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Sample records for diameter-dependent dopant location

  1. Dopant location identification in Nd3+ doped TiO2 nanoparticles

    SciTech Connect

    Li, W.; Frenkel, A.; Woicik, J.; Ni, C.; Shah, S.

    2010-12-03

    Large band gap semiconductors are typically doped in order to enhance their photocatalytic, photovoltaic, and other chemical and optoelectronic properties. The identification of dopant position and its local environment are essential to explore the effect of doping. X ray techniques, including extended x ray absorption fine structure, x ray photoelectron spectroscopy, and x ray diffraction, were performed to analyze the Nd (0 to 1.5 at. %) dopant location and the structural changes associated with the doping in anatase TiO{sub 2} nanoparticles, which were synthesized by metalorganic chemical vapor deposition. Nd ions were determined to have a trivalent chemical state and substitute for Ti{sup 4+} in the TiO{sub 2} structure. The substitutional Nd{sup 3+} ions cause anatase lattice expansion along c direction with a maximum value of 0.15 {angstrom} at 1.5% Nd doping level and the local structure of the dopants changes towards rutile like configuration. The lengths of the nearest neighbor Nd-O and Nd-Ti bonds increase by 0.5-0.8 {angstrom} compared to their counterparts in the pure TiO{sub 2} host structure. The substitutional nature of Nd{sup 3+} dopants explains why they are efficient not only for charge carrier separation but also for visible light absorption in TiO{sub 2}.

  2. 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.

  3. 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.

  4. Diameter dependent thermoelectric properties of individual SnTe nanowires

    DOE PAGESBeta

    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 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

  5. 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 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 nanowire 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.

  6. 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.

  7. Diameter dependent thermoelectric properties of individual SnTe nanowires.

    PubMed

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

    2015-02-21

    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. 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. PMID:25623253

  8. Sb- and Bi-doped Mg2Si: location of the dopants, micro- and nanostructures, electronic structures and thermoelectric properties.

    PubMed

    Farahi, Nader; VanZant, Mathew; Zhao, Jianbao; Tse, John S; Prabhudev, Sagar; Botton, Gianluigi A; Salvador, James R; Borondics, Ferenc; Liu, Zhenxian; Kleinke, Holger

    2014-10-28

    Due to increasing global energy concerns, alternative sustainable methods to create energy such as thermoelectric energy conversion have become increasingly important. Originally, research into thermoelectric materials was focused on tellurides of bismuth and lead because of the exemplary thermoelectric properties of Bi2Te3 and PbTe. These materials, however, contain toxic lead and tellurium, which is also scarce and thus expensive. A viable alternative material may exist in Mg2Si, which needs to be doped and alloyed in order to achieve reasonable thermoelectric efficiency. Doping is a major problem, as p-type doping has thus far not produced competitive efficiencies, and n-type doping is problematic because of the low solubility of the typical dopants Sb and Bi. This investigation shows experimentally that these dopants can indeed replace Si in the crystal lattice, and excess Sb and Bi atoms are present in the grain boundaries in the form of Mg3Sb2 and Mg3Bi2. As a consequence, the carrier concentration is lower than the formal Sb/Bi concentration suggests, and the thermal conductivity is significantly reduced. DFT calculations are in good agreement with the experimental data, including the band gap and the Seebeck coefficient. Overall, this results in competitive efficiencies despite the low carrier concentration. While ball-milling was previously shown to enhance the solubility of the dopants and thus the carrier concentration, this did not lead to enhanced thermoelectric properties. PMID:25005794

  9. Location of trivalent lanthanide dopant energy levels in (Lu{sub 0.5}Gd{sub 0.5}){sub 2}O{sub 3}

    SciTech Connect

    Retot, H.; Viana, B.; Bessiere, A.; Galtayries, A.

    2011-06-15

    The location of Ln{sup 3+} dopant energy levels relative to bands in (Lu{sub 0.5}Gd{sub 0.5}){sub 2}O{sub 3} was studied. A several-steps analysis of XPS measurements on heavy lanthanides sesquioxides Ln{sub 2}O{sub 3} (Ln = Gd, Tb, Dy, Er, Tm, Yb, Lu) and on Sc{sub 2}O{sub 3} and Y{sub 2}O{sub 3} reference materials were used to locate Ln{sup 3+} dopant ground state relative to the top of the valence band in (Lu{sub 0.5}Gd{sub 0.5}){sub 2}O{sub 3} within an error bar of {+-}0.4 eV. The agreement between XPS data and model was found improved relative to previous studies. When compared to XPS analysis, prediction based on optical absorption shows a slight underestimation attributed to the lack of precision in Ce{sup 4+} charge transfer band measurement.

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

    PubMed

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

    2015-01-01

    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. PMID:26490342

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

    PubMed Central

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

    2015-01-01

    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. PMID:26490342

  12. Diameter dependence of the thermal conductivity of InAs nanowires.

    PubMed

    Swinkels, M Y; van Delft, M R; Oliveira, D S; Cavalli, A; Zardo, I; van der Heijden, R W; Bakkers, E P A M

    2015-09-25

    The diameter dependence of the thermal conductivity of InAs nanowires in the range of 40-1500 nm has been measured. We demonstrate a reduction in thermal conductivity of 80% for 40 nm nanowires, opening the way for further design strategies for nanoscaled thermoelectric materials. Furthermore, we investigate the effect of thermal contact in the most common measurement method for nanoscale thermal conductivity. Our study allows for the determination of the thermal contact using existing measurement setups. The thermal contact resistance is found to be comparable to the wire thermal resistance for wires with a diameter of 90 nm and higher. PMID:26329133

  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. Successful location of tin dopant cations on surface sites of anatase-type TiO2 crystallites evidenced by 119Sn Mössbauer spectroscopic probe and XPS techniques

    NASA Astrophysics Data System (ADS)

    Astashkin, R. A.; Fabritchnyi, P. B.; Afanasov, M. I.; Korolenko, M. V.; Wattiaux, A.; Bordère, S.; Labrugère, C.; Delmas, C.

    2013-11-01

    The present study provides the first experimental evidence for the stabilization of tin dopant cations immediately on the surface of an oxide having a tetragonal structure. 119Sn Mössbauer spectra of the dopant, introduced by air annealing into the bulk of anatase microcrystals, showed that it was located, in the tetravalent state, in somewhat distorted octahedral sites of a unique type. On the contrary, the reduced tin species, formed upon subsequent hydrogen annealing the Sn4+-doped samples, are found to occupy different sites being characterized by two sets of the isomer shift δ and quadrupole splitting ΔEQ values (δI = 3.25 mm s-1, ΔEQI = 1.75 mm s-1; and δII = 2.85 mm s-1, ΔEQII = 1.71 mm s-1). Either of them implies both the divalent state of tin atoms and their presence at low-coordination sites that can be assigned to the surface of crystallites. Mössbauer spectra of Sn4+←2+ daughter ions, formed upon contact with air of Sn2+, consist of a symmetrically broadened peak characterized by only slightly different average values of both the isomer shift (<δ> = 0.07 mm s-1) and quadrupole splitting (<ΔEQ> = 0.50 mm s-1), as compared to the δ and ΔEQ values for the bulk-located Sn4+. However, considerable broadening of Sn4+←2+ doublet components (Γ = 0.97 mm s-1) allows one to suggest that these secondary formed ions remain distributed over the non equivalent sites inherited from their Sn2+ precursors. The occurrence of Sn4+←2+ at surface sites is independently proven by XPS measurements that revealed a greater than 10-fold enrichment with tin of 3-5 nm thick surface layers.

  15. Kinetics of PL quenching during single-walled carbon nanotube rebundling and diameter-dependent surfactant interactions.

    PubMed

    McDonald, Timothy J; Engtrakul, Chaiwat; Jones, Marcus; Rumbles, Garry; Heben, Michael J

    2006-12-21

    The kinetics of single-walled carbon nanotube rebundling have been investigated by photoluminescence (PL) spectroscopy. The rate of loss of PL intensity was measured for 12 different nanotubes in three common aqueous surfactants (sodium dodecyl sulfate, SDS; sodium dodecylbenzene sulfonate, SDBS; and sodium cholate, SC) as the surfactant suspensions were diluted to promote nanotube rebundling, quenching of semiconductor nanotube PL, and precipitation. The rate of PL decay was first-order in the concentration of isolated nanotubes, as expected if surfactant desorption is rate-limiting in the rebundling process. Temperature-dependent measurements permitted an Arrhenius analysis from which diameter-dependent activation energies were determined. SDS was found to have very strong diameter dependence for activation energy, with stronger binding to smaller-diameter nanotubes, whereas SDBS displayed a weaker diameter dependence. SC was found to bind strongly to certain nanotubes and weakly to the (10,2) nanotube. The PL emission red shifted with time after dilution as surfactant desorption proceeded. This effect is attributed to an increase in the micropolarity at the nanotube surface. PMID:17165980

  16. Imaging "invisible" dopant atoms in semiconductor nanocrystals.

    PubMed

    Gunawan, Aloysius A; Mkhoyan, K Andre; Wills, Andrew W; Thomas, Malcolm G; Norris, David J

    2011-12-14

    Nanometer-scale semiconductors that contain a few intentionally added impurity atoms can provide new opportunities for controlling electronic properties. However, since the physics of these materials depends strongly on the exact arrangement of the impurities, or dopants, inside the structure, and many impurities of interest cannot be observed with currently available imaging techniques, new methods are needed to determine their location. We combine electron energy loss spectroscopy with annular dark-field scanning transmission electron microscopy (ADF-STEM) to image individual Mn impurities inside ZnSe nanocrystals. While Mn is invisible to conventional ADF-STEM in this host, our experiments and detailed simulations show consistent detection of Mn. Thus, a general path is demonstrated for atomic-scale imaging and identification of individual dopants in a variety of semiconductor nanostructures. PMID:22107439

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. Interface engineering through atomic dopants in HfO2-based gate stacks

    NASA Astrophysics Data System (ADS)

    Zhu, H.; Ramanath, Ganpati; Ramprasad, R.

    2013-09-01

    Controlling the effective work function (ϕeff) of metal electrodes is critical and challenging in metal-oxide-semiconductor field effect transistors. The introduction of atomic dopants (also referred to as "capping" layers) is an emerging approach to controllably modify ϕeff. Here, we investigate the energetic preference of the location of La, Y, Sc, Al, Ce, Ti, and Zr as atomic dopants within a model Pt/HfO2/Si stack and the resulting variation of ϕeff using density functional theory calculations. Our results indicate that all the considered atomic dopants prefer to be situated at the interfaces. The dopant-induced variation of ϕeff is found to be strongly correlated to the dopant electronegativity and location. Dopants at the metal/HfO2 interface decrease ϕeff with increasing dopant electronegativity, while a contrary trend is seen for dopants at the Si/HfO2 interface. These results are consistent with available experimental data for La, Al, and Ti doping. Our findings, especially the identified correlations, have important implications for the further optimization and "scaling down" of transistors.

  2. 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…

  3. Organo-lanthanide complexes as luminescent dopants in polymer waveguides fabricated by hot embossing

    NASA Astrophysics Data System (ADS)

    Moynihan, S.; Van Deun, R.; Binnemans, K.; Krueger, J.; von Papen, G.; Kewell, A.; Crean, G.; Redmond, G.

    2007-08-01

    Lanthanide complexes, Eu(dbm)3(Phen) and Er(dbm)3(Phen), are employed as luminescent dopants within polymer channel waveguide devices fabricated by hot embossing. Spectroscopic properties of the complexes as dopants in the waveguide core polymer are investigated in detail. Judd-Ofelt parameters are calculated for the europium chelate and radiative properties are determined viz. potential for optical amplification. Channel waveguides fabricated by single level embossing are shown to be capable of guiding visible and infrared light emitted following optical excitation of the dopants. Multi-level polymer micro-optical benches incorporating doped channel waveguides and passive locational features for self-alignment and integration of optical fibres are fabricated in a multi-level single-step embossing process and are shown to successfully out-couple the waveguided dopant emission.

  4. 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.

  5. Dopant precipitation in silicon-germanium alloys.

    NASA Technical Reports Server (NTRS)

    Raag, V.

    1972-01-01

    The model commonly used to describe dopant precipitation in silicon-germanium alloys is discussed. The results of an experimental program are fit to the model in order to determine the long-term behavior of the thermoelectric properties of the n-type 80 at. % Si/20 at. % Ge alloy. Thermoelectric property projections to twelve years of operating time are given.

  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. 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. PMID:21288644

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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.

  13. Dopant materials used in the microelectronics industry

    SciTech Connect

    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. 24 references.

  14. Dopant morphology as the factor limiting graphene conductivity

    NASA Astrophysics Data System (ADS)

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

    2015-11-01

    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.

  15. 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

  16. Patterning Superatom Dopants on Transition Metal Dichalcogenides.

    PubMed

    Yu, Jaeeun; Lee, Chul-Ho; Bouilly, Delphine; Han, Minyong; Kim, Philip; Steigerwald, Michael L; Roy, Xavier; Nuckolls, Colin

    2016-05-11

    This study describes a new and simple approach to dope two-dimensional transition metal dichalcogenides (TMDCs) using the superatom Co6Se8(PEt3)6 as the electron dopant. Semiconducting TMDCs are wired into field-effect transistor devices and then immersed into a solution of these superatoms. The degree of doping is determined by the concentration of the superatoms in solution and by the length of time the films are immersed in the dopant solution. Using this chemical approach, we are able to turn mono- and few-layer MoS2 samples from moderately to heavily electron-doped states. The same approach applied on WSe2 films changes their characteristics from hole transporting to electron transporting. Moreover, we show that the superatom doping can be patterned on specific areas of TMDC films. To illustrate the power of this technique, we demonstrate the fabrication of a lateral p-n junction by selectively doping only a portion of the channel in a WSe2 device. Finally, encapsulation of the doped films with crystalline hydrocarbon layers stabilizes their properties in an ambient environment. PMID:27082448

  17. 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.

  18. Dopant segregation at silicon-oxide interfaces

    NASA Astrophysics Data System (ADS)

    Pei, Lirong

    With the fast scaling of MOSFET devices, interfaces between silicon and dielectric layers are becoming increasingly important. However, a physical understanding of dopant segregation at such interfaces using atomic resolution remains elusive in spite of intensive study. In this thesis, As and Sb are selected as dopants to achieve different levels of segregation in equilibrium conditions. This study utilizes a combination of theoretical and experimental concepts. Experimentally, three different methods (SIMS, GI-XRF and high resolution Z-contrast imaging/EELS) are used. Due to the fact that each method has its own artifacts, we use a combination of all of them to allow accurate determination of position and concentration of dopants. Additionally, ab initio calculations provide appropriate structure model by calculating the energy of different preferred segregation sites. After implanting As (1015 and 1016 cm -2) into Czochralski Si (100) wafer at 32keV, a SiO2 layer is thermally grown. Then Si/SiO2 samples are annealed at 900°C for 360min in N2, with a final SiO2 thin film less than 15nm measured by ellipsometry. Combining the above three experimental methods, the segregation of As to the Si/SiO2 interface is observed. The As concentration profiles of both samples are analyzed close to the interface region by EELS, and compared with those measured by GI-XRF and SIMS. A maximum of 4˜5x1021 cm-3 arsenic (10 16 cm-2) and 1.2x1021 cm -3 arsenic (1015 cm-2) are observed at the last monolayer of Si. The total dose loss at the interface of the 10 16 cm-2 As doped sample is 8˜9%. With the incorporation of ab initio calculations, a physical explanation of the segregation mechanism is given based on both theoretical and experimental results. Due to the overlap of Sb, Si and O edges, neither EELS nor GI-XRF can be applied to Sb-concentration profiling in Sb (3x1015 cm-2) doped Si/SiO2 samples, which are annealed at 950°C for 360min, 1000°C for 20 or 60 min separately

  19. Arrangement, Dopant Source, And Method For Making Solar Cells

    DOEpatents

    Rohatgi, Ajeet; Krygowski, Thomas W.

    1999-10-26

    Disclosed is an arrangement, dopant source and method used in the fabrication of photocells that minimize handling of cell wafers and involve a single furnace step. First, dopant sources are created by depositing selected dopants onto both surfaces of source wafers. The concentration of dopant that is placed on the surface is relatively low so that the sources are starved sources. These sources are stacked with photocell wafers in alternating orientation in a furnace. Next, the temperature is raised and thermal diffusion takes place whereby the dopant leaves the source wafers and becomes diffused in a cell wafer creating the junctions necessary for photocells to operate. The concentration of dopant diffused into a single side of the cell wafer is proportional to the concentration placed on the respective dopant source facing the side of the cell wafer. Then, in the same thermal cycle, a layer of oxide is created by introducing oxygen into the furnace environment after sufficient diffusion has taken place. Finally, the cell wafers receive an anti-reflective coating and electrical contacts for the purpose of gathering electrical charge.

  20. 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.

  1. Alumina as a dopant in optical fiber by OVD

    NASA Astrophysics Data System (ADS)

    Wang, Ji

    2014-08-01

    Alumina is an indispensable dopant in modern optical fiber technology, particularly due to its important role played in the recent developments of optical fiber amplifiers and high-power fiber lasers over the last decade or so, which have revolutionized the telecommunication systems, and the industrial laser landscapes, respectively. In this paper, Alumina-doped optical fibers advanced through the outside vapor deposition process and their key attributes in the respective applications are reviewed, with Alumina both as a sole dopant for its potential use in the low-loss transmission lines and as a co-dopant for active use in the high-brightness, high-power fiber laser applications.

  2. 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.

  3. Dopant-mediated oxygen vacancy tuning in ceria nanoparticles.

    PubMed

    Babu, Suresh; Thanneeru, Ranjith; Inerbaev, Talgat; Day, Richard; Masunov, Artëm E; Schulte, Alfons; Seal, Sudipta

    2009-02-25

    Ceria nanoparticles with 20 and 40 at.% RE (RE = Y, Sm, Gd, and Yb) dopants were synthesized through a microemulsion method. Independently of the dopant nature and concentration, nearly monodispersed nanoparticles of size 3-5 nm were observed in high resolution transmission electron microscopic analysis. The ceria lattice either expands or contracts depending on the dopant cation ionic radii, as indicated by x-ray diffraction studies. X-ray photoelectron and Raman spectroscopic studies were used to quantify the cerium oxidation state and oxygen vacancy concentration. The results show the tunability of the oxygen vacancy and Ce(3+) concentrations based on the dopant properties. First principles simulations using the free energy density functional theory method support the observed experimental trends. The reported results establish a relationship between the oxygen vacancies and oxidation states in doped ceria required for tailoring properties in catalytic and biomedical applications. PMID:19417474

  4. Dopant profile engineering of advanced Si MOSFET's using ion implantation

    NASA Astrophysics Data System (ADS)

    Stolk, P. A.; Ponomarev, Y. V.; Schmitz, J.; van Brandenburg, A. C. M. C.; Roes, R.; Montree, A. H.; Woerlee, P. H.

    1999-01-01

    Ion implantation has been used to realize non-uniform, steep retrograde (SR) dopant profiles in the active channel region of advanced Si MOSFET's. After defining the transistor configuration, SR profiles were formed by dopant implantation through the polycrystalline Si gate and the gate oxide (through-the-gate, TG, implantation). The steep nature of the as-implanted profile was retained by applying rapid thermal annealing for dopant activation and implantation damage removal. For NMOS transistors, TG implantation of B yields improved transistor performance through increased carrier mobility, reduced junction capacitances, and reduced susceptibility to short-channel effects. Electrical measurements show that the gate oxide quality is not deteriorated by the ion-induced damage, demonstrating that transistor reliability is preserved. For PMOS transistors, TG implantation of P or As leads to unacceptable source/drain junction broadening as a result of transient enhanced dopant diffusion during thermal activation.

  5. Conducting molecular composites of polypyrrole with electroactive polymeric dopantions

    SciTech Connect

    Cameron, D.A.; Reynolds, J.R.

    1996-10-01

    Polypyrrole is one of the most widely used and studied electroactive polymers due to its good conductivity and stability in air. A variety of low molecular weight and polymeric ions have been used as charge compensating dopants in conductive polypyrrole in its oxidized state. In this work we report the electro-polymerization of polypyrrole films incorporating electroactive N-substituted polyaniline polyelectrolytes as dopant ions.

  6. 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.

  7. 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

  8. Refractive index modification of polymers using nanosized dopants

    NASA Astrophysics Data System (ADS)

    Hanemann, Thomas; Boehm, Johannes; Müller, Claas; Ritzhaupt-Kleissl, Eberhard

    2008-04-01

    The addition of nanosized inorganic or organic dopants to polymers allows the modification of the polymers physical properties enabling the realization of functionalized polymers with new application fields e.g. in microoptics. Exemplarily electron rich organic dopants, solved in polymers, cause a pronounced increase of the refractive index. Polymer based reactive resins like PMMA, solved in MMA, or unsaturated polyester, solved in styrene, can be cured to thermoplastic polymers. The resin's low viscous flow behaviour enables an easy composite formation by solving the organic dopants in the liquid up to a dopant content of 50 wt%, followed by solidification to a thermoplastic. The addition of simple organic molecules like phenanthrene or benzochinoline allows a refractive index elevation at 633 nm from 1.56 up to 1.60 retaining the good transmission properties. In comparison the refractive index of PMMA can be increased from the initial value of 1.49 up to values around 1.58 (@633 nm). All composites show an almost linear correlation between dopant content and refractive index. Using these composites devices like 3dB-couplers or an electrooptical modulator applying injection molded or hot embossed substrates have been realized.

  9. Substituted molecular p-dopants: A theoretical study

    SciTech Connect

    Padmaperuma, Asanga B.

    2012-09-28

    Conductivity dopants with processing properties suitable for industrial applications are of importance to the organic electronics field. However, the number of commercially available organic molecular dopants is limited. The electron acceptor 2,3,5,6-tetrafluoro-7,7,8,8,-tetracyanoquinodimethane (F4-TCNQ) is the most utilized p-dopant; however, it has high volatility and a poor sticking coefficient, which makes it difficult to control doping levels and prevent vacuum system contamination. A design concept for p-type molecular dopants based on the TCNQ core which are substituted to improve processing properties without sacrificing the electronic properties necessary is presented. The correlation between the LUMO energy and the position of substitution as well as the choice of linker is evaluated. The position of substitution as well as the choice of linker has a significant effect on the electronic properties. However, the geometry of the substituted molecules was not significantly distorted from that of the parent F4-TCNQ, and the electron density was delocalized on the TCNQ core. We also put forward four possible molecular dopants with suitable energy levels.

  10. Detecting excitation and magnetization of individual dopants in a semiconductor.

    PubMed

    Khajetoorians, Alexander A; Chilian, Bruno; Wiebe, Jens; Schuwalow, Sergej; Lechermann, Frank; Wiesendanger, Roland

    2010-10-28

    An individual magnetic atom doped into a semiconductor is a promising building block for bottom-up spintronic devices and quantum logic gates. Moreover, it provides a perfect model system for the atomic-scale investigation of fundamental effects such as magnetism in dilute magnetic semiconductors. However, dopants in semiconductors so far have not been studied by magnetically sensitive techniques with atomic resolution that correlate the atomic structure with the dopant's magnetism. Here we show electrical excitation and read-out of a spin associated with a single magnetic dopant in a semiconductor host. We use spin-resolved scanning tunnelling spectroscopy to measure the spin excitations and the magnetization curve of individual iron surface-dopants embedded within a two-dimensional electron gas confined to an indium antimonide (110) surface. The dopants act like isolated quantum spins the states of which are governed by a substantial magnetic anisotropy that forces the spin to lie in the surface plane. This result is corroborated by our first principles calculations. The demonstrated methodology opens new routes for the investigation of sample systems that are more widely studied in the field of spintronics-that is, Mn in GaAs (ref. 5), magnetic ions in semiconductor quantum dots, nitrogen-vacancy centres in diamond and phosphorus spins in silicon. PMID:20981095

  11. 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.

  12. The effect of oxide overlayers on secondary electron dopant mapping.

    PubMed

    Dapor, Maurizio; Jepson, Mark A E; Inkson, Beverley J; Rodenburg, Cornelia

    2009-06-01

    The International Technology Roadmap for Semiconductors ranks dopant profiling as one of the most difficult challenges for analysis of semiconductors. Dopant mapping in the scanning electron microscope (SEM) has the potential to provide a solution. This technique has not yet found widespread application, however, mainly due to the lack of a comprehensive theoretical model, uncertain quantification, and its inability to differentiate doping levels in n-type silicon. Although a Monte Carlo model was recently published that closely matched experimental data obtained in p-doped silicon to data obtained from the theoretical model, a large discrepancy between experimental data obtained for n-type silicon was found. Here we present a Monte Carlo model that provides close matches between experimental and calculated data in both n- and p-type silicon, paving the way for a widespread application of SEM dopant contrast. PMID:19460180

  13. 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.

  14. 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.

  15. Development of an ion beam alignment system for real-time scanning tunneling microscope observation of dopant-ion irradiation

    SciTech Connect

    Kamioka, Takefumi; Sato, Kou; Kazama, Yutaka; Watanabe, Takanobu; Ohdomari, Iwao

    2008-07-15

    An ion beam alignment system has been developed in order to realize real-time scanning tunneling microscope (STM) observation of 'dopant-ion' irradiation that has been difficult due to the low emission intensity of the liquid-metal-ion-source (LMIS) containing dopant atoms. The alignment system is installed in our original ion gun and STM combined system (IG/STM) which is used for in situ STM observation during ion irradiation. By using an absorbed electron image unit and a dummy sample, ion beam alignment operation is drastically simplified and accurized. We demonstrate that sequential STM images during phosphorus-ion irradiation are successfully obtained for sample surfaces of Si(111)-7x7 at room temperature and a high temperature of 500 deg. C. The LMIS-IG/STM equipped with the developed ion beam alignment system would be a powerful tool for microscopic investigation of the dynamic processes of ion irradiation.

  16. Polarization charge as a reconfigurable quasi-dopant in ferroelectric thin films.

    PubMed

    Crassous, Arnaud; Sluka, Tomas; Tagantsev, Alexander K; Setter, Nava

    2015-07-01

    Impurity elements used as dopants are essential to semiconductor technology for controlling the concentration of charge carriers. Their location in the semiconductor crystal is determined during the fabrication process and remains fixed. However, another possibility exists whereby the concentration of charge carriers is modified using polarization charge as a quasi-dopant, which implies the possibility to write, displace, erase and re-create channels having a metallic-type conductivity inside a wide-bandgap semiconductor matrix. Polarization-charge doping is achieved in ferroelectrics by the creation of charged domain walls. The intentional creation of stable charged domain walls has so far only been reported in BaTiO3 single crystals, with a process that involves cooling the material through its phase transition under a strong electric bias, but this is not a viable technology when real-time reconfigurability is sought in working devices. Here, we demonstrate a technique allowing the creation and nanoscale manipulation of charged domain walls and their action as a real-time doping activator in ferroelectric thin films. Stable individual and multiple conductive channels with various lengths from 3 μm to 100 nm were created, erased and recreated in another location, and their high metallic-type conductivity was verified. This takes the idea of hardware reconfigurable electronics one step forward. PMID:26076468

  17. Polarization charge as a reconfigurable quasi-dopant in ferroelectric thin films

    NASA Astrophysics Data System (ADS)

    Crassous, Arnaud; Sluka, Tomas; Tagantsev, Alexander K.; Setter, Nava

    2015-07-01

    Impurity elements used as dopants are essential to semiconductor technology for controlling the concentration of charge carriers. Their location in the semiconductor crystal is determined during the fabrication process and remains fixed. However, another possibility exists whereby the concentration of charge carriers is modified using polarization charge as a quasi-dopant, which implies the possibility to write, displace, erase and re-create channels having a metallic-type conductivity inside a wide-bandgap semiconductor matrix. Polarization-charge doping is achieved in ferroelectrics by the creation of charged domain walls. The intentional creation of stable charged domain walls has so far only been reported in BaTiO3 single crystals, with a process that involves cooling the material through its phase transition under a strong electric bias, but this is not a viable technology when real-time reconfigurability is sought in working devices. Here, we demonstrate a technique allowing the creation and nanoscale manipulation of charged domain walls and their action as a real-time doping activator in ferroelectric thin films. Stable individual and multiple conductive channels with various lengths from 3 μm to 100 nm were created, erased and recreated in another location, and their high metallic-type conductivity was verified. This takes the idea of hardware reconfigurable electronics one step forward.

  18. 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.

  19. 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.

  20. Band engineering of GaN/AlN quantum wells by Si dopants

    SciTech Connect

    Zhuo, Xiaolong; Ni, Jianchao; Li, Jinchai; Lin, Wei; Cai, Duanjun; Li, Shuping E-mail: jykang@xmu.edu.cn; Kang, Junyong E-mail: jykang@xmu.edu.cn

    2014-03-28

    The electronic properties of GaN/AlN quantum wells are engineered by Si doped in different positions with the aid of the first-principle calculations. The local potential where the dopant located is dragged down as a result of negative center induced by the Si atom, leading to a different shift of the potential, and further affects the band bending and carrier distribution. The band profiles are depicted by analyzing the projected densities of states, it is found that the different positions of Si doping lead to a different band bending owing to the modified polarization fields. The spatial distributions of electrons and holes plotted by the partial charge densities reveal that electrons and holes experience redistribution by Si dopant in different positions. The above results demonstrate that the effect of polarization on the band bending has been significantly modulated by Si doped in different positions. Such modification of electronic structure is especially valuable for the fabrication of GaN/AlN QWs under desired control.

  1. Implant activation and redistribution of dopants in GaN

    SciTech Connect

    Zolper, J.C.; Pearton, S.J.; Wilson, R.G.; Stall, R.A.

    1996-07-01

    GaN and related III-Nitride materials (IN, an) have recently been the focus of extensive research for photonic and electronic device applications. As this material system matures, ion implantation doping and isolation is expected to play an important role in advance device demonstrations. To this end, we report the demonstration of implanted p-type doping with Mg+P and Ca as well as n-type doping with Si in GaN. These implanted dopants require annealing 105 approximately1100 {degrees}C to achieve electrical activity, but demonstrate limited redistribution at this temperature. The redistribution of other potential dopants in GaN (such as Be, Zn, and Cd) will also be reported. Results for a GaN junction field effect transistor (JFET), the first GaN device to use implantation doping, will also be presented.

  2. Boosting the Boron Dopant Level in Monolayer Doping by Carboranes.

    PubMed

    Ye, Liang; González-Campo, Arántzazu; Núñez, Rosario; de Jong, Michel P; Kudernac, Tibor; van der Wiel, Wilfred G; Huskens, Jurriaan

    2015-12-16

    Monolayer doping (MLD) presents an alternative method to achieve silicon doping without causing crystal damage, and it has the capability of ultrashallow doping and the doping of nonplanar surfaces. MLD utilizes dopant-containing alkene molecules that form a monolayer on the silicon surface using the well-established hydrosilylation process. Here, we demonstrate that MLD can be extended to high doping levels by designing alkenes with a high content of dopant atoms. Concretely, carborane derivatives, which have 10 B atoms per molecule, were functionalized with an alkene group. MLD using a monolayer of such a derivative yielded up to ten times higher doping levels, as measured by X-ray photoelectron spectroscopy and dynamic secondary mass spectroscopy, compared to an alkene with a single B atom. Sheet resistance measurements showed comparably increased conductivities of the Si substrates. Thermal budget analyses indicate that the doping level can be further optimized by changing the annealing conditions. PMID:26595856

  3. Raman characterization of defects and dopants in graphene.

    PubMed

    Beams, Ryan; Gustavo Cançado, Luiz; Novotny, Lukas

    2015-03-01

    In this article we review Raman studies of defects and dopants in graphene as well as the importance of both for device applications. First a brief overview of Raman spectroscopy of graphene is presented. In the following section we discuss the Raman characterization of three defect types: point defects, edges, and grain boundaries. The next section reviews the dependence of the Raman spectrum on dopants and highlights several common doping techniques. In the final section, several device applications are discussed which exploit doping and defects in graphene. Generally defects degrade the figures of merit for devices, such as carrier mobility and conductivity, whereas doping provides a means to tune the carrier concentration in graphene thereby enabling the engineering of novel material systems. Accurately measuring both the defect density and doping is critical and Raman spectroscopy provides a powerful tool to accomplish this task. PMID:25634863

  4. The role of isoelectronic dopants in organic light emitting diodes

    NASA Astrophysics Data System (ADS)

    Crone, B. K.; Campbell, I. H.; Smith, D. L.

    2007-09-01

    Power efficiency is an important parameter for all OLEDs, and is particularly critical for lighting applications. To maximize the power efficiency one must optimize charge injection, carrier transport, and radiative quantum efficiency, while minimizing energy losses. In this work we discuss how isoelectronic dopants can be used to address these problems. It can be difficult to produce efficient electrical contacts, particularly to large energy gap organic materials, and thus the contacts often limit the performance and stability of OLEDs . Recent results by several groups have attributed improved hole injection in poly (9,9' dioctylfluorene) [PFO] based LEDs to charge trapping, but the origin of the traps is unknown. In order to understand the role of traps in improving injection we studied poly[2-methoxy, 5-(2'- ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) devices with C 60 molecules at the anode to improve hole injection. Isoelectronic dopants are used widely as recombination centers in organic light emitting diodes (OLEDs). In these systems one wants to maximize quantum efficiency by effectively trapping charges on the emitting dopants, while at the same time maximizing power efficiency by maintaining good charge transport. An understanding of the influence of the depth of the dopant on charge capture, and charge transport will aid in optimizing doped organic LEDs. We have looked at the OLED system consisting of the polymer PFO, and the organometallic molecule PhqIr. We show that PhqIr acts as a shallow hole trap in PFO, and that the charge transport and luminescence properties of this system are described by quasi-equilibrium statistics.

  5. The interstitial fraction of diffusivity of common dopants in Si

    NASA Astrophysics Data System (ADS)

    Gossmann, H.-J.; Haynes, T. E.; Stolk, P. A.; Jacobson, D. C.; Gilmer, G. H.; Poate, J. M.; Luftman, H. S.; Mogi, T. K.; Thompson, M. O.

    1997-12-01

    The relative contributions of interstitials and vacancies to diffusion of a dopant A in silicon are specified by the interstitial fraction of diffusivity, fA. Accurate knowledge of fA is required for predictive simulations of Si processing during which the point defect population is perturbed, such as transient enhanced diffusion. While experimental determination of fA is traditionally based on an underdetermined system of equations, we show here that it is actually possible to derive expressions that give meaningful bounds on fA without any further assumptions but that of local equilibrium. By employing a pair of dopants under the same point-defect perturbance, and by utilizing perturbances very far from equilibrium, we obtain experimentally fSb⩽0.012 and fB⩾0.98 at temperatures of ˜800 °C, which are the strictest bounds reported to date. Our results are in agreement with a theoretical expectation that a substitutional dopant in Si should either be a pure vacancy, or a pure interstitial(cy) diffuser.

  6. 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. PMID:16193953

  7. 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.

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

    DOE PAGESBeta

    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 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

  9. Dopant-site-dependent scattering by dislocations in epitaxial films of perovskite semiconductor BaSnO{sub 3}

    SciTech Connect

    Kim, Useong; Park, Chulkwon; Kim, Rokyeon; Mun, Hyo Sik; Kim, Hoon Min; Kim, Namwook; Yu, Jaejun; Char, Kookrin; Ha, Taewoo; Kim, Jae Hoon; Kim, Hyung Joon; Kim, Tai Hoon; Kim, Kee Hoon

    2014-05-01

    We studied the conduction mechanism in Sb-doped BaSnO{sub 3} epitaxial films, and compared its behavior with that of the mechanism of its counterpart, La-doped BaSnO{sub 3}. We found that the electron mobility in BaSnO{sub 3} films was reduced by almost 7 times when the dopant was changed from La to Sb, despite little change in the effective mass of the carriers. This indicates that the scattering rate of conduction electrons in the BaSnO{sub 3} system is strongly affected by the site at which the dopants are located. More importantly, we found that electron scattering by threading dislocations also depends critically on the dopant site. We propose that the large enhancement of scattering by the threading dislocations in Sb-doped BaSnO{sub 3} films is caused by the combination effect of the change in the distribution of Sb impurities in the films, the formation of the Sb impurity clusters near the threading dislocations, and the conduction electron clustering near the Sb impurities.

  10. 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.

  11. Quantum confinement, core level shifts, and dopant segregation in P-doped Si⟨110⟩ nanowires

    NASA Astrophysics Data System (ADS)

    Han, Jiaxin; Chan, Tzu-Liang; Chelikowsky, James R.

    2010-10-01

    We examine P-doped Si⟨110⟩ nanowires by employing a real-space pseudopotential method. We find the defect wave function becomes more localized along the nanowire axis and the donor ionization energy increases, owing to quantum confinement. It is more difficult to dope a P atom into a Si⟨110⟩ nanowire than to dope Si bulk because the formation energy increases with decreasing size. By comparing the formation energy for different P positions within a nanowire, we find that if a P atom at the nanowire surface can overcome the energy barrier close to the surface, there is a tendency for the dopant to reside within the nanowire core. We calculate P core levels shift as P changes position within the nanowire and provide a means for x-ray photoelectron spectroscopy experiments to determine the location of P atoms within a Si nanowire.

  12. 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.

  13. Polymer-Dopant-Systems: Tailoring of Optical and Thermomechanical Properties

    NASA Astrophysics Data System (ADS)

    Hanemann, Thomas; Honnef, Kirsten

    2010-06-01

    For modern application in microoptics the refractive index of polymers can be adjusted in a certain range by the addition of electron-rich organic dopants. As an unwanted side-effect a pronounced plasticizing occurs. In this work the addition of a crosslinker (divinylbenzene) to the unsaturated polyester matrix, doped with phenanthrene for refractive index adjustment, allows for a successful suppression of the plasticizing effect measured after polymerization. Even at high phenanthrene concentrations the glass transition temperature of the initial polymer could be almost retained. An increase of the polymers refractive index from 1.5684 up to a value of 1.6425 could be achieved.

  14. Characterization of microstructure and dopant distribution of laser diffused resistors

    NASA Astrophysics Data System (ADS)

    Liao, Yougui

    In order to completely understand the laser-processing mechanisms and accurately control the electrical and material properties of the LDRs, the research during this thesis was focused on microstructural characterization and dopant distribution measurements of LDRs fabricated under various laser parameters and different initial device structures The aim of the project was to use theses results to improve the accuracy, thermal coefficient of resistance (TCR) and long-term stability of those microdevices. Obtaining accurate quantified electrically activated dopant distribution in the actual microelectronic devices was a real challenge, especially when one considers microdevices (LDRs) having a very small area of few mum 2. By considering a vector as etching rate instead of a scalar (as considered by previous researchers) and by using a novel calibration method, the reliability, reproducibility and accuracy of quantification of dopant concentrations, ranging from 9x1016 to 6x10 19 atoms/cm3, of the dopant evaluation technique have been significantly improved. Therefore, the dopant profiles in the non-irradiated heavily doped regions in our devices were obtained using dopant selective etching (DSE) in combination with cross-sectional transmission electron microscopy (TEM) and focused ion beam (FIB) techniques. Furthermore, the developed method has been applied to our LDRs and the two-dimensional (2D) dopant distributions with wide range of boron concentrations of the resistive links were quantified with spatial resolution of 1 to 5 nm. This results shows that the LDRs with boron concentrations up to ˜0.24x1018 atoms/cm 3 and 8.9x1018 atoms/cm3 can be produced depending on different structures of initial microdevices and laser parameters. Those profiles were accurately compared with numerical simulation results based on heat transfer and diffusion equations. Three-dimensional (3D) and two-dimensional (2D) periodic silicon nanostructures formed by polarized focused Nd

  15. 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

  16. Nanowire dopant measurement using secondary ion mass spectrometry

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

    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.

  17. 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™.

  18. 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

  19. Charge-transfer crystallites as molecular electrical dopants.

    PubMed

    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

  20. 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.

  1. Dopant activation in ion implanted silicon by microwave annealing

    SciTech Connect

    Alford, T. L.; Thompson, D. C.; Mayer, J. W.; Theodore, N. David

    2009-12-01

    Microwaves are used as a processing alternative for the electrical activation of ion implanted dopants and the repair of ion implant damage within silicon. Rutherford backscattering spectra demonstrate that microwave heating reduces the damage resulting from ion implantation of boron or arsenic into silicon. Cross-section transmission electron microscopy and selective area electron diffraction patterns demonstrate that the silicon lattice regains nearly all of its crystallinity after microwave processing of arsenic implanted silicon. Sheet resistance readings indicate the time required for boron or arsenic electrical activation within implanted silicon. Hall measurements demonstrate the extent of dopant activation after microwave heating of implanted silicon. Physical and electrical characterization determined that the mechanism of recrystallization in arsenic implanted silicon is solid phase epitaxial regrowth. The boron implanted silicon samples did not result in enough lattice damage to amorphize the silicon lattice and resulted in low boron activation during microwave annealing even though recrystallization of the Si lattice damage did take place. Despite low boron activation levels, the level of boron activation in this work was higher than that expected from traditional annealing techniques. The kinetics of microwave heating and its effects on implanted Si are also discussed.

  2. Amphoteric behavior and precipitation of Ge dopants in InP

    SciTech Connect

    Yu, K.M.; Moll, A.J.; Walukiewicz, W.

    1996-11-01

    We have directly correlated the electrical behavior, the impurity lattice site location, ion damage, and the local bonding environments of Ge-dopant ions implanted into InP. We have found that after rapid thermal annealing the free electron concentration in the samples implanted at room temperature (RT) are always higher than those implanted at liquid nitrogen temperature (LNT). Although the macroscopic structure seems to be insensitive to the implantation temperature, significantly more local disorder is created in the LNT implanted amorphous layers. Moreover, the amphoteric bonding structure of the Ge atoms is found to be well established already in the as-implanted amorphous InP. After high temperature annealing ({approx_gt}800{degree}C), the Ge atoms rearrange locally with more of the Ge substituting the In site than the P site resulting in {ital n}-type conductivity. The solid solubility of Ge in the InP is measured to be {approximately}1.4{endash}1.6{times}10{sup 20}/cm{sup 3} while the free electron concentration is estimated to saturate at {approximately}3.4{times}10{sup 19}/cm{sup 3}. The relatively low electron concentration can be explained by Ge precipitation and the compensation of Ge{sub In} donors by Ge{sub P} acceptors in the RT implanted case. The further reduction in electron concentration in the LNT implanted samples is believed to be related to the high residual damage found in these samples. The high solubility of Ge in InP can be attributed to the availability of two possible sublattice sites for the dopant and the compensation of the local strains due to the amphoteric substitution of the Ge. The concentration ratio of the Ge{sub In} to Ge{sub P} determined in the heavily implanted material has been used to estimate the difference in the formation energy of Ge substituting those two different sites.

  3. 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.

  4. Ab-initio study of the segregation and electronic properties of neutral and charged B and P dopants in Si and Si/SiO2 nanowires

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

    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/SiO2 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/SiO2 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/SiO2 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.

  5. Eldercare Locator

    MedlinePlus

    ... page content Skip Navigation Department of Health and Human Services Your Browser ... Welcome to the Eldercare Locator, a public service of the U.S. Administration on Aging connecting you to services for older ...

  6. 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.

  7. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

    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 (SiOx) 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 × 1018 cm-3. Our results also indicate that conventional silicon based processes must be carefully reviewed for compound semiconductor device fabrication to prevent unintended doping.

  9. 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.

  10. Charged dopants in semiconductor nanowires under partially periodic boundary conditions

    NASA Astrophysics Data System (ADS)

    Chan, Tzu-Liang; Zhang, S. B.; Chelikowsky, James R.

    2011-06-01

    We develop a one-dimensional, periodic real-space formalism for examining the electronic structure of charged nanowires from first principles. The formalism removes spurious electrostatic interactions between charged unit cells by appropriately specifying a boundary condition for the Kohn-Sham equation. The resultant total energy of the charged system remains finite, and a Madelung-type correction is unnecessary. We demonstrate our scheme by examining the ionization energy of P-doped Si<110> nanowires. We find that there is an effective repulsion between charged P dopants along the nanowire owing to the repulsive interaction of the induced surface charge between adjacent periodic cells. This repulsive interaction decays exponentially with unit cell size instead of a power law behavior assumed in typical charged calculations.

  11. Interplay between quantum confinement and dielectric mismatch for ultrashallow dopants

    NASA Astrophysics Data System (ADS)

    Mol, J. A.; Salfi, J.; Miwa, J. A.; Simmons, M. Y.; Rogge, S.

    2013-06-01

    Understanding the electronic properties of dopants near an interface is a critical challenge for nanoscale devices. We have determined the effect of dielectric mismatch and quantum confinement on the ionization energy of individual acceptors beneath a hydrogen passivated silicon (100) surface. While dielectric mismatch between the vacuum and the silicon at the interface results in an image charge which enhances the binding energy of subsurface acceptors, quantum confinement is shown to reduce the binding energy. Using scanning tunneling spectroscopy we measure resonant transport through the localized states of individual acceptors. Thermal broadening of the conductance peaks provides a direct measure for the absolute energy scale. Our data unambiguously demonstrates that these two independent effects compete with the result that the ionization energy is less than 5 meV lower than the bulk value for acceptors less than a Bohr radius from the interface.

  12. Dopant concentration dependent growth of Fe:ZnO nanostructures

    NASA Astrophysics Data System (ADS)

    Sahai, Anshuman; Goswami, Navendu

    2016-05-01

    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 Zn1-xFexO along with secondary phases of ZnFe2O4 and Fe2O3 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.

  13. Neutron Vibrational Spectroscopy and modeling of polymer/dopant interactions

    NASA Astrophysics Data System (ADS)

    Moule, Adam; Harrelson, Thomas; Cheng, Yongqiang; Ramirez-Cuesta, Anibal; Faller, Roland; Huang, David

    Neutron vibrational spectroscopy (VISION and ORNL) is a powerful technique to determine the configurations of organic species in amorphous samples. We apply this technique to samples of the semiconducting polymer regio-regular P3HT to determine the molecular configurations outside of the crystalline domains, which have never been investigated. Application of density functional theory modeling using crystal field theory and for the single molecule approach yield a variety of configurations of the polymer backbone and side chains. These results demonstrate that only 1% of the volume corresponds to the assumed crystal structure solved using x-ray diffraction. In addition we investigate the configurations of P3HT doped with the molecular dopant F4TCNQ and determine that the charging of the polymer backbone leads to increased side chain stiffness. These results have significant implications for design of organic electronic devices based on thiophenes.

  14. 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.

  15. Theoretical Study of High-Valent Vanadium Oxo-Porphyrins as a Dopant of Crude Oil

    SciTech Connect

    Salcedo, Roberto; Martinez, LMR; Martinez-Magadan, Jose M.

    2001-06-15

    The role played by the vanadyl porphyrinate as a dopant for zeolites in the refinement process of crude oil is analyzed using DFT calculations. The pair formed by the vanadium atom and its bonded oxygen atoms seems to be the responsible items in the dopant reaction. However, the present paper shows the participation of the vanadium atom as being the most important.

  16. Femtosecond-laser hyperdoping silicon in an SF6 atmosphere: Dopant incorporation mechanism

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

    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.

  17. 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.

  18. 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.

  19. A Block Copolymer Self-Assembly Approach for 3D Nanoconfined Dopants in Semiconductors

    NASA Astrophysics Data System (ADS)

    Popere, Bhooshan; Russ, Boris; Chang, William; Heitsch, Andrew; Trefonas, Peter; Segalman, Rachel

    2015-03-01

    Continuous shrinking of electronic circuits presents a new challenge to demonstrate reliable, uniform nanoscale doping. Directed self-assembly (DSA) of block copolymers (BCP) has proved critical in meeting the technology nodes by enabling excellent pitch control for lithography. Yet, controlling the 3D dopant distribution remains a fundamental design challenge. To this end, we have utilized BCP self-assembly in a novel approach to confine dopants to nanoscopic domains within a semiconductor. The periodic nature of these domains affords precise control over the dosage and spatial positions of dopant atoms. Dopant incorporation within the block copolymer domains via hydrogen bonding eliminates the need for tailored synthesis, making the approach highly modular. Rapid thermal annealing of the self-assembled films effectively drives the dopants into the underlying substrate, thus confining them to within 10-20 nm in all dimensions. Additionally, the size, pitch, dopant dosage and the junction depth can be independently varied for a wide range of dopants. Compositional and electronic measurements indicate that the domains are indeed discrete and nanoconfined. Our approach, thereby, enables a facile method for controlled nanoscopic doping in semiconductors.

  20. Preparation and characterization of electropolymerized poly(3,4-ethylenedioxythiophene) thin films with different dopant anions

    NASA Astrophysics Data System (ADS)

    Deguchi, Toshiaki; Tomeoku, Hiroya; Takashiri, Masayuki

    2016-06-01

    We investigated the structural and thermoelectric properties poly(3,4-ethylenedioxythiophene) (PEDOT) films with several dopants (counter ions, ClO4, PF6, and BF4), synthesised by electropolymerization. We first performed cyclic voltammetry analysis to determine the optimum synthesis conditions of the PEDOT thin films. We found that the surface morphology of the PEDOT thin films was dependent on the type of the dopant. The PF6-doped PEDOT (PEDOT:PF6) thin films showed a dense structure, and the PEDOT:ClO4 thin films showed a highly porous microstructure. Fourier transform infrared (FT-IR) spectroscopy showed that all the PEDOT thin films showed similar chemical structures and the p-type state. Regarding their thermoelectric properties, the electrical conductivity of the all the doped PEDOT thin films increased as the dopant concentration increased, with the PEDOT:PF6 thin films showing the highest value. On the other hand, the Seebeck coefficient of the PEDOT thin films with all the dopants decreased as the dopant concentration increased, with the PEDOT:BF4 thin films achieving the highest value. As a result, the PEDOT:BF4 thin films exhibited the highest power factor of 0.75 µW/(m·K2) at a dopant concentration of 1.0 M. We think that the PEDOT microstructure produced using the different types of dopant may affect the thermoelectric properties.

  1. Dopant Profiling of III-V Nanostructures for Electronic Applications

    NASA Astrophysics Data System (ADS)

    Ford, Alexandra Caroline

    2011-12-01

    High electron mobility III-V compound semiconductors such as indium arsenide (InAs) are promising candidates for future active channel materials of electron devices to further enhance device performance. In particular, compound semiconductors heterogeneously integrated on Si substrates have been studied, combining the high mobility of III-V semiconductors and the well-established, low cost processing of Si technology. However, one of the primary challenges of III-V device fabrication is controllable, post-growth dopant profiling. Here InAs nanowires and ultrathin layers (nanoribbons) on SiO2/Si are investigated as the channel material for high performance field-effect transistors (FETs) and post-growth, patterned doping techniques are demonstrated. First, the synthesis of crystalline InAs nanowires with high yield and tunable diameters by using Ni nanoparticles as the catalyst material on SiO 2/Si substrates is demonstrated. The back-gated InAs nanowire FETs have electron field-effect mobilities of ˜4,000 cm2/Vs and ION/IOFF ˜104. The uniformity of the InAs nanowires is demonstrated by large-scale assembly of parallel arrays of nanowires (˜400 nanowires) on SiO2/Si substrates by a contact printing process. This enables high performance, "printable" transistors with 5--10 mA ON currents. Second, an epitaxial transfer method for the integration of ultrathin layers of single-crystalline InAs on SiO2/Si substrates is demonstrated. As a parallel to silicon-on-insulator (SOI) technology, the abbreviation "XOI" is used to represent this compound semiconductor-on-insulator platform. A high quality InAs/dielectric interface is obtained by the use of a thermally grown interfacial InAsOx layer (˜1 nm thick). Top-gated FETs exhibit a peak transconductance of ˜1.6 mS/microm at V DS=0.5V with ION/I OFF >104 and subthreshold swings of 107--150 mV/decade for a channel length of ˜0.5 microm. Next, temperature-dependent I-V and C-V studies of single InAs nanowire FETs are

  2. Quantitative Dopant/Impurity Analysis for ICF Targets

    NASA Astrophysics Data System (ADS)

    Huang, Haibo; Nikroo, Abbas; Stephens, Richard; Eddinger, Samual; Xu, Hongwei; Chen, K. C.; Moreno, Kari

    2008-11-01

    We developed a number of new or improved metrology techniques to measure the spatial distributions of multiple elements in ICF ablator capsules to tight NIF specifications (0.5±0.1 at% Cu, 0.25±0.10 at% Ar, 0.4±0.4 at% O). The elements are either the graded dopants for shock timing, such as Cu in Be, or process-induced impurities, such as Ar and O. Their low concentration, high spatial variation and simultaneous presence make the measurement very difficult. We solved this metrology challenge by combining several techniques: Cu and Ar profiles can be nondestructively measured by operating Contact Radiography (CR) in a differential mode. The result, as well as the O profile, can be checked destructively by a quantitative Energy Dispersive Spectroscopy (EDS) method. Non-spatially resolved methods, such as absorption edge spectroscopy (and to a lesser accuracy, x-ray fluorescence) can calibrate the Ar and Cu measurement in EDS and CR. In addition, oxygen pick-up during mandrel removal can be validated by before-and-after CR and by density change. Use of all these methods gives multiple checks on the reported profiles.

  3. Efficient silicon solar cells with dopant-free asymmetric heterocontacts

    NASA Astrophysics Data System (ADS)

    Bullock, James; Hettick, Mark; Geissbühler, Jonas; Ong, Alison J.; Allen, Thomas; Sutter-Fella, Carolin M.; Chen, Teresa; Ota, Hiroki; Schaler, Ethan W.; de Wolf, Stefaan; Ballif, Christophe; Cuevas, Andrés; Javey, Ali

    2016-03-01

    A salient characteristic of solar cells is their ability to subject photo-generated electrons and holes to pathways of asymmetrical conductivity—‘assisting’ them towards their respective contacts. All commercially available crystalline silicon (c-Si) solar cells achieve this by making use of doping in either near-surface regions or overlying silicon-based films. Despite being commonplace, this approach is hindered by several optoelectronic losses and technological limitations specific to doped silicon. A progressive approach to circumvent these issues involves the replacement of doped-silicon contacts with alternative materials which can also form ‘carrier-selective’ interfaces on c-Si. Here we successfully develop and implement dopant-free electron and hole carrier-selective heterocontacts using alkali metal fluorides and metal oxides, respectively, in combination with passivating intrinsic amorphous silicon interlayers, resulting in power conversion efficiencies approaching 20%. Furthermore, the simplified architectures inherent to this approach allow cell fabrication in only seven low-temperature (≤200 ∘C), lithography-free steps. This is a marked improvement on conventional doped-silicon high-efficiency processes, and highlights potential improvements on both sides of the cost-to-performance ratio for c-Si photovoltaics.

  4. Light Propagation in Liquid Crystals with a Chiral Dopant

    NASA Astrophysics Data System (ADS)

    Lawson, Justin; Saunders, Karl; Gantner, Logan

    2009-11-01

    This project will investigate the design and feasibility of a novel liquid crystal sensor that could be used to detect the presence and amount of foreign biological and/or chemical airborne agents. Such a sensor would have the advantage of being very portable. As such could have particular value in detecting biological or chemical weapons in the field of military operations. It would also be of use in a rapid response to a chemical or biological terrorist attack. The device would operate on the basic principal that when certain types of molecules bind to a liquid crystal molecule, the conformation of the liquid crystal molecule changes. This would in turn lead to a change in the overall arrangement of the liquid crystal, which could be detected using polarized light. In the absence of a contaminant the average molecular direction (optical axis, n ) is constant throughout the liquid crystal. The dopant adds a chirality or twist so that n precesses as a function of depth. We first solve for the reflected and transmitted light off of the air-liquid crystal boundary in the simplified case where there is linear chirality or a spiral configuration which repeats itself over some fixed interval (or pitch). We then generalize for cases in which this repeat distance varies with crystal depth. Finally we will obtain an expression for the contaminated crystal configuration which should depend on time and a diffusion constant and examine how the light properties change with respect to intensity and duration of exposure to the contaminant.

  5. Antimony as an amphoteric dopant in lead telluride

    SciTech Connect

    Jaworski, Christopher M.; Tobola, Janusz; Levin, E.M.; Schmidt-Rohr, Klaus; Heremans, Joseph P.

    2009-09-24

    We elucidate the amphoteric nature of antimony as a dopant in PbTe. Band-structure calculations show that Sb substituting for Pb is a donor and that Sb on the Te site is an acceptor giving rise to a large excess density of states (DOS). Experimentally, in Te-rich Pb{sub 1-x}Sb{sub x}Te samples, {sup 125}Te NMR spectroscopy shows that Sb substitutes for Pb and transport data reveal that it then acts as a simple donor. In Pb-rich PbSb{sub x}Te{sub 1-x} samples, {sup 125}Te NMR shows that little Sb substitutes for Te when samples are prepared above 770 K and then quenched; {sup 207}Pb NMR shows four types of charge carriers, but only a majority hole and a minority electron contribute to transport. Sb acts as an acceptor in PbSb{sub x}Te{sub 1-x}, but the large DOS calculated must correspond to a large concentration of localized holes and the Seebeck coefficient is not enhanced.

  6. D-Limonene as a Chiral Dopant for Thermotropic Liquid Crystalline Systems

    NASA Astrophysics Data System (ADS)

    Zola, Rafael S.; Hurley, Shawn; Yang, Deng-Ke

    2011-06-01

    We used the chiral molecule D-limonene to induce thermotropic cholesteric phases. The methods used to characterize the chiral nematic phase and its features are given. We substituted D-limonene for conventional synthesized chiral dopants in the twisted nematic (TN) displays and showed an improvement in the response time. Despite the large number of synthesized chiral dopants, D-limonene can be used as a dopant for making cholesteric phases having the advantage of being a naturally occurring substance. It is surprising how many more synthesized chiral molecules have been used as the liquid crystal field moves forward in comparison to naturally occurring molecules.

  7. 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.

  8. Measurement of Temperature, Density, and Particle Transport with Localized Dopants in Wire-Array Z Pinches

    NASA Astrophysics Data System (ADS)

    Jones, B.; Deeney, C.; McKenney, J. L.; Ampleford, D. J.; Coverdale, C. A.; Lepell, P. D.; Shelton, K. P.; Safronova, A. S.; Kantsyrev, V. L.; Osborne, G.; Sotnikov, V. I.; Ivanov, V. V.; Fedin, D.; Nalajala, V.; Yilmaz, F.; Shrestha, I.

    2008-03-01

    Axially localized NaF dopants are coated onto Al cylindrical wire arrays in order to act as spectroscopic tracers in the stagnated z-pinch plasma. Non-local-thermodynamic-equilibrium kinetic models fit to Na K-shell lines provide an independent measurement of the density and temperature that is consistent with spectroscopic analysis of K-shell emissions from Al and an alloyed Mg dopant. Axial transport of the Na dopant is observed, enabling quantitative study of instabilities in dense z-pinch plasmas.

  9. Drain current modulation in a nanoscale field-effect-transistor channel by single dopant implantation

    NASA Astrophysics Data System (ADS)

    Johnson, B. C.; Tettamanzi, G. C.; Alves, A. D. C.; Thompson, S.; Yang, C.; Verduijn, J.; Mol, J. A.; Wacquez, R.; Vinet, M.; Sanquer, M.; Rogge, S.; Jamieson, D. N.

    2010-06-01

    We demonstrate single dopant implantation into the channel of a silicon nanoscale metal-oxide-semiconductor field-effect-transistor. This is achieved by monitoring the drain current modulation during ion irradiation. Deterministic doping is crucial for overcoming dopant number variability in present nanoscale devices and for exploiting single atom degrees of freedom. The two main ion stopping processes that induce drain current modulation are examined. We employ 500 keV He ions, in which electronic stopping is dominant, leading to discrete increases in drain current and 14 keV P dopants for which nuclear stopping is dominant leading to discrete decreases in drain current.

  10. 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.

  11. Diameter-dependent solubility of single-walled carbon nanotubes.

    PubMed

    Duque, Juan G; Parra-Vasquez, A Nicholas G; Behabtu, Natnael; Green, Micah J; Higginbotham, Amanda L; Price, B Katherine; Leonard, Ashley D; Schmidt, Howard K; Lounis, Brahim; Tour, James M; Doorn, Stephen K; Cognet, Laurent; Pasquali, Matteo

    2010-06-22

    We study the solubility and dispersibility of as-produced and purified HiPco single-walled carbon nanotubes (SWNTs). Variation in specific operating conditions of the HiPco process are found to lead to significant differences in the respective SWNT solubilities in oleum and surfactant suspensions. The diameter distributions of SWNTs dispersed in surfactant solutions are batch-dependent, as evidenced by luminescence and Raman spectroscopies, but are identical for metallic and semiconducting SWNTs within a batch. We thus find that small diameter SWNTs disperse at higher concentration in aqueous surfactants and dissolve at higher concentration in oleum than do large-diameter SWNTs. These results highlight the importance of controlling SWNT synthesis methods in order to optimize processes dependent on solubility, including macroscopic processing such as fiber spinning, material reinforcement, and films production, as well as for fundamental research in type selective chemistry, optoelectronics, and nanophotonics. PMID:20521799

  12. Diameter Dependence of Planar Defects in InP Nanowires.

    PubMed

    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

  13. Diameter Dependence of the Transport Properties of Antimony Telluride Nanowires

    NASA Astrophysics Data System (ADS)

    Zuev, Yuri; Lee, Jin Sook; Park, Hongkun; Kim, Philip

    2010-03-01

    We report measurements of electronic, thermoelectric, and galvanometric properties of individual semimetallic single crystal antimony telluride (Sb2Te3) nanowires. Microfabricated heater and thermometer electrodes were used to probe the transport properties of the nanowires with diameters in the range of 22 - 95nm and temperatures in the range of 2 - 300K. Temperature dependent resistivity varies depending on nanowire diameter. Thermoelectric power (TEP) measurements indicate hole dominant diffusive thermoelectric generation, with an enhancement of the TEP for smaller diameter wires. The large surface-to-volume ratio of Sb2Te3 nanowires makes them an excellent platform to explore novel phenomena in this predicted topological insulator. We investigate mesoscopic magnetoresistance effects in magnetic fields both parallel and perpendicular to the nanowire axis.

  14. 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. PMID:22700490

  15. Controlling the Adsorption of Carbon Monoxide on Platinum Clusters by Dopant-Induced Electronic Structure Modification.

    PubMed

    Ferrari, Piero; Molina, Luis M; Kaydashev, Vladimir E; Alonso, Julio A; Lievens, Peter; Janssens, Ewald

    2016-09-01

    A major drawback of state-of-the-art proton exchange membrane fuel cells is the CO poisoning of platinum catalysts. It is known that CO poisoning is reduced if platinum alloys are used, but the underlying mechanism therefore is still under debate. We study the influence of dopant atoms on the CO adsorption on small platinum clusters using mass spectrometry experiments and density functional calculations. A significant reduction in the reactivity for Nb- and Mo-doped clusters is attributed to electron transfer from those highly coordinated dopants to the Pt atoms and the concomitant lower CO binding energies. On the other hand Sn and Ag dopants have a lower Pt coordination and have a limited effect on the CO adsorption. Analysis of the density of states demonstrates a correlation of dopant-induced changes in the electronic structure with the enhanced tolerance to CO poisoning. PMID:27464653

  16. 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.

  17. First-principles study of n-type dopants and their clustering in SiC

    NASA Astrophysics Data System (ADS)

    Rurali, R.; Godignon, P.; Rebollo, J.; Hernández, E.; Ordejón, P.

    2003-06-01

    We report the results of an ab initio study of N and P dopants in SiC. We find that while N substitutes most favorably at a C lattice site, P does so preferably at a Si site, except in n-doping and Si-rich 3C-SiC. Furthermore, we consider a series of dopant complexes that could form in high-dose implantation, in order to investigate the dopant activation behavior in this limit. We find that all N complexes considered lead to passivation through the formation of a deep level. For P, the most stable aggregate is still an active dopant, while passivation is only observed for complexes with a higher formation energy. We discuss how these results could help in the understanding of the observed experimental high-dose doping and codoping behavior of these species.

  18. 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. PMID:25607722

  19. 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.

  20. Analysis of the dopant segregation effects at the floating zone growth of large silicon crystals

    NASA Astrophysics Data System (ADS)

    Mühlbauer, A.; Muiznieks, A.; Virbulis, J.

    1997-10-01

    A computer simulation is carried out to study the dopant concentration fields in the molten zone and in the growing crystal for the floating zone (FZ) growth of large (> 100mm) Si crystals with the needle-eye technique and with feed/crystal rotation. The mathematical model developed in the previous work is used to calculate the shape of the molten zone and the velocity field in the melt. The influence of melt convection on the dopant concentration field is considered. The significance of the rotation scheme of the feed rod and crystal on the dopant distribution is investigated. The calculated dopant concentration directly at the growth interface is used to determine the normalized lateral resistivity distribution in the single crystal. The calculated resistivity distributions are compared with lateral spreading resistivity measurements in the single crystal.

  1. Wide Band-Gap Bismuth-based p-Dopants for Opto-Electronic Applications.

    PubMed

    Pecqueur, Sébastien; Maltenberger, Anna; Petrukhina, Marina A; Halik, Marcus; Jaeger, Arndt; Pentlehner, Dominik; Schmid, Günter

    2016-08-22

    Ten new efficient p-dopants for conductivity doping of organic semiconductors for OLEDs are identified. The key advantage of the electrophilic tris(carboxylato) bismuth(III) compounds is the unique low absorption of the resulting doped layers which promotes the efficiency of OLED devices. The combination of these features with their low fabrication cost, volatility, and stability, make these materials very attractive as dopants in organic electronics. PMID:27440434

  2. 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.

  3. 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.

  4. Dopant and self-diffusion in extrinsic n-type silicon isotopically controlled heterostructures

    SciTech Connect

    Silvestri, Hughes H.; Sharp, Ian D.; Bracht, Hartmut A.; Nicols, Sam P.; Beeman, Jeff W.; Hansen, John; Nylandsted-Larsen, Arme; Haller, Eugene E.

    2002-04-01

    We present experimental results of dopant- and self-diffusion in extrinsic silicon doped with As. Multilayers of isotopically controlled {sup 28}Si and natural silicon enable simultaneous analysis of {sup 30}Si diffusion into the {sup 28}Si enriched layers and dopant diffusion throughout the multilayer structure. In order to suppress transient enhanced self- and dopant diffusion caused by ion implantation, we adopted a special approach to dopant introduction. First, an amorphous 250-nm thick Si layer was deposited on top of the Si isotope heterostructure. Then the dopant ions were implanted to a depth such that all the radiation damage resided inside this amorphous cap layer. These samples were annealed for various times and temperatures to study the impact of As diffusion and doping on Si self-diffusion. The Si self-diffusion coefficient and the dopant diffusivity for various extrinsic n-type conditions were determined over a wide temperature range. We observed increased diffusivities that we attribute to the increase in the concentration of the native defect promoting the diffusion.

  5. spds* Tight-Binding Model for Transition Metal Dopants in SiC

    NASA Astrophysics Data System (ADS)

    Kortan, Victoria R.; Şahin, Cüneyt; Flatté, Michael E.

    2014-03-01

    SiC is a well known, wide-band-gap semiconductor with excellent chemical, thermal and mechanical stability. These traits make it an attractive material for high temperature, hostile environment, high power and high frequency device design. A necessary step in the development of SiC technology is the understanding and subsequent control of point defects. In addition to altering optoelectronic properties, single dopants can add effects dependent on the specific dopant species. In particular the d-states of transition metal dopants have been predicted to allow the control of the single Ni spin state with the application of strain in diamond and single Fe dopants in GaAs have a core transition that can be manipulated by a STM and produce a decrease in tunneling current. Here we choose a first and second nearest neighbor spds* tight-binding model to calculate the electronic trends and defect wavefunctions of transition metal dopants in 3C-SiC. Additionally we calculate the exchange interaction between pairs of dopants. This work was supported by an AFOSR MURI.

  6. 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. PMID:26510444

  7. 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.

  8. Comprehensive examination of dopants and defects in BaTiO3 from first principles

    NASA Astrophysics Data System (ADS)

    Sharma, V.; Pilania, G.; Rossetti, G. A., Jr.; Slenes, K.; Ramprasad, R.

    2013-04-01

    An extensive assessment of the physicochemical factors that control the behavior of dopant-related defects in BaTiO3 has been performed using high-throughput first-principles computations. Dopants spanning the Periodic Table—44 in total—including K-As, Rb-Sb, and Cs-Bi were considered, and have allowed us to reveal previously unknown correlations, chemical trends, and the interplay between stability, chemistry, and electrical activity. We quantitatively show that the most important factor that determines dopant stability in BaTiO3 is the dopant ionic size (followed by its oxidation state). Moreover, we are also able to identify definitively dopants that are O vacancy formers and suppressors, and those that would lead to p-type versus n-type conduction. Our results are in agreement with available experimental data (with no violations thus far), and point to an attractive computational route to dopant selection in BaTiO3 as well as in other materials.

  9. 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

    2015-02-01

    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 [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. PMID:25605947

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

    DOE PAGESBeta

    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.; et al

    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

  11. Dopant in Near-Surface Semiconductor Layers of Metal-Insulator-Semiconductor Structures Based on Graded-Gap p-Hg0.78Cd0.22Te Grown by Molecular-Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Voitsekhovskii, A. V.; Nesmelov, S. N.; Dzyadukh, S. M.

    2016-02-01

    Peculiarities in determining the dopant concentration and dopant distribution profile in the near-surface layer of a semiconductor are investigated by measuring the admittance of metal-insulator-semiconductor structures (MIS structures) based on p-Hg0.78Cd0.22Te grown by molecular beam epitaxy. The dopant concentrations in the near-surface layer of the semiconductor are determined by measuring the admittance of MIS structures in the frequency range of 50 kHz to 1 MHz. It is shown that in this frequency range, the capacitance-voltage characteristics of MIS structures based on p-Hg0.78Cd0.22Te with a near-surface graded gap layer demonstrate a high-frequency behavior with respect to the recharge time of surface states located near the Fermi level for an intrinsic semiconductor. The formation time of the inversion layer is decreased by less than two times, if a near-surface graded-gap layer is created. The dopant distribution profile in the near-surface layer of the semiconductor is found, and it is shown that for structures based on p-Hg0.78Cd0.22Te with a near-surface graded-gap layer, the dopant concentration has a minimum near the interface with the insulator. For MIS structure based on n-Hg0.78Cd0.22Te, the dopant concentration is more uniformly distributed in the near-surface layer of the semiconductor.

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

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

    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.

  13. Use of scanning probe microscopies to study dopants at semiconductor surfaces

    NASA Astrophysics Data System (ADS)

    Nelson, Mark William

    Dopants, in semiconductors, are detected as either protrusions or depressions in scanning tunneling microscopy (STM) images. Measured dopant heights for layered semiconductors are considerably larger than for conventional semiconductors. This is interpreted as the influence of dopant induced electrostatic forces between the tip and the sample leading to a structural deformation of the surface around the dopant atoms. To investigate the influence of electrostatic forces, we performed STM measurements on p-type MoS2 at different bias voltages. The bias dependence of the STM images indicates the presence of electrostatic forces. Additional measurements with current imaging tunneling spectroscopy (CITS) show that changes in the density of states at dopant sites play only a minor role and cannot account for the large protrusions observed. Atomic force microscopy (AFM), with an applied D.C. voltage between the cantilever and sample, also confirms the role of electrostatic forces. Recently, we developed a new TappingmodeRTM AFM (TMAFM) based dopant profiling method based on an electrostatic mechanism similar to the STM imaging of dopants in layered semiconductors. TMAFM with an applied bias was used to spatially resolve areas of different doping type and density on silicon patterned via ion implantation. The application of a D.C. bias between the cantilever and sample during the measurement results in a Coulomb interaction between the tip and sample, whose magnitude depends on the spatial variation in the doping density. This effect was utilized to detect areas differing in doping by monitoring the phase angle between the drive frequency and cantilever response while scanning over areas of differing doping density. Measurements at various bias voltages are presented to demonstrate that the phase contrast observed between differently doped areas is directly connected to the bias induced surface potential (band bending) present on these areas. A quantitative investigation

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

    DOEpatents

    Usov, Igor; Arendt, Paul N.

    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.

  15. Dopant profiling and surface analysis of silicon nanowires using capacitance-voltage measurements.

    PubMed

    Garnett, Erik C; Tseng, Yu-Chih; Khanal, Devesh R; Wu, Junqiao; Bokor, Jeffrey; Yang, Peidong

    2009-05-01

    Silicon nanowires are expected to have applications in transistors, sensors, resonators, solar cells and thermoelectric systems. Understanding the surface properties and dopant distribution will be critical for the fabrication of high-performance devices based on nanowires. At present, determination of the dopant concentration depends on a combination of experimental measurements of the mobility and threshold voltage in a nanowire field-effect transistor, a calculated value for the capacitance, and two assumptions--that the dopant distribution is uniform and that the surface (interface) charge density is known. These assumptions can be tested in planar devices with the capacitance-voltage technique. This technique has also been used to determine the mobility of nanowires, but it has not been used to measure surface properties and dopant distributions, despite their influence on the electronic properties of nanowires. Here, we measure the surface (interface) state density and the radial dopant profile of individual silicon nanowire field-effect transistors with the capacitance-voltage technique. PMID:19421217

  16. Molecular Dynamics Approach for Predicting Helical Twisting Powers of Metal Complex Dopants in Nematic Solvents.

    PubMed

    Watanabe, Go; Yoshida, Jun

    2016-07-14

    Nematic liquid crystals of small molecules are known to transform into chiral nematic liquid crystals with supramolecular helical structures upon doping with enantiomeric compounds. Although this phenomenon is well established, the basic mechanism is still unclear. We have previously examined metal complexes with Δ and Λ chiralities as dopants in nematic liquid crystals and have found that slight differences in the molecular structure determine the handedness of the induced helical structure. In this study, we investigated the microscopic arrangement of liquid crystal molecules around metal complex dopants with the aid of molecular dynamics (MD) simulations. There are several restrictions to performing MD simulations of the chiral nematic system; for example, one pitch of the helix usually exceeds one side of an applicable periodic boundary box (∼10(2) nm). In view of these simulation problems, we therefore examined racemic systems in which a pair of Δ- and Λ-isomers of the chiral dopant is mixed with liquid crystal molecules. We selected two different octahedral ruthenium complexes as the chiral dopant molecules. As a result, we accurately calculated the ordering matrix that is essential parameter to estimate the helical twisting power of the chiral dopant based on the surface chirality model. Since the microscopic ordering is experimentally hard to be determined, our new approach with using MD simulations accurately deduced the ordering matrix and, with the aid of the surface chirality model, gave reasonable values for the helical twisting powers of each complex. PMID:27333445

  17. Design of molecularly imprinted conducting polymer protein-sensing films via substrate-dopant binding.

    PubMed

    Komarova, Elena; Aldissi, Matt; Bogomolova, Anastasia

    2015-02-21

    Addressing the challenge of protein biosensing using molecularly imprinted polymers (MIP), we have developed and tested a novel approach to creating sensing conducive polymer films imprinted with a protein substrate, ricin toxin chain A (RTA). Our approach for creating MIP protein sensing films is based on a concept of substrate-guided dopant immobilization with subsequent conducting polymer film formation. In this proof-of-concept work we have tested three macromolecular dopants with strong protein affinity, Ponceau S, Coomassie BB R250 and ι-Carrageenan. The films were formed using sequential interactions of the substrate, dopant and pyrrole, followed by electrochemical polymerization. The films were formed on gold array electrodes allowing for extensive data acquisition. The thickness of the films was optimized to allow for efficient substrate extraction, which was removed by a combination of protease and detergent treatment. The MIP films were tested for substrate rebinding using electrochemical impedance spectroscopy (EIS). The presence of macromolecular dopants was essential for MIP film specificity. Out of three dopants tested, RTA-imprinted polypyrrole films doped with Coomassie BB performed with highest specificity towards detection of RTA with a level of detection (LOD) of 0.1 ng ml(-1). PMID:25574520

  18. Disproportionation, dopant incorporation, and defect clustering in Perovskite-structured NdCoO3.

    PubMed

    Tealdi, Cristina; Malavasi, Lorenzo; Fisher, Craig A J; Islam, M Saiful

    2006-03-23

    Atomistic simulation techniques are used to examine the defect chemistry of perovskite-structured NdCoO(3), a material whose electrochemical properties make it attractive for use in heterogeneous oxidation catalysis, as well as in gas sensors and mixed ionic/electronic conductors. In practice, dopants are added to NdCoO(3) to obtain the desired properties, such as high electrical conductivity and rapid gas adsorption/desorption; thus, a wide range of dopants substituted on both Nd and Co sites are examined. Charge compensation for aliovalent dopants is predicted to occur via formation of oxide ion vacancies; these are understood to be key sites with respect to catalytic and sensor activity. Low activation energies calculated for oxide ion migration are consistent with high oxygen mobilities measured experimentally. Sr and Ca, which occupy Nd sites in the lattice, are found to be the most soluble of the alkaline earth metals, in agreement with experiment. These two dopant ions also have the weakest binding energies for dopant-vacancy cluster formation. Mechanisms of electronic defect formation, critical to the overall transport properties of the material, are also considered. The results suggest that disproportionation of the Co ion to form small polaron species is the most favorable intrinsic defect process. In doped compounds, formation of electronic holes via uptake of oxygen at vacant sites is found to be a low energy process. PMID:16539474

  19. 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.

  20. 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.

  1. Defect development and dopant location due to elevated temperature implantation of InP with MeV zinc ions

    NASA Astrophysics Data System (ADS)

    Krause, H.; Flagmeyer, R.-H.; Vogt, J.; Kling, A.; Butz, T.

    1996-06-01

    Zinc implantations in the MeV energy regime at temperatures of about 200°C within the dose range of 5 × 10 14-1 × 10 16 cm -2 were carried out. The investigations included RBS and PIXE measurements combined with ion channeling in the major crystallographic axes and additionally SNMS and XTEM. The implantation-induced damage is characterized by mobile point defects at the elevated implantation temperature. This results in damaged layers containing point-like defects, but far from amorphization. During rapid thermal annealing the surface up to about 0.6 Rp recovered channeling-perfect, while in a depth of (1-2) Rp a band of extrinsic dislocation loops was formed. Comparing the experimental with the calculated PIXE minimum yields, conclusions about the zinc positions were drawn: Due to the low ZnK aligned yield nearly all zinc atoms occupy substitutional lattice sites in the as-implanted samples. After annealing a remarkable diffusion of zinc combined with lattice site changes is observed.

  2. A model of dopant diffusion through a strongly correlated p-n junction

    NASA Astrophysics Data System (ADS)

    Wieteska, Jedrzej; Brierley, Richard; Guzman-Verri, Gian; Moller, Gunnar; Littlewood, Peter; Littlewood group Collaboration

    The diffusion of charged ions in a solid depends on an equation of state that balances diffusive and screened electrostatic forces, and is well understood in the case of conventional semiconductors and metals. In the case of a strongly-correlated material, the physics is different, and expected to be relevant, for example, in Li-ion battery cathodes. We propose a model of dopant ion motion through a strongly correlated p-n junction. Our approach is to consider diffusive (Nernst-Planck) dynamics of dopants under screened electrostatic interactions computed within a mean-field (Thomas-Fermi) approximation. Dopant profiles as function of time are calculated for a p-n junction held at constant voltage. In the case where filling levels are near a correlation-induced gap, Mott insulating regions can form at the p-n interface and their dynamics is studied.

  3. 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.

  4. 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.

  5. 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. PMID:23623133

  6. Modulation of thermoelectric power factor via radial dopant inhomogeneity in B-doped Si nanowires.

    PubMed

    Zhuge, Fuwei; Yanagida, Takeshi; Fukata, Naoki; Uchida, Ken; Kanai, Masaki; Nagashima, Kazuki; Meng, Gang; He, Yong; Rahong, Sakon; Li, Xiaomin; Kawai, Tomoji

    2014-10-01

    We demonstrate a modulation of thermoelectric power factor via a radial dopant inhomogeneity in B-doped Si nanowires. These nanowires grown via vapor-liquid-solid (VLS) method were naturally composed of a heavily doped outer shell layer and a lightly doped inner core. The thermopower measurements for a single nanowire demonstrated that the power factor values were higher than those of homogeneously B-doped Si nanowires. The field effect measurements revealed the enhancement of hole mobility for these VLS grown B-doped Si nanowires due to the modulation doping effect. This mobility enhancement increases overall electrical conductivity of nanowires without decreasing the Seebeck coefficient value, resulting in the increase of thermoelectric power factor. In addition, we found that tailoring the surface dopant distribution by introducing surface δ-doping can further increase the power factor value. Thus, intentionally tailoring radial dopant inhomogeneity promises a way to modulate the thermoelectric power factor of semiconductor nanowires. PMID:25229842

  7. 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

  8. Peculiarities of Determining the Dopant Concentration in the Near-Surface Layer of a Semiconductor by Measuring the Admittance of MIS Structures Based on P-Hg0.78Cd0.22Te Grown by Molecular Beam Epitaxy

    NASA Astrophysics Data System (ADS)

    Voitsekhovskii, A. V.; Nesmelov, S. N.; Dzyadukh, S. M.

    2016-06-01

    Peculiarities of determining the concentration and distribution profile of dopant in the near-surface layer of a semiconductor by measuring the admittance of MIS structures based on p-Hg0.78Cd0.22Te grown by molecular beam epitaxy are studied. A technique is proposed for the determining the concentration of dopant based on the measurement of the admittance of MIS structures in the frequency range of 50 kHz - 1 MHz. It is shown that in this frequency range, the capacitance-voltage characteristics of MIS structures based on p-Hg0.78Cd0.22Te with a near-surface graded-gap layer have a high- frequency behavior with respect to the recharge time of surface states located near the Fermi level of intrinsic semiconductor. The distribution profile of dopant in the nearsurface layer of the semiconductor is calculated. It is shown that in p-Hg0.78Cd0.22Te with a near-surface graded-gap layer, the dopant concentration has the lowest value near the interface with the insulator.

  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. Simple and highly efficient chiral dopant molecules possessing both rod- and arch-like units.

    PubMed

    Kishikawa, Keiki; Aoyagi, Shota; Kohri, Michinari; Taniguchi, Tatsuo; Takahashi, Masahiro; Kohmoto, Shigeo

    2014-09-14

    A simple chiral dopant molecule (R)-1 with both rod- and arch-like units was prepared, and extremely large helical twisting powers (+123 to +228 μm(-1)) in nematic liquid crystal phases were achieved. We have demonstrated that the introduction of an arch-like unit in addition to rod-like units is highly effective in controlling the helical molecular alignment. As an application of the dopant, induction of blue phases by addition of a small amount of it was achieved. PMID:25041949

  11. Dopant-induced random telegraph signal in nanoscale lateral silicon pn diodes at low temperatures

    SciTech Connect

    Purwiyanti, Sri; Department of Electrical Engineering, University of Indonesia, Depok, 16424 Jakarta ; Nowak, Roland; Division of Sensors and Measuring Systems, Warsaw University of Technology, Sw. A. Boboli 8, 02-525 Warsaw ; Moraru, Daniel; Mizuno, Takeshi; Tabe, Michiharu; Hartanto, Djoko; Jablonski, Ryszard

    2013-12-09

    We studied current-voltage characteristics of nanoscale pn diodes having the junction formed in a laterally patterned ultrathin silicon-on-insulator layer. At temperatures below 30 K, we observed random telegraph signal (RTS) in a range of forward bias. Since RTS is observed only for pn diodes, but not for pin diodes, one dopant among phosphorus donors or boron acceptors facing across the junction is likely responsible for potential changes affecting the current. Based also on potential measurements by low-temperature Kelvin probe force microscope, RTS is ascribed to trapping/detrapping of carriers by/from a single dopant near the farther edge of the depletion region.

  12. Dependence of Ablative Rayleigh—Taylor Instability on High-Z Dopant Concentration

    NASA Astrophysics Data System (ADS)

    Shiroto, Takashi; Ohnishi, Naofumi; Sunahara, Atsushi; Fujioka, Shinsuke

    2016-03-01

    We conducted two-dimensional simulations of inertial confinement fusion targets to evaluate effects of high-Z doping on implosion hydrodynamics. It was found that an ablation structure drastically changes with concentration of dopant material. We also confirmed that even a lightly-doped target can suppress Rayleigh-Taylor instability on short wavelength, while a long-wavelength perturbation is difficult to be suppressed with any dopant concentration. The high-Z doping is thus only effective for a spherical implosion with high-mode perturbations.

  13. Dopant distributions in n-MOSFET structure observed by atom probe tomography.

    PubMed

    Inoue, K; Yano, F; Nishida, A; Takamizawa, H; Tsunomura, T; Nagai, Y; Hasegawa, M

    2009-11-01

    The dopant distributions in an n-type metal-oxide-semiconductor field effect transistor (MOSFET) structure were analyzed by atom probe tomography. The dopant distributions of As, P, and B atoms in a MOSFET structure (gate, gate oxide, channel, source/drain extension, and halo) were obtained. P atoms were segregated at the interface between the poly-Si gate and the gate oxide, and on the grain boundaries of the poly-Si gate, which had an elongated grain structure along the gate height direction. The concentration of B atoms was enriched near the edge of the source/drain extension where the As atoms were implanted. PMID:19775815

  14. Rare Earth Dopant (Nd, Gd, Dy, and Er) Hybridization in Lithium Tetraborate

    NASA Astrophysics Data System (ADS)

    Kelly, Tony; Petrosky, James; McClory, John; Adamiv, Volodymyr; Burak, Yaroslav; Padlyak, Bohdan; Teslyuk, Ihor; Lu, Ning; Wang, Lu; Mei, Wai-Ning; Dowben, Peter

    2014-05-01

    The four dopants (Nd, Gd, Dy, and Er) substitutionally occupy the Li+ sites in lithium tetraborate (Li2B4O7: RE) glasses as determined by analysis of the extended X-ray absorption fine structure. The dopants are coordinated by 6-8 oxygen at a distance of 2.3 to 2.5 Å, depending on the rare earth. The inverse relationship between the RE¬ O coordination distance and rare earth (RE) atomic number is consistent with the expected lanthanide atomic radial contraction with increased atomic number. Through analysis of the X-ray absorption near edge structure, the rare earth dopants adopt the RE3+ valence state. There are indications of strong rare earth 5d hybridization with the trigonal and tetrahedral formations of BO3 and BO4 based on the determination of the rare earth substitutional Li+ site occupancy from the X-ray absorption near edge structure data. The local oxygen disorder around the RE3+ luminescence centers evident in the structural determination of the various glasses, and the hybridization of the RE3+ dopants with the host may contribute to the asymmetry evident in the luminescence emission spectral lines. The luminescence emission spectra are indeed characteristic of the expected f-to-f transitions; however, there is an observed asymmetry in some emission lines.

  15. Gas-Phase Dopant-Induced Conformational Changes Monitored with Transversal Modulation Ion Mobility Spectrometry.

    PubMed

    Meyer, Nicole Andrea; Root, Katharina; Zenobi, Renato; Vidal-de-Miguel, Guillermo

    2016-02-16

    The potential of a Transversal Modulation Ion Mobility Spectrometry (TMIMS) instrument for protein analysis applications has been evaluated. The Collision Cross Section (CCS) of cytochrome c measured with the TMIMS is in agreement with values reported in the literature. Additionally, it enables tandem IMS-IMS prefiltration in dry gas and in vapor doped gas. The chemical specificity of the different dopants enables interesting studies on the structure of proteins as CCS changed strongly depending on the specific dopant. Hexane produced an unexpectedly high CCS shift, which can be utilized to evaluate the exposure of hydrophobic parts of the protein. Alcohols produced higher shifts with a dual behavior: an increase in CCS due to vapor uptake at specific absorption sites, followed by a linear shift typical for unspecific and unstable vapor uptake. The molten globule +8 shows a very specific transition. Initially, its CCS follows the trend of the compact folded states, and then it rapidly increases to the levels of the unfolded states. This strong variation suggests that the +8 charge state undergoes a dopant-induced conformational change. Interestingly, more sterically demanding alcohols seem to unfold the protein more effectively also in the gas phase. This study shows the capabilities of the TMIMS device for protein analysis and how tandem IMS-IMS with dopants could provide better understanding of the conformational changes of proteins. PMID:26845079

  16. 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.

  17. Dopant activation during solid phase crystallization of poly-Si and influence of fluorine and hydrogen

    SciTech Connect

    Kalkan, A.K.; Kingi, R.M.; Fonash, S.J.

    1997-07-01

    Dopant activation for ion implanted solid phase crystallized (SPC) a-Si:H films, deposited by low temperature PECVD, was investigated. The impact of film thickness, the effect of subsequent hydrogenation, and a possible role for fluorine in this process have been studied.

  18. Influence of dopant distribution on the plasmonic properties of indium tin oxide nanocrystals.

    PubMed

    Lounis, Sebastien D; Runnerstrom, Evan L; Bergerud, Amy; Nordlund, Dennis; Milliron, Delia J

    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. PMID:24786283

  19. 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.

  20. 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.

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

    PubMed

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

    2015-12-01

    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. PMID:26403925

  2. 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.

  3. Dopant-assisted reactive low temperature plasma probe for sensitive and specific detection of explosives.

    PubMed

    Chen, Wendong; Hou, Keyong; Hua, Lei; Li, Haiyang

    2015-09-01

    A dopant-assisted reactive low temperature plasma (DARLTP) probe was developed for sensitive and specific detection of explosives by a miniature rectilinear ion trap mass spectrometer. The DARLTP probe was fabricated using a T-shaped quartz tube. The dopant gas was introduced into the plasma stream through a side-tube. Using CH2Cl2 doped wet air as the dopant gas, the detection sensitivities were improved about 4-fold (RDX), 4-fold (PETN), and 3-fold (tetryl) compared with those obtained using the conventional LTP. Furthermore, the formation of [M + (35)Cl](-) and [M + (37)Cl](-) for these explosives enhanced the specificity for their identification. Additionally, the quantities of fragment ions of tetryl and adduct ions such as [RDX + NO2](-) and [PETN + NO2](-) were dramatically reduced, which simplified the mass spectra and avoided the overlap of mass peaks for different explosives. The sensitivity improvement may be attributed to the increased intensity of reactant ion [HNO3 + NO3](-), which was enhanced 4-fold after the introduction of dopant gas. The limits of detection (LODs) for RDX, tetryl, and PETN were down to 3, 6, and 10 pg, respectively. Finally, an explosive mixture was successfully analyzed, demonstrating the potential of the DARLTP probe for qualitative and quantitative analysis of complicated explosives. PMID:26191543

  4. 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''.

  5. 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

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

    NASA Astrophysics Data System (ADS)

    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.

  7. 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

  8. 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.

  9. 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

    2016-04-01

    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.

  10. 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. PMID:27126470

  11. 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. Graphical Abstract ᅟ. PMID:26637323

  12. Hf dopants in γ'-Ni3Al alloy

    NASA Astrophysics Data System (ADS)

    Ivanovski, V. N.; Cekić, B.; Umićević, A.; Belošević-Čavor, J.; Schumacher, G.; Koteski, V.; Barudzija, T.

    2013-08-01

    The Time Differential Perturbed Angular (TDPAC) measurements of nuclear quadrupole interactions (NQIs) at 181Ta ion probe in the polycrystalline intermetallic alloy γ'-Ni3Al doped with 0.2 at. % Hf were performed in the temperature range 78-1230 K, in order to determine the lattice location of Hf atoms in the ordered γ'-Ni3Al structure. The two NQIs obtained are discussed within the present L12 cubic structure and a tetragonal distortion of L12 to another two DO22 and L60 type structures. The first low frequency NQI at the site of the 181Ta ion-probe after substitution of aluminum for hafnium in DO22 at ambient temperature, is vQ1(300 K) = 39(1) MHz with η1 = 0. The corresponding high frequency value on the second crystallographic site in L60, is vQ2(300 K) = 204(14) MHz with η2 = 0.47(11). These two NQI's have different temperature behavior. The presence of both DO22 and L60 tetragonal distortions of the parent cubic L12 lattice, detected after adding 0.2 at. % Hf, are with modulations to the lattice constant (a) with a ratio (c/a), 2.04 and 0.87, respectively. Ab initio calculations of electronic and structural properties and hyperfine parameters at the 181Ta ion probe of the γ'-Ni3Al-0.2 at. % Hf alloy were performed using the full potential augmented plane wave plus local-orbital (APW+lo) method as implemented in the WIEN2k code. The accuracy of the calculations and comparison with the experimental results enabled us to identify the observed hyperfine interactions and to infer the EFG sign that cannot be measured in conventional TDPAC measurements.

  13. Impact of Dopant Compensation on Graded p-n Junctions in Si Nanowires.

    PubMed

    Amit, Iddo; Jeon, Nari; Lauhon, Lincoln J; Rosenwaks, Yossi

    2016-01-13

    The modulation between different doping species required to produce a diode in VLS-grown nanowires (NWs) yields a complex doping profile, both axially and radially, and a gradual junction at the interface. We present a detailed analysis of the dopant distribution around the junction. By combining surface potential measurements, performed by KPFM, with finite element simulations, we show that the highly doped (5 × 10(19) cm(-3)) shell surrounding the NW can screen the junction's built in voltage at shell thickness as low as 3 nm. By comparing NWs with high and low doping contrast at the junction, we show that dopant compensation dramatically decreases the electrostatic width of the junction and results in relatively low leakage currents. PMID:26650197

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

    PubMed

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

    2016-07-01

    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. PMID:26972924

  15. 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.

  16. Profiling the local carrier concentration and dopant distribution across a semiconductor quantum dot

    NASA Astrophysics Data System (ADS)

    Walrath, J. C.; Chang, A. S.; Lin, Y. H.; Huang, S.; Goldman, R. S.

    We profile the local carrier concentration, n, across epitaxial InAs/GaAs quantum dots (QDs) consisting of 3D islands on top of a 2D alloy layer. We use scanning thermoelectric microscopy to profile the temperature gradient-induced voltage, which is converted to a profile of the local Seebeck coefficient, S. The S profile is then converted to a conduction band-edge profile and compared with Poisson-Schrodinger band-edge simulations. Our combined computational-experimental approach suggests a reduced carrier concentration in the QD center in comparison to that of the 2D alloy layer. We further use 3D atom probe tomography, which enables 3D imaging with a few Angstrom resolution, to profile the distribution of Si dopants. We discuss the correlation between the Si dopant distribution and the observed carrier concentration profile.

  17. RETRACTION: Redistribution of infused and implanted dopants in a multilayer structure during annealing of dopant and radiation defects for the production of a system of p-n junctions Redistribution of infused and implanted dopants in a multilayer structure during annealing of dopant and radiation defects for the production of a system of p-n junctions

    NASA Astrophysics Data System (ADS)

    Pankratov, E. L.

    2009-04-01

    It has come to the attention of IOP Publishing that this article should not have been submitted for publication owing to its substantial replication of other published papers by the same author: E L Pankratov 2008 Optimization of laser annealing of radiation defects for production of an implanted-junction rectifier J. Phys. D: Appl. Phys. 41 115105 E L Pankratov 2008 Redistribution of dopant during microwave annealing of a multilayer structure for production p-junction J. Appl. Phys. 103 064320 and E L Pankratov 2008 Redistribution of dopant in a multilayer structure during annealing of radiation defects by laser pulses for production an implanted-junction rectifier Phys. Lett. A 372 4510-4516 Consequently the two papers in Semiconductor Science and Technology and Journal of Physics D: Applied Physics have been retracted by IOP Publishing.

  18. 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.

  19. 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.

  20. 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.

  1. DBR laser with nondynamic plasma grating formed by focused ion beam implanted dopants

    NASA Technical Reports Server (NTRS)

    Boenke, Myra M.; Wu, M. C.; Wang, Shyh; Clark, William M., Jr.; Stevens, Eugene H.

    1989-01-01

    A static plasma grating has been demonstrated experimentally (Wu et al., 1988) in a large-optical-cavity focused-ion-beam-distributed-Bragg-reflector (FIB-DBR) GaAlAs/GaAs laser diode. The grating is formed by implanting stripes of dopants with a focused ion beam. The dopants ionize to form periodic fluctuations in the carrier concentration which, through the Kramers-Kronig relations, form an index grating. A model of the grating strength for optimizaton of the laser design is developed and presented. The computed results show that the coupling coefficient k can be increased by more than an order of magnitude over the 15/cm experimentally. Therefore, FIB-DBR or FIB-distributed-feedback (DFB) lasers with performance comparable to that of conventional DBR (or DFB) lasers can be expected.

  2. Tuning the magnetic interaction between Mn dopants in GaAs

    NASA Astrophysics Data System (ADS)

    Gohlke, David; Gupta, Jay

    2012-02-01

    Manganese can be used as a dopant in gallium arsenide to create a ferromagnetic semiconductor. We use low-temperature scanning tunneling microscopy to study these magnetic properties. The magnetic coupling between Mn dopants in GaAs(110) changes between ferromagnetic and antiferromagnetic depending on the orientation of the acceptors due to the zincblende crystal structure of the surface [Kitchen et al, Nature, 2006]. We have recently reported tuning of the resonance energy for a single Mn acceptor by moving charged atomic point defects [Lee and Gupta, Science, 2010]. Here, we tune the magnetic interaction between surface-layer Mn atoms in the same way. Funding for this research was provided by the Center for Emergent Materials at the Ohio State University, an NSF MRSEC (Award Number DMR-0820414). http://www.physics.ohio-state.edu/˜jgupta/

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

    PubMed

    Hughes-Currie, Rosa B; Ivanovskikh, Konstantin V; R Wells, Jon-Paul; 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. PMID:26941175

  4. 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.

  5. 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.

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

    DOE PAGESBeta

    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 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

  7. 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.

  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. 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. PMID:26588665

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

    PubMed

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

    2016-07-26

    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. 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. 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 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. PMID:27327863

  11. Optical properties of active bismuth centres in silica fibres containing no other dopants

    SciTech Connect

    Bufetov, Igor' A; Semenov, S L; Vel'miskin, V V; Firstov, Sergei V; Dianov, Evgenii M; Bufetova, G A

    2010-09-10

    Optical fibre preforms and fibres with a bismuth-doped silica core containing no other dopants have been fabricated by the powder-in-tube technique. The optical loss has been measured for the first time in such fibres in a wide spectral range, from 190 to 1700 nm. We have studied the luminescence of active bismuth centres and the luminescence lifetime for some of their bands in both the preforms and the fibres drawn out from them. (optical fibres)

  12. 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. PMID:26088609

  13. 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.

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

    PubMed Central

    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.

    2015-01-01

    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 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+/0.5D2 redox potentials – the effective reducing strengths of the dimers – vary little within the series (ca. –1.9 V vs. FeCp2+/0) 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. PMID:26088609

  15. 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

  16. The effect of random dopant fluctuation on threshold voltage and drain current variation in junctionless nanotransistors

    NASA Astrophysics Data System (ADS)

    Rezapour, Arash; Rezapour, Pegah

    2015-09-01

    We investigate the effect of dopant random fluctuation on threshold voltage and drain current variation in a two-gate nanoscale transistor. We used a quantum-corrected technology computer aided design simulation to run the simulation (10000 randomizations). With this simulation, we could study the effects of varying the dimensions (length and width), and thicknesses of oxide and dopant factors of a transistor on the threshold voltage and drain current in subthreshold region (off) and overthreshold (on). It was found that in the subthreshold region the variability of the drain current and threshold voltage is relatively fixed while in the overthreshold region the variability of the threshold voltage and drain current decreases remarkably, despite the slight reduction of gate voltage diffusion (compared with that of the subthreshold). These results have been interpreted by using previously reported models for threshold current variability, load displacement, and simple analytical calculations. Scaling analysis shows that the variability of the characteristics of this semiconductor increases as the effects of the short channel increases. Therefore, with a slight increase of length and a reduction of width, oxide thickness, and dopant factor, we could correct the effect of the short channel.

  17. 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. PMID:26505784

  18. 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.

  19. 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.

  20. Optical Behaviors of Cholesteric Liquid-Crystalline Polyester Composites with Various Chiral Photochromic Dopants.

    PubMed

    Chien, Chih-Chieh; Liu, Jui-Hsiang

    2015-12-15

    New developments in the field of chiral nematic liquid crystals, such as color displays, are now being widely proposed. This article describes the tunable incident reflection band based on composite materials of low-molecular-weight chiroptical dopants and polymeric networks. These materials have advantages including easily manageable color according to a change in the helical pitch of the cholesteric liquid crystal upon exposure to light. A series of novel chiral dopants of isosorbide derivatives containing photochromic groups and three new main-chain liquid crystalline polyesters were synthesized and identified using nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FTIR), and elemental analyses. The phase-transition temperatures and the liquid-crystal phase determination of the synthesized polymers were estimated using DSC, WAXD, and POM analyses. The influence of the dopant concentrations and the solubility in a liquid crystalline polymer blend were also studied. The reflection band of the cholesteric liquid crystalline composites could be adjusted and tuned with a wide range of color variation across the entire visible region. A real image recording of the chiral photochromic liquid crystalline polymer blend was achieved by exposing it to UV light through a mask. PMID:26636344

  1. 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

    2015-02-01

    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. PMID:25602735

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

    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.

  3. 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

    2016-01-01

    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

  4. Design of new anchored p-dopants for high power efficiency OLEDs

    SciTech Connect

    Koech, Phillip K; Sapochak, Linda S; Rainbolt, James E; Cosimbescu, Lelia; Polikarpov, Evgueni; Swensen, James S; Wang, Liang; Padmaperuma, Asanga B; Gaspar, Daniel J

    2009-08-27

    Conductivity doping of charge transporting layers is increasingly becoming attractive for improving power efficiency in OLEDs. However, the number of organic molecular p-dopants is limited for instance the electron acceptor 2,3,5,6-tetrafluoro-7,7,8,8,-tetracyanoquinodimethane (F4-TCNQ) is the most utilized p-dopant. F4-TCNQ can dope most hole transporting materials (HTL), but it is very volatility, and has a low sticking coefficient thus difficult to deposit. Here we present the design of anchored molecular dopants based on the TCNQ core. We first review how the reduction potential of TCNQ core is affected by substitution with alkyl groups of different electronic properties. Electron donating groups have negative effect on the reduction potential of the acceptor. However, attaching electron withdrawing groups such as halogens counteracts the effect of electron donating groups. Using gas phase theoretical calculations we determined that trifluorinated TCNQ can be anchored through a σ-coupled alkyl chain to an inert molecular anchor without sacrificing the electron affinity.

  5. Predicting Low Energy Dopant Implant Profiles in Semiconductors using Molecular Dynamics

    SciTech Connect

    Beardmore, K.M.; Gronbech-Jensen, N.

    1999-05-02

    The authors present a highly efficient molecular dynamics scheme for calculating dopant density profiles in group-IV alloy, and III-V zinc blende structure materials. Their scheme incorporates several necessary methods for reducing computational overhead, plus a rare event algorithm to give statistical accuracy over several orders of magnitude change in the dopant concentration. The code uses a molecular dynamics (MD) model to describe ion-target interactions. Atomic interactions are described by a combination of 'many-body' and pair specific screened Coulomb potentials. Accumulative damage is accounted for using a Kinchin-Pease type model, inelastic energy loss is represented by a Firsov expression, and electronic stopping is described by a modified Brandt-Kitagawa model which contains a single adjustable ion-target dependent parameter. Thus, the program is easily extensible beyond a given validation range, and is therefore truly predictive over a wide range of implant energies and angles. The scheme is especially suited for calculating profiles due to low energy and to situations where a predictive capability is required with the minimum of experimental validation. They give examples of using the code to calculate concentration profiles and 2D 'point response' profiles of dopants in crystalline silicon and gallium-arsenide. Here they can predict the experimental profile over five orders of magnitude for <100> and <110> channeling and for non-channeling implants at energies up to hundreds of keV.

  6. An Efficient Molecular Dynamics Scheme for Predicting Dopant Implant Profiles in Semiconductors

    SciTech Connect

    Beardmore, K.M.; Gronbech-Jensen, N.

    1998-09-15

    The authors present a highly efficient molecular dynamics scheme for calculating the concentration profile of dopants implanted in group-IV alloy, and III-V zinc blende structure materials. The program incorporates methods for reducing computational overhead, plus a rare event algorithm to give statistical accuracy over several orders of magnitude change in the dopant concentration. The code uses a molecular dynamics (MD) model, instead of the binary collision approximation (BCA) used in implant simulators such as TRIM and Marlowe, to describe ion-target interactions. Atomic interactions are described by a combination of 'many-body' and screened Coulomb potentials. Inelastic energy loss is accounted for using a Firsov model, and electronic stopping is described by a Brandt-Kitagawa model which contains the single adjustable parameter for the entire scheme. Thus, the program is easily extensible to new ion-target combinations with the minimum of tuning, and is predictive over a wide range of implant energies and angles. The scheme is especially suited for calculating profiles due to low energy, large angle implants, and for situations where a predictive capability is required with the minimum of experimental validation. They give examples of using their code to calculate concentration profiles and 2D 'point response' profiles of dopants in crystalline silicon, silicon-germanium blends, and gallium-arsenide. They can predict the experimental profiles over five orders of magnitude for <100> and <110> channeling and for non-channeling implants at energies up to hundreds of keV.

  7. Effects of Li and Cu dopants on structural properties of zinc oxide nanorods

    NASA Astrophysics Data System (ADS)

    Kim, Kyung Ho; Jin, Zhuguang; Abe, Yoshio; Kawamura, Midori

    2015-01-01

    We fabricated undoped zinc oxide (ZnO), Li-doped zinc oxide (LZO), and Cu-doped zinc oxide (CZO) nanorods (NRs) on fluorine-doped tin oxide (FTO)-coated glass substrates using chemical solution deposition and investigated their structural properties. With the incorporation of the Li dopant, the length and crystallinity of LZO NRs increased and improved, respectively, compared to that of the ZnO NRs. The average optical transmittance of LZO NRs was slightly lower than that of the ZnO NRs, but otherwise very similar over the visible wavelength region. With the incorporation of the Cu dopant, however, the morphology of the CZO sample was remarkably different from that of the pure ZnO NRs. Rods with a length of ∼12 μm and a diameter of 0.5-1.2 μm were randomly oriented on the substrate, and copper oxide (CuO) nanocrystals were uniformly grown on the surface of substrate. This paper presents a simple way to tune the growth behaviors of the ZnO NRs by adding dopants.

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

    PubMed

    Khaparde, Rohini; Acharya, Smita

    2016-06-15

    Isovalent (Mn, Cd, Cu, Co)-doped-ZnS nanoparticles having size vary in between 2 to 5nm 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 UVVis 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 5nm. 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 UVVis 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. PMID:27037762

  9. 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.

  10. Deionization of Dopants in Silicon Nanofilms Even with Donor Concentration of Greater than 10(19) cm(-3).

    PubMed

    Tanaka, Takahisa; Kurosawa, Yuya; Kadotani, Naotoshi; Takahashi, Tsunaki; Oda, Shunri; Uchida, Ken

    2016-02-10

    Understanding the dopant properties in heavily doped nanoscale semiconductors is essential to design nanoscale devices. We report the deionization or finite ionization energy of dopants in silicon (Si) nanofilms with dopant concentration (ND) of greater than 10(19) cm(-3), which is in contrast to the zero ionization energy (ED) in bulk Si at the same ND. From the comparison of experimentally observed and theoretically calculated ED, we attribute the deionization to the suppression of metal-insulator transition in highly doped nanoscale semiconductors in addition to the quantum confinement and the dielectric mismatch, which greatly increase ED in low-doped nanoscale semiconductors. Thus, for nanoscale transistors, ND should be higher than that estimated from bulk Si dopant properties in order to reduce their resistivity by the metal-insulator transition. PMID:26741540

  11. Variable-angle high-angle annular dark-field imaging: application to three-dimensional dopant atom profiling

    PubMed Central

    Zhang, Jack Y.; Hwang, Jinwoo; Isaac, Brandon J.; Stemmer, Susanne

    2015-01-01

    Variable-angle high-angle annular dark-field (HAADF) imaging in scanning transmission electron microscopy is developed for precise and accurate determination of three-dimensional (3D) dopant atom configurations. Gd-doped SrTiO3 films containing Sr columns containing zero, one, or two Gd dopant atoms are imaged in HAADF mode using two different collection angles. Variable-angle HAADF significantly increases both the precision and accuracy of 3D dopant profiling. Using image simulations, it is shown that the combined information from the two detectors reduces the uncertainty in the dopant depth position measurement and can uniquely identify certain atomic configurations that are indistinguishable with a single detector setting. Additional advances and applications are discussed. PMID:26206489

  12. From Bimetallic Metal-Organic Framework to Porous Carbon: High Surface Area and Multicomponent Active Dopants for Excellent Electrocatalysis.

    PubMed

    Chen, Yu-Zhen; Wang, Chengming; Wu, Zhen-Yu; Xiong, Yujie; Xu, Qiang; Yu, Shu-Hong; Jiang, Hai-Long

    2015-09-01

    Bimetallic metal-organic frameworks are rationally synthesized as templates and employed for porous carbons with retained morphology, high graphitization degree, hierarchical porosity, high surface area, CoNx moiety and uniform N/Co dopant by pyrolysis. The optimized carbon with additional phosphorus dopant exhibits excellent electrocatalytic performance for the oxygen reduction reaction, which is much better than the benchmark Pt/C in alkaline media. PMID:26193083

  13. Hybrid Modulation-Doping of Solution-Processed Ultrathin Layers of ZnO Using Molecular Dopants.

    PubMed

    Schießl, Stefan P; Faber, Hendrik; Lin, Yen-Hung; Rossbauer, Stephan; Wang, Qingxiao; Zhao, Kui; Amassian, Aram; Zaumseil, Jana; Anthopoulos, Thomas D

    2016-05-01

    An alternative doping approach that exploits the use of organic donor/acceptor molecules for the effective tuning of the free electron concentration in quasi-2D ZnO transistor channel layers is reported. The method relies on the deposition of molecular dopants/formulations directly onto the ultrathin ZnO channels. Through careful choice of materials combinations, electron transfer from the dopant molecule to ZnO and vice versa is demonstrated. PMID:26437002

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

    NASA Astrophysics Data System (ADS)

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

    2016-01-01

    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.

  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. 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.

  17. 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

  18. 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%.

  19. 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.

  20. Quantitative dopant distributions in GaAs nanowires using atom probe tomography.

    PubMed

    Du, Sichao; Burgess, Timothy; Gault, Baptiste; Gao, Qiang; Bao, Peite; Li, Li; Cui, Xiangyuan; Kong Yeoh, Wai; Liu, Hongwei; Yao, Lan; Ceguerra, Anna V; Hoe Tan, Hark; Jagadish, Chennupati; Ringer, Simon P; Zheng, Rongkun

    2013-09-01

    Controllable doping of semiconductor nanowires is critical to realize their proposed applications, however precise and reliable characterization of dopant distributions remains challenging. In this article, we demonstrate an atomic-resolution three-dimensional elemental mapping of pristine semiconductor nanowires on growth substrates by using atom probe tomography to tackle this major challenge. This highly transferrable method is able to analyze the full diameter of a nanowire, with a depth resolution better than 0.17 nm thanks to an advanced reconstruction method exploiting the specimen's crystallography, and an enhanced chemical sensitivity of better than 8-fold increase in the signal-to-noise ratio. PMID:23489910

  1. Off-center Tl and Na dopant centers in CsI

    SciTech Connect

    Van Ginhoven, Renee M.; Schultz, P. A.

    2013-12-11

    We use density functional theory calculations to characterize the electronic and structural properties of the Tl and Na dopant centers in CsI. We nd that the Tl and Na centers can accept one or two electrons and couple to long-range relaxations in the surrounding crystal lattice to distort strongly off-center to multiple distinct minima, even without a triplet excitation. The long-range distortions are a mechanism to couple to phonon modes in the crystal, and are expected to play an important role in the phonon-assisted transport of polarons in activated CsI and subsequent light emission in this scintillator.

  2. Removing grain boundaries from three-dimensional colloidal crystals using active dopants.

    PubMed

    van der Meer, B; Dijkstra, M; Filion, L

    2016-07-01

    Using computer simulations we explore how grain boundaries can be removed from three-dimensional colloidal crystals by doping with a small fraction of active colloids. We show that for sufficient self-propulsion, the system is driven into a crystal-fluid coexistence. In this phase separated regime, the active dopants become mobile and spontaneously gather at the grain boundaries. The resulting surface melting and recrystallization of domains result in the motion of the grain boundaries over time and lead to the formation of a large single crystal. However, when the self-propulsion is too low to cause a phase separation, we observe no significant enhancement of grain growth. PMID:27257054

  3. Ternary logic implemented on a single dopant atom field effect silicon transistor

    NASA Astrophysics Data System (ADS)

    Klein, M.; Mol, J. A.; Verduijn, J.; Lansbergen, G. P.; Rogge, S.; Levine, R. D.; Remacle, F.

    2010-01-01

    We provide an experimental proof of principle for a ternary multiplier realized in terms of the charge state of a single dopant atom embedded in a fin field effect transistor (Fin-FET). Robust reading of the logic output is made possible by using two channels to measure the current flowing through the device and the transconductance. A read out procedure that allows for voltage gain is proposed. Long numbers can be multiplied by addressing a sequence of Fin-FET transistors in a row.

  4. Laser ablation at 337 nm of nitrocellulose and nylon sensitized with organic dopants

    NASA Astrophysics Data System (ADS)

    Skordoulis, Constantine D.; Kosmidis, Constantine E.

    1993-05-01

    The laser induced ablative decomposition of nitrocellulose and nylon sensitized with organic dopants (Stilbene 420, Coumarin 120, and Rhodamine 6G) has been studied. Ablation with a low power nitrogen laser is hereby reported for the first time. With the addition of dyes strongly absorbing at 337 nm the photoetching rate of the pure materials can be significantly increased. A two step photochemical mechanism considering the decomposition of the polymers from excited electronic states and the energy transfer process from the dye to the polymer are discussed.

  5. 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%.

  6. Cable-fault locator

    NASA Technical Reports Server (NTRS)

    Cason, R. L.; Mcstay, J. J.; Heymann, A. P., Sr.

    1979-01-01

    Inexpensive system automatically indicates location of short-circuited section of power cable. Monitor does not require that cable be disconnected from its power source or that test signals be applied. Instead, ground-current sensors are installed in manholes or at other selected locations along cable run. When fault occurs, sensors transmit information about fault location to control center. Repair crew can be sent to location and cable can be returned to service with minimum of downtime.

  7. 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…

  8. Incorporation and diffusion of dopants in gallium arsenide, indium phosphide and indium gallium arsenide: Implications for devices

    NASA Astrophysics Data System (ADS)

    Tandon, Ashish

    Incorporation and diffusion of dopants in the InP, InGaAs and GaAs material systems by atmospheric pressure organometallic vapor phase epitaxy (APOMVPE) is discussed. A better understanding of the role point defect mechanisms play in driving dopant diffusion in III-V compounds has been obtained from experimental results. A study of Fermi level pinning at the surface of InP, InGaAs and GaAs is presented to explain the anomalously fast diffusion of dopants (such as Zn and Be which reside on the group III sublattice) observed in the base region of InP/InGaAs HBTs. Experimental results indicated that the Fermi level is not pinned at the surface of InGaAs while it appears to be pinned close to the valence band in InP. The Fermi level pinning at the surface of GaAs was found to vary with the crystal orientation. A solution to the problem of obtaining p-type base in InP/InGaAs HBTs has been presented in the form of carbon doped (p-type) InGaAs. The effects of growth temperature, V/III ratio and dopant source partial pressure on the concentration and mobility of holes in carbon doped InGaAs epilayers are reported. Record doping levels with negligible dopant passivation have been attained for carbon doped InGaAs epilayers. Studies linking dopant passivation to macroscopic defect formation are presented. A culmination of these findings in the growth and fabrication of InP/InGaAs HBTs with low base resistance and moderate gains is reported. A design resulting in the improvement of the collector-base breakdown voltage in InGaAs diodes is also discussed. The chemical treatment and history of the substrate were shown to play an important role in the diffusion of dopants in grown epilayers. Chlorine based compounds, thermal oxidation of the surface and growth of buffer layers (between the substrate and the epilayer) reduced diffusion in the epilayer. Sodium based compounds and anodic oxides tend to enhance dopant diffusion in the epilayer. A theoretical model for calculating

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

    PubMed

    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

  10. 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

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

    NASA Astrophysics Data System (ADS)

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

    2016-07-01

    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.

  12. Schottky barrier formation and reduction at Au/TiO2 interfaces by dopants from quantum simulations

    NASA Astrophysics Data System (ADS)

    Jiao, Yang; Hellman, Anders; Fang, Yurui; Gao, Shiwu; Käll, Mikael

    2015-03-01

    Excitation of localized surface plasmon resonances (LSPRs) in metallic nanoparticles, especially particles made of noble metals, results in efficient light absorption and strong field enhancement, thereby enabling a multitude of nanooptical applications of high current interest. Recently, the possibility of utilizing LSPRs to generate hot electrons has attracted considerable attention. One method to extract and make use of the hot electrons is by attaching the nanoparticles on a semiconductor surface such that excited electrons with proper energy and momentum can be transferred through the Schottky barrier at the interface. Using ab initio calculations for Au/TiO2 interfaces, we investigate dopant induced Schottky barrier height reduction effects. We show that dopant induced polarization at the interface is the dominant reason behind the semiconductor band bending and Schottky barrier formation. Calculations for Nb-dopants at different depths (d) below the interface show that the Schottky barrier height reduction depends on the depth and varies from 0.1 eV at d = 4 nm to up to 1.3 eV when the dopant is situated at the interfacial layer. The calculations also indicate that the Schottky barrier can be tuned by up to 1.5 eV by using different transition metal dopants.

  13. 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. PMID:23549289

  14. 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.

  15. 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.

  16. 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.

  17. 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. PMID:24027227

  18. 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. PMID:26727130

  19. 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.

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

    PubMed

    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. PMID:26167766

  1. 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.

  2. Dopant and carrier concentration in Si in equilibrium with monoclinic SiP precipitates

    NASA Astrophysics Data System (ADS)

    Solmi, S.; Parisini, A.; Angelucci, R.; Armigliato, A.; Nobili, D.; Moro, L.

    1996-03-01

    The behavior of silicon slices very heavily implanted (1.5×1017 cm-2) with phosphorus was investigated by transmission electron microscopy and secondary neutral mass spectrometry (SNMS) after annealing at 800, 850, 900, and 1000 °C. Precipitation of large monoclinic, and partially orthorhombic, SiP particles takes place in the most heavily doped region. From the shape of the SNMS profiles in the dissolution stage of these precipitates, we determined the concentration Csat of P in equilibrium with the conjugate phase: Csat=2.45×1023exp(-0.62/kT) cm-3. This concentration has to be compared with the equilibrium concentration ne of the electrically active dopant. To this end, more accurate determinations of ne were performed on heavily P-doped polysilicon films. It was found that ne=1.3×1022exp(-0.37/kT) cm-3. Hence for T>~750 °C, Csat exceeds ne and the concentration (Csat-ne) of inactive mobile P increases with temperature. The formation and the diffusion behavior of this inactive dopant are in keeping with a preprecipitation phenomenon.

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

    DOE PAGESBeta

    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 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

  4. Characteristics of titanium oxide memristor with coexistence of dopant drift and a tunnel barrier

    NASA Astrophysics Data System (ADS)

    Tian, Xiao-Bo; Xu, Hui

    2014-06-01

    The recent published experimental data of titanium oxide memristor devices which are tested under the same experimental conditions exhibit the strange instability and complexity of these devices. Such undesired characteristics preclude the understanding of the device conductive processes and the memristor-based practical applications. The possibility of the coexistence of dopant drift and tunnel barrier conduction in a memristor provides preliminary explanations for the undesired characteristics. However, current research lacks detailed discussion about the coexistence case. In this paper, dopant drift and tunnel barrier-based theories are first analyzed for studying the relations between parameters and physical variables which affect characteristics of memristors, and then the influences of each parameter change on the conductive behaviors in the single and coexistence cases of the two mechanisms are simulated and discussed respectively. The simulation results provide further explanations of the complex device conduction. Theoretical methods of eliminating or reducing the coexistence of the two mechanisms are proposed, in order to increase the stability of the device conduction. This work also provides the support for optimizing the fabrications of memristor devices with excellent performance.

  5. Modification of dopant profiles due to surface and interface interactions: Applications to semiconductor materials

    SciTech Connect

    Jagannadham, K.; Narayan, J.

    1987-02-01

    The kinetics of segregation of dopant solute atoms in the presence of free surfaces and interfaces are analyzed by solving the diffusion equation with a drift term. The drift term includes the configurational interaction energy associated with an oversize or an undersize atom near a coherent interface when the continuity conditions are satisfied. Both an analytical solution and a numerical procedure are provided to solve the problem by eigenfunction expansion method. A new procedure for evaluating the eigenvalues to include higher-order terms is given. It is further established that an attractive force due to either a soft second phase or a free surface gives rise to a minimum in the concentration profile near the interface while a hard second phase results in a monotonically increasing concentration. The position of the minimum in the concentration profile in the presence of a soft second phase or the slope of the concentration profile in the presence of a hard second phase provides a measure of the strength of the defect and the interaction-energy term which can be compared with experimental observations. In particular, we have considered changes in the dopant profiles in silicon under the influence of the free surface, in silicon with silicon dioxide, gallium arsenide, germanium, magnesium oxide and in germanium with silicon, all deposited as a second phase, respectively.

  6. 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.

  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. 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

  9. 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.

  10. 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.

  11. Dopant effects on 2-ethyl-1-hexanol: A dual-channel impedance spectroscopy and neutron scattering study

    NASA Astrophysics Data System (ADS)

    Singh, Lokendra P.; Raihane, Ahmed; Alba-Simionesco, Christiane; Richert, Ranko

    2015-01-01

    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 (Tg) 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.

  12. Sarsat location algorithms

    NASA Astrophysics Data System (ADS)

    Nardi, Jerry

    The Satellite Aided Search and Rescue (Sarsat) is designed to detect and locate distress beacons using satellite receivers. Algorithms used for calculating the positions of 406 MHz beacons and 121.5/243 MHz beacons are presented. The techniques for matching, resolving and averaging calculated locations from multiple satellite passes are also described along with results pertaining to single pass and multiple pass location estimate accuracy.

  13. 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.

  14. 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.

  15. Improving stability of photoluminescence of ZnSe thin films grown by molecular beam epitaxy by incorporating Cl dopant

    NASA Astrophysics Data System (ADS)

    Wang, J. S.; Chen, W. J.; Yang, C. S.; Tsai, Y. H.; Wang, H. H.; Chen, R. H.; Shen, J. L.; Tsai, C. D.

    2011-01-01

    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/cm2 has a much stronger effect on PL degradation than does thermal heating to a temperature of 150 °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.

  16. 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.

  17. Diffusion of dopant from optical coating and single step formation of pn junction in silicon solar cell and coating thereon

    SciTech Connect

    Yoldas, B. E.; Yoldas, L. A.

    1981-02-17

    The pn juncture in a silicon chip and an oxide coating on its surface are simultaneously formed from clear solution derived from titanium alkoxides, water, alcohol, a suitable acid, and a P or N dopant compound by partial hydrolysis and polymerization. The solution is applied to the surface of a silicon chip. The chip is then heated which converts the solution to a solid oxide coating which meets the antireflective optical film requirements and induces the migration of the dopants into the chip, forming a pn junction in the chip. The method also provides deep and uniform junction formation or diffusion without resulting in excessive carrier concentration.

  18. Influence of damped propagation of dopant on the static and frequency-dependent third nonlinear polarizability of quantum dot

    NASA Astrophysics Data System (ADS)

    Pal, Suvajit; Ghosh, Manas

    2014-07-01

    We investigate the profiles of diagonal components of static and frequency-dependent third nonlinear (γxxxx and γyyyy) polarizability of repulsive impurity doped quantum dots. The dopant impurity potential takes a GAUSSIAN form. We have considered propagation of the dopant within an environment that damps the motion. The study focuses on role of damping strength on the diagonal components of both static and frequency-dependent third nonlinear polarizability of the doped system. The doped system is further exposed to an external electric field of given intensity. Damping subtly modulates the dot-impurity interaction and fabricates the polarizability components in a noticeable manner.

  19. 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

  20. 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.

  1. Dopant characterization in self-regulatory plasma doped fin field-effect transistors by atom probe tomography

    SciTech Connect

    Takamizawa, H.; Shimizu, Y.; Nozawa, Y.; Toyama, T.; Nagai, Y.; Morita, H.; Yabuuchi, Y.; Ogura, M.

    2012-02-27

    Fin field-effect transistors are promising next-generation electronic devices, and the identification of dopant positions is important for their accurate characterization. We report atom probe tomography (APT) of silicon fin structures prepared by a recently developed self-regulatory plasma doping (SRPD) technique. Trenches between fin-arrays were filled using a low-energy focused ion beam to directly deposit silicon, which allowed the analysis of dopant distribution by APT near the surface of an actual fin transistor exposed to air. We directly demonstrate that SRPD can achieve a boron concentration above 1 x 10{sup 20} atoms/cm{sup 3} at the fin sidewall.

  2. The Thermoelectric Properties of Rare Earths as Dopants in InGaAs Films

    NASA Astrophysics Data System (ADS)

    Koltun, Rachel Ann

    Current energy technologies lose over half of the energy input to waste heat. Thermoelectric materials can recover some of this waste heat by converting it into electricity. Thermoelectric devices have no moving parts, so they are low noise and highly reliable, making them particularly suitable for extreme environments. A good thermoelectric has low thermal conductivity to maintain large temperature gradients and high electrical conductivity to effectively transport carriers across that temperature gradient. One of the major challenges in engineering such thermoelectrics is effectively decoupling these parameters. These relationships are quantified in the dimensionless thermoelectric figure of merit, ZT, where a ZT of 1 is considered commercially viable. Doping MBE grown InGaAs films with rare earths forms embedded nanoparticles that have been shown to improve thermoelectric efficiency of InGaAs. Rare earth doping effectively overcomes the problematic relationship between electrical and thermal conductivities. These embedded particles effectively decouple thermal and electrical properties by contributing carriers to increase electrical conductivity as well as forming scattering centers for mid to long wavelength phonons to decrease thermal conductivity. However, the mechanism for carrier generation from rare earths is poorly understood. Comparing different rare earths as dopants in InGaAs, we find a positive correlation with the electrical activation efficiency as the rare earth arsenide nanoparticles are more closely lattice matched to the host matrix. This is in contrast to traditional Si doped InGaAs, which is fully ionized at room temperature. The high doping efficiency of Si leads it to be as good or better of a dopant for thermoelectrics compared to the best rare earths studied. We observe that rare earth doped InGaAs has thermal activation of carriers at high temperature, giving it the potential to be a more efficient thermoelectric in this regime than

  3. 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.

  4. Reversible micromachining locator

    SciTech Connect

    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.

  5. 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.

  6. The influence of dopant distribution on the optoelectronic properties of tin-doped indium oxide nanocrystals and nanocrystal films

    NASA Astrophysics Data System (ADS)

    Lounis, Sebastien Dahmane

    Colloidally prepared nanocrystals of transparent conducting oxide (TCO) semiconductors have emerged in the past decade as an exciting new class of plasmonic materials. In recent years, there has been tremendous progress in developing synthetic methods for the growth of these nanocrystals, basic characterization of their properties, and their successful integration into optoelectronic and electrochemical devices. However, many fundamental questions remain about the physics of localized surface plasmon resonance (LSPR) in these materials, and how their optoelectronic properties derive from their underlying structural properties. In particular, the influence of the concentration and distribution of dopant ions and compensating defects on the optoelectronic properties of TCO nanocrystals has seen little investigation. Indium tin oxide (ITO) is the most widely studied and commercially deployed TCO. Herein we investigate the role of the distribution of tin dopants on the optoelectronic properties of colloidally prepared ITO nanocrystals. Owing to a high free electron density, ITO nanocrystals display strong LSPR absorption in the near infrared. Depending on the particular organic ligands used, they are soluble in various solvents and can readily be integrated into densely packed nanocrystal films with high conductivities. Using a combination of spectroscopic techniques, modeling and simulation of the optical properties of the nanocrystals using the Drude model, and transport measurements, it is demonstrated herein that the radial distribution of tin dopants has a strong effect on the optoelectronic properties of ITO nanocrystals. ITO nanocrystals were synthesized in both surface-segregated and uniformly distributed dopant profiles. Temperature dependent measurements of optical absorbance were first combined with Drude modeling to extract the internal electrical properties of the ITO nanocrystals, demonstrating that they are well-behaved degenerately doped semiconductors

  7. Yb-doped large mode area fibers with depressed clad and dopant confinement

    NASA Astrophysics Data System (ADS)

    Roy, Vincent; Paré, Claude; Laperle, Pierre; Desbiens, Louis; Taillon, Yves

    2016-03-01

    Large mode area fibers with depressed-index cladding layer and confinement of rare-earth dopants can provide effective suppression of high-order modes. A polarization-maintaining Yb-doped double-clad fiber with 35/250 μm core/clad diameter has been fabricated from conventional methods according to this design. The fiber which has an effective mode area close to 500 μm2 yields near diffraction-limited output with beam quality factor M2 close to 1.1 when tested as a power amplifier with a coherent seed light source. Beam pointing measurements provide further evidence for near single-mode behavior as the pointing fluctuations are shown to be negligible once the fiber is coiled to a given diameter.

  8. First-principles study of extensive dopants in wurtzite ZnO

    NASA Astrophysics Data System (ADS)

    Huang, Gui-Yang; Wang, Chong-Yu; Wang, Jian-Tao

    2010-01-01

    Based on comprehensive calculations of the transition energy levels for extensive dopant substitutional (H, Li, Na, K, Ag, B, Al, Ga, In, N, P, As, Sb, Bi, F, Cl, Br, I), we illustrate and check the validity of the first-principle calculations based on GGA and GGA+ U correction method. The results indicate that there still exist large limits for quantitative correct results of first-principle calculations. Nevertheless, some qualitative useful information can be obtained by such calculations. Based on our calculation results, LiZn, NaZn, KZn, NZn and AgZn have the shallowest transition energy level (0/1-) for p-type doping, from shallow to deep.

  9. Local Probes of Strain Texture and Individual Atomic Dopant Sites in Monolayer MoS2

    NASA Astrophysics Data System (ADS)

    Fragapane, Alex H.; Contryman, Alex W.; Li, Hong; Qian, Xiaofeng; Ardakani, Sina Moeini; Gong, Yongji; Wang, Xingli; Weisse, Jeffrey M.; Lee, Chi Hwan; Zhao, Jiheng; Ajayan, Pulickel M.; Li, Ju; Zheng, Xiaolin; Manoharan, Hari C.

    The 2D semiconductor MoS2 is an optically active material uniquely responsive to local perturbations. As an atomically thin membrane with exceptional strength, it can embed wide band gap variations overlapping the visible light spectrum when subjected to biaxial strain, where the modified electronic potential emanating from point-induced tensile strain perturbations mimics the Coulomb potential in a mesoscopic atom. We have realized this ``artificial atom'' concept via monolayer nanoindentation, and demonstrate that a synthetic superlattice of these building blocks forms an optoelectronic crystal capable of broadband light absorption and efficient funneling of photogenerated excitons to points of maximum strain at the artificial-atom nuclei. We also investigate the effects of individual atomic dopant sites through STM/STS, and visualize the atomic-scale local band structure changes. The modification of 2D semiconductors through methods such as strain texturing and doping connects to applications in next generation optoelectronics and photovoltaics.

  10. Site selectivity of dopant cations in Ca3(SiO4)Cl2

    NASA Astrophysics Data System (ADS)

    Gilbert, M. R.

    2014-08-01

    A series of static lattice calculations were performed to determine the site selectivity of cations of differing size and valence when substituted onto the Ca sites of the calcium chlorosilicate (Ca3(SiO4)Cl2) lattice, a potential host phase for the immobilisation of halide-rich wastes arising from the pyrochemical reprocessing of plutonium. Atomic-scale simulations indicate that divalent cations are preferentially substituted onto the Ca1 site, whilst tri- and tetravalent cations are preferentially hosted on the Ca2 site, with the Ca1 site favoured for forming the vacancies necessary to charge-balance the lattice as a whole. Multi-defect calculations reveal that the site selectivity of the dopant cations is dependent on their ionic radii; as the ionic radii of the divalent cations increase, substitution onto the preferred site becomes more and more strongly favoured, whereas the inverse is true of the trivalent cations.

  11. The effect of mixed dopants on the stability of Fricke gel dosimeters

    NASA Astrophysics Data System (ADS)

    Penev, K.; Mequanint, K.

    2013-06-01

    Auto-oxidation and fast diffusion in Fricke gels are major drawbacks to wide-spread application of these gels in 3D dosimetry. Aiming to limit both processes, we used mixed dopants: the ferric-specific ligand xylenol orange with a ferrous-specific ligand (1,10-phenanthroline) and/or a bi-functional cross-linking agent (glyoxal). Markedly improved auto-oxidation stability was observed in the xylenol orange and phenanthroline doped gel at the expense of increased background absorbance and faster diffusion. Addition of glyoxal limited the diffusion rate and led to a partial bleaching of the gel. It is conceivable that these two new compositions may find useful practical application.

  12. 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.

  13. 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. PMID:27131646

  14. Simple structured hybrid WOLEDs based on incomplete energy transfer mechanism: from blue exciplex to orange dopant

    PubMed Central

    Zhang, Tianyou; Zhao, Bo; Chu, Bei; Li, Wenlian; Su, Zisheng; Yan, Xingwu; Liu, Chengyuan; Wu, Hairuo; Gao, Yuan; Jin, Fangming; Hou, Fuhua

    2015-01-01

    Exciplex is well known as a charge transfer state formed between electron-donating and electron-accepting molecules. However, exciplex based organic light emitting diodes (OLED) often performed low efficiencies relative to pure phosphorescent OLED and could hardly be used to construct white OLED (WOLED). In this work, a new mechanism is developed to realize efficient WOLED with extremely simple structure by redistributing the energy of triplet exciplex to both singlet exciplex and the orange dopant. The micro process of energy transfer could be directly examined by detailed photoluminescence decay measurement and time resolved photoluminescence analysis. This strategy overcomes the low reverse intersystem crossing efficiency of blue exciplex and complicated device structure of traditional WOLED, enables us to achieve efficient hybrid WOLEDs. Based on this mechanism, we have successfully constructed both exciplex-fluorescence and exciplex-phosphorescence hybrid WOLEDs with remarkable efficiencies. PMID:25975371

  15. Dual nature of magnetic dopants and competing trends in topological insulators

    NASA Astrophysics Data System (ADS)

    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.

    2016-06-01

    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.

  16. 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

    2016-01-01

    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

  17. 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

  18. Systematic conversion of single walled carbon nanotubes into n-type thermoelectric materials by molecular dopants.

    PubMed

    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

  19. Observation of dopant-induced impurity states in bottom-up graphene nanoribbons

    NASA Astrophysics Data System (ADS)

    Pedramrazi, Zahra; Chen, Chen; Marangoni, Tomas; Cloke, Ryan; Cao, Ting; Louie, Steven; Fischer, Felix; Crommie, Michael

    Graphene nanoribbons (GNRs) provide a means for inducing energy gaps in graphene and are a promising candidate for many nanotechnological applications. New bottom-up fabrication techniques allow the structure of GNRs to be tuned with atomic precision, thus providing new opportunities for modifying their electronic structure. Here we report the synthesis of bottom-up armchair GNRs (AGNRs) with isolated substitutional boron-dopant centers; thus creating localized impurity states in the GNR. These impurities are realized via dilute doping of pristine n =7 AGNRs with sparse boron-containing monomer units, resulting in uniform-width n =7 AGNR segments where only two carbon atoms have been substitutionally replaced by boron atoms. Scanning tunneling microscopy (STM) and spectroscopy (STS) were performed to study the electronic structure of these AGNR impurity systems, enabling us to observe localized mid-gap impurity states.

  20. 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. PMID:26190007

  1. Local environment of Fe dopants in nanoscale Fe : CeO2-x oxygen storage material

    NASA Astrophysics Data System (ADS)

    Meledina, M.; Turner, S.; Galvita, V. V.; Poelman, H.; Marin, G. B.; van Tendeloo, G.

    2015-02-01

    Nanoscale Fe : CeO2-x oxygen storage material for the process of chemical looping has been investigated by advanced transmission electron microscopy and electron energy-loss spectroscopy before and after a model looping procedure, consisting of redox cycles at heightened temperature. Separately, the activity of the nanomaterial has been tested in a toluene total oxidation reaction. The results show that the material consists of ceria nanoparticles, doped with single Fe atoms and small FeOx clusters. The iron ion is partially present as Fe3+ in a solid solution within the ceria lattice. Furthermore, enrichment of reduced Fe2+ species is observed in nanovoids present in the ceria nanoparticles, as well as at the ceria surface. After chemical looping, agglomeration occurs and reduced nanoclusters appear at ceria grain boundaries formed by sintering. These clusters originate from surface Fe2+ aggregation, and from bulk Fe3+, which ``leaks out'' in reduced state after cycling to a slightly more agglomerated form. The activity of Fe : CeO2 during the toluene total oxidation part of the chemical looping cycle is ensured by the dopant Fe in the Fe1-xCexO2 solid solution, and by surface Fe species. These measurements on a model Fe : CeO2-x oxygen storage material give a unique insight into the behavior of dopants within a nanosized ceria host, and allow to interpret a plethora of (doped) cerium oxide-based reactions.Nanoscale Fe : CeO2-x oxygen storage material for the process of chemical looping has been investigated by advanced transmission electron microscopy and electron energy-loss spectroscopy before and after a model looping procedure, consisting of redox cycles at heightened temperature. Separately, the activity of the nanomaterial has been tested in a toluene total oxidation reaction. The results show that the material consists of ceria nanoparticles, doped with single Fe atoms and small FeOx clusters. The iron ion is partially present as Fe3+ in a solid solution

  2. 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.

  3. Tunable proton stopping power of deuterium-tritium by mixing heavy ion dopants for fast ignition

    NASA Astrophysics Data System (ADS)

    Zou, D. B.; Hu, L. X.; Wang, W. Q.; Yang, X. H.; Yu, T. P.; Zhang, G. B.; Ouyang, J. M.; Shao, F. Q.; Zhuo, H. B.

    2016-03-01

    The theoretical model of charged-particle stopping power for the Coulomb logarithm lnΛb ≥ 2 plasma [Phys. Rev. Lett., 20, 3059 (1993)] is extended to investigate the transport of the energetic protons in a compressed deuterium-tritium (DT) pellet mixed with heavy ion dopants. It shows that an increase of mixed-ion charge state and density ratio results in the substantial enhancement of the proton stopping power, which leads to a shorter penetration distance and an earlier appearance of the Bragg peak with a higher magnitude. The effect of hot-spot mix on the proton-driven fast ignition model is discussed. It is found that ignition time required for a small mixed hot-spot can be significantly reduced with slightly increased beam energy. Nevertheless, the ignition cannot maintain for a long time due to increasing alpha-particle penetration distance and energy loss from mechanical work and thermal conduction at high temperatures.

  4. Effect of metallic dopants on potassium acid phthalate (KAP) single crystals

    NASA Astrophysics Data System (ADS)

    Chithambaram, V.; Jerome Das, S.; Arivudai Nambi, R.; Srinivasan, K.; Krishnan, S.

    2010-06-01

    Optically transparent single crystals of Cu 2+ and Zn 2+ doped potassium acid phthalate (KAP) were grown in aqueous solution by slow evaporation technique at room temperature. Single crystal X-ray diffraction analysis confirmed the changes in the lattice parameters of the doped crystals. The presence of functional groups in the crystal lattice has been determined qualitatively by Fourier transform infrared (FTIR) analysis. Optical absorption studies revealed that the doped crystals possess very low absorption in the entire visible region. The dielectric constant has been studied as a function of frequency for the doped crystals at temperatures viz., 328, 348, 368 K. Further the influence of metal dopants on the dielectric behaviour has been studied which clearly exhibited the ferroelectric properties of the crystal.

  5. Simple structured hybrid WOLEDs based on incomplete energy transfer mechanism: from blue exciplex to orange dopant.

    PubMed

    Zhang, Tianyou; Zhao, Bo; Chu, Bei; Li, Wenlian; Su, Zisheng; Yan, Xingwu; Liu, Chengyuan; Wu, Hairuo; Gao, Yuan; Jin, Fangming; Hou, Fuhua

    2015-01-01

    Exciplex is well known as a charge transfer state formed between electron-donating and electron-accepting molecules. However, exciplex based organic light emitting diodes (OLED) often performed low efficiencies relative to pure phosphorescent OLED and could hardly be used to construct white OLED (WOLED). In this work, a new mechanism is developed to realize efficient WOLED with extremely simple structure by redistributing the energy of triplet exciplex to both singlet exciplex and the orange dopant. The micro process of energy transfer could be directly examined by detailed photoluminescence decay measurement and time resolved photoluminescence analysis. This strategy overcomes the low reverse intersystem crossing efficiency of blue exciplex and complicated device structure of traditional WOLED, enables us to achieve efficient hybrid WOLEDs. Based on this mechanism, we have successfully constructed both exciplex-fluorescence and exciplex-phosphorescence hybrid WOLEDs with remarkable efficiencies. PMID:25975371

  6. Novel ferroelectric liquid crystals consisting glassy liquid crystal as chiral dopants

    NASA Astrophysics Data System (ADS)

    Chen, Huang-Ming Philip; Tsai, Yun-Yen; Lin, Chi-Wen; Shieh, Han-Ping David

    2006-08-01

    A series of ferroelectric liquid crystals consisting new glassy liquid crystals (GLCs) as chiral dopants were prepared and evaluated for their potentials in fast switching ability less than 1 ms. The properties of pure ferroelectric glassy liquid crystals (FGLCs) and mixtures were reported in this paper. In particular, the novel FGLC possessing wide chiral smectic C mesophase over 100 °C is able to suppress smectic A phase of host. The mixture containing 2.0 % GLC-1 performs greater alignment ability and higher contrast ratio than R2301 (Clariant, Japan) in a 2 μm pre-made cell (EHC, Japan). These results indicate that novel FLC mixtures consisting glassy liquid crystals present a promising liquid crystal materials for fast switching field sequential color displays.

  7. 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.

  8. 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.

  9. Optical gain and laser generation in bismuth-doped silica fibers free of other dopants.

    PubMed

    Bufetov, Igor A; Melkumov, Mikhail A; Firstov, Sergey V; Shubin, Alexey V; Semenov, Sergey L; Vel'miskin, Vladimir V; Levchenko, Andrey E; Firstova, Elena G; Dianov, Evgeny M

    2011-01-15

    Luminescence emission and excitation spectra of bismuth-doped silica optical fibers free of other dopants have been obtained to construct an emission-excitation map in a wide wavelength range of 400-1600 nm. The main low-lying energy levels of the bismuth active centers in such fibers have been determined. For the first time (to our knowledge), optical gain and lasing have been obtained in such fibers. A gain of 8 dB has been achieved with a pump power of 340 mW, and a cw fiber laser emitting at 1460 nm with an output power of 40 mW and an efficiency of ≈3% has been created. PMID:21263488

  10. Effects of various dopants on NaCl and KCl glow curves

    NASA Astrophysics Data System (ADS)

    Davidson, A. T.; Kozakiewicz, A. G.; Derry, T. E.; Comins, J. D.; Suszynska, M.

    2004-06-01

    We have measured the thermoluminescence of a number of NaCl and KCl crystals following irradiation at ambient temperature with the same dose (10 kGy) of Co-60 γ rays. We compare the TL of pure samples and of samples doped with europium and calcium ions. In the case of NaCl, additional impurities (Ni, Pb, Sr and Cr) have been investigated. The effects of irradiation are determined using optical absorption and thermoluminescence. Factors investigated include the effects of different dopants on TL glow curves and the effects of thermal annealing samples at 400 °C before the irradiation. Changes in TL glow curves relating to changes in the state of aggregation of the impurities produced by pre-irradiation annealing are reported in this paper. Perhaps the most significant effect is a temperature shift of the main glow peak in pre-annealed compared to not pre-annealed samples in the case of Eu doped NaCl. The magnitude of the shift depends on the concentration of the Eu dopant. Shifts are also observed for Ni and Sr impurities in NaCl, but not for Ca and Cr impurities in NaCl. In the case of KCl, glow peaks generally occur at similar temperatures in doped samples and do not shift when doped samples are pre-annealed. Here the main effect of different impurities is to influence the size of the emission and not the structure of the glow curve. Results are discussed in terms of current theories of thermoluminescence.

  11. 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.

  12. Persistent dopants and phase segregation in organolead mixed-halide perovskites

    DOE PAGESBeta

    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 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

  13. 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).

  14. Low-cost copper complexes as p-dopants in solution processable hole transport layers

    NASA Astrophysics Data System (ADS)

    Kellermann, Renate; Taroata, Dan; Maltenberger, Anna; Hartmann, David; Brabec, Christoph J.; Schmid, Guenter

    2015-09-01

    We demonstrate the usage of the Lewis-acidic copper(II)hexafluoroacetylacetonate (Cu(hfac)2) and copper(II)trifluoroacetylacetonate (Cu(tfac)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 × 10-11 S/cm with a dopant concentration of only 2 mol% Cu(hfac)2 and 1.5 × 10-9 S/cm with 5 mol% Cu(tfac)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)2 and 5.6 lm/W with Cu(tfac)2) compared to the OLED with undoped spiro-TTB (3.9 lm/W). The OLED with Cu(hfac)2 doped spiro-TTB showed an over 8 times improved LT50 lifetime of 70 h at a starting luminance of 5000 cd/m2. The LT50 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. 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.

  16. 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+.

  17. Effects of Substitutional Dopants on the Photoresponse of a Polyoxotitanate Cluster.

    PubMed

    Hu, Junyi; Zhan, Lijie; Zhang, Guanyun; Zhang, Qun; Du, Lin; Tung, Chen-Ho; Wang, Yifeng

    2016-09-01

    In this paper, using a simple method, 17 isostructural polyoxotitanates (POTs) were synthesized, including the pristine [Ti12O16(O(i)Pr)16], the monodefected [Ti11O13(O(i)Pr)18], and the heterometal-doped [Ti11O14(O(i)Pr)17(ML)] (M = Mg, Ca, Zn, Cd, Co, or Ni; L = Cl, Br, I, or NO3). The electronic structures of these POTs were determined by UV-vis spectroscopy and DFT calculations. Upon UV irradiation of the POTs, electron spin resonance showed the formation of Ti(III) under anaerobic conditions and superoxide (O2(•-)) in the presence of O2. The photoactivities of the POTs were then probed with Ti(III) production and short-circuit photocurrent experiments. The photophysical processes were studied using steady-state and transient photoluminescence. The results show that within the very similar structures, the deexcitation processes of the photoexcited POTs can be greatly affected by the dopants, which result in enhanced or decreased photoactivities. Co and Ni doping enhances the absorption of the visible light accompanied by serious loss of UV photoactivities. On the other hand, a Ti vacancy (in [Ti11O13(O(i)Pr)18]) does not reduce the band gap of a POT but improves the UV photoactivities by serving as surface reaction site. The POTs were then used as molecular models of titanium oxide nanoparticles to understand some important issues relevant to doped titanate, i.e., coordination environment of the dopant metal, electronic structure, photoactivities, and photophysical processes. Our present findings suggest that for solar energy harvesting applications of titanium oxides like photocatalysis and solar cells substitution of titanium atoms by transition metal ions (like Co and Ni) to extend the absorption edges may not be an efficient way, while loading of Ti vacancies is very effective. PMID:27559825

  18. 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

  19. 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. PMID:22523948

  20. Effect of Sb dopant amount on the structure and electrocatalytic capability of Ti/Sb-SnO2 electrodes in the oxidation of 4-chlorophenol.

    PubMed

    Kong, Jiang-tao; Shi, Shao-yuan; Zhu, Xiu-ping; Ni, Jin-ren

    2007-01-01

    Ti/Sb-SnO2 anodes were prepared by thermal decomposition to examine the influence of the amount of Sb dopant on the structure and electrocatalytic capability of the electrodes in the oxidation of 4-chlorophenol. The physicochemical properties of the Sb-SnO2 coating were markedly influenced by different amounts of Sb dopant. The electrodes, which contained 5% Sb dopant in the coating, presented a much more homogenous surface and much smaller mud-cracks, compared with Ti/Sb-SnO2 electrodes containing 10% or 15% Sb dopant, which exibited larger mud cracks and pores on the surface. However, the main microstructure remained unchanged with the addition of the Sb dopant. No new crystal phase was observed by X-ray diffraction (XRD). The electrochemical oxidation of 4-chlorophenol on the Ti/SnO2 electrode with 5% Sb dopant was inclined to electrochemical combustion; while for those containing more Sb dopant, intermediate species were accumulated. The electrodes with 5% Sb dopant showed the highest efficiency in the bulk electrolysis of 4-chlorophenol at a current density of 20 mA/cm2 for 180 min; and the removal rates of 4-chlorophenol and COD were 51.0% and 48.9%, respectively. PMID:18232235

  1. 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.

  2. The role of the domain size and titanium dopant in nanocrystalline hematite thin films for water photolysis

    DOE PAGESBeta

    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 frommore » 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.« less

  3. Generation of core-shell structures and segregation of dopants in Si/SiO2 nanowires

    NASA Astrophysics Data System (ADS)

    Kim, Sunghyun; Park, Ji-Sang; Chang, K. J.

    2013-03-01

    Oxidized Si nanowires (SiNWs) are usually synthesized by subsequent thermal annealing of as-grown SiNWs. It has been observed that B diffusivity is enhanced during thermal annealing in SiNWs, similar to the phenomena called transient enhanced diffusion or oxidation enhanced diffusion in planar Si/SiO2 interfaces. However, previous theoretical studies have been focused on hydrogen or hydroxyl terminated SiNWs. In this work, we generate realistic atomic models for oxidized SiNWs in which crystalline Si core is sheathed by amorphous SiO2 by using a combined approach of classical molecular dynamics simulations with first-principles density functional calculations. For realistic core-shell structures, we investigate the stability and segregation behavior of B and P dopants. A single substitutional B is more stable in the Si core, with a very small energy variation with the radial position of B. On the other hand, B dopants easily segregate to the oxide shell with the aid of Si self-interstitials generated during thermal oxidation. In contrast to B dopants, P dopants prefer to reside in the Si core even in the presence of Si self-interstitials but tend to aggregate in the Si region near the interface, forming nearest-neighbor donor pairs which are electrically inactive.

  4. 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.

  5. 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.

  6. 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

    2016-01-01

    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

  7. 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.

  8. 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.

  9. Diffusion of ion-implanted group 4 n-type dopants in gallium arsenide and gallium/arsenide-based superlattices

    NASA Astrophysics Data System (ADS)

    Allen, Emily Lin

    1992-09-01

    As semiconductor device dimensions shrink, understanding and controlling dopant diffusion becomes increasingly important. For submicron FET's made in GaAs, dopant diffusion during post-implant anneal is undesirable. In addition, impurity induced intermixing of III-V heterostructures for optoelectronic devices requires a series of carefully controlled diffusion steps. A more complete understanding of the diffusion mechanisms of dopants and point defects in both GaAs and Al(x)Ga(1-x)As is thus required for several advanced technologies. Most of the published parameters for diffusion of dopants in III-V compound semiconductors are from thin film or vapor source diffusions. The effect of implant damage and extended defects on diffusion of implanted dopants in GaAs and Al(x)Ga(1-x)As has not been extensively studied. In this work we measure the carrier concentrations and diffusivities of the ion-implanted Group IV dopants Sn, Ge and Si in GaAs and Al(x)Ga(1-x)As, using SIMS, polaron and SUPREM 3.5 simulations. In the substrate, diffusion is modeled by an effective diffusivity which depends on the square of the electron concentration (n), due to enhancement of the negatively charged Ga vacancy concentration by the n-type doping. In the near-surface implanted region diffusion is suppressed for doses greater than 1 x 10(exp 14)/sq cm. The carrier concentrations for Sn implants are anomalously high in this region, and anomalously low for Ge and Si. Transmission electron microscopy shows that precipitates and dislocations form in the implanted region during annealing for doses greater than 1 x 10(exp 14)/sq cm. These extended defects may influence dopant diffusion by controlling the generation and recombination of point defects. The carrier concentration-dependent diffusion model is applied to interdiffusion of Al and Ga in AlAs/Al(x)Ga(1-x)As superlattice structures. We show that interdiffusion is enhanced more under an oxide film than under a nitride film, while a tungsten

  10. 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.

  11. Infrared horizon locator

    NASA Technical Reports Server (NTRS)

    Jalink, A., Jr. (Inventor)

    1973-01-01

    A precise method and apparatus for locating the earth's infrared horizon from space that is independent of season and latitude is described. First and second integrations of the earth's radiance profile are made from space to earth with the second delayed with respect to the first. The second integration is multiplied by a predetermined constant R and then compared with the first integration. When the two are equal the horizon is located.

  12. 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.

  13. Inuence of Gold-Copper Alloy Catalyst Composition on Crystal Growth and Dopant Distribution in Silicon and Germanium Nanowires

    NASA Astrophysics Data System (ADS)

    Connell, Justin G.

    A combination of local electrode atom probe tomography (LEAP) and transmission electron microscopy characterization were used to investigate growth of and dopant incorporation in silicon and germanium nanowires (Si and GeNWs) via the vapor-liquid- solid (VLS) mechanism. A sample structure was developed that enabled isolation of the catalyst-mediated contribution to doping in individual nanowires during LEAP analysis. As a result, the distribution coefficient - a thermodynamic quantity describing axial junction abruptness - was measured in nanowires for the first time, providing a fundamental framework for comparison of junction abruptness in nanowires. These investigations also enabled the identification of a previously unknown radial anisotropy in dopant incorporation through the catalyst, with variations in dopant concentration across the VLS-defined diameter of the nanowire as large as two orders of magnitude. Finite element modeling of the doping process, coupled with in situ TEM observations reported in the literature, suggests that this radially inhomogeneous dopant distribution is a direct consequence of growth from a faceted liquid-solid interface, rather than the commonly assumed planar interface. Au-Cu alloy catalysts were explored as alternatives to Au-catalyzed VLS nanowire growth as a means to alleviate or eliminate axial and radial doping gradients in nanowires. Both an aqueous solution and electron beam lithographic method for creating Au-Cu alloy catalysts of controlled composition were developed, and GeNW growth was demonstrated from both types of catalyst. LEAP characterization of Au-Cu alloy catalyzed P-doped GeNWs revealed that alloying with Cu results in more abrupt axial doping junctions, as well as a more homogeneous radial distribution of dopants within the VLS-defined diameter of the nanowire.

  14. 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.

  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. Cable fault locator research

    NASA Astrophysics Data System (ADS)

    Cole, C. A.; Honey, S. K.; Petro, J. P.; Phillips, A. C.

    1982-07-01

    Cable fault location and the construction of four field test units are discussed. Swept frequency sounding of mine cables with RF signals was the technique most thoroughly investigated. The swept frequency technique is supplemented with a form of moving target indication to provide a method for locating the position of a technician along a cable and relative to a suspected fault. Separate, more limited investigations involved high voltage time domain reflectometry and acoustical probing of mine cables. Particular areas of research included microprocessor-based control of the swept frequency system, a microprocessor based fast Fourier transform for spectral analysis, and RF synthesizers.

  17. 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.

  18. Dopant induced variations in microstructure and optical properties of CeO{sub 2} nanoparticles

    SciTech Connect

    Mohanty, Bhaskar Chandra; Lee, Jong Won; Yeon, Deuk-Ho; Jo, Yeon-Hwa; Kim, Jong Hak; Cho, Yong Soo

    2011-06-15

    Research highlights: {yields} Dopant (Zr{sup 4+}, La{sup 3+}, and Ca{sup 2+}) induced phase stability, and changes in microstructure and optical properties of CeO{sub 2} nanoparticles have been studied. {yields} The nanoparticles were prepared by hydrothermal synthesis of nitrate solutions. {yields} The results show modification of the unit cell parameter by -0.39, +0.83 and +0.16% for doping of 20% Zr{sup 4+}, La{sup 3+}, and Ca{sup 2+}, respectively. {yields} For each batch prepared, nanoparticles with a narrow size distribution of 5-15 nm have been obtained. These particles are single crystals mostly having polygonal two-dimensional projections. {yields} UV-visible spectra of doped particles exhibit shift of the absorption edge and absorption peak with respect to those of the undoped ones and has been attributed to compensation of Ce{sup 3+} and decreasing crystallite size as result of doping. -- Abstract: Nanocrystalline CeO{sub 2} particles doped in the range of 0-20% of Ca{sup 2+}, La{sup 3+}, and Zr{sup 4+} have been prepared from hydrothermal synthesis of nitrate solutions at 200 {sup o}C and the influences of the dopants on microstructure and optical properties of the nanoparticles have been investigated. The unit cell parameter is found to be modified by -0.39, +0.83 and +0.16% for doping of 20% Zr{sup 4+}, La{sup 3+}, and Ca{sup 2+}, respectively. For each batch prepared, nanoparticles with a narrow size distribution of 5-15 nm have been obtained. A high-resolution transmission electron microscopy investigation reveals that these particles are single crystals mostly having hexagonal, square or circular two-dimensional projections. UV-visible spectra of doped powders exhibit shift of the absorption edge and absorption peak with respect to those of the undoped CeO{sub 2} particles and has been attributed to compensation of Ce{sup 3+} and decreasing crystallite size as result of doping.

  19. 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.

  20. 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...

  1. Location of Spirit's Home

    NASA Technical Reports Server (NTRS)

    2004-01-01

    This image shows where Earth would set on the martian horizon from the perspective of the Mars Exploration Rover Spirit if it were facing northwest atop its lander at Gusev Crater. Earth cannot be seen in this image, but engineers have mapped its location. This image mosaic was taken by the hazard-identification camera onboard Spirit.

  2. Random Dopant Induced Threshold Voltage Lowering and Fluctuations in Sub-0.1 (micron)meter MOSFET's: A 3-D 'Atomistic' Simulation Study

    NASA Technical Reports Server (NTRS)

    Asenov, Asen

    1998-01-01

    A three-dimensional (3-D) "atomistic" simulation study of random dopant induced threshold voltage lowering and fluctuations in sub-0.1 microns MOSFET's is presented. For the first time a systematic analysis of random dopant effects down to an individual dopant level was carried out in 3-D on a scale sufficient to provide quantitative statistical predictions. Efficient algorithms based on a single multigrid solution of the Poisson equation followed by the solution of a simplified current continuity equation are used in the simulations. The effects of various MOSFET design parameters, including the channel length and width, oxide thickness and channel doping, on the threshold voltage lowering and fluctuations are studied using typical samples of 200 atomistically different MOSFET's. The atomistic results for the threshold voltage fluctuations were compared with two analytical models based on dopant number fluctuations. Although the analytical models predict the general trends in the threshold voltage fluctuations, they fail to describe quantitatively the magnitude of the fluctuations. The distribution of the atomistically calculated threshold voltage and its correlation with the number of dopants in the channel of the MOSFET's was analyzed based on a sample of 2500 microscopically different devices. The detailed analysis shows that the threshold voltage fluctuations are determined not only by the fluctuation in the dopant number, but also in the dopant position.

  3. Point Defect Based Two Dimensional Modeling of Dislocation Loops and Stress Effects on Dopant Diffusion in Silicon.

    NASA Astrophysics Data System (ADS)

    Park, Heemyong

    Dopant diffusion in silicon is studied and modeled on the basis of point defect kinetics associated with ion implantation damage. Point defect parameters are extracted from the modeling of transient enhanced dopant diffusion due to oxidation and low dose implant damage without extended defects. The theory of dopant-defect pairing is found to be crucial in modeling the implantation damage effects, and the effective binding energies for boron-defect and phosphorus-defect pairs are experimentally determined. The extracted parameters provide an important reference for further modeling of diffusion under high dose implantation conditions involving extended defects. Evolution of dislocation loops through their interaction with point defects is modeled in two dimensions by accounting for the pressure around the ensemble of loops as well as loop coalescence and dissolution as observed in transmission electron microscopy (TEM) measurements. Assuming an asymmetric triangular density distribution of periodically oriented circular dislocation loops leads to estimation of the effective pressure and an efficient model for the statistical loop -to-loop interaction. Simulation with the model correctly predicts variation of the number of captured silicon atoms and the radii and densities of the dislocation loops during oxidation in agreement with the TEM data. It also shows significant reduction in oxidation enhanced diffusion of boron in a buried layer in agreement with measured profiles, confirming the role of dislocation loops as an efficient sink for interstitials. A point-defect-based atomistic model for the stress effects on dopant diffusion is developed by accounting for variation in formation enthalpy of dopant-defect pairs due to the hydrostatic pressure. Binding energies and diffusivities of dopant-defect pairs under the pressure are modeled and incorporated into diffusion equations. Boron segregation around dislocation loops in silicon is explained by the pressure

  4. Substance Abuse Treatment Facility Locator

    MedlinePlus

    ... Health Services Locator Buprenorphine Physician Locator Find a Facility in Your State To locate the drug and ... Service . Privacy Policy . Home | About the Locator | Find Facilities Near You | Find Facilities by City, County, State ...

  5. 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.

  6. 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.

  7. Effect of ferromagnetic dopants on laser induced optical parameters of bismuth doped CaS phosphors

    NASA Astrophysics Data System (ADS)

    Kumar, Sunil; Jeon, H. C.; Kang, T. W.; Devraj; Sekhon, Jaskanwal; Verma, N. K.; Bhatti, H. S.; Choubey, Ravi Kant

    2015-12-01

    The effect of ferromagnetic impurities (Fe, Co, and Ni) on the laser induced optical parameters of CaS:Bi phosphors has been studied. The studies were done for the Bismuth concentration of 0.4% in CaS phosphors due to the highest value of oscillator strength as reported earlier. The studies were conducted using nitrogen laser as a excitation source in a pulse excitation mode at room temperature. Appreciable changes in the optical properties have been detected after the addition of ferromagnetic impurities in the CaS phosphor doped with bismuth. The nature of the multiple exponential decays remains the same even after the addition of ferromagnetic impurities in the present case of bismuth-doped phosphors which is in agreement with the earlier work reported on other dopants in sulfide type phosphors. As ferromagnetic impurities enhanced the optical parameters of CaS phosphors appreciably, these studies shows that they can be used to control the transition probability and the corresponding optical parameters.

  8. Self-passivation mechanisms in clusters of N dopants in SiC

    NASA Astrophysics Data System (ADS)

    Rurali, R.; Hernández, E.; Godignon, P.; Rebollo, J.; Ordejòn, P.

    2004-02-01

    Although having proved to be one of the most successful n-type dopant in SiC for many applications, nitrogen exhibits a troublesome nature when a high-dose implantation is required. Experimental measurements showed that phosphorus is more suited in such conditions. We proposed previously that the reason may be the self-passivation of the N clusters that are likely to form in the high-concentration limit. In this paper we discuss in details the passivation mechanisms that are relevant for the different N aggregates that can form and that are the ultimate responsible of the low activation rate of high-dose N-implanted SiC. We have found that all the N complexes that are likely to form in SiC do self-passivate. However, the passivation mechanisms are not always the same and they are due in turn to the formation of a bound molecule or to a charge-trapping effect.

  9. 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.

  10. 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. PMID:23003051

  11. Effects of Dopant Concentration on the Mobilities of Molecularly Doped Polymers

    NASA Astrophysics Data System (ADS)

    Gruenbaum, W. T.; Lin, L.-B.; Magin, E. H.; Borsenberger, P. M.

    1997-12-01

    Hole mobilities have been measured for poly(styrene) (PS) doped with triphenylmethane (TPM) and triarylamine (TAA) derivatives with the same dipole moment. The results are described by a formalism based on disorder. According to the formalism, charge transport occurs by hopping through a manifold of localized states that are distributed in energy. The key parameter of the formalism is the width of the hopping site energies. For TPM doped PS, the widths decrease with increasing dilution while for TAA doped PS, the widths increase with dilution. The widths are described by a model based on dipolar disorder. The model is based on the assumption that the total width is comprised of a dipolar component and a van der Waals component. The selection of dopant molecules with the same dipole moment provides a method by which the van der Waals component can be determined from an analysis of the total widths of both. For TPM doped PS, the van der Waals component is constant while for TAA doped PS the van der Waals component increases with increasing dilution. The difference is described by a charge delocalization argument.

  12. Enhanced thermoelectric performance of PEDOT:PSS flexible bulky papers by treatment with secondary dopants.

    PubMed

    Mengistie, Desalegn A; Chen, Chang-Hsiao; Boopathi, Karunakara M; Pranoto, Ferry W; Li, Lain-Jong; Chu, Chih-Wei

    2015-01-14

    For inorganic thermoelectric materials, Seebeck coefficient and electrical conductivity are interdependent, and hence optimization of thermoelectric performance is challenging. In this work we show that thermoelectric performance of PEDOT:PSS can be enhanced by greatly improving its electrical conductivity in contrast to inorganic thermoelectric materials. Free-standing flexible and smooth PEDOT:PSS bulky papers were prepared using vacuum-assisted filtration. The electrical conductivity was enhanced to 640, 800, 1300, and 1900 S cm(-1) by treating PEDOT:PSS with ethylene glycol, polyethylene glycol, methanol, and formic acid, respectively. The Seebeck coefficient did not show significant variation with the tremendous conductivity enhancement being 21.4 and 20.6 μV K(-1) for ethylene glycol- and formic acid-treated papers, respectively. This is because secondary dopants, which increase electrical conductivity, do not change oxidation level of PEDOT. A maximum power factor of 80.6 μW m(-1) K(-2) was shown for formic acid-treated samples, while it was only 29.3 μW m(-1) K(-2) for ethylene glycol treatment. Coupled with intrinsically low thermal conductivity of PEDOT:PSS, ZT ≈ 0.32 was measured at room temperature using Harman method. We investigated the reasons behind the greatly enhanced thermoelectric performance. PMID:25475257

  13. 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.

  14. Hydrogen Storage Properties of Lithium Aluminohydride modified by dopants and mechanochemistry

    SciTech Connect

    Keita Hosokawa

    2002-05-30

    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 NaAlH{sub 4} below 70 atm. They achieved 4 wt.% H{sub 2} reversible capacity by doping NaAlH{sub 4} 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, Zr{sub 27}Ti{sub 9}Ni{sub 38}V{sub 5}Mn{sub 16}Cr{sub 5}, LaNi{sub 4.85}Sn{sub 0.15}, Al{sub 3}Ti, and PdCl{sub 2} were combined with LiAlH{sub 4} by ball-milling to study whether or not LiAlH{sub 4} 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 LiAlH{sub 4} and Li{sub 3}AlH{sub 6} 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.

  15. Hydrogen Storage Properties of Lithium Aluminohydride Modified by Dopants and Mechanochemistry

    SciTech Connect

    Ketia Hosokawa

    2002-06-27

    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 NaAlH{sub 4} below 70 atm. They achieved 4 wt.% H{sub 2} reversible capacity by doping NaAlH{sub 4} 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, Zr{sub 27}Ti{sub 9}Ni{sub 38}V{sub 5}Mn{sub 16}Cr{sub 5}, LaNi{sub 4.85}Sn{sub 0.15}, Al{sub 3}Ti, and PdCl{sub 2} were combined with LiAlH{sub 4} by ball-milling to study whether or not LiAlH{sub 4} 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 LiAlH{sub 4} and Li{sub 3}AlH{sub 6} 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.

  16. 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. PMID:23901106

  17. White organic light-emitting devices employing phosphorescent iridium complex as RGB dopants

    NASA Astrophysics Data System (ADS)

    Song, Ruili; Duan, Yu; Chen, Shufen; Zhao, Yi; Hou, Jingying; Liu, Shiyong

    2007-07-01

    Efficient phosphorescent white organic light-emitting diodes (WOLEDs) were realized by using a bright blue-emitting layer, iridium (III) bis-[(4,6- di-fluoropheny)-pyridinato-N, C2'] picolinate doped 4.4'-bis-(9-carbazolyl)-2, 2'-dimethyl-biphenyl doped, together with tris-(2-phenylpyridine) iridium and bis-(1-phenyl-isoquinoline) acetylacetonate iridium (III) are codoped into a 4,4'-N,N'-dicarbazole- biphenyl layer to provide blue, green and red emission for colour mixing. The device emission colour is controlled by varying dopant concentrations and the thicknesses of blue and green-red layers as well as tuning the thickness of an exciton-blocking layer. The maximum luminance and power efficiency of the WOLED are 42700 cd m-2 at 17 V and 8.48 lm W-1 at 5 V, respectively. The Commission Internationale de 1'Eclairage (CIE) chromaticity coordinate changes from (0.41, 0.42) to (0.37, 0.39) when the luminance ranges from 1000 cd m-2 to 30000 cd m-2.

  18. Copper phthalocyanine as an efficient dopant in development of solar cells

    SciTech Connect

    Inigo, A.R.; Xavier, F.P.; Goldsmith, G.J.

    1997-05-01

    Organic semiconductors having conjugate bonds, such as phthalocyanines, are well known photoconductors. Phthalocyanines absorb light on either side of blue-green region in the visible spectrum. And polyaniline which has conjugate bonds is photosensitive. When polyaniline thin films are prepared with copper phthalocyanine powder the magnitude of absorption of the films not only increases but also broadens, indicating a wide absorption region between 1.7 and 2.3 eV and above 3.0 eV of the visible spectrum. Thus copper phthalocyanine in preparation of thin films is shown to smooth the broadening effect in absorption of solar cells. Attempts are underway to increase the absorption on either end of the visible spectrum, viz., infrared as well as ultraviolet regions, using suitable dopants. This would ensure the overall efficiency of solar cells made of organic photoconductive materials to absorb solar energy from infrared to ultraviolet regions of the optical spectrum, thereby making them more efficient solar energy converters.

  19. 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.

  20. Enhancement of magnetization damping coefficient of permalloy thin films with dilute Nd dopants

    NASA Astrophysics Data System (ADS)

    Luo, C.; Feng, Z.; Fu, Y.; Zhang, W.; Wong, P. K. J.; Kou, Z. X.; Zhai, Y.; Ding, H. F.; Farle, M.; Du, J.; Zhai, H. R.

    2014-05-01

    For spintronics application, which requires fast field switching, it is important to have a kind of soft magnetic material with large damping coefficient. Here, we present the studies of the Nd dopant-level-dependent damping coefficient of Ndx-Py(1-x) thin films (30 nm) in a dilute region utilizing ferromagnetic resonance (FMR). With the Nd content increasing, the film structure was found to be changing from polycrystalline to amorphous when the Nd content is around 3.4%. Meanwhile, the magnetization decreases linearly. Interestingly, we find that along the easy axis, both low coercivity and high hysteresis squareness are simultaneously maintained in the system; i.e., the magnetic softness has been well kept. By theoretical fitting of the angular dependence of the FMR field, the first- and second-order magnetic anisotropy constants, K1 and K2, and the Lande g factor are obtained and discussed quantitatively. The measurements of angular and frequency dependence of the ferromagnetic resonance linewidth, as well as the theoretical fitting by considering the contributions of Gilbert damping, two-magnon scattering, and inhomogeneous broadening, show that the damping coefficient α increases rapidly (about 25-fold) as the Nd content increases to 11.6%, which is mainly due to the enhanced spin-orbit coupling by the Nd additives, supported by x-ray magnetic circular dichroism measurements.

  1. Optical activity and defect/dopant evolution in ZnO implanted with Er

    NASA Astrophysics Data System (ADS)

    Azarov, Alexander; Galeckas, Augustinas; Hallén, Anders; Kuznetsov, Andrej; Monakhov, Edouard; Svensson, Bengt G.

    2015-09-01

    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.

  2. 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.

  3. 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.

  4. Impact of stochastic accelerations on dopant segregation in microgravity semiconductor crystal growth

    NASA Astrophysics Data System (ADS)

    Ruiz, X.; Bitlloch, P.; Ramírez-Piscina, L.; Casademunt, J.

    2012-09-01

    The residual accelerations that are typically present in microgravity environments (g-jitters) contain a broad spectrum of frequencies and may be modeled as stochastic processes. Their effects on the quality of the semiconductor crystals are analyzed here quantitatively with direct numerical simulation. In particular we focus on the dopant segregation effects due to thermosolutal convection as a function of the parameters characterizing the statistics of the stochastic force. The numerical simulation is specified for material parameters of two doped semiconductors (Ge:Ga and GaAs:Se) in realistic conditions of actual microgravity environments. As a general result, we show that the segregation response is strongly dominated by the low-frequency part of the g-jitter spectrum. In addition, we develop a simplified model of the problem based on linear response theory that projects the dynamics into very few effective modes. The model captures remarkably well the segregation effects for an arbitrary time-dependent acceleration of small amplitude, while it implies an enormous reduction of computer demands. This model could be helpful to analyze results from real accelerometric signals and also as a predictive tool for experimental design.

  5. Electronic structure and chemical nature of oxygen dopant states in carbon nanotubes.

    PubMed

    Ma, Xuedan; Adamska, Lyudmyla; Yamaguchi, Hisato; Yalcin, Sibel Ebru; Tretiak, Sergei; Doorn, Stephen K; Htoon, Han

    2014-10-28

    We performed low temperature photoluminescence (PL) studies on individual oxygen-doped single-walled carbon nanotubes (SWCNTs) and correlated our observations to electronic structure simulations. Our experiment reveals multiple sharp asymmetric emission peaks at energies 50-300 meV red-shifted from that of the E11 bright exciton peak. Our simulation suggests an association of these peaks with deep trap states tied to different specific chemical adducts. In addition, oxygen doping is also observed to split the E11 exciton into two or more states with an energy splitting <40 meV. We attribute these states to dark states that are brightened through defect-induced symmetry breaking. While the wave functions of these brightened states are delocalized, those of the deep-trap states are strongly localized and pinned to the dopants. These findings are consistent with our experimental observation of asymmetric broadening of the deep trap emission peaks, which can result from interaction between pinned excitons and one-dimensional phonons. Exciton pinning also increases the sensitivity of the deep traps to the local dielectric environment, leading to a large inhomogeneous broadening. Observations of multiple spectral features on single nanotubes indicate the possibility of different chemical adducts coexisting on a given nanotube. PMID:25265272

  6. Charge transport in molecularly doped polymers at low dopant concentrations: simulation and experiment

    NASA Astrophysics Data System (ADS)

    Hartenstein, B.; Bässler, H.; Heun, S.; Borsenberger, P.; Van der Auweraer, M.; De Schryver, F. C.

    1995-02-01

    A new computational technique has been developed to simulate charge transport in dilute, energetically random, media. The results predict that in materials containing 15-20% hopping sites, the transition from field-assisted to field-saturated drift occurs within a field range of 10 5-10 6 V/cm, lower values referring to lower degrees of energetic disorder. Experimental results are reported for N,N'-diphenyl-N,N'-bis(3-methylphenyl)-[1,1'-biphenyl]-4,4'-diamine (TPD) and 5'-[4-[bis(4-methylphenyl)amino]-phenyl]-N,N,N',N'-tetrakis (4-ethylphenyl) [1,1':3',1″-terphenyl'-4,rt'-diamine (EFTP) doped in either a polycarbonate (PC) or poly(styrene) (PS). While TPD doped PS fulfills all criteria of disorder controlled hopping, a superposition of disorder and polaron effects has to be invoked for EFTP in both PC or PS, the latter resulting from coupling of the charge transfer process to a torsional mode of the dopant molecule. Criteria to separate disorder and polaron effects in experimental data are briefly outlined.

  7. Investigation of lauric acid dopant as a novel carbon source in MgB 2 wire

    NASA Astrophysics Data System (ADS)

    Lee, C. M.; Lee, S. M.; Park, G. C.; Joo, J.; Lim, J. H.; Kang, W. N.; Yi, J. H.; Jun, B.-H.; Kim, C.-J.

    2010-11-01

    We fabricated lauric acid (LA) doped MgB 2 wires and investigated the effects of the LA doping. For the fabrication of the LA-doped MgB 2 wires, B powder was mixed with LA at 0-5 wt.% of the total amount of MgB 2 using an organic solvent, dried, and then the LA-treated B and Mg powders were mixed stoichiometrically. The powder mixture was loaded into an Fe tube and the assemblage was drawn and sintered at 900 °C for 3 h under an argon atmosphere. We observed that the LA doping induced the substitution of C for the B sites in MgB 2 and that the actual content of C increased monotonically with increasing LA doping level. The LA-doped MgB 2 wires exhibited a lower critical temperature ( Tc), but better critical current density ( Jc) behavior in a high magnetic field: the 5 wt.% LA-doped sample had a Jc value of 5.32 × 10 3 A/cm 2, which was 2.17 times higher than that of the pristine sample (2.45 × 10 3 A/cm 2) at 5 K and 6 T, suggesting that LA is an effective C dopant in MgB 2 for enhancing the high-field Jc performance.

  8. 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.

  9. Site location of Al-dopant in ZnO lattice by exploiting the structural and optical characterisation of ZnO:Al thin films

    NASA Astrophysics Data System (ADS)

    Nakrela, A.; Benramdane, N.; Bouzidi, A.; Kebbab, Z.; Medles, M.; Mathieu, C.

    The zinc oxide thin films, highly transparent, doped aluminium were prepared on glass substrates by the reactive chemical spray method. The incorporation nature of Al atoms in the ZnO lattice was determined by X-ray diffraction and optical analyses. Indeed, for low doping ⩽2%, the results of X-ray spectra analysis show a simultaneous reduction of lattice parameters (a and c), this variation, which follows VEGARD's law, tends to indicate a substitution of Zn by Al. By against for doping >2% the increase in the lattice parameters thus the grain sizes, in accordance with the VEGARD's law can be explained by occupation of the interstitial sites by Al atoms. Beyond 4%, the material tends to get disorderly and the crystallites orientation is random. The studied optical properties show that the variation of the optical gap follows a law of the x3/2 form for x < 3% (x is the aluminium atom fraction incorporated in the ZnO lattice). The granular structure is fairly visible and some local growths are disrupted. The crystallite size at low enlargement is coherent with the XRD results.

  10. Dipole Well Location

    Energy Science and Technology Software Center (ESTSC)

    1998-08-03

    The problem here is to model the three-dimensional response of an electromagnetic logging tool to a practical situation which is often encountered in oil and gas exploration. The DWELL code provide the electromagnetic fields on the axis of a borehole due to either an electric or a magnetic dipole located on the same axis. The borehole is cylindrical, and is located within a stratified formation in which the bedding planes are not horizontal. The anglemore » between the normal to the bedding planes and the axis of the borehole may assume any value, or in other words, the borehole axis may be tilted with respect to the bedding planes. Additionally, all of the formation layers may have invasive zones of drilling mud. The operating frequency of the source dipole(s) extends from a few Hertz to hundreds of Megahertz.« less

  11. Electric current locator

    DOEpatents

    King, Paul E.; Woodside, Charles Rigel

    2012-02-07

    The disclosure herein provides an apparatus for location of a quantity of current vectors in an electrical device, where the current vector has a known direction and a known relative magnitude to an input current supplied to the electrical device. Mathematical constants used in Biot-Savart superposition equations are determined for the electrical device, the orientation of the apparatus, and relative magnitude of the current vector and the input current, and the apparatus utilizes magnetic field sensors oriented to a sensing plane to provide current vector location based on the solution of the Biot-Savart superposition equations. Description of required orientations between the apparatus and the electrical device are disclosed and various methods of determining the mathematical constants are presented.

  12. Dipole Well Location

    SciTech Connect

    Newman, Gregory

    1998-08-03

    The problem here is to model the three-dimensional response of an electromagnetic logging tool to a practical situation which is often encountered in oil and gas exploration. The DWELL code provide the electromagnetic fields on the axis of a borehole due to either an electric or a magnetic dipole located on the same axis. The borehole is cylindrical, and is located within a stratified formation in which the bedding planes are not horizontal. The angle between the normal to the bedding planes and the axis of the borehole may assume any value, or in other words, the borehole axis may be tilted with respect to the bedding planes. Additionally, all of the formation layers may have invasive zones of drilling mud. The operating frequency of the source dipole(s) extends from a few Hertz to hundreds of Megahertz.

  13. Underwater hydrophone location survey

    NASA Technical Reports Server (NTRS)

    Cecil, Jack B.

    1993-01-01

    The Atlantic Undersea Test and Evaluation Center (AUTEC) is a U.S. Navy test range located on Andros Island, Bahamas, and a Division of the Naval Undersea Warfare Center (NUWC), Newport, RI. The Headquarters of AUTEC is located at a facility in West Palm Beach, FL. AUTEC's primary mission is to provide the U.S. Navy with a deep-water test and evaluation facility for making underwater acoustic measurements, testing and calibrating sonars, and providing accurate underwater, surface, and in-air tracking data on surface ships, submarines, aircraft, and weapon systems. Many of these programs are in support of Antisubmarine Warfare (ASW), undersea research and development programs, and Fleet assessment and operational readiness trials. Most tests conducted at AUTEC require precise underwater tracking (plus or minus 3 yards) of multiple acoustic signals emitted with the correct waveshape and repetition criteria from either a surface craft or underwater vehicle.

  14. X-ray photoelectron diffraction study of dopant effects in La{sub 0.7}X{sub 0.3}MnO{sub 3} (X = La, Sr, Ca, Ce) thin films

    SciTech Connect

    Raisch, C.; Glaser, M.; Chasse, T.; Langheinrich, C.; Chasse, A.; Werner, R.; Kleiner, R.; Koelle, D.

    2013-02-14

    We present and discuss element-specific x-ray photoelectron diffraction (XPD) patterns of La, Mn, O and the dopant ions Ca, Sr and Ce of various La{sub 0.7}X{sub 0.3}MnO (LXMO) films grown epitaxially on SrTiO{sub 3}(001) substrates. The recorded XPD polar scans are explained in the framework of multiple-scattering cluster calculations, where in general a very good agreement between experimental and theoretical data has been found. Results for all thin films are compatible with a tetragonally distorted cubic perovskite structure with similar MnO{sub 6} network. Strong evidence for Mn-site termination was found in all thin films. Dopant locations on A-type sites were clearly confirmed for Sr in LSMO and Ca in LCMO films by means of XPD polar scans. The absence of surface-sensitive Ce3d diffraction features for Ce in LCeMO points to non-equivalent Ce sites and related near-surface disorder.

  15. Marine cable location system

    SciTech Connect

    Ottsen, H.; Barker, Th.

    1985-04-23

    An acoustic positioning system for locating a marine cable at an exploration site employs a plurality of acoustic transponders, each having a characteristic frequency, at spaced-apart positions along the cable. A marine vessel measures the depth to the transponders as the vessel passes over the cable and measures the slant range from the vessel to each of the acoustic transponders as the vessel travels in a parallel and horizontally offset path to the cable.

  16. Magnetic Location Indicator

    NASA Technical Reports Server (NTRS)

    Stegman, Thomas W.

    1992-01-01

    Ferrofluidic device indicates point of highest magnetic-flux density in workspace. Consists of bubble of ferrofluid in immiscible liquid carrier in clear plastic case. Used in flat block or tube. Axes of centering circle on flat-block version used to mark location of maximum flux density when bubble in circle. Device used to find point on wall corresponding to known point on opposite side of wall.

  17. Ammonia Leak Locator Study

    NASA Technical Reports Server (NTRS)

    Dodge, Franklin T.; Wuest, Martin P.; Deffenbaugh, Danny M.

    1995-01-01

    The thermal control system of International Space Station Alpha will use liquid ammonia as the heat exchange fluid. It is expected that small leaks (of the order perhaps of one pound of ammonia per day) may develop in the lines transporting the ammonia to the various facilities as well as in the heat exchange equipment. Such leaks must be detected and located before the supply of ammonia becomes critically low. For that reason, NASA-JSC has a program underway to evaluate instruments that can detect and locate ultra-small concentrations of ammonia in a high vacuum environment. To be useful, the instrument must be portable and small enough that an astronaut can easily handle it during extravehicular activity. An additional complication in the design of the instrument is that the environment immediately surrounding ISSA will contain small concentrations of many other gases from venting of onboard experiments as well as from other kinds of leaks. These other vapors include water, cabin air, CO2, CO, argon, N2, and ethylene glycol. Altogether, this local environment might have a pressure of the order of 10(exp -7) to 10(exp -6) torr. Southwest Research Institute (SwRI) was contracted by NASA-JSC to provide support to NASA-JSC and its prime contractors in evaluating ammonia-location instruments and to make a preliminary trade study of the advantages and limitations of potential instruments. The present effort builds upon an earlier SwRI study to evaluate ammonia leak detection instruments [Jolly and Deffenbaugh]. The objectives of the present effort include: (1) Estimate the characteristics of representative ammonia leaks; (2) Evaluate the baseline instrument in the light of the estimated ammonia leak characteristics; (3) Propose alternative instrument concepts; and (4) Conduct a trade study of the proposed alternative concepts and recommend promising instruments. The baseline leak-location instrument selected by NASA-JSC was an ion gauge.

  18. 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.

  19. High-performance germanium n+/p junction by nickel-induced dopant activation of implanted phosphorus at low temperature

    NASA Astrophysics Data System (ADS)

    Wei, Huang; Chao, Lu; Jue, Yu; Jiang-Bin, Wei; Chao-Wen, Chen; Jian-Yuan, Wang; Jian-Fang, Xu; Chen, Wang; Cheng, Li; Song-Yan, Chen; Chun-Li, Liu; Hong-Kai, Lai

    2016-05-01

    High-performance Ge n+/p junctions were fabricated at a low formation temperature from 325 °C to 400 °C with a metal(nickel)-induced dopant activation technique. The obtained NiGe electroded Ge n+/p junction has a rectification ratio of 5.6× 104 and a forward current of 387 A/cm2 at ‑1 V bias. The Ni-based metal-induced dopant activation technique is expected to meet the requirement of the shallow junction of Ge MOSFET. Project supported by the National Natural Science Foundation of China (Grant Nos. 61176092 and 61474094), the National Basic Research Program of China (Grant Nos. 2012CB933503 and 2013CB632103), and the National Natural Science Foundation of China–National Research Foundation of Korea Joint Research Project (Grant No. 11311140251).

  20. Spontaneous organisation of ZnS nanoparticles into monocrystalline nanorods with highly enhanced dopant-related emission

    NASA Astrophysics Data System (ADS)

    Manzoor, K.; Aditya, V.; Vadera, S. R.; Kumar, N.; Kutty, T. R. N.

    2005-07-01

    A natural self-assembly process of semiconductor nanoparticles leading to the formation of doped, monocrystalline nanorods with highly enhanced dopant-related luminescence properties is reported. ˜4 nm sized, polycrystalline ZnS nanoparticles of zinc-blende (cubic) structure, doped with Cu+-Al3+ or Mn2+ have been aggregated in the aqueous solution and grown into nanorods of length ˜400 nm and aspect ratio ˜12. Transmission electron microscopic (TEM) images indicate crystal growth mechanisms involving both Ostwald-ripening and particle-to-particle oriented-attachment. Sulphur sulphur catenation is proposed for the covalent-linkage between the attached particles. The nanorods exhibit self-assembly mediated quenching of the lattice defect-related emission accompanied by multifold enhancement in the dopant-related emission. This study demonstrates that the collective behavior of an ensemble of bare nanoparticles, under natural conditions, can lead to the formation of functionalized (doped) nanorods with enhanced luminescence properties.

  1. Sensitivity of CoSi2 precipitation in silicon to extra-low dopant concentrations. I. Experiment

    NASA Astrophysics Data System (ADS)

    Fortuna, F.; Ruault, M.-O.; Borodin, V. A.; Ganchenkova, M. G.; Kaïtasov, O.

    2015-01-01

    We demonstrate that the precipitation of cobalt disilicide phase in silicon during high-temperature (500 °C and 650 °C) implantation is noticeably affected by impurities of phosphorus and boron. Measurements of B-type CoSi2 cluster sizes and number densities as a function of implantation dose indicate that the number density of clusters progressively increases as the phosphorus concentration increases from 7 × 1011 to 8 × 1013 cm-3. A tentative explanation of these observations is proposed based on the previously suggested mechanism of precipitate nucleation, and on the results of first principles calculations summarized in Paper II, published as a follow-up paper. The results imply that utmost care is to be taken when dealing with transition metal precipitation during ion implantation into silicon because variations in the dopant content can affect the reproducibility of results even at extremely low dopant concentrations.

  2. 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.

  3. 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.

  4. Dimeric tetrathiafulvalene linked to pseudo-ortho-[2.2]paracyclophane: chiral electrochromic properties and use as a chiral dopant.

    PubMed

    Kobayakawa, Kosuke; Hasegawa, Masashi; Sasaki, Hiroaki; Endo, Junta; Matsuzawa, Hideyo; Sako, Katsuya; Yoshida, Jun; Mazaki, Yasuhiro

    2014-10-01

    A dimeric tetrathiafulvalene installed into a chiral pseudo-ortho-[2.2]paracyclophane framework was synthesized as a novel chiral electrochromic material. This compound exhibited pronounced chiroptical properties in the UV-Vis-NIR range depending on its redox states without racemization. Each enantiomer was examined as a chiral dopant for nematic liquid crystals (LCs), and the induced helicity of the LC solvent was in accord with that of the tetrathiafulvalene compound. PMID:25146126

  5. Air stable organic salt as an n-type dopant for efficient and stable organic light-emitting diodes.

    PubMed

    Bin, Zhengyang; Duan, Lian; Qiu, Yong

    2015-04-01

    Air-stable and low-temperature-evaporable n-type dopants are highly desired for efficient and stable organic light-emitting diodes (OLEDs). In this work, 2-(2-Methoxyphenyl)-1,3-dimethyl-1H-benzoimidazol-3-ium iodide (o-MeO-DMBI-I), a thermally decomposable precursor of organic radical o-MeO-DMBI, has been employed as a novel n-type dopant in OLEDs, because of its air stability, low decomposition temperature, and lack of atom diffusion. The n-type electrical doping is evidenced by the rapid increase in current density of electron-only devices and the large improvement in conductivity, originated from increased electron concentration in electron-transport layer (ETL) and reduced electron injection barrier. A highly efficient and stable OLED is created using o-MeO-DMBI as an n-type dopant in Bphen. Compared with the control device with its high-temperature-evaporable n-type dopant cesium carbonate (Cs2CO3), o-MeO-DMBI-doped device showed an incredible boom in current efficiency from 28.6 to 42.2 cd/A. Moreover, the lifetime (T(70%)) of o-MeO-DMBI-doped device is 45 h, more than 20 times longer than that of the Cs2CO3-doped device (2 h). The enhanced efficiency and stability are attributed to the improved balance of holes and electrons in the emissive layer, and the eliminated atom diffusion of cesium. PMID:25768295

  6. Structural and orientation effects on electronic energy transfer between silicon quantum dots with dopants and with silver adsorbates

    SciTech Connect

    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, K{sub EET}, between selected identical pairs of crystalline silicon quantum dots systems, either bare, doped with Al or P, or adsorbed with Ag and Ag{sub 3}, 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 Ag{sub 3} 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) K{sub EET} 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.

  7. Generation of Broensted and Lewis acid sites on the surface of silica by addition of dopant cations

    SciTech Connect

    Connell, G.; Dumesic, J.A.

    1987-06-01

    Pyridine adsorption was used to study the acidic properties of silica doped with the following cations: Sc/sup 3 +/, Mg/sup 2 +/, Fe/sup 2 +/, Fe/sup 3 +/, Zn/sup 2 +/, Al/sup 3 +/, and Ga/sup 3 +/. All samples were exposed to pyridine at 423 K and subsequently evacuated at successively higher temperatures to 723 K. Infrared spectra of the adsorbed pyridine indicated that all of these cations generated Lewis acid sites. This can be explained by the presence of coordinatively unsaturated dopant cations on the surface of silica, in accord with a model based on Pauling's electrostatic bond strength rules. The infrared frequency of the 19b band of pyridine adsorbed on these Lewis acid sites was found to increase with increasing electronegativity of the dopant cation. It is suggested that both of these quantities are related to the strength of the Lewis acid sites. Broensted acid sites were also observed by infrared spectroscopy for Sc/sup 3 +/, Al/sup 3 +/, and Ga/sup 3 +/ on silica. These dopant cations are believed to be bonded tetrahedrally on the surface of silica, generating bridging hydroxyl groups between the dopant cation and Si/sup 4 +/. As for zeolite catalysts, the proton associated with these groups and required for charge neutrality is the Broensted acid site. Finally, Broensted acid sites can also be generated on silica by highly electronegative anions, such as HPO/sub 4//sup 2 -/, which generate Broensted acidity in a different manner. 55 references.

  8. 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. PMID:26673846

  9. 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.

  10. Effects of different dopants on switching behavior of HfO2-based resistive random access memory

    NASA Astrophysics Data System (ADS)

    Deng, Ning; Pang, Hua; Wu, Wei

    2014-10-01

    In this study the effects of doping atoms (Al, Cu, and N) with different electro-negativities and ionic radii on resistive switching of HfO2-based resistive random access memory (RRAM) are systematically investigated. The results show that forming voltages and set voltages of Al/Cu-doped devices are reduced. Among all devices, Cu-doped device shows the narrowest device-to-device distributions of set voltage and low resistance. The effects of different dopants on switching behavior are explained with deferent types of CFs formed in HfO2 depending on dopants: oxygen vacancy (Vo) filaments for Al-doped HfO2 devices, hybrid filaments composed of oxygen vacancies and Cu atoms for Cu-doped HfO2 devices, and nitrogen/oxygen vacancy filaments for N-doped HfO2 devices. The results suggest that a metal dopant with a larger electro-negativity than host metal atom offers the best comprehensive performance.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. The effect of the dopant nature on the reactivity, interlayer bonding and electronic properties of dual doped bilayer graphene.

    PubMed

    Denis, Pablo A; Iribarne, Federico

    2016-09-21

    Herein, we report on the structural, chemical reactivity and electronic properties of dual-doped bilayer graphene (DDBG). Only one of the layers was doped with a pair of 3p-2p elements. Aluminum was the only dopant which prefers to interact with the undoped layer. The interlayer interaction energies of DDBG are smaller than those determined for bilayer graphene, except for AlN and AlO DDBG. This effect is due to the presence of weak Al-C interlayer bonds. The dopants increase the reactivity of both the doped and undoped layers. Interestingly, we found that hydrogenation is a method that can be used to switch on/off the interlayer bonding, as it controlled the X-C interlayer distance (X = Al, Si, P, S). The magnetic moment of the systems can be adjusted by the position of the 3p dopant. In effect, when X interacts with the doped layer, the magnetic moment is reduced, while it is maintained when X fails to interact. Finally, we found that the doped layer is able to break the symmetry of the undoped sheet and small gaps can be opened in the band structure of the undoped layer. As observed for single doped monolayer graphene, the most effective element for such purposes is P, which opened gaps close to 0.2 eV. For SiN DDBG, the spin filtering properties are enhanced with respect to the monolayered structure. PMID:27545204

  16. Effects of thickness, dopant type and doping levels of flexible nanoscale polyaniline films on responses to gases

    NASA Astrophysics Data System (ADS)

    Sinha, Mousumi; Panda, Siddhartha

    2015-07-01

    While doped nanoscale (sub-100 nm) polyaniline films have shown interesting behavior with respect to electrical conductivities and thermal sensing, there has been scant attention to responses of such films to gases. In this work, a detailed study on the effects of film thicknesses, doping levels and dopant types on the responses to different gases is presented. The responses to NO2 were higher than to NO and NH3, and the films were unresponsive to N2, O2, CO2 and H2. The responses to NO2 and NH3 increased with decrease in film thickness below about 50 nm and were prominent at lower doping levels, and also were dependent on the type of dopant used. Explanations for the experimental observations were provided based on energy considerations. The modulation of the calculated LUMO levels and band gaps, and the Fermi energy levels at lower film thicknesses and doping levels correlated well with the responses. As the transfer of electrons resulting in the formation of the charge complex depends on the difference between the Fermi level of the film and the Mulliken electronegativity of the gas molecules, this difference in the energy levels also correlated with the effects of different gases and different dopants. Limited tests on the effect of water vapor were conducted.

  17. 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

  18. 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.

  19. Sonar Locator Systems

    NASA Technical Reports Server (NTRS)

    1985-01-01

    An underwater locator device called a Pinger is attached to an airplane's flight recorder for recovery in case of a crash. Burnett Electronics Pinger Model 512 resulted from a Burnett Electronics Laboratory, Inc./Langley Research Center contract for development of a search system for underwater mines. The Pinger's battery-powered transmitter is activated when immersed in water, and sends multidirectional signals for up to 500 hours. When a surface receiver picks up the signal, a diver can retrieve the pinger and the attached airplane flight recorder. Other pingers are used to track whales, mark underwater discoveries and assist oil drilling vessels.

  20. Location of Planet X

    SciTech Connect

    Harrington, R.S.

    1988-10-01

    Observed positions of Uranus and Neptune along with residuals in right ascension and declination are used to constrain the location of a postulated tenth planet. The residuals are converted into residuals in ecliptic longitude and latitude. The results are then combined into seasonal normal points, producing average geocentric residuals spaced slightly more than a year apart that are assumed to represent the equivalent heliocentric average residuals for the observed oppositions. Such a planet is found to most likely reside in the region of Scorpius, with considerably less likelihood that it is in Taurus. 8 references.

  1. Control of the mechanical strength of a bipyridine-based polymeric gel from linear nanofibre to helix with a chiral dopant.

    PubMed

    Choi, Heekyoung; Ahn, Junho; Kim, Sungmin; Kim, Hyungjun; Jung, Jong Hwa

    2016-06-18

    A mixture of building blocks 1 and 2 having hydrazine moieties and aldehyde moieties, respectively, formed a gel by a hydrazone reaction in the absence and presence of cyclohexane diamines as chiral dopants and Fe(2+). In particular, the mechanical strength of the helical gel prepared from 1 and 2 in the presence of a chiral dopant and Fe(2+) was ca. 10-fold stronger as compared to that of the gel prepared from the building blocks 1 and 2 without a chiral dopant and Fe(2+). The improved mechanical strength was attributed to the formation of a helix. The results indicate that the mechanical strength of gels obtained by hydrazone reaction could be controlled by a chiral dopant and Fe(2+). PMID:27226044

  2. METHOD OF LOCATING GROUNDS

    DOEpatents

    Macleish, K.G.

    1958-02-11

    ABS>This patent presents a method for locating a ground in a d-c circult having a number of parallel branches connected across a d-c source or generator. The complete method comprises the steps of locating the ground with reference to the mildpoint of the parallel branches by connecting a potentiometer across the terminals of the circuit and connecting the slider of the potentiometer to ground through a current indicating instrument, adjusting the slider to right or left of the mildpoint so as to cause the instrument to indicate zero, connecting the terminal of the network which is farthest from the ground as thus indicated by the potentiometer to ground through a condenser, impressing a ripple voltage on the circuit, and then measuring the ripple voltage at the midpoint of each parallel branch to find the branch in which is the lowest value of ripple voltage, and then measuring the distribution of the ripple voltage along this branch to determine the point at which the ripple voltage drops off to zero or substantially zero due to the existence of a ground. The invention has particular application where a circuit ground is present which will disappear if the normal circuit voltage is removed.

  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

    Keita Hosokawa

    2002-08-01

    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 NaAlH{sub 4} below 70 atm. They achieved 4 wt.% H{sub 2} reversible capacity by doping NaAlH{sub 4} 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, Zr{sub 27}Ti{sub 9}Ni{sub 38}V{sub 5}Mn{sub 16}Cr{sub 5}, LaNi{sub 4.85}Sn{sub 0.15}, Al{sub 3}Ti, and PdCl{sub 2} were combined , LaNi4.85Sn0.15, Al3Ti, and PdCl2 were combined with LiAlH{sub 4} by ball-milling to study whether or not LiAlH{sub 4} 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 LiAlH{sub 4} and Li{sub 3}AlH{sub 6} 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. TOF-SIMS and laser-SNMS investigations of dopant distribution in nanophosphors

    NASA Astrophysics Data System (ADS)

    Chakraborty, B. R.; Haranath, D.; Chander, Harish; Hellweg, S.; Dambach, S.; Arlinghaus, H. F.

    2005-08-01

    Characterization of industrially important nanophosphors such as ZnS:Mn2+, SrAl2O4:Eu2+, Dy3+ and Gd2O2S:Pr3+ was undertaken with a view to optimize their synthesis methods. To investigate the crystallinity, particle size, efficiency and homogeneity in doping of Mn in ZnS; Eu and Dy in SrAl2O4 and Pr in Gd2O2S, analytical techniques such as XRD, TEM, PL, TOF-SIMS and laser-SNMS were employed. The XRD and TEM studies revealed the average particle sizes to be between 2 and 15 nm. Photoluminescence (PL) studies carried out for the nanophosphors confirm the effectiveness of doping in the host lattices. TOF-SIMS spectral analysis showed the formation of the crystal (host lattice) with the presence of different dopants. The chemical imaging mode of TOF-SIMS suggested homogeneous doping in ZnS:Mn2+ nanophosphor while in the case of SrAl2O4:Eu2+, Dy3+ the degree of homogeneity of doping was found to be considerably less. The broad band of PL in SrAl2O4:Eu2+, Dy3+ nanophosphor may be attributed to such an inhomogeneity to some extent. In the case of Gd2O2S:Pr3+, the PL was found to be brightest at the higher energy region. But because of very low level doping of Pr3+ in the Gd2O2S lattice, additional laser-SNMS studies were carried out for analysing the doping distribution using chemical imaging data, which indicated a high degree of homogeneity.

  6. SILVER DOPANTS FOR TARGETED AND UNTARGETED DIRECT ANALYSIS OF UNSATURATED LIPIDS VIA IR-MALDESI

    PubMed Central

    Meier, Florian; Garrard, Kenneth P.; Muddiman, David C.

    2014-01-01

    RATIONALE Unsaturated lipids play a crucial role in cellular processes as signaling factors, membrane building blocks or energy storage molecules. However, adequate mass spectrometry imaging of this diverse group of molecules remains challenging. In this study we implemented silver cationization for IR-MALDESI direct analysis to enhance the ion abundances for olefinic lipids and facilitate peak assignment. METHODS Trace amounts of silver nitrate were doped into the electrospray solvent of an IR-MALDESI imaging source coupled to an Orbitrap mass analyzer. Calcifediol was examined as a model compound to demonstrate the effect of silver dopants on sensitivity and assay robustness. Dried human serum spots were subsequently analyzed to compare Ag doped solvents with previously described solvent compositions. Mass difference as well as ion abundance ratio filters were employed to interpret results based on the characteristic isotopic pattern of silver. RESULTS Olefinic lipids were readily observed as silver adducts in IR-MALDESI analyses. Silver cationization decreased the limit of detection for calcifediol by at least one order of magnitude and was not affected in complex biological matrices. The ion abundance ratio and mass difference of [M+107Ag+]+ and [M+109Ag+]+ were successfully applied to facilitate the spectral assignment of silver adducts. Overall, silver cationization increased the analyte coverage in human serum by 43% compared with a standard IR-MALDESI approach. CONCLUSIONS Silver cationization has been shown to enhance IR-MALDESI sensitivity and selectivity for unsaturated lipids, even when applied to complex samples. Increased compound coverage, enhanced robustness as well as the developed tools for peak assignment and mapping of isotopic patterns will clearly benefit future mass spectrometry imaging studies. PMID:25303475

  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. 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

  9. Groth Deep Locations Image

    NASA Technical Reports Server (NTRS)

    2003-01-01

    NASA's Galaxy Evolution Explorer photographed this ultraviolet color blowup of the Groth Deep Image on June 22 and June 23, 2003. Hundreds of galaxies are detected in this portion of the image, and the faint red galaxies are believed to be 6 billion light years away. The white boxes show the location of these distant galaxies, of which more than a 100 can be detected in this image. NASA astronomers expect to detect 10,000 such galaxies after extrapolating to the full image at a deeper exposure level.

    The Galaxy Evolution Explorer mission is led by the California Institute of Technology, which is also responsible for the science operations and data analysis. NASA's Jet Propulsion Laboratory, Pasadena, Calif., a division of Caltech, manages the mission and built the science instrument. The mission was developed under NASA's Explorers Program, managed by the Goddard Space Flight Center, Greenbelt, Md. The mission's international partners include South Korea and France.

  10. Object Locating System

    NASA Technical Reports Server (NTRS)

    Arndt, G. Dickey (Inventor); Carl, James R. (Inventor)

    2000-01-01

    A portable system is provided that is operational for determining, with three dimensional resolution, the position of a buried object or approximately positioned object that may move in space or air or gas. The system has a plurality of receivers for detecting the signal front a target antenna and measuring the phase thereof with respect to a reference signal. The relative permittivity and conductivity of the medium in which the object is located is used along with the measured phase signal to determine a distance between the object and each of the plurality of receivers. Knowing these distances. an iteration technique is provided for solving equations simultaneously to provide position coordinates. The system may also be used for tracking movement of an object within close range of the system by sampling and recording subsequent position of the object. A dipole target antenna. when positioned adjacent to a buried object, may be energized using a separate transmitter which couples energy to the target antenna through the medium. The target antenna then preferably resonates at a different frequency, such as a second harmonic of the transmitter frequency.

  11. Submerged marine streamer locator

    SciTech Connect

    Roberts, F.A.

    1987-01-06

    An apparatus is described for use in determining relative to known geographic locations on a sea floor the position of a moving submerged marine seismic streamer while being towed through the sea by an exploration vessel, which comprises: spaced apart acoustic receivers and at least one acoustic transducer-receiver carried by the streamer. The transducer-receiver is capable of emitting acoustic command signals when triggered by means controllable from the moving vessel and the receivers are capable of receiving and distinguishing distinctly different acoustic frequencies to transmit distinguishable signals responsive thereto along the streamer to recording means on the vessel; at least three sea floor transponders spatially displaced from each other at known positions relative to the sea floor and each of the transponders being capable of responding to a single acoustic command signal from the transducer-receiver in the moving streamer while being towed by the vessel. Each of the transponders emits signals of a distinctly different frequency; and means for recording the time interval from initiation of a command signal from the streamer transducer to the receipt of each signal relayed along the streamer from each of the receivers in response to the signals from the transponders. In this way, the distance of each of the streamer receivers from each of the known positions of the transponders may be calculated.

  12. AOTV bow shock location

    NASA Technical Reports Server (NTRS)

    Desautel, D.

    1985-01-01

    Hypersonic bow-shock location and geometry are of central importance to the aerodynamics and aerothermodynamics of aeroassisted orbital transfer vehicles (AOTVs), but they are difficult to predict for a given vehicle configuration. This paper reports experimental measurements of shock standoff distance for the 70 deg cone AOTV configuration in shock-tunnel-test flows at Mach numbers of 3.8 to 7.9 and for angles of attack from 0 deg to 20 deg. The controlling parameter for hypersonic bow-shock standoff distance (for a given forebody shape) is the mean normal-shock density ratio. Values for this parameter in the tests reported are in the same range as those of the drag-brake AOTV perigee regime. Results for standoff distance are compared with those previously reported in the literature for this AOTV configuration. It is concluded that the AOTV shock standoff distance for the conical configuration, based on frustrum (base) radius, is equivalent to that of a sphere with a radius about 35 percent greater than that of the cone; the distance is, therefore, much less than reported in previous studies. Some reasons for the discrepancies between the present and previous are advanced. The smaller standoff distance determined here implies there will be less radiative heat transfer than was previously expected.

  13. Effect of rare earth dopants on the magnetic ordering of frustrated h-YMnO3

    NASA Astrophysics Data System (ADS)

    Sharma, Neetika; Das, A.; Prajapat, C. L.; Singh, M. R.

    2016-12-01

    In this report the combined effects of chemical pressure and R-Mn interaction on the structural and magnetic properties of frustrated h-YMnO3 have been investigated. Towards this, neutron powder diffraction and magnetization measurements were carried out on isostructural compounds Y1-xRxMnO3(R=Yb, Er, Tb, Ho; x≤0.2) with hexagonal structure (P63cm space group). The dopants are evenly distributed between the two Yttrium sites. The unit cell volume shows a linear increase with average A-site ionic radii, . The average apical a and planar p bond lengths are found to increase with . The tilting angle of the MnO5 polyhedron decreases linearly with increase in , whereas the buckling angle remains constant. No significant change in TN (within 10 K) is observed on doping. The temperature variation of the volume indicates an anomalous reduction in volume at TN which is found to be correlated with the square of the antiferromagnetic Mn moment. A spin reorientation behavior (evident from a change in the irreducible representation (IR) Γ3 to Γ4) is observed on decreasing from 1.019 Å (Y) to 1.012 Å (Yb) similar to that reported in external pressure studies on YMnO3. Additional interaction between the doped R and Mn influences the magnetic structure in the case of Ho and Tb doped samples. With Ho doping at Y site, the magnetic structure is described by IR Γ3 alone for 5 K≤T<35 K and a mixture of Γ3 and Γ4 for T≥35 K. However, in Tb doped sample, the magnetic structure is better described by Γ4Tb,Mn IR with additional moment on Tb. The frustration parameter, f reduces from 6 to 1 in the doped samples. A combination of chemical pressure effect and magnetic coupling between the magnetic R ion and Mn moments thus describes the magnetic structures and relieves the frustration effects inherent to the quasi-two dimensional Mn moment ordering.

  14. Anomalous diameter dependence of thermal transport in ultra-narrow Si nanowires

    SciTech Connect

    Karamitaheri, Hossein; Neophytou, Neophytos; Kosina, Hans

    2014-01-14

    We present atomistic valence force field calculations of thermal transport in Si nanowires of diameters from 12 nm down to 1 nm. We show that as the diameter is reduced, the phonon density-of-states and transmission function acquire a finite value at low frequency, in contrast to approaching zero as in the bulk material. It turns out that this effect results in what Ziman described as the “problem of long longitudinal waves” [J. M. Ziman, Electrons and Phonons: The Theory of Transport Phenomena in Solids (Clarendon, Oxford, 1962)], which states that the thermal conductivity of a material increases as its length is increased due to the vanishing scattering for long-wavelength phonons. We show that this thermal transport improvement also appears in nanowires as their diameter is decreased below D = 5 nm (not only as the length increases), originating from the increase in the density of the long wavevector modes. The observation is present under ballistic transport conditions, and further enhanced with the introduction of phonon-phonon scattering. Because of this, in such ultra-narrow nanowires, as the diameter is reduced, phonon transport is dominated more and more by lower energy phonons with longer mean-free paths. We show that ∼80% of the heat is carried by phonons with energies less than 5 meV, most with mean-free paths of several hundreds of nanometers.

  15. Diameter-dependent bending dynamics of single-walled carbon nanotubes in liquids

    PubMed Central

    Fakhri, Nikta; Tsyboulski, Dmitri A.; Cognet, Laurent; Weisman, R. Bruce; Pasquali, Matteo

    2009-01-01

    By relating nanotechnology to soft condensed matter, understanding the mechanics and dynamics of single-walled carbon nanotubes (SWCNTs) in fluids is crucial for both fundamental and applied science. Here, we study the Brownian bending dynamics of individual chirality-assigned SWCNTs in water by fluorescence microscopy. The bending stiffness scales as the cube of the nanotube diameter and the shape relaxation times agree with the semiflexible chain model. This suggests that SWCNTs may be the archetypal semiflexible filaments, highly suited to act as nanoprobes in complex fluids or biological systems. PMID:19706503

  16. Diameter-Dependent Modulus and Melting Behavior in Electrospun Semicrystalline Polymer Fibers

    SciTech Connect

    Y Liu; S Chen; E Zussman; C Korach; W Zhao; M Rafailovich

    2011-12-31

    Confinement of the semicrystalline polymers, poly(ethylene-co-vinyl acetate) (PEVA) and low-density polyethylene (LDPE), produced by electrospinning has been observed to produce fibers with large protrusions, which have not been previously observed in fibers of comparable diameters produced by other methods. SAXS spectra confirmed the crystalline structure and determined that the lamellar spacing was almost unchanged from the bulk. Measurement of the mechanical properties of these fibers, by both shear modulation force microscopy (SMFM) and atomic force acoustic microscopy (AFAM), indicates that the modulii of these fibers increases with decreasing diameter, with the onset at {approx}10 {micro}m, which is an order of magnitude larger than previously reported. Melting point measurements indicate a decrease of more than 7% in T{sub m}/T{sub 0} (where T{sub m} is the melting point of semicrystalline polymer fibers and T{sub 0} is the melting point of the bulk polymer) for fibers ranging from 4 to 10 {micro}m in diameter. The functional form of the decrease followed a universal curve for PEVA, when scaled with T{sub 0}.

  17. Diameter-dependent multiferroic functionality in hybrid core/shell NWs.

    PubMed

    Khan, U; Irfan, M; Li, W J; Adeela, N; Liu, P; Zhang, Q T; Han, X F

    2016-08-11

    A versatile approach towards nanofabrication of highly reproducible Co/BiCoO3 (Co/BCO) core/shell (CS) nanowires (NWs) with different diameters has been adopted by demonstrating easily available and low cost sol-gel and electrodeposition routes. X-ray diffraction (XRD) analysis confirmed the tetragonal system of the BCO nanoshells (NSs) with the space group P4mm. Scanning electron microscopy (SEM) clearly demonstrates the uniform morphology with well aligned CS NWs. The magnetization reversal processes (MRPs), experimentally and with analytical modelling, have been discussed for CS NWs with θ ranging from 0° (in-plane magnetic easy axis) to 90° (out-of-plane magnetic hard axis) with magnetic hysteresis loops and geometrical parameters. Crossover from the vortex to transverse reversal mode on increasing θ has been observed for all diameters. An exchange bias effect has been observed for smaller CS NWs diameters and it is attributed to the shell thickness of ∼25 nm. Furthermore, the magnetic anisotropy effect has been discussed in some detail. PMID:27465910

  18. First-principles simulation on wire diameter dependence of piezoresistivity in zinc oxide nanowires

    NASA Astrophysics Data System (ADS)

    Nakamura, Koichi

    2015-06-01

    The wire dependence of piezoresistivity in wurtzite-type zinc oxide (ZnO) nanowires with a <0001> orientation has been simulated on the basis of the first-principles calculations of model structures. The strain responses to the carrier conductivity of n- or p-doped semiconducting wurtzite-ZnO<0001> nanowire models were calculated using band carrier densities and their corresponding effective masses derived from a one-dimensional band diagram by our original procedure. In this simulation, the conductivities of p-doped thin nanowire models change drastically owing to a longitudinal uniaxial strain because of either the redistribution of holes among subbands with completely different effective masses or the change in the effective mass. As a result, high positive longitudinal gauge factors and piezoresistance coefficients were obtained. On the other hand, for thick nanowire models with wire diameters of more than 1.5 nm, the piezoresistivity of the nanowire itself is essentially low in both the n- and p-doped states.

  19. Transfer of location-specific control to untrained locations.

    PubMed

    Weidler, Blaire J; Bugg, Julie M

    2016-11-01

    Recent research highlights a seemingly flexible and automatic form of cognitive control that is triggered by potent contextual cues, as exemplified by the location-specific proportion congruence effect--reduced compatibility effects in locations associated with a high as compared to low likelihood of conflict. We investigated just how flexible location-specific control is by examining whether novel locations effectively cue control for congruency-unbiased stimuli. In two experiments, biased (mostly compatible or mostly incompatible) training stimuli appeared in distinct locations. During a final block, unbiased (50% compatible) stimuli appeared in novel untrained locations spatially linked to biased locations. The flanker compatibly effect was reduced for unbiased stimuli in novel locations linked to a mostly incompatible compared to a mostly compatible location, indicating transfer. Transfer was observed when stimuli appeared along a linear function (Experiment 1) or in rings of a bullseye (Experiment 2). The novel transfer effects imply that location-specific control is more flexible than previously reported and further counter the complex stimulus-response learning account of location-specific proportion congruence effects. We propose that the representation and retrieval of control settings in untrained locations may depend on environmental support and the presentation of stimuli in novel locations that fall within the same categories of space as trained locations. PMID:26800157

  20. Hydrogen adsorption and storage on palladium-decorated graphene with boron dopants and vacancy defects: A first-principles study

    NASA Astrophysics Data System (ADS)

    Ma, Ling; Zhang, Jian-Min; Xu, Ke-Wei; Ji, Vincent

    2015-02-01

    The geometric stability and hydrogen capacity of Pd-decorated graphene with experimentally realizable boron dopants and various vacancy defects including single carbon vacancy (SV), "585"-type double carbon vacancy (585 DCV) and "555-777"-type double carbon vacancy (555-777 DCV) are investigated using the first-principles calculations based on density functional theory (DFT). It is found that among the four types of defective structures, Pd‧s binding energies on SV and 585 DCV defect graphene sheets exceed the cohesive energy of the Pd metal bulk, thus Pd atoms are well dispersed above defective graphene sheets and effectively prevent Pd clustering. Up to three H2 molecules can bind to Pd atom on graphene with B dopants, SV and 555-777 DCV defects. For the cases of Pd-decorated graphene with B dopants and 555-777 DCV defect, a single H2 or two H2 are molecularly chemisorbed to Pd atom in the form of Pd-H2 Kubas complex, where the stretched H-H bond is relaxed but not dissociated. Out of two adsorbed H2, the third H2 binds to Pd atom by small van der Waals (vdW) forces and the nature of bonding is very weak physisorption. Different from above two cases, three H2 are all molecularly chemisorbed to Pd atom with stretched H-H bond for Pd-decorated SV defect graphene, the hybridization of the Pd-4d orbitals with the H2-σ orbitals and the electrostatic interaction between the Pd cation and the induced H2 dipole both contribute to the H2 molecules binding, and the binding energies of 0.25-0.41 eV/H2 is in the range that can permit H2 molecules recycling at ambient conditions.

  1. Thermoluminescence emission spectra for the LiF:Mg,Cu,Na,Si thermoluminescent materials with various concentrations of the dopants (3-D measurement).

    PubMed

    Lee, J I; Lee, D; Kim, J L; Chang, S Y

    2006-01-01

    The thermoluminescence (TL) emission spectra from LiF TL materials, called KLT-300 (LiF:Mg,Cu,Na,Si) with various dopant concentrations are measured and analysed. These KLT-300 materials were developed by the Korea Atomic Energy Research Institute (KAERI) to achieve an enhancement of the thermal stability in TL readings. Six types of samples are prepared with different dopant concentrations in the following ranges; Mg (0-0.20 mol%), Cu (0-0.05 mol%), Na and Si (0-0.9 mol%). The spectra measurements are carried out for the six types of samples using a TL emission spectra measurement device. The spectra measurement device consists of a monochromator, photomultiplier tube and temperature control unit to thermally stimulate the samples. The measured data shows the light emission during heating of the sample as a function of temperature and wavelength (three-dimensional TL spectra). The spectra were analysed using a method of deconvolution based on gaussian curve. The wavelength of a main peak of the emission spectra changes depending on the existence of the Cu dopant, while intensity of the spectra rapidly changes with the Cu dopant concentrations. The 385 nm emission is mainly observed in all the spectra from the samples with the Cu dopant, but in those from the samples without the Cu dopant a very weak 401 nm emission is mainly observed. However, any change in the wavelength at a main peak of the TL emission spectra from the sample materials with Na and Si dopants is not observed but that in the intensity at a peak of the spectra is observed. PMID:16644972

  2. Chemical vapor deposition of B-doped polycrystalline diamond films: Growth rate and incorporation efficiency of dopants

    NASA Astrophysics Data System (ADS)

    Gonon, P.; Deneuville, A.; Fontaine, F.; Gheeraert, E.; Campargue, A.; Chenevier, M.; Rodolphe, S.

    1995-12-01

    The growth rate and the incorporation efficiency of dopants have been studied in the case of chemical vapor deposition of B-doped polycrystalline diamond films. The deposition rate is found to decrease with the addition of diborane in the gas phase. This is correlated with a modification of the plasma chemistry as observed by emission spectroscopy (decrease in the H/H2, CH/H, and C2/H ratios with the addition of diborane). The concentration of boron incorporated in the films is observed to vary with the square of the boron concentration in the gas phase.

  3. Co-Dopant Influence on the Persistent Luminescence of BaAl2O4:Eu2+,R3+

    NASA Astrophysics Data System (ADS)

    Rodrigues, Lucas C. V.; Hölsä, Jorma; Carvalho, José M.; Pedroso, Cássio C. S.; Lastusaari, Mika; Felinto, Maria C. F. C.; Watanabe, Shigeo; Brito, Hermi F.

    2014-04-01

    The R3+ (rare earth) co-dopants may have a surprisingly important role in persistent luminescence - enhancement of up to 1-3 orders of magnitude may be obtained in the performance of these phosphor materials - depending strongly on the R3+ ion, of course. In this work, the effects of the R3+ co-dopants in the BaAl2O4:Eu2+,R3+ materials were studied using mainly thermoluminescence (TL) and synchrotron radiation XANES methods. In BaAl2O4, the conventional and persistent luminescence both arise from the 4f7→4f65d1 transition of Eu2+, yielding blue-green emission color. The former, in the presence of humidity, turns to more bluish because of creation of an additional Eu2+ luminescence centre which is not, however, visible in persistent luminescence. The trap structure in the non-co-doped BaAl2O4:Eu2+ is rather complex with 4-5 TL bands above room temperature. With R3+ co-doping, this basic structure is modified though no drastic change can be observed. This underlines the fact that even very small changes in the trap depths can produce significant modifications in the persistent luminescence efficiency. It should be remembered that basically the persistent luminescence performance is controlled by the Boltzmann population law depending exponentially on both the temperature and trap depth. Some mechanisms for persistent luminescence have suggested the presence of either divalent R2+ or tetravalent RIV during the charging of the Eu2+ doped materials. The present XANES measurements on BaAl2O4:Eu2+,R3+ confirmed the presence of only the trivalent form of the R3+ co-dopants excluding both of these pathways. It must thus be concluded, that the energy is stored in intrinsic and extrinsic defects created by the synthesis conditions and charge compensation due to R3+ co-doping. Even though the effect of the R3+ co-dopants was carefully exploited and characterized, the differences in the effect of different R3+ ions with very similar chemical and spectroscopic properties could

  4. Low-temperature study of array of dopant atoms on transport behaviors in silicon junctionless nanowire transistor

    SciTech Connect

    Wang, Hao; Han, Weihua Li, Xiaoming; Zhang, Yanbo; Yang, Fuhua

    2014-09-28

    We demonstrate temperature-dependent quantum transport characteristics in silicon junctionless nanowire transistor fabricated on Silicon-on-Insulator substrate by the femtosecond laser lithography. Clear drain-current oscillations originated from dopant-induced quantum dots are observed in the initial stage of the conduction for the silicon nanowire channel at low temperatures. Arrhenius plot of the conductance indicates the transition temperature of 30 K from variable-range hopping to nearest-neighbor hopping, which can be well explained under Mott formalism. The transition of electron hopping behavior is the interplay result between the thermal activation and the Coulomb interaction.

  5. Site-Competition Epitaxy for N-Type and P-Type Dopant Control in CVD Sic Epilayers

    NASA Technical Reports Server (NTRS)

    Larkin, D. J.

    1995-01-01

    The use of site-competition epitaxy, which is based on intentional variation of the Si/C ratio during epitaxy, has now been reproduced in numerous national and international laboratories. However, previous reports have only considered dopant incorporation control for epitaxy on the Si-face 6H-SiC(OOO1) substrates. Presented in this paper is the extension of this technique for control of phosphorous incorporation and also a comparison of controlled doping on C-face 6H-SiC(OOO1) versus Si-face 6H-SiC(OOO1) substrates for aluminum, boron, nitrogen, and phosphorous.

  6. 9. SITE MAP HIGHLIGHTING SIGNIFICANT BUILDINGS AND SHOWING LOCATION LOCATION ...

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

    9. SITE MAP HIGHLIGHTING SIGNIFICANT BUILDINGS AND SHOWING LOCATION LOCATION OF OUTPATIENT CLINIC ADDITION - U.S. Veterans Administration Medical Center, 600 South Seventieth Street, Lincoln, Lancaster County, NE

  7. Evaluation of CO2 and CO dopants in hydrogen to reduce hydrogen permeation in the Stirling engine heater head tube alloy CG-27

    NASA Technical Reports Server (NTRS)

    Misencik, J. A.

    1983-01-01

    Tubes of CG-27 alloy, filled with hydrogen doped with various amounts of carbon dioxide and carbon monoxide, were heated in a diesel fuel fired Stirling engine simulator materials test rig for 100 hours at 820 C and at a gas pressure of 15 MPa to determine the effectiveness of the dopants in reducing hydrogen permeation through the hot tube wall. This was done for clean as-heat treated tubes and also for tubes that had previously been exposed for 100 hours to hydrogen doped with 1.0 volume percent carbon dioxide to determine if the lower levels of dopant could maintain a low hydrogen permeation through the hot tube wall. Carbon dioxide, as a dopant in hydrogen, was most effective in reducing hydrogen permeation through clean tubes and in maintaining low hydrogen permeation after prior exposure to 1.0 volume percent carbon dioxide. Only the lowest level of carbon dioxide (0.05 volume percent) was not as effective in the clean or prior exposed tubes. Carbon monoxide as a dopant in hydrogen was less effective than carbon dioxide at a given concentration level. Of the four dopant levels studied; 1.0, 0.5, 0.2, and 0.05 volume percent carbon monoxide, only the 1.0 and 0.5 volume percent were effective in reducing and maintaining low hydrogen permeation through the CG-27.

  8. Sensitivity of CoSi{sub 2} precipitation in silicon to extra-low dopant concentrations. I. Experiment

    SciTech Connect

    Fortuna, F.; Ruault, M.-O.; Kaïtasov, O.; Borodin, V. A.; Ganchenkova, M. G.

    2015-01-28

    We demonstrate that the precipitation of cobalt disilicide phase in silicon during high-temperature (500 °C and 650 °C) implantation is noticeably affected by impurities of phosphorus and boron. Measurements of B-type CoSi{sub 2} cluster sizes and number densities as a function of implantation dose indicate that the number density of clusters progressively increases as the phosphorus concentration increases from 7 × 10{sup 11} to 8 × 10{sup 13 }cm{sup −3}. A tentative explanation of these observations is proposed based on the previously suggested mechanism of precipitate nucleation, and on the results of first principles calculations summarized in Paper II, published as a follow-up paper. The results imply that utmost care is to be taken when dealing with transition metal precipitation during ion implantation into silicon because variations in the dopant content can affect the reproducibility of results even at extremely low dopant concentrations.

  9. H2 Desorption from MgH2 Surfaces with Steps and Catalyst-Dopants

    SciTech Connect

    Reich, Jason M.; Wang, Lin-Lin; Johnson, Duane D.

    2014-03-10

    Light-metal hydrides, like MgH2, remain under scrutiny as prototypes for reversible H-storage materials. For MgH2, we assess hydrogen desorption/adsorption properties (enthalpy and kinetic barriers) for stepped, catalyst-doped surfaces occurring, e.g., from ball-milling in real samples. Employing density functional theory and simulated annealing in a slab model, we studied initial H2 desorption from stepped surfaces with(out) titanium (Ti) catalytic dopant. Extensive simulated annealing studies were performed to find the dopant’s site preferences. For the most stable initial and final (possibly magnetic) states, nudged elastic band (NEB) calculations were performed to determine the H2-desorption activation energy. We used a moment-transition NEB method to account for the dopant’s transition to the lowest-energy magnetic state at each image along the band. We identify a dopant-related surface-desorption mechanism that reloads via bulk H diffusion. While reproducing the observed bulk enthalpy of desorption, we find a decrease of 0.24 eV (a 14% reduction) in the activation energy on doped stepped surface; together with a 22% reduction on a doped flat surface, this brackets the assessed 18% reduction in kinetic barrier for ball-milled MgH2 samples with low concentration of Ti from experiment.

  10. Cavitating ultrasound hydrogenation of water-soluble olefins employing inert dopants: Studies of activity, selectivity and reaction mechanisms

    SciTech Connect

    Disselkamp, Robert S.; Chajkowski, Sarah M.; Boyles, Kelly R.; Hart, Todd R.; Peden, Charles HF

    2006-12-07

    Here we discuss results obtained as part of a three-year investigation at Pacific Northwest National Laboratory of ultrasound processing to effect selectivity and activity in the hydrogenation of water-soluble olefins on transition metal catalysts. We have shown previously that of the two regimes for ultrasound processing, high-power cavitating and high-power non-cavitating, only the former can effect product selectivity dramatically (> 1000%) whereas the selectivity of the latter was comparable with those obtained in stirred/silent control experiments [R.S. Disselkamp, Y.-H. Chin, C.H.F. Peden, J. Catal., 227, 552 (2005)]. As a means of ensuring the benefits of cavitating ultrasound processing, we introduced the concept of employing inert dopants into the reacting solution. These inert dopants do not partake in solution chemistry but enable a more facile transition from high-power non-cavitating to cavitating conditions during sonication treatment. With cavitation processing conditions ensured, we discuss here results of isotopic H/D substitution for a variety of substrates and illustrate how such isotope dependent chemistries during substrate hydrogenation elucidate detailed mechanistic information about these reaction systems.

  11. EXAFS study of dopant ions with different charges in nanocrystalline anatase: evidence for space-charge segregation of acceptor ions.

    PubMed

    Knauth, Philippe; Chadwick, Alan V; Lippens, Pierre E; Auer, Gerhard

    2009-06-01

    Nanocrystalline TiO(2) (anatase) is an essential oxide for environment and energy applications. A combination of EXAFS spectroscopy and DFT calculations on a series of dopants with quite similar ion radius, but increasing ion charge, show boundary space charge segregation of acceptor cations. The picture illustrates the Fourier-transformed EXAFS spectrum for Sn(4+)-doped TiO(2).A series of dopants, including acceptor ions (Zn(2+), Y(3+)), isovalent ions (Zr(4+), Sn(4+)) as well as a donor ion (Nb(5+)), were studied by EXAFS spectroscopy in nanocrystalline TiO(2) anatase powders and nanoceramics. Similar results were found for nanocrystalline powders and nanocrystalline ceramics, made by hot-pressing the powders. Boundary segregation was observed for the acceptor ions yttrium and zinc, whereas tin, zirconium and niobium ions were placed on substitutional bulk sites and did not segregate, whatever their concentration. These results can be interpreted based on defect thermodynamics, in the framework of a space charge segregation model with positive boundary core, due to excess oxide ion vacancies, and negative space charge regions, where ionized acceptors are segregated. PMID:19425035

  12. spds* Tight-Binding Model for Exchange Interaction Between Transition Metal Dopants in Diamond and SiC

    NASA Astrophysics Data System (ADS)

    Kortan, Victoria R.; Şahin, Cüneyt; Flatté, Michael E.

    2015-03-01

    Diamond and SiC are wide-band-gap semiconductors with long-lived spin lifetimes and promising for quantum information technology device design. Spin initialization, manipulation and readout has already been demonstrated for the NV center in diamond and the divacancy in SiC. Transition metal spin centers offer additional benefits in tetrahedral hosts due to the crystal field splitting of the d-states into localized and extended states. For example, the application of strain in diamond allows switching between two spin states of a single Ni dopant. Here we use a spds* tight-binding model including spin-orbit interaction to describe transition metal spin centers in diamond and 3C-SiC as well as the NV center in diamond and divacancy in 3C-SiC. The energy levels for an isolated dopant are taken from experiment, when available, and density functional theory calculations otherwise. We calculate and compare the wavefunctions of these spin centers, as well as the strength of the exchange interaction between pairs of them. This work was supported by an AFOSR MURI.

  13. Determination of Raman Spectrum of Li28La12Zr8O48 as a Function of Dopant

    NASA Astrophysics Data System (ADS)

    Mukhopadhyay, Saikat; Thompson, Travis; Sakamoto, Jeff; Johannes, Michelle; Stewart, Derek

    2014-03-01

    Li28La12Zr8O48 is a supervalent conductor with a low conductivity tetragonal phase and a high conductivity cubic phase, making it a strong candidate as a practical Li ion rechargeable battery solid electrolyte. The high conductivity phase can be stabilized via supervalent doping that drives Li+ ions out of the lattice, creating vacancies that both relieve the necessity for Li sublattice ordering and provide easier pathways for ionic conduction. The conductivity strongly depends on both doping concentration and site preference. Ta5+ has been suggested as an optimal dopant as it likely substitutes for Zr4+, thereby leaving the Li sublattice undisturbed. However, it is difficult to accurately establish the actual, as compared to nominal, amount of Ta doped into the lattice which, in turn, determines the vacancy concentration and conductivity. In this talk, we will present the variation of Raman intensities of LLZO as a function of Ta concentration to determine the role of dopant and vacancies in deciding measured Raman intensities via first principles calculations based on Density Functional Theory. A direct comparison of calculated and measured Raman spectrum may provide a definitive measure of vacancy concentration.

  14. A study on NiGe-contacted Ge n+/p Ge shallow junction prepared by dopant segregation technique

    NASA Astrophysics Data System (ADS)

    Tsui, Bing-Yue; Shih, Jhe-Ju; Lin, Han-Chi; Lin, Chiung-Yuan

    2015-05-01

    In this work, the effect of dopant segregation on the NiGe/n-Ge contact is studied by experiments and first-principles calculations. Both Al-contacted and NiGe-contacted n+/p junctions were fabricated. Phosphorus and arsenic ions were Implanted Before Germanide (IBG) formation or Implanted After Germanide (IAG) formation. The NiGe-contacted junction always exhibit higher forward current than the Al-contacted junction due to dopant segregation. First principles calculations predict that phosphorus atoms tend to segregate on both NiGe side and Ge side while arsenic atoms tend to segregate at Ge side. Since phosphorus has higher activation level and lower diffusion coefficient than arsenic, we propose a phosphorus IBG + arsenic IAG process. Shallow n+/p junction with junction depth 90 nm below the NiGe/Ge interface is achieved. The lowest and average contact resistivity is 2 × 10-6 Ω cm2 and 6.7 × 10-6 Ω cm2, respectively. Methods which can further reduce the junction depth and contact resistivity are suggested.

  15. 7,7,8,8-Tetracyanoquinodimethane based molecular dopants for p-type doping of OLEDs: A theoretical investigation

    SciTech Connect

    Cosimbescu, Lelia; Padmaperuma, Asanga B.; Gaspar, Daniel J.

    2011-11-15

    The array of organic conductivity dopants used for organic light emitting devices (OLED) to reduce the operating voltage and improve power efficiency is extremely limited. Here we report a comparative theoretical study between newly proposed analogs and the standard state-of-the-art conductivity dopant 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ). We used density functional theory to determine the bond lengths, bond angles and electronic properties, such as the energy of the highest occupied molecular orbital (E{sub HOMO}) and lowest occupied molecular orbital (E{sub LUMO}) states, as well as the triplet energies of the novel structures (ET). The ground state structures of the proposed molecules were optimized at the B3LYP/6-31G* level. The results show that substitution of one or two fluorine groups in the F4-TCNQ core with a substituted phenyl ring or other electron withdrawing moieties, will not substantially affect the geometry of the molecule or its electronic ability to accept electrons. The most significant finding was that the phenyl substitutions onto the TCNQ core are nearly perpendicular to the TCNQ plane, and thus there is no electronic communication between the two rings. This is extremely important, as such extension of the {pi} conjugated system would negatively affect the E{sub LUMO} and thus the electron affinity of the molecule.

  16. Dopant concentration dependent optical and X-Ray induced photoluminescence in Eu3+ doped La2Zr2O7

    NASA Astrophysics Data System (ADS)

    Pokhrel, Madhab; Brik, Mikhail; Mao, Yuanbing

    2015-03-01

    Herein, we will be presenting the dopant (Eu) concentration dependent high density La2Zr2O7 nanoparticles for optical and X-ray scintillation applications by use of X - ray diffraction, Raman, FTIR, scanning electron microscope (SEM), transmission electron microscopy (TEM), optically and X-ray excited photoluminescence (PL). Several theoretical methods have been used in order to investigate the structural, electronic, optical, elastic, dynamic properties of Eu doped La2Zr2O7. It is observed that Eu: La2Zr2O7 shows an intense red luminescence under 258, 322, 394 and 465 nm excitation. The optical intensity of Eu: La2Zr2O7 depends on the dopant concentration of Eu3+. Following high energy excitation with X-rays, Eu: La2Zr2O7 shows an atypical Eu PL response (scintillation) with a red emission. The intense color emission of Eu obtained under 258 nm excitation, the X-ray induced luminescence property along with reportedly high density of La2Zr2O7, makes these nanomaterials attractive for optical and X-ray applications. The authors thank the support from the Defense Threat Reduction Agency (DTRA) of the U.S. Department of Defense (Award #HDTRA1-10-1-0114).

  17. FFTF Asbestos Location Tracking Program

    SciTech Connect

    Reynolds, J.A.

    1994-09-15

    An Asbestos Location Tracking Program was prepared to list, locate, and determine Asbestos content and to provide baseline {open_quotes}good faith{close_quotes} for yearly condition inspections for the FFTF Plant and buildings and grounds.

  18. Impact-Locator Sensor Panels

    NASA Technical Reports Server (NTRS)

    Christiansen, Eric L.; Byers, Terry; Gibbons, Frank

    2008-01-01

    Electronic sensor systems for detecting and locating impacts of rapidly moving particles on spacecraft have been invented. Systems of this type could also be useful on Earth in settings in which the occurrence of impacts and/or the locations of impacts are not immediately obvious and there are requirements to detect and quickly locate impacts to prevent or minimize damage.

  19. DIORAMA Location Type User's Guide

    SciTech Connect

    Terry, James Russell

    2015-01-29

    The purpose of this report is to present the current design and implementation of the DIORAMA location type object (LocationType) and to provide examples and use cases. The LocationType object is included in the diorama-app package in the diorama::types namespace. Abstractly, the object is intended to capture the full time history of the location of an object or reference point. For example, a location may be speci ed as a near-Earth orbit in terms of a two-line element set, in which case the location type is capable of propagating the orbit both forward and backward in time to provide a location for any given time. Alternatively, the location may be speci ed as a xed set of geodetic coordinates (latitude, longitude, and altitude), in which case the geodetic location of the object is expected to remain constant for all time. From an implementation perspective, the location type is de ned as a union of multiple independent objects defi ned in the DIORAMA tle library. Types presently included in the union are listed and described in subsections below, and all conversions or transformation between these location types are handled by utilities provided by the tle library with the exception of the \\special-values" location type.

  20. Spring loaded locator pin assembly

    DOEpatents

    Groll, T.A.; White, J.P.

    1998-03-03

    This invention deals with spring loaded locator pins. Locator pins are sometimes referred to as captured pins. This is a mechanism which locks two items together with the pin that is spring loaded so that it drops into a locator hole on the work piece. 5 figs.

  1. Spring loaded locator pin assembly

    DOEpatents

    Groll, Todd A.; White, James P.

    1998-01-01

    This invention deals with spring loaded locator pins. Locator pins are sometimes referred to as captured pins. This is a mechanism which locks two items together with the pin that is spring loaded so that it drops into a locator hole on the work piece.

  2. NHD INDEXED LOCATIONS FOR GRTS

    EPA Science Inventory

    GRTS locational data for nonpoint source projects. GRTS locations are coded onto route.drain (Transport and Coastline Reach) feature of NHD to create Point Events and Linear Events. GRTS locations are coded onto region.rch (Waterbody Reach) feature of NHD to create NHD Waterbody ...

  3. NHD INDEXED LOCATIONS FOR BEACH

    EPA Science Inventory

    Beach locational data for BEACH Act. Beach locations are coded onto route.drain (Transport and Coastline Reach) feature of NHD to create Point Events and Linear Events. Beach locations are coded onto region.rch (Waterbody Reach) feature of NHD to create NHD Waterbody Shapefiles...

  4. The Impact of an Oxygen Dopant in an ideal Bi_2Sr_2CaCu_2O_8 delta Crystal

    SciTech Connect

    Johnston, S.

    2010-05-04

    Recent scanning tunneling microscopy studies have shown that local nanoscale pairing inhomogenities are correlated with interstitial oxygen dopants in Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8+{delta}}. Combining electrostatic and cluster calculations, in this paper the impact of a dopant on the local Madelung and charge transfer energies, magnetic exchange J, Zhang-Rice mobility, and interactions with the lattice is investigated. It is found that electrostatic modifications locally increases the charge transfer energy and slightly suppresses J. It is further shown that coupling to c-axis phonons is strongly modified near the dopant. The combined effects of electrostatic modifications and coupling to the lattice yield broadened spectral features, reduced charge gap energies, and a sizable local increase of J. This implies a strong local interplay between antiferromagnetism, polarons, and superconducting pairing.

  5. Highly stable and efficient tandem organic light-emitting devices with intermediate connectors using lithium amide as n-type dopant

    NASA Astrophysics Data System (ADS)

    Zhou, Dong-Ying; Zu, Feng-Shuo; Zhang, Ying-Jie; Shi, Xiao-Bo; Aziz, Hany; Liao, Liang-Sheng

    2014-08-01

    In this work, we report thermally decomposable lithium amide (LiNH2) feasible to function as an effective n-type dopant for intermediate connectors in tandem organic light-emitting devices (OLEDs). Metallic lithium, which is released from the decomposition process of LiNH2, is proved by X-ray photoelectron spectroscopy and responsible for n-type electrical doping of electron transporting materials. We demonstrate that tandem OLEDs using LiNH2 and Cs2CO3 as n-type dopants, respectively, give a comparable electroluminescence efficiency and, moreover, the device with LiNH2 has far longer operational lifetime. The results therefore highlight the significance of selecting suitable n-type dopant in intermediate connectors to fabricate high-stability tandem OLEDs.

  6. Highly stable and efficient tandem organic light-emitting devices with intermediate connectors using lithium amide as n-type dopant

    SciTech Connect

    Zhou, Dong-Ying; Zu, Feng-Shuo; Shi, Xiao-Bo; Liao, Liang-Sheng E-mail: lsliao@suda.edu.cn; Zhang, Ying-Jie; Aziz, Hany E-mail: lsliao@suda.edu.cn

    2014-08-25

    In this work, we report thermally decomposable lithium amide (LiNH{sub 2}) feasible to function as an effective n-type dopant for intermediate connectors in tandem organic light-emitting devices (OLEDs). Metallic lithium, which is released from the decomposition process of LiNH{sub 2}, is proved by X-ray photoelectron spectroscopy and responsible for n-type electrical doping of electron transporting materials. We demonstrate that tandem OLEDs using LiNH{sub 2} and Cs{sub 2}CO{sub 3} as n-type dopants, respectively, give a comparable electroluminescence efficiency and, moreover, the device with LiNH{sub 2} has far longer operational lifetime. The results therefore highlight the significance of selecting suitable n-type dopant in intermediate connectors to fabricate high-stability tandem OLEDs.

  7. LETTER TO THE EDITOR: Metal (M) dopant centred local structures, high-pressure synthesis and bulk superconductivity in ?: M = Fe, Co, Ni

    NASA Astrophysics Data System (ADS)

    Shi, F.; Harris, R.; Bresser, W. J.; McDaniel, D.; Boolchand, P.

    1997-05-01

    Depression of 0953-8984/9/21/001/img9 by the dopants Fe or Co, but not Ni, is spectacularly reversed by synthesis of the titled cuprates at high P instead of ambient P of oxygen with 0953-8984/9/21/001/img9 enhanced from 32 to 82 K for M = Fe at x = 0.10. With Fe dopant, Mössbauer spectroscopy reveals a conversion of a tetrahedral (A) into a trigonal bipyramidal coordinated (C) Fe chain site by oxygen addition in the chains upon high-P processing. The A 0953-8984/9/21/001/img11 C site transformation is elucidated and extended to the case of Co dopant, and its consequences for superconducting behaviour discussed.

  8. Increase in the Random Dopant Induced Threshold Fluctuations and Lowering in Sub 100 nm MOSFETs Due to Quantum Effects: A 3-D Density-Gradient Simulation Study

    NASA Technical Reports Server (NTRS)

    Asenov, Asen; Slavcheva, G.; Brown, A. R.; Davies, J. H.; Saini, S.

    2000-01-01

    In this paper we present a detailed simulation study of the influence of quantum mechanical effects in the inversion layer on random dopant induced threshold voltage fluctuations and lowering in sub 100 nm MOSFETs. The simulations have been performed using a 3-D implementation of the density gradient (DG) formalism incorporated in our established 3-D atomistic simulation approach. This results in a self-consistent 3-D quantum mechanical picture, which implies not only the vertical inversion layer quantisation but also the lateral confinement effects related to current filamentation in the 'valleys' of the random potential fluctuations. We have shown that the net result of including quantum mechanical effects, while considering statistical dopant fluctuations, is an increase in both threshold voltage fluctuations and lowering. At the same time, the random dopant induced threshold voltage lowering partially compensates for the quantum mechanical threshold voltage shift in aggressively scaled MOSFETs with ultrathin gate oxides.

  9. Location-based Web Search

    NASA Astrophysics Data System (ADS)

    Ahlers, Dirk; Boll, Susanne

    In recent years, the relation of Web information to a physical location has gained much attention. However, Web content today often carries only an implicit relation to a location. In this chapter, we present a novel location-based search engine that automatically derives spatial context from unstructured Web resources and allows for location-based search: our focused crawler applies heuristics to crawl and analyze Web pages that have a high probability of carrying a spatial relation to a certain region or place; the location extractor identifies the actual location information from the pages; our indexer assigns a geo-context to the pages and makes them available for a later spatial Web search. We illustrate the usage of our spatial Web search for location-based applications that provide information not only right-in-time but also right-on-the-spot.

  10. Diffusion barriers for achieving controlled concentrations of luminescent dopants via diffusion for mask-less RGB color patterning of organic light emitting devices.

    PubMed

    Kajiyama, Yoshitaka; Kajiyama, Koichi; Aziz, Hany

    2015-11-30

    Using molecular diffusion as an approach to introduce organic luminescent dopants for making organic light emitting devices (OLEDs) of different colors on one substrate has the potential to overcome the yield and resolution limitations of the current OLED display technology. In this work, diffusion barriers made of MoO3 and a hole transport material mixture are introduced. The barriers effectively confine the diffusion of the dopants to only the desired depths. With the use of these barriers, OLEDs with highly controlled doping concentrations and performance are fabricated. The barriers thus allow utilizing simple diffusion methods for RGB patterning in OLEDs. PMID:26698710

  11. High Conductivity in Molecularly p-Doped Diketopyrrolopyrrole-Based Polymer: The Impact of a High Dopant Strength and Good Structural Order.

    PubMed

    Karpov, Yevhen; Erdmann, Tim; Raguzin, Ivan; Al-Hussein, Mahmoud; Binner, Marcus; Lappan, Uwe; Stamm, Manfred; Gerasimov, Kirill L; Beryozkina, Tetyana; Bakulev, Vasiliy; Anokhin, Denis V; Ivanov, Dimitri A; Günther, Florian; Gemming, Sibylle; Seifert, Gotthard; Voit, Brigitte; Di Pietro, Riccardo; Kiriy, Anton

    2016-07-01

    [3]-Radialene-based dopant CN6-CP studied herein, with its reduction potential of +0.8 versus Fc/Fc+ and the lowest unoccupied molecular orbital level of -5.87 eV, is the strongest molecular p-dopant reported in the open literature, so far. The efficient p-doping of the donor-acceptor dithienyl-diketopyrrolopyrrole-based copolymer having the highest unoccupied molecular orbital level of -5.49 eV is achieved. The doped films exhibit electrical conductivities up to 70 S cm(-1) . PMID:27172371

  12. Dopants Control Electron-Hole Recombination at Perovskite-TiO₂ Interfaces: Ab Initio Time-Domain Study.

    PubMed

    Long, Run; Prezhdo, Oleg V

    2015-11-24

    TiO2 sensitized with organohalide perovskites gives rise to solar-to-electricity conversion efficiencies reaching close to 20%. Nonradiative electron-hole recombination across the perovskite/TiO2 interface constitutes a major pathway of energy losses, limiting quantum yield of the photoinduced charge. In order to establish the fundamental mechanisms of the energy losses and to propose practical means for controlling the interfacial electron-hole recombination, we applied ab initio nonadiabatic (NA) molecular dynamics to pristine and doped CH3NH3PbI3(100)/TiO2 anatase(001) interfaces. We show that doping by substitution of iodide with chlorine or bromine reduces charge recombination, while replacing lead with tin enhances the recombination. Generally, lighter and faster atoms increase the NA coupling. Since the dopants are lighter than the atoms they replace, one expects a priori that all three dopants should accelerate the recombination. We rationalize the unexpected behavior of chlorine and bromine by three effects. First, the Pb-Cl and Pb-Br bonds are shorter than the Pb-I bond. As a result, Cl and Br atoms are farther away from the TiO2 surface, decreasing the donor-acceptor coupling. In contrast, some iodines form chemical bonds with Ti atoms, increasing the coupling. Second, chlorine and bromine reduce the NA electron-vibrational coupling, because they contribute little to the electron and hole wave functions. Tin increases the coupling, since it is lighter than lead and contributes to the hole wave function. Third, higher frequency modes introduced by chlorine and bromine shorten quantum coherence, thereby decreasing the transition rate. The recombination occurs due to coupling of the electronic subsystem to low-frequency perovskite and TiO2 modes. The simulation shows excellent agreement with the available experimental data and advances our understanding of electronic and vibrational dynamics in perovskite solar cells. The study provides design principles

  13. NHD INDEXED LOCATIONS FOR PCS PIPE SCHEDULE AND FACILITY LOCATIONS

    EPA Science Inventory

    Permit Compliance System (PCS) pipe schedule and facility locations indexed to the National Hydrography Dataset (NHD). PCS pipe schedule and facility locations are coded onto route.drain (Transport and Coastline Reach) feature of NHD to create Point Events. PCS pipe schedule an...

  14. Quantum Mechanical Enhancement of the Random Dopant Induced Threshold Voltage Fluctuations and Lowering in Sub 0.1 Micron MOSFETs

    NASA Technical Reports Server (NTRS)

    Asenov, Asen; Slavcheva, G.; Brown, A. R.; Davies, J. H.; Saini, Subhash

    1999-01-01

    A detailed study of the influence of quantum effects in the inversion layer on the random dopant induced threshold voltage fluctuations and lowering in sub 0.1 micron MOSFETs has been performed. This has been achieved using a full 3D implementation of the density gradient (DG) formalism incorporated in our previously published 3D 'atomistic' simulation approach. This results in a consistent, fully 3D, quantum mechanical picture which implies not only the vertical inversion layer quantisation but also the lateral confinement effects manifested by current filamentation in the 'valleys' of the random potential fluctuations. We have shown that the net result of including quantum mechanical effects, while considering statistical fluctuations, is an increase in both threshold voltage fluctuations and lowering.

  15. Local environment of Mn dopant in ZnO by near-edge x-ray absorption fine structure analysis

    NASA Astrophysics Data System (ADS)

    Kunisu, Masahiro; Oba, Fumiyasu; Ikeno, Hidekazu; Tanaka, Isao; Yamamoto, Tomoyuki

    2005-03-01

    High-resolution near-edge x-ray absorption fine structure (NEXAFS) at MnK edge is employed to probe the local environment of Mn dopant in ZnO. First-principles supercell calculations are systematically made to obtain theoretical NEXAFS. Mn is found to substitute for Zn up to 5at. %Mn in polycrystalline samples sintered at 1623K in air. Presence of Mn3O4 is apparent for samples with higher Mn content. The NEXAFS does not change in the range of Mn concentration from 0.01 to 5at.%, indicating the absence of Mn precipitates. The results are confirmed by examining the polarization dependence of the NEXAFS for a 5at.%-doped ZnO thin film.

  16. A fully 3D atomistic quantum mechanical study on random dopant induced effects in 25nm MOSFETs

    SciTech Connect

    Wang, Lin-Wang; Jiang, Xiang-Wei; Deng, Hui-Xiong; Luo, Jun-Wei; Li, Shu-Shen; Wang, Lin-Wang; Xia, Jian-Bai

    2008-07-11

    We present a fully 3D atomistic quantum mechanical simulation for nanometered MOSFET using a coupled Schroedinger equation and Poisson equation approach. Empirical pseudopotential is used to represent the single particle Hamiltonian and linear combination of bulk band (LCBB) method is used to solve the million atom Schroedinger's equation. We studied gate threshold fluctuations and threshold lowering due to the discrete dopant configurations. We compared our results with semiclassical simulation results. We found quantum mechanical effects increase the threshold fluctuation while decreases the threshold lowering. The increase of threshold fluctuation is in agreement with previous study based on approximated density gradient approach to represent the quantum mechanical effect. However, the decrease in threshold lowering is in contrast with the previous density gradient calculations.

  17. No difference in local structure about a Zn dopant for congruent and stoichiometric LiNbO3

    NASA Astrophysics Data System (ADS)

    Bridges, F.; Mackeen, C.; Kovács, L.

    2016-07-01

    We compare extended x-ray absorption fine structure (EXAFS) data at the Zn K edge for a low concentration of Zn (0.7 mol%) in a stoichiometric crystal with that for higher Zn concentrations (nominally 5 and 9 mol%) in congruent LiNbO3 (LNO). Note that stoichiometric and congruent LNO have significantly different optical properties. We find no significant difference in the local structure about Zn out to 4 Å for the two types of crystals and different dopant levels. Although some earlier theoretical models suggest a self-compensation model with 75% of Zn on a Li site and 25% Zn on Nb, we find no clear evidence for a significant fraction of Zn on the Nb site, and estimate at most 2%-3% of Zn might be ZnN b.

  18. Thermal transport across symmetric tilt grain boundaries in β-SiC: Effect of dopants and temperature

    NASA Astrophysics Data System (ADS)

    Goel, N.; Webb, E. B.; Rickman, J. M.; Oztekin, A.; Neti, S.

    2016-07-01

    The Kapitza resistance at a segregated, low-angle symmetric tilt grain boundary in β-SiC is investigated using non-equilibrium molecular dynamics simulation. In particular, we assess the role of compositional and thermal disorder on the boundary resistance for various doping scenarios. By examining the local vibrational density of states, we identify a subset of modes that are significant for thermal transport in this system. This analysis is complemented by calculations of the projected density of states and a corresponding eigenmode analysis of the dynamical matrix that highlight important phonon polarizations and propagation directions. We also examine the dependence of the Kapitza resistance on temperature and dopant/matrix interaction strength, the latter parameter affecting grain-boundary structure and, hence, phonon scattering.

  19. Diffusion, Clustering, and Magnetic Properties of Mn dopants on a 2x2-T4 GaN(0001) Substrate

    SciTech Connect

    Hao, Shiqiang; Zhang, Zhenyu

    2007-01-01

    Based on extensive rst-principles calculations with density-functional theory (DFT), we propose a growth model of Mn on reconstructed 22-T4 GaN(0001), characterized by substitution of Ga by a Mn adatom via a surface site T4. At lower Mn concentration, Mn dopants distribute in Ga sublattice randomly forming intrinsic DMS. At higher concentration, planar ferromagnetic clusters oriented in (0001) plane are easily formed at lower temperature, but ferrimagnetic zigzag columns along the growth orientation will be formed at higher temperature. Based on these ndings, we qualitatively explain the puzzling experimental observations on TC variations, as well as the dierent magnetic natures in Ga1 xMnxN systems.

  20. Sensitivity of CoSi2 precipitation in silicon to extra-low dopant concentrations. II. First-principles calculations

    NASA Astrophysics Data System (ADS)

    Borodin, V. A.; Ganchenkova, M. G.; Ruault, M.-O.; Fortuna, F.

    2015-01-01

    The paper is the second part of the study on the influence of very low dopant content in silicon on CoSi2 precipitation during high-temperature cobalt ion implantation into transmission electron microscope samples. It deals with the computational justification of various assumptions used in Paper I when rationalizing the kinetics of cobalt clustering in ion-implanted intrinsic silicon (both undoped and containing low concentrations of phosphorus atoms). In particular, it is proven that divacancies are efficient nucleation centers for the new Co-Si phase. It is shown that the capture of vacancies and divacancies on phosphorus atoms increases their lifetime in silicon matrix, but practically does not affect the mechanism of their interaction with interstitial cobalt atoms. Finally, it is demonstrated that the mobility of phosphorus interstitials at temperatures of our experiment is orders of magnitude higher than might be expected from the published literature data.

  1. Coherent coupling of two dopants in a silicon nanowire probed by Landau-Zener-Stückelberg interferometry.

    PubMed

    Dupont-Ferrier, E; Roche, B; Voisin, B; Jehl, X; Wacquez, R; Vinet, M; Sanquer, M; De Franceschi, S

    2013-03-29

    We report on microwave-driven coherent electron transfer between two coupled donors embedded in a silicon nanowire. By increasing the microwave frequency we observe a transition from incoherent to coherent driving revealed by the emergence of a Landau-Zener-Stückelberg quantum interference pattern of the measured current through the donors. This interference pattern is fitted to extract characteristic parameters of the double-donor system. In particular we estimate a charge dephasing time of 0.3±0.1  ns, comparable to other types of charge-based two-level systems. The demonstrated coherent coupling between two dopants is an important step towards donor-based quantum computing devices in silicon. PMID:23581354

  2. Defect induced tunable near infrared emission of Er-CeO2 by heterovalent co-dopants.

    PubMed

    Florea, Mihaela; Avram, Daniel; Cojocaru, Bogdan; Tiseanu, Ion; Parvulescu, Vasile; Tiseanu, Carmen

    2016-07-21

    We investigate the effects of heterovalent co-dopants on the structural and emission properties of 1% Er-CeO2 nanoparticles. The CeO2 oxide host was selected on the basis of its fairly well-understood defect chemistry in either a pure or doped state. As a luminescent activator, Er is acknowledged as an interesting element due to its rich luminescence and excitation properties spanning the visible to near-infrared range. The optically inactive trivalent La and monovalent Li metal ions with a concentration of up to 20% were chosen to presumably generate a variable amount of defects in the Er-CeO2 lattice. It was found that La and Li co-dopants induced distinct changes related to the size, lattice constant, bandgap energy, lattice and surface defects of Er-CeO2. As a result of these changes, a strong modulation of the luminescence intensity and shape was measured using a suite of excitation conditions (charge-transfer absorption band of CeO2, direct/up-conversion into Er absorptions and X-ray excitation modes). The use of Eu as a luminescent probe offered additional information concerning the effects of La/Li co-doping on the local structure surrounding the luminescent activator. Remarkably high percentages of 90 and 98% of the total emission of Er measured between 500 and 1100 nm are measured in the near-infrared region at 980 nm under X-ray and up-conversion excitation at ∼1500 nm, respectively. The optical properties suggest that Li, Er co-doped CeO2 has good potential for therapy and biological imaging. PMID:27333335

  3. Radiotherapy dosimetry and the thermoluminescence characteristics of Ge-doped fibres of differing germanium dopant concentration and outer diameter

    NASA Astrophysics Data System (ADS)

    Noor, N. Mohd; Fadzil, M. S. Ahmad; Ung, N. M.; Maah, M. J.; Mahdiraji, G. A.; Abdul-Rashid, H. A.; Bradley, D. A.

    2016-09-01

    We examine the influence of elevated dopant concentration on the thermoluminescence characteristics of novel Ge-doped silica fibres. Basic dosimetric characteristics of the TL media were obtained, including linearity, reproducibility, energy dependence, fading, minimum detectable dose and glow curve analysis, use being made of a 60Co gamma irradiation facility (mean energy 1.25 MeV) and an electron linear accelerator producing photons at an accelerating potential of 6 and 10 MV. The 6 mol% Ge-doped fibres were found to provide TL response superior to that of 8- and 10 mol% Ge-doped fibres, both for fibres with outer diameter of 241 μm and 604 μm. Concerning reproducibility, obtained under three different test conditions, at <10% the 6 mol% Ge dopant concentration was observed to provide the superior coefficient of variation (CV). In regard to energy dependence, the 10 mol% Ge doped cylindrical fibres produced the largest gradient values at 0.364 and 0.327 for the 241 μm and 604 μm diameter cylindrical fibres respectively and thus the greatest energy dependency. Measured 33 days post irradiation; the 6 mol% Ge doped cylindrical fibres showed the least TL signal loss, at 21% for the 241 μm cylindrical fibre and <40% for the 604 μm cylindrical fibres. The results also revealed that the 6 mol% optical fibres provided the lowest minimum detectable dose, at 0.027 Gy for 6 MV photon beams. Evaluations of these characteristics are supporting development of novel Ge-doped optical fibres for dosimetry in radiotherapy.

  4. Neodymium as a magnesium tetraborate matrix dopant and its applicability in dosimetry and as a temperature sensor

    NASA Astrophysics Data System (ADS)

    Souza, Luiza F.; Antonio, Patrícia L.; Caldas, Linda V. E.; Souza, Divanizia N.

    2015-06-01

    MgB4O7 doped with lanthanides such as Dy3+ and Tm3+ are phosphors with very well established use in routine personal dosimetry. Certain characteristics, for example linearity in a broad dose range, low energy dependence, Zeff=8.5, high sensitivity and a relatively simple thermoluminescent (TL) emission curve make MgB4O7 a good material for thermoluminescent dosimetry. With the aim of analyzing other doping possibilities, this paper presents some preliminary results on the use of Nd3+ as a dopant in the MgB4O7 matrix. Furthermore, we evaluated the effect of using two different lanthanides, Nd and Dy, in the host matrix. In the present work, the phosphors were produced through solid state synthesis and X-ray diffraction confirmed the success of the technique. The TL behavior of MgB4O7:Nd was assessed when irradiated with gamma (60Co) and beta radiation, to determine the effect of the dopant concentration and the dose-response over a broad dose range. We also evaluated the dose-response of MgB4O7:Nd,Dy when irradiated with 60Co. The TL responses of the phosphors were compared with that of MgB4O7:Dy. These preliminary studies show that for the absorbed dose range studied, the sensitivity of MgB4O7:Nd,Dy was 3.8 and 28 times higher than that of MgB4O7:Dy and MgB4O7:Nd. The materials also presented linearity from 5 to 40 Gy. Above this value, the dose response curve exhibited sublinear behavior. These preliminary results will assist in developing a new temperature sensor based on a MgB4O7 dosimeter.

  5. Improved Endurance and Resistive Switching Stability in Ceria Thin Films Due to Charge Transfer Ability of Al Dopant.

    PubMed

    Ismail, M; Ahmed, E; Rana, A M; Hussain, F; Talib, I; Nadeem, M Y; Panda, D; Shah, N A

    2016-03-01

    An improvement in resistive switching (RS) characteristics of CeO2-based devices has been reported by charge transfer through Al metal as a dopant. Moreover, density functional theory (DFT) calculations have been performed to investigate the role of Al-layer sandwiched between CeO2 layers by the Vienna ab initio simulation package (VASP). Total density of states (TDOS) and partial electron density of states (PDOS) have been calculated and analyzed with respect to resistive switching. It is established that the oxygen vacancy based conductive filaments are formed and ruptured in the upper region of CeO2 layer, because of the fact that maximum transport of charge takes place in this region by Al and Ti (top electrode), while the lower region revealed less capability to generate conductive filaments because minimum charge transfer takes place in this region by Al and/or Pt (bottom electrode). The effect of Al and Al2O3 on both the electronic charge transfer from valence to conduction bands and the formation stability of oxygen vacancies in conductive filament have been discussed in detail. Experimental results demonstrated that the Ti/CeO2:Al/Pt sandwich structure exhibits significantly better switching characteristics including lower forming voltage, improved and stable SET/RESET voltages, enhanced endurance of more than 10(4) repetitive switching cycles and large memory window (ROFF/RON > 10(2)) as compared to undoped Ti/CeOx/Pt device. This improvement in memory switching behavior has been attributed to a significant decrease in the formation energy of oxygen vacancies and to the enhanced oxygen vacancies generation within the CeO2 layers owing to charge transferring and oxygen gettering ability of Al-dopant. PMID:26881895

  6. Effects of dopant type and concentration on the femtosecond laser ablation threshold and incubation behaviour of silicon

    NASA Astrophysics Data System (ADS)

    Oosterbeek, Reece N.; Corazza, Carsten; Ashforth, Simon; Simpson, M. Cather

    2016-04-01

    In laser micromachining, the ablation threshold (minimum fluence required to cause ablation) is a key performance parameter and overall indicator of the efficiency of material removal. For pulsed laser micromachining, this important observable depends upon material properties, pulse properties and the number of pulses applied in a complex manner that is not yet well understood. The incubation effect is one example. It manifests as a change in the ablation threshold as a function of number of laser pulses applied and is driven by photoinduced defect accumulation in the material. Here, we study femtosecond (800 nm, 110 fs, 0.1-1 mJ/pulse) micromachining of a material with well-defined initial defect concentrations: doped Si across a range of dopant types and concentrations. The single-pulse ablation threshold (F th,1) was observed to decrease with increasing dopant concentration, from a maximum of 0.70 J/cm2 (±0.02) for undoped Si to 0.51 J/cm2 (±0.01) for highly N-type doped Si. The effect was greater for N-type doped Si than for P-type, consistent with the higher carrier mobility of electrons compared to holes. In contrast, the infinite-pulse ablation threshold (F th, ∞ ) was the same for all doping levels and types. We attribute this asymptotic behaviour to a maximum defect concentration that is independent of the initial defect concentration and type. These results lend insight into the mechanism of multipulse, femtosecond laser ablation.

  7. EPA FACILITY POINT LOCATION FILES

    EPA Science Inventory

    Data includes locations of facilities from which pollutants are discharged. The epapoints.tar.gz file is a gzipped tar file of 14 Arc/Info export files and text documents. The .txt files define the attributes located in the INFO point coverage files. Projections are defined in...

  8. Pan-information Location Map

    NASA Astrophysics Data System (ADS)

    Zhu, X. Y.; Guo, W.; Huang, L.; Hu, T.; Gao, W. X.

    2013-11-01

    A huge amount of information, including geographic, environmental, socio-economic, personal and social network information, has been generated from diverse sources. Most of this information exists separately and is disorderly even if some of it is about the same person, feature, phenomenon or event. Users generally need to collect related information from different sources and then utilize them in applications. An automatic mechanism, therefore, for establishing a connection between potentially-related information will profoundly expand the usefulness of this huge body of information. A connection tie is semantic location describing semantically concepts and attributes of locations as well as relationships between locations, since 80% of information contains some kind of geographic reference but not all of geographic reference has explicit geographic coordinates. Semantic location is an orthogonal form of location representation which can be represented as domain ontology or UML format. Semantic location associates various kinds of information about a same object to provide timely information services according to users' demands, habits, preferences and applications. Based on this idea, a Pan-Information Location Map (PILM) is proposed as a new-style 4D map to associates semantic location-based information dynamically to organize and consolidate the locality and characteristics of corresponding features and events, and delivers on-demand information with a User-Adaptive Smart Display (UASD).

  9. Experiences with Information Locator Services.

    ERIC Educational Resources Information Center

    Christian, Eliot

    1999-01-01

    Relates experiences in developing and promoting services interoperable with the Global Information Locator Service (GILS) standard. Describes sample implementations and touches on the strategic choices made in public policy, standards, and technology. Offers 10 recommendations for successful implementation of an Information Locator Service. (AEF)

  10. Cold War Geopolitics: Embassy Locations.

    ERIC Educational Resources Information Center

    Vogeler, Ingolf

    1995-01-01

    Asserts that the geopolitics of the Cold War can be illustrated by the diplomatic ties among countries, particularly the superpowers and their respective allies. Describes a classroom project in which global patterns of embassy locations are examined and compared. Includes five maps and a chart indicating types of embassy locations. (CFR)

  11. Precision zero-home locator

    DOEpatents

    Stone, W.J.

    1983-10-31

    A zero-home locator includes a fixed phototransistor switch and a moveable actuator including two symmetrical, opposed wedges, each wedge defining a point at which switching occurs. The zero-home location is the average of the positions of the points defined by the wedges.

  12. Mobile Alternative Fueling Station Locator

    SciTech Connect

    Not Available

    2009-04-01

    The Department of Energy's Alternative Fueling Station Locator is available on-the-go via cell phones, BlackBerrys, or other personal handheld devices. The mobile locator allows users to find the five closest biodiesel, electricity, E85, hydrogen, natural gas, and propane fueling sites using Google technology.

  13. Precision zero-home locator

    DOEpatents

    Stone, William J.

    1986-01-01

    A zero-home locator includes a fixed phototransistor switch and a moveable actuator including two symmetrical, opposed wedges, each wedge defining a point at which switching occurs. The zero-home location is the average of the positions of the points defined by the wedges.

  14. Locating Information within Extended Hypermedia

    ERIC Educational Resources Information Center

    Cromley, Jennifer G.; Azevedo, Roger

    2009-01-01

    New literacies researchers have identified a core set of strategies for locating information, one of which is "reading a Web page to locate information that might be present there" (Leu et al. in: Rush, Eakle, Berger (eds) "Secondary school reading and writing: What research reveals for classroom practices," 2007, p. 46). Do middle-school, high…

  15. LLNL Location and Detection Research

    SciTech Connect

    Myers, S C; Harris, D B; Anderson, M L; Walter, W R; Flanagan, M P; Ryall, F

    2003-07-16

    We present two LLNL research projects in the topical areas of location and detection. The first project assesses epicenter accuracy using a multiple-event location algorithm, and the second project employs waveform subspace Correlation to detect and identify events at Fennoscandian mines. Accurately located seismic events are the bases of location calibration. A well-characterized set of calibration events enables new Earth model development, empirical calibration, and validation of models. In a recent study, Bondar et al. (2003) develop network coverage criteria for assessing the accuracy of event locations that are determined using single-event, linearized inversion methods. These criteria are conservative and are meant for application to large bulletins where emphasis is on catalog completeness and any given event location may be improved through detailed analysis or application of advanced algorithms. Relative event location techniques are touted as advancements that may improve absolute location accuracy by (1) ensuring an internally consistent dataset, (2) constraining a subset of events to known locations, and (3) taking advantage of station and event correlation structure. Here we present the preliminary phase of this work in which we use Nevada Test Site (NTS) nuclear explosions, with known locations, to test the effect of travel-time model accuracy on relative location accuracy. Like previous studies, we find that the reference velocity-model and relative-location accuracy are highly correlated. We also find that metrics based on travel-time residual of relocated events are not a reliable for assessing either velocity-model or relative-location accuracy. In the topical area of detection, we develop specialized correlation (subspace) detectors for the principal mines surrounding the ARCES station located in the European Arctic. Our objective is to provide efficient screens for explosions occurring in the mines of the Kola Peninsula (Kovdor, Zapolyarny

  16. To study the effect of dopant NiO concentration and duration of calcinations on structural and optical properties of MgO-NiO nanocomposites

    NASA Astrophysics Data System (ADS)

    Kumar, Rajesh; Praveen, Sharma, Ashwani; Parmar, R.; Dahiya, S.; Kishor, N.

    2016-05-01

    In present work Magnesium oxide (MgO) samples were doped with different concentration of Transition metal Nickel Oxide(NiO) by using Chemical co-precipitation method. The doping levels were varied from NiO (5%, 10%, 15%) and all the samples were calcined at 600°C for 4hrs and 8hrs respectively. Structural analysis of these calcined materials is carried out by X-ray diffraction (XRD) techniques which reveals that average crystalline sizes are in nano region i.e. 21.77nm-31.13 nm and tabulated in table 1. The powder of calcined samples were also characterized by using various other techniques i.e. Scanning Electron Microscopy (SEM), Fourier Transformation Infrared Spectroscopy (FTIR), UV-Visible spectroscopy, Transmission Electron Microscopy (TEM) etc. The effects of dopant concentration, calcined temperature, calcinations duration on samples were studied and also investigate the effect of varying dopant concentration on morphology and optical properties of calcined nanomaterials. From results it was observed that the crystallite size of nanocomposites increases with increases dopant concentration or increases calcinations duration. The optical band gap decreases with increases sintering time and increase with increases dopant concentrations. TEM results coincide with XRD results and show that particles are polycrystalline in nature. FTIR spectra show that for all samples particles are pure in composition and transmission rate increases with calcinations duration.

  17. Dopant Diffusion and Activation in Silicon Nanowires Fabricated by ex Situ Doping: A Correlative Study via Atom-Probe Tomography and Scanning Tunneling Spectroscopy.

    PubMed

    Sun, Zhiyuan; Hazut, Ori; Huang, Bo-Chao; Chiu, Ya-Ping; Chang, Chia-Seng; Yerushalmi, Roie; Lauhon, Lincoln J; Seidman, David N

    2016-07-13

    Dopants play a critical role in modulating the electric properties of semiconducting materials, ranging from bulk to nanoscale semiconductors, nanowires, and quantum dots. The application of traditional doping methods developed for bulk materials involves additional considerations for nanoscale semiconductors because of the influence of surfaces and stochastic fluctuations, which may become significant at the nanometer-scale level. Monolayer doping is an ex situ doping method that permits the post growth doping of nanowires. Herein, using atom-probe tomography (APT) with subnanometer spatial resolution and atomic-ppm detection limit, we study the distributions of boron and phosphorus in ex situ doped silicon nanowires with accurate control. A highly phosphorus doped outer region and a uniformly boron doped interior are observed, which are not predicted by criteria based on bulk silicon. These phenomena are explained by fast interfacial diffusion of phosphorus and enhanced bulk diffusion of boron, respectively. The APT results are compared with scanning tunneling spectroscopy data, which yields information concerning the electrically active dopants. Overall, comparing the information obtained by the two methods permits us to evaluate the diffusivities of each different dopant type at the nanowire oxide, interface, and core regions. The combined data sets permit us to evaluate the electrical activation and compensation of the dopants in different regions of the nanowires and understand the details that lead to the sharp p-i-n junctions formed across the nanowire for the ex situ doping process. PMID:27351447

  18. Stabilization of the high-k tetragonal phase in HfO2: The influence of dopants and temperature from ab initio simulations

    NASA Astrophysics Data System (ADS)

    Fischer, Dominik; Kersch, Alfred

    2008-10-01

    By means of ab initio simulations we investigate the influence of dopants (Si, C, Ge, Sn, Ti, and Ce) on the transition from the monoclinic to the tetragonal phase in HfO2. In this study we focus first on the internal energy only, an approach common to ab initio simulations. In the second step we go beyond this approach in considering the Helmholtz free energy by additionally taking into account the contribution of the phonon density of states. Finally we discuss the change in transition temperature in the regime of thin films based on an empirical model. We find that both the contributions of the internal energy and phonons can be understood in terms of a model relying on the ionic radius of the dopants. Among the investigated dopants silicon is identified to promote the tetragonal phase most efficiently. The effectiveness of the various dopants is compared on the basis of a qualitative phase diagram for doping concentrations up to ˜12%.

  19. In silico optimization of phase-change materials for digital memories: a survey of first-row transition-metal dopants for Ge₂Sb₂Te₅.

    PubMed

    Skelton, J M; Elliott, S R

    2013-05-22

    Phase-change materials are the alloys at the heart of an emerging class of next-generation, non-volatile digital memory technologies. However, the widely studied Ge-Sb-Te system possesses several undesirable properties, and enhancing its properties, e.g. by doping, is an area of active research. Various first-row transition-metal dopants have been shown to impart useful property enhancements, but a systematic study of the entire period has yet to be undertaken, and little has been done to investigate their interaction with the host material at the atomic level. We have carried out first-principles computer simulations of the complete phase-change cycle in Ge2Sb2Te5 doped with each of the ten first-row transition metals. In this article, we present a comprehensive survey of the electronic, magnetic and optical properties of these doped materials. We discuss in detail their atomic-level structure, and relate the microscopic behaviours of the dopant atoms to their influence on the Ge2Sb2Te5 host. By considering an entire family of similar materials, we identify trends and patterns which might be used to predict suitable dopants for optimizing materials for specific phase-change applications. The computational method employed here is general, and this materials-discovery approach could be applied in the future to study other families of potential dopants for such materials. PMID:23628772

  20. Influence of a dopant source on the structural and optical properties of Mn doped ZnGa2O4 thin films

    NASA Astrophysics Data System (ADS)

    Anoop, G.; Mini Krishna, K.; Jayaraj, M. K.

    2008-03-01

    Thin films of ZnGa2O4:Mn2+ were deposited on quartz substrates using an rf magnetron sputtering technique. The sputtering target, ZnGa2O4 doped with 2 at. % manganese, was synthesized by a high temperature solid state reaction. Two different dopant sources were used to incorporate the dopant ions into the target, namely, manganese acetate and manganese oxide. The structural and optical properties of the thin films were studied using XRD, PL and transmission spectra. Polycrystalline ZnGa2O4:Mn with a spinel structure could be grown at an optimized substrate-target distance even at room temperature. No luminescence was observed in the as-deposited films grown using (CH3COO)2Mn as the dopant source in the target. Substrate heating or post-deposition annealing in the reducing ambient didn’t impart any luminescence to the films, ruling out the possibility of Mn2+ incorporation in the films. However, when using MnO as the manganese source in the target, the as-deposited films exhibited green photoluminescent emission (peak maximum at 508 nm) for substrate temperatures at and above 500 °C. This suggests that, in thin films, Mn incorporation and subsequent luminescent outcome is strongly influenced by the dopant source, which is quite different from the bulk phosphor behavior.

  1. Dopant-assisted atmospheric pressure photoionization of patulin in apple juice and apple-based food with liquid chromatography-tandem mass spectrometry.

    PubMed

    Zhang, Kai; Wong, Jon W; Mai, Huy; Trucksess, Mary W

    2014-05-01

    A dopant-assisted atmospheric pressure photoionization (APPI) with liquid chromatography tandem mass spectrometry (LC-MS/MS) method was developed to determine patulin in apple juice and apple-based food. Different dopants, dopant flow rates, and LC separation conditions were evaluated. Using toluene as the dopant, the LC-APPI-MS/MS method achieved a linear calibration from 12.5 to 2000 μg/L (r(2) > 0.99). Matrix-dependent limits of quantitation (LOQs) were from 8 μg/L (solvent) to 12 μg/L (apple juice). [(13)C]-Patulin-fortified apple juice samples were directly analyzed by the LC-APPI-MS/MS method. Other apple-based food was fortified with [(13)C]-patulin, diluted using water (1% formic acid), centrifuged, and filtered, followed by LC-APPI-MS/MS analysis. In clear apple juice, unfiltered apple cider, applesauce, and apple-based baby food, average recoveries were 101 ± 6% (50 μg/kg), 103 ± 5% (250 μg/kg), and 102 ± 5% (1000 μg/kg) (av ± SD, n = 16). Using the suggested method, patulin was detected in 3 of 30 collected market samples with concentrations ranging from

  2. Left-handed properties of manganite-perovskites La{sub 1-x}Sr{sub x}MnO{sub 3} at various dopant concentrations

    SciTech Connect

    Belozorov, D. P.; Girich, A. A.; Tarapov, S. I.; Pogorily, A. M.; Tovstolytkin, A. I.; Belous, A. G.; Solopan, S. A.

    2014-03-15

    The experimental study of Double Negative (DNG) state of electromagnetic wave propagating in lanthanum manganite-perovskites doped with strontium La{sub 1-x}Sr{sub x}MnO{sub 3} is provided firstly below individual Curie temperatures (in ferromagnetic metal state (FM) for La{sub 1-x}Sr{sub x}MnO{sub 3}). Various dopant concentrations are considered for ceramic specimens: x = 0.15;  0.225;  0.3;  0.45;  0.6. It is shown that dependence of the DNG-peak intensity on dopant concentration is sharply non-monotone with maximum at the dopant concentrations x = 0.225 – 0.3. This behaviour follows the change of Curie temperature with increase of dopant concentration in such substances. The obtained dependence of DNG peak intensity supports the opinion concerning the role of disorder in highly doped manganite-perovskite magnetic ceramics under study.

  3. Regional location in western China

    SciTech Connect

    Cogbill, A.H.; Steck, L.K.

    1996-10-01

    Accurately locating seismic events in western China using only regional seismic stations is a challenge. Not only is the number of seismic stations available for locating events small, but most stations available to researchers are often over 10{degree} distant. Here the authors describe the relocation, using regional stations, of both nuclear and earthquake sources near the Lop Nor test site in western China. For such relocations, they used the Earthquake Data Reports provided by the US Geological Survey (USGS) for the reported travel times. Such reports provide a listing of all phases reported to the USGS from stations throughout the world, including many stations in the People`s Republic of China. LocSAT was used as the location code. The authors systematically relocated each event int his study several times, using fewer and fewer stations at reach relocation, with the farther stations being eliminated at each step. They found that location accuracy, judged by comparing solutions from few stations to the solution provided using all available stations, remained good typically until fewer than seven stations remained.With a good station distribution, location accuracy remained surprisingly good (within 7 km) using as few as 3 stations. Because these relocations were computed without good station corrections and without source-specific station corrections (that is, path corrections), they believe that such regional locations can be substantially improved, largely using static station corrections and source-specific station corrections, at least in the Lop nor area, where sources have known locations. Elsewhere in China, one must rely upon known locations of regionally-recorded explosions. Locating such sources is clearly one of the major problems to be overcome before one can provide event locations with any assurance from regional stations.

  4. The radial distribution of dopant (Cr, Nd, Yb, or Ce) in yttrium aluminum garnet (Y 3Al 5O 12) single crystals grown by the micro-pulling-down method

    NASA Astrophysics Data System (ADS)

    Simura, Rayko; Yoshikawa, Akira; Uda, Satoshi

    2009-12-01

    Dopant distribution in yttrium aluminum garnet (YAG:Y 3Al 5O 12) shaped crystal grown via the micro-pulling-down method depends primarily on the distribution coefficient (k0). The solid-favoring dopants (k0>1.0), Cr and Yb, concentrated in the central core of the crystal, while the liquid-favoring dopants (k0<1.0), Nd and Ce, concentrated in the rim. Secondary rare-earth oxide phases were sometimes segregated and crystallized circumferentially with Nd and Ce dopant. The dopant distribution profile was also controlled by the position of the melt entrance hole in the crucible shaper, which was confirmed by SIMPLER calculation. Segregation/distribution coefficients for Cr, Yb, Nd, and Ce in YAG were found to be 1.5, 1.01, 0.1, and 0.01, respectively.

  5. Synthesis and characterization of p-type conductivity dopant 2-(3-(adamantan-1-yl)propyl)-3,5,6-trifluoro-7,7,8,8-tetracyanoquinodimethane

    SciTech Connect

    Rainbolt, James E.; Koech, Phillip K.; Polikarpov, Evgueni; Swensen, James S.; Cosimbescu, Lelia; Von Ruden, Amber L.; Wang, Liang; Sapochak, Linda S.; Padmaperuma, Asanga B.; Gaspar, Daniel J.

    2013-01-22

    We report the synthesis and characterization of 2-(3-(adamantan-1-yl)propyl)-3,5,6-trifluoro-7,7,8,8-tetracyanoquinodimethane (F3TCNQ-Ad1), a substituted analog of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ), designed for p-type conductivity doping. The dopant is designed as a model for substituted alternatives to F4TCNQ that maintain similar electronic properties with the goal of engineering dopants with superior fabrication characteristics over F4TCNQ. We describe the design strategy for F3TCNQ-Ad1 based on molecular modeling predictions that substitution of a single fluorine atom of F4TCNQ has little effect on the electronic properties of the molecule. Photophysical and electrochemical characterization reveal that the adamantyl substituent in F3TCNQ-Ad1 does not significantly alter the electronic properties of the substituted dopant relative to F4TCNQ. Unfortunately, F3TCNQ-Ad1 degrades under standard sublimation conditions, preventing sublimation deposition processing. Instead, hole-only devices were made via solution-processing of the p-doped films with the structure glass/ITO/2.3 x103Å PVK:(MTDATA:dopant)/2.0x102Å Au/1.0x103Å Al, where dopant is either F4TCNQ or F3TCNQ-Ad1. We demonstrate that F3TCNQ-Ad1 increased the conductivity of the films by at least 1,000 times compared to an undoped device.

  6. Experiences with information locator services

    USGS Publications Warehouse

    Christian, E.

    1999-01-01

    Over the last few years, governments and other organizations have been using new technologies to create networked Information Locator Services that help people find information resources. These services not only enhance access to information, but also are designed to support fundamental information policy principles. This article relates experiences in developing and promoting services interoperable with the Global Information Locator Service standard that has now been adopted and promoted in many forums worldwide. The article describes sample implementations and touches on the strategic choices made in public policy, standards, and technology. Ten recommendations are offered for successful implementation of an Information Locator Service. Published by Elsevier Science Ltd. All rights reserved.

  7. Effects of Cu Dopant on Lattice and Optical Properties of ZnS Quantum Dots.

    PubMed

    Shuhua, Lu; Aiji, Wang; Tingfang, Chen; Yinshu, Wang

    2016-04-01

    Doped and undoped ZnS colloidal nanocrystals have drawn much attention due to their versatile applications in the fields of optoelectronics and biotechnology. In this paper, Cu doped ZnS quantum dots were synthesized via the simple thermolysis of ethylxanthate salts. The lattice and optical properties of the nanocrystals were then studied in detail. The quantum dot lattice contracted linearly between Cu concentrations of 0.2-2%, while it continued to contract more gradually as Cu concentrations were further increased from 4 to 6%, due in part to the Cu ions located on the surface of the ZnS lattice. Cu incorporation induces a long tail in absorption at long wavelengths. The PL spectrum shows a red shift at first, and then a blue shift with increases in Cu concentration. Cu doped at low concentrations (0.2-1%) enhanced the emission, while high Cu concentrations (2-6%) quenched emissions. PMID:27451716

  8. Point Source Location Sensitivity Analysis

    NASA Astrophysics Data System (ADS)

    Cox, J. Allen

    1986-11-01

    This paper presents the results of an analysis of point source location accuracy and sensitivity as a function of focal plane geometry, optical blur spot, and location algorithm. Five specific blur spots are treated: gaussian, diffraction-limited circular aperture with and without central obscuration (obscured and clear bessinc, respectively), diffraction-limited rectangular aperture, and a pill box distribution. For each blur spot, location accuracies are calculated for square, rectangular, and hexagonal detector shapes of equal area. The rectangular detectors are arranged on a hexagonal lattice. The two location algorithms consist of standard and generalized centroid techniques. Hexagonal detector arrays are shown to give the best performance under a wide range of conditions.

  9. Mental Health Treatment Program Locator

    MedlinePlus

    ... County or Zip By Name Other Links State Mental Health Agencies Frequently Asked Questions Links Comments or Questions ... a Facility in Your State To locate the mental health treatment programs nearest you, find your State on ...

  10. Bayesian Mulitple-Event Location

    Energy Science and Technology Software Center (ESTSC)

    2010-03-30

    Bayesloc is a statistical model of the multiple seismic location system, including event hypocenters, corrections to model-based travel time predictions, assessments precision for measurement phase arrival times, and phase lavels which indicate phase ray path.

  11. A thermodynamic analysis of native point defect and dopant solubilities in zinc-blende III-V semiconductors

    SciTech Connect

    Hurle, D. T. J.

    2010-06-15

    A thermodynamic model is used to analyze available experimental data relevant to point defects in the binary zinc-blende III-V compounds (Ga,In)-(P,As,Sb). The important point defects and their complexes in each of the materials are identified and included in the model. Essentially all of the available experimental data on dopant solubility, crystal density, and lattice parameter of melt and solution grown crystals and epilayers are reproduced by the model. It extends an earlier study [Hurle, J. Appl. Phys. 85, 6957 (1999)] devoted solely to GaAs. Values for the enthalpy and entropy of formation of both native and dopant related point defects are obtained by fitting to experimental data. In undoped material, vacancies, and interstitials on the Group V sublattice dominate in the vicinity of the melting point (MP) in both the phosphides and arsenides, whereas, in the antimonides, vacancies on both sublattices dominate. The calculated concentrations of the native point defects are used to construct the solidus curves of all the compounds. The charged native point defect concentrations at the MP in four of the six materials are significantly higher than their intrinsic carrier concentrations. Thus the usually assumed high temperature 'intrinsic' electroneutrality condition for undoped material (n=p) is not valid for these materials. In GaSb, the Ga{sub Sb} antisite defect appears to be grown-in from the melt. This contrasts with the As{sub Ga} defect in GaAs for which the concentration grown-in at the MP is negligibly small. Compensation of donor-doped material by donor-Group III vacancy complexes is shown to exist in all the compounds except InP where Group VI doped crystals are uncompensated and in InSb where there is a lack of experimental data. The annealing effects in n{sup +} GaAs, including lattice superdilation, which were shown in the earlier paper to be due to Group III vacancy undersaturation during cooling, are found to be present also in GaSb and In

  12. Locating the LCROSS Impact Craters

    NASA Technical Reports Server (NTRS)

    Marshall, William; Shirley, Mark; Moratto, Zachary; Colaprete, Anthony; Neumann, Gregory A.; Smith, David E.; Hensley, Scott; Wilson, Barbara; Slade, Martin; Kennedy, Brian; Gurrola, Eric; Harcke, Leif

    2012-01-01

    The Lunar CRater Observations and Sensing Satellite (LCROSS) mission impacted a spent Centaur rocket stage into a permanently shadowed region near the lunar south pole. The Sheperding Spacecraft (SSC) separated approx. 9 hours before impact and performed a small braking maneuver in order to observe the Centaur impact plume, looking for evidence of water and other volatiles, before impacting itself. This paper describes the registration of imagery of the LCROSS impact region from the mid- and near-infrared cameras onboard the SSC, as well as from the Goldstone radar. We compare the Centaur impact features, positively identified in the first two, and with a consistent feature in the third, which are interpreted as a 20 m diameter crater surrounded by a 160 m diameter ejecta region. The images are registered to Lunar Reconnaisance Orbiter (LRO) topographical data which allows determination of the impact location. This location is compared with the impact location derived from ground-based tracking and propagation of the spacecraft's trajectory and with locations derived from two hybrid imagery/trajectory methods. The four methods give a weighted average Centaur impact location of -84.6796 deg, -48.7093 deg, with a 1s uncertainty of 115 m along latitude, and 44 m along longitude, just 146 m from the target impact site. Meanwhile, the trajectory-derived SSC impact location is -84.719 deg, -49.61 deg, with a 1 alpha uncertainty of 3 m along the Earth vector and 75 m orthogonal to that, 766 m from the target location and 2.803 km south-west of the Centaur impact. We also detail the Centaur impact angle and SSC instrument pointing errors. Six high-level LCROSS mission requirements are shown to be met by wide margins. We hope that these results facilitate further analyses of the LCROSS experiment data and follow-up observations of the impact region

  13. Microstructure and Secondary Phase Segregation Correlation in Epitaxial/Oriented ZnO Films with Unfavorable Cr Dopant

    SciTech Connect

    Saraf, Laxmikant V.; Zhu, Zihua; Wang, Chong M.; Engelhard, Mark H.

    2009-02-01

    We discuss the effect of microstructure on the secondary phase segregation region and mobility of carbon impurities in case of poorly soluble Cr as a dopant in ZnO thin films. Thin films of Cr:ZnO ~50 nm in thickness were grown by metal organic chemical vapor deposition (MOCVD) of Zn(TMHD) and Cr(TMHD) precursors in reactive oxygen partial pressure environment. For an accurate comparison among the differences among the grain-boundary density and degree of orientation on the secondary phase segregation and impurity mobility, simultaneous thin film growths were carried out on single crystals of Si (100), c-plane oriented Al2O3 (c-ALO) and r-plane oriented Al2O3 (r-ALO) substrates. High-resolution transmission electron microscopy (HRTEM) measurements across the film substrate interface indicate that growths on Si(100) and c-ALO resulted in highly oriented Cr:ZnO films whereas a good epitaxial growth was observed on r-ALO. The trace carbon impurity detection, secondary phase formation and their mobility properties were studied by sensitive x-ray photoelectron spectroscopy (XPS) and time of flight secondary ion mass spectroscopy (ToF-SIMS). We have observed that secondary phase segregation regions occur near the surface for Cr:ZnO films grown on ALO whereas the region moves near the interface for the growth on Si. Considering the presence of grain boundaries in Cr:ZnO grown on c-ALO and Si, it appears to be a weak relationship between grain boundary density and unfavorable dopant mobility as well as preferred segregation region. A near uniform stress distribution observed at r-ALO/ZnO interface indicates good epitaxial growth by domain matching epitaxy process. We also observe that low carbon impurity distribution in the studied thickness regime remains more or less uniform inside Cr:ZnO. This gives strong evidence that trace amount of carbon is soluble in the Cr:ZnO system as a direct result of oxygen vacancy defects.

  14. The dopant type and amount governs the electrochemical performance of graphene platforms for the antioxidant activity quantification

    NASA Astrophysics Data System (ADS)

    Hui, Kai Hwee; Ambrosi, Adriano; Sofer, Zdeněk; Pumera, Martin; Bonanni, Alessandra

    2015-05-01

    Graphene doped with heteroatoms can show new or improved properties as compared to the original undoped material. It has been reported that the type of heteroatoms and the doping conditions can have a strong influence on the electronic and electrochemical properties of the resulting material. Here, we wish to compare the electrochemical behavior of two n-type and two p-type doped graphenes, namely boron-doped graphenes and nitrogen-doped graphenes containing different amounts of heteroatoms. We show that the boron-doped graphene containing a higher amount of dopants provides the best electroanalytical performance in terms of calibration sensitivity, selectivity and linearity of response for the detection of gallic acid normally used as the standard probe for the quantification of antioxidant activity of food and beverages. Our findings demonstrate that the type and amount of heteroatoms used for the doping have a profound influence on the electrochemical detection of gallic acid rather than the structural properties of the materials such as amounts of defects, oxygen functionalities and surface area. This finding has a profound influence on the application of doped graphenes in the field of analytical chemistry.Graphene doped with heteroatoms can show new or improved properties as compared to the original undoped material. It has been reported that the type of heteroatoms and the doping conditions can have a strong influence on the electronic and electrochemical properties of the resulting material. Here, we wish to compare the electrochemical behavior of two n-type and two p-type doped graphenes, namely boron-doped graphenes and nitrogen-doped graphenes containing different amounts of heteroatoms. We show that the boron-doped graphene containing a higher amount of dopants provides the best electroanalytical performance in terms of calibration sensitivity, selectivity and linearity of response for the detection of gallic acid normally used as the standard probe for

  15. URLs: Uniform Resource Locators or Unreliable Resource Locators.

    ERIC Educational Resources Information Center

    Germain, Carol Anne

    2000-01-01

    This research studies the accessibility of 64 URLs (Uniform Resource Locators) cited in 31 academic journal articles. Discusses the role of citations as scholarly links and examines results of this longitudinal study that found an increasing decline in the availability of URL citations to World Wide Web sties. (Contains 22 references.) (Author/LRW)

  16. Wireless Damage Location Sensing System

    NASA Technical Reports Server (NTRS)

    Woodard, Stanley E. (Inventor); Taylor, Bryant Douglas (Inventor)

    2012-01-01

    A wireless damage location sensing system uses a geometric-patterned wireless sensor that resonates in the presence of a time-varying magnetic field to generate a harmonic response that will experience a change when the sensor experiences a change in its geometric pattern. The sensing system also includes a magnetic field response recorder for wirelessly transmitting the time-varying magnetic field and for wirelessly detecting the harmonic response. The sensing system compares the actual harmonic response to a plurality of predetermined harmonic responses. Each predetermined harmonic response is associated with a severing of the sensor at a corresponding known location thereof so that a match between the actual harmonic response and one of the predetermined harmonic responses defines the known location of the severing that is associated therewith.

  17. Facile fabrication of superhydrophobic flower-like polyaniline architectures by using valine as a dopant in polymerization

    NASA Astrophysics Data System (ADS)

    Sun, Jun; Bi, Hong

    2012-03-01

    A facile method was developed to fabricate superhydrophobic, flower-like polyanline (PANI) architectures with hierarchical nanostructures by adding valine in polymerization as a dopant. The water contact angle of the prepared PANI film was measured to be 155.3°, and the hydrophobic surface of the PANI architectures can be tuned easily by varying the polymerization time as well as valine doping quantity. It is believed that valine plays an important role in not only growth of the hierarchical PANI structures but also formation of the superhydrophobic surface, for it provides functional groups such as sbnd COOH, sbnd NH2 and a hydrophobic terminal group which may further increase intra-/inter-molecular interactions including hydrogen bonding, π-π stacking and hydrophobic properties. Similar flower-like PANI architectures have been prepared successfully by employing other amino acids such as threonine, proline and arginine. This method makes it possible for widespread applications of superhydrophobic PANI film due to its simplicity and practicability.

  18. Influence of Nd dopant amount on microstructure and photoluminescence of TiO2:Nd thin films

    NASA Astrophysics Data System (ADS)

    Wojcieszak, Damian; Mazur, Michal; Kaczmarek, Danuta; Morgiel, Jerzy; Zatryb, Grzegorz; Domaradzki, Jaroslaw; Misiewicz, Jan

    2015-10-01

    TiO2 and TiO2:Nd thin films were deposited using reactive magnetron sputtering process from mosaic Ti-Nd targets with various Nd concentration. The thin films were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM) and spectroscopic techniques. Photoluminescence (PL) in the near infrared obtained upon 514.5 nm excitation was also examined. The relationship between the Nd concentration, structural, optical and photoluminescence properties of prepared thin films was investigated and discussed. XRD and TEM measurements showed that an increase in the Nd concentration in the thin films hinders the crystal growth in the deposited coatings. Depending on the Nd amount in the thin films, TiO2 with the rutile, mixed rutile-amorphous or amorphous phase was obtained. Transmittance measurements revealed that addition of Nd dopant to titania matrix did not deteriorate optical transparency of the coatings, however it influenced on the position of the fundamental absorption edge and therefore on the width of optical band gap energy. All TiO2:Nd thin films exhibited PL emission that occurred at ca. 0.91, 1.09 and 1.38 μm. Finally, results obtained for deposited coatings showed that titania with the rutile structure and 1.0 at.% of Nd was the most efficient in VIS to NIR photon conversion.

  19. Dopant Studies in the BaCe0.9-xZrxY0.103- System

    NASA Technical Reports Server (NTRS)

    Zhong, Zhimin; Sayir, Ali; Dynys, Fred; Heimann, Paula

    2003-01-01

    Protonic separation membranes for the hydrogen industry require thermo-chemical stability and high conductance. The perovskite BaCe0.9Y0.1O3- exhibits excellent proton conduction at high temperatures, but shows poor thermo-chemical tability. Substituting Zr for Ce in BaZr0.9Y0.1O3- improves the thermo-chemical stability but reduces proton conduction. The objective of this work was to study the optimization of protonic conductance and thermo-chemical by changing the ratio of Ce to Zr in BaCe0.9-xZrxY0.1O3-. To elucidate the dopant effect, co-precipitation method has been developed to produce single phase perovskites of composition BaCe0.9-xZrxY0.1O3- (0=x=0.9). The co-precipitation method has been optimized to yield high purity and homogeneous powders with a particle size of 100-200 nm in diameter. The sintering characteristics were studied in temperature range of 1400-1600 C. The effect of Zr substitution on sintering behavior and thermo-chemical stability will be reported.

  20. Effect of acid dopants in biodegradable gel polymer electrolyte and the performance in an electrochemical double layer capacitor

    NASA Astrophysics Data System (ADS)

    Sudhakar, Y. N.; Selvakumar, M.; Krishna Bhat, D.

    2015-09-01

    Proton-conducting biodegradable gellan gum gel polymer electrolytes (GPEs) have been prepared using three different dopants, namely ortho-phosphoric (o-H3PO4), sulfuric (H2SO4) and hydrochloric acids (HCl). The GPEs were cross-linked using borax. The polymeric gels were characterized by spectroscopic, thermal, ionic conductivities and dielectric measurements. Proton conductivity was in the range of 5.1 × 10-3 to 3.7 × 10-4 s cm-1 and activation energies were between 0.14 meV and 0.19 meV, at different temperatures. Among the doped acids, the H3PO4 doped GPE exhibited thermal stability at varying temperature. Electrochemical double layer capacitors (EDLCs) were fabricated using activated carbon as electrode material and GPEs. The EDLCs were tested using cyclic voltammetry, ac impedance spectroscopic and galvanostatic charge-discharge techniques. The maximum specific capacitance value was 146 F g-1 at a scan rate of 2 mV s-1. Quite stable values were obtained at a constant current density up to 1000 cycles.

  1. Experimental observation and computational identification of Sc at Cu{sub 16}{sup +}, a stable dopant-encapsulated copper cage

    SciTech Connect

    Veldeman, Nele; Neukermans, Sven; Lievens, Peter; Hoeltzl, Tibor; Minh Tho Nguyen; Veszpremi, Tamas

    2007-07-15

    We report a combined experimental and computational study of scandium doped copper clusters. The clusters are studied with time-of-flight mass spectrometry after laser fragmentation. Enhanced stabilities for specific cluster sizes in the mass abundance spectra are discussed using both electronic (shell closing) and geometric (symmetry) arguments. The exceptional stability observed for Cu{sub 16}Sc{sup +} is investigated in detail computationally. Density functional geometry optimizations at the Becke-Perdew 1986-LANL 2-double-zeta (BP86/LANL2DZ) level result in a Frank-Kasper tetrahedron, encapsulating a scandium atom in a highly coordinated position. The high stability is therefore interpreted in terms of extremely stable dopant encapsulated structures featuring a closed electron shell. The thermodynamic stability, as indicated by the stable backbone and large binding energy per atom, the relatively small ionization energy, and the moderate electron affinity of the neutral Cu{sub 16}Sc cluster show that it has a superatom character, chemically similar to the alkaline-metal atoms.

  2. Influence of the organic solvents on the properties of the phosphoric acid dopant emulsion deposited on multicrystalline silicon wafers

    NASA Astrophysics Data System (ADS)

    Bouhafs, D.; Moussi, A.; Boumaour, M.; Abaïdia, S. E. K.; Mahiou, L.; Messaoud, A.

    2007-05-01

    This study is devoted to the formation of an n+p emitter for multicrystalline silicon (mc-Si) solar cells for photovoltaic (PV) application. The atomization technique has been used to make the emitter from H3PO4 phosphoric acid as a doping source. The doping emulsion has been optimized using several organic solvents. H3PO4 was mixed with one of these solutions: ethanol, 2-butanol, isopropanol alcohol and deionized water. The volume concentration of H3PO4 does not exceed 20% of the total volume emulsion. The deposit characteristics of the emulsion change with the organic solvent. H3PO4 : 2-butanol gives the best deposited layer with acceptable adherence and uniformity on silicon surface. Fourier transform infrared characterizations show the presence of organic and mineral phosphorous bonds in the formed layer. The obtained emitters are characterized by a junction depth in the range 0.2-0.75 µm and a sheet resistance of about 10-90 Ω/square. Such a low cost dopant source combined with a continuous spray process can effectively reduce the cost per Wp of the PV generator.

  3. Asymmetric Dimers of Chiral Azobenzene Dopants Exhibiting Unusual Helical Twisting Power upon Photoswitching in Cholesteric Liquid Crystals.

    PubMed

    Kim, Yuna; Tamaoki, Nobuyuki

    2016-02-01

    In this study, we synthesized asymmetric dimeric chiral molecules as photon-mode chiral switches for reversible tuning of self-assembled helical superstructures. The chiral switches bearing two mesogen units-cholesterol and azobenzene moieties connected through flexible alkylenedioxy bridges-were doped into nematic liquid crystals, resulting in a chiral nematic (cholesteric) phase. Under irradiation with UV light, photoisomerization of the azobenzene units led to unprecedented switching of the cholesteric pitch and helical twisting power (HTP, β), with a higher HTP found in the cis-rich state (bent-form) than in the trans-state (rod-form). We attribute this behavior to the elongated cybotactic smectic clusters disrupting the helical orientation of the molecules in the cholesteric liquid crystals; their reversible decay and reassembly was evidenced upon sequential irradiation with UV and visible light, respectively. In addition to the photoisomerization of the azobenzene units, the odd/even parity of the alkylenedioxy linkers of the dimeric dopants also had a dramatic effect on the transitions of the cybotactic smectic domains. On the basis of the large rotational reorganization of the cholesteric helix and HTP switching (Δβ/βini of up to 50%), we could control the macroscopic rotational motion of microsized glass rods upon irradiating the surface of a cholesteric liquid crystal film featuring a polygonal fingerprint texture using UV and visible light. PMID:26815738

  4. Effect of nitrogen as co-dopant in carbon and boron-doped ZnO clusters

    NASA Astrophysics Data System (ADS)

    Kapila, Neha; Sharma, Gaurav; Mudahar, Isha; Sharma, Hitesh

    2016-05-01

    The effect of N as co-dopant have been investigated on magnetic properties of C and B-doped (ZnO)n clusters (n = 1 - 16) using spin-polarized density functional theory. Total energy calculations show that C and N more stable when substituted at O site, whereas B is more stable at the Zn site. The B:N co-doping is energetically more stable than C:N which is more stable than N:N doping. C and N atoms do not show tendency to form clusters when doped separately. The magnetic moment (MM) of C-doped ZnO clusters is enhanced significantly with N co-doping. The MM of 2 μB, 1 μB and 1 μB per atom is induced due to C, N and B respectively. The MM of 3 μB or 5 μB and 2 μB or 4 μB are observed for co-doping of 2C:N and C:2N respectively. In contrary, the MM in 2B:N and B:2N co-doped (ZnO)n remains 1 μB for n=2-4, 12 and 16. The results are in agreement with the available theoretical results.

  5. Effects of Metal Particle Dopant on Acoustic Attenuation Properties of Silicone Rubber Lens for Medical Echo Array Probe

    NASA Astrophysics Data System (ADS)

    Yamashita, Yohachi (John); Hosono, Yasuharu; Itsumi, Kazuhiro

    2005-06-01

    A low-acoustic-attenuation silicone rubber lens was developed by using a nanometer-size fine metal powder as a dopant for silicone rubber. Ten-nanometer-platinum (Pt)-powder-doped silicone rubber material showed not only a low sound velocity of 0.858 km/s, but also low acoustic attenuation properties, 0.84 dB/mmMHz with an acoustic impedance of 1.37 MRalys. By virtue of its low sound velocity and low attenuation, the Pt-doped silicone rubber provides a better figure of merit (attenuation x sound velocity) for the acoustic lens material of medical array probes than does silicone-rubber doped with conventional inorganic powders, namely, SiO2, TiO2, or Al2O3. The Pt-doped silicone lens material provides increased sensitivity for the high-frequency, 5 to 10-MHz-probe application because it can be used to realize a thinner lens than conventionally used.

  6. Effects of boron dopants of Si (001) substrates on formation of Ge layers by sputter epitaxy method

    NASA Astrophysics Data System (ADS)

    Tsukamoto, Takahiro; Hirose, Nobumitsu; Kasamatsu, Akifumi; Mimura, Takashi; Matsui, Toshiaki; Suda, Yoshiyuki

    2013-10-01

    The formation of Ge layers on boron-doped Si (001) substrates by our sputter epitaxy method has been investigated. The surface morphology of Ge layers grown on Si substrates depends on the substrate resistance, and flat Ge layers are obtained on Si substrates with 0.015 Ω cm resistivity. Highly boron-doped Si substrates cause a transition in the dislocation structure from complex dislocations with 60° dislocation glide planes to 90° pure-edge dislocations, resulting in the formation of flat Ge layers. Furthermore, we have found that the surface morphology of the Ge layers improves with increasing Ge layer thickness. Ge atoms migrating on the deposited Ge layers tend to position themselves at the reactive sites, where the reactivity is related to the number of bonding contacts between the Ge atom and the surface. This modifies the surface morphology, resulting in a flatter surface. Boron dopants together with the sputter epitaxy method effectively suppress the growth of Ge islands and result in the formation of flat Ge layers.

  7. The effect of dopant and optical micro-cavity on the photoluminescence of Mn-doped ZnSe nanobelts

    PubMed Central

    2013-01-01

    Pure and Mn-doped ZnSe nanobelts were synthesized by a convenient thermal evaporation method. Scanning electron microscopy, X-ray powder diffraction, energy dispersive X-ray spectroscopy and corresponding element mapping, and transmission electron microscope were used to examine the morphology, phase structure, crystallinity, composition, and growth direction of as-prepared nanobelts. Raman spectra were used to confirm the effective doping of Mn2+ into ZnSe nanobelts. Micro-photoluminescence (PL) spectra were used to investigate the emission property of as-prepared samples. A dominant trapped-state emission band is observed in single ZnSeMn nanobelt. However, we cannot observe the transition emission of Mn ion in this ZnSeMn nanobelt, which confirm that Mn powder act as poor dopant. There are weak near-bandgap emission and strong 4T1 → 6A1 transition emission of Mn2+ in single ZnSeMnCl2 and ZnSeMn(CH3COO)2 nanobelt. More interesting, the 4T1 → 6A1 transition emission in ZnSeMn(CH3COO)2 nanobelt split into multi-bands. PL mapping of individual splitted sub-bands were carried out to explore the origin of multi-bands. These doped nanobelts with novel multi-bands emission can find application in frequency convertor and wavelength-tunable light emission devices. PMID:23829706

  8. Effects of nitrogen dopants on the atomic step kinetics and electronic structures of O-polar ZnO

    NASA Astrophysics Data System (ADS)

    Wang, Hao; Zhan, Huahan; Zhou, Yinghui; Wu, Yaping; Chen, Xiaohang; Wang, Huiqiong; Kang, Junyong

    2016-02-01

    Oxygen-polar ZnO films are grown in step flow mode by molecular beam epitaxy. Driven by the step flow anisotropy, the growth leads to the occurrence of specific hexagonal pits in the surface. The specific pits are formed by interlacing steps of the {101&cmb.macr;4&cmb.macr;} facets, thus quenching the macroscopic dipole moment along the c-axis and satisfying the stabilization principles. Nitrogen (N) doping trials are then performed on the basis of the stable surface. In doping, growth remains in step flow mode but the step flow anisotropy vanishes, resulting in an obvious change of the surface morphology. Besides, a distinct acceptor state appears by in situ scanning tunneling spectroscopy analysis. First-principles calculations reveal that N readily substitutes for step-edge Zn and acts as NO2 adsorbed at the step edge. Desorption of the NO2 facilitates the formation of NO-VZn shallow acceptor complexes, which contributes to the appearance of the acceptor state. According to the peculiarities of N dopants on the O-polar surface, vicinal O-polar substrates (e.g., {101&cmb.macr;4&cmb.macr;} substrate) are promising in ZnO : N due to the easily achieved step flow growth and high density of step edges for N incorporation.

  9. Effects of boron dopants of Si (001) substrates on formation of Ge layers by sputter epitaxy method

    SciTech Connect

    Tsukamoto, Takahiro; Suda, Yoshiyuki; Hirose, Nobumitsu; Kasamatsu, Akifumi; Mimura, Takashi; Matsui, Toshiaki

    2013-10-21

    The formation of Ge layers on boron-doped Si (001) substrates by our sputter epitaxy method has been investigated. The surface morphology of Ge layers grown on Si substrates depends on the substrate resistance, and flat Ge layers are obtained on Si substrates with 0.015 Ω cm resistivity. Highly boron-doped Si substrates cause a transition in the dislocation structure from complex dislocations with 60° dislocation glide planes to 90° pure-edge dislocations, resulting in the formation of flat Ge layers. Furthermore, we have found that the surface morphology of the Ge layers improves with increasing Ge layer thickness. Ge atoms migrating on the deposited Ge layers tend to position themselves at the reactive sites, where the reactivity is related to the number of bonding contacts between the Ge atom and the surface. This modifies the surface morphology, resulting in a flatter surface. Boron dopants together with the sputter epitaxy method effectively suppress the growth of Ge islands and result in the formation of flat Ge layers.

  10. Evaluation of river pollution of neonicotinoids in Osaka City (Japan) by LC/MS with dopant-assisted photoionisation.

    PubMed

    Yamamoto, Atsushi; Terao, Tomoko; Hisatomi, Hirotaka; Kawasaki, Hideya; Arakawa, Ryuichi

    2012-08-01

    An atmospheric pressure photoionisation (APPI) source for liquid chromatography/mass spectrometry (LC/MS) was applied to determine neonicotinoid pesticides in the aquatic environment. Dopant-assisted APPI was very effective in the ionisation of neonicotinoids. Neonicotinoids generated protonated molecules in APPI with high sensitivity, while adduct ions, such as sodiated molecules, were predominantly generated in conventional electrospray ionisation. The ionisation of neonicotinoids was confirmed by ultra-high-resolution MS. An analytical method coupled with solid phase extraction was developed for acetamiprid, clothianidin, dinotefuran, imidacloprid, nitenpyram, and thiamethoxam. Method detection limits were 0.47 to 2.1 ng L(-1) for six neonicotinoids. Dinotefuran was the most frequent and highest among the neonicotinoids examined in the aquatic environment in Osaka, Japan. The maximum concentration of dinotefuran was 220 ng L(-1). Given the toxicity of neonicotinoids for aquatic creatures, the concentrations observed here were substantially low. The change in concentrations was temporally coincident with the period of the neonicotinoid application. Although rapid photodegradation and some degradation products have been elucidated, the degradation products in the aquatic environment were not identified in the present study. PMID:22767100

  11. Effects of added dopants on various triboluminescent properties of europium dibenzoylmethide triethylammonium (EuD4TEA)

    NASA Astrophysics Data System (ADS)

    Owens, Constance; Fontenot, Ross S.; Bhat, Kamala N.; Aggarwal, Mohan D.

    2014-03-01

    A triboluminescent (TL) material is one that emits light upon pressure, impact, friction, or mechanical shock. TL materials are desirable for investigation because they have the potential to be used as the active element for smart impact sensors. While the material europium dibenzoylmethide triethylammonium (EuD4TEA) produces a TL emission yield that can be observed by the naked eye, it is still not sufficiently bright for use in smart sensor devices. Previous studies have shown that additional materials can be combined with EuD4TEA in order to improve the TL emission yield. In this paper, we discuss the effects of doping on EuD4TEA at different concentrations with a variety of materials on the TL emission yield and decay times. The dopants that were used in this study were nicotine, dibutyl phosphate (DBP), and magnesium. We also discuss both the effects of pH on EuD4TEA, and the doping effects on impact energy. For testing triboluminescent properties, we use a custom-built drop tower that generates triboluminescence by fracturing compounds through impact. Collected data is analyzed using specially written LabVIEW programs.

  12. Predictors of Rural Practice Location

    ERIC Educational Resources Information Center

    Kegel-Flom, Penelope

    1977-01-01

    Attitudes toward the urban environment and place of origin were found to be the best predictors of an optometrist's practice location. Findings of this study imply that optometry students most likely to enter rural practice can be objectively identified early in their training and that the predictive equation presented may be useful in the…

  13. Negative Geography: Locating Things Elsewhere.

    ERIC Educational Resources Information Center

    Stoddard, Robert H.

    The phenomenon of negative geography--the assertion that any location is better than the one selected--is discussed and ways in which this approach differs from traditional geography methodology are analyzed. Case studies of two citizens' groups which protested the relocation of a city mission and halfway house in their neighborhoods illustrate…

  14. Source Identification and Location Techniques

    NASA Technical Reports Server (NTRS)

    Weir, Donald; Bridges, James; Agboola, Femi; Dougherty, Robert

    2001-01-01

    Mr. Weir presented source location results obtained from an engine test as part of the Engine Validation of Noise Reduction Concepts program. Two types of microphone arrays were used in this program to determine the jet noise source distribution for the exhaust from a 4.3 bypass ratio turbofan engine. One was a linear array of 16 microphones located on a 25 ft. sideline and the other was a 103 microphone 3-D "cage" array in the near field of the jet. Data were obtained from a baseline nozzle and from numerous nozzle configuration using chevrons and/or tabs to reduce the jet noise. Mr. Weir presented data from two configurations: the baseline nozzle and a nozzle configuration with chevrons on both the core and bypass nozzles. This chevron configuration had achieved a jet noise reduction of 4 EPNdB in small scale tests conducted at the Glenn Research Center. IR imaging showed that the chevrons produced significant improvements in mixing and greatly reduced the length of the jet potential core. Comparison of source location data from the 1-D phased array showed a shift of the noise sources towards the nozzle and clear reductions of the sources due to the noise reduction devices. Data from the 3-D array showed a single source at a frequency of 125 Hz. located several diameters downstream from the nozzle exit. At 250 and 400 Hz., multiple sources, periodically spaced, appeared to exist downstream of the nozzle. The trend of source location moving toward the nozzle exit with increasing frequency was also observed. The 3-D array data also showed a reduction in source strength with the addition of chevrons. The overall trend of source location with frequency was compared for the two arrays and with classical experience. Similar trends were observed. Although overall trends with frequency and addition of suppression devices were consistent between the data from the 1-D and the 3-D arrays, a comparison of the details of the inferred source locations did show differences. A

  15. Earthquake location in island arcs

    USGS Publications Warehouse

    Engdahl, E.R.; Dewey, J.W.; Fujita, K.

    1982-01-01

    A comprehensive data set of selected teleseismic P-wave arrivals and local-network P- and S-wave arrivals from large earthquakes occurring at all depths within a small section of the central Aleutians is used to examine the general problem of earthquake location in island arcs. Reference hypocenters for this special data set are determined for shallow earthquakes from local-network data and for deep earthquakes from combined local and teleseismic data by joint inversion for structure and location. The high-velocity lithospheric slab beneath the central Aleutians may displace hypocenters that are located using spherically symmetric Earth models; the amount of displacement depends on the position of the earthquakes with respect to the slab and on whether local or teleseismic data are used to locate the earthquakes. Hypocenters for trench and intermediate-depth events appear to be minimally biased by the effects of slab structure on rays to teleseismic stations. However, locations of intermediate-depth events based on only local data are systematically displaced southwards, the magnitude of the displacement being proportional to depth. Shallow-focus events along the main thrust zone, although well located using only local-network data, are severely shifted northwards and deeper, with displacements as large as 50 km, by slab effects on teleseismic travel times. Hypocenters determined by a method that utilizes seismic ray tracing through a three-dimensional velocity model of the subduction zone, derived by thermal modeling, are compared to results obtained by the method of joint hypocenter determination (JHD) that formally assumes a laterally homogeneous velocity model over the source region and treats all raypath anomalies as constant station corrections to the travel-time curve. The ray-tracing method has the theoretical advantage that it accounts for variations in travel-time anomalies within a group of events distributed over a sizable region of a dipping, high

  16. A phononic crystal strip based on silicon for support tether applications in silicon-based MEMS resonators and effects of temperature and dopant on its band gap characteristics

    NASA Astrophysics Data System (ADS)

    Ha, Thi Dep; Bao, JingFu

    2016-04-01

    Phononic crystals (PnCs) and n-type doped silicon technique have been widely employed in silicon-based MEMS resonators to obtain high quality factor (Q) as well as temperature-induced frequency stability. For the PnCs, their band gaps play an important role in the acoustic wave propagation. Also, the temperature and dopant doped into silicon can cause the change in its material properties such as elastic constants, Young's modulus. Therefore, in order to design the simultaneous high Q and frequency stability silicon-based MEMS resonators by two these techniques, a careful design should study effects of temperature and dopant on the band gap characteristics to examine the acoustic wave propagation in the PnC. Based on these, this paper presents (1) a proposed silicon-based PnC strip structure for support tether applications in low frequency silicon-based MEMS resonators, (2) influences of temperature and dopant on band gap characteristics of the PnC strips. The simulation results show that the largest band gap can achieve up to 33.56 at 57.59 MHz and increase 1280.13 % (also increase 131.89 % for ratio of the widest gaps) compared with the counterpart without hole. The band gap properties of the PnC strips is insignificantly effected by temperature and electron doping concentration. Also, the quality factor of two designed length extensional mode MEMS resonators with proposed PnC strip based support tethers is up to 1084.59% and 43846.36% over the same resonators with PnC strip without hole and circled corners, respectively. This theoretical study uses the finite element analysis in COMSOL Multiphysics and MATLAB softwares as simulation tools. This findings provides a background in combination of PnC and dopant techniques for high performance silicon-based MEMS resonators as well as PnC-based MEMS devices.

  17. Achieving high power efficiency and low roll-off OLEDs based on energy transfer from thermally activated delayed excitons to fluorescent dopants.

    PubMed

    Wang, Shipan; Zhang, Yuewei; Chen, Weiping; Wei, Jinbei; Liu, Yu; Wang, Yue

    2015-08-01

    Achieving high power efficiencies at high-brightness levels is still an important issue for organic light-emitting diodes (OLEDs) based on the thermally activated delayed fluorescence (TADF) mechanism. Herein, enhanced electroluminescence efficiencies were achieved in fluorescent OLEDs using a TADF molecule, (4s,6s)-2,4,5,6-tetra(9H-carbazol-9-yl)isophthalonitrile (4CzIPN), as a host and quinacridone derivatives (QA) as fluorescent dopants. PMID:26120606

  18. Regional Location Calibration in Asia

    NASA Astrophysics Data System (ADS)

    Steck, L. K.; Hartse, H.; Aprea, C.; Franks, J.; Velasco, A.; Randall, G.; Bradley, C.; Begnaud, M.; Aguilar-Chang, J.

    2002-12-01

    This paper presents a spectrum of issues and efforts involved in improving seismic location performance worldwide. Our efforts are largely designed around providing validated, rigorously calibrated travel times, azimuths, and slownesses along with accurate error estimates. To do so entails a significant effort that includes data mining, data integration, database management, developing optimal 1-, 2-, and 3-D Earth models, using the Earth models to predict wave propagation, developing corrections and errors for travel times, azimuths, and slownesses, and validation of all products. Results presented here will focus on Asia. For the region around station MAKZ in north-central Asia we have looked at several tens of published 1-D velocity models. For each model, travel time calculations were performed, predictions for P and S arrivals were established, and the predicted times were compared to the observed. We will present best-fit models for tectonic provinces out to regional distances from MAKZ. Previous work has shown that Non-stationary Modified Bayesian Kriging of travel time residuals successfully improves regional seismic event location, and this method is being extended to calculate corrections for azimuth and slowness. The ability to krig over 3-D Earth models is also being implemented. In order to produce the most useful corrections, we require accurate ground truth. For this we are continuing efforts to create a location database consisting of the best available seismic event locations and the most accurate and precise travel times. Building this database relies on participation from universities, other NNSA laboratories, and contacts in private industry. Through the kriging procedure we are able to stabilize location algorithms, but the ultimate usefulness of the corrections themselves is directly related to the quality of the ground truth from which the corrections are derived. Indeed, epicentral mislocations from EvLoc using travel time correction

  19. Effects of Zn2+ and Pb2+ dopants on the activity of Ga2O3-based photocatalysts for water splitting.

    PubMed

    Wang, Xiang; Shen, Shuai; Jin, Shaoqing; Yang, Jingxiu; Li, Mingrun; Wang, Xiuli; Han, Hongxian; Li, Can

    2013-11-28

    Zn-doped and Pb-doped β-Ga2O3-based photocatalysts were prepared by an impregnation method. The photocatalyst based on the Zn-doped β-Ga2O3 shows a greatly enhanced activity in water splitting while the Pb-doped β-Ga2O3 one shows a dramatic decrease in activity. The effects of Zn(2+) and Pb(2+) dopants on the activity of Ga2O3-based photocatalysts for water splitting were investigated by HRTEM, XPS and time-resolved IR spectroscopy. A ZnGa2O4-β-Ga2O3 heterojunction is formed in the surface region of the Zn-doped β-Ga2O3 and a slower decay of photogenerated electrons is observed. The ZnGa2O4-β-Ga2O3 heterojunction exhibits type-II band alignment and facilitates charge separation, thus leading to an enhanced photocatalytic activity for water splitting. Unlike Zn(2+) ions, Pb(2+) ions are coordinated by oxygen atoms to form polyhedra as dopants, resulting in distorted surface structure and fast decay of photogenerated electrons of β-Ga2O3. These results suggest that the Pb dopants act as charge recombination centers expediting the recombination of photogenerated electrons and holes, thus decreasing the photocatalytic activity. PMID:24121670

  20. Dopant Enriched Nitrogen Gas Combined with Sheathless Capillary Electrophoresis-Electrospray Ionization-Mass Spectrometry for Improved Sensitivity and Repeatability in Glycopeptide Analysis.

    PubMed

    Kammeijer, Guinevere S M; Kohler, Isabelle; Jansen, Bas C; Hensbergen, Paul J; Mayboroda, Oleg A; Falck, David; Wuhrer, Manfred

    2016-06-01

    Over the last years, numerous strategies have been proposed to enhance both ionization efficiency and spray stability in electrospray ionization (ESI), in particular for nanospray applications. In nano-liquid chromatography-mass spectrometry (nano-LC-ESI-MS), a better ESI performance has been observed when a coaxial gas flow is added around the ESI emitter. Moreover, enrichment of the gas with an organic dopant has led to an improved desolvation and ionization efficiency with an overall enhanced sensitivity. In this study, the use of a dopant enriched nitrogen (DEN)-gas combined with sheathless capillary electrophoresis (CE)-ESI-MS was evaluated for glycopeptide analysis. Using acetonitrile as a dopant, an increased sensitivity was observed compared to conventional sheathless CE-ESI-MS. Up to 25-fold higher sensitivities for model glycopeptides were obtained, allowing for limits of detection unachieved by state-of-the-art nano-LC-ESI-MS. The effect of DEN-gas on the repeatability and intermediate precision was also investigated. When compared to previously reported nano-LC-ESI-MS measurements, similar values were found for CE-ESI-MS with DEN-gas. The enhanced repeatability fosters the use of DEN-gas sheathless CE-ESI-MS in protein glycosylation analysis, where precision is essential. The use of DEN-gas opens new avenues for highly sensitive sheathless CE-ESI-MS approaches in glycoproteomics research, by significantly improving sensitivity and precision. PMID:27119460