells

    DOEpatents

    Swathirajan, Swathy; Mikhail, Youssef M.

    2001-01-01

    There is provided an electrode structure comprising a current collector sheet and first and second layers of electrode material. Together, the layers improve catalyst utilization and water management.

  7. Electrochemical Atomic Layer Epitaxy

    NASA Astrophysics Data System (ADS)

    Gregory, Brian Wayne

    1992-01-01

    Presented here are initial investigations into an electrochemical method whereby thin films of compound semiconductors are produced by epitaxial growth of the constituent elements. This method is the electrochemical analogue of atomic layer epitaxy (ALE) (a vacuum-based technique which relies on sequential formation of atomic layers of the constituent elements) and has been termed "Electrochemical atomic layer epitaxy" (ECALE). These preliminary studies are centered on the formation of CdTe, though in principle they could be extended to a number of other compound semiconductors. A background introduction on topics relevant to epitaxial growth in electrochemical systems will be presented. Predictions of underpotential behavior in the CdTe system will be made using potential -pH (Pourbaix) diagrams. Development of the method will proceed from our initial studies of Cd and Te underpotential deposition (UPD) on a number of metallic substrates, followed by results demonstrating the ECALE formation of two monolayers of CdTe on polycrystalline and single crystal gold substrates. The final chapter will present current attempts to design and construct an automated, computer-controlled thin-layer electrochemical flow cell, which is to be used for the deposition of thicker layers (up to 1 mu m) of compound semiconductors.

  8. North Polar Layers

    NASA Technical Reports Server (NTRS)

    2004-01-01

    3 December 2004 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows an exposure of finely-detailed layers in the martian north polar region. The polar ice cap, which is made up of frozen water (whereas the south polar cap is mostly frozen carbon dioxide), is underlain by a thick sequence of layers. Some have speculated that these layers may record the history of changes in martian climate during the past few hundreds of millions of years. This picture is located near 86.0oN, 30.2oW, and covers an area approximately 3 km (1.9 mi) across. Sunlight illuminates the scene from the lower left.

  9. Layered Systems Engineering Engines

    NASA Technical Reports Server (NTRS)

    Breidenthal, Julian C.; Overman, Marvin J.

    2009-01-01

    A notation is described for depicting the relationships between multiple, contemporaneous systems engineering efforts undertaken within a multi-layer system-of-systems hierarchy. We combined the concepts of remoteness of activity from the end customer, depiction of activity on a timeline, and data flow to create a new kind of diagram which we call a "Layered Vee Diagram." This notation is an advance over previous notations because it is able to be simultaneously precise about activity, level of granularity, product exchanges, and timing; these advances provide systems engineering managers a significantly improved ability to express and understand the relationships between many systems engineering efforts. Using the new notation, we obtain a key insight into the relationship between project duration and the strategy selected for chaining the systems engineering effort between layers, as well as insights into the costs, opportunities, and risks associated with alternate chaining strategies.

  10. Boundary layer simulator improvement

    NASA Technical Reports Server (NTRS)

    Praharaj, Sarat C.; Schmitz, Craig P.; Nouri, Joseph A.

    1989-01-01

    Boundary Layer Integral Matrix Procedure (BLIMPJ) has been identified by the propulsion community as the rigorous boundary layer program in connection with the existing JANNAF reference programs. The improvements made to BLIMPJ and described herein have potential applications in the design of the future Orbit Transfer Vehicle engines. The turbulence model is validated to include the effects of wall roughness and a way is devised to treat multiple smooth-rough surfaces. A prediction of relaminarization regions is examined as is the combined effects of wall cooling and surface roughness on relaminarization. A turbulence model to represent the effects of constant condensed phase loading is given. A procedure is described for thrust decrement calculation in thick boundary layers by coupling the T-D Kinetics Program and BLIMPJ and a way is provided for thrust loss optimization. Potential experimental studies in rocket nozzles are identified along with the required instrumentation to provide accurate measurements in support of the presented new analytical models.

  11. South Polar Layers

    NASA Technical Reports Server (NTRS)

    2003-01-01

    MGS MOC Release No. MOC2-516, 17 October 2003

    This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows eroded, stair-stepped layers in the south polar region of Mars. These layers have been considered, for the past three decades, to consist of a mixture of dust and ice. The Mars Polar Lander (MPL) mission was designed to test this hypothesis. However, sadly, MPL was lost during descent in December 1999. This exposure of south polar layered material is located near 86.3oS, 187.7oW. The image covers an area 3 km (1.9 mi) wide and is illuminated by sunlight from the upper left.

  12. Superfluid Boundary Layer

    NASA Astrophysics Data System (ADS)

    Stagg, G. W.; Parker, N. G.; Barenghi, C. F.

    2017-03-01

    We model the superfluid flow of liquid helium over the rough surface of a wire (used to experimentally generate turbulence) profiled by atomic force microscopy. Numerical simulations of the Gross-Pitaevskii equation reveal that the sharpest features in the surface induce vortex nucleation both intrinsically (due to the raised local fluid velocity) and extrinsically (providing pinning sites to vortex lines aligned with the flow). Vortex interactions and reconnections contribute to form a dense turbulent layer of vortices with a nonclassical average velocity profile which continually sheds small vortex rings into the bulk. We characterize this layer for various imposed flows. As boundary layers conventionally arise from viscous forces, this result opens up new insight into the nature of superflows.

  13. MHD turbulent mixing layers

    SciTech Connect

    Esquivel, A.; Lazarian, A.; Benjamin, R.A.; Cho, J.; Leitner, S.N.

    2005-09-28

    Turbulent mixing layers have been proposed to explain observations of line ratios of highly ionized elements in the interstellar medium. We present preliminary results of numerical simulations of turbulent mixing layers in a magnetized medium. We developed a MHD code with radiative cooling. The magnetic field is expected to be a controlling factor by suppressing instabilities that lead to the turbulent mixing. Our results suggest that the difference in turbulent mixing in the unmagnetized case as compared to the case of a weak magnetic field, {beta} = Pgas/Pmag {approx} 10, is insignificant. With a more thorough exploration of parameter space, this work will provide more reliable diagnostics of turbulent mixing layers than those available today.

  14. Layered Systems Engineering Engines

    NASA Technical Reports Server (NTRS)

    Breidenthal, Julian C.; Overman, Marvin J.

    2009-01-01

    A notation is described for depicting the relationships between multiple, contemporaneous systems engineering efforts undertaken within a multi-layer system-of-systems hierarchy. We combined the concepts of remoteness of activity from the end customer, depiction of activity on a timeline, and data flow to create a new kind of diagram which we call a "Layered Vee Diagram." This notation is an advance over previous notations because it is able to be simultaneously precise about activity, level of granularity, product exchanges, and timing; these advances provide systems engineering managers a significantly improved ability to express and understand the relationships between many systems engineering efforts. Using the new notation, we obtain a key insight into the relationship between project duration and the strategy selected for chaining the systems engineering effort between layers, as well as insights into the costs, opportunities, and risks associated with alternate chaining strategies.

  15. Layered Topological Crystalline Insulators.

    PubMed

    Kim, Youngkuk; Kane, C L; Mele, E J; Rappe, Andrew M

    2015-08-21

    Topological crystalline insulators (TCIs) are insulating materials whose topological property relies on generic crystalline symmetries. Based on first-principles calculations, we study a three-dimensional (3D) crystal constructed by stacking two-dimensional TCI layers. Depending on the interlayer interaction, the layered crystal can realize diverse 3D topological phases characterized by two mirror Chern numbers (MCNs) (μ1,μ2) defined on inequivalent mirror-invariant planes in the Brillouin zone. As an example, we demonstrate that new TCI phases can be realized in layered materials such as a PbSe (001) monolayer/h-BN heterostructure and can be tuned by mechanical strain. Our results shed light on the role of the MCNs on inequivalent mirror-symmetric planes in reciprocal space and open new possibilities for finding new topological materials.

  16. Layers and Dark Dunes

    NASA Image and Video Library

    2015-04-08

    The target of this observation as seen by ASA Mars Reconnaissance Orbiter is a circular depression in a dark-toned unit associated with a field of cones to the northeast. At the image scale of a Context Camera image, the depression appears to expose layers especially on the sides or walls of the depression, which are overlain by dark sands presumably associated with the dark-toned unit. HiRISE resolution, which is far higher than that of the Context Camera and its larger footprint, can help identify possible layers. http://photojournal.jpl.nasa.gov/catalog/PIA19358

  17. North Polar Layer Exposure

    NASA Technical Reports Server (NTRS)

    2004-01-01

    20 November 2004 Both the north and south polar ice caps overlie a thick accumulation of layered material. For more than three decades, these deposits have been assumed to consist of a mixture of dust and ice. This October 2004 Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows some of the north polar layers exposed on a slope located near 79.1oN, 348.4oW. The image covers an area approximately 3 km (1.9 mi) wide. Sunlight illuminates the scene from the lower left.

  18. Layers Inside 'Endurance'

    NASA Technical Reports Server (NTRS)

    2004-01-01

    This view of rock layers exposed in the upper portion of the inner slope of 'Endurance Crater' was captured by the navigation camera on NASA's Mars Exploration Rover Opportunity from the rover's position inside the crater during Opportunity's 134th sol on June 9, 2004. Scientists and engineers are assessing possible targets and routes among these rocks. The view is looking down into the crater, so the layers at the top of the image lie lower in the crater than the rocks in the foreground.

  19. Layered semiconductor neutron detectors

    DOEpatents

    Mao, Samuel S; Perry, Dale L

    2013-12-10

    Room temperature operating solid state hand held neutron detectors integrate one or more relatively thin layers of a high neutron interaction cross-section element or materials with semiconductor detectors. The high neutron interaction cross-section element (e.g., Gd, B or Li) or materials comprising at least one high neutron interaction cross-section element can be in the form of unstructured layers or micro- or nano-structured arrays. Such architecture provides high efficiency neutron detector devices by capturing substantially more carriers produced from high energy .alpha.-particles or .gamma.-photons generated by neutron interaction.

  20. Sedimentary Rock Layers

    NASA Technical Reports Server (NTRS)

    2004-01-01

    27 January 2004 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows layers of sedimentary rock in a crater in western Arabia Terra. Layered rock records the history of a place, but an orbiter image alone cannot tell the entire story. These materials record some past episodes of deposition of fine-grained material in an impact crater that is much larger than the image shown here. The picture is located near 3.4oN, 358.7oW, and covers an area 3 km (1.9 mi.) wide. Sunlight illuminates the scene from the lower left.

  1. Layers Inside 'Endurance'

    NASA Technical Reports Server (NTRS)

    2004-01-01

    This view of rock layers exposed in the upper portion of the inner slope of 'Endurance Crater' was captured by the navigation camera on NASA's Mars Exploration Rover Opportunity from the rover's position inside the crater during Opportunity's 134th sol on June 9, 2004. Scientists and engineers are assessing possible targets and routes among these rocks. The view is looking down into the crater, so the layers at the top of the image lie lower in the crater than the rocks in the foreground.

  2. Layers Inside 'Endurance'

    NASA Image and Video Library

    2004-06-15

    This view of rock layers exposed in the upper portion of the inner slope of "Endurance Crater" was captured by the navigation camera on NASA's Mars Exploration Rover Opportunity from the rover's position inside the crater during Opportunity's 134th sol on June 9, 2004. Scientists and engineers are assessing possible targets and routes among these rocks. The view is looking down into the crater, so the layers at the top of the image lie lower in the crater than the rocks in the foreground. http://photojournal.jpl.nasa.gov/catalog/PIA06263

  3. Sedimentary Rock Layers

    NASA Technical Reports Server (NTRS)

    2004-01-01

    27 January 2004 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows layers of sedimentary rock in a crater in western Arabia Terra. Layered rock records the history of a place, but an orbiter image alone cannot tell the entire story. These materials record some past episodes of deposition of fine-grained material in an impact crater that is much larger than the image shown here. The picture is located near 3.4oN, 358.7oW, and covers an area 3 km (1.9 mi.) wide. Sunlight illuminates the scene from the lower left.

  4. Layers and Streaks

    NASA Technical Reports Server (NTRS)

    2004-01-01

    6 December 2004 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows an outcrop of light-toned layered rock and a plethora of dark streaks on the floor of a crater in southern Noachis Terra. The streaks were created by dozens of dust devils which disrupted and perhaps removed some of the thin layer of dust that coats the surface. This view is located near 55.5oS, 333.4oW. The scene is illuminated by sunlight from the lower right. The 500 meter scale bar is approximately 547 yards long.

  5. Layers in Melas Chasma

    NASA Technical Reports Server (NTRS)

    2006-01-01

    [figure removed for brevity, see original site] Click on image for larger annotated version

    This scene of layered deposits is from Melas Chasma, part of the Valles Marineris valley network. The area consists of a series of plateaus and cliffs that form a step-like terrain similar to the Grand Staircase-Escalante region of southwest Utah. The upper-right half of the image covers the highest plateau, and lower cliffs and plateaus step down in elevation toward the lower left of the image. Dunes of dark sand commonly cover the flat plateaus and distinct layers of bedrock are exposed in the cliffs. The orientations of these layers may help scientists to understand how the layers formed and the kind of environment that the layers formed in. Black rectangles on the left side of the image are areas where the image data was lost during transmission from Mars Reconnaissance Orbiter to Earth. This subscene [above] shows a series of boulder tracks on the left side of the image. The boulders fell from the cliffs above and left behind a series of small depressions. Each depression was made as the boulder bounced and rolled along the surface. In many cases, the tracks can be followed to the specific boulder that made them. Also visible in this subscene are cross-sections through the layered bedrock. This bedrock likely formed through settling of sand-sized particles out of the air or out of a body of water that has since drained away. These layers are 'cross-bedded', which means that subsequent layers are not parallel to each other but are instead oriented at an angle to other layers. The fact that these layers are cross-bedded indicates that the sand-sized particles were moved horizontally along the surface as they settled, just like sand dunes or ripples at the bottom of a stream. The size and shape of these cross-beds may help scientists to determine if the layers formed underwater or on land.

    Image PSP_001377_1685 was taken by the High Resolution Imaging

  6. Plasmons in layered films

    NASA Astrophysics Data System (ADS)

    Jain, J. K.; Allen, P. B.

    1985-06-01

    A random-phase-approximation theory is given for the electronic collective modes of a film containing N equally spaced layers of two-dimensional electron gas. Raman line shapes are predicted. The Giuliani-Quinn surface-plasmon intensity is enhanced in transmission geometry.

  7. Layer-Cake Earth

    ERIC Educational Resources Information Center

    Tedford, Rebecca; Warny, Sophie

    2006-01-01

    In this article, the authors offer a safe, fun, effective way to introduce geology concepts to elementary school children of all ages: "coring" layer cakes. This activity introduces the concepts and challenges that geologists face and at the same time strengthens students' inferential, observational, and problem-solving skills. It also addresses…

  8. Teaching the Double Layer.

    ERIC Educational Resources Information Center

    Bockris, J. O'M.

    1983-01-01

    Suggests various methods for teaching the double layer in electrochemistry courses. Topics addressed include measuring change in absolute potential difference (PD) at interphase, conventional electrode potential scale, analyzing absolute PD, metal-metal and overlap electron PDs, accumulation of material at interphase, thermodynamics of electrified…

  9. South Polar Layered Slope

    NASA Technical Reports Server (NTRS)

    2003-01-01

    MGS MOC Release No. MOC2-559, 29 November 2003

    Both the north and south polar regions of Mars exhibit thick deposits of layered sediment. These have been known since the Mariner 9 (1972) and Viking (1976-1980) orbiter missions. The layered deposits are considered to contain a record of climate changes that occurred in the relatively recent martian past, but most of that record will have to wait until some time in the future when a lander or people can go there to study them. Meanwhile, pictures such as this from the Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) provide opportunities to view the layers where they are exposed on slopes. Here, numerous layers have been exposed by erosion in the south polar region. The picture was obtained in October 2003 and is located near 86.4oS, 112.4oW. The image covers an area 3 km (1.9 mi) wide, and is illuminated by sunlight from the upper left.

  10. Undoped Buffer Layer Development.

    DTIC Science & Technology

    1984-01-01

    boiled for several hours in aqua regia , followed by boiling for several more hours in deionized water before being dried in air and loaded into the...different from Report) 1S. SUPPLEMENTARY NOTES it. IKy WORDS (Canal... an reverse 4aaIo It eesarav d Ientify by block nuinbr) Epitaxial layer MBE

  11. Layer-Cake Earth

    ERIC Educational Resources Information Center

    Tedford, Rebecca; Warny, Sophie

    2006-01-01

    In this article, the authors offer a safe, fun, effective way to introduce geology concepts to elementary school children of all ages: "coring" layer cakes. This activity introduces the concepts and challenges that geologists face and at the same time strengthens students' inferential, observational, and problem-solving skills. It also addresses…

  12. MITRE sensor layer prototype

    NASA Astrophysics Data System (ADS)

    Duff, Francis; McGarry, Donald; Zasada, David; Foote, Scott

    2009-05-01

    The MITRE Sensor Layer Prototype is an initial design effort to enable every sensor to help create new capabilities through collaborative data sharing. By making both upstream (raw) and downstream (processed) sensor data visible, users can access the specific level, type, and quantities of data needed to create new data products that were never anticipated by the original designers of the individual sensors. The major characteristic that sets sensor data services apart from typical enterprise services is the volume (on the order of multiple terabytes) of raw data that can be generated by most sensors. Traditional tightly coupled processing approaches extract pre-determined information from the incoming raw sensor data, format it, and send it to predetermined users. The community is rapidly reaching the conclusion that tightly coupled sensor processing loses too much potentially critical information.1 Hence upstream (raw and partially processed) data must be extracted, rapidly archived, and advertised to the enterprise for unanticipated uses. The authors believe layered sensing net-centric integration can be achieved through a standardize-encapsulate-syndicateaggregate- manipulate-process paradigm. The Sensor Layer Prototype's technical approach focuses on implementing this proof of concept framework to make sensor data visible, accessible and useful to the enterprise. To achieve this, a "raw" data tap between physical transducers associated with sensor arrays and the embedded sensor signal processing hardware and software has been exploited. Second, we encapsulate and expose both raw and partially processed data to the enterprise within the context of a service-oriented architecture. Third, we advertise the presence of multiple types, and multiple layers of data through geographic-enabled Really Simple Syndication (GeoRSS) services. These GeoRSS feeds are aggregated, manipulated, and filtered by a feed aggregator. After filtering these feeds to bring just the type

  13. Reactivity and applications of layered silicates and layered double hydroxides.

    PubMed

    Selvam, Thangaraj; Inayat, Alexandra; Schwieger, Wilhelm

    2014-07-21

    Layered materials, such as layered sodium silicates and layered double hydroxides (LDHs), are well-known for their remarkable adsorption, intercalation and swelling properties. Their tunable interlayers offer an interesting avenue for the fabrication of pillared nanoporous materials, organic-inorganic hybrid materials and catalysts or catalyst supports. This perspective article provides a summary of the reactivity and applications of layered materials including aluminium-free layered sodium silicates (kanemite, ilerite (RUB-18 or octosilicate) and magadiite) and layered double hydroxides (LDHs). Recent developments in the use of layered sodium silicates as precursors for the preparation of various porous, functional and catalytic materials including zeolites, mesoporous materials, pillared layered silicates, organic-inorganic nanocomposites and synthesis of highly dispersed nanoparticles supported on silica are reviewed in detail. Along this perspective, we have attempted to illustrate the reactivity and transformational potential of LDHs in order to deduce the main differences and similarities between these two types of layered materials.

  14. Boundary layer transition studies

    NASA Technical Reports Server (NTRS)

    Watmuff, Jonathan H.

    1995-01-01

    A small-scale wind tunnel previously used for turbulent boundary layer experiments was modified for two sets of boundary layer transition studies. The first study concerns a laminar separation/turbulent reattachment. The pressure gradient and unit Reynolds number are the same as the fully turbulent flow of Spalart and Watmuff. Without the trip wire, a laminar layer asymptotes to a Falkner & Skan similarity solution in the FPG. Application of the APG causes the layer to separate and a highly turbulent and approximately 2D mean flow reattachment occurs downstream. In an effort to gain some physical insight into the flow processes a small impulsive disturbance was introduced at the C(sub p) minimum. The facility is totally automated and phase-averaged data are measured on a point-by-point basis using unprecedently large grids. The evolution of the disturbance has been tracked all the way into the reattachment region and beyond into the fully turbulent boundary layer. At first, the amplitude decays exponentially with streamwise distance in the APG region, where the layer remains attached, i.e. the layer is viscously stable. After separation, the rate of decay slows, and a point of minimum amplitude is reached where the contours of the wave packet exhibit dispersive characteristics. From this point, exponential growth of the amplitude of the disturbance is observed in the detached shear layer, i.e. the dominant instability mechanism is inviscid. A group of large-scale 3D vortex loops emerges in the vicinity of the reattachment. Remarkably, the second loop retains its identify far downstream in the turbulent boundary layer. The results provide a level of detail usually associated with CFD. Substantial modifications were made to the facility for the second study concerning disturbances generated by Suction Holes for laminar flow Control (LFC). The test section incorporates suction through interchangeable porous test surfaces. Detailed studies have been made using isolated

  15. Boundary layer transition studies

    NASA Astrophysics Data System (ADS)

    Watmuff, Jonathan H.

    1995-02-01

    A small-scale wind tunnel previously used for turbulent boundary layer experiments was modified for two sets of boundary layer transition studies. The first study concerns a laminar separation/turbulent reattachment. The pressure gradient and unit Reynolds number are the same as the fully turbulent flow of Spalart and Watmuff. Without the trip wire, a laminar layer asymptotes to a Falkner & Skan similarity solution in the FPG. Application of the APG causes the layer to separate and a highly turbulent and approximately 2D mean flow reattachment occurs downstream. In an effort to gain some physical insight into the flow processes a small impulsive disturbance was introduced at the C(sub p) minimum. The facility is totally automated and phase-averaged data are measured on a point-by-point basis using unprecedently large grids. The evolution of the disturbance has been tracked all the way into the reattachment region and beyond into the fully turbulent boundary layer. At first, the amplitude decays exponentially with streamwise distance in the APG region, where the layer remains attached, i.e. the layer is viscously stable. After separation, the rate of decay slows, and a point of minimum amplitude is reached where the contours of the wave packet exhibit dispersive characteristics. From this point, exponential growth of the amplitude of the disturbance is observed in the detached shear layer, i.e. the dominant instability mechanism is inviscid. A group of large-scale 3D vortex loops emerges in the vicinity of the reattachment. Remarkably, the second loop retains its identify far downstream in the turbulent boundary layer. The results provide a level of detail usually associated with CFD. Substantial modifications were made to the facility for the second study concerning disturbances generated by Suction Holes for laminar flow Control (LFC). The test section incorporates suction through interchangeable porous test surfaces. Detailed studies have been made using isolated

  16. Peeling Back the Layers

    NASA Technical Reports Server (NTRS)

    2004-01-01

    NASA's Mars Exploration Rover Spirit took this panoramic camera image of the rock target named 'Mazatzal' on sol 77 (March 22, 2004). It is a close-up look at the rock face and the targets that will be brushed and ground by the rock abrasion tool in upcoming sols.

    Mazatzal, like most rocks on Earth and Mars, has layers of material near its surface that provide clues about the history of the rock. Scientists believe that the top layer of Mazatzal is actually a coating of dust and possibly even salts. Under this light coating may be a more solid portion of the rock that has been chemically altered by weathering. Past this layer is the unaltered rock, which may give scientists the best information about how Mazatzal was formed.

    Because each layer reveals information about the formation and subsequent history of Mazatzal, it is important that scientists get a look at each of them. For this reason, they have developed a multi-part strategy to use the rock abrasion tool to systematically peel back Mazatzal's layers and analyze what's underneath with the rover's microscopic imager, and its Moessbauer and alpha particle X-ray spectrometers.

    The strategy began on sol 77 when scientists used the microscopic imager to get a closer look at targets on Mazatzal named 'New York,' 'Illinois' and 'Arizona.' These rock areas were targeted because they posed the best opportunity for successfully using the rock abrasion tool; Arizona also allowed for a close-up look at a range of tones. On sol 78, Spirit's rock abrasion tool will do a light brushing on the Illinois target to preserve some of the surface layers. Then, a brushing of the New York target should remove the top coating of any dust and salts and perhaps reveal the chemically altered rock underneath. Finally, on sol 79, the rock abrasion tool will be commanded to grind into the New York target, which will give scientists the best chance of observing Mazatzal's interior.

    The Mazatzal targets were named

  17. Layered seal for turbomachinery

    DOEpatents

    Sarawate, Neelesh Nandkumar; Morgan, Victor John; Weber, David Wayne

    2015-11-20

    The present application provides seal assemblies for reducing leakages between adjacent components of turbomachinery. The seal assemblies may include outer shims, and at least a portion of the outer shims may be substantially impervious. At least one of the outer shims may be configured for sealing engagement with seal slots of the adjacent components. The seal assemblies may also include at least one of an inner shim and a filler layer positioned between the outer shims. The at least one inner shim may be substantially solid and the at least one filler layer may be relatively porous. The seal assemblies may be sufficiently flexible to account for misalignment between the adjacent components, sufficiently stiff to meet assembly requirements, and sufficiently robust to operating meet requirements associated with turbomachinery.

  18. Crack layer theory

    NASA Technical Reports Server (NTRS)

    Chudnovsky, A.

    1984-01-01

    A damage parameter is introduced in addition to conventional parameters of continuum mechanics and consider a crack surrounded by an array of microdefects within the continuum mechanics framework. A system consisting of the main crack and surrounding damage is called crack layer (CL). Crack layer propagation is an irreversible process. The general framework of the thermodynamics of irreversible processes are employed to identify the driving forces (causes) and to derive the constitutive equation of CL propagation, that is, the relationship between the rates of the crack growth and damage dissemination from one side and the conjugated thermodynamic forces from another. The proposed law of CL propagation is in good agreement with the experimental data on fatigue CL propagation in various materials. The theory also elaborates material toughness characterization.

  19. Sedimentary Rock Layers

    NASA Technical Reports Server (NTRS)

    2003-01-01

    MGS MOC Release No. MOC2-348, 2 May 2003

    This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image acquired in March 2003 shows dozens of repeated layers of sedimentary rock in a western Arabia Terra crater at 8oN, 7oW. Wind has sculpted the layered forms into hills somewhat elongated toward the lower left (southwest). The dark patches at the bottom (south) end of the image are drifts of windblown sand. These sedimentary rocks might indicate that the crater was once the site of a lake--or they may result from deposition by wind in a completely dry, desert environment. Either way, these rocks have something important to say about the geologic history of Mars. The area shown is about 3 km (1.9 mi) wide. Sunlight illuminates the scene from the left.

  20. Layered Rocks in Crater

    NASA Technical Reports Server (NTRS)

    2004-01-01

    19 June 2004 Exposures of layered, sedimentary rock are common on Mars. From the rock outcrops examined by the Mars Exploration Rover, Opportunity, in Meridiani Planum to the sequence in Gale Crater's central mound that is twice the thickness of of the sedimentary rocks exposed by Arizona's Grand Canyon, Mars presents a world of sediment to study. This unusual example, imaged by the Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC), shows eroded layer outcrops in a crater in Terra Tyrrhena near 15.4oS, 270.5oW. Sedimentary rocks provide a record of past climates and events. Perhaps someday the story told by the rocks in this image will be known via careful field work. The image covers an area about 3 km (1.9 mi) wide and is illuminated by sunlight from the left.

  1. Layered Composite Analysis Capability

    NASA Technical Reports Server (NTRS)

    Narayanaswami, R.; Cole, J. G.

    1985-01-01

    Laminated composite material construction is gaining popularity within industry as an attractive alternative to metallic designs where high strength at reduced weights is of prime consideration. This has necessitated the development of an effective analysis capability for the static, dynamic and buckling analyses of structural components constructed of layered composites. Theoretical and user aspects of layered composite analysis and its incorporation into CSA/NASTRAN are discussed. The availability of stress and strain based failure criteria is described which aids the user in reviewing the voluminous output normally produced in such analyses. Simple strategies to obtain minimum weight designs of composite structures are discussed. Several example problems are presented to demonstrate the accuracy and user convenient features of the capability.

  2. Sedimentary Rock Layers

    NASA Technical Reports Server (NTRS)

    2003-01-01

    MGS MOC Release No. MOC2-348, 2 May 2003

    This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image acquired in March 2003 shows dozens of repeated layers of sedimentary rock in a western Arabia Terra crater at 8oN, 7oW. Wind has sculpted the layered forms into hills somewhat elongated toward the lower left (southwest). The dark patches at the bottom (south) end of the image are drifts of windblown sand. These sedimentary rocks might indicate that the crater was once the site of a lake--or they may result from deposition by wind in a completely dry, desert environment. Either way, these rocks have something important to say about the geologic history of Mars. The area shown is about 3 km (1.9 mi) wide. Sunlight illuminates the scene from the left.

  3. Boundary layer simulator improvement

    NASA Technical Reports Server (NTRS)

    Praharaj, S. C.; Schmitz, C.; Frost, C.; Engel, C. D.; Fuller, C. E.; Bender, R. L.; Pond, J.

    1984-01-01

    High chamber pressure expander cycles proposed for orbit transfer vehicles depend primarily on the heat energy transmitted from the combustion products through the thrust wall chamber wall. The heat transfer to the nozzle wall is affected by such variables as wall roughness, relamarization, and the presence of particles in the flow. Motor performance loss for these nozzles with thick boundary layers is inaccurate using the existing procedure coded BLIMPJ. Modifications and innovations to the code are examined. Updated routines are listed.

  4. Origins of Igneous Layering

    NASA Astrophysics Data System (ADS)

    Marsh, Bruce

    Anyone who has ever seen a photo of a layered intrusion, let alone visited one first hand, or even seen a thin section from one, cannot help but be impressed by the stunning record of crystal growth and deposition. Such bodies stand as majestic monuments of undeniable evidence that intricate magmatic processes exist, processes that couple crystallization, convection, and crystal sorting to form rocks so highly ordered and beautiful that they are a wonder to behold. These are the altars to which petrologists must carry their conceived petrologic processes for approval.Although significant in number, the best layered intrusions seem to be found almost always in remote places. Their names, Bushveld, Muskox, Kiglapait, Stillwater, Duke Island, Skaergaard, Rhum, ring through igneous petrology almost as historic military battles (Saratoga, Antietam, Bull Run, Manassas, Gettysburg) do through American history. People who have worked on such bodies are almost folk heros: Wager, Deer, Brown, Jackson, Hess, Irvine, McBirney, Morse; these names are petrologic household words. Yet with all this fanfare and reverence, layered instrusions are nearly thought of as period pieces, extreme examples of what can happen, but not generally what does. This is now all changing with the increasing realization that these bodies are perhaps highly representative of all magmatic bodies. They are simply more dynamically complete, containing more of the full range of interactions, and of course, exposing a more complete record. They are one end of a spectrum containing lava flows, lava lakes, large sills, plutons, and layered intrusions. This book uniquely covers this range with an abundance of first-hand field observations and a good dose of process conceptualization, magma physics, and crystal growth kinetics.

  5. Layered bismuth vanadate ferroelectrics

    SciTech Connect

    Osipyan, V.G.; Savchenko, L.M.; Elbakyan, V.L.; Avakyan, P.B.

    1987-08-01

    The authors synthesize new layered bismuth vanadate ferroelectrics. The x-ray diffraction characteristics of Bi/sub 2/VO/sub 5.5/ are shown. Thermal expansion of ceramics with various compositions are presented, as are the temperature dependences of the dielectric constant of the ceramic with various compositions. Unit-cell parameters, Curie temperature, electrical conductivity and the dielectric characteristics of the compositions studied are shown.

  6. The atmospheric boundary layer

    SciTech Connect

    Garratt, J.R.

    1992-01-01

    This book is aimed at researchers in the atmospheric and associated sciences who require a moderately advanced text on the Atmospheric Boundary Layer (ABL) in which the many links between turbulence, air-surface transfer, boundary-layer structure and dynamics, and numerical modeling are discussed and elaborated upon. Chapter 1 serves as an introduction, with Chapters 2 and 3 dealing with the development of mean and turbulence equations, and the many scaling laws and theories that are the cornerstone of any serious ABL treatment. Modelling of the ABL is crucially dependent for its realism on the surface boundary conditions, and Chapters 4 and 5 deal with aerodynamic and energy considerations, with attention to both dry and wet land surfaces and the sea. The structure of the clear-sky, thermally stratified ABL is treated in Chapter 6, including the convective and stable cases over homogeneous land, the marine ABL and the internal boundary layer at the coastline. Chapter 7 then extends the discussion to the cloudy ABL. This is seen as particularly relevant since the extensive stratocumulus regions over the sub-tropical oceans and stratus regions over the Arctic are now identified as key players in the climate system. Finally, Chapters 8 and 9 bring much of the book's material together in a discussion of appropriate ABL and surface parameterization schemes for the general circulation models of the atmosphere that are being used for climate simulation.

  7. Crater with Exposed Layers

    NASA Image and Video Library

    2017-01-17

    On Earth, geologists can dig holes and pull up core samples to find out what lies beneath the surface. On Mars, geologists cannot dig holes very easily themselves, but a process has been occurring for billions of years that has been digging holes for them: impact cratering. Impact craters form when an asteroid, meteoroid, or comet crashes into a planet's surface, causing an explosion. The energy of the explosion, and the resulting size of the impact crater, depends on the size and density of the impactor, as well as the properties of the surface it hits. In general, the larger and denser the impactor, the larger the crater it will form. The impact crater in this image is a little less than 3 kilometers in diameter. The impact revealed layers when it excavated the Martian surface. Layers can form in a variety of different ways. Multiple lava flows in one area can form stacked sequences, as can deposits from rivers or lakes. Understanding the geology around impact craters and searching for mineralogical data within their layers can help scientists on Earth better understand what the walls of impact craters on Mars expose. http://photojournal.jpl.nasa.gov/catalog/PIA12328

  8. Diversity in S-layers.

    PubMed

    Zhu, Chaohua; Guo, Gang; Ma, Qiqi; Zhang, Fengjuan; Ma, Funing; Liu, Jianping; Xiao, Dao; Yang, Xiaolin; Sun, Ming

    2017-01-01

    Surface layers, referred simply as S-layers, are the two-dimensional crystalline arrays of protein or glycoprotein subunits on cell surface. They are one of the most common outermost envelope components observed in prokaryotic organisms (Archaea and Bacteria). Over the past decades, S-layers have become an issue of increasing interest due to their ubiquitousness, special features and functions. Substantial work in this field provides evidences of an enormous diversity in S-layers. This paper reviews and illustrates the diversity from several different aspects, involving the S-layer-carrying strains, the structure of S-layers, the S-layer proteins and genes, as well as the functions of S-layers.

  9. Modern Thin-Layer Chromatography.

    ERIC Educational Resources Information Center

    Poole, Colin F.; Poole, Salwa K.

    1989-01-01

    Some of the important modern developments of thin-layer chromatography are introduced. Discussed are the theory and instrumentation of thin-layer chromatography including multidimensional and multimodal techniques. Lists 53 references. (CW)

  10. Protecting the ozone layer.

    PubMed

    Munasinghe, M; King, K

    1992-06-01

    Stratospheric ozone layer depletion has been recognized as a problem by the Vienna Convention for the Protection of the Ozone Layer and the 1987 Montreal Protocol (MP). The ozone layer shields the earth from harmful ultraviolet radiation (UV-B), which is more pronounced at the poles and around the equator. Industrialized countries have contributed significantly to the problem by releasing chlorofluorocarbons (CFCs) and halons into the atmosphere. The effect of these chemicals, which were known for their inertness, nonflammability, and nontoxicity, was discovered in 1874. Action to deal with the effects of CFCs and halons was initiated in 1985 in a 49-nation UN meeting. 21 nations signed a protocol limiting ozone depleting substances (ODS): CFCs and halons. Schedules were set based on each country's use in 1986; the target phaseout was set for the year 2000. The MP restricts trade in ODSs and weights the impact of substances to reflect the extent of damage; i.e., halons are 10 times more damaging than CFCs. ODS requirements for developing countries were eased to accommodate scarce resources and the small fraction of ODS emissions. An Interim Multilateral Fund under the Montreal Protocol (IMFMP) was established to provide loans to finance the costs to developing countries in meeting global environmental requirements. The IMFMP is administered by the World Bank, the UN Environmental Program, and the UN Development Program. Financing is available to eligible countries who use .3 kg of ODS/person/year. Rapid phaseout in developed countries has occurred due to strong support from industry and a lower than expected cost. Although there are clear advantages to rapid phaseout, there were no incentives included in the MP for rapid phaseout. Some of the difficulties occur because the schedules set minimum targets at the lowest possible cost. Also, costs cannot be minimized by a country-specific and ODS-specific process. The ways to improve implementation in scheduling and

  11. Unsteady Shear Layers.

    DTIC Science & Technology

    1985-10-29

    plunging airfoils, elliptic jets with mass entrainment and impinging ’ j ets. Additionally, the 3-D vortical flow over a backward facing step was...reattachment length is only about 4 step depths which is much shorter than that in a 2-D J . .1 r r*~ % 4,V rq ~ 4 case. The reattachment line shows a ...Boundary Layers", R.F. Blackwelder and J.H. Haritonidis, J . Fluid Mech., 132, 87, 1983. 2. "Breakdown of Streamwise Vortices near a Wall", J.D

  12. The Keck keyword layer

    NASA Technical Reports Server (NTRS)

    Conrad, A. R.; Lupton, W. F.

    1992-01-01

    Each Keck instrument presents a consistent software view to the user interface programmer. The view consists of a small library of functions, which are identical for all instruments, and a large set of keywords, that vary from instrument to instrument. All knowledge of the underlying task structure is hidden from the application programmer by the keyword layer. Image capture software uses the same function library to collect data for the image header. Because the image capture software and the instrument control software are built on top of the same keyword layer, a given observation can be 'replayed' by extracting keyword-value pairs from the image header and passing them back to the control system. The keyword layer features non-blocking as well as blocking I/O. A non-blocking keyword write operation (such as setting a filter position) specifies a callback to be invoked when the operation is complete. A non-blocking keyword read operation specifies a callback to be invoked whenever the keyword changes state. The keyword-callback style meshes well with the widget-callback style commonly used in X window programs. The first keyword library was built for the two Keck optical instruments. More recently, keyword libraries have been developed for the infrared instruments and for telescope control. Although the underlying mechanisms used for inter-process communication by each of these systems vary widely (Lick MUSIC, Sun RPC, and direct socket I/O, respectively), a basic user interface has been written that can be used with any of these systems. Since the keyword libraries are bound to user interface programs dynamically at run time, only a single set of user interface executables is needed. For example, the same program, 'xshow', can be used to display continuously the telescope's position, the time left in an instrument's exposure, or both values simultaneously. Less generic tools that operate on specific keywords, for example an X display that controls optical

  13. Cooperating systems: Layered MAS

    NASA Technical Reports Server (NTRS)

    Rochowiak, Daniel

    1990-01-01

    Distributed intelligent systems can be distinguished by the models that they use. The model developed focuses on layered multiagent system conceived of as a bureaucracy in which a distributed data base serves as a central means of communication. The various generic bureaus of such a system is described and a basic vocabulary for such systems is presented. In presenting the bureaus and vocabularies, special attention is given to the sorts of reasonings that are appropriate. A bureaucratic model has a hierarchy of master system and work group that organizes E agents and B agents. The master system provides the administrative services and support facilities for the work groups.

  14. Layered Rocks of Melas

    NASA Technical Reports Server (NTRS)

    2004-01-01

    04 August 2004 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows layered sedimentary rock outcrops exposed by erosion in southern Melas Chasma, one of the major Valles Marineris troughs. Such outcrops are common in southern Melas; they resemble the rock outcrops seen in some of the chaotic terrains and other Valles Marineris chasms. This image is located near 11.9oS, 74.6oW, and is about 3 km (1.9 mi) wide. Sunlight illuminates the scene from the lower left.

  15. Layered Rocks in Ritchey

    NASA Technical Reports Server (NTRS)

    2004-01-01

    14 May 2004 This March 2004 Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows light- and dark-toned layered rock outcrops on the floor of Ritchey Crater, located near 28.9oS, 50.8oW. Some or all of these rocks may be sedimentary in origin. Erosion has left a couple of buttes standing on a more erosion-resistant plain. This picture covers an area approximately 3 km (1.9 mi) across and is illuminated by sunlight from the upper left.

  16. Simulation of multilayer homoepitaxial growth on Cu (100) surface

    NASA Astrophysics Data System (ADS)

    Wu, Feng-Min; Lu, Hang-Jun; Wu, Zi-Qin

    2006-04-01

    The processes of multilayer thin Cu films grown on Cu (100) surfaces at elevated temperature (250-400 K) are simulated by mean of kinetic Monte Carlo (KMC) method, where the realistic growth model and physical parameters are used. The effects of small island (dimer and trimer) diffusion, edge diffusion along the islands, exchange of the adatom with an atom in the existing island, as well as mass transport between interlayers are included in the simulation model. Emphasis is placed on revealing the influence of the Ehrlich-Schwoebel (ES) barrier on growth mode and morphology during multilayer thin film growth. We present numerical evidence that the ES barrier does exist for the Cu/Cu(100) system and an ES barrier EB>0.125 eV is estimated from a comparison of the KMC simulation with the realistic experimental images. The transitions of growth modes with growth conditions and the influence of exchange barrier on growth mode are also investigated.

  17. Simulation of Pores Sealing During Homoepitaxy on Si(111) Surface

    DTIC Science & Technology

    2000-06-23

    deposition rate. Simulation results of epitaxial growth on porous surface with 100 x 100 atomic sites (a.s.) at T = 1073 K [ , ] for different surface...s), v is vibration frequency (1/s), k is Boltzmann’s constant, T is substrate temperature (K). Taking v = 1013 s-1, Ed = 1.75 eV ],T = 1073 K for...surface at T = 1073 K for ndif = 10 (high deposition rate). Pores diameter is 10 atomic sites, height is 20 BL, surface porosity P• = 26 %. (a

  18. On the kinetic barriers of graphene homo-epitaxy

    SciTech Connect

    Zhang, Wei; Yu, Xinke; Xie, Ya-Hong; Cahyadi, Erica; Ratsch, Christian

    2014-12-01

    The diffusion processes and kinetic barriers of individual carbon adatoms and clusters on graphene surfaces are investigated to provide fundamental understanding of the physics governing epitaxial growth of multilayer graphene. It is found that individual carbon adatoms form bonds with the underlying graphene whereas the interaction between graphene and carbon clusters, consisting of 6 atoms or more, is very weak being van der Waals in nature. Therefore, small carbon clusters are quite mobile on the graphene surfaces and the diffusion barrier is negligibly small (∼6 meV). This suggests the feasibility of high-quality graphene epitaxial growth at very low growth temperatures with small carbon clusters (e.g., hexagons) as carbon source. We propose that the growth mode is totally different from 3-dimensional bulk materials with the surface mobility of carbon hexagons being the highest over graphene surfaces that gradually decreases with further increase in cluster size.

  19. Layered Manufacturing: Challenges and Opportunities

    DTIC Science & Technology

    2003-04-01

    UNCLASSIFIED Defense Technical Information Center Compilation Part Notice ADP014215 TITLE: Layered Manufacturing : Challenges and Opportunities ...Research Society LL1.4 Layered Manufacturing : Challenges and Opportunities Khershed P. Cooper Materials Science and Technology Division, Naval Research...Laboratory Washington, DC 20375-5343, U.S.A. ABSTRACT Layered Manufacturing (LM) refers to computer-aided manufacturing processes in which parts are made

  20. The Boundary Layer Radiometer

    NASA Astrophysics Data System (ADS)

    Irshad, Ranah; Bowles, N. E.; Calcutt, S. B.; Hurley, J.

    2010-10-01

    The Boundary Layer Radiometer is a small, low mass (<1kg) radiometer with only a single moving part - a scan/calibration mirror. The instrument consists of a three mirror telescope system incorporating an intermediate focus for use with miniature infrared and visible filters. It also has an integrated low power blackbody calibration target to provide long-term calibration stability The instrument may be used as an upward looking boundary layer radiometer for both the terrestrial and Martian atmospheres with appropriate filters for the mid-infrared carbon dioxide band, as well as a visible channel for the detection of aerosol components such as dust. The scan mirror may be used to step through different positions from the local horizon to the zenith, allowing the vertical temperature profile of the atmosphere to be retrieved. The radiometer uses miniature infrared filter assemblies developed for previous space-based instruments by Oxford, Cardiff and Reading Universities. The intermediate focus allows for the use of upstream blocking filters and baffles, which not only simplifies the design of the filters and focal plane assembly, but also reduces the risk of problems due to stray light. Combined with the calibration target this means it has significant advantages over previous generations of small radiometers.

  1. Turbulent boundary layer heat

    NASA Astrophysics Data System (ADS)

    Finson, M. L.; Clarke, A. S.; Wu, P. K. S.

    1981-01-01

    A Reynolds stress model for turbulent boundary layers is used to study surface roughness effects on skin friction and heat transfer. The issues of primary interest are the influence of roughness character (element shape and spacing) and the nature of roughness effects at high Mach numbers. Computations based on the model compare satisfactorily with measurements from experiments involving variations in roughness character, in low speed and modestly supersonic conditions. The more limited data base at hypersonic Mach numbers is also examined with reasonable success, although no quantitative explanation is offered for the reduction of heat transfer with increasing roughness observed by Holden at Me -9.4. The present calculations indicate that the mean velocity is approximately uniform over much of the height range below the tops of the elements, y less than or equal to k. With this constant (roughness velocity,) it is simple to estimate the form drag on the elements. This roughness velocity has been investigated by systematically exercising the present model over ranges of potential parameters. The roughness velocity is found to be primarily a function of the projected element frontal area per unit surface area, thus providing a new and simple method for predicting roughness character effects. The model further suggests that increased boundary layer temperatures should be generated by roughness at high edge Mach numbers, which would tend to reduce skin friction and heat transfer, perhaps below smooth wall levels.

  2. Thin layer chromatography.

    PubMed

    Santiago, Marina; Strobel, Scott

    2013-01-01

    In many experiments, it is important to be able to separate a mixture into its chemical components in order to isolate one compound or to assess the purity of the mixture. Thin layer chromatography (TLC) is one of the easiest and most versatile methods of doing this because of its low cost, simplicity, quick development time, high sensitivity, and good reproducibility. TLC is used by many industries and fields of research, including pharmaceutical production, clinical analysis, industrial chemistry, environmental toxicology, food chemistry, water, inorganic, and pesticide analysis, dye purity, cosmetics, plant materials, and herbal analysis. In its simplest form, glass plates are coated with a uniform layer of silica gel (SiO2). The dissolved sample is placed on the plate, and the plate is inserted into a screw-top jar containing the developing solvent and a piece of filter paper. When the solvent has risen to near the top of the plate, the plate is removed, dried, and visualized using UV light. Variations on this protocol are used for different purposes, including pretreating the sample, changing the sorbent, plate material, the solvent system, the development techniques, and method of detection and visualization or by coupling TLC to other techniques. © 2013 Elsevier Inc. All rights reserved.

  3. Multiresonant layered plasmonic films

    SciTech Connect

    DeVetter, Brent M.; Bernacki, Bruce E.; Bennett, Wendy D.; Schemer-Kohrn, Alan; Alvine, Kyle J.

    2017-01-01

    Multi-resonant nanoplasmonic films have numerous applications in areas such as nonlinear optics, sensing, and tamper indication. While techniques such as focused ion beam milling and electron beam lithography can produce high-quality multi-resonant films, these techniques are expensive, serial processes that are difficult to scale at the manufacturing level. Here, we present the fabrication of multi-resonant nanoplasmonic films using a layered stacking technique. Periodically-spaced gold nanocup substrates were fabricated using self-assembled polystyrene nanospheres followed by oxygen plasma etching and metal deposition via magnetron sputter coating. By adjusting etch parameters and initial nanosphere size, it was possible to achieve an optical response ranging from the visible to the near-infrared. Singly resonant, flexible films were first made by performing peel-off using an adhesive-coated polyolefin film. Through stacking layers of the nanofilm, we demonstrate fabrication of multi-resonant films at a fraction of the cost and effort as compared to top-down lithographic techniques.

  4. Buried oxide layer in silicon

    DOEpatents

    Sadana, Devendra Kumar; Holland, Orin Wayne

    2001-01-01

    A process for forming Silicon-On-Insulator is described incorporating the steps of ion implantation of oxygen into a silicon substrate at elevated temperature, ion implanting oxygen at a temperature below 200.degree. C. at a lower dose to form an amorphous silicon layer, and annealing steps to form a mixture of defective single crystal silicon and polycrystalline silicon or polycrystalline silicon alone and then silicon oxide from the amorphous silicon layer to form a continuous silicon oxide layer below the surface of the silicon substrate to provide an isolated superficial layer of silicon. The invention overcomes the problem of buried isolated islands of silicon oxide forming a discontinuous buried oxide layer.

  5. Metal deposition using seed layers

    DOEpatents

    Feng, Hsein-Ping; Chen, Gang; Bo, Yu; Ren, Zhifeng; Chen, Shuo; Poudel, Bed

    2013-11-12

    Methods of forming a conductive metal layers on substrates are disclosed which employ a seed layer to enhance bonding, especially to smooth, low-roughness or hydrophobic substrates. In one aspect of the invention, the seed layer can be formed by applying nanoparticles onto a surface of the substrate; and the metallization is achieved by electroplating an electrically conducting metal onto the seed layer, whereby the nanoparticles serve as nucleation sites for metal deposition. In another approach, the seed layer can be formed by a self-assembling linker material, such as a sulfur-containing silane material.

  6. Liquefaction mechanism for layered soils

    SciTech Connect

    Fiegel, G.L.; Kutter, B.L. . Dept. of Civil and Environmental Engineering)

    1994-04-01

    Results from four centrifuge model tests are presented. Three of the model tests involve layered soil deposits subject to base shaking; one model test involves a uniform soil deposit of sand subject to base shaking. The layered soil models consisted of fine sand overlain by a layer of relatively impermeable silica flour (silt). Pore-water pressures, accelerations, and settlements were measured during all four tests. Results from the model tests involving layered soils suggest that during liquefaction a water interlayer or very loose zone of soil may develop at the sand-silt interface due to the difference in permeabilities. In each layered model test, boils were observed on the surface of the silt layer. These boils were concentrated in the thinnest zones of the overlying silt layer and provided a vent for the excess pore-water pressure generated in the fine sand.

  7. The multiple layer solar collector

    NASA Astrophysics Data System (ADS)

    Kenna, J. P.

    1983-01-01

    An analytical model is developed for obtaining numerical solutions for differential equations describing the performance of separate layers in a multiple layer solar collector. The configurations comprises heat transfer fluid entering at the top of the collector and travelling down through several layers. A black absorber plate prevents reemission of thermal radiation. The overall performance is shown to depend on the number of layers, the heat transfer coefficient across each layer, and the absorption properties of the working fluid. It is found that the multiple layer system has a performance inferior to that of flat plate selective surface collectors. Air gaps insulating adjacent layers do not raise the efficiency enough to overcome the relative deficiency.

  8. Layers in Galle Crater

    NASA Image and Video Library

    2017-03-31

    This image shows a layered deposit in Galle Crater, located in the Southern cratered highlands. The geologic history of Galle Crater is not well constrained, and it contains a variety of features that have been interpreted as fluvial, lacustrine or glacial deposits. The deposit pictured here contains multiple unconformities (sudden or irregular changes from one deposit to another), indicating periods of erosion and non deposition. The map is projected here at a scale of 25 centimeters (9.8 inches) per pixel. [The original image scale is 25.7 centimeters (10.1 inches) per pixel (with 1 x 1 binning); objects on the order of 77 centimeters (30.3 inches) across are resolved.] North is up. https://photojournal.jpl.nasa.gov/catalog/PIA21575

  9. Wireless physical layer security

    NASA Astrophysics Data System (ADS)

    Poor, H. Vincent; Schaefer, Rafael F.

    2017-01-01

    Security in wireless networks has traditionally been considered to be an issue to be addressed separately from the physical radio transmission aspects of wireless systems. However, with the emergence of new networking architectures that are not amenable to traditional methods of secure communication such as data encryption, there has been an increase in interest in the potential of the physical properties of the radio channel itself to provide communications security. Information theory provides a natural framework for the study of this issue, and there has been considerable recent research devoted to using this framework to develop a greater understanding of the fundamental ability of the so-called physical layer to provide security in wireless networks. Moreover, this approach is also suggestive in many cases of coding techniques that can approach fundamental limits in practice and of techniques for other security tasks such as authentication. This paper provides an overview of these developments.

  10. Wireless physical layer security

    PubMed Central

    Schaefer, Rafael F.

    2017-01-01

    Security in wireless networks has traditionally been considered to be an issue to be addressed separately from the physical radio transmission aspects of wireless systems. However, with the emergence of new networking architectures that are not amenable to traditional methods of secure communication such as data encryption, there has been an increase in interest in the potential of the physical properties of the radio channel itself to provide communications security. Information theory provides a natural framework for the study of this issue, and there has been considerable recent research devoted to using this framework to develop a greater understanding of the fundamental ability of the so-called physical layer to provide security in wireless networks. Moreover, this approach is also suggestive in many cases of coding techniques that can approach fundamental limits in practice and of techniques for other security tasks such as authentication. This paper provides an overview of these developments. PMID:28028211

  11. Improved electrodeposited actinide layers

    NASA Astrophysics Data System (ADS)

    Ingelbrecht, C.; Moens, A.; Eykens, R.; Dean, A.

    1997-02-01

    Electrodeposition is a relatively simple and high-yielding method for producing actinide layers for nuclear targets. A new design of the cell has been used to deposit U, Pu, Np and Am onto metallic backings from isopropanol and onto carbon-coated polyimide films from isobutanol. The current density was 1-3 mA/cm 2. Deposition yields, determined by low geometry alpha-particle counting, were about 65% for Pu and about 90% for other elements. The same technique was used to investigate thickness homogeneity of 239Pu deposits, and it was observed that targets with mean thickness up to about 100 μg/cm 2 were thicker in the centre than at the edge, but for targets above 100 μg/cm 2, this profile was reversed. Modifications to the electrode shape were made in an attempt to improve the thickness uniformity.

  12. ISDC Data Access Layer

    NASA Astrophysics Data System (ADS)

    Jennings, D.; Borkowski, J.; Contessi, T.; Lock, T.; Rohlfs, R.; Walter, R.

    The ISDC Data Access Layer (DAL) is an ANSI C and \\fortran 90 compatible library under development in support of the ESA INTEGRAL mission data analysis software. DALs primary purpose is to isolate the analysis software from the specifics of the data formats while at the same time providing new data abstraction and access capabilities. DAL supports the creation and manipulation of hierarchical data sets which may span multiple files and, in theory, multiple computer systems. A number of Application Programming Interfaces (APIs) are supported by DAL that allow software to view and access data at different levels of complexity. DAL also allows data sets to reside on disk, in conventional memory or in shared memory in a way that is transparent to the user/application.

  13. Templated quasicrystalline molecular layers

    NASA Astrophysics Data System (ADS)

    Smerdon, Joe; Young, Kirsty; Lowe, Michael; Hars, Sanger; Yadav, Thakur; Hesp, David; Dhanak, Vinod; Tsai, An-Pang; Sharma, Hem Raj; McGrath, Ronan

    2014-03-01

    Quasicrystals are materials with long range ordering but no periodicity. We report scanning tunneling microscopy (STM) observations of quasicrystalline molecular layers on five-fold quasicrystal surfaces. The molecules adopt positions and orientations on the surface consistent with the quasicrystalline ordering of the substrate. Carbon-60 adsorbs atop sufficiently-separated Fe atoms on icosahedral Al-Cu-Fe to form a unique quasicrystalline lattice whereas further C60 molecules decorate remaining surface Fe atoms in a quasi-degenerate fashion. Pentacene (Pn) adsorbs at tenfold-symmetric points around surface-bisected rhombic triacontahedral clusters in icosahedral Ag-In-Yb. These systems constitute the first demonstrations of quasicrystalline molecular ordering on a template. EPSRC EP/D05253X/1, EP/D071828/1, UK BIS.

  14. Layer Outcrops and Dunes

    NASA Technical Reports Server (NTRS)

    2003-01-01

    MGS MOC Release No. MOC2-561, 1 December 2003

    This October 2003 Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) picture shows dark, windblown sand dunes amid outcrops of light-toned, sedimentary rock in a crater in western Arabia Terra. The darkest material in the scene is windblown sand; the steep slopes--the slip faces--of the dunes face toward the southwest (lower left), indicating that wind transport of sand has been from the northeast (upper right). The layered mounds are the remains of sedimentary rock that were once more extensive across this crater floor. The image is located near 8.9oN, 1.2oW, and covers an area 3 km (1.9 mi) wide. Sunlight illuminates the scene from the lower left.

  15. Ferroelectrics based absorbing layers

    NASA Astrophysics Data System (ADS)

    Hao, Jianping; Sadaune, Véronique; Burgnies, Ludovic; Lippens, Didier

    2014-07-01

    We show that ferroelectrics-based periodic structure made of BaSrTiO3 (BST) cubes, arrayed onto a metal plate with a thin dielectric spacer film exhibit a dramatic enhancement of absorbance with value close to unity. The enhancement is found around the Mie magnetic resonance of the Ferroelectrics cubes with the backside metal layer stopping any transmitted waves. It also involves quasi-perfect impedance matching resulting in reflection suppression via simultaneous magnetic and electrical activities. In addition, it was shown numerically the existence of a periodicity optimum, which is explained from surface waves analysis along with trade-off between the resonance damping and the intrinsic loss of ferroelectrics cubes. An experimental verification in a hollow waveguide configuration with a good comparison with full-wave numerical modelling is at last reported by measuring the scattering parameters of single and dual BST cubes schemes pointing out coupling effects for densely packed structures.

  16. Layers in Tithonium

    NASA Technical Reports Server (NTRS)

    2003-01-01

    MGS MOC Release No. MOC2-570, 10 December 2003

    This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) picture shows eroded layered bedrock outcrops in the upper walls of one of the depressions in the Tithonium Chasma trough system. Tithonium Chasma is one of the canyons of the Valles Marineris, a vast gouge that--if it occurred on Earth-would span the distance from Los Angeles, California, to New York City. The Valles Marineris canyons were not carved by running water, instead they formed mostly by the combined forces of faulting and mass movement (landslides) as gravity eroded materials from the walls. This image is located near 4.2oS, 85.1oW. The image covers an area approximately 3 km (1.9 mi) wide and is illuminated from the lower left.

  17. Aeolian transport layer.

    PubMed

    Almeida, Murilo P; Andrade, José S; Herrmann, Hans J

    2006-01-13

    We investigate the airborne transport of particles on a granular surface by the saltation mechanism through numerical simulation of particle motion coupled with turbulent flow. We determine the saturated flux q(s) and show that its behavior is consistent with classical empirical relations obtained from wind tunnel measurements. Our results also allow one to propose and explain a new relation valid for small fluxes, namely, q(s) = a(u*-u(t))alpha, where u* and u(t) are the shear and threshold velocities of the wind, respectively, and the scaling exponent is alpha approximately 2. We obtain an expression for the velocity profile of the wind distorted by the particle motion due to the feedback and discover a novel dynamical scaling relation. We also find a new expression for the dependence of the height of the saltation layer as a function of the wind velocity.

  18. Templated, layered manganese phosphate

    DOEpatents

    Thoma, Steven G.; Bonhomme, Francois R.

    2004-08-17

    A new crystalline maganese phosphate composition having an empirical formula: O). The compound was determined to crystallize in the trigonal space group P-3c1 with a=8.8706(4) .ANG., c=26.1580(2) .ANG., and V (volume)=1783 .ANG..sup.3. The structure consists of sheets of corner sharing Mn(II)O.sub.4 and PO.sub.4 tetrahedra with layers of (H.sub.3 NCH.sub.2 CH.sub.2).sub.3 N and water molecules in-between. The pronated (H.sub.3 NCH.sub.2 CH.sub.2).sub.3 N molecules provide charge balancing for the inorganic sheets. A network of hydrogen bonds between water molecules and the inorganic sheets holds the structure together.

  19. Wireless physical layer security.

    PubMed

    Poor, H Vincent; Schaefer, Rafael F

    2017-01-03

    Security in wireless networks has traditionally been considered to be an issue to be addressed separately from the physical radio transmission aspects of wireless systems. However, with the emergence of new networking architectures that are not amenable to traditional methods of secure communication such as data encryption, there has been an increase in interest in the potential of the physical properties of the radio channel itself to provide communications security. Information theory provides a natural framework for the study of this issue, and there has been considerable recent research devoted to using this framework to develop a greater understanding of the fundamental ability of the so-called physical layer to provide security in wireless networks. Moreover, this approach is also suggestive in many cases of coding techniques that can approach fundamental limits in practice and of techniques for other security tasks such as authentication. This paper provides an overview of these developments.

  20. South Polar Layered Deposits

    NASA Technical Reports Server (NTRS)

    2003-01-01

    [figure removed for brevity, see original site]

    Released 17 July 2003

    Similar to ice cores taken from Greenland and Antarctica, Mars also has fine-scale layered deposits in both the north and south polar regions. In this image from the south pole, alternating light and dark bands represent varying amounts of dust or sand mixed in with carbon dioxide ice. These layers are related in part to climate cycles caused by variations in the tilt of Mars' rotational axis, as well as other orbital variations that occur on geologic time scales (tens of thousands of years).

    Image information: VIS instrument. Latitude -80.1, Longitude 260.4 East (99.6 West). 19 meter/pixel resolution.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.

  1. Ozone Layer Observations

    NASA Technical Reports Server (NTRS)

    McPeters, Richard; Bhartia, P. K. (Technical Monitor)

    2002-01-01

    The US National Aeronautics and Space Administration (NASA) has been monitoring the ozone layer from space using optical remote sensing techniques since 1970. With concern over catalytic destruction of ozone (mid-1970s) and the development of the Antarctic ozone hole (mid-1980s), long term ozone monitoring has become the primary focus of NASA's series of ozone measuring instruments. A series of TOMS (Total Ozone Mapping Spectrometer) and SBUV (Solar Backscatter Ultraviolet) instruments has produced a nearly continuous record of global ozone from 1979 to the present. These instruments infer ozone by measuring sunlight backscattered from the atmosphere in the ultraviolet through differential absorption. These measurements have documented a 15 Dobson Unit drop in global average ozone since 1980, and the declines in ozone in the antarctic each October have been far more dramatic. Instruments that measure the ozone vertical distribution, the SBUV and SAGE (Stratospheric Aerosol and Gas Experiment) instruments for example, show that the largest changes are occurring in the lower stratosphere and upper troposphere. The goal of ozone measurement in the next decades will be to document the predicted recovery of the ozone layer as CFC (chlorofluorocarbon) levels decline. This will require a continuation of global measurements of total column ozone on a global basis, but using data from successor instruments to TOMS. Hyperspectral instruments capable of measuring in the UV will be needed for this purpose. Establishing the relative roles of chemistry and dynamics will require instruments to measure ozone in the troposphere and in the stratosphere with good vertical resolution. Instruments that can measure other chemicals important to ozone formation and destruction will also be needed.

  2. Processes for multi-layer devices utilizing layer transfer

    DOEpatents

    Nielson, Gregory N; Sanchez, Carlos Anthony; Tauke-Pedretti, Anna; Kim, Bongsang; Cederberg, Jeffrey; Okandan, Murat; Cruz-Campa, Jose Luis; Resnick, Paul J

    2015-02-03

    A method includes forming a release layer over a donor substrate. A plurality of devices made of a first semiconductor material are formed over the release layer. A first dielectric layer is formed over the plurality of devices such that all exposed surfaces of the plurality of devices are covered by the first dielectric layer. The plurality of devices are chemically attached to a receiving device made of a second semiconductor material different than the first semiconductor material, the receiving device having a receiving substrate attached to a surface of the receiving device opposite the plurality of devices. The release layer is etched to release the donor substrate from the plurality of devices. A second dielectric layer is applied over the plurality of devices and the receiving device to mechanically attach the plurality of devices to the receiving device.

  3. CLARAty Functional-Layer Software

    NASA Technical Reports Server (NTRS)

    Nesnas, Issa; Volpe, Richard; Das, Hari; Mutz, Darren; Petras, Richard; Estlin, Tara

    2003-01-01

    Functional-layer software for the Coupled Layer Architecture for Robotics Autonomy (CLARAty) is being developed. [CLARAty was described in Coupled-Layer Architecture for Advanced Software for Robots (NPO-21218), NASA Tech Briefs, Vol. 26, No. 12 (December 2002), page 48. To recapitulate: CLARAty was proposed to improve the modularity of robotic software while tightening the coupling between planning/execution and control subsystems. Whereas prior robotic software architectures have typically contained three levels, the CLARAty architecture contains two layers: a decision layer and a functional layer.] Just as an operating system provides abstraction from computational hardware, the CLARAty functional-layer software provides for abstraction for the different robotic systems. The functional-layer software establishes interrelated, object-oriented hierarchies that contain active and passive objects that represent the different levels of system abstrations and components. The functional-layer software is decomposed into a set of reusable core components and a set of extended components that adapt the reusable set to specific hardware implementations. The reusable components (a) provide behavior and interface definitions and implementations of basic functionality, (b) provide local executive capabilities, (c) manage local resources, and (d) support state and resource queries by the decision layer. Software for robotic systems can be built by use of these components.

  4. Inter-layer synchronization in multiplex networks of identical layers

    SciTech Connect

    Sevilla-Escoboza, R.; Sendiña-Nadal, I.; Leyva, I.; Buldú, J. M.; Gutiérrez, R.; Boccaletti, S.

    2016-06-15

    Inter-layer synchronization is a distinctive process of multiplex networks whereby each node in a given layer evolves synchronously with all its replicas in other layers, irrespective of whether or not it is synchronized with the other units of the same layer. We analytically derive the necessary conditions for the existence and stability of such a state, and verify numerically the analytical predictions in several cases where such a state emerges. We further inspect its robustness against a progressive de-multiplexing of the network, and provide experimental evidence by means of multiplexes of nonlinear electronic circuits affected by intrinsic noise and parameter mismatch.

  5. Nanostructure Neutron Converter Layer Development

    NASA Technical Reports Server (NTRS)

    Park, Cheol (Inventor); Sauti, Godfrey (Inventor); Kang, Jin Ho (Inventor); Lowther, Sharon E. (Inventor); Thibeault, Sheila A. (Inventor); Bryant, Robert G. (Inventor)

    2016-01-01

    Methods for making a neutron converter layer are provided. The various embodiment methods enable the formation of a single layer neutron converter material. The single layer neutron converter material formed according to the various embodiments may have a high neutron absorption cross section, tailored resistivity providing a good electric field penetration with submicron particles, and a high secondary electron emission coefficient. In an embodiment method a neutron converter layer may be formed by sequential supercritical fluid metallization of a porous nanostructure aerogel or polyimide film. In another embodiment method a neutron converter layer may be formed by simultaneous supercritical fluid metallization of a porous nanostructure aerogel or polyimide film. In a further embodiment method a neutron converter layer may be formed by in-situ metalized aerogel nanostructure development.

  6. Spray coated nanosilver functional layers

    NASA Astrophysics Data System (ADS)

    Krzemiński, J.; Szałapak, J.; Dybowska-Sarapuk, L.; Jakubowska, M.

    2016-09-01

    Silver coatings are highly conductive functional layers. There are many different ways to product the silver coating but most of them need vacuum or high temperature. Spray coating is a technique that is free of this disadvantages - it doesn't need a cleanroom or high temperature. What's more the layer thickness is about 10 μm. In this article the spray coating process of silver nanolayer is described. Four different inks were tested and measured. The layer resistance was measured and show as a graph. After the layer resistance was measured the adhesion test was performed. The pull-off test was performed on testing machine with special self made module. To conclude the article include the test and measurements of spray coated nanosilver functional layers. The layers was examined for the current conductivity and adhesion force.

  7. Excited waves in shear layers

    NASA Technical Reports Server (NTRS)

    Bechert, D. W.

    1982-01-01

    The generation of instability waves in free shear layers is investigated. The model assumes an infinitesimally thin shear layer shed from a semi-infinite plate which is exposed to sound excitation. The acoustical shear layer excitation by a source further away from the plate edge in the downstream direction is very weak while upstream from the plate edge the excitation is relatively efficient. A special solution is given for the source at the plate edge. The theory is then extended to two streams on both sides of the shear layer having different velocities and densities. Furthermore, the excitation of a shear layer in a channel is calculated. A reference quantity is found for the magnitude of the excited instability waves. For a comparison with measurements, numerical computations of the velocity field outside the shear layer were carried out.

  8. Boundary-Layer & health

    NASA Astrophysics Data System (ADS)

    Costigliola, V.

    2010-09-01

    It has long been known that specific atmospheric processes, such as weather and longer-term climatic fluctuations, affect human health. The biometeorological literature refers to this relationship as meteorotropism, defined as a change in an organism that is correlated with a change in atmospheric conditions. Plenty of (patho)physiological functions are affected by those conditions - like the respiratory diseases - and currently it is difficult to put any limits for pathologies developed in reply. Nowadays the importance of atmospheric boundary layer and health is increasingly recognised. A number of epidemiologic studies have reported associations between ambient concentrations of air pollution, specifically particulate pollution, and adverse health effects, even at the relatively low concentrations of pollution found. Since 1995 there have been over twenty-one studies from four continents that have explicitly examined the association between ambient air pollutant mixes and daily mortality. Statistically significant and positive associations have been reported in data from various locations around the world, all with varying air pollutant concentrations, weather conditions, population characteristics and public health policies. Particular role has been given to atmospheric boundary layer processes, the impact of which for specific patient-cohort is, however, not well understood till now. Assessing and monitoring air quality are thus fundamental to improve Europe's welfare. One of current projects run by the "European Medical Association" - PASODOBLE will develop and demonstrate user-driven downstream information services for the regional and local air quality sectors by combining space-based and in-situ data with models in 4 thematic service lines: - Health community support for hospitals, pharmacies, doctors and people at risk - Public information for regions, cities, tourist industry and sporting event organizers - Compliance monitoring support on particulate

  9. Oxygen-reducing catalyst layer

    DOEpatents

    O'Brien, Dennis P [Maplewood, MN; Schmoeckel, Alison K [Stillwater, MN; Vernstrom, George D [Cottage Grove, MN; Atanasoski, Radoslav [Edina, MN; Wood, Thomas E [Stillwater, MN; Yang, Ruizhi [Halifax, CA; Easton, E Bradley [Halifax, CA; Dahn, Jeffrey R [Hubley, CA; O'Neill, David G [Lake Elmo, MN

    2011-03-22

    An oxygen-reducing catalyst layer, and a method of making the oxygen-reducing catalyst layer, where the oxygen-reducing catalyst layer includes a catalytic material film disposed on a substrate with the use of physical vapor deposition and thermal treatment. The catalytic material film includes a transition metal that is substantially free of platinum. At least one of the physical vapor deposition and the thermal treatment is performed in a processing environment comprising a nitrogen-containing gas.

  10. Outer layer effects in wind-farm boundary layers: Coriolis forces and boundary layer height

    NASA Astrophysics Data System (ADS)

    Allaerts, Dries; Meyers, Johan

    2015-11-01

    In LES studies of wind-farm boundary layers, scale separation between the inner and outer region of the atmospheric boundary layer (ABL) is frequently assumed, i.e., wind turbines are presumed to fall within the inner layer and are not affected by outer layer effects. However, modern wind turbine and wind farm design tends towards larger rotor diameters and farm sizes, which means that outer layer effects will become more important. In a prior study, it was already shown for fully-developed wind farms that the ABL height influences the power performance. In this study, we use the in-house LES code SP-Wind to investigate the importance of outer layer effects on wind-farm boundary layers. In a suite of LES cases, the ABL height is varied by imposing a capping inversion with varying inversion strengths. Results indicate the growth of an internal boundary layer (IBL), which is limited in cases with low inversion layers. We further find that flow deceleration combined with Coriolis effects causes a change in wind direction throughout the farm. This effect increases with decreasing boundary layer height, and can result in considerable turbine wake deflection near the end of the farm. The authors are supported by the ERC (ActiveWindFarms, grant no: 306471). Computations were performed on VSC infrastructiure (Flemish Supercomputer Center), funded by the Hercules Foundation and the Flemish Government-department EWI.

  11. Multiple-layer Radiation Absorber

    NASA Astrophysics Data System (ADS)

    Baker, Robert M. L.; Baker, Bonnie Sue

    A structure is discussed for absorbing incident radiation, either electromagnetic (EM) or sound. Such a surface structure is needed, for example, in a highly sensitive high-frequency gravitational wave or HFGW detector such as the Li-Baker. The multi-layer absorber, which is discussed, is constructed with metamaterial [MM] layer or layers on top. This MM is configured for a specific EM or sound radiation frequency band, which absorbs incident EM or sound radiation without reflection. Below these top MM layers is a substrate of conventional EM-radiation absorbing or acoustical absorbing reflective material, such as an array of pyramidal foam absorbers. Incident radiation is partially absorbed by the MM layer or layers, and then it is more absorbed by the lower absorbing and reflecting substrate. The remaining reflected radiation is even further absorbed by the MM layers on its "way out_ so that essentially all of the incident radiation is absorbed _ a nearly perfect black-body absorber. In a HFGW detector a substrate, such as foam absorbers, may outgas into a high vacuum and reduce the capability of the vacuum-producing equipment, however, the layers above this lowest substrate will seal the absorbing and reflecting substrate from any external vacuum. The layers also serve to seal the absorbing material against air or water flow past the surfaces of aircraft, watercraft or submarines. Other applications for such a multiple-level radiation absorber include stealth aircraft, missiles and submarines.

  12. Two-layer Tripole Model

    NASA Astrophysics Data System (ADS)

    Sokolovskiy, M. A.; Verron, J.; Yakovenko, O. I.

    Three-vortex filament problem for the case of both zero average circulation and im- pulse in a 2D two-layer incompressible fluid is investigated. In this framework, a model of tripolar structures is constructed with one vortex located in the upper layer and two vortices situated in the lower layer. Two special cases of the intensity dis- tribution were studied: (-2; 1, 1) ­ a strong central vortex is over two week vortices placed in the lower layer; (-1; 2, -1) ­ a strong central vortex is in the lower layer, and the week vortices are located one in the upper, and the second in the lower layers. The results give two types of stationary axially symmetrical configurations in the first case: a) an ordinary roundabout ­ two lower-layer vortices are rotating in the direction in- duced by the central vortex; b) an inversed roundabout ­ the lower-layer vortices are rotating in the direction opposite to the central upper layer vortex because of the in- tralayer interaction prevalence. In the second case, all three vortices form a colinear configuration and always rotate around the common vorticity center in the direction implied by the stronger vortex. Such configuration received the name of eccentric roundabout. Comparison of calcu- lation results for discrete and finite-core vortices is made. Support of RFBR (Grant 01-05-64646) is gratefully acknowledged.

  13. Secondary polymer layered impregnated tile

    NASA Technical Reports Server (NTRS)

    Tran, Huy K. (Inventor); Rasky, Daniel J. (Inventor); Szalai, Christine E. (Inventor); Carroll, Joseph A. (Inventor); Hsu, Ming-ta S. (Inventor)

    2005-01-01

    A low density organic polymer impregnated preformed fibrous ceramic article includes a plurality of layers. A front layer includes ceramic fibers or carbon fibers or combinations of ceramic fibers and carbon fibers, and is impregnated with an effective amount of at least one organic polymer. A middle layer includes polymer impregnated ceramic fibers. A back layer includes ceramic fibers or carbon fibers or combinations of ceramic fibers and carbon fibers, and is impregnated with an effective amount of at least one low temperature pyrolyzing organic polymer capable of decomposing without depositing residues.

  14. Secondary polymer layered impregnated tile

    NASA Technical Reports Server (NTRS)

    Tran, Huy K. (Inventor); Rasky, Daniel J. (Inventor); Szalai, Christine E. (Inventor); Carroll, Joseph A. (Inventor); Hsu, Ming-ta S. (Inventor)

    2005-01-01

    A low density organic polymer impregnated preformed fibrous ceramic article includes a plurality of layers. A front layer includes ceramic fibers or carbon fibers or combinations of ceramic fibers and carbon fibers, and is impregnated with an effective amount of at least one organic polymer. A middle layer includes polymer impregnated ceramic fibers. A back layer includes ceramic fibers or carbon fibers or combinations of ceramic fibers and carbon fibers, and is impregnated with an effective amount of at least one low temperature pyrolyzing organic polymer capable of decomposing without depositing residues.

  15. Eroded Scallops with Layers

    NASA Image and Video Library

    2017-01-09

    The western Utopia Planitia in the Northern mid-latitudes of Mars is marked by a peculiar type of depression with scalloped edges and by a network of polygonal fractures. The scalloped depressions are typical features; a smooth layered terrain located between 40 and 60 degrees in both hemispheres. Scalloped depressions probably form by removal of ice-rich subsurface material by sublimation (ice transforming directly from a solid to a gaseous state), a process that may still be active today. Isolated scalloped depressions generally have a steep pole-facing scarp and a gentler equator-facing slope. This asymmetry is interpreted as being the result of difference in solar heating. Scalloped depressions may coalesce, leading to the formation of large areas of pitted terrain. The polygonal pattern of fractures resembles permafrost polygons that form in terrestrial polar and high alpine regions by seasonal-to-annual contraction of the permafrost (permanently frozen ground). On Earth, such polygons indicate the presence of ground ice. These landforms most likely show that sub-surface ice is present or has been present geologically recently at these latitudes, and they may slowly be continuing their development at the present time. http://photojournal.jpl.nasa.gov/catalog/PIA13485

  16. The Martian surface layer

    NASA Technical Reports Server (NTRS)

    Christensen, Philip R.; Moore, Henry J.

    1992-01-01

    The global characteristics of the Martian surface layer are discussed on the basis of thermal, albedo, color, and radar data for the region between approximately 60 deg S and 60 deg N. Thermal data reveal the presence of large low- and high-inertia regions of the northern hemisphere, with much of the south covered by material of moderate inertia. There is a strong anticorrelation between inertia and albedo, a correlation between inertia and rock abundance, and, over much of the planet, a correlation of radar-derived density with inertia. Viking Orbiter color data indicate the presence of three major surface materials: low-inertia, bright-red material that is presumably dust; high-inertia, dark-grey material interpreted to be lithic material mixed with palagonitelike dust; and moderate-inertia, dark-red material that is rough at subpixel scales and interpreted to be indurated. Observations from the Viking landing sites show rocks, fines of varying cohesion and crusts. These sites have indications of aeolian erosion and deposition in the recent past.

  17. A POROUS, LAYERED HELIOPAUSE

    SciTech Connect

    Swisdak, M.; Drake, J. F.; Opher, M. E-mail: drake@umd.edu

    2013-09-01

    The picture of the heliopause (HP)-the boundary between the domains of the Sun and the local interstellar medium (LISM)-as a pristine interface with a large rotation in the magnetic field fails to describe recent Voyager 1 (V1) data. Magnetohydrodynamic (MHD) simulations of the global heliosphere reveal that the rotation angle of the magnetic field across the HP at V1 is small. Particle-in-cell simulations, based on cuts through the MHD model at V1's location, suggest that the sectored region of the heliosheath (HS) produces large-scale magnetic islands that reconnect with the interstellar magnetic field while mixing LISM and HS plasma. Cuts across the simulation reveal multiple, anti-correlated jumps in the number densities of LISM and HS particles, similar to those observed, at the magnetic separatrices. A model is presented, based on both the observations and simulations, of the HP as a porous, multi-layered structure threaded by magnetic fields. This model further suggests that contrary to the conclusions of recent papers, V1 has already crossed the HP.

  18. Layer-by-Layer Proteomic Analysis of Mytilus galloprovincialis Shell.

    PubMed

    Gao, Peng; Liao, Zhi; Wang, Xin-Xing; Bao, Lin-Fei; Fan, Mei-Hua; Li, Xiao-Min; Wu, Chang-Wen; Xia, Shu-Wei

    2015-01-01

    Bivalve shell is a biomineralized tissue with various layers/microstructures and excellent mechanical properties. Shell matrix proteins (SMPs) pervade and envelop the mineral crystals and play essential roles in biomineralization. Despite that Mytilus is an economically important bivalve, only few proteomic studies have been performed for the shell, and current knowledge of the SMP set responsible for different shell layers of Mytilus remains largely patchy. In this study, we observed that Mytilus galloprovincialis shell contained three layers, including nacre, fibrous prism, and myostracum that is involved in shell-muscle attachment. A parallel proteomic analysis was performed for these three layers. By combining LC-MS/MS analysis with Mytilus EST database interrogations, a whole set of 113 proteins was identified, and the distribution of these proteins in different shell layers followed a mosaic pattern. For each layer, about a half of identified proteins are unique and the others are shared by two or all of three layers. This is the first description of the protein set exclusive to nacre, myostracum, and fibrous prism in Mytilus shell. Moreover, most of identified proteins in the present study are novel SMPs, which greatly extended biomineralization-related protein data of Mytilus. These results are useful, on one hand, for understanding the roles of SMPs in the deposition of different shell layers. On the other hand, the identified protein set of myostracum provides candidates for further exploring the mechanism of adductor muscle-shell attachment.

  19. Layer-layer competition in multiplex complex networks.

    PubMed

    Gómez-Gardeñes, J; de Domenico, M; Gutiérrez, G; Arenas, A; Gómez, S

    2015-12-13

    The coexistence of multiple types of interactions within social, technological and biological networks has moved the focus of the physics of complex systems towards a multiplex description of the interactions between their constituents. This novel approach has unveiled that the multiplex nature of complex systems has strong influence in the emergence of collective states and their critical properties. Here we address an important issue that is intrinsic to the coexistence of multiple means of interactions within a network: their competition. To this aim, we study a two-layer multiplex in which the activity of users can be localized in each of the layers or shared between them, favouring that neighbouring nodes within a layer focus their activity on the same layer. This framework mimics the coexistence and competition of multiple communication channels, in a way that the prevalence of a particular communication platform emerges as a result of the localization of user activity in one single interaction layer. Our results indicate that there is a transition from localization (use of a preferred layer) to delocalization (combined usage of both layers) and that the prevalence of a particular layer (in the localized state) depends on the structural properties. © 2015 The Author(s).

  20. Layer-by-Layer Proteomic Analysis of Mytilus galloprovincialis Shell

    PubMed Central

    Wang, Xin-xing; Bao, Lin-fei; Fan, Mei-hua; Li, Xiao-min; Wu, Chang-wen; Xia, Shu-wei

    2015-01-01

    Bivalve shell is a biomineralized tissue with various layers/microstructures and excellent mechanical properties. Shell matrix proteins (SMPs) pervade and envelop the mineral crystals and play essential roles in biomineralization. Despite that Mytilus is an economically important bivalve, only few proteomic studies have been performed for the shell, and current knowledge of the SMP set responsible for different shell layers of Mytilus remains largely patchy. In this study, we observed that Mytilus galloprovincialis shell contained three layers, including nacre, fibrous prism, and myostracum that is involved in shell-muscle attachment. A parallel proteomic analysis was performed for these three layers. By combining LC-MS/MS analysis with Mytilus EST database interrogations, a whole set of 113 proteins was identified, and the distribution of these proteins in different shell layers followed a mosaic pattern. For each layer, about a half of identified proteins are unique and the others are shared by two or all of three layers. This is the first description of the protein set exclusive to nacre, myostracum, and fibrous prism in Mytilus shell. Moreover, most of identified proteins in the present study are novel SMPs, which greatly extended biomineralization-related protein data of Mytilus. These results are useful, on one hand, for understanding the roles of SMPs in the deposition of different shell layers. On the other hand, the identified protein set of myostracum provides candidates for further exploring the mechanism of adductor muscle-shell attachment. PMID:26218932

  1. Natural melanin composites by layer-by-layer assembly

    NASA Astrophysics Data System (ADS)

    Eom, Taesik; Shim, Bong Sub

    2015-04-01

    Melanin is an electrically conductive and biocompatible material, because their conjugated backbone structures provide conducting pathways from human skin, eyes, brain, and beyond. So there is a potential of using as materials for the neural interfaces and the implantable devices. Extracted from Sepia officinalis ink, our natural melanin was uniformly dispersed in mostly polar solvents such as water and alcohols. Then, the dispersed melanin was further fabricated to nano-thin layered composites by the layer-by-layer (LBL) assembly technique. Combined with polyvinyl alcohol (PVA), the melanin nanoparticles behave as an LBL counterpart to from finely tuned nanostructured films. The LBL process can adjust the smart performances of the composites by varying the layering conditions and sandwich thickness. We further demonstrated the melanin loading degree of stacked layers, combination nanostructures, electrical properties, and biocompatibility of the resulting composites by UV-vis spectrophotometer, scanning electron microscope (SEM), multimeter, and in-vitro cell test of PC12, respectively.

  2. Layer-by-Layer Assembly of Enzymes on Carbon Nanotubes

    SciTech Connect

    Wang, Jun; Liu, Guodong; Lin, Yuehe

    2008-06-01

    The use of Layer-by-layer techniques for immobilizing several types of enzymes, e.g. glucose oxidase (GOx), horse radish oxidases(HRP), and choline oxidase(CHO) on carbon nanotubes and their applications for biosenseing are presented. The enzyme is immobilized on the negatively charged CNT surface by alternatively assembling a cationic polydiallyldimethyl-ammonium chloride (PDDA) layer and a enzyme layer. The sandwich-like layer structure (PDDA/enzyme/PDDA/CNT) formed by electrostatic assembling provides a favorable microenvironment to keep the bioactivity of enzyme and to prevent enzyme molecule leakage. The morphologies and electrocatalytic acitivity of the resulted enzyme film were characterized using TEM and electrochemical techniques, respectively. It was found that these enzyme-based biosensors are very sensitive, selective for detection of biomolecules, e.g. glucose, choline.

  3. Advanced double layer capacitors

    NASA Technical Reports Server (NTRS)

    Sarangapani, S.; Lessner, P.; Forchione, J.; Laconti, A. B.

    1989-01-01

    There is a need for large amounts of power to be delivered rapidly in a number of airborne and space systems. Conventional, portable power sources, such as batteries, are not suited to delivering high peak power pulses. The charge stored at the electrode-electrolyte double layer is, however, much more assessible on a short time scale. Devices exploiting this concept were fabricated using carbon and metal oxides (Pinnacle Research) as the electrodes and sulfuric acid as the electrolyte. The approach reported, replaces the liquid sulfuric acid electrolyte with a solid ionomer electrolyte. The challenge is to form a solid electrode-solid ionomer electrolyte composite which has a high capacitance per geometric area. The approach to maximize contact between the electrode particles and the ionomer was to impregnate the electrode particles using a liquid ionomer solution and to bond the solvent-free structure to a solid ionomer membrane. Ruthenium dioxide is the electrode material used. Three strategies are being pursued to provide for a high area electrode-ionomer contact: mixing of the RuOx with a small volume of ionomer solution followed by filtration to remove the solvent, and impregnation of the ionomer into an already formed RuOx electrode. RuOx powder and electrodes were examined by non-electrochemical techniques. X-ray diffraction has shown that the material is almost pure RuO2. The electrode structure depends on the processing technique used to introduce the Nafion. Impregnated electrodes have Nafion concentrated near the surface. Electrodes prepared by the evaporation method show large aggregates of crystals surrounded by Nafion.

  4. Multi-layer overlay metrology

    NASA Astrophysics Data System (ADS)

    Ausschnitt, C. P.; Morningstar, J.; Muth, W.; Schneider, J.; Yerdon, R. J.; Binns, L. A.; Smith, N. P.

    2006-03-01

    A novel approach to overlay metrology, called Blossom, maximizes the number of layers measurable within a single optical field of view (FOV). As chip processing proceeds, each layer contributes a set of at least four marks, arranged symmetrically on concentric circles, to create a 90° rotationally invariant array of marks that "blossoms" to fill the FOV. Radial symmetry about the target center is maintained at each layer to minimize susceptibility to metrology lens aberrations. Overlay combinations among detectable marks within the target can be measured simultaneously. In the described embodiment, 28 distinct layers are represented within a 50μm square FOV. Thus, all the layers of a functional chip can be represented in a single target. Blossom achieves several benefits relative to overlay methods currently in practice: * Compression (>30X) of area required for overlay targets. * Nullification of within-target proximity effects. * Suppression of optical mark fidelity (OMF) errors. * Reduction of sensitivity to across-target detection noise.* Elimination of overlay error random walk among layers. * Reference mark redundancy for detection flexibility and robustness. * Integration of multi-layer and within-layer overlay control schema. * Simplification of overlay recipe creation and management. * Capture and visualization of overlay performance through the entire chip fabrication. Blossom results from 65-nm products in manufacturing are described.

  5. Midlatitude sporadic-E layers

    NASA Technical Reports Server (NTRS)

    Miller, K. L.; Smith, L. G.

    1976-01-01

    The partially transparent echo from midlatitude sporadic E layers was recorded by ionosondes between the blanketing frequency and the maximum frequency. The theory that the midlatitude sporadic E layers are not uniform in the horizontal plane but contain localized regions of high electron density was evaluated using data obtained by incoherent scatter radar and found to provide a satisfactory explanation. The main features of midlatitude sporadic E layers are consistent with the convergence of metallic ions as described by the wind shear theory applied to gravity waves and tides. The interference of gravity waves with other gravity waves and tides can be recognized in the altitudes of occurrence and the structure of the layers. Small scale horizontal irregularities are attributed in some cases to critical level effects and in others to fluid instabilities. The convergence of a meteor trail can, under some circumstances, account for localized enhancement of the electron density in the layer.

  6. Boundary-layer moisture regimes

    NASA Technical Reports Server (NTRS)

    Mahrt, L.

    1991-01-01

    Boundary-layer moisture fluctuations are estimated by analyzing HAPEX and FIFE data collected on 52 aircraft flight legs. Moisture fluctuations were given considerable attention in the HAPEX flights, which were 120 km long, and flew 150 m over one area of homogeneous terrain. The repetitions permit statistical consideration of motion characteristics on horizontal scales. Two prototypical boundary layer regimes are discovered: the entrainment-drying boundary layer, and the moistening boundary layer. The latter demonstrates positive moisture skewness close to the surface related to high surface evaporation. The former is characterized by boundary-layer instability, weak surface evaporation, and drier air aloft, leading to unexpected negative moisture skewness. It is noted that 10 km moisture variations with horizontal gradients are often found in narrow zones of horizontal convergence, called mesoscale moisture fronts. A negative moisture to temperature correlation, due to surface energy budget inhomogeneity, is shown to incur large mesoscale variations of relative humidity.

  7. Fragmentation of drying paint layers

    NASA Astrophysics Data System (ADS)

    Bakos, Katinka; Dombi, András; Járai-Szabó, Ferenc; Néda, Zoltán

    2013-11-01

    Fragmentation of thin layers of drying granular materials on a frictional surface are studied both by experiments and computer simulations. Besides a qualitative description of the fragmentation phenomenon, the dependence of the average fragment size as a function of the layer thickness is thoroughly investigated. Experiments are done using a special nail polish, which forms characteristic crack structures during drying. In order to control the layer thickness, we diluted the nail polish in acetone and evaporated in a controlled manner different volumes of this solution on glass surfaces. During the evaporation process we managed to get an instable paint layer, which formed cracks as it dried out. In order to understand the obtained structures a previously developed spring-block model was implemented in a three-dimensional version. The experimental and simulation results proved to be in excellent qualitative and quantitative agreement. An earlier suggested scaling relation between the average fragment size and the layer thickness is reconfirmed.

  8. Lear jet boundary layer/shear layer laser propagation experiments

    NASA Technical Reports Server (NTRS)

    Gilbert, K.

    1980-01-01

    Optical degradations of aircraft turbulent boundary layers with shear layers generated by aerodynamic fences are analyzed. A collimated 2.5 cm diameter helium-neon laser (0.63 microns) traversed the approximate 5 cm thick natural aircraft boundary layer in double pass via a reflective airfoil. In addition, several flights examined shear layer-induced optical degradation. Flight altitudes ranged from 1.5 to 12 km, while Mach numbers were varied from 0.3 to 0.8. Average line spread function (LSF) and Modulation Transfer Function (MTF) data were obtained by averaging a large number of tilt-removed curves. Fourier transforming the resulting average MTF yields an LSF, thus affording a direct comparison of the two optical measurements. Agreement was good for the aerodynamic fence arrangement, but only fair in the case of a turbulent boundary layer. Values of phase variance inferred from the LSF instrument for a single pass through the random flow and corrected for a large aperture ranged from 0.08 to 0.11 waves (lambda = .63 microns) for the boundary layer. Corresponding values for the fence vary from 0.08 to 0.16 waves. Extrapolation of these values to 10.6 microns suggests negligible degradation for a CO2 laser transmitted through a 5 cm thick, subsonic turbulent boundary layer.

  9. Improved CLARAty Functional-Layer/Decision-Layer Interface

    NASA Technical Reports Server (NTRS)

    Estlin, Tara; Rabideau, Gregg; Gaines, Daniel; Johnston, Mark; Chouinard, Caroline; Nessnas, Issa; Shu, I-Hsiang

    2008-01-01

    Improved interface software for communication between the CLARAty Decision and Functional layers has been developed. [The Coupled Layer Architecture for Robotics Autonomy (CLARAty) was described in Coupled-Layer Robotics Architecture for Autonomy (NPO-21218), NASA Tech Briefs, Vol. 26, No. 12 (December 2002), page 48. To recapitulate: the CLARAty architecture was developed to improve the modularity of robotic software while tightening coupling between planning/execution and basic control subsystems. Whereas prior robotic software architectures typically contained three layers, the CLARAty contains two layers: a decision layer (DL) and a functional layer (FL).] Types of communication supported by the present software include sending commands from DL modules to FL modules and sending data updates from FL modules to DL modules. The present software supplants prior interface software that had little error-checking capability, supported data parameters in string form only, supported commanding at only one level of the FL, and supported only limited updates of the state of the robot. The present software offers strong error checking, and supports complex data structures and commanding at multiple levels of the FL, and relative to the prior software, offers a much wider spectrum of state-update capabilities.

  10. The Effect of Nonlinear Critical Layers on Boundary Layer Transition

    NASA Technical Reports Server (NTRS)

    Goldstein, Marvin E.

    1995-01-01

    Asymptotic methods are used to describe the nonlinear self-interaction between pairs of oblique instability modes that eventually develops when initially linear and spatially growing instability waves evolve downstream in nominally two-dimensional and spanwise periodic laminar boundary layers. The first nonlinear reaction takes place locally within a so-called 'critical layer' with the flow outside this layer consisting of a locally parallel mean flow plus an appropriate superposition of linear instability waves. The amplitudes of these waves are determined by either a single integro-differential equation or by a pair of integro-differential equations with quadratic to quartic-type nonlinearities.

  11. D0 layer 0 innermost layer of silicon microstrip tracker

    SciTech Connect

    Hanagaki, K.; /Fermilab

    2006-01-01

    A new inner layer silicon strip detector has been built and will be installed in the existing silicon microstrip tracker in D0. They report on the motivation, design, and performance of this new detector.

  12. Nanoengineering Catalyst Supports via Layer-by Layer Surface Functionalization

    SciTech Connect

    Yan, Wenfu; Mahurin, Shannon Mark; Overbury, Steven {Steve} H; Dai, Sheng

    2006-01-01

    Recent progress in the layer-by-layer surface modification of oxides for the preparation of highly active and stable gold nanocatalysts is briefly reviewed. Through a layer-by-layer surface modification approach, the surfaces of various catalyst supports including both porous and nonporous silica materials and TiO{sub 2} nanoparticles were modified with monolayers or multilayers of distinct metal oxide ultra-thin films. The surface-modified materials were used as supports for Au nanoparticles, resulting in highly active nanocatalysts for low-temperature CO oxidation. Good stability against sintering under high-temperature treatment was achieved for a number of the Au catalysts through surface modification of the support material. The surface modification of supports can be a viable route to control both the composition and structure of support and nanoparticle interfaces, thereby tailoring the stability and activity of the supported catalyst systems.

  13. The role of nonlinear critical layers in boundary layer transition

    NASA Technical Reports Server (NTRS)

    Goldstein, M.E.

    1995-01-01

    Asymptotic methods are used to describe the nonlinear self-interaction between pairs of oblique instability modes that eventually develops when initially linear spatially growing instability waves evolve downstream in nominally two-dimensional laminar boundary layers. The first nonlinear reaction takes place locally within a so-called 'critical layer', with the flow outside this layer consisting of a locally parallel mean flow plus a pair of oblique instability waves - which may or may not be accompanied by an associated plane wave. The amplitudes of these waves, which are completely determined by nonlinear effects within the critical layer, satisfy either a single integro-differential equation or a pair of integro-differential equations with quadratic to quartic-type nonlinearities. The physical implications of these equations are discussed.

  14. On Multiple-Layered Vortices

    NASA Technical Reports Server (NTRS)

    Rossow, Vernon J.

    2011-01-01

    As part of an ongoing effort to find ways to make vortex flow fields decompose more quickly, photographs and observations are presented of vortex flow fields that indicate the presence of multiple layers of fluid rotating about a common axis. A survey of the literature indicates that multiple-layered vortices form in waterspouts, tornadoes and lift-generated vortices of aircraft. An explanation for the appearance of multiple-layered structures in vortices is suggested. The observations and data presented are intended to improve the understanding of the formation and persistence of vortex flow fields.

  15. Layer Communities in Multiplex Networks

    NASA Astrophysics Data System (ADS)

    Kao, Ta-Chu; Porter, Mason A.

    2017-08-01

    Multiplex networks are a type of multilayer network in which entities are connected to each other via multiple types of connections. We propose a method, based on computing pairwise similarities between layers and then doing community detection, for grouping structurally similar layers in multiplex networks. We illustrate our approach using both synthetic and empirical networks, and we are able to find meaningful groups of layers in both cases. For example, we find that airlines that are based in similar geographic locations tend to be grouped together in a multiplex airline network and that related research areas in physics tend to be grouped together in a multiplex collaboration network.

  16. Formation of cracks in layered rock considering layer thickness variations

    NASA Astrophysics Data System (ADS)

    Chang, Xu; Lu, Jianyou; Wang, Shanyong; Wang, Shuren; Liu, Xiliang

    2017-09-01

    The formation mechanisms for layer interface-parallel discontinuities and their interactions with vertical cracks in layered rocks with varying layer thickness are investigated. The interface behaviour between rock layers is modeled by a shear displacement response and rock crack behaviour is described by a damage model. Three typical failures can be captured: (1) vertical cracking, (2) delamination and (3) interface-parallel cracking. The result further indicates these crack modes are determined by a threshold of the interfacial strength. When the interfacial strength is higher than the threshold, a combined pattern of vertical cracking and interface-parallel cracking occurs. If the strength is lower than the threshold, a combined pattern of vertical cracking and interfacial delamination can be found. If the strength for the interface is near the threshold, a combined pattern of interface-parallel cracking, vertical cracking and interfacial delamination occurs. The result shows the interface-parallel discontinuities are induced by interface-delamination, interface-parallel cracks, or their coupling behaviour. Both interfacial delamination and interface-parallel cracking can reduce the tensile stress between two adjacent cracks and thus lead to a saturation state. Layer thickness variations can further influence the infilling process of vertical cracks and the crack spacing to average layer thickness ratios.

  17. Layer-by-Layer Insight into Electrostatic Charge Distribution of Few-Layer Graphene

    PubMed Central

    Rokni, Hossein; Lu, Wei

    2017-01-01

    In few-layer graphene (FLG) systems on a dielectric substrate such as SiO2, the addition of each extra layer of graphene can drastically alter their electronic and structural properties. Here, we map the charge distribution among the individual layers of finite-size FLG systems using a novel spatial discrete model that describes both electrostatic interlayer screening and fringe field effects. Our results reveal that the charge density in the region very close to the edges is screened out an order of magnitude more weakly than that across the central region of the layers. Our discrete model suggests that the interlayer charge screening length in 1–8 layer thick graphene systems depends mostly on the overall gate/molecular doping level rather than on temperature, in particular at an induced charge density >5 × 1012 cm−2, and can reliably be determined to be larger than half the interlayer spacing but shorter than the bilayer thickness. Our model can be used for designing FLG-based devices, and offers a simple rule regarding the charge distribution in FLG: approximately 70%, 20%, 6% and 3% (99% overall) of the total induced charge density reside within the four innermost layers, implying that the gate-induced electric field is not definitely felt by >4th layer. PMID:28220816

  18. Layer-by-Layer Insight into Electrostatic Charge Distribution of Few-Layer Graphene

    NASA Astrophysics Data System (ADS)

    Rokni, Hossein; Lu, Wei

    2017-02-01

    In few-layer graphene (FLG) systems on a dielectric substrate such as SiO2, the addition of each extra layer of graphene can drastically alter their electronic and structural properties. Here, we map the charge distribution among the individual layers of finite-size FLG systems using a novel spatial discrete model that describes both electrostatic interlayer screening and fringe field effects. Our results reveal that the charge density in the region very close to the edges is screened out an order of magnitude more weakly than that across the central region of the layers. Our discrete model suggests that the interlayer charge screening length in 1–8 layer thick graphene systems depends mostly on the overall gate/molecular doping level rather than on temperature, in particular at an induced charge density >5 × 1012 cm‑2, and can reliably be determined to be larger than half the interlayer spacing but shorter than the bilayer thickness. Our model can be used for designing FLG-based devices, and offers a simple rule regarding the charge distribution in FLG: approximately 70%, 20%, 6% and 3% (99% overall) of the total induced charge density reside within the four innermost layers, implying that the gate-induced electric field is not definitely felt by >4th layer.

  19. Inversion layer MOS solar cells

    NASA Technical Reports Server (NTRS)

    Ho, Fat Duen

    1986-01-01

    Inversion layer (IL) Metal Oxide Semiconductor (MOS) solar cells were fabricated. The fabrication technique and problems are discussed. A plan for modeling IL cells is presented. Future work in this area is addressed.

  20. Theory of nonmonotonic double layers

    SciTech Connect

    Kim, K.Y.

    1987-12-01

    A simple graphic method of solving the Vlasov--Poisson system associated with nonlinear eigenvalue conditions for arbitrary potential structures is presented. A general analytic formulation for nonmonotonic double layers is presented and illustrated with some particular closed form solutions. This class of double layers satisfies the time stationary Vlasov--Poisson system while requiring a Sagdeev potential, which is a double-valued function of the physical potential. It follows that any distribution function having a density representation as any integer or noninteger power series of potential can never satisfy the nonmonotonic double-layer boundary conditions. A Korteweg--de Vries-like equation is found showing a relationship among the speed of the nonmonotonic double layer, its scale length, and its degree of asymmetry.

  1. The plasma sheet boundary layer

    NASA Technical Reports Server (NTRS)

    Eastman, T. E.; Frank, L. A.; Peterson, W. K.; Lennartsson, W.

    1984-01-01

    A spatially distinct, temporally variable, transition region between the magnetotail lobes and the central plasma sheet designated the plasma sheet boundary layer has been identified from a survey of particle spectra and three-dimensional distributions as sampled by the ISEE 1 LEPEDEA. The instrumentation and data presentation are described, and the signatures of the magnetotail plasma regimes are presented and discussed for the central plasma sheet and lobe and the plasma sheet boundary layer. Comparisons of plasma parameters and distribution fucntions are made and the evolution of ion velocity distributions within the plasma sheet boundary layer is discussed. The spatial distribution of the plasma sheet boundary layer is considered and ion composition measurements are presented.

  2. Boundary Layer Control on Airfoils.

    ERIC Educational Resources Information Center

    Gerhab, George; Eastlake, Charles

    1991-01-01

    A phenomena, boundary layer control (BLC), produced when visualizing the fluidlike flow of air is described. The use of BLC in modifying aerodynamic characteristics of airfoils, race cars, and boats is discussed. (KR)

  3. WEATHER_Layered-Precipitable-Water

    Atmospheric Science Data Center

    2016-06-23

    ... TOVS (HIRS) clear sky radiances Radiosonde GPS (after 1995) AIRS Level 2 TPW and Layered PW Spatial ... Parameters:  Precipitable Water Order Data:  Earthdata Search:  Earthdata Search SCAR-B ...

  4. Bedding Details in Layered Rock

    NASA Image and Video Library

    2013-10-16

    This beautiful image shows terrific layers and exposed bedrock along a cliff in west Candor Chasma, which is part of the extensive Valles Marineris canyon system as seen by NASA Mars Reconnaissance Orbiter.

  5. Layer-oriented simulation tool.

    PubMed

    Arcidiacono, Carmelo; Diolaiti, Emiliano; Tordi, Massimiliano; Ragazzoni, Roberto; Farinato, Jacopo; Vernet, Elise; Marchetti, Enrico

    2004-08-01

    The Layer-Oriented Simulation Tool (LOST) is a numerical simulation code developed for analysis of the performance of multiconjugate adaptive optics modules following a layer-oriented approach. The LOST code computes the atmospheric layers in terms of phase screens and then propagates the phase delays introduced in the natural guide stars' wave fronts by using geometrical optics approximations. These wave fronts are combined in an optical or numerical way, including the effects of wave-front sensors on measurements in terms of phase noise. The LOST code is described, and two applications to layer-oriented modules are briefly presented. We have focus on the Multiconjugate adaptive optics demonstrator to be mounted upon the Very Large Telescope and on the Near-IR-Visible Adaptive Interferometer for Astronomy (NIRVANA) interferometric system to be installed on the combined focus of the Large Binocular Telescope.

  6. Terraced Craters and Layered Targets

    NASA Image and Video Library

    2013-09-12

    Small impact craters usually have simple bowl shapes; however, when the target material has different layers of different strength, then more complicated crater shapes can emerge as shown in image captured by NASA Mars Reconnaissance Orbiter.

  7. Boundary Layer Control on Airfoils.

    ERIC Educational Resources Information Center

    Gerhab, George; Eastlake, Charles

    1991-01-01

    A phenomena, boundary layer control (BLC), produced when visualizing the fluidlike flow of air is described. The use of BLC in modifying aerodynamic characteristics of airfoils, race cars, and boats is discussed. (KR)

  8. Layers in Arsia Mons Volcano

    NASA Image and Video Library

    2010-10-28

    This observance from NASA Mars Reconnaissance Orbiter covers a pit in the lower West flank of Arsia Mons, one of the four giant volcanos of the Tharsis region. Many layers are exposed in the pit, probably marking individual lava flows.

  9. Modeling the urban boundary layer

    NASA Technical Reports Server (NTRS)

    Bergstrom, R. W., Jr.

    1976-01-01

    A summary and evaluation is given of the Workshop on Modeling the Urban Boundary Layer; held in Las Vegas on May 5, 1975. Edited summaries from each of the session chairpersons are also given. The sessions were: (1) formulation and solution techniques, (2) K-theory versus higher order closure, (3) surface heat and moisture balance, (4) initialization and boundary problems, (5) nocturnal boundary layer, and (6) verification of models.

  10. Shape optimization of damping layers

    NASA Technical Reports Server (NTRS)

    Lin, T.-C.; Scott, R. A.

    1987-01-01

    Shape optimization of unconstrained and constrained damping layers is completed. The specific problem analyzed is a cantilever beam loaded at its tip by a harmonic force. Finite element modeling and mathematical programming techniques are used to obtain the solution. Performance measures are taken to be reduction of maximum diplacement and increase in fatigue lifetime. Results include the improvement, over the uniform treatment case, of these measures when the profile of the damping layer is optimized.

  11. Removing Boundary Layer by Suction

    NASA Technical Reports Server (NTRS)

    Ackeret, J

    1927-01-01

    Through the utilization of the "Magnus effect" on the Flettner rotor ship, the attention of the public has been directed to the underlying physical principle. It has been found that the Prandtl boundary-layer theory furnishes a satisfactory explanation of the observed phenomena. The present article deals with the prevention of this separation or detachment of the flow by drawing the boundary layer into the inside of a body through a slot or slots in its surface.

  12. Evaporation from layered porous media

    NASA Astrophysics Data System (ADS)

    Shokri, N.; Lehmann, P.; Or, D.

    2010-06-01

    Evaporation rates from porous media may vary considerably due to changes in internal transport mechanisms and potential interruption of hydraulic continuity; both are influenced by media pore space properties. Evaporation behavior in layered porous media is affected by thickness and sequence of layering and capillary characteristics of each layer. We propose a composite characteristic length for predicting drying front depth at the end of a period with a high and constant drying rate (stage 1 evaporation) from layered porous media. The model was tested in laboratory experiments using Hele-Shaw cells filled with alternating layers of coarse and fine sands considering different combinations of thicknesses and positions. The presence of textural interfaces affects drying rate, modifies liquid phase configuration, and affects the dynamics of the receding drying front. Neutron radiography measurements were used to delineate dynamics of liquid phase distribution with high temporal and spatial resolution. Results show that air invading an interface between fine and coarse sand layers results in a capillary pressure jump and subsequent relaxation that significantly modify liquid phase distribution compared with evaporation from homogeneous porous media. Insights are potentially useful for designing mulching strategies and capillary barriers aimed at reducing evaporative losses.

  13. Mixing in straight shear layers

    NASA Technical Reports Server (NTRS)

    Karasso, P. S.; Mungal, M. G.

    1992-01-01

    Planar laser-induced fluorescence measurements were performed in a liquid plane mixing layer to extract the probability density function (pdf) of the mixture fraction of a passive scalar across the layer. Three Reynolds number (Re) cases were studied, 10,000, 33,000 and 90,000, with Re based on velocity difference and visual thickness. The results show that a non-marching pdf (central hump invariant from edge to edge of the layer) exists for Re = 10,000 but that a marching type pdf characterizes the Re = 33,000 and Re = 90,000 cases. For all cases, a broad range of mixture fraction values is found at each location across the layer. Streamwise and spanwise ramps across the layer, and structure-to-structure variation were observed and are believed to be responsible for the above behavior of the composition field. Tripping the boundary layer on the high-speed side of the splitter plate for each of the above three cases resulted in increased three-dimensionality and a change in the composition field. Average and average mixed fluid compositions are reported for all cases.

  14. Dynamics of Polyelectrolyte Chains within Layer-by-Layer Assemblies

    NASA Astrophysics Data System (ADS)

    Sukhishvili, Svetlana

    2015-03-01

    Layer-by-layer (LbL) assembly of charged polymers/nanoparticles finds diverse industrial applications ranging from NIR reflective heat-reduction to multi-stage drug delivery. Internal layering of film components lies at the heart of their performance. I will discuss experiments aimed to unravel relationships between center-of-mass diffusion of polyelectrolyte (PE) chains within LbL films, PE molecular characteristics, environmental conditions (salt concentration), and film structure. Upon film annealing in salt solutions, chain diffusion is highly anisotropic (as probed by fluorescence recovery after photobleaching and neutron reflectometry), and is strongly coupled with film structure. For layered LbL films, PE diffusion in the direction parallel to the substrate reveals quasi-Rouse scaling with molecular weight (D ~ M-1) , even for long chains, suggesting that chains disentangle upon adsorption. Finally, I will discuss quantitative aspects of salt-induced PE chain diffusion in directions parallel and perpendicular to the substrate, and their consequences for persistent layering within LbL films. This work was supported by the National Science Foundation under Award DMR-0906474.

  15. Investigation of the Transmission of Sound Through Isotropic, Damped Material Layer(s) Bounded by Seawater

    DTIC Science & Technology

    2008-03-01

    9 A. SINGLE LAYER NORMAL INCIDENCE...9 B. MULTI-LAYER NON- NORMAL INCIDENCE .......................................10 1. Stress/Strain Wave Propagation...10 2. Non- Normal , Multi-Layered, Unattenuated Case ..........................14 3. Non- Normal , Multi-Layer

  16. Double-diffusive layer formation

    NASA Astrophysics Data System (ADS)

    Zaussinger, Florian; Kupka, Friedrich; Hücker, Sebastian; Egbers, Christoph

    2015-04-01

    Double-diffusive convection plays an important role in geo- and astrophysical applications. The special case, where a destabilising temperature gradient counteracts a stabilising solute gradient leads to layering phenomena under certain conditions. Convectively mixed layers sandwiched in diffusive interfaces form a so-called stack. Well-known double-diffusive systems are observed in rift lakes in Africa and even from the coffee drink Latte Macciatto. Stacks of layers are also predicted to occur inside massive stars and inside giant planets. Their dynamics depend on the thermal, the solute and the momentum diffusivities, as well on the ratio of the gradients of the opposing stratifications. Since the layering process cannot be derived from linear stability analysis, the full nonlinear set of equations has to be investigated. Numerical simulations have become feasible for this task, despite the physical processes operate on a vast range of length and time scales, which is challenging for numerical hydrodynamical modelling. The oceanographically relevant case of fresh and salty water is investigated here in further details. The heat and mass transfer is compared with theoretical results and experimental measurements. Additionally, the initial dynamic of layering, the transient behaviour of a stack and the long time evolution are presented using the example of Lake Kivu and the interior of a giant planet.

  17. Mars Surface Layers in Infrared

    NASA Technical Reports Server (NTRS)

    2002-01-01

    (Released 29 May 2002) Infrared imaging from NASA's Mars Odyssey spacecraft shows signs of layering exposed at the surface in a region of Mars called Terra Meridiani. The brightness levels show daytime surface temperatures, which range from about minus 20 degrees to zero degrees Celsius (minus 4 degrees to 32 degrees Fahrenheit). Many of the temperature variations are due to slope effects, with sun-facing slopes warmer than shaded slopes. However, several rock layers can be seen to have distinctly different temperatures, indicating that physical properties vary from layer to layer. These differences suggest that the environment on this part of Mars varied through time as these layers were formed. The image is a mosaic combining four exposures taken by the thermal emission imaging system aboard Odyssey during the first two months of the Odyssey mapping mission, which began in February 2002. The area shown is about 120 kilometers (75 miles) across, at approximately 358 degrees east (2 degrees west) longitude and 3 degrees north latitude.

  18. Mars Surface Layers in Infrared

    NASA Technical Reports Server (NTRS)

    2002-01-01

    Infrared imaging from NASA's Mars Odyssey spacecraft shows signs of layering exposed at the surface in a region of Mars called Terra Meridiani.

    The brightness levels show daytime surface temperatures, which range from about minus 20 degrees to zero degrees Celsius (minus 4 degrees to 32 degrees Fahrenheit). Many of the temperature variations are due to slope effects, with sun-facing slopes warmer than shaded slopes. However, several rock layers can be seen to have distinctly different temperatures, indicating that physical properties vary from layer to layer. These differences suggest that the environment on this part of Mars varied through time as these layers were formed.

    The image is a mosaic combining four exposures taken by the thermal emission imaging system aboard Odyssey during the first two months of the Odyssey mapping mission, which began in February 2002. The area shown is about 120 kilometers (75 miles) across, at approximately 358 degrees east (2 degrees west) longitude and 3 degrees north latitude.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The thermal emission imaging system was provided by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. Lockheed Martin Astronautics, Denver, is the prime contractor for the project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and JPL. JPL is a division of the California Institute of Technology in Pasadena.

  19. Step Free Surface Heteroepitaxy of 3C-SiC Layers on Patterned 4H/6H-SiC Mesas and Cantilevers

    NASA Technical Reports Server (NTRS)

    Neudeck, Philip G.; Powell, J. Anthony; Trunek, Andrew J.; Spry, David J.

    2003-01-01

    Most SiC devices are implemented in homoepitaxial films grown on 4H/6H-SiC wafers with surfaces 3 degrees to 8 degrees off-axis from the (0001) basal plane. This approach has not prevented many substrate crystal defects from propagating into SiC epilayers, and does not permit the realization of SiC heteropolytype devices. This presentation describes recent advances in SiC epitaxial growth that begun to overcome the above shortcomings for arrays of mesas patterned into on-axis 4H/6H-SiC wafers. First, we demonstrated that atomic-scale surface steps can be completely eliminated from 4H/6H-SiC mesas via on-axis homoepitaxial step-flow growth, forming (0001) basal plane surfaces (up to 0.4 mm x 0.4 mm) for larger than previously thought possible. Step-free surface areas were then extended by growth fo thin lateral cantilevers from the mesa tops. These lateral cantilevers enabled substrate defects to be reduced and relocated in homoepitaxial films in a manner not possible with off-axis SiC growth. Finally, growth of vastly improved 3C-SiC heterofilms was achieved on 4H/6H-SiC mesas using the recently develop step-free surface heteroepitaxy process. These epitaxial growth developments should enable improved homojunction and heterojunction silicon carbide prototype devices.

  20. Physics of magnetospheric boundary layers

    NASA Technical Reports Server (NTRS)

    Cairns, Iver H.

    1995-01-01

    This final report was concerned with the ideas that: (1) magnetospheric boundary layers link disparate regions of the magnetosphere-solar wind system together; and (2) global behavior of the magnetosphere can be understood only by understanding its internal linking mechanisms and those with the solar wind. The research project involved simultaneous research on the global-, meso-, and micro-scale physics of the magnetosphere and its boundary layers, which included the bow shock, the magnetosheath, the plasma sheet boundary layer, and the ionosphere. Analytic, numerical, and simulation projects were performed on these subjects, as well as comparisons of theoretical results with observational data. Other related activity included in the research included: (1) prediction of geomagnetic activity; (2) global MHD (magnetohydrodynamic) simulations; (3) Alfven resonance heating; and (4) Critical Ionization Velocity (CIV) effect. In the appendixes are list of personnel involved, list of papers published; and reprints or photocopies of papers produced for this report.

  1. 'Blueberry' Layers Indicate Watery Origins

    NASA Technical Reports Server (NTRS)

    2004-01-01

    This microscopic image, taken at the outcrop region dubbed 'El Capitan' near the Mars Exploration Rover Opportunity's landing site, reveals millimeter-scale (.04 inch-scale) layers in the lower portion. This same layering is hinted at by the fine notches that run horizontally across the sphere-like grain or 'blueberry' in the center left. The thin layers do not appear to deform around the blueberry, indicating that these geologic features are concretions and not impact spherules or ejected volcanic material called lapilli. Concretions are balls of minerals that form in pre-existing wet sediments. This image was taken by the rover's microscopic imager on the 29th martian day, or sol, of its mission. The observed area is about 3 centimeters (1.2 inches) across.

  2. Boundary layer control for airships

    NASA Technical Reports Server (NTRS)

    Pake, F. A.; Pipitone, S. J.

    1975-01-01

    An investigation is summarized of the aerodynamic principle of boundary layer control for nonrigid LTA craft. The project included a wind tunnel test on a BLC body of revolution at zero angle of attack. Theoretical analysis is shown to be in excellent agreement with the test data. Methods are evolved for predicting the boundary layer development on a body of revolution and the suction pumping and propulsive power requirements. These methods are used to predict the performance characteristics of a full-scale airship. The analysis indicates that propulsive power reductions of 15 to 25 percent and endurance improvements of 20 to 40 percent may be realized in employing boundary-layer control to nonrigid airships.

  3. Layered Architecture for Quantum Computing

    NASA Astrophysics Data System (ADS)

    Jones, N. Cody; Van Meter, Rodney; Fowler, Austin G.; McMahon, Peter L.; Kim, Jungsang; Ladd, Thaddeus D.; Yamamoto, Yoshihisa

    2012-07-01

    We develop a layered quantum-computer architecture, which is a systematic framework for tackling the individual challenges of developing a quantum computer while constructing a cohesive device design. We discuss many of the prominent techniques for implementing circuit-model quantum computing and introduce several new methods, with an emphasis on employing surface-code quantum error correction. In doing so, we propose a new quantum-computer architecture based on optical control of quantum dots. The time scales of physical-hardware operations and logical, error-corrected quantum gates differ by several orders of magnitude. By dividing functionality into layers, we can design and analyze subsystems independently, demonstrating the value of our layered architectural approach. Using this concrete hardware platform, we provide resource analysis for executing fault-tolerant quantum algorithms for integer factoring and quantum simulation, finding that the quantum-dot architecture we study could solve such problems on the time scale of days.

  4. Layered Rocks in 'Columbia Hills'

    NASA Technical Reports Server (NTRS)

    2004-01-01

    This black-and-white image shows the first layered rocks scientists have seen close up in Gusev Crater, where NASA's Mars Exploration Rover Spirit landed Jan. 4, 2004. While Spirit's twin rover, Opportunity, reached the stadium-size Endurance Crater on the other side of Mars and began exploring its many layered outcrops in early May, Spirit traveled more than 3.5 kilometers (2.2 miles) to get to this layered bedrock in the 'Columbia Hills.' Scientists are planning to conduct a study of these rocks to determine if they are volcanic or sedimentary in origin, and if they have been chemically altered. Spirit's panoramic camera took this image on sol 217 (Aug. 13, 2004).

  5. Layer-by-layer dielectric breakdown of hexagonal boron nitride.

    PubMed

    Hattori, Yoshiaki; Taniguchi, Takashi; Watanabe, Kenji; Nagashio, Kosuke

    2015-01-27

    Hexagonal boron nitride (BN) is widely used as a substrate and gate insulator for two-dimensional (2D) electronic devices. The studies on insulating properties and electrical reliability of BN itself, however, are quite limited. Here, we report a systematic investigation of the dielectric breakdown characteristics of BN using conductive atomic force microscopy. The electric field strength was found to be ∼ 12 MV/cm, which is comparable to that of conventional SiO2 oxides because of the covalent bonding nature of BN. After the hard dielectric breakdown, the BN fractured like a flower into equilateral triangle fragments. However, when the applied voltage was terminated precisely in the middle of the dielectric breakdown, the formation of a hole that did not penetrate to the bottom metal electrode was clearly observed. Subsequent I-V measurements of the hole indicated that the BN layer remaining in the hole was still electrically inactive. On the basis of these observations, layer-by-layer breakdown was confirmed for BN with regard to both physical fracture and electrical breakdown. Moreover, statistical analysis of the breakdown voltages using a Weibull plot suggested the anisotropic formation of defects. These results are unique to layered materials and unlike the behavior observed for conventional 3D amorphous oxides.

  6. Controlled Layer-by-Layer Etching of MoS₂.

    PubMed

    Lin, TaiZhe; Kang, BaoTao; Jeon, MinHwan; Huffman, Craig; Jeon, JeaHoo; Lee, SungJoo; Han, Wei; Lee, JinYong; Lee, SeHan; Yeom, GeunYoung; Kim, KyongNam

    2015-07-29

    Two-dimensional (2D) metal dichalcogenides like molybdenum disulfide (MoS2) may provide a pathway to high-mobility channel materials that are needed for beyond-complementary metal-oxide-semiconductor (CMOS) devices. Controlling the thickness of these materials at the atomic level will be a key factor in the future development of MoS2 devices. In this study, we propose a layer-by-layer removal of MoS2 using the atomic layer etching (ALET) that is composed of the cyclic processing of chlorine (Cl)-radical adsorption and argon (Ar)(+) ion-beam desorption. MoS2 etching was not observed with only the Cl-radical adsorption or low-energy (<20 eV) Ar(+) ion-beam desorption steps; however, the use of sequential etching that is composed of the Cl-radical adsorption step and a subsequent Ar(+) ion-beam desorption step resulted in the complete etching of one monolayer of MoS2. Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM) indicated the removal of one monolayer of MoS2 with each ALET cycle; therefore, the number of MoS2 layers could be precisely controlled by using this cyclical etch method. In addition, no noticeable damage or etch residue was observed on the exposed MoS2.

  7. The Lowest Atmosphere: Atmospheric Boundary Layer Including Atmospheric Surface Layer.

    DTIC Science & Technology

    1996-04-01

    of motion of the atmosphere— "second order closure"—to such applications as the SCIPUFF -PC code for tracer dispersion (see Sykes, 1994). Now, for...Turbulence, Methuen, London, 2nd Ed., 1955. Sykes, R.I., "The SCIPUFF -PC Code," ARAP Draft Report, 1994. Tennekes, H., "The Atmospheric Boundary Layer

  8. Electrostatic layer-by-layer construction of fibrous TMV biofilms.

    PubMed

    Tiu, Brylee David B; Kernan, Daniel L; Tiu, Sicily B; Wen, Amy M; Zheng, Yi; Pokorski, Jonathan K; Advincula, Rigoberto C; Steinmetz, Nicole F

    2017-01-26

    As nature's choice in designing complex architectures, the bottom-up assembly of nanoscale building blocks offers unique solutions in achieving more complex and smaller morphologies with wide-ranging applications in medicine, energy, and materials science as compared to top-down manufacturing. In this work, we employ charged tobacco mosaic virus (TMV-wt and TMV-lys) nanoparticles in constructing multilayered fibrous networks via electrostatic layer-by-layer (LbL) deposition. In neutral aqueous media, TMV-wt assumes an anionic surface charge. TMV-wt was paired with a genetically engineered TMV-lys variant that displays a corona of lysine side chains on its solvent-exposed surface. The electrostatic interaction between TMV-wt and TMV-lys nanoparticles became the driving force in the highly controlled buildup of the multilayer TMV constructs. Since the resulting morphology closely resembles the 3-dimensional fibrous network of an extracellular matrix (ECM), the capability of the TMV assemblies to support the adhesion of NIH-3T3 fibroblast cells was investigated, demonstrating potential utility in regenerative medicine. Lastly, the layer-by-layer deposition was extended to release the TMV scaffolds as free-standing biomembranes. To demonstrate potential application in drug delivery or vaccine technology, cargo-functionalized TMV biofilms were programmed.

  9. Current driven weak double layers

    NASA Technical Reports Server (NTRS)

    Chanteur, Gerard

    1987-01-01

    Double layers in plasmas can be created by different means. For example, a potential difference forms between two plasmas with different temperatures, in a plasma jet flowing along a converging magnetic field, in a quiescent plasma submitted to an external difference of potential, or in a turbulent plasma carrying an electric charge. The first three cases can be current-free, but not necessarily, although the numerical simulations were made under such conditions for the first two points. Apart from the third case, which is mainly of interest for laboratory experiments, these double layers are good candidates for accelerating the auroral electrons to the few kiloelectron volts observed.

  10. Nonlinear Convection in Mushy Layers

    NASA Technical Reports Server (NTRS)

    Worster, M. Grae; Anderson, Daniel M.; Schulze, T. P.

    1996-01-01

    When alloys solidify in a gravitational field there are complex interactions between solidification and natural, buoyancy-driven convection that can alter the composition and impair the structure of the solid product. The particular focus of this project has been the compositional convection within mushy layers that occurs in situations where the lighter component of the alloy is rejected into the melt during solidification by cooling from below. The linear stability of such a situation was previously described and has been further elucidated in a number of published articles. Here we describe some recent developments in the study of nonlinear evolution of convection in mushy layers.

  11. Three-Dimensional Boundary Layers.

    DTIC Science & Technology

    1985-02-01

    sketched in figure 1 . The model design is des- • cribed in more detail in reference 2. At measuring station 1 the turbulent boundary layer is very...layer methods are increasingly important as their use for design purposes increases. Specific recommendations for future work include the following. 1 ...MEMBERS M. 1 ’Ing. G&n C.Cap~lier Prof. Dr. Jr. J.L. van Ingen Directeur de l’A~rodynamique Department of Aerospace B.P. 72 Engineering% ONERA Delf

  12. Changing the Layers of Mind.

    DTIC Science & Technology

    1987-07-02

    AID-R186 646 CHANGING THE LAYERS OF MIND (U) CARNEGIE-NELLON UNIY i/I PITTSURGH PA DEPT OF PSYCHOLOGY K YANLEHN 62 JUL 6? PCG-12 W90914-86-K-S349...Changing the Layers of Mind Technical Report PCG-12 I Kurt VanLehn Departments of Psychology and Computer Science Carnegie Mellon University Pittsburgh, PA...of Mind Technical Report PCG-12 -- Kurt VanLehn Departments of Psychology and Computer Science 0- Carnegie Mellon University Pittsburgh, PA 15213

  13. Operating System Abstraction Layer (OSAL)

    NASA Technical Reports Server (NTRS)

    Yanchik, Nicholas J.

    2007-01-01

    This viewgraph presentation reviews the concept of the Operating System Abstraction Layer (OSAL) and its benefits. The OSAL is A small layer of software that allows programs to run on many different operating systems and hardware platforms It runs independent of the underlying OS & hardware and it is self-contained. The benefits of OSAL are that it removes dependencies from any one operating system, promotes portable, reusable flight software. It allows for Core Flight software (FSW) to be built for multiple processors and operating systems. The presentation discusses the functionality, the various OSAL releases, and describes the specifications.

  14. The Beauty of Layered Stratigraphy

    NASA Image and Video Library

    2017-01-20

    The layered bedrock in this image was brought from several kilometers of depth during the formation of this 44 kilometer wide crater in the volcanic plains of Lunae Planum. As these layers were exhumed and brought to nearly vertical orientations, faulting and fracturing occurred and breccia dikes formed. Breccias are rocks consisting of angular and sharp fragments, and a dike is a fracture that has been widened by forces pulling apart the rock while simultaneously filling it with rocky materials. Breccia dikes are a common feature in terrestrial craters and can now be recognized in brilliant preservation on Mars. http://photojournal.jpl.nasa.gov/catalog/PIA12178

  15. Preparation of luminescent layered zirconium phosphate nanocomposites by the layer-by-layer technique

    NASA Astrophysics Data System (ADS)

    Jiang, Qun; Liu, Meitang; Ma, Hongwen; Wang, Tianlei; Kuai, Yuqing

    2016-12-01

    In the present work, photoactive cation N, N‧-Dimenthyl-9, 9'-bisacridinium nitrate (BNMA) was assembled with exfoliated layered α-zirconium phosphate (α-ZrP) via an electrostatic layer-by-layer (LBL) assembly method. As a result, the luminescent films which were well-aligned and periodical had been successfully fabricated. Surprisingly, the lifetimes of (BNMA/ZrP)n were found to be prolonged by 16-fold for the first time, due to the isolation effect of inorganic nanosheets and hydrogen ion migration between the interlayers. Therefore, it is testified that α-ZrP can be used as the laminate and has remarkable influences on enhancing the lifetimes of chromophores. We expect that this new discovered effect can enable α-ZrP a kind of new potential material to develop novel light-emitting materials and optical devices.

  16. Doped LZO buffer layers for laminated conductors

    DOEpatents

    Paranthaman, Mariappan Parans [Knoxville, TN; Schoop, Urs [Westborough, MA; Goyal, Amit [Knoxville, TN; Thieme, Cornelis Leo Hans [Westborough, MA; Verebelyi, Darren T [Oxford, MA; Rupich, Martin W [Framingham, MA

    2010-03-23

    A laminated conductor includes a metallic substrate having a surface, a biaxially textured buffer layer supported by the surface of the substrate, the biaxially textured buffer layer comprising LZO and a dopant for mitigating metal diffusion through the LZO, and a biaxially textured conductor layer supported by the biaxially textured buffer layer.

  17. Facilitating mass transport in gas diffusion layer of PEMFC by fabricating micro-porous layer with dry layer preparation

    NASA Astrophysics Data System (ADS)

    Chen, Jian; Xu, Haifeng; Zhang, Huamin; Yi, Baolian

    For a proton exchange membrane fuel cell (PEMFC), dry layer preparation was optimized and applied to fabricate a micro-porous layer (MPL) for a gas diffusion layer (GDL). The MPLs fabricated by dry layer preparation and the conventional wet layer preparation were compared by physical and electrochemical methods. The PEMFC using dry layer MPLs showed better performance than that using wet layer MPLs, especially when the cells were operated under conditions of high oxygen utilization rate and high humidification temperature of air. The mass transport properties of the GDLs with the dry layer MPLs were also better than with the wet layer MPLs, and were found to be related to the pore size distribution in GDLs. The differences in surface morphology and pore size distribution for the GDLs with the dry layer and wet layer MPLs were investigated and analyzed. The dry layer preparation for MPLs was found to be more beneficial for forming meso-pores (pore size in the range of 0.5-15 μm), which are important and advantageous for facilitating gas transport in the GDLs. Moreover, the GDLs with the dry layer MPLs exhibited better electronic conductivity and more stable hydrophobicity than those with the wet layer MPLs. The reproducibility of the dry layer preparation for MPLs was also satisfying.

  18. Simulation of Layered Magma Chambers.

    ERIC Educational Resources Information Center

    Cawthorn, Richard Grant

    1991-01-01

    The principles of magma addition and liquid layering in magma chambers can be demonstrated by dissolving colored crystals. The concepts of density stratification and apparent lack of mixing of miscible liquids is convincingly illustrated with hydrous solutions at room temperature. The behavior of interstitial liquids in "cumulus" piles…

  19. Layering Literacies and Contemporary Learning

    ERIC Educational Resources Information Center

    Abrams, Sandra Schamroth; Russo, Michael P.

    2015-01-01

    This article explores how adolescents layer literacies in and outside school. Findings from a longitudinal study of gaming in a public library, as well as data related to the use of Portal 2 in a New York City middle school classroom, reveal how the students created, showcased, analyzed, and experimented with online and offline artifacts and…

  20. Stability of Boundary Layer Flow.

    DTIC Science & Technology

    1980-03-01

    and Teske (1975). We can conclude (as in the case of ducting) that theoretical models of boundary layer structure and associated radar structure...FI33 (Secret). Hitney, (1978) "Surface Duct Effects," Naval Ocean Systems Center, San Diego, Calif., Report No. TD144. Lewellen, W. S., and M. E. Teske

  1. Space Wire Upper Layer Protocols

    NASA Technical Reports Server (NTRS)

    Rakow, Glenn; Schnurr, Richard; Gilley, Daniel; Parkes, Steve

    2004-01-01

    This viewgraph presentation addresses efforts to provide a streamlined approach for developing SpaceWire Upper layer protocols which allows industry to drive standardized communication solutions for real projects. The presentation proposes a simple packet header that will allow flexibility in implementing a diverse range of protocols.

  2. Layered materials for structural applications

    SciTech Connect

    Lewandowski, J.J.; Ward, C.H.; Jackson, M.R.; Hunt, W.H. Jr.

    1996-12-31

    The symposium, Layered Materials for Structural Applications, was held April 8--11, 1996, in San Francisco, California. This Materials Research Society symposium was supported by contributions from The Air Force Office of Scientific Research and Office of Naval Research. The meeting began with overviews on structural applications of layered systems and highlighted applications such as thermal barrier coatings, aircraft structural components, and wear-resistant coatings for a variety of applications. Processing techniques such as EB deposition processing, reactive sputter deposition, sedimentation processing, pressureless co-sintering, and rapid prototyping via laminated object manufacturing were subsequently covered in a following session. Microstructural stability issues were additionally covered and highlighted as a critical area requiring further investigation. The largest number of papers presented focused on the mechanical behavior and modeling of layered systems and revealed significant effects of layer thickness, spacing, and constituent properties on the fracture and fatigue behavior of such systems. While considerable work has investigated the issues of strength and toughness, less effort has been focused on the behavior of such systems under either cyclic loading or high-temperature conditions. Forty papers have been processed separately for inclusion on the data base.

  3. Physics of magnetospheric boundary layers

    NASA Technical Reports Server (NTRS)

    Cairns, I. H.

    1993-01-01

    The central ideas of this grant are that the magnetospheric boundary layers link disparate regions of the magnetosphere together, and the global behavior of the magnetosphere can be understood only by understanding the linking mechanisms. Accordingly the present grant includes simultaneous research on the global, meso-, and micro-scale physics of the magnetosphere and its boundary layers. These boundary layers include the bow shock, magnetosheath, the plasma sheet boundary layer, and the ionosphere. Analytic, numerical and simulation projects have been performed on these subjects, as well as comparison of theoretical results with observational data. Very good progress has been made, with four papers published or in press and two additional papers submitted for publication during the six month period 1 June - 30 November 1993. At least two projects are currently being written up. In addition, members of the group have given papers at scientific meetings. The further structure of this report is as follows: section two contains brief accounts of research completed during the last six months, while section three describes the research projects intended for the grant's final period.

  4. High Performance Thin Layer Chromatography.

    ERIC Educational Resources Information Center

    Costanzo, Samuel J.

    1984-01-01

    Clarifies where in the scheme of modern chromatography high performance thin layer chromatography (TLC) fits and why in some situations it is a viable alternative to gas and high performance liquid chromatography. New TLC plates, sample applications, plate development, and instrumental techniques are considered. (JN)

  5. Hurricane Boundary-Layer Theory

    DTIC Science & Technology

    2010-01-01

    interpretations offer a broad context in which to understand the role of the boundary layer in hurricane forecast models. A significant result of M3 was the...vortex aloft. In hurricane forecast models, it is necessary to parametrize the effects of the turbulent transfer of heat, moisture and momentum across the

  6. Simulation of Layered Magma Chambers.

    ERIC Educational Resources Information Center

    Cawthorn, Richard Grant

    1991-01-01

    The principles of magma addition and liquid layering in magma chambers can be demonstrated by dissolving colored crystals. The concepts of density stratification and apparent lack of mixing of miscible liquids is convincingly illustrated with hydrous solutions at room temperature. The behavior of interstitial liquids in "cumulus" piles…

  7. Layering Literacies and Contemporary Learning

    ERIC Educational Resources Information Center

    Abrams, Sandra Schamroth; Russo, Michael P.

    2015-01-01

    This article explores how adolescents layer literacies in and outside school. Findings from a longitudinal study of gaming in a public library, as well as data related to the use of Portal 2 in a New York City middle school classroom, reveal how the students created, showcased, analyzed, and experimented with online and offline artifacts and…

  8. High Performance Thin Layer Chromatography.

    ERIC Educational Resources Information Center

    Costanzo, Samuel J.

    1984-01-01

    Clarifies where in the scheme of modern chromatography high performance thin layer chromatography (TLC) fits and why in some situations it is a viable alternative to gas and high performance liquid chromatography. New TLC plates, sample applications, plate development, and instrumental techniques are considered. (JN)

  9. Organic photovoltaic cells utilizing ultrathin sensitizing layer

    DOEpatents

    Rand, Barry P.; Forrest, Stephen R.

    2011-05-24

    A photosensitive device includes a series of organic photoactive layers disposed between two electrodes. Each layer in the series is in direct contact with a next layer in the series. The series is arranged to form at least one donor-acceptor heterojunction, and includes a first organic photoactive layer comprising a first host material serving as a donor, a thin second organic photoactive layer comprising a second host material disposed between the first and a third organic photoactive layer, and the third organic photoactive layer comprising a third host material serving as an acceptor. The first, second, and third host materials are different. The thin second layer serves as an acceptor relative to the first layer or as a donor relative to the third layer.

  10. Chemical solution seed layer for rabits tapes

    DOEpatents

    Goyal, Amit; Paranthaman, Mariappan; Wee, Sung-Hun

    2014-06-10

    A method for making a superconducting article includes the steps of providing a biaxially textured substrate. A seed layer is then deposited. The seed layer includes a double perovskite of the formula A.sub.2B'B''O.sub.6, where A is rare earth or alkaline earth metal and B' and B'' are different rare earth or transition metal cations. A superconductor layer is grown epitaxially such that the superconductor layer is supported by the seed layer.

  11. Tetradymite layer assisted heteroepitaxial growth and applications

    DOEpatents

    Stoica, Vladimir A.; Endicott, Lynn; Clarke, Roy; Uher, Ctirad

    2017-08-01

    A multilayer stack including a substrate, an active layer, and a tetradymite buffer layer positioned between the substrate and the active layer is disclosed. A method for fabricating a multilayer stack including a substrate, a tetradymite buffer layer and an active layer is also disclosed. Use of such stacks may be in photovoltaics, solar cells, light emitting diodes, and night vision arrays, among other applications.

  12. Buffer layer for thin film structures

    DOEpatents

    Foltyn, Stephen R.; Jia, Quanxi; Arendt, Paul N.; Wang, Haiyan

    2010-06-15

    A composite structure including a base substrate and a layer of a mixture of strontium titanate and strontium ruthenate is provided. A superconducting article can include a composite structure including an outermost layer of magnesium oxide, a buffer layer of strontium titanate or a mixture of strontium titanate and strontium ruthenate and a top-layer of a superconducting material such as YBCO upon the buffer layer.

  13. Rapid Prototyping Of Layered Composite Parts

    NASA Technical Reports Server (NTRS)

    Wolff, Edwin D.

    1992-01-01

    Numerically controlled cutting accelerates fabrication of layers. Proposed method derived from stereoscopic lithography. CATIA or CAEDS computer program used to generate three-dimensional mathematical model of prototype part. In model, geometry of part specified in layers, as in stereoscopic lithography. Model data for each layer fed to computer-numerically-controlled ultrasonic cutting machine. Sheet of prepreg (uncured composite material) of specified layer thickness placed in machine and cut, under control of model data, to specified shape of layer.

  14. [A comment on chiral thin layer chromatography].

    PubMed

    Chen, Xuexian; Yuan, Liming

    2016-01-01

    In recent eight years, authors' group has repeated a lot of experiments of chiral thin layer chromatography coming from literature. From the practical opinion, we summarized that there are nine characteristics for chiral thin layer chromatography. Some progresses of chiral thin layer chromatography are reviewed, and the enantioselectivity of a commercial chiral thin layer plate is introduced. The study of vancomycin as the chiral selector in thin layer chromatography is also reported.

  15. Discrete Atomic Layers at the Molecular Level

    NASA Astrophysics Data System (ADS)

    Yorimitsu, Hideki; Bhanuchandra, M.

    2015-12-01

    In this review, we deal with the syntheses of large discrete atomic layers at the molecular level. Spectroscopic measurements as well as X-ray crystallographic analyses lead to unambiguous characterizations of these layers. The molecular atomic layers can be considered to be parts of graphenes and related atomic layers, thereby helping to understand such indefinitely huge atomic layers or serving as seeds for the controlled synthesis of nanocarbons.

  16. Buffer layer for thin film structures

    DOEpatents

    Foltyn, Stephen R.; Jia, Quanxi; Arendt, Paul N.; Wang, Haiyan

    2006-10-31

    A composite structure including a base substrate and a layer of a mixture of strontium titanate and strontium ruthenate is provided. A superconducting article can include a composite structure including an outermost layer of magnesium oxide, a buffer layer of strontium titanate or a mixture of strontium titanate and strontium ruthenate and a top-layer of a superconducting material such as YBCO upon the buffer layer.

  17. Rapid Prototyping Of Layered Composite Parts

    NASA Technical Reports Server (NTRS)

    Wolff, Edwin D.

    1992-01-01

    Numerically controlled cutting accelerates fabrication of layers. Proposed method derived from stereoscopic lithography. CATIA or CAEDS computer program used to generate three-dimensional mathematical model of prototype part. In model, geometry of part specified in layers, as in stereoscopic lithography. Model data for each layer fed to computer-numerically-controlled ultrasonic cutting machine. Sheet of prepreg (uncured composite material) of specified layer thickness placed in machine and cut, under control of model data, to specified shape of layer.

  18. Spraying asymmetry into functional membranes layer-by-layer

    NASA Astrophysics Data System (ADS)

    Krogman, Kevin C.; Lowery, Joseph L.; Zacharia, Nicole S.; Rutledge, Gregory C.; Hammond, Paula T.

    2009-06-01

    As engineers strive to mimic the form and function of naturally occurring materials with synthetic alternatives, the challenges and costs of processing often limit creative innovation. Here we describe a powerful yet economical technique for developing multiple coatings of different morphologies and functions within a single textile membrane, enabling scientists to engineer the properties of a material from the nanoscopic level in commercially viable quantities. By simply varying the flow rate of charged species passing through an electrospun material during spray-assisted layer-by-layer deposition, individual fibres within the matrix can be conformally functionalized for ultrahigh-surface-area catalysis, or bridged to form a networked sublayer with complimentary properties. Exemplified here by the creation of selectively reactive gas purification membranes, the myriad applications of this technology also include self-cleaning fabrics, water purification and protein functionalization of scaffolds for tissue engineering.

  19. Spraying asymmetry into functional membranes layer-by-layer.

    PubMed

    Krogman, Kevin C; Lowery, Joseph L; Zacharia, Nicole S; Rutledge, Gregory C; Hammond, Paula T

    2009-06-01

    As engineers strive to mimic the form and function of naturally occurring materials with synthetic alternatives, the challenges and costs of processing often limit creative innovation. Here we describe a powerful yet economical technique for developing multiple coatings of different morphologies and functions within a single textile membrane, enabling scientists to engineer the properties of a material from the nanoscopic level in commercially viable quantities. By simply varying the flow rate of charged species passing through an electrospun material during spray-assisted layer-by-layer deposition, individual fibres within the matrix can be conformally functionalized for ultrahigh-surface-area catalysis, or bridged to form a networked sublayer with complimentary properties. Exemplified here by the creation of selectively reactive gas purification membranes, the myriad applications of this technology also include self-cleaning fabrics, water purification and protein functionalization of scaffolds for tissue engineering.

  20. Layer-by-layer microcapsules templated on erythrocyte ghost carriers.

    PubMed

    Shaillender, Mutukumaraswamy; Luo, Rongcong; Venkatraman, Subbu S; Neu, Björn

    2011-08-30

    This work reports the fabrication of layer-by-layer (LbL) microcapsules that provide a simple mean for controlling the burst and subsequent release of bioactive agents. Red blood cell (RBC) ghosts were loaded with fluorescently labeled dextran and lysozyme as model compounds via hypotonic dialysis with an encapsulation efficiency of 27-31%. It is demonstrated that these vesicles maintain their shape and integrity and that a uniform distribution of the encapsulated agents within these carriers is achieved. The loaded vesicles were then successfully coated with the biocompatible polyelectrolytes, poly-L-arginine hydrochloride and dextran sulfate. It is demonstrated that the release profiles of the encapsulated molecules can be regulated over a wide range by adjusting the number of polyelectrolyte layers. In addition, the LbL shell also protects the RBC ghost from decomposition thereby potentially preserving the bioactivity of encapsulated drugs or proteins. These microcapsules, consisting of an RBC ghost coated with a polyelectrolyte multilayer, provide a simple mean for the preparation of loaded LbL microcapsules eliminating the core dissolution and post-loading of bioactive agents, which are required for conventional LbL microcapsules.

  1. Layer-by-layer self-assembly of plexcitonic nanoparticles.

    PubMed

    DeLacy, Brendan G; Qiu, Wenjun; Soljačić, Marin; Hsu, Chia Wei; Miller, Owen D; Johnson, Steven G; Joannopoulos, John D

    2013-08-12

    Colloidal suspensions of multilayer nanoparticles composed of a silver core, a polyelectrolyte spacer layer (inner shell), and a J-aggregate cyanine dye outer shell have been prepared for the first time. Absorption properties of the colloid were measured in the visible region. This multilayer architecture served as a framework for examining the coupling of the localized surface plasmon resonance exhibited by the silver core with the molecular exciton exhibited by the J-aggregate outer shell. The polyelectrolyte spacer layer promotes the formation of an excitonic J-aggregate while serving as a means of controlling the plasmon-exciton (i.e. plexciton) coupling strength through changing the distance between the core and the shell. An analytical expression based on Mie Theory and the Transfer Matrix Method was obtained for describing the optical response of these multilayered nanostructures. Computational and experimental results indicate that the absorption wavelength of the J-aggregate form of the dye is dependent on both the distance of the dye layer from the silver core and the degree of dye aggregation.

  2. Polyelectrolyte Layer-by-Layer Assembly on Organic Electrochemical Transistors.

    PubMed

    Pappa, Anna-Maria; Inal, Sahika; Roy, Kirsty; Zhang, Yi; Pitsalidis, Charalampos; Hama, Adel; Pas, Jolien; Malliaras, George G; Owens, Roisin M

    2017-03-29

    Oppositely charged polyelectrolyte multilayers (PEMs) were built up in a layer-by-layer (LbL) assembly on top of the conducting polymer channel of an organic electrochemical transistor (OECT), aiming to combine the advantages of well-established PEMs with a high performance electronic transducer. The multilayered film is a model system to investigate the impact of biofunctionalization on the operation of OECTs comprising a poly(3,4-ethylenedioxythiophene) polystyrenesulfonate (PEDOT:PSS) film as the electrically active layer. Understanding the mechanism of ion injection into the channel that is in direct contact with charged polymer films provides useful insights for novel biosensing applications such as nucleic acid sensing. Moreover, LbL is demonstrated to be a versatile electrode modification tool enabling tailored surface features in terms of thickness, softness, roughness, and charge. LbL assemblies built up on top of conducting polymers will aid the design of new bioelectronic platforms for drug delivery, tissue engineering, and medical diagnostics.

  3. Mars South Polar Layered Deposits

    NASA Technical Reports Server (NTRS)

    2003-01-01

    December 8, 2003

    Remarkable layered deposits covering older, cratered surfaces near Mars' south pole dominate this mosaic of images taken by the camera on NASA's Mars Odyssey spacecraft between Nov. 8 and Nov. 26, 2003. The margin of these layered deposits appears to be eroding poleward, exposing a series of layers in the retreating cliff.

    The mosaic, stitched from eight visible-wavelength images from Odyssey's thermal emission imaging system, covers an area more than 325 kilometers (200 miles) long and 100 kilometers (62 miles) wide. The pictured area lies between 78 degrees and 82 degrees south latitude and between 90 degrees and 104 degrees east longitude.

    [figure removed for brevity, see original site] Click on image for larger view

    A zoom shows details in an area about 75 kilometers (47 miles) by 100 kilometers (62 miles), centered at about 80 degrees south latitude and 99 degrees east longitude. An older impact crater in the left part of the scene is filled with younger deposits from the layered terrain.

    [figure removed for brevity, see original site] Click on image for larger view

    A further zoom emphasizes a small, fresh crater about 350 meters (1,150 feet) in diameter near the center of the scene. The adjacent cliff contains numerous individual layers. An unusual set of small mesas, seen in the lower right part of the image, is being eroded from the polar layered material. The images making up this mosaic have a spatial resolution of 36 meters (118 feet) per pixel, allowing detection of features as small as 75 to 100 meters (246 to 328 feet) across.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for the NASA Office of Space Science, Washington. The thermal emission imaging system on Odyssey was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. Lockheed Martin Space Systems, Denver, is the prime contractor for the Odyssey project, and developed and built

  4. Nonlinear Instability of Liquid Layers.

    NASA Astrophysics Data System (ADS)

    Newhouse, Lori Ann

    The nonlinear instability of two superposed viscous liquid layers in planar and axisymmetric configurations is investigated. In the planar configuration, the light layer fluid is bounded below by a wall and above by a heavy semiinfinite fluid. Gravity drives the instability. In the first axisymmetric configuration, the layer is confined between a cylindrical wall and a core of another fluid. In the second, a thread is suspended in an infinite fluid. Surface tension forces drive the instability in the axisymmetric configurations. The nonlinear evolution of the fluid-fluid interface is computed for layers of arbitrary thickness when their dynamics are fully coupled to those of the second fluid. Under the assumption of creeping flow, the flow field is represented by an interfacial distribution of Green's functions. A Fredholm integral equation of the second kind for the strength of the distribution is derived and then solved using an iterative technique. The Green's functions produce flow fields which are periodic in the direction parallel to the wall and have zero velocity on the wall. For small and moderate surface tension, planar layers evolve into a periodic array of viscous plumes which penetrate into the overlying fluid. The morphology of the plumes depends on the surface tension and the ratio of the fluid viscosities. As the viscosity of the layer increases, the plumes change from a well defined drop on top of a narrow stem to a compact column of rising fluid. The capillary instability of cylindrical interfaces and interfaces in which the core thickness varies in the axial direction are investigated. In both the unbounded and wall bounded configurations, the core evolves into a periodic array of elongated fluid drops connected by thin, almost cylindrical fluid links. The characteristics of the drop-link structure depend on the core thickness, the ratio of the core radius to the wall radius, and the ratio of the fluid viscosities. The factors controlling the

  5. Semi-convective layer formation

    NASA Astrophysics Data System (ADS)

    Zaussinger, F.; Kupka, F.; Egbers, Ch.; Neben, M.; Hücker, S.; Bahr, C.; Schmitt, M.

    2017-05-01

    Semi-convective mixing, as an example of double-diffusive convection, is of general importance in multi-component fluid mixing processes. In astrophysics it occurs when the mean molecular weight gradient caused by a mixture of light material on top of heavier one counteracts the convective instability caused by a temperature gradient. Direct numerical simulations of double-diffusive fluid flows in a realistic stellar or planetary parameter space are currently non-feasible. Hence, a model describing incompressible semi-convection was developed, which allows to investigate semi-convective layer formation. A detailed parameter study with varying Rayleigh number and stability parameter has been performed for the giant planet case. We conclude that semi-convective layering may not play that important role as suggested in earlier works for the planetary case.

  6. Generic properties of layered superconductors

    SciTech Connect

    Klemm, R.A.

    1992-10-01

    A wide variety of layered materials have been found to be superconducting. Among these are graphite intercalation donor compounds, transition metal dichalcogenides, intercalated transition metal dichalcogenides, organic layered superconductors, artificial superlattices, and the cuprates. The normal state properties of all of these compounds are very similar, due to the fact that they all have well-defined Fermi surfaces, and quasi-linear in-plane resistivities at high temperatures. At lower temperatures, charge- or spin-density waves are common in these systems. With the exception of the graphite intercalation compounds, all of the fayered superconductors are type-II, and generally highly anisotropic in their superconducting properties. Dimensional crossover from anisotropic bulk to thin film behavior is common to many of these materials.

  7. Plastic energies in layered superconductors

    SciTech Connect

    Wilkin, N.K.; Moore, M.A.

    1995-08-01

    We estimate the energy cost associated with two pancake vortices colliding in a layered superconductor. It is argued that this energy sets the plastics energy scale and is the analogue of the crossing energy for vortices in the continuum case. The starting point of the calculation is the Lawrence-Doniach version of the Ginzburg-Landau free energy for type-II superconductors. The magnetic fields considered are along the {ital c} direction and assumed to be sufficiently high that the lowest Landau-level approximation is valid. For Bi-2212, where it is known that layering is very important, the results are radically different from what would have been obtained using a three-dimensional anisotropic continuum model. We then use the plastic energy for Bi-2212 to successfully explain recent results from Hellerqvist {ital et} {ital al}. on its longitudinal resistance.

  8. Stability of compressible boundary layers

    NASA Technical Reports Server (NTRS)

    Nayfeh, Ali H.

    1989-01-01

    The stability of compressible 2-D and 3-D boundary layers is reviewed. The stability of 2-D compressible flows differs from that of incompressible flows in two important features: There is more than one mode of instability contributing to the growth of disturbances in supersonic laminar boundary layers and the most unstable first mode wave is 3-D. Whereas viscosity has a destabilizing effect on incompressible flows, it is stabilizing for high supersonic Mach numbers. Whereas cooling stabilizes first mode waves, it destabilizes second mode waves. However, second order waves can be stabilized by suction and favorable pressure gradients. The influence of the nonparallelism on the spatial growth rate of disturbances is evaluated. The growth rate depends on the flow variable as well as the distance from the body. Floquet theory is used to investigate the subharmonic secondary instability.

  9. Deep layer malt drying modelling

    SciTech Connect

    Lopez, A.; Virseda, P.; Martinez, G.; Llorca, M.

    1997-05-01

    In malt production drying operation plays an important role in the total processing cost, however there are not many studies on malt drying modeling and optimization. In this paper a deep layer malt drying mathematical model in the form of four partial differential equations is presented. To determine drying constants, malt thin layer drying experiments at several air temperatures and relative humidities were made. The model were validated at industrial scale. The greatest energy savings, approximately 5.5% in fuel and 7.5% in electric energy, were obtained by an additional (and increased) air recirculation, which is carried out during the last 6 hours of the drying process and a significant decrease of air flow-rate during the last 6 hours of the drying process.

  10. Optimized capping layers for EUV multilayers

    DOEpatents

    Bajt, Sasa; Folta, James A.; Spiller, Eberhard A.

    2004-08-24

    A new capping multilayer structure for EUV-reflective Mo/Si multilayers consists of two layers: A top layer that protects the multilayer structure from the environment and a bottom layer that acts as a diffusion barrier between the top layer and the structure beneath. One embodiment combines a first layer of Ru with a second layer of B.sub.4 C. Another embodiment combines a first layer of Ru with a second layer of Mo. These embodiments have the additional advantage that the reflectivity is also enhanced. Ru has the best oxidation resistance of all materials investigated so far. B.sub.4 C is an excellent barrier against silicide formation while the silicide layer formed at the Si boundary is well controlled.

  11. Waves, Turbulence and Boundary Layers

    DTIC Science & Technology

    2005-09-30

    turbulent bottom boundary layers to account for shallow water wave and streaming effects . OBJECTIVES 1. Derive the three-dimensional, wave...deficiency. 1 Report Documentation Page Form ApprovedOMB No. 0704-0188 Public reporting burden for the collection of information is estimated to average...completing and reviewing the collection of information . Send comments regarding this burden estimate or any other aspect of this collection of

  12. Transition in hypersonic boundary layers

    NASA Astrophysics Data System (ADS)

    Zhang, Chuanhong; Zhu, Yiding; Chen, Xi; Yuan, Huijing; Wu, Jiezhi; Chen, Shiyi; Lee, Cunbiao; Gad-el-Hak, Mohamed

    2015-10-01

    Transition and turbulence production in a hypersonic boundary layer is investigated in a Mach 6 wind tunnel using Rayleigh-scattering visualization, fast-response pressure measurements, and particle image velocimetry. It is found that the second-mode instability is a key modulator of the transition process. Although the second-mode is primarily an acoustic wave, it causes the formation of high-frequency vortical waves, which triggers a fast transition to turbulence.

  13. Explosive shielding by weak layers

    SciTech Connect

    Fourney, W.L.; Dick, R.D.; Weaver, T.A.

    1993-02-01

    This paper presents the results of a series of computations which were carried out to determine the effect that a layer of extremely weak rock embedded in an otherwise strong rock matrix would have on the displacements and velocities which result from the detonation of a nearby explosive source. The motivation for the study was the apparently different measurements obtained on the Mission Cyber Nuclear Event when compared to results obtained from other events of equal yield in similar geologic media.

  14. Explosive shielding by weak layers

    SciTech Connect

    Fourney, W.L.; Dick, R.D.; Weaver, T.A.

    1993-01-01

    This paper presents the results of a series of computations which were carried out to determine the effect that a layer of extremely weak rock embedded in an otherwise strong rock matrix would have on the displacements and velocities which result from the detonation of a nearby explosive source. The motivation for the study was the apparently different measurements obtained on the Mission Cyber Nuclear Event when compared to results obtained from other events of equal yield in similar geologic media.

  15. The Martian Surface Boundary Layer

    NASA Technical Reports Server (NTRS)

    Wilson, G. R.; Joshi, M.

    1999-01-01

    The acquisition of meteorological data from the surface of Mars by the two Viking Landers and Mars Pathfinder make it possible to estimate atmospheric boundary layer parameters and surface properties at three different locations on the planet. Because the Martian atmosphere is so thin the majority of the solar radiance is converted to heat at the surface. The difference between surface and atmospheric temperature can also constraint surface albedo, thermal inertia, and infrared emissivity. The Mars Pathfinder Atmospheric Structure Instrument/Meteorological package (ASI/MET) was the most capable weather monitoring system ever sent to the surface of another planet to date. One of the prime objectives of the ASI/MET package is to characterize the surface boundary layer parameters, particularly the heat and momentum fluxes, scaling temperature and friction velocity, and estimate surface roughness. Other important boundary layer parameters, such as Richardson Number, Monin-Obukhov length, analysis of turbulence characteristics of wind and temperature, and atmospheric stability class can also be determined from these measurements.

  16. Layered sensing with radio (LSWR)

    NASA Astrophysics Data System (ADS)

    Mitra, Atindra K.

    2010-04-01

    An alternative approach to a Layered Sensing System-of-Systems methodology, denoted as LSWR (Layered Sensing With Radio), is outlined in this paper. This is a novel Broadcast-TV-Driven layered sensing technique that shows potential for finding embedded objects within, for example, buildings via leveraging and combining existing commercial satellite technologies with COTS (Commercial Off-the-Shelf) wireless network technologies and state-of-the-art wireless sensor mote technologies. Specifically, compact sensor mote technologies are employed in a cost-effective manner to interface with and control low-cost satellite radio/broadcast tuners. With this approach, initial concepts of this type are investigated via the analysis of compact custom sensor node technology (i.e. wireless sensor mote interfaced with satellite broadcast tuner) integrated onto a UGV (unmanned ground vehicle) robot arm for purposes developing prototype UGV robot systems with passive integrated RF sensors that support, for example, networked thru-wall embedded object detection. The primary category of commercial satellite signal considered for analysis within this paper is known as DVB (Digital Video Broadcast).

  17. Layer transfer by controlled spalling

    NASA Astrophysics Data System (ADS)

    Bedell, Stephen W.; Fogel, Keith; Lauro, Paul; Shahrjerdi, Davood; Ott, John A.; Sadana, Devendra

    2013-04-01

    In this communication, we present what may be the simplest method yet devised for removing surface layers from brittle substrates. The process is called controlled spalling technology (CST) and works by depositing a tensile stressor layer on the surface of a substrate, introducing a crack near the edge of the substrate, and mechanically guiding the crack as a single fracture front across the surface. The entire process is performed at room-temperature using only common laboratory equipment. We present here, for the first time, the specific process conditions required for controlled spalling of Ge <0 0 1> substrates using Ni as the stressor layer. We also illustrate the versatility of CST by removing completed CMOS circuits from a Si wafer and demonstrate functionality of the flexible circuits. Raman spectroscopy of spalled circuits with the Ni stressor intact indicates a residual compressive Si strain of 0.0029, in good agreement with the calculated value of 0.0022. Therefore, CST also permits new opportunities for strain engineering of nanoscale devices.

  18. A laboratory investigation of potential double layers

    NASA Technical Reports Server (NTRS)

    Leung, Philip

    1987-01-01

    In a triple plasma device, the injection of electron current from the source chamber to the target chamber causes the formation of a potential double layer. At a low current density, the space charge of the injected current produces a virtual cathode-type potential double layer. This double layer is stable, and various wave instabilities are observed to associate with this double layer. As the current density is increased, the double layer becomes unstable, and a moving double layer results. As the current density is increased further, the enhanced ionization causes the neutralization of the space charge of the electron beam, and the beam plasma discharge is ignited.

  19. A laboratory investigation of potential double layers

    NASA Technical Reports Server (NTRS)

    Leung, Philip

    1987-01-01

    In a triple plasma device, the injection of electron current from the source chamber to the target chamber causes the formation of a potential double layer. At a low current density, the space charge of the injected current produces a virtual cathode-type potential double layer. This double layer is stable and various wave instabilities are observed to associate with this double layer. As the current density is increased, the double layer becomes unstable and a moving double layer results. As the current density is increased further, the enhanced ionization causes the neutralization of the space charge of the electron beam and the 'beam plasma discharge' is ignited.

  20. A laboratory investigation of potential double layers

    NASA Technical Reports Server (NTRS)

    Leung, Philip

    1987-01-01

    In a triple plasma device, the injection of electron current from the source chamber to the target chamber causes the formation of a potential double layer. At a low current density, the space charge of the injected current produces a virtual cathode-type potential double layer. This double layer is stable and various wave instabilities are observed to associate with this double layer. As the current density is increased, the double layer becomes unstable and a moving double layer results. As the current density is increased further, the enhanced ionization causes the neutralization of the space charge of the electron beam and the 'beam plasma discharge' is ignited.

  1. Boundary layer receptivity and control

    NASA Technical Reports Server (NTRS)

    Hill, D. C.

    1993-01-01

    Receptivity processes initiate natural instabilities in a boundary layer. The instabilities grow and eventually break down to turbulence. Consequently, receptivity questions are a critical element of the analysis of the transition process. Success in modeling the physics of receptivity processes thus has a direct bearing on technological issues of drag reduction. The means by which transitional flows can be controlled is also a major concern: questions of control are tied inevitably to those of receptivity. Adjoint systems provide a highly effective mathematical method for approaching many of the questions associated with both receptivity and control. The long term objective is to develop adjoint methods to handle increasingly complex receptivity questions, and to find systematic procedures for deducing effective control strategies. The most elementary receptivity problem is that in which a parallel boundary layer is forced by time-harmonic sources of various types. The characteristics of the response to such forcing form the building blocks for more complex receptivity mechanisms. The first objective of this year's research effort was to investigate how a parallel Blasius boundary layer responds to general direct forcing. Acoustic disturbances in the freestream can be scattered by flow non-uniformities to produce Tollmien-Schlichting waves. For example, scattering by surface roughness is known to provide an efficient receptivity path. The present effort is directed towards finding a solution by a simple adjoint analysis, because adjoint methods can be extended to more complex problems. In practice, flows are non-parallel and often three-dimensional. Compressibility may also be significant in some cases. Recent developments in the use of Parabolized Stability Equations (PSE) offer a promising possibility. By formulating and solving a set of adjoint parabolized equations, a method for mapping the efficiency with which external forcing excites the three

  2. Layer by layer etching of LaAlSiOx

    NASA Astrophysics Data System (ADS)

    Hayashi, Hisataka

    2016-09-01

    In order to fabricate a gate transistor with high-k oxide materials, removal of high-k oxide films after gate electrode etching is necessary for the formation of ohmic contacts on source and drain regions. It is crucial that the removal process of high-k oxide film by dry etching is highly selective to and low in damage to the Si substrate in order to avoid the degradation of device performances. Sasaki et al. have achieved a high LaAlSiOx-to-Si selectivity of 6.7 using C4F8/Ar/H2 plasma. In the LaAlSiOx etching process using C4F8/Ar/H2 plasma, H2 plays a role in breaking the metal-oxygen bond to enhance etching of LaAlSiOx. Based on this result, the process was decomposed into two steps: a surface modification step using H2 plasma to break the metal-oxygen bond, and a removal step using C4F8/Ar plasma. A sequential layer by layer etching could realize low damage etching, similar to atomic layer etching. Therefore, a sequential LaAlSiOx etching process using a H2 surface modification step followed by a removal step using C4F8/Ar plasma is investigated. Experiments were carried out on 300 mm diameter wafers using the 100/13.56 MHz dual frequency superimposed capacitively coupled plasma reactor. The etching gases were H2 and C4F8/Ar for each step, respectively. Plasma process conditions were 100 MHz power of 1000 W (plasma generation), 13.56MHz power varied from 0 W to 300W (ion energy control). The substrate temperature was 40 °C. 15nm thick LaAlSiOx blanket film was used for evaluation of the etched amount. Film thickness was measured by X-ray fluorescent analysis thickness meter before and after plasma exposure. The etched amount of LaAlSiOx by the C4F8/Ar plasma step doubled with H2 modification. It is confirmed that when the C4F8/Ar plasma treatment time is sufficient to remove the surface modification layer, a self-limiting reaction is realized. Furthermore, it is confirmed that the etched amount per step can be controlled by control of the ion energy of H2

  3. Layers over layer-by-layer assemblies: silanization of polyelectrolyte multilayers.

    PubMed

    Dirani, Ali; Fernandes, Antony E; Wong, Diana Ramirez; Lipnik, Pascale; Poleunis, Claude; Nysten, Bernard; Glinel, Karine; Jonas, Alain M

    2014-08-26

    The functionalization of poly(allylamine hydrochloride)/poly(acrylic acid) (PAH/PAA) polyelectrolyte multilayers by silanes reacted from the gas phase is studied depending on reaction time and temperature, pH of multilayer assembly, and nature of the reacting silane group. Whereas monochlorosilanes only diffuse in the multilayer and graft in limited amount, trichloro- and triethoxysilanes form rapidly a continuous gel layer on the surface of the multilayer, with a thickness of ca. 10-20 nm. The reactivity is lower in the strongly paired regime of the multilayers (neutral assembly conditions) but otherwise is not affected by the pH of multilayer assembly. Silanization considerably broadens the range of possible functionalities for (PAH/PAA) multilayers: hydrophobicity, surface-initiated polymerization, and grafting of fluorescent probes by the formation of disulfide bridges are demonstrated. Conversely, our results also broaden the range of substrates that can be functionalized by silanes, using (PAH/PAA) multilayers as ubiquitous anchoring layers.

  4. Ultrathin-layer chromatography nanostructures modified by atomic layer deposition.

    PubMed

    Jim, S R; Foroughi-Abari, A; Krause, K M; Li, P; Kupsta, M; Taschuk, M T; Cadien, K C; Brett, M J

    2013-07-19

    Stationary phase morphology and surface chemistry dictate the properties of ultrathin-layer chromatography (UTLC) media and interactions with analytes in sample mixtures. In this paper, we combined two powerful thin film deposition techniques to create composite chromatography nanomaterials. Glancing angle deposition (GLAD) produces high surface area columnar microstructures with aligned macropores well-suited for UTLC. Atomic layer deposition (ALD) enables precise fabrication of conformal, nanometer-scale coatings that can tune surfaces of these UTLC films. We coated ∼5μm thick GLAD SiO2 UTLC media with <10nm thick ALD metal oxides (Al2O3, ZrO2, and ZnO) to decouple surface chemistry from the underlying GLAD scaffold microstructure. The effects of ALD coatings on GLAD UTLC media were investigated using transmission electron microscopy (TEM), gas adsorption porosimetry, and lipophilic dye separations. The results collectively show that the most significant changes occur over the first few nanometers of ALD coating. They further demonstrate independent control of film microstructure and surface characteristics. ALD coatings can enhance complex GLAD microstructures to engineer new composite nanomaterials potentially useful in analytical chromatography.

  5. Osteotropic therapy via targeted Layer-by-Layer nanoparticles

    PubMed Central

    Morton, Stephen W.; Shah, Nisarg J.; Quadir, Mohiuddin A.; Deng, Zhou J.; Poon, Zhiyong

    2014-01-01

    Current treatment options for debilitating bone diseases such as osteosarcoma, osteoporosis, and bone metastatic cancer are suboptimal and have low efficacy. New treatment options for these pathologies require targeted therapy that maximizes exposure to the diseased tissue and minimizes off-target side effects. This work investigates an approach for generating functional and targeted drug carriers specifically for treating primary osteosarcoma, a disease in which recurrence is common and the cure rate has remained around 20%. Our approach utilizes the modularity of Layer-by-Layer (LbL) assembly to generate tissue-specific drug carriers for systemic administration. This is accomplished via surface modification of drug-loaded nanoparticles with an aqueous polyelectrolyte, poly(acrylic acid) (PAA), side-chain functionalized with alendronate, a potent clinically-used bisphosphonate. Nanoparticles coated with PAA-Alendronate are observed to bind and internalize rapidly in human osteosarcoma 143B cells. Encapsulation of doxorubicin, a front-line chemotherapeutic, in an LbL-targeted liposome demonstrates potent toxicity in vitro. Active targeting of 143B xenografts in NCR nude mice with the LbL-targeted doxorubicin liposomes promotes enhanced, prolonged tumor accumulation and significantly improved efficacy. This report represents a tunable approach towards the synthesis of drug carriers, in which LbL can enable surface modification of nanoparticles for tissue-specific targeting and treatment. PMID:24124132

  6. Inkjet Deposition of Layer by Layer Assembled Films

    PubMed Central

    Andres, Christine M.; Kotov, Nicholas A.

    2010-01-01

    Layer-by-layer assembly (LBL) can create advanced composites with exceptional properties unavailable by other means, but the laborious deposition process and multiple dipping cycles hamper their utilization in microtechnologies and electronics. Multiple rinse steps provide both structural control and thermodynamic stability to LBL multilayers but they significantly limit their practical applications and contribute significantly to the processing time and waste. Here we demonstrate that by employing inkjet technology one can deliver the necessary quantities of LBL components required for film build-up without excess, eliminating the need for repetitive rinsing steps. This feature differentiates this approach from all other recognized LBL modalities. Using a model system of negatively charged gold nanoparticles and positively charged poly(diallyldimethylammonium) chloride, the material stability, nanoscale control over thickness and particle coverage offered by the inkjet LBL technique are shown to be equal or better than the multilayers made with traditional dipping cycles. The opportunity for fast deposition of complex metallic patterns using a simple inkjet printer was also shown. The additive nature of LBL deposition based on the formation of insoluble nanoparticle-polyelectrolyte complexes of various compositions provides an excellent opportunity for versatile, multi-component, and non-contact patterning for the simple production of stratified patterns that are much needed in advanced devices. PMID:20863114

  7. Layer-by-layer assemblies for antibacterial applications.

    PubMed

    Zhu, Xiaoying; Jun Loh, Xian

    2015-12-01

    The adhesion and proliferation of bacteria on various artificial surfaces affects the functionality of these specific interfaces. To overcome the problems caused by bacterial growth on these surfaces, various antibacterial coatings were developed. In this review, we summarized most of the antibacterial surfaces prepared by the Layer-by-Layer (LbL) assembly approach and classified these LbL films based on their antibacterial mechanisms. In the first group, the bactericidal LbL assemblies which incorporate various biocides including heavy metals, antibiotics, cationic molecules, antimicrobial peptides and enzymes are able to kill surrounding or contacted bacteria. In the second group, we focused on the physical aspects of film surfaces. Bacterial adhesion resistant LbL films have been fabricated to adjust the substrate surface properties such as surface free energy (or wettability), roughness, and surface charge which may affect the adhesion of bacteria. Furthermore, as an enhancement in the antibacterial efficiency, multifunctional LbL assemblies combining both bactericidal and adhesion resistant functionalities were discussed. The advantages and limitations of these antibacterial LbL assemblies were summarized and subsequently directions for future development were proposed.

  8. Layer-by-Layer Assemblies for Cancer Treatment and Diagnosis.

    PubMed

    Liu, Xi Qiu; Picart, Catherine

    2016-02-10

    The layer-by-layer (LbL) technique was introduced in the early 1990s. Since then, it has undergone a series of technological developments, making it possible to engineer various theranostic platforms, such as films and capsules, with precise control at the nanometer and micrometer scales. Recent progress in the applications of LbL assemblies in the field of cancer therapy, diagnosis, and fundamental biological study are highlighted here. The potential of LbL-based systems as drug carriers is discussed, especially with regard to the engineering of innovative stimuli-responsive systems, and their advantageous multifunctionality in the development of new therapeutic tools. Then, the diagnostic functions of LbL assemblies are illustrated for detection and capture of rare cancer cells. Finally, LbL-mimicking extracellular environments demonstrate the emerging potential for the study of cancer cell behavior in vitro. The advantages of LbL systems, important challenges that need to be overcome, and future perspectives in clinical practice are then highlighted.

  9. Layer-by-layer assemblies for cancer treatment and diagnosis

    PubMed Central

    Liu, Xi Qiu; Picart, Catherine

    2016-01-01

    The layer-by-layer (LbL) technique was introduced in the early 90s by Profs Moehwald, Lvov and Decher. Since then, it has undergone a series of technological developments, making it possible to engineer various theranostic platforms such as films and capsules, with precise control at the nanometer and micrometer scales. This Research News article highlights recent progress in the applications of LbL assemblies in the field of cancer therapy, diagnosis and fundamental biology study. The potentials of LbL-based systems as drug carriers are discussed, especially with regard to the engineering of innovative stimuli-responsive systems, and their advantageous multifunctionality in the development of new therapeutic tools. Then, the diagnostic functions of LbL assemblies are illustrated for detection and capture of rare cancer cells. Finally, LbL mimicking extracellular environments demonstrate the emerging potential for the study of cancer cell behaviors in vitro. We conclude by highlighting the advantages of LbL systems, important challenges that need to be overcome, and future perspectives in clinical practice. PMID:26390356

  10. Nanomechanical cleavage of molybdenum disulphide atomic layers.

    PubMed

    Tang, Dai-Ming; Kvashnin, Dmitry G; Najmaei, Sina; Bando, Yoshio; Kimoto, Koji; Koskinen, Pekka; Ajayan, Pulickel M; Yakobson, Boris I; Sorokin, Pavel B; Lou, Jun; Golberg, Dmitri

    2014-04-03

    The discovery of two-dimensional materials became possible due to the mechanical cleavage technique. Despite its simplicity, the as-cleaved materials demonstrated surprising macro-continuity, high crystalline quality and extraordinary mechanical and electrical properties that triggered global research interest. Here such cleavage processes and associated mechanical behaviours are investigated by a direct in situ transmission electron microscopy probing technique, using atomically thin molybdenum disulphide layers as a model material. Our technique demonstrates layer number selective cleavage, from a monolayer to double layer and up to 23 atomic layers. In situ observations combined with molecular dynamics simulations reveal unique layer-dependent bending behaviours, from spontaneous rippling (<5 atomic layers) to homogeneous curving (~ 10 layers) and finally to kinking (20 or more layers), depending on the competition of strain energy and interfacial energy.

  11. Nanomechanical cleavage of molybdenum disulphide atomic layers

    NASA Astrophysics Data System (ADS)

    Tang, Dai-Ming; Kvashnin, Dmitry G.; Najmaei, Sina; Bando, Yoshio; Kimoto, Koji; Koskinen, Pekka; Ajayan, Pulickel M.; Yakobson, Boris I.; Sorokin, Pavel B.; Lou, Jun; Golberg, Dmitri

    2014-04-01

    The discovery of two-dimensional materials became possible due to the mechanical cleavage technique. Despite its simplicity, the as-cleaved materials demonstrated surprising macro-continuity, high crystalline quality and extraordinary mechanical and electrical properties that triggered global research interest. Here such cleavage processes and associated mechanical behaviours are investigated by a direct in situ transmission electron microscopy probing technique, using atomically thin molybdenum disulphide layers as a model material. Our technique demonstrates layer number selective cleavage, from a monolayer to double layer and up to 23 atomic layers. In situ observations combined with molecular dynamics simulations reveal unique layer-dependent bending behaviours, from spontaneous rippling (<5 atomic layers) to homogeneous curving (~ 10 layers) and finally to kinking (20 or more layers), depending on the competition of strain energy and interfacial energy.

  12. Layers in Burns Cliff Examined by Opportunity

    NASA Image and Video Library

    2011-11-21

    NASA Mars Exploration Rover Opportunity studied layers in the Burns Cliff slope of Endurance Crater in 2004. The layers show different types of deposition of sulfate-rich sediments. Opportunity panoramic camera recorded this image.

  13. Black layers on historical architecture.

    PubMed

    Toniolo, Lucia; Zerbi, Carlotta M; Bugini, Roberto

    2009-03-01

    The external surface of any building in urban polluted environment is unavoidably destined to be covered with layers that assume a grey to black colour and are generally called 'black crusts'. These, according to standard protocols and glossary, are deteriorated surface layers of stone material; they can have variable thickness, are hard and fragile and can detach spontaneously from the substrate, which, in general, is quite decayed. Plain visual examination may lead to consider 'black crusts' all similar, whilst only a careful diagnostic investigation can distinguish 'black crusts' and the consequences of their formation on stone substrates. In this paper, various black layers on marble are studied and compared and the morphological and compositional characteristics discussed according to the related mechanisms of formation. Differences between old (hundred years) and recent crusts (30 years) are investigated and pointed out. Samples of black crusts collected from the Milan Cathedral façade (Candoglia Marble) have been studied and compared with the careful and synergic employ of traditional techniques: optical (transmission and reflected VIS light) and electron microscopy, X-ray spectrometry and micro-Fourier transform infrared spectroscopy. Visual examination of loose fragments does not allow to point out outstanding differences amongst the various samples; black layers have similar main mineral components, gypsum and airborne particles, with different spatial distribution. The microscopic studies allowed to point out the porosity differences, the gypsum crystallisation habit, different amount of embedded particles, level and progress of marble decay. The observations lead to define three main types of black crusts: black crust deriving from marble sulphation, compact deposit and encrustation due to exogenic materials deposition. Black crusts show evidence of sulphation in progress, without a clear continuity solution between crust and marble; the lack of

  14. Bioactivity of polycrystalline silicon layers.

    PubMed

    Pramatarova, Lilyana; Pecheva, Emilia; Montgomery, Paul; Dimova-Malinovska, Doriana; Petrov, Todor; Toth, Attila L; Dimitrova, Magdalena

    2008-02-01

    After oxygen, silicon is the second most abundant element in the environment and is present as an impurity in most materials. The widespread occurrence of siliceous biominerals as structural elements in lower plants and animals suggests that Si plays a role in the production and maintenance of connective tissue in higher organisms. It has been shown that the presence of Si is necessary in bones, cartilage and in the formation of connective tissue, as well as in some important metabolic processes. In this work, polycrystalline silicon layers are tested in terms of bioactivity, i.e., their ability to induce hydroxyapatite formation from simulated body fluid. Hydroxyapatite is a biologically compatible material with chemical similarity to the inorganic part of bones and teeth. Polycrystalline silicon layers are obtained by aluminum induced crystallization of Al and amorphous Si thin films deposited sequentially on glass substrates by radio-frequency magnetron sputtering and subsequently annealed in different atmospheres. The hydroxyapatite formation is induced by applying a method of laser-liquid-solid interaction. The method consists of irradiating the samples with laser light while immersed in a solution that is supersaturated with respect to Ca and P. As a result, heterogeneous porous sponge-like carbonate-containing hydroxyapatite is grown on the polysilicon surfaces. Crystals that are spherical in shape, containing Ca, P and O, Na, Cl, Mg, Al, Si and S, as well as well-faceted NaCl crystals are embedded in the hydroxyapatite layer. Enhancement of the hydroxyapatite growth and increased crystallinity is observed due to the applied laser-liquid-solid interaction.

  15. Applications of strained layer superlattices

    NASA Astrophysics Data System (ADS)

    Smith, D. L.; Laurich, B. K.; Mailhiot, C.

    1990-04-01

    Because of different band edge lineups, strain conditions, and growth orientations, various strained layer superlattice (SLS) materials can exhibit qualitatively new physical behavior in their optical properties. Two examples are given of new physical behavior in SLS: strain generated electric fields in polar growth axis superlattices and strained type 2 superlattices. In SLS, large electric fields can be generated by the piezoelectric effect. The fields are largest for SLS with a (111) growth axis; they vanish for SLS with a (100) growth axis. The strain generated electric fields strongly modify the optical properties of the superlattice. Photogenerated electron-hole pairs screen the fields leading to a large nonlinear optical response. Application of an external electric field leads to a large linear electrooptical response. The absorption edge can be either red or blue shifted. Optical studies of (100), (111), and (211) oriented GaInAs/GaAs superlattices confirm the existence of the strain generated electric fields. Small band gap semiconductors are useful for making intrinsic long wavelength infrared detectors. Arbitrarily small band gaps can be reached in the type 2 superlattice InAs/GaSb. However, for band gaps less than 0.1 eV, the layer thicknesses are large and the overlap of electron and hole wavefunctions are small. Thus, the absorption coefficient is too small for useful infrared (IR) detection. Including In in the GaSb introduces strain in he InAs/GaInSb superlattice which shifts the band edges so that small band gaps can be reached in thin layer superlattices. Good absorption at long IR wavelengths is thus achieved.

  16. Multiple-Dynode-Layer Microchannel Plate

    NASA Technical Reports Server (NTRS)

    Woodgate, Bruce E.

    1990-01-01

    Improved microchannel-plate electron image amplifier made of stack of discrete microchannel-plate layers. New plates easier to manufacture because no need to etch long, narrow holes, to draw and bundle thin glass tubes, or to shear plates to give microchannels curvatures necessary for reduction of undesired emission of ions. Discrete dynode layers stacked with slight offset from layer to layer to form microchannel plate with curved channels. Provides for relatively fast recharging of microchannel dynodes, with consequent enhancement of performance.

  17. Assembly of 1D nanofibers into a 2D bi-layered composite nanofibrous film with different functionalities at the two layers via layer-by-layer electrospinning.

    PubMed

    Wang, Zijiao; Ma, Qianli; Dong, Xiangting; Li, Dan; Xi, Xue; Yu, Wensheng; Wang, Jinxian; Liu, Guixia

    2016-12-21

    A two-dimensional (2D) bi-layered composite nanofibrous film assembled by one-dimensional (1D) nanofibers with trifunctionality of electrical conduction, magnetism and photoluminescence has been successfully fabricated by layer-by-layer electrospinning. The composite film consists of a polyaniline (PANI)/Fe3O4 nanoparticle (NP)/polyacrylonitrile (PAN) tuned electrical-magnetic bifunctional layer on one side and a Tb(TTA)3(TPPO)2/polyvinylpyrrolidone (PVP) photoluminescent layer on the other side, and the two layers are tightly combined face-to-face together into the novel bi-layered composite film of trifunctionality. The brand-new film has totally different characteristics at the double layers. The electrical conductivity and magnetism of the electrical-magnetic bifunctional layer can be, respectively, tunable via modulating the PANI and Fe3O4 NP contents, and the highest electrical conductivity can reach up to the order of 10(-2) S cm(-1), and predominant intense green emission at 545 nm is obviously observed in the photoluminescent layer under the excitation of 357 nm single-wavelength ultraviolet light. More importantly, the luminescence intensity of the photoluminescent layer remains almost unaffected by the electrical-magnetic bifunctional layer because the photoluminescent materials have been successfully isolated from dark-colored PANI and Fe3O4 NPs. By comparing with the counterpart single-layered composite nanofibrous film, it is found that the bi-layered composite nanofibrous film has better performance. The novel bi-layered composite nanofibrous film with trifunctionality has potential in the fields of nanodevices, molecular electronics and biomedicine. Furthermore, the design conception and fabrication technique for the bi-layered multifunctional film provide a new and facile strategy towards other films of multifunctionality.

  18. Layered Yardangs in Henry Crater

    NASA Technical Reports Server (NTRS)

    2003-01-01

    MGS MOC Release No. MOC2-389, 12 June 2003

    This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows wind-sculpted remnants of layered sedimentary rock that once completely covered the northwestern floor of Henry Crater, an ancient impact basin located at 11.7oN, 336.4oW. These landforms, shaped somewhat like inverted boat hulls, are 'textbook examples' of a wind erosion form known as a yardang. The image covers an area 2.3 km (1.4 mi) wide; sunlight illuminates the scene from the left.

  19. Coarse Layering at 'Home Plate'

    NASA Technical Reports Server (NTRS)

    2006-01-01

    This image shows coarse-grained layers from around the edge of a low plateau called 'Home Plate' inside Mars' Gusev Crater. One possible origin is material falling to the ground after being thrown aloft by an explosion such as a volcanic eruption or meteorite impact.

    The panoramic camera (Pancam) on NASA's Mars Exploration Rover Spirit acquired the exposures for this image on Spirit's 749th Martian day (Feb. 10, 2006). This view is an approximately true-color rendering mathematically generated from separate images taken through all of the left Pancam's 432-nanometer to 753-nanometer filters.

  20. Emissivity of layered fibrous materials.

    PubMed

    Golombok, M; Shirvill, L C

    1988-09-15

    The radiant energy properties of fibrous materials may be described by an effective surface emissivity, which is a function of the material construction. The important parameters are porosity and the emissivity of the solid component. The layered construction leads to a unit cell model determining radiant heat transfer through the material to the environment. Geometric absorption cross sections are used as radiation view factors in a pseudoenclosed configuration. The emissivities are obtained by comparison to a material made from black fibers and are in qualitative agreement with experimental measurements.

  1. Bursts in inclined layer convection

    NASA Astrophysics Data System (ADS)

    Busse, F. H.; Clever, R. M.

    2000-08-01

    A new instability of longitudinal rolls in an inclined fluid layer heated from below is analyzed in the case of the Prandtl number P=0.71. The instability assumes the form of subharmonic undulations and evolves into a spatially chaotic pattern when the angle of inclination is of the order of 20°. The chaotic state rapidly decays and longitudinal rolls recover until the next burst of chaotic convection occurs. The theoretical findings closely correspond to recent experimental observations by Daniels et al. [Phys. Rev. Lett. (to be published)].

  2. Motor cortex layer 4: less is more

    PubMed Central

    Barbas, Helen; García-Cabezas, Miguel Á.

    2015-01-01

    The stratified motor cortex is variously thought to either lack or contain layer 4. Yamawaki et al. described a functional layer 4 in mouse motor cortex with properties and connections similar to layer 4 in sensory areas. Their results bolster a theoretical framework suggesting all primary cortical areas are equivalent. PMID:25868984

  3. Variability in oak forest herb layer communities

    Treesearch

    J. R. McClenahen; R. P. Long

    1995-01-01

    This study evaluates forest herb-layer sensitivity to annual-scale environmental fluctuation. Specific objectives were to determine the between-year variation in herb-layer community biomass, and to contrast and evaluate the temporal stability of spatial relationships in herb-layer community structure and composition between successive years. Aboveground dry weights of...

  4. The Hole in the Ozone Layer.

    ERIC Educational Resources Information Center

    Hamers, Jeanne S.; Jacob, Anthony T.

    This document contains information on the hole in the ozone layer. Topics discussed include properties of ozone, ozone in the atmosphere, chlorofluorocarbons, stratospheric ozone depletion, effects of ozone depletion on life, regulation of substances that deplete the ozone layer, alternatives to CFCs and Halons, and the future of the ozone layer.…

  5. The Hole in the Ozone Layer.

    ERIC Educational Resources Information Center

    Hamers, Jeanne S.; Jacob, Anthony T.

    This document contains information on the hole in the ozone layer. Topics discussed include properties of ozone, ozone in the atmosphere, chlorofluorocarbons, stratospheric ozone depletion, effects of ozone depletion on life, regulation of substances that deplete the ozone layer, alternatives to CFCs and Halons, and the future of the ozone layer.…

  6. Biaxially textured metal substrate with palladium layer

    DOEpatents

    Robbins, William B [Maplewood, MN

    2002-12-31

    Described is an article comprising a biaxially textured metal substrate and a layer of palladium deposited on at least one major surface of the metal substrate; wherein the palladium layer has desired in-plane and out-of-plane crystallographic orientations, which allow subsequent layers that are applied on the article to also have the desired orientations.

  7. Computer Program Re-layers Engineering Drawings

    NASA Technical Reports Server (NTRS)

    Crosby, Dewey C., III

    1990-01-01

    RULCHK computer program aids in structuring layers of information pertaining to part or assembly designed with software described in article "Software for Drawing Design Details Concurrently" (MFS-28444). Checks and optionally updates structure of layers for part. Enables designer to construct model and annotate its documentation without burden of manually layering part to conform to standards at design time.

  8. Blockfall on the North Polar Layered Deposits

    NASA Image and Video Library

    2014-06-18

    The North Polar layered deposits NPLD are a stack of layers of ice and dust at the North Pole of Mars. The layers are thought to have been deposited over millions of years. This image is from NASA Mars Reconnaissance Orbiter.

  9. Equilibrium states of pancake vortices in layered superconductors: coupling of inter-layer ordering and in-layer ordering

    NASA Astrophysics Data System (ADS)

    Wu, Wenjuan; Zhao, H. J.; Zhou, Wei; Shi, Z. X.

    2016-10-01

    We numerically study the static configurations of pancake vortices in layered superconductors. We analyze how disordering induced by random pinning centers competes with inter-layer ordering and in-layer ordering. In general, for inter-layer ordering, 3D states composed of coupled vortex lines are formed for strong inter-layer coupling strength and weak pinning strength. In contrast, 2D states composed of decoupled individual pancake vortices are formed for weak inter-layer coupling strength and strong pinning strength. For in-layer ordering, with increasing pinning forces, the in-layer structure evolves from crystals to Bragg glasses (BGs), vortex glasses (VGs), and liquid-like structures. Changing the vortex density, an initially fast disordering, then slow ordering procedure is found for both in-layer and inter-layer ordering, which is a possible clue to second peak effect (SPE). The reason behind this non-monotonic behavior is discussed. Our results are summarized in a phase diagram in the plane of ‘inter-layer coupling strength s m versus pinning strength f p.

  10. Multilayer article having stabilized zirconia outer layer and chemical barrier layer

    NASA Technical Reports Server (NTRS)

    Lee, Kang N. (Inventor); Bansal, Narottam P. (Inventor)

    2004-01-01

    A multilayer article includes a substrate that includes at least one of a ceramic compound and a Si-containing metal alloy. An outer layer includes stabilized zirconia. Intermediate layers are located between the outer layer and the substrate and include a mullite-containing layer and a chemical barrier layer. The mullite-containing layer includes 1) mullite or 2) mullite and an alkaline earth metal aluminosilicate. The chemical barrier layer is located between the mullite-containing layer and the outer layer. The chemical barrier layer includes at least one of mullite, hafnia, hafnium silicate and rare earth silicate (e.g., at least one of RE.sub.2 SiO.sub.5 and RE.sub.2 Si.sub.2 O.sub.7 where RE is Sc or Yb). The multilayer article is characterized by the combination of the chemical barrier layer and by its lack of a layer consisting essentially of barium strontium aluminosilicate between the mullite-containing layer and the chemical barrier layer. Such a barium strontium aluminosilicate layer may undesirably lead to the formation of a low melting glass or unnecessarily increase the layer thickness with concomitant reduced durability of the multilayer article. In particular, the chemical barrier layer may include at least one of hafnia, hafnium silicate and rare earth silicate.

  11. Layer-to-layer compression and enhanced optical properties of few-layer graphene nanosheet induced by ion irradiation

    NASA Astrophysics Data System (ADS)

    Shang, Zhen; Tan, Yang; Zhou, Shengqiang; Chen, Feng

    2016-08-01

    We report on the first experimental study of the layer-to-layer compression and enhanced optical properties of few-layer graphene nanosheet by applying ion irradiation. The deformation of graphene layers is investigated both theoretically and experimentally. It is observed that after the irradiation of energetic ion beams, the space between separate graphene layers is reduced due to layer-to-layer compression, resulting in tighter contact of the graphene sheet with the surface of the substrate. This processing enables enhanced interaction of the graphene with the evanescent-field wave near the surface, which induces reinforced polarization-dependent light absorption of the graphene. Utilizing the ion-bombarded graphene nanosheets as saturable absorbers, we have realized efficient Q-switched waveguide lasing with enhanced performance through the interaction of the graphene and evanescent field.

  12. Wetting Layers Close to Coexistence

    NASA Astrophysics Data System (ADS)

    Ripple, Dean Charles

    A substrate immersed in a two component liquid mixture will preferentially adsorb one of the components. I describe in this thesis theoretical and experimental results on the smooth divergence of the thickness of this adsorbed layer as the system is brought close to two phase coexistence. I present a free energy functional which combines a phenomenological equation of state suitable for near critical binary liquids with a mean field treatment of bulk and surface ions. For the system carbon disulfide plus nitromethane on glass, the theory agrees well with experiment for suitable choices of theoretical parameters. Electrical conductivity measurements of the coexisting liquid phases confirm the choice of ion concentration values. By driving a stirred binary liquid mixture off coexistence with a linear temperature ramp, very small perturbations off coexistence are possible. I apply this method to the system perfluoromethylcyclohexane plus methylcyclohexane on Si wafers, measuring the adsorption with DC null ellipsometry. As the distance from coexistence decreases, the layer thickness smoothly increases and shows a crossover from adsorption dominated by the nonzero correlation length to adsorption dominated by dispersion forces, in agreement with theoretical predictions.

  13. 2-Shock layered tuning campaign

    NASA Astrophysics Data System (ADS)

    Masse, Laurent; Dittrich, T.; Khan, S.; Kyrala, G.; Ma, T.; MacLaren, S.; Ralph, J.; Salmonson, J.; Tipton, R.; Los Alamos Natl Lab Team; Lawrence Livermore Natl Lab Team

    2016-10-01

    The 2-Shock platform has been developed to maintain shell sphericity throughout the compression phase of an indirect-drive target implosion and produce a stagnating hot spot in a quasi 1D-like manner. A sub-scale, 1700 _m outer diameter, and thick, 200 _m, uniformly Silicon doped, gas-filled plastic capsule is driven inside a nominal size 5750 _m diameter ignition hohlraum. The hohlraum fill is near vacuum to reduce back-scatter and improve laser/drive coupling. A two-shock pulse of about 1 MJ of laser energy drives the capsule. The thick capsule prevents ablation front feed-through to the imploded core. This platform has demonstrated its efficiency to tune a predictable and reproducible 1-D implosion with a nearly round shape. It has been shown that the high foot performance was dominated by the local defect growth due to the ablation front instability and by the hohlraum radiation asymmetries. The idea here is to take advantage of this 2-Shock platform to design a 1D-like layered implosion and eliminates the deleterious effects of radiation asymmetries and ablation front instability growth. We present the design work and our first experimental results of this near one-dimensional 2-Shock layered design. This work was performed under the auspices of the Lawrence Livermore National Security, LLC, (LLNS) under Contract No. DE-AC52-07NA27344.

  14. Boundary Layer Heights from CALIOP

    NASA Astrophysics Data System (ADS)

    Kuehn, R.; Ackerman, S. A.; Holz, R.; Roubert, L.

    2012-12-01

    This work is focused on the development of a planetary boundary layer (PBL) height retrieval algorithm for CALIOP and validation studies. Our current approach uses a wavelet covariance transform analysis technique to find the top of the boundary layer. We use the methodology similar to that found in Davis et. al. 2000, ours has been developed to work with the lower SNR data provided by CALIOP, and is intended to work autonomously. Concurrently developed with the CALIOP algorithm we will show results from a PBL height retrieval algorithm from profiles of potential temperature, these are derived from Aircraft Meteorological DAta Relay (AMDAR) observations. Results from 5 years of collocated AMDAR - CALIOP retrievals near O'Hare airport demonstrate good agreement between the CALIOP - AMDAR retrievals. In addition, because we are able to make daily retrievals from the AMDAR measurements, we are able to observe the seasonal and annual variation in the PBL height at airports that have sufficient instrumented-aircraft traffic. Also, a comparison has been done between the CALIOP retrievals and the NASA Langley airborne High Spectral Resolution Lidar (HSRL) PBL height retrievals acquired during the GoMACCS experiment. Results of this comparison, like the AMDAR comparison are favorable. Our current work also involves the analysis and verification of the CALIOP PBL height retrieval from the 6 year CALIOP global data set. Results from this analysis will also be presented.

  15. Modelling the transitional boundary layer

    NASA Technical Reports Server (NTRS)

    Narasimha, R.

    1990-01-01

    Recent developments in the modelling of the transition zone in the boundary layer are reviewed (the zone being defined as extending from the station where intermittency begins to depart from zero to that where it is nearly unity). The value of using a new non-dimensional spot formation rate parameter, and the importance of allowing for so-called subtransitions within the transition zone, are both stressed. Models do reasonably well in constant pressure 2-dimensional flows, but in the presence of strong pressure gradients further improvements are needed. The linear combination approach works surprisingly well in most cases, but would not be so successful in situations where a purely laminar boundary layer would separate but a transitional one would not. Intermittency-weighted eddy viscosity methods do not predict peak surface parameters well without the introduction of an overshooting transition function whose connection with the spot theory of transition is obscure. Suggestions are made for further work that now appears necessary for developing improved models of the transition zone.

  16. Dispersal, settling and layer formation.

    PubMed

    Caffrey, James R; Hughes, Barry D; Landman, Kerry A

    2011-07-01

    Motivated by examples in developmental biology and ecology, we develop a model for convection-dominated invasion of a spatial region by initially motile agents which are able to settle permanently. The motion of the motile agents and their rate of settling are affected by the local concentration of settled agents. The model can be formulated as a nonlinear partial differential equation for the time-integrated local concentration of the motile agents, from which the instantaneous density of settled agents and its long-time limit can be extracted. In the limit of zero diffusivity, the partial differential equation is of first order; for application-relevant initial and boundary-value problems, shocks arise in the time-integrated motile agent density, leading to delta-function components in the motile agent density. Furthermore, there are simple solutions for a model of successive layer formation. In addition some analytic results for a one-dimensional system with non-zero diffusivity can also be obtained. A case study, both with and without diffusion, is examined numerically. Some important predictions of the model are insensitive to the specific settling law used and the model offers insight into biological processes involving layered growth or overlapping generations of colonization.

  17. Dense, layered membranes for hydrogen separation

    DOEpatents

    Roark, Shane E.; MacKay, Richard; Mundschau, Michael V.

    2006-02-21

    This invention provides hydrogen-permeable membranes for separation of hydrogen from hydrogen-containing gases. The membranes are multi-layer having a central hydrogen-permeable layer with one or more catalyst layers, barrier layers, and/or protective layers. The invention also relates to membrane reactors employing the hydrogen-permeable membranes of the invention and to methods for separation of hydrogen from a hydrogen-containing gas using the membranes and reactors. The reactors of this invention can be combined with additional reactor systems for direct use of the separated hydrogen.

  18. Aligned Layers of Silver Nano-Fibers

    PubMed Central

    Golovin, Andrii B.; Stromer, Jeremy; Kreminska, Liubov

    2012-01-01

    We describe a new dichroic polarizers made by ordering silver nano-fibers to aligned layers. The aligned layers consist of nano-fibers and self-assembled molecular aggregates of lyotropic liquid crystals. Unidirectional alignment of the layers is achieved by means of mechanical shearing. Aligned layers of silver nano-fibers are partially transparent to a linearly polarized electromagnetic radiation. The unidirectional alignment and density of the silver nano-fibers determine degree of polarization of transmitted light. The aligned layers of silver nano-fibers might be used in optics, microwave applications, and organic electronics. PMID:28817042

  19. Heat generation in double layer capacitors

    NASA Astrophysics Data System (ADS)

    Schiffer, Julia; Linzen, Dirk; Sauer, Dirk Uwe

    Thermal management is a key issue concerning lifetime and performance of double layer capacitors and battery technologies. Double layer capacitor modules for hybrid vehicles are subject to heavy duty cycling conditions and therefore significant heat generation occurs. High temperature causes accelerated aging of the double layer capacitors and hence reduced lifetime. To investigate the thermal behavior of double layer capacitors, thermal measurements during charge/discharge cycles were performed. These measurements show that heat generation in double layer capacitors is the superposition of an irreversible Joule heat generation and a reversible heat generation caused by a change in entropy. A mathematical representation of both parts is provided.

  20. Solar cell with silicon oxynitride dielectric layer

    SciTech Connect

    Shepherd, Michael; Smith, David D

    2015-04-28

    Solar cells with silicon oxynitride dielectric layers and methods of forming silicon oxynitride dielectric layers for solar cell fabrication are described. For example, an emitter region of a solar cell includes a portion of a substrate having a back surface opposite a light receiving surface. A silicon oxynitride (SiO.sub.xN.sub.y, 0layer is disposed on the back surface of the portion of the substrate. A semiconductor layer is disposed on the silicon oxynitride dielectric layer.

  1. Linear instability of curved free shear layers

    NASA Technical Reports Server (NTRS)

    Liou, William W.

    1993-01-01

    The linear inviscid hydrodynamic stability of slightly curved free mixing layers is studied in this paper. The disturbance equation is solved numerically using a shooting technique. Two mean velocity profiles that represent stably and unstably curved free mixing layers are considered. Results are shown for cases of five curvature Richardson numbers. The stability characteristics of the shear layer are found to vary significantly with the introduction of the curvature effects. The results also indicate that, in a manner similar to the Goertler vortices observed in a boundary layer along a concave wall, instability modes of spatially developing streamwise vortex pairs may appear in centrifugally unstable curved mixing layers.

  2. Five layers in a turbulent pipe flow

    NASA Astrophysics Data System (ADS)

    Lee, Jinyoung; Ahn, Junsun; Sung, Hyung Jin

    2016-11-01

    The scaling laws governing the five layers of the mean velocity distribution of a turbulent pipe flow were characterized using the available DNS data (Reτ = 544 , 934, 3008). Excluding the very near-wall and core regions, the buffer, meso- and log layers were identified by examining the streamwise mean momentum equation and the net force spectra. The (outer) log layer was located in the overlap region where the viscous force was negligible. Another (inner) log layer was observed in the buffer layer, in which the viscous force was directly counterbalanced by the turbulent inertia. A meso-layer between the buffer and outer log layers was found to feature viscous effects. The acceleration force of the large-scale motions (LSMs) penetrated the outer log layer at higher Reynolds numbers, as observed in the net force spectra. The acceleration force of the LSMs became strong and was counterbalanced by the deceleration force of the small-scale motions (SSMs), indicating that the inner and outer length scales contributed equally to the meso-layer. The outer log layer was established by forming an extended connection link between the meso- and outer layers. This work was supported by the Creative Research Initiatives (No. 2016-004749) program of the National Research Foundation of Korea (MSIP) and partially supported by KISTI under the Strategic Supercomputing Support Program.

  3. Organic doping of rotated double layer graphene

    SciTech Connect

    George, Lijin; Jaiswal, Manu

    2016-05-06

    Charge transfer techniques have been extensively used as knobs to tune electronic properties of two- dimensional systems, such as, for the modulation of conductivity \\ mobility of single layer graphene and for opening the bandgap in bilayer graphene. The charge injected into the graphene layer shifts the Fermi level away from the minimum density of states point (Dirac point). In this work, we study charge transfer in rotated double-layer graphene achieved by the use of organic dopant, Tetracyanoquinodimethane. Naturally occurring bilayer graphene has a well-defined A-B stacking whereas in rotated double-layer the two graphene layers are randomly stacked with different rotational angles. This rotation is expected to significantly alter the interlayer interaction. Double-layer samples are prepared using layer-by-layer assembly of chemical vapor deposited single-layer graphene and they are identified by characteristic resonance in the Raman spectrum. The charge transfer and distribution of charges between the two graphene layers is studied using Raman spectroscopy and the results are compared with that for single-layer and A-B stacked bilayer graphene doped under identical conditions.

  4. Combined technique for estimating the quality of joining the layers in three-layer pipes

    NASA Astrophysics Data System (ADS)

    Nikulin, S. A.; Rozhnov, A. B.; Nechaikina, T. A.; Rogachev, S. O.; Votinov, S. N.; Zavodchikov, S. Yu.

    2014-04-01

    The prospects of estimating the quality of joining the layers of a three-layer pipe for the fuel claddings of a fast reactor from the results of a combined investigation, which includes computer-assisted quantitative metallography, microindentation, electron-probe microanalysis, and layer-by-layer atomic emission spectroscopy, are discussed.

  5. Holographic recording medium employing a photoconductive layer and a low molecular weight microcrystalline polymeric layer

    NASA Technical Reports Server (NTRS)

    Gange, Robert Allen (Inventor)

    1977-01-01

    A holographic recording medium comprising a conductive substrate, a photoconductive layer and an electrically alterable layer of a linear, low molecular weight hydrocarbon polymer has improved fatigue resistance. An acrylic barrier layer can be interposed between the photoconductive and electrically alterable layers.

  6. S-Layer Protein Self-Assembly

    PubMed Central

    Pum, Dietmar; Toca-Herrera, Jose Luis; Sleytr, Uwe B.

    2013-01-01

    Crystalline S(urface)-layers are the most commonly observed cell surface structures in prokaryotic organisms (bacteria and archaea). S-layers are highly porous protein meshworks with unit cell sizes in the range of 3 to 30 nm, and thicknesses of ~10 nm. One of the key features of S-layer proteins is their intrinsic capability to form self-assembled mono- or double layers in solution, and at interfaces. Basic research on S-layer proteins laid foundation to make use of the unique self-assembly properties of native and, in particular, genetically functionalized S-layer protein lattices, in a broad range of applications in the life and non-life sciences. This contribution briefly summarizes the knowledge about structure, genetics, chemistry, morphogenesis, and function of S-layer proteins and pays particular attention to the self-assembly in solution, and at differently functionalized solid supports. PMID:23354479

  7. Simulation of plasma double-layer structures

    NASA Technical Reports Server (NTRS)

    Borovsky, J. E.; Joyce, G.

    1982-01-01

    Electrostatic plasma double layers are numerically simulated by means of a magnetized 2 1/2 dimensional particle in cell method. The investigation of planar double layers indicates that these one dimensional potential structures are susceptible to periodic disruption by instabilities in the low potential plasmas. Only a slight increase in the double layer thickness with an increase in its obliqueness to the magnetic field is observed. Weak magnetization results in the double layer electric field alignment of accelerated particles and strong magnetization results in their magnetic field alignment. The numerical simulations of spatially periodic two dimensional double layers also exhibit cyclical instability. A morphological invariance in two dimensional double layers with respect to the degree of magnetization implies that the potential structures scale with Debye lengths rather than with gyroradii. Electron beam excited electrostatic electron cyclotron waves and (ion beam driven) solitary waves are present in the plasmas adjacent to the double layers.

  8. Multi-layered proton-conducting electrolyte

    DOEpatents

    Lee, Tae H.; Dorris, Stephen E.; Balachandran, Uthamalingam

    2017-06-27

    The present invention provides a multilayer anode/electrolyte assembly comprising a porous anode substrate and a layered solid electrolyte in contact therewith. The layered solid electrolyte includes a first dense layer of yttrium-doped barium zirconate (BZY), optionally including another metal besides Y, Ba, and Zr (e.g., a lanthanide metal such as Pr) on one surface thereof, a second dense layer of yttrium-doped barium cerate (BCY), and an interfacial layer between and contacting the BZY and BCY layers. The interfacial layer comprises a solid solution of the BZY and BCY electrolytes. The porous anode substrate comprises at least one porous ceramic material that is stable to carbon dioxide and water (e.g., porous BZY), as well as an electrically conductive metal and/or metal oxide (e.g., Ni, NiO, and the like).

  9. S-layers: principles and applications

    PubMed Central

    Sleytr, Uwe B; Schuster, Bernhard; Egelseer, Eva-Maria; Pum, Dietmar

    2014-01-01

    Monomolecular arrays of protein or glycoprotein subunits forming surface layers (S-layers) are one of the most commonly observed prokaryotic cell envelope components. S-layers are generally the most abundantly expressed proteins, have been observed in species of nearly every taxonomical group of walled bacteria, and represent an almost universal feature of archaeal envelopes. The isoporous lattices completely covering the cell surface provide organisms with various selection advantages including functioning as protective coats, molecular sieves and ion traps, as structures involved in surface recognition and cell adhesion, and as antifouling layers. S-layers are also identified to contribute to virulence when present as a structural component of pathogens. In Archaea, most of which possess S-layers as exclusive wall component, they are involved in determining cell shape and cell division. Studies on structure, chemistry, genetics, assembly, function, and evolutionary relationship of S-layers revealed considerable application potential in (nano)biotechnology, biomimetics, biomedicine, and synthetic biology. PMID:24483139

  10. S-layers: principles and applications.

    PubMed

    Sleytr, Uwe B; Schuster, Bernhard; Egelseer, Eva-Maria; Pum, Dietmar

    2014-09-01

    Monomolecular arrays of protein or glycoprotein subunits forming surface layers (S-layers) are one of the most commonly observed prokaryotic cell envelope components. S-layers are generally the most abundantly expressed proteins, have been observed in species of nearly every taxonomical group of walled bacteria, and represent an almost universal feature of archaeal envelopes. The isoporous lattices completely covering the cell surface provide organisms with various selection advantages including functioning as protective coats, molecular sieves and ion traps, as structures involved in surface recognition and cell adhesion, and as antifouling layers. S-layers are also identified to contribute to virulence when present as a structural component of pathogens. In Archaea, most of which possess S-layers as exclusive wall component, they are involved in determining cell shape and cell division. Studies on structure, chemistry, genetics, assembly, function, and evolutionary relationship of S-layers revealed considerable application potential in (nano)biotechnology, biomimetics, biomedicine, and synthetic biology.

  11. Reflective article having a sacrificial cathodic layer

    DOEpatents

    Kabagambe, Benjamin; Buchanan, Michael J.; Scott, Matthew S.; Rearick, Brian K.; Medwick, Paul A.; McCamy, James W.

    2017-09-12

    The present invention relates to reflective articles, such as solar mirrors, that include a sacrificial cathodic layer. The reflective article, more particularly includes a substrate, such as glass, having a multi-layered coating thereon that includes a lead-free sacrificial cathodic layer. The sacrificial cathodic layer includes at least one transition metal, such as a particulate transition metal, which can be in the form of flakes (e.g., zinc flakes). The sacrificial cathodic layer can include an inorganic matrix formed from one or more organo-titanates. Alternatively, the sacrificial cathodic layer can include an organic polymer matrix (e.g., a crosslinked organic polymer matrix formed from an organic polymer and an aminoplast crosslinking agent). The reflective article also includes an outer organic polymer coating, that can be electrodeposited over the sacrificial cathodic layer.

  12. Fundamentals of thin layer chromatography

    SciTech Connect

    Geiss, F.

    1987-01-01

    This comprehensive book on the theory and practice of thin-layer chromatography (TLC) is largely translated from the German original. The text contains a number of appendices, including a list of key equations, a short glossary of terms, and a list of symbols and acronyms. It also contains a list of figures that is perhaps a trifle superfluous. The book lists 299 references and has a four-page subject index. The index may be a little small for a book of nearly 500 pages. This book is a valuable addition to the texts on TLC. It is recommended to those with good mathematics backgrounds and, in particular, to those interested in chromatography theory. It will also be useful to those who employ TLC as an aid in solvent choice for LC.

  13. Layer Precipitable Water (LPW) Briefing

    NASA Technical Reports Server (NTRS)

    Forsythe, John; Kidder, Stan; Fuell, Kevin; LeRoy, Anita

    2013-01-01

    Microwave Integrated Retrieval System (MIRS) provides soundings of specific humidity from a variety of instruments and is combined with AIRS infrared soundings to create a Layered Precipitable Water (LPW) composite product. The LPW provides vertical moisture information in the column instead of just upper levels via WV imagery, or a single column value via TPW products. LPW is created every 3 hours using the last 12 hours worth of data and has a delivery latency of 40 minutes. Weaknesses include discontinuities in the composite. Strengths include seeing through clouds, over land usage, and greater spatial coverage of vertical moisture profiles. Applications of LPW include analysis of horizontal and vertical moisture gradients, verification of NWP moisture, and analysis of atmospheric rivers and other moisture advection. Operational testbed is ongoing to determine viability of wider distribution.

  14. NDAS Hardware Translation Layer Development

    NASA Technical Reports Server (NTRS)

    Nazaretian, Ryan N.; Holladay, Wendy T.

    2011-01-01

    The NASA Data Acquisition System (NDAS) project is aimed to replace all DAS software for NASA s Rocket Testing Facilities. There must be a software-hardware translation layer so the software can properly talk to the hardware. Since the hardware from each test stand varies, drivers for each stand have to be made. These drivers will act more like plugins for the software. If the software is being used in E3, then the software should point to the E3 driver package. If the software is being used at B2, then the software should point to the B2 driver package. The driver packages should also be filled with hardware drivers that are universal to the DAS system. For example, since A1, A2, and B2 all use the Preston 8300AU signal conditioners, then the driver for those three stands should be the same and updated collectively.

  15. Tracer diffusion inside fibrinogen layers

    NASA Astrophysics Data System (ADS)

    Cieśla, Michał; Gudowska-Nowak, Ewa; Sagués, Francesc; Sokolov, Igor M.

    2014-01-01

    We investigate the obstructed motion of tracer (test) particles in crowded environments by carrying simulations of two-dimensional Gaussian random walk in model fibrinogen monolayers of different orientational ordering. The fibrinogen molecules are significantly anisotropic and therefore they can form structures where orientational ordering, similar to the one observed in nematic liquid crystals, appears. The work focuses on the dependence between level of the orientational order (degree of environmental crowding) of fibrinogen molecules inside a layer and non-Fickian character of the diffusion process of spherical tracer particles moving within the domain. It is shown that in general particles motion is subdiffusive and strongly anisotropic, and its characteristic features significantly change with the orientational order parameter, concentration of fibrinogens, and radius of a diffusing probe.

  16. Boundary layer theory and subduction

    SciTech Connect

    Fowler, A.C.

    1993-12-01

    Numerical models of thermally activated convective flow in Earth`s mantle do not resemble active plate tectonics because of their inability to model successfully the process of subduction, other than by the inclusion of artificial weak zones. Here we show, using a boundary layer argument, how the `rigid lid` style of convection favored by thermoviscous fluids leads to lithospheric stresses which may realistically exceed the yield stress and thus cause subduction ot occur through the visoc-plastic failure of lithospheric rock. An explicit criterion for the failure of the lid is given, which is sensitive to the internal viscosity eta(sub a) below the lid. For numbers appropriate to Earth`s mantle, this criterion is approximately eta(sub a) greater than 10(exp 21) Pa s.

  17. Vortex boundary-layer interactions

    NASA Technical Reports Server (NTRS)

    Bradshaw, P.

    1986-01-01

    Parametric studies to identify a vortex generator were completed. Data acquisition in the first chosen configuration, in which a longitudinal vortex pair generated by an isolated delta wing starts to merge with a turbulent boundary layer on a flat plate fairly close to the leading edge is nearly completed. Work on a delta-wing/flat-plate combination, consisting of a flow visualization and hot wire measurements taken with a computer controlled traverse gear and data logging system were completed. Data taking and analysis have continued, and sample results for another cross stream plane are presented. Available data include all mean velocity components, second order mean products of turbulent fluctuations, and third order mean products. Implementation of a faster data logging system was accomplished.

  18. Sensor layers and waveguide layers produced in sol-gel technology

    NASA Astrophysics Data System (ADS)

    Karasinski, Pawel; Zielonka, Iwona

    2003-04-01

    The paper presents the results of investigation studies on the application of sol-gel technology for the production of sensor layers and waveguide layers for the system of planar waveguide sensors. The sensor layers are made up by silica SiO2, which is playing the role of a matrix fixing bromocresol purpole. These layers are sensitive to ammonia. The waveguide layers are produced in a two-component system SiO2:TiO2.

  19. Inter-layer synchronization in non-identical multi-layer networks

    PubMed Central

    Leyva, I.; Sevilla-Escoboza, R.; Sendiña-Nadal, I.; Gutiérrez, R.; Buldú, J.M.; Boccaletti, S.

    2017-01-01

    Inter-layer synchronization is a dynamical process occurring in multi-layer networks composed of identical nodes. This process emerges when all layers are synchronized, while nodes in each layer do not necessarily evolve in unison. So far, the study of such inter-layer synchronization has been restricted to the case in which all layers have an identical connectivity structure. When layers are not identical, the inter-layer synchronous state is no longer a stable solution of the system. Nevertheless, when layers differ in just a few links, an approximate treatment is still feasible, and allows one to gather information on whether and how the system may wander around an inter-layer synchronous configuration. We report the details of an approximate analytical treatment for a two-layer multiplex, which results in the introduction of an extra inertial term accounting for structural differences. Numerical validation of the predictions highlights the usefulness of our approach, especially for small or moderate topological differences in the intra-layer coupling. Moreover, we identify a non-trivial relationship connecting the betweenness centrality of the missing links and the intra-layer coupling strength. Finally, by the use of multiplexed layers of electronic circuits, we study the inter-layer synchronization as a function of the removed links. PMID:28374802

  20. Process Conditions of Forming the Surface Layer of Aluminum Powder Product by Layer-by-layer Laser Sintering

    NASA Astrophysics Data System (ADS)

    Saprykina, N. A.; Saprykin, A. A.; Ibragimov, E. A.; Arkhipova, D. A.

    2016-07-01

    The paper presents data on state of the art in selective laser sintering of products. Layer-by-layer sintering is shown to be a future-oriented technology, making it possible to synthesize products of metal powder materials. Factors, influencing the quality of a sintered product, are revealed in the paper. It presents outcomes of experiments, focused on the dependence of surface layer thickness of sintered aluminum powder PA-4 on laser processing conditions. Basic factors, influencing the quality of a sintered surface layer include laser power, speeds of scanning and moving the laser beam on the layer of powder. Thickness of the sintered layer varies from 0.74 to 1.55 mm, as the result of changing the laser processing conditions.

  1. The smear layer in endodontics - a review.

    PubMed

    Violich, D R; Chandler, N P

    2010-01-01

    Root canal instrumentation produces a layer of organic and inorganic material called the smear layer that may also contain bacteria and their by-products. It can prevent the penetration of intracanal medicaments into dentinal tubules and influence the adaptation of filling materials to canal walls. This article provides an overview of the smear layer, focusing on its relevance to endodontics. The PubMed database was used initially; the reference list for smear layer featured 1277 articles, and for both smear layer dentine and smear layer root canal revealed 1455 publications. Smear layer endodontics disclosed 408 papers. A forward search was undertaken on selected articles and using some author names. Potentially relevant material was also sought in contemporary endodontic texts, whilst older books revealed historic information and primary research not found electronically, such that this paper does not represent a 'classical' review. Data obtained suggests that smear layer removal should enhance canal disinfection. Current methods of smear removal include chemical, ultrasonic and laser techniques - none of which are totally effective throughout the length of all canals or are universally accepted. If smear is to be removed, the method of choice seems to be the alternate use of ethylenediaminetetraacetic acid and sodium hypochlorite solutions. Conflict remains regarding the removal of the smear layer before filling root canals, with investigations required to determine the role of the smear layer in the outcomes of root canal treatment.

  2. Nanomanufacturing : nano-structured materials made layer-by-layer.

    SciTech Connect

    Cox, James V.; Cheng, Shengfeng; Grest, Gary Stephen; Tjiptowidjojo, Kristianto; Reedy, Earl David, Jr.; Fan, Hongyou; Schunk, Peter Randall; Chandross, Michael Evan; Roberts, Scott A.

    2011-10-01

    Large-scale, high-throughput production of nano-structured materials (i.e. nanomanufacturing) is a strategic area in manufacturing, with markets projected to exceed $1T by 2015. Nanomanufacturing is still in its infancy; process/product developments are costly and only touch on potential opportunities enabled by growing nanoscience discoveries. The greatest promise for high-volume manufacturing lies in age-old coating and imprinting operations. For materials with tailored nm-scale structure, imprinting/embossing must be achieved at high speeds (roll-to-roll) and/or over large areas (batch operation) with feature sizes less than 100 nm. Dispersion coatings with nanoparticles can also tailor structure through self- or directed-assembly. Layering films structured with these processes have tremendous potential for efficient manufacturing of microelectronics, photovoltaics and other topical nano-structured devices. This project is designed to perform the requisite R and D to bring Sandia's technology base in computational mechanics to bear on this scale-up problem. Project focus is enforced by addressing a promising imprinting process currently being commercialized.

  3. LDV measurements of turbulent baroclinic boundary layers

    SciTech Connect

    Neuwald, P.; Reichenbach, H.; Kuhl, A.L.

    1993-07-01

    Described here are shock tube experiments of nonsteady, turbulent boundary layers with large density variations. A dense-gas layer was created by injecting Freon through the porous floor of the shock tube. As the shock front propagated along the layer, vorticity was created at the air-Freon interface by an inviscid, baroclinic mechanism. Shadow-schlieren photography was used to visualize the turbulent mixing in this baroclinic boundary layer. Laser-Doppler-Velocimetry (LDV) was used to measure the streamwise velocity histories at 14 heights. After transition, the boundary layer profiles may be approximated by a power-law function u {approximately} u{sup {alpha}} where {alpha} {approx_equal} 3/8. This value lies between the clean flat plate value ({alpha} = 1/7) and the dusty boundary layer value ({alpha} {approx_equal} 0.7), and is controlled by the gas density near the wall.

  4. Microgravity Effects on Plant Boundary Layers

    NASA Technical Reports Server (NTRS)

    Stutte, Gary; Monje, Oscar

    2005-01-01

    The goal of these series of experiment was to determine the effects of microgravity conditions on the developmental boundary layers in roots and leaves and to determine the effects of air flow on boundary layer development. It is hypothesized that microgravity induces larger boundary layers around plant organs because of the absence of buoyancy-driven convection. These larger boundary layers may affect normal metabolic function because they may reduce the fluxes of heat and metabolically active gases (e.g., oxygen, water vapor, and carbon dioxide. These experiments are to test whether there is a change in boundary layer associated with microgravity, quantify the change if it exists, and determine influence of air velocity on boundary layer thickness under different gravity conditions.

  5. Close-up of 'Tetl' Layers

    NASA Technical Reports Server (NTRS)

    2004-01-01

    [figure removed for brevity, see original site] Figure 1

    Alternating layers of more-resisant and less-resistant material make up this portion of a rock called 'Tetl,' on the west spur of the 'Columbia Hills' on Mars. NASA's Mars Exploration Rover Spirit took this picture with its microscopic imager on the rover's 272nd martian day (Oct. 7, 2004). The view covers an area about 3 centimeters (1.2 inches) wide. The layers that are less resistant to eroding away recede in comparison to the more-resistant layers. Granules of apparently harder material can be seen eroding out of some layers. Several possible origins could account for this type of layering. One that scientists are considering for Tetl and similarly layered rocks is from multiple events of volcanic ash falling from the sky or flowing across the land. Another is from episodes of sediment precipitating from a body of water.

  6. Instabilities in a Layer-Multiplying Device

    NASA Astrophysics Data System (ADS)

    Sollogoub, Cyrille; Grandmontagne, Anne; Guinault, Alain

    2011-01-01

    The application of a layer-multiplying device to coextrusion has resulted in a process, called microlayer coextrusion, producing films with ten to thousands of layers of two different polymers. It was shown that this device is quite versatile and can be used to produce new layered systems with improved mechanical, optical, electrical and barrier properties. However, instabilities may occur in the feedblock and/or the layer multiplying unit, affecting the uniformity and the continuity of the created layers. Those instabilities have been widely studied for classical systems with three to five layer structures, while very few studies deal with microlayer coextrusion process. The aim of this paper is to study the flow instabilities in multilayered films. In particular, the role of polymer properties and the effect of some parameters, such as the viscosity ratio, will be investigated.

  7. Layer-by-layer all-transfer-based organic solar cells.

    PubMed

    Kim, Jung Kyu; Kim, Wanjung; Wang, Dong Hwan; Lee, Haksoo; Cho, Sung M; Choi, Dae-Geun; Park, Jong Hyeok

    2013-04-30

    For the first time, we describe a novel cost- and time-effective vacuum-free process to fabricate bulk-heterojunction (BHJ) organic photovoltaics (OPVs) via layer-by-layer selective stamping transfer of all layers. By controlling the surface properties of polyurethane acrylate (PUA) stamping molds with ultraviolet (UV)-ozone (UVO) exposure, poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT/PSS), BHJ layer, and metal cathode were uniformly transferred layer by layer onto each of the bottom layers. Among several interfaces between each layer, we found that the interface between the active layer and metal cathode is a critical factor in obtaining conventional device-like efficiency. To enhance the interfacial connectivity between the BHJ layer and metal cathode and increase electron extraction from the BHJ layer, a titanium oxide (TiOx) interlayer was introduced. Cell performance was optimized by controlling the concentration of TiOx solution. The poly(3-hexylthiophene-2,5-diyl)/[6,6]-phenyl-C61-butyric acid methyl ester (P3HT/PC60BM) BHJ device fabricated by transferring PEDOT/PSS, TiOx/active layer, and Al cathode showed 2.01% power conversion efficiency. This efficiency is not comparable to those of conventional OPVs, but our approach shows the possibility of fabricating OPVs via the layer-by-layer transfer method for the first time.

  8. Manganese containing layer for magnetic recording media

    DOEpatents

    Lambeth, David N.; Lee, Li-Lien; Laughlin, David E.

    1999-01-01

    The present invention provides for a magnetic recording media incorporating Mn-containing layers between a substrate and a magnetic layer to provide media having increased coercivity and lower noise. The Mn-containing layer can be incorporated in a rotating, translating or stationary recording media to operate in conjunction with magnetic transducing heads for recording and reading of magnetic data, as well as other applications. The magnetic recording medium of the invention preferably includes a Co or Co alloy film magnetic layer, and Mn-containing layer, preferably comprised of VMn, TiMn, MnZn, CrMnMo, CrMnW, CrMnV, and CrMnTi, and most preferably a CrMn alloy, disposed between the substrate and the magnetic layer to promote an epitaxial crystalline structure in the magnetic layer. The medium can further include seed layers, preferably polycrystalline MgO for longitudinal media, underlayers, and intermediate layers. Underlayers and intermediate layers are comprised of materials having either an A2 structure or a B2-ordered crystalline structure disposed between the seed layer and the magnetic layer. Materials having an A2 structure are preferably Cr or Cr alloys, such as CrV, CrMo, CrW and CrTi. Materials having a B2-ordered structure having a lattice constant that is substantially comparable to that of Cr, such as those preferably selected from the group consisting of NiAl, AILCo, FeAl, FeTi, CoFe, CoTi, CoHf, CoZr, NiTi, CuBe, CuZn, A-LMn, AlRe, AgMg, and Al.sub.2 FeMn.sub.2, and is most preferably FeAl or NiAl.

  9. FIFE atmospheric boundary layer budget methods

    NASA Technical Reports Server (NTRS)

    Betts, A. K.

    1992-01-01

    The budget methods and the mixed layer model employed to analyze the aircraft data from the First ISLSCP Field Experiment (FIFE) are described. Vector budgets for the mixed layer are discussed on conserved variable diagrams. Theoretical solutions are presented for the critical surface Bowen ratio that produces no boundary layer moistening or equivalent potential temperature rise as a function of the Bowen ratio at the inversion.

  10. Photovoltaic cell with thin CS layer

    SciTech Connect

    Jordan, J.F.; Albright, S.P.

    1994-01-18

    An improved photovoltaic panel and method of forming a photovoltaic panel are disclosed for producing a high efficiency CdS/CdTe photovoltaic cell. The photovoltaic panel of the present invention is initially formed with a substantially thick CdS layer, and the effective thickness of the CdS layer is substantially reduced during regrowth to both form larger diameter CdTe crystals and substantially reduce the effective thickness of the CdS layer. 4 figures.

  11. Method to fabricate layered material compositions

    DOEpatents

    Fleming, James G.; Lin, Shawn-Yu

    2004-11-02

    A new class of processes suited to the fabrication of layered material compositions is disclosed. Layered material compositions are typically three-dimensional structures which can be decomposed into a stack of structured layers. The best known examples are the photonic lattices. The present invention combines the characteristic features of photolithography and chemical-mechanical polishing to permit the direct and facile fabrication of, e.g., photonic lattices having photonic bandgaps in the 0.1-20.mu. spectral range.

  12. Method to fabricate layered material compositions

    DOEpatents

    Fleming, James G.; Lin, Shawn-Yu

    2002-01-01

    A new class of processes suited to the fabrication of layered material compositions is disclosed. Layered material compositions are typically three-dimensional structures which can be decomposed into a stack of structured layers. The best known examples are the photonic lattices. The present invention combines the characteristic features of photolithography and chemical-mechanical polishing to permit the direct and facile fabrication of, e.g., photonic lattices having photonic bandgaps in the 0.1-20.mu. spectral range.

  13. The national tree-list layer

    Treesearch

    Stacy A. Drury; Jason M. Herynk

    2011-01-01

    The National Tree-List Layer (NTLL) project used LANDFIRE map products to produce the first national tree-list map layer that represents tree populations at stand and regional levels. The NTLL was produced in a short time frame to address the needs of Fire and Aviation Management for a map layer that could be used as input for simulating fire-caused tree mortality...

  14. Towards Natural Transition in Compressible Boundary Layers

    DTIC Science & Technology

    2016-06-29

    AFRL-AFOSR-CL-TR-2016-0011 Towards natural transition in compressible boundary layers Marcello Faraco de Medeiros FUNDACAO PARA O INCREMENTO DA...to 29-03-2016 Towards natural transition in compressible boundary layers FA9550-11-1-0354 Marcello A. Faraco de Medeiros Germán Andrés Gaviria...unlimited. 109 Final report Towards natural transition in compressible boundary layers Principal Investigator: Marcello Augusto Faraco de Medeiros

  15. Multi-layer seal for electrochemical devices

    DOEpatents

    Chou, Yeong-Shyung [Richland, WA; Meinhardt, Kerry D [Kennewick, WA; Stevenson, Jeffry W [Richland, WA

    2010-11-16

    Multi-layer seals are provided that find advantageous use for reducing leakage of gases between adjacent components of electrochemical devices. Multi-layer seals of the invention include a gasket body defining first and second opposing surfaces and a compliant interlayer positioned adjacent each of the first and second surfaces. Also provided are methods for making and using the multi-layer seals, and electrochemical devices including said seals.

  16. Multi-layer seal for electrochemical devices

    DOEpatents

    Chou, Yeong-Shyung [Richland, WA; Meinhardt, Kerry D [Kennewick, WA; Stevenson, Jeffry W [Richland, WA

    2010-09-14

    Multi-layer seals are provided that find advantageous use for reducing leakage of gases between adjacent components of electrochemical devices. Multi-layer seals of the invention include a gasket body defining first and second opposing surfaces and a compliant interlayer positioned adjacent each of the first and second surfaces. Also provided are methods for making and using the multi-layer seals, and electrochemical devices including said seals.

  17. Size distributions of boundary-layer clouds

    SciTech Connect

    Stull, R.; Berg, L.; Modzelewski, H.

    1996-04-01

    Scattered fair-weather clouds are triggered by thermals rising from the surface layer. Not all surface layer air is buoyant enough to rise. Also, each thermal has different humidities and temperatures, resulting in interthermal variability of their lifting condensation levels (LCL). For each air parcel in the surface layer, it`s virtual potential temperature and it`s LCL height can be computed.

  18. Superconductive articles including cerium oxide layer

    DOEpatents

    Wu, Xin D.; Muenchausen, Ross E.

    1993-01-01

    A ceramic superconductor comprising a metal oxide substrate, a ceramic high temperature superconductive material, and a intermediate layer of a material having a cubic crystal structure, said layer situated between the substrate and the superconductive material is provided, and a structure for supporting a ceramic superconducting material is provided, said structure comprising a metal oxide substrate, and a layer situated over the surface of the substrate to substantially inhibit interdiffusion between the substrate and a ceramic superconducting material deposited upon said structure.

  19. Unified Parameterization of the Marine Boundary Layer

    DTIC Science & Technology

    2010-09-30

    information if it does not display a currently valid OMB control number. 1. REPORT DATE 2010 2 . REPORT TYPE 3. DATES COVERED 00-00-2010 to 00-00-2010...boundary layer closure for the convective boundary layer 2 . An EDMF approach to the vertical transport of TKE in convective boundary layers 3. EDMF in...4 implementation and extension to shallow cumulus parameterization is in progress. 2   An integrated TKE-based eddy-diffusivity/mass-flux

  20. Nonequilibrium chemistry boundary layer integral matrix procedure

    NASA Technical Reports Server (NTRS)

    Tong, H.; Buckingham, A. C.; Morse, H. L.

    1973-01-01

    The development of an analytic procedure for the calculation of nonequilibrium boundary layer flows over surfaces of arbitrary catalycities is described. An existing equilibrium boundary layer integral matrix code was extended to include nonequilibrium chemistry while retaining all of the general boundary condition features built into the original code. For particular application to the pitch-plane of shuttle type vehicles, an approximate procedure was developed to estimate the nonequilibrium and nonisentropic state at the edge of the boundary layer.

  1. Generalized approach to design multi-layer stacks for enhanced optical detectability of ultrathin layers

    NASA Astrophysics Data System (ADS)

    Hutzler, A.; Matthus, C. D.; Rommel, M.; Frey, L.

    2017-01-01

    The optical detectability of ultrathin conductive films (down to one atomic layer) can be enhanced by choosing distinct layer-stacks. A simple analytical approach using the transfer matrix method is applied for calculating the reflectance of arbitrary multi-layer stack systems with and without the ultrathin layer of interest on top in a wide wavelength range, including both the visible spectrum and the ultraviolet spectrum. Then, the detectability defined by the Michelson contrast was calculated. Performing these calculations for thickness variations of the individual layers in the stack allows determining optimum layer thicknesses, e.g., maximum overall contrast or maximum contrast for a given wavelength. To demonstrate the validity of the methodology, two thin film stacks were investigated, which use p-type silicon as a substrate material and partially covered by a single-layer graphene as a top layer. For each stack, two samples with different layer thicknesses were fabricated and their experimentally determined reflectance was compared to the calculated values. The first system consists of a single SiO2 layer with a thickness of 147 nm and 304 nm, respectively, and the second is a double layer stack consisting of a Si3N4 layer with a thickness of 54 nm and 195 nm, respectively, on top of an 11 nm SiO2 film. The Michelson contrast of single-layer graphene flakes on the latter layer stacks becomes very high (absolute value of more than 0.3) in the visible wavelength range. Additionally, in the UV-B range a large difference in the reflection of selected SiO2 layer thicknesses on silicon substrates with and without single-layer graphene on top is found with a decrease in the measured reflectance of up to 33%. The measured and calculated values showed a high conformity suggesting this approach usable for the calculation of reflectance and transmittance properties of arbitrary layer stack systems including thin conductive layers.

  2. Effect of surface ionization on wetting layers

    NASA Technical Reports Server (NTRS)

    Kayser, R. F.

    1986-01-01

    A surface ionization model due to Langmuir is generalized to liquid mixtures of polar and nonpolar components in contact with ionizable substrates. When a predominantly nonpolar mixture is near a miscibility gap, thick wetting layers of the conjugate polar phase form on the substrate. Such charged layers can be much thicker than similar wetting layers stabilized by dispersion forces. This model may explain the 0.4- to 0.6-micron-thick wetting layers formed in stirred mixtures of nitromethane and carbon disulfide in contact with glass.

  3. Organizing Principles of Cortical Layer 6

    PubMed Central

    Briggs, Farran

    2009-01-01

    Neurons in the deepest layer of mammalian cerebral cortex are morphologically and physiological diverse and are situated in a strategic position to modulate neuronal activity locally and in other structures. The variety of neuronal circuits within which layer 6 neurons participate differs across species and cortical regions. However even amidst this diversity, common organizational features emerge. Examination of the anatomical and physiological characteristics of different classes of layer 6 neuron, each specialized to participate in distinct circuits, provides insight into the functional contributions of layer 6 neurons toward cortical information processing. PMID:20179784

  4. Organic photovoltaic cells utilizing ultrathin sensitizing layer

    DOEpatents

    Forrest, Stephen R.; Yang, Fan; Rand, Barry P.

    2011-09-06

    A photosensitive device includes a plurality of organic photoconductive materials disposed in a stack between a first electrode and a second electrode, including a first continuous layer of donor host material, a second continuous layer of acceptor host material, and at least one other organic photoconductive material disposed as a plurality of discontinuous islands between the first continuous layer and the second continuous layer. Each of these other photoconductive materials has an absorption spectra different from the donor host material and the acceptor host material. Preferably, each of the discontinuous islands consists essentially of a crystallite of the respective organic photoconductive material, and more preferably, the crystallites are nanocrystals.

  5. Two-layer tubes from cubic crystals

    NASA Astrophysics Data System (ADS)

    Goldstein, R. V.; Gorodtsov, V. A.; Lisovenko, D. S.; Volkov, M. A.

    2016-12-01

    Effective Young's moduli and Poisson's ratios of two-layer tubes from cubic crystals have been analyzed theoretically. It is shown (using derived formulas for numerical estimates) that the mechanical properties of two-layer tube composites from auxetics and nonauxetics are not described by the mixture rule. It is demonstrated that the deviation of the effective modulus from the mixture rule predictions rapidly increases with an increase in Young's modulus of the nonauxetic components of a composite. It is established that, combining auxetics and nonauxetics in layered tubes, one can obtain, depending on the packing order in layers, either a strong increase or a decrease in auxeticity.

  6. North Polar Cap Layers and Ledges

    NASA Image and Video Library

    2016-08-24

    At the edge of Mars' permanent North Polar cap, we see an exposure of the internal layers, each with a different mix of water ice, dust and dirt. These layers are believed to correspond to different climate conditions over the past tens of thousands of years. When we zoom in closer, we see that the distinct layers erode differently. Some are stronger and more resistant to erosion, others only weakly cemented. The strong layers form ledges. http://photojournal.jpl.nasa.gov/catalog/PIA21022

  7. Enhanced Densification of SDC Barrier Layers

    SciTech Connect

    Hardy, John S.; Templeton, Jared W.; Lu, Zigui; Stevenson, Jeffry W.

    2011-09-12

    This technical report explores the Enhanced Densification of SCD Barrier Layers A samaria-doped ceria (SDC) barrier layer separates the lanthanum strontium cobalt ferrite (LSCF) cathode from the yttria-stabilized zirconia (YSZ) electrolyte in a solid oxide fuel cell (SOFC) to prevent the formation of electrically resistive interfacial SrZrO{sub 3} layers that arise from the reaction of Sr from the LSCF with Zr from the YSZ. However, the sintering temperature of this SDC layer must be limited to {approx}1200 C to avoid extensive interdiffusion between SDC and YSZ to form a resistive CeO{sub 2}-ZrO{sub 2} solid solution. Therefore, the conventional SDC layer is often porous and therefore not as impervious to Sr-diffusion as would be desired. In the pursuit of improved SOFC performance, efforts have been directed toward increasing the density of the SDC barrier layer without increasing the sintering temperature. The density of the SDC barrier layer can be greatly increased through small amounts of Cu-doping of the SDC powder together with increased solids loading and use of an appropriate binder system in the screen print ink. However, the resulting performance of cells with these barrier layers did not exhibit the expected increase in accordance with that achieved with the prototypical PLD SDC layer. It was determined by XRD that increased sinterability of the SDC also results in increased interdiffusivity between the SDC and YSZ, resulting in formation of a highly resistive solid solution.

  8. Electromechanics and Electrical Breakdown of Particulate Layers

    NASA Astrophysics Data System (ADS)

    Moslehi, Bizhan G. R.

    A comprehensive theory of the electromechanics and electrical breakdown of a current-carrying particulate layer is developed, which takes into account its inhomogeneous nature and mode of compaction. The theory treates the general case of combined surface and volume conduction and takes account of self-compression of the layer due to electrical forces. The electromechanical theory predicts the existence of a remarkably large electrical cohesive stress in the layer due to a strong field enhancement in and around the contact regions. Furthermore, it shows a decrease in the apparent resistivity of the layer with increasing electric field as a result of self-compression. The analysis of electrical breakdown of current -carrying particulate layer predicts the onset of breakdown of the layer in the form of intermittent microsparks in the gap between the contacting particles when the electric field at the contact or in the surrounding gap exceeds the threshold breakdown value. An analysis of the behavior of the layer after breakdown in terms of a simplified equivalent lumped circuit predicts increases of sparking frequency and average current as the applied average field exceeds the threshold average field for the onset of breakdown. The results of measurements on layers of glass beads and fly-ash in a standard resistivity cell are in good agreement with the theoretical predictions for the field-dependent resistivity characteristics. The work has particular significance for electrostatic precipitation and addresses the phenomenon of backdischarge and the questions of the retention, rapping, and reentrainment of precipitation ash layers.

  9. Development of perturbations in the boundary layer

    NASA Technical Reports Server (NTRS)

    Dovgal, A. V.; Kachanov, Y. S.; Kozlov, V. V.; Levchenko, V. Y.; Maksimov, V. P.

    1986-01-01

    The transition of laminar flows into turbulent flows in a boundary layer is discussed. The individual aspects of the transition process, observed under controllable model conditions are examined. The aspect of this problem, namely the development or excitation of the natural oscillations in the boundary layer, the so-called Tollmin-Schlichting waves is covered. Three types of excitation of these waves are considered: (1) distributed generation throughout the boundary layer; (2) generation in the vicinity of the forward edge of a model, having either a sharp edge or an edge with a large radius or curvature, and (3) generation in a developed boundary layer by means of a focused effect.

  10. Electroactive functional hybrid layered nanocomposites

    SciTech Connect

    Destri, Giovanni Li; Torrisi, Vanna; Marletta, Giovanni

    2012-07-11

    Two methodologies to build new nanostructured hybrid layered nanocomposites are presented. The first one involves the preparation of hybrid metal/polymer nanolayers (NLs) by combining two monolayer preparation techniques: Horizontal Precipitation Langmuir Blodgett method (HP-ML), for copolymer monolayers and sputter deposition technique, for Au NLs deposition. The second methodology is aimed to prepare regular arrays of nanopores, with diameter ranging between 40-100 nm, in ultra-thin films of electroactive polymers, to obtain embedded regular arrays of nanopores filled by a further electroactive organic component. The produced hybrid MLs have been characterized by means of X-ray Photoelectron Spectroscopy (XPS), Atomic Force Microscopy (AFM) and Grazing Incidence X-ray Diffraction (GI-XRD). In the first case, current-voltage (I-V) measurements demonstrate that the multilayers exhibit a bipolar conduction behaviour (electrons and holes carriers), with a peculiar transition in the nature of the majority carriers (from holes to electrons) above a threshold number of bilayers. In the second case, it is found that the degree of pore filling, as well as the polymer crystallinity can be easily modulated, prompting the tuning of the photoresponse of the nanocomposites.

  11. WOCE Ocean Surface Layer Group

    NASA Astrophysics Data System (ADS)

    deSzoeke, Roland

    The initial meeting of a U.S. working group to consider the surface layers of the ocean and their role in the World Ocean Circulation Experiment (WOCE) was held January 25, 1985, at the Scripps Institution of Oceanography (SIO) in La Jolla, Calif., under the auspices of the U.S. WOCE Science Steering Committee. Present were A. Bennett (Institute of Ocean Sciences, Sydney, Canada), F. Bretherton (National Center for Atmospheric Research (NCAR), Boulder, Colo.), C. Collins (National Science Foundation (NSF), Washington, D.C.), R. Davis (SIO), R. deSzoeke (Oregon State University (OSU), Corvallis), D. Halpern (University of Washington, Seattle), W. Large (NCAR), J . Luyten (Woods Hole Oceanographic Institution (WHOI), Woods Hole, Mass.), J. McWilliams, (NCAR), W. Nowlin (Texas A&M University, College Station, Tex.), C. Paulson (OSU), C. Rooth (Rosenstiel School of Marine and Atmospheric Sciences, Miami, Fla.), R. Weiss (SIO), R. Weller (WHOI), W. White (SIO), and C. Wunsch (Massachusetts Institute of Technology, Cambridge, Mass.).

  12. The Martian Atmospheric Boundary Layer

    NASA Astrophysics Data System (ADS)

    Petrosyan, A.; Galperin, B.; Larsen, S. E.; Lewis, S. R.; Määttänen, A.; Read, P. L.; Renno, N.; Rogberg, L. P. H. T.; Savijärvi, H.; Siili, T.; Spiga, A.; Toigo, A.; Vázquez, L.

    2011-09-01

    The planetary boundary layer (PBL) represents the part of the atmosphere that is strongly influenced by the presence of the underlying surface and mediates the key interactions between the atmosphere and the surface. On Mars, this represents the lowest 10 km of the atmosphere during the daytime. This portion of the atmosphere is extremely important, both scientifically and operationally, because it is the region within which surface lander spacecraft must operate and also determines exchanges of heat, momentum, dust, water, and other tracers between surface and subsurface reservoirs and the free atmosphere. To date, this region of the atmosphere has been studied directly, by instrumented lander spacecraft, and from orbital remote sensing, though not to the extent that is necessary to fully constrain its character and behavior. Current data strongly suggest that as for the Earth's PBL, classical Monin-Obukhov similarity theory applies reasonably well to the Martian PBL under most conditions, though with some intriguing differences relating to the lower atmospheric density at the Martian surface and the likely greater role of direct radiative heating of the atmosphere within the PBL itself. Most of the modeling techniques used for the PBL on Earth are also being applied to the Martian PBL, including novel uses of very high resolution large eddy simulation methods. We conclude with those aspects of the PBL that require new measurements in order to constrain models and discuss the extent to which anticipated missions to Mars in the near future will fulfill these requirements.

  13. Electrochemical-coupling layer-by-layer (ECC-LbL) assembly.

    PubMed

    Li, Mao; Ishihara, Shinsuke; Akada, Misaho; Liao, Meiyong; Sang, Liwen; Hill, Jonathan P; Krishnan, Venkata; Ma, Yuguang; Ariga, Katsuhiko

    2011-05-18

    Electrochemical-coupling layer-by-layer (ECC-LbL) assembly is introduced as a novel fabrication methodology for preparing layered thin films. This method allows us to covalently immobilize functional units (e.g., porphyrin, fullerene, and fluorene) into thin films having desired thicknesses and designable sequences for both homo- and heteroassemblies while ensuring efficient layer-to-layer electronic interactions. Films were prepared using a conventional electrochemical setup by a simple and inexpensive process from which various layering sequences can be obtained, and the photovoltaic functions of a prototype p/n heterojunction device were demonstrated. © 2011 American Chemical Society

  14. Ordered poly(p-phenylene)/layered double hydroxide ultrathin films with blue luminescence by layer-by-layer assembly.

    PubMed

    Yan, Dongpeng; Lu, Jun; Wei, Min; Han, Jingbin; Ma, Jing; Li, Feng; Evans, David G; Duan, Xue

    2009-01-01

    Lavender layers: A poly(p-phenylene) anionic derivate and exfoliated Mg-Al layered double hydroxide monolayers were assembled into ultrathin films with well-defined blue fluorescence (see picture; the numbers indicate the number of bilayers), long-range order, and high photostability. These films work as multiple quantum-well structures for valence electrons.

  15. Spray Layer-by-Layer Assembled Clay Composite Thin Films as Selective Layers in Reverse Osmosis Membranes.

    PubMed

    Kovacs, Jason R; Liu, Chaoyang; Hammond, Paula T

    2015-06-24

    Spray layer-by-layer assembled thin films containing laponite (LAP) clay exhibit effective salt barrier and water permeability properties when applied as selective layers in reverse osmosis (RO) membranes. Negatively charged LAP platelets were layered with poly(diallyldimethylammonium) (PDAC), poly(allylamine) (PAH), and poly(acrylic acid) (PAA) in bilayer and tetralayer film architectures to generate uniform films on the order of 100 nm thick that bridge a porous poly(ether sulfone) support to form novel RO membranes. Nanostructures were formed of clay layers intercalated in a polymeric matrix that introduced size-exclusion transport mechanisms into the selective layer. Thermal cross-linking of the polymeric matrix was used to increase the mechanical stability of the films and improve salt rejection by constraining swelling during operation. Maximum salt rejection of 89% was observed for the tetralayer film architecture, with an order of magnitude increase in water permeability compared to commercially available TFC-HR membranes. These clay composite thin films could serve as a high-flux alternative to current polymeric RO membranes for wastewater and brackish water treatment as well as potentially for forward osmosis applications. In general, we illustrate that by investigating the composite systems accessed using alternating layer-by-layer assembly in conjunction with complementary covalent cross-linking, it is possible to design thin film membranes with tunable transport properties for water purification applications.

  16. Modeling the summertime Arctic cloudy boundary layer

    SciTech Connect

    Curry, J.A.; Pinto, J.O.; McInnes, K.L.

    1996-04-01

    Global climate models have particular difficulty in simulating the low-level clouds during the Arctic summer. Model problems are exacerbated in the polar regions by the complicated vertical structure of the Arctic boundary layer. The presence of multiple cloud layers, a humidity inversion above cloud top, and vertical fluxes in the cloud that are decoupled from the surface fluxes, identified in Curry et al. (1988), suggest that models containing sophisticated physical parameterizations would be required to accurately model this region. Accurate modeling of the vertical structure of multiple cloud layers in climate models is important for determination of the surface radiative fluxes. This study focuses on the problem of modeling the layered structure of the Arctic summertime boundary-layer clouds and in particular, the representation of the more complex boundary layer type consisting of a stable foggy surface layer surmounted by a cloud-topped mixed layer. A hierarchical modeling/diagnosis approach is used. A case study from the summertime Arctic Stratus Experiment is examined. A high-resolution, one-dimensional model of turbulence and radiation is tested against the observations and is then used in sensitivity studies to infer the optimal conditions for maintaining two separate layers in the Arctic summertime boundary layer. A three-dimensional mesoscale atmospheric model is then used to simulate the interaction of this cloud deck with the large-scale atmospheric dynamics. An assessment of the improvements needed to the parameterizations of the boundary layer, cloud microphysics, and radiation in the 3-D model is made.

  17. Sequential imposed layer epitaxy of cuprate films

    SciTech Connect

    Laguees, M.; Tebbji, H.; Mairet, V.; Hatterer, C.; Beuran, C.F.; Hass, N.; Xu, X.Z. ); Cavellin, C.D. )

    1994-02-01

    Layer-by-layer epitaxy has been used to grow cuprate films since the discovery of high-Tc compounds. This deposition technique is in principle suitable for the growth of layered crystalline structures. However, the sequential deposition of atomic layer by atomic layer of cuprate compounds has presently not been optimized. Nevertheless, this deposition process is the only one which allows one to build artificial cell structures such as Bi[sub 2]Sr[sub 2]Ca[sub (n[minus]1)]Cu[sub n]O[sub y] with n as large as 10. This process will also be the best one to grow films of the so-called infinite layer phase compounds belonging to the Sr[sub 1[minus]x]Ca[sub x]CuO[sub 2] family, in order to improve the transport properties and the morphological properties of the cuprate films. When performed at high substrate temperature (typically more than 600[degree]C), the layer-by-layer epitaxy of cuprates exhibits usually 3D aggregate nucleation. Then the growth of the film no longer obeys the layer-by-layer sequence imposed during the deposition. We present here two experimental situations of true 2D sequential imposed layer epitaxy; the growth at 500[degree]C under atomic oxygen pressure of Bi[sub 2]Sr[sub 2]CuO[sub 6] and of Sr[sub 1[minus]x]Ca[sub y]CuO[sub 2] phases. 20 refs., 2 figs.

  18. Mesoporous layer-by-layer ordered nanohybrids of layered double hydroxide and layered metal oxide: highly active visible light photocatalysts with improved chemical stability.

    PubMed

    Gunjakar, Jayavant L; Kim, Tae Woo; Kim, Hyo Na; Kim, In Young; Hwang, Seong-Ju

    2011-09-28

    Mesoporous layer-by-layer ordered nanohybrids highly active for visible light-induced O(2) generation are synthesized by self-assembly between oppositely charged 2D nanosheets of Zn-Cr-layered double hydroxide (Zn-Cr-LDH) and layered titanium oxide. The layer-by-layer ordering of two kinds of 2D nanosheets is evidenced by powder X-ray diffraction and cross-sectional high resolution-transmission electron microscopy. Upon the interstratification process, the original in-plane atomic arrangements and electronic structures of the component nanosheets remain intact. The obtained heterolayered nanohybrids show a strong absorption of visible light and a remarkably depressed photoluminescence signal, indicating an effective electronic coupling between the two component nanosheets. The self-assembly between 2D inorganic nanosheets leads to the formation of highly porous stacking structure, whose porosity is controllable by changing the ratio of layered titanate/Zn-Cr-LDH. The resultant heterolayered nanohybrids are fairly active for visible light-induced O(2) generation with a rate of ∼1.18 mmol h(-1) g(-1), which is higher than the O(2) production rate (∼0.67 mmol h(-1) g(-1)) by the pristine Zn-Cr-LDH material, that is, one of the most effective visible light photocatalysts for O(2) production, under the same experimental condition. This result highlights an excellent functionality of the Zn-Cr-LDH-layered titanate nanohybrids as efficient visible light active photocatalysts. Of prime interest is that the chemical stability of the Zn-Cr-LDH is significantly improved upon the hybridization, a result of the protection of the LDH lattice by highly stable titanate layer. The present findings clearly demonstrate that the layer-by-layer-ordered assembly between inorganic 2D nanosheets is quite effective not only in improving the photocatalytic activity of the component semiconductors but also in synthesizing novel porous LDH-based hybrid materials with improved chemical

  19. Snow Model for the F-Layer

    NASA Astrophysics Data System (ADS)

    Lasbleis, M.; Hernlund, J. W.; Labrosse, S.

    2015-12-01

    Seismic observations of the Earth's core reveal a complex structure: radial and lateral heterogeneities in seismic anisotropy and attenuation in the solid inner core, but also discrepancies between observed P-wave velocity and homogeneous PREM model in the deep liquid outer core. In this work, we focus on the 200km anomalous layer at the bottom of the outer core that exhibits seismic velocities lower than the PREM model. It has been interpreted as a layer depleted in light elements, whereas the usual model considers that light elements are expelled at the surface of the inner core by freezing of the outer core alloy. Recent models of core formation argued for an early stratified liquid core, and the stratified layers at the top and bottom of the outer core would be a vestige of this primordial stratification. However, freezing of the inner core at the inner core boundary releases light elements that provide buoyancy fluxes that would mix the stratified liquid above with small scale buoyant plumes. To model the F-layer, we consider that the freezing of the iron alloy and the release of light elements have to occur in the bulk of the layer. Iron snow forms and settles in the layer, buffering the thermal and chemical profile to the liquidus. We show that this dynamics can both sustain and stabilize the stratified layer in the liquid outer core while simultaneously matching the seismic observations. However, the expected layer is stable only for a given set of parameters, in particular when a high thermal diffusivity (>100 W/m/K) is employed. If freezing of the iron alloy of the outer core occurs in the bulk of the layer, several assumptions for both the outer and inner core has to be discussed: the F-layer acts as a boundary layer for both composition and temperature, and modifies the quantity of light elements expelled into the outer core as well as the composition that freezes to form the inner core.

  20. Layer by layer: complex analysis with OCT technology

    NASA Astrophysics Data System (ADS)

    Florin, Christian

    2017-03-01

    three-dimensional tomographic image. For 3D measuring technique specially designed ASP- arrays with a very high image rate are available. If ASP- Arrays are coupled with the OCT method, layer thicknesses can be determined without contact, sealing seams can be inspected or geometrical shapes can be measured. From a stack of hundreds of single OCT images, interesting images can be selected and fed to the computer to analyse them.