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Sample records for stacked metallic layers

  1. Complex and Noncentrosymmetric Stacking of Layered Metal Dichalcogenide Materials Created by Screw Dislocations.

    PubMed

    Shearer, Melinda J; Samad, Leith; Zhang, Yi; Zhao, Yuzhou; Puretzky, Alexander; Eliceiri, Kevin W; Wright, John C; Hamers, Robert J; Jin, Song

    2017-03-08

    The interesting and tunable properties of layered metal dichalcogenides heavily depend on their phase and layer stacking. Here, we show and explain how the layer stacking and physical properties of WSe2 are influenced by screw dislocations. A one-to-one correlation of atomic force microscopy and high- and low-frequency Raman spectroscopy of many dislocated WSe2 nanoplates reveals variations in the number and shapes of dislocation spirals and different layer stackings that are determined by the number, rotation, and location of the dislocations. Plates with triangular dislocation spirals form noncentrosymmetric stacking that gives rise to strong second-harmonic generation and enhanced photoluminescence, plates with hexagonal dislocation spirals form the bulk 2H layer stacking commonly observed, and plates containing mixed dislocation shapes have intermediate noncentrosymmetric stackings with mixed properties. Multiple dislocation cores and other complexities can lead to more complex stackings and properties. These previously unobserved properties and layer stackings in WSe2 will be interesting for spintronics and valleytronics.

  2. Low-frequency Raman modes as fingerprints of layer stacking configurations of transition metal dichalcogenides

    NASA Astrophysics Data System (ADS)

    Liang, Liangbo; Puretzky, Alexander; Sumpter, Bobby; Meunier, Vincent; Geohegan, David; David B. Geohegan Team; Vincent Meunier Team

    The tunable optoelectronic properties of stacked two-dimensional (2D) crystal monolayers are determined by their stacking orientation, order, and atomic registry. Atomic-resolution Z-contrast scanning transmission electron microscopy (AR-Z-STEM) can be used to determine the exact atomic registration between different layers in few-layer 2D stacks; however, fast and relatively inexpensive optical characterization techniques are essential for rapid development of the field. Using two- and three-layer MoSe2 and WSe2 crystals synthesized by chemical vapor deposition, we show that the generally unexplored low-frequency (LF) Raman modes (<50 cm-1) that originate from interlayer vibrations can serve as fingerprints to characterize not only the number of layers, but also their stacking configurations [Puretzky and Liang et al, ACS Nano 2015, 9, 6333]. First-principles Raman calculations and group theory analysis corroborate the experimental assignments determined by AR-Z-STEM and show that the calculated LF mode fingerprints are related to the 2D crystal symmetries. Our combined experimental/theoretical work demonstrates the LF Raman modes potentially more effective than HF Raman modes to probe the layer stacking and interlayer interaction for 2D materials. The authors acknowledge support from Eugene P. Wigner Fellowship at the Oak Ridge National Laboratory and the Center for Nanophase Materials Sciences, a DOE Office of Science User Facility.

  3. Low-frequency Raman fingerprints of two-dimensional metal dichalcogenide layer stacking configurations

    SciTech Connect

    Puretzky, Alexander A.; Liang, Liangbo; Li, Xufan; Xiao, Kai; Wang, Kai; Mahjouri-Samani, Masoud; Basile, Leonardo; Idrobo, Juan Carlos; Sumpter, Bobby G.; Meunier, Vincent; Geohegan, David B.

    2015-05-12

    In this study, stacked monolayers of two-dimensional (2D) materials present a new class of hybrid materials with tunable optoelectronic properties determined by their stacking orientation, order, and atomic registry. Atomic-resolution Z-contrast scanning transmission electron microscopy (AR-Z-STEM) and electron energy loss spectroscopy (EELS) can be used to determine the exact atomic registration between different layers, in few-layer 2D stacks, however fast optical characterization techniques are essential for rapid development of the field. Here, using two- and three-layer MoSe2 and WSe2 crystals synthesized by chemical vapor deposition we show that the generally unexplored low frequency (LF) Raman modes (< 50 cm-1) that originate from interlayer vibrations can serve as fingerprints to characterize not only the number of layers, but also their stacking configurations. Ab initio calculations and group theory analysis corroborate the experimental assignments determined by AR-Z-STEM and show that the calculated LF mode fingerprints are related to the 2D crystal symmetries.

  4. Low-Frequency Raman Fingerprints of Two-Dimensional Metal Dichalcogenide Layer Stacking Configurations.

    PubMed

    Puretzky, Alexander A; Liang, Liangbo; Li, Xufan; Xiao, Kai; Wang, Kai; Mahjouri-Samani, Masoud; Basile, Leonardo; Idrobo, Juan Carlos; Sumpter, Bobby G; Meunier, Vincent; Geohegan, David B

    2015-06-23

    The tunable optoelectronic properties of stacked two-dimensional (2D) crystal monolayers are determined by their stacking orientation, order, and atomic registry. Atomic-resolution Z-contrast scanning transmission electron microscopy (AR-Z-STEM) and electron energy loss spectroscopy (EELS) can be used to determine the exact atomic registration between different layers, in few-layer 2D stacks; however, fast optical characterization techniques are essential for rapid development of the field. Here, using two- and three-layer MoSe2 and WSe2 crystals synthesized by chemical vapor deposition, we show that the generally unexplored low frequency (LF) Raman modes (<50 cm(-1)) that originate from interlayer vibrations can serve as fingerprints to characterize not only the number of layers, but also their stacking configurations. Ab initio calculations and group theory analysis corroborate the experimental assignments determined by AR-Z-STEM and show that the calculated LF mode fingerprints are related to the 2D crystal symmetries.

  5. Low-frequency Raman fingerprints of two-dimensional metal dichalcogenide layer stacking configurations

    DOE PAGES

    Puretzky, Alexander A.; Liang, Liangbo; Li, Xufan; ...

    2015-05-12

    In this study, stacked monolayers of two-dimensional (2D) materials present a new class of hybrid materials with tunable optoelectronic properties determined by their stacking orientation, order, and atomic registry. Atomic-resolution Z-contrast scanning transmission electron microscopy (AR-Z-STEM) and electron energy loss spectroscopy (EELS) can be used to determine the exact atomic registration between different layers, in few-layer 2D stacks, however fast optical characterization techniques are essential for rapid development of the field. Here, using two- and three-layer MoSe2 and WSe2 crystals synthesized by chemical vapor deposition we show that the generally unexplored low frequency (LF) Raman modes (< 50 cm-1) thatmore » originate from interlayer vibrations can serve as fingerprints to characterize not only the number of layers, but also their stacking configurations. Ab initio calculations and group theory analysis corroborate the experimental assignments determined by AR-Z-STEM and show that the calculated LF mode fingerprints are related to the 2D crystal symmetries.« less

  6. Preparation of Cu2ZnSnSe4 thin films by selenization of stacked metallic layers

    NASA Astrophysics Data System (ADS)

    Huang, Hou-Ying; Liu, Shang-En

    2013-12-01

    A Cu2ZnSnSe4 (CZTSe) thin film fabricated by selenization of stacked pure metal precursors through e-beam evaporation on Mo-coated soda lime glass substrates worked as thin film solar cell absorber. The selenization was carried out under element Se vapor circumstance at 570 °C for 20 min. The absorber went through chemical bath CdS deposition, sputtered ZnO, ITO and Al electrodes to become a solar cell. Unlike previous works, only simple three-layer metal precursors without any compound were used as evaporation sources. The synthesized CZTSe absorber layer phase was identified by X-ray diffraction. The solar cells were measured by AAA class solar simulator. The absorber layer thickness was measured by scanning electron microscope (SEM). Energy dispersive spectrometer (EDS) was also used for checking metal ratios in the absorber layer. The best efficiency was 4.2%. In this work, we found that there were voids in absorber film bottom. The Cu-top precursors will lead to larger grains, flatter surfaces and larger voids than Sn-top precursors. The Cu-top precursor may also contribute to better selenization which may help prevent Zn loss but cause Sn loss. Finally, this work also showed Cu-poor and Zn-rich will improve conversion efficiency.

  7. CZTS absorber layer for thin film solar cells from electrodeposited metallic stacked precursors (Zn/Cu-Sn)

    NASA Astrophysics Data System (ADS)

    Khalil, M. I.; Atici, O.; Lucotti, A.; Binetti, S.; Le Donne, A.; Magagnin, L.

    2016-08-01

    In the present work, Kesterite-Cu2ZnSnS4 (CZTS) thin films were successfully synthesized from stacked bilayer precursor (Zn/Cu-Sn) through electrodeposition-annealing route. Adherent and homogeneous Cu-poor, Zn-rich stacked metal Cu-Zn-Sn precursors with different compositions were sequentially electrodeposited, in the order of Zn/Cu-Sn onto Mo foil substrates. Subsequently, stacked layers were soft annealed at 350 °C for 20 min in flowing N2 atmosphere in order to improve intermixing of the elements. Then, sulfurization was completed at 585 °C for 15 min in elemental sulfur environment in a quartz tube furnace with N2 atmosphere. Morphological, compositional and structural properties of the films were investigated using SEM, EDS and XRD methods. Raman spectroscopy with two different excitation lines (514.5 and 785 nm), has been carried out on the sulfurized films in order to fully characterize the CZTS phase. Higher excitation wavelength showed more secondary phases, but with low intensities. Glow discharge optical emission spectroscopy (GDOES) has also been performed on films showing well formed Kesterite CZTS along the film thickness as compositions of the elements do not change along the thickness. In order to investigate the electronic structure of the CZTS, Photoluminescence (PL) spectroscopy has been carried out on the films, whose results matched up with the literatures.

  8. Arrays of stacked metal coordination compounds

    DOEpatents

    Bulkowski, John E.

    1986-01-01

    A process is disclosed for preparing novel arrays of metal coordination compounds characterized by arrangement of the metal ions, separated by a linking agent, in stacked order one above the other. The process permits great flexibility in the design of the array. For example, layers of different composition can be added to the array at will.

  9. Arrays of stacked metal coordination compounds

    DOEpatents

    Bulkowski, J.E.

    1986-10-21

    A process is disclosed for preparing novel arrays of metal coordination compounds characterized by arrangement of the metal ions, separated by a linking agent, in stacked order one above the other. The process permits great flexibility in the design of the array. For example, layers of different composition can be added to the array at will. 3 figs.

  10. Effect of metal layer stacking order on the growth of Cu2ZnSnS4thin films

    NASA Astrophysics Data System (ADS)

    Thota, Narayana; Gurubhaskar, M.; Sunil, M. Anantha; Prathap, P.; Subbaiah, Y. P. Venkata; Tiwari, Ashutosh

    2017-02-01

    In this paper we have presented an in-depth study of effect of metallic precursor stacking order on the growth of the Cu2ZnSnS4 (CZTS) thin films. The CZTS films were prepared by employing a two-step process comprising of sequential sputtering of the metal precursors followed by sulfurization. An optimized stacking sequence as well as growth mechanism for obtaining the single phase CZTS has been proposed based on the results of XRD, Raman, XPS, UV-Vis and electrical studies. A combination of Raman analysis and XPS has been carried out to confirm the CZTS phase formation and to detect any minor phases, if present. The occurrence of Raman modes at around 286 and 336 cm-1 for the Zn/Cu/Sn/Cu stack sulfurized at 500 °C indicated the existence of prominent Kesterite CZTS phase. The perfect homogeneous mixing of sequential precursors together with the elemental sulfur was observed in the case of sulfurized stack order of Zn/Cu/Sn/Cu, which yielded single phase CZTS films, and further confirmed by high resolution core level XPS measurements. Stack dependent micro structural features and elemental analysis were also carried out using FESEM attached to EDS. The p-type charge carriers as detected using hot-probe measurement technique and the band-gap energy of ∼1.52 eV as estimated from the absorbance spectrum, suggested that the Zn/Cu/Sn/Cu stack order is most appropriate for realizing single phase CZTS growth using two step method.

  11. 23. Brick coke quencher, brick stack, metal stack to right, ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    23. Brick coke quencher, brick stack, metal stack to right, coke gas pipe to left; in background, BOF building, limestone piles, Levy's Slag Dump. Looking north/northwest - Rouge Steel Company, 3001 Miller Road, Dearborn, MI

  12. UV light induced insulator-metal transition in ultra-thin ZnO/TiOx stacked layer grown by atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Saha, D.; Misra, P.; Joshi, M. P.; Kukreja, L. M.

    2016-08-01

    In the present study, atomic layer deposition has been used to grow a series of Ti incorporated ZnO thin films by vertically stacking different numbers (n = 1-7) of ZnO/TiOx layers on (0001) sapphire substrates. The effects of defect states mediated chemisorption of O2 and/OH groups on the electrical properties of these films have been investigated by illuminating the samples under UV light inside a high vacuum optical cryostat. The ultra-thin film having one stacked layer (n = 1) did not show any change in its electrical resistance upon UV light exposure. On the contrary, marginal drop in the electrical resistivity was measured for the samples with n ≥ 3. Most surprisingly, the sample with n = 2 (thickness ˜ 12 nm) showed an insulator to metal transition upon UV light exposure. The temperature dependent electrical resistivity measurement on the as grown film (n = 2) showed insulating behaviour, i.e., diverging resistivity on extrapolation to T→ 0 K. However, upon UV light exposure, it transformed to a metallic state, i.e., finite resistivity at T → 0 K. Such an insulator-metal transition plausibly arises due to the de-trapping of conduction electrons from the surface defect sites which resulted in an upward shift of the Fermi level above the mobility edge. The low-temperature electron transport properties on the insulating film (n = 2) were investigated by a combined study of zero field electrical resistivity ρ(T) and magnetoresistance (MR) measurements. The observed negative MR was found to be in good agreement with the magnetic field induced suppression of quantum interference between forward-going paths of tunnelling electrons. Both ρ(T) and MR measurements provided strong evidence for the Efros-Shklovskii type variable range hopping conduction in the low-temperature (≤40 K) regime. Such studies on electron transport in ultra-thin n-type doped ZnO films are crucial to achieve optimum functionality with long term reliability of ZnO based transparent

  13. Six-band terahertz metamaterial absorber based on the combination of multiple-order responses of metallic patches in a dual-layer stacked resonance structure

    PubMed Central

    Wang, Ben-Xin; Wang, Gui-Zhen; Sang, Tian; Wang, Ling-Ling

    2017-01-01

    This paper reports on a numerical study of the six-band metamaterial absorber composed of two alternating stack of metallic-dielectric layers on top of a continuous metallic plane. Six obvious resonance peaks with high absorption performance (average larger than 99.37%) are realized. The first, third, fifth, and the second, fourth, sixth resonance absorption bands are attributed to the multiple-order responses (i.e., the 1-, 3- and 5-order responses) of the bottom- and top-layer of the structure, respectively, and thus the absorption mechanism of six-band absorber is due to the combination of two sets of the multiple-order resonances of these two layers. Besides, the size changes of the metallic layers have the ability to tune the frequencies of the six-band absorber. Employing the results, we also present a six-band polarization tunable absorber through varying the sizes of the structure in two orthogonal polarization directions. Moreover, nine-band terahertz absorber can be achieved by using a three-layer stacked structure. Simulation results indicate that the absorber possesses nine distinct resonance bands, and average absorptivities of them are larger than 94.03%. The six-band or nine-band absorbers obtained here have potential applications in many optoelectronic and engineering technology areas. PMID:28120897

  14. Six-band terahertz metamaterial absorber based on the combination of multiple-order responses of metallic patches in a dual-layer stacked resonance structure

    NASA Astrophysics Data System (ADS)

    Wang, Ben-Xin; Wang, Gui-Zhen; Sang, Tian; Wang, Ling-Ling

    2017-01-01

    This paper reports on a numerical study of the six-band metamaterial absorber composed of two alternating stack of metallic-dielectric layers on top of a continuous metallic plane. Six obvious resonance peaks with high absorption performance (average larger than 99.37%) are realized. The first, third, fifth, and the second, fourth, sixth resonance absorption bands are attributed to the multiple-order responses (i.e., the 1-, 3- and 5-order responses) of the bottom- and top-layer of the structure, respectively, and thus the absorption mechanism of six-band absorber is due to the combination of two sets of the multiple-order resonances of these two layers. Besides, the size changes of the metallic layers have the ability to tune the frequencies of the six-band absorber. Employing the results, we also present a six-band polarization tunable absorber through varying the sizes of the structure in two orthogonal polarization directions. Moreover, nine-band terahertz absorber can be achieved by using a three-layer stacked structure. Simulation results indicate that the absorber possesses nine distinct resonance bands, and average absorptivities of them are larger than 94.03%. The six-band or nine-band absorbers obtained here have potential applications in many optoelectronic and engineering technology areas.

  15. Wall energy and wall thickness of exchange-coupled rare-earth transition-metal triple layer stacks

    SciTech Connect

    Raasch, D.; Mathieu, C.

    1997-08-01

    The room-temperature wall energy {sigma}{sub w}=4.0{times}10{sup {minus}3}J/m{sup 2} of an exchange-coupled Tb{sub 19.6}Fe{sub 74.7}Co{sub 5.7}/Dy{sub 28.5}Fe{sub 43.2}Co{sub 28.3} double layer stack can be reduced by introducing a soft magnetic intermediate layer in between both layers exhibiting a significantly smaller anisotropy compared to Tb{endash}FeCo and Dy{endash}FeCo. {sigma}{sub w} will decrease linearly with increasing intermediate layer thickness, d{sub IL}, until the wall is completely located within the intermediate layer for d{sub IL}{ge}d{sub w}, where d{sub w} denotes the wall thickness. Thus, d{sub w} can be obtained from the plot {sigma}{sub w} versus d{sub IL}. We determined {sigma}{sub w} and d{sub w} on Gd{endash}FeCo intermediate layers with different anisotropy behavior (perpendicular and in-plane easy axis) and compared the results with data obtained from Brillouin light-scattering measurements, where exchange stiffness, A, and uniaxial anisotropy, K{sub u}, could be determined. With the knowledge of A and K{sub u}, wall energy and thickness were calculated and showed an excellent agreement with the magnetic measurements. A ten times smaller perpendicular anisotropy of Gd{sub 28.1}Fe{sub 71.9} in comparison to Tb{endash}FeCo and Dy{endash}FeCo resulted in a much smaller {sigma}{sub w}=1.1{times}10{sup {minus}3}J/m{sup 2} and d{sub w}=24nm at 300 K. A Gd{sub 34.1}Fe{sub 61.4}Co{sub 4.5} with in-plane anisotropy at room temperature showed a further reduced {sigma}{sub w}=0.3{times}10{sup {minus}3}J/m{sup 2} and d{sub w}=17nm. The smaller wall energy was a result of a different wall structure compared to perpendicular layers. {copyright} {ital 1997 American Institute of Physics.}

  16. Three-Dimensional Flexible Complementary Metal-Oxide-Semiconductor Logic Circuits Based On Two-Layer Stacks of Single-Walled Carbon Nanotube Networks.

    PubMed

    Zhao, Yudan; Li, Qunqing; Xiao, Xiaoyang; Li, Guanhong; Jin, Yuanhao; Jiang, Kaili; Wang, Jiaping; Fan, Shoushan

    2016-02-23

    We have proposed and fabricated stable and repeatable, flexible, single-walled carbon nanotube (SWCNT) thin film transistor (TFT) complementary metal-oxide-semiconductor (CMOS) integrated circuits based on a three-dimensional (3D) structure. Two layers of SWCNT-TFT devices were stacked, where one layer served as n-type devices and the other one served as p-type devices. On the basis of this method, it is able to save at least half of the area required to construct an inverter and make large-scale and high-density integrated CMOS circuits easier to design and manufacture. The 3D flexible CMOS inverter gain can be as high as 40, and the total noise margin is more than 95%. Moreover, the input and output voltage of the inverter are exactly matched for cascading. 3D flexible CMOS NOR, NAND logic gates, and 15-stage ring oscillators were fabricated on PI substrates with high performance as well. Stable electrical properties of these circuits can be obtained with bending radii as small as 3.16 mm, which shows that such a 3D structure is a reliable architecture and suitable for carbon nanotube electrical applications in complex flexible and wearable electronic devices.

  17. Quasi-dielectric characteristics of stacked metallic metamaterials

    NASA Astrophysics Data System (ADS)

    Tokuda, Yasunori; Takano, Keisuke; Yamaguchi, Yuki; Sakaguchi, Koichiro; Nakajima, Makoto

    2017-03-01

    We investigated the optical transmission properties of quasi-dielectric metamaterials composed of a stack of metallic sub-wavelength slit-array slabs. First, we used simulations to predict the transmission properties, and showed that these characteristics are basically equivalent to those of triple-layered dielectrics below the diffraction-limit frequency. Next, for the experimental demonstrations, we fabricated the metallic slit arrays, and then measured the transmission spectra. By comparison of the theoretical and experimental results, we demonstrated that each slit array acts as an individual quasi-dielectric in the stacked system. Using these metamaterials, a variety of transmission characteristics can be obtained in the terahertz region.

  18. Voltage linearity modulation and polarity dependent conduction in metal-insulator-metal capacitors with atomic-layer-deposited Al{sub 2}O{sub 3}/ZrO{sub 2}/SiO{sub 2} nano-stacks

    SciTech Connect

    Zhu, Bao; Liu, Wen-Jun; Wei, Lei; Zhang, David Wei; Jiang, Anquan; Ding, Shi-Jin

    2015-07-07

    Excellent voltage linearity of metal-insulator-metal (MIM) capacitors is highly required for next generation radio frequency integration circuits. In this work, employing atomic layer deposition technique, we demonstrated how the voltage linearity of MIM capacitors was modulated by adding different thickness of SiO{sub 2} layer to the nano-stack of Al{sub 2}O{sub 3}/ZrO{sub 2}. It was found that the quadratic voltage coefficient of capacitance (α) can be effectively reduced from 1279 to −75 ppm/V{sup 2} with increasing the thickness of SiO{sub 2} from zero to 4 nm, which is more powerful than increasing the thickness of ZrO{sub 2} in the Al{sub 2}O{sub 3}/ZrO{sub 2} stack. This is attributed to counteraction between the positive α for Al{sub 2}O{sub 3}/ZrO{sub 2} and the negative one for SiO{sub 2} in the MIM capacitors with Al{sub 2}O{sub 3}/ZrO{sub 2}/SiO{sub 2} stacks. Interestingly, voltage-polarity dependent conduction behaviors in the MIM capacitors were observed. For electron bottom-injection, the addition of SiO{sub 2} obviously suppressed the leakage current; however, it abnormally increased the leakage current for electron top-injection. These are ascribed to the co-existence of shallow and deep traps in ZrO{sub 2}, and the former is in favor of the field-assisted tunnelling conduction and the latter contributes to the trap-assisted tunnelling process. The above findings will be beneficial to device design and process optimization for high performance MIM capacitors.

  19. Stacked Metal Silicide/Silicon Far-Infrared Detectors

    NASA Technical Reports Server (NTRS)

    Maserjian, Joseph

    1988-01-01

    Selective doping of silicon in proposed metal silicide/silicon Schottky-barrier infrared photodetector increases maximum detectable wavelength. Stacking layers to form multiple Schottky barriers increases quantum efficiency of detector. Detectors of new type enhance capabilities of far-infrared imaging arrays. Grows by molecular-beam epitaxy on silicon waferscontaining very-large-scale integrated circuits. Imaging arrays of detectors made in monolithic units with image-preprocessing circuitry.

  20. Stacking-dependent transport properties in few-layers graphene

    NASA Astrophysics Data System (ADS)

    Lima, Matheus Paes; Padilha, José Eduardo; Pontes, Renato Borges; Fazzio, Adalberto; Silva, Antônio José Roque da

    2017-01-01

    By performing ab initio electronic structure and transport calculations, we investigated the effects of the stacking order (Bernal (AB) and rhombohedral (ABC)) as well as the number of layers, in the electronic structure and charge transport of few-layers graphene (FLG). We observed that for the ABC stack the transport properties are derived from surface states close to the Fermi level connected to dispersive states with an exponential penetration towards the inner layers, whereas for the AB stacking the transport is distributed over all layers. We present a simple model for the resistances as a function of the number of layers which contemplates the different contribution of the surface and inner layers for the transport. However, even if the stackings AB and ABC present completely different electronic and transport properties, both present the same cohesive energies, showing the absence of a thermodynamical preference for a given kind of stacking.

  1. Imaging Stacking Order in Few-Layer Graphene

    SciTech Connect

    C Lui; Z Li; Z Chen; P Klimov; L Brus; T Heinz

    2011-12-31

    Few-layer graphene (FLG) has been predicted to exist in various crystallographic stacking sequences, which can strongly influence the material's electronic properties. We demonstrate an accurate and efficient method to characterize stacking order in FLG using the distinctive features of the Raman 2D-mode. Raman imaging allows us to visualize directly the spatial distribution of Bernal (ABA) and rhombohedral (ABC) stacking in tri- and tetralayer graphene. We find that 15% of exfoliated graphene tri- and tetralayers is composed of micrometer-sized domains of rhombohedral stacking, rather than of usual Bernal stacking. These domains are stable and remain unchanged for temperatures exceeding 800 C.

  2. Enhanced intervalley scattering in artificially stacked double-layer graphene

    NASA Astrophysics Data System (ADS)

    Iqbal, M. Z.; Kelekçi, Özgür; Iqbal, M. W.; Jin, Xiaozhan; Hwang, Chanyong; Eom, Jonghwa

    2014-08-01

    We fabricated artificially stacked double-layer graphene by sequentially transferring graphene grown by chemical vapor deposition. The double-layer graphene was characterized by Raman spectroscopy and transport measurements. A weak localization effect was observed for different charge carrier densities and temperatures. The obtained intervalley scattering rate was unusually high compared to normal Bernal-stacked bilayer or single-layer graphene. The sharp point defects, local deformation, or bending of graphene plane required for intervalley scattering from one Dirac cone to another seemed to be enhanced by the artificially stacked graphene layers.

  3. Laser micromachining as a metallization tool for microfluidic polymer stacks

    NASA Astrophysics Data System (ADS)

    Brettschneider, T.; Dorrer, C.; Czurratis, D.; Zengerle, R.; Daub, M.

    2013-03-01

    A novel assembly approach for the integration of metal structures into polymeric microfluidic systems is described. The presented production process is completely based on a single solid-state laser source, which is used to incorporate metal foils into a polymeric multi-layer stack by laser bonding and ablation processes. Chemical reagents or glues are not required. The polymer stack contains a flexible membrane which can be used for realizing microfluidic valves and pumps. The metal-to-polymer bond was investigated for different metal foils and plasma treatments, yielding a maximum peel strength of Rps = 1.33 N mm-1. A minimum structure size of 10 µm was determined by 3D microscopy of the laser cut line. As an example application, two different metal foils were used in combination to micromachine a standardized type-T thermocouple on a polymer substrate. An additional laser process was developed which allows metal-to-metal welding in close vicinity to the polymer substrate. With this process step, the reliability of the electrical contact could be increased to survive at least 400 PCR temperature cycles at very low contact resistances.

  4. Layer-stacking effect on electronic structures of bilayer arsenene

    NASA Astrophysics Data System (ADS)

    Mi, Kui; Xie, Jiafeng; Si, M. S.; Gao, C. X.

    2017-01-01

    A monolayer of orthorhombic arsenic (arsenene) is a promising candidate for nano-electronic devices due to the uniquely electronic properties. To further extend its practical applications, an additional layer is introduced to tune the electronic structures. Four layer-stacking manners, namely AA-, AB-, AB‧-, and AC-stacking, are constructed and studied through using first-principles calculations. Compared with monolayer, an indirect-direct gap transition is realized in AB-stacking. More importantly, a semimetal feature appears in the AC- and AB‧-stacked bilayers, leaving the electronic structure of AA-stacking trivial. In addition, the energy dispersion around Γ is largely tuned from the layer-stacking effect. To understand the underlying physics, the \\textbf{k}\\cdot\\textbf{p} approximation is taken to address this issue. Our results show that the level repulsion from the additional layer domaintes the anisotropy of energy dispersion around Γ. The works like ours would shed new light on the tunability of the electronic structure in layered arsenene.

  5. Tinv Scaling and Gate Leakage Reduction for n-Type Metal Oxide Semiconductor Field Effect Transistor with HfSix/HfO2 Gate Stack by Interfacial Layer Formation Using Ozone-Water-Last Treatment

    NASA Astrophysics Data System (ADS)

    Oshiyama, Itaru; Tai, Kaori; Hirano, Tomoyuki; Yamaguchi, Shinpei; Tanaka, Kazuaki; Hagimoto, Yoshiya; Uemura, Takayuki; Ando, Takashi; Watanabe, Koji; Yamamoto, Ryo; Kanda, Saori; Wang, Junli; Tateshita, Yasushi; Wakabayashi, Hitoshi; Tagawa, Yukio; Tsukamoto, Masanori; Iwamoto, Hayato; Saito, Masaki; Oshima, Masaharu; Toyoda, Satoshi; Nagashima, Naoki; Kadomura, Shingo

    2008-04-01

    In this paper, we demonstrate a wet treatment for the HfSix/HfO2 gate stack of n-type metal oxide semiconductor field effect transistor (nMOSFET) fabricated by a gate-last process in order to scale down the electrical thickness at inversion state Tinv value and reduce the gate leakage Jg. As a result, we succeeded in scaling down Tinv to 1.41 nm without mobility or Jg degradation by ozone-water-last treatment. We found that a high-density interfacial layer (IFL) is formed owing to the ozone-water-last treatment, and Hf diffusion to the IFL is suppressed, which was analyzed by high-resolution angle-resolved spectroscopy.

  6. Generalized approach to design multi-layer stacks for enhanced optical detectability of ultrathin layers

    NASA Astrophysics Data System (ADS)

    Hutzler, A.; Matthus, C. D.; Rommel, M.; Frey, L.

    2017-01-01

    The optical detectability of ultrathin conductive films (down to one atomic layer) can be enhanced by choosing distinct layer-stacks. A simple analytical approach using the transfer matrix method is applied for calculating the reflectance of arbitrary multi-layer stack systems with and without the ultrathin layer of interest on top in a wide wavelength range, including both the visible spectrum and the ultraviolet spectrum. Then, the detectability defined by the Michelson contrast was calculated. Performing these calculations for thickness variations of the individual layers in the stack allows determining optimum layer thicknesses, e.g., maximum overall contrast or maximum contrast for a given wavelength. To demonstrate the validity of the methodology, two thin film stacks were investigated, which use p-type silicon as a substrate material and partially covered by a single-layer graphene as a top layer. For each stack, two samples with different layer thicknesses were fabricated and their experimentally determined reflectance was compared to the calculated values. The first system consists of a single SiO2 layer with a thickness of 147 nm and 304 nm, respectively, and the second is a double layer stack consisting of a Si3N4 layer with a thickness of 54 nm and 195 nm, respectively, on top of an 11 nm SiO2 film. The Michelson contrast of single-layer graphene flakes on the latter layer stacks becomes very high (absolute value of more than 0.3) in the visible wavelength range. Additionally, in the UV-B range a large difference in the reflection of selected SiO2 layer thicknesses on silicon substrates with and without single-layer graphene on top is found with a decrease in the measured reflectance of up to 33%. The measured and calculated values showed a high conformity suggesting this approach usable for the calculation of reflectance and transmittance properties of arbitrary layer stack systems including thin conductive layers.

  7. Calculated stacking-fault energies of elemental metals

    NASA Astrophysics Data System (ADS)

    Rosengaard, N. M.; Skriver, H. L.

    1993-05-01

    We have performed ab initio calculations of twin, intrinsic, and extrinsic face-centered-cubic stacking faults for all the 3d, 4d, and 5d transition metals by means of a Green's-function technique, based on the linear-muffin-tin-orbitals method within the tight-binding and atomic-sphere approximations. The results are in excellent agreement with recent layer Korringa-Kohn-Rostoker Green's-function calculations where stacking-fault energies for Ni, Cu, Rh, Pd, Ag, Ir, and Au were found by means of the so-called force theorem. We find that the self-consistent fault energies for all the metals in the three transition series vary with atomic number essentially as the calculated structural energy differences between the face-centered-cubic and the hexagonal-close-packed phases. In addition we find that the simple relations between the different types of fault energies predicted by models based on the local atomic coordination are obeyed to a high degree of accuracy.

  8. Tests on Double Layer Metalization

    NASA Technical Reports Server (NTRS)

    Woo, D. S.

    1983-01-01

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

  9. Stacking dependent electronic structures of transition metal dichalcogenides heterobilayer

    NASA Astrophysics Data System (ADS)

    Lee, Yea-Lee; Park, Cheol-Hwan; Ihm, Jisoon

    The systematic study of the electronic structures and optical properties of the transition metal dichalcogenides (TMD) heterobilayers can significantly improve the designing of new electronic and optoelectronic devices. Here, we theoretically study the electronic structures and optical properties of TMD heterobilayers using the first-principles methods. The band structures of TMD heterobilayer are shown to be determined by the band alignments of the each layer, the weak interlayer interactions, and angle dependent stacking patterns. The photoluminescence spectra are investigated using the calculated band structures, and the optical absorption spectra are examined by the GW approximations including the electron-hole interaction through the solution of the Bethe-Salpeter equation. It is expected that the weak interlayer interaction gives rise to the substantial interlayer optical transition which will be corresponding to the interlayer exciton.

  10. Multiple layer identification label using stacked identification symbols

    NASA Technical Reports Server (NTRS)

    Schramm, Harry F. (Inventor)

    2005-01-01

    An automatic identification system and method are provided which employ a machine readable multiple layer label. The label has a plurality of machine readable marking layers stacked one upon another. Each of the marking layers encodes an identification symbol detectable using one or more sensing technologies. The various marking layers may comprise the same marking material or each marking layer may comprise a different medium having characteristics detectable by a different sensing technology. These sensing technologies include x-ray, radar, capacitance, thermal, magnetic and ultrasonic. A complete symbol may be encoded within each marking layer or a symbol may be segmented into fragments which are then divided within a single marking layer or encoded across multiple marking layers.

  11. Silicene beyond mono-layers--different stacking configurations and their properties.

    PubMed

    Kamal, C; Chakrabarti, Aparna; Banerjee, Arup; Deb, S K

    2013-02-27

    We carry out a computational study on the geometric and electronic properties of multi-layers of silicene in different stacking configurations using state-of-the-art ab initio density functional theory based calculations. In this work we investigate the evolution of these properties with increasing number of layers (n) ranging from 1 to 10. Although a mono-layer of silicene possesses properties similar to those of graphene, our results show that the geometric and electronic properties of multi-layers of silicene are strikingly different from those of multi-layers of graphene. We observe that strong inter-layer covalent bonding exists between the layers in multi-layers of silicene as opposed to weak van der Waals bonding which exists between the graphene layers. The inter-layer bonding strongly influences the geometric and electronic structures of these multi-layers. Like bi-layers of graphene, silicene with two different stacking configurations AA and AB exhibits linear and parabolic dispersions around the Fermi level, respectively. However, unlike graphene, for bi-layers of silicene, these dispersion curves are shifted in the band diagram; this is due to the strong inter-layer bonding present in the latter. For n > 3, we study the geometric and electronic properties of multi-layers with four different stacking configurations, namely AAAA, AABB, ABAB and ABC. Our results on cohesive energy show that all the multi-layers considered are energetically stable. Furthermore, we find that the three stacking configurations (AAAA, AABB and ABC) containing tetrahedral coordination have much higher cohesive energy than the Bernal (ABAB) stacking configuration. This is in contrast to the case of multi-layers of graphene, where ABAB is reported to be the lowest energy configuration. We also observe that bands near the Fermi level in lower energy stacking configurations AAAA, AABB and ABC correspond to the surface atoms and these surface states are responsible for the semi-metallic

  12. Dimensional crossover of electron weak localization in ZnO/TiOx stacked layers grown by atomic layer deposition

    NASA Astrophysics Data System (ADS)

    Saha, D.; Misra, P.; Bhartiya, S.; Gupta, M.; Joshi, M. P.; Kukreja, L. M.

    2016-01-01

    We report on the dimensional crossover of electron weak localization in ZnO/TiOx stacked layers having well-defined and spatially-localized Ti dopant profiles along film thickness. These films were grown by in situ incorporation of sub-monolayer TiOx on the growing ZnO film surface and subsequent overgrowth of thin conducting ZnO spacer layer using atomic layer deposition. Film thickness was varied in the range of ˜6-65 nm by vertically stacking different numbers (n = 1-7) of ZnO/TiOx layers of nearly identical dopant-profiles. The evolution of zero-field sheet resistance (R⊙) versus temperature with decreasing film thickness showed a metal to insulator transition. On the metallic side of the metal-insulator transition, R⊙(T) and magnetoresistance data were found to be well corroborated with the theoretical framework of electron weak localization in the diffusive transport regime. The temperature dependence of both R⊙ and inelastic scattering length provided strong evidence for a smooth crossover from 2D to 3D weak localization behaviour. Results of this study provide deeper insight into the electron transport in low-dimensional n-type ZnO/TiOx stacked layers which have potential applications in the field of transparent oxide electronics.

  13. Novel fuel cell stack with coupled metal hydride containers

    NASA Astrophysics Data System (ADS)

    Liu, Zhixiang; Li, Yan; Bu, Qingyuan; Guzy, Christopher J.; Li, Qi; Chen, Weirong; Wang, Cheng

    2016-10-01

    Air-cooled, self-humidifying hydrogen fuel cells are often used for backup and portable power sources, with a metal hydride used as the hydrogen storage material. To provide a stable hydrogen flow to the fuel cell stack, heat must be provided to the metal hydride. Conventionally, the heat released from the exothermic reaction of hydrogen and oxygen in the fuel cell stack to the exhaust air is used to heat a separate metal hydride container. In this case, the heat is only partially used instead of being more closely coupled because of the heat transfer resistances in the system. To achieve better heat integration, a novel scheme is proposed whereby hydrogen storage and single fuel cells are more closely coupled. Based on this idea, metal hydride containers in the form of cooling plates were assembled between each pair of cells in the stack so that the heat could be directly transferred to a metal hydride container of much larger surface-to-volume ratio than conventional separate containers. A heat coupled fuel cell portable power source with 10 cells and 11 metal hydride containers was constructed and the experimental results show that this scheme is beneficial for the heat management of fuel cell stack.

  14. Stacked Ge nanocrystals with ultrathin SiO₂ separation layers.

    PubMed

    Zschintzsch, Manuel; von Borany, Johannes; Jeutter, Nicole M; Mücklich, Arndt

    2011-11-18

    The aim of this work is the tailored growth of Ge nanocrystals (NCs) in (GeO(x)/SiO(2)) multilayers (ML) for photovoltaic applications. For this purpose the fabrication of regularly stacked Ge NCs separated by ultrathin SiO(2) layers is essential to enable charge carrier transport by direct tunnelling. In this paper we report on the fabrication of (GeO(x)/SiO(2))(50) multilayer stacks via reactive dc magnetron sputtering and Ge NCs formation after subsequent annealing. It is shown that magnetron sputtering allows us to deposit very regular ML stacks with a total thickness of about 300 nm, characterized by ultrathin (down to 1 nm) and very smooth (roughness ∼ 0.6 nm) SiO(2) separation layers. A main challenge is to keep these properties for a thermal budget necessary to form Ge NCs. For this reason, the temperature dependence of phase separation. Ge crystallization and ML morphology was investigated by Rutherford backscattering, x-ray scattering, Raman spectroscopy and electron microscopy. The formation of size confined Ge NCs of about 5 nm after annealing of only 550 °C is confirmed. This low thermal budget ensures the suppression of GeO emanation and multilayer stability. Spectroscopic ellipsometry was applied to determine the optical Ge NC bandgap to (1.65 ± 0.5) eV.

  15. Vertically stacked multi-heterostructures of layered materials for logic transistors and complementary inverters

    PubMed Central

    Yu, Woo Jong; Li, Zheng; Zhou, Hailong; Chen, Yu; Wang, Yang; Huang, Yu; Duan, Xiangfeng

    2014-01-01

    The layered materials such as graphene have attracted considerable interest for future electronics. Here we report the vertical integration of multi-heterostructures of layered materials to enable high current density vertical field-effect transistors (VFETs). An n-channel VFET is created by sandwiching few-layer molybdenum disulfide (MoS2) as the semiconducting channel between a monolayer graphene and a metal thin film. The VFETs exhibit a room temperature on-off ratio >103, while at same time deliver a high current density up to 5,000 A/cm2, sufficient for high performance logic applications. This study offers a general strategy for the vertical integration of various layered materials to obtain both p- and n-channel transistors for complementary logic functions. A complementary inverter with larger than unit voltage gain is demonstrated by vertically stacking the layered materials of graphene, Bi2Sr2Co2O8 (p-channel), graphene, MoS2 (n-channel), and metal thin film in sequence. The ability to simultaneously achieve high on-off ratio, high current density, and logic integration in the vertically stacked multi-heterostructures can open up a new dimension for future electronics to enable three-dimensional integration. PMID:23241535

  16. Metal stack optimization for low-power and high-density for N7-N5

    NASA Astrophysics Data System (ADS)

    Raghavan, P.; Firouzi, F.; Matti, L.; Debacker, P.; Baert, R.; Sherazi, S. M. Y.; Trivkovic, D.; Gerousis, V.; Dusa, M.; Ryckaert, J.; Tokei, Z.; Verkest, D.; McIntyre, G.; Ronse, K.

    2016-03-01

    One of the key challenges while scaling logic down to N7 and N5 is the requirement of self-aligned multiple patterning for the metal stack. This comes with a large cost of the backend cost and therefore a careful stack optimization is required. Various layers in the stack have different purposes and therefore their choice of pitch and number of layers is critical. Furthermore, when in ultra scaled dimensions of N7 or N5, the number of patterning options are also much larger ranging from multiple LE, EUV to SADP/SAQP. The right choice of these are also needed patterning techniques that use a full grating of wires like SADP/SAQP techniques introduce high level of metal dummies into the design. This implies a large capacitance penalty to the design therefore having large performance and power penalties. This is often mitigated with extra masking strategies. This paper discusses a holistic view of metal stack optimization from standard cell level all the way to routing and the corresponding trade-off that exist for this space.

  17. Improvement in the breakdown endurance of high-κ dielectric by utilizing stacking technology and adding sufficient interfacial layer.

    PubMed

    Pang, Chin-Sheng; Hwu, Jenn-Gwo

    2014-01-01

    Improvement in the time-zero dielectric breakdown (TZDB) endurance of metal-oxide-semiconductor (MOS) capacitor with stacking structure of Al/HfO2/SiO2/Si is demonstrated in this work. The misalignment of the conduction paths between two stacking layers is believed to be effective to increase the breakdown field of the devices. Meanwhile, the resistance of the dielectric after breakdown for device with stacking structure would be less than that of without stacking structure due to a higher breakdown field and larger breakdown power. In addition, the role of interfacial layer (IL) in the control of the interface trap density (D it) and device reliability is also analyzed. Device with a thicker IL introduces a higher breakdown field and also a lower D it. High-resolution transmission electron microscopy (HRTEM) of the samples with different IL thicknesses is provided to confirm that IL is needed for good interfacial property.

  18. Tunable Hydrophilic or Amphiphilic Coatings: A "Reactive Layer Stack" Approach.

    PubMed

    Frenzel, Ralf; Höhne, Susanne; Hanzelmann, Christian; Schmidt, Thomas; Winkler, René; Drechsler, Astrid; Bittrich, Eva; Eichhorn, Klaus-Jochen; Uhlmann, Petra

    2015-06-17

    Thin films with tunable properties are very interesting for potential applications as functional coatings with, for example, anti-icing or improved easy-to-clean properties. A novel "reactive layer stack" approach was developed to create covalently grafted mono- and multilayers of poly(glycidyl methacrylate)/poly(tert-butyl acrylate) diblock copolymers. Because these copolymers contain poly(glycidyl methacrylate) blocks they behave as self-cross-linking materials after creation of acrylic acid functionalities by splitting off the tert-butyl units. The ellipsometrically determined coating thickness of the resulting hydrophilic multilayers depended linearly on the number of applied layers. Amphiphilic films with tunable wettability were prepared using triblock terpolymers with an additional poly(methyl methacrylate) block. The mechanism of the formation of the (multi)layers was investigated in detail by studying the acidolysis of the surface-linked tert-butyl acrylate blocks by infrared reflection absorbance spectroscopy, accompanied by surface analysis using atomic force microscopy and contact angle measurements. In the case of the amphiphilic and switchable terpolymer layers this reaction was very sensitive to the used acidic reagent.

  19. Metal deposition using seed layers

    DOEpatents

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

    2013-11-12

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

  20. Resin infusion of layered metal/composite hybrid and resulting metal/composite hybrid laminate

    NASA Technical Reports Server (NTRS)

    Cano, Roberto J. (Inventor); Grimsley, Brian W. (Inventor); Weiser, Erik S. (Inventor); Jensen, Brian J. (Inventor)

    2009-01-01

    A method of fabricating a metal/composite hybrid laminate is provided. One or more layered arrangements are stacked on a solid base to form a layered structure. Each layered arrangement is defined by a fibrous material and a perforated metal sheet. A resin in its liquid state is introduced along a portion of the layered structure while a differential pressure is applied across the laminate structure until the resin permeates the fibrous material of each layered arrangement and fills perforations in each perforated metal sheet. The resin is cured thereby yielding a metal/composite hybrid laminate.

  1. Exchange coupling and switching fields of RE—TM double and triple layer stacks for direct overwrite

    NASA Astrophysics Data System (ADS)

    Raasch, D.; Wierenga, H.

    1997-04-01

    The recording properties of common single layer magneto-optical (MO) disks can be improved by introducing exchange coupled rare-earth (RE) transition-metal (TM) films, both from the point of view of capacity and data transfer rate. Direct overwrite (DOW) is a method to double the data transfer rate during writing, because the write process of new bits and the erase process of old bits is performed simultaneously. MO multilayer stacks must exhibit exchange coupling in order to be suitable for DOW. The switching fields of each layer depend on coercive energy, magnetic field energy and the energy of the interface wall between coupled layers. In this paper we discuss the dependence of switching fields on layer thickness and wall energy σw for several double and triple layer stacks. The memory and reference layers are TbFeCo and DyFeCo, respectively. Triple layer stacks have an intermediate layer (GdFe and GdFeCo) to adjust the wall energy. DOW presupposes a weak coupling at 300 K and a strong coupling at higher temperatures. This requires a very thick reference layer in double layer stacks, causing excessive heat capacities. However, for triple layers the DOW demands are met in much thinner stacks as the wall energy is adjusted through the intermediate layer. The wall energy of the intermediate layer is determined by its anisotropy. We studied the anisotropy of evaporated GdFe, GdCo and GdFeCo films as a function of composition. GdCo showed only in-plane anisotropy, while GdFe was perpendicularly magnetized for Fe contents up to 87 at%. Adding Co to GdFe leads to a layer with a temperature dependent easy axis. The carrier-to-noise ratio (CNR) of a series of magneto-optical disks, both double and triple layer stacks, was determined. The maximum CNR of 51.4 dB is comparable to results on a single layer disk with the same memory layer. On triple layer stacks a CNR > 45 dB could be written at a laser power below 9 mW.

  2. Effect of vacancy defects on generalized stacking fault energy of fcc metals.

    PubMed

    Asadi, Ebrahim; Zaeem, Mohsen Asle; Moitra, Amitava; Tschopp, Mark A

    2014-03-19

    Molecular dynamics (MD) and density functional theory (DFT) studies were performed to investigate the influence of vacancy defects on generalized stacking fault (GSF) energy of fcc metals. MEAM and EAM potentials were used for MD simulations, and DFT calculations were performed to test the accuracy of different common parameter sets for MEAM and EAM potentials in predicting GSF with different fractions of vacancy defects. Vacancy defects were placed at the stacking fault plane or at nearby atomic layers. The effect of vacancy defects at the stacking fault plane and the plane directly underneath of it was dominant compared to the effect of vacancies at other adjacent planes. The effects of vacancy fraction, the distance between vacancies, and lateral relaxation of atoms on the GSF curves with vacancy defects were investigated. A very similar variation of normalized SFEs with respect to vacancy fractions were observed for Ni and Cu. MEAM potentials qualitatively captured the effect of vacancies on GSF.

  3. Stacking faults and superstructures in a layered brownmillerite

    PubMed Central

    Krüger, H.; Stöber, S.; Welberry, T. R.; Withers, R. L.; Fitz Gerald, J. D.

    2011-01-01

    Single crystals of Ca4Fe2Mn0.5Ti0.5O9 have been synthesized using a flux method. The structural characterization using single-crystal X-ray diffraction revealed the space group Amma and unit-cell dimensions of a = 5.3510 (6), b = 26.669 (3), c = 5.4914 (6) Å. The structure is isotypic with Sr3NdFe3O9 [Barrier et al. (2005 ▸). Chem. Mater. 17, 6619–6623] and exhibits separated brownmillerite-type layers. One-dimensional diffuse scattering shows that the unit cell is doubled along c by alternating the intra-layer order of tetrahedral chains, causing stacking faults along the b direction. A computer simulation was performed, proving that the observed intensity variations along the diffuse scattering rods originates from two different local structures depending on the configuration of the tetrahedral chains. Selected-area electron diffraction experiments exhibit well ordered regions characterized by satellite reflections corresponding to two different superstructures. Both superstructures can be described using the superspace group A21/m(0βγ)0s, with γ = 0.5 and β ≃ 0.27 or β = 0. PMID:22101537

  4. A metallic interconnect for a solid oxide fuel cell stack

    NASA Astrophysics Data System (ADS)

    England, Diane Mildred

    A solid oxide fuel cell (SOFC) electrochemically converts the chemical energy of reaction into electrical energy. The commercial success of planar, SOFC stack technology has a number of challenges, one of which is the interconnect that electrically and physically connects the cathode of one cell to the anode of an adjacent cell in the SOFC stack and in addition, separates the anodic and cathodic gases. An SOFC stack operating at intermediate temperatures, between 600°C and 800°C, can utilize a metallic alloy as an interconnect material. Since the interconnect of an SOFC stack must operate in both air and fuel environments, the oxidation kinetics, adherence and electronic resistance of the oxide scales formed on commercial alloys were investigated in air and wet hydrogen under thermal cycling conditions to 800°C. The alloy, Haynes 230, exhibited the slowest oxidation kinetics and the lowest area-specific resistance as a function of oxidation time of all the alloys in air at 800°C. However, the area-specific resistance of the oxide scale formed on Haynes 230 in wet hydrogen was unacceptably high after only 500 hours of oxidation, which was attributed to the high resistivity of Cr2O3 in a reducing atmosphere. A study of the electrical conductivity of the minor phase manganese chromite, MnXCr3-XO4, in the oxide scale of Haynes 230, revealed that a composition closer to Mn2CrO4 had significantly higher electrical conductivity than that closer to MnCr 2O4. Haynes 230 was coated with Mn to form a phase closer to the Mn2CrO4 composition for application on the fuel side of the interconnect. U.S. Patent No. 6,054,231 is pending. Although coating a metallic alloy is inexpensive, the stringent economic requirements of SOFC stack technology required an alloy without coating for production applications. As no commercially available alloy, among the 41 alloys investigated, performed to the specifications required, a new alloy was created and designated DME-A2. The oxide scale

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

    DTIC Science & Technology

    2009-01-01

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

  6. Impact of La{sub 2}O{sub 3} interfacial layers on InGaAs metal-oxide-semiconductor interface properties in Al{sub 2}O{sub 3}/La{sub 2}O{sub 3}/InGaAs gate stacks deposited by atomic-layer-deposition

    SciTech Connect

    Chang, C.-Y. Takenaka, M.; Takagi, S.; Ichikawa, O.; Osada, T.; Hata, M.; Yamada, H.

    2015-08-28

    We examine the electrical properties of atomic layer deposition (ALD) La{sub 2}O{sub 3}/InGaAs and Al{sub 2}O{sub 3}/La{sub 2}O{sub 3}/InGaAs metal-oxide-semiconductor (MOS) capacitors. It is found that the thick ALD La{sub 2}O{sub 3}/InGaAs interface provides low interface state density (D{sub it}) with the minimum value of ∼3 × 10{sup 11} cm{sup −2} eV{sup −1}, which is attributable to the excellent La{sub 2}O{sub 3} passivation effect for InGaAs surfaces. It is observed, on the other hand, that there are a large amount of slow traps and border traps in La{sub 2}O{sub 3}. In order to simultaneously satisfy low D{sub it} and small hysteresis, the effectiveness of Al{sub 2}O{sub 3}/La{sub 2}O{sub 3}/InGaAs gate stacks with ultrathin La{sub 2}O{sub 3} interfacial layers is in addition evaluated. The reduction of the La{sub 2}O{sub 3} thickness to 0.4 nm in Al{sub 2}O{sub 3}/La{sub 2}O{sub 3}/InGaAs gate stacks leads to the decrease in hysteresis. On the other hand, D{sub it} of the Al{sub 2}O{sub 3}/La{sub 2}O{sub 3}/InGaAs interfaces becomes higher than that of the La{sub 2}O{sub 3}/InGaAs ones, attributable to the diffusion of Al{sub 2}O{sub 3} through La{sub 2}O{sub 3} into InGaAs and resulting modification of the La{sub 2}O{sub 3}/InGaAs interface structure. As a result of the effective passivation effect of La{sub 2}O{sub 3} on InGaAs, however, the Al{sub 2}O{sub 3}/10 cycle (0.4 nm) La{sub 2}O{sub 3}/InGaAs gate stacks can realize still lower D{sub it} with maintaining small hysteresis and low leakage current than the conventional Al{sub 2}O{sub 3}/InGaAs MOS interfaces.

  7. Nonlocal effect on optic spectrum of a periodic dielectric-metal stack.

    PubMed

    Paredes-Juárez, Alejandro; Iakushev, Denis A; Flores-Desirena, Benito; Makarov, Nykolay M; Pérez-Rodríguez, Felipe

    2014-04-07

    On the basis of the formalism of the Boltzmann kinetic equation for the distribution function of the conduction electrons, the photonic band structure of binary dielectric-metal superlattice is theoretically studied. Using the constitutive nonlocal relation between the electrical current density and the electric field inside the metallic layer, the dispersion equation for photonic eigenmodes in the periodic stack is analytically expressed in terms of the surface impedances at the interfaces of the metal and dielectric layers. In the case of very thin metallic layers, the optic spectrum for the superlattice exhibits narrow pass bands as a result of the strong contrast between the impedances of the dielectric and the metal. The narrow pass bands are attributed to Fabry-Perot resonances in the relatively-thick dielectric layer. The metal nonlocality is well pronounced in the infrared and, therefore, the nonlocal effect upon the photonic band structure of the superlattice can be strong when the Fabry-Perot resonance bands are in that frequency range. Our results for the photonic spectrum have been compared with those obtained within the local Drude-Lorentz model. Noticeably differences not only in the the magnitude, but also in the sign of the real part of the Bloch wave number in the Fabry-Perot resonance bands, have been found.

  8. Fabrication and applications of multi-layer graphene stack on transparent polymer

    NASA Astrophysics Data System (ADS)

    Krajewska, Aleksandra; Pasternak, Iwona; Sobon, Grzegorz; Sotor, Jaroslaw; Przewloka, Aleksandra; Ciuk, Tymoteusz; Sobieski, Jan; Grzonka, Justyna; Abramski, Krzysztof M.; Strupinski, Wlodek

    2017-01-01

    In this report, we demonstrate the preparation method of a multi-layer stack with a pre-defined number of graphene layers, which was obtained using chemical vapor deposition graphene deposited on a copper substrate and subsequently transferred onto a poly(methyl methacrylate) (PMMA) substrate. The prepared multi-layer stack can also be transferred onto an arbitrary substrate and in the end, the polymer can be removed, which in consequence significantly increases the range of possible graphene applications. The multi-layer character was confirmed by optical transmittance measurements and Raman spectroscopy, whereas the microstructure of the multi-layer graphene stack was investigated using Scanning Electron Microscopy. The electrical properties in the function of the number of graphene layers were assessed with standard Hall Effect measurements. Finally, we showed the practical application of the multi-layer graphene stack as a saturable absorber of a mode-locked Er-doped fiber laser.

  9. Dimensional crossover of electron weak localization in ZnO/TiO{sub x} stacked layers grown by atomic layer deposition

    SciTech Connect

    Saha, D. E-mail: pmisra@rrcat.gov.in; Misra, P. E-mail: pmisra@rrcat.gov.in; Joshi, M. P.; Kukreja, L. M.; Bhartiya, S.; Gupta, M.

    2016-01-25

    We report on the dimensional crossover of electron weak localization in ZnO/TiO{sub x} stacked layers having well-defined and spatially-localized Ti dopant profiles along film thickness. These films were grown by in situ incorporation of sub-monolayer TiO{sub x} on the growing ZnO film surface and subsequent overgrowth of thin conducting ZnO spacer layer using atomic layer deposition. Film thickness was varied in the range of ∼6–65 nm by vertically stacking different numbers (n = 1–7) of ZnO/TiO{sub x} layers of nearly identical dopant-profiles. The evolution of zero-field sheet resistance (R{sub ◻}) versus temperature with decreasing film thickness showed a metal to insulator transition. On the metallic side of the metal-insulator transition, R{sub ◻}(T) and magnetoresistance data were found to be well corroborated with the theoretical framework of electron weak localization in the diffusive transport regime. The temperature dependence of both R{sub ◻} and inelastic scattering length provided strong evidence for a smooth crossover from 2D to 3D weak localization behaviour. Results of this study provide deeper insight into the electron transport in low-dimensional n-type ZnO/TiO{sub x} stacked layers which have potential applications in the field of transparent oxide electronics.

  10. Phase Modulator with Terahertz Optical Bandwidth Formed by Multi-Layered Dielectric Stack

    NASA Technical Reports Server (NTRS)

    Keys, Andrew S. (Inventor); Fork, Richard L. (Inventor)

    2005-01-01

    An optical phase modulator includes a bandpass multilayer stack, formed by a plurality of dielectric layers, preferably of GaAs and AlAs, and having a transmission function related to the refractive index of the layers of the stack, for receiving an optical input signal to be phase modulated. A phase modulator device produces a nonmechanical change in the refractive index of each layer of the stack by, e.g., the injection of free carrier, to provide shifting of the transmission function so as to produce phase modulation of the optical input signal and to thereby produce a phase modulated output signal.

  11. Control of layer stacking in CVD graphene under quasi-static condition.

    PubMed

    Subhedar, Kiran M; Sharma, Indu; Dhakate, Sanjay R

    2015-09-14

    The type of layer stacking in bilayer graphene has a significant influence on its electronic properties because of the contrast nature of layer coupling. Herein, different geometries of the reaction site for the growth of bilayer graphene by the chemical vapor deposition (CVD) technique and their effects on the nature of layer stacking are investigated. Micro-Raman mapping and curve fitting analysis confirmed the type of layer stacking for the CVD grown bilayer graphene. The samples grown with sandwiched structure such as quartz/Cu foil/quartz along with a spacer, between the two quartz plates to create a sealed space, resulted in Bernal or AB stacked bilayer graphene while the sample sandwiched without a spacer produced the twisted bilayer graphene. The contrast difference in the layer stacking is a consequence of the difference in the growth mechanism associated with different geometries of the reaction site. The diffusion dominated process under quasi-static control is responsible for the growth of twisted bilayer graphene in sandwiched geometry while surface controlled growth with ample and continual supply of carbon in sandwiched geometry along with a spacer, leads to AB stacked bilayer graphene. Through this new approach, an efficient technique is presented to control the nature of layer stacking.

  12. Two-Dimensional Layered Oxide Structures Tailored by Self-Assembled Layer Stacking via Interfacial Strain

    DOE PAGES

    Zhang, Wenrui; Li, Mingtao; Chen, Aiping; ...

    2016-06-13

    Two-dimensional (2D) nanostructures emerge as one of leading topics in fundamental materials science and could enable next generation nanoelectronic devices. Beyond graphene and molybdenum disulphide, layered complex oxides are another large group of promising 2D candidates because of their strong interplay of intrinsic charge, spin, orbital and lattice. As a fundamental basis of heteroepitaxial thin film growth, interfacial strain can be used to design materials exhibiting new phenomena beyond their conventional form. Here we report the strain-driven self-assembly of Bismuth-based supercells (SC) with a 2D layered structure, and elucidate the fundamental growth mechanism with combined experimental tools and first-principles calculations.more » The study revealed that the new layered structures were formed by the strain-enabled self-assembled atomic layer stacking, i.e., alternative growth of Bi2O2 layer and [Fe0.5Mn0.5]O6 layer. The strain-driven approach is further demonstrated in other SC candidate systems with promising room-temperature multiferroic properties. This well-integrated theoretical and experimental study inspired by the Materials Genome Initiatives opens up a new avenue in searching and designing novel 2D layered complex oxides with enormous promises.« less

  13. Two-Dimensional Layered Oxide Structures Tailored by Self-Assembled Layer Stacking via Interfacial Strain

    SciTech Connect

    Zhang, Wenrui; Li, Mingtao; Chen, Aiping; Li, Leigang; Zhu, Yuanyuan; Xia, Zhenhai; Lu, Ping; Boullay, Philippe; Wu, Lijun; Zhu, Yimei; MacManus-Driscoll, Judith L.; Jia, Quanxi; Zhou, Honghui; Narayan, Jagdish; Zhang, Xinghang; Wang, Haiyan

    2016-06-13

    Two-dimensional (2D) nanostructures emerge as one of leading topics in fundamental materials science and could enable next generation nanoelectronic devices. Beyond graphene and molybdenum disulphide, layered complex oxides are another large group of promising 2D candidates because of their strong interplay of intrinsic charge, spin, orbital and lattice. As a fundamental basis of heteroepitaxial thin film growth, interfacial strain can be used to design materials exhibiting new phenomena beyond their conventional form. Here we report the strain-driven self-assembly of Bismuth-based supercells (SC) with a 2D layered structure, and elucidate the fundamental growth mechanism with combined experimental tools and first-principles calculations. The study revealed that the new layered structures were formed by the strain-enabled self-assembled atomic layer stacking, i.e., alternative growth of Bi2O2 layer and [Fe0.5Mn0.5]O6 layer. The strain-driven approach is further demonstrated in other SC candidate systems with promising room-temperature multiferroic properties. This well-integrated theoretical and experimental study inspired by the Materials Genome Initiatives opens up a new avenue in searching and designing novel 2D layered complex oxides with enormous promises.

  14. Four-Dimensional Lung Treatment Planning in Layer-Stacking Carbon Ion Beam Treatment: Comparison of Layer-Stacking and Conventional Ungated/Gated Irradiation

    SciTech Connect

    Mori, Shinichiro; Kanematsu, Nobuyuki; Asakura, Hiroshi; Sharp, Gregory C.; Kumagai, Motoki; Dobashi, Suguru; Nakajima, Mio; Yamamoto, Naoyoshi; Kandatsu, Susumu; Baba, Masayuki

    2011-06-01

    Purpose: We compared four-dimensional (4D) layer-stacking and conventional carbon ion beam distribution in the treatment of lung cancer between ungated and gated respiratory strategies using 4DCT data sets. Methods and Materials: Twenty lung patients underwent 4DCT imaging under free-breathing conditions. Using planning target volumes (PTVs) at respective respiratory phases, two types of compensating bolus were designed, a full single respiratory cycle for the ungated strategy and an approximately 30% duty cycle for the exhalation-gated strategy. Beams were delivered to the PTVs for the ungated and gated strategies, PTV(ungated) and PTV(gated), respectively, which were calculated by combining the respective PTV(Tn)s by layer-stacking and conventional irradiation. Carbon ion beam dose distribution was calculated as a function of respiratory phase by applying a compensating bolus to 4DCT. Accumulated dose distributions were calculated by applying deformable registration. Results: With the ungated strategy, accumulated dose distributions were satisfactorily provided to the PTV, with D95 values for layer-stacking and conventional irradiation of 94.0% and 96.2%, respectively. V20 for the lung and Dmax for the spinal cord were lower with layer-stacking than with conventional irradiation, whereas Dmax for the skin (14.1 GyE) was significantly lower (21.9 GyE). In addition, dose conformation to the GTV/PTV with layer-stacking irradiation was better with the gated than with the ungated strategy. Conclusions: Gated layer-stacking irradiation allows the delivery of a carbon ion beam to a moving target without significant degradation of dose conformity or the development of hot spots.

  15. Inter-layered clay stacks in Jurassic shales

    NASA Technical Reports Server (NTRS)

    Pye, K.; Krinsley, D. H.

    1983-01-01

    Scanning electron microscopy in the backscattered electron mode is used together with energy-dispersive X-ray microanalysis to show that Lower Jurassic shales from the North Sea Basin contain large numbers of clay mineral stacks up to 150 microns in size. Polished shale sections are examined to determine the size, shape orientation, textural relationships, and internal compositional variations of the clays. Preliminary evidence that the clay stacks are authigenic, and may have formed at shallow burial depths during early diagenesis, is presented.

  16. About zone structure of a stack of a cholesteric liquid crystal and isotropic medium layers

    NASA Astrophysics Data System (ADS)

    Gevorgyan, A. H.; Matinyan, G. K.; Harutyunyan, M. Z.; Harutyunyan, E. M.

    2014-05-01

    The optical properties of a stack of metamaterial-based cholesteric liquid crystal (CLC) layers and isotropic medium layers are investigated. CLCs with two types of chiral nihility are defined. The peculiarities of the reflection spectra of this system are investigated and it is shown that the reflection spectra of the stacks of CLC layers of these two types differ from each other. The influence of: the CLC sublayer thicknesses; incidence angle; local dielectric (magnetic) anisotropy of the CLC layers; refraction indices and thicknesses of the isotropic media layers on the reflection spectra and other optical characteristics of the system is investigated.

  17. Layer-by-layer graphene/TCNQ stacked films as conducting anodes for organic solar cells.

    PubMed

    Hsu, Chang-Lung; Lin, Cheng-Te; Huang, Jen-Hsien; Chu, Chih-Wei; Wei, Kung-Hwa; Li, Lain-Jong

    2012-06-26

    Large-area graphene grown by chemical vapor deposition (CVD) is a promising candidate for transparent conducting electrode applications in flexible optoelectronic devices such as light-emitting diodes or organic solar cells. However, the power conversion efficiency (PCE) of the polymer photovoltaic devices using a pristine CVD graphene anode is still not appealing due to its much lower conductivity than that of conventional indium tin oxide. We report a layer-by-layer molecular doping process on graphene for forming sandwiched graphene/tetracyanoquinodimethane (TCNQ)/graphene stacked films for polymer solar cell anodes, where the TCNQ molecules (as p-dopants) were securely embedded between two graphene layers. Poly(3-hexylthiophene)/phenyl-C61-butyric acid methyl ester (P3HT/PCBM) bulk heterojunction polymer solar cells based on these multilayered graphene/TCNQ anodes are fabricated and characterized. The P3HT/PCBM device with an anode structure composed of two TCNQ layers sandwiched by three CVD graphene layers shows optimum PCE (∼2.58%), which makes the proposed anode film quite attractive for next-generation flexible devices demanding high conductivity and transparency.

  18. Two-Dimensional Layered Oxide Structures Tailored by Self-Assembled Layer Stacking via Interfacial Strain.

    PubMed

    Zhang, Wenrui; Li, Mingtao; Chen, Aiping; Li, Leigang; Zhu, Yuanyuan; Xia, Zhenhai; Lu, Ping; Boullay, Philippe; Wu, Lijun; Zhu, Yimei; MacManus-Driscoll, Judith L; Jia, Quanxi; Zhou, Honghui; Narayan, Jagdish; Zhang, Xinghang; Wang, Haiyan

    2016-07-06

    Study of layered complex oxides emerge as one of leading topics in fundamental materials science because of the strong interplay among intrinsic charge, spin, orbital, and lattice. As a fundamental basis of heteroepitaxial thin film growth, interfacial strain can be used to design materials that exhibit new phenomena beyond their conventional forms. Here, we report a strain-driven self-assembly of bismuth-based supercell (SC) with a two-dimensional (2D) layered structure. With combined experimental analysis and first-principles calculations, we investigated the full SC structure and elucidated the fundamental growth mechanism achieved by the strain-enabled self-assembled atomic layer stacking. The unique SC structure exhibits room-temperature ferroelectricity, enhanced magnetic responses, and a distinct optical bandgap from the conventional double perovskite structure. This study reveals the important role of interfacial strain modulation and atomic rearrangement in self-assembling a layered singe-phase multiferroic thin film, which opens up a promising avenue in the search for and design of novel 2D layered complex oxides with enormous promise.

  19. Influence of stacking fault energy on friction of nanotwinned metals

    NASA Astrophysics Data System (ADS)

    Zhang, J. J.; Wang, Z. F.; Sun, T.; Yan, Y. D.

    2016-12-01

    The unique dislocation-twin boundary (TB) interactions that govern the extraordinary mechanical properties of nanotwinned (NT) metals have the strong intrinsic effect of material energy and the extrinsic effect of feature size. In this work, we perform molecular dynamics (MD) simulations to elucidate fundamental deformation mechanisms of two NT face-centered cubic (FCC) metals (Cu and Pd) under probe-based friction, with an emphasis on evaluating the influence of both material’s intrinsic energy barrier and extrinsic grain size on the microscopic deformation behavior and correlated macroscopic frictional results of the materials. Simulation results reveal that individual deformation modes of dislocation mechanisms, dislocation-TB interactions, TB-associated mechanisms, deformation twinning and grain boundary (GB) accommodation work in parallel in the plastic deformation of the materials, and their competition is strongly influenced by both the intrinsic energy barriers for the nucleation of stacking faults and twin faults, and the extrinsic grain size. Consequently, both the frictional response and worn surface morphology present strong anisotropic characteristics. It is also found that the deformation behavior of NT Pd under a localized multi-axis stress state is significantly different from that which occurs under a uniaxial stress state. These findings will advance the rational design and synthesis of nanostructured materials with advanced frictional properties.

  20. Transistor memory devices with large memory windows, using multi-stacking of densely packed, hydrophobic charge trapping metal nanoparticle array

    NASA Astrophysics Data System (ADS)

    Cho, Ikjun; Kim, Beom Joon; Ryu, Sook Won; Cho, Jeong Ho; Cho, Jinhan

    2014-12-01

    Organic field-effect transistor (OFET) memories have rapidly evolved from low-cost and flexible electronics with relatively low-memory capacities to memory devices that require high-capacity memory such as smart memory cards or solid-state hard drives. Here, we report the high-capacity OFET memories based on the multilayer stacking of densely packed hydrophobic metal NP layers in place of the traditional transistor memory systems based on a single charge trapping layer. We demonstrated that the memory performances of devices could be significantly enhanced by controlling the adsorption isotherm behavior, multilayer stacking structure and hydrophobicity of the metal NPs. For this study, tetraoctylammonium (TOA)-stabilized Au nanoparticles (TOA-AuNPs) were consecutively layer-by-layer (LbL) assembled with an amine-functionalized poly(amidoamine) dendrimer (PAD). The formed (PAD/TOA-AuNP)n films were used as a multilayer stacked charge trapping layer at the interface between the tunneling dielectric layer and the SiO2 gate dielectric layer. For a single AuNP layer (i.e. PAD/TOA-AuNP)1) with a number density of 1.82 × 1012 cm-2, the memory window of the OFET memory device was measured to be approximately 97 V. The multilayer stacked OFET memory devices prepared with four AuNP layers exhibited excellent programmable memory properties (i.e. a large memory window (ΔVth) exceeding 145 V, a fast switching speed (1 μs), a high program/erase (P/E) current ratio (greater than 106) and good electrical reliability) during writing and erasing over a relatively short time scale under an operation voltage of 100 V applied at the gate.

  1. Transistor memory devices with large memory windows, using multi-stacking of densely packed, hydrophobic charge trapping metal nanoparticle array.

    PubMed

    Cho, Ikjun; Kim, Beom Joon; Ryu, Sook Won; Cho, Jeong Ho; Cho, Jinhan

    2014-12-19

    Organic field-effect transistor (OFET) memories have rapidly evolved from low-cost and flexible electronics with relatively low-memory capacities to memory devices that require high-capacity memory such as smart memory cards or solid-state hard drives. Here, we report the high-capacity OFET memories based on the multilayer stacking of densely packed hydrophobic metal NP layers in place of the traditional transistor memory systems based on a single charge trapping layer. We demonstrated that the memory performances of devices could be significantly enhanced by controlling the adsorption isotherm behavior, multilayer stacking structure and hydrophobicity of the metal NPs. For this study, tetraoctylammonium (TOA)-stabilized Au nanoparticles (TOA-Au(NPs)) were consecutively layer-by-layer (LbL) assembled with an amine-functionalized poly(amidoamine) dendrimer (PAD). The formed (PAD/TOA-Au(NP))(n) films were used as a multilayer stacked charge trapping layer at the interface between the tunneling dielectric layer and the SiO2 gate dielectric layer. For a single AuNP layer (i.e. PAD/TOA-Au(NP))1) with a number density of 1.82 × 10(12) cm(-2), the memory window of the OFET memory device was measured to be approximately 97 V. The multilayer stacked OFET memory devices prepared with four Au(NP) layers exhibited excellent programmable memory properties (i.e. a large memory window (ΔV(th)) exceeding 145 V, a fast switching speed (1 μs), a high program/erase (P/E) current ratio (greater than 10(6)) and good electrical reliability) during writing and erasing over a relatively short time scale under an operation voltage of 100 V applied at the gate.

  2. Laminated metal composite formed from low flow stress layers and high flow stress layers using flow constraining elements and making same

    DOEpatents

    Syn, Chol K.; Lesuer, Donald R.

    1995-01-01

    A laminated metal composite of low flow stress layers and high flow stress layers is described which is formed using flow constraining elements, preferably in the shape of rings, individually placed around each of the low flow stress layers while pressure is applied to the stack to bond the layers of the composite together, to thereby restrain the flow of the low flow stress layers from the stack during the bonding. The laminated metal composite of the invention is made by the steps of forming a stack of alternate layers of low flow stress layers and high flow stress layers with each layer of low flow stress material surrounded by an individual flow constraining element, such as a ring, and then applying pressure to the top and bottom surfaces of the resulting stack to bond the dissimilar layers together, for example, by compression rolling the stack. In a preferred embodiment, the individual flow constraining elements surrounding the layers of low flow stress material are formed of a material which may either be the same material as the material comprising the high flow stress layers, or have similar flow stress characteristics to the material comprising the high flow stress layers. Additional sacrificial layers may be added to the top and bottom of the stack to avoid damage to the stack during the bonding step; and these additional layers may then be removed after the bonding step.

  3. Laminated metal composite formed from low flow stress layers and high flow stress layers using flow constraining elements and making same

    DOEpatents

    Syn, C.K.; Lesuer, D.R.

    1995-07-04

    A laminated metal composite of low flow stress layers and high flow stress layers is described which is formed using flow constraining elements, preferably in the shape of rings, individually placed around each of the low flow stress layers while pressure is applied to the stack to bond the layers of the composite together, to thereby restrain the flow of the low flow stress layers from the stack during the bonding. The laminated metal composite of the invention is made by the steps of forming a stack of alternate layers of low flow stress layers and high flow stress layers with each layer of low flow stress material surrounded by an individual flow constraining element, such as a ring, and then applying pressure to the top and bottom surfaces of the resulting stack to bond the dissimilar layers together, for example, by compression rolling the stack. In a preferred embodiment, the individual flow constraining elements surrounding the layers of low flow stress material are formed of a material which may either be the same material as the material comprising the high flow stress layers, or have similar flow stress characteristics to the material comprising the high flow stress layers. Additional sacrificial layers may be added to the top and bottom of the stack to avoid damage to the stack during the bonding step; and these additional layers may then be removed after the bonding step. 5 figs.

  4. Stacking of lamellae in Mg/Al hydrotalcites: Effect of metal ion concentrations on morphology

    SciTech Connect

    Panda, H.S.; Srivastava, R.; Bahadur, D.

    2008-06-03

    A hybrid nanocomposite based on the intercalation of carbonate anion has been synthesized through co-precipitation technique. Powder X-ray diffraction patterns (PXRD) showed pure layered double hydroxide (LDH) phases having crystallite size around 20 and 13 nm in 'a' and 'c' crystallographic directions, respectively. Fourier transform infrared and Raman spectroscopy measurements exhibit shifting of bands with increase of divalent metal ion concentration and it further suggests the presence of carbonate anions. Differential scanning calorimetry (DSC) and thermogravimetry analysis (TGA) exhibit the three stages of thermal degradation, which is characteristic behaviour of layered double hydroxide. CHN and energy dispersive X-ray analysis support the PXRD and spectroscopy results. The nature of charge observed through Zeta potential analyzer is positive. Transmission electron microscope (TEM) exhibits the characteristic LDH platelet morphology with the platelets stacked one above the other.

  5. Modeling boron dose loss in sidewall spacer stacks of complementary metal oxide semiconductor transistors

    NASA Astrophysics Data System (ADS)

    Essa, Z.; Pelletier, B.; Morin, P.; Boulenc, P.; Pakfar, A.; Tavernier, C.; Wacquant, F.; Zechner, C.; Juhel, M.; Autran, J. L.; Cristiano, F.

    2016-12-01

    The presence of capping materials during annealing (activation for example) can substantially impact the silicon junction profiles of Complementary Metal Oxide Semiconductor Field Effect Transistors (CMOSFET), depending on the nature of these layers. In this paper we specifically investigated the boron out-diffusion from a silicon junction into the silicon oxide in presence of a silicon oxide/silicon nitride capping bi-layer similar to the stacks used to form sidewall spacers. After 120 s anneal we observed with secondary ion mass spectrometry (SIMS) substantial boron dose loss in silicon and segregation at the silicon oxide interface related to oxide and nitride material properties, in particular to the hydrogen concentration. We then modeled the boron profiles in both silicon and oxide as a function of the hydrogen static and dynamic in the materials. The exponential-like boron diffusion profiles observed in oxide are reproduced by introducing a long hop mechanism mediated with hydrogen-related defects (HRDs).

  6. Creating CZTS thin films via stacked metallic CVD and sulfurization

    NASA Astrophysics Data System (ADS)

    Bielecki, Anthony

    Cu2ZnSnS4 (CZTS) thin-film photovoltaics is an increasingly important area of research for solar energy due to the high abundance and low toxicity of the elements used. A series of chemical vapor depositions (CVDs) with copper, tin, and zinc precursors were carried out to create layered thin films on quartz substrates. The viability of creating CZTS using these precursors was examined. As far as the author is aware, no work has yet been published on creating CZTS using the particular tin precursor that was used here, Dibutyltin Diacetate. Four different precursor stacking sequences were examined. Depositions were characterized using atomic force microscopy, energy-dispersive x-ray spectroscopy, x-ray diffraction, and four-point resistivity measurements. It was found that the ordering of precursors has a significant effect on the properties of the resulting thin films. The band gap energies were found to range from 1.08 eV to 2.02 eV.

  7. Ternary metal-rich sulfide with a layered structure

    DOEpatents

    Franzen, Hugo F.; Yao, Xiaoqiang

    1993-08-17

    A ternary Nb-Ta-S compound is provided having the atomic formula, Nb.sub.1.72 Ta.sub.3.28 S.sub.2, and exhibiting a layered structure in the sequence S-M3-M2-M1-M2-M3-S wherein S represents sulfur layers and M1, M2, and M3 represent Nb/Ta mixed metal layers. This sequence generates seven sheets stacked along the [001] direction of an approximate body centered cubic crystal structure with relatively weak sulfur-to-sulfur van der Waals type interactions between adjacent sulfur sheets and metal-to-metal bonding within and between adjacent mixed metal sheets.

  8. Reversible loss of Bernal stacking during the deformation of few-layer graphene in nanocomposites.

    PubMed

    Gong, Lei; Young, Robert J; Kinloch, Ian A; Haigh, Sarah J; Warner, Jamie H; Hinks, Jonathan A; Xu, Ziwei; Li, Li; Ding, Feng; Riaz, Ibtsam; Jalil, Rashid; Novoselov, Kostya S

    2013-08-27

    The deformation of nanocomposites containing graphene flakes with different numbers of layers has been investigated with the use of Raman spectroscopy. It has been found that there is a shift of the 2D band to lower wavenumber and that the rate of band shift per unit strain tends to decrease as the number of graphene layers increases. It has been demonstrated that band broadening takes place during tensile deformation for mono- and bilayer graphene but that band narrowing occurs when the number of graphene layers is more than two. It is also found that the characteristic asymmetric shape of the 2D Raman band for the graphene with three or more layers changes to a symmetrical shape above about 0.4% strain and that it reverts to an asymmetric shape on unloading. This change in Raman band shape and width has been interpreted as being due to a reversible loss of Bernal stacking in the few-layer graphene during deformation. It has been shown that the elastic strain energy released from the unloading of the inner graphene layers in the few-layer material (~0.2 meV/atom) is similar to the accepted value of the stacking fault energies of graphite and few layer graphene. It is further shown that this loss of Bernal stacking can be accommodated by the formation of arrays of partial dislocations and stacking faults on the basal plane. The effect of the reversible loss of Bernal stacking upon the electronic structure of few-layer graphene and the possibility of using it to modify the electronic structure of few-layer graphene are discussed.

  9. Reversible Loss of Bernal Stacking during the Deformation of Few-Layer Graphene in Nanocomposites

    PubMed Central

    2013-01-01

    The deformation of nanocomposites containing graphene flakes with different numbers of layers has been investigated with the use of Raman spectroscopy. It has been found that there is a shift of the 2D band to lower wavenumber and that the rate of band shift per unit strain tends to decrease as the number of graphene layers increases. It has been demonstrated that band broadening takes place during tensile deformation for mono- and bilayer graphene but that band narrowing occurs when the number of graphene layers is more than two. It is also found that the characteristic asymmetric shape of the 2D Raman band for the graphene with three or more layers changes to a symmetrical shape above about 0.4% strain and that it reverts to an asymmetric shape on unloading. This change in Raman band shape and width has been interpreted as being due to a reversible loss of Bernal stacking in the few-layer graphene during deformation. It has been shown that the elastic strain energy released from the unloading of the inner graphene layers in the few-layer material (∼0.2 meV/atom) is similar to the accepted value of the stacking fault energies of graphite and few layer graphene. It is further shown that this loss of Bernal stacking can be accommodated by the formation of arrays of partial dislocations and stacking faults on the basal plane. The effect of the reversible loss of Bernal stacking upon the electronic structure of few-layer graphene and the possibility of using it to modify the electronic structure of few-layer graphene are discussed. PMID:23899378

  10. Spin and valley resolved Landau level crossing in tri-layer ABA stacked graphene

    NASA Astrophysics Data System (ADS)

    Datta, Biswajit; Gupta, Vishakha; Borah, Abhinandan; Watanabe, Kenji; Taniguchi, Takashi; Deshmukh, Mandar

    We present quantum Hall measurements on a high quality encapsulated tri-layer graphene device. Low temperature field effect mobility of this device is around 500,000 cm2/Vs and we see SdH oscillations at a magnetic field as low as 0.3 T. Quantum Hall measurements confirm that the chosen tri layer graphene is Bernal (ABA) stacked. Due to the presence of both mass-less monolayer like Dirac fermions and massive bi-layer like Dirac fermions in Bernal stacked tri-layer graphene, there are Landau level crossings between monolayer and bi-layer bands in quantum Hall regime. Although most of the Landau Level crossings are predominantly present on the electron sides, we also observe signatures of the crossings on the hole side. This behaviour is consistent with the asymmetry of electron and hole in ABA tri-layer graphene. We observe a series of crossings of the spin and valley resolved Landau Levels.

  11. Carrier scattering in high-κ/metal gate stacks

    NASA Astrophysics Data System (ADS)

    Zeng, Zaiping; Triozon, François; Niquet, Yann-Michel

    2017-03-01

    A significant degradation of the mobility has been repeatedly observed at low inversion density in high-κ/metal gate metal-oxide-semiconductor field-effect transistors. However, the scattering mechanisms responsible for this degradation are still debated. It is often assumed that the mobility is limited by remote charges (RCS) at the interface between SiO2 and HfO2. However, the amount of charges needed to reproduce the experimental mobilities is usually very high (a few 1013 cm-2), and does not seem to be consistent with the measured threshold voltages. Scattering by localized dipoles hardly solves these discrepancies. Here, we investigate the contribution from three alternative mechanisms in a non-equilibrium Green's functions framework: (i) scattering by band offset fluctuations at the SiO2/HfO2 interface, (ii) scattering by dielectric constant fluctuations in SiO2 and HfO2, and (iii) scattering by workfunction fluctuations in a granular metal gate. None of these mechanisms significantly shifts the threshold voltage. We show that mechanisms (i) and (iii) efficiently scatter the carriers at low inversion densities. This reduces the amount of RCS charges needed to reproduce the experimental data. RCS and these mechanisms show different dependences on the thickness of the HfO2 layer, which might help to identify the dominant contributions.

  12. Photonic density of states of a stack of cholesteric liquid crystals and isotropic medium layers

    NASA Astrophysics Data System (ADS)

    Oganesyan, K. B.; Gevorgyan, A. H.; Kocharian, A. N.; Vardanyan, G. A.; Chilingaryan, Yu. S.; Santrosyan, E. A.; Rostovtsev, Y. V.

    2014-10-01

    We investigated the zone structure peculiarities and the photonic density of states (PDS) of the eigen polarizations (EPs) in the system composed of a stack of layers of a cholesteric liquid crystal (CLC) and an isotropic medium. The problem was solved by Ambartsumian's layer addition modified method. The influence of the CLC sublayer thicknesses and the thicknesses of the isotropic media layers on the reflection an PDS spectra of the system is investigated.

  13. Dynamic Recrystallization of Low Stacking Fault Energy Metals

    DTIC Science & Technology

    2007-11-02

    dynamic recovery" occurs by progressive (slow) transformation of subgrain boundaries (LAGB) into grain boundaries (HAGB) - dynamic recovery is weak ...homogeneous ( weak ∆ρ) - the rate of grain boundary migration is high - the rate of grain boundary migration is low low stacking fault energy materials...Cu, γ-iron and austenitic steels, Ni-base superalloys, ... high stacking fault energy materials: Al, α-iron and ferritic steels, β- titanium

  14. Addressing Raman features of individual layers in isotopically labeled Bernal stacked bilayer graphene

    NASA Astrophysics Data System (ADS)

    Costa, Sara D.; Weis, Johan Ek; Frank, Otakar; Fridrichová, Michaela; Kalbac, Martin

    2016-06-01

    In this report important Raman modes for the evaluation of strain in graphene (the 2D and 2D‧) are analyzed. The isotope labeling is used to disentangle contribution of individual graphene layers of graphene bilayer to the studied Raman modes. It is shown that for Bernal-stacked bilayers, the 2D and the 2D‧ Raman modes have three distinct components that can be assigned to processes originating solely from the top graphene layer, bottom graphene layer, and from a combination of processes originating both from the top and bottom layers. The reported results thus enable addressing the properties of individual graphene layers in graphene bilayer by Raman spectroscopy.

  15. Interplay between intrinsic and stacking-fault magnetic domains in bi-layered manganites

    SciTech Connect

    Hossain, M.A; Burkhardt, Mark H.; Sarkar, S.; Ohldag, H.; Chuang, Y.-D.; Scholl, A.; Young, A.T.; Doran, A.; Dessau, D.S.; Zheng, H.; Mitchell, J.F.; Durr, H.A.; Stohr, J.

    2012-09-11

    We present a low temperature X-ray photoemission electron microscopy study of the bi-layered manganite compound La{sub 1.2}Sr{sub 1.8}Mn{sub 2}O{sub 7} (BL-LSMO) to investigate the influence of stacking faults, which are structurally and magnetically different from the bi-layered host. In BL-LSMO small magnetic moment persists to T* = 300K, well above the Curie temperature of 120K (T{sub C}). Our magnetic images show that 3D stacking faults are responsible for the T* transition. Furthermore, close to the T{sub C}, stacking faults are well coupled to the bi-layered host with latter magnetic domains controlling the spin direction of the stacking faults. Contrary to recent reports, we find that stacking faults do not seed magnetic domains in the host via an exchange spring mechanism and the intrinsic T{sub C} of the BL-LSMO is not lower than 120K.

  16. Microchannel neural interface manufacture by stacking silicone and metal foil laminae

    NASA Astrophysics Data System (ADS)

    Lancashire, Henry T.; Vanhoestenberghe, Anne; Pendegrass, Catherine J.; Ajam, Yazan Al; Magee, Elliot; Donaldson, Nick; Blunn, Gordon W.

    2016-06-01

    Objective. Microchannel neural interfaces (MNIs) overcome problems with recording from peripheral nerves by amplifying signals independent of node of Ranvier position. Selective recording and stimulation using an MNI requires good insulation between microchannels and a high electrode density. We propose that stacking microchannel laminae will improve selectivity over single layer MNI designs due to the increase in electrode number and an improvement in microchannel sealing. Approach. This paper describes a manufacturing method for creating MNIs which overcomes limitations on electrode connectivity and microchannel sealing. Laser cut silicone—metal foil laminae were stacked using plasma bonding to create an array of microchannels containing tripolar electrodes. Electrodes were DC etched and electrode impedance and cyclic voltammetry were tested. Main results. MNIs with 100 μm and 200 μm diameter microchannels were manufactured. High electrode density MNIs are achievable with electrodes present in every microchannel. Electrode impedances of 27.2 ± 19.8 kΩ at 1 kHz were achieved. Following two months of implantation in Lewis rat sciatic nerve, micro-fascicles were observed regenerating through the MNI microchannels. Significance. Selective MNIs with the peripheral nervous system may allow upper limb amputees to control prostheses intuitively.

  17. Large changes of graphene conductance as a function of lattice orientation between stacked layers

    NASA Astrophysics Data System (ADS)

    Lee, Hyunsoo; Qi, Yabing; Kwon, Sangku; Salmeron, Miquel; Park, Jeong Young

    2015-01-01

    Using the conductive tip of an atomic force microscope as an electrode, we found that the electrical conductance of graphite terraces separated by steps can vary by large factors of up to 100, depending on the relative lattice orientation of the surface and subsurface layers. This effect can be attributed to interlayer interactions that, when stacked commensurately in a Bernal sequence (ABAB…), cause the band gap to open. Misaligned layers, on the other hand, behave like graphene. Angular misorientations of a few degrees were found to cause large increases in the conductance of the top layer, with the maximum occurring around 30°. These results suggest new applications for graphene multilayers by stacking layers at various angles to control the resistance of the connected graphene ribbons in devices.

  18. Giant enhancement in vertical conductivity of stacked CVD graphene sheets by self-assembled molecular layers

    NASA Astrophysics Data System (ADS)

    Liu, Yanpeng; Yuan, Li; Yang, Ming; Zheng, Yi; Li, Linjun; Gao, Libo; Nerngchamnong, Nisachol; Nai, Chang Tai; Sangeeth, C. S. Suchand; Feng, Yuan Ping; Nijhuis, Christian A.; Loh, Kian Ping

    2014-11-01

    Layer-by-layer-stacked chemical vapour deposition (CVD) graphene films find applications as transparent and conductive electrodes in solar cells, organic light-emitting diodes and touch panels. Common to lamellar-type systems with anisotropic electron delocalization, the plane-to-plane (vertical) conductivity in such systems is several orders lower than its in-plane conductivity. The poor electronic coupling between the planes is due to the presence of transfer process organic residues and trapped air pocket in wrinkles. Here we show the plane-to-plane tunnelling conductivity of stacked CVD graphene layers can be improved significantly by inserting 1-pyrenebutyric acid N-hydroxysuccinimide ester between the graphene layers. The six orders of magnitude increase in plane-to-plane conductivity is due to hole doping, orbital hybridization, planarization and the exclusion of polymer residues. Our results highlight the importance of interfacial modification for enhancing the performance of LBL-stacked CVD graphene films, which should be applicable to other types of stacked two-dimensional films.

  19. A novel method of fabricating laminated silicone stack actuators with pre-strained dielectric layers

    NASA Astrophysics Data System (ADS)

    Hinitt, Andrew D.; Conn, Andrew T.

    2014-03-01

    In recent studies, stack based Dielectric Elastomer Actuators (DEAs) have been successfully used in haptic feedback and sensing applications. However, limitations in the fabrication method, and materials used to con- struct stack actuators constrain their force and displacement output per unit volume. This paper focuses on a fabrication process enabling a stacked elastomer actuator to withstand the high tensile forces needed for high power applications, such as mimetics for mammalian muscle contraction (i.e prostheses), whilst requiring low voltage for thickness-mode contractile actuation. Spun elastomer layers are bonded together in a pre-strained state using a conductive adhesive filler, forming a Laminated Inter-Penetrating Network (L-IPN) with repeatable and uniform electrode thickness. The resulting structure utilises the stored strain energy of the dielectric elas- tomer to compress the cured electrode composite material. The method is used to fabricate an L-IPN example, which demonstrated that the bonded L-IPN has high tensile strength normal to the lamination. Additionally, the uniformity and retained dielectric layer pre-strain of the L-IPN are confirmed. The described method is envisaged to be used in a semi-automated assembly of large-scale multi-layer stacks of pre-strained dielectric layers possessing a tensile strength in the range generated by mammalian muscle.

  20. Giant enhancement in vertical conductivity of stacked CVD graphene sheets by self-assembled molecular layers.

    PubMed

    Liu, Yanpeng; Yuan, Li; Yang, Ming; Zheng, Yi; Li, Linjun; Gao, Libo; Nerngchamnong, Nisachol; Nai, Chang Tai; Sangeeth, C S Suchand; Feng, Yuan Ping; Nijhuis, Christian A; Loh, Kian Ping

    2014-11-20

    Layer-by-layer-stacked chemical vapour deposition (CVD) graphene films find applications as transparent and conductive electrodes in solar cells, organic light-emitting diodes and touch panels. Common to lamellar-type systems with anisotropic electron delocalization, the plane-to-plane (vertical) conductivity in such systems is several orders lower than its in-plane conductivity. The poor electronic coupling between the planes is due to the presence of transfer process organic residues and trapped air pocket in wrinkles. Here we show the plane-to-plane tunnelling conductivity of stacked CVD graphene layers can be improved significantly by inserting 1-pyrenebutyric acid N-hydroxysuccinimide ester between the graphene layers. The six orders of magnitude increase in plane-to-plane conductivity is due to hole doping, orbital hybridization, planarization and the exclusion of polymer residues. Our results highlight the importance of interfacial modification for enhancing the performance of LBL-stacked CVD graphene films, which should be applicable to other types of stacked two-dimensional films.

  1. Stacking Structures of Few-Layer Graphene Revealed by Phase-Sensitive Infrared Nanoscopy.

    PubMed

    Kim, Deok-Soo; Kwon, Hyuksang; Nikitin, Alexey Yu; Ahn, Seongjin; Martín-Moreno, Luis; García-Vidal, Francisco J; Ryu, Sunmin; Min, Hongki; Kim, Zee Hwan

    2015-07-28

    The stacking orders in few-layer graphene (FLG) strongly influences the electronic properties of the material. To explore the stacking-specific properties of FLG in detail, one needs powerful microscopy techniques that visualize stacking domains with sufficient spatial resolution. We demonstrate that infrared (IR) scattering scanning near-field optical microscopy (sSNOM) directly maps out the stacking domains of FLG with a nanometric resolution, based on the stacking-specific IR conductivities of FLG. The intensity and phase contrasts of sSNOM are compared with the sSNOM contrast model, which is based on the dipolar tip-sample coupling and the theoretical conductivity spectra of FLG, allowing a clear assignment of each FLG domain as Bernal, rhombohedral, or intermediate stacks for tri-, tetra-, and pentalayer graphene. The method offers 10-100 times better spatial resolution than the far-field Raman and infrared spectroscopic methods, yet it allows far more experimental flexibility than the scanning tunneling microscopy and electron microscopy.

  2. Infrared Detectors Containing Stacked Si(1-x)Ge(x)/Si Layers

    NASA Technical Reports Server (NTRS)

    Park, Jin S.; Lin, True-Lon; Jones, Eric; Del Castillo, Hector; Gunapala, Sarath

    1996-01-01

    Long-wavelength-infrared detectors containing multiple layers of high-quality crystalline p(+) Si(1-x)Ge(x) alternating with layers of Si undergoing development. Each detector comprises stack of Si(1-x)Ge(x)/Si heterojunction internal photoemission (HIP) photodetectors. In comparison with older HIP detectors containing single Si(1-x)Ge(x)/Si heterojunctions, developmental detectors feature greater quantum efficiencies and stronger photoresponses.

  3. Rapid and Nondestructive Identification of Polytypism and Stacking Sequences in Few-Layer Molybdenum Diselenide by Raman Spectroscopy

    DOE PAGES

    Lu, Xin; Utama, M. Iqbal Bakti; Lin, Junhao; ...

    2015-07-02

    Various combinations of interlayer shear modes emerge in few-layer molybdenum diselenide grown by chemical vapor deposition depending on the stacking configuration of the sample. Raman measurements may also reveal polytypism and stacking faults, as supported by first principles calculations and high-resolution transmission electron microscopy. Thus, Raman spectroscopy is an important tool in probing stacking-dependent properties in few-layer 2D materials.

  4. Layer-by-layer paper-stacking nanofibrous membranes to deliver adipose-derived stem cells for bone regeneration.

    PubMed

    Wan, Wenbing; Zhang, Shiwen; Ge, Liangpeng; Li, Qingtao; Fang, Xingxing; Yuan, Quan; Zhong, Wen; Ouyang, Jun; Xing, Malcolm

    2015-01-01

    Bone tissue engineering through seeding of stem cells in three-dimensional scaffolds has greatly improved bone regeneration technology, which historically has been a constant challenge. In this study, we researched the use of adipose-derived stem cell (ADSC)-laden layer-by-layer paper-stacking polycaprolactone/gelatin electrospinning nanofibrous membranes for bone regeneration. Using this novel paper-stacking method makes oxygen distribution, nutrition, and waste transportation work more efficiently. ADSCs can also secrete multiple growth factors required for osteogenesis. After the characterization of ADSC surface markers CD29, CD90, and CD49d using flow cytometry, we seeded ADSCs on the membranes and found cells differentiated, with significant expression of the osteogenic-related proteins osteopontin, osteocalcin, and osteoprotegerin. During 4 weeks in vitro, the ADSCs cultured on the paper-stacking membranes in the osteogenic medium exhibited the highest osteogenic-related gene expressions. In vivo, the paper-stacking scaffolds were implanted into the rat calvarial defects (5 mm diameter, one defect per parietal bone) for 12 weeks. Investigating with microcomputer tomography, the ADSC-laden paper-stacking membranes showed the most significant bone reconstruction, and from a morphological perspective, this group occupied 90% of the surface area of the defect, produced the highest bone regeneration volume, and showed the highest bone mineral density of 823.06 mg/cm(3). From hematoxylin and eosin and Masson staining, the new bone tissue was most evident in the ADSC-laden scaffold group. Using quantitative polymerase chain reaction analysis from collected tissues, we found that the ADSC-laden paper-stacking membrane group presented the highest osteogenic-related gene expressions of osteocalcin, osteopontin, osteoprotegerin, bone sialoprotein, runt-related transcription factor 2, and osterix (two to three times higher than the control group, and 1.5 times higher

  5. Biaxially textured metal substrate with palladium layer

    DOEpatents

    Robbins, William B [Maplewood, MN

    2002-12-31

    Described is an article comprising a biaxially textured metal substrate and a layer of palladium deposited on at least one major surface of the metal substrate; wherein the palladium layer has desired in-plane and out-of-plane crystallographic orientations, which allow subsequent layers that are applied on the article to also have the desired orientations.

  6. Comprehensive study and design of scaled metal/high-k/Ge gate stacks with ultrathin aluminum oxide interlayers

    SciTech Connect

    Asahara, Ryohei; Hideshima, Iori; Oka, Hiroshi; Minoura, Yuya; Hosoi, Takuji Shimura, Takayoshi; Watanabe, Heiji; Ogawa, Shingo; Yoshigoe, Akitaka; Teraoka, Yuden

    2015-06-08

    Advanced metal/high-k/Ge gate stacks with a sub-nm equivalent oxide thickness (EOT) and improved interface properties were demonstrated by controlling interface reactions using ultrathin aluminum oxide (AlO{sub x}) interlayers. A step-by-step in situ procedure by deposition of AlO{sub x} and hafnium oxide (HfO{sub x}) layers on Ge and subsequent plasma oxidation was conducted to fabricate Pt/HfO{sub 2}/AlO{sub x}/GeO{sub x}/Ge stacked structures. Comprehensive study by means of physical and electrical characterizations revealed distinct impacts of AlO{sub x} interlayers, plasma oxidation, and metal electrodes serving as capping layers on EOT scaling, improved interface quality, and thermal stability of the stacks. Aggressive EOT scaling down to 0.56 nm and very low interface state density of 2.4 × 10{sup 11 }cm{sup −2}eV{sup −1} with a sub-nm EOT and sufficient thermal stability were achieved by systematic process optimization.

  7. Impact of the Stack Order in Cu-Zn-Sn Metal Precursors on the Properties of Cu2ZnSnS4 Thin Films

    SciTech Connect

    Abusnina, Mohamed; Matin, Mohammad; Moutinho, Helio; Al-Jassim, Mowafak

    2015-06-14

    Cu2ZnSnS4 (CZTS) thin films were grown by the annealing of metallic precursors with different stack orders in sulfur atmosphere. The sequential deposition of the metal layers from single Cu, Zn, and Sn targets on Mo-coated soda-lime glass substrates was carried out using radio-frequency magnetron sputtering. In this work, we investigated the effect of the sequence of metal layers on the chemical, structural, and morphological properties of the final CZTS films using X-ray fluorescence (XRF), X-ray diffraction (XRD), Raman scattering spectroscopy, scanning electron microscopy, and energy-dispersive spectroscopy. The realized stack sequences were Mo/Sn/Zn/Cu, Mo/Sn/Cu/Zn, Mo/Cu/Zn/Sn, Mo/Cu/Sn/Zn, and Mo/Zn/Cu/Sn. XRF measurements revealed notable impact of the metal layers' stacking order in the precursor on the chemical composition. It also showed Sn loss and high Zn concentration in all sulfurized films; however, having Cu on the Sn or Zn/Sn layer showed some minimization of the Sn loss. XRD showed CZTS films with good crystallinity and no evidence of the presence of secondary phases. Changing the precursor stack order did not show any influence on the films' crystallinity or texture. Raman spectroscopy, in contrast, indicated the presence of ZnS phase beside the main CZTS phase. The morphology study showed significant effect on the structure of the final CZTS films depending on the used stack order. Generally, the films that originated from precursors having a Zn layer deposited directly on Mo or as the second layer exhibited better adhesion to the Mo layer and showed fewer or even no voids compared to the other films.

  8. Ceramic TBS/porous metal compliant layer

    NASA Technical Reports Server (NTRS)

    Tolokan, Robert P.; Jarrabet, G. P.

    1992-01-01

    Technetics Corporation manufactures metal fiber materials and components used in aerospace applications. Our technology base is fiber metal porous sheet material made from sinter bonded metal fibers. Fiber metals have percent densities (metal content by volume) from 10 to 65 percent. Various topics are covered and include the following: fiber metal materials, compliant layer thermal bayer coatings (TBC's), pad properties, ceramic/pad TBC design, thermal shock rig, fabrication, and applications.

  9. Direct Free Carrier Photogeneration in Single Layer and Stacked Organic Photovoltaic Devices.

    PubMed

    Chandran, Hrisheekesh Thachoth; Ng, Tsz-Wai; Foo, Yishu; Li, Ho-Wa; Qing, Jian; Liu, Xiao-Ke; Chan, Chiu-Yee; Wong, Fu-Lung; Zapien, Juan Antonio; Tsang, Sai-Wing; Lo, Ming-Fai; Lee, Chun-Sing

    2017-04-03

    High performance organic photovoltaic devices typically rely on type-II P/N junctions for assisting exciton dissociation. Heremans and co-workers recently reported a high efficiency device with a third organic layer which is spatially separated from the active P/N junction; but still contributes to the carrier generation by passing its energy to the P/N junction via a long-range exciton energy transfer mechanism. In this study the authors show that there is an additional mechanism contributing to the high efficiency. Some bipolar materials (e.g., subnaphthalocyanine chloride (SubNc) and subphthalocyanine chloride (SubPc)) are observed to generate free carriers much more effectively than typical organic semiconductors upon photoexcitation. Single-layer devices with SubNc or SubPc sandwiched between two electrodes can give power conversion efficiencies 30 times higher than those of reported single-layer devices. In addition, internal quantum efficiencies (IQEs) of bilayer devices with opposite stacking sequences (i.e., SubNc/SubPc vs SubPc/SubNc) are found to be the sum of IQEs of single layer devices. These results confirm that SubNc and SubPc can directly generate free carriers upon photoexcitation without assistance from a P/N junction. These allow them to be stacked onto each other with reversible sequence or simply stacking onto another P/N junction and contribute to the photocarrier generation.

  10. Amorphous Si waveguides with high-quality stacked gratings for multi-layer Si optical circuits

    NASA Astrophysics Data System (ADS)

    Tokushige, H.; Endo, T.; Saiki, K.; Hiidome, K.; Kitamura, S.; Katsuyama, T.; Tokuda, M.; Takagi, H.; Morita, M.; Ito, Y.; Tsutsui, K.; Wada, Y.; Ikeda, N.; Sugimoto, Y.

    2014-11-01

    To realize a stacked multi-layer silicon-based photonic device, a waveguide with a stacked grating was fabricated by using amorphous Si (a-Si) material, which is suitable for constructing layered structures. The fabrication method was based on forming a flat a-Si layer on a non-flat structure by using only spin-on-glass (SOG) coating technique. The a-Si grating was precisely constructed on the a-Si waveguide with gold alignment marks for electron beam lithography. Transmitted and reflected light power dependence on the grating period, wavelength, and polarization was systematically measured and compared with the designed dependence. As a result, the reflected light power exhibited a characteristic peak structure at a particular wavelength. Remarkable transverse electric/transverse magnetic (TE/TM) mode dependence was also observed. Furthermore, the measured and the designed properties were in excellent agreement with each other. Consequently, the designed structure was well reproduced in the actual stacked structure based on the a-Si material. These results pave the way for novel a-Si based integrated photonic devices such as polarization selectors and wavelength filters, indicating that a-Si is an excellent material for implementing Si-based multi-layer optical circuits.

  11. Removal of stacking-fault tetrahedra by twin boundaries in nanotwinned metals.

    PubMed

    Yu, K Y; Bufford, D; Sun, C; Liu, Y; Wang, H; Kirk, M A; Li, M; Zhang, X

    2013-01-01

    Stacking-fault tetrahedra are detrimental defects in neutron- or proton-irradiated structural metals with face-centered cubic structures. Their removal is very challenging and typically requires annealing at very high temperatures, incorporation of interstitials or interaction with mobile dislocations. Here we present an alternative solution to remove stacking-fault tetrahedra discovered during room temperature, in situ Kr ion irradiation of epitaxial nanotwinned Ag with an average twin spacing of ~8 nm. A large number of stacking-fault tetrahedra were removed during their interactions with abundant coherent twin boundaries. Consequently the density of stacking-fault tetrahedra in irradiated nanotwinned Ag was much lower than that in its bulk counterpart. Two fundamental interaction mechanisms were identified, and compared with predictions by molecular dynamics simulations. In situ studies also revealed a new phenomenon: radiation-induced frequent migration of coherent and incoherent twin boundaries. Potential migration mechanisms are discussed.

  12. Efficiency Enhancement of InGaN-Based Solar Cells via Stacking Layers of Light-Harvesting Nanospheres

    PubMed Central

    Al-Amri, Amal M.; Fu, Po-Han; Lai, Kun-Yu; Wang, Hsin-Ping; Li, Lain-Jong; He, Jr-Hau

    2016-01-01

    An effective light-harvesting scheme for InGaN-based multiple quantum well solar cells is demonstrated using stacking layers of polystyrene nanospheres. Light-harvesting efficiencies on the solar cells covered with varied stacks of nanospheres are evaluated through numerical and experimental methods. The numerical simulation reveals that nanospheres with 3 stacking layers exhibit the most improved optical absorption and haze ratio as compared to those obtained by monolayer nanospheres. The experimental demonstration, agreeing with the theoretical analyses, shows that the application of 3-layer nanospheres improves the conversion efficiency of the solar cell by ~31%. PMID:27339612

  13. Control of the stacking fault areas in pseudomorphic ZnSe layers by photo-molecular beam epitaxy

    NASA Astrophysics Data System (ADS)

    Ohno, Y.; Taishi, T.; Yonenaga, I.; Ichikawa, S.; Hirai, R.; Takeda, S.

    2007-12-01

    Pseudomorphic ZnSe layers on GaAs(0 0 1) were grown by molecular beam epitaxy under the light illumination with photon energy of about 1.8 eV. In the layers, isolated Shockley-type stacking faults on (1 1 1), bordering not on the ZnSe/GaAs interface but on the ZnSe surface, as well as the well-known stacking fault pairs, were formed. The sum of the stacking fault areas was small in comparison with the layers grown by molecular beam epitaxy without light illumination.

  14. Kondo screening and spin excitation in few-layer CoPc molecular assembly stacking on Pb(111) surface: A DFT+HEOM study

    NASA Astrophysics Data System (ADS)

    Wang, Yu; Zheng, Xiao; Yang, Jinlong

    2016-10-01

    Transition metal phthalocyanine molecules adsorbed on a metal substrate exhibit rich spin-related phenomena such as magnetic anisotropy, spin excitation, and Kondo effect. In this work, we investigate theoretically few-layer cobalt phthalocyanine (CoPc) molecular assembly stacking on Pb(111) surface with the use of a combined density functional theory (DFT) and hierarchical equations of motion (HEOM) approach. Calculation results indicate that the local spin properties of CoPc/Pb(111) composites depend critically on the number of adsorption layers. The first layer of CoPc on the Pb(111) surface serves as a spin-insulating buffer, while the CoPc molecules in the second layer exhibit spin-1/2 Kondo effect with a Kondo temperature of about 22 K. In a triple-layer CoPc assembly stacking on Pb(111), the antiferromagnetic coupling between the second and third layers leads to local spin-flip excitations under finite bias voltages, which gives rise to characteristic signatures in the differential conductance spectra. The DFT+HEOM approach thus provides a practical means for investigating the local electronic and spin properties of two-dimensional molecular assemblies adsorbed on the metal surface. The insights obtained from the first-principles based simulations could be useful for experimental manipulation or design of magnetic composite systems.

  15. Study of stacked-emitter layer for high efficiency amorphous/crystalline silicon heterojunction solar cells

    NASA Astrophysics Data System (ADS)

    Lee, Youngseok; Kim, Heewon; Iftiquar, S. M.; Kim, Sunbo; Kim, Sangho; Ahn, Shihyun; Lee, Youn-Jung; Dao, Vinh Ai; Yi, Junsin

    2014-12-01

    A modified emitter, of stacked two layer structure, was investigated for high-efficiency amorphous/crystalline silicon heterojunction (HJ) solar cells. Surface area of the cells was 181.5 cm2. The emitter was designed to achieve a high open circuit voltage (Voc) and fill factor (FF). When doping of the emitter layer was increased, it was observed that the silicon dihydride related structural defects within the films increased, and the Voc of the HJ cell decreased. On the other hand, while the doping concentration of the emitter was reduced the FF of the cell reduced. Therefore, a combination of a high conductivity and low defects of a single emitter layer appears difficult to obtain, yet becomes necessary to improve the cell performance. So, we investigated a stacked-emitter with low-doped/high-doped double layer structure. A low-doped emitter with reduced defect density was deposited over the intrinsic hydrogenated amorphous silicon passivation layer, while the high-doped emitter with high conductivity was deposited over the low-doped emitter. The effects of doping and defect density of the emitter, on the device performance, were elucidated by using computer simulation and an optimized device structure was formulated. The simulation was performed with the help of Automat for the Simulation of Heterostructures simulation software. Finally, based on the simulation results, amorphous/crystalline heterojunction silicon solar cells were optimized by reducing density of defect states in the stacked-emitter structure and we obtained 725 mV, 77.41%, and 19.0% as the open-circuit voltage, fill factor, and photo-voltaic conversion efficiency of the device, respectively.

  16. Stacking sequence and interlayer coupling in few-layer graphene revealed by in situ imaging

    SciTech Connect

    Wang, Zhu-Jun; Dong, Jichen; Cui, Yi; Eres, Gyula; Timpe, Olaf; Fu, Qiang; Ding, Feng; Willinger, Marc-Georg; Schloegl, R.

    2016-10-19

    In the transition from graphene to graphite, the addition of each individual graphene layer modifies the electronic structure and produces a different material with unique properties. Controlled growth of few-layer graphene is therefore of fundamental interest and will provide access to materials with engineered electronic structure. Here we combine isothermal growth and etching experiments with in situ scanning electron microscopy to reveal the stacking sequence and interlayer coupling strength in few-layer graphene. The observed layer-dependent etching rates reveal the relative strength of the graphene graphene and graphene substrate interaction and the resulting mode of adlayer growth. Scanning tunnelling microscopy and density functional theory calculations confirm a strong coupling between graphene edge atoms and platinum. Simulated etching confirms that etching can be viewed as reversed growth. This work demonstrates that real-time imaging under controlled atmosphere is a powerful method for designing synthesis protocols for sp2 carbon nanostructures in between graphene and graphite.

  17. AA stacking, tribological and electronic properties of double-layer graphene with krypton spacer.

    PubMed

    Popov, Andrey M; Lebedeva, Irina V; Knizhnik, Andrey A; Lozovik, Yurii E; Potapkin, Boris V; Poklonski, Nikolai A; Siahlo, Andrei I; Vyrko, Sergey A

    2013-10-21

    Structural, energetic, and tribological characteristics of double-layer graphene with commensurate and incommensurate krypton spacers of nearly monolayer coverage are studied within the van der Waals-corrected density functional theory. It is shown that when the spacer is in the commensurate phase, the graphene layers have the AA stacking. For this phase, the barriers to relative in-plane translational and rotational motion and the shear mode frequency of the graphene layers are calculated. For the incommensurate phase, both of the barriers are found to be negligibly small. A considerable change of tunneling conductance between the graphene layers separated by the commensurate krypton spacer at their relative subangstrom displacement is revealed by the use of the Bardeen method. The possibility of nanoelectromechanical systems based on the studied tribological and electronic properties of the considered heterostructures is discussed.

  18. Stacking sequence and interlayer coupling in few-layer graphene revealed by in situ imaging

    NASA Astrophysics Data System (ADS)

    Wang, Zhu-Jun; Dong, Jichen; Cui, Yi; Eres, Gyula; Timpe, Olaf; Fu, Qiang; Ding, Feng; Schloegl, R.; Willinger, Marc-Georg

    2016-10-01

    In the transition from graphene to graphite, the addition of each individual graphene layer modifies the electronic structure and produces a different material with unique properties. Controlled growth of few-layer graphene is therefore of fundamental interest and will provide access to materials with engineered electronic structure. Here we combine isothermal growth and etching experiments with in situ scanning electron microscopy to reveal the stacking sequence and interlayer coupling strength in few-layer graphene. The observed layer-dependent etching rates reveal the relative strength of the graphene-graphene and graphene-substrate interaction and the resulting mode of adlayer growth. Scanning tunnelling microscopy and density functional theory calculations confirm a strong coupling between graphene edge atoms and platinum. Simulated etching confirms that etching can be viewed as reversed growth. This work demonstrates that real-time imaging under controlled atmosphere is a powerful method for designing synthesis protocols for sp2 carbon nanostructures in between graphene and graphite.

  19. <110> symmetric tilt grain-boundary structures in fcc metals with low stacking-fault energies

    NASA Astrophysics Data System (ADS)

    Rittner, J. D.; Seidman, D. N.

    1996-09-01

    Twenty-one <110> symmetric tilt grain boundaries (GB's) are investigated with atomistic simulations, using an embedded-atom method (EAM) potential for a low stacking-fault energy fcc metal. Lattice statics simulations with a large number of initial configurations are used to identify both the equilibrium and metastable structures at 0 K. The level of difficulty in finding the equilibrium structures is quantitatively assessed. The stability of the structures at an elevated temperature is investigated by Monte Carlo annealing. A form of GB dissociation is identified in a number of the boundaries. These structures are used to develop a dislocation model of GB dissociation by stacking-fault emission. Also, an attempt is made to apply the structural unit model (SUM) to the simulated boundaries and problems that are encountered for GB structures in low stacking-fault energy metals are enumerated and discussed.

  20. CHARACTERIZATION OF POLED SINGLE-LAYER PZT FOR PIEZO STACK IN FUEL INJECTION SYSTEM

    SciTech Connect

    Wang, Hong; Matsunaga, Tadashi; Lin, Hua-Tay

    2010-01-01

    Poled single-layer PZT has been characterized in as-extracted and as-received states. PZT plate specimens in the former were extracted from a stack. Flexure strength of PZT was evaluated by using ball-on-ring and 4-point bend tests. Fractography showed that intergranular fractures dominated the fracture surface and that volume pores were the primary strength-limiting flaws. The electric field effect was investigated by testing the PZT in open circuit and coercive field levels. An asymmetrical response on the biaxial flexure strength with respect to the electric field direction was observed. These experimental results will assist reliability design of the piezo stack that is being considered in fuel injection system.

  1. Centimeter Scale Patterned Growth of Vertically Stacked Few Layer Only 2D MoS2/WS2 van der Waals Heterostructure.

    PubMed

    Choudhary, Nitin; Park, Juhong; Hwang, Jun Yeon; Chung, Hee-Suk; Dumas, Kenneth H; Khondaker, Saiful I; Choi, Wonbong; Jung, Yeonwoong

    2016-05-05

    Two-dimensional (2D) van der Waal (vdW) heterostructures composed of vertically-stacked multiple transition metal dichalcogenides (TMDs) such as molybdenum disulfide (MoS2) and tungsten disulfide (WS2) are envisioned to present unprecedented materials properties unobtainable from any other material systems. Conventional fabrications of these hybrid materials have relied on the low-yield manual exfoliation and stacking of individual 2D TMD layers, which remain impractical for scaled-up applications. Attempts to chemically synthesize these materials have been recently pursued, which are presently limited to randomly and scarcely grown 2D layers with uncontrolled layer numbers on very small areas. Here, we report the chemical vapor deposition (CVD) growth of large-area (>2 cm(2)) patterned 2D vdW heterostructures composed of few layer, vertically-stacked MoS2 and WS2. Detailed structural characterizations by Raman spectroscopy and high-resolution/scanning transmission electron microscopy (HRTEM/STEM) directly evidence the structural integrity of two distinct 2D TMD layers with atomically sharp vdW heterointerfaces. Electrical transport measurements of these materials reveal diode-like behavior with clear current rectification, further confirming the formation of high-quality heterointerfaces. The intrinsic scalability and controllability of the CVD method presented in this study opens up a wide range of opportunities for emerging applications based on the unconventional functionalities of these uniquely structured materials.

  2. Centimeter Scale Patterned Growth of Vertically Stacked Few Layer Only 2D MoS2/WS2 van der Waals Heterostructure

    NASA Astrophysics Data System (ADS)

    Choudhary, Nitin; Park, Juhong; Hwang, Jun Yeon; Chung, Hee-Suk; Dumas, Kenneth H.; Khondaker, Saiful I.; Choi, Wonbong; Jung, Yeonwoong

    2016-05-01

    Two-dimensional (2D) van der Waal (vdW) heterostructures composed of vertically-stacked multiple transition metal dichalcogenides (TMDs) such as molybdenum disulfide (MoS2) and tungsten disulfide (WS2) are envisioned to present unprecedented materials properties unobtainable from any other material systems. Conventional fabrications of these hybrid materials have relied on the low-yield manual exfoliation and stacking of individual 2D TMD layers, which remain impractical for scaled-up applications. Attempts to chemically synthesize these materials have been recently pursued, which are presently limited to randomly and scarcely grown 2D layers with uncontrolled layer numbers on very small areas. Here, we report the chemical vapor deposition (CVD) growth of large-area (>2 cm2) patterned 2D vdW heterostructures composed of few layer, vertically-stacked MoS2 and WS2. Detailed structural characterizations by Raman spectroscopy and high-resolution/scanning transmission electron microscopy (HRTEM/STEM) directly evidence the structural integrity of two distinct 2D TMD layers with atomically sharp vdW heterointerfaces. Electrical transport measurements of these materials reveal diode-like behavior with clear current rectification, further confirming the formation of high-quality heterointerfaces. The intrinsic scalability and controllability of the CVD method presented in this study opens up a wide range of opportunities for emerging applications based on the unconventional functionalities of these uniquely structured materials.

  3. Optical properties of a stack of cholesteric liquid crystal and isotropic medium layers

    SciTech Connect

    Gevorgyan, A. H.

    2015-12-15

    Some new optical properties of a stack consisting of cholesteric liquid crystal (CLC) and isotropic medium layers are studied. The problem is solved by the modified Ambartsumyan method for the summation of layers. Bragg conditions for the photonic band gaps of the proposed system are presented. It is shown that the choice of proper sublayer parameters can be used to control the band structure of the system. In the general case, the effect of full suppression of absorption, which is observed in a finite homogeneous CLC layer, is not detected in the presence of anisotropic absorption in CLC sublayers. It is shown that this effect can be generated in the system under study if certain conditions are imposed on the isotropic sublayer thickness. Under these conditions, the maximum photonic density of states (PDS) increases significantly at the boundaries of the corresponding band. The influence of a change in the CLC sublayer thickness and the system thickness on PDS is investigated.

  4. Optical properties of a stack of cholesteric liquid crystal and isotropic medium layers

    NASA Astrophysics Data System (ADS)

    Gevorgyan, A. H.

    2015-12-01

    Some new optical properties of a stack consisting of cholesteric liquid crystal (CLC) and isotropic medium layers are studied. The problem is solved by the modified Ambartsumyan method for the summation of layers. Bragg conditions for the photonic band gaps of the proposed system are presented. It is shown that the choice of proper sublayer parameters can be used to control the band structure of the system. In the general case, the effect of full suppression of absorption, which is observed in a finite homogeneous CLC layer, is not detected in the presence of anisotropic absorption in CLC sublayers. It is shown that this effect can be generated in the system under study if certain conditions are imposed on the isotropic sublayer thickness. Under these conditions, the maximum photonic density of states (PDS) increases significantly at the boundaries of the corresponding band. The influence of a change in the CLC sublayer thickness and the system thickness on PDS is investigated.

  5. Simple solution route to uniform MoS{sub 2} particles with randomly stacked layers

    SciTech Connect

    Li Qing; Li Ming; Chen Zhiqian; Li Chunmei

    2004-06-08

    MoS{sub 2} particles of uniform size (ca. 70 nm) consisting of random and loosely stacked layers have been synthesized from hydrazine solution with (NH{sub 4}){sub 2}Mo{sub 3}S{sub 13} as the precursor at 180 deg. C for 16 h under hydrothermal conditions. The particles were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HREM). The influences of reaction conditions are discussed while a mechanism is proposed to explain the formation of this peculiar morphology.

  6. Limitations of H- κ stacking: ambiguous results caused by crustal layering

    NASA Astrophysics Data System (ADS)

    Wölbern, I.; Rümpker, G.

    2017-01-01

    Over the past decade, the H- κ stacking technique of Zhu and Kanamori (J Geophys Res 105:2969-2980, 2000) has become a standard tool to determine the crustal thickness H and the bulk crustal vP/vS ratio κ from teleseismic receiver functions. It is obvious that unfavorable noise conditions as well as a complex 3D velocity structure can severely hamper the interpretation of receiver-function data. However, we observe that ambiguities can even arise from a simple 1D layered velocity structure which raises a high potential for misinterpretations. To analyze the feasibility and basic limitations of the H- κ stacking method, we conduct a series of tests based on synthetic data. The impact of different given elementary parameters, related either to the velocity structure or to the data processing, is evaluated in a series of eight individual tests. We deliberately exclude complications such as 3D structural variations and/or noise to show that even a simple 1D velocity structure, involving, e.g., an additional inter-crustal discontinuity, can have significant consequences for the interpretation of the results. However, our modeling suggests that more complex crustal structures may lead to even less reliable results. Additionally, our tests illustrate that time shifts of the maxima in the H- κ domain due to the superposition and merging of individual phases can lead to significantly overestimated vP/vS ratios. In general, the depth to the Moho (or other discontinuities of interest) is less significantly affected. Our tests indicate the necessity to accurately check delay times derived from the maxima of the H- κ stacks against corresponding phases in the receiver functions. Repeating the stacking with varied weighting factors and filter ranges can help to reduce the ambiguities and to avoid possible misinterpretation.

  7. Supramolecular self-assembly of graphene oxide and metal nanoparticles into stacked multilayers by means of a multitasking protein ring

    NASA Astrophysics Data System (ADS)

    Ardini, Matteo; Golia, Giordana; Passaretti, Paolo; Cimini, Annamaria; Pitari, Giuseppina; Giansanti, Francesco; Leandro, Luana Di; Ottaviano, Luca; Perrozzi, Francesco; Santucci, Sandro; Morandi, Vittorio; Ortolani, Luca; Christian, Meganne; Treossi, Emanuele; Palermo, Vincenzo; Angelucci, Francesco; Ippoliti, Rodolfo

    2016-03-01

    Graphene oxide (GO) is rapidly emerging worldwide as a breakthrough precursor material for next-generation devices. However, this requires the transition of its two-dimensional layered structure into more accessible three-dimensional (3D) arrays. Peroxiredoxins (Prx) are a family of multitasking redox enzymes, self-assembling into ring-like architectures. Taking advantage of both their symmetric structure and function, 3D reduced GO-based composites are hereby built up. Results reveal that the ``double-faced'' Prx rings can adhere flat on single GO layers and partially reduce them by their sulfur-containing amino acids, driving their stacking into 3D multi-layer reduced GO-Prx composites. This process occurs in aqueous solution at a very low GO concentration, i.e. 0.2 mg ml-1. Further, protein engineering allows the Prx ring to be enriched with metal binding sites inside its lumen. This feature is exploited to both capture presynthesized gold nanoparticles and grow in situ palladium nanoparticles paving the way to straightforward and ``green'' routes to 3D reduced GO-metal composite materials.Graphene oxide (GO) is rapidly emerging worldwide as a breakthrough precursor material for next-generation devices. However, this requires the transition of its two-dimensional layered structure into more accessible three-dimensional (3D) arrays. Peroxiredoxins (Prx) are a family of multitasking redox enzymes, self-assembling into ring-like architectures. Taking advantage of both their symmetric structure and function, 3D reduced GO-based composites are hereby built up. Results reveal that the ``double-faced'' Prx rings can adhere flat on single GO layers and partially reduce them by their sulfur-containing amino acids, driving their stacking into 3D multi-layer reduced GO-Prx composites. This process occurs in aqueous solution at a very low GO concentration, i.e. 0.2 mg ml-1. Further, protein engineering allows the Prx ring to be enriched with metal binding sites inside its

  8. Graphitic Tribological Layers in Metal-on-Metal Hip Replacements

    NASA Astrophysics Data System (ADS)

    Liao, Y.; Pourzal, R.; Wimmer, M. A.; Jacobs, J. J.; Fischer, A.; Marks, L. D.

    2011-12-01

    Arthritis is a leading cause of disability, and when nonoperative methods have failed, a prosthetic implant is a cost-effective and clinically successful treatment. Metal-on-metal replacements are an attractive implant technology, a lower-wear alternative to metal-on-polyethylene devices. Relatively little is known about how sliding occurs in these implants, except that proteins play a critical role and that there is a tribological layer on the metal surface. We report evidence for graphitic material in the tribological layer in metal-on-metal hip replacements retrieved from patients. As graphite is a solid lubricant, its presence helps to explain why these components exhibit low wear and suggests methods of improving their performance; simultaneously, this raises the issue of the physiological effects of graphitic wear debris.

  9. Basic criteria for formation of growth twins in high stacking fault energy metals

    NASA Astrophysics Data System (ADS)

    Yu, K. Y.; Bufford, D.; Chen, Y.; Liu, Y.; Wang, H.; Zhang, X.

    2013-10-01

    Nanotwinned metals received significant interest lately as twin boundaries may enable simultaneous enhancement of strength, ductility, thermal stability, and radiation tolerance. However, nanotwins have been the privilege of metals with low-to-intermediate stacking fault energy (SFE). Recent scattered studies show that nanotwins could be introduced into high SFE metals, such as Al. In this paper, we examine several sputter-deposited, {111} textured Ag/Al, Cu/Ni, and Cu/Fe multilayers, wherein growth twins were observed in Al, Ni, and face-centered cubic (fcc) Fe. The comparisons lead to two important design criteria that dictate the introduction of growth twins in high SFE metals. The validity of these criteria was then examined in Ag/Ni multilayers. Furthermore, another twin formation mechanism in high SFE metals was discovered in Ag/Ni system.

  10. Shear deformation, ideal strength, and stacking fault formation of fcc metals: A density-functional study of Al and Cu

    NASA Astrophysics Data System (ADS)

    Jahnátek, Michal; Hafner, Jürgen; Krajčí, Marián

    2009-06-01

    Ab initio density-functional calculations have been used to study the response of two face-centered-cubic metals (Al and Cu) to shearing parallel to the close-packed (111) planes along two different directions, [112¯] and [1¯10] . Two different types of deformations—affine and alias—have been investigated. Under an affine shear deformation, all atoms are shifted parallel to the shearing direction by a distance proportional to their distance from the fixed basal plane. In the alias regime, only the top layer is displaced in the shearing direction. In both regimes, calculations have been performed with (pure shear) and without (simple shear) relaxation. For a pure alias shear, due to the interaction between the atoms, the displacement propagates through the sample; this is certainly the most realistic description of the shearing processes. In the pure alias regime, shear deformation, theoretical shear strength, and stacking fault formations may be described on a common footing. For small strains (in the elastic region), affine and alias shears lead to very similar results. Beyond the elastic limit, relaxation has a strong influence of the response on an applied shear strain. The elastic shear moduli are significantly larger for Cu than for Al, but a much higher shear strength is calculated for Al, although the shear strength is limited by the occurrence of a stacking fault instability before the stress maximum is reached. Under ⟨1¯10⟩ {111} shear the analysis of the atomistic deformation mechanism shows that in this case the formation of a stacking fault leads to a splitting of the (1)/(2)[1¯10] dislocation into two partial Shockley dislocations. Due to the repulsive interaction between the atoms in adjacent close-packed planes, the atoms in the top A layer move along (1)/(6)[2¯11] to a position directly above the B layer such that the stable intrinsic stacking fault configuration is the same for both slip systems. The analysis of the variation in the

  11. Molecular dynamics simulations on deformation and fracture of bi-layer graphene with different stacking pattern under tension

    NASA Astrophysics Data System (ADS)

    Jiao, M. D.; Wang, L.; Wang, C. Y.; Zhang, Q.; Ye, S. Y.; Wang, F. Y.

    2016-02-01

    Based on AIREBO (Adaptive Intermolecular Reactive Empirical Bond Order) potential, molecular dynamics simulations (MDs) are performed to study the mechanical behavior of AB- and AA-stacked bi-layer graphene films (BGFs) under tension. Stress-strain relationship is established and deformation mechanism is investigated via morphology analysis. It is found that AA-stacked BGFs show wavy folds, i.e. the structural instability, and the local structure of AB-stacked BGFs transforms into AA-stacked ones during free relaxation. The values of the Young's modulus obtained for AA-stacked zigzag and armchair BGFs are 797.2 GPa and 727.4 GPa, and those of their AB-stacked counterparts are 646.7 GPa and 603.5 GPa, respectively. In comparison with single-layer graphene, low anisotropy is observed for BGFs, especially AB-stacked ones. During the tensile deformation, hexagonal cells at the edge of BGFs are found to transform into pentagonal rings and the number of such defects increases with the rise of tensile strain.

  12. Controlled assembly of layer-by-layer stacking continuous graphene oxide films and their application for actively modulated field electron emission cathodes.

    PubMed

    Huang, Yuan; She, Juncong; Yang, Wenjie; Deng, Shaozhi; Xu, Ningsheng

    2014-04-21

    A featured "vapor transportation" assembly technique was developed to attain layer-by-layer stacking continuous graphene oxide (GO) films on both flat and concavo-concave surfaces. Few-layer (layer number < 10) GO sheets were "evaporated" (carried by water vapor) from the water-dispersed GO suspension and smoothly/uniformly tiled on the substrate surface. We have found evidence of the influence of the deposition time and substrate-liquid separation on the film thickness. A model was proposed for interpreting the assembly process. It was found that a current conditioning would induce a reduction of the GO surface and form an Ohmic contact between the GO-metal interfaces. Accordingly, an actively modulated GO cold cathode was fabricated by locally depositing continuous GO sheets on the drain electrode of a metal-oxide-semiconductor field effect transistor (MOSFET). The field emission current of the GO cathode can be precisely controlled by the MOSFET gate voltage (VGS). A current modulation range from 1 × 10(-10) A to 6.9 × 10(-6) A (4 orders of magnitude) was achieved by tuning the VGS from 0.812 V to 1.728 V. Due to the self-acting positive feedback of the MOSFET, the emission current fluctuation was dramatically reduced from 57.4% (non-control) to 3.4% (controlled). Furthermore, the integrated GO cathode was employed for a lab-prototype display pixel application demonstrating the active modulation of the phosphor luminance, i.e. from 0.01 cd m(-2) to 34.18 cd m(-2).

  13. Controlled assembly of layer-by-layer stacking continuous graphene oxide films and their application for actively modulated field electron emission cathodes

    NASA Astrophysics Data System (ADS)

    Huang, Yuan; She, Juncong; Yang, Wenjie; Deng, Shaozhi; Xu, Ningsheng

    2014-03-01

    A featured ``vapor transportation'' assembly technique was developed to attain layer-by-layer stacking continuous graphene oxide (GO) films on both flat and concavo-concave surfaces. Few-layer (layer number < 10) GO sheets were ``evaporated'' (carried by water vapor) from the water-dispersed GO suspension and smoothly/uniformly tiled on the substrate surface. We have found evidence of the influence of the deposition time and substrate-liquid separation on the film thickness. A model was proposed for interpreting the assembly process. It was found that a current conditioning would induce a reduction of the GO surface and form an Ohmic contact between the GO-metal interfaces. Accordingly, an actively modulated GO cold cathode was fabricated by locally depositing continuous GO sheets on the drain electrode of a metal-oxide-semiconductor field effect transistor (MOSFET). The field emission current of the GO cathode can be precisely controlled by the MOSFET gate voltage (VGS). A current modulation range from 1 × 10-10 A to 6.9 × 10-6 A (4 orders of magnitude) was achieved by tuning the VGS from 0.812 V to 1.728 V. Due to the self-acting positive feedback of the MOSFET, the emission current fluctuation was dramatically reduced from 57.4% (non-control) to 3.4% (controlled). Furthermore, the integrated GO cathode was employed for a lab-prototype display pixel application demonstrating the active modulation of the phosphor luminance, i.e. from 0.01 cd m-2 to 34.18 cd m-2.

  14. Stacking sequence and interlayer coupling in few-layer graphene revealed by in situ imaging

    PubMed Central

    Wang, Zhu-Jun; Dong, Jichen; Cui, Yi; Eres, Gyula; Timpe, Olaf; Fu, Qiang; Ding, Feng; Schloegl, R.; Willinger, Marc-Georg

    2016-01-01

    In the transition from graphene to graphite, the addition of each individual graphene layer modifies the electronic structure and produces a different material with unique properties. Controlled growth of few-layer graphene is therefore of fundamental interest and will provide access to materials with engineered electronic structure. Here we combine isothermal growth and etching experiments with in situ scanning electron microscopy to reveal the stacking sequence and interlayer coupling strength in few-layer graphene. The observed layer-dependent etching rates reveal the relative strength of the graphene–graphene and graphene–substrate interaction and the resulting mode of adlayer growth. Scanning tunnelling microscopy and density functional theory calculations confirm a strong coupling between graphene edge atoms and platinum. Simulated etching confirms that etching can be viewed as reversed growth. This work demonstrates that real-time imaging under controlled atmosphere is a powerful method for designing synthesis protocols for sp2 carbon nanostructures in between graphene and graphite. PMID:27759024

  15. Stacking sequence and interlayer coupling in few-layer graphene revealed by in situ imaging

    DOE PAGES

    Wang, Zhu-Jun; Dong, Jichen; Cui, Yi; ...

    2016-10-19

    In the transition from graphene to graphite, the addition of each individual graphene layer modifies the electronic structure and produces a different material with unique properties. Controlled growth of few-layer graphene is therefore of fundamental interest and will provide access to materials with engineered electronic structure. Here we combine isothermal growth and etching experiments with in situ scanning electron microscopy to reveal the stacking sequence and interlayer coupling strength in few-layer graphene. The observed layer-dependent etching rates reveal the relative strength of the graphene graphene and graphene substrate interaction and the resulting mode of adlayer growth. Scanning tunnelling microscopy andmore » density functional theory calculations confirm a strong coupling between graphene edge atoms and platinum. Simulated etching confirms that etching can be viewed as reversed growth. This work demonstrates that real-time imaging under controlled atmosphere is a powerful method for designing synthesis protocols for sp2 carbon nanostructures in between graphene and graphite.« less

  16. Supramolecular self-assembly of graphene oxide and metal nanoparticles into stacked multilayers by means of a multitasking protein ring.

    PubMed

    Ardini, Matteo; Golia, Giordana; Passaretti, Paolo; Cimini, Annamaria; Pitari, Giuseppina; Giansanti, Francesco; Di Leandro, Luana; Ottaviano, Luca; Perrozzi, Francesco; Santucci, Sandro; Morandi, Vittorio; Ortolani, Luca; Christian, Meganne; Treossi, Emanuele; Palermo, Vincenzo; Angelucci, Francesco; Ippoliti, Rodolfo

    2016-03-28

    Graphene oxide (GO) is rapidly emerging worldwide as a breakthrough precursor material for next-generation devices. However, this requires the transition of its two-dimensional layered structure into more accessible three-dimensional (3D) arrays. Peroxiredoxins (Prx) are a family of multitasking redox enzymes, self-assembling into ring-like architectures. Taking advantage of both their symmetric structure and function, 3D reduced GO-based composites are hereby built up. Results reveal that the "double-faced" Prx rings can adhere flat on single GO layers and partially reduce them by their sulfur-containing amino acids, driving their stacking into 3D multi-layer reduced GO-Prx composites. This process occurs in aqueous solution at a very low GO concentration, i.e. 0.2 mg ml(-1). Further, protein engineering allows the Prx ring to be enriched with metal binding sites inside its lumen. This feature is exploited to both capture presynthesized gold nanoparticles and grow in situ palladium nanoparticles paving the way to straightforward and "green" routes to 3D reduced GO-metal composite materials.

  17. Controlling Optical Properties of Electrodes With Stacked Metallic Thin Films for Polymeric Light-Emitting Diodes and Displays

    NASA Astrophysics Data System (ADS)

    Wu, Elbert Hsing-En; Li, Sheng-Han; Chen, Chieh-Wei; Li, Gang; Xu, Zheng; Yang, Yang

    2005-09-01

    A semi-transparent metallic film and a high optical absorbing film were constructed with stacking metallic films. Both films were used as cathodes for polymeric light-emitting diodes (PLEDs). The semi-transparent film was made of gold/aluminum/gold thin multilayers with its optical transparency of the device reaches as high as ~70% in the visible region without capping layer, and the electrical sheet resistance reduces below 10 Omega/square. During illumination of the PLED, there was approximately 47% of light emitting from the top of the cathode surface, and 53% of light from the ITO side. The high optical absorbing film, also refer to as the black cathode, was constructed with four alternating layers of aluminum-silver, each aluminum or silver layer is 4 nm thick. The PLED with this black cathode demonstrated 126% enhancement of contrast under 1000 lx ambient illumination. The physical properties of these two cathodes were characterized by current-voltage measurement and atomic force microscopy. Ultraviolet-visible transmission spectroscopy and X-ray photoemission spectroscopy were also used to characterize the semi-transparent cathode and the black cathode respectively. For polymer light-emitting device,it is believed that morphology modification at each interface of the cathode plays a crucial role in determining the optical properties and conductivity of the over cathode.

  18. Paleointensity determination of welded tuffs extruded with tephra layers: A new approach to calibration of relative paleointensity stacks

    NASA Astrophysics Data System (ADS)

    Mochizuki, N.; Fujii, S.; Hasegawa, T.; Yamamoto, Y.; Hatakeyama, T.; Okada, M.; Shibuya, H.

    2015-12-01

    For a reliable calibration of a relative paleointensity stack, we proposed a new method for direct comparison of absolute paleointensities (APIs) with relative paleointensities (RPIs) (Mochizuki et al., under review). In the analysis, APIs are directly compared with the RPIs of a RPI stack at six stratigraphic levels: three levels are based on tephrostratigraphic correlations between welded tuffs and corresponding tephra layers in the oxygen isotope stratigraphy, and the other three levels are based on paleomagnetic correlations between RPI minima and transitional geomagnetic fields. In the present study, to increase API data with tephrostratigraphic correlation, we applied the LTD-DHT Shaw paleointensity method (Tsunakawa-Shaw method) to 21 welded tuffs in Japan extruded with widespread tephra layers. We obtained mean paleointensities for 16 of the 21 welded tuffs. Since nine of the 16 welded tuffs were correlated with the tephras recognized in the oxygen isotope stratigraphy, they can be added to the API data used in the direct comparison method. Combining these API data with the reported data, we compared API data with RPIs from the PISO-1500 stack and SINT-800 stack at the 14 stratigraphic levels: eleven levels are based on tephrostratigraphic correlation and the other three levels are based on paleomagnetic correlation. RPIs of the PISO-1500 stack showed a linear relationship with the virtual axial dipole moments (VADMs) calculated from the APIs, indicating that the PISO-1500 stack has a linear relation to the axial dipole moment. PRIs from the SINT-800 stack also have a linear-like trend with the VADMs. This direct comparison method can clarify the relationship between APIs and RPIs of a RPI stack, and thus provide a reliable calibration of the RPI stack to absolute values.

  19. Quantum theory for the nanoscale propagation of light through stacked thin film layers

    NASA Astrophysics Data System (ADS)

    Forbes, Kayn A.; Williams, Mathew D.; Andrews, David L.

    2016-04-01

    Stacked multi-layer films have a range of well-known applications as optical elements. The various types of theory commonly used to describe optical propagation through such structures rarely take account of the quantum nature of light, though phenomena such as Anderson localization can be proven to occur under suitable conditions. In recent and ongoing work based on quantum electrodynamics, it has been shown possible to rigorously reformulate, in photonic terms, the fundamental mechanisms that are involved in reflection and optical transmission through stacked nanolayers. Accounting for sum-over-pathway features in the quantum mechanical description, this theory treats the sequential interactions of photons with material boundaries in terms of individual scattering events. The study entertains an arbitrary number of reflections in systems comprising two or three internally reflective surfaces. Analytical results are secured, without recourse to FTDT (finite-difference time-domain) software or any other finite-element approximations. Quantum interference effects can be readily identified. The new results, which cast the optical characteristics of such structures in terms of simple, constituent-determined properties, are illustrated by model calculations.

  20. Effects of stable and unstable stacking fault energy on dislocation nucleation in nano-crystalline metals

    NASA Astrophysics Data System (ADS)

    Borovikov, Valery; Mendelev, Mikhail I.; King, Alexander H.

    2016-12-01

    Dislocation nucleation from grain boundaries (GB) can control plastic deformation in nano-crystalline metals under certain conditions, but little is known about what controls dislocation nucleation, because when data from different materials are compared, the variations of many interacting properties tend to obscure the effects of any single property. In this study, we seek clarification by applying a unique capability of semi-empirical potentials in molecular dynamics simulations: the potentials can be modified such that all significant material properties but one, are kept constant. Using a set of potentials developed to isolate the effects of stacking fault energy, we show that for a given grain boundary, loading orientation and strain rate, the yield stress depends linearly on both the stable and unstable stacking fault energies. The coefficients of proportionality depend on the GB structure and the value of the yield stress is related to the density of the E structural units in the GB. While the impact of the stable stacking fault energy is easy to understand, the unstable stacking fault energy requires more elucidation and we provide a framework for understanding how it affects the nucleation and propagation process.

  1. Optimization of high-k and gate metal workfunction for improved analog and intermodulation performance of Gate Stack (GS)-GEWE-SiNW MOSFET

    NASA Astrophysics Data System (ADS)

    Gupta, Neha; Chaujar, Rishu

    2016-09-01

    This work optimizes the gate engineering scheme (both gate stack and gate metal workfunction engineering) of Stacked Gate (SG) Gate Electrode Workfunction Engineered (GEWE)-Silicon Nanowire MOSFET at 300 K for improved analog and intermodulation performance. This has been done by evaluating and analyzing the metrics such as Switching Ratio, Subthreshold Swing (SS), Device Efficiency, channel and output resistance, VIP3, IIP3, 1-dB Compression Point, IMD3, HD2 and HD3. Simulation results exhibit that HfO2 as a gate stack exhibit high linearity at a comparatively low gate bias of 0.56 V with higher IIP3 (6.21 dBm) and low IMD3 (9.6 dBm). Further, the characteristics/performance is modulated by adjusting the workfunction difference of metal gate. This study demonstrates that SiNW MOSFET modeled with HfO2 as a gate stack over SiO2 interfacial layer, and gate metal workfunction difference (ΔW) of 4.4 eV can be considered as a promising potential for low power switching component in ICs and Linear RF amplifiers.

  2. Blocking force of a piezoelectric stack actuator made of single crystal layers (PMN-29PT)

    NASA Astrophysics Data System (ADS)

    Tran, K. S.; Phan, H. V.; Lee, H. Y.; Kim, Yongdae; Park, H. C.

    2016-09-01

    In this study, we fabricated and characterized a stack actuator made of forty layers of 1 mm thick PMN-29PT with a cross-sectional area of 10 × 10 mm2. From the measurement of actuation displacement, we confirmed that the piezoelectric strain constant in the direction of thickness of the material is 2000 pm V-1, as suggested by the manufacturer. The blocking forces of the actuator are measured to be 230 N, 369 N, and 478 N for 100 V, 200 V, and 300 V, respectively. The measured blocking forces showed large discrepancies from the estimated blocking forces calculated using linear models, especially for a high voltage application. An empirical equation acquired by fitting the measured blocking forces indicates that the blocking force has a nonlinear relationship with the applied voltage. The measured hysteresis showed a slight nonlinear voltage-stroke relationship and small energy loss.

  3. Clinical characterization of a proton beam continuous uniform scanning system with dose layer stacking

    SciTech Connect

    Farr, J. B.; Mascia, A. E.; Hsi, W.-C.; Allgower, C. E.; Jesseph, F.; Schreuder, A. N.; Wolanski, M.; Nichiporov, D. F.; Anferov, V.

    2008-11-15

    A proton beam delivery system on a gantry with continuous uniform scanning and dose layer stacking at the Midwest Proton Radiotherapy Institute has been commissioned and accepted for clinical use. This paper was motivated by a lack of guidance on the testing and characterization for clinical uniform scanning systems. As such, it describes how these tasks were performed with a uniform scanning beam delivery system. This paper reports the methods used and important dosimetric characteristics of radiation fields produced by the system. The commissioning data include the transverse and longitudinal dose distributions, penumbra, and absolute dose values. Using a 208 MeV cyclotron's proton beam, the system provides field sizes up to 20 and 30 cm in diameter for proton ranges in water up to 27 and 20 cm, respectively. The dose layer stacking method allows for the flexible construction of spread-out Bragg peaks with uniform modulation of up to 15 cm in water, at typical dose rates of 1-3 Gy/min. For measuring relative dose distributions, multielement ion chamber arrays, small-volume ion chambers, and radiographic films were employed. Measurements during the clinical commissioning of the system have shown that the lateral and longitudinal dose uniformity of 2.5% or better can be achieved for all clinically important field sizes and ranges. The measured transverse penumbra widths offer a slight improvement in comparison to those achieved with a double scattering beam spreading technique at the facility. Absolute dose measurements were done using calibrated ion chambers, thermoluminescent and alanine detectors. Dose intercomparisons conducted using various types of detectors traceable to a national standards laboratory indicate that the measured dosimetry data agree with each other within 5%.

  4. Nitrogen-doped amorphous oxide semiconductor thin film transistors with double-stacked channel layers

    NASA Astrophysics Data System (ADS)

    Xie, Haiting; Wu, Qi; Xu, Ling; Zhang, Lei; Liu, Guochao; Dong, Chengyuan

    2016-11-01

    The amorphous oxide semiconductor (AOS) thin film transistors (TFTs) with the double-stacked channel layers (DSCL) combing the amorphous InZnO (a-IZO) films and the nitrogen-doped amorphous InGaZnO (a-IGZO:N) films were proposed and fabricated, which showed the excellent performance with the field-effect mobility of 49.6 cm2 V-1 s-1 and the subthreshold swing of 0.5 V/dec. More interestingly, very stable properties were observed in the bias stress and light illumination tests for these a-IZO/a-IGZO:N TFTs, as seemed to be the evident improvements over the prior arts. The improved performance and stability might be mainly due to the hetero-junctions in the channel layers and less interface/bulk trap density from the in situ nitrogen doping process in the a-IGZO layers. In addition, the passivation effect of the a-IGZO:N films also made some contributions to the stable properties exhibited in these novel DSCL TFTs.

  5. Effect of Thermal Budget on the Electrical Characterization of Atomic Layer Deposited HfSiO/TiN Gate Stack MOSCAP Structure.

    PubMed

    Khan, Z N; Ahmed, S; Ali, M

    2016-01-01

    Metal Oxide Semiconductor (MOS) capacitors (MOSCAP) have been instrumental in making CMOS nano-electronics realized for back-to-back technology nodes. High-k gate stacks including the desirable metal gate processing and its integration into CMOS technology remain an active research area projecting the solution to address the requirements of technology roadmaps. Screening, selection and deposition of high-k gate dielectrics, post-deposition thermal processing, choice of metal gate structure and its post-metal deposition annealing are important parameters to optimize the process and possibly address the energy efficiency of CMOS electronics at nano scales. Atomic layer deposition technique is used throughout this work because of its known deposition kinetics resulting in excellent electrical properties and conformal structure of the device. The dynamics of annealing greatly influence the electrical properties of the gate stack and consequently the reliability of the process as well as manufacturable device. Again, the choice of the annealing technique (migration of thermal flux into the layer), time-temperature cycle and sequence are key parameters influencing the device's output characteristics. This work presents a careful selection of annealing process parameters to provide sufficient thermal budget to Si MOSCAP with atomic layer deposited HfSiO high-k gate dielectric and TiN gate metal. The post-process annealing temperatures in the range of 600°C -1000°C with rapid dwell time provide a better trade-off between the desirable performance of Capacitance-Voltage hysteresis and the leakage current. The defect dynamics is thought to be responsible for the evolution of electrical characteristics in this Si MOSCAP structure specifically designed to tune the trade-off at low frequency for device application.

  6. Effect of Thermal Budget on the Electrical Characterization of Atomic Layer Deposited HfSiO/TiN Gate Stack MOSCAP Structure

    PubMed Central

    Khan, Z. N.; Ahmed, S.; Ali, M.

    2016-01-01

    Metal Oxide Semiconductor (MOS) capacitors (MOSCAP) have been instrumental in making CMOS nano-electronics realized for back-to-back technology nodes. High-k gate stacks including the desirable metal gate processing and its integration into CMOS technology remain an active research area projecting the solution to address the requirements of technology roadmaps. Screening, selection and deposition of high-k gate dielectrics, post-deposition thermal processing, choice of metal gate structure and its post-metal deposition annealing are important parameters to optimize the process and possibly address the energy efficiency of CMOS electronics at nano scales. Atomic layer deposition technique is used throughout this work because of its known deposition kinetics resulting in excellent electrical properties and conformal structure of the device. The dynamics of annealing greatly influence the electrical properties of the gate stack and consequently the reliability of the process as well as manufacturable device. Again, the choice of the annealing technique (migration of thermal flux into the layer), time-temperature cycle and sequence are key parameters influencing the device’s output characteristics. This work presents a careful selection of annealing process parameters to provide sufficient thermal budget to Si MOSCAP with atomic layer deposited HfSiO high-k gate dielectric and TiN gate metal. The post-process annealing temperatures in the range of 600°C -1000°C with rapid dwell time provide a better trade-off between the desirable performance of Capacitance-Voltage hysteresis and the leakage current. The defect dynamics is thought to be responsible for the evolution of electrical characteristics in this Si MOSCAP structure specifically designed to tune the trade-off at low frequency for device application. PMID:27571412

  7. 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.

  8. Photoluminescence quenching and charge transfer in artificial heterostacks of monolayer transition metal dichalcogenides and few-layer black phosphorus.

    PubMed

    Yuan, Jiangtan; Najmaei, Sina; Zhang, Zhuhua; Zhang, Jing; Lei, Sidong; M Ajayan, Pulickel; Yakobson, Boris I; Lou, Jun

    2015-01-27

    Transition metal dichalcogenides monolayers and black phosphorus thin crystals are emerging two-dimensional materials that demonstrated extraordinary optoelectronic properties. Exotic properties and physics may arise when atomic layers of different materials are stacked together to form van der Waals solids. Understanding the important interlayer couplings in such heterostructures could provide avenues for control and creation of characteristics in these artificial stacks. Here we systematically investigate the optical and optoelectronic properties of artificial stacks of molybdenum disulfide, tungsten disulfide, and black phosphorus atomic layers. An anomalous photoluminescence quenching was observed in tungsten disulfide-molybdenum disulfide stacks. This was attributed to a direct to indirect band gap transition of tungsten disulfide in such stacks while molybdenum disulfide maintains its monolayer properties by first-principles calculations. On the other hand, due to the strong build-in electric fields in tungsten disulfide-black phosphorus or molybdenum disulfide-black phosphorus stacks, the excitons can be efficiently splitted despite both the component layers having a direct band gap in these stacks. We further examine optoelectronic properties of tungsten disulfide-molybdenum disulfide artificial stacks and demonstrate their great potentials in future optoelectronic applications.

  9. Molecular dynamics simulation on generalized stacking fault energies of FCC metals under preloading stress

    NASA Astrophysics Data System (ADS)

    Zhang, Liang; Cheng, Lü; Kiet, Tieu; Zhao, Xing; Pei, Lin-Qing; Guillaume, Michal

    2015-08-01

    Molecular dynamics (MD) simulations are performed to investigate the effects of stress on generalized stacking fault (GSF) energy of three fcc metals (Cu, Al, and Ni). The simulation model is deformed by uniaxial tension or compression in each of [111], [11-2], and [1-10] directions, respectively, before shifting the lattice to calculate the GSF curve. Simulation results show that the values of unstable stacking fault energy (γusf), stable stacking fault energy (γsf), and unstable twin fault energy (γutf) of the three elements can change with the preloaded tensile or compressive stress in different directions. The ratio of γsf/γusf, which is related to the energy barrier for full dislocation nucleation, and the ratio of γutf/γusf, which is related to the energy barrier for twinning formation are plotted each as a function of the preloading stress. The results of this study reveal that the stress state can change the energy barrier of defect nucleation in the crystal lattice, and thereby can play an important role in the deformation mechanism of nanocrystalline material. Project supported by Australia Research Council Discovery Projects (Grant No. DP130103973). L. Zhang, X. Zhao and L. Q. Pei were financially supported by the China Scholarship Council (CSC).

  10. Orbital reconstruction in nonpolar tetravalent transition-metal oxide layers

    NASA Astrophysics Data System (ADS)

    Bogdanov, Nikolay A.; Katukuri, Vamshi M.; Romhányi, Judit; Yushankhai, Viktor; Kataev, Vladislav; Büchner, Bernd; van den Brink, Jeroen; Hozoi, Liviu

    2015-06-01

    A promising route to tailoring the electronic properties of quantum materials and devices rests on the idea of orbital engineering in multilayered oxide heterostructures. Here we show that the interplay of interlayer charge imbalance and ligand distortions provides a knob for tuning the sequence of electronic levels even in intrinsically stacked oxides. We resolve in this regard the d-level structure of layered Sr2IrO4 by electron spin resonance. While canonical ligand-field theory predicts g||-factors less than 2 for positive tetragonal distortions as present in Sr2IrO4, the experiment indicates g|| is greater than 2. This implies that the iridium d levels are inverted with respect to their normal ordering. State-of-the-art electronic-structure calculations confirm the level switching in Sr2IrO4, whereas we find them in Ba2IrO4 to be instead normally ordered. Given the nonpolar character of the metal-oxygen layers, our findings highlight the tetravalent transition-metal 214 oxides as ideal platforms to explore d-orbital reconstruction in the context of oxide electronics.

  11. Structure change, layer sliding, and metallization in high-pressure MoS2

    NASA Astrophysics Data System (ADS)

    Tosatti, Erio; Hromadova, Liliana; Martonak, Roman

    2013-03-01

    Based on ab initio calculations and metadynamics simulations, we predict that 2H-MoS2, a layered insulator, will metallize under pressures in excess of 20-30 GPa. In the same pressure range, simulations and enthalpy optimization predict a structural transition. Reminiscent of this material's frictional properties, free mutual sliding of layers takes place at this transition, where the original 2Hc stacking changes to a 2Ha stacking typical of 2H-NbSe2, a transformation which explains for the first time previously mysterious X-ray diffraction data. Phonon and electron phonon calculations suggest that metallic pristine MoS2 will require ultrahigh pressures in order to develop superconductivity. Supported by EU-Japan Project LEMSUPER, by a SNF Sinergia Project, and by the Slovak Research and Development Agency

  12. Structural and thermodynamic consideration of metal oxide doped GeO{sub 2} for gate stack formation on germanium

    SciTech Connect

    Lu, Cimang Lee, Choong Hyun; Zhang, Wenfeng; Nishimura, Tomonori; Nagashio, Kosuke; Toriumi, Akira

    2014-11-07

    A systematic investigation was carried out on the material and electrical properties of metal oxide doped germanium dioxide (M-GeO{sub 2}) on Ge. We propose two criteria on the selection of desirable M-GeO{sub 2} for gate stack formation on Ge. First, metal oxides with larger cation radii show stronger ability in modifying GeO{sub 2} network, benefiting the thermal stability and water resistance in M-GeO{sub 2}/Ge stacks. Second, metal oxides with a positive Gibbs free energy for germanidation are required for good interface properties of M-GeO{sub 2}/Ge stacks in terms of preventing the Ge-M metallic bond formation. Aggressive equivalent oxide thickness scaling to 0.5 nm is also demonstrated based on these understandings.

  13. Observation of dopant-profile independent electron transport in sub-monolayer TiO{sub x} stacked ZnO thin films grown by atomic layer deposition

    SciTech Connect

    Saha, D. E-mail: pmisra@rrcat.gov.in; Misra, P. E-mail: pmisra@rrcat.gov.in; Joshi, M. P.; Kukreja, L. M.; Das, Gangadhar

    2016-01-18

    Dopant-profile independent electron transport has been observed through a combined study of temperature dependent electrical resistivity and magnetoresistance measurements on a series of Ti incorporated ZnO thin films with varying degree of static-disorder. These films were grown by atomic layer deposition through in-situ vertical stacking of multiple sub-monolayers of TiO{sub x} in ZnO. Upon decreasing ZnO spacer layer thickness, electron transport smoothly evolved from a good metallic to an incipient non-metallic regime due to the intricate interplay of screening of spatial potential fluctuations and strength of static-disorder in the films. Temperature dependent phase-coherence length as extracted from the magnetotransport measurement revealed insignificant role of inter sub-monolayer scattering as an additional channel for electron dephasing, indicating that films were homogeneously disordered three-dimensional electronic systems irrespective of their dopant-profiles. Results of this study are worthy enough for both fundamental physics perspective and efficient applications of multi-stacked ZnO/TiO{sub x} structures in the emerging field of transparent oxide electronics.

  14. Design of wide-angle solar-selective absorbers using aperiodic metal-dielectric stacks.

    PubMed

    Sergeant, Nicholas P; Pincon, Olivier; Agrawal, Mukul; Peumans, Peter

    2009-12-07

    Spectral control of the emissivity of surfaces is essential in applications such as solar thermal and thermophotovoltaic energy conversion in order to achieve the highest conversion efficiencies possible. We investigated the spectral performance of planar aperiodic metal-dielectric multilayer coatings for these applications. The response of the coatings was optimized for a target operational temperature using needle-optimization based on a transfer matrix approach. Excellent spectral selectivity was achieved over a wide angular range. These aperiodic metal-dielectric stacks have the potential to significantly increase the efficiency of thermophotovoltaic and solar thermal conversion systems. Optimal coatings for concentrated solar thermal conversion were modeled to have a thermal emissivity <7% at 720K while absorbing >94% of the incident light. In addition, optimized coatings for solar thermophotovoltaic applications were modeled to have thermal emissivity <16% at 1750K while absorbing >85% of the concentrated solar radiation.

  15. Effects of stacking fault energy on defect formation process in face-centered cubic metals

    NASA Astrophysics Data System (ADS)

    Okita, Taira; Yang, Yingjuan; Hirabayashi, Junichi; Itakura, Mitsuhiro; Suzuki, Katsuyuki

    2016-05-01

    To elucidate the effect of stacking fault energies (SFEs) on defect formation by the collision cascade process for face-centred cubic metals, we used six sets of interatomic potentials with different SFEs while keeping the other properties almost identical. Molecular dynamic simulations of the collision cascade were carried out using these potentials with primary knock-on atom energies (EPKA) of 10 and 20 keV at 100 K. Neither the number of residual defects nor the size distributions for both self-interstitial atom (SIA) type and vacancy type clusters were affected by the difference in the SFE. In the case of EPKA = 20 keV, the ratio of glissile SIA clusters increased as the SFE decreased, which was not expected by a prediction based on the classical dislocation theory. The trend did not change after annealing at 1100 K for 100 ps. For vacancy clusters, few stacking fault tetrahedrons (SFTs) formed before the annealing. However, lower SFEs tended to increase the SFT fraction after the annealing, where large vacancy clusters formed at considerable densities. The findings of this study can be used to characterise the defect formation process in low SFE metals such as austenitic stainless steels.

  16. Optical Tamm states above the bulk plasma frequency at a Bragg stack/metal interface

    NASA Astrophysics Data System (ADS)

    Brand, S.; Kaliteevski, M. A.; Abram, R. A.

    2009-02-01

    We demonstrate theoretically that surface-plasmon polaritons, a form of optical Tamm state, can occur at the interface between a metal and a Bragg reflector at frequencies above the bulk plasma frequency of the metal. The frequencies of the excitations are within the photonic band gap of the Bragg reflector which provides the required evanescent decay on that side of the interface. At finite in-plane wave vector, the low value of the permittivity of the metal above its plasma frequency can lead to an imaginary normal wave vector component in the metal, which provides the localization on the other side of the interface. It is proposed that the necessary conditions can be realized using a GaAs/AlAs Bragg stack coated with a suitable conducting metal oxide having a bulk plasma frequency of 1 eV, but the concept is valid for other systems given an appropriate plasma frequency and photonic band-gap structure. The dispersion relations of the plasmon polaritons in the structures considered are calculated for both possible polarizations, and it is shown how the excitations result in distinct features in the predicted reflectivity spectra.

  17. Stacking faults on (001) in transition-metal disilicides with the C11{sub b} structure

    SciTech Connect

    Ito, K.; Nakamoto, T.; Inui, H.; Yamaguchi, M.

    1997-12-31

    Stacking faults on (001) in MoSi{sub 2} and WSi{sub 2} with the C11{sub b} structure have been characterized by transmission electron microscopy (TEM), using their single crystals grown by the floating-zone method. Although WSi{sub 2} contains a high density of stacking faults, only several faults are observed in MoSi{sub 2}. For both crystals, (001) faults are characterized to be of the Frank-type in which two successive (001) Si layers are removed from the lattice, giving rise to a displacement vector parallel to [001]. When the displacement vector of faults is expressed in the form of R = 1/n[001], however, their n values are slightly deviated from the exact value of 3, because of dilatation of the lattice in the direction perpendicular to the fault, which is caused by the repulsive interaction between Mo (W) layers above and below the fault. Matching of experimental high-resolution TEM images with calculated ones indicates n values to be 3.12 {+-} 0.10 and 3.34 {+-} 0.10 for MoSi{sub 2} and WSi{sub 2}, respectively.

  18. Synthesis and characterization of petal type CZTS by stacked layer reactive sputtering

    NASA Astrophysics Data System (ADS)

    Singh, Om Pal; Parmar, R.; Gour, K. S.; Dalai, M. K.; Tawale, Jai; Singh, S. P.; Singh, Vidya Nand

    2015-12-01

    Here we present a method to grow the petal type structure of CZTS thin film on soda lime glass substrate using the stacked layer reactive sputtering and post-depostion annealing in N2 atmosphere. Optical bandgap of the petal type structure of CZTS was determined using UV-VIS spectroscopy and the value was 1.5 eV. In XRD analysis, (112) plane having highest intensity and other supporting planes with low intensity peaks corresponding to (200), (220) and (312) revealed the presence of CZTS phase. It was further confirmed by the Raman analysis, where the Raman peaks at 288 cm-1, 335 cm-1 and 353 cm-1 revealed the presence of CZTS phase. Petal type growth was observed in the scanning electron microscopy analysis. Elemental analysis was done by the EDAX. In EDAX analysis, It is observed that sample was Sn rich which may be responsible for petal type growth. Petal type growth of CZTS may be helpful in increasing the performance of the CZTS based thin film solar cell by phenomena of light scattering and enhanced surface area.

  19. Resonant frequency and hysteresis of a stack actuator made of single crystal (PMN-29PT) layers

    NASA Astrophysics Data System (ADS)

    Tran, K. S.; Lee, H. Y.; Kim, Y.; Park, H. C.

    2016-12-01

    In this study, we have presented the dynamic behavior of a piezoelectric stack actuator made of forty layers of single-crystal (PMN-29PT) with an area of 10 × 10 mm2 and thickness of 1 mm. To conduct a dynamic test of the actuator, we built a test apparatus with dummy weights that was placed over the top of the actuator to measure the actuation displacement. The resonant frequencies of the actuator with and without the dummy weight were determined as the excitation frequencies where a significant increase in the actuation displacement could be observed. We also proposed an analytical multi-degree-of-freedom (MDOF) model of the actuator to analytically predict the resonant frequency. Finite element analyses were conducted to validate the analytically predicted and measured resonant frequencies. With no dummy weight, the resonant frequency of the actuator was measured at 730.00 Hz, which was 0.70% higher than the one calculated by the MDOF model and 0.10% smaller than that of the finite element model. With a dummy weight, the measured resonant frequency was lower than 730.00 Hz and close enough to those computed by the MDOF model and the finite element model. The hysteresis curves of the actuator at various frequencies indicated that the actuator might incur a small energy loss.

  20. Water tank experiment of gas diffusion from a stack in stably and unstably stratified layers under calm conditions

    NASA Astrophysics Data System (ADS)

    Ohba, R.; Kakishima, S.; Ito, S.

    Water tank experiments were conducted to investigate plume rrise and diffusion of gases discharged from a stack under calm conditions with stable and unstable thermal stratifications. First, tracer liquid with fluorescent dye and salt was emitted from a model of a stack in a stably stratified layer and the behavior of a plume was recorded by video camera. Using these results. we obtained formulae for plume rise height, and horizontal and vertical width of a plume as a function of thedensimetric Froude number, stability ratio and time. After the completion of these experiments under stable conditions, an unstably stratified layer was developed from a ground surface by heating a floor and the resulting concentration distribution was measured with electric conductivity probes. Using these results, we analyzed the height of the convection layer and concentration distribution as a function of the overall Richardson number and time.

  1. [Co/Ni]-CoFeB hybrid free layer stack materials for high density magnetic random access memory applications

    NASA Astrophysics Data System (ADS)

    Liu, E.; Swerts, J.; Couet, S.; Mertens, S.; Tomczak, Y.; Lin, T.; Spampinato, V.; Franquet, A.; Van Elshocht, S.; Kar, G.; Furnemont, A.; De Boeck, J.

    2016-03-01

    Alternative free layer materials with high perpendicular anisotropy are researched to provide spin-transfer-torque magnetic random access memory stacks' sufficient thermal stability at critical dimensions of 20 nm and below. We demonstrate a high tunnel magetoresistance (TMR) MgO-based magnetic tunnel junction stack with a hybrid free layer design made of a [Co/Ni] multilayer and CoFeB. The seed material on which the [Co/Ni] multilayer is deposited determines its switching characteristics. When deposited on a Pt seed layer, soft magnetic switching behavior with high squareness is obtained. When deposited on a NiCr seed, the perpendicular anisotropy remains high, but the squareness is low and coercivity exceeds 1000 Oe. Interdiffusion of the seed material with the [Co/Ni] multilayers is found to be responsible for the different switching characteristics. In optimized stacks, a TMR of 165% and low resistance-area (RA) product of 7.0 Ω μm2 are attained for free layers with an effective perpendicular magnetic anisotropy energy of 1.25 erg/cm2, which suggests that the hybrid free layer materials may be a viable candidate for high density magnetic random access memory applications.

  2. Advanced atom chips with two metal layers.

    SciTech Connect

    Stevens, James E.; Blain, Matthew Glenn; Benito, Francisco M.; Biedermann, Grant

    2010-12-01

    A design concept, device layout, and monolithic microfabrication processing sequence have been developed for a dual-metal layer atom chip for next-generation positional control of ultracold ensembles of trapped atoms. Atom chips are intriguing systems for precision metrology and quantum information that use ultracold atoms on microfabricated chips. Using magnetic fields generated by current carrying wires, atoms are confined via the Zeeman effect and controllably positioned near optical resonators. Current state-of-the-art atom chips are single-layer or hybrid-integrated multilayer devices with limited flexibility and repeatability. An attractive feature of multi-level metallization is the ability to construct more complicated conductor patterns and thereby realize the complex magnetic potentials necessary for the more precise spatial and temporal control of atoms that is required. Here, we have designed a true, monolithically integrated, planarized, multi-metal-layer atom chip for demonstrating crossed-wire conductor patterns that trap and controllably transport atoms across the chip surface to targets of interest.

  3. Two stacked tandem white organic light-emitting diodes employing WO3 as a charge generation layer

    NASA Astrophysics Data System (ADS)

    Bin, Jong-Kwan; Lee, Na Yeon; Lee, SeungJae; Seo, Bomin; Yang, JoongHwan; Kim, Jinook; Yoon, Soo Young; Kang, InByeong

    2016-09-01

    Recently, many studies have been conducted to improve the electroluminescence (EL) performance of organic lightemitting diodes (OLEDs) by using appropriate organic or inorganic materials as charge generation layer (CGL) for their application such as full color displays, backlight units, and general lighting source. In a stacked tandem white organic light-emitting diodes (WOLEDs), a few emitting units are electrically interconnected by a CGL, which plays the role of generating charge carriers, and then facilitate the injection of it into adjacent emitting units. In the present study, twostacked WOLEDs were fabricated by using tungsten oxide (WO3) as inorganic charge generation layer and 1,4,5,8,9,11- hexaazatriphenylene hexacarbonitrile (HAT-CN) as organic charge generation layer (P-CGL). Organic P-CGL materials were used due to their ease of use in OLED fabrication as compared to their inorganic counterparts. To obtain high efficiency, we demonstrate two-stacked tandem WOLEDs as follows: ITO/HIL/HTL/HTL'/B-EML/ETL/N-CGL/P-CGL (WO3 or HAT-CN)/HTL″/YG-EML/ETL/LiF/Al. The tandem devices with blue- and yellow-green emitting layers were sensitive to the thickness of an adjacent layer, hole transporting layer for the YG emitting layer. The WOLEDs containing the WO3 as charge generation layer reach a higher power efficiency of 19.1 lm/W and the current efficiency of 51.2 cd/A with the white color coordinate of (0.316, 0.318) than the power efficiency of 13.9 lm/W, and the current efficiency of 43.7 cd/A for organic CGL, HAT-CN at 10 mA/cm2, respectively. This performance with inserting WO3 as CGL exhibited the highest performance with excellent CIE color coordinates in the two-stacked tandem OLEDs.

  4. 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.

  5. Zone structure and polarization properties of the stack of a metamaterial-based cholesteric liquid crystal and isotropic medium layers

    NASA Astrophysics Data System (ADS)

    Gevorgyan, A. H.; Matinyan, G. K.

    2014-05-01

    The optical properties of a stack of metamaterial-based cholesteric liquid crystal (CLC) layers and isotropic medium layers are investigated. The problem is solved by a modification of Ambartsumian's layer addition method. CLCs with two types of chiral nihility are defined. The peculiarities of the reflection spectra of this system are investigated and it is shown that the reflection spectra of the stacks of CLC layers of these two types differ from each other. Besides, in contrast to the single CLC layer case, these systems have multiple photonic band gaps. There are two types of such gaps: those selective with respect to polarization of the incident light and nonselective ones. It is shown that the system eigenpolarizations mainly coincide with the quasi-orthogonal, quasi-circular polarizations for normally incident light, except the regions of diffraction reflection selective with respect to the polarization of incident light. The influence of the CLC sublayer thick-nesses, the incidence angle, the local dielectric (magnetic) anisotropy of the CLC layers, and the refractive indices and thicknesses of the isotropic media layers on the reflection spectra and other optical characteristics of the system is investigated.

  6. Photovoltaic device having light transmitting electrically conductive stacked films

    DOEpatents

    Weber, Michael F.; Tran, Nang T.; Jeffrey, Frank R.; Gilbert, James R.; Aspen, Frank E.

    1990-07-10

    A light transmitting electrically conductive stacked film, useful as a light transmitting electrode, including a first light transmitting electrically conductive layer, having a first optical thickness, a second light transmitting layer, having a second optical thickness different from the optical thickness of the first layer, and an electrically conductive metallic layer interposed between and in initimate contact with the first and second layers.

  7. Tight-binding study of stacking fault energies and the Rice criterion of ductility in the fcc metals

    NASA Astrophysics Data System (ADS)

    Mehl, Michael J.; Papaconstantopoulos, Dimitrios A.; Kioussis, Nicholas; Herbranson, M.

    2000-02-01

    We have used the Naval Research Laboratory (NRL) tight-binding (TB) method to calculate the generalized stacking fault energy and the Rice ductility criterion in the fcc metals Al, Cu, Rh, Pd, Ag, Ir, Pt, Au, and Pb. The method works well for all classes of metals, i.e., simple metals, noble metals, and transition metals. We compared our results with full potential linear-muffin-tin orbital and embedded atom method (EAM) calculations, as well as experiment, and found good agreement. This is impressive, since the NRL-TB approach only fits to first-principles full-potential linearized augmented plane-wave equations of state and band structures for cubic systems. Comparable accuracy with EAM potentials can be achieved only by fitting to the stacking fault energy.

  8. CZTSe solar cells prepared by electrodeposition of Cu/Sn/Zn stack layer followed by selenization at low Se pressure

    PubMed Central

    2014-01-01

    Cu2ZnSnSe4 (CZTSe) thin films are prepared by the electrodeposition of stack copper/tin/zinc (Cu/Sn/Zn) precursors, followed by selenization with a tin source at a substrate temperature of 530°C. Three selenization processes were performed herein to study the effects of the source of tin on the quality of CZTSe thin films that are formed at low Se pressure. Much elemental Sn is lost from CZTSe thin films during selenization without a source of tin. The loss of Sn from CZTSe thin films in selenization was suppressed herein using a tin source at 400°C (A2) or 530°C (A3). A copper-poor and zinc-rich CZTSe absorber layer with Cu/Sn, Zn/Sn, Cu/(Zn + Sn), and Zn/(Cu + Zn + Sn) with metallic element ratios of 1.86, 1.24, 0.83, and 0.3, respectively, was obtained in a selenization with a tin source at 530°C. The crystallized CZTSe thin film exhibited an increasingly (112)-preferred orientation at higher tin selenide (SnSe x ) partial pressure. The lack of any obvious Mo-Se phase-related diffraction peaks in the X-ray diffraction (XRD) diffraction patterns may have arisen from the low Se pressure in the selenization processes. The scanning electron microscope (SEM) images reveal a compact surface morphology and a moderate grain size. CZTSe solar cells with an efficiency of 4.81% were produced by the low-cost fabrication process that is elucidated herein. PMID:25593559

  9. CZTSe solar cells prepared by electrodeposition of Cu/Sn/Zn stack layer followed by selenization at low Se pressure

    NASA Astrophysics Data System (ADS)

    Yao, Liyong; Ao, Jianping; Jeng, Ming-Jer; Bi, Jinlian; Gao, Shoushuai; He, Qing; Zhou, Zhiqiang; Sun, Guozhong; Sun, Yun; Chang, Liann-Be; Chen, Jian-Wun

    2014-12-01

    Cu2ZnSnSe4 (CZTSe) thin films are prepared by the electrodeposition of stack copper/tin/zinc (Cu/Sn/Zn) precursors, followed by selenization with a tin source at a substrate temperature of 530°C. Three selenization processes were performed herein to study the effects of the source of tin on the quality of CZTSe thin films that are formed at low Se pressure. Much elemental Sn is lost from CZTSe thin films during selenization without a source of tin. The loss of Sn from CZTSe thin films in selenization was suppressed herein using a tin source at 400°C (A2) or 530°C (A3). A copper-poor and zinc-rich CZTSe absorber layer with Cu/Sn, Zn/Sn, Cu/(Zn + Sn), and Zn/(Cu + Zn + Sn) with metallic element ratios of 1.86, 1.24, 0.83, and 0.3, respectively, was obtained in a selenization with a tin source at 530°C. The crystallized CZTSe thin film exhibited an increasingly (112)-preferred orientation at higher tin selenide (SnSe x ) partial pressure. The lack of any obvious Mo-Se phase-related diffraction peaks in the X-ray diffraction (XRD) diffraction patterns may have arisen from the low Se pressure in the selenization processes. The scanning electron microscope (SEM) images reveal a compact surface morphology and a moderate grain size. CZTSe solar cells with an efficiency of 4.81% were produced by the low-cost fabrication process that is elucidated herein.

  10. CZTSe solar cells prepared by electrodeposition of Cu/Sn/Zn stack layer followed by selenization at low Se pressure.

    PubMed

    Yao, Liyong; Ao, Jianping; Jeng, Ming-Jer; Bi, Jinlian; Gao, Shoushuai; He, Qing; Zhou, Zhiqiang; Sun, Guozhong; Sun, Yun; Chang, Liann-Be; Chen, Jian-Wun

    2014-01-01

    Cu2ZnSnSe4 (CZTSe) thin films are prepared by the electrodeposition of stack copper/tin/zinc (Cu/Sn/Zn) precursors, followed by selenization with a tin source at a substrate temperature of 530°C. Three selenization processes were performed herein to study the effects of the source of tin on the quality of CZTSe thin films that are formed at low Se pressure. Much elemental Sn is lost from CZTSe thin films during selenization without a source of tin. The loss of Sn from CZTSe thin films in selenization was suppressed herein using a tin source at 400°C (A2) or 530°C (A3). A copper-poor and zinc-rich CZTSe absorber layer with Cu/Sn, Zn/Sn, Cu/(Zn + Sn), and Zn/(Cu + Zn + Sn) with metallic element ratios of 1.86, 1.24, 0.83, and 0.3, respectively, was obtained in a selenization with a tin source at 530°C. The crystallized CZTSe thin film exhibited an increasingly (112)-preferred orientation at higher tin selenide (SnSe x ) partial pressure. The lack of any obvious Mo-Se phase-related diffraction peaks in the X-ray diffraction (XRD) diffraction patterns may have arisen from the low Se pressure in the selenization processes. The scanning electron microscope (SEM) images reveal a compact surface morphology and a moderate grain size. CZTSe solar cells with an efficiency of 4.81% were produced by the low-cost fabrication process that is elucidated herein.

  11. Ab initio calculations of generalized-stacking-fault energy surfaces and surface energies for FCC metals

    NASA Astrophysics Data System (ADS)

    Wu, Xiao-Zhi; Wang, Rui; Wang, Shao-Feng; Wei, Qun-Yi

    2010-08-01

    The ab initio calculations have been used to study the generalized-stacking-fault energy (GSFE) surfaces and surface energies for the closed-packed (1 1 1) plane in FCC metals Cu, Ag, Au, Ni, Al, Rh, Ir, Pd, Pt, and Pb. The GSFE curves along <112> (1 1 1) direction and <110> (1 1 1) direction, and surface energies have been calculated from first principles. Based on the translational symmetry of the GSFE surfaces, the fitted expressions have been obtained from the Fourier series. Our results of the GSFEs and surface energies agree better with experimental results. The metals Al, Pd, and Pt have low γ/γI value, so full dislocation will be observed easily; while Cu, Ag, Au, and Ni have large γ/γI value, so it is preferred to create partial dislocation. From the calculations of surface energies, it is confirmed that the VIII column elements Ni, Rh, Ir, Pd, and Pt have higher surface energies than other metals.

  12. Effective Schottky Barrier Height Lowering of Metal/n-Ge with a TiO2/GeO2 Interlayer Stack.

    PubMed

    Kim, Gwang-Sik; Kim, Sun-Woo; Kim, Seung-Hwan; Park, June; Seo, Yujin; Cho, Byung Jin; Shin, Changhwan; Shim, Joon Hyung; Yu, Hyun-Yong

    2016-12-28

    A perfect ohmic contact formation technique for low-resistance source/drain (S/D) contact of germanium (Ge) n-channel metal-oxide-semiconductor field-effect transistors (MOSFETs) is developed. A metal-interlayer-semiconductor (M-I-S) structure with an ultrathin TiO2/GeO2 interlayer stack is introduced into the contact scheme to alleviate Fermi-level pinning (FLP), and reduce the electron Schottky barrier height (SBH). The TiO2 interlayer can alleviate FLP by preventing formation of metal-induced gap states (MIGS) with its very low tunneling resistance and series resistance and can provide very small electron energy barrier at the metal/TiO2 interface. The GeO2 layer can induce further alleviation of FLP by reducing interface state density (Dit) on Ge which is one of main causes of FLP. Moreover, the proposed TiO2/GeO2 stack can minimize interface dipole formation which induces the SBH increase. The M-I-S structure incorporating the TiO2/GeO2 interlayer stack achieves a perfect ohmic characteristic, which has proved unattainable with a single interlayer. FLP can be perfectly alleviated, and the SBH of the metal/n-Ge can be tremendously reduced. The proposed structure (Ti/TiO2/GeO2/n-Ge) exhibits 0.193 eV of effective electron SBH which achieves 0.36 eV of SBH reduction from that of the Ti/n-Ge structure. The proposed M-I-S structure can be suggested as a promising S/D contact technique for nanoscale Ge n-channel transistors to overcome the large electron SBH problem caused by severe FLP.

  13. Long-Wavelength Stacked SiGe/Si Heterojunction Internal Photoemission Infrared Detectors Using Multiple SiGe/Si Layers

    NASA Technical Reports Server (NTRS)

    Park, J. S.; Lin, T. L.; Jones, E. W.; Castillo, H. M. Del; Gunapala, S. D.

    1994-01-01

    Utilizing low temperature silicon molecular beam epitaxy (MBE) growth, long-wavelength stacked SiGe/Si heterojunction internal photoemission (HIP) infrared detectors with multiple SiGe/Si layers have been fabricated and demonstrated. Using an elemental boron source, high doping concentrations (approximately equal to 4 x 10(sup 20) cm(sup -3)) has been achieved and high crystalline quality multiple Si(sub 0.7)Ge(sub 0.3)/Si layers have been obtained. The detector structure consists of several periods of degenerately boron doped (approximately equal to 4 x 10(sup 20) cm(sup -3)) thin (less than or equal to 50 u Si(sub 0.7)Ge(sub 0.3) layers and undoped thick (approximately equal to 300u Si layers. The multiple p(sup +) - Si(sub 0.7)Ge(sub 0.3)/undoped-Si layers show strong infrared absorption in the long-wavelength regime mainly through free carrier absorption. The stacked Si(sub 0.7)Ge(sub 0.3)/Si HIP detectors with p = 4 x 10(sup 20) cm(sup -3) exhibit strong photoresponse at wavelengths ranging from 2 to 20 (micro)m with quantum efficiencies of about 4% and 1.5% at 10 and 15 (micro)m wavelengths, respectively. The detectors show near ideal thermionic-emission limited dark current characteristics.

  14. Stacking fault energy of face-centered cubic metals: thermodynamic and ab initio approaches

    NASA Astrophysics Data System (ADS)

    Li, Ruihuan; Lu, Song; Kim, Dongyoo; Schönecker, Stephan; Zhao, Jijun; Kwon, Se Kyun; Vitos, Levente

    2016-10-01

    The formation energy of the interface between face-centered cubic (fcc) and hexagonal close packed (hcp) structures is a key parameter in determining the stacking fault energy (SFE) of fcc metals and alloys using thermodynamic calculations. It is often assumed that the contribution of the planar fault energy to the SFE has the same order of magnitude as the bulk part, and thus the lack of precise information about it can become the limiting factor in thermodynamic predictions. Here, we differentiate between the interfacial energy for the coherent fcc(1 1 1)/hcp(0 0 0 1) interface and the ‘pseudo-interfacial energy’ that enters the thermodynamic expression for the SFE. Using first-principles calculations, we determine the coherent and pseudo-interfacial energies for six elemental metals (Al, Ni, Cu, Ag, Pt, and Au) and three paramagnetic Fe-Cr-Ni alloys. Our results show that the two interfacial energies significantly differ from each other. We observe a strong chemistry dependence for both interfacial energies. The calculated pseudo-interfacial energies for the Fe-Cr-Ni steels agree well with the available literature data. We discuss the effects of strain on the description of planar faults via thermodynamic and ab initio approaches.

  15. Diffusion barrier performance of novel Ti/TaN double layers for Cu metallization

    NASA Astrophysics Data System (ADS)

    Zhou, Y. M.; He, M. Z.; Xie, Z.

    2014-10-01

    Novel Ti/TaN double layers offering good stability as a barrier against Cu metallization have been made achievable by annealing in vacuum better than 1 × 10-3 Pa. Ti/TaN double layers were formed on SiO2/Si substrates by DC magnetron sputtering and then the properties of Cu/Ti/TaN/SiO2/Si film stacks were studied. It was found that the Ti/TaN double layers provide good diffusion barrier between Cu and SiO2/Si up to 750 °C for 30 min. The XRD, Auger and EDS results show that the Cu-Si compounds like Cu3Si were formed by Cu diffusion through Ti/TaN barrier for the 800 °C annealed samples. It seems that the improved diffusion barrier property of Cu/Ti/TaN/SiO2/Si stack is due to the diffusion of nitrogen along the grain boundaries in Ti layer, which would decrease the defects in Ti film and block the diffusion path for Cu diffusion with increasing annealing temperature. The failure mechanism of Ti/TaN bi-layer is similar to the Cu/TaN/Si metallization system in which Cu atoms diffuse through the grain boundary of barrier and react with silicon to form Cu3Si.

  16. Aerosol-Jet-Printing silicone layers and electrodes for stacked dielectric elastomer actuators in one processing device

    NASA Astrophysics Data System (ADS)

    Reitelshöfer, Sebastian; Göttler, Michael; Schmidt, Philip; Treffer, Philipp; Landgraf, Maximilian; Franke, Jörg

    2016-04-01

    In this contribution we present recent findings of our efforts to qualify the so called Aerosol-Jet-Printing process as an additive manufacturing approach for stacked dielectric elastomer actuators (DEA). With the presented system we are able to print the two essential structural elements dielectric layer and electrode in one machine. The system is capable of generating RTV-2 silicone layers made of Wacker Elastosil P 7670. Therefore, two aerosol streams of both precursor components A and B are generated in parallel and mixed in one printing nozzle that is attached to a 4-axis kinematic. At maximum speed the printing of one circular Elastosil layer with a calculated thickness of 10 μm and a diameter of 1 cm takes 12 seconds while the process keeps stable for 4.5 hours allowing a quite high overall material output and the generation of numerous silicone layers. By adding a second printing nozzle and the infrastructure to generate a third aerosol, the system is also capable of printing inks with conductive particles in parallel to the silicone. We have printed a reduced graphene oxide (rGO) ink prepared in our lab to generate electrodes on VHB 4905, Elastosil foils and finally on Aerosol-Jet-Printed Elastosil layers. With rGO ink printed on Elastosil foil, layers with a 4-point measured sheet resistance as low as 4 kΩ can be realized leaving room for improving the electrode printing time, which at the moment is not as good as the quite good time-frame for printing the silicone layers. Up to now we have used the system to print a fully functional two-layer stacked DEA to demonstrate the principle of continuously 3D printing actuators.

  17. Interfacial layer growth condition dependent carrier transport mechanisms in HfO2/SiO2 gate stacks

    NASA Astrophysics Data System (ADS)

    Sahoo, S. K.; Misra, D.

    2012-06-01

    The temperature and field dependent leakage current in HfO2/SiO2 gate stack for in situ steam grown and chemical interfacial layers (ILs) are studied in the temperature range of 20 °C to 105 °C. Poole-Frenkel mechanism in high field whereas Ohmic conduction in low field region are dominant for both devices. Leakage current decreases whereas both trap energy level (ϕt) and activation energy (Ea) increase for chemically grown IL devices. The trap level energy, (ϕt) ˜ 0.2 eV, indicates that doubly charged oxygen vacancies (V2-) are the active electron traps which contribute to the leakage current in these gate stacks.

  18. Anisotropy of Earth's D'' layer and stacking faults in the MgSiO3 post-perovskite phase.

    PubMed

    Oganov, Artem R; Martonák, Roman; Laio, Alessandro; Raiteri, Paolo; Parrinello, Michele

    2005-12-22

    The post-perovskite phase of (Mg,Fe)SiO3 is believed to be the main mineral phase of the Earth's lowermost mantle (the D'' layer). Its properties explain numerous geophysical observations associated with this layer-for example, the D'' discontinuity, its topography and seismic anisotropy within the layer. Here we use a novel simulation technique, first-principles metadynamics, to identify a family of low-energy polytypic stacking-fault structures intermediate between the perovskite and post-perovskite phases. Metadynamics trajectories identify plane sliding involving the formation of stacking faults as the most favourable pathway for the phase transition, and as a likely mechanism for plastic deformation of perovskite and post-perovskite. In particular, the predicted slip planes are {010} for perovskite (consistent with experiment) and {110} for post-perovskite (in contrast to the previously expected {010} slip planes). Dominant slip planes define the lattice preferred orientation and elastic anisotropy of the texture. The {110} slip planes in post-perovskite require a much smaller degree of lattice preferred orientation to explain geophysical observations of shear-wave anisotropy in the D'' layer.

  19. Electron Scattering at Surfaces of Epitaxial Metal Layers

    NASA Astrophysics Data System (ADS)

    Chawla, Jasmeet Singh

    and without thin epitaxial TiN(001) wetting layers and are studied for structure, crystalline quality, surface morphology, density and composition by a combination of x-ray diffraction theta-2theta scans, o-rocking curves, pole figures, reciprocal space mapping, Rutherford backscattering, x-ray reflectometry and transmission electron microscopy. The TiN(001) surface suppresses Cu and Ag dewetting, yielding lower defect density, no twinning, and smaller surface roughness than if grown on MgO(001). Textured polycrystalline Cu(111) layers 25-50-nm-thick are deposited on a stack of 7.5-nm-Ta on SiO2/Si(001), and subsequent in situ annealing at 350°C followed by sputter etching in Ar plasma yields Cu layers with independently variable thickness and grain size. Cu nanowires, 75 to 350 nm wide, are fabricated from Cu layers with different average grain size using a subtractive patterning process. In situ electron transport measurements at room temperature in vacuum and at 77 K in liquid nitrogen for single-crystal Cu and Ag layers is consistent with the Fuchs-Sondheimer (FS) model and indicates specular scattering at the metal-vacuum boundary with an average specularity parameter p = 0.8 and 0.6, respectively. In contrast, layers measured ex situ show diffuse surface scattering due to sub-monolayer oxidation. Also, addition of Ta atoms on Cu(001) surface perturbs the smooth interface potential and results in completely diffuse scattering at the Cu-Ta interface, and in turn, a higher resistivity of single-crystal Cu layers. In situ exposure of Cu(001) layers to O2 between 10 -3 and 105 Pa-s results in a sequential increase, decrease and increase of the electrical resistance which is attributed to specular surface scattering for clean Cu(001) and for surfaces with a complete adsorbed monolayer, but diffuse scattering at partial coverage and after chemical oxidation. Electron transport measurements for polycrystalline Cu layers and wires show a 10-15% and 7-9% decrease in

  20. Direct observation of both contact and remote oxygen scavenging of GeO{sub 2} in a metal-oxide-semiconductor stack

    SciTech Connect

    Fadida, S. Shekhter, P.; Eizenberg, M.; Cvetko, D.; Floreano, L.; Verdini, A.; Kymissis, I.

    2014-10-28

    In the path to incorporating Ge based metal-oxide-semiconductor into modern nano-electronics, one of the main issues is the oxide-semiconductor interface quality. Here, the reactivity of Ti on Ge stacks and the scavenging effect of Ti were studied using synchrotron X-ray photoelectron spectroscopy measurements, with an in-situ metal deposition and high resolution transmission electron microscopy imaging. Oxygen removal from the Ge surface was observed both in direct contact as well as remotely through an Al{sub 2}O{sub 3} layer. The scavenging effect was studied in situ at room temperature and after annealing. We find that the reactivity of Ti can be utilized for improved scaling of Ge based devices.

  1. Silver doped metal layers for medical applications

    NASA Astrophysics Data System (ADS)

    Kocourek, T.; Jelínek, M.; Mikšovský, J.; Jurek, K.; Weiserová, M.

    2014-04-01

    Biological, physical and mechanical properties of silver-doped layers of titanium alloy Ti6Al4V and 316L steel prepared by pulsed laser deposition were studied. Metallic silver-doped coatings could be a new route for antibacterial protection in medicine. Thin films of silver and silver-doped materials were synthesized using KrF excimer laser deposition. The materials were ablated from two targets, which were composed either from titanium alloy with silver segments or from steel with silver segments. The concentration of silver ranged from 1.54 at% to 4.32 at% for steel and from 3.04 at% to 13.05 at% for titanium alloy. The layer properties such as silver content, structure, adhesion, surface wettability, and antibacterial efficacy (evaluated by Escherichia coli and Bacillus subtilis bacteria) were measured. Film adhesion was studied using scratch test. The antibacterial efficacy changed with silver doping up to 99.9 %. Our investigation was focused on minimum Ag concentration needed to reach high antibacterial efficiency, high film adhesion, and hardness.

  2. Isolation and characterization of nanosheets containing few layers of the Aurivillius family of oxides and metal-organic compounds

    SciTech Connect

    Sreedhara, M.B.; Prasad, B.E.; Moirangthem, Monali; Murugavel, R.; Rao, C.N.R.

    2015-04-15

    Nanosheets containing few-layers of ferroelectric Aurivillius family of oxides, Bi{sub 2}A{sub n−1}B{sub n}O{sub 3n+3} (where A=Bi{sup 3+}, Ba{sup 2+} etc. and B=Ti{sup 4+}, Fe{sup 3+} etc.) with n=3, 4, 5, 6 and 7 have been prepared by reaction with n-butyllithium, followed by exfoliation in water. The few-layer samples have been characterized by Tyndall cones, atomic force microscopy, optical spectroscopy and other techniques. The few-layer species have a thickness corresponding to a fraction of the c-parameter along which axis the perovskite layers are stacked. Magnetization measurements have been carried out on the few-layer samples containing iron. Few-layer species of a few layered metal-organic compounds have been obtained by ultrasonication and characterized by Tyndall cones, atomic force microscopy, optical spectroscopy and magnetic measurements. Significant changes in the optical spectra and magnetic properties are found in the few-layer species compared to the bulk samples. Few-layer species of the Aurivillius family of oxides may find uses as thin layer dielectrics in photovoltaics and other applications. - Graphical abstract: Exfoliation of the layered Aurivillius oxides into few-layer nanosheets by chemical Li intercalation using n-BuLi followed by reaction in water. Exfoliation of the layered metal-organic compounds into few-layer nanosheets by ultrasonication. - Highlights: • Few-layer nanosheets of Aurivillius family of oxides with perovskite layers have been generated by lithium intercalation. • Few-layer nanosheets of few layered metal-organic compounds have been generated by ultrasonication. • Few-layer nanosheets of the Aurivillius oxides have been characterized by AFM, TEM and optical spectroscopy. • Aurivillius oxides containing Fe show layer dependent magnetic properties. • Exfoliated few-layer metal-organic compounds show changes in spectroscopic and magnetic properties compared with bulk materials.

  3. Synthesis of Stacked-Cup Carbon Nanotubes in a Metal Free Low Temperature System

    NASA Technical Reports Server (NTRS)

    Kimura, Yuki; Nuth, Joseph A.; Johnson, Natasha M.; Farmer, Kevin D.; Roberts, Kenneth P.; Hussaini, Syed R.

    2011-01-01

    Stacked-cup carbon nanotubes were formed by either Fischer-Tropsch type or Haber Bosch type reactions in a metal free system. Graphite particles were used as the catalyst. The samples were heated at 600 C in a gas mixture of CO 75 Torr, N2 75 Torr and H2 550 Torr for three days. Trans mission electron microscope analysis of the catalyst surface at the completion of the experiment recognized the growth of nanotubes. They were 10-50 nm in diameter and approximately 1 micrometer in length. They had a hollow channel of 5-20 nm in the center. The nanotubes may have grown on graphite surfaces by the CO disproportionation reaction and the surface tension of the carbon nucleus may have determined the diameter. Although, generally, the diameter of a carbon nanotube depends on the size of the cataly1ic particles, the diameter of the nanotubes on graphite particles was independent of the particle size and significantly confined within a narrow range compared with that produced using catalytic amorphous iron-silicate nanoparticles. Therefore, they must have an unknown formation process that is different than the generally accepted mechanism.

  4. Photoinduced switching to metallic states in the two-dimensional organic Mott insulator dimethylphenazine-tetrafluorotetracyanoquinodimethane with anisotropic molecular stacks

    NASA Astrophysics Data System (ADS)

    Matsuzaki, Hiroyuki; Ohkura, Masa-aki; Ishige, Yu; Nogami, Yoshio; Okamoto, Hiroshi

    2015-06-01

    A photoinduced phase transition was investigated in an organic charge-transfer (CT) complex M2P -TCNQ F4 , [M2P : 5,10-dihydro-5,10-dimethylphenazine, donor (D) molecule; TCNQ F4 : 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane, acceptor (A) molecule] by means of femtosecond pump-probe reflection spectroscopy. This is an ionic compound and has a peculiar two-dimensional (2D) molecular arrangement; the same A (or D) molecules arrange along the [100] direction, and A and D molecules alternately arrange along the [111] direction. It results in a strongly anisotropic two-dimensional electronic structure. This compound shows a structural and magnetic phase transition at 122 K below which the two neighboring molecules are dimerized along both the [100] and [111] directions. We demonstrate that two kinds of photoinduced phase transitions occur by irradiation of a femtosecond laser pulse; in the high-temperature lattice-uniform phase, a quasi-one-dimensional (1D) metallic state along the AA(DD) stack is generated, and in the low-temperature lattice-dimerized phase, a quasi-2D metallic state is initially produced and molecular dimerizations are subsequently released. Mixed-stack CT compounds consisting of DA stacks are generally insulators or semiconductors in the ground state. Here, such a dynamical metallization in the DA stack is demonstrated. The release of the dimerizations drives several kinds of coherent oscillations which play an important role in the stabilization of the lattice-dimerized phase. The mechanisms of those photoinduced phase transitions are discussed in terms of the magnitudes of the anisotropic bandwidths and molecular dimerizations along two different directions of the molecular stacks.

  5. Selective realignment of the exchange biased magnetization direction in spintronic layer stacks using continuous and pulsed laser radiation

    NASA Astrophysics Data System (ADS)

    Berthold, I.; Müller, M.; Ebert, R.; Schille, J.; Löschner, U.; Exner, H.; Matthes, P.; Albrecht, M.

    2014-03-01

    We report on selective realignment of the magnetization direction of the exchange biased ferromagnetic layer in two different spintronic layer stacks using laser radiation. The exchange bias effect occurs in an antiferromagnetic/ferromagnetic bilayer system when cooled in an external magnetic field below the Néel temperature and results in a shift of the ferromagnetic hysteresis loop with increased coercivity. The effect is utilized to pin the magnetization direction of the reference ferromagnetic layer in spin valve systems. We investigated the realignment of the pinned magnetization direction in a spin valve system with in plane exchange bias and in a Co/Pt multilayer with perpendicular exchange bias. The layer stacks were heated above the Néel temperature in a defined lateral area by using rapidly deflected laser radiation. Two different laser assisted annealing techniques were investigated applying either continuous or pulsed laser radiation. During laser annealing, the sample was subjected to an external magnetic field in order to selectively realign the magnetization direction of the pinned ferromagnetic layer. Magnetic structuring was performed by heating narrow single tracks as well as irradiating single pulses. By using a magneto optical sensor in combination with a polarization microscope, the magnetic structures have been visualized. After laser annealing of larger-scaled areas, the exchange bias field strength and the coercive field strength were analyzed using a magneto optical Kerr effect set up (MOKE). The impact of the processing parameters laser peak intensity, laser pulse duration, scan speed (continuous wave) and magnetic field strength on the resulting reversed exchange bias field was evaluated.

  6. Analysis of Al diffusion processes in TiN barrier layers for the application in silicon solar cell metallization

    NASA Astrophysics Data System (ADS)

    Kumm, J.; Samadi, H.; Chacko, R. V.; Hartmann, P.; Wolf, A.

    2016-07-01

    An evaporated Al layer is known as an excellent rear metallization for highly efficient solar cells, but suffers from incompatibility with a common solder process. To enable solar cell-interconnection and module integration, in this work the Al layer is complemented with a solder stack of TiN/Ti/Ag or TiN/NiV/Ag, in which the TiN layer acts as an Al diffusion barrier. X-ray photoelectron spectroscopy measurements prove that diffusion of Al through the stack and the formation of an Al2O3 layer on the stack's surface are responsible for a loss of solderability after a strong post-metallization anneal, which is often mandatory to improve contact resistance and passivation quality. An optimization of the reactive TiN sputter process results in a densification of the TiN layer, which improves its barrier quality against Al diffusion. However, measurements with X-ray diffraction and scanning electron microscopy show that small grains with vertical grain boundaries persist, which still offer fast diffusion paths. Therefore, the concept of stuffing is introduced. By incorporating oxygen into the grain boundaries of the sputtered TiN layer, Al diffusion is strongly reduced as confirmed by secondary ion mass spectroscopy profiles. A quantitative analysis reveals a one order of magnitude lower Al diffusion coefficient for stuffed TiN layers. This metallization system maintains its solderability even after strong post-metallization annealing at 425 °C for 15 min. This paper thus presents an industrially feasible, conventionally solderable, and long-term stable metallization scheme for highly efficient silicon solar cells.

  7. Temperature Dependent Border Trap Response Produced by a Defective Interfacial Oxide Layer in Al2O3/InGaAs Gate Stacks.

    PubMed

    Tang, Kechao; Meng, Andrew C; Droopad, Ravi; McIntyre, Paul C

    2016-11-09

    Intentional oxidation of an As2-decapped (100) In0.57Ga0.43As substrate by additional H2O dosing during initial Al2O3 gate dielectric atomic layer deposition (ALD) increases the interface trap density (Dit), lowers the band edge photoluminescence (PL) intensity, and generates Ga-oxide detected by X-ray photoelectron spectroscopy (XPS). Aberration-corrected high resolution transmission electron microscopy (TEM) reveals formation of an amorphous interfacial layer which is distinct from the Al2O3 dielectric and which is not present without the additional H2O dosing. Observation of a temperature dependent border trap response, associated with the frequency dispersion of the accumulation capacitance and conductance of metal-oxide-semiconductor (MOS) structures, is found to be correlated with the presence of this defective interfacial layer. MOS capacitors prepared with additional H2O dosing show a notable decrease (∼20%) of accumulation dispersion over 5 kHz to 500 kHz when the measurement temperature decreases from room temperature to 77 K, while capacitors prepared with an abrupt Al2O3/InGaAs interface display little change (<2%) with temperature. Similar temperature-dependent border trap response is also observed when the (100) InGaAs surface is treated with a previously reported HCl(aq) wet cleaning procedure prior to Al2O3 ALD. These results point out the sensitivity of the temperature dependence of the border trap response in metal oxide/III-V MOS gate stacks to the presence of processing-induced interface oxide layers, which alter the dynamics of carrier trapping at defects that are not located at the semiconductor interface.

  8. Ultraviolet laser damage and optical properties of high-refractive-index single layers, multiple layers, and high/low index multilayer stacks

    NASA Astrophysics Data System (ADS)

    McInnes, Hazel A.; Andrew, James E.; Bazin, Nicholas J.; Morris, A. J.; Porter, K. J.

    1998-04-01

    Laser induced damage thresholds, measured using N-on-1 and R-on-1 testing, of single layer high index zirconia and hafnia coatings, derived from nitric or acetic acid stabilized sol-gel processing, are reported. Single layer acetic acid, nitric acid and base catalyzed silica sol-gel coatings have also been tested. The sol-gels were dip coated onto fused silica substrates at a rate of 3mm/s. The refractive index of the materials were measured using transmission spectra of multiple pairs of high and low refractive index materials. Absorption in the UV region was similarly measured with multiple layers of the same material and fitting to a Beer's law behavior. The high index materials used were zirconia or hafnia, the low index material was silica. The compatibility of the various combinations of high and low index materials for physical stacking without cracking, achieving high reflectivity and high damage thresholds are discussed and compared.

  9. Shear, Bulk, and Young's Moduli of Clay/Polymer Nanocomposites Containing the Stacks of Intercalated Layers as Pseudoparticles

    NASA Astrophysics Data System (ADS)

    Zare, Yasser

    2016-10-01

    The pseudoparticles include the stacks of intercalated layers in the case of incomplete clay exfoliation in clay/polymer nanocomposites. In this article, the effects of pseudoparticle properties on the shear, bulk, and Young's moduli of nanocomposites are studied using the Norris model. The properties of pseudoparticles are determined in some samples by the experimental data of Young's modulus and the roles of pseudoparticles in the shear, bulk, and Young's moduli of nanocomposites are discussed. The calculations show a good agreement with the experimental data when the pseudoparticles are taken into account in the samples. A low number of clay layers in the pseudoparticles present high moduli in nanocomposites. Moreover, the Poisson ratio and Young's modulus of polymer matrix play different roles in the shear, bulk, and Young's moduli of nanocomposites.

  10. High holding voltage segmentation stacking silicon-controlled-rectifier structure with field implant as body ties blocking layer

    NASA Astrophysics Data System (ADS)

    Yen, Shiang-Shiou; Cheng, Chun-Hu; Lan, Yu-Pin; Chiu, Yu-Chien; Fan, Chia-Chi; Hsu, Hsiao-Hsuan; Chang, Shao-Chin; Jiang, Zhe-Wei; Hung, Li-Yue; Tsai, Chi-Chung; Chang, Chun-Yen

    2016-04-01

    High electrostatic discharge (ESD) protection robustness and good transient-induced latchup immunity are two important issues for high voltage integrate circuit application. In this study, we report a high-voltage-n-type-field (HVNF) implantation to act as the body ties blocking layer in segmented topology silicon-controlled-rectifier (SCR) structure in 0.11 µm 32 V high voltage process. This body ties blocking layer eliminate the elevated triggered voltage in segmented technique. Using a large resistance as shunt resistor in resistor assisted triggered SCRs stacking structure, the double snapback phenomenon is eliminate. The series SCR could be decoupled a sufficient voltage drop to turned-on when a very low current flow through the shunt resistor. The holding voltage and the failure current of 22 V and 3.4 A are achieved in the best condition of segmented topology SCR stacking structure, respectively. It improves the latchup immunity at high voltage ICs application. On the other hand, the triggered voltage almost keep the same value which is identical to SCR single cell without using segmented topology.

  11. Commissioning of a conformal irradiation system for heavy-ion radiotherapy using a layer-stacking method

    SciTech Connect

    Kanai, Tatsuaki; Kanematsu, Nobuyuki; Minohara, Shinichi; Komori, Masataka; Torikoshi, Masami; Asakura, Hiroshi; Ikeda, Noritoshi; Uno, Takayuki; Takei, Yuka

    2006-08-15

    The commissioning of conformal radiotherapy system using heavy-ion beams at the Heavy Ion Medical Accelerator in Chiba (HIMAC) is described in detail. The system at HIMAC was upgraded for a clinical trial using a new technique: large spot uniform scanning with conformal layer stacking. The system was developed to localize the irradiation dose to the target volume more effectively than with the old system. With the present passive irradiation method using a ridge filter, a scatterer, a pair of wobbler magnets, and a multileaf collimator, the width of the spread-out Bragg peak (SOBP) in the radiation field could not be changed. With dynamic control of the beam-modifying devices during irradiation, a more conformal radiotherapy could be achieved. In order to safely perform treatments with this conformal therapy, the moving devices should be watched during irradiation and the synchronousness among the devices should be verified. This system, which has to be safe for patient irradiations, was constructed and tested for safety and for the quality of the dose localization realized. Through these commissioning tests, we were successfully able to prepare the conformal technique using layer stacking for patients. Subsequent to commissioning the technique has been applied to patients in clinical trials.

  12. The role of the substrate on the dispersion in accumulation in III-V compound semiconductor based metal-oxide-semiconductor gate stacks

    SciTech Connect

    Krylov, Igor; Ritter, Dan; Eizenberg, Moshe

    2015-09-07

    Dispersion in accumulation is a widely observed phenomenon in metal-oxide-semiconductor gate stacks based on III-V compound semiconductors. The physical origin of this phenomenon is attributed to border traps located in the dielectric material adjacent to the semiconductor. Here, we study the role of the semiconductor substrate on the electrical quality of the first layers at atomic layer deposited (ALD) dielectrics. For this purpose, either Al{sub 2}O{sub 3} or HfO{sub 2} dielectrics with variable thicknesses were deposited simultaneously on two technology important semiconductors—InGaAs and InP. Significantly larger dispersion was observed in InP based gate stacks compared to those based on InGaAs. The observed difference is attributed to a higher border trap density in dielectrics deposited on InP compared to those deposited on InGaAs. We therefore conclude that the substrate plays an important role in the determination of the electrical quality of the first dielectric monolayers deposited by ALD. An additional observation is that larger dispersion was obtained in HfO{sub 2} based capacitors compared to Al{sub 2}O{sub 3} based capacitors, deposited on the same semiconductor. This phenomenon is attributed to the lower conduction band offset rather than to a higher border trap density.

  13. Impact Electrochemistry of Layered Transition Metal Dichalcogenides.

    PubMed

    Lim, Chee Shan; Tan, Shu Min; Sofer, Zdeněk; Pumera, Martin

    2015-08-25

    Layered transition metal dichalcogenides (TMDs) exhibit paramount importance in the electrocatalysis of the hydrogen evolution reaction. It is crucial to determine the size of the electrocatalytic particles as well as to establish their electrocatalytic activity, which occurs at the edges of these particles. Here, we show that individual TMD (MoS2, MoSe2, WS2, or WSe2; in general MX2) nanoparticles impacting an electrode surface provide well-defined current "spikes" in both the cathodic and anodic regions. These spikes originate from direct oxidation of the nanoparticles (from M(4+) to M(6+)) at the anodic region and from the electrocatalytic currents generated upon hydrogen evolution in the cathodic region. The positive correlation between the frequency of the impacts and the concentration of TMD nanoparticles is also demonstrated here, enabling determination of the concentration of TMD nanoparticles in colloidal form. In addition, the size of individual TMD nanoparticles can be evaluated using the charge passed during every spike. The capability of detecting both the "indirect" catalytic effect of an impacting TMD nanoparticle as well as "direct" oxidation indicates that the frequency of impacts in both the "indirect" and "direct" scenarios are comparable. This suggests that all TMD nanoparticles, which are electrochemically oxidizable (thus capable of donating electrons to electrodes), are also capable of catalyzing the hydrogen reduction reaction.

  14. Stacking sequence determines Raman intensities of observed interlayer shear modes in 2D layered materials--A general bond polarizability model.

    PubMed

    Luo, Xin; Lu, Xin; Cong, Chunxiao; Yu, Ting; Xiong, Qihua; Quek, Su Ying

    2015-10-15

    2D layered materials have recently attracted tremendous interest due to their fascinating properties and potential applications. The interlayer interactions are much weaker than the intralayer bonds, allowing the as-synthesized materials to exhibit different stacking sequences, leading to different physical properties. Here, we show that regardless of the space group of the 2D materials, the Raman frequencies of the interlayer shear modes observed under the typical z(xx)z configuration blue shift for AB stacked materials, and red shift for ABC stacked materials, as the number of layers increases. Our predictions are made using an intuitive bond polarizability model which shows that stacking sequence plays a key role in determining which interlayer shear modes lead to the largest change in polarizability (Raman intensity); the modes with the largest Raman intensity determining the frequency trends. We present direct evidence for these conclusions by studying the Raman modes in few layer graphene, MoS2, MoSe2, WSe2 and Bi2Se3, using both first principles calculations and Raman spectroscopy. This study sheds light on the influence of stacking sequence on the Raman intensities of intrinsic interlayer modes in 2D layered materials in general, and leads to a practical way of identifying the stacking sequence in these materials.

  15. Fermi level pinning in metal/Al{sub 2}O{sub 3}/InGaAs gate stack after post metallization annealing

    SciTech Connect

    Winter, R.; Krylov, I.; Cytermann, C.; Eizenberg, M.; Tang, K.; Ahn, J.; McIntyre, P. C.

    2015-08-07

    The effect of post metal deposition annealing on the effective work function in metal/Al{sub 2}O{sub 3}/InGaAs gate stacks was investigated. The effective work functions of different metal gates (Al, Au, and Pt) were measured. Flat band voltage shifts for these and other metals studied suggest that their Fermi levels become pinned after the post-metallization vacuum annealing. Moreover, there is a difference between the measured effective work functions of Al and Pt, and the reported vacuum work function of these metals after annealing. We propose that this phenomenon is caused by charging of indium and gallium induced traps at the annealed metal/Al{sub 2}O{sub 3} interface.

  16. Solder for oxide layer-building metals and alloys

    DOEpatents

    Kronberg, J.W.

    1992-09-15

    A low temperature solder and method for soldering an oxide layer-building metal such as aluminum, titanium, tantalum or stainless steel is disclosed. The composition comprises tin and zinc; germanium as a wetting agent; preferably small amounts of copper and antimony; and a grit, such as silicon carbide. The grit abrades any oxide layer formed on the surface of the metal as the germanium penetrates beneath and loosens the oxide layer to provide good metal-to-metal contact. The germanium comprises less than approximately 10% by weight of the solder composition so that it provides sufficient wetting action but does not result in a melting temperature above approximately 300 C. The method comprises the steps rubbing the solder against the metal surface so the grit in the solder abrades the surface while heating the surface until the solder begins to melt and the germanium penetrates the oxide layer, then brushing aside any oxide layer loosened by the solder.

  17. Solder for oxide layer-building metals and alloys

    DOEpatents

    Kronberg, James W.

    1992-01-01

    A low temperature solder and method for soldering an oxide layer-building metal such as aluminum, titanium, tantalum or stainless steel. The comosition comprises tin and zinc; germanium as a wetting agent; preferably small amounts of copper and antimony; and a grit, such as silicon carbide. The grit abrades any oxide layer formed on the surface of the metal as the germanium penetrates beneath and loosens the oxide layer to provide good metal-to-metal contact. The germanium comprises less than aproximatley 10% by weight of the solder composition so that it provides sufficient wetting action but does not result in a melting temperature above approximately 300.degree. C. The method comprises the steps rubbing the solder against the metal surface so the grit in the solder abrades the surface while heating the surface until the solder begins to melt and the germanium penetrates the oxide layer, then brushing aside any oxide layer loosened by the solder.

  18. Correlation of bandgap reduction with inversion response in (Si)GeSn/high-k/metal stacks.

    PubMed

    Schulte-Braucks, Christian; Narimani, Keyvan; Glass, Stefan; von den Driesch, Nils; Hartmann, Jean-Michel; Ikonic, Zoran; Afanas'ev, Valeri V; Zhao, Qing-Tai; Mantl, Siegfried; Buca, Dan

    2017-02-21

    The bandgap tunability of (Si)GeSn group IV semiconductors opens a new era in Si-technology. Depending on the Si/Sn contents, direct and indirect bandgaps in the range of 0.4 eV to 0.8 eV can be obtained, offering a broad spectrum of both photonic and low power electronic applications. In this work, we systematically studied capacitance-voltage characteristics of high-k/metal gate stacks formed on GeSn and SiGeSn alloys with Sn-contents ranging from 0 to 14 at.% and Si-contents from 0 to 10 at.% particularly focusing on the minority carrier inversion response. A clear correlation between the Sn-induced shrinkage of the bandgap energy and enhanced minority carrier response was confirmed using temperature and frequency dependent capacitance voltage-measurements, in good agreement with k.p theory predictions and photoluminescence measurements of the analyzed epilayers as reported earlier. The enhanced minority generation rate for higher Sn-contents can be firmly linked to the bandgap reduction in the GeSn epilayer without significant influence of substrate/interface effects. It thus offers a unique possibility to analyze intrinsic defects in (Si)GeSn epilayers. The extracted dominant defect level for minority carrier inversion lies approximately 0.4 eV above the valence band edge in the studied Sn-content range (0 to12.5 at.%). This finding is of critical importance since it shows that the presence of Sn by itself does not impair the minority carrier lifetime. Therefore, the continuous improvement of (Si)GeSn material quality should yield longer non-radiative recombination times which are required for the fabrication of efficient light detectors and to obtain room temperature lasing action.

  19. Effect of stacking fault energy on mechanism of plastic deformation in nanotwinned FCC metals

    DOE PAGES

    Borovikov, Valery; Mendelev, Mikhail I.; King, Alexander H.; ...

    2015-05-15

    Starting from a semi-empirical potential designed for Cu, we have developed a series of potentials that provide essentially constant values of all significant (calculated) materials properties except for the intrinsic stacking fault energy, which varies over a range that encompasses the lowest and highest values observed in nature. In addition, these potentials were employed in molecular dynamics (MD) simulations to investigate how stacking fault energy affects the mechanical behavior of nanotwinned face-centered cubic (FCC) materials. The results indicate that properties such as yield strength and microstructural stability do not vary systematically with stacking fault energy, but rather fall into twomore » distinct regimes corresponding to 'low' and 'high' stacking fault energies.« less

  20. Effect of stacking fault energy on mechanism of plastic deformation in nanotwinned FCC metals

    SciTech Connect

    Borovikov, Valery; Mendelev, Mikhail I.; King, Alexander H.; LeSar, Richard

    2015-05-15

    Starting from a semi-empirical potential designed for Cu, we have developed a series of potentials that provide essentially constant values of all significant (calculated) materials properties except for the intrinsic stacking fault energy, which varies over a range that encompasses the lowest and highest values observed in nature. In addition, these potentials were employed in molecular dynamics (MD) simulations to investigate how stacking fault energy affects the mechanical behavior of nanotwinned face-centered cubic (FCC) materials. The results indicate that properties such as yield strength and microstructural stability do not vary systematically with stacking fault energy, but rather fall into two distinct regimes corresponding to 'low' and 'high' stacking fault energies.

  1. A Three-Stage Inverter-Based Stacked Power Amplifier in 65 nm Complementary Metal Oxide Semiconductor Process

    NASA Astrophysics Data System (ADS)

    Kiumarsi, Hamid; Mizuochi, Yutaka; Ito, Hiroyuki; Ishihara, Noboru; Masu, Kazuya

    2012-02-01

    A three-stage inverter-based stacked power amplifier (PA) in complementary metal oxide semiconductor (CMOS) process is proposed to overcome low breakdown voltage problem of scaled CMOS technologies. Unlike previous reported stacked PAs which radio frequency choke (RFC) was inevitable, we proposed stacked nMOS and pMOS transistors which effectively eliminates use of RFC. By properly setting self-biased circuits' and transistors' parameters, output impedance could reach up to 50 Ω which together with not employing the RFC makes this topology very appealing for the scalable PA realization. As a proof of concept, a three-stage PA using 65 nm CMOS technology is implemented. With a 6 V power supply for the third stage, the fabricated PA shows a small-signal gain of 36 dB, a saturated output power of 16 dBm and a maximum power added efficiency of 10% at 1 GHz. Using a 7.5 V of power supply, saturated output power reaches 18 dBm. To the best of our knowledge, this is the first reported inverter-based stacked PA.

  2. Formation and Characterization of Stacked Nanoscale Layers of Polymers and Silanes on Silicon Surfaces

    NASA Astrophysics Data System (ADS)

    Ochoa, Rosie; Davis, Brian; Conley, Hiram; Hurd, Katie; Linford, Matthew R.; Davis, Robert C.

    2008-10-01

    Chemical surface patterning at the nanoscale is a critical component of chemically directed assembly of nanoscale devices or sensitive biological molecules onto surfaces. Complete and consistent formation of nanoscale layers of silanes and polymers is a necessary first step for chemical patterning. We explored methods of silanizing silicon substrates for the purpose of functionalizing the surfaces. The chemical functionalization, stability, flatness, and repeatability of the process was characterized by use of ellipsometry, water contact angle, and Atomic Force Microscopy (AFM). We found that forming the highest quality functionalized surfaces was accomplished through use of chemical vapor deposition (CVD). Specifically, surfaces were plasma cleaned and hydrolyzed before the silane was applied. A polymer layer less then 2 nm in thickness was electrostatically bound to the silane layer. The chemical functionalization, stability, flatness, and repeatability of the process was also characterized for the polymer layer using ellipsometry, water contact angle, and AFM.

  3. Systematic study of interfacial reactions induced by metal electrodes in high-k/InGaAs gate stacks

    NASA Astrophysics Data System (ADS)

    Yoshida, S.; Lin, D.; Vais, A.; Alian, A.; Franco, J.; El Kazzi, S.; Mols, Y.; Miyanami, Y.; Nakazawa, M.; Collaert, N.; Watanabe, H.; Thean, A.

    2016-10-01

    We systematically studied the effects of metal electrodes on high-k/InGaAs gate stacks and observed that the remote reactions—both oxidation and reduction—at the interface between the high-k dielectrics and InGaAs were thermodynamically initiated by the metal electrodes. Metal electrodes with negative Gibbs free energies (e.g., Pd) resulted in the oxidation of the InGaAs surface during the forming-gas annealing. In contrast, with TiN electrodes, which have a positive Gibbs free energy, the native III-V oxides underwent the reduction between the high-k dielectrics and InGaAs. We demonstrated that the reduction of native III-V oxides by metal electrodes improved the interface quality of the high-k/InGaAs gate stacks and produced an interface trap density (Dit) at the mid-gap with a value as low as 5.2 × 1011 cm-2 eV-1 with a scaled capacitance-equivalent thickness.

  4. Compositional modulated atomic layer stacking and uniaxial magnetocrystalline anisotropy of CoPt alloy sputtered films with close-packed plane orientation

    SciTech Connect

    Saito, Shin Nozawa, Naoki; Hinata, Shintaro; Takahashi, Migaku; Shibuya, Kazunari; Hoshino, Kazuya; Awaya, Satoru

    2015-05-07

    An atomic layer stacking structure in hexagonal close packed (hcp) Co{sub 100−x}Pt{sub x} alloy films with c-plane sheet texture was directly observed by a high-angle annular dark-field imaging scanning transmission electron microscopy. The analysis of sequential and/or compositional atomic layer stacking structure and uniaxial magnetocrystalline anisotropy (K{sub u} = K{sub u1} + K{sub u2}) revealed that (1) integrated intensity of the superlattice diffraction takes the maximum at x = 20 at. % and shows broadening feature against x for the film fabricated under the substrate temperature (T{sub sub}) of 400 °C. (2) Compositional separation structure in atomic layers is formed for the films fabricated under T{sub sub} = 400 °C. A sequential alternative stacking of atomic layers with different compositions is hardly formed in the film with x = 50 at. %, whereas easily formed in the film with x = 20 at. %. This peculiar atomic layer stacking structure consists of in-plane-disordered Pt-rich and Pt-poor layers, which is completely different from the so-called atomic site ordered structure. (3) A face centered cubic atomic layer stacking as faults appeared in the host hcp atomic layer stacking exists in accompanies with irregularities for the periodicity of the compositional modulation atomic layers. (4) K{sub u1} takes the maximum of 1.4 × 10{sup 7 }erg/cm{sup 3} at around x = 20 at. %, whereas K{sub u2} takes the maximum of 0.7 × 10{sup 7 }erg/cm{sup 3} at around x = 40 at. %, which results in the maximum of 1.8 × 10{sup 7 }erg/cm{sup 3} of K{sub u} at x = 30 at. % and a shoulder in compositional dependence of K{sub u} in the range of x = 30–60 at. %. Not only compositional separation of atomic layers but also sequential alternative stacking of different compositional layers is quite important to improve essential uniaxial magnetocrystalline anisotropy.

  5. White-light emitting thin film electroluminescent devices with stacked SrS:Ce/CaS:Eu active layers

    NASA Astrophysics Data System (ADS)

    Ono, Yoshimasa A.; Fuyama, Moriaki; Onisawa, Ken-ichi; Tamura, Katsumi; Ando, Masahiko

    1989-12-01

    By stacking blue-green emitting SrS:Ce and red-emitting CaS:Eu active layers, white-light emitting electroluminescent (EL) devices were fabricated. Luminance improvement and EL characteristics of SrS:Ce and CaS:Eu EL devices were discussed. The electrooptical characteristics of white-light emitting EL devices with stacked SrS:Ce/CaS:Eu active layers were presented. Color changed from blue-green to white by changing the voltage or frequency. Finally, feasibility of multicolor EL devices by using the fabricated white-light emitting EL devices with color filters were discussed. UFpg5523,5527 UFid992922JAP UFttIn situ ac magnetic susceptibility of gadolinium thin films UFauF. H. SalasSUPa),b) and M. Mirabal-GarciaaSUPc) UFloInstitut fuur Atom- und Festkourperphysik, Freie Universitaut Berlin, D-1000 Berlin 33, ufquadFederal Republic of Germany UFsd(Received 27 April 1989; accepted for publication 3 August 1989) UFabWe report measurements of the ac magnetic susceptibility on Gd(0001)/W(110) thin films grown in ultrahigh vacuum. The measurements were made by using a pickup coil, in which the geometry and the number of turns were optimized. We applied an alternating magnetic field of about 2 Grms at frequencies of 180 and 340 Hz. The growth mode and the deposition rate of the Gd films were determined by performing conventional Auger electron spectroscopy during film growth. In films with thickness larger than 10 nm our technique is sensitive up to 1016 atoms/Grms , which allowed us to study the critical behavior of the magnetic susceptibility as the Curie temperature is approached from above, TT+C . A sharp maximum, which may be related to the Hopkinson effect, is observed at a temperature TH 289 K.

  6. On the nature of the stacking interaction between two graphene layers

    NASA Astrophysics Data System (ADS)

    Wang, Weizhou; Zhang, Yu; Sun, Tao; Wang, Yi-Bo

    2015-01-01

    The interlayer interaction energy and its components of the bilayer graphene were obtained by extrapolation of the interlayer interaction energies and their components of the dimers formed by graphene with benzene, naphthalene, anthracene, phenanthrene, pyrene, tetracene, perylene, pentacene and hexacene. The resulting interaction energy of the bilayer graphene is -1.82 kcal/mol (or -79 meV) per carbon atom. The dispersion energy represents 70% of the total attractive energy between two graphene layers. In contrast, the electrostatic component is responsible for 25% of the total attractive interaction and the induction term contributes 5% to the stability of two graphene layers.

  7. AB stacked few layer graphene growth by chemical vapor deposition on single crystal Rh(1 1 1) and electronic structure characterization

    NASA Astrophysics Data System (ADS)

    Kordatos, Apostolis; Kelaidis, Nikolaos; Giamini, Sigiava Aminalragia; Marquez-Velasco, Jose; Xenogiannopoulou, Evangelia; Tsipas, Polychronis; Kordas, George; Dimoulas, Athanasios

    2016-04-01

    Graphene synthesis on single crystal Rh(1 1 1) catalytic substrates is performed by Chemical Vapor Deposition (CVD) at 1000 °C and atmospheric pressure. Raman analysis shows full substrate coverage with few layer graphene. It is found that the cool-down rate strongly affects the graphene stacking order. When lowered, the percentage of AB (Bernal) -stacked regions increases, leading to an almost full AB stacking order. When increased, the percentage of AB-stacked graphene regions decreases to a point where almost a full non AB-stacked graphene is grown. For a slow cool-down rate, graphene with AB stacking order and good epitaxial orientation with the substrate is achieved. This is indicated mainly by Raman characterization and confirmed by Reflection high-energy electron diffraction (RHEED) imaging. Additional Scanning Tunneling Microscopy (STM) topography data confirm that the grown graphene is mainly an AB-stacked structure. The electronic structure of the graphene/Rh(1 1 1) system is examined by Angle resolved Photo-Emission Spectroscopy (ARPES), where σ and π bands of graphene, are observed. Graphene's ΓK direction is aligned with the ΓK direction of the substrate, indicating no significant contribution from rotated domains.

  8. hcp metal nanoclusters with hexagonal A-A bilayer stacking stabilized by enhanced covalent bonding

    SciTech Connect

    Li, Shunfang; Li, Haisheng; Xue, Xinlian; Jia, Yu; Guo, Zheng Xiao; Zhang, Zhenyu; Gong, Xingao

    2010-01-01

    First-principles total energy calculations within density functional theory have been performed to study the geometric and electronic structures of Ru{sub n} nanoclusters of varying size n (14{<=}n{<=}42). Strikingly, for the size range of n=14 to 38, the clusters always prefer a hexagonal bilayer structure with A-A stacking, rather than some of the more closely packed forms, or bilayer with A-B stacking. Such an intriguing 'molecular double-wheel' form is stabilized by substantially enhanced interlayer covalent bonding associated with strong s-d hybridization. Similar A-A stacking is also observed in the ground states or low-lying isomers of the clusters composed of other hcp elements, such as Os, Tc, Re, and Co. Note that these 'molecular double-wheels' show enhanced chemical activity toward H{sub 2}O splitting relative to their bulk counterpart, implying its potential applications as nanocatalysts.

  9. The energy components of stacked chromatin layers explain the morphology, dimensions and mechanical properties of metaphase chromosomes

    PubMed Central

    Daban, Joan-Ramon

    2014-01-01

    The measurement of the dimensions of metaphase chromosomes in different animal and plant karyotypes prepared in different laboratories indicates that chromatids have a great variety of sizes which are dependent on the amount of DNA that they contain. However, all chromatids are elongated cylinders that have relatively similar shape proportions (length to diameter ratio approx. 13). To explain this geometry, it is considered that chromosomes are self-organizing structures formed by stacked layers of planar chromatin and that the energy of nucleosome–nucleosome interactions between chromatin layers inside the chromatid is approximately 3.6 × 10−20 J per nucleosome, which is the value reported by other authors for internucleosome interactions in chromatin fibres. Nucleosomes in the periphery of the chromatid are in contact with the medium; they cannot fully interact with bulk chromatin within layers and this generates a surface potential that destabilizes the structure. Chromatids are smooth cylinders because this morphology has a lower surface energy than structures having irregular surfaces. The elongated shape of chromatids can be explained if the destabilizing surface potential is higher in the telomeres (approx. 0.16 mJ m−2) than in the lateral surface (approx. 0.012 mJ m−2). The results obtained by other authors in experimental studies of chromosome mechanics have been used to test the proposed supramolecular structure. It is demonstrated quantitatively that internucleosome interactions between chromatin layers can justify the work required for elastic chromosome stretching (approx. 0.1 pJ for large chromosomes). The high amount of work (up to approx. 10 pJ) required for large chromosome extensions is probably absorbed by chromatin layers through a mechanism involving nucleosome unwrapping. PMID:24402918

  10. Structure and stacking-fault energy in metals Al, Pd, Pt, Ir, and Rh

    NASA Astrophysics Data System (ADS)

    Cai, J.; Wang, F.; Lu, C.; Wang, Y. Y.

    2004-06-01

    The generalized stacking faults of Al, Pd, Pt, Ir, and Rh are investigated by a parametrized tight-binding potential. The stacking-fault energies (SFEs) are calculated to be in good agreement with experimental data, except for Al. More important, it is found that the SFE of Pt may be reduced by 14% by atom relaxation while the effect of atom relaxation on the SFEs of Al, Pd, Ir, and Rh are small. Thus, it is concluded that the effect of atom relaxation on SFE should be important, especially for an alloy system where radii difference between two constituting elements is large.

  11. 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.

  12. Energy dissipation in intercalated carbon nanotube forests with metal layers

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Vertically aligned carbon nanotube (CNT) forests were synthesized to study their quasi-static mechanical properties in a layered configuration with metallization. The top and bottom surfaces of CNT forests were metalized with Ag, Fe, and In using paste, sputtering, and thermal evaporation, respectiv...

  13. Lipid Layer-based Corrosion Monitoring on Metal Substrates

    DTIC Science & Technology

    2013-04-01

    explore lipid layers as a potential biosensor for corrosion. It is hypothesized that applying a lipid layer to metals will allow for corrosion monitoring...Corrosion monitoring, lipid layers, biosensor 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF ABSTRACT UU 18. NUMBER OF PAGES 14 19a...occurs as the material’s surface is oxidized in an electrochemical reaction, commonly in the presence of oxygen and water, which initially causes

  14. Chromium oxide as a metal diffusion barrier layer: An x-ray absorption fine structure spectroscopy study

    NASA Astrophysics Data System (ADS)

    Ahamad Mohiddon, Md.; Lakshun Naidu, K.; Ghanashyam Krishna, M.; Dalba, G.; Ahmed, S. I.; Rocca, F.

    2014-01-01

    The interaction at the interface between chromium and amorphous Silicon (a-Si) films in the presence of a sandwich layer of chromium oxide is investigated using X-ray absorption fine structure (XAFS) spectroscopy. The oxidized interface was created, in situ, prior to the deposition of a 400 nm tick a-Si layer over a 50 nm tick Cr layer. The entire stack of substrate/metallic Cr/Cr2O3/a-Si was then annealed at temperatures from 300 up to 700 °C. Analysis of the near edge and extended regions of each XAFS spectrum shows that only a small fraction of Cr is able to diffuse through the oxide layer up to 500 °C, while the remaining fraction is buried under the oxide layer in the form of metallic Cr. At higher temperatures, diffusion through the oxide layer is enhanced and the diffused metallic Cr reacts with a-Si to form CrSi2. At 700 °C, the film contains Cr2O3 and CrSi2 without evidence of unreacted metallic Cr. The activation energy and diffusion coefficient of Cr are quantitatively determined in the two temperature regions, one where the oxide acts as diffusion barrier and another where it is transparent to Cr diffusion. It is thus demonstrated that chromium oxide can be used as a diffusion barrier to prevent metal diffusion into a-Si.

  15. Two-dimensionally stacked heterometallic layers hosting a discrete chair dodecameric ring of water clusters: synthesis and structural study.

    PubMed

    Kenfack Tsobnang, Patrice; Wenger, Emmanuel; Biache, Coralie; Lambi Ngolui, John; Ponou, Siméon; Dahaoui, Slimane; Lecomte, Claude

    2014-10-01

    The stacked two-dimensional supramolecular compound catena-{Co(amp)3Cr(ox)3·6H2O} (amp = 2-picolylamine, ox = oxalate) has been synthesized from the bimolecular approach using hydrogen bonds. It is built from layers in which both Co(amp)(3+) (D) and Cr(ox)(3-) (A) ions are bonded in a repeating DADADA… pattern along the a and c axes by multiple hydrogen bonds. These layers host a well resolved R12 dodecameric discrete ring of water clusters built by six independent molecules located around the 2c centrosymmetric Wyckoff positions of the P21/n space group in which the compound crystallizes. These clusters are ranged along the [001] direction, occupy 733.5 Å(3) (22.0%) of the unit cell and have a chair conformation via 12 hydrogen bonds. The water molecules of the cluster are linked with stronger hydrogen bonds than those between the cluster and its host, which explains the single continuous step of the dehydration process of the compound.

  16. Charge Modeling for Metal Layer on Insulating Substrate

    NASA Astrophysics Data System (ADS)

    Okai, Nobuhiro; Yano, Tasuku; Sohda, Yasunari

    2011-06-01

    A charging model for magnification variation in the observation of a metal pattern on an insulating substrate using a scanning electron microscope is proposed. To calculate the time evolution of charging, we replace electron trajectory with current. Negative charging of the metal layer is observed and is caused by the current from the anode, which is set above the sample, to the metal layer. The origin of the current is tertiary electrons produced by backscattered electrons colliding with the anode. By controlling tertiary-electron trajectories through the application of bias voltage to the anode, the magnification variation can be reduced to almost zero.

  17. A further comparison of graphene and thin metal layers for plasmonics.

    PubMed

    He, Xiaoyong; Gao, Pingqi; Shi, Wangzhou

    2016-05-21

    Which one is much more suitable for plasmonic materials, graphene or metal? To address this problem well, the plasmonic properties of thin metal sheets at different thicknesses have been investigated and compared with a graphene layer. As demonstration examples, the propagation properties of insulator-metal-insulator and metamaterials (MMs) structures are also shown. The results manifest that the plasmonic properties of the graphene layer are comparable to that of thin metal sheets with the thickness of tens of nanometers. For the graphene MMs structure, by using the periodic stack structure in the active region, the resonant transmission strength significantly improves. At the optimum period number, 3-5 periods of graphene/SiO2, the graphene MMs structure manifests good frequency and amplitude tunable properties simultaneously, and the resonant strength is also strong with large values of the Q-factor. Therefore, graphene is a good tunable plasmonic material. The results are very helpful to develop novel graphene plasmonic devices, such as modulators, antenna and filters.

  18. A further comparison of graphene and thin metal layers for plasmonics

    NASA Astrophysics Data System (ADS)

    He, Xiaoyong; Gao, Pingqi; Shi, Wangzhou

    2016-05-01

    Which one is much more suitable for plasmonic materials, graphene or metal? To address this problem well, the plasmonic properties of thin metal sheets at different thicknesses have been investigated and compared with a graphene layer. As demonstration examples, the propagation properties of insulator-metal-insulator and metamaterials (MMs) structures are also shown. The results manifest that the plasmonic properties of the graphene layer are comparable to that of thin metal sheets with the thickness of tens of nanometers. For the graphene MMs structure, by using the periodic stack structure in the active region, the resonant transmission strength significantly improves. At the optimum period number, 3-5 periods of graphene/SiO2, the graphene MMs structure manifests good frequency and amplitude tunable properties simultaneously, and the resonant strength is also strong with large values of the Q-factor. Therefore, graphene is a good tunable plasmonic material. The results are very helpful to develop novel graphene plasmonic devices, such as modulators, antenna and filters.

  19. Preparation of novel layer-stack hexagonal CdO micro-rods by a pre-oxidation and subsequent evaporation process

    SciTech Connect

    Peng, Kun; Jiang, Pan; Zhu, Jiajun; Zhou, Lingping; Li, Deyi

    2014-12-15

    Graphical abstract: Layer-stack hexagonal cadmium oxide (CdO) micro-rods were prepared. - Highlights: • Novel hexagonal layer-stack structure CdO micro-rods were synthesized by a thermal evaporation method. • The pre-oxidation, vapor pressure and substrate nature play a key role on the formation of CdO rods. • The formation mechanism of CdO micro-rods was explained. - Abstract: Novel layer-stack hexagonal cadmium oxide (CdO) micro-rods were prepared by pre-oxidizing Cd granules and subsequent thermal oxidation under normal atmospheric pressure. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were performed to characterize the phase structure and microstructure. The pre-oxidation process, vapor pressure and substrate nature were the key factors for the formation of CdO micro-rods. The diameter of micro-rod and surface rough increased with increasing of thermal evaporation temperature, the length of micro-rod increased with the increasing of evaporation time. The formation of hexagonal layer-stack structure was explained by a vapor–solid mechanism.

  20. Method of adhesion between an oxide layer and a metal layer

    DOEpatents

    Jennison, Dwight R.; Bogicevic, Alexander; Kelber, Jeffry A.; Chambers, Scott A.

    2004-09-14

    A method of controlling the wetting characteristics and increasing the adhesion between a metal and an oxide layer. By introducing a negatively-charged species to the surface of an oxide layer, layer-by-layer growth of metal deposited onto the oxide surface is promoted, increasing the adhesion strength of the metal-oxide interface. The negatively-charged species can either be deposited onto the oxide surface or a compound can be deposited that dissociates on, or reacts with, the surface to form the negatively-charged species. The deposited metal adatoms can thereby bond laterally to the negatively-charged species as well as vertically to the oxide surface as well as react with the negatively charged species, be oxidized, and incorporated on or into the surface of the oxide.

  1. Chemistry of layered d-metal pnictide oxides and their potential as candidates for new superconductors

    PubMed Central

    Ozawa, Tadashi C; Kauzlarich, Susan M

    2008-01-01

    Layered d-metal pnictide oxides are a unique class of compounds which consist of characteristic d-metal pnictide layers and metal oxide layers. More than 100 of these layered compounds, including the recently discovered Fe-based superconducting pnictide oxides, can be classified into nine structure types. These structure types and the chemical and physical properties of the characteristic d-metal pnictide layers and metal oxide layers of the layered d-metal pnictide oxides are reviewed and discussed. Furthermore, possible approaches to design new superconductors based on these layered d-metal pnictide oxides are proposed. PMID:27877997

  2. 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 0layer 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.

  3. Design of Al2O3/SiO2 laminated stacks with multiple interface dipole layers to achieve large flatband voltage shifts of MOS capacitors

    NASA Astrophysics Data System (ADS)

    Kamata, Hironobu; Kita, Koji

    2017-03-01

    We studied the dipole induced flatband voltage (VFB) shifts of Si MOS capacitors with Al2O3/SiO2/Al2O3/SiO2/Si laminated stacks ((Al2O3/SiO2)n/Si, n = 2) designed for a large positive shift of VFB. The VFB shift caused by each dipole layer was determined from capacitance-voltage characteristics by excluding the effect of fixed charges. Due to the additivity of multiple dipole layers in the laminated stack, a large VFB shift (>1 V) was observed. In our experimental condition, the dipole layers at Al2O3-on-SiO2 interfaces were selectively formed, while those at SiO2-on-Al2O3 interfaces were effectively suppressed. The validity of such additivity of VFB shifts induced by selectively formed dipole layers was also experimentally demonstrated for n ≥ 3 laminated stacks. An introduction of multiple dipole layers is applicable for a threshold voltage tuning in a wider range than the tuning with a single dipole layer.

  4. Single-layer transition metal sulfide catalysts

    DOEpatents

    Thoma, Steven G.

    2011-05-31

    Transition Metal Sulfides (TMS), such as molybdenum disulfide (MoS.sub.2), are the petroleum industry's "workhorse" catalysts for upgrading heavy petroleum feedstocks and removing sulfur, nitrogen and other pollutants from fuels. We have developed an improved synthesis technique to produce SLTMS catalysts, such as molybdenum disulfide, with potentially greater activity and specificity than those currently available. Applications for this technology include heavy feed upgrading, in-situ catalysis, bio-fuel conversion and coal liquefaction.

  5. Metallorganic chemical vapor deposition and atomic layer deposition approaches for the growth of hafnium-based thin films from dialkylamide precursors for advanced CMOS gate stack applications

    NASA Astrophysics Data System (ADS)

    Consiglio, Steven P.

    To continue the rapid progress of the semiconductor industry as described by Moore's Law, the feasibility of new material systems for front end of the line (FEOL) process technologies needs to be investigated, since the currently employed polysilicon/SiO2-based transistor system is reaching its fundamental scaling limits. Revolutionary breakthroughs in complementary-metal-oxide-semiconductor (CMOS) technology were recently announced by Intel Corporation and International Business Machines Corporation (IBM), with both organizations revealing significant progress in the implementation of hafnium-based high-k dielectrics along with metal gates. This announcement was heralded by Gordon Moore as "...the biggest change in transistor technology since the introduction of polysilicon gate MOS transistors in the late 1960s." Accordingly, the study described herein focuses on the growth of Hf-based dielectrics and Hf-based metal gates using chemical vapor-based deposition methods, specifically metallorganic chemical vapor deposition (MOCVD) and atomic layer deposition (ALD). A family of Hf source complexes that has received much attention recently due to their desirable properties for implementation in wafer scale manufacturing is the Hf dialkylamide precursors. These precursors are room temperature liquids and possess sufficient volatility and desirable decomposition characteristics for both MOCVD and ALD processing. Another benefit of using these sources is the existence of chemically compatible Si dialkylamide sources as co-precursors for use in Hf silicate growth. The first part of this study investigates properties of MOCVD-deposited HfO2 and HfSixOy using dimethylamido Hf and Si precursor sources using a customized MOCVD reactor. The second part of this study involves a study of wet and dry surface pre-treatments for ALD growth of HfO2 using tetrakis(ethylmethylamido)hafnium in a wafer scale manufacturing environment. The third part of this study is an investigation of

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

    DOEpatents

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

    2002-08-27

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

  7. Thermodynamics of elastic strength of the metal surface layer

    NASA Astrophysics Data System (ADS)

    Andreev, Yu. Ya.; Kiselev, D. A.

    2013-07-01

    This paper presents a physicochemical model that establishes a connection between the elastic strength of the surface layer (SL) of metal and its surface Gibbs energy. The elastic limit of SL along the low-index face of the metal single crystal under stress during the transition from elastic to plastic deformation was calculated. Calculation shows that the elastic limit of metal SL with fcc and bcc structures is approximately three orders of magnitude higher than the yield strength of these metals in bulk and close to nanohardness of the metals, in particular; for Cu(111) и Al(111), it is 5.3 and 2.8 GPa, respectively. In the light of the proposed model, the effect of lowering the elastic strength of metal SL due to adsorption of surfactant is formulated.

  8. Indium gallium zinc oxide layer used to decrease optical reflection loss at intermediate adhesive region for fabricating mechanical stacked multijunction solar cells

    NASA Astrophysics Data System (ADS)

    Sameshima, Toshiyuki; Nimura, Takeshi; Sugawara, Takashi; Ogawa, Yoshihiro; Yoshidomi, Shinya; Kimura, Shunsuke; Hasumi, Masahiko

    2017-01-01

    Reduction of optical reflection loss is discussed in three mechanical stacked samples: top crystalline silicon and bottom crystalline germanium substrates, top crystalline GaAs and bottom crystalline silicon substrates, and top crystalline GaP and bottom crystalline silicon substrates using an epoxy-type adhesive with a reflective index of 1.47. Transparent conductive Indium gallium zinc oxide (IGZO) layers with a refractive index of 1.85 were used as antireflection layers. IGZO layers were formed on the bottom surface of the top substrate and the top surface of the bottom substrate of the three stacked samples with thicknesses of 188, 130, and 102 nm. The insertion of IGZO layers decreased the optical reflectivity of the stacked samples. The IGZO layers provided high effective optical absorbency of bottom substrates of 0.925, 0.943, and 0.931, respectively, for light wavelength regions for light in which the top substrates were transparent and the bottom substrates were opaque.

  9. Methods of Fabricating a Layer of Metallic Glass-Based Material Using Immersion and Pouring Techniques

    NASA Technical Reports Server (NTRS)

    Hofmann, Douglas (Inventor)

    2015-01-01

    Systems and methods in accordance with embodiments of the invention implement layers of metallic glass-based materials. In one embodiment, a method of fabricating a layer of metallic glass includes: applying a coating layer of liquid phase metallic glass to an object, the coating layer being applied in a sufficient quantity such that the surface tension of the liquid phase metallic glass causes the coating layer to have a smooth surface; where the metallic glass has a critical cooling rate less than 1000 K/s; and cooling the coating layer of liquid phase metallic glass to form a layer of solid phase metallic glass.

  10. Divergent layer topologies in divalent metal aliphatic dicarboxylate coordination polymers containing 3-pyridylmethylnicotinamide

    NASA Astrophysics Data System (ADS)

    White, Charmaine L.; Torres Salgado, Maria D.; Mizzi, Jessica E.; LaDuca, Robert L.

    2015-12-01

    Hydrothermal reaction of the requisite metal salt, an aliphatic dicarboxylic acid, and the hydrogen-bonding capable dipyridylamide ligand 3-pyridylmethylnicotinamide (3-pmna) resulted in four coordination polymers whose connectedness and layer topology depend on the metal coordination environment and dicarboxylate binding mode. These new crystalline phases were characterized by single crystal X-ray diffraction. [Cu(ox)(3-pmna)]n (1, ox = oxalate) manifests stacked 3-connected (6,3) herringbone layer motifs. {[Cd(mal)(3-pmna)(H2O)]·3H2O}n (2, mal = malonate) shows a 4-connected (4,4) grid topology with entrained water molecule trimeric chains in the interlamellar regions. {[Cd2(suc)2(3-pmna)(H2O)2]·3H2O}n (3, suc = succinate) possesses {Cd2O2} dimer-based [Cd(suc)]n layers pillared by 3-pmna ligands into a 5-connected sandwich motif with 4862 topology. {[Cd(glu)(3-pmna)(H2O)]·3H2O}n (4, glu = glutarate) manifests a rippled (4,4) grid topology. Luminescent behavior in the cadmium complexes is ascribed to intra-ligand molecular orbital transitions. Thermal decomposition behavior is also discussed herein.

  11. Contacts and transport characteristics of few-layer transition metal dichalcogenides

    NASA Astrophysics Data System (ADS)

    Wang, Junjie; Li, Jing; Shevrin, Jacob; Nguyen, An; Mallouk, Tom; Zhu, J.; Rhodes, Daniel; Balicas, Luis; Watanabe, K.; Taniguchi, T.

    2014-03-01

    Two-dimensional layered transition metal dichalcogenides (TMDs) are potentially useful for electronic and optoelectronic applications. However, the lack of reliable methods to make ohmic contacts has been a major challenge. This work addresses two aspects of this challenge, i.e. interface cleanness and conductivity of the material in the contact area. Using gentle Ar ion milling immediately before the deposition of metal electrodes, we can completely remove polymer residue from prior lithography without significantly damaging the few-layer TMD sheet. Gate stacks made of Au and HfO2 films can inject carriers up to 3 ×1013 cm-2. We make van der Pauw devices of few-layer (< 5 L) TMD (MoS2, WS2, WSe2) sheets using Ti/Au contacts with area < 2 (um)2 and observe contact resistance less than 10 k Ω at high carrier densities, where the sheet conductance is well above 2e2/h. We eliminate hysteresis in the transfer curve of TMD devices by pulsing the gate voltage. Ambipolar conduction is observed in WSe2 devices, with an on/off ratio exceeding 106 for both electrons and holes. WSe2 devices supported on h-BN show field-effect (hole) mobility > 100 cm2/(Vs) at 300K. We discuss the effects of the various approaches taken above.

  12. The Thermomagnetic Instability in Superconducting Films with Adjacent Metal Layer

    NASA Astrophysics Data System (ADS)

    Vestgården, J. I.; Galperin, Y. M.; Johansen, T. H.

    2013-12-01

    Dendritic flux avalanches is a frequently encountered consequence of the thermomagnetic instability in type-II superconducting films. The avalanches, which are potentially harmful for superconductor-based devices, can be suppressed by an adjacent normal metal layer, even when the two layers are not in thermal contact. The suppression of the avalanches in this case is due to so-called magnetic braking, caused by eddy currents generated in the metal layer by propagating magnetic flux. We develop a theory of magnetic braking by analyzing coupled electrodynamics and heat flow in a superconductor-normal metal bilayer. The equations are solved by linearization and by numerical simulation of the avalanche dynamics. We find that in an uncoated superconductor, even a uniform thermomagnetic instability can develop into a dendritic flux avalanche. The mechanism is that a small non-uniformity caused by the electromagnetic non-locality induces a flux-flow hot spot at a random position. The hot spot quickly develops into a finger, which at high speeds penetrates into the superconductor, forming a branching structure. Magnetic braking slows the avalanches, and if the normal metal conductivity is sufficiently high, it can suppress the formation of the dendritic structure. During avalanches, the braking by the normal metal layer prevents the temperature from exceeding the transition temperature of the superconductor. Analytical criteria for the instability threshold are developed using the linear stability analysis. The criteria are found to match quantitatively the instability onsets obtained in simulations.

  13. Gaussian beam incident on the one-dimensional diffraction gratings with the high-K metal gate stack structures.

    PubMed

    Kuo, Hung-Fei; Frederick

    2014-04-01

    Optical scatterometry has attracted extensive interest in extracting the geometric shape information of nanolithography patterns because of the trend of shrinking device size and complicated stack structure. RCWA is the numerical algorithm implemented in the current scatterometry tool to calculate the diffraction efficiency. However, the known weakness for the RCWA method is the analysis of metallic gratings illuminated by the TM wave. This research applies the FDTD method using the Gaussian beam excitation source to analyze the diffraction efficiency of HKMG gratings for the use in the optical scatterometry and verifies the numerical diffraction efficiency discrepancy between the Gaussian beam and plane wave excitation methods. The numerical study is carried out with the line/space nanolithography patterns on the HKMG process stacks at 45 nm node technology. The nanolithography patterns are modeled as 1-D surface relief gratings. The 0th order diffraction efficiency is analyzed as a function of CDs, SWAs, incident angles and pitches of the gratings. The study presents the impact of the polarizations of the incident waves on the diffraction efficiency. In addition, this research investigates the phase of the 0th diffraction order as a function of the SWAs and illustrates the corresponding SWA parameter effect on the phase distribution. This research suggests the minimum beam radius to converge the numerical diffraction efficiency using Gaussian beam excitation to it using the plan wave.

  14. Monolayer and/or few-layer graphene on metal or metal-coated substrates

    DOEpatents

    Sutter, Peter Werner; Sutter, Eli Anguelova

    2015-04-14

    Disclosed is monolayer and/or few-layer graphene on metal or metal-coated substrates. Embodiments include graphene mirrors. In an example, a mirror includes a substrate that has a surface exhibiting a curvature operable to focus an incident beam onto a focal plane. A graphene layer conformally adheres to the substrate, and is operable to protect the substrate surface from degradation due to the incident beam and an ambient environment.

  15. PASSIVATION LAYER STABILITY OF A METALLIC ALLOY WASTE FORM

    SciTech Connect

    Williamson, M.; Mickalonis, J.; Fisher, D.; Sindelar, R.

    2010-08-16

    Alloy waste form development under the Waste Forms Campaign of the DOE-NE Fuel Cycle Research & Development program includes the process development and characterization of an alloy system to incorporate metal species from the waste streams generated during nuclear fuel recycling. This report describes the tests and results from the FY10 activities to further investigate an Fe-based waste form that uses 300-series stainless steel as the base alloy in an induction furnace melt process to incorporate the waste species from a closed nuclear fuel recycle separations scheme. This report is focused on the initial activities to investigate the formation of oxyhydroxide layer(s) that would be expected to develop on the Fe-based waste form as it corrodes under aqueous repository conditions. Corrosion tests were used to evaluate the stability of the layer(s) that can act as a passivation layer against further corrosion and would affect waste form durability in a disposal environment.

  16. Alloyed 2D Metal-Semiconductor Atomic Layer Junctions.

    PubMed

    Kim, Ah Ra; Kim, Yonghun; Nam, Jaewook; Chung, Hee-Suk; Kim, Dong Jae; Kwon, Jung-Dae; Park, Sang Won; Park, Jucheol; Choi, Sun Young; Lee, Byoung Hun; Park, Ji Hyeon; Lee, Kyu Hwan; Kim, Dong-Ho; Choi, Sung Mook; Ajayan, Pulickel M; Hahm, Myung Gwan; Cho, Byungjin

    2016-03-09

    Heterostructures of compositionally and electronically variant two-dimensional (2D) atomic layers are viable building blocks for ultrathin optoelectronic devices. We show that the composition of interfacial transition region between semiconducting WSe2 atomic layer channels and metallic NbSe2 contact layers can be engineered through interfacial doping with Nb atoms. WxNb1-xSe2 interfacial regions considerably lower the potential barrier height of the junction, significantly improving the performance of the corresponding WSe2-based field-effect transistor devices. The creation of such alloyed 2D junctions between dissimilar atomic layer domains could be the most important factor in controlling the electronic properties of 2D junctions and the design and fabrication of 2D atomic layer devices.

  17. Advanced optical interference filters based on metal and dielectric layers.

    PubMed

    Begou, Thomas; Lemarchand, Fabien; Lumeau, Julien

    2016-09-05

    In this paper, we investigate the design and the fabrication of an advanced optical interference filter based on metal and dielectric layers. This filter respects the specifications of the 2016 OIC manufacturing problem contest. We study and present all the challenges and solutions that allowed achieving a low deviation between the fabricated prototype and the target.

  18. Abrupt Depletion Layer Approximation for the Metal Insulator Semiconductor Diode.

    ERIC Educational Resources Information Center

    Jones, Kenneth

    1979-01-01

    Determines the excess surface change carrier density, surface potential, and relative capacitance of a metal insulator semiconductor diode as a function of the gate voltage, using the precise questions and the equations derived with the abrupt depletion layer approximation. (Author/GA)

  19. Trap-limited photovoltage in ultrathin metal oxide layers

    NASA Astrophysics Data System (ADS)

    Dittrich, Th.; Duzhko, V.; Koch, F.; Kytin, V.; Rappich, J.

    2002-04-01

    Photovoltage signals were observed at ultrathin metal oxide (TiO2,Cu2O, ZnO)/ metal structures by transient and spectral photovoltage (PV) techniques. The sign, the spectral behavior and the time-dependent relaxation of the PV are determined by the nature of the traps in the metal oxide layers. At lower temperatures, the relaxation of the PV signal in TiO2 layers is controlled by recombination due to the overlap of the wave functions of the spatially separated electrons and holes. At higher temperatures, thermal emission accelerates the recombination process. The Bohr radius of trapped holes, the tail of the exponential approximation of electronic states distribution above the valence band, the density of states at the valence band edge were obtained for TiO2 layers by using the proposed model of trap limited PV. The concept of trap limited PV gives a general tool for the investigation of excess carrier separation in ultrathin metal oxide or semiconductor layers with trap states.

  20. Perfect polar stacking of parallel beloamphiphile layers. Synthesis, structure and solid-state optical properties of the unsymmetrical acetophenone azine DCA.

    PubMed

    Glaser, Rainer; Knotts, Nathan; Yu, Ping; Li, Linghui; Chandrasekhar, Meera; Martin, Christopher; Barnes, Charles L

    2006-06-21

    Extraordinary high degrees of polar order can be achieved by a rational design that involves the polar stacking of parallel beloamphiphile monolayers (PBAM). This strategy is exemplified by the acetophenone azines MCA (4-methoxy-4'-chloroacetophenone azine) and DCA (4-decoxy-4'-chloroacetophenone azine). The beloamphiphile design aims to achieve strong lateral interactions by way of arene-arene, azine-azine, arene-azine and halogen-bonding interactions. Dipole-induced interactions and halogen bonding dominate interlayer interactions and halogen bonding is shown to effect the layer stacking. Crystals of DCA contain PBAMs with perfect polar order and perfect polar layer stacking, while crystals of MCA features perfect polar order only in one of two layers and layer stacking is polar but not entirely perfect. We report the synthesis of the beloamphiphile DCA, its crystal structure, and we present a comparative discussion of the structures and intermolecular interactions of MCA and DCA. Absorbance and photoluminescence measurements have been carried out for solutions of DCA and for DCA crystals. DCA exhibits a broad emission centered at 2.5 eV when excited with UV radiation. The nonlinear optical response was studied by measuring second harmonic generation (SHG). Strong SHG signals have been observed due to the polar alignment and the DCA crystal's NLO response is 34 times larger than that of urea. Optimization of the beloamphiphile and systematic SAR studies of the polar organic crystals, which are now possible for the very first time, will further improve the performance of this new class of functional organic materials. The materials are organic semiconductors and show promise as blue emitters, as nonlinear optical materials and as OLED materials.

  1. Optimisation on the two-layer stack gamma detectors of CsI(Tl) coupled with a pin photodiode for non-destructive testing.

    PubMed

    Bai, Jin Hyoung; Whang, Joo Ho

    2011-07-01

    This paper proposed the two-layer stack scintillator-coupled photodiode detector to improve the measurement accuracy of the gamma-ray scanning. Both MCNPX and DETECT97 code were used to design the detector. The two manufactured two-layer stack gamma detectors were used to measure the density profile of the distillation column of the radiographic non-intrusive process diagnostic area. To compare the measurement accuracy of the density profile through the non-destructive transmission test, the relative error of the four fluids used for the process diagnostics was analysed. To summarise the measurement results with regard to the relative error of the NaI(Tl) detector and the manufactured detector by material as well as the total relative error, the total relative error of the NaI(Tl) detector was about 15.7 %, whereas that of the two-layer stack CsI(Tl) with photodiode detectors were about 5 %. This paper confirmed that the measurement accuracy of the detector proposed was improved by about three times as compared with the NaI(Tl) detector mostly used for non-destructive testing.

  2. Meteoric metal layers in the atmosphere of Mars

    NASA Astrophysics Data System (ADS)

    Plane, John; Whalley, Charlotte

    Radio occultation measurements from several spacecraft (e.g., Mars Express, Mars Global Sur-veyor) have revealed the presence of a "third" ion layer in the Martian atmosphere, which occurs sporadically around 90 km. Because this is the aerobraking region of the atmosphere, and the layers resemble sporadic E layers observed in the terrestrial atmosphere, it has been proposed that these layers consist of metallic ions (principally Fe+ and Mg+ ). A major problem with this hypothesis is that we have shown recently that metallic ions re-combine rapidly in a CO2 -rich atmosphere, both because of the efficiency of CO2 as the "third body" and because of the very low temperatures (about 140 K). In fact, both Fe+ and Mg+ form CO2 cluster ions about 200 times faster than current Mars models predict. These cluster ions should rapidly be destroyed by dissociative recombination with electrons, so that sporadic layers containing metallic ions would have lifetimes of only minutes. We will present a new laboratory study of all the reactions that appear to be required to solve this problem. Most importantly, we will show that the reactions of molecular magnesium ions (Mg+ .CO2 , MgO2 + and MgO+ ) with atomic O are about 20 times faster than expected. The laboratory will then be used to construct a new model of the Martian upper atmosphere, which demonstrates that the sporadic third layers must largely be composed of Mg+ and not Fe+ . These layers should then have lifetimes of more than 10 hours, in accord with observations from Mars Express made on successive orbits.

  3. Optically sensitive devices based on Pt nano particles fabricated by atomic layer deposition and embedded in a dielectric stack

    NASA Astrophysics Data System (ADS)

    Mikhelashvili, V.; Padmanabhan, R.; Meyler, B.; Yofis, S.; Atiya, G.; Cohen-Hyams, Z.; Weindling, S.; Ankonina, G.; Salzman, J.; Kaplan, W. D.; Eisenstein, G.

    2015-10-01

    We report a series of metal insulator semiconductor devices with embedded Pt nano particles (NPs) fabricated using a low temperature atomic layer deposition process. Optically sensitive nonvolatile memory cells as well as optical sensors: (i) varactors, whose capacitance-voltage characteristics, nonlinearity, and peak capacitance are strongly dependent on illumination intensity; (ii) highly linear photo detectors whose responsivity is enhanced due to the Pt NPs. Both single devices and back to back pairs of diodes were used. The different configurations enable a variety of functionalities with many potential applications in biomedical sensing, environmental surveying, simple imagers for consumer electronics and military uses. The simplicity and planar configuration of the proposed devices makes them suitable for standard CMOS fabrication technology.

  4. Optically sensitive devices based on Pt nano particles fabricated by atomic layer deposition and embedded in a dielectric stack

    SciTech Connect

    Mikhelashvili, V.; Padmanabhan, R.; Eisenstein, G.; Meyler, B.; Yofis, S.; Weindling, S.; Salzman, J.; Atiya, G.; Cohen-Hyams, Z.; Kaplan, W. D.; Ankonina, G.

    2015-10-07

    We report a series of metal insulator semiconductor devices with embedded Pt nano particles (NPs) fabricated using a low temperature atomic layer deposition process. Optically sensitive nonvolatile memory cells as well as optical sensors: (i) varactors, whose capacitance-voltage characteristics, nonlinearity, and peak capacitance are strongly dependent on illumination intensity; (ii) highly linear photo detectors whose responsivity is enhanced due to the Pt NPs. Both single devices and back to back pairs of diodes were used. The different configurations enable a variety of functionalities with many potential applications in biomedical sensing, environmental surveying, simple imagers for consumer electronics and military uses. The simplicity and planar configuration of the proposed devices makes them suitable for standard CMOS fabrication technology.

  5. Solution processed metal oxide thin film hole transport layers for high performance organic solar cells

    DOEpatents

    Steirer, K. Xerxes; Berry, Joseph J.; Chesin, Jordan P.; Lloyd, Matthew T.; Widjonarko, Nicodemus Edwin; Miedaner, Alexander; Curtis, Calvin J.; Ginley, David S.; Olson, Dana C.

    2017-01-10

    A method for the application of solution processed metal oxide hole transport layers in organic photovoltaic devices and related organic electronics devices is disclosed. The metal oxide may be derived from a metal-organic precursor enabling solution processing of an amorphous, p-type metal oxide. An organic photovoltaic device having solution processed, metal oxide, thin-film hole transport layer.

  6. Effect of metallation, substituents and inter/intra-molecular polarization on electronic couplings for hole transport in stacked porphyrin dyads.

    PubMed

    Hernández-Fernández, F; Pavanello, M; Visscher, L

    2016-08-03

    We carried out a systematic study of the hole transport properties for a series of symmetrically stacked porphyrin dimers. In the first part of this study, we evaluated the sensitivity of electronic couplings to orbital relaxation due to molecular ionization and intermolecular interactions for a series of halogenated porphyrins. The effect of polarization was estimated by comparing electronic couplings from fragment orbital density functional theory (FODFT) and frozen density embedding electron transfer (FDE-CT). For the dimers considered, the effect of polarization was estimated to be less than 20%, in line with previous studies on different molecular dimers. Thus, we decided to employ a computationally cheaper FODFT method to continue our study of the effect of metals and substituents on the electronic couplings for hole transfer. We find that, compared to the non-metallated porphyrins, Ni, Fe and Pt significantly reduce the coupling, while Zn, Ti, Cd and Pd increase it. The effect of substituents was studied on a series of meso-substituted porphyrins (meso-tetrapyridineporphyrin, meso-tetraphenylporphyrin and derivatives) for which we could relate a reduction of the coupling to steric effects that reduce the overlap between the frontier orbitals of the monomers.

  7. Self assembled multi-layer nanocomposite of graphene and metal oxide materials

    DOEpatents

    Liu, Jun; Aksay, Ilhan A; Choi, Daiwon; Kou, Rong; Nie, Zimin; Wang, Donghai; Yang, Zhenguo

    2015-04-28

    Nanocomposite materials having at least two layers, each layer consisting of one metal oxide bonded to at least one graphene layer were developed. The nanocomposite materials will typically have many alternating layers of metal oxides and graphene layers, bonded in a sandwich type construction and will be incorporated into an electrochemical or energy storage device.

  8. Self assembled multi-layer nanocomposite of graphene and metal oxide materials

    DOEpatents

    Liu, Jun; Choi, Daiwon; Kou, Rong; Nie, Zimin; Wang, Donghai; Yang, Zhenguo

    2014-09-16

    Nanocomposite materials having at least two layers, each layer consisting of one metal oxide bonded to at least one graphene layer were developed. The nanocomposite materials will typically have many alternating layers of metal oxides and graphene layers, bonded in a sandwich type construction and will be incorporated into an electrochemical or energy storage device.

  9. Self assembled multi-layer nanocomposite of graphene and metal oxide materials

    DOEpatents

    Liu, Jun; Aksay, Ilhan A; Choi, Daiwon; Kou, Rong; Nie, Zimin; Wang, Donghai; Yang, Zhenguo

    2013-10-22

    Nanocomposite materials having at least two layers, each layer consisting of one metal oxide bonded to at least one graphene layer were developed. The nanocomposite materials will typically have many alternating layers of metal oxides and graphene layers, bonded in a sandwich type construction and will be incorporated into an electrochemical or energy storage device.

  10. Anisotropy in layered half-metallic Heusler alloy superlattices

    SciTech Connect

    Azadani, Javad G.; Munira, Kamaram; Sivakumar, Chockalingam; Butler, William H.; Romero, Jonathon; Ma, Jianhua; Ghosh, Avik W.

    2016-01-28

    We show that when two Heusler alloys are layered in the [001], [110], or [111] directions for various thicknesses to form a superlattice, the Slater-Pauling rule may still be satisfied and the resulting superlattice is often half-metallic with gaps comparable to or larger than those of its constituents. In addition, uniaxial magnetocrystalline anisotropy is induced because of the differences in the electronic structure of the two Heuslers in the superlattice. Various full-full, full-half, and half-half Heusler superlattices are studied, and potential half-metallic superlattices with perpendicular magnetocrystalline anisotropy are identified.

  11. Anisotropy in layered half-metallic Heusler alloy superlattices

    NASA Astrophysics Data System (ADS)

    Azadani, Javad G.; Munira, Kamaram; Romero, Jonathon; Ma, Jianhua; Sivakumar, Chockalingam; Ghosh, Avik W.; Butler, William H.

    2016-01-01

    We show that when two Heusler alloys are layered in the [001], [110], or [111] directions for various thicknesses to form a superlattice, the Slater-Pauling rule may still be satisfied and the resulting superlattice is often half-metallic with gaps comparable to or larger than those of its constituents. In addition, uniaxial magnetocrystalline anisotropy is induced because of the differences in the electronic structure of the two Heuslers in the superlattice. Various full-full, full-half, and half-half Heusler superlattices are studied, and potential half-metallic superlattices with perpendicular magnetocrystalline anisotropy are identified.

  12. Layered Post-Transition-Metal Dichalcogenides (X-M-M-X) and Their Properties.

    PubMed

    Luxa, Jan; Wang, Yong; Sofer, Zdenek; Pumera, Martin

    2016-12-23

    A(III) B(VI) chalcogenides are an interesting group of layered semiconductors with several attractive properties, such as tunable band gaps and the formation of solid solutions. Unlike the typically sandwiched structure of transition-metal dichalcogenides, A(III) B(VI) layered chalcogenides with hexagonal symmetry are stacked through the X-M-M-X motif, in which M is gallium and indium, and X is sulfur, selenium, and tellurium. In view of the inadequate study of the electrochemical properties and great interest in layered materials towards energy-related research, herein the inherent electrochemistry of GaS, GaSe, GaTe, and InSe has been studied, as well as the exploration of their potential as hydrogen evolution reaction (HER) electrocatalysts. All four materials show redox peaks during cyclic voltammetry measurements. Furthermore, insights into catalysis of the HER are provided; these indicate the conductivity and number of active sites of the materials. All of these findings have important implications on their possible applications.

  13. Hydrogen permeation resistant layers for liquid metal reactors

    SciTech Connect

    McGuire, J.C.

    1980-03-01

    Reviewing the literature in the tritium diffusion field one can readily see a wide divergence in results for both the response of permeation rate to pressure, and the effect of oxide layers on total permeation rates. The basic mechanism of protective oxide layers is discussed. Two coatings which are less hydrogen permeable than the best naturally occurring oxide are described. The work described is part of an HEDL-ANL cooperative research program on Tritium Permeation in Liquid Metal Cooled Reactors. This includes permeation work on hydrogen, deuterium, and tritium with the hydrogen-deuterium research leading to the developments presented.

  14. Metal-Organic Frameworks for Thin-Layer Chromatographic Applications.

    PubMed

    Schenk, Claudia; Kutzscher, Christel; Drache, Franziska; Helten, Stella; Senkovska, Irena; Kaskel, Stefan

    2017-01-25

    Preparation of thin-layer chromatographic (TLC) plates based on metal-organic frameworks (MOFs) as porous stationary phases is described. DUT-67 (DUT = Dresden University of Technology), a zirconium based MOF, was used in combination with a fluorescent indicator as stationary phase for analyzing a small selection of a wide spectrum of relevant analytes. The successful separation of benzaldehyde from trans-cinnamaldehyde and 4-aminophenol from 2-aminotoluene is reported as a model system using optimized eluent mixtures containing acetic acid.

  15. Al2O3/SiON stack layers for effective surface passivation and anti-reflection of high efficiency n-type c-Si solar cells

    NASA Astrophysics Data System (ADS)

    Thi Thanh Nguyen, Huong; Balaji, Nagarajan; Park, Cheolmin; Triet, Nguyen Minh; Le, Anh Huy Tuan; Lee, Seunghwan; Jeon, Minhan; Oh, Donhyun; Dao, Vinh Ai; Yi, Junsin

    2017-02-01

    Excellent surface passivation and anti-reflection properties of double-stack layers is a prerequisite for high efficiency of n-type c-Si solar cells. The high positive fixed charge (Q f) density of N-rich hydrogenated amorphous silicon nitride (a-SiNx:H) films plays a poor role in boron emitter passivation. The more the refractive index ( n ) of a-SiNx:H is decreased, the more the positive Q f of a-SiNx:H is increased. Hydrogenated amorphous silicon oxynitride (SiON) films possess the properties of amorphous silicon oxide (a-SiOx) and a-SiNx:H with variable n and less positive Q f compared with a-SiNx:H. In this study, we investigated the passivation and anti-reflection properties of Al2O3/SiON stacks. Initially, a SiON layer was deposited by plasma enhanced chemical vapor deposition with variable n and its chemical composition was analyzed by Fourier transform infrared spectroscopy. Then, the SiON layer was deposited as a capping layer on a 10 nm thick Al2O3 layer, and the electrical and optical properties were analyzed. The SiON capping layer with n = 1.47 and a thickness of 70 nm resulted in an interface trap density of 4.74 = 1010 cm-2 eV-1 and Q f of -2.59 = 1012 cm-2 with a substantial improvement in lifetime of 1.52 ms after industrial firing. The incorporation of an Al2O3/SiON stack on the front side of the n-type solar cells results in an energy conversion efficiency of 18.34% compared to the one with Al2O3/a-SiNx:H showing 17.55% efficiency. The short circuit current density and open circuit voltage increase by up to 0.83 mA cm-2 and 12 mV, respectively, compared to the Al2O3/a-SiNx:H stack on the front side of the n-type solar cells due to the good anti-reflection and front side surface passivation.

  16. Exceeding 4% external quantum efficiency in ultraviolet organic light-emitting diode using PEDOT:PSS/MoOx double-stacked hole injection layer

    NASA Astrophysics Data System (ADS)

    Zhang, Xiaowen; You, Fengjiao; Liu, Shiqi; Mo, Bingjie; Zhang, Zheling; Xiong, Jian; Cai, Ping; Xue, Xiaogang; Zhang, Jian; Wei, Bin

    2017-01-01

    An effective and simple method has been explored to construct an efficient ultraviolet organic light-emitting diode (OLED) by incorporating poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)/MoOx double-stacked hole injection layer (HIL) and slightly retarding electron injection for achieving extremely balanced charge carriers. The device produces 4.6% external quantum efficiency with an attractive ultraviolet emission peak of 377 nm and full width at half maximum of 35 nm. Ultraviolet photoelectron spectroscopy and impedance spectroscopy analysis determine the substantially enhanced hole injection capacity of PEDOT:PSS/MoOx double-stacked HIL, which accordingly contributes to optimizing carrier balance. The results pave a way to advancing OLED in potential application towards short wavelength emission.

  17. Microstructure and Mechanical Properties of Nanostructured 1050/6061 Aluminum Alloy Fabricated by Four-Layer Stack Accumulative Roll-Bonding.

    PubMed

    Lee, Seong-Hee; Lee, Seong Ro

    2015-07-01

    An ultrafine grained AA1050/AA6061 Al alloy sheet was successfully fabricated by four-layer stack ARB process. The ARB of AA1050 and AA6061 alloy sheets was performed up to 3 cycles without a lubricant at ambient temperature. The sample fabricated by the ARB was a multi-layer aluminum alloy sheet in which AA1050 and AA6061 layers are alternately stacked. The layer thickness of the each alloy became thinner and elongated to the rolling direction with increasing the number of ARB cycles. The tensile strength increased with the ARB, it reached about 347 MPa which is almost 2.4 times that of the starting material. The grain size decreased with increasing of the number of ARB cycles, became about 190 nm in thickness after 3 cycles. The variation of mechanical properties with the ARB was similar to those of the other ARB processed materials. However, the texture development was different from those of the conventional ARB processed materials.

  18. Layer-selective half-metallicity in bilayer graphene nanoribbons

    NASA Astrophysics Data System (ADS)

    Jeon, Gi Wan; Lee, Kyu Won; Lee, Cheol Eui

    2015-05-01

    Half-metallicity recently predicted in the zigzag-edge graphene nanoribbons (ZGNRs) and the hydrogenated carbon nanotubes (CNTs) enables fully spin-polarized electric currents, providing a basis for carbon-based spintronics. In both carbon systems, the half-metallicity arises from the edge-localized electron states under an electric field, lowering the critical electric field Dc for the half-metallicity being an issue in recent works on ZGNRs. A properly chosen direction of the electric field alone has been predicted to significantly reduce Dc in the hydrogenated CNTs, which in this work turned out to be the case in narrow bilayer ZGNRs (biZGNRs). Here, our simple model based on the electrostatic potential difference between the edges predicts that for wide biZGNRs of width greater than ~2.0 nm (10 zigzag carbon chains), only one layer of the biZGNRs becomes half-metallic leaving the other layer insulating as confirmed by our density functional theory (DFT) calculations. The electric field-induced switching of the spin-polarized current path is believed to open a new route to graphene-based spintronics applications.

  19. Tailoring capping layers to reduce stress gradients in copper metallization

    NASA Astrophysics Data System (ADS)

    Murray, Conal E.; Priyadarshini, Deepika; Nguyen, Son; Ryan, E. Todd

    2016-12-01

    Capping layers for back-end-of-line metallization, which primarily serve as diffusion barriers to prevent contamination, also play a role in mitigating electromigration in the underlying conductive material. Stress gradients can be generated in copper metallization due to the conditions associated with the capping process. To study the effects of deposition and subsequent annealing on the mechanical response of copper films with various capping schemes, we employed a combination of conventional and glancing incidence X-ray diffraction techniques to quantify the stress gradient maxima. The Cu films with dielectric caps, such as silicon nitride, can exhibit large gradients that decrease slightly with thermal cycling. However, Co and TaN-based metallic capping layers create significantly lower stress gradient maxima in copper features both before and after annealing. The different evolution of stress gradients in Cu films with dielectric and metallic caps due to thermal cycling reveals the interaction of dislocation-mediated, plastic deformation with the cap/Cu interface.

  20. Self-Limiting Layer Synthesis of Transition Metal Dichalcogenides

    NASA Astrophysics Data System (ADS)

    Kim, Youngjun; Song, Jeong-Gyu; Park, Yong Ju; Ryu, Gyeong Hee; Lee, Su Jeong; Kim, Jin Sung; Jeon, Pyo Jin; Lee, Chang Wan; Woo, Whang Je; Choi, Taejin; Jung, Hanearl; Lee, Han-Bo-Ram; Myoung, Jae-Min; Im, Seongil; Lee, Zonghoon; Ahn, Jong-Hyun; Park, Jusang; Kim, Hyungjun

    2016-01-01

    This work reports the self-limiting synthesis of an atomically thin, two dimensional transition metal dichalcogenides (2D TMDCs) in the form of MoS2. The layer controllability and large area uniformity essential for electronic and optical device applications is achieved through atomic layer deposition in what is named self-limiting layer synthesis (SLS); a process in which the number of layers is determined by temperature rather than process cycles due to the chemically inactive nature of 2D MoS2. Through spectroscopic and microscopic investigation it is demonstrated that SLS is capable of producing MoS2 with a wafer-scale (~10 cm) layer-number uniformity of more than 90%, which when used as the active layer in a top-gated field-effect transistor, produces an on/off ratio as high as 108. This process is also shown to be applicable to WSe2, with a PN diode fabricated from a MoS2/WSe2 heterostructure exhibiting gate-tunable rectifying characteristics.

  1. Self-Limiting Layer Synthesis of Transition Metal Dichalcogenides

    PubMed Central

    Kim, Youngjun; Song, Jeong-Gyu; Park, Yong Ju; Ryu, Gyeong Hee; Lee, Su Jeong; Kim, Jin Sung; Jeon, Pyo Jin; Lee, Chang Wan; Woo, Whang Je; Choi, Taejin; Jung, Hanearl; Lee, Han-Bo-Ram; Myoung, Jae-Min; Im, Seongil; Lee, Zonghoon; Ahn, Jong-Hyun; Park, Jusang; Kim, Hyungjun

    2016-01-01

    This work reports the self-limiting synthesis of an atomically thin, two dimensional transition metal dichalcogenides (2D TMDCs) in the form of MoS2. The layer controllability and large area uniformity essential for electronic and optical device applications is achieved through atomic layer deposition in what is named self-limiting layer synthesis (SLS); a process in which the number of layers is determined by temperature rather than process cycles due to the chemically inactive nature of 2D MoS2. Through spectroscopic and microscopic investigation it is demonstrated that SLS is capable of producing MoS2 with a wafer-scale (~10 cm) layer-number uniformity of more than 90%, which when used as the active layer in a top-gated field-effect transistor, produces an on/off ratio as high as 108. This process is also shown to be applicable to WSe2, with a PN diode fabricated from a MoS2/WSe2 heterostructure exhibiting gate-tunable rectifying characteristics. PMID:26725854

  2. Improved thermal stability and electrical properties of atomic layer deposited HfO{sub 2}/AlN high-k gate dielectric stacks on GaAs

    SciTech Connect

    Cao, Yan-Qiang; Li, Xin; Zhu, Lin; Cao, Zheng-Yi; Wu, Di; Li, Ai-Dong

    2015-01-15

    The thermal stability and electrical properties of atomic layer deposited HfO{sub 2}/AlN high-k gate dielectric stacks on GaAs were investigated. Compared to HfO{sub 2}/Al{sub 2}O{sub 3} gate dielectric, significant improvements in interfacial quality as well as electrical characteristics after postdeposition annealing are confirmed by constructing HfO{sub 2}/AlN dielectric stacks. The chemical states were carefully explored by the x-ray photoelectron spectroscopy, which indicates the AlN layers effectively prevent from the formation of defective native oxides at elevated temperatures. In addition, it is found that NH{sub 3} plasma during AlN plasma-enhanced atomic layer deposition also has the self-cleaning effect as Al(CH{sub 3}){sub 3} in removing native oxides. The passivating AlN layers suppress the formation of interfacial oxide and trap charge, leading to the decrease of capacitance equivalent thickness after annealing. Moreover, HfO{sub 2}/AlN/GaAs sample has a much lower leakage current density of 2.23 × 10{sup −4} A/cm{sup 2} than HfO{sub 2}/Al{sub 2}O{sub 3}/GaAs sample of 2.58 × 10{sup −2} A/cm{sup 2}. For the HfO{sub 2}/AlN/GaAs sample annealed at 500 °C, it has a lowest interface trap density value of 2.11 × 10{sup 11} eV{sup −1} cm{sup −2}. These results indicate that adopting HfO{sub 2}/AlN dielectric stacks may be a promising approach for the realization of high quality GaAs-based transistor devices.

  3. Fabrication of Ta2O5/GeNx gate insulator stack for Ge metal-insulator-semiconductor structures by electron-cyclotron-resonance plasma nitridation and sputtering deposition techniques

    NASA Astrophysics Data System (ADS)

    Otani, Yohei; Itayama, Yasuhiro; Tanaka, Takuo; Fukuda, Yukio; Toyota, Hiroshi; Ono, Toshiro; Mitsui, Minoru; Nakagawa, Kiyokazu

    2007-04-01

    The authors have fabricated germanium (Ge) metal-insulator-semiconductor (MIS) structures with a 7-nm-thick tantalum pentaoxide (Ta2O5)/2-nm-thick germanium nitride (GeNx) gate insulator stack by electron-cyclotron-resonance plasma nitridation and sputtering deposition. They found that pure GeNx ultrathin layers can be formed by the direct plasma nitridation of the Ge surface without substrate heating. X-ray photoelectron spectroscopy revealed no oxidation of the GeNx layer after the Ta2O5 sputtering deposition. The fabricated MIS capacitor with a capacitance equivalent thickness of 4.3nm showed excellent leakage current characteristics. The interface trap density obtained by the modified conductance method was 4×1011cm-2eV-1 at the midgap.

  4. Combining a multi deposition multi annealing technique with a scavenging (Ti) to improve the high-k/metal gate stack performance for a gate-last process

    NASA Astrophysics Data System (ADS)

    ShuXiang, Zhang; Hong, Yang; Bo, Tang; Zhaoyun, Tang; Yefeng, Xu; Jing, Xu; Jiang, Yan

    2014-10-01

    ALD HfO2 films fabricated by a novel multi deposition multi annealing (MDMA) technique are investigated, we have included samples both with and without a Ti scavenging layer. As compared to the reference gate stack treated by conventional one-time deposition and annealing (D&A), devices receiving MDMA show a significant reduction in leakage current. Meanwhile, EOT growth is effectively controlled by the Ti scavenging layer. This improvement strongly correlates with the cycle number of D&A (while keeping the total annealing time and total dielectrics thickness the same). Transmission electron microscope and energy-dispersive X-ray spectroscopy analysis suggests that oxygen incorporation into both the high-k film and the interfacial layer is likely to be responsible for the improvement of the device. This novel MDMA is promising for the development of gate stack technology in a gate last integration scheme.

  5. Epitaxial ZnO/LiNbO{sub 3}/ZnO stacked layer waveguide for application to thin-film Pockels sensors

    SciTech Connect

    Akazawa, Housei Fukuda, Hiroshi

    2015-05-15

    We produced slab waveguides consisting of a LiNbO{sub 3} (LN) core layer that was sandwiched with Al-doped ZnO cladding layers. The ZnO/LN/ZnO stacked layers were grown on sapphire C-planes by electron cyclotron resonance (ECR) plasma sputtering and were subjected to structural, electrical, and optical characterizations. X-ray diffraction confirmed that the ZnO and LN layers were epitaxial without containing misoriented crystallites. The presence of 60°-rotational variants of ZnO and LN crystalline domains were identified from X-ray pole figures. Cross-sectional transmission electron microscopy images revealed a c-axis orientated columnar texture for LN crystals, which ensured operation as electro-optic sensors based on optical anisotropy along longitudinal and transversal directions. The interfacial roughness between the LN core and ZnO bottom layers as well as that between the ZnO top and the LN core layers was less than 20 nm, which agreed with surface images observed with atomic force microscopy. Outgrowth of triangular LN crystalline domains produced large roughness at the LN film surface. The RMS roughness of the LN film surface was twice that of the same structure grown on sapphire A-planes. Vertical optical transmittance of the stacked films was higher than 85% within the visible and infrared wavelength range. Following the approach adopted by Teng and Man [Appl. Phys. Lett. 56, 1734 (1990)], ac Pockels coefficients of r{sub 33} = 24-28 pm/V were derived for c-axis oriented LN films grown on low-resistive Si substrates. Light propagation within a ZnO/LN/ZnO slab waveguide as well as within a ZnO single layer waveguide was confirmed. The birefringence of these waveguides was 0.11 for the former and 0.05 for the latter.

  6. Mesoporous layer-by-layer ordered nanohybrids of layered double hydroxide and layered metal oxide: highly active visible light photocatalysts with improved chemical stability.

    PubMed

    Gunjakar, Jayavant L; Kim, Tae Woo; Kim, Hyo Na; Kim, In Young; Hwang, Seong-Ju

    2011-09-28

    Mesoporous layer-by-layer ordered nanohybrids highly active for visible light-induced O(2) generation are synthesized by self-assembly between oppositely charged 2D nanosheets of Zn-Cr-layered double hydroxide (Zn-Cr-LDH) and layered titanium oxide. The layer-by-layer ordering of two kinds of 2D nanosheets is evidenced by powder X-ray diffraction and cross-sectional high resolution-transmission electron microscopy. Upon the interstratification process, the original in-plane atomic arrangements and electronic structures of the component nanosheets remain intact. The obtained heterolayered nanohybrids show a strong absorption of visible light and a remarkably depressed photoluminescence signal, indicating an effective electronic coupling between the two component nanosheets. The self-assembly between 2D inorganic nanosheets leads to the formation of highly porous stacking structure, whose porosity is controllable by changing the ratio of layered titanate/Zn-Cr-LDH. The resultant heterolayered nanohybrids are fairly active for visible light-induced O(2) generation with a rate of ∼1.18 mmol h(-1) g(-1), which is higher than the O(2) production rate (∼0.67 mmol h(-1) g(-1)) by the pristine Zn-Cr-LDH material, that is, one of the most effective visible light photocatalysts for O(2) production, under the same experimental condition. This result highlights an excellent functionality of the Zn-Cr-LDH-layered titanate nanohybrids as efficient visible light active photocatalysts. Of prime interest is that the chemical stability of the Zn-Cr-LDH is significantly improved upon the hybridization, a result of the protection of the LDH lattice by highly stable titanate layer. The present findings clearly demonstrate that the layer-by-layer-ordered assembly between inorganic 2D nanosheets is quite effective not only in improving the photocatalytic activity of the component semiconductors but also in synthesizing novel porous LDH-based hybrid materials with improved chemical

  7. Enhancement of Thermal Conductance at Metal-Dielectric Interfaces Using Subnanometer Metal Adhesion Layers

    NASA Astrophysics Data System (ADS)

    Jeong, Minyoung; Freedman, Justin P.; Liang, Hongliang Joe; Chow, Cheng-Ming; Sokalski, Vincent M.; Bain, James A.; Malen, Jonathan A.

    2016-01-01

    We show that the use of subnanometer adhesion layers significantly enhances the thermal interface conductance at metal-dielectric interfaces. A metal-dielectric interface between Au and sapphire (Al2O3) is considered using Cu (low optical loss) and Cr (high optical loss) as adhesion layers. To enable high throughput measurements, each adhesion layer is deposited as a wedge such that a continuous range of thicknesses could be sampled. Our measurements of thermal interface conductance at the metal-Al2O3 interface made using frequency-domain thermoreflectance show that a 1-nm-thick adhesion layer of Cu or Cr is sufficient to enhance the thermal interface conductance by more than a factor of 2 or 4, respectively, relative to the pure Au/Al2O3 interface. The enhancement agrees with the diffuse-mismatch-model-based predictions of accumulated thermal conductance versus adhesion-layer thickness assuming that it contributes phonons with wavelengths less than its thickness, while those with longer wavelengths transmit directly from the Au.

  8. Iridium Interfacial Stack (IRIS)

    NASA Technical Reports Server (NTRS)

    Spry, David James (Inventor)

    2015-01-01

    An iridium interfacial stack ("IrIS") and a method for producing the same are provided. The IrIS may include ordered layers of TaSi.sub.2, platinum, iridium, and platinum, and may be placed on top of a titanium layer and a silicon carbide layer. The IrIS may prevent, reduce, or mitigate against diffusion of elements such as oxygen, platinum, and gold through at least some of its layers.

  9. Selective and low temperature transition metal intercalation in layered tellurides

    PubMed Central

    Yajima, Takeshi; Koshiko, Masaki; Zhang, Yaoqing; Oguchi, Tamio; Yu, Wen; Kato, Daichi; Kobayashi, Yoji; Orikasa, Yuki; Yamamoto, Takafumi; Uchimoto, Yoshiharu; Green, Mark A.; Kageyama, Hiroshi

    2016-01-01

    Layered materials embrace rich intercalation reactions to accommodate high concentrations of foreign species within their structures, and find many applications spanning from energy storage, ion exchange to secondary batteries. Light alkali metals are generally most easily intercalated due to their light mass, high charge/volume ratio and in many cases strong reducing properties. An evolving area of materials chemistry, however, is to capture metals selectively, which is of technological and environmental significance but rather unexplored. Here we show that the layered telluride T2PTe2 (T=Ti, Zr) displays exclusive insertion of transition metals (for example, Cd, Zn) as opposed to alkali cations, with tetrahedral coordination preference to tellurium. Interestingly, the intercalation reactions proceed in solid state and at surprisingly low temperatures (for example, 80 °C for cadmium in Ti2PTe2). The current method of controlling selectivity provides opportunities in the search for new materials for various applications that used to be possible only in a liquid. PMID:27966540

  10. Selective and low temperature transition metal intercalation in layered tellurides

    NASA Astrophysics Data System (ADS)

    Yajima, Takeshi; Koshiko, Masaki; Zhang, Yaoqing; Oguchi, Tamio; Yu, Wen; Kato, Daichi; Kobayashi, Yoji; Orikasa, Yuki; Yamamoto, Takafumi; Uchimoto, Yoshiharu; Green, Mark A.; Kageyama, Hiroshi

    2016-12-01

    Layered materials embrace rich intercalation reactions to accommodate high concentrations of foreign species within their structures, and find many applications spanning from energy storage, ion exchange to secondary batteries. Light alkali metals are generally most easily intercalated due to their light mass, high charge/volume ratio and in many cases strong reducing properties. An evolving area of materials chemistry, however, is to capture metals selectively, which is of technological and environmental significance but rather unexplored. Here we show that the layered telluride T2PTe2 (T=Ti, Zr) displays exclusive insertion of transition metals (for example, Cd, Zn) as opposed to alkali cations, with tetrahedral coordination preference to tellurium. Interestingly, the intercalation reactions proceed in solid state and at surprisingly low temperatures (for example, 80 °C for cadmium in Ti2PTe2). The current method of controlling selectivity provides opportunities in the search for new materials for various applications that used to be possible only in a liquid.

  11. High aspect ratio iridescent three-dimensional metal–insulator–metal capacitors using atomic layer deposition

    SciTech Connect

    Burke, Micheal Blake, Alan; Djara, Vladimir; O'Connell, Dan; Povey, Ian M.; Cherkaoui, Karim; Monaghan, Scott; Scully, Jim; Murphy, Richard; Hurley, Paul K.; Pemble, Martyn E.; Quinn, Aidan J.

    2015-01-01

    The authors report on the structural and electrical properties of TiN/Al{sub 2}O{sub 3}/TiN metal–insulator–metal (MIM) capacitor structures in submicron three-dimensional (3D) trench geometries with an aspect ratio of ∼30. A simplified process route was employed where the three layers for the MIM stack were deposited using atomic layer deposition (ALD) in a single run at a process temperature of 250 °C. The TiN top and bottom electrodes were deposited via plasma-enhanced ALD using a tetrakis(dimethylamino)titanium precursor. 3D trench devices yielded capacitance densities of 36 fF/μm{sup 2} and quality factors >65 at low frequency (200 Hz), with low leakage current densities (<3 nA/cm{sup 2} at 1 V). These devices also show strong optical iridescence which, when combined with the covert embedded capacitance, show potential for system in package (SiP) anticounterfeiting applications.

  12. Van Der Waals heterogeneous layer-layer carbon nanostructures involving π···H-C-C-H···π···H-C-C-H stacking based on graphene and graphane sheets.

    PubMed

    Yuan, Kun; Zhao, Rui-Sheng; Zheng, Jia-Jia; Zheng, Hong; Nagase, Shigeru; Zhao, Sheng-Dun; Liu, Yan-Zhi; Zhao, Xiang

    2017-04-15

    Noncovalent interactions involving aromatic rings, such as π···π stacking, CH···π are very essential for supramolecular carbon nanostructures. Graphite is a typical homogenous carbon matter based on π···π stacking of graphene sheets. Even in systems not involving aromatic groups, the stability of diamondoid dimer and layer-layer graphane dimer originates from C - H···H - C noncovalent interaction. In this article, the structures and properties of novel heterogeneous layer-layer carbon-nanostructures involving π···H-C-C-H···π···H-C-C-H stacking based on [n]-graphane and [n]-graphene and their derivatives are theoretically investigated for n = 16-54 using dispersion corrected density functional theory B3LYP-D3 method. Energy decomposition analysis shows that dispersion interaction is the most important for the stabilization of both double- and multi-layer-layer [n]-graphane@graphene. Binding energy between graphane and graphene sheets shows that there is a distinct additive nature of CH···π interaction. For comparison and simplicity, the concept of H-H bond energy equivalent number of carbon atoms (noted as NHEQ), is used to describe the strength of these noncovalent interactions. The NHEQ of the graphene dimers, graphane dimers, and double-layered graphane@graphene are 103, 143, and 110, indicating that the strength of C-H···π interaction is close to that of π···π and much stronger than that of C-H···H-C in large size systems. Additionally, frontier molecular orbital, electron density difference and visualized noncovalent interaction regions are discussed for deeply understanding the nature of the C-H···π stacking interaction in construction of heterogeneous layer-layer graphane@graphene structures. We hope that the present study would be helpful for creations of new functional supramolecular materials based on graphane and graphene carbon nano-structures. © 2017 Wiley Periodicals, Inc.

  13. Lowering the environmental impact of high-kappa/ metal gate stack surface preparation processes

    NASA Astrophysics Data System (ADS)

    Zamani, Davoud

    ABSTRACT Hafnium based oxides and silicates are promising high-κ dielectrics to replace SiO2 as gate material for state-of-the-art semiconductor devices. However, integrating these new high-κ materials into the existing complementary metal-oxide semiconductor (CMOS) process remains a challenge. One particular area of concern is the use of large amounts of HF during wet etching of hafnium based oxides and silicates. The patterning of thin films of these materials is accomplished by wet etching in HF solutions. The use of HF allows dissolution of hafnium as an anionic fluoride complex. Etch selectivity with respect to SiO2 is achieved by appropriately diluting the solutions and using slightly elevated temperatures. From an ESH point of view, it would be beneficial to develop methods which would lower the use of HF. The first objective of this study is to find new chemistries and developments of new wet etch methods to reduce fluoride consumption during wet etching of hafnium based high-κ materials. Another related issue with major environmental impact is the usage of large amounts of rinsing water for removal of HF in post-etch cleaning step. Both of these require a better understanding of the HF interaction with the high-κ surface during the etching, cleaning, and rinsing processes. During the rinse, the cleaning chemical is removed from the wafers. Ensuring optimal resource usage and cycle time during the rinse requires a sound understanding and quantitative description of the transport effects that dominate the removal rate of the cleaning chemicals from the surfaces. Multiple processes, such as desorption and re-adsorption, diffusion, migration and convection, all factor into the removal rate of the cleaning chemical during the rinse. Any of these processes can be the removal rate limiting process, the bottleneck of the rinse. In fact, the process limiting the removal rate generally changes as the rinse progresses, offering the opportunity to save resources

  14. Different forms of antiparallel stacking of hydrogen-bonded antidromic rings in the solid state: polymorphism with virtually the same unit cell and two-dimensional isostructurality with alternating layers.

    PubMed

    Kálmán, Alajos; Fábián, László; Argay, Gyula; Bernáth, Gábor; Gyarmati, Zsuzsanna Cs

    2004-12-01

    As a continuation of a systematic structural analysis of 2-hydroxycycloalkanecarboxylic acids and their carboxamide analogs, the effects of antidromic rings [Jeffrey & Saenger (1991). Hydrogen Bonding in Biological Structures. Berlin, Heidelberg: Springer Verlag] upon the layer stacking of cyclopentane and cycloheptane derivatives are compared. Determination of the structure of trans-2-hydroxycycloheptanecarboxylic acid (2) led to the discovery of two polymorphs with virtually the same unit cell [Kalman et al. (2003). J. Am. Chem. Soc. 125, 34-35]. (i) The layer stacking of the antidromic rings for the whole single crystal is antiparallel (2b). (ii) The antidromic rings and the 21 axis are parallel (2a), consequently the domains of the single crystal must be antiparallel. While their polymorphism is solvent-controlled, they illustrate a novel form of two-dimensional isostructurality. Antiparallel layer stacking is again demonstrated by trans-2-hydroxycycloheptanecarboxamide (3) (space group Pbca). It is built up from layers isostructural with those in the homologous trans-2-hydroxycyclopentanecarboxamide (4) [Kalman et al. (2001). Acta Cryst. B57, 539-550], but in this structure (space group Pca21) the layers are stacked in parallel mode. Similar to (2a) and (2b), the antiparallel layer stacking in (3) versus their parallel array in (4) illustrates the two-dimensional isostructurality with alternating layer orientations. Although (3) and (4) display isostructurality, they are not isomorphous.

  15. Towards a global model of the meteoric metal layers

    NASA Astrophysics Data System (ADS)

    Plane, John; Feng, Wuhu; Marsh, Daniel; Janches, Diego; Chipperfield, Martyn; Burrows, John P.; Sinnhuber, Miriam

    This paper will describe a major new initiative to develop a global model of the Na, Fe, Ca and Mg layers which are produced in the upper mesosphere and lower thermosphere by mete-oric ablation. The 4M (Multi-scale Modelling of Mesospheric Metals) project brings together three components: the injection of meteoric constituents into the atmosphere; the neutral and ion-molecule chemistries of these four metals; and a general circulation model of the whole atmosphere. The injection rates are calculated by combining the meteoric input function (MIF), an astro-nomical model which determines the meteoric size distribution and infall velocity distribution as a function of location and time, and a chemical ablation model (CABMOD), which calcu-lates the ablation rates of the different meteoric elements for a meteoroid of specified mass and velocity. The atmospheric chemistries of Na, Fe, Ca and Mg are now quite well understood: the kinetics of most of their important atmospheric reactions have been studied in the laboratory under appropriate conditions. This has enabled 1-dimensional models of these metallic layers to be produced, which compare satisfactorily with observations by ground-based lidar and space-borne spectrometers. The global model which has been chosen for the 4M project is the Whole Atmosphere Chemistry Climate Model (WACCM), developed at NCAR (Boulder). The model extends from 0 -140 km and includes a full treatment of neutral chemistry and lower E region ion chemistry. We will present the initial results on modelling the global Na and Fe layers.

  16. Analysis of Si-SiO2 Interface Using Charge Pumping Method with Various Capping Materials between Gate Stacks and Inter Layer Dielectric in NAND Flash Memory

    NASA Astrophysics Data System (ADS)

    Kim, Nam-Kyeong; Kim, Se-Jun; Park, Kyoung-Hwan; Choi, Eun-Seok; Lee, Min-Kyu; Kim, Hyeon-Soo; Noh, Keum-Hwan; Om, Jae-Chul; Lee, Hee-Kee; Bae, Gi-Hyun

    2006-09-01

    We report the dependence of Si-SiO2 interface trap density after Fowler-Nordheim (F/N) stress on various capping materials between gate stacks and an inter layer dielectric (ILD) in a NAND Flash memory cell. The interface trap density was characterized by charge pumping method (CPM). When the capping layer is an oxide, the Nit after F/N stress is approximately 2× 1011 cm-2, which is about 50% smaller than that with a nitride layer. We found that the oxide layer causes compressive stress whereas the nitride layer causes a relatively high tensile stress in the underlying substrate by measuring the warp change of the substrate. To correlate the interface state density and data retention characteristics, we measured Vt shift after high-temperature baking. When an oxide capping layer is used, the retention characteristics of memory devices are greatly improved compared to the nitride capping case. These results show a good correlation between the interface characteristics and mechanical stress behaviors.

  17. Tunable magnetic resonance in double layered metallic structures.

    PubMed

    Zhou, L; Zhu, Y Y

    2011-12-01

    Double layered metallic gratings have been investigated both theoretically and experimentally. The authors have reported that tunable magnetic resonance (MR) can be achieved by modulating the vertical chirped width dh which could be controlled conveniently in the common electron and/or ion beam microfabrications. The linear relationship between MR wavelength and dh has been reported. By introducing the difference of electric and magnetic penetration depth, an analytic formula deduced from a modified LC model has shown good agreement with the simulation results, and an effective width for trapezoidal sandwiched microstructures has been presented. Our results may provide an alternative choice for tunable MR and broad bandwidth of magnetic metamaterials.

  18. Layered Metal Thiophosphite Materials: Magnetic, Electrochemical, and Electronic Properties.

    PubMed

    Mayorga-Martinez, Carmen C; Sofer, Zdeněk; Sedmidubský, David; Huber, Štěpán; Eng, Alex Yong Sheng; Pumera, Martin

    2017-03-29

    Beyond graphene, transitional metal dichalcogenides, and black phosphorus, there are other layered materials called metal thiophosphites (MPSx), which are recently attracting the attention of scientists. Here we present the synthesis, structural and morphological characterization, magnetic properties, electrochemical performance, and the calculated density of states of different layered metal thiophosphite materials with a general formula MPSx, and as a result of varying the metal component, we obtain CrPS4, MnPS3, FePS3, CoPS3, NiPS3, ZnPS3, CdPS3, GaPS4, SnPS3, and BiPS4. SnPS3, ZnPS3, CdPS3, GaPS4, and BiPS4 exhibit only diamagnetic behavior due to core electrons. By contrast, trisulfides with M = Mn, Fe, Co, and Ni, as well as CrPS4, are paramagnetic at high temperatures and undergo a transition to antiferromagnetic state on cooling. Within the trisulfides series the Néel temperature characterizing the transition from paramagnetic to antiferromagnetic phase increases with the increasing atomic number and the orbital component enhancing the total effective magnetic moment. Interestingly, in terms of catalysis NiPS3, CoPS3, and BiPS4 show the highest efficiency for hydrogen evolution reaction (HER), while for the oxygen evolution reaction (OER) the highest performance is observed for CoPS3. Finally, MnPS3 presents the highest oxygen reduction reaction (ORR) activity compared to the other MPSx studied here. This great catalytic performance reported for these MPSx demonstrates their promising capabilities in energy applications.

  19. Effect of the deformation temperature on the structural refinement of BCC metals with a high stacking fault energy during high pressure torsion

    NASA Astrophysics Data System (ADS)

    Voronova, L. M.; Chashchukhina, T. I.; Gapontseva, T. M.; Krasnoperova, Yu. G.; Degtyarev, M. V.; Pilyugin, V. P.

    2016-10-01

    The structural evolution in bcc metals (molybdenum, niobium) with a high stacking fault energy (300 and 200 mJ/m-2, respectively) is studied during high pressure torsion in Bridgman anvils at temperatures of 290 and 80 K. It is established that cryogenic deformation of these metals does not result in twinning; however, banded structures are formed at the initial stage of deformation. Misoriented kink bands, which inhibit the formation of a homogeneous submicrocrystalline structure similarly to twins, form in molybdenum. The banded structures in niobium are characterized by low-angle misorientations; they do not suppress the formation of a submicrocrystalline structure and the refinement of microcrystallites to nanosizes.

  20. Novel hetero-layered materials with tunable direct band gaps by sandwiching different metal disulfides and diselenides.

    PubMed

    Terrones, Humberto; López-Urías, Florentino; Terrones, Mauricio

    2013-01-01

    Although bulk hexagonal phases of layered semiconducting transition metal dichalcogenides (STMD) such as MoS2, WS2, WSe2 and MoSe2 exhibit indirect band gaps, a mono-layer of STMD possesses a direct band gap which could be used in the construction of novel optoelectronic devices, catalysts, sensors and valleytronic components. Unfortunately, the direct band gap only occurs for mono-layered STMD. We have found, using first principles calculations, that by alternating individual layers of different STMD (MoS2, WS2, WSe2 and MoSe2) with particular stackings, it is possible to generate direct band gap bi-layers ranging from 0.79 eV to 1.157 eV. Interestingly, in this direct band gap, electrons and holes are physically separated and localized in different layers. We foresee that the alternation of different STMD would result in the fabrication of materials with unprecedented optical and physico-chemical properties that would need further experimental and theoretical investigations.

  1. Novel hetero-layered materials with tunable direct band gaps by sandwiching different metal disulfides and diselenides

    PubMed Central

    Terrones, Humberto; López-Urías, Florentino; Terrones, Mauricio

    2013-01-01

    Although bulk hexagonal phases of layered semiconducting transition metal dichalcogenides (STMD) such as MoS2, WS2, WSe2 and MoSe2 exhibit indirect band gaps, a mono-layer of STMD possesses a direct band gap which could be used in the construction of novel optoelectronic devices, catalysts, sensors and valleytronic components. Unfortunately, the direct band gap only occurs for mono-layered STMD. We have found, using first principles calculations, that by alternating individual layers of different STMD (MoS2, WS2, WSe2 and MoSe2) with particular stackings, it is possible to generate direct band gap bi-layers ranging from 0.79 eV to 1.157 eV. Interestingly, in this direct band gap, electrons and holes are physically separated and localized in different layers. We foresee that the alternation of different STMD would result in the fabrication of materials with unprecedented optical and physico-chemical properties that would need further experimental and theoretical investigations. PMID:23528957

  2. Effect of spacer layer thickness on structural and optical properties of multi-stack InAs/GaAsSb quantum dots

    SciTech Connect

    Kim, Yeongho; Ban, Keun-Yong Honsberg, Christiana B.; Boley, Allison; Smith, David J.

    2015-10-26

    The structural and optical properties of ten-stack InAs/GaAsSb quantum dots (QDs) with different spacer layer thicknesses (d{sub s} = 2, 5, 10, and 15 nm) are reported. X-ray diffraction analysis reveals that the strain relaxation of the GaAsSb spacers increases linearly from 0% to 67% with larger d{sub s} due to higher elastic stress between the spacer and GaAs matrix. In addition, the dislocation density in the spacers with d{sub s} = 10 nm is lowest as a result of reduced residual strain. The photoluminescence peak energy from the QDs does not change monotonically with increasing d{sub s} due to the competing effects of decreased compressive strain and weak electronic coupling of stacked QD layers. The QD structure with d{sub s} = 10 nm is demonstrated to have improved luminescence properties and higher carrier thermal stability.

  3. High-performance enhancement-mode AlGaN/GaN MOS-HEMTs with fluorinated stack gate dielectrics and thin barrier layer

    NASA Astrophysics Data System (ADS)

    Tao, Gao; Ruimin, Xu; Kai, Zhang; Yuechan, Kong; Jianjun, Zhou; Cen, Kong; Xinxin, Yu; Xun, Dong; Tangsheng, Chen

    2016-06-01

    We present high-performance enhancement-mode AlGaN/GaN metal—oxide—semiconductor high-electron mobility transistors (MOS-HEMTs) by a fluorinated gate dielectric technique. A nanolaminate of an Al2O3/La x Al1-x O 3/Al2O3 stack (x≈0.33) grown by atomic layer deposition is employed to avoid fluorine ions implantation into the scaled barrier layer. Fabricated enhancement-mode MOS-HEMTs exhibit an excellent performance as compared to those with the conventional dielectric-last technique, delivering a large maximum drain current of 916 mA/mm and simultaneously a high peak transconductance of 342 mS/mm. The balanced DC characteristics indicate that advanced gate stack dielectrics combined with buffered fluorine ions implantation have a great potential for high speed GaN E/D-mode integrated circuit applications. Project supported by the National Natural Science Foundation of China (Nos. 61504125, 61474101, 61106130 61076120, 61505181), and the Natural Science Foundation of Jiangsu Province of China (Nos. BK20131072, BE2012007, BK2012516).

  4. Cross-stacked carbon nanotube film as an additional built-in current collector and adsorption layer for high-performance lithium sulfur batteries

    NASA Astrophysics Data System (ADS)

    Sun, Li; Kong, Weibang; Li, Mengya; Wu, Hengcai; Jiang, Kaili; Li, Qunqing; Zhang, Yihe; Wang, Jiaping; Fan, Shoushan

    2016-02-01

    Cross-stacked carbon nanotube (CNT) film is proposed as an additional built-in current collector and adsorption layer in sulfur cathodes for advanced lithium sulfur (Li-S) batteries. On one hand, the CNT film with high conductivity, microstructural rough surface, high flexibility and mechanical durability retains stable and direct electronic contact with the sulfur cathode materials, therefore decreasing internal resistivity and suppressing polarization of the cathode. On the other hand, the highly porous structure and the high surface area of the CNT film provide abundant adsorption points to support and confine sulfur cathode materials, alleviate their aggregation and promote high sulfur utilization. Moreover, the lightweight and compact structure of the CNT film adds no extra weight or volume to the sulfur cathode, benefitting the improvement of energy densities. Based on these characteristics, the sulfur cathode with a 100-layer cross-stacked CNT film presents excellent rate performances with capacities of 986, 922 and 874 mAh g-1 at cycling rates of 0.2C, 0.5C and 1C for sulfur loading of 60 wt%, corresponding to an improvement of 52%, 109% and 146% compared to that without a CNT film. Promising cycling performances are also demonstrated, offering great potential for scaled-up production of sulfur cathodes for Li-S batteries.

  5. Unidirectional transmission in non-symmetric gratings containing metallic layers.

    PubMed

    Serebryannikov, A E; Ozbay, Ekmel

    2009-08-03

    The mechanism of achieving unidirectional transmission in the gratings, which only contain isotropic dielectric and metallic layers, is suggested and numerically validated. It is shown that significant transmission in one direction and nearly zero transmission in the opposite direction can be obtained in the same intrinsically isotropic gratings as those studied recently in A. E. Serebryannikov and E. Ozbay, Opt. Express 17, 278 (2009), but at a non-zero angle of incidence. The tilting, non-symmetric features of the grating and the presence of a metallic layer with a small positive real part of the index of refraction are the conditions that are necessary for obtaining the unidirectionality. Single- and multibeam operational regimes are demonstrated. The frequency and angle ranges of the unidirectional transmission can be estimated by using the conventional framework based on isofrequency dispersion contours and construction lines that properly take into account the periodic features of the interfaces, but should then be corrected because of the tunneling arising within the adjacent ranges. After proper optimization, this mechanism is expected to become an alternative to that based on the use of anisotropic materials.

  6. Wear mechanisms in metal-on-metal bearings: the importance of tribochemical reaction layers.

    PubMed

    Wimmer, Markus A; Fischer, Alfons; Büscher, Robin; Pourzal, Robin; Sprecher, Christoph; Hauert, Roland; Jacobs, Joshua J

    2010-04-01

    Metal-on-metal (MoM) bearings are at the forefront in hip resurfacing arthroplasty. Because of their good wear characteristics and design flexibility, MoM bearings are gaining wider acceptance with market share reaching nearly 10% worldwide. However, concerns remain regarding potential detrimental effects of metal particulates and ion release. Growing evidence is emerging that the local cell response is related to the amount of debris generated by these bearing couples. Thus, an urgent clinical need exists to delineate the mechanisms of debris generation to further reduce wear and its adverse effects. In this study, we investigated the microstructural and chemical composition of the tribochemical reaction layers forming at the contacting surfaces of metallic bearings during sliding motion. Using X-ray photoelectron spectroscopy and transmission electron microscopy with coupled energy dispersive X-ray and electron energy loss spectroscopy, we found that the tribolayers are nanocrystalline in structure, and that they incorporate organic material stemming from the synovial fluid. This process, which has been termed "mechanical mixing," changes the bearing surface of the uppermost 50 to 200 nm from pure metallic to an organic composite material. It hinders direct metal contact (thus preventing adhesion) and limits wear. This novel finding of a mechanically mixed zone of nanocrystalline metal and organic constituents provides the basis for understanding particle release and may help in identifying new strategies to reduce MoM wear.

  7. 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.

  8. Transition metal dichalcogenides and beyond: synthesis, properties, and applications of single- and few-layer nanosheets.

    PubMed

    Lv, Ruitao; Robinson, Joshua A; Schaak, Raymond E; Sun, Du; Sun, Yifan; Mallouk, Thomas E; Terrones, Mauricio

    2015-01-20

    CONSPECTUS: In the wake of the discovery of the remarkable electronic and physical properties of graphene, a vibrant research area on two-dimensional (2D) layered materials has emerged during the past decade. Transition metal dichalcogenides (TMDs) represent an alternative group of 2D layered materials that differ from the semimetallic character of graphene. They exhibit diverse properties that depend on their composition and can be semiconductors (e.g., MoS2, WS2), semimetals (e.g., WTe2, TiSe2), true metals (e.g., NbS2, VSe2), and superconductors (e.g., NbSe2, TaS2). The properties of TMDs can also be tailored according to the crystalline structure and the number and stacking sequence of layers in their crystals and thin films. For example, 2H-MoS2 is semiconducting, whereas 1T-MoS2 is metallic. Bulk 2H-MoS2 possesses an indirect band gap, but when 2H-MoS2 is exfoliated into monolayers, it exhibits direct electronic and optical band gaps, which leads to enhanced photoluminescence. Therefore, it is important to learn to control the growth of 2D TMD structures in order to exploit their properties in energy conversion and storage, catalysis, sensing, memory devices, and other applications. In this Account, we first introduce the history and structural basics of TMDs. We then briefly introduce the Raman fingerprints of TMDs of different layer numbers. Then, we summarize our progress on the controlled synthesis of 2D layered materials using wet chemical approaches, chemical exfoliation, and chemical vapor deposition (CVD). It is now possible to control the number of layers when synthesizing these materials, and novel van der Waals heterostructures (e.g., MoS2/graphene, WSe2/graphene, hBN/graphene) have recently been successfully assembled. Finally, the unique optical, electrical, photovoltaic, and catalytic properties of few-layered TMDs are summarized and discussed. In particular, their enhanced photoluminescence (PL), photosensing, photovoltaic conversion, and

  9. Issues involved in the atomic layer deposition of metals

    NASA Astrophysics Data System (ADS)

    Grubbs, Robert Kimes

    Auger Electron Spectroscopy (AES) was used to study the nucleation and growth of tungsten on aluminum oxide surfaces. Tungsten metal was deposited using Atomic Layer Deposition (ALD) techniques. ALD uses sequential surface reactions to deposit material with atomic layer control. W ALD is performed using sequential exposures of WF6 and Si2H6. The step-wise nature of W ALD allows nucleation studies to be performed by analyzing the W surface concentration after each ALD reaction. Nucleation and growth regions can be identified by quantifying the AES signal intensities from both the W surface and the Al2O3 substrate. W nucleation occurred in 3 ALD reaction cycles. The AES results yielded a nucleation rate of 1.0 A/ALD cycle and a growth rate of ≈3 A/ALD cycle. AES studies also explored the nucleation and growth of Al2O3 on W. Al2O3 nucleated in 1 ALD cycle giving a nucleation rate of 3.5 A/ALD cycle and a subsequent growth rate of 1.0 A/ALD cycle. Mass spectrometry was then used to study the ALD reaction chemistry of tungsten deposition. Because of the step-wise nature of the W ALD chemistry, each W ALD reaction could be studied independently. The gaseous mass products were identified from both the WF6 and Si2H6 reactions. H2, HF and SiF4 mass products were observed for the WF6 reaction. The Si2H6 reaction displayed a room temperature reaction and a 200°C reaction. Products from the room temperature Si2H6 reaction were H2 and SiF3H. The reaction at 200°C yielded only H2 as a reaction product. H2 desorption from the surface contributes to the 200°C Si2H6 reaction. AES was used to confirm that the gas phase reaction products are correlated with a change in the surface species. Atomic hydrogen reduction of metal halides and oganometallic compounds provides another method for depositing metals with atomic layer control. The quantity of atomic hydrogen necessary to perform this chemistry is critical to the metal ALD process. A thermocouple probe was constructed to

  10. Modeling and Simulation of Ballistic Penetration of Ceramic-Polymer-Metal Layered Systems

    DTIC Science & Technology

    2016-01-01

    ARL-RP-0562 ● JAN 2016 US Army Research Laboratory Modeling and Simulation of Ballistic Penetration of Ceramic- Polymer -Metal...Penetration of Ceramic- Polymer -Metal Layered Systems by JD Clayton Weapons and Materials Research Directorate, ARL Reprinted from...Modeling and Simulation of Ballistic Penetration of Ceramic- Polymer -Metal Layered Systems 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM

  11. Electronic, Mechanical, and Dielectric Properties of Two-Dimensional Atomic Layers of Noble Metals

    NASA Astrophysics Data System (ADS)

    Kapoor, Pooja; Kumar, Jagdish; Kumar, Arun; Kumar, Ashok; Ahluwalia, P. K.

    2017-01-01

    We present density functional theory-based electronic, mechanical, and dielectric properties of monolayers and bilayers of noble metals (Au, Ag, Cu, and Pt) taken with graphene-like hexagonal structure. The Au, Ag, and Pt bilayers stabilize in AA-stacked configuration, while the Cu bilayer favors the AB stacking pattern. The quantum ballistic conductance of the noble-metal mono- and bilayers is remarkably increased compared with their bulk counterparts. Among the studied systems, the tensile strength is found to be highest for the Pt monolayer and bilayer. The noble metals in mono- and bilayer form show distinctly different electron energy loss spectra and reflectance spectra due to the quantum confinement effect on going from bulk to the monolayer limit. Such tunability of the electronic and dielectric properties of noble metals by reducing the degrees of freedom of electrons offers promise for their use in nanoelectronics and optoelectronics applications.

  12. Ultraviolet photodetectors based on ZnO nanorods-seed layer effect and metal oxide modifying layer effect.

    PubMed

    Zhou, Hai; Fang, Guojia; Liu, Nishuang; Zhao, Xingzhong

    2011-02-15

    Pt/ZnO nanorod (NR) and Pt/modified ZnO NR Schottky barrier ultraviolet (UV) photodetectors (PDs) were prepared with different seed layers and metal oxide modifying layer materials. In this paper, we discussed the effect of metal oxide modifying layer on the performance of UV PDs pre- and post-deposition annealing at 300°C, respectively. For Schottky barrier UV PDs with different seed layers, the MgZnO seed layer-PDs without metal oxide coating showed bigger responsivity and larger detectivity (Dλ*) than those of PDs with ZnO seed layer, and the reason was illustrated through energy band theory and the electron transport mechanism. Also the ratio of D254* to D546* was calculated above 8 × 102 for all PDs, which demonstrated that our PDs showed high selectivity for detecting UV light with less influence of light with long wavelength.

  13. Two methods of tuning threshold voltage of bulk FinFETs with replacement high-k metal-gate stacks

    NASA Astrophysics Data System (ADS)

    Xu, Miao; Zhu, Huilong; Zhang, Yanbo; Xu, Qiuxia; Zhang, Yongkui; Qin, Changliang; Zhang, Qingzhu; Yin, Huaxiang; Xu, Hao; Chen, Shuai; Luo, Jun; Li, Chunlong; Zhao, Chao; Ye, Tianchun

    2017-03-01

    In this work, we propose two threshold voltage (VTH) tuning methods for bulk FinFETs with replacement high-k metal gate. The first method is to perform a vertical implantation into fin structure after dummy gate removal, self-aligned forming halo & punch through stop pocket (halo & PTSP) doping profile. The second method is to execute P+/BF2+ ion implantations into the single common work function (WF) layer in N-/P-FinFETs, respectively. These two methods have been investigated by TCAD simulations and MOS-capacitor experiments respectively, and then integrated into FinFET fabrication successfully. Experimental results show that the halo & PTSP doping profile can reduce VTH roll off and total variation. With P+/BF2+ doped WF layer, the VTH-sat shift -0.43 V/+1.26 V for N-FinFETs and -0.75 V/+0.11 V for P-FinFETs, respectively, with gate length of 500 nm. The proposed two methods are simple and effective for FinFET VTH tuning, and have potential for future application of massive production.

  14. Metal-semiconductor-metal neutron detectors based on hexagonal boron nitride epitaxial layers

    NASA Astrophysics Data System (ADS)

    Majety, S.; Li, J.; Cao, X. K.; Dahal, R.; Lin, J. Y.; Jiang, H. X.

    2012-10-01

    Hexagonal boron nitride (hBN) possesses extraordinary potential for solid-state neutron detector applications. This stems from the fact that the boron-10 (10B) isotope has a capture cross-section of 3840 barns for thermal neutrons that is orders of magnitude larger than other isotopes. Epitaxial layers of hBN have been synthesized by metal organic chemical vapor deposition (MOCVD). Experimental measurements indicated that the thermal neutron absorption coefficient and length of natural hBN epilayers are about 0.0036 μm-1 and 277 μm, respectively. To partially address the key requirement of long carrier lifetime and diffusion length for a solid-state neutron detector, micro-strip metal-semiconductor-metal detectors were fabricated and tested. A good current response was generated in these detectors using continuous irradiation with a thermal neutron beam, corresponding to an effective conversion efficiency approaching ~80% for absorbed neutrons.

  15. Vertical Bipolar Charge Plasma Transistor with Buried Metal Layer

    PubMed Central

    Nadda, Kanika; Kumar, M. Jagadesh

    2015-01-01

    A self-aligned vertical Bipolar Charge Plasma Transistor (V-BCPT) with a buried metal layer between undoped silicon and buried oxide of the silicon-on-insulator substrate, is reported in this paper. Using two-dimensional device simulation, the electrical performance of the proposed device is evaluated in detail. Our simulation results demonstrate that the V-BCPT not only has very high current gain but also exhibits high BVCEO · fT product making it highly suitable for mixed signal high speed circuits. The proposed device structure is also suitable for realizing doping-less bipolar charge plasma transistor using compound semiconductors such as GaAs, SiC with low thermal budgets. The device is also immune to non-ideal current crowding effects cropping up at high current densities. PMID:25597295

  16. Vertical bipolar charge plasma transistor with buried metal layer.

    PubMed

    Nadda, Kanika; Kumar, M Jagadesh

    2015-01-19

    A self-aligned vertical Bipolar Charge Plasma Transistor (V-BCPT) with a buried metal layer between undoped silicon and buried oxide of the silicon-on-insulator substrate, is reported in this paper. Using two-dimensional device simulation, the electrical performance of the proposed device is evaluated in detail. Our simulation results demonstrate that the V-BCPT not only has very high current gain but also exhibits high BVCEO · f(T) product making it highly suitable for mixed signal high speed circuits. The proposed device structure is also suitable for realizing doping-less bipolar charge plasma transistor using compound semiconductors such as GaAs, SiC with low thermal budgets. The device is also immune to non-ideal current crowding effects cropping up at high current densities.

  17. Method for producing functionally graded nanocrystalline layer on metal surface

    DOEpatents

    Ajayi, Oyelayo O.; Hershberger, Jeffrey G.

    2010-03-23

    An improved process for the creation or formation of nanocrystalline layers on substrates' surfaces is provided. The process involves "prescuffing" the surface of a substrate such as a metal by allowing friction to occur on the surface by a load-bearing entity making rubbing contact and moving along and on the substrate's surface. The "prescuffing" action is terminated when the coefficient of friction between the surface and the noise is rising significantly. Often, the significant rise in the coefficient of friction is signaled by a change in pitch of the scuffing action sound emanating from the buffeted surface. The "prescuffing" gives rise to a harder and smoother surface which withstands better any inadequate lubrication that may take place when the "prescuffed" surface is contacted by other surfaces.

  18. π(+)-π(+) stacking of imidazolium cations enhances molecular layering of room temperature ionic liquids at their interfaces.

    PubMed

    Tang, Fujie; Ohto, Tatsuhiko; Hasegawa, Taisuke; Bonn, Mischa; Nagata, Yuki

    2017-01-25

    The interfacial structure of room temperature ionic liquids (RTILs) controls many of the unique properties of RTILs, such as the high capacitance of RTILs and the efficiency of charge transport between RTILs and electrodes. RTILs have been experimentally shown to exhibit interfacial molecular layering structures over a 10 Å length scale. However, the driving force behind the formation of these layered structures has not been resolved. Here, we report ab initio molecular dynamics simulations of imidazolium RTIL/air and RTIL/graphene interfaces along with force field molecular dynamics simulations. We find that the π(+)-π(+) interaction of imidazolium cations enhances the layering structure of RTILs, despite the electrostatic repulsion. The length scales of the molecular layering at the RTIL/air and RTIL/graphene interfaces are very similar, manifesting the limited effect of the substrate on the interfacial organization of RTILs.

  19. Inhibiting Metal Oxide Atomic Layer Deposition: Beyond Zinc Oxide.

    PubMed

    Sampson, Matthew D; Emery, Jonathan D; Pellin, Michael J; Martinson, Alex B F

    2017-04-05

    Atomic layer deposition (ALD) of several metal oxides is selectivity inhibited on alkanethiol self-assembled monolayers (SAMs) on Au, and the eventual nucleation mechanism is investigated. The inhibition ability of the SAM is significantly improved by the in situ H2-plasma pretreatment of the Au substrate prior to the gas-phase deposition of a long-chain alkanethiol, 1-dodecanethiol (DDT). This more rigorous surface preparation inhibits even aggressive oxide ALD precursors, including trimethylaluminum and water, for at least 20 cycles. We study the effect that the ALD precursor purge times, growth temperature, alkanethiol chain length, alkanethiol deposition time, and plasma treatment time have on Al2O3 ALD inhibition. This is the first example of Al2O3 ALD inhibition from a vapor-deposited SAM. The inhibitions of Al2O3, ZnO, and MnO ALD processes are compared, revealing the versatility of this selective surface treatment. Atomic force microscopy and grazing-incidence X-ray fluorescence further reveal insight into the mechanism by which the well-defined surface chemistry of ALD may eventually be circumvented to allow metal oxide nucleation and growth on SAM-modified surfaces.

  20. Silver-doped metal layers for medical applications

    NASA Astrophysics Data System (ADS)

    Kocourek, T.; Jelínek, M.; Mikšovský, J.; Jurek, K.; Weiserová, M.

    2014-08-01

    Biological, physical and mechanical properties of silver-doped layers of titanium alloy Ti6Al4V and 316 L steel prepared by pulsed laser deposition were studied. Metallic silver-doped coatings could be a new route for antibacterial protection in medicine. Thin films of silver and silver-doped materials were synthesized using KrF excimer laser deposition. The materials were ablated from two targets, which were composed either from titanium alloy with silver segments or from steel with silver segments. The concentration of silver ranged from 1.54 to 4.32 at% for steel and from 3.04 to 13.05 at% for titanium alloy. The layer properties such as silver content, structure, adhesion, surface wettability, and antibacterial efficiency (evaluated by Escherichia coli and Bacillus subtilis bacteria) were measured. Film adhesion was studied using a scratch test. The antibacterial efficiency changed with silver doping up to 99.9 %. Our investigation was focused on the minimum Ag concentration needed to reach high antibacterial efficiency, high film adhesion, and hardness.

  1. Low Threshold Voltage and High Mobility N-Channel Metal-Oxide-Semiconductor Field-Effect Transistor Using Hf-Si/HfO2 Gate Stack Fabricated by Gate-Last Process

    NASA Astrophysics Data System (ADS)

    Ando, Takashi; Hirano, Tomoyuki; Tai, Kaori; Yamaguchi, Shinpei; Yoshida, Shinichi; Iwamoto, Hayato; Kadomura, Shingo; Watanabe, Heiji

    2010-01-01

    Systematic characterization of Hf-Si/HfO2 gate stacks revealed two mobility degradation modes. One is carrier scattering by fixed charges and/or trapped charges induced by the crystallization in the thick HfO2 case (inversion oxide thickness, Tinv> 1.6 nm). The other is the Hf penetration into the interfacial layer with the Si substrate in the thin HfO2 case (Tinv< 1.6 nm) for the Hf-rich electrode. It was demonstrated that careful optimization of the HfO2 thickness and the Hf-Si composition can suppress both modes. As a result, a high electron mobility equivalent to that of n+polycrystalline silicon (poly-Si)/SiO2 (248 cm2 V-1 s-1 at Eeff=1 MV/cm) was obtained at Tinv of 1.47 nm. Moreover, the effective work function of the optimized Hf-Si/HfO2 gate stack is located within 50 mV from the Si band edge (Ec). An extremely high Ion of 1165 µA/µm (at Ioff = 81 nA/µm) at Vdd=1.0 V was demonstrated for a 45 nm gate n-channel metal-oxide-semiconductor field-effect transistor (n-MOSFET) without strain enhanced technology.

  2. Relationship between structural changes, hydrogen content and annealing in stacks of ultrathin Si/Ge amorphous layers

    PubMed Central

    2011-01-01

    Hydrogenated multilayers (MLs) of a-Si/a-Ge have been analysed to establish the reasons of H release during annealing that has been seen to bring about structural modifications even up to well-detectable surface degradation. Analyses carried out on single layers of a-Si and a-Ge show that H is released from its bond to the host lattice atom and that it escapes from the layer much more efficiently in a-Ge than in a-Si because of the smaller binding energy of the H-Ge bond and probably of a greater weakness of the Ge lattice. This should support the previous hypothesis that the structural degradation of a-Si/a-Ge MLs primary starts with the formation of H bubbles in the Ge layers. PMID:21711697

  3. Relationship between structural changes, hydrogen content and annealing in stacks of ultrathin Si/Ge amorphous layers.

    PubMed

    Frigeri, Cesare; Serényi, Miklós; Khánh, Nguyen Quoc; Csik, Attila; Riesz, Ferenc; Erdélyi, Zoltán; Nasi, Lucia; Beke, Dezső László; Boyen, Hans-Gerd

    2011-03-01

    Hydrogenated multilayers (MLs) of a-Si/a-Ge have been analysed to establish the reasons of H release during annealing that has been seen to bring about structural modifications even up to well-detectable surface degradation. Analyses carried out on single layers of a-Si and a-Ge show that H is released from its bond to the host lattice atom and that it escapes from the layer much more efficiently in a-Ge than in a-Si because of the smaller binding energy of the H-Ge bond and probably of a greater weakness of the Ge lattice. This should support the previous hypothesis that the structural degradation of a-Si/a-Ge MLs primary starts with the formation of H bubbles in the Ge layers.

  4. Avoiding chromium transport from stainless steel interconnects into contact layers and oxygen electrodes in intermediate temperature solid oxide electrolysis stacks

    NASA Astrophysics Data System (ADS)

    Schlupp, Meike V. F.; Kim, Ji Woo; Brevet, Aude; Rado, Cyril; Couturier, Karine; Vogt, Ulrich F.; Lefebvre-Joud, Florence; Züttel, Andreas

    2014-12-01

    We investigated the ability of (La0.8Sr0.2)(Mn0.5Co0.5)O3-δ (LSMC) and La(Ni0.6Fe0.4)O3-δ (LNF) contact coatings to avoid the transport of Cr from steel interconnects to solid oxide electrolysis electrodes, especially to the anode. The transport of chromium from commercial Crofer 22 APU (ThyssenKrupp) and K41X (AISI441, Aperam Isbergues) steels through LSMC and LNF contact coatings into adjacent (La0.8Sr0.2)MnO3-δ (LSM) oxygen electrodes was investigated in an oxygen atmosphere at 700 °C. Chromium concentrations of up to 4 atom% were detected in the contact coatings after thermal treatments for 3000 h, which also lead to the presence of chromium in adjacent LSM electrodes. Introduction of a dense (Co,Mn)3O4 coating between steel and contact coating was necessary to prevent the diffusion of chromium into contact coatings and electrodes and should lead to extended stack performance and lifetime.

  5. Solid-state dewetting of single- and bilayer Au-W thin films: Unraveling the role of individual layer thickness, stacking sequence and oxidation on morphology evolution

    NASA Astrophysics Data System (ADS)

    Herz, A.; Franz, A.; Theska, F.; Hentschel, M.; Kups, Th.; Wang, D.; Schaaf, P.

    2016-03-01

    Self-assembly of ultrathin Au, W, and Au-W bilayer thin films is investigated using a rapid thermal annealing technique in an inert ambient. The solid-state dewetting of Au films is briefly revisited in order to emphasize the role of initial film thickness. W films deposited onto SiO2 evolve into needle-like nanocrystals rather than forming particle-like agglomerates upon annealing at elevated temperatures. Transmission electron microscopy reveals that such nanocrystals actually consist of tungsten (VI) oxide (WO3) which is related to an anisotropic oxide crystal growth out of the thin film. The evolution of W films is highly sensitive to the presence of any residual oxygen. Combination of both the dewetting of Au and the oxide crystal growth of WO3 is realized by using various bilayer film configurations of the immiscible Au and W. At low temperature, Au dewetting is initiated while oxide crystal growth is still suppressed. Depending on the stacking sequence of the Au-W bilayer thin film, W acts either as a substrate or as a passivation layer for the dewetting of Au. Being the ground layer, W changes the wettability of Au which clearly modifies its initial state for the dewetting. Being the top layer, W prevents Au from dewetting regardless of Au film thickness. Moreover, regular pattern formation of Au-WO3 nanoparticles is observed at high temperature demonstrating how bilayer thin film dewetting can create unique nanostructure arrangements.

  6. The stratum corneum comprises three layers with distinct metal-ion barrier properties

    PubMed Central

    Kubo, Akiharu; Ishizaki, Itsuko; Kubo, Akiko; Kawasaki, Hiroshi; Nagao, Keisuke; Ohashi, Yoshiharu; Amagai, Masayuki

    2013-01-01

    The stratum corneum (SC), the outermost barrier of mammalian bodies, consists of layers of cornified keratinocytes with intercellular spaces sealed with lipids. The insolubility of the SC has hampered in-depth analysis, and the SC has been considered a homogeneous barrier. Here, we applied time-of-flight secondary ion mass spectrometry to demonstrate that the SC consists of three layers with distinct properties. Arginine, a major component of filaggrin-derived natural moisturizing factors, was concentrated in the middle layer, suggesting that this layer functions in skin hydration. Topical application of metal ions revealed that the outer layer allowed their passive influx and efflux, while the middle and lower layers exhibited distinct barrier properties, depending on the metal tested. Notably, filaggrin deficiency abrogated the lower layer barrier, allowing specific metal ions to permeate viable layers. These findings elucidate the multi-layered barrier function of the SC and its defects in filaggrin-deficient atopic disease patients. PMID:23615774

  7. Control of the optical and crystalline properties of TiO{sub 2} in visible-light active TiO{sub 2}/TiN bi-layer thin-film stacks

    SciTech Connect

    Smith, Wilson; Fakhouri, Houssam; Pulpytel, Jerome; Arefi-Khonsari, Farzaneh

    2012-01-15

    Multi-layered thin films of TiO{sub 2} and TiN were created by rf reactive magnetron sputtering, and their crystalline, optical, and photoelectrochemical properties were measured. The overall composition of the films (TiO{sub 2}-to-TiN ratio) was kept constant with the height of each film. The number of layers and thickness of each layer was controlled to create bi-layer thin films that were composed of: 9 bi-layers, 18 bi-layers, 27 bi-layers, 36 bi-layers, and 45 bi-layers. XRD patterns were observed for each film after annealing to measure the grain size and composition of anatase and rutile as a function of temperature. It was found that the phase-transition temperature is able to be substantially controlled (between 550 deg. C and 850 deg. C) for the anatase to rutile transition by varying the number of layers/thickness of each layer. In addition, bi-layer stacking significantly affected the film's optical properties by lowering the bandgap into the visible-light region, and also showed up to three times the improvement in photoelectrochemical performance under uv and visible irradiation. Overall, bi-layer stacking of TiO{sub 2}/TiN films has shown a unique and highly desirable control over several important physical characteristics that can be beneficial for many applications, such as high-temperature sensors and optoelectronic devices.

  8. Imaging the Structure of Grains, Grain Boundaries, and Stacking Sequences in Single and Multi-Layer Graphene

    NASA Astrophysics Data System (ADS)

    Muller, David

    2012-02-01

    Graphene can be produced by chemical vapor deposition (CVD) on copper substrates on up to meter scales [1, 2], making their polycrystallinity [3,4] almost unavoidable. By combining aberration-corrected scanning transmission electron microscopy and dark-field transmission electron microscopy, we image graphene grains and grain boundaries across six orders of magnitude. Atomic-resolution images of graphene grain boundaries reveal that different grains can stitch together via pentagon-heptagon pairs. We use diffraction-filtered electron imaging to map the shape and orientation of several hundred grains and boundaries over fields of view of a hundred microns. Single, double and multilayer graphene can be differentiated, and the stacking sequence and relative abundance of sequences can be directly imaged. These images reveal an intricate patchwork of grains with structural details depending strongly on growth conditions. The imaging techniques enabled studies of the structure, properties, and control of graphene grains and grain boundaries [5]. [4pt] [1] X. Li et al., Science 324, 1312 (2009).[0pt] [2] S. Bae et al., Nature Nanotechnol. 5, 574 (2010).[0pt] [3] J. M. Wofford, et al., Nano Lett., (2010).[0pt] [4] P. Y. Huang, et al., Nature 469, 389--392 (2011); arXiv:1009.4714, (2010)[0pt] [5] In collaboration with Pinshane Y. Huang, C. S. Ruiz-Vargas, A. M. van der Zande, A. W. Tsen, L. Brown, R. Hovden, F. Ghahari, W. S. Whitney, M.P. Levendorf, J. W. Kevek, S. Garg, J. S. Alden, C. J. Hustedt, Y. Zhu, N. Petrone, J. Hone, J. Park, P. L. McEuen

  9. Stacked insulator induction accelerator gaps

    SciTech Connect

    Houck, T.I.; Westenskow, G.A.; Kim, J.S.; Eylon, S.; Henestroza, E.; Yu, S.S.; Vanecek, D.

    1997-05-01

    Stacked insulators, with alternating layers of insulating material and conducting film, have been shown to support high surface electrical field stresses. We have investigated the application of the stacked insulator technology to the design of induction accelerator modules for the Relativistic-Klystron Two-Beam Accelerator program. The rf properties of the accelerating gaps using stacked insulators, particularly the impedance at frequencies above the beam pipe cutoff frequency, are investigated. Low impedance is critical for Relativistic-Klystron Two-Beam Accelerator applications where a high current, bunched beam is trsnsported through many accelerating gaps. An induction accelerator module designs using a stacked insulator is presented.

  10. Ordering and spin waves in NaNi O2 : A stacked quantum ferromagnet

    NASA Astrophysics Data System (ADS)

    Lewis, M. J.; Gaulin, B. D.; Filion, L.; Kallin, C.; Berlinsky, A. J.; Dabkowska, H. A.; Qiu, Y.; Copley, J. R. D.

    2005-07-01

    Neutron scattering measurements on powder NaNiO2 reveal magnetic Bragg peaks and spin waves characteristic of strongly correlated s=1/2 magnetic moments arranged in ferromagnetic layers which are stacked antiferromagnetically. This structure lends itself to stacking sequence frustration in the presence of mixing between nickel and alkali metal sites, possibly providing a natural explanation for the enigmatic spin glass state of the isostructural compound, LiNiO2 .

  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. Dislocated double-layer metal gratings: an efficient unidirectional coupler.

    PubMed

    Liu, Tianran; Shen, Yang; Shin, Wonseok; Zhu, Qiangzhong; Fan, Shanhui; Jin, Chongjun

    2014-07-09

    We propose theoretically and demonstrate experimentally a dislocated double-layer metal grating structure, which operates as a unidirectional coupler capable of launching surface plasmon polaritons in a desired direction under normal illumination. The structure consists of a slanted dielectric grating sandwiched between two gold gratings. The upper gold grating has a nonzero lateral relative displacement with respect to the lower one. Numerical simulations show that a grating structure with 7 periods can convert 49% of normally incident light into surface plasmons with a contrast ratio of 78 between the powers of the surface plasmons launched in two opposite directions. We explain the unidirectional coupling phenomenon by the dislocation-induced interference of the diffracted waves from the upper and lower gold gratings. Furthermore, we developed a simple and cost-effective technique to fabricate the structure via tilted two-beam interference lithography and subsequent shadow deposition of gold. The experimental results demonstrate a coupling efficiency of 36% and a contrast ratio of 43. The relatively simple periodic nature of our structure lends itself to large-scale low-cost fabrication and simple theoretical analysis. Also, unlike the previous unidirectional couplers based on aperiodic structures, the design parameters of our unidirectional coupler can be determined analytically. Therefore, this structure can be an important component for surface-plasmon-based nanophotonic circuits by providing an efficient interface between free-space and surface plasmon waves.

  13. Hybrid functional studies of defects in layered transition metal oxides

    NASA Astrophysics Data System (ADS)

    Hoang, Khang; Johannes, Michelle

    2014-03-01

    Layered oxides LiMO2 (M is a transition metal) have been studied extensively for Li-ion battery cathodes. It is known that defects have strong impact on the electrochemical performance. A detailed understanding of native point defects in LiMO2 is however still lacking, thus hindering rational design of more complex materials for battery applications. In fact, first-principles defect calculations in LiMO2 are quite challenging because standard density functional theory (DFT) calculations using the generalized gradient approximation (GGA) of the exchange-correlation functional fail to reproduce the correct physics. The GGA+U extension can produce reasonable results, but the transferability of U across the compounds is limited. In this talk, we present our DFT studies of defects in LiMO2 (M=Co, Ni) using the Heyd-Scuseria-Ernzerhof (HSE) screened hybrid functional. The dominant point defects will be identified and compared with experiment; and their impact on the structural stability and the charge (electronic and ionic) and mass transport will be addressed. We will also discuss possible shortcomings of the HSE functional in the study of these electron-correlated materials.

  14. 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.

  15. Low resistance barrier layer for isolating, adhering, and passivating copper metal in semiconductor fabrication

    DOEpatents

    Weihs, Timothy P.; Barbee, Jr., Troy W.

    2002-01-01

    Cubic or metastable cubic refractory metal carbides act as barrier layers to isolate, adhere, and passivate copper in semiconductor fabrication. One or more barrier layers of the metal carbide are deposited in conjunction with copper metallizations to form a multilayer characterized by a cubic crystal structure with a strong (100) texture. Suitable barrier layer materials include refractory transition metal carbides such as vanadium carbide (VC), niobium carbide (NbC), tantalum carbide (TaC), chromium carbide (Cr.sub.3 C.sub.2), tungsten carbide (WC), and molybdenum carbide (MoC).

  16. Multi-scale analysis of the diffusion barrier layer of gadolinia-doped ceria in a solid oxide fuel cell operated in a stack for 3000 h

    NASA Astrophysics Data System (ADS)

    Morales, M.; Miguel-Pérez, V.; Tarancón, A.; Slodczyk, A.; Torrell, M.; Ballesteros, B.; Ouweltjes, J. P.; Bassat, J. M.; Montinaro, D.; Morata, A.

    2017-03-01

    The state-of-the-art materials for SOFCs are yttria-stabilized zirconia as electrolyte and lanthanum strontium cobalt ferrite as cathode. However, the formation of insulating phases between them requires the use of diffusion barriers, typically made of gadolinia doped ceria. The study of the stability of this layer during the fabrication and in operando is currently one of the major goals of the SOFC industry. In this work, the cation inter-diffusion at the cathode/barrier layer/electrolyte region is analysed for an anode-supported cell industrially fabricated by conventional techniques, assembled in a short-stack and tested under real operation conditions for 3000 h. A comprehensive study of this cell, and an equivalent non-operated one, is performed in order to understand the inter-diffusion mechanisms with possible effects on the final performance. The analyses evidence that the cation diffusion is occurring during the fabrication process. Despite the significant diffusion of Ce,Gd, Zr, Y and Sr cations, the formation of typically reported CGO-YSZ solid solution is not observed while the presence of isolated grains of SrZrO3 is proved. All in all, this study presents new insights into the stability of the typically employed diffusion barriers for solid oxide cells that will guide future strategies to improve their performance and durability.

  17. Improving Metal-Oxide-Metal (MOM) Diode Performance Via the Optimization of the Oxide Layer

    NASA Astrophysics Data System (ADS)

    Dodd, Linzi E.; Shenton, Samantha A.; Gallant, Andrew J.; Wood, David

    2015-05-01

    Small area metal-oxide-metal (MOM) diodes are being investigated in many research groups for the detection of THz frequency radiation. In order to create a high-speed rectifying device, the central oxide layer of the MOM structure must be thin and have known physical characteristics. The thickness, structure and uniformity of the oxide can be controlled during the fabrication process. In the work presented here, the effects of both oxygen plasma concentration and annealing temperature during fabrication of MOM diodes have been explored. It has been found that, by reducing the oxygen gas concentration from previous work, the layer can be more repeatable and uniform. Furthermore, for an anneal temperature up to a threshold temperature in the to range, the performance of the diodes is excellent, with a value of zero-bias curvature coefficient (CCZB) that can be up to . For higher temperature treatments, the value of CCZB decreases to a maximum of . Similar trends in AC tests can be seen for voltage and current responsivity values.

  18. Metallic wave-impedance matching layers for broadband terahertz optical systems.

    PubMed

    Kröll, Josef; Darmo, Juraj; Unterrainer, Karl

    2007-05-28

    We examine the potential of ultra-thin metallic layers for broadband wave-impedance matching in the terahertz frequency range. The metallic layer is modeled using Fresnel formulae for stratified optical medium. Experimental data for chromium and indium-tin-oxide layers, measured using time-domain terahertz spectroscopy over the frequency range 0.4 - 4.5 THz, are compared with theoretical results.

  19. Thermal analysis of double-layer metal films during femtosecond laser heating

    NASA Astrophysics Data System (ADS)

    Chen, A. M.; Jiang, Y. F.; Sui, L. Z.; Liu, H.; Jin, M. X.; Ding, D. J.

    2011-05-01

    In this paper, the primary interest is the heat effect of the bottom-layer metal on the temperature distribution of the top-layer metal in a double-layer metal structure during femtosecond laser irradiation. The evolution of the surface electron and lattice temperature depends a lot on the thermal parameters of the substrate. The damage threshold can be increased by using a substrate material with high electron-lattice coupling factor. Next, we choose chrome as the bottom-layer material. The results of modeling show that the surface lattice temperature of top-layer gold can be reduced remarkably. For a fixed entire thickness of the double-layer film, there is an optimal proportion of top and bottom layers for which the damage threshold is the highest possible. Also, for increasing the damage threshold, a substrate with higher melting temperature should be chosen.

  20. Linear increase of the modal gain in 1.3 µm InAs/GaAs quantum dot lasers containing up to seven-stacked QD layers.

    PubMed

    Salhi, A; Rainò, G; Fortunato, L; Tasco, V; Martiradonna, L; Todaro, M T; De Giorgi, M; Cingolani, R; Passaseo, A; Luna, E; Trampert, A; De Vittorio, M

    2008-07-09

    The authors have recently demonstrated the enhancement of the quantum dot laser modal gain, linearly scaling with the number of stacked QD layers. These results allowed the achievement of multi-quantum dot (MQD) lasers, the zero-dimensional counterpart of MQW lasers, with a modal gain as high as 42 cm(-1), in a seven-layer structure. A detailed investigation of the structural and optical properties was performed on laser structures with three, five and seven QD layers. Such an investigation clearly shows that the high uniformity of QD layer features is responsible for the linear increase of the modal gain and its high value.

  1. Structural color-tunable mesoporous bragg stack layers based on graft copolymer self-assembly for high-efficiency solid-state dye-sensitized solar cells

    NASA Astrophysics Data System (ADS)

    Lee, Chang Soo; Park, Jung Tae; Kim, Jong Hak

    2016-08-01

    We present a facile fabrication route for structural color-tunable mesoporous Bragg stack (BS) layers based on the self-assembly of a cost-effective graft copolymer. The mesoporous BS layers are prepared through the alternating deposition of organized mesoporous-TiO2 (OM-TiO2) and -SiO2 (OM-SiO2) films on the non-conducting side of the counter electrode in dye-sensitized solar cells (DSSCs). The OM layers with controlled porosity, pore size, and refractive index are templated with amphiphilic graft copolymers consisting of poly(vinyl chloride) backbones and poly(oxyethylene methacrylate) side chains, i.e., PVC-g-POEM. The morphology and properties of the structural color-tunable mesoporous BS-functionalized electrodes are characterized using energy filtered transmission electron microscopy (EF-TEM), field emission-scanning electron microscopy (FE-SEM), spectroscopic ellipsometry, and reflectance spectroscopy. The solid-state DSSCs (ssDSSCs) based on a structural color-tunable mesoporous BS counter electrode with a single-component solid electrolyte show an energy conversion efficiency (η) of 7.1%, which is much greater than that of conventional nanocrystalline TiO2-based cells and one of the highest values for N719 dye-based ssDSSCs. The enhancement of η is due to the enhancement of current density (Jsc), attributed to the improved light harvesting properties without considerable decrease in fill factor (FF) or open-circuit voltage (Voc), as confirmed by incident photon-to-electron conversion efficiency (IPCE) and electrochemical impedance spectroscopy (EIS).

  2. Stacking Up

    ERIC Educational Resources Information Center

    Naylor, Jim

    2005-01-01

    Chimneys and stacks appear to be strong and indestructible, but chimneys begin to deteriorate from the moment they are built. Early on, no signs are apparent; but deterioration accelerates in subsequent years, and major repairs are soon needed instead of minor maintenance. With proper attention, most structures can be repaired and continue to…

  3. 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.

  4. Experimental investigation on coupling flows between liquid and liquid metal layers

    NASA Astrophysics Data System (ADS)

    Yano, Kanako; Tasaka, Yuji; Murai, Yuichi; Takeda, Yasushi; Yanagisawa, Takatoshi

    2008-11-01

    This study aims to clarify coupling of flows between liquid metal and other usual liquids, e.g. water or oil, in fluid dynamical systems. In past studies for two-layer Rayleigh-Bénard system where the immiscible two liquids are layered, two types of coupling were observed; these are called as ``mechanical coupling'' and ``thermal coupling.'' As a typical character of low Pr fluid, large-scale structure in the liquid metal layer has oscillating motion. In this study we investigate ``thermal coupling'' especially how the oscillation of cells in the liquid metal layer propagates to the upper liquid layer and vice versa by changing a ratio of the height of the layers and viscosity of the upper layer fluid. Visualization of the liquid metal motion was conducted by means of ultrasonic velocity profiling, and then the oscillating motion is expressed on the space-time velocity map. PIV measurement of the upper, transparent fluid layer shows the modulation of the convective motion due to the oscillation in the liquid metal layer. Point-wise measurement of temperature at several positions in the fluid layer represents the modulation quantitatively.

  5. 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.

  6. Effect of GeO2 deposition temperature in atomic layer deposition on electrical properties of Ge gate stack

    NASA Astrophysics Data System (ADS)

    Kanematsu, Masayuki; Shibayama, Shigehisa; Sakashita, Mitsuo; Takeuchi, Wakana; Nakatsuka, Osamu; Zaima, Shigeaki

    2016-08-01

    We investigated the effect of GeO2 deposition temperature (T depo) on electronic properties of Al/Al2O3/GeO2/Ge MOS capacitors. Capacitance-voltage characteristics show frequency dispersions under depletion and strong inversion conditions, which can be attributed from the interface states at the atomic layer deposition (ALD)-GeO2/Ge interface and from the defect states in the quasi-neutral region in the Ge substrate, respectively. We found that the interface state density (D it) shows similar values and energy distributions as T depo decreases to 200 from 300 °C, while a higher D it is observed at a T depo of 150 °C. Also, from the temperature dependence of conductance, the frequency dispersion under the strong inversion condition can be related to the minority carrier diffusion to the quasi-neutral region of the Ge substrate. The frequency dependence of conductance reveals that the undesirable increment of the bulk defect density can be suppressed by decreasing T depo. In this study, the bulk defect density in a MOS capacitor prepared at a T depo of 200 °C decreases one tenth compared with that at a T depo of 300 °C. The ALD of GeO2 at a low temperature of around 200 °C is effective for both obtaining a low D it and preventing the undesirable introduction of bulk defect density.

  7. New Method to Determine the Schottky Barrier in Few-Layer Black Phosphorus Metal Contacts.

    PubMed

    Lee, Su Yeong; Yun, Won Seok; Lee, J D

    2017-03-01

    Schottky barrier height and carrier polarity are seminal concepts for a practical device application of the interface between semiconductor and metal electrode. Investigation of those concepts is usually made by a conventional method such as the Schottky-Mott rule, incorporating the metal work function and semiconductor electron affinity, or the Fermi level pinning effect, resulting from the metal-induced gap states. Both manners are, however, basically applied to the bulk semiconductor metal contacts. To explore few-layer black phosphorus metal contacts far from the realm of bulk, we propose a new method to determine the Schottky barrier by scrutinizing the layer-by-layer phosphorus electronic structure from the first-principles calculation combined with the state-of-the-art band unfolding technique. In this study, using the new method, we calculate the Schottky barrier height and determine the contact polarity of Ti, Sc, and Al metal contacts to few-layer (mono-, bi-, tri-, and quadlayer) black phosphorus. This gives a significant physical insight toward the utmost layer-by-layer manipulation of electronic properties of few-layer semiconductor metal contacts.

  8. Considerably improved photovoltaic performance of carbon nanotube-based solar cells using metal oxide layers.

    PubMed

    Wang, Feijiu; Kozawa, Daichi; Miyauchi, Yuhei; Hiraoka, Kazushi; Mouri, Shinichiro; Ohno, Yutaka; Matsuda, Kazunari

    2015-02-18

    Carbon nanotube-based solar cells have been extensively studied from the perspective of potential application. Here we demonstrated a significant improvement of the carbon nanotube solar cells by the use of metal oxide layers for efficient carrier transport. The metal oxides also serve as an antireflection layer and an efficient carrier dopant, leading to a reduction in the loss of the incident solar light and an increase in the photocurrent, respectively. As a consequence, the photovoltaic performance of both p-single-walled carbon nanotube (SWNT)/n-Si and n-SWNT/p-Si heterojunction solar cells using MoOx and ZnO layers is improved, resulting in very high photovoltaic conversion efficiencies of 17.0 and 4.0%, respectively. These findings regarding the use of metal oxides as multifunctional layers suggest that metal oxide layers could improve the performance of various electronic devices based on carbon nanotubes.

  9. Considerably improved photovoltaic performance of carbon nanotube-based solar cells using metal oxide layers

    NASA Astrophysics Data System (ADS)

    Wang, Feijiu; Kozawa, Daichi; Miyauchi, Yuhei; Hiraoka, Kazushi; Mouri, Shinichiro; Ohno, Yutaka; Matsuda, Kazunari

    2015-02-01

    Carbon nanotube-based solar cells have been extensively studied from the perspective of potential application. Here we demonstrated a significant improvement of the carbon nanotube solar cells by the use of metal oxide layers for efficient carrier transport. The metal oxides also serve as an antireflection layer and an efficient carrier dopant, leading to a reduction in the loss of the incident solar light and an increase in the photocurrent, respectively. As a consequence, the photovoltaic performance of both p-single-walled carbon nanotube (SWNT)/n-Si and n-SWNT/p-Si heterojunction solar cells using MoOx and ZnO layers is improved, resulting in very high photovoltaic conversion efficiencies of 17.0 and 4.0%, respectively. These findings regarding the use of metal oxides as multifunctional layers suggest that metal oxide layers could improve the performance of various electronic devices based on carbon nanotubes.

  10. Polarization-dependent plasmonic coupling in dual-layer metallic structures at terahertz frequencies.

    PubMed

    Zhang, Zhong Xiang; Chan, Kam Tai

    2011-01-31

    Dual-layer metallic wire-hole structures were fabricated and their terahertz transmission properties were measured. They exhibit polarization-dependent transmittance with large extinction ratios. Simulation and experimental results on structures with different wire-to-hole orientations provide strong evidence that the resonance peaks are caused by plasmonic coupling between the two metallic layers. A simplified LC-circuit model is proposed to explain the coupling mechanism and to estimate the peak frequencies. Our results suggest that specific electromagnetic response can be achieved by appropriate design of the geometrical patterns on the two metallic layers and a suitable polarization of the incident wave.

  11. Structural and electrical characteristics of ALD-HfO2/n-Si gate stack with SiON interfacial layer for advanced CMOS technology

    NASA Astrophysics Data System (ADS)

    Gupta, Richa; Rajput, Renu; Prasher, Rakesh; Vaid, Rakesh

    2016-09-01

    We report the fabrication of an ultra-thin silicon oxynitride (SiON) as an interfacial layer (IL) for n-Si/ALD-HfO2 gate stack with reduced leakage current. The XRD, AFM, FTIR, FESEM and EDAX characterizations have been performed for structural and morphological studies. Electrical parameters such as dielectric constant (K), interface trap density (Dit), leakage current density (J), effective oxide charge (Qeff), barrier height (Φbo), ideality factor (ƞ), breakdown-voltage (Vbr) and series resistance (Rs) were extracted through C-V, G-V and I-V measurements. The determined values of K, Dit, J, Qeff, Φbo, ƞ, Vbr and Rs are 14.4, 0.5 × 10 11 eV-1 cm-2, 2.2 × 10-9 A/cm2, 0.3 × 1013 cm-2, 0.42, 2.1, -0.33 and 14.5 MΩ respectively. SiON growth prior to HfO2 deposition has curtailed the problem of high leakage current density and interfacial traps due to sufficient amount of N2 incorporated at the interface.

  12. Polytypism in LaOBi S2 -type compounds based on different three-dimensional stacking sequences of two-dimensional Bi S2 layers

    NASA Astrophysics Data System (ADS)

    Liu, Qihang; Zhang, Xiuwen; Zunger, Alex

    2016-05-01

    LaOBi S2 -type materials have drawn much attention recently because of various interesting physical properties, such as low-temperature superconductivity, hidden spin polarization, and electrically tunable Dirac cones. However, it was generally assumed that each LaOBi S2 -type compound has a unique and specific crystallographic structure (with a space group P 4 /nmm) separated from other phases. Using first-principles total energy and stability calculations we confirm that the previous assignment of the P 4 /nmm structure to LaOBi S2 is incorrect. Furthermore, we find that the unstable structure is replaced by a family of energetically closely spaced modifications (polytypes) differing by the layer sequences and orientations. We find that the local Bi-S distortion leads to three polytypes of LaOBi S2 with different stacking patterns of the distorted Bi S2 layers. The energy difference between the polytypes of LaOBi S2 is merely ˜1 meV/u.c., indicating the possible coexistence of all polytypes in the real sample and that the particular distribution of polytypes may be growth induced. The in-plane distortion can be suppressed by pressure, leading to a phase transition from polytypes to the high-symmetry P 4 /nmm structure with a pressure larger than 2.5 GPa. In addition, different choices of the intermediate atoms (replacing La) or active atoms (Bi S2 ) could also manifest different ground-state structures. One can thus tune the distortion and the ground state by pressure or by substituting covalence atoms in the LaOBi S2 family.

  13. Electronically decoupled stacking fault tetrahedra embedded in Au(111) films

    PubMed Central

    Schouteden, Koen; Amin-Ahmadi, Behnam; Li, Zhe; Muzychenko, Dmitry; Schryvers, Dominique; Van Haesendonck, Chris

    2016-01-01

    Stacking faults are known as defective structures in crystalline materials that typically lower the structural quality of the material. Here, we show that a particular type of defect, that is, stacking fault tetrahedra (SFTs), exhibits pronounced quantized electronic behaviour, revealing a potential synthetic route to decoupled nanoparticles in metal films. We report on the electronic properties of SFTs that exist in Au(111) films, as evidenced by scanning tunnelling microscopy and confirmed by transmission electron microscopy. We find that the SFTs reveal a remarkable decoupling from their metal surroundings, leading to pronounced energy level quantization effects within the SFTs. The electronic behaviour of the SFTs can be described well by the particle-in-a-box model. Our findings demonstrate that controlled preparation of SFTs may offer an alternative way to achieve well-decoupled nanoparticles of high crystalline quality in metal thin films without the need of thin insulating layers. PMID:28008910

  14. Electronically decoupled stacking fault tetrahedra embedded in Au(111) films

    NASA Astrophysics Data System (ADS)

    Schouteden, Koen; Amin-Ahmadi, Behnam; Li, Zhe; Muzychenko, Dmitry; Schryvers, Dominique; Van Haesendonck, Chris

    2016-12-01

    Stacking faults are known as defective structures in crystalline materials that typically lower the structural quality of the material. Here, we show that a particular type of defect, that is, stacking fault tetrahedra (SFTs), exhibits pronounced quantized electronic behaviour, revealing a potential synthetic route to decoupled nanoparticles in metal films. We report on the electronic properties of SFTs that exist in Au(111) films, as evidenced by scanning tunnelling microscopy and confirmed by transmission electron microscopy. We find that the SFTs reveal a remarkable decoupling from their metal surroundings, leading to pronounced energy level quantization effects within the SFTs. The electronic behaviour of the SFTs can be described well by the particle-in-a-box model. Our findings demonstrate that controlled preparation of SFTs may offer an alternative way to achieve well-decoupled nanoparticles of high crystalline quality in metal thin films without the need of thin insulating layers.

  15. Electronically decoupled stacking fault tetrahedra embedded in Au(111) films.

    PubMed

    Schouteden, Koen; Amin-Ahmadi, Behnam; Li, Zhe; Muzychenko, Dmitry; Schryvers, Dominique; Van Haesendonck, Chris

    2016-12-23

    Stacking faults are known as defective structures in crystalline materials that typically lower the structural quality of the material. Here, we show that a particular type of defect, that is, stacking fault tetrahedra (SFTs), exhibits pronounced quantized electronic behaviour, revealing a potential synthetic route to decoupled nanoparticles in metal films. We report on the electronic properties of SFTs that exist in Au(111) films, as evidenced by scanning tunnelling microscopy and confirmed by transmission electron microscopy. We find that the SFTs reveal a remarkable decoupling from their metal surroundings, leading to pronounced energy level quantization effects within the SFTs. The electronic behaviour of the SFTs can be described well by the particle-in-a-box model. Our findings demonstrate that controlled preparation of SFTs may offer an alternative way to achieve well-decoupled nanoparticles of high crystalline quality in metal thin films without the need of thin insulating layers.

  16. The Deep2 Galaxy Redshift Survey: Mean Ages and Metallicities ofRed Field Galaxies at Z ~; 0.9 from Stacked Keck/Deimos Spectra

    SciTech Connect

    Schiavon, Ricardo P.; Faber, S.M.; Konidaris, Nicholas; Graves,Genevieve; Willmer, Christopher N.A.; Weiner, Benjamin J.; Coil, AlisonL.; Cooper, Michael C.; Davis, Marc; Harker, Justin; Koo, David C.; Newman, Jeffrey A.; Yan, Renbin

    2006-10-19

    As part of the DEEP2 galaxy redshift survey, we analyze absorption line strengths in stacked Keck/DEIMOS spectra of red field galaxies with weak to no emission lines, at redshifts 0.7 {approx}< z {approx}< 1. Comparison with models of stellar population synthesis shows that red galaxies at z {approx} 0:9 have mean luminosity-weighted ages of the order of only 1 Gyr and at least solar metallicities. These ages cannot be reconciled with a scenario where all stars evolved passively after forming at very high z. Rather, a significant fraction of stars can be no more than 1 Gyr old, which means that some star formation in the stacked populations continued to at least z {approx} 1:2. Furthermore, a comparison of these distant galaxies with a local SDSS sample, using stellar populations synthesis models, shows that the drop in the equivalent width of H{delta} from z {approx} 0:9 to 0.1 is less than predicted by passively evolving models. This admits of two interpretations: either each individual galaxy experiences continuing low-level star formation, or the red-sequence galaxy population from z {approx} 0:9 to 0.1 is continually being added to by new galaxies with younger stars.

  17. Combining field-amplified sample stacking with moving reaction boundary electrophoresis on a paper chip for the preconcentration and separation of metal ions.

    PubMed

    Ouyang, Liangfei; Liu, Qian; Liang, Heng

    2017-02-01

    A common drawback of paper-based separation devices is their poor detection limit. In this study, we combined field-amplified sample stacking with moving reaction boundary electrophoresis on a paper chip with six array channels for the parallel separation and concentration of multiple samples. With a new hyphenated technique, the brown I2 from the Fe(3+) /I(-) oxidation-reduction reaction emerged near the boundary between the dilute ethylene diamine tetraacetic acid and potassium iodide and highly concentrated KCl solutions. For the separation and concentration of three components, Cr(3+) , Cu(2+) , and Fe(3+) , the Fe(3+) detection limit was improved at least 266-fold by comparing the hyphenated technique with moving reaction boundary electrophoresis. The detection limit of Fe(3+) was found to be as low as 0.34 ng (20 μM) on the paper chip. We also demonstrated the analysis of a real sample of four metal ions, with detection limits as follows: 0.16 μg Cr(3+) , 1.5 μg Ni(2+) , 0.64 μg Cu(2+) , and 1.5 μg Co(2+) . The synergy of field-amplified sample stacking and moving reaction boundary electrophoresis in the micron paper-based array channels dramatically improved the detection limit and throughput of paper-based electrophoresis.

  18. Image stacking approach to increase sensitivity of fluorescence detection using a low cost complementary metal-oxide-semiconductor (CMOS) webcam

    PubMed Central

    Balsam, Joshua; Bruck, Hugh Alan; Kostov, Yordan; Rasooly, Avraham

    2013-01-01

    Optical technologies are important for biological analysis. Current biomedical optical analyses rely on high-cost, high-sensitivity optical detectors such as photomultipliers, avalanched photodiodes or cooled CCD cameras. In contrast, Webcams, mobile phones and other popular consumer electronics use lower-sensitivity, lower-cost optical components such as photodiodes or CMOS sensors. In order for consumer electronics devices, such as webcams, to be useful for biomedical analysis, they must have increased sensitivity. We combined two strategies to increase the sensitivity of CMOS-based fluorescence detector. We captured hundreds of low sensitivity images using a Webcam in video mode, instead of a single image typically used in cooled CCD devices.We then used a computational approach consisting of an image stacking algorithm to remove the noise by combining all of the images into a single image. While video mode is widely used for dynamic scene imaging (e.g. movies or time-lapse photography), it is not used to capture a single static image, which removes noise and increases sensitivity by more than thirty fold. The portable, battery-operated Webcam-based fluorometer system developed here consists of five modules: (1) a low cost CMOS Webcam to monitor light emission, (2) a plate to perform assays, (3) filters and multi-wavelength LED illuminator for fluorophore excitation, (4) a portable computer to acquire and analyze images, and (5) image stacking software for image enhancement. The samples consisted of various concentrations of fluorescein, ranging from 30 μM to 1000 μM, in a 36-well miniature plate. In the single frame mode, the fluorometer's limit-of-detection (LOD) for fluorescein is ∼1000 μM, which is relatively insensitive. However, when used in video mode combined with image stacking enhancement, the LOD is dramatically reduced to 30 μM, sensitivity which is similar to that of state-of-the-art ELISA plate photomultiplier-based readers. Numerous medical

  19. Superior Stable and Long Life Sodium Metal Anodes Achieved by Atomic Layer Deposition.

    PubMed

    Zhao, Yang; Goncharova, Lyudmila V; Lushington, Andrew; Sun, Qian; Yadegari, Hossein; Wang, Biqiong; Xiao, Wei; Li, Ruying; Sun, Xueliang

    2017-03-03

    Na-metal batteries are considered as the promising alternative candidate for Li-ion battery beneficial from the wide availability and low cost of sodium, high theoretical specific capacity, and high energy density based on the plating/stripping processes and lowest electrochemical potential. For Na-metal batteries, the crucial problem on metallic Na is one of the biggest challenges. Mossy or dendritic growth of Na occurs in the repetitive Na stripping/plating process with an unstable solid electrolyte interphase layer of nonuniform ionic flux, which can not only lead to the low Coulombic efficiency, but also can create short circuit risks, resulting in possible burning or explosion. In this communication, the atomic layer deposition of Al2 O3 coating is first demonstrated for the protection of metallic Na anode for Na-metal batteries. By protecting Na foil with ultrathin Al2 O3 layer, the dendrites and mossy Na formation have been effectively suppressed and lifetime has been significantly improved. Furthermore, the thickness of protective layer has been further optimized with 25 cycles of Al2 O3 layer presenting the best performance over 500 cycles. The novel design of atomic layer deposition protected metal Na anode may bring in new opportunities to the realization of the next-generation high energy-density Na metal batteries.

  20. Series resistance effect on time zero dielectrics breakdown characteristics of MOSCAP with ultra-thin EOT high-k/metal gate stacks

    NASA Astrophysics Data System (ADS)

    Hao, Xu; Hong, Yang; Yanrong, Wang; Wenwu, Wang; Guangxing, Wan; Shangqing, Ren; Weichun, Luo; Luwei, Qi; Chao, Zhao; Dapeng, Chen; Xinyu, Liu; Tianchun, Ye

    2016-05-01

    The time zero dielectric breakdown characteristics of MOSCAP with ultra-thin EOT high-k metal gate stacks are studied. The TZDB results show an abnormal area dependence due to the series resistance effect. The series resistance components extracted from the Fowler-Nordheim tunneling relation are attributed to the spreading resistance due to the asymmetry electrodes. Based on a series model to eliminate the series resistance effect, an area acceleration dependence is obtained by correcting the TZDB results. The area dependence follows Poisson area scaling rules, which indicates that the mechanism of TZDB is the same as TDDB and could be considered as a trap generation process. Project supported by the National High Technology Research and Development Program (863 Program) of China (No. SS2015AA010601), the National Natural Science Foundation of China (Nos. 61176091, 61306129), and the Opening Project of the Key Laboratory of Microelectronics Devices & Integrated Technology, Institute of Microelectronics, Chinese Academy of Sciences.

  1. Surface plasmon dispersion engineering via double-metallic AU/AG layers for nitride light-emitting diodes

    DOEpatents

    Tansu, Nelson; Zhao, Hongping; Zhang, Jing; Liu, Guangyu

    2014-04-01

    A double-metallic deposition process is used whereby adjacent layers of different metals are deposited on a substrate. The surface plasmon frequency of a base layer of a first metal is tuned by the surface plasmon frequency of a second layer of a second metal formed thereon. The amount of tuning is dependent upon the thickness of the metallic layers, and thus tuning can be achieved by varying the thicknesses of one or both of the metallic layers. In a preferred embodiment directed to enhanced LED technology in the green spectrum regime, a double-metallic Au/Ag layer comprising a base layer of gold (Au) followed by a second layer of silver (Ag) formed thereon is deposited on top of InGaN/GaN quantum wells (QWs) on a sapphire/GaN substrate.

  2. The Deformation of the Multi-Layered Panel of Sheet Metals Under Elevated Temperatures

    NASA Astrophysics Data System (ADS)

    Lee, Sang-Wook; Woo, Dong-Uk

    A Molten Carbonate Fuel Cell (MCFC) stack consists of several layered unit cells. In each unit cell, the stiff structure of the separator plate contains the softer components, such as electrodes. When surface pressure acts on the stack over an extended period of time at elevated temperatures, the stiffness of the separator plate tends to degrade. Moreover, the demands for large electrode area (to increase the electric capacity of a unit cell) and thinner separator plates (to reduce weight) complicate the design of a separator plate with high stiffness. To evaluate the stiffness of the separator plate at elevated temperatures, we design and test a tiny, multi-layered separator plate specimen using a three-point bending tool. To determine the optimal structure of the separator plate, we investigate three design factors: angle, pitch and height. We adopt the Taguchi method to evaluate the experiments, and use finite element analysis to examine the experimental results. Based on these results, pitch is the most effective of these factors. As the pitch narrows, the stiffness of the separator plate increases. Therefore, we propose the pitch factor as a design criterion for the separator plate of the MCFC stack.

  3. Thermal analysis of thin multi-layer metal films during femtosecond laser heating

    NASA Astrophysics Data System (ADS)

    Karakas, A.; Tunc, M.; Camdali, Ü.

    2010-12-01

    Multi-layer metals films are widely used in modern engineering applications such as gold-coated metal mirrors used in high power laser systems. A transient heat flux model is derived to analyze multi-layer metal films under laser heating. The two separate system composed of electrons and the lattice is considered to take into account the electron-lattice interaction. The present model predicted the effects of underlying chromium's thermal properties on temperature rise of the top gold layer. The effects of two adjacent and different metals with different electron-lattice coupling factors are analyzed for the heating mechanism of different lattices. The derived transient model combined with the two different conservation equations for the lattice and electrons are applied for the ultra short-pulse laser heating of a multi-layer film composed of gold and chromium.

  4. Modeling Metallic Ion Transport During the Lifetime of an Intermediate Layer

    NASA Astrophysics Data System (ADS)

    Bishop, R. L.; Earle, G. D.

    2001-05-01

    Intermediate layers are one of several phenomena that occur at midlatitudes in the nighttime E region. These ionization layers which typically form on the bottomside of the F region, are frequently observed by the Arecibo Incoherent Scatter Facility. Although their occurrence is relatively common, they exhibit diverse structure. Their altitude of formation, vertical thickness, and motion show significant nightly variations. Layer structure is influenced by a number of factors including composition, electric fields, and fluctuations in the neutral wind field. A numerical simulation has been employed to investigate the effects of composition on layer development. Specifically, the simulation, named LEAD (Layer Evolution And Dynamics), explores the transport of metallic ions during the formation and subsequent motion of a layer due to a time varying meridional wind field. We discuss the relative molecular/metallic ratio inside the layer during its evolution, the time scales for metallic ion dominance within the layer, and the motion of metallic ions in the adjacent altitude regions. We present animated results from LEAD which allow detailed inspection of ion composition variations throughout the process of layer evolution and descent.

  5. 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.

  6. Improvement of corrosion resistance of transparent conductive multilayer coating consisting of silver layers and transparent metal oxide layers

    SciTech Connect

    Koike, Katsuhiko; Yamazaki, Fumiharu; Okamura, Tomoyuki; Fukuda, Shin

    2007-05-15

    An optical filter for plasma display panel (PDP) requires an electromagnetic shield with very high ability. The authors investigated a transparent conductive multilayer coating consisting of silver (Ag) layers and transparent metal oxide layers. The durability of the multilayer sputter coating, including the silver layer, is very sensitive to the surrounding atmosphere. For example, after an exposure test they found discolored points on the multilayer sputter coatings, possibly caused by migration of silver atoms in the silver layers. In their investigation, they modified the top surface of the multilayer sputter coatings with transition metals to improve the corrosion resistance of the multilayer coating. Specifically, they deposited transition metals 0.5-2 nm thick on the top surface of the multilayer coatings by sputtering. They chose indium tin oxide (ITO) as the transparent metal oxide. They applied the multilayer sputter coatings of seven layers to a polyethylene terephthalate (PET) film substrate. A cross-sectional structure of the film with the multilayer coatings is PET film/ITO/Ag/ITO/Ag/ITO/Ag/ITO. They evaluated the corrosion resistance of the films by a salt-water immersion test. In the test, they immersed the film with multilayer coatings into salt water, and then evaluated the appearance, transmittance, and electrical resistance of the multilayer coatings. They investigated several transition metals as the modifying material, and found that titanium and tantalum drastically improved the resistance of the multilayer coatings to the salt-water exposure without a significant decline in transmittance. They also investigated the relation between elapsed time after deposition of the modifying materials and resistance to the salt water. Furthermore, they investigated the effects of a heat treatment and an oxide plasma treatment on resistance to the salt water.

  7. Electrical characterization of thulium silicate interfacial layers for integration in high-k/metal gate CMOS technology

    NASA Astrophysics Data System (ADS)

    Dentoni Litta, Eugenio; Hellström, Per-Erik; Henkel, Christoph; Östling, Mikael

    2014-08-01

    This work presents a characterization of the electrical properties of thulium silicate thin films, within the scope of a possible application as IL (interfacial layer) in scaled high-k/metal gate CMOS technology. Silicate formation is investigated over a wide temperature range (500-900 °C) through integration in MOS capacitor structures and analysis of the resulting electrical properties. The results are compared to those obtained from equivalent devices integrating lanthanum silicate interfacial layers. The thulium silicate IL is formed through a gate-last CMOS-compatible process flow, providing IL EOT of 0.1-0.3 nm at low formation temperature and interface state density at flatband condition below 2 × 1011 cm-2 eV-1. The effects of a possible integration in a gate-first process flow with a maximum thermal budget of 1000 °C are also evaluated, achieving an IL EOT of 0.2-0.5 nm, an interface state density at flatband condition ∼1 × 1011 cm-2 eV-1 and a reduction in gate leakage current density of one order of magnitude compared to the same stack without IL.

  8. Iridium Interfacial Stack - IrIS

    NASA Technical Reports Server (NTRS)

    Spry, David

    2012-01-01

    Iridium Interfacial Stack (IrIS) is the sputter deposition of high-purity tantalum silicide (TaSi2-400 nm)/platinum (Pt-200 nm)/iridium (Ir-200 nm)/platinum (Pt-200 nm) in an ultra-high vacuum system followed by a 600 C anneal in nitrogen for 30 minutes. IrIS simultaneously acts as both a bond metal and a diffusion barrier. This bondable metallization that also acts as a diffusion barrier can prevent oxygen from air and gold from the wire-bond from infiltrating silicon carbide (SiC) monolithically integrated circuits (ICs) operating above 500 C in air for over 1,000 hours. This TaSi2/Pt/Ir/Pt metallization is easily bonded for electrical connection to off-chip circuitry and does not require extra anneals or masking steps. There are two ways that IrIS can be used in SiC ICs for applications above 500 C: it can be put directly on a SiC ohmic contact metal, such as Ti, or be used as a bond metal residing on top of an interconnect metal. For simplicity, only the use as a bond metal is discussed. The layer thickness ratio of TaSi2 to the first Pt layer deposited thereon should be 2:1. This will allow Si from the TaSi2 to react with the Pt to form Pt2Si during the 600 C anneal carried out after all layers have been deposited. The Ir layer does not readily form a silicide at 600 C, and thereby prevents the Si from migrating into the top-most Pt layer during future anneals and high-temperature IC operation. The second (i.e., top-most) deposited Pt layer needs to be about 200 nm to enable easy wire bonding. The thickness of 200 nm for Ir was chosen for initial experiments; further optimization of the Ir layer thickness may be possible via further experimentation. Ir itself is not easily wire-bonded because of its hardness and much higher melting point than Pt. Below the iridium layer, the TaSi2 and Pt react and form desired Pt2Si during the post-deposition anneal while above the iridium layer remains pure Pt as desired to facilitate easy and strong wire-bonding to the Si

  9. Emerging interface dipole versus screening effect in copolymer/metal nano-layered systems

    NASA Astrophysics Data System (ADS)

    Torrisi, V.; Ruffino, F.; Liscio, A.; Grimaldi, M. G.; Marletta, G.

    2015-12-01

    Despite to the importance on the charge carrier injection and transport at organic/metal interface, there is yet an incomplete estimation of the various contribution to the overall dipole. This work shows how the mapping of the surface potential performed by Kelvin Probe Force Microscopy (KPFM) allows the direct observation of the interface dipole within an organic/metal multilayered structure. Moreover, we show how the sub-surface sensitivity of the KPFM depends on the thickness and surface coverage of the metallic layer. This paper proposes a way to control the surface potential of the exposed layer of an hybrid layered system by controlling the interface dipole at the organic/metal interface as a function of the nanometer scale thickness and the surface coverage of the metallic layer. We obtained a layered system constituted by repeated sequence of a copolymer film, poly(n-butylacrylate)-b-polyacrilic acid, and Au layer. We compared the results obtained by means of scanning probe microscopy technique with the results of the KPFM technique, that allows us to obtain high-contrast images of the underlying layer of copolymer behind a typical threshold, on the nanoscale, of the thickness of the metal layer. We considered the effect of the morphology of the gold layer on the covered area at different thicknesses by using the scanning electron microscopy technique. This finding represents a step forward towards the using of dynamic atomic force microscopy based characterization to explore the electrical properties of the sub-surface states of layered nanohybrid, that is a critical point for nanohybrid applications in sensors and energy storage devices.

  10. Double sporadic metal layers as observed by colocated Fe and Na lidars at Wuhan, China

    NASA Astrophysics Data System (ADS)

    Wang, Xiaodong; Yi, Fan; Huang, Kaiming

    2017-02-01

    In this paper, we report a set of double sporadic layer events observed by Fe and Na lidars over Wuhan, China. The two sporadic metal layers above normal layer were named as upper and middle sporadic metal layers, respectively. In these events, the upper, middle, and normal Fe layers presented altitude separately. There were nine double sporadic Fe events observed in 163 nights during 2010-2013. Eight of the nine events were observed in summer. The maximum ratios of peak density for upper and middle sporadic Fe layers to normal Fe layer were up to 375% and 225%, respectively. The peak altitudes of upper (middle) sporadic Fe layers were in the range of 102-107 km (95-98.5 km). The double sporadic Fe layers lasted more than 2 h. Interestingly, we found that density enhancement occurred simultaneously in upper, middle, and normal Fe layers on two events. On the nine Fe events, there existed five nights of colocated Na lidar observations. We found that double sporadic Na and Fe layers simultaneously appeared. They presented similar structures, altitudes, and temporal variations in all five compared events. A little different from Fe, the middle sporadic Na layer was not separated from Na main layer maybe for the wide altitude range of Na main layer. The ratios of upper (middle) sporadic Fe and Na peak values were in the range of 6.6-52 (0.57-6.58). While the exact formation mechanism responsible for double sporadic metal layers is still unclear, some possible explanations and corresponding observations are discussed.

  11. Spectral and total temperature-dependent emissivities of few-layer structures on a metallic substrate.

    PubMed

    Blandre, Etienne; Chapuis, Pierre-Olivier; Vaillon, Rodolphe

    2016-01-25

    We investigate the thermal radiative emission of few-layer structures deposited on a metallic substrate and its dependence on temperature with the Fluctuational Electrodynamics approach. We highlight the impact of the variations of the optical properties of metallic layers on their temperature-dependent emissivity. Fabry-Pérot spectral selection involving at most two transparent layers and one thin reflective layer leads to well-defined peaks and to the amplification of the substrate emission. For a single Fabry-Pérot layer on a reflective substrate, an optimal thickness that maximizes the emissivity of the structure can be determined at each temperature. A thin lossy layer deposited on the previous structure can enhance interference phenomena, and the analysis of the participation of each layer to the emission shows that the thin layer is the main source of emission. Eventually, we investigate a system with two Fabry-Pérot layers and a metallic thin layer, and we show that an optimal architecture can be found. The total hemispherical emissivity can be increased by one order of magnitude compared to the substrate emissivity.

  12. Stacking orders induced direct band gap in bilayer MoSe2-WSe2 lateral heterostructures

    PubMed Central

    Hu, Xiaohui; Kou, Liangzhi; Sun, Litao

    2016-01-01

    The direct band gap of monolayer semiconducting transition-metal dichalcogenides (STMDs) enables a host of new optical and electrical properties. However, bilayer STMDs are indirect band gap semiconductors, which limits its applicability for high-efficiency optoelectronic devices. Here, we report that the direct band gap can be achieved in bilayer MoSe2-WSe2 lateral heterostructures by alternating stacking orders. Specifically, when Se atoms from opposite layers are stacked directly on top of each other, AA and A’B stacked heterostructures show weaker interlayer coupling, larger interlayer distance and direct band gap. Whereas, when Se atoms from opposite layers are staggered, AA’, AB and AB’ stacked heterostructures exhibit stronger interlayer coupling, shorter interlayer distance and indirect band gap. Thus, the direct/indirect band gap can be controllable in bilayer MoSe2-WSe2 lateral heterostructures. In addition, the calculated sliding barriers indicate that the stacking orders of bilayer MoSe2-WSe2 lateral heterostructures can be easily formed by sliding one layer with respect to the other. The novel direct band gap in bilayer MoSe2-WSe2 lateral heterostructures provides possible application for high-efficiency optoelectronic devices. The results also show that the stacking order is an effective strategy to induce and tune the band gap of layered STMDs. PMID:27528196

  13. Surface and Interface Chemistry for Gate Stacks on Silicon

    NASA Astrophysics Data System (ADS)

    Frank, M. M.; Chabal, Y. J.

    This chapter addresses the fundamental silicon surface science associated with the continued progress of nanoelectronics along the path prescribed by Moore's law. Focus is on hydrogen passivation layers and on ultrathin oxide films encountered during silicon cleaning and gate stack formation in the fabrication of metal-oxide-semiconductor field-effect transistors (MOSFETs). Three main topics are addressed. (i) First, the current practices and understanding of silicon cleaning in aqueous solutions are reviewed, including oxidizing chemistries and cleans leading to a hydrogen passivation layer. The dependence of the final surface termination and morphology/roughness on reactant choice and pH and the influence of impurities such as dissolved oxygen or metal ions are discussed. (ii) Next, the stability of hydrogen-terminated silicon in oxidizing liquid and gas phase environments is considered. In particular, the remarkable stability of hydrogen-terminated silicon surface in pure water vapor is discussed in the context of atomic layer deposition (ALD) of high-permittivity (high-k) gate dielectrics where water is often used as an oxygen precursor. Evidence is also provided for co-operative action between oxygen and water vapor that accelerates surface oxidation in humid air. (iii) Finally, the fabrication of hafnium-, zirconium- and aluminum-based high-k gate stacks is described, focusing on the continued importance of the silicon/silicon oxide interface. This includes a review of silicon surface preparation by wet or gas phase processing and its impact on high-k nucleation during ALD growth, and the consideration of gate stack capacitance and carrier mobility. In conclusion, two issues are highlighted: the impact of oxygen vacancies on the electrical characteristics of high-k MOS devices, and the way alloyed metal ions (such as Al in Hf-based gate stacks) in contact with the interfacial silicon oxide layer can be used to control flatband and threshold voltages.

  14. Proliferation of the synovial lining cell layer in suggested metal hypersensitivity.

    PubMed

    Burkandt, Andreas; Katzer, Alexander; Thaler, Karlheinz; Von Baehr, Volker; Friedrich, Reinhard E; Rüther, Wolfgang; Amling, Michael; Zustin, Jozef

    2011-01-01

    Synovial tissues in joints with prostheses display characteristic morphological changes in cases with aseptic failure, particularly macrophage infiltration. Since proliferation of the synovial lining cell layer represents a feature characteristic of autoimmune joint diseases, the possibility of morphological changes of the synovial lining cell layer in periprosthetic tissues was investigated. Synovial biopsies from five groups of morphologically well-defined lesions (osteoarthritis, rheumatoid arthritis, aseptic loosened metal-on-polyethylene and metal-on-metal arthroplasty and suggested metal hypersensitivity) were compared using a conventional staining method and immunohistochemistry. The synovial lining cell layer was substantially enlarged in both rheumatoid arthritis and cases suggestive of metal hypersensitivity. Macrophage infiltrates were apparent in rheumatoid arthritis and all specimens from retrieved hip arthroplasties. Although both synovial and subsynovial macrophages were positive for CD163 (indicating synovial M2 macrophages), the remaining fibroblast-like synoviocytes and scattered stromal fibroblasts showed a positive reaction with the D2-40 antibody (indicating fibroblast-like synoviocytes). Furthermore, in contrast to CD163-positive macrophages, the enlarged D2-40-positive fibroblast-like synoviocytes displayed cytoplasmatic tubular projections. Proliferation of the periprosthetic synovial lining cell layer occurred in cases with unexplained groin pain following metal-on-metal hip resurfacing arthroplasty, suggestive of hypersensitivity. Despite some important study limitations, the present observation adds to the evidence that metal hypersensitivity shares characteristic morphological features with autoimmune diseases of the joints.

  15. Construction of layered structures on valve metal alloys by microplasma oxidation

    NASA Astrophysics Data System (ADS)

    Baranova, T. A.; Chubenko, A. K.; Mamaev, A. I.; Mamaeva, V. A.; Kovalskaya, Ya B.

    2016-11-01

    Process of layered structure materials creation based on aluminum alloys is presented. Microplasma texturing method, microplasma oxidation method and chemical metallization method were used to create these structures. Non-conductive nonmetallic inorganic coatings were produced by microplasma oxidation method. Obtained structures showed high durability under thermal stress loads due to substrate metal - non-conductive nonmetallic inorganic coating phase boundary texturing.

  16. Lateral amorphous selenium metal-insulator-semiconductor-insulator-metal photodetectors using ultrathin dielectric blocking layers for dark current suppression

    NASA Astrophysics Data System (ADS)

    Chang, Cheng-Yi; Pan, Fu-Ming; Lin, Jian-Siang; Yu, Tung-Yuan; Li, Yi-Ming; Chen, Chieh-Yang

    2016-12-01

    We fabricated amorphous selenium (a-Se) photodetectors with a lateral metal-insulator-semiconductor-insulator-metal (MISIM) device structure. Thermal aluminum oxide, plasma-enhanced chemical vapor deposited silicon nitride, and thermal atomic layer deposited (ALD) aluminum oxide and hafnium oxide (ALD-HfO2) were used as the electron and hole blocking layers of the MISIM photodetectors for dark current suppression. A reduction in the dark current by three orders of magnitude can be achieved at electric fields between 10 and 30 V/μm. The effective dark current suppression is primarily ascribed to electric field lowering in the dielectric layers as a result of charge trapping in deep levels. Photogenerated carriers in the a-Se layer can be transported across the blocking layers to the Al electrodes via Fowler-Nordheim tunneling because a high electric field develops in the ultrathin dielectric layers under illumination. Since the a-Se MISIM photodetectors have a very low dark current without significant degradation in the photoresponse, the signal contrast is greatly improved. The MISIM photodetector with the ALD-HfO2 blocking layer has an optimal signal contrast more than 500 times the contrast of the photodetector without a blocking layer at 15 V/μm.

  17. Photoresponse of double-stacked graphene to Infrared radiation.

    PubMed

    Gowda, Prarthana; Mohapatra, Dipti R; Misra, Abha

    2015-10-14

    We report the photoresponse of stacked graphene layers towards infrared radiation. Graphene is stacked in two configurations, namely, crossed and parallel layers. Raman analysis demonstrated a strong interaction among the stacked graphene layers. Graphene in the crossed configuration exhibited the presence of both negative and positive conductivities; however, other configurations of graphene exhibited positive conductivity only. The presence of negative photoconductivity is proposed to be due to oxygen or oxygen-related functional group absorbents that are trapped in between two monolayers of graphene and act as scattering centers for free carriers. An interesting trend is reported in differential conductivity when stacked layers are compared with multilayers and parallel-stacked graphene layers.

  18. Photoresponse of double-stacked graphene to Infrared radiation

    NASA Astrophysics Data System (ADS)

    Gowda, Prarthana; Mohapatra, Dipti R.; Misra, Abha

    2015-09-01

    We report the photoresponse of stacked graphene layers towards infrared radiation. Graphene is stacked in two configurations, namely, crossed and parallel layers. Raman analysis demonstrated a strong interaction among the stacked graphene layers. Graphene in the crossed configuration exhibited the presence of both negative and positive conductivities; however, other configurations of graphene exhibited positive conductivity only. The presence of negative photoconductivity is proposed to be due to oxygen or oxygen-related functional group absorbents that are trapped in between two monolayers of graphene and act as scattering centers for free carriers. An interesting trend is reported in differential conductivity when stacked layers are compared with multilayers and parallel-stacked graphene layers.

  19. Effect of spacer layer thickness on multi-stacked InGaAs quantum dots grown on GaAs (311)B substrate for application to intermediate band solar cells

    NASA Astrophysics Data System (ADS)

    Shoji, Yasushi; Narahara, Kohei; Tanaka, Hideharu; Kita, Takashi; Akimoto, Katsuhiro; Okada, Yoshitaka

    2012-04-01

    We have investigated the properties of multi-stacked layers of self-organized In0.4Ga0.6As quantum dots (QDs) on GaAs (311)B grown by molecular beam epitaxy. We found that a high degree of in-plane ordering of QDs structure with a six-fold symmetry was maintained though the growth has been performed at a higher growth rate than the conventional conditions. The dependence of photoluminescence characteristics on spacer layer thickness showed an increasing degree of electronic coupling between the stacked QDs for thinner spacer layers. The external quantum efficiency for an InGaAs/GaAs quantum dot solar cell (QDSC) with a thin spacer layer thickness increased in the longer wavelength range due to additive contribution from QD layers inserted in the intrinsic region. Furthermore, a photocurrent production by 2-step photon absorption has been observed at room temperature for the InGaAs/GaAs QDSC with a spacer layer thickness of 15 nm.

  20. LOW VELOCITY IMPACT RESPONSE OF A LAMINATED COMPOSITE TUBE WITH A METALLIC BUMPER LAYER

    SciTech Connect

    Ibekwe, S.I.; Li, G.; Pang, S.S.; and Smith, B. H.

    2006-07-01

    A thin metallic sheet was bonded to the outer surface of a laminated composite curved beam as a bumper layer. It was believed that a metallic bumper layer such as an aluminum thin sheet would be able to intercept any lateral impacting force and absorb impact energy through plastic deformation. Since aluminum is comparatively light weight, a thin sheet will not result in a significant increase in structural weight. Results showed that impact damage occurred primarily in the bumper layer, thereby resulting in a much higher residual bending strength compared to the control specimen.

  1. Atomic-Scale Tuning of Layered Binary Metal Oxides for High Temperature Moving Assemblies

    DTIC Science & Technology

    2015-06-01

    AFRL-OSR-VA-TR-2015-0166 Atomic -Scale Tuning of Layered Binary Metal OxideS ASHLIE MARTINI UNIVERSITY OF CALIFORNIA MERCED Final Report 06/01/2015...COVERED (From - To)      01-05-2012 to 30-04-2015 4.  TITLE AND SUBTITLE Atomic -Scale Tuning of Layered Binary Metal Oxides for High Temperature Moving...understand, at an atomic level, the material properties that influence the thermal, mechanical and tribological behavior of intrinsically layered binary

  2. Layer-by-Layer Deposition with Polymers Containing Nitrilotriacetate, A Convenient Route to Fabricate Metal- and Protein-Binding Films.

    PubMed

    Wijeratne, Salinda; Liu, Weijing; Dong, Jinlan; Ning, Wenjing; Ratnayake, Nishanka Dilini; Walker, Kevin D; Bruening, Merlin L

    2016-04-27

    This paper describes a convenient synthesis of nitrilotriacetate (NTA)-containing polymers and subsequent layer-by-layer adsorption of these polymers on flat surfaces and in membrane pores. The resulting films form NTA-metal-ion complexes and capture 2-3 mmol of metal ions per mL of film. Moreover, these coatings bind multilayers of polyhistidine-tagged proteins through association with NTA-metal-ion complexes. Inclusion of acrylic acid repeat units in NTA-containing copolymers promotes swelling to increase protein binding in films on Au-coated wafers. Adsorption of NTA-containing films in porous nylon membranes gives materials that capture ∼46 mg of His-tagged ubiquitin per mL. However, the binding capacity decreases with the protein molecular weight. Due to the high affinity of NTA for metal ions, the modified membranes show modest leaching of Ni(2+) in binding and rinsing buffers. Adsorption of NTA-containing polymers is a simple method to create metal- and protein-binding films and may, with future enhancement of stability, facilitate development of disposable membranes that rapidly purify tagged proteins.

  3. Role of surface-reaction layer in HBr/fluorocarbon-based plasma with nitrogen addition formed by high-aspect-ratio etching of polycrystalline silicon and SiO2 stacks

    NASA Astrophysics Data System (ADS)

    Iwase, Taku; Matsui, Miyako; Yokogawa, Kenetsu; Arase, Takao; Mori, Masahito

    2016-06-01

    The etching of polycrystalline silicon (poly-Si)/SiO2 stacks by using VHF plasma was studied for three-dimensional NAND fabrication. One critical goal is achieving both a vertical profile and high throughput for multiple-stack etching. While the conventional process consists of multiple steps for each stacked layer, in this study, HBr/fluorocarbon-based gas chemistry was investigated to achieve a single-step etching process to reduce process time. By analyzing the dependence on wafer temperature, we improved both the etching profile and rate at a low temperature. The etching mechanism is examined considering the composition of the surface reaction layer. X-ray photoelectron spectroscopy (XPS) analysis revealed that the adsorption of N-H and Br was enhanced at a low temperature, resulting in a reduced carbon-based-polymer thickness and enhanced Si etching. Finally, a vertical profile was obtained as a result of the formation of a thin and reactive surface-reaction layer at a low wafer temperature.

  4. Newtype single-layer magnetic semiconductor in transition-metal dichalcogenides VX2 (X = S, Se and Te)

    PubMed Central

    Fuh, Huei-Ru; Chang, Ching-Ray; Wang, Yin-Kuo; Evans, Richard F. L.; Chantrell, Roy W.; Jeng, Horng-Tay

    2016-01-01

    We present a newtype 2-dimensional (2D) magnetic semiconductor based on transition-metal dichalcogenides VX2 (X = S, Se and Te) via first-principles calculations. The obtained indirect band gaps of monolayer VS2, VSe2, and VTe2 given from the generalized gradient approximation (GGA) are respectively 0.05, 0.22, and 0.20 eV, all with integer magnetic moments of 1.0 μB. The GGA plus on-site Coulomb interaction U (GGA + U) enhances the exchange splittings and raises the energy gap up to 0.38~0.65 eV. By adopting the GW approximation, we obtain converged G0W0 gaps of 1.3, 1.2, and 0.7 eV for VS2, VSe2, and VTe2 monolayers, respectively. They agree very well with our calculated HSE gaps of 1.1, 1.2, and 0.6 eV, respectively. The gap sizes as well as the metal-insulator transitions are tunable by applying the in-plane strain and/or changing the number of stacking layers. The Monte Carlo simulations illustrate very high Curie-temperatures of 292, 472, and 553 K for VS2, VSe2, and VTe2 monolayers, respectively. They are nearly or well beyond the room temperature. Combining the semiconducting energy gap, the 100% spin polarized valence and conduction bands, the room temperature TC, and the in-plane magnetic anisotropy together in a single layer VX2, this newtype 2D magnetic semiconductor shows great potential in future spintronics. PMID:27601195

  5. Noise and vibration level reduction by covering metal structures with layers of damping materials. [considering viscoelastic insulation layers

    NASA Technical Reports Server (NTRS)

    Rugina, I.; Paven, H. T. O.

    1974-01-01

    One of the most important methods of reducing the noise and vibration level is the damping of the secondary sources, such as metal plates, often used in vehicle structures, by means of covering materials with high internal viscosity. Damping layers are chosen at an optimum thickness corresponding to the frequency and temperature range in which a certain structure works. The structure's response corresponding to various real situations is analyzed by means of a measuring chain including electroacoustical or electromechanical transducers. The experimental results provide the dependence of the loss factor and damping transmission coefficient as a function of the damping layer thickness or of the frequency for various viscoelastic covering materials.

  6. Current density and catalyst-coated membrane resistance distribution of hydro-formed metallic bipolar plate fuel cell short stack with 250 cm2 active area

    NASA Astrophysics Data System (ADS)

    Haase, S.; Moser, M.; Hirschfeld, J. A.; Jozwiak, K.

    2016-01-01

    An automotive fuel cell with an active area of 250 cm2 is investigated in a 4-cell short stack with a current and temperature distribution device next to the bipolar plate with 560 current and 140 temperature segments. The electrical conductivities of the bipolar plate and gas diffusion layer assembly are determined ex-situ with this current scan shunt module. The applied fuel cell consists of bipolar plates constructed of 75-μm-thick, welded stainless-steel foils and a graphitic coating. The electrical conductivities of the bipolar plate and gas diffusion layer assembly are determined ex-situ with this module with a 6% deviation in in-plane conductivity. The current density distribution is evaluated up to 2.4 A cm-2. The entire cell's investigated volumetric power density is 4.7 kW l-1, and its gravimetric power density is 4.3 kW kg-1 at an average cell voltage of 0.5 V. The current density distribution is determined without influencing the operating cell. In addition, the current density distribution in the catalyst-coated membrane and its effective resistivity distribution with a finite volume discretisation of Ohm's law are evaluated. The deviation between the current density distributions in the catalyst-coated membrane and the bipolar plate is determined.

  7. Atomic layer deposition to prevent metal transfer from implants: An X-ray fluorescence study

    NASA Astrophysics Data System (ADS)

    Bilo, Fabjola; Borgese, Laura; Prost, Josef; Rauwolf, Mirjam; Turyanskaya, Anna; Wobrauschek, Peter; Kregsamer, Peter; Streli, Christina; Pazzaglia, Ugo; Depero, Laura E.

    2015-12-01

    We show that Atomic Layer Deposition is a suitable coating technique to prevent metal diffusion from medical implants. The metal distribution in animal bone tissue with inserted bare and coated Co-Cr alloys was evaluated by means of micro X-ray fluorescence mapping. In the uncoated implant, the migration of Co and Cr particles from the bare alloy in the biological tissues is observed just after one month and the number of particles significantly increases after two months. In contrast, no metal diffusion was detected in the implant coated with TiO2. Instead, a gradient distribution of the metals was found, from the alloy surface going into the tissue. No significant change was detected after two months of aging. As expected, the thicker is the TiO2 layer, the lower is the metal migration.

  8. Metallic layer-by-layer photonic crystals for linearly-polarized thermal emission and thermophotovoltaic device including same

    DOEpatents

    Lee, Jae-Hwang; Ho, Kai-Ming; Constant, Kristen P.

    2016-07-26

    Metallic thermal emitters consisting of two layers of differently structured nickel gratings on a homogeneous nickel layer are fabricated by soft lithography and studied for polarized thermal radiation. A thermal emitter in combination with a sub-wavelength grating shows a high extinction ratio, with a maximum value close to 5, in a wide mid-infrared range from 3.2 to 7.8 .mu.m, as well as high emissivity up to 0.65 at a wavelength of 3.7 .mu.m. All measurements show good agreement with theoretical predictions. Numerical simulations reveal that a high electric field exists within the localized air space surrounded by the gratings and the intensified electric-field is only observed for the polarizations perpendicular to the top sub-wavelength grating. This result suggests how the emissivity of a metal can be selectively enhanced at a certain range of wavelengths for a given polarization.

  9. Copper Benzenetricarboxylate Metal-Organic Framework Nucleation Mechanisms on Metal Oxide Powders and Thin Films formed by Atomic Layer Deposition.

    PubMed

    Lemaire, Paul C; Zhao, Junjie; Williams, Philip S; Walls, Howard J; Shepherd, Sarah D; Losego, Mark D; Peterson, Gregory W; Parsons, Gregory N

    2016-04-13

    Chemically functional microporous metal-organic framework (MOF) crystals are attractive for filtration and gas storage applications, and recent results show that they can be immobilized on high surface area substrates, such as fiber mats. However, fundamental knowledge is still lacking regarding initial key reaction steps in thin film MOF nucleation and growth. We find that thin inorganic nucleation layers formed by atomic layer deposition (ALD) can promote solvothermal growth of copper benzenetricarboxylate MOF (Cu-BTC) on various substrate surfaces. The nature of the ALD material affects the MOF nucleation time, crystal size and morphology, and the resulting MOF surface area per unit mass. To understand MOF nucleation mechanisms, we investigate detailed Cu-BTC MOF nucleation behavior on metal oxide powders and Al2O3, ZnO, and TiO2 layers formed by ALD on polypropylene substrates. Studying both combined and sequential MOF reactant exposure conditions, we find that during solvothermal synthesis ALD metal oxides can react with the MOF metal precursor to form double hydroxy salts that can further convert to Cu-BTC MOF. The acidic organic linker can also etch or react with the surface to form MOF from an oxide metal source, which can also function as a nucleation agent for Cu-BTC in the mixed solvothermal solution. We discuss the implications of these results for better controlled thin film MOF nucleation and growth.

  10. Spin Transport in Single Layer Transition Metal Dichalcogenides

    NASA Astrophysics Data System (ADS)

    Phillips, Michael; Aji, Vivek

    Inversion symmetry breaking and strong spin orbit coupling in two dimensional transition metal dichalcogenides leads to interesting new phenomena such as the valley hall and spin hall effects. The nontrivial Berry curvature of the bands yields transverse spin currents in applied field. In this talk we characterize the spin transport in hole-doped systems. Due to the large spin-splitting, time-reversal invariance, and the large separation of hole pockets in momentum space, spin flip scattering involves inter-valley processes with large momentum. As such, one expects large spin life times and a large spin hall angle. We analyze the robustness of the phenomena to various scattering processes and explore the viability of transition metal dichalcogenides for spintronic applications. We acknowledge the support of the NSF via Grant NSF DMR-1506707.

  11. Metallic stereostructured layer: An approach for broadband polarization state manipulation

    SciTech Connect

    Xiong, Xiang; Hu, Yuan-Sheng; Jiang, Shang-Chi; Hu, Yu-Hui; Fan, Ren-Hao; Ma, Guo-Bin; Shu, Da-Jun; Peng, Ru-Wen; Wang, Mu

    2014-11-17

    In this letter, we report a full-metallic broadband wave plate assembled by standing metallic L-shaped stereostructures (LSSs). We show that with an array of LSSs, high polarization conversion ratio is achieved within a broad frequency band. Moreover, by rotating the orientation of the array of LSSs, the electric components of the reflection beam in two orthogonal directions and their phase difference can be independently tuned. In this way, all the polarization states on the Poincaré sphere can be realized. As examples, the functionalities of a quarter wave plate and a half wave plate are experimentally demonstrated with both reflection spectra and focal-plane-array imaging. Our designing provides a unique approach in realizing the broadband wave plate to manipulate the polarization state of light.

  12. Multistep soft chemistry method for valence reduction in transition metal oxides with triangular (CdI2-type) layers.

    PubMed

    Blakely, Colin K; Bruno, Shaun R; Poltavets, Viktor V

    2014-03-14

    Transition metal (M) oxides with MO2 triangular layers demonstrate a variety of physical properties depending on the metal oxidation states. In the known compounds, metal oxidation states are limited to either 3+ or mixed-valent 3+/4+. A multistep soft chemistry synthetic route for novel phases with M(2+/3+)O2 triangular layers is reported.

  13. Modulation of spin-orbit torque efficiency by thickness control of heavy metal layers in Co/Pt multilayers

    NASA Astrophysics Data System (ADS)

    Sethi, P.; Krishnia, S.; Li, S. H.; Lew, W. S.

    2017-03-01

    We investigate and quantify spin-orbit torque (SOT) strength by current induced effective in-plane magnetic fields and spin Hall angle (SHA) using AC harmonic Hall voltage measurements techniques on Ta/Pt/Co/Pt/Co/Ta thin film structures. The proposed Co/Pt thin film double stack gives property enhancement on thermal stability and perpendicular magnetization anisotropy strength over the single stack Pt/Co/Ta. In the proposed Co/Pt double stack we observed that increasing the Ta capping thickness to three times enhances the SHA in similar order, consistent with larger spin injection efficiency. Doubling the Pt spacer layer thickness reduces the SHA by nearly 1.4 times, due to partial cancellation of SOT by bottom layer Pt, negating the increase from the top Co/Pt interface. The in-plane current threshold for magnetization switching is lower with the increase of the SHA.

  14. Layer-number dependent high-frequency vibration modes in few-layer transition metal dichalcogenides induced by interlayer couplings

    NASA Astrophysics Data System (ADS)

    Tan, Qing-Hai; Zhang, Xin; Luo, Xiang-Dong; Zhang, Jun; Tan, Ping-Heng

    2017-03-01

    Two-dimensional transition metal dichalcogenides (TMDs) have attracted extensive attention due to their many novel properties. The atoms within each layer in two-dimensional TMDs are joined together by covalent bonds, while van der Waals interactions combine the layers together. This makes its lattice dynamics layer-number dependent. The evolutions of ultralow frequency (< 50 cm‑1) modes, such as shear and layer-breathing modes have been well-established. Here, we review the layer-number dependent high-frequency (> 50 cm‑1) vibration modes in few-layer TMDs and demonstrate how the interlayer coupling leads to the splitting of high-frequency vibration modes, known as Davydov splitting. Such Davydov splitting can be well described by a van der Waals model, which directly links the splitting with the interlayer coupling. Our review expands the understanding on the effect of interlayer coupling on the high-frequency vibration modes in TMDs and other two-dimensional materials. Project supported by the National Basic Research Program of China (No. 2016YFA0301200), the National Natural Science Foundation of China (Nos. 11225421, 11474277, 11434010, 61474067, 11604326, 11574305 and 51527901), and the National Young 1000 Talent Plan of China.

  15. Enhancing current-induced torques by abutting additional spin polarizer layer to nonmagnetic metal layer.

    PubMed

    Go, Gyungchoon; Lee, Kyung-Jin; Kim, Young Keun

    2017-04-04

    Recently, the switching of a perpendicularly magnetized ferromagnet (FM) by injecting an in-plane current into an attached non-magnet (NM) has become of emerging technological interest. This magnetization switching is attributed to the spin-orbit torque (SOT) originating from the strong spin-orbit coupling of the NM layer. However, the switching efficiency of the NM/FM structure itself may be insufficient for practical use, as for example, in spin transfer torque (STT)-based magnetic random access memory (MRAM) devices. Here we investigate spin torque in an NM/FM structure with an additional spin polarizer (SP) layer abutted to the NM layer. In addition to the SOT contribution, a spin-polarized current from the SP layer creates an extra spin chemical potential difference at the NM/FM interface and gives rise to a STT on the FM layer. We show that, using typical parameters including device width, thickness, spin diffusion length, and the spin Hall angle, the spin torque from the SP layer can be much larger than that from the spin Hall effect (SHE) of the NM.

  16. Enhancing current-induced torques by abutting additional spin polarizer layer to nonmagnetic metal layer

    PubMed Central

    Go, Gyungchoon; Lee, Kyung-Jin; Kim, Young Keun

    2017-01-01

    Recently, the switching of a perpendicularly magnetized ferromagnet (FM) by injecting an in-plane current into an attached non-magnet (NM) has become of emerging technological interest. This magnetization switching is attributed to the spin-orbit torque (SOT) originating from the strong spin-orbit coupling of the NM layer. However, the switching efficiency of the NM/FM structure itself may be insufficient for practical use, as for example, in spin transfer torque (STT)-based magnetic random access memory (MRAM) devices. Here we investigate spin torque in an NM/FM structure with an additional spin polarizer (SP) layer abutted to the NM layer. In addition to the SOT contribution, a spin-polarized current from the SP layer creates an extra spin chemical potential difference at the NM/FM interface and gives rise to a STT on the FM layer. We show that, using typical parameters including device width, thickness, spin diffusion length, and the spin Hall angle, the spin torque from the SP layer can be much larger than that from the spin Hall effect (SHE) of the NM. PMID:28374805

  17. Diverse and tunable electronic structures of single-layer metal phosphorus trichalcogenides for photocatalytic water splitting

    SciTech Connect

    Liu, Jian; Li, Xi-Bo; Wang, Da; Liu, Li-Min E-mail: limin.liu@csrc.ac.cn; Lau, Woon-Ming; Peng, Ping E-mail: limin.liu@csrc.ac.cn

    2014-02-07

    The family of bulk metal phosphorus trichalcogenides (APX{sub 3}, A = M{sup II}, M{sub 0.5}{sup I}M{sub 0.5}{sup III}; X = S, Se; M{sup I}, M{sup II}, and M{sup III} represent Group-I, Group-II, and Group-III metals, respectively) has attracted great attentions because such materials not only own magnetic and ferroelectric properties, but also exhibit excellent properties in hydrogen storage and lithium battery because of the layered structures. Many layered materials have been exfoliated into two-dimensional (2D) materials, and they show distinct electronic properties compared with their bulks. Here we present a systematical study of single-layer metal phosphorus trichalcogenides by density functional theory calculations. The results show that the single layer metal phosphorus trichalcogenides have very low formation energies, which indicates that the exfoliation of single layer APX{sub 3} should not be difficult. The family of single layer metal phosphorus trichalcogenides exhibits a large range of band gaps from 1.77 to 3.94 eV, and the electronic structures are greatly affected by the metal or the chalcogenide atoms. The calculated band edges of metal phosphorus trichalcogenides further reveal that single-layer ZnPSe{sub 3}, CdPSe{sub 3}, Ag{sub 0.5}Sc{sub 0.5}PSe{sub 3}, and Ag{sub 0.5}In{sub 0.5}PX{sub 3} (X = S and Se) have both suitable band gaps for visible-light driving and sufficient over-potentials for water splitting. More fascinatingly, single-layer Ag{sub 0.5}Sc{sub 0.5}PSe{sub 3} is a direct band gap semiconductor, and the calculated optical absorption further convinces that such materials own outstanding properties for light absorption. Such results demonstrate that the single layer metal phosphorus trichalcogenides own high stability, versatile electronic properties, and high optical absorption, thus such materials have great chances to be high efficient photocatalysts for water-splitting.

  18. Corrosion of Metal Films with Defective Surface Protection Layers.

    DTIC Science & Technology

    1980-07-01

    Evaporation 5 x I0- 100-150 25-35 S-Gun Sputtering 2 x 10-3 (argon) 6 35 was applied and patterned. Aqua regia was used to remove the platinum down to...Dielectric Layers Electrochemical Measurements Aluminum Thin Films Surface pH Measurements Gold Thin Films TRACT (Contfne o- reverse aide Hf nec.eary...between lines and line resis- tance were monitored at intervals. In one case, the potential was reversed after a certain time. Cathodic corrosion was

  19. Co-based alloys design based on first-principles calculations: Influence of transition metal and rare-earth alloying element on stacking fault energy

    NASA Astrophysics Data System (ADS)

    Achmad, Tria Laksana; Fu, Wenxiang; Chen, Hao; Zhang, Chi; Yang, Zhi-Gang

    2017-01-01

    The main idea of alloy design is to reduce costs and time required by the traditional (trial and error) method, then finding a new way to develop the efficiency of the alloy design is necessary. In this study, we proposed a new approach to the design of Co-based alloys. It is based on the concept that lowering the ratio of stable and unstable stacking fault energy (SFE) could bring a significant increase in the tendency of partial dislocation accumulation and FCC to HCP phase transformation then enhance mechanical properties. Through the advance development of the computing techniques, first-principles density-functional-theory (DFT) calculations are capable of providing highly accurate structural modeling at the atomic scale without any experimental data. The first-principles calculated results show that the addition of some transition metal (Cr, Mo, W, Re, Os, Ir) and rare-earth (Sc, Y, La, Sm) alloying elements would decrease both stable and unstable SFE of pure Co. The dominant deformation mechanism of binary Co-4.5 at.% X (X = alloying element) is extended partial dislocation. Our study reveals Re, W, Mo and La as the most promising alloying additions for the Co-based alloys design with superior performances. Furthermore, the underlying mechanisms for the SFE reduction can be explained regarding the electronic structure.

  20. Plasmonically sensitized metal-oxide electron extraction layers for organic solar cells

    PubMed Central

    Trost, S.; Becker, T.; Zilberberg, K.; Behrendt, A.; Polywka, A.; Heiderhoff, R.; Görrn, P.; Riedl, T.

    2015-01-01

    ZnO and TiOx are commonly used as electron extraction layers (EELs) in organic solar cells (OSCs). A general phenomenon of OSCs incorporating these metal-oxides is the requirement to illuminate the devices with UV light in order to improve device characteristics. This may cause severe problems if UV to VIS down-conversion is applied or if the UV spectral range (λ < 400 nm) is blocked to achieve an improved device lifetime. In this work, silver nanoparticles (AgNP) are used to plasmonically sensitize metal-oxide based EELs in the vicinity (1–20 nm) of the metal-oxide/organic interface. We evidence that plasmonically sensitized metal-oxide layers facilitate electron extraction and afford well-behaved highly efficient OSCs, even without the typical requirement of UV exposure. It is shown that in the plasmonically sensitized metal-oxides the illumination with visible light lowers the WF due to desorption of previously ionosorbed oxygen, in analogy to the process found in neat metal oxides upon UV exposure, only. As underlying mechanism the transfer of hot holes from the metal to the oxide upon illumination with hν < Eg is verified. The general applicability of this concept to most common metal-oxides (e.g. TiOx and ZnO) in combination with different photoactive organic materials is demonstrated. PMID:25592174

  1. Simple metal under tensile stress: layer-dependent herringbone reconstruction of thin potassium films on graphite

    PubMed Central

    Yin, Feng; Kulju, Sampo; Koskinen, Pekka; Akola, Jaakko; Palmer, Richard E.

    2015-01-01

    While understanding the properties of materials under stress is fundamentally important, designing experiments to probe the effects of large tensile stress is difficult. Here tensile stress is created in thin films of potassium (up to 4 atomic layers) by epitaxial growth on a rigid support, graphite. We find that this “simple” metal shows a long-range, periodic “herringbone” reconstruction, observed in 2- and 3- (but not 1- and 4-) layer films by low-temperature scanning tunneling microscopy (STM). Such a pattern has never been observed in a simple metal. Density functional theory (DFT)simulations indicate that the reconstruction consists of self-aligned stripes of enhanced atom density formed to relieve the tensile strain. At the same time marked layer-dependent charging effects lead to substantial variation in the apparent STM layer heights. PMID:25959681

  2. Theory of strain in single-layer transition metal dichalcogenides

    NASA Astrophysics Data System (ADS)

    Rostami, Habib; Roldán, Rafael; Cappelluti, Emmanuele; Asgari, Reza; Guinea, Francisco

    2015-11-01

    Strain engineering has emerged as a powerful tool to modify the optical and electronic properties of two-dimensional crystals. Here we perform a systematic study of strained semiconducting transition metal dichalcogenides. The effect of strain is considered within a full Slater-Koster tight-binding model, which provides us with the band structure in the whole Brillouin zone (BZ). From this, we derive an effective low-energy model valid around the K point of the BZ, which includes terms up to second order in momentum and strain. For a generic profile of strain, we show that the solutions for this model can be expressed in terms of the harmonic oscillator and double quantum well models, for the valence and conduction bands respectively. We further study the shift of the position of the electron and hole band edges due to uniform strain. Finally, we discuss the importance of spin-strain coupling in these 2D semiconducting materials.

  3. Ultrathin two-dimensional atomic crystals as stable interfacial layer for improvement of lithium metal anode.

    PubMed

    Yan, Kai; Lee, Hyun-Wook; Gao, Teng; Zheng, Guangyuan; Yao, Hongbin; Wang, Haotian; Lu, Zhenda; Zhou, Yu; Liang, Zheng; Liu, Zhongfan; Chu, Steven; Cui, Yi

    2014-10-08

    Stable cycling of lithium metal anode is challenging due to the dendritic lithium formation and high chemical reactivity of lithium with electrolyte and nearly all the materials. Here, we demonstrate a promising novel electrode design by growing two-dimensional (2D) atomic crystal layers including hexagonal boron nitride (h-BN) and graphene directly on Cu metal current collectors. Lithium ions were able to penetrate through the point and line defects of the 2D layers during the electrochemical deposition, leading to sandwiched lithium metal between ultrathin 2D layers and Cu. The 2D layers afford an excellent interfacial protection of Li metal due to their remarkable chemical stability as well as mechanical strength and flexibility, resulting from the strong intralayer bonds and ultrathin thickness. Smooth Li metal deposition without dendritic and mossy Li formation was realized. We showed stable cycling over 50 cycles with Coulombic efficiency ∼97% in organic carbonate electrolyte with current density and areal capacity up to the practical value of 2.0 mA/cm(2)and 5.0 mAh/cm(2), respectively, which is a significant improvement over the unprotected electrodes in the same electrolyte.

  4. FTIR spectroscopy structural analysis of the interaction between Lactobacillus kefir S-layers and metal ions

    NASA Astrophysics Data System (ADS)

    Gerbino, E.; Mobili, P.; Tymczyszyn, E.; Fausto, R.; Gómez-Zavaglia, A.

    2011-02-01

    FTIR spectroscopy was used to structurally characterize the interaction of S-layer proteins extracted from two strains of Lactobacillus kefir (the aggregating CIDCA 8348 and the non-aggregating JCM 5818) with metal ions (Cd +2, Zn +2, Pb +2 and Ni +2). The infrared spectra indicate that the metal/protein interaction occurs mainly through the carboxylate groups of the side chains of Asp and Glut residues, with some contribution of the NH groups belonging to the peptide backbone. The frequency separation between the νCOO - anti-symmetric and symmetric stretching vibrations in the spectra of the S-layers in presence of the metal ions was found to be ca. 190 cm -1 for S-layer CIDCA 8348 and ca. 170 cm -1 for JCM 5818, denoting an unidentate coordination in both cases. Changes in the secondary structures of the S-layers induced by the interaction with the metal ions were also noticed: a general trend to increase the amount of β-sheet structures and to reduce the amount of α-helices was observed. These changes allow the proteins to adjust their structure to the presence of the metal ions at minimum energy expense, and accordingly, these adjustments were found to be more important for the bigger ions.

  5. Process for preparation of a seed layer for selective metal deposition

    DOEpatents

    Bernhardt, Anthony F.

    1992-01-01

    Disclosed is a process for selective metal deposition comprising of the steps of: a. formation of an initial surface on a substrate, said initial surface being comprised of at least two layers of which the uppermost is inert, b. exposing the surface to a source of heat in pre-determined places wherein surface activation is desired, and c. deposition of metal on activated portions of said surface.

  6. Transport Properties of the Layered Transition Metal Oxypnictide Sr2ScMPO3 with MP layers (M =Mn, Ni and Co0.5Fe0.5)

    NASA Astrophysics Data System (ADS)

    Okada, S.; Kamihara, Y.; Ohkubo, N.; Ban, S.; Matoba, M.

    2014-12-01

    Polycrystalline samples of novel oxypnictides, Sr2ScMPO3, with MP layer (M = Mn, Ni and Co0.5Fe0.5) were synthesized, and their resistivities and Seebeck coefficients were measured. Sr2ScMPO3 crystallizes in a stacked, layered structure comprised of a ThCr2Si2- type MP layer alternating with a K2NiF4-type Sr2ScO3 layer. Sr2ScMnPO3 is an insulator at room temperature. The resistivities (ρ) of Sr2ScNiPO3 and Sr2ScCo0.5Fe0.5PO3 decrease with decreasing temperature like a metal. The Seebeck coefficients (S) of these materials are negative at room temperature. For Sr2ScNiPO3, S initially decreases slightly with decreasing temperature, and increases with decreasing temperature below 50 K. However, for Sr2ScCo0.5Fe0.5PO3, S increases with decreasing temperature, and attains to a positive value below 270 K.

  7. Fuel cell stack arrangements

    DOEpatents

    Kothmann, Richard E.; Somers, Edward V.

    1982-01-01

    Arrangements of stacks of fuel cells and ducts, for fuel cells operating with separate fuel, oxidant and coolant streams. An even number of stacks are arranged generally end-to-end in a loop. Ducts located at the juncture of consecutive stacks of the loop feed oxidant or fuel to or from the two consecutive stacks, each individual duct communicating with two stacks. A coolant fluid flows from outside the loop, into and through cooling channels of the stack, and is discharged into an enclosure duct formed within the loop by the stacks and seals at the junctures at the stacks.

  8. Synthesis and stabilization of supported metal catalysts by atomic layer deposition.

    PubMed

    Lu, Junling; Elam, Jeffrey W; Stair, Peter C

    2013-08-20

    Supported metal nanoparticles are among the most important catalysts for many practical reactions, including petroleum refining, automobile exhaust treatment, and Fischer-Tropsch synthesis. The catalytic performance strongly depends on the size, composition, and structure of the metal nanoparticles, as well as the underlying support. Scientists have used conventional synthesis methods including impregnation, ion exchange, and deposition-precipitation to control and tune these factors, to establish structure-performance relationships, and to develop better catalysts. Meanwhile, chemists have improved the stability of metal nanoparticles against sintering by the application of protective layers, such as polymers and oxides that encapsulate the metal particle. This often leads to decreased catalytic activity due to a lack of precise control over the thickness of the protective layer. A promising method of catalyst synthesis is atomic layer deposition (ALD). ALD is a variation on chemical vapor deposition in which metals, oxides, and other materials are deposited on surfaces by a sequence of self-limiting reactions. The self-limiting character of these reactions makes it possible to achieve uniform deposits on high-surface-area porous solids. Therefore, design and synthesis of advanced catalysts on the nanoscale becomes possible through precise control over the structure and composition of the underlying support, the catalytic active sites, and the protective layer. In this Account, we describe our advances in the synthesis and stabilization of supported metal catalysts by ALD. After a short introduction to the technique of ALD, we show several strategies for metal catalyst synthesis by ALD that take advantage of its self-limiting feature. Monometallic and bimetallic catalysts with precise control over the metal particle size, composition, and structure were achieved by combining ALD sequences, surface treatments, and deposition temperature control. Next, we describe

  9. Corrosion protected, multi-layer fuel cell interface

    DOEpatents

    Feigenbaum, Haim; Pudick, Sheldon; Wang, Chiu L.

    1986-01-01

    An improved interface configuration for use between adjacent elements of a fuel cell stack. The interface is impervious to gas and liquid and provides resistance to corrosion by the electrolyte of the fuel cell. The multi-layer configuration for the interface comprises a non-cupreous metal-coated metallic element to which is film-bonded a conductive layer by hot pressing a resin therebetween. The multi-layer arrangement provides bridging electrical contact.

  10. Angular and positional dependence of Purcell effect for layered metal-dielectric structures

    NASA Astrophysics Data System (ADS)

    Gubaydullin, A. R.; Mazlin, V. A.; Ivanov, K. A.; Kaliteevski, M. A.; Balocco, C.

    2016-04-01

    We study the angular dependence of the spontaneous emission enhancement of a dipole source inserted into a layered metal-dielectric metamaterial. We analyse the dependence of Purcell effect from the position of the dipole in the layered hyperbolic media. We analyse the impact of the complex structure of eigenmodes of the system operating in hyperbolic regime. We have shown that the spontaneous emission rate of the dipole emitter depends on its position, which mainly affect the interaction with Langmuir modes.

  11. Lightweight Stacks of Direct Methanol Fuel Cells

    NASA Technical Reports Server (NTRS)

    Narayanan, Sekharipuram; Valdez, Thomas

    2004-01-01

    An improved design concept for direct methanol fuel cells makes it possible to construct fuel-cell stacks that can weigh as little as one-third as much as do conventional bipolar fuel-cell stacks of equal power. The structural-support components of the improved cells and stacks can be made of relatively inexpensive plastics. Moreover, in comparison with conventional bipolar fuel-cell stacks, the improved fuel-cell stacks can be assembled, disassembled, and diagnosed for malfunctions more easily. These improvements are expected to bring portable direct methanol fuel cells and stacks closer to commercialization. In a conventional bipolar fuel-cell stack, the cells are interspersed with bipolar plates (also called biplates), which are structural components that serve to interconnect the cells and distribute the reactants (methanol and air). The cells and biplates are sandwiched between metal end plates. Usually, the stack is held together under pressure by tie rods that clamp the end plates. The bipolar stack configuration offers the advantage of very low internal electrical resistance. However, when the power output of a stack is only a few watts, the very low internal resistance of a bipolar stack is not absolutely necessary for keeping the internal power loss acceptably low.

  12. Active diagenetic formation of metal-rich layers in N. E. Atlantic sediments

    NASA Astrophysics Data System (ADS)

    Wallace, H. E.; Thomson, J.; Wilson, T. R. S.; Weaver, P. P. E.; Higgs, N. C.; Hydes, D. J.

    1988-06-01

    Sediment cores from the Porcupine Abyssal Plain exhibit an indurated layer 0.5-3 cm thick at depths of approximately 50 cm. This is some 15-20 cm below the glacial/Holocene transition as interpreted by radiocarbon dating and the palaeontological criteria of RUDDIMAN and MCINTYRE (1981). The layer is forming currently at the oxic/post-oxic boundary in the sediments, as revealed by pore water data: O 2 and NO -3 are present in solution above the layer, while Fe 2+, Mn 2+, PO 3-4 and NH +4 are present in solution below, and all these species show concentration gradients indicating fluxes into the layer. These data are consistent with the hypothesis for the initiation and sustained formation of such layers proposed by WILSONet al. (1986a,b). The elements Mn, Ni, Co, Fe, P, V, Cu, Zn and U are all enriched to varying degrees in the vicinity of the layer. Some differential stratification of these elements in the vertical, consistent with a redox control, is observed at one site with a 0.5 cm layer, with Mn, Ni and Co above, Fe, P, V and Cu in the layer, and U below. At another site the metal-rich layer has higher Fe and P concentrations and is more indurated. Here all enrichments except Co are contained within a single layer sample, 3 cm thick.

  13. APCVD Transition Metal Oxides - Functional Layers in "Smart windows"

    NASA Astrophysics Data System (ADS)

    Gesheva, K. A.; Ivanova, T. M.; Bodurov, G. K.

    2014-11-01

    Transition metal oxides (TMO) exhibit electrochromic effect. Under a small voltage they change their optical transmittance from transparent to collored (absorbing) state. The individual material can manifest its electrochromic properties only when it is part of electrochromic (EC) multilayer system. Smart window is controlling the energy of solar flux entering the building or car and makes the interiors comfortable and energy utilization more effective. Recently the efforts of material researchers in this field are directed to price decreasing. APCVD technology is considered as promissing as this process permits flowthrough large-scale production process. The paper presents results on device optimization based on WO3-MoO3 working electrode. Extensive research reveals that WO3-MoO3 structure combines positive features of single oxides: excellent electrochromic performance of WO3 and better kinetic properties of MoO3 deposition. The achieved color efficiency of APCVD WO3-MoO3 films is 200cm2/C and optical modulation of 65-70% are practically favorable electrochromic characteristics. To respond to low cost requirement, the expensive hexacarbonyl can be replaced with acetylacetonate. We have started with this precursor to fabricate mixed WxV1-xO3 films. The films possess excellent surface coverage and high growth-rate. CVD deposition of VO2, a promissing thermochromic thin film material is also presented.

  14. Control of electronic properties of 2D carbides (MXenes) by manipulating their transition metal layers

    DOE PAGES

    Anasori, Babak; Shi, Chenyang; Moon, Eun Ju; ...

    2016-02-24

    In this paper, a transition from metallic to semiconducting-like behavior has been demonstrated in two-dimensional (2D) transition metal carbides by replacing titanium with molybdenum in the outer transition metal (M) layers of M3C2 and M4C3 MXenes. The MXene structure consists of n + 1 layers of near-close packed M layers with C or N occupying the octahedral site between them in an [MX]nM arrangement. Recently, two new families of ordered 2D double transition metal carbides MXenes were discovered, M'2M"C2 and M'2M"2C3 – where M' and M" are two different early transition metals, such as Mo, Cr, Ta, Nb, V, andmore » Ti. The M' atoms only occupy the outer layers and the M" atoms fill the middle layers. In other words, M' atomic layers sandwich the middle M"–C layers. Using X-ray atomic pair distribution function (PDF) analysis on Mo2TiC2 and Mo2Ti2C3 MXenes, we present the first quantitative analysis of structures of these novel materials and experimentally confirm that Mo atoms are in the outer layers of the [MC]nM structures. The electronic properties of these Mo-containing MXenes are compared with their Ti3C2 counterparts, and are found to be no longer metallic-like conductors; instead the resistance increases mildly with decreasing temperatures. Density functional theory (DFT) calculations suggest that OH terminated Mo–Ti MXenes are semiconductors with narrow band gaps. Measurements of the temperature dependencies of conductivities and magnetoresistances have confirmed that Mo2TiC2Tx exhibits semiconductor-like transport behavior, while Ti3C2Tx is a metal. Finally, this finding opens new avenues for the control of the electronic and optical applications of MXenes and for exploring new applications, in which semiconducting properties are required.« less

  15. Control of electronic properties of 2D carbides (MXenes) by manipulating their transition metal layers

    SciTech Connect

    Anasori, Babak; Shi, Chenyang; Moon, Eun Ju; Xie, Yu; Voigt, Cooper A.; Kent, Paul R. C.; May, Steven J.; Billinge, Simon J. L.; Barsoum, Michel W.; Gogotsi, Yury

    2016-02-24

    In this paper, a transition from metallic to semiconducting-like behavior has been demonstrated in two-dimensional (2D) transition metal carbides by replacing titanium with molybdenum in the outer transition metal (M) layers of M3C2 and M4C3 MXenes. The MXene structure consists of n + 1 layers of near-close packed M layers with C or N occupying the octahedral site between them in an [MX]nM arrangement. Recently, two new families of ordered 2D double transition metal carbides MXenes were discovered, M'2M"C2 and M'2M"2C3 – where M' and M" are two different early transition metals, such as Mo, Cr, Ta, Nb, V, and Ti. The M' atoms only occupy the outer layers and the M" atoms fill the middle layers. In other words, M' atomic layers sandwich the middle M"–C layers. Using X-ray atomic pair distribution function (PDF) analysis on Mo2TiC2 and Mo2Ti2C3 MXenes, we present the first quantitative analysis of structures of these novel materials and experimentally confirm that Mo atoms are in the outer layers of the [MC]nM structures. The electronic properties of these Mo-containing MXenes are compared with their Ti3C2 counterparts, and are found to be no longer metallic-like conductors; instead the resistance increases mildly with decreasing temperatures. Density functional theory (DFT) calculations suggest that OH terminated Mo–Ti MXenes are semiconductors with narrow band gaps. Measurements of the temperature dependencies of conductivities and magnetoresistances have confirmed that Mo2TiC2Tx exhibits semiconductor-like transport behavior, while Ti3C2Tx is a metal. Finally, this finding opens new avenues for the control of the electronic and optical applications of MXenes and for exploring new applications, in

  16. Laminated metal composite formed from low flow stress layers and high flow stress layers using flow constraining elements and method of making same

    SciTech Connect

    Syn, C.K.; Lesuer, D.R.

    1994-12-31

    This invention relates to a laminated metal composite, comprising alternating layers of low flow stress material and high flow stress material, and formed using flow constraining elements around each low flow stress layer; and a method of making same. A composite is a combination of at least two chemically distinct materials with a distinct interface separating the two materials. A metal matrix composite (MMC) is a composite material composed of a metal and a nonmetallic reinforcing agent such as silicon carbide (SiC) or graphite in continuous or discontinuous fiber, whisker, or discrete particulate form. A laminate is a material composed of several bonded layers. It is possible to have a laminate composed of multi-layers of a single type of material bonded to each other. However, such a laminate would not be considered to be a composite. The term {open_quotes}laminated metal composite{close_quotes} (LMC), as used herein, is intended to include a structural material composed of: (1) layers of metal or metal alloys interleaved with (2) a different metal, a metal alloy, or a metal matrix composite (MMC) containing strengthening agents.

  17. High performance pseudocapacitor based on 2D layered metal chalcogenide nanocrystals.

    PubMed

    Muller, Guillaume A; Cook, John B; Kim, Hyung-Seok; Tolbert, Sarah H; Dunn, Bruce

    2015-03-11

    Single-layer and few-layer transition metal dichalcogenides have been extensively studied for their electronic properties, but their energy-storage potential has not been well explored. This paper describes the structural and electrochemical properties of few-layer TiS2 nanocrystals. The two-dimensional morphology leads to very different behavior, compared to corresponding bulk materials. Only small structural changes occur during lithiation/delithiation and charge storage characteristics are consistent with intercalation pseudocapacitance, leading to materials that exhibit both high energy and power density.

  18. Bilayer SnS2: Tunable stacking sequence by charging and loading pressure

    NASA Astrophysics Data System (ADS)

    Bacaksiz, C.; Cahangirov, S.; Rubio, A.; Senger, R. T.; Peeters, F. M.; Sahin, H.

    2016-03-01

    Employing density functional theory-based methods, we investigate monolayer and bilayer structures of hexagonal SnS2, which is a recently synthesized monolayer metal dichalcogenide. Comparison of the 1 H and 1 T phases of monolayer SnS2 confirms the ground state to be the 1 T phase. In its bilayer structure we examine different stacking configurations of the two layers. It is found that the interlayer coupling in bilayer SnS2 is weaker than that of typical transition-metal dichalcogenides so that alternative stacking orders have similar structural parameters and they are separated with low energy barriers. A possible signature of the stacking order in the SnS2 bilayer has been sought in the calculated absorbance and reflectivity spectra. We also study the effects of the external electric field, charging, and loading pressure on the characteristic properties of bilayer SnS2. It is found that (i) the electric field increases the coupling between the layers at its preferred stacking order, so the barrier height increases, (ii) the bang gap value can be tuned by the external E field and under sufficient E field, the bilayer SnS2 can become a semimetal, (iii) the most favorable stacking order can be switched by charging, and (iv) a loading pressure exceeding 3 GPa changes the stacking order. The E-field tunable band gap and easily tunable stacking sequence of SnS2 layers make this 2D crystal structure a good candidate for field effect transistor and nanoscale lubricant applications.

  19. Alleviation of fermi-level pinning effect at metal/germanium interface by the insertion of graphene layers

    SciTech Connect

    Baek, Seung-heon Chris; Seo, Yu-Jin; Oh, Joong Gun; Albert Park, Min Gyu; Bong, Jae Hoon; Yoon, Seong Jun; Lee, Seok-Hee; Seo, Minsu; Park, Seung-young; Park, Byong-Guk

    2014-08-18

    In this paper, we report the alleviation of the Fermi-level pinning on metal/n-germanium (Ge) contact by the insertion of multiple layers of single-layer graphene (SLG) at the metal/n-Ge interface. A decrease in the Schottky barrier height with an increase in the number of inserted SLG layers was observed, which supports the contention that Fermi-level pinning at metal/n-Ge contact originates from the metal-induced gap states at the metal/n-Ge interface. The modulation of Schottky barrier height by varying the number of inserted SLG layers (m) can bring about the use of Ge as the next-generation complementary metal-oxide-semiconductor material. Furthermore, the inserted SLG layers can be used as the tunnel barrier for spin injection into Ge substrate for spin-based transistors.

  20. Characteristics of Spontaneous Emission of Polarized Atoms in Metal Dielectric Multiple Layer Structures

    NASA Astrophysics Data System (ADS)

    Zhao, Li-Ming; Gu, Ben-Yuan; Zhou, Yun-Song

    2007-11-01

    The spontaneous emission (SE) progress of polarized atoms in a stratified structure of air-dielectric(D0)-metal(M)-dielectric(D1)-air can be controlled effectively by changing the thickness of the D1 layer and rotating the polarized direction of atoms. It is found that the normalized SE rate of atoms located inside the D0 layer crucially depends on the atomic position and the thickness of the D1 layer. When the atom is located near the D0-M interface, the normalized atomic SE rate as a function of the atomic position is abruptly onset for the thin D1 layer. However, with the increasing thickness of the D1 layer, the corresponding curve profile exhibits plateau and stays nearly unchanged. The substantial change of the SE rate stems from the excitation of the surface plasmon polaritons in metal-dielectric interface, and the feature crucially depends on the thickness of D1 layer. If atoms are positioned near the D0-air interface, the substantial variation of the normalized SE rate appears when rotating the polarized direction of atoms. These findings manifest that the atomic SE processes can be flexibly controlled by altering the thickness of the dielectric layer D1 or rotating the orientation of the polarization of atoms.

  1. Effect of electron collecting metal oxide layer in normal and inverted structure polymer solar cells

    SciTech Connect

    Ng, A.; Liu, X.; Sun, Y. C.; Djurišić, A. B.; Ng, A. M. C.; Chan, W. K.

    2013-12-04

    We performed a systematic study of the effect of electron collecting metal oxide layer on the performance of P3HT: PCBM solar cells. Zinc oxide (ZnO) or titanium dioxide (TiO{sub 2}) buffer layers were prepared by either e-beam evaporation or solution processing method. We also compared the photovoltaic performance of inserting the buffer layer between indium tin oxide (ITO) and the polymer layer for the inverted structure (ITO/ ZnO or TiO{sub 2}/P3HT:PCBM/V{sub 2}O{sub 5}/Au) as well as inserting the buffers layers between the polymer and the aluminum electrode for the conventional structure (ITO/V{sub 2}O{sub 5}/P3HT:PCBM/ZnO or TiO{sub 2}/Al). The results are shown in detail.

  2. Large area nanoscale metal meshes for use as transparent conductive layers

    NASA Astrophysics Data System (ADS)

    Jin, Yuanhao; Li, Qunqing; Chen, Mo; Li, Guanhong; Zhao, Yudan; Xiao, Xiaoyang; Wang, Jiaping; Jiang, Kaili; Fan, Shoushan

    2015-10-01

    We report on the experimental realization of using super-aligned carbon nanotubes (SACNTs) as etching masks for the fabrication of large area nanoscale metal meshes. This method can easily be extended to different metals on both rigid and flexible substrates. The as-fabricated metal meshes, including the ones made of gold, copper, and aluminum, are suitable for use as transparent conductive layers (TCLs). The metal meshes, which are similar to the SACNT networks in their dimensional features of tens of nanometers, exhibit compatible performance in terms of optical transmittance and sheet resistance. Moreover, because the metal meshes are fabricated as an integrated material, there is no junction resistance between the interconnected metal nanostructures, which markedly lowers their sheet resistance at high temperatures. The fabrication of such an effective etching mask involves a simple drawing process of the SACNT networks prepared and a common deposition process. This approach should be easy to extend to various research fields and has broad prospects in commercial applications.We report on the experimental realization of using super-aligned carbon nanotubes (SACNTs) as etching masks for the fabrication of large area nanoscale metal meshes. This method can easily be extended to different metals on both rigid and flexible substrates. The as-fabricated metal meshes, including the ones made of gold, copper, and aluminum, are suitable for use as transparent conductive layers (TCLs). The metal meshes, which are similar to the SACNT networks in their dimensional features of tens of nanometers, exhibit compatible performance in terms of optical transmittance and sheet resistance. Moreover, because the metal meshes are fabricated as an integrated material, there is no junction resistance between the interconnected metal nanostructures, which markedly lowers their sheet resistance at high temperatures. The fabrication of such an effective etching mask involves a simple

  3. A fluorescent, photochromic and thermochromic trifunctional material based on a layered metal-viologen complex.

    PubMed

    Wan, Fang; Qiu, Li-Xia; Zhou, Liang-Liang; Sun, Yan-Qiong; You, Yi

    2015-11-14

    The azide anion as an energy acceptor and an electron donor has been introduced into a metal-viologen compound to form a 2D layered viologen-based trifunctional material, which exhibits the rare discolored function of reversible photochromism and thermochromism. Interestingly, its fluorescence can be switched by visible light irradiation and heating in air.

  4. Elasto-plastic analysis of interface layers for fiber reinforced metal matrix composites

    NASA Technical Reports Server (NTRS)

    Doghri, I.; Leckie, F. A.

    1991-01-01

    The mismatch in coefficients of thermal expansion (CTE) of fiber and matrix in metal matrix composites reinforced with ceramic fibers induces high thermal stresses in the matrix. Elasto-plastic analyses - with different degrees of simplification and modelization - show that an interface layer with a sufficiently high CTE can reduce the tensile hoop stress in the matrix substantially.

  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. 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.

  7. Metallic conduction induced by direct anion site doping in layered SnSe2

    PubMed Central

    Kim, Sang Il; Hwang, Sungwoo; Kim, Se Yun; Lee, Woo-Jin; Jung, Doh Won; Moon, Kyoung-Seok; Park, Hee Jung; Cho, Young-Jin; Cho, Yong-Hee; Kim, Jung-Hwa; Yun, Dong-Jin; Lee, Kyu Hyoung; Han, In-taek; Lee, Kimoon; Sohn, Yoonchul

    2016-01-01

    The emergence of metallic conduction in layered dichalcogenide semiconductor materials by chemical doping is one of key issues for two-dimensional (2D) materials engineering. At present, doping methods for layered dichalcogenide materials have been limited to an ion intercalation between layer units or electrostatic carrier doping by electrical bias owing to the absence of appropriate substitutional dopant for increasing the carrier concentration. Here, we report the occurrence of metallic conduction in the layered dichalcogenide of SnSe2 by the direct Se-site doping with Cl as a shallow electron donor. The total carrier concentration up to ~1020 cm−3 is achieved by Cl substitutional doping, resulting in the improved conductivity value of ~170 S·cm−1 from ~1.7 S·cm−1 for non-doped SnSe2. When the carrier concentration exceeds ~1019 cm−3, the conduction mechanism is changed from hopping to degenerate conduction, exhibiting metal-insulator transition behavior. Detailed band structure calculation reveals that the hybridized s-p orbital from Sn 5s and Se 4p states is responsible for the degenerate metallic conduction in electron-doped SnSe2. PMID:26792630

  8. Preparation of silica stabilized Tobacco mosaic virus templates for the production of metal and layered nanoparticles.

    PubMed

    Royston, Elizabeth S; Brown, Adam D; Harris, Michael T; Culver, James N

    2009-04-15

    The use of biological molecules as templates for the production of metal nanoparticles and wires is often limited by the stability of the bio-template and its affinity for nucleating metal deposition. In this study, Tobacco mosaic virus (TMV) was used as a model bio-template to investigate the use of silica coatings as a means to both enhance template stability and increase its affinity for metal ions. Results indicate that the unmodified TMV particle can function as a template for the growth of thin (<1 nm) silica layers. However, this thin silica shell did not enhance the stability of the template during metal deposition. To increase silica growth on the TMV template, a pretreatment with aniline was used to produce a uniform silica attractive surface. Aniline pretreated templates yielded significant silica layers of >20 nm in thickness. These silica shells conferred a high degree of stability to the TMV particle and promoted the deposition of various metal nanoparticles through conventional silica mineralization chemistries. This process provides a simple and robust method for the layering of inorganics onto a biological template.

  9. Electrochemical cell stack assembly

    DOEpatents

    Jacobson, Craig P.; Visco, Steven J.; De Jonghe, Lutgard C.

    2010-06-22

    Multiple stacks of tubular electrochemical cells having a dense electrolyte disposed between an anode and a cathode preferably deposited as thin films arranged in parallel on stamped conductive interconnect sheets or ferrules. The stack allows one or more electrochemical cell to malfunction without disabling the entire stack. Stack efficiency is enhanced through simplified gas manifolding, gas recycling, reduced operating temperature and improved heat distribution.

  10. Heat-resistant organic molecular layer as a joint interface for metal reduction on plastics surfaces

    NASA Astrophysics Data System (ADS)

    Sang, Jing; Aisawa, Sumio; Hirahara, Hidetoshi; Kudo, Takahiro; Mori, Kunio

    2016-04-01

    Heat-resistant organic molecular layers have been fabricated by triazine-based silane coupling agent for metal reduction on plastic surfaces using adsorption method. These molecular layers were used as an interfacial layer between polyamide (PA6) and metal solution to reduce Ag+ ion to Ag0. The interfacial behaviors of triazine molecular layer at the interfaces between PA6 and Ag solution were investigated using quartz crystal microbalance (QCM). The kinetics of molecular adsorption on PA6 was investigated by using triazine-based silane coupling agent solutions at different pH and concentration. X-ray photoelectron spectroscopy (XPS), atomic force microscope (AFM), and local nano thermal analysis were employed to characterize the surfaces and interfaces. The nano thermal analysis results show that molecular layers of triazine-based silane coupling agent greatly improved heat resistance of PA6 resin from 170 °C up to 230 °C. This research developed an in-depth insight for molecular behaviors of triazine-based silane coupling agent at the PA6 and Ag solution interfaces and should be of significant value for interfacial research between plastics and metal solution in plating industry.

  11. Combustion zone durability program-B. Task VIII. Sputter deposited ceramic and metallic coatings. Executive summary. [Graded metal; metal/ceramic layered; dense surface ceramic

    SciTech Connect

    Patten, J. W.; Moss, R. W.; Hays, D. D.

    1980-11-01

    The graded metal coatings are of the CoCrAlY type modified by including high Cr surface compositions, gradients in Cr and Al composition, underlayers and graded Pt additions, and Hf substitutions for Y. The metal ceramic layered coatings consist of alternate metal (Ni, Ni-Cr, CoCrAlY or Pt) and ceramic (Al/sub 2/O/sub 3/ or ZrO/sub 2/ + Y) layers. Investigations of dense surface ceramic coatings are directed towards methods for obtaining adherent impermeable ceramic protective coatings for gas turbine hot section components. Increased coating adherence is being sought through two coating designs intended to accomodate expansion and modulus mismatches at the coating-substrate interface.

  12. Electronic and magnetic properties of single-layer M P X3 metal phosphorous trichalcogenides

    NASA Astrophysics Data System (ADS)

    Chittari, Bheema Lingam; Park, Youngju; Lee, Dongkyu; Han, Moonsup; MacDonald, Allan H.; Hwang, Euyheon; Jung, Jeil

    2016-11-01

    We survey the electronic structure and magnetic properties of two-dimensional (2D) M P X3 (M =V,Cr,Mn,Fe,Co,Ni,Cu,Zn, and X =S,Se,Te ) transition-metal chalcogenophosphates to shed light on their potential role as single-layer van der Waals materials that possess magnetic order. Our ab initio calculations predict that most of these single-layer materials are antiferromagnetic semiconductors. The band gaps of the antiferromagnetic states decrease as the atomic number of the chalcogen atom increases (from S to Se to Te), leading in some cases to half-metallic ferromagnetic states or to nonmagnetic metallic states. We find that the competition between antiferromagnetic and ferromagnetic states can be substantially influenced by gating and by strain engineering. The sensitive interdependence we find between magnetic, structural, and electronic properties establishes the potential of this 2D materials class for applications in spintronics.

  13. Ab initio study of magnetic single layer MPX3 metal-phosphorous-trichalcogenides

    NASA Astrophysics Data System (ADS)

    Chittari, Bheema Lingam; Hwang, Euyheon; Jung, Jeil; MacDonald, Allan H.

    We analyze the electronic structure of two dimensional (2D) MPX3 (M= V, Cr, Mn, Fe, Co, Ni, Cu, Zn, and X = S, Se, Te) transition metal thiophosphates, viewing them as single layer van der Waals materials that can exhibit magnetic order. Our ab initio calculations for MPX3 single layer compounds predict both semiconducting phases with variable band gap sizes and metallic phases, and an intimate interplay between magnetic order and the presence of a gap. A systematic trend of decreasing band gaps in antiferromagnetic states is observed as the chalcogen atoms S, Se, and Te change from smaller to larger atomic number, Ferromagnetic, antiferromagnetic, and nonmagnetic phases, and lattice constant changes accompanied by distortions in crystal symmetry, occur as the metal atom is varied. The sensitive interdependence between magnetic, structural, and electronic properties suggests the important potential of this class of 2D magnetic van der Waals materials for strain and field-effect carrier tunable spintronics.

  14. Mode propagation in optical nanowaveguides with dielectric cores and surrounding metal layers.

    PubMed

    Lapchuk, Anatoly S; Shin, Dongho; Jeong, Ho-Seop; Kyong, Chun Su; Shin, Dong-Ik

    2005-12-10

    The mode spectrum in an optical nanowaveguide consisting of a dielectric-core layer surrounded by two identical metal layers is investigated. A simple model based on mode matching to predict the properties of mode propagation in such optical nanowaveguides is proposed. It is shown that quasi-TM00 and quasi-TM10 modes supported by an optical microstrip line do not have a cutoff frequency, regardless of the size of the metal strips, the thickness of the dielectric slab, and the cross-sectional shape. The transverse size of the TM00 mode supported by a nanosized microstrip line was found to be approximately equal to the transverse dimension of the microstrip line. In closed rectangular and elliptical nanowaveguides, i.e., in which all dielectric surfaces are covered with metal films, the cross-sectional shape of the waveguide should be stretched along one side to produce propagation conditions for the fundamental mode.

  15. Core–Shell Nanoparticle Coating as an Interfacial Layer for Dendrite-Free Lithium Metal Anodes

    PubMed Central

    2017-01-01

    Lithium metal based batteries represent a major challenge and opportunity in enabling a variety of devices requiring high-energy-density storage. However, dendritic lithium growth has limited the practical application of lithium metal anodes. Here we report a nanoporous, flexible and electrochemically stable coating of silica@poly(methyl methacrylate) (SiO2@PMMA) core–shell nanospheres as an interfacial layer on lithium metal anode. This interfacial layer is capable of inhibiting Li dendrite growth while sustaining ionic flux through it, which is attributed to the nanoscaled pores formed among the nanospheres. Enhanced Coulombic efficiencies during lithium charge/discharge cycles have been achieved at various current densities and areal capacities. PMID:28280780

  16. Layer modeling of zinc removal from metallic mixture of waste printed circuit boards by vacuum distillation.

    PubMed

    Gao, Yujie; Li, Xingang; Ding, Hui

    2015-08-01

    A layer model was established to elucidate the mechanism of zinc removal from the metallic mixture of waste printed circuit boards by vacuum distillation. The removal process was optimized by response surface methodology, and the optimum operating conditions were the chamber pressure of 0.1Pa, heating temperature of 923K, heating time of 60.0min, particle size of 70 mesh (0.212mm) and initial mass of 5.25g. Evaporation efficiency of zinc, the response variable, was 99.79%, which indicates that the zinc can be efficiently removed. Based on the experimental results, a mathematical model, which bears on layer structure, evaporation, mass transfer and condensation, interprets the mechanism of the variable effects. Especially, in order to reveal blocking effect on the zinc removal, the Blake-Kozeny-Burke-Plummer equation was introduced into the mass transfer process. The layer model can be applied to a wider range of metal removal by vacuum distillation.

  17. Multilayered thermal insulation formed of zirconia bonded layers of zirconia fibers and metal oxide fibers and method for making same

    DOEpatents

    Wrenn, Jr., George E.; Holcombe, Jr., Cressie E.

    1988-01-01

    A multilayered thermal insulating composite is formed of a first layer of zirconia-bonded zirconia fibers for utilization near the hot phase or surface of a furnace or the like. A second layer of zirconia-bonded metal oxide fibers is attached to the zirconia fiber layer by a transition layer formed of intermingled zirconia fibers and metal oxide fibers. The thermal insulation is fabricated by vacuum molding with the layers being sequentially applied from aqueous solutions containing the fibers to a configured mandrel. A portion of the solution containing the fibers forming the first layer is intermixed with the solution containing the fibers of the second layer for forming the layer of mixed fibers. The two layers of fibers joined together by the transition layer are saturated with a solution of zirconium oxynitrate which provides a zirconia matrix for the composite when the fibers are sintered together at their nexi.

  18. Multilayered thermal insulation formed of zirconia bonded layers of zirconia fibers and metal oxide fibers and method for making same

    DOEpatents

    Wrenn, G.E. Jr.; Holcombe, C.E. Jr.

    1988-09-13

    A multilayered thermal insulating composite is formed of a first layer of zirconia-bonded zirconia fibers for utilization near the hot phase or surface of a furnace or the like. A second layer of zirconia-bonded metal oxide fibers is attached to the zirconia fiber layer by a transition layer formed of intermingled zirconia fibers and metal oxide fibers. The thermal insulation is fabricated by vacuum molding with the layers being sequentially applied from aqueous solutions containing the fibers to a configured mandrel. A portion of the solution containing the fibers forming the first layer is intermixed with the solution containing the fibers of the second layer for forming the layer of mixed fibers. The two layers of fibers joined together by the transition layer are saturated with a solution of zirconium oxynitrate which provides a zirconia matrix for the composite when the fibers are sintered together at their nexi.

  19. Atomic layer deposition of metal oxide patterns on nonwoven fiber mats using localized physical compression.

    PubMed

    Sweet, William J; Oldham, Christopher J; Parsons, Gregory N

    2014-06-25

    Patterning is an essential part of many industrial processes from printing to semiconductor manufacturing. In this work, we demonstrate a new method to pattern and selectively coat nonwoven textiles by atomic layer deposition (ALD) using compressive mask patterning. A physical mask combined with mechanical compression allows lateral definition and fidelity of the ALD coating to be controlled. We produce features of several sizes on different nonwoven fiber materials and demonstrate the ability to limit diffusion effects to within <200 μm of the pattern edge. Lateral and vertical penetration of reactive growth species into nonwoven mats is investigated by plan-view and cross-sectional imaging. Vertical growth is also analyzed by imaging coating depth into fiber mat stacks. We develop a fully quantitative transport model that describes well the effect of fiber structure and mechanical compression on the extent of coating under the physical mask. This method could be implemented for high-volume patterning for applications including flexible electronics.

  20. Intercalation of highly dispersed metal nanoclusters into a layered metal oxide for photocatalytic overall water splitting.

    PubMed

    Oshima, Takayoshi; Lu, Daling; Ishitani, Osamu; Maeda, Kazuhiko

    2015-02-23

    Metal nanoclusters (involving metals such as platinum) with a diameter smaller than 1 nm were deposited on the interlayer nanospace of KCa2 Nb3 O10 using the electrostatic attraction between a cationic metal complex (e.g., [Pt(NH3 )4 ]Cl2 ) and a negatively charged two-dimensional Ca2 Nb3 O10 (-) sheet, without the aid of any additional reagent. The material obtained possessed eight-fold greater photocatalytic activity for water splitting into H2 and O2 under band-gap irradiation than the previously reported analog using a RuO2 promoter. This study highlighted the superior functionality of Pt nanoclusters with diameters smaller than 1 nm for photocatalytic overall water splitting. This material shows the greatest efficiency among nanosheet-based photocatalysts reported to date.

  1. Transmission enhancement based on strong interference in metal-semiconductor layered film for energy harvesting.

    PubMed

    Li, Qiang; Du, Kaikai; Mao, Kening; Fang, Xu; Zhao, Ding; Ye, Hui; Qiu, Min

    2016-07-12

    A fundamental strategy to enhance optical transmission through a continuous metallic film based on strong interference dominated by interface phase shift is developed. In a metallic film coated with a thin semiconductor film, both transmission and absorption are simultaneously enhanced as a result of dramatically reduced reflection. For a 50-nm-thick Ag film, experimental transmission enhancement factors of 4.5 and 9.5 are realized by exploiting Ag/Si non-symmetric and Si/Ag/Si symmetric geometries, respectively. These planar layered films for transmission enhancement feature ultrathin thickness, broadband and wide-angle operation, and reduced resistance. Considering one of their potential applications as transparent metal electrodes in solar cells, a calculated 182% enhancement in the total transmission efficiency relative to a single metallic film is expected. This strategy relies on no patterned nanostructures and thereby may power up a wide spectrum of energy-harvesting applications such as thin-film photovoltaics and surface photocatalysis.

  2. Transmission enhancement based on strong interference in metal-semiconductor layered film for energy harvesting

    NASA Astrophysics Data System (ADS)

    Li, Qiang; Du, Kaikai; Mao, Kening; Fang, Xu; Zhao, Ding; Ye, Hui; Qiu, Min

    2016-07-01

    A fundamental strategy to enhance optical transmission through a continuous metallic film based on strong interference dominated by interface phase shift is developed. In a metallic film coated with a thin semiconductor film, both transmission and absorption are simultaneously enhanced as a result of dramatically reduced reflection. For a 50-nm-thick Ag film, experimental transmission enhancement factors of 4.5 and 9.5 are realized by exploiting Ag/Si non-symmetric and Si/Ag/Si symmetric geometries, respectively. These planar layered films for transmission enhancement feature ultrathin thickness, broadband and wide-angle operation, and reduced resistance. Considering one of their potential applications as transparent metal electrodes in solar cells, a calculated 182% enhancement in the total transmission efficiency relative to a single metallic film is expected. This strategy relies on no patterned nanostructures and thereby may power up a wide spectrum of energy-harvesting applications such as thin-film photovoltaics and surface photocatalysis.

  3. Engineering damping in insulating magnet-metal bilayers using ultrathin spacer layers

    NASA Astrophysics Data System (ADS)

    Aradhya, Sriharsha V.; Jermain, Colin L.; Paik, Hanjong; Heron, John T.; Schlom, Darrell G.; Ralph, Daniel C.; Buhrman, Robert A.

    2015-03-01

    Insulating magnetic materials, particularly yttrium iron garnet (YIG), are of significant interest for fundamental research as well as technological applications. Thus far copper spacer layers of ~10 nm - 1 μm thickness sandwiched between YIG and heavy metal films have been shown to modulate the damping of the magnetic layer either higher or lower. We report on the effect of ultrathin nonmagnetic spacer layers on the damping of YIG with different heavy metal overlayers. We start with YIG films grown by oxide molecular beam epitaxy with thicknesses below 20 nm and Gilbert damping as low as 0.0005. We observe that a spacer layer can increase the damping by 50% in YIG/spacer/Ta samples compared to YIG/Ta, and the increase can be as large 500% for YIG/spacer/Pt compared to YIG/Pt. These observations suggest a significant increase in the effective spin mixing conductance at the YIG-heavy metal interface that might be used to improve the efficiency of the spin torque produced by the spin Hall effect.

  4. Pressure induced metallization with absence of structural transition in layered molybdenum diselenide

    SciTech Connect

    Zhao, Zhao; Zhang, Haijun; Yuan, Hongtao; Wang, Shibing; Lin, Yu; Zeng, Qiaoshi; Xu, Gang; Liu, Zhenxian; Solanki, G. K.; Patel, K. D.; Cui, Yi; Hwang, Harold Y.; Mao, Wendy L.

    2015-06-19

    Layered transition-metal dichalcogenides have emerged as exciting material systems with atomically thin geometries and unique electronic properties. Pressure is a powerful tool for continuously tuning their crystal and electronic structures away from the pristine states. Here, we systematically investigated the pressurized behavior of MoSe2 up to ~60 GPa using multiple experimental techniques and ab-initio calculations. MoSe2 evolves from an anisotropic two-dimensional layered network to a three-dimensional structure without a structural transition, which is a complete contrast to MoS2. The role of the chalcogenide anions in stabilizing different layered patterns is underscored by our layer sliding calculations. MoSe2 possesses highly tunable transport properties under pressure, determined by the gradual narrowing of its band-gap followed by metallization. The continuous tuning of its electronic structure and band-gap in the range of visible light to infrared suggest possible energy-variable optoelectronics applications in pressurized transition-metal dichalcogenides.

  5. Pressure induced metallization with absence of structural transition in layered molybdenum diselenide

    DOE PAGES

    Zhao, Zhao; Zhang, Haijun; Yuan, Hongtao; ...

    2015-06-19

    Layered transition-metal dichalcogenides have emerged as exciting material systems with atomically thin geometries and unique electronic properties. Pressure is a powerful tool for continuously tuning their crystal and electronic structures away from the pristine states. Here, we systematically investigated the pressurized behavior of MoSe2 up to ~60 GPa using multiple experimental techniques and ab-initio calculations. MoSe2 evolves from an anisotropic two-dimensional layered network to a three-dimensional structure without a structural transition, which is a complete contrast to MoS2. The role of the chalcogenide anions in stabilizing different layered patterns is underscored by our layer sliding calculations. MoSe2 possesses highly tunablemore » transport properties under pressure, determined by the gradual narrowing of its band-gap followed by metallization. The continuous tuning of its electronic structure and band-gap in the range of visible light to infrared suggest possible energy-variable optoelectronics applications in pressurized transition-metal dichalcogenides.« less

  6. Exchange coupling in metallic multilayers with a top FeRh layer

    NASA Astrophysics Data System (ADS)

    Yamada, S.; Tanikawa, K.; Hirayama, J.; Kanashima, T.; Taniyama, T.; Hamaya, K.

    2016-05-01

    We study magnetic properties of metallic multilayers with FeRh/ferromagnet interfaces grown by low-temperature molecular beam epitaxy. Room-temperature coercivity of the ferromagnetic layers is significantly enhanced after the growth of FeRh, proving the existence of the exchange coupling between the antiferromagnetic FeRh layer and the ferromagnetic layer. However, exchange bias is not clearly observed probably due to the presence of disordered structures, which result from the lattice strain at the FeRh/ferromagnet interfaces due to the lattice mismatch. We infer that the lattice matched interface between FeRh and ferromagnetic layers is a key parameter for controlling magnetic switching fields in such multilayer systems.

  7. Enablement of DSA for VIA layer with a metal SIT process flow

    NASA Astrophysics Data System (ADS)

    Schneider, L.; Farys, V.; Serret, E.; Fenouillet-Beranger, C.

    2016-03-01

    For technologies beyond 10 nm, 1D gridded designs are commonly used. This practice is common particularly in the case of Self-Aligned Double Patterning (SADP) metal processes where Vertical Interconnect Access (VIA) connecting metal line layers are placed along a discrete grid thus limiting the number of VIA pitches. In order to create a Vertical Interconnect Access (VIA) layer, graphoepitaxy Directed Self-Assembly (DSA) is the prevailing candidate. The technique relies on the creation of a confinement guide using optical microlithography methods, in which the BCP is allowed to separate into distinct regions. The resulting patterns are etched to obtain an ordered VIA layer. Guiding pattern variations impact directly on the placement of the target and one must ensure that it does not interfere with circuit performance. To prevent flaws, design rules are set. In this study, for the first time, an original framework is presented to find a consistent set of design rules for enabling the use of DSA in a production flow using Self Aligned Double Patterning (SADP) for metal line layer printing. In order to meet electrical requirements, the intersecting area between VIA and metal lines must be sufficient to ensure correct electrical connection. The intersecting area is driven by both VIA placement variability and metal line printing variability. Based on multiple process assumptions for a 10 nm node, the Monte Carlo method is used to set a maximum threshold for VIA placement error. In addition, to determine a consistent set of design rules, representative test structures have been created and tested with our in-house placement estimator: the topological skeleton of the guiding pattern [1]. Using this technique, structures with deviation above the maximum tolerated threshold are considered as infeasible and the appropriate set of design rules is extracted. In a final step, the design rules are verified with further test structures that are randomly generated using

  8. Exclusion of metal oxide by an RF sputtered Ti layer in flexible perovskite solar cells: energetic interface between a Ti layer and an organic charge transporting layer.

    PubMed

    Ameen, Sadia; Akhtar, M Shaheer; Seo, Hyung-Kee; Nazeeruddin, Mohammad Khaja; Shin, Hyung-Shik

    2015-04-14

    In this work, the effects of a titanium (Ti) layer on the charge transport and recombination rates of flexible perovskite solar cells were studied. Ti as an efficient barrier layer was deposited directly on PET-ITO flexible substrates through RF magnetic sputtering using a Ti-source and a pressure of ∼5 mTorr. A Ti coated PET-ITO was used for the fabrication of a flexible perovskite solar cell without using any metal oxide layer. The fabricated flexible perovskite solar cell was composed of a PET-ITO/Ti/perovskite (CH3NH3PbI3)/organic hole transport layer of 2,2',7,7'-tetrakis [N,N'-di-p-methoxyphenylamine]-9,9'-spirobifluorene (spiro-OMeTAD)-Li-TFSI/Ag. A high conversion efficiency of ∼8.39% along with a high short circuit current (JSC) of ∼15.24 mA cm(-2), an open circuit voltage (VOC) of ∼0.830 V and a high fill factor (FF) of ∼0.66 was accomplished by the fabricated flexible perovskite solar cell under a light illumination of ∼100 mW cm(-2) (1.5 AM). Intensity-modulated photocurrent (IMPS)/photovoltage spectroscopy (IMVS) studies demonstrated that the fabricated flexible perovskite solar cell considerably reduced the recombination rate.

  9. Future manufacturing techniques for stacked MCM interconnections

    NASA Astrophysics Data System (ADS)

    Carson, R. F.; Seigal, P. K.; Craft, D. C.; Lovejoy, M. L.

    1994-06-01

    As multichip modules (MCMs) grow in chip count and complexity, increasingly large numbers of input/output (I/O) channels will be required for connection to other MCMs or printed wiring boards. In applications such as digital signal processing, large increases in processing density (number of operations in a given volume) can be obtained in stacked MCM arrangements. The potential pin counts and required I/O densities in these stacked architectures will push beyond the limits of present interlevel coupling techniques. This problem is particularly acute if easy separation of layers is needed to meet MCM testing and yield requirements. Solutions to this problem include the use of laser-drilled, metal-filled electrical vias in the MCM substrate and also optoelectronic data channels that operate in large arrays. These arrays will emit and detect signals traveling perpendicular to the surface of the MCM. All of these approaches will require packaging and alignment that makes use of advanced MCM manufacturing techniques.

  10. Super-resolution and nonlinear absorption with metallodielectric stacks

    NASA Astrophysics Data System (ADS)

    Katte, Nkorni

    We investigate sub-wavelength imaging, i.e. super-resolution, in metal-dielectric film systems, which are simply referred to as metallodielectrics. Our simulations incorporate experimentally derived material dielectric dispersion properties across the visible region. For demonstration purposes we designed metallodielectric stacks for super-resolution containing GaP and TiO2, dielectric films, and either Ag or Au as the metallic materials. Using the known optical properties of the constituent materials found designs that could be good candidates for super-resolution. We did not have the resources to fabricate these samples; however, based on our computer simulations we are confident that the designed samples would produce super-resolution approaching one-twentieth of a wavelength in air. We examined for the first time the broad bandwidth of the super-resolution phenomenon in metallodielectrics. We validate the results using the finite element method (FEM) and the transfer matrix method (TMM). We also show that the measurement of super-resolution is highly dependent on the distance of the probe from the exit surface; high resolution at the exit plane can quickly decay with a few tens of nanometers when high resolution is sought. Secondly we numerically studied the nonlinear optical transmission of an optical beam through heterogeneous metallodielectric stacks under the action of nonlinear absorption. One film layer is a metal and the other layer is a dielectric; the heterogeneous material is called a metallodielectric stack (MDS). In these studies we also used applied FEM with two-dimensional transverse effects and TMM simulation techniques. Our samples consisted of Ag/ZnS, Ag/SiO 2 and Cu/ZnS. We numerically simulate using two transverse dimensions in our FEM codes, Z-scan experiments for two different MDS designs and draw general observations from these cases. We experimentally examined the nonlinear absorption effect in samples of Ag/SiO2 when irradiated by a

  11. Micro-layers of polystyrene film preventing metal oxidation: implications in cultural heritage conservation

    NASA Astrophysics Data System (ADS)

    Giambi, Francesca; Carretti, Emiliano; Dei, Luigi; Baglioni, Piero

    2014-12-01

    Protection of surfaces directly exposed to the detrimental action of degradative agents (i.e. oxygen, air pollutants and bacteria) is one of the most important challenges in the field of conservation of works of art. Metallic objects are subjected to specific surface corrosion phenomena that, over the years, make mandatory the research of innovative materials that should avoid the direct contact between the metal surface and the weathering agents. In this paper, the set-up, characterisation and application of a new reversible material for preserving metal artefacts are reported. Micro-layers constituted of low-adhesive polystyrene (PS) films obtained from recycling waste packaging materials made of expanded PS were studied. The morphology and thickness of PS films were characterised by optical, atomic force and scanning electron microscopy (SEM). A further check on thickness was carried out by means of visible spectrophotometry doping the films with a hydrophobic dye. Thermal properties of the PS micro-layers were studied by means of differential scanning calorimetry coupled with optical microscopy. Permeability of the PS films to water vapour was also determined. The potential of the low-adhesive PS films, that enabled an easy removal in case of film deterioration, for preventing metal oxidation was investigated on brass specimens by simulating standard artificial corrosion programmes. Morphological and chemical (coupling the energy-dispersive X-rays spectrometry to SEM measurements) analyses carried out on these metal samples showed promising results in terms of surface protection against corrosion.

  12. Performance limits of tunnel transistors based on mono-layer transition-metal dichalcogenides

    NASA Astrophysics Data System (ADS)

    Jiang, Xiang-Wei; Li, Shu-Shen

    2014-05-01

    Performance limits of tunnel field-effect transistors based on mono-layer transition metal dichalcogenides are investigated through numerical quantum mechanical simulations. The atomic mono-layer nature of the devices results in a much smaller natural length λ, leading to much larger electric field inside the tunneling diodes. As a result, the inter-band tunneling currents are found to be very high as long as ultra-thin high-k gate dielectric is possible. The highest on-state driving current is found to be close to 600 μA/μm at Vg = Vd = 0.5 V when 2 nm thin HfO2 layer is used for gate dielectric, outperforming most of the conventional semiconductor tunnel transistors. In the five simulated transition-metal dichalcogenides, mono-layer WSe2 based tunnel field-effect transistor shows the best potential. Deep analysis reveals that there is plenty room to further enhance the device performance by either geometry, alloy, or strain engineering on these mono-layer materials.

  13. Performance limits of tunnel transistors based on mono-layer transition-metal dichalcogenides

    SciTech Connect

    Jiang, Xiang-Wei Li, Shu-Shen

    2014-05-12

    Performance limits of tunnel field-effect transistors based on mono-layer transition metal dichalcogenides are investigated through numerical quantum mechanical simulations. The atomic mono-layer nature of the devices results in a much smaller natural length λ, leading to much larger electric field inside the tunneling diodes. As a result, the inter-band tunneling currents are found to be very high as long as ultra-thin high-k gate dielectric is possible. The highest on-state driving current is found to be close to 600 μA/μm at V{sub g} = V{sub d} = 0.5 V when 2 nm thin HfO{sub 2} layer is used for gate dielectric, outperforming most of the conventional semiconductor tunnel transistors. In the five simulated transition-metal dichalcogenides, mono-layer WSe{sub 2} based tunnel field-effect transistor shows the best potential. Deep analysis reveals that there is plenty room to further enhance the device performance by either geometry, alloy, or strain engineering on these mono-layer materials.

  14. Fabrication and design of metal nano-accordion structures using atomic layer deposition and interference lithography.

    PubMed

    Min, J-H; Bagal, A; Mundy, J Z; Oldham, C J; Wu, B-I; Parsons, G N; Chang, C-H

    2016-03-07

    Metal nanostructures have attractive electrical and thermal properties as well as structural stability, and are important for applications in flexible conductors. In this study, we have developed a method to fabricate and control novel complex platinum nanostructures with accordion-like profile using atomic layer deposition on lithographically patterned polymer templates. The template removal process results in unique structural transformation of the nanostructure profile, which has been studied and modeled. Using different template duty cycles and aspect ratios, we have demonstrated a wide variety of cross-sectional profiles from wavy geometry to pipe array patterns. These complex thin metal nanostructures can find applications in flexible/stretchable electronics, photonics and nanofluidics.

  15. Optical properties of surface layers of Co-based amorphous metallic alloys

    NASA Astrophysics Data System (ADS)

    Poperenko, L. V.; Kravets, V. G.; Lysenko, S. I.; Vinnichenko, K. L.

    2005-04-01

    The modification of roughness and structure of the surface layers of a cobalt-based amorphous metal alloy after thermal treatment at elevated and cryogenic temperatures and under the influence of an external magnetic field is studied by light scattering and atomic force microscopy. The parameters of the surface roughness were calculated from the measured indicatrices of light scattering. It is shown that heating of the metal ribbons to T=350-475 °C partially relieves stresses arising in the course of the ribbon preparation and increases the surface roughness compared to freshly prepared samples.

  16. Transient temperature of liquid on micro metal layer heated by pulsed laser

    NASA Astrophysics Data System (ADS)

    Li, Ji; Zhang, Zhengfang; Liu, Dengying

    1999-06-01

    In this paper the transient temperature of liquid on micro metal layer heated by pulsed high energy laser is simulated by numerical method, especially around the theoretical homogeneous boiling point(THBP). The relationship between temperature rising rate and laser fluence is obtained; and under different temperature rising rate the distributions of temperature in liquid and metal around the THBP are obtained. With numerical simulation the relation between the temperature rising rate and laser parameters (fluence and pulse width) is known and so in the future the rapid transient boiling phenomenon could be studied and analyzed.

  17. Effects of fiber and interfacial layer architectures on the thermoplastic response of metal matrix composites

    NASA Technical Reports Server (NTRS)

    Pindera, Marek-Jerzy; Freed, Alan D.; Arnold, Steven M.

    1992-01-01

    Examined here is the effect of fiber and interfacial layer morphologies on thermal fields in metal matrix composites (MMCs). A micromechanics model based on an arbitrarily layered concentric cylinder configuration is used to calculate thermal stress fields in MMCs subjected to spatially uniform temperature changes. The fiber is modelled as a layered material with isotropic or orthotropic elastic layers, whereas the surrounding matrix, including interfacial layers, is treated as a strain-hardening, elastoplastic, von Mises solid with temperature-dependent parameters. The solution to the boundary-value problem of an arbitrarily layered concentric cylinder under the prescribed thermal loading is obtained using the local/global stiffness matrix formulation originally developed for stress analysis of multilayered elastic media. Examples are provided that illustrate how the morphology of the SCS6 silicon carbide fiber and the use of multiple compliant layers at the fiber/matrix interface affect the evolution of residual stresses in SiC/Ti composites during fabrication cool-down.

  18. Origin of interfacial perpendicular magnetic anisotropy in MgO/CoFe/metallic capping layer structures.

    PubMed

    Peng, Shouzhong; Wang, Mengxing; Yang, Hongxin; Zeng, Lang; Nan, Jiang; Zhou, Jiaqi; Zhang, Youguang; Hallal, Ali; Chshiev, Mairbek; Wang, Kang L; Zhang, Qianfan; Zhao, Weisheng

    2015-12-11

    Spin-transfer-torque magnetic random access memory (STT-MRAM) attracts extensive attentions due to its non-volatility, high density and low power consumption. The core device in STT-MRAM is CoFeB/MgO-based magnetic tunnel junction (MTJ), which possesses a high tunnel magnetoresistance ratio as well as a large value of perpendicular magnetic anisotropy (PMA). It has been experimentally proven that a capping layer coating on CoFeB layer is essential to obtain a strong PMA. However, the physical mechanism of such effect remains unclear. In this paper, we investigate the origin of the PMA in MgO/CoFe/metallic capping layer structures by using a first-principles computation scheme. The trend of PMA variation with different capping materials agrees well with experimental results. We find that interfacial PMA in the three-layer structures comes from both the MgO/CoFe and CoFe/capping layer interfaces, which can be analyzed separately. Furthermore, the PMAs in the CoFe/capping layer interfaces are analyzed through resolving the magnetic anisotropy energy by layer and orbital. The variation of PMA with different capping materials is attributed to the different hybridizations of both d and p orbitals via spin-orbit coupling. This work can significantly benefit the research and development of nanoscale STT-MRAM.

  19. Origin of interfacial perpendicular magnetic anisotropy in MgO/CoFe/metallic capping layer structures

    PubMed Central

    Peng, Shouzhong; Wang, Mengxing; Yang, Hongxin; Zeng, Lang; Nan, Jiang; Zhou, Jiaqi; Zhang, Youguang; Hallal, Ali; Chshiev, Mairbek; Wang, Kang L.; Zhang, Qianfan; Zhao, Weisheng

    2015-01-01

    Spin-transfer-torque magnetic random access memory (STT-MRAM) attracts extensive attentions due to its non-volatility, high density and low power consumption. The core device in STT-MRAM is CoFeB/MgO-based magnetic tunnel junction (MTJ), which possesses a high tunnel magnetoresistance ratio as well as a large value of perpendicular magnetic anisotropy (PMA). It has been experimentally proven that a capping layer coating on CoFeB layer is essential to obtain a strong PMA. However, the physical mechanism of such effect remains unclear. In this paper, we investigate the origin of the PMA in MgO/CoFe/metallic capping layer structures by using a first-principles computation scheme. The trend of PMA variation with different capping materials agrees well with experimental results. We find that interfacial PMA in the three-layer structures comes from both the MgO/CoFe and CoFe/capping layer interfaces, which can be analyzed separately. Furthermore, the PMAs in the CoFe/capping layer interfaces are analyzed through resolving the magnetic anisotropy energy by layer and orbital. The variation of PMA with different capping materials is attributed to the different hybridizations of both d and p orbitals via spin-orbit coupling. This work can significantly benefit the research and development of nanoscale STT-MRAM. PMID:26656721

  20. Origin of interfacial perpendicular magnetic anisotropy in MgO/CoFe/metallic capping layer structures

    NASA Astrophysics Data System (ADS)

    Peng, Shouzhong; Wang, Mengxing; Yang, Hongxin; Zeng, Lang; Nan, Jiang; Zhou, Jiaqi; Zhang, Youguang; Hallal, Ali; Chshiev, Mairbek; Wang, Kang L.; Zhang, Qianfan; Zhao, Weisheng

    2015-12-01

    Spin-transfer-torque magnetic random access memory (STT-MRAM) attracts extensive attentions due to its non-volatility, high density and low power consumption. The core device in STT-MRAM is CoFeB/MgO-based magnetic tunnel junction (MTJ), which possesses a high tunnel magnetoresistance ratio as well as a large value of perpendicular magnetic anisotropy (PMA). It has been experimentally proven that a capping layer coating on CoFeB layer is essential to obtain a strong PMA. However, the physical mechanism of such effect remains unclear. In this paper, we investigate the origin of the PMA in MgO/CoFe/metallic capping layer structures by using a first-principles computation scheme. The trend of PMA variation with different capping materials agrees well with experimental results. We find that interfacial PMA in the three-layer structures comes from both the MgO/CoFe and CoFe/capping layer interfaces, which can be analyzed separately. Furthermore, the PMAs in the CoFe/capping layer interfaces are analyzed through resolving the magnetic anisotropy energy by layer and orbital. The variation of PMA with different capping materials is attributed to the different hybridizations of both d and p orbitals via spin-orbit coupling. This work can significantly benefit the research and development of nanoscale STT-MRAM.

  1. A metal-semiconductor-metal detector based on ZnO nanowires grown on a graphene layer

    NASA Astrophysics Data System (ADS)

    Xu, Qiang; Cheng, Qijin; Zhong, Jinxiang; Cai, Weiwei; Zhang, Zifeng; Wu, Zhengyun; Zhang, Fengyan

    2014-02-01

    High quality ZnO nanowires (NWs) were grown on a graphene layer by a hydrothermal method. The ZnO NWs revealed higher uniform surface morphology and better structural properties than ZnO NWs grown on SiO2/Si substrate. A low dark current metal-semiconductor-metal photodetector based on ZnO NWs with Au Schottky contact has also been fabricated. The photodetector displays a low dark current of 1.53 nA at 1 V bias and a large UV-to-visible rejection ratio (up to four orders), which are significantly improved compared to conventional ZnO NW photodetectors. The improvement in UV detection performance is attributed to the existence of a surface plasmon at the interface of the ZnO and the graphene.

  2. A metal-semiconductor-metal detector based on ZnO nanowires grown on a graphene layer.

    PubMed

    Xu, Qiang; Cheng, Qijin; Zhong, Jinxiang; Cai, Weiwei; Zhang, Zifeng; Wu, Zhengyun; Zhang, Fengyan

    2014-02-07

    High quality ZnO nanowires (NWs) were grown on a graphene layer by a hydrothermal method. The ZnO NWs revealed higher uniform surface morphology and better structural properties than ZnO NWs grown on SiO2/Si substrate. A low dark current metal-semiconductor-metal photodetector based on ZnO NWs with Au Schottky contact has also been fabricated. The photodetector displays a low dark current of 1.53 nA at 1 V bias and a large UV-to-visible rejection ratio (up to four orders), which are significantly improved compared to conventional ZnO NW photodetectors. The improvement in UV detection performance is attributed to the existence of a surface plasmon at the interface of the ZnO and the graphene.

  3. Metal Surface Modification for Obtaining Nano- and Sub-Nanostructured Protective Layers.

    PubMed

    Ledovskykh, Volodymyr; Vyshnevska, Yuliya; Brazhnyk, Igor; Levchenko, Sergiy

    2017-12-01

    Regularities of the phase protective layer formation in multicomponent systems involving inhibitors with different mechanism of protective action have been investigated. It was shown that optimization of the composition of the inhibition mixture allows to obtain higher protective efficiency owing to improved microstructure of the phase layer. It was found that mechanism of the film formation in the presence of NaNO2-PHMG is due to deposition of slightly soluble PHMG-Fe complexes on the metal surface. On the basis of the proposed mechanism, the advanced surface engineering methods for obtaining nanoscaled and sub-nanostructured functional coatings may be developed.

  4. Enhanced Magnetoelectric Coupling in Layered Structure of Piezoelectric Bimorph and Metallic Alloy

    NASA Astrophysics Data System (ADS)

    Petrov, V. M.; Bichurin, M. I.; Lavrentyeva, K. V.; Leontiev, V. S.

    2016-08-01

    We have investigated the enhanced magnetoelectric (ME) coupling in a layered structure of piezoelectric bimorph and magnetostrictive metallic alloy. The observed ME coefficient in the piezoelectric bimorph-based structure was found to be two times higher than in the traditional piezoelectric/magnetostrictive bilayer. The observed enhancement in ME coupling strength is related to equal signs of induced voltage in both lead zirconate titanate layers with opposite poling directions due to the flexural deformations. The piezoelectric bimorph-based structure has promising potential for sensor and technological applications.

  5. Synthesis and Characterization of Layered Double Hydroxides Containing Optically Active Transition Metal Ion

    NASA Astrophysics Data System (ADS)

    Tyagi, S. B.; Kharkwal, Aneeta; Nitu; Kharkwal, Mamta; Sharma, Raghunandan

    2017-01-01

    The acetate intercalated layered double hydroxides of Zn and Mn, have been synthesized by chimie douce method. The materials were characterized by XRD, TGA, CHN, IR, XPS, SEM-EDX and UV-visible spectroscopy. The photoluminescence properties was also studied. The optical properties of layered hydroxides are active transition metal ion dependent, particularly d1-10 system plays an important role. Simultaneously the role of host - guest orientation has been considered the basis of photoluminescence. Acetate ion can be exchanged with iodide and sulphate ions. The decomposed product resulted the pure phase Mn doped zinc oxide are also reported.

  6. Metal Surface Modification for Obtaining Nano- and Sub-Nanostructured Protective Layers

    NASA Astrophysics Data System (ADS)

    Ledovskykh, Volodymyr; Vyshnevska, Yuliya; Brazhnyk, Igor; Levchenko, Sergiy

    2017-03-01

    Regularities of the phase protective layer formation in multicomponent systems involving inhibitors with different mechanism of protective action have been investigated. It was shown that optimization of the composition of the inhibition mixture allows to obtain higher protective efficiency owing to improved microstructure of the phase layer. It was found that mechanism of the film formation in the presence of NaNO2-PHMG is due to deposition of slightly soluble PHMG-Fe complexes on the metal surface. On the basis of the proposed mechanism, the advanced surface engineering methods for obtaining nanoscaled and sub-nanostructured functional coatings may be developed.

  7. Anion exchange kinetics of nanodimensional layered metal hydroxides: use of isoconversional analysis.

    PubMed

    Majoni, Stephen; Hossenlopp, Jeanne M

    2010-12-16

    Anion exchange reactions of nanodimensional layered metal hydroxide compounds are utilized to create materials with targeted physical and chemical properties and also as a means for controlled release of intercalated anions. The kinetics of this important class of reaction are generally characterized by model-based approaches. In this work, a different approach based on isothermal, isoconversional analysis was utilized to determine effective activation energies with respect to extent of reaction. Two different layered metal hydroxide materials were chosen for reaction with chloride anions, using a temperature range of 30-60 °C. The concentrations of anions released into solution and the changes in polycrystalline solid phases were evaluated using model-based (Avrami-Erofe'ev nucleation-growth model) and model-free (integral isoconversional) methods. The results demonstrate the utility of the isoconversional approach for identifying when fitting to a single model is not appropriate, particularly for characterizing the temperature dependence of the reaction kinetics.

  8. Anisotropy in the optical properties of bulk and layered transition metal dichalcogenide ReS2

    NASA Astrophysics Data System (ADS)

    Das, Suvadip; Pradhan, Nihar; Garcia, Carlos; Rhodes, Daniel; McGill, Stephen; Balicas, Luis; Manousakis, Efstratios

    Unlike most transition metal dichalcogenides, ReS2 in the distorted 1T' phase, is a direct gap semiconductor. We measured the temperature dependent photoluminescence in both bulk and layered ReS2 and examined the evolution of the peaks with the number of layers. We obtained strong signatures of optical anisotropy in the absorption spectroscopy and photocurrent response which makes this material a potential candidate for optoelectronic applications. Many body calculations including electron-hole interactions as implemented in the GW+BSE approach, agrees with the strong anisotropy in the optical properties of bulk and monolayer ReS2. A shift in the excitonic peaks by about 0.8 eV introduced by solving the Bethe-Salpeter equation indicates strong contribution from excitonic bound states in this transition metal dichalcogenide.

  9. Synthesis, characterization and application of two-dimensional layered metal hydroxides for environmental remediation purposes

    NASA Astrophysics Data System (ADS)

    Machingauta, Cleopas

    Two-dimensional layered nano composites, which include layered double hydroxides (LDHs), hydroxy double salts (HDSs) and layered hydroxide salts (LHSs) are able to intercalate different molecular species within their gallery space. These materials have a tunable structural composition which has made them applicable as fire retardants, adsorbents, catalysts, catalyst support materials, and ion exchangers. Thermal treatment of these materials results in destruction of the layers and formation of mixed metal oxides (MMOs) and spinels. MMOs have the ability to adsorb anions from solution and may also regenerate layered structures through a phenomenon known as memory effect. Zinc-nickel hydroxy nitrate was used for the uptake of a series of halogenated acetates (HAs). HAs are pollutants introduced into water systems as by-products of water chlorination and pesticide degradation; their sequestration from water is thus crucial. Optimization of layered materials for controlled uptake requires an understanding of their ion-exchange kinetics and thermodynamics. Exchange kinetics of these anions was monitored using ex-situ PXRD, UV-vis, HPLC and FTIR. It was revealed that exchange rates and uptake efficiencies are related to electronic spatial extents and the charge on carboxyl-oxygen atoms. In addition, acetate and nitrate-based HDSs were used to explore how altering the hydroxide layer affects uptake of acetate/nitrate ions. Changing the metal identities affects the interaction of the anions with the layers. From FTIR, we observed that nitrates coordinate in a D3h and Cs/C 2v symmetry; the nitrates in D3h symmetry were easily exchangeable. Interlayer hydrogen bonding was also revealed to be dependent on metal identity. Substituting divalent cations with trivalent cations produces materials with a higher charge density than HDSs and LHSs. A comparison of the uptake efficiency of zinc-aluminum, zinc-gallium and zinc-nickel hydroxy nitrates was performed using trichloroacetic

  10. Antibacterial and bioactive calcium titanate layers formed on Ti metal and its alloys.

    PubMed

    Kizuki, Takashi; Matsushita, Tomiharu; Kokubo, Tadashi

    2014-07-01

    An antibacterial and bioactive titanium (Ti)-based material was developed for use as a bone substitute under load-bearing conditions. As previously reported, Ti metal was successively subjected to NaOH, CaCl2, heat, and water treatments to form a calcium-deficient calcium titanate layer on its surface. When placed in a simulated body fluid (SBF), this bioactive Ti formed an apatite layer on its surface and tightly bonded to bones in the body. To address concerns regarding deep infection during orthopedic surgery, Ag(+) ions were incorporated on the surface of this bioactive Ti metal to impart antibacterial properties. Ti metal was first soaked in a 5 M NaOH solution to form a 1 μm-thick sodium hydrogen titanate layer on the surface and then in a 100 mM CaCl2 solution to form a calcium hydrogen titanate layer via replacement of the Na(+) ions with Ca(2+) ions. The Ti material was subsequently heated at 600 °C for 1 h to transform the calcium hydrogen titanate into calcium titanate. This heat-treated titanium metal was then soaked in 0.01-10 mM AgNO3 solutions at 80 °C for 24 h. As a result, 0.1-0.82 at.% Ag(+) ions and a small amount of H3O(+) ions were incorporated into the surface calcium titanate layers. The resultant products formed apatite on their surface in an SBF, released 0.35-3.24 ppm Ag(+) ion into the fetal bovine serum within 24 h, and exhibited a strong antibacterial effect against Staphylococcus aureus. These results suggest that the present Ti metals should exhibit strong antibacterial properties in the living body in addition to tightly bonding to the surrounding bone through the apatite layer that forms on their surfaces in the body.

  11. Cold Expansion and Interference for Extending the Fatigue Life of Multi- Layer Metal Joints

    DTIC Science & Technology

    1993-10-01

    quickly rupture any oxide film, leading to cold welding of the asperities and then their fracture from high strain fatigue . Material is thus transferred...MELBOURNE, VICTORIA Research Report 17 COLD EXPANSION AND INTERFERENCE FOR EXTENDING THE FATIGUE LIFE OF MULTI-LAYER METAL, JOINTS by . . . J.M. FINNEY...AND TECHNOLOGY ORGANISATION ",1 AERONAUTICAL RESEARCH LABORATORY Research Report 17 COLD EXVANSION AND INTERFERENCE FOR EXTENDING THE FATIGUE LIFE OF

  12. Thin-layer chromatographie separation of alkaline earth metals on diethylaminoethyl cellulose.

    PubMed

    Ishida, K

    1969-12-01

    Thin-layer Chromatographic behaviour of magnesium, calcium, strontium and barium on diethylaminoethyl cellulose has been investigated in methanol-nitric acid mixtures. R(f) values are in the order magnesium > calcium > strontium > barium. The differences in R(f) values are large enough to allow good separations of the four metal ions from each other. The best separation is obtained by the ascending technique with methanol-8M nitric acid (20:1, v v ).

  13. Ag/Ni Metallization Bilayer: A Functional Layer for Highly Efficient Polycrystalline SnSe Thermoelectric Modules

    NASA Astrophysics Data System (ADS)

    Park, Sang Hyun; Jin, Younghwan; Ahn, Kyunghan; Chung, In; Yoo, Chung-Yul

    2017-02-01

    The structural and electrical characteristics of Ag/Ni bilayer metallization on polycrystalline thermoelectric SnSe were investigated. Two difficulties with thermoelectric SnSe metallization were identified for Ag and Ni single layers: Sn diffusion into the Ag metallization layer and unexpected cracks in the Ni metallization layer. The proposed Ag/Ni bilayer was prepared by hot-pressing, demonstrating successful metallization on the SnSe surface without interfacial cracks or elemental penetration into the metallization layer. Structural analysis revealed that the Ni layer reacts with SnSe, forming several crystalline phases during metallization that are beneficial for reducing contact resistance. Detailed investigation of the Ni/SnSe interface layer confirms columnar Ni-Sn intermetallic phases [(Ni3Sn and Ni3Sn2) and Ni5.63SnSe2] that suppress Sn diffusion into the Ag layer. Electrical specific-contact resistivity (5.32 × 10-4 Ω cm2) of the Ag/Ni bilayer requires further modification for development of high-efficiency polycrystalline SnSe thermoelectric modules.

  14. A pH-gradient induced method for wetting metal-layer embedded nanopores

    NASA Astrophysics Data System (ADS)

    Balagurusamy, Venkat; Stolovitzky, Gustavo

    2015-03-01

    Solid-state nanopores made on a single layer of Silicon nitride are wet by a number of methods by different workers. Typically, they involve using some low-surface tension liquid like iso propyl alcohol for pre-wetting before filling with the electrolyte solution of interest e.g., a buffered KCl solution both sides of the chamber that partition the nanopore. These methods can also be preceded by a cleaning step which may involve either oxygen plasma or piranha treatment. However we found that these methods were not successful in wetting certain batches of nanopores drilled in a stack of Si3N4/SiO2/TiN/SiO2/TiN/SiO2/TiN/SiO2/Si3N4 layers. We found that applying buffer solutions at different pH on the two sides of the nanopore greatly accelerated the wetting process from days to few hours and resulted in nanopores with near linear I-V behavior for high salt concentration buffer solutions. We will describe this method and the results for a number of nanopores. Nanopores wet with this pH gradient method translocate DNA molecules like nanopores wet by other methods mentioned here. We believe that the actual mechanism of this wetting process is influenced strongly by the pH effect on SiO2 surface. Efforts are underway to understand the working of this wetting method by quantum computer simulation methods.

  15. Single-Layer Limit of Metallic Indium Overlayers on Si(111).

    PubMed

    Park, Jae Whan; Kang, Myung Ho

    2016-09-09

    Density-functional calculations are used to identify one-atom-thick metallic In phases grown on the Si(111) surface, which have long been sought in quest of the ultimate two-dimensional (2D) limit of metallic properties. We predict two metastable single-layer In phases, one sqrt[7]×sqrt[3] phase with a coverage of 1.4 monolayer (ML; here 1 ML refers to one In atom per top Si atom) and the other sqrt[7]×sqrt[7] phase with 1.43 ML, which indeed agree with experimental evidences. Both phases reveal quasi-1D arrangements of protruded In atoms, leading to 2D-metallic but anisotropic band structures and Fermi surfaces. This directional feature contrasts with the free-electron-like In-overlayer properties that are known to persist up to the double-layer thickness, implying that the ultimate 2D limit of In overlayers may have been achieved in previous studies of double-layer In phases.

  16. Design technology co-optimization for 14/10nm metal1 double patterning layer

    NASA Astrophysics Data System (ADS)

    Duan, Yingli; Su, Xiaojing; Chen, Ying; Su, Yajuan; Shao, Feng; Zhang, Recco; Lei, Junjiang; Wei, Yayi

    2016-03-01

    Design and technology co-optimization (DTCO) can satisfy the needs of the design, generate robust design rule, and avoid unfriendly patterns at the early stage of design to ensure a high level of manufacturability of the product by the technical capability of the present process. The DTCO methodology in this paper includes design rule translation, layout analysis, model validation, hotspots classification and design rule optimization mainly. The correlation of the DTCO and double patterning (DPT) can optimize the related design rule and generate friendlier layout which meets the requirement of the 14/10nm technology node. The experiment demonstrates the methodology of DPT-compliant DTCO which is applied to a metal1 layer from the 14/10nm node. The DTCO workflow proposed in our job is an efficient solution for optimizing the design rules for 14/10 nm tech node Metal1 layer. And the paper also discussed and did the verification about how to tune the design rule of the U-shape and L-shape structures in a DPT-aware metal layer.

  17. Atomic-layer-deposition-assisted formation of carbon nanoflakes on metal oxides and energy storage application.

    PubMed

    Guan, Cao; Zeng, Zhiyuan; Li, Xianglin; Cao, Xiehong; Fan, Yu; Xia, Xinhui; Pan, Guoxiang; Zhang, Hua; Fan, Hong Jin

    2014-01-29

    Nanostructured carbon is widely used in energy storage devices (e.g., Li-ion and Li-air batteries and supercapacitors). A new method is developed for the generation of carbon nanoflakes on various metal oxide nanostructures by combining atomic layer deposition (ALD) and glucose carbonization. Various metal oxide@nanoflake carbon (MO@f-C) core-branch nanostructures are obtained. For the mechanism, it is proposed that the ALD Al2 O3 and glucose form a composite layer. Upon thermal annealing, the composite layer becomes fragmented and moves outward, accompanied by carbon deposition on the alumina skeleton. When tested as electrochemical supercapacitor electrode, the hierarchical MO@f-C nanostructures exhibit better properties compared with the pristine metal oxides or the carbon coating without ALD. The enhancement can be ascribed to increased specific surface areas and electric conductivity due to the carbon flake coating. This peculiar carbon coating method with the unique hierarchical nanostructure may provide a new insight into the preparation of 'oxides + carbon' hybrid electrode materials for energy storage applications.

  18. Origin of photogenerated carrier recombination at the metal-active layer interface in polymer solar cells.

    PubMed

    Kumar, Mukesh; Dubey, Ashish; Reza, Khan Mamun; Adhikari, Nirmal; Qiao, Qiquan; Bommisetty, Venkat

    2015-11-07

    The role of the metal-active layer interface in photogenerated recombination has been investigated using nanoscale current sensing atomic force microscopy (CS-AFM) and intensity modulated photocurrent spectroscopy (IMPS) in as-deposited, pre-annealed and post-annealed bulk heterojunction (BHJ) solar cells. Aluminum (Al) confined post-annealed BHJ solar cells exhibited a significantly improved device efficiency compared to pre-annealed BHJ solar cells having similar photocarrier harvesting ability in the active layer. The nanoscale topography and CS-AFM results indicate a uniform PCBM rich phase at the metal-active layer interface in the post-annealed cells, but PCBM segregation in the pre-annealed cells. These two different annealing processes showed different carrier dynamics revealed using IMPS under various light intensities. The IMPS results suggest reduced photo generated carrier recombination in uniform PCBM rich post-annealed BHJ solar cells. This study reveals the importance of the metal-bend interface in BHJ solar cells in order to obtain efficient charge carrier extraction for high efficiency.

  19. Thin-film composite materials as a dielectric layer for flexible metal-insulator-metal capacitors.

    PubMed

    Tiwari, Jitendra N; Meena, Jagan Singh; Wu, Chung-Shu; Tiwari, Rajanish N; Chu, Min-Ching; Chang, Feng-Chih; Ko, Fu-Hsiang

    2010-09-24

    A new organic-organic nanoscale composite thin-film (NCTF) dielectric has been synthesized by solution deposition of 1-bromoadamantane and triblock copolymer (Pluronic P123, BASF, EO20-PO70-EO20), in which the precursor solution has been achieved with organic additives. We have used a sol-gel process to make a metal-insulator-metal capacitor (MIM) comprising a nanoscale (10 nm-thick) thin-film on a flexible polyimide (PI) substrate at room temperature. Scanning electron microscope and atomic force microscope revealed that the deposited NCTFs were crack-free, uniform, highly resistant to moisture absorption, and well adhered on the Au-Cr/PI. The electrical properties of 1-bromoadamantane-P123 NCTF were characterized by dielectric constant, capacitance, and leakage current measurements. The 1-bromoadamantane-P123 NCTF on the PI substrate showed a low leakage current density of 5.5 x 10(-11) A cm(-2) and good capacitance of 2.4 fF at 1 MHz. In addition, the calculated dielectric constant of 1-bromoadamantane-P123 NCTF was 1.9, making them suitable candidates for use in future flexible electronic devices as a stable intermetal dielectric. The electrical insulating properties of 1-bromoadamantane-P123 NCTF have been improved due to the optimized dipole moments of the van der Waals interactions.

  20. Extraordinary terahertz transmission through a double-layer metal array with closed ring resonators

    NASA Astrophysics Data System (ADS)

    Guo, Yadong; Yuan, Zongheng; Yuan, Yuyang; Wang, Sheng; Zhang, Wentao

    2016-07-01

    In this paper, we numerically investigate the transmission properties of a terahertz metamaterial. This metamaterial is composed of metal-dielectric-metal, which consists of metallic layers with an air hole array and one coaxial closed ring resonator in the air hole. The metamaterial in the THz range of 0.2-1 THz has three transmission peaks. We provide an explanation of the transmission peaks by means of the surface plasmon polaritons and magnetic polaritons resonance based on the distribution of the surface current. Then according to the magnetic polaritons resonance, the equivalent circuit model of the metamaterial is established. The effects of geometric parameters on the transmission peaks are discussed and studied by an equivalent circuit model and surface plasmon polaritons dispersion relation. Our metamaterial promises dual-band potential applications such as filters.

  1. Friction modifier using adherent metallic multilayered or mixed element layer conversion coatings

    NASA Technical Reports Server (NTRS)

    Schramm, Harry F. (Inventor); Defalco, Frank G. (Inventor); Starks, Sr., Lloyd L. (Inventor)

    2012-01-01

    A process for creating conversion coatings and spin, drawing, and extrusion finishes for surfaces, wherein the conversion coatings and spin, drawing, and extrusion finishes contain potassium, phosphorus, nitrogen, silicon, and one or more non-alkaline metals. The process comprises forming a first aqueous solution of silicate, potassium hydroxide, and ammonium hydroxide; forming a second aqueous solution of water, phosphoric acid, ammonium hydroxide, an alkali metal hydroxide, and one or more non-alkaline metals, and then combining the first solution with the second solution to form a final solution. This final solution forms an anti-friction multi-layer conversion coating or a spin, drawing, and extrusion finish on a surface when applied to the surface, either directly or as an additive in lubricating fluids.

  2. Atomic layer deposition by reaction of molecular oxygen with tetrakisdimethylamido-metal precursors

    SciTech Connect

    Provine, J Schindler, Peter; Torgersen, Jan; Kim, Hyo Jin; Karnthaler, Hans-Peter; Prinz, Fritz B.

    2016-01-15

    Tetrakisdimethylamido (TDMA) based precursors are commonly used to deposit metal oxides such as TiO{sub 2}, ZrO{sub 2}, and HfO{sub 2} by means of chemical vapor deposition and atomic layer deposition (ALD). Both thermal and plasma enhanced ALD (PEALD) have been demonstrated with TDMA-metal precursors. While the reactions of TDMA-type precursors with water and oxygen plasma have been studied in the past, their reactivity with pure O{sub 2} has been overlooked. This paper reports on experimental evaluation of the reaction of molecular oxygen (O{sub 2}) and several metal organic precursors based on TDMA ligands. The effect of O{sub 2} exposure duration and substrate temperature on deposition and film morphology is evaluated and compared to thermal reactions with H{sub 2}O and PEALD with O{sub 2} plasma.

  3. Photocatalytic Water Oxidation over Metal Oxide Nanosheets Having a Three-Layer Perovskite Structure.

    PubMed

    Oshima, Takayoshi; Eguchi, Miharu; Maeda, Kazuhiko

    2016-02-19

    Metal oxide nanosheets having a three-layer perovskite structure were studied as photocatalysts for water oxidation in the presence of IO3 (-) as a reversible electron acceptor. This work examined the effects of the lateral dimensions and composition of the nanosheets as well as metal oxide co-catalysts deposited on the restacked nanosheets. Depositing metal oxides capable of promoting reduction reactions on the nanosheets were found to promote the water oxidation activity. In contrast, the lateral dimensions and the degree of crystallinity of the nanosheets had little effect on the activity. Experimental results demonstrated that the reduction of IO3 (-) is the rate-limiting step in this reaction and that nanosheets with less distorted structures are advantageous with regard to increasing both light absorption and the mobility of photoexcited charge carriers.

  4. Probing Critical Point Energies of Transition Metal Dichalcogenides: Surprising Indirect Gap of Single Layer WSe2.

    PubMed

    Zhang, Chendong; Chen, Yuxuan; Johnson, Amber; Li, Ming-Yang; Li, Lain-Jong; Mende, Patrick C; Feenstra, Randall M; Shih, Chih-Kang

    2015-10-14

    By using a comprehensive form of scanning tunneling spectroscopy, we have revealed detailed quasi-particle electronic structures in transition metal dichalcogenides, including the quasi-particle gaps, critical point energy locations, and their origins in the Brillouin zones. We show that single layer WSe2 surprisingly has an indirect quasi-particle gap with the conduction band minimum located at the Q-point (instead of K), albeit the two states are nearly degenerate. We have further observed rich quasi-particle electronic structures of transition metal dichalcogenides as a function of atomic structures and spin-orbit couplings. Such a local probe for detailed electronic structures in conduction and valence bands will be ideal to investigate how electronic structures of transition metal dichalcogenides are influenced by variations of local environment.

  5. Contact resistance at planar metal contacts on bilayer graphene and effects of molecular insertion layers.

    PubMed

    Nouchi, Ryo

    2017-03-01

    The possible origins of metal-bilayer graphene (BLG) contact resistance are investigated by taking into consideration the bandgap formed by interfacial charge transfer at the metal contacts. Our results show that a charge injection barrier (Schottky barrier) does not contribute to the contact resistance because the BLG under the contacts is always degenerately doped. We also showed that the contact-doping-induced increase in the density of states (DOS) of BLG under the metal contacts decreases the contact resistance owing to enhanced charge carrier tunnelling at the contacts. The contact doping can be enhanced by inserting molecular dopant layers into the metal contacts. However, carrier tunnelling through the insertion layer increases the contact resistance, and thus, alternative device structures should be employed. Finally, we showed that the inter-band transport by variable range hopping via in-gap states is the largest contributor to contact resistance when the carrier type of the gated channel is opposite to the contact doping carrier type. This indicates that the strategy of contact resistance reduction by the contact-doping-induced increase in the DOS is effective only for a single channel transport branch (n- or p-type) depending on the contact doping carrier type.

  6. Metal to insulator quantum-phase transition in few-layered ReS2

    NASA Astrophysics Data System (ADS)

    Pradhan, Nihar; McCreary, Amber; Rhodes, Daniel; Lu, Zhenguang; Smirnov, Dmitry; Manousakis, Efstratios; Feng, Simin; Namburu, Raju; Dubey, Madan; Hight Walker, Angela; Terrones, Humberto; Terrones, Mauricio; Dobrosavljevic, Vladimir; Balicas, Luis

    ReS2 a layer-independent direct band-gap semiconductor of 1.5 eV implies a potential for its use in optoelectronic applications. Here, we present an overall evaluation of transport and anisotropic Raman of few-layered ReS2 FET. ReS2 exfoliated on SiO2 behaves as an n-type semiconductor with an intrinsic carrier mobility surpassing μi ~30 cm2/Vs at T = 300 K which increases up to ~350 cm2/vs at 2 K. Semiconducting behavior is observed at low electron densities n, but at high values of nthe resistivity decreases by a factor >7 upon cooling to 2 K and displays a metallicT2 -dependence. The electric-field induced metallic state observed in MoS2 was recently claimed to result from a percolation type of transition. Instead, through a scaling analysis of the conductivity as a function of Tand n, we find that the metallic state of ReS2 results from a second-order metal to insulator transition driven by electronic correlations. Supported by U.S. Army Research Office MURI Grant No. W911NF-11-1-0362.

  7. Metal to insulator quantum-phase transition in few-layered ReS2

    NASA Astrophysics Data System (ADS)

    Pradhan, Nihar; Rhodes, Daniel; Lu, Zhenguang; Smirnov, Dmitry; Manousakis, Efstratios; Dobrosavljevic, Vladimir; Balicas, Luis; McCreary, Amber; Feng, Simin; Terrones, Maurico; Namburu, Raju; Dubey, Madan; Hight Walker, Angela; Terrones, Humberto

    ReS2 a layer-independent direct band-gap semiconductor of 1.5 eV implies a potential for its use in optoelectronic applications. Here, we present an overall evaluation of transport and anisotropic Raman of few-layered ReS2 FET. ReS2 exfoliated on SiO2 behaves as an n-type semiconductor with an intrinsic carrier mobility surpassing μi ~ 30cm2 /Vs at T = 300 K which increases up to ~ 350cm2 /vs at 2 K. Semiconducting behavior is observed at low electron densities n, but at high values of nthe resistivity decreases by a factor > 7 upon cooling to 2 K and displays a metallicT2-dependence. The electric-field induced metallic state observed in MoS2 was recently claimed to result from a percolation type of transition. Instead, through a scaling analysis of the conductivity as a function of Tand n, we find that the metallic state of ReS2 results from a second-order metal to insulator transition driven by electronic correlations. Supported by U.S. Army Research Office MURI Grant No. W911NF-11-1-0362.

  8. New First Order Raman-active Modes in Few Layered Transition Metal Dichalcogenides

    PubMed Central

    Terrones, H.; Corro, E. Del; Feng, S.; Poumirol, J. M.; Rhodes, D.; Smirnov, D.; Pradhan, N. R.; Lin, Z.; Nguyen, M. A. T.; Elías, A. L.; Mallouk, T. E.; Balicas, L.; Pimenta, M. A.; Terrones, M.

    2014-01-01

    Although the main Raman features of semiconducting transition metal dichalcogenides are well known for the monolayer and bulk, there are important differences exhibited by few layered systems which have not been fully addressed. WSe2 samples were synthesized and ab-initio calculations carried out. We calculated phonon dispersions and Raman-active modes in layered systems: WSe2, MoSe2, WS2 and MoS2 ranging from monolayers to five-layers and the bulk. First, we confirmed that as the number of layers increase, the E′, E″ and E2g modes shift to lower frequencies, and the A′1 and A1g modes shift to higher frequencies. Second, new high frequency first order A′1 and A1g modes appear, explaining recently reported experimental data for WSe2, MoSe2 and MoS2. Third, splitting of modes around A′1 and A1g is found which explains those observed in MoSe2. Finally, exterior and interior layers possess different vibrational frequencies. Therefore, it is now possible to precisely identify few-layered STMD. PMID:24572993

  9. Embbeded dipolar vortices driven by Lorentz forces in a shallow liquid metal layer

    NASA Astrophysics Data System (ADS)

    Lara, Cinthya G.; Cuevas, Sergio

    2014-11-01

    We present an experimental and numerical study of the vortex pattern that results from the action of a localized Lorentz force in a thin liquid metal layer (GaInSn) contained in a square box. The fluid motion is generated by the interaction of a uniform D.C. current and a non-uniform magnetic field produced by square-shaped permanent magnet much smaller that the container. Unlike the simple vortex dipole created by a localized Lorentz force in a layer of electrolyte, a more complex vortex pattern is formed in a liquid metal layer. Experiments show the appearance of two ``embedded'' vortex dipoles with a quasi-stagnat zone in the region of highest magnetic field intensity. The observed pattern can be explained by noticing that the localized magnetic field acts as a magnetic obstacle for the imposed flow. Using the Ultrasonic Doppler Velocimetry technique, we obtained the velocity profiles along the symmetry axis. We developed a quasi-two-dimensional numerical model that takes into account the effect of the boundary layers adhered to the bottom wall, the Hartmann friction and the induced effects. Numerical simulations show a satisfactory qualitative and quantitative agreement with the experimental results. Work supported by CONACYT, Mexico under Project 131399. C. G. Lara acknowledges a grant from CONACYT.

  10. Gluing together metallic and covalent layers to form Ru2C under ambient conditions.

    PubMed

    Sun, Weiwei; Li, Yunguo; Zhu, Li; Ma, Yanming; Di Marco, Igor; Johansson, Börje; Korzhavyi, Pavel

    2015-04-21

    Ru2C has recently been synthesised at high pressure and high temperature, and was assumed to have a structure with space group P3̅m1. However, subsequent theoretical work has revealed that this structure is unstable under ambient conditions, which motivated us to look for the stable structure. In this work, we explore the structures of Ru2C by using an unbiased swarm structure searching algorithm. The structures with R3m and R3̅m symmetries have been found to be lower in energy than the P3̅m1 structure, at the same time being dynamically stable under ambient conditions. These layered structures consist of alternating Ru bilayers and C monolayers in the R3m structure, and alternating Ru tetra-layers and C bilayers in the R3̅m structure. The C layers are more evenly distributed and more covalently bound to the Ru layers in the R3m structure than in the R3̅m structure. Instead, in the R3̅m structure there exists more Ru-Ru metallic bonding, which has a crucial role in diminishing the hardness of this material. Our findings should stimulate further explorations of the structures and properties of the heavy transition metal carbides and nitrides, potentially leading to industrial applications.

  11. Metallic adhesion layer induced plasmon damping and molecular linker as a nondamping alternative.

    PubMed

    Habteyes, Terefe G; Dhuey, Scott; Wood, Erin; Gargas, Daniel; Cabrini, Stefano; Schuck, P James; Alivisatos, A Paul; Leone, Stephen R

    2012-06-26

    Drastic chemical interface plasmon damping is induced by the ultrathin (∼2 nm) titanium (Ti) adhesion layer; alternatively, molecular adhesion is implemented for lithographic fabrication of plasmonic nanostructures without significant distortion of the plasmonic characteristics. As determined from the homogeneous linewidth of the resonance scattering spectrum of individual gold nanorods, an ultrathin Ti layer reduces the plasmon dephasing time significantly, and it reduces the plasmon scattering amplitude drastically. The increased damping rate and decreased plasmon amplitude are due to the dissipative dielectric function of Ti and the chemical interface plasmon damping where the conduction electrons are transferred across the metal-metal interface. In addition, a pronounced red shift due to the Ti adhesion layer, more than predicted using electromagnetic simulation, suggests the prevalence of interfacial reactions. By extending the experiment to conductively coupled ring-rod nanostructures, it is shown that a sharp Fano-like resonance feature is smeared out due to the Ti layer. Alternatively, vapor deposition of (3-mercaptopropyl)trimethoxysilane on gently cleaned and activated lithographic patterns functionalizes the glass surface sufficiently to link the gold nanostructures to the surface by sulfur-gold chemical bonds without observable plasmon damping effects.

  12. Revealing extraordinary tensile plasticity in layered Ti-Al metal composite

    NASA Astrophysics Data System (ADS)

    Huang, M.; Fan, G. H.; Geng, L.; Cao, G. J.; Du, Y.; Wu, H.; Zhang, T. T.; Kang, H. J.; Wang, T. M.; Du, G. H.; Xie, H. L.

    2016-12-01

    Layered Ti-Al metal composite (LMC) fabricated by hot-pressing and hot-rolling process displays higher ductility than that of both components. In this paper, a combination of digital image correlation (DIC) and X-ray tomography revealed that strain delocalization and constrained crack distribution are the origin of extraordinary tensile ductility. Strain delocalization was derived from the transfer of strain partitioning between Ti and Al layer, which relieved effectively the strain localization of LMC. Furthermore, the extensive cracks of LMC were restricted in the interface due to constraint effect. Layered architecture constrained the distribution of cracks and significantly relieved the strain localization. Meanwhile, the transfer of strain partitioning and constrained crack distribution were believed to inhibit the strain localization of Ti and change the deformation mechanisms of Ti. Our finding enriches current understanding about simultaneously improving the strength and ductility by structural design.

  13. Electro-vortex flows in a square layer of liquid metal

    NASA Astrophysics Data System (ADS)

    Kolesnichenko, I.; Khripchenko, S.; Buchenau, D.; Gerbeth, G.

    2005-03-01

    We study electro-vortex flows generated by electro-magnetic forces in a shallow square layer of liquid metal. The force driving the flow is produced by the interaction between the electric current flowing through the layer and its own magnetic field. Rotational parts of that force are particularly caused by ferromagnetic yokes placed around the layer. Depending of the position and type of those yokes flows of one-, two- or four-eddies are initiated. The basic flow structure and the related velocity oscillations have been investigated both by experimental techniques using the ultrasound Doppler velocimetry and by numerical calculations. Compared to the single vortex flow the double vortex flow shows a much higher level of large-scale velocity oscillations. The theoretical model turned out to be in good agreement with the experimental data. Figs 11, Refs 15.

  14. Transitions metal dichalcogenides: Growth, fermiology studies, and few-layered transport properties

    NASA Astrophysics Data System (ADS)

    Rhodes, Daniel

    Transition metal dichalcogenides (TMDs or TMDCs) have garnered much interest recently due to their weakly layered structures, allowing for mechanical exfoliation down to a single atomic layer. As such, it is pertinent to re-examine the bulk properties of these materials in order to completely understand and predict what is happening in the few-layered limit. A large majority of these systems were first investigated in the 1950s and 1960s. As such, many of the current growth methods rely on these reports, making new growth techniques for lowering defects of importance as well. In this thesis, both topics are taken into consideration and discussed, though the latter remains to be investigated in much more detail and should be the work of future research efforts. (Abstract shortened by ProQuest.).

  15. Interface-controlled layer exchange in metal-induced crystallization of germanium thin films

    NASA Astrophysics Data System (ADS)

    Hu, Shu; Marshall, Ann F.; McIntyre, Paul C.

    2010-08-01

    Low-temperature synthesis of polycrystalline germanium (poly-Ge) thin films is of great interest in thin-film photovoltaic and electronics applications. We demonstrate metal (Al)-induced crystallization to form poly-Ge thin films on both glass and polymer substrates at temperatures as low as 200 °C. An interfacial diffusion control layer, intentionally interposed between the Al and the underlying amorphous Ge (a-Ge) layer, is found to achieve layer exchange while suppressing uncontrolled Ge crystallization within the bilayer samples. Germanium thin films with micron-size grains and (111)-preferred orientation are prepared by controlled Ge nucleation and Ge lateral overgrowth of Al during a-Ge crystallization.

  16. Revealing extraordinary tensile plasticity in layered Ti-Al metal composite

    PubMed Central

    Huang, M.; Fan, G. H.; Geng, L.; Cao, G. J.; Du, Y.; Wu, H.; Zhang, T. T.; Kang, H. J.; Wang, T. M.; Du, G. H.; Xie, H. L.

    2016-01-01

    Layered Ti-Al metal composite (LMC) fabricated by hot-pressing and hot-rolling process displays higher ductility than that of both components. In this paper, a combination of digital image correlation (DIC) and X-ray tomography revealed that strain delocalization and constrained crack distribution are the origin of extraordinary tensile ductility. Strain delocalization was derived from the transfer of strain partitioning between Ti and Al layer, which relieved effectively the strain localization of LMC. Furthermore, the extensive cracks of LMC were restricted in the interface due to constraint effect. Layered architecture constrained the distribution of cracks and significantly relieved the strain localization. Meanwhile, the transfer of strain partitioning and constrained crack distribution were believed to inhibit the strain localization of Ti and change the deformation mechanisms of Ti. Our finding enriches current understanding about simultaneously improving the strength and ductility by structural design. PMID:27917923

  17. Zero-line modes at stacking faulted domain walls in multilayer graphene

    NASA Astrophysics Data System (ADS)

    Lee, Changhee; Kim, Gunn; Jung, Jeil; Min, Hongki

    2016-09-01

    Rhombohedral multilayer graphene is a physical realization of the chiral two-dimensional electron gas that can host zero-line modes (ZLMs), also known as kink states, when the local gap opened by inversion symmetry breaking potential changes sign in real space. Here we study how the variations in the local stacking coordination of multilayer graphene affects the formation of the ZLMs. Our analysis indicates that the valley Hall effect develops whenever an interlayer potential difference is able to open up a band gap in stacking faulted multilayer graphene, and that ZLMs can appear at the domain walls separating two distinct regions with imperfect rhombohedral stacking configurations. Based on a tight-binding formulation with distant hopping terms between carbon atoms, we first show that topologically distinct domains characterized by the valley Chern number are separated by a metallic region connecting AA and AA' stacking line in the layer translation vector space. We find that gapless states appear at the interface between the two stacking faulted domains with different layer translation or with opposite perpendicular electric field if their valley Chern numbers are different.

  18. Metallization of Epitaxial VO2 Films by Ionic Liquid Gating through Initially Insulating TiO2 Layers.

    PubMed

    Passarello, Donata; Altendorf, Simone G; Jeong, Jaewoo; Samant, Mahesh G; Parkin, Stuart S P

    2016-09-14

    Ionic liquid gating has been shown to metallize initially insulating layers formed from several different oxide materials. Of these vanadium dioxide (VO2) is of especial interest because it itself is metallic at temperatures above its metal-insulator transition. Recent studies have shown that the mechanism of ionic liquid gated induced metallization is entirely distinct from that of the thermally driven metal-insulator transition and is derived from oxygen migration through volume channels along the (001) direction of the rutile structure of VO2. Here we show that it is possible to metallize the entire volume of 10 nm thick layers of VO2 buried under layers of rutile titanium dioxide (TiO2) up to 10 nm thick. Key to this process is the alignment of volume channels in the respective oxide layers, which have the same rutile structure with clamped in-plane lattice constants. The metallization of the VO2 layers is accompanied by large structural expansions of up to ∼6.5% in the out-of-plane direction, but the structure of the TiO2 layer is hardly affected by gating. The TiO2 layers become weakly conducting during the gating process, but in contrast to the VO2 layers, the conductivity disappears on exposure to air. Indeed, even after air exposure, X-ray photoelectron spectroscopy studies show that the VO2 films have a reduced oxygen content after metallization. Ionic liquid gating of the VO2 films through initially insulating TiO2 layers is not consistent with conventional models that have assumed the gate induced carriers are of electrostatic origin.

  19. Wearable solar cells by stacking textile electrodes.

    PubMed

    Pan, Shaowu; Yang, Zhibin; Chen, Peining; Deng, Jue; Li, Houpu; Peng, Huisheng

    2014-06-10

    A new and general method to produce flexible, wearable dye-sensitized solar cell (DSC) textiles by the stacking of two textile electrodes has been developed. A metal-textile electrode that was made from micrometer-sized metal wires was used as a working electrode, while the textile counter electrode was woven from highly aligned carbon nanotube fibers with high mechanical strengths and electrical conductivities. The resulting DSC textile exhibited a high energy conversion efficiency that was well maintained under bending. Compared with the woven DSC textiles that are based on wire-shaped devices, this stacked DSC textile unexpectedly exhibited a unique deformation from a rectangle to a parallelogram, which is highly desired in portable electronics. This lightweight and wearable stacked DSC textile is superior to conventional planar DSCs because the energy conversion efficiency of the stacked DSC textile was independent of the angle of incident light.

  20. A difference in using atomic layer deposition or physical vapour deposition TiN as electrode material in metal-insulator-metal and metal-insulator-silicon capacitors.

    PubMed

    Groenland, A W; Wolters, R A M; Kovalgin, A Y; Schmitz, J

    2011-09-01

    In this work, metal-insulator-metal (MIM) and metal-insulator-silicon (MIS) capacitors are studied using titanium nitride (TiN) as the electrode material. The effect of structural defects on the electrical properties on MIS and MIM capacitors is studied for various electrode configurations. In the MIM capacitors the bottom electrode is a patterned 100 nm TiN layer (called BE type 1), deposited via sputtering, while MIS capacitors have a flat bottom electrode (called BE type 2-silicon substrate). A high quality 50-100 nm thick SiO2 layer, made by inductively-coupled plasma CVD at 150 degrees C, is deposited as a dielectric on top of both types of bottom electrodes. BE type 1 (MIM) capacitors have a varying from low to high concentration of structural defects in the SiO2 layer. BE type 2 (MIS) capacitors have a low concentration of structural defects and are used as a reference. Two sets of each capacitor design are fabricated with the TiN top electrode deposited either via physical vapour deposition (PVD, i.e., sputtering) or atomic layer deposition (ALD). The MIM and MIS capacitors are electrically characterized in terms of the leakage current at an electric field of 0.1 MV/cm (I leak) and for different structural defect concentrations. It is shown that the structural defects only show up in the electrical characteristics of BE type 1 capacitors with an ALD TiN-based top electrode. This is due to the excellent step coverage of the ALD process. This work clearly demonstrates the sensitivity to process-induced structural defects, when ALD is used as a step in process integration of conductors on insulation materials.

  1. Anion-intercalated layered double hydroxides modified test strips for detection of heavy metal ions.

    PubMed

    Wang, Nan; Sun, Jianchao; Fan, Hai; Ai, Shiyun

    2016-01-01

    In this work, a novel approach for facile and rapid detection of heavy metal ions using anion-intercalated layered double hydroxides (LDHs) modified test strips is demonstrated. By intercalating Fe(CN)6(4-) or S(2-) anions into the interlayers of LDHs on the filter paper, various heavy metal ions can be easily detected based on the color change before and after reaction between the anions and the heavy metal ions. Upon the dropping of heavy metal ions solutions to the test strips, the colors of the test strips changed instantly, which can be easily observed by naked eyes. With the decrease of the concentration, the color depth changed obviously. The lowest detection concentration can be up to 1×10(-6) mol L(-1). Due to the easily intercalation of anions into the interlayer of the LDHs on test trips, this procedure provides a general method for the construction of LDHs modified test strips for detection of heavy metal ions. The stability of the prepared test strips is investigated. Furthermore, all the results were highly reproducible. The test strips may have potential applications in environmental monitoring fields.

  2. Vapor phase hydrogenation of furfural over nickel mixed metal oxide catalysts derived from layered double hydroxides

    SciTech Connect

    Sulmonetti, Taylor P.; Pang, Simon H.; Claure, Micaela Taborga; Lee, Sungsik; Cullen, David A.; Agrawal, Pradeep K.; Jones, Christopher W.

    2016-05-01

    The hydrogenation of furfural is investigated over various reduced nickel mixed metal oxides derived from layered double hydroxides (LDHs) containing Ni-Mg-Al and Ni-Co-Al. Upon reduction, relatively large Ni(0) domains develop in the Ni-Mg-Al catalysts, whereas in the Ni-Co-Al catalysts smaller metal particles of Ni(0) and Co(0), potentially as alloys, are formed, as evidenced by XAS, XPS, STEM and EELS. All the reduced Ni catalysts display similar selectivities towards major hydrogenation products (furfuryl alcohol and tetrahydrofurfuryl alcohol), though the side products varied with the catalyst composition. The 1.1Ni-0.8Co-Al catalyst showed the greatest activity per titrated site when compared to the other catalysts, with promising activity compared to related catalysts in the literature. The use of base metal catalysts for hydrogenation of furanic compounds may be a promising alternative to the well-studied precious metal catalysts for making biomass-derived chemicals if catalyst selectivity can be improved in future work by alloying or tuning metal-oxide support interactions.

  3. Vapor phase hydrogenation of furfural over nickel mixed metal oxide catalysts derived from layered double hydroxides

    DOE PAGES

    Sulmonetti, Taylor P.; Pang, Simon H.; Claure, Micaela Taborga; ...

    2016-03-09

    The hydrogenation of furfural is investigated over various reduced nickel mixed metal oxides derived from layered double hydroxides (LDHs) containing Ni-Mg-Al and Ni-Co-Al. Upon reduction, relatively large Ni(0) domains develop in the Ni-Mg-Al catalysts, whereas in the Ni-Co-Al catalysts smaller metal particles of Ni(0) and Co(0), potentially as alloys, are formed, as evidenced by XAS, XPS, STEM and EELS. All the reduced Ni catalysts display similar selectivities towards major hydrogenation products (furfuryl alcohol and tetrahydrofurfuryl alcohol), though the side products varied with the catalyst composition. The 1.1Ni-0.8Co-Al catalyst showed the greatest activity per titrated site when compared to the othermore » catalysts, with promising activity compared to related catalysts in the literature. In conclusion, the use of base metal catalysts for hydrogenation of furanic compounds may be a promising alternative to the well-studied precious metal catalysts for making biomass-derived chemicals if catalyst selectivity can be improved in future work by alloying or tuning metal-oxide support interactions.« less

  4. Vapor phase hydrogenation of furfural over nickel mixed metal oxide catalysts derived from layered double hydroxides

    SciTech Connect

    Sulmonetti, Taylor P.; Pang, Simon H.; Claure, Micaela Taborga; Lee, Sungsik; Cullen, David A.; Agrawal, Pradeep K.; Jones, Christopher W.

    2016-03-09

    The hydrogenation of furfural is investigated over various reduced nickel mixed metal oxides derived from layered double hydroxides (LDHs) containing Ni-Mg-Al and Ni-Co-Al. Upon reduction, relatively large Ni(0) domains develop in the Ni-Mg-Al catalysts, whereas in the Ni-Co-Al catalysts smaller metal particles of Ni(0) and Co(0), potentially as alloys, are formed, as evidenced by XAS, XPS, STEM and EELS. All the reduced Ni catalysts display similar selectivities towards major hydrogenation products (furfuryl alcohol and tetrahydrofurfuryl alcohol), though the side products varied with the catalyst composition. The 1.1Ni-0.8Co-Al catalyst showed the greatest activity per titrated site when compared to the other catalysts, with promising activity compared to related catalysts in the literature. In conclusion, the use of base metal catalysts for hydrogenation of furanic compounds may be a promising alternative to the well-studied precious metal catalysts for making biomass-derived chemicals if catalyst selectivity can be improved in future work by alloying or tuning metal-oxide support interactions.

  5. Selectivity of layered double hydroxides and their derivative mixed metal oxides as sorbents of hydrogen sulfide.

    PubMed

    Othman, Mohamed A; Zahid, Waleed M; Abasaeed, Ahmed E

    2013-06-15

    In the context of finding high efficient sorbent materials for removing hydrogen sulfide (H2S) from air stream, a screening study was performed to find the best combination of metals for the synthesis of layered double hydroxides (LDHs) and their derivative mixed metal oxides. Based on selectivity of 998 natural mineral species of sulfur-containing compounds, Cu(2+), Ni(2+) and Zn(2+) were selected as divalent metals, and Fe(3+), Al(3+) and Cr(3+) as trivalent metals to synthesis the LDHs sorbents. 10 LDHs materials and their calcined mixed metal oxides, Ni(0.66)Al(0.34), Cu(0.35)Ni(0.32)Al(0.33), Zn(0.66)Al(0.34), Cu(0.36)Zn(0.32)Al(0.32), Ni(0.64)Fe(0.36), Cu(0.35)Ni(0.31)Fe(0.34), Ni(0.66)Cr(0.34), Cu(0.35)Ni(0.31)Cr(0.34), Zn(0.66)Cr(0.34), Cu(0.33)Zn(0.32)Cr(0.35) were synthesized, characterized chemically and physically, and then tested using breakthrough test to determine their sulfur uptake. Ni(0.64)Fe(0.36) mixed metal oxides was found to have the best uptake of hydrogen sulfide (136 mg H₂S/g). Regeneration of spent Ni(0.64)Fe(0.36) mixed metal oxides was studied using two different mixture solutions, NaCl/NaOH and acetate-buffer/NaCl/NaOH. The latter mixture successfully desorbed the sulfur from the Ni0.64Fe0.36 sorbent for 2 cycles of regeneration/sorption.

  6. Stacking with stochastic cooling

    NASA Astrophysics Data System (ADS)

    Caspers, Fritz; Möhl, Dieter

    2004-10-01

    Accumulation of large stacks of antiprotons or ions with the aid of stochastic cooling is more delicate than cooling a constant intensity beam. Basically the difficulty stems from the fact that the optimized gain and the cooling rate are inversely proportional to the number of particles 'seen' by the cooling system. Therefore, to maintain fast stacking, the newly injected batch has to be strongly 'protected' from the Schottky noise of the stack. Vice versa the stack has to be efficiently 'shielded' against the high gain cooling system for the injected beam. In the antiproton accumulators with stacking ratios up to 105 the problem is solved by radial separation of the injection and the stack orbits in a region of large dispersion. An array of several tapered cooling systems with a matched gain profile provides a continuous particle flux towards the high-density stack core. Shielding of the different systems from each other is obtained both through the spatial separation and via the revolution frequencies (filters). In the 'old AA', where the antiproton collection and stacking was done in one single ring, the injected beam was further shielded during cooling by means of a movable shutter. The complexity of these systems is very high. For more modest stacking ratios, one might use azimuthal rather than radial separation of stack and injected beam. Schematically half of the circumference would be used to accept and cool new beam and the remainder to house the stack. Fast gating is then required between the high gain cooling of the injected beam and the low gain stack cooling. RF-gymnastics are used to merge the pre-cooled batch with the stack, to re-create free space for the next injection, and to capture the new batch. This scheme is less demanding for the storage ring lattice, but at the expense of some reduction in stacking rate. The talk reviews the 'radial' separation schemes and also gives some considerations to the 'azimuthal' schemes.

  7. Single-layer CVD-grown graphene decorated with metal nanoparticles as a promising biosensing platform.

    PubMed

    Gutés, Albert; Carraro, Carlo; Maboudian, Roya

    2012-03-15

    A new approach to the development of a single-layer graphene sensor decorated with metal nanoparticles is presented. Chemical vapor deposition is used to grow single layer graphene on copper. Decoration of the single-layer graphene is achieved by electroless deposition of Au nanoparticles using the copper substrate as a source of electrons. Transfer of the decorated single-layer graphene on glassy carbon electrodes offers a sensitive platform for biosensor development. As a proof of concept, 10 units of glucose oxidase were deposited on the surface in a Nafion matrix to stabilize the enzyme as well as to prevent interference from ascorbic acid and uric acid. Amperometric linear response calibration in the μmoll(-1) is obtained. The presented methodology enables highly sensitive platforms for biosensor development, providing a scalable roll-to-roll production with a much more reproducible scheme when compared to the graphene biosensors reported previously based on drop-cast of multi-layer graphene suspensions.

  8. Chromatic Mechanical Response in 2-D Layered Transition Metal Dichalcogenide (TMDs) based Nanocomposites

    NASA Astrophysics Data System (ADS)

    Rahneshin, Vahid; Khosravi, Farhad; Ziolkowska, Dominika A.; Jasinski, Jacek B.; Panchapakesan, Balaji

    2016-10-01

    The ability to convert photons of different wavelengths directly into mechanical motion is of significant interest in many energy conversion and reconfigurable technologies. Here, using few layer 2H-MoS2 nanosheets, layer by layer process of nanocomposite fabrication, and strain engineering, we demonstrate a reversible and chromatic mechanical response in MoS2-nanocomposites between 405 nm to 808 nm with large stress release. The chromatic mechanical response originates from the d orbitals and is related to the strength of the direct exciton resonance A and B of the few layer 2H-MoS2 affecting optical absorption and subsequent mechanical response of the nanocomposite. Applying uniaxial tensile strains to the semiconducting few-layer 2H-MoS2 crystals in the nanocomposite resulted in spatially varying energy levels inside the nanocomposite that enhanced the broadband optical absorption up to 2.3 eV and subsequent mechanical response. The unique photomechanical response in 2H-MoS2 based nanocomposites is a result of the rich d electron physics not available to nanocomposites based on sp bonded graphene and carbon nanotubes, as well as nanocomposite based on metallic nanoparticles. The reversible strain dependent optical absorption suggest applications in broad range of energy conversion technologies that is not achievable using conventional thin film semiconductors.

  9. Chromatic Mechanical Response in 2-D Layered Transition Metal Dichalcogenide (TMDs) based Nanocomposites

    PubMed Central

    Rahneshin, Vahid; Khosravi, Farhad; Ziolkowska, Dominika A.; Jasinski, Jacek B.; Panchapakesan, Balaji

    2016-01-01

    The ability to convert photons of different wavelengths directly into mechanical motion is of significant interest in many energy conversion and reconfigurable technologies. Here, using few layer 2H-MoS2 nanosheets, layer by layer process of nanocomposite fabrication, and strain engineering, we demonstrate a reversible and chromatic mechanical response in MoS2-nanocomposites between 405 nm to 808 nm with large stress release. The chromatic mechanical response originates from the d orbitals and is related to the strength of the direct exciton resonance A and B of the few layer 2H-MoS2 affecting optical absorption and subsequent mechanical response of the nanocomposite. Applying uniaxial tensile strains to the semiconducting few-layer 2H-MoS2 crystals in the nanocomposite resulted in spatially varying energy levels inside the nanocomposite that enhanced the broadband optical absorption up to 2.3 eV and subsequent mechanical response. The unique photomechanical response in 2H-MoS2 based nanocomposites is a result of the rich d electron physics not available to nanocomposites based on sp bonded graphene and carbon nanotubes, as well as nanocomposite based on metallic nanoparticles. The reversible strain dependent optical absorption suggest applications in broad range of energy conversion technologies that is not achievable using conventional thin film semiconductors. PMID:27713550

  10. Chromatic Mechanical Response in 2-D Layered Transition Metal Dichalcogenide (TMDs) based Nanocomposites.

    PubMed

    Rahneshin, Vahid; Khosravi, Farhad; Ziolkowska, Dominika A; Jasinski, Jacek B; Panchapakesan, Balaji

    2016-10-07

    The ability to convert photons of different wavelengths directly into mechanical motion is of significant interest in many energy conversion and reconfigurable technologies. Here, using few layer 2H-MoS2 nanosheets, layer by layer process of nanocomposite fabrication, and strain engineering, we demonstrate a reversible and chromatic mechanical response in MoS2-nanocomposites between 405 nm to 808 nm with large stress release. The chromatic mechanical response originates from the d orbitals and is related to the strength of the direct exciton resonance A and B of the few layer 2H-MoS2 affecting optical absorption and subsequent mechanical response of the nanocomposite. Applying uniaxial tensile strains to the semiconducting few-layer 2H-MoS2 crystals in the nanocomposite resulted in spatially varying energy levels inside the nanocomposite that enhanced the broadband optical absorption up to 2.3 eV and subsequent mechanical response. The unique photomechanical response in 2H-MoS2 based nanocomposites is a result of the rich d electron physics not available to nanocomposites based on sp bonded graphene and carbon nanotubes, as well as nanocomposite based on metallic nanoparticles. The reversible strain dependent optical absorption suggest applications in broad range of energy conversion technologies that is not achievable using conventional thin film semiconductors.

  11. Modeling hydrodynamic flows in plasma fluxes when depositing metal layer on the surface of catalyst converters

    NASA Astrophysics Data System (ADS)

    Chinakhov, D. A.; Sarychev, V. D.; Granovsky, A. Yu; Solodsky, S. A.; Nevsky, S. A.; Konovalov, S. V.

    2017-01-01

    Air pollution with harmful substances resulting from combustion of liquid hydrocarbons and emitted into atmosphere became one of the global environmental problems in the late 20th century. The systems of neutralization capable to reduce toxicity of exhaust gases several times are very important for making environmentally safer combustion products discharged into the atmosphere. As revealed in the literature review, one of the most promising purification procedures is neutralization of burnt gases by catalyst converter systems. The principal working element in the converter is a catalytic layer of metals deposited on ceramics, with thickness 20-60 micron and a well-developed micro-relief. The paper presents a thoroughly substantiated new procedure of deposing a nano-scale surface layer of metal-catalyst particles, furthering the utilization of catalysts on a new level. The paper provides description of mathematical models and computational researches into plasma fluxes under high-frequency impulse input delivered to electrode material, explorations of developing Kelvin-Helmholtz, Marangoni and magnetic hydrodynamic instabilities on the surface of liquid electrode metal droplet in the nano-scale range of wavelengths to obtain a flow of nano-meter particles of cathode material. The authors have outlined a physical and mathematical model of magnetic and hydrodynamic instability for the case of melt flowing on the boundary with the molten metal with the purpose to predict the interphase shape and mutual effect of formed plasma jet and liquid metal droplet on the electrode in the nano-scale range of wavelengths at high-frequency impact on the boundary “electrode-liquid layer”.

  12. Short protection device for stack of electrolytic cells

    DOEpatents

    Katz, Murray; Schroll, Craig R.

    1985-10-22

    Electrical short protection is provided in an electrolytic cell stack by the combination of a thin, nonporous ceramic shield and a noble metal foil disposed on opposite sides of the sealing medium in a gas manifold gasket. The thin ceramic shield, such as alumina, is placed between the porous gasket and the cell stack face at the margins of the negative end plate to the most negative cells to impede ion current flow. The noble metal foil, for instance gold, is electrically coupled to the negative potential of the stack to collect positive ions at a harmless location away from the stack face. Consequently, corrosion products from the stack structure deposit on the foil rather than on the stack face to eliminate electrical shorting of cells at the negative end of the stack.

  13. Orientation of diamagnetic layered transition metal oxide particles in 1-tesla magnetic fields.

    PubMed

    Sklute, Elizabeth C; Eguchi, Miharu; Henderson, Camden N; Angelone, Mark S; Yennawar, Hemant P; Mallouk, Thomas E

    2011-02-16

    The magnetic field-driven orientation of microcrystals of six diamagnetic layered transition metal oxides (HLaNb(2)O(7), HCa(2)Nb(3)O(10)·0.5H(2)O, KNaCa(2)Nb(4)O(13), KTiTaO(5), KTiNbO(5), and H(2.2)K(1.8)Nb(6)O(17)·nH(2)O) suspended in epoxy resins was studied by X-ray diffraction using permanent magnets producing a 0.8 T field. Although the degree of orientation, quantified as the Hermans order parameter, was strongly affected by the particle size distribution, in all cases microcrystals with ∼1-2 μm lateral dimensions were found to orient with the magnetic field vector in the layer plane. Control of the orientation of ionically conducting layered oxides is of interest for practical applications in batteries and fuel cells. The consistent direction of orientation of the lamellar oxides studied can be rationalized in the framework of a quantitative bond anisotropy model developed by Uyeda (Phys. Chem. Miner.1993, 20, 77-80). The asymmetry of metal-oxygen bonding at the faces of the octahedral layers results in long and short M-O bonds perpendicular to the plane of the sheets. This distortion of the M-O octahedra, which is a structural feature of almost all layered materials that contain octahedral bonding frameworks, gives rise to the diamagnetic anisotropy and results in an easy axis or plane of magnetization in the plane of the sheets.

  14. Metallicity of Ca2Cu6P5 with single and double copper-pnictide layers

    DOE PAGES

    Li, Li; Parker, David; Chi, Miaofang; ...

    2016-02-16

    We report thermodynamic and transport properties, and also theoretical calculations, for Cu-based compound Ca2Cu6P5 and compare with CaCu2-δP2. Both materials have layers of edge-sharing copper pnictide tetrahedral CuP4, similar to Fe–As and Fe–Se layers (with FeAs4, FeSe4) in the iron-based superconductors. Despite the presence of this similar transition-metal pnictide layer, we find that both Ca2Cu6P5 and CaCu2-δP2 have temperature-independent magnetic susceptibility and show metallic behavior with no evidence of either magnetic ordering or superconductivity down to 1.8 K CaCu2-δP2 is slightly off-stoichiometric, with δ = 0.14. Theoretical calculations suggest that unlike Fe 3d-based magnetic materials with a large density ofmore » states (DOS) at the Fermi surface, Cu have comparatively low DOS, with the majority of the 3d spectral weight located well below Fermi level. The room-temperature resistivity value of Ca2Cu6P5 is only 9 μΩ-cm, due to a substantial plasma frequency and an inferred electron-phonon coupling λ of 0.073 (significantly smaller than that of metallic Cu). Also, microscopy result shows that Cu–Cu distance along the c-axis within the double layers can be very short (2.5 Å), even shorter than metallic elemental copper bond (2.56 Å). The value of dρ/dT for CaCu2-δP2 at 300 K is approximately three times larger than in Ca2Cu6P5, which suggests the likelihood of stronger electron-phonon coupling. Lastly, this study shows that the details of Cu–P layers and bonding are important for their transport characteristics. In addition, it emphasizes the remarkable character of the DOS of ‘122’ iron-based materials, despite much structural similarities.« less

  15. Fundamental studies of diffusion barriers for copper metallization and atomic layer deposited high-kappa films

    NASA Astrophysics Data System (ADS)

    Majumder, Prodyut

    Copper is used as interconnect material due to its lower resistivity, higher melting point and higher electromigration resistance than those of Al. However, Cu diffuses rapidly into Si and SiO2, to form Cu-silicides at temperatures as low as 200°C. Being highly resistive, Cu-silicides are detrimental in the performance of the integrated circuits. The continued downscaling of device dimensions has placed a high priority on the development of thin diffusion barrier layers in copper metallization. The effectiveness and performance of Mo-based bi-layers, such as Mo/WN, Mo/Ti, and Mo/TiN, and a ternary single layer, Mo-V nitride, deposited using magnetron sputtering are investigated in this work. The Cu/barrier film(s)/Si structures are annealed at high temperatures in N2 and the interactions between the layers along with the possible formation of any anneal-induced reaction products are evaluated using different techniques. The formation of Cu3Si due to the intermixing of Cu and Si is indicative of barrier breakdown. The decreasing device dimensions in microelectronic circuits set high demands for film conformality as the barrier layer thickness is anticipated to decrease to 1.9 nm for the 25 nm node (by 2015). In order to meet future requirement of ultrathin barriers, the apparently counter-intuitive approach of using insulating films, such as HfO2 and Al2O 3, deposited using atomic layer deposition (ALD) technique has been studied and revealed interesting and promising results. In microelectronics fabrication, there is also a need for thin films with high dielectric constant (kappa) in order to continue device dimension reduction of logic and memory devices. With conventional SiO2 based materials, continued scale minimization mandates single digit atomic layer thicknesses of the dielectric layers that lead to the ultimate limitation of quantum mechanical tunneling. To overcome this limitation, high-kappa metal oxides have been recognized as future gate dielectrics

  16. Improved adhesion of Cu on pre-etched polytetrafluoroethylene by PECVD deposited thin metallic layers

    NASA Astrophysics Data System (ADS)

    Haag, C.; Suhr, H.

    1988-10-01

    The adhesion of copper to PTFE has been studied with regard to the influence of a pretreatment in discharges of reactive gases, such as O2 and CF4/O2, and a subsequent deposition of thin metallic interlayers of Pd, Pt, Au, and Cu by PECVD methods. Adhesion forces could be enhanced by about the factor of 10 compared with merely pretreated surfaces up to 5 N/mm, which, as scanning electron micrographs prove, corresponds to the tensile strength of the bulk material. SIMS spectra of the back surface of a peeled copper stripe show the typical signals of PTFE. The thermal stability of the layers was established by dipping the samples into a tin bath of 540 K. The enhanced adhesion is not only due to the changes in surface morphology by etching. It can be attributed to chemical effects, i. e. chemical bonds between substrate atoms and the interlayer, and physical effects, caused by implantation of metal ions into the upper surface layers accompanied by a probable electron transfer from PTFE to metal.

  17. Long-Term Passivation of Strongly Interacting Metals with Single-Layer Graphene

    PubMed Central

    2015-01-01

    The long-term (>18 months) protection of Ni surfaces against oxidation under atmospheric conditions is demonstrated by coverage with single-layer graphene, formed by chemical vapor deposition. In situ, depth-resolved X-ray photoelectron spectroscopy of various graphene-coated transition metals reveals that a strong graphene–metal interaction is of key importance in achieving this long-term protection. This strong interaction prevents the rapid intercalation of oxidizing species at the graphene–metal interface and thus suppresses oxidation of the substrate surface. Furthermore, the ability of the substrate to locally form a passivating oxide close to defects or damaged regions in the graphene overlayer is critical in plugging these defects and preventing oxidation from proceeding through the bulk of the substrate. We thus provide a clear rationale for understanding the extent to which two-dimensional materials can protect different substrates and highlight the key implications for applications of these materials as barrier layers to prevent oxidation. PMID:26499041

  18. Contact resistance at planar metal contacts on bilayer graphene and effects of molecular insertion layers

    NASA Astrophysics Data System (ADS)

    Nouchi, Ryo

    2017-03-01

    The possible origins of metal–bilayer graphene (BLG) contact resistance are investigated by taking into consideration the bandgap formed by interfacial charge transfer at the metal contacts. Our results show that a charge injection barrier (Schottky barrier) does not contribute to the contact resistance because the BLG under the contacts is always degenerately doped. We also showed that the contact-doping-induced increase in the density of states (DOS) of BLG under the metal contacts decreases the contact resistance owing to enhanced charge carrier tunnelling at the contacts. The contact doping can be enhanced by inserting molecular dopant layers into the metal contacts. However, carrier tunnelling through the insertion layer increases the contact resistance, and thus, alternative device structures should be employed. Finally, we showed that the inter-band transport by variable range hopping via in-gap states is the largest contributor to contact resistance when the carrier type of the gated channel is opposite to the contact doping carrier type. This indicates that the strategy of contact resistance reduction by the contact-doping-induced increase in the DOS is effective only for a single channel transport branch (n- or p-type) depending on the contact doping carrier type.

  19. Growth and spectroscopic characterization of monolayer and few-layer hexagonal boron nitride on metal substrates

    NASA Astrophysics Data System (ADS)

    Feigelson, Boris N.; Bermudez, Victor M.; Hite, Jennifer K.; Robinson, Zachary R.; Wheeler, Virginia D.; Sridhara, Karthik; Hernández, Sandra C.

    2015-02-01

    Atomically thin two dimensional hexagonal boron nitride (2D h-BN) is one of the key materials in the development of new van der Waals heterostructures due to its outstanding properties including an atomically smooth surface, high thermal conductivity, high mechanical strength, chemical inertness and high electrical resistance. The development of 2D h-BN growth is still in the early stages and largely depends on rapid and accurate characterization of the grown monolayer or few layers h-BN films. This paper demonstrates a new approach to characterizing monolayer h-BN films directly on metal substrates by grazing-incidence infrared reflection absorption spectroscopy (IRRAS). Using h-BN films grown by atmospheric-pressure chemical vapor deposition on Cu and Ni substrates, two new sub-bands are found for the A2u out-of-plane stretching mode. It is shown, using both experimental and computational methods, that the lower-energy sub-band is related to 2D h-BN coupled with substrate, while the higher energy sub-band is related to decoupled (or free-standing) 2D h-BN. It is further shown that this newly-observed fine structure in the A2u mode can be used to assess, quickly and easily, the homogeneity of the h-BN-metal interface and the effects of metal surface contamination on adhesion of the layer.

  20. Ultra-Flexible, Invisible Thin-Film Transistors Enabled by Amorphous Metal Oxide/Polymer Channel Layer Blends

    DTIC Science & Technology

    2015-02-25

    Transistors Enabled by Amorphous Metal Oxide/Polymer Channel Layer Blends Xinge Yu , Li Zeng , Nanjia Zhou , Peijun Guo , Fengyuan Shi , Donald B...chemical vapor deposition processes. Thus, a key issue for inexpensive large-scale roll-to-roll production is to enable MO TFT manu- facturing with...4. TITLE AND SUBTITLE Ultra-Flexible, ’Invisible’ Thin-Film Transistors Enabled by Amorphous Metal Oxide/Polymer Channel Layer Blends 5a. CONTRACT

  1. Deposition temperature dependence of material and Si surface passivation properties of O{sub 3}-based atomic layer deposited Al{sub 2}O{sub 3}-based films and stacks

    SciTech Connect

    Bordihn, Stefan; Mertens, Verena; Müller, Jörg W.; Kessels, W. M. M.

    2014-01-15

    The material composition and the Si surface passivation of aluminum oxide (Al{sub 2}O{sub 3}) films prepared by atomic layer deposition using Al(CH{sub 3}){sub 3} and O{sub 3} as precursors were investigated for deposition temperatures (T{sub Dep}) between 200 °C and 500 °C. The growth per cycle decreased with increasing deposition temperature due to a lower Al deposition rate. In contrast the material composition was hardly affected except for the hydrogen concentration, which decreased from [H] = 3 at. % at 200 °C to [H] < 0.5 at. % at 400 °C and 500 °C. The surface passivation performance was investigated after annealing at 300 °C–450 °C and also after firing steps in the typical temperature range of 800 °C–925 °C. A similar high level of the surface passivation performance, i.e., surface recombination velocity values <10 cm/s, was obtained after annealing and firing. Investigations of Al{sub 2}O{sub 3}/SiN{sub x} stacks complemented the work and revealed similar levels of surface passivation as single-layer Al{sub 2}O{sub 3} films, both for the chemical and field-effect passivation. The fixed charge density in the Al{sub 2}O{sub 3}/SiN{sub x} stacks, reflecting the field-effect passivation, was reduced by one order of magnitude from 3·10{sup 12} cm{sup −2} to 3·10{sup 11} cm{sup −2} when T{sub Dep} was increased from 300 °C to 500 °C. The level of the chemical passivation changed as well, but the total level of the surface passivation was hardly affected by the value of T{sub Dep}. When firing films prepared at of low T{sub Dep}, blistering of the films occurred and this strongly reduced the surface passivation. These results presented in this work demonstrate that a high level of surface passivation can be achieved for Al{sub 2}O{sub 3}-based films and stacks over a wide range of conditions when the combination of deposition temperature and annealing or firing temperature is carefully chosen.

  2. LONG-TERM PERFORMANCE OF SOLID OXIDE STACKS WITH ELECTRODE-SUPPORTED CELLS OPERATING IN THE STEAM ELECTROLYSIS MODE

    SciTech Connect

    J. E. O'Brien; R. C. O'Brien; X. Zhang; G. Tao; B. J. Butler

    2011-11-01

    Performance characterization and durability testing have been completed on two five-cell high-temperature electrolysis stacks constructed with advanced cell and stack technologies. The solid oxide cells incorporate a negative-electrode-supported multi-layer design with nickel-zirconia cermet negative electrodes, thin-film yttria-stabilized zirconia electrolytes, and multi-layer lanthanum ferrite-based positive electrodes. The per-cell active area is 100 cm2. The stack is internally manifolded with compliant mica-glass seals. Treated metallic interconnects with integral flow channels separate the cells. Stack compression is accomplished by means of a custom spring-loaded test fixture. Initial stack performance characterization was determined through a series of DC potential sweeps in both fuel cell and electrolysis modes of operation. Results of these sweeps indicated very good initial performance, with area-specific resistance values less than 0.5 ?.cm2. Long-term durability testing was performed with A test duration of 1000 hours. Overall performance degradation was less than 10% over the 1000-hour period. Final stack performance characterization was again determined by a series of DC potential sweeps at the same flow conditions as the initial sweeps in both electrolysis and fuel cell modes of operation. A final sweep in the fuel cell mode indicated a power density of 0.356 W/cm2, with average per-cell voltage of 0.71 V at a current of 50 A.

  3. Shift and elimination of microwave Fabry-Perot resonances in a dielectric covered with a thin metal layer

    NASA Astrophysics Data System (ADS)

    Ragulis, Paulius; Simniškis, Rimantas; Kancleris, Žilvinas

    2015-04-01

    In this paper, we consider a plane electromagnetic wave incident onto a dielectric plate, which has one surface covered with a thin layer of metal. An oblique incident angle was considered for the TE (s polarization in optic) and TM (p polarization) plane waves. The thin metal layer is treated as an infinitesimal thickness. It was characterized by a surface conductivity and accounted for by a tangential magnetic field component step induced by the current flow in the metal layer. Compact expressions, which describe the reflection, transmission and absorption in a dielectric plate covered with a thin layer of metal, have been obtained. It was shown that by choosing the appropriate surface conductivity, the Fabry-Perot transmission resonances can be shifted to the position where the maximum reflection is observed in the case of an uncovered dielectric. On the other hand, the elimination of the Fabry-Perot resonances can be also achieved by choosing a proper metal surface conductivity. Measurements of the reflection from the glass covered with a thin layer of metal have been performed in a wide microwave frequency range (2-12 GHz) revealing a large difference in the measured reflection coefficient from the dielectric and metalized surfaces. The measured results fit well with those calculated by employing analytical expressions obtained in this paper.

  4. Capacitance of the double electrical layer on the copper-group metals in molten alkali metal halides

    NASA Astrophysics Data System (ADS)

    Kirillova, E. V.; Stepanov, V. P.

    2016-08-01

    The electrochemical impedance is measured to study the capacitance of the double electrical layer of metallic Au, Ag, and Cu as a function of potential and temperature in nine molten salts, namely, the chlorides, bromides, and iodides of sodium, potassium, and cesium. The C- E curve of a gold electrode has an additional minimum in the anodic branch. This minimum for silver is less pronounced and is only observed at low ac signal frequencies in cesium halides. The additional minimum is not detected for copper in any salt under study. This phenomenon is explained on the assumption that the adsorption of halide anions on a positively charged electrode surface has a predominantly chemical rather than an electrostatic character. The specific adsorption in this case is accompanied by charge transfer through the interface and the formation of an adsorbent-adsorbate covalent bond.

  5. Synthesis, crystal structure, and ionic conductivity of a new layered metal phosphate, Li2Sr2Al(PO4)3

    NASA Astrophysics Data System (ADS)

    Kim, Sung-Chul; Kwak, Hyun-Jung; Yoo, Chung-Yul; Yun, Hoseop; Kim, Seung-Joo

    2016-11-01

    A new layered metal phosphate, Li2Sr2Al(PO4)3, was synthesized in the form of either a single-crystal or polycrystalline powder using the molten hydroxide flux method or a solid-state reaction, respectively. Li2Sr2Al(PO4)3 crystallizes to the P21/n (Z=4) monoclinic space group with lattice parameters a≈4.95 Å, b≈22.06 Å, c≈8.63 Å, and β≈91.5°. The structure is composed of stacked [LiSrAl(PO4)2] layers alternating regularly with [LiSrPO4] layers. In the [LiSrAl(PO4)2] sublattice, the AlO6 octahedra and PO4 tetrahedra are tilted cooperatively to form an anionic, corrugated, two-dimensional [Al(PO4)2]3- framework that can be regarded as a "distorted-glaserite" structure. The [LiSrPO4] sublattice is that of a layered block containing a six-membered ring formed from alternating linkages of LiO4 and PO4 tetrahedra. The six-membered rings show a boat-type arrangement with the up(U) or down(D) pointing sequence, UUDUUD. The interspace between the two sublattices generates a two-dimensional pathway for Li+ ion conduction. The impedance measurement indicated that Li2Sr2Al(PO4)3 had a moderate ion conductivity (σ≈1.30×10-4 S cm-1 at 667 K), with an activation energy Ea≈1.02 eV.

  6. Nanostructural model of metal-insulator transition in layered LixZrNCl superconductors

    NASA Astrophysics Data System (ADS)

    Phillips, J. C.

    2008-03-01

    The self-organized dopant percolative filamentary model, entirely orbital in character (no fictive spins), has recently quantitatively and specifically explained chemical trends in ceramic layered cuprate superconductors. Here, this model explains the observation of an abrupt jump ΔTc(x) in LixZrNCl powders over a wide composition range Δx , as well as many other features in the resistivity, lattice constants, Raman spectra, upper critical field, and Meissner volume factor. The ceramic data confirm one-dimensional features in realistic structural models of three-dimensional metal-insulator transitions that had been previously only hypothetical. These data provide a “missing link” between the metal-insulator transition in semiconductor impurity bands and cuprate superconductors. They show that all three material families are united by exhibiting an intermediate phase, absent from crystals, but seen in many properties of network glasses.

  7. Evidence of photo-induced dynamic competition of metallic and insulating phase in a layered manganite.

    PubMed

    Li, Yuelin; Walko, Donald A; Li, Qing'an; Liu, Yaohua; Rosenkranz, Stephan; Zheng, Hong; Mitchell, J F

    2015-12-16

    We show evidence that the competition between the antiferromagetic metallic phase and the charge- and orbital-ordered insulating phase at the reentrant phase boundary of a layered manganite, La0.99Sr2.01Mn2O7, can be manipulated using ultrafast optical excitation. The time-dependent evolution of the Jahn-Teller superlattice reflection, which indicates the formation of the charge and orbital order, was measured at different laser fluences. The laser-induced enhancement and reduction the Jahn-Teller reflection intensity shows a reversal of sign between earlier (~10 ns) and later (~150 ns) time delays during the relaxation after photo excitation. This effect is consistent with a scenario whereby the laser excitation modulates the local competition between the metallic and the insulating phases.

  8. Evidence of photo-induced dynamic competition of metallic and insulating phase in a layered manganite

    DOE PAGES

    Li, Yuelin; Walko, Daonld A.; Li, Qing'an; ...

    2015-11-17

    We show evidence that the competition between the antiferromagetic metallic phase and the charge- and orbital-ordered insulating phase at the reentrant phase boundary of a layered manganite, LaSr2Mn2O7, can be manipulated using ultrafast optical excitation. The time-dependent evolution of the Jahn-Teller superlattice reflection, which indicates the formation of the charge and orbital order, was measured at different laser fluences. The laser-induced enhancement and reduction the Jahn-Teller reflection intensity shows a reversal of sign between earlier (~10 ns) and later (~150 ns) time delays during the relaxation after photo excitation. This effect is consistent with a scenario whereby the laser excitationmore » modulates the local competition between the metallic and the insulating phases.« less

  9. Evidence of photo-induced dynamic competition of metallic and insulating phase in a layered manganite

    SciTech Connect

    Li, Yuelin; Walko, Daonld A.; Li, Qing'an; Liu, Yaohua; Rosenkranz, Stephen; Zheng, Hong; Mitchell, J. F.

    2015-11-17

    We show evidence that the competition between the antiferromagetic metallic phase and the charge- and orbital-ordered insulating phase at the reentrant phase boundary of a layered manganite, LaSr2Mn2O7, can be manipulated using ultrafast optical excitation. The time-dependent evolution of the Jahn-Teller superlattice reflection, which indicates the formation of the charge and orbital order, was measured at different laser fluences. The laser-induced enhancement and reduction the Jahn-Teller reflection intensity shows a reversal of sign between earlier (~10 ns) and later (~150 ns) time delays during the relaxation after photo excitation. This effect is consistent with a scenario whereby the laser excitation modulates the local competition between the metallic and the insulating phases.

  10. Evidence of Photo-induced Dynamic Competition of Metallic and Insulating Phase in a Layered Manganite.

    SciTech Connect

    Li, Yuelin; Walko, Donald A.; Li, Qing'an; Liu, Yaohua; Rosenkranz, Stephan; Zheng, Hong; Mitchell, J. F.

    2015-12-16

    We show evidence that the competition between the antiferromagetic metallic phase and the charge- and orbital-ordered insulating phase at the reentrant phase boundary of a layered manganite, LaSr2Mn2O7, can be manipulated using ultrafast optical excitation. The time- dependent evolution of the Jahn-Teller superlattice reflection, which indicates the formation of the charge and orbital order, was measured at different laser fluences. The laser-induced enhancement and reduction the Jahn-Teller reflection intensity shows a reversal of sign between earlier (~10 ns) and later (~150 ns) time delays during the relaxation after photo excitation. This effect is consistent with a scenario whereby the laser excitation modulates the local competition between the metallic and the insulating phases.

  11. Nanolithography in evanescent near field by using nano-filmed noble metal layers

    NASA Astrophysics Data System (ADS)

    Yang, Yong; Hu, Song; Yao, Hanmin; Cheng, Guanxiao; Yan, Wei

    2007-12-01

    Nanolithography has been investigated by using optical proximity exposure in the evanescent near field in nano-filmed noble metals. Sub-diffraction-limited feature size can be resolved by using i-line illumination exposure. Compared with the model of original superlens, we separated the superlens 100nm away from the mask, under the illumination of i-line light, the initial simulation shows that the sub-diffraction-limited feature as small as 60nm linewidth with 120nm pitch can be clearly resolved without hard contact between mask and nano-filmed noble metal. By proper design of the materials and the parameters of nano-filmed layers, better resolution can be realized.

  12. Determination of heavy metals by thin-layer chromatography-square-wave anodic stripping voltammetry

    SciTech Connect

    Aldstadt, J.H.; Dewald, H.D. )

    1992-12-15

    A square-wave anodic stripping voltammetric method is described for low parts per million determination of heavy metals separated by thin-layer chromatography (TLC). Heavy metal samples are separated on carboxymethyl cellulose TLC plates and detected by anodic stripping voltammetry (ASV) using a cellulose dialysis membrane-covered mercury film electrode (CM-MFE) placed directly on the TLC plate surface in a thin film of supporting electrolyte solution. The fast scan rates possible in square-wave voltammetry during the stripping step eliminate the need to deoxygenate the sample. Results are presented for a mixture of Pb(II), Cd(II), Cu(II), and Zn(II). Calibration curves for Pb(II) were linear over the range 10-500 ng, with a relative standard deviation of the peak current over a set of eight separate 100-ng Pb(II) samples of 16%. 25 refs., 7 figs.

  13. Metal based gas diffusion layers for enhanced fuel cell performance at high current densities

    NASA Astrophysics Data System (ADS)

    Hussain, Nabeel; Van Steen, Eric; Tanaka, Shiro; Levecque, Pieter

    2017-01-01

    The gas diffusion layer strongly influences the performance and durability of polymer electrolyte fuel cells. A major drawback of current carbon fiber based GDLs is the non-controlled variation in porosity resulting in a random micro-structure. Moreover, when subjected to compression these materials show significant reduction in porosity and permeability leading to water management problems and mass transfer losses within the fuel cell. This study investigated the use of uniform perforated metal sheets as GDLs in conjunction with microchannel flowfields. A metal sheet design with a pitch of 110 μm and a hole diameter of 60 μm in combination with an MPL showed superior performance in the high current density region compared to a commercially available carbon paper based GDL in a single cell environment. Fuel cell testing with different oxidants (air, heliox and oxygen) indicate that the metal sheet offers both superior diffusion and reduced flooding in comparison to the carbon based GDL. The presence of the MPL has been found to be critical to the functionality of the metal sheet suggesting that the MPL design may represent an important optimisation parameter for further improvements in performance.

  14. Layered reduced graphene oxide with nanoscale interlayer gaps as a stable host for lithium metal anodes

    NASA Astrophysics Data System (ADS)

    Lin, Dingchang; Liu, Yayuan; Liang, Zheng; Lee, Hyun-Wook; Sun, Jie; Wang, Haotian; Yan, Kai; Xie, Jin; Cui, Yi

    2016-07-01

    Metallic lithium is a promising anode candidate for future high-energy-density lithium batteries. It is a light-weight material, and has the highest theoretical capacity (3,860 mAh g-1) and the lowest electrochemical potential of all candidates. There are, however, at least three major hurdles before lithium metal anodes can become a viable technology: uneven and dendritic lithium deposition, unstable solid electrolyte interphase and almost infinite relative dimension change during cycling. Previous research has tackled the first two issues, but the last is still mostly unsolved. Here we report a composite lithium metal anode that exhibits low dimension variation (˜20%) during cycling and good mechanical flexibility. The anode is composed of 7 wt% ‘lithiophilic’ layered reduced graphene oxide with nanoscale gaps that can host metallic lithium. The anode retains up to ˜3,390 mAh g-1 of capacity, exhibits low overpotential (˜80 mV at 3 mA cm-2) and a flat voltage profile in a carbonate electrolyte. A full-cell battery with a LiCoO2 cathode shows good rate capability and flat voltage profiles.

  15. Lithium Metal Anodes with an Adaptive "Solid-Liquid" Interfacial Protective Layer.

    PubMed

    Liu, Kai; Pei, Allen; Lee, Hye Ryoung; Kong, Biao; Liu, Nian; Lin, Dingchang; Liu, Yayuan; Liu, Chong; Hsu, Po-Chun; Bao, Zhenan; Cui, Yi

    2017-04-05

    Lithium metal is an attractive anode for the next generation of high energy density lithium-ion batteries due to its high specific capacity (3,860 mAh g(-1)) and lowest overall anode potential. However, the key issue is that the static solid electrolyte interphase cannot match the dynamic volume changes of the Li anode, resulting in side reactions, dendrite growth, and poor electrodeposition behavior, which prevent its practical applications. Here, we show that the "solid-liquid" hybrid behavior of a dynamically cross-linked polymer enables its use as an excellent adaptive interfacial layer for Li metal anodes. The dynamic polymer can reversibly switch between its "liquid" and "solid" properties in response to the rate of lithium growth to provide uniform surface coverage and dendrite suppression, respectively, thereby enabling the stable operation of lithium metal electrodes. We believe that this example of engineering an adaptive Li/electrolyte interface brings about a new and promising way to address the intrinsic problems of lithium metal anodes.

  16. Solution-Processed Metal Oxides as Efficient Carrier Transport Layers for Organic Photovoltaics.

    PubMed

    Choy, Wallace C H; Zhang, Di

    2016-01-27

    Carrier (electron and hole) transport layers (CTLs) are essential components for boosting the performance of various organic optoelectronic devices such as organic solar cells and organic light-emitting diodes. Considering the drawbacks of conventional CTLs (easily oxidized/unstable, demanding/costly fabrication, etc.), transition metal oxides with good carrier transport/extraction and superior stability have drawn extensive research interest as CTLs for next-generation devices. In recent years, many research efforts have been made toward the development of solution-based metal oxide CTLs with the focus on low- or even room-temperature processes, which can potentially be compatible with the deposition processes of organic materials and can significantly contribute to the low-cost and scale-up of organic devices. Here, the recent progress of different types of solution-processed metal oxide CTLs are systematically reviewed in the context of organic photovoltaics, from synthesis approaches to device performance. Different approaches for further enhancing the performance of solution-based metal oxide CTLs are also discussed, which may push the future development of this exciting field.

  17. Charge generation layers comprising transition metal-oxide/organic interfaces: Electronic structure and charge generation mechanism

    NASA Astrophysics Data System (ADS)

    Meyer, J.; Kröger, M.; Hamwi, S.; Gnam, F.; Riedl, T.; Kowalsky, W.; Kahn, A.

    2010-05-01

    The energetics of an archetype charge generation layer (CGL) architecture comprising of 4,4',4″-tris(N-carbazolyl)triphenylamine (TCTA), tungsten oxide (WO3), and bathophenanthroline (BPhen) n-doped with cesium carbonate (Cs2CO3) are determined by ultraviolet and inverse photoemission spectroscopy. We show that the charge generation process occurs at the interface between the hole-transport material (TCTA) and WO3 and not, as commonly assumed, at the interface between WO3 and the n-doped electron-transport material (BPhen:Cs2CO3). However, the n-doped layer is also essential to the realization of an efficient CGL structure. The charge generation mechanism occurs via electron transfer from the TCTA highest occupied molecular orbital level to the transition metal-oxide conduction band.

  18. Flat metallic surface gratings with sub-10 nm gaps controlled by atomic-layer deposition

    NASA Astrophysics Data System (ADS)

    Chen, Borui; Ji, Dengxin; Cheney, Alec; Zhang, Nan; Song, Haomin; Zeng, Xie; Thomay, Tim; Gan, Qiaoqiang; Cartwright, Alexander

    2016-09-01

    Atomic layer lithography is a recently reported new technology to fabricate deep-subwavelength features down to 1-2 nm, based on combinations of electron beam lithography (EBL) and atomic layer deposition (ALD). However, the patterning area is relatively small as limited by EBL, and the fabrication yield is not very high due to technical challenges. Here we report an improved procedure to fabricate flat metallic surfaces with sub-10 nm features based on ALD processes. To demonstrate the scalability of the new manufacturing method, we combine the ALD process with large area optical interference patterning, which is particularly promising for the development of practical applications for nanoelectronics and nanophotonics with extremely strong confinement of electromagnetic fields.

  19. Metallic atomically-thin layered silicon epitaxially grown on silicene/ZrB2

    DOE PAGES

    Gill, Tobias; Fleurence, Antoine; Warner, Ben; ...

    2017-01-19

    We observe a new two-dimensional (2D) silicon crystal, using low energy electron diffraction (LEED) and scanning tunnelling microscopy (STM) and it's formed by depositing additional Si atoms onto spontaneously-formed epitaxial silicene on a ZrB2 thin film. From scanning tunnelling spectroscopy (STS) studies, we find that this atomically-thin layered silicon has distinctly different electronic properties. Angle resolved photoelectron spectroscopy (ARPES) reveals that, in sharp contrast to epitaxial silicene, the layered silicon exhibits significantly enhanced density of states at the Fermi level resulting from newly formed metallic bands. Furthermore, the 2D growth of this material could allow for direct contacting to themore » silicene surface and demonstrates the dramatic changes in electronic structure that can occur by the addition of even a single monolayer amount of material in 2D systems.« less

  20. Metallic atomically-thin layered silicon epitaxially grown on silicene/ZrB 2

    DOE PAGES

    Gill, Tobias G.; Fleurence, Antoine; Warner, Ben; ...

    2017-02-17

    We observe a new two-dimensional (2D) silicon crystal, using low energy electron diffraction (LEED) and scanning tunnelling microscopy (STM) and it's formed by depositing additional Si atoms onto spontaneously-formed epitaxial silicene on a ZrB2 thin film. From scanning tunnelling spectroscopy (STS) studies, we find that this atomically-thin layered silicon has distinctly different electronic properties. Angle resolved photoelectron spectroscopy (ARPES) reveals that, in sharp contrast to epitaxial silicene, the layered silicon exhibits significantly enhanced density of states at the Fermi level resulting from newly formed metallic bands. Furthermore, the 2D growth of this material could allow for direct contacting to themore » silicene surface and demonstrates the dramatic changes in electronic structure that can occur by the addition of even a single monolayer amount of material in 2D systems.« less