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Sample records for buffer layer thickness

  1. Thick lanthanum zirconate buffer layers from water-based precursor solutions on Ni-5%W substrates

    SciTech Connect

    Narayanan, Vyshnavi; Lommens, Petra; De Buysser, Klaartje; Huehne, Ruben; Van Driessche, Isabel

    2011-11-15

    In this work, water-based precursor solutions suitable for dip-coating of thick La{sub 2}Zr{sub 2}O{sub 7} (LZO) buffer layers for coated conductors on Ni-5%W substrates were developed. The solutions were prepared based on chelate chemistry using water as the main solvent. The effect of polymer addition on the maximum crack-free thickness of the deposited films was investigated. This novel solution preparation method revealed the possibility to grow single, crack-free layers with thicknesses ranging 100-280 nm with good crystallinity and an in-plane grain misalignment with average FWHM of 6.55{sup o}. TEM studies illustrated the presence of nanovoids, typical for CSD-LZO films annealed under Ar-5%H{sub 2} gas flow. The appropriate buffer layer action of the film in preventing the Ni diffusion was studied using XPS. It was found that the Ni diffusion was restricted to the first 30 nm of a 140 nm thick film. The surface texture of the film was improved using a seed layer. - Graphical abstract: Thick LZO buffer layers from water-based precursor solutions were synthesized and their crystallinity, microstructure and buffer layer action were studied. The buffer layer action of the LZO layer was substantial to restrict the Ni penetration within 30 nm of a 140 nm thick film. Highlights: > LZO buffer layers with high thicknesses for use in coated conductors were prepared. > Prepared from water-based solutions. > Polymeric PVP increases the crack-free critical thickness of thick films. > Thick films showed good barrier action against Ni penetration. > Seed layers promote epitaxial growth of thick layers.

  2. Influence of homo buffer layer thickness on the quality of ZnO epilayers.

    PubMed

    Eid, E A; Fouda, A N

    2015-10-01

    ZnO buffer layers with different thicknesses were deposited on a-plane sapphire substrates at 300 °C. ZnO epilayers were grown on ZnO buffers at 600 °C by radio-frequency magnetron sputtering and vacuum annealed at 900 °C for an hour. Influence of nucleation layer thickness on the structural and quality of ZnO thin films was investigated using X-ray diffraction (XRD), atomic force microscopy (AFM), and Raman spectroscopy. The best ZnO film quality was obtained with the ZnO buffer layer of 45 nm thick which provided the smoothest surface with RMS value of 0.3 nm. X-ray diffraction measurements reveal that the films have a single phase wurtzite structure with (0001) preferred crystal orientation. As evident from narrow FWHM of ZnO (0002) rocking curve, ZnO buffer can serve as a good template for the growth of high-quality ZnO films with little tilt. In addition, the micro-Raman scattering measurements at room temperature revealed the existence of Raman active phonon modes of ZnO; A1(TO), A1(LO) and E2(high). The latter two modes were not observed in thin buffer layer beside the dis-appearance of E2(low) mode in all films. PMID:25950638

  3. Effect of CeO{sub 2} buffer layer thickness on the structures and properties of YBCO coated conductors.

    SciTech Connect

    Li, M.; Zhao, X.; Ma, B.; Dorris, S. E.; Balachandran, U.; Maroni, V. A.; Wuhan Univ.

    2007-01-01

    Biaxially textured YBa{sub 2}Cu{sub 3}O{sub 7-x} (YBCO) films were grown on inclined-substrate-deposited (ISD) MgO-textured metal substrates by pulsed laser deposition. CeO{sub 2} was deposited as a buffer layer prior to YBCO growth. CeO{sub 2} layers of different thickness were prepared to evaluate the thickness dependence of the YBCO films. The biaxial alignment features of the films were examined by X-ray diffraction 2{theta}-scans, pole-figure, {phi}-scans and rocking curves of {Omega} angles. The significant influence of the CeO{sub 2} thickness on the structure and properties of the YBCO films were demonstrated and the optimal thickness was found to be about 10 nm. High values of T{sub c} = 91 K and J{sub c} = 5.5 x 10{sup 5} A/cm{sup 2} were obtained on YBCO films with optimal CeO{sub 2} thickness at 77 K in zero field. The possible mechanisms responsible for the dependence of the structure and the properties of the YBCO films on the thickness of the CeO{sub 2} buffer layers are discussed.

  4. Effects of low-temperature buffer-layer thickness and growth temperature on the SEE sensitivity of GaAs HIGFET circuits

    SciTech Connect

    Weatherford, T.R.; Fouts, D.J.; Marshall, P.W. |; Marshall, C.J.; Mathes, B.; LaMacchia, M.

    1997-12-01

    Heavy-ion Single Event Effects (SEE) test results reveal the role of growth temperature and buffer layer thickness in the use of a low-temperature grown GaAs (LT GaAs) buffer layer for suppressing SEE sensitivity in GaAs HIGFET circuits.

  5. Enhanced performance and stability in PBDTTT-C-T : PC70 BM polymer solar cells by optimizing thickness of NiOx buffer layers

    NASA Astrophysics Data System (ADS)

    Fan, Xi; Fang, Guojia; Cheng, Fei; Qin, Pingli; Huang, Huihui; Li, Yongfang

    2013-07-01

    We report efficient polymer solar cells (PSCs) based on PBDTTT-C-T : PC70BM with a NiOx anode buffer layer (thickness of 3-15 nm) prepared by radio-frequency magnetron sputtering deposition. The PSC with the optimum NiOx buffer layer thickness of 9 nm showed the highest power conversion efficiency of 7.42% with Voc of 0.75 V, Jsc of 15.82 mA cm-2 and FF of 62.5%, which was higher than that of the PSCs with a PEDOT : PSS buffer layer. Moreover, compared with the PSCs with a PEDOT : PSS buffer layer, the PSCs with the optimum NiOx buffer layer exhibited a better stability under N2 atmosphere. The results indicate that the sputtered 9 nm thick NiOx buffer layer is superior to the PEDOT : PSS buffer layer not only for better performance but also for improved long-term stability. The optimized NiOx buffer layer thickness possesses an appropriate energy level matching with PBDTTT-C-T, which results in effective hole collection and improved photovoltaic performance.

  6. Impact of buffer layer and Pt thickness on the interface structure and magnetic properties in (Co/Pt) multilayers.

    PubMed

    Bersweiler, M; Dumesnil, K; Lacour, D; Hehn, M

    2016-08-24

    The influence of Pt thickness on the interface structure (roughness / intermixing) and magnetic properties has been investigated for (Co / Pt) multilayers sputtered on a Pt or a thin oxide (MgO or AlO x ) buffer layer. When Pt thickness increases from 1.2 nm-2.2 nm, we observe that the effective anisotropy increases with the Pt thickness, simultaneously with the decrease of roughness, i.e. the occurrence of sharper interfaces. Perpendicular magnetic anisotropy (PMA) is still achieved on the oxide buffer layers, but with a lower effective anisotropy correlated to more perturbed interfaces. The detailed analysis of the saturation magnetization shows that: (i) M s is significantly enhanced in the case of rough/intermixed interfaces, which is attributed to and discussed in the framework of Pt induced polarization, (ii) the change in volume dipolar anisotropy is the main factor responsible for the reduction of K eff for systems grown on oxides. Beyond the major role of volume dipolar contribution that reduces PMA, a supplemental positive contribution promoting PMA can be invoked for rough interfaces and large M s (deposit on oxide). This contribution is consistent with a dipolar surface anisotropy term and increases for rough interfaces, in contrast to the Néel surface anisotropy. These opposite variations may interestingly lead to an enhanced anisotropy in (Co / Pt) stackings grown on oxides compared to systems deposited on Pt, i.e. with sharper interfaces. PMID:27351776

  7. Impact of buffer layer and Pt thickness on the interface structure and magnetic properties in (Co/Pt) multilayers

    NASA Astrophysics Data System (ADS)

    Bersweiler, M.; Dumesnil, K.; Lacour, D.; Hehn, M.

    2016-08-01

    The influence of Pt thickness on the interface structure (roughness / intermixing) and magnetic properties has been investigated for (Co / Pt) multilayers sputtered on a Pt or a thin oxide (MgO or AlO x ) buffer layer. When Pt thickness increases from 1.2 nm–2.2 nm, we observe that the effective anisotropy increases with the Pt thickness, simultaneously with the decrease of roughness, i.e. the occurrence of sharper interfaces. Perpendicular magnetic anisotropy (PMA) is still achieved on the oxide buffer layers, but with a lower effective anisotropy correlated to more perturbed interfaces. The detailed analysis of the saturation magnetization shows that: (i) M s is significantly enhanced in the case of rough/intermixed interfaces, which is attributed to and discussed in the framework of Pt induced polarization, (ii) the change in volume dipolar anisotropy is the main factor responsible for the reduction of K eff for systems grown on oxides. Beyond the major role of volume dipolar contribution that reduces PMA, a supplemental positive contribution promoting PMA can be invoked for rough interfaces and large M s (deposit on oxide). This contribution is consistent with a dipolar surface anisotropy term and increases for rough interfaces, in contrast to the Néel surface anisotropy. These opposite variations may interestingly lead to an enhanced anisotropy in (Co / Pt) stackings grown on oxides compared to systems deposited on Pt, i.e. with sharper interfaces.

  8. Effects of AlN buffer layer thickness on the crystallinity and surface morphology of 10-µm-thick a-plane AlN films grown on r-plane sapphire substrates

    NASA Astrophysics Data System (ADS)

    Lin, Chia-Hung; Tamaki, Shinya; Yamashita, Yasuhiro; Miyake, Hideto; Hiramatsu, Kazumasa

    2016-08-01

    10-µm-thick a-plane AlN(11\\bar{2}0) films containing a low-temperature AlN (LT-AlN) buffer layer and a high-temperature AlN (HT-AlN) film were prepared on r-plane sapphire (1\\bar{1}02) substrates. The crystallinity of all the samples with different LT-AlN buffer layer thicknesses was improved after thermal annealing and HT-AlN growth, mainly owing to the elimination of domain boundaries and the concurrent suppression of facet formation. The optimum crystallinity of HT-AlN films was obtained with full widths at half maximum of the X-ray rocking curves of 660 arcsec for AlN(11\\bar{2}0)\\parallel [1\\bar{1}00]AlN and 840 arcsec for (0002) using a 200-nm-thick LT-AlN buffer layer.

  9. Strain-free GaN thick films grown on single crystalline ZnO buffer layer with in situ lift-off technique

    SciTech Connect

    Lee, S. W.; Minegishi, T.; Lee, W. H.; Goto, H.; Lee, H. J.; Lee, S. H.; Lee, Hyo-Jong; Ha, J. S.; Goto, T.; Hanada, T.; Cho, M. W.; Yao, T.

    2007-02-05

    Strain-free freestanding GaN layers were prepared by in situ lift-off process using a ZnO buffer as a sacrificing layer. Thin Zn-polar ZnO layers were deposited on c-plane sapphire substrates, which was followed by the growth of Ga-polar GaN layers both by molecular beam epitaxy (MBE). The MBE-grown GaN layer acted as a protecting layer against decomposition of the ZnO layer and as a seeding layer for GaN growth. The ZnO layer was completely in situ etched off during growth of thick GaN layers at low temperature by hydride vapor phase epitaxy. Hence freestanding GaN layers were obtained for the consecutive growth of high-temperature GaN thick layers. The lattice constants of freestanding GaN agree with those of strain-free GaN bulk. Extensive microphotoluminescence study indicates that strain-free states extend throughout the high-temperature grown GaN layers.

  10. Growth of thick La2Zr2O7 buffer layers for coated conductors by polymer-assisted chemical solution deposition

    NASA Astrophysics Data System (ADS)

    Zhang, Xin; Zhao, Yong; Xia, Yudong; Guo, Chunsheng; Cheng, C. H.; Zhang, Yong; Zhang, Han

    2015-06-01

    La2Zr2O7 (LZO) epitaxial films have been deposited on LaAlO3 (LAO) (1 0 0) single-crystal surface and bi-axially textured NiW (2 0 0) alloy substrate by polymer-assisted chemical solution deposition, and afterwards studied with XRD, SEM and AFM approaches. Highly in-plane and out-of-plane oriented, dense, smooth, crack free and with a sufficient thickness (>240 nm) LZO buffer layers have been obtained on LAO (1 0 0) single-crystal surface; The films deposited on NiW (2 0 0) alloy substrate are also found with high degree in-plane and out-of-plane texturing, good density with pin-hole-free, micro-crack-free nature and a thickness of 300 nm. Highly epitaxial 500 nm thick YBa2Cu3O7-x (YBCO) thin film exhibits the self-field critical current density (Jc) reached 1.3 MA/cm2 at 77 K .These results demonstrate the LZO epi-films obtained with current techniques have potential to be a buffer layer for REBCO coated conductors.

  11. Design and characterization of thick InxGa1-xAs metamorphic buffer layers grown by hydride vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    Schulte, K. L.; Zutter, B. T.; Wood, A. W.; Babcock, S. E.; Kuech, T. F.

    2014-03-01

    Thick InxGa1-xAs metamorphic buffer layers (MBLs) grown by hydride vapor phase epitaxy (HVPE) were studied. Relationships between MBL properties and growth parameters such as grading rate, cap layer thickness, final xInAs, and deposition temperature (TD) were explored. The MBLs were characterized by measurement of in-plane residual strain (ɛ¦¦), surface etch pit density (EPD), and surface roughness. Capping layer thickness had a strong effect on strain relaxation, with thickly capped samples exhibiting the lowest ɛ¦¦. EPD was higher in samples with thicker caps, reflecting their increased relaxation through dislocation generation. ɛ¦¦ and EPD were weakly affected by the grading rate, making capping layer thickness the primary structural parameter which controls these properties. MBLs graded in discrete steps had similar properties to MBLs with continuous grading. In samples with identical thickness and 10-step grading style, ɛ¦¦ increased almost linearly with final xInAs, while total relaxation stayed relatively constant. Relaxation as a function of xInAs could be described by an equilibrium model in which dislocation nucleation is impeded by the energy of the existing dislocation array. EPD was constant from xInAs = 0 to 0.24 then increased exponentially, which is related to the increased dislocation interaction and blocking seen at higher dislocation densities. RMS roughness increased with xInAs above a certain strain rate (0.15%/µm) samples grown below this level possessed large surface hillocks and high roughness values. The elimination of hillocks at higher values of xInAs is attributed to increased density of surface steps and is related to the out-of-plane component of the burgers vector of the dominant type of 60° dislocation. TD did not affect ɛ¦¦ for samples with a given xInAs. EPD tended to increase with TD, indicating dislocation glide likely is impeded at higher temperatures.

  12. 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.

  13. Evolution of epilayer tilt in thick InxGa1-xAs metamorphic buffer layers grown by hydride vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    Schulte, K. L.; Strand, M. T.; Kuech, T. F.

    2015-09-01

    Tilt behavior in thick InxGa1-xAs metamorphic buffer layers (MBLs) grown by hydride vapor phase epitaxy (HVPE) was measured by high-resolution reciprocal space mapping. Step-graded and continuously-graded structures, grown on nominally (001) oriented GaAs substrates, were analyzed. Tilt was measured as a function of position in a step-graded MBL. It was found that the tilt was strongest near the edges and tended to point toward the sample center. Step-grading induced a nearly linear tilt increase with xInAs, while tilt increased slowly below xInAs~0.10 then increased more sharply with In concentration in continuously-graded samples. The tilt behavior could be described by a model in which the tilt is attributed to imbalances in dislocations that result from cross-slip within a glide length of the sample edge. This finding implies that dislocation multiplication by cross slip is an important strain relief mechanism during the growth of these MBLs. Strategies for minimizing tilt in HVPE MBLs are discussed.

  14. 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.

  15. 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.

  16. Thick (>20 µm) and high-resistivity carbon-doped GaN-buffer layers grown by metalorganic vapor phase epitaxy on n-type GaN substrates

    NASA Astrophysics Data System (ADS)

    Tsuchiya, Tomonobu; Terano, Akihisa; Mochizuki, Kazuhiro

    2016-05-01

    To improve the performance of GaN power devices, we have investigated the crystalline quality of thick (>20 µm) carbon-doped GaN layers on n-type GaN substrates and templates. The surface morphologies and X-ray rocking curves of carbon-doped GaN layers were improved by using GaN substrates. However, the crystalline quality degraded when the carbon concentration was too high (1 × 1020 cm‑3), even in the case of GaN substrates. High breakdown voltages (approximately 7 kV under a lateral configuration) were obtained for the carbon-doped GaN layers on n-type GaN substrates when the carbon concentration was 5 × 1019 cm‑3. These results indicate that lateral power devices with high breakdown voltage can be fabricated by using thick carbon-doped GaN buffer layers, even on n-type GaN substrates.

  17. Photo-induced wettability of TiO{sub 2} film with Au buffer layer

    SciTech Connect

    Purkayastha, Debarun Dhar; Sangani, L. D. Varma; Krishna, M. Ghanashyam; Madhurima, V.

    2014-04-24

    The effect of thickness of Au buffer layer (15-25 nm) between TiO{sub 2} film and substrate on the wettability of TiO{sub 2} films is reported. TiO{sub 2} films grown on Au buffer layer have a higher contact angle of 96-;100° as compared to 47.6o for the film grown without buffer layer. The transition from hydrophobicity to hydrophilicity under UV irradiation occurs within 10 min. for the buffer layered films whereas it is almost 30 min. for the film grown without buffer layer. The enhanced photo induced hydrophilicity is shown to be surface energy driven.

  18. Buffer layers for coated conductors

    DOEpatents

    Stan, Liliana; Jia, Quanxi; Foltyn, Stephen R.

    2011-08-23

    A composite structure is provided including a base substrate, an IBAD oriented material upon the base substrate, and a cubic metal oxide material selected from the group consisting of rare earth zirconates and rare earth hafnates upon the IBAD oriented material. Additionally, an article is provided including a base substrate, an IBAD oriented material upon the base substrate, a cubic metal oxide material selected from the group consisting of rare earth zirconates and rare earth hafnates upon the IBAD oriented material, and a thick film upon the cubic metal oxide material. Finally, a superconducting article is provided including a base substrate, an IBAD oriented material upon the base substrate, a cubic metal oxide material selected from the group consisting of rare earth zirconates and rare earth hafnates upon the IBAD oriented material, and an yttrium barium copper oxide material upon the cubic metal oxide material.

  19. Leakage effects in n-GaAs MESFET with n-GaAs buffer layer

    NASA Technical Reports Server (NTRS)

    Wang, Y. C.; Bahrami, M.

    1983-01-01

    Whereas improvement of the interface between the active layer and the buffer layer has been demonstrated, the leakage effects can be important if the buffer layer resistivity is not sufficiently high and/or the buffer layer thickness is not sufficiently small. It was found that two buffer leakage currents exist from the channel under the gate to the source and from drain to the channel in addition to the buffer leakage resistance between drain and source. It is shown that for a 1 micron gate-length n-GaAs MESFET, if the buffer layer resistivity is 12 OHM-CM and the buffer layer thickness h is 2 microns, the performance of the device degrades drastically. It is suggested that h should be below 2 microns.

  20. Buffer layers on biaxially textured metal substrates

    DOEpatents

    Shoup, Shara S.; Paranthamam, Mariappan; Beach, David B.; Kroeger, Donald M.; Goyal, Amit

    2001-01-01

    A method is disclosed for forming a biaxially textured buffer layer on a biaxially oriented metal substrate by using a sol-gel coating technique followed by pyrolyzing/annealing in a reducing atmosphere. This method is advantageous for providing substrates for depositing electronically active materials thereon.

  1. Electrodeposited Biaxially Textured Buffer Layers for YBCO Superconductors

    SciTech Connect

    Bhattacharya, R.; Phok, S.; Zhao, W.; Norman, A.

    2009-06-01

    Non-vacuum electrodeposition (ED) was used to prepare simplified Gd{sub 2}O{sub 3}/Gd{sub 2}Zr{sub 2}O{sub 7} and CeO{sub 2}/Gd{sub 2}Zr{sub 2}O{sub 7} buffer layers on a Ni-W substrate. Post-annealing conditions of electrodeposited precursor films were optimized to obtain high-quality biaxially textured buffer layers. The buffer layers were characterized by X-ray diffraction, optical profiling, and transmission electron microscopy (TEM). The effect of the cap layer thickness on the surface morphology and texture of the buffers was also studied. The microstructure of CeO{sub 2}/Gd{sub 2}Zr{sub 2}O{sub 7} was analyzed and compared to Gd{sub 2}O{sub 3}/Gd{sub 2}Zr{sub 2}O{sub 7}. The high-resolution TEM shows biaxially textured crystalline elctrodeposited Gd{sub 2}O{sub 3} and CeO{sub 2} cap layers on the electrodeposited Gd{sub 2}Zr{sub 2}O{sub 7} layers without any defects. YBa{sub 2}Cu{sub 3}O{sub 7}-delta (YBCO) superconductor was deposited by pulsed laser deposition (PLD) on the simplified ED-Gd{sub 2}O{sub 3}/Gd{sub 2}Zr{sub 2}O{sub 7} and ED-CeO{sub 2}/Gd{sub 2}Zr{sub 2}O{sub 7} buffers. Transport current density of 3.3 MA/cm{sup 2} at 77 K was obtained for PLD YBCO deposited on ED-Gd{sub 2}O{sub 3}/Gd{sub 2}Zr{sub 2}O{sub 7} buffer layers.

  2. buffer Layer Growth, the Thickness Dependence of Jc in Coated Conductors, Local Identification of Current Limiting Mechanisms and Participation in the Wire Development Group

    SciTech Connect

    Larbalestier, David; Hellstron, Eric; Abraimov, Dmytro

    2011-12-17

    The primary thrusts of our work were to provide critical understanding of how best to enhance the current-carrying capacity of coated conductors. These include the deconstruction of Jc as a function of fim thickness, the growth of in situ films incorporating strong pinning centers and the use of a suite of position-sensitive tools that enable location and analysis of key areas where current-limiting occurs.

  3. An ultra-thin buffer layer for Ge epitaxial layers on Si

    SciTech Connect

    Kawano, M.; Yamada, S.; Tanikawa, K.; Miyao, M.; Hamaya, K.; Sawano, K.

    2013-03-25

    Using an Fe{sub 3}Si insertion layer, we study epitaxial growth of Ge layers on a Si substrate by a low-temperature molecular beam epitaxy technique. When we insert only a 10-nm-thick Fe{sub 3}Si layer in between Si and Ge, epitaxial Ge layers can be obtained on Si. The detailed structural characterizations reveal that a large lattice mismatch of {approx}4% is completely relaxed in the Fe{sub 3}Si layer. This means that the Fe{sub 3}Si layers can become ultra-thin buffer layers for Ge on Si. This method will give a way to realize a universal buffer layer for Ge, GaAs, and related devices on a Si platform.

  4. Aerosol buffering of marine boundary layer cloudiness

    NASA Astrophysics Data System (ADS)

    Kazil, J.; Feingold, G.; Wang, H.

    2010-12-01

    The role of aerosol particles in maintaining a cloudy boundary layer in the remote marine environment is explored. It has previously been shown that precipitation can result in the transition from a closed- to open-cellular state but that the boundary layer cannot maintain this open-cell state without a resupply of particles. Potential sources include wind-driven production of sea salt particles from the ocean, nucleation from the gas phase, and entrainment from the free troposphere. Here we investigate with model simulations how the interplay of cloud properties, aerosol production, and boundary layer dynamics results in aerosol sources acting as a buffer against processes that destabilize cloudiness and the dynamic state of the marine boundary layer. For example, at nighttime, cloud liquid water increases in the absence of solar heating, resulting in increased precipitation, stronger cloud top cooling, accelerated boundary layer turbulence, and faster surface wind speeds. Faster surface wind speeds drive an enhanced flux of sea salt aerosol, at a time when aerosol particles are scavenged more readily by enhanced precipitation. In contrast, absorption of solar radiation during daytime reduces cloud water, decelerates boundary layer turbulence, reduces surface wind speeds, and therefore slows surface emissions. This is compensated by nucleation of small aerosol particles from the gas phase in response to the nigh complete removal of cloud condensation nuclei in precipitating open cell walls. These newly formed particles need to grow to larger sizes before they can serve as cloud condensation nuclei (CCN), but will likely contribute to the CCN population during the nighttime and, together with ocean emissions, buffer the system against precipitation removal.

  5. Buffer layers and articles for electronic devices

    DOEpatents

    Paranthaman, Mariappan P.; Aytug, Tolga; Christen, David K.; Feenstra, Roeland; Goyal, Amit

    2004-07-20

    Materials for depositing buffer layers on biaxially textured and untextured metallic and metal oxide substrates for use in the manufacture of superconducting and other electronic articles comprise RMnO.sub.3, R.sub.1-x A.sub.x MnO.sub.3, and combinations thereof; wherein R includes an element selected from the group consisting of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y, and A includes an element selected from the group consisting of Be, Mg, Ca, Sr, Ba, and Ra.

  6. Back contact buffer layer for thin-film solar cells

    DOEpatents

    Compaan, Alvin D.; Plotnikov, Victor V.

    2014-09-09

    A photovoltaic cell structure is disclosed that includes a buffer/passivation layer at a CdTe/Back contact interface. The buffer/passivation layer is formed from the same material that forms the n-type semiconductor active layer. In one embodiment, the buffer layer and the n-type semiconductor active layer are formed from cadmium sulfide (CdS). A method of forming a photovoltaic cell includes the step of forming the semiconductor active layers and the buffer/passivation layer within the same deposition chamber and using the same material source.

  7. Effect of buffer layer on the voltage responsivity of the pyroelectric thermal sensors prepared with PZT ceramics

    NASA Astrophysics Data System (ADS)

    Lee, Moon-Ho; Hwang, Ha R.; Bae, Seong-Ho

    1997-08-01

    The pyroelectric thermal detectors were prepared with lead zirconate titanate (PZT) ceramics, where a signal electrode had a structure of Au/metallic buffer/(PZT ceramic). The effect of buffer layer on the voltage responsivity was investigated with a response to step signal, taken by dynamic pyroelectric measurement. Pyroelectric ceramic wafer was prepared by mixed oxide technique. Au layer (thickness: 50 nm) and metallic buffers (thickness: 0 - 20 nm) of Cr, NiCr (80/20), and Ti were prepared by dc magnetron sputtering. In order to improve the light absorptivity, an Au-black was coated on Au signal electrode by thermal evaporation. At steady state, the output voltage (Vo) was decreased with increasing chopping frequency in the range of 1 - 100 Hz. A sensor without buffer showed the severe time-drift and instability in the output signal. However, the sensors with buffer layer showed the stable outputs. For step radiations, rising time (tp), peak voltage (Vp), and initial slope (k) of the output voltage were dependent upon the thickness and materials of buffer layer. The mechanical and electrical contacts between Au electrode and PZT ceramics were improved by inserting the metallic buffer layer. Considering the characteristics of the output voltage, the optimum thickness of buffer layer was about 15 - 20 nm, and the sensors with Ti buffer of 15 - 20 nm in thickness showed the good detectivity. Therefore, the stability and reliability of the thermal sensors could be improved by use of appropriate buffer layer.

  8. Effect of Oxide Buffer Layer on the Thermochromic Properties of VO2 Thin Films

    NASA Astrophysics Data System (ADS)

    Koo, Hyun; Xu, Lu; Ko, Kyeong-Eun; Ahn, Seunghyun; Chang, Se-Hong; Park, Chan

    2013-12-01

    VO2 thin films were deposited on soda lime glass substrates with ZnO, TiO2, SnO2, and CeO2 thin films applied as buffer layers between the VO2 films and the substrates in order to investigate the effect of buffer layer on the formation and the thermochromic properties of VO2 film. Buffer layers with thicknesses over 50 nm were found to affect the formation of VO2 film, which was confirmed by XRD spectra. By using ZnO, TiO2, and SnO2 buffer layers, monoclinic VO2 (VO2(M)) film was successfully fabricated on soda lime glass at 370 °C. On the contrary, films of VO2(B), which is known to have no phase transition near room temperature, were formed rather than VO2(M) when the film was deposited on CeO2 buffer layer at the same film deposition temperature. The excellent thermochromic properties of the films deposited on ZnO, TiO2, and SnO2 buffer layers were confirmed from the temperature dependence of electrical resistivity from room temperature to 80 °C. Especially, due to the tendency of ZnO thin film to grow with a high degree of preferred orientation on soda lime glass at low temperature, the VO2 film deposited on ZnO buffer layer exhibits the best thermochromic properties compared to those on other buffer layer materials used in this study. These results suggest that deposition of VO2 films on soda lime glass at low temperature with excellent thermochromic properties can be achieved by considering the buffer layer material having structural similarity with VO2. Moreover, the degree of crystallization of buffer layer is also related with that of VO2 film, and thus ZnO can be one of the most effective buffer layer materials.

  9. 1,3,5-Tris(phenyl-2-benzimidazole)-benzene cathode buffer layer thickness dependence in solution-processable organic solar cell based on 1,4,8,11,15,18,22,25-octahexylphthalocyanine

    NASA Astrophysics Data System (ADS)

    De Roméo Banoukepa, Gilles; Fujii, Akihiko; Shimizu, Yo; Ozaki, Masanori

    2015-04-01

    Studies on the insertion effects of a cathode buffer layer on bulk heterojunction organic solar cell based on 1,4,8,11,15,18,22,25-octahexylphthalocyanine (C6PcH2) and 1-(3-methoxy-carbonyl)-propyl-1-1-phenyl-(6,6)C61 (PCBM) by using 1,3,5-tris(phenyl-2-benzimidazole)-benzene (TPBi) as a cathode buffer layer material have been carried out. The external quantum efficiency and the short-circuit current markedly increased, resulting in the enhancement of the power conversion efficiency. The solar cell performance has been discussed from the atomic force microscopy, photoelectron yield spectroscopy and X-ray photoelectron spectroscopy measurements.

  10. Simulation study on single event burnout in linear doping buffer layer engineered power VDMOSFET

    NASA Astrophysics Data System (ADS)

    Yunpeng, Jia; Hongyuan, Su; Rui, Jin; Dongqing, Hu; Yu, Wu

    2016-02-01

    The addition of a buffer layer can improve the device's secondary breakdown voltage, thus, improving the single event burnout (SEB) threshold voltage. In this paper, an N type linear doping buffer layer is proposed. According to quasi-stationary avalanche simulation and heavy ion beam simulation, the results show that an optimized linear doping buffer layer is critical. As SEB is induced by heavy ions impacting, the electric field of an optimized linear doping buffer device is much lower than that with an optimized constant doping buffer layer at a given buffer layer thickness and the same biasing voltages. Secondary breakdown voltage and the parasitic bipolar turn-on current are much higher than those with the optimized constant doping buffer layer. So the linear buffer layer is more advantageous to improving the device's SEB performance. Project supported by the National Natural Science Foundation of China (No. 61176071), the Doctoral Fund of Ministry of Education of China (No. 20111103120016), and the Science and Technology Program of State Grid Corporation of China (No. SGRI-WD-71-13-006).

  11. Buffer layers for REBCO films for use in superconducting devices

    DOEpatents

    Goyal, Amit; Wee, Sung-Hun

    2014-06-10

    A superconducting article includes a substrate having a biaxially textured surface. A biaxially textured buffer layer, which can be a cap layer, is supported by the substrate. The buffer 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 transition metal cations. A biaxially textured superconductor layer is deposited so as to be supported by the buffer layer. A method of making a superconducting article is also disclosed.

  12. Current isolating epitaxial buffer layers for high voltage photodiode array

    DOEpatents

    Morse, Jeffrey D.; Cooper, Gregory A.

    2002-01-01

    An array of photodiodes in series on a common semi-insulating substrate has a non-conductive buffer layer between the photodiodes and the semi-insulating substrate. The buffer layer reduces current injection leakage between the photodiodes of the array and allows optical energy to be converted to high voltage electrical energy.

  13. Buffer layers on metal alloy substrates for superconducting tapes

    DOEpatents

    Jia, Quanxi; Foltyn, Stephen R.; Arendt, Paul N.; Groves, James R.

    2004-10-05

    An article including a substrate, at least one intermediate layer upon the surface of the substrate, a layer of an oriented cubic oxide material having a rock-salt-like structure upon the at least one intermediate layer, and a layer of a SrRuO.sub.3 buffer material upon the oriented cubic oxide material layer is provided together with additional layers such as a HTS top-layer of YBCO directly upon the layer of a SrRuO.sub.3 buffer material layer. With a HTS top-layer of YBCO upon at least one layer of the SrRuO.sub.3 buffer material in such an article, J.sub.c 's of up to 1.3.times.10.sup.6 A/cm.sup.2 have been demonstrated with projected I.sub.c 's of over 200 Amperes across a sample 1 cm wide.

  14. Mitigation of substrate defects in reticles using multilayer buffer layers

    DOEpatents

    Mirkarimi, Paul B.; Bajt, Sasa; Stearns, Daniel G.

    2001-01-01

    A multilayer film is used as a buffer layer to minimize the size of defects on a reticle substrate prior to deposition of a reflective coating on the substrate. The multilayer buffer layer deposited intermediate the reticle substrate and the reflective coating produces a smoothing of small particles and other defects on the reticle substrate. The reduction in defect size is controlled by surface relaxation during the buffer layer growth process and by the degree of intermixing and volume contraction of the materials at the multilayer interfaces. The buffer layers are deposited at near-normal incidence via a low particulate ion beam sputtering process. The growth surface of the buffer layer may also be heated by a secondary ion source to increase the degree of intermixing and improve the mitigation of defects.

  15. Magneto-optical properties of Co /Ge(100) with ultrathin Ag buffer layers

    NASA Astrophysics Data System (ADS)

    Su, C. W.; Tsay, J. S.; Hwang, C. H.; Yao, Y. D.

    2005-05-01

    Magnetic properties of Co films (<2nm) with Ag buffer layers (<0.7nm) grown on Ge(100) at room temperature and 200K were studied by surface magneto-optical Kerr effect. Without the buffer, the films reveal in-plane magnetic anisotropy even Co and Ge forms nonmagnetic interfacial alloys. The hysteresis due to intercalation of Ag can be detected at thinner Co thicknesses. The buffer can effectively cutoff the intermixing of Co and Ge. As the thickness of Ag is reduced, out-of-plane magnetic anisotropy due to the interface interactions between Co /Ag and Co /Ge was discovered and was only at 200K.

  16. Methods for improved growth of group III nitride buffer layers

    DOEpatents

    Melnik, Yurity; Chen, Lu; Kojiri, Hidehiro

    2014-07-15

    Methods are disclosed for growing high crystal quality group III-nitride epitaxial layers with advanced multiple buffer layer techniques. In an embodiment, a method includes forming group III-nitride buffer layers that contain aluminum on suitable substrate in a processing chamber of a hydride vapor phase epitaxy processing system. A hydrogen halide or halogen gas is flowing into the growth zone during deposition of buffer layers to suppress homogeneous particle formation. Some combinations of low temperature buffers that contain aluminum (e.g., AlN, AlGaN) and high temperature buffers that contain aluminum (e.g., AlN, AlGaN) may be used to improve crystal quality and morphology of subsequently grown group III-nitride epitaxial layers. The buffer may be deposited on the substrate, or on the surface of another buffer. The additional buffer layers may be added as interlayers in group III-nitride layers (e.g., GaN, AlGaN, AlN).

  17. Controlling optical polarization of {11-22} semipolar multiple quantum wells using relaxed underlying InGaN buffer layers

    NASA Astrophysics Data System (ADS)

    Okada, Narihito; Okamura, Yasuhiro; Uchida, Katsumi; Tadatomo, Kazuyuki

    2016-08-01

    We successfully fabricated {11-22} multiple quantum wells (MQWs) having different emission peak wavelengths on partially or completely relaxed thick InGaN buffer layers with different In contents formed on a semipolar {11-22} GaN layer, which was grown on a patterned r-plane sapphire substrate. The polarization properties changed significantly with changing in In content and thickness for InGaN buffer layer. For the same In content of the InGaN buffer layer, the optical polarization changed with an increase in the thickness of the underlying InGaN buffer layer, indicating a change in the relaxation ratio of the InGaN buffer layer. Similarly, for the same thickness of the InGaN buffer layer, the optical polarization changed by changing In content of the InGaN buffer layer. Thus, the degree of optical polarization could be controlled by varying the In content of the underlying InGaN buffer layer.

  18. Enhanced adhesion for LIGA microfabrication by using a buffer layer

    DOEpatents

    Bajikar, Sateesh S.; De Carlo, Francesco; Song, Joshua J.

    2001-01-01

    The present invention is an improvement on the LIGA microfabrication process wherein a buffer layer is applied to the upper or working surface of a substrate prior to the placement of a resist onto the surface of the substrate. The buffer layer is made from an inert low-Z material (low atomic weight), a material that absorbs secondary X-rays emissions from the substrate that are generated from the substrate upon exposure to a primary X-rays source. Suitable materials for the buffer layer include polyamides and polyimide. The preferred polyimide is synthesized form pyromellitic anhydride and oxydianiline (PMDA-ODA).

  19. Enhanced adhesion for LIGA microfabrication by using a buffer layer

    SciTech Connect

    Bajikar, Sateesh S.; De Carlo, Francesco; Song, Joshua J.

    2004-01-27

    The present invention is an improvement on the LIGA microfabrication process wherein a buffer layer is applied to the upper or working surface of a substrate prior to the placement of a resist onto the surface of the substrate. The buffer layer is made from an inert low-Z material (low atomic weight), a material that absorbs secondary X-rays emissions from the substrate that are generated from the substrate upon exposure to a primary X-rays source. Suitable materials for the buffer layer include polyamides and polyimide. The preferred polyimide is synthesized form pyromellitic anhydride and oxydianiline (PMDA-ODA).

  20. Buffer layer effect on ZnO nanorods growth alignment

    NASA Astrophysics Data System (ADS)

    Zhao, Dongxu; Andreazza, Caroline; Andreazza, Pascal; Ma, Jiangang; Liu, Yichun; Shen, Dezhen

    2005-06-01

    Vertical aligned ZnO nanorods array was fabricated on Si with introducing a ZnO thin film as a buffer layer. Two different nucleation mechanisms were found in growth process. With using Au catalyst, Zn vapor could diffuse into Au nanoclusters with forming a solid solution. Then the ZnO nucleation site is mainly on the catalyst by oxidation of Au/Zn alloy. Without catalyst, nucleation could occur directly on the surface of buffer layer by homoepitaxy. The density and the size of ZnO nanorods could be governed by morphological character of catalyst and buffer layer. The nanorods growth is followed by vapor-solid mechanism.

  1. On buffer layers as non-reflecting computational boundaries

    NASA Technical Reports Server (NTRS)

    Hayder, M. Ehtesham; Turkel, Eli L.

    1996-01-01

    We examine an absorbing buffer layer technique for use as a non-reflecting boundary condition in the numerical simulation of flows. One such formulation was by Ta'asan and Nark for the linearized Euler equations. They modified the flow inside the buffer zone to artificially make it supersonic in the layer. We examine how this approach can be extended to the nonlinear Euler equations. We consider both a conservative and a non-conservative form modifying the governing equations in the buffer layer. We compare this with the case that the governing equations in the layer are the same as in the interior domain. We test the effectiveness of these buffer layers by a simulation of an excited axisymmetric jet based on a nonlinear compressible Navier-Stokes equations.

  2. Buffer layers for high-Tc thin films on sapphire

    NASA Technical Reports Server (NTRS)

    Wu, X. D.; Foltyn, S. R.; Muenchausen, R. E.; Cooke, D. W.; Pique, A.; Kalokitis, D.; Pendrick, V.; Belohoubek, E.

    1992-01-01

    Buffer layers of various oxides including CeO2 and yttrium-stabilized zirconia (YSZ) have been deposited on R-plane sapphire. The orientation and crystallinity of the layers were optimized to promote epitaxial growth of YBa2Cu3O(7-delta) (YBCO) thin films. An ion beam channeling minimum yield of about 3 percent was obtained in the CeO2 layer on sapphire, indicating excellent crystallinity of the buffer layer. Among the buffer materials used, CeO2 was found to be the best one for YBCO thin films on R-plane sapphire. High Tc and Jc were obtained in YBCO thin films on sapphire with buffer layers. Surface resistances of the YBCO films were about 4 mOmega at 77 K and 25 GHz.

  3. Degradation Characteristics of MgO Based Magnetic Tunnel Junction Caused by Surface Roughness of Ta/Ru Buffer Layers.

    PubMed

    Lee, Jung Min; Choi, Chul Min; Sukegawa, Hiroaki; Lee, Jeong Yong; Mitani, Seiji; Song, Yun-Heub

    2016-01-01

    We investigated how surface roughness of a Ta/Ru buffer layer affects the degradation characteristics on MgO-based magnetic tunnel junctions (MTJs). MTJs with worse surface roughness on the buffer layer showed increased resistance drift and degraded time-dependent dielectric breakdown (TDDB) characteristics. We suggest that this resulted from reduced MgO thickness on the MTJ with worse surface roughness on the buffer layer, which was estimated by the TDDB and analytic approach. As a result, surface roughness of the buffer layer is a critical factors that impacts the reliability of MTJs, and it should be controlled to have the smallest roughness value as possible. PMID:27398503

  4. Rare earth zirconium oxide buffer layers on metal substrates

    DOEpatents

    Williams, Robert K.; Paranthaman, Mariappan; Chirayil, Thomas G.; Lee, Dominic F.; Goyal, Amit; Feenstra, Roeland

    2001-01-01

    A laminate article comprises a substrate and a biaxially textured (RE.sub.x A.sub.(1-x)).sub.2 O.sub.2-(x/2) buffer layer over the substrate, wherein 0buffer layer can be deposited using sol-gel or metal-organic decomposition. The laminate article can include a layer of YBCO over the (RE.sub.x A.sub.(1-x)).sub.2 O.sub.2-(x/2) buffer layer. A layer of CeO.sub.2 between the YBCO layer and the (RE.sub.x A.sub.(1-x)).sub.2 O.sub.2-(x/2) buffer layer can also be include. Further included can be a layer of YSZ between the CeO.sub.2 layer and the (RE.sub.x A.sub.(1-x)).sub.2 O.sub.2-(x/2) buffer layer. The substrate can be a biaxially textured metal, such as nickel. A method of forming the laminate article is also disclosed.

  5. GaAs buffer layer technique for vertical nanowire growth on Si substrate

    SciTech Connect

    Xu, Xiaoqing Parizi, Kokab B.; Huo, Yijie; Kang, Yangsen; Philip Wong, H.-S.; Li, Yang

    2014-02-24

    Gold catalyzed vapor-liquid-solid method is widely applied to III–V nanowire (NW) growth on Si substrate. However, the easy oxidation of Si, possible Si contamination in the NWs, high defect density in the NWs, and high sensitivity of the NW morphology to growth conditions largely limit its controllability. In this work, we developed a buffer layer technique by introducing a GaAs thin film with predefined polarity as a template. It is found that samples grown on these buffer layers all have high vertical NW yields in general, due to the single-orientation of the buffer layers. Low temperature buffer with smoother surface leads to highest yield of vertical NWs, while high temperature (HT) buffer with better crystallinity results in perfect NW quality. The defect-free property we observed here is very promising for optoelectronic device applications based on GaAs NW. Moreover, the buffer layers can eliminate Si contamination by preventing Si-Au alloy formation and by increasing the thickness of the Si diffusion barrier, thus providing more flexibility to vertical NW growth. The buffer layer technique we demonstrated here could be easily extended to other III-V on Si system for electronic and photonic applications.

  6. Method of depositing buffer layers on biaxially textured metal substrates

    DOEpatents

    Beach, David B.; Morrell, Jonathan S.; Paranthaman, Mariappan; Chirayil, Thomas; Specht, Eliot D.; Goyal, Amit

    2002-08-27

    A laminate article comprises a substrate and a biaxially textured (RE.sup.1.sub.x RE.sup.2.sub.(1-x)).sub.2 O.sub.3 buffer layer over the substrate, wherein 0buffer layer can be deposited using sol-gel or metal-organic decomposition. The laminate article can include a layer of YBCO over the (RE.sup.1.sub.x RE.sup.2.sub.(1-x)).sub.2 O.sub.3 buffer layer. A layer of CeO.sub.2 between the YBCO layer and the (RE.sup.1.sub.x RE.sup.2.sub.(1-x)).sub.2 O.sub.3 buffer can also be include. Further included can be a layer of YSZ between the CeO.sub.2 layer and the (RE.sup.1.sub.x RE.sup.2.sub.(1-x)).sub.2 O.sub.3 buffer layer. The substrate can be a biaxially textured metal, such as nickel. A method of forming the laminate article is also disclosed.

  7. Hafnium nitride buffer layers for growth of GaN on silicon

    DOEpatents

    Armitage, Robert D.; Weber, Eicke R.

    2005-08-16

    Gallium nitride is grown by plasma-assisted molecular-beam epitaxy on (111) and (001) silicon substrates using hafnium nitride buffer layers. Wurtzite GaN epitaxial layers are obtained on both the (111) and (001) HfN/Si surfaces, with crack-free thickness up to 1.2 {character pullout}m. However, growth on the (001) surface results in nearly stress-free films, suggesting that much thicker crack-free layers could be obtained.

  8. Characterization of AlInN/AlN/GaN Heterostructures with Different AlN Buffer Thickness

    NASA Astrophysics Data System (ADS)

    Çörekçi, S.; Dugan, S.; Öztürk, M. K.; Çetin, S. Ş.; Çakmak, M.; Özçelik, S.; Özbay, E.

    2016-05-01

    Two AlInN/AlN/GaN heterostructures with 280-nm- and 400-nm-thick AlN buffer grown on sapphire substrates by metal-organic chemical vapor deposition (MOCVD) have been investigated by x-ray diffraction (XRD), atomic force microscopy (AFM), photoluminescence (PL) and Hall-effect measurements. The symmetric (0002) plane with respect to the asymmetric (10bar{1} 2) plane in the 280-nm-thick AlN buffer has a higher crystal quality, as opposed to the 400-nm-thick buffer. The thinner buffer improves the crystallinity of both (0002) and (10bar{1} 2) planes in the GaN layers, it also provides a sizeable reduction in dislocation density of GaN. Furthermore, the lower buffer thickness leads to a good quality surface with an rms roughness of 0.30 nm and a dark spot density of 4.0 × 108 cm-2. The optical and transport properties of the AlInN/AlN/GaN structure with the relatively thin buffer are compatible with the enhancement in its structural quality, as verified by XRD and AFM results.

  9. Characterization of AlInN/AlN/GaN Heterostructures with Different AlN Buffer Thickness

    NASA Astrophysics Data System (ADS)

    Çörekçi, S.; Dugan, S.; Öztürk, M. K.; Çetin, S. Ş.; Çakmak, M.; Özçelik, S.; Özbay, E.

    2016-07-01

    Two AlInN/AlN/GaN heterostructures with 280-nm- and 400-nm-thick AlN buffer grown on sapphire substrates by metal-organic chemical vapor deposition (MOCVD) have been investigated by x-ray diffraction (XRD), atomic force microscopy (AFM), photoluminescence (PL) and Hall-effect measurements. The symmetric (0002) plane with respect to the asymmetric (10bar{1}2) plane in the 280-nm-thick AlN buffer has a higher crystal quality, as opposed to the 400-nm-thick buffer. The thinner buffer improves the crystallinity of both (0002) and (10bar{1}2) planes in the GaN layers, it also provides a sizeable reduction in dislocation density of GaN. Furthermore, the lower buffer thickness leads to a good quality surface with an rms roughness of 0.30 nm and a dark spot density of 4.0 × 108 cm-2. The optical and transport properties of the AlInN/AlN/GaN structure with the relatively thin buffer are compatible with the enhancement in its structural quality, as verified by XRD and AFM results.

  10. Buffer layers on metal alloy substrates for superconducting tapes

    DOEpatents

    Jia, Quanxi; Foltyn, Stephen R.; Arendt, Paul N.; Groves, James R.

    2004-06-29

    An article including a substrate, a layer of an inert oxide material upon the surface of the substrate, a layer of an amorphous oxide or oxynitride material upon the inert oxide material layer, a layer of an oriented cubic oxide material having a rock-salt-like structure upon the amorphous oxide material layer, and a layer of a SrRuO.sub.3 buffer material upon the oriented cubic oxide material layer is provided together with additional layers such as a HTS top-layer of YBCO directly upon the layer of a SrRuO.sub.3 buffer material layer. With a HTS top-layer of YBCO upon at least one layer of the SrRuO.sub.3 buffer material in such an article, J.sub.c 's of up to 1.3.times.10.sup.6 A/cm.sup.2 have been demonstrated with projected IC's of over 200 Amperes across a sample 1 cm wide.

  11. Growth of InSb on GaAs Using InAlSb Buffer Layers

    SciTech Connect

    BIEFELD, ROBERT M.; PHILLIPS, JAMIE D.

    1999-09-20

    We report the growth of InSb on GaAs using InAlSb buffers of high interest for magnetic field sensors. We have grown samples by metal-organic chemical vapor deposition consisting of {approximately} 0.55 {micro}m thick InSb layers with resistive InAlSb buffers on GaAs substrates with measured electron nobilities of {approximately}40,000 cm{sup 2}/V.s. We have investigated the In{sub 1{minus}x}Al{sub x}Sb buffers for compositions x{le}0.22 and have found that the best results are obtained near x=0.12 due to the tradeoff of buffer layer bandgap and lattice mismatch.

  12. Conductive and robust nitride buffer layers on biaxially textured substrates

    DOEpatents

    Sankar, Sambasivan [Chicago, IL; Goyal, Amit [Knoxville, TN; Barnett, Scott A [Evanston, IL; Kim, Ilwon [Skokie, IL; Kroeger, Donald M [Knoxville, TN

    2009-03-31

    The present invention relates to epitaxial, electrically conducting and mechanically robust, cubic nitride buffer layers deposited epitaxially on biaxially textured substrates such as metals and alloys. The invention comprises of a biaxially textured substrate with epitaxial layers of nitrides. The invention also discloses a method to form such epitaxial layers using a high rate deposition method as well as without the use of forming gases. The invention further comprises epitaxial layers of oxides on the biaxially textured nitride layer. In some embodiments the article further comprises electromagnetic devices which may have superconducting properties.

  13. Conductive and robust nitride buffer layers on biaxially textured substrates

    DOEpatents

    Sankar, Sambasivan; Goyal, Amit; Barnett, Scott A.; Kim, Ilwon; Kroeger, Donald M.

    2004-08-31

    The present invention relates to epitaxial, electrically conducting and mechanically robust, cubic nitride buffer layers deposited epitaxially on biaxially textured substrates such as metal and alloys. The invention comprises of a biaxially textured substrate with epitaxial layers of nitrides. The invention also discloses a method to form such epitaxial layers using a high rate deposition method as well as without the use of forming gases. The invention further comprises epitaxial layers of oxides on the biaxially textured nitride layers. In some embodiments the article further comprises electromagnetic devices which may be super conducting properties.

  14. CoFe2O4/buffer layer ultrathin heterostructures on Si(001)

    NASA Astrophysics Data System (ADS)

    Bachelet, R.; de Coux, P.; Warot-Fonrose, B.; Skumryev, V.; Fontcuberta, J.; Sánchez, F.

    2011-10-01

    Epitaxial films of ferromagnetic CoFe2O4 (CFO) were grown by pulsed laser deposition on Si(001) buffered with ultrathin yttria-stabilized zirconia (YSZ) layers in a single process. Reflection high-energy electron diffraction was used to monitor in real time the crystallization of YSZ, allowing the fabrication of epitaxial YSZ buffers with thickness of about 2 nm. CFO films, with thicknesses in the 2-50 nm range were subsequently deposited. The magnetization of the CFO films is close to the bulk value. The ultrathin CFO/YSZ heterostructures have very flat morphology (0.1 nm roughness) and thin interfacial SiOx layer (about 2 nm thick) making them suitable for integration in tunnel (e.g., spin injection) devices.

  15. Substrate surface treatment and YSZ buffer layers by IBAD method for coated conductors

    NASA Astrophysics Data System (ADS)

    Feng, F.; Liu, R.; Chen, H.; Shi, K.; Wang, Z.; Wu, W.; Han, Z.

    2009-10-01

    In this work, an Ion Beam Assisted Deposition (IBAD) system was utilized to fabricate Yttria-Stabilized Zirconia (YSZ) template films for coated conductors. The surface of the Hastelloy C276 substrate was modified by rolling and electropolishing. The effect of the electropolishing parameters of the substrate on the texture of the YSZ buffer layers was studied. The electropolishing current and time were optimized for short samples of 1 cm×1 cm square shape as 1 A and 60 s, respectively. And the relationship between the roughness of the substrate surface and the texture of the YSZ layer is discussed. Reel-to-reel metal tape moving apparatus was installed and used to produce meter-long buffer layer for coated conductors. The YSZ template film was deposited by IBAD method on meter-long Hastelloy tape with tape shifting speed of 15-20 m/h, and the thickness of the buffer layer was up to about 1.7 μm. The Hastelloy substrate surface was measured by Atomic Force Microscope. The thickness of the YSZ films over length was measured by Thermal Field Emission Scan Electronic Microscopy. X Ray Diffraction Ω-scan and ϕ-scan measurements were performed in order to examine the out-of-plane and in-plane texture of the YSZ buffer layers, respectively.

  16. Characterization of mismatched SiGe grown on low temperature Si buffer layers by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Linder, K. K.; Zhang, F. C.; Rieh, J.-S.; Bhattacharya, P.

    1997-05-01

    Several types of buffer layer structures, including superlattice and step-graded layers, have been employed to reduce the threading dislocation in SiGe epitaxial layers. A new technique, using a 0.1 μm thick Si buffer grown at 450°C by molecular beam epitaxy, provides the best results. For a 0.5 μm thick Si 0.85Ge 0.15 layer, the dislocation density is ⩽ 10 5cm -2. Hall measurements indicate an improvement in the hole mobility of a 1 μm thick Boron doped Si 0.7Ge 0.3 layer. A {SiGe}/{Si} heterojunction bipolar transistor has been fabricated exploiting the low temperature Si buffer. Transmission electron microscopy of the structure does not indicate any evidence of threading dislocations.

  17. Thickness-Dependent Properties of YBCO Films Grown on GZO/CLO-Buffered NiW Substrates

    NASA Astrophysics Data System (ADS)

    Malmivirta, M.; Huhtinen, H.; Zhao, Y.; Grivel, J.-C.; Paturi, P.

    2016-07-01

    To study the role of novel Gd_2 Zr_2 O_7 /Ce_{0.9} La_{0.1} O_2 buffer layer structure on a biaxially textured NiW substrate, a set of YBa_2 Cu_3 O_{7-δ } (YBCO) films with different thicknesses were prepared by pulsed laser deposition (PLD). Interface imperfections as well as thickness-dependent structural properties were observed in the YBCO thin films. The structure is also reflected into the improved superconducting properties with the highest critical current densities in films with intermediate thicknesses. Therefore, it can be concluded that the existing buffer layers need more optimization before they can be successfully used for films with various thicknesses. This issue is linked to the extremely susceptible growth method of PLD when compared to the commonly used chemical deposition methods. Nevertheless, PLD-grown films can give a hint on what to concentrate to be able to further improve the buffer layer structures for future coated conductor technologies.

  18. Effect of ZnO seed layer on the morphology and optical properties of ZnO nanorods grown on GaN buffer layers

    SciTech Connect

    Nandi, R. Mohan, S. Major, S. S.; Srinivasa, R. S.

    2014-04-24

    ZnO nanorods were grown by chemical bath deposition on sputtered, polycrystalline GaN buffer layers with and without ZnO seed layer. Scanning electron microscopy and X-ray diffraction show that the ZnO nanorods on GaN buffer layers are not vertically well aligned. Photoluminescence spectrum of ZnO nanorods grown on GaN buffer layer, however exhibits a much stronger near-band-edge emission and negligible defect emission, compared to the nanorods grown on ZnO buffer layer. These features are attributed to gallium incorporation at the ZnO-GaN interface. The introduction of a thin (25 nm) ZnO seed layer on GaN buffer layer significantly improves the morphology and vertical alignment of ZnO-NRs without sacrificing the high optical quality of ZnO nanorods on GaN buffer layer. The presence of a thick (200 nm) ZnO seed layer completely masks the effect of the underlying GaN buffer layer on the morphology and optical properties of nanorods.

  19. Formation of CeO 2 buffer layer using multi-plume PLD

    NASA Astrophysics Data System (ADS)

    Sutoh, Y.; Nakaoka, K.; Miura, M.; Matsuda, J.; Nakanishi, T.; Nakai, A.; Yoshizumi, M.; Izumi, T.; Miyata, S.; Iijima, Y.; Yamada, Y.; Shiohara, Y.; Saitoh, T.

    2008-09-01

    The CeO 2 buffer layer was fabricated using the multi-plume pulsed laser deposition (PLD) method with different deposition rates controlled by the excimer laser energy and frequency on the Gd 2Zr 2O 7 template tape formed by the ion-beam assisted deposition (IBAD) with 14° of Δ φ (full width at half maximum (FWHM) value of X-ray diffraction φ-scan for Gd 2Zr 2O 7 (2 2 2) pole). The laser conditions with high pulse energy and low frequency resulted in a highly textured in-plane grain alignment (Δ φ). The surface roughness and Δ φ values were improved by increasing the thickness of the CeO 2 buffer layer. YBCO films with the thickness of 1 μm and 1.6 μm were further deposited by the advanced trifluoroacetates-metal organic deposition (TFA-MOD) on the CeO 2 buffered substrates with the deposition rate of 0.15 and 0.5 μm/min. The Jc values of 2.5 MA/cm 2 and 2 MA/cm 2 were obtained, respectively. High Jc films could be deposited on the CeO 2 buffer layer even at high deposition rate by the multi-plume deposition.

  20. The growth of various buffer layer structures and their influence on the quality of (CdHg)Te epilayers

    NASA Astrophysics Data System (ADS)

    Gouws, G. J.; Muller, R. J.; Bowden, R. S.

    1993-05-01

    The suitability of various buffer layer structures on (100) GaAs for (CdHg)Te growth by organometallic vapour phase epitaxy (OMVPE) was investigated. The preferred epitaxial orientation of {(100)GaAs}/{(111)CdTe} was found to be unsuitable due to the formation of electrically active defects in the material. An intermediate ZnTe layer was used to select the (100) orientation and (100) CdTe layers were when deposited on this ZnTe layer. The quality of the resultant CdTe buffer was found to critically depend on the thickness of this intermediate ZnTe buffer, with a ZnTe thickness of approximately 500 Å producing the best CdTe buffer. (CdHg)Te epilayers grown on these {ZnTe}/{CdTe} buffers had improved electrical properties, but still suffered from a poor surface morphology. This surface morphology could be improved by using a lattice matched Cd 0.96Zn 0.04Te alloy as the final buffer layer, but the surface pyramids typical of the (100) orientation could never be completely eliminated.

  1. Non-polar a-plane ZnO films grown on r-Al2O3 substrates using GaN buffer layers

    NASA Astrophysics Data System (ADS)

    Xu, C. X.; Chen, W.; Pan, X. H.; Chen, S. S.; Ye, Z. Z.; Huang, J. Y.

    2016-09-01

    In this work, GaN buffer layer has been used to grow non-polar a-plane ZnO films by laser-assisted and plasma-assisted molecular beam epitaxy. The thickness of GaN buffer layer ranges from ∼3 to 12 nm. The GaN buffer thickness effect on the properties of a-plane ZnO thin films is carefully investigated. The results show that the surface morphology, crystal quality and optical properties of a-plane ZnO films are strongly correlated with the thickness of GaN buffer layer. It was found that with 6 nm GaN buffer layer, a-plane ZnO films display the best crystal quality with X-ray diffraction rocking curve full-width at half-maximum of only 161 arcsec for the (101) reflection.

  2. Improved nonlinear slot waveguides using dielectric buffer layers: properties of TM waves.

    PubMed

    Elsawy, Mahmoud M R; Renversez, Gilles

    2016-04-01

    We propose an improved version of the symmetric metal slot waveguides with a Kerr-type nonlinear dielectric core adding linear dielectric buffer layers between the metal regions and the core. Using a finite element method to compute the stationary nonlinear modes, we provide the full phase diagrams of its main transverse magnetic modes as a function of the total power, buffer layer, and core thicknesses that are more complex than the ones of the simple nonlinear metal slot. We show that these modes can exhibit spatial transitions toward specific modes of the new structure as a function of power. We also demonstrate that, for the main modes, the losses are reduced compared to the previous structures, and that they can now decrease with power. Finally, we describe the stability properties of the main stationary solutions using nonlinear FDTD simulations. PMID:27192282

  3. Buffer influence on magnetic dead layer, critical current, and thermal stability in magnetic tunnel junctions with perpendicular magnetic anisotropy

    NASA Astrophysics Data System (ADS)

    Frankowski, Marek; Żywczak, Antoni; Czapkiewicz, Maciej; Zietek, Sławomir; Kanak, Jarosław; Banasik, Monika; Powroźnik, Wiesław; Skowroński, Witold; Checiński, Jakub; Wrona, Jerzy; Głowiński, Hubert; Dubowik, Janusz; Ansermet, Jean-Philippe; Stobiecki, Tomasz

    2015-06-01

    We present a detailed study of Ta/Ru-based buffers and their influence on features crucial from the point of view of applications of Magnetic Tunnel Junctions (MTJs) such as critical switching current and thermal stability. We study buffer/FeCoB/MgO/Ta/Ru and buffer/MgO/FeCoB/Ta/Ru layers, investigating the crystallographic texture, the roughness of the buffers, the magnetic domain pattern, the magnetic dead layer thickness, and the perpendicular magnetic anisotropy fields for each sample. Additionally, we examine the effect of the current induced magnetization switching for complete nanopillar MTJs with lateral dimensions of 270 × 180 nm. Buffer Ta 5/Ru 10/Ta 3 (thicknesses in nm), which has the thickest dead layer, exhibits a much larger thermal stability factor (63 compared to 32.5) while featuring a slightly lower critical current density value (1.25 MA/cm2 compared to 1.5 MA/cm2) than the buffer with the thinnest dead layer Ta 5/Ru 20/Ta 5. We can account for these results by considering the difference in damping which compensates for the difference in the switching barrier heights.

  4. Effect of Alloy 625 Buffer Layer on Hardfacing of Modified 9Cr-1Mo Steel Using Nickel Base Hardfacing Alloy

    NASA Astrophysics Data System (ADS)

    Chakraborty, Gopa; Das, C. R.; Albert, S. K.; Bhaduri, A. K.; Murugesan, S.; Dasgupta, Arup

    2016-04-01

    Dashpot piston, made up of modified 9Cr-1Mo steel, is a part of diverse safety rod used for safe shutdown of a nuclear reactor. This component was hardfaced using nickel base AWS ER NiCr-B alloy and extensive cracking was experienced during direct deposition of this alloy on dashpot piston. Cracking reduced considerably and the component was successfully hardfaced by application of Inconel 625 as buffer layer prior to hardface deposition. Hence, a separate study was undertaken to investigate the role of buffer layer in reducing the cracking and on the microstructure of the hardfaced deposit. Results indicate that in the direct deposition of hardfacing alloy on modified 9Cr-1Mo steel, both heat-affected zone (HAZ) formed and the deposit layer are hard making the thickness of the hard layer formed equal to combined thickness of both HAZ and deposit. This hard layer is unable to absorb thermal stresses resulting in the cracking of the deposit. By providing a buffer layer of Alloy 625 followed by a post-weld heat treatment, HAZ formed in the modified 9Cr-1Mo steel is effectively tempered, and HAZ formed during the subsequent deposition of the hardfacing alloy over the Alloy 625 buffer layer is almost completely confined to Alloy 625, which does not harden. This reduces the cracking susceptibility of the deposit. Further, unlike in the case of direct deposition on modified 9Cr-1Mo steel, dilution of the deposit by Ni-base buffer layer does not alter the hardness of the deposit and desired hardness on the deposit surface could be achieved even with lower thickness of the deposit. This gives an option for reducing the recommended thickness of the deposit, which can also reduce the risk of cracking.

  5. Investigation of hole injection enhancement by MoO{sub 3} buffer layer in organic light emitting diodes

    SciTech Connect

    Haitao, Xu; Xiang, Zhou

    2013-12-28

    An MoO{sub 3} buffer layer prepared by thermal evaporation as hole injection layer was investigated in organic light emitting diodes. The MoO{sub 3} film inserted between the anode and hole transport layer decreased the operating voltage and enhanced power efficiency. Introduction of 1 nm MoO{sub 3} film, which was found to be the optimum layer thickness, resulted in 45% increase in efficiency compared with traditional ITO anode. Results from atomic force microscopy and photoemission spectroscopy showed that smooth surface morphology and suitable energy level alignment of ITO/MoO{sub 3} interface facilitated hole injection and transport. The hole injection and transport mechanism at the ITO/MoO{sub 3} interface in thin and thick buffer layers were analyzed.

  6. Cobalt disilicide buffer layer for YBCO film on silicon

    SciTech Connect

    Belousov, I.; Rudenko, E.; Linzen, S.; Seidel, P.

    1997-02-01

    The CoSi{sub 2} films were used as buffer layers of YBCO/CoSi{sub 2}/Si(100), YBCO/ZrO{sub 2}/CoSi{sub 2}/Si(100) and YBCO/CeO{sub 2}/YSZ/CoSi{sub 2}/epi-Si/Al{sub 2}O{sub 3} heterostructures in this work. Transition temperatures of YBCO films were obtained up to 86K for YBCO films deposited by laser ablation on the top of CeO{sub 2}/YSZ/CoSi{sub 2}/Si/Al{sub 2}O{sub 3} structure. Local nucleation on the crystal defects of silicon, the phenomenon of lateral directed growth (DLG) and agglomeration of CoSi{sub 2} phase are responsible for grain boundaries (GB) position in CoSi{sub 2} layer and its roughness. The roughness was decreased using an additional Zr film on the top structure.

  7. Buffer layers on rolled nickel or copper as superconductor substrates

    DOEpatents

    Paranthaman, Mariappan; Lee, Dominic F.; Kroeger, Donald M.; Goyal, Amit

    2000-01-01

    Buffer layer architectures are epitaxially deposited on biaxially-textured rolled substrates of nickel and/or copper and their alloys for high current conductors, and more particularly buffer layer architectures such as Y.sub.2 O.sub.3 /Ni, YSZ/Y.sub.2 O.sub.3 /Ni, Yb.sub.2 O.sub.3 /Ni, Yb.sub.2 O.sub.3 /Y.sub.2 O.sub.3 /Ni, Yb.sub.2 O.sub.3 /CeO.sub.2 /Ni, RE.sub.2 O.sub.3 /Ni (RE=Rare Earth), and Yb.sub.2 O.sub.3 /YSZ/CeO.sub.2 /Ni, Y.sub.2 O.sub.3 /Cu, YSZ/Y.sub.2 O.sub.3 /Cu, Yb.sub.2 O.sub.3 /Cu, Yb.sub.2 O.sub.3 /Y.sub.2 O.sub.3 /Cu, Yb.sub.2 O.sub.3 /CeO.sub.2 /Cu, RE.sub.2 O.sub.3 /Cu, and Yb.sub.2 O.sub.3 /YSZ/CeO.sub.2 /Cu. Deposition methods include physical vapor deposition techniques which include electron-beam evaporation, rf magnetron sputtering, pulsed laser deposition, thermal evaporation, and solution precursor approach, which includes chemical vapor deposition, combustion CVD, metal-organic decomposition, sol-gel processing, and plasma spray.

  8. Morphology and arrangement of InN nanocolumns deposited by radio-frequency sputtering: Effect of the buffer layer

    NASA Astrophysics Data System (ADS)

    Monteagudo-Lerma, L.; Valdueza-Felip, S.; Núñez-Cascajero, A.; Ruiz, A.; González-Herráez, M.; Monroy, E.; Naranjo, F. B.

    2016-01-01

    We present the structural and optical properties of (0001)-oriented nanocolumnar films of InN deposited on c-sapphire substrates by radio-frequency reactive sputtering. It is observed that the column density and dimensions are highly dependent on the growth parameters of the buffer layer. We investigate four buffer layers consisting of (i) 30 nm of low-growth-rate InN, (ii) 30 nm of AlN deposited on the unbiased substrate (us), (iii) 30 nm of AlN deposited on the reverse-biased substrate (bs), and (iv) a 60-nm-thick bilayer consisting of 30-nm-thick bs-AlN deposited on top of 30-nm-thick us-AlN. Differences in the layer nucleation process due to the buffer layer induce variations of the column density in the range of (2.5-16)×109 cm-2, and of the column diameter in the range of 87-176 nm. Best results in terms of mosaicity are obtained using the bs-AlN buffer layer, which leads to a full width at half-maximum of the InN(0002) rocking curve of 1.2°. A residual compressive strain is still present in the nanocolumns. All samples exhibit room temperature photoluminescence emission at ~1.6 eV, and an apparent optical band gap at ~1.7 eV estimated from linear optical transmittance measurements.

  9. Structure and magnetic properties of ultrathin Ni films on Pt(111) with Co buffer layers

    NASA Astrophysics Data System (ADS)

    Shern, C. S.; Ho, H. Y.; Lin, S. H.; Su, C. W.

    2004-12-01

    The growth mode and the structure of ultrathin Ni films on Pt(111) with Co buffer layers were studied by low-energy electron diffraction (LEED) and Auger electron spectroscopy. The comparative study of the magnetic properties between Ni/Pt(111) and Ni/1 ML Co/Pt(111) was investigated by magneto-optical Kerr effect. The oscillation of the specular beam of LEED and the Auger uptake curve were used to calibrate the thickness of Ni overlayers and to study the growth mode of Ni thin films on 1 ML Co/Pt(111) . The study of the alloy formation for Ni/1 ML Co/Pt(111) showed that the temperature for mixing Ni and Co in the upper interface without diffusing into the bulk of Pt is independent of the thickness of Ni overlayers. By further increasing the temperature, Co and Ni diffuse into Pt bulk simultaneously to form Co-Pt , Ni-Pt , and Ni-Co-Pt alloys. The temperature of the formation of these alloys is dependent on the Ni thickness. Studies of the magnetic properties showed that the easy axis of the magnetization changed from the cant to the out-of-plane direction when the Co buffer layer was inserted on Ni/Pt(111) . The alloy formation causes some interesting changes in the polar Kerr signal. The enhancement in the out-of-plane magnetization of Ni/Co/Pt(111) is mainly contributed by the formation of Co-Pt alloy.

  10. Doped Y.sub.2O.sub.3 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

    2007-08-21

    A laminated conductor includes a metallic substrate having a surface, a biaxially textured buffer layer supported by the surface of the metallic substrate, the biaxially textured buffer layer comprising Y.sub.2O.sub.3 and a dopant for blocking cation diffusion through the Y.sub.2O.sub.3, and a biaxially textured conductor layer supported by the biaxially textured buffer layer.

  11. A study on intermediate buffer layer of coated Fiber Bragg Grating cryogenic temperature sensors

    NASA Astrophysics Data System (ADS)

    Freitas, R.; Araujo, F.; Araujo, J.; Neumann, H.; Ramalingam, R.

    2015-12-01

    The sensor characteristics of a coated Fiber Bragg grating (FBG) thermal sensor for cryogenic temperatures depends mainly on the coating materials. The sensitivity of the coated FBG can be improved by enhancing the effective thermal strain transfer between the different layers and the bare FBG. The dual coated FBG's has a primary layer and the secondary layer. The primary coating acts as an intermediate buffer between the secondary coating and the bare FBG. The outer secondary coating is normally made of metals with high thermal expansion coefficient. In this work, a detailed study is carried out on chromium and titanium intermediate buffer layers with various coating thicknesses and combinations. To improve the sensitivity, the secondary coating layer was tested with Indium, Lead and Tin. The sensors were then calibrated in a cryogenic temperature calibration facility at Institute of Technical Physics (ITEP), Karlsruhe Institute of Technology. The sensors were subjected to several thermal cycles between 4.2 and 80 K to study the sensor performance and its thermal characteristics. The sensor exhibits a Bragg wavelength shift of 13pm at 20K. The commercially available detection equipment with a resolution of 1pm can result in a temperature resolution of 0.076 K at 20K.

  12. Improvement of the interfacial Dzyaloshinskii-Moriya interaction by introducing a Ta buffer layer

    SciTech Connect

    Kim, Nam-Hui; Jung, Jinyong; Cho, Jaehun; You, Chun-Yeol; Han, Dong-Soo; Kim, June-Seo Swagten, Henk J. M.

    2015-10-05

    We report systematic measurements of the interfacial Dzyaloshinskii-Moriya interaction (iDMI) by employing Brillouin light scattering in Pt/Co/AlO{sub x} and Ta/Pt/Co/AlO{sub x} structures. By introducing a tantalum buffer layer, the saturation magnetization and the interfacial perpendicular magnetic anisotropy are significantly improved due to the better interface between heavy metal and ferromagnetic layer. From the frequency shift between Stokes- and anti-Stokes spin-waves, we successively obtain considerably larger iDM energy densities (D{sub max} = 1.65 ± 0.13 mJ/m{sup 2} at t{sub Co} = 1.35 nm) upon adding the Ta buffer layer, despite the nominally identical interface materials. Moreover, the energy density shows an inverse proportionality with the Co layer thickness, which is the critical clue that the observed iDMI is indeed originating from the interface between the Pt and Co layers.

  13. Superconducting composite with multilayer patterns and multiple buffer layers

    DOEpatents

    Wu, X.D.; Muenchausen, R.E.

    1993-10-12

    An article of manufacture is described including a substrate, a patterned interlayer of a material selected from the group consisting of magnesium oxide, barium-titanium oxide or barium-zirconium oxide, the patterned interlayer material overcoated with a secondary interlayer material of yttria-stabilized zirconia or magnesium-aluminum oxide, upon the surface of the substrate whereby an intermediate article with an exposed surface of both the overcoated patterned interlayer and the substrate is formed, a coating of a buffer layer selected from the group consisting of cerium oxide, yttrium oxide, curium oxide, dysprosium oxide, erbium oxide, europium oxide, iron oxide, gadolinium oxide, holmium oxide, indium oxide, lanthanum oxide, manganese oxide, lutetium oxide, neodymium oxide, praseodymium oxide, plutonium oxide, samarium oxide, terbium oxide, thallium oxide, thulium oxide, yttrium oxide and ytterbium oxide over the entire exposed surface of the intermediate article, and, a ceramic superconductor. 5 figures.

  14. Buffer effects of Ag layers on magneto-optical Co/Ge(1 0 0) ultrathin films

    NASA Astrophysics Data System (ADS)

    Su, C. W.; Tsay, J. S.; Yao, Y. D.

    2006-09-01

    Magnetic properties of the Co/Ag/Ge(1 0 0) films grown at room temperature and 200 K were studied by the surface magneto-optical Kerr effect (SMOKE). More than 1.5 monolayer Ag buffer layers not only effectively block the interdiffusion between the capped Co layers and the Ge(1 0 0) substrate but also stabilize the magnetic phase. The temperature and thickness dependence on coercivity measurements show that interactions upon the interfaces are strongly correlated to the microstructures.

  15. Reducing interface recombination for Cu(In,Ga)Se{sub 2} by atomic layer deposited buffer layers

    SciTech Connect

    Hultqvist, Adam; Bent, Stacey F.; Li, Jian V.; Kuciauskas, Darius; Dippo, Patricia; Contreras, Miguel A.; Levi, Dean H.

    2015-07-20

    Partial CuInGaSe{sub 2} (CIGS) solar cell stacks with different atomic layer deposited buffer layers and pretreatments were analyzed by photoluminescence (PL) and capacitance voltage (CV) measurements to investigate the buffer layer/CIGS interface. Atomic layer deposited ZnS, ZnO, and SnO{sub x} buffer layers were compared with chemical bath deposited CdS buffer layers. Band bending, charge density, and interface state density were extracted from the CV measurement using an analysis technique new to CIGS. The surface recombination velocity calculated from the density of interface traps for a ZnS/CIGS stack shows a remarkably low value of 810 cm/s, approaching the range of single crystalline II–VI systems. Both the PL spectra and its lifetime depend on the buffer layer; thus, these measurements are not only sensitive to the absorber but also to the absorber/buffer layer system. Pretreatment of the CIGS prior to the buffer layer deposition plays a significant role on the electrical properties for the same buffer layer/CIGS stack, further illuminating the importance of good interface formation. Finally, ZnS is found to be the best performing buffer layer in this study, especially if the CIGS surface is pretreated with potassium cyanide.

  16. Effect of Reaction Temperature of CdS Buffer Layers by Chemical Bath Deposition Method.

    PubMed

    Kim, Hye Jin; Kim, Chae-Woong; Jung, Duk Young; Jeong, Chaehwan

    2016-05-01

    This study investigated CdS deposition on a Cu(In,Ga)Se2 (CIGS) film via chemical bath deposition (CBD) in order to obtain a high-quality optimized buffer layer. The thickness and reaction temperature (from 50 degrees C to 65 degrees C) were investigated, and we found that an increase in the reaction temperature during CBD, resulted in a thicker CdS layer. We obtained a thin film with a thickness of 50 nm at a reaction temperature of 60 degrees C, which also exhibited the highest photoelectric conversion efficiency for use in solar cells. Room temperature time-resolved photoluminescence (TR-PL) measurements were performed on the Cu(In,Ga)Se2 (CIGS) thin film and CdS/CIGS samples to determine the recombination process of the photo-generated minority carrier. The device performance was found to be dependent on the thickness of the CdS layer. As the thickness of the CdS increases, the fill factor and the series resistance increased to 61.66% and decreased to 8.35 Ω, respectively. The best condition was observed at a reaction temperature of 60 degrees C, and its conversion efficiency was 12.20%. PMID:27483883

  17. Lattice-matched HfN buffer layers for epitaxy of GaN on Si

    SciTech Connect

    Armitage, Robert; Yang, Qing; Feick, Henning; Gebauer, Joerg; Weber, Eicke R.; Shinkai, Satoko; Sasaki, Katsutaka

    2002-05-08

    Gallium nitride is grown by plasma-assisted molecular-beam epitaxy on (111) and (001) silicon substrates using sputter-deposited hafnium nitride buffer layers. Wurtzite GaN epitaxial layers are obtained on both the (111) and (001) HfN/Si surfaces, with crack-free thickness up to 1.2 (mu)m. Initial results for GaN grown on the (111) surface show a photoluminescence peak width of 17 meV at 11 K, and an asymmetric x-ray rocking curve width of 20 arcmin. Wurtzite GaN on HfN/Si(001) shows reduced structural quality and peculiar low-temperature luminescence features. However, growth on the (001) surface results in nearly stress-free films, suggesting that much thicker crack-free layers could be obtained.

  18. Annealing of an AlN buffer layer in N2-CO for growth of a high-quality AlN film on sapphire

    NASA Astrophysics Data System (ADS)

    Miyake, Hideto; Nishio, Gou; Suzuki, Shuhei; Hiramatsu, Kazumasa; Fukuyama, Hiroyuki; Kaur, Jesbains; Kuwano, Noriyuki

    2016-02-01

    The annealing of an AlN buffer layer in a carbon-saturated N2-CO gas on a sapphire substrate was investigated. The crystal quality of the buffer layer was significantly improved by annealing at 1650-1700 °C. An AlN buffer layer with a thickness of 300 nm was grown by metalorganic vapor phase epitaxy (MOVPE), and was annealed at 1700 °C for 1 h. We fabricated a 2-µm-thick AlN layer on the annealed AlN buffer layer by MOVPE. The full widths at half maximum of the (0002)- and (10\\bar{1}2)-plane X-ray rocking curves were 16 and 154 arcsec, respectively, and the threading dislocation density was 4.7 × 108 cm-2.

  19. Development of Solution Buffer Layers for RABiTS Based YBCO Coated Conductors

    SciTech Connect

    Paranthaman, Mariappan Parans; Qiu, Xiaofeng; List III, Frederick Alyious; Zhang, Yifei; Li, Xiaoping; Sathyamurthy, Srivatsan; Thieme, C. L. H.; Rupich, M. W.

    2011-01-01

    Abstract The main objective of this research is to find a suitable alternate solution based seed layer for the standard RABiTS three-layer architecture of physical vapor deposited CeO cap/YSZ barrier/Y O seed on Ni-5%W metal tape. In the present work, we have identified CeO buffer layer as a potential replacement for Y O seeds. Using a metal-organic deposition (MOD) process, we have grown smooth, crack-free, epitaxial thin films of CeO (pure and Zr, Cu and Gd-doped) directly on biaxially textured Ni-5W substrates in short lengths. Detailed XRD studies indicate that a single epitaxial CeO phase with slightly improved out-of-plane texture compared to the texture of the underlying Ni-W substrates can be achieved in pure, undoped CeO samples. We have also demonstrated the growth of YSZ barrier layers on pure CeO seeds using sputtering. Both sputtered CeO cap layers and MOD-YBCO films were grown epitaxially on these YSZ-buffered MOD-CeO /Ni-5W substrates. High critical currents per unit width, of 264 A/cm (critical current density, of 3.3 MA/cm ) at 77 K and 0.01 T was achieved for 0.8 m thick MOD-YBCO films grown on MOD-CeO seeds. These results indicate that CeO films can be grown directly on Ni-5W substrates and still support high performance YBCO coated conductors. This work holds promise for a route for producing low-cost buffer architecture for RABiTS based YBCO coated conductors.

  20. Development of Solution Buffer Layers for RABiTS Based YBCO Coated Conductors

    SciTech Connect

    Paranthaman, Mariappan Parans; Qiu, Xiaofeng; Kim, Kyunghoon; Shi, D.; Zhang, Yifei; Li, Xiaoping; Sathyamurthy, Srivatsan; Thieme, C. L. H.; Rupich, M. W.

    2010-01-01

    The main objective of this research is to find a suitable alternate solution based seed layer for the standard RABiTS three-layer architecture of physical vapor deposited CeO2 cap/YSZ barrier/Y2O3 seed on Ni-5%W metal tape. In the present work, we have identified CeO2 buffer layer as a potential replacement for Y2O3 seeds. Using a metal-organic deposition (MOD) process, we have grown smooth, crack-free, epitaxial thin films of CeO2 (both pure and Zr, Cu and Gd-doped) directly on biaxially textured Ni-5W substrates in short lengths. Detailed XRD studies indicate that a single epitaxial CeO2 phase with slightly improved out-of-plane texture compared to the texture of underlying Ni-W substrates can be achieved in pure, undoped CeO2 samples. We have also demonstrated the growth of YSZ barrier layers on pure CeO2 seeds using sputtering. Both sputtered CeO2 cap layers and MOD-YBCO films were grown epitaxially on these YSZ-buffered MOD-CeO2/Ni-5W substrates. High critical currents per unit width, Ic of 264 A/cm (critical current density, Jc of 3.3 MA/cm2) at 77 K and 0.01 T was achieved for 0.8 m thick MOD-YBCO films grown on MOD-CeO2 seeds. These results indicate that CeO2 films can be grown directly on Ni-5W substrates and still support high performance YBCO coated conductors. This work holds promise for a route for producing low-cost buffer architecture for RABiTS based YBCO coated conductors.

  1. Development of buffer layers by chemical solution deposition for YBCO coated conductors

    NASA Astrophysics Data System (ADS)

    Akin, Yalcin

    Short length YBCO coated conductors have been fabricated by vacuum thin film deposition techniques. However, the fabrication process increases the cost, and makes them impractical to use for commercial applications even if they are fabricated in kilometer lengths. YBCO coated conductors could be available in the market with a cheaper price by developing non-vacuum deposition techniques. The objective of this research was to investigate development of buffer layers by chemical solution deposition technique for YBCO coated conductors. Buffer layer structures are mainly used to prevent metal ion diffusion, and to reduce the lattice mismatch between YBCO and the metallic substrate. The technical approach, which was adapted here, is the reel-to-reel sol-gel dip coating process to fabricate long length coatings by developing buffer layers' chemical solutions. Rolling assisted biaxially textured Ni substrates were used for deposition of buffer layers. Cold rolled Ni strips were heat-treated at certain conditions to form biaxially textured structure, which became templates for textured growth of buffer layers that is necessary to obtain high critical current in the coated conductors. CeO2 was chosen as a buffer layers because it has been recognized as one of the best cap layers. Growth of highly textured, crack free, pinhole free and smooth CeO2 buffer layers have been demonstrated by chemical solution deposition technique on biaxially textured substrates. A new buffer layer with pseudocubic lattice parameters matching YBCO, (Eu0.893Yb0.107)2O3, was developed for the first time by using a mixture of Eu2O 3 and Yb2O3 to eliminate lattice mismatch, which adversely affected the critical current of the coated conductors. Highly textured (Eu0.893Yb0.107)2O3 buffer layers were deposited on biaxially textured Ni substrates by chemical solution deposition technique. Finally, the growth of CeO2 and (Eu0.893Yb 0.107)2O3 buffer layers were investigated on oxide layers because both Ce

  2. Graphene Growth on Pre-patterned Copper Film with Nickel as a Buffer Layer

    NASA Astrophysics Data System (ADS)

    Li, Yang; Deng, Wu-Zhu; Wang, Dong-Zhao; Chen, Yang-Yang; Zhou, Wen-Li

    2015-11-01

    Selective graphene growth has been simultaneously achieved on oxidized silicon substrate with three kinds of pre-patterned rectangular metal films, i.e., Cu/Ni double layer, and Ni and Cu single layer film, by atmospheric chemical vapor deposition at 1020°C. The top graphene maintains the micron-scale patterning of the metal film underneath. It was found that single layer graphene growth is more favorable on the Cu/Ni double layer film than on either single layer. The morphology and structure study of the pre-patterned metal substrates before and after graphene growth indicated that Ni functions as a buffer layer to significantly weaken the lattice mismatch between the copper and silicon substrate, resulting in a smoother and larger grain-sized Cu surface. It is also suggested that Ni diffuses to the Cu surface and participates in the graphene growth during the chemical vapor deposition (CVD) process. Defect-free single layer graphene growth can be obtained when the ratio of Cu/Ni is appropriate with respect to their thickness and the feature size of rectangular patterning.

  3. Superconducting composite with multilayer patterns and multiple buffer layers

    DOEpatents

    Wu, Xin D.; Muenchausen, Ross E.

    1993-01-01

    An article of manufacture including a substrate, a patterned interlayer of a material selected from the group consisting of magnesium oxide, barium-titanium oxide or barium-zirconium oxide, the patterned interlayer material overcoated with a secondary interlayer material of yttria-stabilized zirconia or magnesium-aluminum oxide, upon the surface of the substrate whereby an intermediate article with an exposed surface of both the overcoated patterned interlayer and the substrate is formed, a coating of a buffer layer selected from the group consisting of cerium oxide, yttrium oxide, curium oxide, dysprosium oxide, erbium oxide, europium oxide, iron oxide, gadolinium oxide, holmium oxide, indium oxide, lanthanum oxide, manganese oxide, lutetium oxide, neodymium oxide, praseodymium oxide, plutonium oxide, samarium oxide, terbium oxide, thallium oxide, thulium oxide, yttrium oxide and ytterbium oxide over the entire exposed surface of the intermediate article, and, a ceramic superco n FIELD OF THE INVENTION The present invention relates to the field of superconducting articles having two distinct regions of superconductive material with differing in-plane orientations whereby the conductivity across the boundary between the two regions can be tailored. This invention is the result of a contract with the Department of Energy (Contract No. W-7405-ENG-36).

  4. Method of deforming a biaxially textured buffer layer on a textured metallic substrate and articles therefrom

    DOEpatents

    Lee, Dominic F.; Kroeger, Donald M.; Goyal, Amit

    2000-01-01

    The present invention provides methods and biaxially textured articles having a deformed epitaxial layer formed therefrom for use with high temperature superconductors, photovoltaic, ferroelectric, or optical devices. A buffer layer is epitaxially deposited onto biaxially-textured substrates and then mechanically deformed. The deformation process minimizes or eliminates grooves, or other irregularities, formed on the buffer layer while maintaining the biaxial texture of the buffer layer. Advantageously, the biaxial texture of the buffer layer is not altered during subsequent heat treatments of the deformed buffer. The present invention provides mechanical densification procedures which can be incorporated into the processing of superconducting films through the powder deposit or precursor approaches without incurring unfavorable high-angle grain boundaries.

  5. Preferentially oriented BaTiO3 thin films deposited on silicon with thin intermediate buffer layers

    PubMed Central

    2013-01-01

    Barium titanate (BaTiO3) thin films are prepared by conventional 2-methoxy ethanol-based chemical solution deposition. We report highly c-axis-oriented BaTiO3 thin films grown on silicon substrates, coated with a lanthanum oxynitrate buffer layer of 8.9 nm. The influence of the intermediate buffer layer on the crystallization of BaTiO3 film is investigated. The annealing temperature and buffer layer sintering conditions are optimized to obtain good crystal growth. X-ray diffraction measurements show the growth of highly oriented BaTiO3 thin films having a single perovskite phase with tetragonal geometry. The scanning electron microscopy and atomic force microscopy studies indicate the presence of smooth, crack-free, uniform layers, with densely packed crystal grains on the silicon surface. A BaTiO3 film of 150-nm thickness, deposited on a buffer layer of 7.2 nm, shows a dielectric constant of 270, remnant polarization (2Pr) of 5 μC/cm2, and coercive field (Ec) of 60 kV/cm. PMID:23391429

  6. Method of depositing an electrically conductive oxide buffer layer on a textured substrate and articles formed therefrom

    DOEpatents

    Paranthaman, M. Parans; Aytug, Tolga; Christen, David K.

    2003-09-09

    An article with an improved buffer layer architecture includes a substrate having a textured metal surface, and an electrically conductive lanthanum metal oxide epitaxial buffer layer on the surface of the substrate. The article can also include an epitaxial superconducting layer deposited on the epitaxial buffer layer. An epitaxial capping layer can be placed between the epitaxial buffer layer and the superconducting layer. A method for preparing an epitaxial article includes providing a substrate with a metal surface and depositing on the metal surface a lanthanum metal oxide epitaxial buffer layer. The method can further include depositing a superconducting layer on the epitaxial buffer layer, and depositing an epitaxial capping layer between the epitaxial buffer layer and the superconducting layer.

  7. Method of depositing an electrically conductive oxide buffer layer on a textured substrate and articles formed therefrom

    DOEpatents

    Paranthaman, M. Parans; Aytug, Tolga; Christen, David K.

    2005-10-18

    An article with an improved buffer layer architecture includes a substrate having a textured metal surface, and an electrically conductive lanthanum metal oxide epitaxial buffer layer on the surface of the substrate. The article can also include an epitaxial superconducting layer deposited on the epitaxial buffer layer. An epitaxial capping layer can be placed between the epitaxial buffer layer and the superconducting layer. A method for preparing an epitaxial article includes providing a substrate with a metal surface and depositing on the metal surface a lanthanum metal oxide epitaxial buffer layer. The method can further include depositing a superconducting layer on the epitaxial buffer layer, and depositing an epitaxial capping layer between the epitaxial buffer layer and the superconducting layer.

  8. High Jc YBCO coated conductors on non-magnetic metallic substrate using YSZ-based buffer layer architecture

    NASA Astrophysics Data System (ADS)

    Celentano, G.; Boffa, V.; Ciontea, L.; Fabbri, F.; Galluzzi, V.; Gambardella, U.; Mancini, A.; Petrisor, T.; Rogai, R.; Rufoloni, A.; Varesi, E.

    2002-08-01

    Biaxially aligned YBa 2Cu 3O 7- δ (YBCO) thick films were deposited by pulsed laser ablation technique on cube textured non-magnetic Ni 89V 11 (Ni-V) substrate, using CeO 2/YSZ/CeO 2/NiO buffer layer architecture. The first NiO seed layer was formed by epitaxial oxidation of the Ni-V substrate. Structural analyses show typical full width at half maximum values of φ- and ω-scans less than 10° and 8°, respectively. The highest value obtained for the critical current density at 77 K and zero magnetic field was 6×10 5 A cm -2, which is close to that obtained for YBCO films grown on CeO 2/NiO buffer layer architecture.

  9. Performance improvement of phase-change memory cell using AlSb3Te and atomic layer deposition TiO2 buffer layer

    PubMed Central

    2013-01-01

    A phase change memory (PCM) cell with atomic layer deposition titanium dioxide bottom heating layer is investigated. The crystalline titanium dioxide heating layer promotes the temperature rise in the AlSb3Te layer which causes the reduction in the reset voltage compared to a conventional phase change memory cell. The improvement in thermal efficiency of the PCM cell mainly originates from the low thermal conductivity of the crystalline titanium dioxide material. Among the various thicknesses of the TiO2 buffer layer, 4 nm was the most appropriate thickness that maximized the improvement with negligible sacrifice of the other device performances, such as the reset/set resistance ratio, voltage window, and endurance. PMID:23414571

  10. Alloying of Co ultrathin films on Pt(111) with Ag buffer layers

    NASA Astrophysics Data System (ADS)

    Shern, C. S.; Su, C. W.; Wu, Y. E.; Fu, T. Y.

    2000-07-01

    The structure at the interfaces of Co/Ag/Pt(111) was studied by low-energy electron diffraction, ultraviolet photoelectron spectroscopy, Auger electron spectroscopy, and depth profiling. An atomic exchange occurs between Co and Ag before the formation of a Co-Pt alloy. Ag atoms start moving to the top at 425 K when the coverage of Co is one monolayer. The temperature of the complete exchange between Ag atoms and Co atoms is dependent on the thickness of the Ag buffer layer. The Co-Pt alloy develops after the atomic exchange is complete. The especially small surface free energy of Ag and large strain energy in this system are proposed as the driving force for the exchange.

  11. Microstructures of YBa2Cu3Oy Layers Deposited on Conductive Layer-Buffered Metal Tapes

    NASA Astrophysics Data System (ADS)

    Ichinose, Ataru; Hashimoto, Masayuki; Horii, Shigeru; Doi, Toshiya

    REBa2Cu3Oy (REBCO; RE: rare-earth elements)-coated conductors (CCs) have high potential for use in superconducting devices. In particular, REBCO CCs are useful for superconducting devices working at relatively high temperatures near 77 K. The important issues in their applications are high performance, reliability and low cost. To date, sufficient performance for some applications has almost been achieved by considerable efforts. The establishment of the reliability of superconducting devices is under way at present. The issue of low cost must be resolved to realize the application of superconducting devices in the near future. Therefore, we have attempted several ways to reduce the cost of REBCO CCs. The coated conductors using a Nb-doped SrTiO3 buffer layer and Ni-plated Cu and stainless steel laminate metal tapes have recently been developed to eliminate the use of electric stabilization layers of Cu and Ag, which are expected to reduce the material cost. Good superconducting properties are obtained at 77 K. The critical current density (JC) at 77 K under a magnetic self-field is determined to be more than 2x106 A/cm2. The microstructures of the CCs are analyzed by transmission electron microscopy to obtain a much higher quality. By microscopic structure analysis, an overgrowth of the buffer layer is observed at a grain boundary of the metal substrate, which is one of the reasons for the high JC.

  12. Control of Sn Precipitation and Strain Relaxation in Compositionally Step-Graded Ge1-xSnx Buffer Layers for Tensile-Strained Ge Layers

    NASA Astrophysics Data System (ADS)

    Shimura, Yosuke; Tsutsui, Norimasa; Nakatsuka, Osamu; Sakai, Akira; Zaima, Shigeaki

    2009-04-01

    We investigated the relationship between Sn precipitation and strain relaxation in Ge1-xSnx buffer layers grown by the compositionally step-graded (CSG) method on a virtual Ge substrate. We found that the strain in the upper Ge1-xSnx layers is reduced by Sn precipitation rather than the lateral propagation of misfit dislocations at the interfaces of upper Ge1-xSnx layers in the CSG method. The critical misfit strain was increased to 5.8 ×10-3 compared with that in our previous work by lowering the temperature of the postdeposition annealing, and a Sn content of 6.3% in the Ge1-xSnx buffer layer was achieved with a large degree of strain relaxation using only two stacked layers of the CSG structure. An in-plane tensile strain of 0.62% in a 30-nm-thick Ge layer fabricated on these Ge1-xSnx buffer layers was achieved.

  13. Method for making MgO buffer layers on rolled nickel or copper as superconductor substrates

    DOEpatents

    Paranthaman, Mariappan; Goyal, Amit; Kroeger, Donald M.; List, III, Frederic A.

    2002-01-01

    Buffer layer architectures are epitaxially deposited on biaxially-textured rolled-Ni and/or Cu substrates for high current conductors, and more particularly buffer layer architectures such as MgO/Ag/Pt/Ni, MgO/Ag/Pd/Ni, MgO/Ag/Ni, MgO/Ag/Pd/Cu, MgO/Ag/Pt/Cu, and MgO/Ag/Cu. Techniques used to deposit these buffer layers include electron beam evaporation, thermal evaporation, rf magnetron sputtering, pulsed laser deposition, metal-organic chemical vapor deposition (MOCVD), combustion CVD, and spray pyrolysis.

  14. MgO buffer layers on rolled nickel or copper as superconductor substrates

    DOEpatents

    Paranthaman, Mariappan; Goyal, Amit; Kroeger, Donald M.; List, III, Frederic A.

    2001-01-01

    Buffer layer architectures are epitaxially deposited on biaxially-textured rolled-Ni and/or Cu substrates for high current conductors, and more particularly buffer layer architectures such as MgO/Ag/Pt/Ni, MgO/Ag/Pd/Ni, MgO/Ag/Ni, MgO/Ag/Pd/Cu, MgO/Ag/Pt/Cu, and MgO/Ag/Cu. Techniques used to deposit these buffer layers include electron beam evaporation, thermal evaporation, rf magnetron sputtering, pulsed laser deposition, metal-organic chemical vapor deposition (MOCVD), combustion CVD, and spray pyrolysis.

  15. Critical CuI buffer layer surface density for organic molecular crystal orientation change

    SciTech Connect

    Ahn, Kwangseok; Kim, Jong Beom; Lee, Dong Ryeol; Kim, Hyo Jung; Lee, Hyun Hwi

    2015-01-21

    We have determined the critical surface density of the CuI buffer layer inserted to change the preferred orientation of copper phthalocyanine (CuPc) crystals grown on the buffer layer. X-ray reflectivity measurements were performed to obtain the density profiles of the buffer layers and out-of-plane and 2D grazing-incidence X-ray diffraction measurements were performed to determine the preferred orientations of the molecular crystals. Remarkably, it was found that the preferred orientation of the CuPc film is completely changed from edge-on (1 0 0) to face-on (1 1 −2) by a CuI buffer layer with a very low surface density, so low that a large proportion of the substrate surface is bare.

  16. Lattice curvature generation in graded InxGa1-xAs/GaAs buffer layers

    NASA Astrophysics Data System (ADS)

    Natali, M.; Romanato, F.; Napolitani, E.; de Salvador, D.; Drigo, A. V.

    2000-10-01

    Position dependent lattice tilts in InGaAs/GaAs(001) compositionally graded buffer layers are investigated. The lateral dependence of the tilt defines a concave buffer layer curvature of up to 3 deg cm-1. The buffer layer curvature is associated with a distribution of the misfit dislocation Burgers vectors that varies nearly linearly across the sample. The origin of this peculiar distribution is discussed and is explained in terms of a Burgers-vector selection rule, which governs the cross slip of gliding threading dislocations and that has been experimentally observed by Capano in Phys. Rev. B 45, 11 768 (1992). A quantitative model of lattice curvature formation is presented that satisfactorily accounts for the main features of the observed buffer layer curvature.

  17. Reliability of Intra-Retinal Layer Thickness Estimates

    PubMed Central

    Oberwahrenbrock, Timm; Weinhold, Maria; Mikolajczak, Janine; Zimmermann, Hanna; Paul, Friedemann; Beckers, Ingeborg; Brandt, Alexander U.

    2015-01-01

    Purpose Measurement of intra-retinal layer thickness using optical coherence tomography (OCT) has become increasingly prominent in multiple sclerosis (MS) research. Nevertheless, the approaches used for determining the mean layer thicknesses vary greatly. Insufficient data exist on the reliability of different thickness estimates, which is crucial for their application in clinical studies. This study addresses this lack by evaluating the repeatability of different thickness estimates. Methods Studies that used intra-retinal layer segmentation of macular OCT scans in patients with MS were retrieved from PubMed. To investigate the repeatability of previously applied layer estimation approaches, we generated datasets of repeating measurements of 15 healthy subjects and 13 multiple sclerosis patients using two OCT devices (Cirrus HD-OCT and Spectralis SD-OCT). We calculated each thickness estimate in each repeated session and analyzed repeatability using intra-class correlation coefficients and coefficients of repeatability. Results We identified 27 articles, eleven of them used the Spectralis SD-OCT, nine Cirrus HD-OCT, two studies used both devices and two studies applied RTVue-100. Topcon OCT-1000, Stratus OCT and a research device were used in one study each. In the studies that used the Spectralis, ten different thickness estimates were identified, while thickness estimates of the Cirrus OCT were based on two different scan settings. In the simulation dataset, thickness estimates averaging larger areas showed an excellent repeatability for all retinal layers except the outer plexiform layer (OPL). Conclusions Given the good reliability, the thickness estimate of the 6mm-diameter area around the fovea should be favored when OCT is used in clinical research. Assessment of the OPL was weak in general and needs further investigation before OPL thickness can be used as a reliable parameter. PMID:26349053

  18. Characterization of MFIS Structure with Dy-Doped ZrO2 Buffer Layer

    NASA Astrophysics Data System (ADS)

    Im, J. H.; Ah, G. Z.; Han, D. H.; Park, B. E.

    2011-12-01

    To evaluate the feasibility of DZO thin film as an insulating buffer layer for ferroelectric gate field effect transistors (Fe-FETs) with a metal-ferroelectric-insulator-semiconductor (MFIS) structure, we fabricated DZO/Si and BLT/DZO/Si structures by a sol-gel method. Equivalent oxide thickness (EOT) values of the DZO thin films were about 12.4nm, 11.9nm, 11.2nm and 11.1 nm for 650 °C, 700 °C 750 °C, and 800 °C,, respectively. Hysteresis was observed in all capacitance-voltage (C-V) curves of the DZO/Si structures, but hysteresis of the 750-°C-annealed film was negligible. The leakage current densities of the DZO thin films on Si showed the good characteristics regardless of the annealing temperature variations. The C-V characteristics of Au/300-nm-thick BLT/750-°C-annealed DZO/Si structure showed clockwise hysteresis loops, and the memory window width increased as the bias voltage increased. The maximum value of the memory window width was about 1.9 V at ±7 V.

  19. Growth of lanthanum manganate buffer layers for coated conductors via a metal-organic decomposition process

    NASA Astrophysics Data System (ADS)

    Venkataraman, Kartik

    LaMnO3 (LMO) was identified as a possible buffer material for YBa2Cu3O7-x conductors due to its diffusion barrier properties and close lattice match with YBa2Cu 3O7-x. Growth of LMO films via a metal-organic decomposition (MOD) process on Ni, Ni-5at.%W (Ni-5W), and single crystal SrTiO3 substrates was investigated. Phase-pure LMO was grown via MOD on Ni and SrTiO 3 substrates at temperatures and oxygen pressures within a thermodynamic "process window" wherein LMO, Ni, Ni-5W, and SrTiO3 are all stable components. LMO could not be grown on Ni-5W in the "process window" because tungsten diffused from the substrate into the overlying film, where it reacted to form La and Mn tungstates. The kinetics of tungstate formation and crystallization of phase-pure LMO from the La and Mn acetate precursors are competitive in the temperature range explored (850--1100°C). Temperatures <850°C might mitigate tungsten diffusion from the substrate to the film sufficiently to obviate tungstate formation, but LMO films deposited via MOD require temperatures ≥850°C for nucleation and grain growth. Using a Y2O3 seed layer on Ni-5W to block tungsten from diffusing into the LMO film was explored; however, Y2O3 reacts with tungsten in the "process window" at 850--1100°C. Tungsten diffusion into Y2O3 can be blocked if epitaxial, crack-free NiWO4 and NiO layers are formed at the interface between Ni-5W and Y2O3. NiWO 4 only grows epitaxially if the overlying NiO and buffer layers are thick enough to mechanically suppress (011)-oriented NiWO4 grain growth. This is not the case when a bare 75 nm-thick Y2O3 film on Ni-5W is processed at 850°C. These studies show that the Ni-5W substrate must be at a low temperature to prevent tungsten diffusion, whereas the LMO precursor film must be at elevated temperature to crystallize. An excimer laser-assisted MOD process was used where a Y2O 3-coated Ni-5W substrate was held at 500°C in air and the pulsed laser photo-thermally heated the Y2O3 and LMO

  20. The effect of the carbon nanotube buffer layer on the performance of a Li metal battery

    NASA Astrophysics Data System (ADS)

    Zhang, Ding; Zhou, Yi; Liu, Changhong; Fan, Shoushan

    2016-05-01

    Lithium (Li) metal is one of the most promising candidates as an anode for the next-generation energy storage systems because of its high specific capacity and lowest negative electrochemical potential. But the growth of Li dendrites limits the application of the Li metal battery. In this work, a type of modified Li metal battery with a carbon nanotube (CNT) buffer layer inserted between the separator and the Li metal electrode was reported. The electrochemical results show that the modified batteries have a much better rate capability and cycling performance than the conventional Li metal batteries. The mechanism study by electrochemical impedance spectroscopy reveals that the modified battery has a smaller charge transfer resistance and larger Li ion diffusion coefficient during the deposition process on the Li electrode than the conventional Li metal batteries. Symmetric battery tests show that the interfacial behavior of the Li metal electrode with the buffer layer is more stable than the naked Li metal electrode. The morphological characterization of the CNT buffer layer and Li metal lamina reveals that the CNT buffer layer has restrained the growth of Li dendrites. The CNT buffer layer has great potential to solve the safety problem of the Li metal battery.Lithium (Li) metal is one of the most promising candidates as an anode for the next-generation energy storage systems because of its high specific capacity and lowest negative electrochemical potential. But the growth of Li dendrites limits the application of the Li metal battery. In this work, a type of modified Li metal battery with a carbon nanotube (CNT) buffer layer inserted between the separator and the Li metal electrode was reported. The electrochemical results show that the modified batteries have a much better rate capability and cycling performance than the conventional Li metal batteries. The mechanism study by electrochemical impedance spectroscopy reveals that the modified battery has a

  1. Nanometer-Scale Epitaxial Strain Release in Perovskite Heterostructures Using 'SrAlOx' Sliding Buffer Layers

    SciTech Connect

    Bell, Christopher

    2011-08-11

    We demonstrate the strain release of LaAlO{sub 3} epitaxial film on SrTiO{sub 3} (001) by inserting ultra-thin 'SrAlO{sub x}' buffer layers. Although SrAlO{sub x} is not a perovskite, nor stable as a single phase in bulk, epitaxy stabilizes the perovskite structure up to a thickness of 2 unit cells (uc). At a critical thickness of 3 uc of SrAlO{sub x}, the interlayer acts as a sliding buffer layer, and abruptly relieves the lattice mismatch between the LaAlO{sub 3} filmand the SrTiO{sub 3} substrate, while maintaining crystallinity. This technique may provide a general approach for strain relaxation of perovskite film far below the thermodynamic critical thickness. A central issue in heteroepitaxial filmgrowth is the inevitable difference in lattice constants between the filmand substrate. Due to this lattice mismatch, thin film are subjected to microstructural strain, which can have a significan effect on the filmproperties. This challenge is especially prominent in the rapidly developing fiel of oxide electronics, where much interest is focused on incorporating the emergent physical properties of oxides in devices. Although strain can be used to great effect to engineer unusual ground states, it is often deleterious for bulk first-orde phase transitions, which are suppressed by the strain and symmetry constraints of the substrate. While there are some reports discussing the control of the lattice mismatch in oxides using thick buffer layers, the materials choice, lattice-tunable range, and control of misfit dislocations are still limited. In this Letter, we report the fabrication of strain-relaxed LaAlO{sub 3} (LAO) thin film on SrTiO{sub 3} (STO) (001) using very thin 'SrAlO{sub x}' (SAO) buffer layers. Whereas for 1 or 2 pseudo-perovskite unit cells (uc) of SAO, the subsequent LAO filmis strained to the substrate, at a critical thickness of 3 uc the SAO interlayer abruptly relieves the lattice mismatch between the LAO and the STO, although maintaining the

  2. Crystallization of amorphous silicon thin films using nanoenergetic intermolecular materials with buffer layers

    NASA Astrophysics Data System (ADS)

    Lee, Choong Hee; Jeong, Tae Hoon; Kim, Do Kyung; Jeong, Woong Hee; Kang, Myung-Koo; Hwang, Tae Hyung; Kim, Hyun Jae

    2009-02-01

    Optimization of the crystallization of amorphous silicon (a-Si) using a mixture of nanoenergetic materials of iron oxide/aluminum (Fe 2O 3/Al) was studied. To achieve high-quality polycrystalline Si (poly-Si) thin films, silicon oxide (SiO 2) and silver (Ag) layer were deposited on the a-Si as buffer layers to prevent the metal diffusion in a-Si during thermite reaction and to transport the thermal energy released from nanoenergetic materials, respectively. Raman measurement was used to define the crystallinity of poly-Si. For molar ratio of Al and Fe of 2 with 100-nm-thick-SiO 2, Raman measurement showed the 519.59 cm -1 of peak position and the 5.08 cm -1 of full width at half maximum with 353 MPa of low tensile stress indicating high quality poly-Si thin film. These results showed that optimized thermite reaction could be used successfully in crystallization of a-Si to high -quality poly-Si thin films.

  3. Photovoltaic devices comprising zinc stannate buffer layer and method for making

    DOEpatents

    Wu, Xuanzhi; Sheldon, Peter; Coutts, Timothy J.

    2001-01-01

    A photovoltaic device has a buffer layer zinc stannate Zn.sub.2 SnO.sub.4 disposed between the semiconductor junction structure and the transparent conducting oxide (TCO) layer to prevent formation of localized junctions with the TCO through a thin window semiconductor layer, to prevent shunting through etched grain boundaries of semiconductors, and to relieve stresses and improve adhesion between these layers.

  4. Thick growing multilayer nanobrick wall thin films: super gas barrier with very few layers.

    PubMed

    Guin, Tyler; Krecker, Michelle; Hagen, David Austin; Grunlan, Jaime C

    2014-06-24

    Recent work with multilayer nanocoatings composed of polyelectrolytes and clay has demonstrated the ability to prepare super gas barrier layers from water that rival inorganic CVD-based films (e.g., SiOx). In an effort to reduce the number of layers required to achieve a very low oxygen transmission rate (OTR (<0.01 cc/m(2)·day·atm)) in these nanocoatings, buffered cationic chitosan (CH) and vermiculite clay (VMT) were deposited using layer-by-layer (LbL) assembly. Buffering the chitosan solution and its rinse with 50 mM Trizma base increased the thickness of these films by an order of magnitude. The OTR of a 1.6-μm-thick, six-bilayer film was 0.009 cc/m(2)·day·atm, making this the best gas barrier reported for such a small number of layers. This simple modification to the LbL process could likely be applied more universally to produce films with the desired properties much more quickly. PMID:24914613

  5. Epitaxial NbN/AlN/NbN tunnel junctions on Si substrates with TiN buffer layers

    NASA Astrophysics Data System (ADS)

    Sun, Rui; Makise, Kazumasa; Zhang, Lu; Terai, Hirotaka; Wang, Zhen

    2016-06-01

    We have developed epitaxial NbN/AlN/NbN tunnel junctions on Si (100) substrates with a TiN buffer layer. A 50-nm-thick (200)-oriented TiN thin film was introduced as the buffer layer for epitaxial growth of NbN/AlN/NbN trilayers on Si substrates. The fabricated NbN/AlN/NbN junctions demonstrated excellent tunneling properties with a high gap voltage of 5.5 mV, a large IcRN product of 3.8 mV, a sharp quasiparticle current rise with a ΔVg of 0.4 mV, and a small subgap leakage current. The junction quality factor Rsg/RN was about 23 for the junction with a Jc of 47 A/cm2 and was about 6 for the junction with a Jc of 3.0 kA/cm2. X-ray diffraction and transmission electron microscopy observations showed that the NbN/AlN/NbN trilayers were grown epitaxially on the (200)-orientated TiN buffer layer and had a highly crystalline structure with the (200) orientation.

  6. Growth mechanisms of GaSb heteroepitaxial films on Si with an AlSb buffer layer

    SciTech Connect

    Vajargah, S. Hosseini; Botton, G. A.; Brockhouse Institute for Materials Research, McMaster University, Hamilton, Ontario L8S 4M1; Canadian Centre for Electron Microscopy, McMaster University, Hamilton, Ontario L8S 4M1 ; Ghanad-Tavakoli, S.; Preston, J. S.; Kleiman, R. N.; Centre for Emerging Device Technologies, McMaster University, Hamilton, Ontario L8S 4L7; Department of Engineering Physics, McMaster University, Hamilton, Ontario L8S 4L7

    2013-09-21

    The initial growth stages of GaSb epilayers on Si substrates and the role of the AlSb buffer layer were studied by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). Heteroepitaxy of GaSb and AlSb on Si both occur by Volmer-Weber (i.e., island mode) growth. However, the AlSb and GaSb islands have distinctly different characteristics as revealed through an atomic-resolution structural study using Z-contrast of HAADF-STEM imaging. While GaSb islands are sparse and three dimensional, AlSb islands are numerous and flattened. The introduction of 3D island-forming AlSb buffer layer facilitates the nucleation of GaSb islands. The AlSb islands-assisted nucleation of GaSb islands results in the formation of drastically higher quality planar film at a significantly smaller thickness of films. The interface of the AlSb and GaSb epilayers with the Si substrate was further investigated with energy dispersive X-ray spectrometry to elucidate the key role of the AlSb buffer layer in the growth of GaSb epilayers on Si substrates.

  7. Buffer layer annealing effects on the magnetization reversal process in Pd/Co/Pd systems

    NASA Astrophysics Data System (ADS)

    Fassatoui, A.; Belhi, R.; Vogel, J.; Abdelmoula, K.

    2016-12-01

    We have investigated the effect of annealing the buffer layer on the magnetization reversal behavior in Pd/Co/Pd thin films using magneto-optical Kerr microscopy. It was found that annealing the buffer layer at 150 °C for 1 h decreases the coercivity and increases the saturation magnetization and the effective magnetic anisotropy constant. This study also shows that the annealing induces a change of the magnetization reversal from a mixed nucleation and domain wall propagation process to one dominated by domain wall propagation. This result demonstrates that the main effect of annealing the buffer layer is to decrease the domain wall pinning in the Co layer, favoring the domain wall propagation mode.

  8. The effect of the carbon nanotube buffer layer on the performance of a Li metal battery.

    PubMed

    Zhang, Ding; Zhou, Yi; Liu, Changhong; Fan, Shoushan

    2016-06-01

    Lithium (Li) metal is one of the most promising candidates as an anode for the next-generation energy storage systems because of its high specific capacity and lowest negative electrochemical potential. But the growth of Li dendrites limits the application of the Li metal battery. In this work, a type of modified Li metal battery with a carbon nanotube (CNT) buffer layer inserted between the separator and the Li metal electrode was reported. The electrochemical results show that the modified batteries have a much better rate capability and cycling performance than the conventional Li metal batteries. The mechanism study by electrochemical impedance spectroscopy reveals that the modified battery has a smaller charge transfer resistance and larger Li ion diffusion coefficient during the deposition process on the Li electrode than the conventional Li metal batteries. Symmetric battery tests show that the interfacial behavior of the Li metal electrode with the buffer layer is more stable than the naked Li metal electrode. The morphological characterization of the CNT buffer layer and Li metal lamina reveals that the CNT buffer layer has restrained the growth of Li dendrites. The CNT buffer layer has great potential to solve the safety problem of the Li metal battery. PMID:27181758

  9. Improving performance of inverted organic solar cells using ZTO nanoparticles as cathode buffer layer

    NASA Astrophysics Data System (ADS)

    Tsai, Meng-Yen; Cheng, Wen-Hui; Jeng, Jiann-Shing; Chen, Jen-Sue

    2016-06-01

    In this study, a low-temperature solution-processed zinc tin oxide (ZTO) films are successfully utilized as the cathode buffer layer in the inverted organic P3HT:PCBM bulk heterojunction solar cells. ZTO film cathode buffer layer with an appropriate Sn-doping concentration outperforms the zinc oxide (ZnO) film with an improved power conversion efficiency (1.96% (ZTO film) vs. 1.56% (ZnO film)). Furthermore, ZTO nanoparticles (NPs) are also synthesized via low-temperature solution route and the device with ZTO NPs buffer layer exhibits a significant improvement in device performance to reach a PCE of 2.60%. The crystallinity of the cathode buffer layer plays an influential factor in the performance. From impedance spectroscopy analysis, a correlation between short circuit current (Jsc), carrier life time (τavg) and, thus, PCE is observed. The interplay between composition and crystallinity of the cathode buffer layers is discussed to find their influences on the solar cell performance.

  10. Transport Studies on Nanometer Thick YBa2Cu3O7-δ Multilayers Using Y0.4Pr0.6Cu3O7 and PrBa2(Cu0.8Ga0.2)3O7 as Buffer Layers

    NASA Astrophysics Data System (ADS)

    Wu, Ke; Tipparach, Udom.; Chen, Tar-Pin; Li, Qi; Zeng, X. H.; Wert, E.; Wagner, John. L.; Chen, Quark Y.; Wang, J. T.; Yang, Hong-Chang; Horng, Herng-Er

    We have fabricated PrBa2[Cu1-xGax]3O7 (PBGCO) ceramic samples for x = 0.05, 0.10, 0.15 and 0.20. The electrical resistivities of these samples are many orders of magnitude higher than that of PrBa2Cu3O7 (Pr123) while the other physical properties remain much the same. PBGCO therefore may be a possible buffer layer for YBa2Cu3O7-δ (Y123) superlattices/multilayers. For this reason YBa2Cu3O7-δ/PrBa2(Cu0.8Ga0.2)3O7 (Y123/PBCGO) and YBa2Cu3O7-δ/Y0.4Pr0.6Ba2Cu3O7 (Y123/YPBCO) superlattices were fabricated and their transport properties were studied. It is found that although PBGCO is better for insulating Y123 films in trilayers, inter-Y123 layer coupling exists between separated Y123 layer.

  11. Synthesis of Vertically Aligned ZnO Nanorods on Ni-Based Buffer Layers Using a Thermal Evaporation Process

    NASA Astrophysics Data System (ADS)

    Kuo, Dong-Hau; He, Jheng-Yu; Huang, Ying-Sheng

    2012-03-01

    Uniform, vertically aligned ZnO nanorods have been grown mainly on Au-coated and ZnO-coated sapphire substrates, ZnO- and GaN-coated substrates, or self-catalyzing substrates. Conventionally, Ni-coated substrates have resulted in thick rods with diameter more than 250 nm, rods with nonuniform distribution in diameter, or rods with an alignment problem. In the best result in this paper, slender, uniform, vertically aligned, solely UV-emitting ZnO nanorods with diameter of 110 ± 25 nm and length of 30 ± 10 μm have been successfully grown at 700°C for 2 h on sapphire substrates covered with Ni-based buffer layers by using metallic zinc and oxygen as reactants. Scanning electron microscopy and room-temperature photoluminescence have been used to investigate the effects of process conditions on the slenderness and vertical alignment of the ZnO rods. To develop the desired ZnO nanorods, etched sapphire substrates, a second metallic Sn buffer layer on top of a spin-coated nickel oxide layer, polyvinyl alcohol binder at 10% concentration in solution of iron nitrate, and pyrolysis and reduction reactions were involved. Defect photoemission for thick ZnO rods is attributed to insufficient oxygen supply during the growth process with fixed oxygen flow rate.

  12. Evaluation of methods for application of epitaxial layers of superconductor and buffer layers

    SciTech Connect

    1997-06-01

    The recent achievements in a number of laboratories of critical currents in excess of 1.0x10{sup 6} amp/cm{sup 2} at 77K in YBCO deposited over suitably textured buffer/substrate composites have stimulated interest in the potential applications of coated conductors at high temperatures and high magnetic fields. As of today, two different approaches for obtaining the textured substrates have been identified. These are: Los Alamos National Laboratory`s (LANL) ion-beam assisted deposition called IBAD, to obtain a highly textured yttria-stabilized zirconia (YSZ) buffer on nickel alloy strips, and Oak Ridge National Laboratory`s (ORNL) rolling assisted, bi-axial texturized substrate option called RABiTS. Similarly, based on the published literature, the available options to form High Temperature Superconductor (HTS) films on metallic, semi-metallic or ceramic substrates can be divided into: physical methods, and non-physical or chemical methods. Under these two major groups, the schemes being proposed consist of: - Sputtering - Electron-Beam Evaporation - Flash Evaporation - Molecular Beam Epitaxy - Laser Ablation - Electrophoresis - Chemical Vapor Deposition (Including Metal-Organic Chemical Vapor Deposition) - Sol-Gel - Metal-Organic Decomposition - Electrodeposition, and - Aerosol/Spray Pyrolysis. In general, a spool- to-spool or reel-to-reel type of continuous manufacturing scheme developed out of any of the above techniques, would consist of: - Preparation of Substrate Material - Preparation and Application of the Buffer Layer(s) - Preparation and Application of the HTS Material and Required Post-Annealing, and - Preparation and Application of the External Protective Layer. These operations would be affected by various process parameters which can be classified into: Chemistry and Material Related Parameters; and Engineering and Environmental Based Parameters. Thus, one can see that for successful development of the coated conductors manufacturing process, an

  13. [Study on the Effects of Alq₃:CsF Composite Cathode Buffer Layer on the Performances of CuPc/C₆₀ Solar Cells].

    PubMed

    Zhao, Huan-bin; Sun, Qin-jun; Zhou, Miao; Gao, Li-yan; Hao, Yu-ying; Shi, Fang

    2016-02-01

    This paper introduces the methods improving the performance and stability of copper-phthalocyanine(CuPc) / fullerene (C₆₀) small molecule solar cells by using tris-(8-hydroxyquinoline) aluminum(Alq₃): cesium fluoride(CsF) composite cathode buffer layer. The device with Alq₃:CsF composite cathode buffer layer with a 4 wt. % CsF at a thickness of 5 nm exhibits a power conversion efficiency (PCE) of up to 0.76%, which is an improvement of 49%, compared to a device with single Alq₃ cathode buffer layer and half-lifetime of the cell in air at ambient circumstance without any encapsulation is almost 9.8 hours, 6 times higher than that of without buffer layer, so the stability is maintained. The main reason of the device performance improvement is that doping of CsF can adjust the interface energy alignment, optimize the electronic transmission characteristics of Alq₃ and improve the short circuit current and the fill factor of the device using ultraviolet-visible absorption, external quantum efficiency and single-electron devices. Placed composite cathode buffer layer devices with different time in the air, by comparing and analyzing current voltage curve, Alq₃:CsF can maintain a good stability as Alq₃. Alq₃:CsF layer can block the diffusion of oxygen and moisture so completely as to improve the lifetime of the device. PMID:27209725

  14. Silver hollow optical fibers with acrylic silicone resin coating as buffer layer for sturdy structure

    NASA Astrophysics Data System (ADS)

    Iwai, Katsumasa; Takaku, Hiroyuki; Miyagi, Mitsunobu; Shi, Yi-Wei; Zhu, Xiao-Song; Matsuura, Yuji

    2016-03-01

    For sturdy silver hollow optical fibers, acrylic silicone resin is newly used as a buffer layer between an inner silver layer and a silica capillary. This acrylic silicone resin film prevents the glass surface from chemical and mechanical micro damages during silver plating process, which deteriorate mechanical strength of the hollow fibers. In addition, it keeps high adhesion of the silver layer with the glass surface. We discuss improvement of mechanical strength of the hollow glass fibers without deterioration of optical properties.

  15. Effect of buffer layer and external stress on magnetic properties of flexible FeGa films

    NASA Astrophysics Data System (ADS)

    Zhang, Xiaoshan; Zhan, Qingfeng; Dai, Guohong; Liu, Yiwei; Zuo, Zhenghu; Yang, Huali; Chen, Bin; Li, Run-Wei

    2013-05-01

    We systematically investigated the effect of a Ta buffer layer and external stress on the magnetic properties of magnetostrictive Fe81Ga19 films deposited on flexible polyethylene terephthalate (PET) substrates. The Ta buffer layers could effectively smoothen the rough surface of PET. As a result, the FeGa films grown on Ta buffer layers exhibit a weaker uniaxial magnetic anisotropy and lower coercivity, as compared to those films directly grown on PET substrates. By inward and outward bending the FeGa/Ta/PET samples, external in-plane compressive and tensile stresses were applied to the magnetic films. Due to the inverse magnetostrictive effect of FeGa, both the coercivity and squareness of hysteresis loops for FeGa/Ta films could be well tuned under various strains.

  16. Microstructure of GaN epitaxy on SiC using AlN buffer layers

    SciTech Connect

    Ponce, F.A.; Krusor, B.S.; Major, J.S. Jr.; Plano, W.E.; Welch, D.F.

    1995-07-17

    The crystalline structure of GaN epilayers on (0001) SiC substrates has been studied using x-ray diffraction and transmission microscopy. The films were grown by metalorganic chemical vapor deposition, using AlN buffer layers. X-ray diffraction measurements show negligible strain in the epilayer, and a long-range variation in orientation. Transmission electron lattice images show that the AlN buffer layer consists of small crystallites. The nature of the buffer layer and its interfaces with the substrate and the GaN film is discussed. The defect structure of the GaN film away from the substrate consists mostly of threading dislocations with a density of {similar_to}10{sup 9} cm{sup {minus}2}. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.

  17. Growth and micro structural studies on Yittria Stabilized Zirconia (YSZ) and Strontium Titanate (STO) buffer layers

    NASA Technical Reports Server (NTRS)

    Srinivas, S.; Pinto, R.; Pai, S. P.; Dsousa, D. P.; Apte, P. R.; Kumar, D.; Purandare, S. C.; Bhatnagar, A. K.

    1995-01-01

    Microstructure of Yittria Stabilized Zirconia (YSZ) and Strontium Titanate (STO) of radio frequency magnetron sputtered buffer layers was studied at various sputtering conditions on Si (100), Sapphire and LaAlO3 (100) substrates. The effect of substrate temperatures up to 800 C and sputtering gas pressures in the range of 50 mTorr. of growth conditions was studied. The buffer layers of YSZ and STO showed a strong tendency for columnar growth was observed above 15 mTorr sputtering gas pressure and at high substrate temperatures. Post annealing of these films in oxygen atmosphere reduced the oxygen deficiency and strain generated during growth of the films. Strong c-axis oriented superconducting YBa2Cu3O7-x (YBCO) thin films were obtained on these buffer layers using pulsed laser ablation technique. YBCO films deposited on multilayers of YSZ and STO were shown to have better superconducting properties.

  18. Buffer layer between a planar optical concentrator and a solar cell

    SciTech Connect

    Solano, Manuel E.; Barber, Greg D.; Lakhtakia, Akhlesh; Faryad, Muhammad; Monk, Peter B.; Mallouk, Thomas E.

    2015-09-15

    The effect of inserting a buffer layer between a periodically multilayered isotropic dielectric (PMLID) material acting as a planar optical concentrator and a photovoltaic solar cell was theoretically investigated. The substitution of the photovoltaic material by a cheaper dielectric material in a large area of the structure could reduce the fabrication costs without significantly reducing the efficiency of the solar cell. Both crystalline silicon (c-Si) and gallium arsenide (GaAs) were considered as the photovoltaic material. We found that the buffer layer can act as an antireflection coating at the interface of the PMLID and the photovoltaic materials, and the structure increases the spectrally averaged electron-hole pair density by 36% for c-Si and 38% for GaAs compared to the structure without buffer layer. Numerical evidence indicates that the optimal structure is robust with respect to small changes in the grating profile.

  19. Buffer layer between a planar optical concentrator and a solar cell

    NASA Astrophysics Data System (ADS)

    Solano, Manuel E.; Barber, Greg D.; Lakhtakia, Akhlesh; Faryad, Muhammad; Monk, Peter B.; Mallouk, Thomas E.

    2015-09-01

    The effect of inserting a buffer layer between a periodically multilayered isotropic dielectric (PMLID) material acting as a planar optical concentrator and a photovoltaic solar cell was theoretically investigated. The substitution of the photovoltaic material by a cheaper dielectric material in a large area of the structure could reduce the fabrication costs without significantly reducing the efficiency of the solar cell. Both crystalline silicon (c-Si) and gallium arsenide (GaAs) were considered as the photovoltaic material. We found that the buffer layer can act as an antireflection coating at the interface of the PMLID and the photovoltaic materials, and the structure increases the spectrally averaged electron-hole pair density by 36% for c-Si and 38% for GaAs compared to the structure without buffer layer. Numerical evidence indicates that the optimal structure is robust with respect to small changes in the grating profile.

  20. Coercivity enhancement of Nd-Fe-B thin film magnets by Dy buffer and capping layers

    NASA Astrophysics Data System (ADS)

    You, C. Y.; Wang, J. W.; Lu, Z. X.

    2012-04-01

    The Dy layer was inserted into the structure of SiO2/Ti/Nd-Fe-B/Ti as the buffer or capping layer of the Nd-Fe-B layer. The insertions of Dy layers had no significant influence on the film texture with the easy axis mainly perpendicular to the film plane. The film without Dy layer gave the out-of-plane coercivity of 533 kA/m, maximum magnetic energy product (BH)max of 245 kJ/m3. With a Dy buffer layer, the out-of-plane coercivity and (BH)max were increased to 1074 kA/m, 291 kJ/m3 respectively. The film with Dy capping layer had a coercivity of 1035 kA/m and (BH)max of 286 kJ/m3. Microstructure observations showed that the Nd-rich phases were evolved into grain boundaries from triple junctions by a Dy buffer layer deposition, resulting in a well magnetic decoupling of Nd2Fe14B neighboring grains. Through capping a Dy layer, the environment of grain boundaries had been improved and some Dy diffused into Nd2Fe14B phases, which contributed to the enhancement of magnetic performance.

  1. Surface Plasmon Resonance Enhanced Polymer Solar Cells by Thermally Evaporating Au into Buffer Layer.

    PubMed

    Yao, Mengnan; Jia, Xu; Liu, Yan; Guo, Wenbin; Shen, Liang; Ruan, Shengping

    2015-08-26

    Generally, the surface plasmon resonance (SPR) effect of metal nanoparticles is widely applied on polymer solar cells (PSCs) to improve device performance by doping method into solution. Herein, a diameter-controlled thermally evaporation method was used to realize Au nanoparticles (Au NPs) doping into WO3 anode buffer layer in inverted PSCs. The surface energy differences between Au and WO3 inevitably lead to Au growing up through the process from nucleation, isolated island, aggregation of metal islands to continuous films along with the process of evaporation. The atom force microscopy (AFM) images indicate that critical thickness of Au film formation is 8 nm, which is in accordance with current density-voltage (J-V) and incident photon-to-electron conversion efficiency (IPCE) measurement results of optimal device performance. The power conversion efficiency (PCE) with 8 nm Au is dramatically improved from 4.67 ± 0.13% to 6.63 ± 0.17% compared to the one without Au. Moreover, the optical absorption enhancement is demonstrated by steady state photoluminescence (PL), which agrees well with transmission spectrum. The optical and electrical improvement all suggest that thermal evaporation is the appropriate method to further enhance device performance. PMID:26230868

  2. Automated segmentation of intraretinal layers from spectral-domain macular OCT: reproducibility of layer thickness measurements

    NASA Astrophysics Data System (ADS)

    Lee, Kyungmoo; Abràmoff, Michael D.; Sonka, Milan; Garvin, Mona K.

    2011-03-01

    Changes in intraretinal layer thickness occur in a variety of diseases such as glaucoma, macular edema and diabetes. To segment the intraretinal layers from macular spectral-domain OCT (SD-OCT) scans, we previously introduced an automated multiscale 3-D graph search method and validated its performance by computing unsigned border positioning differences when compared with human expert tracings. However, it is also important to study the reproducibility of resulting layer thickness measurements, as layer thickness is a commonly used clinical parameter. In this work, twenty eight (14 x 2) repeated macular OCT volumes were acquired from the right eyes of 14 normal subjects using two Zeiss-Cirrus SD-OCT scanners. After segmentation of 10 intraretinal layers and rigid registration of layer thickness maps from the repeated OCT scans, the thickness difference of each layer was calculated. The overall mean global and regional thickness differences of 10 intraretinal layers were 0.46 +/- 0.25 μm (1.70 +/- 0.72 %) and 1.16 +/- 0.84 μm (4.03 +/- 2.05 %), respectively. No specific local region showed a consistent thickness difference across the layers.

  3. Determination of graphene layer thickness using optical image processing

    NASA Astrophysics Data System (ADS)

    Cook, Monica; Mani, R. G.

    2015-03-01

    Graphene, a single atomic layer of carbon arranged in a hexagonal lattice structure, is a valuable material in a wide range of research. A significant impediment to graphene research is the need to manually characterize the thickness of high-quality graphene produced via mechanical exfoliation. Traditional methods of characterizing the layer thickness of graphene, including Raman spectroscopy and atomic force microscopy, require expensive equipment and can be damaging to the graphene sample. We examine here a known alternative method for quantitatively determining the layer thickness of graphene on SiO2/Si based on optical image processing, which is quick, inexpensive, and non-invasive. Using RGB images of a candidate graphene sample and a background image, taken with a simple optical microscope and charge-coupled device (CCD) camera, we process the images with an algorithm based on Fresnel's law to obtain the contrast spectrum. Each layer of graphene exhibits a unique contrast spectrum for its particular substrate, which is measured and used for accurate layer identification. We also discuss how this algorithm can be generalized to characterize the thickness of other promising two-dimensional materials as well as more complex structures on a variety of substrates.

  4. Exciton-blocking phosphonic acid-treated anode buffer layers for organic photovoltaics

    NASA Astrophysics Data System (ADS)

    Zimmerman, Jeramy D.; Song, Byeongseop; Griffith, Olga; Forrest, Stephen R.

    2013-12-01

    We demonstrate significant improvements in power conversion efficiency of bilayer organic photovoltaics by replacing the exciton-quenching MoO3 anode buffer layer with an exciton-blocking benzylphosphonic acid (BPA)-treated MoO3 or NiO layer. We show that the phosphonic acid treatment creates buffers that block up to 70% of excitons without sacrificing the hole extraction efficiency. Compared to untreated MoO3 anode buffers, BPA-treated NiO buffers exhibit a ˜ 25% increase in the near-infrared spectral response in diphenylanilo functionalized squaraine (DPSQ)/C60-based bilayer devices, increasing the power conversion efficiency under 1 sun AM1.5G simulated solar illumination from 4.8 ± 0.2% to 5.4 ± 0.3%. The efficiency can be further increased to 5.9 ± 0.3% by incorporating a highly conductive exciton blocking bathophenanthroline (BPhen):C60 cathode buffer. We find similar increases in efficiency in two other small-molecule photovoltaic systems, indicating the generality of the phosphonic acid-treated buffer approach to enhance exciton blocking.

  5. The role of buffer layers and double windows layers in a solar cell CZTS performances

    NASA Astrophysics Data System (ADS)

    Mebarkia, C.; Dib, D.; Zerfaoui, H.; Belghit, R.

    2016-07-01

    In the overall context of the diversification of the use of natural resources, the use of renewable energy including solar photovoltaic has become increasingly indispensable. As such, the development of a new generation of photovoltaic cells based on CuZnSnS4 (CZTS) looks promising. Cu2ZnSnS4 (CZTS) is a new film absorber, with good physical properties (band gap energy 1.4-1.6 eV with a large absorption coefficient over 104 cm-1). Indeed, the performance of these cells exceeded 30% in recent years. In the present paper, our work based on modeling and numerical simulation, we used SCAPS to study the performance of solar cells based on Cu2ZnSnS4 (CZTS) and thus evaluate the electrical efficiency η for typical structures of n-ZnO:Al / i-ZnO / n-CdS / p-CZTS and n-ITO / n-ZnO:Al / n-CdS /p-CZTS. Furthermore, the influence of the change of CdS by ZnSeand In2S3buffer layer was treated in this paper.

  6. A Proposal of Evaluation of Frost Layer Thickness

    NASA Astrophysics Data System (ADS)

    Yotsumoto, Hiroyuki; Ishihara, Isao; Tanio, Kenichi; Matsumoto, Ryosuke

    The frosting is an unsteady phenomenon occurs simultaneously with heat and mass transfer. Both the heat and water vapor in the humid air reach the surface of the frost layer and transfer to the cold surface. The frost surface plays an important role as an interface of heat and mass transfer between air-flow and ice-air composite solid layer. However, since the frost layer surface consists of ice and air, and is rough and unsteady, any specific definition of the frost layer thickness is not found. This paper tried to give the definition. The frost layer thickness was measured by using a micro photo-sensing device combined with a light emitter and receiver traversing normal to the frost surface. During traversing the device, a peak response from the device indicates the vertical position corresponding to the maximum frost area exposed to the emitted light i.e. air around the frost inside the frost layer. This position is defined as the frost layer position and it could give an effective frost layer.

  7. Methods of producing free-standing semiconductors using sacrificial buffer layers and recyclable substrates

    SciTech Connect

    Ptak, Aaron Joseph; Lin, Yong; Norman, Andrew; Alberi, Kirstin

    2015-05-26

    A method of producing semiconductor materials and devices that incorporate the semiconductor materials are provided. In particular, a method is provided of producing a semiconductor material, such as a III-V semiconductor, on a spinel substrate using a sacrificial buffer layer, and devices such as photovoltaic cells that incorporate the semiconductor materials. The sacrificial buffer material and semiconductor materials may be deposited using lattice-matching epitaxy or coincident site lattice-matching epitaxy, resulting in a close degree of lattice matching between the substrate material and deposited material for a wide variety of material compositions. The sacrificial buffer layer may be dissolved using an epitaxial liftoff technique in order to separate the semiconductor device from the spinel substrate, and the spinel substrate may be reused in the subsequent fabrication of other semiconductor devices. The low-defect density semiconductor materials produced using this method result in the enhanced performance of the semiconductor devices that incorporate the semiconductor materials.

  8. Anisotropic layers with through-thickness thermal and material variations

    SciTech Connect

    Ferrari, M. )

    1992-09-01

    The thermoelastic problem of an inhomogeneous anisotropic layer with material properties that vary smoothly through the thickness is examined. The problem is solved via a semiinverse technique, relying on the assumptions of the simply-connectedness of the body. The solution is applicable to the analysis of materials with chemical composition gradients and/or temperature-dependent material properties. 14 refs.

  9. Benzocyclobutene (BCB) Polymer as Amphibious Buffer Layer for Graphene Field-Effect Transistor.

    PubMed

    Wu, Yun; Zou, Jianjun; Huo, Shuai; Lu, Haiyan; Kong, Yuecan; Chen, Tangshen; Wu, Wei; Xu, Jingxia

    2015-08-01

    Owing to the scattering and trapping effects, the interfaces of dielectric/graphene or substrate/graphene can tailor the performance of field-effect transistor (FET). In this letter, the polymer of benzocyclobutene (BCB) was used as an amphibious buffer layer and located at between the layers of substrate and graphene and between the layers of dielectric and graphene. Interestingly, with the help of nonpolar and hydrophobic BCB buffer layer, the large-scale top-gated, chemical vapor deposited (CVD) graphene transistors was prepared on Si/SiO2 substrate, its cutoff frequency (fT) and the maximum cutoff frequency (fmax) of the graphene field-effect transistor (GFET) can be reached at 12 GHz and 11 GHz, respectively. PMID:26369142

  10. 'Buffer-layer' technique for the growth of single crystal SiC on Si

    NASA Astrophysics Data System (ADS)

    Addamiano, A.; Sprague, J. A.

    1984-03-01

    The nature of the buffer layers needed for the single-crystal deposition of cubic SiC on Si substrates has been studied. The preparation of chemically formed surface layers of SiC on (100) Si wafers is described. The reaction-grown films of SiC were examined by reflection high-energy electron diffraction using an incident electron energy of 200 keV and by SEM using incident electron energies of 20 and 200 keV. It is concluded that the buffer layer obtained at about 1400 C is a stressed monocrystalline layer of cubic SiC whose crystals contain considerable imperfections. The stresses are due to quenching to room temperature because of the large difference between the thermal expansion coefficients of Si and SiC.

  11. Interface characterization of nanometer scale CdS buffer layer in chalcopyrite solar cell

    NASA Astrophysics Data System (ADS)

    Lin, Shih-Hung; Cheng, Tzu-Huan

    2016-06-01

    The buffer layer of a chalcopyrite solar cell plays an important role in optical responses of open circuit voltage (V oc) and short circuit current (J sc). A CdS buffer layer is applicable on the nanometer scale owing to its high carrier concentration and n-type semiconductor behavior in chalcopyrite solar cells. The thin buffer layer also contributes to the passivation of the absorber surface to reduce defect recombination loss. Non-destructive metrological parameters such as photoluminescence (PL) intensity, external quantum efficiency (EQE), and depth-resolved photovoltage are used to characterize the interface quality of CdS/chalcopyrite. The defects and dangling bonds at the absorber surface will cause interface recombination and reduce the cell performance in build-in voltage distribution. Post annealing can improve Cd ion diffusion from the buffer layer to the absorber surface and reduce the density of defects and dangling bonds. After thermal annealing, the EQE, PL intensity, and minority carrier lifetime are improved.

  12. Effect of buffer layer on thermochromic performances of VO2 films fabricated by magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Zhu, Benqin; Tao, Haizheng; Zhao, Xiujian

    2016-03-01

    As a well-developed industrial fabricating method, magnetron sputtering technique has its distinct advantages for the large-scale production. In order to investigate the effect of buffer layer on the formation and thermochromic performances of VO2 films, using RF magnetron sputtering method, we fabricated three kinds of buffer layers SiO2, TiO2 and SnO2 on soda lime float-glass. Then according to the reactive DC magnetron sputtering method, VO2 films were deposited. Due to the restriction of heat treatment temperature when using soda lime float-glass as substrates, dense rutile phase TiO2 cannot be formed, leading to the formation of vanadium oxide compounds containing Na ions. When using SnO2 as buffer layer, we found that relatively high pure VO2 can be deposited more easily. In addition, compared with the effect of SiO2 buffer layer, we observed an enhanced visible transparency, a decreased infrared emissivity, which should be mainly originated from the modified morphology and/or the hetero-structured VO2/SnO2 interface.

  13. Growth and micro structural studies on Yittria Stabilized Zirconia (YSZ) and Strontium Titanate (STO) buffer layers

    SciTech Connect

    Srinivas, S.; Bhatnagar, A.K.; Pinto, R.

    1994-12-31

    Microstructure of Yittria Stabilized Zirconia (YSZ) and Strontium Titanate (STO) of radio frequency magnetron sputtered buffer layers was studied at various sputtering conditions on Si<100>, Sapphire and LaAlO{sub 3} <100> substrates. The effect of substrate temperatures upto 800 C and sputtering gas pressures in the range of 50 mTorr. of growth conditions was studied. The buffer layers of YSZ and STO showed a strong tendency for columnar structure with variation growth conditions. The buffer layers of YSZ and STO showed orientation. The tendency for columnar growth was observed above 15 mTorr sputtering gas pressure and at high substrate temperatures. Post annealing of these films in oxygen atmosphere reduced the oxygen deficiency and strain generated during growth of the films. Strong c-axis oriented superconducting YBa{sub 2}Cu{sub 9}O{sub 7-x} (YBCO) thin films were obtained on these buffer layers using pulsed laser ablation technique. YBCO films deposited on multilayers of YSZ and STO were shown to have better superconducting properties.

  14. Sol-gel deposition of buffer layers on biaxially textured metal substances

    DOEpatents

    Shoup, Shara S.; Paranthamam, Mariappan; Beach, David B.; Kroeger, Donald M.; Goyal, Amit

    2000-01-01

    A method is disclosed for forming a biaxially textured buffer layer on a biaxially oriented metal substrate by using a sol-gel coating technique followed by pyrolyzing/annealing in a reducing atmosphere. This method is advantageous for providing substrates for depositing electronically active materials thereon.

  15. Grafted polymers inside cylindrical tubes: Chain stretching vs layer thickness

    NASA Astrophysics Data System (ADS)

    Suo, Tongchuan; Whitmore, Mark D.

    2013-04-01

    We present a study of the detailed structure of grafted polymer chains and the layers they form inside cylindrical tubes, using the finitely extensible nonlinear elastic chain model and numerical self-consistent field theory. For very large tube radius, the chain stretching and layer thicknesses are the same as for polymers grafted to a planar surface. For decreasing radius, our calculations indicate that the layer almost always gets thinner, although there can be situations where it is very slightly thicker. However, we find that this thinning is not necessarily due to changes to the polymers: in fact, the root-mean-squared layer thickness would decrease even if the polymers themselves are completely unchanged. Furthermore, we find that the polymer stretching can increase at the same time that the layer thickness decreases. These apparent paradoxes are resolved by analyzing and distinguishing between the volume fraction profiles and monomer number distributions in these systems, including how they change and why. We also find that, in a given system, parts of each polymer move towards the curved surface and parts away from it, and that these differences are key to understanding the behavior.

  16. Retinal nerve fiber layer and ganglion cell-inner plexiform layer thickness in children with obesity

    PubMed Central

    Demir, Selim; Özer, Samet; Alim, Sait; Güneş, Alper; Ortak, Hüseyin; Yılmaz, Resul

    2016-01-01

    AIM To evaluate retinal nerve fiber layer (RNFL) thickness analysis of peripapillary optic nerve head (PONH) and macula as well as ganglion cell-inner plexiform layer (GCIPL) thickness in obese children. METHODS Eighty-five children with obesity and 30 controls were included in the study. The thicknesses of the PONH and macula of each subject's right eye were measured by high-resolution spectral-domain optic coherence tomography (OCT). RESULTS The RNFL thicknesses of central macular and PONH were similar between the groups (all P>0.05). The GCIPL thickness was also similar between the groups. However, the RNFL thickness of temporal outer macula were 261.7±13.7 and 268.9±14.3 µm for the obesity and the control group, respectively (P=0.034). CONCLUSION Obesity may cause a reduction in temporal outer macular RNFL thickness. PMID:27158616

  17. High-Quality AgGaTe2 Layers on Si Substrates with Ag2Te Buffer Layers

    NASA Astrophysics Data System (ADS)

    Uruno, Aya; Kobayashi, Masakazu

    2016-05-01

    AgGaTe2 layers were successfully grown on Si substrates by the close-spaced sublimation method. The Si substrates were confirmed to be etched during AgGaTe2 layer growth when the layer was grown directly on the substrate. To eliminate melt-back etching, a buffer layer of Ag2Te was introduced. It was found that the Ag2Te buffer layer changed into the AgGaTe2 layer during the growth process, and a uniform AgGaTe2 layer with an abrupt interface was formed. Both the diffusion of Ga into Ag2Te and the growth of AgGaTe2 occurred simultaneously. It was confirmed that uniform AgGaTe2 layers could be formed without any traces of the Ag2Te layer or melt-back etching by tuning the growth parameters. A solar cell was also fabricated using the p-AgGaTe2/n-Si heterojunction. This solar cell showed conversion efficiency of approximately 3%.

  18. High-Quality AgGaTe2 Layers on Si Substrates with Ag2Te Buffer Layers

    NASA Astrophysics Data System (ADS)

    Uruno, Aya; Kobayashi, Masakazu

    2016-09-01

    AgGaTe2 layers were successfully grown on Si substrates by the close-spaced sublimation method. The Si substrates were confirmed to be etched during AgGaTe2 layer growth when the layer was grown directly on the substrate. To eliminate melt-back etching, a buffer layer of Ag2Te was introduced. It was found that the Ag2Te buffer layer changed into the AgGaTe2 layer during the growth process, and a uniform AgGaTe2 layer with an abrupt interface was formed. Both the diffusion of Ga into Ag2Te and the growth of AgGaTe2 occurred simultaneously. It was confirmed that uniform AgGaTe2 layers could be formed without any traces of the Ag2Te layer or melt-back etching by tuning the growth parameters. A solar cell was also fabricated using the p-AgGaTe2/n-Si heterojunction. This solar cell showed conversion efficiency of approximately 3%.

  19. EXAMINATION OF DISLOCATIONS IN LATTICE-MISMATCHED GaInAs/BUFFER LAYER/GaAs FOR III-V PHOTOVOLTAICS

    SciTech Connect

    Levander, A.; Geisz, J.

    2007-01-01

    Dislocations act as sites for nonradiative electron/hole pair recombination, which reduces the effi ciency of photovoltaics. Lattice-matched materials can be grown on top of one another without forming a high density of dislocations. However, when the growth of lattice-mismatched (LMM) materials is attempted, many dislocations result from the relaxation of strain in the crystal structure. In an attempt to reduce the number of dislocations that propagate into a solar device when using LMM materials, a compositionally step-graded buffer is placed between the two LMM materials. In order to confi ne the dislocations to the buffer layer and therefore increase material quality and device effi ciency, the growth temperature and thickness of the buffer layer were varied. A GaInP compositionally graded buffer and GaInAs p-n junction were grown on a GaAs substrate in a metal-organic chemical vapor deposition (MOCVD) system. A multibeam optical stress sensor (MOSS) and X-ray diffraction (XRD) were used to characterize the strain in the epilayers. Electrical and optoelectronic properties were measured using a probe station and multimeter setup, solar simulator, and a quantum effi ciency instrument. It was determined that device functionality was highly dependent on the growth temperature of the graded buffer. As growth temperature increased, so did the dislocation density in the device despite an increase in the dislocation velocity, which should have increased the dislocation annihilation rate and the diffusion of dislocations to the edge of the crystal. The thickness of the graded buffer also affected device effi ciency with thinner samples performing poorly. The thinner graded buffer layers had high internal resistances from reduced carrier concentrations. In terms of effi ciency, the empirically derived recipe developed by the scientists at the National Renewable Energy Laboratory (NREL) produced the highest quality cells.

  20. Near independence of OLED operating voltage on transport layer thickness

    SciTech Connect

    Swensen, James S.; Wang, Liang; Polikarpov, Evgueni; Rainbolt, James E.; Koech, Phillip K.; Cosimbescu, Lelia; Padmaperuma, Asanga B.

    2013-01-01

    We report organic light emitting devices (OLEDs) with weak drive voltage dependence on the thickness of the hole transport layer (HTL) for thicknesses up to 1150 Å using the N,N′-Bis(naphthalen-1-yl)-N,N′-bis(phenyl)-benzidine (α-NPD) and N,N'-bis(3-methyl phenyl)-N,N'-diphenyl-[1,1'-biphenyl]-4,4'diamine (TPD), both of which have hole mobilities in the range of 2 × 10-3 cm2V-1s-1. Lower mobility HTL materials show larger operating voltage dependence on thickness. The near independence of the operating voltage for high mobility transport material thickness was only observed when the energy barrier for charge injection into the transport material was minimized. To ensure low injection barriers, a thin film of 2-(3-(adamantan-1-yl)propyl)-3,5,6-trifluorotetracyanoquinodimethane (F3TCNQ-Adl) was cast from solution onto the ITO surface. These results indicate that thick transport layers can be integrated into OLED stacks without the need for bulk conductivity doping.

  1. Terahertz reflection interferometry for automobile paint layer thickness measurement

    NASA Astrophysics Data System (ADS)

    Rahman, Aunik; Tator, Kenneth; Rahman, Anis

    2015-05-01

    Non-destructive terahertz reflection interferometry offers many advantages for sub-surface inspection such as interrogation of hidden defects and measurement of layers' thicknesses. Here, we describe a terahertz reflection interferometry (TRI) technique for non-contact measurement of paint panels where the paint is comprised of different layers of primer, basecoat, topcoat and clearcoat. Terahertz interferograms were generated by reflection from different layers of paints on a metallic substrate. These interferograms' peak spacing arising from the delay-time response of respective layers, allow one to model the thicknesses of the constituent layers. Interferograms generated at different incident angles show that the interferograms are more pronounced at certain angles than others. This "optimum" angle is also a function of different paint and substrate combinations. An automated angular scanning algorithm helps visualizing the evolution of the interferograms as a function of incident angle and also enables the identification of optimum reflection angle for a given paint-substrate combination. Additionally, scanning at different points on a substrate reveals that there are observable variations from one point to another of the same sample over its entire surface area. This ability may be used as a quality control tool for in-situ inspection in a production line. Keywords: Terahertz reflective interferometry, Paint and coating layers, Non-destructive

  2. Compression response of thick layer composite laminates with through-the-thickness reinforcement

    NASA Technical Reports Server (NTRS)

    Farley, Gary L.; Smith, Barry T.; Maiden, Janice

    1992-01-01

    Compression and compression-after-impact (CAI) tests were conducted on seven different AS4-3501-6 (0/90) 0.64-cm thick composite laminates. Four of the seven laminates had through-the-thickness (TTT) reinforcement fibers. Two TTT reinforcement methods, stitching and integral weaving, and two reinforcement fibers, Kevlar and carbon, were used. The remaining three laminates were made without TTT reinforcements and were tested to establish a baseline for comparison with the laminates having TTT reinforcement. Six of the seven laminates consisted of nine thick layers whereas the seventh material was composed of 46 thin plies. The use of thick-layer material has the potential for reducing structural part cost because of the reduced part count (layers of material). The compression strengths of the TTT reinforced laminates were approximately one half those of the materials without TTT reinforcements. However, the CAI strengths of the TTT reinforced materials were approximately twice those of materials without TTT reinforcements. The improvement in CAI strength is due to an increase in interlaminar strength produced by the TTT reinforcement. Stitched laminates had slightly higher compression and CAI strengths than the integrally woven laminates.

  3. Improved performance of microcrystalline silicon solar cell with graded-band-gap silicon oxide buffer layer

    NASA Astrophysics Data System (ADS)

    Shi, Zhen-Liang; Ji, Yun; Yu, Wei; Yang, Yan-Bin; Cong, Ri-Dong; Chen, Ying-Juan; Li, Xiao-Wei; Fu, Guang-Sheng

    2015-07-01

    Microcrystalline silicon (μc-Si:H) solar cell with graded band gap microcrystalline silicon oxide (μc-SiOx:H) buffer layer is prepared by plasma enhanced chemical vapor deposition and exhibits improved performance compared with the cell without it. The buffer layer moderates the band gap mismatch by reducing the barrier of the p/i interface, which promotes the nucleation of the i-layer and effectively eliminates the incubation layer, and then enhances the collection efficiency of the cell in the short wavelength region of the spectrum. The p/i interface defect density also decreases from 2.2 × 1012 cm-2 to 5.0 × 1011 cm-2. This graded buffer layer allows to simplify the deposition process for the μc-Si:H solar cell application. Project supported by the Key Basic Research Project of Hebei Province, China (Grant Nos. 12963930D and 12963929D), the Natural Science Foundation of Hebei Province, China (Grant Nos. F2013201250 and E2012201059), and the Science and Technology Research Projects of the Education Department of Hebei Province, China (Grant No. ZH2012030).

  4. Magnetooptical and crystalline properties of sputtered garnet ferrite film on spinel ferrite buffer layer

    NASA Astrophysics Data System (ADS)

    Furuya, Akinori; Sasaki, Ai-ichiro; Morimura, Hiroki; Kagami, Osamu; Tanabe, Takaya

    2016-09-01

    The purpose of this study is to provide garnet films for volumetric magnetic holography. Volumetric magnetic holography usually employs an easily obtainable short-wavelength laser (visible light, not infrared light) with a large diffraction intensity. Bi-substituted garnet ferrite with a large Faraday rotation is promising for volumetric magnetic holography applications in the visible light region. However, a garnet film without a deteriorated layer must be obtained because a deteriorated layer (minute polycrystalline grains containing an amorphous phase) is formed during the initial deposition on a glass substrate. In particular, the required magnetooptical properties have not been obtained in a thin garnet film (100 nm or less) after annealing (1 h, 700 °C, oxygen atmosphere). Therefore, there is a need for excellent garnet films with the required magnetooptical (MO) properties even if the films are thin. By using a spinel ferrite buffer layer for garnet film deposition, we could obtain a thin garnet film with excellent MO properties. We determined the effect of the initial buffer layer on the crystallinity of the deposited garnet films by observing the film cross section. In addition, we undertook a qualitative estimation of the influence of the crystallinity and optical properties of the garnet film on a glass substrate with a spinel ferrite buffer layer.

  5. Quantification of cell-free layer thickness and cell distribution of blood by optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Lauri, Janne; Bykov, Alexander; Fabritius, Tapio

    2016-04-01

    A high-speed optical coherence tomography (OCT) with 1-μm axial resolution was applied to assess the thickness of a cell-free layer (CFL) and a spatial distribution of red blood cells (RBC) next to the microchannel wall. The experiments were performed in vitro in a plain glass microchannel with a width of 2 mm and height of 0.2 mm. RBCs were suspended in phosphate buffered saline solution at the hematocrit level of 45%. Flow rates of 0.1 to 0.5 ml/h were used to compensate gravity induced CFL. The results indicate that OCT can be efficiently used for the quantification of CFL thickness and spatial distribution of RBCs in microcirculatory blood flow.

  6. Ultraviolet-ozone-treated PEDOT:PSS as anode buffer layer for organic solar cells

    PubMed Central

    2012-01-01

    Ultraviolet-ozone-treated poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS)was used as the anode buffer layer in copper phthalocyanine (CuPc)/fullerene-based solar cells. The power conversion efficiency of the cells with appropriated UV-ozone treatment was found to increase about 20% compared to the reference cell. The improved performance is attributed to the increased work function of the PEDOT:PSS layer, which improves the contact condition between PEDOT:PSS and CuPc, hence increasing the extraction efficiency of the photogenerated holes and decreasing the recombination probability of holes and electrons in the active organic layers. PMID:22901365

  7. Solution-processed In2S3 buffer layer for chalcopyrite thin film solar cells

    NASA Astrophysics Data System (ADS)

    Wang, Lan; Lin, Xianzhong; Ennaoui, Ahmed; Wolf, Christian; Lux-Steiner, Martha Ch.; Klenk, Reiner

    2016-02-01

    We report a route to deposit In2S3 thin films from air-stable, low-cost molecular precursor inks for Cd-free buffer layers in chalcopyrite-based thin film solar cells. Different precursor compositions and processing conditions were studied to define a reproducible and robust process. By adjusting the ink properties, this method can be applied in different printing and coating techniques. Here we report on two techniques, namely spin-coating and inkjet printing. Active area efficiencies of 12.8% and 12.2% have been achieved for In2S3-buffered solar cells respectively, matching the performance of CdS-buffered cells prepared with the same batch of absorbers.

  8. Coincident site lattice-matched growth of semiconductors on substrates using compliant buffer layers

    DOEpatents

    Norman, Andrew

    2016-08-23

    A method of producing semiconductor materials and devices that incorporate the semiconductor materials are provided. In particular, a method is provided of producing a semiconductor material, such as a III-V semiconductor, on a silicon substrate using a compliant buffer layer, and devices such as photovoltaic cells that incorporate the semiconductor materials. The compliant buffer material and semiconductor materials may be deposited using coincident site lattice-matching epitaxy, resulting in a close degree of lattice matching between the substrate material and deposited material for a wide variety of material compositions. The coincident site lattice matching epitaxial process, as well as the use of a ductile buffer material, reduce the internal stresses and associated crystal defects within the deposited semiconductor materials fabricated using the disclosed method. As a result, the semiconductor devices provided herein possess enhanced performance characteristics due to a relatively low density of crystal defects.

  9. Tuning the interfacial hole injection barrier between p-type organic materials and Co using a MoO{sub 3} buffer layer

    SciTech Connect

    Wang Yuzhan; Wee, Andrew T. S.; Cao Liang; Qi Dongchen; Chen Wei; Gao Xingyu

    2012-08-01

    We demonstrate that the interfacial hole injection barrier {Delta}{sub h} between p-type organic materials (i.e., CuPc and pentacene) and Co substrate can be tuned by the insertion of a MoO{sub 3} buffer layer. Using ultraviolet photoemission spectroscopy, it was found that the introduction of MoO{sub 3} buffer layer effectively reduces the hole injection barrier from 0.8 eV to 0.4 eV for the CuPc/Co interface, and from 1.0 eV to 0.4 eV for the pentacene/Co interface, respectively. In addition, by varying the thickness of the buffer, the tuning effect of {Delta}{sub h} is shown to be independent of the thickness of MoO{sub 3} interlayer at both CuPc/Co and pentacene/Co interfaces. This Fermi level pinning effect can be explained by the integer charge-transfer model. Therefore, the MoO{sub 3} buffer layer has the potential to be applied in p-type organic spin valve devices to improve the device performance via reducing the interfacial hole injection barrier.

  10. Leidenfrost point and estimate of the vapour layer thickness

    NASA Astrophysics Data System (ADS)

    Gianino, Concetto

    2008-11-01

    In this article I describe an experiment involving the Leidenfrost phenomenon, which is the long lifetime of a water drop when it is deposited on a metal that is much hotter than the boiling point of water. The experiment was carried out with high-school students. The Leidenfrost point is measured and the heat laws are used to estimate the thickness of the vapour layer, d≈0.06 mm, which prevents the drop from touching the hotplate.

  11. Effects of buffer layers on the structural and electronic properties of InSb films

    SciTech Connect

    Weng, X.; Rudawski, N.G.; Wang, P.T.; Goldman, R.S.; Partin, D.L.; Heremans, J.

    2005-02-15

    We have investigated the effects of various buffer layers on the structural and electronic properties of n-doped InSb films. We find a significant decrease in room-temperature electron mobility of InSb films grown on low-misfit GaSb buffers, and a significant increase in room-temperature electron mobility of InSb films grown on high-misfit InAlSb or step-graded GaSb+InAlSb buffers, in comparison with those grown directly on GaAs. Plan-view transmission electron microscopy (TEM) indicates a significant increase in threading dislocation density for InSb films grown on the low-misfit buffers, and a significant decrease in threading dislocation density for InSb films grown on high-misfit or step-graded buffers, in comparison with those grown directly on GaAs. Cross-sectional TEM reveals the role of the film/buffer interfaces in the nucleation (filtering) of threading dislocations for the low-misfit (high-misfit and step-graded) buffers. A quantitative analysis of electron mobility and carrier-concentration dependence on threading dislocation density suggests that electron scattering from the lattice dilation associated with threading dislocations has a stronger effect on electron mobility than electron scattering from the depletion potential surrounding the dislocations. Furthermore, while lattice dilation is the predominant mobility-limiting factor in these n-doped InSb films, ionized impurity scattering associated with dopants also plays a role in limiting the electron mobility.

  12. MBE grown III-V strain relaxed buffer layers and superlattices characterized by atomic force microscopy

    SciTech Connect

    Howard, A.J.; Fritz, I.J.; Drummond, T.J.; Olsen, J.A.; Hammons, B.E.; Kurtz, S.R.; Brennan, T.M.

    1993-11-01

    Using atomic force microscopy (AFM), the authors have investigated the effects of growth temperature and dopant incorporation on the surface morphology of MBE grown graded buffer layers and strained layer superlattices (SLSs) in the InGaAlAs/GaAs and InAsSb/InSb material systems. The AFM results show quantitatively that over the temperature range from 380 to 545 C, graded in{sub x}Al{sub 1{minus}x}As(x = 0.05 {minus} 0.32) buffer layers grown at high temperatures ({approximately}520 C), and graded In{sub x}Ga{sub 1{minus}x}As (x = 0.05 {minus} 0.33) buffer layers and In{sub 0.4}Ga{sub 0.6}As/In{sub 0.26}Al{sub 0.35}Ga{sub 0.39}As SLSs grown at low temperatures ({approximately}400 C) have the lowest RMS roughness. Also, for SLSs InAs{sub 0.21}Sb{sub 0.79}/InSb, undoped layers grown at 470 C were smoother than undoped layers grown at 420 C and Be-doped layers grown at 470 C. These results illustrate the role of surface tension in the growth of strained layer materials near the melting temperature of the InAs{sub x}Sb{sub {minus}x}/InSb superlattice. Nomarski interference and transmission electron microscopies, IR photoluminescence, x-ray diffraction, and photocurrent spectroscopy were also used to evaluate the relative quality of the material but usually, the results were not conclusive.

  13. Structural and electrical properties of Pb(Zr,Ti)O3 thin films on NiCr substrate modified by LaNiO3 and PbTiO3 buffer layers

    NASA Astrophysics Data System (ADS)

    He, Liang; Cheng, Jinrong; Meng, Zhongyan

    2004-12-01

    Ferroelectric Pb(Zr,Ti)O3 (PZT) thin films were deposited onto the NiCr (NC) substrate by using sol-gel techniques. LaNiO3 (LNO) and PbTiO3 (PT) buffer layers have been introduced to grow single-phase perovskite PZT thin films at the lower temperature of 550°C. The (110) preferred orientation of PZT thin films was favored using LNO and PT buffer layers. Dielectric constant and remnant polarization of PZT thin films on NC with a LNO buffer layer achieved ~ 430 and 13 μC/cm2 respectively. The ferroelectric P-E loops of PZT thin films were shifted towards the positive field by introducing LNO buffer layers. In addition, the coercive field and internal bias field increased with increasing the thickness of LNO layer.

  14. Performance of organic photovoltaics using an ytterbium trifluoride n-type buffer layer

    NASA Astrophysics Data System (ADS)

    Ji, Chan Hyuk; Jang, Ji Min; Oh, Se Young

    2016-03-01

    Ytterbium trifluoride (YbF3) was used as an n-type cathode buffer layer in conventional poly(3-hexylthiophene):[6,6]-phenyl C61 butyric acid methyl ester (P3HT:PC60BM) bulk heterojunction (BHJ) organic photovoltaic cells. This buffer layer acts as an electron-transport layer and improves the open circuit voltage ( V oc), power conversion efficiency (PCE), and interfacial durability of the device. The physical properties and performance of the device were studied using impedance spectroscopy, photocurrent measurements, ultraviolet photoelectron spectroscopy, and atomic force microscopy. The PCE reached to 3.2% with a 65% fill factor under 1 sun irradiation. The PCE decreased to half of its original value after 120 h at room temperature in air or 24 h at 70°C in air. Comparison with Yb and TiOx cathode buffer layers reveals that YbF3 has superior performance and longevity. These findings suggest that YbF3 has the potential to replace costly device encapsulation. [Figure not available: see fulltext.

  15. Electron dynamics of the buffer layer and bilayer graphene on SiC

    SciTech Connect

    Shearer, Alex J.; Caplins, Benjamin W.; Suich, David E.; Harris, Charles B.; Johns, James E.; Hersam, Mark C.

    2014-06-09

    Angle- and time-resolved two-photon photoemission (TPPE) was used to investigate electronic states in the buffer layer of 4H-SiC(0001). An image potential state (IPS) series was observed on this strongly surface-bound buffer layer, and dispersion measurements indicated free-electron-like behavior for all states in this series. These results were compared with TPPE taken on bilayer graphene, which also show the existence of a free-electron-like IPS series. Lifetimes for the n = 2, and n = 3 states were obtained from time-resolved TPPE; slightly increased lifetimes were observed in the bilayer graphene sample for the n = 2 the n = 3 states. Despite the large band gap of graphene at the center of the Brillouin zone, the lifetime results demonstrate that the graphene layers do not behave as a simple tunneling barrier, suggesting that the buffer layer and graphene overlayers play a direct role in the decay of IPS electrons.

  16. Exploring Cd-Zn-O-S alloys for optimal buffer layers in thin-film photovoltaics

    NASA Astrophysics Data System (ADS)

    Varley, J.; He, X.; Mackie, N.; Rockett, A.; Lordi, V.

    2015-03-01

    The development of thin-film photovoltaics has largely focused on alternative absorber materials, while the choices for other layers in the solar cell stack have remained somewhat limited. In particular, cadmium sulfide (CdS) is widely used as the buffer layer in typical record devices utilizing absorbers like Cu(In,Ga)Se2 (CIGSe) or Cu2ZnSnS4 (CZTS) despite leading to a loss of solar photocurrent due to its band gap of 2.4 eV. While different buffers such as Zn(S,O,OH) are beginning to become competitive with CdS, the identification of additional wider-band gap alternatives with electrical properties comparable to or better than CdS is highly desirable. Here we use hybrid functional calculations to characterize CdxZn1-xOyS1-y candidate buffer layers in the quaternary phase space composed by Cd, Zn, O, and S. We focus on the band gaps and band offsets of the alloys to assess strategies for improving absorption losses from conventional CdS buffers while maintaining similar conduction band offsets known to facilitate good device performance. We also consider additional criteria such as lattice matching to identify regions in the composition space that may provide improved epitaxy to CIGSe and CZTS absorbers. Lastly, we incorporate our calculated alloy properties into simulations of typical CIGSe devices to identify the CdxZn1-xOyS1-y buffer compositions that lead to the best performance. This work performed under the auspices of the USDoE by LLNL under Contract DE-AC52-07NA27344 and funded by the DoE EERE through the SunShot BRIDGE program.

  17. Reel-to-reel deposition of epitaxial double-sided MgO buffer layers for coated conductors

    NASA Astrophysics Data System (ADS)

    Xue, Yan; Xiong, Jie; Zhang, Yahui; Zhang, Fei; Zhao, Rui-Peng; Hui, Wang; Wang, Quiling; Cheng, Guo; Zhao, Xiao-Hui; Tao, Bo-Wan

    2016-06-01

    We have successfully employed a double-sided process to deposit MgO buffer layers on both sides of amorphous Y2O3 surface for double-sided YBa2Cu3O7-δ (YBCO) coated conductors (CCs) for the first time, the structure of which is of great prospect to improve the performance and cut the production cost. The biaxial textures of MgO buffer layer are noticeably affected by the ion energy and film thickness, which is demonstrated by X-ray diffraction. The best biaxial texture of double-sided MgO films shows ω-scan of (002) MgO and Φ-scan of (220) MgO yield full width at half maximum values of 4° and 7.8° for one side, respectively, as well as 3.5° and 6.7° for the other side. The subsequent double-sided YBCO films are deposited on the as-prepared MgO template with entire critical current of over 300 A/cm for both sides.

  18. Minimum Wind Dynamic Soaring Trajectories under Boundary Layer Thickness Limits

    NASA Astrophysics Data System (ADS)

    Bousquet, Gabriel; Triantafyllou, Michael; Slotine, Jean-Jacques

    2015-11-01

    Dynamic soaring is the flight technique where a glider, either avian or manmade, extracts its propulsive energy from the non-uniformity of horizontal winds. Albatrosses have been recorded to fly an impressive 5000 km/week at no energy cost of their own. In the sharp boundary layer limit, we show that the popular image, where the glider travels in a succession of half turns, is suboptimal for travel speed, airspeed, and soaring ability. Instead, we show that the strategy that maximizes the three criteria simultaneously is a succession of infinitely small arc-circles connecting transitions between the calm and windy layers. The model is consistent with the recordings of albatross flight patterns. This lowers the required wind speed for dynamic soaring by over 50% compared to previous beliefs. In the thick boundary layer limit, energetic considerations allow us to predict a minimum wind gradient necessary for sustained soaring consistent with numerical models.

  19. Selective growth of Pb islands on graphene/SiC buffer layers

    SciTech Connect

    Liu, X. T.; Miao, Y. P.; Ma, D. Y.; Hu, T. W.; Ma, F. E-mail: kwxu@mail.xjtu.edu.cn; Chu, Paul K.; Xu, K. W. E-mail: kwxu@mail.xjtu.edu.cn

    2015-02-14

    Graphene is fabricated by thermal decomposition of silicon carbide (SiC) and Pb islands are deposited by Pb flux in molecular beam epitaxy chamber. It is found that graphene domains and SiC buffer layer coexist. Selective growth of Pb islands on SiC buffer layer rather than on graphene domains is observed. It can be ascribed to the higher adsorption energy of Pb atoms on the 6√(3) reconstruction of SiC. However, once Pb islands nucleate on graphene domains, they will grow very large owing to the lower diffusion barrier of Pb atoms on graphene. The results are consistent with first-principle calculations. Since Pb atoms on graphene are nearly free-standing, Pb islands grow in even-number mode.

  20. Ultrathin Polyaniline-based Buffer Layer for Highly Efficient Polymer Solar Cells with Wide Applicability

    PubMed Central

    Zhao, Wenchao; Ye, Long; Zhang, Shaoqing; Fan, Bin; Sun, Mingliang; Hou, Jianhui

    2014-01-01

    Interfacial buffer layers often attribute the improved device performance in organic optoelectronic device. Herein, a water-soluble hydrochloric acid doped polyanilines (HAPAN) were utilized as p-type electrode buffer layer in highly efficient polymer solar cells (PSC) based on PBDTTT-EFT and several representative polymers. The PBDTTT-EFT-based conventional PSC featuring ultrathin HAPAN (1.3 nm) delivered high PCE approximately 9%, which is one of the highest values among conventional PSC devices. Moreover, ultrathin HAPAN also exhibited wide applicability in a variety of efficient photovoltaic polymers including PBDTTT-C-T, PTB7, PBDTBDD, PBTTDPP-T, PDPP3T and P3HT. The excellent performances were originated from the high transparency, small film roughness and suitable work function. PMID:25300365

  1. Protein adsorption on poly(N-isopropylacrylamide)-modified silicon surfaces: effects of grafted layer thickness and protein size.

    PubMed

    Yu, Qian; Zhang, Yanxia; Chen, Hong; Wu, Zhaoqiang; Huang, He; Cheng, Chi

    2010-04-01

    In this work, we investigated the protein adsorption on the end-tethered thermoresponsive poly(N-isopropylacrylamide) (PNIPAAm) brushes with varying grafted layer thickness prepared via surface-initiated atom transfer radical polymerization (SI-ATRP) on initiator-immobilized silicon surfaces. The thickness of a grafted layer was modulated by adjusting reaction time and/or solvent composition. The surface properties as a function of thickness were investigated by water contact angle, X-ray photoelectron spectroscopy (XPS), and atomic force microscope (AFM). The influence of PNIPAAm-grafted layer thickness on human serum albumin (HSA) adsorption in phosphate-buffered saline (PBS) (pH 7.4) at different temperature was evaluated using a radiolabeling method. In a lower thickness range (<15 nm), protein adsorption on PNIPAAm-grafted layer shows a thermoresponsive change in a certain extent, but the variation is not remarkable. However, it is interesting to observe that these surfaces exhibit good protein-resistant property. For the surface with a PNIPAAm thickness of 13.4 nm, the HSA adsorption level measured at room temperature was approximately 7 ng/cm2, corresponding to a reduction of 97% compared to the unmodified silicon surface. For thicker PNIPAAm-grafted surface with thickness of 38.1 nm, the adsorption results of three proteins (HSA, fibrinogen, and lysozyme) with different sizes and charges indicate that the PNIPAAm-modified surface exhibits a size-sensitive property of protein adsorption. PMID:20045297

  2. ZnS/Zn(O,OH)S-based buffer layer deposition for solar cells

    DOEpatents

    Bhattacharya, Raghu N.

    2009-11-03

    The invention provides CBD ZnS/Zn(O,OH)S and spray deposited ZnS/Zn(O,OH)S buffer layers prepared from a solution of zinc salt, thiourea and ammonium hydroxide dissolved in a non-aqueous/aqueous solvent mixture or in 100% non-aqueous solvent. Non-aqueous solvents useful in the invention include methanol, isopropanol and triethyl-amine. One-step deposition procedures are described for CIS, CIGS and other solar cell devices.

  3. Law-of-the-wall buffer layer explained by a simplified cospectral budget model

    NASA Astrophysics Data System (ADS)

    Mccoll, K. A.; Katul, G. G.; Gentine, P.; Entekhabi, D.

    2015-12-01

    A series of recent studies have shown that a model of the turbulent vertical velocity variance spectrum (Fvv) combined with a simplified cospectral budget can reproduce many macroscopic flow properties of turbulent wall-bounded flows, including various features of the mean-velocity profile (MVP), i.e., the "law of the wall". While the theory reasonably models the MVP's logarithmic layer, the modelled buffer layer displays insufficient curvature compared to measurements at moderate Reynolds number. The theory is re-examined here using a DNS dataset at moderate Reynolds number. Starting with several hypotheses for the cause of the 'missing' curvature, it is shown that it is mainly due to mismatches between (i) the modelled and DNS-observed pressure-strain terms in the cospectral budget and (ii) the DNS-observed Fvv and the idealized form used in the previous model. By replacing the current parameterization for the pressure-strain term with an expansive version that directly accounts for the presence of a wall, the modelled and DNS reported pressure-strain profiles match each other in the buffer and logarithmic layers. Forcing the new model with DNS-reported Fvv rather than the idealized form previously used reproduces the missing buffer layer curvature to high fidelity thereby confirming the "spectral link" between Fvv and the MVP. A major departure between the idealized Fvv previously employed and those reported from DNS is the invariance with distance from the wall of the cross-over scale to the inertial subrange in Fvv. This invariance is presumably due to the presence of streaks within the buffer region whose dimensions do not scale with distance from the wall. Comparisons between DNS reported and modeled cospectra are also discussed. A broad implication of this work is that much of the macroscopic properties of the flow (such as the MVP) may be derived from the energy distribution in turbulent eddies (i.e., Fvv) representing the microstates of the flow.

  4. A study of the factors effecting layer thickness uniformity and layer breakup in microlayered coextruded films

    NASA Astrophysics Data System (ADS)

    Ghumman, Bhavjit Singh

    Microlayer coextrusion offers the opportunity to economically commercialize the production of nanometer thick film. A major obstacle towards commercialization is the non-uniform thickness of these layers and their breakup into droplets, which is also known as a scattering instability. Prior research had indicated a strong interaction between material properties and process parameters. Therefore, the focus of this research effort was to better understand and then identify the coextrusion parameters and material properties that governed the layer non-uniformity and scattering. Initial studies had indicated that there existed an interaction between the two extruders, which gave rise to pressure fluctuations and non-uniform flow. The interaction of the two extruders was studied by analyzing the pressure signals at the two extruders and the junction of the two streams. A response surface method was used to analyze the two extruders individually, the number of layer multiplying elements and finally the interaction between the two extruders and the effect they had on pressure, surging, flow rate and torque. Although the interaction of the two extruders did result in higher backpressures, it did not decrease the output. The output was independent of the screw speed of the other extruder, however it did influence the melting mechanics along the screw. The more shear sensitive PMMA showed a greater degree of sensitivity than the Newtonian PC. The influence of primary; coextrusion, and secondary; chill roll, processing on the final layer thickness was studied in a second set of experiments. For this purpose primary coextrusion process parameters such as screw speed ratio, die temperature and core melt temperature were changed and the effect on the layer thickness uniformity was studied. Similarly secondary process parameters such as nip gap and chill roll speed were also investigated. Thickness was measured using an Atomic Force Microscope (AFM). The screw speed ratio was the

  5. High performance polymer solar cells with as-prepared zirconium acetylacetonate film as cathode buffer layer.

    PubMed

    Tan, Zhan'ao; Li, Shusheng; Wang, Fuzhi; Qian, Deping; Lin, Jun; Hou, Jianhui; Li, Yongfang

    2014-01-01

    Low-work-function active metals are commonly used as cathode in polymer solar cells (PSCs), but sensitivity of the active metals towards moisture and oxygen results in poor stability of the devices. Therefore, solution-proceessable and stable cathode buffer layer is of great importance for the application of PSCs. Here we demonstrate high performance PSCs by employing as-prepared zirconium acetylacetonate (a-ZrAcac) film spin-cast from its ethanol solution as cathode buffer layer. The PSCs based on a low bandgap polymer PBDTBDD as donor and PC60BM as acceptor with a-ZrAcac/Al cathode demonstrated an average power conversion efficiency (PCE) of 8.75% which is significantly improved than that of the devices with traditional Ca/Al cathode. The improved photovoltaic performance is benefitted from the decreased series resistance and enhanced light harvest of the PSCs with the a-ZrAcac/Al cathode. The results indicate that a-ZrAcac is a promising high performance cathode buffer layer for fabricating large area flexible PSCs. PMID:24732976

  6. Performance enhancement in inverted solar cells by interfacial modification of ZnO nanoparticle buffer layer.

    PubMed

    Ambade, Swapnil B; Ambade, Rohan B; Kim, Seojin; Park, Hanok; Yoo, Dong Jin; Leel, Soo-Hyoung

    2014-11-01

    Polymer solar cells (PSCs) have attracted increasing attention in recent years. The rapid progress and mounting interest suggest the feasibility of PSC commercialization. However, critical issues such as stability and the weak nature of their interfaces posses quite a challenge. In the context of improving stability, PSCs with inverted geometry consising of inorganic oxide layer acting as an n-buffer offer quite the panacea. Zinc oxide (ZnO) is one of the most preferred semiconducting wide band gap oxides as an efficient cathode layer that effectively extracts and transports photoelectrons from the acceptor to the conducting indium-doped tin oxide (ITO) due to its high conductivity and transparency. However, the existence of a back charge transfer from metal oxides to electron-donating conjugated polymer and poor contact with the bulk heterojunction (BHJ) active layer results in serious interfacial recombination and leads to relatively low photovoltaic performance. One approach to improving the performance and charge selectivity of these types of inverted devices consists of modifying the interface between the inorganic metal oxide (e.g., ZnO) and organic active layer using a sub-monolayer of interfacial materials (e.g., functional dyes). In this work, we demonstrate that the photovoltaic parameters of inverted solar cells comprising a thin overlayer of functional dyes over ZnO nanoparticle as an n-buffer layer are highly influenced by the anchoring groups they possess. While an inverted PSC containing an n-buffer of only ZnO exhibited an overall power conversion efficiency (PCE) of 2.87%, the devices with an interlayer of dyes containing functional cyano-carboxylic, cyano-cyano, and carboxylic groups exhibited PCE of 3.52%, 3.39%, and 3.21%, respectively, due to increased forward charge collection resulting from enhanced electronic coupling between the ZnO and BHJ active layers. PMID:25958563

  7. UV-ozone-treated ultra-thin NaF film as anode buffer layer on organic light emitting devices.

    PubMed

    Chen, Yu-Cheng; Kao, Po-Ching; Chu, Sheng-Yuan

    2010-06-21

    An ultra-thin NaF film was thermally deposited between ITO and NPB as the buffer layer and then treated with the ultraviolet (UV) ozone, in the fabrication of organic light emitting diodes (ITO/NaF/NPB/Alq(3)/LiF/Al) to study its effect on hole-injection properties. The treatment drastically transforms the role of NaF film from hole-blocking to hole-injecting. This transformation is elucidated using hole-only devices, energy band measurement, surface energy, surface polarity, and X-ray photoelectron spectra. With the optimal thickness (3 nm) of the UV-ozone-treated NaF layer, the device performance is significantly improved, with a turn-on voltage, maximum luminance, and maximum current efficiency of 2.5 V, 15700 cd/m(2), and 4.9 cd/A, respectively. Results show that NaF film is not only a hole-blocking layer, but also a promising hole-injecting layer after UV-ozone treatment. PMID:20588585

  8. Performance improvement of polymer solar cells by using a solution processible titanium chelate as cathode buffer layer

    NASA Astrophysics Data System (ADS)

    Tan, Zhan'ao; Yang, Chunhe; Zhou, Erjun; Wang, Xiang; Li, Yongfang

    2007-07-01

    A solution processible titanium chelate, titanium (diisopropoxide) bis (2,4-pentanedionate) (TIPD), was used as the cathode buffer layer in the polymer solar cells (PSCs) based on the blend of poly[2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene] and [6,6]-phenyl-C61-butyric acid methyl ester. Introducing TIPD buffer layer reduced the interface resistance between the active layer and Al electrode, leading to a lower device resistance. The power conversion efficiency of the PSC with TIPD buffer layer reached 2.52% under the illumination of AM1.5, 100mW/cm2, which is increased by 51.8% in comparison with that (1.66%) of the device without TIPD buffer layer under the same experimental conditions.

  9. Usage of Neural Network to Predict Aluminium Oxide Layer Thickness

    PubMed Central

    Michal, Peter; Vagaská, Alena; Gombár, Miroslav; Kmec, Ján; Spišák, Emil; Kučerka, Daniel

    2015-01-01

    This paper shows an influence of chemical composition of used electrolyte, such as amount of sulphuric acid in electrolyte, amount of aluminium cations in electrolyte and amount of oxalic acid in electrolyte, and operating parameters of process of anodic oxidation of aluminium such as the temperature of electrolyte, anodizing time, and voltage applied during anodizing process. The paper shows the influence of those parameters on the resulting thickness of aluminium oxide layer. The impact of these variables is shown by using central composite design of experiment for six factors (amount of sulphuric acid, amount of oxalic acid, amount of aluminium cations, electrolyte temperature, anodizing time, and applied voltage) and by usage of the cubic neural unit with Levenberg-Marquardt algorithm during the results evaluation. The paper also deals with current densities of 1 A·dm−2 and 3 A·dm−2 for creating aluminium oxide layer. PMID:25922850

  10. Neutron supermirrors: an accurate theory for layer thickness computation

    NASA Astrophysics Data System (ADS)

    Bray, Michael

    2001-11-01

    We present a new theory for the computation of Super-Mirror stacks, using accurate formulas derived from the classical optics field. Approximations are introduced into the computation, but at a later stage than existing theories, providing a more rigorous treatment of the problem. The final result is a continuous thickness stack, whose properties can be determined at the outset of the design. We find that the well-known fourth power dependence of number of layers versus maximum angle is (of course) asymptotically correct. We find a formula giving directly the relation between desired reflectance, maximum angle, and number of layers (for a given pair of materials). Note: The author of this article, a classical opticist, has limited knowledge of the Neutron world, and begs forgiveness for any shortcomings, erroneous assumptions and/or misinterpretation of previous authors' work on the subject.

  11. Usage of neural network to predict aluminium oxide layer thickness.

    PubMed

    Michal, Peter; Vagaská, Alena; Gombár, Miroslav; Kmec, Ján; Spišák, Emil; Kučerka, Daniel

    2015-01-01

    This paper shows an influence of chemical composition of used electrolyte, such as amount of sulphuric acid in electrolyte, amount of aluminium cations in electrolyte and amount of oxalic acid in electrolyte, and operating parameters of process of anodic oxidation of aluminium such as the temperature of electrolyte, anodizing time, and voltage applied during anodizing process. The paper shows the influence of those parameters on the resulting thickness of aluminium oxide layer. The impact of these variables is shown by using central composite design of experiment for six factors (amount of sulphuric acid, amount of oxalic acid, amount of aluminium cations, electrolyte temperature, anodizing time, and applied voltage) and by usage of the cubic neural unit with Levenberg-Marquardt algorithm during the results evaluation. The paper also deals with current densities of 1 A · dm(-2) and 3 A · dm(-2) for creating aluminium oxide layer. PMID:25922850

  12. Thickness dependence of structural and transport properties of Co-doped BaFe2As2 on Fe buffered MgO substrates

    NASA Astrophysics Data System (ADS)

    Iida, Kazumasa; Hänisch, Jens; Trommler, Sascha; Haindl, Silvia; Kurth, Fritz; Hühne, Ruben; Schultz, Ludwig; Holzapfel, Bernhard

    2011-12-01

    We have investigated the influence of the superconducting layer thickness, d, on the structural and transport properties of Co-doped BaFe2As2 films deposited on Fe buffered MgO substrates by pulsed laser deposition. The superconducting transition temperature and the texture quality of Co-doped BaFe2As2 films improve with increasing d due to a gradual relief of the tensile strain. For d >= 90 nm an additional 110 textured component of Co-doped BaFe2As2 was observed, which leads to an upward shift in the angle-dependent critical current density at H \\parallel c . These results indicate that the grain boundaries created by the 110 textured component may contribute to the c-axis pinning.

  13. Ultrasonic eggshell thickness measurement for selection of layers.

    PubMed

    Kibala, Lucyna; Rozempolska-Rucinska, Iwona; Kasperek, Kornel; Zieba, Grzegorz; Lukaszewicz, Marek

    2015-10-01

    This study aimed to develop a methodology for using ultrasonic technology (USG) to record eggshell thickness for selection of layers. Genetic correlations between eggshell strength and its thickness have been reported to be around 0.8, making shell thickness a selection index candidate element. Applying ultrasonic devices to measure shell thickness leaves an egg intact for further handling. In this study, eggs from 2 purebred populations of Rhode Island White (RIW) and Rhode Island Red (RIR) hens were collected on a single day in the 33rd week of the farm laying calendar from 2,414 RIR and 4,525 RIW hens. Beginning from the large end of the egg, measurements were taken at 5 latitudes: 0º (USG0), 45º (USG45), 90º (USG90), 135º (USG135), and 180º (USG180). To estimate the repeatability of readings, measurements were repeated at each parallel on 3 meridians. Electronic micrometer measurement ( EMM: ) were taken with an electronic micrometer predominantly at the wider end of eggs from 2,397 RIR and 4,447 RIW hens. A multiple-trait statistical model fit the fixed effect of year-of-hatch × hatch-within-year, and random effects due to repeated measurements (except EMM) and an animal's additive genetic component. The shell was thinnest in the region where chicks break it upon hatching (USG0, USG45). Heritabilities of shell thickness in different regions of the shell ranged from 0.09 to 0.19 (EMM) in RIW and from 0.12 to 0.23 (EMM) in RIR and were highest for USG45 and USG0. Because the measurement repeatabilities were all above 0.90, our recommendation for balancing egg strength against hatching ease is to take a single measurement of USG45. Due to high positive genetic correlations between shell thickness in different regions of the shell its thickness in the pointed end region will be modified accordingly, in response to selection for USG45. PMID:26316340

  14. Epitaxial strontium titanate films grown by atomic layer deposition on SrTiO{sub 3}-buffered Si(001) substrates

    SciTech Connect

    McDaniel, Martin D.; Posadas, Agham; Ngo, Thong Q.; Dhamdhere, Ajit; Smith, David J.; Demkov, Alexander A.; Ekerdt, John G.

    2013-01-15

    Epitaxial strontium titanate (STO) films have been grown by atomic layer deposition (ALD) on Si(001) substrates with a thin STO buffer layer grown by molecular beam epitaxy (MBE). Four unit cells of STO grown by MBE serve as the surface template for ALD growth. The STO films grown by ALD are crystalline as-deposited with minimal, if any, amorphous SiO{sub x} layer at the STO-Si interface. The growth of STO was achieved using bis(triisopropylcyclopentadienyl)-strontium, titanium tetraisopropoxide, and water as the coreactants at a substrate temperature of 250 Degree-Sign C. In situ x-ray photoelectron spectroscopy (XPS) analysis revealed that the ALD process did not induce additional Si-O bonding at the STO-Si interface. Postdeposition XPS analysis also revealed sporadic carbon incorporation in the as-deposited films. However, annealing at a temperature of 250 Degree-Sign C for 30 min in moderate to high vacuum (10{sup -6}-10{sup -9} Torr) removed the carbon species. Higher annealing temperatures (>275 Degree-Sign C) gave rise to a small increase in Si-O bonding, as indicated by XPS, but no reduced Ti species were observed. X-ray diffraction revealed that the as-deposited STO films were c-axis oriented and fully crystalline. A rocking curve around the STO(002) reflection gave a full width at half maximum of 0.30 Degree-Sign {+-} 0.06 Degree-Sign for film thicknesses ranging from 5 to 25 nm. Cross-sectional transmission electron microscopy revealed that the STO films were continuous with conformal growth to the substrate and smooth interfaces between the ALD- and MBE-grown STO. Overall, the results indicate that thick, crystalline STO can be grown on Si(001) substrates by ALD with minimal formation of an amorphous SiO{sub x} layer using a four-unit-cell STO buffer layer grown by MBE to serve as the surface template.

  15. Tracing the sub-photospheric layers of optically thick winds

    NASA Astrophysics Data System (ADS)

    Graefener, G.

    2013-06-01

    Towards the end of their evolution hot massive stars develop strong stellar winds and appear as emission line stars, such as WR stars or LBVs. The quanitative description of the mass loss in these important pre-SN phases is hampered by unkowns such as wind clumping and porosity, and by an incomplete theoretical understanding of optically thick stellar winds. Even the stellar radii in these phases are badly undestood as they are often variable (LBVs), or deviate from theoretical expectations (WR stars). Here we present a new semi-empirical method that helps to tackle these problems. By analysing a large sample of Galactic WR stars we gain information about deep wind layers near the sonic point which are otherwise not directly observable. We find evidence that these layers are clumped, with clumping factors comparable to the ones observed in the winds of WR stars. Moreover, density and temperature near the sonic point seem to follow a relation which is ubiqitous for optically thick winds, and which may be responsible for the peculiar radius properties of these objects.

  16. Highly Reliable 0.15 μm/14 F2 Cell Ferroelectric Random Access Memory Capacitor Using SrRuO3 Buffer Layer

    NASA Astrophysics Data System (ADS)

    Heo, Jang‑Eun; Bae, Byoung‑Jae; Yoo, Dong‑Chul; Nam, Sang‑Don; Lim, Ji‑Eun; Im, Dong‑Hyun; Joo, Suk‑Ho; Jung, Yong‑Ju; Choi, Suk‑Hun; Park, Soon‑Oh; Kim, Hee‑Seok; Chung, U‑In; Moon, Joo‑Tae

    2006-04-01

    We investigated a novel technique of modifying the interface between a Pb(ZrxTi1-x)O3 (PZT) thin film and electrodes for high density 64 Mbit ferroelectric random access memory (FRAM) device. Using a SrRuO3 buffer layer, we successfully developed highly reliable 0.15 μm/14 F2 cell FRAM capacitors with 75-nm-thick polycrystalline PZT thin films. The SrRuO3 buffer layer greatly enhanced ferroelectric characteristics due to the decrease in interfacial defect density. In PZT capacitors with a total thickness of 180 nm for whole capacitor stack, a remnant polarization of approximately 42 μC/cm2 was measured with a 1.4 V operation. In addition, an opposite state remnant polarization loss of less than 15% was observed after baking at 150 °C for 100 h. In particular, we found that the SrRuO3 buffer layer also played a key role in inhibiting the diffusion of Pb and O from the PZT thin films.

  17. Numerical Analysis of In2S3 Layer Thickness, Band Gap and Doping Density for Effective Performance of a CIGS Solar Cell Using SCAPS

    NASA Astrophysics Data System (ADS)

    Khoshsirat, Nima; Md Yunus, Nurul Amziah

    2016-07-01

    The effect of indium sulfide buffer layer's geometrical and electro-optical properties on the Copper-Indium-Gallium-diSelenide solar cell performance using numerical simulation is investigated. The numerical simulation software used is a solar cell capacitance simulator in (SCAPS). The innermost impacts of buffer layer thickness, band gap, and doping density on the cells output parameters such as open circuit voltage, short circuit current density, fill factor, and the efficiency were extensively simulated. The results show that the cell efficiency, which was innovatively illustrated as a two-dimensional contour plot function, depends on the buffer layer electron affinity and doping density by keeping all the other parameters at a steady state. The analysis, which was made from this numerical simulation, has revealed that the optimum electron affinity is to be 4.25 ± 0.2 eV and donor density of the buffer layer is over 1× 10 ^{17} cm^{-3} . It is also shown that the cell with an optimum thin buffer layer has higher performance and efficiency due to the lower optical absorption of the buffer layer.

  18. Buffer Layer Effects on Tandem InGaAs TPV Devices

    NASA Technical Reports Server (NTRS)

    Wilt, David M.; Wehrer, Rebecca J.; Maurer, William F.

    2004-01-01

    Single junction indium gallium arsenide (InGaAs) based TPV devices have demonstrated efficiencies in excess of 20% at radiator temperatures of 1058 C. Modeling suggests that efficiency improvements in single bandgap devices should continue although they will eventually plateau. One approach for extending efficiencies beyond the single bandgap limit is to follow the technique taken in the solar cell field, namely tandem TPV cells. Tandem photovoltaic devices are traditionally composed of cells of decreasing bandgap, connected electrically and optically in series. The incident light impinges upon the highest bandgap first. This device acts as a sieve, absorbing the high-energy photons, while allowing the remainder to pass through to the underlying cell(s), and so on. Tandem devices reduce the energy lost to overexcitation as well as reducing the current density (Jsc). Reduced Jsc results in lower resistive losses and enables the use of thinner and lower doped lateral current conducting layers as well as a higher pitch grid design. Fabricating TPV tandem devices utilizing InGaAs for all of the component cells in a two cell tandem necessitates the inclusion of a buffer layer in-between the high bandgap device (In0.53 Ga0.47As - 0.74eV) and the low bandgap device (In0.66Ga0.34As - 0.63eV) to accommodate the approximately 1% lattice strain generated due to the change in InGaAs composition. To incorporate only a single buffer layer structure, we have investigated the use of the indium phosphide (InP) substrate as a superstrate. Thus the high-bandgap, lattice- matched device is deposited first, followed by the buffer structure and the low-bandgap cell. The near perfect transparency of the high bandgap (1.35eV) iron-doped InP permits the device to be oriented such that the light enters through the substrate. In this paper we examine the impact of the buffer layer on the underlying lattice-matched InGaAs device. 0.74eV InGaAs devices were produced in a variety of

  19. Characterization of ZrO2 buffer layers for sequentially evaporated Y-Ba-CuO on Si and Al2O3 substrates

    NASA Technical Reports Server (NTRS)

    Valco, George J.; Rohrer, Norman J.; Pouch, John J.; Warner, Joseph D.; Bhasin, Kul B.

    1988-01-01

    Thin film high temperature superconductors have the potential to change the microwave technology for space communications systems. For such applications it is desirable that the films be formed on substrates such as Al2O3 which have good microwave properties. The use of ZrO2 buffer layers between Y-Ba-Cu-O and the substrate has been investigated. These superconducting films have been formed by multilayer sequential electron beam evaporation of Cu, BaF2 and Y with subsequent annealing. The three layer sequence of Y/BaF2/Cu is repeated four times for a total of twelve layers. Such a multilayer film, approximately 1 micron thick, deposited directly on SrTiO3 and annealed at 900 C for 45 min produces a film with a superconducting onset of 93 K and critical temperature of 85 K. Auger electron spectroscopy in conjunction with argon ion sputtering was used to obtain the distribution of each element as a function of depth for an unannealed film, the annealed film on SrTiO3 and annealed films on ZrO2 buffer layers. The individual layers were apparent. After annealing, the bulk of the film on SrTiO3 is observed to be fairly uniform while films on the substrates with buffer layers are less uniform. The Y-Ba-Cu-O/ZrO2 interface is broad with a long Ba tail into the ZrO2, suggesting interaction between the film and the buffer layer. The underlying ZrO2/Si interface is sharper. The detailed Auger results are presented and compared with samples annealed at different temperatures and durations.

  20. Versatile buffer layer architectures based on Ge1-xSnx alloys

    NASA Astrophysics Data System (ADS)

    Roucka, R.; Tolle, J.; Cook, C.; Chizmeshya, A. V. G.; Kouvetakis, J.; D'Costa, V.; Menendez, J.; Chen, Zhihao D.; Zollner, S.

    2005-05-01

    We describe methodologies for integration of compound semiconductors with Si via buffer layers and templates based on the GeSn system. These layers exhibit atomically flat surface morphologies, low defect densities, tunable thermal expansion coefficients, and unique ductile properties, which enable them to readily absorb differential stresses produced by mismatched overlayers. They also provide a continuous selection of lattice parameters higher than that of Ge, which allows lattice matching with technologically useful III-V compounds. Using this approach we have demonstrated growth of GaAs, GeSiSn, and pure Ge layers at low temperatures on Si(100). These materials display extremely high-quality structural, morphological, and optical properties opening the possibility of versatile integration schemes directly on silicon.

  1. ZnO buffer layer for metal films on silicon substrates

    DOEpatents

    Ihlefeld, Jon

    2014-09-16

    Dramatic improvements in metallization integrity and electroceramic thin film performance can be achieved by the use of the ZnO buffer layer to minimize interfacial energy between metallization and adhesion layers. In particular, the invention provides a substrate metallization method utilizing a ZnO adhesion layer that has a high work of adhesion, which in turn enables processing under thermal budgets typically reserved for more exotic ceramic, single-crystal, or metal foil substrates. Embodiments of the present invention can be used in a broad range of applications beyond ferroelectric capacitors, including microelectromechanical systems, micro-printed heaters and sensors, and electrochemical energy storage, where integrity of metallized silicon to high temperatures is necessary.

  2. Effects of the nano-tubular anodic TiO2 buffer layer on bioactive hydroxyapatite coating.

    PubMed

    Piao, Zhonglie; Qiu, Jijun; Wu, Yongqing; Park, Se-Jeong; He, Weizhen; Timur, A; Ryu, Su-Chak; Kim, Hyung-Kook; Hwang, Yoon-Hwae

    2011-01-01

    We studied the effect of nano-tubular anodic TiO2 buffer layers on hydroxyapatite (HA) coating. The pulsed laser deposition (PLD) method was used to deposit HA on a well arranged nano-tubular anodic TiO2 (NT-ATO) buffer layer prepared by an electrochemical anodization technique. The surface morphology and chemical composition of HA coatings were characterized by using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and contact angle measurement. We found that crystalline HA coatings show well arranged porous morphologies with a favorable surface wettability. We also found that an anodic nano-tubular TiO2 buffer layer with a relatively short tube length shows a better coating morphology. The deposition process of HA on the nanotubular TiO2 buffer layer was also proposed. PMID:21446441

  3. ZnO-SiO2 solar-blind photodetectors on flexible polyethersulfone substrate with organosilicon buffer layer

    NASA Astrophysics Data System (ADS)

    Lai, Wei-Chih; Chen, Jiun-Ting; Yang, Ya-Yu

    2013-05-01

    The ZnO-SiO2 nanocomposite solar-blind metal-semiconductor-metal photodetectors (PDs) on flexible polyethersulfone (PES) with an organosilicon (SiOx(CH3)) buffer layer improved the -10 V-biased responsivity of PDs illuminated wavelength of 240 nm from 0.75 A/W (without SiOx(CH3) buffer layer) to 3.86 A/W and the deep-ultraviolet (DUV)-visible rejection ratio of PDs from 8.10 × 104 (without SiOx(CH3) buffer layer) to 1.75 × 105. Moreover, the inserted SiOx(CH3) buffer layer would reduce the responsivity and DUV-visible rejection ratio of degradation of the severely bended ZnO-SiO2 nanocomposite PDs on PES.

  4. Co-solvent enhanced zinc oxysulfide buffer layers in Kesterite copper zinc tin selenide solar cells.

    PubMed

    Steirer, K Xerxes; Garris, Rebekah L; Li, Jian V; Dzara, Michael J; Ndione, Paul F; Ramanathan, Kannan; Repins, Ingrid; Teeter, Glenn; Perkins, Craig L

    2015-06-21

    A co-solvent, dimethylsulfoxide (DMSO), is added to the aqueous chemical "bath" deposition (CBD) process used to grow ZnOS buffer layers for thin film Cu2ZnSnSe4 (CZTSe) solar cells. Device performance improves markedly as fill factors increase from 0.17 to 0.51 upon the co-solvent addition. X-ray photoelectron spectroscopy (XPS) analyses are presented for quasi-in situ CZTSe/CBD-ZnOS interfaces prepared under an inert atmosphere and yield valence band offsets equal to -1.0 eV for both ZnOS preparations. When combined with optical band gap data, conduction band offsets exceed 1 eV for the water and the water/DMSO solutions. XPS measurements show increased downward band bending in the CZTSe absorber layer when the ZnOS buffer layer is deposited from water only. Admittance spectroscopy data shows that the ZnOS deposited from water increases the built-in potential (Vbi) yet these solar cells perform poorly compared to those made with DMSO added. The band energy offsets imply an alternate form of transport through this junction. Possible mechanisms are discussed, which circumvent the otherwise large conduction band spike between CZTSe and ZnOS, and improve functionality with the low-band gap absorber, CZTSe (Eg = 0.96 eV). PMID:26000570

  5. Structure, Optical Absorption, and Performance of Organic Solar Cells Improved by Gold Nanoparticles in Buffer Layers.

    PubMed

    Yang, Yingguo; Feng, Shanglei; Li, Meng; Wu, Zhongwei; Fang, Xiao; Wang, Fei; Geng, Dongping; Yang, Tieying; Li, Xiaolong; Sun, Baoquan; Gao, Xingyu

    2015-11-11

    11-Mercaptoundecanoic acid (MUA)-stabilized gold nanoparticles (AuNPs) embedded in copper phthalocyanine (CuPc) were used as a buffer layer between a poly(3-hexyl-thiophene) (P3HT)/[6,6]-phenyl C61-butyric acid methyl ester (PCBM) bulk heterojunction and anodic indium-tin oxide (ITO) substrate. As systematic synchrotron-based grazing incidence X-ray diffraction (GIXRD) experiments demonstrated that the AuNPs present in the buffer layer can improve the microstructure of the active layer with a better lamella packing of P3HT from the surface to the interior, UV-visible absorption spectrum measurements revealed enhanced optical absorption due to the localized surface plasma resonance (LSPR) generated by the AuNPs. The device of ITO/poly(3,4-ethylenedioxythiophene):polystyrenesulfonate/CuPc:MUA-stabilized AuNPs/P3HT:PCBM/LiF/Al was found with over 24% enhancement of power conversion efficiency (PCE) in comparison with reference devices without AuNPs. This remarkable improvement in PCE should be partially attributed to LSPR generated by the AuNPs and partially to improved crystallization as well as preferred orientation order of P3HT due to the presence of the AuNPs, which would promote more applications of metal NPs in the organic photovoltaic devices and other organic multilayer devices. PMID:26477556

  6. Surface plasmon enhanced organic solar cells with a MoO3 buffer layer.

    PubMed

    Su, Zisheng; Wang, Lidan; Li, Yantao; Zhang, Guang; Zhao, Haifeng; Yang, Haigui; Ma, Yuejia; Chu, Bei; Li, Wenlian

    2013-12-26

    High-efficiency surface plasmon enhanced 1,1-bis-(4-bis(4-methyl-phenyl)-amino-phenyl)-cyclohexane:C70 small molecular bulk heterojunction organic solar cells with a MoO3 anode buffer layer have been demonstrated. The optimized device based on thermal evaporated Ag nanoparticles (NPs) shows a power conversion efficiency of 5.42%, which is 17% higher than the reference device. The improvement is attributed to both the enhanced conductivity and increased absorption due to the near-field enhancement of the localized surface plasmon resonance of Ag NPs. PMID:24320799

  7. a Spatio-Temporal Framework for Modeling Active Layer Thickness

    NASA Astrophysics Data System (ADS)

    Touyz, J.; Streletskiy, D. A.; Nelson, F. E.; Apanasovich, T. V.

    2015-07-01

    The Arctic is experiencing an unprecedented rate of environmental and climate change. The active layer (the uppermost layer of soil between the atmosphere and permafrost that freezes in winter and thaws in summer) is sensitive to both climatic and environmental changes, and plays an important role in the functioning, planning, and economic activities of Arctic human and natural ecosystems. This study develops a methodology for modeling and estimating spatial-temporal variations in active layer thickness (ALT) using data from several sites of the Circumpolar Active Layer Monitoring network, and demonstrates its use in spatial-temporal interpolation. The simplest model's stochastic component exhibits no spatial or spatio-temporal dependency and is referred to as the naïve model, against which we evaluate the performance of the other models, which assume that the stochastic component exhibits either spatial or spatio-temporal dependency. The methods used to fit the models are then discussed, along with point forecasting. We compare the predicted fit of the various models at key study sites located in the North Slope of Alaska and demonstrate the advantages of space-time models through a series of error statistics such as mean squared error, mean absolute and percent deviance from observed data. We find the difference in performance between the spatio-temporal and remaining models is significant for all three error statistics. The best stochastic spatio-temporal model increases predictive accuracy, compared to the naïve model, of 33.3%, 36.2% and 32.5% on average across the three error metrics at the key sites for a one-year hold out period.

  8. Development of Production PVD-AIN Buffer Layer System and Processes to Reduce Epitaxy Costs and Increase LED Efficiency

    SciTech Connect

    Cerio, Frank

    2013-09-14

    The DOE has set aggressive goals for solid state lighting (SSL) adoption, which require manufacturing and quality improvements for virtually all process steps leading to an LED luminaire product. The goals pertinent to this proposed project are to reduce the cost and improve the quality of the epitaxial growth processes used to build LED structures. The objectives outlined in this proposal focus on achieving cost reduction and performance improvements over state-of-the-art, using technologies that are low in cost and amenable to high efficiency manufacturing. The objectives of the outlined proposal focus on cost reductions in epitaxial growth by reducing epitaxy layer thickness and hetero-epitaxial strain, and by enabling the use of larger, less expensive silicon substrates and would be accomplished through the introduction of a high productivity reactive sputtering system and an effective sputtered aluminum-nitride (AlN) buffer/nucleation layer process. Success of the proposed project could enable efficient adoption of GaN on-silicon (GaN/Si) epitaxial technology on 150mm silicon substrates. The reduction in epitaxy cost per cm{sup 2} using 150mm GaN-on-Si technology derives from (1) a reduction in cost of ownership and increase in throughput for the buffer deposition process via the elimination of MOCVD buffer layers and other throughput and CoO enhancements, (2) improvement in brightness through reductions in defect density, (3) reduction in substrate cost through the replacement of sapphire with silicon, and (4) reduction in non-ESD yield loss through reductions in wafer bow and temperature variation. The adoption of 150mm GaN/Si processing will also facilitate significant cost reductions in subsequent wafer fabrication manufacturing costs. There were three phases to this project. These three phases overlap in order to aggressively facilitate a commercially available production GaN/Si capability. In Phase I of the project, the repeatability of the performance

  9. Accretion disk boundary layers in cataclysmic variables. 1: Optically thick boundary layers

    NASA Technical Reports Server (NTRS)

    Popham, Robert; Narayan, Ramesh

    1995-01-01

    We develop numerical models of accretions disks in cataclysmic variables (CVs), including and emphasizing the boundary layer region where the accretion disk meets the accreting white dwarf. We confine ourselves to solutions where the boundary layer region is vertically optically thick, and find that these solutions share several common features. The angular and radial velocities of the accreting material drop rapidly in a dynamical boundary layer, which has a radial width approximately 1%-3% of the white dwarf radius. The energy dissipated in this region diffuses through the inner part of the disk and is radiated from the disk surface in a thermal boundary layer, which has a radial width comparable to the disk thickness, approximately 5%-15% of the white dwarf radius. We examine the dependence of the boundary layer structure on the mass accretion rate, the white dwarf mass and rotation rate, and the viscosity parameter alpha. We delineate the boundary between optically thick and optically thin boundary layer solutions as a function of these parameters and suggest that by means of a careful comparison with observations it may be possible to estimate alpha in CVs. We derive an expression for the total boundary layer luminosities as a function of the parameters and show that it agrees well with the luminosites of our numerical solutions. Finally, we calcuate simple blackbody continuum spectra of the boundary layer and disk emission for our solutions and compare these to soft X-ray, EUV, and He II emission-line observations of CVs. We show that, through such comparisons, it may be possible to determine the rotation rates of the accreting stars in CVs, and perhaps also the white dwarf masses and the accretion rates. The spectra are quite insensitive to alpha, so the uncertainty in this parameter does not affect such comparisons.

  10. Mild oxygen plasma treated PEDOT:PSS as anode buffer layer for vacuum deposited organic light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Zhou, Yunfei; Yuan, Yongbo; Lian, Jiarong; Zhang, Jie; Pang, Hongqi; Cao, Lingfang; Zhou, Xiang

    2006-08-01

    The surface morphology of PEDOT:PSS after mild oxygen plasma treatment were investigated by scanning electron microscopy and atomic force microscopy. The nanometer-scale islands on the surface of treated PEDOT:PSS were observed. Vacuum deposited organic light-emitting diodes (OLEDs) with treated PEDOT:PSS as anode buffer layer had been fabricated. The OLEDs with an appropriately treated PEDOT:PSS as anode buffer layer exhibited significantly enhanced lifetime and decreased driving voltage. The results suggest that the appropriate mild oxygen plasma treatment of PEDOT:PSS layers may be useful for the improvement of the interface with the hole transport layer and enhanced device performance.

  11. Thickness-induced structural phase transformation of layered gallium telluride.

    PubMed

    Zhao, Q; Wang, T; Miao, Y; Ma, F; Xie, Y; Ma, X; Gu, Y; Li, J; He, J; Chen, B; Xi, S; Xu, L; Zhen, H; Yin, Z; Li, J; Ren, J; Jie, W

    2016-07-28

    The thickness-dependent electronic states and physical properties of two-dimensional materials suggest great potential applications in electronic and optoelectronic devices. However, the enhanced surface effect in ultra-thin materials might significantly influence the structural stability, as well as the device reliability. Here, we report a spontaneous phase transformation of gallium telluride (GaTe) that occurred when the bulk was exfoliated to a few layers. Transmission electron microscopy (TEM) results indicate a structural variation from a monoclinic to a hexagonal structure. Raman spectra suggest a critical thickness for the structural transformation. First-principle calculations and thermodynamic analysis show that the surface energy and the interlayer interaction compete to dominate structural stability in the thinning process. A two-stage transformation process from monoclinic (m) to tetragonal (T) and then from tetragonal to hexagonal (h) is proposed to understand the phase transformation. The results demonstrate the crucial role of interlayer interactions in the structural stability, which provides a phase engineering strategy for device applications. PMID:27198938

  12. Dependence of Gold Nanoparticle Radiosensitization on Functionalizing Layer Thickness.

    PubMed

    Spaas, Cedric; Dok, Rüveyda; Deschaume, Olivier; De Roo, Bert; Vervaele, Mattias; Seo, Jin Won; Bartic, Carmen; Hoet, Peter; Van den Heuvel, Frank; Nuyts, Sandra; Locquet, Jean-Pierre

    2016-04-01

    Gold nanoparticles functionalized with polyethylene glycol of different chain lengths are used to determine the influence of the capping layer thickness on the radiosensitizing effect of the particles. The size variations in organic coating, built up with polyethylene glycol polymers of molecular weight 1-20 kDa, allow an evaluation of the decrease in dose enhancement percentages caused by the gold nanoparticles at different radial distances from their surface. With localized eradication of malignant cells as a primary focus, radiosensitization is most effective after internalization in the nucleus. For this reason, we performed controlled radiation experiments, with doses up to 20 Gy and particle diameters in a range of 5-30 nm, and studied the relaxation pattern of supercoiled DNA. Subsequent gel electrophoresis of the suspensions was performed to evaluate the molecular damage and consecutively quantify the gold nanoparticle sensitization. In conclusion, on average up to 58.4% of the radiosensitizing efficiency was lost when the radial dimensions of the functionalizing layer were increased from 4.1 to 15.3 nm. These results serve as an experimental supplement for biophysical simulations and demonstrate the influence of an important parameter in the development of nanomaterials for targeted therapies in cancer radiotherapy. PMID:26950059

  13. Fabrication of YSZ buffer layer by single source MOCVD technique for YBCO coated conductor

    NASA Astrophysics Data System (ADS)

    Jun, Byung-Hyuk; Sun, Jong-Won; Kim, Ho-Jin; Lee, Dong-Wook; Jung, Choong-Hwan; Park, Soon-Dong; Kim, Chan-Joong

    2003-10-01

    Yttria stabilized zirconia (YSZ) buffer layers were deposited by a metal organic chemical vapor deposition technique using a single liquid source for the application of YBa 2Cu 3O 7- δ (YBCO) coated conductor. Y:Zr mole ratio was 0.2:0.8, and tetrahydrofuran (THF) was used as a solvent. The (1 0 0) single crystal MgO substrate was used for searching the deposition conditions. Bi-axially oriented CeO 2 and NiO films were fabricated on {1 0 0} <0 0 1> textured Ni substrate by the same method and used as templates. At a constant working pressure of 10 Torr, the deposition temperatures (660-800 °C) and oxygen flow rates (100-500 sccm) were changed to find the optimum deposition condition. The best (1 0 0) oriented YSZ film on MgO was obtained at 740 °C and O 2 flow rate of 300 sccm. For a YSZ buffer layer with this deposition condition on a CeO 2/Ni template, full width half maximum values of the in-plane ( ϕ-scan) and out-of-plane ( ω-scan) alignments were 10.6° and 9.8°, respectively. The SEM image of YSZ film on CeO 2/Ni showed surface morphologies without microcracks. The film deposition rate was about 100 nm/min.

  14. Hydrogenated amorphous silicon thin film solar cell with buffer layer of DNA-CTMA biopolymer

    NASA Astrophysics Data System (ADS)

    Son, Won-Ho; Reddy, M. Siva Pratap; Choi, Sie-Young

    2014-05-01

    The characteristics of nip-type a-Si:H thin film solar cells based on DNA-CTMA biopolymer was investigated. The DNA-CTMA was used as the buffer layer in nip-type a-Si:H solar cell. The Eopt of the DNA-CTMA biopolymer was measured with UV-VIS spectrometer. The Eopt of DNA-CTMA was determined as 3.96 eV by the plot of (Ahν)2 versus hν. All films of amorphous materials were deposited by PECVD method. The solar cell with a simple structure of glass/ITO/n-a-Si:H/i-a-Si:H/p-a-Si:H/DNA-CTMA/Al was fabricated. The various values of Voc, Jsc, FF, and conversion efficiency η were measured under 100 mW/cm2 (AM 1.5) solar simulator irradiation. Consequently, the resulting in solar cell showed an enhancement in conversion efficiency η compared to conventional nip-type a-Si:H solar cell without buffer layer of DNA-CTMA biopolymer.

  15. Buffer layers on metal surfaces having biaxial texture as superconductor substrates

    DOEpatents

    Paranthaman, Mariappan; Lee, Dominic F.; Kroeger, Donald M.; Goyal, Amit

    2000-01-01

    Buffer layer architectures are epitaxially deposited on biaxially-textured rolled substrates of nickel and/or copper and their alloys for high current conductors, and more particularly buffer layer architectures such as Y.sub.2 O.sub.3 /Ni, YSZ/Y.sub.2 O.sub.3 /Ni, RE.sub.2 O.sub.3 /Ni, (RE=Rare Earth), RE.sub.2 O.sub.3 /Y.sub.2 O.sub.3 /Ni, RE.sub.2 O.sub.3 /CeO.sub.2 /Ni, and RE.sub.2 O.sub.3 /YSZ/CeO.sub.2 /Ni, Y.sub.2 O.sub.3 /Cu, YSZ/Y.sub.2 O.sub.3 /Cu, RE.sub.2 O.sub.3 /Cu, RE.sub.2 O.sub.3 /Y.sub.2 O.sub.3 /Cu, RE.sub.2 O.sub.3 /CeO.sub.2 /Cu, and RE.sub.2 O.sub.3 /YSZ/CeO.sub.2 /Cu. Deposition methods include physical vapor deposition techniques which include electron-beam evaporation, rf magnetron sputtering, pulsed laser deposition, thermal evaporation, and solution precursor approaches, which include chemical vapor deposition, combustion CVD, metal-organic decomposition, sol-gel processing, and plasma spray.

  16. Calcium manganate: A promising candidate as buffer layer for hybrid halide perovskite photovoltaic-thermoelectric systems

    SciTech Connect

    Zhao, Pengjun; Wang, Hongguang; Kong, Wenwen; Xu, Jinbao Wang, Lei; Ren, Wei; Bian, Liang; Chang, Aimin

    2014-11-21

    We have systematically studied the feasibility of CaMnO{sub 3} thin film, an n-type perovskite, to be utilized as the buffer layer for hybrid halide perovskite photovoltaic-thermoelectric device. Locations of the conduction band and the valence band, spontaneous polarization performance, and optical properties were investigated. Results indicate the energy band of CaMnO{sub 3} can match up well with that of CH{sub 3}NH{sub 3}PbI{sub 3} on separating electron-hole pairs. In addition, the consistent polarization angle helps enlarge the open circuit voltage of the composite system. Besides, CaMnO{sub 3} film shows large absorption coefficient and low extinction coefficient under visible irradiation, demonstrating high carrier concentration, which is beneficial to the current density. More importantly, benign thermoelectric properties enable CaMnO{sub 3} film to assimilate phonon vibration from CH{sub 3}NH3PbI{sub 3}. All the above features lead to a bright future of CaMnO{sub 3} film, which can be a promising candidate as a buffer layer for hybrid halide perovskite photovoltaic-thermoelectric systems.

  17. Uncovering the role of cathode buffer layer in organic solar cells

    NASA Astrophysics Data System (ADS)

    Qi, Boyuan; Zhang, Zhi-Guo; Wang, Jizheng

    2015-01-01

    Organic solar cells (OSCs) as the third generation photovoltaic devices have drawn intense research, for their ability to be easily deposited by low-cost solution coating technologies. However the cathode in conventional OSCs, Ca, can be only deposited by thermal evaporation and is highly unstable in ambient. Therefore various solution processible cathode buffer layers (CBLs) are synthesized as substitute of Ca and show excellent effect in optimizing performance of OSCs. Yet, there is still no universal consensus on the mechanism that how CBL works, which is evidently a critical scientific issue that should be addressed. In this article detailed studies are targeted on the interfacial physics at the interface between active layer and cathode (with and without treatment of a polar CBL) by using ultraviolet photoelectron spectroscopy, capacitance-voltage measurement, and impedance spectroscopy. The experimental data demonstrate that CBL mainly takes effect in three ways: suppressing surface states at the surface of active layer, protecting the active layer from being damaged by thermally evaporated cathode, and changing the energy level alignment by forming dipole moments with active layer and/or cathode. Our findings here provide a comprehensive picture of interfacial physics in devices with and without CBL.

  18. Uncovering the role of cathode buffer layer in organic solar cells.

    PubMed

    Qi, Boyuan; Zhang, Zhi-Guo; Wang, Jizheng

    2015-01-01

    Organic solar cells (OSCs) as the third generation photovoltaic devices have drawn intense research, for their ability to be easily deposited by low-cost solution coating technologies. However the cathode in conventional OSCs, Ca, can be only deposited by thermal evaporation and is highly unstable in ambient. Therefore various solution processible cathode buffer layers (CBLs) are synthesized as substitute of Ca and show excellent effect in optimizing performance of OSCs. Yet, there is still no universal consensus on the mechanism that how CBL works, which is evidently a critical scientific issue that should be addressed. In this article detailed studies are targeted on the interfacial physics at the interface between active layer and cathode (with and without treatment of a polar CBL) by using ultraviolet photoelectron spectroscopy, capacitance-voltage measurement, and impedance spectroscopy. The experimental data demonstrate that CBL mainly takes effect in three ways: suppressing surface states at the surface of active layer, protecting the active layer from being damaged by thermally evaporated cathode, and changing the energy level alignment by forming dipole moments with active layer and/or cathode. Our findings here provide a comprehensive picture of interfacial physics in devices with and without CBL. PMID:25588623

  19. Engineered oxide thin films as 100% lattice match buffer layers for YBCO coated conductors

    NASA Astrophysics Data System (ADS)

    Akin, Y.; Heiba, Z. K.; Sigmund, W.; Hascicek, Y. S.

    2003-12-01

    One of the most important qualities of buffer layers for RE-BCO coated conductors' growth is close lattice match with RE-BCO. However, there is no natural material with a 100% lattice match with RE-BCO. In this study mixtures of europium oxide (Eu 2O 3) and ytterbium oxide (Yb 2O 3), (Eu 1- uYb u) 2O 3 (0.0⩽ u⩽1.0), were investigated as a candidate buffer layer that could have same lattice parameter as YBa 2Cu 3O 7- δ(YBCO). Because the pseudocubic lattice parameter of Eu 2O 3 is bigger, and that of Yb 2O 3 is smaller than lattice parameter of YBCO, and the mixed oxides with appropriate ratio would have same lattice parameter of YBCO. The mixtures were prepared using metal-organic precursor by sol-gel process, and it was found that all mixed samples are single phase, complete solid solutions, and have same crystal system over the whole range of " u". Lattice parameters of mixed (Eu 1- uYb u) 2O 3 oxide powders were changed between 10.86831 and 10.42828 Å which are lattice parameter of Eu 2O 3 and Yb 2O 3, respectively by changing the ratio of Eu/Yb in the mixture. Phase and lattice parameter analysis revealed that pseudocubic lattice parameter of (Eu 0.893Yb 0.107) 2O 3 is 3.82 Å which is same as the lattice parameter of YBCO. Textured (Eu 0.893Yb 0.107) 2O 3 buffer layers were grown on biaxially textured-Ni (1 0 0) substrates. The solution was prepared from Europium and Ytterbium 2,4-pentadioanate, and was deposited on the Ni substrates using a reel-to-reel sol-gel dip coating system. The textured films were annealed at 1150 °C for 10 min under 4% H 2-Ar gas flow. Extensive texture analysis has been done to characterize the texture of (Eu 0.893Yb 0.107) 2O 3 buffer layers. X-ray diffraction (XRD) of the buffer layer showed strong out-of-plane orientation on Ni tape. The (Eu 0.893Yb 0.107) 2O 3 (2 2 2) pole figure indicated a single cube-on-cube textured structure. The omega and phi scans revealed good out-of-plane and in-plane alignments. The full

  20. Artificially MoO3 graded ITO anodes for acidic buffer layer free organic photovoltaics

    NASA Astrophysics Data System (ADS)

    Lee, Hye-Min; Kim, Seok-Soon; Kim, Han-Ki

    2016-02-01

    We report characteristics of MoO3 graded ITO anodes prepared by a RF/DC graded sputtering for acidic poly(3,4-ethylene dioxylene thiophene):poly(styrene sulfonic acid) (PEDOT:PSS)-free organic solar cells (OSCs). Graded sputtering of the MoO3 buffer layer on top of the ITO layer produced MoO3 graded ITO anodes with a sheet resistance of 12.67 Ω/square, a resistivity of 2.54 × 10-4 Ω cm, and an optical transmittance of 86.78%, all of which were comparable to a conventional ITO anode. In addition, the MoO3 graded ITO electrode showed a greater work function of 4.92 eV than that (4.6 eV) of an ITO anode, which is beneficial for hole extraction from an organic active layer. Due to the high work function of MoO3 graded ITO electrodes, the acidic PEDOT:PSS-free OSCs fabricated on the MoO3 graded ITO electrode exhibited a power conversion efficiency 3.60% greater than that of a PEDOT:PSS-free OSC on the conventional ITO anode. The successful operation of PEDOT:PSS-free OSCs indicates simpler fabrication steps for cost-effective OSCs and elimination of interfacial reactions caused by the acidic PEDOT:PSS layer for reliable OSCs.

  1. The role of Ag buffer layer in Fe islands growth on Ge (111) surfaces

    SciTech Connect

    Fu, Tsu-Yi Wu, Jia-Yuan; Jhou, Ming-Kuan; Hsu, Hung-Chan

    2015-05-07

    Sub-monolayer iron atoms were deposited at room temperature on Ge (111)-c(2 × 8) substrates with and without Ag buffer layers. The behavior of Fe islands growth was investigated by using scanning tunneling microscope (STM) after different annealing temperatures. STM images show that iron atoms will cause defects and holes on substrates at room temperature. As the annealing temperature rises, iron atoms pull out germanium to form various kinds of alloyed islands. However, the silver layer can protect the Ag/Ge(111)-(√3×√3) reconstruction from forming defects. The phase diagram shows that ring, dot, and triangular defects were only found on Ge (111)-c(2 × 8) substrates. The kinds of islands found in Fe/Ge system are similar to Fe/Ag/Ge system. It indicates that Ge atoms were pulled out to form islands at high annealing temperatures whether there was a Ag layer or not. But a few differences in big pyramidal or strip islands show that the silver layer affects the development of islands by changing the surface symmetry and diffusion coefficient. The structure characters of various islands are also discussed.

  2. Semi-insulating Sn-Zr-O: Tunable resistance buffer layers

    SciTech Connect

    Barnes, Teresa M.; Burst, James M.; Reese, Matthew O.; Perkins, Craig L.

    2015-03-02

    Highly resistive and transparent (HRT) buffer layers are critical components of solar cells and other opto-electronic devices. HRT layers are often undoped transparent conducting oxides. However, these oxides can be too conductive to form an optimal HRT. Here, we present a method to produce HRT layers with tunable electrical resistivity, despite the presence of high concentrations of unintentionally or intentionally added dopants in the film. This method relies on alloying wide-bandgap, high-k dielectric materials (e.g., ZrO{sub 2}) into the host oxide to tune the resistivity. We demonstrate Sn{sub x}Zr{sub 1−x}O{sub 2}:F films with tunable resistivities varying from 0.001 to 10 Ω cm, which are controlled by the Zr mole fraction in the films. Increasing Zr suppresses carriers by expanding the bandgap almost entirely by shifting the valence-band position, which allows the HRT layers to maintain good conduction-band alignment for a low-resistance front contact.

  3. Improved performance of organic light-emitting devices with plasma treated ITO surface and plasma polymerized methyl methacrylate buffer layer

    NASA Astrophysics Data System (ADS)

    Lim, Jae-Sung; Shin, Paik-Kyun

    2007-02-01

    Transparent indium-tin-oxide (ITO) anode surface was modified using O 3 plasma and organic ultra-thin buffer layers were deposited on the ITO surface using 13.56 MHz rf plasma polymerization technique. A plasma polymerized methyl methacrylate (ppMMA) ultra-thin buffer layer was deposited between the ITO anode and hole transporting layer (HTL). The plasma polymerization of the buffer layer was carried out at a homemade capacitively coupled plasma (CCP) equipment. N, N'-Diphenyl- N, N'-bis(3-methylphenyl)-1,1'-diphenyl-4,4'-diamine (TPD) as HTL, Tris(8-hydroxy-quinolinato)aluminum (Alq 3) as both emitting layer (EML)/electron transporting layer (ETL), and aluminum layer as cathode were deposited using thermal evaporation technique. Electroluminescence (EL) efficiency, operating voltage and stability of the organic light-emitting devices (OLEDs) were investigated in order to study the effect of the plasma surface treatment of the ITO anode and role of plasma polymerized methyl methacrylate as an organic ultra-thin buffer layer.

  4. Growth and characterization of metamorphic InxGa1-xAs/InAlAs (x >= 0.8) modulation doped heterostructures on GaAs using a linearly graded In(AlGa)as buffer layer

    NASA Astrophysics Data System (ADS)

    Wang, S. M.; Karlsson, C.; Rorsman, N.; Bergh, M.; Olsson, E.; Andersson, T. G.

    1997-01-01

    Metamorphic InxGa1-xAs/InAlAs (x >= 0.8) modulation doped heterostructures have been grown on GaAs using a linearly graded In(AlGa)As buffer layer, and their structural and electric properties have been investigated. Surface morphology was found to depend on growth temperature and graded buffer thickness. Low growth temperature resulted in a relatively smooth surface with a minimum root-mean-square roughness value of 4-7 nm. The In(AlGa)As graded buffer effectively prevented dislocations from threading into the top layers. The epilayer grown on the graded buffer was tilted and not fully relaxed. High electron mobility and sheet density were achieved. The highest mobility value was 13740 cm2/Vs with a carrier density of 1.9 · 1012 cm-2 at 300 K. These values are comparable with InP-based InGaAs/InAlAs modulation doped heterostructures.

  5. Determination of layer-thickness variation in periodic multilayer by x-ray reflectivity

    SciTech Connect

    Jiang Hui; Zhu Jingtao; Xu Jing; Wang Xiaoqiang; Wang Zhanshan; Watanabe, Makoto

    2010-05-15

    A method basically determining individual layer thicknesses in actual periodic multilayers has been developed, that solves simultaneous equations of positions of peaks appearing in wavelet transform curve of x-ray grazing incidence reflectivity. The determination was demonstrated on a Ni/C periodic multilayer fabricated by magnetron sputtering. Using the layer thicknesses obtained by the method, further accurate of thickness, roughness, and density of each layer was performed by Parratt's model. The special feature that the topmost and bottom-most layers were thicker than other layers was clearly observed. The former is attributed to oxidation and the latter is attributed to the effect of deposition on thick substrate. The mean fluctuations of other layers are 2.6% in C layers and 4.2% in Ni layers attributed to random fluctuations at deposition. Numerical analysis and statistical hypothesis tests have been carried out to discuss noncumulative and cumulative layer-thickness fluctuations in fabrication process.

  6. Oxygen inhibition layer of composite resins: effects of layer thickness and surface layer treatment on the interlayer bond strength.

    PubMed

    Bijelic-Donova, Jasmina; Garoushi, Sufyan; Lassila, Lippo V J; Vallittu, Pekka K

    2015-02-01

    An oxygen inhibition layer develops on surfaces exposed to air during polymerization of particulate filling composite. This study assessed the thickness of the oxygen inhibition layer of short-fiber-reinforced composite in comparison with conventional particulate filling composites. The effect of an oxygen inhibition layer on the shear bond strength of incrementally placed particulate filling composite layers was also evaluated. Four different restorative composites were selected: everX Posterior (a short-fiber-reinforced composite), Z250, SupremeXT, and Silorane. All composites were evaluated regarding the thickness of the oxygen inhibition layer and for shear bond strength. An equal amount of each composite was polymerized in air between two glass plates and the thickness of the oxygen inhibition layer was measured using a stereomicroscope. Cylindrical-shaped specimens were prepared for measurement of shear bond strength by placing incrementally two layers of the same composite material. Before applying the second composite layer, the first increment's bonding site was treated as follows: grinding with 1,000-grit silicon-carbide (SiC) abrasive paper, or treatment with ethanol or with water-spray. The inhibition depth was lowest (11.6 μm) for water-sprayed Silorane and greatest (22.9 μm) for the water-sprayed short-fiber-reinforced composite. The shear bond strength ranged from 5.8 MPa (ground Silorane) to 36.4 MPa (water-sprayed SupremeXT). The presence of an oxygen inhibition layer enhanced the interlayer shear bond strength of all investigated materials, but its absence resulted in cohesive and mixed failures only with the short-fiber-reinforced composite. Thus, more durable adhesion with short-fiber-reinforced composite is expected. PMID:25556290

  7. Improvement of Performance and Stability of Polymer Photovoltaic Cells by WO3/CUPC as Anode Buffer Layers

    NASA Astrophysics Data System (ADS)

    Varnamkhasti, M. G.; Shahriaria, E.

    2015-05-01

    In this work, bulk-hetrojunction polymer photovoltaic cells based on poly-(3-hexylthiophene) (P3HT): [6,6]-phenyl C61 butyric acid methyl ester (PCBM) were fabricated with tungsten oxide (WO3) and copper phthalocyanine (CuPc) as anodic buffer layers. The WO3 plays an important role in reducing the interfacial resistance, efficiently extracting holes and good band structure matching between the work function of the anode and the highest occupied molecular orbital of the organic material. The insertion of CuPc improves the device In this work, bulk-hetrojunction polymer photovoltaic cells based on poly-(3-hexylthiophene) (P3HT): [6, 6]-phenyl C61 butyric acid methylester (PCBM) were fabricated with tungsten oxide (WO3) and copper phthalocyanine (CuPc) as anodic buffer layers. The WO3 plays animportant role in reducing the interfacial resistance, efficiently extracting holes and good band structure matching between the workfunction of the anode and the highest occupied molecular orbital of the organic material. The insertion of CuPc improves the device performance and expands the absorption spectra range of the photovoltaic devices. The effects of WO3 and CuPc thickness on the performance of the photovoltaic devices were investigated. The optimum thicknesses of WO3 and CuPc were 10 nm and 8 nm, respectively. The obtained power conversion efficiency of optimized cell was about 4.21%. Also, the device performance was analyzed based on thesurface roughness of bare ITO and ITO that was covered with poly (3, 4-ethylenedioxythiophene): poly (styrene sulfonate) (PEDOT:PSS) or WO3/CuPc. The device stability in an ambient atmosphere without encapsulation under continuous light irradiation was also investigated.For the cell with PEDOT:PSS, the power conversion efficiency reduced down to 50% of the maximum value (half-life) after light irradiation for 12 h, while the half-life of device for WO3/CuPc was about 120 h. Therefore, the lifetime of unpackaged devices was improved with

  8. A sputtered CdS buffer layer for co-electrodeposited Cu2ZnSnS4 solar cells with 6.6% efficiency.

    PubMed

    Tao, Jiahua; Zhang, Kezhi; Zhang, Chuanjun; Chen, Leilei; Cao, Huiyi; Liu, Junfeng; Jiang, Jinchun; Sun, Lin; Yang, Pingxiong; Chu, Junhao

    2015-06-28

    Cu2ZnSnS4 thin films with thicknesses ranging from 0.35 to 1.85 μm and micron-sized grains (0.5-1.5 μm) were synthesized using co-electrodeposited Cu-Zn-Sn-S precursors with different deposition times. Here we have introduced a sputtered CdS buffer layer for the development of CZTS solar cells for the first time, which enables breakthrough efficiencies up to 6.6%. PMID:26027699

  9. Electron density and currents of AlN/GaN high electron mobility transistors with thin GaN/AlN buffer layer

    SciTech Connect

    Bairamis, A.; Zervos, Ch.; Georgakilas, A.; Adikimenakis, A.; Kostopoulos, A.; Kayambaki, M.; Tsagaraki, K.; Konstantinidis, G.

    2014-09-15

    AlN/GaN high electron mobility transistor (HEMT) structures with thin GaN/AlN buffer layer have been analyzed theoretically and experimentally, and the effects of the AlN barrier and GaN buffer layer thicknesses on two-dimensional electron gas (2DEG) density and transport properties have been evaluated. HEMT structures consisting of [300 nm GaN/ 200 nm AlN] buffer layer on sapphire were grown by plasma-assisted molecular beam epitaxy and exhibited a remarkable agreement with the theoretical calculations, suggesting a negligible influence of the crystalline defects that increase near the heteroepitaxial interface. The 2DEG density varied from 6.8 × 10{sup 12} to 2.1 × 10{sup 13} cm{sup −2} as the AlN barrier thickness increased from 2.2 to 4.5 nm, while a 4.5 nm AlN barrier would result to 3.1 × 10{sup 13} cm{sup −2} on a GaN buffer layer. The 3.0 nm AlN barrier structure exhibited the highest 2DEG mobility of 900 cm{sup 2}/Vs for a density of 1.3 × 10{sup 13} cm{sup −2}. The results were also confirmed by the performance of 1 μm gate-length transistors. The scaling of AlN barrier thickness from 1.5 nm to 4.5 nm could modify the drain-source saturation current, for zero gate-source voltage, from zero (normally off condition) to 0.63 A/mm. The maximum drain-source current was 1.1 A/mm for AlN barrier thickness of 3.0 nm and 3.7 nm, and the maximum extrinsic transconductance was 320 mS/mm for 3.0 nm AlN barrier.

  10. Enhancing electrochemical performance by control of transport properties in buffer layers--solid oxide fuel/electrolyser cells.

    PubMed

    Ramasamy, Devaraj; Nasani, Narendar; Brandão, Ana D; Pérez Coll, Domingo; Fagg, Duncan P

    2015-05-01

    The current work demonstrates how tailoring the transport properties of thin ceria-based buffer layers in solid oxide fuel or electrolyser cells can provide the necessary phase stability against chemical interaction at the electrolyte/electrode interface, while also providing radical improvements in the electrochemical performance of the oxygen electrode. Half cells of Ce0.8R0.2O2-δ + 2 mol% Co buffer layers (where R = Gd, Pr) with Nd2NiO4+δ electrodes were fabricated by spin coating on dense YSZ electrolyte supports. Dramatic decreases in polarization resistance, Rp, of up to an order of magnitude, could be achieved in the order, Pr ≪ Gd < no buffer layer. The current article shows how this improvement can be related to increased levels of ambipolar conductivity in the mixed conducting buffer layer, which provides an additional parallel path for electrochemical reaction. This is an important breakthrough as it shows how electrode polarization resistance can be substantially improved, in otherwise identical electrochemical cells, solely by tailoring the transport properties of thin intermediate buffer layers. PMID:25857870

  11. Reduction of dislocation density in mismatched SiGe/Si using a low-temperature Si buffer layer

    NASA Astrophysics Data System (ADS)

    Linder, K. K.; Zhang, F. C.; Rieh, J.-S.; Bhattacharya, P.; Houghton, D.

    1997-06-01

    The reduction of the dislocation density in relaxed SiGe/Si heterostructures using a low-temperature Si(LT-Si) buffer has been investigated. We have shown that a 0.1 μm LT-Si buffer reduces the threading dislocation density in mismatched Si0.85Ge0.15/Si epitaxial layers as low as ˜104cm-2. Samples were grown by both gas-source molecular beam epitaxy and ultrahigh vacuum chemical vapor deposition.

  12. Effects of Soil Property Uncertainty on Projected Active Layer Thickness

    NASA Astrophysics Data System (ADS)

    Harp, D. R.; Atchley, A. L.; Coon, E.; Painter, S. L.; Wilson, C. J.; Romanovsky, V. E.; Liljedahl, A.

    2014-12-01

    Uncertainty in future climate is often assumed to contribute the largest uncertainty to active layer thickness (ALT) projections. However, the impact of soil property uncertainty on these projections may be significant. In this research, we evaluate the contribution of soil property uncertainty on ALT projections at the Barrow Environmental Observatory, Alaska. The effect of variations in porosity, thermal conductivity, saturation, and water retention properties of peat and mineral soil are evaluated. The micro-topography of ice wedge polygons present at the site is included in the analysis using three 1D column models to represent polygon center, rim and trough features. The Arctic Terrestrial Simulator (ATS) is used to model multiphase thermal and hydrological processes in the subsurface. We apply the Null-Space Monte Carlo (NSMC) algorithm to identify an ensemble of soil property combinations that produce simulated temperature profiles that are consistent with temperature measurements available from the site. ALT is simulated for the ensemble of soil property combinations for four climate scenarios. The uncertainty in ALT due to soil properties within and across climate scenarios is evaluated. This work was supported by LANL Laboratory Directed Research and Development Project LDRD201200068DR and by the The Next-Generation Ecosystem Experiments (NGEE Arctic) project. NGEE-Arctic is supported by the Office of Biological and Environmental Research in the DOE Office of Science.

  13. Composite Fermion Spin Polarization Energy with Finite Layer Thickness

    NASA Astrophysics Data System (ADS)

    Shayegan, Mansour; Liu, Yang; Hasdemir, Sukret; Pfeiffer, Loren; West, Ken; Baldwin, Kirk

    2014-03-01

    We study the spin polarization transitions of fractional quantum Hall (FQH) states in the filling range 1 < ν < 2 in symmetric quantum wells (QWs), as a function of density. Our results reveal a strong well-width dependence of the critical density nC and ratio between the Zeeman energy (EZ) normalized to the Coulomb energy (e2 / 4 πɛlB), above which a certain FQH state becomes spin polarized. For example, the ν = 7 / 5 FQH state becomes spin polarized at about 3 times higher density or 1.7 times larger EZ in the 31-nm-wide QW than in the 65-nm-wide QW. This well-width dependence of the spin polarization stems from by the finite electron layer thickness in these QWs and the resulting softening of the Coulomb interaction. We acknowledge support through the DOE BES (DE-FG02-00-ER45841) for measurements, and the Gordon and Betty Moore Foundation (Grant GBMF2719), Keck Foundation, and the NSF (DMR-0904117, DMR-1305691 and MRSEC DMR-0819860) for sample fabrication. Work at Arg.

  14. Towards NOAA Forecasts of Permafrost Active Layer Thickness

    NASA Astrophysics Data System (ADS)

    Livezey, M. M.; Jonassen, R. G.; Horsfall, F. M. C.; Jafarov, E. E.; Schaefer, K. M.

    2014-12-01

    NOAA's implementation of its 2014 Arctic Action Plan (AAP) lacks services related to permafrost change yet the Interagency Working Group on Coordination of Domestic Energy Development and Permitting in Alaska noted that warming permafrost challenges land-based development and calls for agencies to provide focused information needed by decision-makers. To address this we propose to link NOAA's existing seasonal forecasts of temperature and precipitation with a high-resolution model of the thermal state of permafrost (Jafarov et al., 2012) to provide near-term (one year ahead) forecasts of active layer thickness (ALT). Such forecasts would be an official NOAA statement of the expected thermal state of permafrost ALT in Alaska and would require: (1) long-term climate outlooks, (2) a permafrost model, (3) detailed specification of local spatial and vertical controls upon soil thermal state, (4) high-resolution vertical measurements of that thermal state, and (5) demonstration of forecast skill in pilot studies. Pilot efforts should focus on oil pipelines where the cost can be justified. With skillful forecasts, engineers could reduce costs of monitoring and repair as well as ecosystem damage by positioning equipment to more rapidly respond to predicted disruptions.

  15. The role of buffer layer between TCO and p-layer in improving series resistance and carrier recombination of a-Si:H solar cells

    SciTech Connect

    Yoon, Kichan; Shin, Chonghoon; Lee, Youn-Jung; Kim, Youngkuk; Park, Hyeongsik; Baek, Seungsin; Yi, Junsin

    2012-10-15

    The properties of the window layer and transparent conducting oxide (TCO)/p interface in silicon based thin-film solar cells are important factors in determining the cell efficiency. As the potential barrier got larger at the interface, the transmission of photo-generated holes were impeded and the recombination of photo-generated electrons diffusing back toward the TCO interface were enhanced leading to a deterioration of the fill factor. In this paper different p-layers were studied. It was found that using p-type hydrogenated amorphous silicon oxide (a-SiO{sub x}:H) layer as the window layer along with a 5 nm buffer layer which reduced the barrier at the fluorine doped tin oxide (SnO{sub 2}:F) TCO/p-layer interface, improved the cell efficiency. a-SiO{sub x}:H was used as the buffer layer. With the buffer layer between TCO and p-type a-SiO{sub x}:H, the potential barrier dropped from 0.506 eV to 0.472 eV. This lowered barrier results in increased short circuit current density (J{sub sc}) and fill factor (FF). With the buffer layer, J{sub sc} increased from 11.9 mA/cm{sup 2} to 13.35 mA/cm{sup 2} and FF increased from 73.22% to 74.91%.

  16. Investigation of polycrystalline thin-film CuInSe{sub 2} solar cells based on ZnSe and ZnO buffer layers. Final report, February 16, 1992--November 15, 1995

    SciTech Connect

    Olsen, L C

    1996-06-01

    The major objective of this program was to determine the potential of ZnSe and ZnO buffer layers in solar cells based on CuInSe{sub 2} and related alloys. Experimental studies were carried out with CIS and CIGSS substrates. ZnSe films were deposited by a CVD process which involved the reaction of a zinc adduct and H{sub 2}Se. Al/ZnSe/CIS test cells were used for process development. Test cell performance aided in determining the optimum thickness for ZnSe buffer layers to be in the range of 150 {angstrom} to 200 {angstrom} for Siemens CIS material, and between 80 {angstrom} and 120 {angstrom} for the graded absorber material. If the buffer layers exceeded these values significantly, the short-circuit current would be reduced to zero. The best efficiency achieved for a ZnSe/CIS cell was an active area value of 9.2%. In general, deposition of a conductive ZnO film on top of a ZnSe/CIS structure resulted in either shunted or inflected I-V characteristics. Two approaches were investigated for depositing ZnO buffer layers, namely, chemical bath deposition and CVD. CVD ZnO buffer layers are grown by reacting a zinc adduct with tetrahydrofuran. Best results were obtained for ZnO buffer layers grown with a substrate temperature ca. 225--250 C. These studies concentrated on Siemens graded absorber material (CIGSS). ZnO/CIS solar cells have been fabricated by first depositing a ZnO buffer layer, followed by deposition of a low resistivity ZnO top contact layer and an Al/Ag collector grid. Several cells were fabricated with an area of 0.44 cm{sup 2} that have total area efficiencies greater than 11%. To date, the best performing ZnO/CIS cell had a total area efficiency of 11.3%. In general, the authors find that ZnO buffer layers should have a resistivity > 1,000 ohm-cm and have a thickness from 200 {angstrom} to 600 {angstrom}. CIS cells studies with ZnO buffer layers grown by CBD also show promise. Finally, simulation studies were carried out using the 1-D code, PC-1D.

  17. Direct electron injection into an oxide insulator using a cathode buffer layer

    PubMed Central

    Lee, Eungkyu; Lee, Jinwon; Kim, Ji-Hoon; Lim, Keon-Hee; Seok Byun, Jun; Ko, Jieun; Dong Kim, Young; Park, Yongsup; Kim, Youn Sang

    2015-01-01

    Injecting charge carriers into the mobile bands of an inorganic oxide insulator (for example, SiO2, HfO2) is a highly complicated task, or even impossible without external energy sources such as photons. This is because oxide insulators exhibit very low electron affinity and high ionization energy levels. Here we show that a ZnO layer acting as a cathode buffer layer permits direct electron injection into the conduction bands of various oxide insulators (for example, SiO2, Ta2O5, HfO2, Al2O3) from a metal cathode. Studies of current–voltage characteristics reveal that the current ohmically passes through the ZnO/oxide-insulator interface. Our findings suggests that the oxide insulators could be used for simply fabricated, transparent and highly stable electronic valves. With this strategy, we demonstrate an electrostatic discharging diode that uses 100-nm SiO2 as an active layer exhibiting an on/off ratio of ∼107, and protects the ZnO thin-film transistors from high electrical stresses. PMID:25864642

  18. Direct electron injection into an oxide insulator using a cathode buffer layer.

    PubMed

    Lee, Eungkyu; Lee, Jinwon; Kim, Ji-Hoon; Lim, Keon-Hee; Seok Byun, Jun; Ko, Jieun; Dong Kim, Young; Park, Yongsup; Kim, Youn Sang

    2015-01-01

    Injecting charge carriers into the mobile bands of an inorganic oxide insulator (for example, SiO2, HfO2) is a highly complicated task, or even impossible without external energy sources such as photons. This is because oxide insulators exhibit very low electron affinity and high ionization energy levels. Here we show that a ZnO layer acting as a cathode buffer layer permits direct electron injection into the conduction bands of various oxide insulators (for example, SiO2, Ta2O5, HfO2, Al2O3) from a metal cathode. Studies of current-voltage characteristics reveal that the current ohmically passes through the ZnO/oxide-insulator interface. Our findings suggests that the oxide insulators could be used for simply fabricated, transparent and highly stable electronic valves. With this strategy, we demonstrate an electrostatic discharging diode that uses 100-nm SiO2 as an active layer exhibiting an on/off ratio of ∼10(7), and protects the ZnO thin-film transistors from high electrical stresses. PMID:25864642

  19. Power Conversion Efficiency and Device Stability Improvement of Inverted Perovskite Solar Cells by Using a ZnO:PFN Composite Cathode Buffer Layer.

    PubMed

    Jia, Xiaorui; Zhang, Lianping; Luo, Qun; Lu, Hui; Li, Xueyuan; Xie, Zhongzhi; Yang, Yongzhen; Li, Yan-Qing; Liu, Xuguang; Ma, Chang-Qi

    2016-07-20

    We have demonstrated in this article that both power conversion efficiency (PCE) and performance stability of inverted planar heterojunction perovskite solar cells can be improved by using a ZnO:PFN nanocomposite (PFN: poly[(9,9-bis(3'-(N,N-dimethylamion)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctyl)-fluorene]) as the cathode buffer layer (CBL). This nanocomposite could form a compact and defect-less CBL film on the perovskite/PC61BM surface (PC61BM: phenyl-C61-butyric acid methyl ester). In addition, the high conductivity of the nanocomposite layer makes it works well at a layer thickness of 150 nm. Both advantages of the composite layer are helpful in reducing interface charge recombination and improving device performance. The power conversion efficiency (PCE) of the best ZnO:PFN CBL based device was measured to be 12.76%, which is higher than that of device without CBL (9.00%), or device with ZnO (7.93%) or PFN (11.30%) as the cathode buffer layer. In addition, the long-term stability is improved by using ZnO:PFN composite cathode buffer layer when compare to that of the reference cells. Almost no degradation of open circuit voltage (VOC) and fill factor (FF) was found for the device having ZnO:PFN, suggesting that ZnO:PFN is able to stabilize the interface property and consequently improve the solar cell performance stability. PMID:27349330

  20. Improvement of electron mobility in La:BaSnO3 thin films by insertion of an atomically flat insulating (Sr,Ba)SnO3 buffer layer

    NASA Astrophysics Data System (ADS)

    Shiogai, Junichi; Nishihara, Kazuki; Sato, Kazuhisa; Tsukazaki, Atsushi

    2016-06-01

    One perovskite oxide, ASnO3 (A = Sr, Ba), is a candidate for use as a transparent conductive oxide with high electron mobility in single crystalline form. However, the electron mobility of films grown on SrTiO3 substrates does not reach the bulk value, probably because of dislocation scattering that originates from the large lattice mismatch. This study investigates the effect of insertion of bilayer BaSnO3 / (Sr,Ba)SnO3 for buffering this large lattice mismatch between La:BaSnO3 and SrTiO3 substrate. The insertion of 200-nm-thick BaSnO3 on (Sr,Ba)SnO3 bilayer buffer structures reduces the number of dislocations and improves surface smoothness of the films after annealing as proved respectively by scanning transmission electron microscopy and atomic force microscopy. A systematic investigation of BaSnO3 buffer layer thickness dependence on Hall mobility of the electron transport in La:BaSnO3 shows that the highest obtained value of mobility is 78 cm2V-1s-1 because of its fewer dislocations. High electron mobility films based on perovskite BaSnO3 can provide a good platform for transparent-conducting-oxide electronic devices and for creation of fascinating perovskite heterostructures.

  1. Growth of III-V nitrides and buffer layer investigation by pulsed laser deposition

    NASA Astrophysics Data System (ADS)

    Huang, Tzu-Fang

    1999-11-01

    III-V nitrides have been investigated intensively due to the enormous interest in optoelectronic device applications in the green, blue, violet, and near-ultraviolet regions. Advances in III-V nitride materials for short wavelength light sources will lead to both a revolution in optical disk storage, as higher densities can be achieved with short wavelengths, and a major impact on imaging and graphic technology as high quality red, green, and blue light-emitting diodes (LED) and lasers become available. High quality GaN films have mostly been prepared by metal-organic vapor phase epitaxy (MOCVD), molecular beam epitaxy (MBE) and vapor phase epitaxy (VPE). Compared to these techniques, pulsed laser deposition (PLD) is a relatively new growth technique used widely for the growth of oxide thin films. However, several advantages of PLD make it worthy of study as a method of growing nitrides. The congruent ablation achieved with short UV-laser pulses allows deposition of a multicomponent material by employing a single target and the ability for depositing a wide variety of materials. This advantage makes PLD very suitable for growing multilayer structures sequentially in the same chamber and investigating the effect of buffer layers. Moreover, the strong nonequilibrium growth conditions of PLD may lead to different nucleation and growth processes. In this work, GaN and (Al,Ga)N films have been epitaxially grown on (0001) sapphire substrate by PLD, which has been successfully applied to controlling the lattice constant and band gap of (Al,Ga)N. Room-temperature photoluminescence of PLD-GaN exhibits a strong band edge emission at 3.4eV. The threading dislocations of GaN are predominantly screw dislocations with Burgers vector of <0001> while edge dislocations with Burgers vector of 1/3<11-20> are the dominant ones in GaN grown by MBE, MOCVD and VPE. This variation observed in defect characteristics may come from the difference in nucleation and growth kinetics between PLD

  2. Epitaxial CeO2 buffer layers for YBa2Cu3O(7-delta) films on sapphire

    NASA Astrophysics Data System (ADS)

    Maul, M.; Schulte, B.; Haeussler, P.; Frank, G.; Steinborn, T.; Fuess, H.; Adrian, H.

    1993-08-01

    The paper reports the successful in situ preparation of thin epitaxial CeO2 buffer layers and YBa2Cu3O(7-delta) (YBCO) films on (1 -1 0 2) Al2O3 substrates by electron beam coevaporation, using an evaporation system (Leybold L560) with four sources. Electron beam sources were used for Y, Ba, and Ce, while Cu was evaporated from a resistively heated tungsten boat. The buffer layers show very smooth surfaces and structural properties close to those of a single crystal. High quality YBCO films grown on these buffer layers have Tc not 88 K or above and j(c) values of 10 exp 6 A/sq cm or greater.

  3. Thickness of the Meniscal Lamellar Layer: Correlation with Indentation Stiffness and Comparison of Normal and Abnormally Thick Layers by Using Multiparametric Ultrashort Echo Time MR Imaging.

    PubMed

    Choi, Ja-Young; Biswas, Reni; Bae, Won C; Healey, Robert; Im, Michael; Statum, Sheronda; Chang, Eric Y; Du, Jiang; Bydder, Graeme M; D'Lima, Darryl; Chung, Christine B

    2016-07-01

    Purpose To determine the relationship between lamellar layer thickness on ultrashort echo time (UTE) magnetic resonance (MR) images and indentation stiffness of human menisci and to compare quantitative MR imaging values between two groups with normal and abnormally thick lamellar layers. Materials and Methods This was a HIPAA-compliant, institutional review board-approved study. Nine meniscal pieces were obtained from seven donors without gross meniscal pathologic results (mean age, 57.4 years ± 14.5 [standard deviation]). UTE MR imaging and T2, UTE T2*, and UTE T1ρ mapping were performed. The presence of abnormal lamellar layer thickening was determined and thicknesses were measured. Indentation testing was performed. Correlation between the thickness and indentation stiffness was assessed, and mean quantitative MR imaging values were compared between the groups. Results Thirteen normal lamellar layers had mean thickness of 232 μm ± 85 and indentation peak force of 1.37 g ± 0.87. Four abnormally thick lamellar layers showed mean thickness of 353.14 μm ± 98.36 and peak force 0.72 g ± 0.31. In most cases, normal thicknesses showed highly positive correlation with the indentation peak force (r = 0.493-0.912; P < .001 to .05). However, the thickness in two abnormal lamellar layers showed highly negative correlation (r = -0.90, P < .001; and r = -0.23, P = .042) and no significant correlation in the others. T2, UTE T2*, and UTE T1ρ values in abnormally thick lamellar layers were increased compared with values in normal lamellar layers, although only the UTE T2* value showed significant difference (P = .010). Conclusion Variation of lamellar layer thickness in normal human menisci was evident on two-dimensional UTE images. In normal lamellar layers, thickness is highly and positively correlated with surface indentation stiffness. UTE T2* values may be used to differentiate between normal and abnormally thickened lamellar layers. (©) RSNA, 2016. PMID:26829523

  4. Obtaining Thickness Maps of Corneal Layers Using the Optimal Algorithm for Intracorneal Layer Segmentation

    PubMed Central

    Rabbani, Hossein; Kazemian Jahromi, Mahdi; Jorjandi, Sahar; Mehri Dehnavi, Alireza; Hajizadeh, Fedra; Peyman, Alireza

    2016-01-01

    Optical Coherence Tomography (OCT) is one of the most informative methodologies in ophthalmology and provides cross sectional images from anterior and posterior segments of the eye. Corneal diseases can be diagnosed by these images and corneal thickness maps can also assist in the treatment and diagnosis. The need for automatic segmentation of cross sectional images is inevitable since manual segmentation is time consuming and imprecise. In this paper, segmentation methods such as Gaussian Mixture Model (GMM), Graph Cut, and Level Set are used for automatic segmentation of three clinically important corneal layer boundaries on OCT images. Using the segmentation of the boundaries in three-dimensional corneal data, we obtained thickness maps of the layers which are created by these borders. Mean and standard deviation of the thickness values for normal subjects in epithelial, stromal, and whole cornea are calculated in central, superior, inferior, nasal, and temporal zones (centered on the center of pupil). To evaluate our approach, the automatic boundary results are compared with the boundaries segmented manually by two corneal specialists. The quantitative results show that GMM method segments the desired boundaries with the best accuracy. PMID:27247559

  5. Effects of BaBi2Ta2O9 thin buffer layer on crystallization and electrical properties of CaBi2Ta2O9 thin films on Pt-coated silicon

    NASA Astrophysics Data System (ADS)

    Kato, Kazumi; Suzuki, Kazuyuki; Nishizawa, Kaori; Miki, Takeshi

    2001-05-01

    Non-c-axis oriented CaBi2Ta2O9 (CBT) thin films have been successfully deposited via the triple alkoxide solution method on Pt-coated Si substrates by inserting BaBi2Ta2O9 (BBT) thin buffer layers. The BBT thin buffer layer, which was prepared on Pt-coated Si, was a key material for suppression of the nonpolar c-axis orientation and promoting the ferroelectric structure perpendicular to the in-plane direction of CBT thin film. The annealing temperature and thickness of the BBT thin buffer layers affected the dielectric, ferroelectric, and fatigue properties of the stacked CBT/BBT thin films. The resultant 650 °C annealed CBT/BBT(30 nm) thin film exhibited good P-E hysteresis properties and fatigue behaviors.

  6. Effects of buffer layer and thermal annealing on the performance of hybrid Cu2S/PVK electrically bistable devices

    NASA Astrophysics Data System (ADS)

    Li, Xu; Lu, Yue; Guan, Li; Li, Jiantao; Wang, Yichao; Dong, Guoyi; Tang, Aiwei; Teng, Feng

    2016-09-01

    Hybrid organic/inorganic electrically bistable devices (EBDs) based on Cu2S/PVK nanocomposites have been fabricated by using a simple spin-coating method. An obvious electrical bistability is observed in the current-voltage (I-V) characteristics of the devices, and the presence of the buffer layer and the annealing process have an important effect on the enhancement of the ON/OFF current ratios. Different electrical conduction mechanisms are responsible for the charge switching of the devices in the presence and absence of the buffer layer.

  7. Improved performance of polymer solar cells by using inorganic, organic, and doped cathode buffer layers

    NASA Astrophysics Data System (ADS)

    Taohong, Wang; Changbo, Chen; Kunping, Guo; Guo, Chen; Tao, Xu; Bin, Wei

    2016-03-01

    The interface between the active layer and the electrode is one of the most critical factors that could affect the device performance of polymer solar cells. In this work, based on the typical poly(3-hexylthiophene):[6,6]-phenyl C61-butyric acid methyl ester (P3HT:PCBM) polymer solar cell, we studied the effect of the cathode buffer layer (CBL) between the top metal electrode and the active layer on the device performance. Several inorganic and organic materials commonly used as the electron injection layer in an organic light-emitting diode (OLED) were employed as the CBL in the P3HT:PCBM polymer solar cells. Our results demonstrate that the inorganic and organic materials like Cs2CO3, bathophenanthroline (Bphen), and 8-hydroxyquinolatolithium (Liq) can be used as CBL to efficiently improve the device performance of the P3HT:PCBM polymer solar cells. The P3HT:PCBM devices employed various CBLs possess power conversion efficiencies (PCEs) of 3.0%-3.3%, which are ca. 50% improved compared to that of the device without CBL. Furthermore, by using the doped organic materials Bphen:Cs2CO3 and Bphen:Liq as the CBL, the PCE of the P3HT:PCBM device will be further improved to 3.5%, which is ca. 70% higher than that of the device without a CBL and ca. 10% increased compared with that of the devices with a neat inorganic or organic CBL. Project supported by the National Natural Science Foundation of China (Grant No. 61204014), the “Chenguang” Project (13CG42) supported by Shanghai Municipal Education Commission and Shanghai Education Development Foundation, China, and the Shanghai University Young Teacher Training Program of Shanghai Municipality, China.

  8. Layer-by-layer Assembly of Thick, Cu2+-Chelating Films

    PubMed Central

    Wijeratne, Salinda; Bruening, Merlin L.; Baker, Gregory L.

    2013-01-01

    Layer-by-layer adsorption of protonated poly(allylamine) (PAH) and deprotonated poly(N,N-dicarboxymethylallyl amine) (PDCMAA) yields thick films with a high density of iminodiacetic acid (IDA) ligands that bind metal ions. When film deposition occurs at pH 3.0, PAH/PDCMAA bilayer thicknesses reach 200 nm, and Cu2+ binding capacities are ~2.5 mmoles per cm3 of film. (PAH/PDCMAA)10 films deposited at pH 3.0 are 4- to 8-fold thicker than films formed at pH 5.0, 7.0, or 9.0, presumably because of the low charge density on PDCMAA chains at pH 3.0. However, with normalization to film thickness, all films bind similar amounts of Cu2+ from pH 4.1 solutions of CuSO4. In μm-thick films, equilibration of binding sites with Cu2+ requires ~4 h due to a low Cu2+ diffusion coefficient (~2.6×10−12 cm2/sec). Sorption isotherms determined at several temperatures show that Cu2+ binding is endothermic with a positive entropy (binding constants increase with increasing temperature), presumably because metal-ion complexation involves displacement of both a proton from IDA and water molecules from Cu2+. (PAH/PDCMAA)10 films retain their binding capacity over 4 absorption/elution cycles and may prove useful in metal-ion scavenging, catalysis, and protein binding. PMID:24044576

  9. Inversion of thicknesses of multi-layered structures from eddy current testing measurements.

    PubMed

    Huang, Ping-jie; Wu, Zhao-tong

    2004-01-01

    Luquire et al.'s impedance change model of a rectangular cross section probe coil above a structure with an arbitrary number of parallel layers was used to study the principle of measuring thicknesses of multi-layered structures in terms of eddy current testing voltage measurements. An experimental system for multi-layered thickness measurement was developed and several fitting models to formulate the relationships between detected impedance/voltage measurements and thickness are put forward using least square method. The determination of multi-layered thicknesses was investigated after inversing the voltage outputs of the detecting system. The best fitting and inversion models are presented. PMID:14663858

  10. Evaluation of methods for application of epitaxial buffer and superconductor layers

    SciTech Connect

    1999-03-30

    The recent achievements of critical currents exceeding million amperes per square centimeter at 77K in YBCO deposited over suitably textured substrate have stimulated interest in the potential applications of coated conductors at high temperatures and in high magnetic fields. Currently, ion-beam assisted deposition (IBAD), and rolling assisted bi-axially textured substrate (RABiTS), represent two available options for obtaining textured substrates. For applying suitable coatings of buffer and high temperature superconductor (HTS) material over textured substrates, several options are available which include sputtering, electron-beam evaporation, laser ablation, electrophoresis, chemical vapor deposition (including metal organics chemical vapor deposition), sol-gel, metal organics decomposition, electrodeposition and aerosol/spray pyrolysis. A commercial continuous long-length wire/tape manufacturing scheme developed out of any suitable combination of the above techniques would consist of operations involving preparation of the substrate and application of buffer, HTS and passivation/insulation materials and special treatment steps such as post-annealing. These operations can be effected by various process parameters that can be classified into chemistry, materials, engineering and environmental related parameters. Under the DOE-sponsored program, to carry out an engineering evaluation, first, the process flow schemes were developed for various candidate options identifying the major operating steps, process conditions, and process streams. Next, to evaluate quantifiable parameters such as process severity (e.g. temperature and pressure), coating thickness and deposition rate for HTS material, achieved maximum J{sub c} value (for films >1{micro}m thick) and cost of chemical and material utilization efficiency, the multi-attribute method was used to determine attributes/merits for various parameters and candidate options. To determine similar attribute values for the

  11. Control of metamorphic buffer structure and device performance of InxGa1-xAs epitaxial layers fabricated by metal organic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Nguyen, H. Q.; Yu, H. W.; Luc, Q. H.; Tang, Y. Z.; Phan, V. T. H.; Hsu, C. H.; Chang, E. Y.; Tseng, Y. C.

    2014-12-01

    Using a step-graded (SG) buffer structure via metal-organic chemical vapor deposition, we demonstrate a high suitability of In0.5Ga0.5As epitaxial layers on a GaAs substrate for electronic device application. Taking advantage of the technique’s precise control, we were able to increase the number of SG layers to achieve a fairly low dislocation density (˜106 cm-2), while keeping each individual SG layer slightly exceeding the critical thickness (˜80 nm) for strain relaxation. This met the demanded but contradictory requirements, and even offered excellent scalability by lowering the whole buffer structure down to 2.3 μm. This scalability overwhelmingly excels the forefront studies. The effects of the SG misfit strain on the crystal quality and surface morphology of In0.5Ga0.5As epitaxial layers were carefully investigated, and were correlated to threading dislocation (TD) blocking mechanisms. From microstructural analyses, TDs can be blocked effectively through self-annihilation reactions, or hindered randomly by misfit dislocation mechanisms. Growth conditions for avoiding phase separation were also explored and identified. The buffer-improved, high-quality In0.5Ga0.5As epitaxial layers enabled a high-performance, metal-oxide-semiconductor capacitor on a GaAs substrate. The devices displayed remarkable capacitance-voltage responses with small frequency dispersion. A promising interface trap density of 3 × 1012 eV-1 cm-2 in a conductance test was also obtained. These electrical performances are competitive to those using lattice-coherent but pricey InGaAs/InP systems.

  12. Effect of Ag doping and insulator buffer layer on the memory mechanism of polymer nanocomposites

    NASA Astrophysics Data System (ADS)

    Kaur, Ramneek; Kaur, Jagdish; Tripathi, S. K.

    2015-07-01

    Resistive memory devices based on nanocomposites have attracted great potential for future applications in electronic and optoelectronic devices. The successful synthesis of aqueous CdSe nanoparticles has been provided with UV-Vis and Photoluminescence spectroscopy. The two terminal planar devices of CdSe nanocomposite have been fabricated. The effect of Ag doping and additional dielectric buffer layers on the memory devices have been studied by current-voltage (I-V) and capacitance-voltage (C-V) measurements. The devices show hysteresis loops in both positive and negative bias directions. The memory window has been found to be increased with both Ag doping and PVA layer addition. The charge carrier transport mechanism in the memory devices has been studied by fitting the I-V characteristics with the theoretical model, Space charge conduction model (SCLC). C-V hysteresis loop in both positive and negative bias directions indicate that both the electrons and holes are responsible for memory mechanism of the devices. The switching mechanism of the memory devices has been explained by charge trapping/detrapping model. The retention characteristics show good stability and reliability of the devices.

  13. Optimisation of a carbon doped buffer layer for AlGaN/GaN HEMT devices

    NASA Astrophysics Data System (ADS)

    Gamarra, Piero; Lacam, Cedric; Tordjman, Maurice; Splettstösser, Jörg; Schauwecker, Bernd; di Forte-Poisson, Marie-Antoinette

    2015-03-01

    This work reports on the optimisation of carbon doping GaN buffer layer (BL) for AlGaN/GaN HEMT (high electron mobility transistor) structures, grown by low pressure metal-organic vapour phase epitaxy (LP-MOVPE) on 3 in. SiC semi-insulating substrates. The incorporation of carbon impurities in GaN is studied as a function of the growth conditions, without using an external carbon source. We observed that the C incorporation can be effectively controlled over more than one order of magnitude by tuning the reactor pressure and the growth temperature, without degradation of the crystalline properties of the GaN layers. HEMT structures with a specific barrier design were grown with different carbon dopings in the GaN BL and processed into transistors to evaluate the impact of the BL doping on the device performances. A significant improvement of the HEMT drain leakage current and of the breakdown voltage was obtained by increasing the carbon incorporation in the GaN BL. The RF performances of the devices show a trade-off between leakage currents and trapping phenomena which are enhanced by the use of carbon doping, limiting the delivered output power. An output power as high as 6.5 W/mm with a Power Added Efficiency of 70% has been achieved at 2 GHz by the HEMT structures with the lowest carbon doping in the BL.

  14. Effect of Mg doping in ZnO buffer layer on ZnO thin film devices for electronic applications

    NASA Astrophysics Data System (ADS)

    Giri, Pushpa; Chakrabarti, P.

    2016-05-01

    Zinc Oxide (ZnO) thin films have been grown on p-silicon (Si) substrate using magnesium doped ZnO (Mg: ZnO) buffer layer by radio-frequency (RF) sputtering method. In this paper, we have optimized the concentration of Mg (0-5 atomic percent (at. %)) ZnO buffer layer to examine its effect on ZnO thin film based devices for electronic and optoelectronic applications. The crystalline nature, morphology and topography of the surface of the thin film have been characterized. The optical as well as electrical properties of the active ZnO film can be tailored by varying the concentration of Mg in the buffer layer. The crystallite size in the active ZnO thin film was found to increase with the Mg concentration in the buffer layer in the range of 0-3 at. % and subsequently decrease with increasing Mg atom concentration in the ZnO. The same was verified by the surface morphology and topography studies carried out with scanning electron microscope (SEM) and atomic electron microscopy (AFM) respectively. The reflectance in the visible region was measured to be less than 80% and found to decrease with increase in Mg concentration from 0 to 3 at. % in the buffer region. The optical bandgap was initially found to increase from 3.02 eV to 3.74 eV by increasing the Mg content from 0 to 3 at. % but subsequently decreases and drops down to 3.43 eV for a concentration of 5 at. %. The study of an Au:Pd/ZnO Schottky diode reveals that for optimum doping of the buffer layer the device exhibits superior rectifying behavior. The barrier height, ideality factor, rectification ratio, reverse saturation current and series resistance of the Schottky diode were extracted from the measured current voltage (I-V) characteristics.

  15. Assembly and organization of poly(3-hexylthiophene) brushes and their potential use as novel anode buffer layers for organic photovoltaics.

    PubMed

    Alonzo, José; Kochemba, W Michael; Pickel, Deanna L; Ramanathan, Muruganathan; Sun, Zhenzhong; Li, Dawen; Chen, Jihua; Sumpter, Bobby G; Heller, William T; Kilbey, S Michael

    2013-10-01

    Buffer layers that control electrochemical reactions and physical interactions at electrode/film interfaces are key components of an organic photovoltaic cell. Here the structure and properties of layers of semi-rigid poly(3-hexylthiophene) (P3HT) chains tethered at a surface are investigated, and these functional systems are applied in an organic photovoltaic device. Areal density of P3HT chains is readily tuned through the choice of polymer molecular weight and annealing conditions, and insights from optical absorption spectroscopy and semiempirical quantum calculation methods suggest that tethering causes intrachain defects that affect co-facial π-stacking of brush chains. Because of their ability to modify oxide surfaces, P3HT brushes are utilized as an anode buffer layer in a P3HT-PCBM (phenyl-C₆₁-butyric acid methyl ester) bulk heterojunction device. Current-voltage characterization shows a significant enhancement in short circuit current, suggesting the potential of these novel nanostructured buffer layers to replace the PEDOT:PSS buffer layer typically applied in traditional P3HT-PCBM solar cells. PMID:23955069

  16. Carbon doped GaN buffer layer using propane for high electron mobility transistor applications: Growth and device results

    SciTech Connect

    Li, X.; Nilsson, D.; Danielsson, Ö.; Pedersen, H.; Janzén, E.; Forsberg, U.; Bergsten, J.; Rorsman, N.

    2015-12-28

    The creation of a semi insulating (SI) buffer layer in AlGaN/GaN High Electron Mobility Transistor (HEMT) devices is crucial for preventing a current path beneath the two-dimensional electron gas (2DEG). In this investigation, we evaluate the use of a gaseous carbon gas precursor, propane, for creating a SI GaN buffer layer in a HEMT structure. The carbon doped profile, using propane gas, is a two stepped profile with a high carbon doping (1.5 × 10{sup 18 }cm{sup −3}) epitaxial layer closest to the substrate and a lower doped layer (3 × 10{sup 16 }cm{sup −3}) closest to the 2DEG channel. Secondary Ion Mass Spectrometry measurement shows a uniform incorporation versus depth, and no memory effect from carbon doping can be seen. The high carbon doping (1.5 × 10{sup 18 }cm{sup −3}) does not influence the surface morphology, and a roughness root-mean-square value of 0.43 nm is obtained from Atomic Force Microscopy. High resolution X-ray diffraction measurements show very sharp peaks and no structural degradation can be seen related to the heavy carbon doped layer. HEMTs are fabricated and show an extremely low drain induced barrier lowering value of 0.1 mV/V, demonstrating an excellent buffer isolation. The carbon doped GaN buffer layer using propane gas is compared to samples using carbon from the trimethylgallium molecule, showing equally low leakage currents, demonstrating the capability of growing highly resistive buffer layers using a gaseous carbon source.

  17. Retinal nerve fiber layer thickness and retinal vessel calibers in children with thalassemia minor

    PubMed Central

    Acer, Semra; Balcı, Yasemin I; Pekel, Gökhan; Ongun, Tuğba T; Polat, Aziz; Çetin, Ebru N; Yağcı, Ramazan

    2016-01-01

    Objectives: Evaluation of the peripapillary retinal nerve fiber layer thickness, subfoveal choroidal thickness, and retinal vessel caliber measurements in children with thalassemia minor. Methods: In this cross-sectional and comparative study, 30 thalassemia minor patients and 36 controls were included. Heidelberg spectral domain optical coherence tomography was used for peripapillary retinal nerve fiber layer thickness, subfoveal choroidal thickness, and retinal vessel caliber measurements. Results: There was no statistically significant difference in retinal nerve fiber layer thickness and subfoveal choroidal thickness between the two groups (p > 0.05). There was no correlation between retinal nerve fiber layer thickness and hemoglobin values. Both the arterioral and venular calibers were higher in thalassemia minor group (p < 0.05). Conclusion: There is increased retinal arterioral and venular calibers in children with thalassemia minor compared with controls. PMID:27540484

  18. Preparation of a thick polymer brush layer composed of poly(2-methacryloyloxyethyl phosphorylcholine) by surface-initiated atom transfer radical polymerization and analysis of protein adsorption resistance.

    PubMed

    Inoue, Yuuki; Onodera, Yuya; Ishihara, Kazuhiko

    2016-05-01

    The purpose of this study was to prepare a thick polymer brush layer composed of poly(2-methacryloyloxyethyl phosphorylcholine (MPC)) and assess its resistance to protein adsorption from the dissolved state of poly(MPC) chains in an aqueous condition. The thick poly(MPC) brush layer was prepared through the surface-initiated atom transfer radical polymerization (SI-ATRP) of MPC with a free initiator from an initiator-immobilized substrate at given [Monomer]/[Free initiator] ratios. The ellipsometric thickness of the poly(MPC) brush layers could be controlled by the polymerization degree of the poly(MPC) chains. The thickness of the poly(MPC) brush layer in an aqueous medium was larger than that in air, and this tendency became clearer when the polymerization degree of the poly(MPC) increased. The maximum thickness of the poly(MPC) brush layer in an aqueous medium was around 110nm. The static air contact angle of the poly(MPC) brush layer in water indicated a reasonably hydrophilic nature, which was independent of the thickness of the poly(MPC) brush layer at the surface. This result occurred because the hydrated state of the poly(MPC) chains is not influenced by the environment surrounding them. Finally, as measured with a quartz crystal microbalance, the amount of protein adsorbed from a fetal bovine serum solution (10% in phosphate-buffered saline) on the original substrate was 420ng/cm(2). However, the poly(MPC) brush layer reduced this value dramatically to less than 50ng/cm(2). This effect was independent of the thickness of the poly(MPC) brush layer for thicknesses between 20nm and about 110nm. These results indicated that the surface covered with a poly(MPC) brush layer is a promising platform to avoid biofouling and could also be applied to analyze the reactions of biological molecules with a high signal/noise ratio. PMID:26896657

  19. Thickness Mapping of Eleven Retinal Layers Segmented Using the Diffusion Maps Method in Normal Eyes

    PubMed Central

    Kafieh, Raheleh; Rabbani, Hossein; Abramoff, Michael D.; Sonka, Milan

    2015-01-01

    This study was conducted to determine the thickness map of eleven retinal layers in normal subjects by spectral domain optical coherence tomography (SD-OCT) and evaluate their association with sex and age. Mean regional retinal thickness of 11 retinal layers was obtained by automatic three-dimensional diffusion map based method in 112 normal eyes of 76 Iranian subjects. We applied our previously reported 3D intraretinal fast layer segmentation which does not require edge-based image information but rather relies on regional image texture. The thickness maps are compared among 9 macular sectors within 3 concentric circles as defined by ETDRS. The thickness map of central foveal area in layers 1, 3, and 4 displayed the minimum thickness. Maximum thickness was observed in nasal to the fovea of layer 1 and in a circular pattern in the parafoveal retinal area of layers 2, 3, and 4 and in central foveal area of layer 6. Temporal and inferior quadrants of the total retinal thickness and most of other quadrants of layer 1 were significantly greater in the men than in the women. Surrounding eight sectors of total retinal thickness and a limited number of sectors in layers 1 and 4 significantly correlated with age. PMID:25960888

  20. Cloud layer thicknesses from a combination of surface and upper-air observations

    NASA Technical Reports Server (NTRS)

    Poore, Kirk D.; Wang, Junhong; Rossow, William B.

    1995-01-01

    Cloud layer thicknesses are derived from base and top altitudes by combining 14 years (1975-1988) of surface and upper-air observations at 63 sites in the Northern Hemisphere. Rawinsonde observations are employed to determine the locations of cloud-layer top and base by testing for dewpoint temperature depressions below some threshold value. Surface observations serve as quality checks on the rawinsonde-determined cloud properties and provide cloud amount and cloud-type information. The dataset provides layer-cloud amount, cloud type, high, middle, or low height classes, cloud-top heights, base heights and layer thicknesses, covering a range of latitudes from 0 deg to 80 deg N. All data comes from land sites: 34 are located in continental interiors, 14 are near coasts, and 15 are on islands. The uncertainties in the derived cloud properties are discussed. For clouds classified by low-, mid-, and high-top altitudes, there are strong latitudinal and seasonal variations in the layer thickness only for high clouds. High-cloud layer thickness increases with latitude and exhibits different seasonal variations in different latitude zones: in summer, high-cloud layer thickness is a maximum in the Tropics but a minimum at high latitudes. For clouds classified into three types by base altitude or into six standard morphological types, latitudinal and seasonal variations in layer thickness are very small. The thickness of the clear surface layer decreases with latitude and reaches a summer minimum in the Tropics and summer maximum at higher latitudes over land, but does not vary much over the ocean. Tropical clouds occur in three base-altitude groups and the layer thickness of each group increases linearly with top altitude. Extratropical clouds exhibit two groups, one with layer thickness proportional to their cloud-top altitude and one with small (less than or equal to 1000 m) layer thickness independent of cloud-top altitude.

  1. Metaporous layer to overcome the thickness constraint for broadband sound absorption

    SciTech Connect

    Yang, Jieun; Lee, Joong Seok; Kim, Yoon Young

    2015-05-07

    The sound absorption of a porous layer is affected by its thickness, especially in a low-frequency range. If a hard-backed porous layer contains periodical arrangements of rigid partitions that are coordinated parallel and perpendicular to the direction of incoming sound waves, the lower bound of the effective sound absorption can be lowered much more and the overall absorption performance enhanced. The consequence of rigid partitioning in a porous layer is to make the first thickness resonance mode in the layer appear at much lower frequencies compared to that in the original homogeneous porous layer with the same thickness. Moreover, appropriate partitioning yields multiple thickness resonances with higher absorption peaks through impedance matching. The physics of the partitioned porous layer, or the metaporous layer, is theoretically investigated in this study.

  2. Solution Processing of Cadmium Sulfide Buffer Layer and Aluminum-Doped Zinc Oxide Window Layer for Thin Films Solar Cells

    NASA Astrophysics Data System (ADS)

    Alam, Mahboob; Islam, Mohammad; Achour, Amine; Hayat, Ansar; Ahsan, Bilal; Rasheed, Haroon; Salam, Shahzad; Mujahid, Mohammad

    2014-07-01

    Cadmium sulfide (CdS) and aluminum-doped zinc oxide (Al:ZnO) thin films are used as buffer layer and front window layer, respectively, in thin film solar cells. CdS and Al:ZnO thin films were produced using chemical bath deposition (CBD) and sol-gel technique, respectively. For CBD CdS, the effect of bath composition and temperature, dipping time and annealing temperature on film properties was investigated. The CdS films are found to be polycrystalline with metastable cubic crystal structure, dense, crack-free surface morphology and the crystallite size of either few nanometers or 12-17 nm depending on bath composition. In case of CdS films produced with 1:2 ratio of Cd and S precursors, spectrophotometer studies indicate quantum confinement effect, owing to extremely small crystallite size, with an increase in Eg value from 2.42 eV (for bulk CdS) to 3.76 eV along with a shift in the absorption edge toward 330 nm wavelength. The optimum annealing temperature is 400°C beyond which film properties deteriorate through S evaporation and CdO formation. On the other hand, Al:ZnO films prepared via spin coating of precursor sols containing 0.90-1.10 at.% Al show that, with an increase in Al concentration, the average grain size increases from 28 nm to 131 nm with an associated decrease in root-mean-square roughness. The minimum value of electrical resistivity, measured for the films prepared using 0.95 at.% Al in the precursor sol, is 2.7 × 10-4 Ω ṡ cm. The electrical resistivity value rises upon further increase in Al doping level due to introduction of lattice defects and Al segregation to the grain boundary area, thus limiting electron transport through it.

  3. Effects of Membrane- and Catalyst-layer-thickness Nonuniformitiesin Polymer-electrolyte Fuel Cells

    SciTech Connect

    Weber, Adam Z.; Newman, John

    2006-09-01

    In this paper, results from mathematical, pseudo 2-D simulations are shown for four different along-the-channel thickness distributions of both the membrane and cathode catalyst layer. The results and subsequent analysis clearly demonstrate that for the membrane thickness distributions, cell performance is affected a few percent under low relative-humidity conditions and that the position along the gas channel is more important than the local thickness variations. However, for the catalyst-layer thickness distributions, global performance is not impacted, although for saturated conditions there is a large variability in the local temperature and performance depending on the thickness.

  4. Cd-Zn-O-S alloys for optimal buffer layers in thin-film photovoltaics (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Varley, Joel B.; He, Xiaoqing; Mackie, Neil; Rockett, Angus A.; Lordi, Vincenzo

    2015-09-01

    Advances in thin-film photovoltaics have largely focused on modifying the absorber layer(s), while the choices for other layers in the solar cell stack have remained somewhat limited. In particular, cadmium sulfide (CdS) is widely used as the buffer layer in typical record devices utilizing absorbers like Cu(In,Ga)Se2 (CIGSe) or Cu2ZnSnS4 (CZTS) despite leading to a loss of solar photocurrent due to its band gap of 2.4 eV. While different buffers such as Zn(S,O,OH) are beginning to become competitive with CdS, the identification of additional wider-band gap alternatives with electrical properties comparable to or better than CdS is highly desirable. Here we use hybrid density functional calculations to characterize CdxZn1-xOyS1-y candidate buffer layers in the quaternary phase space composed by Cd, Zn, O, and S. We focus on the band gaps and band offsets of the alloys to assess strategies for improving absorption losses from conventional CdS buffers while maintaining similar conduction band offsets known to facilitate good device performance. We also consider additional criteria such as lattice matching to identify regions in the composition space that may provide improved epitaxy to CIGSe and CZTS absorbers. Lastly, we incorporate our calculated alloy properties into device model simulations of typical CIGSe devices to identify the CdxZn1-xOyS1-y buffer compositions that lead to the best performance. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344 and funded by the Department of Energy office of Energy Efficiency and Renewable Energy (EERE) through the SunShot Bridging Research Interactions through collaborative Development Grants in Energy (BRIDGE) program.

  5. Characterization and optimization of residual layer thickness during UV imprint process for singlemode waveguide fabrication

    NASA Astrophysics Data System (ADS)

    An, Shinmo; Lee, Hyun-Shik; Park, Se-Guen; O, Beom-Hoan; Lee, Seung-Gol; Lee, El-Hang

    2009-02-01

    We report on the fabrication and characterization of a residual layer resulting from UV imprinting of singlemode optical waveguide. We have measured the residual thickness formed from the imprinting process for several-um-size singlemode waveguide fabrication using the parameters of the imprinting pressure, dropped volume, and viscosity of the used polymer. We found that the residual layer thickness is dependent on both the initial polymer volume and process pressure and the initial polymer volume is more critical than process pressure. Viscosity of polymer also affects the residual layer thickness, the lowest residual layer thickness of 29nm is achieved with nano-imprinting resin, 0.3uL volume, and imprint pressure more than 20bar. Even with optical resin, the residual layer thickness of 60nm is achieved with 0.3uL volume and imprinting pressure of 30bar.

  6. Enhancement in electrical properties of ITO/PEDOT:PSS/PTCDA/Ag by using calcium buffer layer

    NASA Astrophysics Data System (ADS)

    Tahir, Muhammad; Hassan Sayyad, Muhammad; Wahab, Fazal; Aziz, Fakhra; Ullah, Irfan; Khan, Gulzar

    2015-06-01

    This paper reports on electrical characterization of ITO/PEDOT:PSS/PTCDA/Ca/Ag device based on 3,4,9,10-perylene tetracarboxylic dianhydride (PTCDA) and calcium (Ca) buffer layer with improved junction properties. The I-V characteristics have been utilized to extract various electrical parameters such as ideality factor (n), barrier height (ϕB) and series resistance Rs, which are found to be 1.9, 0.79 eV and 2.5 kΩ, respectively. The device shows good rectifying behavior, with a rectification ratio of 528, and also field-lowering mechanism with a linear dependence of log I on V1/2. The device reported in the present work shows 50% improvement in the rectification ratio and ideality factor as compared to our previously fabricated device. It appears from the experimental data that the transport mechanism in the PTCDA thin film is dominated by the Poole-Frenkel model of thermionic emission, which may be associated with high density of structural defects or traps present in the film.

  7. Rayleigh-Taylor growth and imprint reduction using foam buffer layers on the Omega Laser

    NASA Astrophysics Data System (ADS)

    Watt, R. G.; Duke, J. R.; Elliot, N. E.; Gobby, P. L.; Hollis, R. V.; Kopp, R. A.; Mason, R. J.; Pollak, G.; Wilson, D. C.; Willi, O.; Kalantar, D. H.; Boehly, T. R.; Knauer, J. P.; Meyerhofer, D. D.; Smalyuk, V. A.; Verdon, C. P.

    1997-11-01

    A serious concern for directly driven ICF implosions is the asymmetry imparted to the capsule by laser drive nonuniformities. A distributed phase plate (DPP) with speckle pattern averaged over several coherence times by smoothing with spectral dispersion (SSD) still retains an ``early time imprint''. A supersonically preheated foam, with Au preheat layer, may reduce this imprint, by creating a low density, high temperature thermal plasma between the absorption and ablation surfaces. We report on experiments using machined polystyrene (PS) foams at 30 mg/cc on the Omega laser at 351 nm. The Rayleigh-Taylor growth of intentional solid substrate mass modulations was measured. Similar observed growth with and without foam suggests at most minor isentrope changes in the solid due to the presence of the foam. Significant reduction in the imprint from the OMEGA beams with DPP and distributed polarization rotators (DPR) but without smoothing by spectral dispersion (SSD) is observed when a foam buffer is employed. Recent experimental results will be shown and compared to simulations.

  8. Improving the performance of perovskite solar cells with glycerol-doped PEDOT:PSS buffer layer

    NASA Astrophysics Data System (ADS)

    Jian-Feng, Li; Chuang, Zhao; Heng, Zhang; Jun-Feng, Tong; Peng, Zhang; Chun-Yan, Yang; Yang-Jun, Xia; Duo-Wang, Fan

    2016-02-01

    In this paper, we investigate the effects of glycerol doping on transmittance, conductivity and surface morphology of poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate)) (PEDOT:PSS) and its influence on the performance of perovskite solar cells. . The conductivity of PEDOT:PSS is improved obviously by doping glycerol. The maximum of the conductivity is 0.89 S/cm when the doping concentration reaches 6 wt%, which increases about 127 times compared with undoped. The perovskite solar cells are fabricated with a configuration of indium tin oxide (ITO)/PEDOT:PSS/CH3NH3PbI3/PC61BM/Al, where PEDOT:PSS and PC61BM are used as hole and electron transport layers, respectively. The results show an improvement of hole charge transport as well as an increase of short-circuit current density and a reduction of series resistance, owing to the higher conductivity of the doped PEDOT:PSS. Consequently, it improves the whole performance of perovskite solar cell. The power conversion efficiency (PCE) of the device is improved from 8.57% to 11.03% under AM 1.5 G (100 mW/cm2 illumination) after the buffer layer has been modified. Project supported by the National Natural Science Foundation of China (Grant Nos. 61264002, 61166002, 91333206, and 51463011), the Natural Science Foundation of Gansu Province, China (Grant No. 1308RJZA159), the New Century Excellent Talents in University of Ministry of Education of China (Grant No. NCET-13-0840), the Research Project of Graduate Teacher of Gansu Province, China (Grant No. 2014A-0042), and the Postdoctoral Science Foundation from Lanzhou Jiaotong University, China.

  9. The effect of chain rigidity on the interfacial layer thickness and dynamics of polymer nanocomposites

    NASA Astrophysics Data System (ADS)

    Cheng, Shiwang; Carrillo, Jan-Michael Y.; Carroll, Bobby; Sumpter, Bobby G.; Sokolov, Alexei P.

    There are growing experimental evidences showing the existence of an interfacial layer that has a finite thickness with slowing down dynamics in polymer nanocomposites (PNCs). Moreover, it is believed that the interfacial layer plays a significant role on various macroscopic properties of PNCs. A thicker interfacial layer is found to have more pronounced effect on the macroscopic properties such as the mechanical enhancement. However, it is not clear what molecular parameter controls the interfacial layer thickness. Inspired by our recent computer simulations that showed the chain rigidity correlated well with the interfacial layer thickness, we performed systematic experimental studies on different polymer nanocomposites by varying the chain stiffness. Combining small-angle X-ray scattering, broadband dielectric spectroscopy and temperature modulated differential scanning calorimetry, we find a good correlation between the polymer Kuhn length and the thickness of the interfacial layer, confirming the earlier computer simulations results. Our findings provide a direct guidance for the design of new PNCs with desired properties.

  10. Optimization of the Energy Level Alignment between the Photoactive Layer and the Cathode Contact Utilizing Solution-Processed Hafnium Acetylacetonate as Buffer Layer for Efficient Polymer Solar Cells.

    PubMed

    Yu, Lu; Li, Qiuxiang; Shi, Zhenzhen; Liu, Hao; Wang, Yaping; Wang, Fuzhi; Zhang, Bing; Dai, Songyuan; Lin, Jun; Tan, Zhan'ao

    2016-01-13

    The insertion of an appropriate interfacial buffer layer between the photoactive layer and the contact electrodes makes a great impact on the performance of polymer solar cells (PSCs). Ideal interfacial buffer layers could minimize the interfacial traps and the interfacial barriers caused by the incompatibility between the photoactive layer and the electrodes. In this work, we utilized solution-processed hafnium(IV) acetylacetonate (Hf(acac)4) as an effective cathode buffer layer (CBL) in PSCs to optimize the energy level alignment between the photoactive layer and the cathode contact, with the short-circuit current density (Jsc), open-circuit voltage (Voc), and fill factor (FF) all simultaneously improved with Hf(acac)4 CBL, leading to enhanced power conversion efficiencies (PCEs). Ultraviolet photoemission spectroscopy (UPS) and scanning Kelvin probe microscopy (SKPM) were performed to confirm that the interfacial dipoles were formed with the same orientation direction as the built-in potential between the photoactive layer and Hf(acac)4 CBL, benefiting the exciton separation and electron transport/extraction. In addition, the optical characteristics and surface morphology of the Hf(acac)4 CBL were also investigated. PMID:26684416

  11. Change in Tear Film Lipid Layer Thickness, Corneal Thickness, Volume and Topography after Superficial Cauterization for Conjunctivochalasis

    PubMed Central

    Chan, Tommy C. Y.; Ye, Cong; Ng, Paul KF; Li, Emmy Y. M.; Yuen, Hunter K. L.; Jhanji, Vishal

    2015-01-01

    We evaluated the change in tear film lipid layer thickness, corneal thickness, volume and topography after superficial cauterization of symptomatic conjunctivochalasis. Bilateral superficial conjunctival cauterization was performed in 36 eyes of 18 patients with symptomatic conjunctivochalasis. The mean age of patients (12 males, 6 females) was 68.6 ± 10.9 years (range: 44–83 years). Preoperatively, 28 eyes (77.8%) had grade 1 conjunctivochalasis, and 8 eyes (22.2%) had grade 2 conjunctivochalasis. At 1 month postoperatively, the severity of conjunctivochalasis decreased significantly (p < 0.001) and 29 eyes (80.6%) had grade 0 conjunctivochalasis whereas 7 eyes (19.4%) had grade 1 conjunctivochalasis. The mean Ocular Surface Disease Index score decreased from 31.5 ± 15.2 preoperatively to 21.5 ± 14.2 at the end of 1 month postoperatively (p = 0.001). There was a statistically significant increase in mean tear film lipid layer thickness 1 month after the surgery (49.6 ± 16.1 nm vs 62.6 ± 21.6 nm; p < 0.001). The central corneal thickness, thinnest corneal thickness and corneal volume decreased significantly postoperatively (p < 0.001). Our study showed that superficial conjunctival cauterization is an effective technique for management of conjunctivochalasis in the short term. An increase in tear film lipid layer thickness along with a decrease in corneal thickness and volume were observed after surgical correction of conjunctivochalasis. PMID:26184418

  12. Simultaneous enhancement of photovoltage and charge transfer in Cu2O-based photocathode using buffer and protective layers

    NASA Astrophysics Data System (ADS)

    Li, Changli; Hisatomi, Takashi; Watanabe, Osamu; Nakabayashi, Mamiko; Shibata, Naoya; Domen, Kazunari; Delaunay, Jean-Jacques

    2016-07-01

    Coating n-type buffer and protective layers on Cu2O may be an effective means to improve the photoelectrochemical (PEC) water-splitting performance of Cu2O-based photocathodes. In this letter, the functions of the buffer layer and protective layer on Cu2O are examined. It is found that a Ga2O3 buffer layer can form a buried junction with Cu2O, which inhibits Cu2O self-reduction as well as increases the photovoltage through a small conduction band offset between the two semiconductors. The introduction of a TiO2 thin protective layer not only improves the stability of the photocathode but also enhances the electron transfer from the photocathode surface into the electrolyte, thus resulting in an increase in photocurrent at positive potentials. These results show that the selection of overlayers with appropriate conduction band positions provides an effective strategy for obtaining a high photovoltage and high photocurrent in PEC systems.

  13. Strain states of AlN/GaN-stress mitigating layer and their effect on GaN buffer layer grown by ammonia molecular beam epitaxy on 100-mm Si(111)

    SciTech Connect

    Ravikiran, L.; Radhakrishnan, K.; Agrawal, M.; Dharmarasu, N.; Munawar Basha, S.

    2013-09-28

    The effect of strain states of AlN/GaN-stress mitigating layer (SML) on buried crack density and its subsequent influence on the residual stresses in GaN buffer layers grown using ammonia-molecular beam epitaxy on 100-mm Si(111) substrate has been investigated. Different stages involved in the formation of buried cracks, which are crack initialization, growth of relaxed AlN layer, and subsequent lateral over growth, are identified using in-situ curvature measurements. While the increase of GaN thickness in AlN/GaN-SML enhanced its compressive strain relaxation and resulted in reduced buried crack spacing, the variation of AlN thickness did not show any effect on the crack spacing. Moreover, the decrease in the crack spacing (or increase in the buried crack density) was found to reduce the residual compression in 1st and 2nd GaN layers of AlN/GaN-SML structure. The higher buried crack density relaxed the compressive strain in 1st GaN layer, which further reduced its ability to compensate the tensile stress generated during substrate cool down, and hence resulted in lower residual compressive stress in 2nd GaN layer.

  14. Tantalum as a buffer layer in diamond-like carbon coated artificial hip joints.

    PubMed

    Kiuru, Mirjami; Alakoski, Esa; Tiainen, Veli-Matti; Lappalainen, Reijo; Anttila, Asko

    2003-07-15

    The acid resistance of tantalum coated and uncoated human hip joint prostheses was studied with commercial CrCoMo acetabular cups. The samples were exposed to 10% HCl solution and the quantities of dissolved Cr, Co, and Mo were measured with proton-induced X-ray emission (PIXE). The absolute quantities were obtained with the use of Cr and Se solution standards. Tantalum coatings (thicknesses 4-6 microm) were prepared in vacuum with magnetron sputtering. Tantalum coating decreased the corrosion rate by a factor of 10(6). As a spinoff from recent wear tests on artificial hip joints it was shown that tantalum has excellent mechanical properties as an intermediate layer of diamond-like carbon (DLC) coatings. When tantalum was tested together with DLC on three metal-on-metal hip joint pairs in a hip simulator, no observable defects occurred during 15 million walking cycles with a periodic 50-300-kg load (Paul curve). PMID:12808604

  15. Enhanced adhesion buffer layer for deep x-ray lithography using hard x-rays.

    SciTech Connect

    De Carlo, F.

    1998-08-28

    The first step in the fabrication of microstructure using deep x-ray lithography (DXRL) is the irradiation of a x-ray sensitive resist like polymethylmethacrylate (PMMA) by hard x-rays. At the Advanced Photon Source, a dedicated beamline allows the proper exposure of very thick (several mm) resists. To fabricate electroformed metal microstructure with heights of several mm, a PMMA sheet is glued onto a metallic plating base. An important requirement is that the PMMA layer must adhere well to the plating base. The adhesion is greatly reduced by the penetration of even a small fraction of hard x-rays through the mask absorber into the substrate. In this work we will show a novel technique to improve the adhesion of PMMA onto high-Z substrates for DXRL. Results of the improved adhesion are shown for different exposure/substrate conditions.

  16. Ultra-thin fluoropolymer buffer layer as an anode stabilizer of organic light emitting devices

    NASA Astrophysics Data System (ADS)

    Yang, Nam Chul; Lee, Jaeho; Song, Myung-Won; Ahn, Nari; Kim, Mu-Hyun; Lee, Songtaek; Doo Chin, Byung

    2007-08-01

    We have investigated the effect of thin fluoro-acrylic polymer as an anode stabilizer on the lifetime of an organic light emitting device (OLED). Surface chemical properties of commercial fluoropolymer, FC-722 (Fluorad™ of 3M), on indium-tin oxide (ITO) were characterized by x-ray photoemission spectroscopy. An OLED with 1 nm thick fluoropolymeric film showed identical brightness and efficiency behaviour and improved operational stability compared with the reference device with UV-O3 treated ITO. The improvement in the lifetime was accompanied by the suppression of the voltage increase at the initial stage of constant-current driving, which can be attributed to the action of the FC-722 layer by smoothing the ITO surface. Fluoropolymer coating, therefore, improves the lifetime of the small molecular OLED by the simple and reliable anode-stabilizing process.

  17. Study of the thickness of liquid layers by moiré deflectometry.

    PubMed

    Yogev, D; Efrima, S; Kafri, O

    1988-10-01

    We suggest and demonstrate a novel method for studying the thickness of thin liquid layers. The method is based on ray-deflection analysis of a beam reflected from the edge of the layer and on studying the topography of the layer. PMID:19746084

  18. The Effect of Axial Length on the Thickness of Intraretinal Layers of the Macula

    PubMed Central

    Szigeti, Andrea; Tátrai, Erika; Varga, Boglárka Enikő; Szamosi, Anna; DeBuc, Delia Cabrera; Nagy, Zoltán Zsolt; Németh, János; Somfai, Gábor Márk

    2015-01-01

    Purpose The aim of this study was to evaluate the effect of axial length (AL) on the thickness of intraretinal layers in the macula using optical coherence tomography (OCT) image analysis. Methods Fifty three randomly selected eyes of 53 healthy subjects were recruited for this study. The median age of the participants was 29 years (range: 6 to 67 years). AL was measured for each eye using a Lenstar LS 900 device. OCT imaging of the macula was also performed by Stratus OCT. OCTRIMA software was used to process the raw OCT scans and to determine the weighted mean thickness of 6 intraretinal layers and the total retina. Partial correlation test was performed to assess the correlation between the AL and the thickness values. Results Total retinal thickness showed moderate negative correlation with AL (r = -0.378, p = 0.0007), while no correlation was observed between the thickness of the retinal nerve fiber layer (RNFL), ganglion cell layer (GCC), retinal pigment epithelium (RPE) and AL. Moderate negative correlation was observed also between the thickness of the ganglion cell layer and inner plexiform layer complex (GCL+IPL), inner nuclear layer (INL), outer plexiform layer (OPL), outer nuclear layer (ONL) and AL which were more pronounced in the peripheral ring (r = -0.402, p = 0.004; r = -0.429, p = 0.002; r = -0.360, p = 0.01; r = -0.448, p = 0.001). Conclusions Our results have shown that the thickness of the nuclear layers and the total retina is correlated with AL. The reason underlying this could be the lateral stretching capability of these layers; however, further research is warranted to prove this theory. Our results suggest that the effect of AL on retinal layers should be taken into account in future studies. PMID:26544553

  19. An ultrasonic theoretical and experimental approach to determine thickness and wave speed in layered media.

    PubMed

    de Sousa, Ana Valéria Greco; Pereira, Wagner Coelho de Albuquerque; Machado, João Carlos

    2007-02-01

    This work presents an ultrasonic method to characterize the layers of a stratified medium, using independent measurements of wave speed and thickness of each layer. The model, based on geometrical acoustics, includes refraction. Two transducers are used: one active (3.4 MHz) and a hydrophone as a receptor, which is moved laterally through 15 positions. The distance between the transducers and the delay between the echoes, from the interfaces separating the layers, received by them are used to estimate the speed and thickness. Three types of layered phantoms were used: Ph1 made with alcohol/acrylic, Ph2 made with polyvinyl chloride/water/acrylic, and Ph3 made with acrylic/water/polyvinyl chloride. The experimental results for speed of sound and layer thickness presented an experimental mean relative error, for thickness and wave speed, lower than 7.0% and 6.6%, respectively. PMID:17328335

  20. Flexible PTB7:PC71BM bulk heterojunction solar cells with a LiF buffer layer

    NASA Astrophysics Data System (ADS)

    Yanagidate, Tatsuki; Fujii, Shunjiro; Ohzeki, Masaya; Yanagi, Yuichiro; Arai, Yuki; Okukawa, Takanori; Yoshida, Akira; Kataura, Hiromichi; Nishioka, Yasushiro

    2014-02-01

    Bulk heterojunction solar cells were fabricated using poly[4,8-bis[(2-ethylhexyl)oxy]benzo [1,2-b:4,5-b‧]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]-thiophenediyl] (PTB7) and [6,6]-phenyl C71 butyric acid methyl ester (PC71BM) after a layer of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) was deposited on a flexible indium tin oxide (ITO)-coated polyethylene terephthalate substrate. The fabricated structures were Al/LiF/PTB7:PC71BM/PEDOT:PSS/ITO with or without a lithium fluoride (LiF) buffer layer, and the effect of the LiF buffer layer on the performance of the solar cells was investigated. The LiF layer significantly increased the open-circuit voltages and fill factors of the solar cells, presumably because of the work function shift of the aluminum cathode. As a result, the conversion efficiency increased from 2.31 to 4.02% owing to the presence of the LiF layer. From the results of a stability test, it was concluded that the inserted LiF layer acted as a shielding and scavenging protector, which prevented the intrusion of some chemical species into the active layer, thereby improving the lifetime of the unpakcaged devices.

  1. Effect of layer thickness on the properties of nickel thermal sprayed steel

    NASA Astrophysics Data System (ADS)

    Nurisna, Zuhri; Triyono, Muhayat, Nurul; Wijayanta, Agung Tri

    2016-03-01

    Thermal arc spray nickel coating is widely used for decorative and functional applications, by improving corrosion resistance, wear resistance, heat resistence or by modifying other properties of the coated materials. There are several properties have been studied. Layer thickness of nickel thermal sprayed steel may be make harder the substrate surface. In this study, the effect of layer thickness of nickel thermal sprayed steel has been investigated. The rectangular substrate specimens were coated by Ni-5 wt.% Al using wire arc spray method. The thickness of coating layers were in range from 0.4 to 1.0 mm. Different thickness of coating layers were conducted to investigate their effect on hardness and morphology. The coating layer was examined by using microvickers and scanning electron microscope with EDX attachment. Generally, the hardness at the interface increased with increasing thickness of coating layers for all specimens due to higher heat input during spraying process. Morphology analysis result that during spraying process aluminum would react with surrounding oxygen and form aluminum oxide at outer surface of splat. Moreover, porosity was formed in coating layers. However, presence porosity is not related to thickness of coating material. The thicker coating layer resulted highesr of hardness and bond strength.

  2. Inversion of lunar regolith layer thickness with CELMS data using BPNN method

    NASA Astrophysics Data System (ADS)

    Meng, Zhiguo; Xu, Yi; Zheng, Yongchun; Zhu, Yongchao; Jia, Yu; Chen, Shengbo

    2014-10-01

    Inversion of the lunar regolith layer thickness is one of the scientific objectives of current Moon research. In this paper, the global lunar regolith layer thickness is inversed with the back propagation neural network (BPNN) technique. First, the radiative transfer simulation is employed to study the relationship between the lunar regolith layer thickness d and the observed brightness temperature TB's. The simulation results show that the parameters such as the surface roughness σ, slope θs and the (FeO+TiO2) abundance S have strong influence on the observed TB's. Therefore, TB's, σ, θs and S are selected as the inputs of the BPNN network. Next, the four-layer BPNN network with seven-dimension input and two hidden layers is constructed by taking nonlinearity into account with sigmoid functions. Then, BPNN network is trained with the corresponding parameters collected in Apollo landing sites. To tackle issues introduced by the small number of the training samples, the six-dimension similarity degree is introduced to indicate similarities of the inversion results to the correspondent training samples. Thus, the output lunar regolith layer thickness is defined as the sum of the product of the similarity degree and the thickness at the corresponding landing site. Once training phase finishes, the lunar regolith layer thickness can be inversed speedily with the four-channel TB's concluded from the CELMS data, σ and θs estimated from LOLA data and S derived from Clementine UV/vis data. the inversed thickness agrees well with the values estimated by ground-based radar data in low latitude regions. The results indicate that the thickness in the maria varies from about 0.5 m to 12 m, and the mean is about 6.52 m; while the thickness in highlands is a bit thicker than the previous estimation, where the thickness varies widely from 10 m to 31.5 m, and the mean thickness is about 16.8 m. In addition, the relation between the ages, the (FeO+TiO2) abundance and the

  3. Air-bridged lateral growth of an Al0.98Ga0.02N layer by introduction of porosity in an AlN buffer

    NASA Astrophysics Data System (ADS)

    Wang, T.; Bai, J.; Parbrook, P. J.; Cullis, A. G.

    2005-10-01

    We demonstrated air-bridged lateral growth of an Al0.98Ga0.02N layer with significant dislocation reduction by introduction of a porous AlN buffer underneath via metalorganic chemical vapor deposition. By modifying growth conditions, a porous AlN layer and an atomically flat AlN layer have been obtained for comparison, confirmed by atomic force microscopy. An Al0.98Ga0.02N layer was subsequently grown on both the porous AlN layer and the atomically flat AlN layer under identical conditions. Significant dislocation reduction was achieved for the Al0.98Ga0.02N layer grown on the porous AlN buffer layer, compared to the layer grown on the atomically flat AlN layer, as observed by transmission electron microscopy. Clear bubbles from the layer grown on the porous AlN buffer layer have been observed, while in contrast, there was not any bubble from the layer on the flat AlN buffer, confirming the mechanism of lateral growth for dislocation reduction. Asymmetric x-ray diffraction studies also indicated that the crystal quality was dramatically improved using the porous AlN buffer layer.

  4. Probing temperature gradients within the GaN buffer layer of AlGaN/GaN high electron mobility transistors with Raman thermography

    SciTech Connect

    Hodges, C. Pomeroy, J.; Kuball, M.

    2014-02-14

    We demonstrate the ability of confocal Raman thermography using a spatial filter and azimuthal polarization to probe vertical temperature gradients within the GaN buffer layer of operating AlGaN/GaN high electron mobility transistors. Temperature gradients in the GaN layer are measured by using offset focal planes to minimize the contribution from different regions of the GaN buffer. The measured temperature gradient is in good agreement with a thermal simulation treating the GaN thermal conductivity as homogeneous throughout the layer and including a low thermal conductivity nucleation layer to model the heat flow between the buffer and substrate.

  5. Evidence for a non-linear relationship between fracture spacing and layer thickness

    NASA Astrophysics Data System (ADS)

    Mandal, Nibir; Deb, Sanjitendra Krishna; Khan, Debdarpan

    1994-09-01

    In experiments, extension fractures were generated in rigid layers of Plaster of Paris resting on a viscous substratum (pitch). The experimental results predict a non-linear relationship between the spacing of fractures in uniform brittle layers and layer thickness for fractures generated by the tractional force of embeddins weak rocks. We derive an equation which relates the critical fracture spacing ( λc) with layer thickness ( b), tensile strength of the layer material/viscosity of the embedding medium ratio ( τo/ η) and bulk strain rate ( ɛ˙b). The equation shows that the spacing increases as a function of the square root of the layer thickness. The theory also predicts that the fracture spacing depends on the strain rate when the embedding weak medium is viscous.

  6. Graphene on a metal surface with an h-BN buffer layer: gap opening and N-doping

    NASA Astrophysics Data System (ADS)

    Wang, Tao; Lu, Yunhao; Feng, Y. P.

    2016-04-01

    Graphene grown on a metal surface, Cu(111), with a boron-nitride (h-BN) buffer layer is studied. Our first-principles calculations reveal that charge is transferred from the copper substrate to graphene through the h-BN buffer layer which results in n-doped graphene in the absence of a gate voltage. More importantly, a gap of 0.2 eV, which is comparable to that of a typical narrow gap semiconductor, opens just 0.5 eV below the Fermi level at the Dirac point. The Fermi level can be easily shifted inside this gap to make graphene a semiconductor, which is crucial for graphene-based electronic devices. A graphene-based p-n junction can be realized with graphene eptaxially grown on a metal surface.

  7. Investigation of noble metal substrates and buffer layers for BiSrCaCuO thin films

    NASA Astrophysics Data System (ADS)

    Matthiesen, M. M.; Rubin, L. M.; Williams, K. E.; Rudman, D. A.

    Noble metal buffer layers and substrates for Bi2Sr2CaCu2O8 (BSCCO) films were investigated using bulk ceramic processing and thin-film techniques. Highly oriented, superconducting BSCCO films were fabricated on polycrystalline Ag substrates and on Ag/MgO and Ag/YSZ structures. Such films could not be produced on Au or Pt substrates under any annealing conditions. In addition, superconducting BSCCO films could not be produced on Ag/Al2O3, Ag/SiO2/Si, or Ag/(Haynes 230 alloy) structures using high annealing temperatures (870 C). However, oriented although poorly connected, superconducting BSCCO films were fabricated on Ag/Al2O3 structures by using lower annealing temperatures (820 C). Once lower processing temperatures are optimized, Ag may be usable as a buffer layer for BSCCO films.

  8. Investigations into alterntive substrate, absorber, and buffer layer processing for Cu(In,Ga)Se{sub 2}-based solar cells

    SciTech Connect

    Tuttle, J.R.; Berens, T.A.; Keane, J.

    1996-05-01

    High-performance Cu(In,Ga)Se{sub 2}(CIGS)-based solar cells are presently fabricated within a narrow range of processing options. In this contribution, alternative substrate, absorber, and buffer layer processing is considered. Cell performance varies considerably when alternative substrates are employed. These variations are narrowed with the addition of Na via a Na{sub 2}S compound. Sputtered and electrodeposited CIGS precursors and completed absorbers show promise as alternatives to evaporation. A recrystallization process is required to improve their quality. (In,Ga){sub y}Se buffer layers contribute to cell performance above 10. Further improvements in these alternatives will lead to combined cell performance greater than 10% in the near term.

  9. Control of Threshold Voltage for Top-Gated Ambipolar Field-Effect Transistor by Gate Buffer Layer.

    PubMed

    Khim, Dongyoon; Shin, Eul-Yong; Xu, Yong; Park, Won-Tae; Jin, Sung-Ho; Noh, Yong-Young

    2016-07-13

    The threshold voltage and onset voltage for p-channel and n-channel regimes of solution-processed ambipolar organic transistors with top-gate/bottom-contact (TG/BC) geometry were effectively tuned by gate buffer layers in between the gate electrode and the dielectric. The work function of a pristine Al gate electrode (-4.1 eV) was modified by cesium carbonate and vanadium oxide to -2.1 and -5.1 eV, respectively, which could control the flat-band voltage, leading to a remarkable shift of transfer curves in both negative and positive gate voltage directions without any side effects. One important feature is that the mobility of transistors is not very sensitive to the gate buffer layer. This method is simple but useful for electronic devices where the threshold voltage should be precisely controlled, such as ambipolar circuits, memory devices, and light-emitting device applications. PMID:27323003

  10. Thermally robust perpendicular Co/Pd-based synthetic antiferromagnetic coupling enabled by a W capping or buffer layer

    NASA Astrophysics Data System (ADS)

    Lee, Ja-Bin; An, Gwang-Guk; Yang, Seung-Mo; Park, Hae-Soo; Chung, Woo-Seong; Hong, Jin-Pyo

    2016-02-01

    Perpendicularly magnetized tunnel junctions (p-MTJs) that contain synthetic antiferromagnetic (SAF) frames show promise as reliable building blocks to meet the demands of perpendicular magnetic anisotropy (PMA)-based spintronic devices. In particular, Co/Pd multilayer-based SAFs have been widely employed due to their outstanding PMA features. However, the widespread utilization of Co/Pd multilayer SAFs coupled with an adjacent CoFeB reference layer (RL) is still a challenge due to the structural discontinuity or intermixing that occurs during high temperature annealing. Thus, we address the thermally robust characteristics of Co/Pd multilayer SAFs by controlling a W layer as a potential buffer or capping layer. The W-capped Co/Pd multilayer SAF, which acts as a pinning layer, exhibited a wide-range plateau with sharp spin-flip and near-zero remanence at the zero field. Structural analysis of the W-capped multilayer SAF exhibited single-crystal-like c-axis oriented crystalline features after annealing at 400 °C, thereby demonstrating the applicability of these frames. In addition, when the W layer serving as a buffer layer in the Co/Pd multilayer SAF was coupled with a conventional CoFeB RL, higher annealing stability up to 425 °C and prominent antiferromagnetic coupling behavior were obtained.

  11. Thermally robust perpendicular Co/Pd-based synthetic antiferromagnetic coupling enabled by a W capping or buffer layer

    PubMed Central

    Lee, Ja-Bin; An, Gwang-Guk; Yang, Seung-Mo; Park, Hae-Soo; Chung, Woo-Seong; Hong, Jin-Pyo

    2016-01-01

    Perpendicularly magnetized tunnel junctions (p-MTJs) that contain synthetic antiferromagnetic (SAF) frames show promise as reliable building blocks to meet the demands of perpendicular magnetic anisotropy (PMA)-based spintronic devices. In particular, Co/Pd multilayer-based SAFs have been widely employed due to their outstanding PMA features. However, the widespread utilization of Co/Pd multilayer SAFs coupled with an adjacent CoFeB reference layer (RL) is still a challenge due to the structural discontinuity or intermixing that occurs during high temperature annealing. Thus, we address the thermally robust characteristics of Co/Pd multilayer SAFs by controlling a W layer as a potential buffer or capping layer. The W-capped Co/Pd multilayer SAF, which acts as a pinning layer, exhibited a wide-range plateau with sharp spin-flip and near-zero remanence at the zero field. Structural analysis of the W-capped multilayer SAF exhibited single-crystal-like c-axis oriented crystalline features after annealing at 400 °C, thereby demonstrating the applicability of these frames. In addition, when the W layer serving as a buffer layer in the Co/Pd multilayer SAF was coupled with a conventional CoFeB RL, higher annealing stability up to 425 °C and prominent antiferromagnetic coupling behavior were obtained. PMID:26887790

  12. Thermally robust perpendicular Co/Pd-based synthetic antiferromagnetic coupling enabled by a W capping or buffer layer.

    PubMed

    Lee, Ja-Bin; An, Gwang-Guk; Yang, Seung-Mo; Park, Hae-Soo; Chung, Woo-Seong; Hong, Jin-Pyo

    2016-01-01

    Perpendicularly magnetized tunnel junctions (p-MTJs) that contain synthetic antiferromagnetic (SAF) frames show promise as reliable building blocks to meet the demands of perpendicular magnetic anisotropy (PMA)-based spintronic devices. In particular, Co/Pd multilayer-based SAFs have been widely employed due to their outstanding PMA features. However, the widespread utilization of Co/Pd multilayer SAFs coupled with an adjacent CoFeB reference layer (RL) is still a challenge due to the structural discontinuity or intermixing that occurs during high temperature annealing. Thus, we address the thermally robust characteristics of Co/Pd multilayer SAFs by controlling a W layer as a potential buffer or capping layer. The W-capped Co/Pd multilayer SAF, which acts as a pinning layer, exhibited a wide-range plateau with sharp spin-flip and near-zero remanence at the zero field. Structural analysis of the W-capped multilayer SAF exhibited single-crystal-like c-axis oriented crystalline features after annealing at 400 °C, thereby demonstrating the applicability of these frames. In addition, when the W layer serving as a buffer layer in the Co/Pd multilayer SAF was coupled with a conventional CoFeB RL, higher annealing stability up to 425 °C and prominent antiferromagnetic coupling behavior were obtained. PMID:26887790

  13. Detection of charged particles in thick hydrogenated amorphous silicon layers

    SciTech Connect

    Fujieda, I.; Cho, G.; Kaplan, S.N.; Perez-Mendez, V.; Qureshi, S.; Ward, W.; Street, R.A.

    1988-03-01

    We show our results in detecting particles of various linear energy transfer, including minimum ionizing electrons from a Sr-90 source with 5 to 12 micron thick n-i-p and p-i-n diodes. We measured W ( average energy to produce one electron-hole pair) using 17keV filtered xray pulses with a result W = 6.0 /+-/ 0.2eV. This is consistent with the expected value for a semiconductor with band gap of 1.7 to 1.9eV. With heavily ionizing particles such as 6 MeV alphas and 1 to 2 MeV protons, there was some loss of signal due to recombination in the particle track. The minimum ionizing electrons showed no sign of recombination. Applications to pixel and strip detectors for physics experiments and medical imaging will be discussed. 7 refs., 8 figs.

  14. Microstructure of a high Jc, laser-ablated YBa 2Cu 3O 7- δ/sol-gel deposited NdGaO 3 buffer layer/(001) SrTiO 3 multi-layer structure

    NASA Astrophysics Data System (ADS)

    Yang, Chau-Yun; Ichinose, Ataru; Babcock, S. E.; Morrell, J. S.; Mathis, J. E.; Verebelyi, D. T.; Paranthaman, M.; Beach, D. B.; Christen, D. K.

    A YBa 2Cu 3O 7- δ (YBCO) film with a transport critical current density ( Jc) value of 1 mA/cm 2 (77 K, 0 T) was grown on a solution deposited NdGaO 3 (NGO) buffer layer on (100) SrTiO 3 (STO). The 25-nm thick NGO buffer layer was dip-coated onto the STO single crystal from a solution of metal methoxyethoxides in 2-methoxyethanol. Pulsed laser deposition (PLD) was used to grow a 250-nm-thick YBCO film on the NGO. The epitaxial relationships are cube-on-cube throughout the structure when the pseudo cubic and pseudo tetragonal unit cells are used to describe the NGO and YBCO crystal structures, respectively: (001) YBCO∥(001) NGO∥(001) STO and [100] YBCO∥[100] NGO∥[100] STO. High resolution scanning electron microscopy (SEM) of the bare NGO surface revealed ∼40 nm diameter pinholes with number density of ∼2×10 13 m -2, corresponding to an area fraction coverage of 2.5%, in an otherwise featureless surface. Cross-sectional transmission electron microscopy (TEM) showed that these pinholes penetrate to the STO; otherwise the NGO layer was uniformly thick to within approximately ±5 nm and defect free. The X-ray diffraction φ- and ω-scans indicated that the YBCO film was highly oriented with a full-width-half maximum peak breadth of 1.14° for in-plane and 0.46° for out-of-plane alignment, respectively. The film contained sparse a-axis oriented grains, an appreciable density of (001) stacking faults and apparently insulating second phase precipitates of the type that typically litter the surface of PLD films. All of these defects are typical of YBCO thin films. High-resolution cross-sectional TEM images indicate that no chemical reaction occurs at the YBCO/NGO interface.

  15. Hydride vapor phase epitaxy growth of GaN on sapphire with ZnO buffer layers

    NASA Astrophysics Data System (ADS)

    Gu, S.; Zhang, R.; Shi, Y.; Zheng, Y.; Zhang, L.; Kuech, T. F.

    The initial stages and subsequent growth of GaN on sapphire using ZnO buffer layers is reported for the hydride vapor phase epitaxy technique. A high gas-phase supersaturation in the growth ambient was used to favor a rapid initial growth on the substrate. A subsequent growth step was employed under conditions that favor a high lateral growth rate in order to promote the coalescence of the initial islands and provide optimal material properties. The specific gas-phase mole fractions of the GaCl and NH3 at the growth front control both the vertical and lateral growth rates. The use of a two-step growth process in the GaN growth leads to a controlled morphology and improved material properties for GaN materials when grown with a ZnO buffer layer. An optimized set of growth conditions, utilizing this two-step process, was found to also improve the growth directly on sapphire without a ZnO buffer layer.

  16. Growth modes of InN (000-1) on GaN buffer layers on sapphire

    SciTech Connect

    Liu Bing; Kitajima, Takeshi; Chen Dongxue; Leone, Stephen R.

    2005-03-01

    In this work, using atomic force microscopy and scanning tunneling microscopy, we study the surface morphologies of epitaxial InN films grown by plasma-assisted molecular beam epitaxy with intervening GaN buffer layers on sapphire substrates. On smooth GaN buffer layers, nucleation and evolution of three-dimensional InN islands at various coverages and growth temperatures are investigated. The shapes of the InN islands are observed to be predominantly mesalike with large flat (000-1) tops, which suggests a possible role of indium as a surfactant. Rough GaN buffer layers composed of dense small GaN islands are found to significantly improve uniform InN wetting of the substrates, on which atomically smooth InN films are obtained that show the characteristics of step-flow growth. Scanning tunneling microscopy imaging reveals the defect-mediated surface morphology of smooth InN films, including surface terminations of screw dislocations and a high density of shallow surface pits with depths less than 0.3 nm. The mechanisms of the three-dimensional island size and shape evolution and formation of defects on smooth surfaces are considered.

  17. Growth modes of InN(000-1) on GaN buffer layers on sapphire

    SciTech Connect

    Liu, Bing; Kitajima, Takeshi; Chen, Dongxue; Leone, Stephen R.

    2005-01-24

    In this work, using atomic force microscopy and scanning tunneling microscopy, we study the surface morphologies of epitaxial InN films grown by plasma-assisted molecular beam epitaxy with intervening GaN buffer layers on sapphire substrates. On smooth GaN buffer layers, nucleation and evolution of three-dimensional InN islands at various coverages and growth temperatures are investigated. The shapes of the InN islands are observed to be predominantly mesa-like with large flat (000-1) tops, which suggests a possible role of indium as a surfactant. Rough GaN buffer layers composed of dense small GaN islands are found to significantly improve uniform InN wetting of the substrates, on which atomically smooth InN films are obtained that show the characteristics of step-flow growth. Scanning tunneling microscopy imaging reveals the defect-mediated surface morphology of smooth InN films, including surface terminations of screw dislocations and a high density of shallow surface pits with depths less than 0.3 nm. The mechanisms of the three-dimensional island size and shape evolution and formation of defects on smooth surfaces are considered.

  18. Atomically flat Ge buffer layers and alternating shutter growth of CaGe2 for large area germanane

    NASA Astrophysics Data System (ADS)

    Xu, Jinsong; Katoch, Jyoti; Ahmed, Adam; Pinchuk, Igor; Williams, Robert; McComb, David; Kawakami, Roland

    Germanane (GeH), which is converted from CaGe2 by soaking in HCl acid, has recently attracted interest because of its novel properties, such as large band gap (1.56eV), spin orbit coupling and predictions of high mobility (18000 cm2/Vs). Previously CaGe2 was successfully grown on Ge(111) substrates by molecular beam epitaxy (MBE) growth. But there were cracks between µm-sized islands, which is not desirable for scientific study and application, and limits the material quality. By growing atomically flat Ge buffer layers and using alternating shutter MBE growth, we are able to grow crack-free, large area films of CaGe2 films. Reflection high energy electron diffraction (RHEED) patterns of Ge buffer layer and CaGe2 indicates high quality two dimensional surfaces, which is further confirmed by atomic force microscopy (AFM), showing atomically flat and uniform Ge buffer layer and CaGe2. The appearance of Laue oscillation in X-ray diffraction (XRD) and Kiessig fringes in X-ray reflectivity (XRR) proves the uniformity of CaGe2 film and the smoothness of the interface. The high quality of CaGe2 film makes it promising to explore novel properties of GeH. Funded by NSF MRSEC DMR-1420451.

  19. Monte Carlo modeling (MCML) of light propagation in skin layers for detection of fat thickness

    NASA Astrophysics Data System (ADS)

    Nilubol, Chonnipa; Treerattrakoon, Kiatnida; Mohammed, Waleed S.

    2010-05-01

    Nowadays, most activities require lesser physical actions, which could ultimately lead to accumulation of excessive body fat. The main roles of body fat are to store energy and acts as various kinds of insulators for the body. The thickness of fat layers can be measured to indicate fat-body weight ratio. Exceeding the body-mass index (BMI) could lead to many illnesses regarding obesity. Consequently, many studies have proposed various principles and techniques to measure the amount of fat within one's body. In this paper, infrared interactance in skin layers is studied for investigation of the influence of fat thickness upon photon travelling pattern in skin tissues using Monte Carlo model (MCML). Photon propagation is numerically simulated in simplified multi-layered tissues. The optical coefficients of each skin layers are accounted for different traveling paths of photons that move through random motion. The thickness of fat layer is varied, and changing in optical parameters is observed. Then the statistically obtained data are computed and analyzed for the effect of the fat layer upon reflection percentage using different wavelengths. The calculations have shown increment in the slope of change of reflection percentage versus fat thickness, when using infrared compare to visible light. This technique can be used to construct a mobile device that is capable of measuring the volume fraction of melanin and blood in the epidermis layer and dermis layer, to calculate for the necessary optical coefficients that would be necessary for measurement of fat thickness.

  20. Layer thickness-dependent phonon properties and thermal conductivity of MoS2

    NASA Astrophysics Data System (ADS)

    Gu, Xiaokun; Li, Baowen; Yang, Ronggui

    2016-02-01

    For conventional materials, the thermal conductivity of thin films is usually suppressed when the thickness decreases due to phonon-boundary scattering. However, this is not necessarily true for the van der Waals solids if the thickness is reduced to only a few layers. In this letter, the layer thickness-dependent phonon properties and thermal conductivity in the few-layer MoS2 are studied using the first-principles-based Peierls-Boltzmann transport equation approach. The basal-plane thermal conductivity of 10-μm-long samples is found to monotonically reduce from 138 W/mK to 98 W/mK for naturally occurring MoS2, and from 155 W/mK to 115 W/mK for isotopically pure MoS2, when its thickness increases from one layer to three layers. The thermal conductivity of tri-layer MoS2 approaches to that of bulk MoS2. Both the change of phonon dispersion and the thickness-induced anharmonicity are important for explaining such a thermal conductivity reduction. The increased anharmonicity in bi-layer MoS2 results in stronger phonon scattering for ZAi modes, which is linked to the breakdown of the symmetry in single-layer MoS2.

  1. Microstructure evolution with varied layer thickness in magnetron-sputtered Ni/C multilayer films

    PubMed Central

    Peng, Jichang; Li, Wenbin; Huang, Qiushi; Wang, Zhanshan

    2016-01-01

    The microstructure evolution of magnetron-sputtered Ni/C multilayers was investigated by varying the Ni and C layer thickness in the region of a few nanometers. For the samples having 2.6-nm-thick C layers, the interface width increases from 0.37 to 0.81 nm as the Ni layer thickness decreases from 4.3 to 1.3 nm. Especially for the samples with Ni layers less than 2.0 nm, the interface width changes significantly due to the discontinuously distributed Ni crystallites. For the samples having 2.8-nm-thick Ni layers, the interface width increases from 0.37 to 0.59 nm when the C layer thickness decreases from 4.3 to 0.7 nm. The evolution of interface microstructures with varied Ni and C layers is explained based on a proposed simple growth model of Ni and C layers. PMID:27515586

  2. Y1Ba2Cu3O(6+delta) growth on thin Y-enhanced SiO2 buffer layers on silicon

    NASA Technical Reports Server (NTRS)

    Robin, T.; Mesarwi, A.; Wu, N. J.; Fan, W. C.; Espoir, L.; Ignatiev, A.; Sega, R.

    1991-01-01

    SiO2 buffer layers as thin as 2 nm have been developed for use in the growth of Y1Ba2Cu3O(6+delta) thin films on silicon substrates. The SiO2 layers are formed through Y enhancement of silicon oxidation, and are highly stoichiometric. Y1Ba2Cu3O(6+delta) film growth on silicon with thin buffer layers has shown c orientation and Tc0 = 78 K.

  3. The effects of the porous buffer layer and doping with dysprosium on internal stresses in the GaInP:Dy/por-GaAs/GaAs(100) heterostructures

    SciTech Connect

    Seredin, P. V.; Gordienko, N. N.; Glotov, A. V.; Zhurbina, I. A.; Domashevskaya, E. P.; Arsent'ev, I. N. Shishkov, M. V.

    2009-08-15

    In structures with a porous buffer layer, residual internal stresses caused by a mismatch between the crystal-lattice parameters of the epitaxial GaInP alloy and the GaAs substrate are redistributed to the porous layer that acts as a buffer and is conducive to disappearance of internal stresses. Doping of the epitaxial layer with dysprosium exerts a similar effect on the internal stresses in the film-substrate structure.

  4. Dependence of deposition parameters and layer thickness on the characteristics of Nd-Fe-B thin films

    NASA Astrophysics Data System (ADS)

    Madeswaran, S.; Tokumaru, R.; Tamano, S.; Goto, S.; Tokiwa, K.; Watanabe, T.

    2009-11-01

    Textured Nd-Fe-B thin films with hard magnetic properties were prepared on a Ta (110) buffer layered glass substrates using radio frequency (RF) sputtering deposition. We investigated the influence of substrate temperature, sputtering gas pressure, RF power and film thickness on their microstructural and magnetic properties. Composition in the Nd-Fe-B thin films prepared using the same target with an Nd/Fe ratio of 0.32 was markedly changed (varied between 0.21 and 0.31) depending on the Ar pressure and the RF power. Well-textured Nd-Fe-B films grown at a deposition pressure of 7.0 Pa, a temperature of 550 °C, and a power of 100 W revealed better magnetic properties: Jr = 1.1 T, Hc = 1130 kA/m and BH(max) = 236 kJ/m3.

  5. Ink-jet printing of SrTiO3 buffer layers from aqueous solutions

    NASA Astrophysics Data System (ADS)

    Pollefeyt, G.; Clerick, S.; Vermeir, P.; Feys, J.; Hühne, R.; Lommens, P.; Van Driessche, I.

    2014-09-01

    In this work, fully a-axis oriented SrTiO3 thin films were synthesized by ink-jet printing of water-based precursor inks. The developed precursor solution or ‘ink’ was optimized in terms of rheology, leading to the ejection of single droplets showing a maximum contact angle of 12° on (100) oriented single crystal LaAlO3 substrates. By using the appropriate ink-jet deposition parameters and thermal treatment, well-textured and dense SrTiO3 films of 130 nm thickness were obtained. The biaxial texture is maintained up to the surface of the films, leading to the formation of (h00)-oriented terraces. As shown by transmission electron microscopy, excellent texture transfer was achieved from the SrTiO3 film to the YBa2Cu3O7 - δ layer deposited by pulsed laser deposition. Outstanding superconducting properties were obtained with critical current densities up to 3.6 MA cm-2 in self-field at 77 K, demonstrating that these sustainable SrTiO3 films meet the requirements to be used as growing template for high quality superconducting coatings.

  6. Observation of three crystalline layers in hydrothermally grown BiFeO{sub 3} thick films

    SciTech Connect

    Lee, T. K.; Sung, K. D.; Jung, J. H.; Kim, T. H.; Ko, J.-H.

    2014-11-21

    We report the observation of three different crystalline layers in hydrothermally grown BiFeO{sub 3} (BFO) thick films on SrRuO{sub 3}/SrTiO{sub 3} substrates. High-resolution X-ray diffraction and transmission electron microcopy results suggest that compressively strained, partially relaxed epitaxial layers, and a mixture of polycrystalline and amorphous BFO layers, were successively formed from the bottom to the top of the films. The resistance and capacitance of the mixed layer were significantly lower than those of the epitaxial layers. The atomic concentrations of Bi and Fe in the mixed layer were fluctuating for each point. Based on the observed three crystalline layers, we have discussed the growth mechanism and the leakage current of hydrothermally grown BFO thick films.

  7. Zn0.85Cd0.15Se active layers on graded-composition InxGa1-xAs buffer layers

    NASA Astrophysics Data System (ADS)

    Müller, B. H.; Lantier, R.; Sorba, L.; Heun, S.; Rubini, S.; Lazzarino, M.; Franciosi, A.; Napolitani, E.; Romanato, F.; Drigo, A. V.; Lazzarini, L.; Salviati, G.

    1999-06-01

    We investigated the structural and optical properties of Zn0.85Cd0.15Se epilayers for blue optical emission on lattice-matched InxGa1-xAs buffer layers. Both the II-VI layers and the III-V buffers were grown by molecular beam epitaxy on GaAs(001) wafers. A parabolic In concentration profile within the graded-composition InxGa1-xAs buffers was selected to control strain relaxation and minimize the concentration of threading dislocations. Dislocation-free II-VI growth was readily achieved on the graded buffers, with a Rutherford backscattering yield ratio reduced by a factor of 3 and a deep-level emission intensity reduced by over two orders of magnitude relative to those observed following direct II-VI growth on GaAs. The surface morphology of the materials, however, was found to replicate the crosshatched pattern of the underlying InxGa1-xAs substrates.

  8. Effect of Thickness on Surface Morphology of Silver Nanoparticle Layer During Furnace Sintering

    NASA Astrophysics Data System (ADS)

    Moon, Yoon Jae; Kang, Heuiseok; Kang, Kyungtae; Moon, Seung-Jae; Young hwang, Jun

    2015-04-01

    In printed electronics applications, specific resistances of conductive lines are critical to the performance of the devices. The specific resistance of a silver (Ag) nanoparticle electrode is affected by surface morphology of the layered nanoparticles which were sintered by the heat treatment after printing. In this work, the relationship between surface morphology and specific resistance was investigated with various sintering temperatures and various layer thicknesses of Ag nanoparticle ink. Ag nanoparticles with an average size of approximately 50 nm were spin-coated on Eagle XG glass substrates with various spin speed to change the layer thickness of Ag nanoparticles from 200 nm to 900 nm. Coated Ag nanoparticle layers were heated from 150°C to 450°C for 30 min in a furnace. The result showed that higher sintering temperature produces larger grains in an Ag layer and decreases specific resistance of the layer, but that the maximum allowable heating temperature is limited by the thickness of the layer. When grain size exceeded the thickness of the layer, the morphology of the Ag nanoparticles changed to submicron-sized islands and the Ag layers did not have electrical conductivity any more.

  9. Plasma versus thermal annealing for the Au-catalyst growth of ZnO nanocones and nanowires on Al-doped ZnO buffer layers

    NASA Astrophysics Data System (ADS)

    Güell, Frank; Martínez-Alanis, Paulina R.; Roso, Sergio; Salas-Pérez, Carlos I.; García-Sánchez, Mario F.; Santana, Guillermo; Marel Monroy, B.

    2016-06-01

    We successfully synthesized ZnO nanocones and nanowires over polycrystalline Al-doped ZnO (AZO) buffer layers on fused silica substrates by a vapor-transport process using Au-catalyst thin films. Different Au film thicknesses were thermal or plasma annealed in order to analyze their influence on the ZnO nanostructure growth morphology. Striking differences have been observed. Thermal annealing generates a distribution of Au nanoclusters and plasma annealing induces a fragmentation of the Au thin films. While ZnO nanowires are found in the thermal-annealed samples, ZnO nanocones and nanowires have been obtained on the plasma-annealed samples. Enhancement of the preferred c-axis (0001) growth orientation was demonstrated by x-ray diffraction when the ZnO nanocones and nanowires have been grown over the AZO buffer layer. The transmittance spectra of the ZnO nanocones and nanowires show a gradual increase from 375 to 900 nm, and photoluminescence characterization pointed out high concentration of defects leading to observation of a broad emission band in the visible range from 420 to 800 nm. The maximum emission intensity peak position of the broad visible band is related to the thickness of the Au-catalyst for the thermal-annealed samples and to the plasma power for the plasma-annealed samples. Finally, we proposed a model for the plasma versus thermal annealing of the Au-catalyst for the growth of the ZnO nanocones and nanowires. These results are promising for renewable energy applications, in particular for its potential application in solar cells.

  10. Effect of anode buffer layer on the efficiency of inverted quantum-dot light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Ram Cho, Ye; Kang, Pil-Gu; Shin, Dong Heon; Kim, Ji-Hoon; Maeng, Min-Jae; Sakong, Jeonghun; Hong, Jong-Am; Park, Yongsup; Suh, Min Chul

    2016-01-01

    The impact of anode buffer layers (ABLs) on the performance of CdSe quantum-dot light-emitting diodes (QLED) with a ZnO nanoparticle (NP) electron-transport layer and 4,4‧-cyclohexylidenebis[N,N-bis(4-methylphenyl)benzenamine] (TAPC) hole-transport layer was studied. Either MoO3 or 1,4,5,8,9,11-hexaazatriphenylene hexacarbonitrile (HAT-CN) was used as the ABL. The QLED with a HAT-CN ABL exhibited better luminance performance, while the ultraviolet photoelectron spectroscopy and hole-only devices indicated that MoO3 was a superior hole injector. These results suggest that the QLED with a MoO3 ABL suffered from a severe charge carrier imbalance. Therefore, electron injection through the ZnO NP layer must be improved to further enhance the QLED performance.

  11. High rate buffer layer for IBAD MgO coated conductors

    DOEpatents

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

    2007-08-21

    Articles are provided including a base substrate having a layer of an oriented material thereon, and, a layer of hafnium oxide upon the layer of an oriented material. The layer of hafnium oxide can further include a secondary oxide such as cerium oxide, yttrium oxide, lanthanum oxide, scandium oxide, calcium oxide and magnesium oxide. Such articles can further include thin films of high temperature superconductive oxides such as YBCO upon the layer of hafnium oxide or layer of hafnium oxide and secondary oxide.

  12. The effects of buffer layers on the performance and stability of flexible InGaZnO thin film transistors on polyimide substrates

    NASA Astrophysics Data System (ADS)

    Ok, Kyung-Chul; Ko Park, Sang-Hee; Hwang, Chi-Sun; Kim, H.; Soo Shin, Hyun; Bae, Jonguk; Park, Jin-Seong

    2014-02-01

    We demonstrated the fabrication of flexible amorphous indium gallium zinc oxide thin-film transistors (TFTs) on high-temperature polyimide (PI) substrates, which were debonded from the carrier glass after TFT fabrication. The application of appropriate buffer layers on the PI substrates affected the TFT performance and stability. The adoption of the SiNx/AlOx buffer layers as water and hydrogen diffusion barriers significantly improved the device performance and stability against the thermal annealing and negative bias stress, compared to single SiNx or SiOx buffer layers. The substrates could be bent down to a radius of curvature of 15 mm and the devices remained normally functional.

  13. High-performance hybrid buffer layer using 1,4,5,8,9,11-hexaazatriphenylenehexacarbonitrile/molybdenum oxide in inverted top-emitting organic light-emitting diodes.

    PubMed

    Park, Cheol Hwee; Lee, Hyun Jun; Hwang, Ju Hyun; Kim, Kyu Nyun; Shim, Yong Sub; Jung, Sun-Gyu; Park, Chan Hyuk; Park, Young Wook; Ju, Byeong-Kwon

    2015-03-25

    A high-performance 1,4,5,8,9,11-hexaazatriphenylenehexacarbonitrile (HATCN)/molybdenum oxide (MoO3) hybrid buffer layer with high hole-injection efficiency and superior plasma resistance under the sputtering process was developed. The HATCN enhances the hole-injection efficiency, and the MoO3 effectively protects the underlying organic layers from plasma damage during deposition by sputtering. This improves the characteristics of inverted top-emitting organic light-emitting diodes using a top transparent conductive oxide electrode. The device using the hybrid buffer layer showed the highest electroluminescence characteristics among devices with other buffer layers. The high hole-injection efficiency of HATCN was shown by the J-F curve of hole-only devices, and the plasma protection performance of MoO3 was shown by atomic force microscope surface morphology images of the buffer layer film after O2 plasma treatment. PMID:25761363

  14. Epitaxial c-axis oriented BaTiO{sub 3} thin films on SrTiO{sub 3}-buffered Si(001) by atomic layer deposition

    SciTech Connect

    Ngo, Thong Q.; McDaniel, Martin D.; Ekerdt, John G.; Posadas, Agham B.; Demkov, Alexander A.; Hu, Chengqing; Yu, Edward T.; Bruley, John

    2014-02-24

    Atomic layer deposition (ALD) of epitaxial c-axis oriented BaTiO{sub 3} (BTO) on Si(001) using a thin (1.6 nm) buffer layer of SrTiO{sub 3} (STO) grown by molecular beam epitaxy is reported. The ALD growth of crystalline BTO films at 225  °C used barium bis(triisopropylcyclopentadienyl), titanium tetraisopropoxide, and water as co-reactants. X-ray diffraction (XRD) reveals a high degree of crystallinity and c-axis orientation of as-deposited BTO films. Crystallinity is improved after vacuum annealing at 600  °C. Two-dimensional XRD confirms the tetragonal structure and orientation of 7–20-nm thick films. The effect of the annealing process on the BTO structure is discussed. A clean STO/Si interface is found using in-situ X-ray photoelectron spectroscopy and confirmed by cross-sectional scanning transmission electron microscopy. The capacitance-voltage characteristics of 7–20 nm-thick BTO films are examined and show an effective dielectric constant of ∼660 for the heterostructure.

  15. Effect of layer thickness on device response of silicon heavily supersaturated with sulfur

    NASA Astrophysics Data System (ADS)

    Hutchinson, David; Mathews, Jay; Sullivan, Joseph T.; Akey, Austin; Aziz, Michael J.; Buonassisi, Tonio; Persans, Peter; Warrender, Jeffrey M.

    2016-05-01

    We report on a simple experiment in which the thickness of a hyperdoped silicon layer, supersaturated with sulfur by ion implantation followed by pulsed laser melting and rapid solidification, is systematically varied at constant average sulfur concentration, by varying the implantation energy, dose, and laser fluence. Contacts are deposited and the external quantum efficiency (EQE) is measured for visible wavelengths. We posit that the sulfur layer primarily absorbs light but contributes negligible photocurrent, and we seek to support this by analyzing the EQE data for the different layer thicknesses in two interlocking ways. In the first, we use the measured concentration depth profiles to obtain the approximate layer thicknesses, and, for each wavelength, fit the EQE vs. layer thickness curve to obtain the absorption coefficient of hyperdoped silicon for that wavelength. Comparison to literature values for the hyperdoped silicon absorption coefficients [S.H. Pan et al. Applied Physics Letters 98, 121913 (2011)] shows good agreement. Next, we essentially run this process in reverse; we fit with Beer's law the curves of EQE vs. hyperdoped silicon absorption coefficient for those wavelengths that are primarily absorbed in the hyperdoped silicon layer, and find that the layer thicknesses obtained from the fit are in good agreement with the original values obtained from the depth profiles. We conclude that the data support our interpretation of the hyperdoped silicon layer as providing negligible photocurrent at high S concentrations. This work validates the absorption data of Pan et al. [Applied Physics Letters 98, 121913 (2011)], and is consistent with reports of short mobility-lifetime products in hyperdoped layers. It suggests that for optoelectronic devices containing hyperdoped layers, the most important contribution to the above band gap photoresponse may be due to photons absorbed below the hyperdoped layer.

  16. Optical Coherence Tomography Assisted Retinal Nerve Fibre Layer Thickness Profile in High Myopia

    PubMed Central

    Malakar, Mousumi; Askari, Syed Nasir; Ashraf, Humayun; Ahuja, Anupam; Asghar, Adil

    2015-01-01

    Introduction: To evaluate the association of high myopia with retinal nerve fibre layer (RNFL) thickness by Fourier domain optical coherence tomography (FD OCT). Materials and Methods: Fifty highly myopic eyes (25 patients) and forty emmetropic eyes (20 Normal subject) were randomly selected after excluding concomitant ophthalmic disorder and RNFL thickness measured using the Fourier domain optical coherence tomography (FD OCT). Results: The overall mean RNFL thickness in the myopic groups and control were 87.89 μm and 111.64 μm respectively. The mean retinal nerve fibre thickness was significantly less in myopic eyes as compared to control group (p =0.0001). Retinal nerve fibre layer thickness shows topographic double hump pattern in both the groups (myopes and emmetropes). Conclusion: Retinal nerve fibre thickness was significantly less in myopic eyes as compared to emmetropic eyes. The retinal nerve fibre layer thinning in high myopes may be confused with open angle glaucoma, a disease also prevalent in high myopes. There is therefore a need to have retinal nerve fibre layer thickness normogram for high myopes of a given population group to avoid wrong interpretation. PMID:25859476

  17. Influences and interactions of inundation, peat, and snow on active layer thickness

    DOE PAGESBeta

    Atchley, Adam L.; Coon, Ethan T.; Painter, Scott L.; Harp, Dylan R.; Wilson, Cathy J.

    2016-05-18

    The effect of three environmental conditions: 1) thickness of organic soil, 2) snow depth, and 3) soil moisture content or water table height above and below the soil surface, on active layer thickness (ALT) are investigated using an ensemble of 1D thermal hydrology models. Sensitivity analyses of the ensemble exposed the isolated influence of each environmental condition on ALT and their multivariate interactions. The primary and interactive influences are illustrated in the form of color maps of ALT change. Results show that organic layer acts as a strong insulator, and its thickness is the dominant control of ALT, but themore » strength of the effect of organic layer thickness is dependent on the saturation state. Snow depth, subsurface saturation, and ponded water depth are strongly codependent and positively correlated to ALT.« less

  18. Influences of Peat, Surface and Subsurface Water, and Snow on Active Layer Thickness

    SciTech Connect

    Atchley, Adam; Coon, Ethan T.; Painter, Scott L; Harp, Dylan; Wilson, Cathy

    2016-01-01

    The effect of three environmental conditions: 1) thickness of organic soil, 2) snow depth, and 3) soil moisture content or water table height above and below the soil surface, on active layer thickness (ALT) are investigated using an ensemble of 1D thermal hydrology models. Sensitivity analyses of the ensemble exposed the isolated influence of each environmental condition on ALT and their multivariate interactions. The primary and interactive influences are illustrated in the form of color maps of ALT change. Results show that organic layer acts as a strong insulator, and its thickness is the dominant control of ALT, but the strength of the effect of organic layer thickness is dependent on the saturation state. Snow depth, subsurface saturation, and ponded water depth are strongly codependent and positively correlated to ALT.

  19. Influences of Peat, Surface and Subsurface Water, and Snow on Active Layer Thickness

    DOE PAGESBeta

    Atchley, Adam; Coon, Ethan T.; Painter, Scott L; Harp, Dylan; Wilson, Cathy

    2016-01-01

    The effect of three environmental conditions: 1) thickness of organic soil, 2) snow depth, and 3) soil moisture content or water table height above and below the soil surface, on active layer thickness (ALT) are investigated using an ensemble of 1D thermal hydrology models. Sensitivity analyses of the ensemble exposed the isolated influence of each environmental condition on ALT and their multivariate interactions. The primary and interactive influences are illustrated in the form of color maps of ALT change. Results show that organic layer acts as a strong insulator, and its thickness is the dominant control of ALT, but themore » strength of the effect of organic layer thickness is dependent on the saturation state. Snow depth, subsurface saturation, and ponded water depth are strongly codependent and positively correlated to ALT.« less

  20. Characteristics of blue organic light emitting diodes with different thick emitting layers

    NASA Astrophysics Data System (ADS)

    Li, Chong; Tsuboi, Taiju; Huang, Wei

    2014-08-01

    We fabricated blue organic light emitting diodes (called blue OLEDs) with emitting layer (EML) of diphenylanthracene derivative 9,10-di(2-naphthyl)anthracene (ADN) doped with blue-emitting DSA-ph (1-4-di-[4-(N,N-di-phenyl)amino]styryl-benzene) to investigate how the thickness of EML and hole injection layer (HIL) influences the electroluminescence characteristics. The driving voltage was observed to increase with increasing EML thickness from 15 nm to 70 nm. The maximum external quantum efficiency of 6.2% and the maximum current efficiency of 14 cd/A were obtained from the OLED with 35 nm thick EML and 75 nm thick HIL. High luminance of 120,000 cd/m2 was obtained at 7.5 V from OLED with 15 nm thick EML.

  1. [Research advances of retinal nerve fiber layer thickness and its association with myopia].

    PubMed

    Kang, M T; Ran, A R; Wang, N L; Li, S M

    2016-05-11

    Recently, the distribution characteristics of retinal nerve fiber layer thickness in myopic population have raised scholars' attention. The retinal nerve fiber layer thickness is varied with different refractive statuses, and is correlated to many factors like age, eye elongation, and fundus changes. Further exploration of the relationship between myopia and retinal structure and function will promote our understanding and knowledge of the pathogenesis of myopia. The article reviews the structure characteristics of the retinal nerve fiber layer, its associations with demographic characteristics, its characteristics in myopia, and the structural-functional relationship.(Chin J Ophthalmol, 2016, 52: 396-400). PMID:27220715

  2. Assessment of the Correlation between Crust and its Estimated Elastic Layer Thickness in Iran

    NASA Astrophysics Data System (ADS)

    Abbaszadeh, Majid; Nikkhoo, Mehdi

    2010-05-01

    Although crust plates movements are usually just under few centimeters during a year, it can deform elastic layer of rocks on the faults and, as a result, energy stores in the layer. Sometimes, just in a few seconds, the accumulated energy within the layer releases suddenly and an earthquake occur. The effective elastic thickness of lithosphere has a prominent role to predict the focal depth of earthquakes and their magnitude, as well. Since lithosphere is flexed by the mass of topography on the earth's surface, the spectral analysis of topography and gravity anomaly is an appropriate method to assess the flexure of lithosphere and estimate its elastic layer thickness. In this paper, by spectral analysis of free-air gravity anomaly and topography signals which were generated respectively from EIGEN-GL04C and ETOPO5 global models; elastic layer thickness in different regions of Iran are calculated. Comparing the crust thickness (obtained from CRUST2.0 model) and the estimated elastic layer thickness, a statistically significant correlation between the two parameters could be seen.

  3. Enhanced photocurrent density in graphene/Si based solar cell (GSSC) by optimizing active layer thickness

    SciTech Connect

    Rosikhin, Ahmad Hidayat, Aulia Fikri; Syuhada, Ibnu; Winata, Toto

    2015-12-29

    Thickness dependent photocurrent density in active layer of graphene/Si based solar cell has been investigated via analytical – simulation study. This report is a preliminary comparison of experimental and analytical investigation of graphene/Si based solar cell. Graphene sheet was interfaced with Si thin film forming heterojunction solar cell that was treated as a device model for photocurrent generator. Such current can be enhanced by optimizing active layer thickness and involving metal oxide as supporting layer to shift photons absorption. In this case there are two type of devices model with and without TiO{sub 2} in which the silicon thickness varied at 20 – 100 nm. All of them have examined and also compared with each other to obtain an optimum value. From this calculation it found that generated currents almost linear with thickness but there are saturated conditions that no more enhancements will be achieved. Furthermore TiO{sub 2} layer is effectively increases photon absorption but reducing device stability, maximum current is fluctuates enough. This may caused by the disturbance of excitons diffusion and resistivity inside each layer. Finally by controlling active layer thickness, it is quite useful to estimate optimization in order to develop the next solar cell devices.

  4. Miniature fuel cell with monolithically fabricated Si electrodes - Uniformity of Catalyst Layer Thickness -

    NASA Astrophysics Data System (ADS)

    Morisawa, Itsuki; Suzuki, Takahiro; Katayama, Noboru; Dowaki, Kiyoshi; Hayase, Masanori

    2014-11-01

    Uniformity of catalyst layer thickness was improved to obtained higher output with our miniature fuel cells. Though the miniature fuel cells demonstrated high power density about 500mW/cm2 with 1 mm2 reaction area, it was difficult to maintain the power density with larger reaction area and careful observation of the prototypes revealed that the porous Si layer, which should be etched away completely, remained on the channel bottoms. Nonuniform porous Pt catalyst layer thickness was suspicious for the residual porous Si, and rotation of the plating vessel in the Pt deposition process was performed to mitigate variation of the catalyst layer thickness. Though the power density was still low with larger reaction area, the larger output was successfully obtained with the vessel rotation.

  5. Effect of por-SiC buffer layer on the parameters of thin Er2O3 layers on silicon carbide substrates

    NASA Astrophysics Data System (ADS)

    Bacherikov, Yu Yu; Konakova, R. V.; Okhrimenko, O. B.; Berezovska, N. I.; Kapitanchuk, L. M.; Svetlichnyi, A. M.; Svetlichnaya, L. A.

    2015-04-01

    Using optical absorption and Auger spectrometry techniques, we studied the effect of rapid thermal annealing (RTA) on the properties of erbium oxide films deposited onto a porous silicon carbide buffer layer formed on 4H-SiC substrates. An analysis of atomic composition of the films under investigation as a function of RTA duration was performed. It is shown that phase composition of erbium oxide films on silicon carbide substrates with a porous SiC layer can be changed by varying RTA duration.

  6. Effects of interfacial layer wettability and thickness on the coating morphology and sirolimus release for drug-eluting stent.

    PubMed

    Bedair, Tarek M; Yu, Seung Jung; Im, Sung Gap; Park, Bang Ju; Joung, Yoon Ki; Han, Dong Keun

    2015-12-15

    Drug-eluting stents (DESs) have been used to treat coronary artery diseases by placing in the arteries. However, current DESs still suffer from polymer coating defects such as delamination and peeling-off that follows stent deployment. Such coating defects could increase the roughness of DES and might act as a source of late or very late thrombosis and might increase the incident of restenosis. In this regard, we modified the cobalt-chromium (Co-Cr) alloy surface with hydrophilic poly(2-hydroxyethyl methacrylate) (PHEMA) or hydrophobic poly(2-hydroxyethyl methacrylate)-grafted-poly(caprolactone) (PHEMA-g-PCL) brushes. The resulting surfaces were biocompatible and biodegradable, which could act as anchoring layer for the drug-in-polymer matrix coating. The two modifications were characterized by ATR-FTIR, XPS, water contact angle measurements, SEM and AFM. On the control and modified Co-Cr samples, a sirolimus (SRL)-containing poly(D,L-lactide) (PDLLA) were ultrasonically spray-coated, and the drug release was examined for 8weeks under physiological conditions. The results demonstrated that PHEMA as a primer coating improved the coating stability and degradation morphology, and drug release profile for short-term as compared to control Co-Cr, but fails after 7weeks in physiological buffer. On the other hand, the hydrophobic PHEMA-g-PCL brushes not only enhanced the stability and degradation morphology of the PDLLA coating layer, but also sustained SRL release for long-term. At 8-week of release test, the surface morphologies and release profiles of coated PDLLA layers verified the beneficial effect of hydrophobic PCL brushes as well as their thickness on coating stability. Our study concludes that 200nm thickness of PHEMA-g-PCL as interfacial layer affects the stability and degradation morphology of the biodegradable coating intensively to be applied for various biodegradable-based DESs. PMID:26319336

  7. Molecular beam epitaxy growth of SrO buffer layers on graphite and graphene for the integration of complex oxides

    DOE PAGESBeta

    Ahmed, Adam S.; Wen, Hua; Ohta, Taisuke; Pinchuk, Igor V.; Zhu, Tiancong; Beechem, Thomas; Kawakami, Roland K.

    2016-04-27

    Here, we report the successful growth of high-quality SrO films on highly-ordered pyrolytic graphite (HOPG) and single-layer graphene by molecular beam epitaxy. The SrO layers have (001) orientation as confirmed by X-ray diffraction (XRD) while atomic force microscopy measurements show continuous pinhole-free films having rms surface roughness of <1.5 Å. Moreover, transport measurements of exfoliated graphene, after SrO deposition, show a strong dependence between the Dirac point and Sr oxidation. As a result, the SrO is leveraged as a buffer layer for more complex oxide integration via the demonstration of (001) oriented SrTiO3 grown atop a SrO/HOPG stack.

  8. Molecular beam epitaxy growth of SrO buffer layers on graphite and graphene for the integration of complex oxides

    NASA Astrophysics Data System (ADS)

    Ahmed, Adam S.; Wen, Hua; Ohta, Taisuke; Pinchuk, Igor V.; Zhu, Tiancong; Beechem, Thomas; Kawakami, Roland K.

    2016-08-01

    We report the successful growth of high-quality SrO films on highly-ordered pyrolytic graphite (HOPG) and single-layer graphene by molecular beam epitaxy. The SrO layers have (001) orientation as confirmed by X-ray diffraction (XRD) while atomic force microscopy measurements show continuous pinhole-free films having rms surface roughness of <1.5 Å. Transport measurements of exfoliated graphene after SrO deposition show a strong dependence between the Dirac point and Sr oxidation. Subsequently, the SrO is leveraged as a buffer layer for more complex oxide integration via the demonstration of (001) oriented SrTiO3 grown atop a SrO/HOPG stack.

  9. Transmission Electron Microscope Study on Electrodeposited Gd2O3 and Gd2Zr2O7 Buffer Layers forYBa2Cu307-..delta.. Superconductors

    SciTech Connect

    Zhao, W.; Norman, A.; Phok, S.; Bhattacharya, R.

    2008-01-01

    We have investigated the microstructures of electrodeposited Gd{sub 2}O{sub 3} (GO) and Gd{sub 2}Zr{sub 2}O{sub 7} (GZO) buffer layers for YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} (YBCO) superconductors with conventional transmission electron microscopy (TEM). A high density of nanoscale voids was present in the GZO buffer layers. No voids were observed in GO buffer layers grown on GZO. YBCO superconductor grown on the GO/GZO buffer layer structure produced a critical current density (J{sub c}) of 3.3 x 10{sup 6} A/cm{sup 2} at 77 K in zero field.

  10. TEM study of dislocations structure in In0.82Ga0.18As/InP heterostructure with InGaAs as buffer layer

    NASA Astrophysics Data System (ADS)

    Zhao, Liang; Guo, Zuo-xing; Yuan, De-zeng; Wei, Qiu-lin; Zhao, Lei

    2016-05-01

    In order to improve the quality of detector, In x Ga1- x As ( x=0.82) buffer layer has been introduced in In0.82Ga0.18As/InP heterostructure. Dislocation behavior of the multilayer is analyzed through plane and cross section [110] by transmission electron microscopy (TEM) and high resolution transmission electron microscopy (HRTEM). The dislocations are effectively suppressed in In x Ga1- x As ( x=0.82) buffer layer, and the density of dislocations in epilayer is reduced obviously. No lattice mismatch between buffer layer and epilayer results in no misfit dislocation (MD). The threading dislocations (TDs) are directly related to the multiplication of the MDs in buffer layer.

  11. Deposition of LaMnO 3 buffer layer on IBAD-MgO template by reactive DC sputtering

    NASA Astrophysics Data System (ADS)

    Kim, H. S.; Oh, S. S.; Ha, H. S.; Ko, R. K.; Ha, D. W.; Kim, T. H.; Youm, D. J.; Lee, N. J.; Moon, S. H.; Yoo, S. I.; Park, C.

    2009-10-01

    The deposition conditions of LaMnO 3 (LMO) buffer layer on Ion Beam Assisted Deposition (IBAD)-MgO template by reactive DC sputtering were investigated. We developed a specially designed chamber for reactive DC magnetron sputtering. The deposition chamber was composed of two sputtering guns with the mixed metallic target of La (50 at%) + Mn (50 at%), halogen lamp heater, QCM (Quartz Crystal Microbalance), RGA (Residual Gas Analyzer) and reel to reel tape moving system. We investigated the effect of oxygen flow rate on the deposition rate of LMO layer. We found that there was an optimal range of oxygen flow rate to have the desired layer. Above the range, the deposition rate decreased sharply and plasma was unstable. Below the range, the deposited layer was partially metallic. We investigated the effect of substrate temperature on the texturing of LMO layer. The texturing of LMO layer was improved by increasing the substrate temperature. We investigated the effect of deposition rate on the texturing of LMO layer. The LMO layer has a good texture in the deposition rate range of 0.07-0.21 nm/s. We confirmed that deposition rate had little effect on the texturing of LMO layer in the deposition rate range. Sm 1Ba 2Cu 3O 7-d superconducting layer was deposited on the LMO(reactive)/IBAD-MgO template. I c and J c were 81.6 A and 1 MA/cm 2. This means that LMO layer deposited by reactive DC sputtering shows a good performance in superconductor coated conductor.

  12. Analysis of Retinal Layer Thicknesses and Their Clinical Correlation in Patients with Traumatic Optic Neuropathy

    PubMed Central

    Lee, Ju-Yeun; Cho, Kyuyeon; Park, Kyung-Ah; Oh, Sei Yeul

    2016-01-01

    The aims of this study were 1) To evaluate retinal nerve fiber layer (fRNFL) thickness and ganglion cell layer plus inner plexiform layer (GCIPL) thickness at the fovea in eyes affected with traumatic optic neuropathy (TON) compared with contralateral normal eyes, 2) to further evaluate these thicknesses within 3 weeks following trauma (defined as “early TON”), and 3) to investigate the relationship between these retinal layer thicknesses and visual function in TON eyes. Twenty-nine patients with unilateral TON were included. Horizontal and vertical spectral-domain optical coherence tomography (SD-OCT) scans of the fovea were taken in patients with unilateral TON. The main outcome measure was thickness of the entire retina, fRNFL, and GCIPL in eight areas. Thickness of each retinal layer was compared between affected and unaffected eyes. The correlation between the thickness of each retinal layer and visual function parameters, including best corrected visual acuity, color vision, P100 latency, and P100 amplitude in visual evoked potential (VEP), mean deviation (MD) and visual field index (VFI) in Humphrey visual field analysis in TON eyes was analyzed. Thicknesses of the entire retina, fRNFL, and GCIPL in SD-OCT were significantly thinner (3–36%) in all measurement areas of TON eyes compared to those in healthy eyes (all p<0.05). Whereas, only GCIPL in the outer nasal, superior, and inferior areas was significantly thinner (5–10%) in the early TON eyes than that in the control eyes (all p<0.01). A significant correlation was detected between retinal layer thicknesses and visual function parameters including color vision, P100 latency and P100 amplitude in VEP, MD, and VFI (particularly P100 latency, MD, and VFI) (r = -0.70 to 0.84). Among the retinal layers analyzed in this study, GCIPL (particularly in the superior and inferior areas) was most correlated with these five visual function parameters (r = -0.70 to 0.71). Therefore, evaluation of morphological

  13. Aspects of the SrO-CuO-TiO2 Ternary System Related to the Deposition of SrTiO3 and Copper-Doped SrTiO3 Thin-Film Buffer Layers

    SciTech Connect

    A. Ayala

    2004-12-20

    YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} (YBCO) coated conductors are promising materials for large-scale superconductivity applications. One version of a YBCO coated conductor is based on ion beam assisted deposition (IBAD) of magnesium oxide (MgO) onto polycrystalline metal substrates. SrTiO{sub 3} (STO) is often deposited by physical vapor deposition (PVD) methods as a buffer layer between the YBCO and IBAD MgO due to its chemical stability and lattice mismatch of only {approx}1.5% with YBCO. In this work, some aspects of the stability of STO with respect to copper (Cu) and chemical solution deposition of STO on IBAD MgO templates were examined. Solubility limits of Cu in STO were established by processing Cu-doped STO powders by conventional bulk preparation techniques. The maximum solubility of Cu in STO was {approx}1% as determined by transmission electron microscopy (TEM) and Rietveld refinements of x-ray diffraction (XRD) data. XRD analysis, performed in collaboration with NIST, on powder compositions on the STO/SrCuO{sub 2} tie line did not identify any ternary phases. SrCu{sub 0.10}Ti{sub 0.90}O{sub y} buffer layers were prepared by pulsed laser deposition (PLD) and CSD on IBAD MgO flexible metallic textured tapes. TEM analysis of a {approx}100 nm thick SrCu{sub 0.10}Ti{sub 0.90}O{sub y} buffer layer deposited by PLD showed a smooth Cu-doped STO/MgO interface. A {approx}600 nm thick YBCO film, deposited onto the SrCu{sub 0.10}Ti{sub 0.90}O{sub y} buffer by PLD, exhibited a T{sub c} of 87 K and critical current density (J{sub c}) of {approx}1 MA/cm{sup 2}. STO and Cu-doped STO thin films by CSD were {approx}30 nm thick. The in plane alignment (FWHM) after deposition of the STO improved by {approx}1{sup o} while it degraded by {approx}2{sup o} with the SrCu{sub 0.05}TiO{sub y} buffer. YBCO was deposited by PLD on the STO and SrCu{sub 0.05}TiO{sub y} buffers. The in plane alignment (FWHM) of the YBCO with the STO buffer layer slightly improved while that of the

  14. Surface effect on the magnetoelectric response of magnetoelectric layered composite with nanoscale thickness

    NASA Astrophysics Data System (ADS)

    Yu, GuoLiang; Zhang, HuaiWu

    2015-02-01

    A theoretical model is proposed to study the ME effect in the layered ME composite with nanoscale thickness, which taking into account the surface effect. The layered ME composites nano structure is treated as a bulk core plus two surface layers with zero thickness. The influence on the structure overall properties resulted from the surface effect is modeled by a spring force exerting on the boundary of the bulk core. Using the derived equations, the so-called effective Miller-Shenoy coefficient, static and electromechanical resonance (EMR) properties of the nanoscale thickness ME composite for the extensional-bending coupling deformations are analyzed theoretically. At the same time, the effect of the substrate on ME effect is theoretically studied by altering the thickness ratio of the substrate. Numerical results shows the effective properties and the static and EMR properties of the composites are size-dependent, and surface effect have non-ignored effects on the ME effect. Besides, the EMR frequency in nano-thickness composites are expected to occur at very low frequencies compared to nominal dimensional composites. The EMR frequency shows an increase with increasing substrate thickness, and predicts a maximum in the EMR ME coefficient at small but nonvanishing substrate thickness.

  15. Hierarchical rendering of trees from precomputed multi-layer z-buffers

    SciTech Connect

    Max, N.

    1996-02-01

    Chen and Williams show how precomputed z-buffer images from different fixed viewing positions can be reprojected to produce an image for a new viewpoint. Here images are precomputed for twigs and branches at various levels in the hierarchical structure of a tree, and adaptively combined, depending on the position of the new viewpoint. The precomputed images contain multiple z levels to avoid missing pixels in the reconstruction, subpixel masks for anti-aliasing, and colors and normals for shading after reprojection.

  16. Effects of Strain and Buffer Layer on Interfacial Magnetization in Sr2CrReO6 Films

    NASA Astrophysics Data System (ADS)

    Liu, Yaohua; Te Velthuis, S. G. E.; Glavic, A.; Ambaye, H.; Lauter, V.; Lucy, J. M.; Yang, F. Y.

    2015-03-01

    Magnetic double-perovskite Sr2CrReO6 (SCRO) has several functional properties including a TC > 500 K, high spin polarization, large spin-orbit interaction, and semiconducting behavior in highly ordered films. However, fabrication of highly ordered films is still challenging, and progress toward device applications requires an in-depth understanding of the electronic and magnetic properties, especially at interfaces. We have investigated how the Cr/Re antisite disorder and strain affect the interfacial magnetization in SCRO films via x-ray and polarized neutron reflectometry. We find that the magnetization of SCRO films is reduced near the interface with the substrate. The width of this interfacial layer weakly depends on the strain and decreases when a SrCr0.5Nb0.5O3 (SCNO) buffer layer is used to reduce the antisite disorder. Interestingly, for the SCRO film deposited on a SCNO buffer layer, the region with reduced magnetization is wider than the antisite disorder region at the SCRO/SCNO interface, suggesting that antisite disorder is not the only mechanism reducing the magnetization. Work at ANL was supported by the DOE-BES, MSE, at OSU by the Center for Emergent Materials, a NSF MRSEC (DMR-1420451), at ORNL by DOE-BES, Scientific User Facilities Division.

  17. Assessment of Layer Thickness and Interface Quality in CoP Electrodeposited Multilayers.

    PubMed

    Lucas, Irene; Ciudad, David; Plaza, Manuel; Ruiz-Gómez, Sandra; Aroca, Claudio; Pérez, Lucas

    2016-07-27

    The magnetic properties of CoP electrodeposited alloys can be easily controlled by layering the alloys and modulating the P content of the different layers by using pulse plating in the electrodeposition process. However, because of its amorphous nature, the study of the interface quality, which is a limitation for the optimization of the soft magnetic properties of these alloys, becomes a complex task. In this work, we use Rutherford backscattering spectroscopy (RBS) to determine that electrodeposited Co0.74P0.26/Co0.83P0.17 amorphous multilayers with layers down to 20 nm-thick are composed by well-defined layers with interfacial roughness below 3 nm. We have also determined, using magnetostriction measurements, that 4 nm is the lower limitation for the layer thickness. Below this thickness, the layers are mixed and the magnetic behavior of the multilayered films is similar to that shown by single layers, thus going from in-plane to out-of-plane magnetic anisotropy. Therefore, these results establish the range in which the magnetic properties of these alloys can be controlled by layering. PMID:27381897

  18. Focusing of dipole radiation by a negative index chiral layer. 1. A thick layer as compared with the wavelength

    SciTech Connect

    Guzatov, D V; Klimov, V V

    2014-09-30

    We have derived and investigated the analytical expressions for the fields of scattered radiation of an electric dipole source by a chiral (bi-isotropic) layer with arbitrary permittivity and permeability and arbitrary thickness. It is shown that in the negativeindex chiral layer the focus spot of dipole radiation is split due to excitation of right- and left-hand circularly polarised waves. The conditions are found under which the waves with one of the polarisations can be suppressed, which leads to a substantial improvement of the focusing properties of the chiral layer. (metamaterials)

  19. Variation of bone layer thicknesses and trabecular volume fraction in the adult male human calvarium.

    PubMed

    Boruah, Sourabh; Paskoff, Glenn R; Shender, Barry S; Subit, Damien L; Salzar, Robert S; Crandall, Jeff R

    2015-08-01

    The human calvarium is a sandwich structure with two dense layers of cortical bone separated by porous cancellous bone. The variation of the three dimensional geometry, including the layer thicknesses and the volume fraction of the cancellous layer across the population, is unavailable in the current literature. This information is of particular importance to mathematical models of the human head used to simulate mechanical response. Although the target geometry for these models is the median geometry of the population, the best attempt so far has been the scaling of a unique geometry based on a few median anthropometric measurements of the head. However, this method does not represent the median geometry. This paper reports the average three dimensional geometry of the calvarium from X-ray computed tomography (CT) imaging and layer thickness and trabecular volume fraction from micro CT (μCT) imaging of ten adult male post-mortem human surrogates (PMHS). Skull bone samples have been obtained and μCT imaging was done at a resolution of 30 μm. Monte Carlo simulation was done to estimate the variance in these measurements due to the uncertainty in image segmentation. The layer thickness data has been averaged over areas of 5mm(2). The outer cortical layer was found to be significantly (p < 0.01; Student's t test) thicker than the inner layer (median of thickness ratio 1.68). Although there was significant location to location difference in all the layer thicknesses and volume fraction measurements, there was no trend. Average distribution and the variance of these metrics on the calvarium have been shown. The findings have been reported as colormaps on a 2D projection of the cranial vault. PMID:25920690

  20. Plasma assisted molecular beam epitaxy growth and effect of varying buffer thickness on the formation of ultra-thin In{sub 0.17}Al{sub 0.83}N/GaN heterostructure on Si(111)

    SciTech Connect

    Chowdhury, Subhra; Biswas, Dhrubes

    2015-02-23

    This work reports on the detailed plasma-assisted molecular beam epitaxy (PAMBE) growth of ultra-thin In{sub 0.17}Al{sub 0.83}N/GaN heterostructures on Si(111) substrate with three different buffer thickness (600 nm, 400 nm, and 200 nm). Growth through critical optimization of growth conditions is followed by the investigation of impact of varying buffer thickness on the formation of ultra-thin 1.5 nm, In{sub 0.17}Al{sub 0.83}N–1.25 nm, GaN–1.5 nm, In{sub 0.17}Al{sub 0.83}N heterostructure, in terms of threading dislocation (TD) density. Analysis reveals a drastic reduction of TD density from the order 10{sup 10 }cm{sup −2} to 10{sup 8 }cm{sup −2} with increasing buffer thickness resulting smooth ultra-thin active region for thick buffer structure. Increasing strain with decreasing buffer thickness is studied through reciprocal space mapping analysis. Surface morphology through atomic force microscopy analysis also supports our study by observing an increase of pits and root mean square value (0.89 nm, 1.2 nm, and 1.45 nm) with decreasing buffer thickness which are resulted due to the internal strain and TDs.

  1. Formation of perovskite BiFeO3(001) films on refined Pt(111) electrode layer with reduced thickness on glass substrates

    NASA Astrophysics Data System (ADS)

    Chang, H. W.; Yuan, F. T.; Tien, S. H.; Tu, K. T.; Wang, C. R.; Jen, S. U.

    2014-05-01

    Structure and ferroelectric properties of multiferroic BiFeO3 (001) films grown on Pt(111) buffer layer with thicknesses of 5-50 nm on glass substrate at 500 °C have been studied. (001) texture of the perovskite BiFeO3 (BFO) could be developed. Grain size and morphology of the BFO(001) films were closely related to those of Pt electrode although no epitaxial growth was evidenced. The optimized BFO layer which exhibited the ferroelectric performance comparable to those with SrRuO3 under layer could be achieved in the samples with Pt thickness in the range of 10 to 20 nm. Different from the polycrystalline BFO/SrRuO3 films, large grain size for 50-nm-thick Pt underlayer causes degeneration of both the ferroelectric properties and the (001)-texture due to the formation of the secondary B2O3 phase. On the other hand, reducing Pt thickness to 5 nm resulted in the induction of the pinholes and thus the increase of the leakage current density. The presented results reveal that a smooth interface between the Pt electrode and BFO layer is essential to achieve good ferroelectric properties.

  2. Prediction of Layer Thickness in Molten Borax Bath with Genetic Evolutionary Programming

    NASA Astrophysics Data System (ADS)

    Taylan, Fatih

    2011-04-01

    In this study, the vanadium carbide coating in molten borax bath process is modeled by evolutionary genetic programming (GEP) with bath composition (borax percentage, ferro vanadium (Fe-V) percentage, boric acid percentage), bath temperature, immersion time, and layer thickness data. Five inputs and one output data exist in the model. The percentage of borax, Fe-V, and boric acid, temperature, and immersion time parameters are used as input data and the layer thickness value is used as output data. For selected bath components, immersion time, and temperature variables, the layer thicknesses are derived from the mathematical expression. The results of the mathematical expressions are compared to that of experimental data; it is determined that the derived mathematical expression has an accuracy of 89%.

  3. Relaxation processes of a thick granular layer at seismic slip rates

    NASA Astrophysics Data System (ADS)

    Kuwano, O.; Nakatani, M.; Hatano, T.; Sakaguchi, H.

    2013-12-01

    We report on laboratory experiments designed to explore transient responses of a thick granular layer following a step change in slip velocity at seismic slip rates. Experiments were performed at constant normal stresses of 10-30kPa using a ring shear apparatus with inner/outer diameters of 15mm/25mm. We measure the friction coefficient and thickness of glass beads layer at sliding velocities between 0.5 and 3 m/s. Experimental results show that the friction coefficient and layer thickness suddenly increases/decrease as sudden increase/decrease of sliding velocity and then exponentially decay to new steady state with characteristic slip length. We found that characteristic slip length is of the order of 10m. The response to a velocity step decreases simply symmetric to that to a velocity step increase.

  4. Effect of Thickness of a Water Repellent Soil Layer on Soil Evaporation Rate

    NASA Astrophysics Data System (ADS)

    Ahn, S.; Im, S.; Doerr, S.

    2012-04-01

    A water repellent soil layer overlying wettable soil is known to affect soil evaporation. This effect can be beneficial for water conservation in areas where water is scarce. Little is known, however, about the effect of the thickness of the water repellent layer. The thickness of this layer can vary widely, and particularly after wildfire, with the soil temperature reached and the duration of the fire. This study was conducted to investigate the effect of thickness of a top layer of water repellent soil on soil evaporation rate. In order to isolate the thickness from other possible factors, fully wettable standard sand (300~600 microns) was used. Extreme water repellency (WDPT > 24 hours) was generated by 'baking' the sand mixed with oven-dried pine needles (fresh needles of Pinus densiflora) at the mass ratio of 1:13 (needle:soil) at 185°C for 18 hours. The thicknesses of water repellent layers were 1, 2, 3 and 7 cm on top of wettable soil. Fully wettable soil columns were prepared as a control. Soil columns (8 cm diameter, 10 cm height) were covered with nylon mesh. Tap water (50 ml, saturating 3 cm of a soil column) was injected with hypoderm syringes from three different directions at the bottom level. The injection holes were sealed with hot-melt adhesive immediately after injection. The rate of soil evaporation through the soil surface was measured by weight change under isothermal condition of 40°C. Five replications were made for each. A trend of negative correlation between the thickness of water repellent top layer and soil evaporation rate is discussed in this contribution.

  5. Diurnal changes in retinal nerve fiber layer thickness with obstructive sleep apnea/hypopnea syndrome

    PubMed Central

    Chirapapaisan, Niphon; Likitgorn, Techawit; Pleumchitchom, Mintra; Sakiyalak, Darin; Banhiran, Wish; Saiman, Manatsawin; Chuenkongkaew, Wanicha

    2016-01-01

    AIM To compare the retinal nerve fiber layer (RNFL) thickness in the morning and evening in Thai patients with varying degrees of obstructive sleep apnea/hypopnea syndrome (OSAHS). METHODS In this cross-sectional study, potential OSAHS patients at Siriraj Hospital underwent polysomnography to determine the severity of OSAHS and an eye examination (including best corrected visual acuity, slit-lamp examination, and Goldmann applanation tonometry). RNFL thickness was recorded once in the morning and once in the evening, using spectral domain optical coherence tomography. Thickness was expressed as an average and given for each quadrant. Patients with ocular or systemic diseases that might affect RNFL thickness were excluded. RESULTS Forty-one eyes of 41 patients were classified into 4 OSAHS groups. The average and mean RNFL thickness in most of the four quadrants of the severe OSAHS group trended toward being less than those in the comparable quadrants of the other groups in both the morning and evening. In the moderate OSAHS group, the average RNFL thickness and temporal and superior quadrant thickness in the morning were significantly higher than in the evening (P=0.01, P=0.01, and P=0.03, respectively). In the severe OSAHS group, the inferior quadrant thickness in the morning was significantly higher than in the evening (P=0.03). CONCLUSION The RNFL thickness in the morning was higher than in the evening in moderate OSAHS. PMID:27500104

  6. Reduction in retinal nerve fiber layer thickness in young adults with autism spectrum disorders.

    PubMed

    Emberti Gialloreti, Leonardo; Pardini, Matteo; Benassi, Francesca; Marciano, Sara; Amore, Mario; Mutolo, Maria Giulia; Porfirio, Maria Cristina; Curatolo, Paolo

    2014-04-01

    Recent years have seen an increase in the use of retinal nerve fiber layer (RNFL) evaluation as an easy-to-use, reproducible, proxy-measure of brain structural abnormalities. Here, we evaluated RNFL thickness in a group of subjects with high functioning autism (HFA) or with Asperger Syndrome (AS) to its potential as a tool to study autism pathophysiology. All subjects underwent high-resolution spectral domain optical coherence tomography to evaluate RNFL thickness. HFA subjects presented with reduced global RNFL thickness compared both to AS subjects and controls. AS subjects showed a reduced nasal quadrant RNFL thickness compared to controls. Verbal-IQ/performance-IQ discrepancy correlated with RNFL thickness. Our data suggest that RNFL evaluation could help in the development of biological markers of autism pathophysiology. PMID:24014196

  7. Redefining electrical double layer thickness in narrow confinements: Effect of solvent polarization

    NASA Astrophysics Data System (ADS)

    Das, Siddhartha; Chakraborty, Suman; Mitra, Sushanta K.

    2012-05-01

    In this paper we delineate the consequences of field-dependent solvent polarization in the electric double layer (EDL) electrostatic potential distribution, and the effective EDL thickness in narrow nanofluidic confinements with thick (or overlapping) EDLs. The EDL, formed at the interface between a charged substrate and an electrolyte solution, induces a large electric field spanning across few nanometer distances from the interface. As a result, a polar solvent like water gets polarized, making its relative permittivity a function of the EDL electric field. This affects the overall EDL electrostatic potential distribution and most importantly, leads to a significant reduction of the effective EDL thickness, with the extent of the reduction being dictated by the value of field independent EDL thickness, strength of the solvent polarization, and the substrate-liquid interfacial electrostatic potential. Such a finding will necessitate redefining the classical EDL thickness, which will be of overwhelming significance in nanofluidic transport.

  8. Distortions to current-voltage curves of cigs cells with sputtered Zinc(Oxygen,Sulfur) buffer layers

    NASA Astrophysics Data System (ADS)

    Song, Tao

    Sputtered-deposited Zn(O,S) is an attractive alternative to CdS for Cu(In,Ga)Se 2 (CIGS) thin-film solar cells' buffer layer. It has a higher band gap and thus allows greater blue photon collection to achieve higher photon current. The primary goal of the thesis is to investigate the effects of the secondary barrier at the buffer-absorber interface on the distortions to current-voltage (J-V) curves of sputtered-Zn(O,S)/CIGS solar cells. A straightforward photodiode model is employed in the numerical simulation to explain the physical mechanisms of the experimental J-V distortions including J-V crossover and red kink. It is shown that the secondary barrier is influenced by both the internal material properties, such as the conduction-band offset (CBO) and the doping density of Zn(O,S), and the external conditions, such as the light intensity and operating temperature. A key parameter for the sputter deposition of Zn(O,S) has been the oxygen fraction in the argon beam. It is found that the CBO varies with the oxygen fraction in the argon beam at a fixed temperature. With a greater CBO (DeltaEC>0.3 eV), the resulting energy barrier limits the electron current flowing across the interface and thus leads to the J-V distortion. Two different ZnS targets, non-indium and indium-doped one, were used to deposit the Zn(O,S) buffer layer. At the same oxygen fraction in argon beam, a non-In-doped Zn(O,S) buffer with a smaller amount of doping forms a greater secondary barrier to limit the electron current due to the compensation of the Zn(O,S) buffer layer. In addition, the temperature-dependent J-V crossover can be explained by the temperature-dependent impact of the secondary barrier - at lower temperature in the dark, the maximum distortion-free barrier is reduced and results in a more serious current limitation, indicating a greater J-V crossover. It is also found that, under low-intensity illumination, there is a lower doping density of Zn(O,S) due to a smaller amount of

  9. Study of the effects of GaN buffer layer quality on the dc characteristics of AlGaN/GaN high electron mobility transistors

    DOE PAGESBeta

    Ahn, Shihyun; Zhu, Weidi; Dong, Chen; Le, Lingcong; Hwang, Ya-Hsi; Kim, Byung-Jae; Ren, Fan; Pearton, Stephen J.; Lind, Aaron G.; Jones, Kevin S.; et al

    2015-04-21

    Here we studied the effect of buffer layer quality on dc characteristics of AlGaN/GaN high electron mobility (HEMTs). AlGaN/GaN HEMT structures with 2 and 5 μm GaN buffer layers on sapphire substrates from two different vendors with the same Al concentration of AlGaN were used. The defect densities of HEMT structures with 2 and 5 μm GaN buffer layer were 7 × 109 and 5 × 108 cm₋2, respectively, as measured by transmission electron microscopy. There was little difference in drain saturation current or in transfer characteristics in HEMTs on these two types of buffer. However, there was no dispersionmore » observed on the nonpassivated HEMTs with 5 μm GaN buffer layer for gate-lag pulsed measurement at 100 kHz, which was in sharp contrast to the 71% drain current reduction for the HEMT with 2 μm GaN buffer layer.« less

  10. Study of the effects of GaN buffer layer quality on the dc characteristics of AlGaN/GaN high electron mobility transistors

    SciTech Connect

    Ahn, Shihyun; Zhu, Weidi; Dong, Chen; Le, Lingcong; Hwang, Ya-Hsi; Kim, Byung-Jae; Ren, Fan; Pearton, Stephen J.; Lind, Aaron G.; Jones, Kevin S.; Kravchenko, I. I.; Zhang, Ming-Lan

    2015-04-21

    Here we studied the effect of buffer layer quality on dc characteristics of AlGaN/GaN high electron mobility (HEMTs). AlGaN/GaN HEMT structures with 2 and 5 μm GaN buffer layers on sapphire substrates from two different vendors with the same Al concentration of AlGaN were used. The defect densities of HEMT structures with 2 and 5 μm GaN buffer layer were 7 × 109 and 5 × 108 cm₋2, respectively, as measured by transmission electron microscopy. There was little difference in drain saturation current or in transfer characteristics in HEMTs on these two types of buffer. However, there was no dispersion observed on the nonpassivated HEMTs with 5 μm GaN buffer layer for gate-lag pulsed measurement at 100 kHz, which was in sharp contrast to the 71% drain current reduction for the HEMT with 2 μm GaN buffer layer.

  11. Micrometer-Thick Graphene Oxide-Layered Double Hydroxide Nacre-Inspired Coatings and Their Properties.

    PubMed

    Yan, You-Xian; Yao, Hong-Bin; Mao, Li-Bo; Asiri, Abdullah M; Alamry, Khalid A; Marwani, Hadi M; Yu, Shu-Hong

    2016-02-10

    Robust, functional, and flame retardant coatings are attractive in various fields such as building construction, food packaging, electronics encapsulation, and so on. Here, strong, colorful, and fire-retardant micrometer-thick hybrid coatings are reported, which can be constructed via an enhanced layer-by-layer assembly of graphene oxide (GO) nanosheets and layered double hydroxide (LDH) nanoplatelets. The fabricated GO-LDH hybrid coatings show uniform nacre-like layered structures that endow them good mechanic properties with Young's modulus of ≈ 18 GPa and hardness of ≈ 0.68 GPa. In addition, the GO-LDH hybrid coatings exhibit nacre-like iridescence and attractive flame retardancy as well due to their well-defined 2D microstructures. This kind of nacre-inspired GO-LDH hybrid thick coatings will be applied in various fields in future due to their high strength and multifunctionalities. PMID:26682698

  12. Controlled gentamicin release from multi-layered electrospun nanofibrous structures of various thicknesses.

    PubMed

    Sirc, Jakub; Kubinova, Sarka; Hobzova, Radka; Stranska, Denisa; Kozlik, Petr; Bosakova, Zuzana; Marekova, Dana; Holan, Vladimir; Sykova, Eva; Michalek, Jiri

    2012-01-01

    Polyvinyl alcohol nanofibers incorporating the wide spectrum antibiotic gentamicin were prepared by Nanospider™ needleless technology. A polyvinyl alcohol layer, serving as a drug reservoir, was covered from both sides by polyurethane layers of various thicknesses. The multilayered structure of the nanofibers was observed using scanning electron microscopy, the porosity was characterized by mercury porosimetry, and nitrogen adsorption/desorption measurements were used to determine specific surface areas. The stability of the gentamicin released from the electrospun layers was proved by high-performance liquid chromatography (HPLC) and inhibition of bacterial growth. Drug release was investigated using in vitro experiments with HPLC/MS quantification, while the antimicrobial efficacy was evaluated on Gram-positive Staphylococcus aureus and Gram-negative Pseudomonas aeruginosa. Both experiments proved that the released gentamicin retained its activity and showed that the retention of the drug in the nanofibers was prolonged with the increasing thickness of the covering layers. PMID:23071393

  13. Selective and non-selective deposition of thick polysilicon layers for adaptive mirror device

    NASA Astrophysics Data System (ADS)

    Bartek, M.; Vdovin, G. V.; Wolffenbuttel, R. F.

    1997-09-01

    Two IC-process-compatible fabrication schemes, based on the selective and non-selective deposition of a thick polysilicon layer in an epitaxial reactor, are used for adaptive micromirror device fabrication. The micromirror consists of a composite diaphragm (a 0960-1317/7/3/014/img1 square-shaped silicon nitride membrane on which an additional 0960-1317/7/3/014/img2 thick polycrystalline silicon layer with a circular aperture is formed) coated with a 0960-1317/7/3/014/img3 reflective aluminium layer on a bulk micromachined 10.5 mm by 10.5 mm square silicon frame. The additional polycrystalline silicon layer with a circular aperture improves the optical properties of a deflected square-shaped silicon nitride membrane resulting from anisotropic KOH etching.

  14. DEVELOPMENT OF IN-SITU CONTROL DIAGNOSTICS FOR APPLICATION OF EPITAXIAL SUPERCONDUCTOR AND BUFFER LAYERS

    SciTech Connect

    B.C. Winkleman; T.V. Giel, Jr.; J. Cunningham

    1999-06-30

    The recent achievements of critical currents in excess of 1x10{sup 6}amp/cm{sup 2} at 77K in YBCO deposited over suitably textured buffer/substrate composites have stimulated interest in the potential fabrication of these coated conductors as wire. Numerous approaches and manufacturing schemes for producing coated conductor wire are currently being developed. Recently, under the U. S. Department of Energy (DOE's) sponsorship, the University of Tennessee Space Institute (UTSI) performed an extensive evaluation of leading coated conductor processing options. In general, it is our feeling that the science and chemistry that are being developed in the coated conductor wire program now need proper engineering evaluation to define the most viable options for a commercial fabrication process. All fabrication processes will need process control measurements. This report provides a specific review of the needs and available technologies for process control for many of the coated conductor processing options. This report also addresses generic process monitoring areas in which additional research and development is needed. The concentration is on the two different approaches for obtaining the textured substrates that have been identified as viable candidates. These are the Los Alamos National Laboratory's (LANL) ion-beam assisted deposition, called IBAD, to obtain a highly textured yttria-stabilized zirconia (YSZ) buffer on nickel alloy strips, and Oak Ridge National Laboratory's (ORNL) rolling assisted, bi-axially textured substrate option called RABiTS{trademark}.

  15. Development of in-situ control diagnostics for application of epitaxial superconductor and buffer layers

    SciTech Connect

    B.C. Winkleman; T.V. Giel; Jason Cunningham

    1999-07-30

    The recent achievements of critical currents in excess of 1 x 10{sup 6} amp/cm{sup 2} at 77 K in YBCO deposited over suitably textured buffer/substrate composites have stimulated interest in the potential fabrication of these coated conductors as wire. Numerous approaches and manufacturing schemes for producing coated conductor wire are currently being developed. Recently, under the US DOE's sponsorship, the University of Tennessee Space Institute performed an extensive evaluation of leading coated conductor processing options. In general, it is their feeling that the science and chemistry that are being developed in the coated conductor wire program now need proper engineering evaluation to define the most viable options for a commercial fabrication process. All fabrication processes will need process control measurements. This report provides a specific review of the needs and available technologies for process control for many of the coated conductor processing options. This report also addresses generic process monitoring areas in which additional research and development is needed. The concentration is on the two different approaches for obtaining the textured substrates that have been identified as viable candidates. These are the Los Alamos National Laboratory's ion-beam assisted deposition, called IBAD, to obtain a highly textured yttria-stabilized zirconia (YSZ) buffer on nickel alloy strips, and Oak Ridge National Laboratory's rolling assisted, bi-axially textured substrate option called RABiTS{trademark}.

  16. Thickness dependence of curvature, strain, and response time in ionic electroactive polymer actuators fabricated via layer-by-layer assembly

    NASA Astrophysics Data System (ADS)

    Montazami, Reza; Liu, Sheng; Liu, Yang; Wang, Dong; Zhang, Qiming; Heflin, James R.

    2011-05-01

    Ionic electroactive polymer (IEAP) actuators containing porous conductive network composites (CNCs) and ionic liquids can result in high strain and fast response times. Incorporation of spherical gold nanoparticles in the CNC enhances conductivity and porosity, while maintaining relatively small thickness. This leads to improved mechanical strain and bending curvature of the actuators. We have employed the layer-by-layer self-assembly technique to fabricate a CNC with enhanced curvature (0.43 mm-1) and large net intrinsic strain (6.1%). The results demonstrate that curvature and net strain of IEAP actuators due to motion of the anions increase linearly with the thickness of the CNC as a result of the increased volume in which the anions can be stored. In addition, after subtracting the curvature of a bare Nafion actuator without a CNC, it is found that the net intrinsic strain of the CNC layer is independent of thickness for the range of 20-80 nm, indicating that the entire CNC volume contributes equivalently to the actuator motion. Furthermore, the response time of the actuator due to anion motion is independent of CNC thickness, suggesting that traversal through the Nafion membrane is the limiting factor in the anion motion.

  17. Mechanism for interfacial adhesion strength of an ion beam mixed Cu/polyimide with a thin buffer layer

    NASA Astrophysics Data System (ADS)

    Chang, G. S.; Chae, K. H.; Whang, C. N.; Kurmaev, E. Z.; Zatsepin, D. A.; Winarski, R. P.; Ederer, D. L.; Moewes, A.; Lee, Y. P.

    1999-01-01

    A Cu (400 Å)/Al (50 Å)/polyimide system showed larger adhesion strength than that of Cu (400 Å)/polyimide after N2+ ion beam mixing. X-ray emission spectroscopy was performed to elucidate the mechanism of adhesion enhancement of the ion beam mixed Cu (400 Å)/polyimide with a thin Al buffer layer. Cu L2,3 x-ray emission spectra showed the formation of a CuAl2O4 layer which is strongly correlated with the large adhesion strength of a Cu/Al/polyimide. A decrease in adhesion strength at an ion dose higher than 5×1015cm-2 was also explained by the formation of an amorphous carbon. This was understood by investigating C Kα x-ray emission spectra. The overall spectroscopic results were in accordance with the behavior of quantitative adhesion strength.

  18. Development of mid-frequency AC reactive magnetron sputtering for fast deposition of Y2O3 buffer layers

    NASA Astrophysics Data System (ADS)

    Xiong, Jie; Xia, Yudong; Xue, Yan; Zhang, Fei; Guo, Pei; Zhao, Xiaohui; Tao, Bowan

    2014-02-01

    A reel-to-reel magnetron sputtering system with mid-frequency alternating current (AC) power supply was used to deposit double-sided Y2O3 seed layer on biaxially textured Ni-5 at.%W tape for YBa2Cu3O7-δ coated conductors. A reactive sputtering process was carried out using two opposite symmetrical sputtering guns with metallic yttrium targets and water vapor for oxidizing the sputtered metallic atoms. The voltage control mode of the power supply was used and the influence of the cathode voltage and ArH2 pressure were systematically investigated. Subsequently yttrium-stabilized zirconia (YSZ) barrier and CeO2 cap layers were deposited on the Y2O3 buffered substrates in sequence, indicating high quality and uniform double-sided structure and surface morphology of such the architecture.

  19. Electrical resistivity of assembled transparent inorganic oxide nanoparticle thin layers: Influence of silica, insulating impurities and surfactant layer thickness

    PubMed Central

    Bubenhofer, Stephanie B.; Schumacher, Christoph M.; Koehler, Fabian M.; Luechinger, Norman A.; Sotiriou, Georgios A.; Grass, Robert N.; Stark, Wendelin J.

    2013-01-01

    Transparent, conductive layers prepared from nanoparticle dispersion of doped oxides are highly sensitive to impurities. Currently investigated cost efficient and fast production of thin conducting films for use in consumer electronics relies on wet processing such as spin and/or dip coating of surfactant-stabilized nanoparticle dispersions. This inherently results in entrainment of organic and inorganic impurities into the conducting layer leading to largely varying electrical conductivity. Therefore this study provides a systematic investigation on the effect of insulating surfactants, small organic molecules and silica in terms of pressure dependent electrical conductivity as a result of different core/shell structure (layer thickness). Application of high temperature flame synthesis gives access to antimony-doped tin oxide (ATO) nanoparticles with high purity. This well-defined starting material was then subjected to representative film preparation processes using organic additives. In addition ATO nanoparticles were prepared with a homogeneous inorganic silica layer (silica layer thickness from 0.7 to 2 nm). Testing both organic and inorganic shell materials for the electronic transport through the nanoparticle composite allowed a systematic study on the influence of surface adsorbates (e.g. organic, insulating materials on the conducting nanoparticle’s surface) in comparison to well-known insulators such as silica. Insulating impurities or shells revealed a dominant influence of tunneling effect on the overall layer resistance. Mechanical relaxation phenomena were found for 2 nm insulating shells for both large polymer surfactants and (inorganic) SiO2 shells. PMID:22545730

  20. Improved electrical properties of PbZrTiO3/BiFeO3 multilayers with ZnO buffer layer

    NASA Astrophysics Data System (ADS)

    Dutta, Shankar; Pandey, Akhilesh; Yadav, I.; Thakur, O. P.; Laishram, R.; Pal, Ramjay; Chatterjee, Ratnamala

    2012-10-01

    In this study, the effect of ZnO buffer layer on the electrical properties of PbZrTiO3/BiFeO3 (PZT/BFO) multilayers has been reported. For this, PZT/BFO multilayers were spin-coated with and without ZnO buffer layer on platinized silicon wafers. X-ray diffraction results of both the films showed polycrystalline phase pure perovskite structure. Both the films show a dense and homogeneous grain structure. The electric properties of the films were measured. The ZnO buffered multilayer thin film showed ˜3 times improvement in remnant polarization compared to the multilayer thin film with no buffer. The buffered samples were found to have higher dielectric constant (1000 at 100 Hz) compared to that of sample (580 at 100 Hz)) with no buffer. Dielectric constants of both the films were found to be ˜30% tunable at 5 V. The buffered film also showed low leakage current density and higher dielectric breakdown compared to the multilayer thin film without buffer.

  1. Effects of accumulated film layers on the accuracy of quartz film thickness monitors

    NASA Technical Reports Server (NTRS)

    Heyman, J. S.; Miller, W. E.

    1978-01-01

    The effect of accumulation layers on the accuracy of quartz thin-film thickness monitors is evaluated. Use of an expanded plane wave ultrasonic propagation theory correctly accounts for observed experimental data. The magnitude of the maximum errors calculated for simply reversing the order of a series of aluminum gold deposits is on the order of 5%. If one totally neglects intervening layers, multiple film propagation and nonlinearity can produce errors greater than 50%.

  2. On the meaning of the diffusion layer thickness for slow electrode reactions.

    PubMed

    Molina, A; González, J; Laborda, E; Compton, R G

    2013-02-21

    A key concept underpinning electrochemical science is that of the diffusion layer - the zone of depletion around an electrode accompanying electrolysis. The size of this zone can be found either from the simulated or measured concentration profiles (yielding the 'true' diffusion layer thickness) or, in the case of the Nernst ('linear') diffusion layer by extrapolating the concentration gradient at the electrode surface to the distance at which the concentration takes its bulk value. The latter concept is very well developed in the case of fast (so-called reversible) electrode processes, however the study of the linear diffusion layer has received scant attention in the case of slow charge transfer processes, despite its study being of great interest in the analysis of the influence of different experimental variables which determine the electrochemical response. Analytical explicit solutions for the concentration profiles, surface concentrations and real and linear diffusion layers corresponding to the application of a potential step to a slow charge transfer process are presented. From these expressions the dependence of the diffusion layer thickness on the potential, pulse time, heterogeneous rate constant and ratio of bulk concentrations of electroactive species and of diffusion coefficients is quantified. A profound influence of the reversibility degree of the charge transfer on the diffusion layer thickness is clear, showing that for non-reversible processes the real and linear diffusion layers reveal a minimum thickness which coincides with the equilibrium potential of the redox couple in the former case and with the reversible half-wave potential in the latter one. PMID:23301247

  3. Synthesis of grafted phosphorylcholine polymer layers as specific recognition ligands for C-reactive protein focused on grafting density and thickness to achieve highly sensitive detection.

    PubMed

    Kamon, Yuri; Kitayama, Yukiya; Itakura, Akiko N; Fukazawa, Kyoko; Ishihara, Kazuhiko; Takeuchi, Toshifumi

    2015-04-21

    We studied the effects of layer thickness and grafting density of poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) thin layers as specific ligands for the highly sensitive binding of C-reactive protein (CRP). PMPC layer thickness was controlled by surface-initiated activators generated by electron transfer for atom transfer radical polymerization (AGET ATRP). PMPC grafting density was controlled by utilizing mixed self-assembled monolayers with different incorporation ratios of the bis[2-(2-bromoisobutyryloxy)undecyl] disulfide ATRP initiator, as modulated by altering the feed molar ratio with (11-mercaptoundecyl)tetra(ethylene glycol). X-ray photoelectron spectroscopy and ellipsometry measurements were used to characterize the modified surfaces. PMPC grafting densities were estimated from polymer thickness and the molecular weight obtained from sacrificial initiator during surface-initiated AGET ATRP. The effects of thickness and grafting density of the obtained PMPC layers on CRP binding performance were investigated using surface plasmon resonance employing a 10 mM Tris-HCl running buffer containing 140 mM NaCl and 2 mM CaCl2 (pH 7.4). Furthermore, the non-specific binding properties of the obtained layers were investigated using human serum albumin (HSA) as a reference protein. The PMPC layer which has 4.6 nm of thickness and 1.27 chains per nm(2) of grafting density showed highly sensitive CRP detection (limit of detection: 4.4 ng mL(-1)) with low non-specific HSA adsorption, which was improved 10 times than our previous report of 50 ng mL(-1). PMID:25783194

  4. Microstructural evaluation of Sb-adjusted Al{sub 0.5}Ga{sub 0.5}As{sub 1{minus}y}Sb{sub y} buffer layer systems for IR applications

    SciTech Connect

    Chen, E.; Paine, D.C.; Uppal, P.; Ahearn, J.S.; Nichols, K.; Charache, G.W.

    1998-06-01

    The authors report on a transmission electron microscopy (TEM) study of Sb-adjusted quaternary Al{sub 0.5}Ga{sub 0.5}As{sub 1{minus}y}Sb{sub y} buffer-layers grown on <001> GaAs substrates. A series of structures were grown by MBE at 470 C that utilize a multilayer grading scheme in which the Sb content of Al{sub 0.5}Ga{sub 0.5}As{sub 1{minus}y}Sb{sub y} buffer-layers grown on <001> GaAs substrates. A series of structures were grown by MBe at 470 C that utilize a multilayer grading scheme in which the Sb content of Al{sub 0.5}Ga{sub 0.5}As{sub 1{minus}y}Sb{sub y} is successively increased in a series of 125 nm thick layers. Post growth analysis using conventional bright field and weak beam dark field imaging of these buffer layers in cross-section reveals that the interface misfit dislocations are primarily of the 60{degree} type and are distributed through out the interfaces of the buffer layer. When optimized, the authors have shown, using plan view and cross-sectional TEM, that this approach can reduce the threading defect density to below the detectability limit of TEM (< 10{sup 5}/cm{sup 2}) and preserve growth surface planarity. The Sb-graded approach was used to fabricate two 2.2 {micro}m power converter structures fabricated using InGaAs grown on Sb-based buffer layers on GaAs substrates. A microstructural and electrical characterization was performed on these device structures and the results are contrasted with a sample in which InP was selected as the substrate. Microstructure, defect density and device performance in these not-yet-optimized Sb-based buffer layers compares favorably to equivalent devices fabricated using InP substrates.

  5. Influence of thickness and permeability of endothelial surface layer on transmission of shear stress in capillaries

    NASA Astrophysics Data System (ADS)

    Zhang, SongPeng; Zhang, XiangJun; Tian, Yu; Meng, YongGang; Lipowsky, Herbert

    2015-07-01

    The molecular coating on the surface of microvascular endothelium has been identified as a barrier to transvascular exchange of solutes. With a thickness of hundreds of nanometers, this endothelial surface layer (ESL) has been treated as a porous domain within which fluid shear stresses are dissipated and transmitted to the solid matrix to initiate mechanotransduction events. The present study aims to examine the effects of the ESL thickness and permeability on the transmission of shear stress throughout the ESL. Our results indicate that fluid shear stresses rapidly decrease to insignificant levels within a thin transition layer near the outer boundary of the ESL with a thickness on the order of ten nanometers. The thickness of the transition zone between free fluid and the porous layer was found to be proportional to the square root of the Darcy permeability. As the permeability is reduced ten-fold, the interfacial fluid and solid matrix shear stress gradients increase exponentially two-fold. While the interfacial fluid shear stress is positively related to the ESL thickness, the transmitted matrix stress is reduced by about 50% as the ESL thickness is decreased from 500 to 100 nm, which may occur under pathological conditions. Thus, thickness and permeability of the ESL are two main factors that determine flow features and the apportionment of shear stresses between the fluid and solid phases of the ESL. These results may shed light on the mechanisms of force transmission through the ESL and the pathological events caused by alterations in thickness and permeability of the ESL.

  6. GaN Epitaxial Layer Grown with Conductive Al(x)Ga(1-x)N Buffer Layer on SiC Substrate Using Metal Organic Chemical Vapor Deposition.

    PubMed

    So, Byeongchan; Lee, Kyungbae; Lee, Kyungjae; Heo, Cheon; Pyeon, Jaedo; Ko, Kwangse; Jang, Jongjin; Nam, Okhyun

    2016-05-01

    This study investigated GaN epitaxial layer growth with a conductive Al(x)Ga(1-x)N buffer layer on n-type 4H-SiC by high-temperature metalorganic chemical vapor deposition (HT-MOCVD). The Al composition of the Al(x)Ga(1-x)N buffer was varied from 0% to 100%. In terms of the crystal quality of the GaN layer, 79% Al was the optimal composition of the Al(x)Ga(1-x)N buffer layer in our experiment. A vertical conductive structure was fabricated to measure the current voltage (I-V) characteristics as a function of Al composition, and the I-V curves showed that the resistance increased with increasing Al concentration of the Al(x)Ga(1-x)N buffer layer. PMID:27483845

  7. Preparation and properties of highly (100)-oriented Pb(Zr{sub 0.2}Ti{sub 0.8})O{sub 3} thin film prepared by rf magnetron sputtering with a PbO{sub x} buffer layer

    SciTech Connect

    Wu, Jiagang; Zhu, Jiliang; Xiao, Dingquan; Zhu, Jianguo; Tan, Junzhe; Zhang, Qinglei

    2007-05-01

    A method for fabrication of highly (100)-oriented Pb(Zr{sub 0.2}Ti{sub 0.8})O{sub 3} (PZT) thin films by rf magnetron sputtering with a special buffer of PbO{sub x} (RFMS-SBP) was developed. With this method, highly (100)-oriented Pb(Zr{sub 0.2}Ti{sub 0.8})O{sub 3} thin films were prepared on the PbO{sub x}/Pt(111)/Ti/SiO{sub 2}/Si(100) substrates, and the preferential (100) orientation of the Pb(Zr{sub 0.2}Ti{sub 0.8})O{sub 3} film is 92%. The (100) orientation of the PbO{sub x} buffer layer leads to the (100) orientation of the PZT thin films, and the thickness of the buffer layer plays a significant role on the phase purity and electrical properties of the films. Highly (100)-oriented Pb(Zr{sub 0.2}Ti{sub 0.8})O{sub 3} thin films with proper thickness of PbO{sub x} buffer layer possess good electrical properties with larger remnant polarization P{sub r} (69.7 {mu}C/cm{sup 2}), lower coercive field E{sub c} (92.4 kV/cm), and good pyroelectric coefficient at room temperature (2.6x10{sup -8} C/cm{sup 2} K). The butterfly-shaped {epsilon}-E characteristic curve gives the evidence of the improved in-plane ferroelectric property in the films.

  8. Lack of Correlation Between Diabetic Macular Edema and Thickness of the Peripapillary Retinal Nerve Fibre Layer

    PubMed Central

    Alkuraya, Hisham S.; Al-Gehedan, Saeed M.; Alsharif, Abdulrahman M.; Alasbali, Tariq; Lotfy, Nancy M.; Khandekar, Rajiv

    2016-01-01

    Introduction: We compared the thickness of the peripapillary retinal nerve fiber layer (RNFL) in patients with diabetic macular edema (DME) and/against the thickness in the normal population. Methods: This cross-sectional study compared the RNFL thickness in patients with DME (DME group) using optical coherence tomography (OCT) to a comparable group of healthy (nondiabetic) patients (control group). Measurements were performed in different/the four peripapillary quadrants and in the macula region for the fovea, parafoveal, and perifoveal areas. The mean RNFL thickness was compared between both groups. Results: There were fifty eyes of fifty nonglaucomatous diabetic patients with DME (29 with nonproliferative diabetic retinopathy [PDR] and 21 with PDR), and fifty eyes in the control group. The macular regions were significantly thicker in the DME group compared to the control group. The central foveal thickness was 149 μ thicker in eyes with DME compared to the control group (P < 0.001). The difference in total RNFL thickness between groups was not significant (4.4 μ [95% confidence interval: −3.1 to +12]). The between-group differences in peripapillary RNFL thickness by age group, glycemic control, history of intravitreal treatments, and refractive errors were not statistically significant (P > 0.05, all comparisons). Conclusion: Peripapillary RNFL thickness measurements were not significantly influenced by DME. Hence, OCT parameters could be used to monitor/early detect glaucomatous eyes even in the presence of DME. PMID:27555707

  9. Holographic Characteristics of an Acrylamide/Bisacrylamide Photopolymer in 40 1000 µm Thick Layers

    NASA Astrophysics Data System (ADS)

    Ortuño, M.; Gallego, S.; García, C.; Pascual, I.; Neipp, C.; Beléndez, A.

    2005-01-01

    In this study we analyze the holographic behaviour of an acrylamide/bisacrylamide photopolymer in layers that range in thickness from 40 to 1000 µm. The photopolymer is composed of acrylamide as polymerizable monomer, N,N' methylene-bis-acrylamide as crosslinker, triethanolamine as radical generator, yellowish eosin as sensitizer and polyvinyl alcohol as binder. The composition and method of depositing the solution varies depending on the desired thickness of the final layer. For each thickness we analyze the holographic behaviour of the material during recording of unslanted diffraction gratings using a continuous argon laser (514 nm) at an intensity of 5 mW/cm2. The response of the material is monitored in real time with an He-Ne laser. The results obtained for the different parameters evaluated vary considerably depends on the layer thickness. Therefore, the different potential applications of the material (fabrication of holographic optical elements, use as recording material in holographic interferometry, or manufacture of holographic memories) depends on its thickness.

  10. Thickness Considerations of Two-Dimensional Layered Semiconductors for Transistor Applications.

    PubMed

    Zhang, Youwei; Li, Hui; Wang, Haomin; Xie, Hong; Liu, Ran; Zhang, Shi-Li; Qiu, Zhi-Jun

    2016-01-01

    Layered two-dimensional semiconductors have attracted tremendous attention owing to their demonstrated excellent transistor switching characteristics with a large ratio of on-state to off-state current, Ion/Ioff. However, the depletion-mode nature of the transistors sets a limit on the thickness of the layered semiconductor films primarily determined by a given Ion/Ioff as an acceptable specification. Identifying the optimum thickness range is of significance for material synthesis and device fabrication. Here, we systematically investigate the thickness-dependent switching behavior of transistors with a wide thickness range of multilayer-MoS2 films. A difference in Ion/Ioff by several orders of magnitude is observed when the film thickness, t, approaches a critical depletion width. The decrease in Ion/Ioff is exponential for t between 20 nm and 100 nm, by a factor of 10 for each additional 10 nm. For t larger than 100 nm, Ion/Ioff approaches unity. Simulation using technical computer-aided tools established for silicon technology faithfully reproduces the experimentally determined scaling behavior of Ion/Ioff with t. This excellent agreement confirms that multilayer-MoS2 films can be approximated as a homogeneous semiconductor with high surface conductivity that tends to deteriorate Ion/Ioff. Our findings are helpful in guiding material synthesis and designing advanced field-effect transistors based on the layered semiconductors. PMID:27403803

  11. Thickness Considerations of Two-Dimensional Layered Semiconductors for Transistor Applications

    NASA Astrophysics Data System (ADS)

    Zhang, Youwei; Li, Hui; Wang, Haomin; Xie, Hong; Liu, Ran; Zhang, Shi-Li; Qiu, Zhi-Jun

    2016-07-01

    Layered two-dimensional semiconductors have attracted tremendous attention owing to their demonstrated excellent transistor switching characteristics with a large ratio of on-state to off-state current, Ion/Ioff. However, the depletion-mode nature of the transistors sets a limit on the thickness of the layered semiconductor films primarily determined by a given Ion/Ioff as an acceptable specification. Identifying the optimum thickness range is of significance for material synthesis and device fabrication. Here, we systematically investigate the thickness-dependent switching behavior of transistors with a wide thickness range of multilayer-MoS2 films. A difference in Ion/Ioff by several orders of magnitude is observed when the film thickness, t, approaches a critical depletion width. The decrease in Ion/Ioff is exponential for t between 20 nm and 100 nm, by a factor of 10 for each additional 10 nm. For t larger than 100 nm, Ion/Ioff approaches unity. Simulation using technical computer-aided tools established for silicon technology faithfully reproduces the experimentally determined scaling behavior of Ion/Ioff with t. This excellent agreement confirms that multilayer-MoS2 films can be approximated as a homogeneous semiconductor with high surface conductivity that tends to deteriorate Ion/Ioff. Our findings are helpful in guiding material synthesis and designing advanced field-effect transistors based on the layered semiconductors.

  12. Thickness Considerations of Two-Dimensional Layered Semiconductors for Transistor Applications

    PubMed Central

    Zhang, Youwei; Li, Hui; Wang, Haomin; Xie, Hong; Liu, Ran; Zhang, Shi-Li; Qiu, Zhi-Jun

    2016-01-01

    Layered two-dimensional semiconductors have attracted tremendous attention owing to their demonstrated excellent transistor switching characteristics with a large ratio of on-state to off-state current, Ion/Ioff. However, the depletion-mode nature of the transistors sets a limit on the thickness of the layered semiconductor films primarily determined by a given Ion/Ioff as an acceptable specification. Identifying the optimum thickness range is of significance for material synthesis and device fabrication. Here, we systematically investigate the thickness-dependent switching behavior of transistors with a wide thickness range of multilayer-MoS2 films. A difference in Ion/Ioff by several orders of magnitude is observed when the film thickness, t, approaches a critical depletion width. The decrease in Ion/Ioff is exponential for t between 20 nm and 100 nm, by a factor of 10 for each additional 10 nm. For t larger than 100 nm, Ion/Ioff approaches unity. Simulation using technical computer-aided tools established for silicon technology faithfully reproduces the experimentally determined scaling behavior of Ion/Ioff with t. This excellent agreement confirms that multilayer-MoS2 films can be approximated as a homogeneous semiconductor with high surface conductivity that tends to deteriorate Ion/Ioff. Our findings are helpful in guiding material synthesis and designing advanced field-effect transistors based on the layered semiconductors. PMID:27403803

  13. Reduction in Retinal Nerve Fiber Layer Thickness in Young Adults with Autism Spectrum Disorders

    ERIC Educational Resources Information Center

    Emberti Gialloreti, Leonardo; Pardini, Matteo; Benassi, Francesca; Marciano, Sara; Amore, Mario; Mutolo, Maria Giulia; Porfirio, Maria Cristina; Curatolo, Paolo

    2014-01-01

    Recent years have seen an increase in the use of retinal nerve fiber layer (RNFL) evaluation as an easy-to-use, reproducible, proxy-measure of brain structural abnormalities. Here, we evaluated RNFL thickness in a group of subjects with high functioning autism (HFA) or with Asperger Syndrome (AS) to its potential as a tool to study autism…

  14. Relationship between Retinal Layer Thickness and the Visual Field in Early Age-Related Macular Degeneration

    PubMed Central

    Acton, Jennifer H.; Smith, R. Theodore; Hood, Donald C.; Greenstein, Vivienne C.

    2012-01-01

    Purpose. To quantify and compare the structural and functional changes in subjects with early age-related macular degeneration (AMD), using spectral-domain optical coherence tomography (SD-OCT) and microperimetry. Methods. Twenty-one eyes of 21 subjects with early AMD were examined. MP-1 10-2 visual fields (VFs) and SD-OCT line and detail volume scans were acquired. The thicknesses of the outer segment (OS; distance between inner segment ellipsoid band and upper retinal pigment epithelium [RPE] border) and RPE layers and elevation of the RPE from Bruch's membrane were measured using a computer-aided manual segmentation technique. Thickness values were compared with those for 15 controls, and values at locations with VF total deviation defects were compared with values at nondefect locations at equivalent eccentricities. Results. Sixteen of 21 eyes with AMD had VF defects. Compared with controls, line scans showed significant thinning of the OS layer (P = 0.006) and thickening and elevation of the RPE (P = 0.037, P = 0.002). The OS layer was significantly thinner in locations with VF defects compared with locations without defects (P = 0.003). There was a negligible difference between the retinal layer thickness values of the 5 eyes without VF defects and the values of normal controls. Conclusions. In early AMD, when VF defects were present, there was significant thinning of the OS layer and thickening and elevation of the RPE. OS layer thinning was significantly associated with decreased visual sensitivity, consistent with known photoreceptor loss in early AMD. For AMD subjects without VF defects, thickness values were normal. The results highlight the clinical utility of both SD-OCT retinal layer quantification and VF testing in early AMD. PMID:23074210

  15. Effect of Electrolyte Concentration on the Stern Layer Thickness at a Charged Interface.

    PubMed

    Brown, Matthew A; Goel, Alok; Abbas, Zareen

    2016-03-01

    The chemistry and physics of charged interfaces is regulated by the structure of the electrical double layer (EDL). Herein we quantify the average thickness of the Stern layer at the silica (SiO2 ) nanoparticle/aqueous electrolyte interface as a function of NaCl concentration following direct measurement of the nanoparticles' surface potential by X-ray photoelectron spectroscopy (XPS). We find the Stern layer compresses (becomes thinner) as the electrolyte concentration is increased. This finding provides a simple and intuitive picture of the EDL that explains the concurrent increase in surface charge density, but decrease in surface and zeta potentials, as the electrolyte concentration is increased. PMID:26880184

  16. Self-assembled, aligned ZnO nanorod buffer layers for high-current-density, inverted organic photovoltaics.

    PubMed

    Rao, Arun D; Karalatti, Suresh; Thomas, Tiju; Ramamurthy, Praveen C

    2014-10-01

    Two different soft-chemical, self-assembly-based solution approaches are employed to grow zinc oxide (ZnO) nanorods with controlled texture. The methods used involve seeding and growth on a substrate. Nanorods with various aspect ratios (1-5) and diameters (15-65 nm) are grown. Obtaining highly oriented rods is determined by the way the substrate is mounted within the chemical bath. Furthermore, a preheat and centrifugation step is essential for the optimization of the growth solution. In the best samples, we obtain ZnO nanorods that are almost entirely oriented in the (002) direction; this is desirable since electron mobility of ZnO is highest along this crystallographic axis. When used as the buffer layer of inverted organic photovoltaics (I-OPVs), these one-dimensional (1D) nanostructures offer: (a) direct paths for charge transport and (b) high interfacial area for electron collection. The morphological, structural, and optical properties of ZnO nanorods are studied using scanning electron microscopy, X-ray diffraction, and ultraviolet-visible light (UV-vis) absorption spectroscopy. Furthermore, the surface chemical features of ZnO films are studied using X-ray photoelectron spectroscopy and contact angle measurements. Using as-grown ZnO, inverted OPVs are fabricated and characterized. For improving device performance, the ZnO nanorods are subjected to UV-ozone irradiation. UV-ozone treated ZnO nanorods show: (i) improvement in optical transmission, (ii) increased wetting of active organic components, and (iii) increased concentration of Zn-O surface bonds. These observations correlate well with improved device performance. The devices fabricated using these optimized buffer layers have an efficiency of ∼3.2% and a fill factor of 0.50; this is comparable to the best I-OPVs reported that use a P3HT-PCBM active layer. PMID:25238197

  17. Optical properties of InGaAs linear graded buffer layers on GaAs grown by metalorganic chemical vapor deposition

    NASA Astrophysics Data System (ADS)

    Lee, B.; Baek, J. H.; Lee, J. H.; Choi, S. W.; Jung, S. D.; Han, W. S.; Lee, E. H.

    1996-05-01

    We report optical characteristics of linear graded InxGa1-xAs (XIn=0-0.58) buffer layers grown on GaAs by low-pressure metalorganic chemical vapor deposition. Two types of wirelike surface structures were observed from the layers grown at two different temperatures. Low-temperature photoluminescence (PL) and double-crystal x-ray diffractometric measurements indicate that the PL energy and the relaxation of the graded layers were strongly dependent on the top surface structure. InGaAs cap layers were grown on top of the graded buffer layers with a variation of indium composition. A strong PL signal was observed from the top region of the graded layer grown with a lattice-matched cap layer. It suggests that the top region of the grade, similar to a graded well structure, is compressively strained but is of high structural quality without dislocations.

  18. Improved high temperature integration of Al{sub 2}O{sub 3} on MoS{sub 2} by using a metal oxide buffer layer

    SciTech Connect

    Son, Seokki; Choi, Moonseok; Kim, Dohyung; Choi, Changhwan; Yu, Sunmoon

    2015-01-12

    We deposited a metal oxide buffer layer before atomic layer deposition (ALD) of Al{sub 2}O{sub 3} onto exfoliated molybdenum disulfide (MoS{sub 2}) in order to accomplish enhanced integration. We demonstrate that even at a high temperature, functionalization of MoS{sub 2} by means of a metal oxide buffer layer can effectively provide nucleation sites for ALD precursors, enabling much better surface coverage of Al{sub 2}O{sub 3}. It is shown that using a metal oxide buffer layer not only allows high temperature ALD process, resulting in highly improved quality of Al{sub 2}O{sub 3}/MoS{sub 2} interface, but also leaves MoS{sub 2} intact.

  19. Growth of wurtzite and zinc-blende phased GaN on silicon (100) substrate with sputtered AlN buffer layer

    NASA Astrophysics Data System (ADS)

    Pang, Wen-Yuan; Lo, Ikai; Wu, Sean; Lin, Zhi-Xun; Shih, Cheng-Hung; Lin, Yu-Chiao; Wang, Ying-Chieh; Hu, Chia-Hsuan; Hsu, Gary Z. L.

    2013-11-01

    GaN films were grown by plasma-assisted molecular beam epitaxy with a sputtered AlN buffer layer on Si (100) substrate. From the analyses of X-ray diffraction (XRD), transmission electron microscopy (TEM) and photoluminescence (PL) measurements, we showed that the variant M-plane, A-plane and c-plane GaN wurtzite structures can be achieved by the selection of crystalline orientation of sputtered AlN buffer layer and the control of epitaxial growth temperature. We also found that the GaN layer grown on sputtered AlN buffer layer can be converted to GaN zinc-blende structure at the epitaxial growth temperature higher than 750 °C and under Ga-rich condition.

  20. Presence and function of a thick mucous layer rich in polysaccharides around Bacillus subtilis spores.

    PubMed

    Faille, Christine; Ronse, Annette; Dewailly, Etienne; Slomianny, Christian; Maes, Emmanuel; Krzewinski, Frédéric; Guerardel, Yann

    2014-01-01

    This study was designed to establish the presence and function of the mucous layer surrounding spores of Bacillus subtilis. First, an external layer of variable thickness and regularity was often observed on B. subtilis spores. Further analyses were performed on B. subtilis 98/7 spores surrounded by a thick layer. The mechanical removal of the layer did not affect their resistance to heat or their ability to germinate but rendered the spore less hydrophilic, more adherent to stainless steel, and more resistant to cleaning. This layer was mainly composed of 6-deoxyhexoses, ie rhamnose, 3-O-methyl-rhamnose and quinovose, but also of glucosamine and muramic lactam, known also to be a part of the bacterial peptidoglycan. The specific hydrolysis of the peptidoglycan using lysozyme altered the structure of the required mucous layer and affected the physico-chemical properties of the spores. Such an outermost mucous layer has also been seen on spores of B. licheniformis and B. clausii isolated from food environments. PMID:25115519

  1. Influence of bulk turbulence and entrance boundary layer thickness on the curved duct flow field

    NASA Technical Reports Server (NTRS)

    Crawford, R. A.

    1988-01-01

    The influence of bulk turbulence and boundary layer thickness on the secondary flow development in a square, 90 degree turning duct was investigated. A three-dimensional laser velocimetry system was utilized to measure the mean and fluctuating components of velocity at six cross-planes in the duct. The results from this investigation, with entrance boundary layer thickness of 20 percent, were compared with the thin boundary layer results documented in NASA CR-174811. The axial velocity profiles, cross-flow velocities, and turbulence intensities were compared and evaluated with regard to the influence of bulk turbulence intensity and boundary layer thickness, and the influence was significant. The results of this investigation expand the 90 degree curved duct experimental data base to higher turbulence levels and thicker entrance boundary layers. The experimental results provide a challenging benchmark data base for computational fluid dynamics code development and validation. The variation of inlet bulk turbulence intensity provides additional information to aid in turbulence model evaluation.

  2. A nitrilo-tri-acetic-acid/acetic acid route for the deposition of epitaxial cerium oxide films as high temperature superconductor buffer layers

    SciTech Connect

    Thuy, T.T.; Lommens, P.; Narayanan, V.; Van de Velde, N.; De Buysser, K.; Herman, G.G.; Cloet, V.; Van Driessche, I.

    2010-09-15

    A water based cerium oxide precursor solution using nitrilo-tri-acetic-acid (NTA) and acetic acid as complexing agents is described in detail. This precursor solution is used for the deposition of epitaxial CeO{sub 2} layers on Ni-5at%W substrates by dip-coating. The influence of the complexation behavior on the formation of transparent, homogeneous solutions and gels has been studied. It is found that ethylenediamine plays an important role in the gelification. The growth conditions for cerium oxide films were Ar-5% gas processing atmosphere, a solution concentration level of 0.25 M, a dwell time of 60 min at 900 {sup o}C and 5-30 min at 1050 {sup o}C. X-ray diffraction (XRD), scanning electron microscope (SEM), atomic force microscopy (AFM), pole figures and spectroscopic ellipsometry were used to characterize the CeO{sub 2} films with different thicknesses. Attenuated total reflection-Fourier transform infrared (ATR-FTIR) was used to determine the carbon residue level in the surface of the cerium oxide film, which was found to be lower than 0.01%. Textured films with a thickness of 50 nm were obtained. - Graphical abstract: Study of the complexation and hydrolysis behavior of Ce{sup 4+} ions in the presence of nitrilo-tri-acetic acid and the subsequent development of an aqueous chemical solution deposition route suited for the processing of textured CeO{sub 2} buffer layers on Ni-W tapes.

  3. Time-domain ultrasonic measurement of the thickness of a sub-half-wavelength elastic layer

    NASA Astrophysics Data System (ADS)

    Zhu, Changyi; Kinra, Vikram K.

    1992-07-01

    A technique is reported for the ultrasonic nondestructive measurement of the thickness of extremely thin (sub-wavelength) adhesive layers in adhesively bonded joints without the use of Fourier transforms. The entire ultrasonic NDE is carried out in the time domain and can be used by a trained technician without a college education. Aluminum plates ranging in thickness from 0.089 to 12.675 mm were tested using a 1-MHz transducer. The error was found to be one percent for h/lambda (specimen thickness/wavelength) down to 0.010. In dimensional terms, plates with a thickness of 100 microns can be measured with an accuracy of + or - 1 micron. This technique can also be used in conjunction with the electromagnetic-acoustic transducer technology in which only low-frequency transducers are presently available.

  4. Influences and interactions of inundation, peat, and snow on active layer thickness

    NASA Astrophysics Data System (ADS)

    Atchley, Adam L.; Coon, Ethan T.; Painter, Scott L.; Harp, Dylan R.; Wilson, Cathy J.

    2016-05-01

    Active layer thickness (ALT), the uppermost layer of soil that thaws on an annual basis, is a direct control on the amount of organic carbon potentially available for decomposition and release to the atmosphere as carbon-rich Arctic permafrost soils thaw in a warming climate. We investigate how key site characteristics affect ALT using an integrated surface/subsurface permafrost thermal hydrology model. ALT is most sensitive to organic layer thickness followed by snow depth but is relatively insensitive to the amount of water on the landscape with other conditions held fixed. The weak ALT sensitivity to subsurface saturation suggests that changes in Arctic landscape hydrology may only have a minor effect on future ALT. However, surface inundation amplifies the sensitivities to the other parameters and under large snowpacks can trigger the formation of near-surface taliks.

  5. Thickness-dependent coercivity of ultrathin Co films on a rough substrate: Cu-buffered Si(111)

    NASA Astrophysics Data System (ADS)

    Min, H.-G.; Kim, S.-H.; Li, M.; Wedding, J. B.; Wang, G.-C.

    1998-03-01

    The hysteresis loops, of Co films with thicknesses ranging from 12- to 80-monolayer-equivalent (MLE) coverages grown by thermal evaporation on a Cu-covered Si(111) surface, were measured in situ by the surface magneto-optic Kerr effect (SMOKE) technique. The hysteresis loops were measured as a function of Co coverage under an external sinusoidal magnetic field at fixed driving frequency. The coercivity Hc of the Co film versus thickness t followed a power law t- n with n=0.4±0.1 between 12 and 44 MLE, and stabilized after 44 MLE, up to the 80 MLE studied. The surface morphology of the 80-MLE Co film was imaged ex situ by atomic force microscopy (AFM) and scanning tunneling microscopy (STM), revealing cauliflower-like islands that were rough both in the short and long range. Analysis of the height-height correlation function for the largest image gave measurements of the effective roughness exponent α (˜0.8), the vertical interface width w(˜2500 Å), and the lateral correlation length ξ(˜10 000 Å). We suggest that the coercivity changed in part due to changes in roughness of the Co films, deposited on a rough substrate; the spatial roughness would create an additional surface anisotropy, contributing to a fluctuation in the domain wall energy, resulting in a roughness-dependent coercivity.

  6. Resputtering effect during MgO buffer layer deposition by magnetron sputtering for superconducting coated conductors

    SciTech Connect

    Xiao, Shaozhu; Shi, Kai; Deng, Shutong; Han, Zhenghe; Feng, Feng Lu, Hongyuan; Qu, Timing; Zhu, Yuping; Huang, Rongxia

    2015-07-15

    In this study, MgO thin films were deposited by radio-frequency magnetron sputtering. The film thickness in the deposition area directly facing the target center obviously decreased compared with that in other areas. This reduction in thickness could be attributed to the resputtering effect resulting from bombardment by energetic particles mainly comprising oxygen atoms and negative oxygen ions. The influences of deposition position and sputtering pressure on the deposition rate were investigated. Resputtering altered the orientation of the MgO film from (111) to (001) when the film was deposited on a single crystal yttria-stabilized zirconia substrate. The density distribution of energetic particles was calculated on the basis of the measured thicknesses of the MgO films deposited at different positions. The divergence angle of the energetic particle flux was estimated to be approximately 15°. The energetic particle flux might be similar to the assisting ion flux in the ion beam assisted deposition process and could affect the orientation of the MgO film growth.

  7. Layer thickness and period as design parameters to tailor pyroelectric properties in ferroelectric superlattices

    SciTech Connect

    Misirlioglu, I. B.; Alpay, S. P.

    2014-10-27

    We theoretically examine the pyroelectric properties of ferroelectric-paraelectric superlattices as a function of layer thickness and configuration using non-linear thermodynamics coupled with electrostatic and electromechanical interactions between layers. We specifically study PbZr{sub 0.3}Ti{sub 0.7}O{sub 3}/SrTiO{sub 3} superlattices. The pyroelectric properties of such constructs consisting of relatively thin repeating units are shown to exceed the pyroelectric response of monolithic PbZr{sub 0.3}Ti{sub 0.7}O{sub 3} films. This is related to periodic internal electric fields generated due to the polarization mismatch between layers that allows tailoring of the shift in the transition temperature. Our results indicate that higher and electric field sensitive pyroresponse can be achieved from layer-by-layer engineered ferroelectric heterostructures.

  8. Retinal nerve fiber layer thickness in normal Indian pediatric population measured with optical coherence tomography.

    PubMed

    Pawar, Neelam; Maheshwari, Devendra; Ravindran, Meenakshi; Ramakrishnan, Renagappa

    2013-11-11

    Purpose: To measure the peripapillary retinal nerve fiber layer (RNFL) thickness in normal Indian pediatric population. Subjects and Methods: 120 normal Indian children ages 5-17 years presenting to the Pediatric Clinic were included in this observational cross-sectional study. RNFL thickness was measured with stratus optical coherence tomography (OCT). Children with strabismus or amblyopia, with neurological, metabolic, vascular, or other disorders and those with abnormal optic discs were excluded. One eye of each subject was randomly selected for statistical analysis. The effect of age, refraction and gender on RNFL thickness was investigated statistically. Result: OCT measurements were obtained in 120 of 130 (92.3%) subjects. Mean age was 10.8 ± 3.24 years (range 5-17). Average RNFL thickness was (± SD) 106.11 ± 9.5 μm (range 82.26-146.25). The RNFL was thickest inferiorly (134.10 ± 16.16 μm) and superiorly (133.44 ± 15.50 μm), thinner nasally (84.26 ± 16.43 μm), and thinnest temporally (70.72 ± 14.80 μm). In univariate regression analysis, age had no statistical significant effect on RNFL thickness (P = 0.7249) and refraction had a significant effect on RNFL thickness (P = 0.0008). Conclusion: OCT can be used to measure RNFL thickness in children. Refraction had an effect on RNFL thickness. In normal children, variation in RNFL thickness is large. The normative data provided by this study may assist in identifying changes in RNFL thickness in Indian children. PMID:24212231

  9. Correlation of Retinal Nerve Fiber Layer Thickness and Axial Length on Fourier Domain Optical Coherence Tomography

    PubMed Central

    Dhasmana, Renu; Nagpal, R.C.

    2016-01-01

    Introduction The assessment of the peripapillary Retinal Nerve Fiber Layer (RNFL) thickness has been an important tool for evaluating and diagnosing glaucoma and its progression. Literature suggests that myopic eyes are at an increased risk for developing glaucoma. This study gives an insight into the relationship of RNFL thickness to the axial length in normal population. Aim To correlate the RNFL thickness and the axial length in normal individuals with Fourier domain Optical Coherence Tomography (OCT). Materials and Methods In the current study, 298 eyes of 149 normal individuals (10 years or older) with or without refractive error were recruited. The RNFL thickness was measured using Optovue (RTVue) three-dimensional Fourier domain OCT. Results We observed an inverse relationship between average RNFL thickness and increasing axial length(p=0.003). Maximum RNFL thickness was seen in the Infero-Temporal (IT) quadrant and minimum in the Supero-Nasal (SN) quadrant. RNFL thickness did not show any tendency to decline with age using the Pearsons correlation (r=0.07). Females had an increased RNFL thickness in the Supero-Temporal (ST) and Infero-Nasal (IN) quadrant (p-value 0.046 and 0.02) in comparison to males. There was a statistically significant thinning in Ganglion Cell Complex (GCC) with increasing axial length (p-value 0.000) Conclusion The current study suggests that the average RNFL thickness does not decrease with age. The RNFL and GCC thickness shows an inverse correlation with axial length of the eyeball hence observations have to be carefully interpreted in myopic eyes. Clinicians need to keep the anatomical variations in RNFL for better patient management. PMID:27190850

  10. Choroidal Haller's and Sattler's Layer Thickness Measurement Using 3-Dimensional 1060-nm Optical Coherence Tomography

    PubMed Central

    Esmaeelpour, Marieh; Kajic, Vedran; Zabihian, Behrooz; Othara, Richu; Ansari-Shahrezaei, Siamak; Kellner, Lukas; Krebs, Ilse; Nemetz, Susanne; Kraus, Martin F.; Hornegger, Joachim; Fujimoto, James G.; Drexler, Wolfgang; Binder, Susanne

    2014-01-01

    Objectives To examine the feasibility of automatically segmented choroidal vessels in three-dimensional (3D) 1060-nmOCT by testing repeatability in healthy and AMD eyes and by mapping Haller's and Sattler's layer thickness in healthy eyes Methods Fifty-five eyes (from 45 healthy subjects and 10 with non-neovascular age-related macular degeneration (AMD) subjects) were imaged by 3D-1060-nmOCT over a 36°x36° field of view. Haller's and Sattler's layer were automatically segmented, mapped and averaged across the Early Treatment Diabetic Retinopathy Study grid. For ten AMD eyes and ten healthy eyes, imaging was repeated within the same session and on another day. Outcomes were the repeatability agreement of Haller's and Sattler's layer thicknesses in healthy and AMD eyes, the validation with ICGA and the statistical analysis of the effect of age and axial eye length (AL) on both healthy choroidalsublayers. Results The coefficients of repeatability for Sattler's and Haller's layers were 35% and 21% in healthy eyes and 44% and 31% in AMD eyes, respectively. The mean±SD healthy central submacular field thickness for Sattler's and Haller's was 87±56 µm and 141±50 µm, respectively, with a significant relationship for AL (P<.001). Conclusions Automated Sattler's and Haller's thickness segmentation generates rapid 3D measurements with a repeatability correspondingto reported manual segmentation. Sublayers in healthy eyes thinnedsignificantly with increasing AL. In the presence of the thinned Sattler's layer in AMD, careful measurement interpretation is needed. Automatic choroidal vascular layer mapping may help to explain if pathological choroidal thinning affects medium and large choroidal vasculature in addition to choriocapillaris loss. PMID:24911446

  11. Effect of buffer structures on AlGaN/GaN high electron mobility transistor reliability

    SciTech Connect

    Liu, L.; Xi, Y. Y.; Ren, F.; Pearton, S. J.; Laboutin, O.; Cao, Yu; Johnson, Wayne J.; Kravchenko, Ivan I

    2012-01-01

    AlGaN/GaN high electron mobility transistors (HEMTs) with three different types of buffer layers, including a GaN/AlGaN composite layer, or 1 or 2 lm GaN thick layers, were fabricated and their reliability compared. The HEMTs with the thick GaN buffer layer showed the lowest critical voltage (Vcri) during off-state drain step-stress, but this was increased by around 50% and 100% for devices with the composite AlGaN/GaN buffer layers or thinner GaN buffers, respectively. The Voff - state for HEMTs with thin GaN and composite buffers were 100 V, however, this degraded to 50 60V for devices with thick GaN buffers due to the difference in peak electric field near the gate edge. A similar trend was observed in the isolation breakdown voltage measurements, with the highest Viso achieved based on thin GaN or composite buffer designs (600 700 V), while a much smaller Viso of 200V was measured on HEMTs with the thick GaN buffer layers. These results demonstrate the strong influence of buffer structure and defect density on AlGaN/GaN HEMT performance and reliability.

  12. Prospective Study on Retinal Nerve Fibre Layer Thickness Changes in Isolated Unilateral Retrobulbar Optic Neuritis

    PubMed Central

    Yau, Gordon S. K.; Lee, Jacky W. Y.; Lau, Patrick P. K.; Tam, Victor T. Y.; Wong, Winnie W. Y.; Yuen, Can Y. F.

    2013-01-01

    Purpose. To investigate the retinal nerve fibre layer (RNFL) thickness after unilateral acute optic neuritis using optical coherence tomography (OCT). Patients and Methods. This prospective cohort study recruited consecutive patients with a first episode of isolated, unilateral acute optic neuritis. RNFL thickness and visual acuity (VA) of the attack and normal fellow eye were measured at presentation and 3 months in both the treatment and nontreatment groups. Results. 11 subjects received systemic steroids and 9 were treated conservatively. The baseline RNFL thickness was similar in the attack and fellow eye (P ≥ 0.4). At 3 months, the attack eye had a thinner temporal (P = 0.02) and average (P = 0.05) RNFL compared to the fellow eye. At 3 months, the attack eye had significant RNFL thinning in the 4 quadrants and average thickness (P ≤ 0.0002) compared to baseline. The RNFL thickness between the treatment and nontreatment groups was similar at baseline and 3 months (P ≥ 0.1). Treatment offered better VA at 3 months (0.1 ± 0.2 versus 0.3 ± 0.2 LogMAR, P = 0.04). Conclusion. Generalized RNFL thinning occurred at 3 months after a first episode of acute optic neuritis most significantly in the temporal quadrant and average thickness. Visual improvement with treatment was independent of RNFL thickness. PMID:24459442

  13. Effect of rear-surface buffer layer on performance of lift-off Cu(In,Ga)Se2 solar cells

    NASA Astrophysics Data System (ADS)

    Aoyagi, Kenta; Tamura, Akihiro; Takakura, Hideyuki; Minemoto, Takashi

    2014-01-01

    The effect of an Au and MoOx rear-surface buffer layer inserted between Cu(In,Ga)Se2 (CIGS) and ZnO:Al on solar cell performances was examined. The lift-off CIGS solar cell without a rear-surface buffer layer showed particular characteristics of two series-connected diodes in the reverse direction, and its short-circuit current density was almost zero. In contrast, the Au or MoOx rear-surface buffer layer improved these characteristics. Although the lift-off CIGS solar cell with the Au rear-surface buffer layer showed shunt characteristics and low efficiency, the efficiency of the lift-off CIGS solar cell with the MoOx rear-surface buffer layer was approximately 50% of that of substrate-type CIGS solar cells. Diode parameters of lift-off CIGS solar cells were determined by fitting analysis of current density-voltage curves using a proposed new equivalent circuit model for lift-off CIGS solar cells.

  14. Improved UV photoresponse properties of high-quality ZnO thin films through the use of a ZnO buffer layer on flexible polyimide substrates

    NASA Astrophysics Data System (ADS)

    Kim, Mincheol; Leem, Jae-Young; Son, Jeong-Sik

    2016-03-01

    An oxidized ZnO buffer layer was prepared by using thermal oxidation of a Zn buffer layer on a polyimide (PI) substrate; then, ZnO thin films with (sample 1) and without (sample 2) an oxidized ZnO buffer layer were grown by using the sol-gel spin-coating method. The intensities of the ZnO (002) diffraction peaks observed in sample 1 were stronger than those observed in sample 2, implying that the crystal quality was enhanced by the oxidized ZnO buffer layer. Moreover, the residual stress of sample 1 was reduced compared to that of sample 2 due to the decreased number of defects. Sample 2 exhibited defect-related deep-level orange-yellow emissions, which almost disappeared with the introduction of the ZnO buffer layer (sample 1). The values of the responsivity were 0.733 (sample 1) and 0.066 (sample 2) mA/W; therefore, the proposed method could provide a pathway to the easy fabrication of fast-response UV sensors.

  15. Optimization of the ZnS Buffer Layer by Chemical Bath Deposition for Cu(In,Ga)Se2 Solar Cells.

    PubMed

    Jeon, Dong-Hwan; Hwang, Dae-Kue; Kim, Dae-Hwan; Kang, Jin-Kyu; Lee, Chang-Seop

    2016-05-01

    We evaluated a ZnS buffer layer prepared using a chemical bath deposition (CBD) process for application in cadmium-free Cu(In,Ga)Se2 (CIGS) solar cells. The ZnS buffer layer showed good transmittance (above 90%) in the spectral range from 300 to 800 nm and was non-toxic compared with the CdS buffer layers normally used in CIGS solar cells. The CBD process was affected by several deposition conditions. The deposition rate was dependent on the ammonia concentration (complexing agent). When the ammonia concentration was either too high or low, a decrease in the deposition rate was observed. In addition, post heat treatments at high temperatures had detrimental influences on the ZnS buffer layers because portions of the ZnS thin films were transformed into ZnO. With optimized deposition conditions, a CIGS solar cell with a ZnS buffer layer showed an efficiency of 14.18% with a 0.23 cm2 active area under 100 mW/cm2 illumination. PMID:27483938

  16. Ideal p-n Diode Current Equation for Organic Heterojunction using a Buffer Layer: Derivation and Numerical Study

    NASA Astrophysics Data System (ADS)

    Kim, SeongMin; Ha, Jaewook; Kim, Jin-Baek

    2016-04-01

    The equation of p-n diode current-voltage (J-V) of an organic heterojunction (HJ) including a hole and electron buffer layer is derived, and its characteristics are numerically simulated based on a polaron-pair model Giebink et al. (Forrest, Phys. Rev. B 82; 1-12, 2010). In particular, the correlation between a fraction of the potential drop for an electron/hole buffer ( δ e - b / δ h - b ) and for a donor (D)/acceptor (A) ( δ D / δ A ) is numerically investigated for J-V curves. As a result, the lowest diode current (DC) is obtained for the condition of δ e - b + δ A ≅ 0 or δ D + δ h - b ≅ 1. It is suggested that it is important to characterize the lowest DC curve for the state of D/A blending with a condition of a fraction of the potential drop ( δ e - b / δ h - b ). Under these circumstances, the transport of holes ( h +) from a DC source at the reverse bias is effectively limited.

  17. Hydrodynamic thickness of petroleum oil adsorbed layers in the pores of reservoir rocks.

    PubMed

    Alkafeef, Saad F; Algharaib, Meshal K; Alajmi, Abdullah F

    2006-06-01

    The hydrodynamic thickness delta of adsorbed petroleum (crude) oil layers into the pores of sandstone rocks, through which the liquid flows, has been studied by Poiseuille's flow law and the evolution of (electrical) streaming current. The adsorption of petroleum oil is accompanied by a numerical reduction in the (negative) surface potential of the pore walls, eventually stabilizing at a small positive potential, attributed to the oil macromolecules themselves. After increasing to around 30% of the pore radius, the adsorbed layer thickness delta stopped growing either with time or with concentrations of asphaltene in the flowing liquid. The adsorption thickness is confirmed with the blockage value of the rock pores' area determined by the combination of streaming current and streaming potential measurements. This behavior is attributed to the effect on the disjoining pressure across the adsorbed layer, as described by Derjaguin and Churaev, of which the polymolecular adsorption films lose their stability long before their thickness has approached the radius of the rock pore. PMID:16414057

  18. Finding the lost open-circuit voltage in polymer solar cells by UV-ozone treatment of the nickel acetate anode buffer layer.

    PubMed

    Wang, Fuzhi; Sun, Gang; Li, Cong; Liu, Jiyan; Hu, Siqian; Zheng, Hua; Tan, Zhan'ao; Li, Yongfang

    2014-06-25

    Efficient polymer solar cells (PSCs) with enhanced open-circuit voltage (Voc) are fabricated by introducing solution-processed and UV-ozone (UVO)-treated nickel acetate (O-NiAc) as an anode buffer layer. According to X-ray photoelectron spectroscopy data, NiAc partially decomposed to NiOOH during the UVO treatment. NiOOH is a dipole species, which leads to an increase in the work function (as confirmed by ultraviolet photoemission spectroscopy), thus benefitting the formation of ohmic contact between the anode and photoactive layer and leading to increased Voc. In addition, the UVO treatment improves the wettability between the substrate and solvent of the active layer, which facilitates the formation of an upper photoactive layer with better morphology. Further, the O-NiAc layer can decrease the series resistance (Rs) and increase the parallel resistance (Rp) of the devices, inducing enhanced Voc in comparison with the as-prepared NiAc-buffered control devices without UVO treatment. For PSCs based on the P3HT:PCBM system, Voc increases from 0.50 to 0.60 V after the NiAc buffer layer undergoes UVO treatment. Similarly, in the P3HT:ICBA system, the Voc value of the device with a UVO-treated NiAc buffer layer increases from 0.78 to 0.88 V, showing an enhanced power conversion efficiency of 6.64%. PMID:24878826

  19. Influence of emissive layer thickness on electrical characteristics of polyfluorene copolymer based polymer light emitting diodes

    NASA Astrophysics Data System (ADS)

    Das, D.; Gopikrishna, P.; Singh, A.; Dey, A.; Iyer, P. K.

    2016-04-01

    Polymer light emitting diodes (PLEDs) with a device configuration of ITO/PEDOT:PSS/PFONPN01 [Poly [2,7-(9,9’-dioctylfluorene)-co-N-phenyl-1,8-naphthalimide (99:01)]/LiF/Al have been fabricated by varying the emissive layer (EML) thickness (40/65/80/130 nm) and the influence of EML thickness on the electrical characteristics of PLED has been studied. PLED can be modelled as a simple combination of resistors and capacitors. The impedance spectroscopy analysis showed that the devices with different EML thickness had different values of parallel resistance (RP) and the parallel capacitance (CP). The impedance of the devices is found to increase with increasing EML thickness resulting in an increase in the driving voltage. The device with an emissive layer thickness of 80nm, spin coated from a solution of concentration 15 mg/mL is found to give the best device performance with a maximum brightness value of 5226 cd/m2.

  20. Influence of liquid-layer thickness on pulmonary surfactant spreading and collapse.

    PubMed

    Siebert, Trina A; Rugonyi, Sandra

    2008-11-15

    Pulmonary surfactant spreads on the thin ( approximately 0.1 microm) liquid layer that lines the alveoli, forming a film that reduces surface tension and allows normal respiration. Pulmonary surfactant deposited in vitro on liquid layers that are several orders of magnitude thicker, however, does not reach the low surface tensions ( approximately 0.001 N/m) achieved in the lungs during exhalation when the surfactant film compresses. This is due to collapse, a surface phase transition during which the surfactant film, rather than decreasing surface tension by increasing its surface density, becomes thicker at constant surface tension ( approximately 0.024 N/m). Formation of the collapse phase requires transport of surfactant to collapse sites, and this transport can be hindered in thinner liquid layers by viscous resistance to motion. Our objective is to determine the effect of the liquid-layer thickness on surfactant transport, which might affect surfactant collapse. To this end, we developed a mathematical model that accounts for the effect of the liquid-layer thickness on surfactant transport, and focused on surfactant spreading and collapse. Model simulations showed a marked decrease in collapse rates for thinner liquid layers, but this decrease was not enough to completely explain differences in surfactant film behavior between in vitro and in situ experiments. PMID:18676658

  1. Leaping shampoo glides on a 500-nm-thick lubricating air layer

    NASA Astrophysics Data System (ADS)

    Li, Erqiang; Lee, Sanghyun; Marston, Jeremy; Bonito, Andrea; Thoroddsen, Sigurdur

    2013-11-01

    When a stream of shampoo is fed onto a pool in one's hand, a jet can leap sideways or rebound from the liquid surface in an intriguing phenomenon known as the Kaye effect. Earlier studies have debated whether non-Newtonian effects are the underlying cause of this phenomenon, making the jet glide on top of a shear-thinning liquid layer, or whether an entrained air layer is responsible. Herein we show unambiguously that the jet slides on a lubricating air layer [Lee et al., Phys. Rev. E 87, 061001 (2013)]. We identify this layer by looking through the pool liquid and observing its rupture into fine micro-bubbles. The resulting micro-bubble sizes suggest that the thickness of this air layer is around 500 nm. This thickness estimate is also supported by the tangential deceleration of the jet during the rebounding, with the shear stress within the thin air layer sufficient for the observed deceleration. Particle tracking within the jet shows uniform velocity, with no pronounced shear, which would be required for shear-thinning effects. The role of the surfactant may primarily be to stabilize the air film.

  2. Quantification of photoreceptor layer thickness in different macular pathologies using ultrahigh-resolution optical coherence tomography

    NASA Astrophysics Data System (ADS)

    Drexler, Wolfgang; Hermann, Boris; Unterhuber, Angelika; Sattmann, Harald; Wirtitsch, Matthias; Stur, Michael; Scholda, Christoph; Ergun, Erdem; Anger, Elisabeth; Ko, Tony H.; Schubert, Christian; Ahnelt, Peter K.; Fujimoto, James G.; Fercher, Adolf F.

    2004-07-01

    In vivo ultrahigh resolution ophthalmic OCT has been performed in more than 300 eyes of 200 patients with several retinal pathologies, demonstrating unprecedented visualization of all major intraretinal layers, in particular the photoreceptor layer. Visualization as well as quantification of the inner and outer segment of the photoreceptor layer especially in the foveal region has been acvhieved. In normal subjects the photoreceptor layer thickness in the center of the fovea is about of 90 μm, approximately equally distributed to the inner and the outer photoreceptor segment. In the parafoveal region this thickness is reduced to ~50 μm (~30 μm for the inner and ~20 μm for the outer segment). This is in good agreement with well known increase of cone outer segments in the central foveal region. Photoreceptor layer impairment in different macular pathologies like macular hole, central serous chorioretinopathy, age related macular degeneration, foveomacular dystrophies, Stargardt dystrophy as well as retinitis pigmentosa has been investigated. Photoreceptor layer loss significantly correlated with visual acuity (R2 = 0.6, p < 0.001) and microperimetry findings for the first time in 22 eyes with Stargardt dystrophy. Visualization and quantification of photoreceptor inner and outer segment using ultrahigh resolution OCT has the potential to improve early ophthalmic diagnosis, contributes to a better understanding of pathogenesis of retinal diseases as well as might have impact in the development and monitoring of novel therapy approaches.

  3. Growth and Characterization of La2Zr2O7 Buffer Layers Deposited by Chemical Solution Deposition

    NASA Astrophysics Data System (ADS)

    Armenio, A. Angrisani; Augieri, A.; Fabbri, F.; Freda, R.; Galluzzi, V.; Mancini, A.; Rizzo, F.; Rufoloni, A.; Vannozzi, A.; Sotgiu, G.; Pompeo, N.; Torokhtii, K.; Silva, E.; Bemporad, E.; Contini, G.; Celentano, G.

    The deposition and characterization of La2Zr2O7 thin films deposited by metal-organic decomposition method on both single crystal SrTiO3 and cube textured Ni-5 at.%W substrates are presented. Metal acetylacetonates in propionic acid solution was used. The results showed that LZO films are epitaxially grown with smooth surface with rms roughness around 2 nm. YBa2Cu3O7-δ films, deposited by pulsed laser deposition technique on LZO buffer layers, showed critical temperature of 90 K and critical current density in self magnetic field Jc = 1.6 and 13 MA/cm2 at 77 K and 4.2 K, respectively. A better Jc retention in magnetic field for YBCO films deposited on LZO/STO than YBCO on bare STO is observed indicating a rather strong vortex pinning as confirmed by microwave measurements.

  4. Enhanced electron extraction capability of polymer solar cells via modifying the cathode buffer layer with inorganic quantum dots.

    PubMed

    Li, Zhiqi; Li, Shujun; Zhang, Zhihui; Zhang, Xinyuan; Li, Jingfeng; Liu, Chunyu; Shen, Liang; Guo, Wenbin; Ruan, Shengping

    2016-04-20

    Enhanced performance of polymer solar cells (PSCs) based on the blend of poly[N-9''-hepta-decanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)] (PCDTBT):[6,6]-phenyl-C70-butyric acid methyl ester (PC71BM) is demonstrated by titanium dioxide (TiO2) interface modification via CuInS2/ZnS quantum dots (CZdots). Devices with a TiO2/CZdots composite buffer layer exhibit both a high short-circuit current density (Jsc) and fill factor (FF), leading to a power conversion efficiency (PCE) up to 7.01%. The charge transport recombination mechanisms are investigated by an impedance behavior model, which indicates that TiO2 interfacial modification results in not only increasing the electron extraction but also reducing impedance. This study provides an important and beneficial approach to develop high efficiency PSCs. PMID:27055908

  5. Nano LaAlO3 buffer layer-assisted tunneling current in manganite p-n heterojunction

    NASA Astrophysics Data System (ADS)

    Ma, Jun-Jie; Wang, Deng-Jing; Huang, Hai-Lin; Wang, Ru-Wu; Li, Yun-Bao

    2015-10-01

    An oxide p-n heterojunction composed of a 150-nm La0.67Ca0.33MnO3 (LCMO) film, 0.05 wt% Nb doped SrTiO3 substrate (STON), and sandwiched 5-nm LaAlO3 (LAO) thin film is fabricated with the pulsed laser deposition technique and the interfacial transport properties are experimentally studied. The rectifying behavior of the junction is in agreement with Newman’s equation, indicating that tunneling is the dominant process for the carriers to pass through the interface while thermal emission is the dominant transport model of an LCMO/STON heterojunction with no LAO buffer layer. Project supported by the National Natural Science Foundation of China (Grant No. 10804089).

  6. Thickness effect of catalyst layer on silicon nanowires morphology and features

    NASA Astrophysics Data System (ADS)

    Hamidinezhad, Habib

    2016-02-01

    Silicon nanowires (SiNWs) have been synthesized on gold layer-coated silicon substrates via plasma enhanced chemical vapor deposition method (PECVD). Various thicknesses of Au layers were coated on Si (111) substrates using radio frequency magnetron sputtering. Field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDX), and transmission electron microscopy (TEM) were used to characterize the morphology, compositions, and structures of the samples. The results show that the sample consisted of single-crystalline SiNWs with the diameters ranging from 40 to 160 nm and length up to 3 μm. It was observed that the diameter of SiNWs increases with increasing of Au catalyst layers thickness. Raman spectra display peaks with narrow and asymmetric shape at 518 cm-1 for the SiNWs, indicating the high crystalline nature of the samples. A possible growth mechanism is proposed for the formation of nanowires (NWs). It has been found that the features of SiNWs depend on the thickness of Au layers.

  7. Toward Efficient Thick Active PTB7 Photovoltaic Layers Using Diphenyl Ether as a Solvent Additive.

    PubMed

    Zheng, Yifan; Goh, Tenghooi; Fan, Pu; Shi, Wei; Yu, Junsheng; Taylor, André D

    2016-06-22

    The development of thick organic photovoltaics (OPV) could increase absorption in the active layer and ease manufacturing constraints in large-scale solar panel production. However, the efficiencies of most low-bandgap OPVs decrease substantially when the active layers exceed ∼100 nm in thickness (because of low crystallinity and a short exciton diffusion length). Herein, we report the use of solvent additive diphenyl ether (DPE) that facilitates the fabrication of thick (180 nm) active layers and triples the power conversion efficiency (PCE) of conventional thienothiophene-co-benzodithiophene polymer (PTB7)-based OPVs from 1.75 to 6.19%. These results demonstrate a PCE 20% higher than those of conventional (PTB7)-based OPV devices using 1,8-diiodooctane. Morphology studies reveal that DPE promotes the formation of nanofibrillar networks and ordered packing of PTB7 in the active layer that facilitate charge transport over longer distances. We further demonstrate that DPE improves the fill factor and photocurrent collection by enhancing the overall optical absorption, reducing the series resistance, and suppressing bimolecular recombination. PMID:27253271

  8. Retinal Nerve Fiber Layer Thickness Measurement Comparison Using Spectral Domain and Swept Source Optical Coherence Tomography

    PubMed Central

    Ha, Ahnul; Lee, Seung Hyen; Lee, Eun Ji

    2016-01-01

    Purpose To investigate the retinal nerve fiber layer (RNFL) thickness concordance when measured by spectral domain (SD) and swept source (SS) optical coherence tomography (OCT), and to compare glaucoma-discriminating capability. Methods RNFL thicknesses were measured with the scan circle, centered on the optic nerve head, in 55 healthy, 41 glaucoma suspected, and 87 glaucomatous eyes. The RNFL thickness measured by the SD-OCT (sdRNFL thickness) and SS-OCT (ssRNFL thickness) were compared using the t-test. Bland-Altman analysis was performed to examine their agreement. We compared areas under the receiver operating characteristics curve and examined sdRNFL and ssRNFL thickness for discriminating glaucomatous eyes from healthy eyes, and from glaucoma suspect eyes. Results The average ssRNFL thickness was significantly greater than sdRNFL thickness in healthy (110.0 ± 7.9 vs. 100.1 ± 6.8 µm, p < 0.001), glaucoma suspect (96.8 ± 9.3 vs. 89.6 ± 7.9 µm, p < 0.001), and glaucomatous eyes (74.3 ± 14.2 vs. 69.1 ± 12.4 µm, p = 0.011). Bland-Altman analysis showed that there was a tendency for the difference between ssRNFL and sdRNFL to increase in eyes with thicker RNFL. The area under the curves of the average sdRNFL and ssRNFL thickness for discriminating glaucomatous eyes from healthy eyes (0.984 vs. 0.986, p = 0.491) and glaucoma suspect eyes (0.936 vs. 0.918, p = 0.132) were comparable. Conclusions There was a tendency for ssRNFL thickness to increase, compared with sdRNFL thickness, in eyes with thicker RNFL. The ssRNFL thickness had comparable diagnostic capability compared with sdRNFL thickness for discriminating glaucomatous eyes from healthy eyes and glaucoma suspect eyes. PMID:27051263

  9. Structural and morphological properties of GaN buffer layers grown by ammonia molecular beam epitaxy on SiC substrates for AlGaN/GaN high electron mobility transistors

    SciTech Connect

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

    2008-05-01

    The impact of growth conditions on the surface morphology and structural properties of ammonia molecular beam epitaxy GaN buffers layers on SiC substrates was investigated. The threading dislocation (TD) density was found to decrease with decreasing NH{sub 3}:Ga flux ratio, which corresponded to an increase in surface roughness and reduction in residual compressive lattice mismatch stress. Furthermore, the dislocation density and compressive stress decreased for increasing buffer thickness. TD inclination was proposed to account for these observations. Optimized surface morphologies were realized at high NH{sub 3}:Ga flux ratios and were characterized by monolayer-high steps, spiral hillocks, and pyramidal mounds, with rms roughness of {approx}1.0 nm over 2x2 {mu}m{sup 2} atomic force microscopy images. Smooth surface morphologies were realized over a large range of growth temperatures and fluxes, and growth rates of up to 1 {mu}m/h were achieved. TD densities in the buffers as low as 3x10{sup 9} cm{sup -2} were demonstrated. These buffers were highly insulating and were used in recently reported AlGaN/GaN HEMTs with power densities of >11 W/mm at 4 and 10 GHz.

  10. Lidar Descriptions of Mixing-Layer Thickness Characteristics in a Complex Terrain/Coastal Environment.

    NASA Astrophysics Data System (ADS)

    McElroy, James L.; Smith, Ted B.

    1991-05-01

    Airborne lidar and supplementary measurements made during a major study of air chemistry in southern California (SCCCAMP 1985) provided a rare opportunity to examine atmospheric boundary-layer structure in a coastal area with complex terrain. This structure results from a combination of daytime heating or convection in the boundary layer (CBL), the intrusion of a marine layer into the inland areas, the thermal internal boundary layer (TIBL) formed within the marine onshore flow, inland growth of the TIBL, interactions of the CBL and the TIBL, and airflow interactions with terrain features.Measurements showed offshore mixing-layer thicknesses during SCCCAMP to be quite uniform spatially and day to day at 100-200 m. Movement of this layer onshore occurred readily with terrain that sloped gradually upward (e.g., to 300 m MSL at 50 km inland), but was effectively blocked by a 400-500 m high coastal ridge. In the higher terrain beyond the coastal ridge, aerosol layers aloft were often created as a result of deep convection and of a combination of onshore flow and heated, upslope airflow activity. Such aerosol layers can extend far offshore when embedded in reverse circulations aloft.The forward boundary of the marine layer was quite sharp, resembling a miniature cold front. Within the marine layer the onshore flow initiates a TIBL at the coastline, which increases in depth with distance inland due to roughness and convective influences. A coherent marine layer with imbedded TIBL was maintained for inland distances of 20-50 km, depending on terrain. Intense heating occurred inland prior to the arrival and undercutting by the marine front. The resulting, effective mixing layer increased in thickness from a few hundred meters to nearly two kilometers in a very short distance.Comparisons of a representative, physically based TIBL and convective mixing-layer models with observed data indicate that they generally do a credible job of estimating the depth of the marine layer

  11. Metal-oxide buffer layer for maintaining topological bumpy surface underlayer of columnar CoPt-SiO2 granular media deposited at high substrate temperature

    NASA Astrophysics Data System (ADS)

    Tham, Kim Kong; Hinata, Shintaro; Saito, Shin; Takahashi, Migaku

    2015-05-01

    Investigation of surface topography for underlayer with various metal-oxide buffer layer (BL) materials for magnetic recording media is reported. In the previous study, it was found out that the application of a high substrate temperature deposition process to a granular layer with a magnetic alloy and a non-magnetic oxide material, such as CoPtCr-SiO2, will induce lamellar and spherical grains due to the flattening of the underlayer bumpy surface by recrystallization. By depositing a CoCr-SiO2 BL onto the Ru underlayer at room temperature, CoCr grains grow epitaxially onto Ru grains and SiO2 segregates to Ru boundaries. Consequently, bumpy surface morphology of the underlayer is maintained even though heated to around 400 °C before depositing the granular layer. Therefore, CoPt magnetic grains of a Co82.4Pt17.6- 27.7 vol. % SiO2 granular film deposited on the underlayer grow epitaxially on CoCr grains with columnar structure. As a result, high average Ku⊥ of around 6.7 × 106 erg/cm3 can be obtained. Among the studied BL materials, CoCr-SiO2 shows the highest thermal resistance with root mean square surface roughness (Rq) of around 1.7 nm after heating at around 400 °C. To obtain columnar magnetic grains with critical thickness more than 13 nm, underlayer with Rq more than 1.6 nm is needed.

  12. The effects of buffer layers on the performance and stability of flexible InGaZnO thin film transistors on polyimide substrates

    SciTech Connect

    Ok, Kyung-Chul; Park, Jin-Seong E-mail: jsparklime@hanyang.ac.kr; Ko Park, Sang-Hee; Kim, H. E-mail: jsparklime@hanyang.ac.kr; Hwang, Chi-Sun; Soo Shin, Hyun; Bae, Jonguk

    2014-02-10

    We demonstrated the fabrication of flexible amorphous indium gallium zinc oxide thin-film transistors (TFTs) on high-temperature polyimide (PI) substrates, which were debonded from the carrier glass after TFT fabrication. The application of appropriate buffer layers on the PI substrates affected the TFT performance and stability. The adoption of the SiN{sub x}/AlO{sub x} buffer layers as water and hydrogen diffusion barriers significantly improved the device performance and stability against the thermal annealing and negative bias stress, compared to single SiN{sub x} or SiO{sub x} buffer layers. The substrates could be bent down to a radius of curvature of 15 mm and the devices remained normally functional.

  13. Effect of dopent on the structural and optical properties of ZnS thin film as a buffer layer in solar cell application

    SciTech Connect

    Vashistha, Indu B. Sharma, S. K.; Sharma, Mahesh C.; Sharma, Ramphal

    2015-08-28

    In order to find the suitable alternative of toxic CdS buffer layer, deposition of pure ZnS and doped with Al by chemical bath deposition method have been reported. Further as grown pure and doped thin films have been annealed at 150°C. The structural and surface morphological properties have been characterized by X-Ray diffraction (XRD) and Atomic Force Microscope (AFM).The XRD analysis shows that annealed thin film has been polycrystalline in nature with sphalerite cubic crystal structure and AFM images indicate increment in grain size as well as growth of crystals after annealing. Optical measurement data give band gap of 3.5 eV which is ideal band gap for buffer layer for solar cell suggesting that the obtained ZnS buffer layer is suitable in a low-cost solar cell.

  14. Influence of electron transport layer thickness on optical properties of organic light-emitting diodes

    SciTech Connect

    Liu, Guohong; Liu, Yong; Li, Baojun; Zhou, Xiang

    2015-06-07

    We investigate experimentally and theoretically the influence of electron transport layer (ETL) thickness on properties of typical N,N′-diphenyl-N,N′-bis(1-naphthyl)-[1,1′-biphthyl]-4,4′-diamine (NPB)/tris-(8-hydroxyquinoline) aluminum (Alq{sub 3}) heterojunction based organic light-emitting diodes (OLEDs), where the thickness of ETL is varied to adjust the distance between the emitting zone and the metal electrode. The devices showed a maximum current efficiency of 3.8 cd/A when the ETL thickness is around 50 nm corresponding to an emitter-cathode distance of 80 nm, and a second maximum current efficiency of 2.6 cd/A when the ETL thickness is around 210 nm corresponding to an emitter-cathode distance of 240 nm. We adopt a rigorous electromagnetic approach that takes parameters, such as dipole orientation, polarization, light emitting angle, exciton recombination zone, and diffusion length into account to model the optical properties of devices as a function of varying ETL thickness. Our simulation results are accurately consistent with the experimental results with a widely varying thickness of ETL, indicating that the theoretical model may be helpful to design high efficiency OLEDs.

  15. Alloy formation of Ni ultrathin films on Pt(1 1 1) with Ag buffer layers

    NASA Astrophysics Data System (ADS)

    Ho, H. Y.; Su, C. W.; Chu, Y. W.; Shern, C. S.

    2004-10-01

    Low-energy electron diffraction (LEED), Auger electron spectroscopy (AES), and depth profiling were used to study growth mode and structure in the interfaces of Ni/Ag/Pt(1 1 1). An atomic exchange occurs between Ni and Ag when the annealing temperature is high enough and the starting exchange temperature does not depend on the thickness of Ni. Nevertheless, the complete exchange temperature is higher when the coverage of Ni increases. Experimental evidence shows that the Ni-Pt alloy develops after the atomic exchange between Ag and Ni is complete. The atomic exchange between Ag and Ni, and the formation of Ni-Pt alloy were confirmed by the depth profile. The mechanisms of the atomic exchange are discussed.

  16. Reduced interface recombination in Cu2ZnSnS4 solar cells with atomic layer deposition Zn1-xSnxOy buffer layers

    NASA Astrophysics Data System (ADS)

    Platzer-Björkman, C.; Frisk, C.; Larsen, J. K.; Ericson, T.; Li, S.-Y.; Scragg, J. J. S.; Keller, J.; Larsson, F.; Törndahl, T.

    2015-12-01

    Cu2ZnSnS4 (CZTS) solar cells typically include a CdS buffer layer in between the CZTS and ZnO front contact. For sulfide CZTS, with a bandgap around 1.5 eV, the band alignment between CZTS and CdS is not ideal ("cliff-like"), which enhances interface recombination. In this work, we show how a Zn1-xSnxOy (ZTO) buffer layer can replace CdS, resulting in improved open circuit voltages (Voc) for CZTS devices. The ZTO is deposited by atomic layer deposition (ALD), with a process previously developed for Cu(In,Ga)Se2 solar cells. By varying the ALD process temperature, the position of the conduction band minimum of the ZTO is varied in relation to that of CZTS. A ZTO process at 95 °C is found to give higher Voc and efficiency as compared with the CdS reference devices. For a ZTO process at 120 °C, where the conduction band alignment is expected to be the same as for CdS, the Voc and efficiency is similar to the CdS reference. Further increase in conduction band minimum by lowering the deposition temperature to 80 °C shows blocking of forward current and reduced fill factor, consistent with barrier formation at the junction. Temperature-dependent current voltage analysis gives an activation energy for recombination of 1.36 eV for the best ZTO device compared with 0.98 eV for CdS. We argue that the Voc of the best ZTO devices is limited by bulk recombination, in agreement with a room temperature photoluminescence peak at around 1.3 eV for both devices, while the CdS device is limited by interface recombination.

  17. Electrically Active Defects in GaN Layers Grown With and Without Fe-doped Buffers by Metal-organic Chemical Vapor Deposition

    NASA Astrophysics Data System (ADS)

    Umana-Membreno, G. A.; Parish, G.; Fichtenbaum, N.; Keller, S.; Mishra, U. K.; Nener, B. D.

    2008-05-01

    Electrically active defects in n-GaN films grown with and without an Fe-doped buffer layer have been investigated using conventional and optical deep-level transient spectroscopy (DLTS). Conventional DLTS revealed three well- defined electron traps with activation energies E a of 0.21, 0.53, and 0.8 eV. The concentration of the 0.21 and 0.8 eV defects was found to be slightly higher in the sample without the Fe-doped buffer, whereas the concentration of the 0.53 eV trap was higher in the sample with the Fe-doped buffer. A minority carrier trap with E a ≈ 0.65 eV was detected in both samples using optical DLTS; its concentration was ˜40% higher in the sample without the Fe-doped buffer. Mobility spectrum analysis and multiple magnetic-field measurements revealed that the electron mobility in the topmost layer of both samples was similar, but that the sample without the Fe-doped buffer layer was affected by parallel conduction through underlying layers with lower electron mobility.

  18. Aerodynamically-driven condensate layer thickness distributions on isothermal cylindrical surfaces

    NASA Technical Reports Server (NTRS)

    Rosner, D. E.; Gunes, D.; Nazih-Anous, N.

    1983-01-01

    A simple yet rather general mathematical model is presented for predicting the distribution of condensate layer thickness when aerodynamic shear is the dominant mechanism of liquid flow along the surface. The Newtonian condensate film is treated using well-known thin-layer (lubrication theory) approximations, and condensate supply is taken to be the result of either convective diffusion or inertial impaction. Illustrative calculations for a circular cylinder in a crossflow at Re = 100,000 reveal the consequences of alternate condensate arrival mechanisms and the existence of thicker reverse-flow films behind the position of gas boundary-layer separation. The present formulation is readily generalized to include transient liquid layer flows on noncircular objects of variable surface temperature, as encountered in turbine-blade materials testing or operation.

  19. Measurement and correlation of aerodynamic heating to surface corrugation stiffened structures in thick turbulent boundary layers

    NASA Technical Reports Server (NTRS)

    Brandon, H. J.; Masek, R. V.

    1974-01-01

    The flow conditions for which heating distributions were measured on corrugated surfaces and wavy walls in turbulent boundary layers are shown, along with the ratio of the displacement thickness to the roughness height versus the local edge Mach number for an equivalent smooth surface. The present data are seen to greatly extend the range of data available on corrugated surfaces in turbulent boundary layers. These data were obtained by testing fullscale corrugation roughened panels in the wall boundary layer of a supersonic and hypersonic wind tunnel. The experimental program used to obtain the data is described. The data are analyzed and correlated in terms of the pertinent flow and geometric parameters. The developed correlations are compared with the available thin boundary layer data, as well as with previously published correlation techniques.

  20. Improved performance of P-type DSCs with a compact blocking layer coated by different thicknesses

    NASA Astrophysics Data System (ADS)

    Ho, Phuong; Bao, Le Quoc; Cheruku, Rajesh; Kim, Jae Hong

    2016-07-01

    The introduction of different thicknesses of a compact NiO blocking layer coating with different spin speeds on FTO and followed by a coating of photoactive NiO electrode for p-type dye-sensitized solar cells (p-DSCs). This study examined the fabrication of a compact NiO blocking layer by decomposing an ethanolic precursor solution of nickel acetate tetrahydrate. The DCBZ dye used as the photosensitizer for the NiO electrode in the p-DSCs device and their performances have been analyzed. The enhancement of photovoltaic performance and resulted from an increase in the power conversion efficiency (η). The electrochemical impedance spectroscopy (EIS) measurement demonstrated that charge recombination was suppressed when a compact NiO blocking layer was applied. The results showed that the best p-DSC was achieved by employing 3000 rpm spin-coated process for different times of blocking layer.

  1. Impact of varying buffer thickness generated strain and threading dislocations on the formation of plasma assisted MBE grown ultra-thin AlGaN/GaN heterostructure on silicon

    SciTech Connect

    Chowdhury, Subhra; Biswas, Dhrubes

    2015-05-15

    Plasma-assisted molecular beam epitaxy (PAMBE) growth of ultra-thin Al{sub 0.2}Ga{sub 0.8}N/GaN heterostructures on Si(111) substrate with three buffer thickness (600 nm/400 nm/200 nm) have been reported. An unique growth process has been developed that supports lower temperature epitaxy of GaN buffer which minimizes thermally generated tensile strain through appropriate nitridation and AlN initiated epitaxy for achieving high quality GaN buffer which supports such ultra-thin heterostructures in the range of 10-15Å. It is followed by investigations of role of buffer thickness on formation of ultra-thin Al{sub 0.2}Ga{sub 0.8}N/GaN heterostructure, in terms of stress-strain and threading dislocation (TD). Structural characterization were performed by High-Resolution X-Ray Diffraction (HRXRD), room-temperature Photoluminescence (RT-PL), High Resolution Transmission Electron Microscopy (HRTEM) and Atomic Force Microscopy (AFM). Analysis revealed increasing biaxial tensile stress of 0.6918 ± 0.04, 1.1084, 1.1814 GPa in heterostructures with decreasing buffer thickness of 600, 400, 200 nm respectively which are summed up with residual tensile strain causing red-shift in RT-PL peak. Also, increasing buffer thickness drastically reduced TD density from the order 10{sup 10} cm{sup −2} to 10{sup 8} cm{sup −2}. Surface morphology through AFM leads to decrease of pits and root mean square value with increasing buffer thickness which are resulted due to reduction of combined effect of strain and TDs.

  2. Wire or no wire-Depends on the catalyst layer thickness

    NASA Astrophysics Data System (ADS)

    Li, Feng Ji; Zhang, Sam; Lee, Jyh-Wei; Zhao, Dongliang

    2013-10-01

    Crystalline silicon (Si) nanowire could be directly grown from Si wafer upon thermal annealing in the presence of catalyst such as gold (Au). However, the role of the catalyst layer thickness is yet elucidated. In this work, 10 nm, 20 nm, and 40 nm Au layers were respectively sputtered on Si wafer substrates, followed by 2 min thermal annealing at 1000 °C under Ar atmosphere, to find the relationship between the catalyst layer thickness and formation of the nanowire. Results show that in the case of thin layer of catalyst, crystalline-Si/amorphous-SiOx coaxial nanowires grew. But with thicker layers of catalyst, no wires were found but crystalline Au particles capsulated with amorphous SiOx. The catalyst and nanowire morphologies and structures were carefully examined through a scanning electron microscope, X-ray diffraction, transmission electron microscopy, energy dispersive X-ray spectroscopy and selected area diffraction. A model is developed to explain the formation mechanism of the Si/SiOx and Au/SiOx core-shell nanostructures.

  3. Influence of the layer thickness in plasmonic gold nanoparticles produced by thermal evaporation

    PubMed Central

    Gaspar, D.; Pimentel, A. C.; Mateus, T.; Leitão, J. P.; Soares, J.; Falcão, B. P.; Araújo, A.; Vicente, A.; Filonovich, S. A.; Águas, H.; Martins, R.; Ferreira, I.

    2013-01-01

    Metallic nanoparticles (NPs) have received recently considerable interest of photonic and photovoltaic communities. In this work, we report the optoelectronic properties of gold NPs (Au-NPs) obtained by depositing very thin gold layers on glass substrates through thermal evaporation electron-beam assisted process. The effect of mass thickness of the layer was evaluated. The polycrystalline Au-NPs, with grain sizes of 14 and 19 nm tend to be elongated in one direction as the mass thickness increase. A 2 nm layer deposited at 250°C led to the formation of Au-NPs with 10-20 nm average size, obtained by SEM images, while for a 5 nm layer the wide size elongates from 25 to 150 nm with a mean at 75 nm. In the near infrared region was observed an absorption enhancement of amorphous silicon films deposited onto the Au-NPs layers with a corresponding increase in the PL peak for the same wavelength region. PMID:23552055

  4. Mointoring Thickness Deviations in Planar Multi-Layered Elastic Structures Using Impedance Signatures

    SciTech Connect

    Fisher, K A

    2007-01-26

    In this letter, a low frequency ultrasonic resonance technique that operates in the (20 - 80 kHz) regime is presented that demonstrates detection of thickness changes on the order of +/- 10{micro}m. This measurement capability is a result of the direct correlation between the electrical impedance of an electro-acoustic transducer and the mechanical loading it experiences when placed in contact with a layered elastic structure. The relative frequency shifts of the resonances peaks can be estimated through a simple one-dimensional transmission model. Separate experimental measurements confirm this technique to be sensitive to subtle changes in the underlying layered elastic structure.

  5. Measurement of thermal noise in multilayer coatings with optimized layer thickness

    SciTech Connect

    Villar, Akira E.; Black, Eric D.; DeSalvo, Riccardo; Libbrecht, Kenneth G.; Michel, Christophe; Morgado, Nazario; Pinard, Laurent; Pinto, Innocenzo M.; Pierro, Vincenzo; Galdi, Vincenzo; Principe, Maria; Taurasi, Ilaria

    2010-06-15

    A standard quarter-wavelength multilayer optical coating will produce the highest reflectivity for a given number of coating layers, but in general it will not yield the lowest thermal noise for a prescribed reflectivity. Coatings with the layer thicknesses optimized to minimize thermal noise could be useful in future generation interferometric gravitational wave detectors where coating thermal noise is expected to limit the sensitivity of the instrument. We present the results of direct measurements of the thermal noise of a standard quarter-wavelength coating and a low noise optimized coating. The measurements indicate a reduction in thermal noise in line with modeling predictions.

  6. Correlation of Retinal Nerve Fiber Layer Thickness and Visual Fields in Glaucoma: A broken stick model

    PubMed Central

    Alasil, Tarek; Wang, Kaidi; Yu, Fei; Field, Matthew G.; Lee, Hang; Baniasadi, Neda; de Boer, Johannes F.; Coleman, Anne L.; Chen, Teresa C.

    2015-01-01

    Purpose To determine the retinal nerve fiber layer (RNFL) thickness at which visual field (VF) damage becomes detectable and associated with structural loss. Design Retrospective cross-sectional study. Methods Eighty seven healthy and 108 glaucoma subjects (one eye per subject) were recruited from an academic institution. All patients had VF examinations (Swedish Interactive Threshold Algorithm 24-2 test of the Humphrey visual field analyzer 750i; Carl Zeiss Meditec, Dublin, CA) and spectral domain optical coherence tomography RNFL scans (Spectralis, Heidelberg Engineering, Heidelberg, Germany). Comparison of RNFL thicknesses values with VF threshold values showed a plateau of VF threshold values at high RNFL thickness values and then a sharp decrease at lower RNFL thickness values. A broken stick statistical analysis was utilized to estimate the tipping point at which RNFL thickness values are associated with VF defects. The slope for the association between structure and function was computed for data above and below the tipping point. Results The mean RNFL thickness value that was associated with initial VF loss was 89 μm. The superior RNFL thickness value that was associated with initial corresponding inferior VF loss was 100 μm. The inferior RNFL thickness value that was associated with initial corresponding superior VF loss was 73 μm. The differences between all the slopes above and below the aforementioned tipping points were statistically significant (p<0.001). Conclusions In open angle glaucoma, substantial RNFL thinning or structural loss appears to be necessary before functional visual field defects become detectable. PMID:24487047

  7. Thickness effects on the Coulomb drag rate in double quantum layer systems

    NASA Astrophysics Data System (ADS)

    Vazifehshenas, T.; Eskourchi, A.

    2007-02-01

    In this paper, we have investigated the effect of quantum layer thickness on Coulomb drag phenomenon in a double quantum well (DQW) system, in which the electrons momentum can transfer from one layer to another. We have applied the full random phase approximation (RPA) in dynamical dielectric matrix of this coupled two-dimensional electron gas (2DEG) system in order to obtain an improved result for temperature-dependent rate of momentum transfer. We have calculated the drag rate transresistivity for various well thicknesses at low and intermediate temperatures in Fermi-scale and for different electron gas densities. It has been obtained that the Coulomb drag rate increases with increasing the well width when the separation between the wells remains unchanged.

  8. Growth of Sputtered-Aluminum Oxide Thin Films on si (100) and si (111) Substrates with Al2O3 Buffer Layer

    NASA Astrophysics Data System (ADS)

    Lim, Wei Qiang; Shanmugan, Subramani; Devarajan, Mutharasu

    2016-03-01

    Aluminum oxide (Al2O3) thin films with Al2O3 buffer layer were deposited on Si (100) and Si (111) substrates using RF magnetron sputtering of Al2O3 target in Ar atmosphere. The synthesized films were then annealed at the temperature of 400∘C, 600∘C and 800∘C in nitrogen (N2) environment for 6h. Structural properties and surface morphology are examined by using X-Ray Diffraction (XRD), Field Emission Scanning Electron Microscope (FESEM) and Atomic Force Microscope (AFM). XRD analysis indicated that different orientation of Al2O3 were formed with different intensities due to increase in the annealing temperature. From FESEM cross-section analysis results, it is observed that the thickness of films were increased as the annealing temperature increased. EDX analysis shows that the concentration of aluminum and oxygen on both the Si substrates increased with the increase in annealing temperature. The surface roughness of the films were found to be decreased first when the annealing temperature is increased to 400∘C, yet the roughness increased when the annealing temperature is further increased to 800∘C.

  9. Improving source/drain contact resistance of amorphous indium–gallium–zinc-oxide thin-film transistors using an n+-ZnO buffer layer

    NASA Astrophysics Data System (ADS)

    Hung, Chien-Hsiung; Wang, Shui-Jinn; Lin, Chieh; Wu, Chien-Hung; Chen, Yen-Han; Liu, Pang-Yi; Tu, Yung-Chun; Lin, Tseng-Hsing

    2016-06-01

    To avoid high temperature annealing in improving the source/drain (S/D) resistance (R DS) of amorphous indium–gallium–zinc-oxide (α-IGZO) thin-film transistors (TFTs) for flexible electronics, a simple and efficient technique using a sputtering-deposited n+-ZnO buffer layer (BL) sandwiched between the S/D electrode and the α-IGZO channel is proposed and demonstrated. It shows that the R DS of α-IGZO TFTs with the proposed n+-ZnO BL is reduced to 8.1 × 103 Ω as compared with 6.1 × 104 Ω of the conventional one. The facilitation of carrier tunneling between the S/D electrode and the α-IGZO channel through the use of the n+-ZnO BL to lower the effective barrier height therein is responsible for the R DS reduction. Effects of the chamber pressure on the carrier concentration of the sputtering-deposited n+-ZnO BL and the thickness of the BL on the degree of improvement in the performance of α-IGZO TFTs are analyzed and discussed.

  10. Strain-driven synthesis of <112> direction InAs nanowires in V-grooved trenches on Si using InP/GaAs buffer layers

    NASA Astrophysics Data System (ADS)

    Li, Shiyan; Zhou, Xuliang; Kong, Xiangting; Li, Mengke; Mi, Junping; Wang, Mengqi; Pan, Jiaoqing

    2016-09-01

    The catalyst-free metal organic vapor phase epitaxial growth of InAs nanowires on silicon (001) substrates is investigated by using selectively grown InP/GaAs buffer layers in V-grooved trenches. A strain-driven mechanism of self-aligned <112> direction InAs nanowires growing is proposed and demonstrated by the transmission electron microscopy measurement. The morphology of InAs nanowires is tapered in diameter and exhibits a hexagonal cross-section. The defect-free InAs nanowire shows a pure zinc blende crystal structure and an epitaxial relationship with InP buffer layer.

  11. Theoretical Determination of The Optimum Thickness of Perylene Layer in Bilayer Phthalocyanine/Perylene Photovoltaic Device

    NASA Astrophysics Data System (ADS)

    Pratiwi, Herlina; Siahaan, Timothy; Satriawan, Mirza; Nurwantoro, Pekik; Triyana, Kuwat

    2009-09-01

    We do theoretical study on thickness of the active layers in a heterojunction bilayer thin film photovoltaic device based on copper phthalocyanine (CuPc)/perylene that gives the highest Incident Photon to Current Efficiency (IPCE). The device we study consists Glass (1 mm)/ITO (Indium Tin Oxide, 120 nm)/CuPc (50 nm)/PTCDA (3, 4, 9, 10-perylenetetracarboxylic dianhydride, x nm)/Ag (40 nm), where x is the thickness of the PTCDA layer that we calculate here. The calculation is based on assumption that the photocurrent generation process is the result of the creation of photogenerated excitons, which difuse before dissociated at the CuPc/PTCDA interface following the diffusion equation, by internal optical electric field that comes from light exposure. We also assume that almost all photocurrent is created in the CuPc/PTCDA interface. Because the order of the thickness of the active layers is the same or smaller than of the wavelength of visible light, we take into account the effect of reflection and interference in the calculation of internal optical electric field distribution inside the device by making use complex indices of refraction of the active materials in our calculation. The modulus of it is proportional with the number generated excitons. The general solution of the exciton diffusion equation was used for calculating the photocurrent and the IPCE. Here, we find the optimum thickness of PTCDA layer that gives greatest IPCE at the wavelength of 344 nm and 467 nm, which are the wavelengths at which the absorption coefficients of CuPc and PTCDA, respectively, reach the maximum values.

  12. Macular Microcysts in Mitochondrial Optic Neuropathies: Prevalence and Retinal Layer Thickness Measurements

    PubMed Central

    Carbonelli, Michele; La Morgia, Chiara; Savini, Giacomo; Cascavilla, Maria Lucia; Borrelli, Enrico; Chicani, Filipe; do V. F. Ramos, Carolina; Salomao, Solange R.; Parisi, Vincenzo; Sebag, Jerry; Bandello, Francesco; Sadun, Alfredo A.; Carelli, Valerio; Barboni, Piero

    2015-01-01

    Purpose To investigate the thickness of the retinal layers and to assess the prevalence of macular microcysts (MM) in the inner nuclear layer (INL) of patients with mitochondrial optic neuropathies (MON). Methods All patients with molecularly confirmed MON, i.e. Leber’s Hereditary Optic Neuropathy (LHON) and Dominant Optic Atrophy (DOA), referred between 2010 and 2012 were enrolled. Eight patients with MM were compared with two control groups: MON patients without MM matched by age, peripapillary retinal nerve fiber layer (RNFL) thickness, and visual acuity, as well as age-matched controls. Retinal segmentation was performed using specific Optical coherence tomography (OCT) software (Carl Zeiss Meditec). Macular segmentation thickness values of the three groups were compared by one-way analysis of variance with Bonferroni post hoc corrections. Results MM were identified in 5/90 (5.6%) patients with LHON and 3/58 (5.2%) with DOA. The INL was thicker in patients with MON compared to controls regardless of the presence of MM [133.1±7μm vs 122.3±9μm in MM patients (p<0.01) and 128.5±8μm vs. 122.3±9μm in no-MM patients (p<0.05)], however the outer nuclear layer (ONL) was thicker in patients with MM (101.4±1mμ) compared to patients without MM [77.5±8mμ (p<0.001)] and controls [78.4±7mμ (p<0.001)]. ONL thickness did not significantly differ between patients without MM and controls. Conclusion The prevalence of MM in MON is low (5-6%), but associated with ONL thickening. We speculate that in MON patients with MM, vitreo-retinal traction contributes to the thickening of ONL as well as to the production of cystic spaces. PMID:26047507

  13. Oscillating layer thickness and vortices generated in oscillation of finite plate

    NASA Astrophysics Data System (ADS)

    Sin, V. K.; Wong, I. K.

    2016-06-01

    Moving mesh strategy is used in the model of flow induced by oscillating finite plate through software - COMSOL Multiphysics. Flow is assumed to be laminar and arbitrary Lagrangian-Eulerian method is used for moving mesh in the simulation. Oscillating layer thickness is found which is different from the analytical solution by 2 to 3 times depends on the oscillating frequency. Vortices are also observed near the oscillating finite plate because of the edge effect of the finite plate.

  14. Enhanced Lifetime of Polymer Solar Cells by Surface Passivation of Metal Oxide Buffer Layers.

    PubMed

    Venkatesan, Swaminathan; Ngo, Evan; Khatiwada, Devendra; Zhang, Cheng; Qiao, Qiquan

    2015-07-29

    The role of electron selective interfaces on the performance and lifetime of polymer solar cells were compared and analyzed. Bilayer interfaces consisting of metal oxide films with cationic polymer modification namely poly ethylenimine ethoxylated (PEIE) were found to enhance device lifetime compared to bare metal oxide films when used as an electron selective cathode interface. Devices utilizing surface-modified metal oxide layers showed enhanced lifetimes, retaining up to 85% of their original efficiency when stored in ambient atmosphere for 180 days without any encapsulation. The work function and surface potential of zinc oxide (ZnO) and ZnO/PEIE interlayers were evaluated using Kelvin probe and Kelvin probe force microscopy (KPFM) respectively. Kelvin probe measurements showed a smaller reduction in work function of ZnO/PEIE films compared to bare ZnO films when aged in atmospheric conditions. KPFM measurements showed that the surface potential of the ZnO surface drastically reduces when stored in ambient air for 7 days because of surface oxidation. Surface oxidation of the interface led to a substantial decrease in the performance in aged devices. The enhancement in the lifetime of devices with a bilayer interface was correlated to the suppressed surface oxidation of the metal oxide layers. The PEIE passivated surface retained a lower Fermi level when aged, which led to lower trap-assisted recombination at the polymer-cathode interface. Further photocharge extraction by linearly increasing voltage (Photo-CELIV) measurements were performed on fresh and aged samples to evaluate the field required to extract maximum charges. Fresh devices with a bare ZnO cathode interlayer required a lower field than devices with ZnO/PEIE cathode interface. However, aged devices with ZnO required a much higher field to extract charges while aged devices with ZnO/PEIE showed a minor increase compared to the fresh devices. Results indicate that surface modification can act as a

  15. Multi-pulse LIBDE of fused silica at different thicknesses of the organic absorber layer

    NASA Astrophysics Data System (ADS)

    Pan, Yunxiang; Ehrhardt, Martin; Lorenz, Pierre; Han, Bing; Hopp, Bela; Vass, Csaba; Ni, Xiaowu; Zimmer, Klaus

    2015-12-01

    Laser-induced etching techniques feature several unique characteristics that enable ultraprecise machining of transparent materials. However, LIBDE (laser-induced back side dry etching) and LIBWE (laser-induced back side wet etching) are preferentially studied due to experimental feasibilities either using a very thin or a bulk absorber at the rear side of the transparent material. This study aims to fill the gap by examining the thickness dependence of the absorbing material. Multi-pulse-LIBDE (MP-LIBDE) of fused silica using different thick photoresist absorber layers (dL = 0.2-11.7 μm) was performed with a KrF excimer laser (λ = 248 nm, tp ≈ 20 ns). The influence of several experimental parameters, such as laser fluence, pulse number, film thickness, on the ablation morphology and the etching rate were investigated. Especially at moderate fluences (F = 0.7-1.5 J/cm2) MP-LIBDE and LIBWE show several similar process characteristics such as the etching rate dependence on the laser fluence and the pulse number with a typical etching rate of approx. 12 nm at 1 J/cm2. However, the specific etching rate values depend on the absorber layer thickness, for instance. The morphology of the etched surface is smooth with a roughness of below 5 nm rms. Further, the modification of the surface has been observed and will be discussed in relation to the multi-pulse laser etching mechanism.

  16. Effects of the Thickness of Niobium Surface Oxide Layers on Field Emission

    SciTech Connect

    A.T. Wu, S. Jin, J.D. Mammosser, R.A. Rimmer, X.Y. Lu, K. Zhao

    2011-09-01

    Field emission on the inner surfaces of niobium superconducting radio frequency cavities is still one of the major obstacles for reaching high accelerating gradients for SRF community. Our previous experimental results* seemed to imply that the threshold of field emission was related to the thickness of Nb surface oxide layers. In this contribution, a more detailed study on the influences of the surface oxide layers on the field emission on Nb surfaces will be reported. By anodization technique, the thickness of the surface pentoxide layer was artificially fabricated from 3 nm up to 460 nm. A home-made scanning field emission microscope was employed to perform the scans on the surfaces. Emitters were characterized using a scanning electron microscope together with an energy dispersive x-ray analyzer. The SFEM experimental results were analyzed in terms of surface morphology and oxide thickness of Nb samples and chemical composition and geographic shape of the emitters. A model based on the classic electromagnetic theory was developed trying to understand the experimental results. Possibly implications for Nb SRF cavity applications from this study will be discussed.

  17. Melanoma thickness measurement in two-layer tissue phantoms using pulsed photothermal radiometry (PPTR)

    NASA Astrophysics Data System (ADS)

    Wang, Tianyi; Qiu, Jinze; Paranjape, Amit; Milner, Thomas E.

    2009-02-01

    Melanoma is a malignant tumor of melanocytes which are found predominantly in skin. Melanoma is one of the rarer types of skin cancer but causes the majority of skin cancer related deaths. The staging of malignant melanoma using Breslow thickness is important because of the relationship to survival rate after five years. Pulsed photothermal radiometry (PPTR) is based on the time-resolved acquisition of infrared (IR) emission from a sample after pulsed laser exposure. PPTR can be used to investigate the relationship between melanoma thickness and detected radiometric temperature using two-layer tissue phantoms. We used a Monte Carlo simulation to mimic light transport in melanoma and employed a three-dimensional heat transfer model to obtain simulated radiometric temperature increase and, in comparison, we also conducted PPTR experiments to confirm our simulation results. Simulation and experimental results show similar trends: thicker absorbing layers corresponding to deeper lesions produce slower radiometric temperature decays. A quantitative relationship exists between PPTR radiometric temperature decay time and thickness of the absorbing layer in tissue phantoms.

  18. Macular Ganglion Cell Inner Plexiform Layer Thickness in Glaucomatous Eyes with Localized Retinal Nerve Fiber Layer Defects

    PubMed Central

    Zhang, Chunwei; Tatham, Andrew J.; Abe, Ricardo Y.; Hammel, Na’ama; Belghith, Akram; Weinreb, Robert N.; Medeiros, Felipe A.; Liebmann, Jeffrey M.; Girkin, Christopher A.; Zangwill, Linda M.

    2016-01-01

    Purpose To investigate macular ganglion cell–inner plexiform layer (mGCIPL) thickness in glaucomatous eyes with visible localized retinal nerve fiber layer (RNFL) defects on stereophotographs. Methods 112 healthy and 149 glaucomatous eyes from the Diagnostic Innovations in Glaucoma Study (DIGS) and the African Descent and Glaucoma Evaluation Study (ADAGES) subjects had standard automated perimetry (SAP), optical coherence tomography (OCT) imaging of the macula and optic nerve head, and stereoscopic optic disc photography. Masked observers identified localized RNFL defects by grading of stereophotographs. Result 47 eyes had visible localized RNFL defects on stereophotographs. Eyes with visible localized RNFL defects had significantly thinner mGCIPL thickness compared to healthy eyes (68.3 ± 11.4 μm versus 79.2 ± 6.6 μm respectively, P<0.001) and similar mGCIPL thickness to glaucomatous eyes without localized RNFL defects (68.6 ± 11.2 μm, P = 1.000). The average mGCIPL thickness in eyes with RNFL defects was 14% less than similarly aged healthy controls. For 29 eyes with a visible RNFL defect in just one hemiretina (superior or inferior) mGCIPL was thinnest in the same hemiretina in 26 eyes (90%). Eyes with inferior-temporal RNFL defects also had significantly thinner inferior-temporal mGCIPL (P<0.001) and inferior mGCIPL (P = 0.030) compared to glaucomatous eyes without a visible RNFL defect. Conclusion The current study indicates that presence of a localized RNFL defect is likely to indicate significant macular damage, particularly in the region of the macular that topographically corresponds to the location of the RNFL defect. PMID:27537107

  19. High current density and high PVCR Si/Si 1-xGe x DQW RTD formed with quadruple-layer buffer

    NASA Astrophysics Data System (ADS)

    Maekawa, Hirotaka; Sano, Yoshihiro; Ueno, Chihiro; Suda, Yoshiyuki

    2007-04-01

    As a strain-relief relaxed Si 1-xGe x buffer that is used for type II band offset formation, we have proposed a quadruple-Si 1-xGe x-layer (QL) buffer where misfit dislocations are evenly distributed in the lower two interfaces and a buffer surface with good crystallinity was obtained. The crystallinity of the buffer surface does not degrade by high P doping with a P concentration of ˜10 19 cm -3 during the buffer growth. A vertical-type electron-tunneling Si/Si 1-xGe x resonant tunneling diode (RTD) formed with the highly P-doped QL buffer exhibits a high current density and a high peak-to-valley current ratio (PVCR) value. A planer-type electron-tunneling Si/ Si 1-xGe x RTD formed with the same buffer using tetramethyl ammonium hydroxide (TMAH) etching and polyimide insulator, which is better suited for device integration, also exhibits a high current density and a high PVCR value and good initial static performance reproducibility.

  20. Predicting the Equilibrium Deuterium-Tritium Fuel Layer Thickness Profile in an Indirect-Drive Hohlraum Capsule

    SciTech Connect

    Sanchez, Jorge J.; Giedt, Warren H.

    2004-03-15

    A numerical procedure for calculating the equilibrium thickness distribution of a thin layer of deuterium and tritium on the inner surface of an indirect drive target sphere ({approx}2.0 mm in diameter) is described. Starting with an assumed uniform thickness layer and with specified thermal boundary conditions, the temperature distribution throughout the capsule and hohlraum (including natural convection in the hohlraum gas) is calculated. Results are used to make a first estimate of the final non-uniform thickness distribution of the layer. This thickness distribution is then used to make a second calculation of the temperature distribution with the same boundary conditions. Legendre polynomial coefficients are evaluated for the two temperature distributions and the two thickness profiles. Final equilibrium Legendre coefficients are determined by linear extrapolation. From these coefficients, the equilibrium layer thickness can be computed.

  1. Predicting the Equilibrium Deuterium-Tritium Fuel Layer Thickness Profile in an Indirect-Drive Hohlraum Capsule

    SciTech Connect

    Sanchez, J J; Giedt, W H

    2003-09-02

    A numerical procedure for calculating the equilibrium thickness distribution of a thin layer of deuterium and tritium on the inner surface of an indirect drive target sphere ({approx} 2.0 mm in diameter) is described. Starting with an assumed uniform thickness layer and with specified thermal boundary conditions, the temperature distribution throughout the capsule and hohlraum (including natural convection in the hohlraum gas) is calculated. Results are used to make a first estimate of the final non-uniform thickness distribution of the layer. This thickness distribution is then used to make a second calculation of the temperature distribution with the same boundary conditions. Legendre polynomial coefficients are evaluated for the two temperature distributions and the two thickness profiles. Final equilibrium Legendre coefficients are determined by linear extrapolation. From these coefficients, the equilibrium layer thickness can be computed.

  2. AlGaN/GaN field effect transistors for power electronics—Effect of finite GaN layer thickness on thermal characteristics

    SciTech Connect

    Hodges, C. Anaya Calvo, J.; Kuball, M.; Stoffels, S.; Marcon, D.

    2013-11-11

    AlGaN/GaN heterostructure field effect transistors with a 150 nm thick GaN channel within stacked Al{sub x}Ga{sub 1−x}N layers were investigated using Raman thermography. By fitting a thermal simulation to the measured temperatures, the thermal conductivity of the GaN channel was determined to be 60 W m{sup −1} K{sup −1}, over 50% less than typical GaN epilayers, causing an increased peak channel temperature. This agrees with a nanoscale model. A low thermal conductivity AlGaN buffer means the GaN spreads heat; its properties are important for device thermal characteristics. When designing power devices with thin GaN layers, as well as electrical considerations, the reduced channel thermal conductivity must be considered.

  3. Growth of ZnO(0001) on GaN(0001)/4H-SiC buffer layers by plasma-assisted hybrid molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Adolph, David; Tingberg, Tobias; Ive, Tommy

    2015-09-01

    Plasma-assisted molecular beam epitaxy was used to grow ZnO(0001) layers on GaN(0001)/4H-SiC buffer layers deposited in the same growth chamber equipped with both N- and O-plasma sources. The GaN buffer layers were grown immediately before initiating the growth of ZnO. Using a substrate temperature of 445 °C and an O2 flow rate of 2.5 standard cubic centimeters per minute, we obtained ZnO layers with statistically smooth surfaces having a root-mean-square roughness of 0.3 nm and a peak-to-valley distance of 3 nm as revealed by atomic force microscopy. The full-width-at-half-maximum for x-ray rocking curves obtained across the ZnO(0002) and ZnO(10 1 bar 5) reflections was 198 and 948 arcsec, respectively. These values indicated that the mosaicity of the ZnO layer was comparable to the corresponding values of the underlying GaN buffer layer. Reciprocal space maps showed that the in-plane relaxation of the GaN and ZnO layers was 82% and 73%, respectively, and that the relaxation occurred abruptly during the growth. Room-temperature Hall-effect measurements revealed that the layers were inherently n-type and had an electron concentration of 1×1019 cm-3 and a Hall mobility of 51 cm2/V s.

  4. Ultrasonographic evaluation of relative gastrointestinal layer thickness in cats without clinical evidence of gastrointestinal tract disease.

    PubMed

    Winter, Matthew D; Londono, Leonel; Berry, Clifford R; Hernandez, Jorge A

    2014-02-01

    The objectives of this study were (1) to measure normal thickness values of the muscularis, submucosal, mucosal and serosal layers in each gastrointestinal (GI) segment (gastric fundus, body and pyloric antrum; duodenum; jejunum; ileum; colon), and (2) to calculate a ratio of muscularis and mucosal layer thickness to aortic diameter measured at the level of the celiac artery (Musc:Ao and Muc:Ao) in each GI segment in a sample of healthy cats. Ultrasonographic examination of the GI tract was performed, and measurements of the individual layers in each GI segment were obtained in 38 healthy cats without clinical evidence of disease. The muscularis layer was significantly thickest in the ileum, compared with other segments, and it was thicker than the submucosa in all segments except the colon. The mucosa was the thickest layer in all segments, and was thickest in the duodenum and ileum. Measurements of the submucosal and serosal layers were not significantly different between all segments. Musc:Ao and Muc:Ao in each segment were 0.12 and 0.25 (gastric fundus), 0.12 and 0.18 (gastric body), 0.11 and 0.16 (pyloric antrum), 0.08 and 0.27 (duodenum), 0.08 and 0.22 (jejunum), 0.14 and 0.25 (ileum), and 0.05 and 0.08 (colon), respectively. Musc:Ao and Muc:Ao are clinically relevant values that can be used to objectively identify thickening of the muscularis and mucosal layers in response to GI diseases. PMID:23906704

  5. Vertically Oriented Growth of GaN Nanorods on Si Using Graphene as an Atomically Thin Buffer Layer.

    PubMed

    Heilmann, Martin; Munshi, A Mazid; Sarau, George; Göbelt, Manuela; Tessarek, Christian; Fauske, Vidar T; van Helvoort, Antonius T J; Yang, Jianfeng; Latzel, Michael; Hoffmann, Björn; Conibeer, Gavin; Weman, Helge; Christiansen, Silke

    2016-06-01

    The monolithic integration of wurtzite GaN on Si via metal-organic vapor phase epitaxy is strongly hampered by lattice and thermal mismatch as well as meltback etching. This study presents single-layer graphene as an atomically thin buffer layer for c-axis-oriented growth of vertically aligned GaN nanorods mediated by nanometer-sized AlGaN nucleation islands. Nanostructures of similar morphology are demonstrated on graphene-covered Si(111) as well as Si(100). High crystal and optical quality of the nanorods are evidenced through scanning transmission electron microscopy, micro-Raman, and cathodoluminescence measurements supported by finite-difference time-domain simulations. Current-voltage characteristics revealed high vertical conduction of the as-grown GaN nanorods through the Si substrates. These findings are substantial to advance the integration of GaN-based devices on any substrates of choice that sustains the GaN growth temperatures, thereby permitting novel designs of GaN-based heterojunction device concepts. PMID:27124605

  6. To determine ice layer thickness of Europa by high energy neutrino

    NASA Astrophysics Data System (ADS)

    Shoji, D.; Kurita, K.; Tanaka, H. K.

    2010-12-01

    Europa, the second closest Galilean satellite is one of the targets which are suspected to have an internal ocean. Detection and characterization of the internal ocean is one of the main subjects for Europa orbiter exploration. Although the gravitational data has shown the thickness of the surface H2O layer of 80-170km[1], it can not determine the phase of H2O. The variations in the magnetic field associated with the induced current in the internal ocean can determine the thickness of the layer of ice if satellite's orbits satisfy the required conditions. Observations of tidal amplitude forced by Jupiter can also resolve the thickness of the surface lithosphere[2]. At moment because of the lack of observational constraints there exist two contrasting models:thick ice layer model and thin model. Here we propose new method to detect the ocean directly based on the radiation by high energy neutrino interacted with matter. Schaefer et al[3] have proposed a similar method to determine ice layer thickness. We will focus on the detection of internal ocean for Europa and present the method is suitable for actual situations of Europa exploration by numerical simulations. Neutrino is famous for its traveling at long distance without any interaction with matter. When high energy neutrinos traverse in Europa hadronic showers are produced by the weak interaction with the nucleons that makes the body of Europa. These hadronic showers induces excess electrons. Because of these excess electrons, Cherenkov photons are emitted. When this radiation occurs in the ice layer, radiations whose wave length is over 10cm should be coherent because the scale of the shower becomes small (a few cm) in the ice, which is called as Askaryan effect[3]. Thus, the intensity of the radiation whose frequency is a few GHz should be enhanced. Since ice has a much longer attenuation length than water, the radiations which occur in the surface ice layer could be detected by the antenna outside Europa but

  7. Investigation of CdZnS Buffer Layers on the Performance of CuInGaSe2 and CuGaSe2 Solar Cells

    SciTech Connect

    Song, J.; Li, S. S.; Chen, L.; Noufi, R.; Anderson, T. J.; Crisalle, O. D.

    2006-01-01

    Cu(In,Ga)Se{sub 2} (CIGS) and CuGaSe{sub 2} (CGS) solar cells were fabricated using Cd{sub 1-x}Zn{sub x}S (CdZnS) buffer layers prepared by chemical bath deposition (CBD) with relative Zn compositions in the CBD bath values of X{sub bath} = 0 (i.e., pure CdS), 0.1, 0.2, 0.3, 0.4, and 0.5. The cell performance parameters of CIGS and CGS films treated with a KCN solution were investigated and compared to cells without KCN treatment. It was found that absorber films treated with KCN etching prior to the buffer CBD step show an improved cell performance for both the CIGS and CGS cells deposited with either CdS or CdZnS buffer layer. A CIGS cell with CdZnS buffer layer of X{sub bath} = 0.2 produced a 13% AM1.5G conversion efficiency with higher V{sub oc}, J{sub sc}, and FF values as compared to the CdZnS/CIGS cells with different Zn contents. Results of photo- J-V and quantum efficiency (QE) measurements reveal that the CGS cell with CdZnS buffer layer of X{sub bath} = 0.3 performed better than the CGS cell deposited with a pure CdS buffer layer. This result is suggested as a result of an increased photocurrent at shorter wavelengths and a more favorable conduction band-offset at the CdZnS/CGS junction.

  8. Determination of the thickness and orientation of few-layer tungsten ditelluride using polarized Raman spectroscopy

    NASA Astrophysics Data System (ADS)

    Kim, Minjung; Han, Songhee; Kim, Jung Hwa; Lee, Jae-Ung; Lee, Zonghoon; Cheong, Hyeonsik

    2016-09-01

    Orthorhombic tungsten ditelluride (WTe2), with a distorted 1T structure, exhibits a large magnetoresistance that depends on the orientation, and its electrical characteristics changes from semimetallic to insulating as the thickness decreases. Through polarized Raman spectroscopy in combination with transmission electron diffraction, we establish a reliable method to determine the thickness and crystallographic orientation of few-layer WTe2. The Raman spectrum shows a pronounced dependence on the polarization of the excitation laser. We found that the separation between two Raman peaks at ∼90 cm‑1 and at 80–86 cm‑1, depending on thickness, is a reliable fingerprint for determination of the thickness. For determination of the crystallographic orientation, the polarization dependence of the A 1 modes, measured with the 632.8 nm excitation, turns out to be the most reliable. We also discovered that the polarization behaviors of some of the Raman peaks depend on the excitation wavelength as well as thickness, indicating a close interplay between the band structure and anisotropic Raman scattering cross section.

  9. Enhancing cell-free layer thickness by bypass channels in a wall.

    PubMed

    Saadatmand, M; Shimogonya, Y; Yamaguchi, T; Ishikawa, T

    2016-07-26

    When blood flows near a wall, red blood cells (RBCs) drift away from the wall and a cell-free layer (CFL) is formed adjacent to the wall. Controlling the CFL thickness is important for preventing adhesion of cells in the design of biomedical devices. In this study, a novel wall configuration with stenoses and bypass channels is proposed to increase the CFL thickness. We found that the presence of bypass channels modified the spatial distribution of cells and substantially increased the CFL downstream of the stenosis. A single-bypass geometry with 5% hematocrit (Hct) blood flow showed a 1.7μm increase in CFL thickness compared to without the bypass. In the case of three bypass channels, a 3μm increase in CFL thickness was observed. The CFL enhancement was observed up to 10% Hct, but no significant enhancement of CFL was indicated for 20% Hct blood flow. The mechanism of the CFL enhancement was investigated using a numerical simulation of the flow field. The results showed that the distance between each streamline and the corner of the stenosis compared with size of RBC was important parameter in regulating CFL thickness. These results show the potential of the proposed mechanism to prevent adhesion of cells to biomedical devices. PMID:26803337

  10. Long wavelength emitting GaInN quantum wells on metamorphic GaInN buffer layers with enlarged in-plane lattice parameter

    SciTech Connect

    Däubler, J. Passow, T.; Aidam, R.; Köhler, K.; Kirste, L.; Kunzer, M.; Wagner, J.

    2014-09-15

    Metamorphic (i.e., linear composition graded) GaInN buffer layers with an increased in-plane lattice parameter, grown by plasma-assisted molecular beam epitaxy, were used as templates for metal organic vapor phase epitaxy (MOVPE) grown GaInN/GaInN quantum wells (QWs), emitting in the green to red spectral region. A composition pulling effect was observed allowing considerable higher growth temperatures for the QWs for a given In composition. The internal quantum efficiency (IQE) of the QWs was determined by temperature and excitation power density dependent photoluminescence (PL) spectroscopy. An increase in IQE by a factor of two was found for green emitting QWs grown on metamorphic GaInN buffer compared to reference samples grown on standard GaN buffer layers. The ratio of room temperature to low temperature intensity PL of the red emitting QWs were found to be comparable to the PL efficiency of green emitting QWs, both grown on metamorphic GaInN buffers. The excitation density and well width dependence of the IQE indicate a reduction of the quantum confined Stark effect upon growth on GaInN buffer layers with increased in-plane lattice parameter.

  11. Quality-enhanced In{sub 0.3}Ga{sub 0.7}As film grown on GaAs substrate with an ultrathin amorphous In{sub 0.6}Ga{sub 0.4}As buffer layer

    SciTech Connect

    Gao, Fangliang; Li, Guoqiang

    2014-01-27

    Using low-temperature molecular beam epitaxy, amorphous In{sub 0.6}Ga{sub 0.4}As layers have been grown on GaAs substrates to act as buffer layers for the subsequent epitaxial growth of In{sub 0.3}Ga{sub 0.7}As films. It is revealed that the crystallinity of as-grown In{sub 0.3}Ga{sub 0.7}As films is strongly affected by the thickness of the large-mismatched amorphous In{sub 0.6}Ga{sub 0.4}As buffer layer. Given an optimized thickness of 2 nm, this amorphous In{sub 0.6}Ga{sub 0.4}As buffer layer can efficiently release the misfit strain between the In{sub 0.3}Ga{sub 0.7}As epi-layer and the GaAs substrate, trap the threading and misfit dislocations from propagating to the following In{sub 0.3}Ga{sub 0.7}As epi-layer, and reduce the surface fluctuation of the as-grown In{sub 0.3}Ga{sub 0.7}As, leading to a high-quality In{sub 0.3}Ga{sub 0.7}As film with competitive crystallinity to that grown on GaAs substrate using compositionally graded In{sub x}Ga{sub 1-x}As metamorphic buffer layers. Considering the complexity of the application of the conventional In{sub x}Ga{sub 1-x}As graded buffer layers, this work demonstrates a much simpler approach to achieve high-quality In{sub 0.3}Ga{sub 0.7}As film on GaAs substrate and, therefore, is of huge potential for the InGaAs-based high-efficiency photovoltaic industry.

  12. On-Line Thickness Measurement for Two-Layer Systems on Polymer Electronic Devices

    PubMed Central

    Grassi, Ana Perez; Tremmel, Anton J.; Koch, Alexander W.; El-Khozondar, Hala J.

    2013-01-01

    During the manufacturing of printed electronic circuits, different layers of coatings are applied successively on a substrate. The correct thickness of such layers is essential for guaranteeing the electronic behavior of the final product and must therefore be controlled thoroughly. This paper presents a model for measuring two-layer systems through thin film reflectometry (TFR). The model considers irregular interfaces and distortions introduced by the setup and the vertical vibration movements caused by the production process. The results show that the introduction of these latter variables is indispensable to obtain correct thickness values. The proposed approach is applied to a typical configuration of polymer electronics on transparent and non-transparent substrates. We compare our results to those obtained using a profilometer. The high degree of agreement between both measurements validates the model and suggests that the proposed measurement method can be used in industrial applications requiring fast and non-contact inspection of two-layer systems. Moreover, this approach can be used for other kinds of materials with known optical parameters. PMID:24253192

  13. Lithospheric strength and its relationship to the elastic and seismogenic layer thickness

    NASA Astrophysics Data System (ADS)

    Watts, A. B.; Burov, E. B.

    2003-08-01

    Plate flexure is a phenomenon that describes how the lithosphere responds to long-term (>105 yr) geological loads. By comparing the flexure in the vicinity of ice, volcano, and sediment loads to predictions based on simple plate models it has been possible to estimate the effective elastic thickness of the lithosphere, Te. In the oceans, Te is the range 2-50 km and is determined mainly by plate and load age. The continents, in contrast, are characterised by Te values of up to 80 km and greater. Rheological considerations based on data from experimental rock mechanics suggest that Te reflects the integrated brittle, elastic and ductile strength of the lithosphere. Te differs, therefore, from the seismogenic layer thickness, Ts, which is indicative of the depth to which anelastic deformation occurs as unstable frictional sliding. Despite differences in their time scales, Te and Ts are similar in the oceans where loading reduces the initial mechanical thickness to values that generally coincide with the thickness of the brittle layer. They differ, however, in continents, which, unlike oceans, are characterised by a multi-layer rheology. As a result, Te≫Ts in cratons, many convergent zones, and some rifts. Most rifts, however, are characterised by a low Te that has been variously attributed to a young thermal age of the rifted lithosphere, thinning and heating at the time of rifting, and yielding due to post-rift sediment loading. Irrespective of their origin, the Wilson cycle makes it possible for low values to be inherited by foreland basins which, in turn, helps explain why similarities between Te and Ts extend beyond rifts into other tectonic regions such as orogenic belts and, occasionally, the cratons themselves.

  14. Thickness-dependent Dielectric Constant of Few-layer In2Se3 Nano-flakes

    NASA Astrophysics Data System (ADS)

    Wu, Di; Pak, Alexander; Liu, Yingnan; Wu, Xiaoyu; Ren, Yuan; Tsai, Yu-Hao; Lin, Min; Peng, Hailin; Hwang, Gyeong; Lai, Keji

    2015-03-01

    The dielectric constant or relative permittivity of active materials in electronic devices is a critical parameter for charging and screening effects. For layered two-dimensional (2D) materials, it is of great interest to understand how their dielectric constants depend on dimensionalities and the arrangement of crystal lattices. Here we present both experimental and theoretical investigations on the dielectric constant of few-layer In2Se3 nano-flakes grown on mica substrates by van der Waals epitaxy. A nondestructive microwave impedance microscope (MIM) is employed to simultaneously quantify the number of layers and local electrical and optical properties. The measured effective dielectric constant increases monotonically as a function of the thickness and saturates to the bulk value at around 6-8 quintuple layers. The same trend of layer-dependent dielectric constant is also revealed through a density functional theory approach. Our results of the dielectric response are expected to be significant for the applications of layered materials in nano-devices.

  15. Impact of silicon epitaxial thickness layer in high power diode devices

    NASA Astrophysics Data System (ADS)

    Mee, Cheh Chai; Arshad, M. K. Md.; Hashim, U.; Fathil, M. F. M.

    2016-07-01

    The p-i-n diode is one of the earliest semiconductor devices developed for power circuit application. It is formed with the intrinsically doped i.e. i-layer sandwiched between the p-type and n-type layers. In this paper, we focus on the integration of the intrinsic region of silicon p-i-n diode to the current-voltage characteristics. In our structure, n-type refers to the bulk substrate and intrinsic region refers to the epitaxial layer of the silicon substrate. We make a thickness variation in the intrinsic region of p-i-n diode and how it affects diode performance. An additional layer is added on the epitaxial layer during the process to control the diffusion from the bottom of bulk substrate. Result shows that intrinsic layer optimization has successfully enhances the diode device robustness in terms of diode current-voltage characteristics, which reflects better manufacturing yield and improve the final product performance.

  16. High Cubic-Phase Purity InN on MgO (001) Using Cubic-Phase GaN as a Buffer Layer

    SciTech Connect

    Sanorpim, S.; Kuntharin, S.; Parinyataramas, J.; Yaguchi, H.; Iwahashi, Y.; Orihara, M.; Hijikata, Y.; Yoshida, S.

    2011-12-23

    High cubic-phase purity InN films were grown on MgO (001) substrates by molecular beam epitaxy with a cubic-phase GaN buffer layer. The cubic phase purity of the InN grown layers has been analyzed by high resolution X-ray diffraction, {mu}-Raman scattering and transmission electron microscopy. It is evidenced that the hexagonal-phase content in the InN overlayer much depends on hexagonal-phase content in the cubic-phase GaN buffer layer and increases with increasing the hexagonal-phase GaN content. From Raman scattering measurements, in addition, the InN layer with lowest hexagonal component (6%), only Raman characteristics of cubic TO{sub InN} and LO{sub InN} modes were observed, indicating a formation of a small amount of stacking faults, which does not affect on vibrational property.

  17. Improved dielectric properties of lead zirconate titanate thin films deposited on metal foils with LaNiO3 buffer layers

    NASA Astrophysics Data System (ADS)

    Zou, Q.; Ruda, H. E.; Yacobi, B. G.

    2001-02-01

    Improved dielectric properties of lead zirconate titanate (PZT) films deposited on a variety of foils using buffer layers are reported. Foils include titanium, stainless steel, and nickel with LaNiO3(LNO) buffer layers which were prepared by sol-gel processing. High dielectric constant (330 for stainless steel, 420 for titanium, and 450 for nickel foils), low dielectric loss (<2.2% for titanium and 8% for stainless steel), symmetric ferroelectric C-V characteristics and P-E curves were obtained. The LNO layers are shown to provide an effective diffusion barrier for Ni and Cr and to restrict oxide layer formation (i.e., TiOx or NiOx) between the PZT film and the metallic foils during annealing in air.

  18. Attenuation Tomography of Body Waves in Thickness-varying Layered Media

    NASA Astrophysics Data System (ADS)

    Cao, H.; Zhou, H.

    2006-12-01

    The intrinsic attenuation of seismic waves, which is quantified as inverse to the quality factor (Q) of a medium, is a well-publicized and yet poorly studied subject. While it is common to deduce Q values from measured dispersion data for surface waves, previous studies on the intrinsic attenuation of body waves have relied on measurements of the waveform of first arrivals or reflections. Better understanding is needed for both solid Earth geophysics and applied seismology to quantify the contributing factors to seismic attenuation and decompose Q from other factors because Q is closely related to rock property and fluid saturation. This study focuses on forward modeling and tomographic inversion for the Q values in thickness-varying layered media. Many of the existing theoretical Q models work in such media. Our work is an extension of the deformable- layer tomography (Zhou, 2004) to dissipative media. In the first phase of this study, we evaluated, through numerical modeling the various factors contributing to the attenuation of body waves. Theoretically, there are intrinsic attenuation, which is related to rock and pore fluid properties, and attenuation due to wave propagation effects, such as geometrical spreading and energy partition across interfaces (transmission and reflection). We made several representative numerical models, and conducted forward modeling using both wave theory and ray theory to quantify the amount of the attenuation of body waves due to different factors. In the second phase, we are integrating the forward modeling with the deformable-layer tomography algorithm to develop means to invert for Q distribution in thickness-varying layer media. While the deformable-layer tomography determines layer velocities and geometry, the current work intends to invert for Q values of the thickness-varying model layers as well as parameters associated with interface energy partition and geometric spreading. In the third phase, we plan to apply the

  19. Optical quantification of epithelial layer thickness as a measure of oral inflammation

    NASA Astrophysics Data System (ADS)

    Hattery, David W.; Hattery, Brenda; Hassan, Moinuddin; Chernomordik, Victor V.; Vogel, Abby; Hekmat, Farid; Gandjbakhche, Amir H.

    2003-06-01

    For individuals with cancer risk factors, reducing tissue inflammation may reduce the risk of developing cancer. This is the basis of several clinical trials evaluating potential chemoprevention drugs. These trials require quantitative assessments of inflammation which, for the oral epithelium, are traditionally provided by punch biopsies. To reduce patient discomfort and morbidity, we have developed a non-invasive alternative using diffuse reflectance spectroscopy. Though any optical system has the potential for probing near-surface structures, traditional methods of accounting for scattering of photons are generally invalid for typical epithelial thicknesses. We have previously developed a theory that is valid in this regime and validated it with Monte Carlo simulations. We use a differential measure with acute sensitivity to small changes in layer scattering coefficients. To assess the capability of the approach to quantify epithelial thickness, detailed Monte Carlo simulations and measurements on phantom models of a two layered structure have been performed. Preliminary results from this work show that our key feature varies less than 20 percent despite four-fold changes in scattering coefficients and ten-fold changes in absorption coefficients. This indicates that the method will be of practical clinical value for quantifying epithelial thickness in vivo.

  20. Superconducting layer thickness dependence of magnetic relaxation property in CVD processed YGdBCO coated conductors

    NASA Astrophysics Data System (ADS)

    Takahashi, Y.; Kiuchi, M.; Otabe, E. S.; Matsushita, T.; Shikimachi, K.; Watanabe, T.; Kashima, N.; Nagaya, S.

    2011-11-01

    One of the most important properties of coated conductors for Superconducting Magnetic Energy Storage (SMES) is the relaxation property of persistent superconducting current. This property can be quantitatively characterized by the apparent pinning potential U0∗. In this paper, the dependence of U0∗ on the thickness of superconducting layer d is investigated in the range of 0.33-1.43 μm at the temperature range of 20-30 K and in magnetic fields up to 6.5 T for Y 0.7Gd 0.3Ba 2Cu 3O 7- δ coated conductors. It was found that the value of critical current density did not appreciably depend on d at 20 K. This indicates that no structural deterioration of superconducting layer occurs during the process of increasing thickness. U0∗ increases and then tends to decrease with an increasing magnetic field. The magnetic field at which U0∗ starts to decrease increases with increasing thickness. This property was analyzed using the flux creep-flow model. Application of scaling law is examined for the dependence of U0∗ on magnetic field and temperature. It was found that the dependence could be expressed using scaling parameters B,U0 peak∗ in the temperature range 20-30 K.

  1. Quantifying the Distribution and Landscape Controls of Peatlands and Organic Layer Thickness within Alaska

    NASA Astrophysics Data System (ADS)

    Wylie, B. K.; Pastick, N.; Jorgenson, T.; Nield, S.; Johnson, K. D.

    2014-12-01

    The northern circumpolar region is estimated to contain 50 % of the global belowground carbon pool and is experiencing climate change at rates higher than anywhere else globally. Surface organic horizons associated with these immense carbon pools are important to ecosystem functioning in terms of soil moisture and temperature regulations, permafrost degradation, successional trajectories, and soil respiration levels. However, fire-induced changes to surface organics and their distribution are poorly understood, especially on landscape scales. These ambiguities make future predictions uncertain for these significant carbon pools, which have the potential for significant feedbacks to global warming. Moreover, given the significant impacts and increasing severity and amount of fires in boreal systems, the spatial quantification of post-fire surface organic thickness is important for ecosystem model calibrations and comparisons, and can improve future projections of vegetation types and albedo, carbon stocks and fluxes, and future thaw depths. Here we present the results of pioneering studies that quantified the distribution and controls of peatlands and soil organic layer thickness in Alaska through the use of statistical models, field data, spatial analyses, and remote sensing (Landsat). Our empirical modeling approach enabled us to produce medium-resolution (30-m pixels) maps of peatlands and organic layer thickness throughout Alaska, which is important for land management practices and enhances the understanding of the risk and feedbacks associated with fires and climate feedbacks.

  2. Weakly nonlinear Rayleigh-Taylor instability of a finite-thickness fluid layer

    SciTech Connect

    Wang, L. F. Ye, W. H. Liu, Jie; He, X. T.; Guo, H. Y.; Wu, J. F. Zhang, W. Y.

    2014-12-15

    A weakly nonlinear (WN) model has been developed for the Rayleigh-Taylor instability of a finite-thickness incompressible fluid layer (slab). We derive the coupling evolution equations for perturbations on the (upper) “linearly stable” and (lower) “linearly unstable” interfaces of the slab. Expressions of temporal evolutions of the amplitudes of the perturbation first three harmonics on the upper and lower interfaces are obtained. The classical feedthrough (interface coupling) solution obtained by Taylor [Proc. R. Soc. London A 201, 192 (1950)] is readily recovered by the first-order results. Our third-order model can depict the WN perturbation growth and the saturation of linear (exponential) growth of the perturbation fundamental mode on both interfaces. The dependence of the WN perturbation growth and the slab distortion on the normalized layer thickness (kd) is analytically investigated via the third-order solutions. Comparison is made with Jacobs-Catton's formula [J. W. Jacobs and I. Catton, J. Fluid Mech. 187, 329 (1988)] of the position of the “linearly unstable” interface. Using a reduced formula, the saturation amplitude of linear growth of the perturbation fundamental mode is studied. It is found that the finite-thickness effects play a dominant role in the WN evolution of the slab, especially when kd < 1. Thus, it should be included in applications where the interface coupling effects are important, such as inertial confinement fusion implosions and supernova explosions.

  3. Impact of CoFe buffer layers on the structural and electronic properties of the Co2MnSi/MgO interface

    NASA Astrophysics Data System (ADS)

    Fetzer, Roman; Liu, Hong-xi; Stadtmüller, Benjamin; Uemura, Tetsuya; Yamamoto, Masafumi; Aeschlimann, Martin; Cinchetti, Mirko

    2016-05-01

    The latest improvement of MgO-based magnetic tunnel junctions has been achieved by the combination of CoFe buffer layers and potentially half-metallic ultrathin Co2MnSi electrodes. By this, tunnel magnetoresistance ratios of almost 2000% could be obtained. However, a complete understanding of the underlying processes leading to this enhancement is not yet given. We present a comprehensive study regarding the structural and electronic spin properties of the CoFe(30 nm)-buffered Co2MnSi(3 nm)/MgO(2 nm) buried interface identical to the one formed in actual devices. Low energy electron diffraction experiments show that the ultrathin Co2MnSi layer adopts the lattice constant of the underlying CoFe buffer layer, leading to improved structural conditions at the interface to MgO. In contrast, the Co2MnSi/MgO interface spin polarization at the Fermi level is not affected by the magnetic CoFe buffer layer, as found by interface-sensitive spin-resolved extremely low energy photoemission spectroscopy.

  4. High-power SiC MESFET using a dual p-buffer layer for an S-band power amplifier

    NASA Astrophysics Data System (ADS)

    Deng, Xiao-Chuan; Sun, He; Rao, Cheng-Yuan; Zhang, Bo

    2013-01-01

    A silicon carbide (SiC) based metal semiconductor field effect transistor (MESFET) is fabricated by using a standard SiC MESFET structure with the application of a dual p-buffer layer and a multi-recessed gate to the process for an S-band power amplifier. The lower doped upper-buffer layer serves to maintain the channel current, while the higher doped lower-buffer layer is used to provide excellent electron confinement in the channel layer. A 20-mm gate periphery SiC MESFET biased at a drain voltage of 85 V demonstrates a pulsed wave saturated output power of 94 W, a linear gain of 11.7 dB, and a maximum power added efficiency of 24.3% at 3.4 GHz. These results are improved compared with those of the conventional single p-buffer MESFET fabricated in this work using the same process. A radio-frequency power output greater than 4.7 W/mm is achieved, showing the potential as a high-voltage operation device for high-power solid-state amplifier applications.

  5. Decreased retinal nerve fiber layer thickness in patients with obstructive sleep apnea syndrome

    PubMed Central

    Sun, Cheng-Lin; Zhou, Li-Xiao; Dang, Yalong; Huo, Yin-Ping; Shi, Lei; Chang, Yong-Jie

    2016-01-01

    Abstract Objective: To investigate the changes of retinal nerve fiber layer (RNFL) thickness in obstructive sleep apnea syndrome (OSAS) patients. Methods: Relevant studies were selected from 3 major literature databases (PubMed, Cochrane Library, and EMBASE) without language restriction. Main inclusion criteria is that a case-control study in which RNFL thickness was measured by a commercial available optical coherence tomography (OCT) in OSAS patients. Meta-analysis was performed using STATA 12.0 software. Efficacy estimates were evaluated by weighted mean difference with corresponding 95% confidence intervals (CIs). Primary outcome evaluations were: the average changes of RNFL thickness in total OSAS patients, subgroup analysis of RNFL thickness changes in patients of different OSAS stages, and subgroup analysis of 4-quadrant RNFL thickness changes in total OSAS patients. Results: Of the initial 327 literatures, 8 case-control studies with 763 eyes of OSA patients and 474 eyes of healthy controls were included (NOS scores ≥6). For the people of total OSAS, there had an average 2.92 μm decreased RNFL thickness compared with controls (95% CI: −4.61 to −1.24, P = 0.001). For subgroup analysis of OSAS in different stages, the average changes of RNFL thickness in mild, moderate, severe, and moderate to severe OSAS were 2.05 (95% CI: −4.40 to 0.30, P = 0.088), 2.32 (95% CI: −5.04 to 0.40, P = 0.094), 4.21 (95% CI: −8.36 to −0.06, P = 0.047), and 4.02 (95% CI: −7.65 to −0.40, P = 0.03), respectively. For subgroup analysis of 4-quadrant, the average changes of RNFL thickness in Superior, Nasal, Inferior, and Temporal quadrant were 2.43 (95% CI: −4.28 to −0.57, P = 0.01), 1.41 (95% CI: −3.33 to 0.51, P = 0.151), 3.75 (95% CI: −6.92 to −0.59, P = 0.02), and 0.98 (95% CI: −2.49 to 0.53, P = 0.203), respectively. Conclusion: Our study suggests that RNFL thickness in OSAS patients is much thinner than

  6. The Correlation of Retinal Nerve Fiber Layer Thickness With Blood Pressure in a Chinese Hypertensive Population

    PubMed Central

    Gangwani, Rita A.; Lee, Jacky W.Y.; Mo, H.Y.; Sum, Rita; Kwong, Alfred S.K.; Wang, Jenny H.L.; Tsui, Wendy W.S.; Chan, Jonathan C.H.; Lai, Jimmy S.M.

    2015-01-01

    Abstract To investigate the association between retinal nerve fiber layer (RNFL) thickness and blood pressure (BP) in subjects with systemic hypertension. Subjects with systemic hypertension on anti-hypertensive medications were screened by fundus photography and referred for glaucoma work-up if there was enlarged vertical cup-to-disc (VCDR) ratio ≥0.6, VCDR asymmetry ≥0.2, or optic disc hemorrhage. Workup included a complete ophthalmological examination, Humphrey visual field test, and RNFL thickness measurement by optical coherence tomography. The intraocular pressure (IOP) and RNFL thicknesses (global and quadrant) were averaged from both eyes and the means were correlated with: the systolic BP (SBP), diastolic BP (DBP), and mean arterial pressure (MAP) using Pearson correlation. Among 4000 screened hypertensive subjects, 133 were referred for glaucoma workup and 110 completed the workup. Of the 4000 screened subjects, 1.3% had glaucoma (0.9% had normal tension glaucoma [NTG], 0.2% had primary open angle glaucoma, and 0.2% had primary angle closure glaucoma), whereas 0.3% were NTG suspects. The SBP was negatively correlated with the mean superior RNFL thickness (P = 0.01). The DBP was negatively correlated with the mean global (P = 0.03), superior (P = 0.02), and nasal (P = 0.003) RNFL thickness. The MAP was negatively correlated with the mean global (P = 0.01), superior (P = 0.002), and nasal (P = 0.004) RNFL thickness while positively correlated with the mean IOP (P = 0.02). In medically treated hypertensive subjects, glaucoma was present in 1.3%, with NTG being most prevalent. MAP control may help with IOP lowering and RNFL preservation, although future prospective studies will be needed. PMID:26061324

  7. Electrocaloric properties of ferroelectric-paraelectric superlattices controlled by the thickness of paraelectric layer in a wide temperature range

    SciTech Connect

    Ma, D. C.; Lin, S. P.; Chen, W. J.; Zheng, Yue Xiong, W. M.; Wang, Biao

    2014-10-15

    As functions of the paraelectric layer thickness, misfit strain and temperature, the electrocaloric properties of ferroelectric-paraelectric superlattices are investigated using a time-dependent Ginzburg-Landau thermodynamic model. Ferroelectric phase transition driven by the relative thickness of the superlattice is found to dramatically impact the electrocaloric response. Near the phase transition temperature, the magnitude of the electrocaloric effect is maximized and shifted to lower temperatures by increasing the relative thickness of paraelectric layer. Theoretical calculations also imply that the electrocaloric effect of the superlattices depends not only on the relative thickness of paraelectric layer but also on misfit strain. Furthermore, control of the relative thickness of paraelectric layer and the misfit strain can change availably both the magnitude and the temperature sensitivity of the electrocaloric effect, which suggests that ferroelectric-paraelectric superlattices may be promising candidates for use in cooling devices in a wide temperature range.

  8. Thickness-dependent electron mobility of single and few-layer MoS2 thin-film transistors

    NASA Astrophysics Data System (ADS)

    Kim, Ji Heon; Kim, Tae Ho; Lee, Hyunjea; Park, Young Ran; Choi, Woong; Lee, Cheol Jin

    2016-06-01

    We investigated the dependence of electron mobility on the thickness of MoS2 nanosheets by fabricating bottom-gate single and few-layer MoS2 thin-film transistors with SiO2 gate dielectrics and Au electrodes. All the fabricated MoS2 transistors showed on/off-current ratio of ˜107 and saturated output characteristics without high-k capping layers. As the MoS2 thickness increased from 1 to 6 layers, the field-effect mobility of the fabricated MoS2 transistors increased from ˜10 to ˜18 cm2V-1s-1. The increased subthreshold swing of the fabricated transistors with MoS2 thickness suggests that the increase of MoS2 mobility with thickness may be related to the dependence of the contact resistance and the dielectric constant of MoS2 layer on its thickness.

  9. The effects of ultraviolet-ozone-treated ultra-thin MnO-doped ZnO film as anode buffer layer on the electrical characteristics of organic light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Lu, Hsin-Wei; Kao, Po-Ching; Juang, Yung-Der; Chu, Sheng-Yuan

    2015-11-01

    In this study, the efficiency of organic light-emitting diodes (OLEDs) was enhanced by depositing an MnO-doped ZnO film as a buffer layer between the indium tin oxide (ITO) electrode and the α-naphthylphenylbiphenyldiamine hole transport layer. The enhancement mechanism was systematically investigated, and the X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy results revealed the formation of the UV-ozone-treated MnO-doped ZnO film. With this film, the work function increased from 4.8 eV (standard ITO electrode (˜ 10 ±5 Ω/◻ )) to 5.27 eV (UV-ozone-treated MnO-doped ZnO deposited on the ITO electrode with 1 wt. % for 1 nm), while the surface roughness of the UV-ozone-treated MnO-doped ZnO film was smoother than that of the ITO electrode. The deposited UV-ozone-treated MnO-doped ZnO film increased the surface energy and polarity of the ITO surface, as determined from contact angle measurements. Further, results from admittance spectroscopy showed that the inserted UV-ozone-treated MnO-doped ZnO film increased the capacitance and conductance of the OLEDs. It was also found that the carrier injection increased in the space-charge region when the UV-ozone-treated MnO-doped ZnO buffer layer was inserted. Moreover, the turn-on voltage of the devices decreased from 3.8 V to 3.2 V, the luminance increased from 7588 cd/m2 to 20 350 cd/m2, and the current efficiency increased from 3.2 cd/A to 5.8 cd/A when a 1 nm-thick UV-ozone-treated MnO-doped ZnO film with 1 wt. % was inserted as a buffer layer in the OLEDs.

  10. Is Retinal Nerve Fiber Layer Thickness Change Related to Headache Lateralization in Migraine?

    PubMed Central

    Demirci, Seden; Tok, Levent; Tok, Ozlem; Demirci, Serpil; Kutluhan, Süleyman

    2016-01-01

    Purpose To evaluate retinal nerve fiber layer (RNFL) thickness in migraine patients with unilateral headache. Methods A total of 58 patients diagnosed with migraine headache consistently occurring on the same side and 58 age- and sex-matched healthy subjects were evaluated in this cross-sectional study. RNFL thickness was measured using spectral-domain optical coherence tomography, and the side with the headache was com-pared with the contralateral side as well as with the results of healthy subjects. Results The mean patient age was 33.05 ± 8.83 years, and that of the healthy subjects was 31.44 ± 8.64 years (p = 0.32). The mean duration of disease was 10.29 ± 9.03 years. The average and nasal RNFL thicknesses were significantly thinner on the side of headache and on the contralateral side compared to control eyes (p < 0.05, for all). Thinning was higher on the side of the headache compared to the contralateral side; however, this difference was not statistically significant. Conclusions The RNFL thicknesses were thinner on the side of the headache compared to the contralateral side in the migraine patients with unilateral headache, but this difference was not statistically significant. PMID:27051262

  11. Thickness Effect of Al-Doped ZnO Window Layer on Damp-Heat Stability of CuInGaSe2 Solar Cells

    SciTech Connect

    Pern, F. J.; Mansfield, L.; DeHart, C.; Glick, S. H.; Yan, F.; Noufi, R.

    2011-01-01

    We investigated the damp heat (DH) stability of CuInGaSe{sub 2} (CIGS) solar cells as a function of thickness of the Al-doped ZnO (AZO) window layer from the 'standard' 0.12 {micro}m to a modest 0.50 {micro}m over an underlying 0.10-{micro}m intrinsic ZnO buffer layer. The CIGS cells were prepared with external electrical contact using fine Au wire to the tiny 'standard' Ni/Al (0.05 {micro}m/3 {micro}m) metal grid contact pads. Bare cell coupons and sample sets encapsulated in a specially designed, Al-frame test structure with an opening for moisture ingress control using a TPT backsheet were exposed to DH at 85 C and 85% relative humidity, and characterized by current-voltage (I-V), quantum efficiency (QE), and (electrochemical) impedance spectroscopy (ECIS). The results show that bare cells exhibited rapid degradation within 50-100 h, accompanied by film wrinkling and delamination and corrosion of Mo and AlNi grid, regardless of AZO thickness. In contrast, the encapsulated cells did not show film wrinkling, delamination, and Mo corrosion after 168 h DH exposure; but the trend of efficiency degradation rate showed a weak correlation to the AZO thickness.

  12. Thickness Effect of Al-Doped ZnO Window Layer on Damp Heat Stability of CuInGaSe2 Solar Cells: Preprint

    SciTech Connect

    Pern, F. J.; Mansfield, L.; DeHart, C.; Glick, S. H.; Yan, F.; Noufi, R.

    2011-07-01

    We investigated the damp heat (DH) stability of CuInGaSe2 (CIGS) solar cells as a function of thickness of the Al-doped ZnO (AZO) window layer from the 'standard' 0.12 μm to a modest 0.50 μm over an underlying 0.10-μm intrinsic ZnO buffer layer. The CIGS cells were prepared with external electrical contact using fine Au wire to the tiny 'standard' Ni/Al (0.05 μm/3 μm) metal grid contact pads. Bare cell coupons and sample sets encapsulated in a specially designed, Al-frame test structure with an opening for moisture ingress control using a TPT backsheet were exposed to DH at 85oC and 85% relative humidity, and characterized by current-voltage (I-V), quantum efficiency (QE), and (electrochemical) impedance spectroscopy (ECIS). The results show that bare cells exhibited rapid degradation within 50-100 h, accompanied by film wrinkling and delamination and corrosion of Mo and AlNi grid, regardless of AZO thickness. In contrast, the encapsulated cells did not show film wrinkling, delamination, and Mo corrosion after 168 h DH exposure; but the trend of efficiency degradation rate showed a weak correlation to the AZO thickness.

  13. A metal-oxide-semiconductor radiation dosimeter with a thick and defect-rich oxide layer

    NASA Astrophysics Data System (ADS)

    Liu, Hongrui; Yang, Yuhao; Zhang, Jinwen

    2016-04-01

    Enhancing the density of defects in the oxide layer is the main factor in improving the sensitivity of a metal-oxide-semiconductor (MOS) radiation dosimeter. This paper reports a novel MOS dosimeter with a very thick and defect-rich oxide layer fabricated by MEMS technology. The category of defects in SiO2 and their possible effect on the radiation dose sensing was analyzed. Then, we proposed combining deep-reactive-ion etching, thermal oxidation and low pressure chemical vapor deposition to realize an oxide layer containing multiple and large interfaces which can increase defects significantly. The trench-and-beam structure of silicon was considered in detail. The fabrication process was developed for obtaining a thick and compact MEMS-made SiO2. Our devices were irradiated by γ-rays of 60Co at 2 Gy per minute for 2 h and a thermally stimulated current (TSC) method was used to determine the readout of the dosimeters. Results show that there is a peak current of about 450 nA, indicating a total TSC charge of 158 μC and sensitivity of 1.1 μC mm-3·Gy, which is 40 times the sensitivity of previous MOS dosimeters.

  14. Anisotropic structural and optical properties of semi-polar (11–22) GaN grown on m-plane sapphire using double AlN buffer layers

    PubMed Central

    Zhao, Guijuan; Wang, Lianshan; Yang, Shaoyan; Li, Huijie; Wei, Hongyuan; Han, Dongyue; Wang, Zhanguo

    2016-01-01

    We report the anisotropic structural and optical properties of semi-polar (11–22) GaN grown on m-plane sapphire using a three-step growth method which consisted of a low temperature AlN buffer layer, followed by a high temperature AlN buffer layer and GaN growth. By introducing double AlN buffer layers, we substantially improve the crystal and optical qualities of semi-polar (11–22) GaN, and significantly reduce the density of stacking faults and dislocations. The high resolution x-ray diffraction measurement revealed that the in-plane anisotropic structural characteristics of GaN layer are azimuthal dependent. Transmission electron microscopy analysis showed that the majority of dislocations in the GaN epitaxial layer grown on m-sapphire are the mixed-type and the orientation of GaN layer was rotated 58.4° against the substrate. The room temperature photoluminescence (PL) spectra showed the PL intensity and wavelength have polarization dependence along parallel and perpendicular to the [1–100] axis (polarization degrees ~ 0.63). The realization of a high polarization semi-polar GaN would be useful to achieve III-nitride based lighting emission device for displays and backlighting. PMID:26861595

  15. Anisotropic structural and optical properties of semi-polar (11-22) GaN grown on m-plane sapphire using double AlN buffer layers

    NASA Astrophysics Data System (ADS)

    Zhao, Guijuan; Wang, Lianshan; Yang, Shaoyan; Li, Huijie; Wei, Hongyuan; Han, Dongyue; Wang, Zhanguo

    2016-02-01

    We report the anisotropic structural and optical properties of semi-polar (11-22) GaN grown on m-plane sapphire using a three-step growth method which consisted of a low temperature AlN buffer layer, followed by a high temperature AlN buffer layer and GaN growth. By introducing double AlN buffer layers, we substantially improve the crystal and optical qualities of semi-polar (11-22) GaN, and significantly reduce the density of stacking faults and dislocations. The high resolution x-ray diffraction measurement revealed that the in-plane anisotropic structural characteristics of GaN layer are azimuthal dependent. Transmission electron microscopy analysis showed that the majority of dislocations in the GaN epitaxial layer grown on m-sapphire are the mixed-type and the orientation of GaN layer was rotated 58.4° against the substrate. The room temperature photoluminescence (PL) spectra showed the PL intensity and wavelength have polarization dependence along parallel and perpendicular to the [1-100] axis (polarization degrees ~ 0.63). The realization of a high polarization semi-polar GaN would be useful to achieve III-nitride based lighting emission device for displays and backlighting.

  16. Anisotropic structural and optical properties of semi-polar (11-22) GaN grown on m-plane sapphire using double AlN buffer layers.

    PubMed

    Zhao, Guijuan; Wang, Lianshan; Yang, Shaoyan; Li, Huijie; Wei, Hongyuan; Han, Dongyue; Wang, Zhanguo

    2016-01-01

    We report the anisotropic structural and optical properties of semi-polar (11-22) GaN grown on m-plane sapphire using a three-step growth method which consisted of a low temperature AlN buffer layer, followed by a high temperature AlN buffer layer and GaN growth. By introducing double AlN buffer layers, we substantially improve the crystal and optical qualities of semi-polar (11-22) GaN, and significantly reduce the density of stacking faults and dislocations. The high resolution x-ray diffraction measurement revealed that the in-plane anisotropic structural characteristics of GaN layer are azimuthal dependent. Transmission electron microscopy analysis showed that the majority of dislocations in the GaN epitaxial layer grown on m-sapphire are the mixed-type and the orientation of GaN layer was rotated 58.4° against the substrate. The room temperature photoluminescence (PL) spectra showed the PL intensity and wavelength have polarization dependence along parallel and perpendicular to the [1-100] axis (polarization degrees ~ 0.63). The realization of a high polarization semi-polar GaN would be useful to achieve III-nitride based lighting emission device for displays and backlighting. PMID:26861595

  17. UV-ozone-treated MoO3 as the hole-collecting buffer layer for high-efficiency solution-processed SQ:PC71BM photovoltaic devices

    NASA Astrophysics Data System (ADS)

    Yang, Qian-Qian; Yang, Dao-Bin; Zhao, Su-Ling; Huang, Yan; Xu, Zheng; Gong, Wei; Fan, Xing; Liu, Zhi-Fang; Huang, Qing-Yu; Xu, Xu-Rong

    2014-03-01

    The enhanced performance of a squaraine compound, with 2,4-bis[4-(N,N-diisobutylamino)-2,6-dihydroxyphenyl] squaraine as the donor and [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) as the acceptor, in solution-processed organic photovoltaic devices is obtained by using UV-ozone-treated MoO3 as the hole-collecting buffer layer. The optimized thickness of the MoO3 layer is 8 nm, at which the device shows the best power conversion efficiency (PCE) among all devices, resulting from a balance of optical absorption and charge transport. After being treated by UV-ozone for 10 min, the transmittance of the MoO3 film is almost unchanged. Atomic force microscopy results show that the treated surface morphology is improved. A high PCE of 3.99% under AM 1.5 G illumination (100 mW/cm2) is obtained.

  18. Thickness-Dependent Dielectric Constant of Few-Layer In₂Se₃ Nanoflakes.

    PubMed

    Wu, Di; Pak, Alexander J; Liu, Yingnan; Zhou, Yu; Wu, Xiaoyu; Zhu, Yihan; Lin, Min; Han, Yu; Ren, Yuan; Peng, Hailin; Tsai, Yu-Hao; Hwang, Gyeong S; Lai, Keji

    2015-12-01

    The dielectric constant or relative permittivity (ε(r)) of a dielectric material, which describes how the net electric field in the medium is reduced with respect to the external field, is a parameter of critical importance for charging and screening in electronic devices. Such a fundamental material property is intimately related to not only the polarizability of individual atoms but also the specific atomic arrangement in the crystal lattice. In this Letter, we present both experimental and theoretical investigations on the dielectric constant of few-layer In2Se3 nanoflakes grown on mica substrates by van der Waals epitaxy. A nondestructive microwave impedance microscope is employed to simultaneously quantify the number of layers and local electrical properties. The measured ε(r) increases monotonically as a function of the thickness and saturates to the bulk value at around 6-8 quintuple layers. The same trend of layer-dependent dielectric constant is also revealed by first-principles calculations. Our results of the dielectric response, being ubiquitously applicable to layered 2D semiconductors, are expected to be significant for this vibrant research field. PMID:26575786

  19. The impact of layer thickness on the performance of additively manufactured lapping tools

    NASA Astrophysics Data System (ADS)

    Williams, Wesley B.

    2015-10-01

    Lower cost additive manufacturing (AM) machines which have emerged in recent years are capable of producing tools, jigs, and fixtures that are useful in optical fabrication. In particular, AM tooling has been shown to be useful in lapping glass workpieces. Various AM machines are distinguished by the processes, materials, build times, and build resolution they provide. This research investigates the impact of varied build resolution (specifically layer resolution) on the lapping performance of tools built using the stereolithographic assembly (SLA) process in 50 μm and 100 μm layer thicknesses with a methacrylate photopolymer resin on a high resolution desktop printer. As with previous work, the lapping tools were shown to remove workpiece material during the lapping process, but the tools themselves also experienced significant wear on the order of 2-3 times the mass loss of the glass workpieces. The tool wear rates for the 100 μm and 50 μm layer tools were comparable, but the 50 μm layer tool was 74% more effective at removing material from the glass workpiece, which is attributed to some abrasive particles being trapped in the coarser surface of the 100 um layer tooling and not being available to interact with the glass workpiece. Considering the tool wear, these additively manufactured tools are most appropriate for prototype tooling where the low cost (<$45) and quick turnaround make them attractive when compared to a machined tool.

  20. Atmospheric pressure spatial atomic layer deposition web coating with in situ monitoring of film thickness

    SciTech Connect

    Yersak, Alexander S.; Lee, Yung C.; Spencer, Joseph A.; Groner, Markus D.

    2014-01-15

    Spectral reflectometry was implemented as a method for in situ thickness monitoring in a spatial atomic layer deposition (ALD) system. Al{sub 2}O{sub 3} films were grown on a moving polymer web substrate at 100 °C using an atmospheric pressure ALD web coating system, with film growth of 0.11–0.13 nm/cycle. The modular coating head design and the in situ monitoring allowed for the characterization and optimization of the trimethylaluminum and water precursor exposures, purge flows, and web speed. A thickness uniformity of ±2% was achieved across the web. ALD cycle times as low as 76 ms were demonstrated with a web speed of 1 m/s and a vertical gap height of 0.5 mm. This atmospheric pressure ALD system with in situ process control demonstrates the feasibility of low-cost, high throughput roll-to-roll ALD.

  1. Influences and interactions of inundation, peat, and snow on active layer thickness: Modeling Archive

    DOE Data Explorer

    Scott Painter; Ethan Coon; Cathy Wilson; Dylan Harp; Adam Atchley

    2016-04-21

    This Modeling Archive is in support of an NGEE Arctic publication currently in review [4/2016]. The Advanced Terrestrial Simulator (ATS) was used to simulate thermal hydrological conditions across varied environmental conditions for an ensemble of 1D models of Arctic permafrost. The thickness of organic soil is varied from 2 to 40cm, snow depth is varied from approximately 0 to 1.2 meters, water table depth was varied from -51cm below the soil surface to 31 cm above the soil surface. A total of 15,960 ensemble members are included. Data produced includes the third and fourth simulation year: active layer thickness, time of deepest thaw depth, temperature of the unfrozen soil, and unfrozen liquid saturation, for each ensemble member. Input files used to run the ensemble are also included.

  2. Highly accurate thickness measurement of multi-layered automotive paints using terahertz technology

    NASA Astrophysics Data System (ADS)

    Krimi, Soufiene; Klier, Jens; Jonuscheit, Joachim; von Freymann, Georg; Urbansky, Ralph; Beigang, René

    2016-07-01

    In this contribution, we present a highly accurate approach for thickness measurements of multi-layered automotive paints using terahertz time domain spectroscopy in reflection geometry. The proposed method combines the benefits of a model-based material parameters extraction method to calibrate the paint coatings, a generalized Rouard's method to simulate the terahertz radiation behavior within arbitrary thin films, and the robustness of a powerful evolutionary optimization algorithm to increase the sensitivity of the minimum thickness measurement limit. Within the framework of this work, a self-calibration model is introduced, which takes into consideration the real industrial challenges such as the effect of wet-on-wet spray in the painting process.

  3. An evaluation of phase separated, self-assembled LaMnO3-MgO nanocomposite films directly on IBAD-MgO as buffer layers for flux pinning enhancements in YBa2YCu3O7-& coated conductors

    SciTech Connect

    Polat, Ozgur; Aytug, Tolga; Paranthaman, Mariappan Parans; Leonard, Keith J; Lupini, Andrew R; Pennycook, Stephen J; Meyer III, Harry M; Kim, Kyunghoon; Qiu, Xiaofeng; Cook, Sylvester W; Thompson, James R; Christen, David K; Goyal, Amit; Selvamanickam, V.; Xiong, X.

    2010-01-01

    Technological applications of high temperature superconductors (HTS) require high critical current density, Jc, under operation at high magnetic field strengths. This requires effective flux pinning by introducing artificial defects through creative processing. In this work, we evaluated the feasibility of mixed-phase LaMnO3:MgO (LMO:MgO) films as a potential cap buffer layer for the epitaxial growth and enhanced performance of YBa2Cu3O7-d (YBCO) films. Such composite films were sputter deposited directly on IBAD-MgO templates (with no additional homo-epitaxial MgO layer) and revealed the formation of two phase-separated, but at the same time vertically aligned, self-assembled composite nanostructures that extend throughout the entire thickness of the film. The YBCO coatings deposited on these nanostructured cap layers showed correlated c-axis pinning and improved in-field Jc performance compared to those of YBCO films fabricated on standard LMO buffers. Microstructural characterization revealed additional extended disorder in the YBCO matrix. The present results demonstrate the feasibility of novel and potentially practical approaches in the pursuit of more efficient, economical, and high performance superconducting devices.

  4. Chemiluminescence flow biosensor for glucose using Mg-Al carbonate layered double hydroxides as catalysts and buffer solutions.

    PubMed

    Wang, Zhihua; Liu, Fang; Lu, Chao

    2012-01-01

    In this work, serving as supports in immobilizing luminol reagent, catalysts of luminol chemiluminescence (CL), and buffer solutions for the CL reaction, Mg-Al-CO(3) layered double hydroxides (LDHs) were found to trigger luminol CL in weak acid solutions (pH 5.8). The silica sol-gel with glucose oxidase and horseradish peroxidase was immobilized in the first half of the inside surface of a clear quartz tube, and luminol-hybrid Mg-Al-CO(3) LDHs were packed in the second half. Therefore, a novel CL flow-through biosensor for glucose was constructed in weak acid solutions. The CL intensity was linear with glucose concentration in the range of 0.005-1.0mM, and the detection limit for glucose (S/N=3) was 0.1 μM. The proposed biosensor exhibited excellent stability, high reproducibility and high selectivity for the determination of glucose and has been successfully applied to determine glucose in human plasma samples with satisfactory results. The success of this work has broken the bottleneck of the pH incompatibility between luminol CL and enzyme activity. PMID:22770831

  5. Magnetic properties of nano-patterned GaMnAs films grown on ZnCdSe buffer layers

    NASA Astrophysics Data System (ADS)

    Dong, Sining; Li, Xiang; Kanzyuba, Vasily; Yoo, Taehee; Liu, Xinyu; Dobrowolska, Malgorzata; Furdyna, Jacek

    Magnetic semiconductor nanostructures are attracting intense attention, both because of their fundamental physical properties, and because of the promise which they hold for building smaller, faster and more energy-efficient devices. In this study we report successful MBE growth of GaMnAs films on the GaAs (100) substrates with ZnCdSe buffer layers, which results in perpendicular magnetic easy axis in the GaMnAs films. The GaMnAs/ZnCdSe films have been etched into nano-stripe shapes with various widths below 200nm by e-beam lithography, which resulted in a new geometry of interest for perpendicular magnetic recording. Magnetic anisotropy of as-grown GaMnAs films and nano-stripes was then studied by SQUID magnetometry. The results indicate that the GaMnAs films consist of magnetic domains with magnetization normal to the film plane, having rather high coercivety, which survives after nanofabrication. This is also confirmed by the dynamics of the domain motion as shown by AC susceptibility measurements. These findings are of interest for understanding the magnetic anisotropy mechanisms in GaMnAs and its domain structures, as well as for designing of nano-sized spintronic devices which require hard ferromagnetic behavior with perpendicular easy axes. This work was supported by the National Science Foundation Grant DMR1400432.

  6. Characterization of Zn(O,S) Buffer Layers for Cu(In,Ga)Se2 Solar Cells.

    PubMed

    Choi, Ji Hyun; Jung, Sung Hee; Chung, Chee Won

    2016-05-01

    Zn(O,S) thin films were deposited using a ZnS target under Ar/O2 gases by radio-frequency magnetron sputtering. As the O2 concentration increased, the deposition rates of the Zn(O,S) films decreased due to increase of O-. The crystalline structure of Zn(O,S) was maintained at up to 0.6% O2, while the films became unstable at the condition exceeding 0.8% O2. This was attributed to incomplete nucleation and film growth on the substrate at the room temperature. Additionally, optical emission spectroscopy analysis indicated that an increased O- intensity at high O2 concentration was responsible for the slow deposition rate and increased oxygen concentration of the films. X-ray diffraction and scanning electron microscopy revealed the formation of a Zn(O,S) crystal structure with partial substitution of O for S and uniform and dense grains of the films. X-ray photoelectron spectroscopy showed that the Zn(O,S) films have a uniform composition of each element and consisted of a mixed crystal structure of Zn(O,S) with Zn-O bonding. Overall, the results of this study confirmed that Zn(O,S) films deposited by radio-frequency sputtering using Ar/O2 gas at room temperature can be applied to Cu(In,Ga)Se2 solar cells as a buffer layer. PMID:27483934

  7. Biaxially oriented CdTe films on glass substrate through nanostructured Ge/CaF2 buffer layers

    NASA Astrophysics Data System (ADS)

    Lord, R. J.; Su, P.-Y.; Bhat, I.; Zhang, S. B.; Lu, T.-M.; Wang, G.-C.

    2015-09-01

    Heteroepitaxial CdTe films were grown by metal organic chemical vapor deposition on glass substrates through nanostructured Ge/CaF2 buffer layers which were biaxially oriented. It allows us to explore the structural properties of multilayer biaxial semiconductor films which possess small angle grain boundaries and to test the principle of a solar cell made of such low-cost, low-growth-temperature semiconductor films. Through the x-ray diffraction and x-ray pole figure analysis, the heteroepitaxial relationships of the mutilayered films are determined as [111] in the out-of-plane direction and <1\\bar{1}0>CdTe//<1\\bar{1}0>Ge//{< \\bar{1}10> }{{{CaF}}2} in the in-plane direction. The I-V curves measured from an ITO/CdS/CdTe/Ge/CaF2/glass solar cell test structure shows a power conversion efficiency of ˜η = 1.26%, illustrating the initial success of such an approach. The observed non-ideal efficiency is believed to be due to a low shunt resistance and high series resistance as well as some residual large-angle grain boundary effects, leaving room for significant further improvement.

  8. Measured Propagation Characteristics of Finite Ground Coplanar Waveguide on Silicon with a Thick Polyimide Interface Layer

    NASA Technical Reports Server (NTRS)

    Ponchak, George E.; Papapolymerou, John; Tentzeris, Emmanouil M.; Williams, W. O. (Technical Monitor)

    2002-01-01

    Measured propagation characteristics of Finite Ground Coplanar (FGC) waveguide on silicon substrates with resistivities spanning 3 orders of magnitude (0.1 to 15.5 Ohm cm) and a 20 micron thick polyimide interface layer is presented as a function of the FGC geometry. Results show that there is an optimum FGC geometry for minimum loss, and silicon with a resistivity of 0.1 Ohm cm has greater loss than substrates with higher and lower resistivity. Lastly, substrates with a resistivity of 10 Ohm cm or greater have acceptable loss.

  9. The application of thick hydrogenated amorphous silicon layers to charged particle and x-ray detection

    SciTech Connect

    Perez-Mendez, V.; Cho, G.; Fujieda, I.; Kaplan, S.N.; Qureshi, S.; Street, R.A.

    1989-04-01

    We outline the characteristics of thick hydrogenated amorphous silicon layers which are optimized for the detection of charged particles, x-rays and ..gamma..-rays. Signal amplitude as a function of the linear energy transfer of various particles are given. Noise sources generated by the detector material and by the thin film electronics - a-Si:H or polysilicon proposed for pixel position sensitive detectors readout are described, and their relative amplitudes are calculated. Temperature and neutron radiation effects on leakage currents and the corresponding noise changes are presented. 17 refs., 12 figs., 2 tabs.

  10. Thickness dependence of the levitation performance of double-layer high-temperature superconductor bulks above a magnetic rail

    NASA Astrophysics Data System (ADS)

    Sun, R. X.; Zheng, J.; Liao, X. L.; Che, T.; Gou, Y. F.; He, D. B.; Deng, Z. G.

    2014-10-01

    A double-layer high-temperature superconductor (HTSC) arrangement was proposed and proved to be able to bring improvements to both levitation force and guidance force compared with present single-layer HTSC arrangement. To fully exploit the applied magnetic field by a magnetic rail, the thickness dependence of a double-layer HTSC arrangement on the levitation performance was further investigated in the paper. In this study, the lower-layer bulk was polished step by step to different thicknesses, and the upper-layer bulk with constant thickness was directly superimposed on the lower-layer one. The levitation force and the force relaxation of the double-layer HTSC arrangement were measured above a Halbach magnetic rail. Experimental result shows that a bigger levitation force and a less levitation force decay could be achieved by optimizing the thickness of the lower-layer bulk HTSC. This thickness optimization method could be applied together with former reported double-layer HTSC arrangement method with aligned growth sector boundaries pattern. This series of study on the optimized combination method do bring a significant improvement on the levitation performance of present HTS maglev systems.

  11. Reflectance Decreases before Thickness Changes in the Retinal Nerve Fiber Layer in Glaucomatous Retinas

    PubMed Central

    Zhou, Ye; Kong, Wei; Knighton, Robert W.

    2011-01-01

    Purpose. Glaucoma damages the retinal never fiber layer (RNFL). RNFL thickness, measured with optical coherence tomography (OCT), is often used in clinical assessment of the damage. In this study the relation between the RNFL reflectance and thickness at early stages of glaucoma was investigated. Methods. A rat model of glaucoma was used that involved laser photocoagulation of the trabecular meshwork. The reflectance of the RNFL in an isolated retina was measured, followed by immunohistochemical staining of the axonal cytoskeleton. RNFL thickness was measured by confocal fluorescence imaging. RNFL reflectance was calculated for bundle areas located at radii of 0.22, 0.33, and 0.44 mm from the optic nerve head (ONH) center. Linear regression was used to study the relation between reflectance and thickness. For glaucomatous eyes, only those bundles with no apparent structural damage were used. Results. Bundles in 11 control retinas and 10 treated retinas were examined. Bundle thickness of both groups at each radius was similar (P = 0.89). The reflectance of the bundles at radii of 0.33 and 0.44 mm was found to be similar in both control and treated retinas (P > 0.5). However, the reflectance of the bundles at the 0.22-mm radius decreased significantly in the treated group (P = 0.005). Conclusions. Elevation of intraocular pressure causes decrease in RNFL reflectance for bundles near the ONH. Change in RNFL reflectance precedes thinning of the RNFL. The results suggest that a decrease in RNFL reflectance near the ONH is an early sign of glaucomatous damage. PMID:21730345

  12. Spatial coherence effect on layer thickness determination in narrowband full-field optical coherence tomography

    SciTech Connect

    Safrani, Avner; Abdulhalim, Ibrahim

    2011-06-20

    Longitudinal spatial coherence (LSC) is determined by the spatial frequency content of an optical beam. The use of lenses with a high numerical aperture (NA) in full-field optical coherence tomography and a narrowband light source makes the LSC length much shorter than the temporal coherence length, hence suggesting that high-resolution 3D images of biological and multilayered samples can be obtained based on the low LSC. A simplified model is derived, supported by experimental results, which describes the expected interference output signal of multilayered samples when high-NA lenses are used together with a narrowband light source. An expression for the correction factor for the layer thickness determination is found valid for high-NA objectives. Additionally, the method was applied to a strongly scattering layer, demonstrating the potential of this method for high-resolution imaging of scattering media.

  13. Anatomy and physiology of the thick-tufted layer 5 pyramidal neuron

    PubMed Central

    Ramaswamy, Srikanth; Markram, Henry

    2015-01-01

    The thick-tufted layer 5 (TTL5) pyramidal neuron is one of the most extensively studied neuron types in the mammalian neocortex and has become a benchmark for understanding information processing in excitatory neurons. By virtue of having the widest local axonal and dendritic arborization, the TTL5 neuron encompasses various local neocortical neurons and thereby defines the dimensions of neocortical microcircuitry. The TTL5 neuron integrates input across all neocortical layers and is the principal output pathway funneling information flow to subcortical structures. Several studies over the past decades have investigated the anatomy, physiology, synaptology, and pathophysiology of the TTL5 neuron. This review summarizes key discoveries and identifies potential avenues of research to facilitate an integrated and unifying understanding on the role of a central neuron in the neocortex. PMID:26167146

  14. Effect of AlN buffer layer properties on the morphology and polarity of GaN nanowires grown by molecular beam epitaxy

    SciTech Connect

    Brubaker, Matt D.; Rourke, Devin M.; Sanford, Norman A.; Bertness, Kris A.; Bright, Victor M.

    2011-09-01

    Low-temperature AlN buffer layers grown via plasma-assisted molecular beam epitaxy on Si (111) were found to significantly affect the subsequent growth morphology of GaN nanowires. The AlN buffer layers exhibited nanowire-like columnar protrusions, with their size, shape, and tilt determined by the AlN V/III flux ratio. GaN nanowires were frequently observed to adopt the structural characteristics of the underlying AlN columns, including the size and the degree of tilt. Piezoresponse force microscopy and polarity-sensitive etching indicate that the AlN films and the protruding columns have a mixed crystallographic polarity. Convergent beam electron diffraction indicates that GaN nanowires are Ga-polar, suggesting that Al-polar columns are nanowire nucleation sites for Ga-polar nanowires. GaN nanowires of low density could be grown on AlN buffers that were predominantly N-polar with isolated Al-polar columns, indicating a high growth rate for Ga-polar nanowires and suppressed growth of N-polar nanowires under typical growth conditions. AlN buffer layers grown under slightly N-rich conditions (V/III flux ratio = 1.0 to 1.3) were found to provide a favorable growth surface for low-density, coalescence-free nanowires.

  15. Reduction in edge dislocation density in corundum-structured α-Ga2O3 layers on sapphire substrates with quasi-graded α-(Al,Ga)2O3 buffer layers

    NASA Astrophysics Data System (ADS)

    Jinno, Riena; Uchida, Takayuki; Kaneko, Kentaro; Fujita, Shizuo

    2016-07-01

    Efforts have been made to reduce the density of defects in corundum-structured α-Ga2O3 thin films on sapphire substrates by applying quasi-graded α-(Al x Ga1‑ x )2O3 buffer layers. Transmission electron microscopy images revealed that most strains were located in the α-(Al x Ga1‑ x )2O3 buffer layers, and that the total density of dislocations in the α-Ga2O3 thin films was successfully decreased by more than one order of magnitude compared with that without buffer layers, that is, the screw and edge dislocation densities were about 3 × 108 and 6 × 108 cm‑2, respectively.

  16. Realizing the full potential of Remotely Sensed Active Layer Thickness (ReSALT) Products

    NASA Astrophysics Data System (ADS)

    Schaefer, K. M.; Chen, A.; Liu, L.; Parsekian, A.; Jafarov, E. E.; Panda, S. K.; Zebker, H. A.

    2015-12-01

    The Remotely Sensed Active Layer Thickness (ReSALT) product uses the Interferometric Synthetic Aperture Radar (InSAR) technique to measure ground subsidence, active layer thickness (ALT), and thermokarst activity in permafrost regions. ReSALT supports research for the Arctic-Boreal Vulnerability Experiment (ABoVE) field campaign in Alaska and northwest Canada and is a precursor for a potential Nasa-Isro Synthetic Aperture Radar (NISAR) product. ALT is a critical parameter for monitoring the status of permafrost and thermokarst activity is one of the key drivers of change in permafrost regions. The ReSALT product currently includes 1) long-term subsidence trends resulting from the melting and subsequent drainage of excess ground ice in permafrost-affected soils, 2) seasonal subsidence resulting from the expansion of soil water into ice as the active layer freezes and thaws, and 3) ALT estimated from the seasonal subsidence assuming a vertical profile of water within the soil column. ReSALT includes uncertainties for all parameters and is validated against in situ measurements from the Circumpolar Active Layer Monitoring (CALM) network, Ground Penetrating Radar and mechanical probe measurements. We present high resolution ReSALT products on the North Slope of Alaska: Prudhoe Bay, Barrow, Toolik Lake, Happy Valley, and the Anaktuvuk fire zone. We believe that the ReSALT product could be expanded to include maps of individual thermokarst features identified as spatial anomalies in the subsidence trends, with quantified expansion rates. We illustrate the technique with multiple examples of thermokarst features on the North Slope of Alaska. Knowing the locations and expansion rates for individual features allows us to evaluate risks to human infrastructure. Our results highlight the untapped potential of the InSAR technique to remotely sense ALT and thermokarst dynamics over large areas of the Arctic.

  17. MoO3 as a Cathode Buffer Layer Material for the Improvement of Planar pn-Heterojunction Organic Solar Cell Performance

    NASA Astrophysics Data System (ADS)

    Kageyama, Hiroshi; Kajii, Hirotake; Ohmori, Yutaka; Shirota, Yasuhiko

    2011-03-01

    The use of MoO3 as a cathode buffer layer inserted between LiF and Al improved the power conversion efficiency (PCE) of planar pn-heterojunction organic solar cells (OSCs) by reducing exciton quenching at the interface between the n-type organic active layer and the electrode. The cell using an amorphous molecular material, tris[4-(5-phenylthiophen-2-yl)phenyl]amine, as a p-type organic semiconductor, C70 as an n-type organic semiconductor and MoO3 as a cathode buffer layer exhibited a PCE of 3.3% under AM1.5G illumination (100 mW cm-2), which is of the highest level among those for planar pn-heterojunction OSCs using amorphous molecular materials as donor materials.

  18. Realization of high quality epitaxial current- perpendicular-to-plane giant magnetoresistive pseudo spin-valves on Si(001) wafer using NiAl buffer layer

    NASA Astrophysics Data System (ADS)

    Chen, Jiamin; Liu, J.; Sakuraba, Y.; Sukegawa, H.; Li, S.; Hono, K.

    2016-05-01

    In this letter, we report a NiAl buffer layer as a template for the integration of epitaxial current-perpendicular-plane-giant magnetoresistive (CPP-GMR) devices on a Si(001) single crystalline substrate. By depositing NiAl on a Si wafer at an elevated temperature of 500 °C, a smooth and epitaxial B2-type NiAl(001) layer was obtained. The surface roughness was further improved by depositing Ag on the NiAl layer and applying subsequent annealing process. The epitaxial CPP-GMR devices grown on the buffered Si(001) substrate present a large magnetoresistive output comparable with that of the devices grown on an MgO(001) substrate, demonstrating the possibility of epitaxial spintronic devices with a NiAl templated Si wafer for practical applications.

  19. Fractal analysis and atomic force microscopy measurements of surface roughness for Hastelloy C276 substrates and amorphous alumina buffer layers in coated conductors

    NASA Astrophysics Data System (ADS)

    Feng, F.; Shi, K.; Xiao, S.-Z.; Zhang, Y.-Y.; Zhao, Z.-J.; Wang, Z.; Wei, J.-J.; Han, Z.

    2012-02-01

    In coated conductors, surface roughness of metallic substrates and buffer layers could significantly affect the texture of subsequently deposited buffer layers and the critical current density of superconductor layer. Atomic force microscopy (AFM) is usually utilized to measure surface roughness. However, the roughness values are actually relevant to scan scale. Fractal geometry could be exerted to analyze the scaling performance of surface roughness. In this study, four samples were prepared, which were electro polished Hastelloy C276 substrate, mechanically polished Hastelloy C276 substrate and the amorphous alumina buffer layers deposited on both the substrates by ion beam deposition. The surface roughness, described by root mean squared (RMS) and arithmetic average (Ra) values, was analyzed considering the scan scale of AFM measurements. The surfaces of amorphous alumina layers were found to be fractal in nature because of the scaling performance of roughness, while the surfaces of Hastelloy substrates were not. The flatten modification of AFM images was discussed. And the calculation of surface roughness in smaller parts divided from the whole AFM images was studied, compared with the results of actual AFM measurements of the same scan scales.

  20. Changes in Inner and Outer Retinal Layer Thicknesses after Vitrectomy for Idiopathic Macular Hole: Implications for Visual Prognosis

    PubMed Central

    Hashimoto, Yuki; Saito, Wataru; Fujiya, Akio; Yoshizawa, Chikako; Hirooka, Kiriko; Mori, Shohei; Noda, Kousuke; Ishida, Susumu

    2015-01-01

    Purpose To investigate sequential post-operative thickness changes in inner and outer retinal layers in eyes with an idiopathic macular hole (MH). Methods Retrospective case series. Twenty-four eyes of 23 patients who had received pars plana vitrectomy (PPV) for the closure of MH were included in the study. Spectral domain optical coherence tomography C-scan was used to automatically measure the mean thickness of the inner and outer retinal layers pre-operatively and up to 6 months following surgery. The photoreceptor outer segment (PROS) length was measured manually and was used to assess its relationship with best-corrected visual acuity (BCVA). Results Compared with the pre-operative thickness, the inner layers significantly thinned during follow-up (P = 0.02), particularly in the parafoveal (P = 0.01), but not perifoveal, area. The post-operative inner layer thinning ranged from the ganglion cell layer to the inner plexiform layer (P = 0.002), whereas the nerve fiber layer was unaltered. Outer layer thickness was significantly greater post-operatively (P = 0.002), and especially the PROS lengthened not only in the fovea but also in the parafovea (P < 0.001). Six months after surgery, BCVA was significantly correlated exclusively with the elongated foveal PROS (R = 0.42, P = 0.03), but not with any of the other thickness parameters examined. Conclusions Following PPV for MH, retinal inner layers other than the nerve fiber layer thinned, suggestive of subclinical thickening in the inner layers where no cyst was evident pre-operatively. In contrast, retinal outer layer thickness significantly increased, potentially as a result of PROS elongation linking tightly with favorable visual prognosis in MH eyes. PMID:26291526

  1. Lubiprostone Decreases Mouse Colonic Inner Mucus Layer Thickness and Alters Intestinal Microbiota

    PubMed Central

    Musch, Mark W.; Wang, Yunwei; Claud, Erika C.

    2013-01-01

    Background Lubiprostone has been used to treat constipation through its effects to stimulate Cl− secretion, resulting in water and electrolyte secretion. Aim Potential associated changes in intestinal mucus and the colonizing bacteria (microbiome) have not been studied. As mucus obstructions may play a role in cystic fibrosis, the hypothesis that lubiprostone alters intestinal mucus and the microbiome was investigated. Methods Ion transport studies were performed ex vivo. For mucus and microbiome studies, mice were gavaged daily with lubiprostone or vehicle. Mucin from intestinal sections was analyzed in Carnoy’s fixed tissues stained with Alcian blue. Microbiome composition was analyzed by 16S rRNA gene-based sequencing. Results Lubiprostone stimulated short circuit current in all mouse intestinal segments after both serosal and mucosal additions, albeit at lower concentrations in the latter. Current was Cl-dependent and blocked by mucosal diphenylcarboxylic acid, serosal bumetanide, and serosal Ba++. The CFTR inhibitor CFTRinh172 had a marginal effect. Mucus near epithelial cells (inner layer mucus) was not present in the small intestine of any mice. Proximal colon inner mucus layer was thicker in ΔF/ΔF compared with +/ΔF and +/+ mice. Lubiprostone decreased inner mucus layer thickness in both proximal and distal colon of all mice. Furthermore, lubiprostone altered the intestinal microbiome by increasing abundance of Lactobacillus and Alistipes. Conclusions Lubiprostone activates non-CFTR Cl− secretion and alters the colonic inner mucus layer, which is associated with changes in the composition of the enteric microbiome. PMID:23329012

  2. Properties of single shear layer instabilities and vortex-induced excitation mechanisms of thick plates

    NASA Astrophysics Data System (ADS)

    Billeter, P.

    2004-04-01

    The basic findings of an experimental investigation of flow-induced vibrations of gate plates with multiple degrees of freedom are presented. The study focused on the fluid dynamic behaviour of the single shear layer separating from a thick rectangular plate. The principal aim of the study was to further the physical understanding of instability-induced excitation mechanisms (IIE) involving shear layer instabilities and vortex generation. It is shown that this type of gate vibration is caused by two dominant excitation mechanisms: cross-flow and streamwise impinging-leading-edge-vortex (ILEV) excitation and streamwise body-resonant leading-edge-vortex-shedding (BR-LEVS) excitation. The first mechanism is caused by the local interaction of the shear layer underneath the gate plate with the trailing edge of the gate lip. The second mechanism is produced by the instability of the shear layer in the tailwater of the gate, with the instability being necessarily triggered by the elastic motion of the flow separation at the leading edge of the gate. Former address. Laboratory of Hydraulics (VAW), Swiss Federal Institute of Technology (ETH), Zurich, Switzerland.

  3. A procedure to mathematically amend possible thickness disuniformities in gel-layer dosimetry

    NASA Astrophysics Data System (ADS)

    Carrara, Mauro; Gambarini, Grazia; Bartesaghi, Giacomo; Fallai, Carlo; Negri, Anna

    2009-05-01

    The continuous development of conformal radiotherapies requires a corresponding improvement of dosimetric techniques. Fricke gel-layer dosimetry, coupled with a suitably developed software, has proven to be a reliable technique for 3D absorbed dose distribution verification. The method is based on the evaluation of the light transmitted by gel-layers due to the fact that th optical density difference between irradiated and non irraddiated dosimeters is proportional to the absorbed dose. Measurement are performed by means of a planar illumination source and a computer-controlled CCD camera. Recently, adoption of gel layers with increased superficial dimensions has evidenced a possible thickness disuniformity of layers, thus introducing a new source of measurement inaccuracy. In this work, a method to mathematically amend this possible source of error is proposed. Dose profiles along the central axis of phantoms irradiated with X-ray therapy and Boron Neutron Capture Therapy fields, obtained with and without the application of the proposed correction procedure, were compared with ionization chamber measurements and Monte Carlo simulations, respectively. The obtained results show a good reliability of the proposed procedure.

  4. Optimization of electrode geometry and piezoelectric layer thickness of a deformable mirror

    NASA Astrophysics Data System (ADS)

    Kruchenko, Alexey V.; Nováková, Kateřina; Mokrý, Pavel

    2013-04-01

    Deformable mirrors are the most commonly used wavefront correctors in adaptive optics systems. Nowadays, many applications of adaptive optics to astronomical telescopes, high power laser systems, and similar fast response optical devices require large diameter deformable mirrors with a fast response time and high actuator stroke. In order to satisfy such requirements, deformable mirrors based on piezoelectric layer composite structures have become a subject of intense scientific research during last two decades. In this paper, we present an optimization of several geometric parameters of a deformable mirror that consists of a nickel reflective layer deposited on top of a thin lead zirconate titanate (PZT) piezoelectric disk. Honeycomb structure of gold electrodes is deposited on the bottom of the PZT layer. The analysis of the optimal thickness ratio between the PZT and nickel layers is performed to get the maximum actuator stroke using the finite element method. The effect of inter-electrode distance on the actuator stroke and influence function is investigated. Applicability and manufacturing issues are discussed.

  5. Peripapillary retinal nerve fiber layer thickness in patients with iron deficiency anemia

    PubMed Central

    Cikmazkara, Ipek; Ugurlu, Seyda Karadeniz

    2016-01-01

    Purpose: To evaluate the effect of iron deficiency anemia (IDA) on peripapillary retinal nerve fiber layer (RNFL) thickness with optical coherence tomography (OCT). Materials and Methods: 102 female patients who had IDA (hemoglobin <12 g/dl, serum transferrin saturation <15%, serum iron <50 μg/dl, and serum ferritin <15 μg/dl) were enrolled in the study. Optic disc and RNFL parameters obtained by Cirrus high-definition OCT 4000 were compared with those of 49 age and sex-matched nonanemic individuals. The time between blood analysis and OCT measurements was 3.14 ± 5.6 (range, 0–28) days in the anemia group, and 3.5 ± 6.7 (range, 0–27) days in the control group (P = 0.76). Results: Average ages of 102 patients and 49 control subjects were 35.76 ± 10.112 (range, 18–66) years, and 36.08 ± 8.416 (range, 19–57) years (P = 0.850), respectively. The average RNFL thickness was 94.67 ± 9.380 in the anemia group, and 100.22 ± 9.12 in the control group (P = 0.001). Temporal, nasal, and lower quadrant average RNFL thicknesses of IDA group were thinner than the control group (P = 0.001, P = 0.013, P = 0.008). Upper quadrant RNFL thicknesses in IDA and control groups were similar. Correlation analysis revealed positive correlation between mean RNFL thickness and hemoglobin (r = 0.273), iron (r = 0.177), ferritin (r = 0.163), and transferrin saturations (r = 0.185), while a negative correlation was found between total iron binding capacity (r = −0.199) and mean RNFL thickness. Conclusions: Peripapillary RNFL thickness measured by OCT is thinner in adult female patients with IDA. It may have a significant influence on the management of many disorders such as glaucoma and neuro-ophthalmological diseases. PMID:27146929

  6. Thickness-dependent charge transport in few-layer MoS2 field-effect transistors

    NASA Astrophysics Data System (ADS)

    Lin, Ming-Wei; Kravchenko, Ivan I.; Fowlkes, Jason; Li, Xufan; Puretzky, Alexander A.; Rouleau, Christopher M.; Geohegan, David B.; Xiao, Kai

    2016-04-01

    Molybdenum disulfide (MoS2) is currently under intensive study because of its exceptional optical and electrical properties in few-layer form. However, how charge transport mechanisms vary with the number of layers in MoS2 flakes remains unclear. Here, exfoliated flakes of MoS2 with various thicknesses were successfully fabricated into field-effect transistors (FETs) to measure the thickness and temperature dependences of electrical mobility. For these MoS2 FETs, measurements at both 295 K and 77 K revealed the maximum mobility for layer thicknesses between 5 layers (˜3.6 nm) and 10 layers (˜7 nm), with ˜70 cm2 V-1 s-1 measured for 5 layer devices at 295 K. Temperature-dependent mobility measurements revealed that the mobility rises with increasing temperature to a maximum. This maximum occurs at increasing temperature with increasing layer thickness, possibly due to strong Coulomb scattering from charge impurities or weakened electron-phonon interactions for thicker devices. Temperature-dependent conductivity measurements for different gate voltages revealed a metal-to-insulator transition for devices thinner than 10 layers, which may enable new memory and switching applications. This study advances the understanding of fundamental charge transport mechanisms in few-layer MoS2, and indicates the promise of few-layer transition metal dichalcogenides as candidates for potential optoelectronic applications.

  7. Thickness-dependent charge transport in few-layer MoS2 field-effect transistors.

    PubMed

    Lin, Ming-Wei; Kravchenko, Ivan I; Fowlkes, Jason; Li, Xufan; Puretzky, Alexander A; Rouleau, Christopher M; Geohegan, David B; Xiao, Kai

    2016-04-22

    Molybdenum disulfide (MoS2) is currently under intensive study because of its exceptional optical and electrical properties in few-layer form. However, how charge transport mechanisms vary with the number of layers in MoS2 flakes remains unclear. Here, exfoliated flakes of MoS2 with various thicknesses were successfully fabricated into field-effect transistors (FETs) to measure the thickness and temperature dependences of electrical mobility. For these MoS2 FETs, measurements at both 295 K and 77 K revealed the maximum mobility for layer thicknesses between 5 layers (∼3.6 nm) and 10 layers (∼7 nm), with ∼70 cm(2) V(-1) s(-1) measured for 5 layer devices at 295 K. Temperature-dependent mobility measurements revealed that the mobility rises with increasing temperature to a maximum. This maximum occurs at increasing temperature with increasing layer thickness, possibly due to strong Coulomb scattering from charge impurities or weakened electron-phonon interactions for thicker devices. Temperature-dependent conductivity measurements for different gate voltages revealed a metal-to-insulator transition for devices thinner than 10 layers, which may enable new memory and switching applications. This study advances the understanding of fundamental charge transport mechanisms in few-layer MoS2, and indicates the promise of few-layer transition metal dichalcogenides as candidates for potential optoelectronic applications. PMID:26963583

  8. Moderately large vibrations of doubly curved shallow open shells composed of thick layers

    NASA Astrophysics Data System (ADS)

    Adam, Christoph

    2007-02-01

    This paper addresses nonlinear flexural vibrations of shallow shells composed of three thick layers with different shear flexibility, which are symmetrically arranged with respect to the middle surface. The considered shell structures of polygonal planform are hard hinged simply supported (i.e. all in-plane rotations and the bending moment vanish) with the edges fully restraint against displacements in any direction. The kinematic field equations are formulated by layerwise application of a first-order shear deformation theory. A modification of Berger's theory is employed to model the nonlinear characteristics of the structural response. The continuity of the transverse shear stress across the interfaces is specified according to Hooke's law, and subsequently the equations of motion of this higher order problem can be derived in analogy to a homogeneous single-layer shear deformable shallow shell. Numerical results of rectangular shallow shells in nonlinear steady-state vibration are presented for various ratios of shell rise to thickness, and non-dimensional load amplitude.

  9. Effect of optic nerve sheath fenestration for idiopathic intracranial hypertension on retinal nerve fiber layer thickness.

    PubMed

    Starks, Victoria; Gilliland, Grant; Vrcek, Ivan; Gilliland, Connor

    2016-01-01

    The objective of the study was to evaluate whether optic nerve sheath fenestration in patients with idiopathic intracranial hypertension was associated with improvement in visual field pattern deviation and optical coherence tomography retinal nerve fiber layer thickness.The records of 13 eyes of 11 patients who underwent optic nerve sheath fenestration were reviewed. The subjects were patients of a clinical practice in Dallas, Texas. Charts were reviewed for pre- and postoperative visual field pattern deviation (PD) and retinal nerve fiber layer thickness (RNFL).PD and RNFL significantly improved after surgery. Average PD preoperatively was 8.51 DB and postoperatively was 4.80 DB (p = 0.0002). Average RNFL preoperatively was 113.63 and postoperatively was 102.70 (p = 0.01). The preoperative PD and RNFL did not correlate strongly.Our results demonstrate that PD and RNFL are improved after optic nerve sheath fenestration. The pre- and postoperative RNFL values were compared to the average RNFL value of healthy optic nerves obtained from the literature. Post-ONSF RNFL values were significantly closer to the normal value than preoperative. RNFL is an objective parameter for monitoring the optic nerve after optic nerve sheath fenestration. This study adds to the evidence that OCT RNFL may be an effective monitoring tool for patients with IIH and that it continues to be a useful parameter after ONSF. PMID:26928128

  10. Area-Selective Atomic Layer Deposition: Conformal Coating, Subnanometer Thickness Control, and Smart Positioning.

    PubMed

    Fang, Ming; Ho, Johnny C

    2015-09-22

    Transistors have already been made three-dimensional (3D), with device channels (i.e., fins in trigate field-effect transistor (FinFET) technology) that are taller, thinner, and closer together in order to enhance device performance and lower active power consumption. As device scaling continues, these transistors will require more advanced, fabrication-enabling technologies for the conformal deposition of high-κ dielectric layers on their 3D channels with accurate position alignment and thickness control down to the subnanometer scale. Among many competing techniques, area-selective atomic layer deposition (AS-ALD) is a promising method that is well suited to the requirements without the use of complicated, complementary metal-oxide semiconductor (CMOS)-incompatible processes. However, further progress is limited by poor area selectivity for thicker films formed via a higher number of ALD cycles as well as the prolonged processing time. In this issue of ACS Nano, Professor Stacy Bent and her research group demonstrate a straightforward self-correcting ALD approach, combining selective deposition with a postprocess mild chemical etching, which enables selective deposition of dielectric films with thicknesses and processing times at least 10 times larger and 48 times shorter, respectively, than those obtained by conventional AS-ALD processes. These advances present an important technological breakthrough that may drive the AS-ALD technique a step closer toward industrial applications in electronics, catalysis, and photonics, etc. where more efficient device fabrication processes are needed. PMID:26351731

  11. Coupled annealing temperature and layer thickness effect on strengthening mechanisms of Ti/Ni multilayer thin films

    NASA Astrophysics Data System (ADS)

    Yang, Zhou; Wang, Junlan

    2016-03-01

    A systematic study was performed on mechanical and microstructural properties of Ti/Ni multilayers with layer thickness from 200 nm to 6 nm and annealing temperature from room temperature to 500 °C. Based on the observed hardness evolution, a coupled layer-thickness and annealing-temperature dependent strengthening mechanism map is proposed. For as-deposited films, the deformation behavior follows the traditional trend of dislocation mediated strengthening to grain boundary mediated softening with decreasing layer thickness. For annealed films, grain boundary relaxation is considered to be the initial strengthening mechanism with higher activation temperature required for thicker layers. Under further annealing, solid solution hardening, intermetallic precipitation hardening, and fully intermixed alloy structure continue to strengthen the thin layered films, while recrystallization and grain-growth lead to the eventual softening of thick layered films. For the films with intermediate layer thickness, a strong orientation dependent hardness behavior is exhibited under high temperature annealing due to mechanism switch from grain growth softening to intermetallic precipitation hardening when changing the loading orientation from perpendicular to parallel to the layer interfaces.

  12. Strain relaxation of thick (11–22) semipolar InGaN layer for long wavelength nitride-based device

    SciTech Connect

    Kim, Jaehwan; Min, Daehong; Jang, Jongjin; Lee, Kyuseung; Chae, Sooryong; Nam, Okhyun

    2014-10-28

    In this study, the properties of thick stress-relaxed (11–22) semipolar InGaN layers were investigated. Owing to the inclination of growth orientation, misfit dislocations (MDs) occurred at the heterointerface when the strain state of the (11–22) semipolar InGaN layers reached the critical point. We found that unlike InGaN layers based on polar and nonpolar growth orientations, the surface morphologies of the stress-relaxed (11–22) semipolar InGaN layers did not differ from each other and were similar to the morphology of the underlying GaN layer. In addition, misfit strain across the whole InGaN layer was gradually relaxed by MD formation at the heterointerface. To minimize the effect of surface roughness and defects in GaN layers on the InGaN layer, we conducted further investigation on a thick (11–22) semipolar InGaN layer grown on an epitaxial lateral overgrown GaN template. We found that the lateral indium composition across the whole stress-relaxed InGaN layer was almost uniform. Therefore, thick stress-relaxed (11–22) semipolar InGaN layers are suitable candidates for use as underlying layers in long-wavelength devices, as they can be used to control strain accumulation in the heterostructure active region without additional influence of surface roughness.

  13. Sodium chloride crystallization from thin liquid sheets, thick layers, and sessile drops in microgravity

    NASA Astrophysics Data System (ADS)

    Fontana, Pietro; Pettit, Donald; Cristoforetti, Samantha

    2015-10-01

    Crystallization from aqueous sodium chloride solutions as thin liquid sheets, 0.2-0.7 mm thick, with two free surfaces supported by a wire frame, thick liquid layers, 4-6 mm thick, with two free surfaces supported by metal frame, and hemispherical sessile drops, 20-32 mm diameter, supported by a flat polycarbonate surface or an initially flat gelatin film, were carried out under microgravity on the International Space Station (ISS). Different crystal morphologies resulted based on the fluid geometry: tabular hoppers, hopper cubes, circular [111]-oriented crystals, and dendrites. The addition of polyethylene glycol (PEG-3350) inhibited the hopper growth resulting in flat-faced surfaces. In sessile drops, 1-4 mm tabular hopper crystals formed on the free surface and moved to the fixed contact line at the support (polycarbonate or gelatin) self-assembling into a shell. Ring formation created by sessile drop evaporation to dryness was observed but with crystals 100 times larger than particles in terrestrially formed coffee rings. No hopper pyramids formed. By choosing solution geometries offered by microgravity, we found it was possible to selectively grow crystals of preferred morphologies.

  14. Thermal and Environmental Stability of Semi-Transparent Perovskite Solar Cells for Tandems Enabled by a Solution-Processed Nanoparticle Buffer Layer and Sputtered ITO Electrode.

    PubMed

    Bush, Kevin A; Bailie, Colin D; Chen, Ye; Bowring, Andrea R; Wang, Wei; Ma, Wen; Leijtens, Tomas; Moghadam, Farhad; McGehee, Michael D

    2016-05-01

    A sputtered oxide layer enabled by a solution-processed oxide nanoparticle buffer layer to protect underlying layers is used to make semi-transparent perovskite solar cells. Single-junction semi-transparent cells are 12.3% efficient, and mechanically stacked tandems on silicon solar cells are 18.0% efficient. The semi-transparent perovskite solar cell has a T 80 lifetime of 124 h when operated at the maximum power point at 100 °C without additional sealing in ambient atmosphere under visible illumination. PMID:26880196

  15. Pulsed laser deposition of hydroxyapatite thin films on Ti-5Al-2.5Fe substrates with and without buffer layers

    NASA Astrophysics Data System (ADS)

    Nelea, V.; Ristoscu, C.; Chiritescu, C.; Ghica, C.; Mihailescu, I. N.; Pelletier, H.; Mille, P.; Cornet, A.

    2000-12-01

    We present a method for processing hydroxyapatite (HA) thin films on Ti-5Al-2.5Fe substrates. The films were grown by pulsed laser deposition (PLD) in vacuum at room temperature, using a KrF∗ excimer laser. The amorphous as-deposited HA films were recrystallized in ambient air by a thermal treatment at 550°C. The best results have been obtained when inserting a buffer layer of ceramic materials (TiN, ZrO2 or Al2O3). The films were characterized by complementary techniques: grazing incidence X-ray diffraction (GIXRD), scanning electron microscopy (SEM), cross-section transmission electron microscopy (XTEM), SAED, energy dispersive X-ray spectroscopy (EDS) and nanoindentation. The samples with buffer interlayer preserve the stoichiometry are completely recrystallized and present better mechanical characteristics as compared with that without buffer interlayer.

  16. Low current operation of GaN-based blue-violet laser diodes fabricated on sapphire substrate using high-temperature-grown single-crystal AlN buffer layer

    NASA Astrophysics Data System (ADS)

    Ohba, Yasuo; Gotoda, Toru; Kaneko, Kei

    2007-01-01

    Low current laser operation at 405 nm has been demonstrated for the first time for the devices fabricated on sapphire substrates by metalorganic chemical vapor deposition (MOCVD) using a high-temperature-grown single-crystal AlN buffer. The thick optical guiding layers were adopted to improve optical confinement. The device structure was the 2-μm-wide ridge-stripe type without facet coating. The minimum threshold current and current density were 60 mA and 3.8 kA/cm 2 for cavity lengths of 500 mm and 1 mm, respectively. These data were comparable to those reported using the special dislocation reduction techniques. The threshold current density linearly decreases with decreasing inverse of cavity length. It was expected that the low threshold current density ranging from 1 to 2 kA/cm 2 could be realized by adapting high reflection coating for laser facets. This expected current density was comparable to values realized for devices grown on the thick freestanding GaN as substrates. These findings support the promising potential of the HT-AlN buffer technique for production of advanced short-wavelength light-emitting devices on sapphire substrates.

  17. Optical in-situ monitoring system for simultaneous measurement of thickness and curvature of thick layer stacks during hydride vapor phase epitaxy growth of GaN

    NASA Astrophysics Data System (ADS)

    Semmelroth, K.; Berwian, P.; Schröter, C.; Leibiger, G.; Schönleber, M.; Friedrich, J.

    2015-10-01

    For improved real-time process control we integrated a novel optical in-situ monitoring system in a vertical reactor for hydride vapor phase epitaxy (HVPE) growth of gallium nitride (GaN) bulk crystals. The in-situ monitoring system consists of a fiber-optical interferometric sensor in combination with an optimized differential measuring head. The system only needs one small optical path perpendicular to the center of the layer stack typically consisting of sapphire as substrate and GaN. It can handle sample distances up to 1 m without difficulty. The in-situ monitoring system is simultaneously measuring the optical layer thicknesses of the GaN/sapphire layer stack and the absolute change of the distance between the measuring head and the backside of the layer stack. From this data it is possible to calculate the thickness of the growing GaN up to a thickness of about 1000 μm and the absolute change in curvature of the layer stack. The performance of the in-situ monitoring system is shown and discussed based on the measured interference signals recorded during a short-time and a long-time HVPE growth run.

  18. Effect of pectin on jejunal glucose absorption and unstirred layer thickness in normal man.

    PubMed Central

    Flourie, B; Vidon, N; Florent, C H; Bernier, J J

    1984-01-01

    The effect of high methoxy apple pectin, a carbohydrate gelling agent, on the intestinal absorption of glucose, water, and sodium was studied in man. The effect of intraluminal fibre was evaluated in 22 healthy volunteers by the intestinal perfusion technique under an occlusive balloon. The test solutions (NaCl 130 mM, KCl 5 mM, glucose or mannitol 30 mM, PEG 4000 5 g/l) were perfused just beyond the ligament of Treitz at a rate of 10 ml/min. A 25 cm segment was studied. Three concentrations of pectin were tested: 6, 10, and 15 g/l. The effect of this pectin at two concentrations, 6 and 10 g/l, on the jejunal unstirred layer thickness was evaluated in nine other healthy subjects by an electrical technique. In mannitol solution, pectin reversed water and sodium absorption, whatever its concentration was, while in glucose solution it significantly reduced absorption of water and sodium at 10 and 15 g/l only (p less than 0.01). It significantly reduced glucose absorption at all concentrations (p less than 0.01). This reduction was found to be correlated with the solution viscosity (p less than 0.01). Pectin did not alter the glucose dependent sodium transport but increased significantly (p less than 0.001) the unstirred layer thickness. These results suggested that, in healthy man, pectin acutely given may impair intestinal absorption by means of an increased unstirred layer resistance. This effect could contribute to the diminished postprandial glycaemia observed in human subjects fed pectin. PMID:6432635

  19. Effect of pectin on jejunal glucose absorption and unstirred layer thickness in normal man.

    PubMed

    Flourie, B; Vidon, N; Florent, C H; Bernier, J J

    1984-09-01

    The effect of high methoxy apple pectin, a carbohydrate gelling agent, on the intestinal absorption of glucose, water, and sodium was studied in man. The effect of intraluminal fibre was evaluated in 22 healthy volunteers by the intestinal perfusion technique under an occlusive balloon. The test solutions (NaCl 130 mM, KCl 5 mM, glucose or mannitol 30 mM, PEG 4000 5 g/l) were perfused just beyond the ligament of Treitz at a rate of 10 ml/min. A 25 cm segment was studied. Three concentrations of pectin were tested: 6, 10, and 15 g/l. The effect of this pectin at two concentrations, 6 and 10 g/l, on the jejunal unstirred layer thickness was evaluated in nine other healthy subjects by an electrical technique. In mannitol solution, pectin reversed water and sodium absorption, whatever its concentration was, while in glucose solution it significantly reduced absorption of water and sodium at 10 and 15 g/l only (p less than 0.01). It significantly reduced glucose absorption at all concentrations (p less than 0.01). This reduction was found to be correlated with the solution viscosity (p less than 0.01). Pectin did not alter the glucose dependent sodium transport but increased significantly (p less than 0.001) the unstirred layer thickness. These results suggested that, in healthy man, pectin acutely given may impair intestinal absorption by means of an increased unstirred layer resistance. This effect could contribute to the diminished postprandial glycaemia observed in human subjects fed pectin. PMID:6432635

  20. Thickness determination of few-layer hexagonal boron nitride films by scanning electron microscopy and Auger electron spectroscopy

    SciTech Connect

    Sutter, P. Sutter, E.

    2014-09-01

    We assess scanning electron microscopy (SEM) and Auger electron spectroscopy (AES) for thickness measurements on few-layer hexagonal boron nitride (h-BN), the layered dielectric of choice for integration with graphene and other two-dimensional materials. Observations on h-BN islands with large, atomically flat terraces show that the secondary electron intensity in SEM reflects monolayer height changes in films up to least 10 atomic layers thickness. From a quantitative analysis of AES data, the energy-dependent electron escape depth in h-BN films is deduced. The results show that AES is suitable for absolute thickness measurements of few-layer h-BN of 1 to 6 layers.