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Sample records for diameter-dependent dopant location

  1. Diameter-dependent dopant location in silicon and germanium nanowires

    PubMed Central

    Xie, Ping; Hu, Yongjie; Fang, Ying; Huang, Jinlin; Lieber, Charles M.

    2009-01-01

    We report studies defining the diameter-dependent location of electrically active dopants in silicon (Si) and germanium (Ge) nanowires (NWs) prepared by nanocluster catalyzed vapor-liquid-solid (VLS) growth without measurable competing homogeneous decomposition and surface overcoating. The location of active dopants was assessed from electrical transport measurements before and after removal of controlled thicknesses of material from NW surfaces by low-temperature chemical oxidation and etching. These measurements show a well-defined transition from bulk-like to surface doping as the diameter is decreased <22–25 nm for n- and p-type Si NWs, although the surface dopant concentration is also enriched in the larger diameter Si NWs. Similar diameter-dependent results were also observed for n-type Ge NWs, suggesting that surface dopant segregation may be general for small diameter NWs synthesized by the VLS approach. Natural surface doping of small diameter semiconductor NWs is distinct from many top-down fabricated NWs, explains enhanced transport properties of these NWs and could yield robust properties in ultrasmall devices often dominated by random dopant fluctuations. PMID:19706402

  2. Exact location of dopants below the Si(001):H surface from scanning tunneling microscopy and density functional theory

    NASA Astrophysics Data System (ADS)

    Brázdová, Veronika; Bowler, David R.; Sinthiptharakoon, Kitiphat; Studer, Philipp; Rahnejat, Adam; Curson, Neil J.; Schofield, Steven R.; Fisher, Andrew J.

    2017-02-01

    Control of dopants in silicon remains crucial to tailoring the properties of electronic materials for integrated circuits. Silicon is also finding new applications in coherent quantum devices, as a magnetically quiet environment for impurity orbitals. The ionization energies and shapes of the dopant orbitals depend on the surfaces and interfaces with which they interact. The location of the dopant and local environment effects will therefore determine the functionality of both future quantum information processors and next-generation semiconductor devices. Here we match observed dopant wave functions from scanning tunneling microscopy (STM) to images simulated from first-principles density functional theory (DFT) calculations and precisely determine the substitutional sites of neutral As dopants between 5 and 15 Å below the Si(001):H surface. We gain a full understanding of the interaction of the donor state with the surface and the transition between the bulk dopant and the dopants in the surface layer.

  3. Three-dimensional location of a single dopant with atomic precision by aberration-corrected scanning transmission electron microscopy.

    PubMed

    Ishikawa, Ryo; Lupini, Andrew R; Findlay, Scott D; Taniguchi, Takashi; Pennycook, Stephen J

    2014-01-01

    Materials properties, such as optical and electronic response, can be greatly enhanced by isolated single dopants. Determining the full three-dimensional single-dopant defect structure and spatial distribution is therefore critical to understanding and adequately tuning functional properties. Combining quantitative Z-contrast scanning transmission electron microscopy images with image simulations, we show the direct determination of the atomic-scale depth location of an optically active, single atom Ce dopant embedded within wurtzite-type AlN. The method represents a powerful new tool for reconstructing three-dimensional information from a single, two-dimensional image.

  4. Diameter-dependent hydrophobicity in carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Kyakuno, Haruka; Fukasawa, Mamoru; Ichimura, Ryota; Matsuda, Kazuyuki; Nakai, Yusuke; Miyata, Yasumitsu; Saito, Takeshi; Maniwa, Yutaka

    2016-08-01

    Single-wall carbon nanotubes (SWCNTs) are a good model system that provides atomically smooth nanocavities. It has been reported that water-SWCNTs exhibit hydrophobicity depending on the temperature T and the SWCNT diameter D. SWCNTs adsorb water molecules spontaneously in their cylindrical pores around room temperature, whereas they exhibit a hydrophilic-hydrophobic transition or wet-dry transition (WDT) at a critical temperature Twd ≈ 220-230 K and above a critical diameter Dc ≈ 1.4-1.6 nm. However, details of the WDT phenomenon and its mechanism remain unknown. Here, we report a systematic experimental study involving X-ray diffraction, optical microscopy, and differential scanning calorimetry. It is found that water molecules inside thick SWCNTs (D > Dc) evaporate and condense into ice Ih outside the SWCNTs at Twd upon cooling, and the ice Ih evaporates and condenses inside the SWCNTs upon heating. On the other hand, residual water trapped inside the SWCNTs below Twd freezes. Molecular dynamics simulations indicate that upon lowering T, the hydrophobicity of thick SWCNTs increases without any structural transition, while the water inside thin SWCNTs (D < Dc) exhibits a structural transition, forming an ordered ice. This ice has a well-developed hydrogen bonding network adapting to the cylindrical pores of the SWCNTs. Thus, the unusual diameter dependence of the WDT is attributed to the adaptability of the structure of water to the pore dimension and shape.

  5. Wire diameter dependence in the catalytic decomposition of H2

    NASA Astrophysics Data System (ADS)

    Umemoto, Hironobu

    2014-01-01

    Jansen et al. have demonstrated that the dissociaiton rate of H2 molecules on hot wire surfaces, normalized per unit surface area, depends on the wire diameter based on the electrical power consumption measurements [J. Appl. Phys. 66, 5749 (1989)]. Mathematical modeling calculations have also been presented to support their experimental results. In the present paper, it is shown that such a wire diameter dependence cannot be observed and that the H-atom density normalized by the wire surface area depends little on the wire diameter. Modeling calculations also show that the wire diameter dependence of the dissociation rate cannot be expected under typical decomposition conditions.

  6. Diameter dependent thermoelectric properties of individual SnTe nanowires

    DOE PAGES

    Xu, E. Z.; Li, Z.; Martinez, J. A.; ...

    2015-01-15

    The lead-free compound tin telluride (SnTe) has recently been suggested to be a potentially promising thermoelectric material because of its similar electronic band structure as the well-known lead telluride. Here we report on the first thermoelectric study of individual single crystalline SnTe nanowires (NWs) with different diameters ranging from ~200 to ~1000 nm. Measurements of thermopower S, electrical conductivity σ, and thermal conductivity κ were carried out on the same nanowires over a temperature range of 25 - 300 K. While σ does not show a strong diameter dependence, the thermopower increases by a factor of 2 when the nanowiremore » diameter is decreased from 1000 nm to 200 nm. The thermal conductivities of the measured NWs are only about half of that of the bulk SnTe, which may arise from the enhanced phonon-grain boundary and phonon-defect scatterings. Temperature dependent figure-of-merit ZT was determined and the maximum value at room temperature is ~3 times higher than what was obtained in bulk samples of comparable carrier density.« less

  7. Diameter dependent thermoelectric properties of individual SnTe nanowires

    SciTech Connect

    Xu, E. Z.; Li, Z.; Martinez, J. A.; Sinitsyn, N.; Htoon, H.; Li, Nan; Swartzentruber, B.; Hollingsworth, J. A.; Wang, Jian; Zhang, S. X.

    2015-01-15

    The lead-free compound tin telluride (SnTe) has recently been suggested to be a promising thermoelectric material. In this work, we report on the first thermoelectric study of individual single-crystalline SnTe nanowires with different diameters ranging from ~ 218 to ~ 913 nm. Measurements of thermopower S, electrical conductivity σ and thermal conductivity κ were carried out on the same nanowires over a temperature range of 25 - 300 K. While the electrical conductivity does not show a strong diameter dependence, the thermopower increases by a factor of two when the nanowire diameter is decreased from ~ 913 nm to ~ 218 nm. The thermal conductivity of the measured NWs is lower than that of the bulk SnTe, which may arise from the enhanced phonon - surface boundary scattering and phonon-defect scattering. Lastly, temperature dependent figure of merit ZT was determined for individual nanowires and the achieved maximum value at room temperature is about three times higher than that in bulk samples of comparable carrier density.

  8. Diameter dependent electron transfer kinetics in semiconductor-enzyme complexes.

    PubMed

    Brown, Katherine A; Song, Qing; Mulder, David W; King, Paul W

    2014-10-28

    Excited state electron transfer (ET) is a fundamental step for the catalytic conversion of solar energy into chemical energy. To understand the properties controlling ET between photoexcited nanoparticles and catalysts, the ET kinetics were measured for solution-phase complexes of CdTe quantum dots and Clostridium acetobutylicum [FeFe]-hydrogenase I (CaI) using time-resolved photoluminescence spectroscopy. Over a 2.0-3.5 nm diameter range of CdTe nanoparticles, the observed ET rate (kET) was sensitive to CaI concentration. To account for diameter effects on CaI binding, a Langmuir isotherm and two geometric binding models were created to estimate maximal CaI affinities and coverages at saturating concentrations. Normalizing the ET kinetics to CaI surface coverage for each CdTe diameter led to k(ET) values that were insensitive to diameter, despite a decrease in the free energy for photoexcited ET (ΔGET) with increasing diameter. The turnover frequency (TOF) of CaI in CdTe-CaI complexes was measured at several molar ratios. Normalization for diameter-dependent changes in CaI coverage showed an increase in TOF with diameter. These results suggest that k(ET) and H2 production for CdTe-CaI complexes are not strictly controlled by ΔG(ET) and that other factors must be considered.

  9. Diameter Dependent Thermoelectric Properties of Individual SnTe Nanowires

    NASA Astrophysics Data System (ADS)

    Xu, E. Z.; Li, Z.; Martinez, J.; Sinitsyn, N.; Htoon, H.; Li, N.; Swartzentruber, B.; Hollingsworth, J.; Wang, J.; Zhang, S. X.

    2015-03-01

    Tin telluride (SnTe), a newly discovered topological crystalline insulator, has recently been suggested to be a promising thermoelectric material. In this work, we report on a systematic study of the thermoelectric properties of individual single-crystalline SnTe nanowires with different diameters. Measurements of thermopower, electrical conductivity and thermal conductivity were carried out on the same nanowires over a temperature range of 25 - 300 K. While the electrical conductivity does not show a strong diameter dependence, we found that the thermopower increases by a factor of two when the nanowire diameter is decreased from 913 nm to 218 nm. The thermal conductivity of the measured NWs is lower than that of the bulk SnTe, which may be attributed to the enhanced phonon - surface boundary scattering and phonon-defect scattering. We further calculated the temperature dependent figure of merit ZT for each individual nanowire. This work was performed, in part, at the Center for Integrated Nanotechnologies, an Office of Science User Facility operated for the U.S. Department of Energy (DOE) Office of Science by Los Alamos National Laboratory (Contract DE-AC52-06NA25396) and Sandia National Laboratories (Contract DE-AC04-94AL85000). We acknowledge support by the Los Alamos LDRD program.

  10. Diameter dependent thermoelectric properties of individual SnTe nanowires

    DOE PAGES

    Xu, E. Z.; Li, Z.; Martinez, J. A.; ...

    2015-01-15

    The lead-free compound tin telluride (SnTe) has recently been suggested to be a promising thermoelectric material. In this work, we report on the first thermoelectric study of individual single-crystalline SnTe nanowires with different diameters ranging from ~ 218 to ~ 913 nm. Measurements of thermopower S, electrical conductivity σ and thermal conductivity κ were carried out on the same nanowires over a temperature range of 25 - 300 K. While the electrical conductivity does not show a strong diameter dependence, the thermopower increases by a factor of two when the nanowire diameter is decreased from ~ 913 nm to ~more » 218 nm. The thermal conductivity of the measured NWs is lower than that of the bulk SnTe, which may arise from the enhanced phonon - surface boundary scattering and phonon-defect scattering. Lastly, temperature dependent figure of merit ZT was determined for individual nanowires and the achieved maximum value at room temperature is about three times higher than that in bulk samples of comparable carrier density.« less

  11. Diameter-dependent bending modulus of individual multiwall boron nitride nanotubes.

    PubMed

    Tanur, Adrienne E; Wang, Jiesheng; Reddy, Arava L M; Lamont, Daniel N; Yap, Yoke Khin; Walker, Gilbert C

    2013-04-25

    The mechanical properties of individual multiwall boron nitride nanotubes (MWBNNTs) synthesized by a growth-vapor-trapping chemical vapor deposition method are investigated by a three-point bending technique via atomic force microscopy. Multiple locations on suspended tubes are probed in order to determine the boundary conditions of the supported tube ends. The bending moduli (EB) calculated for 20 tubes with diameters ranging from 18 to 58 nm confirm the exceptional mechanical properties of MWBNNTs, with an average EB of 760 ± 30 GPa. For the first time, the bending moduli of MWBNNTs are observed to increase with decreasing diameter, ranging from 100 ± 20 GPa to as high as 1800 ± 300 GPa. This diameter dependence is evaluated by Timoshenko beam theory. The Young's modulus and shear modulus were determined to be 1800 ± 300 and 7 ± 1 GPa, respectively, for a trimmed data set of 16 tubes. The low shear modulus of MWBNNTs is the reason for the detected diameter-dependent bending modulus and is likely due to the presence of interwall shearing between the crystalline and faceted helical nanotube structures of MWBNNTs.

  12. Diameter Dependence of Lattice Thermal Conductivity of Single-Walled Carbon Nanotubes: Study from Ab Initio.

    PubMed

    Yue, Sheng-Ying; Ouyang, Tao; Hu, Ming

    2015-10-22

    The effects of temperature, tube length, defects, and surface functionalization on the thermal conductivity (κ) of single-walled carbon nanotubes (SWCNTs) were well documented in literature. However, diameter dependence of thermal conductivity of SWCNTs received less attentions. So far, diverse trends of the diameter dependence have been discussed by different methods and all the previous results were based on empirical interatomic potentials. In this paper, we emphasize to clarify accurate κ values of SWCNTs with different diameters and in-plane κ of graphene. All the studies were under the framework of anharmonic lattice dynamics and Boltzmann transport equation (BTE) based on first principle calculations. We try to infer the right trend of diameter dependent thermal conductivity of SWCNTs. We infer that graphene is the limitation as SWCNT with an infinite diameter. We analyzed the thermal conductivity contributions from each phonon mode in SWCNTs to explain the trend. Meanwhile, we also identify the extremely low thermal conductivity of ultra-thin SWCNTs.

  13. Diameter-dependent electronic transport properties of Au-catalyst/Ge-nanowire Schottky diodes

    SciTech Connect

    Picraux, S Thomas; Leonard, Francois; Swartzentruber, Brian S; Talin, A Alee

    2008-01-01

    We present electronic transport measurements in individual Au-catalyst/Ge-nanowire interfaces demonstrating the presence of a Schottky barrier. Surprisingly, the small-bias conductance density increases with decreasing diameter. Theoretical calculations suggest that this effect arises because electron-hole recombination in the depletion region is the dominant charge transport mechanism, with a diameter dependence of both the depletion width and the electron-hole recombination time. The recombination time is dominated by surface contributions and depends linearly on the nanowire diameter.

  14. Strong diameter-dependence of nanowire emission coupled to waveguide modes

    NASA Astrophysics Data System (ADS)

    van Dam, Dick; Abujetas, Diego R.; Sánchez-Gil, José A.; Haverkort, Jos E. M.; Bakkers, Erik P. A. M.; Gómez Rivas, Jaime

    2016-03-01

    The emission from nanowires can couple to waveguide modes supported by the nanowire geometry, thus governing the far-field angular pattern. To investigate the geometry-induced coupling of the emission to waveguide modes, we acquire Fourier microscopy images of the photoluminescence of nanowires with diameters ranging from 143 to 208 nm. From the investigated diameter range, we conclude that a few nanometers difference in diameter can abruptly change the coupling of the emission to a specific mode. Moreover, we observe a diameter-dependent width of the Gaussian-shaped angular pattern in the far-field emission. This dependence is understood in terms of interference of the guided modes, which emit at the end facets of the nanowire. Our results are important for the design of quantum emitters, solid state lighting, and photovoltaic devices based on nanowires.

  15. CdSe nanocrystals: controlled growth and diameter-dependent photoluminescence

    NASA Astrophysics Data System (ADS)

    Zhang, Qiang; Yang, Ping; Chen, Hsueh Shin; Huang, Baibiao; Shen, Jianxing

    2014-02-01

    Phosphonic and carboxylic acids were used as capping agents to fabricate CdSe nanocrystals (NCs) through organic synthesis, leading to a controlled growth of the NCs with adjustable morphologies from dots to rods. The binding energies and steric hindrance of ligands dramatically affected the growth kinetics of CdSe NCs, and therefore the resulting geometry of NCs. The detailed investigations of ligand effect on the growth of NCs and an efficient control over the NCs morphology were presented. CdSe nanorods (NRs) with various aspect ratios were created for studying relation between the diameter of NRs and photoluminescence (PL). Consequently, a synergic use of PL spectra and transmission electron microscopy images allowed us to systematically investigate the relationship between morphology and PL properties of as-prepared CdSe rods. The PL properties of CdSe NRs were finally found to be strongly diameter dependent and weakly related to their lengths.

  16. Strong diameter-dependence of nanowire emission coupled to waveguide modes

    SciTech Connect

    Dam, Dick van Haverkort, Jos E. M.; Abujetas, Diego R.; Sánchez-Gil, José A.; Bakkers, Erik P. A. M.; Gómez Rivas, Jaime

    2016-03-21

    The emission from nanowires can couple to waveguide modes supported by the nanowire geometry, thus governing the far-field angular pattern. To investigate the geometry-induced coupling of the emission to waveguide modes, we acquire Fourier microscopy images of the photoluminescence of nanowires with diameters ranging from 143 to 208 nm. From the investigated diameter range, we conclude that a few nanometers difference in diameter can abruptly change the coupling of the emission to a specific mode. Moreover, we observe a diameter-dependent width of the Gaussian-shaped angular pattern in the far-field emission. This dependence is understood in terms of interference of the guided modes, which emit at the end facets of the nanowire. Our results are important for the design of quantum emitters, solid state lighting, and photovoltaic devices based on nanowires.

  17. Probing Intrawire, Interwire, and Diameter-Dependent Variations in Silicon Nanowire Surface Trap Density with Pump-Probe Microscopy.

    PubMed

    Cating, Emma E M; Pinion, Christopher W; Christesen, Joseph D; Christie, Caleb A; Grumstrup, Erik M; Cahoon, James F; Papanikolas, John M

    2017-10-11

    Surface trap density in silicon nanowires (NWs) plays a key role in the performance of many semiconductor NW-based devices. We use pump-probe microscopy to characterize the surface recombination dynamics on a point-by-point basis in 301 silicon NWs grown using the vapor-liquid-solid (VLS) method. The surface recombination velocity (S), a metric of the surface quality that is directly proportional to trap density, is determined by the relationship S = d/4τ from measurements of the recombination lifetime (τ) and NW diameter (d) at distinct spatial locations in individual NWs. We find that S varies by as much as 2 orders of magnitude between NWs grown at the same time but varies only by a factor of 2 or three within an individual NW. Although we find that, as expected, smaller-diameter NWs exhibit shorter τ, we also find that smaller wires exhibit higher values of S; this indicates that τ is shorter both because of the geometrical effect of smaller d and because of a poorer quality surface. These results highlight the need to consider interwire heterogeneity as well as diameter-dependent surface effects when fabricating NW-based devices.

  18. Diameter Dependence of Giant Magneto-Impedance Effect in Co-BASED Melt Extracted Amorphous Wires

    NASA Astrophysics Data System (ADS)

    Zhang, Shuling; Xing, Dawei; Sun, Jianfei

    2011-06-01

    Naked Co68.25Fe4.5Si12.25B15 amorphous wires of 67μm, 56μm, 52μm, 47μm and 31μm in diameter are produced by melt extraction method. Their giant magneto impedance (GMI) effect is investigated at frequencies from 0.1MHz to13MHz. Significant diameter dependence of GMI effect is studied. Thicker wires exhibit strong GMI effect and have clear characteristic frequencies at which their impedance ratio ΔZ/Z are largest. Largest impedance response is obtained in 67μm wires with the ΔZ/Z of 442% and field sensitivity of 71.5%/Oe. Wires of 31μm in diameter show increasing ΔZ/Z as frequency and have a steady field sensitivity of 30.7-33.6%/Oe in a wide frequency range from 3MHz to 13MHz. The different frequency dependence of GMI effect is discussed in the light of the skin effect. These amorphous wires are suitable for applications in high performance field sensors and can fit different demand.

  19. Limits in detecting an individual dopant atom embedded in a crystal.

    PubMed

    Mittal, Anudha; Mkhoyan, K Andre

    2011-07-01

    Annular dark field scanning transmission electron microscope (ADF-STEM) images allow detection of individual dopant atoms located on the surface of or inside a crystal. Contrast between intensities of an atomic column containing a dopant atom and a pure atomic column in ADF-STEM image depends strongly on specimen parameters and microscope conditions. Analysis of multislice-based simulations of ADF-STEM images of crystals doped with one substitutional dopant atom for a wide range of crystal thicknesses, types and locations of dopant atom inside the crystal, and crystals with different atoms reveal some interesting trends and non-intuitive behaviours in visibility of the dopant atom. The results provide practical guidelines to determine the optimal microscope and specimen conditions to detect a dopant atom in experiment, obtain information about the 3-d location of a dopant atom, and recognize cases where detecting a single dopant atom is not possible. Copyright © 2011 Elsevier B.V. All rights reserved.

  20. Introduction of a Nozzle Throat Diameter Dependency into the SRM Dust Size Distribution

    NASA Astrophysics Data System (ADS)

    Stabroth, S.; Wegener, P.; Oswald, M.; Wiedemann, C.; Klinkrad, H.; Vörsmann, P.

    In the exhaust gas of SRM (Solid Rocket Motor) firings, a considerable amount of very small aluminium oxide (Al2O3) particles is generally included. In order to increase motor performance and to dampen burn instabilities, aluminium is used as an additive in the propellant. During the burn process this aluminium is transformed into Al2O3. A large number of small dust particles (< 1 μ m up to about 50 μ m) is generated continuously during a burn. At the end of a burn, a second group of much larger fragments from an Al2O3 slag pool clustering inside the motor leaves the nozzle. The ESA space debris population model MASTER-2001 considers 1,032 SRM firings with the associated generation of SRM slag and dust. The resulting Al2O3 population is a major contribution to the micron size space debris environment in Earth orbit. For the modelling of each SRM dust release event a detailed knowledge of the size distribution is essential. However, the knowledge of the particle size distribution after passing the nozzle throat is poor. The current dust implementation in the MASTER-2001 space debris model therefore assumes an average motor size, since information on the actual motor size is normally not available in common databases. Thus, a fixed distribution is identically used for large upper stages as well as small apogee motors. This assumption can lead to an over-representation of large dust in regions, where mainly apogee motors are used (i.e. GEO) and an under-representation in lower altitudes, where large stages predominate. In this paper, a concept for the improvement of SRM dust size modelling is discussed. It will be shown that an introduction of a nozzle throat diameter dependency into the dust size distribution could lead to a more precise modelling of SRM dust release events. Investigations showed that there is a good correlation between the propellant mass flow and the nozzle's throat diameter, which is in turn the determining term for the actual diameter

  1. Spatial metrology of dopants in silicon with exact lattice site precision.

    PubMed

    Usman, M; Bocquel, J; Salfi, J; Voisin, B; Tankasala, A; Rahman, R; Simmons, M Y; Rogge, S; Hollenberg, L C L

    2016-09-01

    Scaling of Si-based nanoelectronics has reached the regime where device function is affected not only by the presence of individual dopants, but also by their positions in the crystal. Determination of the precise dopant location is an unsolved problem in applications from channel doping in ultrascaled transistors to quantum information processing. Here, we establish a metrology combining low-temperature scanning tunnelling microscopy (STM) imaging and a comprehensive quantum treatment of the dopant-STM system to pinpoint the exact coordinates of the dopant in the Si crystal. The technique is underpinned by the observation that STM images contain atomic-sized features in ordered patterns that are highly sensitive to the STM tip orbital and the absolute dopant lattice site. The demonstrated ability to determine the locations of P and As dopants to 5 nm depths will provide critical information for the design and optimization of nanoscale devices for classical and quantum computing applications.

  2. Spatial metrology of dopants in silicon with exact lattice site precision

    NASA Astrophysics Data System (ADS)

    Usman, M.; Bocquel, J.; Salfi, J.; Voisin, B.; Tankasala, A.; Rahman, R.; Simmons, M. Y.; Rogge, S.; Hollenberg, L. C. L.

    2016-09-01

    Scaling of Si-based nanoelectronics has reached the regime where device function is affected not only by the presence of individual dopants, but also by their positions in the crystal. Determination of the precise dopant location is an unsolved problem in applications from channel doping in ultrascaled transistors to quantum information processing. Here, we establish a metrology combining low-temperature scanning tunnelling microscopy (STM) imaging and a comprehensive quantum treatment of the dopant-STM system to pinpoint the exact coordinates of the dopant in the Si crystal. The technique is underpinned by the observation that STM images contain atomic-sized features in ordered patterns that are highly sensitive to the STM tip orbital and the absolute dopant lattice site. The demonstrated ability to determine the locations of P and As dopants to 5 nm depths will provide critical information for the design and optimization of nanoscale devices for classical and quantum computing applications.

  3. Diameter dependence of TO phonon frequencies and the Kohn anomaly in armchair single-wall carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Telg, Hagen; Hároz, Erik H.; Duque, Juan G.; Tu, Xiaomin; Khripin, Constantine Y.; Fagan, Jeffrey A.; Zheng, Ming; Kono, Junichiro; Doorn, Stephen K.

    2014-12-01

    We present resonant Raman scattering experiments on nanotube samples enriched in metallic armchair single-wall carbon nanotubes (SWCNTs). We establish the transverse optical (ATO) phonon frequency for the (5,5) through (10,10) armchair species, ranging in diameter from 0.68 to 1.36 nm. The frequencies show a strong diameter dependence similar to that previously observed in semiconducting nanotubes. We show that the ATO frequencies in armchair SWCNTs are dramatically upshifted from those of semiconducting SWCNTs. Furthermore, using electrochemical doping, we demonstrated that the ATO frequencies in armchair SWCNTs are independent of the position of the Fermi level. These results suggest that the upshift is a result of a Kohn anomaly involving a forward-scattering mechanism of electrons close to the Fermi level. This is in contrast to the well-known Kohn anomaly that dominates the downshift of the ALO and E2 g phonons in nonarmchair metallic SWCNTs and graphene, respectively.

  4. Diameter dependent polarization in ZnO/MgO disk-in-wire emitters: Multiscale modeling of optical quantum efficiency

    NASA Astrophysics Data System (ADS)

    Al-Qahtani, Saad Mubarak; Abdullah, Abdulmuin Mostafa A.; Nishat, Md. Rezaul Karim; Ahmed, Shaikh S.

    2017-03-01

    A multiscale computational study is performed to investigate how electronic structure, optical transitions, and terminal characteristics of nanostructured ZnO/MgO disk-in-wire emitters are governed by an intricate coupling of size-quantization, atomicity, and built-in structural and polarization fields. As for the models, an 8-band sp3 (with spin) atomistic tight-binding basis set was used to construct the Hamiltonian of the device in wurtzite crystal symmetry. Strain and the associated distortions of bond directions and bond lengths were modeled via the valence force-field (VFF) molecular mechanics framework. Specifically, in this work, a recently proposed ab initio based diameter-dependent model for the piezoelectric fields was implemented, which, as compared to the conventional diameter-independent model, was found to curb the influence of spontaneous (pyroelectric) polarization significantly. This particular finding is further illustrated through the calculation of electronic bandgap and localization of wavefunctions, optical emission characteristics, and the internal quantum efficiency of the device.

  5. Nonmonotonic Diameter Dependence of Thermal Conductivity of Extremely Thin Si Nanowires: Competition between Hydrodynamic Phonon Flow and Boundary Scattering.

    PubMed

    Zhou, Yanguang; Zhang, Xiaoliang; Hu, Ming

    2017-02-08

    By carefully and systematically performing Green-Kubo equilibrium molecular dynamics simulations, we report that the thermal conductivity (κ) of Si nanowires (NWs) does not diverge but converges and increases steeply when NW diameter (D) becomes extremely small (dκ/dD < 0), a long debate of one-dimensional heat conduction in history. The κ of the thinnest possible Si NWs reaches a superhigh level that is as large as more than 1 order of magnitude higher than its bulk counterpart. The abnormality is explained in terms of the dominant normal (N) process (energy and momentum conservation) of low frequency acoustic phonons that induces hydrodynamic phonon flow in the Si NWs without being scattered. With D increasing, the downward shift of optical phonons triggers strong Umklapp (U) scattering with acoustic phonons and attenuates the N process, leading to the regime of phonon boundary scattering (dκ/dD < 0). The two competing mechanisms result in nonmonotonic diameter dependence of κ with minima at critical diameter of 2-3 nm. Our results unambiguously demonstrate the converged κ and the clear trend of κ ∼ D for extremely thin Si NWs by fully elucidating the competition between the hydrodynamic phonon flow and phonon boundary scattering.

  6. Cirrus Dopant Nano-Composite Coatings

    DTIC Science & Technology

    2014-11-01

    Dopant • How it works • What it does • Development path Cirrus Dopant • One-step additive for electrolytic/ electroless • Nano...turns • Dispersion strengthening & grain refinement Process • Electroless • DC Plating • Pulse Plating Dopant • Aqueous • Organic...Application beyond Au Cirrus Dopant R&D progress so far … … all with industry partners … … all with commercial baths formulations. 15 microns Electroless

  7. Activation of shallow dopants in II-VI compounds

    SciTech Connect

    Walukiewicz, W.

    1995-08-01

    The amphoteric native defect model is applied to the understanding of the variations in the dopant activation efficiency in II-VI compounds. It is shown that the location of the common energy reference, the Fermi level stabilization energy, relative to the band edges can be used to determine the doping induced reduction of the formation energy and the enhancement of the concentration of compensating native defects. The model is applied to the most extensively studied compound semiconductors as well as to ternary and quaternary alloys. The effects of the compound ionicity on the dopant activation are briefly discussed.

  8. New photosensitive dopants for liquid argon

    NASA Astrophysics Data System (ADS)

    Anderson, D. F.

    1986-05-01

    Thirteen photosensitive dopants for liquid argon are presented, and the criteria for selecting prospective new dopants are discussed. A substantial improvement in energy resolution for 5.5 MeV alpha particles is measured in liquid argon when a photosensitive dopant is added.

  9. Surface Interactions of Organic Dopants

    NASA Astrophysics Data System (ADS)

    Johnson, Andrew Morgan

    1985-12-01

    In this study, electron tunneling spectroscopy and x-ray photoelectron spectroscopy (XPS) are used in order to examine the interaction of organic dopants with the aluminum oxide surface. When high bias voltages are applied to tunnel junctions, the tunneling barriers are observed to shift toward higher conductivity for a variety of dopants and cover electrodes. These shifts are characterized by increases throughout the IV characteristic. The inelastic tunneling spectrum is also affected. After shifting, there is a turnover in the background of the IET spectrum combined with a loss of mode intensity after the turnover. Finally, the calculated barrier model, TRAPSQR, is affected. After shifting, the barrier heights corresponding to the AlOx -dopant interface are reduced and the overall barrier thickness is increased. The voltage induced shifts have a well defined threshold voltage which is dependent on the dopant, cover electrode, and past history of the junction. If the bias voltage to the junction is less than the threshold voltage, V(,th), no shifting occurs. If the bias voltage exceeds V(,th) for a sufficiently long time, shifting occurs and the new, higher bias voltage becomes the threshold voltage. The voltage and time dependence of the shift voltage are studied in detail in the body of this text. Finally, the voltage induced shifts are reversible. If, after shifting, the junction is warmed up to room temperature and then re-cooled to 4.2K, the resulting IV characteristic and second derivative spectrum resulting will be that of an unshifted junction. Shifting behavior may then be reproduced exactly as before. Using XPS, dopant molecules with NO(,2) groups on an AlOx substrate are studied. Shifts in the position of the N1s peak which correspond to charge transfer to the surface are observed and identified with a weak surface bond. The observed charge transfer is dependent on the dopant molecule and is slightly dependent on the presence of trace amounts of other

  10. SU-F-18C-11: Diameter Dependency of the Radial Dose Distribution in a Long Polyethylene Cylinder

    SciTech Connect

    Bakalyar, D; McKenney, S; Feng, W

    2014-06-15

    Purpose: The radial dose distribution in the central plane of a long cylinder following a long CT scan depends upon the diameter and composition of the cylinder. An understanding of this behavior is required for determining the spatial average of the dose in the central plane. Polyethylene, the material for construction of the TG200/ICRU phantom (30 cm in diameter) was used for this study. Size effects are germane to the principles incorporated in size specific dose estimates (SSDE); thus diameter dependency was explored as well. Method: ssuming a uniform cylinder and cylindrically symmetric conditions of irradiation, the dose distribution can be described using a radial function. This function must be an even function of the radial distance due to the conditions of symmetry. Two effects are accounted for: The direct beam makes its weakest contribution at the center while the contribution due to scatter is strongest at the center and drops off abruptly at the outer radius. An analytic function incorporating these features was fit to Monte Carlo results determined for infinite polyethylene cylinders of various diameters. A further feature of this function is that it is integrable. Results: Symmetry and continuity dictate a local extremum at the center which is a minimum for the larger sizes. The competing effects described above can Resultin an absolute maximum occurring between the center and outer edge of the cylinders. For the smallest cylinders, the maximum dose may occur at the center. Conclusion: An integrable, analytic function can be used to characterize the radial dependency of dose for cylindrical CT phantoms of various sizes. One use for this is to help determine average dose distribution over the central cylinder plane when equilibrium dose has been reached.

  11. Structural Effects of Lanthanide Dopants on Alumina

    PubMed Central

    Patel, Ketan; Blair, Victoria; Douglas, Justin; Dai, Qilin; Liu, Yaohua; Ren, Shenqiang; Brennan, Raymond

    2017-01-01

    Lanthanide (Ln3+) doping in alumina has shown great promise for stabilizing and promoting desirable phase formation to achieve optimized physical and chemical properties. However, doping alumina with Ln elements is generally accompanied by formation of new phases (i.e. LnAlO3, Ln2O3), and therefore inclusion of Ln-doping mechanisms for phase stabilization of the alumina lattice is indispensable. In this study, Ln-doping (400 ppm) of the alumina lattice crucially delays the onset of phase transformation and enables phase population control, which is achieved without the formation of new phases. The delay in phase transition (θ → α), and alteration of powder morphology, particle dimensions, and composition ratios between α- and θ-alumina phases are studied using a combination of solid state nuclear magnetic resonance, electron microscopy, digital scanning calorimetry, and high resolution X-ray diffraction with refinement fitting. Loading alumina with a sparse concentration of Ln-dopants suggests that the dopants reside in the vacant octahedral locations within the alumina lattice, where complete conversion into the thermodynamically stable α-domain is shown in dysprosium (Dy)- and lutetium (Lu)-doped alumina. This study opens up the potential to control the structure and phase composition of Ln-doped alumina for emerging applications. PMID:28059121

  12. Structural Effects of Lanthanide Dopants on Alumina

    DOE PAGES

    Patel, Ketan; Blair, Victoria; Douglas, Justin; ...

    2017-01-06

    Lanthanide (Ln3+) doping in alumina has shown great promise for stabilizing and promoting desirable phase formation to achieve optimized physical and chemical properties. However, doping alumina with Ln elements is generally accompanied by formation of new phases (i.e. LnAlO3, Ln2O3), and therefore inclusion of Ln-doping mechanisms for phase stabilization of the alumina lattice is indispensable. In this study, Ln-doping (400 ppm) of the alumina lattice crucially delays the onset of phase transformation and enables phase population control, which is achieved without the formation of new phases. In addition, the delay in phase transition (θ → α), and alteration of powdermore » morphology, particle dimensions, and composition ratios between α- and θ-alumina phases are studied using a combination of solid state nuclear magnetic resonance, electron microscopy, digital scanning calorimetry, and high resolution X-ray diffraction with refinement fitting. Loading alumina with a sparse concentration of Ln-dopants suggests that the dopants reside in the vacant octahedral locations within the alumina lattice, where complete conversion into the thermodynamically stable α-domain is shown in dysprosium (Dy)- and lutetium (Lu)-doped alumina. Lastly, this study opens up the potential to control the structure and phase composition of Ln-doped alumina for emerging applications.« less

  13. Structural Effects of Lanthanide Dopants on Alumina

    NASA Astrophysics Data System (ADS)

    Patel, Ketan; Blair, Victoria; Douglas, Justin; Dai, Qilin; Liu, Yaohua; Ren, Shenqiang; Brennan, Raymond

    2017-01-01

    Lanthanide (Ln3+) doping in alumina has shown great promise for stabilizing and promoting desirable phase formation to achieve optimized physical and chemical properties. However, doping alumina with Ln elements is generally accompanied by formation of new phases (i.e. LnAlO3, Ln2O3), and therefore inclusion of Ln-doping mechanisms for phase stabilization of the alumina lattice is indispensable. In this study, Ln-doping (400 ppm) of the alumina lattice crucially delays the onset of phase transformation and enables phase population control, which is achieved without the formation of new phases. The delay in phase transition (θ → α), and alteration of powder morphology, particle dimensions, and composition ratios between α- and θ-alumina phases are studied using a combination of solid state nuclear magnetic resonance, electron microscopy, digital scanning calorimetry, and high resolution X-ray diffraction with refinement fitting. Loading alumina with a sparse concentration of Ln-dopants suggests that the dopants reside in the vacant octahedral locations within the alumina lattice, where complete conversion into the thermodynamically stable α-domain is shown in dysprosium (Dy)- and lutetium (Lu)-doped alumina. This study opens up the potential to control the structure and phase composition of Ln-doped alumina for emerging applications.

  14. Dopant diffusion in tungsten silicide

    SciTech Connect

    Pan, P.; Hsieh, N.; Geipel, H.J. Jr.; Slusser, G.J.

    1982-04-01

    The dopant (B, P, and As) redistribution in a silicide on polycrystalline silicon structure after annealing at 800 and 1000 /sup 0/C was studied. The distribution of boron was found to be quite different from these of phosphorus and arsenic. At 1000 /sup 0/C, the distribution coefficient for boron at the WSi/sub 2//polycrystalline silicon interface was found to be 2.7. The solubilities of phosphorus and arsenic in WSi/sub 2/ at 1000 /sup 0/C were estimated to be 6 x 10/sup 19/ and 1.6 x 10/sup 19/ atoms/cm/sup 3/, respectively. At 800 /sup 0/C, the diffusion coefficient for the dopants was found to be equal to, or greater than 3.3 x 10/sup -12/ cm/sup 2//s, which is at least three orders of magnitude larger than in silicon.

  15. Dopant Distribution in NIF Beryllium Ablator Capsules

    NASA Astrophysics Data System (ADS)

    Huang, H.; Xu, H. W.; Youngblood, K. P.; Wall, D. R.; Stephens, R. B.; Moreno, K. A.; Nikroo, A.; Salmonson, J. D.; Haan, S. W.; Wu, K. J.; Wang, Y. M.; Hamza, A. V.

    2012-10-01

    Good implosion performance requires capsule ablator material with spherically uniform x-ray opacity, which is controlled by one of several dopants (Cu, Si, Al, etc.) in the Be shell. During production, the dopant concentration is radially stepped. However, the various Be-dopant interactions result in vastly different dopant distribution patterns, some quite inhomogeneous. We have characterized these structures and established the phenomenological basis and the magnitudes of the inhomogeneity both in spatial length scales and in atomic percent. We will discuss the case of inhomogeneous Cu diffusion in detail, followed by discussions of other dopants and the estimate of the impact of these structures on target implosion.

  16. Dopant-Induced Plasmon Decay in Graphene.

    PubMed

    Novko, Dino

    2017-10-05

    Chemically doped graphene could support plasmon excitations up to telecommunication or even visible frequencies. Apart from that, the presence of dopant may influence electron scattering mechanisms in graphene and thus impact the plasmon decay rate. Here I study from first principles these effects in single-layer and bilayer graphene doped with various alkali and alkaline earth metals. I find new dopant-activated damping channels: loss due to out-of-plane graphene and in-plane dopant vibrations, and electron transitions between graphene and dopant states. The latter excitations interact with the graphene plasmon, and together they form a new hybrid mode. The study points out a strong dependence of these features on the type of dopants and the number of layers, which could be used as a tuning mechanism in future graphene-based plasmonic devices.

  17. Transient enhanced diffusion and gettering of dopants in ion implanted silicon

    SciTech Connect

    Pennycook, S.J.; Narayan, J.; Culbertson, R.J.

    1984-01-01

    We have studied in detail the transient enhanced diffusion observed during furnace or rapid-thermal-annealing of ion-implanted Si. We show that the effect originates in the trapping of Si atoms by dopant atoms during implantation, which are retained during solid-phase-epitaxial (SPE) growth but released by subsequent annealing to cause a transient dopant precipitation or profile broadening. The interstitials condense to form a band of dislocation loops located at the peak of the dopant profile, which may be distinct from the band formed at the original amorphous/crystalline interface. The band can develop into a network and effectively getter the dopant. We discuss the conditions under which the various effects may or may not be observed, and discuss conflicting observations on As/sup +/ implanted Si.

  18. Automatic Replenishment Of Dopant In Silicon Growth

    NASA Technical Reports Server (NTRS)

    Kochka, E. L.

    1988-01-01

    Dopant incorporated feed pellets to maintain required concentration. Technique of continuous replenishment of dopant in silicon melt helps ensure correct resistivity in solid silicon grown from melt. Technique used in dendritic-web growth process in which ribbon of silicon continously pulled from molten material. Providing uniform doping and resistivity in ribbon technique enables production of high-quality silicon ribbon at high yields for use in semiconductor devices.

  19. Prospects for photosensitive dopants in liquid argon

    SciTech Connect

    Anderson, D.F.

    1990-12-01

    Evidence is presented that the addition of a few ppM of a photosensitive dopant to a U/liquid argon or Pb/liquid argon calorimeter will make a substantial reduction in the e/{pi} ratio. Previous results indicating high voltage problems and no change in the e/{pi} ratio in tests of photosensitive dopants with the Fermilab D0 experiment's U/liquid argon tests calorimeter are also explained. 13 refs., 3 figs.

  20. Location, Location, Location!

    ERIC Educational Resources Information Center

    Ramsdell, Kristin

    2004-01-01

    Of prime importance in real estate, location is also a key element in the appeal of romances. Popular geographic settings and historical periods sell, unpopular ones do not--not always with a logical explanation, as the author discovered when she conducted a survey on this topic last year. (Why, for example, are the French Revolution and the…

  1. Location, Location, Location!

    ERIC Educational Resources Information Center

    Ramsdell, Kristin

    2004-01-01

    Of prime importance in real estate, location is also a key element in the appeal of romances. Popular geographic settings and historical periods sell, unpopular ones do not--not always with a logical explanation, as the author discovered when she conducted a survey on this topic last year. (Why, for example, are the French Revolution and the…

  2. Numerical algorithms for the atomistic dopant profiling of semiconductor materials

    NASA Astrophysics Data System (ADS)

    Aghaei Anvigh, Samira

    In this dissertation, we investigate the possibility to use scanning microscopy such as scanning capacitance microscopy (SCM) and scanning spreading resistance microscopy (SSRM) for the "atomistic" dopant profiling of semiconductor materials. For this purpose, we first analyze the discrete effects of random dopant fluctuations (RDF) on SCM and SSRM measurements with nanoscale probes and show that RDF significantly affects the differential capacitance and spreading resistance of the SCM and SSRM measurements if the dimension of the probe is below 50 nm. Then, we develop a mathematical algorithm to compute the spatial coordinates of the ionized impurities in the depletion region using a set of scanning microscopy measurements. The proposed numerical algorithm is then applied to extract the (x, y, z) coordinates of ionized impurities in the depletion region in the case of a few semiconductor materials with different doping configuration. The numerical algorithm developed to solve the above inverse problem is based on the evaluation of doping sensitivity functions of the differential capacitance, which show how sensitive the differential capacitance is to doping variations at different locations. To develop the numerical algorithm we first express the doping sensitivity functions in terms of the Gâteaux derivative of the differential capacitance, use Riesz representation theorem, and then apply a gradient optimization approach to compute the locations of the dopants. The algorithm is verified numerically using 2-D simulations, in which the C-V curves are measured at 3 different locations on the surface of the semiconductor. Although the cases studied in this dissertation are much idealized and, in reality, the C-V measurements are subject to noise and other experimental errors, it is shown that if the differential capacitance is measured precisely, SCM measurements can be potentially used for the "atomistic" profiling of ionized impurities in doped semiconductors.

  3. Development of dopant-free conductive bioelastomers

    PubMed Central

    Xu, Cancan; Huang, Yihui; Yepez, Gerardo; Wei, Zi; Liu, Fuqiang; Bugarin, Alejandro; Tang, Liping; Hong, Yi

    2016-01-01

    Conductive biodegradable materials are of great interest for various biomedical applications, such as tissue repair and bioelectronics. They generally consist of multiple components, including biodegradable polymer/non-degradable conductive polymer/dopant, biodegradable conductive polymer/dopant or biodegradable polymer/non-degradable inorganic additives. The dopants or additives induce material instability that can be complex and possibly toxic. Material softness and elasticity are also highly expected for soft tissue repair and soft electronics. To address these concerns, we designed a unicomponent dopant-free conductive polyurethane elastomer (DCPU) by chemically linking biodegradable segments, conductive segments, and dopant molecules into one polymer chain. The DCPU films which had robust mechanical properties with high elasticity and conductivity can be degraded enzymatically and by hydrolysis. It exhibited great electrical stability in physiological environment with charge. Mouse 3T3 fibroblasts survived and proliferated on these films exhibiting good cytocompatibility. Polymer degradation products were non-toxic. DCPU could also be processed into a porous scaffold and in an in vivo subcutaneous implantation model, exhibited good tissue compatibility with extensive cell infiltration over 2 weeks. Such biodegradable DCPU with good flexibility and elasticity, processability, and electrical stability may find broad applications for tissue repair and soft/stretchable/wearable bioelectronics. PMID:27686216

  4. Visualizing Individual Nitrogen Dopants in Monolayer Graphene

    SciTech Connect

    Hybertsen, M.S.; Zhao, L.; He, R.; Rim, K.T.; Kim, K.S.; Zhou, H.; Gutierrez, C.; Chockalingam, S.; Arguello, C.; Palova, L.; Reichman, D.R.; Heinz, T.F.; Kim, P.; Pinczuk, A.; Flynn, G.W.; Pasupathy, A.N.

    2011-08-19

    In monolayer graphene, substitutional doping during growth can be used to alter its electronic properties. We used scanning tunneling microscopy, Raman spectroscopy, x-ray spectroscopy, and first principles calculations to characterize individual nitrogen dopants in monolayer graphene grown on a copper substrate. Individual nitrogen atoms were incorporated as graphitic dopants, and a fraction of the extra electron on each nitrogen atom was delocalized into the graphene lattice. The electronic structure of nitrogen-doped graphene was strongly modified only within a few lattice spacings of the site of the nitrogen dopant. These findings show that chemical doping is a promising route to achieving high-quality graphene films with a large carrier concentration.

  5. Visualizing Individual Nitrogen Dopants in Monolayer Graphene

    SciTech Connect

    L Zhao; R He; K Rim; T Schiros; K Kim; H Zhou; C Gutierrez; S Chockalingam; C Arguello; et al.

    2011-12-31

    In monolayer graphene, substitutional doping during growth can be used to alter its electronic properties. We used scanning tunneling microscopy, Raman spectroscopy, x-ray spectroscopy, and first principles calculations to characterize individual nitrogen dopants in monolayer graphene grown on a copper substrate. Individual nitrogen atoms were incorporated as graphitic dopants, and a fraction of the extra electron on each nitrogen atom was delocalized into the graphene lattice. The electronic structure of nitrogen-doped graphene was strongly modified only within a few lattice spacings of the site of the nitrogen dopant. These findings show that chemical doping is a promising route to achieving high-quality graphene films with a large carrier concentration.

  6. Liquid-phase electroepitaxy - Dopant segregation

    NASA Technical Reports Server (NTRS)

    Lagowski, J.; Jastrzebski, L.; Gatos, H. C.

    1980-01-01

    A theoretical model is presented which accounts for the dopant segregation in liquid-phase electroepitaxy in terms of dopant transport in the liquid phase (by electromigration and diffusion), the growth velocity, and the Peltier effect at the substrate-solution interface. The contribution of dopant electromigration to the magnitude of the effective segregation coefficient is dominant in the absence of convection; the contribution of the Peltier effect becomes significant only in the presence of pronounced convection. Quantitative expressions which relate the segregation coefficient to the growth parameters also permit the determination of the diffusion constant and electromigration mobility of the dopant in the liquid phase. The model was found to be in good agreement with the measured segregation characteristics of Sn in the electroepitaxial growth of GaAs from Ga-As solutions. For Sn in Ga-As solution at 900 C the diffusion constant was found to be 4 x 10 to the -5 sq cm/s and the electromigration velocity (toward the substrate with a positive polarity 2 x 10 to the -5 cm/s current density of 10 A/sq cm.

  7. Phototropic liquid crystal materials containing naphthopyran dopants

    NASA Astrophysics Data System (ADS)

    Rumi, Mariacristina; Cazzell, Seth; Kosa, Tamas; Sukhomlinova, Ludmila; Taheri, Bahman; Bunning, Timothy; White, Timothy

    2015-03-01

    Dopant molecules dispersed in a liquid crystalline material usually affects the order of the system and the transition temperature between various phases. If the dopants undergo photoisomerization between conformers with different shapes, the interactions with the liquid crystal molecules can be different for the material in the dark and during exposure to light of appropriate wavelength. This can be used to achieve isothermal photoinduced phase transitions (phototropism). With proper selection of materials components, both order-to-disorder and disorder-to-order photoinduced transition have been demonstrated. Isothermal order-increasing transitions have been observed recently using naphthopyran derivatives as dopants. We are investigating the changes in order parameter and transition temperature of liquid crystal mixtures containing naphthopyrans and how they are related to exposure conditions and to the concentration and molecular structure of the dopants. We are also studying the nature of the photoinduced phase transitions, and comparing the behavior with that of azobenzene-doped mixtures, in which exposure to light leads to a decrease, instead of an increase, in the order of the system.

  8. Dopant penetration studies through Hf silicate

    NASA Astrophysics Data System (ADS)

    Quevedo-Lopez, M. A.; Visokay, M. R.; Chambers, J. J.; Bevan, M. J.; LiFatou, A.; Colombo, L.; Kim, M. J.; Gnade, B. E.; Wallace, R. M.

    2005-02-01

    We present a study of the penetration of B, P, and As through Hf silicate (HfSixOy) and the effect of N incorporation in Hf silicate (HfSixOyNz) on dopant penetration from doped polycrystalline silicon capping layers. The extent of penetration through Hf silicate was found to be dependent upon the thermal annealing budget for each dopant investigated as follows: B(T⩾950°C/60s), P(T⩾1000°C/20s), and As (T⩾1050°C/60s). We propose that the enhanced diffusion observed for these dopants in HfSixOy, compared with that of SiO2 films, is related to grain boundary formation resulting from HfSixOy film crystallization. We also find that, as in the case of SiO2, N incorporation inhibits dopant (B, P, and As) diffusion through the Hf silicate and thus penetration into the underlying Si substrate. Only B penetration is clearly observed through HfSiON films for anneals at 1050 °C for durations of 10 s or longer. The calculated B diffusivity through the HfSixOyNz layer is D0=5.2×10-15cm2/s.

  9. Liquid-phase electroepitaxy - Dopant segregation

    NASA Technical Reports Server (NTRS)

    Lagowski, J.; Jastrzebski, L.; Gatos, H. C.

    1980-01-01

    A theoretical model is presented which accounts for the dopant segregation in liquid-phase electroepitaxy in terms of dopant transport in the liquid phase (by electromigration and diffusion), the growth velocity, and the Peltier effect at the substrate-solution interface. The contribution of dopant electromigration to the magnitude of the effective segregation coefficient is dominant in the absence of convection; the contribution of the Peltier effect becomes significant only in the presence of pronounced convection. Quantitative expressions which relate the segregation coefficient to the growth parameters also permit the determination of the diffusion constant and electromigration mobility of the dopant in the liquid phase. The model was found to be in good agreement with the measured segregation characteristics of Sn in the electroepitaxial growth of GaAs from Ga-As solutions. For Sn in Ga-As solution at 900 C the diffusion constant was found to be 4 x 10 to the -5 sq cm/s and the electromigration velocity (toward the substrate with a positive polarity 2 x 10 to the -5 cm/s current density of 10 A/sq cm.

  10. Atom-probe for FinFET dopant characterization.

    PubMed

    Kambham, A K; Mody, J; Gilbert, M; Koelling, S; Vandervorst, W

    2011-05-01

    With the continuous shrinking of transistors and advent of new transistor architectures to keep in pace with Moore's law and ITRS goals, there is a rising interest in multigate 3D-devices like FinFETs where the channel is surrounded by gates on multiple surfaces. The performance of these devices depends on the dimensions and the spatial distribution of dopants in source/drain regions of the device. As a result there is a need for new metrology approach/technique to characterize quantitatively the dopant distribution in these devices with nanometer precision in 3D. In recent years, atom probe tomography (APT) has shown its ability to analyze semiconductor and thin insulator materials effectively with sub-nm resolution in 3D. In this paper we will discuss the methodology used to study FinFET-based structures using APT. Whereas challenges and solutions for sample preparation linked to the limited fin dimensions already have been reported before, we report here an approach to prepare fin structures for APT, which based on their processing history (trenches filled with Si) are in principle invisible in FIB and SEM. Hence alternative solutions in locating and positioning them on the APT-tip are presented. We also report on the use of the atom probe results on FinFETs to understand the role of different dopant implantation angles (10° and 45°) when attempting conformal doping of FinFETs and provide a quantitative comparison with alternative approaches such as 1D secondary ion mass spectrometry (SIMS) and theoretical model values. Copyright © 2011 Elsevier B.V. All rights reserved.

  11. Dopant Incorporation Efficiency in CVD Silicon Carbide Epilayers

    NASA Technical Reports Server (NTRS)

    Larkin, D. J.

    1996-01-01

    In order to ensure reproducible and reliable SiC semiconductor device characteristics, controlled dopant incorporation must be accomplished. Some of the many factors which greatly influence dopant incorporation are the site-competition effect, SiC(0001) substrate polarity, substrate temperature, and the dopant-source reactor concentration. In this paper, dopant incorporation is considered and compared for various dopants in the context of dopant incorporation efficiency. By using secondary ion mass spectrometry (SIMS), the relative dopant incorporation efficiencies were calculated by dividing the SIMS determined dopant concentration in the resulting epitaxial layer by the intentional gas phase dopant concentration used during the SiC CVD. Specifically, the relative magnitudes of dopant incorporation efficiencies for nitrogen, phosphorus, and boron in 6H-SiC (0001) Si-face epitaxial layers are compared as a function of the site-competition effect and the dopant-source reactor concentrations. This serves as a first approximation for comparison of the relative 'doping potencies' of some common dopants used in SiC CVD epitaxial growth.

  12. Analytical model for random dopant fluctuation in double-gate MOSFET in the subthreshold region using macroscopic modeling method

    NASA Astrophysics Data System (ADS)

    Shin, Yong Hyeon; Yun, Ilgu

    2016-12-01

    An analytical model is proposed for the random dopant fluctuation (RDF) in a symmetric double-gate metal-oxidesemiconductor field-effect-transistor (DG MOSFET) in the subthreshold region. Unintended impurity dopants cannot be absolutely prevented during the device fabrication; hence, it is important to analytically model the fluctuations in the electrical characteristics caused by these impurity dopants. Therefore, a macroscopic modeling method is applied to represent the impurity dopants in DG MOSFETs. With this method, the two-dimensional (2D) Poisson equation is separated into a basic analytical DG MOSFET model with channel doping concentration NA and an impurity-dopant-related term with local doping concentration NRD confined in a specific rectangular area. To solve the second term, the manually solvable 2D Green's function for DG MOSFETs is used. Through calculation of the channel potential (ϕ(x, y)), the variations in the drive current (IDS) and threshold voltage (Vth) are extracted from the analytical model. All results from the analytical model for an impurity dopant in a DG MOSFET are examined by comparisons with the commercially available 2D numerical simulation results, with respect to various oxide thicknesses (tox), channel lengths (L), and location of impurity dopants.

  13. Dopant-Catalyzed Singlet Exciton Fission.

    PubMed

    Snamina, Mateusz; Petelenz, Piotr

    2017-01-04

    In acene-based molecular crystals, singlet exciton fission occurs through superexchange mediated by two virtual charge-transfer states. Hence, it is sensitive to their energies, which depend on the local environment. The crucial point is the balance between the charge-quadrupole interactions within the pair of molecules directly involved in the process and those with the surrounding crystal matrix, which are governed by local symmetry and may be influenced by breaking this symmetry. This happens, for example, in the vicinity of a vacancy or an impurity and in the latter case is complemented by polarization energy and potentially by dipolar contributions. Our model calculations indicate that the superexchange coupling is sensitive enough to these factors to enable fission to be catalyzed by judiciously designed dopant molecules. In favorable cases, dipolar dopants are expected to increase the fission rate by an order of magnitude.

  14. Synthesis of chiral dopants based on carbohydrates.

    PubMed

    Tsuruta, Toru; Koyama, Tetsuo; Yasutake, Mikio; Hatano, Ken; Matsuoka, Koji

    2014-07-01

    Chiral dopants based on carbohydrates for nematic liquid crystals were synthesized from D-glucose, and their helical twisting power (HTP) values were evaluated. The chiral dopants induced helices in the host nematic liquid crystals. An acetyl derivative having an ether-type glycosidic linkage between carbohydrate and a mesogenic moiety showed the highest HTP value of 10.4 μm(-1), while an acetyl derivative having an anomeric ester-type linkage did not show any HTP. It was surprising that this molecule had no HTP despite the presence of chirality in the molecule. A relationship between HTP and specific rotation was not observed in this study. Copyright © 2014 Elsevier Ltd. All rights reserved.

  15. Deposition of dopant impurities and pulsed energy drive-in

    DOEpatents

    Wickboldt, Paul; Carey, Paul G.; Smith, Patrick M.; Ellingboe, Albert R.

    2008-01-01

    A semiconductor doping process which enhances the dopant incorporation achievable using the Gas Immersion Laser Doping (GILD) technique. The enhanced doping is achieved by first depositing a thin layer of dopant atoms on a semiconductor surface followed by exposure to one or more pulses from either a laser or an ion-beam which melt a portion of the semiconductor to a desired depth, thus causing the dopant atoms to be incorporated into the molten region. After the molten region recrystallizes the dopant atoms are electrically active. The dopant atoms are deposited by plasma enhanced chemical vapor deposition (PECVD) or other known deposition techniques.

  16. Deposition of dopant impurities and pulsed energy drive-in

    DOEpatents

    Wickboldt, Paul; Carey, Paul G.; Smith, Patrick M.; Ellingboe, Albert R.

    1999-01-01

    A semiconductor doping process which enhances the dopant incorporation achievable using the Gas Immersion Laser Doping (GILD) technique. The enhanced doping is achieved by first depositing a thin layer of dopant atoms on a semiconductor surface followed by exposure to one or more pulses from either a laser or an ion-beam which melt a portion of the semiconductor to a desired depth, thus causing the dopant atoms to be incorporated into the molten region. After the molten region recrystallizes the dopant atoms are electrically active. The dopant atoms are deposited by plasma enhanced chemical vapor deposition (PECVD) or other known deposition techniques.

  17. Deposition of dopant impurities and pulsed energy drive-in

    DOEpatents

    Wickboldt, P.; Carey, P.G.; Smith, P.M.; Ellingboe, A.R.

    1999-06-29

    A semiconductor doping process which enhances the dopant incorporation achievable using the Gas Immersion Laser Doping (GILD) technique is disclosed. The enhanced doping is achieved by first depositing a thin layer of dopant atoms on a semiconductor surface followed by exposure to one or more pulses from either a laser or an ion-beam which melt a portion of the semiconductor to a desired depth, thus causing the dopant atoms to be incorporated into the molten region. After the molten region recrystallizes the dopant atoms are electrically active. The dopant atoms are deposited by plasma enhanced chemical vapor deposition (PECVD) or other known deposition techniques. 2 figs.

  18. Deposition of dopant impurities and pulsed energy drive-in

    DOEpatents

    Wickboldt, Paul; Carey, Paul G.; Smith, Patrick M.; Ellingboe, Albert R.

    2008-01-01

    A semiconductor doping process which enhances the dopant incorporation achievable using the Gas Immersion Laser Doping (GILD) technique. The enhanced doping is achieved by first depositing a thin layer of dopant atoms on a semiconductor surface followed by exposure to one or more pulses from either a laser or an ion-beam which melt a portion of the semiconductor to a desired depth, thus causing the dopant atoms to be incorporated into the molten region. After the molten region recrystallizes the dopant atoms are electrically active. The dopant atoms are deposited by plasma enhanced chemical vapor deposition (PECVD) or other known deposition techniques.

  19. Quantum interference and correlations in single dopants and exchange-coupled dopants in silicon

    NASA Astrophysics Data System (ADS)

    Salfi, Joe

    2015-03-01

    Quantum electronics exploiting the highly coherent states of single dopants in silicon invariably requires interactions between states and interfaces, and inter-dopant coupling by exchange interactions. We have developed a low temperature STM scheme for spatially resolved single-electron transport in a device-like environment, providing the first wave-function measurements of single donors and exchange-coupled acceptors in silicon. For single donors, we directly observed valley quantum interference due to linear superpositions of the valleys, and found that valley degrees of freedom are highly robust to the symmetry-breaking perturbation of nearby (3 nm) surfaces. For exchange-coupled acceptors, we measured the singlet-triplet splitting, and from the spatial tunneling probability, extracted enough information about the 2-body wavefunction amplitudes to determine the entanglement entropy, a measure of the quantum inseparability (quantum correlations) generated by the interactions between indistinguishable particles. Entanglement entropy of the J=3/2 holes was found to increase with increasing dopant distance, as Coulomb interactions overcome tunneling, coherently localizing spin towards a Heitler-London singlet, mimicing S=1/2 particles. In the future these capabilities will be exploited to peer into the inner workings of few-dopant quantum devices and shed new light on multi-dopant correlated states, engineered atom-by-atom. Work done collaboratively with J. A. Mol, R. Rahman, G. Klimeck, M. Y. Simmons, L. C. L. Hollenberg, and S. Rogge. Primary financial support from the ARC.

  20. Controlling Dopant Profiles in Hyperdoped Silicon by Modifying Dopant Evaporation Rates During Pulsed Laser Melting

    SciTech Connect

    Recht, D.; Sullivan, J. T.; Reedy, R.; Buonassisi, T.; Aziz, M. J.

    2012-03-12

    We describe a method to control the sub-surface dopant profile in 'hyperdoped' silicon fabricated by ion implantation and pulsed laser melting. Dipping silicon ion implanted with sulfur into hydrofluoric acid prior to nanosecond pulsed laser melting leads to a tenfold increase in the rate of sulfur evaporation from the surface of the melt. This results in an 80% reduction of the near-surface dopant concentration, effectively embedding the hyperdoped region in a layer up to 180 nm beneath the surface. This method should facilitate the development of blocked impurity band devices.

  1. Bonding of dopants to irradiated polymers

    NASA Astrophysics Data System (ADS)

    Fink, D.; Klett, R.; Hnatowicz, V.; Vacik, J.; Mathis, C.; Omichi, H.; Hosoi, F.; Chadderton, L. T.; Wang, L.

    1996-08-01

    Latent tracks are formed in polyimide, polypropylene and polyethylene by irradiation with 0.5 to 3 GeV heavy ions. They are then doped with aqueous LiCl, organo- {Li}/{THF}, or {C60}/{THF} solutions for well-defined periods after the irradiation. Subsequently, the excess of non-trapped Li dopant fraction is washed out. The remaining lithium-doped polymer zones along the latent ion tracks are studied here. The depth distribution of the bonding efficiency, as determined by neutron depth profiling, points out an electronic nature of the bonding process.

  2. Dopant materials used in the microelectronics industry.

    PubMed

    Lewis, D R

    1986-01-01

    Advances in microelectronics have transformed the occupational environment of the electronics industry. Large quantities of potentially hazardous materials are now in routine use as integrated circuit manufacturing becomes more complex and specialized. While the acute hazards associated with these dopant materials are clear, the subacute and chronic effects are less evident. Many of these elements are trace elements in humans and may play roles in health and disease in minute concentrations. Early detection and prevention of adverse health effects requires both astute medical surveillance, industrial hygiene, and safety engineering efforts to eliminate the sources of exposure to workers.

  3. Atom devices based on single dopants in silicon nanostructures

    PubMed Central

    2011-01-01

    Silicon field-effect transistors have now reached gate lengths of only a few tens of nanometers, containing a countable number of dopants in the channel. Such technological trend brought us to a research stage on devices working with one or a few dopant atoms. In this work, we review our most recent studies on key atom devices with fundamental structures of silicon-on-insulator MOSFETs, such as single-dopant transistors, preliminary memory devices, single-electron turnstile devices and photonic devices, in which electron tunneling mediated by single dopant atoms is the essential transport mechanism. Furthermore, observation of individual dopant potential in the channel by Kelvin probe force microscopy is also presented. These results may pave the way for the development of a new device technology, i.e., single-dopant atom electronics. PMID:21801408

  4. Energetics of neutral Si dopants in InGaAs: An ab initio and semiempirical Tersoff model study

    NASA Astrophysics Data System (ADS)

    Lee, Cheng-Wei; Lukose, Binit; Thompson, Michael O.; Clancy, Paulette

    2015-03-01

    A roadblock in utilizing III-V semiconductors for scaled-down electronic devices is their poor dopant activation. As a first step to unravel the dopant behavior in InGaAs, we studied the tendency for dopant formation computationally using two approaches: ab initio and semiempirical methods. We studied a number of structural possibilities, such as the impact of local sites and local and global environments. We will show that the dopant we considered here, Si, has discrete preferences for certain sites and the nature of its surroundings. Substitutional defects are clearly preferred over interstitial locations. We shall show that cation ordering has an impact on dopant energetics. Critically, for large-scale simulations of dopant diffusion in InGaAs alloys, we also present a parameterization of the Abell-Tersoff semiempirical potential for pairwise interactions between silicon atoms and each of the elements constituting InGaAs. In the absence of experimental data, reference parameters for estimating the Tersoff values were obtained using ab initio pseudopotential calculations (density functional theory and generalized gradient approximations). These sets of Tersoff parameters were optimized to describe the bulk structural properties of the mostly theoretical alloys Si-As, Si-Ga, and Si-In. We demonstrate the transferability of these parameters by predicting formation energies of extrinsic point "defects" of Si on a variety of sites in ternary InGaAs alloys with different local compositional configurations, both random and ordered. Tersoff model predictions of the extrinsic "substitution energy" of a Si dopant on a cationic lattice site were found to be independent of the composition of the dopant's second nearest neighbors, but were affected by the strain induced by a local arrangement of In and Ga cationic atoms. This finding is important since common deposition processes used to create InGaAs may lead to specifically ordered patterns within the cation sublattice.

  5. Dopants and defects in conductive oxide spinels

    NASA Astrophysics Data System (ADS)

    Zakutayev, Andriy; Perkins, John; Parilla, Phillip; Paudel, Tula; Lany, Staphan; Ginely, David; Zunger, Alex

    2011-03-01

    We will discuss the effects of extrinsic and intrinsic imperfections (dopants and defects) in a group of conductive oxide materials related to Co3O4. Co3O4 is a spinel with Co2+ and Co3+ on tetrahedral and octahedral sites, respectively. Doping of Co3O4 with Zn and Ni represent two limiting cases: Zn2+ ions have a preference to occupy tetrahedral (Co2+) sites and are predicted to be unable to dope effectively; Ni2+ ions have a preference to occupy octahedral (Co3+) sites, so these atoms are expected to be efficient dopants. We found that substitution of Co3O4 spinel with up to 33 percent of Zn and Ni results in formation of ZnCo2O4 normal spinel and NiCo2O4 inverse spinel, and causes 100-fold and 1000-fold increases in conductivity, respectively, matching the predicted trend. Increase in Zn and Ni concentraion up to 40 percent cause phase separation of ZnO and NiO and leveling out of the conductivity. The conductivity decreases sharply above 50-60 percent Zn and Ni substitution level. Small differences with the theoretical predictions may be explained by non-equilibrium character of the thin film deposition process. This work was supported by the ``Center for Inverse Design'' EFRC of the Department of Energy.

  6. Direct evidence of dopant segregation in Gd-doped ceria

    NASA Astrophysics Data System (ADS)

    Li, Zhi-Peng; Mori, Toshiyuki; Auchterlonie, Graeme John; Zou, Jin; Drennan, John

    2011-02-01

    Microstructures and segregations of dopants and associated oxygen vacancies in gadolinium-doped ceria (GDC) have been characterized by high-resolution transmission electron microscopy (HRTEM) and scanning TEM (STEM). Diffuse scattering was detected in 25 at. % GDC (25GDC) in comparison to 10GDC, which is ascribed to nanodomain formation in 25GDC. HRTEM, dark-field, and STEM Z-contrast imaging investigations all provide direct evidence for dopant segregation in doped ceria. It is illustrated that dopant cations cannot only segregate in grain interior forming larger nanodomains but also at grain boundary forming smaller ones. Detailed analyses about nanodomain formation and related dopant segregation behaviors are then elucidated.

  7. Anomalous dynamics of interstitial dopants in soft crystals

    NASA Astrophysics Data System (ADS)

    Tauber, Justin; Higler, Ruben; Sprakel, Joris

    2016-11-01

    The dynamics of interstitial dopants govern the properties of a wide variety of doped crystalline materials. To describe the hopping dynamics of such interstitial impurities, classical approaches often assume that dopant particles do not interact and travel through a static potential energy landscape. Here we show, using computer simulations, how these assumptions and the resulting predictions from classical Eyring-type theories break down in entropically stabilized body-centered cubic (BCC) crystals due to the thermal excitations of the crystalline matrix. Deviations are particularly severe close to melting where the lattice becomes weak and dopant dynamics exhibit strongly localized and heterogeneous dynamics. We attribute these anomalies to the failure of both assumptions underlying the classical description: (i) The instantaneous potential field experienced by dopants becomes largely disordered due to thermal fluctuations and (ii) elastic interactions cause strong dopant-dopant interactions even at low doping fractions. These results illustrate how describing nonclassical dopant dynamics requires taking the effective disordered potential energy landscape of strongly excited crystals and dopant-dopant interactions into account.

  8. Topological engineering of glass for modulating chemical state of dopants.

    PubMed

    Zhou, Shifeng; Guo, Qiangbing; Inoue, Hiroyuki; Ye, Qun; Masuno, Atsunobu; Zheng, Binbin; Yu, Yongze; Qiu, Jianrong

    2014-12-17

    A novel approach to modulating the chemical state of dopants by engineering the topological features of a glass matrix is presented. The method allows selective stabilization of dopants on a wide range of length scales, from dispersed ions to aggregated clusters to nanoparticles, leading to various intriguing optical phenomena, such as great emission enhancement and ultra-broadband optical amplification.

  9. Dopant-induced stress in microfabricated silicon devices

    NASA Astrophysics Data System (ADS)

    Sievilä, P.; Mäkinen, J.; Tilli, M.; Tittonen, I.

    2013-07-01

    The modification of material characteristics by introducing dopant atoms into a crystal lattice is a fundamental basis for modern micro- and nanosystems technology. In this work, the uneven distribution of dopants is shown to have a remarkable effect on the residual stress and the consequent deformation of released, mechanical silicon structures. In particular, the focus is on segregation of initial dopants inside the bulk silicon which takes place in such fabrication processes as thermal oxidation. A theoretical model based on perceiving the dopant-induced change in Si crystal lattice parameter is developed. We experimentally investigate a series of silicon-on-insulator wafers, including samples with dopant types B, P, and Sb, and concentrations in the range from 1015 to 5 × 1019 atoms cm-3. Released cantilevers are fabricated as test structures and the residual stress is determined by measuring their final curvature. Experimental results are compared with the modelled values obtained utilizing the dopant profiles determined by secondary ion mass spectrometry and concentration distribution simulations. The use of lightly doped substrates or the selection of processes not modifying the underlying Si surface (e.g., plasma enhanced chemical vapour deposition PECVD or metal deposition) is shown to be an effective solution for minimizing the dopant redistribution-induced stress. Besides the scientific impact, knowledge of the stress generated by dopants is of great significance for industrial manufacturing of a wide range of micro- and nanomechanical systems.

  10. Time-resolved single dopant charge dynamics in silicon

    NASA Astrophysics Data System (ADS)

    Rashidi, Mohammad; Burgess, Jacob A. J.; Taucer, Marco; Achal, Roshan; Pitters, Jason L.; Loth, Sebastian; Wolkow, Robert A.

    2016-10-01

    As the ultimate miniaturization of semiconductor devices approaches, it is imperative that the effects of single dopants be clarified. Beyond providing insight into functions and limitations of conventional devices, such information enables identification of new device concepts. Investigating single dopants requires sub-nanometre spatial resolution, making scanning tunnelling microscopy an ideal tool. However, dopant dynamics involve processes occurring at nanosecond timescales, posing a significant challenge to experiment. Here we use time-resolved scanning tunnelling microscopy and spectroscopy to probe and study transport through a dangling bond on silicon before the system relaxes or adjusts to accommodate an applied electric field. Atomically resolved, electronic pump-probe scanning tunnelling microscopy permits unprecedented, quantitative measurement of time-resolved single dopant ionization dynamics. Tunnelling through the surface dangling bond makes measurement of a signal that would otherwise be too weak to detect feasible. Distinct ionization and neutralization rates of a single dopant are measured and the physical process controlling those are identified.

  11. Dopant ink composition and method of fabricating a solar cell there from

    DOEpatents

    Loscutoff, Paul; Wu, Kahn; Molesa, Steven Edward

    2015-03-31

    Dopant ink compositions and methods of fabricating solar cells there from are described. A dopant ink composition may include a cross-linkable matrix precursor, a bound dopant species, and a solvent. A method of fabricating a solar cell may include delivering a dopant ink composition to a region above a substrate. The dopant ink composition includes a cross-linkable matrix precursor, a bound dopant species, and a solvent. The method also includes baking the dopant ink composition to remove a substantial portion of the solvent of the dopant ink composition, curing the baked dopant ink composition to cross-link a substantial portion of the cross-linkable matrix precursor of the dopant ink composition, and driving dopants from the cured dopant ink composition toward the substrate.

  12. Impact of dopant concentrations on emitter formation with spin on dopant source in n-type crystalline silicon solar cells

    SciTech Connect

    Singha, Bandana; Solanki, Chetan Singh

    2016-05-06

    Use of a suitable dopant source for emitter formation is an essential requirement in n-type crystalline silicon solar cells. Boron spin on dopant source, used as alternative to mostly used BBr{sub 3} liquid source, can yield an emitter with less diffusion induced defects under controlled conditions. Different concentrations of commercially available spin on dopant source is used and optimized in this work for sheet resistance values of the emitter ranging from 30 Ω/□ to 70 Ω/□ with emitter doping concentrations suitable for ohmic contacts. The dopant concentrations diluted with different ratios improves the carrier lifetime and thus improves the emitter performance. Hence use of suitable dopant source is essential in forming emitters in n-type crystalline silicon solar cells.

  13. Anomalous dynamics of interstitial dopants in soft crystals

    PubMed Central

    Tauber, Justin; Higler, Ruben; Sprakel, Joris

    2016-01-01

    The dynamics of interstitial dopants govern the properties of a wide variety of doped crystalline materials. To describe the hopping dynamics of such interstitial impurities, classical approaches often assume that dopant particles do not interact and travel through a static potential energy landscape. Here we show, using computer simulations, how these assumptions and the resulting predictions from classical Eyring-type theories break down in entropically stabilized body-centered cubic (BCC) crystals due to the thermal excitations of the crystalline matrix. Deviations are particularly severe close to melting where the lattice becomes weak and dopant dynamics exhibit strongly localized and heterogeneous dynamics. We attribute these anomalies to the failure of both assumptions underlying the classical description: (i) The instantaneous potential field experienced by dopants becomes largely disordered due to thermal fluctuations and (ii) elastic interactions cause strong dopant–dopant interactions even at low doping fractions. These results illustrate how describing nonclassical dopant dynamics requires taking the effective disordered potential energy landscape of strongly excited crystals and dopant–dopant interactions into account. PMID:27856751

  14. Local Lattice Structure and Dopant Occupancy of Doped Lithium Niobate Crystals

    NASA Astrophysics Data System (ADS)

    Zhang, Zhigang; Xue, Dongfeng

    We present a systematic study of the local distortions produced upon doping metal ions to lithium niobate (LiNbO3, LN) single crystals. The impurity bond length can be predicted by a radial force constant model, when the dopant ions substitute for Li+ or Nb5+ ions in the LN crystallographic frame. From the viewpoint of constituent chemical bonds, the lattice energy can be described as the function of bond valence on the basis of Born-Haber cycle for the formation of an ionic oxide MmOn. The dopant occupancy in the LN matrix can be determined by comparing the deviation of its lattice energy in different locations at both Li+ and Nb5+ sites, on the basis of the bond length relaxation of impurity ions, which can agree well with the experiment results. The effect of impurity ions on the property modification of LN crystals is also discussed according to our calculated results.

  15. Transition-metal dopants in tetrahedrally bonded semiconductors: Symmetry and exchange interactions from tight-binding models

    NASA Astrophysics Data System (ADS)

    Kortan, Victoria Ramaker

    It has become increasingly apparent that the future of electronic devices can and will rely on the functionality provided by single or few dopant atoms. The most scalable physical system for quantum technologies, i.e. sensing, communication and computation, are spins in crystal lattices. Diamond is an excellent host crystal offering long room temperature spin coherence times and there has been exceptional experimental work done with the nitrogen vacancy center in diamond demonstrating many forms of spin control. Transition metal dopants have additional advantages, large spin-orbit interaction and internal core levels, that are not present in the nitrogen vacancy center. This work explores the implications of the internal degrees of freedom associated with the core d levels using a tight-binding model and the Koster-Slater technique. The core d levels split into two separate symmetry states in tetrahedral bonding environments and result in two levels with different wavefunction spatial extents. For 4 d semiconductors, e.g. GaAs, this is reproduced in the tight-binding model by adding a set of d orbitals on the location of the transition metal impurity and modifying the hopping parameters from impurity to its nearest neighbors. This model does not work in the case of 3d semiconductors, e.g. diamond, where there is no physical reason to drastically alter the hopping from 3 d dopant to host and the difference in wavefunction extent is not as pronounced. In the case of iron dopants in gallium arsenide the split symmetry levels in the band gap are responsible for a decrease in tunneling current when measured with a scanning tunneling microscope due to interference between two elastic tunneling paths and comparison between wavefunction measurements and tight-binding calculations provides information regarding material parameters. In the case of transition metal dopants in diamond there is less distinction between the symmetry split d levels. When considering pairs of

  16. Diffusion of n-type dopants in germanium

    SciTech Connect

    Chroneos, A.; Bracht, H.

    2014-03-15

    Germanium is being actively considered by the semiconductor community as a mainstream material for nanoelectronic applications. Germanium has advantageous materials properties; however, its dopant-defect interactions are less understood as compared to the mainstream material, silicon. The understanding of self- and dopant diffusion is essential to form well defined doped regions. Although p-type dopants such as boron exhibit limited diffusion, n-type dopants such as phosphorous, arsenic, and antimony diffuse quickly via vacancy-mediated diffusion mechanisms. In the present review, we mainly focus on the impact of intrinsic defects on the diffusion mechanisms of donor atoms and point defect engineering strategies to restrain donor atom diffusion and to enhance their electrical activation.

  17. Extended OLED operational lifetime through phosphorescent dopant profile management

    DOEpatents

    Forrest, Stephen R.; Zhang, Yifan

    2017-05-30

    This disclosure relates, at least in part, an organic light emitting device, which in some embodiments comprises an anode; a cathode; a first emissive layer disposed between the anode and the cathode, the first emissive layer comprising an electron transporting compound and a phosphorescent emissive dopant compound; and wherein the phosphorescent emissive dopant compound has a concentration gradient, in the emissive layer, which varies from the cathode side of the first emissive layer to the anode side of the emissive layer.

  18. Dopant morphology as the factor limiting graphene conductivity

    PubMed Central

    Hofmann, Mario; Hsieh, Ya-Ping; Chang, Kai-Wen; Tsai, He-Guang; Chen, Tzung-Te

    2015-01-01

    Graphene’s low intrinsic carrier concentration necessitates extrinsic doping to enhance its conductivity and improve its performance for application as electrodes or transparent conductors. Despite this importance limited knowledge of the doping process at application-relevant conditions exists. Employing in-situ carrier transport and Raman characterization of different dopants, we here explore the fundamental mechanisms limiting the effectiveness of doping at different doping levels. Three distinct transport regimes for increasing dopant concentration could be identified. First the agglomeration of dopants into clusters provides a route to increase the graphene conductivity through formation of ordered scatterers. As the cluster grows, the charge transfer efficiency between graphene and additional dopants decreases due to emerging polarization effects. Finally, large dopant clusters hinder the carrier motion and cause percolative transport that leads to an unexpected change of the Hall effect. The presented results help identifying the range of beneficial doping density and guide the choice of suitable dopants for graphene’s future applications. PMID:26617255

  19. Quantification of Shallow-junction Dopant Loss during CMOS Process

    SciTech Connect

    Buh, G.H.; Park, T.; Jee, Y.; Hong, S.J.; Ryoo, C.; Yoo, J.; Lee, J.W.; Yon, G.H.; Jun, C.S.; Shin, Y.G.; Chung, U.-In; Moon, J.T.

    2005-09-09

    We analyzed dopant concentration and profiles in source drain extension (SDE) by using in-line low energy electron induced x-ray emission spectrometry (LEXES), four point probe (FPP), and secondary ion mass spectroscopy (SIMS). By monitoring the dopant dose with LEXES, dopant loss in implantation and annealing process was successfully quantified. To measure the actual SDE sheet resistance in CMOS device structure without probe penetration in FPP, we fabricated a simple SDE sheet-resistance test structure (SSTS) by modifying a conventional CMOS process. It was found that the sheet resistances determined with SSTS are larger than those measured with FPP. There are three mechanisms of dopants loss in CMOS process: 1) wet-etching removal during photo resist cleaning, 2) out-diffusion, and 3) deactivation by post-thermal process. We quantified the loss of the dopant in SDE during the CMOS process, and found that the wet-etching removal and out-diffusion are the most significant causes for dopant loss in n-SDE and p-SDE, respectively.

  20. Calibrated nanoscale dopant profiling using a scanning microwave microscope

    SciTech Connect

    Huber, H. P.; Hochleitner, M.; Hinterdorfer, P.; Humer, I.; Smoliner, J.; Fenner, M.; Moertelmaier, M.; Rankl, C.; Tanbakuchi, H.; Kienberger, F.; Imtiaz, A.; Wallis, T. M.; Kabos, P.; Kopanski, J. J.

    2012-01-01

    The scanning microwave microscope is used for calibrated capacitance spectroscopy and spatially resolved dopant profiling measurements. It consists of an atomic force microscope combined with a vector network analyzer operating between 1-20 GHz. On silicon semiconductor calibration samples with doping concentrations ranging from 10{sup 15} to 10{sup 20} atoms/cm{sup 3}, calibrated capacitance-voltage curves as well as derivative dC/dV curves were acquired. The change of the capacitance and the dC/dV signal is directly related to the dopant concentration allowing for quantitative dopant profiling. The method was tested on various samples with known dopant concentration and the resolution of dopant profiling determined to 20% while the absolute accuracy is within an order of magnitude. Using a modeling approach the dopant profiling calibration curves were analyzed with respect to varying tip diameter and oxide thickness allowing for improvements of the calibration accuracy. Bipolar samples were investigated and nano-scale defect structures and p-n junction interfaces imaged showing potential applications for the study of semiconductor device performance and failure analysis.

  1. Atom location by electron channeling analysis

    SciTech Connect

    Pennycook, S.J.

    1984-07-01

    For many years the orientation dependence of the characteristic x-ray emission close to a Bragg reflection has been regarded as a hindrance to accurate microanalysis, and a random incident beam direction has always been recommended for accurate composition analysis. However, this orientation dependence can be put to use to extract information on the lattice location of foreign atoms within the crystalline matrix. Here a generalization of the technique is described which is applicable to any crystal structure including monatomic crystals, and can quantitatively determine substitutional fractions of impurities. The technique was referred to as electron channeling analysis, by analogy with the closely related and widely used bulk technique of ion channeling analysis, and was developed for lattice location studies of dopants in semiconductors at high spatial resolution. Only two spectra are required for each channeling analysis, one in each of the channeling conditions described above. If the matrix and dopant x-ray yields vary identically between the two orientations then the dopant necessarily lies within the reflecting matrix planes. If the dopant x-ray yield does not vary the dopant atoms are randomly located with respect to the matrix planes. 10 references, 2 figures.

  2. Three dimensional mapping of Fe dopants in ceria nanocrystals using direct spectroscopic electron tomography.

    PubMed

    Goris, Bart; Meledina, Maria; Turner, Stuart; Zhong, Zhichao; Batenburg, K Joost; Bals, Sara

    2016-12-01

    Electron tomography is a powerful technique for the 3D characterization of the morphology of nanostructures. Nevertheless, resolving the chemical composition of complex nanostructures in 3D remains challenging and the number of studies in which electron energy loss spectroscopy (EELS) is combined with tomography is limited. During the last decade, dedicated reconstruction algorithms have been developed for HAADF-STEM tomography using prior knowledge about the investigated sample. Here, we will use the prior knowledge that the experimental spectrum of each reconstructed voxel is a linear combination of a well-known set of references spectra in a so-called direct spectroscopic tomography technique. Based on a simulation experiment, it is shown that this technique provides superior results in comparison to conventional reconstruction methods for spectroscopic data, especially for spectrum images containing a relatively low signal to noise ratio. Next, this technique is used to investigate the spatial distribution of Fe dopants in Fe:Ceria nanoparticles in 3D. It is shown that the presence of the Fe(2+) dopants is correlated with a reduction of the Ce atoms from Ce(4+) towards Ce(3+). In addition, it is demonstrated that most of the Fe dopants are located near the voids inside the nanoparticle.

  3. Method for enhancing the solubility of dopants in silicon

    DOEpatents

    Sadigh, Babak; Lenosky, Thomas J.; De La Rubia, Tomas Diaz

    2003-09-30

    A method for enhancing the equilibrium solid solubility of dopants in silicon, germanium and silicon-germanium alloys. The method involves subjecting silicon-based substrate to biaxial or compression strain. It has been determined that boron solubility was largely enhanced (more than 100%) by a compressive bi-axial strain, based on a size-mismatch theory since the boron atoms are smaller than the silicon atoms. It has been found that the large enhancement or mixing properties of dopants in silicon and germanium substrates is primarily governed by their, and to second order by their size-mismatch with the substrate. Further, it has been determined that the dopant solubility enhancement with strain is most effective when the charge and the size-mismatch of the impurity favor the same type of strain. Thus, the solid solubility of small p-type (e.g., boron) as well as large n-type (e.g., arsenic) dopants can be raised most dramatically by appropriate bi-axial (compressive) strain, and that solubility of a large p-type dopant (e.g, indium) in silicon will be raised due to size-mismatch with silicon, which favors tensile strain, while its negative charge prefers compressive strain, and thus the two effects counteract each other.

  4. Thermal stability of dopants in laser annealed silicon

    NASA Astrophysics Data System (ADS)

    Takamura, Y.; Jain, S. H.; Griffin, P. B.; Plummer, J. D.

    2002-07-01

    As semiconductor device dimensions continue to decrease, the main challenge in the area of junction formation involves decreasing the junction depth while simultaneously decreasing the sheet resistance. Laser annealing is being investigated as an alternative to rapid thermal annealing to repair the damage from ion implantation and to activate the dopants. With this technique, uniform, box-shaped profiles are obtained, with dopant concentrations that can exceed equilibrium solubility limits at normal processing temperatures. Unfortunately, these super-saturated dopant concentrations exist in a metastable state and deactivate upon further thermal processing. In this article, we describe a comprehensive study of the deactivation kinetics of common dopants (P, B, and Sb) across a range of concentrations and annealing conditions. For comparison, As deactivation data from the literature is also presented. P and As deactivate substantially at temperatures as low as 500 degC, while Sb at moderate concentrations and B remain fully active until 700 to 800 degC. It is proposed that As and P deactivate through the formation of small dopant-defect clusters while B deactivates through precipitation. The proximity to the surface is shown to be a second-order effect.

  5. Time-resolved single dopant charge dynamics in silicon

    PubMed Central

    Rashidi, Mohammad; Burgess, Jacob A. J.; Taucer, Marco; Achal, Roshan; Pitters, Jason L.; Loth, Sebastian; Wolkow, Robert A.

    2016-01-01

    As the ultimate miniaturization of semiconductor devices approaches, it is imperative that the effects of single dopants be clarified. Beyond providing insight into functions and limitations of conventional devices, such information enables identification of new device concepts. Investigating single dopants requires sub-nanometre spatial resolution, making scanning tunnelling microscopy an ideal tool. However, dopant dynamics involve processes occurring at nanosecond timescales, posing a significant challenge to experiment. Here we use time-resolved scanning tunnelling microscopy and spectroscopy to probe and study transport through a dangling bond on silicon before the system relaxes or adjusts to accommodate an applied electric field. Atomically resolved, electronic pump-probe scanning tunnelling microscopy permits unprecedented, quantitative measurement of time-resolved single dopant ionization dynamics. Tunnelling through the surface dangling bond makes measurement of a signal that would otherwise be too weak to detect feasible. Distinct ionization and neutralization rates of a single dopant are measured and the physical process controlling those are identified. PMID:27782125

  6. Single-electron capacitance spectroscopy of individual dopants in silicon.

    PubMed

    Gasseller, M; DeNinno, M; Loo, R; Harrison, J F; Caymax, M; Rogge, S; Tessmer, S H

    2011-12-14

    Motivated by recent transport experiments and proposed atomic-scale semiconductor devices, we present measurements that extend the reach of scanned-probe methods to discern the properties of individual dopants tens of nanometers below the surface of a silicon sample. Using a capacitance-based approach, we have both spatially resolved individual subsurface boron acceptors and detected spectroscopically single holes entering and leaving these minute systems of atoms. A resonance identified as the B+ state is shown to shift in energy from acceptor to acceptor. We examine this behavior with respect to nearest-neighbor distances. By directly measuring the quantum levels and testing the effect of dopant-dopant interactions, this method represents a valuable tool for the development of future atomic-scale semiconductor devices.

  7. Spatial Distribution of Dopant Incorporation in CdTe

    SciTech Connect

    Guthrey, Harvey; Moseley, John; Colegrove, Eric; Burst, James; Albin, David; Metzger, Wyatt; Al-Jassim, Mowafak

    2016-11-21

    In this work we use state-of-the-art cathodoluminescence (CL) spectrum imaging that provides spectrum-per-pixel mapping of the CL emission to examine how dopant elements are incorporated into CdTe. Emission spectra and intensity are used to monitor the spatial distribution of additional charge carriers through characteristic variations in the CL emission based on theoretical modeling. Our results show that grain boundaries play a role in the incorporation of dopants in CdTe, whether intrinsic or extrinsic. This type of analysis is crucial for providing feedback to design different processing schedules that optimize dopant incorporation in CdTe photovoltaic material, which has struggled to reach high carrier concentration values. Here, we present results on CdTe films exposed to copper, phosphorus, and intrinsic doping treatments.

  8. Non-equilibrium Green's functions study of discrete dopants variability on an ultra-scaled FinFET

    SciTech Connect

    Valin, R. Martinez, A.; Barker, J. R.

    2015-04-28

    In this paper, we study the effect of random discrete dopants on the performance of a 6.6 nm channel length silicon FinFET. The discrete dopants have been distributed randomly in the source/drain region of the device. Due to the small dimensions of the FinFET, a quantum transport formalism based on the non-equilibrium Green's functions has been deployed. The transfer characteristics for several devices that differ in location and number of dopants have been calculated. Our results demonstrate that discrete dopants modify the effective channel length and the height of the source/drain barrier, consequently changing the channel control of the charge. This effect becomes more significant at high drain bias. As a consequence, there is a strong effect on the variability of the on-current, off-current, sub-threshold slope, and threshold voltage. Finally, we have also calculated the mean and standard deviation of these parameters to quantify their variability. The obtained results show that the variability at high drain bias is 1.75 larger than at low drain bias. However, the variability of the on-current, off-current, and sub-threshold slope remains independent of the drain bias. In addition, we have found that a large source to drain current by tunnelling current occurs at low gate bias.

  9. Sodium dopants in helium clusters: Structure, equilibrium and submersion kinetics

    SciTech Connect

    Calvo, F.

    2015-12-31

    Alkali impurities bind to helium nanodroplets very differently depending on their size and charge state, large neutral or charged dopants being wetted by the droplet whereas small neutral impurities prefer to reside aside. Using various computational modeling tools such as quantum Monte Carlo and path-integral molecular dynamics simulations, we have revisited some aspects of the physical chemistry of helium droplets interacting with sodium impurities, including the onset of snowball formation in presence of many-body polarization forces, the transition from non-wetted to wetted behavior in larger sodium clusters, and the kinetics of submersion of small dopants after sudden ionization.

  10. Redistribution of Implanted Dopants in GaN

    SciTech Connect

    Fu, M.; Gao, X.A.; Han, J.; Pearton, S.J.; Rieger, D.J.; Scarvepalli, V. Sekhar, J.A.; Shul, R.J.; Singh, R.K.; Wilson, R.G.; Zavada, J.M.; Zolper, J.C.

    1998-11-20

    Donor (S, Se and Te) and acceptor (Mg, Be and C) dopants have been implanted into GaN at doses of 3-5x1014 cm-2 and annealed at temperatures up to 1450 *C. No redistribution of any of the elements is detectable by Secondary Ion Mass Spectrometry, except for Be, which displays an apparent damage-assisted diffusion at 900 "C. At higher temperatures there is no further movement of the Be, suggesting that the point defect flux that assists motion at lower temperatures has been annealed. Effective diffusivities are <2X 1013 cm2.sec-1 at 1450 `C for each of the dopants in GaN.

  11. Encoding abrupt and uniform dopant profiles in vapor-liquid-solid nanowires by suppressing the reservoir effect of the liquid catalyst.

    PubMed

    Christesen, Joseph D; Pinion, Christopher W; Zhang, Xing; McBride, James R; Cahoon, James F

    2014-11-25

    Semiconductor nanowires (NWs) are often synthesized by the vapor-liquid-solid (VLS) mechanism, a process in which a liquid droplet-supplied with precursors in the vapor phase-catalyzes the growth of a solid, crystalline NW. By changing the supply of precursors, the NW composition can be altered as it grows to create axial heterostructures, which are applicable to a range of technologies. The abruptness of the heterojunction is mediated by the liquid catalyst, which can act as a reservoir of material and impose a lower limit on the junction width. Here, we demonstrate that this "reservoir effect" is not a fundamental limitation and can be suppressed by selection of specific VLS reaction conditions. For Au-catalyzed Si NWs doped with P, we evaluate dopant profiles under a variety of synthetic conditions using a combination of elemental imaging with energy-dispersive X-ray spectroscopy and dopant-dependent wet-chemical etching. We observe a diameter-dependent reservoir effect under most conditions. However, at sufficiently slow NW growth rates (≤250 nm/min) and low reactor pressures (≤40 Torr), the dopant profiles are diameter independent and radially uniform with abrupt, sub-10 nm axial transitions. A kinetic model of NW doping, including the microscopic processes of (1) P incorporation into the liquid catalyst, (2) P evaporation from the catalyst, and (3) P crystallization in the Si NW, quantitatively explains the results and shows that suppression of the reservoir effect can be achieved when P evaporation is much faster than P crystallization. We expect similar reaction conditions can be developed for other NW systems and will facilitate the development of NW-based technologies that require uniform and abrupt heterostructures.

  12. Multiple dopant injection system for small rocket engines

    NASA Technical Reports Server (NTRS)

    Sakala, G. G.; Raines, N. G.

    1992-01-01

    The Diagnostics Test Facility (DTF) at NASA's Stennis Space Center (SSC) was designed and built to provide a standard rocket engine exhaust plume for use in the research and development of engine health monitoring instrumentation. A 1000 lb thrust class liquid oxygen (LOX)-gaseous hydrogen (GH2) fueled rocket engine is used as the subscale plume source to simulate the SSME during experimentation and instrument development. The ability of the DTF to provide efficient, and low cost test operations makes it uniquely suited for plume diagnostic experimentation. The most unique feature of the DTF is the Multiple Dopant Injection System (MDIS) that is used to seed the exhaust plume with the desired element or metal alloy. The dopant injection takes place at the fuel injector, yielding a very uniform and homogeneous distribution of the seeding material in the exhaust plume. The MDIS allows during a single test firing of the DTF, the seeding of the exhaust plume with up to three different dopants and also provides distilled water base lines between the dopants. A number of plume diagnostic-related experiments have already utilized the unique capabilities of the DTF.

  13. Multiple dopant injection system for small rocket engines

    NASA Astrophysics Data System (ADS)

    Sakala, G. G.; Raines, N. G.

    1992-07-01

    The Diagnostics Test Facility (DTF) at NASA's Stennis Space Center (SSC) was designed and built to provide a standard rocket engine exhaust plume for use in the research and development of engine health monitoring instrumentation. A 1000 lb thrust class liquid oxygen (LOX)-gaseous hydrogen (GH2) fueled rocket engine is used as the subscale plume source to simulate the SSME during experimentation and instrument development. The ability of the DTF to provide efficient, and low cost test operations makes it uniquely suited for plume diagnostic experimentation. The most unique feature of the DTF is the Multiple Dopant Injection System (MDIS) that is used to seed the exhaust plume with the desired element or metal alloy. The dopant injection takes place at the fuel injector, yielding a very uniform and homogeneous distribution of the seeding material in the exhaust plume. The MDIS allows during a single test firing of the DTF, the seeding of the exhaust plume with up to three different dopants and also provides distilled water base lines between the dopants. A number of plume diagnostic-related experiments have already utilized the unique capabilities of the DTF.

  14. Change of Electronic Structures by Dopant-Induced Local Strain

    NASA Astrophysics Data System (ADS)

    Hyeong Kim, Gyu; Jeong, Sukmin

    2015-06-01

    Ag-induced Si(111)- surfaces (-Ag) exhibit unusual electronic structures that cannot be explained by the conventional rigid band model and charge transfer model. The (-Ag surfaces feature a free-electron-like parabolic band, the S1 band, that selectively shifts downward upon the adsorption of noble metal or alkali metal adatoms. Furthermore, the downward shift of S1 is independent of the type of dopants, Au, Ag, and Na. According to charge transfer analysis, Au adatoms accumulate electrons from the substrate and become negatively charged, whereas Na adatoms become positively charged, which indicates that S1 should shift in the opposite direction for both the adatoms. Investigation of calculated structures, calculation of model structures, and tight-binding analysis disclose that the changes in the electronic structure are closely related to the average Ag-Ag distance in the substrate and have their origin in the local strain induced by dopants (adatoms). This explanation implies that the electronic structure is irrespective of the dopant characters itself and paves a new way for understanding the electronic structures associated with the presence of dopants.

  15. Dopant profiling in the TEM, progress towards quantitative electron holography

    SciTech Connect

    Cooper, David; Truche, Robert; Chabli, Amal; Twitchett-Harrison, Alison C.; Midgley, Paul A.; Dunin-Borkowski, Rafal E.

    2007-09-26

    Off-axis electron holography has been used to characterise the dopant potential in GaAs p-n junctions. We show that the measured potential across the junctions is affected by both FIB specimen preparation and by charging in the TEM and suggest methods that can be used to minimise these problems.

  16. Functional dopant profiling of optical coherent transient materials

    NASA Astrophysics Data System (ADS)

    Kiruluta, Andrew J. M.

    A new novel method that functionally maps the distribution of dopants in a photon echo material is proposed that relies on imposing a set of linear orthogonal gradient magnetic fields for a controlled hyperfine splitting of energy levels to create characteristic quantum beats when illuminated with a laser pulse with sufficient bandwidth to interrogate these levels. In this approach, a spectroscopic finger print of the dopant sites due to concentration and field susceptibilities in the sample is achieved through a Fourier decomposition of the radiative relaxation decay in an approach analogous to nuclear magnetic resonance (NMR) spectroscopy due to the imposition of a controlled spatial-spectral encoding scheme. An example of such an interrogative approach uses a three pulse stimulated sequence necessary to probe a gradient resolved voxel. This three pulse approach can be combined with the conventional confocal imaging technique to provide information about the underlying chemistry of dopant distribution along each imaging plane which is useful in guiding the design and manufacturing process of optical crystals. In combination with gradient induced quantum beats, the entire inhomogeneous bandwidth can be interrogated. The proposed approach would scan this entire bandwidth at much faster rate enabling characterization of a large number of crystals than is currently possible through mechanical scanning with a confocal microscopy based spectroscopic technique as well as providing functional dopant profiling which is not currently possible with conventional approaches.

  17. Relaxation dynamics of orientationally disordered plastic crystals: effect of dopants.

    PubMed

    Singh, L P; Murthy, S S N; Bräuniger, T; Zimmermann, H

    2008-02-14

    We have examined the relaxation that occurs in the supercooled plastic crystalline phases of pentachloronitrobenzene (PCNB), dichlorotetramethylbenzene (DCTMB), trichlorotrimethylbenzene (TCTMB) along with some of their deuterated samples, and 1-cyanoadamantane (CNADM) in the presence of intentionally added dopants. The experimental techniques used in the present study are dielectric spectroscopy and differential scanning calorimetry (DSC). Only one relaxation process similar to that of the primary (or alpha-) relaxation characteristic of glass-forming materials is found, but there is no indication of any observable secondary relaxation within the resolution of our experimental setup. The alpha-process can reasonably be described by a Havriliak-Negami (HN) shape function throughout the frequency range. However, in the case of PCNB the dielectric strength (Delta epsilon) of the above said alpha-process does not change appreciably with temperature, though interestingly, a small addition of a dopant such as pentachlorobenzene (PCB), trichlorobenzene (TCB), and chloroadamantane (CLADM) to the molten state of PCNB drastically lowers the dielectric strength by a factor of 4 to 8. Powder X-ray diffraction measurements at room temperature and DSC data do not indicate any appreciable change in the crystalline structure. It is noticed that the effect of PCB as a dopant on the magnitude of alpha-process of CNADM is moderate, whereas both PCB and TCB as dopants show a much reduced effect on the relaxation in DCTMB and TCTMB. It is suggested that the drastic changes in the dielectric strength of the alpha-process is due to the rotational hindrance caused by the presence of a small number of dopant molecules in the host crystalline lattice. In the above context, the possibility of a certain degree of antiparallel ordering of dipoles is also discussed.

  18. Structure and segregation of dopant-defect complexes at grain boundaries in nanocrystalline doped ceria.

    PubMed

    Dholabhai, Pratik P; Aguiar, Jeffery A; Wu, Longjia; Holesinger, Terry G; Aoki, Toshihiro; Castro, Ricardo H R; Uberuaga, Blas P

    2015-06-21

    Grain boundaries (GBs) dictate vital properties of nanocrystalline doped ceria. Thus, to understand and predict its properties, knowledge of the interaction between dopant-defect complexes and GBs is crucial. Here, we report atomistic simulations, corroborated with first principles calculations, elucidating the fundamental dopant-defect interactions at model GBs in gadolinium-doped and manganese-doped ceria. Gadolinium and manganese are aliovalent dopants, accommodated in ceria via a dopant-defect complex. While the behavior of isolated dopants and vacancies is expected to depend on the local atomic structure at GBs, the added structural complexity associated with dopant-defect complexes is found to have key implications on GB segregation. Compared to the grain interior, energies of different dopant-defect arrangements vary significantly at the GBs. As opposed to bulk, the stability of oxygen vacancy is found to be sensitive to the dopant arrangement at GBs. Manganese exhibits a stronger propensity for segregation to GBs than gadolinium, revealing that accommodation of dopant-defect clusters depends on the nature of dopants. Segregation strength is found to depend on the GB character, a result qualitatively supported by our experimental observations based on scanning transmission electron microscopy. The present results indicate that segregation energies, availability of favorable sites, and overall stronger binding of dopant-defect complexes would influence ionic conductivity across GBs in nanocrystalline doped ceria. Our comprehensive investigation emphasizes the critical role of dopant-defect interactions at GBs in governing functional properties in fluorite-structured ionic conductors.

  19. Valences of dopants in Eu2+ persistent luminescence materials

    NASA Astrophysics Data System (ADS)

    Lastusaari, M.; Brito, H. F.; Carlson, S.; Hölsä, J.; Laamanen, T.; Rodrigues, L. C. V.; Welter, E.

    2014-04-01

    The existence and effect of different rare earth (R2+/3+/IV) ions in SrAl2O4:Eu2+,R3+ and M2MgSi2O7:Eu2+,R3+ (M: Sr, Ba) persistent luminescence materials was studied with XANES (x-ray absorption near edge structure) measurements at HASYLAB/DESY (Hamburg, Germany) and MAX-lab (Lund, Sweden). The experiments were carried out at 298 K for selected rare earth (co-)dopants (Eu2+; Ce3+, Nd3+, Sm3+, Dy3+ and Yb3+). The co-existence of Eu2+ and Eu3+ was observed in all materials. The co-dopants were always in the trivalent form.

  20. Simulation and bonding of dopants in nanocrystalline diamond.

    PubMed

    Barnard, A S; Russo, S P; Snook, I K

    2005-09-01

    The doping of the wide-band gap semiconductor diamond has led to the invention of many electronic and optoelectronic devices. Impurities can be introduced into diamond during chemical vapor deposition or high pressure-high temperature growth, resulting in materials with unusual physical and chemical properties. For electronic applications one of the main objectives in the doping of diamond is the production of p-type and n-type semiconductors materials; however, the study of dopants in diamond nanoparticles is considered important for use in nanodevices, or as qubits for quantum computing. Such devices require that bonding of dopants in nanodiamond must be positioned substitutionally at a lattice site, and must exhibit minimal or no possibility of diffusion to the nanocrystallite surface. In light of these requirements, a number of computational studies have been undertaken to examine the stability of various dopants in various forms of nanocrystalline diamond. Presented here is a review of some such studies, undertaken using quantum mechanical based simulation methods, to provide an overview of the crystal stability of doped nanodiamond for use in diamondoid nanodevices.

  1. Microwave modulation characteristics of twisted liquid crystals with chiral dopant

    NASA Astrophysics Data System (ADS)

    Yuan, Rui; Xing, Hongyu; Ye, Wenjiang

    2017-01-01

    Adding a chiral dopant in twisted nematic (TN) liquid crystal cell can stabilize the orientation of liquid crystal molecules, particularly in high TN (HTN) or super TN (STN) liquid crystal cells. The difference in pitches in liquid crystal is induced by the chiral dopant, and these different pitches affect the orientation of liquid crystal director under an external applied voltage and influence the characteristics of microwave modulation. To illustrate this point, the microwave phase shift per unit length (MPSL) versus voltage is calculated on the basis of the elastic theory of liquid crystal and the finite-difference iterative method. Enhancing the pitch induced by the chiral dopant in liquid crystal increases the MPSLs, but the stability of the twisted structures is decreased. Thus, appropriate pitches of 100d, 4d, and 2d can be applied in TN, HTN, and STN cells with cell gap d to enhance the characteristics of microwave modulation and stabilize the structures in twisted cell. This method can improve the characteristics of liquid crystal microwave modulators such that the operating voltage and the size of such phase shifters can be decreased.

  2. Introducing and manipulating magnetic dopant exchange interactions in semiconductor nanowires

    NASA Astrophysics Data System (ADS)

    Hegde, Manu; Hosein, Ian D.; Sabergharesou, Tahereh; Farvid, Shokouh S.; Radovanovic, Pavle V.

    2013-09-01

    The ability to control both spin and charge degrees of freedom in semiconductor nanostructrures is at heart of spintronic and quantum information technologies. Magnetically-doped semiconductor nanowires have emerged as a promising platform for spintronics, which warrants the exploration of their synthesis, electronic structure, and magnetic properties. Here we demonstrate the preparation of manganese-doped GaN and SnO2 nanowires by chemical vapor deposition and solvothermal methods, respectively. The investigation of both systems by electron microscopy and x-ray absorption spectroscopy at ensemble and single nanowire levels indicates that manganese dopants exist in a dual oxidation state, Mn2+ and Mn3+, with Mn2+ being the majority species. X-ray magnetic circular dichroism studies of individual nanowires suggest ferromagnetic interactions of manganese dopants, and the nanowire orientation-dependent magnetization owing to the magnetocrystalline anisotropy. The results of these studies demonstrate quantitative determination of the dopant electronic structure at the molecular level, and allow for a prediction of the magnetic properties of diluted magnetic semiconductor nanowires based on their orientation and geometry.

  3. Cation dopant distributions in nanostructures of transition-metal doped ZnO:Monte Carlo simulations

    SciTech Connect

    Droubay, Timothy C.; Kaspar, Tiffany C.; Kaspar, Bryce P.; Chambers, Scott A.

    2009-02-01

    The path from trace doping to solid solution formation involves an intermediate regime in which the doping level is a few to several atomic percent. In this regime, dopant-dopant interactions, which are driven by the spatial arrangement of dopants, are critical factors in determining the resulting properties. Conventional wisdom counts on simple probabilistic methods for predicting dopant distributions. Here, we use Monte Carlo simulations to show that widely used, straightforward statistical models, such as that of Behringer1, are accurate only in the limit of infinitesimally small surface–to-volume ratio. For epitaxial films and nanoparticles, where much of the current interest resides, dopant distributions depend strongly on the surface-to-volume ratio. We present empirical expressions that accurately predict dopant bonding configurations as a function of film or particle size, shape and dopant concentration for doped ZnO, a material of particular interest in semiconductor spintronics.

  4. Photoluminescence imaging of solitary dopant sites in covalently doped single-wall carbon nanotubes

    DOE PAGES

    Hartmann, Nicolai F.; Yalcin, Sibel Ebru; Adamska, Lyudmyla; ...

    2015-11-11

    Covalent dopants in semiconducting single wall carbon nanotubes (SWCNTs) are becoming important as routes for introducing new photoluminescent emitting states with potential for enhanced quantum yields, new functionality, and as species capable of near-IR room-temperature single photon emission. The origin and behavior of the dopant-induced emission is thus important to understand as a key requirement for successful room-T photonics and optoelectronics applications. Here, we use direct correlated two-color photoluminescence imaging to probe how the interplay between the SWCNT bright E11 exciton and solitary dopant sites yields the dopant-induced emission for three different dopant species: oxygen, 4-methoxybenzene, and 4-bromobenzene. We introducemore » a route to control dopant functionalization to a low level as a means for introducing spatially well-separated solitary dopant sites. Resolution of emission from solitary dopant sites and correlation to their impact on E11 emission allows confirmation of dopants as trapping sites for localization of E11 excitons following their diffusive transport to the dopant site. Imaging of the dopant emission also reveals photoluminescence intermittency (blinking), with blinking dynamics being dependent on the specific dopant. Density functional theory calculations were performed to evaluate the stability of dopants and delineate the possible mechanisms of blinking. Furthermore, theoretical modeling suggests that the trapping of free charges in the potential well created by permanent dipoles introduced by dopant atoms/groups is likely responsible for the blinking, with the strongest effects being predicted and observed for oxygen-doped SWCNTs.« less

  5. Photoluminescence imaging of solitary dopant sites in covalently doped single-wall carbon nanotubes

    SciTech Connect

    Hartmann, Nicolai F.; Yalcin, Sibel Ebru; Adamska, Lyudmyla; Haroz, Erik H.; Ma, Xuedan; Tretiak, Sergei; Htoon, Han; Doorn, Stephen K.

    2015-11-11

    Covalent dopants in semiconducting single wall carbon nanotubes (SWCNTs) are becoming important as routes for introducing new photoluminescent emitting states with potential for enhanced quantum yields, new functionality, and as species capable of near-IR room-temperature single photon emission. The origin and behavior of the dopant-induced emission is thus important to understand as a key requirement for successful room-T photonics and optoelectronics applications. Here, we use direct correlated two-color photoluminescence imaging to probe how the interplay between the SWCNT bright E11 exciton and solitary dopant sites yields the dopant-induced emission for three different dopant species: oxygen, 4-methoxybenzene, and 4-bromobenzene. We introduce a route to control dopant functionalization to a low level as a means for introducing spatially well-separated solitary dopant sites. Resolution of emission from solitary dopant sites and correlation to their impact on E11 emission allows confirmation of dopants as trapping sites for localization of E11 excitons following their diffusive transport to the dopant site. Imaging of the dopant emission also reveals photoluminescence intermittency (blinking), with blinking dynamics being dependent on the specific dopant. Density functional theory calculations were performed to evaluate the stability of dopants and delineate the possible mechanisms of blinking. Furthermore, theoretical modeling suggests that the trapping of free charges in the potential well created by permanent dipoles introduced by dopant atoms/groups is likely responsible for the blinking, with the strongest effects being predicted and observed for oxygen-doped SWCNTs.

  6. Influence of electron–phonon interactions in single dopant nanowire transistors

    SciTech Connect

    Carrillo-Nuñez, H. Bescond, M. Cavassilas, N.; Dib, E.; Lannoo, M.

    2014-10-28

    Single dopant nanowire transistors can be viewed as the ultimate miniaturization of nano electronic devices. In this work, we theoretically investigate the influence of the electron-phonon coupling on their transport properties using a non-equilibrium Green's function approach in the self-consistent Born approximation. For an impurity located at the center of the wire we find that, at room temperature, acoustic phonons broaden the impurity level so that the bistability predicted in the ballistic regime is suppressed. Optical phonons are found to have a beneficial impact on carrier transport via a phonon-assisted tunneling effect. We discuss the position and temperature dependence of these effects, showing that such systems might be very promising for engineering of ultimate devices.

  7. The Effect of Rare Earth Dopants on UO2 Oxidation

    SciTech Connect

    Hanson, Brady D.; Cumblidge, Stephen E.; Scheele, Randall D.; Sell, Rachel L.

    2003-06-01

    Recent work by Hanson [1] has demonstrated a clear dependence of the oxidation of Light Water Reactor spent fuel on burnup. Oxidation of spent fuel was shown to proceed via the two-step reaction UO2?UO2.4?UO2.67+x, where the U3O8-like phase does not form until conversion to UO2.4 is complete. The temperature-dependent activation energy (Ea) of the transition from UO2.4 to the hyperstoichiometric U3O8 was found to be {approx}150 kJ mol-1. Each MWD/kg M burnup added {approx}1.0 kJ mol-1. The work of McEachern et.al. [2], Choi et. al. [3], and You et. al. [4] have all verified this oxidation dependence on SIMFUEL or unirradiated doped-UO2. All present work agrees that the soluble actinides or fission products that substitute in the U matrix act to delay the onset of U3O8. However, no single model exists to explain the observed behavior, including the fact that most dopants actually allow an earlier onset for UO2.4 formation. The present work is part of a Nuclear Energy Research Initiative project attempting to develop a UO2-based matrix capable of achieving extended burnups by including soluble dopants. The resulting fuel should be highly oxidation and dissolution resistant, which will be beneficial during accident scenarios or for disposal in a geologic repository. In addition, the stabilized matrix may help delay the onset of fuel restructuring that occurs at higher burnups. Initial results of the oxidation tests to quantify effects as a function of ionic radii and charge of the dopant are presented.

  8. A theoretical study of dopant atom detection and probe behavior in STEM

    NASA Astrophysics Data System (ADS)

    Mittal, Anudha

    Very detailed information about the atomic and electronic structure of materials can be obtained via atomic-scale resolution scanning transmission electron microscopy (STEM). These experiments reach the limits of current microscopes, which means that optimal experimental design is a key ingredient in success. The step following experiment, extraction of information from experimental data is also complex. Comprehension of experimental data depends on comparison with simulated data and on fundamental understanding of aspects of scattering behavior. The research projects discussed in this thesis are formulated within three large concepts. 1. Usage of simulation to suggest experimental technique for observation of a particular structural feature.. Two specific structural features are explored. One is the characterization of a substitutional dopant atom in a crystal. Annular dark field scanning transmission electron microscope (ADF-STEM) images allow detection of individual dopant atoms in a crystal based on contrast between intensities of doped and non-doped column in the image. The magnitude of the said contrast is heavily influenced by specimen and microscope parameters. Analysis of multislice-based simulations of ADF-STEM images of crystals doped with one substitutional dopant atom for a wide range of crystal thicknesses, types and locations of dopant atom inside the crystal, and crystals with different atoms revealed trends and non-intuitive behaviors in visibility of the dopant atom. The results provide practical guidelines for the optimal experimental setup regarding both the microscope and specimen conditions in order to characterize the presence and location of a dopant atom. Furthermore, the simulations help in recognizing the cases where detecting a single dopant atom via ADF-STEM imaging is not possible. The second is a more specific case of detecting intrinsic twist in MoS2 nanotubes. Objective molecular dynamics simulations coupled with a density

  9. Radial Dopant Placement for Tuning Plasmonic Properties in Metal Oxide Nanocrystals.

    PubMed

    Crockett, Brandon M; Jansons, Adam W; Koskela, Kristopher M; Johnson, Darren W; Hutchison, James E

    2017-08-22

    Doped metal oxide nanocrystals that exhibit tunable localized surface plasmon resonances (LSPRs) represent an intriguing class of nanomaterials that show promise for a variety of applications from spectroscopy to sensing. LSPRs arise in these materials through the introduction of aliovalent dopants and lattice oxygen vacancies. Tuning the LSPR shape and energy is generally accomplished through controlling the concentration or identity of dopants in a nanocrystal, but the lack of finer synthetic control leaves several fundamental questions unanswered regarding the effects of radial dopant placement, size, and nanocrystalline architecture on the LSPR energy and damping. Here, we present a layer-by-layer synthetic method for core/shell nanocrystals that permits exquisite and independent control over radial dopant placement, absolute dopant concentration, and nanocrystal size. Using Sn-doped In2O3 (ITO) as a model LSPR system, we synthesized ITO/In2O3 core/shell as well as In2O3/ITO core/shell nanocrystals with varying shell thickness, and investigated the resulting optical properties. We observed profound influence of radial dopant placement on the energy and linewidth of the LSPR response, noting (among other findings) that core-localized dopants produce the highest values for LSPR energies per dopant concentration, and display the lowest damping in comparison to nanocrystals with shell-localized or homogeneously distributed dopants. Inactive Sn dopants present on ITO nanocrystal surfaces are activated upon the addition of a subnanometer thick undoped In2O3 shell. We show how LSPR energy can be tuned fully independent of dopant concentration, relying solely on core/shell architecture. Finally, the impacts of radial dopant placement on damping, independent of LSPR energy, are explored.

  10. A Safe Solution to Dopant Gas Desorption from Metal Surfaces

    NASA Astrophysics Data System (ADS)

    Nakanoya, Tsutomu; Egami, Maki

    2006-11-01

    TOXICAPTURE™ is used to further minimize trace toxic dopant gas inside cylinder valve outlets, which, over time, may desorb from metal surfaces. When outlet caps or connections to ion source gas cylinders are disconnected in order to perform installations or bottle changes, there always is some risk that toxic fumes resulting from desorption of the metal surface in contact with dopant gas are released in air and inhaled by the operator. TOXICAPTURE™ is a simple and easy solution to reduce this risk that may damage human health or may pollute clean room environment. TOXICAPTURE™ will react with the poison gas vapor to form nontoxic and solid material through irreversible chemical reactions. TOXICAPTURE™ prevents contamination and corrosion on gas contact surfaces of gas pipings, pressure regulators, pneumatic valves, mass flow controllers, and other parts in a gas box. TOXICAPTURE™ is highly effective in shortening the time to achieve high vacuum and in extending the lifetime of devices in the gas box. In this paper, we introduce the structure, functions, reactivity, applications, and effectivity of TOXICAPTURE™.

  11. Single-atom spectroscopy of phosphorus dopants implanted into graphene

    NASA Astrophysics Data System (ADS)

    Susi, Toma; Hardcastle, Trevor P.; Hofsäss, Hans; Mittelberger, Andreas; Pennycook, Timothy J.; Mangler, Clemens; Drummond-Brydson, Rik; Scott, Andrew J.; Meyer, Jannik C.; Kotakoski, Jani

    2017-06-01

    One of the keys behind the success of modern semiconductor technology has been the ion implantation of silicon, which allows its electronic properties to be tailored. For similar purposes, heteroatoms have been introduced into carbon nanomaterials both during growth and using post-growth methods. However, due to the nature of the samples, it has been challenging to determine whether the heteroatoms have been incorporated into the lattice as intended. Direct observations have so far been limited to N and B dopants, and incidental Si impurities. Furthermore, ion implantation of these materials is challenging due to the requirement of very low ion energies and atomically clean surfaces. Here, we provide the first atomic-resolution imaging and electron energy loss spectroscopy (EELS) evidence of phosphorus atoms in the graphene lattice, implanted by low-energy ion irradiation. The measured P L 2,3-edge shows excellent agreement with an ab initio spectrum simulation, conclusively identifying the P in a buckled substitutional configuration. While advancing the use of EELS for single-atom spectroscopy, our results demonstrate the viability of phosphorus as a lattice dopant in sp 2-bonded carbon structures and provide its unmistakable fingerprint for further studies.

  12. Charge-transfer crystallites as molecular electrical dopants

    PubMed Central

    Méndez, Henry; Heimel, Georg; Winkler, Stefanie; Frisch, Johannes; Opitz, Andreas; Sauer, Katrein; Wegner, Berthold; Oehzelt, Martin; Röthel, Christian; Duhm, Steffen; Többens, Daniel; Koch, Norbert; Salzmann, Ingo

    2015-01-01

    Ground-state integer charge transfer is commonly regarded as the basic mechanism of molecular electrical doping in both, conjugated polymers and oligomers. Here, we demonstrate that fundamentally different processes can occur in the two types of organic semiconductors instead. Using complementary experimental techniques supported by theory, we contrast a polythiophene, where molecular p-doping leads to integer charge transfer reportedly localized to one quaterthiophene backbone segment, to the quaterthiophene oligomer itself. Despite a comparable relative increase in conductivity, we observe only partial charge transfer for the latter. In contrast to the parent polymer, pronounced intermolecular frontier-orbital hybridization of oligomer and dopant in 1:1 mixed-stack co-crystallites leads to the emergence of empty electronic states within the energy gap of the surrounding quaterthiophene matrix. It is their Fermi–Dirac occupation that yields mobile charge carriers and, therefore, the co-crystallites—rather than individual acceptor molecules—should be regarded as the dopants in such systems. PMID:26440403

  13. Nanowire dopant measurement using secondary ion mass spectrometry

    SciTech Connect

    Chia, A. C. E.; Boulanger, J. P.; Wood, B. A.; LaPierre, R. R.; Dhindsa, N.; Saini, S. S.

    2015-09-21

    A method is presented to improve the quantitative determination of dopant concentration in semiconductor nanowire (NW) arrays using secondary ion mass spectrometry (SIMS). SIMS measurements were used to determine Be dopant concentrations in a Be-doped GaAs thin film and NW arrays of various pitches that were dry-etched from the same film. A comparison of these measurements revealed a factor of 3 to 12 difference, depending on the NW array pitch, between the secondary Be ion yields of the film and the NW arrays, despite being identically doped. This was due to matrix effects and ion beam mixing of Be from the NWs into the surrounding benzocyclobutene that was used to fill the space between the NWs. This indicates the need for etched NWs to be used as doping standards instead of 2D films when evaluating NWs of unknown doping by SIMS. Using the etched NWs as doping standards, NW arrays of various pitches grown by the vapour-liquid-solid mechanism were characterized by SIMS to yield valuable insights into doping mechanisms.

  14. Ab-initio study of the segregation and electronic properties of neutral and charged B and P dopants in Si and Si/SiO{sub 2} nanowires

    SciTech Connect

    Schoeters, Bob; Leenaerts, Ortwin Partoens, Bart; Pourtois, Geoffrey

    2015-09-14

    We perform first-principles calculations to investigate the preferred positions of B and P dopants, both neutral and in their preferred charge state, in Si and Si/SiO{sub 2} core-shell nanowires (NWs). In order to understand the observed trends in the formation energy, we isolate the different effects that determine these formation energies. By making the distinction between the unrelaxed and the relaxed formation energy, we separate the impact of the relaxation from that of the chemical environment. The unrelaxed formation energies are determined by three effects: (i) the effect of strain caused by size mismatch between the dopant and the host atoms, (ii) the local position of the band edges, and (iii) a screening effect. In the case of the SiNW (Si/SiO{sub 2} NW), these effects result in an increase of the formation energy away from the center (interface). The effect of relaxation depends on the relative size mismatch between the dopant and host atoms. A large size mismatch causes substantial relaxation that reduces the formation energy considerably, with the relaxation being more pronounced towards the edge of the wires. These effects explain the surface segregation of the B dopants in a SiNW, since the atomic relaxation induces a continuous drop of the formation energy towards the edge. However, for the P dopants, the formation energy starts to rise when moving from the center but drops to a minimum just next to the surface, indicating a different type of behavior. It also explains that the preferential location for B dopants in Si/SiO{sub 2} core-shell NWs is inside the oxide shell just next to the interface, whereas the P dopants prefer the positions next to the interface inside the Si core, which is in agreement with recent experiments. These preferred locations have an important impact on the electronic properties of these core-shell NWs. Our simulations indicate the possibility of hole gas formation when B segregates into the oxide shell.

  15. Towards chiral distributions of dopants in microporous frameworks: helicoidal supramolecular arrangement of (1R,2S)-ephedrine and transfer of chirality.

    PubMed

    Gómez-Hortigüela, Luis; Álvaro-Muñoz, Teresa; Bernardo-Maestro, Beatriz; Pérez-Pariente, Joaquín

    2015-01-07

    A molecular-mechanics computational study is performed in order to analyze the arrangement of (1R,2S)-(-)-ephedrine molecules within the 12-MR channels of the AFI aluminophosphate microporous framework and the influence on the spatial distribution of dopants embedded in the tetrahedral network. Results showed that ephedrine molecules arrange exclusively as dimers by π-π stacking of the aromatic rings within the AFI channels. Interestingly, the asymmetric nature of ephedrine and the presence of H-bond-forming groups (NH2 and OH) involve a preferential orientation where consecutive dimers within the channels are rotated by an angle of +30°; this is driven by the establishment of inter-dimer H-bonds. This preferential orientation leads to the development of a supramolecular enantiomerically-pure helicoidal (chiral) arrangement of ephedrine dimers. In addition, the computational results demonstrate that the particular molecular structure of ephedrine imparts a strong trend to attract negative charges to the vicinity of the NH2(+) positively-charged groups. Hence divalent dopants such as Mg, whose replacement by trivalent Al in the aluminophosphate network involves the generation of a negative charge, will tend to locate close to the NH2(+) molecular groups, suggesting that an imprinting of the organic arrangement to the spatial distribution of dopants would be feasible. Combined with the trend of ephedrine to arrange in a helicoidal fashion, an enantiomerically-pure helicoidal distribution of dopants would be expected, thus inducing a new type of chirality in microporous materials.

  16. Location Privacy

    NASA Astrophysics Data System (ADS)

    Meng, Xiaofeng; Chen, Jidong

    With rapid development of sensor and wireless mobile devices, it is easy to access mobile users' location information anytime and anywhere. On one hand, LBS is becoming more and more valuable and important. On the other hand, location privacy issues raised by such applications have also gained more attention. However, due to the specificity of location information, traditional privacy-preserving techniques in data publishing cannot be used. In this chapter, we will introduce location privacy, and analyze the challenges of location privacy-preserving, and give a survey of existing work including the system architecture, location anonymity and query processing.

  17. Dopant selection for control of charge carrier density and mobility in amorphous indium oxide thin-film transistors: Comparison between Si- and W-dopants

    SciTech Connect

    Mitoma, Nobuhiko E-mail: TSUKAGOSHI.Kazuhito@nims.go.jp; Kizu, Takio; Lin, Meng-Fang; Tsukagoshi, Kazuhito E-mail: TSUKAGOSHI.Kazuhito@nims.go.jp; Aikawa, Shinya; Ou-Yang, Wei; Gao, Xu; Fujiwara, Akihiko

    2015-01-26

    The dependence of oxygen vacancy suppression on dopant species in amorphous indium oxide (a-InO{sub x}) thin film transistors (TFTs) is reported. In a-InO{sub x} TFTs incorporating equivalent atom densities of Si- and W-dopants, absorption of oxygen in the host a-InO{sub x} matrix was found to depend on difference of Gibbs free energy of the dopants for oxidation. For fully oxidized films, the extracted channel conductivity was higher in the a-InO{sub x} TFTs containing dopants of small ionic radius. This can be explained by a reduction in the ionic scattering cross sectional area caused by charge screening effects.

  18. Location | FNLCR

    Cancer.gov

    The Frederick National Laboratory for Cancer Research campus is located 50 miles northwest of Washington, D.C., and 50 miles west of Baltimore, Maryland, in Frederick, Maryland. Satellite locations include leased and government facilities extending s

  19. Effective distribution coefficient of silicon dopants during magnetic Czochralski growth

    NASA Astrophysics Data System (ADS)

    Series, R. W.; Hurle, D. T. J.; Barraclough, K. G.

    1985-09-01

    Silicon crystals have been grown under axial magnetic fields of up to 0.2 T. At 0.05 T the field starts to interact with the melt and dopant incorporation becomes erratic. As the field is increased to 0.2 T the interaction becomes more controlled and it is seen that the effective distribution coefficient (keff) moves towards unity. A theory based on the analysis by Burton, Prim and Slichter of the dependence of the effective distribution coefficient (keff) on growth and crystal rotation rates in Czochralski growth is extended to include the effect of an imposed steady axial magnetic field. The flow fields incorporated into the theory are based on the analysis of the hydromagnetic flow at a rotating disc due to Kakutani (1962). It is shown that keff approaches unity as the field increases.

  20. Behavior of volatile dopants (P, Sb) in Czochralski silicon growth

    NASA Astrophysics Data System (ADS)

    Porrini, M.; Scala, R.; Voronkov, V. V.

    2017-02-01

    The evaporation from the silicon melt, during Czochralski process, is an important effect for Phosphorus and Antimony dopants. The evaporation rate γ was deduced from the measured axial profile of the resistivity converted into the concentration. For the heavily doped crystals, the value of γ is very similar for both P and Sb: in the order of 5.5×10-5 cm/s (which is significantly lower than the previously reported evaporation rates). It was concluded that the rate-limiting step for the evaporation process is neither the evaporation reaction itself nor the impurity transport through the flowing gas, but rather the transport through the melt that strongly depends on the melt convection. For low Phosphorus concentration, the transport through the gas is severely slowed-down - due to a change in the dominant gaseous species, from P2 to P1 - and becomes a limiting step. The evaporation rate is decreased and, in fact, becomes negligible.

  1. Recognizing nitrogen dopant atoms in graphene using atomic force microscopy

    NASA Astrophysics Data System (ADS)

    van der Heijden, Nadine J.; Smith, Daniël; Calogero, Gaetano; Koster, Rik S.; Vanmaekelbergh, Daniel; van Huis, Marijn A.; Swart, Ingmar

    2016-06-01

    Doping graphene by heteroatoms such as nitrogen presents an attractive route to control the position of the Fermi level in the material. We prepared N-doped graphene on Cu(111) and Ir(111) surfaces via chemical vapor deposition of two different molecules. Using scanning tunneling microscopy images as a benchmark, we show that the position of the dopant atoms can be determined using atomic force microscopy. Specifically, the frequency shift-distance curves Δ f (z ) acquired above a N atom are significantly different from the curves measured over a C atom. Similar behavior was found for N-doped graphene on Cu(111) and Ir(111). The results are corroborated by density functional theory calculations employing a van der Waals functional.

  2. Accurate measurement of the helical twisting power of chiral dopants

    NASA Astrophysics Data System (ADS)

    Kosa, Tamas; Bodnar, Volodymyr; Taheri, Bahman; Palffy-Muhoray, Peter

    2002-03-01

    We propose a method for the accurate determination of the helical twisting power (HTP) of chiral dopants. In the usual Cano-wedge method, the wedge angle is determined from the far-field separation of laser beams reflected from the windows of the test cell. Here we propose to use an optical fiber based spectrometer to accurately measure the cell thickness. Knowing the cell thickness at the positions of the disclination lines allows determination of the HTP. We show that this extension of the Cano-wedge method greatly increases the accuracy with which the HTP is determined. We show the usefulness of this method by determining the HTP of ZLI811 in a variety of hosts with negative dielectric anisotropy.

  3. Nanocarbon for Oxygen Reduction Electrocatalysis: Dopants, Edges, and Defects.

    PubMed

    Tang, Cheng; Zhang, Qiang

    2017-01-09

    The oxygen reduction reaction (ORR) is the cornerstone of various sustainable energy-conversion technologies. Metal-free nanocarbon electrocatalysts with competitive activity, enhanced durability, and satisfactory cost, have been proposed as the most promising substitute for precious-metal catalysts. However, their further development is still primarily based on trial-and-error approaches due to the controversial knowledge of critical active sites and mechanisms. Herein, the activity origins of nanocarbon-based ORR electro-catalysts are comprehensively reviewed and correlated, considering the dopants, edges, and defects. Analogously, they can effectively modify the charge/spin distribution on the sp(2) -conjugated carbon matrix, leading to optimized intermediate chemisorption and facilitated electron transfer. Specific doping at defective edges is expected to render practical applications for metal-free nanocarbon electrocatalysts.

  4. Mechanism for Increasing Dopant Incorporation in Semiconductors Via Doped Nanostructures

    SciTech Connect

    Kuskovsky,I.; Gu, Y.; Gong, Y.; Yan, H.; Lau, J.; Noyan, I.; Neumark, G.; Maksimov, O.; Zhou, X.; et al.

    2006-01-01

    A long-standing problem for ZnSe (and related alloys) has been to obtain good p-type doping. Recent work has given about an order-of-magnitude improvement in such doping by use of Te as a 'codopant' to facilitate the introduction of an acceptor dopant (N), since it is known that p-ZnTe can be obtained quite readily; the Te was introduced in submonolayer quantities via planar ({delta}) doping during molecular beam epitaxy. Here, we examine the mechanism of this improved doping. We show that it resides in the formation of ZnTe-rich nanoislands, with the N embedded in these. This result is obtained by studies involving transmission electron microscopy, high-resolution x-ray diffraction, secondary-ion mass spectroscopy, and temperature quenching of photoluminescence. We note that these nanoislands appear quite unique, in providing doping of semiconductors, and thus are of great interest of their own.

  5. Nanoscale doping of compound semiconductors by solid phase dopant diffusion

    SciTech Connect

    Ahn, Jaehyun Koh, Donghyi; Roy, Anupam; Banerjee, Sanjay K.; Chou, Harry; Kim, Taegon; Song, Jonghan

    2016-03-21

    Achieving damage-free, uniform, abrupt, ultra-shallow junctions while simultaneously controlling the doping concentration on the nanoscale is an ongoing challenge to the scaling down of electronic device dimensions. Here, we demonstrate a simple method of effectively doping ΙΙΙ-V compound semiconductors, specifically InGaAs, by a solid phase doping source. This method is based on the in-diffusion of oxygen and/or silicon from a deposited non-stoichiometric silicon dioxide (SiO{sub x}) film on InGaAs, which then acts as donors upon activation by annealing. The dopant profile and concentration can be controlled by the deposited film thickness and thermal annealing parameters, giving active carrier concentration of 1.4 × 10{sup 18 }cm{sup −3}. Our results also indicate that conventional silicon based processes must be carefully reviewed for compound semiconductor device fabrication to prevent unintended doping.

  6. Influence of dopants on defect formation in GaN

    SciTech Connect

    Liliental-Weber, Z.; Jasinski, J.; Benamara, M.; Grzegory, I.; Porowski, S.; Lampert, D.J.H.; Eiting, C.J.; Dupuis R.D.

    2001-10-15

    Influence of p-dopants (Mg and Be) on the structure of GaN has been studied using Transmission Electron Microscopy (TEM). Bulk GaN:Mg and GaN:Be crystals grown by a high pressure and high temperature process and GaN:Mg grown by metal-organic chemical-vapor deposition (MOCVD) have been studied. Structural dependence on growth polarity was observed in the bulk crystals. Spontaneous ordering in bulk GaN:Mg on c-plane (formation of Mg-rich planar defects with characteristics of inversion domains) was observed for growth in the N to Ga polar direction (N polarity). On the opposite site of the crystal (growth in the Ga to N polar direction) Mg-rich pyramidal defects empty inside (pinholes) were observed. Both these defects were also observed in MOCVD grown crystals. Pyramidal defects were also observed in the bulk GaN:Be crystals.

  7. Towards bipolar atomic scale dopant devices defined by STM-lithography

    NASA Astrophysics Data System (ADS)

    Fuhrer, Andreas; Köster, Sigrun; Pascher, Nikola

    2015-03-01

    Dopant device fabrication with hydrogen resist lithography has been demonstrated only for n-type dopants. The reason for this is the ease with which phosphorus can be incorporated and activated after gas phase doping with phosphine. Specifically, incorporation on the silicon (001) surface can be achieved at 350°C while keeping the hydrogen resist intact and thus avoiding surface diffusion of the dopants. Here, we present new results on p-type δ-doping of silicon, towards the fabrication of bipolar dopant devices with hydrogen resist lithography. Using diborane as a gas-phase dopant source, Hall bar devices were fabricated to extract hole densities and mobilities in cryogenic magneto-transport experiments. Furthermore, the dependence of these parameters on diborane dose and dopant activation temperatures is investigated. We find that gas-phase doping with diborane is compatible with hydrogen resist lithography and dopant structures can be patterned using the STM. However, activation of the boron dopants currently still leads to significant diffusion and therefore blurring of the patterned devices. We will discuss the prospects of further optimising this and present a possible path forward towards bipolar atomic scale device fabrication with the STM. Support from EU grants PAMS, SiSpin, SiAM and from Swiss NCCR QSIT is gratefully acknowledged.

  8. Dopant gas effect on silicon chemical vapor depositions: A surface potential model

    NASA Technical Reports Server (NTRS)

    Chang, C. A.

    1975-01-01

    A surface potential model is proposed to consistently explain the known dopant gas effects on silicon chemical vapor deposition. This model predicts that the effects of the same dopant gases on the diamond deposition rate using methane and carbon tetrachloride should be opposite and similar to those of silane, respectively. Available data are in agreement with this prediction.

  9. Tuning deep dopants to shallow ones in 2D semiconductors by substrate screening: The case of XS (X = Cl, Br, I) in MoS2

    NASA Astrophysics Data System (ADS)

    Ma, Jie; Yu, Zhi Gen; Zhang, Yong-Wei

    2017-04-01

    Doping plays a key role in modulating electronic properties of 2D semiconductors, and thus is vitally important for next-generation nanoelectronics and optoelectronics devices. However, how to effectively tune the dopant ionization energy (IE) so as to achieve robust and controllable n -type or p -type conductivities in 2D semiconductors is still a significant challenge. Here, using first-principles calculations, we demonstrate an effective IE-tuning route for 2D semiconductors using dielectric substrates. Taking XS (X = Cl, Br, I) in MoS2 as examples, we show that the dielectric substrate is able to tune deep dopants to shallow ones, and the dopant IE depends on which S layer the dopant is located in. Specifically, the IE of IS is reduced from 0.63 eV for the freestanding MoS2, to 0.39 eV when MoS2 is on a SiO2 substrate, further to 0.17 eV when MoS2 is on an Al2O3 substrate, and the IEs of IS in the inner and outer S layers differ by 0.22 eV with an Al2O3 substrate. Correspondingly, the carrier concentrations can be tuned by selecting different substrates or doping layers. We reveal that the remarkable IE reduction is originated from the electronic and ionic screenings of the substrate. Our results not only shed light on the substrate screening effects on the dopant properties, but also suggest a practical route to achieve controllable n -type or p -type carrier concentrations for 2D semiconductors.

  10. Defect and dopant properties of MgTa{sub 2}O{sub 6}

    SciTech Connect

    Tealdi, Cristina; Saiful Islam, M.; Malavasi, Lorenzo . E-mail: lorenzo.malavasi@unipv.it; Flor, Giorgio

    2004-11-01

    Atomistic computer simulation techniques have been used, for the first time, to reproduce the crystal structure of MgTa{sub 2}O{sub 6} and to investigate the defect chemistry and dopant properties of this material. The calculated defect energetics suggest that the concentration of intrinsic atomic defects in this phase is insignificant and that the system is probably stable to both oxidation and reduction. Dopant solution energy versus ion size trends are found for both isovalent and aliovalent dopant incorporation at Mg and Ta sites. Divalent dopants (e.g. Ca, Cu) preferentially occupy the Mg site whereas dopants with higher charge (e.g. Sc, Zr, Nb) are more favorable on the Ta site. High migration activation energies (>2eV) predict limited ionic conductivity in this material.

  11. The effect of dopant incorporation on the elastic properties of Ti metal

    NASA Astrophysics Data System (ADS)

    Wilson, N. C.; McGregor, K.; Gibson, M. A.; Russo, S. P.

    2015-01-01

    The effect of dopant atoms on the structural and elastic properties of α titanium is examined through the use of density functional theory. The effect of 66 dopant atoms, from H through the third row transition metal elements, were considered in this study. In all cases the dopant concentration was approximately 3 at%, with substitutional incorporation investigated for all atoms considered and interstitial incorporation investigated for a smaller subset of elements. Interstitial incorporation was calculated to be more energetically favourable for the elements H, B to F, S and Cl with these dopants coordinating octahedrally with the surrounding Ti atoms, while substitutional incorporation was found to be more stable for the other elements. The five independent single crystal elastic constants are calculated, along with the bulk and shear moduli. The energetics and mechanically stability associated with the alloying of various dopants is also discussed.

  12. Comparison of Boron diffused emitters from BN, BSoD and H3BO3 dopants

    NASA Astrophysics Data System (ADS)

    Singha, Bandana; Singh Solanki, Chetan

    2016-12-01

    In this work, we are comparing different limited boron dopant sources for the emitter formation in n-type c-Si solar cells. High purity boric acid solution, commercially available boron spin on dopant and boron nitride solid source are used for comparison of emitter doping profiles for the same time and temperature conditions of diffusion. The characterizations done for the similar sheet resistance values for all the dopant sources show different surface morphologies and different device parameters. The measured emitter saturation current densities (Joe) are more than 20 fA cm-2 for all the dopant sources. The bulk carrier lifetimes measured for different diffusion conditions and different solar cell parameters for the similar sheet resistance values show the best result for boric acid diffusion and the least for BN solid source. So, different dopant sources result in different emitter and cell performances.

  13. Femtosecond-laser hyperdoping silicon in an SF{sub 6} atmosphere: Dopant incorporation mechanism

    SciTech Connect

    Sher, Meng-Ju; Mangan, Niall M.; Lin, Yu-Ting; Brenner, Michael P.; Smith, Matthew J.; Gradečak, Silvija; Marbach, Sophie; Schneider, Tobias M.; Mazur, Eric

    2015-03-28

    In this paper, we examine the fundamental processes that occur during femtosecond-laser hyperdoping of silicon with a gas-phase dopant precursor. We probe the dopant concentration profile as a function of the number of laser pulses and pressure of the dopant precursor (sulfur hexafluoride). In contrast to previous studies, we show the hyperdoped layer is single crystalline. From the dose dependence on pressure, we conclude that surface adsorbed molecules are the dominant source of the dopant atoms. Using numerical simulation, we estimate the change in flux with increasing number of laser pulses to fit the concentration profiles. We hypothesize that the native oxide plays an important role in setting the surface boundary condition. As a result of the removal of the native oxide by successive laser pulses, dopant incorporation is more efficient during the later stage of laser irradiation.

  14. Optical characterizations of doped silicon nanocrystals grown by co-implantation of Si and dopants in SiO₂

    SciTech Connect

    Frégnaux, M.; Khelifi, R.; Muller, D.; Mathiot, D.

    2014-10-14

    Co-implantation, with overlapping implantation projected ranges, of Si and doping species (P, As, and B) followed by a thermal annealing step is a viable route to form doped Si nanocrystals (NCs) embedded in silica (SiO₂). In this paper, we investigate optical characterizations of both doped and un-doped Si-NCs prepared by this method. The effective NC presence in the oxide layer and their crystallinity is verified by Raman spectrometry. Photoluminescence (PL) and PL excitation measurements reveal quantum confinement effects and a gradual PL quenching with increasing dopant concentrations. In un-doped NC, the measured Stokes shift remains constant and its value ~0.2 eV is almost twice the Si–O vibration energy. This suggests that a possible radiative recombination path is a fundamental transition assisted by a local phonon. PL lifetime investigations show that PL time-decays follow a stretched exponential. Using a statistical model for luminescence quenching, a typical NC diameter close to 2 nm is obtained for As- and P-doped samples, consistent with our previous atomic probe tomography (APT) analyses. APT also demonstrated that n-type dopant (P and As) are efficiently introduced in the NC core, whereas p-type dopant (B) are located at the NC/SiO₂ interface. This last observation could explain the failure of the luminescence-quenching model to determine NC size in B-doped samples. All together, these experimental observations question on possible different carrier recombination paths in P or As doped NC compared to B one's.

  15. Anderson-Mott transition in arrays of a few dopant atoms in a silicon transistor.

    PubMed

    Prati, Enrico; Hori, Masahiro; Guagliardo, Filippo; Ferrari, Giorgio; Shinada, Takahiro

    2012-07-01

    Dopant atoms are used to control the properties of semiconductors in most electronic devices. Recent advances such as single-ion implantation have allowed the precise positioning of single dopants in semiconductors as well as the fabrication of single-atom transistors, representing steps forward in the realization of quantum circuits. However, the interactions between dopant atoms have only been studied in systems containing large numbers of dopants, so it has not been possible to explore fundamental phenomena such as the Anderson-Mott transition between conduction by sequential tunnelling through isolated dopant atoms, and conduction through thermally activated impurity Hubbard bands. Here, we observe the Anderson-Mott transition at low temperatures in silicon transistors containing arrays of two, four or six arsenic dopant atoms that have been deterministically implanted along the channel of the device. The transition is induced by controlling the spacing between dopant atoms. Furthermore, at the critical density between tunnelling and band transport regimes, we are able to change the phase of the electron system from a frozen Wigner-like phase to a Fermi glass by increasing the temperature. Our results open up new approaches for the investigation of coherent transport, band engineering and strongly correlated systems in condensed-matter physics.

  16. First-principles Study of the NiGe/Ge Schottky Barrier Height under Dopant Segregation

    NASA Astrophysics Data System (ADS)

    Lin, Chiung-Yuan; Lin, Han-Chi

    2015-03-01

    Traditional Si-based MOSFETs are approaching its fundamental scaling limits, and Ge has been comprehensively explored as a potential channel material to replace Si due to its high intrinsic carrier mobility for further performance enhancement. Nevertheless, strong Fermi-level pinning near the valence band edge of Ge leads to high electron Schottky barrier height. Dopant segregation technique has been proposed to achieve shallower junction depth and heavier dopant concentration for NiGe/Ge. However, the role of dopants at the NiGe/Ge interface is not clear. In this study, first-principles calculations are employed to nail down the most stable dopant position and to obtain the physical Schottky barrier height (by HSE06 hybrid functional) of the NiGe/Ge contact. For the conventional n-type dopant such as phosphorous and arsenic, our calculations show that those two elements may be segregated at the interface, while the reduction of the Schottky barrier height is insignificant. This implies that the experimental improvement of the NiGe/n-type Ge junction by dopant are mainly attributed to the increased dopant concentration around the interface. The authors acknowledge financial support from the Taiwan Ministry of Science and Technology (under Grant No. MOST 103-2112-M-009-004-).

  17. Photorefractive effect in ferroelectric liquid crystal blends containing terthiophene photoconductive chiral dopants

    NASA Astrophysics Data System (ADS)

    Sasaki, Takeo; Yoshino, Masanori

    2016-04-01

    Ferroelectric liquid crystalline mixtures composed of a smectic liquid crystal, a photoconductive chiral dopant, and an electron trap reagent exhibit a large photorefractivity with a rapid response. It is expected that the photorefractive FLC blends can be utilized in dynamic amplification of moving optical signals. In the present study, the photorefractive properties of the ferroelectric liquid crystal blends containing different photoconductive chiral dopants were examined. The durability of the photoconductive chiral dopants during laser irradiation was investigated. Tthe effect of the conduction of photogenerated ionic species on the photorefractivity decay was clarified.

  18. Carrier injection engineering in nanowire transistors via dopant and shape monitoring of the access regions

    SciTech Connect

    Berrada, Salim Bescond, Marc Cavassilas, Nicolas; Raymond, Laurent; Lannoo, Michel

    2015-10-12

    This work theoretically studies the influence of both the geometry and the discrete nature of dopants of the access regions in ultra-scaled nanowire transistors. By means of self-consistent quantum transport simulations, we show that discrete dopants induce quasi-localized states which govern carrier injection into the channel. Carrier injection can be enhanced by taking advantage of the dielectric confinement occurring in these access regions. We demonstrate that the optimization of access resistance can be obtained by a careful control of shape and dopant position. These results pave the way for contact resistance engineering in forthcoming device generations.

  19. Influence of surface reconstruction on dopant incorporation and transport properties of GaAs(Bi) alloys

    NASA Astrophysics Data System (ADS)

    Field, R. L.; Occena, J.; Jen, T.; Del Gaudio, D.; Yarlagadda, B.; Kurdak, C.; Goldman, R. S.

    2016-12-01

    We report on the influence of surface reconstruction on silicon dopant incorporation and transport properties during molecular-beam epitaxy of GaAs(Bi) alloys. GaAs(Bi) growth with an (n × 3) reconstruction leads to n-type conductivity, while growth with a (2 × 1) reconstruction leads to p-type conductivity. We hypothesize that the presence or absence of surface arsenic dimers prevents or enables dopant incorporation into arsenic lattice sites. We consider the influence of bismuth anions on arsenic-dimer mediated dopant incorporation and the resulting electronic transport properties, demonstrating the applicability of this mechanism to mixed anion semiconductor alloys.

  20. Dopants adsorbed as single atoms prevent degradation of catalysts

    NASA Astrophysics Data System (ADS)

    Wang, Sanwu; Borisevich, Albina Y.; Rashkeev, Sergey N.; Glazoff, Michael V.; Sohlberg, Karl; Pennycook, Stephen J.; Pantelides, Sokrates T.

    2004-03-01

    The design of catalysts with desired chemical and thermal properties is viewed as a grand challenge for scientists and engineers. For operation at high temperatures, stability against structural transformations is a key requirement. Although doping has been found to impede degradation, the lack of atomistic understanding of the pertinent mechanism has hindered optimization. For example, porous γ-Al2O3, a widely used catalyst and catalytic support, transforms to non-porous α-Al2O3 at ~1,100 °C (refs 7-10). Doping with La raises the transformation temperature to ~1,250 °C, but it has not been possible to establish if La atoms enter the bulk, adsorb on surfaces as single atoms or clusters, or form surface compounds. Here, we use direct imaging by aberration-corrected Z-contrast scanning transmission electron microscopy coupled with extended X-ray absorption fine structure and first-principles calculations to demonstrate that, contrary to expectations, stabilization is achieved by isolated La atoms adsorbed on the surface. Strong binding and mutual repulsion of La atoms effectively pin the surface and inhibit both sintering and the transformation to α-Al2O3. The results provide the first guidelines for the choice of dopants to prevent thermal degradation of catalysts and other porous materials.

  1. Dopant concentration dependent growth of Fe:ZnO nanostructures

    SciTech Connect

    Sahai, Anshuman; Goswami, Navendu

    2016-05-23

    Systematic investigations of structural properties of 1-10% Fe doped ZnO nanostructure (Fe:ZnO NS) prepared via chemical precipitation method have been reported. Structural properties were probed thoroughly employing scanning electron microscope (SEM) and transmission electron microscope (TEM), energy dispersive X-ray (EDAX) analysis and X-ray diffraction (XRD). Morphological transformation of nanostructures (NS) with Fe incorporation is evident in SEM/TEM images. Nanoparticles (NP) obtained with 1% Fe, evolve to nanorods (NR) for 3% Fe; NR transform to nanocones (NC) (for 5% and 7% Fe) and finally NC transform to nanoflakes (NF) at 10% Fe. Morover, primary phase of Zn{sub 1-x}Fe{sub x}O along with secondary phases of ZnFe{sub 2}O{sub 4} and Fe{sub 2}O{sub 3} were also revealed through XRD measurements. Based on collective XRD, SEM, TEM, and EDAX interpretations, a model for morphological evolution of NS was proposed and the pivotal role of Fe dopant was deciphered.

  2. Comparison of Cathodoluminescent and Photoluminescent Emission Spectra of LuPO4 with Different Dopants

    SciTech Connect

    Goedeke, Shawn; Hollerman, William Andrew; Allison, Stephen W; Gray, P A; Lewis, Linda A; Smithwick III, Robert W; Boatner, Lynn A; Glasgow, David C; Wise, H.

    2008-01-01

    The current interest in returning human exploration to the Moon and Mars makes cost-effective and low-mass health monitoring sensors essential for spacecraft development. In space, there are many surface measurements that are required to monitor the condition of the spacecraft including: surface temperature, radiation dose, and impact. Through the use of tailored phosphors, these conditions can be monitored. Practical space-based phosphor sensors will depend heavily upon research investigating the resistance of phosphors to ionizing radiation and their ability to anneal or 'self-heal' from damage caused by ionizing radiation. For the present research, a group of lutetium orthophosphate (LuPO{sub 4}) crystals with dopants including europium, erbium, and neodymium were characterized. Cathodoluminescence (CL) testing was performed using the low energy electron system located at the NASA Marshall Space Flight Center in Huntsville, Alabama. The data were collected using an Ocean Optics HR4000 spectrometer and a fiber optic feed-through. Previous research has shown that increases in both beam energy and current density improved the CL fluorescence yield. While the total electron dose was small, the intention was to maximize the number of irradiated materials. Additionally, these samples were evaluated using a PTI Quantum Master Spectrophotometer to determine the photoluminescence emission spectra.

  3. Theoretical study on the effect of dopant positions and dopant density on transport properties of a BN co-doped SiC nanotube

    NASA Astrophysics Data System (ADS)

    Choudhary, Sudhanshu; Qureshi, S.

    2013-01-01

    We investigate the effect of dopant (boron ‘B’-nitrogen ‘N’) position and density on electronic transport properties of a BN co-doped silicon carbide nanotube (SiCNT). The results show an increase in conductance when both BN impurities are far in space from each other. Orbital delocalization and appearance of new electronic states around Fermi level contribute to the current when this spacing is increased. On the other hand, a reduction in SiCNT conductivity was observed when BN dopant density was increased. This is attributed to the electronic states moving away from the Fermi level and orbital localization at higher bias voltages.

  4. Controlling the dopant dose in silicon by mixed-monolayer doping.

    PubMed

    Ye, Liang; Pujari, Sidharam P; Zuilhof, Han; Kudernac, Tibor; de Jong, Michel P; van der Wiel, Wilfred G; Huskens, Jurriaan

    2015-02-11

    Molecular monolayer doping (MLD) presents an alternative to achieve doping of silicon in a nondestructive way and holds potential for realizing ultrashallow junctions and doping of nonplanar surfaces. Here, we report the mixing of dopant-containing alkenes with alkenes that lack this functionality at various ratios to control the dopant concentration in the resulting monolayer and concomitantly the dopant dose in the silicon substrate. The mixed monolayers were grafted onto hydrogen-terminated silicon using well-established hydrosilylation chemistry. Contact angle measurements, X-ray photon spectroscopy (XPS) on the boron-containing monolayers, and Auger electron spectroscopy on the phosphorus-containing monolayers show clear trends as a function of the dopant-containing alkene concentration. Dynamic secondary-ion mass spectroscopy (D-SIMS) and Van der Pauw resistance measurements on the in-diffused samples show an effective tuning of the doping concentration in silicon.

  5. Dopant effects on the superconductivity of YBa2Cu3O7 ceramics

    NASA Astrophysics Data System (ADS)

    Yan, M. F.; Rhodes, W. W.; Gallagher, P. K.

    1988-02-01

    The effect of dopants on the superconductivity of YBa2Cu3O7 ceramics was investigated, comparing the effects of SrTiO3 and 17 different oxide dopants (namely, Ca, Sc, La, and Zr with possible substitution in the yttrium sites; K, Sr, and Pb in the barium sites; and Li, Mg, Fe, Co, Ni, Zn, Al, Ti, Nb, and Si in the copper sites). The results showed that these dopants can be classified into four categories, depending on their solubilities and substitution into different cation sites of the YBa2Cu3O7 perovskite. The effects of these dopants on the transition temperature of the superconductivity of YBa2Cu3O7 and on the integrity of the superconducting phase are discussed.

  6. The dopant dependent photocatalytic activity of polyaniline towards the degradation of Rose Bengal dye

    NASA Astrophysics Data System (ADS)

    Chatterjee, Mukulika Jana; Banerjee, Dipali; Ghosh, Amrita; Mondal, Anup

    2016-05-01

    Polyaniline (PANI) with two different dopants, hydrochloric acid (HCl) and bismuth nitrate (Bi (NO3)3), were synthesized to investigate the effect of dopant on photocatalytic degradation of Rose Bengal, an organic dye, in presence of sunlight. PANI, synthesized by in situ polymerization was characterized by FESEM images, FTIR and UV-Vis spectra. FESEM images show rod like structures obtained for both the dopants. FTIR spectra confirms the formation of conducting PANI with the presence of C=N, C=C stretching modes in quinoid and benzenoid units. Band gap of PANI has been obtained from UV-Vis spectrum. Doped polyaniline exhibited a fast degradation of dye by 98.62 % & 98.12 % within 5 min & 8 min under visible light illumination for the dopant HCl & Bi (NO3)3 respectively.

  7. A method of dopant electron energy spectrum parameterization for calculation of single-electron nanodevices

    NASA Astrophysics Data System (ADS)

    Shorokhov, V. V.

    2017-05-01

    Solitary dopants in semiconductors and dielectrics that possess stable electron structures and interesting physical properties may be used as building blocks of quantum computers and sensor systems that operate based on new physical principles. This study proposes a phenomenological method of parameterization for a single-particle energy spectrum of dopant valence electrons in crystalline semiconductors and dielectrics that takes electron-electron interactions into account. It is proposed to take electron-electron interactions in the framework of the outer electron shell model into account. The proposed method is applied to construct the procedure for the determination of the effective dopant outer shell capacity and the method for calculation of the tunneling current in a single-electron device with one or several active dopants-charge centers.

  8. Charge separation technique for metal-oxide-silicon capacitors in the presence of hydrogen deactivated dopants

    SciTech Connect

    Witczak, Steven C.; Winokur, Peter S.; Lacoe, Ronald C.; Mayer, Donald C.

    2000-06-01

    An improved charge separation technique for metal-oxide-silicon (MOS) capacitors is presented which accounts for the deactivation of substrate dopants by hydrogen at elevated irradiation temperatures or small irradiation biases. Using high-frequency capacitance-voltage measurements, radiation-induced inversion voltage shifts are separated into components due to oxide trapped charge, interface traps, and deactivated dopants, where the latter is computed from a reduction in Si capacitance. In the limit of no radiation-induced dopant deactivation, this approach reduces to the standard midgap charge separation technique used widely for the analysis of room-temperature irradiations. The technique is demonstrated on a p-type MOS capacitor irradiated with {sup 60}Co {gamma} rays at 100 degree sign C and zero bias, where the dopant deactivation is significant.(c) 2000 American Institute of Physics.

  9. Dopant-controlled single-electron pumping through a metallic island

    NASA Astrophysics Data System (ADS)

    Wenz, Tobias; Hohls, Frank; Jehl, Xavier; Sanquer, Marc; Barraud, Sylvain; Klochan, Jevgeny; Barinovs, Girts; Kashcheyevs, Vyacheslavs

    2016-05-01

    We investigate a hybrid metallic island/single dopant electron pump based on fully depleted silicon-on-insulator technology. Electron transfer between the central metallic island and the leads is controlled by resonant tunneling through single phosphorus dopants in the barriers. Top gates above the barriers are used to control the resonance conditions. Applying radio frequency signals to the gates, non-adiabatic quantized electron pumping is achieved. A simple deterministic model is presented and confirmed by comparing measurements with simulations.

  10. Dopant-controlled single-electron pumping through a metallic island

    SciTech Connect

    Wenz, Tobias Hohls, Frank; Jehl, Xavier; Sanquer, Marc; Barraud, Sylvain; Klochan, Jevgeny; Barinovs, Girts; Kashcheyevs, Vyacheslavs

    2016-05-23

    We investigate a hybrid metallic island/single dopant electron pump based on fully depleted silicon-on-insulator technology. Electron transfer between the central metallic island and the leads is controlled by resonant tunneling through single phosphorus dopants in the barriers. Top gates above the barriers are used to control the resonance conditions. Applying radio frequency signals to the gates, non-adiabatic quantized electron pumping is achieved. A simple deterministic model is presented and confirmed by comparing measurements with simulations.

  11. Quantitative Two-Dimensional Dopant Profile Measurement on Semiconductors by Scanning Probe Microscopy.

    NASA Astrophysics Data System (ADS)

    Huang, Yunji

    1995-01-01

    A Scanning Capacitance Microscope (SCM) has been built to measure two-dimensional (2D) dopant density profiles on semiconductor materials. A quasi-one-dimensional(1D) analytical model has been constructed for inverting the measured SCM data to dopant profile. Local Capacitance -Voltage (C-V) measurements have been performed on n ^+/n and p^+/n ion implanted silicon wafers and systematic results have been obtained. Dopant profile measurements by SCM have been performed on both top surfaces and cross-sectional surfaces of ion implanted silicon wafers. After inversion, a good agreement has been found between the SCM profile and the profiles obtained by other independent methods such as Secondary Ion Mass Spectrometry (SIMS), Spreading Resistance Profiling (SRP), and process simulation (SUPREM IV). The dissertation presented here consists of four chapters. The first chapter introduces the dopant profile measurement and gives a review of existing doping profiling methods. The advantages of SCM for dopant profile measurement are discussed in this chapter. The second chapter concentrates on the instrumentation of SCM, SCM tip preparation, and silicon sample preparation for dopant profile measurement by SCM. The third chapter describes the tip/sample modeling by which the measured capacitance signal is inverted to dopant profile. The calculation of the electrostatic force between a tip and semiconductor sample as a function of dopant density is also presented in this chapter. Finally, in the fourth chapter, the SCM measurement results are presented and the inverted 2D profiles are compared with the results obtained by other independent methods. A discussion about measurement sensitivity, spatial resolution, modeling errors, and future works is presented.

  12. Theory of defects and dopants in amorphous and crystalline semiconductors

    NASA Astrophysics Data System (ADS)

    Stumm, Petra

    In this dissertation the structural and electronic consequences of defects and dopants in amorphous and crystalline semiconductors are investigated. The research that I have done explores these possibilities on a theoretical level. This work is aimed towards comprising a detailed study of the atomic scale structure and electrical properties of elemental and nitrogen doped ta-C. Further, results on a investigation of native defects in crystalline and amorphous GaN are reported. First principles methods are used for these calculations. Two structural tetrahedral amorphous carbon models were introduced, whose properties were in agreement with the available experimental data. The topological and electronic properties for different N doping concentrations were investigated. Substitutional N occurred in tetrahedral and pi bonded sites, which resulted in an increase of the Fermi energy, while N incorporation in strained network sites induced structural changes that lead to an increase in the spsp2 fraction of the material. Molecular dynamics simulations were employed to study defects in GaN, where charge transfer between the ions is included in an approximate fashion. We find good agreement for the band structure of wurtzite and zincblende GaN compared to other recent calculations, suggesting the suitability of our method to describe GaN. A 96 atom GaN supercell is used to study the relaxations and electronic properties of common defects in the crystal structure, including Ga and N vacancies and antisites. The prevalent conduction mechanisms in nitrogen doped tetrahedral amorphous carbon are identified and discussed. These results are compared to the recent experimental reports on N doping of ta-C and we find that the non-doping 3-fold N incorporation (Nsbsp{3}{0}) is energetically most likely, which explains the low doping efficiency seen in experiments. The electronic signatures of intrinsic defects in GaN are analyzed. Also, two 64 atom models of amorphous GaN at

  13. Predicting the optimal dopant concentration in gadolinium doped ceria: a kinetic lattice Monte Carlo approach

    NASA Astrophysics Data System (ADS)

    Dholabhai, Pratik P.; Anwar, Shahriar; Adams, James B.; Crozier, Peter A.; Sharma, Renu

    2012-01-01

    Gadolinium doped ceria (GDC) is a promising alternative electrolyte material for solid oxide fuel cells that offers the possibility of operation in the intermediate temperature range (773-1073 K). To determine the optimal dopant concentration in GDC, we have employed a systematic approach of applying a 3D kinetic lattice Monte Carlo (KLMC) model of vacancy diffusion in conjunction with previously calculated activation energies for vacancy migration in GDC as inputs. KLMC simulations were performed including the vacancy repelling effects in GDC. Increasing the dopant concentration increases the vacancy concentration, which increases the ionic conductivity. However, at higher concentrations, vacancy-vacancy repulsion impedes vacancy diffusion, and together with vacancy trapping by dopants decreases the ionic conductivity. The maximum ionic conductivity is predicted to occur at ≈20% to 25% mole fraction of Gd dopant. Placing Gd dopants in pairs, instead of randomly, was found to decrease the conductivity by ≈50%. Overall, the trends in ionic conductivity results obtained using the KLMC model developed in this work are in reasonable agreement with the available experimental data. This KLMC model can be applied to a variety of ceria-based electrolyte materials for predicting the optimum dopant concentration.

  14. Dopant size effects on novel functionalities: High-temperature interfacial superconductivity.

    PubMed

    Suyolcu, Y Eren; Wang, Yi; Baiutti, Federico; Al-Temimy, Ameer; Gregori, Giuliano; Cristiani, Georg; Sigle, Wilfried; Maier, Joachim; van Aken, Peter A; Logvenov, Gennady

    2017-03-28

    Among the range of complex interactions, especially at the interfaces of epitaxial oxide systems, contributing to the occurrence of intriguing effects, a predominant role is played by the local structural parameters. In this study, oxide molecular beam epitaxy grown lanthanum cuprate-based bilayers (consisting of a metallic (M) and an insulating phase (I)), in which high-temperature superconductivity arises as a consequence of interface effects, are considered. With the aim of assessing the role of the dopant size on local crystal structure and chemistry, and on the interface functionalities, different dopants (Ca(2+), Sr(2+) and, Ba(2+)) are employed in the M-phase, and the M-I bilayers are investigated by complementary techniques, including spherical-aberration-corrected scanning transmission electron microscopy. A series of exciting outcomes are found: (i) the average out-of-plane lattice parameter of the bilayers is linearly dependent on the dopant ion size, (ii) each dopant redistributes at the interface with a characteristic diffusion length, and (iii) the superconductivity properties are highly dependent on the dopant of choice. Hence, this study highlights the profound impact of the dopant size and related interface chemistry on the functionalities of superconducting oxide systems.

  15. Measurement of lateral dopant diffusion in rapid thermal annealed W-polycide gate structures

    SciTech Connect

    Schiml, T.; Bevk, J.; Furtsch, M.; Georgiou, G.E.; Cirelli, R.; Mansfield, W.M.; Silverman, P.J.; Luftman, H.S.

    1996-12-01

    Lateral dopant diffusion is a well known problem in dual-gate W-polycide CMOS devices. The authors have recently demonstrated that RTA processing helps to alleviate this problem and at the same time ensures sufficient dopant activation. However, due to the complex micro-structural changes in both poly-Si and WSi{sub x} (x {approximately} 2.5) layers during the RTA process, the time dependence of the diffusion processes and dopant distribution are difficult to predict. Consequently, the process optimization and device simulations are rather unreliable. They describe a new experimental technique to measure lateral dopant diffusion and 2-dimensional dopant distribution in RTA processed W-polycide structures using conventional SIMS analysis of lithographically defined test structures. The experiments show that the technique is capable of measuring lateral dopant diffusion over distances between one and tens of microns without losing the vertical resolution of conventional SIMS profiling. The technique can be used to study diffusion processes in a variety of materials and multi-layer structures.

  16. Numerical study on the radial dopant distribution in micro-pulling-down crystal growth

    NASA Astrophysics Data System (ADS)

    Zeng, Zhong; Qiao, Long; Liu, Yaping; Yokota, Yuui; Kawazoe, Yoshiyuki; Yoshikawa, Akira

    2016-01-01

    To improve the dopant homogeneity in the radial direction, the micro-pulling-down apparatus was modified for Ce-doped Y3Al5O12 (Ce3+:YAG) crystal growth. Two effective crucible variants, diffusion-channel and multi-channel crucibles, were adopted to alleviate the inhomogeneity of dopant concentration in the radial direction. In the diffusion-channel model, two different inclination angles were investigated. The results demonstrate that the radial dopant distribution at the melt-crystal interface (i.e., the growth front) is improved notably by using the diffusion-channel crucible. Furthermore, the better radial distribution is achieved with the larger inclination angle. In the multi-channel model, more capillary-channels result in a smaller inflow velocity from every single capillary-channel with the same growth rate. Therefore, the effect of inflow on the dopant distribution is reduced, and thus the radial dopant homogeneity is improved apparently. Besides, although the symmetry of concentration distribution along the azimuthal direction is broken in the multi-channel model, the whole homogeneity of dopant at the melt-crystal interface is ameliorated.

  17. Properties of Dopants in HfOx for Improving the Performance of Nonvolatile Memory

    NASA Astrophysics Data System (ADS)

    Duncan, Dan; Magyari-Köpe, Blanka; Nishi, Yoshio

    2017-03-01

    Doping is an increasingly popular technique for improving the characteristics of cutting-edge HfOx nonvolatile memory devices, but relatively few dopant species have been investigated. In this work, the properties of 50 different cation and anion dopants in HfOx are explored using density-functional theory and are corroborated with experimental data. Depending on the atomic species, dopants are found to preferentially form on either substitutional or interstitial lattice sites and to reduce the formation energy of oxygen vacancies in the surrounding oxide. The behavior of cation dopants in HfOx is also found to be well predicted by six properties: dopant valence, atomic radius, native-oxide enthalpy of formation, coordination number, magnetization, and charge transfer with the HfOx lattice. These results can be used to optimize dopant selection for tuning of the switching characteristics of HfOx -based resistance-change random-access-memory and conductive-bridge random-access-memory devices.

  18. Benefitting from Dopant Loss and Ostwald Ripening in Mn Doping of II-VI Semiconductor Nanocrystals.

    PubMed

    Zhai, You; Shim, Moonsub

    2015-12-01

    Annealing or growth at high temperatures for an extended period of time is considered detrimental for most synthetic strategies for high-quality Mn-doped II-VI semiconductor nanocrystals. It can lead to the broadening of size distribution and, more importantly, to the loss of dopants. Here, we examine how ripening can be beneficial to doping in a simple "heat-up" approach, where high dopant concentrations can be achieved. We discuss the interplay of the loss of dopants, Ostwald ripening, and the clustering of Mn near the surface during nanocrystal growth. Smaller nanocrystals in a reaction batch, on average, exhibit higher undesirable band-edge photoluminescence (PL) and lower desirable dopant PL. The optimization of dopant loss and the removal of such smaller undesirable nanocrystals through Ostwald ripening along with surface exchange/passivation to remove Mn clustering lead to high Mn PL quantum yields (45 to 55 %) for ZnSxSe1-x, ZnS, CdS, and CdSxSe1-x host nanocrystals. These results provide an improved understanding of the doping process in a simple and potentially scalable synthetic strategy for achieving "pure" and bright dopant emission.

  19. Benefitting from Dopant Loss and Ostwald Ripening in Mn Doping of II-VI Semiconductor Nanocrystals

    NASA Astrophysics Data System (ADS)

    Zhai, You; Shim, Moonsub

    2015-10-01

    Annealing or growth at high temperatures for an extended period of time is considered detrimental for most synthetic strategies for high-quality Mn-doped II-VI semiconductor nanocrystals. It can lead to the broadening of size distribution and, more importantly, to the loss of dopants. Here, we examine how ripening can be beneficial to doping in a simple "heat-up" approach, where high dopant concentrations can be achieved. We discuss the interplay of the loss of dopants, Ostwald ripening, and the clustering of Mn near the surface during nanocrystal growth. Smaller nanocrystals in a reaction batch, on average, exhibit higher undesirable band-edge photoluminescence (PL) and lower desirable dopant PL. The optimization of dopant loss and the removal of such smaller undesirable nanocrystals through Ostwald ripening along with surface exchange/passivation to remove Mn clustering lead to high Mn PL quantum yields (45 to 55 %) for ZnSxSe1-x, ZnS, CdS, and CdSxSe1-x host nanocrystals. These results provide an improved understanding of the doping process in a simple and potentially scalable synthetic strategy for achieving "pure" and bright dopant emission.

  20. Effect of Al3+ co-doping on the dopant local structure, optical properties, and exciton dynamics in Cu+-doped ZnSe nanocrystals.

    PubMed

    Gul, Sheraz; Cooper, Jason Kyle; Glans, Per-Anders; Guo, Jinghua; Yachandra, Vittal K; Yano, Junko; Zhang, Jin Zhong

    2013-10-22

    The dopant local structure and optical properties of Cu-doped ZnSe (ZnSe:Cu) and Cu and Al co-doped ZnSe (ZnSe:Cu,Al) nanocrystals (NCs) were studied with an emphasis on understanding the impact of introducing Al as a co-dopant. Quantum-confined NCs with zinc blende crystal structure and particle size of 6 ± 0.6 Å were synthesized using a wet chemical route. The local structure of the Cu dopant, studied by extended X-ray absorption fine structure, indicated that Cu in ZnSe:Cu NCs occupies a site that is neither substitutional nor interstitial and is adjacent to a Se vacancy. Additionally, we estimated that approximately 25 ± 8% of Cu was located on the surface of the NC. Al(3+) co-doping aids in Cu doping by accounting for the charge imbalance originated by Cu(+) doping and consequently reduces surface Cu doping. The Cu ions remain distorted from the center of the tetrahedron to one of the triangular faces. The lifetime of the dopant-related photoluminescence was found to increase from 550 ± 60 to 700 ± 60 ns after Al co-doping. DFT calculations were used to obtain the density of states of a model system to help explain the optical properties and dynamics processes observed. This study demonstrates that co-doping using different cations with complementary oxidation states is an effective method to enhance optical properties of doped semiconductor NCs of interest for various photonics applications.

  1. Imaging Dirac-mass disorder from magnetic dopant atoms in the ferromagnetic topological insulator Crx(Bi0.1Sb0.9)2-xTe3

    PubMed Central

    Lee, Inhee; Kim, Chung Koo; Lee, Jinho; Billinge, Simon J. L.; Zhong, Ruidan; Schneeloch, John A.; Liu, Tiansheng; Valla, Tonica; Tranquada, John M.; Gu, Genda; Davis, J. C. Séamus

    2015-01-01

    To achieve and use the most exotic electronic phenomena predicted for the surface states of 3D topological insulators (TIs), it is necessary to open a “Dirac-mass gap” in their spectrum by breaking time-reversal symmetry. Use of magnetic dopant atoms to generate a ferromagnetic state is the most widely applied approach. However, it is unknown how the spatial arrangements of the magnetic dopant atoms influence the Dirac-mass gap at the atomic scale or, conversely, whether the ferromagnetic interactions between dopant atoms are influenced by the topological surface states. Here we image the locations of the magnetic (Cr) dopant atoms in the ferromagnetic TI Cr0.08(Bi0.1Sb0.9)1.92Te3. Simultaneous visualization of the Dirac-mass gap Δ(r) reveals its intense disorder, which we demonstrate is directly related to fluctuations in n(r), the Cr atom areal density in the termination layer. We find the relationship of surface-state Fermi wavevectors to the anisotropic structure of Δ(r) not inconsistent with predictions for surface ferromagnetism mediated by those states. Moreover, despite the intense Dirac-mass disorder, the anticipated relationship Δ(r)∝n(r) is confirmed throughout and exhibits an electron–dopant interaction energy J* = 145 meV·nm2. These observations reveal how magnetic dopant atoms actually generate the TI mass gap locally and that, to achieve the novel physics expected of time-reversal symmetry breaking TI materials, control of the resulting Dirac-mass gap disorder will be essential. PMID:25605947

  2. Imaging Dirac-mass disorder from magnetic dopant atoms in the ferromagnetic topological insulator Crx(Bi0.1Sb0.9)2-xTe3

    DOE PAGES

    Lee, Inhee; Kim, Chung Koo; Lee, Jinho; ...

    2015-01-20

    To achieve and use the most exotic electronic phenomena predicted for the surface states of 3D topological insulators (TIs), it is necessary to open a “Dirac-mass gap” in their spectrum by breaking time-reversal symmetry. Use of magnetic dopant atoms to generate a ferromagnetic state is the most widely applied approach. However, it is unknown how the spatial arrangements of the magnetic dopant atoms influence the Dirac-mass gap at the atomic scale or, conversely, whether the ferromagnetic interactions between dopant atoms are influenced by the topological surface states. Here we image the locations of the magnetic (Cr) dopant atoms in themore » ferromagnetic TI Cr₀.₀₈(Bi₀.₁Sb₀.₉)₁.₉₂Te₃. Simultaneous visualization of the Dirac-mass gap Δ(r) reveals its intense disorder, which we demonstrate is directly related to fluctuations in n(r), the Cr atom areal density in the termination layer. We find the relationship of surface-state Fermi wavevectors to the anisotropic structure of Δ(r) not inconsistent with predictions for surface ferromagnetism mediated by those states. Moreover, despite the intense Dirac-mass disorder, the anticipated relationship Δ(r)∝n(r) is confirmed throughout and exhibits an electron–dopant interaction energy J* = 145 meV·nm². In addition, these observations reveal how magnetic dopant atoms actually generate the TI mass gap locally and that, to achieve the novel physics expected of time-reversal symmetry breaking TI materials, control of the resulting Dirac-mass gap disorder will be essential.« less

  3. Imaging Dirac-mass disorder from magnetic dopant atoms in the ferromagnetic topological insulator Crx(Bi0.1Sb0.9)2-xTe3.

    PubMed

    Lee, Inhee; Kim, Chung Koo; Lee, Jinho; Billinge, Simon J L; Zhong, Ruidan; Schneeloch, John A; Liu, Tiansheng; Valla, Tonica; Tranquada, John M; Gu, Genda; Davis, J C Séamus

    2015-02-03

    To achieve and use the most exotic electronic phenomena predicted for the surface states of 3D topological insulators (TIs), it is necessary to open a "Dirac-mass gap" in their spectrum by breaking time-reversal symmetry. Use of magnetic dopant atoms to generate a ferromagnetic state is the most widely applied approach. However, it is unknown how the spatial arrangements of the magnetic dopant atoms influence the Dirac-mass gap at the atomic scale or, conversely, whether the ferromagnetic interactions between dopant atoms are influenced by the topological surface states. Here we image the locations of the magnetic (Cr) dopant atoms in the ferromagnetic TI Cr0.08(Bi0.1Sb0.9)1.92Te3. Simultaneous visualization of the Dirac-mass gap Δ(r) reveals its intense disorder, which we demonstrate is directly related to fluctuations in n(r), the Cr atom areal density in the termination layer. We find the relationship of surface-state Fermi wavevectors to the anisotropic structure of Δ(r) not inconsistent with predictions for surface ferromagnetism mediated by those states. Moreover, despite the intense Dirac-mass disorder, the anticipated relationship [Formula: see text] is confirmed throughout and exhibits an electron-dopant interaction energy J* = 145 meV·nm(2). These observations reveal how magnetic dopant atoms actually generate the TI mass gap locally and that, to achieve the novel physics expected of time-reversal symmetry breaking TI materials, control of the resulting Dirac-mass gap disorder will be essential.

  4. Dopant-induced stabilization of rhombohedral LiMn O2 against Jahn-Teller distortion

    NASA Astrophysics Data System (ADS)

    Prasad, R.; Benedek, R.; Thackeray, M. M.

    2005-04-01

    Dopants introduced into layered LiMnO2 , a candidate cathode material for lithium batteries, tend to suppress the Jahn-Teller-effect-driven monoclinic distortion (symmetry C2/m ) in favor of the layered rhombohedral structure (R3¯m) , which has superior Li insertion/extraction cycling properties. First-principles calculations, within the Local-Spin-Density-Approximation Generalized-Gradient-Approximation (LSDA-GGA) framework, implemented in the VASP code, are performed for 3d transition-metal, as well as Mg, Zn, Al, and N dopants, in order to assess their relative effectiveness in stabilizing the R3¯m symmetry. At the concentration x=0.25 , the selected cation dopants (with the exception of Co and Fe) are found to adopt the same oxidation state (divalent or trivalent) in both monoclinic and rhombohedral structures. Transition metals earlier than Fe are trivalent, whereas those later than Co are divalent. Co in monoclinic LiMnO2 exhibits (stable) trivalent and (metastable) divalent states that are only narrowly different in energy. Fe is trivalent in the monoclinic structure, but is mixed valent in the rhombohedral structure. Divalent dopants (which oxidize a neighboring Mn to the [non-Jahn-Teller-active] 4+ oxidation state) promote rhombohedral structure stabilization to a greater extent than trivalent dopants. Within the class of divalent dopants, the filled shell systems Mg and Zn are more effective than those with partially filled eg shells. Within the class of trivalent dopants, those with partially filled t2g shells are more effective than those with filled or empty shells. Breathing mode (Q1) and Jahn-Teller active ( Q2 , Q3 ) phonon coordinates of transition metal octahedra are analyzed.

  5. Incorporation of dopant impurities into a silicon oxynitride matrix containing silicon nanocrystals

    SciTech Connect

    Ehrhardt, Fabien; Muller, Dominique; Slaoui, Abdelilah Ferblantier, Gérald; Ulhaq-Bouillet, Corinne

    2016-05-07

    Dopant impurities, such as gallium (Ga), indium (In), and phosphorus (P), were incorporated into silicon-rich silicon oxynitride (SRSON) thin films by the ion implantation technique. To form silicon nanoparticles, the implanted layers were thermally annealed at temperatures up to 1100 °C for 60 min. This thermal treatment generates a phase separation of the silicon nanoparticles from the SRSON matrix in the presence of the dopant atoms. We report on the position of the dopant species within the host matrix and relative to the silicon nanoparticles, as well as on the effect of the dopants on the crystalline structure and the size of the Si nanoparticles. The energy-filtered transmission electron microscopy technique is thoroughly used to identify the chemical species. The distribution of the dopant elements within the SRSON compound is determined using Rutherford backscattering spectroscopy. Energy dispersive X-ray mapping coupled with spectral imaging of silicon plasmons was performed to spatially localize at the nanoscale the dopant impurities and the silicon nanoparticles in the SRSON films. Three different behaviors were observed according to the implanted dopant type (Ga, In, or P). The In-doped SRSON layers clearly showed separated nanoparticles based on indium, InOx, or silicon. In contrast, in the P-doped SRSON layers, Si and P are completely miscible. A high concentration of P atoms was found within the Si nanoparticles. Lastly, in Ga-doped SRSON the Ga atoms formed large nanoparticles close to the SRSON surface, while the Si nanoparticles were localized in the bulk of the SRSON layer. In this work, we shed light on the mechanisms responsible for these three different behaviors.

  6. Titanium dioxide nanotube membranes for solar energy conversion: effect of deep and shallow dopants.

    PubMed

    Ding, Yuchen; Nagpal, Prashant

    2017-04-12

    Nanostructured titanium dioxide (TiO2) has been intensively investigated as a material of choice for solar energy conversion in photocatalytic, photoelectrochemical, photovoltaic, and other photosensitized devices for converting light into chemical feedstocks or electricity. Towards management of light absorption in TiO2, while the nanotubular structure improves light absorption and simultaneous charge transfer to mitigate problems due to the indirect bandgap of the semiconductor, typically dopants are used to improve light absorption of incident solar irradiation in the wide bandgap of TiO2. While these dopants can be critical to the success of these solar energy conversion devices, their effect on photophysical and photoelectrochemical properties and detailed photokinetics are relatively under-studied. Here, we show the effect of deep and shallow metal dopants on the kinetics of photogenerated charged carriers in TiO2 and the resulting effect on photocatalytic and photoelectrochemical processes using these nanotube membranes. We performed a detailed optical, electronic, voltammetry and electrochemical impedance study to understand the effect of shallow and deep metal dopants (using undoped and niobium- and copper-doped TiO2 nanotubes) on light absorption, charge transport and charge transfer processes. Using wireless photocatalytic methylene blue degradation and carbon dioxide reduction, and wired photoelectrochemical device measurements, we elucidate the effect of different dopants on solar-to-fuel conversion efficiency and simultaneously describe the photokinetics using a model, to help design better energy conversion devices.

  7. Non-metallic dopant modulation of conductivity in substoichiometric tantalum pentoxide: A first-principles study

    NASA Astrophysics Data System (ADS)

    Bondi, Robert J.; Fox, Brian P.; Marinella, Matthew J.

    2017-06-01

    We apply density-functional theory calculations to predict dopant modulation of electrical conductivity (σo) for seven dopants (C, Si, Ge, H, F, N, and B) sampled at 18 quantum molecular dynamics configurations of five independent insertion sites into two (high/low) baseline references of σo in amorphous Ta2O5, where each reference contains a single, neutral O vacancy center (VO0). From this statistical population (n = 1260), we analyze defect levels, physical structure, and valence charge distributions to characterize nanoscale modification of the atomistic structure in local dopant neighborhoods. C is the most effective dopant at lowering Ta2Ox σo, while also exhibiting an amphoteric doping behavior by either donating or accepting charge depending on the host oxide matrix. Both B and F robustly increase Ta2Ox σo, although F does so through elimination of Ta high charge outliers, while B insertion conversely creates high charge O outliers through favorable BO3 group formation, especially in the low σo reference. While N applications to dope and passivate oxides are prevalent, we found that N exacerbates the stochasticity of σo we sought to mitigate; sensitivity to the N insertion site and some propensity to form N-O bond chemistries appear responsible. We use direct first-principles predictions of σo to explore feasible Ta2O5 dopants to engineer improved oxides with lower variance and greater repeatability to advance the manufacturability of resistive memory technologies.

  8. A dopant for improved sensitivity in easy ambient sonic-spray ionization mass spectrometry.

    PubMed

    Santos, Jandyson M; Vendramini, Pedro H; Schwab, Nicolas V; Eberlin, Marcos N; de Morais, Damila R

    2016-01-01

    Recently, 3-nitrobenzonitrile (3-NBN) has been used to improve sensitivity of sonic-spray ionization mass spectrometry. Easy ambient sonic-spray ionization (EASI) is one of the simplest, gentlest and most used spray-based desorption/ionization ambient techniques, but limited sensitivity has been commonly taken as its major drawback. Herein we investigate the use of 3-NBN as a dopant in EASI-MS for improved sensitivity. Using a few typical EASI samples as test cases, the presence of 10 ppm (µg ml(-1) ) of 3-NBN in the spray solvent showed two to fourfold gains in EASI-MS sensitivity as measured both by total ion current and S/N ratios, accompanied with significant reductions in chemical noise. Sensitivity for DESI using 3-NBN as a dopant also improved and dopant DESI versus dopant EASI sensitivities were compared. The use of solvent dopants seems therefore to be a promising strategy to improve sensitivity for spray-based ambient MS techniques. Copyright © 2015 John Wiley & Sons, Ltd.

  9. Method for implantation of high dopant concentrations in wide band gap materials

    DOEpatents

    Usov, Igor [Los Alamos, NM; Arendt, Paul N [Los Alamos, NM

    2009-09-15

    A method that combines alternate low/medium ion dose implantation with rapid thermal annealing at relatively low temperatures. At least one dopant is implanted in one of a single crystal and an epitaxial film of the wide band gap compound by a plurality of implantation cycles. The number of implantation cycles is sufficient to implant a predetermined concentration of the dopant in one of the single crystal and the epitaxial film. Each of the implantation cycles includes the steps of: implanting a portion of the predetermined concentration of the one dopant in one of the single crystal and the epitaxial film; annealing one of the single crystal and the epitaxial film and implanted portion at a predetermined temperature for a predetermined time to repair damage to one of the single crystal and the epitaxial film caused by implantation and activates the implanted dopant; and cooling the annealed single crystal and implanted portion to a temperature of less than about 100.degree. C. This combination produces high concentrations of dopants, while minimizing the defect concentration.

  10. Electron-donor dopant, method of improving conductivity of polymers by doping therewith, and a polymer so treated

    DOEpatents

    Liepins, Raimond; Aldissi, Mahmoud

    1988-01-01

    Polymers with conjugated backbones, both polyacetylene and polyaromatic heterocyclic types, are doped with electron-donor agents to increase their electrical conductivity. The electron-donor agents are either electride dopants made in the presence of lithium or dopants derived from alkalides made in the presence of lithium. The dopants also contain a metal such as cesium and a trapping agent such as a crown ether.

  11. Electron-donor dopant, method of improving conductivity of polymers by doping therewith, and a polymer so treated

    DOEpatents

    Liepins, R.; Aldissi, M.

    1984-07-27

    Polymers with conjugated backbones, both polyacetylene and polyaromatic heterocyclic types, are doped with electron-donor agents to increase their electrical conductivity. The electron-donor agents are either electride dopants made in the presence of lithium or dopants derived from alkalides made in the presence of lithium. The dopants also contain a metal such as cesium and a trapping agent such as a crown ether.

  12. Impact of different dopants on the switching properties of ferroelectric hafniumoxide

    NASA Astrophysics Data System (ADS)

    Schroeder, Uwe; Yurchuk, Ekaterina; Müller, Johannes; Martin, Dominik; Schenk, Tony; Polakowski, Patrick; Adelmann, Christoph; Popovici, Mihaela I.; Kalinin, Sergei V.; Mikolajick, Thomas

    2014-08-01

    The wake-up behavior of ferroelectric thin film capacitors based on doped hafnium oxide dielectrics in TiN-based metal-insulator-metal structures is reported. After field cycling a remanent polarization up to 40 µC/cm2 and a high coercive field of about 1 MV/cm was observed. Doping of HfO2 by different dopants with a crystal radius ranging from 54 pm (Si) to 132 pm (Sr) was evaluated. In all cases, an improved polarization-voltage hysteresis after wake-up cycling is visible. For smaller dopant atoms like Si and Al stronger pinching of the polarization hysteresis appeared with increasing dopant concentration and proved to be stable during cycling.

  13. Nanoporous Ge thin film production combining Ge sputtering and dopant implantation.

    PubMed

    Toinin, Jacques Perrin; Portavoce, Alain; Hoummada, Khalid; Texier, Michaël; Bertoglio, Maxime; Bernardini, Sandrine; Abbarchi, Marco; Chow, Lee

    2015-01-01

    In this work a novel process allowing for the production of nanoporous Ge thin films is presented. This process uses the combination of two techniques: Ge sputtering on SiO2 and dopant ion implantation. The process entails four successive steps: (i) Ge sputtering on SiO2, (ii) implantation preannealing, (iii) high-dose dopant implantation, and (iv) implantation postannealing. Scanning electron microscopy and transmission electron microscopy were used to characterize the morphology of the Ge film at different process steps under different postannealing conditions. For the same postannealing conditions, the Ge film topology was shown to be similar for different implantation doses and different dopants. However, the film topology can be controlled by adjusting the postannealing conditions.

  14. Influence of pentavalent dopant addition to polarization and bioactivity of hydroxyapatite.

    PubMed

    Dhal, Jharana; Bose, Susmita; Bandyopadhyay, Amit

    2013-07-01

    Influence of pentavalent tantalum doping in bulk hydroxyapatite (HAp) ceramics has been investigated for polarizability and bioactivity. Phase analysis from X-ray diffraction measurement indicates that increasing dopant concentration decreased the amount of HAp phase and increased β-TCP and/or α-TCP phases during sintering at 1250 °C in a muffle furnace. Results from thermally stimulated depolarization current (TSDC) measurements showed that doping hindered charge storage ability in HAp ceramics, and doped samples stored fewer charge compared to pure HAp. However, doping enhanced wettability of HAp samples, which was improved further due to polarization. In vitro human osteoblast cell-material interaction study revealed an increase in bioactivity due to dopant addition and polarization compared to pure HAp. This increase in bioactivity was attributed to the increase in wettability due to surface charge and dopant addition.

  15. Fine-Tuning the Properties of Doped Multifunctional Materials by Controlled Reduction of Dopants.

    PubMed

    Barroux, Hugo; Jiang, Tengfei; Paul, Camille; Massuyeau, Florian; Génois, Romain; Gordon, Elijah E; Whangbo, Myung-Hwan; Jobic, Stéphane; Gautier, Romain

    2017-03-02

    The physical properties of doped multifunctional compounds are commonly tuned by controlling the amount of dopants, but this control is limited because all the properties are influenced simultaneously by this single parameter. Here, we present a strategy that enables the fine-tuning of a specific combination of properties by controlling the reduction of dopants. The feasibility of this approach was demonstrated by optimizing the near-IR photoluminescence of strontium titanate SrTiO3 :Ni for potential applications in biomedicine for a range of absorbance in the visible/near-IR region. We discussed how material properties, such as luminescence, conductivity, or photocatalytic properties can be designed by carefully controlling the ratio of dopants in different oxidation states.

  16. N-type doping of poly(p-phenylene vinylene) with air-stable dopants

    NASA Astrophysics Data System (ADS)

    Lu, Mingtao; Nicolai, Herman T.; Wetzelaer, Gert-Jan A. H.; Blom, Paul W. M.

    2011-10-01

    The electron transport in poly(p-phenylene vinylene) (PPV) derivatives blended with the air-stable n-type dopant (4-(1,3-dimethyl-2,3-dihydro-1H-benzoimidazol-2-yl)phenyl)dimethylamine (N-DMBI) is investigated. This dopant is activated after thin film deposition by annealing and strongly enhances the electron transport due to filling of electron traps as well as donation of free electrons to the lowest unoccupied molecular orbital (LUMO) of PPV. As a result, the electron current in a doped device exceeds the trap-free hole current. The total generated free electron density in the LUMO by the dopant typically amounts to 1023 m-3.

  17. Light amplification by photorefractive ferroelectric liquid crystal blends containing quarter-thiophene photoconductive chiral dopant

    NASA Astrophysics Data System (ADS)

    Sasaki, T.; Hara, T.; Yamamoto, Y.; Naka, Y.; Le, K. V.

    2017-05-01

    The photorefractive effect is a phenomenon that forms a rewritable hologram in a material. This phenomenon can be utilized in devices including 3D displays, optical tomography, novelty filters, phase conjugate wave generators, and optical amplification. Ferroelectric liquid crystal blends composed of a smectic liquid crystalline mixture, a photoconductive chiral dopant, and an electron trap reagent exhibit significant photorefractivity together with rapid responses. As such, they allow the dynamic amplification of moving optical signals. The photoconductive chiral dopants used in the previous study are ter-thiphene derivatives so that the photorefractive effect was examined at 488 nm. In the present work, chiral dopants possessing quarter-thiphene chromophore were synthesized and the photorefractive effect of the FLC blends at longer wavelength was demonstrated.

  18. Optical, electrical, and photovoltaic properties of PbS thin films by anionic and cationic dopants

    NASA Astrophysics Data System (ADS)

    Cheraghizade, Mohsen; Jamali-Sheini, Farid; Yousefi, Ramin

    2017-06-01

    Lead sulfide (PbS) thin films were deposited by CVD method to examine the effects of anionic and cationic dopants on optical and electrical properties for photovoltaic applications. XRD diffractograms verified the formation of cubic phase of multicrystalline PbS thin films. FESEM images showed surface morphologies in nano-dimensions (rods and flowers). UV-Vis-NIR spectrum revealed absorbance in the visible and NIR regions for all samples, in which dopants decreased the intensity of absorbance. Se as an anionic dopant for PbS thin films increased electrical resistance, acceptor concentrations, and crystallite defects, and decreased flat-band voltage and depletion width. Finally, photovoltaic measurements indicated that Zn-doped PbS thin film, as a photovoltaic cell, exhibited higher conversion efficiency and external quantum efficiency (EQE).

  19. Effect of Cu-Dopant on the Structural, Magnetic and Electrical Properties of ZnO

    NASA Astrophysics Data System (ADS)

    Aryanto, D.; Kurniawan, C.; Subhan, A.; Sudiro, T.; Sebayang, P.; Ginting, M.; Siregar, S. M. K.; Nasruddin, M. N.

    2017-05-01

    Zn1- x Cu x O (x = 0, 2, 3, and 4 at.%) was synthesized by using solid-state reaction technique. The ZnO and CuO powders were mixed and then milled by using high-speed shaker mill. The influence of Cu dopants on the structure, magnetic, and electrical properties was investigated by using XRD, VSM, and I-V and C-V measurements. The XRD analysis showed that the Zn1- x Cu x O had hexagonal wurtzite polycrystalline. The diffraction intensity decreased and the peak position shifted directly to a higher 2θ angle with increasing the dopant concentration. Furthermore, the lattice parameters decreased when the ZnO was doped with x = 0.04, which indicated that the crystal structure changed. The increase of Cu dopants was believed to affect the magnetic and electrical properties of ZnO.

  20. Interdiffusion in the MgO-Al2O3 spinel with or without some dopants

    NASA Astrophysics Data System (ADS)

    Zhang, P.; Debroy, T.; Seetharaman, S.

    1996-08-01

    With a view to seek an improved understanding of the DIMOX process, interdiffusion of polycrystalline MgO and Al2O3 in the temperature range 1473 to 1873 K was studied by diffusion couple experiments. The interdiffusivities in the spinel layer were calculated as functions of composition and temperature. The spinel portion of the phase diagram in the system MgO-Al2O3 was determined from carefully measured compositions at the phase boundaries, and the low temperature spinel region of the phase diagram was confirmed from the present results. For Zn2+ as dopant in alumina, the growth rate of spinel thickness seems to increase when compared with that of the diffusion couples without dopant. The samples containing Si4+ as dopant reveal the formation of a glass phase, and the effect of Si4+ on the diffusion process appears to be negligible.

  1. Study of dopant concentrations on thermally induced mode instability in high-power fiber amplifiers

    NASA Astrophysics Data System (ADS)

    Tao, Rumao; Ma, Pengfei; Wang, Xiaolin; Zhou, Pu; Liu, Zejin

    2016-06-01

    The dependence of mode instabilities (MIs) on ytterbium dopant concentrations in high-power fiber amplifiers has been investigated. It is theoretically shown that, by only varying the fiber length to maintain the same total small-signal pump absorption, the MI threshold is independent of dopant concentration. MI thresholds of gain fibers with ytterbium dopant concentrations of 5.93  ×  1025 m-3 and 1.02  ×  1026 m-3 have been measured which exhibit similar MI thresholds and agree with the theoretical results. The result indicates that heavy doping of active fiber can be adopted to suppress nonlinear effects without decreasing the MI threshold. This provides a method of maximizing the power output of fiber laser, taking into account the stimulated Brillouin scattering, stimulated Raman Scattering, and MI thresholds simultaneously.

  2. Influence of Pentavalent Dopant Addition to Polarization and Bioactivity of Hydroxyapatite

    PubMed Central

    Dhal, Jharana; Bose, Susmita; Bandyopadhyay, Amit

    2013-01-01

    Influence of pentavalent tantalum doping in bulk hydroxyapatite (HAp) ceramics has been investigated for polarizability and bioactivity. Phase analysis from X-ray diffraction measurement indicates that increasing dopant concentration decreased the amount of HAp phase and increased β-TCP and/or α-TCP phases during sintering at 1250 °C in a muffle furnace. Results from thermally stimulated depolarization current (TSDC) measurements showed that doping hindered charge storage ability in HAp ceramics, and doped samples stored fewer charge compared to pure HAp. However, doping enhanced wettability of HAp samples, which was improved further due to polarization. In vitro human osteoblast cell-materials interactions study revealed an increase in bioactivity due to dopant addition and polarization compared to pure HAp. This increase in bioactivity was attributed to the increase in wettability due to surface charge and dopant addition. PMID:23623133

  3. Ion Profiling of Implanted Dopants in Si (001) with Excess Vacancy Concentration

    SciTech Connect

    Dalponte, M.; Boudinov, H.; Goncharova, L. V.; Feng, T.; Garfunkel, E.; Gustafsson, T.

    2007-09-26

    Medium energy ion scattering (MEIS) was used to study the distribution of ion-implanted As and Sb dopants in Si with excess vacancies and SIMOX substrates as well as the effects of thermal treatments. Extra vacancies in Si were generated by N or O pre-implantation at high temperatures. Under these conditions, effects related to the different chemical nature of the pre-implanted species are expected. The annealing behavior and depth distribution of the Sb atoms differed for O compared to N pre-implanted Si. After long annealing times, the oxygen containing samples (SIMOX and O pre-implanted Si) presented higher substitutionality. The nitrogen pre-implanted Si presented the lowest amount of segregated Sb and a more uniform dopant distribution. For both N and O pre-implanted samples a large dopant loss to the atmosphere during annealing was observed.

  4. Nanoporous Ge thin film production combining Ge sputtering and dopant implantation

    PubMed Central

    Portavoce, Alain; Hoummada, Khalid; Texier, Michaël; Bertoglio, Maxime; Bernardini, Sandrine; Abbarchi, Marco; Chow, Lee

    2015-01-01

    Summary In this work a novel process allowing for the production of nanoporous Ge thin films is presented. This process uses the combination of two techniques: Ge sputtering on SiO2 and dopant ion implantation. The process entails four successive steps: (i) Ge sputtering on SiO2, (ii) implantation preannealing, (iii) high-dose dopant implantation, and (iv) implantation postannealing. Scanning electron microscopy and transmission electron microscopy were used to characterize the morphology of the Ge film at different process steps under different postannealing conditions. For the same postannealing conditions, the Ge film topology was shown to be similar for different implantation doses and different dopants. However, the film topology can be controlled by adjusting the postannealing conditions. PMID:25821672

  5. Role of Entropy in the Expulsion of Dopants from Optically Trapped Colloidal Assemblies

    NASA Astrophysics Data System (ADS)

    Kakoty, Hreedish; Banerjee, Rajarshi; Dasgupta, Chandan; Ghosh, Ambarish

    2016-12-01

    Controlling an assembly of colloidal particles under external forces can be helpful in developing soft nanomaterials with novel functionalities. How external impurities organize within such confined systems is of fundamental and technological interest, especially when the system sizes are so small that even a single dopant can interact with an appreciable fraction of the system. To address this question, we use a defocused laser beam to form two-dimensional colloidal crystallites containing foreign dopants. Our studies reveal a surprising position dependence in the fate of dopants getting either spontaneously expelled or permanently internalized within the crystallite. This phenomenon arises due to the subtle interplay between the effects of external confinement and the role of entropy in the thermodynamics of small assemblies of interacting particles.

  6. Spatial luminescence imaging of dopant incorporation in CdTe Films

    DOE PAGES

    Guthrey, Harvey; Moseley, John; Colegrove, Eric; ...

    2017-01-25

    State-of-the-art cathodoluminescence (CL) spectrum imaging with spectrum-per-pixel CL emission mapping is applied to spatially profile how dopant elements are incorporated into Cadmium telluride (CdTe). Emission spectra and intensity monitor the spatial distribution of additional charge carriers through characteristic variations in the CL emission based on computational modeling. Our results show that grain boundaries play a role in incorporating dopants in CdTe exposed to copper, phosphorus, and intrinsic point defects in CdTe. Furthermore, the image analysis provides critical, unique feedback to understand dopant incorporation and activation in the inhomogeneous CdTe material, which has struggled to reach high levels of hole density.

  7. Atomic-scale imaging of dopant atoms and clusters in Yb-doped optical fibers

    NASA Astrophysics Data System (ADS)

    Najafi, H.; Pilz, S.; El Sayed, A.; Boas, J.; Kummer, D.; Romano, V.

    2016-04-01

    Fabrication of Ytterbium-doped active fibers with different designs, compositions and high Yb concentration has attracted an intense interest. For making highly Yb-doped fibers, co-dopants like phosphorous (P) and aluminum (Al) are also employed in order to modify refractive index and increase Yb solubility, avoiding clusters and phase segregations. Indeed, Yb-clustering results in quenching effects and increased propagation losses due to energy transfer between clustered ions. Therefore, the chemical composition and phase homogeneity of the fiber core have key influences on the performance of an active fiber. However, conventional fabrication techniques such as MCVD (modified chemical vapor deposition) and OVD (outside vapor deposition) are approaching the limit. In this contribution, we have developed an approach for fabrication of such active fibres based on granulated silica derived from the sol-gel process. The advantage of this method is the fabrication of active fibers with high dopant contents and homogeneity. Here, using high angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) in atomic scale, we report the direct, nano-scale and atomic-resolution observation of individual Yb dopant and co-dopant (i.e. Al, P) atoms for different fabricated fibers. The chemical mapping from STEM-EDX shows an extremely homogeneous distribution of the dopants and co-dopants in nano-scale for our fabrication protocol. However in atomic resolution, we also identified the possible Yb clusters in the range of 10 atoms within the core structure. The size, structure, and distribution of these clusters are determined with an Yb-atom detection efficiency of almost 100% by STEM.

  8. Recent progress of dopant-free organic hole-transporting materials in perovskite solar cells

    NASA Astrophysics Data System (ADS)

    Dongxue, Liu; Liu, Yongsheng

    2017-01-01

    Organic-inorganic hybrid perovskite solar cells have undergone especially intense research and transformation over the past seven years due to their enormous progress in conversion efficiencies. In this perspective, we review the latest developments of conventional perovskite solar cells with a main focus on dopant-free organic hole transporting materials (HTMs). Regarding the rapid progress of perovskite solar cells, stability of devices using dopant-free HTMs are also discussed to help readers understand the challenges and opportunities in high performance and stable perovskite solar cells. Project supported by the Scientific Research Starting Foundation for Overseas Introduced Talents of College of Chemistry, Nankai University.

  9. Investigation of dopant clustering and segregation to defects in semiconductors using atom probe tomography

    NASA Astrophysics Data System (ADS)

    Blavette, D.; Duguay, S.

    2016-05-01

    The role of atom probe tomography in the investigation of clustering and segregation of dopants to lattice defects in semiconductors is highlighted on the basis of some selected salient illustrations obtained at the Groupe de Physique des Matériaux of Rouen (France). The instrument is shown to be able to map out the 3D distribution of chemical species in the three dimensions of space at the ultimate scale. Results related to clustering, segregation of dopants (As, B, and P) to grain boundaries, dislocation loops, and extended defects in silicon are discussed.

  10. Negative differential resistance induced by SiNx co-dopant in armchair graphene nanoribbon

    NASA Astrophysics Data System (ADS)

    Cheng, Cai-Ping; Hu, Hui-Fang; Zhang, Zhao-Jin; Liu, Quanhui; Chen, Ying; Peng, Ping

    2014-11-01

    By adopting density functional theory in combination with nonequilibrium Green's functions, we investigated the electronic structure and transport properties of silicon/nitrogen (Si/N) co-doping armchair graphene nanoribbons (AGNRs) with SiNx co-dopant incorporated in neighboring carbon atoms. The results demonstrate that the electronic structure can be modulated by introducing SiNx co-dopants in AGNRs. The striking negative differential resistance behaviors in the range of low bias can be observed in Si/N co-doped AGNR devices. These remarkable properties suggest the potential application of Si/N co-doping AGNRs in molectronics.

  11. Toward a predictive atomistic model of ion implantation and dopant diffusion in silicon

    SciTech Connect

    Caturla, M.; Johnson, M.D.; Zhu, J.

    1998-09-18

    We review the development and application of kinetic Monte Carlo simulations to investigate defect and dopant diffusion in ion implanted silicon. In these type of Monte Carlo models, defects and dopants are treated at the atomic scale, and move according to reaction rates given as input principles. These input parameters can be obtained from first principles calculations and/or empirical molecular dynamics simulations, or can be extracted from fits to experimental data. Time and length scales differing several orders of magnitude can be followed with this method, allowing for direct comparison with experiments. The different approaches are explained and some results presented.

  12. Investigation of dopant clustering and segregation to defects in semiconductors using atom probe tomography

    SciTech Connect

    Blavette, D. Duguay, S.

    2016-05-14

    The role of atom probe tomography in the investigation of clustering and segregation of dopants to lattice defects in semiconductors is highlighted on the basis of some selected salient illustrations obtained at the Groupe de Physique des Matériaux of Rouen (France). The instrument is shown to be able to map out the 3D distribution of chemical species in the three dimensions of space at the ultimate scale. Results related to clustering, segregation of dopants (As, B, and P) to grain boundaries, dislocation loops, and extended defects in silicon are discussed.

  13. Addition of photosensitive dopants to the D0 liquid argon calorimeter

    SciTech Connect

    Amos, N.A.; Anderson, D.F.

    1992-10-01

    The addition of photosensitive dopants to liquid argon greatly enhances the signal from heavily ionizing particles. Since binding energy losses we correlated with the heavily ionizing component in hadronic showers, the addition of photosensitive dopants has been suggested as a mechanism to tune the e/[pi] ratio in liquid argon calorimeters. A measurement was performed at the FNAL test beam, adding 4 ppM tetramethylgermanium to the D[phi] uranium-liquid argon calorimeter. An increase in response for electromagnetic and hadronic showers was observed, with no net change in the e/[pi] ratio.

  14. Addition of photosensitive dopants to the D0 liquid argon calorimeter

    SciTech Connect

    Amos, N.A.; Anderson, D.F.; The D0 Collaboration

    1992-10-01

    The addition of photosensitive dopants to liquid argon greatly enhances the signal from heavily ionizing particles. Since binding energy losses we correlated with the heavily ionizing component in hadronic showers, the addition of photosensitive dopants has been suggested as a mechanism to tune the e/{pi} ratio in liquid argon calorimeters. A measurement was performed at the FNAL test beam, adding 4 ppM tetramethylgermanium to the D{phi} uranium-liquid argon calorimeter. An increase in response for electromagnetic and hadronic showers was observed, with no net change in the e/{pi} ratio.

  15. Diameter-dependent wetting of tungsten disulfide nanotubes.

    PubMed

    Goldbart, Ohad; Cohen, Sidney R; Kaplan-Ashiri, Ifat; Glazyrina, Polina; Wagner, H Daniel; Enyashin, Andrey; Tenne, Reshef

    2016-11-29

    The simple process of a liquid wetting a solid surface is controlled by a plethora of factors-surface texture, liquid droplet size and shape, energetics of both liquid and solid surfaces, as well as their interface. Studying these events at the nanoscale provides insights into the molecular basis of wetting. Nanotube wetting studies are particularly challenging due to their unique shape and small size. Nonetheless, the success of nanotubes, particularly inorganic ones, as fillers in composite materials makes it essential to understand how common liquids wet them. Here, we present a comprehensive wetting study of individual tungsten disulfide nanotubes by water. We reveal the nature of interaction at the inert outer wall and show that remarkably high wetting forces are attained on small, open-ended nanotubes due to capillary aspiration into the hollow core. This study provides a theoretical and experimental paradigm for this intricate problem.

  16. Nanofiber diameter-dependent MAPK activity in osteoblasts.

    PubMed

    Jaiswal, Devina; Brown, Justin L

    2012-11-01

    The major challenge for bone tissue engineering lies in the fabrication of scaffolds that can mimic the extracellular matrix and promote osteogenesis. Electrospun fibers are being widely researched for this application due to high porosity, interconnectivity, and mechanical strength of the fibrous scaffolds. Electrospun poly methyl methacrylate (PMMA, 2.416 ± 0.100 μm) fibers were fabricated and etched using a 60% propylene glycol methyl ether acetate (PGMEA)/limonene (vol/vol) solution to obtain fiber diameters ranging from 2.5 to 0.5 μm in a time-dependent manner. The morphology of the fibrous scaffolds was evaluated using scanning electron microscopy and cellular compatibility with etchant-treated scaffold was assessed using immunoflurescence. Mitogen-activated protein kinases (MAPK) activation in response to different fiber diameter was evaluated with western blot as well as quantitative in-cell western. We report that electrospun micro-fibers can be etched to 0.552 ± 0.047 μm diameter without producing beads. Osteoblasts adhered to the fibers and a change in fiber diameter played a major role in modulating the activation of extracellular signal-regulated kinase (ERK) and p38 kinases with 0.882 ± 0.091 μm diameter fibers producing an inverse effect on ERK and p38 phosphorylation. These results indicate that nanofibers produced by wet etching can be effectively utilized to produce diameters that can differentially modulate MAPK activation patterns. Copyright © 2012 Wiley Periodicals, Inc.

  17. Diameter-dependent wetting of tungsten disulfide nanotubes

    PubMed Central

    Goldbart, Ohad; Cohen, Sidney R.; Kaplan-Ashiri, Ifat; Glazyrina, Polina; Wagner, H. Daniel; Enyashin, Andrey; Tenne, Reshef

    2016-01-01

    The simple process of a liquid wetting a solid surface is controlled by a plethora of factors—surface texture, liquid droplet size and shape, energetics of both liquid and solid surfaces, as well as their interface. Studying these events at the nanoscale provides insights into the molecular basis of wetting. Nanotube wetting studies are particularly challenging due to their unique shape and small size. Nonetheless, the success of nanotubes, particularly inorganic ones, as fillers in composite materials makes it essential to understand how common liquids wet them. Here, we present a comprehensive wetting study of individual tungsten disulfide nanotubes by water. We reveal the nature of interaction at the inert outer wall and show that remarkably high wetting forces are attained on small, open-ended nanotubes due to capillary aspiration into the hollow core. This study provides a theoretical and experimental paradigm for this intricate problem. PMID:27856759

  18. Diameter Dependence of Planar Defects in InP Nanowires

    NASA Astrophysics Data System (ADS)

    Wang, Fengyun; Wang, Chao; Wang, Yiqian; Zhang, Minghuan; Han, Zhenlian; Yip, Senpo; Shen, Lifan; Han, Ning; Pun, Edwin Y. B.; Ho, Johnny C.

    2016-09-01

    In this work, extensive characterization and complementary theoretical analysis have been carried out on Au-catalyzed InP nanowires in order to understand the planar defect formation as a function of nanowire diameter. From the detailed transmission electron microscopic measurements, the density of stacking faults and twin defects are found to monotonically decrease as the nanowire diameter is decreased to 10 nm, and the chemical analysis clearly indicates the drastic impact of In catalytic supersaturation in Au nanoparticles on the minimized planar defect formation in miniaturized nanowires. Specifically, during the chemical vapor deposition of InP nanowires, a significant amount of planar defects is created when the catalyst seed sizes are increased with the lower degree of In supersaturation as dictated by the Gibbs-Thomson effect, and an insufficient In diffusion (or Au-rich enhancement) would lead to a reduced and non-uniform In precipitation at the NW growing interface. The results presented here provide an insight into the fabrication of “bottom-up” InP NWs with minimized defect concentration which are suitable for various device applications.

  19. Diameter Dependence of Planar Defects in InP Nanowires

    PubMed Central

    Wang, Fengyun; Wang, Chao; Wang, Yiqian; Zhang, Minghuan; Han, Zhenlian; Yip, SenPo; Shen, Lifan; Han, Ning; Pun, Edwin Y. B.; Ho, Johnny C.

    2016-01-01

    In this work, extensive characterization and complementary theoretical analysis have been carried out on Au-catalyzed InP nanowires in order to understand the planar defect formation as a function of nanowire diameter. From the detailed transmission electron microscopic measurements, the density of stacking faults and twin defects are found to monotonically decrease as the nanowire diameter is decreased to 10 nm, and the chemical analysis clearly indicates the drastic impact of In catalytic supersaturation in Au nanoparticles on the minimized planar defect formation in miniaturized nanowires. Specifically, during the chemical vapor deposition of InP nanowires, a significant amount of planar defects is created when the catalyst seed sizes are increased with the lower degree of In supersaturation as dictated by the Gibbs-Thomson effect, and an insufficient In diffusion (or Au-rich enhancement) would lead to a reduced and non-uniform In precipitation at the NW growing interface. The results presented here provide an insight into the fabrication of “bottom-up” InP NWs with minimized defect concentration which are suitable for various device applications. PMID:27616584

  20. The ionization mechanisms in direct and dopant-assisted atmospheric pressure photoionization and atmospheric pressure laser ionization.

    PubMed

    Kauppila, Tiina J; Kersten, Hendrik; Benter, Thorsten

    2014-11-01

    A novel, gas-tight API interface for gas chromatography-mass spectrometry was used to study the ionization mechanism in direct and dopant-assisted atmospheric pressure photoionization (APPI) and atmospheric pressure laser ionization (APLI). Eight analytes (ethylbenzene, bromobenzene, naphthalene, anthracene, benzaldehyde, pyridine, quinolone, and acridine) with varying ionization energies (IEs) and proton affinities (PAs), and four common APPI dopants (toluene, acetone, anisole, and chlorobenzene) were chosen. All the studied compounds were ionized by direct APPI, forming mainly molecular ions. Addition of dopants suppressed the signal of the analytes with IEs above the IE of the dopant. For compounds with suitable IEs or Pas, the dopants increased the ionization efficiency as the analytes could be ionized through dopant-mediated gas-phase reactions, such as charge exchange, proton transfer, and other rather unexpected reactions, such as formation of [M + 77](+) in the presence of chlorobenzene. Experiments with deuterated toluene as the dopant verified that in case of proton transfer, the proton originated from the dopant instead of proton-bound solvent clusters, as in conventional open or non-tight APPI sources. In direct APLI using a 266 nm laser, a narrower range of compounds was ionized than in direct APPI, because of exceedingly high IEs or unfavorable two-photon absorption cross-sections. Introduction of dopants in the APLI system changed the ionization mechanism to similar dopant-mediated gas-phase reactions with the dopant as in APPI, which produced mainly ions of the same form as in APPI, and ionized a wider range of analytes than direct APLI.

  1. Quantitative Measurements of the Temperature-Dependent Microscopic and Macroscopic Dynamics of a Molecular Dopant in a Conjugated Polymer

    DOE PAGES

    Li, Jun; Koshnick, Correy; Diallo, Souleymane O.; ...

    2017-07-14

    Understanding the nature of dopant dynamics in the solid state is critical for improving the longevity and stability of organic electronic devices and for optimizing the doping-induced solubility control (DISC) patterning method. In this work, we use quasi-elastic neutron scattering (QENS) and fluorescence quenching techniques to develop a comprehensive picture of both the microscopic and macroscopic dynamics of the soluble p-type molecular dopant tetrafluoromethyloxycarbonyltricyanoquinodimethane (F4MCTCNQ) in the conductive polymer poly(3-hexylthiophene-2,5-diyl) (P3HT). Specifically, fast dynamics (ps–ns) of the dopant, such as the methyl and the methoxycarbonyl group rotations, are observed in QENS experiments. From confocal fluorescence microscope experiments, longer-range/slower dopant diffusionmore » (ms–days) is captured. However, in order to fit these data, it is necessary to incorporate a Langmuir isotherm equilibrium between the neutral and ionized dopant molecules. Ionized F4MCTCNQ is strongly favored by the equilibrium, but it diffuses 3 orders of magnitude slower than neutral species. Moreover, the macroscopic diffusion is found to depend mostly on the minority concentration of neutral dopant molecules in the film. Lastly, the global diffusion coefficient of the monoester-substituted dopant F4MCTCNQ is shown to be more than an order of magnitude smaller than that of the widely used dopant F4TCNQ.« less

  2. The Influence of Dopants on the Effectiveness of Alginate Beads in Immobilized Cell Reactors.

    PubMed

    Nordmeier, Akira; Chidambaram, Dev

    2016-04-01

    Zymomonas mobilis immobilized in doped calcium alginate (Ca-alginate) was successfully employed for the production of ethanol in an immobilized cell reactor. Polyethylene oxide and F127 dimethacrylate were evaluated as potential dopants for Ca-alginate beads to decrease lag time and increase initial ethanol yield. The influence of the type and concentration of the dopant on the effectiveness of the microbe immobilized in Ca-alginate beads to produce ethanol was studied, and results were compared to the widely used 2 % Ca-alginate with no dopants, which acted as control. Immobilized cell reactors that were operated using beads doped with 0.25 % polyethylene oxide (PEO) reached an ethanol yield of ∼70 % in 24 h, which was significantly higher than an ethanol yield of 25 % obtained for the control reactor operated using undoped Ca-alginate beads. This study shows that the use of water-soluble dopants can potentially reduce the lag phase and thus improve the initial production yield of immobilized cell reactors, likely due to an increase in porosity and diffusion rate of the doped beads.

  3. Detecting excitation and magnetization of individual dopants in a semiconductor two-dimensional electron gas

    NASA Astrophysics Data System (ADS)

    Wiebe, Jens

    2011-03-01

    Magnetic atoms doped into a semiconductor are the building blocks for bottom up spintronic and quantum logic devices. They also provide model systems for the investigation of fundamental effects. In order to correlate the dopant's atomic structure with its magnetism magnetically sensitive techniques with atomic resolution are a prerequisite. Here, I show electrical excitation and read-out [ 1 ] of single magnetic dopant associated spins in a two-dimensional electron gas (2DEG) confined to a semiconductor surface [ 2 ] using spin-resolved scanning tunneling spectroscopy [ 3 ] . I will review our real-space study of the quantum Hall transition in the 2DEG [ 2 ] and of the magnetic properties of the dopants [ 1 ] . Finally, I will demonstrate that the dopant serves as an atomic scale probe for local magnetometry of the 2DEG. This work was done in collaboration with A. A. Khajetoorians, B. Chillian, S. Schuwalow, F. Lechermann, K. Hashimoto, C. Sohrmann, T. Inaoka, F. Meier, Y. Hirayama, R. A. Römer, M. Morgenstern, and R. Wiesendanger. [ 1 ] A. A. Khajetoorians et al., Nature 467, 1084 (2010). [ 2 ] K. Hashimoto et al., Phys. Rev. Lett. 101, 256802 (2008). [ 3 ] J. Wiebe et al., Rev. Sci. Instrum. 75, 4871 (2004). We acknowledge financial support from ERC Advanced Grant ``FURORE'', by the DFG via SFB668 and GrK1286, and by the city of Hamburg via the cluster of excellence ``Nanospintronics''.

  4. Effect of bromine-dopant on radiation-driven Rayleigh-Taylor instability in plastic foil

    NASA Astrophysics Data System (ADS)

    Xu, Binbin; Ma, Yanyun; Yang, Xiaohu; Tang, Wenhui; Ge, Zheyi; Zhao, Yuan; Ke, Yanzhao; Kawata, Shiego

    2017-10-01

    Effects of bromine (Br) dopant on the growth of radiation-driven ablative Rayleigh-Taylor instability (RTI) in plastic foils are studied by radiation hydrodynamics simulations and theoretical analysis. It is found that the Br-dopant in plastic foil reduces the seed of ablative RTI. The main reasons of the reduction are attributed to the smaller oscillation amplitude of ablative Richtmyer-Meshkov instability (RMI) induced by the smaller post-shock sound speed, and the smaller oscillation frequency of ablative RMI induced by the smaller ablation velocity and blow-off plasma velocity. The Br-dopant also decreases the linear growth rate of ablative RTI due to the smaller acceleration. Treating the perturbation growth as a function of foil’s displacement, the perturbation growth would increase in Br-doped foil at the phase of ablative RTI, which is attributed to the decrease of the ablation velocity and the density gradient scale length. The results are helpful for further understanding the influence of high-Z dopant on the radiation-driven ablative RTI.

  5. Theory and simulation of dopant implantation and diffusion in SiGe

    NASA Astrophysics Data System (ADS)

    Liu, Chun-Li; Orlowski, Marius; Thean, Aaron; Beardmore, Keith; Barr, Alex; White, Ted; Nguyen, Bich-Yen; Rueda, Hernan; Liu, Xiang-Yang

    2003-09-01

    Strained Si-based technology has imposed a new challenge for understanding dopant implantation and diffusion in SiGe that is often used as the buffer layer for a strained Si cap layer. In this work, we describe our latest modeling effort investigating the difference in dopant implantation and diffusion between Si and SiGe. A lattice expansion theory was developed to account for the volume change due to Ge in Si and its effect on defect formation enthalpy. The theory predicts that As diffusion in SiGe is enhanced by a factor of 10, P diffusion by a factor of 2, and B diffusion is retarded by a factor of 6, when compared to bulk Si. These predictions are consistent with experiment. Dopant profiles for As, P, and B were simulatedusing process simulators FLOOPS and DIOS. The simulated profiles are in good agreement with experiment. Dopant implantation was simulated using REED-MD. The results showed a noticeable difference in peak and tail positions SiGe compared to Si. (

  6. Tunneling in Systems of Coupled Dopant-Atoms in Silicon Nano-devices

    NASA Astrophysics Data System (ADS)

    Moraru, Daniel; Samanta, Arup; Tyszka, Krzysztof; Anh, Le The; Muruganathan, Manoharan; Mizuno, Takeshi; Jablonski, Ryszard; Mizuta, Hiroshi; Tabe, Michiharu

    2015-09-01

    Following the rapid development of the electronics industry and technology, it is expected that future electronic devices will operate based on functional units at the level of electrically active molecules or even atoms. One pathway to observe and characterize such fundamental operation is to focus on identifying isolated or coupled dopants in nanoscale silicon transistors, the building blocks of present electronics. Here, we review some of the recent progress in the research along this direction, with a focus on devices fabricated with simple and CMOS-compatible-processing technology. We present results from a scanning probe method (Kelvin probe force microscopy) which show direct observation of dopant-induced potential modulations. We also discuss tunneling transport behavior based on the analysis of low-temperature I- V characteristics for devices representative for different regimes of doping concentration, i.e., different inter-dopant coupling strengths. This overview outlines the present status of the field, opening also directions toward practical implementation of dopant-atom devices.

  7. In situ control of polymer helicity with a non-covalently bound photoresponsive molecular motor dopant.

    PubMed

    van Leeuwen, Thomas; Heideman, G Henrieke; Zhao, Depeng; Wezenberg, Sander J; Feringa, Ben L

    2017-06-13

    The transfer of chirality from a molecular motor to a dynamic helical polymer via ionic interactions was investigated. A dopant with photoswitchable chirality was able to induce a preferred helicity in a poly(phenylacetylene) polymer and the helicity is inverted upon irradiation. The findings described herein will advance the development of functional and responsive polymeric systems.

  8. A fixed-grid method for transient simulations of dopant segregation in VGF-RMF growth

    NASA Astrophysics Data System (ADS)

    Nikrityuk, Petr A.; Pätzold, Olf; Stelter, Michael

    2012-01-01

    In this work a fixed-grid, virtual-front tracking model originally developed for modeling dendritic growth has been adopted for transient simulations of dopant segregation in vertical gradient freeze (VGF) melt growth of Ga-doped germanium under the influence of a rotating magnetic field (RMF). The interfacial Stefan conditions for temperature and solute are formulated in volumetric terms in energy and solute conservation equations, which allow the interface to be tracked implicitly with no need to calculate the growth velocity. The model and the code are validated against an analytical solution for the transient solidification of a binary alloy at constant velocity. The numerical results show the strong relationship between the melt flow pattern and the dopant concentration in the crystal grown. The better melt mixing during growth under the influence of RMF is found to have a significant impact on the axial and radial macrosegregation of dopants. Simulation results are in good qualitative agreement with previous experimental observations of the dopant segregation in VGF-RMF growth, which now are seen ass a direct consequence of the mixing state of the melt.

  9. Dopant-vacancy binding effects in Li-doped magnesium hydride

    NASA Astrophysics Data System (ADS)

    Smith, Kyle C.; Fisher, Timothy S.; Waghmare, Umesh V.; Grau-Crespo, Ricardo

    2010-10-01

    We use a combination of ab initio calculations and statistical mechanics to investigate the substitution of Li+ for Mg2+ in magnesium hydride (MgH2) accompanied by the formation of hydrogen vacancies with positive charge (with respect to the original ion at the site). We show that the binding energy between dopants and vacancy defects leads to a significant fraction of trapped vacancies and therefore a dramatic reduction in the number of free vacancies available for diffusion. The concentration of free vacancies initially increases with dopant concentration but reaches a maximum at around 1mol% Li doping and slowly decreases with further doping. At the optimal level of doping, the corresponding concentration of free vacancies is much higher than the equilibrium concentrations of charged and neutral vacancies in pure MgH2 at typical hydrogen storage conditions. We also show that Li-doped MgH2 is thermodynamically metastable with respect to phase separation into pure magnesium and lithium hydrides at any significant Li concentration, even after considering the stabilization provided by dopant-vacancy interactions and configurational entropic effects. Our results suggest that lithium doping may enhance hydrogen diffusion hydride but only to a limited extent determined by an optimal dopant concentration and conditioned to the stability of the doped phase.

  10. Effect of rare-earth-dopants on Bragg gratings recording in PTR glasses

    NASA Astrophysics Data System (ADS)

    Nikonorov, N. V.; Ivanov, S. A.; Kozlova, D. A.; Pichugin, I. S.

    2017-05-01

    In present paper, we represent a study on the effect of RE dopants (lanthanum, erbium, ytterbium, and neodymium) on the process of the photo-thermo-induced (PTI) crystallization. During this work, we investigated each step of the PTI crystallization process including silver particle formation, growth of shell and nanocrystal. To perform these observations, we reduced the temperature of thermal treatment below the glass transition temperature to slow down all processes inside the glass. We found out that the silver nanoparticles formation process does not depend from the concentration of RE ions and is the same as in case of the parent PTR glass. In other hand the growth kinetics of AgBr-NaBr shell and NaF nanocrystals differ from the parent glass and depend on RE concentration. Our observations show no difference in final position of plasmon resonance, which means that the PTI crystallization process itself stays the same and is not affected by the RE dopants. Further study shows that utmost achievable refractive index change falls off with rare earth dopant concentration increase mainly due to the bond formed between dopant and fluorine. This bond prevents fluorine from participation in crystallization process thus overall volume fraction of the crystalline phase decreases. This effect can be corrected by addition of fluorine in the chemical composition of the glass at the synthesis. In conclusion, we show that refractive index change in doped glass with appropriate concentration of additional fluorine is same as in the parent glass (1500 ppm).

  11. Sugar Amphiphiles as Revealing Dopants for Induced Chiral Nematic Lyotropic Liquid Crystals.

    PubMed

    von Minden, Hans Markus; Vill, Volkmar; Pape, Martin; Hiltrop, Karl

    2001-04-01

    The existence of phase chirality in lyotropic liquid crystals still raises questions. The mechanisms behind the transfer of chirality throughout the long-range orientational order are not yet obvious. Guest/host systems with chiral dopants in achiral host phases offer the capability of systematic investigations. We demonstrate that the large amount of accessible sugar amphiphiles exhibits remarkable structure/property relations. Their helical twisting power HTP increases strongly with the number of sugar units of a dopant molecule. The spatial range of the chirality information reaching from a chirally doped micelle to adjacent aggregates is essential for the development of phase chirality. The induced twist of the lyotropic nematic host phase is highly sensitive to small changes of the sugar type (e.g., galacto- to glucopyranose). Depending on the nature of the host phase, either the alpha- or the beta-linkage of the sugar to the hydrophobic moiety of the sugar dopant results in larger HTP values. We propose that our amphiphilic sugar derivatives act like antennae to transfer chirality information. Their effectiveness as chiral dopants is due to a hydrophobic anchoring within the micelles and an extension of their chiral moiety far into the intermicellar region. The chirality transfer works especially well if the hydrophilic and chiral sugar moieties are oriented toward a neighboring micelle in the direction of the helix axis. Copyright 2001 Academic Press.

  12. Influence of Dopant Distribution on the Plasmonic Properties of Indium Tin Oxide Nanocrystals

    SciTech Connect

    Lounis, SD; Runnerstrom, EL; Bergerud, A; Nordlund, D; Milliron, DJ

    2014-05-14

    Doped metal oxide nanocrystals represent an exciting frontier for colloidal synthesis of plasmonic materials, displaying unique optoelectronic properties and showing promise for a variety of applications. However, fundamental questions about the nature of doping in these materials remain. In this article, the strong influence of radial dopant distribution on the optoelectronic properties of colloidal indium tin oxide nanocrystals is reported. Comparing elemental depth-profiling by X-ray photoelectron spectroscopy (XPS) with detailed modeling and simulation of the optical extinction of these nanocrystals using the Drude model for free electrons, a correlation between surface segregation of tin ions and the average activation of dopants is observed. A strong influence of surface segregation of tin on the line shape of the localized surface plasmon resonance (LSPR) is also reported. Samples with tin segregated near the surface show a symmetric line shape that suggests weak or no damping of the plasmon by ionized impurities. It is suggested that segregation of tin near the surface facilitates compensation of the dopant ions by electronic defects and oxygen interstitials, thus reducing activation. A core shell model is proposed to explain the observed differences in line shape. These results demonstrate the nuanced role of dopant distribution in determining the optoelectronic properties of semiconductor nanocrystals and suggest that more detailed study of the distribution and structure of defects in plasmonic colloidal nanocrystals is warranted.

  13. Self- and dopant diffusion in extrinsic boron doped isotopically controlled silicon multilayer structures

    SciTech Connect

    Sharp, Ian D.; Bracht, Hartmut A.; Silvestri, Hughes H.; Nicols, Samuel P.; Beeman, Jeffrey W.; Hansen, John L.; Nylandsted Larsen, Arne; Haller, Eugene E.

    2002-04-01

    Isotopically controlled silicon multilayer structures were used to measure the enhancement of self- and dopant diffusion in extrinsic boron doped silicon. {sup 30}Si was used as a tracer through a multilayer structure of alternating natural Si and enriched {sup 28}Si layers. Low energy, high resolution secondary ion mass spectrometry (SIMS) allowed for simultaneous measurement of self- and dopant diffusion profiles of samples annealed at temperatures between 850 C and 1100 C. A specially designed ion- implanted amorphous Si surface layer was used as a dopant source to suppress excess defects in the multilayer structure, thereby eliminating transient enhanced diffusion (TED) behavior. Self- and dopant diffusion coefficients, diffusion mechanisms, and native defect charge states were determined from computer-aided modeling, based on differential equations describing the diffusion processes. We present a quantitative description of B diffusion enhanced self-diffusion in silicon and conclude that the diffusion of both B and Si is mainly mediated by neutral and singly positively charged self-interstitials under p-type doping. No significant contribution of vacancies to either B or Si diffusion is observed.

  14. Two-dimensional dopant analysis in silicon using chemical etching and transmission electron microscopy

    NASA Astrophysics Data System (ADS)

    Neogi, Suneeta Shamanna

    The purpose of this research has been to develop a methodologoy to map two-dimensional dopant distributions in silicon and investigate the factors that influence the interpretation of the results. The analysis exploits the image contrast obtained by transmission electron microscopy (TEM) using cross-section specimens which have undergone selective chemical etching. The appearance of iso-thickness contours in a selectively etched TEM sample must represent iso-concentration contours when imaged under constant diffraction conditions. The application of this technique is two-fold: (1) to establish a physical metrology of semiconductor devices for the purpose of research and development efforts that impact on future nodes outlined in the semiconductor roadmap and (2) to provide physical data for validation of simulation tools in technology computer aided design (TCAD). The research involves an investigation into the selective removal of doped regions for both test and device structures, followed by an analysis to obtain two-dimensional (2-D) dopant profiles. The critical issues which arise in the development of a methodology to profile dopant distributions and which are addressed in this investigation are, wedge technique versus conventional dimple and ion-mill procedures for thin-film preparation, thin-film versus bulk chemical etching, data acquisition using TEM and choice of diffraction conditions, sensitivity in terms of the etch detection limit, resolution influenced by the effective extinction length of the operating reflection, digital image processing to extract profiles from thickness contours, calibration of the 2-D profiles using a one-dimensional (1-D) calibrator and role of structure/dopant interactions such as stress, interfaces and point defects in test structures and real device structures containing additional processing sequences. Selective chemical etching in combination with TEM has the sensitivity, resolution and reproducibility required to be used

  15. 1,8-Naphthalimides in phosphorescent organic LEDs: the interplay between dopant, exciplex, and host emission.

    PubMed

    Kolosov, Dmitry; Adamovich, Vadim; Djurovich, Peter; Thompson, Mark E; Adachi, Chihaya

    2002-08-21

    Four different 1,8-naphthalimide derivatives were examined in phosphorescent organic light emitting diodes (OLEDs), i.e., 1,8-naphthalimide, N-phenyl-1,8-naphthalimide, N-2,6-dibromophenyl-1,8-naphthalimide (niBr), and bis-N,N-1,8-naphthalimide. Photoluminescence from all four naphthalimides have violet-blue fluorescence and phosphorescent bands between 550 and 650 nm (visible at 77 K). While all four compounds gave good glassy films when doped with a phosphorescent dopant, only the niBr films remained glassy for extended periods. OLED studies focused on niBr, with two different architectures. One OLED structure (type 1) had the niBr layer as a doped luminescent layer and an undoped niBr layer to act as a hole-blocking layer. The alternate structure (type 2) utilizes a doped CBP layer as the luminescent layer and the niBr layer is used as a hole-blocking layer only (CBP = 4,4'-N,N'-dicarbazolylbiphenyl). Type 1 and 2 OLEDs were prepared with green, yellow, and red emissive phosphorescent dopants (Irppy, btIr, and btpIr, respectively). The dopants were organometallic Ir complexes, previously shown to give highly efficient OLEDs. Of the three dopants, the btpIr-based OLEDs showed the best device performance in both structures (peak efficiencies for type 2: 3.2% and 2.3 lum/W at 6.3 V; type 1: 1.7% and 1.3 lm/W at 6.1 V). The green and yellow dopants gave very similar performance in both type 1 and 2 devices (peak efficiencies are 0.2-0.3%), which were significantly poorer than the btpIr-based OLEDs. The emission spectrum of the btIr- and btpIr-based devices (type 1 and 2) are the same as the solution photoluminescence spectrum of the dopant alone, while the Irppy device gives a broad red emission line (lambda(max) = 640 nm). The red Irppy.niBr emission line is assigned to an Irppy.niBr exciplex. The type 2 Irppy-based device gave a voltage-dependent spectrum, with the red emission observed at low bias (4-8 V), switching over to strong green emission as the bias was

  16. Photoswitching of ferroelectric liquid crystals using chiral thioindigo dopants: The development of a photochemical switch hitter.

    PubMed

    Lemieux, Robert P

    2004-01-01

    By virtue of its spontaneous polarization (PS), a ferroelectric SmC* liquid crystal can be switched between two states corresponding to opposite molecular tilt orientations using an electric field, thus producing an ON-OFF light shutter between crossed polarizers. Considerable efforts have been made over the past decade to develop photonic FLC light shutters because of their potential uses in dynamic holography and optical data storage. The ON-OFF switching of a FLC light shutter can be triggered by light via a photoinversion of PS using a photochromic dopant. The spontaneous polarization is a chiral bulk property that can be left-handed (negative) or right-handed (positive), depending on the absolute configuration of the chiral component of the SmC* phase. In the approach described herein, the magnitude of PS is modulated via the photoisomerization of a chiral thioindigo dopant that undergoes a large increase in transverse dipole moment upon trans-cis photoisomerization. The sign of PS is photoinverted using an "ambidextrous" thioindigo dopant containing a chiral 2-octyloxy side chain that is coupled to the thioindigo core and induces a positive PS, and a chiral 2,3-difluorooctyloxy side chain that is decoupled from the core and induces a negative PS. In the trans form, the 2,3-difluorooctyloxy side chain predominates and the net PS induced by the dopant is negative. However, upon trans-cis-photoisomerization, the increase in transverse dipole moment of the 2-octyloxy/thioindigo unit raises its induced PS over that of the decoupled 2,3-difluorooctyloxy side chain, and thus inverts the net sign of PS induced by the dopant from negative to positive.

  17. A Thermodynamic Study of Dopant Interfacial Segregation Effect on Nanostability and Mechanical Properties

    NASA Astrophysics Data System (ADS)

    Wu, Longjia

    Nanoparticles, with great surface area and high surface to volume ratio, have been widely applied in many applications due to their unique size related effects. However, this high surface area character of nanoparticles also brings great excess energy to the whole system, making the system unstable and even causing the failure of nanoparticles, especially at higher temperatures. In order to maintain nanocrystalline structure of the materials, nanostability enhancement is of great significance in nanotechnology. It is well known that the global driving force for particles growth is to eliminate the excess energy brought by surface and grain boundary. Therefore, interfacial energetics has a great influence on the nanostability of the materials. And according to previous studies, dopant interfacial segregation could be a potential way to control the interfacial energetics of the nanoparticles and possibly lead to an improved nanostability. Furthermore, the interfacial energetics even can affect mechanical properties of nano-grain ceramic materials based on recent research. The main goals of the present work were to experimentally measure the interfacial energies of nanoparticles as well as nano-grain ceramics, modify the interfacial energetics through dopant segregation effect and engineer the nanostability and mechanical properties of the nanocrystalline materials through interfacial energetics modification. To achieve this goal, Mn cation has been chosen to introduce Mn interfacial segregation on ceria nanoparticles, and La cation has been added to 12 mol% yttria stabilized zirconia (12YSZ) and magnesium aluminate spinel (MAO) two-phase nano-grain ceramics to cause La interfacial segregation. Both of the dopant segregation phenomena were directly proved by electron energy loss spectroscopy (EELS). To quantify the dopant segregation effect on the interfacial energies, high-temperature oxide melt drop solution calorimetry, water adsorption calorimetry and differential

  18. Charge Exchange Reaction in Dopant-Assisted Atmospheric Pressure Chemical Ionization and Atmospheric Pressure Photoionization

    NASA Astrophysics Data System (ADS)

    Vaikkinen, Anu; Kauppila, Tiina J.; Kostiainen, Risto

    2016-08-01

    The efficiencies of charge exchange reaction in dopant-assisted atmospheric pressure chemical ionization (DA-APCI) and dopant-assisted atmospheric pressure photoionization (DA-APPI) mass spectrometry (MS) were compared by flow injection analysis. Fourteen individual compounds and a commercial mixture of 16 polycyclic aromatic hydrocarbons were chosen as model analytes to cover a wide range of polarities, gas-phase ionization energies, and proton affinities. Chlorobenzene was used as the dopant, and methanol/water (80/20) as the solvent. In both techniques, analytes formed the same ions (radical cations, protonated molecules, and/or fragments). However, in DA-APCI, the relative efficiency of charge exchange versus proton transfer was lower than in DA-APPI. This is suggested to be because in DA-APCI both dopant and solvent clusters can be ionized, and the formed reagent ions can react with the analytes via competing charge exchange and proton transfer reactions. In DA-APPI, on the other hand, the main reagents are dopant-derived radical cations, which favor ionization of analytes via charge exchange. The efficiency of charge exchange in both DA-APPI and DA-APCI was shown to depend heavily on the solvent flow rate, with best efficiency seen at lowest flow rates studied (0.05 and 0.1 mL/min). Both DA-APCI and DA-APPI showed the radical cation of chlorobenzene at 0.05-0.1 mL/min flow rate, but at increasing flow rate, the abundance of chlorobenzene M+. decreased and reagent ion populations deriving from different gas-phase chemistry were recorded. The formation of these reagent ions explains the decreasing ionization efficiency and the differences in charge exchange between the techniques.

  19. Charge Exchange Reaction in Dopant-Assisted Atmospheric Pressure Chemical Ionization and Atmospheric Pressure Photoionization.

    PubMed

    Vaikkinen, Anu; Kauppila, Tiina J; Kostiainen, Risto

    2016-08-01

    The efficiencies of charge exchange reaction in dopant-assisted atmospheric pressure chemical ionization (DA-APCI) and dopant-assisted atmospheric pressure photoionization (DA-APPI) mass spectrometry (MS) were compared by flow injection analysis. Fourteen individual compounds and a commercial mixture of 16 polycyclic aromatic hydrocarbons were chosen as model analytes to cover a wide range of polarities, gas-phase ionization energies, and proton affinities. Chlorobenzene was used as the dopant, and methanol/water (80/20) as the solvent. In both techniques, analytes formed the same ions (radical cations, protonated molecules, and/or fragments). However, in DA-APCI, the relative efficiency of charge exchange versus proton transfer was lower than in DA-APPI. This is suggested to be because in DA-APCI both dopant and solvent clusters can be ionized, and the formed reagent ions can react with the analytes via competing charge exchange and proton transfer reactions. In DA-APPI, on the other hand, the main reagents are dopant-derived radical cations, which favor ionization of analytes via charge exchange. The efficiency of charge exchange in both DA-APPI and DA-APCI was shown to depend heavily on the solvent flow rate, with best efficiency seen at lowest flow rates studied (0.05 and 0.1 mL/min). Both DA-APCI and DA-APPI showed the radical cation of chlorobenzene at 0.05-0.1 mL/min flow rate, but at increasing flow rate, the abundance of chlorobenzene M(+.) decreased and reagent ion populations deriving from different gas-phase chemistry were recorded. The formation of these reagent ions explains the decreasing ionization efficiency and the differences in charge exchange between the techniques. Graphical Abstract ᅟ.

  20. Nucleophilic Aromatic Substitution Between Halogenated Benzene Dopants and Nucleophiles in Atmospheric Pressure Photoionization.

    PubMed

    Kauppila, Tiina J; Haack, Alexander; Kroll, Kai; Kersten, Hendrik; Benter, Thorsten

    2016-03-01

    In a preceding work with dopant assisted-atmospheric pressure photoionization (DA-APPI), an abundant ion at [M + 77](+) was observed in the spectra of pyridine and quinoline with chlorobenzene dopant. This contribution aims to reveal the identity and route of formation of this species, and to systematically investigate structurally related analytes and dopants. Compounds containing N-, O-, and S-lone pairs were investigated with APPI in the presence of fluoro-, chloro-, bromo-, and iodobenzene dopants. Computational calculations on a density functional theory (DFT) level were carried out to study the reaction mechanism for pyridine and the different halobenzenes. The experimental and computational results indicated that the [M + 77](+) ion was formed by nucleophilic aromatic ipso-substitution between the halobenzene radical cation and nucleophilic analytes. The reaction was most efficient for N-heteroaromatic compounds, and it was weakened by sterical effects and enhanced by resonance stabilization. The reaction was most efficient with chloro-, bromo-, and iodobenzenes, whereas with fluorobenzene the reaction was scarcely observed. The calculated Gibbs free energies for the reaction between pyridine and the halobenzenes were shown to increase in the order I < Br < Cl < F. The reaction was found endergonic for fluorobenzene due to the strong C-F bonding, and exergonic for the other halobenzenes. For fluoro- and chlorobenzenes the reaction was shown to proceed through an intermediate state corresponding to [M + dopant](+), which was highly stable for fluorobenzene. For the bulkier bromine and iodine, this intermediate did not exist, but the halogens were shown to detach already during the approach by the nucleophile.

  1. Non-metallic dopant modulation of conductivity in substoichiometric tantalum pentoxide: A first-principles study

    DOE PAGES

    Bondi, Robert J.; Fox, Brian P.; Marinella, Matthew J.

    2017-06-01

    Here, we apply density-functional theory calculations to predict dopant modulation of electrical conductivity (σo) for seven dopants (C, Si, Ge, H, F, N, and B) sampled at 18 quantum molecular dynamics configurations of five independent insertion sites into two (high/low) baseline references of σo in amorphous Ta2O5, where each reference contains a single, neutral O vacancy center (VO0). From this statistical population (n = 1260), we analyze defect levels, physical structure, and valence charge distributions to characterize nanoscale modification of the atomistic structure in local dopant neighborhoods. C is the most effective dopant at lowering Ta2Ox σo, while also exhibitingmore » an amphoteric doping behavior by either donating or accepting charge depending on the host oxide matrix. Both B and F robustly increase Ta2Ox σo, although F does so through elimination of Ta high charge outliers, while B insertion conversely creates high charge O outliers through favorable BO3 group formation, especially in the low σo reference. While N applications to dope and passivate oxides are prevalent, we also found that N exacerbates the stochasticity of σo we sought to mitigate; sensitivity to the N insertion site and some propensity to form N-O bond chemistries appear responsible. Finally, we use direct first-principles predictions of σo to explore feasible Ta2O5 dopants to engineer improved oxides with lower variance and greater repeatability to advance the manufacturability of resistive memory technologies.« less

  2. Ab initio study of dopant-defect interactions in graphene sheets and graphene nano-ribbons

    NASA Astrophysics Data System (ADS)

    Tawalbeh, Tarek

    Theoretical studies of nanostructured systems, such as doped, defective and pristine graphene and graphene nanoribbons, present a major challenge to conventional computational methods. This thesis presents ab initio calculations based on density functional theory (DFT) to study the structural and electronic properties of doped and defective graphene and graphene 'nanoribbons. Our calculations are carried-out using density-functional pseudopotential approximations combined with the generalized gradient approximation (GGA) for the exchange-correlation functional. Structural optimizations are executed by iterative force minimization using the conjugate gradient algorithm. We investigate the effect of dopants and point defects on graphene and graphene nanoribbons and study the interactions between the two. Binding energies, equilibrium geometries, charge transfer, and exchange-splitting-induced magnetism are calculated. The dependence of dopant-defect separation distance on interaction energy and interaction energy is examined in detail. We find that the interaction energy for on-defect dopant sites is dominated by how well defect geometry accommodates the dopant-carbon interatomic distance. Depending on the site dopant-defect interaction is either attractive or repulsive. Stone-Wales defect-nitrogen pairing was found to induce exchange splitting and magnetism in certain configurations. Nitrogen was also found to passivate single-vacancy dangling bonds and eliminate exchange-splitting induced magnetism; vacancy-nitrogen interactions were found to be mostly attractive. Boron-vacancy pairing can result in a favorable symmetric sp3 configuration, this is the only vacancy-boron pairing were dangling bonds are passivated and magnetism is eliminated; other favorable boron-vacancy pairings maintain exchange splitting and can in some cases enhance it. We found that the effect of dopant-defect separation distance follows a simple inverse power law. Our results indicate that

  3. Electron probe microanalysis of the dopant concentrations in complex perovskite ferroelectrics

    NASA Astrophysics Data System (ADS)

    Samardžija, Z.

    2016-02-01

    Quantitative EPMA-WDS microanalyses were applied for the compositional characterisation of complex perovskite ferroelectrics based on cerium-doped barium titanate, a solid solution between lead-magnesium-niobate/lead-titanate and niobium-doped barium- bismuth-titanate. The analyses were optimized for high analytical sensitivity, precision and an ultimate accuracy of ≈ ± 1 % relative. The inherent problem with the WDS peak overlap of the Ce-Lα1 and Ba-Lβ1,4 spectral lines was solved by introducing overlap-correction methods in order to obtain consistent quantitative results for the Ce-doped BaTiO3. The quantitative results made it possible to obtain accurate chemical formulae for these materials, to determine the solubility of the dopants as well as to define the mode of the dopant incorporation and the charge-compensation mechanisms.

  4. Finite element simulations of electrostatic dopant potentials in thin semiconductor specimens for electron holography.

    PubMed

    Somodi, P K; Twitchett-Harrison, A C; Midgley, P A; Kardynał, B E; Barnes, C H W; Dunin-Borkowski, R E

    2013-11-01

    Two-dimensional finite element simulations of electrostatic dopant potentials in parallel-sided semiconductor specimens that contain p-n junctions are used to assess the effect of the electrical state of the surface of a thin specimen on projected potentials measured using off-axis electron holography in the transmission electron microscope. For a specimen that is constrained to have an equipotential surface, the simulations show that the step in the projected potential across a p-n junction is always lower than would be predicted from the properties of the bulk device, but is relatively insensitive to the value of the surface state energy, especially for thicker specimens and higher dopant concentrations. The depletion width measured from the projected potential, however, has a complicated dependence on specimen thickness. The results of the simulations are of broader interest for understanding the influence of surfaces and interfaces on electrostatic potentials in nanoscale semiconductor devices.

  5. Transparent organic p-dopant in carbon nanotubes: bis(trifluoromethanesulfonyl)imide.

    PubMed

    Kim, Soo Min; Jo, Young Woo; Kim, Ki Kang; Duong, Dinh Loc; Shin, Hyeon-Jin; Han, Jong Hun; Choi, Jae-Young; Kong, Jing; Lee, Young Hee

    2010-11-23

    We propose bis(trifluoromethanesulfonyl)imide [(CF(3)SO(2))(2)N](-) (TFSI) as a transparent strong electron-withdrawing p-type dopant in carbon nanotubes (CNTs). The conventional p-dopant, AuCl(3), has several drawbacks, such as hygroscopic effect, formation of Au clusters, decrease in transmittance, and high cost in spite of the significant increase in conductivity. TFSI is converted from bis(trifluoromethanesulfonyl)amine (TFSA) by accepting electrons from CNTs, subsequently losing a proton as a characteristic of a Brønsted acid, and has an inductive effect from atoms with high electronegativity, such as halogen, oxygen, and nitrogen. TFSI produced a similar improvement in conductivity to AuCl(3), while maintaining high thermal stability, and no appreciable change in transmittance with no cluster formation. The effectiveness of TFSI was compared with that of other derivatives.

  6. Continuous or discrete: Tuning the energy level alignment of organic layers with alkali dopants

    NASA Astrophysics Data System (ADS)

    Ules, Thomas; Lüftner, Daniel; Reinisch, Eva Maria; Koller, Georg; Puschnig, Peter; Ramsey, Michael G.

    2016-11-01

    This paper investigates the effects of cesium (Cs) deposited on pentacene (5A) and sexiphenyl (6P) monolayers on the Ag(110) substrate. The process of doping and the energy level alignment are studied quantitatively and contrasted. While ultimately for both molecules lowest unoccupied molecular orbital (LUMO) filling on charge transfer upon Cs dosing is observed, the doping processes are tellingly different. In the case of 5A, hybrid molecule-substrate states and doping states coexist at lowest Cs exposures, while for 6P doping states appear only after Cs has completely decoupled the monolayer from the substrate. With the support of density functional theory calculations, this different behavior is rationalized by the local character of electrostatic potential changes induced by dopants in relation to the spatial extent of the molecules. This also has severe effects on the energy level alignment, which for most dopant/molecule systems cannot be considered continuous but discrete.

  7. Investigation of deep level transient spectroscopy (DLTS) of dopant ZnO-based varistors

    NASA Astrophysics Data System (ADS)

    Ammar, A. H.; Farag, A. A. M.

    2010-03-01

    This work shows that the use of conventional analytical procedures to investigate the deep centers from the deep levels transient spectroscopy (DLTS) for ZnO varistors doped with single, double and ternary dopants of Bi 2O 3, CoO and MnO 2. This is to clarify the effect of these doping atoms on the conductivity of ZnO varistors. The results showed that the doping with Bi 2O 3 +CoO leads to a decrease in the conductivity while doping with Bi 2O 3+MnO 2 increased the conductivity and the three dopants together showed a compensating effect. The DLTS characterizing parameters such as minority-carrier capture cross-section, σ, effective density of states in the minority-carrier band, N D, energy separation between the trap level and the minority-carrier band, Δ E t and electron trap density, N t for each doped varistor were also calculated.

  8. Characterization of Spin-on Dopant by Sol-gel Method

    NASA Astrophysics Data System (ADS)

    Kamil, S. Ahmad; Ibrahim, K.; Aziz, A. Abdul

    2008-05-01

    P-N junction is a basic building block for many important electron devices from as simple as a solar cell to very complicated integrated circuit. In this work, spin-on dopant (SOD) was used as the diffusion source in order to create p-n junction. SOD was prepared by using sol gel method. The spin-on dopant solution ingredients contain tetraethylorthosilicate (TEOS), isopropanol (IPA), distilled water (H2O), acetone and phosphoric acid (H3PO4). The coated silicon wafers were put inside the conventional furnace for predepostion and drive in oxidation. Effect caused by varying the molarity of the acid were observed and studied using Hall Effect measurement by comparing their differences in sheet resistance, mobility, resistivity as well as sheet and bulk concentaration.

  9. Geometric Frustration of 2D Dopants in Silicon: Surpassing Electrical Saturation

    SciTech Connect

    Citrin, P.H.; Muller, D.A.; Gossmann, H.; Northrup, P.A.; Vanfleet, R.

    1999-10-01

    A novel application of scanning transmission electron microscopy, combined with data from x-ray absorption spectroscopy, establishes that high concentrations of n -type Sb dopants distributed within a two-dimensional (2D) layer in Si can contribute up to an order of magnitude higher free-carrier density than similar dopant concentrations distributed over a three-dimensional region. This difference is explained using a simple model in which formation of electrically deactivating centers is inhibited by solely geometric constraints. It should be possible to extend these ideas for obtaining even higher free-carrier densities in Si from 2D layers of Sb and other group V donors. {copyright} {ital 1999} {ital The American Physical Society }

  10. Carrier density and lifetime for different dopants in single-crystal and polycrystalline CdTe

    DOE PAGES

    Burst, James M.; Farrell, Stuart B.; Albin, David S.; ...

    2016-11-01

    CdTe defect chemistry is adjusted by annealing samples with excess Cd or Te vapor with and without extrinsic dopants. We observe that Group I (Cu and Na) elements can increase hole density above 1016 cm-3, but compromise lifetime and stability. By post-deposition incorporation of a Group V dopant (P) in a Cd-rich ambient, lifetimes of 30 ns with 1016 cm-3 hole density are achieved in single-crystal and polycrystalline CdTe without CdCl2 or Cu. Furthermore, phosphorus doping appears to be thermally stable. In conclusion, this combination of long lifetime, high carrier concentration, and improved stability can help overcome historic barriers formore » CdTe solar cell development.« less

  11. Heterovalent Dopant Incorporation for Bandgap and Type Engineering of Perovskite Crystals.

    PubMed

    Abdelhady, Ahmed L; Saidaminov, Makhsud I; Murali, Banavoth; Adinolfi, Valerio; Voznyy, Oleksandr; Katsiev, Khabiboulakh; Alarousu, Erkki; Comin, Riccardo; Dursun, Ibrahim; Sinatra, Lutfan; Sargent, Edward H; Mohammed, Omar F; Bakr, Osman M

    2016-01-21

    Controllable doping of semiconductors is a fundamental technological requirement for electronic and optoelectronic devices. As intrinsic semiconductors, hybrid perovskites have so far been a phenomenal success in photovoltaics. The inability to dope these materials heterovalently (or aliovalently) has greatly limited their wider utilizations in electronics. Here we show an efficient in situ chemical route that achieves the controlled incorporation of trivalent cations (Bi(3+), Au(3+), or In(3+)) by exploiting the retrograde solubility behavior of perovskites. We term the new method dopant incorporation in the retrograde regime. We achieve Bi(3+) incorporation that leads to bandgap tuning (∼300 meV), 10(4) fold enhancement in electrical conductivity, and a change in the sign of majority charge carriers from positive to negative. This work demonstrates the successful incorporation of dopants into perovskite crystals while preserving the host lattice structure, opening new avenues to tailor the electronic and optoelectronic properties of this rapidly emerging class of solution-processed semiconductors.

  12. Enhanced flux pinning in GdBaCuO bulk superconductors by Zr dopants

    NASA Astrophysics Data System (ADS)

    Xu, C.; Hu, A.; Ichihara, M.; Sakai, N.; Izumi, M.; Hirabayashi, I.

    2007-10-01

    We, respectively, fabricated GdBa2Cu3O7-δ (Gd123) single domain superconductors by melt growth process in air with Gd2Ba4CuZrOx (GdZr2411) and nanosize ZrO2 dopants. The microstructures and superconducting properties were investigated by scanning/transmission electron microscopy (SEM/TEM) and SQUID. GdZr2411 and BaZrO3 particles with the average size of 50 nm were observed in the GdZr2411 and nanosize ZrO2 doped Gd123 bulks by TEM, respectively. Critical current density (Jc) was enhanced up to 100,000 A/cm2 at 77 K and self-field with 0.4 mol% nano-sized ZrO2. The present study also showed that small amount GdZr2411 dopants (8 mol%, ratio to Gd123) were effective to induce a δTc-type pinning.

  13. Effectiveness of a dopant in U-Zr metallic fuel to prevent lanthanide migration

    SciTech Connect

    Kim, Yeon Soo; Wieneck, T.; O'Hare, E.; Fortner, J.

    2013-07-01

    The advanced fast reactor concepts to achieve ultra-high burnup (about 50%) without requiring refueling by way of using metallic alloy fuel have gained interest. Fission product lanthanide accumulation at high burnup is substantial and its migration to cladding and reaction with cladding is a potential life-limiting phenomenon. As a means to solve this problem, adding an element that forms stable compounds with lanthanides to immobilize them has been proposed. The theoretical assessment shows that indium, thallium, gallium, and antimony are good candidates. Except for Sb, because these elements are low-melting temperature elements, liquid metal embrittlement of cladding is a concern if large sized agglomerates exist contacting the cladding. Alloy characterization of as-fabricated samples was performed to examine the effectiveness of the dopant addition method using optical microscopy and scanning electron microscopy. Although preliminary, the present results showed that indium is a better dopant to immobilize lanthanides.

  14. Radiation tolerant polymeric films through the incorporation of small molecule dopants in the polymer matrix

    SciTech Connect

    Lenhart, Joseph L.; Cole, Phillip J.; Cole, Shannon M.; Schroeder, John L.; Belcher, Michael E.

    2008-01-15

    Radiation induced conductivity (RIC) in semicrystalline polyethylene terephthalate (PET) films can be reduced by incorporating small molecule electron traps into the polymer. The electron traps contained an aromatic core with strong electron withdrawing functionality pendant to the core and were incorporated into the PET film by immersing the polymer in a solution of dopant and solvent at elevated temperatures. The chemical functionality of the electron trapping molecule and the number of pendant functional groups had a strong impact on the equilibrium doping level and the most effective doping solvent. In addition, all of the electron traps exhibited effectiveness at reducing the RIC. The technique of incorporating small molecule dopants into the polymer matrix in order to reduce the RIC can potentially be exploited with other polymers films and coatings utilized in electronics devices such as encapsulants, conformal coatings, and polymeric underfills.

  15. Influence of absorber layer dopants on performance of Ge/Si single photon avalanche diodes

    NASA Astrophysics Data System (ADS)

    Pilgrim, Neil J.; Ikonic, Zoran; Kelsall, Robert W.

    2013-04-01

    Monte Carlo electronic transport simulations are applied to investigate the influence of the Ge absorber layer on the performance of Ge/Si single photon avalanche diodes. Ge dopant type and concentration control the internal electric field gradients, which directly influence the probabilistic distribution of times from the point of charge photo-generation to that of transmission over the Ge/Si heterojunction. The electric field adjacent to the heterointerface is found to be the dominant factor in achieving rapid transmission, leading to a preference for p-type dopants in the Ge absorber. The contribution to jitter from the Ge layer is estimated and appears relatively independent of bias, though scales near-linearly with layer height.

  16. 3-D Atomic-Scale Mapping of Manganese Dopants in Lead Sulfide Nanowires

    SciTech Connect

    Isheim, Dieter; Kaszpurenko, Jason; Yu, Dong; Mao, Zugang; Seidman, David N.; Arslan, Ilke

    2012-03-22

    Dopants in nanowires, whether intentional or unintentional, can ultimately control the material's properties and therefore need to be understood on the atomic scale. We study vapor-liquid-solid grown manganese-doped lead sulfide nanowires by atom-probe tomography for the first time for lead salt materials. The three-dimensional chemical concentration maps at the atomic scale demonstrate a radial distribution profile of Mn ions, with a concentration of only 0.18 at.% and 0.01 at.% for MnCl2 and Mn-acetate precursors, respectively. The ability to characterize these small concentrations of dopant atoms in Pb1-xMnxS nanowires (x = 0.0036 and 0.0002), important for spintronic and thermoelectric devices, sets a platform for similar analyses for all nanostructures. First-principles calculations confirm that Mn atoms substitute for Pb in the PbS structure.

  17. Two-dimensional dopant profiling of gallium nitride p-n junctions by scanning capacitance microscopy

    NASA Astrophysics Data System (ADS)

    Lamhamdi, M.; Cayrel, F.; Frayssinet, E.; Bazin, A. E.; Yvon, A.; Collard, E.; Cordier, Y.; Alquier, D.

    2016-04-01

    Two-dimensional imaging of dopant profiles for n and p-type regions are relevant for the development of new power semiconductors, especially for gallium nitride (GaN) for which classical profiling techniques are not adapted. This is a challenging task since it needs a technique with simultaneously good sensitivity, high spatial resolution and high dopant gradient resolution. To face these challenges, scanning capacitance microscopy combined with Atomic Force Microscopy is a good candidate, presenting reproducible results, as demonstrated in literature. In this work, we attempt to distinguish reliably and qualitatively the various doping concentrations and type at p-n and unipolar junctions. For both p-n and unipolar junctions three kinds of samples were prepared and measured separately. The space-charge region of the p-n metallurgical junction, giving rise to different contrasts under SCM imaging, is clearly observed, enlightening the interest of the SCM technique.

  18. The determination of dopant ion valence distributions in insulating crystals using XANES measurements.

    PubMed

    Hughes-Currie, Rosa B; Ivanovskikh, Konstantin V; Wells, Jon-Paul R; Reid, Michael F; Gordon, Robert A

    2016-04-06

    Ytterbium-doped wide-bandgap fluoride crystals CaF2, SrF2 and NaMgF3 have been measured using x-ray absorption near edge structure (XANES) on the L3 edge to determine the ratio of trivalent to divalent Yb ions present in the crystals. This study improves upon previous XANES measurements of dopant ion valency by taking into account the x-ray emission transition probabilities for the divalent and trivalent species instead of simply assuming that the relative concentrations may be determined by the ratio of the x-ray excitation band areas. Trivalent to divalent ratios as high as 5 are inferred even at low total dopant ion concentrations of 0.05 mol% Yb.

  19. The determination of dopant ion valence distributions in insulating crystals using XANES measurements

    NASA Astrophysics Data System (ADS)

    Hughes-Currie, Rosa B.; Ivanovskikh, Konstantin V.; Wells, Jon-Paul R.; Reid, Michael F.; Gordon, Robert A.

    2016-04-01

    Ytterbium-doped wide-bandgap fluoride crystals CaF2, SrF2 and NaMgF3 have been measured using x-ray absorption near edge structure (XANES) on the L3 edge to determine the ratio of trivalent to divalent Yb ions present in the crystals. This study improves upon previous XANES measurements of dopant ion valency by taking into account the x-ray emission transition probabilities for the divalent and trivalent species instead of simply assuming that the relative concentrations may be determined by the ratio of the x-ray excitation band areas. Trivalent to divalent ratios as high as 5 are inferred even at low total dopant ion concentrations of 0.05 mol% Yb.

  20. The roles played by Ag and Al dopants in controlling the electrical properties of ZnO varistors

    NASA Astrophysics Data System (ADS)

    Fan, Jiwei; Freer, Robert

    1995-05-01

    Four sets of ZnO-based ceramic varistors (reference samples-ZNR; doped with aluminium-AL; doped with silver-AG; doped with aluminium and silver-AA) have been prepared by the conventional mixed oxide route. The current-voltage (I-V) characteristics, determined at current densities up to 1 mA/cm2, yielded nonlinear coefficients (α) of 38, 60, 22 and 56, respectively. Dc and ac degradation tests were performed at 115 °C. Ac impedance analysis was used to determine grain (rg) and grain boundary (Rb) resistances; capacitance-voltage analysis enabled the donor density (Nd) and the barrier height (φ) to be determined. Doping the varistors with Al increased Nd, reduced rg, and improved the I-V characteristics, but caused an increase in Zn interstitials which degraded the stability. In contrast, Ag acts as an amphoteric dopant in ZnO causing a decrease in Nd, an increase in rg and Rb, and a reduction in α ; Ag located in the interstitial sites is able to block the formation and migration of new Zn interstitials, thereby improving the stability. Doping with both Al and Ag at optimum levels gives benefits from both additives, i.e., Al doping (increases Nd and decreases rg) improves nonlinearity, while Ag doping (blocks the formation and migration of Zn interstitials) improves the stability of ZnO varistors.

  1. High Resolution Dopant Profiles Revealed by Atom Probe Tomography and STEM-EBIC for CdTe Based Solar Cells

    DOE PAGES

    Poplawsky, Jonathan D.; Li, Chen; Paudel, Naba; ...

    2016-01-01

    Segregated elements and their diffusion profiles within grain boundaries and interfaces resulting from post deposition heat treatments are revealed using atom probe tomography (APT), scanning transmission electron microscopy (STEM), and electron beam induced current (EBIC) techniques. The results demonstrate how these techniques complement each other to provide conclusive evidence for locations of space charge regions and mechanisms that create them at the nanoscale. Most importantly, a Cl dopant profile that extends ~5 nm into CdTe grains interfacing the CdS is shown using APT and STEM synergy, which has been shown to push the pn-junction into the CdTe layer indicative ofmore » a homojunction (revealed by STEM EBIC). In addition, Cu and Cl concentrations within grain boundaries within several nms and µms from the CdS/CdTe interface are compared, Na segregation of <0.1% is detected, and S variations of ~1–3% are witnessed between CdTe grains close to the CdS/CdTe interface. The segregation and diffusion of these elements directly impacts on the material properties, such as band gap energy and n/p type properties. Optimization of the interfacial and grain boundary doping will lead to higher efficiency solar cells.« less

  2. High Resolution Dopant Profiles Revealed by Atom Probe Tomography and STEM-EBIC for CdTe Based Solar Cells

    SciTech Connect

    Poplawsky, Jonathan D.; Li, Chen; Paudel, Naba; Guo, Wei; Yan, Yanfa; Pennycook, Stephen J.

    2016-01-01

    Segregated elements and their diffusion profiles within grain boundaries and interfaces resulting from post deposition heat treatments are revealed using atom probe tomography (APT), scanning transmission electron microscopy (STEM), and electron beam induced current (EBIC) techniques. The results demonstrate how these techniques complement each other to provide conclusive evidence for locations of space charge regions and mechanisms that create them at the nanoscale. Most importantly, a Cl dopant profile that extends ~5 nm into CdTe grains interfacing the CdS is shown using APT and STEM synergy, which has been shown to push the pn-junction into the CdTe layer indicative of a homojunction (revealed by STEM EBIC). In addition, Cu and Cl concentrations within grain boundaries within several nms and µms from the CdS/CdTe interface are compared, Na segregation of <0.1% is detected, and S variations of ~1–3% are witnessed between CdTe grains close to the CdS/CdTe interface. The segregation and diffusion of these elements directly impacts on the material properties, such as band gap energy and n/p type properties. Optimization of the interfacial and grain boundary doping will lead to higher efficiency solar cells.

  3. Atomistic Interrogation of B–N Co-dopant Structures and Their Electronic Effects in Graphene

    DOE PAGES

    Schiros, Theanne; Nordlund, Dennis; Palova, Lucia; ...

    2016-06-21

    Chemical doping has been demonstrated to be an effective method for producing high-quality, large-area graphene with controlled carrier concentrations and an atomically tailored work function. Furthermore, the emergent optoelectronic properties and surface reactivity of carbon nanostructures are dictated by the microstructure of atomic dopants. Co-doping of graphene with boron and nitrogen offers the possibility to further tune the electronic properties of graphene at the atomic level, potentially creating p- and n-type domains in a single carbon sheet, opening a gap between valence and conduction bands in the 2-D semimetal. When using a suite of high-resolution synchrotron-based X-ray techniques, scanning tunnelingmore » microscopy, and density functional theory based computation we visualize and characterize B–N dopant bond structures and their electronic effects at the atomic level in single-layer graphene grown on a copper substrate. We find there is a thermodynamic driving force for B and N atoms to cluster into BNC structures in graphene, rather than randomly distribute into isolated B and N graphitic dopants, although under the present growth conditions, kinetics limit segregation of large B–N domains. We also observe that the doping effect of these BNC structures, which open a small band gap in graphene, follows the B:N ratio (B > N, p-type; B < N, n-type; B=N, neutral). We attribute this to the comparable electron-withdrawing and -donating effects, respectively, of individual graphitic B and N dopants, although local electrostatics also play a role in the work function change.« less

  4. Atomistic Interrogation of B–N Co-dopant Structures and Their Electronic Effects in Graphene

    SciTech Connect

    Schiros, Theanne; Nordlund, Dennis; Palova, Lucia; Zhao, Liuyan; Levendorf, Mark; Jaye, Cherno; Reichman, David; Park, Jiwoong; Hybertsen, Mark; Pasupathy, Abhay

    2016-06-21

    Chemical doping has been demonstrated to be an effective method for producing high-quality, large-area graphene with controlled carrier concentrations and an atomically tailored work function. Furthermore, the emergent optoelectronic properties and surface reactivity of carbon nanostructures are dictated by the microstructure of atomic dopants. Co-doping of graphene with boron and nitrogen offers the possibility to further tune the electronic properties of graphene at the atomic level, potentially creating p- and n-type domains in a single carbon sheet, opening a gap between valence and conduction bands in the 2-D semimetal. When using a suite of high-resolution synchrotron-based X-ray techniques, scanning tunneling microscopy, and density functional theory based computation we visualize and characterize B–N dopant bond structures and their electronic effects at the atomic level in single-layer graphene grown on a copper substrate. We find there is a thermodynamic driving force for B and N atoms to cluster into BNC structures in graphene, rather than randomly distribute into isolated B and N graphitic dopants, although under the present growth conditions, kinetics limit segregation of large B–N domains. We also observe that the doping effect of these BNC structures, which open a small band gap in graphene, follows the B:N ratio (B > N, p-type; B < N, n-type; B=N, neutral). We attribute this to the comparable electron-withdrawing and -donating effects, respectively, of individual graphitic B and N dopants, although local electrostatics also play a role in the work function change.

  5. Effect of dopants on crystal structure and thermal properties of pentaglycerine

    SciTech Connect

    Chandra, D.; Ding, W.

    1989-03-01

    The overall objective of this research program is to develop practical solid-state thermal energy storage materials. Research is focused on polyalcohol {open_quotes}Plastic Crystals{close_quotes} which undergo crystallographic changes at constant transition temperature absorbing or releasing amounts of latent heat. The known pure polyalcohols have high transition temperatures; therefore, adjustment of transformation temperature is important to develop practical materials. The approach taken is to introduce substitutional and interstitial dopants so as to strain the lattice of the host crystal which results in lowering the transition temperature. Current research is on temperature adjustment of pentaglycerine [PG] (C{sub 5}H{sub 12}O{sub 3}) initiated approximately four months ago. Results, so far, show that the substitutional dopants are more effective in reducing the transition temperature than interstitial dopants. The results in the first phase of this program show that the transition temperature of PG reduced significantly by using trimethylol propane [TMP] (C{sub 6}H{sub 14}O{sub 3}), 2-amino 2-methyl 1,3 propanediol [AMPL] (C{sub 4}H{sub 11}NO{sub 2}) as dopants. It appears that some of these doped samples have near room temperature transitions; however, these results are not conclusive at this time. Recently, it was discovered that TMP has an additional solid-solid phase transformation, slightly below room temperature. Crystal structure analyses showed some surprising results with regards to thermal expansion behavior of PG. Several sets of low as well as high temperature data were obtained from the pure and doped PG to characterize the structural changes, if any, and the thermal expansions. Research is in progress on crystal structure and thermal analyses.

  6. Influence of dopant substitution mechanism on catalytic properties within hierarchical architectures

    NASA Astrophysics Data System (ADS)

    Newland, Stephanie H.; Sinkler, Wharton; Mezza, Thomas; Bare, Simon R.; Raja, Robert

    2016-07-01

    A range of hierarchically porous (HP) AlPO-5 catalysts, with isomorphously substituted transition metal ions, have been synthesized using an organosilane as a soft template. By employing a range of structural and spectroscopic characterization protocols, the properties of the dopant-substituted species within the HP architectures have been carefully evaluated. The resulting nature of the active site is shown to have a direct impact on the ensuing catalytic properties in the liquid-phase Beckmann rearrangement of cyclic ketones.

  7. Direct Electrical Probing of Periodic Modulation of Zinc-Dopant Distributions in Planar Gallium Arsenide Nanowires.

    PubMed

    Choi, Wonsik; Seabron, Eric; Mohseni, Parsian K; Kim, Jeong Dong; Gokus, Tobias; Cernescu, Adrian; Pochet, Pascal; Johnson, Harley T; Wilson, William L; Li, Xiuling

    2017-02-28

    Selective lateral epitaxial (SLE) semiconductor nanowires (NWs), with their perfect in-plane epitaxial alignment, ability to form lateral complex p-n junctions in situ, and compatibility with planar processing, are a distinctive platform for next-generation device development. However, the incorporation and distribution of impurity dopants in these planar NWs via the vapor-liquid-solid growth mechanism remain relatively unexplored. Here, we present a detailed study of SLE planar GaAs NWs containing multiple alternating axial segments doped with Si and Zn impurities by metalorganic chemical vapor deposition. The dopant profile of the lateral multi-p-n junction GaAs NWs was imaged simultaneously with nanowire topography using scanning microwave impedance microscopy and correlated with infrared scattering-type near-field optical microscopy. Our results provide unambiguous evidence that Zn dopants in the periodically twinned and topologically corrugated p-type segments are preferentially segregated at twin plane boundaries, while Si impurity atoms are uniformly distributed within the n-type segments of the NWs. These results are further supported by microwave impedance modulation microscopy. The density functional theory based modeling shows that the presence of Zn dopant atoms reduces the formation energy of these twin planes, and the effect becomes significantly stronger with a slight increase of Zn concentration. This implies that the twin formation is expected to appear when a threshold planar concentration of Zn is achieved, making the onset and twin periodicity dependent on both Zn concentration and nanowire diameter, in perfect agreement with our experimental observations.

  8. Final results from the SDC dopant search for new green wavelength shifting (WLS) fibers: Volume 1

    SciTech Connect

    Pla-Dalmau, A.; Foster, G.W.; Zhang, G.

    1993-12-01

    A scintillating tile/fiber design had been selected for the SDC calorimeter. It consisted of scintillator plates embedded with a wavelength shifting (WLS) fiber which was spliced to a clear fiber. Based on the results from previous radiation damage studies on different scintillating materials, SCSN38 had been chosen for the scintillating tile and BCF91 or Y7 for the WLS fiber. SCSN38 is a blue-emitting scintillator and both WLS fibers use K-27, a green-emitting compound, as dopant. K-27 has a decay time of approximately 12 ns which is long in comparison to that of most blue-emitting materials. Of all the factors that affect the speed of the scintillator tile/fiber calorimeter, the lifetime of the green-emitting dopant is the dominant component. To increase the speed of the calorimeter, it would be desirable that the green WLS fibers utilized had lifetimes between 3 and 5 ns. However, currently available green WLS fibers exhibit decay times between 7 and 12 ns. Development of new green-emitting WLS fibers with short decay times must be investigated. The goal of this project was to search for commercially available fluorescent compounds with {lambda}{sub abs} = 400--450 nm, {lambda}{sub em} = 450--550 nm, {tau} = 3--7 ns, and quantum efficiency of minimum 0.7 (current K-27 baseline). Large Stokes shift and low self-absorption were not important requirements since the optical pathlength for the shifted light was small. Characterization of the spectroscopic properties of these compounds after styrene polymerization is important since this is an essential part of the manufacturing of WLS fibers. This summary presents the transmittance and fluorescence data for each dopant tested. However, many fluorescence measurements using different excitation wavelengths and orientations were recorded. Volume 1 presents a plot for each dopant combining transmittance and the most representative fluorescence measurement.

  9. Final results from the SDC dopant search for new green wavelength shifting (WLS) fibers, volume 1

    NASA Astrophysics Data System (ADS)

    Pla-Dalmau, A.; Foster, G. W.; Zhang, G.

    1993-12-01

    A scintillating tile/fiber design had been selected for the SDC calorimeter. It consisted of scintillator plates embedded with a wavelength shifting (WLS) fiber which was spliced to a clear fiber. Based on the results from previous radiation damage studies on different scintillating materials, SCSN38 had been chosen for the scintillating tile and BCF91 or Y7 for the WLS fiber. SCSN38 is a blue-emitting scintillator and both WLS fibers use K-27, a green-emitting compound, as dopant. K-27 has a decay time of approximately 12 ns which is long in comparison to that of most blue-emitting materials. Of all the factors that affect the speed of the scintillator tile/fiber calorimeter, the lifetime of the green-emitting dopant is the dominant component. To increase the speed of the calorimeter, it would be desirable that the green WLS fibers utilized had lifetimes between 3 and 5 ns. However, currently available green WLS fibers exhibit decay times between 7 and 12 ns. Development of new green-emitting WLS fibers with short decay times must be investigated. The goal of this project was to search for commercially available fluorescent compounds with lambda(sub abs) = 400-450 nm, lambda(sub em) = 450-550 nm, tau = 3-7 ns, and quantum efficiency of minimum 0.7 (current K-27 baseline). Large Stokes shift and low self-absorption were not important requirements since the optical pathlength for the shifted light was small. Characterization of the spectroscopic properties of these compounds after styrene polymerization is important since this is an essential part of the manufacturing of WLS fibers. This summary presents the transmittance and fluorescence data for each dopant tested. However, many fluorescence measurements using different excitation wavelengths and orientations were recorded. Volume 1 presents a plot for each dopant combining transmittance and the most representative fluorescence measurement.

  10. Atomistic Interrogation of B–N Co-dopant Structures and Their Electronic Effects in Graphene

    SciTech Connect

    Schiros, Theanne; Nordlund, Dennis; Palova, Lucia; Zhao, Liuyan; Levendorf, Mark; Jaye, Cherno; Reichman, David; Park, Jiwoong; Hybertsen, Mark; Pasupathy, Abhay

    2016-06-21

    Chemical doping has been demonstrated to be an effective method for producing high-quality, large-area graphene with controlled carrier concentrations and an atomically tailored work function. Furthermore, the emergent optoelectronic properties and surface reactivity of carbon nanostructures are dictated by the microstructure of atomic dopants. Co-doping of graphene with boron and nitrogen offers the possibility to further tune the electronic properties of graphene at the atomic level, potentially creating p- and n-type domains in a single carbon sheet, opening a gap between valence and conduction bands in the 2-D semimetal. When using a suite of high-resolution synchrotron-based X-ray techniques, scanning tunneling microscopy, and density functional theory based computation we visualize and characterize B–N dopant bond structures and their electronic effects at the atomic level in single-layer graphene grown on a copper substrate. We find there is a thermodynamic driving force for B and N atoms to cluster into BNC structures in graphene, rather than randomly distribute into isolated B and N graphitic dopants, although under the present growth conditions, kinetics limit segregation of large B–N domains. We also observe that the doping effect of these BNC structures, which open a small band gap in graphene, follows the B:N ratio (B > N, p-type; B < N, n-type; B=N, neutral). We attribute this to the comparable electron-withdrawing and -donating effects, respectively, of individual graphitic B and N dopants, although local electrostatics also play a role in the work function change.

  11. Dopant-Enabled Supramolecular Approach for Controlled Synthesis of Nanostructured Conductive Polymer Hydrogels.

    PubMed

    Wang, Yaqun; Shi, Ye; Pan, Lijia; Ding, Yu; Zhao, Yu; Li, Yun; Shi, Yi; Yu, Guihua

    2015-11-11

    Conducting polymer hydrogels emerge as a novel class of polymeric materials that show great potential in many energy, environmental, and biomedical devices. We describe here for the first time a general supramolecular approach toward controlled in situ synthesis of one-dimensional nanostructured conductive hydrogels (polypyrrole (PPy) as a model system) using a rational dopant counterion, which is a disc-shaped liquid crystal molecular copper phthalocyanine-3,4',4″,4‴-tetrasulfonic acid tetrasodium salt (CuPcTs). The dopant molecule CuPcTs cross-linked the PPy chains to form a three-dimensional network that gelated into a hydrogel. The PPy hydrogel could be synthesized in bulk quantities with uniform morphology of self-assembled interconnected nanofibers. The tetra-functional dopant favors a supramolecular self-assembly mechanism to form one-dimensional PPy nanostructures. Furthermore, the enhanced interchain charge transport of CuPcTs doped PPy resulted in greatly enhanced conductivity and pseudocapacitance compared with pristine PPy.

  12. Investigating lanthanide dopant distributions in Yttrium Aluminum Garnet (YAG) using solid state paramagnetic NMR.

    PubMed

    McCarty, Ryan J; Stebbins, Jonathan F

    2016-10-01

    This paper demonstrates the approach of using paramagnetic effects observed in NMR spectra to investigate the distribution of lanthanide dopant cations in YAG (yttrium aluminum garnet, Y3Al5O12) optical materials, as a complimentary technique to optical spectroscopy and other standard methods of characterization. We investigate the effects of Ce(3+), Nd(3+), Yb(3+), Tm(3+), and Tm(3+)-Cr(3+) on (27)Al and (89)Y NMR spectra. We note shifted resonances for both AlO4 and AlO6 sites. In some cases, multiple shifted peaks are observable, and some of these can be empirically assigned to dopant cations in known configurations to the observed nuclides. In many cases, AlO6 peaks shifted by more than one magnetic neighbor can be detected. In general, we observe that the measured intensities of shifted resonances, when spinning sidebands are included, are consistent with predictions from models with dopant cations that are randomly distributed throughout the lattice. In at least one set of (27)Al spectra, we identify two sub-peaks possibly resulting from two paramagnetic cations with magnetically coupled spin states neighboring the observed nucleus. We identify systematic changes in the spectra related to known parameters describing the magnetic effects of lanthanide cations, such as larger shift distances when the expectation value of electron spins is greater. We lastly comment on the promise of this technique in future analyses of laser and other crystalline oxide materials. Copyright © 2016 Elsevier Inc. All rights reserved.

  13. Mechanism of enhanced photocatalytic activities on tungsten trioxide doped with sulfur: Dopant-type effects

    NASA Astrophysics Data System (ADS)

    Li, Dan; Huang, Wei-Qing; Xie, Zhong; Xu, Liang; Yang, Yin-Cai; Hu, Wangyu; Huang, Gui-Fang

    2016-09-01

    The enhanced photocatalytic activity of tungsten trioxide (WO3) has been observed experimentally via doping with S element as different dopant types. Herein, a comparative study on the effect of different types of S dopant and native vacancy defects on the electronic structure and optical properties of WO3 is presented by using hybrid Heyd-Scuseria-Ernzerhof 2006 (HSE06) density functional methods. Six possible models (SO-WO3, SW-WO3, VO-WO3, VW-WO3, SO + VW-WO3 and SW + VO-WO3) based on WO3 are tentatively put forward. It is found that cationic S doping (the substitution of W by S) is more favorable than anionic S doping (replacing O with S), and both cases become easier to form as native vacancy defect is accompanied. The electronic structures of doped WO3 depend on the type of dopant: anionic S doping results into three isolated levels in the upper part of valence band, while cationic S doping only induces an effective band gap reduction, which is critical for efficient light-to-current conversion. Interestingly, the isolated states near gap of WO3 would appear as long as native vacancy defects exist. The introduced levels or reduced band gaps make the systems responsed to the visible light, even further to a range of 400-700 nm. These findings can rationalize the available experimental results and pave the way for developing WO3-based photocatalysts.

  14. Quantum simulation of the Hubbard model with dopant atoms in silicon

    PubMed Central

    Salfi, J.; Mol, J. A.; Rahman, R.; Klimeck, G.; Simmons, M. Y.; Hollenberg, L. C. L.; Rogge, S.

    2016-01-01

    In quantum simulation, many-body phenomena are probed in controllable quantum systems. Recently, simulation of Bose–Hubbard Hamiltonians using cold atoms revealed previously hidden local correlations. However, fermionic many-body Hubbard phenomena such as unconventional superconductivity and spin liquids are more difficult to simulate using cold atoms. To date the required single-site measurements and cooling remain problematic, while only ensemble measurements have been achieved. Here we simulate a two-site Hubbard Hamiltonian at low effective temperatures with single-site resolution using subsurface dopants in silicon. We measure quasi-particle tunnelling maps of spin-resolved states with atomic resolution, finding interference processes from which the entanglement entropy and Hubbard interactions are quantified. Entanglement, determined by spin and orbital degrees of freedom, increases with increasing valence bond length. We find separation-tunable Hubbard interaction strengths that are suitable for simulating strongly correlated phenomena in larger arrays of dopants, establishing dopants as a platform for quantum simulation of the Hubbard model. PMID:27094205

  15. Instability of the Characteristic Emissions of Dopant Tb in ZnO Hexagonal Pyramids

    NASA Astrophysics Data System (ADS)

    Zhai, Bao-gai; Ma, Qing-lan; Huang, Yuan Ming

    2017-02-01

    Tb-doped ZnO hexagonal pyramids with the doping level of 0.1 mol.% were synthesized by thermal decomposing the mixture of zinc nitrate and terbium nitrate at 500°C in an air-filled furnace. The crystal structures and photoluminescent properties of Tb-doped ZnO hexagonal pyramids were analyzed with a scanning electron microscope, x-ray diffractometer, fluorescence spectrophotometer and photoluminescence excitation spectrophotometer. Four characteristic emission peaks of Tb3+ ions were recorded over the broad green luminescent band of ZnO, at 488 nm, 544 nm, 584 nm and 620 nm for Tb-doped ZnO hexagonal pyramids. The characteristic emissions of the rare-earth dopant in Tb-doped ZnO were found to be unstable when stored in air. The 544-nm emission of dopant Tb in ZnO lost 12%, 37%, 78%, and 100% of its original intensity after stored in air for 2 months, 4 months, 6 months, and 8 months, respectively. With the help of calculated band structures, our results suggest that the instability of the characteristic emissions of dopant Tb in ZnO can be attributed to the possible expulsion of Tb out of the ZnO host.

  16. Spontaneous reorientation from planar to homeotropic alignment in dual-frequency mixture doped with chiral dopant

    NASA Astrophysics Data System (ADS)

    Perkowski, Paweł; Mrukiewicz, Mateusz; Chojnowska, Olga; Piecek, Wiktor; Dąbrowski, Roman

    2014-11-01

    We investigate a dual-frequency (DF) nematic mixture by means of the dielectric spectroscopy. A chiral dopant has been added to the DF matrix. A pure DF matrix as well as three samples with increasing concentration of chiral dopant (DF*) have been prepared. Investigated samples have shown a selective reflection band, according to a helical pitch induced in proportion to the chiral dopant amount. Such system promises a great application potential as a selective light reflecting shutter or spectral filter due to nearly symmetrical switching times and defectless structures. When we put the non-doped DF mixture into homogenous (HG) oriented cell we found that planar orientation is permanent on both cooling and heating cycles. In the case of DF* chiral mixtures, the behavior changes substantially. One can observe that the oriented virgin planar structure of DF* within the HG cell starts to change its orientation to homeotropic one at different temperature. When heating is continued the homeotropic orientation in the HG cell is preserved up to the clearing temperature. Upon a subsequent cooling from the isotropic state, the homeotropic orientation is preserved within the whole mesogenic state. The effect of induction of the homeotropic state observed within HG cells is analyzed and discussed.

  17. Nitrogen oxides as dopants for the detection of aromatic compounds with ion mobility spectrometry.

    PubMed

    Gaik, Urszula; Sillanpää, Mika; Witkiewicz, Zygfryd; Puton, Jarosław

    2017-03-03

    Limits of detection (LODs) in ion mobility spectrometry (IMS) strictly depend on ionization of the analyte. Especially challenging is ionization of compounds with relatively low proton affinity (PA) such as aromatic compounds. To change the course of ion-molecule reactions and enhance the performance of the IMS spectrometer, substances called dopants are introduced into the carrier gas. In this work, we present the results of studies of detection using nitrogen oxides (NOx) dopants. Three aromatic compounds, benzene, toluene, toluene diisocyanate and, for comparison, two compounds with high PA, dimethyl methylphosphonate (DMMP) and triethyl phosphate (TEP), were selected as analytes. The influence of water vapour on these analyses was also studied. Experiments were carried out with a generator of gas mixtures that allowed for the simultaneous introduction of three substances into the carrier gas. The experiments showed that the use of NOx dopants significantly decreases LODs for aromatic compounds and does not affect the detection of compounds with high PA. The water vapour significantly disturbs the detection of aromatic compounds; however, doping with NOx allows to reduce the effect of humidity. Graphical Abstract Two possible ionization mechanisms of aromatic compounds in ion mobility spectrometry: proton transfer reaction and adduct formation.

  18. Effect of isovalent dopants on photodegradation ability of ZnS nanoparticles

    NASA Astrophysics Data System (ADS)

    Khaparde, Rohini; Acharya, Smita

    2016-06-01

    Isovalent (Mn, Cd, Cu, Co)-doped-ZnS nanoparticles having size vary in between 2 to 5 nm are synthesized by co-precipitation route. Their photocatalytic activity for decoloration of Cango Red and Malachite Green dyes is tested in visible radiation under natural conditions. Structural and morphological features of the samples are investigated by X-ray diffraction, Raman spectroscopy, Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM) and UVsbnd Vis spectrometer. Single phase zinc blende structure of as-synthesized undoped and doped-ZnS is confirmed by XRD and revealed by Rietveld fitting. SEM and TEM images show ultrafine nanoparticles having size in the range of 2 to 5 nm. UV-Vis absorption spectra exhibit blue shift in absorption edge of undoped and doped ZnS as compared to bulk counterpart. The photocatalytic activity as a function of dopant concentration and irradiation time is systematically studied. The rate of de-coloration of dyes is detected by UVsbnd Vis absorption spectroscopy and organic dye mineralization is confirmed by table of carbon (TOC) study. The photocatalytic activity of Mn-doped ZnS is highest amongst all dopants; however Co as a dopant is found to reduce photocatalytic activity than pure ZnS.

  19. Deep Level Tight-Binding Model for Transition Metal Dopant States in Diamond

    NASA Astrophysics Data System (ADS)

    Kortan, Victoria; Sahin, Cuneyt; Flatté, Michael

    2012-02-01

    Diamond is a promising system for quantum information processing [1], providing the possibility of single-spin-photon entanglement, as well as the potential for high-speed spin manipulation at room temperature (such as has been demonstrated for the electronic spin associated with an NV center [2]). Ion implantation has been demonstrated for controllable positioning of NV centers; in principle other dopants could be so implanted as well. For example, transition-metal dopants could potentially be used as optically and electrically active single spin qubits [3]. Here we use a deep level tight binding model to study the electronic trends and defect wave functions of transition-metal dopants in diamond. Starting with the Green's functions of homogeneous diamond (within an spds* tight-binding model), a Koster-Slater approach is used to evaluate the defect state. This work is supported by an AFOSR MURI.[4pt] [1] A. M. Stoneham, A. H. Harker and G. W. Morley, J. Phys.: Condns. Matter 21, 364222 (2009).[0pt] [2] R. Hanson, O. Gywat and D. D. Awschalom, Phys. Rev. B. 74, 161203(r) (2006).[0pt] [3] R. Larico, et. al., Phys. Rev. B. 79, 115202 (2009).

  20. Density functional theory study of dopants in polycrystalline TiO2

    NASA Astrophysics Data System (ADS)

    Körner, Wolfgang; Elsässer, Christian

    2011-05-01

    We present a density functional theory (DFT) study of doped rutile and anatase TiO2 in which we investigate the impact of grain boundaries on the physics of atomic defects. The main goal is to obtain information about the positions of the defect levels generated by an oxygen vacancy, a titanium interstitial, cation dopants Nb, Al, and Ga, and an anion dopant N in the electronic band gap having in mind the application of TiO2 as a transparent conducting oxide (TCO) or its use in heterogeneous catalysis. Due to the known deficiency of the local density approximation (LDA) of DFT to yield accurate values for band gap energies for insulators such as TiO2, a self-interaction correction (SIC) to the LDA is employed. The main result of our study is that grain boundaries do affect the defect formation energies as well as the position and shape of the dopant-induced electronic energy levels significantly with respect to the single crystal. According to our study Nb doping may lead to n-conducting TiO2 whereas doping with N, Al, or Ga is not promising in order to achieve p-conducting TiO2. Furthermore an increase in the photoconductivity of TiO2:N and the colorlessness of TiO2:Al may be explained by our results.

  1. Dopant effects on charge transport to enhance performance of phosphorescent white organic light emitting diodes

    SciTech Connect

    Zhu, Liping; Chen, Jiangshan; Ma, Dongge

    2015-11-07

    We compared the performance of phosphorescent white organic light emitting diodes (WOLEDs) with red-blue-green and green-blue-red sequent emissive layers. It was found that the influence of red and green dopants on electron and hole transport in emissive layers leads to the large difference in the efficiency of fabricated WOLEDs. This improvement mechanism is well investigated by the current density-voltage characteristics of single-carrier devices based on dopant doped emissive layers and the comparison of electroluminescent and photoluminescence spectra, and attributed to the different change of charge carrier transport by the dopants. The optimized device achieves a maximum power efficiency, current efficiency, and external quantum efficiency of 37.0 lm/W, 38.7 cd/A, and 17.7%, respectively, which are only reduced to 32.8 lm/W, 38.5 cd/A, and 17.3% at 1000 cd/m{sup 2} luminance. The critical current density is as high as 210 mA/cm{sup 2}. It can be seen that the efficiency roll-off in phosphorescent WOLEDs can be well improved by effectively designing the structure of emissive layers.

  2. Discrete random distribution of source dopants in nanowire tunnel transistors (TFETs)

    NASA Astrophysics Data System (ADS)

    Sylvia, Somaia; Abul Khayer, M.; Alam, Khairul; Park, Hong-Hyun; Klimeck, Gerhard; Lake, Roger

    2013-03-01

    InAs and InSb nanowire (NW) tunnel field effect transistors (TFETs) require highly degenerate source doping to support the high electric fields in the tunnel region. For a target on-current of 1 μA , the doping requirement may be as high as 1 . 5 ×1020cm-3 in a NW with diameter as low as 4 nm. The small size of these devices demand that the dopants near tunneling region be treated discretely. Therefore, the effects resulting from the random distribution of dopant atoms in the source of a TFET are studied for 30 test devices. Comparing with the transfer characteristics of the same device simulated with a continuum doping model, our results show (1) a spread of I - V toward the positive gate voltage axis, (2) the same average threshold voltage, (3) an average 62% reduction in the on current, and (4) a slight degradation of the subthreshold slope. Random fluctuations in both the number and placement of dopants will be discussed. Also, as the channel length is scaled down, direct tunneling through the channel starts limiting the device performance. Therefore, a comparison of materials is also performed, showing their ability to block direct tunneling for sub-10 nm channel FETs and TFETs. This work was supported in part by the Center on Functional Engineered Nano Architectonics and the Materials, Structures and Devices Focus Center, under the Focus Center Research Program, and by the National Science Foundation under Grant OCI-0749140

  3. New cyclometalated iridium(III) complex as a phosphorescent dopant in organic light emitting devices

    NASA Astrophysics Data System (ADS)

    Ivanov, P.; Tomova, R.; Petrova, P.; Stanimirov, S.; Petkov, I.

    2014-05-01

    A new cyclometalated iridium (III) bis[2-(4-chlorophenyl)benzothiazolato-N,C2]-acetylacetonate, (Cl-bt)2Ir(acac), was synthesized and identified by 1H NMR and elemental analysis. The application was studied of the new compound as a dopant in the hole transporting layer (HTL) of the following organic light emitting diode (OLED) structure: HTL/EL/ETL, where HTL was 4,4'-bis(9H-carbazol-9-yl)biphenyl (CBP) or N,N'-bis(3-methylphenyl)-N,N'-diphenylbenzidine (TPD), incorporated in a poly(N-vinylcarbazole) (PVK) matrix; EL was an electroluminescent layer of bis(8-hydroxy-2-methylquinoline)-(4-phenylpheno-xy) aluminum (BAlq); and ETL was an electron-transporting layer of bis[2-(2-benzothiazoly) phenolato]zinc(II) (Zn(btz)2). We established that the electroluminescence spectra of the OLEDs at different dopant concentrations were basically the sum of the greenish-blue emission of BAlq and the yellowish-green emission of the Ir complex. It was also found that increasing the dopant concentration resulted in an increase in the relative electroluminescent intensity of the Ir complex emission, while that of BAlq decreased, thus a fine tuning of the OLED color was observed.

  4. Effects of Dopant Ionic Radius on Cerium Reduction in Epitaxial Cerium Oxide Thin Films

    DOE PAGES

    Yang, Nan; Orgiani, Pasquale; Di Bartolomeo, Elisabetta; ...

    2017-04-17

    The role of trivalent rare-earth dopants in ceria epitaxial films on surface ion exchange reactivity and ion conductivity has been systematically studied. Single-crystal epitaxial films with unique crystal orientation and micro-structure nature have allowed us to rule out the influence of structural defects on both transport and surface ion exchange properties. The films conductivities were larger than those reported in literature for both polycrystalline ceramic pellets and crystalline films. An increase in oxygen vacancies and Ce3+ concentration while decreasing the dopant ionic radius from La3+ to Yb3+ was observed, thus explaining the measured increased activation energy and enhanced surface reactivity.more » The more significant ability of smaller dopant ionic radius in releasing the stress strength induced by the larger Ce3+ ionic radius allows promoting the formation of oxygen vacancies and Ce3+, which are two precious species in determining the efficiency of ion transport and surface ion exchange processes. This can open new perspectives in designing ceria-based materials in tailoring functional properties, either ion migration or surface reactivity, by rational cation substitutions.« less

  5. Simulations of Ar gas-puff implosions on Z with a Xe dopant

    NASA Astrophysics Data System (ADS)

    Tangri, Varun; Giuliani, J. L.; Velikovich, A. L.; Ouart, N. D.; Dasgupta, A.; Thornhill, J. W.; Apruzese, J. P.; Harvey-Thompson, A. J.; Jones, B.; Jennings, C. A.

    2016-10-01

    A recent experiment on the Z machine at SNL indicated that the presence of a small fraction of Xe (0.8% by number in the center jet) in a Ar gas puff shot had a significant effect on the emitted K-shell radiation. In presence of the Xe dopant, the Ar K-shell yield dramatically reduced from 373 +/-9 to 129 +/-9 kJ. The peak K-shell power was also significantly lower and accompanied by two nearly equal peaks. A second shot without the Xe dopant consisted of a single peak. We present radiation-magnetohydrodynamic simulations of these shots [Z2603 (with Xe) and Z2605 (without Xe)] using the using the Mach2-TCRE code with a tabulated collisional radiative equilibrium model. Detailed numerical simulations exploring the impact of the Xe dopant on the implosion dynamics and the resultant K-shell radiation will be presented. Analysis of a time- and space resolved synthetic K-shell spectra would also be presented. Work supported by the DOE/NNSA. SNL is a multi-program laboratory operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Company, for the U.S. Department of Energy's NNSA under contract DE-AC04-94AL85000.

  6. Quantum simulation of the Hubbard model with dopant atoms in silicon.

    PubMed

    Salfi, J; Mol, J A; Rahman, R; Klimeck, G; Simmons, M Y; Hollenberg, L C L; Rogge, S

    2016-04-20

    In quantum simulation, many-body phenomena are probed in controllable quantum systems. Recently, simulation of Bose-Hubbard Hamiltonians using cold atoms revealed previously hidden local correlations. However, fermionic many-body Hubbard phenomena such as unconventional superconductivity and spin liquids are more difficult to simulate using cold atoms. To date the required single-site measurements and cooling remain problematic, while only ensemble measurements have been achieved. Here we simulate a two-site Hubbard Hamiltonian at low effective temperatures with single-site resolution using subsurface dopants in silicon. We measure quasi-particle tunnelling maps of spin-resolved states with atomic resolution, finding interference processes from which the entanglement entropy and Hubbard interactions are quantified. Entanglement, determined by spin and orbital degrees of freedom, increases with increasing valence bond length. We find separation-tunable Hubbard interaction strengths that are suitable for simulating strongly correlated phenomena in larger arrays of dopants, establishing dopants as a platform for quantum simulation of the Hubbard model.

  7. Structure-property-composition relationships in doped zinc oxides: enhanced photocatalytic activity with rare earth dopants.

    PubMed

    Goodall, Josephine B M; Illsley, Derek; Lines, Robert; Makwana, Neel M; Darr, Jawwad A

    2015-02-09

    In this paper, we demonstrate the use of continuous hydrothermal flow synthesis (CHFS) technology to rapidly produce a library of 56 crystalline (doped) zinc oxide nanopowders and two undoped samples, each with different particle properties. Each sample was produced in series from the mixing of an aqueous stream of basic zinc nitrate (and dopant ion or modifier) solution with a flow of superheated water (at 450 °C and 24.1 MPa), whereupon a crystalline nanoparticle slurry was rapidly formed. Each composition was collected in series, cleaned, freeze-dried, and then characterized using analytical methods, including powder X-ray diffraction, transmission electron microscopy, Brunauer-Emmett-Teller surface area measurement, X-ray photoelectron spectroscopy, and UV-vis spectrophotometry. Photocatalytic activity of the samples toward the decolorization of methylene blue dye was assessed, and the results revealed that transition metal dopants tended to reduce the photoactivity while rare earth ions, in general, increased the photocatalytic activity. In general, low dopant concentrations were more beneficial to having greater photodecolorization in all cases.

  8. n-Dopants Based on Dimers of Benzimidazoline Radicals: Structures and Mechanism of Redox Reactions.

    PubMed

    Zhang, Siyuan; Naab, Benjamin D; Jucov, Evgheni V; Parkin, Sean; Evans, Eric G B; Millhauser, Glenn L; Timofeeva, Tatiana V; Risko, Chad; Brédas, Jean-Luc; Bao, Zhenan; Barlow, Stephen; Marder, Seth R

    2015-07-20

    Dimers of 2-substituted N,N'-dimethylbenzimidazoline radicals, (2-Y-DMBI)2 (Y=cyclohexyl (Cyc), ferrocenyl (Fc), ruthenocenyl (Rc)), have recently been reported as n-dopants for organic semiconductors. Here their structural and energetic characteristics are reported, along with the mechanisms by which they react with acceptors, A (PCBM, TIPS-pentacene), in solution. X-ray data and DFT calculations both indicate a longer C-C bond for (2-Cyc-DMBI)2 than (2-Fc-DMBI)2 , yet DFT and ESR data show that the latter dissociates more readily due to stabilization of the radical by Fc. Depending on the energetics of dimer (D2 ) dissociation and of D2 -to-A electron transfer, D2 reacts with A to form D(+) and A(-) by either of two mechanisms, differing in whether the first step is endergonic dissociation or endergonic electron transfer. However, the D(+) /0.5 D2 redox potentials-the effective reducing strengths of the dimers-vary little within the series (ca. -1.9 V vs. FeCp2 (+/0) ) (Cp=cyclopentadienyl) due to cancelation of trends in the D(+/0) potential and D2 dissociation energy. The implications of these findings for use of these dimers as n-dopants, and for future dopant design, are discussed.

  9. Enhanced dopant solubility and visible-light absorption in Cr-N co-doped TiO2 nanoclusters

    SciTech Connect

    Chiodi, Dr Mirco; Cheney, Christine; Vilmercati, Paolo; Cavaliere, Emanuele; Mannella, Norman; Gavioli, Luca; Weitering, Harm H

    2012-01-01

    A major obstacle toward employing TiO2 as an efficient photoactive material is related to its large optical band gap, strongly limiting visible light absorption. Substitutional doping with both donors and acceptors (co-doping) potentially leads to a significant band gap reduction, but the effectiveness of the co-doping approach remains limited by the low solubility of dopants inside TiO2. Here we show that nanostructured Cr and N co-doped TiO2 thin films can be obtained by Supersonic Cluster Beam Deposition (SCBD) with a high concentration of dopants and a strongly reduced band gap. Complementary spectroscopic investigations show that doping effectively occurs into substitutional lattice sites, inducing dopant levels in the gap that are remarkably delocalized. The high surface-to-volume ratio, typical of SCBD nanostructured films, likely facilitates the dopant incorporation. The present results indicate that SCBD films are highly promising photoactive nanophase materials.

  10. Selection of dopants to enhance hydrogen diffusion rates in MgH2 and NaMgH3

    NASA Astrophysics Data System (ADS)

    Hao, Shiqiang; Sholl, David S.

    2009-04-01

    The transport properties of hydrogen in metal hydrides are crucial to the kinetics of H2 storage in these materials. Previous first-principles calculations and experiments have shown that H transport in MgH2 and NaMgH3 is dominated by charged defects. This creates the possibility of enhancing hydrogen diffusion in these materials by adding dopants that alter the population of the relevant charged defects. We describe a comprehensive set of first-principles calculations examining dopants in MgH2 and NaMgH3 for this purpose. Only a small number of elemental dopants are found to have favorable properties, but these dopants could increase the diffusivity of H by two to three orders of magnitude relative to the undoped materials.

  11. Coupling of erbium dopants to yttrium orthosilicate photonic crystal cavities for on-chip optical quantum memories

    SciTech Connect

    Miyazono, Evan; Zhong, Tian; Craiciu, Ioana; Kindem, Jonathan M.; Faraon, Andrei

    2016-01-04

    Erbium dopants in crystals exhibit highly coherent optical transitions well suited for solid-state optical quantum memories operating in the telecom band. Here, we demonstrate coupling of erbium dopant ions in yttrium orthosilicate to a photonic crystal cavity fabricated directly in the host crystal using focused ion beam milling. The coupling leads to reduction of the photoluminescence lifetime and enhancement of the optical depth in microns-long devices, which will enable on-chip quantum memories.

  12. Energy transfer to porphyrin derivative dopants in polymer light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Higgins, R. W. T.; Monkman, A. P.; Nothofer, H.-G.; Scherf, U.

    2002-01-01

    The device physics of bilayer polymer light-emitting diodes that utilize energy transfer to various porphyrin derivatives were investigated. The emissive host, α,ω-bis[N,N-di(4-methylphenyl) aminophenyl]-poly(9,9-bis(2-ethylhexyl)fluoren-2,7-diyl) (PF2/6am4), was doped to a variety of concentrations between 0.5 and 4 wt. % with 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrin zinc(II) (ZnOEP), 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrin palladium(II) (PdOEP), and 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrin platinum(II) (PtOEP). The electroluminescent devices showed a maximum external quantum efficiency (EQE) of 1.19%, 0.22%, 1.08%, and 2.75% for undoped APFO, PF2/6am4:ZnOEP, PF2/6am4:PdOEP, and PF2/6am4:PtOEP blends, respectively. We attribute this variation in performance of the blends to be a product of both the luminescence quantum yield of the dopant molecules, which we take from the literature as 0.065, 0.2, and 0.5 for ZnOEP, PdOEP, and PtOEP, respectively, and the dopant excited state lifetime. We observe that at high brightness the EQE of the doped devices falls below that of the undoped device and we attribute this high-end falloff in performance to the excited state lifetimes of the dopant molecules, which determine at which current density devices exhibit peak efficiency. Past this peak in efficiency, we propose that saturation of the dopant sites is the major factor in detrimental device performance, which has wide reaching consequences for any future design that utilizes energy transfer of dopant molecules.

  13. Quantitative measurement of active dopant density distribution in phosphorus-implanted monocrystalline silicon solar cell using scanning nonlinear dielectric microscopy

    NASA Astrophysics Data System (ADS)

    Hirose, K.; Tanahashi, K.; Takato, H.; Cho, Y.

    2017-07-01

    The performance of silicon (Si) solar cells is dependent on the active dopant distribution in emitters. Estimation of the dopant distribution in a Si solar cell fabricated by ion implantation is difficult due to the pyramidal surface texture of the emitter. Here, we investigate the active dopant distribution in a P-implanted Si solar cell using scanning nonlinear dielectric microscopy (SNDM). SNDM and dC/dz-SNDM are complementarily applied to visualize the carrier distribution in the cross section of the Si solar cell. The carrier density in the emitter is calibrated using the SNDM data obtained from Si standard samples. The results show that the dopant distribution can be described as the sum of two Gaussian functions distributed over the vertical direction of the pyramidal faces. The three-dimensional (3D) dopant distribution is estimated from the superposition of the P distributions at each pyramidal face. The estimated 3D dopant distribution is in good agreement with the SNDM measurement results.

  14. Imaging Dirac-Mass Disorder from Magnetic Dopant-Atoms in the Ferromagnetic Topological Insulator Crx(Bi0.1Sb0.9)2-x Te3 - Part I

    NASA Astrophysics Data System (ADS)

    Kim, Chung Koo; Lee, Inhee; Lee, Jinho; Billinge, Simon; Zhong, Ruidan; Schneeloch, John; Liu, Tiansheng; Tranquada, John; Gu, Genda; Davis, J. C. Seamus

    2015-03-01

    Topological insulators (TI) have a gapless surface state of Dirac fermions protected by the time reversal symmetry (TRS). However, TRS can be broken in the ferromagnetic state induced by magnetic doping. This leads to the opening of ``mass gap'' at the Dirac point. Such a gap is predicted to involve many exotic phenomena for which understanding the microscopic role of magnetic dopants is critical. But it is unknown how the spatial arrangements of the magnetic dopant atoms influence the Dirac-mass gap at the atomic scale. Here we image the locations of the magnetic (Cr) dopant atoms in the ferromagnetic TI Cr0.08(Bi0.1Sb0.9)1.92 Te3. Simultaneous visualization of the Dirac-mass gap Δ(r) reveals its intense disorder, which we demonstrate directly is related to fluctuations in n(r), the areal Cr atom density at the surface. The relationship of the surface-state Fermi wavevectors to both the correlation length and anisotropic structure of Δ(r) are found consistent with predictions for ferromagnetism mediated by the surface states.

  15. Imaging Dirac-mass disorder from magnetic dopant atoms in the ferromagnetic topological insulator Crx(Bi0.1Sb0.9)2-xTe3

    SciTech Connect

    Lee, Inhee; Kim, Chung Koo; Lee, Jinho; Billinge, Simon J. L.; Zhong, Ruidan D.; Schneeloch, John A.; Liu, Tiansheng S.; Valla, Tonica; Tranquada, John M.; Gu, Genda D.; Davis, J. C. Séamus

    2015-01-20

    To achieve and use the most exotic electronic phenomena predicted for the surface states of 3D topological insulators (TIs), it is necessary to open a “Dirac-mass gap” in their spectrum by breaking time-reversal symmetry. Use of magnetic dopant atoms to generate a ferromagnetic state is the most widely applied approach. However, it is unknown how the spatial arrangements of the magnetic dopant atoms influence the Dirac-mass gap at the atomic scale or, conversely, whether the ferromagnetic interactions between dopant atoms are influenced by the topological surface states. Here we image the locations of the magnetic (Cr) dopant atoms in the ferromagnetic TI Cr₀.₀₈(Bi₀.₁Sb₀.₉)₁.₉₂Te₃. Simultaneous visualization of the Dirac-mass gap Δ(r) reveals its intense disorder, which we demonstrate is directly related to fluctuations in n(r), the Cr atom areal density in the termination layer. We find the relationship of surface-state Fermi wavevectors to the anisotropic structure of Δ(r) not inconsistent with predictions for surface ferromagnetism mediated by those states. Moreover, despite the intense Dirac-mass disorder, the anticipated relationship Δ(r)∝n(r) is confirmed throughout and exhibits an electron–dopant interaction energy J* = 145 meV·nm². In addition, these observations reveal how magnetic dopant atoms actually generate the TI mass gap locally and that, to achieve the novel physics expected of time-reversal symmetry breaking TI materials, control of the resulting Dirac-mass gap disorder will be essential.

  16. Molecular Electrical Doping of Organic Semiconductors: Fundamental Mechanisms and Emerging Dopant Design Rules.

    PubMed

    Salzmann, Ingo; Heimel, Georg; Oehzelt, Martin; Winkler, Stefanie; Koch, Norbert

    2016-03-15

    Today's information society depends on our ability to controllably dope inorganic semiconductors, such as silicon, thereby tuning their electrical properties to application-specific demands. For optoelectronic devices, organic semiconductors, that is, conjugated polymers and molecules, have emerged as superior alternative owing to the ease of tuning their optical gap through chemical variability and their potential for low-cost, large-area processing on flexible substrates. There, the potential of molecular electrical doping for improving the performance of, for example, organic light-emitting devices or organic solar cells has only recently been established. The doping efficiency, however, remains conspicuously low, highlighting the fact that the underlying mechanisms of molecular doping in organic semiconductors are only little understood compared with their inorganic counterparts. Here, we review the broad range of phenomena observed upon molecularly doping organic semiconductors and identify two distinctly different scenarios: the pairwise formation of both organic semiconductor and dopant ions on one hand and the emergence of ground state charge transfer complexes between organic semiconductor and dopant through supramolecular hybridization of their respective frontier molecular orbitals on the other hand. Evidence for the occurrence of these two scenarios is subsequently discussed on the basis of the characteristic and strikingly different signatures of the individual species involved in the respective doping processes in a variety of spectroscopic techniques. The critical importance of a statistical view of doping, rather than a bimolecular picture, is then highlighted by employing numerical simulations, which reveal one of the main differences between inorganic and organic semiconductors to be their respective density of electronic states and the doping induced changes thereof. Engineering the density of states of doped organic semiconductors, the Fermi

  17. Dopants diffusion in a thin film SIMOX structure and its computer simulation

    NASA Astrophysics Data System (ADS)

    Zuoyu, Shi; Chenglu, Lin; Wenhua, Zhu; Shichang, Zou; Hemment, P. L. F.

    1994-02-01

    Oxygen ions with energy 90 or 200 keV and doses of 1.2 or 1.8×10 18 O +/cm 2 respectively were implanted into p-type (100) single crystal wafers followed by annealing at 1300°C for 5 h in a nitrogen environment to form a SIMOX (Separation by IMplanted OXygen) structure. During implantation the substrates were heated and the temperature was maintained at 650°C. 50 and 100 keV As + ions with doses ranging from 10 14 to 10 16/cm 2 were implanted into the SIMOX substrates. After implantation the samples were annealed at 900°C for 30 min or at 1100 or 1200°C for 15 or 20 s. Secondary ion mass spectroscopy (SIMS), Rutherford backscattering and channeling (RBS/C), automatic spreading resistance (ASR), and stripping Hall measurement were used to characterize the electrical properties of the SIMOX samples and the diffusion behavior of the arsenic atoms during the anneal. A computer program simulating dopant diffusion in SIMOX (SODDIS) was implemented, this being based upon the well-known SUPREM III program. Computer simulation and experiment showed (i) the buried SiO 2 layer in SIMOX acts as a very good barrier to dopant diffusion, (ii) the diffusion of arsenic in SIMOX is more rapid than in bulk silicon, and (iii) the electrical activity of the dopant in thin film SIMOX samples is dependent upon the implantation and anneal conditions, and also upon the defects present in the SIMOX material.

  18. The Effect of Rare Earth Dopants in Crystal Structure of Bi-2212 Superconductor

    NASA Astrophysics Data System (ADS)

    Suharta, W. G.; Widagda, IGA.; Putra, K.; Suyanto, H.

    2017-03-01

    Bi2Sr2CaCu2O8+∂ samples have been successfully synthesized by doping rare earth (RE) variations using wet-mixing method. Samples calcined at 600°C for 3 hours and sintered at 850°C for 10 hours. The purpose of research is to determine the effect of the RE dopant on the microscopic structure of BSCRECO superconductors. Therefore, the research was conducted characterization by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscope (SEM). Measurements with XRD could be carried out and crystal system of Bi2Sr2CaCu2O8+∂ with rare earth (RE) dopants could be determined clearly. Generally, crystallization has occurred very well demonstrated by the diffraction peaks are sharp, which is dominated by the emergence of Bi-2212 phase. Search match results of XRD spectrum showed Bi2Sr2CuOx (2201) and Ca2CuO3 (21) as an impurity phase with small intensity. Also, that is showing volume fraction from 85 to 92% and orthorombic value for all samples from 5 to 7%. The effect of RE dopants resulted a shift angle 2θ and changes in the volume of the unit cells of each sample. The value of the unit cell volume of the largest to smallest is BS(CN)CO, BS(CNG)CO, BS(CNEG)CO, BS(CNE)CO, BS(CG)CO, BS(CEG)CO and BS(CE)CO. Measurement with FTIR showed the bending vibration absorption by CO3 2- in the wavelength range between 1500 and 1520 cm-1, vibration of M-O between 420 and 650 cm-1, the complex formation of BSCCO in the wavelength range between 1690 and 1700 cm-1. Measurement with SEM showed rod shape with particle size in hundreds nanometer.

  19. Tunable emission of Cu (Mn)-doped ZnInS quantum dots via dopant interaction.

    PubMed

    Zhu, Jiatao; Mei, Shiliang; Yang, Wu; Zhang, Guilin; Chen, Qiuhang; Zhang, Wanlu; Guo, Ruiqian

    2017-11-15

    In this work, transition metal ion- doped zinc-based quantum dots (QDs) are synthesized via a greener controllable method to avoid the toxicity of the traditional cadmium-based QDs and broaden the tunable emission. Herein, the tunable emission of Cu-doped ZnInS/ZnS core-shell QDs (Cu:ZnInS/ZnS) can cover from 500 to 620nm by varying the Cu dopant concentration from 1 to 20% and the maximum quantum yield can reach 49.8%. Based on the single-doped QDs, Cu,Mn co-doped ZnInS/ZnS core-shell QDs (Cu,Mn:ZnInS/ZnS) with a photoluminance (PL) quantum yield of 30.4% are obtained. All the as-synthesized QDs have the zinc blende structure and the average size is about 3.55nm. Besides, the interaction mechanism between the Cu and Mn dopant luminescence centers is proposed in this work, which is rarely investigated in the previous report. Diffusion priority and energy transfer between these two dopants are supposed to play an important role in the co-doped QDs and Cu ions could affect the splitting of Mn d states. Color coordinates of these doped QDs show the line-tunability from (0.200, 0.397) to (0.408, 0.508) on the Commission Internationale de L'Eclairage (CIE) chromatic diagram, showing a promising potential in high-quality white light output by integration of these QDs with blue chips. Copyright © 2017 Elsevier Inc. All rights reserved.

  20. Ab initio modeling of vacancies, antisites, and Si dopants in ordered InGaAs

    NASA Astrophysics Data System (ADS)

    Wang, Jingyang; Lukose, Binit; Thompson, Michael O.; Clancy, Paulette

    2017-01-01

    In0.53Ga0.47As, a III-V compound semiconductor with high electron mobility, is expected to bring better performance than silicon in next-generation n-type MOSFET devices. However, one major challenge to its wide scale adoption is the difficulty of obtaining high enough dopant activation. For Si-doped InGaAs, the best current experimental result, involving 10 min of furnace annealing at temperatures above 700 °C, yields a free electron concentration of 1.4 ×1019 cm-3, a value that still falls short of requirement for practical applications. In this paper, we investigate the origin of low dopant activation in InGaAs by calculating formation energies for a wide variety of single point defects (Si substutionals, Si tetrahedral interstitials, vacancies, and antisites) in Si-doped In0.5Ga0.5As in a CuAu-I type crystal structure. We find that (1) a high electron concentration can only be achieved under In/Ga-poor growth conditions, while As-poor conditions inhibit n-type doping; and (2) in heavily n-doped samples, cation vacancies VIn/Ga-3 contribute the most to the compensation of excess Si donors via the Si III - VIII mechanism (III = In/Ga), thus becoming the limiting factor to higher dopant activation. Under the most favorable growth conditions for n-doping, we find the maximum carrier concentration to be 5.2 ×1018 cm-3 under thermal equilibrium, within an order of magnitude of the best experimental value.

  1. Characterisation of active dopants in boron-doped self-assembled silicon nanostructures

    NASA Astrophysics Data System (ADS)

    Puthen Veettil, Binesh; Zhang, Tian; Chin, Robert Lee; Jia, Xuguang; Nomoto, Keita; Yang, Terry Chien-Jen; Lin, Ziyun; Wu, Lingfeng; Rexiati, Reyifate; Gutsch, Sebastian; Conibeer, Gavin; Perez-Würfl, Ivan

    2016-10-01

    Doping of silicon nanocrystals has become an important topic due to its potential to enable the fabrication of environmentally friendly and cost-effective optoelectronic and photovoltaic devices. However, doping of silicon nanocrystals has been proven difficult and most of the structural and electronic properties are still not well understood. In this work, the intrinsic and boron-doped self-assembled silicon nanocrystals were prepared and mainly characterised by the transient current method to study the behaviour of charge carriers in these materials. Our experiments quantified the amount of electrically active boron dopants that contributed to charge transport. From this, the boron doping efficiency in the nanocrystal superlattice was estimated.

  2. A Semiconductor Material And Method For Enhancing Solubility Of A Dopant Therein

    DOEpatents

    Sadigh, Babak; Lenosky, Thomas J.; Diaz de la Rubia, Tomas; Giles, Martin; Caturla, Maria-Jose; Ozolins, Vidvuds; Asta, Mark; Theiss, Silva; Foad, Majeed; Quong, Andrew

    2005-03-29

    A method for enhancing the equilibrium solubility of boron ad indium in silicon. The method involves first-principles quantum mechanical calculations to determine the temperature dependence of the equilibrium solubility of two important p-type dopants in silicon, namely boron and indium, under various strain conditions. The equilibrium thermodynamic solubility of size-mismatched impurities, such as boron and indium in silicon, can be raised significantly if the silicon substrate is strained appropriately. For example, for boron, a 1% compressive strain raises the equilibrium solubility by 100% at 1100.degree. C.; and for indium, a 1% tensile strain at 1100.degree. C., corresponds to an enhancement of the solubility by 200%.

  3. Semiconductor material and method for enhancing solubility of a dopant therein

    DOEpatents

    Sadigh, Babak; Lenosky, Thomas J.; Rubia, Tomas Diaz; Giles, Martin; Caturla, Maria-Jose; Ozolins, Vidvuds; Asta, Mark; Theiss, Silva; Foad, Majeed; Quong, Andrew

    2003-09-09

    A method for enhancing the equilibrium solubility of boron and indium in silicon. The method involves first-principles quantum mechanical calculations to determine the temperature dependence of the equilibrium solubility of two important p-type dopants in silicon, namely boron and indium, under various strain conditions. The equilibrium thermodynamic solubility of size-mismatched impurities, such as boron and indium in silicon, can be raised significantly if the silicon substrate is strained appropriately. For example, for boron, a 1% compressive strain raises the equilibrium solubility by 100% at 1100.degree. C.; and for indium, a 1% tensile strain at 1100.degree. C., corresponds to an enhancement of the solubility by 200%.

  4. Incorporation of the dopants Si and Be into GaAs nanowires

    NASA Astrophysics Data System (ADS)

    Hilse, M.; Ramsteiner, M.; Breuer, S.; Geelhaar, L.; Riechert, H.

    2010-05-01

    We studied the doping with Si and Be of GaAs nanowires (NWRs) grown by molecular beam epitaxy. Regarding the NW morphology, no influence was observed for Si doping but high Be doping concentrations cause a kinking and tapering of the NWRs. We investigated local vibrational modes by means of resonant Raman scattering to determine the incorporation sites of the dopant atoms. For Si doping, both donors on Ga sites and acceptors on As sites have been observed. Be was found to be incorporated as an acceptor on Ga sites. However, at high doping concentration, Be is also incorporated on interstitial sites.

  5. Impact of Random Dopant Fluctuation on Size-Dependence of Contact Resistance

    NASA Astrophysics Data System (ADS)

    Matsuzawa, Kazuya

    2011-12-01

    Reducing the size of semiconductor devices causes contact in deca-nano size. Substantial fluctuation of contact resistance is anticipated owing to the reduction of impurity atoms in the contact holes. In this study, the impact of the random dopant fluctuation on the contact resistance is revealed by three-dimensional device simulation with a Schottky contact model. The standard deviation of the contact resistance could become 50%, dominated by the number of impurity atoms in the depletion layer formed by the Schottky barrier. The average value of the contact resistance could increase as the impurity concentration decreases because of the reduction of the tunneling path.

  6. Extending the Lifetime of Perovskite Solar Cells using a Perfluorinated Dopant.

    PubMed

    Salado, Manuel; Ramos, F Javier; Manzanares, Valentin M; Gao, Peng; Nazeeruddin, Mohammad Khaja; Dyson, Paul J; Ahmad, Shahzada

    2016-09-22

    The principle limitation of perovskite solar cells is related to their instability and, hence, their limited lifetime. Herein, we employ an imidazolium iodide dopant, 1-methyl-3-(1H,1H,2H,2H-nonafluorohexyl)-imidazolium iodide, containing a perfluorous appendage, which leads to prolonged (unencapsulated, under Ar atmosphere) device activities exceeding 100 days without compromising the power conversion efficiency and other photovoltaic parameters. The extended lifetime of the device can be attributed, at least in part, to the hydrophobic nature of the imidazolium iodide salt. The functionalization of the perovskite material was found to have negligible influence on the perovskite crystal structure.

  7. First principles investigations of single dopants in diamond and silicon carbide

    NASA Astrophysics Data System (ADS)

    Hu, Wenhao

    In the most recent two decades, the development of impurity controls with ultra-high precision in semiconductors motivates people to put more and more attentions on the solotronic devices, whose properties depend on one or a few dopants. One of the most promising applications of solotronic device is the qubit in quantum computing. In the procedure of exploring qubit candidates, the most straightforward challenges we need face include that the qubit must be highly isolated and can be initialized/manipulated efficiently with high fidelities. It has been proved that qubits based on single defects have excellent performances as quits. For instance, the NV center in diamond forms a ground spin triplet which can be manipulated at room temperature with electromagnetic fields. This work focuses on searching for new single defects as qubit candidates with density functional theory. Lanthanides element possesses excellent optical characteristics and extremely long nuclear coherence time. Therefore, combining it into the diamond platform can be possible design for integrated quantum information processing devices in the future. To investigate the stability of lanthanides dopants in the diamond matrix, the formation energies of charge states of complexes are calculated. The broadening of Eu(III) peak in the photoluminescence spectrum can be verified according to the existence of more than stable configuration and steady 4f electron occupation. In the case of transition-metal dopant in the silicon carbide, it is found that both silicon and carbon substituted nickels in 3C-SiC shows a magnetic-antimagnetic transition under applied strains. The virtual hopping rate of electrons strongly depends on the distance between the spin pair residing in the nickel and dangling bonds. Therefore, the Heisenberg exchange coupling between them can be adjusted subtly by controlling the external strain. According to the spin Hamiltonian of the defect, the spin state can be manipulated

  8. DETERMINATION OF OXALATE ION DOPANT LEVEL IN POLYPYRROLE USING FT-IR.

    PubMed

    Miller, Eric T; Benally, Kristal J; GreyEyes, Shawn D; McKenzie, Jason T

    A pellet method using standard addition and FT-IR was used to estimate oxalate ion doping levels in electrosynthesized polypyrrole. The method is useful for materials where removal of analyte from an insoluble material is problematic. Here, electrosynthesized oxalate doped polypyrrole is dispersed in potassium bromide. Spikes of sodium oxalate are added and the mixtures pressed into pellets. The oxalate carbonyl absorption peak is then used to quantify the amount of oxalate present in the polypyrrole. The mass fraction of oxalate dopant in polypyrrole was determined to be 0.4 ± 0.1 % and coincides with the original synthesis solution composition.

  9. Spin on Dopants for High-Performance Single-Crystal Silicon Transistors on Flexible Plastic Substrates

    DTIC Science & Technology

    2005-03-23

    Lett. 84, 5398 s2004d. 6Y. Sun and J. A. Rogers, Nano Lett. 4, 1953 s2004d; Y. Sun , D.-Y. Khang , F. Hua, K. Hurley, R. G. Nuzzo, and J. A. Rogers...York, 1981d. 11T. Sekitani, Y. Kato, S . Iba, H. Shinaoka, and T . Someya, Appl. Phys. Lett. 86, 073511 s2005d; S . H. Won, J. K. Chung, C. B. Lee, H. C...Spin on dopants for high-performance single-crystal silicon transistors on flexible plastic substrates Z.- T . Zhu, E. Menard, K. Hurley, R. G. Nuzzo

  10. Nondestructive method for quantifying thallium dopant concentrations in CsI:Tl crystals.

    PubMed

    Miller, Stuart R; Ovechkina, Elena E; Bennett, Paul; Brecher, Charles

    2013-12-01

    We report a quantitative method for using X-ray fluorescence (XRF) to nondestructively measure the true content of Tl dopant in CsI:Tl scintillator crystals. The instrument is the handheld LeadTracer™, originally developed at RMD Instruments for measuring Pb concentration in electronic components. We describe both the measurement technique and specific findings on how changes in crystal size and growth parameters affect Tl concentration. This method is also applicable to numerous other activator ions important to scintillators, such as Ce(3+) and Eu(2+). © 2013 Elsevier Ltd. All rights reserved.

  11. Temperature dependence of terahertz optical transitions from boron and phosphorus dopant impurities in silicon

    NASA Astrophysics Data System (ADS)

    Lynch, S. A.; Townsend, P.; Matmon, G.; Paul, D. J.; Bain, M.; Gamble, H. S.; Zhang, J.; Ikonic, Z.; Kelsall, R. W.; Harrison, P.

    2005-09-01

    There has been considerable interest in using impurity dopants in silicon, such as boron and phosphorus, since it was demonstrated that such materials can show emission in the THz region of the electromagnetic spectrum. The measured temperature dependence of these transitions in this letter shows that the most optimistic maximum operating temperature of such an impurity-based laser is 90 K. In a real device with current flowing and associated Joule heating, the actual operating range is likely to be much narrower and it is therefore unlikely that such a device would have a maximum operating temperature above 40 K.

  12. Enhancing ionic conductivity of bulk single-crystal yttria-stabilized zirconia by tailoring dopant distribution

    SciTech Connect

    Lee, E.; Prinz, F. B.; Cai, W.

    2011-02-11

    We present an ab initio–based kinetic Monte Carlo model for ionic conductivity in single-crystal yttria-stabilized zirconia. Ionic interactions are taken into account by combining density functional theory calculations and the cluster expansion method and are found to be essential in reproducing the effective activation energy observed in experiments. The model predicts that the effective energy barrier can be reduced by 0.15–0.25 eV by arranging the dopant ions into a superlattice.

  13. Substrate heating and emitter dopant effects in laser-annealed solar cells

    NASA Astrophysics Data System (ADS)

    Young, R. T.; Wood, R. F.; Christie, W. H.; Jellison, G. E., Jr.

    1981-08-01

    Experimental evidence is presented to demonstrate that substrate heating during pulsed-laser annealing (PLA) of ion-implanted silicon can significantly improve the electrical properties of the laser-recrystallized region, due to regrowth velocity reduction. Use of the optimum PLA condition shows qualitative agreement with theoretical predictions in that (1) the open-circuit voltage and fill factor of ion-implanted, laser-annealed solar cells are improved by the increase of emitter dopant concentrations, while (2) the short-circuit current remains fairly constant.

  14. Substitutional Co dopant on the GaAs(110) surface: A first principles study

    NASA Astrophysics Data System (ADS)

    Fang, Zhou; Yi, Zhijun

    2016-12-01

    Using the first principles ground state method, the electronic properties of single Co dopant replacing one Ga atom on the GaAs(110) surface are studied. Our calculated local density of states (LDOS) at Co site presents several distinct peaks above the valence band maximum (VBM), and this agrees with recent experiments. Moreover, the calculated STM images at bias voltages of 2 eV and -2 eV also agree with experiments. We discussed the origin of Co impurity induced distinct peaks, which can be characterized with the hybridization between Co d orbitals and p-like orbitals of surface As and Ga atoms.

  15. Perovskite Solar Cells Employing Dopant-Free Organic Hole Transport Materials with Tunable Energy Levels.

    PubMed

    Liu, Yongsheng; Hong, Ziruo; Chen, Qi; Chen, Huajun; Chang, Wei-Hsuan; Yang, Yang Michael; Song, Tze-Bin; Yang, Yang

    2016-01-20

    Conjugated small-molecule hole-transport materials (HTMs) with tunable energy levels are designed and synthesized for efficient perovskite solar cells. A champion device with efficiency of 16.2% is demonstrated using a dopant-free DERDTS-TBDT HTM, while the DORDTS-DFBT-HTM-based device shows an inferior performance of 6.2% due to its low hole mobility and unmatched HOMO level with the valence band of perovskite film. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  16. Optimizing the Dopant and Carrier Concentration of Ca5Al2Sb6 for High Thermoelectric Efficiency

    PubMed Central

    Yan, Yuli; Zhang, Guangbiao; Wang, Chao; Peng, Chengxiao; Zhang, Peihong; Wang, Yuanxu; Ren, Wei

    2016-01-01

    The effects of doping on the transport properties of Ca5Al2Sb6 are investigated using first-principles electronic structure methods and Boltzmann transport theory. The calculated results show that a maximum ZT value of 1.45 is achieved with an optimum carrier concentration at 1000 K. However, experimental studies have shown that the maximum ZT value is no more than 1 at 1000 K. By comparing the calculated Seebeck coefficient with experimental values, we find that the low dopant solubility in this material is not conductive to achieve the optimum carrier concentration, leading a smaller experimental value of the maximum ZT. Interestingly, the calculated dopant formation energies suggest that optimum carrier concentrations can be achieved when the dopants and Sb atoms have similar electronic configurations. Therefore, it might be possible to achieve a maximum ZT value of 1.45 at 1000 K with suitable dopants. These results provide a valuable theoretical guidance for the synthesis of high-performance bulk thermoelectric materials through dopants optimization. PMID:27406178

  17. Simple dopant-free hole-transporting materials with p-π conjugated structure for stable perovskite solar cells

    NASA Astrophysics Data System (ADS)

    Sun, Mengna; Liu, Xueyuan; Zhang, Fei; Liu, Hongli; Liu, Xicheng; Wang, Shirong; Xiao, Yin; Li, Dongmei; Meng, Qingbo; Li, Xianggao

    2017-09-01

    Two simple hole-transporting materials, Me-QTPA and Me-BPZTPA, which consist of p-π conjugated structure, have been synthesized and studied in solid-state perovskite solar cells. Me-QTPA and Me-BPZTPA show outstanding thermal stabilities and appropriate HOMO levels; in addition, these two materials show wide band gaps, thus they can block the electron transport and hence suppress the carrier recombination. The solution-processed CH3NH3PbI3-based device using dopant-free Me-QTPA and Me-BPZTPA can achieve a power conversion efficiency of 9.07% and 8.16%, respectively. The perovskite solar cells with dopant-free Me-QTPA show better performance than the cells with dopant-free spiro-OMeTAD, especially in long-term stability. The power conversion efficiency for the perovskite solar cells with dopant-free Me-QTPA remains almost constant after 600 h. The dopant-free Me-QTPA layer shows strong hydrophobicity with a contact angle of 101.6° to water, which indicates that Me-QTPA has a promising long-term stability at room temperature.

  18. Dopant-specific unzipping of carbon nanotubes for intact crystalline graphene nanostructures

    PubMed Central

    Lim, Joonwon; Narayan Maiti, Uday; Kim, Na-Young; Narayan, Rekha; Jun Lee, Won; Sung Choi, Dong; Oh, Youngtak; Min Lee, Ju; Yong Lee, Gil; Hun Kang, Seok; Kim, Hyunwoo; Kim, Yong-Hyun; Ouk Kim, Sang

    2016-01-01

    Atomic level engineering of graphene-based materials is in high demand to enable customize structures and properties for different applications. Unzipping of the graphene plane is a potential means to this end, but uncontrollable damage of the two-dimensional crystalline framework during harsh unzipping reaction has remained a key challenge. Here we present heteroatom dopant-specific unzipping of carbon nanotubes as a reliable and controllable route to customized intact crystalline graphene-based nanostructures. Substitutional pyridinic nitrogen dopant sites at carbon nanotubes can selectively initiate the unzipping of graphene side walls at a relatively low electrochemical potential (0.6 V). The resultant nanostructures consisting of unzipped graphene nanoribbons wrapping around carbon nanotube cores maintain the intact two-dimensional crystallinity with well-defined atomic configuration at the unzipped edges. Large surface area and robust electrical connectivity of the synergistic nanostructure demonstrate ultrahigh-power supercapacitor performance, which can serve for AC filtering with the record high rate capability of −85° of phase angle at 120 Hz. PMID:26796993

  19. Electrical properties of tin-doped zinc oxide nanostructures doped at different dopant concentrations

    NASA Astrophysics Data System (ADS)

    Nasir, M. F.; Zainol, M. N.; Hannas, M.; Mamat, M. H.; Rahman, S. A.; Rusop, Mohamad

    2016-07-01

    This project has been focused on the electrical and optical properties respectively on the effect of Tin doped zinc oxide (ZnO) thin films at different dopant concentrations. These thin films were doped with different Sn dopant concentrations at 1 at%, 2 at%, 3 at%, 4 at% and 5 at% was selected as the parameter to optimize the thin films quality while the annealing temperature is fixed 500 °C. Sn doped ZnO solutions were deposited onto the glass substrates using sol-gel spin coating method. This project was involved with three phases, which are thin films preparation, deposition and characterization. The thin films were characterized using Current Voltage (I-V) measurement and ultraviolet-visible-near-infrared (UV-vis-NIR) spectrophotometer (Perkin Elmer Lambda 750) for electrical properties and optical properties. The electrical properties show that the resistivity is the lowest at 4 at% Sn doping concentration with the value 3.08 × 103 Ωcm-1. The absorption coefficient spectrum obtained shows all films exhibit very low absorption in the visible (400-800nm) and near infrared (NIR) (>800nm) range but exhibit high absorption in the UV range.

  20. Effect of Dopants on the Adsorption of Carbon Dioxide on Ceria Surfaces

    DOE PAGES

    Li, Meijun; Tumuluri, Uma; Wu, Zili; ...

    2015-09-25

    Here, high-surface-area nanosized CeO2 and M-doped CeO2 (M=Cu, La, Zr, and Mg) prepared by a surfactant-templated method were tested for CO2 adsorption. Cu, La, and Zr are doped into the lattice of CeO2, whereas Mg is dispersed on the CeO2 surface. The doping of Cu and La into CeO2 leads to an increase of the CO2 adsorption capacity, whereas the doping of Zr has little or no effect. The addition of Mg causes a decrease of the CO2 adsorption capacity at a low Mg content and a gradual increase at a higher content. The CO2 adsorption capacity follows the sequencemore » Cu-CeO2>La-CeO2>Zr-CeO2≈CeO2>Mg-CeO2 at low dopant contents, in line with the relative amount of defect sites in the samples. It is the defect sites on the surface, not in the bulk of CeO2, modified by the dopants that play the vital role in CO2 chemisorption. Lastly, the role of surface oxygen vacancies is further supported by an in situ IR spectroscopic study of the surface chemistry during CO2 adsorption on the doped CeO2.« less

  1. Anomalous behaviour of dopants in atmospheric pressure MOVPE of InP

    NASA Astrophysics Data System (ADS)

    Cole, S.; Evans, J. S.; Harlow, M. J.; Nelson, A. W.; Wong, S.

    1988-12-01

    The doping level of p-type InP doped with Zn or Cd, incorporated into various structures, has been investigated as a function of the gaseous ambient to which the structure is exposed during cooling from typical MOVPE growth temperatures. It is found that the doping level is strongly dependent on this ambient. If AsH 3 is present the doping level is lower by up to an order of magnitude than if PH 3 is used, which in turn gives a doping level lower by up to a factor of two than H 2 alone. Both MOVPE grown epilayers and Czochralski grown bulk crystals have been studied and found to behave similarly. SIMS experiments show that this is due to electrical deactivation rather than loss of the dopant species itself. n-Type InP and n- or p-type GaAs do not appear to be affected. Significant quantities of atomic H are found in samples exposed to the hydrides during cooling, consistent with their pyrolysis being catalysed by the semiconductor surface. The anomalous doping level phenomena are discussed in terms of a model involving deactivation of the dopant by complex formation with H, as observed by Johnson et al. in GaAs exposed to a hydrogen plasma.

  2. Interactions between Mn dopant and oxygen vacancy for insulation performance of BaTiO3

    NASA Astrophysics Data System (ADS)

    Chikada, Shunsuke; Kubota, Teppei; Honda, Atsushi; Higai, Shin'ichi; Motoyoshi, Yasuhiro; Wada, Nobuyuki; Shiratsuyu, Kosuke

    2016-10-01

    We performed first-principles calculations and electron spin resonance (ESR) measurements on Mn-doped perovskite BaTiO3 (BT) ceramics in order to investigate the interactions between Mn dopant and O vacancy (VO). We discovered the following two. First, VOs are stabilized at the nearest neighbor O site of Mn at a Ti site and this results in the suppression of VO diffusion. Second, electrons generated by the formation of VOs are trapped in unoccupied Mn-3d orbitals in the BT bandgap. This indicates that the valence state of Mn changes according to the VO density. We synthesized Mn-doped BT by varying the partial pressure of O2 gas and examined the Mn valence states with ESR measurements. We successfully observed that the majority type of Mn ions (2+, 3+, and 4+) depends on O2 gas pressure of the firing atmosphere. According to these theoretical and experimental investigations, we concluded that Mn dopants have two effects, i.e., VO and electron carrier trapping. Moreover, the mechanisms of Mn doping in BT improved the insulation resistance, and the reliability of BT-based ceramic capacitors/condensers were thoroughly examined.

  3. Effects of dopants on the biomechanical properties of conducting polymer films on platinum electrodes.

    PubMed

    Baek, Sungchul; Green, Rylie A; Poole-Warren, Laura A

    2014-08-01

    Conducting polymers have often been described in literature as a coating for metal electrodes which will dampen the mechanical mismatch with neural tissue, encouraging intimate cell interactions. However, there is very limited quantitative analysis of conducting polymer mechanics and the relation to tissue interactions. This article systematically analyses the impact of coating platinum (Pt) electrodes with the conducting polymer poly(ethylene dioxythiophene) (PEDOT) doped with a series of common anions which have been explored for neural interfacing applications. Nanoindentation was used to determine the coating modulus and it was found that the polymer stiffness increased as the size of the dopant ion was increased, with PEDOT doped with polystyrene sulfonate (PSS) having the highest modulus at 3.2 GPa. This was more than double that of the ClO4 doped PEDOT at 1.3 GPa. Similarly, the electrical properties of these materials were shown to have a size dependent behavior with the smaller anions producing PEDOT films with the highest charge transfer capacity and lowest impedance. Coating stiffness was found to have a negligible effect on in vitro neural cell survival and differentiation, but rather polymer surface morphology, dopant toxicity and mobility is found to have the greatest impact.

  4. Electrical properties of tin-doped zinc oxide nanostructures doped at different dopant concentrations

    SciTech Connect

    Nasir, M. F. Zainol, M. N. Hannas, M.; Mamat, M. H. Rusop, Mohamad; Rahman, S. A.

    2016-07-06

    This project has been focused on the electrical and optical properties respectively on the effect of Tin doped zinc oxide (ZnO) thin films at different dopant concentrations. These thin films were doped with different Sn dopant concentrations at 1 at%, 2 at%, 3 at%, 4 at% and 5 at% was selected as the parameter to optimize the thin films quality while the annealing temperature is fixed 500 °C. Sn doped ZnO solutions were deposited onto the glass substrates using sol-gel spin coating method. This project was involved with three phases, which are thin films preparation, deposition and characterization. The thin films were characterized using Current Voltage (I-V) measurement and ultraviolet-visible-near-infrared (UV-vis-NIR) spectrophotometer (Perkin Elmer Lambda 750) for electrical properties and optical properties. The electrical properties show that the resistivity is the lowest at 4 at% Sn doping concentration with the value 3.08 × 10{sup 3} Ωcm{sup −1}. The absorption coefficient spectrum obtained shows all films exhibit very low absorption in the visible (400-800 nm) and near infrared (NIR) (>800 nm) range but exhibit high absorption in the UV range.

  5. Origin of electrolyte-dopant dependent sulfur poisoning of SOFC anodes.

    PubMed

    Zeng, ZhenHua; Björketun, Mårten E; Ebbesen, Sune; Mogensen, Mogens B; Rossmeisl, Jan

    2013-05-14

    The mechanisms governing the sulfur poisoning of the triple phase boundary (TPB) of Ni-XSZ (X2O3 stabilized zirconia) anodes have been investigated using density functional theory. The calculated sulfur adsorption energies reveal a clear correlation between the size of the cation dopant X(3+) and the sulfur tolerance of the Ni-XSZ anode; the smaller the ionic radius, the higher the sulfur tolerance. The mechanistic study shows that the size of X(3+) strongly influences XSZ's surface energy, which in turn determines the adhesion of Ni to XSZ. The Ni-XSZ interaction has a direct impact on the Ni-S interaction and on the relative stability of reconstructed and pristine Ni(100) facets at the TPB. Together, these two effects control the sulfur adsorption on the Ni atoms at the TPB. The established relationships explain experimentally observed dopant-dependent anode performances and provide a blueprint for the future search for and preparation of highly sulfur tolerant anodes.

  6. Effect of dopant ions on piezo-response of polyaniline-poly(vinylidine flouride) blends

    NASA Astrophysics Data System (ADS)

    Radhakrishnan, S.; Kar, Swarendu B.

    2002-11-01

    Electromechanical sensors and actuators are important for robotic and aerospace applications. Among various material, poly(vinylidene fluoride) ir its co-polymers are known to exhibit high piezosensitivity. However, due to their higher electrical resistivity the input impedance of subsequent signal processign circuits is required to be very high. A novel technique to decrease the impedance would be blending PVDF with conducting polyaniline (PANI) but without affecting the piezosensitivyt of PVDF. Polyaniline (PANI) was synthesized by well known standard chemical route using dopants HCl and dodecyl benzene sulfonic acid. These PANI powder were blended with PVDF which was first dissolved in DMAc at 50 degrees C to which were added requisite amounts of two types of PANI ranging from 2 to 25 wt percent, stirred for 24 hours to form a homogeneous mixture which was cast in glass petri-dish, followed by complete solvent evaporation at 50 degrees C and then drying under vacuum for 24 hours to give films of PANI-PVDF blends. The piezo-sensitivity of these blends was measured before and after poling in electrical field. The sensitivity factor was dependent on the composition, type of dopant as well as the electric polarization of the blend. The HCl doped PANI blends in PVDF were highly piezo-sensitive than other blend compositions. These various results have been explained on the basis of compatibility, discrete domain formation, nonlinear conduction process for charge transport, orientation of dipoles, and trapping of space charge at inter-domain sites.

  7. Dopant-specific unzipping of carbon nanotubes for intact crystalline graphene nanostructures

    NASA Astrophysics Data System (ADS)

    Lim, Joonwon; Narayan Maiti, Uday; Kim, Na-Young; Narayan, Rekha; Jun Lee, Won; Sung Choi, Dong; Oh, Youngtak; Min Lee, Ju; Yong Lee, Gil; Hun Kang, Seok; Kim, Hyunwoo; Kim, Yong-Hyun; Ouk Kim, Sang

    2016-01-01

    Atomic level engineering of graphene-based materials is in high demand to enable customize structures and properties for different applications. Unzipping of the graphene plane is a potential means to this end, but uncontrollable damage of the two-dimensional crystalline framework during harsh unzipping reaction has remained a key challenge. Here we present heteroatom dopant-specific unzipping of carbon nanotubes as a reliable and controllable route to customized intact crystalline graphene-based nanostructures. Substitutional pyridinic nitrogen dopant sites at carbon nanotubes can selectively initiate the unzipping of graphene side walls at a relatively low electrochemical potential (0.6 V). The resultant nanostructures consisting of unzipped graphene nanoribbons wrapping around carbon nanotube cores maintain the intact two-dimensional crystallinity with well-defined atomic configuration at the unzipped edges. Large surface area and robust electrical connectivity of the synergistic nanostructure demonstrate ultrahigh-power supercapacitor performance, which can serve for AC filtering with the record high rate capability of -85° of phase angle at 120 Hz.

  8. Role of magnetic dopants in the phase diagram of Sm 1111 pnictides: The case of Mn

    NASA Astrophysics Data System (ADS)

    Lamura, G.; Shiroka, T.; Bordignon, S.; Sanna, S.; Moroni, M.; De Renzi, R.; Carretta, P.; Biswas, P. K.; Caglieris, F.; Putti, M.; Wurmehl, S.; Singh, S. J.; Shimoyama, J.; Gastiasoro, M. N.; Andersen, B. M.

    2016-12-01

    The deliberate insertion of magnetic Mn dopants in the Fe sites of the optimally doped SmFeAsO0.88F0.12 iron-based superconductor can modify in a controlled way its electronic properties. The resulting phase diagram was investigated across a wide range of manganese contents (x ) by means of muon-spin spectroscopy (μ SR ), both in zero and in transverse fields, to probe the magnetic and the superconducting order, respectively. The pure superconducting phase (at x <0.03 ) is replaced by a crossover region at intermediate Mn values (0.03 ≤x <0.08 ), where superconductivity coexists with static magnetic order. After completely suppressing superconductivity for x =0.08 , a further increase in Mn content reinforces the natural tendency towards antiferromagnetic correlations among the magnetic Mn ions. The sharp drop of Tc and the induced magnetic order in the presence of magnetic disorder/dopants, such as Mn, are both consistent with a recent theoretical model of unconventional superconductors (M. N. Gastiasoro et al., Phys. Rev. Lett. 117, 257002 (2016), 10.1103/PhysRevLett.117.257002), which includes correlation-enhanced RKKY couplings between the impurity moments.

  9. Laser and voltage manipulation of bistable Si dopants in the GaAs (110) surface

    NASA Astrophysics Data System (ADS)

    Smakman, E. P.; van Bree, J.; Koenraad, P. M.

    2013-02-01

    Bistable behavior of single Si dopants in the (110) surface layer of GaAs was studied with a scanning tunneling microscope (STM). The Si atom acts as either a positively charged substitutional donor or a negatively charged interstitial. Its configuration can switch under the influence of a local biased STM tip. To independently manipulate the charge state, the sample was illuminated by a laser during STM operation. The Si atom can be reversibly switched between its positive and negative charge states by turning the laser on and off, respectively. This process occurs mostly with the photon energy tuned above the band gap of GaAs, indicating that photogenerated electron-hole pairs play an important role in the process. The occupation of the donor and interstitial configurations depends on the carrier dynamics, i.e., the possibility of the electrons to escape or to be captured. If the tip-induced band bending is large enough, it is possible for electrons to tunnel into the conduction band and the donor configuration is observed. Another escape path is created when the sample is illuminated and photogenerated holes can recombine with the bound electrons of the dopant.

  10. Theoretical investigation of single dopant in core/shell nanocrystal in magnetic field

    NASA Astrophysics Data System (ADS)

    Talbi, A.; Feddi, E.; Oukerroum, A.; Assaid, E.; Dujardin, F.; Addou, M.

    2015-09-01

    The control of single dopant or "solitary dopant" in semiconductors constitute a challenge to achieve new range of tunable optoelectronic devices. Knowing that the properties of doped monocrystals are very sensitive to different external perturbations, the aim of this study is to understand the effect of a magnetic field on the ground state energy of an off-center ionized donor in a core/shell quantum dot (CSQD). The binding energies with and without an applied magnetic field are determined by the Ritz variational method taking into account the electron-impurity correlation in the trial wave function deduced from the second-order perturbation. It has been found that the external magnetic field affects strongly the binding energy, and its effect varies as a function of the core radius and the shell thickness. We have shown the existence of a threshold ratio (a / b) crit which represents the limit between the tridimensional and the spherical surface confinement. In addition our analysis demonstrates the important influence of the position of ionized donor in the shell material.

  11. On substrate dopant engineering for ET-SOI MOSFETs with UT-BOX

    NASA Astrophysics Data System (ADS)

    Hao, Wu; Miao, Xu; Guangxing, Wan; Huilong, Zhu; Lichuan, Zhao; Xiaodong, Tong; Chao, Zhao; Dapeng, Chen; Tianchun, Ye

    2014-11-01

    The importance of substrate doping engineering for extremely thin SOI MOSFETs with ultra-thin buried oxide (ES-UB-MOSFETs) is demonstrated by simulation. A new substrate/backgate doping engineering, lateral non-uniform dopant distributions (LNDD) is investigated in ES-UB-MOSFETs. The effects of LNDD on device performance, Vt-roll-off, channel mobility and random dopant fluctuation (RDF) are studied and optimized. Fixing the long channel threshold voltage (Vt) at 0.3 V, ES-UB-MOSFETs with lateral uniform doping in the substrate and forward back bias can scale only to 35 nm, meanwhile LNDD enables ES-UB-MOSFETs to scale to a 20 nm gate length, which is 43% smaller. The LNDD degradation is 10% of the carrier mobility both for nMOS and pMOS, but it is canceled out by a good short channel effect controlled by the LNDD. Fixing Vt at 0.3 V, in long channel devices, due to more channel doping concentration for the LNDD technique, the RDF in LNDD controlled ES-UB-MOSFETs is worse than in back-bias controlled ES-UB-MOSFETs, but in the short channel, the RDF for LNDD controlled ES-UB-MOSFET is better due to its self-adaption of substrate doping engineering by using a fixed thickness inner-spacer. A novel process flow to form LNDD is proposed and simulated.

  12. Exciton-to-Dopant Energy Transfer in Mn-Doped Cesium Lead Halide Perovskite Nanocrystals.

    PubMed

    Parobek, David; Roman, Benjamin J; Dong, Yitong; Jin, Ho; Lee, Elbert; Sheldon, Matthew; Son, Dong Hee

    2016-12-14

    We report the one-pot synthesis of colloidal Mn-doped cesium lead halide (CsPbX3) perovskite nanocrystals and efficient intraparticle energy transfer between the exciton and dopant ions resulting in intense sensitized Mn luminescence. Mn-doped CsPbCl3 and CsPb(Cl/Br)3 nanocrystals maintained the same lattice structure and crystallinity as their undoped counterparts with nearly identical lattice parameters at ∼0.2% doping concentrations and no signature of phase separation. The strong sensitized luminescence from d-d transition of Mn(2+) ions upon band-edge excitation of the CsPbX3 host is indicative of sufficiently strong exchange coupling between the charge carriers of the host and dopant d electrons mediating the energy transfer, essential for obtaining unique properties of magnetically doped quantum dots. Highly homogeneous spectral characteristics of Mn luminescence from an ensemble of Mn-doped CsPbX3 nanocrystals and well-defined electron paramagnetic resonance spectra of Mn(2+) in host CsPbX3 nanocrystal lattices suggest relatively uniform doping sites, likely from substitutional doping at Pb(2+). These observations indicate that CsPbX3 nanocrystals, possessing many superior optical and electronic characteristics, can be utilized as a new platform for magnetically doped quantum dots expanding the range of optical, electronic, and magnetic functionality.

  13. Room-temperature single-photon generation from solitary dopants of carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Ma, Xuedan; Hartmann, Nicolai F.; Baldwin, Jon K. S.; Doorn, Stephen K.; Htoon, Han

    2015-08-01

    On-demand single-photon sources capable of operating at room temperature and the telecom wavelength range of 1,300-1,500 nm hold the key to the realization of novel technologies that span from sub-diffraction imaging to quantum key distribution and photonic quantum information processing. Here, we show that incorporation of undoped (6,5) single-walled carbon nanotubes into a SiO2 matrix can lead to the creation of solitary oxygen dopant states capable of fluctuation-free, room-temperature single-photon emission in the 1,100-1,300 nm wavelength range. We investigated the effects of temperature on photoluminescence emission efficiencies, fluctuations and decay dynamics of the dopant states and determined the conditions most suitable for the observation of single-photon emission. This emission can in principle be extended to 1,500 nm by doping of smaller-bandgap single-walled carbon nanotubes. This easy tunability presents a distinct advantage over existing defect centre single-photon emitters (for example, diamond defect centres). Our SiO2-encapsulated sample also presents exciting opportunities to apply Si/SiO2-based micro/nano-device fabrication techniques in the development of electrically driven single-photon sources and integration of these sources into quantum photonic devices and networks.

  14. Correlation Between High Gas Sensitivity and Dopant Structure in W-doped ZnO

    NASA Astrophysics Data System (ADS)

    Fukami, Shun; Taguchi, Munetaka; Adachi, Yutaka; Sakaguchi, Isao; Watanabe, Ken; Kinoshita, Toyohiko; Muro, Takayuki; Matsushita, Tomohiro; Matsui, Fumihiko; Daimon, Hiroshi; Suzuki, Taku T.

    2017-06-01

    W-doped ZnO films are synthesized by pulsed laser deposition on Al2 O3 (11 2 ¯ 0 ) substrate, and their gas-sensing properties are investigated. Significantly improved sensitivity and response time to ethanol vapor are achieved. In order to study the relation between high sensing performance and local structure around the dopant W site, we carry out two-dimensional photoelectron diffraction on W-doped ZnO thin films at two different annealing temperatures (600 and 1000 °C ). The photoelectron-intensity angular-distribution (PIAD) patterns of Zn 3 p and W 4 f core levels show the presence of forward-focusing peaks of very different relative intensities in the bulk and surface. From the PIAD patterns and their circular dichroism, we find clear evidence for the substitution of a segregated W atom into a Zn site in the second atomic layer. The result shows a direct relationship between the drastic increase in gas-sensing performance via W doping and the segregation of W at the surface. It also demonstrates that this photoelectron-diffraction measurement is a powerful tool for the study of the local structure of dopant sites in gas-sensing materials.

  15. Mitigating valley-driven localization in atomically thin dopant chains in Si

    NASA Astrophysics Data System (ADS)

    Dusko, Amintor; Saraiva, A. L.; Koiller, Belita

    2016-09-01

    A theoretical study of the localization properties of nanowires of dopants in silicon (Si) fabricated by ionic implantation or scanning tunnel microscope lithography is presented for a model incorporating the currently unavoidable imprecision in individual donor positioning. Experiments have shown that Ohm's law holds in some cases, in apparent defiance to the Anderson localization theory in one dimension. We investigate how valley interference affects the traditional theory of electronic structure of disordered systems. Each isolated donor orbital is realistically described by multivalley effective-mass theory. We extend this model to describe chains of donors as a linear combination of dopant orbitals. Disorder in donor positioning is taken into account, leading to an intricate disorder distribution of hoppings between nearest-neighbor donor sites (donor-donor tunnel coupling)—an effect of valley interference. A decay length, related to the usual localization length, is obtained for phosphorous (P) donor chains from a transfer-matrix approach and is further compared with the chain length. We quantitatively determine the impact of uncertainties δ R in the implantation position relative to a target and also compare our results with those obtained without valley interference. We analyze systematically the aimed interdonor separation dependence (R0) and show that fairly diluted donor chains (R0=7.7 nm) may be as long as 100 nm before the effective onset of Anderson localization, as long as the positioning error is under a lattice parameter (δ R <0.543 nm).

  16. Modulating the Electronic and Optical Properties of Tetragonal ZnSe Monolayers by Chalcogen Dopants.

    PubMed

    Zhou, Jia; Li, Yang; Wu, Xiaohong; Qin, Wei

    2016-07-04

    The recently proposed three-atom-thick single-layer ZnSe sheet demonstrates a strong quantum confinement effect by exhibiting a large enhancement of band gap relative to the zinc blende (ZB) bulk phase. In this work, we aim at investigating the electronic and optical properties of this ultrathin tetragonal ZnSe single-layer sheet with various chalcogen dopant atoms, based on density functional theory (DFT). We find that these single-layer sheets with dopant atoms are still direct-band semiconductors with tunable band gaps, which can lead to strong light absorption and potential applications in solar energy harvesting. Theoretical optical absorbance results show that the S-doped ZnSe monolayer exhibits a higher absorption performance compared to other doped and undoped ZnSe monolayers. These findings pave a way for the modulation of novel ultrathin tetragonal ZnSe monolayers for a wealth of potential optoelectronic applications. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  17. Application of Lithium Chloride Dopant in Fabrication of CdTe Solar Cells

    NASA Astrophysics Data System (ADS)

    Xu, Hang; Zeng, Guanggen; Feng, Lianghuan; Wu, Lili; Liu, Cai; Ren, Shengqiang; Li, Kang; Li, Bing; Li, Wei; Wang, Wenwu; Zhang, Jingquan

    2017-02-01

    We report use of lithium chloride (LiCl) as a non-Cd dopant to deal with the environmental issues associated with use of traditional CdCl2 dopant in CdTe solar cells. It has been found that, after LiCl treatment, device performance parameters including external quantum efficiency and conversion efficiency were improved considerably, being comparable to those of a counterpart treated with CdCl2. The optimal efficiency of 9.58% was obtained at 405°C, and V oc as high as ˜737.3 mV was obtained at 385°C. Thorough study of the properties of the CdTe film treated by LiCl by x-ray diffraction analysis, scanning electron microscopy, x-ray photoelectron spectroscopy, and secondary-ion mass spectroscopy further verified the feasibility of posttreatment with nontoxic LiCl for fabrication of CdTe photovoltaic devices. The doping level of p-type CdTe thin film was improved by lithium. This represents a nontoxic approach for fabrication of commercial CdS/CdTe thin-film solar cells with better performance.

  18. Effect of Dopants on the Adsorption of Carbon Dioxide on Ceria Surfaces.

    PubMed

    Li, Meijun; Tumuluri, Uma; Wu, Zili; Dai, Sheng

    2015-11-01

    High-surface-area nanosized CeO2 and M-doped CeO2 (M=Cu, La, Zr, and Mg) prepared by a surfactant-templated method were tested for CO2 adsorption. Cu, La, and Zr are doped into the lattice of CeO2, whereas Mg is dispersed on the CeO2 surface. The doping of Cu and La into CeO2 leads to an increase of the CO2 adsorption capacity, whereas the doping of Zr has little or no effect. The addition of Mg causes a decrease of the CO2 adsorption capacity at a low Mg content and a gradual increase at a higher content. The CO2 adsorption capacity follows the sequence Cu-CeO2 >La-CeO2 >Zr-CeO2 ≈CeO2 >Mg-CeO2 at low dopant contents, in line with the relative amount of defect sites in the samples. It is the defect sites on the surface, not in the bulk of CeO2, modified by the dopants that play the vital role in CO2 chemisorption. The role of surface oxygen vacancies is further supported by an in situ IR spectroscopic study of the surface chemistry during CO2 adsorption on the doped CeO2.

  19. Role of dopant counter-anion functionality in polyaniline salts/blends and implications to morphology

    SciTech Connect

    Hopkins, A.R.; Rasmussen, P.G.; Basheer, R.A.; Annis, B.K.; Wignall, G.D.

    1997-04-01

    Polyanilines are of particular current interest primarily due to their relative ease of synthesis, low cost and stable conductivity in air. The insulating, polyaniline emeraldine base (PANI-EB) form becomes electrically conducting by preferential protonation or doping the imine nitrogen sites to yield an electrically conducting polyaniline emeraldine salt (PANI-ES). In this paper, wide and small angle X-ray scattering techniques (i.e., WAXS and SAXS) and light microscopy are used to characterize the influence of the dopant`s structure on the morphology of both polyaniline salt and blend. In an attempt to modify the morphology of the PANI-ES, the authors have evaluated a number of doping acids (i.e., methane sulfonic acid (HMSA), butane sulfonic acid (HBSA), dodecyl benzene sulfonic acid (HDBSA) and camphor sulfonic acid (HCSA)) that vary in size and polarity to better understanding the role of the acid in PANI-ES`s morphology and the resulting electrical conductivity. The other goal was to investigate the effect of the counter-anion structure on the nature of the phase separated PANI-ES network. The shape of the PANI-ES network in the host polycaprolactam has important implications on the nature of conduction behavior and the final electrical conductivity of the blend.

  20. Role of dopant counter-anion functionality in polyaniline salts/blends and implications to morphology

    SciTech Connect

    Hopkins, A.R.; Rasmussen, P.G.; Basheer, R.A.; Annis, B.K.; Wignall, G.D.

    1997-03-01

    In this paper, wide and small angle X-ray scattering techniques (i.e., WAXS and SAXS) and light microscopy are used to characterize the influence of the dopant`s structure on the morphology of both polyaniline salt and blend. In an attempt to modify the morphology of the PANI-ES, the authors have evaluated a number of doping acids (i.e., methane sulfonic acid (HMSA), butane sulfonic acid (HBSA), dodecyl benzene sulfonic acid (HDBSA) and camphor sulfonic acid (HCSA)) that vary in size and polarity to better understand the role of the acid in PANI-ES`s morphology and the resulting electrical conductivity. These salts were solution blended with polycaprolactam using hexafluoro-2-propanol (HFIP) as a solvent. The other goal was to investigate the effect of the counter-anion structure on the nature of the phase separated PANI-ES network. The shape of the PANI-ES network in the host polycaprolactam has important implications on the nature of conduction behavior and the final electrical conductivity of the blend.

  1. Preparation and characterization of electrodeposited SnS:In thin films: Effect of In dopant

    NASA Astrophysics Data System (ADS)

    Kafashan, Hosein; Balak, Zohre

    2017-09-01

    SnS:In thin films were grown on fluorine doped tin oxide (FTO) substrate by cathodic electrodeposition technique. The solution was containing 2 mM SnCl2 and 16 mM Na2S2O3 and different amounts of 1 mM InCl3 as In-dopant. The pH, bath temperature, deposition time, and deposition potential (E) were fixed at 2.1, 60 °C, 30 min, and - 1 V, respectively. The XRD results showed that the synthesized films were polycrystalline orthorhombic SnS. The XPS results demonstrated that the films were composed of Sn, S and In. According to the FESEM images, an increase in In-dopant concentration leads to a change in morphology from grain-like to sheet-like having a nanoscale thickness of 20-80 nm and fiber-like. The PL spectra of undoped SnS exhibited four emission peaks including a UV peak, two blue emission peaks, and an IR emission peak. According to the UV-Vis spectra, the direct band gap of SnS:In thin films was estimated to be 1.40-1.66 eV.

  2. High thermoelectric figure of merit by resonant dopant in half-Heusler alloys

    NASA Astrophysics Data System (ADS)

    Chen, Long; Liu, Yamei; He, Jian; Tritt, Terry M.; Poon, S. Joseph

    2017-06-01

    Half-Heusler alloys have been one of the benchmark high temperature thermoelectric materials owing to their thermal stability and promising figure of merit ZT. Simonson et al. early showed that small amounts of vanadium doped in Hf0.75Zr0.25NiSn enhanced the Seebeck coefficient and correlated the change with the increased density of states near the Fermi level. We herein report a systematic study on the role of vanadium (V), niobium (Nb), and tantalum (Ta) as prospective resonant dopants in enhancing the ZT of n-type half-Heusler alloys based on Hf0.6Zr0.4NiSn0.995Sb0.005. The V doping was found to increase the Seebeck coefficient in the temperature range 300-1000 K, consistent with a resonant doping scheme. In contrast, Nb and Ta act as normal n-type dopants, as evident by the systematic decrease in electrical resistivity and Seebeck coefficient. The combination of enhanced Seebeck coefficient due to the presence of V resonant states and the reduced thermal conductivity has led to a state-of-the-art ZT of 1.3 near 850 K in n-type (Hf0.6Zr0.4)0.99V0.01NiSn0.995Sb0.005 alloys.

  3. Multi-Excitonic Emission from Solitary Dopant States of Carbon Nanotubes

    NASA Astrophysics Data System (ADS)

    Htoon, H.; Ma, X.; Hartmann, N. F.; Adamska, L.; Velizhanin, K. A.; Tretiak, S.; Baldwin, J. K. S.; Doorn, S. K.

    Oxygen doping of single wall carbon nanotubes (SWCNTs) has been rapidly emerging as an effective mean for introduction of new functionalities. Recently, through demonstration of fluctuation free, room temperature single photon generation, we established these states as a new type of solid-state two level atom with potentials in quantum information technologies. This study further showed that while some doped tubes were characterized with a near complete photon antibunching, significant numbers of doped tubes exhibit some degree of photon bunching indicating that they emit more than one photon in one excitation cycle. Here in this work, by separating slow and fast photons in the time domain, we show for the first time that the multiple photon emissions originated from higher order multi-exciton states of solitary dopants. We also show that such multi-exciton states can allow emission of photon pairs with efficiency as high as 20-30% of single exciton emission. With this work, we bring out multi-excitonic processes of the solitary dopant states as a new area to be explored for potential applications in lasing, entangled photon generation and carrier multiplication.

  4. High-resolution patterning electronic polymers using dopant induced solubility control (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Moule, Adam J.; Jacobs, Ian E.; Li, Jun; Burg, Stephanie L.; Bilsky, David J.; Rotondo, Brandon T.; Stroeve, Pieter

    2015-08-01

    Organic electronics promise to provide flexible, large-area circuitry such as photovoltaics, displays, and light emitting diodes that can be fabricated inexpensively from solutions. A major obstacle to this vision is that most conjugated organic materials are miscible, making solution-based fabrication of multilayer or micro- to nanoscale patterned films problematic. Here we demonstrate that the solubility of prototypical conductive polymer poly(3-hexylthiophene) (P3HT) can be reversibly "switched off" using high electron affinity molecular dopants, then later recovered with light or a suitable dedoping solution. Using this technique, we are able to stack mutually soluble materials and laterally pattern polymer films using evaporation of dopants through a shadow mask or with light, achieving sub-micrometer, optically limited feature sizes. After forming these structures, the films can be dedoped without disrupting the patterned features; dedoped films have identical optical characteristics, charge carrier mobilities, and NMR spectra as as-cast P3HT films. This method greatly simplifies solution-based device fabrication, is easily adaptable to current manufacturing workflows, and is potentially generalizable to other classes of materials.

  5. Distribution of dopant ions around poly(3,4-ethylenedioxythiophene) chains: a theoretical study.

    PubMed

    Casanovas, Jordi; Zanuy, David; Alemán, Carlos

    2017-04-12

    The effect of counterions and multiple polymer chains on the properties and structure of poly(3,4-ethylenedioxythiophene) (PEDOT) doped with ClO4(-) has been examined using density functional theory (DFT) calculations with periodic boundary conditions (PBCs). Calculations on a one-dimensional periodic model with four explicit polymer repeat units and two ClO4(-) molecules indicate that the latter are separated as much as possible, with the salt structure and band gap obtained from such ClO4(-) distribution being in excellent agreement with those determined experimentally. On the other hand, DFT calculations on periodic models that include two chains indicate that neighboring PEDOT chains are shifted along the molecular axis by a half of the repeat unit length, with dopant ions intercalated between the polymer molecules acting as cement. In order to support these structural features, classical molecular dynamics (MD) simulations have been performed on a multiphasic system consisting of 69 explicit PEDOT chains anchored onto a steel surface, explicit ClO4(-) anions embedded in the polymer matrix, and an acetonitrile phase layer onto the polymer matrix. Analyses of the radial distribution functions indicate that the all-anti conformation, the relative disposition of adjacent PEDOT chains and the distribution of ClO4(-) dopant ions are fully consistent with periodic DFT predictions. The agreement between two such different methodologies allows reinforcing the microscopic understanding of the PEDOT film structure.

  6. In Situ Measurement of Voltage-Induced Stress in Conducting Polymers with Redox-Active Dopants.

    PubMed

    Sen, Sujat; Kim, Sung Yeol; Palmore, Lia R; Jin, Shenghua; Jadhav, Nitin; Chason, Eric; Palmore, G Tayhas R

    2016-09-14

    Minimization of stress-induced mechanical rupture and delamination of conducting polymer (CP) films is desirable to prevent failure of devices based on these materials. Thus, precise in situ measurement of voltage-induced stress within these films should provide insight into the cause of these failure mechanisms. The evolution of stress in films of polypyrrole (pPy), doped with indigo carmine (IC), was measured in different electrochemical environments using the multibeam optical stress sensor (MOSS) technique. The stress in these films gradually increases to a constant value during voltage cycling, revealing an initial break-in period for CP films. The nature of the ions involved in charge compensation of pPy[IC] during voltage cycling was determined from electrochemical quartz crystal microbalance (EQCM) data. The magnitude of the voltage-induced stress within pPy[IC] at neutral pH correlated with the radius of the hydrated mobile ion in the order Li(+) > Na(+) > K(+). At acidic pH, the IC dopant in pPy[IC] undergoes reversible oxidation and reduction within the range of potentials investigated, providing a secondary contribution to the observed voltage-induced stress. We report on the novel stress response of these polymers due to the presence of pH-dependent redox-active dopants and how it can affect material performance.

  7. Effect of Gd dopant concentration on the defect engineering in ceria nanostructures

    SciTech Connect

    Sakar, M.; Rajkumar, Rubini; Tripathy, S.; Balakumar, S.

    2012-12-15

    Graphical abstract: Display Omitted Highlights: ► Investigates the ionic conductivity of defect engineered Gd doped nano scale ceria. ► Reveals that there exists an optimum concentration of dopant to engineer ceria with large O{sub 2} vacancies. ► For the first time the Nanosponge morphology observed in the Gd doped nanoceria. ► It is observed that 5% of Gd in ceria is optimum to induce appropriate amount of defects. ► Thereby an enhanced ionic conductivity is achieved in 5% Gd doped ceria. -- Abstract: In this study, the fabrication and characterization of pure and gadolinium (Gd) doped ceria nanostructures (Ce{sub 1−x}Gd{sub x}O{sub 2−δ} where x = 0.05, 0.1 and 0.2) are investigated. The origin of defect formation has been systematically investigated by XRD and UV-Visible Raman. All the fabricated ceria are found to be “Nanosponge” morphology which is observed by using FESEM technique. The charge transfer of O{sup 2−} ions and Ce{sup 3+}/Ce{sup 4+} in the ceria host due to these defect structures are studied by UV–DRS. Impedance analysis is showed an enhanced ionic conductivity for 5% Gd doped ceria compared to other concentration of Gd, revealing that the dopant concentration is a critical parameter in engineering a large number of vacancy defects in ceria nanostructures.

  8. The effect of low levels of dopants upon the formation and properties of beta-phase molybdenum nitride

    SciTech Connect

    Cairns, A.G.; Gallagher, J.G.; Hargreaves, J.S.J.; Mckay, D.; Rico, J.L.; Wilson, K.

    2010-03-15

    The addition of 1 wt% Pd, Au, Ni and Cu dopants has been demonstrated to strongly alter the morphology of beta-phase molybdenum nitride prepared by treatment of MoO{sub 3} with a 3/1 H{sub 2}/N{sub 2} mixture at 750 deg. C. Furthermore, the addition of Pd significantly enhances the surface area and the formation of the nitride phase. It is proposed that the facile formation of molybdenum bronzes in this system is important in this respect. The dopants have also been observed to modify the denitridation characteristics of the beta-phase, with an overall reduction of the proportion of NH{sub 3} formed upon using a 3/1 H{sub 2}/Ar mixture with respect to the undoped sample. - Graphical abstract: Low levels of Pd, Au, Ni and Cu dopant have significant effects upon the morphology, formation and dentitridation characteristics of beta-phase molybdenum nitride.

  9. Dopant effects on 2-ethyl-1-hexanol: A dual-channel impedance spectroscopy and neutron scattering study

    SciTech Connect

    Singh, Lokendra P.; Richert, Ranko; Raihane, Ahmed; Alba-Simionesco, Christiane

    2015-01-07

    A two-channel impedance technique has been used to study the relaxation behavior of 2-ethyl-1-hexanol with polar and non-polar dopants at the few percent concentration level over a wide temperature and frequency range. The non-polar dopants shift both the Debye and the primary structural relaxation time in the same direction, to shorter times for 3-methylpentane and to longer times for squalane, consistent with the relative glass transition temperatures (T{sub g}) of the components. By contrast, polar dopants such as water or methanol modify the α-process towards slower dynamics and increased amplitude, while the Debye process is accelerated and with a decreased amplitude. This effect of adding water to alcohol is explained by water promoting more compact structures with reduced Kirkwood correlation factors. This picture is consistent with a shift in the neutron scattering pre-peak to lower scattering vectors and with simulation work on alcohol-water systems.

  10. Identification of dopant-induced point defects and their effect on the performance of CZT detectors (Conference Presentation)

    NASA Astrophysics Data System (ADS)

    Gul, Rubi; Bolotnikov, Aleksey E.; Camarda, Giuseppe S.; Cui, Yonggang; Didic, Václav; Egarievwe, Stephen U.; Hossain, Anwar; Roy, Utpal N.; Yang, Ge; James, Ralph B.

    2016-09-01

    In our prior research we investigated room-temperature radiation detectors (CZT, CMT, CdMgTe, CTS, among other compound semiconductors) for point defects related to different dopants and impurities. In this talk we will report on our most recent research on newly grown CZT crystals doped with In, In+Al, In+Ni, and In+Sn. The main focus will be on the study of dopant-induced point defects using deep-level current transient spectroscopy (i-DLTS). In addition the performance, ? product, gamma-ray spectral response and internal electric field of the detectors were measured and correlated with the dopant-induced point defects and their concentrations. Characterization of the detectors was carried out using i-DLTS for the point defects, Pockels effect for the internal electric-field distribution, and γ-ray spectroscopy for the spectral properties.

  11. Microscopic distribution of metal dopants and anion vacancies in Fe-doped BaTiO3-δ single crystals

    NASA Astrophysics Data System (ADS)

    Chakraborty, Tanushree; Meneghini, Carlo; Aquilanti, Giuliana; Ray, Sugata

    2013-06-01

    A detailed microscopic structural study on two single crystalline dilute magnetic oxides, BaTi0.95Fe0.05O3-δ with and without perceptible δ, has been carried out. Although it has been reported earlier that varying δ significantly affects high temperature ferromagnetism, the real distribution/redistribution of vacancies and dopant Fe ions inside the 6H hexagonal structure was never probed. This study reveals that oxygen vacancies reduce the dopant Fe3+ ions to Fe2+ and mostly accumulate around these Fe2+ ions. Another distinct trend is the tendency of the dopant Fe ions to get closer instead of being distributed randomly, thereby creating {{Fe}}_{2}^{2+}{{O}}_{9-{\\delta }^{\\prime}} like dimers within the 6H hexagonal unit cell. This experimental observation definitively confirms previous hypotheses based on theoretical models.

  12. Perspective analysis of tri gate germanium tunneling field-effect transistor with dopant segregation region at source/drain

    NASA Astrophysics Data System (ADS)

    Liu, Liang-kui; Shi, Cheng; Zhang, Yi-bo; Sun, Lei

    2017-04-01

    A tri gate Ge-based tunneling field-effect transistor (TFET) has been numerically studied with technology computer aided design (TCAD) tools. Dopant segregated Schottky source/drain is applied to the device structure design (DS-TFET). The characteristics of the DS-TFET are compared and analyzed comprehensively. It is found that the performance of n-channel tri gate DS-TFET with a positive bias is insensitive to the dopant concentration and barrier height at n-type drain, and that the dopant concentration and barrier height at a p-type source considerably affect the device performance. The domination of electron current in the entire BTBT current of this device accounts for this phenomenon and the tri-gate DS-TFET is proved to have a higher performance than its dual-gate counterpart.

  13. Significant improvement in dopant emission and lifetime in water soluble Cu:ZnSe/ZnS nanocrystals

    NASA Astrophysics Data System (ADS)

    Saikia, K.; Deb, P.; Mondal, B.; Kalita, E.

    2014-03-01

    We report here the enhanced dopant emission in Cu:ZnSe/ZnS core-shell nanocrystals (NCs) through an aqueous route in ambient conditions. A three-fold quantum enhancement in luminescence has been achieved by developing a ZnS inert shell as compared to the pristine doped NCs. The internal doping of Cu after shell growth, signifying localization of Cu2+ t2 energy states in the deep band gap, has shown a significant improvement in dopant excited state lifetime. The long lifetime related to Cu dopant emission is the longest lifetime ever reported for copper doped zinc based NCs developed through an aqueous route. The good colloidal as well as the luminescence stability of these highly efficient doped NCs mean they have great potential for use in biomedical imaging applications.

  14. Locative Inversion in Cantonese.

    ERIC Educational Resources Information Center

    Mok, Sui-Sang

    This study investigates the phenomenon of "Locative Inversion" in Cantonese. The term "Locative Inversion" indicates that the locative phrase (LP) syntactic process in Cantonese and the appears at the sentence-initial position and its logical subject occurs postverbally. It is demonstrated that this Locative Inversion is a…

  15. Location, Location, Location: Development of Spatiotemporal Sequence Learning in Infancy

    ERIC Educational Resources Information Center

    Kirkham, Natasha Z.; Slemmer, Jonathan A.; Richardson, Daniel C.; Johnson, Scott P.

    2007-01-01

    We investigated infants' sensitivity to spatiotemporal structure. In Experiment 1, circles appeared in a statistically defined spatial pattern. At test 11-month-olds, but not 8-month-olds, looked longer at a novel spatial sequence. Experiment 2 presented different color/shape stimuli, but only the location sequence was violated during test;…

  16. Location, Location, Location: Development of Spatiotemporal Sequence Learning in Infancy

    ERIC Educational Resources Information Center

    Kirkham, Natasha Z.; Slemmer, Jonathan A.; Richardson, Daniel C.; Johnson, Scott P.

    2007-01-01

    We investigated infants' sensitivity to spatiotemporal structure. In Experiment 1, circles appeared in a statistically defined spatial pattern. At test 11-month-olds, but not 8-month-olds, looked longer at a novel spatial sequence. Experiment 2 presented different color/shape stimuli, but only the location sequence was violated during test;…

  17. High efficient white organic light-emitting diodes with single emissive layer using phosphorescent red, green, and blue dopants

    NASA Astrophysics Data System (ADS)

    Kim, You-Hyun; Wai Cheah, Kok; Young Kim, Woo

    2013-07-01

    Phosphorescent white organic light-emitting diodes (PHWOLEDs) with single emissive layer were fabricated by co-doping phosphorescent blue, green, and red emitters with different concentrations. WOLEDs using Ir(piq)3 and Ir(ppy)3 as red and green dopants along with 8% of Firpic as blue dopant with host materials of 4CzPBP in the emissive layer were compared under various doping ratio between Ir(piq)3 and Ir(ppy)3. Triplet-triplet Dexter energy transfer in single emissive PHWOLEDs including three primary colors was saturated from higher triplet energy levels to lower triplet energy levels directly.

  18. Maskless RGB color patterning of vacuum-deposited small molecule OLED displays by diffusion of luminescent dopant molecules.

    PubMed

    Kajiyama, Yoshitaka; Kajiyama, Koichi; Aziz, Hany

    2015-06-29

    A maskless RGB color patterning technique based on diffusion of luminescent dopant molecules is proposed here for vacuum-deposited small molecule OLED displays. The proposed maskless color patterning technique enables us to overcome challenging issues in OLED display manufacturing arising from shadow mask limitations. This approach utilizes selective diffusion of luminescent dopant molecules from a donor substrate to an acceptor substrate. Results show that sufficiently high doping levels can be achieved through this technique and that devices with performance similar to those produced by standard co-deposition can be easily produced. Red, green and blue OLEDs are successfully fabricated side by side on one substrate using this technique.

  19. Effect of solvent and dopant on poly(3,4-ethylenedioxythiophene) thin films by atomic force microscope lithography.

    PubMed

    Kim, Yong-il; Kim, Hyunsook; Lee, Haiwon

    2008-09-01

    AMF anodization lithography was performed on organic thin films with conducting polymers which is poly(3,4-ethylenedioxythiophene). The conductivity of PEDOT thin films was changed by different dopants and organic solvents. Two different dopants are poly(4-styrenesulfonate) and di(2-ethylhexyl)-sulfosuccinate. Also, DMF and IPA were used to prepare the PEDOT thin films doped with PSS and DEHS on silicon surface. The conductivities of these PEDOT variants were compared by obtaining their I-V curves between tip and thin films using AFM. Silicon oxide nanopatterns with higher aspect ratios can be obtained from the films with higher conductivity.

  20. The role of the domain size and titanium dopant in nanocrystalline hematite thin films for water photolysis

    NASA Astrophysics Data System (ADS)

    Yan, Danhua; Tao, Jing; Kisslinger, Kim; Cen, Jiajie; Wu, Qiyuan; Orlov, Alexander; Liu, Mingzhao

    2015-11-01

    Here we develop a novel technique for preparing high quality Ti-doped hematite thin films for photoelectrochemical (PEC) water splitting, through sputtering deposition of metallic iron films from an iron target embedded with titanium (dopants) pellets, followed by a thermal oxidation step that turns the metal films into doped hematite. It is found that the hematite domain size can be tuned from ~10 nm to over 100 nm by adjusting the sputtering atmosphere from more oxidative to mostly inert. The better crystallinity at a larger domain size ensures excellent PEC water splitting performance, leading to record high photocurrent from pure planar hematite thin films on FTO substrates. Titanium doping further enhances the PEC performance of hematite photoanodes. The photocurrent is improved by 50%, with a titanium dopant concentration as low as 0.5 atom%. It is also found that the role of the titanium dopant in improving the PEC performance is not apparently related to the films' electrical conductivity which had been widely believed, but is more likely due to the passivation of surface defects by the titanium dopants.Here we develop a novel technique for preparing high quality Ti-doped hematite thin films for photoelectrochemical (PEC) water splitting, through sputtering deposition of metallic iron films from an iron target embedded with titanium (dopants) pellets, followed by a thermal oxidation step that turns the metal films into doped hematite. It is found that the hematite domain size can be tuned from ~10 nm to over 100 nm by adjusting the sputtering atmosphere from more oxidative to mostly inert. The better crystallinity at a larger domain size ensures excellent PEC water splitting performance, leading to record high photocurrent from pure planar hematite thin films on FTO substrates. Titanium doping further enhances the PEC performance of hematite photoanodes. The photocurrent is improved by 50%, with a titanium dopant concentration as low as 0.5 atom%. It is

  1. Dopant mapping of Be δ-doped layers in GaAs tailored by counterdoping using scanning tunneling microscopy

    NASA Astrophysics Data System (ADS)

    Ebert, Ph.; Landrock, S.; Chiu, Y. P.; Breuer, U.; Dunin-Borkowski, R. E.

    2012-11-01

    The effect of counterdoping on the Be dopant distribution in delta (δ)-doped layers embedded in Si-doped and intrinsic GaAs is investigated by cross-sectional scanning tunneling microscopy. δ-doped layers in intrinsic GaAs exhibit a large spreading, whereas those surrounded by Si-doped GaAs remain spatially localized. The different spreading is explained by the Fermi-level pinning at the growth surface, which leads to an increased Ga vacancies concentration with increasing Si counterdoping. The Ga vacancies act as sinks for the diffusing Be dopant atoms, hence retarding the spreading.

  2. Current-voltage spectroscopy of dopant-induced quantum-dots in heavily n-doped junctionless nanowire transistors

    SciTech Connect

    Wang, Hao; Han, Weihua Ma, Liuhong; Li, Xiaoming; Hong, Wenting; Yang, Fuhua

    2014-03-31

    We demonstrate current-voltage spectroscopy of dopant-induced quantum dots in heavily n-doped junctionless nanowire transistors (JNTs) at low temperatures. The similar multiple-split current peak features for both single-channel and multiple-channel JNTs are found at the initial stage of conduction below the temperature of 75 K. The temperature stability of the pinch-off voltage, affected by activated electrons from defects and donor ionization, has been effectively improved by the 20 nm-width nanowires. The transition temperature for single electron tunneling to thermal activated transport is dependent on the ionization energy of dopants.

  3. Improving stability of photoluminescence of ZnSe thin films grown by molecular beam epitaxy by incorporating Cl dopant

    SciTech Connect

    Wang, J. S.; Shen, J. L.; Chen, W. J.; Tsai, Y. H.; Wang, H. H.; Yang, C. S.; Chen, R. H.; Tsai, C. D.

    2011-01-10

    This investigation studies the effect of chlorine (Cl) dopant in ZnSe thin films that were grown by molecular beam epitaxy on their photoluminescence (PL) and the stability thereof. Free excitonic emission was observed at room-temperature in the Cl-doped sample. Photon irradiation with a wavelength of 404 nm and a power density of 9.1 W/cm{sup 2} has a much stronger effect on PL degradation than does thermal heating to a temperature of 150 deg. C. Additionally, this study shows that the generation of nonradiative centers by both photon irradiation and thermal heating can be greatly inhibited by incorporating Cl dopant.

  4. Gradient-index POF without dopants: how the optical properties can be controlled by sole temperature treatment

    NASA Astrophysics Data System (ADS)

    Bunge, C.-A.; Schüppert, M.; Beckers, M.; Stepniak, G.; Vad, T.; Seide, G.; Gries, T.

    2016-09-01

    In this paper we present a novel melt-spinning fabrication process for graded-index polymer optical fibers that completely avoids additional dopants for the formation of the refractive-index profile. In the presented process the meltspun fiber is rapidly cooled down so that the inner and outer parts of the fiber solidify at different speeds resulting in a density gradient. This density variation leads to a refractive-index profile without any further dopants. We present achieved results for fibers made of PMMA, and also first preliminary results for bio polymers such as TPU.

  5. Double-hole-mediated coupling of dopants and its impact on band gap engineering in TiO2.

    PubMed

    Yin, Wan-Jian; Wei, Su-Huai; Al-Jassim, Mowafak M; Yan, Yanfa

    2011-02-11

    A double-hole-mediated coupling of dopants is unraveled and confirmed in TiO2 by density-functional theory calculations. We find that when a dopant complex on neighboring oxygen sites in TiO2 has net two holes, the holes will strongly couple to each other through significant lattice relaxation. The coupling results in the formation of fully filled impurity bands lying above the valence band of TiO2, leading to a much more effective band gap reduction than that induced by monodoping or conventional donor-acceptor codoping. Our results suggest a new path for semiconductor band gap engineering.

  6. Electron-donor dopant, method of improving conductivity of polymers by doping therewith, and a polymer so treated

    SciTech Connect

    Liepins, R.; Aldissi, M.

    1988-07-05

    The electrically conductive material is described comprising a polymer with a conjugated backbone selected from the group consisting of polyacetylene, polypyrrone, and polyphenylquinoxaline, the polymer being electron-donor doped to a controlled degree with an agent derived from an electride dopant or a dopant derived from an alkalide both of which contain a trapping agent being selected from the group consisting of: a crown ether, 1,4,7,10,13,16-hexaoxacyclooctadecane, cryptand, methyl ether cyclodextrin, spherand, methyl ether calixarene, podand, and an octopus molecule, the agent being made in the presence of lithium.

  7. Effect of low temperature oxidation (LTO) in reducing boron skin in boron spin on dopant diffused emitter

    SciTech Connect

    Singha, Bandana; Solanki, Chetan Singh

    2016-05-06

    Formation of boron skin is an unavoidable phenomenon in p-type emitter formation with boron dopant source. The boron skin thickness is generally less than 100 nm and difficult to remove by chemical and physical means. Low temperature oxidation (LTO) used in this work is useful in removing boron skin thickness up to 30 nm and improves the emitter performance. The effective minority carrier lifetime gets improved by more than 30% after using LTO and leakage current of the emitter gets lowered by 100 times thereby showing the importance of low temperature oxidation in boron spin on dopant diffused emitters.

  8. Modeling and de-embedding the interferometric scanning microwave microscopy by means of dopant profile calibration

    SciTech Connect

    Michalas, L. Marcelli, R.; Wang, F.; Brillard, C.; Theron, D.

    2015-11-30

    This paper presents the full modeling and a methodology for de-embedding the interferometric scanning microwave microscopy measurements by means of dopant profile calibration. A Si calibration sample with different boron-doping level areas is used to that end. The analysis of the experimentally obtained S{sub 11} amplitudes based on the proposed model confirms the validity of the methodology. As a specific finding, changes in the tip radius between new and used tips have been clearly identified, leading to values for the effective tip radius in the range of 45 nm to 85 nm, respectively. Experimental results are also discussed in terms of the effective area concept, taking into consideration details related to the nature of tip-to-sample interaction.

  9. Restoring the lattice of Si-based atom probe reconstructions for enhanced information on dopant positioning.

    PubMed

    Breen, Andrew J; Moody, Michael P; Ceguerra, Anna V; Gault, Baptiste; Araullo-Peters, Vicente J; Ringer, Simon P

    2015-12-01

    The following manuscript presents a novel approach for creating lattice based models of Sb-doped Si directly from atom probe reconstructions for the purposes of improving information on dopant positioning and directly informing quantum mechanics based materials modeling approaches. Sophisticated crystallographic analysis techniques are used to detect latent crystal structure within the atom probe reconstructions with unprecedented accuracy. A distortion correction algorithm is then developed to precisely calibrate the detected crystal structure to the theoretically known diamond cubic lattice. The reconstructed atoms are then positioned on their most likely lattice positions. Simulations are then used to determine the accuracy of such an approach and show that improvements to short-range order measurements are possible for noise levels and detector efficiencies comparable with experimentally collected atom probe data.

  10. Spin dynamics and magnetic interactions of Mn dopants in the topological insulator Bi2Te3

    NASA Astrophysics Data System (ADS)

    Zimmermann, S.; Steckel, F.; Hess, C.; Ji, H. W.; Hor, Y. S.; Cava, R. J.; Büchner, B.; Kataev, V.

    2016-09-01

    The magnetic and electronic properties of the magnetically doped topological insulator Bi2 -xMnxTe3 were studied using electron-spin resonance (ESR) and measurements of static magnetization and electrical transport. The investigated high-quality single crystals of Bi2 -xMnxTe3 show a ferromagnetic phase transition for x ≥0.04 at TC≈12 K. The Hall measurements reveal a p -type finite charge-carrier density. Measurements of the temperature dependence of the ESR signal of Mn dopants for different orientations of the external magnetic field give evidence that the localized Mn moments interact with the mobile charge carriers leading to Ruderman-Kittel-Kasuya-Yosida-type ferromagnetic coupling between the Mn spins of order 2-3 meV. Furthermore, ESR reveals a low-dimensional character of magnetic correlations that persist far above the ferromagnetic ordering temperature.

  11. Contributed Review: A review of the investigation of rare-earth dopant profiles in optical fibers

    NASA Astrophysics Data System (ADS)

    Sidiroglou, F.; Roberts, A.; Baxter, G.

    2016-04-01

    Rare-earth doped optical fibers have captivated the interest of many researchers around the world across the past three decades. The growth of this research field has been stimulated primarily through their application in optical communications as fiber lasers and amplifiers, although rare-earth doped optical fiber based devices are now finding important uses in many other scientific and industrial areas (for example, medicine, sensing, the military, and material processing). Such wide commercial interest has provided a strong incentive for innovative fiber designs, alternative glass compositions, and novel fabrication processes. A prerequisite for the ongoing progress of this research field is developing the capacity to provide high resolution information about the rare-earth dopant distribution profiles within the optical fibers. This paper constitutes a comprehensive review of the imaging techniques that have been utilized in the analysis of the distribution of the rare-earth ion erbium within the core of optical fibers.

  12. Systematic Conversion of Single Walled Carbon Nanotubes into n-type Thermoelectric Materials by Molecular Dopants

    PubMed Central

    Nonoguchi, Yoshiyuki; Ohashi, Kenji; Kanazawa, Rui; Ashiba, Koji; Hata, Kenji; Nakagawa, Tetsuya; Adachi, Chihaya; Tanase, Tomoaki; Kawai, Tsuyoshi

    2013-01-01

    Thermoelectrics is a challenging issue for modern and future energy conversion and recovery technology. Carbon nanotubes are promising active thermoelectic materials owing to their narrow bandgap energy and high charge carrier mobility, and they can be integrated into flexible thermoelectrics that can recover any waste heat. We here report air-stable n-type single walled carbon nanotubes with a variety of weak electron donors in the range of HOMO level between ca. −4.4 eV and ca. −5.6 eV, in which partial uphill electron injection from the dopant to the conduction band of single walled carbon nanotubes is dominant. We display flexible films of the doped single walled carbon nanotubes possessing significantly large thermoelectric effect, which is applicable to flexible ambient thermoelectric modules. PMID:24276090

  13. Quantum-chemical modeling of boron and noble gas dopants in silicon

    NASA Technical Reports Server (NTRS)

    Aronowitz, S.

    1983-01-01

    The electron effects of the presence of boron and noble gas dopants in a model silicon lattice were investigated using a self-consistent charge extended Hueckel program. The extent of electronic interaction of the noble gas with the lattice is given by: Kr greater than Ar greater than Ne. Theoretically, boron diffusion in the presence of neon, argon or krypton was examined using a self-consistent charge extended Hueckel program. The net energy of interaction between boron and neon is strongly repulsive while argon-boron exhibits a region of relative stability; krypton exhibits behavior similar to argon though no region of stability was found for the range of separations used in the calculations. Finally, it is noted, from the relative energy of the topmost filled molecular orbital associated with boron (in an interstitial position), that activation of the boron does not require boron movement but can be accomplished by indirect transitions.

  14. Atomic scale models of Ion implantation and dopant diffusion in silicon

    SciTech Connect

    Caturla, M; Johnson, M; Lenosky, T; Sadigh, B; Theiss, S K; Zhu, J; de la Rubia, T D

    1999-03-01

    We review our recent work on an atomistic approach to the development of predictive process simulation tools. First principles methods, molecular dynamics simulations, and experimental results are used to construct a database of defect and dopant energetics in Si. This is used as input for kinetic Monte Carlo simulations. C and B trapping of the Si self- interstitial is shown to help explain the enormous disparity in its measured diffusivity. Excellent agreement is found between experiments and simulations of transient enhanced diffusion following 20-80 keV B implants into Si, and with those of 50 keV Si implants into complex B-doped structures. Our simulations predict novel behavior of the time evolution of the electrically active B fraction during annealing.

  15. Quantum-chemical modeling of boron and noble gas dopants in silicon

    NASA Technical Reports Server (NTRS)

    Aronowitz, S.

    1983-01-01

    The electron effects of the presence of boron and noble gas dopants in a model silicon lattice were investigated using a self-consistent charge extended Hueckel program. The extent of electronic interaction of the noble gas with the lattice is given by: Kr greater than Ar greater than Ne. Theoretically, boron diffusion in the presence of neon, argon or krypton was examined using a self-consistent charge extended Hueckel program. The net energy of interaction between boron and neon is strongly repulsive while argon-boron exhibits a region of relative stability; krypton exhibits behavior similar to argon though no region of stability was found for the range of separations used in the calculations. Finally, it is noted, from the relative energy of the topmost filled molecular orbital associated with boron (in an interstitial position), that activation of the boron does not require boron movement but can be accomplished by indirect transitions.

  16. Effect of dopant concentration on photoluminescence properties of Gd2O3:Eu3+

    NASA Astrophysics Data System (ADS)

    Selvalakshmi, T.; Bose, A. Chandra

    2013-02-01

    Red-emitting Gd2-xO3:Eux3+(x = 2,4,6at%) was synthesized by sol-gel method and its optical properties were studied. The formation of Gd2O3 and the presence of metal oxygen bond were confirmed from X-ray diffraction (XRD) and fourier transform infrared (FTIR) spectroscopy studies. Incorporation of Eu3+ in Gd3+ site was proved qualitatively by Energy dispersive X-ray analysis (EDX). A strong charge transfer band (CTB) at 254 nm was observed in the excitation spectra with varying intensity for different dopant concentrations. Photoluminescence (PL) spectra reported red emission peak at 611 nm corresponding to 5D0-7F2 transition between Eu3+ energy levels. Concentration quenching occurred at 2 at % and its critical distance was calculated. Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) studies was carried out to study the morphological variations.

  17. Contributed Review: A review of the investigation of rare-earth dopant profiles in optical fibers

    SciTech Connect

    Sidiroglou, F.; Baxter, G.; Roberts, A.

    2016-04-15

    Rare-earth doped optical fibers have captivated the interest of many researchers around the world across the past three decades. The growth of this research field has been stimulated primarily through their application in optical communications as fiber lasers and amplifiers, although rare-earth doped optical fiber based devices are now finding important uses in many other scientific and industrial areas (for example, medicine, sensing, the military, and material processing). Such wide commercial interest has provided a strong incentive for innovative fiber designs, alternative glass compositions, and novel fabrication processes. A prerequisite for the ongoing progress of this research field is developing the capacity to provide high resolution information about the rare-earth dopant distribution profiles within the optical fibers. This paper constitutes a comprehensive review of the imaging techniques that have been utilized in the analysis of the distribution of the rare-earth ion erbium within the core of optical fibers.

  18. Electric-field-dependent charge delocalization from dopant atoms in silicon junctionless nanowire transistor

    NASA Astrophysics Data System (ADS)

    Wang, Hao; Han, Wei-Hua; Zhao, Xiao-Song; Zhang, Wang; Lyu, Qi-Feng; Ma, Liu-Hong; Yang, Fu-Hua

    2016-10-01

    We study electric-field-dependent charge delocalization from dopant atoms in a silicon junctionless nanowire transistor by low-temperature electron transport measurement. The Arrhenius plot of the temperature-dependent conductance demonstrates the transport behaviors of variable-range hopping (below 30 K) and nearest-neighbor hopping (above 30 K). The activation energy for the charge delocalization gradually decreases due to the confinement potential of the conduction channel decreasing from the threshold voltage to the flatband voltage. With the increase of the source-drain bias, the activation energy increases in a temperature range from 30 K to 100 K at a fixed gate voltage, but decreases above the temperature of 100 K. Project supported partly by the National Key R & D Program of China (Grant No. 2016YFA02005003) and the National Natural Science Foundation of China (Grant Nos. 61376096 and 61327813).

  19. Systematic Conversion of Single Walled Carbon Nanotubes into n-type Thermoelectric Materials by Molecular Dopants

    NASA Astrophysics Data System (ADS)

    Nonoguchi, Yoshiyuki; Ohashi, Kenji; Kanazawa, Rui; Ashiba, Koji; Hata, Kenji; Nakagawa, Tetsuya; Adachi, Chihaya; Tanase, Tomoaki; Kawai, Tsuyoshi

    2013-11-01

    Thermoelectrics is a challenging issue for modern and future energy conversion and recovery technology. Carbon nanotubes are promising active thermoelectic materials owing to their narrow bandgap energy and high charge carrier mobility, and they can be integrated into flexible thermoelectrics that can recover any waste heat. We here report air-stable n-type single walled carbon nanotubes with a variety of weak electron donors in the range of HOMO level between ca. -4.4 eV and ca. -5.6 eV, in which partial uphill electron injection from the dopant to the conduction band of single walled carbon nanotubes is dominant. We display flexible films of the doped single walled carbon nanotubes possessing significantly large thermoelectric effect, which is applicable to flexible ambient thermoelectric modules.

  20. Contributed Review: A review of the investigation of rare-earth dopant profiles in optical fibers.

    PubMed

    Sidiroglou, F; Roberts, A; Baxter, G

    2016-04-01

    Rare-earth doped optical fibers have captivated the interest of many researchers around the world across the past three decades. The growth of this research field has been stimulated primarily through their application in optical communications as fiber lasers and amplifiers, although rare-earth doped optical fiber based devices are now finding important uses in many other scientific and industrial areas (for example, medicine, sensing, the military, and material processing). Such wide commercial interest has provided a strong incentive for innovative fiber designs, alternative glass compositions, and novel fabrication processes. A prerequisite for the ongoing progress of this research field is developing the capacity to provide high resolution information about the rare-earth dopant distribution profiles within the optical fibers. This paper constitutes a comprehensive review of the imaging techniques that have been utilized in the analysis of the distribution of the rare-earth ion erbium within the core of optical fibers.

  1. Dual nature of magnetic dopants and competing trends in topological insulators.

    PubMed

    Sessi, Paolo; Biswas, Rudro R; Bathon, Thomas; Storz, Oliver; Wilfert, Stefan; Barla, Alessandro; Kokh, Konstantin A; Tereshchenko, Oleg E; Fauth, Kai; Bode, Matthias; Balatsky, Alexander V

    2016-06-27

    Topological insulators interacting with magnetic impurities have been reported to host several unconventional effects. These phenomena are described within the framework of gapping Dirac quasiparticles due to broken time-reversal symmetry. However, the overwhelming majority of studies demonstrate the presence of a finite density of states near the Dirac point even once topological insulators become magnetic. Here, we map the response of topological states to magnetic impurities at the atomic scale. We demonstrate that magnetic order and gapless states can coexist. We show how this is the result of the delicate balance between two opposite trends, that is, gap opening and emergence of a Dirac node impurity band, both induced by the magnetic dopants. Our results evidence a more intricate and rich scenario with respect to the once generally assumed, showing how different electronic and magnetic states may be generated and controlled in this fascinating class of materials.

  2. Doping Versatile n-Type Organic Semiconductors via Room Temperature Solution-Processable Anionic Dopants.

    PubMed

    Chueh, Chu-Chen; Li, Chang-Zhi; Ding, Feizhi; Li, Zhong'an; Cernetic, Nathan; Li, Xiaosong; Jen, Alex K-Y

    2017-01-11

    In this study, we describe a facile solution-processing method to effectively dope versatile n-type organic semiconductors, including fullerene, n-type small molecules, and graphene by commercially available ammonium and phosphonium salts via in situ anion-induced electron transfer. In addition to the Lewis basicity of anions, we unveiled that the ionic binding strength between the cation and anion of the salts is also crucial in modulating the electron transfer strength of the dopants to affect the resulting doping efficiency. Furthermore, combined with the rational design of n-type molecules, an n-doped organic semiconductor is demonstrated to be thermally and environmentally stable. This finding provides a simple and generally applicable method to make highly efficient n-doped conductors which complements the well-established p-doped organics such as PEDOT:PSS for organic electronic applications.

  3. Ionized dopant concentrations at the heavily doped surface of a silicon solar cell

    NASA Technical Reports Server (NTRS)

    Weinberg, I.; Broder, J. D.; Mazaris, G. A., Jr.; Hsu, L.

    1978-01-01

    Data are combined with concentrations obtained by a bulk measurement method using successive layer removal with measurements of Hall effect and resistivity. From the MOS (metal-oxide-semiconductor) measurements it is found that the ionized dopant concentration N has the value (1.4 + or - 0.1) x 10 to the 20th power/cu cm at distances between 100 and 220 nm from the n(+) surface. The bulk measurement technique yields average values of N over layers whose thickness is 2000 nm. Results show that, at the higher concentrations encountered at the n(+) surface, the MOS C-V technique, when combined with a bulk measurement method, can be used to evaluate the effects of materials preparation methodologies on the surface and near surface concentrations of silicon cells.

  4. Dual nature of magnetic dopants and competing trends in topological insulators

    PubMed Central

    Sessi, Paolo; Biswas, Rudro R.; Bathon, Thomas; Storz, Oliver; Wilfert, Stefan; Barla, Alessandro; Kokh, Konstantin A.; Tereshchenko, Oleg E.; Fauth, Kai; Bode, Matthias; Balatsky, Alexander V.

    2016-01-01

    Topological insulators interacting with magnetic impurities have been reported to host several unconventional effects. These phenomena are described within the framework of gapping Dirac quasiparticles due to broken time-reversal symmetry. However, the overwhelming majority of studies demonstrate the presence of a finite density of states near the Dirac point even once topological insulators become magnetic. Here, we map the response of topological states to magnetic impurities at the atomic scale. We demonstrate that magnetic order and gapless states can coexist. We show how this is the result of the delicate balance between two opposite trends, that is, gap opening and emergence of a Dirac node impurity band, both induced by the magnetic dopants. Our results evidence a more intricate and rich scenario with respect to the once generally assumed, showing how different electronic and magnetic states may be generated and controlled in this fascinating class of materials. PMID:27345240

  5. Influence of dopants on supercontinuum generation during the femtosecond laser filamentation in water

    NASA Astrophysics Data System (ADS)

    Li, He; Shi, Zhe; Wang, Xiaowei; Sui, Laizhi; Li, Suyu; Jin, Mingxing

    2017-08-01

    Our experiments show that lactose as one of organic substance and nitric acid as one of inorganic substance added into distilled water can influence the supercontinuum generation in aqueous solution irradiated by the ultrashort femtosecond laser pulses. It is found that once the dopants are added into the water, the supercontinuum generation is suppressed to different extent, and the supercontinuum suppression is enhanced by increasing the concentrations of lactose solution and nitric acid solution. Through the analysis, we find that the capture of electrons by the solvent, and spectral absorption or scattering by the solution may also result in the supercontinuum suppression. These studies will be helpful to understanding of the supercontinuum generation during femtosecond filamentation in liquid samples.

  6. Effect of Dopants on the Adsorption of Carbon Dioxide on Ceria Surfaces

    SciTech Connect

    Li, Meijun; Tumuluri, Uma; Wu, Zili; Dai, Sheng

    2015-09-25

    Here, high-surface-area nanosized CeO2 and M-doped CeO2 (M=Cu, La, Zr, and Mg) prepared by a surfactant-templated method were tested for CO2 adsorption. Cu, La, and Zr are doped into the lattice of CeO2, whereas Mg is dispersed on the CeO2 surface. The doping of Cu and La into CeO2 leads to an increase of the CO2 adsorption capacity, whereas the doping of Zr has little or no effect. The addition of Mg causes a decrease of the CO2 adsorption capacity at a low Mg content and a gradual increase at a higher content. The CO2 adsorption capacity follows the sequence Cu-CeO2>La-CeO2>Zr-CeO2≈CeO2>Mg-CeO2 at low dopant contents, in line with the relative amount of defect sites in the samples. It is the defect sites on the surface, not in the bulk of CeO2, modified by the dopants that play the vital role in CO2 chemisorption. Lastly, the role of surface oxygen vacancies is further supported by an in situ IR spectroscopic study of the surface chemistry during CO2 adsorption on the doped CeO2.

  7. Dopant-assisted negative photoionization ion mobility spectrometry for sensitive detection of explosives.

    PubMed

    Cheng, Shasha; Dou, Jian; Wang, Weiguo; Chen, Chuang; Hua, Lei; Zhou, Qinghua; Hou, Keyong; Li, Jinghua; Li, Haiyang

    2013-01-02

    Ion mobility spectrometry (IMS) is a key trace detection technique for explosives and the development of a simple, stable, and efficient nonradioactive ionization source is highly demanded. A dopant-assisted negative photoionization (DANP) source has been developed for IMS, which uses a commercial VUV krypton lamp to ionize acetone as the source of electrons to produce negative reactant ions in air. With 20 ppm of acetone as the dopant, a stable current of reactant ions of 1.35 nA was achieved. The reactant ions were identified to be CO(3)(-)(H(2)O)(n) (K(0) = 2.44 cm(2) V(-1) s(-1)) by atmospheric pressure time-of-flight mass spectrometry, while the reactant ions in (63)Ni source were O(2)(-)(H(2)O)(n) (K(0) = 2.30 cm(2) V(-1) s(-1)). Finally, its capabilities for detection of common explosives including ammonium nitrate fuel oil (ANFO), 2,4,6-trinitrotoluene (TNT), N-nitrobis(2-hydroxyethyl)amine dinitrate (DINA), and pentaerythritol tetranitrate (PETN) were evaluated, and the limits of detection of 10 pg (ANFO), 80 pg (TNT), and 100 pg (DINA) with a linear range of 2 orders of magnitude were achieved. The time-of-flight mass spectra obtained with use of DANP source clearly indicated that PETN and DINA can be directly ionized by the ion-association reaction of CO(3)(-) to form PETN·CO(3)(-) and DINA·CO(3)(-) adduct ions, which result in good sensitivity for the DANP source. The excellent stability, good sensitivity, and especially the better separation between the reactant and product ion peaks make the DANP a potential nonradioactive ionization source for IMS.

  8. Dopant induced bandgap narrowing in Y-doped zinc oxide nanostructures.

    PubMed

    Yogamalar, Rajeswari; Venkateswaran, Pedinti S; Benzigar, Mercy R; Ariga, Katsuhiko; Vinu, Ajayan; Bose, A Chandra

    2012-01-01

    In this report, hydrothermal synthesis and the absorption properties of the cubic shaped zinc oxide nanostructures doped with different amount of yttrium (Y) metal cation (0 to 15 at.%) are demonstrated. The structural and optical properties of chemically synthesized pure and Y doped ZnO powders are investigated by using powder X-ray diffraction (XRD), field emission scanning electron spectroscopy (FESEM) and transmission electron microscopy (TEM), ultraviolet-visible (UV-vis) absorbance, photoluminescence (PL), and Fourier transform infra-red spectroscopy (FT-IR). It is found that the dopant ions stabilize in wurtzite hexagonal phase of ZnO upto the concentration of less than 6 at.%, which is mainly due to the fact that the ZnO lattice expands and the optical bandgap energy decreases at this level. Increasing the dopant concentration to greater than 6 at.% leads to a contraction of the lattice, which in turn produces a significant structural disorder evidenced by shift in the XRD peaks due to additional interstitial incorporation of Y. The vibrational modes of the metal oxide groups have been identified from the IR transmission spectra. The optical absorption results show that the optical bandgap energy of Y:ZnO nanocrystals is much less as compared to that of the pure bulk ZnO particles. Doping ZnO with trivalent Y produces excess number of electrons in the conduction band and thus, shifts the absorption edge and narrows down to 80 meV approximately. PL spectra are used to study the dependence of doping on the deep-level emission, which show an enhanced blue emission after Y doping. The existence of near band edge (NBE) emission and blue emission, related to zinc interstitials are observed in the luminescence spectra of Zn(1-x)Y(x)O nanostructures.

  9. Persistent dopants and phase segregation in organolead mixed-halide perovskites

    SciTech Connect

    Rosales, Bryan A.; Men, Long; Cady, Sarah D.; Hanrahan, Michael P.; Rossini, Aaron J.; Vela, Javier

    2016-07-25

    Organolead mixed-halide perovskites such as CH3NH3PbX3–aX'a (X, X' = I, Br, Cl) are interesting semiconductors because of their low cost, high photovoltaic power conversion efficiencies, enhanced moisture stability, and band gap tunability. Using a combination of optical absorption spectroscopy, powder X-ray diffraction (XRD), and, for the first time, 207Pb solid state nuclear magnetic resonance (ssNMR), we probe the extent of alloying and phase segregation in these materials. Because 207Pb ssNMR chemical shifts are highly sensitive to local coordination and electronic structure, and vary linearly with halogen electronegativity and band gap, this technique can provide the true chemical speciation and composition of organolead mixed-halide perovskites. We specifically investigate samples made by three different preparative methods: solution phase synthesis, thermal annealing, and solid phase synthesis. 207Pb ssNMR reveals that nonstoichiometric dopants and semicrystalline phases are prevalent in samples made by solution phase synthesis. We show that these nanodomains are persistent after thermal annealing up to 200 °C. Further, a novel solid phase synthesis that starts from the parent, single-halide perovskites can suppress phase segregation but not the formation of dopants. Our observations are consistent with the presence of miscibility gaps and spontaneous spinodal decomposition of the mixed-halide perovskites at room temperature. This underscores how strongly different synthetic procedures impact the nanostructuring and composition of organolead halide perovskites. In conclusion, better optoelectronic properties and improved device stability and performance may be achieved through careful manipulation of the different phases and nanodomains present in these materials.

  10. Biocompatibility of Polypyrrole with Human Primary Osteoblasts and the Effect of Dopants.

    PubMed

    Fahlgren, Anna; Bratengeier, Cornelia; Gelmi, Amy; Semeins, Cornelis M; Klein-Nulend, Jenneke; Jager, Edwin W H; Bakker, Astrid D

    2015-01-01

    Polypyrrole (PPy) is a conducting polymer that enables controlled drug release upon electrical stimulation. We characterized the biocompatibility of PPy with human primary osteoblasts, and the effect of dopants. We investigated the biocompatibility of PPy comprising various dopants, i.e. p-toluene sulfonate (PPy-pTS), chondroitin sulfate (PPy-CS), or dodecylbenzenesulfonate (PPy-DBS), with human primary osteoblasts. PPy-DBS showed the roughest appearance of all surfaces tested, and its wettability was similar to the gold-coated control. The average number of attached cells was 45% higher on PPy-DBS than on PPy-CS or PPy-pTS, although gene expression of the proliferation marker Ki-67 was similar in osteoblasts on all surfaces tested. Osteoblasts seeded on PPy-DBS or gold showed similar vinculin attachment points, vinculin area per cell area, actin filament structure, and Feret's diameter, while cells seeded on PPY-CS or PPY-pTS showed disturbed focal adhesions and were enlarged with disorganized actin filaments. Osteoblasts grown on PPy-DBS or gold showed enhanced alkaline phosphatase activity and osteocalcin gene expression, but reduced osteopontin gene expression compared to cells grown on PPy-pTS and PPy-CS. In conclusion, PPy doped with DBS showed excellent biocompatibility, which resulted in maintaining focal adhesions, cell morphology, cell number, alkaline phosphatase activity, and osteocalcin gene expression. Taken together, conducting polymers doped with DBS are well tolerated by osteoblasts. Our results could provide a basis for the development of novel orthopedic or dental implants with controlled release of antibiotics and pharmaceutics that fight infections or focally enhance bone formation in a tightly controlled manner.

  11. Persistent dopants and phase segregation in organolead mixed-halide perovskites

    DOE PAGES

    Rosales, Bryan A.; Men, Long; Cady, Sarah D.; ...

    2016-07-25

    Organolead mixed-halide perovskites such as CH3NH3PbX3–aX'a (X, X' = I, Br, Cl) are interesting semiconductors because of their low cost, high photovoltaic power conversion efficiencies, enhanced moisture stability, and band gap tunability. Using a combination of optical absorption spectroscopy, powder X-ray diffraction (XRD), and, for the first time, 207Pb solid state nuclear magnetic resonance (ssNMR), we probe the extent of alloying and phase segregation in these materials. Because 207Pb ssNMR chemical shifts are highly sensitive to local coordination and electronic structure, and vary linearly with halogen electronegativity and band gap, this technique can provide the true chemical speciation and compositionmore » of organolead mixed-halide perovskites. We specifically investigate samples made by three different preparative methods: solution phase synthesis, thermal annealing, and solid phase synthesis. 207Pb ssNMR reveals that nonstoichiometric dopants and semicrystalline phases are prevalent in samples made by solution phase synthesis. We show that these nanodomains are persistent after thermal annealing up to 200 °C. Further, a novel solid phase synthesis that starts from the parent, single-halide perovskites can suppress phase segregation but not the formation of dopants. Our observations are consistent with the presence of miscibility gaps and spontaneous spinodal decomposition of the mixed-halide perovskites at room temperature. This underscores how strongly different synthetic procedures impact the nanostructuring and composition of organolead halide perovskites. In conclusion, better optoelectronic properties and improved device stability and performance may be achieved through careful manipulation of the different phases and nanodomains present in these materials.« less

  12. Effects of co-dopants on the magnetic properties of Ni-Zn ferrites

    NASA Astrophysics Data System (ADS)

    Wang, Sea-Fue; Hsu, Yung-Fu; Chou, Kai-Mou; Tsai, Jeng-Ting

    2015-01-01

    In this study, substitution of co-dopants into the Ni0.4Zn0.6Fe2O4 ceramic was performed. Al3+, Sn4+ and Ti4+ ions were added to the Ni0.4Zn0.4Li0.10Fe2.10O4 ceramic to improve magnetic properties. After sintering, all samples were indexed on a spinel structure and no detectable second phase was observed. When the concentration of dopants increased, the grain size of the Ni-Zn ferrites increased from 1.40 to 6.05 μm and the saturation magnetization declined from 428.8 emu/cm3 to 374.0 emu/cm3. Amongst the systems investigated, the Ni0.4Zn0.4Li0.10Al0.050Fe2.050O4, Ni0.4Zn0.425Li0.10Ti0.025Fe2.050O4, and Ni0.4Zn0.450Li0.10Ti0.050Fe2.000O4 ceramics revealed promising magnetic properties for applications. The measured initial permeability and quality factor were respectively 291.9 and 45.1 for the Ni0.4Zn0.4Li0.10Al0.050Fe2.050O4 ceramic, 316.9 and 42.5 for the Ni0.4Zn0.425Li0.10Ti0.025Fe2.050O4 ceramic, 429.4 and 34.8 for the Ni0.4Zn0.450Li0.10Ti0.050Fe2.000O4 ceramic. The high initial permeability and quality factor values associated with good electrical resistivity (>106 Ω-cm) qualify the ceramics for high frequency applications.

  13. The effect of dopants on the redox performance, microstructure and phase formation of ceria

    NASA Astrophysics Data System (ADS)

    Bonk, Alexander; Maier, Annika C.; Schlupp, Meike V. F.; Burnat, Dariusz; Remhof, Arndt; Delmelle, Renaud; Steinfeld, Aldo; Vogt, Ulrich F.

    2015-12-01

    A solid state reaction is employed to investigate the influence of ZrO2, HfO2, Pr6O11, TiO2 and Li2O doping on CeO2 for a possible use in solar thermochemical redox cycles. Ceramics with a macroscopic interconnected porosity, necessary for high mass transport during redox cycles, are produced by the addition of spherical carbon particles prior to sintering. Partial closure of porosity is detectable when CeO2 is doped with Pr, Zr or Hf, while Li co-doping retains interconnected porosity more effectively than other doped or pristine ceria samples. In dense ceramics, microstructures reveal a reduction of the average grain size of pristine CeO2 with increasing Zr and Hf dopant concentration. These trends are validated using Pechini synthesized materials of the same composition. The reduction in grain size is even more pronounced for Pr doped CeO2 and Li doped Hf0.1Ce0.9O2, while TiO2 doping induces softening of samples under operating conditions (>1500 °C) limiting its use for high temperature applications. The redox performance of MxCe1-xO2-δ (M = Zr, Hf; 0 ≤ x ≤ 0.2) can be increased significantly with increasing Zr and Hf dopant concentration. At x = 0.2 (Zr, Hf) the fuel production rates are doubled as compared to pristine CeO2. The redox performance of Hf doped CeO2 remains stable upon co-doping with Li+.

  14. Low-cost copper complexes as p-dopants in solution processable hole transport layers

    SciTech Connect

    Kellermann, Renate; Taroata, Dan; Maltenberger, Anna; Hartmann, David; Schmid, Guenter; Brabec, Christoph J.

    2015-09-07

    We demonstrate the usage of the Lewis-acidic copper(II)hexafluoroacetylacetonate (Cu(hfac){sub 2}) and copper(II)trifluoroacetylacetonate (Cu(tfac){sub 2}) as low-cost p-dopants for conductivity enhancement of solution processable hole transport layers based on small molecules in organic light emitting diodes (OLEDs). The materials were clearly soluble in mixtures of environmentally friendly anisole and xylene and spin-coated under ambient atmosphere. Enhancements of two and four orders of magnitude, reaching 4.0 × 10{sup −11} S/cm with a dopant concentration of only 2 mol% Cu(hfac){sub 2} and 1.5 × 10{sup −9} S/cm with 5 mol% Cu(tfac){sub 2} in 2,2′,7,7′-tetra(N,N-ditolyl)amino-9,9-spiro-bifluorene (spiro-TTB), respectively, were achieved. Red light emitting diodes were fabricated with reduced driving voltages and enhanced current and power efficiencies (8.6 lm/W with Cu(hfac){sub 2} and 5.6 lm/W with Cu(tfac){sub 2}) compared to the OLED with undoped spiro-TTB (3.9 lm/W). The OLED with Cu(hfac){sub 2} doped spiro-TTB showed an over 8 times improved LT{sub 50} lifetime of 70 h at a starting luminance of 5000 cd/m{sup 2}. The LT{sub 50} lifetime of the reference OLED with PEDOT:PSS was only 8 h. Both non-optimized OLEDs were operated at similar driving voltage and power efficiency.

  15. Persistent dopants and phase segregation in organolead mixed-halide perovskites

    SciTech Connect

    Rosales, Bryan A.; Men, Long; Cady, Sarah D.; Hanrahan, Michael P.; Rossini, Aaron J.; Vela, Javier

    2016-07-25

    Organolead mixed-halide perovskites such as CH3NH3PbX3–aX'a (X, X' = I, Br, Cl) are interesting semiconductors because of their low cost, high photovoltaic power conversion efficiencies, enhanced moisture stability, and band gap tunability. Using a combination of optical absorption spectroscopy, powder X-ray diffraction (XRD), and, for the first time, 207Pb solid state nuclear magnetic resonance (ssNMR), we probe the extent of alloying and phase segregation in these materials. Because 207Pb ssNMR chemical shifts are highly sensitive to local coordination and electronic structure, and vary linearly with halogen electronegativity and band gap, this technique can provide the true chemical speciation and composition of organolead mixed-halide perovskites. We specifically investigate samples made by three different preparative methods: solution phase synthesis, thermal annealing, and solid phase synthesis. 207Pb ssNMR reveals that nonstoichiometric dopants and semicrystalline phases are prevalent in samples made by solution phase synthesis. We show that these nanodomains are persistent after thermal annealing up to 200 °C. Further, a novel solid phase synthesis that starts from the parent, single-halide perovskites can suppress phase segregation but not the formation of dopants. Our observations are consistent with the presence of miscibility gaps and spontaneous spinodal decomposition of the mixed-halide perovskites at room temperature. This underscores how strongly different synthetic procedures impact the nanostructuring and composition of organolead halide perovskites. In conclusion, better optoelectronic properties and improved device stability and performance may be achieved through careful manipulation of the different phases and nanodomains present in these materials.

  16. Biocompatibility of Polypyrrole with Human Primary Osteoblasts and the Effect of Dopants

    PubMed Central

    Fahlgren, Anna; Bratengeier, Cornelia; Gelmi, Amy; Semeins, Cornelis M.; Klein-Nulend, Jenneke; Jager, Edwin W. H.; Bakker, Astrid D.

    2015-01-01

    Polypyrrole (PPy) is a conducting polymer that enables controlled drug release upon electrical stimulation. We characterized the biocompatibility of PPy with human primary osteoblasts, and the effect of dopants. We investigated the biocompatibility of PPy comprising various dopants, i.e. p-toluene sulfonate (PPy-pTS), chondroitin sulfate (PPy-CS), or dodecylbenzenesulfonate (PPy-DBS), with human primary osteoblasts. PPy-DBS showed the roughest appearance of all surfaces tested, and its wettability was similar to the gold-coated control. The average number of attached cells was 45% higher on PPy-DBS than on PPy-CS or PPy-pTS, although gene expression of the proliferation marker Ki-67 was similar in osteoblasts on all surfaces tested. Osteoblasts seeded on PPy-DBS or gold showed similar vinculin attachment points, vinculin area per cell area, actin filament structure, and Feret’s diameter, while cells seeded on PPY-CS or PPY-pTS showed disturbed focal adhesions and were enlarged with disorganized actin filaments. Osteoblasts grown on PPy-DBS or gold showed enhanced alkaline phosphatase activity and osteocalcin gene expression, but reduced osteopontin gene expression compared to cells grown on PPy-pTS and PPy-CS. In conclusion, PPy doped with DBS showed excellent biocompatibility, which resulted in maintaining focal adhesions, cell morphology, cell number, alkaline phosphatase activity, and osteocalcin gene expression. Taken together, conducting polymers doped with DBS are well tolerated by osteoblasts. Our results could provide a basis for the development of novel orthopedic or dental implants with controlled release of antibiotics and pharmaceutics that fight infections or focally enhance bone formation in a tightly controlled manner. PMID:26225862

  17. Effects of Chromium Dopant on Ultraviolet Photoresponsivity of ZnO Nanorods

    NASA Astrophysics Data System (ADS)

    Mokhtari, S.; Safa, S.; Khayatian, A.; Azimirad, R.

    2017-02-01

    Structural and optical properties of bare ZnO nanorods, ZnO-encapsulated ZnO nanorods, and Cr-doped ZnO-encapsulated ZnO nanorods have been investigated. Encapsulated ZnO nanorods were grown using a simple two-stage method in which ZnO nanorods were first grown on a glass substrate directly from a hydrothermal bath, then encapsulated with a thin layer of Cr-doped ZnO by dip coating. Comparative study of x-ray diffraction patterns showed that Cr was successfully incorporated into the shell layer of ZnO nanorods. Moreover, energy-dispersive x-ray spectroscopy confirmed presence of Cr in this sample. It was observed that the thickness of the shell layer around the core of the ZnO nanorods was at least about 20 nm. Transmission electron microscopy of bare ZnO nanorods revealed single-crystalline structure. Based on optical results, both the encapsulation process and addition of Cr dopant decreased the optical bandgap of the samples. Indeed, the optical bandgap values of Cr-doped ZnO-encapsulated ZnO nanorods, ZnO-encapsulated ZnO nanorods, and bare ZnO nanorods were 2.89 eV, 3.15 eV, and 3.34 eV, respectively. The ultraviolet (UV) parameters demonstrated that incorporation of Cr dopant into the shell layer of ZnO nanorods considerably facilitated formation and transportation of photogenerated carriers, optimizing their performance as a practical UV detector. As a result, the photocurrent of the Cr-doped ZnO-encapsulated ZnO nanorods was the highest (0.6 mA), compared with ZnO-encapsulated ZnO nanorods and bare ZnO nanorods (0.21 mA and 0.06 mA, respectively).

  18. Effects of Chromium Dopant on Ultraviolet Photoresponsivity of ZnO Nanorods

    NASA Astrophysics Data System (ADS)

    Mokhtari, S.; Safa, S.; Khayatian, A.; Azimirad, R.

    2017-07-01

    Structural and optical properties of bare ZnO nanorods, ZnO-encapsulated ZnO nanorods, and Cr-doped ZnO-encapsulated ZnO nanorods have been investigated. Encapsulated ZnO nanorods were grown using a simple two-stage method in which ZnO nanorods were first grown on a glass substrate directly from a hydrothermal bath, then encapsulated with a thin layer of Cr-doped ZnO by dip coating. Comparative study of x-ray diffraction patterns showed that Cr was successfully incorporated into the shell layer of ZnO nanorods. Moreover, energy-dispersive x-ray spectroscopy confirmed presence of Cr in this sample. It was observed that the thickness of the shell layer around the core of the ZnO nanorods was at least about 20 nm. Transmission electron microscopy of bare ZnO nanorods revealed single-crystalline structure. Based on optical results, both the encapsulation process and addition of Cr dopant decreased the optical bandgap of the samples. Indeed, the optical bandgap values of Cr-doped ZnO-encapsulated ZnO nanorods, ZnO-encapsulated ZnO nanorods, and bare ZnO nanorods were 2.89 eV, 3.15 eV, and 3.34 eV, respectively. The ultraviolet (UV) parameters demonstrated that incorporation of Cr dopant into the shell layer of ZnO nanorods considerably facilitated formation and transportation of photogenerated carriers, optimizing their performance as a practical UV detector. As a result, the photocurrent of the Cr-doped ZnO-encapsulated ZnO nanorods was the highest (0.6 mA), compared with ZnO-encapsulated ZnO nanorods and bare ZnO nanorods (0.21 mA and 0.06 mA, respectively).

  19. Theoretical Spin-Orbit Spectroscopy of cl Dopants in Solid Parahydrogen

    NASA Astrophysics Data System (ADS)

    Hinde, Robert

    2012-06-01

    Solid parahydrogen (pH_2) matrices containing open-shell (^2P) Cl and Br atoms as substitutional impurities exhibit several infrared (IR) absorption features associated with intermolecular interactions between the halogen atom and nearby pH_2 molecules. These dopant-induced IR absorption features are associated with (i) spin-orbit (SO) excitation of the halogen atom, and (ii) cooperative excitations in which a single IR photon both triggers SO excitation of the halogen atom and excites the H-H stretching coordinate of a nearby pH_2 molecule. The IR spectral features thus contain detailed information about the interaction between the open-shell halogen atom and the surrounding pH_2 molecules, and in particular tell us about the coupling between the atom's electronic degrees of freedom and the nuclear motion of its H_2 neighbors. Here we present recent progress towards understanding these features in Cl-doped solid pH_2. This system represents an arena for testing theoretical approaches that generate many-body, non-pairwise-additive potential energy functions for the dopant--matrix interaction by combining multiple low-lying Cl--H_2 pair potential energy functions. Our analysis must account for the fact that the individual pH_2 molecules in the doped solid undergo large amplitude zero-point motions; we use quantum Monte Carlo simulations to model these zero-point motions. We interpret our findings in terms of a reduced dimensionality model that provides a qualitative understanding of the role that matrix zero-point motions play in the observed spectra. P. L. Raston and D. T. Anderson, J. Chem. Phys. 126, 021106 (2007) S. C. Kettwich, L. O. Paulson, P. L. Raston and D. T. Anderson, J. Phys. Chem. A 112, 11153 (2008). I .F. Silvera, Rev. Mod. Phys. 52, 393 (1980). R. J. Hinde, Comput. Phys. Commun. 182, 2339 (2011).

  20. The LMOP Locator

    EPA Pesticide Factsheets

    This page contains the LMOP Locator, a tool that allows a user to geographically search for facilities that can potentially utilize LFG, or for landfills located near a facility that is interested in utilizing LFG.

  1. Location | FNLCR Staging

    Cancer.gov

    The Frederick National Laboratory for Cancer Research campus is located 50 miles northwest of Washington, D.C., and 50 miles west of Baltimore, Maryland, in Frederick, Maryland. Satellite locations include leased and government facilities extending s

  2. Doped Graphene for DNA Analysis: the Electrochemical Signal is Strongly Influenced by the Kind of Dopant and the Nucleobase Structure

    PubMed Central

    Tian, Huidi; Wang, Lu; Sofer, Zdenek; Pumera, Martin; Bonanni, Alessandra

    2016-01-01

    Doping graphene with heteroatoms can alter the electronic and electrochemical properties of the starting material. Contrasting properties should be expected when the doping is carried out with electron donating species (n-type dopants) or with electron withdrawing species (p-type dopants). This in turn can have a profound influence on the electroanalytical performance of the doped material being used for the detection of specific probes. Here we investigate the electrochemical oxidation of DNA bases adenine, guanine, thymine and cytosine on two heteroatom-doped graphene platforms namely boron-doped graphene (p-type dopant) and nitrogen-doped graphene (n-type dopant). We found that overall, boron–doped graphene provided the best response in terms of electrochemical signal sensitivity for all bases. This is due to the electron deficiency of boron-doped graphene, which can promote the oxidation of DNA bases, as opposed to nitrogen-doped graphene which possesses an excess of electrons. Moreover, also the structure of the nucleobase was found to have significant influence on the obtained signal. Our study may open new frontiers in the electrochemical detection of DNA bases which is the first step for label-free DNA analysis. PMID:27623951

  3. Influence of Dopant Loading on the Photo- and Electrochemical Properties of (N, O)-Co-doped Graphene.

    PubMed

    Baldoví, Hermenegildo G; Albarracín, Ferran; Álvaro, Mercedes; Ferrer, Belén; García, Hermenegildo

    2015-07-20

    A series of (N, O)-co-doped graphenes with different N and O loadings are prepared by the pyrolysis of natural chitosan. When the percentage of dopant increases, the conduction-band potential and charge-separation quantum yield increase, whereas the charge-separation lifetime decreases.

  4. Investigation of iodine dopant amount effects on dye-sensitized hierarchically structured ZnO solar cells

    SciTech Connect

    Zheng, Yan-Zhen; Ding, Haiyang; Tao, Xia; Chen, Jian-Feng

    2014-07-01

    Highlights: • The effect of I amount on the photovoltaic performance was investigated. • The enhancement in η of ZnO:I DSSCs was from 38% to 77% compared with ZnO DSSCs. • Appropriate I doping enhanced light harness and inhibited charge recombination. - Abstract: We prepare a series of iodine doped zinc oxide monodisperse aggregates (ZnO:I) with various iodine concentrations as the photoanodes of dye-sensitized solar cells (DSSCs) to study iodine dopant amount-dependent photovoltaic performance. The iodine-doped DSSCs achieve overall conversion efficiency (η) of 3.6–4.6%. The enhancement in η of ZnO:I DSSCs is from 38% to 77% as compared to undoped ZnO DSSCs. The significantly enhanced η of DSSCs is found to be correlated with iodine dopant amount. The optimum iodine dopant amount is determined to be 2.3 wt% by X-ray photoelectron spectroscopy. Furthermore, the incident photon to current conversion efficiency and electrochemical impedance spectroscopy data reveal a systematic correlation between photovoltaic properties and the iodine dopant amount. The enhancement of open-circuit potential of ZnO:I cells is arising from negative shift of their flat-band potential, as demonstrated by Mott–Schottky measurement.

  5. Effective dopant activation by susceptor-assisted microwave annealing of low energy boron implanted and phosphorus implanted silicon

    SciTech Connect

    Zhao, Zhao; Vemuri, Rajitha N. P.; Alford, T. L.; David Theodore, N.; Lu, Wei; Lau, S. S.; Lanz, A.

    2013-12-28

    Rapid processing and reduced end-of-range diffusion result from susceptor-assisted microwave (MW) annealing, making this technique an efficient processing alternative for electrically activating dopants within ion-implanted semiconductors. Sheet resistance and Hall measurements provide evidence of electrical activation. Susceptor-assisted MW annealing, of ion-implanted Si, enables more effective dopant activation and at lower temperatures than required for rapid thermal annealing (RTA). Raman spectroscopy and ion channeling analyses are used to monitor the extent of ion implantation damage and recrystallization. The presence and behavior of extended defects are monitored by cross-section transmission electron microscopy. Phosphorus implanted Si samples experience effective electrical activation upon MW annealing. On the other hand, when boron implanted Si is MW annealed, the growth of extended defects results in reduced crystalline quality that hinders the electrical activation process. Further comparison of dopant diffusion resulting from MW annealing and rapid thermal annealing is performed using secondary ion mass spectroscopy. MW annealed ion implanted samples show less end-of-range diffusion when compared to RTA samples. In particular, MW annealed P{sup +} implanted samples achieve no visible diffusion and equivalent electrical activation at a lower temperature and with a shorter time-duration of annealing compared to RTA. In this study, the peak temperature attained during annealing does not depend on the dopant species or dose, for susceptor-assisted MW annealing of ion-implanted Si.

  6. Anomalous radial and angular strain relaxation around dilute p-, isoelectronic-, and n-type dopants in Si crystal

    NASA Astrophysics Data System (ADS)

    Zhao, Mingshu; Dong, Juncai; Chen, Dongliang

    2017-02-01

    Doping is widely applied in yielding desirable properties and functions in silicon technology; thus, fully understanding the relaxation mechanism for lattice-mismatch strain is of fundamental importance. Here we systematically study the local lattice distortion near dilute IIIA-, IVA-, and VA-group substitutional dopants in Si crystal using density functional theory, and anomalous radial and angular strain relaxation modes are first revealed. Both the nearest-neighbor (NN) bond-distances and the tetrahedral bond-angles are found to exhibit completely opposite dependence on the electronic configurations for the low Z (Z<26) and high Z (Z>26) dopants. More surprisingly, negative and positive angular shifts for the second NN twelve Si2 atoms are unveiled surrounding the p- and n-type dopants, respectively. While electron localization function shows that the doped hole and electron are highly localized near the dopants, hence being responsible for the abnormal angular shifts, a universal radial strain relaxation mechanism dominated by a competition of the Coulomb interactions among the ion-core, bond-charge, and the localized hole or electron is also proposed. These findings may prove to be instrumental in precise design of silicon-based solotronics.

  7. The role of the domain size and titanium dopant in nanocrystalline hematite thin films for water photolysis

    SciTech Connect

    Yan, Danhua; Tao, Jing; Kisslinger, Kim; Cen, Jiajie; Wu, Qiyuan; Orlov, Alexander; Liu, Mingzhao

    2015-10-13

    In this study, we develop a novel technique for preparing high quality Ti-doped hematite thin films for photoelectrochemical (PEC) water splitting, through sputtering deposition of metallic iron films from an iron target embedded with titanium (dopants) pellets, followed by a thermal oxidation step that turns the metal films into doped hematite. It is found that the hematite domain size can be tuned from ~10 nm to over 100 nm by adjusting the sputtering atmosphere from more oxidative to mostly inert. The better crystallinity at a larger domain size ensures excellent PEC water splitting performance, leading to record high photocurrent from pure planar hematite thin films on FTO substrates. Titanium doping further enhances the PEC performance of hematite photoanodes. The photocurrent is improved by 50%, with a titanium dopant concentration as low as 0.5 atom%. It is also found that the role of the titanium dopant in improving the PEC performance is not apparently related to the films’ electrical conductivity which had been widely believed, but is more likely due to the passivation of surface defects by the titanium dopants.

  8. The role of the domain size and titanium dopant in nanocrystalline hematite thin films for water photolysis

    DOE PAGES

    Yan, Danhua; Tao, Jing; Kisslinger, Kim; ...

    2015-10-13

    Here we develop a novel technique for preparing high quality Ti-doped hematite thin films for photoelectrochemical (PEC) water splitting, through sputtering deposition of metallic iron films from an iron target embedded with titanium (dopants) pellets, followed by a thermal oxidation step that turns the metal films into doped hematite. It is found that the hematite domain size can be tuned from ~10 nm to over 100 nm by adjusting the sputtering atmosphere from more oxidative to mostly inert. The better crystallinity at a larger domain size ensures excellent PEC water splitting performance, leading to record high photocurrent from pure planarmore » hematite thin films on FTO substrates. Titanium doping further enhances the PEC performance of hematite photoanodes. The photocurrent is improved by 50%, with a titanium dopant concentration as low as 0.5 atom%. As a result, it is also found that the role of the titanium dopant in improving the PEC performance is not apparently related to the films’ electrical conductivity which had been widely believed, but is more likely due to the passivation of surface defects by the titanium dopants.« less

  9. Direct observation of dopant distribution in GaAs compound semiconductors using phase-shifting electron holography and Lorentz microscopy.

    PubMed

    Sasaki, Hirokazu; Otomo, Shinya; Minato, Ryuichiro; Yamamoto, Kazuo; Hirayama, Tsukasa

    2014-06-01

    Phase-shifting electron holography and Lorentz microscopy were used to map dopant distributions in GaAs compound semiconductors with step-like dopant concentration. Transmission electron microscope specimens were prepared using a triple beam focused ion beam (FIB) system, which combines a Ga ion beam, a scanning electron microscope, and an Ar ion beam to remove the FIB damaged layers. The p-n junctions were clearly observed in both under-focused and over-focused Lorentz microscopy images. A phase image was obtained by using a phase-shifting reconstruction method to simultaneously achieve high sensitivity and high spatial resolution. Differences in dopant concentrations between 1 × 10(19) cm(-3) and 1 × 10(18) cm(-3) regions were clearly observed by using phase-shifting electron holography. We also interpreted phase profiles quantitatively by considering inactive layers induced by ion implantation during the FIB process. The thickness of an inactive layer at different dopant concentration area can be measured from the phase image.

  10. Efficient 3D 'Atomistic' Simulation Technique for Studying of Random Dopant Induced Threshold Voltage Lowering and Fluctuations in Decanano MOSFETs

    NASA Technical Reports Server (NTRS)

    Asenov, Asen

    1998-01-01

    A 3D 'atomistic' simulation technique to study random dopant induced threshold voltage lowering and fluctuations in sub 0.1 micron MOSFETs is presented. It allows statistical analysis of random impurity effects down to the individual impurity level. Efficient algorithms based on a single solution of Poisson's equation, followed by the solution of a simplified current continuity equation are used in the simulations.

  11. Doped Graphene for DNA Analysis: the Electrochemical Signal is Strongly Influenced by the Kind of Dopant and the Nucleobase Structure

    NASA Astrophysics Data System (ADS)

    Tian, Huidi; Wang, Lu; Sofer, Zdenek; Pumera, Martin; Bonanni, Alessandra

    2016-09-01

    Doping graphene with heteroatoms can alter the electronic and electrochemical properties of the starting material. Contrasting properties should be expected when the doping is carried out with electron donating species (n-type dopants) or with electron withdrawing species (p-type dopants). This in turn can have a profound influence on the electroanalytical performance of the doped material being used for the detection of specific probes. Here we investigate the electrochemical oxidation of DNA bases adenine, guanine, thymine and cytosine on two heteroatom-doped graphene platforms namely boron-doped graphene (p-type dopant) and nitrogen-doped graphene (n-type dopant). We found that overall, boron–doped graphene provided the best response in terms of electrochemical signal sensitivity for all bases. This is due to the electron deficiency of boron-doped graphene, which can promote the oxidation of DNA bases, as opposed to nitrogen-doped graphene which possesses an excess of electrons. Moreover, also the structure of the nucleobase was found to have significant influence on the obtained signal. Our study may open new frontiers in the electrochemical detection of DNA bases which is the first step for label-free DNA analysis.

  12. Doped Graphene for DNA Analysis: the Electrochemical Signal is Strongly Influenced by the Kind of Dopant and the Nucleobase Structure.

    PubMed

    Tian, Huidi; Wang, Lu; Sofer, Zdenek; Pumera, Martin; Bonanni, Alessandra

    2016-09-14

    Doping graphene with heteroatoms can alter the electronic and electrochemical properties of the starting material. Contrasting properties should be expected when the doping is carried out with electron donating species (n-type dopants) or with electron withdrawing species (p-type dopants). This in turn can have a profound influence on the electroanalytical performance of the doped material being used for the detection of specific probes. Here we investigate the electrochemical oxidation of DNA bases adenine, guanine, thymine and cytosine on two heteroatom-doped graphene platforms namely boron-doped graphene (p-type dopant) and nitrogen-doped graphene (n-type dopant). We found that overall, boron-doped graphene provided the best response in terms of electrochemical signal sensitivity for all bases. This is due to the electron deficiency of boron-doped graphene, which can promote the oxidation of DNA bases, as opposed to nitrogen-doped graphene which possesses an excess of electrons. Moreover, also the structure of the nucleobase was found to have significant influence on the obtained signal. Our study may open new frontiers in the electrochemical detection of DNA bases which is the first step for label-free DNA analysis.

  13. Effects of In, Al and Sn dopants on the structural and optical properties of ZnO thin films.

    PubMed

    Caglar, Yasemin; Ilican, Saliha; Caglar, Mujdat; Yakuphanoglu, Fahrettin

    2007-07-01

    Effect of In, Al and Sn dopants on the optical and structural properties of ZnO thin films have been investigated by X-ray diffraction technique and optical characterization method. X-ray diffraction patterns confirm that the films have polycrystalline nature. The thin films have (002) as the preferred orientation. This (002) preferred orientation is due to the minimal surface energy which the hexagonal structure, c-plane to the ZnO crystallites, corresponds to the densest packed plane. The grain size values of the films are found to be 29.0, 35.2 and 39.5 nm for In, Al and Sn doped ZnO thin films, respectively. The optical band gaps of the films were calculated. The absorption edge shifts to the lower wavelengths with In, Al and Sn dopants. The inclusion of dopant into films expands also width of localized states as E(UIn)>E(UAl)>E(USn). The refractive index dispersion curves obey the single oscillator model. The dispersion parameters and optical constants of the films were determined. These parameters changed with In, Al and Sn dopants.

  14. Random Dopant Threshold Voltage Fluctuations in 50 nm Epitaxial Channel MOSFETs: A 3D 'Atomoc' Simulation Study

    NASA Technical Reports Server (NTRS)

    Asenov, Asen

    2000-01-01

    3D 'atomistic' simulations are used to study random dopant related threshold voltage fluctuations in 50 nm MOSFETs. Comparisons are made between conventionally doped transistors and transistors with thin epitaxial silicon layers on heavily doped silicon. Issues related to both the optimum threshold voltage control and the suppression of the threshold voltage dispersion are addressed.

  15. Location, Location, Location: Where Do Location-Based Services Fit into Your Institution's Social Media Mix?

    ERIC Educational Resources Information Center

    Nekritz, Tim

    2011-01-01

    Foursquare is a location-based social networking service that allows users to share their location with friends. Some college administrators have been thinking about whether and how to take the leap into location-based services, which are also known as geosocial networking services. These platforms, which often incorporate gaming elements like…

  16. Location, Location, Location: Where Do Location-Based Services Fit into Your Institution's Social Media Mix?

    ERIC Educational Resources Information Center

    Nekritz, Tim

    2011-01-01

    Foursquare is a location-based social networking service that allows users to share their location with friends. Some college administrators have been thinking about whether and how to take the leap into location-based services, which are also known as geosocial networking services. These platforms, which often incorporate gaming elements like…

  17. Locatives in Kpelle.

    ERIC Educational Resources Information Center

    Kuha, Mai

    This paper examines the differences between locative expressions in Kpelle and English, based on the dialect of one native speaker of Kpelle. It discusses the crucial role of the reference object in defining the meaning of locatives in Kpelle, in contrast to English, where the characteristics of the object to be located are less important. An…

  18. Non-classical behaviour of higher valence dopants in chromium (III) oxide by a Cr vacancy compensation mechanism

    NASA Astrophysics Data System (ADS)

    Carey, John J.; Nolan, Michael

    2017-10-01

    Modification of metal oxides with dopants that have a stable oxidation in their parent oxides which is higher than the host system is expected to introduce extra electrons into the material to improve carrier mobility. This is essential for applications in catalysis, SOFCs and solar energy materials. Density functional theory calculations are used to investigate the change in electronic and geometric structure of chromium (III) oxide by higher valence dopants, namely; Ce, Ti, V and Zr. For single metal doping, we find that the dopants with variable oxidation states, Ce, Ti and V, adopt a valence state of  +3, while Zr dopant has a  +4 oxidation state and reduces a neighbouring Cr cation. Chromium vacancy formation is greatly enhanced for all dopants, and favoured over oxygen vacancy formation. The Cr vacancies generate holes which oxidise Ce, Ti and V from  +3 to  +4, while also oxidising lattice oxygen sites. For Zr doping, the generated holes oxidise the reduced Cr2+ cation back to Cr3+ and also two lattice oxygen atoms. Three metal atoms in the bulk lattice facilitate spontaneous Cr vacancy from charge compensation. A non-classical compensation mechanism is observed for Ce, Ti and V; all three metals are oxidised from  +3 to  +4, which explains experimental observations that these metals have a  +4 oxidation state in Cr2O3. Charge compensation of the three Zr metals proceeds by a classical higher valence doping mechanism; the three dopants reduce three Cr cations, which are subsequently charge compensated by a Cr vacancy oxidising three Cr2+ to Cr3+. The compensated structures are the correct ground state electronic structure for these doped systems, and used as a platform to investigate cation/anion vacancy formation. Unlike the single metal doped bulks, preference is now given for oxygen vacancy formation over Cr vacancy formation, indicating that the dopants increase the reducibility of Cr2O3 with Ce doping showing the strongest

  19. Sleeping at work: not all about location, location, location.

    PubMed

    Jay, Sarah M; Aisbett, Brad; Sprajcer, Madeline; Ferguson, Sally A

    2015-02-01

    Working arrangements in industries that use non-standard hours sometimes necessitate an 'onsite' workforce where workers sleep in accommodation within or adjacent to the workplace. Of particular relevance to these workers is the widely held (and largely anecdotal) assumption that sleep at home is better than sleep away, particularly when away for work. This narrative review explores the idea that sleep outcomes in these unique work situations are the product of an interaction between numerous factors including timing and duration of breaks, commute length, sleeping environment (noise, movement, vibration, light), circadian phase, demographic factors and familiarity with the sleep location. Based on the data presented in this review, it is our contention that the location of sleep, whilst important, is secondary to other factors such as the timing and duration of sleep periods. We suggest that future research should include measures that allow conceptualisation of other critical factors such as familiarity with the sleeping environment. Copyright © 2014 Elsevier Ltd. All rights reserved.

  20. Effect of cation dopants in zirconia on interfacial properties in nickel/zirconia systems: an atomistic modeling study

    NASA Astrophysics Data System (ADS)

    Iskandarov, Albert M.; Ding, Yingna; Umeno, Yoshitaka

    2017-02-01

    Cation doping is often used to stabilize the cubic or tetragonal phase of zirconia for enhanced thermomechanical and electrochemical properties. In the present paper we report a combined density functional theory (DFT) and molecular dynamics study of the effect of Sc, Y, and Ce dopants on properties of Ni/\\text{Zr}{{\\text{O}}2} interfaces and nickel sintering. First, we develop an MD model that is based on DFT data for various nickel/zirconia interfaces. Then, we employ the model to simulate Ni nanoparticles coalescing on a zirconia surface. The results show the possibility of particle migration by means of fast sliding over the surface when the work of separation is small (<1.0\\text{J} {{\\text{m}}-2} ). The sliding observed for the O-terminated Ni(1 1 1)/\\text{Zr}{{\\text{O}}2} (1 1 1) interface is not affected by dopants in zirconia because the work of separation of the doped interface stays small. The most pronounced effect of the dopants is observed for the Zr-terminated Ni(1 1 1)/\\text{Zr}{{\\text{O}}2} (1 1 1) interface, which possesses a large work of separation (4.4\\text{J} {{\\text{m}}-2} ) and thus restricts the sliding mechanism of Ni nanoparticle migration. DFT calculations for the interface revealed that dopants with a smaller covalent radius result in a larger energy barriers for Ni diffusion. We analyze this effect and discuss how it can be used to suppress nickel sintering by using the dopant selection.

  1. Ionization of EPA contaminants in direct and dopant-assisted atmospheric pressure photoionization and atmospheric pressure laser ionization.

    PubMed

    Kauppila, Tiina J; Kersten, Hendrik; Benter, Thorsten

    2015-06-01

    Seventy-seven EPA priority environmental pollutants were analyzed using gas chromatography-mass spectrometry (GC-MS) equipped with an optimized atmospheric pressure photoionization (APPI) and an atmospheric pressure laser ionization (APLI) interface with and without dopants. The analyzed compounds included e.g., polycyclic aromatic hydrocarbons (PAHs), nitro compounds, halogenated compounds, aromatic compounds with phenolic, acidic, alcohol, and amino groups, phthalate and adipatic esters, and aliphatic ethers. Toluene, anisole, chlorobenzene, and acetone were tested as dopants. The widest range of analytes was ionized using direct APPI (66/77 compounds). The introduction of dopants decreased the amount of compounds ionized in APPI (e.g., 54/77 with toluene), but in many cases the ionization efficiency increased. While in direct APPI the formation of molecular ions via photoionization was the main ionization reaction, dopant-assisted (DA) APPI promoted ionization reactions, such as charge exchange and proton transfer. Direct APLI ionized a much smaller amount of compounds than APPI (41/77 compounds), showing selectivity towards compounds with low ionization energies (IEs) and long-lived resonantly excited intermediate states. DA-APLI, however, was able to ionize a higher amount of compounds (e.g. 51/77 with toluene), as the ionization took place entirely through dopant-assisted ion/molecule reactions similar to those in DA-APPI. Best ionization efficiency in APPI and APLI (both direct and DA) was obtained for PAHs and aromatics with O- and N-functionalities, whereas nitro compounds and aliphatic ethers were the most difficult to ionize. Halogenated aromatics and esters were (mainly) ionized in APPI, but not in APLI.

  2. Density functional theory study of dopant effect on formation energy of intrinsic point defects in germanium crystals

    NASA Astrophysics Data System (ADS)

    Yamaoka, S.; Kobayashi, K.; Sueoka, K.; Vanhellemont, J.

    2017-09-01

    During the last decade the use of single crystal germanium (Ge) layers and structures in combination with silicon (Si) substrates has led to a revival of defect research on Ge. Ge is used because of the much higher carrier mobility compared to Si, allowing to design devices operating at much higher frequencies. A major issue for the use of Ge single crystal wafers is the fact that all Czochralski-grown Ge (CZ-Ge) crystals are vacancy-rich and contain vacancy clusters that are much larger than the ones in Si. In contrast to Si, control of intrinsic point defect concentrations has not yet been realized at the same level in Ge crystals due to the lack of experimental data especially on dopant effects. In this study, we have evaluated with density functional theory (DFT) calculations the dopant effect on the formation energy (Ef) of the uncharged vacancy (V) and self-interstitial (I) in Ge and compared the results with those for Si. The dependence of the total thermal equilibrium concentrations of point defects (sum of free V or I and V or I paired with dopant atoms) at melting temperature on the type and concentration of various dopants is obtained. It was found that (1) Ge crystals will be more V-rich by Tl, In, Sb, Sn, As and P doping, (2) Ge crystals will be more I-rich by Ga, C and B doping, (3) Si doping has negligible impact. The dopant impact on Ef of V and I in Ge has a narrower range and is smaller than that in Si. The obtained results are useful to control grown-in V and I concentrations, and will perhaps also allow to develop defect-free ;perfect; Ge crystals.

  3. Ionization of EPA Contaminants in Direct and Dopant-Assisted Atmospheric Pressure Photoionization and Atmospheric Pressure Laser Ionization

    NASA Astrophysics Data System (ADS)

    Kauppila, Tiina J.; Kersten, Hendrik; Benter, Thorsten

    2015-06-01

    Seventy-seven EPA priority environmental pollutants were analyzed using gas chromatography-mass spectrometry (GC-MS) equipped with an optimized atmospheric pressure photoionization (APPI) and an atmospheric pressure laser ionization (APLI) interface with and without dopants. The analyzed compounds included e.g., polycyclic aromatic hydrocarbons (PAHs), nitro compounds, halogenated compounds, aromatic compounds with phenolic, acidic, alcohol, and amino groups, phthalate and adipatic esters, and aliphatic ethers. Toluene, anisole, chlorobenzene, and acetone were tested as dopants. The widest range of analytes was ionized using direct APPI (66/77 compounds). The introduction of dopants decreased the amount of compounds ionized in APPI (e.g., 54/77 with toluene), but in many cases the ionization efficiency increased. While in direct APPI the formation of molecular ions via photoionization was the main ionization reaction, dopant-assisted (DA) APPI promoted ionization reactions, such as charge exchange and proton transfer. Direct APLI ionized a much smaller amount of compounds than APPI (41/77 compounds), showing selectivity towards compounds with low ionization energies (IEs) and long-lived resonantly excited intermediate states. DA-APLI, however, was able to ionize a higher amount of compounds (e.g. 51/77 with toluene), as the ionization took place entirely through dopant-assisted ion/molecule reactions similar to those in DA-APPI. Best ionization efficiency in APPI and APLI (both direct and DA) was obtained for PAHs and aromatics with O- and N-functionalities, whereas nitro compounds and aliphatic ethers were the most difficult to ionize. Halogenated aromatics and esters were (mainly) ionized in APPI, but not in APLI.

  4. Operational gunshot location system

    NASA Astrophysics Data System (ADS)

    Showen, Robert

    1997-02-01

    The nation's first operational trial of a gunshot location system is underway in Redwood City, California. The system uses acoustic sensors widely distributed over an impacted community. The impulses received at each sensor allow triangulation of the gunfire location and prompt police dispatch. A computer display shows gunfire location superimposed on a map showing property boundaries. Police are responding to system events immediately and in a community-policing investigative role.

  5. Wet, dry, Dopants and Defects - an Integrated View of Diffusion in Olivine as a Prototypical Silicate

    NASA Astrophysics Data System (ADS)

    Dohmen, R.; Costa, F.; Chakraborty, S.

    2008-12-01

    Knowledge of diffusion coefficients of different species in minerals is a necessary pre-requisite for understanding and modeling the compositional evolution of rocks. Their use to determine time scales of various geological processes, to understand the reaction mechanisms and rheological behavior of rocks and minerals, and to evaluate the significance of dates and temperatures obtained from geochronometers and geothermometers, is becoming routine. However, many aspects of diffusion behavior of minerals remain enigmatic. Two of these are: (1) Do the presence of small amounts of impurities ("dopants") affect diffusion rates, and if yes, how? (2) Water is known to enhance transport rates, but exactly at what conditions and how does the wet to dry transition occur? Can it be predicted? These questions can be approached by developing an appropriate description of the diffusion process in terms of point defect thermodynamics. The large body of systematic diffusion data and natural observations in olivine makes it the mineral of choice to explore this avenue. Diffusion coefficients for various cations as well as O are known typically as a function of temperature, and often as a function of other variables such as pressure, oxygen fugacity or water fugacity. We developed a quantitative point defect model that allows the role of trace elements (i.e. dopants in the terminology of material science) in controlling transport properties to be quantified [1]. In addition we explored the nature of wet to dry transition of these transport properties in olivine [2]. We have now combined these approaches to develop an integrated scheme for describing point defect chemistry and transport properties of olivine containing arbitrary trace elements, in the presence or absence of water. The approach is perfectly general and can be extended to any other mineral provided enough data are available. Oxygen fugacity is known to affect transport rates of Fe-bearing silicates but the extent of

  6. Parachute recovery location aids

    NASA Technical Reports Server (NTRS)

    Silbert, M. N.; Moltedo, A. D.; Bedy, E. P., Sr.

    1986-01-01

    This paper presents various types of location aid devices that may be used individually or in some combination to locate parachutes designed for the recovery of scientific data and instrumentation that have impacted on the earth's surface. Systems may be used on either recovery parachute systems or high altitude parachute systems. It is noted that all location aids are passive during the data gathering period of flight. Initial results of test data from two types of direction finder receivers are presented as well as their application and use with parachute borne and other location transmitters.

  7. Reversible micromachining locator

    DOEpatents

    Salzer, L.J.; Foreman, L.R.

    1999-08-31

    This invention provides a device which includes a locator, a kinematic mount positioned on a conventional tooling machine, a part carrier disposed on the locator and a retainer ring. The locator has disposed therein a plurality of steel balls, placed in an equidistant position circumferentially around the locator. The kinematic mount includes a plurality of magnets which are in registry with the steel balls on the locator. In operation, a blank part to be machined is placed between a surface of a locator and the retainer ring (fitting within the part carrier). When the locator (with a blank part to be machined) is coupled to the kinematic mount, the part is thus exposed for the desired machining process. Because the locator is removably attachable to the kinematic mount, it can easily be removed from the mount, reversed, and reinserted onto the mount for additional machining. Further, the locator can likewise be removed from the mount and placed onto another tooling machine having a properly aligned kinematic mount. Because of the unique design and use of magnetic forces of the present invention, positioning errors of less than 0.25 micrometer for each machining process can be achieved. 7 figs.

  8. Reversible micromachining locator

    DOEpatents

    Salzer, Leander J.; Foreman, Larry R.

    1999-01-01

    This invention provides a device which includes a locator, a kinematic mount positioned on a conventional tooling machine, a part carrier disposed on the locator and a retainer ring. The locator has disposed therein a plurality of steel balls, placed in an equidistant position circumferentially around the locator. The kinematic mount includes a plurality of magnets which are in registry with the steel balls on the locator. In operation, a blank part to be machined is placed between a surface of a locator and the retainer ring (fitting within the part carrier). When the locator (with a blank part to be machined) is coupled to the kinematic mount, the part is thus exposed for the desired machining process. Because the locator is removably attachable to the kinematic mount, it can easily be removed from the mount, reversed, and reinserted onto the mount for additional machining. Further, the locator can likewise be removed from the mount and placed onto another tooling machine having a properly aligned kinematic mount. Because of the unique design and use of magnetic forces of the present invention, positioning errors of less than 0.25 micrometer for each machining process can be achieved.

  9. Heterogeneity of nervous system mitochondria: location, location, location!

    PubMed

    Dubinsky, Janet M

    2009-08-01

    Mitochondrial impairments have been associated with many neurological disorders, from inborn errors of metabolism or genetic disorders to age and environmentally linked diseases of aging (DiMauro S., Schon E.A. 2008. Mitochondrial disorders in the nervous system. Annu. Rev., Neurosci. 31, 91-123.). In these disorders, specific nervous system components or brain regions appear to be initially more susceptible to the triggering event or pathological process. Such regional variation in susceptibility to multiple types of stressors raises the possibility that inherent differences in mitochondrial function may mediate some aspect of pathogenesis. Regional differences in the distribution or number of mitochondria, mitochondrial enzyme activities, enzyme expression levels, mitochondrial genes or availability of necessary metabolites become attractive explanations for selective vulnerability of a nervous system structure. While regionally selective mitochondrial vulnerability has been documented, regional variations in other cellular and tissue characteristics may also contribute to metabolic impairment. Such environmental variables include high tonic firing rates, neurotransmitter phenotype, location of mitochondria within a neuron, or the varied tissue perfusion pressure of different cerebral arterial branches. These contextual variables exert regionally distinct regulatory influences on mitochondria to tune their energy production to local demands. Thus to understand variations in mitochondrial functioning and consequent selective vulnerability to injury, the organelle must be placed within the context of its cellular, functional, developmental and neuroanatomical environment.

  10. The effect of diketopyrrolopyrrole (DPP) group inclusion in p-cyanophenyl end-capped oligothiophene used as a dopant in P3HT:PCBM BHJ solar cells.

    PubMed

    Manninen, V M; Heiskanen, J P; Pankov, D; Kastinen, T; Hukka, T I; Hormi, O E O; Lemmetyinen, H J

    2014-10-01

    In this work, two p-cyanophenyl end-capped oligothiophenes, and , were compared as dopants in the P3HT:PC60BM bulk heterojunction (BHJ) layer of inverted organic solar cells. Inclusion of significantly increased the average efficiency of the solar cells, while the increase using doping in the cell efficiency was minor. In the BHJ photoactive layer, the dopant molecules are close to and interact with P3HT and PC60BM molecules. Intra- and intermolecular interactions of the dopant molecules with P3HT and PC60BM were studied in chloroform solutions. Energy or electron transfer from the dopant molecules to PC60BM takes place as the fluorescence emission intensity and lifetime of the dopant molecules decreased in the presence of PC60BM. In the case of doping with , doped cells had higher absorbance than the non-doped reference cell and doping broadens the cell absorption to the near IR-region. Thus, the dopant molecules act as additional light absorbers in the photoactive layer and transfer energy or electrons to PC60BM, which increases the short circuit current and power conversion efficiency of the cell. Also, the emission of the cells doped with decreased when compared to that of the reference cell. In this case, P3HT can give electrons or energy to dopant molecules and the cell current and efficiency are further increased.

  11. Object locating system

    DOEpatents

    Novak, James L.; Petterson, Ben

    1998-06-09

    A sensing system locates an object by sensing the object's effect on electric fields. The object's effect on the mutual capacitance of electrode pairs varies according to the distance between the object and the electrodes. A single electrode pair can sense the distance from the object to the electrodes. Multiple electrode pairs can more precisely locate the object in one or more dimensions.

  12. Acoustic emission source location

    NASA Astrophysics Data System (ADS)

    Promboon, Yajai

    The objective of the research program was development of reliable source location techniques. The study comprised two phases. First, the research focused on development of source location methods for homogeneous plates. The specimens used in the program were steel railroad tank cars. Source location methods were developed and demonstrated for empty and water filled tanks. The second phase of the research was an exploratory study of source location method for fiber reinforced composites. Theoretical analysis and experimental measurement of wave propagation were carried out. This data provided the basis for development of a method using the intersection of the group velocity curves for the first three wave propagation modes. Simplex optimization was used to calculate the location of the source. Additional source location methods have been investigated and critically examined. Emphasis has been placed on evaluating different methods for determining the time of arrival of a wave. The behavior of wave in a water filled tank was studied and source location methods suitable for use in this situation have been examined through experiment and theory. Particular attention is paid to the problem caused by leaky Lamb waves. A preliminary study into the use of neural networks for source location in fiber reinforced composites was included in the research program. A preliminary neural network model and the results from training and testing data are reported.

  13. Reversible micromachining locator

    DOEpatents

    Salzer, Leander J.; Foreman, Larry R.

    2002-01-01

    A locator with a part support is used to hold a part onto the kinematic mount of a tooling machine so that the part can be held in or replaced in exactly the same position relative to the cutting tool for machining different surfaces of the part or for performing different machining operations on the same or different surfaces of the part. The locator has disposed therein a plurality of steel balls placed at equidistant positions around the planar surface of the locator and the kinematic mount has a plurality of magnets which alternate with grooves which accommodate the portions of the steel balls projecting from the locator. The part support holds the part to be machined securely in place in the locator. The locator can be easily detached from the kinematic mount, turned over, and replaced onto the same kinematic mount or another kinematic mount on another tooling machine without removing the part to be machined from the locator so that there is no need to touch or reposition the part within the locator, thereby assuring exact replication of the position of the part in relation to the cutting tool on the tooling machine for each machining operation on the part.

  14. Automatic vehicle location system

    NASA Technical Reports Server (NTRS)

    Hansen, G. R., Jr. (Inventor)

    1973-01-01

    An automatic vehicle detection system is disclosed, in which each vehicle whose location is to be detected carries active means which interact with passive elements at each location to be identified. The passive elements comprise a plurality of passive loops arranged in a sequence along the travel direction. Each of the loops is tuned to a chosen frequency so that the sequence of the frequencies defines the location code. As the vehicle traverses the sequence of the loops as it passes over each loop, signals only at the frequency of the loop being passed over are coupled from a vehicle transmitter to a vehicle receiver. The frequencies of the received signals in the receiver produce outputs which together represent a code of the traversed location. The code location is defined by a painted pattern which reflects light to a vehicle carried detector whose output is used to derive the code defined by the pattern.

  15. Mitigating laser imprint in direct-drive inertial confinement fusion implosions with high-Z dopants.

    PubMed

    Hu, S X; Fiksel, G; Goncharov, V N; Skupsky, S; Meyerhofer, D D; Smalyuk, V A

    2012-05-11

    Nonuniformities seeded by both long- and short-wavelength laser perturbations can grow via Rayleigh-Taylor (RT) instability in direct-drive inertial confinement fusion, leading to performance reduction in low-adiabat implosions. To mitigate the effect of laser imprinting on target performance, spherical RT experiments have been performed on OMEGA using Si- or Ge-doped plastic targets in a cone-in-shell configuration. Compared to a pure plastic target, radiation preheating from these high-Z dopants (Si/Ge) increases the ablation velocity and the standoff distance between the ablation front and laser-deposition region, thereby reducing both the imprinting efficiency and the RT growth rate. Experiments showed a factor of 2-3 reduction in the laser-imprinting efficiency and a reduced RT growth rate, leading to significant (3-5 times) reduction in the σ(rms) of shell ρR modulation for Si- or Ge-doped targets. These features are reproduced by radiation-hydrodynamics simulations using the two-dimensional hydrocode DRACO.

  16. Theory of metal/rare-gas clusters: aspects of open-shell atomic dopants

    NASA Astrophysics Data System (ADS)

    Boatz, J. A.; Hinde, R. J.; Sheehy, J. A.; Langhoff, P. W.

    2003-05-01

    Studies are reported of the structures and vibronic spectra of metal/rare-gas clusters and their ions employing new theoretical methods devised recently for these purposes. Particular attention is addressed to open-shell atomic dopants (B, Al,...), in which cases the theory must include anisotropic (M-Rg) and spin-orbit interactions in the ground states, the avoided crossings of nearly degenerate electronically excited potential energy surfaces, and significant fragmentation following the cluster ionization commonly employed in experimental detection schemes. Detailed computational applications of the theory are reported of AlArN clusters (N = 2 to 54), and comparisons made with the results of multi-photon excitation and ionization measurements. The significantly different structures of the neutral and ionic clusters predicted in these cases, in which Al is largely external to the Ar cluster and the Al^+ ion is inside the cluster, indicates that fragmentation plays a central role in the interpretation of the experiments. The cluster spectra are seen to be highly sensitive to the details of the atomic Ar arrangements around the Al chromophore, and, accordingly, the measurements provide useful spectroscopic probes of the nature and evolution of the Al trapping sites with increasing degree of solvation when the complex electronic and vibrational phenomena underlying the data are appropriately interpreted theoretically.

  17. Computer modelling of the reduction of rare earth dopants in barium aluminate

    SciTech Connect

    Rezende, Marcos V. dos S; Valerio, Mario E.G.; Jackson, Robert A.

    2011-08-15

    Long lasting phosphorescence in barium aluminates can be achieved by doping with rare earth ions in divalent charge states. The rare earth ions are initially in a trivalent charge state, but are reduced to a divalent charge state before being doped into the material. In this paper, the reduction of trivalent rare earth ions in the BaAl{sub 2}O{sub 4} lattice is studied by computer simulation, with the energetics of the whole reduction and doping process being modelled by two methods, one based on single ion doping and one which allows dopant concentrations to be taken into account. A range of different reduction schemes are considered and the most energetically favourable schemes identified. - Graphical abstract: The doping and subsequent reduction of a rare earth ion into the barium aluminate lattice. Highlights: > The doping of barium aluminate with rare earth ions reduced in a range of atmospheres has been modelled. > The overall solution energy for the doping process for each ion in each reducing atmosphere is calculated using two methods. > The lowest energy reduction process is predicted and compared with experimental results.

  18. Electronic transport through carbon nanotubes - effect of contacts, topological defects, dopants and chemisorbed impurities

    SciTech Connect

    Maiti, A; Hoekstra, J; Andzelm, J; Govind, N; Ricca, A; Svizhenko, A; Mehrez, H; Anantram, M P

    2005-02-11

    Electronics based on carbon nanotubes (CNT) has received a lot of attention recently because of its tremendous application potential, such as active components and interconnects in nanochips, nanoelectromechanical systems (NEMS), display devices, and chemical and biological sensors. However, as with most nanoelectronic systems, successful commercial deployment implies structural control at the molecular level. To this end, it is clearly necessary to understand the effect of contacts, topological defects, dopants, and chemisorbed atoms and molecules on the electronic transport through CNT's. This paper summarizes our computational efforts to address some of the above questions. Examples include: wetting properties and bonding strength of metal contacts on the CNT surface, the effect of Stone-Wales defects on the chemisorption of O{sub 2} and NH3, and how such chemisorbed species and defects effect the electronic transmission and conductance. Our approach is based on first-principles density functional theory (DFT) to compute equilibrium structures, and nonequilibrium Green's function (NEGF) methods, using both DFT and semi-empirical tight-binding formalisms, for computing electronic transport properties.

  19. Gain-shift induced by dopant concentration ratio in a Thulium-Bismuth doped fiber amplifier.

    PubMed

    Emami, Siamak Dawazdah; Zarifi, Atieh; Rashid, Hairul Azhar Abdul; Muhammad, Ahmad Razif; Paul, Mukul Chandra; Halder, Arindam; Bhadra, Shyamal Kumar; Ahmad, Harith; Harun, Sulaiman Wadi

    2014-03-24

    This paper details the effect of Thulium and Bismuth concentration ratio on gain-shift at 1800 nm and 1400 nm band in a Thulium-Bismuth Doped Fiber Amplifier (TBDFA). The effect of Thulium and Bismuth's concentration ratio on gain shifting is experimentally established and subsequently numerically modeled. The analysis is carried out via the cross relaxation and energy transfer processes between the two dopants. The energy transfer in this process was studied through experimental and numerical analysis of three samples with different Tm/Bi concentration ratio of 2, 0.5 and 0.2, respectively. The optimized length for the three samples (TBDFA-1, TBDFA-2 and TBDFA-3) was determined and set at 6.5, 4 and 5.5 m, respectively. In addition, the experimental result of Thulium Doped Fiber Amplifier (TDFA) was compared with the earlier TBDFA samples. The gain for TBDFA-1, with the highest Tm/Bi ratio, showed no shift at the 1800 nm region, while TBDFA-2 and TBDFA-3, possessing a lower Tm/Bi concentration ratio, shifted to the region of 1950 and 1960 nm, respectively. The gain shifting from 1460 nm to 1490 nm is also observed. The numerical model demonstrates that the common 3F4 layer for 1460 nm emission (3H4→3F4), and 1800 nm emission (3F4→3H6)inversely affects the 1460 nm and 1800 nm gain shifting.

  20. Dopant effect of yttrium and the growth and adherence of alumina on nickel-aluminum alloys

    NASA Technical Reports Server (NTRS)

    Anderson, A. B.; Mehandru, S. P.; Smialek, J. L.

    1985-01-01

    The atom superposition and electron delocalization molecular orbital theory and large cluster models have been employed to study cation vacancy diffusion in alpha-Al2O3 and the bonding of alpha-Al2O3 to nickel, aluminum, and yttrium surfaces. Al(3+) diffusion barriers in alpha-Al2O3 by the vacancy mechanism are in reasonable agreement with experiment. The barrier to Y(3+) diffusion is predicted to be much higher. Since addition of yttrium to transition metal alloys is known to reduce the growth rate and stress convolutions in protective alumina scales, this result suggests the rate-limiting step in scale growth is cation vacancy diffusion. This may partially explain the beneficial effect of yttrium dopants on scale adhesion. The theory also predicts a very strong bonding between alumina and yttrium at the surface of the alloy. This may also be important to the adhesion phenomenon. It is also found that aluminum and yttrium atoms bond very strongly to nickel because of charge transfer from their higher lying valence orbitals to the lower lying nickel s-d band.

  1. High thermoelectric performance by resonant dopant indium in nanostructured SnTe

    PubMed Central

    Zhang, Qian; Liao, Bolin; Lan, Yucheng; Lukas, Kevin; Liu, Weishu; Esfarjani, Keivan; Opeil, Cyril; Broido, David; Chen, Gang; Ren, Zhifeng

    2013-01-01

    From an environmental perspective, lead-free SnTe would be preferable for solid-state waste heat recovery if its thermoelectric figure-of-merit could be brought close to that of the lead-containing chalcogenides. In this work, we studied the thermoelectric properties of nanostructured SnTe with different dopants, and found indium-doped SnTe showed extraordinarily large Seebeck coefficients that cannot be explained properly by the conventional two-valence band model. We attributed this enhancement of Seebeck coefficients to resonant levels created by the indium impurities inside the valence band, supported by the first-principles simulations. This, together with the lower thermal conductivity resulting from the decreased grain size by ball milling and hot pressing, improved both the peak and average nondimensional figure-of-merit (ZT) significantly. A peak ZT of ∼1.1 was obtained in 0.25 atom % In-doped SnTe at about 873 K. PMID:23901106

  2. Optical activity and defect/dopant evolution in ZnO implanted with Er

    SciTech Connect

    Azarov, Alexander; Galeckas, Augustinas; Kuznetsov, Andrej; Monakhov, Edouard; Svensson, Bengt G.; Hallén, Anders

    2015-09-28

    The effects of annealing on the optical properties and defect/dopant evolution in wurtzite (0001) ZnO single crystals implanted with Er ions are studied using a combination of Rutherford backscattering/channeling spectrometry and photoluminescence measurements. The results suggest a lattice recovery behavior dependent on ion dose and involving formation/evolution of an anomalous multipeak defect distribution, thermal stability of optically active Er complexes, and Er outdiffusion. An intermediate defect band occurring between the surface and ion-induced defects in the bulk is stable up to 900 °C and has a photoluminescence signature around 420 nm well corresponding to Zn interstitials. The optical activity of the Er atoms reaches a maximum after annealing at 700 °C but is not directly associated to the ideal Zn site configuration, since the Er substitutional fraction is maximal already in the as-implanted state. In its turn, annealing at temperatures above 700 °C leads to dissociation of the optically active Er complexes with subsequent outdiffusion of Er accompanied by the efficient lattice recovery.

  3. Dopant-mediated structural and magnetic properties of TbMnO3

    NASA Astrophysics Data System (ADS)

    Sharma, Vinit; McDannald, A.; Staruch, M.; Ramprasad, R.; Jain, M.

    2015-07-01

    Structural and magnetic properties of the doped terbium manganites (Tb,A)MnO3 (A = Gd, Dy, and Ho) have been investigated using first-principles calculations and further confirmed by subsequent experimental studies. Both computational and experimental studies suggest that compared to the parent material, namely, TbMnO3 (with a magnetic moment of 9.7 μ B for Tb3+) Dy- and Ho-ion substituted TbMnO3 results in an increase in the magnetic susceptibility at low fields ( ≤ 10.6 μ B for Dy3+ and Ho3+). The observed spiral-spin AFM order in TbMnO3 is stable with respect to the dopant substitutions, which modify the Mn-O-Mn bond angles and lead to stronger the ferromagnetic component of the magnetic moment. Given the fact that magnetic ordering in TbMnO3 causes the ferroelectricity, this is an important step in the field of the magnetically driven ferroelectricity in the class of magnetoelectric multiferroics, which traditionally have low magnetic moments due to the predominantly antiferromagnetic order. In addition, the present study reveals important insights on the phenomenological coupling mechanism in detail, which is essential in order to design new materials with enhanced magneto-electric effects at higher temperatures.

  4. AlN/h-BN Heterostructures for Mg Dopant-Free Deep Ultraviolet Photonics.

    PubMed

    Laleyan, David Arto; Zhao, Songrui; Woo, Steffi Y; Tran, Hong Nhung; Le, Huy Binh; Szkopek, Thomas; Guo, Hong; Botton, Gianluigi A; Mi, Zetian

    2017-06-14

    Aluminum-rich AlGaN is the ideal material system for emerging solid-state deep-ultraviolet (DUV) light sources. Devices operating in the near-UV spectral range have been realized; to date, however, the achievement of high-efficiency light-emitting diodes (LEDs) operating in the UV-C band (200-280 nm specifically) has been hindered by the extremely inefficient p-type conduction in AlGaN and the lack of DUV-transparent conductive electrodes. Here, we show that these critical challenges can be addressed by Mg dopant-free Al(Ga)N/h-BN nanowire heterostructures. By exploiting the acceptor-like boron vacancy formation, we have demonstrated that h-BN can function as a highly conductive, DUV-transparent electrode; the hole concentration is ∼10(20) cm(-3) at room temperature, which is 10 orders of magnitude higher than that previously measured for Mg-doped AlN epilayers. We have further demonstrated the first Al(Ga)N/h-BN LED, which exhibits strong emission at ∼210 nm. This work also reports the first achievement of Mg-free III-nitride LEDs that can exhibit high electrical efficiency (80% at 20 A/cm(2)).

  5. Summary of the radiation damage studies of the SDC dopants in polystyrene

    SciTech Connect

    Pla-Dalmau, A.; Foster, G.W.; Zhang, G.

    1993-12-22

    Approximately 80 commercially available fluorescent organic compounds were studied as dopants in a polystyrene matrix for possible use in wavelength shifting (WLS) fibers. The goal was to find a new green- emitting WLS fiber which would outperform in light yield and decay time the currently available fiber doped with K-27. Therefore the fluorescent compounds of interest should exhibit the following spectroscopic characteristics in polystyrene: {lambda}{sub abs} = 400--450 nm,{lambda}{sub em} = 450--550 nm, {tau} = 3--7 ns and quantum efficiency of minimum 0.7. Polystyrene samples doped with different fluorescent compounds were prepared and characterized. Of all the compounds tested, only a series of coumarins exhibited the spectroscopic characteristics of interest. Radiation damage studies had to be performed on these samples in order to condusively determine if they were better candidates than K-27 for green WLS fibers. AU samples except those showing opacity or deep coloration were irradiated. They were, however, separated in two sets. Radiation damage set No. 20 was mainly formed by the coumarin derivatives. Radiation damage set No. 22 was based on the remaining samples. The irradiations were performed at the Phoenix Memorial Laboratory using a {sup 60}Co source. Both sets were exposed to a total dose of 10 Mrad in air, at a dose rate of 1.8 Mrad/h. Transmittance measurements were recorded before and after irradiation, and after annealing. After irradiation, the samples were annealed in oxygen to accelerate the recovery process.

  6. Dopant effect of yttrium and the growth and adherence of alumina on nickel-aluminum alloys

    NASA Technical Reports Server (NTRS)

    Anderson, A. B.; Mehandru, S. P.; Smialek, J. L.

    1985-01-01

    The atom superposition and electron delocalization molecular orbital theory and large cluster models have been employed to study cation vacancy diffusion in alpha-Al2O3 and the bonding of alpha-Al2O3 to nickel, aluminum, and yttrium surfaces. Al(3+) diffusion barriers in alpha-Al2O3 by the vacancy mechanism are in reasonable agreement with experiment. The barrier to Y(3+) diffusion is predicted to be much higher. Since addition of yttrium to transition metal alloys is known to reduce the growth rate and stress convolutions in protective alumina scales, this result suggests the rate-limiting step in scale growth is cation vacancy diffusion. This may partially explain the beneficial effect of yttrium dopants on scale adhesion. The theory also predicts a very strong bonding between alumina and yttrium at the surface of the alloy. This may also be important to the adhesion phenomenon. It is also found that aluminum and yttrium atoms bond very strongly to nickel because of charge transfer from their higher lying valence orbitals to the lower lying nickel s-d band.

  7. Solution Electrochemiluminescent Cell with a High Luminance Using an Ion Conductive Assistant Dopant

    NASA Astrophysics Data System (ADS)

    Nishimura, Kazuki; Hamada, Yuji; Tsujioka, Tsuyoshi; Matsuta, Shigeki; Shibata, Kenichi; Fuyuki, Takashi

    2001-12-01

    Conventional solution electrochemiluminescent (SECL) cells have a low luminance. In this paper, we propose an ion conductive assistant dopant (ICAD) system to improve the luminance of SECL cells. The SECL cell is assumed to have a simple structure of [transparent electrode/emitting solution/transparent electrode]. The solution of the cell consists of a mixed solvent (o-dichlorobenzene/acetonitrile=2/1 (vol/vol)), rubrene used as the emitting material, and 1,2-diphenoxyethane used as the ICAD@. When voltage is applied to this SECL cell, the cell achieves a luminance of 183 cd/m2 and a luminous efficiency of 1.5 cd/A at 8 V with yellow emission. On the other hand, an SECL cell without an ICAD results in a low luminance of 0.3 cd/m2 at 8 V, corresponding to a conventional SECL cell. The ICAD improves the luminance 600 times by enhancing the ion conduction of rubrene cations in the solution. Furthermore, when the mixed solvent (o-dichlorobenzene/toluene=2/1 (vol/vol)), which has a high voltage resistance, is used in the SECL cell, the cell obtains a maximum luminance of 986 cd/m2 at 80 V@. The features of the SECL cell are a simple cell structure and a transparent emitting area. SECL cells are expected to be used in unique displays with a see-through function for automobiles, windows, information equipment, and so on.

  8. Lattice damage, boron diffusion, and dopant activation in BF/sub 2/ implanted layers

    SciTech Connect

    Queirolo, G.; Caprara, P.; Meda, L.; Guareschi, C.; Anderle, M.; Ottaviani, G.; Armigliato, A.

    1987-11-01

    The properties of boron-doped silicon layers obtained by ion implantation using BF/sub 2//sup +/ molecular ions are studied with Rutherford backscattering spectrometry, transmission electron microscopy, secondary ion mass spectrometry, and with incremental sheet resistance and sheet Hall coefficient measurements by the anodic sectioning method. The implantation step is responsible for the formation of interstitial aggregates at the amorphous/crystal interface. The size of these aggregates, and hence the total number of defects involved, depends on the implant conditions, and is different for samples implanted in the two systems used (a medium current and a high current implanter). During a high temperature (900-1000/sup 0/C) diffusion step in an inert atmosphere, the aggregates anneal out and induce an interstitial oversaturation. As a consequence diffusion enhancement is observed which was modeled simulating the creation of the excess of interstitials with a thermal treatment in a partially oxidizing atmosphere (oxidation-enhanced diffusion). The carrier concentration profiles are nearly identical for samples implanted in the two systems and show an incomplete dopant activation in the diffusion tail.

  9. Dopant titrating ion mobility spectrometry for trace exhaled nitric oxide detection.

    PubMed

    Peng, Liying; Hua, Lei; Li, Enyou; Wang, Weiguo; Zhou, Qinghua; Wang, Xin; Wang, Changsong; Li, Jinghua; Li, Haiyang

    2015-01-05

    Ion mobility spectrometry (IMS) is a promising non-invasive tool for the analysis of exhaled gas and exhaled nitric oxide (NO), a biomarker for diagnosis of respiratory diseases. However, the high moisture in exhaled gas always brings about extra overlapping ion peaks and results in poor identification ability. In this paper, p-benzoquinone (PBQ) was introduced into IMS to eliminate the interference of overlapping ion peaks and realize the selective identification of NO. The overlapping ions caused by moisture were titrated by PBQ and then converted to hydrated PBQ anions (C6H4[Formula: see text](H2O)n). The NO concentration could be determined by quantifying gas phase hydrated nitrite anions (N[Formula: see text](H2O)n), product ions of NO. Under optimized conditions, a limit of detection (LOD) of about 1.4 ppbv and a linear range of 10-200 ppbv were obtained for NO even in 100% relative humidity (RH) purified air. Furthermore, this established method was applied to measure hourly the exhaled NO of eight healthy volunteers, and real-time monitoring the exhaled NO of an esophageal carcinoma patient during radical surgery. These results revealed the potential of the current dopant titrating IMS method in the measurement of exhaled NO for medical disease diagnosis.

  10. Schottky Barrier Height Tuning via the Dopant Segregation Technique through Low-Temperature Microwave Annealing.

    PubMed

    Fu, Chaochao; Zhou, Xiangbiao; Wang, Yan; Xu, Peng; Xu, Ming; Wu, Dongping; Luo, Jun; Zhao, Chao; Zhang, Shi-Li

    2016-04-27

    The Schottky junction source/drain structure has great potential to replace the traditional p/n junction source/drain structure of the future ultra-scaled metal-oxide-semiconductor field effect transistors (MOSFETs), as it can form ultimately shallow junctions. However, the effective Schottky barrier height (SBH) of the Schottky junction needs to be tuned to be lower than 100 meV in order to obtain a high driving current. In this paper, microwave annealing is employed to modify the effective SBH of NiSi on Si via boron or arsenic dopant segregation. The barrier height decreased from 0.4-0.7 eV to 0.2-0.1 eV for both conduction polarities by annealing below 400 °C. Compared with the required temperature in traditional rapid thermal annealing, the temperature demanded in microwave annealing is ~60 °C lower, and the mechanisms of this observation are briefly discussed. Microwave annealing is hence of high interest to future semiconductor processing owing to its unique capability of forming the metal/semiconductor contact at a remarkably lower temperature.

  11. Schottky Barrier Height Tuning via the Dopant Segregation Technique through Low-Temperature Microwave Annealing

    PubMed Central

    Fu, Chaochao; Zhou, Xiangbiao; Wang, Yan; Xu, Peng; Xu, Ming; Wu, Dongping; Luo, Jun; Zhao, Chao; Zhang, Shi-Li

    2016-01-01

    The Schottky junction source/drain structure has great potential to replace the traditional p/n junction source/drain structure of the future ultra-scaled metal-oxide-semiconductor field effect transistors (MOSFETs), as it can form ultimately shallow junctions. However, the effective Schottky barrier height (SBH) of the Schottky junction needs to be tuned to be lower than 100 meV in order to obtain a high driving current. In this paper, microwave annealing is employed to modify the effective SBH of NiSi on Si via boron or arsenic dopant segregation. The barrier height decreased from 0.4–0.7 eV to 0.2–0.1 eV for both conduction polarities by annealing below 400 °C. Compared with the required temperature in traditional rapid thermal annealing, the temperature demanded in microwave annealing is ~60 °C lower, and the mechanisms of this observation are briefly discussed. Microwave annealing is hence of high interest to future semiconductor processing owing to its unique capability of forming the metal/semiconductor contact at a remarkably lower temperature. PMID:28773440

  12. Hydrogen adsorption and storage on Palladium - functionalized graphene with NH-dopant: A first principles calculation

    NASA Astrophysics Data System (ADS)

    Faye, Omar; Szpunar, Jerzy A.; Szpunar, Barbara; Beye, Aboubaker Chedikh

    2017-01-01

    We conducted a detailed theoretical investigation of the structural and electronic properties of single and double sided Pd-functionalized graphene and NH-doped Pd-functionalized graphene, which are shown to be efficient materials for hydrogen storage. Nitrene radical dopant was an effective addition required for enhancing the Pd binding on the graphene sheet as well as the storage of hydrogen. We found that up to eight H2 molecules could be adsorbed by double-sided Pd-functionalized graphene at 0 K with an average binding energy in the range 1.315-0.567 eVA gravimetric hydrogen density of 3.622 wt% was reached in the Pd-functionalized graphene on both sides. The binding mechanism of H2 molecules came not only the polarization mechanism between Pd and H atoms but also from the binding of the Pd atoms on the graphene sheet and the orbital hybridization. The most crucial part of our work is measuring the effect of nitrene radical on the H2 adsorption on Pd-functionalized graphene. Our calculations predicted that the addition of NH radicals on Pd-functionalized graphene enhance the binding of H2 molecules, which helps also to avoid the desorption of Pd(H2)n (n = 1-5) complexes from graphene sheet. Our results also predict Pd-functionalized NH-doped graphene is a potential hydrogen storage medium for on-board applications.

  13. Polycrystalline silicon carbide dopant profiles obtained through a scanning nano-Schottky contact

    NASA Astrophysics Data System (ADS)

    Golt, M. C.; Strawhecker, K. E.; Bratcher, M. S.; Shanholtz, E. R.

    2016-07-01

    The unique thermo-electro-mechanical properties of polycrystalline silicon carbide (poly-SiC) make it a desirable candidate for structural and electronic materials for operation in extreme environments. Necessitated by the need to understand how processing additives influence poly-SiC structure and electrical properties, the distribution of lattice defects and impurities across a specimen of hot-pressed 6H poly-SiC processed with p-type additives was visualized with high spatial resolution using a conductive atomic force microscopy approach in which a contact forming a nano-Schottky interface is scanned across the sample. The results reveal very intricate structures within poly-SiC, with each grain having a complex core-rim structure. This complexity results from the influence the additives have on the evolution of the microstructure during processing. It was found that the highest conductivities localized at rims as well as at the interface between the rim and the core. The conductivity of the cores is less than the conductivity of the rims due to a lower concentration of dopant. Analysis of the observed conductivities and current-voltage curves is presented in the context of nano-Schottky contact regimes where the conventional understanding of charge transport to diode operation is no longer valid.

  14. High thermoelectric performance by resonant dopant indium in nanostructured SnTe.

    PubMed

    Zhang, Qian; Liao, Bolin; Lan, Yucheng; Lukas, Kevin; Liu, Weishu; Esfarjani, Keivan; Opeil, Cyril; Broido, David; Chen, Gang; Ren, Zhifeng

    2013-08-13

    From an environmental perspective, lead-free SnTe would be preferable for solid-state waste heat recovery if its thermoelectric figure-of-merit could be brought close to that of the lead-containing chalcogenides. In this work, we studied the thermoelectric properties of nanostructured SnTe with different dopants, and found indium-doped SnTe showed extraordinarily large Seebeck coefficients that cannot be explained properly by the conventional two-valence band model. We attributed this enhancement of Seebeck coefficients to resonant levels created by the indium impurities inside the valence band, supported by the first-principles simulations. This, together with the lower thermal conductivity resulting from the decreased grain size by ball milling and hot pressing, improved both the peak and average nondimensional figure-of-merit (ZT) significantly. A peak ZT of ∼1.1 was obtained in 0.25 atom % In-doped SnTe at about 873 K.

  15. Ultra-low Contact Resistivity of PtHf Silicide Utilizing Dopant Segregation Process

    NASA Astrophysics Data System (ADS)

    Ohmi, Shun-ichiro; Chen, Mengyi; Masahiro, Yasushi

    2016-12-01

    We investigated the dopant segregation (DS) process for PtHf silicide to realize low contact resistivity. After the patterning of SiO2 hard mask and heavily doped n+ diffusion region formation on p-Si(100) substrates, 20 nm-thick PtHf-alloy thin film with 10 nm-thick HfN encapsulating layer was deposited in situ utilizing a PtHf-alloy target by RF magnetron sputtering at room temperature. Then, PH3 ion implantation was carried out for DS followed by silicidation at 450-500°C/5-60 min in N2/4.9%H2 ambient. After Al electrode formation, a sintering process was carried out at 400°C/20 min in N2/4.9%H2 ambient. Ultra-low contact resistivity was achieved for fabricated PtHSi with a DS process on the order of 2.5 × 10-8 Ω cm2 evaluated by the cross-bridge Kelvin resistor method.

  16. A Probabilistic Finite State Logic Machine Realized Experimentally on a Single Dopant Atom.

    PubMed

    Fresch, Barbara; Bocquel, Juanita; Rogge, Sven; Levine, R D; Remacle, F

    2017-03-08

    Exploiting the potential of nanoscale devices for logic processing requires the implementation of computing functionalities departing from the conventional switching paradigm. We report on the design and the experimental realization of a probabilistic finite state machine in a single phosphorus donor atom placed in a silicon matrix electrically addressed and probed by scanning tunneling spectroscopy (STS). The single atom logic unit simulates the flow of visitors in a maze whose topology is determined by the dynamics of the electronic transport through the states of the dopant. By considering the simplest case of a unique charge state for which three electronic states can be resolved, we demonstrate an efficient solution of the following problem: in a maze of four connected rooms, what is the optimal combination of door opening rates in order to maximize the time that visitors spend in one specific chamber? The implementation takes advantage of the stochastic nature of electron tunneling, while the output remains the macroscopic current whose reading can be realized with standard techniques and does not require single electron sensitivity.

  17. Probing the local structure of dilute Cu dopants in fluorescent ZnS nanocrystals using EXAFS.

    PubMed

    Car, Brad; Medling, Scott; Corrado, Carley; Bridges, Frank; Zhang, Jin Z

    2011-10-05

    A local structure study of ZnS nanocrystals, doped with very low concentrations of Cu, was carried out using the EXAFS technique to better understand how Cu substitutes into the host lattice and forms Cu luminescence centers. We show that a large fraction of the Cu have three nearest neighbor S atoms and the Cu-S bond is significantly shortened compared to Zn-S, by ∼0.08 Å. In addition, the second neighbor Cu-Cu peak is extremely small. We propose that Cu occupies an interior site next to a S(2-) vacancy, with the Cu displaced towards the remaining S(2-) and away from the vacancy; such a displacement immediately explains the lack of a significant Cu-Cu peak in the data. There is no evidence for interstitial Cu sites (Cu(i)), indicating that no more than 2% of the Cu are Cu(i.) This study provides new insights into the local structure of the Cu dopant in ZnS without the presence of CuS nanoprecipitates that are present at higher Cu doping levels.

  18. Probing the local structure of dilute Cu dopants in fluorescent ZnS nanocrystals using EXAFS

    NASA Astrophysics Data System (ADS)

    Car, Brad; Medling, Scott; Corrado, Carley; Bridges, Frank; Zhang, Jin Z.

    2011-10-01

    A local structure study of ZnS nanocrystals, doped with very low concentrations of Cu, was carried out using the EXAFS technique to better understand how Cu substitutes into the host lattice and forms Cu luminescence centers. We show that a large fraction of the Cu have three nearest neighbor S atoms and the Cu-S bond is significantly shortened compared to Zn-S, by ~0.08 Å. In addition, the second neighbor Cu-Cu peak is extremely small. We propose that Cu occupies an interior site next to a S2- vacancy, with the Cu displaced towards the remaining S2- and away from the vacancy; such a displacement immediately explains the lack of a significant Cu-Cu peak in the data. There is no evidence for interstitial Cu sites (Cui), indicating that no more than 2% of the Cu are Cui. This study provides new insights into the local structure of the Cu dopant in ZnS without the presence of CuS nanoprecipitates that are present at higher Cu doping levels.

  19. The study of dopant segregation behavior during the growth of GaAs in microgravity

    NASA Technical Reports Server (NTRS)

    Matthiesen, David H.; Majewski, J. A.

    1994-01-01

    An investigation into the segregation behavior of selenium doped gallium arsenide during directional solidification in the microgravity environment was conducted using the Crystal Growth Furnace (CGF) aboard the first United States Microgravity Laboratory (USML-1). The two crystals grown were 1.5 cm in diameter and 16.5 cm in length with an initial melt length of 14 cm. Two translation periods were executed, the first at 2.5 microns/s and after a specified time, which was different between the two experiments, the translation rate was doubled to 5.0 microns/s. The translation was then stopped and the remaining sample melt was solidified using a gradient freeze technique in the first sample and a rapid solidification in the second experiment. Measurement of the selenium dopant distribution, using quantitative infrared transmission imaging, indicates that the first sample initially achieved diffusion controlled growth as desired. However, after about 1 cm of growth, the segregation behavior was driven from a diffusion controlled growth regime to a complete mixing regime. Measurements in the second flight sample indicated that the growth was always in a complete mixing regime. In both experiments, voids in the center line of the crystal, indicative of bubble entrapment, were found to correlate with the position in the crystal when the translation rates were doubled.

  20. Dopant-Free Hole-Transporting Materials for Stable and Efficient Perovskite Solar Cells.

    PubMed

    Paek, Sanghyun; Qin, Peng; Lee, Yonghui; Cho, Kyung Taek; Gao, Peng; Grancini, Giulia; Oveisi, Emad; Gratia, Paul; Rakstys, Kasparas; Al-Muhtaseb, Shaheen A; Ludwig, Christian; Ko, Jaejung; Nazeeruddin, Mohammad Khaja

    2017-07-17

    Molecularly engineered novel dopant-free hole-transporting materials for perovskite solar cells (PSCs) combined with mixed-perovskite (FAPbI3 )0.85 (MAPbBr3 )0.15 (MA: CH3 NH3(+) , FA: NH=CHNH3(+) ) that exhibit an excellent power conversion efficiency of 18.9% under AM 1.5 conditions are investigated. The mobilities of FA-CN, and TPA-CN are determined to be 1.2 × 10(-4) cm(2) V(-1) s(-1) and 1.1 × 10(-4) cm(2) V(-1) s(-1) , respectively. Exceptional stability up to 500 h is measured with the PSC based on FA-CN. Additionally, it is found that the maximum power output collected after 1300 h remained 65% of its initial value. This opens up new avenue for efficient and stable PSCs exploring new materials as alternatives to Spiro-OMeTAD. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  1. Polycrystalline silicon carbide dopant profiles obtained through a scanning nano-Schottky contact

    SciTech Connect

    Golt, M. C.; Strawhecker, K. E.; Bratcher, M. S.; Shanholtz, E. R.

    2016-07-14

    The unique thermo-electro-mechanical properties of polycrystalline silicon carbide (poly-SiC) make it a desirable candidate for structural and electronic materials for operation in extreme environments. Necessitated by the need to understand how processing additives influence poly-SiC structure and electrical properties, the distribution of lattice defects and impurities across a specimen of hot-pressed 6H poly-SiC processed with p-type additives was visualized with high spatial resolution using a conductive atomic force microscopy approach in which a contact forming a nano-Schottky interface is scanned across the sample. The results reveal very intricate structures within poly-SiC, with each grain having a complex core-rim structure. This complexity results from the influence the additives have on the evolution of the microstructure during processing. It was found that the highest conductivities localized at rims as well as at the interface between the rim and the core. The conductivity of the cores is less than the conductivity of the rims due to a lower concentration of dopant. Analysis of the observed conductivities and current-voltage curves is presented in the context of nano-Schottky contact regimes where the conventional understanding of charge transport to diode operation is no longer valid.

  2. Preparation of monotectic alloys having a controlled microstructure by directional solidification under dopant-induced interface breakdown

    NASA Technical Reports Server (NTRS)

    Parr, R. A.; Johnston, M. H.; Mcclure, J. C.

    1980-01-01

    Monotectic alloys having aligned spherical particles of rods of the minor component dispersed in a matrix of the major component are prepared by forming a melt containing predetermined amounts of the major and minor components of a chosen monotectic system, providing in the melt a dopant capable of breaking down the liquid solid interface for the chosen alloy, and directionally solidfying the melt at a selected temperature gradient and a selected rate of movement of the liquid-solid interface (growth rate). Shaping of the minor component into spheres or rods and the spacing between them are controlled by the amount of dopant and the temperature gradient and growth rate values. Specific alloy systems include Al Bi, Al Pb and Zn Bi, using a transition element such as iron.

  3. Electrical and optical properties of SrTiO3 nanopowders: Effect of different dopants Ba and Ag

    NASA Astrophysics Data System (ADS)

    Ghasemifard, Mahdi; Ghamari, Misagh; Iziy, Meysam

    2016-05-01

    Using strontium-titanium salts precursor, nanopowders (STO-based-NPs) were successfully synthesized by controlled gel-combustion method. Citric and nitric acids in an optimum ratio were used as the fuel and oxidizer agents, respectively. After heat treatment at 850∘C, the crystalline structure of the products was investigated by X-ray diffraction. The effects of Ba and Ag dopants on particle size distribution were discussed by transmission electron microscopy (TEM). The optical and dielectric parameters such as energy band gap (Eg), real and imaginary parts of refractive index, dielectric function and energy loss function of nanopowders have been investigated by UV-Vis and FTIR spectra. The band gap of SrTiO3 increased with increasing Ba, Ag and Ba-Ag. Different atomic radii of dopants are responsible for changing optical and dielectric parameters due to the altered orbital configuration of the lattice structure.

  4. Rational design of dipolar chromophore as an efficient dopant-free hole-transporting material for perovskite solar cells

    SciTech Connect

    Li, Zhong’an; Zhu, Zonglong; Chueh, Chu -Chen; Jo, Sae Byeok; Luo, Jingdong; Jang, Sei -Hum; Jen, Alex K. -Y.

    2016-08-23

    In this paper, an electron donor-acceptor (D-A) substituted dipolar chromophore (BTPA-TCNE) is developed to serve as an efficient dopant-free hole-transporting material (HTM) for perovskite solar cells (PVSCs). BTPA-TCNE is synthesized via a simple reaction between a triphenylamine-based Michler’s base and tetracyanoethylene. This chromophore possesses a zwitterionic resonance structure in the ground state, as evidenced by X-ray crystallography and transient absorption spectroscopies. Moreover, BTPA-TCNE shows an antiparallel molecular packing (i.e., centrosymmetric dimers) in its crystalline state, which cancels out its overall molecular dipole moment to facilitate charge transport. Finally, BTPA-TCNE can be employed as an effective dopant-free HTM to realize an efficient (PCE ≈ 17.0%) PVSC in the conventional n-i-p configuration, outperforming the control device with doped spiro-OMeTAD HTM.

  5. Rational design of dipolar chromophore as an efficient dopant-free hole-transporting material for perovskite solar cells

    DOE PAGES

    Li, Zhong’an; Zhu, Zonglong; Chueh, Chu -Chen; ...

    2016-08-23

    In this paper, an electron donor-acceptor (D-A) substituted dipolar chromophore (BTPA-TCNE) is developed to serve as an efficient dopant-free hole-transporting material (HTM) for perovskite solar cells (PVSCs). BTPA-TCNE is synthesized via a simple reaction between a triphenylamine-based Michler’s base and tetracyanoethylene. This chromophore possesses a zwitterionic resonance structure in the ground state, as evidenced by X-ray crystallography and transient absorption spectroscopies. Moreover, BTPA-TCNE shows an antiparallel molecular packing (i.e., centrosymmetric dimers) in its crystalline state, which cancels out its overall molecular dipole moment to facilitate charge transport. Finally, BTPA-TCNE can be employed as an effective dopant-free HTM to realize anmore » efficient (PCE ≈ 17.0%) PVSC in the conventional n-i-p configuration, outperforming the control device with doped spiro-OMeTAD HTM.« less

  6. Rational design of dipolar chromophore as an efficient dopant-free hole-transporting material for perovskite solar cells

    SciTech Connect

    Li, Zhong’an; Zhu, Zonglong; Chueh, Chu -Chen; Jo, Sae Byeok; Luo, Jingdong; Jang, Sei -Hum; Jen, Alex K. -Y.

    2016-08-23

    In this paper, an electron donor-acceptor (D-A) substituted dipolar chromophore (BTPA-TCNE) is developed to serve as an efficient dopant-free hole-transporting material (HTM) for perovskite solar cells (PVSCs). BTPA-TCNE is synthesized via a simple reaction between a triphenylamine-based Michler’s base and tetracyanoethylene. This chromophore possesses a zwitterionic resonance structure in the ground state, as evidenced by X-ray crystallography and transient absorption spectroscopies. Moreover, BTPA-TCNE shows an antiparallel molecular packing (i.e., centrosymmetric dimers) in its crystalline state, which cancels out its overall molecular dipole moment to facilitate charge transport. Finally, BTPA-TCNE can be employed as an effective dopant-free HTM to realize an efficient (PCE ≈ 17.0%) PVSC in the conventional n-i-p configuration, outperforming the control device with doped spiro-OMeTAD HTM.

  7. Sensors Locate Radio Interference

    NASA Technical Reports Server (NTRS)

    2009-01-01

    After receiving a NASA Small Business Innovation Research (SBIR) contract from Kennedy Space Center, Soneticom Inc., based in West Melbourne, Florida, created algorithms for time difference of arrival and radio interferometry, which it used in its Lynx Location System (LLS) to locate electromagnetic interference that can disrupt radio communications. Soneticom is collaborating with the Federal Aviation Administration (FAA) to install and test the LLS at its field test center in New Jersey in preparation for deploying the LLS at commercial airports. The software collects data from each sensor in order to compute the location of the interfering emitter.

  8. Mn2+-Doped CdSe/CdS Core/Multishell Colloidal Quantum Wells Enabling Tunable Carrier-Dopant Exchange Interactions

    NASA Astrophysics Data System (ADS)

    Delikanli, Savas; Scrace, Thomas; Murphy, Joseph; Barman, Biblop; Tsai, Yutsung; Zhang, Peiyao; Hernandez-Martinez, Pedro Ludwig; Christodoulides, Joseph; Cartwright, Alexander N.; Petrou, Athos; Demir, Hilmi Volkan

    We report the manifestations of carrier-dopant exchange interactions in colloidal Mn2+-doped CdSe/CdS core/multishell quantum wells. In our solution-processed quantum well heterostructures, Mn2+ was incorporated by growing a Cd0.985Mn0:015S monolayer shell on undoped CdSe nanoplatelets using the colloidal atomic layer deposition technique. The carrier-magnetic ion exchange interaction effects are tunable through wave function engineering. This is realized by controlling the spatial overlap between the carrier wave functions with the manganese ions through adjusting the location, composition, and number of the CdSe, Cd1-xMnxS, and CdS layers. Our colloidal quantum wells, which exhibit magneto-optical properties analogous to those of epitaxially grown quantum wells, offer new opportunities for solution-processed spin-based semiconductor devices. H.V.D. acknowledges support from EU-FP7 Nanophotonics4Energy NoE, TUBITAK, NRF-CRP-6-2010-02 and A*STAR of Singapore. Work at the University at Buffalo was supported by NSF DMR 1305770.

  9. A comprehensive study on the structural evolution of HfO2 thin films doped with various dopants

    DOE PAGES

    Park, Min Hyuk; Schenk, Tony; Fancher, Christopher M.; ...

    2017-04-19

    The origin of the unexpected ferroelectricity in doped HfO2 thin films is now considered to be the formation of a non-centrosymmetric Pca21 orthorhombic phase. Due to the polycrystalline nature of the films as well as their extremely small thickness (~10 nm) and mixed orientation and phase composition, structural analysis of doped HfO2 thin films remains a challenging task. As a further complication, the structural similarities of the orthorhombic and tetragonal phase are difficult to distinguish by typical structural analysis techniques such as X-ray diffraction. To resolve this issue, the changes in the grazing incidence X-ray diffraction (GIXRD) patterns of HfO2more » films doped with Si, Al, and Gd are systematically examined. For all dopants, the shift of o111/t101 diffraction peak is observed with increasing atomic layer deposition (ALD) cycle ratio, and this shift is thought to originate from the orthorhombic to P42/nmc tetragonal phase transition with decreasing aspect ratio (2a/(b + c) for orthorhombic and c/a for the tetragonal phase). For quantitative phase analysis, Rietveld refinement is applied to the GIXRD patterns. A progressive phase transition from P21/c monoclinic to orthorhombic to tetragonal is confirmed for all dopants, and a strong relationship between orthorhombic phase fraction and remanent polarization value is uniquely demonstrated. The concentration range for the ferroelectric properties was the narrowest for the Si-doped HfO2 films. As a result, the dopant size is believed to strongly affect the concentration range for the ferroelectric phase stabilization, since small dopants can strongly decrease the free energy of the tetragonal phase due to their shorter metal–oxygen bonds.« less

  10. Dopant-Free GaN/AlN/AlGaN Radial Nanowire Heterostructures as High Electron Mobility Transistors

    DTIC Science & Technology

    2016-06-07

    microscopy (TEM) studies reveal that the GaN/ AlN/AlGaN radial nanowire heterostructures are dislocation -free single crystals. In addition, the...due to a reduction or elimination of impurity scattering by separating the dopants and surface potential fluctuations from the conduction channel . We...AlN/AlGaN radial nanowire heterostructures are dislocation -free single crystals. In addition, the thicknesses and compositions of the individual AlN

  11. The effect of high-Z dopant on laser-driven acceleration of a thin plastic target

    NASA Astrophysics Data System (ADS)

    Badziak, J.; Kasperczuk, A.; Parys, P.; Pisarczyk, T.; Rosiński, M.; Ryć, L.; Wołowski, J.; Suchańska, R.; Krása, J.; Krousky, E.; Láska, L.; Mašek, K.; Pfeifer, M.; Rohlena, K.; Skala, J.; Ullschmied, J.; Dhareshwar, L. J.; Földes, I. B.; Suta, T.; Borrielli, A.; Mezzasalma, A.; Torrisi, L.; Pisarczyk, P.

    2008-05-01

    Acceleration of a thin (10 or 20μm) plastic foil by 120J, 0.438μm, 0.3ns laser pulse of intensity up to 1015W/cm2 has been investigated. It is shown that the introducing a high-Z dopant to the foil causes an increase in the ablating plasma density, velocity, and collimation which, in turn, results in a remarkably higher kinetic energy and energy fluence of the flyer foil.

  12. Structural and orientation effects on electronic energy transfer between silicon quantum dots with dopants and with silver adsorbates.

    PubMed

    Vinson, N; Freitag, H; Micha, D A

    2014-06-28

    Starting from the atomic structure of silicon quantum dots (QDs), and utilizing ab initio electronic structure calculations within the Förster resonance energy transfer (FRET) treatment, a model has been developed to characterize electronic excitation energy transfer between QDs. Electronic energy transfer rates, KEET, between selected identical pairs of crystalline silicon quantum dots systems, either bare, doped with Al or P, or adsorbed with Ag and Ag3, have been calculated and analyzed to extend previous work on light absorption by QDs. The effects of their size and relative orientation on energy transfer rates for each system have also been considered. Using time-dependent density functional theory and the hybrid functional HSE06, the FRET treatment was employed to model electronic energy transfer rates within the dipole-dipole interaction approximation. Calculations with adsorbed Ag show that: (a) addition of Ag increases rates up to 100 times, (b) addition of Ag3 increases rates up to 1000 times, (c) collinear alignment of permanent dipoles increases transfer rates by an order of magnitude compared to parallel orientation, and (d) smaller QD-size increases transfer due to greater electronic orbitals overlap. Calculations with dopants show that: (a) p-type and n-type dopants enhance energy transfer up to two orders of magnitude, (b) surface-doping with P and center-doping with Al show the greatest rates, and (c) KEET is largest for collinear permanent dipoles when the dopant is on the outer surface and for parallel permanent dipoles when the dopant is inside the QD.

  13. Uranium Location Database Compilation

    EPA Pesticide Factsheets

    EPA has compiled mine location information from federal, state, and Tribal agencies into a single database as part of its investigation into the potential environmental hazards of wastes from abandoned uranium mines in the western United States.

  14. Electronic apex locators.

    PubMed

    Gordon, M P J; Chandler, N P

    2004-07-01

    Prior to root canal treatment at least one undistorted radiograph is required to assess canal morphology. The apical extent of instrumentation and the final root filling have a role in treatment success, and are primarily determined radiographically. Electronic apex locators reduce the number of radiographs required and assist where radiographic methods create difficulty. They may also indicate cases where the apical foramen is some distance from the radiographic apex. Other roles include the detection of root canal perforation. A review of the literature focussed first on the subject of electronic apex location. A second review used the names of apex location devices. From the combined searches, 113 pertinent articles in English were found. This paper reviews the development, action, use and types of electronic apex locators.

  15. Locations Accessible | FNLCR

    Cancer.gov

    The Frederick National Laboratory for Cancer Research campus is located 50 miles northwest of Washington, D.C., and 50 miles west of Baltimore, Maryland, in Frederick, Maryland.Operations and Technical Support contractor Leidos Biomedical Resea

  16. Locations Accessible | FNLCR Staging

    Cancer.gov

    The Frederick National Laboratory for Cancer Research campus is located 50 miles northwest of Washington, D.C., and 50 miles west of Baltimore, Maryland, in Frederick, Maryland.Operations and Technical Support contractor Leidos Biomedical Resea

  17. Finding the Correct Location.

    ERIC Educational Resources Information Center

    Seiter, David M.

    1988-01-01

    Provides educational resources from ERIC (Educational Resources Information Center) to help teachers find the material to teach the five themes of geography. An annotated bibliography of seven ERIC documents on geographic location is provided. (LS)

  18. Smart Location Mapping

    EPA Pesticide Factsheets

    The Smart Location Database, Access to Jobs and Workers via Transit, and National Walkability Index tools can help assess indicators related to the built environment, transit accessibility, and walkability.

  19. Atomic-scale quantification of interdiffusion and dopant localization in GeSbTe-based memory devices

    NASA Astrophysics Data System (ADS)

    Chae, B.-G.; Seol, J.-B.; Song, J.-H.; Jung, W.-Y.; Hwang, H.; Park, C.-G.

    2016-09-01

    Fabrication of phase-change memory devices at modest or ambient temperatures leads to nanoscale compositional variations in phase-transition layers, where amorphous-polycrystalline phase change takes place via electrical switching, and can alter the device's performances. Here, by transmission electron microscopy and atom probe tomography, we address that thermal annealing at 400 °C for 20 min induces an elemental interdiffusion in the devices consisting of TiN (top electrode), carbon-doped GeSbTe (phase-transition layer), and TiSiN (bottom heater). With respect to the employed annealing process, the Ge atoms of GeSbTe layer have diffused into TiSiN layer at a given sample volume, while the Ti atoms of TiSiN layer into GeSbTe layer. Furthermore, non-random nature of dopant distribution in the GeSbTe materials leads to a Ti-localization including dopants at the GeSbTe/TiSiN interfaces. Our findings have two important implications: First, the annealing-driven interdiffusion of Ge and Ti is a predominant mechanism responsible for nanoscale compositional variations in GeSbTe layer; second, such an interdiffusion and the resultant dopant localization play a crucial role on the driving force for amorphous-polycrystalline transition of GeSbTe-based memory devices.

  20. Polysilicon Gate Enhancement of the Random Dopant Induced Threshold Voltage Fluctuations in Sub-100 nm MOSFET's with Ultrathin Gate Oxide

    NASA Technical Reports Server (NTRS)

    Asenov, Asen; Saini, Subhash

    2000-01-01

    In this paper, we investigate various aspects of the polysilicon gate influence on the random dopant induced threshold voltage fluctuations in sub-100 nm MOSFET's with ultrathin gate oxides. The study is done by using an efficient statistical three-dimensional (3-D) "atomistic" simulation technique described else-where. MOSFET's with uniform channel doping and with low doped epitaxial channels have been investigated. The simulations reveal that even in devices with a single crystal gate the gate depletion and the random dopants in it are responsible for a substantial fraction of the threshold voltage fluctuations when the gate oxide is scaled-in the range of 1-2 nm. Simulation experiments have been used in order to separate the enhancement in the threshold voltage fluctuations due to an effective increase in the oxide thickness associated with the gate depletion from the direct influence of the random dopants in the gate depletion layer. The results of the experiments show that the both factors contribute to the enhancement of the threshold voltage fluctuations, but the effective increase in the oxide-thickness has a dominant effect in the investigated range of devices. Simulations illustrating the effect or the polysilicon grain boundaries on the threshold voltage variation are also presented.

  1. A reliable method for the counting and control of single ions for single-dopant controlled devices.

    PubMed

    Shinada, T; Kurosawa, T; Nakayama, H; Zhu, Y; Hori, M; Ohdomari, I

    2008-08-27

    By 2016, transistor device size will be just 10 nm. However, a transistor that is doped at a typical concentration of 10(18) atoms cm(-3) has only one dopant atom in the active channel region. Therefore, it can be predicted that conventional doping methods such as ion implantation and thermal diffusion will not be available ten years from now. We have been developing a single-ion implantation (SII) method that enables us to implant dopant ions one-by-one into semiconductors until the desired number is reached. Here we report a simple but reliable method to control the number of single-dopant atoms by detecting the change in drain current induced by single-ion implantation. The drain current decreases in a stepwise fashion as a result of the clusters of displaced Si atoms created by every single-ion incidence. This result indicates that the single-ion detection method we have developed is capable of detecting single-ion incidence with 100% efficiency. Our method potentially could pave the way to future single-atom devices, including a solid-state quantum computer.

  2. Highly efficient blue organic light-emitting diodes using dual emissive layers with host-dopant system

    NASA Astrophysics Data System (ADS)

    Lee, Bo Mi; Yu, Hyeong Hwa; Kim, You Hyun; Kim, Nam Ho; Yoon, Ju An; Mascher, Peter; Kim, Woo Young

    2012-10-01

    In this study, we fabricated highly efficient blue organic light-emitting diodes by designing different emitting layer structures with fluorescent host and dopant materials of 4,4-bis(2,2-diphenylyinyl)-1,10-biphenyl (DPVBi) and 9,10- bis(2-naphthyl) anthracene (ADN) as host materials and 4,4'-bis(9-ethyl-3-carbazovinylene)-1,1'biphenyl (BCzVBi) as a dopant material to demonstrate electrical and optical improvements. Best enhancement in luminance and luminous efficiency were achieved by a quantum well structure and energy transfer between host and dopant materials in device F as of 8668cd/m2 at 8V and 5.16 Cd/A at 103.20 mA/cm2 respectively. Among the blue OLED devices doped by BCzVBi, device B emits the deepest blue emission with Commission Internationale de l'É clairage (CIExy) coordinates of (0.157, 0.117) at 8V.

  3. Probing the effect of intrinsic defects and dopants on the structural evolution and optical properties of ZnO nanocrystallites

    SciTech Connect

    Panda, N. R.; Sahu, D.; Acharya, B. S.; Nayak, P.

    2015-06-24

    Role of intrinsic defects and external impurities in modifying the structural and optical properties of ZnO nanostructures has been studied and discussed. ZnO nanocrystallites doped with B, N and S elements have been prepared by ultrasound assisted wet chemical method. Structural evolution of ZnO in presence of dopant ions has been studied by XRD and electron microscopic measurements. Elemental analysis like XPS has been carried out to ascertain the dopant configuration. A variation in crystallographic parameters and microstructure is found to be observed as impurity is incorporated into ZnO. This has been explained on the basis of the substitution of dopant at Zn{sup 2+} and O{sup −} sites rearranging the lattice. Optical absorption measurements and PL studies reflect a change in band gap of ZnO by impurity adsorption. Most of the cases, the band gap is found to be broadened which has been explained in the line of Moss-Burstein effect. The excitonic emission in ZnO is observed to blue shift supporting the above results and the defect emissions also get modified in terms of position and intensity. New PL bands observed have been assigned to the transitions related to the defect states present in the band gap of ZnO along with intrinsic defects.

  4. Reversibility, dopant desorption, and tunneling in the temperature-dependent conductivity of type-separated, conductive carbon nanotube networks.

    PubMed

    Barnes, Teresa M; Blackburn, Jeffrey L; van de Lagemaat, Jao; Coutts, Timothy J; Heben, Michael J

    2008-09-23

    We present a comprehensive study of the effects of doping and temperature on the conductivity of single-walled carbon nanotube (SWNT) networks. We investigated nearly type-pure networks as well as networks comprising precisely tuned mixtures of metallic and semiconducting tubes. Networks were studied in their as-produced state and after treatments with nitric acid, thionyl chloride, and hydrazine to explore the effects of both intentional and adventitious doping. For intentionally and adventitiously doped networks, the sheet resistance (R(s)) exhibits an irreversible increase with temperature above approximately 350 K. Dopant desorption is shown to be the main cause of this increase and the observed hysteresis in the temperature-dependent resistivity. Both thermal and chemical dedoping produced networks free of hysteresis. Temperature-programmed desorption data showed that dopants are most strongly bound to the metallic tubes and that networks consisting of metallic tubes exhibit the best thermal stability. At temperatures below the dopant desorption threshold, conductivity in the networks is primarily controlled by thermally assisted tunneling through barriers at the intertube or interbundle junctions.

  5. Measurement of 3-dimensional dopant distribution in InGaAs microdiscs grown selectively on Si (111)

    NASA Astrophysics Data System (ADS)

    Watanabe, Tohma; Takeuchi, Miyuki; Nakano, Yoshiaki; Sugiyama, Masakazu

    2017-04-01

    The control of the dopant profile in 3-dimentional InGaAs microdiscs on Si (111) is essential for their device applications. However, such profiles can never be controlled by simply changing the supply of dopant precursors during the growth of microdiscs. This is because a variety of crystal planes, such as (111), {-110}, and irregular planes near the corners, surround a hexagonal pillar of InGaAs and the incorporation efficiency of dopant elements depends significantly on the kind of planes involved. We here observed the distributions of sulfur and zinc in p-i-n InGaAs microdiscs by both cross-sectional scanning capacitance microscopy (SCM) and secondary-ion mass spectrometry using focused ion beam (NanoSIMS). Even though the InGaAs shell was grown on the microdiscs using dimethylzinc (DMZn), no p-type region was found on the top of the microdiscs and the p-type region existed on the sidewall of the discs alone. This result suggested that the zinc incorporation efficiency on InGaAs (111) plane is much lower than that on {-110} planes. Complete encapsulation of the microdiscs with p-type region was possible by the post-diffusion of zinc during exposure to a mixture of tertiarybutylarsine (TBAs) and DMZn after the growth of InGaAs microdiscs.

  6. Effects of various dopants on properties of GaAs tunneling junctions and p-i-n solar cells

    NASA Astrophysics Data System (ADS)

    Sodabanlu, Hassanet; Watanabe, Kentaroh; Sugiyama, Masakazu; Nakano, Yoshiaki

    2017-08-01

    Several GaAs tunneling junctions (TJs) and p-i-n single junction solar cells grown using a planetary metalorganic vapor phase epitaxy (MOVPE) reactor utilizing various dopant species including Zn, C, S, and Te were investigated. The incorporation of Te atoms into GaAs was approximately two orders larger than that of S atoms. Although only 30% of Te atoms could be electrically activated, a carrier concentration of 1019 cm-3 was achieved. Highly C-doped GaAs was successfully obtained by decreasing the growth temperature and increasing the amount of H2 carrier gas in order to prevent the predecomposition of CBr4 dopant gas. A hole concentration of about 1020 cm-3 was realized with a growth temperature of 450 °C. The C-Te-doped GaAs TJ exhibited the best ohmic tunneling behavior with a resistivity of 12.5 mΩ·cm2, while the others had diode characteristics. The GaAs solar cell grown with the Zn-S dopant showed the highest conversion efficiency ascribed to a longer minority carrier lifetime.

  7. Measurement of Small Molecular Dopant F4TCNQ and C60F36 Diffusion in Organic Bilayer Architectures.

    PubMed

    Li, Jun; Rochester, Chris W; Jacobs, Ian E; Friedrich, Stephan; Stroeve, Pieter; Riede, Moritz; Moulé, Adam J

    2015-12-30

    The diffusion of molecules through and between organic layers is a serious stability concern in organic electronic devices. In this work, the temperature-dependent diffusion of molecular dopants through small molecule hole transport layers is observed. Specifically we investigate bilayer stacks of small molecules used for hole transport (MeO-TPD) and p-type dopants (F4TCNQ and C60F36) used in hole injection layers for organic light emitting diodes and hole collection electrodes for organic photovoltaics. With the use of absorbance spectroscopy, photoluminescence spectroscopy, neutron reflectometry, and near-edge X-ray absorption fine structure spectroscopy, we are able to obtain a comprehensive picture of the diffusion of fluorinated small molecules through MeO-TPD layers. F4TCNQ spontaneously diffuses into the MeO-TPD material even at room temperature, while C60F36, a much bulkier molecule, is shown to have a substantially higher morphological stability. This study highlights that the differences in size/geometry and thermal properties of small molecular dopants can have a significant impact on their diffusion in organic device architectures.

  8. Simulation and comparative study of tunneling field effect transistors with dopant-segregated Schottky source/drain

    NASA Astrophysics Data System (ADS)

    Zhang, Yi Bo; Sun, Lei; Xu, Hao; Han, Jing Wen

    2016-04-01

    Dopant-segregated Schottky source/drain tunneling field effect transistors (STFET) are investigated in this paper. The working mechanisms of STFET and the influence of device parameters are studied with Synopsys Sentaurus. Schottky source/drain MOSFETs possess several advantages over conventional MOSFETs, and dopant segregation can be feasibly achieved within current silicidation process. With dopant segregation, highly doped regions can be obtained after silicidation, which is necessary for band-to-band tunneling. With proper parameter setting, STFET can achieve comparable performance as TFET. High segregation doping for STFET is required to increase band-to-band tunneling probability and suppress bipolar behaviors. Increasing the electron barrier height at source side helps to provide larger drive current and higher on/off ratio. It is also found that STFET’s on-state performance is irrelevant to the segregation length when the segregation length is larger than a certain value. Furthermore, STFET is also insensitive to the Schottky barrier at drain side when the Schottky barrier at source side is fixed, which would relax the requirement for source/drain fabrication.

  9. Observation of early shell-dopant mix in OMEGA direct-drive implosions and comparisons with radiation-hydrodynamic simulations

    SciTech Connect

    Baumgaertel, J. A.; Bradley, P. A.; Hsu, S. C.; Cobble, J. A.; Hakel, P.; Tregillis, I. L.; Krasheninnikova, N. S.; Murphy, T. J.; Schmitt, M. J.; Shah, R. C.; Obrey, K. D.; Batha, S.; Johns, H.; Joshi, T.; Mayes, D.; Mancini, R. C.; Nagayama, T.

    2014-05-15

    Temporally, spatially, and spectrally resolved x-ray image data from direct-drive implosions on OMEGA were interpreted with the aid of radiation-hydrodynamic simulations. Neither clean calculations nor those using a turbulent mix model can explain fully the observed migration of shell-dopant material (titanium) into the core. Shell-dopant migration was observed via time-dependent, spatially integrated spectra, and spatially and spectrally resolved x-ray images of capsule implosions and resultant dopant emissions. The titanium emission was centrally peaked in narrowband x-ray images. In post-processed clean simulations, the peak titanium emission forms in a ring in self-emission images as the capsule implodes. Post-processed simulations with mix reproduce trends in time-dependent, spatially integrated spectra, as well having centrally peaked Ti emission in synthetic multiple monochromatic imager. However, mix simulations still do not transport Ti to the core as is observed in the experiment. This suggests that phenomena in addition to the turbulent mix must be responsible for the transport of Ti. Simple diffusion estimates are unable to explain the early Ti mix into the core. Mechanisms suggested for further study are capsule surface roughness, illumination non-uniformity, and shock entrainment.

  10. X-ray absorption near edge spectroscopy with a superconducting detector for nitrogen dopants in SiC

    PubMed Central

    Ohkubo, M.; Shiki, S.; Ukibe, M.; Matsubayashi, N.; Kitajima, Y.; Nagamachi, S.

    2012-01-01

    Fluorescence-yield X-ray absorption fine structure (FY-XAFS) is extensively used for investigating atomic-scale local structures around specific elements in functional materials. However, conventional FY-XAFS instruments frequently cannot cover trace light elements, for example dopants in wide gap semiconductors, because of insufficient energy resolution of semiconductor X-ray detectors. Here we introduce a superconducting XAFS (SC-XAFS) apparatus to measure X-ray absorption near-edge structure (XANES) of n-type dopant N atoms (4 ×1019 cm−3) implanted at 500°C into 4H-SiC substrates annealed subsequently. The XANES spectra and ab initio multiple scattering calculations indicate that the N atoms almost completely substitute for the C sites, associated with a possible existence of local CN regions, in the as-implanted state. This is a reason why hot implantation is necessary for dopant activation in ion implantation. The SC-XAFS apparatus may play an important role in improving doping processes for energy-saving wide-gap semiconductors and other functional materials. PMID:23152937

  11. Interdiffusion in the MgO-Al{sub 2}O{sub 3} spinel with or without some dopants

    SciTech Connect

    Zhang, P.; Seetharaman, S.; Debroy, T.

    1996-08-01

    With a view to seek an improved understanding of the DIMOX process, interdiffusion of polycrystalline MgO and Al{sub 2}O{sub 3} in the temperature range 1,473 to 1,873 K was studied by diffusion couple experiments. The interdiffusivities in the spinel layer were calculated as functions of composition and temperature. The spinel portion of the phase diagram in the system MgO-Al{sub 2}O{sub 3} was determined from carefully measured compositions at the phase boundaries, and the low temperature spinel region of the phase diagram was confirmed from the present results. For Zn{sup 2+} as dopant in alumina, the growth rate of spinel thickness seems to increase when compared with that of the diffusion couples without dopant. The samples containing Si{sup 4+} as dopant reveal the formation of a glass phase, and the effect of Si{sup 4+} on the diffusion process appears to be negligible.

  12. New cyclometalated Iridium(III) beta-dicetone complex as phosphorescent dopant in Organic light emitting devices

    NASA Astrophysics Data System (ADS)

    Ivanov, P.; Petrova, P.; Stanimirov, S.; Tomova, R.

    2017-01-01

    A new Bis[4-(benzothiazolato-N,C2‧-2-yl)-N,N-dimethylaniline]Iridium(III) acetylacetonate (Me2N-bt) 2Ir(acac) was synthesized and identified by 1H NMR and elemental analysis. The application of the new compound as a dopant in the hole transporting layer (HTL) of Organic light emitting diode (OLED) structure: HTL/EL/ETL, where HTL was N,N’-bis(3-methylphenyl)-N,N’-diphenylbenzidine (TPD), incorporated in Poly(N-vinylcarbazole) (PVK) matrix, EL - electroluminescent layer of Bis(8-hydroxy-2-methylquinoline)-(4-phenylpheno-xy)aluminum (BAlq) and ETL - electron-transporting layer of Tris-(8-hydroxyquinoline) aluminum (Alq3) or Bis[2-(2-benzothiazoly) phenolato]zinc (Zn(btz)2). We established that the electroluminescent spectra of OLEDs at different concentrations of the dopant were basically the sum of the greenish-blue emission of BAlq and yellowish-green emission of Ir complex. It was found that with increasing of the dopant concentration the relative electroluminescent intensity of Iridium complex emission increased and this of BAlq decreased and as a result the fine tuning of OLED color was observed.

  13. Grain boundary segregation of cation dopants in {alpha}-Al{sub 2}O{sub 3} scales

    SciTech Connect

    Pint, B.A.; Alexander, K.B.

    1996-12-31

    A Fe-20at.%Cr-10%Al matrix was dispersed with a wide range of different oxides in order to study the effect of oxygen-active dopants on the high-temperature growth and adhesion of {alpha}-Al{sub 2}O{sub 3} scales. Effect of these various cation dopants on the alumina scale microstructure was correlated with dopant ion segregation to the {alpha}-Al{sub 2}O{sub 3} grain boundaries using analytical electron microscopy. Elements such as Mn and V showed little effect on the oxide scale and were not observed to segregate. Elements such as Y and Gd resulted in finer, more columnar {alpha}-Al{sub 2}O{sub 3} grains and were segregated to scale grain boundaries. However, Ti, Ta, Ca, and Nb also were found to segregate but had a lesser effect on scale morphology. This indicates that cation segregation to scale grain boundaries is not a sufficient condition to achieve beneficial oxidation effects. The driving force for segregation in growing alumina scales is discussed.

  14. Local structures around 3d metal dopants in topological insulator Bi2Se3 studied by EXAFS measurements

    NASA Astrophysics Data System (ADS)

    Liu, Zhen; Wei, Xinyuan; Wang, Jiajia; Pan, Hong; Ji, Fuhao; Xi, Fuchun; Zhang, Jing; Hu, Tiandou; Zhang, Shuo; Jiang, Zheng; Wen, Wen; Huang, Yuying; Ye, Mao; Yang, Zhongqin; Qiao, Shan

    2014-09-01

    Transition-metal-doped Bi2Se3 crystals, X0.05Bi2Se3 (X =Cr, Co, Ni, and Cu), are prepared and studied by powder x-ray diffraction and extended x-ray absorption fine structure (EXAFS) measurements to get the local structures around the dopants. Cr atoms substitute Bi atoms and Co atoms may substitute Bi atoms or form Co3Se4 (C2/m) clusters. Cu is also found taking the Bi substitutional site, which differs from the reported superconductor phase of Cu-doped Bi2Se3, suggesting the dependence of site occupancy of Cu in Bi2Se3 on the process of sample growing. For Ni0.05Bi2Se3, Ni atoms form Ni3Se4 (C2/m) clusters. The nearest neighbors of X (X =Cr, Co, and Cu) are Se atoms, and the X-Se bond lengths are extracted from EXAFS as 2.50 Å for Cr-Se, 2.40 Å for Co-Se, and 2.38 Å for Cu-Se, which show the direct evidences of dramatic structural relaxations around 3d dopants. The bond information of local structures around dopants is valuable for subsequent theoretical studies, and can hardly be obtained from other techniques.

  15. Highly Soluble p-Terphenyl and Fluorene Derivatives as Efficient Dopants in Plastic Scintillators for Sensitive Nuclear Material Detection.

    PubMed

    Sellinger, Alan; Yemam, Henok A; Mahl, Adam; Greife, Uwe; Tinkham, Jonathan; Koubek, Joshua

    2017-04-10

    Plastic scintillators are commonly used as first-line detectors for special nuclear materials. Current state-of-the-art plastic scintillators based on poly(vinyltoluene) (PVT) matrices containing high loadings (>15.0 wt%) of 2,5-diphenyloxazole (PPO) offer neutron signal discrimination in gamma radiation background (termed pulse shape discrimination, PSD), however they suffer from poor mechanical properties. In this work, a series of p-terphenyl and fluorene derivatives were synthesized and used as dopants in PVT based plastic scintillators as possible alternatives to PPO to address the mechanical property issue and to study the PSD mechanism. The derivatives were synthesized from low cost starting materials in high yields using simple chemistry. The photophysical and thermal properties were investigated for their influence on radiation sensitivity/detection performance, and mechanical stability. A direct correlation was found between the melting point of the dopants and the subsequent mechanical properties of the PVT based plastic scintillators. Select fluorene derivatives produced scintillator samples whose mechanical properties exceeded those of the commercial PPO based scintillators while producing acceptable PSD capabilities. The physical properties of the synthesized dopants were also investigated to examine their effect on the samples. Planar derivatives of fluorene were found to be highly soluble in PVT matrices with little to no aggregation induced effects.

  16. Reversibility, Dopant Desorption, and Tunneling in the Temperature-Dependent Conductivity of Type-Separated, Conductive Carbon Nanotube Networks

    SciTech Connect

    Barnes, T. M.; Blackburn, J. L.; van de Lagemaat, J.; Coutts, T. J.; Heben, M. J.

    2008-09-01

    We present a comprehensive study of the effects of doping and temperature on the conductivity of single-walled carbon nanotube (SWNT) networks. We investigated nearly type-pure networks as well as networks comprising precisely tuned mixtures of metallic and semiconducting tubes. Networks were studied in their as-produced state and after treatments with nitric acid, thionyl chloride, and hydrazine to explore the effects of both intentional and adventitious doping. For intentionally and adventitiously doped networks, the sheet resistance (R{sub s}) exhibits an irreversible increase with temperature above {approx}350 K. Dopant desorption is shown to be the main cause of this increase and the observed hysteresis in the temperature-dependent resistivity. Both thermal and chemical dedoping produced networks free of hysteresis. Temperature-programmed desorption data showed that dopants are most strongly bound to the metallic tubes and that networks consisting of metallic tubes exhibit the best thermal stability. At temperatures below the dopant desorption threshold, conductivity in the networks is primarily controlled by thermally assisted tunneling through barriers at the intertube or interbundle junctions.

  17. Lunar Impact Flash Locations

    NASA Technical Reports Server (NTRS)

    Moser, D. E.; Suggs, R. M.; Kupferschmidt, L.; Feldman, J.

    2015-01-01

    A bright impact flash detected by the NASA Lunar Impact Monitoring Program in March 2013 brought into focus the importance of determining the impact flash location. A process for locating the impact flash, and presumably its associated crater, was developed using commercially available software tools. The process was successfully applied to the March 2013 impact flash and put into production on an additional 300 impact flashes. The goal today: provide a description of the geolocation technique developed.

  18. Object locating system

    DOEpatents

    Novak, J.L.; Petterson, B.

    1998-06-09

    A sensing system locates an object by sensing the object`s effect on electric fields. The object`s effect on the mutual capacitance of electrode pairs varies according to the distance between the object and the electrodes. A single electrode pair can sense the distance from the object to the electrodes. Multiple electrode pairs can more precisely locate the object in one or more dimensions. 12 figs.

  19. Dopant induced single electron tunneling within the sub-bands of single silicon NW tri-gate junctionless n-MOSFET

    NASA Astrophysics Data System (ADS)

    Uddin, Wasi; Georgiev, Yordan M.; Maity, Sarmistha; Das, Samaresh

    2017-09-01

    We report 1D electron transport of silicon junctionless tri-gate n-type transistor at 4.2 K. The step like curve observed in the current voltage characteristic suggests 1D transport. Besides the current steps for 1D transport, we found multiple spikes within individual steps, which we relate to inter-band single electron tunneling, mediated by the charged dopants available in the channel region. Clear Coulomb diamonds were observed in the stability diagram of the device. It is shown that a uniformly doped silicon nanowire can provide us the window for the single electron tunnelling. Back-gate versus front-gate color plot, where current is in a color scale, shows a crossover of the increased conduction region. This is a clear indication of the dopant-dopant interaction. It has been shown that back-gate biasing can be used to tune the coupling strength between the dopants.

  20. Control of the binding energy by tuning the single dopant position, magnetic field strength and shell thickness in ZnS/CdSe core/shell quantum dot

    NASA Astrophysics Data System (ADS)

    Talbi, A.; Feddi, E.; Zouitine, A.; Haouari, M. El; Zazoui, M.; Oukerroum, A.; Dujardin, F.; Assaid, E.; Addou, M.

    2016-10-01

    Recently, the new tunable optoelectronic devices associated to the inclusion of the single dopant are in continuous emergence. Combined to other effects such as magnetic field, geometrical confinement and dielectric discontinuity, it can constitute an approach to adjusting new transitions. In this paper, we present a theoretical investigation of magnetic field, donor position and quantum confinement effects on the ground state binding energy of single dopant confined in ZnS/CdSe core/shell quantum dot. Within the framework of the effective mass approximation, the Schrödinger equation was numerically been solved by using the Ritz variational method under the finite potential barrier. The results show that the binding energy is very affected by the core/shell sizes and by the external magnetic field. It has been shown that the single dopant energy transitions can be controlled by tuning the dopant position and/or the field strength.

  1. The big red shift of photoluminescence of Mn dopants in strained CdS: a case study of Mn-doped MnS-CdS heteronanostructures.

    PubMed

    Zuo, Taisen; Sun, Zhipeng; Zhao, Yuliang; Jiang, Xiaoming; Gao, Xueyun

    2010-05-19

    The red photoluminescence of Mn dopants in MnS-CdS heteronanostructures has been observed for the first time. The red photoluminescence at 650 nm derives from emission due to the (4)T(1) --> (6)A(1) transition of Mn(2+) dopants in a CdS matrix exposed to gigapascal-level lattice stress. HRTEM, FFT, XRD, and optical studies revealed that the lattice of Mn-doped CdS is compressed to match that of MnS when CdS crystallizes at the MnS surface to form MnS-CdS heteronanostructures. The photoluminescence decay times of such Mn dopants are on the order of nanoseconds because of the spin-flip interactions between Mn dopants and free carriers in the CdS matrix.

  2. Thermal equilibrium concentration of intrinsic point defects in heavily doped silicon crystals - Theoretical study of formation energy and formation entropy in area of influence of dopant atoms-

    NASA Astrophysics Data System (ADS)

    Kobayashi, K.; Yamaoka, S.; Sueoka, K.; Vanhellemont, J.

    2017-09-01

    It is well known that p-type, neutral and n-type dopants affect the intrinsic point defect (vacancy V and self-interstitial I) behavior in single crystal Si. By the interaction with V and/or I, (1) growing Si crystals become more V- or I-rich, (2) oxygen precipitation is enhanced or retarded, and (3) dopant diffusion is enhanced or retarded, depending on the type and concentration of dopant atoms. Since these interactions affect a wide range of Si properties ranging from as-grown crystal quality to LSI performance, numerical simulations are used to predict and to control the behavior of both dopant atoms and intrinsic point defects. In most cases, the thermal equilibrium concentrations of dopant-point defect pairs are evaluated using the mass action law by taking only the binding energy of closest pair to each other into account. The impacts of dopant atoms on the formation of V and I more distant than 1st neighbor and on the change of formation entropy are usually neglected. In this study, we have evaluated the thermal equilibrium concentrations of intrinsic point defects in heavily doped Si crystals. Density functional theory (DFT) calculations were performed to obtain the formation energy (Ef) of the uncharged V and I at all sites in a 64-atom supercell around a substitutional p-type (B, Ga, In, and Tl), neutral (C, Ge, and Sn) and n-type (P, As, and Sb) dopant atom. The formation (vibration) entropies (Sf) of free I, V and I, V at 1st neighboring site from B, C, Sn, P and As atoms were also calculated with the linear response method. The dependences of the thermal equilibrium concentrations of trapped and total intrinsic point defects (sum of free I or V and I or V trapped with dopant atoms) on the concentrations of B, C, Sn, P and As in Si were obtained. Furthermore, the present evaluations well explain the experimental results of the so-called ;Voronkov criterion; in B and C doped Si, and also the observed dopant dependent void sizes in P and As doped Si

  3. Electronic and Magnetic Properties of Encapsulated MoS2 Quantum Dots: The Case of Noble Metal Nanoparticle Dopants.

    PubMed

    Loh, Guan Chee

    2016-04-18

    With the rise of 2D materials, such as graphene and transition metal dichalcogenides, as viable materials for numerous experimental applications, it becomes more necessary to maintain fine control of their properties. One expedient and efficacious technique to regulate their properties is surface functionalization. In this study, DFT calculations are performed on triangular MoS2 quantum dots (QDs) either partially or completely doped with nanoparticles (NPs) of the noble metals Au, Ag, and Pt. The effects of these dopants on the geometry, electronic properties, magnetic properties, and chemical bonding of the QDs are investigated. The calculations show that the structural stability of the QDs is reduced by Au or Ag dopants, whereas Pt dopants have a contrasting effect. The NPs diminish the metallicity of the QD, the extent of which is contingent on the number of NPs adsorbed on the QD. However, these NPs exert distinctly disparate charge transfer effects-Ag NPs n-dope the QDs, whereas Au and Pt NPs either n- or p-dope. The molecular electrostatic potential maps of the occupied states show that metallic states are removed from the doping sites. Notwithstanding the decrease of magnetization in all three types of hybrid QD, the distribution of spin density in the Pt-doped QD is inherently different from that in the other QDs. Bond analyses using the quantum theory of atoms in molecules and the crystal orbital Hamilton population suggest that bonds between the Pt NPs and the QDs are the most covalent and the strongest, followed by the Au-QD bonds, and then Ag-QD bonds. The versatility of these hybrid QDs is further examined by applying an external electric field in the three orthogonal orientations, and comparing their properties with those in the absence of the electric field. There are two primary observations: 1) dopants at the tail, head and tail, and in the fully encased configuration are most effective in modifying the distribution of metallic states if the

  4. Hydrogen Storage Properties of Lithium Aluminohydride Modified by Dopants and Mechanochemistry

    SciTech Connect

    Hosokawa, Ketia

    2002-01-01

    Alkali metal aluminohydrides have high potential as solid hydrogen storage materials. They have been known for their irreversible dehydrogenation process below 100 atm until Bogdanovic et al succeeded in the re-hydrogenation of NaAlH4 below 70 atm. They achieved 4 wt.% H2 reversible capacity by doping NaAlH4 with Ti and/or Fe organo-metallic compounds as catalysts. This suggests that other alkali and, possibly alkaline earth metal aluminohydrides can be used for reversible hydrogen storage when modified by proper dopants. In this research, Zr27Ti9Ni38V5Mn16Cr5, LaNi 4.85Sn0.15, Al3Ti, and PdCl2 were combined with LiAlH4 by ball-milling to study whether or not LiAlH4 is capable to both absorb and desorb hydrogen near ambient conditions. X-ray powder diffraction, differential thermal analysis, and scanning electron microscopy were employed for sample characterizations. All four compounds worked as catalysts in the dehydrogenation reactions of both LiAlH4 and Li3AlH6 by inducing the decomposition at lower temperature. However, none of them was applicable as catalyst in the reverse hydrogenation reaction at low to moderate hydrogen pressure.

  5. Hydrogen Storage Properties of Lithium Aluminohydride Modified by Dopants and Mechanochemistry

    SciTech Connect

    Hosokawa, Keita

    2002-01-01

    Alkali metal aluminohydrides have high potential as solid hydrogen storage materials. They have been known for their irreversible dehydrogenation process below 100 atm until Bogdanovic et al [1, 2] succeeded in the re-hydrogenation of NaAlH4 below 70 atm. They achieved 4 wt.% H2 reversible capacity by doping NaAlH4 with Ti and/or Fe organo-metalic compounds as catalysts. This suggests that other alkali and, possibly alkaline earth metal aluminohydrides can be used for reversible hydrogen storage when modified by proper dopants. In this research, Zr27Ti9Ni38V5Mn16Cr5, LaNi4.85Sn0.15, Al3Ti, and PdCl2 were combined , LaNi4.85Sn0.15, Al3Ti, and PdCl2 were combined with LiAlH4 by ball-milling to study whether or not LiAlH4 is capable to both absorb and desorb hydrogen near ambient conditions. X-ray powder diffraction, differential thermal analysis, and scanning electron microscopy were employed for sample characterizations. All four compounds worked as catalysts in the dehydrogenation reactions of both LiAlH4 and Li3AlH6 by inducing the decomposition at lower temperature. However, none of them was applicable as catalyst in the reverse hydrogenation reaction at low to moderate hydrogen pressure.

  6. Hydrogen Storage Properties of Lithium Aluminohydride modified by dopants and mechanochemistry

    SciTech Connect

    Hosokawa, Keita

    2002-01-01

    Alkali metal aluminohydrides have high potential as solid hydrogen storage materials. They have been known for their irreversible dehydrogenation process below 100 atm until Bogdanovic et al [1, 2] succeeded in the re-hydrogenation of NaAlH4 below 70 atm. They achieved 4 wt.% H2 reversible capacity by doping NaAlH4 with Ti and/or Fe organo-metalic compounds as catalysts. This suggests that other alkali and, possibly alkaline earth metal aluminohydrides can be used for reversible hydrogen storage when modified by proper dopants. In this research, Zr27Ti9Ni38V5Mn16Cr5, LaNi4.85Sn0.15, Al3Ti, and PdCl2 were combined with LiAlH4 by ball-milling to study whether or not LiAlH4 is capable to both absorb and desorb hydrogen near ambient conditions. X-ray powder diffraction, differential thermal analysis, and scanning electron microscopy were employed for sample characterizations. All four compounds worked as catalysts in the dehydrogenation reactions of both LiAlH4 and Li3AlH6 by inducing the decomposition at lower temperature. However, none of them was applicable as catalyst in the reverse hydrogenation reaction at low to moderate hydrogen pressure.

  7. Organic dopant added polyvinylidene fluoride based solid polymer electrolytes for dye-sensitized solar cells

    NASA Astrophysics Data System (ADS)

    Senthil, R. A.; Theerthagiri, J.; Madhavan, J.

    2016-02-01

    The effect of phenothiazine (PTZ) as dopant on PVDF/KI/I2 electrolyte was studied for the fabrication of efficient dye-sensitized solar cell (DSSC). The different weight percentage (wt%) ratios (0, 20, 30, 40 and 50%) of PTZ doped PVDF/KI/I2 electrolyte films were prepared by solution casting method using DMF as a solvent. The following techniques such as Fourier transform infrared (FT-IR), differential scanning calorimetry (DSC), X-ray diffractometer (XRD) and AC-impedance analysis have been employed to characterize the prepared polymer electrolyte films. The FT-IR studies revealed the complex formation between PVDF/KI/I2 and PTZ. The crystalline and amorphous nature of polymer electrolytes were confirmed by DSC and XRD analysis respectively. The ionic conductivities of polymer electrolyte films were calculated from the AC-impedance analysis. The undoped PVDF/KI/I2 electrolyte exhibited the ionic conductivity of 4.68×10-6 S cm-1 and this value was increased to 7.43×10-5 S cm-1 when PTZ was added to PVDF/KI/I2 electrolyte. On comparison with different wt% ratios, the maximum ionic conductivity was observed for 20% PTZ-PVDF/KI/I2 electrolyte. A DSSC assembled with the optimized wt % of PTZ doped PVDF/KI/I2 electrolyte exhibited a power conversion efficiency of 2.92%, than the undoped PVDF/KI/I2 electrolyte (1.41%) at similar conditions. Hence, the 20% PTZ-PVDF/KI/I2 electrolyte was found to be optimal for DSSC applications.

  8. Dopant mapping in thin FIB prepared silicon samples by Off-Axis Electron Holography.

    PubMed

    Pantzer, Adi; Vakahy, Atsmon; Eliyahou, Zohar; Levi, George; Horvitz, Dror; Kohn, Amit

    2014-03-01

    Modern semiconductor devices function due to accurate dopant distribution. Off-Axis Electron Holography (OAEH) in the transmission electron microscope (TEM) can map quantitatively the electrostatic potential in semiconductors with high spatial resolution. For the microelectronics industry, ongoing reduction of device dimensions, 3D device geometry, and failure analysis of specific devices require preparation of thin TEM samples, under 70 nm thick, by focused ion beam (FIB). Such thicknesses, which are considerably thinner than the values reported to date in the literature, are challenging due to FIB induced damage and surface depletion effects. Here, we report on preparation of TEM samples of silicon PN junctions in the FIB completed by low-energy (5 keV) ion milling, which reduced amorphization of the silicon to 10nm thick. Additional perpendicular FIB sectioning enabled a direct measurement of the TEM sample thickness in order to determine accurately the crystalline thickness of the sample. Consequently, we find that the low-energy milling also resulted in a negligible thickness of electrically inactive regions, approximately 4nm thick. The influence of TEM sample thickness, FIB induced damage and doping concentrations on the accuracy of the OAEH measurements were examined by comparison to secondary ion mass spectrometry measurements as well as to 1D and 3D simulations of the electrostatic potentials. We conclude that for TEM samples down to 100 nm thick, OAEH measurements of Si-based PN junctions, for the doping levels examined here, resulted in quantitative mapping of potential variations, within ~0.1 V. For thinner TEM samples, down to 20 nm thick, mapping of potential variations is qualitative, due to a reduced accuracy of ~0.3 V. This article is dedicated to the memory of Zohar Eliyahou. Copyright © 2014 Elsevier B.V. All rights reserved.

  9. Chemical nature of boron and nitrogen dopant atoms in graphene strongly influences its electronic properties.

    PubMed

    Lazar, Petr; Zbořil, Radek; Pumera, Martin; Otyepka, Michal

    2014-07-21

    Boron and nitrogen doped graphenes are highly promising materials for electrochemical applications, such as energy storage, generation and sensing. The doped graphenes can be prepared by a broad variety of chemical approaches. The substitution of a carbon atom should induce n-type behavior in the case of nitrogen and p-type behavior in the case of boron-doped graphene; however, the real situation is more complex. The electrochemical experiments show that boron-doped graphene prepared by hydroboration reaction exhibits similar properties as the nitrogen doped graphene; according to theory, the electrochemical behavior of B and N doped graphenes should be opposite. Here we analyze the electronic structure of N/B-doped graphene (at ∼5% coverage) by theoretical calculations. We consider graphene doped by both substitution and addition reactions. The density of states (DOS) plots show that graphene doped by substitution of the carbon atom by N/B behaves as expected, i.e., as an n/p-doped material. N-doped graphene also has a lower value of the workfunction (3.10 eV) with respect to that of the pristine graphene (4.31 eV), whereas the workfunction of B-doped graphene is increased to the value of 5.57 eV. On the other hand, the workfunctions of graphene doped by addition of -NH2 (4.77 eV) and -BH2 (4.54 eV) groups are both slightly increased and therefore the chemical nature of the dopant is less distinguishable. This shows that mode of doping depends significantly on the synthesis method used, as it leads to different types of behaviour, and, in turn, different electronic and electrochemical properties of doped graphene, as observed in electrocatalytic experiments. This study has a tremendous impact on the design of doped graphene systems from the point of view of synthetic chemistry.

  10. Impact of zirconium dopants on the lasing efficiency of Raman microcavity laser

    NASA Astrophysics Data System (ADS)

    Choi, Hyungwoo; Armani, Andrea M.

    2017-02-01

    Whispering Gallery Mode (WGM) silica microresonators are a particularly unique group of microcavities in the sense that they can confine light inside the device for an extended period of time while maintaining a high quality (Q) factor due to the total internal reflection. As a result, WGM resonators have high circulating optical power, which can cause nonlinear optical processes such as stimulated Raman scattering (SRS). It has been demonstrated that SRS has been observed in various WGM silica microresonators with the sub-mW Raman lasing threshold. However, in case of the Raman lasing efficiency, it is limited by the intrinsic property of silica itself, which is the Raman gain coefficient. Therefore, in the present work, we introduce a hybrid silica toroidal microcavity in order to enhance the Raman lasing efficiency. First, we synthesize a suite of silica sol-gels doped with a range of Zirconium (Zr) concentrations and integrate the material with silica toroidal microresonator. The intrinsic Raman gain of the Zr-doped silica is measured using Raman spectroscopy, and the values show a clear dependence on Zr dopant concentrations. The lasing performance is characterized using a 765 nm pump source, and the Raman emissions for the coated devices are detected at 790 nm and longer. The lasing emission and characteristic threshold curves are quantified using both an optical spectrum analyzer and an optical spectrograph. The lasing slope efficiency of exhibits a marked increase from 3.37% to 47.43% as the Zr concentration increases due to the Raman gain improvement. These values are particularly notable as they are the unidirectional, not bidirectional, lasing efficiencies.

  11. Tuning near-gap electronic structure, interface charge transfer and visible light response of hybrid doped graphene and Ag3PO4 composite: Dopant effects

    PubMed Central

    He, Chao-Ni; Huang, Wei-Qing; Xu, Liang; Yang, Yin-Cai; Zhou, Bing-Xin; Huang, Gui-Fang; Peng, P.; Liu, Wu-Ming

    2016-01-01

    The enhanced photocatalytic performance of doped graphene (GR)/semiconductor nanocomposites have recently been widely observed, but an understanding of the underlying mechanisms behind it is still out of reach. As a model system to study the dopant effects, we investigate the electronic structures and optical properties of doped GR/Ag3PO4 nanocomposites using the first-principles calculations, demonstrating that the band gap, near-gap electronic structure and interface charge transfer of the doped GR/Ag3PO4(100) composite can be tuned by the dopants. Interestingly, the doping atom and C atoms bonded to dopant become active sites for photocatalysis because they are positively or negatively charged due to the charge redistribution caused by interaction. The dopants can enhance the visible light absorption and photoinduced electron transfer. We propose that the N atom may be one of the most appropriate dopants for the GR/Ag3PO4 photocatalyst. This work can rationalize the available experimental results about N-doped GR-semiconductor composites, and enriches our understanding on the dopant effects in the doped GR-based composites for developing high-performance photocatalysts. PMID:26923338

  12. Using Pt Dopant and Sol Gel Technology for Sensitivity Enhancement of TiO2/SnO2Humidity Sensors.

    PubMed

    Chang, Wen-Yang; Ke, Wen-Wang; Hsieh, Yu-Sheng; Kuo, Nai-Hao; Lin, Yu-Cheng

    2005-01-01

    The sensitivity of the humidity sensor based on hybrid thin films of nanostructure TiO2/SnO2with Pt dopant was successfully increased. The humidity-sensitive materials, TiO2/SnO3, were prepared by sol gel technology. The microstructure of the sensing film after calcination was investigated by the Field Emission gun Scanning Electron Microscopy (FESEM) and revealed that the metal oxide hybrid had about 10 nm grain size. For studying the effect of Pt dopant on the humidity-sensitive responses, 1 ml to 10 ml of Pt standard solution was added into the colloidal solution. To compare the humidity sensor of Pt dopant with that of no Pt dopant, operational frequencies and electrode spacing were set under the relative humidity from 30 % to 95 % at the ambient temperature of 22 °C. We demonstrated that adding Pt dopant remarkably enhanced the sensitivity of TiO2/SnO2humidity sensor, and further decreased the TiO2/SnO2 resistance, which was 3.3 times lower than that without Pt dopant at the high humidity.

  13. iLocater

    NASA Astrophysics Data System (ADS)

    Crepp, Justin R.

    2013-01-01

    We present the science case and optical design for iLocater: a precision NIR Doppler spectrometer for the Large Binocular Telescope. iLocater is the world's first AO-fed ultra-stable RV instrument. By working at the diffraction limit, the instrument has spatial dimensions less than 0.5 cubic-meters (the size of a travel carry-on bag), and is thus physically smaller than comparable seeing-limited spectrographs. The benefits of a small point-spread function are three-fold: (1) high spectral resolution; (2) a smaller and thus more stable instrument; (3) smaller and thus less expensive optics. iLocater will operate in the Y-band, achieve R=110,000 spectral resolution, and identify terrestrial planets orbiting in the habitable zone of nearby M-dwarf stars.

  14. RFI emitter location techniques

    NASA Technical Reports Server (NTRS)

    Rao, B. L. J.

    1973-01-01

    The possibility is discussed of using Doppler techniques for determining the location of ground based emitters causing radio frequency interference with low orbiting satellites. An error analysis indicates that it is possible to find the emitter location within an error range of 2 n.mi. The parameters which determine the required satellite receiver characteristic are discussed briefly along with the non-real time signal processing which may by used in obtaining the Doppler curve. Finally, the required characteristics of the satellite antenna are analyzed.

  15. Marine cable location system

    SciTech Connect

    Zachariadis, R.G.

    1984-05-01

    An acoustic positioning system locates a marine cable at an exploration site, such cable employing a plurality of hydrophones at spaced-apart positions along the cable. A marine vessel measures water depth to the cable as the vessel passes over the cable and interrogates the hydrophones with sonar pulses along a slant range as the vessel travels in a parallel and horizontally offset path to the cable. The location of the hydrophones is determined from the recordings of water depth and slant range.

  16. LOCATING AREAS OF CONCERN

    EPA Science Inventory

    A simple method to locate changes in vegetation cover, which can be used to identify areas under stress. The method only requires inexpensive NDVI data. The use of remotely sensed data is far more cost-effective than field studies and can be performed more quickly. Local knowledg...

  17. LOCATING AREAS OF CONCERN

    EPA Science Inventory

    A simple method to locate changes in vegetation cover, which can be used to identify areas under stress. The method only requires inexpensive NDVI data. The use of remotely sensed data is far more cost-effective than field studies and can be performed more quickly. Local knowledg...

  18. Particle impact location detector

    NASA Technical Reports Server (NTRS)

    Auer, S. O.

    1974-01-01

    Detector includes delay lines connected to each detector surface strip. When several particles strike different strips simultaneously, pulses generated by each strip are time delayed by certain intervals. Delay time for each strip is known. By observing time delay in pulse, it is possible to locate strip that is struck by particle.

  19. Uranium Location Database

    EPA Pesticide Factsheets

    A GIS compiled locational database in Microsoft Access of ~15,000 mines with uranium occurrence or production, primarily in the western United States. The metadata was cooperatively compiled from Federal and State agency data sets and enables the user to conduct geographic and analytical studies on mine impacts on the public and environment.

  20. Optimal Facility-Location.

    PubMed

    Goldman, A J

    2006-01-01

    Dr. Christoph Witzgall, the honoree of this Symposium, can count among his many contributions to applied mathematics and mathematical operations research a body of widely-recognized work on the optimal location of facilities. The present paper offers to non-specialists a sketch of that field and its evolution, with emphasis on areas most closely related to Witzgall's research at NBS/NIST.