Science.gov

Sample records for stacked metallic layers

  1. White light emission from GaN stack layers doped by different rare-earth metals

    NASA Astrophysics Data System (ADS)

    Zhang, Lei; Liu, Chang

    2015-02-01

    Experimental progress of electroluminescence devices (ELDs) employing GaN doped with rare-earth metals had been significantly made targeting RGB displays. However, reports on the theoretical models to design the devices and the applications were limited. Our previous paper proposed a device model using the quantum collision theory and Judd-Ofelt approximation to design the ELDs for white light illumination. In the present study, the model is modified by considering the light extraction efficiency and optical loss during propagating in the films. To improve the luminous efficiency, an ELD with three stack layers of GaN:Tm/GaN:Er/GaN:Eu is proposed and designed. The model predicts that the color of the integrated light can be controlled by applied voltage, thickness of each doping layer and doping concentrations of the rare earth metals. The luminous efficacy of white light emission at a bias of -100 V is calculated to be 274 lm/W, which is much higher than that of fluorescent lumps. The proposed ELD will open a door to efficient solid-state lighting.

  2. 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.

  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

    DOE PAGES

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

    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

  5. 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.

  6. Weak Van der Waals Stacking, Wide-Range Band Gap, and Raman Study on Ultrathin Layers of Metal Phosphorus Trichalcogenides.

    PubMed

    Du, Ke-zhao; Wang, Xing-zhi; Liu, Yang; Hu, Peng; Utama, M Iqbal Bakti; Gan, Chee Kwan; Xiong, Qihua; Kloc, Christian

    2016-02-23

    2D semiconducting metal phosphorus trichalcogenides, particularly the bulk crystals of MPS3 (M = Fe, Mn, Ni, Cd and Zn) sulfides and MPSe3 (M = Fe and Mn) selenides, have been synthesized, crystallized and exfoliated into monolayers. The Raman spectra of monolayer FePS3 and 3-layer FePSe3 show the strong intralayer vibrations and structural stability of the atomically thin layers under ambient condition. The band gaps can be adjusted by element choices in the range of 1.3-3.5 eV. The wide-range band gaps suggest their optoelectronic applications in a broad wavelength range. The calculated cleavage energies of MPS3 are smaller than that of graphite. Therefore, the monolayers used for building of heterostructures by van der Waals stacking could be considered as the candidates for artificial 2D materials with unusual ferroelectric and magnetic properties.

  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, 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.

  9. 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.

  10. 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

  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. 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.}

  13. An effective work-function tuning method of nMOSCAP with high-k/metal gate by TiN/TaN double-layer stack thickness

    NASA Astrophysics Data System (ADS)

    Xueli, Ma; Hong, Yang; Wenwu, Wang; Huaxiang, Yin; Huilong, Zhu; Chao, Zhao; Dapeng, Chen; Tianchun, Ye

    2014-09-01

    We evaluated the TiN/TaN/TiAl triple-layer to modulate the effective work function (EWF) of a metal gate stack for the n-type metal-oxide-semiconductor (NMOS) devices application by varying the TiN/TaN thickness. In this paper, the effective work function of EWF ranges from 4.22 to 4.56 eV with different thicknesses of TiN and TaN. The thinner TiN and/or thinner in situ TaN capping, the closer to conduction band of silicon the EWF is, which is appropriate for 2-D planar NMOS. Mid-gap work function behavior is observed with thicker TiN, thicker in situ TaN capping, indicating a strong potential candidate of metal gate material for replacement gate processed three-dimensional devices such as FIN shaped field effect transistors. The physical understandings of the sensitivity of EWF to TiN and TaN thickness are proposed. The thicker TiN prevents the Al diffusion then induces the EWF to shift to mid-gap. However, the TaN plays a different role in effective work function tuning from TiN, due to the Ta—O dipoles formed at the interface between the metal gate and the high-k layer.

  14. Van der Waals stacked 2D layered materials for optoelectronics

    NASA Astrophysics Data System (ADS)

    Zhang, Wenjing; Wang, Qixing; Chen, Yu; Wang, Zhuo; Wee, Andrew T. S.

    2016-06-01

    The band gaps of many atomically thin 2D layered materials such as graphene, black phosphorus, monolayer semiconducting transition metal dichalcogenides and hBN range from 0 to 6 eV. These isolated atomic planes can be reassembled into hybrid heterostructures made layer by layer in a precisely chosen sequence. Thus, the electronic properties of 2D materials can be engineered by van der Waals stacking, and the interlayer coupling can be tuned, which opens up avenues for creating new material systems with rich functionalities and novel physical properties. Early studies suggest that van der Waals stacked 2D materials work exceptionally well, dramatically enriching the optoelectronics applications of 2D materials. Here we review recent progress in van der Waals stacked 2D materials, and discuss their potential applications in optoelectronics.

  15. 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. PMID:26768020

  16. 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.

  17. Band engineering in transition metal dichalcogenides: Stacked versus lateral heterostructures

    NASA Astrophysics Data System (ADS)

    Guo, Yuzheng; Robertson, John

    2016-06-01

    We calculate a large difference in the band alignments for transition metal dichalcogenide (TMD) heterojunctions when arranged in the stacked layer or lateral (in-plane) geometries, using direct supercell calculations. The stacked case follows the unpinned limit of the electron affinity rule, whereas the lateral geometry follows the strongly pinned limit of alignment of charge neutrality levels. TMDs therefore provide one of the few clear tests of band alignment models, whereas three-dimensional semiconductors give less stringent tests because of accidental chemical trends in their properties.

  18. Highly ordered ultralong magnetic nanowires wrapped in stacked graphene layers

    PubMed Central

    El Mel, Abdel-Aziz; Duvail, Jean-Luc; Gautron, Eric; Xu, Wei; Choi, Chang-Hwan; Angleraud, Benoit; Granier, Agnès

    2012-01-01

    Summary We report on the synthesis and magnetic characterization of ultralong (1 cm) arrays of highly ordered coaxial nanowires with nickel cores and graphene stacking shells (also known as metal-filled carbon nanotubes). Carbon-containing nickel nanowires are first grown on a nanograted surface by magnetron sputtering. Then, a post-annealing treatment favors the metal-catalyzed crystallization of carbon into stacked graphene layers rolled around the nickel cores. The observed uniaxial magnetic anisotropy field oriented along the nanowire axis is an indication that the shape anisotropy dominates the dipolar coupling between the wires. We further show that the thermal treatment induces a decrease in the coercivity of the nanowire arrays. This reflects an enhancement of the quality of the nickel nanowires after annealing attributed to a decrease of the roughness of the nickel surface and to a reduction of the defect density. This new type of graphene–ferromagnetic-metal nanowire appears to be an interesting building block for spintronic applications. PMID:23365798

  19. In-layer stacking competition during ice growth

    NASA Astrophysics Data System (ADS)

    Choi, Saehyun; Jang, Eunseon; Kim, Jun Soo

    2014-01-01

    When ice grows, the growth rates are unequal along different growth directions and some layers contain planar defective regions. With the aim of helping to understand these phenomena, we report the molecular dynamics simulations of ice growth on the basal and prismatic faces of initial hexagonal ice, using the TIP5P-E water model. By presenting the time evolution of the two-dimensional density profiles of water molecules in each layer and the kinetics of layer formation during ice growth at the temperature of 11 K supercooling, we show that two forms of ice arrangements, hexagonal and cubic, develop competitively within the same ice layer on the basal face, whereas such in-layer stacking-competition is insignificant on the prismatic face. It is shown that, on the basal face, the occurrence of significant in-layer stacking competition in one of the layers significantly delays the layer formation in several overlying layers and explains the overall delay in ice growth on the basal face compared to that on the prismatic face. In addition, it is observed that large planar defects form on the basal face, as a consequence of the long-lasting in-layer stacking competition when the overlying layer grows rapidly.

  20. AA-stacked bilayer square ice between graphene layers

    NASA Astrophysics Data System (ADS)

    Sobrino Fernandez Mario, M.; Neek-Amal, M.; Peeters, F. M.

    2015-12-01

    Water confined between two graphene layers with a separation of a few Å forms a layered two-dimensional ice structure. Using large scale molecular dynamics simulations with the adoptable ReaxFF interatomic potential we found that flat monolayer ice with a rhombic-square structure nucleates between the graphene layers which is nonpolar and nonferroelectric. We provide different energetic considerations and H-bonding results that explain the interlayer and intralayer properties of two-dimensional ice. The controversial AA stacking found experimentally [Algara-Siller et al., Nature (London) 519, 443 (2015), 10.1038/nature14295] is consistent with our minimum-energy crystal structure of bilayer ice. Furthermore, we predict that an odd number of layers of ice has the same lattice structure as monolayer ice, while an even number of ice layers exhibits the square ice AA stacking of bilayer ice.

  1. 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.

  2. Significant effect of stacking on the electronic and optical properties of few-layer black phosphorus

    NASA Astrophysics Data System (ADS)

    Ćakır, Deniz; Sevik, Cem; Peeters, Francois M.

    2015-10-01

    The effect of the number of stacking layers and the type of stacking on the electronic and optical properties of bilayer and trilayer black phosphorus are investigated by using first-principles calculations within the framework of density functional theory. We find that inclusion of many-body effects (i.e., electron-electron and electron-hole interactions) modifies strongly both the electronic and optical properties of black phosphorus. While trilayer black phosphorus with a particular stacking type is found to be a metal by using semilocal functionals, it is predicted to have an electronic band gap of 0.82 eV when many-body effects are taken into account within the G0W0 scheme. Though different stacking types result in similar energetics, the size of the band gap and the optical response of bilayer and trilayer phosphorene are very sensitive to the number of layers and the stacking type. Regardless of the number of layers and the type of stacking, bilayer and trilayer black phosphorus are direct band gap semiconductors whose band gaps vary within a range of 0.3 eV. Stacking arrangements that are different from the ground state structure in both bilayer and trilayer black phosphorus exhibit significant modified valence bands along the zigzag direction and result in larger hole effective masses. The optical gap of bilayer (trilayer) black phosphorus varies by 0.4 (0.6) eV when changing the stacking type. The calculated binding energy of the bound exciton hardly changes with the type of stacking and is found to be 0.44 (0.30) eV for bilayer (trilayer) phosphorous.

  3. 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.

  4. 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

  5. Nanostructured Anodic Multilayer Dielectric Stacked Metal-Insulator-Metal Capacitors.

    PubMed

    Karthik, R; Kannadassan, D; Baghini, Maryam Shojaei; Mallick, P S

    2015-12-01

    This paper presents the fabrication of Al2O3/TiO2/Al2O3 metal-insulator-metal (MIM) capacitor using anodization technique. High capacitance density of > 3.5 fF/μm2, low quadratic voltage coefficient of capacitance of < 115 ppm/V2 and a low leakage current density of 4.457 x 10(-11) A/cm2 at 3 V are achieved which are suitable for analog and mixed signal applications. We found that the anodization voltage played a major role in electrical and structural properties of the thin film. This work suggests that the anodization method can offer crystalline multilayer dielectric stack required for high performance MIM capacitor.

  6. 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.

  7. Stacking fault and twinning in nanocrystalline metals.

    SciTech Connect

    Liao, Xiaozhou; Zhao, Y.; Srivilliputhur, S. G.; Zhou, F.; Lavernia, E. J.; Baskes, M. I.; Zhu, Y. T.; Xu, H. F.

    2004-01-01

    Nanocrystalline Al processed by cryogenic ball-milling and nanocrystalline Cu processed by high-pressure torsion at a very low strain rate and at room temperature were investigated using high-resolution transmission electron microscopy. For nanocrystalline Al, we observed partial dislocation emission from grain boundaries, which consequently resulted in deformation stacking faults and twinning. We also observed deformation twins formed via two other mechanisms recently predicted by molecular dynamic simulations. These results are surprising because (1) partial dislocation emission from grain boundaries has not been experimentally observed although it has been predicted by simulations and (2) deformation stacking faults and twinning have not been reported in Al due to its high stacking fault energy. For nanocrystalline Cu, we found that twinning becomes a major deformation mechanism, which contrasts with the literature reports that deformation twinning in coarse-grained Cu occurs only under high strain rate and/or low temperature conditions and that reducing grain sizes suppresses deformation twinning. The investigation of the twinning morphology suggests that twins and stacking faults in nanocrystalline Cu were formed through partial dislocation emissions from grain boundaries. This mechanism differs from the pole mechanism operating in coarse-grained Cu.

  8. 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.

  9. Enforced Layer-by-Layer Stacking of Energetic Salts towards High-Performance Insensitive Energetic Materials.

    PubMed

    Zhang, Jiaheng; Mitchell, Lauren A; Parrish, Damon A; Shreeve, Jean'ne M

    2015-08-26

    Development of modern high-performance insensitive energetic materials is significant because of the increasing demands for both military and civilian applications. Here we propose a rapid and facile strategy called the "layer hydrogen bonding pairing approach" to organize energetic molecules via layer-by-layer stacking, which grants access to tunable energetic materials with targeted properties. Using this strategy, an unusual energetic salt, hydroxylammonium 4-amino-furazan-3-yl-tetrazol-1-olate, with good detonation performances and excellent sensitivities, was designed, synthesized, and fully characterized. In addition, the expected unique layer-by-layer structure with a high crystal packing coefficient was confirmed by single-crystal X-ray crystallography. Calculations indicate that the layer-stacking structure of this material can absorb the mechanical stimuli-induced kinetic energy by converting it to layer sliding, which results in low sensitivity.

  10. 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

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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

  16. 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.

  17. Piezoelectric two-layer stacks of cellular polypropylene ferroelectrets: transducer response at audio and ultrasound frequencies.

    PubMed

    Wegener, Michael; Bergweiler, Steffen; Wirges, Werner; Pucher, Andreas; Tuncer, Enis; Gerhard-Multhaupt, Reimund

    2005-09-01

    Piezoelectric cellular polypropylene films, so-called ferroelectrets, are assembled in a stack with two active transducer layers. The stack is characterized with respect to its linear and quadratic response in a frequency range from 1 kHz to 80 kHz. A relatively smooth frequency response in the sound-pressure level is found for the individual layers as well as for both layers driven in phase. The piezoelectric response of the two-layer stack is twice the response of an individual layer over a rather broad frequency range. Furthermore, the influence of the preparation conditions on the resonance frequency and the effect of the quadratic distortion on the radiated sound are investigated both for the individual transducer films in the stack and for the stack system as a whole. PMID:16285459

  18. Ductilizing Bulk Metallic Glass Composite by Tailoring Stacking Fault Energy

    NASA Astrophysics Data System (ADS)

    Wu, Y.; Zhou, D. Q.; Song, W. L.; Wang, H.; Zhang, Z. Y.; Ma, D.; Wang, X. L.; Lu, Z. P.

    2012-12-01

    Martensitic transformation was successfully introduced to bulk metallic glasses as the reinforcement micromechanism. In this Letter, it was found that the twinning property of the reinforcing crystals can be dramatically improved by reducing the stacking fault energy through microalloying, which effectively alters the electron charge density redistribution on the slipping plane. The enhanced twinning propensity promotes the martensitic transformation of the reinforcing austenite and, consequently, improves plastic stability and the macroscopic tensile ductility. In addition, a general rule to identify effective microalloying elements based on their electronegativity and atomic size was proposed.

  19. Stacking Fault Enriching the Electronic and Transport Properties of Few-Layer Phosphorenes and Black Phosphorus.

    PubMed

    Lei, Shuangying; Wang, Han; Huang, Lan; Sun, Yi-Yang; Zhang, Shengbai

    2016-02-10

    Interface engineering is critical for enriching the electronic and transport properties of two-dimensional materials. Here, we identify a new stacking, named Aδ, in few-layer phosphorenes (FLPs) and black phosphorus (BP) based on first-principles calculation. With its low formation energy, the Aδ stacking could exist in FLPs and BP as a stacking fault. The presence of the Aδ stacking fault induces a direct to indirect transition of the band gap in FLPs. It also affects the carrier mobilities by significantly increasing the carrier effective masses. More importantly, the Aδ stacking enables the fabrication of a whole spectrum of lateral junctions with all the type-I, II, and III alignments simply through the manipulation of the van der Waals stacking without resorting to any chemical modification. This is achieved by the widely tunable electron affinity and ionization potential of FLPs and BP with the Aδ stacking. PMID:26799596

  20. Stacking Fault Enriching the Electronic and Transport Properties of Few-Layer Phosphorenes and Black Phosphorus.

    PubMed

    Lei, Shuangying; Wang, Han; Huang, Lan; Sun, Yi-Yang; Zhang, Shengbai

    2016-02-10

    Interface engineering is critical for enriching the electronic and transport properties of two-dimensional materials. Here, we identify a new stacking, named Aδ, in few-layer phosphorenes (FLPs) and black phosphorus (BP) based on first-principles calculation. With its low formation energy, the Aδ stacking could exist in FLPs and BP as a stacking fault. The presence of the Aδ stacking fault induces a direct to indirect transition of the band gap in FLPs. It also affects the carrier mobilities by significantly increasing the carrier effective masses. More importantly, the Aδ stacking enables the fabrication of a whole spectrum of lateral junctions with all the type-I, II, and III alignments simply through the manipulation of the van der Waals stacking without resorting to any chemical modification. This is achieved by the widely tunable electron affinity and ionization potential of FLPs and BP with the Aδ stacking.

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

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

    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 (AlOx) interlayers. A step-by-step in situ procedure by deposition of AlOx and hafnium oxide (HfOx) layers on Ge and subsequent plasma oxidation was conducted to fabricate Pt/HfO2/AlOx/GeOx/Ge stacked structures. Comprehensive study by means of physical and electrical characterizations revealed distinct impacts of AlOx 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 × 1011 cm-2eV-1 with a sub-nm EOT and sufficient thermal stability were achieved by systematic process optimization.

  2. 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.

  3. 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.

  4. Development of a laser-speckle-based measurement principle for the evaluation of mechanical deformation of stacked metal sheets

    NASA Astrophysics Data System (ADS)

    Halder, Clemens; Thurner, Thomas; Mair, Mathias

    2014-05-01

    Stacks of metal plates are widely used in electrical motors, transformers and generators to reduce for eddy current loss in their magnetic circuit. To model the mechanical behavior of such special material structures a profound knowledge of the underlying physical processes is needed. This paper describes a highly specialized optical sensor system utilizing the laser-speckle-effect for non-contacting strain and displacement measurements of stacked metal plates. In order to gain insights into the mechanical changes of stacked metal structures during defined mechanical load, a certain kind of spatially resolving digital laser speckle photography has been used to measure displacements between individual layers of the stacked metal sheets at high resolution. The developed speckle template matching algorithm takes into account for the very special surface structure and the given loading behavior. The sensor system is capable of acquiring displacement fields with a resolution in the order of a single micron at video rate and beyond, enabling the real time observation of load experiments on stacked metal plate structures.

  5. 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.

  6. Metal Gate (TiN, TiC, TaN) Film Stack Stress

    NASA Astrophysics Data System (ADS)

    Bello, A. F.; Paul, Abhijeet; Kim, Hoon

    2015-10-01

    Successful stress engineering in semiconductor device structures must consider all the contributions to the stress field including those not typically considered for stress, such as work function metal (WFM) gate layers that are used to tune to the desired work function level. These films induce stress especially since they are so close to the channel region. In this study we measure stress from blanket layer films and combinations of TiN, TiC, and TaN deposited on Hf oxide, at thicknesses that are typically used for advanced metal-oxide-semiconductor field-effect transistor (MOSFET) devices. Tungsten (W) deposited on top of the WFM layer stacks is also measured. For combination film stacks, the stress is measured after each deposition step. The induced stress from the WFM is significant, in the range of hundreds of MPa, and varies according to the thickness and processing conditions such as annealing temperature and time, etc. Results from these blanket film measurements were used as a guide for technology computer-aided design (TCAD) modeling of the stress field in FinFET structures with design rules comparable to 10-nm technology. The tensor stress components identify areas of compressive and tensile stress and with a magnitude similar to expected results. The stress field could be used to calculate the FinFET device performance, and in this case an example is provided with the relative improvement in drain current.

  7. 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

    2016-07-01

    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. PMID:27295399

  8. 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

    2016-07-01

    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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. 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. PMID:25426661

  14. Left handed dispersion of a stack of subwavelength hole metal arrays at terahertz frequencies

    NASA Astrophysics Data System (ADS)

    Croënne, Charles; Garet, Frédéric; Lheurette, Éric; Coutaz, Jean-Louis; Lippens, Didier

    2009-03-01

    We report on the electromagnetic response of a stack of subwavelength hole metal arrays. The samples were designed for exhibiting left handed dispersion branches under normal incidence, and their transmissivities were optimized via the fabrication of elliptical-shaped holes. They are constituted of benzocyclobutene layers with tens of micron thicknesses and submicron-thick gold films patterned by photolithography. Experimental evidence, achieved by time-domain terahertz spectroscopy and supported by full wave simulations, of a ground left handed dispersion branch is found around 0.45 THz. The insertion losses are -3 dB for a five-layer structure, this good level being explained by the matching of the impedance.

  15. 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.

  16. High frequency clipper like behavior of tri-layer nickel oxide stack

    NASA Astrophysics Data System (ADS)

    Koiry, S. P.; Ratnadurai, R.; Krishnan, S.; Bhansali, S.

    2012-04-01

    We report on AC propagation in vertically stacked tri-layer nickel oxide (NiO) film with gradient in oxide composition. These studies reveal that the stacked film clips both positive and negative peaks of the AC signals and these clipping characteristics are analogous to a symmetrical clipper. These characteristics are obtained without using any clipper circuit elements like diodes or transistors and DC power source. We propose that the clipping characteristic of NiO stack is a result of space charge generated during signal propagation.

  17. 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

  18. 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. PMID:23899378

  19. Imaging layer number and stacking order through formulating Raman fingerprints obtained from hexagonal single crystals of few layer graphene

    NASA Astrophysics Data System (ADS)

    Hwang, Jih-Shang; Lin, Yu-Hsiang; Hwang, Jeong-Yuan; Chang, Railing; Chattopadhyay, Surojit; Chen, Chang-Jiang; Chen, Peilin; Chiang, Hai-Pang; Tsai, Tsong-Ru; Chen, Li-Chyong; Chen, Kuei-Hsien

    2013-01-01

    Quantitative mapping of layer number and stacking order for CVD-grown graphene layers is realized by formulating Raman fingerprints obtained on two stepwise stacked graphene single-crystal domains with AB Bernal and turbostratic stacking (with ˜30°interlayer rotation), respectively. The integrated peak area ratio of the G band to the Si band, AG/ASi, is proven to be a good fingerprint for layer number determination, while the area ratio of the 2D and G bands, A2D/AG, is shown to differentiate effectively between the two different stacking orders. The two fingerprints are well formulated and resolve, quantitatively, the layer number and stacking type of various graphene domains that used to rely on tedious transmission electron microscopy for structural analysis. The approach is also noticeable in easy discrimination of the turbostratic graphene region (˜30° rotation), the structure of which resembles the well known high-mobility graphene R30/R2± fault pairs found on the vacuum-annealed C-face SiC and suggests an electron mobility reaching 14 700 cm3 V-1 s-1. The methodology may shed light on monitoring and control of high-quality graphene growth, and thereby facilitate future mass production of potential high-speed graphene applications.

  20. Electrical response in atomic layer deposited Al:ZnO with varying stack thickness

    SciTech Connect

    Mundle, R.; Pradhan, A. K.

    2014-05-14

    We report on the effects of stacking of the macrocycles in atomic layer deposited (ALD) Al:ZnO thin films on the structural and electrical properties. There is a large change in the resistivity ranging from as high as 1.19 × 10{sup −3} Ω cm for 760 growth cycles film down to as low as 7.9 × 10{sup −4} Ω cm for the 4000 cycles. The electrical transport demonstrates a transition from a semiconductor behavior at 760 cycles to a metallic behavior in the 4000 cycle, due to an increase in electron scattering as well as increase in the carrier concentration. However, interestingly the carrier concentration sharply increases with increasing macrocycles containing Al and Zn, exhibiting a nearly metal-like behavior in thicker films. We anticipate that the change in Zn-vacancy, V{sub zn}, formation energy is related to the increase in surface area of the ALD precursor deposition plane. The increase in V{sub zn} density allows for more adsorption of Al-precursor into the doped monolayer, showing interesting electrical properties.

  1. Impact of Physical Vapor Deposition-Based In situ Fabrication Method on Metal/High-k Gate Stacks

    NASA Astrophysics Data System (ADS)

    Watanabe, Heiji; Horie, Shinya; Minami, Takashi; Kitano, Naomu; Kosuda, Motomu; Shimura, Takayoshi; Yasutake, Kiyoshi

    2007-04-01

    We proposed an in situ method for fabricating metal/high-k gate stacks. High-quality Hf silicate gate dielectrics were formed by utilizing a solid phase interface reaction (SPIR) between a metal Hf layer and an SiO2 underlayer, and TiN electrodes were continuously grown on the gate dielectrics using a low-damage sputtering system without exposure to air. We investigated the optimum SPIR conditions for TiN/HfSiO gate stacks, such as the thicknesses of the metal Hf and oxide underlayers, in situ annealing temperature, and oxygen pressure. The results indicate that the in situ method can be used to precisely control the SPIR to form silicate films and improve the electrical properties at metal/high-k interfaces. We demonstrated that the scaling of equivalent oxide thickness (EOT) was achieved and that the carbon impurity content at the gate stacks was successfully reduced by in situ silicate formation and continuous electrode deposition. As a consequence, we obtained excellent EOT versus gate leakage characteristics and succeeded in improving the hysteresis of capacitance-voltage curves for the TiN/HfSiO gate stacks.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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

    2014-01-01

    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. PMID:25410480

  8. 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.

  9. 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.

  10. 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

  11. 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

  12. 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; Luo, Xin; Zhao, Yanyuan; Zhang, Jun; Pantelides, Sokrates T.; Zhou, Wu; Quek, Su Ying; Xiong, Qihua

    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.

  13. 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.

  14. 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.

  15. Layer-stacked tin disulfide nanorods in silica nanoreactors with improved lithium storage capabilities.

    PubMed

    Wu, Ping; Du, Ning; Zhang, Hui; Liu, Jie; Chang, Lantao; Wang, Lei; Yang, Deren; Jiang, Jian-Zhong

    2012-07-01

    A new structure of layered materials, layer-stacked nanorod, has been fabricated through an entirely new template-engaged structural transformation methodology. The formation of layer-stacked hexagonal tin disulfide (SnS(2)) nanorods has been demonstrated as an example by using tetragonal tin (Sn) nanorods as sacrificing templates and silica (SiO(2)) as nanoreactors. In addition, the structural transformation process probably involves the formation of orthorhombic tin sulfide (SnS) nanorods as an intermediate product. The rod-like morphology and single-crystal feature of the Sn templates are well preserved in both SnS(2) and SnS products due to the nanoscale confinement in silica. Owing to its unique structural characteristics, the SnS(2)-SiO(2) nanorod anode exhibits excellent capacity retention and improved rate capability, facilitating its application in lithium ion batteries with long cycle life and high power density.

  16. 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.

  17. 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.

  18. 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.

  19. Resonant tunneling through discrete quantum states in stacked atomic-layered MoS2.

    PubMed

    Nguyen, Linh-Nam; Lan, Yann-Wen; Chen, Jyun-Hong; Chang, Tay-Rong; Zhong, Yuan-Liang; Jeng, Horng-Tay; Li, Lain-Jong; Chen, Chii-Dong

    2014-05-14

    Two-dimensional crystals can be assembled into three-dimensional stacks with atomic layer precision, which have already shown plenty of fascinating physical phenomena and been used for prototype vertical-field-effect-transistors.1,2 In this work, interlayer electron tunneling in stacked high-quality crystalline MoS2 films were investigated. A trilayered MoS2 film was sandwiched between top and bottom electrodes with an adjacent bottom gate, and the discrete energy levels in each layer could be tuned by bias and gate voltages. When the discrete energy levels aligned, a resonant tunneling peak appeared in the current-voltage characteristics. The peak position shifts linearly with perpendicular magnetic field, indicating formation of Landau levels. From this linear dependence, the effective mass and Fermi velocity are determined and are confirmed by electronic structure calculations. These fundamental parameters are useful for exploitation of its unique properties.

  20. Multiplane-induced widening of stacking faults in fcc metals

    NASA Astrophysics Data System (ADS)

    Shehadeh, Mutasem A.; Lu, G.; Chen, Z.; Kioussis, N.; Ghoniem, N. M.

    2007-10-01

    Using an ab initio-based parametric dislocation dynamics approach we show that Shockley partials on successive glide planes greatly assist the widening of stacking faults (SFs) in Al and Ag. This effect is amplified when all trailing partials are pinned. Subsequent placement of Shockley partials on adjacent planes enhances further the widening of the SF width. In sharp contrast, dislocations with zero net Burgers vector across three successive planes form very compact cores in both Al and Ag, in agreement with recent experiments.

  1. Microscopic theoretical model study of band gap opening in AA-stacked bi-layer graphene

    NASA Astrophysics Data System (ADS)

    Sahu, Sivabrata; Parashar, S. K. S.; Rout, G. C.

    2016-05-01

    We address here a tight-binding theoretical model calculation for AA-stacked bi-layer graphene taking into account of a biased potential between two layers to study the density of states and the band dispersion within the total Brillouin zone. We have calculated the electronic Green's function for electron operator corresponding to A and B sub lattices by Zubarev's Green's function technique from which the electronic density of states and the electron band energy dispersion are calculated. The numerically computed density of states and band energy dispersions are investigated by tuning the biased potential to exhibit the band gap by varying the different physical parameters.

  2. 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

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

    PubMed

    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

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

    NASA Astrophysics Data System (ADS)

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

    2016-06-01

    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%.

  5. A new method for the characterisation and quantitative speciation of base metal smelter stack particulates.

    PubMed

    Skeaff, James M; Thibault, Yves; Hardy, David J

    2011-06-01

    Base metal smelters may be a source of particulates containing metals of environmental concern released to the atmosphere. Knowledge of the quantitative chemical speciation of particulate releases from base metal smelters will be of value in smelter emission fingerprinting, site-specific risk assessments, predictions of the behaviour of smelter stack particulates released to the environment and in resolving liability issues related to current and historic releases. Accordingly, we have developed an innovative approach comprising bulk chemical analysis, a leaching procedure, X-ray diffraction analysis and scanning electron microscopy/electron probe microanalysis characterisation in a step-wise apportioning procedure to derive the quantitative speciation of particulate samples from the stacks of three copper smelters designated as A, B and C. For the A smelter stack particulates, the major calculated percentages were 29 CuSO(4), 20 ZnSO(4).H(2)O, 13 (Cu(0.94)Zn(0.06))(2)(AsO(4))(OH), 11 PbSO(4) and four As(2)O(3). For the B smelter stack particulates, the primary calculated percentages were 20 ZnSO(4).H(2)O, 20 PbSO(4), 12 CuSO(4) and nine As(2)O(3). Finally, we calculated that the C smelter stack particulates mostly comprised 34 ZnSO(4).H(2)O, 19 (Cu(0.84)Zn(0.16))(AsO(3)OH), 11 PbSO(4), 10 As(2)O(3) and nine Zn(3)(AsO(4))(2). Between 56% and 67% by weight of the smelter stack particulates, including the As, was soluble in water. For these and other operations, the data and approach may be useful in estimating metals partitioning among water, soil and sediment, as well as predictions of the effects of the stack particulates released to the environment. PMID:20676929

  6. Size-dependent melting of single and stacked silver alkanethiolate layers: experiment and phenomenological model

    NASA Astrophysics Data System (ADS)

    Ye, Zichao; de La Rama, Lito; Hu, Liang; Efremov, Mikhail; Allen, Leslie

    2015-03-01

    We report a systematic study of melting of silver alkanethiolate (AgSCn) lamellar crystals. A new synthesis method enables us to control their thickness by either modulating alkanethiol chain length (n = 7-18) or stacking them to a specific layer number (m = 1-10). Nanocalorimetry shows stepwise increase in the melting point, Tm, of single layer AgSCn as an increment of chain length. Layer stacking also results in a size-dependent melting. An odd/even alternation is observed in the Tm of 2, 3, and 4-layer lamellae, but absent in that of single and multilayer samples. We develop a phenomenological model for lamellae melting based on the cumulative excess free energy contributions of four spatially separate regions in AgSCn crystal: free surface, Ag -S central plane, substrate interface, and interlayer interface. Surface excess free energy is revealed to be independent of chain length. The selective appearance of the odd/even effect is due to the significant stabilization of interlayer interfaces of odd-chain samples, possibly due to registration/packing. Such interface stabilization occurs most significantly for 2-layer samples. XRD results support the model as the measured van der Waals gap is smaller for crystals with odd chains. Supported by NSF-DMR-1409953 and NSF-DMR-1006385.

  7. 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.

  8. 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.

  9. Modulating the interface quality and electrical properties of HfTiO/InGaAs gate stack by atomic-layer-deposition-derived Al₂O₃ passivation layer.

    PubMed

    He, Gang; Gao, Juan; Chen, Hanshuang; Cui, Jingbiao; Sun, Zhaoqi; Chen, Xiaoshuang

    2014-12-24

    In current work, the effect of the growth cycles of atomic-layer-deposition (ALD) derived ultrathin Al2O3 interfacial passivation layer on the interface chemistry and electrical properties of MOS capacitors based on sputtering-derived HfTiO as gate dielectric on InGaAs substrate. Significant suppression of formation of Ga-O and As-O bond from InGaAs surface after deposition of ALD Al2O3 with growth cycles of 20 has been achieved. X-ray photoelectron spectroscopy (XPS) measurements have confirmed that suppressing the formation of interfacial layer at HfTiO/InGaAs interface can be achieved by introducing the Al2O3 interface passivation layer. Meanwhile, increased conduction band offset and reduced valence band offset have been observed for HfTiO/Al2O3/InGaAs gate stack. Electrical measurements of MOS capacitor with HfTiO/Al2O3/InGaAs gate stacks with dielectric thickness of ∼4 nm indicate improved electrical performance. A low interface-state density of (∼1.9) × 10(12) eV(-1) cm(-2) with low frequency dispersion ( ∼ 3.52%), small border trap density of 2.6 × 10(12) cm(-2), and low leakage current of 1.17 × 10(-5) A/cm(2) at applied gate voltage of 1 V have been obtained. The involved leakage current conduction mechanisms for metal-oxide-semiconductor (MOS) capacitor devices with and without Al2O3 interface control layer also have been discussed in detail.

  10. Layer-stacked tin disulfide nanorods in silica nanoreactors with improved lithium storage capabilities

    NASA Astrophysics Data System (ADS)

    Wu, Ping; Du, Ning; Zhang, Hui; Liu, Jie; Chang, Lantao; Wang, Lei; Yang, Deren; Jiang, Jian-Zhong

    2012-06-01

    A new structure of layered materials, layer-stacked nanorod, has been fabricated through an entirely new template-engaged structural transformation methodology. The formation of layer-stacked hexagonal tin disulfide (SnS2) nanorods has been demonstrated as an example by using tetragonal tin (Sn) nanorods as sacrificing templates and silica (SiO2) as nanoreactors. In addition, the structural transformation process probably involves the formation of orthorhombic tin sulfide (SnS) nanorods as an intermediate product. The rod-like morphology and single-crystal feature of the Sn templates are well preserved in both SnS2 and SnS products due to the nanoscale confinement in silica. Owing to its unique structural characteristics, the SnS2-SiO2 nanorod anode exhibits excellent capacity retention and improved rate capability, facilitating its application in lithium ion batteries with long cycle life and high power density.A new structure of layered materials, layer-stacked nanorod, has been fabricated through an entirely new template-engaged structural transformation methodology. The formation of layer-stacked hexagonal tin disulfide (SnS2) nanorods has been demonstrated as an example by using tetragonal tin (Sn) nanorods as sacrificing templates and silica (SiO2) as nanoreactors. In addition, the structural transformation process probably involves the formation of orthorhombic tin sulfide (SnS) nanorods as an intermediate product. The rod-like morphology and single-crystal feature of the Sn templates are well preserved in both SnS2 and SnS products due to the nanoscale confinement in silica. Owing to its unique structural characteristics, the SnS2-SiO2 nanorod anode exhibits excellent capacity retention and improved rate capability, facilitating its application in lithium ion batteries with long cycle life and high power density. Electronic supplementary information (ESI) available: Detailed experimental procedures, EDX elemental mapping, XPS, IFFT, XRD and SEM images. See

  11. Three dimensional optical twisters-driven helically stacked multi-layered microrotors

    NASA Astrophysics Data System (ADS)

    Xavier, Jolly; Dasgupta, Raktim; Ahlawat, Sunita; Joseph, Joby; Kumar Gupta, Pradeep

    2012-03-01

    We demonstrate tunable helically stacked multi-layered microrotors realized in vortex-embedded three dimensional (3D) optical twister patterns. Intensity-tunable annular irradiance profiles with higher order vortex are generated as well as simultaneously unfolded by phase-engineered multiple plane wave interference. In the individually tunable 3D helical bright arms of these unfolded vortex structures, 2 μm silica beads are optically trapped as spiraling multilayered handles of multi-armed microrotors. Further, multiple rows of such microrotors are parallelly actuated with controllable sense of rotation. We also present our observation on helical 3D stacking of micro-particles in these longitudinally gyrating multi-armed rotor traps.

  12. 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.

  13. Direct observation of bias-dependence potential distribution in metal/HfO{sub 2} gate stack structures by hard x-ray photoelectron spectroscopy under device operation

    SciTech Connect

    Yamashita, Y.; Yoshikawa, H.; Kobayashi, K.; Chikyo, T.

    2014-01-28

    Although gate stack structures with high-k materials have been extensively investigated, there are some issues to be solved for the formation of high quality gate stack structures. In the present study, we employed hard x-ray photoelectron spectroscopy in operating devices. This method allows us to investigate bias dependent electronic states, while keeping device structures intact. Using this method, we have investigated electronic states and potential distribution in gate metal/HfO{sub 2} gate stack structures under device operation. Analysis of the core levels shifts as a function of the bias voltage indicated that a potential drop occurred at the Pt/HfO{sub 2} interface for a Pt/HfO{sub 2} gate structure, while a potential gradient was not observed at the Ru/HfO{sub 2} interface for a Ru/HfO{sub 2} gate structure. Angle resolved photoelectron spectroscopy revealed that a thicker SiO{sub 2} layer was formed at the Pt/HfO{sub 2} interface, indicating that the origin of potential drop at Pt/HfO{sub 2} interface is formation of the thick SiO{sub 2} layer at the interface. The formation of the thick SiO{sub 2} layer at the metal/high-k interface might concern the Fermi level pinning, which is observed in metal/high-k gate stack structures.

  14. 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.

  15. 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.

  16. 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.

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

    PubMed Central

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

    2016-01-01

    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. PMID:27147503

  18. Dependence of spin-pumping spin Hall effect measurements on layer thicknesses and stacking order

    NASA Astrophysics Data System (ADS)

    Vlaminck, V.; Pearson, J. E.; Bader, S. D.; Hoffmann, A.

    2013-08-01

    Voltages generated from inverse spin Hall and anisotropic magnetoresistance effects via spin pumping in ferromagnetic (F)/nonmagnetic (N) bilayers are investigated by means of a broadband ferromagnetic resonance approach. Varying the nonmagnetic layer thickness enables the determination of the spin diffusion length in Pd of 5.5 ± 0.5 nm. We also observe a systematic change of the voltage line shape when reversing the stacking order of the F/N bilayer, which is qualitatively consistent with expectations from spin Hall effects. However, even after independent calibration of the precession angle, systematic quantitative discrepancies in analyzing the data with spin Hall effects remain.

  19. Optical fiber oxygen sensor using layer-by-layer stacked porous composite membranes

    NASA Astrophysics Data System (ADS)

    Ban, Sayuri; Hosoki, Ai; Nishiyama, Michiko; Seki, Atsushi; Watanabe, Kazuhiro

    2016-03-01

    Optical fiber oxygen sensors have attractive attentions such as no oxygen consume, thin size, light weight, flexibility, and immunity to electromagnetic interference. Ruthenium (Ru) complexes are known as luminescent materials whose luminescent light is quenched depending on oxygen concentrations when concentrations of Ru complexes are fixed. They emit phosphorescence with the wavelength of around 620 nm as exited light with the wavelength of 450 nm is irradiated into Ru complexes. As a result, phosphorescence is quenched depending on oxygen concentrations. Conventional optical fiber oxygen sensors have employed large core-diameter such as 1000 μm in order to obtain quenching abundantly, hence they have large transmission loss. Therefore, they have little practicability in the case of remote monitoring system, for example undersea explorations. In this paper, we have successfully developed a novel optical fiber oxygen sensor with transmission GI multi-mode fiber whose core diameter is 62.5 μm and cladding diameter is 125 μm. The sensing portion was fabricated on an end of the fiber with porous composite membranes which is made by glass beads and polyallylamine in Layer-by-Layer technique. The composite membranes immobilized Ru complexes. In experiments, in order to investigate characteristics of the number of layers for porous composite membranes, we tested several kinds of sensors having such as 5-, 50- and 125-layers and confirmed phosphorescent intensity and change of phosphorescence against existence of oxygen. As a result, 5-layer and 50-layer sensors showed best sensitivity and reproducibility.

  20. Structural Analysis and Direct Imaging of Rotational Stacking Faults in Few-Layer Graphene Synthesized from Solid Botanical Precursor

    NASA Astrophysics Data System (ADS)

    Kalita, Golap; Wakita, Koichi; Umeno, Masayoshi

    2011-07-01

    Here, we report the structural analysis and rotational stacking faults of few-layer graphene sheets derived by the controlled pyrolysis of the solid botanical derivative camphor (C10H16O). The second-order Raman spectra of the sheets show that the graphene layers are more than one single layer, and the numbers of layers can be controlled by adjusting the amount of camphor pyrolyzed. Transmission electron microscopy images show a minimum of 3 layers for thinner graphene sheets and a maximum of 12 layers for thicker graphene sheets. Low-voltage aberration-corrected high-resolution transmission electron microscopy is also carried out to gain insight into the hexagonal structure and stacking of graphene layers. The transmission electron microscopy study showed the presence of moiré patterns with a relative rotation between graphene layers.

  1. 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

  2. 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.

  3. Efficiency Enhancement of Nanotextured Black Silicon Solar Cells Using Al2O3/TiO2 Dual-Layer Passivation Stack Prepared by Atomic Layer Deposition.

    PubMed

    Wang, Wei-Cheng; Tsai, Meng-Chen; Yang, Jason; Hsu, Chuck; Chen, Miin-Jang

    2015-05-20

    In this study, efficient nanotextured black silicon (NBSi) solar cells composed of silicon nanowire arrays and an Al2O3/TiO2 dual-layer passivation stack on the n(+) emitter were fabricated. The highly conformal Al2O3 and TiO2 surface passivation layers were deposited on the high-aspect-ratio surface of the NBSi wafers using atomic layer deposition. Instead of the single Al2O3 passivation layer with a negative oxide charge density, the Al2O3/TiO2 dual-layer passivation stack treated with forming gas annealing provides a high positive oxide charge density and a low interfacial state density, which are essential for the effective field-effect and chemical passivation of the n(+) emitter. In addition, the Al2O3/TiO2 dual-layer passivation stack suppresses the total reflectance over a broad range of wavelengths (400-1000 nm). Therefore, with the Al2O3/TiO2 dual-layer passivation stack, the short-circuit current density and efficiency of the NBSi solar cell were increased by 11% and 20%, respectively. In conclusion, a high efficiency of 18.5% was achieved with the NBSi solar cells by using the n(+)-emitter/p-base structure passivated with the Al2O3/TiO2 stack.

  4. Efficiency Enhancement of Nanotextured Black Silicon Solar Cells Using Al2O3/TiO2 Dual-Layer Passivation Stack Prepared by Atomic Layer Deposition.

    PubMed

    Wang, Wei-Cheng; Tsai, Meng-Chen; Yang, Jason; Hsu, Chuck; Chen, Miin-Jang

    2015-05-20

    In this study, efficient nanotextured black silicon (NBSi) solar cells composed of silicon nanowire arrays and an Al2O3/TiO2 dual-layer passivation stack on the n(+) emitter were fabricated. The highly conformal Al2O3 and TiO2 surface passivation layers were deposited on the high-aspect-ratio surface of the NBSi wafers using atomic layer deposition. Instead of the single Al2O3 passivation layer with a negative oxide charge density, the Al2O3/TiO2 dual-layer passivation stack treated with forming gas annealing provides a high positive oxide charge density and a low interfacial state density, which are essential for the effective field-effect and chemical passivation of the n(+) emitter. In addition, the Al2O3/TiO2 dual-layer passivation stack suppresses the total reflectance over a broad range of wavelengths (400-1000 nm). Therefore, with the Al2O3/TiO2 dual-layer passivation stack, the short-circuit current density and efficiency of the NBSi solar cell were increased by 11% and 20%, respectively. In conclusion, a high efficiency of 18.5% was achieved with the NBSi solar cells by using the n(+)-emitter/p-base structure passivated with the Al2O3/TiO2 stack. PMID:25919200

  5. 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.

  6. 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

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

    SciTech Connect

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

    2013-10-28

    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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. Fabricating large-area metallic woodpile photonic crystals using stacking and rolling.

    PubMed

    Ibbotson, Lindsey A; Baumberg, Jeremy J

    2013-08-01

    Stacking thin polymer films supporting metal nanowire gratings provides a simple route, demonstrated here, to producing large-area metallic woodpile structures with high throughput. Under appropriate conditions the grating films can spontaneously roll up, giving a rapid and controllable method of creating multilayers. The resulting three-dimensional (3D) wire structures are flexible and potentially stretchable. Since this process can be extended to include a wide variety of functional materials, it opens up the manufacture of many tailored 3D optical metamaterials.

  13. 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.

  14. 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. PMID:26952635

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

    PubMed Central

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

    2008-01-01

    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%. PMID:19070228

  16. 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.

  17. GO-induced assembly of gelatin toward stacked layer-like porous carbon for advanced supercapacitors.

    PubMed

    Zhang, Xiaomeng; Jiao, Yanqing; Sun, Li; Wang, Lei; Wu, Aiping; Yan, Haijing; Meng, Meichen; Tian, Chungui; Jiang, Baojiang; Fu, Honggang

    2016-01-28

    Layer-like nanocarbons with high surface area and good conductivity are promising materials for supercapacitors due to their good ability for effective charge-transfer and mass-transfer. In this paper, stacked layer-like porous carbon containing RGO (reduced graphene oxides) (LPCG) was constructed via the GO-induced assembly of gelatin followed by carbonization and activation processes. Under suitable conditions, LPCG-based materials with a thickness of about 100 nm and a high specific surface area (up to 1476 m(2) g(-1)) could be obtained. In the materials, the closed combination of RGO and porous carbon can be observed, which is favourable for the development of the synergistic effects of both components. The presence of GO can not only enhance the conductivity of LPCG-based materials, but also is essential for the formation of a thin carbon sheet with a stacked structure. Otherwise, the plate-like, non-stacked carbon with a thickness of about 500 nm could be formed in the absence of RGO. The porous structure along with the presence of RGO allows rapid charge-transfer and easy access and diffusion of electrolyte ions. As a result, the materials exhibited a high discharge specific capacitance (455 F g(-1) at 0.5 A g(-1), 366 F g(-1) at 1 A g(-1)), good rate capability (221 F g(-1) at density 30 A g(-1)) and good cycling stability. In aqueous electrolytes, the energy density could be up to 9.32 W h kg(-1) at a relatively low power density of 500 W kg(-1) with a good cycling stability (>96% over 5000 cycles). It was found that (1) the rational combination of RGO and porous carbon is essential for enhancing the capacitance performance and improving the cycling stability and (2) the high conductivity is favorable for improving the rate performance of the materials. The LPCG-based materials have extensive potential for practical applications in energy storage and conversion devices.

  18. 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.

  19. Buffer layers on biaxially textured metal substrates

    DOEpatents

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

    2001-01-01

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

  20. GO-induced assembly of gelatin toward stacked layer-like porous carbon for advanced supercapacitors

    NASA Astrophysics Data System (ADS)

    Zhang, Xiaomeng; Jiao, Yanqing; Sun, Li; Wang, Lei; Wu, Aiping; Yan, Haijing; Meng, Meichen; Tian, Chungui; Jiang, Baojiang; Fu, Honggang

    2016-01-01

    Layer-like nanocarbons with high surface area and good conductivity are promising materials for supercapacitors due to their good ability for effective charge-transfer and mass-transfer. In this paper, stacked layer-like porous carbon containing RGO (reduced graphene oxides) (LPCG) was constructed via the GO-induced assembly of gelatin followed by carbonization and activation processes. Under suitable conditions, LPCG-based materials with a thickness of about 100 nm and a high specific surface area (up to 1476 m2 g-1) could be obtained. In the materials, the closed combination of RGO and porous carbon can be observed, which is favourable for the development of the synergistic effects of both components. The presence of GO can not only enhance the conductivity of LPCG-based materials, but also is essential for the formation of a thin carbon sheet with a stacked structure. Otherwise, the plate-like, non-stacked carbon with a thickness of about 500 nm could be formed in the absence of RGO. The porous structure along with the presence of RGO allows rapid charge-transfer and easy access and diffusion of electrolyte ions. As a result, the materials exhibited a high discharge specific capacitance (455 F g-1 at 0.5 A g-1, 366 F g-1 at 1 A g-1), good rate capability (221 F g-1 at density 30 A g-1) and good cycling stability. In aqueous electrolytes, the energy density could be up to 9.32 W h kg-1 at a relatively low power density of 500 W kg-1 with a good cycling stability (>96% over 5000 cycles). It was found that (1) the rational combination of RGO and porous carbon is essential for enhancing the capacitance performance and improving the cycling stability and (2) the high conductivity is favorable for improving the rate performance of the materials. The LPCG-based materials have extensive potential for practical applications in energy storage and conversion devices.Layer-like nanocarbons with high surface area and good conductivity are promising materials for

  1. 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

  2. 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.

  3. 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. PMID:27571412

  4. Vertically Stacked Graphene/Transition-Metal-Dichalcogenides/Graphene Heterojunction Devices for High Performance Photodetectors

    NASA Astrophysics Data System (ADS)

    Heo, Jinseong; Jeong, Heejeong; Lee, Jaeho; Lee, Kiyoung; Lee, Eun-Kyu; Lee, Sangyeob; Cho, Yeonchoo; Byun, Kyung-Eun; Lee, Chang-Won; Park, Seongjun; Hwang, Sungwoo

    Photodetectors based on vertically stacked graphene heterojunctions have advantages of short transit length for photo-generated carriers and large sensing area, thus implying fast response time and high responsivity. Previously, vertically stacked Graphene (Gr)/Transition-Metal-Dichalcogenide (TMDC)/Gr junctions were introduced for optoelectronic devices, showing high current on and off ratio as well as photoresponsivity. But for high performance photodetectors, both thorough and comparative study in terms of the figures of merit such as photoresponse time and photoresponsivity depending on different TMDC materials is crucial. Here, we report fast response time (28 us) and high responsivity (20 A/W) from Gr/WSe2 and MoS2/Gr, respectively. At the same time, those devices operate as p- and n-type barrier-variable transistors, respectively, being a potential building block for optoelectronic system on a chip.

  5. 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.

  6. A highly photoreflective and heat-insulating alumina film composed of stacked mesoporous layers in hierarchical structure.

    PubMed

    Kodaira, Tetsuya; Suzuki, Yo-Hei; Nagai, Naofumi; Matsuda, Gozo; Mizukami, Fujio

    2015-10-21

    An alumina film with highly photoreflective and heat-insulating properties can be simply synthesized using a sol of fibrous boehmite with an additive. The entangled fibers bring about mesopores among them and form stacked 2D nonwoven-like nanosheets. The porosity and the layered structure of alumina accompanying the heat resistivity provide the upper properties that are usually difficult to realize simultaneously.

  7. Wafer-scale double-layer stacked Au/Al2O3@Au nanosphere structure with tunable nanospacing for surface-enhanced Raman scattering.

    PubMed

    Hu, Zhaosheng; Liu, Zhe; Li, Lin; Quan, Baogang; Li, Yunlong; Li, Junjie; Gu, Changzhi

    2014-10-15

    Fabricating perfect plasmonic nanostructures has been a major challenge in surface enhanced Raman scattering (SERS) research. Here, a double-layer stacked Au/Al2O3@Au nanosphere structures is designed on the silicon wafer to bring high density, high intensity "hot spots" effect. A simply reproducible high-throughput approach is shown to fabricate feasibly this plasmonic nanostructures by rapid thermal annealing (RTA) and atomic layer deposition process (ALD). The double-layer stacked Au nanospheres construct a three-dimensional plasmonic nanostructure with tunable nanospacing and high-density nanojunctions between adjacent Au nanospheres by ultrathin Al2O3 isolation layer, producing highly strong plasmonic coupling so that the electromagnetic near-field is greatly enhanced to obtain a highly uniform increase of SERS with an enhancement factor (EF) of over 10(7). Both heterogeneous nanosphere group (Au/Al2O@Ag) and pyramid-shaped arrays structure substrate can help to increase the SERS signals further, with a EF of nearly 10(9). These wafer-scale, high density homo/hetero-metal-nanosphere arrays with tunable nanojunction between adjacent shell-isolated nanospheres have significant implications for ultrasensitive Raman detection, molecular electronics, and nanophotonics.

  8. 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

  9. A wide-angle broadband polarization-dependent absorber with stacked metal-dielectric grating

    NASA Astrophysics Data System (ADS)

    Liao, Yan-Lin; Zhao, Yan

    2016-07-01

    We report an absorber in the mid-infrared regime by using stacked metal-dielectric grating structure. The simulation results show that the minimal absorption magnitude is larger than 0.8 in the broadband range for angles up to 60° for TM polarization (magnetic field is parallel to grating grooves). At the same time, absorption for TE polarization (electric field is parallel to grating grooves) is negligible. Furthermore, such broadband absorption for TM polarization can be tuned by shrinking or enlarging the grating parameters. This absorber is a good candidate for potential applications such as polarization detectors and polarizers.

  10. 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).

  11. 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.

  12. Observation of dopant-profile independent electron transport in sub-monolayer TiOx stacked ZnO thin films grown by atomic layer deposition

    NASA Astrophysics Data System (ADS)

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

    2016-01-01

    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 TiOx 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/TiOx structures in the emerging field of transparent oxide electronics.

  13. Stacked thin layers of metaphase chromatin explain the geometry of chromosome rearrangements and banding.

    PubMed

    Daban, Joan-Ramon

    2015-10-08

    The three-dimensional organization of tightly condensed chromatin within metaphase chromosomes has been one of the most challenging problems in structural biology since the discovery of the nucleosome. This study shows that chromosome images obtained from typical banded karyotypes and from different multicolour cytogenetic analyses can be used to gain information about the internal structure of chromosomes. Chromatin bands and the connection surfaces in sister chromatid exchanges and in cancer translocations are planar and orthogonal to the chromosome axis. Chromosome stretching produces band splitting and even the thinnest bands are orthogonal and well defined, indicating that short stretches of DNA can occupy completely the chromosome cross-section. These observations impose strong physical constraints on models that attempt to explain chromatin folding in chromosomes. The thin-plate model, which consists of many stacked layers of planar chromatin perpendicular to the chromosome axis, is compatible with the observed orientation of bands, with the existence of thin bands, and with band splitting; it is also compatible with the orthogonal orientation and planar geometry of the connection surfaces in chromosome rearrangements. The results obtained provide a consistent interpretation of the chromosome structural properties that are used in clinical cytogenetics for the diagnosis of hereditary diseases and cancers.

  14. 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.

  15. [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.

  16. THE MASS-METALLICITY RELATION WITH THE DIRECT METHOD ON STACKED SPECTRA OF SDSS GALAXIES

    SciTech Connect

    Andrews, Brett H.; Martini, Paul

    2013-03-10

    The relation between galaxy stellar mass and gas-phase metallicity is a sensitive diagnostic of the main processes that drive galaxy evolution, namely cosmological gas inflow, metal production in stars, and gas outflow via galactic winds. We employed the direct method to measure the metallicities of {approx}200,000 star-forming galaxies from the Sloan Digital Sky Survey that were stacked in bins of (1) stellar mass and (2) both stellar mass and star formation rate (SFR) to significantly enhance the signal-to-noise ratio of the weak [O III] {lambda}4363 and [O II] {lambda}{lambda}7320, 7330 auroral lines required to apply the direct method. These metallicity measurements span three decades in stellar mass from log(M{sub *}/M{sub Sun }) = 7.4-10.5, which allows the direct method mass-metallicity relation to simultaneously capture the high-mass turnover and extend a full decade lower in mass than previous studies that employed more uncertain strong line methods. The direct method mass-metallicity relation rises steeply at low mass (O/H {proportional_to} M{sub *} {sup 1/2}) until it turns over at log(M{sub *}/M{sub Sun }) = 8.9 and asymptotes to 12 + log(O/H) = 8.8 at high mass. The direct method mass-metallicity relation has a steeper slope, a lower turnover mass, and a factor of two to three greater dependence on SFR than strong line mass-metallicity relations. Furthermore, the SFR-dependence appears monotonic with stellar mass, unlike strong line mass-metallicity relations. We also measure the N/O abundance ratio, an important tracer of star formation history, and find the clear signature of primary and secondary nitrogen enrichment. N/O correlates tightly with oxygen abundance, and even more so with stellar mass.

  17. 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.

  18. 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.

  19. Laser evaporation of metal sandwich layers for improved IC metallization

    NASA Astrophysics Data System (ADS)

    Pielmeier, R.; Bollmann, D.; Haberger, K.

    1990-12-01

    With the further shrink of IC dimensions, metallization becomes the most crucial layer because conductivity and contact resistivity determine the RC constants and thus the speed of the circuits. With our Q-switched Nd:YAG laser we have evaporated different materials (Al, Ti, W, Pt, Au), alloys (Ta-Si) and dielectrics (ZrO 2, Al 2O 3). We also produced sandwich layers (Al-Au, Ti-Al). The layers were investigated with regard to deposition rate, homogeneity, adhesion, step coverage and surface roughness. Deposition rates in the order of 60 nm/min were achieved. At a power of 10 W and a repetition rate of about 5 kHz we could form ohmic contacts to silicon with a good step coverage in the contact.

  20. Whispering gallery mode nanodisk resonator based on layered metal-dielectric waveguide.

    PubMed

    Lou, Fei; Yan, Min; Thylen, Lars; Qiu, Min; Wosinski, Lech

    2014-04-01

    This paper proposes a layered metal-dielectric waveguide consisting of a stack of alternating metal and dielectric films which enables an ultracompact mode confinement. The properties of whispering gallery modes supported by disk resonators based on such waveguides are investigated for achieving a large Purcell factor. We show that by stacking three layers of 10 nm thick silver with two layers of 50 nm dielectric layers (of refractive index n) in sequence, the disk radius can be as small as 61 nm ∼λ(0)/(7n) and the mode volume is only 0.0175(λ(0)/(2n))(3). When operating at 40 K, the cavity's Q-factor can be ~670; Purcell factor can be as large as 2.3×10(4), which is more than five times larger than that achievable in a metal-dielectric-metal disk cavity in the same condition. When more dielectric layers with smaller thicknesses are used, even more compact confinement can be achieved. For example, the radius of a cavity consisting of seven dielectric-layer waveguide can be shrunk down to λ(0)/(13.5n), corresponding to a mode volume of 0.005λ(0)/(2n))(3), and Purcell factor can be enhanced to 7.3×10(4) at 40 K. The influence of parameters like thicknesses of dielectric and metal films, cavity size, and number of dielectric layers is also comprehensively studied. The proposed waveguide and nanodisk cavity provide an alternative for ultracompact light confinement, and can find applications where a strong light-matter interaction is necessary.

  1. 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.

  2. 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

  3. 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. PMID:25593559

  4. Design of non-polarizing cut-off filters based on dielectric-metal-dielectric stacks.

    PubMed

    Cai, Qing-Yuan; Luo, Hai-Han; Zheng, Yu-Xiang; Liu, Ding-Quan

    2013-08-12

    Cut-off filters are usually operating at oblique incidence and exhibit polarization dependence properties. We propose a simple approach to design cut-off filters with low linear polarization sensitivity (LPS) based on dielectric-metal-dielectric (DMD) stacks. The designing method is derived from the theory of optical film characteristic matrix. The admittance loci of the film are adjusted to achieve similar spectral properties of s- and p-polarized light at oblique incidence. Different film structures are designed non-polarizing at different angles of incidence with the method. The results show that the designing method is efficient for designing non-polarizing cut-off filters, which are widely used in non-polarizing optical system.

  5. Effect of π-π+ stacking on the layering of ionic liquids confined to an amorphous carbon surface.

    PubMed

    Gong, Xiao; Kozbial, Andrew; Rose, Franck; Li, Lei

    2015-04-01

    In the current paper, AFM studies were conducted on nanometer-thick ionic liquids (ILs) confined to an amorphous carbon (AC) surface, which is critical to the design of the next-generation media lubricant for hard disk drives (HDDs). The results indicated that the existence of the delocalized ring in the cation is critical to layering of ILs. Extended layering was observed only when there is imidazolium ring in the cation. When the imidazolium ring is replaced by an aliphatic moiety, "drop-on-layer" (dewetting) structure was observed. On the basis of the experimental results, we proposed that π-π+ stacking between sp(2) carbon in the AC and the imidazolium cation in the ILs is the key to the extended layering of ILs at the ILs/AC interface. PMID:25808335

  6. 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.

  7. 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.

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

    PubMed

    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. PMID:27484794

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

    PubMed

    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.

  10. 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.

  11. Oxide film on metal substrate reduced to form metal-oxide-metal layer structure

    NASA Technical Reports Server (NTRS)

    Youngdahl, C. A.

    1967-01-01

    Electrically conductive layer of zirconium on a zirconium-oxide film residing on a zirconium substrate is formed by reducing the oxide in a sodium-calcium solution. The reduced metal remains on the oxide surface as an adherent layer and seems to form a barrier that inhibits further reaction.

  12. Atomic layer deposition of metal sulfide materials.

    PubMed

    Dasgupta, Neil P; Meng, Xiangbo; Elam, Jeffrey W; Martinson, Alex B F

    2015-02-17

    CONSPECTUS: The field of nanoscience is delivering increasingly intricate yet elegant geometric structures incorporating an ever-expanding palette of materials. Atomic layer deposition (ALD) is a powerful driver of this field, providing exceptionally conformal coatings spanning the periodic table and atomic-scale precision independent of substrate geometry. This versatility is intrinsic to ALD and results from sequential and self-limiting surface reactions. This characteristic facilitates digital synthesis, in which the film grows linearly with the number of reaction cycles. While the majority of ALD processes identified to date produce metal oxides, novel applications in areas such as energy storage, catalysis, and nanophotonics are motivating interest in sulfide materials. Recent progress in ALD of sulfides has expanded the diversity of accessible materials as well as a more complete understanding of the unique chalcogenide surface chemistry. ALD of sulfide materials typically uses metalorganic precursors and hydrogen sulfide (H2S). As in oxide ALD, the precursor chemistry is critical to controlling both the film growth and properties including roughness, crystallinity, and impurity levels. By modification of the precursor sequence, multicomponent sulfides have been deposited, although challenges remain because of the higher propensity for cation exchange reactions, greater diffusion rates, and unintentional annealing of this more labile class of materials. A deeper understanding of these surface chemical reactions has been achieved through a combination of in situ studies and quantum-chemical calculations. As this understanding matures, so does our ability to deterministically tailor film properties to new applications and more sophisticated devices. This Account highlights the attributes of ALD chemistry that are unique to metal sulfides and surveys recent applications of these materials in photovoltaics, energy storage, and photonics. Within each application

  13. 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.

  14. Coupling and Stacking Order of ReS2 Atomic Layers Revealed by Ultralow-Frequency Raman Spectroscopy.

    PubMed

    He, Rui; Yan, Jia-An; Yin, Zongyou; Ye, Zhipeng; Ye, Gaihua; Cheng, Jason; Li, Ju; Lui, C H

    2016-02-10

    We investigate the ultralow-frequency Raman response of atomically thin ReS2, a special type of two-dimensional (2D) semiconductors with unique distorted 1T structure. Bilayer and few-layer ReS2 exhibit rich Raman spectra at frequencies below 50 cm(-1), where a panoply of interlayer shear and breathing modes are observed. The emergence of these interlayer phonon modes indicate that the ReS2 layers are coupled and orderly stacked. Whereas the interlayer breathing modes behave similarly to those in other 2D layered crystals, the shear modes exhibit distinctive behavior due to the in-plane lattice distortion. In particular, the two shear modes in bilayer ReS2 are nondegenerate and clearly resolved in the Raman spectrum, in contrast to the doubly degenerate shear modes in other 2D materials. By carrying out comprehensive first-principles calculations, we can account for the frequency and Raman intensity of the interlayer modes and determine the stacking order in bilayer ReS2.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. New layered metal oxides as positive electrode materials for room-temperature sodium-ion batteries

    NASA Astrophysics Data System (ADS)

    Mu, Lin-Qin; Hu, Yong-Sheng; Chen, Li-Quan

    2015-03-01

    In order to achieve better Na storage performance, most layered oxide positive electrode materials contain toxic and expensive transition metals Ni and/or Co, which are also widely used for lithium-ion batteries. Here we report a new quaternary layered oxide consisting of Cu, Fe, Mn, and Ti transition metals with O3-type oxygen stacking as a positive electrode for room-temperature sodium-ion batteries. The material can be simply prepared by a high-temperature solid-state reaction route and delivers a reversible capacity of 94 mAh/g with an average storage voltage of 3.2 V. This paves the way for cheaper and non-toxic batteries with high Na storage performance. Project supported by the National Natural Science Foundation of China (Grant Nos. 51222210 and 11234013) and the One Hundred Talent Project of the Chinese Academy of Sciences.

  2. 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.

  3. 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.

  4. 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

    2015-01-01

    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. PMID:26469313

  5. Electrical characterization of the metal ferroelectric oxide semiconductor and metal ferroelectric nitride semiconductor gate stacks for ferroelectric field effect transistors

    NASA Astrophysics Data System (ADS)

    Verma, Ram Mohan; Rao, Ashwath; Singh, B. R.

    2014-03-01

    This paper presents our work on electrical characterization of metal-ferroelectric-oxide-semiconductor (MFeOS) and metal-ferroelectric-nitride-semiconductor (MFeNS) structures for nonvolatile memory applications. Thin films of lead zirconate titanate (PZT: 35:65) have been used as ferroelectric material on 2.5-5 nm thick thermally grown SiO2 and Si3N4 as buffer layer for MFeOS and MFeNS structures, respectively. Capacitance-Voltage (C-V) and Current-Voltage (I-V) characteristics were used for electrical characterization. Our comparative results reveal that the MFeNS structure with 2.5 nm thick buffer layer has higher memory window of about 3.6 V as compared to 3 V for similar MFeOS structure. Also superior electrical properties such as lower leakage current and higher dielectric strength were observed in MFeNS structures. Higher nitridation time was observed to deteriorate the polarization characteristics resulting in reduced memory window. The highest memory window of 6.5 V was observed for SiO2 buffer layer thickness of 5 nm. We also observed that the annealing temperature influences the leakage current characteristic and memory window of these structures.

  6. 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.

  7. 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.

  8. Thermally stable, sub-nanometer equivalent oxide thickness gate stack for gate-first In0.53Ga0.47As metal-oxide-semiconductor field-effect-transistors

    NASA Astrophysics Data System (ADS)

    El Kazzi, M.; Czornomaz, L.; Rossel, C.; Gerl, C.; Caimi, D.; Siegwart, H.; Fompeyrine, J.; Marchiori, C.

    2012-02-01

    Metal-oxide-semiconductor (MOS) capacitors were fabricated by depositing composite 2 nm HfO2/1 nm Al2O3/1 nm a-Si gate stacks on p-In0.53Ga0.47As/InP (001) substrates. Thanks to the presence of the Al2O3 barrier layer, a minimum amount of the a-Si passivating layer is oxidized during the whole fabrication process. The capacitors exhibit excellent electrical characteristics with scaled equivalent oxide thickness (EOT) of 0.89 nm and mid-gap interface state density of 5 × 1011 eV-1 cm-2 upon post-metallization anneal up to 550 °C. Gate-first, self-aligned MOS field-effect-transistors were fabricated with a similar 5 nm HfO2/1 nm Al2O3/1 nm a-Si gate stack and raised source and drain (600 °C for 30 min). Owing to the excellent thermal stability of the stack, no degradation of the gate stack/semiconductor interface is observed, as demonstrated by the excellent capacitance vs voltage characteristics and the good mobility values (peak at 1030 cm2 V-1 s-1 and 740 cm2 V-1 s-1 at carrier density of 6.5 × 1012 cm-2) for a 1.3 nm EOT.

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

    DOE PAGES

    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 twomore » distinct regimes corresponding to 'low' and 'high' stacking fault energies.« less

  10. 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.

  11. 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.

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

    PubMed

    Daban, Joan-Ramon

    2014-03-01

    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

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

    PubMed

    Daban, Joan-Ramon

    2014-03-01

    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.

  14. 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...

  15. Layer-by-layer synthesis of metal-containing conducting polymers: caged metal centers for interlayer charge transport.

    PubMed

    Liu, Wenjun; Huang, Weijie; Pink, Maren; Lee, Dongwhan

    2010-09-01

    Metal-templated [2 + 3]-type cocondensation of a pi-extended boronic acid and nioxime furnished a series of cage molecules, which were electropolymerized to prepare metal-containing conducting polymers (MCPs). Despite sharing essentially isostructural organic scaffolds, these materials display metal-dependent electrochemical properties as evidenced by different redox windows observed for M = Co, Fe, Ru. Consecutive electropolymerization using two different monomers furnished bilayer MCPs having different metals in each layer. In addition to functioning as heavy atom markers in cross-sectional analysis by FIB and EDX, redox-active metal centers participate in voltage-dependent interlayer electron transport to give rise to cyclic voltammograms that are distinctively different from those of each layer alone or random copolymers. A simple electrochemical technique can thus be used as a straightforward diagnostic tool to investigate the structural ordering of electrically conductive layered materials. PMID:20690667

  16. 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.

  17. Effect of impurity doping on tunneling conductance in AB-stacked bi-layer graphene: A tight-binding study

    NASA Astrophysics Data System (ADS)

    Rout, G. C.; Sahu, Sivabrata; Panda, S. K.

    2016-04-01

    We report here a microscopic tight-binding model calculation for AB-stacked bilayer graphene in presence of biasing potential between the two layers and the impurity effects to study the evolution of the total density of states with special emphasis on opening of band gap near Dirac point. We have calculated the electron Green's functions for both the A and B sub-lattices by Zubarev technique. The imaginary part of the Green's function gives the partial and total density of states of electrons. The density of states are computed numerically for 1000 × 1000 grid points of the electron momentum. The evolution of the opening of band gap near van-Hove singularities as well as near Dirac point is investigated by varying the different interlayer hoppings and the biasing potentials. The inter layer hopping splits the density of states at van-Hove singularities and produces a V-shaped gap near Dirac point. Further the biasing potential introduces a U shaped gap near Dirac point with a density minimum at the applied potential(i.e. at V/2).

  18. Specular spectral profilometry on metal layers

    NASA Astrophysics Data System (ADS)

    Bao, Junwei; Niu, Xinhui; Jakatdar, Nickhil H.; Spanos, Costas J.; Bendik, Joseph J.

    2000-06-01

    With the advent of deep sub-micron semiconductor technology, metrology for metal interconnects becomes more critical. In addition to the line width, information about the height and the sidewall profile is needed to ensure good circuit performance. Conventional metrology tools such as CD SEMs and AFMs are either unable to measure the profile, or too slow for production process control. Scatterometry is a promising candidate as in situ, full-profile metrology tool. In this method, scattering of broadband light (240 nm to 760 nm) on periodical structures is simulated by approximating the structure with a finite series of Fourier expansion terms. By comparing the measured spectrum and the simulated spectra for various possible profiles in a precalculated library, the profile can be extracted. Previous work has shown good results on resist structures. For metal structures, however, more diffraction orders need to be included to accurately simulate light scattering. In this study, a library for 0.22 micrometer line and 0.44 micrometer space metal grating structures is generated using 31 orders. The profiles of metal grating structures of the same size are extracted using this library. Our data shows that the correlation between CD-SEM and scatterometry-based profile extraction appears to be related to the sidewall angle of the profile. These discrepancies will be analyzed and discussed.

  19. Real-time analysis of metals in stack gas using argon/air inductively coupled plasma with optical emission spectrometry

    NASA Astrophysics Data System (ADS)

    Meyer, Gerhard; Seltzer, Michael D.

    1999-02-01

    The design and operation of an instrument capable of continuous, real-time detection of hazardous air pollutant metals in the effluent of boilers, incinerators, and furnaces is reported. A commercially available inductively coupled argon plasma spectrometer, modified for introduction of sample air, provides sensitivity for several metals comparable to that of EPA-approved manual methods, with an analysis result reported every 1 to 2 minutes. Achievable detection limits for the present list of hazardous air pollutant metals range from 0.1 to 20 (mu) g/dry standard cubic meter. Air is isokinetically extracted from a stack or duct and introduced into the argon plasma through an innovative sample transport interface. Data is reported after every measurement cycle and immediately archived to a control computer, where the information is available to a local area network. The entire instrument is automated, and is enclosed in a shelter that can be placed as near as possible to the stack. The measurement of sample losses in the transport line is also discussed.

  20. Closed and open-ended stacking fault tetrahedra formation along the interfaces of Cu-Al nanolayered metals

    NASA Astrophysics Data System (ADS)

    Li, Ruizhi; Beng Chew, Huck

    2015-09-01

    Stacking fault tetrahedra (SFTs) are volume defects that typically form by the clustering of vacancies in face-centred cubic (FCC) metals. Here, we report a dislocation-based mechanism of SFT formation initiated from the semi-coherent interfaces of Cu-Al nanoscale multilayered metals subjected to out-of-plane tension. Our molecular dynamics simulations show that Shockley partials are first emitted into the Cu interlayers from the dissociated misfit dislocations along the Cu-Al interface and interact to form SFTs above the triangular intrinsic stacking faults along the interface. Under further deformation, Shockley partials are also emitted into the Al interlayers and interact to form SFTs above the triangular FCC planes along the interface. The resulting dislocation structure comprises closed SFTs within the Cu interlayers which are tied across the Cu-Al interfaces to open-ended SFTs within the Al interlayers. This unique plastic deformation mechanism results in considerable strain hardening of the Cu-Al nanolayered metal, which achieves its highest tensile strength at a critical interlayer thickness of ~4 nm corresponding to the highest possible density of complete SFTs within the nanolayer structure.

  1. Sliding charge density wave in the monophosphate tungsten bronze (PO2)4(WO3)2m with alternate stacking of m=4 and m=6 WO3 layers

    NASA Astrophysics Data System (ADS)

    Foury-Leylekian, P.; Sandré, E.; Ravy, S.; Pouget, J.-P.; Elkaim, E.; Roussel, P.; Groult, D.; Labbé, Ph.

    2002-08-01

    The monophosphate tungsten bronzes (PO2)4(WO3)2m form family of two-dimensional metals which exhibit charge density wave (CDW) instabilities. These materials are generally built by the regular stacking of (a,b) layers in which chains made of segments of m WO6 octahedra directed along the a and a+/-b directions are delimited. Their electronic structure thus originates from quasi-one-dimensional (1D) bands located on these chains. As a consequence their Fermi surface (FS) exhibits large flat portions whose nesting gives rise to successive CDW instabilities. Here we present a structural study of the CDW instability of the (PO2)4(WO3)10 member formed by the alternate stacking of layers built with segments of m=4 and m=6 WO6 octahedra. Its ab initio electronic structure calculation shows that the FS of this member exhibits large flat portions which can be extremely well nested. Its best nesting wave vector accounts for the modulation wave vector stabilized by the CDW transition which occurs at 156 K. Because of the regular stacking of layers of different m values the FS is slightly split. The unusual thermal dependence of the x-ray satellite intensity provides evidence that the two types of layers become modulated at different temperature. This also leads to a slight thermal sliding of the CDW-nesting modulation wave vector, which can be accounted for within the framework of a Landau-Ginzburg theory. In addition, the observation of a global hysteresis in the thermal cycling of the satellite intensity, as well as the degradation of the interlayer order upon cooling, suggest the formation of a disordered lattice of dilute solitons. Such solitons allow to accomodate the charge transferred between the two types of layer. Finally the relevance of local charge transfers, at intergrowth defects, for example, to create pinned discommensurations that break the CDW coherence is emphasized in this whole family of bronzes.

  2. 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.

  3. 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.

  4. Oxygen vacancy defect engineering using atomic layer deposited HfAlOx in multi-layered gate stack

    NASA Astrophysics Data System (ADS)

    Bhuyian, M. N.; Sengupta, R.; Vurikiti, P.; Misra, D.

    2016-05-01

    This work evaluates the defects in high quality atomic layer deposited (ALD) HfAlOx with extremely low Al (<3% Al/(Al + Hf)) incorporation in the Hf based high-k dielectrics. The defect activation energy estimated by the high temperature current voltage measurement shows that the charged oxygen vacancies, V+/V2+, are the primary source of defects in these dielectrics. When Al is added in HfO2, the V+ type defects with a defect activation energy of Ea ˜ 0.2 eV modify to V2+ type to Ea ˜ 0.1 eV with reference to the Si conduction band. When devices were stressed in the gate injection mode for 1000 s, more V+ type defects are generated and Ea reverts back to ˜0.2 eV. Since Al has a less number of valence electrons than do Hf, the change in the co-ordination number due to Al incorporation seems to contribute to the defect level modifications. Additionally, the stress induced leakage current behavior observed at 20 °C and at 125 °C demonstrates that the addition of Al in HfO2 contributed to suppressed trap generation process. This further supports the defect engineering model as reduced flat-band voltage shifts were observed at 20 °C and at 125 °C.

  5. 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.

  6. 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.

  7. Single-layer transition metal sulfide catalysts

    SciTech Connect

    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.

  8. 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.

  9. Oxidation precursor dependence of atomic layer deposited Al2O3 films in a-Si:H(i)/Al2O3 surface passivation stacks.

    PubMed

    Xiang, Yuren; Zhou, Chunlan; Jia, Endong; Wang, Wenjing

    2015-01-01

    In order to obtain a good passivation of a silicon surface, more and more stack passivation schemes have been used in high-efficiency silicon solar cell fabrication. In this work, we prepared a-Si:H(i)/Al2O3 stacks on KOH solution-polished n-type solar grade mono-silicon(100) wafers. For the Al2O3 film deposition, both thermal atomic layer deposition (T-ALD) and plasma enhanced atomic layer deposition (PE-ALD) were used. Interface trap density spectra were obtained for Si passivation with a-Si films and a-Si:H(i)/Al2O3 stacks by a non-contact corona C-V technique. After the fabrication of a-Si:H(i)/Al2O3 stacks, the minimum interface trap density was reduced from original 3 × 10(12) to 1 × 10(12) cm(-2) eV(-1), the surface total charge density increased by nearly one order of magnitude for PE-ALD samples and about 0.4 × 10(12) cm(-2) for a T-ALD sample, and the carrier lifetimes increased by a factor of three (from about 10 μs to about 30 μs). Combining these results with an X-ray photoelectron spectroscopy analysis, we discussed the influence of an oxidation precursor for ALD Al2O3 deposition on Al2O3 single layers and a-Si:H(i)/Al2O3 stack surface passivation from field-effect passivation and chemical passivation perspectives. In addition, the influence of the stack fabrication process on the a-Si film structure was also discussed in this study.

  10. 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

  11. 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.

  12. Universal Transfer and Stacking of Chemical Vapor Deposition Grown Two-Dimensional Atomic Layers with Water-Soluble Polymer Mediator.

    PubMed

    Lu, Zhixing; Sun, Lifei; Xu, Guanchen; Zheng, Jingying; Zhang, Qi; Wang, Jingyi; Jiao, Liying

    2016-05-24

    Chemical vapor deposition (CVD) has shown great potential in synthesizing various high-quality two-dimensional (2D) transition metal dichalcogenides (TMDCs). However, the nondestruction transfer of these CVD-grown 2D TMDCs at a high yield remains a key challenge for applying these emerging materials in various aspects. To address this challenge, we designed a water-soluble transfer mediator consisting of two polymers, polyvinylpyrrolidone (PVP) and poly(vinyl alcohol) (PVA), which can form strong interactions with CVD-grown 2D TMDCs for the nondestruction transfer of these materials. With this mediator, we realized the physical transfer of CVD-grown MoS2 flakes and several other 2D TMDCs, including 2D alloys and heterostructures to a wide range of substrates at a high yield of >90% with well-retained properties as evidenced by various microscopic, spectroscopic, and electrical measurements. Field-effect transistors (FETs) made on thus-transferred CVD-grown MoS2 monolayers exhibited obviously higher mobility than those transferred by chemical method. We also constructed several artificial 2D crystals showing very strong interlayer coupling by the multiple transfer of CVD-grown 2D TMDCs monolayers with this approach. This transfer approach will make versatile CVD-grown 2D materials and their artificial stacks with pristine qualities easily accessible for both fundamental studies and practical applications. PMID:27158832

  13. Universal Transfer and Stacking of Chemical Vapor Deposition Grown Two-Dimensional Atomic Layers with Water-Soluble Polymer Mediator.

    PubMed

    Lu, Zhixing; Sun, Lifei; Xu, Guanchen; Zheng, Jingying; Zhang, Qi; Wang, Jingyi; Jiao, Liying

    2016-05-24

    Chemical vapor deposition (CVD) has shown great potential in synthesizing various high-quality two-dimensional (2D) transition metal dichalcogenides (TMDCs). However, the nondestruction transfer of these CVD-grown 2D TMDCs at a high yield remains a key challenge for applying these emerging materials in various aspects. To address this challenge, we designed a water-soluble transfer mediator consisting of two polymers, polyvinylpyrrolidone (PVP) and poly(vinyl alcohol) (PVA), which can form strong interactions with CVD-grown 2D TMDCs for the nondestruction transfer of these materials. With this mediator, we realized the physical transfer of CVD-grown MoS2 flakes and several other 2D TMDCs, including 2D alloys and heterostructures to a wide range of substrates at a high yield of >90% with well-retained properties as evidenced by various microscopic, spectroscopic, and electrical measurements. Field-effect transistors (FETs) made on thus-transferred CVD-grown MoS2 monolayers exhibited obviously higher mobility than those transferred by chemical method. We also constructed several artificial 2D crystals showing very strong interlayer coupling by the multiple transfer of CVD-grown 2D TMDCs monolayers with this approach. This transfer approach will make versatile CVD-grown 2D materials and their artificial stacks with pristine qualities easily accessible for both fundamental studies and practical applications.

  14. Multi-Scale Mechanical Probing Techniques To Investigate The Stability Of BEOL Layer Stacks With Sub-100 nm Structures

    NASA Astrophysics Data System (ADS)

    Geisler, Holm; Lehr, Matthias U.; Platz, Alexander; Mayer, Ulrich; Hofmann, Petra; Engelmann, Hans-Jürgen

    2011-09-01

    The stress levels induced by chip-package interaction (CPI) impose an increased risk of mechanical failure on advanced backend-of-line (BEOL) layer stacks in microelectronic circuits if they contain fragile ultralow-k (ULK) interlayer dielectric (ILD) films. On the one hand, multilevel finite element modeling is used to assess the potential risk at an early stage of the development of new microelectronic products. On the other hand, the theoretical models need as accurate as possible materials parameters as an input to provide realistic results. Moreover, it is highly desirable to have multi-scale experimental probes available which can provide complementary data to support the modeling calculations. The present paper provides an overview about various mechanical probing techniques which operate on the scale of less than 100 nm up to more than 100 μm. In this way, typical feature sizes are covered which occur from the package level via solder bumps or copper pillars down to small Cu/ULK interconnect structures. The experimental approaches are based on nanoindentation with lateral force detection and in-situ scanning probe microscopy (SPM) imaging capabilities, and they include a novel technique named bump assisted BEOL stability indentation (BABSI) test. Especially, the interrelation between small-scale mechanical properties of ULK dielectric films and stresses acting on larger scales are quantitatively assessed by means of the experimental approaches described here.

  15. 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.

  16. 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.

  17. Growth of transition metals on cerium tungstate model catalyst layers

    NASA Astrophysics Data System (ADS)

    Skála, T.; Tsud, N.; Stetsovych, V.; Mysliveček, J.; Matolín, V.

    2016-10-01

    Two model catalytic metal/oxide systems were investigated by photoelectron spectroscopy and scanning tunneling microscopy. The mixed-oxide support was a cerium tungstate epitaxial thin layer grown in situ on the W(1 1 0) single crystal. Active particles consisted of palladium and platinum 3D islands deposited on the tungstate surface at 300 K. Both metals were found to interact weakly with the oxide support and the original chemical state of both support and metals was mostly preserved. Electronic and morphological changes are discussed during the metal growth and after post-annealing at temperatures up to 700 K. Partial transition-metal coalescence and self-cleaning from the CO and carbon impurities were observed.

  18. Growth of transition metals on cerium tungstate model catalyst layers.

    PubMed

    Skála, T; Tsud, N; Stetsovych, V; Mysliveček, J; Matolín, V

    2016-10-01

    Two model catalytic metal/oxide systems were investigated by photoelectron spectroscopy and scanning tunneling microscopy. The mixed-oxide support was a cerium tungstate epitaxial thin layer grown in situ on the W(1 1 0) single crystal. Active particles consisted of palladium and platinum 3D islands deposited on the tungstate surface at 300 K. Both metals were found to interact weakly with the oxide support and the original chemical state of both support and metals was mostly preserved. Electronic and morphological changes are discussed during the metal growth and after post-annealing at temperatures up to 700 K. Partial transition-metal coalescence and self-cleaning from the CO and carbon impurities were observed. PMID:27494195

  19. 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

    2016-03-01

    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.

  20. 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

    2016-03-01

    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. PMID:26839956

  1. 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.

  2. 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.

  3. Asymmetric Flexible Supercapacitor Stack

    PubMed Central

    2008-01-01

    Electrical double layer supercapacitor is very significant in the field of electrical energy storage which can be the solution for the current revolution in the electronic devices like mobile phones, camera flashes which needs flexible and miniaturized energy storage device with all non-aqueous components. The multiwalled carbon nanotubes (MWNTs) have been synthesized by catalytic chemical vapor deposition technique over hydrogen decrepitated Mischmetal (Mm) based AB3alloy hydride. The polymer dispersed MWNTs have been obtained by insitu polymerization and the metal oxide/MWNTs were synthesized by sol-gel method. Morphological characterizations of polymer dispersed MWNTs have been carried out using scanning electron microscopy (SEM), transmission electron microscopy (TEM and HRTEM). An assymetric double supercapacitor stack has been fabricated using polymer/MWNTs and metal oxide/MWNTs coated over flexible carbon fabric as electrodes and nafion®membrane as a solid electrolyte. Electrochemical performance of the supercapacitor stack has been investigated using cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy.

  4. 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)

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

    PubMed

    Begou, Thomas; Lemarchand, Fabien; Lumeau, Julien

    2016-09-01

    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. PMID:27607695

  6. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

    Nanosheets containing few-layers of ferroelectric Aurivillius family of oxides, Bi2An-1BnO3n+3 (where A=Bi3+, Ba2+ etc. and B=Ti4+, Fe3+ 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.

  8. Theoretical and Monte Carlo optimization of a stacked three-layer flat-panel x-ray imager for applications in multi-spectral diagnostic medical imaging

    NASA Astrophysics Data System (ADS)

    Lopez Maurino, Sebastian; Badano, Aldo; Cunningham, Ian A.; Karim, Karim S.

    2016-03-01

    We propose a new design of a stacked three-layer flat-panel x-ray detector for dual-energy (DE) imaging. Each layer consists of its own scintillator of individual thickness and an underlying thin-film-transistor-based flat-panel. Three images are obtained simultaneously in the detector during the same x-ray exposure, thereby eliminating any motion artifacts. The detector operation is two-fold: a conventional radiography image can be obtained by combining all three layers' images, while a DE subtraction image can be obtained from the front and back layers' images, where the middle layer acts as a mid-filter that helps achieve spectral separation. We proceed to optimize the detector parameters for two sample imaging tasks that could particularly benefit from this new detector by obtaining the best possible signal to noise ratio per root entrance exposure using well-established theoretical models adapted to fit our new design. These results are compared to a conventional DE temporal subtraction detector and a single-shot DE subtraction detector with a copper mid-filter, both of which underwent the same theoretical optimization. The findings are then validated using advanced Monte Carlo simulations for all optimized detector setups. Given the performance expected from initial results and the recent decrease in price for digital x-ray detectors, the simplicity of the three-layer stacked imager approach appears promising to usher in a new generation of multi-spectral digital x-ray diagnostics.

  9. Atomic Layer Deposition of Metal Oxide Thin Films on Metallic Substrates

    NASA Astrophysics Data System (ADS)

    Foroughi Abari, Ali

    Atomic layer deposition (ALD) is a powerful ultra-thin film deposition technique that uses sequential self-limiting surface reactions to provide conformal atomic scale film growth. Deposition of ALD films on many substrate systems has been studied before; however, limited data is available on deposition on metallic surfaces. The investigation of the growth of Al 2O3, HfO2, and ZrO2 as three technologically important metal oxides on metallic substrates is the subject of this thesis. Al2O3, HfO2, and ZrO2 films were grown by ALD on silicon, as a well-studied substrate, in different operating conditions to investigate the effect of process parameters on film properties. To study the growth of oxides on metals, thin metallic substrates were prepared by sputter deposition on silicon wafers and then were transferred to the ALD chamber where the film growth was monitored by in-situ spectroscopic ellipsometry. The transfer was performed via a load lock system without breaking the vacuum to preserve the pristine metal surface. Formation of a thin interfacial layer of metal oxide was observed during the initial moments of plasma enhanced ALD, that was due to the exposure of metal surface to oxygen plasma. In-situ spectroscopic ellipsometry was used to accurately measure the thickness change of the growing films including the interfacial layer. The thickness of this interfacial oxide layer depended on various process parameters including deposition temperature, order of precursors and plasma pulse length. The interfacial oxide layer was absent during the conventional thermal ALD. However, thermal ALD of oxides on metals exhibited substrate-inhibited growth, especially at higher deposition temperatures. With the knowledge of ALD growth characteristics on metals, metal-insulator-metal (MIM) devices were fabricated by both thermal and plasma enhanced ALD and electrically characterized. The presence of the interfacial oxide layer altered the device performance by changing the

  10. The evaluation of stack metal emissions from hazardous waste incinerators: assessing human exposure through noninhalation pathways.

    PubMed Central

    Sedman, R M; Polisini, J M; Esparza, J R

    1994-01-01

    Potential public health effects associated with exposure to metal emissions from hazardous waste incinerators through noninhalation pathways were evaluated. Instead of relying on modeling the movement of toxicants through various environmental media, an approach based on estimating changes from baseline levels of exposure was employed. Changes in soil and water As, Cd, Hg, Pb, Cr, and Be concentrations that result from incinerator emissions were first determined. Estimates of changes in human exposure due to direct contact with shallow soil or the ingestion of surface water were then ascertained. Projected changes in dietary intakes of metals due to incinerator emissions were estimated based on changes from baseline dietary intakes that are monitored in U.S. Food and Drug Administration total diet studies. Changes from baseline intake were deemed to be proportional to the projected changes in soil or surface water metal concentrations. Human exposure to metals emitted from nine hazardous waste incinerators were then evaluated. Metal emissions from certain facilities resulted in tangible human exposure through noninhalation pathways. However, the analysis indicated that the deposition of metals from ambient air would result in substantially greater human exposure through noninhalation pathways than the emissions from most of the facilities. PMID:7925180

  11. Impedance of a coil near an imperfectly layered metal structure: The layer approximation

    NASA Astrophysics Data System (ADS)

    Satveli, Radhika; Moulder, John C.; Wang, Bing; Rose, James H.

    1996-03-01

    Changes in the impedance of a coil next to a one-dimensional layered conductor due to three-dimensional changes in the conductivity are studied. Eddy current probes are often used to inspect layered one-dimensional, nonmagnetic metal structures whose electrical conductivity varies primarily with depth beneath the surface. We present a perturbation method, the ``layer approximation,'' which yields simple and readily evaluated formulas for changes in the impedance of a small coil due to localized three-dimensional variations in the conductivity. The layer approximation is constructed to be accurate when the conductivity change due to the defect is small or the defect is nearly one-dimensional. The impedance is calculated and reported for a variety of defects in layered metal structures: voids, inclusions, interfacial roughness, and fasteners. We test the ``robustness'' of the layer approximation using an extreme case, a flat-bottom hole in an aluminum plate, as a ``benchmark.'' Both experimental measurements and more exact theoretical calculations are reported. Impedance measurements were made with a Hewlett-Packard 4194A impedance analyzer for a right-cylindrical flat-bottom hole in a 1-mm-thick 2024 aluminum alloy plate; the hole was on the side opposite to the coil. Frequencies were varied from 2.5 to 50 kHz. We also calculated the change in the impedance for this benchmark problem using the numerically exact volume integral method. For this benchmark problem, the layer approximation is in good agreement with experiment and more exact theory.

  12. Comparative study of the synthesis of layered transition metal molybdates

    SciTech Connect

    Mitchell, S.; Gomez-Aviles, A.; Gardner, C.; Jones, W.

    2010-01-15

    Mixed metal oxides (MMOs) prepared by the mild thermal decomposition of layered double hydroxides (LDHs) differ in their reactivity on exposure to aqueous molybdate containing solutions. In this study, we investigate the reactivity of some T-Al containing MMOs (T=Co, Ni, Cu or Zn) towards the formation of layered transition metal molybdates (LTMs) possessing the general formula AT{sub 2}(OH)(MoO{sub 4}){sub 2}.H{sub 2}O, where A=NH{sub 4}{sup +}, Na{sup +} or K{sup +}. The phase selectivity of the reaction was studied with respect to the source of molybdate, the ratio of T to Mo and the reaction pH. LTMs were obtained on reaction of Cu-Al and Zn-Al containing MMOs with aqueous solutions of ammonium heptamolybdate. Rehydration of these oxides in the presence of sodium or potassium molybdate yielded a rehydrated LDH phase as the only crystalline product. The LTM products obtained by the rehydration of MMO precursors were compared with LTMs prepared by direct precipitation from the metal salts in order to study the influence of preparative route on their chemical and physical properties. Differences were noted in the composition, morphology and thermal properties of the resulting products. - Graphical abstract: Mixed metal oxides (MMOs) derived from layered double hydroxide precursors differ in their reactivity on exposure to aqueous molybdate containing solutions. We investigate the influence of the molybdate source, the rehydration pH and the ratio of T/Mo on the reactivity of some T-Al containing MMOs (T=Co, Ni, Cu or Zn) towards the formation of layered transition metal molybdates of general formula AT{sub 2}(OH)(MoO{sub 4}){sub 2}.H{sub 2}O (where A{sup +}=NH{sub 4}{sup +}, K{sup +} or Na{sup +}).

  13. Size effect and odd-even alternation in the melting of single and stacked AgSCn layers: synthesis and nanocalorimetry measurements.

    PubMed

    de la Rama, Lito P; Hu, Liang; Ye, Zichao; Efremov, Mikhail Y; Allen, Leslie H

    2013-09-25

    We report a systematic study of melting of layered lamella of silver alkanethiolates (AgSCn). A new synthesis method allows us to independently change the thickness of the crystal in two ways-by modulating chain length (n = 7-18) and by stacking these crystals to a specific layer number (m = 1-10). This method produces magic size lamella, having a well-spaced discrete melting point, Tm, distribution. Nanocalorimetry shows stepwise increases in Tm, as the lamella thickness increases by integer increments of chain length. The relationship between Tm and the inverse thickness follows the linear scaling law of Gibbs-Thomson effect. Layer stacking dramatically changes the degree and nature of size-effect melting. There is odd/even effect in stacked 2, 3, and 4 layers. Tm values of single-layer and multilayer samples do not show noticeable odd/even alternation. We develop a phenomenological model of size effect based on the cumulative excess free energy, G(excess), contributions of four spatially separate regions of the crystal: surface, Ag-S central plane, substrate interface, and interlayer interface. The selective appearance of the odd/even effect is due to the significant stabilization (1.4 kJ/mol) of interlamellae interfaces of odd-chain samples, possibly due to registration/packing. Stabilization occurs only for the mobile lamellae situated close to the free surface, and thus 2-layer samples show the highest degree of stabilization. X-ray diffraction shows that the chains are tilted 18° with respect to the basal plane normal but that the van der Waals gap is 0.3 Å smaller for crystals with odd chains.

  14. 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.

  15. 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.

  16. 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.

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

    SciTech Connect

    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.

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

    SciTech Connect

    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.

  19. Ultimate Backside Sample Preparation For Ultra Thin High-k/Metal Gate Stack Characterization

    NASA Astrophysics Data System (ADS)

    Py, M.; Veillerot, M.; Martinez, E.; Fabbri, J. M.; Boujamaa, R.; Barnes, J. P.; Bertin, F.

    2011-11-01

    Backside sample preparation is a well known method to help circumvent undesired effects and artifacts in the analysis of a sample or device structure. However it remains challenging in the case of thin layers analysis since only a fraction of the original sample must remain while removing all of the substrate and maintaining a smooth and flat surface suitable for analysis. Here we present a method adapted to the preparation of ultra thin layers grown on pure Si substrates. It consists in a mechanical polishing up to a few remaining microns, followed by a dedicated wet etch. This method can be operated in a routine fashion and yields an extremely flat and smooth surface, without any remaining Si from substrate. It therefore allows precise analysis of the layers of interests with various characterization techniques.

  20. Final Report - Subfreezing Start/Stop Protocol for an Advanced Metallic Open Flowfield Fuel Cell Stack

    SciTech Connect

    Conti, Amedeo

    2010-09-28

    For fuel cells to be commercially viable as powerplants in automotive applications, the ability to survive and start reliably in cold climates (as low as -40C) is a must. Since fuel cells are water-based energy systems, this requirement is a significant technical challenge. Water transport studies are imperative for achieving DOE targets for fuel cell startup time from subfreezing conditions. Stack components must be selected that endure thermal and humidity cycling over the operating range, and operating strategies must be devised that enable the fuel cell to start, i.e. generate power and heat up sufficiently before ice extinguishes the galvanic reactions, and afford evacuation of a sufficient amount of water, using a limited amount of auxiliary power, at shutdown. The objective of the CIRRUS program was to advance the state of the art in fuel cell operability under subfreezing conditions, consistent with requirements for applications involving such conditions (e.g. automotive, forklifts, backup power systems, and APUs) and DOE targets, specifically to: • Demonstrate repeatable achievement of 50% rated power in less than 30 seconds from a -20C start condition, using less than 5 MJ auxiliary energy over the complete start/stop cycle. • Demonstrate unassisted start capability from an initial temperature of -40C.

  1. Entropic separations of mixtures of aromatics by selective face-to-face molecular stacking in one-dimensional channels of metal-organic frameworks and zeolites.

    PubMed

    Torres-Knoop, Ariana; Balestra, Salvador R G; Krishna, Rajamani; Calero, Sofía; Dubbeldam, David

    2015-02-23

    Separation of challenging mixtures using metal-organic frameworks can be achieved by an entropy-driven mechanism, where one of the components can arrange into a "face-to-face" stacking, thus reducing its "footprint" and reaching a higher saturation loading.

  2. [Trace analysis of heavy metal ions in electroplate waste water by capillary electrophoresis with visual offline sample stacking via moving neutralization boundary].

    PubMed

    Fan, Yinping; Li, Shan; Fan, Liuyin; Cao, Chengxi

    2012-08-01

    A moving neutralization boundary (MNB) was developed as a novel model of visual offline sample stacking for the trace analysis of heavy metal ions (HMIs) by capillary zone electrophoresis (CZE). In the stacking system, the motion direction of MNB to cathode was used with 2.1 mmol/L HCl-98 mmol/L KCl-trace metal ions in the anodic solution and 4.0 mmol/L NaOH-96 mmol/L KCl in the cathodic solution. The voltage was constant at 180 V and the flow rate of the anolyte and catholyte was 1 mL/min. The metal ions in the gel after stacking were detected by capillary electrophoresis. The calibration curves showed good linear relationship (r > or = 0.998 5) in the concentration range used in the experiments. The pre-concentration factors were up to 80 - 150 and the limits of detection (LODs) were 0.163, 0.256, 0.077, 0.153, 0.203, 0.062 and 0.142 mg/L for Cu(II), Zn(II), Ni(II), Mg(II), Ca(II), Cr(III) and Fe(III), respectively, obviously lower than the national standards. The intra-day and inter-day assay precisions were good (the relative standard deviations (RSDs) less than 7.42%). Finally, the developed method has been successfully used for the stacking and the detection of heavy metal ions in electroplate waste water.

  3. Self-Limiting Layer Synthesis of Transition Metal Dichalcogenides.

    PubMed

    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 10(8). 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

  4. 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

  5. Adsorption of metal adatoms on single-layer phosphorene.

    PubMed

    Kulish, Vadym V; Malyi, Oleksandr I; Persson, Clas; Wu, Ping

    2015-01-14

    Single- or few-layer phosphorene is a novel two-dimensional direct-bandgap nanomaterial. Based on first-principles calculations, we present a systematic study on the binding energy, geometry, magnetic moment and electronic structure of 20 different adatoms adsorbed on phosphorene. The adatoms cover a wide range of valences, including s and p valence metals, 3d transition metals, noble metals, semiconductors, hydrogen and oxygen. We find that adsorbed adatoms produce a rich diversity of structural, electronic and magnetic properties. Our work demonstrates that phosphorene forms strong bonds with all studied adatoms while still preserving its structural integrity. The adsorption energies of adatoms on phosphorene are more than twice higher than on graphene, while the largest distortions of phosphorene are only ∼0.1-0.2 Å. The charge carrier type in phosphorene can be widely tuned by adatom adsorption. The unique combination of high reactivity with good structural stability is very promising for potential applications of phosphorene.

  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. Non-destructive observation of in-grown stacking faults in 4H-SiC epitaxial layer using mirror electron microscope

    SciTech Connect

    Hasegawa, Masaki; Ohno, Toshiyuki

    2011-10-01

    Mirror electron microscope (MEM) observation has been conducted for a 4-{mu}m-thick n-doped 4H-SiC epitaxial layer. If the sample is simultaneously illuminated with ultraviolet (UV) light of a slightly greater energy than the bandgap energy of 4H-SiC, in-grown stacking faults (IGSFs) can be clearly observed in MEM images. These observations were performed non-destructively, as almost all irradiated electrons returned without impinging the sample surface due to the negative voltage applied to the sample. High spatial resolution observation via MEM showed that multiple IGSFs were stacked up. The phenomenon in which the contrast of the IGSFs vanished in the absence of UV illumination and under UV illumination with a lower energy than the bandgap energy revealed that the origin of the contrast was the negative charging of IGSFs trapping electrons excited by UV light.

  8. Layer Stack Design of High Density Read-Only-Memory Discs for Near-Field Systems using a Solid Immersion Lens

    NASA Astrophysics Data System (ADS)

    Kitano, Kazutoshi; Yamaguchi, Atsushi; Miura, Masahiro; Horikawa, Kunihiko; Tagiri, Takao; Muramatsu, Eiji; Taniguchi, Shoji; Yokogawa, Fumihiko

    2009-03-01

    For high numerical aperture (NA) near-field systems using a solid immersion lens, layer stack types of first-surface read-only-memory (ROM) discs have been investigated. Complicated interactions of high-NA incident and diffracted waves with surface waves occur in multilayer-stacked subwavelength structures on the discs. Therefore, vector diffraction simulation in consideration of these effects is indispensable for the optimization of the disc structures. We used rigorous coupled wave analysis to numerically calculate readout signals from the discs. On the basis of the simulation results, we actually fabricated high-density ROM media. Consequently, a significantly low jitter of 6.8% was obtained for 100 Gbyte ROM media with a designed structure in an NA 2.0 system.

  9. 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.

  10. 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.

  11. Protein Induces Layer-by-Layer Exfoliation of Transition Metal Dichalcogenides.

    PubMed

    Guan, Guijian; Zhang, Shuangyuan; Liu, Shuhua; Cai, Yongqing; Low, Michelle; Teng, Choon Peng; Phang, In Yee; Cheng, Yuan; Duei, Koh Leng; Srinivasan, Bharathi Madurai; Zheng, Yuangang; Zhang, Yong-Wei; Han, Ming-Yong

    2015-05-20

    Here, we report a general and facile method for effective layer-by-layer exfoliation of transition metal dichalcogenides (TMDs) and graphite in water by using protein, bovine serum albumin (BSA) to produce single-layer nanosheets, which cannot be achieved using other commonly used bio- and synthetic polymers. Besides serving as an effective exfoliating agent, BSA can also function as a strong stabilizing agent against reaggregation of single-layer nanosheets for greatly improving their biocompatibility in biomedical applications. With significantly increased surface area, single-layer MoS2 nanosheets also exhibit a much higher binding capacity to pesticides and a much larger specific capacitance. The protein exfoliation process is carefully investigated with various control experiments and density functional theory simulations. It is interesting to find that the nonpolar groups of protein can firmly bind to TMD layers or graphene to expose polar groups in water, facilitating the effective exfoliation of single-layer nanosheets in aqueous solution. The present work will enable to optimize the fabrication of various 2D materials at high yield and large scale, and bring more opportunities to investigate the unique properties of 2D materials and exploit their novel applications. PMID:25936424

  12. 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.

  13. Epitaxial ZnO/LiNbO3/ZnO stacked layer waveguide for application to thin-film Pockels sensors

    NASA Astrophysics Data System (ADS)

    Akazawa, Housei; Fukuda, Hiroshi

    2015-05-01

    We produced slab waveguides consisting of a LiNbO3 (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 r33 = 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.

  14. Stacking Principle and Magic Sizes of Transition Metal Nanoclusters Based on Generalized Wulff Construction

    NASA Astrophysics Data System (ADS)

    Li, S. F.; Zhao, X. J.; Xu, X. S.; Gao, Y. F.; Zhang, Zhenyu

    2013-09-01

    Nanoclusters with extra stability at certain cluster sizes are known as magic clusters with exotic properties. The classic Wulff construction principle, which stipulates that the preferred structure of a cluster should minimize its total surface energy, is often invoked in determining the cluster magicity, resulting in close-shelled Mackay icosahedronal clusters with odd-numbered magic sizes of 13, 55, 147, etc. Here we use transition metal clusters around size 55 as prototypical examples to demonstrate that, in the nanometer regime, the classic Wulff construction principle needs to be generalized to primarily emphasize the edge atom effect instead of the surface energy. Specifically, our detailed calculations show that nanoclusters with much shorter total edge lengths but substantially enlarged total surface areas are energetically much more stable. As a consequence, a large majority of the nanoclusters within the 3d-, 4d-, and 5d-transition metal series are found to be fcc or hcp crystal fragments with much lower edge energies, and the widely perceived magic size of 55 is shifted to its nearby even numbers.

  15. Stacking principle and magic sizes of transition metal nanoclusters based on generalized Wulff construction.

    PubMed

    Li, S F; Zhao, X J; Xu, X S; Gao, Y F; Zhang, Zhenyu

    2013-09-13

    Nanoclusters with extra stability at certain cluster sizes are known as magic clusters with exotic properties. The classic Wulff construction principle, which stipulates that the preferred structure of a cluster should minimize its total surface energy, is often invoked in determining the cluster magicity, resulting in close-shelled Mackay icosahedronal clusters with odd-numbered magic sizes of 13, 55, 147, etc. Here we use transition metal clusters around size 55 as prototypical examples to demonstrate that, in the nanometer regime, the classic Wulff construction principle needs to be generalized to primarily emphasize the edge atom effect instead of the surface energy. Specifically, our detailed calculations show that nanoclusters with much shorter total edge lengths but substantially enlarged total surface areas are energetically much more stable. As a consequence, a large majority of the nanoclusters within the 3d-, 4d-, and 5d-transition metal series are found to be fcc or hcp crystal fragments with much lower edge energies, and the widely perceived magic size of 55 is shifted to its nearby even numbers.

  16. Polarized thermal radiation by layer-by-layer metallic emitters with sub-wavelength grating.

    PubMed

    Lee, Jae-Hwang; Leung, Wai; Kim, Tae Guen; Constant, Kristen; Ho, Kai-Ming

    2008-06-01

    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 mum, as well as high emissivity up to 0.65 at a wavelength of 3.7 microm. 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. PMID:18545587

  17. 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.

  18. The effect of stabilizer on the trapped field of stacks of superconducting tape magnetized by a pulsed field

    NASA Astrophysics Data System (ADS)

    Page, A. G.; Patel, A.; Baskys, A.; Hopkins, S. C.; Kalitka, V.; Molodyk, A.; Glowacki, B. A.

    2015-08-01

    Stacks of high temperature superconducting tape, magnetized using pulsed fields, provide a new type of permanent magnet using superconductors. To optimize the trapped field in such stacks, the role of stabilization layers was investigated by pulse magnetizing a 12 mm square stack of 15 tape layers over a temperature range of 15-77 K. The stacks consisted of commercial tape with a silver stabilizer of 1-3 μm or tape with an additional 20 μm layer of copper on top of 1 μm of silver. It was found that the trapped field and flux are relatively insensitive to the stabilizer thickness, and 1 μm of silver only, led to the highest trapped field. An FEM model was also developed for a stack that considered for the first time both the actual thickness of metallic and superconducting layers, to investigate the effect of heating and heat transfer when a stack of tapes is magnetized.

  19. Dynamic Control of Optical Response in Layered Metal Chalcogenide Nanoplates.

    PubMed

    Liu, Yanping; Tom, Kyle; Wang, Xi; Huang, Chunming; Yuan, Hongtao; Ding, Hong; Ko, Changhyun; Suh, Joonki; Pan, Lawrence; Persson, Kristin A; Yao, Jie

    2016-01-13

    Tunable optical transitions in ultrathin layered 2-dimensional (2D) materials unveil the electronic structures of materials and provide exciting prospects for potential applications in optics and photonics. Here, we present our realization of dynamic optical modulation of layered metal chalcogenide nanoplates using ionic liquid (IL) gating over a wide spectral range. The IL gating significantly increased the tuning range of the Fermi level and, as a result, substantially altered the optical transitions in the nanoplates. Using heavily n-doped Bi2Se3 nanoplates, we substantially modulated the light transmission through the ultrathin layer. A tunable, high-transmission spectral window in the visible to near-infrared region has been observed due to simultaneous shifts of both the plasma edge and absorption edge of the material. On the other hand, optical response of multilayer MoSe2 flakes gated by IL has shown enhanced transmission in both positive and negative biases, which is consistent with their ambipolar electrical behavior. The electrically controlled optical property tuning in metal chalcogenide material systems provides new opportunities for potential applications, such as wide spectral range optical modulators, optical filters, and electrically controlled smart windows with extremely low material consumption.

  20. Dynamic Control of Optical Response in Layered Metal Chalcogenide Nanoplates.

    PubMed

    Liu, Yanping; Tom, Kyle; Wang, Xi; Huang, Chunming; Yuan, Hongtao; Ding, Hong; Ko, Changhyun; Suh, Joonki; Pan, Lawrence; Persson, Kristin A; Yao, Jie

    2016-01-13

    Tunable optical transitions in ultrathin layered 2-dimensional (2D) materials unveil the electronic structures of materials and provide exciting prospects for potential applications in optics and photonics. Here, we present our realization of dynamic optical modulation of layered metal chalcogenide nanoplates using ionic liquid (IL) gating over a wide spectral range. The IL gating significantly increased the tuning range of the Fermi level and, as a result, substantially altered the optical transitions in the nanoplates. Using heavily n-doped Bi2Se3 nanoplates, we substantially modulated the light transmission through the ultrathin layer. A tunable, high-transmission spectral window in the visible to near-infrared region has been observed due to simultaneous shifts of both the plasma edge and absorption edge of the material. On the other hand, optical response of multilayer MoSe2 flakes gated by IL has shown enhanced transmission in both positive and negative biases, which is consistent with their ambipolar electrical behavior. The electrically controlled optical property tuning in metal chalcogenide material systems provides new opportunities for potential applications, such as wide spectral range optical modulators, optical filters, and electrically controlled smart windows with extremely low material consumption. PMID:26599063

  1. 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.

  2. Nucleation and Early Stages of Layer-by-Layer Growth of Metal Organic Frameworks on Surfaces

    PubMed Central

    2015-01-01

    High resolution atomic force microscopy (AFM) is used to resolve the evolution of crystallites of a metal organic framework (HKUST-1) grown on Au(111) using a liquid-phase layer-by-layer methodology. The nucleation and faceting of individual crystallites is followed by repeatedly imaging the same submicron region after each cycle of growth and we find that the growing surface is terminated by {111} facets leading to the formation of pyramidal nanostructures for [100] oriented crystallites, and triangular [111] islands with typical lateral dimensions of tens of nanometres. AFM images reveal that crystallites can grow by 5–10 layers in each cycle. The growth rate depends on crystallographic orientation and the morphology of the gold substrate, and we demonstrate that under these conditions the growth is nanocrystalline with a morphology determined by the minimum energy surface. PMID:26709359

  3. 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.

  4. A tong-like fluorescence sensor for metal ions: perfect conformational switch of hinge sugar by pyrene stacking.

    PubMed

    Yuasa, Hideya; Miyagawa, Naofusa; Nakatani, Masatoshi; Izumi, Masayuki; Hashimoto, Hironobu

    2004-12-21

    Carbohydrates are among the potential materials for molecular devices, since they are abundant natural resources. However, their rigidity has restricted their use for movable devices. Hinge sugars, 2,4-diamino-2,4-dideoxy-xylopyranosides, shed light on the use of carbohydrates as movable components, as demonstrated by the motion by which all four equatorial substituents can change to an axial orientation in synchronization with a chelation-driven 4C1-1C4 ring flip. In this study, we synthesized a tong-like metal ion sensor, 1,3-di-O-pyrenylmethylated hinge sugar (1), and its model compound, methyl 2,4-di-O-pyrenecarbonyl-xylopyranoside (2), to extend the abilities of hinge sugars as molecular components. From observations of the solvent-dependent conformational and fluorescent behavior of 2, we found that the pyrene stacking assists the 1C4 formation of xylopyranoside by 1.7 kcal mol(-1). We also found that compound 1 produced excimer fluorescence by chelation to Pt2+, Zn2+, Cd2+, Mg2+ or Mn2+, and unexpectedly by addition of acids. 1H NMR measurements ascribed this behavior to the 4C1-1C4 ring flip of hinge sugar in response to chelation or protonation at N2, and revealed rapid and perfect 1C4 formation in the case of Zn2+. These findings will extend the scope of hinge sugars as movable components.

  5. Heavy metal sorption in the lichen cationactive layer.

    PubMed

    Andrzej, Kłos; Małgorzata, Rajfur; Maria, Wacławek; Witold, Wacławek

    2007-09-01

    Results of copper ion sorption in lichens owing to the ion exchange between the surroundings (aqueous solution) and the lichen cationactive layer have been presented. It indicates that the course of sorption of these ions, similarly as in the case of cations of other heavy metals, depends on the concentration and type of cations naturally found in lichen surroundings: H+, Na+, K+, Mg2+ and Ca2+. A determination method of heavy metal concentration in lichen surroundings has been proposed. It consists in exposure of transplanted lichens in the presence of salts that provide precisely determined, artificial salinity of precipitation with which the lichens are in contact. The studies were conducted on Hypogymnia physodes lichens.

  6. Spin and pseudospins in layered transition metal dichalcogenides

    SciTech Connect

    Xu, Xiaodong; Yao, Wang; Xiao, Di; Heinz, Tony F.

    2014-01-01

    The recent emergence of two-dimensional layered materials in particular the transition metal dichalcogenides provides a new laboratory for exploring the internal quantum degrees of freedom of electrons and their potential for new electronics. These degrees of freedom are the real electron spin, the layer pseudospin, and the valley pseudospin. New methods for the quantum control of the spin and these pseudospins arise from the existence of Berry phase-related physical properties and strong spin orbit coupling. The former leads to the versatile control of the valley pseudospin, whereas the latter gives rise to an interplay between the spin and the pseudospins. Here, we provide a brief review of both theoretical and experimental advances in this field.

  7. Low Temperature Deposition of High-k/Metal Gate Stacks on High-Sn Content (Si)GeSn-Alloys.

    PubMed

    Schulte-Braucks, C; von den Driesch, N; Glass, S; Tiedemann, A T; Breuer, U; Besmehn, A; Hartmann, J-M; Ikonic, Z; Zhao, Q T; Mantl, S; Buca, D

    2016-05-25

    (Si)GeSn is an emerging group IV alloy system offering new exciting properties, with great potential for low power electronics due to the fundamental direct band gap and prospects as high mobility material. In this Article, we present a systematic study of HfO2/TaN high-k/metal gate stacks on (Si)GeSn ternary alloys and low temperature processes for large scale integration of Sn based alloys. Our investigations indicate that SiGeSn ternaries show enhanced thermal stability compared to GeSn binaries, allowing the use of the existing Si technology. Despite the multielemental interface and large Sn content of up to 14 atom %, the HfO2/(Si)GeSn capacitors show small frequency dispersion and stretch-out. The formed TaN/HfO2/(Si)GeSn capacitors present a low leakage current of 2 × 10(-8) A/cm(2) at -1 V and a high breakdown field of ∼8 MV/cm. For large Sn content SiGeSn/GeSn direct band gap heterostructures, process temperatures below 350 °C are required for integration. We developed an atomic vapor deposition process for TaN metal gate on HfO2 high-k dielectric and validated it by resistivity as well as temperature and frequency dependent capacitance-voltage measurements of capacitors on SiGeSn and GeSn. The densities of interface traps are deduced to be in the low 10(12) cm(-2) eV(-1) range and do not depend on the Sn-concentration. The new processes developed here are compatible with (Si)GeSn integration in large scale applications. PMID:27149260

  8. Polyheteroaromatic layers on commodity metals (CIPL)-passivation, corrosion protection

    SciTech Connect

    Beck, F.; Haase, V.; Schroetz, M.

    1996-01-01

    Filmforming anodic polymerizations of pyrrole, thiophene or aniline and their derivatives on commodity metals, predominantly iron, are possible only in a few solvent/electrolyte systems. Even then, these processes compete with the anodic dissolution of the metal in the course of the initial active/passive transition. The influence of current densities, (co)solvent molecules and monomers is studied by chronopotentiometry. Corrosion protection capability is characterized analytically and by electrochemical impedance spectroscopy (EIS) in aerated acetate buffered 0.1 M NaCl. Samples with 1{endash}100 nm nominal coating thickness (d{sub n}) do not differ very much from the nontreated iron. The prevalence of a metal/metal oxide formation/dissolution process at the beginning is concluded therefrom. Adsorption of the monomers alone has no effect as well, however. This is attributed to a (partial) oxide coverage at pH 4.7 and a low degree of coverage for the molecules. Remarkable corrosion protection is only detectable in some cases at a nominal thickness d{sub n}{approx_equal}1 {mu}m, where dark and well adhering polymer layers are observed. This seems mainly due to a barrier action effect, cf. {section} 9. Inhibition of electrochemical partial processes linked to the corrosion itself does not seem to play a role. The realization of the corrosion inhibiting polymer layer (CIPL) strategy seems to be possible only through prepassivation or dip coating by prefabricated polymer solutions. This means an additional step in both cases. {copyright} {ital 1996 American Institute of Physics.}

  9. Electrical and Mechanical Properties of Through-Silicon Vias and Bonding Layers in Stacked Wafers for 3D Integrated Circuits

    NASA Astrophysics Data System (ADS)

    Hwang, Sung-Hwan; Kim, Byoung-Joon; Lee, Ho-Young; Joo, Young-Chang

    2012-02-01

    Thermal stress issues in a three-dimensional (3D) stacked wafer system were examined using finite-element analysis of the stacked wafers. This paper elucidates the effects of the bonding dimensions on mechanical failure and the keep-away zone, where devices cannot be located because of the stress in the Si. The key factors in decreasing the thermal strain were the bonding diameter and thickness. When the bonding diameter decreased from 40 μm to 12 μm, the equivalent strain decreased by 83%. It is noteworthy that the keep-away zone also decreased from 17 μm to zero when the bonding diameter decreased from 40 μm to 12 μm. When the bonding thickness doubled, the equivalent strain decreased by 44%. The effects of the dimensions and arrangement of through-silicon vias (TSV) were also analyzed. Small TSV diameter and pitch are important to decrease the equivalent strain, especially when the amount of Cu per unit volume is fixed. When the TSV diameter and pitch decreased fourfold, the equivalent strain decreased by 70%. The effects of TSV height and the number of die stacks were not significant, because the underfill acted as a buffer against thermal strain.

  10. Quantum chemical simulations of atomic layer deposition of metal oxides and metal nitrides

    NASA Astrophysics Data System (ADS)

    Xu, Ye

    Scaling of SiO2 gate dielectrics to extend the miniaturization of complementary metal oxide semiconductor (CMOS) devices in accordance with Moore's Law has resulted in unacceptable tunneling current leakage levels. The projection that this challenge could significantly limit CMOS performance has prompted the intense search for alternative gate dielectric materials that can achieve high capacitances with physically thicker films which minimize tunneling leakage current. Atomic layer deposition is an ideal deposition method for high-k films because it controls the film thickness with atomic layer precision and can achieve high film conformality and uniformity. We use density functional theory (DFT) to explore chemical reactions involved in ALD processes at the atomic level. We have investigated different metal precursors for ALD process. Compared to halides, metal alkylamides are more favorable on nitrided silicon surfaces and subsequent film growth. Likewise, hafnium alkylamide is more favorable than water to initiate the nucleation on hydrogen terminated silicon surfaces. For deposition on organic self-assembled monolayers, different end groups significantly affect the selectivity towards ALD reactions. The chemical mechanisms involved in ALD of hafnium nitride, aluminum nitride are developed which provide an understanding to the difficulty in producing oxygen free metal nitrides by ALD. By combining ALD of metal oxide and metal nitride, a new method for incorporating nitrogen into oxide films is proposed. In TMA and ozone reaction, it's found that by-product water can be a catalyzer for this reaction.

  11. Template-Free 3D Microprinting of Metals Using a Force-Controlled Nanopipette for Layer-by-Layer Electrodeposition.

    PubMed

    Hirt, Luca; Ihle, Stephan; Pan, Zhijian; Dorwling-Carter, Livie; Reiser, Alain; Wheeler, Jeffrey M; Spolenak, Ralph; Vörös, János; Zambelli, Tomaso

    2016-03-23

    A novel 3D printing method for voxel-by-voxel metal printing is presented. Hollow atomic force microscopy (AFM) cantilevers are used to locally supply metal ions in an electrochemical cell, enabling a localized electroplating reaction. By exploiting the deflection feedback of these probes, electrochemical 3D metal printing is, for the first time, demonstrated in a layer-by-layer fashion, enabling the fabrication of arbitrary-shaped geometries.

  12. Template-Free 3D Microprinting of Metals Using a Force-Controlled Nanopipette for Layer-by-Layer Electrodeposition.

    PubMed

    Hirt, Luca; Ihle, Stephan; Pan, Zhijian; Dorwling-Carter, Livie; Reiser, Alain; Wheeler, Jeffrey M; Spolenak, Ralph; Vörös, János; Zambelli, Tomaso

    2016-03-23

    A novel 3D printing method for voxel-by-voxel metal printing is presented. Hollow atomic force microscopy (AFM) cantilevers are used to locally supply metal ions in an electrochemical cell, enabling a localized electroplating reaction. By exploiting the deflection feedback of these probes, electrochemical 3D metal printing is, for the first time, demonstrated in a layer-by-layer fashion, enabling the fabrication of arbitrary-shaped geometries. PMID:26783090

  13. 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.

  14. Stacked optical antennas

    NASA Astrophysics Data System (ADS)

    Pohl, Dieter W.; Rodrigo, Sergio G.; Novotny, Lukas

    2011-01-01

    We propose and analyze a stacked optical antenna (SOA). It is characterized by a stacked structure of its arms at the center, and an interstitial gap layer (IGL) in between, which plays the role of the feed gap. Because of its in-plane arrangement, the IGL can be fabricated by standard planar deposition techniques providing high accuracy and control. A SOA can be an enabling element for several technologies, in particular for optical detection, communication, and encryption besides applications in microscopy.

  15. 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

  16. 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

  17. 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.

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

    NASA Astrophysics Data System (ADS)

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

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

  19. Reversible transition between bipolar and unipolar resistive switching in Cu2O/Ga2O3 binary oxide stacked layer

    NASA Astrophysics Data System (ADS)

    Zhi, Y. S.; Li, P. G.; Wang, P. C.; Guo, D. Y.; An, Y. H.; Wu, Z. P.; Chu, X. L.; Shen, J. Q.; Tang, W. H.; Li, C. R.

    2016-01-01

    Both unipolar resistive switching (URS) and bipolar resistive switching (BRS) behaviors are observed in Cu2O/Ga2O3 stacked layer. The conversion between BRS and URS is controllable and reversible. The switching operations in BRS mode requires smaller voltage than that in the URS mode. The oxygen vacancies closed to the Cu2O/Ga2O3 interface contributes to the BRS, and the bias-controlling filament formation/rupture in depletion layer is considered to contribute to the URS. The URS happens only in the negative voltage part due to the nature of directionality of the p-n junction. The process reported here can be developed to design memory device.

  20. Preparation and characterization of the heterojunction of CuInSe2/CdS thin films prepared by stacked elemental layer technique

    NASA Astrophysics Data System (ADS)

    Sharma, Mahesh C.; Vashistha, Indu B.; Vijay, Y. K.

    2013-06-01

    In the present paper, we reported heterojunction of CuInSe2/CdS thin films prepared by stacking elemental layers (SEL) technique in a vacuum 2×10-5 Torr. The as-grown CuInSe2/CdS thin films have been annealed at 300 °C in air for heating time 1h for improving the interface and crystallinity of the heterojunction. As-grown and annealed heterojunction of CuInSe2/CdS thin films have been characterized for compositional, morphological and electrical properties by energy dispersive X-ray (EDAX) analysis, scanning electron microscopy (SEM) and I-V response respectively. The presence of observed and expected elements in the EDAX spectra confirms the elemental compositions in CuInSe2/CdS thin films. Surface morphology of as-grown stacked layers and annealed thin films have been confirmed by SEM images. The dark I-V characteristics show that a recombination mechanism controls the transport of charge carriers across the junction. On illumination, appreciable changes in the I-V characteristics and photovoltaic effects have been observed. The enhancement in solar energy conversion efficiency has been observed a value of about 0.68% after annealing.

  1. 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.

  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. Metal-phthalocyanine ordered layers on Au(110): Metal-dependent adsorption energy

    SciTech Connect

    Massimi, Lorenzo Angelucci, Marco; Gargiani, Pierluigi; Betti, Maria Grazia; Montoro, Silvia; Mariani, Carlo

    2014-06-28

    Iron-phthalocyanine and cobalt-phthalocyanine chains, assembled along the Au(110)-(1×2) reconstructed channels, present a strong interaction with the Au metallic states, via the central metal ion. X-ray photoemission spectroscopy from the metal-2p core-levels and valence band high-resolution ultraviolet photoelectron spectroscopy bring to light signatures of the interaction of the metal-phthalocyanine single-layer with gold. The charge transfer from Au to the molecule causes the emerging of a metal-2p core level component at lower binding energy with respect to that measured in the molecular thin films, while the core-levels associated to the organic macrocycle (C and N 1s) are less influenced by the adsorption, and the macrocycles stabilize the interaction, inducing a strong interface dipole. Temperature Programmed Desorption experiments and photoemission as a function of temperature allow to estimate the adsorption energy for the thin-films, mainly due to the molecule-molecule van der Waals interaction, while the FePc and CoPc single-layers remain adsorbed on the Au surface up to at least 820 K.

  4. Layering effects on low frequency modes in n-layered MX2 transition metal dichalcogenides.

    PubMed

    Cammarata, Antonio; Polcar, Tomas

    2016-02-14

    n-Layered (n = 2, 3, 4) MX2 transition metal dichalcogenides (M = Mo, W; X = S, Se, Te) have been studied using DFT techniques. Long-range van der Waals forces have been modeled using the Grimme correction to capture interlayer interactions. We study the dynamic and electronic dependence of atomic displacement on the number of layers. We find that the displacement patterns mainly affected by a change in the layer number are low-frequency modes at Γ and A k-points; such modes are connected with the intrinsic tribological response. We disentangle electro-phonon coupling by combining orbital polarization, covalency and cophonicity analysis with phonon band calculations. We find that the frequency dependence on the number of layers and the atomic type has a non-trivial relation with the electronic charge distribution in the interlayer region. We show that the interlayer electronic density can be adjusted by appropriately tuning M-X cophonicity, acting as a knob to control vibrational frequencies, hence the intrinsic frictional response. The present results can be exploited to study the electro-phonon coupling effects in TMD-based materials beyond tribological applications. PMID:26806673

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

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

    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 ( D λ*) 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 D 254* to D 546* 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.

  6. 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.

    2016-08-01

    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.

  7. 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.

  8. 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

  9. Metal-doped graphene layers composed with boron nitride-graphene as an insulator: a nano-capacitor.

    PubMed

    Monajjemi, Majid

    2014-11-01

    A model of a nanoscale dielectric capacitor composed of a few dopants has been investigated in this study. This capacitor includes metallic graphene layers which are separated by an insulating medium containing a few h-BN layers. It has been observed that the elements from group IIIA of the periodic table are more suitable as dopants for hetero-structures of the {metallic graphene/hBN/metallic graphene} capacitors compared to those from groups IA or IIA. In this study, we have specifically focused on the dielectric properties of different graphene/h-BN/graphene including their hetero-structure counterparts, i.e., Boron-graphene/h-BN/Boron-graphene, Al-graphene/h-BN/Al-graphene, Mg-graphene/h-BN/Mg-graphene, and Be-graphene/h-BN/Be-graphene stacks for monolayer form of dielectrics. Moreover, we studied the multi dielectric properties of different (h-BN)n/graphene hetero-structures of Boron-graphene/(h-BN)n/Boron-graphene. PMID:25359456

  10. Electron-electron scattering-induced channel hot electron injection in nanoscale n-channel metal-oxide-semiconductor field-effect-transistors with high-k/metal gate stacks

    SciTech Connect

    Tsai, Jyun-Yu; Liu, Kuan-Ju; Lu, Ying-Hsin; Liu, Xi-Wen; Chang, Ting-Chang; Chen, Ching-En; Ho, Szu-Han; Tseng, Tseung-Yuen; Cheng, Osbert; Huang, Cheng-Tung; Lu, Ching-Sen

    2014-10-06

    This work investigates electron-electron scattering (EES)-induced channel hot electron (CHE) injection in nanoscale n-channel metal-oxide-semiconductor field-effect-transistors (n-MOSFETs) with high-k/metal gate stacks. Many groups have proposed new models (i.e., single-particle and multiple-particle process) to well explain the hot carrier degradation in nanoscale devices and all mechanisms focused on Si-H bond dissociation at the Si/SiO{sub 2} interface. However, for high-k dielectric devices, experiment results show that the channel hot carrier trapping in the pre-existing high-k bulk defects is the main degradation mechanism. Therefore, we propose a model of EES-induced CHE injection to illustrate the trapping-dominant mechanism in nanoscale n-MOSFETs with high-k/metal gate stacks.

  11. 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.

  12. 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.

  13. 12-Metal 36-membered ring based W(V)-Co(II) layers showing spin-glass behavior.

    PubMed

    Zhao, Liang; Duan, Ran; Zhuang, Peng-Fei; Zheng, Hui; Jiao, Cheng-Qi; Wang, Jun-Li; He, Cheng; Liu, Tao

    2015-07-28

    The present study describes the designed synthesis, X-ray structures, and magnetic properties of two 2D cyano bridged heterobimetallic W(V)-Co(II) networks, {[W(CN)8]2[Co(phpy)4]3}·2CH3OH·2H2O (1) and {[W(CN)8]2[Co(4-spy)4]3}·6H2O (2) (phpy = 4-phenylpyridine, 4-spy = 4-styrylpyridine). Both compounds consist of cyano-bridged 12-metal 36-membered ring units, Co6W6(CN)12, joined by organic linkers into a 2D plane. The layer presents a corrugated configuration in compound 1 and a plane configuration in compound 2 due to different π-π stacking interactions. Magnetic measurements reveal that both 1 and 2 have a transition to the spin glass-like phase due to competitive magnetic interactions. PMID:26076432

  14. 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.

  15. Metallic few-layered VS2 ultrathin nanosheets: high two-dimensional conductivity for in-plane supercapacitors.

    PubMed

    Feng, Jun; Sun, Xu; Wu, Changzheng; Peng, Lele; Lin, Chenwen; Hu, Shuanglin; Yang, Jinlong; Xie, Yi

    2011-11-01

    With the rapid development of portable electronics, such as e-paper and other flexible devices, practical power sources with ultrathin geometries become an important prerequisite, in which supercapacitors with in-plane configurations are recently emerging as a favorable and competitive candidate. As is known, electrode materials with two-dimensional (2D) permeable channels, high-conductivity structural scaffolds, and high specific surface areas are the indispensible requirements for the development of in-plane supercapacitors with superior performance, while it is difficult for the presently available inorganic materials to make the best in all aspects. In this sense, vanadium disulfide (VS(2)) presents an ideal material platform due to its synergic properties of metallic nature and exfoliative characteristic brought by the conducting S-V-S layers stacked up by weak van der Waals interlayer interactions, offering great potential as high-performance in-plane supercapacitor electrodes. Herein, we developed a unique ammonia-assisted strategy to exfoliate bulk VS(2) flakes into ultrathin VS(2) nanosheets stacked with less than five S-V-S single layers, representing a brand new two-dimensional material having metallic behavior aside from graphene. Moreover, highly conductive VS(2) thin films were successfully assembled for constructing the electrodes of in-plane supercapacitors. As is expected, a specific capacitance of 4760 μF/cm(2) was realized here in a 150 nm in-plane configuration, of which no obvious degradation was observed even after 1000 charge/discharge cycles, offering as a new in-plane supercapacitor with high performance based on quasi-two-dimensional materials.

  16. Indium-gallium-zinc-oxide layer used to increase light transmittance efficiency of adhesive layer for stacked-type multijunction solar cells

    NASA Astrophysics Data System (ADS)

    Yoshidomi, Shinya; Kimura, Shunsuke; Hasumi, Masahiko; Sameshima, Toshiyuki

    2015-11-01

    We report the increase in transmittance efficiency of the intermediate layer for multijunction solar cells caused by the indium-gallium-zinc-oxide (IGZO) layer used as the antireflection layer. Si substrates coated with a 200-nm-thick IGZO layer with a refractive index of 1.85 were prepared. The resistivity of the IGZO layer was increased from 0.0069 (as-deposited) to 0.032 Ω cm by heat treatment at 350 °C for 1 h to prevent free-carrier optical absorption. Samples with the Si/IGZO/adhesive/IGZO/Si structure were fabricated. The average transmissivity for wavelengths between 1200 and 1600 nm was 49%, which was close to 55% of single-crystal silicon substrates. A high effective transmittance efficiency of 89% was experimentally achieved. The numerical calculation showed in an effective transmittance efficiency of 99% for 170-nm-thick antireflection layers with a resistivity of 0.6 Ω cm and a refractive index of 2.1.

  17. 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

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

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

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

  19. 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.

  20. Liquid exfoliation of alkyl-ether functionalised layered metal-organic frameworks to nanosheets.

    PubMed

    Foster, Jonathan A; Henke, Sebastian; Schneemann, Andreas; Fischer, Roland A; Cheetham, Anthony K

    2016-08-18

    We report the synthesis of a 2D-layered metal-organic framework incorporating weakly interacting chains designed to aid exfoliation of the layers into nanosheets. Dispersion of the nanosheets exposes labile metal-sites which are shown to exchange solvent molecules allowing the nanosheets to act as sensors in suspension.

  1. Liquid exfoliation of alkyl-ether functionalised layered metal-organic frameworks to nanosheets.

    PubMed

    Foster, Jonathan A; Henke, Sebastian; Schneemann, Andreas; Fischer, Roland A; Cheetham, Anthony K

    2016-08-18

    We report the synthesis of a 2D-layered metal-organic framework incorporating weakly interacting chains designed to aid exfoliation of the layers into nanosheets. Dispersion of the nanosheets exposes labile metal-sites which are shown to exchange solvent molecules allowing the nanosheets to act as sensors in suspension. PMID:27452790

  2. Synthesis Single Layer Transition Metal Dichalcogenides with Chemical Vapor Deposition

    NASA Astrophysics Data System (ADS)

    Li, Yi-Hsien; Wang, Han; Yu, Lili; Fang, Wenjing; Palacios, Tomas; Li, Lain-Jong; Kong, Jing

    2013-03-01

    Recently, monolayers of layered transition metal dichalcogenides (LTMD), such as MX2 (M =Mo, W and X =S, Se), have been reported to exhibit significant spin-valley coupling and optoelectronic performances because of the unique structural symmetry and band structures. Monolayers in this class of materials offered a burgeoning field in fundamental physics, energy harvesting, electronics and optoelectronics. However, most studies to date are hindered with great challenges on the synthesis and transfer of high quality LTMD monolayers. Hence, a feasible synthetic process to overcome the challenges is essential. Here, we demonstrate the growth of high-quality MS2 (M =Mo, W) monolayers using ambient-pressure-chemical-vapor-deposition (APCVD) with the seeding of aromatic molecules. Electronic transport and optical performances of the as-grown MS2 monolayers are comparable to those of exfoliated MS2 monolayers. The growth of MS2 monolayer is achieved on various surfaces. Growth mechanism on the novel synthetic process is investigated. Understanding and better control of seeds for the novel growth on the class of materials may stimulate the progress in the emerging filed.

  3. 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).

  4. 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.

  5. Properties of silicon dioxide layers with embedded metal nanocrystals produced by oxidation of Si:Me mixture.

    PubMed

    Novikau, Andrei; Gaiduk, Peter; Maksimova, Ksenia; Zenkevich, Andrei

    2011-02-16

    A two-dimensional layers of metal (Me) nanocrystals embedded in SiO2 were produced by pulsed laser deposition of uniformly mixed Si:Me film followed by its furnace oxidation and rapid thermal annealing. The kinetics of the film oxidation and the structural properties of the prepared samples were investigated by Rutherford backscattering spectrometry, and transmission electron microscopy, respectively. The electrical properties of the selected SiO2:Me nanocomposite films were evaluated by measuring C-V and I-V characteristics on a metal-oxide-semiconductor stack. It is found that Me segregation induced by Si:Me mixture oxidation results in the formation of a high density of Me and silicide nanocrystals in thin film SiO2 matrix. Strong evidence of oxidation temperature as well as impurity type effect on the charge storage in crystalline Me-nanodot layer is demonstrated by the hysteresis behavior of the high-frequency C-V curves.

  6. Phase coexistence and metal-insulator transition in few-layer phosphorene: a computational study.

    PubMed

    Guan, Jie; Zhu, Zhen; Tománek, David

    2014-07-25

    Based on ab initio density functional calculations, we propose γ-P and δ-P as two additional stable structural phases of layered phosphorus besides the layered α-P (black) and β-P (blue) phosphorus allotropes. Monolayers of some of these allotropes have a wide band gap, whereas others, including γ-P, show a metal-insulator transition caused by in-layer strain or changing the number of layers. An unforeseen benefit is the possibility to connect different structural phases at no energy cost. This becomes particularly valuable in assembling heterostructures with well-defined metallic and semiconducting regions in one contiguous layer.

  7. X-ray characterization of stacked InP/(InGa)As:C HBT and InP/(InGa)As HEMT layer sequences grown by LP-MOVPE using non-gaseous sources

    NASA Astrophysics Data System (ADS)

    Velling, P.; Keiper, D.; Brennemann, A.; Agethen, M.; Janssen, G.; Bertenburg, R. M.

    2003-02-01

    Stacked layer sequences of InP-based HBT and HEMT are of interest for today's (OC-768) and tomorrows (OC-3072, 100 Gbit Ethernet) communication standards. The better low noise performance of the HEMT can be combined with the driver capability of the HBT while also a PIN-photodiode can be provided by the HBT base-collector-diode. However this results in a complex procedure for MOVPE growth process development. For a reliable fabrication of complex radio frequency (opto-)electronic circuit applications a quantitative InP process technology control is necessary starting at the level of device epilayer stacks. In this report the detailed characterization of stacked InP/(InGa)As:C HBT and InP/(InGa)As HEMT layer sequences is carried out by non-destructive X-ray analysis. Based on X-ray measurements in 004- and 002-reflection a detailed analysis of complex device layer stacks is purposed. As a result, an automatic calculation of layer parameters, e.g. thickness and composition is possible, reducing the turn-around time for the statistical process control (SPC).

  8. Buffer layers on metal alloy substrates for superconducting tapes

    DOEpatents

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

    2004-06-29

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

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

    PubMed

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

    2016-06-01

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

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

    PubMed

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

    2016-06-01

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

  11. 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).

  12. Structural evolution and the control of defects in atomic layer deposited HfO2-Al2O3 stacked films on GaAs.

    PubMed

    Kang, Yu-Seon; Kim, Dae-Kyoung; Jeong, Kwang-Sik; Cho, Mann-Ho; Kim, Chung Yi; Chung, Kwun-Bum; Kim, Hyoungsub; Kim, Dong-Chan

    2013-03-01

    The structural characteristics and interfacial reactions of bilayered dielectric stacks of 3 nm HfO2/2 nm Al2O3 and 3 nm Al2O3/2 nm HfO2 on GaAs, prepared by atomic layer deposition (ALD), were examined during film growth and the postannealing process. During the postdeposition annealing (PDA) of the Al2O3/HfO2/GaAs structures at 700 °C, large amounts of Ga oxides were generated between the Al2O3 and HfO2 films as the result of interfacial reactions between interdiffused oxygen impurities and out-diffused atomic Ga. However, in the case of the HfO2/Al2O3/GaAs structures, the presence of an Al2O3 buffer layer effectively blocked the out-diffusion of atomic Ga, thus suppressing the formation of Ga oxide. Microstructural analyses showed that HfO2 films that were deposited on Al2O3/GaAs had completely crystallized during the PDA process, even at 700 °C, because of the Al2O3 diffusion barrier. Capacitance-voltage measurements showed a relatively large frequency dispersion of the Al2O3/HfO2/GaAs structure in accumulation capacitance compared to the HfO2/Al2O3/GaAs structure due to a higher interface state density. Conductance results revealed that the Al2O3 buffer layer on GaAs resulted in a significant reduction in gap states in GaAs. The induced gap state in the Al2O3/HfO2/GaAs structure originated from the out-diffusion of atomic Ga into the HfO2 film. Density functional theory calculations supported this conclusion.

  13. 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.

  14. 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.

  15. 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.

  16. 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

    2015-01-01

    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.

  17. The demonstration of colossal magneto-capacitance effect with the promising gate stack characteristics on Ge (100) by the magnetic gate stack design

    NASA Astrophysics Data System (ADS)

    Liao, M.-H.; Huang, S.-C.

    2014-06-01

    The tetragonal-phase BaTiO3 as the high dielectric (HK) layer and the magnetic FePt film as the metal gate (MG) are proposed to be the gate stack scheme on the Ge (100) substrate. The ˜75% dielectric constant (κ-value) improvement, ˜100X gate leakage (Jg) reduction, and the promising Jg-equivalent-oxide-thickness (EOT) gate stack characteristics are achieved in this work with the colossal magneto-capacitance effect. The perpendicular magnetic field from the magnetic FePt MG film couples and triggers the more dipoles in the BaTiO3 HK layer and then results in the super gate capacitance (Cgate) and κ-value. Super Jg-EOT gate stack characteristics with the magnetic gate stack design on the high mobility (Ge) substrate demonstrated in this work provides the useful solution for the future low power mobile device design.

  18. Influence of metal bonding layer on strain transfer performance of FBG

    NASA Astrophysics Data System (ADS)

    Liu, Hao; Chen, Weimin; Zhang, Peng; Liu, Li; Shu, Yuejie; Wu, Jun

    2013-01-01

    Metal bonding layer seriously affects the strain transfer performance of Fiber Bragg Grating (FBG). Based on the mode of FBG strain transfer, the influence of the length, the thickness, Poisson's ratio, elasticity modulus of metal bonding layer on the strain transfer coefficient of FBG is analyzed by numerical simulation. FBG is packaged to steel wire using metal bonding technology of FBG. The tensile tests of different bonding lengths and elasticity modulus are carried out. The result shows the strain transfer coefficient of FBGs are 0.9848,0.962 and their average strain sensitivities are 1.076 pm/μɛ,1.099 pm/μɛ when the metal bonding layer is zinc, whose lengths are 15mm, 20mm, respectively. The strain transfer coefficient of FBG packaged by metal bonding layer raises 8.9 percent compared to epoxy glue package. The preliminary experimental results show that the strain transfer coefficient increases with the length of metal bonding layer, decreases with the thickness of metal bonding layer and the influence of Poisson's ratio can be ignored. The experiment result is general agreement with the analysis and provides guidance for metal package of FBG.

  19. Influence of the metal work function on the photocatalytic properties of TiO2 layers on metals.

    PubMed

    Freitag, Janna; Bahnemann, Detlef W

    2015-08-24

    The photocatalytic properties of titanium dioxide (TiO2 ) layers on different metal plates are investigated. The metal-semiconductor interface can be described as a Schottky contact, and is part of a depletion layer for the majority carriers in the semiconductor. Many researchers have demonstrated an increase in the photocatalytic activity, due to the formation of a metal-semiconductor contact that are obtained by deposition of small metal islands on the semiconductor. Nevertheless, the influence of a Schottky contact remains uncertain, sparking much interest in this field. The immobilization of nanoparticulate TiO2 layers by dip-coating on different metal substrates results in the formation of a Schottky contact. The recombination rate of photoinduced electron-hole pairs decreases at this interface provided that the thickness of the thin TiO2 layer has a similar magnitude to the depletion layer. The degradation of dichloroacetic acid in aqueous solution and of acetaldehyde in a gas mixture is investigated to obtain information concerning the influence of the metal work function of the back contact on the efficiency of the photocatalytic process.

  20. 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…

  1. 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.

  2. Diverse and tunable electronic structures of single-layer metal phosphorus trichalcogenides for photocatalytic water splitting.

    PubMed

    Liu, Jian; Li, Xi-Bo; Wang, Da; Lau, Woon-Ming; Peng, Ping; Liu, Li-Min

    2014-02-01

    The family of bulk metal phosphorus trichalcogenides (APX3, A = M(II), M(I)(0.5)M(III)(0.5); X = S, Se; M(I), M(II), and M(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 APX3 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 ZnPSe3, CdPSe3, Ag0.5Sc0.5PSe3, and Ag0.5In0.5PX3 (X = S and Se) have both suitable band gaps for visible-light driving and sufficient over-potentials for water splitting. More fascinatingly, single-layer Ag0.5Sc0.5PSe3 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.

  3. Isotopic stack: measurement of heavy cosmic rays

    SciTech Connect

    Beaujean, R.; Schmidt, M.; Enge, W.; Siegmon, G.; Krause, J.; Fischer, E.

    1984-07-13

    A stack of plastic nuclear track detectors was exposed to heavy cosmic rays on the pallet of Spacelab 1. Some layers of the stack were rotated with respect to the main stack to determine the arrival time of the particles. After return of the stack the latent particle tracks are revealed by chemical etching. Under the optical microscope the charge, mass, energy, and impact direction of the particles can be deduced from the track geometry.

  4. Proximity Effect in BSCCO Intrinsic Josephson Junctions Contacted with a Normal Metal Layer

    NASA Astrophysics Data System (ADS)

    Suzuki, Minoru; Koizumi, Masayuki; Ohmaki, Masayuki; Kakeya, Itsuhiro; Shukrinov, Yu. M.

    Superconductivity proximity effect is numerically evaluated based on McMillan's tunneling proximity model for a sandwich of a normal metal layer on top of the surface superconducting layer of intrinsic Josephson junctions in a Bi2Sr2CaCu2O8+δ (BSCCO) crystal. Due to the very thin thickness of 0.3 nm of the superconducting layer in IJJs, the surface layer is subject to influence of the proximity effect when the top layer is contacted with a normal metal layer. The effect manifests itself as a significant change in the characteristics of the IJJ surface Josephson junction. It is found that when the superconducting layer thickness is smaller than 0.6 nm, the pair potential reduces significantly, leading to an almost complete suppression of the critical Josephson current density for the surface junction. This result can partly explain the experimental results on the IJJ characteristics of a mesa type structure.

  5. 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.

  6. 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.

  7. Strengthening effect of single-atomic-layer graphene in metal-graphene nanolayered composites.

    PubMed

    Kim, Youbin; Lee, Jinsup; Yeom, Min Sun; Shin, Jae Won; Kim, Hyungjun; Cui, Yi; Kysar, Jeffrey W; Hone, James; Jung, Yousung; Jeon, Seokwoo; Han, Seung Min

    2013-01-01

    Graphene is a single-atomic-layer material with excellent mechanical properties and has the potential to enhance the strength of composites. Its two-dimensional geometry, high intrinsic strength and modulus can effectively constrain dislocation motion, resulting in the significant strengthening of metals. Here we demonstrate a new material design in the form of a nanolayered composite consisting of alternating layers of metal (copper or nickel) and monolayer graphene that has ultra-high strengths of 1.5 and 4.0 GPa for copper-graphene with 70-nm repeat layer spacing and nickel-graphene with 100-nm repeat layer spacing, respectively. The ultra-high strengths of these metal-graphene nanolayered structures indicate the effectiveness of graphene in blocking dislocation propagation across the metal-graphene interface. Ex situ and in situ transmission electron microscopy compression tests and molecular dynamics simulations confirm a build-up of dislocations at the graphene interface. PMID:23820590

  8. 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.

  9. 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.

  10. Embedding Metal in the Interface of a p-n Heterojunction with a Stack Design for Superior Z-Scheme Photocatalytic Hydrogen Evolution.

    PubMed

    Yin, Wenjie; Bai, Lijie; Zhu, Yuzhen; Zhong, Shuxian; Zhao, Leihong; Li, Zhengquan; Bai, Song

    2016-09-01

    The construction of a p-n heterojunction is an efficient strategy to resolve the limited light absorption and serious charge-carrier recombination in semiconductors and enhance the photocatalytic activity. However, the promotion effect is greatly limited by poor interfacial charge transfer efficiency as well as reduced redox ability of charge carriers. In this work, we demonstrate that the embedding of metal Pd into the interface between n-type C3N4 and p-type Cu2O can further enhance the interfacial charge transfer and increase the redox ability of charge carriers through the design of the C3N4-Pd-Cu2O stack nanostructure. The embedded Pd nanocubes in the stack structure not only trap the charge carriers from the semiconductors in promoting the electron-hole separation but also act as a Z-scheme "bridge" in keeping the strong reduction/oxidation ability of the electrons/holes for surface reactions. Furthermore, Pd nanocubes also increase the bonding strength between the two semiconductors. Enabled by this unique design, the hydrogen evolution achieved is dramatically higher than that of its counterpart C3N4-Cu2O structure without Pd embedding. The apparent quantum efficiency (AQE) is 0.9% at 420 nm for the designed C3N4-Pd-Cu2O. This work highlights the rational interfacial design of heterojunctions for enhanced photocatalytic performance. PMID:27538462

  11. 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

  12. 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.

  13. 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.

  14. 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. PMID:26832589

  15. 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.

  16. The impact of energy barrier height on border traps in the metal insulator semicondoctor gate stacks on III-V semiconductors

    NASA Astrophysics Data System (ADS)

    Yoshida, Shinichi; Taniguchi, Satoshi; Minari, Hideki; Lin, Dennis; Ivanov, Tsvetan; Watanabe, Heiji; Nakazawa, Masashi; Collaert, Nadine; Thean, Aaron

    2016-08-01

    We investigated the effect of a thin interfacial layer (IL) made of silicon or germanium between high-k dielectrics and III-V semiconductors on the frequency dispersion of the capacitance-voltage (C-V) curves in detail. We demonstrated experimentally that the frequency dispersion at accumulation voltage is strongly dependent on the energy barrier height (ΦB) between high-k dielectrics and semiconductors. It was revealed that the improvement of frequency dispersion for n-type III-V semiconductors with IL is attributed to the increase in ΦB realized by inserting Ge IL. Moreover, the border trap density did not necessarily decrease with IL through the assessment of border trap density using a distributed bulk-oxide trap model. Finally, we proved that it is important to increase ΦB to suppress the carrier exchange and improve high-k/III-V gate stack reliability.

  17. The impact of energy barrier height on border traps in the metal insulator semicondoctor gate stacks on III–V semiconductors

    NASA Astrophysics Data System (ADS)

    Yoshida, Shinichi; Taniguchi, Satoshi; Minari, Hideki; Lin, Dennis; Ivanov, Tsvetan; Watanabe, Heiji; Nakazawa, Masashi; Collaert, Nadine; Thean, Aaron

    2016-08-01

    We investigated the effect of a thin interfacial layer (IL) made of silicon or germanium between high-k dielectrics and III–V semiconductors on the frequency dispersion of the capacitance–voltage (C–V) curves in detail. We demonstrated experimentally that the frequency dispersion at accumulation voltage is strongly dependent on the energy barrier height (ΦB) between high-k dielectrics and semiconductors. It was revealed that the improvement of frequency dispersion for n-type III–V semiconductors with IL is attributed to the increase in ΦB realized by inserting Ge IL. Moreover, the border trap density did not necessarily decrease with IL through the assessment of border trap density using a distributed bulk-oxide trap model. Finally, we proved that it is important to increase ΦB to suppress the carrier exchange and improve high-k/III–V gate stack reliability.

  18. In situ ceramic layer growth on coated fuel particles dispersed in a zirconium metal matrix

    SciTech Connect

    Terrani, Kurt A; Silva, G W Chinthaka M; Kiggans, Jim; Cai, Zhonghou; Shin, Dongwon; Snead, Lance Lewis

    2013-01-01

    The extent and nature of the chemical interaction between the outermost coating layer of coated fuel particles embedded in zirconium metal during fabrication of metal matrix microencapsulated fuels was examined. Various particles with outermost coating layers of pyrocarbon, SiC, and ZrC have been investigated in this study. ZrC-Zr interaction was least substantial while PyC-Zr reaction can be exploited to produce a ZrC layer at the interface in an in situ manner. The thickness of the ZrC layer in the latter case can be controlled by adjusting the time and temperature during processing. The kinetics of ZrC layer growth is significantly faster from what is predicted using literature carbon diffusivity data in ZrC. SiC-Zr interaction is more complex and results in formation of various chemical phases in a layered aggregate morphology at the interface.

  19. In situ ceramic layer growth on coated fuel particles dispersed in a zirconium metal matrix

    NASA Astrophysics Data System (ADS)

    Terrani, K. A.; Silva, C. M.; Kiggans, J. O.; Cai, Z.; Shin, D.; Snead, L. L.

    2013-06-01

    The extent and nature of the chemical interaction between the outermost coating layer of coated fuel particles embedded in zirconium metal during fabrication of metal matrix microencapsulated fuels were examined. Various particles with outermost coating layers of pyrocarbon, SiC, and ZrC have been investigated in this study. ZrC-Zr interaction was the least substantial, while the PyC-Zr reaction can be exploited to produce a ZrC layer at the interface in an in situ manner. The thickness of the ZrC layer in the latter case can be controlled by adjusting the time and temperature during processing. The kinetics of ZrC layer growth is significantly faster from what is predicted using literature carbon diffusivity data in ZrC. SiC-Zr interaction is more complex and results in formation of various chemical phases in a layered aggregate morphology at the interface.

  20. Elliptical metallic hollow fiber inner-coated with non-uniform dielectric layer.

    PubMed

    Tang, Xiaoli; Yu, Zhuzheng; Tu, Xuecou; Chen, Jian; Argyros, Alexander; Kuhlmey, Boris T; Shi, Yiwei

    2015-08-24

    We report on the fabrication and characterization of an elliptical hollow fiber inner coated with a silver layer and a dielectric layer for polarization maintaining and low loss transmission of terahertz (THz) radiation. The primary purpose of adding the dielectric layer is to prevent the silver layer from oxidation. The thickness of the dielectric layer is non-uniform owing to the surface tension of the coating, which was initially applied as a liquid. Transmission loss and polarization maintenance are experimentally characterized. Effects of the dielectric layer on transmission properties are analyzed by comparing the fiber to Ag-only fiber. Results show that a dielectric layer with thickness less than λ/10 can effectively decreases the power distributed on the metal surface and thus can practically reduce loss resulting from roughness of the silver layer. Bending effects on transmission loss and polarization maintenance are also investigated.

  1. 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. PMID:27042860

  2. 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.

  3. 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.

  4. Schottky source/drain germanium-based metal-oxide-semiconductor field-effect transistors with self-aligned NiGe/Ge junction and aggressively scaled high-k gate stack

    NASA Astrophysics Data System (ADS)

    Hosoi, Takuji; Minoura, Yuya; Asahara, Ryohei; Oka, Hiroshi; Shimura, Takayoshi; Watanabe, Heiji

    2015-12-01

    Schottky source/drain (S/D) Ge-based metal-oxide-semiconductor field-effect transistors (MOSFETs) were fabricated by combining high permittivity (high-k) gate stacks with ultrathin AlOx interlayers and Fermi level depinning process by means of phosphorous ion implantation into NiGe/Ge contacts. Improved thermal stability of the metal/high-k/Ge stacks enabled self-aligned integration scheme for Schottky S/D complementary MOS applications. Significantly reduced parasitic resistance and aggressively scaled high-k gate stacks with sub-1-nm equivalent oxide thickness were demonstrated for both p- and n-channel Schottky Ge-FETs with the proposed combined technology.

  5. 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

  6. Stacking orders induced direct band gap in bilayer MoSe2-WSe2 lateral heterostructures.

    PubMed

    Hu, Xiaohui; Kou, Liangzhi; Sun, Litao

    2016-08-16

    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.

  7. Stacking orders induced direct band gap in bilayer MoSe2-WSe2 lateral heterostructures

    NASA Astrophysics Data System (ADS)

    Hu, Xiaohui; Kou, Liangzhi; Sun, Litao

    2016-08-01

    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.

  8. Stacking orders induced direct band gap in bilayer MoSe2-WSe2 lateral heterostructures.

    PubMed

    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

  9. Spin tuning of electron-doped metal-phthalocyanine layers.

    PubMed

    Stepanow, Sebastian; Lodi Rizzini, Alberto; Krull, Cornelius; Kavich, Jerald; Cezar, Julio C; Yakhou-Harris, Flora; Sheverdyaeva, Polina M; Moras, Paolo; Carbone, Carlo; Ceballos, Gustavo; Mugarza, Aitor; Gambardella, Pietro

    2014-04-01

    The spin state of organic-based magnets at interfaces is to a great extent determined by the organic environment and the nature of the spin-carrying metal center, which is further subject to modifications by the adsorbate-substrate coupling. Direct chemical doping offers an additional route for tailoring the electronic and magnetic characteristics of molecular magnets. Here we present a systematic investigation of the effects of alkali metal doping on the charge state and crystal field of 3d metal ions in Cu, Ni, Fe, and Mn phthalocyanine (Pc) monolayers adsorbed on Ag. Combined X-ray absorption spectroscopy and ligand field multiplet calculations show that Cu(II), Ni(II), and Fe(II) ions reduce to Cu(I), Ni(I), and Fe(I) upon alkali metal adsorption, whereas Mn maintains its formal oxidation state. The strength of the crystal field at the Ni, Fe, and Mn sites is strongly reduced upon doping. The combined effect of these changes is that the magnetic moment of high- and low-spin ions such as Cu and Ni can be entirely turned off or on, respectively, whereas the magnetic configuration of MnPc can be changed from intermediate (3/2) to high (5/2) spin. In the case of FePc a 10-fold increase of the orbital magnetic moment accompanies charge transfer and a transition to a high-spin state.

  10. Epitaxial Gd2O3 on strained Si1-xGex layers for next generation complementary metal oxide semiconductor device application

    NASA Astrophysics Data System (ADS)

    Ghosh, Kankat; Das, Sudipta; Fissel, A.; Osten, H. J.; Laha, Apurba

    2013-10-01

    Strained Si1-xGex (x = 0.1-0.4) layers were grown on Si(111) and Si(001) substrates using molecular beam epitaxy followed by the growth of epitaxial Gd2O3 thin films on Si1-xGex layers using same technique. Pt/Gd2O3/Si1-xGex/Si stacks fabricated by several in situ process steps exhibit excellent electrical properties. Surface and microstructural analysis of both Si1-xGex and Gd2O3 layers carried out by different in situ and ex situ tools reveal a relaxed epi-Gd2O3 layer on a strained Si1-xGex layer on both Si(111) and Si(001) substrates with sharp interfaces between the oxide and the SiGe layer. Standard electrical measurements, such as capacitance-voltage and leakage current analysis, demonstrate promising electrical properties for such metal oxide semiconductor capacitors. A capacitance equivalent thickness as low as 1.20 nm with associated leakage current density of 2.0 mA/cm2 was obtained for devices with 4.5 nm thin oxide films where the density of interface trap (Dit) was only ˜1011 cm-2 eV-1.

  11. 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

  12. Newtype single-layer magnetic semiconductor in transition-metal dichalcogenides VX2 (X = S, Se and Te)

    NASA Astrophysics Data System (ADS)

    Fuh, Huei-Ru; Chang, Ching-Ray; Wang, Yin-Kuo; Evans, Richard F. L.; Chantrell, Roy W.; Jeng, Horng-Tay

    2016-09-01

    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.

  13. Newtype single-layer magnetic semiconductor in transition-metal dichalcogenides VX2 (X = S, Se and Te).

    PubMed

    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

  14. Numerical simulation of mark formation in dual-stack phase-change recording

    NASA Astrophysics Data System (ADS)

    Meinders, E. R.; Borg, H. J.; Lankhorst, M. H. R.; Hellmig, J.; Mijiritskii, A. V.

    2002-06-01

    Dual-stack phase-change recording is an option to further increase the data capacity of rewritable optical disks. Such disks consist of two recording stacks that are both recorded and read from the same side of the disk. Consequently, the first recording stack needs therefore to be semitransparent to allow recording in the second recording stack. Thick nontransparent metal layers can therefore not be used in the first recording stack, which makes the first recording stack the most challenging stack from a thermal point of view. A numerical model based on crystal growth was developed to study formation and erasure of amorphous marks in phase-change stacks that are based on fast-growth doped SbTe phase-change materials. The validity of the model was demonstrated from transmission electron microscopy analyses of recorded marks that showed a good correspondence with the calculated mark shapes in a conventional single-stack recording stack. The model was subsequently applied to analyze formation and erasure of marks in slow-cooling phase-change stacks for digital versatile disk, (DVD) and digital video recording (DVR) recording conditions. The effect of the recording velocity, the erase power, and the crystal growth velocity on the erasability of amorphous marks was simulated. The calculated phenomena are in good agreement with the phenomena observed from DVD and DVR erasability measurements. Mark formation in slow-cooling recording stacks is characterized by severe recrystallization during writing. Two possible solutions are indicated in this article, aiming at reducing the heat accumulation and the resulting recrystallization during writing of amorphous marks. Additional semitransparent heat sinks improve the mark formation considerably but also require higher write powers. Another solution is the application of modified write strategies. Modeling and recorder results are discussed for both approaches.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. Layered metal sulfides: Exceptionally selective agents for radioactive strontium removal

    PubMed Central

    Manos, Manolis J.; Ding, Nan; Kanatzidis, Mercouri G.

    2008-01-01

    In this article, we report the family of robust layered sulfides K2xMnxSn3-xS6 (x = 0.5–0.95) (KMS-1). These materials feature hexagonal [MnxSn3-xS6]2x− slabs of the CdI2 type and contain highly mobile K+ ions in their interlayer space that are easily exchangeable with other cations and particularly strontium. KMS-1 display outstanding preference for strontium ions in highly alkaline solutions containing extremely large excess of sodium cations as well as in acidic environment where most alternative adsorbents with oxygen ligands are nearly inactive. The implication of these results is that simple layered sulfides should be considered for the efficient remediation of certain nuclear wastes. PMID:18316731

  1. Topological phase transition in layered transition metal dichalcogenides

    NASA Astrophysics Data System (ADS)

    Choe, Duk-Hyun; Sung, Ha-Jun; Chang, Kee Joo

    Despite considerable interests in transition metal dichalcogenides (TMDs), such as MX2 with M = (Mo, W) and X = (S, Se, Te), the physical origin of their topological nature is still in its infancy. The conventional view of topological phase transition (TPT) in TMDs is that the band inversion occurs between the metal d and chalcogen p orbital bands. More precisely, the former is pulled down below the latter. Here we introduce an explicit scheme for analyzing TPT in topological materials and find that the TPT in TMDs is different from the conventional speculation. When the 1T phase undergoes a structural transformation to the 1T' phase in monolayer MX2, the band topology changes from trivial to non-trivial, leading to the TPT. We discuss the exact role of the metal d and chalcogen p orbital bands during the TPT. Our finding would provide clear guidelines for understanding the topological nature not only in TMDs but also in other topological materials yet to be explored.

  2. Multi-Component Organic Layers on Metal Substrates.

    PubMed

    Goiri, Elizabeth; Borghetti, Patrizia; El-Sayed, Afaf; Ortega, J Enrique; de Oteyza, Dimas G

    2016-02-17

    Increasingly high hopes are being placed on organic semiconductors for a variety of applications. Progress along these lines, however, requires the design and growth of increasingly complex systems with well-defined structural and electronic properties. These issues have been studied and reviewed extensively in single-component layers, but the focus is gradually shifting towards more complex and functional multi-component assemblies such as donor-acceptor networks. These blends show different properties from those of the corresponding single-component layers, and the understanding on how these properties depend on the different supramolecular environment of multi-component assemblies is crucial for the advancement of organic devices. Here, our understanding of two-dimensional multi-component layers on solid substrates is reviewed. Regarding the structure, the driving forces behind the self-assembly of these systems are described. Regarding the electronic properties, recent insights into how these are affected as the molecule's supramolecular environment changes are explained. Key information for the design and controlled growth of complex, functional multicomponent structures by self-assembly is summarized.

  3. Stitching 2D polymeric layers into flexible interpenetrated metal-organic frameworks within single crystals.

    PubMed

    Zhang, Zi-Xuan; Ding, Ni-Ni; Zhang, Wen-Hua; Chen, Jin-Xiang; Young, David J; Hor, T S Andy

    2014-04-25

    A 2D coordination polymer prepared with bulky diethylformamide solvates exhibits channels which allow dipyridyl bridging ligands to diffuse into the crystal lattice. The absorbed dipyridyls thread through the pores of one layer and substitute the surface diethylformamide molecules on the neighboring layers to stitch alternate layers to form flexible interpenetrated metal-orgaic frameworks. The threading process also results in exchange of the bulky diethylformamide solvates for aqua to minimize congestion and, more strikingly, forces the slippage of two-dimensional layers, while still maintaining crystallinity. PMID:24692130

  4. 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.

  5. Interphase layer optimization for metal matrix composites with fabrication considerations

    NASA Technical Reports Server (NTRS)

    Morel, M.; Saravanos, D. A.; Chamis, C. C.

    1991-01-01

    A methodology is presented to reduce the final matrix microstresses for metal matrix composites by concurrently optimizing the interphase characteristics and fabrication process. Application cases include interphase tailoring with and without fabrication considerations for two material systems, graphite/copper and silicon carbide/titanium. Results indicate that concurrent interphase/fabrication optimization produces significant reductions in the matrix residual stresses and strong coupling between interphase and fabrication tailoring. The interphase coefficient of thermal expansion and the fabrication consolidation pressure are the most important design parameters and must be concurrently optimized to further reduce the microstresses to more desirable magnitudes.

  6. Graphene oxide monolayers as atomically thin seeding layers for atomic layer deposition of metal oxides

    NASA Astrophysics Data System (ADS)

    Nourbakhsh, Amirhasan; Adelmann, Christoph; Song, Yi; Lee, Chang Seung; Asselberghs, Inge; Huyghebaert, Cedric; Brizzi, Simone; Tallarida, Massimo; Schmeißer, Dieter; van Elshocht, Sven; Heyns, Marc; Kong, Jing; Palacios, Tomás; de Gendt, Stefan

    2015-06-01

    Graphene oxide (GO) was explored as an atomically-thin transferable seed layer for the atomic layer deposition (ALD) of dielectric materials on any substrate of choice. This approach does not require specific chemical groups on the target surface to initiate ALD. This establishes GO as a unique interface which enables the growth of dielectric materials on a wide range of substrate materials and opens up numerous prospects for applications. In this work, a mild oxygen plasma treatment was used to oxidize graphene monolayers with well-controlled and tunable density of epoxide functional groups. This was confirmed by synchrotron-radiation photoelectron spectroscopy. In addition, density functional theory calculations were carried out on representative epoxidized graphene monolayer models to correlate the capacitive properties of GO with its electronic structure. Capacitance-voltage measurements showed that the capacitive behavior of Al2O3/GO depends on the oxidation level of GO. Finally, GO was successfully used as an ALD seed layer for the deposition of Al2O3 on chemically inert single layer graphene, resulting in high performance top-gated field-effect transistors.Graphene oxide (GO) was explored as an atomically-thin transferable seed layer for the atomic layer deposition (ALD) of dielectric materials on any substrate of choice. This approach does not require specific chemical groups on the target surface to initiate ALD. This establishes GO as a unique interface which enables the growth of dielectric materials on a wide range of substrate materials and opens up numerous prospects for applications. In this work, a mild oxygen plasma treatment was used to oxidize graphene monolayers with well-controlled and tunable density of epoxide functional groups. This was confirmed by synchrotron-radiation photoelectron spectroscopy. In addition, density functional theory calculations were carried out on representative epoxidized graphene monolayer models to correlate the

  7. 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.

  8. Effect of hydrogen in controlling the structural orientation of ZnO:Ga:H as transparent conducting oxide films suitable for applications in stacked layer devices.

    PubMed

    Mondal, Praloy; Das, Debajyoti

    2016-07-27

    consequence of the increased carrier concentration. Highly conducting and transparent c-axis oriented ZnO:Ga:H films grown by a device compatible process at a low TS are extremely useful for various stacked layer thin film devices, including solar cells.

  9. Effect of hydrogen in controlling the structural orientation of ZnO:Ga:H as transparent conducting oxide films suitable for applications in stacked layer devices.

    PubMed

    Mondal, Praloy; Das, Debajyoti

    2016-07-27

    consequence of the increased carrier concentration. Highly conducting and transparent c-axis oriented ZnO:Ga:H films grown by a device compatible process at a low TS are extremely useful for various stacked layer thin film devices, including solar cells. PMID:27401012

  10. Graphene oxide monolayers as atomically thin seeding layers for atomic layer deposition of metal oxides.

    PubMed

    Nourbakhsh, Amirhasan; Adelmann, Christoph; Song, Yi; Lee, Chang Seung; Asselberghs, Inge; Huyghebaert, Cedric; Brizzi, Simone; Tallarida, Massimo; Schmeisser, Dieter; Van Elshocht, Sven; Heyns, Marc; Kong, Jing; Palacios, Tomás; De Gendt, Stefan

    2015-06-28

    Graphene oxide (GO) was explored as an atomically-thin transferable seed layer for the atomic layer deposition (ALD) of dielectric materials on any substrate of choice. This approach does not require specific chemical groups on the target surface to initiate ALD. This establishes GO as a unique interface which enables the growth of dielectric materials on a wide range of substrate materials and opens up numerous prospects for applications. In this work, a mild oxygen plasma treatment was used to oxidize graphene monolayers with well-controlled and tunable density of epoxide functional groups. This was confirmed by synchrotron-radiation photoelectron spectroscopy. In addition, density functional theory calculations were carried out on representative epoxidized graphene monolayer models to correlate the capacitive properties of GO with its electronic structure. Capacitance-voltage measurements showed that the capacitive behavior of Al2O3/GO depends on the oxidation level of GO. Finally, GO was successfully used as an ALD seed layer for the deposition of Al2O3 on chemically inert single layer graphene, resulting in high performance top-gated field-effect transistors.

  11. One-Step Synthesis of MoS₂/WS₂ Layered Heterostructures and Catalytic Activity of Defective Transition Metal Dichalcogenide Films.

    PubMed

    Woods, John M; Jung, Yeonwoong; Xie, Yujun; Liu, Wen; Liu, Yanhui; Wang, Hailiang; Cha, Judy J

    2016-02-23

    Transition metal dichalcogenides (TMDCs) are a promising class of two-dimensional (2D) materials for use in applications such as 2D electronics, optoelectronics, and catalysis. Due to the van der Waals (vdW) bonding between layers, vdW heterostructures can be constructed between two different species of TMDCs. Most studies employ exfoliation or co-vapor growth schemes, which are limited by the small size and uneven distribution of heterostructures on the growth substrate. In this work we demonstrate a one-step synthesis procedure for large-area vdW heterostructures between horizontal TMDCs MoS2 and WS2. The synthesis procedure is scalable and provides patterning ability, which is critical for electronic applications in integrated circuits. We demonstrate rectification characteristics of large-area MoS2/WS2 stacks. In addition, hydrogen evolution reaction performance was measured in these horizontal MoS2 and WS2 thin films, which indicate that, in addition to the catalytically active sulfur edge sites, defect sites may serve as catalyst sites. PMID:26836122

  12. Midlatitude sporadic-E layers and vertical metallic ion drift profiles

    NASA Astrophysics Data System (ADS)

    Royrvik, O.

    1983-02-01

    An investigation of the relationship between the occurrence of midlatitude sporadic-E-layers and convergent points in the ion drift profiles has been made using the 430 MHz incoherent scatter radar at the Arecibo Observatory. Electron concentration profiles were obtained using a 13 baud Barker coded pulse yielding 600 m range resolution, while a 5-pulse sequence with 2.4 km range resolution was used to obtain line-of-sight ion drift velocities. With some exceptions, observed sporadic-E layers occur near convergent points in the vertical metallic ion drift profile, and vertical motions of these layers follow the vertical motions of the convergent point. A sudden increase in the altitude of a sporadic-E layer has been observed. This is attributed to the disappearance of the convergent point, releasing the layer, followed by an ascent of the layer to the closest overlying convergent point.

  13. Effects of Cu/In compositional ratio on the characteristics of CuInS2 absorber layers prepared by sulfurization of metallic precursors

    NASA Astrophysics Data System (ADS)

    Lee, Seung Hwan; Shin, Seung Wook; Han, Jun Hee; Lee, Jeong Yong; Kang, Myeong Gil; Agawane, G. L.; Yun, Jae Ho; Moon, Jong Ha; Kim, Jin Hyeok

    2012-04-01

    This paper investigates the effects of the Cu/In compositional ratio on morphological, structural and optical properties of CuInS2 (CIS) absorber layers formed by sulfurization of In/Cu stacked precursors. In/Cu stacked precursors were prepared on Mo-coated soda-lime glass substrates by DC magnetron sputtering method. The Cu/In compositional ratio in the precursor thin film was varied from 0.55 to 1.44. The as-deposited stacked precursor thin films were sulfurized using a tubular furnace annealing system in a mixture of N2 (95%) + H2S (5%) atmosphere at 450°C for 1 hour. X-ray diffraction patterns and Raman spectra results showed that the sulfurized thin films contained both tetragonal CIS and a Cu-based secondary phase, except for the film with a Cu/In compositional ratio of 0.55. Field emission-scanning electron microscopy study showed that the microstructure of the sulfurized CIS thin films became denser with increasing Cu/In compositional ratio. Optical properties of the CIS thin films showed that all the CIS thin films had a good absorption coefficient over 104 cm-1 in the visible region. The direct band gap energy of the sulfurized CIS thin films decreased from 1.39 eV to 1.08 eV with increasing Cu/In compositional ratio. These results demonstrated the effect of the Cu/In compositional ratio on the properties of the CIS thin films and the consequent importance of precisely controlling the metal ratio in the precursor film in order to control the properties of absorber layers in thin film solar cells.

  14. Maximal light-energy transfer through a dielectric/metal-layered electrode on a photoactive device.

    PubMed

    Kim, Kyoung-Ho; Park, Q-Han

    2014-01-27

    We report the fabrication of an optimized low reflective dielectric/metal-layered electrode that provides significant electrical conductivity and light transparency in the near-infrared wavelength regime. By making the metal film thickness thick enough and choosing a proper dielectric layer with a certain thickness, we show that our suggested electrode significantly reduces the light reflection while preserving high electrical conductivity. We demonstrate our optimized electrodes present a highly conductive surface with a sheet resistance of 5.2 Ω/sq and a high light transmittance of near 85% in the near-infrared regime. We also apply our optimized electrode to thin-film organic photovoltaic devices and show the electrode helps in absorbing light energy inside an active layer. We believe that this simple but powerful layered electrode will pave the way for designing transparent electrodes on photoactive devices.

  15. Simple metal under tensile stress: layer-dependent herringbone reconstruction of thin potassium films on graphite

    NASA Astrophysics Data System (ADS)

    Yin, Feng; Kulju, Sampo; Koskinen, Pekka; Akola, Jaakko; Palmer, Richard E.

    2015-05-01

    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.

  16. 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

  17. 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

  18. Next-Generation Lithium Metal Anode Engineering via Atomic Layer Deposition.

    PubMed

    Kozen, Alexander C; Lin, Chuan-Fu; Pearse, Alexander J; Schroeder, Marshall A; Han, Xiaogang; Hu, Liangbing; Lee, Sang-Bok; Rubloff, Gary W; Noked, Malachi

    2015-06-23

    Lithium metal is considered to be the most promising anode for next-generation batteries due to its high energy density of 3840 mAh g(-1). However, the extreme reactivity of the Li surface can induce parasitic reactions with solvents, contamination, and shuttled active species in the electrolyte, reducing the performance of batteries employing Li metal anodes. One promising solution to this issue is application of thin chemical protection layers to the Li metal surface. Using a custom-made ultrahigh vacuum integrated deposition and characterization system, we demonstrate atomic layer deposition (ALD) of protection layers directly on Li metal with exquisite thickness control. We demonstrate as a proof-of-concept that a 14 nm thick ALD Al2O3 layer can protect the Li surface from corrosion due to atmosphere, sulfur, and electrolyte exposure. Using Li-S battery cells as a test system, we demonstrate an improved capacity retention using ALD-protected anodes over cells assembled with bare Li metal anodes for up to 100 cycles. PMID:25970127

  19. Next-Generation Lithium Metal Anode Engineering via Atomic Layer Deposition.

    PubMed

    Kozen, Alexander C; Lin, Chuan-Fu; Pearse, Alexander J; Schroeder, Marshall A; Han, Xiaogang; Hu, Liangbing; Lee, Sang-Bok; Rubloff, Gary W; Noked, Malachi

    2015-06-23

    Lithium metal is considered to be the most promising anode for next-generation batteries due to its high energy density of 3840 mAh g(-1). However, the extreme reactivity of the Li surface can induce parasitic reactions with solvents, contamination, and shuttled active species in the electrolyte, reducing the performance of batteries employing Li metal anodes. One promising solution to this issue is application of thin chemical protection layers to the Li metal surface. Using a custom-made ultrahigh vacuum integrated deposition and characterization system, we demonstrate atomic layer deposition (ALD) of protection layers directly on Li metal with exquisite thickness control. We demonstrate as a proof-of-concept that a 14 nm thick ALD Al2O3 layer can protect the Li surface from corrosion due to atmosphere, sulfur, and electrolyte exposure. Using Li-S battery cells as a test system, we demonstrate an improved capacity retention using ALD-protected anodes over cells assembled with bare Li metal anodes for up to 100 cycles.

  20. 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

    2014-10-01

    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.

  1. 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.

  2. 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.

  3. 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.

  4. Charge Transfer Stabilization of Late Transition Metal Oxide Nanoparticles on a Layered Niobate Support.

    PubMed

    Strayer, Megan E; Senftle, Thomas P; Winterstein, Jonathan P; Vargas-Barbosa, Nella M; Sharma, Renu; Rioux, Robert M; Janik, Michael J; Mallouk, Thomas E

    2015-12-30

    Interfacial interactions between late transition metal/metal oxide nanoparticles and oxide supports impact catalytic activity and stability. Here, we report the use of isothermal titration calorimetry (ITC), electron microscopy and density functional theory (DFT) to explore periodic trends in the heats of nanoparticle-support interactions for late transition metal and metal oxide nanoparticles on layered niobate and silicate supports. Data for Co(OH)2, hydroxyiridate-capped IrOx·nH2O, Ni(OH)2, CuO, and Ag2O nanoparticles were added to previously reported data for Rh(OH)3 grown on nanosheets of TBA0.24H0.76Ca2Nb3O10 and a layered silicate. ITC measurements showed stronger bonding energies in the order Ag < Cu ≈ Ni ≈ Co < Rh < Ir on the niobate support, as expected from trends in M-O bond energies. Nanoparticles with exothermic heats of interaction were stabilized against sintering. In contrast, ITC measurements showed endothermic interactions of Cu, Ni, and Rh oxide/hydroxide nanoparticles with the silicate and poor resistance to sintering. These trends in interfacial energies were corroborated by DFT calculations using single-atom and four-atom cluster models of metal/metal oxide nanoparticles. Density of states and charge density difference calculations reveal that strongly bonded metals (Rh, Ir) transfer d-electron density from the adsorbed cluster to niobium atoms in the support; this mixing is absent in weakly binding metals, such as Ag and Au, and in all metals on the layered silicate support. The large differences between the behavior of nanoparticles on niobate and silicate supports highlight the importance of d-orbital interactions between the nanoparticle and support in controlling the nanoparticles' stability. PMID:26651875

  5. 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.

  6. 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.

  7. Control of electronic properties of 2D carbides (MXenes) by manipulating their transition metal layers

    DOE PAGES

    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, 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

  8. Solvent-free synthesis of new metal phosphites with double-layered, pillared-layered, and framework structures

    NASA Astrophysics Data System (ADS)

    Liu, Lin; Zhang, Wei; Shi, Zhonghua; Chen, Yaoqiang; Lin, Zhien

    2014-12-01

    Three new metal phosphites, formulated as (H3O)2·Mn2(HPO3)3 (1), Co(bpy) (H2O) (HPO3) (2), and H2tmpda·Zn3(HPO3)4 (3), have been synthesized under solvent-free conditions, where bpy = 4,4‧-bipyridine, and tmpda = N,N,N‧,N‧-tetramethyl-1,3-propanediamine. Compound 1 has a double-layered structure with a thickness of 5.68 Å. Compound 2 has an inorganic-organic hybrid framework with cobalt phosphite layers pillared by bpy ligands. Compound 3 has a three-dimensional open-framework structure containing 8-ring channels. The temperature dependence of the magnetic susceptibility of compounds 1 and 2 were also investigated.

  9. 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.

  10. 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.

  11. 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.

  12. Layer-by-layer growth of metal-metal bonded supramolecular thin films and its use in the fabrication of lateral nanoscale devices.

    PubMed

    Lin, Chun; Kagan, Cherie R

    2003-01-15

    Layer-by-layer self-assembly of metal-metal bonded supramolecules is demonstrated and utilized to fabricate lateral nanoelectronic devices. Mercaptoethylpyridine is used to bind to Au substrates and to template the sequential assembly of alternating layers of redox active dirhodium complexes [Rh2(DAniF)2]2(O2CCH2CO2)2 (DAniF = N,N'-di-p-anisylformamidinate) and conjugated organic ligands trans-1,2-bis(4-pyridyl)ethylene. Optical spectroscopy and atomic force microscopy show that the structure and composition of these thin films are similar to those found in tightly packed single crystals. Electrochemical studies of these films grown on Au substrates reveal a reversible oxidation wave at approximately 406 mV, corresponding to the one electron oxidation of the Rh24+ center. This directed assembly technique has been used to fabricate lateral nano-electronic devices in which the supramolecules span the channels. Tailoring the chemistry of the templating ligand enables assembly on desired surfaces and engineering the chemistry of the supramolecules' dimetal units and coordinating ligands may tune the device characteristics.

  13. 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.

  14. Metallic conduction induced by direct anion site doping in layered SnSe2.

    PubMed

    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 ~10(20) 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 ~10(19) 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

  15. Metallic conduction induced by direct anion site doping in layered SnSe2

    NASA Astrophysics Data System (ADS)

    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.

  16. 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.

  17. 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

  18. 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.

  19. Tin disulfide-an emerging layered metal dichalcogenide semiconductor: materials properties and device characteristics.

    PubMed

    Huang, Yuan; Sutter, Eli; Sadowski, Jerzy T; Cotlet, Mircea; Monti, Oliver L A; Racke, David A; Neupane, Mahesh R; Wickramaratne, Darshana; Lake, Roger K; Parkinson, Bruce A; Sutter, Peter

    2014-10-28

    Layered metal dichalcogenides have attracted significant interest as a family of single- and few-layer materials that show new physics and are of interest for device applications. Here, we report a comprehensive characterization of the properties of tin disulfide (SnS2), an emerging semiconducting metal dichalcogenide, down to the monolayer limit. Using flakes exfoliated from layered bulk crystals, we establish the characteristics of single- and few-layer SnS2 in optical and atomic force microscopy, Raman spectroscopy and transmission electron microscopy. Band structure measurements in conjunction with ab initio calculations and photoluminescence spectroscopy show that SnS2 is an indirect bandgap semiconductor over the entire thickness range from bulk to single-layer. Field effect transport in SnS2 supported by SiO2/Si suggests predominant scattering by centers at the support interface. Ultrathin transistors show on-off current ratios >10(6), as well as carrier mobilities up to 230 cm(2)/(V s), minimal hysteresis, and near-ideal subthreshold swing for devices screened by a high-k (deionized water) top gate. SnS2 transistors are efficient photodetectors but, similar to other metal dichalcogenides, show a relatively slow response to pulsed irradiation, likely due to adsorbate-induced long-lived extrinsic trap states.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. Impact of thin metal layer on the optical and electrical properties of indium-doped-tin oxide and aluminum-doped-zinc oxide layers

    NASA Astrophysics Data System (ADS)

    Kumar, Melvin David; Park, Yun Chang; Kim, Joondong

    2015-06-01

    The distinguished transparent conductive oxide (TCO) layers like indium-doped-tin oxide (ITO) and aluminum-doped-zinc oxide (AZO) layers were prepared in different combinations with and without thin Ni metal layer. The optical and electrical properties of prepared samples were analyzed and compared with the objective to understand the role and influence of the Ni layer in each TCO combination. The highest transmittance value of 91.49% was exhibited by prepared AZO layers. Even though if the transmittance of Ni inserting TCO layers was marginally reduced than that of the ordinary TCO samples, they exhibited balanced optical properties with enhanced electrical properties. Carrier concentration of indium doped tin-oxide and aluminum doped zinc oxide (ITO/AZO) bilayer sample is increased more than double the times when the Ni layer was inserted between ITO and AZO. Thin layer of Ni in between TCO layers reduced sheet resistance and offered substantial transmittance, so that the figure of merit (FOM) value of Ni embedding TCOs was greater than that of TCOs without Ni layer. The ITO/Ni/AZO combination provided optimum results in all the electrical properties. As compared to other TCO/metal combinations, the overall performance of ITO/Ni/AZO tri-layer combination was appreciable. These results show that the optical and electrical properties of TCO layers could be enhanced by inserting a Ni layer with optimum thickness in between them.

  6. Role of metallic substrate on the plasmon modes in double-layer graphene structures

    NASA Astrophysics Data System (ADS)

    Cruz, G. Gonzalez de la

    2015-07-01

    Novel heterostructures combining different layered materials offer new opportunities for applications and fundamental studies of collective excitations driven by interlayer Coulomb interactions. In this work, we have investigated the influence of the metallic-like substrate on the plasmon spectrum of a double layer graphene system and a structure consisting of conventional two-dimensional electron gas (2DEG) immersed in a semiconductor quantum well and a graphene sheet with an interlayer separation of d. Long-range Coulomb interactions between substrate and graphene layered systems lead a new set of spectrum plasmons. At long wavelengths (q→0) the acoustic modes (ω~q) depend, besides on the carrier density in each layer, on the distance between the first carrier layer and the substrate in both structures. Furthermore, in the relativistic/nonrelativistic layered structure an undamped acoustic mode emerges for a certain interlayer critical distance dc. On the other hand, the optical plasmon modes emerging from the coupling of the double-layer systems and the substrate, both start at finite frequency at q=0 in contrast to the collective excitation spectrum ω~q1/2 reported in the literature for double-layer graphene structures.

  7. Influence of face-centered-cubic texturing of Co2Fe6B2 pinned layer on tunneling magnetoresistance ratio decrease in Co2Fe6B2/MgO-based p-MTJ spin valves stacked with a [Co/Pd]n-SyAF layer

    NASA Astrophysics Data System (ADS)

    Takemura, Yasutaka; Lee, Du-Yeong; Lee, Seung-Eun; Chae, Kyo-Suk; Shim, Tae-Hun; Lian, Guoda; Kim, moon; Park, Jea-Gun

    2015-05-01

    The TMR ratio of Co2Fe6B2/MgO-based p-MTJ spin valves stacked with a [Co/Pd]n-SyAF layer decreased rapidly when the ex situ magnetic annealing temperature (Tex) was increased from 275 to 325 °C, and this decrease was associated with degradation of the Co2Fe6B2 pinned layer rather than the Co2Fe6B2 free layer. At a Tex above 325 °C the amorphous Co2Fe6B2 pinned layer was transformed into a face-centered-cubic (fcc) crystalline layer textured from [Co/Pd]n-SyAF, abruptly reducing the Δ1 coherence tunneling of perpendicular-spin-torque electrons between the (100) MgO tunneling barrier and the fcc Co2Fe6B2 pinned layer.

  8. Rapid self-start of polymer electrolyte fuel cell stacks from subfreezing temperatures

    NASA Astrophysics Data System (ADS)

    Ahluwalia, R. K.; Wang, X.

    Polymer electrolyte fuel cell (PEFC) systems for light-duty vehicles must be able to start unassisted and rapidly from temperatures below -20 °C. Managing buildup of ice within the porous cathode catalyst and electrode structure is the key to self-starting a PEFC stack from subfreezing temperatures. The stack temperature must be raised above the melting point of ice before the ice completely covers the cathode catalyst and shuts down the electrochemical reaction. For rapid and robust self-start it is desirable to operate the stack near the short-circuit conditions. This mode of operation maximizes hydrogen utilization, favors production of waste heat that is absorbed by the stack, and delays complete loss of effective electrochemical surface area by causing a large fraction of the ice to form in the gas diffusion layer rather than in the cathode catalyst layer. Preheating the feed gases, using the power generated to electrically heat the stack, and operating pressures have only small effect on the ability to self-start or the startup time. In subfreezing weather, the stack shut-down protocol should include flowing ambient air through the hot cathode passages to vaporize liquid water remaining in the cathode catalyst. Self-start is faster and more robust if the bipolar plates are made from metal rather than graphite.

  9. Electrochemical cell stack assembly

    SciTech Connect

    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. 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.

  11. 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.

  12. 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.

  13. Ambipolar Transport and Gate-Induced Superconductivity in Layered Transition Metal Dichalcogenides

    NASA Astrophysics Data System (ADS)

    Shi, Wu; Ye, Jianting; Zhang, Yijing; Suzuki, Ryuji; Saito, Yu; Iwasa, Yoshihiro

    2014-03-01

    Transition metal dichalcogenides (TMDs) are well known van der Waals layered materials that are easy to be exfoliated into atomically flat nano scale flakes. Owing to high efficiency of electrical double layer (EDL) dielectrics, thin flakes of TMDs have achieved high performance ambipolar transistor operation and established metallic states with high mobility, which are ideal for inducing superconductivity. Here, we report a comprehensive study of ambipolar transport behaviors in the EDL transistors (EDLTs) of MoS2, MoSe2 and MoTe2 thin flakes down to 2 K. In comparison, MoSe2 EDLT displayed a well-balanced ambipolar transistor operation while the other two showed opposite predominance in electron and hole accumulation, respectively. By modulation of carrier densities, the metal insulator transition (MIT) was observed in both electron and hole transport measurements. Particularly, superconducting transitions were reached after the formation of metallic states in the electron side. The phase diagram of transition temperature-carrier density was established and a dome-shaped structure was confirmed, revealing a universal feature of gate-induce superconductivity in layered band insulators. Present address: University of Groningen.

  14. Half Metallic Digital Ferromagnetic Heterostructure Composed of a (Delta)-doped Layer of Mn in Si

    SciTech Connect

    Qian, M C; Fong, C Y; Liu, K; Pickett, W E; Pask, J E; Yang, L H

    2006-05-30

    The authors propose and investigate the properties of a digital ferromagnetic heterostructure (DFH) consisting of a {delta}-doped layer of Mn in Si, using ab initio electronic-structure methods. They find that (1) ferromagnetic order of the Mn layer is energetically favorable relative to antiferromagnetic, and (2) the heterostructure is a two-dimensional half metallic system. The metallic behavior is contributed by three majority-spin bands originating from hybridized Mn-d and nearest-neighbor Si-p states, and the corresponding carriers are responsible for the ferromagnetic order in the Mn layer. The minority-spin channel has a calculated semiconducting gap of 0.25 eV. Analysis of the total and partial densities of states, band structure, Fermi surfaces and associated charge density reveals the marked two-dimensional nature of the half metallicity. The band lineup is found to be favorable for retaining the half metal character to near the Curie temperature (T{sub C}). Being Si based and possibly having a high T{sub C} as suggested by an experiment on dilutely doped Mn in Si, the heterostructure may be of special interest for integration into mature Si technologies for spintronic applications.

  15. Predictive double-layer modeling of metal sorption in mine-drainage systems

    SciTech Connect

    Smith, K.S.; Plumlee, G.S.; Ranville, J.F.; Macalady, D.L.

    1996-10-01

    Previous comparison of predictive double-layer modeling and empirically derived metal-partitioning data has validated the use of the double-layer model to predict metal sorption reactions in iron-rich mine-drainage systems. The double-layer model subsequently has been used to model data collected from several mine-drainage sites in Colorado with diverse geochemistry and geology. This work demonstrates that metal partitioning between dissolved and sediment phases can be predictively modeled simply by knowing the water chemistry and the amount of suspended iron-rich particulates present in the system. Sorption on such iron-rich suspended sediments appears to control metal and arsenic partitioning between dissolved and sediment phases, with sorption on bed sediment playing a limited role. At pH > 5, Pb and As are largely sorbed by iron-rich suspended sediments and Cu is partially sorbed; Zn, Cd, and Ni usually remain dissolved throughout the pH range of 3 to 8.

  16. Pressure induced metallization with absence of structural transition in layered molybdenum diselenide

    DOE PAGES

    Zhao, Zhao; Zhang, Haijun; Yuan, Hongtao; Wang, Shibing; Lin, Yu; Zeng, Qiaoshi; Xu, Gang; Liu, Zhenxian; Solanki, G. K.; Patel, K. D.; et al

    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

  17. Pressure induced metallization with absence of structural transition in layered molybdenum diselenide

    PubMed Central

    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.

    2015-01-01

    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. PMID:26088416

  18. 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.

  19. Investigation of thin-layer chromatography properties of some transition metal complexes based on ditiocarbamates.

    PubMed

    Ergül, Soner

    2006-10-01

    Sodium diethyldithiocarbamate (DEDTC) and ammonium pyrolidinedithiocarbamate (PyDTC) are prepared as their Co or Cu (M) complexes [M(DEDTC)(2) and M(PyDTC)(2), respectively]. The complexes are prepared by reactions of DEDTC and PyDTC with metal (II) nitrates, and they are examined for chromatographic properties using thin-layer chromatography systems. These complexes and their mixtures are spotted on the activated and non-activated 250-microm thick thin layers of commercial silica gel (Si-60GF(254)). Pure toluene and a toluene-cyclohexane mixture (3:1, v/v) are used as mobile phases for running the complexes. These chromatographic systems are successfully used for the qualitative analysis of the corresponding metal cations and the separation of components in both M(DEDTC)(2) and M(PyDTC)(2) complex mixtures. In addition, non-activated layers are more successful than activated layers. This study may be useful in understanding the effects of stationary and mobile phase properties, retention mechanisms, and the effects of the nature of metal and ligand type on the chromatographic behavior and parameters [e.g., retention factors, theoretical plate numbers, and resolution] of the complexes. PMID:17059680

  20. Atomic layer deposition of Hf{sub x}Al{sub y}C{sub z} as a work function material in metal gate MOS devices

    SciTech Connect

    Lee, Albert Fuchigami, Nobi; Pisharoty, Divya; Hong, Zhendong; Haywood, Ed; Joshi, Amol; Mujumdar, Salil; Bodke, Ashish; Karlsson, Olov; Kim, Hoon; Choi, Kisik; Besser, Paul

    2014-01-15

    As advanced silicon semiconductor devices are transitioning from planar to 3D structures, new materials and processes are needed to control the device characteristics. Atomic layer deposition (ALD) of Hf{sub x}Al{sub y}C{sub z} films using hafnium chloride and trimethylaluminum precursors was combined with postdeposition anneals and ALD liners to control the device characteristics in high-k metal-gate devices. Combinatorial process methods and technologies were employed for rapid electrical and materials characterization of various materials stacks. The effective work function in metal–oxide–semiconductor capacitor devices with the Hf{sub x}Al{sub y}C{sub z} layer coupled with an ALD HfO{sub 2} dielectric was quantified to be mid-gap at ∼4.6 eV. Thus, Hf{sub x}Al{sub y}C{sub z} is a promising metal gate work function material that allows for the tuning of device threshold voltages (V{sub th}) for anticipated multi-V{sub th} integrated circuit devices.

  1. 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

  2. Characterization of the Electric Double Layer Formation Dynamics of a Metal/Ionic Liquid/Metal Structure.

    PubMed

    Schmidt, Elliot; Shi, Sha; Ruden, P Paul; Frisbie, C Daniel

    2016-06-15

    Although ionic liquids (ILs) have been used extensively in recent years as a high-capacitance "dielectric" in electric double layer transistors, the dynamics of the double layer formation have remained relatively unexplored. Better understanding of the dynamics and relaxation processes involved in electric double layer formation will guide device optimization, particularly with regard to switching speed. In this paper, we explore the dynamical characteristics of an IL in a metal/ionic liquid/metal (M/IL/M) capacitor. In particular, we examine a Au/IL/Au structure where the IL is 1-butyl-1-methylpyrrolidinium tris(pentafluoroethyl)trifluorophosphate. The experiments consist of frequency-dependent impedance measurements and time-dependent current vs voltage measurements for applied linear voltage ramps and abrupt voltage steps. The parameters of an equivalent circuit model are determined by fits to the impedance vs frequency data and subsequently verified by calculating the current vs voltage characteristics for the applied potential profiles. The data analysis indicates that the dynamics of the structure are characterized by a wide distribution of relaxation times spanning the range of less than microseconds to longer than seconds. Possible causes for these time scales are discussed. PMID:27213215

  3. Factors affecting metal concentrations in the upper sediment layer of intertidal reedbeds along the river Scheldt.

    PubMed

    Du Laing, Gijs; Vandecasteele, Bart; De Grauwe, Pieter; Moors, Wouter; Lesage, Els; Meers, Erik; Tack, Filip M G; Verloo, Marc G

    2007-05-01

    Factors that play a role in determining metal accumulation in sediments of 26 intertidal marshes which are mainly vegetated by reed plants (Phragmites australis) were assessed along the Scheldt estuary (Belgium and The Netherlands). In the upper 20 cm sediment layer, several physico-chemical properties (clay, silt and sand content, organic matter, carbonate and chloride content, pH and conductivity) and aqua regia extractable metals (Cd, Cr, Cu, Ni, Pb, Zn) were determined. The sediments were significantly contaminated with trace metals. The Cd concentrations often exceeded the Flemish soil remediation thresholds for nature areas, whereas Cr, Cu and Zn levels indicated moderate contamination. Pb concentrations occasionally were high, whereas Ni concentrations leaned towards background values. Organic matter was the single most important predictor variable for total metal contents in regression models, except for Cr. Additional significant predictor variables were clay or chloride content, depending on the metal. Observed metal concentrations at sites within a range of a few km from specific point-sources of metals (e.g. shipyards, industrial areas with metallurgic activities, affluents, major motorways) were somewhat higher than predicted by the models, whereas they were lower than predicted at sites which are regularly subjected to flooding by water of high salinity. The ratio between observed and predicted concentrations seems to be a valuable tool for the identification of areas which are specifically impacted by point sources. PMID:17492090

  4. Electromigration in aluminum/silicon/copper metallization due to the presence of a thin oxide layer

    NASA Astrophysics Data System (ADS)

    Koh, K. A.; Chua, S. J.

    1997-09-01

    The effect of a thin layer of SiO2 (50 nm) on the electromigration behavior of Al/ 0.8wt.%Si/0.5wt.%Cu metallization, passivated by spin-on-glass, phosphorus silicate glass and silicon nitride as part of the complementary metal oxide semiconductor technology fabrication process was studied. It is found that voids were formed along the edge of the metallization line as opposed to formation at triple point of grain boundaries. At the same stress current of 1 × 106 A/cm2, thicker metallization layer (600 nm) showed an improvement in median time to failure (MTF) (1.4 times) with smaller void size (0.2 to 0.4 μm) over one without an underlying oxide, whereas if the metallization thickness is thin (300 nm), the MTF is degraded (0.6 times) with larger void size formed (0.3 to 1.0 μm).

  5. 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.

  6. 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.

  7. 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.

  8. Microstructures and properties of ceramic particle-reinforced metal matrix composite layers produced by laser cladding

    NASA Astrophysics Data System (ADS)

    Zhang, Qingmao; He, Jingjiang; Liu, Wenjin; Zhong, Minlin

    2005-01-01

    Different weight ratio of titanium, zirconium, WC and Fe-based alloy powders were mixed, and cladded onto a medium carbon steel substrate using a 3kW continuous wave CO2 laser, aiming at producing Ceramic particles- reinforced metal matrix composites (MMCs) layers. The microstructures of the layers are typical hypoeutectic, and the major phases are Ni3Si2, TiSi2, Fe3C, FeNi, MC, Fe7Mo3, Fe3B, γ(residual austenite) and M(martensite). The microstructure morphologies of MMCs layers are dendrites/cells. The MC-type reinforcements are in situ synthesis Carbides which main compositions consist of transition elements Zr, Ti, W. The MC-type particles distributed within dendrite and interdendritic regions with different volume fractions for single and overlapping clad layers. The MMCs layers are dense and free of cracks with a good metallurgical bonding between the layer and substrate. The addition ratio of WC in the mixtures has the remarkable effect on the microhardness of clad layers.

  9. 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

  10. Effect of metal films on the photostabilities of emissive organic layers as probed by fluorescence microscopy

    NASA Astrophysics Data System (ADS)

    Abbas, Sikandar; Peteanu, Linda A.

    2015-09-01

    Realization of energy efficient and cost effective electroluminescence applications of conjugated polymers, like organic light emitting diodes (OLEDs), requires a complete understanding of photo-chemical processes at metal-polymer interfaces. Therefore it is useful to study the effects of metal films on the photoluminescence of emissive organic layer fabricated on it. While investigating these processes we observed an interesting and unexpected phenomenon that, when conjugated polymer is deposited on thin gold film substrates, it exhibits remarkable photo-stability relative to that deposited on glass, even in the presence of molecular oxygen. This paper addresses the photo-stability enhancement by thin Au films and explores the photochemical mechanism behind it.

  11. Release of multi-layer metal structure in MEMS devices by dry etching technique

    NASA Astrophysics Data System (ADS)

    Das, N. C.

    2002-04-01

    Reactive ion etching technique was used to remove interleave photoresist layer for free standing metal structure in microelectromechanical systems (MEMS) devices. Mixture of oxygen and CF 4 gas was used to get isotropic etching profile. Etching process was optimized to get large metal structure of 100×100 μm 2 without any surface bending. The etching rate of 0.7 μm/min at 60 W of RIE plasma power is found to be optimum process for the particular application. The reported dry release technique is fully compatible with standard silicon IC processing and hence can be used for hybridize process used in MEMS array application.

  12. Structure of ultrathin oxide layers on metal surfaces from grazing scattering of fast atoms

    NASA Astrophysics Data System (ADS)

    Winter, H.; Seifert, J.; Blauth, D.; Busch, M.; Schüller, A.; Wethekam, S.

    2009-10-01

    The structure of ultrathin oxide layers grown on metal substrates is investigated by grazing scattering of fast atoms from the film surface. We present three recent experimental techniques which allow us to study the structure of ordered oxide films on metal substrates in detail. (1) A new variant of a triangulation method with fast atoms based on the detection of emitted electrons, (2) rainbow scattering under axial surface channeling conditions, and (3) fast atom diffraction (FAD) for studies on the structure of oxide films. Our examples demonstrate the attractive features of grazing fast atom scattering as a powerful analytical tool in surface physics.

  13. 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.

  14. Strain-induced semiconductor to metal transition in few-layer black phosphorus from first principles

    NASA Astrophysics Data System (ADS)

    Ju, Weiwei; Li, Tongwei; Wang, Hui; Yong, Yongliang; Sun, Jinfeng

    2015-02-01

    Electronic structures of few-layer black phosphorus (BP) with biaxial strain are investigated by using methods based on density functional theory. The compressive strain can result in a semiconductor-metal transition (SMT) for few-layer BP, whereas the tensile strain only affects the band gaps. The critical compressive strain for the SMT is larger in the thinner 2D BP. The band structures and charge densities are calculated in order to provide imperative understanding on SMT. With the compressive strain, the energy of conduction bands moves down, which is induced by the structural change and is essential reason of SMT.

  15. Dependence of reactive metal layer on resistive switching in a bi-layer structure Ta/HfOx filament type resistive random access memory

    NASA Astrophysics Data System (ADS)

    Lee, Daeseok; Woo, Jiyong; Park, Sangsu; Cha, Euijun; Lee, Sangheon; Hwang, Hyunsang

    2014-02-01

    The dependence of reactive metal layer on resistive switching characteristics is investigated in a bi-layer structural Ta/HfOx filament type resistive random access memory (ReRAM). By increasing the oxygen absorption rate of the reactive metal layer, formation of an induced resistive switching region that led to significant changes in the resistive switching characteristics of the ReRAM was observed. Electrical and physical analyses showed that the induced TaOx-resistive switching region can result in self-compliance behavior, uniform resistive switching, and a gradual set process, which can be utilized for low power and analog operations.

  16. 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

  17. Characteristics of laser ultrasound interaction with multi-layered dissimilar metals adhesive interface by numerical simulation

    NASA Astrophysics Data System (ADS)

    Zhang, Kuanshuang; Zhou, Zhenggan; Zhou, Jianghua; Sun, Guangkai

    2015-10-01

    The characteristics of laser-generated ultrasonic wave interaction with multi-layered dissimilar metals adhesive interface are investigated by finite element method (FEM). The physical model of laser-generated ultrasonic wave in the multi-layered dissimilar metals adhesive structure is built. The surface temperature evolution with different laser power densities is analyzed to obtain the parameters of pulsed laser with thermoelastic regime. The differences of laser ultrasonic waves with different center frequencies measured at the center of laser irradiation would verify the interfacial features of adhesive structures. The optimum frequency range and probe point would be beneficial for the detection of the small void defect. The numerical results indicate that the different frequency range and probe points would evidently influence the identification and quantitative characterization of the small void defect. The research findings would lay a foundation for testing interfacial integrity.

  18. 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.

  19. 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.

  20. 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

    2016-10-01

    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.

  1. Prediction of transmittance spectra for transparent composite electrodes with ultra-thin metal layers

    NASA Astrophysics Data System (ADS)

    Zhao, Zhao; Khorasani, Arash Elhami; Theodore, N. D.; Dhar, A.; Alford, T. L.

    2015-11-01

    Recent interest in indium-free transparent composite-electrodes (TCEs) has motivated theoretical and experimental efforts to better understand and enhance their electrical and optical properties. Various tools have been developed to calculate the optical transmittance of multilayer thin-film structures based on the transfer-matrix method. However, the factors that affect the accuracy of these calculations have not been investigated very much. In this study, two sets of TCEs, TiO2/Au/TiO2 and TiO2/Ag/TiO2, were fabricated to study the factors that affect the accuracy of transmittance predictions. We found that the predicted transmittance can deviate significantly from measured transmittance for TCEs that have ultra-thin plasmonic metal layers. The ultrathin metal layer in the TCE is typically discontinuous. When light interacts with the metallic islands in this discontinuous layer, localized surface plasmons are generated. This causes extra light absorption, which then leads to the actual transmittance being lower than the predicted transmittance.

  2. 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.

  3. Single-Layer Limit of Metallic Indium Overlayers on Si(111).

    PubMed

    Park, Jae Whan; Kang, Myung Ho

    2016-09-01

    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. PMID:27661703

  4. Single-Layer Limit of Metallic Indium Overlayers on Si(111)

    NASA Astrophysics Data System (ADS)

    Park, Jae Whan; Kang, Myung Ho

    2016-09-01

    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 √{7 }×√{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 √{7 }×√{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.

  5. Prediction of transmittance spectra for transparent composite electrodes with ultra-thin metal layers

    SciTech Connect

    Zhao, Zhao; Alford, T. L.; Khorasani, Arash Elhami; Theodore, N. D.; Dhar, A.

    2015-11-28

    Recent interest in indium-free transparent composite-electrodes (TCEs) has motivated theoretical and experimental efforts to better understand and enhance their electrical and optical properties. Various tools have been developed to calculate the optical transmittance of multilayer thin-film structures based on the transfer-matrix method. However, the factors that affect the accuracy of these calculations have not been investigated very much. In this study, two sets of TCEs, TiO{sub 2}/Au/TiO{sub 2} and TiO{sub 2}/Ag/TiO{sub 2}, were fabricated to study the factors that affect the accuracy of transmittance predictions. We found that the predicted transmittance can deviate significantly from measured transmittance for TCEs that have ultra-thin plasmonic metal layers. The ultrathin metal layer in the TCE is typically discontinuous. When light interacts with the metallic islands in this discontinuous layer, localized surface plasmons are generated. This causes extra light absorption, which then leads to the actual transmittance being lower than the predicted transmittance.

  6. 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

    2015-11-01

    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. PMID:26431263

  7. 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.

  8. The role of ZrN capping layer deposited on ultra-thin high-k Zr-doped yttrium oxide for metal-gate metal-insulator-semiconductor applications

    NASA Astrophysics Data System (ADS)

    Juan, Pi-Chun; Mong, Fan-Chen; Huang, Jen-Hung

    2013-08-01

    Metal-gate MIS structures with and without ZrN capping layer on high-k Y2O3:Zr/Y2O3 stack were fabricated. The binding energies and depth profiles were investigated by x-ray photoelectron spectroscopy (XPS). The x-ray diffraction (XRD) patterns were compared. It is found that Ti out-diffusion into Zr-based high-k dielectric becomes lesser with the insertion of ZrN capping layer. The electrical properties of current-voltage (I-V) and capacitance-voltage (C-V) characteristics were measured in the postannealing temperature range of 550-850 °C. According to the defect reaction model, Zr cation vacancies are associated with the concentration of Ti ion by a transition from +3 to +2 states. The amount of Zr cation vacancies is quantified and equal to a half of Ti substitution amount at Zr site. The reduction in cation vacancies at high temperatures can well explain the decrease in ΔVFB for samples with ZrN layer. In contrast, an excess of Ti outdiffusion will produce the interstitial defects in high-k films without ZrN capping.

  9. Improved air stability of perovskite solar cells via solution-processed metal oxide transport layers.

    PubMed

    You, Jingbi; Meng, Lei; Song, Tze-Bin; Guo, Tzung-Fang; Yang, Yang Michael; Chang, Wei-Hsuan; Hong, Ziruo; Chen, Huajun; Zhou, Huanping; Chen, Qi; Liu, Yongsheng; De Marco, Nicholas; Yang, Yang

    2016-01-01

    Lead halide perovskite solar cells have recently attracted tremendous attention because of their excellent photovoltaic efficiencies. However, the poor stability of both the perovskite material and the charge transport layers has so far prevented the fabrication of devices that can withstand sustained operation under normal conditions. Here, we report a solution-processed lead halide perovskite solar cell that has p-type NiO(x) and n-type ZnO nanoparticles as hole and electron transport layers, respectively, and shows improved stability against water and oxygen degradation when compared with devices with organic charge transport layers. Our cells have a p-i-n structure (glass/indium tin oxide/NiO(x)/perovskite/ZnO/Al), in which the ZnO layer isolates the perovskite and Al layers, thus preventing degradation. After 60 days storage in air at room temperature, our all-metal-oxide devices retain about 90% of their original efficiency, unlike control devices made with organic transport layers, which undergo a complete degradation after just 5 days. The initial power conversion efficiency of our devices is 14.6 ± 1.5%, with an uncertified maximum value of 16.1%.

  10. Improved air stability of perovskite solar cells via solution-processed metal oxide transport layers

    NASA Astrophysics Data System (ADS)

    You, Jingbi; Meng, Lei; Song, Tze-Bin; Guo, Tzung-Fang; Yang, Yang (Michael); Chang, Wei-Hsuan; Hong, Ziruo; Chen, Huajun; Zhou, Huanping; Chen, Qi; Liu, Yongsheng; De Marco, Nicholas; Yang, Yang

    2016-01-01

    Lead halide perovskite solar cells have recently attracted tremendous attention because of their excellent photovoltaic efficiencies. However, the poor stability of both the perovskite material and the charge transport layers has so far prevented the fabrication of devices that can withstand sustained operation under normal conditions. Here, we report a solution-processed lead halide perovskite solar cell that has p-type NiOx and n-type ZnO nanoparticles as hole and electron transport layers, respectively, and shows improved stability against water and oxygen degradation when compared with devices with organic charge transport layers. Our cells have a p-i-n structure (glass/indium tin oxide/NiOx/perovskite/ZnO/Al), in which the ZnO layer isolates the perovskite and Al layers, thus preventing degradation. After 60 days storage in air at room temperature, our all-metal-oxide devices retain about 90% of their original efficiency, unlike control devices made with organic transport layers, which undergo a complete degradation after just 5 days. The initial power conversion efficiency of our devices is 14.6 ± 1.5%, with an uncertified maximum value of 16.1%.

  11. 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.

  12. Observations of Metal Ions in the Meteoroid Layer of the Ionosphere of Mars

    NASA Astrophysics Data System (ADS)

    Benna, Mehdi; Grebowsky, Joseph M.; Mahaffy, Paul

    2016-10-01

    We report the results of the observations of metal ions in the ionosphere of Mars by the Neutral Gas and Ion Mass Spectrometer (NGIMS). These observations were conducted during the five "deep dip" campaigns of the Mars Atmosphere and Volatile Evolution mission (MAVEN), during which the periapsis altitude of the spacecraft altitude is lowered from its nominal 150 km to ~125 km. The observations revealed the presence of Na+, Mg+, and Fe+ in the ionosphere with peak abundance ranging from 1 to 10 ions/cm3 at the periapsis altitude. While, the relative abundance of these metals ions varies from a deep dip campaigns to another, their altitude profile exhibit correlated structures with the neutral atmosphere. These structure may be indicative of the transport processes that carry the metals upward from the main ablation layer to the spacecraft's altitude.

  13. Fabrication and design of metal nano-accordion structures using atomic layer deposition and interference lithography

    NASA Astrophysics Data System (ADS)

    Min, J.-H.; Bagal, A.; Mundy, J. Z.; Oldham, C. J.; Wu, B.-I.; Parsons, G. N.; Chang, C.-H.

    2016-02-01

    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.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. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr08566g

  14. 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.

  15. 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.

  16. 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.

  17. [XPS characterization of auto-reconditioning layer on worn metal surfaces].

    PubMed

    Yang, He; Zhang, Zheng-ye; Li, Sheng-hua; Jin, Yuan-sheng

    2005-06-01

    An auto-reconditioner package for in situ reconditioning of worn surfaces of machinery parts under normal running was applied to diesel engines of DF locomotives. A reconditioning layer was generated on the cylinder bore after running a mileage of 300,000 km, and no wear was measured for the piston rings and cylinder bores. Evaluations with SEM, nanohardness tester and XPS indicated that the protective layer assumed a thickness of 8-10 microm, a nano-hardness twice as high as that of the cast iron substrate, and a main elemental composition of Fe, O and C corresponding to the existence of Fe3O4 and Fe3C. A possible formation mechanism of the protective layer was suggested based on the mechanochemical activation of metal surfaces and the catalytic activation of the auto-reconditioner molecules.

  18. Effect of metal base layer on the absorptance and emittance of sputtered graded metal-carbon selective absorbing surfaces

    NASA Astrophysics Data System (ADS)

    Harding, G. L.; Craig, S.

    1981-08-01

    Solar absorptance and temperature-dependent emittance is measured for graded metal-carbon films deposited onto smooth aluminum, copper, nickel, and stainless steel base layers, sputter-deposited onto glass tubes at relatively low argon pressure (approximately 0.5 Pa), and deposited onto textured copper using argon pressures 3 to 40 Pa. Absorptance measurements are made on surfaces deposited onto small plane glass slides attached to a glass tube in the coating system, and emittance measurements are made on coated tubes, assembled into glass envelopes. Both the small planar specimens of selective surface and coated tubes were inserted in continuously evacuated glass envelopes and annealed at 500 C for approximately 1 hr. It is shown that solar absorptance varies by only 1-2% for the different base layers, whereas the emittance of surfaces based on nickel and stainless steel is considerably higher than for surfaces based on copper and aluminum. Small changes occur in absorptances and emittances after annealing. It is concluded that the optimum selective surface for evacuated collectors used with mirrors of low concentrations consists of graded metal-carbon overlaid with smooth copper.

  19. High-contrast top-emitting organic light-emitting diodes with a Ni/ZnS/CuPc/Ni contrast-enhancing stack and a ZnS anti-reflection layer

    NASA Astrophysics Data System (ADS)

    Chen, Shufen; Xie, Jun; Yang, Yang; Chen, Chunyan; Huang, Wei

    2010-09-01

    High-contrast top-emitting organic light-emitting diodes are successfully fabricated using a Ni/ZnS/copper-phthalocyanine (CuPc)/Ni contrast-enhancing stack (CES) and a ZnS anti-reflection (AR) layer. The CES and AR layer that are outside the active region reduce the complexity of the device design although their utilization affects the device electrical performance due to morphological deterioration of the device films. After the thickness optimization of the CES and AR coating, high contrast ratios of 139.4 : 1 and 462.3 : 1 are obtained under on-state luminances of 300 and 1000 cd m-2 and an ambient luminance of 140 lux. The reduced reflectance of ambient illumination is mainly due to the anti-reflection ZnS layer and the strong absorption of ambient illumination by the Ni layers, where the CES structure is beneficial for the absorption of ambient illumination by the interfacial reflection of Ni/ZnS and CuPc/Ni.

  20. The different diffusive transport behaviours of some metals in layers of Peru Basin surface sediment

    NASA Astrophysics Data System (ADS)

    Fritsche, Ulrich; Koschinsky, Andrea; Winkler, Andreas

    Diffusion experiments with a duration of 90 days were carried out with radio tracers in an oxic and a suboxic sediment layer from two deep-sea sediment cores. Diffusion coefficients, breakthrough and time-lag values were determined and the results checked by modelling. Only small differences of diffusive transport were observed for Na and Cs during the four experiments; Na behaved as a perfect conservative tracer, and the somewhat stronger uptake of Cs in one sample was caused by preferential absorption by illite that was enriched in this sample. The significant differences between the four experiments for the diffusion parameters of Mn, Zn, Co, and Cd correlate with the differing chemical compositions of the sediment layers; higher Mn oxide concentrations in the sample led to slower diffusion through the sediment sample and to significant sorption of the diffusing heavy metals. This result confirms the dominating role of Mn oxide phases in controlling the diffusive exchange of heavy metals between deep-sea sediment and bottom water. Sediment resuspension of the oxic surface layer, such as during potential ferromanganese nodule mining in the deep-sea, would be followed by increased diffusive flux of dissolved heavy metals, especially Mn, from suboxic sediment layers to the new disturbed sediment-bottom-water interface. According to our modelling, the Mn flux from the oxic sediment surface of 0.3 mg m -2 yr -1 in the undisturbed state would increase to up to several mg m -2 yr -1 within the first few weeks after disturbance. Depending on the time necessary until a stable oxic and Mn oxide rich layer is again re-established, a total Mn 2+ release of 54 mg m -2 was calculated if the original state is reached within 100 yr, in contrast to only 3.5 mg m -2 for 5 yr of re-establishment. The fluxes of the other heavy metals would be smaller, corresponding to their lower pore water concentrations in the suboxic layer compared to Mn.

  1. Investigation of Thickness Dependence of Metal Layer in Al/Mo/4H-SiC Schottky Barrier Diodes.

    PubMed

    Lee, Seula; Lee, Jinseon; Kang, Tai-Young; Kyoung, Sinsu; Jung, Eun Sik; Kim, Kyung Hwan

    2015-11-01

    In this paper, we present the preparation and characterization of Schottky barrier diodes based on silicon carbide with various Schottky metal layer thickness values. In this structure, molybdenum and aluminum were employed as the Schottky barrier metal and top electrode, respectively. Schottky metal layers were deposited with thicknesses ranging from 1000 to 3000 Å, and top electrodes were deposited with thickness as much as 3000 Å. The deposition of both metal layers was performed using the facing target sputtering (FTS) method, and the fabricated samples were annealed with the tubular furnace at 300 degrees C under argon ambient for 10 min. The Schottky barrier height, series resistance, and ideality factor was calculated from the forward I-V characteristic curve using the methods proposed by Cheung and Cheung, and by Norde. For as-deposited Schottky diodes, we observed an increase of the threshold voltage (V(T)) as the thickness of the Schottky metal layer increased. After the annealing, the Schottky barrier heights (SBHs) of the diodes, including Schottky metal layers of over 2000 Å, increased. In the case of the Schottky metal layer deposited to 1000 Å, the barrier heights decreased due to the annealing process. This may have been caused by the interfacial penetration phenomenon through the Schottky metal layer. For variations of V(T), the SBH changed with a similar tendency. The ideality factor and series resistance showed no significant changes before or after annealing. This indicates that this annealing condition is appropriate for Mo SiC structures. Our results confirm that it is possible to control V(T) by adjusting the thickness of the Schottky metal layer.

  2. Investigation of Thickness Dependence of Metal Layer in Al/Mo/4H-SiC Schottky Barrier Diodes.

    PubMed

    Lee, Seula; Lee, Jinseon; Kang, Tai-Young; Kyoung, Sinsu; Jung, Eun Sik; Kim, Kyung Hwan

    2015-11-01

    In this paper, we present the preparation and characterization of Schottky barrier diodes based on silicon carbide with various Schottky metal layer thickness values. In this structure, molybdenum and aluminum were employed as the Schottky barrier metal and top electrode, respectively. Schottky metal layers were deposited with thicknesses ranging from 1000 to 3000 Å, and top electrodes were deposited with thickness as much as 3000 Å. The deposition of both metal layers was performed using the facing target sputtering (FTS) method, and the fabricated samples were annealed with the tubular furnace at 300 degrees C under argon ambient for 10 min. The Schottky barrier height, series resistance, and ideality factor was calculated from the forward I-V characteristic curve using the methods proposed by Cheung and Cheung, and by Norde. For as-deposited Schottky diodes, we observed an increase of the threshold voltage (V(T)) as the thickness of the Schottky metal layer increased. After the annealing, the Schottky barrier heights (SBHs) of the diodes, including Schottky metal layers of over 2000 Å, increased. In the case of the Schottky metal layer deposited to 1000 Å, the barrier heights decreased due to the annealing process. This may have been caused by the interfacial penetration phenomenon through the Schottky metal layer. For variations of V(T), the SBH changed with a similar tendency. The ideality factor and series resistance showed no significant changes before or after annealing. This indicates that this annealing condition is appropriate for Mo SiC structures. Our results confirm that it is possible to control V(T) by adjusting the thickness of the Schottky metal layer. PMID:26726688

  3. 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. PMID:27479461

  4. 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; 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 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

  5. Electrical Characterization of Metal-Ferroelectric-Insulator- Semiconductor having Double Layered Insulator for Memory Applications

    NASA Astrophysics Data System (ADS)

    Ismail, L. N.; Wahid, M. H.; Habibah, Z.; Herman, S. H.; Rozana, M. D.; Rusop, M.

    2014-08-01

    Metal-ferroelectric-insulator-semiconductor (MFIS) devices were successfully fabricated using poly(vinylidene fluoride-trifluoroethylene) (PVDF-TrFE) and poly (methyl methacrylate): titanium dioxide (PMMA:TiO2) nanocomposite as ferroelectric and insulator films, respectively on n-type silicon (n-Si) substrate. Both ferroelectric and insulator films were prepared by sol-gel spin coating method. The electrical behaviour of metal-ferroelectric-metal (MFM) structure with PVDF-TrFE film and metal-insulator- metal (MIM) structure PMMA:TiO2 film exhibited different current characteristics. The capacitance of the MFIS devices was found to be 0.42 and 0.29 nF at frequency of 1kHz and 1 MHz respectively. Meanwhile, the dielectric loss values are constant (~60 × 10-3) in the frequency range from 100 Hz to 100 kHz. I-V results for MFIS are much higher than MIM and MFM is due to there is a trapped holes/electron located at the semiconductor- insulator interface which contributes to high leakage current in the MFIS device. We conclude, although interposing the PMMA :TiO2 nanocomposite insulator layer between the semiconductor and Al electrodes degrades the MFIS performance, nevertheless, they remain sufficiently good for use in organic electronic devices.

  6. 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.

  7. 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.

  8. Chameleonic electrochemical metallization cells: dual-layer solid electrolyte-inducing various switching behaviours.

    PubMed

    Lim, Hyungkwang; Soni, Rohit; Kim, Dohun; Kim, Guhyun; Kornijcuk, Vladimir; Kim, Inho; Park, Jong-Keuk; Hwang, Cheol Seong; Jeong, Doo Seok

    2016-08-25

    We present 'unusual' resistive switching behaviours in electrochemical metallization (ECM) cells utilizing a dual-layer (SiOx/GeSex: SiOx on GeSex) solid electrolyte (SE). The observed switching behaviour markedly varies with the thickness of the upper SiOx layer and compliance current: (i) monostable switching, (ii) counter-eightwise bipolar switching, and (iii) combination of monostable and eightwise bipolar switching behaviours. Focusing on cases (i) and (iii), electrical and chemical analyses on these chameleonic cells were performed in an attempt to gain clues to the understanding of the observed complexity. The chemical analysis indicated the upper SiOx layer as a chemical potential well for Cu ions-Cu ions were largely confined in the well. This non-uniform distribution of Cu across the SE perhaps hints at the mechanism for the complex behaviour; it may be a 'zero-sum game' between SiOx and GeSex layers, in which the two layers fight over the limited number of Cu atoms/ions. PMID:27510607

  9. 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.

  10. 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

  11. Fullerenes as adhesive layers for mechanical peeling of metallic, molecular and polymer thin films.

    PubMed

    Wieland, Maria B; Slater, Anna G; Mangham, Barry; Champness, Neil R; Beton, Peter H

    2014-01-01

    We show that thin films of C60 with a thickness ranging from 10 to 100 nm can promote adhesion between a Au thin film deposited on mica and a solution-deposited layer of the elastomer polymethyldisolaxane (PDMS). This molecular adhesion facilitates the removal of the gold film from the mica support by peeling and provides a new approach to template stripping which avoids the use of conventional adhesive layers. The fullerene adhesion layers may also be used to remove organic monolayers and thin films as well as two-dimensional polymers which are pre-formed on the gold surface and have monolayer thickness. Following the removal from the mica support the monolayers may be isolated and transferred to a dielectric surface by etching of the gold thin film, mechanical transfer and removal of the fullerene layer by annealing/dissolution. The use of this molecular adhesive layer provides a new route to transfer polymeric films from metal substrates to other surfaces as we demonstrate for an assembly of covalently-coupled porphyrins.

  12. 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.

  13. Layer Formation On Metal Surfaces In Lead-Bismuth At High Temperatures In Presence Of Zirconium

    SciTech Connect

    Loewen, Eric Paul; Yount, Hannah J.; Volk, Kevin; Kumar, Arvind

    2003-09-01

    If the operating temperature lead–bismuth cooled fission reactor could be extended to 800 °C, they could produce hydrogen directly from water. A key issue for the deployment of this technology at these temperatures is the corrosion of the fuel cladding and structural materials by the lead–bismuth. Corrosion studies of several metals were performed to correlate the interaction layer formation rate as a function of time, temperature, and alloy compositions. The interaction layer is defined as the narrow band between the alloy substrate and the solidified lead–bismuth eutectic on the surface. Coupons of HT-9, 410, 316L, and F22 were tested at 550 and 650 °C for 1000 h inside a zirconium corrosion cell. The oxygen potential ranged from approximately 10-22 to 10-19 Pa. Analyses were performed on the coupons to determine the depth of the interaction layer and the composition, at each time step (100, 300, and 1000 h). The thickness of the interaction layer on F22 at 550 °C was 25.3 µm, the highest of all the alloys tested, whereas at 650 °C, the layer thickness was only 5.6 µm, the lowest of all the alloys tested. The growth of the interaction layer on F22 at 650 °C was suppressed, owing to the presence of Zr (at 1500 wppm) in the LBE. In the case of 316L, the interaction layers of 4.9 and 10.6 µm were formed at 550 and 650 °C, respectively.

  14. Metallicity of Ca2Cu6P5 with single and double copper-pnictide layers

    DOE PAGES

    Li, Li; Parker, David; Chi, Miaofang; Tsoi, Georgiy M.; Vohra, Yogesh K.; Sefat, Athena S.

    2016-02-16

    Here, we report thermodynamic and transport properties, and also theoretical calculations, for Cu-based compound Ca2Cu6P5 and compare with CaCu2-dP2. 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 densitymore » of 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. 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. Novel Synthetic Methods of NbS2 and other Layered Transition Metal Dichalcogenides

    NASA Astrophysics Data System (ADS)

    Cooper, Brian

    2014-03-01

    Research on layered transition metal dichalcogenides (LTMDs - compounds of the form MX2, with M as a metal and X as any member of group 16 in the periodic table) has accelerated since the discovery of graphene. Although much progress in graphene research has been made, there are still many hurdles to clear, and prudence has made requisite parallel courses in research. LTMDs exhibit similar features to graphene; namely they are relatively easy to exfoliate, and have symmetries consistent with hexagonal crystal structure, but unlike graphene, these compounds represent a spanning set of the materials under investigation in various scientific branches (e.g. superconductors, semiconductors, topological insulators, etc.). We shall report a novel approach the synthesis, manipulation, and device design of these materials. In our attempts to better understand the role of doping Nb into the MoS2 and WS2 systems, we serendipitously realized the merits, which previously lay quiescent, of studying NbS2 itself. A metallic dichalcogenide, NbS2 exhibits both charge density wave and superconducting phase transitions below respective appropriate temperatures. Studying mono, bi, and tri-layer systems have afforded us the opportunities to probe not only the details of quantum confinement effects in the NbS2 system, but also how these effects percolate through and affect the various properties of other dichalcogenidal systems.

  16. Long-Term Passivation of Strongly Interacting Metals with Single-Layer Graphene.

    PubMed

    Weatherup, Robert S; D'Arsié, Lorenzo; Cabrero-Vilatela, Andrea; Caneva, Sabina; Blume, Raoul; Robertson, John; Schloegl, Robert; Hofmann, Stephan

    2015-11-18

    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

  17. Layered spherical carbon composites with nanoparticles of different metals grown simultaneously inside and outside.

    PubMed

    Tang, Shaochun; Vongehr, Sascha; Meng, Xiangkang

    2012-03-01

    We report a general one-step route to place nanoparticles (NPs) of different noble metals controllably into interior or surface locations of submicron nanoporous carbon spheres (CSs). In particular, Pd and Au NPs can be easily put either inside or outside of the CSs by selecting these metals' differently charged precursor ions. Employing mixed precursor solutions, the method allows different metals to grow simultaneously yet selectively in the separate locations, thus resulting in composites with a complex layered structure, for example Pd or Au outside and Ag inside, Au or Pt outside and Pd inside, and other combinations. The synthesis is fast and needs no additional steps like a functionalization of surfaces. It crucially involves microwave heating, the power setting of which further influences the locations and sizes of the NPs especially in the interior of the amorphous carbon matrix. The three-dimensional composite structures are analyzed by transmission electron microscopy and energy dispersed x-ray spectroscopy combined with quantitative analysis by comparison with simulation. The UV-visible absorption of monometallic and layered composites is compared. The involved mechanisms leading to the selective decoration are discussed; important aspects being the charge of the precursor ions and selective microwave absorption.

  18. 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

  19. Layered transition metal dichalcogenides: promising near-lattice-matched substrates for GaN growth

    NASA Astrophysics Data System (ADS)

    Gupta, Priti; Rahman, A. A.; Subramanian, Shruti; Gupta, Shalini; Thamizhavel, Arumugam; Orlova, Tatyana; Rouvimov, Sergei; Vishwanath, Suresh; Protasenko, Vladimir; Laskar, Masihhur R.; Xing, Huili Grace; Jena, Debdeep; Bhattacharya, Arnab

    2016-03-01

    Most III-nitride semiconductors are grown on non-lattice-matched substrates like sapphire or silicon due to the extreme difficulty of obtaining a native GaN substrate. We show that several layered transition-metal dichalcogenides are closely lattice-matched to GaN and report the growth of GaN on a range of such layered materials. We report detailed studies of the growth of GaN on mechanically-exfoliated flakes WS2 and MoS2 by metalorganic vapour phase epitaxy. Structural and optical characterization show that strain-free, single-crystal islands of GaN are obtained on the underlying chalcogenide flakes. We obtain strong near-band-edge emission from these layers, and analyse their temperature-dependent photoluminescence properties. We also report a proof-of-concept demonstration of large-area growth of GaN on CVD MoS2. Our results show that the transition-metal dichalcogenides can serve as novel near-lattice-matched substrates for nitride growth.

  20. Layered transition metal dichalcogenides: promising near-lattice-matched substrates for GaN growth.

    PubMed

    Gupta, Priti; Rahman, A A; Subramanian, Shruti; Gupta, Shalini; Thamizhavel, Arumugam; Orlova, Tatyana; Rouvimov, Sergei; Vishwanath, Suresh; Protasenko, Vladimir; Laskar, Masihhur R; Xing, Huili Grace; Jena, Debdeep; Bhattacharya, Arnab

    2016-03-30

    Most III-nitride semiconductors are grown on non-lattice-matched substrates like sapphire or silicon due to the extreme difficulty of obtaining a native GaN substrate. We show that several layered transition-metal dichalcogenides are closely lattice-matched to GaN and report the growth of GaN on a range of such layered materials. We report detailed studies of the growth of GaN on mechanically-exfoliated flakes WS2 and MoS2 by metalorganic vapour phase epitaxy. Structural and optical characterization show that strain-free, single-crystal islands of GaN are obtained on the underlying chalcogenide flakes. We obtain strong near-band-edge emission from these layers, and analyse their temperature-dependent photoluminescence properties. We also report a proof-of-concept demonstration of large-area growth of GaN on CVD MoS2. Our results show that the transition-metal dichalcogenides can serve as novel near-lattice-matched substrates for nitride growth.

  1. Layered transition metal dichalcogenides: promising near-lattice-matched substrates for GaN growth

    PubMed Central

    Gupta, Priti; Rahman, A. A.; Subramanian, Shruti; Gupta, Shalini; Thamizhavel, Arumugam; Orlova, Tatyana; Rouvimov, Sergei; Vishwanath, Suresh; Protasenko, Vladimir; Laskar, Masihhur R.; Xing, Huili Grace; Jena, Debdeep; Bhattacharya, Arnab

    2016-01-01

    Most III-nitride semiconductors are grown on non-lattice-matched substrates like sapphire or silicon due to the extreme difficulty of obtaining a native GaN substrate. We show that several layered transition-metal dichalcogenides are closely lattice-matched to GaN and report the growth of GaN on a range of such layered materials. We report detailed studies of the growth of GaN on mechanically-exfoliated flakes WS2 and MoS2 by metalorganic vapour phase epitaxy. Structural and optical characterization show that strain-free, single-crystal islands of GaN are obtained on the underlying chalcogenide flakes. We obtain strong near-band-edge emission from these layers, and analyse their temperature-dependent photoluminescence properties. We also report a proof-of-concept demonstration of large-area growth of GaN on CVD MoS2. Our results show that the transition-metal dichalcogenides can serve as novel near-lattice-matched substrates for nitride growth. PMID:27025461

  2. 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.

  3. Observations and Modeling of Sporadic Metal Layers over the Arecibo Observatory

    NASA Astrophysics Data System (ADS)

    Delgado Gilewski, Ruben

    Nighttime observations of the atmospheric potassium and iron layers were performed using lidar, between September 2001 and December 2005, to determine the frequency and characteristics of potassium (Ks) and iron (Fes) sporadic metal layers over the Arecibo Observatory. Ks and Fes were observed to occur once every six hours of measurements, lasting about 90 minutes. Occurrence probability, peak height and full width half maxima (FWHM), strength factor and duration were determined from 1312 and 299 hours of observations for potassium and iron, respectively. Ab initio and density functional calculations were carried out to calculate the geometry and vibrational frequencies of the neutral and ionic form of KN2 and KCO2 to study the binding energy, the adiabatic ionization energy (AIE), and the vertical ionization energy (VIE). KCO 2+ and KN2+ have a significant role in Ks, acting as sinks and reservoirs in the ligand-switching recombination reactions used to describe the mesospheric potassium ion-chemistry. Finally, we present an analysis of two separate and distinct sporadic layer events in the mesosphere and lower thermosphere region above the Arecibo Observatory. One sporadic event was a high altitude layer, in which both atomic and ion sporadic layers were positioned above 100 km altitude. This represents a rather typical sporadic layer visible in both ions and neutrals at Arecibo. The other observation was less typical, with a lower altitude and more diffuse sporadic E layer, extending from below 90 km to above 95 km, which dissipated coincident with growth of a sporadic neutral K layer. We analyze these separate events using a temperature-dependent chemical model. First, we find that the high altitude layer of 12--13 June 2002 has a distinct and important temperature dependence, and that the neutral layer would not have formed had the temperature profile matched the MSIS-90 model. Second, the temperature dependent chemistry model reproduced K+ in close agreement

  4. Evolution of magnetic layers stacking sequence within the magnetic structure of Ho(CoxNi1-x)2B2C

    NASA Astrophysics Data System (ADS)

    ElMassalami, M.; Takeya, H.; Ouladdiaf, B.; Gomes, A. M.; Paiva, T.; dos Santos, R. R.

    2014-12-01

    We evaluated the influence of Co substitution on the magnetic structure of Ho(CoxNi1-x)2B2C (x=0.2, 0.4, 0.6, 0.8) using neutron diffraction, magnetization and specific heat studies. Different modes are stabilized: an AFM k=(0,0,1) mode for x=0.2, a spiral k=(0,0,0.49) mode for x=0.4, a spiral k=(0,0,0.26) mode for x=0.6, and a FM k=(0,0,0) mode for x=0.8. Recalling that for x=0.0, k=(0,0,1) while for x=1.0, k=(0,0,0), then all these magnetic structures can be visualized as a variation in the stacking sequence, along the z-axis, of the intra-planar FM-coupled Ho sheets as such Co substitution controls the z-component of the k=(0,0,ux) vector where ux=0,0.26,0.49, or 1. We discuss this inference and the observation that in spite of such a diversity of magnetic structures, the critical temperatures and the saturated moments are only weakly influenced by substitution.

  5. 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.

  6. 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.

  7. 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; 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 excitationmore » modulates the local competition between the metallic and the insulating phases.« less

  8. 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.

  9. Self-Supporting Metal-Organic Layers as Single-Site Solid Catalysts.

    PubMed

    Cao, Lingyun; Lin, Zekai; Peng, Fei; Wang, Weiwei; Huang, Ruiyun; Wang, Cheng; Yan, Jiawei; Liang, Jie; Zhang, Zhiming; Zhang, Teng; Long, Lasheng; Sun, Junliang; Lin, Wenbin

    2016-04-11

    Metal-organic layers (MOLs) represent an emerging class of tunable and functionalizable two-dimensional materials. In this work, the scalable solvothermal synthesis of self-supporting MOLs composed of [Hf6O4(OH)4(HCO2)6] secondary building units (SBUs) and benzene-1,3,5-tribenzoate (BTB) bridging ligands is reported. The MOL structures were directly imaged by TEM and AFM, and doped with 4'-(4-benzoate)-(2,2',2''-terpyridine)-5,5''-dicarboxylate (TPY) before being coordinated with iron centers to afford highly active and reusable single-site solid catalysts for the hydrosilylation of terminal olefins. MOL-based heterogeneous catalysts are free from the diffusional constraints placed on all known porous solid catalysts, including metal-organic frameworks. This work uncovers an entirely new strategy for designing single-site solid catalysts and opens the door to a new class of two-dimensional coordination materials with molecular functionalities.

  10. Optical response in nanostructured thin metal films with dielectric over-layers

    NASA Astrophysics Data System (ADS)

    Smith, G. B.; Maaroof, A. I.

    2004-12-01

    Thin metal films which contain nano-size pores yield higher than expected transmittance and larger than expected times for transmission of near infra red radiation. An optically equivalent layer with complex refractive index (n*, k*) can model measured specular transmittance and reflectance, when scattering is weak. The way surface plasmon effects impact on these measured indices is considered. A strongly elevated n* is linked to trad the time for a surface plasmon to re-radiate and hence delay transmission times, and reduced imaginary part k*, to resonant channelling via voids. Measurement of n* thus allows an estimate of trad. The sensitivity of (n*, k*) to surface effects is illustrated using an insulating overlayer to modify the surface states. Resultant measured changes in n*, k* are substantial. Results are for two nanostructured metal systems characterised with 400,000× scanning electron microscopy.

  11. 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

    2016-03-01

    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. PMID:26863903

  12. 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.

  13. Metal-Insulator Transition of the New One-Dimensional Organic Conductors with Complete Uniform Stacks: (DMEDO-TTF)2X (X = ClO4 and BF4)

    NASA Astrophysics Data System (ADS)

    Kumeta, Shohei; Kawamoto, Tadashi; Shirahata, Takashi; Misaki, Yohji; Mori, Takehiko

    2016-09-01

    The structural, transport, and magnetic properties of the new organic conductors (DMEDO-TTF)2X (X = ClO4 and BF4), where DMEDO-TTF is dimethyl(ethylenedioxy)tetrathiafulvalene, have been investigated. These compounds have a complete uniform stack structure, indicating that a quasi-one-dimensional 3/4-filled band without a dimerization gap is realized. The ClO4 and BF4 salts show a first-order metal-insulator (MI) transition at approximately 190 and 210 K, respectively, in the cooling process. The ground state is a nonmagnetic insulator on the basis of magnetic susceptibility measurements. Low-temperature X-ray diffraction measurements show that the MI transition originates in the anion ordering transition with a superstructure wave vector of q = (0,1/2,0) corresponding to the stacking direction; the uniform donor stacking structure changes to the tetramerized structure with a large shift of the donors. The shift of the anion toward the central two donors in a tetramer indicates that the insulating phase is a charge-density-wave state.

  14. Charge generation layers comprising transition metal-oxide/organic interfaces. Electronic structure and charge generation mechanism

    SciTech Connect

    Meyer, Jens; Kröger, M.; Hamwi, S.; Gnam, F.; Riedl, T.; Kowalsky, W.; Kahn, Antoine

    2010-01-01

    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 (Cs2 CO3 ) are determined by ultraviolet and inverse photoemissionspectroscopy. 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:Cs2 CO3 ) . 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.

  15. Flat metallic surface gratings with sub-10 nm gaps controlled by atomic-layer deposition.

    PubMed

    Chen, Borui; Ji, Dengxin; Cheney, Alec; Zhang, Nan; Song, Haomin; Zeng, Xie; Thomay, Tim; Gan, Qiaoqiang; Cartwright, Alexander

    2016-09-16

    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.

  16. Flat metallic surface gratings with sub-10 nm gaps controlled by atomic-layer deposition.

    PubMed

    Chen, Borui; Ji, Dengxin; Cheney, Alec; Zhang, Nan; Song, Haomin; Zeng, Xie; Thomay, Tim; Gan, Qiaoqiang; Cartwright, Alexander

    2016-09-16

    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. PMID:27505713

  17. 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.

  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. Chemical routes to modify, uplift, and detach a silicene layer from a metal substrate.

    PubMed

    Tsetseris, Leonidas; Kaltsas, Dimitrios

    2014-03-21

    Experimental studies have shown that honeycomb silicene layers can grow on various metal substrates. Here we demonstrate using first-principles calculations that hydrogenation and calcium intercalation can be employed to break bonds between a silicene overlayer and a silver surface. The end result of the former process is the creation of a silicane mono-layer, a wide band-gap semiconductor. In this way, the Si overlayer can eventually be etched away, in agreement with pertinent experiments. Ca intercalation, on the other hand, lifts the silicene sheet up without destroying its sp(2) honeycomb bonding. Both approaches augment thus the functionalities of silicene overlayers by creating two-dimensional materials with distinct properties.

  20. 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.

  1. Silicon Layer Intercalation and Interface Properties between Graphene and Metal hosts

    NASA Astrophysics Data System (ADS)

    Wang, Yeliang; Mao, Jinhai; Meng, Lei; Gao, Hongjun; Junfeng He Collaboration; Shixuan Du Collaboration; Xingjiang Zhou Collaboration; A. H. Castro Neto Collaboration

    2013-03-01

    Graphene is being considered as a contender as the reference material with extraordinary properties for a post-CMOS technology. The availability of high quality and large scale single crystal graphene is fundamental for it to fulfill its promise in electronic applications. Graphene is usually grown on a metallic substrate from which it has to be transferred before it can be used. However, uncontrolled shear and strain, associated with the transfer and the presence of extended domains, lead to unavoidable tearing, rendering it useless for scalable production. We propose a way to overcome this bottleneck and produce high quality, free standing graphene by intercalating Si in graphene epitaxially grown on metals, like Ru(0001) & Ir(111). This G/Si/metal architecture, produced by the silicon-layer intercalation approach (SIA), was characterized by STM/STS, Raman, and angle resolved electron photoemission spectroscopy (ARPES) and proves the high structural and electronic qualities of the new composite. The SIA eliminates the need for the graphene transfer and also allows for an atomic control of the distance between the graphene and the metal. Graphene Research Center, Singapore National University.

  2. Transmission enhancement based on strong interference in metal-semiconductor layered film for energy harvesting

    PubMed Central

    Li, Qiang; Du, Kaikai; Mao, Kening; Fang, Xu; Zhao, Ding; Ye, Hui; Qiu, Min

    2016-01-01

    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. PMID:27404510

  3. 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

    2016-01-01

    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. PMID:27404510

  4. 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.

  5. Layered reduced graphene oxide with nanoscale interlayer gaps as a stable host for lithium metal anodes.

    PubMed

    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.

  6. 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.

  7. Concurrent tailoring of fabrication process and interphase layer to reduce residual stresses in metal matrix composites

    NASA Technical Reports Server (NTRS)

    Saravanos, D. A.; Chamis, C. C.; Morel, M.

    1991-01-01

    A methodology is presented to reduce the residual matrix stresses in continuous fiber metal matrix composites (MMC) by optimizing the fabrication process and interphase layer characteristics. The response of the fabricated MMC was simulated based on nonlinear micromechanics. Application cases include fabrication tailoring, interphase tailoring, and concurrent fabrication-interphase optimization. Two composite systems, silicon carbide/titanium and graphite/copper, are considered. Results illustrate the merits of each approach, indicate that concurrent fabrication/interphase optimization produces significant reductions in the matrix residual stresses and demonstrate the strong coupling between fabrication and interphase tailoring.

  8. Post heat treatment effects on double layer metal structures for VLSI applications

    NASA Technical Reports Server (NTRS)

    Wade, T. E.; Trotter, J. D.

    1978-01-01

    The realization of high yield double layer metal systems using wet chemistry processes and the ability to extend yields beyond that attainable with wet chemistry by means of post sintering processes at temperatures below 500 C for potential applications in very large scale integration structures were studied. Yields in excess of 98% and average total contact resistance of less than 150 ohms and 200 ohms were realized for a series of 560 vias of 0.5 X 0.5 mils and 0.2 X 0.2 mils in size, respectively.

  9. Effect of Individual Layer Shape on the Mechanical Properties of Dissimilar Al Alloys Laminated Metal Composite Sheets

    NASA Astrophysics Data System (ADS)

    Chen, Zejun; Wu, Xia; Hu, Hongbo; Chen, Quanzhong; Liu, Qing

    2014-03-01

    For the dissimilar laminated metal composite sheets (LMCS) fabricated by roll bonding technology, the great differences of mechanical properties between the constituent metals lead to the non-uniform deformation and individual layer necking. The individual layer shape affects the mechanical properties and microstructure of dissimilar LMCS. The Al/Al alloy (1100/7075) LMCS with the same thickness and ratio of dissimilar metals, but different individual layer shapes, have been successfully fabricated by hot accumulative roll bonding in conjunction with cold rolling technology. Some effective methods (such as sheet crown, warp degree, and slant angle) were presented to quantitatively evaluate the individual layer shape and necking of constituent metals. The microstructure and mechanical properties of 1100/7075 LMCS with different individual layer shapes were investigated. The effects of bonding interface on the mechanical properties were obtained based on the assessment of individual layer shapes and necking. The strength and elongation of LMCS decrease with the increase of variation of individual layer shapes and necking when the number of layers keeps constant. The research results offer some theoretical guides and references for adjusting the control measures of compatibility deformation, optimizing the hot roll bonding technologies, and designing the novel high-performance dissimilar LMCS.

  10. Double Layer Charging for Conductivity Enhancement of Pure Metallic and Semiconducting Single Wall Carbon Nanotubes

    NASA Astrophysics Data System (ADS)

    Mayo, Nathanael; Kuznetsov, Alexander; Zakhidov, Anvar

    2011-03-01

    Injecting high electronic charge densities can profoundly change the optical, electrical, and magnetic properties of materials. Evidence suggests a possibility of significantly improving conductivity of carbon nanotubes through double layer charge injection. Double layer charge injection can prove to be a powerful method when applied to carbon nanotubes because of theirs high surface area and chemical stability. Investigation has commenced on the effect of charging on various types of carbon nanotubes, specifically 99% purified single wall semiconducting and single wall metallic tubes. An electrical double layer is electrochemically introduced upon a sheet of carbon nanotubes via application of potential (up to +/- 5 volts) to a sample immersed in ionic-liquid-based electrolyte. Resistance of carbon nanotube as a function of applied charging voltage is recorded to determine the effects of charge injection. Results show that the electrical double layer considerably reduces the resistance across both samples. ESR/LFMA studies combined with low temperature magnetic and transport measurements are conducted to search for charge injection induced superconductivity in carbon nanotubes. Supported by AFOSR grant FA 9550-09-1-0384.

  11. Tunable near-infrared optical properties of three-layered metal nanoshells.

    PubMed

    Wu, Dajian; Xu, Xiaodong; Liu, Xiaojun

    2008-08-21

    The extinction spectra of a three-layered metal nanoshell, which consists of a particle with a dielectric core, a middle Ag (Au) layer, and an outer Au (Ag) shell, have been investigated by means of the Mie theory. With a decrease in the outer shell thickness or the middle layer thickness, the wavelengths of the localized surface plasmon resonance (LSPR) for SiO(2)-Ag-Au (SiO(2)-Au-Ag) nanoshells show distinct redshifts and the full widths at half maximum (FWHMs) for the dipole peaks in the extinction spectra decrease first and then increase. We have further investigated the influence of the embedding medium on the LSPRs for SiO(2)-Ag-Au and SiO(2)-Au-Ag nanoshells and found that the resonance wavelengths of the particles show redshift and the FWHM of the dipole peak increases with increasing the dielectric constant of the embedding medium. The calculated results indicate that the LSPR of the three-layered gold-silver nanoshells can be controlled to the near-infrared region by changing the geometry, which has practical biomedical application. PMID:19044796

  12. Pressure-Free Bonding of Metallic Plates with Ni Affinity Layers Using Cu Nanoparticles

    NASA Astrophysics Data System (ADS)

    Ishizaki, Toshitaka; Akedo, Kunio; Satoh, Toshikazu; Watanabe, Ryota

    2014-01-01

    This study investigated the pressure-free bonding of metallic plates using Cu nanoparticles capped by fatty acid and amine as the bonding material. The application of Ni layers to Cu plates prior to bonding significantly improved their adhesion to sintered Cu nanoparticles, resulting in higher strengths even without pressure compared to samples bonded using an ordinary Pb-rich solder at a similar temperature. The shear strength could be enhanced if the thickness of Ni layers was larger than 1 nm. The same effect was also observed when Al plates with Ni layers were bonded by Cu nanoparticles. In contrast, Ti, Mn, and Cr layers were found to be ineffective with regard to improving bond strength. Cu plates bonded by Cu nanoparticles capped by fatty acid and amine with different alkyl chain lengths from 6 to 18 showed an optimal strength with a length of 10, where the Cu particles were small enough to sinter effectively but not so small as to oxidize.

  13. Control of valence and conduction band energies in layered transition metal phosphates via surface functionalization.

    PubMed

    Lentz, Levi C; Kolb, Brian; Kolpak, Alexie M

    2016-05-18

    Layered transition metal phosphates and phosphites (TMPs) are a class of materials composed of layers of 2D sheets bound together via van der Waals interactions and/or hydrogen bonds. Explored primarily for use in proton transfer, their unique chemical tunability also makes TMPs of interest for forming large-scale hybrid materials. Further, unlike many layered materials, TMPs can readily be solution exfoliated to form single 2D sheets or bilayers, making them exciting candidates for a variety of applications. However, the electronic properties of TMPs have largely been unstudied to date. In this work, we use first-principles computations to investigate the atomic and electronic structure of TMPs with a variety of stoichiometries. We demonstrate that there exists a strong linear relationship between the band gap and the ionic radius of the transition metal cation in these materials, and show that this relationship, which opens opportunities for engineering new compositions with a wide range of band gaps, arises from constraints imposed by the phosphorus-oxygen bond geometry. In addition, we find that the energies of the valence and conduction band edges can be systematically tuned over a range of ∼3 eV via modification of the functional group extending from the phosphorus. Based on the Hammett constant of this functional group, we identify a simple, predictive relationship for the ionization potential and electron affinity of layered TMPs. Our results thus provide guidelines for systematic design of TMP-derived functional materials, which may enable new approaches for optimizing charge transfer in electronics, photovoltaics, electrocatalysts, and other applications. PMID:27157509

  14. Control of valence and conduction band energies in layered transition metal phosphates via surface functionalization.

    PubMed

    Lentz, Levi C; Kolb, Brian; Kolpak, Alexie M

    2016-05-18

    Layered transition metal phosphates and phosphites (TMPs) are a class of materials composed of layers of 2D sheets bound together via van der Waals interactions and/or hydrogen bonds. Explored primarily for use in proton transfer, their unique chemical tunability also makes TMPs of interest for forming large-scale hybrid materials. Further, unlike many layered materials, TMPs can readily be solution exfoliated to form single 2D sheets or bilayers, making them exciting candidates for a variety of applications. However, the electronic properties of TMPs have largely been unstudied to date. In this work, we use first-principles computations to investigate the atomic and electronic structure of TMPs with a variety of stoichiometries. We demonstrate that there exists a strong linear relationship between the band gap and the ionic radius of the transition metal cation in these materials, and show that this relationship, which opens opportunities for engineering new compositions with a wide range of band gaps, arises from constraints imposed by the phosphorus-oxygen bond geometry. In addition, we find that the energies of the valence and conduction band edges can be systematically tuned over a range of ∼3 eV via modification of the functional group extending from the phosphorus. Based on the Hammett constant of this functional group, we identify a simple, predictive relationship for the ionization potential and electron affinity of layered TMPs. Our results thus provide guidelines for systematic design of TMP-derived functional materials, which may enable new approaches for optimizing charge transfer in electronics, photovoltaics, electrocatalysts, and other applications.

  15. Enhanced Lifetime of Polymer Solar Cells by Surface Passivation of Metal Oxide Buffer Layers.

    PubMed

    Venkatesan, Swaminathan; Ngo, Evan; Khatiwada, Devendra; Zhang, Cheng; Qiao, Qiquan

    2015-07-29

    The role of electron selective interfaces on the performance and lifetime of polymer solar cells were compared and analyzed. Bilayer interfaces consisting of metal oxide films with cationic polymer modification namely poly ethylenimine ethoxylated (PEIE) were found to enhance device lifetime compared to bare metal oxide films when used as an electron selective cathode interface. Devices utilizing surface-modified metal oxide layers showed enhanced lifetimes, retaining up to 85% of their original efficiency when stored in ambient atmosphere for 180 days without any encapsulation. The work function and surface potential of zinc oxide (ZnO) and ZnO/PEIE interlayers were evaluated using Kelvin probe and Kelvin probe force microscopy (KPFM) respectively. Kelvin probe measurements showed a smaller reduction in work function of ZnO/PEIE films compared to bare ZnO films when aged in atmospheric conditions. KPFM measurements showed that the surface potential of the ZnO surface drastically reduces when stored in ambient air for 7 days because of surface oxidation. Surface oxidation of the interface led to a substantial decrease in the performance in aged devices. The enhancement in the lifetime of devices with a bilayer interface was correlated to the suppressed surface oxidation of the metal oxide layers. The PEIE passivated surface retained a lower Fermi level when aged, which led to lower trap-assisted recombination at the polymer-cathode interface. Further photocharge extraction by linearly increasing voltage (Photo-CELIV) measurements were performed on fresh and aged samples to evaluate the field required to extract maximum charges. Fresh devices with a bare ZnO cathode interlayer required a lower field than devices with ZnO/PEIE cathode interface. However, aged devices with ZnO required a much higher field to extract charges while aged devices with ZnO/PEIE showed a minor increase compared to the fresh devices. Results indicate that surface modification can act as a

  16. 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.

  17. Ultrathin cobalt-alloyed barrier layers for copper metallization by a new seeding and electroless-deposition process

    NASA Astrophysics Data System (ADS)

    Chen, Sung-Te; Liu, Yuan-Yu; Chen, Giin-Shan

    2015-11-01

    Pioneering activation-seeding processes grow catalytic particles with sizes exceeding 10 nm due to agglomeration, and thus are unable to act as a template for electroless deposition of a barrier layer with a thickness of 10 nm or less, which is desperately needed for the incoming ULSI copper interconnecting technology. In this work, the capacity of a seeding process to grow a continuous Co-P barrier layer of 8-nm thickness on thermally oxidized SiO2 layers using electroless deposition will be demonstrated. The Co-P barrier layer works effectively in retarding (a) Cu agglomeration and (b) Cu diffusion into the dielectric layer subjected to thermal annealing. Evidently, thermal stability of the Cu film on SiO2 is markedly strengthened by interposing the 8-nm-thick barrier layer. The mechanism of the interposed barrier layer in enhancing thermal stability of the metallization layer is currently under investigation.

  18. Modeling small-signal response of GaN-based metal-insulator-semiconductor high electron mobility transistor gate stack in spill-over regime: Effect of barrier resistance and interface states

    SciTech Connect

    Capriotti, M. E-mail: dionyz.pogany@tuwien.ac.at; Fleury, C.; Oposich, M.; Bethge, O.; Strasser, G.; Pogany, D. E-mail: dionyz.pogany@tuwien.ac.at; Lagger, P.; Ostermaier, C.

    2015-01-14

    We provide theoretical and simulation analysis of the small signal response of SiO{sub 2}/AlGaN/GaN metal insulator semiconductor (MIS) capacitors from depletion to spill over region, where the AlGaN/SiO{sub 2} interface is accumulated with free electrons. A lumped element model of the gate stack, including the response of traps at the III-N/dielectric interface, is proposed and represented in terms of equivalent parallel capacitance, C{sub p}, and conductance, G{sub p}. C{sub p} -voltage and G{sub p} -voltage dependences are modelled taking into account bias dependent AlGaN barrier dynamic resistance R{sub br} and the effective channel resistance. In particular, in the spill-over region, the drop of C{sub p} with the frequency increase can be explained even without taking into account the response of interface traps, solely by considering the intrinsic response of the gate stack (i.e., no trap effects) and the decrease of R{sub br} with the applied forward bias. Furthermore, we show the limitations of the conductance method for the evaluation of the density of interface traps, D{sub it}, from the G{sub p}/ω vs. angular frequency ω curves. A peak in G{sub p}/ω vs. ω occurs even without traps, merely due to the intrinsic frequency response of gate stack. Moreover, the amplitude of the G{sub p}/ω vs. ω peak saturates at high D{sub it}, which can lead to underestimation of D{sub it}. Understanding the complex interplay between the intrinsic gate stack response and the effect of interface traps is relevant for the development of normally on and normally off MIS high electron mobility transistors with stable threshold voltage.

  19. Modeling small-signal response of GaN-based metal-insulator-semiconductor high electron mobility transistor gate stack in spill-over regime: Effect of barrier resistance and interface states

    NASA Astrophysics Data System (ADS)

    Capriotti, M.; Lagger, P.; Fleury, C.; Oposich, M.; Bethge, O.; Ostermaier, C.; Strasser, G.; Pogany, D.

    2015-01-01

    We provide theoretical and simulation analysis of the small signal response of SiO2/AlGaN/GaN metal insulator semiconductor (MIS) capacitors from depletion to spill over region, where the AlGaN/SiO2 interface is accumulated with free electrons. A lumped element model of the gate stack, including the response of traps at the III-N/dielectric interface, is proposed and represented in terms of equivalent parallel capacitance, Cp, and conductance, Gp. Cp -voltage and Gp -voltage dependences are modelled taking into account bias dependent AlGaN barrier dynamic resistance Rbr and the effective channel resistance. In particular, in the spill-over region, the drop of Cp with the frequency increase can be explained even without taking into account the response of interface traps, solely by considering the intrinsic response of the gate stack (i.e., no trap effects) and the decrease of Rbr with the applied forward bias. Furthermore, we show the limitations of the conductance method for the evaluation of the density of interface traps, Dit, from the Gp/ω vs. angular frequency ω curves. A peak in Gp/ω vs. ω occurs even without traps, merely due to the intrinsic frequency response of gate stack. Moreover, the amplitude of the Gp/ω vs. ω peak saturates at high Dit, which can lead to underestimation of Dit. Understanding the complex interplay between the intrinsic gate stack response and the effect of interface traps is relevant for the development of normally on and normally off MIS high electron mobility transistors with stable threshold voltage.

  20. 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.