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Sample records for buffer layer thickness

  1. The roles of buffer layer thickness on the properties of the ZnO epitaxial films

    NASA Astrophysics Data System (ADS)

    Tang, Kun; Huang, Shimin; Gu, Shulin; Zhu, Shunming; Ye, Jiandong; Xu, Zhonghua; Zheng, Youdou

    2016-12-01

    In this article, the authors have investigated the optimization of the buffer thickness for obtaining high-quality ZnO epi-films on sapphire substrates. The growth mechanism of the buffers with different thickness has been clearly revealed, including the initial nucleation and vertical growth, the subsequent lateral growth with small grain coalescence, and the final vertical growth along the existing larger grains. Overall, the quality of the buffer improves with increasing thickness except the deformed surface morphology. However, by a full-scale evaluation of the properties for the epi-layers, the quality of the epi-film is briefly determined by the surface morphology of the buffer, rather than the structural, optical, or electrical properties of it. The best quality epi-layer has been grown on the buffer with a smooth surface and well-coalescent grains. Meanwhile, due to the huge lattice mismatch between sapphire and ZnO, dislocations are inevitably formed during the growth of buffers. More importantly, as the film grows thicker, the dislocations may attracting other smaller dislocations and defects to reduce the total line energy and thus result in the formation of V-shape defects, which are connected with the bottom of the threading dislocations in the buffers. The V-defects appear as deep and large hexagonal pits from top view and they may act as electron traps which would affect the free carrier concentration of the epi-layers.

  2. Optimal Cu buffer layer thickness for growing epitaxial Co overlayers on Si(111)7 x 7

    SciTech Connect

    Ivanov, Yu. P.; Zotov, A. V.; Ilin, A. I.; Davydenko, A. V.

    2011-10-15

    Using scanning tunneling microscopy, reflection high energy diffraction and magnetic optical Kerr effect measurements, growth mode and the magnetic properties of epitaxial Co films on Si(111) with epitaxial Cu(111) buffer layers of various thicknesses have been studied. The strained 3.5-monolayer-thick Cu/Si(111) film has been found to be an optimal buffer, in which case an almost ideal layer-by-layer like growth of Co is observed up to six Co monolayers, due to a negligible lattice mismatch. The coercivity of Co films grown in this layer-by-layer like fashion has been determined to be about 10 Oe, testifying to the high quality of the formed Co film and Co/Cu interface. Changeover of the Co film growth mode from layer-by-layer like to multilayer has been found to result in the transition of the film magnetic properties from isotropic to markedly uniaxially anisotropic.

  3. Threading dislocations in GaAs epitaxial layers on various thickness Ge buffers on 300 mm Si substrates

    NASA Astrophysics Data System (ADS)

    Bogumilowicz, Y.; Hartmann, J. M.; Rochat, N.; Salaun, A.; Martin, M.; Bassani, F.; Baron, T.; David, S.; Bao, X.-Y.; Sanchez, E.

    2016-11-01

    We have grown GaAs epitaxial layers on Ge buffers, themselves on Si (001) substrates, using an Applied Materials 300 mm metal organic chemical vapor deposition tool. We varied the Ge buffer thickness between 0.36 and 1.38 μm and studied the properties of a 0.27 μm thick GaAs layer on top. We found that increasing the Ge buffer thickness yielded smoother GaAs films with an rms surface roughness as low as 0.5 nm obtained on a 5×5 μm2 area. The bow of the substrate increased following a linear law with the epitaxial stack thickness up to 240 μm for a 1.65 μm stack. We have also characterized the threading dislocations present in the GaAs layers using X-ray diffraction and cathodoluminescence. Increasing the Ge buffer thickness resulted in lower threading dislocation densities, enabling us to obtain anti-phase boundary - free GaAs films with a threading dislocation density as low as 3×107 cm-2. In addition, atomic force microscopy surface topology measurements showed the presence of pits in the GaAs layers whose density agreed well with other threading dislocation density assessments. It thus seems that threading dislocations can in certain cases induce some growth rate variations, making them visible in as-grown GaAs films. Using thicker Ge buffers results in smoother films with less threading dislocations, with the side effect of increasing the bow on the wafer. If bow is not an issue, this is a practical approach to improve the GaAs (on Ge buffer) on silicon quality.

  4. Characteristics of GaN-based light emitting diodes with different thicknesses of buffer layer grown by HVPE and MOCVD

    NASA Astrophysics Data System (ADS)

    Tian, Pengfei; Edwards, Paul R.; Wallace, Michael J.; Martin, Robert W.; McKendry, Jonathan J. D.; Gu, Erdan; Dawson, Martin D.; Qiu, Zhi-Jun; Jia, Chuanyu; Chen, Zhizhong; Zhang, Guoyi; Zheng, Lirong; Liu, Ran

    2017-02-01

    GaN-based light emitting diodes (LEDs) have been fabricated on sapphire substrates with different thicknesses of GaN buffer layer grown by a combination of hydride vapor phase epitaxy and metalorganic chemical vapor deposition. We analyzed the LED efficiency and modulation characteristics with buffer thicknesses of 12 μm and 30 μm. With the buffer thickness increase, cathodoluminescence hyperspectral imaging shows that the dislocation density in the buffer layer decreases from  ∼1.3  ×  108 cm‑2 to  ∼1.0  ×  108 cm‑2, and Raman spectra suggest that the compressive stress in the quantum wells is partly relaxed, which leads to a large blue shift in the peak emission wavelength of the photoluminescence and electroluminescent spectra. The combined effects of the low dislocation density and stress relaxation lead to improvements in the efficiency of LEDs with the 30 μm GaN buffer, but the electrical-to-optical modulation bandwidth is higher for the LEDs with the 12 μm GaN buffer. A rate equation analysis suggests that defect-related nonradiative recombination can help increase the modulation bandwidth but reduce the LED efficiency at low currents, suggesting that a compromise should be made in the choice of defect density.

  5. 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.

  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.

  7. Crack-free thick (∼5 µm) α-Ga2O3 films on sapphire substrates with α-(Al,Ga)2O3 buffer layers

    NASA Astrophysics Data System (ADS)

    Oda, Masaya; Kaneko, Kentaro; Fujita, Shizuo; Hitora, Toshimi

    2016-12-01

    To obtain crack-free thick α-Ga2O3 films on sapphire substrates, effects and behaviors of buffer layers have been investigated. With the growth of an α-Ga2O3 layer, there appeared an unintentionally formed layer in the sample, which was associated with stress accumulation and could be the seed for crack generation. We obtained a thick (∼5 µm) α-Ga2O3 layer on a sapphire substrate with the insertion of α-(Al0.12Ga0.88)2O3/α-(Al0.02Ga0.98)2O3 buffer layers, and for this sample, we did not observe the intermediate layer, suggesting that the buffer layers were effective for eliminating the stress accumulation at the α-Ga2O3/sapphire interface region.

  8. Aqueous Chemical Solution Deposition of Novel, Thick and Dense Lattice-Matched Single Buffer Layers Suitable for YBCO Coated Conductors: Preparation and Characterization

    PubMed Central

    Narayanan, Vyshnavi; Van Steenberge, Sigelinde; Lommens, Petra; Van Driessche, Isabel

    2012-01-01

    In this work we present the preparation and characterization of cerium doped lanthanum zirconate (LCZO) films and non-stoichiometric lanthanum zirconate (LZO) buffer layers on metallic Ni-5% W substrates using chemical solution deposition (CSD), starting from aqueous precursor solutions. La2Zr2O7 films doped with varying percentages of Ce at constant La concentration (La0.5CexZr1−xOy) were prepared as well as non-stoichiometric La0.5+xZr0.5−xOy buffer layers with different percentages of La and Zr ratios. The variation in the composition of these thin films enables the creation of novel buffer layers with tailored lattice parameters. This leads to different lattice mismatches with the YBa2Cu3O7−x (YBCO) superconducting layer on top and with the buffer layers or substrate underneath. This possibility of minimized lattice mismatch should allow the use of one single buffer layer instead of the current complicated buffer architectures such as Ni-(5% W)/LZO/LZO/CeO2. Here, single, crack-free LCZO and non-stoichiometric LZO layers with thicknesses of up to 140 nm could be obtained in one single CSD step. The crystallinity and microstructure of these layers were studied by XRD, and SEM and the effective buffer layer action was studied using XPS depth profiling.

  9. Capacitance-voltage and retention characteristics of Pt/SrBi2Ta2O9/HfO2/Si structures with various buffer layer thickness

    NASA Astrophysics Data System (ADS)

    Tang, M. H.; Sun, Z. H.; Zhou, Y. C.; Sugiyama, Y.; Ishiwara, H.

    2009-05-01

    The metal-ferroelectric-insulator-semiconductor (MFIS) structure diodes with SrBi2Ta2O9 (SBT) as ferroelectric thin film and HfO2 as insulating buffer layer were fabricated. The electrical properties of MFIS structure were investigated for different HfO2 buffer layer thickness. The experimental results show that the memory window extended significantly as the HfO2 layer thickness increased from 6 to 10 nm. It is also observed that the leakage current was reduced to about 10-10 A at applied voltage of 4 V, and the high and low capacitances remained distinguishable for over 8 h even if we extrapolate the measured data to 10 years.

  10. Buffer layer optimization for high efficiency CIGS solar cells

    NASA Astrophysics Data System (ADS)

    Severino, N.; Bednar, N.; Adamovic, N.

    2016-10-01

    This work presents a study concerning the numerical optimization of a buffer layer for high efficiency CIGS solar cells. The dependence of the solar cell properties on the buffer layer material, the layer thickness, the type and density of defects within the same layer were numerically investigated and analysed. Promising results were obtained with alternative Cd-free buffer layers (ZnSnO, InS and ZnS) in place of the standard CdS.

  11. Undoped Buffer Layer Development.

    DTIC Science & Technology

    1984-01-01

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

  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. Effect of different thickness crystalline SiC buffer layers on the ordering of MgB{sub 2} films probed by extended x-ray absorption fine structure

    SciTech Connect

    Putri, W. B. K.; Tran, D. H.; Kang, B.; Lee, O. Y.; Kang, W. N.; Miyanaga, T.; Yang, D. S.

    2014-03-07

    Extended X-ray absorption fine structure (EXAFS) spectroscopy is a powerful method to investigate the local structure of thin films. Here, we have studied EXAFS of MgB{sub 2} films grown on SiC buffer layers. Crystalline SiC buffer layers with different thickness of 70, 100, and 130 nm were deposited on the Al{sub 2}O{sub 3} (0001) substrates by using a pulsed laser deposition method, and then MgB{sub 2} films were grown on the SiC buffer layer by using a hybrid physical-chemical vapor deposition technique. Transition temperature of MgB{sub 2} film decreased with increasing thickness of SiC buffer layer. However, the T{sub c} dropping went no farther than 100 nm-thick-SiC. This uncommon behavior of transition temperature is likely to be created from electron-phonon interaction in MgB{sub 2} films, which is believed to be related to the ordering of MgB{sub 2} atomic bonds, especially in the ordering of Mg–Mg bonds. Analysis from Mg K-edge EXAFS measurements showed interesting ordering behavior of MgB{sub 2} films. It is noticeable that the ordering of Mg–B bonds is found to decrease monotonically with the increase in SiC thickness of the MgB{sub 2} films, while the opposite happens with the ordering in Mg–Mg bonds. Based on these results, crystalline SiC buffer layers in MgB{sub 2} films seemingly have evident effects on the alteration of the local structure of the MgB{sub 2} film.

  14. Buffer layer for thin film structures

    SciTech Connect

    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.

  15. 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.

  16. 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.

  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. 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.

  19. 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.

  20. 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.

  1. Lightwave coupler utilizing a tapered buffer layer.

    PubMed

    Kishioka, K

    1988-06-01

    We discuss the performance of a lightwave coupler utilizing a tapered buffer layer. The coupler with a ridge waveguide is fabricated on a glass substrate and high coupling efficiencies of 75% and 50% are measured for the operations of coupling from the waveguide to a light beam and from the laser beam into the waveguide, respectively. Further, experimental results of the rigid connection between the optical fiber and the waveguide are demonstrated. We also describe how the coupler differs from the conventional tapered guiding-layer coupler.

  2. 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.

  3. 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.

  4. Buffer layer investigations on MFIS capacitors consisting of ferroelectric poly[vinylidene fluoride trifluoroethylene

    NASA Astrophysics Data System (ADS)

    Henkel, K.; Seime, B.; Paloumpa, I.; Müller, K.; Schmeißer, D.

    2010-02-01

    In this paper we present capacitance-voltage (CV) measurements on metal-ferroelectric-insulator-semiconductor (MFIS) capacitors with poly[vinylidene fluoride trifluoroethylene] (P[VDF/TrFE] as ferroelectric layer and SiO2, Al2O3 and HfO2 as buffering insulator layer. In order to discuss our data in a quantitative manner we perform fits to the data based on a model proposed by Miller and McWorther. The improvement of the polarization values and subsequently its effect on the hysteresis of the CV curve by the successive shrinking of the buffer layer thickness and the following choice of a high-k buffer material is demonstrated. Our data underline that a saturated polarization of P[VDF/TrFE] cannot be controlled with a SiO2 buffer layer and the insertion of a high-k buffer layer is essential for further improvements of the characteristics of MFIS stacks.

  5. 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.

  6. Thin film photovoltaic devices with a minimally conductive buffer layer

    DOEpatents

    Barnes, Teresa M.; Burst, James

    2016-11-15

    A thin film photovoltaic device (100) with a tunable, minimally conductive buffer (128) layer is provided. The photovoltaic device (100) may include a back contact (150), a transparent front contact stack (120), and an absorber (140) positioned between the front contact stack (120) and the back contact (150). The front contact stack (120) may include a low resistivity transparent conductive oxide (TCO) layer (124) and a buffer layer (128) that is proximate to the absorber layer (140). The photovoltaic device (100) may also include a window layer (130) between the buffer layer (128) and the absorber (140). In some cases, the buffer layer (128) is minimally conductive, with its resistivity being tunable, and the buffer layer (128) may be formed as an alloy from a host oxide and a high-permittivity oxide. The high-permittivity oxide may further be chosen to have a bandgap greater than the host oxide.

  7. 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.

  8. High Jc coated conductors with a simple buffer layer architecture

    NASA Astrophysics Data System (ADS)

    Gianni, L.; Baldini, A.; Bindi, M.; Gauzzi, A.; Rampino, S.; Zannella, S.

    2005-10-01

    We report on the in situ route for the continuous fabrication of YBCO coated conductors (CC) by thermal co-evaporation. CC architecture consists of YBCO film grown on biaxially textured Ni-alloys tapes buffered with a single layer of CeO2. The buffer layer deposition has been optimized by either e-beam or thermal evaporation using respectively ceria or metallic cerium. Best results have been obtained on CeO2 film, with a thickness less or equal than 100 nm, grown in a reducing atmosphere at 690 °C with a growth rate of 2.4 Å/s. The optimal samples exhibit a highly biaxial texture, as indicated by FWHM values in the range of 5-8° and 4-6° for respectively in- and out-of-plane orientations. The layers are characterized by an uniform and crack-free surface with an average roughness lower than 10 nm. SIMS analysis confirms the effectiveness of CeO2 buffer layer against Ni interdiffusion. This template allows to obtain YBCO films strong textured, with good superconductive properties. YBCO texture data are equivalent the CeO2 ones. Midpoint critical temperature, Tc, falls reproducibly in 87-88 K range, with transition widths ΔTc < 2-3 K. Critical current density, Jc, up to 2 MA/cm2 at 77 K in self-field, have been achieved in a meter long CC corresponding to Ic/width value of 130 A/cm-width. Uniformity and reproducibility of long CC properties are under optimization.

  9. 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).

  10. 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.

  11. 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.

  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. 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.

  14. 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).

  15. Perpendicular magnetization of CoFeB on top of an amorphous buffer layer

    NASA Astrophysics Data System (ADS)

    Kim, Dongseok; Jung, K. Y.; Joo, Sungjung; Jang, Youngjae; Hong, Jinki; Lee, B. C.; You, C. Y.; Cho, J. H.; Kim, M. Y.; Rhie, K.

    2015-01-01

    Perpendicular magnetic anisotropy was observed in sputtered FeZr/CoFeB/MgO multilayers. A thin paramagnetic amorphous FeZr layer was used as a buffer layer and perpendicular anisotropy was obtained by annealing the samples without an external magnetic field. The critical CoFeB thickness for perpendicular anisotropy was 1.8 nm; the anisotropy changes from out-of-plane to in-plane as the CoFeB thickness increases beyond this point. Perpendicular anisotropy was also enhanced when a Ta layer was capped on top of the MgO layer. The amorphous buffer provided better perpendicular anisotropy than previously reported Ta buffer, and it may be applied to perpendicular magnetization MRAM devices where good uniformity of tunnel junctions is required.

  16. 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.

  17. 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.

  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

    DOEpatents

    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. 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.

  1. 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.

  2. 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.

  3. 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.

  4. Dependence of Magnetic Properties of Co/Pt Multilayers on Deposition Temperature of Pt Buffer Layers

    NASA Astrophysics Data System (ADS)

    Shiomi, Shigeru; Nishimura, Tomotaka; Kobayashi, Tadashi; Masuda, Morio

    1993-04-01

    A 15-nm-thick Pt buffer layer was deposited on a glass slide at temperature Ts(Ptbuf) ranging from 30 to 300°C by e-gun evaporation. Following the cooling in vacuum to ambient temperature, Co and Pt layers have been alternately deposited on it. Very large perpendicular anisotropy and coercivity have been obtained at Ts(Ptbuf) higher than 200°C. The (111) preferred orientation of the Co/Pt multilayer as well as the Pt buffer layer became more pronounced with elevating Ts(Ptbuf), to which the enhancement of perpendicular anisotropy with elevating Ts(Ptbuf) might be ascribable.

  5. YSZ buffer layers and YBCO superconducting tapes with enhanced biaxial alignment and properties

    NASA Astrophysics Data System (ADS)

    Savvides, N.; Gnanarajan, S.

    2003-05-01

    Commercial applications of YBa 2Cu 3O 7 (YBCO) superconducting cables require viable and scalable manufacturing processes. We have investigated the evolution of the biaxial alignment of yttria-stabilized zirconia (YSZ) buffer layers with increasing film thickness (50-900 nm) and report on a method of fabricating highly aligned YBCO tapes using a thin epitaxial YSZ buffer layer as template. The method employs magnetron and ion beam assisted deposition (IBAD) techniques followed by epitaxial growth to produce the buffer architectures IBAD-YSZ and epi-YSZ/IBAD-YSZ onto optically polished hastelloy metal substrates. Subsequent in situ deposition of YBCO films is used to determine the biaxial alignment at the surface of the buffer architecture, and to show that 100-200 nm thick epi-YSZ layers suffice to yield YBCO tapes that have enhanced biaxial alignment (Δ φ=9-10°) and high critical current densities: J c(77 K)=(1-2)×10 6 A cm -2 and J c(5 K,1 T)=8×10 6 A cm -2. Atomic force microscopy of the surface microstructure of the YSZ buffer layers and YBCO films reveals some grain coarsening in the epi-YSZ layers compared to the IBAD-YSZ layers while the YBCO tapes show significant outgrowths (∼200 nm) and large grains (800-1200 nm) that are similar to high- Jc YBCO films grown on single crystal MgO(1 0 0) substrates.

  6. Organic Photovoltaic Cells with Improved Performance Using Bathophenanthroline as a Buffer Layer

    NASA Astrophysics Data System (ADS)

    Wang, Na-na; Yu, Jun-sheng; Lin, Hui; Jiang, Ya-dong

    2010-02-01

    The role of bathophenanthroline (Bphen) as a buffer layer inserted between fullerene (C60) and Ag cathode in organic photovoltaic (OPV) cell was discussed. By introducing Bphen as a buffer layer with thicknes from 0 to 2.5 nm, the power conversion efficiency of the OPV cell based on copper phthalocyanine (CuPc) and C60 was increased from 0.87% to 2.25% under AM 1.5 solar illumination at an intensity of 100 mW/cm2, which was higher than that of bathocuproine used as a buffer layer. The photocurrent-voltage characteristics showed that Bphen effectively improves electron transport through C60 layer into Ag electrode and leads to balance charge carrier transport capability. The influence of Bphen thickness on OPV cells was also investigated. Furthermore, the absorption spectrum shows that an additional Bphen layer enhances the light harvest capability of CuPc/C60.

  7. Steady incompressible variable thickness shear layer aerodynamics

    NASA Technical Reports Server (NTRS)

    Chi, M. R.

    1976-01-01

    A shear flow aerodynamic theory for steady incompressible flows is presented for both the lifting and non lifting problems. The slow variation of the boundary layer thickness is considered. The slowly varying behavior is treated by using multitime scales. The analysis begins with the elementary wavy wall problem and, through Fourier superpositions over the wave number space, the shear flow equivalents to the aerodynamic transfer functions of classical potential flow are obtained. The aerodynamic transfer functions provide integral equations which relate the wall pressure and the upwash. Computational results are presented for the pressure distribution, the lift coefficient, and the center of pressure travel along a two dimensional flat plate in a shear flow. The aerodynamic load is decreased by the shear layer, compared to the potential flow. The variable thickness shear layer decreases it less than the uniform thickness shear layer based upon equal maximum shear layer thicknesses.

  8. 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.

  9. Matching characteristics of different buffer layers with VO2 thin films

    NASA Astrophysics Data System (ADS)

    Yang, Kai; Zhang, Dongping; Liu, Yi; Guan, Tianrui; Qin, Xiaonan; Zhong, Aihua; Cai, Xingmin; Fan, Ping; Lv, Weizhong

    2016-10-01

    VO2 thin films were fabricated by reactive DC magnetron sputtering on different buffer layers of MgF2, Al2O3 and TiO2, respectively. The crystallinity and orientation relationship, thickness of VO2 thin films, atoms vibrational modes, optical and electrical property, surface morphology of films were characterized by X-ray diffraction, Raman scattering microscopy, step profiler, spectrophotometer, four-probe technique, and scanning electron microscopy, respectively. XRD results investigated that the films have preferential crystalline planes VO2 (011). The crystallinity of VO2 films grown on TiO2 buffer layers are superior to VO2 directly deposited on soda-lime glass. The Raman bands of the VO2 films correspond to an Ag symmetry mode of VO2 (M). The sample prepared on 100nm TiO2 buffer layer appears nanorods structure, and exhibits remarkable solar energy modulation ability as high as 5.82% in full spectrum and 23% in near infrared spectrum. Cross-sectional SEM image of the thin films samples indicate that MgF2 buffer layer has clear interface with VO2 layer. But there are serious interdiffusion phenomenons between Al2O3, TiO2 buffer layer with VO2 layer.

  10. Strain compensation in a semiconducting device structure using an intentionally mismatched uniform buffer layer

    NASA Astrophysics Data System (ADS)

    Kujofsa, Tedi; Ayers, John E.

    2016-12-01

    The extent of strain relaxation in semiconducting device heterostructures has important implications in the design of high electron mobility transistors, light-emitting diodes, and laser diodes, in which the residual strain affects the device characteristics. In this work, we develop the theoretical framework for understanding strain compensation in a semiconductor device layer using a uniform buffer layer which can be intentionally mismatched to the material above. Specifically, we determined the critical condition for complete strain compensation in the device layer by intentionally introducing a compositional mismatch at the device-buffer interface. We present minimum energy calculations and show that for a given device layer with fixed mismatch and layer thickness, the buffer layer may be designed with the appropriate combination of thickness and mismatch such that the device layer will have zero residual strain in equilibrium. Such a structure can be referred to as a completely strain-compensated design. In the more general case, there may be partial strain compensation, and we give a simple physics-based Gaussian-type function describing the residual strain in the device layer. We have applied this general framework to In x Ga1-x As/GaAs (001) heterostructures for the purpose of illustration, but the work is applicable to any diamond or zinc blende (001) heteroepitaxial material system.

  11. Accelerating the L10 ordering transition of FePt(001) nanograins using composite buffer layers

    NASA Astrophysics Data System (ADS)

    Li, Guoqing; Zheng, Yuanping; Hayashi, Kenichi; Takanashi, Koki

    2011-07-01

    This paper reports fabrication of 2-nm-thick L10 FePt films at a low substrate temperature of 400 °C using composite MgO and FeAl buffer layers on (001) MgO substrates. The FeAl buffer layer is crucial in promoting the ordered L10 growth of (001) FePt by allowing additional heat uptake. The MgO buffer layer prevents interlayer diffusion of FeAl into the FePt films and induces (001) texture growth. The deposited FePt films consist of isolated nanograins about 13 nm in size. These films have (001) texture and perpendicular magnetic anisotropy with a coercivity of up to 19 kOe. They have potential applications in perpendicular magnetic recording.

  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. 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.

    2017-01-01

    To study the role of novel Gd_2Zr_2O_7/Ce_{0.9}La_{0.1}O_2 buffer layer structure on a biaxially textured NiW substrate, a set of YBa_2Cu_3O_{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.

  15. Epitaxial growth of cadmium telluride films on silicon with a buffer silicon carbide layer

    NASA Astrophysics Data System (ADS)

    Antipov, V. V.; Kukushkin, S. A.; Osipov, A. V.

    2017-02-01

    An epitaxial 1-3-μm-thick cadmium telluride film has been grown on silicon with a buffer silicon carbide layer using the method of open thermal evaporation and condensation in vacuum for the first time. The optimum substrate temperature was 500°C at an evaporator temperature of 580°C, and the growth time was 4 s. In order to provide more qualitative growth of cadmium telluride, a high-quality 100-nm-thick buffer silicon carbide layer was previously synthesized on the silicon surface using the method of topochemical substitution of atoms. The ellipsometric, Raman, X-ray diffraction, and electron-diffraction analyses showed a high structural perfection of the CdTe layer in the absence of a polycrystalline phase.

  16. Substrate-induced magnetism in epitaxial graphene buffer layers.

    PubMed

    Ramasubramaniam, A; Medhekar, N V; Shenoy, V B

    2009-07-08

    Magnetism in graphene is of fundamental as well as technological interest, with potential applications in molecular magnets and spintronic devices. While defects and/or adsorbates in freestanding graphene nanoribbons and graphene sheets have been shown to cause itinerant magnetism, controlling the density and distribution of defects and adsorbates is in general difficult. We show from first principles calculations that graphene buffer layers on SiC(0001) can also show intrinsic magnetism. The formation of graphene-substrate chemical bonds disrupts the graphene pi-bonds and causes localization of graphene states near the Fermi level. Exchange interactions between these states lead to itinerant magnetism in the graphene buffer layer. We demonstrate the occurrence of magnetism in graphene buffer layers on both bulk-terminated as well as more realistic adatom-terminated SiC(0001) surfaces. Our calculations show that adatom density has a profound effect on the spin distribution in the graphene buffer layer, thereby providing a means of engineering magnetism in epitaxial graphene.

  17. Optimization of CdS Buffer Layer for High Efficiency CIGS Solar Cells.

    PubMed

    Kim, Donguk; Jang, Yong-Jun; Jung, Ho-Sung; Kim, Minha; Baek, Dohyun; Yi, Junsin; Lee, Jaehyeong; Choi, Youngkwan

    2016-05-01

    In present work, effects of the thickness on the structural and optical properties of chemically deposited CdS thin films were investigated. In addition, we fabricated Cu(In, Ga)Se2 solar cells with various thicknesses of CdS buffer layer and optimized the thickness for a high efficiency. When the CdS thin films were thicker, the crystallinity improved but the transmittance decreased. The short-circuit current density (J(sc)) and the fill factor are the major efficiency limiting factors for the CIGS solar cells. As the thickness of the CdS buffer layer, the open-circuit voltage (V(oc)) and the fill factor increased, whereas the J(sc) slightly decreased. The improvement of the fill factor and thus efficiency resulted from larger shunt resistance. For the solar cells without a high resistive intrinsic ZnO layer, the highest efficiency was acquired at the thickness of 89 nm. With further increasing the thickness, the J(sc) decreased significantly, resulting in poor efficiency.

  18. Buffer layer engineering on graphene via various oxidation methods for atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Takahashi, Nobuaki; Nagashio, Kosuke

    2016-12-01

    The integration of a high-k oxide on graphene using atomic layer deposition requires an electrically reliable buffer layer. In this study, Y was selected as the buffer layer due to its highest oxidation ability among the rare-earth elements, and various oxidation methods (atmospheric, and high-pressure O2 and ozone annealing) were applied to the Y metal buffer layer. By optimizing the oxidation conditions of the top-gate insulator, we successfully improved the capacitance of the top gate Y2O3 insulator and demonstrated a large I on/I off ratio for bilayer graphene under an external electric field.

  19. Semiconducting chalcogenide buffer layer for oxide heteroepitaxy on Si(001)

    NASA Astrophysics Data System (ADS)

    Schmidt, D. A.; Ohta, Taisuke; Lu, C.-Y.; Bostwick, Aaron A.; Yu, Q.; Rotenberg, Eli; Ohuchi, F. S.; Olmstead, Marjorie A.

    2006-05-01

    We report controlled laminar growth of a crystalline transition metal oxide on Si(001) without SiOx or silicide formation by utilizing the chalcogenide semiconductor gallium sesquiselenide (Ga2Se3) as a nonreactive buffer layer. Initial nucleation of both pure and Co-doped anatase (TiO2) is along Ga2Se3 nanowire structures, coalescing to a flat, multidomain film within two molecular layers. Arsenic-terminated Si(001) [Si(001):As] is stable against pure O2, but oxidizes when both Ti and O2 are present. The Si -TiO2 valence band offset using either buffer layer is about 2.8eV, producing a staggered band alignment.

  20. 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.

  1. Advanced titania buffer layer architectures prepared by chemical solution deposition

    NASA Astrophysics Data System (ADS)

    Kunert, J.; Bäcker, M.; Brunkahl, O.; Wesolowski, D.; Edney, C.; Clem, P.; Thomas, N.; Liersch, A.

    2011-08-01

    Chemical solution deposition (CSD) was used to grow high-quality (100) oriented films of SrTiO3 (STO) on CSD CaTiO3 (CTO), Ba0.1Ca0.9TiO3 (BCT) and STO seed and template layers. These template films bridge the lattice misfit between STO and the nickel-tungsten (NiW) substrate, assisting in dense growth of textured STO. Additional niobium (Nb) doping of the STO buffer layer reduces oxygen diffusion which is necessary to avoid undesired oxidation of the NiW. The investigated templates offer suitable alternatives to established standard buffer systems like La2Zr2O7 (LZO) and CeO2 for coated conductors.

  2. Epitaxial MOD-YSZ buffer layers on IBAD-YSZ substrates

    NASA Astrophysics Data System (ADS)

    Jarzina, H.; Sievers, S.; Jooss, Ch; Freyhardt, H. C.; Lobinger, P.; Roesky, H. W.

    2005-03-01

    There are a number of reports on the epitaxial growth of MOD buffer layers for coated conductors. However, the quality of superconducting films deposited on top of these layers is often poor. We demonstrate that Y Ba2Cu3O7 (YBCO) layers with a high critical current density of 20 MA cm-2 (8 K) can be deposited on MOD-YSZ (ZrO2:10 mol% Y2O3) which has been grown epitaxially on YSZ(001) single crystals. Furthermore, high jc YBCO films are obtained on a MOD-YSZ buffer deposited on an IBAD (ion-beam-assisted-deposition)-YSZ substrate. In this case, critical current densities of 11 MA cm-2 (8 K) are observed. Finally, multilayers of MOD-YSZ on IBAD-YSZ substrates are prepared, where the development of texture with increasing film thickness is discussed as well as its possible technological impact.

  3. Plasmonic absorption enhancement in organic solar cells by nano disks in a buffer layer

    NASA Astrophysics Data System (ADS)

    Kim, Inho; Seok Jeong, Doo; Seong Lee, Taek; Seong Lee, Wook; Lee, Kyeong-Seok

    2012-05-01

    We demonstrate using finite-difference-time-domain calculations that embedding Ag nano disks (NDs) in the buffer layers of thin P3HT:PCBM organic solar cells can enhance optical absorption in the active layers at specific wavelength range. We show that the aspect ratio of the NDs is a key parameter for strong plasmonic absorption enhancement. Two different plasmonic absorption bands are observed stemming from optical refractive index differences among the layers surrounding the NDs in the solar cell devices. One absorption band by the surface plasmon mode localized at the interface of indium tin oxide/ND, which is undesirable for plasmonic absorption enhancement in the active layer, become negligible as the aspect ratio of the diameter-to-height increased. The other absorption band by the dipole-like surface plasmon mode, which plays a main role in enhancing the absorption in the active layer, is spectrally tunable by adjusting the aspect ratio of the NDs. The influences of diameter, height, and coverage of the NDs on optical absorption in the active layer are discussed. Embedding the optimal size NDs in the buffer layer leads to the enhanced total absorption in the 50 nm thick active layer by 16% relative to that without the NDs, and the optical absorption keeps enhanced with increasing the active layer thickness up to 90 nm. However, further increases in the active layer thickness are detrimental to absorption enhancement, which is considered to be caused by destructive interference between scattered light by the NDs and incident light.

  4. Efficient quantum dot light-emitting diodes with solution-processable molybdenum oxide as the anode buffer layer

    NASA Astrophysics Data System (ADS)

    He, Shaojian; Li, Shusheng; Wang, Fuzhi; Wang, Andrew Y.; Lin, Jun; Tan, Zhan'ao

    2013-05-01

    Quantum dot light-emitting diodes (QD-LEDs) are characterized by pure and saturated emission colors with narrow bandwidth. Optimization of the device interface is an effective way to achieve stable and high-performance QD-LEDs. Here we utilized solution-processed molybdenum oxide (MoOx) as the anode buffer layer on ITO to build efficient QD-LEDs. Using MoOx as the anode buffer layer provides the QD-LED with good Ohmic contact and a small charge transfer resistance. The device luminance is nearly independent of the thickness of the MoOx anode buffer layer. The QD-LEDs with a MoOx anode buffer layer exhibit a maximum luminance and luminous efficiency of 5230 cd m-2 and 0.67 cd A-1 for the yellow emission at 580 nm, and 7842 cd m-2 and 1.49 cd A-1 for the red emission at 610 nm, respectively.

  5. GaN on Silicon Substrate with AlN Buffer Layer for UV Photodiode

    NASA Astrophysics Data System (ADS)

    Chuah, L. S.; Thahab, S. M.; Hassan, Z.

    Nitrogen plasma-assisted molecular beam epitaxy (PAMBE) deposited GaN thin films on (111) n-type silicon substrate with different thickness AlN buffer layers are investigated and distinguished by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM) and Raman scattering. The thickness of AlN buffer layer ranged from 200 nm to 300 nm. Besides that, the electrical characteristics of the GaN thin film for ultraviolet detecting utilizations are studied by calculating the photo current/dark current ratio on a metal-semiconductor-metal (MSM) photodiode with and without the illumination of Hg-lamp source. The devices have been tested over room temperature (RT). The photocurrent analysis, together with the study of Schottky barrier height (SBH) development, ascertain that the principal mechanism of photo transport is thermionic emission. The photocurrent value is rigorously dependent on Schottky barrier height. The GaN/AlN(200 nm)/n-Si MSM photodiode produces the highest photo/dark current ratio for the lowest strain that consists of the GaN film grown on the AlN (200 nm) buffer layer.

  6. Crystallinity of YBCO thin films on an MgO substrate using an amorphous buffer layer deposited at a low temperature

    NASA Astrophysics Data System (ADS)

    Nakamura, Y.; Kudo, S.; Mukaida, M.; Ohshima, S.

    2002-10-01

    We have investigated crystallinity of YBCO films on an MgO substrate using an amorphous buffer layer. The evaluated films are obtained as follows: an amorphous YBCO buffer layer is deposited on the MgO substrate at a low temperature (200 °C); and then, an amorphous buffer layer is crystallized by the thermal annealing at a high temperature from 910 to 1030 °C; finally, main YBCO film is grown on the crystalline YBCO buffer layer over the MgO substrate. A significant improvement in the crystalline quality of the YBCO films was achieved, when amorphous buffer layers of 100 nm in thickness were crystallized by annealing temperature 950 °C and then annealing is continued for 1 h in air atmosphere. We confirmed that YBCO films grown on a well-crystallized buffer layer had better crystallinity than ones on bare MgO substrate, which has substantially large lattice mismatch.

  7. Development of buffer layers on 30 mm wide textured metal substrates for REBCO coated conductors

    NASA Astrophysics Data System (ADS)

    Yamaguchi, T.; Ota, H.; Ohki, K.; Konishi, M.; Ohmatsu, K.

    2010-11-01

    We have been studying REBa2Cu3Ox (RE: rare earth elements) coated conductors on clad-type substrates. We developed coated conductors on the 10 mm wide clad-type tape, and succeeded in obtaining the maximum critical current of 380 A/cm with the 2.0 μm thick GdBa2Cu3Ox superconducting film. At present, we are trying to widen the tape width from 10 mm to 30 mm in order to increase production throughput. We report our recent progress on scaling-up of the buffer layers and their properties. The buffer layers consisted of three layers; CeO2 as the seed layer, yttrium-stabilized zirconia (YSZ) as the diffusion barrier layer and CeO2 as the lattice matching layer. They were grown by the RF-sputtering method and the electron beam evaporation technique (EB). EB deposition has possibility of higher throughput compared with the RF-sputtering. The intensity ratio of (2 0 0) to (2 0 0) + (1 1 1) for the lattice matching layer showed as high as 98%. The uniform properties of 40 m long and 30 mm wide substrates were successfully produced by all sputtering method. Additionally, the tape travel speed of the seed layer can be increased from 7 m/h (RF-sputtering deposition) to 10 m/h (EB deposition) on short sample (0.3 m long).

  8. Alloys containing antimony as metamorphic buffer layer for device applications

    NASA Astrophysics Data System (ADS)

    Rodriguez, Benny Perez

    This work explores the stress/strain relaxation kinetics in metamorphic buffer layers of GaAs1-xSbx/GaAs (001) grown by molecular beam epitaxy. The real-time stress/strain evolution was obtained using an in situ multi-beam optical sensor measurement, and combined with detailed analysis from x-ray diffraction, transmission electron microscopy, and atomic force microscopy. Several distinct stages of the strain relaxation were observed during growth of GaAs1-xSbx constant composition buffer layers, which are separated into three main regimes: pseudomorphic growth, fast strain relaxation and saturation. Constant composition layers of GaAs0.5Sb0.5/GaAs initially relax elastically followed by the rapid nucleation of both 60° and pure edge dislocations. The saturation regime is distinguished by coalescence of small islands that appears to trigger the formation of threading dislocations. The strain relaxation profile for GaAs0.5Sb0.5, GaAs0.61Sb0.39, and In0.2Ga0.8As films were modeled using Dodson and Tsao's model of effective stress, with a new representation for elastic interactions of misfit dislocations. The model results agree with the experimental data and show that repulsive interaction of misfit dislocations is responsible for the large residual stress. Using this model, estimated line dislocation densities are in good agreement with the values obtained experimentally. This could have potential application in the design of metamorphic buffer layers because our observations are made in real time on individual growth, without the need of external characterization to measure the dislocation density. In addition, this model offers new insights in estimating the dislocation glide energy for simulation purposes. Linearly graded GaAs1-xSbx films resulted in a decreased Sb incorporation, higher residual stress, and bifurcation in the tilt of the sample. Less aggressive grading resulted in more uniform incorporation and lower residual stress. Step graded films resulted in

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. Defect Reduction in Epitaxial Growth Using Superlattice Buffer Layers

    DTIC Science & Technology

    1988-07-01

    Katsuyama, Y. J. Yang and S. M. Bedair, Electron Dev. Lett., vol. 8, p. 240, 1987. 0 -15 -" Journal of (ryOstal (io iih 77 (108(,) ,xQ 9i4 S9 North-I...layer facilitat the csea of Gaosu 3 (5% in H2) + 500 sccm of H , and ed cross-sectional thickness measurements. trimethylgallium (TMG) + 500 sccm of H

  14. Layer coupling and read disturbances in a buffered magnetic logic environment

    NASA Astrophysics Data System (ADS)

    Windbacher, Thomas; Makarov, Alexander; Sverdlov, Viktor; Selberherr, Siegfried

    2016-10-01

    There are two major obstacles impeding computing systems from further advancements: The power dissipation due to leakage and the energy spent for the information transfer between memory and processor(s). The first issue is commonly handled by shutting down unused circuit parts, however, when the dormant circuits are turned on again, their previous state must be recovered. This is commonly realized by retrieving the required information from the memory, which exacerbates the limited bandwidth between memory and processor(s). In order to circumvent these limitations, we have proposed a non-volatile buffered magnetic logic grid with instant-on capability. Non-volatile magnetic flip flops and spin-transfer torque majority gates are combined to a compact regular structure, which enables a small layout foot print as well as it guarantees the reduction of the information transfer due to a shared buffer. In the proposed structure the information is passed from one magnetic layer to another by first running a current through the magnetic layer to be read, which subsequently generates a magnetization orientation encoded spin-transfer torque, when the polarized electron spins enter the next layer. Since the current passing through the junction also exerts a spin-transfer torque on the read layer, its magnetization orientation could be destabilized which might cause a read disturbance. However, during our simulations it was also found out that the stray fields of neighboring layers have a non-negligible influence on the proposed copy operation. In this work we investigate these potential read disturbances in detail for a 2-bit shift register for varying stray field strength by changing the thickness of the interconnection layer. We found that for closer proximity the acting stray fields not only stabilize but also speed up the copy procedure, while for increasing interconnection layer thickness oscillating domain walls are formed and the copy operation becomes unreliable.

  15. 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.

  16. 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.

  17. 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%.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. System for etching thick aluminum layers minimizes bridging and undercutting

    NASA Technical Reports Server (NTRS)

    1966-01-01

    Four step photoresist process for etching thick aluminum layers for semiconductor device contacts produces uniform contact surfaces, eliminates bridging, minimizes undercutting, and may be used on various materials of any thickness.

  3. The effect of employing the p/i buffer layers and in-situ hydrogen treatment for transparent a-Si:H solar cells.

    PubMed

    Lee, Da Jung; Yun, Sun Jin; Park, Min A; Lim, Jung Wook

    2014-05-01

    In this study, we describe the effects of various thicknesses of triple p/i buffer layers and hydrogen treatment on various performances in the fabrication of transparent a-Si:H solar cells. For the increment of buffer layer thickness, V(oc) increases steadily and J(sc) firstly increases and then decreases. The triple buffer layers also enhance the transmittance as well as conversion efficiency. For hydrogen plasma treatment, overall performances were enhanced with plasma power due to the passivation of dangling bonds at p/i interface. Therefore, the usage of triple buffer layers with proper treatment is beneficial to obtaining transparent a-Si:H solar cells with high quality.

  4. Enhancing the blocking temperature of perpendicular-exchange biased Cr2O3 thin films using buffer layers

    NASA Astrophysics Data System (ADS)

    Shimomura, Naoki; Pati, Satya Prakash; Nozaki, Tomohiro; Shibata, Tatsuo; Sahashi, Masashi

    2017-02-01

    In this study, we investigated the effect of buffer layers on the blocking temperature (TB) of perpendicular exchange bias of thin Cr2O3/Co exchange coupled films with a Ru spacer and revealed a high TB of 260 K for 20-nm-thick Cr2O3 thin films. By comparing the TB values of the 20-nm-thick Cr2O3 films on Pt and α-Fe2O3 buffers, we investigated the lattice strain effect on the TB. We show that higher TB values can be obtained using an α-Fe2O3 buffer, which is likely because of the lattice strain-induced increase in Cr2O3 magnetocrystalline anisotropy.

  5. Multilayers Diamond-Like Carbon Film with Germanium Buffer Layers by Pulsed Laser Deposition

    NASA Astrophysics Data System (ADS)

    Cheng, Y.; Lu, Y. M.; Guo, Y. L.; Huang, G. J.; Wang, S. Y.; Tian, F. T.

    Multilayer diamond-like carbon film with germanium buffer layers, which was composed of several thick DLC layers and thin germanium island “layers” and named as Ge-DLC film, was prepared on the germanium substrate by ultraviolet laser. The Ge-DLC film had almost same surface roughness as the pure DLC film. Hardness of the Ge-DLC film was above 48.1GPa, which was almost the same as that of pure DLC film. Meanwhile, compared to the pure DLC film, the critical load of Ge-DLC film on the germanium substrate increased from 81.6mN to 143.8mN. Moreover, Ge-DLC film on germanium substrates had no change after fastness tests. The results showed that Ge-DLC film not only kept high hardness but also had higher critical load than that of pure DLC film. Therefore, it could be used as practical protective films.

  6. Characterization of Cu buffer layers for growth of L10-FeNi thin films

    NASA Astrophysics Data System (ADS)

    Mizuguchi, M.; Sekiya, S.; Takanashi, K.

    2010-05-01

    A Cu(001) layer was fabricated on a Au(001) layer to investigate the use of Cu as a buffer layer for growing L10-FeNi thin films. The epitaxial growth of a Cu buffer layer was observed using reflection high-energy electron diffraction. The flatness of the layer improved drastically with an increase in the substrate temperature although the layer was an alloy (AuCu3). An FeNi thin film was epitaxially grown on the AuCu3 buffer layer by alternate monatomic layer deposition and the formation of an L10-FeNi ordered alloy was expected. The AuCu3 buffer layer is thus a promising candidate material for the growth of L10-FeNi thin films.

  7. 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).

  8. Heterointegration of III-V on silicon using a crystalline oxide buffer layer

    NASA Astrophysics Data System (ADS)

    Bhatnagar, K.; Rojas-Ramirez, J. S.; Contreras-Guerrero, R.; Caro, M.; Droopad, R.

    2015-09-01

    The integration of III-V compound semiconductors with Si can combine the cost advantage and maturity of Si technology with the superior performance of III-V materials. We have achieved the heteroepitaxial growth of III-V compound semiconductors on a crystalline SrTiO3 buffer layer grown on Si(0 0 1) substrates. A two-step growth process utilizing a high temperature nucleation layer of GaAs, followed by a low-temperature GaAs layer at a higher growth rate was employed to achieve highly crystalline thick GaAs layers on the SrTiO3/Si substrates with low surface roughness as seen by AFM. The effect of the GaAs nucleation layer on different surface terminations for the SrTiO3 layer was studied for both on axis and miscut wafers, which led to the conclusion that the Sr terminated surface on miscut substrates provides the best GaAs films. Using GaAs/STO/Si as virtual substrates, we have optimized the growth of high quality GaSb using the interfacial misfit (IMF) dislocation array technique. This work can lead to the possibility of realizing infrared detectors and next-generation high mobility III-V CMOS within the existing Si substrate infrastructure.

  9. Enhancement of perpendicular magnetic anisotropy and coercivity in ultrathin Ru/Co/Ru films through the buffer layer engineering

    NASA Astrophysics Data System (ADS)

    Kolesnikov, Alexander G.; Stebliy, Maxim E.; Ognev, Alexey V.; Samardak, Alexander S.; Fedorets, Aleksandr N.; Plotnikov, Vladimir S.; Han, Xiufeng; Chebotkevich, Ludmila A.

    2016-10-01

    We present results on a study of the interplay between microstructure and the magnetic properties of ultrathin Ru/Co/Ru films with perpendicular magnetic anisotropy (PMA). To induce PMA in the Co layer, we experimentally determined thicknesses of the buffer and capping layers of Ru. The maximum value of PMA was observed for the Co thickness of 0.9 nm with the 3 nm thick capping layer. The effective anisotropy field (H eff) and coercive force (H c) of the Co layer are very sensitive to the Ru buffer layer thickness (t b). The values of H eff and H c increase approximately by two and ten times, correspondingly, when t b changes from 6 to 20 nm, owing to an increase in volume fraction of the crystalline phase as a result of the grains’ growth. PMA is found to be mainly enhanced by elastic strains induced by the lattice mismatch on the Ru/Co and Co/Ru interfaces, leading to the deformation of the Co lattice. The surface impact is determined to be less than 10% of the magneto-elastic contribution to the effective anisotropy. Observation of the magnetic domain structure by means of polar Kerr microscopy reveals that out-of-plane magnetization reversal occurs through the nucleation, growth, and annihilation of domains, where the average size drastically rises with the increasing t b.

  10. 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.

  11. 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.

  12. 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.

  13. Efficient quantum dot light-emitting diodes with solution-processable molybdenum oxide as the anode buffer layer.

    PubMed

    He, Shaojian; Li, Shusheng; Wang, Fuzhi; Wang, Andrew Y; Lin, Jun; Tan, Zhan'ao

    2013-05-03

    Quantum dot light-emitting diodes (QD-LEDs) are characterized by pure and saturated emission colors with narrow bandwidth. Optimization of the device interface is an effective way to achieve stable and high-performance QD-LEDs. Here we utilized solution-processed molybdenum oxide (MoOx) as the anode buffer layer on ITO to build efficient QD-LEDs. Using MoOx as the anode buffer layer provides the QD-LED with good Ohmic contact and a small charge transfer resistance. The device luminance is nearly independent of the thickness of the MoOx anode buffer layer. The QD-LEDs with a MoOx anode buffer layer exhibit a maximum luminance and luminous efficiency of 5230 cd m(-2) and 0.67 cd A(-1) for the yellow emission at 580 nm, and 7842 cd m(-2) and 1.49 cd A(-1) for the red emission at 610 nm, respectively.

  14. Improved performance and stability of organic light-emitting devices with silicon oxy-nitride buffer layer

    NASA Astrophysics Data System (ADS)

    Poon, C. O.; Wong, F. L.; Tong, S. W.; Zhang, R. Q.; Lee, C. S.; Lee, S. T.

    2003-08-01

    The use of silicon oxy-nitride (SiOxNy) as an anode buffer layer in organic light-emitting devices (OLEDs) with a configuration of indium tin oxide (ITO)/SiOxNy/α-naphtylphenyliphenyl diamine (NPB)/8-hydroxyquinoline aluminum/Mg:Ag has been studied. With a SiOxNy buffer layer several angstroms thick, the device efficiency increased from 3.0 to 3.8 cd/A. The buffer layer also protected the ITO surface from contamination due to air exposure. Upon exposing the cleaned ITO substrate to air for one day before device fabrication, the device current efficiency and turn-on voltage degraded to 2.1 cd/A and 4.3 V, respectively, from 3 cd/A and 3.3 V for the device fabricated on an as-cleaned ITO surface. In contrast, devices prepared on air-exposed SiOxNy/ITO surface had almost the same current efficiency (3.85 cd/A) and turn on voltage (3.7 V) comparing to devices (3.8 cd/A and 3.7 V) fabricated on freshly prepared SiOxNy/ITO surface. The results suggested that SiOxNy is a promising anode buffer layer for OLEDs, for both efficiency and stability enhancements.

  15. New Approach to Depositing Yttria-Stabilized Zirconia Buffer Layers for Coated Conductors (Postprint)

    DTIC Science & Technology

    2012-02-01

    distribution unlimited. See additional restrictions described on inside pages STINFO COPY © 2003 Materials Research Society AIR... additional layer in the buffer layer stack—a transient nickel layer deposited directly on the substrate. Regardless of the substrate and protective layers...Ridge Na- tional Laboratory ( ORNL ), Oak Ridge, TN, were precleaned in organic solvents (acetone, ethanol, chloro- form) using ultrasonic agitation

  16. The role of hydrogenated amorphous silicon oxide buffer layer on improving the performance of hydrogenated amorphous silicon germanium single-junction solar cells

    NASA Astrophysics Data System (ADS)

    Sritharathikhun, Jaran; Inthisang, Sorapong; Krajangsang, Taweewat; Krudtad, Patipan; Jaroensathainchok, Suttinan; Hongsingtong, Aswin; Limmanee, Amornrat; Sriprapha, Kobsak

    2016-12-01

    Hydrogenated amorphous silicon oxide (a-Si1-xOx:H) film was used as a buffer layer at the p-layer (μc-Si1-xOx:H)/i-layer (a-Si1-xGex:H) interface for a narrow band gap hydrogenated amorphous silicon germanium (a-Si1-xGex:H) single-junction solar cell. The a-Si1-xOx:H film was deposited by plasma enhanced chemical vapor deposition (PECVD) at 40 MHz in a same processing chamber as depositing the p-type layer. An optimization of the thickness of the a-Si1-xOx:H buffer layer and the CO2/SiH4 ratio was performed in the fabrication of the a-Si1-xGex:H single junction solar cells. By using the wide band gap a-Si1-xOx:H buffer layer with optimum thickness and CO2/SiH4 ratio, the solar cells showed an improvement in the open-circuit voltage (Voc), fill factor (FF), and short circuit current density (Jsc), compared with the solar cells fabricated using the conventional a-Si:H buffer layer. The experimental results indicated the excellent potential of the wide-gap a-Si1-xOx:H buffer layers for narrow band gap a-Si1-xGex:H single junction solar cells.

  17. Microstructures of GaN Buffer Layers Grown on Si(111) Using Rapic Thermal Process Low-Pressure Metalorganic Chemical Vapor Deposition

    NASA Astrophysics Data System (ADS)

    Peng, Chen; Bo, Shen; Jian-Min, Zhu; Zhi-Zhong, Chen; Yu-Gang, Zhou; Shi-Yong, Xie; Rong, Zhang; Ping, Han; Shu-Lin, Gu; You-Dou, Zheng; Shu-Sheng, Jiang; Duan, Feng; Z, Huang C.

    2000-03-01

    Microstructures of GaN buffer layers grown on Si (111) substrates using rapid thermal process low-pressure metalorganic chemical vapor deposition are investigated by an atomic force microscope (AFM) and a high-resolution transmission electron microscope (HRTEM). AFM images show that the islands appear in the GaN buffer layer after annealing at high temperature. Cross-sectional HRTEM micrographs of the buffer region of these samples indicate that there are bunched steps on the surface of the Si substrate and a lot of domains in GaN misorienting each other with small angles. The boundaries of those domains locate near the bunched steps, and the regions of the film on a terrace between steps have the same crystal orientation. An amorphous-like layer, about 3 nm thick, can also be observed between the GaN buffer layer and the Si substrate.

  18. 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.

  19. 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.

  20. 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.

  1. Growth Optimization of YBa2NbO6 Buffer Layers (Postprint)

    DTIC Science & Technology

    2012-02-01

    single crystals, and IBAD MgO buffered Inconel substrates has been investigated. X-ray diffraction confirms the epitaxial growth of highly h00 oriented...YBNO thin films on single crystal substrates and IBAD MgO buffered Inconel substrates. The best average surface roughness of the YBNO films...diffraction, crystal, buffered, inconel , epitaxial, films, substrates, layers, growth, investigated, sufficient, preliminary, critical 16. SECURITY

  2. 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

  3. Thickness of the retinal nerve fiber layer in primate eyes.

    PubMed

    Radius, R L

    1980-09-01

    Thickness of the retinal nerve fiber layer is studied in the eyes of three primate species. Measurements are made at various points throughout the fundus, including the peripapillary, arcuate, macular (area centralis), equatorial, and peripheral parts of the retina. Anatomic findings are compared with the clinical appearance of retinal light reflexes in these way. It is proposed that the nature of this light reflex is, in part, determined by the thickness of the retinal nerve fiber layer.

  4. Efficient organic photovoltaic devices using a combination of exciton blocking layer and anodic buffer layer

    NASA Astrophysics Data System (ADS)

    Chan, M. Y.; Lee, C. S.; Lai, S. L.; Fung, M. K.; Wong, F. L.; Sun, H. Y.; Lau, K. M.; Lee, S. T.

    2006-11-01

    By using bathophenanthroline (BPhen) as an exciton blocking layer (EBL) at the organic/cathode contact of a standard copper phthalocyanine/C60 organic photovoltaic (OPV) device, power conversion efficiency was substantially increased from 0.86% to 2.64%. The BPhen-based devices showed a 45% increase in power conversion efficiency over that of an equivalent device with an EBL of bathocuproine. The performance improvement was analyzed in terms of the electron energy levels, optical transparencies and electron mobilities of the two EBLs. Based on these results, the roles of and requirements for an effective EBL were discussed. Combining the use of BPhen and a WO3 anodic buffer layer further increased the power conversion efficiency of the OPV device to 3.33%.

  5. R.F. Sputtering Deposition of Buffer Layers for Si/YBCO Integrated Microelectronics

    NASA Astrophysics Data System (ADS)

    Rombolà, G.; Ballarini, V.; Chiodoni, A.; Gozzelino, L.; Mezzetti, E.; Minetti, B.; Pirri, C. F.; Tresso, E.; Camerlingo, C.

    The aim of the present work is the optimization of the Si/buffer-layer/YBCO multilayer deposition process so as to grow superconducting films of quality suitable for device applications. The structural properties of the Si/CeO2 system, obtained by RF magnetron sputtering of CeO2 targets in Ar atmosphere, have been studied. More than 50 films have been deposited and some of them submitted to post-deposition annealing treatments both in N2 and O2 atmospheres. The presence of an unwanted amorphous SiO2 layer at the Si/CeO2 interface compromises the YBCO c-axis orientation, and therefore the sharpness of the R versus T transition. A newly designed deposition system has been realized: it has been specially conceived for obtaining bi- and tri-layers, adopting two targets in YSZ and CeO2, respectively. Results on YSZ/Si and CeO2/YSZ/Si systems obtained with the new machine are presented and discussed: (100) oriented YSZ films with nominal thickness of 40 nm have been obtained. The CeO2 film subsequently deposited has the desired (100) orientation. The YBCO film, in the final YBCO/YSZ/CeO2/Si configuration, is c-axis oriented.

  6. Tailoring the magnetic anisotropy of CoFeB/MgO stacks onto W with a Ta buffer layer

    NASA Astrophysics Data System (ADS)

    Kaidatzis, Andreas; Bran, Cristina; Psycharis, Vasilios; Vázquez, Manuel; García-Martín, José Miguel; Niarchos, Dimitrios

    2015-06-01

    The emergence of perpendicular magnetic anisotropy (PMA) in CoFeB/MgO stacks deposited on W using a Ta buffer layer is studied as a function of Ta and CoFeB layer thickness and annealing temperature. It is shown that very thin Ta "dusting" layers (thickness between 0.3 and 1 nm) enhance PMA of CoFeB layers grown on top of W. We find that Ta thickness is a crucial factor affecting magnetic anisotropy and it needs to be scaled proportionally to CoFeB thickness for obtaining PMA. Stacks without Ta have in-plane anisotropy, verifying the "PMA-enhancing" role of Ta. The maximum effective PMA energy ( 3.6 ×106 erg/cm3) is obtained for a stack with 1.4 nm of CoFeB and 1 nm of Ta and after annealing at 350 °C . Besides, PMA can be obtained even at the as-deposited state for certain thicknesses. This W-based CoFeB/MgO system could enable the development of low power consumption, high density, and non-volatile magnetic memories.

  7. 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.

  8. Pulsed Laser Deposition of YBCO With Yttrium Oxide Buffer Layers (Postprint)

    DTIC Science & Technology

    2012-02-01

    AFRL-RZ-WP-TP-2012-0092 PULSED LASER DEPOSITION OF YBCO WITH YTTRIUM OXIDE BUFFER LAYERS (POSTPRINT) Paul N. Barnes, Timothy J. Haugan...Paper Postprint 01 January 2002 – 01 January 2004 4. TITLE AND SUBTITLE PULSED LASER DEPOSITION OF YBCO WITH YTTRIUM OXIDE BUFFER LAYERS (POSTPRINT...Textured metallic substrate based HTS coated conductors with the YBCO /CeO2/YSZ/CeO2/Ni architecture have already been shown to exhibit high current

  9. New layer thickness parameterization of diffusive convection in the ocean

    NASA Astrophysics Data System (ADS)

    Zhou, Sheng-Qi; Lu, Yuan-Zheng; Song, Xue-Long; Fer, Ilker

    2016-03-01

    In the present study, a new parameterization is proposed to describe the convecting layer thickness in diffusive convection. By using in situ observational data of diffusive convection in the lakes and oceans, a wide range of stratification and buoyancy flux is obtained, where the buoyancy frequency N varies between 10-4 and 0.1 s-1 and the heat-related buoyancy flux qT varies between 10-12 and 10-7 m2 s-3. We construct an intrinsic thickness scale, H0 =[qT3 / (κTN8) ] 1 / 4, here κT is the thermal diffusivity. H0 is suggested to be the scale of an energy-containing eddy and it can be alternatively represented as H0 = ηRebPr1/4, here η is the dissipation length scale, Reb is the buoyant Reynolds number, and Pr is the Prandtl number. It is found that the convective layer thickness H is directly linked to the stability ratio Rρ and H0 with the form of H ∼ (Rρ - 1)2H0. The layer thickness can be explained by the convective instability mechanism. To each convective layer, its thickness H reaches a stable value when its thermal boundary layer develops to be a new convecting layer.

  10. Zn (O,S) buffer layers by atomic layer deposition in Cu (In,Ga)Se2 based thin film solar cells: Band alignment and sulfur gradient

    NASA Astrophysics Data System (ADS)

    Platzer-Björkman, C.; Törndahl, T.; Abou-Ras, D.; Malmström, J.; Kessler, J.; Stolt, L.

    2006-08-01

    Thin film solar cells with the structure sodalimeglass /Mo/Cu(In,Ga)Se2/Zn(O,S)/ZnO/ZnO:Al are studied for varying thickness and sulfur content of the Zn (O,S) buffer layer. These Zn (O,S) layers were deposited by atomic layer deposition (ALD) at 120°C. Devices with no or small concentrations of sulfur in the buffer layer show low open-circuit voltages. This is explained by the cliff, or negative conduction-band offset (CBO), of -0.2eV measured by photoelectron spectroscopy (PES) and optical methods for the Cu (In,Ga)Se2 (CIGS)/ZnO interface. Devices with ZnS buffer layers exhibit very low photocurrent. This is expected from the large positive CBO (spike) of 1.2eV measured for the CIGS /ZnS interface. For devices with Zn (O,S) buffer layers, two different deposition recipes were found to yield devices with efficiencies equal to or above reference devices in which standard CdS buffer layers were used; ultrathin Zn (O,S) layers with S /Zn ratios of 0.8-0.9, and Zn (O,S) layers of around 30nm with average S /Zn ratios of 0.3. The sulfur concentration increases towards the CIGS interface as revealed by transmission electron microscopy and in vacuo PES measurements. The occurrence of this sulfur gradient in ALD-Zn (O,S) is explained by longer incubation time for ZnO growth compared to ZnS growth. For the Zn (O,S) film with high sulfur content, the CBO is large which causes blocking of the photocurrent unless the film is ultrathin. For the Zn (O,S) film with lower sulfur content, a CBO of 0.2eV is obtained which is close to ideal, according to simulations. Efficiencies of up to 16.4% are obtained for devices with this buffer layer.

  11. 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.

  12. 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.

  13. Efficiency enhancement of polymer solar cells by applying poly(vinylpyrrolidone) as a cathode buffer layer via spin coating or self-assembly.

    PubMed

    Wang, Haitao; Zhang, Wenfeng; Xu, Chenhui; Bi, Xianghong; Chen, Boxue; Yang, Shangfeng

    2013-01-01

    A non-conjugated polymer poly(vinylpyrrolidone) (PVP) was applied as a new cathode buffer layer in P3HT:PCBM bulk heterojunction polymer solar cells (BHJ-PSCs), by means of either spin coating or self-assembly, resulting in significant efficiency enhancement. For the case of incorporation of PVP by spin coating, power conversion efficiency (PCE) of the ITO/PEDOT:PSS/P3HT:PCBM/PVP/Al BHJ-PSC device (3.90%) is enhanced by 29% under the optimum PVP spin-coating speed of 3000 rpm, which leads to the optimum thickness of PVP layer of ~3 nm. Such an efficiency enhancement is found to be primarily due to the increase of the short-circuit current (J(sc)) (31% enhancement), suggesting that the charge collection increases upon the incorporation of a PVP cathode buffer layer, which originates from the conjunct effects of the formation of a dipole layer between P3HT:PCBM active layer and Al electrodes, the chemical reactions of PVP molecules with Al atoms, and the increase of the roughness of the top Al film. Incorporation of PVP layer by doping PVP directly into the P3HT:PCBM active layer leads to an enhancement of PCE by 13% under the optimum PVP doping ratio of 3%, and this is interpreted by the migration of PVP molecules to the surface of the active layer via self-assembly, resulting in the formation of the PVP cathode buffer layer. While the formation of the PVP cathode buffer layer is fulfilled by both fabrication methods (spin coating and self-assembly), the dependence of the enhancement of the device performance on the thickness of the PVP cathode buffer layer formed by self-assembly or spin coating is different, because of the different aggregation microstructures of the PVP interlayer.

  14. 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.

  15. Quality-enhanced AlN epitaxial films grown on c-sapphire using ZnO buffer layer for SAW applications

    NASA Astrophysics Data System (ADS)

    Fu, Sulei; Li, Qi; Gao, Shuang; Wang, Guangyue; Zeng, Fei; Pan, Feng

    2017-04-01

    AlN epitaxial films with a thin ZnO buffer layer were successfully deposited on c-sapphire by DC magnetron sputtering for surface acoustic wave (SAW) applications. The effect of ZnO buffer layer thickness on structural properties of AlN epitaxial films and the related SAW properties were investigated systematically. The results revealed that a thin ZnO buffer layer can significantly enhance the crystalline quality of AlN films and release the strain in AlN films. The AlN films were epitaxially grown on ZnO buffered-substrate with orientation relationship of (0001) [ 10 1 bar 0 ] AlN//(0001) [ 10 1 bar 0 ] ZnO//(0001) [2 bar 110 ] Al2O3. High frequency SAW devices with a center frequency of 1.4 GHz, a phase velocity of 5600 m/s were achieved on the obtained AlN films. The optimum ZnO buffer layer thickness was found to be 10 nm, resulting in high-quality epitaxial AlN films with a FWHM value of the rocking curve of 0.84°, nearly zero stress and low insertion loss of SAW devices. This work offers an effective approach to achieve high-quality AlN epitaxial films on sapphire substrates for the applications of AlN-based SAW devices.

  16. 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.

  17. 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

    2016-06-07

    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.

  18. Masking ability of opaque thickness on layered metal-ceramic.

    PubMed

    Pieper, Cari M; Waldemarin, Renato Fa; Camacho, Guilherme B

    2016-09-01

    This study evaluated the masking ability of two opaques applied in different thicknesses. Eighty NiCr metal discs 16 mm in diameter and 1.0 mm thick were prepared. The disks were divided into 8 groups (n = 10). Ceramic opaque in paste (groups 1 to 4) or powder (groups 5 to 8) presentations were applied. They were machined with aluminum oxide burs to the following thicknesses: G1 and G5 = 0.10 mm; G2 and G6 = 0.15 mm; G3 and G7 = 0.20 mm and G4 and G8 = 0.30 mm. Dentin ceramic 0.7 mm thick was applied over these discs, sintered and glazed according manufacturer's instructions. Color was assessed with a Minolta CR10 spectrocolorimeter on the CIELab scale. Powder opaque had higher values on (L) and (ΔE) variables, and lower values on (a) and (b) variables compared to paste opaque. For opaque thickness, 0.10 mm had higher ΔE than all other thicknesses. L values were higher for 0.20 mm and 0.30 mm. Lowest and highest a* values were observed for 0.10 mm and 0.30 mm, respectively. No difference was observed for b* values. There were differences between paste and powder opaque types; 0.10 mm thickness behaves differently from the other thicknesses, with higher ΔE, while 0.15 mm does not differ statistically from thicker layers.

  19. Amorphous carbon buffer layers for separating free gallium nitride films

    NASA Astrophysics Data System (ADS)

    Altakhov, A. S.; Gorbunov, R. I.; Kasharina, L. A.; Latyshev, F. E.; Tarala, V. A.; Shreter, Yu. G.

    2016-11-01

    The possibility of using amorphous diamond-like carbon (DLC) films for self-separation of gallium nitride (GaN) layers grown by hydride vapor-phase epitaxy has been analyzed. DLC films have been synthesized by plasma-enhanced chemical vapor deposition under low pressure on sapphire (Al2O3) substrates with a (0001) crystallographic orientation. The samples have been studied by the methods of Raman scattering and X-ray diffraction analysis. It is shown that thin DLC films affect only slightly the processes of nucleation and growth of gallium nitride films. Notably, the strength of the "GaN film-Al2O3" substrate interface decreases, which facilitates separation of the GaN layers.

  20. 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

  1. Mapping liquefiable layer thickness for seismic hazard assessment

    SciTech Connect

    O`Rourke, T.D.; Pease, J.W.

    1997-01-01

    Investigations of liquefaction sites, combining subsurface mapping and evaluation of liquefaction damage, are summarized for four areas in San Francisco affected by 1906 and 1989 earthquakes, where more than 950 borehole and sounding records were collected and analyzed. The maps developed from this database provide a comprehensive picture of subsurface conditions with substantial practical value. Postliquefaction settlement, horizontal displacement caused by lateral spread, and earthquake damage to buried pipelines are shown to be related closely with the thickness of underlying liquefiable soil. The influence of surface and liquefiable layer thicknesses on liquefaction damage is evaluated. Mapping liquefiable layer thickness is shown to be an excellent means of locating areas of potentially severe liquefaction, which is adapted easily to geographic information systems (GIS) for planning and design purposes.

  2. Hydrothermal Growth and Application of ZnO Nanowire Films with ZnO and TiO2 Buffer Layers in Dye-Sensitized Solar Cells

    NASA Astrophysics Data System (ADS)

    Yang, Weiguang; Wan, Farong; Chen, Siwei; Jiang, Chunhua

    2009-12-01

    This paper reports the effects of the seed layers prepared by spin-coating and dip-coating methods on the morphology and density of ZnO nanowire arrays, thus on the performance of ZnO nanowire-based dye-sensitized solar cells (DSSCs). The nanowire films with the thick ZnO buffer layer (~0.8-1 μm thick) can improve the open circuit voltage of the DSSCs through suppressing carrier recombination, however, and cause the decrease of dye loading absorbed on ZnO nanowires. In order to further investigate the effect of TiO2 buffer layer on the performance of ZnO nanowire-based DSSCs, compared with the ZnO nanowire-based DSSCs without a compact TiO2 buffer layer, the photovoltaic conversion efficiency and open circuit voltage of the ZnO DSSCs with the compact TiO2 layer (~50 nm thick) were improved by 3.9-12.5 and 2.4-41.7%, respectively. This can be attributed to the introduction of the compact TiO2 layer prepared by sputtering method, which effectively suppressed carrier recombination occurring across both the film-electrolyte interface and the substrate-electrolyte interface.

  3. Quantification of retinal layer thickness changes in acute macular neuroretinopathy

    PubMed Central

    Munk, Marion R; Beck, Marco; Kolb, Simone; Larsen, Michael; Hamann, Steffen; Valmaggia, Christophe; Zinkernagel, Martin S

    2017-01-01

    Purpose To quantitatively evaluate retinal layer thickness changes in acute macular neuroretinopathy (AMN). Methods AMN areas were identified using near-infrared reflectance (NIR) images. Intraretinal layer segmentation using Heidelberg software was performed. The inbuilt ETDRS -grid was moved onto the AMN lesion and the mean retinal layer thicknesses of the central grid were recorded and compared with the corresponding area of the fellow eye at initial presentation and during follow-up. Results Eleven patients were included (mean age 26±6 years). AMN lesions at baseline had a significantly thinner outer nuclear layer (ONL) (51±21 µm vs 73±17 µm, p=0.002). The other layers, including inner nuclear layer (37±8 µm vs 38±6 µm, p=0.9) and outer plexiform layer (OPL) (45±19 µm vs 33±16 µm, p=0.1) did not show significant differences between the study eyes and fellow eyes. Adjacent to NIR image lesions, areas of OPL thickening were identified (study eye: 50±14 µm vs fellow eye: 39±16 µm, p=0.005) with corresponding thinning of ONL (study eye: 52±16 µm vs fellow eye: 69±16 µm, p=0.002). Conclusions AMN presents with characteristic quantitative retinal changes and the extent of the lesion may be more extensive than initially presumed from NIR image lesions. PMID:27170518

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. Ferroelectric properties of multi-layer LiTaO 3 thin films with Ta IIO 5 buffer

    NASA Astrophysics Data System (ADS)

    Zhang, De-Yin; Peng, Wei-Dong; Li, Jin-Hua; Li, Kun; Huang, Da-Gui

    2007-12-01

    The new sol-gel derived multi-layer LiTaO 3 thin films with Ta IIO 5 buffer layer were prepared on Pt/Ti/SiO2/Si substrate using lithium ethoxide and tantalum ethoxide as starting materials. The sol of Ta IIO 5 was firstly covered on the substrate by spin coating at 6500rpm for 50s and then a rapid annealing at 650°C for 2min to form an about 20nm thick Ta IIO 5 buffer layer. Multi-layer LiTaO 3 thin films were made over Ta IIO 5 buffer by repeated spin coating at 4000rpm for 30s and then a rapid annealing process at 700°C for 3min. The spectrum of XRD show the crystalline orientation of thin film type Ta IIO 5 is different compared to powder type Ta IIO 5. The SEM micrograph of the cross section shows the prepared sample is uniform, smooth and crack-free on the surface and the thickness of LiTaO 3 thin film is 0.341μm. The ferroelectric hysteresis loop and leakage current of the prepared sample have been measured using Al/LiTaO 3/Ta IIO 5/Pt structure electrode by a ferroelectric material analyzer PLC-100. The remanent polarization and coercive field of the prepared sample polarized at 13V were 3.4μC/cm2 and 185kV/cm respectively. The leakage current of the prepared sample was 2.66x10 -7A at 71.43kV/cm .Experimental results show the prepared sample of LiTaO 3 thin film with Ta IIO 5 buffer has good ferroelectric properties. Ta IIO 5 buffer introduction between LiTaO 3 thin film and Pt substrate can effectively decrease the leakage current and improve the properties of uncooled LiTaO 3 infrared device.

  9. Nearly 4-Inch-Diameter Free-Standing GaN Wafer Fabricated by Hydride Vapor Phase Epitaxy with Pit-Inducing Buffer Layer

    NASA Astrophysics Data System (ADS)

    Sato, Tadashige; Okano, Shinya; Goto, Takenari; Yao, Takafumi; Seto, Ritsu; Sato, Akira; Goto, Hideki

    2013-08-01

    A free-standing GaN wafer was fabricated by depositing a GaN buffer that induced the formation of pits (hereafter, pit-inducing GaN buffer) on a low-temperature-grown GaN buffer on the sapphire substrate. A high-temperature-grown GaN layer was grown on the pit-inducing GaN buffer that induced the formation of pits on the high-temperature-grown GaN layer. The pit-inducing buffer suppresses crack formation in the thick GaN film thereby releasing growth stress. Thermal stress in GaN on a sapphire system is also discussed on the basis of calculations utilizing a bilayer model. We have succeeded in the fabrication of a nearly 4-in.-diameter free-standing GaN thick wafer with a pit-inducing GaN buffer by one-stop hydride vapor phase epitaxy, which will lead to a low-cost fabrication of free-standing GaN wafers.

  10. Structure and dielectric tunability of (Pb 0.5Ba 0.5)ZrO 3 thin films derived on (Sr 0.95La 0.05)TiO 3 buffer-layered substrates

    NASA Astrophysics Data System (ADS)

    Hao, Xihong; Zhai, Jiwei; Zhou, Jing; Yang, Jichun; Song, Xiwen; An, Shengli

    2010-02-01

    In present work, (Pb 0.5Ba 0.5)ZrO 3 (PBZ) thin films with a thickness of 840 nm were successfully fabricated on (Sr 0.95La 0.05)TiO 3 (SLT) buffer-layered Pt(1 1 1)/TiO 2/SiO 2/Si(1 0 0) substrates via the sol-gel technique. The effects of SLT buffer layer on the microstructure and electrical properties of PBZ thin films were investigated systemically. X-ray diffraction (XRD) and scanning electron microscopy (SEM) results indicated that PBZ thin films on SLT buffer-layered substrates showed a more uniform structure with a random orientation. Dielectric measurements illustrated that PBZ films with SLT buffer layer displayed larger dielectric constant, improved tunability and enhanced figure of merit (FOM). Moreover, leakage current of PBZ films was also reduced by SLT buffer layer.

  11. The scaling transition of Nu number and boundary layer thickness in RB convection

    NASA Astrophysics Data System (ADS)

    Zou, Hong-Yue; Chen, Xi; She, Zhen-Su

    2016-11-01

    A quantitative theory is developed for the vertical mean temperature profile (MTP) and mean velocity profile (MVP) in turbulent Rayleigh-Benard Convection (RBC), which explains the experimental and numerical observations of logarithmic law in MTP and the Rayleigh number (Ra)-dependence of its coefficient A. The theory extends a symmetry analysis of canonical wall-bounded turbulent flows, which allows to extract accurate Ra scaling of the sub-layer, buffer layer and log-layer thicknesses from the empirical data over a wide range of Ra. In particular, the scaling of the multi-layer thicknesses predicts that the log-law coefficient A follows a -0.121 scaling, which agrees well with the experimental data. More interestingly, a scaling transition is discovered for the kinetic sublayer thickness around Ra of 1010, which yields a scaling transition of Nu from 1/3 to 0.38. We also develop a new explanation for mean temperature logarithmic law: the effect of inverse pressure gradient drives plumes upwards near the side wall, and yields a similarity between temperature and momentum transport in the vertical direction.

  12. 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.

  13. Indium Tin Oxide Electrode with an Ultrathin Al Buffer Layer for Flexible Organic Light Emitting Diode

    NASA Astrophysics Data System (ADS)

    Sim, Boyeon; Hwang, Hyeonseok; Ryu, Seungyoon; Baik, Hongkoo; Lee, Myeongkyu

    2010-06-01

    This paper reports that the mechanical and electrical stability of indium tin oxide (ITO) film deposited on flexible plastic substrate can be much enhanced with a thin Al buffer layer while maintaining a visible transmittance over 75%. The improved stability is attributed to the effective elastic mismatch between the film and the substrate reduced by a ductile interlayer. A polymer light emitting diode fabricated using an ITO/Al anode exhibited a luminance of 13,000 cd/m2 with a current efficiency of 16 cd/A. Bending-induced degradation of the device performance was also alleviated when a mechanical buffer layer was inserted.

  14. CdS/CdTe thin-film solar cell with a zinc stannate buffer layer

    NASA Astrophysics Data System (ADS)

    Wu, X.; Sheldon, P.; Mahathongdy, Y.; Ribelin, R.; Mason, A.; Moutinho, H. R.; Coutts, T. J.

    1999-03-01

    This paper describes an improved CdS/CdTe polycrystalline thin-film solar-cell device structure that integrates a zinc stannate (Zn2SnO4 or ZTO) buffer layer between the transparent conductive oxide (TCO) layer and the CdS window layer. Zinc stannate films have a high bandgap, high transmittance, low absorptance, and low surface roughness. In addition, these films are chemically stable and exhibit higher resistivities that are roughly matched to that of the CdS window layer in the device structure. Preliminary device results have demonstrated that by integrating a ZTO buffer layer in both SnO2-based and Cd2SnO4 (CTO)-based CdS/CdTe devices, performance and reproducibility can be significantly enhanced.

  15. Assessing the Relationship between Central Corneal Thickness and Retinal Nerve Fiber Layer Thickness in Healthy Subjects

    PubMed Central

    Mumcuoglu, Tarkan; Townsend, Kelly A; Wollstein, Gadi; Ishikawa, Hiroshi; Bilonick, Richard A; Sung, Kyung Rim; Kagemann, Larry; Schuman, Joel S

    2008-01-01

    Purpose To determine the relationship between central corneal thickness (CCT) and retinal nerve fiber layer (RNFL) thickness obtained by scanning laser polarimetry (GDx-VCC; Carl Zeiss Meditec, Dublin, CA) confocal scanning laser ophthalmoscopy (HRT II; Heidelberg Engineering, Heidelberg, Germany) and optical coherence tomography (Stratus OCT; Carl Zeiss Meditec, Dublin, CA). Design Multi-center clinical trial, retrospective cross-sectional study. Methods One hundred and nine healthy subjects from the Advanced Imaging in Glaucoma Study were enrolled in this study. All subjects had a standard clinical examination, including visual field and good quality scans from all three imaging devices. Central corneal thickness was measured using an ultrasonic pachymeter. A linear mixed effects model was used to assess the relationship between RNFL thickness and CCT, accounting for clustering of eyes within subjects, testing site, ethnicity, family history of glaucoma, axial length intraocular pressure and visual field global indices. Results For OCT and GDx, there was a slight non-statistically significant positive relationship between CCT and RNFL thickness. For HRT, there was a slight non-statistically significant negative relationship between CCT and RNFL thickness. Relationships for each device were found to differ between sites. Conclusions CCT was not statistically significantly related to RNFL thickness in healthy eyes. PMID:18657796

  16. 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.

  17. 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.

  18. Measuring for thickness distribution of recording layer of PLH

    NASA Astrophysics Data System (ADS)

    Zhang, Xiao-Chun; Guo, Lurong; Guo, Yongkang

    1991-07-01

    An interference microscope is employed to take a photo of the interfering fringes, and its density is analyzed by a computer image system to measure the thickness distribution of a photolithographic hologram (PLH). This method is much more simple than that of SEM. The theory of measuring is presented in the paper. The authors measured the distributions of photolithographic gratings before and after the etching process. Comparing both the thickness distributions of corresponding recording layers, some primary rules of pattern transfer process by etching were identified.

  19. 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.

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

    DOEpatents

    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.

  1. 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.

  2. 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.

  3. Turbulent Boundary Layer Thickness Estimation Method and Apparatus

    DTIC Science & Technology

    2003-04-02

    correlation coefficient is computed with measured data from the recorded voltage. A laboratory non- dimensional value of the correlation coefficient is independently determined from laboratory data. The real non-dimensional value is compared with the laboratory non-dimensional value to obtain a boundary layer thickness having a value which minimizes a difference between the values of the real non-dimensional value and the laboratory non-dimensional

  4. 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.

  5. 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.

  6. 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.

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

    SciTech Connect

    Shoup, S.S.; Paranthamam, M.; Beach, D.B.; Kroeger, D.M.; Goyal, A.

    2000-06-20

    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.

  8. Characterization of Cu buffer layers for growth of L1{sub 0}-FeNi thin films

    SciTech Connect

    Mizuguchi, M.; Sekiya, S.; Takanashi, K.

    2010-05-15

    A Cu(001) layer was fabricated on a Au(001) layer to investigate the use of Cu as a buffer layer for growing L1{sub 0}-FeNi thin films. The epitaxial growth of a Cu buffer layer was observed using reflection high-energy electron diffraction. The flatness of the layer improved drastically with an increase in the substrate temperature although the layer was an alloy (AuCu{sub 3}). An FeNi thin film was epitaxially grown on the AuCu{sub 3} buffer layer by alternate monatomic layer deposition and the formation of an L1{sub 0}-FeNi ordered alloy was expected. The AuCu{sub 3} buffer layer is thus a promising candidate material for the growth of L1{sub 0}-FeNi thin films.

  9. Final Report: Rational Design of Wide Band Gap Buffer Layers for High-Efficiency Thin-Film Photovoltaics

    SciTech Connect

    Lordi, Vincenzo

    2016-09-30

    The main objective of this project is to enable rational design of wide band gap buffer layer materials for CIGS thin-film PV by building understanding of the correlation of atomic-scale defects in the buffer layer and at the buffer/absorber interface with device electrical properties. Optimized wide band gap buffers are needed to reduce efficiency loss from parasitic absorption in the buffer. The approach uses first-principles materials simulations coupled with nanoscale analytical electron microscopy as well as device electrical characterization. Materials and devices are produced by an industrial partner in a manufacturing line to maximize relevance, with the goal of enabling R&D of new buffer layer compositions or deposition processes to push device efficiencies above 21%. Cadmium sulfide (CdS) is the reference material for analysis, as the prototypical high-performing buffer material.

  10. 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.

  11. Layer-based buffer aware rate adaptation design for SHVC video streaming

    NASA Astrophysics Data System (ADS)

    Gudumasu, Srinivas; Hamza, Ahmed; Asbun, Eduardo; He, Yong; Ye, Yan

    2016-09-01

    This paper proposes a layer based buffer aware rate adaptation design which is able to avoid abrupt video quality fluctuation, reduce re-buffering latency and improve bandwidth utilization when compared to a conventional simulcast based adaptive streaming system. The proposed adaptation design schedules DASH segment requests based on the estimated bandwidth, dependencies among video layers and layer buffer fullness. Scalable HEVC video coding is the latest state-of-art video coding technique that can alleviate various issues caused by simulcast based adaptive video streaming. With scalable coded video streams, the video is encoded once into a number of layers representing different qualities and/or resolutions: a base layer (BL) and one or more enhancement layers (EL), each incrementally enhancing the quality of the lower layers. Such layer based coding structure allows fine granularity rate adaptation for the video streaming applications. Two video streaming use cases are presented in this paper. The first use case is to stream HD SHVC video over a wireless network where available bandwidth varies, and the performance comparison between proposed layer-based streaming approach and conventional simulcast streaming approach is provided. The second use case is to stream 4K/UHD SHVC video over a hybrid access network that consists of a 5G millimeter wave high-speed wireless link and a conventional wired or WiFi network. The simulation results verify that the proposed layer based rate adaptation approach is able to utilize the bandwidth more efficiently. As a result, a more consistent viewing experience with higher quality video content and minimal video quality fluctuations can be presented to the user.

  12. 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.

  13. Improvement of luminescence properties of GaN buffer layer for fast nitride scintillator structures

    NASA Astrophysics Data System (ADS)

    Hubáček, T.; Hospodková, A.; Oswald, J.; Kuldová, K.; Pangrác, J.

    2017-04-01

    We have optimized technology of GaN buffer layer growth with respect to the application in fast scintillation structures. The deep defect luminescence so called yellow band (YB) with decay time up to tens of microseconds is undesired for these applications and should be suppressed or at least the ratio of intensities of excitonic to YB maximum has to be considerably increased. The required photoluminescence properties were achieved by optimization of growth parameters of nucleation and coalescence layer on sapphire substrate. We have shown that decrease of NH3 flow, decrease of coalescence temperature, increase of nucleation time and nucleation pressure lead to improvement of the structure and luminescence properties of the buffer layer. Results indicate a significant increased ratio of excitonic/YB luminescence intensity.

  14. From front contact to back contact in cadmium telluride/cadmium sulfide solar cells: Buffer layer and interfacial layer

    NASA Astrophysics Data System (ADS)

    Roussillon, Yann

    Cadmium telluride (CdTe) polycrystalline thin film solar cells, with their near optimum direct band-gap of 1.4 eV matching almost perfectly the sun radiation spectrum, are a strong contender as a less expensive alternative, among photovoltaic materials, than the more commonly used silicon-based cells. Polycrystalline solar cells are usually deposited over large areas. Such devices often exhibit strong fluctuations (nonuniformities) in electronic properties, which originate from deposition and post-deposition processes, and are detrimental to the device performance. Therefore their effects need to be constrained. A new approach in this work was, when a CdS/CdTe solar cell is exposed to light and immersed in a proper electrolyte, fluctuations in surface potential can drive electrochemical reactions which result in a nonuniform interfacial layer that could balance the original nonuniformity. This approach improved the device efficiency for CdS/CdTe photovoltaic devices from 1--3% to 11--12%. Cadmium sulfide (CdS), used as a window layer and heterojunction partner to CdTe, is electrically inactive and absorb light energies above its band-gap of 2.4 eV. Therefore, to maximize the device efficiency, a thin US layer needs to be used. However, more defects, such as pinholes, are likely to be present in the film, leading to shunts. A resistive transparent layer, called buffer layer, is therefore deposited before CdS. A key observation was that the open-circuit voltage (Voc) for cells made using a buffer layer was high, around 800 mV, similar to cells without buffer layer after Cu doping. The standard p-n junction theory cannot explain this phenomena, therefore an alternative junction mechanism, similar to metal-insulator-semiconductor devices, was developed. Furthermore, alternative Cu-free back-contacts were used in conjunction with a buffer layer. The Voc of the devices was found to be dependent of the back contact used. This change occurs as the back-contact junction

  15. Thirty-Day-Long Data Retention in Ferroelectric-Gate Field-Effect Transistors with HfO2 Buffer Layers

    NASA Astrophysics Data System (ADS)

    Takahashi, Kazuhiro; Aizawa, Koji; Park, Byung-Eun; Ishiwara, Hiroshi

    2005-08-01

    Metal-ferroelectric-insulator-semiconductor (MFIS) diodes and p-channel MFIS field-effect transistors (FETs) were fabricated and their electrical properties were characterized. These MFIS structures were formed using HfO2 as an insulating buffer layer, and SrBi2Ta2O9 (SBT) and (Bi,La)4Ti3O12 (BLT) as ferroelectric films. HfO2 buffer layers of about 8 nm physical thickness were deposited by ultrahigh-vacuum (UHV) electron-beam evaporation, then ferroelectric films of about 400 nm thickness were deposited by sol-gel spin coating. The fabricated p-channel MFIS-FETs with the SBT/HfO2 gate structure exhibited a drain current on/off ratio larger than 103 even after 30 days had elapsed. It was also found that the degradation of ferroelectricity was not pronounced even after applying 2.2× 1011 bipolar pulses.

  16. Retinal Nerve Fiber Layer Thickness in Amblyopic Eyes

    PubMed Central

    Repka, Michael X.; Kraker, Raymond T.; Tamkins, Susanna M.; Suh, Donny W.; Sala, Nicholas A.; Beck, Roy W.

    2010-01-01

    Purpose To compare the peripapillary retinal nerve fiber layer (RNFL) thickness of amblyopic and fellow eyes. We hypothesized that the RNFL of the amblyopic eye might be thinner. Design Prospective cross-sectional observational case series Methods Optical coherence tomography (OCT) of the peripapillary RNFL thickness of amblyopic and fellow eyes was performed in 37 patients age 7 to 12 years (mean 9.2 ± 1.5) with unilateral strabismic, anisometropic or combined mechanism amblyopia enrolled in a randomized treatment trial. Results Mean global RNFL thickness of the amblyopic and fellow eyes was 111.4 microns and 109.6 microns, respectively (mean difference = 1.8 microns thicker in the amblyopic eyes, 95% confidence interval -0.6 to +4.3 microns). The amblyopic eye was 8 or more microns thicker than the fellow eye in 9 patients (24%); the fellow eye was 8 or more microns thicker than the amblyopic eye in 2 patients (5%); and the difference was within test-retest variability (7 microns) in 26 patients (70%). Conclusions Our findings do not indicate that peripapillary RNFL thickness is thinner in eyes with moderate amblyopia compared with their fellow eyes. PMID:19327749

  17. Oil shale ash-layer thickness and char combustion kinetics

    SciTech Connect

    Aldis, D.F.; Singleton, M.F.; Watkins, B.E.; Thorsness, C.B.; Cena, R.J.

    1992-04-15

    A Hot-Recycled-Solids (HRS) oil shale retort is being studied at Lawrence Livermore National Laboratory. In the HRS process, raw shale is heated by mixing it with burnt retorted shale. Retorted shale is oil shale which has been heated in an oxygen deficient atmosphere to pyrolyze organic carbon, as kerogen into oil, gas, and a nonvolatile carbon rich residue, char. In the HRS retort process, the char in the spent shale is subsequently exposed to an oxygen environment. Some of the char, starting on the outer surface of the shale particle, is burned, liberating heat. In the HRS retort, the endothermic pyrolysis step is supported by heat from the exothermic char combustion step. The rate of char combustion is controlled by three resistances; the resistance of oxygen mass transfer through the gas film surrounding the solid particle, resistance to mass transfer through a ash layer which forms on the outside of the solid particles as the char is oxidized and the resistance due to the intrinsic chemical reaction rate of char and oxygen. In order to estimate the rate of combustion of the char in a typical oil shale particle, each of these resistances must be accurately estimated. We begin by modeling the influence of ash layer thickness on the over all combustion rate of oil shale char. We then present our experimental measurements of the ash layer thickness of oil shale which has been processed in the HRS retort.

  18. Direct charge carrier injection into Ga2O3 thin films using an In2O3 cathode buffer layer: their optical, electrical and surface state properties

    NASA Astrophysics Data System (ADS)

    Cui, W.; Zhao, X. L.; An, Y. H.; Guo, D. Y.; Qing, X. Y.; Wu, Z. P.; Li, P. G.; Li, L. H.; Cui, C.; Tang, W. H.

    2017-04-01

    Conductive Ga2O3 thin films with an In2O3 buffer layer have been prepared on c-plane sapphire substrates using a laser molecular beam epitaxy technique. The effects of the In2O3 buffer layer on the structure and optical, electrical and surface state properties of the Ga2O3 films have been studied. The change in conductivity of the thin films is attributed to different thicknesses of the In2O3 buffer layer, which determine the concentration of charge carriers injected into the upper Ga2O3 layer from the interface of the bilayer thin films. In addition, the increase in flat band voltage shift and capacitance values as the In2O3 buffer layer thickens are attributed to the increase in surface state density, which also contributes to the rapid shrinkage of the optical band gap of the Ga2O3. With transparency to visible light, high n-type conduction and the ability to tune the optical band gap and surface state density, we propose that Ga2O3/In2O3 bilayer thin film is an ideal n-type semiconductor for fabrication of transparent power devices, solar cell electrodes and gas sensors.

  19. 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.

  20. 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.

  1. Pyroelectric and dielectric properties of ferroelectric films with interposed dielectric buffer layers

    NASA Astrophysics Data System (ADS)

    Espinal, Y.; Kesim, M. T.; Misirlioglu, I. B.; Trolier-McKinstry, S.; Mantese, J. V.; Alpay, S. P.

    2014-12-01

    The dielectric and pyroelectric properties of c-domain ferroelectric films with linear dielectric buffer layers were investigated theoretically. Computations were carried out for multilayers consisting of PbZr0.2Ti0.8O3 with Al2O3, SiO2, Si3N4, HfO2, and TiO2 buffers on metalized Si. It is shown that the dielectric and pyroelectric properties of such multilayers can be increased by the presence of the buffer compared to ferroelectric monolayers. Calculations for PbZr0.2Ti0.8O3 films with 1% Al2O3 interposed between electrodes on Si show that the dielectric and pyroelectric coefficients are 310 and 0.070 μC cm-2 °C-1, respectively. Both values are higher than the intrinsic response of PbZr0.2Ti0.8O3 monolayer on Si.

  2. 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%.

  3. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2005-02-01

    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.

  5. 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.

  6. 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.

  7. 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.

  8. 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

  9. Effect of magnetic structural processing on structure and texture of La2Zr2O7 buffer layers

    NASA Astrophysics Data System (ADS)

    Chibirova, F. Kh.; Kotina, G. V.; Bovina, E. A.; Tarasova, D. V.; Polisan, A. A.; Parkhomenko, Yu. N.

    2016-11-01

    Epitaxial CeO2 seed layer and La2Zr2O7 (LZO) buffer layers were deposited on biaxially-textured Ni-5 at.% W (NiW) tape substrate by liquid-phase polymer assisted nanoparticles deposition (PAND) method. LZO layers deposited by PAND have consistently shown tilting of the c-axis toward the direction of the sample’s surface normal. A new approach increasing the sharpening of the buffer texture by magnetic structural processing (MSP) of buffer layers was tested. The LZO layers, deposited on the seed and buffer layers after MSP, have dense and smooth surface structure, and more importantly, significantly improved out-of-plane texture, compared with the LZO layers that were deposited on a layer without MSP. Transmission electron microscopy study confirmed the c-axis tilting of CeO2 and LZO layers and revealed the absence of interfaces between LZO layers which have been grown on the layers after MSP. There are very small (2-4 nm) gated pores in the single-crystal structure of LZO layers that are not typical for structure of LZO layers obtained by liquid-phase methods. Thus the LZO buffer layers can serve as an effective metal-ion diffusion barrier.

  10. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

    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.

  12. 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.

  13. 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.

  14. Growth and characterization of CdS buffer layers by CBD and MOCVD

    SciTech Connect

    Morrone, A.A.; Huang, C.; Li, S.S.

    1999-03-01

    Thin film CdS has been widely used in thin-film photovoltaic devices. The most efficient Cu(In,&hthinsp;Ga)Se{sub 2} (CIGS) solar cells reported to date utilized a thin CdS buffer layer prepared by a reactive solution growth technique known as chemical bath deposition (CBD). Considerable effort has been directed to better understand the role and find a replacement for the CBD CdS process in CIGS-based solar cells. We reported a low temperature ({approximately}150&hthinsp;{degree}C) Metalorganic Chemical Vapor Deposition (MOCVD) CdS thin film buffer layer process for CIGS absorbers. Many prior studies have reported that CBD CdS contains a mixture of crystal structures. Recent investigations of CBD CdS thin films by ellipsometry suggested a multilayer structure. In this study we compare CdS thin films prepared by CBD and MOCVD and the effects of annealing. TED and XRD are used to characterize the crystal structure, the film microstructure is studied by HRTEM, and the optical properties are studied by Raman and spectrophotometry. All of these characterization techniques reveal superior crystalline film quality for CdS films grown by MOCVD compared to those grown by CBD. Dual Beam Optical Modulation (DBOM) studies showed that the MOCVD and CBD CdS buffer layer processes have nearly the same effect on CIGS absorbers when combined with a cadmium partial electrolyte aqueous dip. {copyright} {ital 1999 American Institute of Physics.}

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

    PubMed Central

    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

  16. 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.

  17. Multi-filamentary REBCO tapes fabricated by scratching a buffer layer along the tape longitudinal direction

    NASA Astrophysics Data System (ADS)

    Kurihara, Chihaya; Fujita, Shinji; Nakamura, Naonori; Igarashi, Mitsunori; Iijima, Yasuhiro; Higashikawa, Kohei; Uetsuhara, Dai; Kiss, Takanobu; Iwakuma, Masataka

    2016-11-01

    A method for making multi-filamentary REBCO tapes by only scratching buffer layer was developed for coil application which requires accurate magnetic fields. By continuous Ic measurement, we found that our new multi-filamentary tape could provide almost equal Ic compared to conventional tapes. Then, using EBSD and RTR-SHPM methods, a divided structure of REBCO layer was surely confirmed. AC loss was also decreased. Furthermore, the result of delamination test of our new multi-filamentary tape showed enough mechanical property. As a result, we have succeeded in developing 100 m class multi-filamentary tape for superconducting coil.

  18. 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.

  19. Improvement of photovoltaic efficiency of dye-sensitized solar cell by introducing highly transparent nanoporous TiO2 buffer layer.

    PubMed

    Kim, Yong Joo; Kim, Hark Jin; Lee, Mi Hyeon; Lim, Goo Il; Song, Hye Young; Choi, Young Sik; Park, Nam-Gyu; Lee, Chongmu; Lee, Wan In

    2010-01-01

    13 nm-sized highly-dispersible TiO2 nanoparticle was synthesized by solvothermal reaction of titanium isopropoxide in a basic condition with tetrabutylammonium hydroxide (TBAH). The prepared TiO2 nanoparticle was applied to fabrication of the transparent nanoporous TiO2 layer with 1.2 microm-thickness. By introducing this buffer layer between FTO and main TiO2 layer in the dye-sensitized solar cell (DSSC), the photovoltaic conversion efficiency was improved from 5.92% to 7.13%. Due to the excellent antireflective role of nanoporous TiO2 buffer layer, the transmittance of FTO glass was increased by 9.2%, and this seemed to be one of the major factors in enhancing photovoltaic conversion efficiency. Moreover, the presence of nanoporous TiO2 buffer layer induces excellent adhesion between FTO and main TiO2 layer, as well as it suppresses the back reaction by blocking direct contact between I3- and FTO electrode.

  20. 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.

  1. Direct numerical simulation of turbulent boundary layer with constant thickness

    NASA Astrophysics Data System (ADS)

    Yao, Yichen; Xu, Chunxiao; Huang, Weixi

    2016-11-01

    Direct numerical simulation is performed to turbulent boundary layer (TBL) with constant thickness at Reθ = 1420 . Periodic boundary condition is applied in the streamwise direction, and a mean body force equivalent to the convection term in the mean momentum equation is imposed in this direction. The body force is calculated using the published TBL data of Schlatter and Orlu (2010) at Reθ = 1420 . The presently simulated TBL is compared with the conventional TBL and turbulent channel flow at the prescribed Reynolds number. The turbulent statistics agrees well with that of Schlatter and Orlu (2010). The pre-multiplied energy spectra in current simulation also present high similarity with the conventional TBL, while differ obviously with those in turbulent channel. The successful replication of turbulent boundary in the current simulation provides an alternative method for boundary layer simulation with much less computational cost. Meanwhile, in aspect of both turbulent statistics and flow structures, the current results indicate that the differences between turbulent channel and boundary layer flow mainly caused by the discrepancy in driving force distribution rather than the periodic boundary restriction. National Natural Science Foundation of China (Project No. 11490551, 11472154, 11322221, 11132005).

  2. Spatio-temporal modeling of Active Layer Thickness

    NASA Astrophysics Data System (ADS)

    Touyz, J.; Apanasovich, T. V.; Streletskiy, D. A.; Shiklomanov, N. I.

    2015-12-01

    Arctic Regions are 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 climate and environmental changes and plays an important role in the functioning of Arctic ecosystems, planning, and economic activities. Knowledge about spatio-temporal variability of ALT is crucial for environmental and engineering applications. The objective of this study is to provide the methodology to model and estimate spatio-temporal variation in the active layer thickness (ALT) at several sites located in the Circumpolar region spanning the Alaska North Slope, and to demonstrate its use in spatio-temporal interpolation as well as time-forward prediction. In our data analysis we estimate a parametric trend and examine residuals for the presence of spatial and temporal dependence. We propose models that provide a description of residual space-time variability in ALT. Formulations that take into account interaction among spatial and temporal components are also developed. Moreover, we compare our models to naive models in which residual spatio-temporal and temporal correlations are not considered. The predicted root mean squared and absolute errors are significantly reduced when our approach is employed. While the methodology is developed in the context of ALT, it can also be applied to model and predict other environmental variables which use similar spatio-temporal sampling designs.

  3. Formation of a Buffer Layer for Graphene on C-Face SiC{0001}

    NASA Astrophysics Data System (ADS)

    He, Guowei; Srivastava, N.; Feenstra, R. M.

    2014-04-01

    Graphene films prepared by heating the SiC surface (the C-face of the {0001} surface) in a Si-rich environment have been studied using low-energy electron diffraction (LEED) and low-energy electron microscopy. Upon graphitization, an interface with symmetry is observed by in situ LEED. After oxidation, the interface displays symmetry. Electron reflectivity measurements indicate that these interface structures arise from a graphene-like "buffer layer" that forms between the graphene and the SiC, similar to that observed on Si-face SiC. From a dynamical LEED structure calculation for the oxidized C-face surface, it is found to consist of a graphene layer sitting on top of a silicate (Si2O3) layer, with the silicate layer having the well-known structure as previously studied on bare SiC surfaces. Based on this result, the structure of the interface prior to oxidation is discussed.

  4. Improved hole-injection and power efficiency of organic light-emitting diodes using an ultrathin cerium fluoride buffer layer

    NASA Astrophysics Data System (ADS)

    Lu, Hsin-Wei; Kao, Po-Ching; Chu, Sheng-Yuan

    2016-09-01

    In this study, the efficiency of organic light-emitting diodes (OLEDs) was enhanced by depositing a CeF3 film as an ultra-thin buffer layer between the ITO and NPB hole transport layer, with the structure configuration ITO/CeF3 (1 nm)/NPB (40 nm)/Alq3 (60 nm)/LiF (1 nm)/Al (150 nm). The enhancement mechanism was systematically investigated via several approaches. The work function increased from 4.8 eV (standard ITO electrode) to 5.2 eV (1-nm-thick UV-ozone treated CeF3 film deposited on the ITO electrode). The turn-on voltage decreased from 4.2 V to 4.0 V at 1 mA/cm2, the luminance increased from 7588 cd/m2 to 10820 cd/m2, and the current efficiency increased from 3.2 cd/A to 3.5 cd/A when the 1-nm-thick UV-ozone treated CeF3 film was inserted into the OLEDs.

  5. Dummy Fill Aware Buffer Insertion after Layer Assignment Based on an Effective Estimation Model

    NASA Astrophysics Data System (ADS)

    Jia, Yanming; Cai, Yici; Hong, Xianlong

    This paper studies the impact of dummy fill for chemical mechanical polishing (CMP)-induced capacitance variation on buffer insertion based on a virtual CMP fill estimation model. Compared with existing methods, our algorithm is more feasible by performing buffer insertion not in post-process but during early physical design. Our contributions are threefold. First, we introduce an improved fast dummy fill amount estimation algorithm based on [4], and use some speedup techniques (tile merging, fill factor and amount assigning) for early estimation. Second, based on some reasonable assumptions, we present an optimum virtual dummy fill method to estimate dummy position and the effect on the interconnect capacitance. Then the dummy fill estimation model was verified by our experiments. Third, we use this model in early buffer insertion after layer assignment considering the effects of dummy fill. Experimental results verified the necessity of early dummy fill estimation and the validity of our algorithm. Buffer insertion considering dummy fill during early physical design is necessary and our algorithm is promising.

  6. 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

    2016-11-01

    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.

  7. Study of optical waveguide sensor using metamaterial as buffer layer with non-linear cladding and substrate

    NASA Astrophysics Data System (ADS)

    Kumar, Santosh; Kumari, Anamika; Raghuwanshi, Sanjeev K.

    2015-05-01

    In this paper, dispersion equation of optical waveguide using metamaterial as buffer layer with non-linear cladding and substrate is pointed. The sensitivity of TE in metamaterial optical waveguide sensor is computed mathematically. The impacts of buffer layer with non-linear cladding and substrate on metamaterial optical waveguide sensor are also tried out. The effects of various parameters on sensitivity of sensor are obtained through MATLAB. It is expected that metamaterial as buffer layer with non-linear cladding and substrate profile has a huge application in leaky fibre sensor, gas sensor and chemical sensor for oil and under grounds mining industries.

  8. Reduction in retinal nerve fiber layer thickness in migraine patients.

    PubMed

    Gipponi, Stefano; Scaroni, Niccolò; Venturelli, Elisabetta; Forbice, Eliana; Rao, Renata; Liberini, Paolo; Padovani, Alessandro; Semeraro, Francesco

    2013-06-01

    Migraine is a common disorder and its pathogenesis remains still unclear. Several hypotheses about the mechanisms involved in the pathogenesis of migraine have been proposed, but the issue is still far from being fully clarified. Neurovascular system remains one of the most important mechanisms involved in the pathogenesis of migraine and it could be possible that hypoperfusion might involve other areas besides brain, including the retina. This is, for example, of particular interest in a form of migraine, the retinal migraine, which has been associated with hypoperfusion and vasoconstriction of the retinal vasculature. Although vasoconstriction of cerebral and retinal blood vessels is a transient phenomenon, the chronic nature of the migraine might cause permanent structural abnormalities of the brain and also of the retina. On this basis, a few studies have evaluated whether retina is involved in migraine patients: Tan et al. have not found differences in retinal nerve fiber layer (RNFL) thickness between migraine patients and healthy subjects, while Martinez et al. have shown that RNFL in the temporal retinic quadrant of migraineurs is thinner than in normal people. The aim of our study was to analyze if there are differences in retinal nerve fiber layer thickness between migraine patients and normal subjects by studying 24 consecutive migraine patients who presented at the Headache Center of our Neurological Department. Migraine diagnosis has been made according to the International Classification of Headache disorder (ICHD-II). Patients have been recruited according to strict inclusion criteria; then patients have undergone a complete ophthalmological examination at the Ophthalmological Department. All patients and controls who met the ophthalmological criteria have been examined with ocular coherence tomography spectral domain (OCT-SD) after pupillary dilation. OCT-SD is an optical system designed to acquire the retinal layer images simultaneously with fundus

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

    NASA Astrophysics Data System (ADS)

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

    2011-11-01

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

  10. Investigation of AlGaN/GaN high electron mobility transistor structures on 200-mm silicon (111) substrates employing different buffer layer configurations

    NASA Astrophysics Data System (ADS)

    Lee, H.-P.; Perozek, J.; Rosario, L. D.; Bayram, C.

    2016-11-01

    AlGaN/GaN high electron mobility transistor (HEMT) structures are grown on 200-mm diameter Si(111) substrates by using three different buffer layer configurations: (a) Thick-GaN/3 × {AlxGa1‑xN}/AlN, (b) Thin-GaN/3 × {AlxGa1‑xN}/AlN, and (c) Thin-GaN/AlN, so as to have crack-free and low-bow (<50 μm) wafer. Scanning electron microscopy, energy-dispersive X-ray spectroscopy, high resolution-cross section transmission electron microscopy, optical microscopy, atomic-force microscopy, cathodoluminescence, Raman spectroscopy, X-ray diffraction (ω/2θ scan and symmetric/asymmetric ω scan (rocking curve scan), reciprocal space mapping) and Hall effect measurements are employed to study the structural, optical, and electrical properties of these AlGaN/GaN HEMT structures. The effects of buffer layer stacks (i.e. thickness and content) on defectivity, stress, and two-dimensional electron gas (2DEG) mobility and 2DEG concentration are reported. It is shown that 2DEG characteristics are heavily affected by the employed buffer layers between AlGaN/GaN HEMT structures and Si(111) substrates. Particularly, we report that in-plane stress in the GaN layer affects the 2DEG mobility and 2DEG carrier concentration significantly. Buffer layer engineering is shown to be essential for achieving high 2DEG mobility (>1800 cm2/V•s) and 2DEG carrier concentration (>1.0 × 1013 cm‑2) on Si(111) substrates.

  11. Investigation of AlGaN/GaN high electron mobility transistor structures on 200-mm silicon (111) substrates employing different buffer layer configurations

    PubMed Central

    Lee, H.-P.; Perozek, J.; Rosario, L. D.; Bayram, C.

    2016-01-01

    AlGaN/GaN high electron mobility transistor (HEMT) structures are grown on 200-mm diameter Si(111) substrates by using three different buffer layer configurations: (a) Thick-GaN/3 × {AlxGa1−xN}/AlN, (b) Thin-GaN/3 × {AlxGa1−xN}/AlN, and (c) Thin-GaN/AlN, so as to have crack-free and low-bow (<50 μm) wafer. Scanning electron microscopy, energy-dispersive X-ray spectroscopy, high resolution-cross section transmission electron microscopy, optical microscopy, atomic-force microscopy, cathodoluminescence, Raman spectroscopy, X-ray diffraction (ω/2θ scan and symmetric/asymmetric ω scan (rocking curve scan), reciprocal space mapping) and Hall effect measurements are employed to study the structural, optical, and electrical properties of these AlGaN/GaN HEMT structures. The effects of buffer layer stacks (i.e. thickness and content) on defectivity, stress, and two-dimensional electron gas (2DEG) mobility and 2DEG concentration are reported. It is shown that 2DEG characteristics are heavily affected by the employed buffer layers between AlGaN/GaN HEMT structures and Si(111) substrates. Particularly, we report that in-plane stress in the GaN layer affects the 2DEG mobility and 2DEG carrier concentration significantly. Buffer layer engineering is shown to be essential for achieving high 2DEG mobility (>1800 cm2/V∙s) and 2DEG carrier concentration (>1.0 × 1013 cm−2) on Si(111) substrates. PMID:27869222

  12. Fibronectin layers by matrix-assisted pulsed laser evaporation from saline buffer-based cryogenic targets.

    PubMed

    Sima, F; Davidson, P; Pauthe, E; Sima, L E; Gallet, O; Mihailescu, I N; Anselme, K

    2011-10-01

    The deposition of fibronectin (FN) from saline buffer-based cryogenic targets by matrix-assisted pulsed laser evaporation (MAPLE) onto silicon substrates is reported. A uniform distribution of FN was revealed by Ponceau staining after control experiments on nitrocellulose paper. Well-organized particulates with heights from hundreds of nanometers up to more than 1 μm packed in homogeneous layers were evidenced by optical microscopy and profilometry on Si substrates. Atomic force microscopy images showed regions composed of buffer and FN aggregates forming a compact film. Comparison of infrared spectra of drop-cast and MAPLE-deposited FN confirmed the preservation of composition and showed no degradation of the protein. The protein deposition on Si was confirmed by antibody staining. Small aggregates and fluorescent fibrils were visualized by fluorescence microscopy. Superior attachment of human osteoprogenitor cells cultivated for 3 h proved the presence of stable and intact FN molecules after transfer.

  13. Cell poking: quantitative analysis of indentation of thick viscoelastic layers.

    PubMed

    Duszyk, M; Schwab, B; Zahalak, G I; Qian, H; Elson, E L

    1989-04-01

    A recently introduced device, the cell poker, measures the force required to indent the exposed surface of a cell adherent to a rigid substratum. The cell poker has provided phenomenological information about the viscoelastic properties of several different types of cells, about mechanical changes triggered by external stimuli, and about the role of the cytoskeleton in these mechanical functions. Except in special cases, however, it has not been possible to extract quantitative estimates of viscosity and elasticity moduli from cell poker measurements. This paper presents cell poker measurements of well characterized viscoelastic polymeric materials, polydimethylsiloxanes of different degrees of polymerization, in a simple shape, a flat, thick layer, which for our purposes can be treated as a half space. Analysis of the measurements in terms of a linear viscoelasticity theory yields viscosity values for three polymer samples in agreement with those determined by measurements on a macroscopic scale. Theoretical analysis further indicates that the measured limiting static elasticity of the layers may result from the tension generated at the interface between the polymer and water. This work demonstrates the possibility of obtaining quantitative viscoelastic material properties from cell poker measurements and represents the first step in extending these quantitative studies to more complicated structures including cells.

  14. Cell poking: quantitative analysis of indentation of thick viscoelastic layers.

    PubMed Central

    Duszyk, M; Schwab, B; Zahalak, G I; Qian, H; Elson, E L

    1989-01-01

    A recently introduced device, the cell poker, measures the force required to indent the exposed surface of a cell adherent to a rigid substratum. The cell poker has provided phenomenological information about the viscoelastic properties of several different types of cells, about mechanical changes triggered by external stimuli, and about the role of the cytoskeleton in these mechanical functions. Except in special cases, however, it has not been possible to extract quantitative estimates of viscosity and elasticity moduli from cell poker measurements. This paper presents cell poker measurements of well characterized viscoelastic polymeric materials, polydimethylsiloxanes of different degrees of polymerization, in a simple shape, a flat, thick layer, which for our purposes can be treated as a half space. Analysis of the measurements in terms of a linear viscoelasticity theory yields viscosity values for three polymer samples in agreement with those determined by measurements on a macroscopic scale. Theoretical analysis further indicates that the measured limiting static elasticity of the layers may result from the tension generated at the interface between the polymer and water. This work demonstrates the possibility of obtaining quantitative viscoelastic material properties from cell poker measurements and represents the first step in extending these quantitative studies to more complicated structures including cells. PMID:2720066

  15. An all chemical solution deposition approach for the growth of highly textured CeO2 cap layers on La2Zr2O7-buffered long lengths of biaxially textured Ni W substrates for YBCO-coated conductors

    NASA Astrophysics Data System (ADS)

    Engel, S.; Knoth, K.; Hühne, R.; Schultz, L.; Holzapfel, B.

    2005-10-01

    A reel-to-reel, dip coating process has been developed to continuously deposit epitaxial La2Zr2O7 (LZO) and CeO2 on 5 m long cube-textured {100} (001)Ni tapes. Recent results for La2Zr2O7 and CeO2 buffer layers deposited on long lengths of Ni substrate for the realization of YBa2Cu3O7-x (YBCO)-coated conductors are presented. The major achievement is the development of a new all chemical solution deposition (CSD) process leading to the formation of highly textured buffer layers at moderate annealing temperatures. Reproducible highly textured, dense and crack-free LZO buffer layers and CeO2 cap layers were obtained for annealing temperatures as low as 900 °C in a reducing atmosphere (Ar-5 at.%-H2). The thickness of the LZO buffer layers was determined to be (200 ± 10) nm per single coating; prepared cerium oxide layers showed a thickness of 60 nm ± 10 nm. Pulsed laser deposition (PLD) was used to grow YBCO films on these substrates. A Tc 0 of T = 90.5 K and ΔTc = 1.4 K was obtained on PLD-YBCO/CSD-CeO2 /CSD-LZO/Ni-5 at.% W, which shows the outstanding features of this new buffer layer architecture processed by CSD. The large layer thickness combined with low annealing temperatures is the main advantage of this new process for low-cost buffer layer deposition on Ni-RABiTS (rolling-assisted biaxially textured substrates).

  16. 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.

  17. 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

  18. SrO(001) on graphene: a universal buffer layer for integration of complex oxides

    NASA Astrophysics Data System (ADS)

    Ahmed, Adam; Wen, Hua; Pinchuk, Igor; Zhu, Tiancong; Kawakami, Roland

    2015-03-01

    We report the successful growth of high-quality crystalline SrO on highly-ordered pyrolytic graphite (HOPG) and single layer graphene by molecular beam epitaxy. The epitaxial SrO layers have (001) orientation as confirmed by x-ray diffraction (XRD), and atomic force microscopy measurements show rms surface roughness of optimal films to be 1.2 Å. Transport measurements of exfoliated graphene after SrO deposition show a strong dependence between the Dirac point and Sr oxidation. To show the utility of SrO as a buffer layer for complex oxide integration, we grew perovskite crystal SrTiO3 on SrO, and it was also confirmed to have (001) orientation from x-ray diffraction. This materials advancement opens the door to integration of many other complex oxides to explore novel correlated electron physics in graphene.

  19. 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.

  20. Controversy of critical layer thickness for InGaAs/GaAs strained-layer epitaxy

    SciTech Connect

    Gourley, P.L.; Fritz, I.J.; Dawson, L.R.

    1988-02-01

    The critical layer thickness for In/sub x/Ga/sub 1-//sub x/As layers in In/sub x/Ga/sub 1-//sub x/As/GaAs single strained quantum wells (SSQW's) and strained-layer superlattices (SLS's) are investigated. Photoluminescence microscopy (PLM) images and x-ray rocking curves for two series of SSQW and SLS structures corresponding to many different layer thicknesses were obtained. We find that the PLM technique, which directly images dislocations and is sensitive to low dislocation densities, is much more suitable for determining the onset of dislocation creation. The x-ray technique can detect lattice relaxation by dislocations but only at relatively high densities of dislocations. Using the former technique, we determine critical thicknesses of 190 A for SSQW's and 250 A for SLS's with xapprox. =0.2. These results are near the theoretical predictions of J. W. Matthews, S. Mader, and T. B. Light (J. Appl. Phys. 41, 3800 (1970)) (150 and 300 A, respectively) and are much lower than results obtained by x-ray or other techniques which sense lattice relaxation.

  1. Effect of buffer layers on performance of organic photovoltaic devices based on copper phthalocyanine-perylene dye heterojunction

    NASA Astrophysics Data System (ADS)

    Signerski, R.; Jarosz, G.

    2011-12-01

    The work presents the results of research on the systems formed from thin films of copper phthalocyanine (CuPc), N-N'-dimethylperylene-3,4,9,10-dicarboximide (MePTCDI), electrodes of ITO and Ag, and from buffer layers: MoO3 at ITO and BCP at Ag. We have observed the effect of each buffer layer on voltage dependence of dark current and photocurrent, and on open circuit voltage-light intensity relationship. The system with both buffer layers exhibited the highest values of open circuit voltage and fill factor. The buffer layers improve transport of charge carriers within near-electrode regions, reduce dissociation of excitons on electrodes and reveal processes of charge carrier generation and recombination within the CuPc/MePTCDI junction.

  2. Design of optimal buffer layers for CuInGaSe2 thin-film solar cells(Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Lordi, Vincenzo; Varley, Joel B.; He, Xiaoqing; Rockett, Angus A.; Bailey, Jeff; Zapalac, Geordie H.; Mackie, Neil; Poplavskyy, Dmitry; Bayman, Atiye

    2016-09-01

    Optimizing the buffer layer in manufactured thin-film PV is essential to maximize device efficiency. Here, we describe a combined synthesis, characterization, and theory effort to design optimal buffers based on the (Cd,Zn)(O,S) alloy system for CIGS devices. Optimization of buffer composition and absorber/buffer interface properties in light of several competing requirements for maximum device efficiency were performed, along with process variations to control the film and interface quality. The most relevant buffer properties controlling performance include band gap, conduction band offset with absorber, dopability, interface quality, and film crystallinity. Control of an all-PVD deposition process enabled variation of buffer composition, crystallinity, doping, and quality of the absorber/buffer interface. Analytical electron microscopy was used to characterize the film composition and morphology, while hybrid density functional theory was used to predict optimal compositions and growth parameters based on computed material properties. Process variations were developed to produce layers with controlled crystallinity, varying from amorphous to fully epitaxial, depending primarily on oxygen content. Elemental intermixing between buffer and absorber, particularly involving Cd and Cu, also is controlled and significantly affects device performance. Secondary phase formation at the interface is observed for some conditions and may be detrimental depending on the morphology. Theoretical calculations suggest optimal composition ranges for the buffer based on a suite of computed properties and drive process optimizations connected with observed film properties. Prepared by LLNL under Contract DE-AC52-07NA27344.

  3. a Novel pt and Npt Mixed Igbt Having a New n-BUFFER Layer

    NASA Astrophysics Data System (ADS)

    Zhang, Fei; Luo, Shuhua; Zhang, Liang; Wang, Wei; Yu, Wen; Li, Chengfang; Sun, Xiaowei

    For the first time, a novel mixed insulated gate bipolar transistor (MIGBT) is proposed and verified by two-dimensional (2D) mixed device-circuit simulations. The structure of the proposed device is almost identical with that of the conventional IGBT, except for the buffer layer which is formed by employing the n+/n- structure, so that the trade-off relation between the conduction and switching losses is greatly improved and efficiently decoupled. Furthermore, the proposed device exhibits larger forward blocking voltage and positive temperature coefficient of the forward voltage drop, facilitating parallel integration.

  4. 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

  5. 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.

  6. 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.

  7. Body centered cubic buffer layers for enhanced lateral grain growth of Co/Cu multilayers

    NASA Astrophysics Data System (ADS)

    Tsunoda, Masakiyo; Takahashi, Daisuke; Takahashi, Migaku

    2003-05-01

    The effect of buffer layers (BLs) on metallurgical microstructure and giant magnetoresistance of Co/Cu multilayers fabricated on them is discussed. The lateral grain size and the magnetoresistance (MR) ratio of multilayers are generally enlarged with changing the chemical composition of BLs toward a limiting concentration, within the range where the solid solution of body-centered-cubic (bcc) structure is formed. A guiding principle for material research for the BLs, which realize flat interfaces with large lateral grain size in the multilayers, is deduced from the correlation between the MR ratio of the multilayers and the surface energy of bcc BLs: the difference between the surface energy of BL (γS) and the interfacial energy (γSL) in Young-Dupré's equation (cos θ=(γS-γSL)/γL) should agree with the surface energy of Co layer (γL), which is deposited first on the BL.

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

    PubMed Central

    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

  9. Growth and superconductivity of REBCO bulk processed by a seed/buffer layer/precursor construction

    NASA Astrophysics Data System (ADS)

    Y Li, T.; Cheng, L.; Yan, S. B.; Sun, L. J.; Yao, X.; Yoshida, Y.; Ikuta, H.

    2010-12-01

    The buffer layer has been used, for the first time, in the cold-seeding melt-growth (MG) process for REBCO superconductor bulks. In this modified method, a mini pellet was inserted between the seed and the bulk precursor. Notably, the chemical contamination, from the seed material (either REBCO films or SmBCO/NdBCO crystals), was mostly absorbed by the mini pellet. Thus a uniformly high Tc REBCO bulk was readily gained. Secondly, the higher limits of the maximum processing temperature (Tmax) were evidently raised, which is promisingly beneficial for broadening the growth window and overcoming the self-nucleation in the growth of large-sized bulk. In short, the success of this work is that it protects the bulk from seed-induced contamination, and breaks the limit of Tmax caused by the intrinsic properties of the seed material. By means of this simple seed/buffer layer/precursor construction, we successfully fabricated a large single grain of GdBCO bulk superconductor with a diameter of 56 mm.

  10. 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.

  11. 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.

  12. 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.

  13. Preparation of electron buffer layer with crystalline ZnO nanoparticles in inverted organic photovoltaic cells

    NASA Astrophysics Data System (ADS)

    Lee, Donghwan; Kang, Taeho; Choi, Yoon-Young; Oh, Seong-Geun

    2017-06-01

    Zinc oxide (ZnO) nanoparticles synthesized through sol-gel method were used to fabricate the electron buffer layer in inverted organic photovoltaic cells (OPVs) after thermal treatment. To investigate the effect of thermal treatment on the formation of crystalline ZnO nanoparticles, the amorphous ZnO nanoparticles were treated via hydrothermal method. The crystalline phase of ZnO with well-ordered structure could be obtained when the amorphous phase of ZnO was processed under hydrothermal treatment at 170 °C. The crystalline structure of ZnO thin film in inverted organic solar cell could be obtained under relatively low annealing temperature by using thermally treated ZnO nanoparticles. The OPVs fabricated by using crystalline ZnO nanoparticles for electron buffer layer exhibited higher efficiency than the conventional ZnO nanoparticles. The best power conversion efficiency (PCE) was achieved for 7.16% through the ZnO film using the crystalline ZnO nanoparticles. The proposed method to prepared ZnO nanoparticles (NPs) could effectively reduce energy consumption during the fabrication of OPVs, which would greatly contribute to advantages such as lower manufacturing costs, higher productivity and application on flexible substrates.

  14. Understanding Coulomb Scattering Mechanism in Monolayer MoS2 Channel in the Presence of h-BN Buffer Layer.

    PubMed

    Joo, Min-Kyu; Moon, Byoung Hee; Ji, Hyunjin; Han, Gang Hee; Kim, Hyun; Lee, Gwanmu; Lim, Seong Chu; Suh, Dongseok; Lee, Young Hee

    2017-02-08

    As the thickness becomes thinner, the importance of Coulomb scattering in two-dimensional layered materials increases because of the close proximity between channel and interfacial layer and the reduced screening effects. The Coulomb scattering in the channel is usually obscured mainly by the Schottky barrier at the contact in the noise measurements. Here, we report low-temperature (T) noise measurements to understand the Coulomb scattering mechanism in the MoS2 channel in the presence of h-BN buffer layer on the silicon dioxide (SiO2) insulating layer. One essential measure in the noise analysis is the Coulomb scattering parameter (αSC) which is different for channel materials and electron excess doping concentrations. This was extracted exclusively from a 4-probe method by eliminating the Schottky contact effect. We found that the presence of h-BN on SiO2 provides the suppression of αSC twice, the reduction of interfacial traps density by 100 times, and the lowered Schottky barrier noise by 50 times compared to those on SiO2 at T = 25 K. These improvements enable us to successfully identify the main noise source in the channel, which is the trapping-detrapping process at gate dielectrics rather than the charged impurities localized at the channel, as confirmed by fitting the noise features to the carrier number and correlated mobility fluctuation model. Further, the reduction in contact noise at low temperature in our system is attributed to inhomogeneous distributed Schottky barrier height distribution in the metal-MoS2 contact region.

  15. 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

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

    PubMed

    Rabbani, Hossein; Kafieh, Rahele; 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.

  17. MIS and MFIS Devices: DyScO3 as a gate-oxide and buffer-layer

    NASA Astrophysics Data System (ADS)

    Melgarejo, R.; Karan, N. K.; Saavedra-Arias, J.; Pradhan, D. K.; Thomas, R.; Katiyar, R. S.

    2008-03-01

    Metal-Ferroelectric-Insulator-Semiconductor (MFIS) structure is of importance in nonvolatile memories, as insulating buffer layer that prevents interdiffusion between the ferroelectric (FE) and the Si substrate. However, insulating layer has some disadvantages viz. generation of depolarization field in FE film and increase of operation voltage. To overcome this, it is important to find a FE with low ɛr (compared to normal FE) and an insulating buffer layer with high ɛr (compared to ɛr = 3.9 of SiO2). High-k materials viz. LaAlO3, SiN, HfO2, HfAlO etc. have been studied as buffer layers in the MFIS structures and as gate-oxide in metal-insulator-silicon (MIS). Recently, a novel gate dielectric material, DyScO3 was considered and studies indicate that crystallization temperature significantly increased and the film on Si remained amorphous even at 1000 C annealing. Considering the requirements on crystallization temperature, ɛr, electrical stability for high-k buffer layers, DyScO3 seems to be very promising for future MFIS device applications. Therefore, the evaluations of MOCVD grown DyScO3 as gate-oxide for MIS and the buffer layers for Bi3.25La0.75Ti3O12 based MFIS structures are presented.

  18. Growth and characterization aluminum gallium nitride/gallium nitride heterostructures on silicon(111) wafers using various buffer layers

    NASA Astrophysics Data System (ADS)

    Venugopal, Rajesh

    Devices based on nitride wide bandgap semiconductors are suitable for several promising applications such as blue lasers, LEDs, HEMTs etc. Due to the absence of bulk nitride crystals, nitride films are grown on lattice mismatched substrates like Al2O3 and 6H-SiC. However from a cost and integration standpoint silicon would be the substrate of choice for the growth of these materials. Nitride heterostructure growth on large area Si(111) is hence attempted by Metal Organic Chemical Vapor Deposition (MOCVD) in an modified AIX 200/4 system. The large lattice and thermal mismatch prevents the direct deposition of GaN on Si and also causes GaN layers grown on Si to crack severely. It is hence necessary to use buffer layers to alleviate this lattice and thermal mismatch. Several buffer layer schemes are used for this purpose. The crystal quality of the AlGaN/GaN heterostructures grown under various conditions on these buffers are studied using several methods like Photoluminescence, X-ray diffraction, Electron Microscopy etc. The quality of heterostructures grown on these buffers is compared in order to identify the strengths and weaknesses of each buffer and to also map the effects of process parameters on nitride layers deposited on each buffer.

  19. 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.

  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. Investigations on crack generation mechanism and crack reduction by buffer layer insertion in thermal-plasma-jet crystallization of amorphous silicon films on glass substrate

    NASA Astrophysics Data System (ADS)

    Tanaka, Keisuke; Hayashi, Shohei; Morisaki, Seiji; Higashi, Seiichiro

    2015-01-01

    The crack generation mechanism and the effect of crack reduction by buffer SiO2 layer insertion in thermal-plasma-jet (TPJ) crystallization of an amorphous silicon film on a glass substrate have been investigated. The crack generation was clearly observed 13.7 s after TPJ irradiation using a high-speed camera, which indicates that cracks are generated not during heating, but during cooling. From the measurement and simulation of substrate deformations, it was clarified that the substrate deformed convexly during heating and it consequently deformed concavely after cooling owing to the substrate surface densification. This result indicated that the tensile stress generated by the concave deformation is the origin of cracks. The deposition of the buffer SiO2 layer generated compressive stress, which minimizes accumulation of tensile stress after TPJ annealing. The number of cracks in unit length significantly decreased owing to the decrease in tensile stress with the increase in the thickness of the buffer SiO2 layer.

  3. Effects of Cd-free buffer layer for CuInSe{sub 2} thin-film solar cells

    SciTech Connect

    Nii, T.; Sugiyama, I.; Kase, T.; Sato, M.; Kaniyama, Y.; Kuriyagawa, S.; Kushiya, K.; Takeshita, H.

    1994-12-31

    ZnO buffer layer by a chemical-bath deposition (CBD) method is developed in this study to improve the interface quality between n-ZnO window layer and p-CuInSe{sub 2} (CIS) thin-film absorber in CIS thin-film solar cells as one of the approaches to the fabrication of Cd-free thin-film solar cells. The optimization of the fabrication conditions of CBD-ZnO leads to the efficiency of about 10%. These results indicate the CBD-ZnO buffer layer has rather high capability to fabricate high-efficiency CIS thin-film solar cells.

  4. Performance improvement of MEH-PPV:PCBM solar cells using bathocuproine and bathophenanthroline as the buffer layers

    NASA Astrophysics Data System (ADS)

    Liu Xiao, Dong; Zhao, Su-Ling; Xu, Zheng; Zhang, Fu-Jun; Zhang, Tian-Hui; Gong, Wei; Yan, Guang; Kong, Chao; Wang, Yong-Sheng; Xu, Xu-Rong

    2011-06-01

    In this work, bathocuproine (BCP) and bathophenanthroline (Bphen), commonly used in small-molecule organic solar cells (OSCs), are adopted as the buffer layers to improve the performance of the polymer solar cells (PSCs) based on poly(2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV): [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) bulk heterojunction. By inserting BCP or Bphen between the active layer and the top cathode, all the performance parameters are dramatically improved. The power conversion efficiency is increased by about 70% and 120% with 5-nm BCP and 12-nm Bphen layers, respectively, when compared with that of the devices without any buffer layer. The performance enhancement is attributed to BCP or Bphen (i) increasing the optical field, and hence the absorption in the active layer, (ii) effectively blocking the excitons generated in MEH-PPV from quenching at organic/aluminum (Al) interface due to the large band-gap of BCP or Bphen, which results in a significant reduction in series resistance (Rs), and (iii) preventing damage to the active layer during the metal deposition. Compared with the traditional device using LiF as the buffer layer, the BCP-based devices show a comparable efficiency, while the Bphen-based devices show a much larger efficiency. This is due to the higher electron mobility in Bphen than that in BCP, which facilitates the electron transport and extraction through the buffer layer to the cathode.

  5. Effect of organic buffer layer in the electrical properties of amorphous-indium gallium zinc oxide thin film transistor.

    PubMed

    Wang, Jian-Xun; Hyung, Gun Woo; Li, Zhao-Hui; Son, Sung-Yong; Kwon, Sang Jik; Kim, Young Kwan; Cho, Eou Sik

    2012-07-01

    In this research, we reported on the fabrication of top-contact amorphous-indium gallium zinc oxide (a-IGZO) thin-film transistors (TFTs) with an organic buffer layer between inorganic gate dielectric and active layer in order to improve the electrical properties of devices. By inserting an organic buffer layer, it was possible to make an affirmation of the improvements in the electrical characteristics of a-IGZO TFTs such as subthreshold slope (SS), on/off current ratio (I(ON/OFF)), off-state current, and saturation field-effect mobility (muFE). The a-IGZO TFTs with the cross-linked polyvinyl alcohol (c-PVA) buffer layer exhibited the pronounced improvements of the muFE (17.4 cm2/Vs), SS (0.9 V/decade), and I(ON/OFF) (8.9 x 10(6)).

  6. Dislocation annihilation in regrown GaN on nanoporous GaN template with optimization of buffer layer growth

    NASA Astrophysics Data System (ADS)

    Soh, C. B.; Hartono, H.; Chow, S. Y.; Chua, S. J.; Fitzgerald, E. A.

    2007-01-01

    Nanoporous GaN template has been fabricated by electrochemical etching to give hexagonal pits with nanoscale pores of size 20-50nm in the underlying grains. The effect of GaN buffer layer grown at various temperatures from 650to1015°C on these as-fabricated nanopores templates is investigated by transmission electron microscopy. The buffer layer grown at the optimized temperature of 850°C partially fill up the pores and voids with annihilation of threading dislocations, serving as an excellent template for high-quality GaN growth. This phenomenon is, however, not observed for the samples grown with other temperature buffer layers. Micro-Raman measurements show significant strain relaxation and improvement in the crystal quality of the overgrown GaN layer on nanoporous GaN template as compared to overgrown on conventional GaN template.

  7. 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.

  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. Magnetic and magnetoresistance studies of nanometric electrodeposited Co films and Co/Cu layered structures: Influence of magnetic layer thickness

    NASA Astrophysics Data System (ADS)

    Zsurzsa, S.; Péter, L.; Kiss, L. F.; Bakonyi, I.

    2017-01-01

    The magnetic properties and the magnetoresistance behavior were investigated for electrodeposited nanoscale Co films, Co/Cu/Co sandwiches and Co/Cu multilayers with individual Co layer thicknesses ranging from 1 nm to 20 nm. The measured saturation magnetization values confirmed that the nominal and actual layer thicknesses are in fairly good agreement. All three types of layered structure exhibited anisotropic magnetoresistance for thick magnetic layers whereas the Co/Cu/Co sandwiches and Co/Cu multilayers with thinner magnetic layers exhibited giant magnetoresistance (GMR), the GMR magnitude being the largest for the thinnest Co layers. The decreasing values of the relative remanence and the coercive field when reducing the Co layer thickness down to below about 3 nm indicated the presence of superparamagnetic (SPM) regions in the magnetic layers which could be more firmly evidenced for these samples by a decomposition of the magnetoresistance vs. field curves into a ferromagnetic and an SPM contribution. For thicker magnetic layers, the dependence of the coercivity (Hc) on magnetic layer thickness (d) could be described for each of the layered structure types by the usual equation Hc=Hco+a/dn with an exponent around n=1. The common value of n suggests a similar mechanism for the magnetization reversal by domain wall motion in all three structure types and hints also at the absence of coupling between magnetic layers in the Co/Cu/Co sandwiches and Co/Cu multilayers.

  10. 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.

  11. Inverted Organic Solar Cells with Improved Performance using Varied Cathode Buffer Layers

    NASA Astrophysics Data System (ADS)

    Guan, Zhi-qiang; Yu, Jun-sheng; Zang, Yue; Zeng, Xing-xin

    2012-10-01

    Organic solar cells with inverted planar heterojunction structure based on subphthalocyanine and C60 were fabricated using several kinds of materials as cathode buffer layer (CBL), including tris-8-hydroxy-quinolinato aluminum (Alq3), bathophenanthroline (Bphen), bathocuproine, 2,3,8,9,14,15-hexakis-dodecyl-sulfanyl-5,6,11,12,17,18-hexaazatrinaphthylene (HATNA), and an inorganic compound of Cs2CO3. The influence of the lowest unoccupied molecular orbital level and the electron mobility of organic CBL on the solar cells performance was compared. The results showed that Alq3, Bphen, and HATNA could significantly improve the device performance. The highest efficiency was obtained from device with annealed HATNA as CBL and increased for more than 7 times compared with device without CBL. Furthermore, the simulation results with space charge-limited current theory indicated that the Schottky barrier at the organic/electrode interface in inverted OSC structure was reduced for 27% by inserting HATNA CBL.

  12. Compact hematite buffer layer as a promoter of nanorod photoanode performances

    PubMed Central

    Milan, R.; Cattarin, S.; Comisso, N.; Baratto, C.; Kaunisto, K.; Tkachenko, N. V.; Concina, I.

    2016-01-01

    The effect of a thin α-Fe2O3 compact buffer layer (BL) on the photoelectrochemical performances of a bare α-Fe2O3 nanorods photoanode is investigated. The BL is prepared through a simple spray deposition onto a fluorine-doped tin oxide (FTO) conducting glass substrate before the growth of a α-Fe2O3 nanorods via a hydrothermal process. Insertion of the hematite BL between the FTO and the nanorods markedly enhances the generated photocurrent, by limiting undesired losses of photogenerated charges at the FTO||electrolyte interface. The proposed approach warrants a marked improvement of material performances, with no additional thermal treatment and no use/dispersion of rare or toxic species, in agreement with the principles of green chemistry. PMID:27733756

  13. Compact hematite buffer layer as a promoter of nanorod photoanode performances

    NASA Astrophysics Data System (ADS)

    Milan, R.; Cattarin, S.; Comisso, N.; Baratto, C.; Kaunisto, K.; Tkachenko, N. V.; Concina, I.

    2016-10-01

    The effect of a thin α-Fe2O3 compact buffer layer (BL) on the photoelectrochemical performances of a bare α-Fe2O3 nanorods photoanode is investigated. The BL is prepared through a simple spray deposition onto a fluorine-doped tin oxide (FTO) conducting glass substrate before the growth of a α-Fe2O3 nanorods via a hydrothermal process. Insertion of the hematite BL between the FTO and the nanorods markedly enhances the generated photocurrent, by limiting undesired losses of photogenerated charges at the FTO||electrolyte interface. The proposed approach warrants a marked improvement of material performances, with no additional thermal treatment and no use/dispersion of rare or toxic species, in agreement with the principles of green chemistry.

  14. Interlaced, Nanostructured Interface with Graphene Buffer Layer Reduces Thermal Boundary Resistance in Nano/Microelectronic Systems.

    PubMed

    Tao, Lei; Theruvakkattil Sreenivasan, Sreeprasad; Shahsavari, Rouzbeh

    2017-01-11

    Improving heat transfer in hybrid nano/microelectronic systems is a challenge, mainly due to the high thermal boundary resistance (TBR) across the interface. Herein, we focus on gallium nitride (GaN)/diamond interface-as a model system with various high power, high temperature, and optoelectronic applications-and perform extensive reverse nonequilibrium molecular dynamics simulations, decoding the interplay between the pillar length, size, shape, hierarchy, density, arrangement, system size, and the interfacial heat transfer mechanisms to substantially reduce TBR in GaN-on-diamond devices. We found that changing the conventional planar interface to nanoengineered, interlaced architecture with optimal geometry results in >80% reduction in TBR. Moreover, introduction of conformal graphene buffer layer further reduces the TBR by ∼33%. Our findings demonstrate that the enhanced generation of intermediate frequency phonons activates the dominant group velocities, resulting in reduced TBR. This work has important implications on experimental studies, opening up a new space for engineering hybrid nano/microelectronics.

  15. 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

  16. Growth of Atomically Flat Ultra-Thin Ag Films on Si(111) by Introducing a √3 × √3-Ga Buffer Layer

    NASA Astrophysics Data System (ADS)

    He, Jie-Hui; Jiang, Li-Qun; Qiu, Jing-Lan; Chen, Lan; Wu, Ke-Hui

    2014-12-01

    It is known that, when Ag is deposited on Si(111)-7×7 substrates in a conventional growth procedure at room temperature, no atomically flat Ag film could be obtained. We use scanning tunneling microscopy and low-energy electron diffraction to investigate the growth of ultra-thin Ag films on the Si(111) substrates at room temperature. Our study reveals that, upon introducing a Si(111)-√3 × √3-Ga buffer layer, atomically flat Ag films can easily grow on Si(111) with a critical thickness of two monolayers. Moreover, Ag film growth follows a layer-by-layer mode with further deposition. This novel growth behavior of Ag can be explained in terms of a free electron model (i.e., particle in a box) and kinetic Monte Carlo simulations.

  17. 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.

  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 110 nm. 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 420 ng/cm(2). However, the poly(MPC) brush layer reduced this value dramatically to less than 50 ng/cm(2). This effect was independent of the thickness of the poly(MPC) brush layer for thicknesses between 20 nm and about 110 nm. 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.

  19. 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.

  20. Reduction of threading dislocation density for AlN epilayer via a highly compressive-stressed buffer layer

    NASA Astrophysics Data System (ADS)

    Huang, Jun; Niu, Mu Tong; Zhang, Ji Cai; Wang, Wei; wang, Jian Feng; Xu, Ke

    2017-02-01

    Crystalline qualities of three AlN films grown by cold-wall high temperature hydride vapor phase epitaxy (CW-HT-HVPE) on c-plane sapphire substrates, with different AlN buffer layers (BLs) deposited either by CW-HT-HVPE or by hot-wall low temperature hydride vapor phase epitaxy (HW-LT-HVPE), have been studied. The best film quality was obtained on a 500-nm-thick AlN BL grown by HW-LT-HVPE at 1000 ℃. In this case,the AlN epilayer has the lowest full-width at half-maximum (FWHM) values of the (0002) and (10-12) x-ray rocking curve peaks of 295 and 306 arcsec, respectively, corresponding to the screw and edge threading dislocation (TD) densities of 1.9×108 cm-2 and 5.2×108 cm-2. This improvement in crystal quality of the AlN film can be attributed to the high compressive-stress of BL grown by HW-LT-HVPE,which facilitate the inclination and annihilation of TDs.

  1. Solution-dispersed CuO nanoparticles anode buffer layer: Effect of ultrasonic agitation duration on photovoltaic performance

    NASA Astrophysics Data System (ADS)

    Sabri, Nasehah Syamin; Yap, Chi Chin; Yahaya, Muhammad; Salleh, Muhamad Mat; Jumali, Mohammad Hafizuddin Haji

    2016-11-01

    The performance of inverted type hybrid organic solar cell based on poly(3-hexyltheopene):[6,6]-phenyl C61-butyric acid methyl ester (P3HT:PCBM) can be improved by adding an anode buffer layer of copper oxide (CuO). CuO that serves as an electron blocking layer which could effectively reduce the charge recombination at the photoactive layer (P3HT:PCBM)/silver (Ag) interfaces. At the same time, Cuo anode buffer layer could accelerate the holes collection from the photoactive layer to the top electrode. In this study we investigated the effects of ultrasonic agitation duration in preparation of solution-dispersed CuO anode buffer layer on the performance of the devices with a configuration of fluorine tin oxide (FTO)/zinc oxide (ZnO) nanorod arrays/P3HT:PCBM/ CuO/Ag. Different durations of ultrasonic agitation (0, 5, 15 and 25 min) were used for CuO nanoparticles solution dispersion to obtain the optimum particle size distribution of CuO. It was found that the smallest average particle size of CuO was obtained by applying the ultrasonic agitation for longest duration of 25 min. The highest power conversion efficiency of 1.22% was recorded from the device incorporating with CuO anode buffer layer with the smallest average particle size. It is believed that CuO anode buffer layer with the smallest average particle size had the least agglomerates, thus leading to better film formation and contact surface area.

  2. 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.

  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. Contribution of the buffer layer to the Raman spectrum of epitaxial graphene on SiC(0001)

    NASA Astrophysics Data System (ADS)

    Fromm, F.; Oliveira, M. H., Jr.; Molina-Sánchez, A.; Hundhausen, M.; Lopes, J. M. J.; Riechert, H.; Wirtz, L.; Seyller, T.

    2013-04-01

    We report a Raman study of the so-called buffer layer with (6\\sqrt 3\\times 6\\sqrt 3)R30^{\\circ } periodicity which forms the intrinsic interface structure between epitaxial graphene and SiC(0001). We show that this interface structure leads to a non-vanishing signal in the Raman spectrum at frequencies in the range of the D- and G-band of graphene and discuss its shape and intensity. Ab initio phonon calculations reveal that these features can be attributed to the vibrational density of states of the buffer layer.

  5. Oceanic Double-Diffusive Layer Thicknesses in the Presence of Turbulence

    NASA Astrophysics Data System (ADS)

    Shibley, Nicole; Timmermans, Mary-Louise

    2016-11-01

    Double-diffusive stratification in the ocean is characterized by staircase structures consisting of mixed layers separated by high-gradient interfaces in temperature and salinity. Several past studies have examined mechanisms that govern the observed thicknesses of staircase mixed layers. In one formalism, the mixed-layer thickness is set by layer formation that arises when a heat source is applied at the base of water that is stably-stratified in salinity; in another, the equilibrium thickness of mixed layers has been explained as the product of "merging," where thin layers continue to grow until they reach a thickness determined by a criterion relating the ratio of heat flux to salt flux and the density ratio. We extend the above two theories to consider the influence of turbulence on mixed-layer thicknesses. The study has implications for the Arctic Ocean where double-diffusive staircases are widely present, and mixed-layer thicknesses are well-resolved by ocean measurements. Our theoretical framework provides a means to determine turbulent diffusivities (in regions where microstructure measurements are not available) by considering only observations of density ratio, stratification, and layer thicknesses.

  6. 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

  7. Control of metamorphic buffer structure and device performance of In(x)Ga(1-x)As epitaxial layers fabricated by metal organic chemical vapor deposition.

    PubMed

    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

    2014-12-05

    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 (∼10(6) 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 × 10(12) 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.

  8. 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.

  9. Structural and electrical properties of metal ferroelectric insulator semiconductor structure of Al/SrBi2Ta2O9/HfO2/Si using HfO2 as buffer layer

    NASA Astrophysics Data System (ADS)

    Roy, A.; Dhar, A.; Bhattacharya, D.; Ray, S. K.

    2008-05-01

    Ferroelectric SrBi2Ta2O9 (SBT) thin films have been deposited by the radio-frequency magnetron sputtering technique on bare p-Si as well as on HfO2 insulating buffer p-Si. XRD patterns revealed the formation of a well-crystallized SBT perovskite thin film on the HfO2 buffer layer. The electrical properties of the metal-ferroelectric-insulator-semiconductor (MFIS) structure were characterized by varying thicknesses of the HfO2 layer. The MFIS structure exhibits a maximum clockwise C-V memory window of 1.60 V when the thickness of the HfO2 layer was 12 nm with a lower leakage current density of 6.20 × 10-7 A cm-2 at a positive applied voltage of 7 V. However, the memory window reaches a maximum value of 0.7 V at a bias voltage of ±5 and then decreases due to charge injection in the case of the insulating buffer layer thickness of 3 nm. The density of oxide trapped charges at/near the buffer layer-ferroelectric interface is studied by the voltage stress method. Capacitance-voltage (C-V) and leakage current density (J-V) characteristics of the Al/SBT/HfO2/Si(1 0 0) capacitor indicate that the introduction of the HfO2 buffer layer prevents interfacial diffusion between the SBT thin film and the Si substrate effectively and improves the interface quality. Furthermore, the Al/SBT/HfO2/Si structures exhibit excellent retention characteristics, the high and low capacitance values clearly distinguishable for over 1 h and 30 min. This shows that the proposed Al/SrBi2Ta2O9/HfO2/Si structure is ideally suitable for high performance ferroelectric memories.

  10. Effect of age and sex on retinal layer thickness and volume in normal eyes

    PubMed Central

    Won, Jae Yon; Kim, Sung Eun; Park, Young-Hoon

    2016-01-01

    Abstract The aim of the study was to evaluate the effect of sex and age on the thickness of the retinal layer in normal eyes using spectral-domain optical coherence tomography (SD-OCT). Fifty healthy subjects between the ages of 20 and 80 had their retinal layers measured using SD-OCT at Seoul St. Mary's Hospital. Mean thickness and volume were measured for 9 retinal layers in the fovea, the pericentral ring, and the peripheral ring. The differences of sex- and age-related thickness and volume in each retinal layer were analyzed. The retinal nerve fiber layer (RNFL), ganglion cell layer (GCL), inner plexiform layer (IPL), inner nuclear layer (INL), and outer plexiform layer (OPL) were thinnest in the fovea area, whereas the outer nuclear layer (ONL), photoreceptor layer (PHL), and retinal pigment epithelium (RPE) were thickest at similar locations. Mean thickness of the RNFL, GCL, IPL, and OPL was significantly greater in men than women. However, mean thickness of the ONL was greater in women than in men. When compared between patients < 30 years and > 60 years of age, the thickness and volume of peripheral RNFL, GCL, and pericentral and peripheral IPL were significantly larger in the younger group than the older group. Conversely, the thickness and volume of foveal INL and IR were larger in the older group than in the younger group. The thickness and volume of the retinal layer in normal eyes significantly vary depending on age and sex. These results should be considered when evaluating layer analysis in retinal disease. PMID:27861391

  11. Aqueous Solution Processed Photoconductive Cathode Interlayer for High Performance Polymer Solar Cells with Thick Interlayer and Thick Active Layer.

    PubMed

    Nian, Li; Chen, Zhenhui; Herbst, Stefanie; Li, Qingyuan; Yu, Chengzhuo; Jiang, Xiaofang; Dong, Huanli; Li, Fenghong; Liu, Linlin; Würthner, Frank; Chen, Junwu; Xie, Zengqi; Ma, Yuguang

    2016-09-01

    An aqueous-solution-processed photoconductive cathode interlayer is developed, in which the photoinduced charge transfer brings multiple advantages such as increased conductivity and electron mobility, as well as reduced work function. Average power conversion efficiency over 10% is achieved even when the thickness of the cathode interlayer and active layer is up to 100 and 300 nm, respectively.

  12. An exactly solvable model for calculating critical misfit and thickness in epitaxial superlattices - Layers of equal elastic constants and thicknesses

    NASA Technical Reports Server (NTRS)

    Van Der Merwe, Jan H.; Jesser, W. A.

    1988-01-01

    A parabolic interaction potential has been used to develop a model for calculating the misfit dislocation (MD) energy in the case of a superlattice of alternating layers of materials with equal elastic constants and thicknesses. The model, which is believed to be a good one for small misfits and to have some merit for covalent bonded materials, is exactly solvable for the critical thickness above which it is energetically favorable to lose coherency by the introduction of MDs into the interfaces. It was found, for a given misfit f, that the critical thickness for epitaxial superlattices free from their substrate is somewhat more than four times that for a single epilayer on a thick substrate. Furthermore, the critical thickness varies almost inversely with misfit to the power 1.22 when Poisson's ratio is 1/3. It was also shown that the critical misfit f(c) obtained by equating maximal misfit strain and MD energies is a significant overestimate of f(c). The results for a superlattice are compared with those of a thin layer on a thick substrate.

  13. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

    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 × 1018 cm-3) epitaxial layer closest to the substrate and a lower doped layer (3 × 1016 cm-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 × 1018 cm-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.

  15. 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.

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

    PubMed

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

    2015-07-17

    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.

  17. Barrier efficiency of sponge-like La2Zr2O7 buffer layers for YBCO-coated conductors

    NASA Astrophysics Data System (ADS)

    Molina, Leopoldo; Tan, Haiyan; Biermans, Ellen; Batenburg, Kees J.; Verbeeck, Jo; Bals, Sara; Van Tendeloo, Gustaaf

    2011-06-01

    Solution derived La2Zr2O7 films have drawn much attention for potential applications as thermal barriers or low-cost buffer layers for coated conductor technology. Annealing and coating parameters strongly affect the microstructure of La2Zr2O7, but different film processing methods can yield similar microstructural features such as nanovoids and nanometer-sized La2Zr2O7 grains. Nanoporosity is a typical feature found in such films and the implications for the functionality of the films are investigated by a combination of scanning transmission electron microscopy (STEM), electron energy-loss spectroscopy (EELS) and quantitative electron tomography. Chemical solution based La2Zr2O7 films deposited on flexible Ni-5 at.%W substrates with a {100}lang001rang biaxial texture were prepared for an in-depth characterization. A sponge-like structure composed of nanometer-sized voids is revealed by high-angle annular dark-field scanning transmission electron microscopy in combination with electron tomography. A three-dimensional quantification of nanovoids in the La2Zr2O7 film is obtained on a local scale. Mostly non-interconnected highly faceted nanovoids compromise more than one-fifth of the investigated sample volume. The diffusion barrier efficiency of a 170 nm thick La2Zr2O7 film is investigated by STEM-EELS, yielding a 1.8 ± 0.2 nm oxide layer beyond which no significant nickel diffusion can be detected and intermixing is observed. This is of particular significance for the functionality of YBa2Cu3O7 - δ coated conductor architectures based on solution derived La2Zr2O7 films as diffusion barriers.

  18. Epitaxial MgB2 thin films on ZrB2 buffer layers: structural characterization by synchrotron radiation

    NASA Astrophysics Data System (ADS)

    Ferrando, V.; Tarantini, C.; Bellingeri, E.; Manfrinetti, P.; Pallecchi, I.; Marré, D.; Plantevin, O.; Putti, M.; Felici, R.; Ferdeghini, C.

    2004-12-01

    Structural and superconducting properties of magnesium diboride thin films grown by pulsed laser deposition on zirconium diboride buffer layers were studied. We demonstrate that the ZrB2 layer is compatible with the MgB2 two step deposition process. Synchrotron radiation measurements, in particular anomalous diffraction measurements, allowed us to separate MgB2 peaks from ZrB2 ones and revealed that both layers have a single in plane orientation with a sharp interface between them. Moreover, the buffer layer avoids oxygen contamination from the sapphire substrate. The critical temperature of this film is near 37.6 K and the upper critical field measured at the Grenoble High Magnetic Field Laboratory up to 20.3 T is comparable with the highest ones reported in literature.

  19. Direct determination of the thickness of stratospheric layers from single-channel satellite radiance measurements.

    NASA Technical Reports Server (NTRS)

    Quiroz, R. S.; Gelman, M. E.

    1972-01-01

    The direct use of measured radiances for determining the thickness of stratospheric layers is investigated. Layers based at 100-10 mb, with upper boundaries at 10-0.5 mb, are investigated using a carefully selected family of stratospheric temperature profiles and computed radiances. On the basis of physical reasoning, a high correlation of thickness with radiance is anticipated for deep layers, such as the 100- to 2-mb layer (from about 15 to 43 km), that emit a substantial part of the infrared energy reaching a satellite radiometer in a particular channel. Empirical regression curves relating thickness and radiance are developed and are compared with blackbody curves obtained by substituting the blackbody temperature in the hydrostatic equation. Maximum thickness-radiance correlation is found, for each infrared channel, for the layer having the best agreement of empirical and blackbody curves.

  20. Dependence of Curie temperature on Pt layer thickness in Co/Pt system

    NASA Astrophysics Data System (ADS)

    Koyama, T.; Obinata, A.; Hibino, Y.; Hirohata, A.; Kuerbanjiang, B.; Lazarov, V. K.; Chiba, D.

    2015-03-01

    The Pt thickness dependence of the Curie temperature of perpendicularly magnetized ultra-thin (Pt/)Co/Pt films has been investigated by magnetization measurements. The Curie temperature and the saturation magnetic moment increase with the Co layer thickness and even with the Pt layer thickness. The Curie temperature is found to have linear dependence on the total magnetic moment of the system and the coefficients of the linear fits are almost identical, regardless of whether the thicknesses of the ferromagnetic Co layer or the Pt layer are varied. The Curie temperature also increases with the magnetic anisotropy, but no systematic dependence is observed. These results suggest that the magnetic moment induced in the Pt layer by the ferromagnetic proximity effect plays a significant role in determining the Curie temperatures of such two-dimensional ferromagnetic systems.

  1. 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

  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. Incorporation of La in epitaxial SrTiO3 thin films grown by atomic layer deposition on SrTiO3-buffered Si (001) substrates

    NASA Astrophysics Data System (ADS)

    McDaniel, Martin D.; Posadas, Agham; Ngo, Thong Q.; Karako, Christine M.; Bruley, John; Frank, Martin M.; Narayanan, Vijay; Demkov, Alexander A.; Ekerdt, John G.

    2014-06-01

    Strontium titanate, SrTiO3 (STO), thin films incorporated with lanthanum are grown on Si (001) substrates at a thickness range of 5-25 nm. Atomic layer deposition (ALD) is used to grow the LaxSr1-xTiO3 (La:STO) films after buffering the Si (001) substrate with four-unit-cells of STO deposited by molecular beam epitaxy. The crystalline structure and orientation of the La:STO films are confirmed via reflection high-energy electron diffraction, X-ray diffraction, and cross-sectional transmission electron microscopy. The low temperature ALD growth (˜225 °C) and post-deposition annealing at 550 °C for 5 min maintains an abrupt interface between Si (001) and the crystalline oxide. Higher annealing temperatures (650 °C) show more complete La activation with film resistivities of ˜2.0 × 10-2 Ω cm for 20-nm-thick La:STO (x ˜ 0.15); however, the STO-Si interface is slightly degraded due to the increased annealing temperature. To demonstrate the selective incorporation of lanthanum by ALD, a layered heterostructure is grown with an undoped STO layer sandwiched between two conductive La:STO layers. Based on this work, an epitaxial oxide stack centered on La:STO and BaTiO3 integrated with Si is envisioned as a material candidate for a ferroelectric field-effect transistor.

  4. Thickness measurement of multi-layer conductive coatings using multifrequency eddy current techniques

    NASA Astrophysics Data System (ADS)

    Zhang, Dejun; Yu, Yating; Lai, Chao; Tian, Guiyun

    2016-07-01

    To ensure the key structural performance in high-temperature and high-stress environments, thermal barrier coatings (TBCs) are often adopted in engineering. The thickness of these multi-layer conductive coatings is an important quality indicator. In order to measure the thickness of multi-layer conductive coatings, a new measurement approach is presented using eddy current testing techniques, and then, an inversion algorithm is proposed and proved efficient and applicable, of which the maximum experimental relative error is within 10%. Therefore, the new approach can be effectively applied to thickness measurement of multi-layer conductive coatings such as TBCs.

  5. 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.

  6. 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.

  7. 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)

    NASA Astrophysics Data System (ADS)

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

    2013-09-01

    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.

  8. Evanescent field response to immunoassay layer thickness on planar waveguides

    NASA Astrophysics Data System (ADS)

    Yan, Rongjin; Yuan, Guangwei; Stephens, Matthew D.; He, Xinya; Henry, Charles S.; Dandy, David S.; Lear, Kevin L.

    2008-09-01

    The response of a compact photonic immunoassay biosensor based on a planar waveguide to variation in antigen (C-reactive protein) concentration as well as waveguide ridge height has been investigated. Near-field scanning optical microscope measurements indicate 1.7%/nm and 3.3%/nm top surface optical intensity modulation due to changes in effective adlayer thickness on waveguides with 16.5 and 10nm ridge heights, respectively. Beam propagation method simulations are in good agreement with the experimental sensitivities as well as the observation of leaky mode interference both within and after the adlayer region.

  9. Pavement thickness and stabilised foundation layer assessment using ground-coupled GPR

    NASA Astrophysics Data System (ADS)

    Hu, Jinhui; Vennapusa, Pavana K. R.; White, David J.; Beresnev, Igor

    2016-07-01

    Experimental results from field and laboratory investigations using a ground-coupled ground penetrating radar (GPR), dielectric measurement, magnetic imaging tomography (MIT) and dynamic cone penetrometer (DCP) tests are presented. Dielectric properties of asphalt pavement and stabilised and unstabilised pavement foundation materials were evaluated in the laboratory in frozen and unfrozen conditions. Laboratory test results showed that dielectric properties of materials back-calculated from GPR in comparison to dielectric gauge measurements are strongly correlated and repeatable. For chemically stabilised materials, curing time affected the dielectric properties of the materials. Field tests were conducted on asphalt pavement test sections with different foundation materials (stabilised and unstabilised layers), drainage conditions and layer thicknesses. GPR and MIT results were used to determine asphalt layer thicknesses and were compared with measured core thicknesses, while GPR and DCP were used to assess foundation layer profiles. Asphalt thicknesses estimated from GPR showed an average error of about 11% using the dielectric gauge values as input. The average error reduced to about 4% when calibrated with cores thicknesses. MIT results showed thicknesses that are about 9% higher than estimated using GPR. Foundation layer thicknesses could not be measured using GPR due to variations in moisture conditions between the test sections, which is partly attributed to variations in gradation and drainage characteristics of the subbase layer.

  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.

  11. Study the spatial variability of organic soil layer thickness within Barataria Bay marshes, Louisiana

    SciTech Connect

    Hudnall, W.H.; Dharmasri, L.C.; Holladay, K.W.; Pelletier, R.

    1997-08-01

    Marshes convert to open water at a high rate in Louisiana. Organic layers degrade in eroding marshes. Organic accretion results in thick organic layers that help to maintain healthy marshes. Thin organic layers may be characteristic of erodible marshes that convert into open water. Thickness of the surface organic layer is a significant soil morphological feature that may indicate the status of the marsh. Soil morphology can show a significant spatial variability within marshes. Accretion rates and the landscape may be disturbed by hurricane activity, presence of channels, open water areas, and man made changes. Understanding spatial variability of organic layer thickness will enable one to delineate critical marsh areas and plan marsh management strategies. Study of multi-dimensional variability may help to understand the spatial variability of soil morphological characteristics and prominent pedogenic processes that can be related to a landscape-soil model. Thickness of surface organic layer (or depth to mineral horizon) was measured using grids at 200 m intervals established within one square mile area in saline and brackish marsh. The soils had a variable organic layer thickness over sandy or clayey alluvium. Data were used to generate thickness contour maps. Soil morphology indicated a considerable spatial variability within the saline and brackish marshes.

  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. 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. Measurement of excited layer thickness in highly photo-excited GaAs

    NASA Astrophysics Data System (ADS)

    Liang, Lingliang; Tian, Jinshou; Wang, Tao; Wu, Shengli; Li, Fuli; Gao, Guilong

    2016-10-01

    Highly photo-excited layer thickness in GaAs is measured using a pump probe arrangement. A normally incident pump illumination spatially modulated by a mask will induce a corresponding refractive index change distribution in the depth direction due to edge scattering and attenuation absorption effect, which can deflect the probe beam passing through this excited region. Maximum deflection of the probe beam will be limited by the thickness of excited layer, and thus can also be employed to measure the thickness of the photo-excited layer of the material. Theoretical calculation confirms the experimental results. This method can find its application in measurements of photo-excited layer thickness of many kinds of materials and be significant to study the characteristics of materials in laser machining, grating and waveguide fabricating.

  15. Effect of spacer layer thickness on magnetic interactions in self-assembled single domain iron nanoparticles

    SciTech Connect

    Herndon, Nichole B; Ho, S; Abiade, J.; Pai, Devdas M.; Sankar, Jag; Pennycook, Stephen J

    2009-01-01

    The magnetic characteristics of iron nanoparticles embedded in an alumina thin film matrix have been studied as a function of spacer layer thickness. Alumina as well as iron nanoparticles were deposited in a multilayered geometry using sequential pulsed laser deposition. The role of spacer layer thickness was investigated by making layered thin film composites with three different spacer layer thicknesses 6, 12, and 18 nm with fixed iron particle size of 13 nm. Intralayer magnetic interactions being the same in each sample, the variation in coercivity and saturation magnetization is attributed to thickness dependent interlayer magnetic interactions of three types: exchange, strong dipolar, and weak dipolar. A thin film composite multilayer structure offers a continuously tunable strength of interparticle dipole-dipole interaction and is thus well suited for studies of the influence of interaction on the magnetic properties of small magnetic particle systems.

  16. Asymmetric transmission of acoustic waves in a layer thickness distribution gradient structure using metamaterials

    NASA Astrophysics Data System (ADS)

    Chen, Jung-San; Chang, I.-Ling; Huang, Wan-Ting; Chen, Lien-Wen; Huang, Guan-Hua

    2016-09-01

    This research presents an innovative asymmetric transmission design using alternate layers of water and metamaterial with complex mass density. The directional transmission behavior of acoustic waves is observed numerically inside the composite structure with gradient layer thickness distribution and the rectifying performance of the present design is evaluated. The layer thickness distributions with arithmetic and geometric gradients are considered and the effect of gradient thickness on asymmetric wave propagation is systematically investigated using finite element simulation. The numerical results indicate that the maximum pressure density and transmission through the proposed structure are significantly influenced by the wave propagation direction over a wide range of audible frequencies. Tailoring the thickness of the layered structure enables the manipulation of asymmetric wave propagation within the desired frequency range. In conclusion, the proposed design offers a new possibility for developing directional-dependent acoustic devices.

  17. Quantitative Raman spectrum and reliable thickness identification for atomic layers on insulating substrates.

    PubMed

    Li, Song-Lin; Miyazaki, Hisao; Song, Haisheng; Kuramochi, Hiromi; Nakaharai, Shu; Tsukagoshi, Kazuhito

    2012-08-28

    We demonstrate the possibility in quantifying the Raman intensities for both specimen and substrate layers in a common stacked experimental configuration and, consequently, propose a general and rapid thickness identification technique for atomic-scale layers on dielectric substrates. Unprecedentedly wide-range Raman data for atomically flat MoS(2) flakes are collected to compare with theoretical models. We reveal that all intensity features can be accurately captured when including optical interference effect. Surprisingly, we find that even freely suspended chalcogenide few-layer flakes have a stronger Raman response than that from the bulk phase. Importantly, despite the oscillating intensity of specimen spectrum versus thickness, the substrate weighted spectral intensity becomes monotonic. Combined with its sensitivity to specimen thickness, we suggest this quantity can be used to rapidly determine the accurate thickness for atomic layers.

  18. 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.

  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. 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

  1. Preparation and properties of highly (100)-oriented Pb(Zr0.2Ti0.8)O3 thin film prepared by rf magnetron sputtering with a PbOx buffer layer

    NASA Astrophysics Data System (ADS)

    Wu, Jiagang; Zhu, Jiliang; Xiao, Dingquan; Zhu, Jianguo; Tan, Junzhe; Zhang, Qinglei

    2007-05-01

    A method for fabrication of highly (100)-oriented Pb(Zr0.2Ti0.8)O3 (PZT) thin films by rf magnetron sputtering with a special buffer of PbOx (RFMS-SBP) was developed. With this method, highly (100)-oriented Pb(Zr0.2Ti0.8)O3 thin films were prepared on the PbOx/Pt(111)/Ti/SiO2/Si(100) substrates, and the preferential (100) orientation of the Pb(Zr0.2Ti0.8)O3 film is 92%. The (100) orientation of the PbOx 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(Zr0.2Ti0.8)O3 thin films with proper thickness of PbOx buffer layer possess good electrical properties with larger remnant polarization Pr (69.7 μC/cm2), lower coercive field Ec (92.4 kV/cm), and good pyroelectric coefficient at room temperature (2.6×10-8 C/cm2 K). The butterfly-shaped ɛ-E characteristic curve gives the evidence of the improved in-plane ferroelectric property in the films.

  2. Electron channel mobility in silicon-doped Ga2O3 MOSFETs with a resistive buffer layer

    NASA Astrophysics Data System (ADS)

    Wong, Man Hoi; Sasaki, Kohei; Kuramata, Akito; Yamakoshi, Shigenobu; Higashiwaki, Masataka

    2016-12-01

    The electron mobility in depletion-mode lateral β-Ga2O3(010) metal-oxide-semiconductor field-effect transistors (MOSFETs) with an n-channel formed by Si-ion (Si+) implantation doping was extracted using low-field electrical measurements on FET structures. An undoped Ga2O3 buffer layer protected the channel against charge compensation by suppressing outdiffusion of deep Fe acceptors from the semi-insulating substrate. The molecular beam epitaxy growth temperature was identified as a key process parameter for eliminating parasitic conduction at the buffer/substrate growth interface. Devices with a resistive buffer showed room temperature channel mobilities of 90-100 cm2 V-1 s-1 at carrier concentrations of low- to mid-1017 cm-3, with small in-plane mobility anisotropy of 10-15% ascribable to anisotropic carrier scattering.

  3. Enhanced field emission from ZnO nanowire arrays utilizing MgO buffer between seed layer and silicon substrate

    NASA Astrophysics Data System (ADS)

    Chen, Si; Chen, Jiangtao; Liu, Jianlin; Qi, Jing; Wang, Yuhua

    2016-11-01

    Field emitters based on ZnO nanowires and other nanomaterials are promising high-brightness electron sources for field emission display, microscopy and other applications. The performance of a ZnO nanowire field emitter is linked to the quality, conductivity and alignment of the nanowires on a substrate, therefore requiring ways to improve these parameters. Here, ZnO nanowire arrays were grown on ZnO seed layer on silicon substrate with MgO buffer between the seed layer and Si. The turn-on field and enhancement factor of these nanowire arrays are 3.79 V/μm and 3754, respectively. These properties are improved greatly compared to those of ZnO nanowire arrays grown on ZnO seed layer without MgO buffer, which are 5.06 V/μm and 1697, respectively. The enhanced field emission properties can be attributed to better electron transport in seed layer, and better nanowire alignment because of MgO buffer.

  4. 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.

  5. 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.

  6. Development of Buffer Layer Technologies for LWIR and VLWIR HgCdTe Integration on Si

    DTIC Science & Technology

    2007-11-02

    the-art HgCdTe films ) can only be achieved on a Si(211)B surface orientation. Since Si-based digital electronics utilizes the (100) orientation...for the large lattice mismatch (and crystallographic orientation change) are urgently needed to overcome these problems. Currently ZnTe/ CdTe ...technologies are based on i) the use of ultrathin, GeSi films as obedient buffers ii) wafer bonding of lattice-matched buffers. Summary of the most

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

    DOE PAGES

    Atchley, Adam L.; Coon, Ethan T.; Painter, Scott L.; ...

    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

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

    SciTech Connect

    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 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.

  9. 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.

  10. Chemical Bath Deposited Zinc Sulfide Buffer Layers for Copper Indium Gallium Sulfur-selenide Solar Cells and Device Analysis

    SciTech Connect

    Kundu, Sambhu N.; Olsen, Larry C.

    2005-01-03

    Cd free CIGSS thin film solar cell structures with a MgF2/TCO/CGD-ZnS/CIGSS/Mo/SLG structure have been fabricated using chemical bath deposited (CBD)-ZnS buffer layers and high quality CIGSS absorber layers supplied from Shell Solar Industries. The use of CBD-ZnS, which is a higher band gap materials than CdS, improved the quantum efficiency of fabricated cells at lower wavelengths, leading to an increase in short circuit current. The best cell to date yielded an active area (0.43 cm2) efficiency of 13.3%. This paper also presents a discussion of the issues relating to the use of the CBD-ZnS buffer materials for improving device performance.

  11. Advanced Architecture for Colloidal PbS Quantum Dot Solar Cells Exploiting a CdSe Quantum Dot Buffer Layer.

    PubMed

    Zhao, Tianshuo; Goodwin, Earl D; Guo, Jiacen; Wang, Han; Diroll, Benjamin T; Murray, Christopher B; Kagan, Cherie R

    2016-09-22

    Advanced architectures are required to further improve the performance of colloidal PbS heterojunction quantum dot solar cells. Here, we introduce a CdI2-treated CdSe quantum dot buffer layer at the junction between ZnO nanoparticles and PbS quantum dots in the solar cells. We exploit the surface- and size-tunable electronic properties of the CdSe quantum dots to optimize its carrier concentration and energy band alignment in the heterojunction. We combine optical, electrical, and analytical measurements to show that the CdSe quantum dot buffer layer suppresses interface recombination and contributes additional photogenerated carriers, increasing the open-circuit voltage and short-circuit current of PbS quantum dot solar cells, leading to a 25% increase in solar power conversion efficiency.

  12. Influences of thicknesses and structures of barrier cap layers on As ion profiles and implant damages in HgCdTe epilayers

    NASA Astrophysics Data System (ADS)

    Shi, Changzhi; Lin, Chun; Wei, Yanfeng; Chen, Lu; Ye, Zhenhua

    2016-05-01

    The barrier cap layer (BCL) is considered to be able to absorb partially implant induced damages during ion implantation, thus its structure and property could impact the result of ion implantation. In this paper, for As ion implantation in HgCdTe, the different BCLs were deposited on the CdZnTe-based (LPE) and GaAs-based (MBE) HgCdTe epilayers, respectively. Then, the influences of thicknesses and structures of these BCLs on dopant profiles and implant damages were investigated. The as-grown BCLs include thermally evaporated (TE) ZnS, TE CdTe, electron beam evaporated (EBE) CdTe and in-situ CdTe/ZnTe grown by MBE. The SIMS profiles and TEM characterization indicate: For TE ZnS BCLs, there exists an optimized thickness to obtain the deepest As indiffusion after high temperature annealing, and the end-of-range (EOR) depth is linearly proportional to the thickness ratio of a-MCT layer/damage layer. For TE CdTe BCLs, the barrier layer induced channeling effect (BLICE) occurs to the thin BCL samples, while this effect is suppressed in the thick BCL samples. The phenomenon might be due to that the blocking effect of the layered structure inside each crystal column becomes dominate in the thick BCL samples. Additionally, the EBE CdTe BCL with layered structure can suppress effectively the BLICE effect; in the in-situ CdTe/ZnTe BCL, the short defect layer generated in the CdTe buffer layer and the amorphization of the ZnTe layer during ion implantation also play a significant role in suppressing the BLICE effect.

  13. 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.

  14. 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

    2016-02-18

    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.

  15. 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

  16. Ratiometric analysis of in vivo retinal layer thicknesses in multiple sclerosis

    NASA Astrophysics Data System (ADS)

    Bhaduri, Basanta; Nolan, Ryan M.; Shelton, Ryan L.; Pilutti, Lara A.; Motl, Robert W.; Boppart, Stephen A.

    2016-09-01

    We performed ratiometric analysis of retinal optical coherence tomography images for the first time in multiple sclerosis (MS) patients. The ratiometric analysis identified differences in several retinal layer thickness ratios in the cohort of MS subjects without a history of optic neuritis (ON) compared to healthy control (HC) subjects, and there was no difference in standard retinal nerve fiber layer thickness (RNFLT). The difference in such ratios between HC subjects and those with mild MS-disability, without a difference in RNFLT, further suggests the possibility of using layer ratiometric analysis for detecting early retinal changes in MS. Ratiometric analysis may be useful and potentially more sensitive for detecting disease changes in MS.

  17. 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.

  18. Improving fatigue resistance of Pb(Zr,Ti)O3 thin films by using PbZrO3 buffer layers

    NASA Astrophysics Data System (ADS)

    Mensur Alkoy, Ebru; Uchiyama, Kiyoshi; Shiosaki, Tadashi; Alkoy, Sedat

    2006-05-01

    Ferroelectric Pb(Zr0.52Ti0.48)O3 (PZT) thin films with PbZrO3 (PZ) buffer layers were prepared on Pt(111)/Ti/SiO2/Si(100) substrates using a hybrid rf magnetron sputtering and sol-gel process. Texture of PZT films was found to depend on Pb content of PZ buffer layers. Buffered PZT films displayed comparable ferroelectric properties (2Pr=38-53 μC/cm2,2Ec=136-170 kV/cm) with unbuffered PZT. Asymmetric leakage current and fatigue behavior with superior fatigue resistance was observed in PZ buffered PZT compared to unbuffered films. PZ buffer layers were found to affect crystallization and texture of PZT, and act as a capacitive interface layer possibly blocking charge injection from electrodes.

  19. Retinal nerve fiber layer thickness and neuropsychiatric manifestations in systemic lupus erythematosus.

    PubMed

    Shulman, S; Shorer, R; Wollman, J; Dotan, G; Paran, D

    2017-01-01

    Background Cognitive impairment is frequent in systemic lupus erythematosus. Atrophy of the corpus callosum and hippocampus have been reported in patients with systemic lupus erythematosus, and diffusion tensor imaging studies have shown impaired white matter integrity, suggesting that white matter damage in systemic lupus erythematosus may underlie the cognitive impairment as well as other neuropsychiatric systemic lupus erythematosus manifestations. Retinal nerve fiber layer thickness, as assessed by optical coherence tomography, has been suggested as a biomarker for white matter damage in neurologic disorders such as multiple sclerosis, Alzheimer's disease and Parkinson's disease. Retinal nerve fiber layer thinning may occur early, even in patients with mild clinical symptoms. Aim The objective of this study was to assess the association of retinal nerve fiber layer thickness, as a biomarker of white matter damage in systemic lupus erythematosus patients, with neuropsychiatric systemic lupus erythematosus manifestations, including cognitive impairment. Methods Twenty-one consecutive patients with systemic lupus erythematosus underwent neuropsychological testing using a validated computerized battery of tests as well as the Rey-Auditory verbal learning test. All 21 patients, as well as 11 healthy, age matched controls, underwent optical coherence tomography testing to assess retinal nerve fiber layer thickness. Correlations between retinal nerve fiber layer thickness and results in eight cognitive domains assessed by the computerized battery of tests as well as the Rey-Auditory verbal learning test were assessed in patients with systemic lupus erythematosus, with and without neuropsychiatric systemic lupus erythematosus, and compared to retinal nerve fiber layer thickness in healthy controls. Results No statistically significant correlation was found between retinal nerve fiber layer thickness in patients with systemic lupus erythematosus as compared to healthy

  20. 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.

  1. Fabrication and electrochemical properties of insoluble fullerene-diamine adduct thin-films as buffer layer by alternate immersion process

    NASA Astrophysics Data System (ADS)

    Saito, Jo; Akiyama, Tsuyoshi; Suzuki, Atsushi; Oku, Takeo

    2017-01-01

    Insoluble fullerene-diamine adduct thin-films consisting of C60 and 1,2-diaminoethane were easily fabricated on an electrode by an alternate immersion process. Formation of the C60-diamine adduct films were confirmed using transmission absorption spectroscopy and atomic force microscopy. An inverted-type organic solar cells were fabricated by using the C60-diamine adduct film as the electron transport layer. The resultant photoelectric conversation performance of the solar cells suggested that photocurrent is generated via the photoexcitation of polythiophene. The result suggests that the present insoluble fullerene-diamine adduct films worked as buffer layer for organic thin-film solar cells.

  2. Enhanced Efficiency of Polymer Light-Emitting Diodes by Dispersing Dehydrated Nanotube Titanic Acid in the Hole-buffer Layer

    NASA Astrophysics Data System (ADS)

    Qian, L.; Xu, Z.; Teng, F.; Duan, X.-X.; Jin, Z.-S.; Du, Z.-L.; Li, F.-S.; Zheng, M.-J.; Wang, Y.-S.

    2007-06-01

    Efficiency of polymer light-emitting diodes (PLEDs) with poly(2-methoxy-5-(2-ethyl hexyloxy)- p-phenylene vinylene) (MEH-PPV) as an emitting layer was improved if a dehydrated nanotubed titanic acid (DNTA) doped hole-buffer layer polyethylene dioxythiophene (PEDOT) was used. Photoluminescence (PL) and Raman spectra indicated a stronger interaction between DNTA and sulfur atom in thiophene of PEDOT, which suppresses the chemical interaction between vinylene of MEH-PPV and thiophene of PEDOT. The interaction decreases the defect states in an interface region to result in enhancement in device efficiency, even though the hole transporting ability of PEDOT was decreased.

  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. 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.

  5. 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.

  6. 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

  7. 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.

  8. Thin layer thickness measurements by zero group velocity Lamb mode resonances.

    PubMed

    Cès, Maximin; Clorennec, Dominique; Royer, Daniel; Prada, Claire

    2011-11-01

    Local and non-contact measurements of the thickness of thin layers deposited on a thick plate have been performed by using zero group velocity (ZGV) Lamb modes. It was shown that the shift of the resonance frequency is proportional to the mass loading through a factor which depends on the mechanical properties of the layer and of the substrate. In the experiments, ZGV Lamb modes were generated by a Nd:YAG pulsed laser and the displacement normal to the plate surface was measured by an optical interferometer. Measurements performed at the same point that the generation on the non-coated face of the plate demonstrated that thin gold layers of a few hundred nanometers were detected through a 1.5-mm thick Duralumin plate. The shift of the resonance frequency (1.9 MHz) of the fundamental ZGV mode is proportional to the layer thickness: typically 10 kHz per μm. Taking into account the influence of the temperature, a 240-nm gold layer was measured with a ±4% uncertainty. This thickness has been verified on the coated face with an optical profiling system.

  9. Chemically deposited La2Zr2O7 buffer layers for YBCO-coated conductors: film growth and microstructure

    NASA Astrophysics Data System (ADS)

    Molina, L.; Knoth, K.; Engel, S.; Holzapfel, B.; Eibl, O.

    2006-11-01

    An adequate buffer layer architecture is of great importance for YBa2Cu3O7-δ (YBCO)-coated conductor fabrication. We present a transmission electron microscopy (TEM) analysis of La2Zr2O7 (LZO) buffer layers on biaxially textured Ni-5 at.%W substrates for YBCO-coated conductors prepared by chemical solution deposition (CSD). The LZO thin films were heat-treated at 900 and 1050 °C respectively. Electron diffraction patterns, and bright and dark-field images were used to determine the microstructure, texture and the nanoporosity of the films. By x-ray diffraction the films were found to be [100] oriented and strongly biaxially textured. Although x-ray diffraction suggests an epitaxial growth of LZO on Ni it was shown by TEM that this was not the case. The grain size of the films is between 100 and 300 nm and therefore much smaller than the Ni grain size of 40 µm. Appropriate acquisition conditions for scanning electron microscopy (SEM) and TEM imaging are given to identify the nanogranularity of the films. For the film annealed at 1050 °C high-resolution SEM images clearly show a polycrystalline LZO microstructure and the grain size can readily be determined. Electron diffraction rings are more pronounced than for the film annealed at 900 °C, indicating a higher level of polycrystallinity in the film. SEM images of the film annealed at 900 °C yield no evidence of a polycrystalline microstructure; only single misoriented LZO grains separated by 500 nm are observed. Nanovoids 10-40 nm in size were found in the LZO buffer layers with a high density. The voids had approximately cuboid shape, indicating an anisotropy of the surface energy in LZO. The surface planes of the voids were identified as {111} lattice planes. Despite the nanoporosity, which is a typical feature of CSD-grown buffer layers, the LZO buffer layers act as efficient Ni diffusion barriers. Energy dispersive x-ray microanalysis (EDX) in the transmission electron microscope yielded the composition of

  10. Large enhanced perpendicular magnetic anisotropy in CoFeB/MgO system with the typical Ta buffer replaced by an Hf layer

    NASA Astrophysics Data System (ADS)

    Liu, T.; Cai, J. W.; Sun, Li

    2012-09-01

    By systematically comparing the magnetic properties of the Ta/CoFeB/Ta and MgO/CoFeB/MgO structures with and without a submonolayer of MgO, Ta, V, Nb, Hf and W inserted in the middle of the CoFeB layer, we have proved that the observed perpendicular magnetic anisotropy (PMA) in Ta/CoFeB/MgO sandwiches is solely originated from the CoFeB/MgO interface with the Ta buffer acting to enhance the CoFeB/MgO interface anisotropy significantly. Moreover, replacing Ta with Hf causes the CoFeB/MgO interfacial PMA further enhanced by 35%, and the CoFeB layer with perpendicular magnetization has a much larger critical thickness accordingly, leaving a wider thickness margin for the CoFeB/MgO-based perpendicular magnetic tunnel junction optimization. Also the sputter deposited thin Hf films are amorphous with low surface roughness. These results will ensure the Hf/CoFeB/MgO more promising material system for PMA device development.

  11. 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.

  12. Simple electrodepositing of CoFe/Cu multilayers: Effect of ferromagnetic layer thicknesses

    NASA Astrophysics Data System (ADS)

    Tekgül, Atakan; Alper, Mürsel; Kockar, Hakan

    2017-01-01

    The CoFe/Cu magnetic multilayers were produced by changing CoFe ferromagnetic layers from 3 nm to 10 nm using electrodeposition. By now, the thinnest Cu (0.5 nm) layer thicknesses were used to see whether the GMR effect in the multilayers can be obtained or not since the pinning of non-magnetic layer between the ferromagnetic layers is required. For the proper depositions, the cyclic voltammograms was used, and the current-time transients were obtained. The Cu and CoFe layers were deposited at a cathode potential of -0.3 and -1.5 V with respect to saturated calomel electrode, respectively. From the XRD patterns, the multilayers were shown to be fcc crystal structures. For the magnetization measurements, saturation magnetization increases from 160 to 600 kA/m from 3 to 8 nm ferromagnetic layer thicknesses. And, the coercivity values increase until the 8 nm of the CoFe layer thickness. It is seen that the thin Cu layer (fixed at 0.5 nm) and pinholes support the random magnetization orientation and thus all multilayers exhibited the giant magnetoresistance (GMR) effect, and the highest GMR value was observed about 5.5%. And, the variation of GMR field sensitivity was calculated. The results show that the GMR and GMR sensitivity are compatible among the multilayers. The CoFe/Cu magnetic multilayers having GMR properties are used in GMR sensors and hard disk drive of the nano-technological devices.

  13. A nanoporous AlN layer patterned by anodic aluminum oxide and its application as a buffer layer in a GaN-based light-emitting diode.

    PubMed

    Chen, Lung-Chien; Wang, Chih-Kai; Huang, Jenn-Bin; Hong, Lu-Sheng

    2009-02-25

    This work investigates a nanoporous aluminum nitride (AlN) layer prepared using an anodic aluminum oxide (AAO) process and its application as a buffer layer for a GaN-based light-emitting diode (LED) fabricated on sapphire substrate. Following this AAO process, the average pore spacing and pore diameter of the nanoporous AlN layer were in the ranges 180-200 nm and 100-150 nm, respectively. The light output power of the GaN-based LED with a nanoporous AlN layer was about 53% higher than that of a GaN-based LED without a nanoporous AlN layer at an injection current of 20 mA. At an injection current of 80 mA, the light output power was increased by about 34%.

  14. Cd-free CIGS solar cells with buffer layer based on the In2S3 derivatives.

    PubMed

    Kim, Kihwan; Larina, Liudmila; Yun, Jae Ho; Yoon, Kyung Hoon; Kwon, HyukSang; Ahn, Byung Tae

    2013-06-21

    This study guided by device evaluations was conducted to reveal the reasons for the loss of the photo-generated carriers in CIGS cells with the buffer based on In2S3 derivatives. Chemical bath deposited Inx(OOH,S)y films have been employed as a Cd-free buffer layers. When compared to solar cells with CdS buffer layer, the Cu0.9(In0.7,Ga0.3)Se2.1 (Eg = 1.18 eV) cells with the Inx(OOH,S)y buffer exhibited strong voltage-dependent carrier collection and poor spectral response above 500 nm, presumably, due to energy barrier at the junction. In order to improve the charge collection by upward shift of the conduction band minimum of CIGS absorber, Inx(OOH,S)y/Cu0.9(In0.55,Ga0.45)Se2.1 (Eg = 1.30 eV) solar cells were also fabricated and their spectral responses were examined. When compared to the Cu0.9(In0.7,Ga0.3)Se2.1 cells, the improved spectral response and voltage dependent carrier collection were obtained. Nevertheless, considerable loss in charge collection above 500 nm was still observed. The efficiency reached 9.3% while the Cu0.9(In0.7,Ga0.3)Se2.1 cell exhibited only the efficiency of 3.4%. Finally, CIGS (Eg = 1.18 eV) solar cells with n-ZnO/i-ZnO/Inx(OOH,S)y/CdS/CIGS and n-ZnO/i-ZnO/CdS/Inx(OOH,S)y/CIGS configurations were fabricated. The influence of the TCO/buffer interface on the device characteristics was also addressed by means of comparison between the characteristics of two cells employing different interfaces. A 13.0% efficient cell has been achieved from n-ZnO/i-ZnO/CdS/Inx(OOH,S)y/CIGS configuration. The obtained data suggested that the limitation of the device efficiency was mainly related to the i-ZnO/Inx(OOH,S)y interface. The experimental results provide the knowledge base for further optimization of the interface properties to form high-quality p-n junction in the CIGS solar cells employing the CBD In2S3 buffer layer.

  15. The polarization of a nanoparticle surrounded by a thick electric double layer.

    PubMed

    Zhao, Hui; Bau, Haim H

    2009-05-15

    The polarization of a charged, dielectric, nanoparticle enveloped by a thick electric double layer and subjected to a uniform, alternating electric field is studied theoretically with the standard model (the Poisson-Nernst-Planck PNP equations). The dipole coefficient (f) is calculated as a function of the electric field's frequency and the double layer's thickness (lambda(D)). For a weakly charged particle with a small zeta potential zeta, an approximate, analytic expression for the dipole moment coefficient, accurate within O(zeta(2)), is derived. Two processes contribute to the dipole moment: the ion transport in the electric double layer under the action of the electric field and the particle's electrophoretic motion. As the thickness of the electric double layer increases so does the importance of the latter. In contrast to the case of the thin electric double layer, the particle with the thick double layer exhibits only high-frequency dispersion. The theoretical predictions are compared and favorably agree with experimental data, leading one to conclude that the standard, PNP based-model adequately represents the behavior of nanoparticles subject to electric fields.

  16. Influence of water layer thickness on hard tissue ablation with pulsed CO2 laser

    NASA Astrophysics Data System (ADS)

    Zhang, Xianzeng; Zhan, Zhenlin; Liu, Haishan; Zhao, Haibin; Xie, Shusen; Ye, Qing

    2012-03-01

    The theory of hard tissue ablation reported for IR lasers is based on a process of thermomechanical interaction, which is explained by the absorption of the radiation in the water component of the tissue. The microexplosion of the water is the cause of tissue fragments being blasted from hard tissue. The aim of this study is to evaluate the influence of the interdependence of water layer thickness and incident radiant exposure on ablation performance. A total of 282 specimens of bovine shank bone were irradiated with a pulse CO2 laser. Irradiation was carried out in groups: without a water layer and with a static water layer of thickness ranging from 0.2 to 1.2 mm. Each group was subdivided into five subgroups for different radiant exposures ranging from 18 to 84 J/cm2, respectively. The incision geometry, surface morphology, and microstructure of the cut walls as well as thermal injury were examined as a function of the water layer thickness at different radiant exposures. Our results demonstrate that the additional water layer is actually a mediator of laser-tissue interaction. There exists a critical thickness of water layer for a given radiant exposure, at which the additional water layer plays multiple roles, not only acting as a cleaner to produce a clean cut but also as a coolant to prevent bone heating and reduce thermal injury, but also helping to improve the regularity of the cut shape, smooth the cut surface, and enhance ablation rate and efficiency. The results suggest that desired ablation results depend on optimal selection of both water layer thickness and radiant exposure.

  17. Influence of water layer thickness on hard tissue ablation with pulsed CO2 laser.

    PubMed

    Zhang, Xianzeng; Zhan, Zhenlin; Liu, Haishan; Zhao, Haibin; Xie, Shusen; Ye, Qing

    2012-03-01

    The theory of hard tissue ablation reported for IR lasers is based on a process of thermomechanical interaction, which is explained by the absorption of the radiation in the water component of the tissue. The microexplosion of the water is the cause of tissue fragments being blasted from hard tissue. The aim of this study is to evaluate the influence of the interdependence of water layer thickness and incident radiant exposure on ablation performance. A total of 282 specimens of bovine shank bone were irradiated with a pulse CO(2) laser. Irradiation was carried out in groups: without a water layer and with a static water layer of thickness ranging from 0.2 to 1.2 mm. Each group was subdivided into five subgroups for different radiant exposures ranging from 18 to 84 J/cm(2), respectively. The incision geometry, surface morphology, and microstructure of the cut walls as well as thermal injury were examined as a function of the water layer thickness at different radiant exposures. Our results demonstrate that the additional water layer is actually a mediator of laser-tissue interaction. There exists a critical thickness of water layer for a given radiant exposure, at which the additional water layer plays multiple roles, not only acting as a cleaner to produce a clean cut but also as a coolant to prevent bone heating and reduce thermal injury, but also helping to improve the regularity of the cut shape, smooth the cut surface, and enhance ablation rate and efficiency. The results suggest that desired ablation results depend on optimal selection of both water layer thickness and radiant exposure.

  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. Improved performances of organic light-emitting diodes with mixed layer and metal oxide as anode buffer

    NASA Astrophysics Data System (ADS)

    Xue, Qin; Liu, Shouyin; Zhang, Shiming; Chen, Ping; Zhao, Yi; Liu, Shiyong

    2013-01-01

    We fabricated organic light-emitting devices (OLEDs) employing 2-methyl-9,10-di(2-naphthyl)-anthracene (MADN) as hole-transport material (HTM) instead of commonly used N,N'-bis-(1-naphthyl)-N,N'-diphenyl,1,1'-biphenyl-4,4'-diamine (NPB). After inserting a 0.9 nm thick molybdenum oxide (MoOx) layer at the indium tin oxide (ITO)/MADN interface and a 5 nm thick mixed layer at the organic/organic heterojunction interface, the power conversion efficiency of the device can be increased by 4-fold.

  20. Measurement of the dead layer thickness in a p-type point contact germanium detector

    NASA Astrophysics Data System (ADS)

    Jiang, Hao; Yue, Qian; Li, Yu-Lan; Kang, Ke-Jun; Li, Yuan-Jing; Li, Jin; Lin, Shin-Ted; Liu, Shu-Kui; Ma, Hao; Ma, Jing-Lu; Su, Jian; Tsz-King Wong, Henry; Yang, Li-Tao; Zhao, Wei; Zeng, Zhi

    2016-09-01

    A 994 g mass p-type PCGe detector has been deployed during the first phase of the China Dark matter EXperiment, aiming at direct searches for light weakly interacting massive particles. Measuring the thickness of the dead layer of a p-type germanium detector is an issue of major importance since it determines the fiducial mass of the detector. This work reports a method using an uncollimated 133Ba source to determine the dead layer thickness. The experimental design, data analysis and Monte Carlo simulation processes, as well as the statistical and systematic uncertainties are described. A dead layer thickness of 1.02 mm was obtained based on a comparison between the experimental data and the simulated results. Supported by National Natural Science Foundation of China (10935005, 10945002, 11275107, 11175099)

  1. 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%.

  2. Preparation of SmBiO3 buffer layer on YSZ substrate by an improved chemical solution deposition route

    NASA Astrophysics Data System (ADS)

    Zhu, Xiaolei; Pu, Minghua; Zhao, Yong

    2016-12-01

    A quick route for chemical solution deposition (CSD) has been developed to prepare SmBiO3 (SBO) layers on yttria stabilized zirconia (YSZ) substrates rapidly by using of solid state decomposition (SSD) technique. The proper conditions for volatilization of lactic acid, which as solvent in precursor coated layer, and SBO growth are 115°C for 30 min and 794°C for 60 min in flowing Ar gas. The coated layers are amorphous structure of mixture oxides and quasi-crystal structure of SBO before and after growth, respectively. The total time by this quick CSD route for organic solvent volatilization, salts decomposed and layer growth is not up to 2 h, which are much less than that needed for traditional CSD of over 10 h. SBO layer is directly epitaxial growth on YSZ substrate without any lattice rotation. SBO layer prepared by this quick route as well as that by traditional route are suitable for the growth of YBCO. The superconducting transition temperature and critical current density of the coated YBCO layer on SBO/YSZ obtained by this quick route are up to 90 K and 1.66 MA/cm2. These results may be the usable reference for continuous preparation of SBO buffer layer on IBAD-YSZ/Ni-based alloy tapes.

  3. 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.

  4. Designing and adjusting the thickness of polyvinylpyrrolidone waveguide layer on plasmonic nanofilm for humidity sensing

    NASA Astrophysics Data System (ADS)

    Feng, Zhiqing; Bai, Lan; Guo, Lijiao; Cao, Baosheng; Wu, Jinlei; He, Yangyang

    2017-01-01

    We developed a fast response and high-resolution plasmonic waveguide sensor for sensing environmental humidity by converting the optical signal in the visible light region. The sensor was designed as a layer-on-layer film structure in which the hydrophilic polymer of polyvinylpyrrolidone (PVP) film served as the waveguide layer and was dip-coated onto the plasmonic gold (Au) nanofilm for sensing the environmental humidity. The amount of the absorbed water molecules on the PVP layer could affect the refractive index and thickness of the PVP, leading to a shift of the surface plasmon resonance peak position of Au nanofilm at the different order modes of the waveguide. The theoretic calculations indicated that the optimal thickness of the waveguide layer on the Au nanofilm ranged from 550 to 650 nm. By adjusting the thickness of the PVP layer to 560 nm, the high-resolution optical signals were observed in the visible light region with the humidity shifts ranging from 11% to 85% relative humidity (RH). Our work details a successful attempt to design and prepare the plasmonic waveguide sensor with the lost-cost polymer as the sensing layer for real-time detection of environmental humidity.

  5. Correlation between active layer thickness and ambient gas stability in IGZO thin-film transistors

    NASA Astrophysics Data System (ADS)

    Gao, Xu; Lin, Meng-Fang; Mao, Bao-Hua; Shimizu, Maki; Mitoma, Nobuhiko; Kizu, Takio; Ou-Yang, Wei; Nabatame, Toshihide; Liu, Zhi; Tsukagoshi, Kazuhito; Wang, Sui-Dong

    2017-01-01

    Decreasing the active layer thickness has been recently reported as an alternative way to achieve fully depleted oxide thin-film transistors for the realization of low-voltage operations. However, the correlation between the active layer thickness and device resistivity to environmental changes is still unclear, which is important for the optimized design of oxide thin-film transistors. In this work, the ambient gas stability of IGZO thin-film transistors is found to be strongly correlated to the IGZO thickness. The TFT with the thinnest IGZO layer shows the highest intrinsic electron mobility in a vacuum, which is greatly reduced after exposure to O2/air. The device with a thick IGZO layer shows similar electron mobility in O2/air, whereas the mobility variation measured in the vacuum is absent. The thickness dependent ambient gas stability is attributed to a high-mobility region in the IGZO surface vicinity with less sputtering-induced damage, which will become electron depleted in O2/air due to the electron transfer to adsorbed gas molecules. The O2 adsorption and deduced IGZO surface band bending is demonstrated by the ambient-pressure x-ray photoemission spectroscopy results.

  6. Photovoltaic properties of Cu2ZnSnS4 cells fabricated using ZnSnO and ZnSnO/CdS buffer layers

    NASA Astrophysics Data System (ADS)

    Tajima, Shin; Umehara, Mitsutaro; Mise, Takahiro

    2016-11-01

    To improve the photovoltaic properties of Cu2ZnSnS4 (CZTS) photovoltaic cells, we investigated the use of novel buffer layer materials. We found that Zn1- x Sn x O y fabricated by atomic layer deposition functioned as an effective buffer layer. The short-circuit current density increased by 10% because of a decrease in the absorption loss in the short-wavelength region. With Zn0.70Sn0.30O y layers, the conversion efficiency was 5.7%. To reduce interface recombination, a thin CdS layer was inserted between the ZnSnO and CZTS layers. The CZTS cells fabricated using ZnSnO/CdS double buffer layers showed a high open-circuit voltage of 0.81 V.

  7. 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

  8. Effect of separating layer thickness on W/Si multilayer replication.

    PubMed

    Wang, Fangfang; Mu, Baozhong; Jin, Huijun; Yang, Xiajun; Zhu, Jingtao; Wang, Zhanshan

    2011-08-15

    The direct replication of W/Si multilayers and the effect of separating layer thickness on the performance of the multilayer before and after replication are investigated systematically. Platinum separating layers with different layer thicknesses were first deposited onto different supersmooth mandrels and then W/Si multilayers with the similar structure were deposited onto these Pt-coated mandrels by using a high vacuum DC magnetron sputtering system. After the deposition, these multilayers were replicated onto the commercially available float glass substrates by epoxy replication technique. These multilayers before and after replication are characterized by grazing-incident X-ray reflectance measurement and atomic force microscope. The measured results show that before and after replication, the reflectivity curves are much similar to those calculated and the surface roughness of each sample is close to that of the mandrel, when the separating layer thickness is larger than 1.5 nm. These results reveal that the W/Si multilayer with the separating layer thickness larger than 1.5 nm can be successfully replicated onto a substrate without modification of the structure, significant increase of surface roughness or apparent change of reflectivity.

  9. 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.

  10. Stress dependence in Fe89Co11 Si multilayers on layer thicknesses

    NASA Astrophysics Data System (ADS)

    Teichert, Anke; Krist, Thomas; Mezei, Ferenc

    2006-11-01

    We report on a study of the stress developing in materials which are used for polarising neutron supermirrors. The stress was examined as function of the thickness of Si and Fe89Co11 layers in multilayer systems. The samples were produced in a triode sputter machine. The bending of the samples was measured on a profilometer and the stress was calculated with the Stoney formula. The samples were characterized with polarized neutron and X-ray reflectometry and XRD. It was found that an increase in layer thickness leads to decreasing compressive stress for FeCo layers and to decreasing tensile stress for Si layers. A formula is given which allows to estimate the resulting stress.

  11. Empirical model predicting the layer thickness and porosity of p-type mesoporous silicon

    NASA Astrophysics Data System (ADS)

    Wolter, Sascha J.; Geisler, Dennis; Hensen, Jan; Köntges, Marc; Kajari-Schröder, Sarah; Bahnemann, Detlef W.; Brendel, Rolf

    2017-04-01

    Porous silicon is a promising material for a wide range of applications because of its versatile layer properties and the convenient preparation by electrochemical etching. Nevertheless, the quantitative dependency of the layer thickness and porosity on the etching process parameters is yet unknown. We have developed an empirical model to predict the porosity and layer thickness of p-type mesoporous silicon prepared by electrochemical etching. The impact of the process parameters such as current density, etching time and concentration of hydrogen fluoride is evaluated by ellipsometry. The main influences on the porosity of the porous silicon are the current density, the etching time and their product while the etch rate is dominated by the current density, the concentration of hydrogen fluoride and their product. The developed model predicts the resulting layer properties of a certain porosification process and can, for example be used to enhance the utilization of the employed chemicals.

  12. Laser generated guided waves and finite element modeling for the thickness gauging of thin layers

    SciTech Connect

    Lefevre, F.; Jenot, F.; Ouaftouh, M.; Duquennoy, M.; Ourak, M.

    2010-03-15

    In this paper, nondestructive testing has been performed on a thin gold layer deposited on a 2 in. silicon wafer. Guided waves were generated and studied using a laser ultrasonic setup and a two-dimensional fast Fourier transform technique was employed to obtain the dispersion curves. A gold layer thickness of 1.33 {mu}m has been determined with a {+-}5% margin of error using the shape of the two first propagating modes, assuming for the substrate and the layer an uncertainty on the elastic parameters of {+-}2.5%. A finite element model has been implemented to validate the data post-treatment and the experimental results. A good agreement between the numerical simulation, the analytical modeling and the experimentations has been observed. This method was considered suitable for thickness layer higher than 0.7 {mu}m.

  13. Determination of Mean Thickness of an Oxide Layer on a Silicon Sphere by Spectroscopic Ellipsometry

    NASA Astrophysics Data System (ADS)

    Zhang, Ji-Tao; Li, Yan; Luo, Zhi-Yong; Wu, Xue-Jian

    2010-05-01

    One of the biggest obstacles to reduce the uncertainty of the Avogadro constant NA is such that there will be an oxide layers on the surface of a silicon sphere. The thickness of this layer is measured by a modified spectroscopic ellipsometer, which can eliminate the influence of the curved surface, and the results are calibrated by x-ray reflectivity. Fifty positions distributed nearly uniformly on the surface of the silicon sphere are measured twice. The results show that the mean thickness of the overall oxide layer is 3.75 nm with the standard uncertainty of 0.21 nm, which means that the relative uncertainty component of NA owing to this layer can be reduced to 1.2 × 10-8.

  14. Tear lipid layer thickness with eye drops in meibomian gland dysfunction

    PubMed Central

    Fogt, Jennifer S; Kowalski, Matthew J; King-Smith, P Ewen; Epitropolous, Alice T; Hendershot, Andrew J; Lembach, Carrie; Maszczak, John Paul; Jones-Jordan, Lisa A; Barr, Joseph T

    2016-01-01

    Purpose The aim of this study was to evaluate the efficacy of a lipid containing emollient eye drop, Soothe XP, which was reformulated in 2014 with a more stable preservative and buffer system, compared to a control, non-emollient, eye drop (Systane Ultra) in improving lipid layer thickness (LLT) in subjects with dry eye due to meibomian gland dysfunction (MGD). Patients and methods This prospective single-center, open-label, cross-over, examiner masked-study enrolled subjects aged 30–75 years with lipid-deficient dry eye and a clinical diagnosis of MGD as determined by a slit lamp examination, an evaluation of meibomian gland drop out with meibography, and a standard patient evaluation of eye dryness questionnaire of >5. Eligibility was then determined by a LLT of <75 nm at baseline and the inability to increase LLT ≥15 nm with three blinks, as determined by interferometric methods. Subjects were randomized to receive a single emollient or non-emollient eye drop at Visit 1 and were crossed over for the alternate treatment at Visit 2. At each visit, LLT was measured prior to and 15 minutes following the instillation of the assigned eye drop. The primary endpoint was the change in LLT from baseline. Results Subjects (n=40) were enrolled and 35 completed the two study arms. Mean (±SD) patient age was 55.7 years (10.9) and 69% were female. Mean (±SD) LLT at baseline was 49.5 nm (9.2). Instillation of Soothe XP resulted in an increase in LLT to 77.5 nm (29.3) 15 minutes following drop instillation, which is an increase of 28.0 nm (27.4) (P<0.001). In contrast, LLT 15 minutes after the instillation of Systane Ultra was 50.8 nm (14.1), which was not statistically significant when compared to the baseline LLT. Conclusion In this study of subjects with MGD, the emollient, or lipid containing eye drop, increased the LLT of tears when measured 15 minutes after instilling a single eye drop. PMID:27853352

  15. 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.

  16. Molecular beam epitaxy growth of SrO buffer layers on graphite and graphene for the integration of complex oxides

    SciTech Connect

    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.

  17. Surface electronic structure of ZrB2 buffer layers for GaN growth on Si wafers

    NASA Astrophysics Data System (ADS)

    Yamada-Takamura, Yukiko; Bussolotti, Fabio; Fleurence, Antoine; Bera, Sambhunath; Friedlein, Rainer

    2010-08-01

    The electronic structure of epitaxial, predominantly single-crystalline thin films of zirconium diboride (ZrB2), a lattice-matching, conductive ceramic to GaN, grown on Si(111) was studied using angle-resolved ultraviolet photoelectron spectroscopy. The existence of Zr-derived surface states dispersing along the Γ¯-M¯ direction indicates a metallic character provided by a two-dimensional Zr-layer at the surface. Together with the measured work function, the results demonstrate that the surface electronic properties of such thin ZrB2(0001) buffer layers are comparable to those of the single crystals promising excellent conduction between nitride layers and the substrate in vertical light-emitting diodes on economic substrates.

  18. 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%.

  19. Characterizing ultrathin and thick organic layers by surface plasmon resonance three-wavelength and waveguide mode analysis.

    PubMed

    Granqvist, Niko; Liang, Huamin; Laurila, Terhi; Sadowski, Janusz; Yliperttula, Marjo; Viitala, Tapani

    2013-07-09

    A three-wavelength angular-scanning surface plasmon resonance based analysis has been utilized for characterizing optical properties of organic nanometer-thick layers with a wide range of thicknesses. The thickness and refractive index were determined for sample layers with thicknesses ranging from subnanometer to hundreds of nanometers. The analysis approach allows for simultaneous determination of both the refractive index and thickness without prior knowledge of either the refractive index or the thickness of the sample layers and without the help of other instruments, as opposed to current methods and approaches for characterizing optical properties of organic nanometer-thick layers. The applicability of the three-wavelength angular-scanning surface plasmon resonance approach for characterizing thin and thick organic layers was demonstrated by ex situ deposited mono- and multilayers of stearic acid and hydrogenated soy phosphatidylcholine and in situ layer-by-layer deposition of two different polyelectrolyte multilayer systems. In addition to the three-wavelength angular-scanning surface plasmon resonance approach, another surface plasmon resonance optical phenomenon, i.e., the surface plasmon resonance waveguide mode, was utilized to characterize organic sample layers whose thicknesses border the micrometer scale. This was demonstrated by characterizing both in situ layer-by-layer deposited polyelectrolyte multilayer systems and an ex situ deposited spin-coated polymer layer.

  20. Aspects of the strontium oxide-copper oxide-titanium dioxide ternary system related to the deposition of strontium titanate and copper doped strontium titanate thin film buffer layers

    NASA Astrophysics Data System (ADS)

    Ayala, Alicia

    YBa2Cu3O7-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. SrTiO3 (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 ˜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 ˜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 2 tie line did not identify any ternary phases. SrCu0.10Ti0.90Oy buffer layers were prepared by pulsed laser deposition (PLD) and CSD on IBAD MgO flexible metallic textured tapes. TEM analysis of a ˜100 nm thick SrCu0.10Ti 0.90Oy buffer layer deposited by PLD showed a smooth Cu-doped STO/MgO interface. A ˜600 nm thick YBCO film, deposited onto the SrCu 0.10Ti0.90Oy buffer by PLD, exhibited a T c of 87 K and critical current density (Jc) of ˜1 MA/cm 2. STO and Cu-doped STO thin films by CSD were ˜30 nm thick. The in plane alignment (FWHM) after deposition of the STO improved by ˜1° while it degraded by ˜2° with the SrCu0.05TiOy buffer. YBCO was deposited by PLD on the STO and SrCu0.05TiO y buffers. The in plane alignment (FWHM) of the YBCO with the STO buffer layer slightly improved while that of the YBCO with the SrCu0.05TiO y buffer layer remained constant. A goal of the CSD approach to fabrication of coated conductors is process simplicity. In this study, single layer

  1. 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.

  2. 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.

  3. 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.

  4. 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).

  5. 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

  6. 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.

  7. Effect of the Platinum Electroplated Layer Thickness on the Coatings' Microstructure

    NASA Astrophysics Data System (ADS)

    Zagula-Yavorska, Maryana; Gancarczyk, Kamil; Sieniawski, Jan

    2017-03-01

    CMSX 4 and Inconel 625 superalloys were coated by platinum layers (3 and 7 μm thick) in the electroplating process. The heat treatment of platinum layers (at 1,050 ˚C for 2 h) was performed to increase platinum adherence to the superalloys substrate. The diffusion zone obtained on CMSX 4 superalloy (3 and 7 μm platinum thick before heat treatment) consisted of two phases: γ-Ni(Al, Cr) and (Al0.25Pt0.75)Ni3. The diffusion zone obtained on Inconel 625 superalloy (3 μm platinum thick before heat treatment) consisted of the α-Pt(Ni, Cr, Al) phase. Moreover, γ-Ni(Cr, Al) phase was identified. The X-ray diffraction (XRD) results revealed the presence of platinum in the diffusion zone of the heat-treated coating (7 μm platinum thick) on Inconel 625 superalloy. The surface roughness parameter Ra of heat-treated coatings increased with the increase of platinum layers thickness. This was due to the unequal mass flow of platinum and nickel.

  8. 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.

  9. Thickness of retinal layers in the foveas of children with anisometropic amblyopia

    PubMed Central

    Zhou, Jinjing; Gu, Zhouqun; Huang, Shenghai; Li, Heming; Qin, Zhuoer; Yu, Xinping

    2017-01-01

    Purpose To use highly precise spectral-domain optical coherence tomography (SD-OCT) to determine whether there were structural abnormalities in the layers of different regions of the fovea in children with anisometropic amblyopia. Methods Eighteen children (mean age 7.8 years old; range 5–11 years) with unilateral anisometropic amblyopia and 18 age-matched control subjects participated. Foveal thickness was measured with an enhanced depth imaging system, SD-OCT and segmented into layers using custom developed software. The thickness of each layer of the fovea was compared among amblyopic eyes, fellow eyes and control eyes with optical magnification correction for axial length and statistical correction for age and sex. Results The total thickness and each intra-ocular layer of the central fovea were the same for each group. However, the amblyopic eyes were significantly thicker than the normal control eyes in 2 of 4 quadrants of the peripheral retina. Exploring intra-retinal layers in these two quadrants, the nasal nerve fiber layer (NFL) and inferior inner nuclear layer (INL)were significantly thicker in amblyopic eyes than in control eyes (p = 0.01 and 0.012, respectively, by ANCOVA). Conclusion The SD-OCT data revealed marginal differences in some foveal layers at peripheral locations and indicated that structural differences might exist between individuals with amblyopia and visually normal control subjects. However, the differences were scattered and represented no identifiable pattern. More studies with large samples and precise locations of the retinal layers must be performed to extend the present results. PMID:28328978

  10. Ground-penetrating radar reveals ice thickness and undisturbed englacial layers at Kilimanjaro's Northern Ice Field

    NASA Astrophysics Data System (ADS)

    Bohleber, Pascal; Sold, Leo; Hardy, Douglas R.; Schwikowski, Margit; Klenk, Patrick; Fischer, Andrea; Sirguey, Pascal; Cullen, Nicolas J.; Potocki, Mariusz; Hoffmann, Helene; Mayewski, Paul

    2017-02-01

    Although its Holocene glacier history is still subject to debate, the ongoing iconic decline of Kilimanjaro's largest remaining ice body, the Northern Ice Field (NIF), has been documented extensively based on surface and photogrammetric measurements. The study presented here adds, for the first time, ground-penetrating radar (GPR) data at centre frequencies of 100 and 200 MHz to investigate bed topography, ice thickness and internal stratigraphy at NIF. The direct comparison of the GPR signal to the visible glacier stratigraphy at NIF's vertical walls is used to validate ice thickness and reveals that the major internal reflections seen by GPR can be associated with dust layers. Internal reflections can be traced consistently within our 200 MHz profiles, indicating an uninterrupted, spatially coherent internal layering within NIF's central flat area. We show that, at least for the upper 30 m, it is possible to follow isochrone layers between two former NIF ice core drilling sites and a sampling site on NIF's vertical wall. As a result, these isochrone layers provide constraints for future attempts at linking age-depth information obtained from multiple locations at NIF. The GPR profiles reveal an ice thickness ranging between (6.1 ± 0.5) and (53.5 ± 1.0) m. Combining these data with a very high resolution digital elevation model we spatially extrapolate ice thickness and give an estimate of the total ice volume remaining at NIF's southern portion as (12.0 ± 0.3) × 106 m3.

  11. Pseudoepitaxial transrotational structures in 14 nm-thick NiSi layers on [001] silicon.

    PubMed

    Alberti, Alessandra; Bongiorno, Corrado; Cafra, Brunella; Mannino, Giovanni; Rimini, Emanuele; Metzger, Till; Mocuta, Cristian; Kammler, Thorsten; Feudel, Thomas

    2005-10-01

    In a system consisting of two different lattices, structural stability is ensured when an epitaxial relationship occurs between them and allows the system to retain the stress whilst avoiding the formation of a polycrystalline film. The phenomenon occurs if the film thickness does not exceed a critical value. Here we show that in spite of its orthorhombic structure, a 14 nm-thick NiSi layer can three-dimensionally adapt to the cubic Si lattice by forming transrotational domains. Each domain arises by the continuous bending of the NiSi lattice, maintaining a close relationship with the substrate structure. The presence of transrotational domains does not cause a roughening of the layer, but instead it improves the structural and electrical stability of the silicide in comparison with a 24 nm-thick layer formed using the same annealing process. These results have relevant implications for the thickness scaling of NiSi layers which are currently used as metallizations of electronic devices.

  12. 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…

  13. Superconducting, surface and interface properties of Ho(123) and Bi(2212) films on sapphire with cerium oxide buffer layers

    NASA Astrophysics Data System (ADS)

    Castro, L. F.; Suryanarayanan, R.; Das, A.; Bacca, E.; Gómez, M. E.; Lopera, W.; Prieto, P.; Kreisler, A.; Martin, J. C.

    1995-09-01

    We report on the X-ray diffraction, secondary ion mass spectrometry, and atomic force microscopy on Ho(123) and Bi(2212) films dc sputtered in pure oxygen atmosphere onto heated sapphire substrates with CeO 2 buffer layers. The films were c-axis oriented. The Ho(123) films had a T c of 88 K but had a relatively high room temperature resistivity of 400 μΩcm. The Bi(2212) films showed a broad transition and a low T c of 46 K. The data may be explained by a certain amount of Al diffusion and inhomogenous grain growth.

  14. Effect of layer thickness setting on deposition characteristics in direct energy deposition (DED) process

    NASA Astrophysics Data System (ADS)

    Shim, Do-Sik; Baek, Gyeong-Yun; Seo, Jin-Seon; Shin, Gwang-Yong; Kim, Kee-Poong; Lee, Ki-Yong

    2016-12-01

    Direct energy deposition is an additive manufacturing technique that involves the melting of metal powder with a high-powered laser beam and is used to build a variety of components. In laser-assisted metal deposition, the mechanical and metallurgical properties achieved are influenced by many factors. This paper addresses methods for selecting an appropriate layer thickness setting, which is an important parameter in layer-by-layer deposition manufacturing. A new procedure is proposed for determining the layer thickness setting for use in slicing of a part based on the single-layer height for a given depositing condition. This procedure was compared with a conventional method that uses an empirically determined layer thickness and with a feedback control method. The micro-hardness distribution, location of the melting pool, and microstructures of the deposited layers after deposition of a simple target shape were investigated for each procedure. The experimental results show that even though the feedback control method is the most effective method for obtaining the desired geometry, the deposited region was characterized by inhomogeneity of micro-hardness due to the time-variable depositing conditions involved. The largest dimensional error was associated with the conventional deposition procedure, which produced a rise in the melting zone due to over-deposition with respect to the slicing thickness, especially at the high laser power level considered. In contrast, the proposed procedure produced a stable melting zone position during deposition, which resulted in the deposited part having reasonable dimensional accuracy and uniform micro-hardness throughout the deposited region.

  15. 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

  16. Determining mean thickness of the oxide layer by mapping the surface of a silicon sphere.

    PubMed

    Zhang, Jitao; Li, Yan; Wu, Xuejian; Luo, Zhiyong; Wei, Haoyun

    2010-03-29

    To determine Avogadro constant with a relative uncertainty of better than 2 x 10(-8), the mean thickness of the oxide layer grown non-uniformly on the silicon sphere should be determined with about 0.1 nm uncertainty. An effective and flexible mapping strategy is proposed, which is insensitive to the angle resolution of the sphere-rotating mechanism. In this method, a sphere-rotating mechanism is associated with spectroscopic ellipsometer to determine the distribution of the layer, and a weighted mean method based on equal-area projection theory is applied to estimate the mean thickness. The spectroscopic ellipsometer is calibrated by X-ray reflectivity method. Within 12 hours, eight hundred positions on the silicon sphere are measured twice. The mean thickness is determined to be 4.23 nm with an uncertainty of 0.13 nm, which is in the acceptable level for the Avogadro project.

  17. Improved properties of barium strontium titanate thin films grown on copper foils by pulsed laser deposition using a self-buffered layer.

    SciTech Connect

    Liu, S.; Ma, B.; Narayanan, M.; Balachandran, U.

    2012-01-01

    Ba{sub 0.6}Sr{sub 0.4}TiO{sub 3} (BST) films were deposited by pulsed laser deposition on copper foils with low-temperature self-buffered layers. The deposition conditions included a low oxygen partial pressure and a temperature of 700 C to crystallize the films without the formation of secondary phases and substrate oxidation. The results from x-ray diffraction and scanning electron microscopy indicated that the microstructure of the BST films strongly depended on the growth temperature. The use of the self-buffered layer improved the dielectric properties of the deposited BST films. The leakage current density of the BST films on the copper foil was 4.4 x 10{sup -9} A cm{sup -2} and 3.3 x 10{sup -6} A cm{sup -2} with and without the self-buffered layer, respectively. The ferroelectric hysteresis loop for the BST thin film with buffer layer was slim, in contrast to the distorted loop observed for the film without the buffer layer. The permittivity (7 0 0) and dielectric loss tangent (0.013) of the BST film on the copper foil with self-buffered layer at room temperature were comparable to those of the film on metal and single-crystal substrates.

  18. Epitaxial growth of BaHfO3 buffer layer and its structure degeneration analysed by Raman spectrum.

    PubMed

    Zheng, Jiahui; Fan, Feng; Yan, Xiangfa; Lu, Yuming; Liang, Yu; Bai, Chuanyi; Liu, Zhiyong; Guo, Yanqun; Cai, Chuanbing

    2016-01-01

    BaHfO3 (BHO) has been proposed as a new cap layer material for YBa2Cu3O7-δ (YBCO) coated conductors. Highly c-axis oriented BHO cap layer has been deposited on ion-beam assisted deposition-MgO buffered Hastelloy tapes by direct-current-magnetron sputtering method. The epi-growth of BHO films combined with its properties is investigated in details. The degenerated cubic crystal structure of BHO film is confirmed by Raman spectrum analysis. XRD θ-2θ scan, φ-scan and ω-scan reveal an excellent c-axis alignment with good in-plane and out-of-plane textures for BHO cap layers. SEM and AFM investigations show BHO cap layer a dense and crack-free morphology. Subsequently pure c-axis orientation YBCO film was epitaxial grown on such BHO cap layer successfully, shown BaHfO3 a potential cap layer material for coated conductors.

  19. 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.

  20. Dependence of seed layer thickness on sensitivity of nano-ZnO cholesterol biosensor

    NASA Astrophysics Data System (ADS)

    Lu, Yang-Ming; Wang, Po-Chin; Tang, Jian-Fu; Chu, Sheng-Yuan

    2017-01-01

    The anemone-like ZnO nanostructures have been synthesized by hydrothermal method and were further adsorbed immobilized cholesterol oxidase (ChOx) as a nano-biosensor. In this study, the sensitivity of biosensor were improved by varying the thickness of the ZnO seed layer. The SEM analysis showed changes in thickness of seed layer will not affect the morphologies of anemone-like ZnO nanostructures. The X-ray Diffraction patterns showed that the (002) plane of anemone-like ZnO grown on various thickness of the seed layer was more prouded than other crystal plane. Abioelectrode (ChOx/ZnO/ITO/glass) grown on the 30nm of ZnO seed layer with high sensitivity of 57.533μAmM-1cm-2 (1.488 μA (mg/dl) -1cm-2), a wide sensitive range from 25 to 500 mg/dl. It is concluded that the thinner sputtered ZnO seed layer for growing anemone-like ZnO nanostructure can effectively improve the sensitivity of the ZnO biosensor.

  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. Influence of bulk turbulence and entrance boundary layer thickness on the curved duct flow field

    NASA Astrophysics Data System (ADS)

    Crawford, R. A.

    1988-11-01

    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.

  3. Ultrasound-based measurement of liquid-layer thickness: A novel time-domain approach

    NASA Astrophysics Data System (ADS)

    Praher, Bernhard; Steinbichler, Georg

    2017-01-01

    Measuring the thickness of a thin liquid layer between two solid materials is important when the adequate separation of metallic parts by a lubricant film (e.g., in bearings or mechanical seals) is to be assessed. The challenge in using ultrasound-based systems for such measurements is that the signal from the liquid layer is a superposition of multiple reflections. We have developed an algorithm for reconstructing this superimposed signal in the time domain. By comparing simulated and measured signals, the time-of-flight of the ultrasonic pulse in a layer can be estimated. With the longitudinal sound velocity known, the layer thickness can then be calculated. In laboratory measurements, we validate successfully (maximum relative error 4.9%) our algorithm for layer thicknesses ranging from 30 μm to 200 μm. Furthermore, we tested our method in the high-temperature environment of polymer processing by measuring the clearance between screw and barrel in the plasticisation unit of an injection moulding machine. The results of such measurements can indicate (i) the wear status of the tribo-mechanical screw-barrel system and (ii) unsuitable process conditions.

  4. The effect of h-BN buffer layers in bilayer graphene on Co (111)

    NASA Astrophysics Data System (ADS)

    Li, Can; Liu, Yan; Zhang, Bin; Wang, Tao; Guo, Qing; Sheng, Kuang; Yin, You

    2015-05-01

    Understanding of the interface of Co/graphene is essential for applications of graphene-based devices, as well as in the process of graphene synthesis. In this paper, the Co/graphene interface, including five structures of bilayer graphene (BLG) on Co (111) surface with bilayer or monolayer BN buffer sheets, is investigated by using density functional theory calculations. The corresponding atomic and electronic structures and Mulliken charge populations are also analyzed. The bilayer BN sheets are found to be the thinnest insulator for the backside Co metal gate, which shields BLG from Co substrate pining, decreases the charges influenced by the substrate, and improves BLG transport mobility.

  5. 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

  6. Physical properties of new iron arsenide oxide with thick perovskite-type oxide layer

    NASA Astrophysics Data System (ADS)

    Kawaguchi, Naoto; Ogino, Hiraku; Kishio, Koji; Shimoyama, Junichi

    2010-03-01

    Since the discovery of high-Tc superconductivity in LaFeAsO, a large number of layered compounds having anti-fluorite type Fe- or Ni-pnictide layer have been discovered. Among them, a series of pnictide oxides having perovskite-type oxide layersfootnotetextH. Ogino et al., Supercond. Sci. Technol. 22 (2009) 075008 are attractive because of their chemical flexibility particularly at the perovskite-type oxide layer, which may results in new compounds. In the present study, various physical properties have been investigated for the new iron pnictide oxides with thick perovskite-type blocking layers, i.e., large interlayer distance between Fe-layers more than 1.7 nm. These samples showed metallic and paramagnetic behaviors in resistivity and magnetization measurements, respectively, down to 2 K without any signs of superconductivity and other anomalies. Relationship among crystal structure, constituent elements and physical properties will be discussed for the newly discovered system.

  7. Optical coherence tomography layer thickness characterization of a mock artery during angioplasty balloon deployment

    NASA Astrophysics Data System (ADS)

    Azarnoush, Hamed; Vergnole, Sébastien; Boulet, Benoît; Lamouche, Guy

    2011-03-01

    Optical coherence tomography (OCT) is used to study the deformation of a mock artery in an angioplasty simulation setup. An OCT probe integrated in a balloon catheter provides intraluminal real-time images during balloon inflation. Swept-source OCT is used for imaging. A 4 mm semi-compliant polyurethane balloon is used for experiments. The balloon is inflated inside a custom-built multi-layer artery phantom. The phantom has three layers to mock artery layers, namely, intima, media and adventitia. Semi-automatic segmentation of phantom layers is performed to provide a detailed assessment of the phantom deformation at various inflation pressures. Characterization of luminal diameter and thickness of different layers of the mock artery is provided for various inflation pressures.

  8. Retinal Fibre Layer Thickness Measurement in Normal Paediatric Population in Sweden Using Optical Coherence Tomography

    PubMed Central

    Ntoula, Evangelia

    2016-01-01

    Purpose. To evaluate the correlation between peripapillary retinal nerve fibre layer (RNFL) thickness and both age and refraction error in healthy children using optical coherence tomography (OCT). Patients and Methods. 80 healthy children with a mean age of 9.1 years (range 3.8 to 16.7 years) undergoing routine ocular examination at the orthoptic section of the Ophthalmology Department were recruited for this cross-sectional study. After applying cycloplegia, the peripapillary RNFL thickness was measured in both eyes using the Topcon 3D OCT 2000 device. Results. 138 eyes were included in the analysis. The average refractive error (SE) was +1.7 D (range −5.25 to +7.25 D). The mean total RNFL thickness was 105 μm ± 10.3, the mean superior RNFL thickness was 112.7 μm ± 16.5, and the mean inferior RNFL thickness was 132.6 μm ± 18.3. We found no statistically significant effect of age on RNFL thickness (ANOVA, f = 0.33, p = 0.56). Refraction was proven to have a statistically significant effect (ANOVA, f = 67.1, p < 0.05) in RNFL measurements. Conclusions. Data obtained from this study may assist in establishing a normative database for a paediatric population. Refraction error should be taken into consideration due to its statistically significant correlation with RNFL thickness. PMID:27980862

  9. 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

  10. 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.

  11. 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}.

  12. 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}.

  13. Study of the effects of GaN buffer layer quality on the dc characteristics of AlGaN/GaN high electron mobility transistors

    DOE PAGES

    Ahn, Shihyun; Zhu, Weidi; Dong, Chen; ...

    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

  14. 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.

  15. Evaluation of AlGaN/GaN high electron mobility transistors grown on ZrTi buffer layers with sapphire substrates

    SciTech Connect

    Ren, Fan; Pearton, Stephen J.; Ahn, Shihyun; Lin, Yi -Hsuan; Machuca, Francisco; Weiss, Robert; Welsh, Alex; McCartney, Martha R.; Smith, David J.; Kravchenko, Ivan I.

    2016-09-21

    Here, AlGaN/GaN high electron mobility transistors (HEMTs) have been grown on sapphire substrates, using ZrTi buffer layers to provide in-plane lattice-matching to hexagonal GaN. X-ray diffraction (XRD) as well as cross-section transmission electron microscopy (TEM) were used to assess the quality of the HEMT structure. The XRD 2θ scans showed full-width-at-half-maximum values of 0.16°, 0.07°, and 0.08° for ZrTi alloy, GaN buffer layer, and the entire HEMT structure, respectively. TEM studies of the GaN buffer layer and the AlN/ZrTi/AlN stack showed the importance of growing thin AlN buffer layers on the ZrTi layer prior to growth of the GaN buffer layer. The density of threading dislocations in the GaN channel layer of the HEMT structure was estimated to be in the 108 cm–2 range. The HEMT device exhibited a saturation drain current density of 820 mA/mm, and the channel of the fabricated HEMTs could be well modulated. A cutoff frequency (fT) of 8.9 GHz and a maximum frequency of oscillation (fmax) of 17.3 GHz were achieved for HEMTs with gate dimensions of 1 × 200 μm.

  16. Graphene/nitrogen-functionalized graphene quantum dot hybrid broadband photodetectors with a buffer layer of boron nitride nanosheets.

    PubMed

    Tetsuka, Hiroyuki; Nagoya, Akihiro; Tamura, Shin-Ichi

    2016-12-01

    A high performance hybrid broadband photodetector with graphene/nitrogen-functionalized graphene quantum dots (NGQDs@GFET) is developed using boron nitride nanosheets (BN-NSs) as a buffer layer to facilitate the separation and transport of photoexcited carriers from the NGQD absorber. The NGQDs@GFET photodetector with the buffer layer of BN-NSs exhibits enhanced photoresponsivity and detectivity in the deep ultraviolet region of ca. 2.3 × 10(6) A W(-1) and ca. 5.5 × 10(13) Jones without the application of a backgate voltage. The high level of photoresponsivity persists into the near-infrared region (ca. 3.4 × 10(2) A W(-1) and 8.0 × 10(9) Jones). In addition, application in flexible photodetectors is demonstrated by the construction of a structure on a polyethylene terephthalate (PET) substrate. We further show the feasibility of using our flexible photodetectors towards the practical application of infrared photoreflectors. Together with the potential application of flexible photodetectors and infrared photoreflectors, the proposed hybrid photodetectors have potential for use in future graphene-based optoelectronic devices.

  17. Interface roughness of double buffer layer of GaN film grown on Si(1 1 1) substrate using GIXR analysis

    NASA Astrophysics Data System (ADS)

    Yamamoto, Y.; Yamabe, N.; Ohachi, T.

    2011-03-01

    A double buffer layer (DBL), interface reaction epitaxy (IRE) AlN/β-Si3N4/Si, grown by an IRE of β-Si3N4 and AlN films on Si, was fabricated to improve the crystalline quality of successively grown 30 nm GaN on a 30 nm AlN buffer layer using plasma-assisted molecular beam epitaxy (PA-MBE). The DBL was first prepared by surface nitridation of Si and successively prepared by IRE between the deposited Al and N atoms in β-Si3N4. Both the AlN buffer layer on the DBL and GaN film on the AlN buffer layer were grown by activity-modulation migration enhanced epitaxy (AM-MEE). Hetero epitaxial grown films of GaN(30 nm)/AlN buffer(30 nm)/DBL/Si(1 1 1) were prepared for analysis using a three layer model of grazing incidence-angle X-ray reflectivity (GIXR), which consisted of three layers of GaN, AlN buffer and Si and of the three interfaces of the GaN surface, GaN/AlN buffer and AlN buffer/DBL/Si. The nitridation temperature dependence of the interface roughness of the DBL was measured to be 0.5 and 0.6 nm, for nitridation temperatures of 780 and 830 °C, respectively. The full width at half maximum (FWHM) of rocking curve GaN(0 0 0 2) measured by X-ray diffraction (XRD) for nitridation temperatures of 780 and 830 °C were 58.2 and 55.2 arcmin, respectively.

  18. Peculiarities of strain relaxation in linearly graded InxGa1-xAs/GaAs(001) metamorphic buffer layers grown by molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Sorokin, S. V.; Klimko, G. V.; Sedova, I. V.; Sitnikova, A. A.; Kirilenko, D. A.; Baidakova, M. V.; Yagovkina, M. A.; Komissarova, T. A.; Belyaev, K. G.; Ivanov, S. V.

    2016-12-01

    This paper presents a comprehensive study of structural, optical and electrical properties of heterostructures with linearly graded InxGa1-xAs metamorphic buffer layers (MBLs) grown by molecular beam epitaxy on GaAs (001) substrates. The low density of threading dislocations (well below 106 cm-2) in 1-μm-thick In0.3Ga0.7As layers grown atop of the linearly graded InxGa1-xAs/GaAs MBLs has been confirmed by using transmission electron microscopy (TEM). X-ray diffraction (XRD) data demonstrate good agreement between the experimentally measured In step-back and its calculations in the frames of existing models. Combining the XRD reciprocal space maps (RSM) of the structures and the spatially-resolved selective area electron diffraction measurements by cross-sectional TEM in depth-profiled RSM diagrams allowed direct visualization of the strain relaxation dynamics during the MBL growth. Strong effect of the azimuth angle and the value of an unintentional initial miscut of nominally (001) oriented GaAs substrate on the strain relaxation dynamics was observed.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. Strength and thickness of the layer of materials used for ceramic veneers bonding.

    PubMed

    Mazurek, Karolina; Mierzwińska-Nastalska, Elżbieta; Molak, Rafał; Kożuchowski, Mariusz; Pakieła, Zbigniew

    2012-01-01

    The use of adhesive bonding systems and composites in prosthetic dentistry brought improved and more aesthetic prosthetic restorations. The adhesive bonding of porcelain veneers is based on the micromechanical and chemical bond between tooth surface, cement layer and ceramic material. The aim of the study was to measure the thickness of the material layer formed during cementing of a ceramic restoration, and - in the second part of the study - to test tension of these cements. The materials investigated comprised dual-curing materials: Variolink II, KoNroot Cem, KoNroot Cem Viscous and Panavia F 2.0, as well as a light-curing composite: Variolink Veneer. The thickness was measured with the use of ZIP Lite 250 optical gauging apparatus. SEM microscope - Hitachi Tabletop Microscope TM-100 - was used to analyse the characteristics of an adhesive bond and filler particle size of particular materials. Tension tests of the cements under study were carried out on the MTS Q Test 10 static electrodynamic apparatus. The tests showed that KoNroot Cem exhibited the best mechanical properties of bonding to enamel and dentin among the materials tested. Variolink II base light-curing cement formed the thinnest layer. All the materials tested formed the layer not exceeding 1/3 of ceramic restoration thickness.

  4. Cooperative Lamb shift in an atomic vapor layer of nanometer thickness.

    PubMed

    Keaveney, J; Sargsyan, A; Krohn, U; Hughes, I G; Sarkisyan, D; Adams, C S

    2012-04-27

    We present an experimental measurement of the cooperative Lamb shift and the Lorentz shift using a nanothickness atomic vapor layer with tunable thickness and atomic density. The cooperative Lamb shift arises due to the exchange of virtual photons between identical atoms. The interference between the forward and backward propagating virtual fields is confirmed by the thickness dependence of the shift, which has a spatial frequency equal to twice that of the optical field. The demonstration of cooperative interactions in an easily scalable system opens the door to a new domain for nonlinear optics.

  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. Characterization of Pt/Bi3.15Nd0.85Ti3O12/HfO2/Si structure using a hafnium oxide as buffer layer for ferroelectric-gate field effect transistors

    NASA Astrophysics Data System (ADS)

    Xie, Dan; Luo, Yafeng; Han, Xueguang; Ren, Tianling; Liu, Litian

    2009-12-01

    We have investigated the structural and electrical properties of metal-ferroelectric-insulator-semiconductor (MFIS) capacitors with Bi3.15Nd0.85Ti3O12 (BNdT) thin film deposited on Si and hafnium oxide (HfO2)/Si substrates. Microstructural analysis reveals the formation of well-crystallized BNdT perovskite film and good interface between BNdT film and HfO2 buffer layer. Pt/BNdT/HfO2/Si structure exhibits a memory window of 1.12 V at an operation voltage of 3.5 V. The width of memory window for the MFIS structure varies with increasing thickness of HfO2 layer, and 4-nm-thickness is optimum. The results from the fatigue test indicate a slight degradation of the memory window after 1010 switching cycles. These properties are encouraging for the development of ferroelectric memory transistors.

  7. Device performance and lifetime of polymer:fullerene solar cells with UV-ozone-irradiated hole-collecting buffer layers.

    PubMed

    Lee, Seungsoo; Nam, Sungho; Lee, Hyena; Kim, Hwajeong; Kim, Youngkyoo

    2011-11-18

    We report the influence of UV-ozone irradiation of the hole-collecting buffer layers on the performance and lifetime of polymer:fullerene solar cells. UV-ozone irradiation was targeted at the surface of the poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) layers by varying the irradiation time up to 600 s. The change of the surface characteristics in the PEDOT:PSS after UV-ozone irradiation was measured by employing optical absorption spectroscopy, photoelectron yield spectroscopy, and contact angle measurements, while Raman and X-ray photoelectron spectroscopy techniques were introduced for more microscopic analysis. Results showed that the UV-ozone irradiation changed the chemical structure/composition of the surface of the PEDOT:PSS layers leading to the gradual increase of ionization potential with irradiation time in the presence of up-and-down variations in the contact angle (polarity). This surface property change was attributed to the formation of oxidative components, as evidenced by XPS and Auger electron images, which affected the sheet resistance of the PEDOT:PSS layers. Interestingly, device performance was slightly improved by short irradiation (up to 10 s), whereas it was gradually decreased by further irradiation. The short-duration illumination test showed that the lifetime of solar cells with the UV-ozone irradiated PEDOT:PSS layer was improved due to the protective role of the oxidative components formed upon UV-ozone irradiation against the attack of sulfonic acid groups in the PEDOT:PSS layer to the active layer.

  8. Influence of electron transport layer thickness on optical properties of organic light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Liu, Guohong; Liu, Yong; Li, Baojun; Zhou, Xiang

    2015-06-01

    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 (Alq3) 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.

  9. Evaluation of retinal nerve fiber layer thickness profile in thyroid ophthalmopathy without optic nerve dysfunction

    PubMed Central

    Mugdha, Kumari; Kaur, Apjit; Sinha, Neha; Saxena, Sandeep

    2016-01-01

    AIM To evaluate retinal nerve fiber layer (RNFL) thickness profile in patients of thyroid ophthalmopathy with no clinical signs of optic nerve dysfunction. METHODS A prospective, case-control, observational study conducted at a tertiary care centre. Inclusion criteria consisted of patients with eyelid retraction in association with any one of: biochemical thyroid dysfunction, exophthalmos, or extraocular muscle involvement; or thyroid dysfunction in association with either exophthalmos or extra-ocular muscle involvement; or a clinical activity score (CAS)>3/7. Two measurements of RNFL thickness were done for each eye, by Cirrus HD-optical coherence tomography 6mo apart. RESULTS Mean age of the sample was 38.75y (range 13-70y) with 18 males and 22 females. Average RNFL thickness at first visit was 92.06±12.44 µm, significantly lower than control group (101.28±6.64 µm) (P=0.0001). Thickness of inferior quadrant decreased from 118.2±21.27 µm to 115.0±22.27 µm after 6mo (P=0.02). There was no correlation between the change in CAS and RNFL thickness. CONCLUSION Decreased RNFL thickness is an important feature of thyroid orbitopathy, which is an inherent outcome of compressive optic neuropathy of any etiology. Subclinical RNFL damage continues in the absence of clinical activity of the disease. RNFL evaluation is essential in Grave's disease and active intervention may be warranted in the presence of significant damage. PMID:27990368

  10. 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.

  11. Identification of atmospheric boundary layer thickness using doppler radar datas and WRF - ARW model in Merauke

    NASA Astrophysics Data System (ADS)

    Putri, R. J. A.; Setyawan, T.

    2017-01-01

    In the synoptic scale, one of the important meteorological parameter is the atmospheric boundary layer. Aside from being a supporter of the parameters in weather and climate models, knowing the thickness of the layer of the atmosphere can help identify aerosols and the strength of the vertical mixing of pollutants in it. The vertical wind profile data from C-band Doppler radar Mopah-Merauke which is operated by BMKG through Mopah-Merauke Meteorological Station can be used to identify the peak of Atmospheric Boundaryu Layer (ABL). ABL peak marked by increasing wind shear over the layer blending. Samples in January 2015 as a representative in the wet and in July 2015 as the representation of a dry month, shows that ABL heights using WRF models show that in July (sunny weather) ABL height values higher than in January (cloudy)

  12. 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.

  13. 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

    2016-09-01

    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.

  14. Aerodynamically-driven condensate layer thickness distributions on isothermal cylindrical surfaces

    NASA Astrophysics Data System (ADS)

    Rosner, D. E.; Gunes, D.; Nazih-Anous, N.

    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.

  15. 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.

  16. The effects of ultra-thin cerium fluoride film as the anode buffer layer on the electrical characteristics of organic light emitting diodes

    NASA Astrophysics Data System (ADS)

    Lu, Hsin-Wei; Tsai, Cheng-Che; Hong, Cheng-Shong; Kao, Po-Ching; Juang, Yung-Der; Chu, Sheng-Yuan

    2016-11-01

    In this study, the efficiency of organic light-emitting diodes (OLEDs) was enhanced by depositing a CeF3film as an ultra-thin buffer layer between the indium tin oxide (ITO) electrode and α-naphthylphenylbiphenyldiamine (NPB) hole transport layer, with the structure configuration ITO/CeF3 (0.5, 1, and 1.5 nm)/α-naphthylphenylbiphenyl diamine (NPB) (40 nm)/tris(8-hydroxyquinoline) aluminum (Alq3) (60 nm)/lithium fluoride (LiF) (1 nm)/Al (150 nm). The enhancement mechanism was systematically investigated via several approaches. The X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy results revealed the formation of the UV-ozone treated CeF3 film. The work function increased from 4.8 eV (standard ITO electrode) to 5.22 eV (0.5-nm-thick UV-ozone treated CeF3 film deposited on the ITO electrode). The surface roughness of the UV-ozone treated CeF3 film was smoother than that of the standard ITO electrode. Further, the UV-ozone treated CeF3 film increased both the surface energy and polarity, as determined from contact angle measurements. In addition, admittance spectroscopy measurements showed an increased capacitance and conductance of the OLEDs. Accordingly, the turn-on voltage decreased from 4.2 V to 3.6 V at 1 mA/cm2, the luminance increased from 7588 cd/m2 to 24760 cd/m2, and the current efficiency increased from 3.2 cd/A to 3.8 cd/A when the 0.5-nm-thick UV-ozone treated CeF3 film was inserted into the OLEDs.

  17. Ca/Alq3 hybrid cathode buffer layer for the optimization of organic solar cells based on a planar heterojunction

    NASA Astrophysics Data System (ADS)

    El Jouad, Z.; Barkat, L.; Stephant, N.; Cattin, L.; Hamzaoui, N.; Khelil, A.; Ghamnia, M.; Addou, M.; Morsli, M.; Béchu, S.; Cabanetos, C.; Richard-Plouet, M.; Blanchard, P.; Bernède, J. C.

    2016-11-01

    Use of efficient anode cathode buffer layer (CBL) is crucial to improve the efficiency of organic photovoltaic cells. Here we show that using a double CBL, Ca/Alq3, allows improving significantly cell performances. The insertion of Ca layer facilitates electron harvesting and blocks hole collection, leading to improved charge selectivity and reduced leakage current, whereas Alq3 blocks excitons. After optimisation of this Ca/Alq3 CBL using CuPc as electron donor, it is shown that it is also efficient when SubPc is substituted to CuPc in the cells. In that case we show that the morphology of the SubPc layer, and therefore the efficiency of the cells, strongly depends on the deposition rate of the SubPc film. It is necessary to deposit slowly (0.02 nm/s) the SubPc films because at higher deposition rate (0.06 nm/s) the films are porous, which induces leakage currents and deterioration of the cell performances. The SubPc layers whose formations are kinetically driven at low deposition rates are more uniform, whereas those deposited faster exhibit high densities of pinholes.

  18. 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.

  19. 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

    2014-10-08

    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.

  20. A method for determining the thickness of tribological performing thin layers formed by selective transfer

    NASA Astrophysics Data System (ADS)

    Ilie, Filip; Chisiu, Georgiana; Ipate, George

    2017-02-01

    A new stage in the research of the unconventional friction couples (alloys or pseudo-alloys in thin layers) to implement them in the designing and execution of machines is represented by the modern friction couples which are based on selective transfer (transfer of a material from one element of the friction couple to the other in the presence of a lubricant forming a superficial layer, antifriction, very thin, the order of several microns, which behaves very well to friction and wear). A selective transfer can be achieved with certainty in a friction couple, lubricated with glycerine or with a special lubricant, if in the friction area there is a material from alloys on based copper. The thin superficial layer formed through selective transfer in the friction process of a friction couple is made of the elements of the alloy based on copper, where the copper is predominant. Hence results the practical necessity to determine the thickness of superficial thin layers (0.1 - 4 μm) obtained in the friction couples, by selective transfer (mass selective transfer through diffusion from one element of the friction couple to another, in conditions of local energies favourable to the transfer process and in the presence of relative motion). The aim of this paper is presenting and explaining a methodology for determining the thickness of layers formed by selective transfer, in the friction process, on the surfaces of elements friction couples.

  1. A novel ellipsometer for measuring thickness of oxide layer on the surface of silicon sphere

    NASA Astrophysics Data System (ADS)

    Zhang, Jitao; Li, Yan

    2008-03-01

    The Avogadro constant NA is used as one of the several possible routes to redefinition of the kilogram in metrology today. Usually in order to accurately determine NA, the volume of a perfect single crystal silicon sphere of nearly 1 kg mass should be measured with a high relative uncertainty, i.e. about 1×10 -8. However, the oxide layer grown on the surface of the silicon sphere causes a remarkable systematic difference between the measured and real diameters. A novel ellipsometer has been developed to determine the thickness of the oxide layer accurately and automatically. The arrangement of this instrument is suitable for measuring the layer on the sphere surface. What's more, the measuring is faster by optimizing the parameters and developing the algorithm of calculating the thickness and refractive index of the oxide layer. The preliminary simulation result has present. Thus, the uncertainty of the diameter measurement caused by the oxide layer can be observably reduced. And the further improving of this ellipsometer is discussed in the end.

  2. A preliminary investigation into the relationship between ocular surface temperature and lipid layer thickness.

    PubMed

    Giraldez, Maria Jesus; Naroo, Shehzad A; Resua, Carlos Garcia

    2009-08-01

    The aim of this study was to establish the relationship between OST, tear film stability as assessed by NIBUT and subjective evaluation of the lipid layer thickness in a young, asymptomatic, sample group (N=29). Non-invasive tear break-up time (NIBUT) and tear lipid layer structure were evaluated through a slit-lamp mounted Tearscope Plus. A self-calibrating infrared thermography camera was used to record two OST values (one immediately post-blink and one immediately pre the subsequent blink). The most common lipid layer pattern observed was the amorphous pattern (48.3%). Differences between post- and pre-blink OST values were observed (paired t-test; p<0.001). Significant differences of pre-blink OST values were observed between the closed marmoreal group with that from the amorphous and flow groups (Tukey post hoc test, p<0.05). There were no differences of NIBUT values between each lipid layer thickness (Kruskal-Wallis test; p=0.152). A no significant tendency for higher OST in eyes with increased NIBUT was observed. This study suggests that higher OST values could be associated with thicker tear lipid layer in normal subjects. The lack of significant results in relation with tear film stability may be due to only normal subjects were included.

  3. 19.5%-Efficient CuIn1-xGaxSe2 Photovoltaic Cells Using A Cd-Zn-S Buffer Layer

    SciTech Connect

    Bhattacharya. R. N.

    2008-01-01

    CuIn1-xGaxSe2 (CIGS) solar cell junctions prepared by chemical-bath-deposited (CBD) Zn1-xCdxS (CdZnS), ZnS, and CdS buffer layers are discussed. A 19.52%-efficient, CIGS-based, thin-film photovoltaic device has been fabricated using a single-layer CBD CdZnS buffer layer. The mechanism that creates extensive hydroxide and oxide impurities in CBD-ZnS and CBD-CdZnS thin films (compared to CBD-CdS thin film) is presented.

  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. High performance organic photovoltaics with zinc oxide and graphene oxide buffer layers

    NASA Astrophysics Data System (ADS)

    Mohd Yusoff, Abd Rashid Bin; Kim, Hyeong Pil; Jang, Jin

    2014-01-01

    We report air stable inverted organic photovoltaics (OPVs) incorporating graphene oxide (GO) and solution processed zinc oxide (ZnO) as hole transport and electron transport layers, respectively. Both the hole transport layer and the electron transport layer (HTL and ETL) are of advantage in high transparency and environmental stability. The use of GO and ZnO in poly(2,7-carbazole) derivative (PCDTBT):fullerene derivative (PC70BM)-based inverted OPVs leads to an improved device stability and enhanced high open circuit voltage (Voc) of 0.81 V, a short-circuit current density (Jsc) of 14.10 mA cm-2, and a fill factor (FF) of 54.44 along with a power conversion efficiency of 6.20%.

  6. Spacer-thickness dependence of interlayer exchange coupling in GaMnAs/InGaAs/GaMnAs trilayers grown on ZnCdSe buffers

    NASA Astrophysics Data System (ADS)

    Tivakornsasithorn, Kritsanu; Yoo, Taehee; Lee, Hakjoon; Choi, Seonghoon; Lee, Sanghoon; Liu, Xinyu; Dobrowolska, M.; Furdyna, Jacek K.

    2017-03-01

    Interlayer exchange coupling (IEC) between GaMnAs layers in GaMnAs/InGaAs/GaMnAs tri-layers was studied by magnetization measurements. Minor hysteresis loops are observed to shift in a direction indicating the presence of ferromagnetic (FM) IEC in the structures. The strength of the FM IEC clearly exhibits an exponential decrease with respect to nonmagnetic InGaAs spacer thickness. The fitting of the spacer thickness dependence of the FM IEC to an exponential decay function provides a decay length of 3.3±0.3 nm, which is relatively large compared to metallic multilayers, indicating a long ranged IEC in systems based on GaMnAs.

  7. Retinal nerve fiber layer thickness analysis in suspected malingerers with optic disc temporal pallor

    PubMed Central

    Civelekler, Mustafa; Halili, Ismail; Gundogan, Faith C; Sobaci, Gungor

    2009-01-01

    Purpose: To investigate the value of temporal retinal nerve fiber layer (RNFLtemporal) thickness in the prediction of malingering. Materials and Methods: This prospective, cross-sectional study was conducted on 33 military conscripts with optic disc temporal pallor (ODTP) and 33 age-and sex-matched healthy controls. Initial visual acuity (VAi) and visual acuity after simulation examination techniques (VAaset) were assessed. The subjects whose VAaset were two or more lines higher than VAi were determined as malingerers. Thickness of the peripapillary RNFL was determined with OCT (Stratus OCT™, Carl Zeiss Meditec, Inc.). RNFLtemporal thickness of the subjects were categorized into one of the 1+ to 4+ groups according to 50% confidence interval (CI), 25% CI and 5% CI values which were assessed in the control group. The VAs were converted to LogMAR-VAs for statistical comparisons. Results: A significant difference was found only in the temporal quadrant of RNFL thickness in subjects with ODTP (P=0.002). Mean LogMAR-VA increased significantly after SETs (P<0.001). Sensitivity, specificity, positive and negative predictive values of categorized RNFLtemporal thickness in diagnosing malingering were 84.6%, 75.0%, 68.8%, 88.2%, respectively. ROC curve showed that RNFLtemporal thickness of 67.5 μm is a significant cut-off point in determining malingering (P=0.001, area under the curve:0.862). The correlations between LogMAR-VAs and RNFLtemporal thicknesses were significant; the correlation coefficient for LogMAR-VAi was lower than the correlation for LogMAR-VAaset (r=−0.447, P=0.009 for LogMAR-VAi; r=−0.676, P<0.001 for LogMAR-VAaset). Conclusions: RNFLtemporal thickness assessment may be a valuable tool in determining malingering in subjects with ODTP objectively. PMID:19700875

  8. Quantum transport modeling of the symmetric Fe/FeO0.5/MgO magnetic tunnel junction: the effects of correlations in the buffer layer.

    PubMed

    Timoshevskii, Vladimir; Hu, Yibin; Marcotte, Étienne; Guo, Hong

    2014-01-08

    We report ab initio simulations of quantum transport properties of Fe/MgO/Fe trilayer structures with FeO0.5 buffer iron oxide layer, where on-site Coulomb interaction is explicitly taken into account by local density approximation + Hubbard U approach. We show that on-site Coulomb repulsion in the iron-oxygen layer can cause a dramatic drop of the tunnel magnetoresistance of the system. We present an understanding of microscopic details of this phenomenon, connecting it to localization of electronic states of particular symmetry, which takes place in the buffer Fe-O layer, when on-site Coulomb repulsion is introduced. We further study the possible influence of the symmetry reduction in the buffer Fe-O layer on the transport properties of the Fe/MgO/Fe interface.

  9. 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.

  10. Investigation of void formation beneath thin AlN layers by decomposition of sapphire substrates for self-separation of thick AlN layers grown by HVPE

    NASA Astrophysics Data System (ADS)

    Kumagai, Yoshinao; Enatsu, Yuuki; Ishizuki, Masanari; Kubota, Yuki; Tajima, Jumpei; Nagashima, Toru; Murakami, Hisashi; Takada, Kazuya; Koukitu, Akinori

    2010-09-01

    Void formation at the interface between thick AlN layers and (0 0 0 1) sapphire substrates was investigated to form a predefined separation point of the thick AlN layers for the preparation of freestanding AlN substrates by hydride vapor phase epitaxy (HVPE). By heating 50-200 nm thick intermediate AlN layers above 1400 °C in a gas flow containing H 2 and NH 3, voids were formed beneath the AlN layers by the decomposition reaction of sapphire with hydrogen diffusing to the interface. The volume of the sapphire decomposed at the interface increased as the temperature and time of the heat treatment was increased and as the thickness of the AlN layer decreased. Thick AlN layers subsequently grown at 1450 °C after the formation of voids beneath the intermediate AlN layer with a thickness of 100 nm or above self-separated from the sapphire substrates during post-growth cooling with the aid of voids. The 79 μm thick freestanding AlN substrate obtained using a 200 nm thick intermediate AlN layer had a flat surface with no pits, high optical transparency at wavelengths above 208.1 nm, and a dislocation density of 1.5×10 8 cm -2.

  11. Two-wavelengths laser-speckle technique for thickness determination of transparent layers on rough surfaces

    NASA Astrophysics Data System (ADS)

    Lettner, J.; Zagar, B. G.

    2013-11-01

    In this work, a non-contacting laser-speckle technique and two different implementations thereof for measuring the thickness of thin transparent liquid layers on optically rough surfaces are presented. The optical system allows large stand-off distances and can be used in harsh environments and industrial applications. The thickness of the (oil) coating can be measured down into the μm range, which is below that of the surface roughness. The distribution of the coating depends on adhesive and cohesive forces, the temperature and primarily on the surface topography itself. The thickness of transparent coatings can be evaluated statistically considering wavelengths and roughness. We describe the two measurement principles and the data processing, present measurement results and discuss the advantages and disadvantages of both methods. For a better understanding, the theoretical considerations of the diffraction of sinusoidal phase gratings in the Fraunhofer region will be given.

  12. An Integrated Observational and Model Synthesis Approach to Examine Dominant Environmental Controls on Active Layer Thickness

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

    The active layer thickness (ALT) - the annual maximum depth of soil with above 0°C temperatures - in part determines the volume of carbon-rich stores available for decomposition and therefore potential greenhouse gas release into the atmosphere from Arctic tundra. However, understanding and predicting ALT in polygonal tundra landscapes is difficult due to the complex nature of hydrothermal atmospheric-surface-subsurface interactions in freezing/thawing soil. Simply deconvolving effects of single environmental controls on ALT is not possible with measurements alone as processes act in concert to drive thaw depth formation. Process-rich models of thermal hydrological dynamics, conversely, are a valuable tool for understanding the dominant controls and uncertainties in predicting permafrost conditions. By integrating observational data with known physical relationships to form process-rich models, synthetic experiments can then be used to explore a breadth of environmental conditions encountered and the effect of each environmental attribute may be assessed. Here a process rich thermal hydrology model, The Advanced Terrestrial Simulator, has been created and calibrated using observed data from Barrow, AK. An ensemble of 1D thermal hydrologic models were simulated that span a range of three environmental factors 1) thickness of organic rich soil, 2) snow depth, and 3) soil moisture content, to investigate the role of each factor on ALT. Results show that organic layer thickness acts as a strong insulator and is the dominant control of ALT, but the strength of the effect of organic layer thickness is also dependent on the saturation state. Using the ensemble results, the effect of peat thickness on ALT was then examined on a 2D domain. 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

  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. Minimum Thickness Requirements for Asphalt Surface Course and Base Layer in Airfield Pavements

    DTIC Science & Technology

    2011-08-01

    e.g., Donovan and Tutumluer 2008, 2009; Tao et al. 2010), a waterproof surface, protection from foreign object damage (FOD), and a durable surface...mechanisms for premature deterioration, and quantify the service life of thin asphalt concrete pavements. Six sections with different layer...32,500 7,794 The full-scale test data analysis led to a conclusion that the Department of Defense’s (DoD) minimum asphalt concrete thickness

  15. 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

  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. 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.

  19. 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

  20. 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.

  1. 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.

  2. 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

  3. 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.

  4. Evaluation of AlGaN/GaN high electron mobility transistors grown on ZrTi buffer layers with sapphire substrates

    DOE PAGES

    Ren, Fan; Pearton, Stephen J.; Ahn, Shihyun; ...

    2016-09-21

    Here, AlGaN/GaN high electron mobility transistors (HEMTs) have been grown on sapphire substrates, using ZrTi buffer layers to provide in-plane lattice-matching to hexagonal GaN. X-ray diffraction (XRD) as well as cross-section transmission electron microscopy (TEM) were used to assess the quality of the HEMT structure. The XRD 2θ scans showed full-width-at-half-maximum values of 0.16°, 0.07°, and 0.08° for ZrTi alloy, GaN buffer layer, and the entire HEMT structure, respectively. TEM studies of the GaN buffer layer and the AlN/ZrTi/AlN stack showed the importance of growing thin AlN buffer layers on the ZrTi layer prior to growth of the GaN buffermore » layer. The density of threading dislocations in the GaN channel layer of the HEMT structure was estimated to be in the 108 cm–2 range. The HEMT device exhibited a saturation drain current density of 820 mA/mm, and the channel of the fabricated HEMTs could be well modulated. A cutoff frequency (fT) of 8.9 GHz and a maximum frequency of oscillation (fmax) of 17.3 GHz were achieved for HEMTs with gate dimensions of 1 × 200 μm.« less

  5. 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%.

  6. Plasma expander viscosity effects on red cell-free layer thickness after moderate hemodilution.

    PubMed

    Yalcin, Ozlem; Wang, Qi; Johnson, Paul C; Palmer, Andre F; Cabrales, Pedro

    2011-01-01

    The objective of the study was to investigate the effects of plasma viscosity after hemodilution on the thickness of the erythrocyte cell free layer (CFL) and on the interface between the flowing column of erythrocytes and the vascular endothelium. The erythrocyte CFL thickness was measured in the rat cremaster muscle preparation. Plasma viscosity was modified in an isovolemic hemodilution, in which the systemic hematocrit (Hctsys) was lowered to 30%. The plasma expanders (PE) of similar nature and different viscosities were generated by glutaraldehyde polymerization of human serum albumin (HSA) at various molar ratios glutaraldehyde to HSA: (i) unpolymerized HSA; (ii) PolyHSA24:1, molar ratio = 24 and (iii) PolyHSA60:1, molar ratio = 60. The HSA viscosities determined at 200 s(-1) were 1.1, 4.2 and 6.0 dyn x cm(-2), respectively. CFL thickness, vessel diameter and blood flow velocity were measured, while volumetric flow, shear rate and stress were calculated. Hemodilution with PolyHSA60:1 increased plasma viscosity and the blood showed marked shear thinning behavior. CFL thickness decreased as plasma viscosity increased after hemodilution; thus the CFL thickness with HSA and PolyHSA24:1 increased compared to baseline. Conversely, the CFL thickness of PolyHSA60:1 was not different from baseline. Blood flow increased with both PolyHSA's compared to baseline. Wall shear rate and shear stress increased for PolyHSA60:1 compared to HSA and PolyHSA24:1, respectively. In conclusion, PE viscosity determined plasma viscosity after hemodilution and affected erythrocyte column hydrodynamics, changing the velocity profile, CFL thickness, and wall shear stress. This study relates the perfusion caused by PolyHSA60:1 to hemodynamic changes induced by the rheological properties of blood diluted with PolyHSA60:1.

  7. Amphiphilic fullerene/ZnO hybrids as cathode buffer layers to improve charge selectivity of inverted polymer solar cells

    NASA Astrophysics Data System (ADS)

    Hu, Ting; Chen, Lie; Yuan, Kai; Chen, Yiwang

    2015-05-01

    Two types of novel fullerene derivative/ZnO hybrids were prepared by physically blending amphiphilic fullerene-end-capped poly(ethylene glycol) (C60-PEG) with ZnO nanocrystals (ZnO/C60-PEG) and by in situ grown ZnO from C60-PEG (ZnO@C60-PEG) at relatively low temperatures. The C60-PEG could act as n-doping on the ZnO while the PEG side chain of C60-PEG could passivate the defects of the ZnO at the same time, consequently increasing the lowest unoccupied molecular orbital (LUMO) level. Compared with the ZnO/C60-PEG by the physical blend approach, the ZnO@C60-PEG by the growth approach showed a more favorable morphology and higher electron mobility by developing a homogeneous network. As a consequence, the efficiency of the inverted polymer solar cells based on thieno[3,4-b]-thiophene/benzodithiophene (PTB7):[6,6]-phenyl C71-butyric acid methyl ester (PC71BM) is raised to 8.0% for the ZnO@C60-PEG cathode buffer layer and to 7.5% for the ZnO/C60-PEG cathode buffer layer with improved long-term stability.Two types of novel fullerene derivative/ZnO hybrids were prepared by physically blending amphiphilic fullerene-end-capped poly(ethylene glycol) (C60-PEG) with ZnO nanocrystals (ZnO/C60-PEG) and by in situ grown ZnO from C60-PEG (ZnO@C60-PEG) at relatively low temperatures. The C60-PEG could act as n-doping on the ZnO while the PEG side chain of C60-PEG could passivate the defects of the ZnO at the same time, consequently increasing the lowest unoccupied molecular orbital (LUMO) level. Compared with the ZnO/C60-PEG by the physical blend approach, the ZnO@C60-PEG by the growth approach showed a more favorable morphology and higher electron mobility by developing a homogeneous network. As a consequence, the efficiency of the inverted polymer solar cells based on thieno[3,4-b]-thiophene/benzodithiophene (PTB7):[6,6]-phenyl C71-butyric acid methyl ester (PC71BM) is raised to 8.0% for the ZnO@C60-PEG cathode buffer layer and to 7.5% for the ZnO/C60-PEG cathode buffer layer

  8. Magnetic anisotropy of crystalline Fe films grown on (001) GaAs substrates using Ge buffer layers

    NASA Astrophysics Data System (ADS)

    Bac, Seul-Ki; Lee, Hakjoon; Lee, Sangyeop; Choi, Seonghoon; Yoo, Taehee; Lee, Sanghoon; Liu, X.; Furdyna, J. K.

    2016-05-01

    Magnetic anisotropy of Fe films grown on (001) GaAs substrates using Ge buffer layers were investigated by planar Hall effect measurements. In addition to phenomena arising from dominant cubic symmetry of the Fe specimen, the study of angular dependence of magnetization reversal revealed breaking of this symmetry in the form of systematic asymmetric shifts of magnetic hysteresis loops around the <110 > crystallographic directions. We ascribe such symmetry breaking to an admixture of uniaxial anisotropy associated with the [100] direction in the Fe film. To determine the parameters associated with this uniaxial anisotropy, we quantitatively analyze the asymmetric shifts of the hysteresis loop centers from the <110 > directions. Even though the value of these parameters turns out to be relatively small compared to that of the cubic anisotropy (by about two orders of magnitude), they survive up to room temperature.

  9. 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).

  10. Solvent effects of a dimethyldicyanoquinonediimine buffer layer as N-type material on the performance of organic photovoltaic cells.

    PubMed

    Yang, Eui Yeol; Oh, Se Young

    2014-08-01

    In the present work, we have fabricated organic photovoltaic cells consisting of ITO/PEDOT:PSS/P3HT:PCBM/DMDCNQI/Al using a dip-coating method with various solvent systems. We have investigated solvent effects (such as solubility, viscosity and vapor pressure) in deposition of a thin DMDCNQI buffer layer on the performance of organic photovoltaic cells. The solvent system which had low viscosity and good solubility properties, made a dense and uniform DMDCNQI ultra thin film, resulting in a high performance device. In particular, a prepared organic photovoltaic cell was fabricated using a cosolvent system (methanol:methylenechloride = 3:1) and showed a maximum power conversion efficiency of 4.53%.

  11. 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.

  12. 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.

  13. 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.

  14. Field electron emission of layered Bi2Se3 nanosheets with atom-thick sharp edges

    NASA Astrophysics Data System (ADS)

    Huang, Huihui; Li, Yuan; Li, Qi; Li, Borui; Song, Zengcai; Huang, Wenxiao; Zhao, Chujun; Zhang, Han; Wen, Shuangchun; Carroll, David; Fang, Guojia

    2014-06-01

    Field electron emission properties of solution processed few-layer Bi2Se3 nanosheets are studied for the first time, which exhibit a low turn-on field of 2.3 V μm-1, a high field enhancement factor of up to 6860 and good field emission stability. This performance is better than that of the as reported layered MoS2f sheets and is comparable to that of single layer graphene films. The efficient field emission behaviours are found to be not only attributed to their lower work function but also related to their numerous sharp edges or protrusion decorated structure based on our simulation results. Besides, the contribution of possible two-dimensional electron gas surface states of atom-thick layered Bi2Se3 nanosheets is discussed in this paper. We anticipate that these solution processed layered Bi2Se3 nanosheets have great potential as robust high-performance vertical structure electron emitters for future light weight and highly flexible vacuum micro/nano-electronic device applications.Field electron emission properties of solution processed few-layer Bi2Se3 nanosheets are studied for the first time, which exhibit a low turn-on field of 2.3 V μm-1, a high field enhancement factor of up to 6860 and good field emission stability. This performance is better than that of the as reported layered MoS2f sheets and is comparable to that of single layer graphene films. The efficient field emission behaviours are found to be not only attributed to their lower work function but also related to their numerous sharp edges or protrusion decorated structure based on our simulation results. Besides, the contribution of possible two-dimensional electron gas surface states of atom-thick layered Bi2Se3 nanosheets is discussed in this paper. We anticipate that these solution processed layered Bi2Se3 nanosheets have great potential as robust high-performance vertical structure electron emitters for future light weight and highly flexible vacuum micro/nano-electronic device applications

  15. Air processed organic photovoltaic devices incorporating a MoOx anode buffer layer

    NASA Astrophysics Data System (ADS)

    Bovill, Edward S. R.; Griffin, Jonathan; Wang, Tao; Kingsley, James W.; Yi, Hunan; Iraqi, Ahmed; Buckley, Alastair R.; Lidzey, David G.

    2013-05-01

    Molybdenum oxide (MoOx) has been shown to act as an efficient hole extraction layer in organic photovoltaic (OPV) devices. However, exposing MoOx films to air is problematic as it is hygroscopic; the uptake of moisture having a negative impact on its electronic properties. Here, we use spectroscopic ellipsometry to characterise the uptake of water, and fabricate PCDTBT:PC70BM based OPVs to determine its effects on device performance. We then show that thermally annealing MoOx reduces its hygroscopicity, permitting it to be processed in air. Using this process, we create air-processsed OPVs having PCEs (power conversion efficiencies) of up to 5.36%.

  16. 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.

  17. 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.

  18. Effect of thermal annealing treatment with titanium chelate on buffer layer in inverted polymer solar cells

    NASA Astrophysics Data System (ADS)

    Liu, Zhiyong; Wang, Ning; Fu, Yan

    2016-12-01

    The solution processable electron extraction layer (EEL) is crucial for polymer solar cells (PSCs). Here, we investigated titanium (diisopropoxide) bis(2,4-pentanedionate) (TIPD) as an EEL and fabricated inverted PSCs with a blend of poly(3-hexylthiophene) (P3HT) and indene-C60 bisadduct (ICBA) acting as the photoactive layer, with a structure of ITO/TIPD/P3HT:ICBA/MoO3/Ag. After thermal annealing treatment at 150 °C for 15 min, the PSC performances increased from 3.85% to 6.84% and they achieve stable power conversion efficiency (PCE), with a similar PCE compared with TiO2 as an EEL by the vacuum evaporated method. Fourier transform infrared spectroscopy (FTIR) and ultraviolet photoelectron spectroscopy (UPS) confirmed that the TIPD decomposed and formed the Tidbnd O bond, and the energy level of the lowest unoccupied molecular orbital and the highest occupied molecular orbital increased. The space charge limited current (SCLC) measurements further confirmed the improvement in electron collection and the transport ability using TIPD as the EEL and thermal annealing.

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

    PubMed Central

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

    2016-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-10-01

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

  1. Impact of layer thickness and well orientation on caprock integrity for geologic carbon storage

    DOE PAGES

    Newell, P.; Martinez, M. J.; Eichhubl, P.

    2016-07-29

    Economic feasibility of geologic carbon storage demands sustaining large storage rates without damaging caprock seals. Reactivation of pre-existing or newly formed fractures may provide a leakage pathway across caprock layers. In this paper, we apply an equivalent continuum approach within a finite element framework to model the fluid-pressure-induced reactivation of pre-existing fractures within the caprock, during high-rate injection of super-critical CO2 into a brine-saturated reservoir in a hypothetical system, using realistic geomechanical and fluid properties. We investigate the impact of reservoir to caprock layer thickness, wellbore orientation, and injection rate on overall performance of the system with respect to caprockmore » failure and leakage. We find that vertical wells result in locally higher reservoir pressures relative to horizontal injection wells for the same injection rate, with high pressure inducing caprock leakage along reactivated opening-mode fractures in the caprock. After prolonged injection, leakage along reactivated fractures in the caprock is always higher for vertical than horizontal injection wells. Furthermore, we find that low ratios of reservoir to caprock thickness favor high excess pressure and thus fracture reactivation in the caprock. Finally, injection into thick reservoir units thus lowers the risk associated with CO2 leakage.« less

  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. Weakly nonlinear Rayleigh-Taylor instability of a finite-thickness fluid layer

    NASA Astrophysics Data System (ADS)

    Wang, L. F.; Guo, H. Y.; Wu, J. F.; Ye, W. H.; Liu, Jie; Zhang, W. Y.; He, X. T.

    2014-12-01

    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.

  4. Facile synthesis of few-layer graphene with a controllable thickness using rapid thermal annealing.

    PubMed

    Chu, Jae Hwan; Kwak, Jinsung; Kwon, Tae-Yang; Park, Soon-Dong; Go, Heungseok; Kim, Sung Youb; Park, Kibog; Kang, Seoktae; Kwon, Soon-Yong

    2012-03-01

    Few-layer graphene films with a controllable thickness were grown on a nickel surface by rapid thermal annealing (RTA) under vacuum. The instability of nickel films in air facilitates the spontaneous formation of ultrathin (<2-3 nm) carbon- and oxygen-containing compounds on a nickel surface; thus, the high-temperature annealing of the nickel samples without the introduction of intentional carbon-containing precursors results in the formation of graphene films. From annealing temperature and ambient studies during RTA, it was found that the evaporation of oxygen atoms from the surface is the dominant factor affecting the formation of graphene films. The thickness of the graphene layers is strongly dependent on the RTA temperature and time, and the resulting films have a limited thickness (<2 nm), even for an extended RTA time. The transferred films have a low sheet resistance of ~0.9 ± 0.4 kΩ/sq, with ~94% ± 2% optical transparency, making them useful for applications as flexible transparent conductors.

  5. Impact of layer thickness and well orientation on caprock integrity for geologic carbon storage

    SciTech Connect

    Newell, P.; Martinez, M. J.; Eichhubl, P.

    2016-07-29

    Economic feasibility of geologic carbon storage demands sustaining large storage rates without damaging caprock seals. Reactivation of pre-existing or newly formed fractures may provide a leakage pathway across caprock layers. In this paper, we apply an equivalent continuum approach within a finite element framework to model the fluid-pressure-induced reactivation of pre-existing fractures within the caprock, during high-rate injection of super-critical CO2 into a brine-saturated reservoir in a hypothetical system, using realistic geomechanical and fluid properties. We investigate the impact of reservoir to caprock layer thickness, wellbore orientation, and injection rate on overall performance of the system with respect to caprock failure and leakage. We find that vertical wells result in locally higher reservoir pressures relative to horizontal injection wells for the same injection rate, with high pressure inducing caprock leakage along reactivated opening-mode fractures in the caprock. After prolonged injection, leakage along reactivated fractures in the caprock is always higher for vertical than horizontal injection wells. Furthermore, we find that low ratios of reservoir to caprock thickness favor high excess pressure and thus fracture reactivation in the caprock. Finally, injection into thick reservoir units thus lowers the risk associated with CO2 leakage.

  6. 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

  7. Growth of thick GaN layers on laser-processed sapphire substrate by hydride vapor phase epitaxy

    NASA Astrophysics Data System (ADS)

    Koyama, Koji; Aida, Hideo; Kim, Seong-Woo; Ikejiri, Kenjiro; Doi, Toshiro; Yamazaki, Tsutomu

    2014-10-01

    A 600 μm thick GaN layer was successfully grown by hydride vapor phase epitaxy by replacing the standard sapphire substrate with that processed by a focused laser beam within the substrate. The effects of the laser processing on the curvature and cracking of the GaN layer were investigated. Microscopic observations of the interior of the thick GaN layer revealed that the laser-processed substrate suppressed the generation of microcracks in the GaN layer. In addition, the laser processing was also found to reduce the change in the curvature during the GaN layer growth in comparison to that on the standard substrate. It is shown that the overlapping microcracks observed in the GaN layer on the standard sapphire substrate lead to serious cracking after thick GaN layer growth.

  8. 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.

  9. 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.

  10. Retinal nerve fiber layer thickness in prematurity is correlated with stage of retinopathy of prematurity

    PubMed Central

    Park, K-A; Oh, S Y

    2015-01-01

    Purpose To compare retinal nerve fiber layer (RNFL) thickness profiles between preterm and full-term children and to investigate factors affecting the RNFL distribution in preterm children. Methods We performed Spectral domain optical coherence tomography (SD-OCT) peripapillary RNFL circular scan centered on the optic disc in 50 premature and 58 full-term children. RNFL thickness profiles were compared between preterm and full-term children using a linear regression model. Among preterm patients in this study, 20 patients previously received laser treatment for severe retinopathy of prematurity (ROP). Results Global average, nasal, and superior disc RNFL thickness profiles were significantly smaller in preterm children (92.70±16.57 μm, 56.02±17.04 μm, and 108.74±27.36 μm, respectively) compared with full-term children (101.63±9.21 μm, P=0.006, 69.14±14.15 μm, P<0.001, and superior, 129.11±18.14 μm, P<0.001, respectively). Multivariable analysis revealed that ROP stage was inversely correlated with nasal RNFL thickness (P=0.010). Conclusions Our SD-OCT data demonstrate decreased global average, nasal, and superior disc RNFL thicknesses in preterm children. ROP stage was inversely correlated with nasal RNFL thickness. Further studies are needed to better understand the association between these structural changes and visual functions in preterm children. PMID:26403327

  11. Effect of suction on macular thickness and retinal nerve fiber layer thickness during LASIK used femtosecond laser and Moria M2 microkeratome

    PubMed Central

    Zhang, Jing; Zhou, Yue-Hua

    2015-01-01

    AIM To compare the effect of suction on the macular thickness and retinal nerve fiber layer (RNFL) thickness during laser in situ keratomileusis (LASIK) used Ziemer FEMTO LDV femtosecond laser (Ziemer group) and Moria M2 automated microkeratome (Moria group) for flap creation. METHODS Fourier-domain optical coherence tomography (FD-OCT) was used to measure macular thickness, ganglion cell complex thickness and (RNFL) thickness of 204 eyes of 102 patients with the Ziemer femtosecond laser (102 eyes) and the Moria M2 microkeratome (102 eyes) before surgery and 30min; 1, 3d; 1wk; 1, 3mo; 1y after surgery. RESULTS The average foveal thickness and parafoveal retinal thickness 30min after the surgery were statistically more than that before surgery (Ziemer P<0.001, P=0.003 and Moria P=0.001, P=0.006) and the effect was less in the Ziemer group than that in the Moria group (P all<0.05). The ganglion cell complex thickness was not significantly changed in both groups (P all>0.05). The RNFL thickness was statistically less 30min after surgery in both groups (P=0.014, P<0.001), but the influence was less in Ziemer group than that in Moria group (P=0.038). However, the RNFL thickness had recovered to the preoperative level only 1d after surgery. CONCLUSION The suction of femtosecond laser and mechanical microkeratome led to the increase in macular central fovea thickness and the decrease in RNFL thickness values at the early stage after LASIK. The effect of suction on macular and the RNFL thicknesses in Ziemer group is smaller than that in Moria group. PMID:26309879

  12. Metal ferroelectric insulator Si devices using HfTaO buffer layers

    NASA Astrophysics Data System (ADS)

    Lu, Xu-bing; Maruyama, Kenji; Ishiwara, Hiroshi

    2008-04-01

    Metal-ferroelectric-insulator-Si (MFIS) diodes and transistors using Pt/Sr0.8Bi2.2Ta2O9 (SBT)/HfTaO/Si gate structures were fabricated. HfTaO films were deposited at room temperature by electron beam evaporation under a background vacuum of ~1.5 × 10-9 Torr. By process optimization of post-deposition annealing, a small effective oxide thickness of 1.6 nm, a small leakage current of 2.4 × 10-4 A cm-2 at a voltage shifted from the flat band voltage by 1 V and a negligible hysteresis loop were obtained for Al/HfTaO (4 nm)/Si diodes. The MFIS diodes were fabricated by the deposition of SBT films on the HfTaO (4 nm)/Si substrate using chemical solution deposition. A memory window of 0.62 V was obtained for Pt/SBT (300 nm)/HfTaO (4 nm)/Si diodes for a voltage sweep between +4 V and -4 V. P-channel ferroelectric-gate transistors were fabricated using the same gate structure, which showed a memory window of 0.6 V and good long-term retention characteristics. A drain current ON/OFF ratio as high as 103 was attained at a fixed reading voltage of -0.7 V even after over 104 s has elapsed.

  13. RF-MBE growth of cubic AlN on MgO (001) substrates via 2-step c-GaN buffer layer

    NASA Astrophysics Data System (ADS)

    Kakuda, M.; Morikawa, S.; Kuboya, S.; Katayama, R.; Yaguchi, H.; Onabe, K.

    2013-09-01

    We fabricated cubic AlN (c-AlN) films on MgO (001) substrates via 2-step c-GaN buffer layer by radio-frequency-plasma-assisted molecular beam epitaxy (RF-MBE). The effect of low temperature c-GaN buffer layer on the surface flatness and crystal quality of c-AlN was investigated by AFM and XRD reciprocal space mapping analysis. We examined optical properties of the c-AlN film by spectroscopic ellipsometry. The absorption edge by the direct transition of the c-AlN film was 5.95 eV caused by the hexagonal phase incorporation.

  14. Effects of Varied Cleaning Methods on Ni-5% W Substrate for Dip-Coating of Water-based Buffer Layers: An X-ray Photoelectron Spectroscopy Study

    PubMed Central

    Narayanan, Vyshnavi; Bruneel, Els; Hühne, Ruben; van Driessche, Isabel

    2012-01-01

    This work describes various combinations of cleaning methods involved in the preparation of Ni-5% W substrates for the deposition of buffer layers using water-based solvents. The substrate has been studied for its surface properties using X-ray photoelectron spectroscopy (XPS). The contaminants in the substrates have been quantified and the appropriate cleaning method was chosen in terms of contaminants level and showing good surface crystallinity to further consider them for depositing chemical solution-based buffer layers for Y1Ba2Cu3Oy (YBCO) coated conductors.

  15. Thickness related textural properties of retinal nerve fiber layer in color fundus images.

    PubMed

    Odstrcilik, Jan; Kolar, Radim; Tornow, Ralf-Peter; Jan, Jiri; Budai, Attila; Mayer, Markus; Vodakova, Martina; Laemmer, Robert; Lamos, Martin; Kuna, Zdenek; Gazarek, Jiri; Kubena, Tomas; Cernosek, Pavel; Ronzhina, Marina

    2014-09-01

    Images of ocular fundus are routinely utilized in ophthalmology. Since an examination using fundus camera is relatively fast and cheap procedure, it can be used as a proper diagnostic tool for screening of retinal diseases such as the glaucoma. One of the glaucoma symptoms is progressive atrophy of the retinal nerve fiber layer (RNFL) resulting in variations of the RNFL thickness. Here, we introduce a novel approach to capture these variations using computer-aided analysis of the RNFL textural appearance in standard and easily available color fundus images. The proposed method uses the features based on Gaussian Markov random fields and local binary patterns, together with various regression models for prediction of the RNFL thickness. The approach allows description of the changes in RNFL texture, directly reflecting variations in the RNFL thickness. Evaluation of the method is carried out on 16 normal ("healthy") and 8 glaucomatous eyes. We achieved significant correlation (normals: ρ=0.72±0.14; p≪0.05, glaucomatous: ρ=0.58±0.10; p≪0.05) between values of the model predicted output and the RNFL thickness measured by optical coherence tomography, which is currently regarded as a standard glaucoma assessment device. The evaluation thus revealed good applicability of the proposed approach to measure possible RNFL thinning.

  16. 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

  17. Macular and retinal nerve fiber layer thickness in Japanese measured by Stratus optical coherence tomography.

    PubMed

    Oshitari, Toshiyuki; Hanawa, Katsuhiro; Adachi-Usami, Emiko

    2007-06-01

    The purpose of this study was to determine the thickness of the macula and the retinal nerve fiber layer (RNFL) in Japanese subjects by Stratus optical coherence tomography (OCT), and to compare the findings with the normative data of subjects from the United States of America (USA). Sixty-one eyes from 31 healthy subjects were used for the measurement of the macular thickness, and 60 eyes from 30 healthy subjects were used for the RNFL thickness measurements. The values obtained from the Japanese subjects were compared with the corresponding values in healthy subjects from the USA. The superior, nasal, temporal, and inferior macular sectors and the mean and inferior areas of the RNFL in the Japanese subjects were significantly thicker than the corresponding areas of normal subjects in the USA (272 +/- 13 vs 255 +/- 17 mum, 274 +/- 12 vs 267 +/- 16 mum, 262 +/- 12 vs 251 +/- 13 mum, 268 +/- 13 vs 260 +/- 15 mum; p < 0.0001, 104 +/- 11 vs 100 +/- 12 mum, 134 +/- 20 vs. 126 +/- 18 mum; p = 0.0167, 0.0047, respectively). In conclusion, the significantly thicker macular regions and RNFL in the Japanese indicate not only that there are racial differences in retinal thicknesses but also that the normative values provided by the Stratus OCT should not be used for different races.

  18. Magnetohydrodynamic effects on a charged colloidal sphere with arbitrary double-layer thickness

    NASA Astrophysics Data System (ADS)

    Hsieh, Tzu H.; Keh, Huan J.

    2010-10-01

    An analytical study is presented for the magnetohydrodynamic (MHD) effects on a translating and rotating colloidal sphere in an arbitrary electrolyte solution prescribed with a general flow field and a uniform magnetic field at a steady state. The electric double layer surrounding the charged particle may have an arbitrary thickness relative to the particle radius. Through the use of a simple perturbation method, the Stokes equations modified with an electric force term, including the Lorentz force contribution, are dealt by using a generalized reciprocal theorem. Using the equilibrium double-layer potential distribution from solving the linearized Poisson-Boltzmann equation, we obtain closed-form formulas for the translational and angular velocities of the spherical particle induced by the MHD effects to the leading order. It is found that the MHD effects on the particle movement associated with the translation and rotation of the particle and the ambient fluid are monotonically increasing functions of κa, where κ is the Debye screening parameter and a is the particle radius. Any pure rotational Stokes flow of the electrolyte solution in the presence of the magnetic field exerts no MHD effect on the particle directly in the case of a very thick double layer (κa →0). The MHD effect caused by the pure straining flow of the electrolyte solution can drive the particle to rotate, but it makes no contribution to the translation of the particle.

  19. Interfacial properties of hydrophilized poly(lactic-co-glycolic acid) layers with various thicknesses.

    PubMed

    Gyulai, G; Pénzes, Cs B; Mohai, M; Lohner, T; Petrik, P; Kurunczi, S; Kiss, É

    2011-10-15

    Biodegradable polyesters such as poly(lactic-co-glycolic acid) copolymers (PLGA) are preferred materials for drug carrier systems although their surface hydrophobicity greatly limits their use in controlled drug delivery. PLGA thin films on a solid support blended with PEG-containing compound (Pluronic) were used as model systems to study the interfacial interactions with aqueous media. Degree of surface hydrophilization was assessed by wettability, and X-ray photoelectron spectroscopy (XPS) measurements. Protein adsorption behavior was investigated by in situ spectroscopic ellipsometry. The degree of protein adsorption showed a good correlation with the hydrophilicity, and surface composition. Unexpectedly, the layer thickness was found to have a great impact on the interfacial characteristics of the polymer films in the investigated regime (20-200 nm). Thick layers presented higher hydrophilicity and great resistance to protein adsorption. That special behavior was explained as the result of the swelling of the polymer film combined with the partial dissolution of Pluronic from the layer. This finding might promote the rational design of surface modified biocompatible nanoparticles.

  20. Endoscopic full-thickness resection for gastric submucosal tumors arising from the muscularis propria layer

    PubMed Central

    Huang, Liu-Ye; Cui, Jun; Lin, Shu-Juan; Zhang, Bo; Wu, Cheng-Rong

    2014-01-01

    AIM: To evaluate the efficacy, safety and feasibility of endoscopic full-thickness resection (EFR) for the treatment of gastric submucosal tumors (SMTs) arising from the muscularis propria. METHODS: A total of 35 gastric SMTs arising from the muscularis propria layer were resected by EFR between January 2010 and September 2013. EFR consists of five major steps: injecting normal saline into the submucosa; pre-cutting the mucosal and submucosal layers around the lesion; making a circumferential incision as deep as the muscularis propria around the lesion using endoscopic submucosal dissection and an incision into the serosal layer around the lesion with a Hook knife; a full-thickness resection of the tumor, including the serosal layer with a Hook or IT knife; and closing the gastric wall with metallic clips. RESULTS: Of the 35 gastric SMTs, 14 were located at the fundus, and 21 at the corpus. EFR removed all of the SMTs successfully, and the complete resection rate was 100%. The mean operation time was 90 min (60-155 min), the mean hospitalization time was 6.0 d (4-10 d), and the mean tumor size was 2.8 cm (2.0-4.5 cm). Pathological examination confirmed the presence of gastric stromal tumors in 25 patients, leiomyomas in 7 and gastric autonomous nerve tumors in 2. No gastric bleeding, peritonitis or abdominal abscess occurred after EFR. Postoperative contrast roentgenography on the third day detected no contrast extravasation into the abdominal cavity. The mean follow-up period was 6 mo, with no lesion residue or recurrence noted. CONCLUSION: EFR is efficacious, safe and minimally invasive for patients with gastric SMTs arising from the muscularis propria layer. This technique is able to resect deep gastric lesions while providing precise pathological information about the lesion. With the development of EFR, the indications of endoscopic resection might be extended. PMID:25320536

  1. What is the copper thin film thickness effect on thermal properties of NiTi/Cu bi-layer?

    NASA Astrophysics Data System (ADS)

    Fazeli, Sara; Vahedpour, Morteza; Khatiboleslam Sadrnezhaad, Sayed

    2017-02-01

    Molecular dynamics (MD) simulation was used to study of thermal properties of NiTi/Cu. Embedded atom method (EAM) potentials for describing of inter-atomic interaction and Nose–Hoover thermostat and barostat are employed. The melting of the bi-layers was considered by studying the temperature dependence of the cohesive energy and mean square displacement. To highlight the differences between bi-layers with various copper layer thickness, the effect of copper film thickness on thermal properties containing the cohesive energy, melting point, isobaric heat capacity and latent heat of fusion was estimated. The results show that thermal properties of bi-layer systems are higher than that of their corresponding of pure NiTi. But, these properties of bi-layer systems approximately are independent of copper film thicknesses. The mean square displacement (MSD) results show that, the diffusion coefficients enhance upon increasing of copper film thickness in a linear performance.

  2. The direct growth of SrTiO 3 (100) layers on silicon (100) substrates; application as a buffer layer for the growth of DyBa 2Cu 3O 7- δ thin films

    NASA Astrophysics Data System (ADS)

    Méchin, L.; Gerritsma, G. J.; Garcia Lopez, J.

    1999-10-01

    Highly (100)-oriented SrTiO 3 thin films were sputtered on Si (100) substrates. After the optimization of the deposition conditions, the fraction of (110)-oriented material in the SrTiO 3 films was about 3%, but the rocking curve of the SrTiO 3 (200) peak was quite large (full width at half maximum (FWHM) ∼2.3°). Indeed grain boundaries crossing the whole SrTiO 3 film and an amorphous layer between Si and SrTiO 3 could be observed by transmission electron microscopy. DyBa 2Cu 3O 7- δ (DBCO) films were successively sputtered on the polycrystalline SrTiO 3 layers on Si. An Auger analysis revealed the presence of barium at the Si/SrTiO 3 interface that presumably diffused along the grain boundaries through SrTiO 3 to form barium silicates. By reducing both the DBCO deposition temperature and the SrTiO 3 thickness, we could prevent this diffusion and improve the electrical properties ( R300/ R100∼1 and Tc ( R=0) in the 40-60 K range). The specific problems for the growth of DBCO thin film on SrTiO 3-buffered silicon substrates by sputter deposition are finally pointed out.

  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. In-plane thermal conductivity of sub-20 nm thick suspended mono-crystalline Si layers

    NASA Astrophysics Data System (ADS)

    Ferrando-Villalba, P.; Lopeandia, A. F.; Abad, Ll; Llobet, J.; Molina-Ruiz, M.; Garcia, G.; Gerbolès, M.; Alvarez, F. X.; Goñi, A. R.; Muñoz-Pascual, F. J.; Rodríguez-Viejo, J.

    2014-05-01

    We measure the thermal conductivity of a 17.5-nm-thick single crystalline Si layer by using a suspended structure developed from a silicon-on-insulator wafer, in which the Si layer bridges the suspended platforms. The obtained value of 19 Wm-1 K-1 at room temperature represents a tenfold reduction with respect to bulk Si. This design paves the way for subsequent lateral nanostructuration of the layer with lithographic techniques, to define different geometries such as Si nanowires, nanostrips or phononic grids. As a proof of concept, nanostrips of 0.5 × 10 μm have been defined by focused ion beam (FIB) in the ultrathin Si layer. After the FIB cutting process with Ga ions at 30 kV and 100 pA, the measured thermal conductivity dramatically decreased to 1.7 Wm-1 K-1, indicating that the structure became severely damaged (amorphous). Re-crystallization of the structure was promoted by laser annealing while monitoring the Raman spectra. The thermal conductivity of the layer increased again to a value of 9.5 Wm-1 K-1 at room temperature, below that of the single crystalline material due to phonon scattering at the grain boundaries.

  5. 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.

  6. In-plane thermal conductivity of sub-20 nm thick suspended mono-crystalline Si layers.

    PubMed

    Ferrando-Villalba, P; Lopeandia, A F; Abad, Ll; Llobet, J; Molina-Ruiz, M; Garcia, G; Gerbolès, M; Alvarez, F X; Goñi, A R; Muñoz-Pascual, F J; Rodríguez-Viejo, J

    2014-05-09

    We measure the thermal conductivity of a 17.5-nm-thick single crystalline Si layer by using a suspended structure developed from a silicon-on-insulator wafer, in which the Si layer bridges the suspended platforms. The obtained value of 19 Wm(-1) K(-1) at room temperature represents a tenfold reduction with respect to bulk Si. This design paves the way for subsequent lateral nanostructuration of the layer with lithographic techniques, to define different geometries such as Si nanowires, nanostrips or phononic grids. As a proof of concept, nanostrips of 0.5 × 10 μm have been defined by focused ion beam (FIB) in the ultrathin Si layer. After the FIB cutting process with Ga ions at 30 kV and 100 pA, the measured thermal conductivity dramatically decreased to 1.7 Wm(-1) K(-1), indicating that the structure became severely damaged (amorphous). Re-crystallization of the structure was promoted by laser annealing while monitoring the Raman spectra. The thermal conductivity of the layer increased again to a value of 9.5 Wm(-1) K(-1) at room temperature, below that of the single crystalline material due to phonon scattering at the grain boundaries.

  7. 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

    2015-12-09

    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.

  8. 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.

  9. 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.

  10. Thin-film encapsulation of organic electronic devices based on vacuum evaporated lithium fluoride as protective buffer layer

    NASA Astrophysics Data System (ADS)

    Peng, Yingquan; Ding, Sihan; Wen, Zhanwei; Xu, Sunan; Lv, Wenli; Xu, Ziqiang; Yang, Yuhuan; Wang, Ying; Wei, Yi; Tang, Ying

    2017-03-01

    Encapsulation is indispensable for organic thin-film electronic devices to ensure reliable operation and long-term stability. For thin-film encapsulating organic electronic devices, insulating polymers and inorganic metal oxides thin films are widely used. However, spin-coating of insulating polymers directly on organic electronic devices may destroy or introduce unwanted impurities in the underlying organic active layers. And also, sputtering of inorganic metal oxides may damage the underlying organic semiconductors. Here, we demonstrated that by utilizing vacuum evaporated lithium fluoride (LiF) as protective buffer layer, spin-coated insulating polymer polyvinyl alcohol (PVA), and sputtered inorganic material Er2O3, can be successfully applied for thin film encapsulation of copper phthalocyanine (CuPc)-based organic diodes. By encapsulating with LiF/PVA/LiF trilayer and LiF/Er2O3 bilayer films, the device lifetime improvements of 10 and 15 times can be achieved. These methods should be applicable for thin-film encapsulation of all kinds of organic electronic devices. Moisture-induced hole trapping, and Al top electrode oxidation are suggest to be the origins of current decay for the LiF/PVA/LiF trilayer and LiF/Er2O3 bilayer films encapsulated devices, respectively.

  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. 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. 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.

  14. Charge trapping properties of the HfO2 layer with various thicknesses for charge trap flash memory applications

    NASA Astrophysics Data System (ADS)

    You, Hee-Wook; Cho, Won-Ju

    2010-03-01

    MHOS (metal-HfO2-SiO2-Si) structure capacitors were fabricated to investigate the charge trapping properties of HfO2 layer with various thicknesses for the applications of charge trap flash (CTF) memory devices. Also, the centroid of charge trap in HfO2 layer was extracted by constant current stress method and compared with that of conventional Si3N4 layer. The gate leakage current of MHOS capacitor due to tunneling was significantly reduced by stacking the HfO2 trap layer on thin SiO2 tunnel layer. The MHOS capacitors showed a larger memory window than the MNOS (metal-Si3N4-SiO2-Si) capacitors at the same trap layer thickness, because the HfO2 layer has better charge trapping efficiency than the Si3N4 layer. It is found that ultrathin HfO2 trap layer with a thickness of 2 nm stored almost the same charges with Si3N4 layer with a thickness of 7 nm. Consequently, the application of ultrathin HfO2 to charge storage layer can considerably improve the performance and enhance the high density of CTF memory.

  15. 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.

  16. Longitudinal Change of Circumpapillary Retinal Nerve Fiber Layer Thickness in Children with Optic Pathway Gliomas

    PubMed Central

    Avery, Robert A.; Cnaan, Avital; Schuman, Joel S.; Trimboli-Heidler, Carmelina; Chen, Chieh-Li; Packer, Roger J.; Ishikawa, Hiroshi

    2015-01-01

    Purpose To evaluate longitudinal changes in circumpapillary retinal nerve fiber layer (RNFL) thickness, as measured by spectral-domain optical coherence tomography (SD-OCT), in children with optic pathway gliomas. Design Longitudinal cohort study Methods Global and quadrant specific circumpapillary RNFL thickness measures were acquired using either a hand-held during sedation or a table-top SD-OCT in children old enough to cooperate. Vision loss was defined as either a 0.2 logMAR decline in visual acuity, or progression of visual field. Percent change in circumpapillary RNFL thickness in eyes experiencing vision loss was compared to eyes with stable vision. Results Fifty-five eyes completed two-hundred fifty study visits. Ten eyes (18%) from 7 patients experienced a new episode of vision loss during the study and 45 (82%) eyes from 39 patients demonstrated stable vision across study visits. Percent decline of RNFL thickness between the baseline visit and first event of vision loss event was greatest in the superior (−14%) and inferior (−10%) quadrants as well as global average (−13%). Using a threshold of ≥ 10% decline in RNFL, the positive and negative predictive value for vision loss when two or more anatomic sectors were affected was 100% and 94%, respectively. Conclusions Children experiencing vision loss from their optic pathway gliomas frequently demonstrate a ≥ 10% decline of RNFL thickness in one or more anatomic sectors. Global average and the inferior quadrant demonstrated the best positive and negative predictive values. Circumpapillary RNFL is a surrogate marker of vision and could be helpful in making treatment decisions for children with optic pathway gliomas. PMID:26231306

  17. Comparison of retinal nerve fiber layer thickness in patients having pseudo exfoliation syndrome with healthy adults

    PubMed Central

    Yasmeen, Naila; Fatima, Nauroz; Qamar-ul-Islam

    2016-01-01

    Objective: To compare mean retinal nerve fiber layer (RNFL) thickness in patients having pseudo exfoliation (PXF) with normal age matched controls using spectral domain optical coherence tomography (SD-OCT). Methods: This was a case control study conducted at Armed Forces Institute of Ophthalmology (AFIO) Rawalpindi from 12 June 2013 to 12 January 2014. Seventy eyes (Group A - 35 patients with PXF and Group B - 35 healthy age matched subjects) of more than 40 years of age were included in the study. Intraocular pressure (IOP) was measured with Goldmann applanation tonometer (GAT) and peripapillary RNFL thickness was measured in four quadrants with SD-OCT (Topcon 3D OCT-1000 Mark II) in all subjects. Data was analyzed using the SPSS version 14. Results: Mean age of group A (PXF patients) was 65.63 ± 8.47 years and of group B (Healthy subjects) was 64.31 ± 6.51 years (p = 0.470). Both groups were gender matched with male preponderance (p = 0.673). Mean IOP in each group was 13.80 ± 2.59 mm Hg, and 13.49 ± 2.07 mm Hg respectively (p= 0.578). Mean average peripapillary RNFL thickness was 77.46 ± 12.17 µm in group A and 83.96 ± 10.58 µm in group B. Statistically significant differences were detected between two groups for mean average RNFL thickness (p= 0.020) and mean RNFL thickness in inferior quadrant (p=0.014). Conclusion: PXF patients with normal IOP and visual fields have thin RNFL as compared to healthy age matched controls. Therefore routine assessment and follow up of PXF patients with OCT may help in early diagnosis of PXF glaucoma. PMID:28083059

  18. 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

  19. Resistivity due to weak double layers - A model for auroral arc thickness

    NASA Technical Reports Server (NTRS)

    Prakash, Manju; Lysak, Robert L.

    1992-01-01

    We have calculated the resistivity due to a sequence of fluctuating weak double layers aligned parallel to the ambient magnetic field line. The average response of an electron drifting through a 1D randomly oriented array of WDLs is studied using a test particle approach. The average is taken over the randomly fluctuating values of the electric field associated with the double layers. Based on our calculations, we estimate that a 350 eV electron energy the thickness of the visual auroral arc is about 2.5 km and that of the auroral fine structure as about 250 m when mapped down to the ionosphere. The significance of our calculations is discussed in the context of magnetosphere-ionosphere coupling.

  20. The computation of thick axisymmetric boundary layers and wakes around bodies of revolution

    NASA Astrophysics Data System (ADS)

    Markatos, N. C.

    The paper is concerned with the computational investigation of thick, axisymmetric, turbulent boundary layers and wakes around bodies of revolution. The procedures employed take full account of the influence of longitudinal and transverse surface curvatures and normal pressure gradients on the development of the boundary layer and wake, and also the viscous-inviscid interaction in the tail region of the body. The method makes it possible to calculate the static pressure and the velocity profiles along the body as well as the drag components; and it is applicable to both two- and three-dimensional situations, enabling, for example, the prediction of flows around ships' and submarines' hulls to be made. The application of the fully-elliptic calculation procedure to a body of revolution is described, and comparisons made between predictions and experimental measurements. The calculated axial variation of skin friction and pressure coefficient, and the velocity profiles are shown to be in fair agreement with experimental values.

  1. Properties of PZT thick film made on LTCC substrates with dielectric intermediate layers

    NASA Astrophysics Data System (ADS)

    DÄ browski, Arkadiusz; Golonka, Leszek

    2016-11-01

    Results of experiments on application of various interlayers between LTCC (Low Temperature Cofired Ceramics) substrate and thick-film PZT (Lead Zirconate - Titanate) are described in this work. Thick-film intermediate layers were based on several dielectric materials: TiN, Al2O3, SiC, TiO2, SiC, YSZ, BN. Seven screen printable pastes were prepared on the base of powders of mentioned materials with addition of glass and organic vehicle. The substrates were made of 951 (DuPont), CeramTapeGC (CeramTec) and HL2000 (Heraeus) LTCC tapes. Sandwich type transducers, consisting of barrier layer, gold bottom electrode, PZT layer and silver top electrode were prepared and characterized. Basic piezoelectric parameters - permittivity, effective charge constant (d33(eff)) and remanent polarization were determined. The best properties were obtained for substrates made of 951. In general, interlayers based on TiO2, SiC and Al2O3 improved permittivity and charge constant comparing to bare substrates. For example, for 951 substrate the PZT layer exhibited d33(eff) equal to 160, 215, 250 and 230 pC/N for bare substrate, TiO2 interlayer, SiC interlayer and Al2O3 interlayer, respectively. In case of CeramTape GC substrates determined permittivity was equal to 215, 245, 235 and 275 for bare substrate, TiO2 interlayer, SiC interlayer and Al2O3 interlayer, respectively. In case of TiN and BN materials the parameters were considerably deteriorated.

  2. 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

  3. Auto-assembly of nanometer thick, water soluble layers of plasmid DNA complexed with diamines and basic amino acids on graphite: Greatest DNA protection is obtained with arginine.

    PubMed

    Khalil, T T; Boulanouar, O; Heintz, O; Fromm, M

    2017-02-01

    We have investigated the ability of diamines as well as basic amino acids to condense DNA onto highly ordered pyrolytic graphite with minimum damage after re-dissolution in water. Based on a bibliographic survey we briefly summarize DNA binding properties with diamines as compared to basic amino acids. Thus, solutions of DNA complexed with these linkers were drop-cast in order to deposit ultra-thin layers on the surface of HOPG in the absence or presence of Tris buffer. Atomic Force Microscopy analyses showed that, at a fixed ligand-DNA mixing ratio of 16, the mean thickness of the layers can be statistically predicted to lie in the range 0-50nm with a maximum standard deviation ±6nm, using a simple linear law depending on the DNA concentration. The morphology of the layers appears to be ligand-dependent. While the layers containing diamines present holes, those formed in the presence of basic amino acids, except for lysine, are much more compact and dense. X-ray Photoelectron Spectroscopy measurements provide compositional information indicating that, compared to the maximum number of DNA sites to which the ligands may bind, the basic amino acids Arg and His are present in large excess. Conservation of the supercoiled topology of the DNA plasmids was studied after recovery of the complex layers in water. Remarkably, arginine has the best protection capabilities whether Tris was present or not in the initial solution.

  4. 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

  5. Diagnostic Ability of Retinal Nerve Fiber Layer Thickness Deviation Map for Localized and Diffuse Retinal Nerve Fiber Layer Defects

    PubMed Central

    Shin, Joong Won; Seong, Mincheol; Lee, Jung Wook; Hong, Eun Hee

    2017-01-01

    Purpose. To evaluate the diagnostic ability of the retinal nerve fiber layer (RNFL) deviation map for glaucoma with localized or diffuse RNFL defects. Methods. Eyes of 139 glaucoma patients and 165 healthy subjects were enrolled. All participants were imaged with Cirrus HD-OCT (Carl Zeiss Meditec, Dublin, CA, USA). A RNFL defect was defined as at least 10 contiguous red (<1% level) superpixels in RNFL deviation map. The area, location, and angular width of RNFL defects were automatically measured. We compared sensitivities, specificities, and area under the receiver operating characteristic curves (AUCs) of RNFL deviation map and circumpapillary RNFL thickness for localized and diffuse RNFL defects. Subgroup analysis was performed according to the severity of glaucoma. Results. For localized defects, the area of RNFL defects (AUC, 0.991; sensitivity, 97%; specificity, 90%) in deviation map showed a higher diagnostic performance (p = 0.002) than the best circumpapillary RNFL parameter (inferior RNFL thickness; AUC, 0.914; sensitivity, 79%; specificity, 92%). For diffuse defects, there was no significant difference between the RNFL deviation map and circumpapillary RNFL parameters. In mild glaucoma with localized defect, RNFL deviation map showed a better diagnostic performance than circumpapillary RNFL measurement. Conclusions. RNFL deviation map is a useful tool for evaluating glaucoma regardless of localized or diffuse defect type and has advantages over circumpapillary RNFL measurement for detecting localized RNFL defects. PMID:28168048

  6. 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.

  7. High-efficiency inverted polymer solar cells controlled by the thickness of polyethylenimine ethoxylated (PEIE) interfacial layers.

    PubMed

    Li, Ping; Wang, Gang; Cai, Lun; Ding, Baofu; Zhou, Dachen; Hu, Yi; Zhang, Yujun; Xiang, Jin; Wan, Keming; Chen, Lijia; Alameh, Kamal; Song, Qunliang

    2014-11-21

    In this work, we investigate the effect of the thickness of the polyethylenimine ethoxylated (PEIE) interface layer on the performance of two types of polymer solar cells based on inverted poly(3-hexylthiophene) (P3HT):phenyl C61-butryric acid methyl ester (PCBM) and thieno[3,4-b]thiophene/benzodithiophene (PTB7):[6,6]-phenyl C71-butyric acid methyl ester (PC71BM). Maximum power conversion efficiencies of 4.18% and 7.40% were achieved at a 5.02 nm thick PEIE interface layer, for the above-mentioned solar cell types, respectively. The optimized PEIE layer provides a strong enough dipole for the best charge collection while maintaining charge tunneling ability. Optical transmittance and atomic force microscopy measurements indicate that all PEIE films have the same high transmittance and smooth surface morphology, ruling out the influence of the PEIE layer on these two parameters. The measured external quantum efficiencies for the devices with thick PEIE layers are quite similar to those of the optimized devices, indicating the poor charge collection ability of thick PEIE layers. The relatively low performance of devices with a PEIE layer of thickness less than 5 nm is the result of a weak dipole and partial coverage of the PEIE layer on ITO.

  8. Thickness scaling effect on interfacial barrier and electrical contact to two-dimensional MoS2 layers.

    PubMed

    Li, Song-Lin; Komatsu, Katsuyoshi; Nakaharai, Shu; Lin, Yen-Fu; Yamamoto, Mahito; Duan, Xiangfeng; Tsukagoshi, Kazuhito

    2014-12-23

    Understanding the interfacial electrical properties between metallic electrodes and low-dimensional semiconductors is essential for both fundamental science and practical applications. Here we report the observation of thickness reduction induced crossover of electrical contact at Au/MoS2 interfaces. For MoS2 thicker than 5 layers, the contact resistivity slightly decreases with reducing MoS2 thickness. By contrast, the contact resistivity sharply increases with reducing MoS2 thickness below 5 layers, mainly governed by the quantum confinement effect. We find that the interfacial potential barrier can be finely tailored from 0.3 to 0.6 eV by merely varying MoS2 thickness. A full evolution diagram of energy level alignment is also drawn to elucidate the thickness scaling effect. The finding of tailoring interfacial properties with channel thickness represents a useful approach controlling the metal/semiconductor interfaces which may result in conceptually innovative functionalities.

  9. 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.

  10. Validity of the "thin" and "thick" double-layer assumptions to model streaming currents in porous media

    NASA Astrophysics Data System (ADS)

    Leinov, E.; Jackson, M.

    2012-12-01

    Measurements of the streaming potential component of the spontaneous potential have been used to characterize groundwater flow and subsurface hydraulic properties in numerous studies. Streaming potentials in porous media arise from the electrical double layer which forms at solid-fluid interfaces. The solid surfaces typically become electrically charged, in which case an excess of counter-charge accumulates in the adjacent fluid. If the fluid is induced to flow by an external pressure gradient, then some of the excess charge within the diffuse part of the double layer is transported with the flow, giving rise to a streaming current. Divergence of the streaming current density establishes an electrical potential, termed the streaming potential. Within the diffuse layer, the Poisson-Boltzmann equation is typically used to describe the variation in electrical potential with distance from the solid surface. In many subsurface settings, it is reasonable to assume that the thickness of the diffuse layer is small compared to the pore radius. This is the so-called 'thin double layer assumption', which has been invoked by numerous authors to model streaming potentials in porous media. However, a number of recent papers have proposed a different approach, in which the thickness of the diffuse layer is assumed to be large compared to the pore radius. This is the so-called 'thick double layer assumption' in which the excess charge density within the pore is assumed to be constant and independent of distance from the solid surface. The advantage of both the 'thin' and 'thick' double layer assumptions is that calculation of the streaming current is greatly simplified. However, perhaps surprisingly, the conditions for which these assumptions are valid have not been determined quantitatively, yet they have a significant impact on the interpretation of streaming potential measurements in natural systems. We use a simple capillary tubes to model investigate the validity of the thin

  11. 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.

  12. 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.

  13. 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.

  14. Peripapillary Retinal Nerve Fiber Layer Thickness and the Evolution of Cognitive Performance in an Elderly Population

    PubMed Central

    Méndez-Gómez, Juan Luis; Rougier, Marie-Bénédicte; Tellouck, Laury; Korobelnik, Jean-François; Schweitzer, Cédric; Delyfer, Marie-Noëlle; Amieva, Hélène; Dartigues, Jean-François; Delcourt, Cécile; Helmer, Catherine

    2017-01-01

    Retinal nerve fiber layer (RNFL) thickness is reduced in Alzheimer’s patients. However, whether it is associated with early evolution of cognitive function is unknown. Within 427 participants from the Three-City-Alienor longitudinal population-based cohort, we explored the relationship between peripapillary RNFL thicknesses and the evolution of cognitive performance. RNFL was assessed at baseline by spectral domain optical coherence tomography; cognitive performances were assessed at baseline and at 2 years, with the Mini–Mental State Examination, the Isaacs’ set test, and the Free and Cued Selective Reminding Test (FCSRT). Multivariate linear mixed models were performed. The RNFL was not associated with initial cognitive performance. Nevertheless, a thicker RNFL was significantly associated with a better cognitive evolution over time in the free delayed recall (p = 0.0037) and free + cued delayed recall (p = 0.0043) scores of the FCSRT, particularly in the temporal, superotemporal, and inferotemporal segments. No associations were found with other cognitive tests. The RNFL was associated with changes in scores that assess episodic memory. RNFL thickness could reflect a higher risk of developing cognitive impairment over time. PMID:28373855

  15. Mechanism insight into the effect of I/P buffer layer on the performance of NIP-type hydrogenated microcrystalline silicon solar cells

    NASA Astrophysics Data System (ADS)

    Bai, Lisha; Liu, Bofei; Zhao, Jing; Suo, Song; Hou, Guofu; Zhang, Dekun; Sun, Jian; Wei, Changchun; Zhao, Ying; Zhang, Xiaodan

    2015-05-01

    A simulation and experimental study on the effect of the buffer layer at the I/P interface on the performance of NIP-type hydrogenated microcrystalline silicon (μc-Si:H) single-junction solar cells is presented. Device-quality hydrogenated amorphous silicon (a-Si:H) material as a buffer layer at the I/P interface obviously improves the performance of NIP-type μc-Si:H single-junction solar cells. In addition to the well-known mechanism that an a-Si:H I/P buffer layer can reduce the recombination current density at I/P interfaces, the optically and electrically calibrated simulations and supporting experimental results in this study illustrate that the performance improvement also originates from the mitigation of the electric screening effect due to the reduced defect density at the I/P interfaces, which reinforces the bulk electric field. Integrating an optimized hydrogen profiling strategy and adding a-Si:H I/P buffer layer yielded an initial efficiency of 9.20% for μc-Si:H single-junction solar cells with an active area of 0.27 cm2. This study may provide new ideas of further improving the performance of NIP-type μc-Si:H single-junction solar cells by mitigating the electric screening effect.

  16. Electronic consequences of random layer-thickness fluctuations in AlAs/GaAs superlattices

    NASA Astrophysics Data System (ADS)

    Mäder, Kurt A.; Wang, Lin-Wang; Zunger, Alex

    1995-12-01

    We study the effects of a few types of atomic disorder on the electronic and optical properties of AlAs/GaAs (001) and (111) superlattices: (i) atomic intermixing across the interfaces; (ii) replacing a single monolayer in a superlattice by one containing the opposite atomic type (isoelectronic δ doping); and (iii) random layer-thickness fluctuations in superlattices (SL). Type (i) is an example of lateral disorder, while types (ii) and (iii) are examples of vertical disorder. Using three-dimensional empirical pseudopotential theory and a plane-wave basis, we calculate the band gaps, electronic wave functions, and optical matrix elements for systems containing up to 2000 atoms in the computational unit cell. Spin-orbit interactions are omitted. Computationally much less costly effective-mass calculations are used to evaluate the density of states and eigenstates away from the band edges in vertically disordered SLs. Our main findings are: (i) Chemical intermixing across the interface can significantly shift the SL energy levels and even change the identity (e.g., symmetry) of the conduction-band minimum in AlAs/GaAs SLs; (ii) any amount of thickness fluctuations in SLs leads to band-edge wave-function localization; (iii) these fluctuation-induced bound states will emit photons at energies below the ``intrinsic'' absorption edge (red shift of photoluminescence); (iv) monolayer fluctuations in thick superlattices create a gap level whose energy is pinned at the value produced by a single δ layer with ``wrong'' thickness; (v) (001) AlAs/GaAs SLs with monolayer thickness fluctuations have a direct band gap, while the ideal (001) superlattices are indirect for n<4; (vi) there is no mobility edge for vertical transport in a disordered superlattice, because all the states are localized; however, the density of states retains some of the features of the ordered-superlattice counterpart. We find quantitative agreement with experiments on intentionally disordered SLs [A

  17. Interpretation of Isopycnal Layer Thickness Advection in Terms of Eddy-Topography Interaction

    NASA Astrophysics Data System (ADS)

    Liu, Chuanyu; Koehl, Armin; Stammer, Detlef

    2013-04-01

    Spatially varying amplitude of the eddy isopycnal layer thickness diffusivity Kgm and the layer thickness advection Kgmskew of the modified Gent and McWilliams parameterization are estimated using two different approaches: the adjoint estimation from a global data assimilation system and the inversion calculation according to divergent buoyancy eddy flux-mean buoyancy gradient relation using results from idealized eddy resolving numerical models with various bottom topographies. This work focuses on the properties of Kgmskew. From the adjoint estimation, large Kgmskew values are found along meandering currents and predominantly positive (negative) over the deep ocean and negative (positive) over seamounts in the southern (northern) hemisphere, implying close relation to the 'Neptune effect" parameterization by Holloway in which the eddy induced mean velocity stream function is represented by -fHL, where H is the bottom depth, f the Coriolis parameter and L a length scale. In the inversion calculation, divergent buoyancy eddy fluxes are obtained by removing the rotational components from the total buoyancy eddy fluxes through Helmholtz-Hodge decomposition. Though subject to topographic length scale, the inversed Kgmskew reveals characteristics of both f and H, and interactions with the mean current, inter-confirming the adjoint estimation results. Applying this parameterization for Kgmskew in the general circulation model produces cold domes and anti-cyclonic circulations over seamounts, which reduces common model biases there. By construction, the original thickness advection Kgmskew redistributes potential energy and the original "Neptune effect" parameterization improves potential vorticity conservation, applying the latter into the former as suggested in the present study thus more correctly reproduces the potential vorticity structure over a sloping topography while conserving the total potential energy.

  18. 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.

  19. Fabrication of Sr silicate buffer layer on Si(100) substrate by pulsed laser deposition using a SrO target

    SciTech Connect

    Imanaka, Atsuhiro; Sasaki, Tsubasa; Hotta, Yasushi Satoh, Shin-ichi

    2014-09-01

    The authors fabricated 2 × 1 Sr-reconstructed Si(100) substrates using thin SrO layers, and used them to direct growth of crystalline perovskite oxide on Si. The SrO layers used to reconstruct the Si(100) substrates were grown by pulsed laser deposition from a SrO single crystal target, followed by postdeposition-annealing (PDA) of the SrO/Si(100) structure. In situ observations of reflective high-energy electron diffraction during PDA confirmed a 2 × 1 reconstruction of the Si surface and x-ray photoemission spectroscopy of the annealed samples confirmed the existence of Sr atoms in a silicate phase, which indicated that a 2 × 1 Sr-reconstructed Si surface was achieved. The optimal fabrication conditions were annealing at 720 °C for 1 min and an equivalent SrO layer thickness (ML{sub eq}) of 2.5 ML{sub eq}. The temperature condition was very narrow, at 720 ± 20 °C, for an acceptable product. Subsequently, the authors demonstrated the growth of crystalline SrTiO{sub 3} films on the 2 × 1 Sr-reconstructed Si(100) surfaces.

  20. 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