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Sample records for ga co-doping effect

  1. Enhanced stability of Eu in GaN nanoparticles: Effects of Si co-doping

    SciTech Connect

    Kaur, Prabhsharan; Sekhon, S. S.; Zavada, J. M.; Kumar, Vijay

    2015-06-14

    Ab initio calculations on Eu doped (GaN){sub n} (n = 12, 13, and 32) nanoparticles show that Eu doping in nanoparticles is favorable compared with bulk GaN as a large fraction of atoms lie on the surface where strain can be released compared with bulk where often Eu doping is associated with a N vacancy. Co-doping of Si further facilitates Eu doping as strain from an oversized Eu atom and an undersized Si atom is compensated. These results along with low symmetry sites in nanoparticles make them attractive for developing strongly luminescent nanomaterials. The atomic and electronic structures are discussed using generalized gradient approximation (GGA) for the exchange-correlation energy as well as GGA + U formalism. In all cases of Eu (Eu + Si) doping, the magnetic moments are localized on the Eu site with a large value of 6μ{sub B} (7μ{sub B}). Our results suggest that co-doping can be a very useful way to achieve rare-earth doping in different hosts for optoelectronic materials.

  2. Effects of doping concentration and co-doping with cerium on the luminescence properties of Gd3Ga5O12:Cr3+ for thermometry applications

    NASA Astrophysics Data System (ADS)

    Pareja, Jhon; Litterscheid, Christian; Molina, Alejandro; Albert, Barbara; Kaiser, Bernhard; Dreizler, Andreas

    2015-09-01

    The accuracy of surface temperature measurements using thermographic phosphors relies on an extensive knowledge of the temperature-dependent properties of the phosphor. This paper addresses the effects of doping concentration and co-doping with cerium on the luminescence properties of the Gd3Ga5O12:Cr3+ phosphor. High-crystallinity Gd3Ga5O12:Cr3+,Ce3+ powder samples (GGG:Cr,Ce) with different Cr3+ and Ce3+ concentrations were synthesized, and their luminescence spectra as well as their decay lifetime properties were characterized after UV laser excitation. Results revealed that the concentration quenching decreases the luminescence lifetime at concentrations above 0.5 mol% Cr3+ while the emission spectrum remains independent of the Cr3+ concentration. Co-doping with small amounts of Ce3+ improves the temperature-dependent luminescence characteristics by reducing the afterglow and producing fairly mono-exponential luminescence decays without changing the lifetime.

  3. Effect of Mg2+ ions co-doping on timing performance and radiation tolerance of Cerium doped Gd3Al2Ga3O12 crystals

    NASA Astrophysics Data System (ADS)

    Lucchini, M. T.; Babin, V.; Bohacek, P.; Gundacker, S.; Kamada, K.; Nikl, M.; Petrosyan, A.; Yoshikawa, A.; Auffray, E.

    2016-04-01

    Inorganic scintillators with high density and high light yield are of major interest for applications in medical imaging and high energy physics detectors. In this work, the optical and scintillation properties of Mg co-doped Ce:Gd3Al2Ga3O12 crystals, grown using Czochralski technique, have been investigated and compared with Ce:Gd3Al2Ga3O12 ones prepared with identical technology. Improvements in the timing performance of the Mg co-doped samples with respect to Ce:Gd3Al2Ga3O12 ones have been measured, namely a substantial shortening of the rise time and scintillation decay components and lower afterglow were achieved. In particular, a significantly better coincidence time resolution of 233 ps FWHM, being a fundamental parameter for TOF-PET devices, has been observed in Mg co-doped crystals. The samples have also shown a good radiation tolerance under high doses of γ-rays, making them suitable candidates for applications in harsh radiation environments, such as detectors at future collider experiments.

  4. Energetics and magnetism of Co-doped GaN(0001) surfaces: A first-principles study

    SciTech Connect

    Qin, Zhenzhen; Xiong, Zhihua Chen, Lanli; Qin, Guangzhao

    2014-12-14

    A comprehensive first-principles study of the energetics, electronic, and magnetic properties of Co-doped GaN(0001) thin films are presented and the effect of surface structure on the magnetic coupling between Co atoms is demonstrated. It is found that Co atoms prefer to substitute the surface Ga sites in different growth conditions. In particular, a CoN/GaN interface structure with Co atoms replacing the first Ga layer is preferred under N-rich and moderately Ga-rich conditions, while CoGa{sub x}/GaN interface is found to be energetically stable under extremely Ga-rich conditions. It is worth noted that the antiferromagnetic coupling between Co atoms is favorable in clean GaN(0001) surface, but the existence of ferromagnetism would be expected to occur as Co concentration increased in Ga-bilayer GaN(0001) surface. Our study provides the theoretical understanding for experimental research on Co-doped GaN films and might promise the Co:GaN system potential applications in spin injection devices.

  5. Ceria co-doping: synergistic or average effect?

    PubMed

    Burbano, Mario; Nadin, Sian; Marrocchelli, Dario; Salanne, Mathieu; Watson, Graeme W

    2014-05-14

    Ceria (CeO2) co-doping has been suggested as a means to achieve ionic conductivities that are significantly higher than those in singly doped systems. Rekindled interest in this topic over the last decade has given rise to claims of much improved performance. The present study makes use of computer simulations to investigate the bulk ionic conductivity of rare earth (RE) doped ceria, where RE = Sc, Gd, Sm, Nd and La. The results from the singly doped systems are compared to those from ceria co-doped with Nd/Sm and Sc/La. The pattern that emerges from the conductivity data is consistent with the dominance of local lattice strains from individual defects, rather than the synergistic co-doping effect reported recently, and as a result, no enhancement in the conductivity of co-doped samples is observed. PMID:24658460

  6. Ab-initio study on electronic and magnetic properties of (Ga,Co) co-doped ZnO

    NASA Astrophysics Data System (ADS)

    González-García, A.; Mendoza-Estrada, V.; López-Pérez, W.; Pinilla-Castellanos, C.; González-Hernández, R.

    2016-08-01

    Using first-principles calculations based on density functional theory within GGA formalism, we have studied the electronic structure and magnetic properties of (Ga,Co) co-doped ZnO system. The effect of impurity distances on ferromagnetic and antiferromagnetic ground state in Co0.056Zn0.944O has been studied. For the closest Co-Co distance, a ferromagnetic ground state with total magnetic moment of ∼⃒3.00μB per Co atom has been found. The electronic structure also displays a nearly halfmetallic order. Conversely, for the farthest Co-Co distance an antiferromagnetic ground state was found for Co0.056Zn0.944O. When Zn2+ ions are replaced by Ga ions in Co0.056Zn0.944O, the new (Ga,Co) co-doped ZnO system is more energetically stable. It has also been found that Ga-doping reduces the Co0.056Zn0.944O band gap due to the sp-d exchange interactions, which is in good agreement with the experimental data. Moreover, the Ga-doping changes the nearly halmetallic order of Co0.056Zn0944O to metallic. Results also show that Ga0.029Co0.056Zn0.915O is still ferromagnetic with a total magnetic moment of ∼⃒3.00μB per Co atom. It was also found that the ferromagnetic ground state in (Ga,Co) co-doped ZnO vanishes as Ga concentration increases.

  7. Sol-gel derived Al-Ga co-doped transparent conducting oxide ZnO thin films

    NASA Astrophysics Data System (ADS)

    Serrao, Felcy Jyothi; Sandeep, K. M.; Bhat, Shreesha; Dharmaprakash, S. M.

    2016-05-01

    Transparent conducting ZnO doped with Al, Ga and co-doped Al and Ga (1:1) (AGZO) thin films were grown on glass substrates by cost effective sol-gel spin coating method. The XRD results showed that all the films are polycrystalline in nature and highly textured along the (002) plane. Enhanced grain size was observed in the case of AGZO thin films. The transmittance of all the films was more than 83% in the visible region of light. The electrical properties such as carrier concentration and mobility values are increased in case of AGZO compared to that of Al and Ga doped ZnO thin films. The minimum resistivity of 2.54 × 10-3 Ω cm was observed in AGZO thin film. The co-doped AGZO thin films exhibited minimum resistivity and high optical transmittance, indicate that co-doped ZnO thin films could be used in transparent electronics mainly in display applications.

  8. Reverse magnetostructural transformation in Co-doped NiMnGa multifunctional alloys

    NASA Astrophysics Data System (ADS)

    Fabbrici, S.; Albertini, F.; Paoluzi, A.; Bolzoni, F.; Cabassi, R.; Solzi, M.; Righi, L.; Calestani, G.

    2009-07-01

    We studied the composition dependence of the structural and magnetic properties of Co-doped Ni-Mn-Ga alloys around the Mn-rich composition Ni50Mn30Ga20. By varying the Co and Mn content we have been able to tune the critical temperatures. In particular, in a suitable composition range, the Curie temperature of martensite is lower than Curie temperature of austenite and lower than martensitic transformation temperature, giving rise to a paramagnetic gap between magnetically ordered martensite and austenite and to the occurrence of a reverse magnetostructural transformation.

  9. Control of selforganized magnetic nanocrystals aggregation in (Ga,Fe)N by co-doping with shallow donors and acceptors

    NASA Astrophysics Data System (ADS)

    Bonanni, A.; Navarro-Quezada, A.; Li, T.; Kiecana, M.; Sawicki, M.; Dietl, T.

    2008-03-01

    A number of possible room temperature functionalities has recently been proposed for magnetically doped semiconductors, in which spinodal decomposition leads to the self-organized formation of coherent ferromagnetic nanodots or nanocolumns [1]. It has also been suggested that the decomposition can be controlled in a wide range by growth conditions and co-doping [2]. We have extended our previous structural and magnetic studies of (Ga,Fe)N [3] by examining the effects of Si and Mg co-doping. As before, we have found the magnetic response to consist of a paramagnetic signal from substitutional Fe and of a ferromagnetic component due to Fe1-xN nanocrystals. Our results demonstrate that the co-doping reduces the fractional concentration of Fe contributing to the nanocrystals. This shows that tuning of the Fermi energy by changing the charge state of the transition metal ions affects their aggregation, as proposed recently [2].1. H.Katayama-Yosida et al., phys.stat. sol. (a) 204, 15 (2007); T.Dietl, arXiv:0711.0343. 2. S.Kuroda et al., Nature Mat. 6, 440 (2007). 3. A.Bonanni et al., Phys. Rev. B 75, 125210 (2007).

  10. Isoelectronic co-doping

    DOEpatents

    Mascarenhas, Angelo

    2004-11-09

    Isoelectronic co-doping of semiconductor compounds and alloys with deep acceptors and deep donors is used to decrease bandgap, to increase concentration of the dopant constituents in the resulting alloys, and to increase carrier mobilities lifetimes. Group III-V compounds and alloys, such as GaAs and GaP, are isoelectronically co-doped with, for example, N and Bi, to customize solar cells, thermal voltaic cells, light emitting diodes, photodetectors, and lasers on GaP, InP, GaAs, Ge, and Si substrates. Isoelectronically co-doped Group II-VI compounds and alloys are also included.

  11. Enhancement of 1.5 μm emission under 980 nm resonant excitation in Er and Yb co-doped GaN epilayers

    NASA Astrophysics Data System (ADS)

    Wang, Q. W.; Li, J.; Lin, J. Y.; Jiang, H. X.

    2016-10-01

    The Erbium (Er) doped GaN is a promising gain medium for optical amplifiers and solid-state high energy lasers due to its high thermal conductivity, wide bandgap, mechanical hardness, and ability to emit in the highly useful 1.5 μm window. Finding the mechanisms to enhance the optical absorption efficiency at a resonant pump wavelength and emission efficiency at 1.5 μm is highly desirable. We report here the in-situ synthesis of the Er and Yb co-doped GaN epilayers (Er + Yb:GaN) by metal-organic chemical vapor deposition (MOCVD). It was observed that the 1.5 μm emission intensity of the Er doped GaN (Er:GaN) under 980 nm resonant pump can be boosted by a factor of 7 by co-doping the sample with Yb. The temperature dependent PL emission at 1.5 μm in the Er + Yb:GaN epilayers under an above bandgap excitation revealed a small thermal quenching of 12% from 10 to 300 K. From these results, it can be inferred that the process of energy transfer from Yb3+ to Er3+ ions is highly efficient, and non-radiative recombination channels are limited in the Er + Yb:GaN epilayers synthesized in-situ by MOCVD. Our results point to an effective way to improve the emission efficiency of the Er doped GaN for optical amplification and lasing applications.

  12. (Ga,N) and (Cu,Ga) Co-Doped ZnO Films for Improving Photoelectrochemical Response for Solar Driven Hydrogen Production

    SciTech Connect

    Shet, S.

    2010-01-01

    In this study, Bandgap-reduced p-type ZnO thin films were synthesized through Cu and Ga co-doping. The ZnO:(Cu,Ga) films were synthesized by RF magnetron sputtering in O2 gas ambient at room temperature and then annealed at 500{sup o} in air for 2 hours. We found that the carrier concentration tuning does not significantly change the bandgap and crystallinity of the ZnO:Cu films. However, it can optimize the carrier concentration and thus dramatically enhance PEC response for the bandgap-reduced p-type ZnO thin films. The co-doped ZnO:(Ga,N) films were deposited by co-sputtering at room temperature, followed by post-annealing at 500{sup o}. We found that the ZnO:(Ga,N) films exhibited greatly enhanced crystallinity compared to ZnO:N films doped with pure N. Furthermore, the ZnO:(Ga,N) films showed much higher N-incorporation than ZnO:N films. As a result, the ZnO:(Ga,N) films showed significantly higher photocurrents than ZnO:N films.

  13. Co-doping effects of Gd and Ag on YBCO films derived by metalorganic deposition

    NASA Astrophysics Data System (ADS)

    Sun, Meijuan; Liu, Zhiyong; Bai, Chuanyi; Guo, Yanqun; Lu, Yuming; Fan, Feng; Cai, Chuanbing

    2015-12-01

    Y1-xGdxBa2Cu3O7-δ-Ag (x = 0, 0.25, 0.5, 0.75, 1) thin films were prepared on oxide buffered Hastelloy substrates by low fluorine metalorganic depostion (MOD) process. The effects of co-doping of Ag and Gd on the microstructures and superconducting properties of YBCO thin films are investigated with respect to improvement on texture and superconducting performance in case of optimized doping content. It is found that optimum addition of Ag and Gd may lead to better c-axis orientation, superior surface microstructure and finally give rise to much improvement of superconducting performance.

  14. Vibrationally induced center reconfiguration in co-doped GaN:Eu, Mg epitaxial layers: Local hydrogen migration vs. activation of non-radiative channels

    SciTech Connect

    Mitchell, B.; Dierolf, V.; Lee, D.; Lee, D.; Fujiwara, Y.

    2013-12-09

    Europium doped gallium nitride (GaN:Eu) is a promising candidate as a material for red light emitting diodes. When Mg was co-doped into GaN:Eu, additional incorporation environments were discovered that show high excitation efficiency at room temperature and have been attributed to the coupling of Mg-H complexes to the majority Eu site. Electron beam irradiation, indirect and resonant (direct) laser excitation were found to modify these complexes, indicating that vibrational energy alone can trigger the migration of the H while the presence of additional charges and excess energy controls the type of reconfiguration and the activation of non-radiative decay channels.

  15. Sol-gel production of Cu/Al co-doped zinc oxide: Effect of Al co-doping concentration on its structure and optoelectronic properties

    NASA Astrophysics Data System (ADS)

    Bu, Ian Yi-Yu

    2014-12-01

    Sol-gel deposition of ZnO:Cu:Al thin films were co-doped different Cu:Al ratio. The optoelectronic and structural properties of the resultant film were evaluated using scanning electron microscopy, X-ray diffraction, energy dispersive spectroscopy, photoluminescence spectroscopy and UV-VIS spectroscopy. It was found that the Al content leads to narrowing of the band gap and that excessive Al doping concentration greater than 5 at% degrade the film's properties.

  16. Co-co-doping Effect on Superconducting Properties of 112-Type Ca0.8La0.2FeAs2 Single Crystals

    NASA Astrophysics Data System (ADS)

    Xing, Xiangzhuo; Zhou, Wei; Xu, Baozhang; Li, Na; Sun, Yiran; Zhang, Yufeng; Shi, Zhixiang

    2015-07-01

    We systematically investigated the Co-co-doping effects in Ca0.8La0.2FeAs2 superconductors. The superconducting transition temperature (Tc) decreases almost linearly with increasing Co content. Simultaneously, it is found that the (Ca,La)112 phase is so sensitive to the Co doping level that chemical phase separation becomes more and more apparent as a result of formation of the (Ca,La)122 phase. The maximum Co doping level for 112 phase seems very low, indicating a quite cruel growth condition for 112 compared with other IBSs.

  17. Effects of F- on the optical and spectroscopic properties of Yb3+/Al3+-co-doped silica glass

    NASA Astrophysics Data System (ADS)

    Xu, Wenbin; Yu, Chunlei; Wang, Shikai; Lou, Fengguang; Feng, Suya; Wang, Meng; Zhou, Qinling; Chen, Danping; Hu, Lili; Guzik, Malgorzata; Boulon, Georges

    2015-04-01

    Yb3+/Al3+-co-doped silica glasses with different F- content were prepared in this work by sol-gel method combined with high temperature sintering. XRF, FTIR and XPS methods were used to confirm the presence of F-. The effects of F- on the optical and spectroscopic properties of these glasses have been investigated. It is worth to notice that the F-/Si4+ mass ratio equal to 9% is a significant value showing a real change in the variation trends of numerous following parameters: refractive index, UV absorption edge, absorption and emission cross sections, scalar crystal-field NJ and fluorescent lifetimes. Furthermore, introduction of F- can adjust the refractive index of Yb3+/Al3+-co-doped silica glass and it is useful for large mode area (LMA) fibers.

  18. Enhanced magnetocaloric effect in a Co-doped Heusler Mn50Ni37Co3In10 unidirectional crystal

    NASA Astrophysics Data System (ADS)

    Ren, Jian; Feng, Shutong; Fang, Yue; Zhai, Qijie; Luo, Zhiping; Zheng, Hongxing

    2016-11-01

    A high-pressure optical zone-melting technique was employed to grow a Mn-rich Heusler Mn50Ni37Co3In10 unidirectional crystal in the present study. It was found that the Co-doped Mn50Ni37Co3In10 unidirectional crystal showed a low magnetic hysteretic loss and a widened working temperature interval in the vicinity of the martensitic transformation. The inverse magnetic entropy change (∆SM) reached 7.84 Jkg-1K-1 around 237.5 K under a magnetic field change of 30 kOe, and the corresponding effective refrigeration capacity (RCeff) was about 127.2 Jkg-1. The experimental results demonstrated a high potential to develop high-performance Mn-rich Heusler Mn-Ni-In magnetocaloric materials by means of Co doping in combination with the high-pressure optical zone-melting fabrication technique.

  19. Effects of acceptor-donor complexes on electronic structure properties in co-doped TiO2: A first-principles study

    NASA Astrophysics Data System (ADS)

    Zhang, L.; Cai, L. L.; Yuan, X. B.; Hu, G. C.; Ren, J. F.

    2016-07-01

    We theoretically investigate the doping effects induced by impurity complexes on the electronic structures of anatase TiO2 based on the density functional theory. Mono-doping and co-doping effects are discussed separately. The results show that the impurity doping can make the band-edges shift. The induced defect levels in the band gaps by impurity doping reduce the band gap predominantly. The compensated acceptor-donor pairs in the co-doped TiO2 will improve the photoelectrochemical activity. From the calculations, it is also found that (S+Zr)-co-doped TiO2 has the ideal band gap and band edge, at the same time, the binding energy is higher than other systems, so (S+Zr)-co-doping in TiO2 is more promise in photoelectrochemical experiments.

  20. Effects of Co doping on the metamagnetic states of the ferromagnetic fcc Fe-Co alloy.

    PubMed

    Ortiz-Chi, Filiberto; Aguayo, Aarón; de Coss, Romeo

    2013-01-16

    The evolution of the metamagnetic states in the ferromagnetic face centered cubic (fcc) Fe(1-x)Co(x) alloy as a function of Co concentration has been studied by means of first-principles calculations. The ground state properties were obtained using the full-potential linear augmented plane wave method and the generalized gradient approximation for the exchange-correlation functional. The alloying was modeled using the virtual crystal approximation and the magnetic states were obtained from the calculations of the total energy as a function of the spin moment, using the fixed spin moment method. For ferromagnetic fcc Fe, the binding-energy curve shows metamagnetic behavior, with two minima corresponding to a small-volume, low-spin (LS) state and a large-volume, high-spin (HS) state, which are separated by a small energy (E(LS) ≲ E(HS)). The evolution of the magnetic moment, the exchange integral (J), and the binding-energy curve is analyzed in the whole range of Co concentrations (x). The magnetic moment corresponding to the HS state decreases monotonically from 2.6 μ(B)/atom in fcc Fe to 1.7 μ(B)/atom in fcc Co. In contrast, the exchange integral for the HS state shows a maximum at around x = 0.45. The thermal dependence of the lattice parameter is evaluated with a method based on statistical mechanics using the binding-energy curve as an effective potential. It is observed that the behavior of the lattice parameter with temperature is tuned by Co doping, from negative thermal expansion in fcc Fe to positive thermal expansion in fcc Co, through the modification of the energetics of the metamagnetic states.

  1. Magneto-optical spectrum and the effective excitonic Zeeman splitting energies of Mn and Co-doped CdSe nanowires

    SciTech Connect

    Xiong, Wen; Chen, Wensuo

    2013-12-21

    The electronic structure of Mn and Co-doped CdSe nanowires are calculated based on the six-band k·p effective-mass theory. Through the calculation, it is found that the splitting energies of the degenerate hole states in Mn-doped CdSe nanowires are larger than that in Co-doped CdSe nanowires when the concentration of these two kinds of magnetic ions is the same. In order to analysis the magneto-optical spectrum of Mn and Co-doped CdSe nanowires, the four lowest electron states and the four highest hole states are sorted when the magnetic field is applied, and the 10 lowest optical transitions between the conduction subbands and the valence subbands at the Γ point in Mn and Co-doped CdSe nanowires are shown in the paper, it is found that the order of the optical transitions at the Γ point almost do not change although two different kinds of magnetic ions are doped in CdSe nanowires. Finally, the effective excitonic Zeeman splitting energies at the Γ point are found to increase almost linearly with the increase of the concentration of the magnetic ions and the magnetic field; meanwhile, the giant positive effective excitonic g factors in Mn and Co-doped CdSe nanowires are predicted based on our theoretical calculation.

  2. Effect of co-doping Tm3+ ions on the emission properties of Dy3+ ions in tellurite glasses

    NASA Astrophysics Data System (ADS)

    Sasikala, T.; Rama Moorthy, L.; Mohan Babu, A.; Srinivasa Rao, T.

    2013-07-01

    The present work reports the absorption, photoluminescence and decay properties of singly doped Dy3+ and co-doped Dy3+/Tm3+ ions in TeO2+ZnO+K2O+CaO (TZKC) glasses prepared by the melt quenching technique. The glassy nature of the host glass has been confirmed by X-ray diffraction analysis and the primary vibrational modes were determined from the Raman spectrum. Judd-Ofelt (JO) analysis has been used to calculate the radiative transition rates, branching ratios and radiative lifetime of the emitting 4F9/2 state. The effect of co-doping of different concentrations of Tm3+ ions on the emission properties of Dy3+ ions has been investigated. The decay profiles of the 4F9/2 level were fitted to double exponential as well as Inokuti-Hirayama (IH) model to determine the energy transfer rates between Dy3+ and Tm3+ ions. The energy transfer rates found to increase with the increase of Tm3+ ions concentration. The chromaticity coordinates and color purity of the emitted light for all glasses were determined.

  3. Electrical properties of Ge crystals and effective Schottky barrier height of NiGe/Ge junctions modified by P and chalcogen (S, Se, or Te) co-doping

    NASA Astrophysics Data System (ADS)

    Koike, Masahiro; Kamimuta, Yuuichi; Tezuka, Tsutomu; Yamabe, Kikuo

    2016-09-01

    The electrical properties of Ge crystals and the effective Schottky barrier height (SBH) of NiGe/Ge diodes fabricated by P and/or chalcogen (S, Se, or Te) doping were investigated for Ge n-channel metal-oxide-semiconductor field-effect transistors with a NiGe/n+Ge junction. The electron concentration in Ge was increased more by co-doping with chalcogen and P than by doping with P alone. Moreover, SBH values were decreased in NiGe/nGe diodes and increased in NiGe/pGe diodes compared with undoped NiGe/Ge by both P doping and P and chalcogen co-doping. Co-doping with Te and P was most effective in modifying the SBH.

  4. Effect of Co doping on the structural and dielectric properties of ZnO nanoparticles

    NASA Astrophysics Data System (ADS)

    Ram, Mast; Bala, Kanchan; Sharma, Hakikat; Negi, N. S.

    2016-05-01

    This paper reports on the synthesis of Co doped Zn1-xCoxO (x= 0.0, 0.01, 0.02, 0.03 and 0.05) nanoparticles by solution combustion method using urea as a fuel. The Structural and dielectric properties of the samples were studied. Crystallite sizes were obtained from X-ray diffraction (XRD) patterns whose values decreased with increase in Co concentration. The XRD study reveals that Co2+ ions substitute the Zn2+ ion without changing the wurtzite structure of pristine ZnO up to Co concentrations of 5%. The dielectric constants, dielectric loss (tanδ) and ac conductivity (σac) were studied as the function of frequency and composition, which have been explained by Maxwell-Wagner type interfacial polarization and discussed Koops phenomenological theory.

  5. Effect of Co Doping on the Structural, Optical and Magnetic Properties of ZnO Nanoparticles

    SciTech Connect

    Hays, Jason; Reddy, K. M.; Graces, N. Y.; Engelhard, Mark H.; Shutthanandan, V.; Luo, M.; Xu, Changqing; Giles, N. C.; Wang, Chong M.; Thevuthasan, Suntharampillai; Punnoose, Alex

    2007-07-04

    We report the results of a detailed investigation of sol-gel synthesized nanoscale Zn1-xCoxO powders processed at 350 °C with 0 @ x @ 0.12 to understand how the structural, morphological, optical and magnetic properties of ZnO are modified by Co doping, in addition to searching for the theoretically predicated ferromagnetism. With x increasing to 0.03, both lattice parameters a and c of the hexagonal ZnO decreased suggesting substitutional doping of Co at the tetrahedral Zn2+ sites. For x > 0.03, these trends reversed and the lattice showed a gradual expansion as x approached 0.12, probably due to additional interstitial incorporation of Co. Raman spectroscopy measurements showed a rapid change in the ZnO peak positions for x > 0.03 suggesting significant disorder and changes in the ZnO structure, in support of additional interstitial Co doping possibility. Combined x-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance spectroscopy, photoluminescence spectroscopy and diffuse reflectance spectroscopy showed clear evidence for tetrahedrally coordinated high spin Co2+ ions occupying the lattice sites of ZnO host system, which became saturated for x > 0.03. Magnetic measurements showed a paramagnetic behavior in Zn1-xCoxO with increasing antiferromagnetic interactions as x increased to 0.10. Surprisingly, a weak ferromagnetic behavior was observed for the sample with x = 0.12 with a characteristic hysteresis loop showing a coercivity Hc ~ 350 Oe, 25% remanence Mr, a low saturation magnetization Ms ~ 0.04 emu/g and with a Curie temperature Tc ~ 540 K. The XPS data collected from Zn1-xCoxO samples showed a gradual increase in the oxygen concentration, changing the oxygen deficient undoped ZnO to an excess oxygen state for x = 0.12. This indicates that such high Co concentrations and appropriate oxygen stoichiometry may be needed to achieve adequate ferromagnetic exchange coupling between the incorporated Co2+ ions.

  6. Effect of Co doping on catalytic activity of small Pt clusters

    NASA Astrophysics Data System (ADS)

    Dhilip Kumar, T. J.; Zhou, Chenggang; Cheng, Hansong; Forrey, Robert C.; Balakrishnan, N.

    2008-03-01

    Platinum is the most widely used catalyst in fuel cell electrodes. Designing improved catalysts with low or no platinum content is one of the grand challenges in fuel cell research. Here, we investigate electronic structures of Pt4 and Pt3Co clusters and report a comparative study of adsorption of H2, O2, and CO molecules on the two clusters using density functional theory. The adsorption studies show that H2 undergoes dissociative chemisorption on the tetrahedral clusters in head on and side on approaches at Pt centers. O2 dissociation occurs primarily in three and four center coordinations and CO prefers to adsorb on Pt or Co atop atoms. The adsorption energy of O2 is found to be higher for the Co doped cluster. For CO, the Pt atop orientation is preferred for both Pt4 and Pt3Co tetrahedral clusters. Adsorption of CO molecule on tetrahedral Pt3Co in side on approach leads to isomerization to planar rhombus geometry. An analysis of Hirshfeld charge distribution shows that the clusters become more polarized after adsorption of the molecules.

  7. Effect of Co doping on catalytic activity of small Pt clusters.

    PubMed

    Dhilip Kumar, T J; Zhou, Chenggang; Cheng, Hansong; Forrey, Robert C; Balakrishnan, N

    2008-03-28

    Platinum is the most widely used catalyst in fuel cell electrodes. Designing improved catalysts with low or no platinum content is one of the grand challenges in fuel cell research. Here, we investigate electronic structures of Pt(4) and Pt(3)Co clusters and report a comparative study of adsorption of H(2), O(2), and CO molecules on the two clusters using density functional theory. The adsorption studies show that H(2) undergoes dissociative chemisorption on the tetrahedral clusters in head on and side on approaches at Pt centers. O(2) dissociation occurs primarily in three and four center coordinations and CO prefers to adsorb on Pt or Co atop atoms. The adsorption energy of O(2) is found to be higher for the Co doped cluster. For CO, the Pt atop orientation is preferred for both Pt(4) and Pt(3)Co tetrahedral clusters. Adsorption of CO molecule on tetrahedral Pt(3)Co in side on approach leads to isomerization to planar rhombus geometry. An analysis of Hirshfeld charge distribution shows that the clusters become more polarized after adsorption of the molecules. PMID:18376957

  8. Large power factor and anomalous Hall effect and their correlation with observed linear magneto resistance in Co-doped Bi2Se3 3D topological insulator

    NASA Astrophysics Data System (ADS)

    Singh, Rahul; Shukla, K. K.; Kumar, A.; Okram, G. S.; Singh, D.; Ganeshan, V.; Lakhani, Archana; Ghosh, A. K.; Chatterjee, Sandip

    2016-09-01

    Magnetoresistance (MR), thermo power, magnetization and Hall effect measurements have been performed on Co-doped Bi2Se3 topological insulators. The undoped sample shows that the maximum MR as a destructive interference due to a π-Berry phase leads to a decrease of MR. As the Co is doped, the linearity in MR is increased. The observed MR of Bi2Se3 can be explained with the classical model. The low temperature MR behavior of Co doped samples cannot be explained with the same model, but can be explained with the quantum linear MR model. Magnetization behavior indicates the establishment of ferromagnetic ordering with Co doping. Hall effect data also supports the establishment of ferromagnetic ordering in Co-doped Bi2Se3 samples by showing the anomalous Hall effect. Furthermore, when spectral weight suppression is insignificant, Bi2Se3 behaves as a dilute magnetic semiconductor. Moreover, the maximum power factor is observed when time reversal symmetry (TRS) is maintained. As the TRS is broken the power factor value is decreased, which indicates that with the rise of Dirac cone above the Fermi level the anomalous Hall effect and linearity in MR increase and the power factor decreases.

  9. Large power factor and anomalous Hall effect and their correlation with observed linear magneto resistance in Co-doped Bi2Se3 3D topological insulator.

    PubMed

    Singh, Rahul; Shukla, K K; Kumar, A; Okram, G S; Singh, D; Ganeshan, V; Lakhani, Archana; Ghosh, A K; Chatterjee, Sandip

    2016-09-21

    Magnetoresistance (MR), thermo power, magnetization and Hall effect measurements have been performed on Co-doped Bi2Se3 topological insulators. The undoped sample shows that the maximum MR as a destructive interference due to a π-Berry phase leads to a decrease of MR. As the Co is doped, the linearity in MR is increased. The observed MR of Bi2Se3 can be explained with the classical model. The low temperature MR behavior of Co doped samples cannot be explained with the same model, but can be explained with the quantum linear MR model. Magnetization behavior indicates the establishment of ferromagnetic ordering with Co doping. Hall effect data also supports the establishment of ferromagnetic ordering in Co-doped Bi2Se3 samples by showing the anomalous Hall effect. Furthermore, when spectral weight suppression is insignificant, Bi2Se3 behaves as a dilute magnetic semiconductor. Moreover, the maximum power factor is observed when time reversal symmetry (TRS) is maintained. As the TRS is broken the power factor value is decreased, which indicates that with the rise of Dirac cone above the Fermi level the anomalous Hall effect and linearity in MR increase and the power factor decreases. PMID:27419361

  10. The combined effect of alumina and silica co-doping on the ageing resistance of 3Y-TZP bioceramics.

    PubMed

    Samodurova, Anastasia; Kocjan, Andraž; Swain, Michael V; Kosmač, Tomaž

    2015-01-01

    The combined effect of alumina and silica co-doping on the ageing resistance of 3Y-TZP bioceramics was investigated. In order to differentiate between the distinct contributions of two dopants to the overall resistance to low-temperature degradation (LTD), specimens were prepared by infiltration of silica sol into pre-sintered 3Y-TZP pellets, produced from commercially available powders, which were alumina-free or contained 0.05 and 0.25 wt.%. After sintering, specimens were exposed to accelerated ageing in distilled water at 134°C for 6-48 h. X-ray diffraction was applied to quantify the tetragonal-to-monoclinic (t-m) phase transformation associated with the LTD, while a focused ion beam-scanning electron microscopy technique was employed to study the microstructural features in the transformed layer. The results showed that the minor alumina and/or silica additions did not drastically change the densities, grain sizes or mechanical properties of 3Y-TZP, but they did significantly reduce LTD. The addition of either alumina or silica has the potential to influence both the nucleation and the propagation of moisture-induced transformation, but in different ways and to different extents. The co-doped ceramics exhibited predominantly transgranular fracture, reflecting strong grain boundaries (limiting microcracking of the transformed layer), for alumina doping, and rounded grains with a glassy phase at multiple grain junctions (reducing internal stresses) for silica-doped material. These two additives evidently have different dominant mechanisms associated with the deceleration of LTD of 3Y-TZP, but their combination increases resistance to ageing, importantly, without reducing the fracture toughness of this popular biomaterial. PMID:25234155

  11. The effect of the starting powders particle size on the electrical properties of sintered Co doped ZnO varistors

    NASA Astrophysics Data System (ADS)

    Hamdelou, S.; Guergouri, K.; Arab, L.

    2014-11-01

    Pure and Co doped zinc oxide nanopowders have been synthesized by sol-gel route. The obtained powders, after calcination in air at 550, 650, 750 and 850 °C, were consolidated and sintered using microwaves. The effect of sintering temperature on the density and electrical properties was investigated. The best characteristics are obtained using a sintering temperature equal to 1,075 °C. The powders and sintered samples are characterized by X-ray diffraction, microstructure images, density and electrical measurements. The studied nanopowders have: a density of 5.22 (g/cm3), a breakdown voltage of 446.5 V/mm and a coefficient of non-linearity of 11.48 for ZnO doped with 7 mol% Co, and a density of 5.19 (g/cm3), a breakdown voltage of 292.5 V/mm and a non-linearity coefficient of 11.62 for ZnO doped with 5 mol% Co. The XRD results indicate that pure and Co doped ZnO powders are solid solutions crystallizing in pure würtzite structure, and consisted of a mixture of nanoparticles with an average grain size between 36 and 210 nm. The grain size decreases with increasing Co concentration and reaches its lowest value at 7 mol% Co and increases with increasing temperature. On the other hand the increase of Co concentration leads to a decrease of the porosity and an increase of the density of samples sintered at 1,070 °C and leads also to an increase of the electric field (E) in the non-linear area. The samples of 5 mol% Co sintered at 1,075 °C, show that the non-linear coefficient α decreases by increasing of calcined temperature, therefore increases with decreasing of grain and particle sizes.

  12. Effects of (La, Sr) co-doping on electrical conduction and magnetic properties of BiFeO3 nanoparticles

    NASA Astrophysics Data System (ADS)

    Liu, Li; Wang, Shouyu; Yin, Zi; Liu, Weifang; Xu, Xunling; Zhang, Chuang; Li, Xiu; Yang, Jiabin

    2016-09-01

    Multiferroic material as a photovoltaic material has gained considerable attention in recent years. Nanoparticles (NPs) La0.1Bi0.9‑xSrxFeOy (LBSF, x = 0, 0.2, 0.4) with dopant Sr2+ ions were synthesized by the sol–gel method. A systematic change in the crystal structure from rhombohedral to tetragonal upon increasing Sr doping was observed. There is an obvious change in the particle size from 180 nm to 50 nm with increasing Sr substitution into LBFO. It was found that Sr doping effectively narrows the band gap from ∼ 2.08 eV to ∼ 1.94 eV, while it leads to an apparent enhancement in the electrical conductivity of LBSF NPs, making a transition from insulator to semiconductor. This suggests an effective way to modulate the conductivity of BiFeO3-based multiferroic materials with pure phase by co-doping with La and Sr at the A sites of BiFeO3. Project supported by the National Natural Science Foundation of China (Grant Nos. 11104202 and 51572193).

  13. Effects of (La, Sr) co-doping on electrical conduction and magnetic properties of BiFeO3 nanoparticles

    NASA Astrophysics Data System (ADS)

    Liu, Li; Wang, Shouyu; Yin, Zi; Liu, Weifang; Xu, Xunling; Zhang, Chuang; Li, Xiu; Yang, Jiabin

    2016-09-01

    Multiferroic material as a photovoltaic material has gained considerable attention in recent years. Nanoparticles (NPs) La0.1Bi0.9-xSrxFeOy (LBSF, x = 0, 0.2, 0.4) with dopant Sr2+ ions were synthesized by the sol-gel method. A systematic change in the crystal structure from rhombohedral to tetragonal upon increasing Sr doping was observed. There is an obvious change in the particle size from 180 nm to 50 nm with increasing Sr substitution into LBFO. It was found that Sr doping effectively narrows the band gap from ˜ 2.08 eV to ˜ 1.94 eV, while it leads to an apparent enhancement in the electrical conductivity of LBSF NPs, making a transition from insulator to semiconductor. This suggests an effective way to modulate the conductivity of BiFeO3-based multiferroic materials with pure phase by co-doping with La and Sr at the A sites of BiFeO3. Project supported by the National Natural Science Foundation of China (Grant Nos. 11104202 and 51572193).

  14. Effect of WO 3 on the spectroscopic properties in Er 3+/Yb 3+ co-doped bismuth-borate glasses

    NASA Astrophysics Data System (ADS)

    Wang, Jun; Zhou, Yaxun; Dai, Shixun; Xu, Tiefeng; Nie, Qiuhua

    2007-11-01

    The spectroscopic properties of Er 3+/Yb 3+ co-doped Bi 2O 3-B 2O 3-WO 3 (BBW) glasses were analyzed and discussed. The effect of WO 3 content on the absorption spectra, the Judd-Ofelt parameters Ω t ( t=2, 4, 6), emission spectra and the lifetime of the 4I 13/2 level and the quantum efficiency of Er 3+: 4I 13/2→ 4I 15/2 transition were also investigated. With the substitution of WO 3 for B 2O 3, the measured lifetime of the 4I 13/2 level and the quantum efficiency of Er 3+: 4I 13/2→ 4I 15/2 transition increase from 0.98 to 1.31 ms and from 38.2% to 49.2%, respectively. The effective width of emission band and the emission cross-section both decrease slightly. And the emission spectra is analyzed via the different curve ( σe- σa) of BBW glasses, the influence of OH - is also discussed.

  15. The effect of K-na co-doping on the formation and particle size of Bi-2212 phase

    NASA Astrophysics Data System (ADS)

    Kır, M. Ebru; Özkurt, Berdan; Aytekin, M. Ersin

    2016-06-01

    Superconducting K-Na co-doped Bi2Sr2KxCa1Cu1.75Na0.25Oy (x=0, 0.05, 0.1 and 0.25) ceramics are prepared by a solid-state reaction method. It is clearly determined from XRD data that the characteristic peaks of Bi-2212 phase are observed in all samples. The resistivity measurements show that Tc (onset) values is gradually increasing as K content is increased. It is also found that K-Na co-doping influence the grain sizes for Bi-2212 phase significantly. The critical current densities as a function of magnetic field have been calculated from M-H hysteresis loops of samples according to Bean's critical model, indicating that K-Na co-doping cause higher Jc values than the pure ones.

  16. A clear effect of charge compensation through Na+ co-doping on the luminescence spectra and decay kinetics of Nd3+-doped CaAl4O7

    NASA Astrophysics Data System (ADS)

    Puchalska, M.; Watras, A.

    2016-06-01

    We present a detailed analysis of luminescence behavior of singly Nd3+ doped and Nd3+, Na+ co-doped calcium aluminates powders: Ca1-xNdxAl4O7 and Ca1-2xNdxNaxAl4O7 (x=0.001-0.1). Relatively intense Nd3+ luminescence in IR region corresponding to typical 4F3/2→4IJ (J=9/2-13/2) transitions with maximum located at about 1079 nm was obtained in all samples on direct excitation into f-f levels. The effect of dopant concentration and charge compensation by co-doping with Na+ ions on morphology and optical properties were studied. The results show that both, the Nd3+ concentration and the alkali metal co-doping affected the optical properties but had no influence on the powders morphology. The studies of luminescence spectra (298 and 77 K) in a function of dopant concentration showed an increasing distortion of the local symmetry of Nd3+with raising activator content due to certain defects created in the crystal lattice. On the other hand Na+ addition led to significant narrowing of absorption and luminescence bands and also a reduction of the number of their components, showing smaller disturbance of Nd3+ ions local symmetries. Consequently, charge compensated by Na+ co-doping materials showed significantly enhanced Nd3+ luminescence. The decrease of emission intensity and luminescence lifetimes with increase of activator concentration was attributed mainly to phonon-assisted cross-relaxation processes between Nd3+ ions. Analysis with Inokuti-Hirayama model indicated dipole-dipole mechanism of ion-ion interaction. Na+ addition led to much smaller concentration quenching due to smaller clustering of dopant ions in CaAl4O7 lattice.

  17. Effect of annealing atmosphere on photoluminescence and gas sensing of solution-combustion-synthesized Al, Pd co-doped ZnO nanoparticles

    NASA Astrophysics Data System (ADS)

    Li, Yan; Liu, Min; Lv, Tan; Wang, Qiong; Zou, Yun-ling; Lian, Xiao-xue; Liu, Hong-peng

    2015-11-01

    Al, Pd co-doped ZnO nanoparticles (NPs) synthesized using a solution combustion method and subsequent annealing process under various atmospheres, including air, nitrogen, and hydrogen, were characterized using x-ray diffraction, energy-dispersive x-ray spectroscopy, field-emission scanning electron microscopy, transmission electron microscopy, and photoluminescence spectroscopy. The gas-sensing properties of the sensors based on the NPs were also examined. The results indicated that the Al, Pd co-doped ZnO NPs, with an average crystallite size of 10 nm, exhibited enhanced gas-sensing performance compared with that of pure ZnO and Al-doped ZnO. The response of the Al, Pd co-doped ZnO NPs annealed in N2 to ethanol (49.22) was nearly 5.7 times higher than that to acetone (8.61) and approximately 20 - 27 times higher than that to benzene (2.38), carbon monoxide (2.23), and methane (1.78), which demonstrates their excellent selectivity to ethanol versus other gases. This high ethanol response can be attributed to the combined effects of the small size, Schottky barrier, lattice defects, and catalysis. [Figure not available: see fulltext.

  18. Effect of SiO2 content on the thermal stability and spectroscopic properties of Er/Yb co-doped tellurite borate glasses

    NASA Astrophysics Data System (ADS)

    Xu, Tiefeng; Zhang, Xudong; Dai, Shixun; Nie, Qiuhua; Shen, Xiang; Zhang, Xianghua

    2007-02-01

    Er/Yb co-doped (85-x) TeO2- 15B2O3- xSiO2 (TBS x=0, 5, 10, 15, 20 mol%) glasses had been prepared. Effect of SiO2 content on the thermal stability and spectroscopic properties of Er/Yb co-doped tellurite borate glasses have been investigated. With SiO2 content increasing from 0 to 20 mol%, the Tg and Tx, the fluorescence full width at half maximum (FWHM), the peak of stimulated emission cross-section ( σpeak), the measured lifetime ( τm) and quantum efficiency ( η) change from 398C, 530C, 75 nm, 5.7×10-21 cm2, 1.84 ms, 56.4% to 419C, 593C, 71 nm, 7.5×10-21 cm2, 2.38 ms, 70.6%, respectively. The results indicate that for Er/Yb co-doped tellurite borate glasses, introducing a suitable amount of SiO2 content is helpful for the improvement of thermal stability and the incremental of the lifetime of I13/24 level and quantum efficiency of Er:I13/24→I15/24 transition, while keeping the FWHM relatively large.

  19. Evidences of grain boundary capacitance effect on the colossal dielectric permittivity in (Nb + In) co-doped TiO2 ceramics

    PubMed Central

    Li, Jinglei; Li, Fei; Li, Chao; Yang, Guang; Xu, Zhuo; Zhang, Shujun

    2015-01-01

    The (Nb + In) co-doped TiO2 ceramics were synthesized by conventional solid-state sintering (CSSS) and spark plasma sintering (SPS) methods. The phases and microstructures were studied by X-ray diffraction, Raman spectra, field-emission scanning electron microscopy and transmission electron microscopy, indicating that both samples were in pure rutile phase while showing significant difference in grain size. The dielectric and I–V behaviors of SPS and CSSS samples were investigated. Though both possess colossal permittivity (CP), the SPS samples exhibited much higher dielectric permittivity/loss factor and lower breakdown electric field when compared to their CSSS counterparts. To further explore the origin of CP in co-doped TiO2 ceramics, the I–V behavior was studied on single grain and grain boundary in CSSS sample. The nearly ohmic I–V behavior was observed in single grain, while GBs showed nonlinear behavior and much higher resistance. The higher dielectric permittivity and lower breakdown electric field in SPS samples, thus, were thought to be associated with the feature of SPS, by which reduced space charges and/or impurity segregation can be achieved at grain boundaries. The present results support that the grain boundary capacitance effect plays an important role in the CP and nonlinear I–V behavior of (Nb + In) co-doped TiO2 ceramics. PMID:25656713

  20. Thermal conductivity of bulk GaN—Effects of oxygen, magnesium doping, and strain field compensation

    SciTech Connect

    Simon, Roland B.; Anaya, Julian; Kuball, Martin

    2014-11-17

    The effect of oxygen doping (n-type) and oxygen (O)-magnesium (Mg) co-doping (semi-insulating) on the thermal conductivity of ammonothermal bulk GaN was studied via 3-omega measurements and a modified Callaway model. Oxygen doping was shown to significantly reduce thermal conductivity, whereas O-Mg co-doped GaN exhibited a thermal conductivity close to that of undoped GaN. The latter was attributed to a decreased phonon scattering rate due the compensation of impurity-generated strain fields as a result of dopant-complex formation. The results have great implications for GaN electronic and optoelectronic device applications on bulk GaN substrates.

  1. Study of synergistic effect of Sc and C co-doping on the enhancement of visible light photo-catalytic activity of TiO2

    NASA Astrophysics Data System (ADS)

    Nasir, Muhammad; Lei, Juying; Iqbal, Waheed; Zhang, Jinlong

    2016-02-01

    Scandium and carbon co-doped TiO2 catalyst was prepared through a simple sol-gel synthesis method by using scandium nitrate as scandium dopant precursor, glucose as carbon precursor and tetrabutyl orthotitanate as titanium precursor and calcined them at 450 °C for 3 h. The characterizations of the prepared samples were accomplished through X-ray diffraction (XRD), transmission electron microscopy (TEM), UV-visible diffuse reflectance spectroscopy (UV-Vis DRS), photoluminescence spectroscopy (PL), Fourier transformation infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) and Brunauer-Emmett-Teller (BET). The X-ray diffraction results of the samples showed the decrease in the crystal size of the sample with the subsequent increase in the specific surface area as shown by Brunauer-Emmett-Teller. The UV-visible diffuse reflectance spectroscopy displayed the blue shift in the absorption together with the photoluminescence spectroscopy revealed the decrease in the recombination of electrons and holes by the addition of the scandium and then after the certain optimum value, the further increase of the scandium further increased the recombination of electrons and holes. The photo-catalytic activity of the samples was investigated with the help of photo-catalytic degradation of Acid orange 7 under visible light irradiation. The degradation of Acid orange 7 was highly increased for the Sc and C co-doped samples compared to the single C doped sample. And the sample 0.2 Sc/C-TiO2 had the maximum increase. The enhanced photo-catalytic performance was due the decrease of the crystal size, increase of the surface area, increase in the surface hydroxyl groups, and increase of the lifetime of the electrons and holes because of the synergistic effect of the Sc and C co-doping in TiO2.

  2. Effect of co-doping Tm{sup 3+} ions on the emission properties of Dy{sup 3+} ions in tellurite glasses

    SciTech Connect

    Sasikala, T.; Rama Moorthy, L.; Mohan Babu, A.; Srinivasa Rao, T.

    2013-07-15

    The present work reports the absorption, photoluminescence and decay properties of singly doped Dy{sup 3+} and co-doped Dy{sup 3+}/Tm{sup 3+} ions in TeO{sub 2}+ZnO+K{sub 2}O+CaO (TZKC) glasses prepared by the melt quenching technique. The glassy nature of the host glass has been confirmed by X-ray diffraction analysis and the primary vibrational modes were determined from the Raman spectrum. Judd–Ofelt (JO) analysis has been used to calculate the radiative transition rates, branching ratios and radiative lifetime of the emitting {sup 4}F{sub 9/2} state. The effect of co-doping of different concentrations of Tm{sup 3+} ions on the emission properties of Dy{sup 3+} ions has been investigated. The decay profiles of the {sup 4}F{sub 9/2} level were fitted to double exponential as well as Inokuti–Hirayama (IH) model to determine the energy transfer rates between Dy{sup 3+} and Tm{sup 3+} ions. The energy transfer rates found to increase with the increase of Tm{sup 3+} ions concentration. The chromaticity coordinates and color purity of the emitted light for all glasses were determined. - Graphical abstract: The graphical abstract shows the emission spectra of Dy{sup 3+}, Tm{sup 3+} and Dy{sup 3+}/Tm{sup 3+} co-doped TZKC glasses recorded by exciting at 355 nm wavelength. - Highlights: • Zinc tellurite glasses doped with Dy{sup 3+}, Tm{sup 3+} and Dy{sup 3+}/Tm{sup 3+} ions were prepared. • XRD, DTA and Raman spectral measurements were recorded to know the nature of host. • Energy transfer occurs from Dy{sup 3+} ions to Tm{sup 3+} ions. • The color purity of the emitted light was determined.

  3. γ irradiation induced effects on bismuth active centres and related photoluminescence properties of Bi/Er co-doped optical fibres.

    PubMed

    Sporea, D; Mihai, L; Neguţ, D; Luo, Yanhua; Yan, Binbin; Ding, Mingjie; Wei, Shuen; Peng, Gang-Ding

    2016-01-01

    We investigate the effects of γ irradiation on bismuth active centres (BACs) and related photoluminescence properties of bismuth/erbium co-doped silica fibre (BEDF), [Si] ~28, [Ge] ~1.60, [Al] ~0.10, [Er] ~ <0.10 and [Bi] ~0.10 atom%, fabricated by in-situ solution doping and Modified Chemical Vapor Deposition (MCVD). The samples were irradiated at 1 kGy, 5 kGy, 15 kGy, 30 kGy and 50 kGy doses, and dose rate of 5.5 kGy/h, at room temperature. The optical properties of BEDF samples are tested before and after γ irradiation. We found that high dose γ irradiation could significantly influence the formation and composition of BACs and their photoluminescence performance, as important changes in absorption and emission properties associated with the 830 nm pump produces the direct evidence of γ irradiation effects on BAC-Si. We notice that the saturable to unsaturable absorption ratio at pump wavelength could be increased with high dose γ irradiation, indicating that emission and pump efficiency could be increased by γ irradiation. Our experimental results also reveal good radiation survivability of the BEDF under low and moderate γ irradiation. Our investigation suggests the existence of irradiation related processing available for tailoring the photoluminescence properties and performance of bismuth doped/co-doped fibres. PMID:27440386

  4. γ irradiation induced effects on bismuth active centres and related photoluminescence properties of Bi/Er co-doped optical fibres

    PubMed Central

    Sporea, D.; Mihai, L.; Neguţ, D.; Luo, Yanhua; Yan, Binbin; Ding, Mingjie; Wei, Shuen; Peng, Gang-Ding

    2016-01-01

    We investigate the effects of γ irradiation on bismuth active centres (BACs) and related photoluminescence properties of bismuth/erbium co-doped silica fibre (BEDF), [Si] ~28, [Ge] ~1.60, [Al] ~0.10, [Er] ~ <0.10 and [Bi] ~0.10 atom%, fabricated by in-situ solution doping and Modified Chemical Vapor Deposition (MCVD). The samples were irradiated at 1 kGy, 5 kGy, 15 kGy, 30 kGy and 50 kGy doses, and dose rate of 5.5 kGy/h, at room temperature. The optical properties of BEDF samples are tested before and after γ irradiation. We found that high dose γ irradiation could significantly influence the formation and composition of BACs and their photoluminescence performance, as important changes in absorption and emission properties associated with the 830 nm pump produces the direct evidence of γ irradiation effects on BAC-Si. We notice that the saturable to unsaturable absorption ratio at pump wavelength could be increased with high dose γ irradiation, indicating that emission and pump efficiency could be increased by γ irradiation. Our experimental results also reveal good radiation survivability of the BEDF under low and moderate γ irradiation. Our investigation suggests the existence of irradiation related processing available for tailoring the photoluminescence properties and performance of bismuth doped/co-doped fibres. PMID:27440386

  5. γ irradiation induced effects on bismuth active centres and related photoluminescence properties of Bi/Er co-doped optical fibres

    NASA Astrophysics Data System (ADS)

    Sporea, D.; Mihai, L.; Neguţ, D.; Luo, Yanhua; Yan, Binbin; Ding, Mingjie; Wei, Shuen; Peng, Gang-Ding

    2016-07-01

    We investigate the effects of γ irradiation on bismuth active centres (BACs) and related photoluminescence properties of bismuth/erbium co-doped silica fibre (BEDF), [Si] ~28, [Ge] ~1.60, [Al] ~0.10, [Er] ~ <0.10 and [Bi] ~0.10 atom%, fabricated by in-situ solution doping and Modified Chemical Vapor Deposition (MCVD). The samples were irradiated at 1 kGy, 5 kGy, 15 kGy, 30 kGy and 50 kGy doses, and dose rate of 5.5 kGy/h, at room temperature. The optical properties of BEDF samples are tested before and after γ irradiation. We found that high dose γ irradiation could significantly influence the formation and composition of BACs and their photoluminescence performance, as important changes in absorption and emission properties associated with the 830 nm pump produces the direct evidence of γ irradiation effects on BAC-Si. We notice that the saturable to unsaturable absorption ratio at pump wavelength could be increased with high dose γ irradiation, indicating that emission and pump efficiency could be increased by γ irradiation. Our experimental results also reveal good radiation survivability of the BEDF under low and moderate γ irradiation. Our investigation suggests the existence of irradiation related processing available for tailoring the photoluminescence properties and performance of bismuth doped/co-doped fibres.

  6. Effect of Er3+ and Yb3+ co-doping on the performance of a ZnO-based DSSC

    NASA Astrophysics Data System (ADS)

    Tsege, Ermias Libnedengel; Vu, Hong Ha Thi; Atabaev, Timur Sh.; Kim, Hyung-Kook; Hwang, Yoon-Hwae

    2016-06-01

    Zinc-oxide (ZnO) nanoparticles (NPs) co-doped with different concentrations of rare-earth ions of erbium and ytterbium, (ZnO: Er3+, Yb3+) were synthesized for applications to ZnO-based dye sensitized solar cells (DSSC). The composite NPs used for the photoelectrode (PE) were synthesized using a simple co-precipitation technique. X-ray diffraction and scanning electron microscopy measurements on the prepared samples revealed a single phase wurzite ZnO powder with approximate sizes in the range from 15 to 20 nm. Photoluminescence (PL) measurements confirmed that the synthesized composite NPs had a good up-conversion (UPC) property. The prepared powders were directly used to make PEs for DSSCs. The photovoltaic efficiency of the DSSCs was enhanced compared to that of pure ZnO-based DSSCs. Particularly, the PE made up of ZnO: Er3+, Yb3+ NPs with 4 wt% of Er3+ and Yb3+ generates a short-circuit current density ( J sc ) of 4.794 mA·cm -2 and an open circuit voltage ( V oc ) of 0.602 V with an efficiency ( η) of 1.58%. The result indicates a 48.4% J sc improvement compared to a pure ZnO PE-based DSSC. The photocurrent improvement is due to an increase in the light-harvesting capacity of the PEs attained through the UPC property of ZnO: Er3+, Yb3+ NPs. As confirmed by PL and electrochemical impedance spectra (EIS), the use of ZnO: Er3+,Yb3+ NPs as PEs for DSSCs enhances charge concentration and transport as a result of n-type doping. However, all ZnO: Er3+, Yb3+ NP based PEs exhibited a lower V oc as a result of a down shift in the Fermi energy, which affects the overall efficiency of the cell.

  7. Effect of Co doping on structural, optical, magnetic and dielectric properties of Bi{sub 2}Fe{sub 4}O{sub 9}

    SciTech Connect

    Mohapatra, S. R.; Sahu, B.; Singh, A. K.; Kaushik, S. D.

    2015-06-24

    Polycrystalline Bi{sub 2}Fe{sub 4}O{sub 9} and 2% Co doped Bi{sub 2}Fe{sub 4}O{sub 9} were prepared by solid state reaction route. X-ray diffraction (XRD) result reveals that there is no change in the crystal structure due to Co doping and the compound has orthorhombic structure. UV-visible spectroscopy confirms the decrease in band gap due Co doping. Zero field cooled magnetization measurement at 100 Oe magnetic field shows substantial decrease in the magnetic transition temperature. Room temperature frequency dependent dielectric permittivity at 1V DC bias shows ∼10% increase in Co doped sample with respect to pure Bi{sub 2}Fe{sub 4}O{sub 9}.

  8. Effect of substrate temperature on transparent conducting Al and F co-doped ZnO thin films prepared by rf magnetron sputtering

    NASA Astrophysics Data System (ADS)

    Wang, Fang-Hsing; Chang, Chiao-Lu

    2016-05-01

    ZnO is a wide bandgap semiconductor that has many potential applications such as solar cells, thin film transistors, light emitting diodes, and gas/biological sensors. In this study, a composite ceramic ZnO target containing 1 wt% Al2O3 and 1.5 wt% ZnF2 was prepared and used to deposit transparent conducting Al and F co-doped zinc oxide (AFZO) thin films on glass substrates by radio frequency magnetron sputtering. The effect of substrate temperatures ranging from room temperature (RT) to 200 °C on structural, morphological, electrical, chemical, and optical properties of the deposited thin films were investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), Hall effect measurement, X-ray photoelectron spectroscopy, secondary ion mass spectrometry, and UV-vis spectrophotometer. The XRD results showed that all the AFZO thin films had a (0 0 2) diffraction peak, indicating a typical wurtzite structure with a preferential orientation of the c-axis perpendicular to the substrate. The FE-SEM and AFM analyses indicated that the crystallinity and grain size of the films were enhanced while the surface roughness decreased as the substrate temperature increased. Results of Hall effect measurement showed that Al and F co-doping decreased the resistivity more effectively than single-doping (either Al or F doping) in ZnO thin films. The resistivity of the AFZO thin films decreased from 5.48 × 10-4 to 2.88 × 10-4 Ω-cm as the substrate temperature increased from RT to 200 °C due to the increased carrier concentration and Hall mobility. The optical transmittances of all the AFZO thin films were over 92% in the wavelength range of 400-800 nm regardless of substrate temperature. The blue-shift of absorption edge accompanied the rise of the optical band gap, which conformed to the Burstein-Moss effect. The developed AFZO thin films are suitable as transparent conducting electrodes for various optoelectronic

  9. The effects of co-doping GeO II and Al 3+ on ytterbium-doped silica-based fiber

    NASA Astrophysics Data System (ADS)

    Wang, Lin; Yan, Fengping; Fu, Yongjun; Li, Yifang; Gong, Taorong; Liu, Peng; Jian, Shuisheng

    2007-11-01

    Four types of YDFs with different Al 3+ concentration and mole content of GeO II were manufactured and the refractive index and absorption spectra of these fibers were explored. With the comparison of four YDFs and detailed analyze, it was found that higher Al 3+ concentration leads to more GeO II volatilization, which results in the refractive index decrease. Therefore, mole content of GeO II should be increased when co-doping Al 3+ in YDF to maintain numerical aperture. Meanwhile, the temperature of making porous layer should be controlled exactly to obtain good repetition of Al 3+- codoped YDF as the little change of temperature has little effect on mole content of GeO II and SiO II but has great effect on compactness of porous layer. By drawing the fiber and testing the related parameters, the results show that the optimum temperature range for making soot layer should between 1440°C and 1480°C where the absorption coefficients were as high as 620dB/m with better repeatability. Finally, the ratio of GeO II to SiO II should be controlled to obtain long fluorescence lifetime for fabricating highly ytterbium-doped fiber with required numerical aperture.

  10. Effective visible light-active boron and europium co-doped BiVO4 synthesized by sol-gel method for photodegradion of methyl orange.

    PubMed

    Wang, Min; Che, Yinsheng; Niu, Chao; Dang, Mingyan; Dong, Duo

    2013-11-15

    Eu-B co-doped BiVO4 visible-light-driven photocatalysts have been synthesized using the sol-gel method. The resulting materials were characterized by a series of joint techniques, including XPS, XRD, SEM, BET, and UV-vis DRS analyses. Compared with BiVO4 and B-BiVO4 photocatalysts, the Eu-B-BiVO4 photocatalysts exhibited much higher photocatalytic activity for methyl orange (MO) degradation under visible light irradiation. The optimal Eu doping content is 0.8 mol%. It was revealed that boron and europium were doped into the lattice of BiVO4 and this led to more surface oxygen vacancies, high specific surface areas, small crystallite size, a narrower band gap and intense light absorbance in the visible region. The doped Eu(III) cations can help in the separation of photogenerated electrons. The synergistic effects of boron and europium in doped BiVO4 were the main reason for improving visible light photocatalytic activity.

  11. Boron, bismuth co-doping of gallium arsenide and other compounds for photonic and heterojunction bipolar transistor devices

    DOEpatents

    Mascarenhas, Angelo

    2015-07-07

    Isoelectronic co-doping of semiconductor compounds and alloys with acceptors and deep donors is sued to decrease bandgap, to increase concentration of the dopant constituents in the resulting alloys, and to increase carrier mobilities lifetimes. For example, Group III-V compounds and alloys, such as GaAs and GaP, are isoelectronically co-doped with, for example, B and Bi, to customize solar cells, and other semiconductor devices. Isoelectronically co-doped Group II-VI compounds and alloys are also included.

  12. Sn/Be Sequentially co-doped Hematite Photoanodes for Enhanced Photoelectrochemical Water Oxidation: Effect of Be2+ as co-dopant

    PubMed Central

    Annamalai, Alagappan; Lee, Hyun Hwi; Choi, Sun Hee; Lee, Su Yong; Gracia-Espino, Eduardo; Subramanian, Arunprabaharan; Park, Jaedeuk; Kong, Ki-jeong; Jang, Jum Suk

    2016-01-01

    For ex-situ co-doping methods, sintering at high temperatures enables rapid diffusion of Sn4+ and Be2+ dopants into hematite (α–Fe2O3) lattices, without altering the nanorod morphology or damaging their crystallinity. Sn/Be co-doping results in a remarkable enhancement in photocurrent (1.7 mA/cm2) compared to pristine α–Fe2O3 (0.7 mA/cm2), and Sn4+ mono-doped α-Fe2O3 photoanodes (1.0 mA/cm2). From first-principles calculations, we found that Sn4+ doping induced a shallow donor level below the conduction band minimum, which does not contribute to increase electrical conductivity and photocurrent because of its localized nature. Additionally, Sn4+-doping induce local micro-strain and a decreased Fe-O bond ordering. When Be2+ was co-doped with Sn4+-doped α–Fe2O3 photoanodes, the conduction band recovered its original state, without localized impurities peaks, also a reduction in micro-strain and increased Fe-O bond ordering is observed. Also the sequence in which the ex-situ co-doping is carried out is very crucial, as Be/Sn co-doping sequence induces many under-coordinated O atoms resulting in a higher micro-strain and lower charge separation efficiency resulting undesired electron recombination. Here, we perform a detailed systematic characterization using XRD, FESEM, XPS and comprehensive electrochemical and photoelectrochemical studies, along with sophisticated synchrotron diffraction studies and extended X-ray absorption fine structure. PMID:27005757

  13. Sn/Be Sequentially co-doped Hematite Photoanodes for Enhanced Photoelectrochemical Water Oxidation: Effect of Be2+ as co-dopant

    NASA Astrophysics Data System (ADS)

    Annamalai, Alagappan; Lee, Hyun Hwi; Choi, Sun Hee; Lee, Su Yong; Gracia-Espino, Eduardo; Subramanian, Arunprabaharan; Park, Jaedeuk; Kong, Ki-Jeong; Jang, Jum Suk

    2016-03-01

    For ex-situ co-doping methods, sintering at high temperatures enables rapid diffusion of Sn4+ and Be2+ dopants into hematite (α-Fe2O3) lattices, without altering the nanorod morphology or damaging their crystallinity. Sn/Be co-doping results in a remarkable enhancement in photocurrent (1.7 mA/cm2) compared to pristine α-Fe2O3 (0.7 mA/cm2), and Sn4+ mono-doped α-Fe2O3 photoanodes (1.0 mA/cm2). From first-principles calculations, we found that Sn4+ doping induced a shallow donor level below the conduction band minimum, which does not contribute to increase electrical conductivity and photocurrent because of its localized nature. Additionally, Sn4+-doping induce local micro-strain and a decreased Fe-O bond ordering. When Be2+ was co-doped with Sn4+-doped α-Fe2O3 photoanodes, the conduction band recovered its original state, without localized impurities peaks, also a reduction in micro-strain and increased Fe-O bond ordering is observed. Also the sequence in which the ex-situ co-doping is carried out is very crucial, as Be/Sn co-doping sequence induces many under-coordinated O atoms resulting in a higher micro-strain and lower charge separation efficiency resulting undesired electron recombination. Here, we perform a detailed systematic characterization using XRD, FESEM, XPS and comprehensive electrochemical and photoelectrochemical studies, along with sophisticated synchrotron diffraction studies and extended X-ray absorption fine structure.

  14. Samarium and Nitrogen Co-Doped Bi2 WO6 Photocatalysts: Synergistic Effect of Sm(3+) /Sm(2+) Redox Centers and N-Doped Level for Enhancing Visible-Light Photocatalytic Activity.

    PubMed

    Wang, Fangzhi; Li, Wenjun; Gu, Shaonan; Li, Hongda; Wu, Xue; Liu, Xintong

    2016-08-26

    Samarium and nitrogen co-doped Bi2 WO6 nanosheets were successfully synthesized by using a hydrothermal method. The crystal structures, morphology, elemental compositions, and optical properties of the prepared samples were investigated. The incorporation of samarium and nitrogen ions into Bi2 WO6 was proved by X-ray diffraction, energy dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy. UV/Vis diffuse reflectance spectroscopy indicated that the samarium and nitrogen co-doped Bi2 WO6 possessed strong visible-light absorption. Remarkably, the samarium and nitrogen co-doped Bi2 WO6 exhibited higher photocatalytic activity than single-doped and pure Bi2 WO6 under visible-light irradiation. Radical trapping experiments indicated that holes (h(+) ) and superoxide radicals ((.) O2 (-) ) were the main active species. The results of photoluminescence spectroscopy and photocurrent measurements demonstrated that the recombination rate of the photogenerated electrons and holes pairs was greatly depressed. The enhanced activity was attributed to the synergistic effect of the in-built Sm(3+) /Sm(2+) redox pair centers and the N-doped level. The mechanism of the excellent photocatalytic activity of Sm-N-Bi2 WO6 is also discussed.

  15. Analysis of thermal and structural properties of germanate glasses co-doped with Yb3+/Tb3+ ions

    NASA Astrophysics Data System (ADS)

    Zmojda, J.; Kochanowicz, M.; Miluski, P.; Dorosz, D.; Jelen, P.; Sitarz, M.

    2014-10-01

    In the work the new glass compositions in the GeO2-GaO-BaO system have been prepared and thermal, structural properties of in germanate glasses co-doped with Yb3+/Tb3+ions were studied. Glasses were obtained by conventional high-temperature melt-quenching technique. The study of the crystallization kinetics processes of glasses co-doped with 0.7Yb2O3:0.7Tb2O3 was performed with DSC measurements. The activation energies have been calculated using Freedman analysis and verified with the Flynn-Wall-Ozawa method. In this order, the DSC curves have been registered with different heating rates, between 5 and 15 degrees/min. The structure of fabricated glasses has been studied by infrared and Raman spectroscopes. The effect of heat treatment on the structural properties was determined. In all glass samples the dominated infrared absorbance band at 800 cm-1 corresponds to asymmetric stretching motions of GeO4 tetrahedra containing bridging (Ge-O(Ge)) and non-bridging (Ge-O-) oxygens. Additionally, the influence of heat treatment on the luminescent properties was evaluated. Strong luminescence at 489, 543, 586 and 621 nm corresponding to 5D4 → 7FJ (J = 6, 5, 4, 3) transitions was measured. The highest upconversion emission intensity was obtained in the germanate glass co-doped with 0.7Yb2O3/0.7Tb2O3.

  16. Effect of co-doped SnO{sub 2} nanoparticles on photoluminescence of cu-doped potassium lithium borate glass

    SciTech Connect

    Namma, Haydar Aboud; Wagiran, H.; Hussin, R.; Ariwahjoedi, B.

    2012-09-26

    The SnO{sub 2} co-doped lithium potassium borate glasses doped with 0.05, 0.10, 0.25 and 0.50 mol% of Cu were synthesized by the melt quenching technique. The SnO{sub 2} co-dope was added to the compounds in the amounts of 0.05, 0.10, and 0.20 mol%. The photoluminescent spectrum for different concentrations of copper was studied. It was observed that the intensity of blue emission (450, 490 nm) varies with concentration mol%. In addition, with different concentration of SnO{sub 2} to 0.10 mol% Cu, the influence of the luminescence has been observed to enhance intensity and shifted to blue and red (490, 535 nm) emissions.

  17. The effect of sulfur and zirconium Co-doping on the oxidation of NiCrAl

    NASA Technical Reports Server (NTRS)

    Smialek, James L.

    1987-01-01

    The adhesion behavior of Al2O3 scales formed on NiCrAl+Zr alloys was examined as a function of both sulfur and zirconium doping levels. In general, very high levels of zirconium were required to counteract the detrimental effects of sulfur. A sulfur-zirconium adherence map was constructed, as determined from the oxidation and spalling behavior in 1100 C cyclic tests. For low sulfur alloys, the amount of zirconium required for adherence at any given sulfur level can be described by Zr greater than 600 S sup 0.2 (in ppma). These results underscore the importance of sulfur to adhesion mechanisms and suggests that sulfur gettering is a first order effect of reactive element additions to MCrAl alloys.

  18. The effect of sulfur and zirconium co-doping on the oxidation of NiCrAl

    NASA Technical Reports Server (NTRS)

    Smialek, James L.

    1988-01-01

    The adhesion behavior of Al2O3 scales formed on NiCrAl+Zr alloys was examined as a function of both sulfur and zirconium doping levels. In general, very high levels of zirconium were required to counteract the detrimental effects of sulfur. A sulfur-zirconium adherence map was constructed, as determined from the oxidation and spalling behavior in 1100 C cyclic tests. For low sulfur alloys (less than 500 ppma), the amount of zirconium required for adherence at any given sulfur level can be described by Zr greater than 600 S(0.2) (in ppma). These results underscore the importance of sulfur to adhesion mechanisms and suggest that sulfur gettering is a first order effect of reactive element additions to MCrAl alloys.

  19. Co doped ZnO nanowires as visible light photocatalysts

    NASA Astrophysics Data System (ADS)

    Šutka, Andris; Käämbre, Tanel; Pärna, Rainer; Juhnevica, Inna; Maiorov, Mihael; Joost, Urmas; Kisand, Vambola

    2016-06-01

    High aspect ratio cobalt doped ZnO nanowires showing strong photocatalytic activity and moderate ferromagnetic behaviour were successfully synthesized using a solvothermal method and characterized by scanning electron microscopy (SEM), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), X-ray absorption spectroscopy (XAS), vibrating sample magnetometry (VSM) and UV-visible absorption spectroscopy. The photocatalytic activities evaluated for visible light driven degradation of an aqueous methylene orange (MO) solution were higher than for Co doped ZnO nanoparticles at the same doping level and synthesized by the same synthesis route. The rate constant for MO visible light photocatalytic degradation was 1.9·10-3 min-1 in case of nanoparticles and 4.2·10-3 min-1 in case of nanowires. We observe strongly enhanced visible light photocatalytic activity for moderate Co doping levels, with an optimum at a composition of Zn0.95Co0.05O. The enhanced photocatalytic activities of Co doped ZnO nanowires were attributed to the combined effects of enhanced visible light absorption at the Co sites in ZnO nanowires, and improved separation efficiency of photogenerated charge carriers at optimal Co doping.

  20. Effect of annealing on the luminescence properties of YVO₄:Dy³⁺ phosphor on co-doping Pb²⁺ ions.

    PubMed

    Devi, Ch Victory; Singh, N Rajmuhon

    2015-07-01

    Pb(2+) co-doped YVO4:Dy(3+) phosphors have been synthesized at a relatively low temperature of 120°C via ethylene glycol route. The samples are further annealed at 500 and 900°C. The prepared samples were characterized by XRD, SEM, spectra energy dispersive analysis of X-ray (EDAX) and photoluminescence spectroscopy. XRD patterns of all samples are well indexed with single tetragonal phase of YVO4. The emission intensity of Dy(3+) is significantly enhanced on co-doping Pb(2+) ions. The highest emission is obtained at 7 at.% Pb(2+) for 900°C annealed samples. Both emission intensity and decay lifetime increases on annealing the samples from 500 to 900°C. On co-doping Pb(2+) into YVO4:Dy(3+) phosphors, the emission color falls near the white region and then shift towards yellow region on annealing from 500 to 900°C thereby indicating that annealing temperature play a role on tuning the color of the phosphors. As well as the emission color of the phosphors remain the same even on changing the excitation wavelengths from 280 nm, which would serve as potential phosphors for white emission in LED applications. PMID:25827617

  1. Effect of Co doping, capping agent and optical-structural studies of ZnO:Co2+ nanoparticles

    NASA Astrophysics Data System (ADS)

    Taheri Otaqsara, S. M.

    2011-08-01

    Co2+ doped ZnO nanoparticles (NPs) using PEG as a capping agent were prepared by colloidal wet-chemical method. The structure, morphology and characteristics of as-prepared samples were investigated. X-ray diffraction patterns studies revealed wurtzite crystal phase. STM-TEM micrographs show a spherical shape and nearly well distribution with an average particle size of ~15-20 nm. UV-VIS spectra show the presence of exciton peak at 349 nm which can be effectively tuned versus cobalt doping and PEG concentration. PL studies were done under the excitation of 347 nm, which exhibited a UV (~386 nm) and visible (blue-orange) emission peak because of free-exciton recombination and oxygen vacancy.

  2. Al-Mg co-doping effect on optical and magnetic properties of ZnO nanopowders

    NASA Astrophysics Data System (ADS)

    Si, Xiaodong; Liu, Yongsheng; Wu, Xinfang; Lei, Wei; Lin, Jia; Gao, Tian; Zheng, Li

    2015-07-01

    Zn0.97 - xMgxAl0.03O (x = 0 , 0.01 , 0.03 and 0.05) nanoparticles were prepared by hydrothermal growth, and their optical and magnetic properties were systematically studied by the X-ray diffraction (XRD), the UV-visible spectrophotometer, the infrared spectrometer and the physical properties measurement system (PPMS). These results showed that all the nanopowders had hexagonal wurtzite structures. With increasing the content of Mg, the strength of the (110) intensity peak increased. When Mg atoms were not incorporated into the Zn0.97Al0.03O lattice, the infrared light transmittance was higher than that of other groups of samples. In the UV range, the absorption decreased with the increase of the concentration of Mg. Mg doping weakened the magnetic property of the nanoparticles at room temperature. The zero-field-cooled (ZFC) and field-cooled (FC) magnetization curves were separated with the decrease of temperature due to the pinning effect between the ferromagnetic domain and antiferromagnetic domain.

  3. Effect of Co doping on the structural, magnetic and electron transport properties of Mn2PtSn Heusler alloy

    NASA Astrophysics Data System (ADS)

    Kharel, Parashu; Huh, Yung; Nelson, Austin; Shah, Valloppilly; Skomski, Ralph; Sellmyer, David

    2014-03-01

    Materials with high magnetic anisotropy and Curie temperature well above room temperature have huge potential for a range of applications including permanent magnet, high density recording and spintronic devices. Tetragonal Mn2PtSn is one such Heuslar compounds which has been predicted to have very high magnetic anisotropy but its low Curie temperature (Tc = 374 K) is a drawback. Our experimental investigation of the rapidly quenched nanostructured ribbons shows that a single phase Mn2PtSn in the tetragonal structure cannot be easily prepared without the substitution of an external element. We have found that a partial replacement of Pt with Co in Mn2PtSn stabilizes the tetragonal structure and also improves the magnetic properties. The experimentally observed values of the room-temperature saturation magnetization (Ms) and Curie temperature (Tc) are respectively 35 emu/g and 385 K for Mn2PtSn and 43 emu/g and 516 K for Mn2Pt0.3Co0.7Sn. The effect of cobalt on the magnetic anisotropy and electron transport properties of this material will be discussed. This research is supported by NSF-MRSEC (DMR-0820521).

  4. Co-doping of Ag into Mn:ZnSe Quantum Dots: Giving Optical Filtering effect with Improved Monochromaticity

    PubMed Central

    Hu, Zhiyang; Xu, Shuhong; Xu, Xiaojing; Wang, Zhaochong; Wang, Zhuyuan; Wang, Chunlei; Cui, Yiping

    2015-01-01

    In optics, when polychromatic light is filtered by an optical filter, the monochromaticity of the light can be improved. In this work, we reported that Ag dopant atoms could be used as an optical filter for nanosized Mn:ZnSe quantum dots (QDs). If no Ag doping, aqueous Mn:ZnSe QDs have low monochromaticity due to coexisting of strong ZnSe band gap emission, ZnSe trap emission, and Mn dopant emission. After doping of Ag into QDs, ZnSe band gap and ZnSe trap emissions can be filtered, leaving only Mn dopant emission with improved monochromaticity. The mechanism for the optical filtering effect of Ag was investigated. The results indicate that the doping of Ag will introduce a new faster deactivation process from ZnSe conduction band to Ag energy level, leading to less electrons deactived via ZnSe band gap emission and ZnSe trap emission. As a result, only Mn dopant emission is left. PMID:26446850

  5. Photodegradation of ibuprofen by TiO2 co-doping with urea and functionalized CNT irradiated with visible light - Effect of doping content and pH.

    PubMed

    Yuan, Ching; Hung, Chung-Hsuang; Li, Huei-Wen; Chang, Wei-Hsian

    2016-07-01

    Ibuprofen (IBP) is one kind of non-steroidal anti-inflammatory drugs (NSAIDs), which are classified as Pharmaceuticals and Personal Care Products (PPCPs). IBP possesses bioactive property and the substantial use of IBP results in a harmful impact on bioreceptors even in small concentrations. Accordingly, the treatment of these wastewaters is important before discharging them into the ecosystem. The photodegradation of IBP with TiO2 co-doped with functionalized CNTs (CNT-COOH and CNT-COCl) and urea, named as N-doping CNT/TiO2, irradiated with visible light of 410 nm was investigated in this study. The titanium tetrachloride was used as the precursor of Ti. The N-doping CNT-COCl/TiO2 photocatalysts exhibited a better crystalline structure and smaller crystal size than the N-doping CNT-COOH/TiO2 photocatalyst. It might largely ascribe to strong binding between acyl chloride functional group and TiO2. About 85.0%-86.0% of IBP was degraded with N-doping CNT/TiO2 within 120 min at natural condition, which obeyed the pseudo first order reaction and the rate constant was 4.45 × 10(-3)-1.22 × 10(-2) min(-1) and 5.03 × 10(-3)-1.47 × 10(-2) min(-1) for N-doping CNT-COOH/TiO2 and N-doping CNT-COCl/TiO2, respectively. The best IBP degradation of 87.9%-89.0% was found at pH 5, which indicated superoxide radicals (O2(-)) played a key role. The optimal pH was majorly dominated by the nature of IBP and N-doping CNT/TiO2. A successful synergy effect of TiO2 and dopants was exhibited and this mainly attributed to the strong binding strength by functional group of acyl chloride (COCl) and carboxylic acid (COOH). In summary, IBP could be effectively photodegraded by the fabricated N-doping CNT/TiO2 photocatalysts.

  6. Effects of post-annealing and cobalt co-doping on superconducting properties of (Ca,Pr)Fe2As2 single crystals

    NASA Astrophysics Data System (ADS)

    Okada, T.; Ogino, H.; Yakita, H.; Yamamoto, A.; Kishio, K.; Shimoyama, J.

    2014-10-01

    In order to clarify the origin of anomalous superconductivity in (Ca,RE)Fe2As2 system, Pr doped and Pr,Co co-doped CaFe2As2 single crystals were grown by the FeAs flux method. These samples showed two-step superconducting transition with Tc1 = 25-42 K, and Tc2 < 16 K, suggesting that (Ca,RE)Fe2As2 system has two superconducting components. Post-annealing performed for these crystals in evacuated quartz ampoules at various temperatures revealed that post-annealing at ∼400 °C increased the c-axis length for all samples. This indicates that as-grown crystals have a certain level of strain, which is released by post-annealing at ∼400 °C. Superconducting properties also changed dramatically by post-annealing. After annealing at 400 °C, some of the co-doped samples showed large superconducting volume fraction corresponding to the perfect diamagnetism below Tc2 and high Jc values of 104-105 A cm-2 at 2 K in low field, indicating the bulk superconductivity of (Ca,RE)Fe2As2 phase occurred below Tc2. On the contrary, the superconducting volume fraction above Tc2 was always very small, suggesting that 40 K-class superconductivity observed in this system is originating in the local superconductivity in the crystal.

  7. Formation and Characteristics of Anatase-Type Titania Solid Solution Nanoparticles Doped with Nb5+ M (M = Ga3+, Al3+, Sc3+)

    NASA Astrophysics Data System (ADS)

    Hirano, Masanori; Ito, Takaharu

    2011-10-01

    Anatase-type titania solid solutions co-doped with Nb5+ and cation M (M = Ga3+, Al3+, Sc3+) with composition Ti1-2XNbXMXO2 were directly formed as nanoparticles from precursor solutions of TiOSO4, NbCl5, and metal salts (Ga(SO4)3, Al(NO3)3, and Sc(NO3)3) under mild hydrothermal conditions at 180 °C for 5 h using the hydrolysis of urea. The effect of co-doped cation M on the formation and properties of anatase-type titania solid solutions was investigated. The region of anatse-type solid solution depended on the co-doped cation M. The composition range of anatase-type titania solid solution in the case of M = Sc3+ was much wider than that in the case of M = Ga3+ and Al3+. The increase in the amount of co-doped cation M = Ga3+, Al3+ enhanced the crystallite growth of anatase solid solutions under the hydrothermal conditions. The solid solutions co-doped with M = Al3+ showed the most improved photocatalytic activity in the three cations. The anatase-to-rutile phase transformation of solid solutions was promoted at lower temperature via the presence of co-doped cation M = Ga3+.

  8. Characterization of afterglow-related spectroscopic effects in vacuum sintered Tb3+, Sr2+ co-doped Lu2O3 ceramics

    NASA Astrophysics Data System (ADS)

    Chen, Shi; Yang, Yan; Zhou, Guohong; Wu, Yiquan; Liu, Peng; Zhang, Fang; Wang, Shiwei; Trojan-Piegza, Joanna; Zych, Eugeniusz

    2012-12-01

    Persistent luminescence phosphors, Tb3+, Sr2+ co-doped Lu2O3 ceramics were fabricated under vacuum at 1870 °C. A strong green color afterglow could be observed after excitation with 254 nm UV radiation. The afterglow was found to be roughly doubled in intensity upon stimulation with violet or blue-green photons (˜400-600 nm) as well as upon IR radiation (˜800-980 nm). Hence, the enhancement of the green afterglow could also be attained by means of natural sunlight. Short wavelength UV radiation was found to induce an extrinsic absorption band below about 600 nm and extending into the deep UV. This was mirrored by a simultaneous decrease of the absorption by Tb3+ around 230-320 nm. The extrinsic absorption seemed to contain at least two overlapping components which supposedly resulted from a band related to Tb4+/Tb3+-h and a feature resulting from F/F+ centers created upon irradiation with short UV. This absorption was shown to be reversible, as it disappeared after a short heat treatment at about 300 °C as well as with continuous irradiation of ˜400 nm radiation.

  9. Synthesis and spectroscopic characterization of YPO{sub 4} activated with Tb{sup 3+} and effect of Bi{sup 3+} co-doping on the luminescence properties

    SciTech Connect

    Angiuli, Fabio; Cavalli, Enrico; Belletti, Alessandro

    2012-08-15

    Single crystals of YPO{sub 4}:Tb{sup 3+}(1%) have been grown from Pb{sub 2}P{sub 2}O{sub 7} flux and their emission dynamics have been characterized by steady state and time resolved optical spectroscopy. The investigation has then been extended to green emitting phosphors with composition Y{sub 0.95-x}Tb{sub 0.05}Bi{sub x}PO{sub 4} (x=0, 0.0025, 0.005, 0.01, 0.025), synthesized by the Pechini sol-gel method and by solid state reaction. The former procedure has yielded higher quality materials in terms of size and morphology of the particles and of emission performance. The effect of the Bi{sup 3+} co-doping on the emission properties has been related to the Bi{sup 3+}{yields}Tb{sup 3+} energy transfer process as well as to the influence of the bismuth ions on the optical properties of the host lattice. - Graphical abstract: The intensity of the 370 nm excited luminescence increases with the Bi{sup 3+} content. A possible mechanism accounting for this behavior is proposed and discussed. Highlights: Black-Right-Pointing-Pointer Green emitting YPO{sub 4}:Tb{sup 3+} phosphors were synthesized by different methods. Black-Right-Pointing-Pointer The emission dynamics have been investigated under different experimental conditions. Black-Right-Pointing-Pointer The co-doping with Bi{sup 3+} ions increases the emission performance of the phosphors.

  10. Effect of different surfactants on structural and optical properties of Ce3+ and Tb3+ co-doped BiPO4 nanostructures

    NASA Astrophysics Data System (ADS)

    Lakshminarayana, G.; Dao, T. D.; Chen, K.; Sharma, Manoj; Takeda, T.; Brik, M. G.; Kityk, I. V.; Singh, Sarabjot; Nagao, T.

    2015-01-01

    In this paper we report on the Ce3+ and Tb3+ ions co-doped bismuth phosphate (BiPO4) nanostructures that were synthesized by a simple precipitation method using different surfactants such as glycerol/H2O, glycerol/ethylene glycol, oleic acid, and ethylene glycol. The structural (X-ray diffraction, scanning electron microscopy, tunneling electron microscopy), functional groups analysis (Fourier transform infrared and Raman spectroscopy), thermal (thermogravimetry and differential thermal analysis), and optical (photoluminescence, photoluminescence-excitation) properties were investigated. The structural and morphological analysis confirms the pure hexagonal crystal structure of the synthesized nanostructures. From the measured Fourier transform infrared (FTIR) and Raman spectra various functional groups such as υ3 stretching vibration of the PO4 group, and δ(O-P-O) and υ4 (PO4) vibrations including the υ2 and υ1 bending modes of the PO4 units are identified. Based on the thermal analysis, for all the studied samples an exothermic peak between 680 °C and 700 °C was observed due to phase transition from hexagonal to high temperature monoclinic. The Ce3+and Tb3+ codoped samples show spectrally broad 5d → 4f luminescence in the blue (centered at 459 nm) wavelength region under the direct optical excitation of Ce3+ at 417 nm. Similarly, Tb3+ has revealed four main emission bands (5D4 → 7F6, 5, 4 and 3) at 490 nm, 545 nm, 585 nm and 621 nm with 378 nm (7F6 → 5G6) as the excitation wavelength, including three more weak emission bands at 647 nm, 669 nm, and 681 nm which could be assigned to 5D4 → 7F2, 1, 0 emission transitions. Among them, 545 nm (5D4 → 7F5) has shown bright green emission. The Ce3+ and Tb3+ codoped sample synthesized with pure oleic acid have shown relatively high green emission intensity for Tb3+, and relatively weak blue emission intensity for Ce3+ under their respective optical excitation wavelengths.

  11. Characterization of co-doped (In, N): ZnO by indigenous thermopower measurement system

    NASA Astrophysics Data System (ADS)

    Kedia, Sanjay Kumar; Singh, Anil; Chaudhary, Sujeet

    2016-05-01

    The thermopower measurement of (In, N) co-doped ZnO thin films have been carried out using indigenous high and low temperature thermopower measurement system. The compact thermopower measurement system has been designed, developed, tested in house. The sensitivity and accuracy of indigenous thermopower system have been investigated by measuring thermopower of standard samples like Cu, Ni, Sb etc. It has been also investigated by the comparison of carrier concentration using Hall Effect and Thermopower measurement of these (In, N) co-doped ZnO thin films. The constant temperature gradient between hot and cold junction has been maintained by using the temperature controller. The room temperature and low temperature Seebeck coefficient measurements were performed on these co-doped ZnO samples. A series of experiments have been performed to detect the p-type conductivity in co-doped ZnO thin films, particularly at low temperature. The negative Seebeck coefficient observed down to 40 K established the n-type behavior in these co-doped samples.

  12. Band gap tuning and room temperature ferromagnetism in Co doped Zinc stannate nanostructures

    NASA Astrophysics Data System (ADS)

    Sumithra, S.; Victor Jaya, N.

    2016-07-01

    The effect of Co doping on structural, optical and magnetic behavior of pure and Co doped Zinc stannate (ZTO) nanostructures was investigated. Pure and Co (1%, 3% & 5%) doped Zn2SnO4 compounds were prepared through simple precipitation route. Formation of cubic inverse spinel structure and metal oxide vibrations of the samples were investigated using XRD and FTIR. Co doping influences the crystallite size producing micro strain in ZTO lattice. Poly dispersed rod like shape of the particles was examined by FESEM. Elemental composition of prepared samples was identified by EDAX analysis. Optical Absorption spectra shows significant red shift on increasing the dopant concentration which indicates the reduction in optical band gap. Visible luminescence observed from photoluminescence studies confirms the presence of oxygen vacancies and trap sites in the lattice. Magnetization analysis reveals the enhanced ferromagnetic behavior in all Co doped ZTO samples. The amplified ferromagnetic ordering in Co doped ZTO compounds has been explained in terms of defects serving as free spin polarized prophetic carriers.

  13. Suppression of boron-oxygen defects in Czochralski silicon by carbon co-doping

    SciTech Connect

    Wu, Yichao; Yu, Xuegong He, Hang; Chen, Peng; Yang, Deren

    2015-03-09

    We have investigated the influence of carbon co-doping on the formation of boron-oxygen defects in Czochralski silicon. It is found that carbon can effectively suppress the formation of boron-oxygen defects. Based on our experiments and first-principle theoretical calculations, it is believed that this effect is attributed to the formation of more energetically favorable carbon-oxygen complexes. Moreover, the diffusion of oxygen dimers in carbon co-doped silicon also becomes more difficult. All these phenomena should be associated with the tensile stress field induced by carbon doping in silicon.

  14. Magnetic and ferroelectric properties of Zn and Mn co-doped BaTiO3

    NASA Astrophysics Data System (ADS)

    Keshari Das, Sangram; Kumar Roul, Binod

    2015-06-01

    This paper reports an approach to obtaining multiferroic properties in co-doped (Zn:Mn) BaTiO3 near room temperature. Interestingly, an unusual magnetic hysteresis loop is observed in the co-doped compositions in which the central portion of the loop is squeezed. However, in the composition Ba0.9Zn0.1Ti0.9Mn0.1O3, a broad magnetic hysteresis loop is observed. Such a magnetic effect is attributed to the coexistence of antiferromagnetic and ferromagnetic exchange interactions in the system. The observation of the above type of magnetic properties is likely to be due to the presence of exchange interactions between Mn ions. A lossy-type of ferroelectric hysteresis loop is also observed in co-doped ceramic compositions near room temperature. Author S. K. Das supported financially by CSIR, New Delhi (Grant No. 09/750 (0005)/2009-EMR-I).

  15. Nitrogen and Phosphorous Co-Doped Graphene Monolith for Supercapacitors.

    PubMed

    Wen, Yangyang; Rufford, Thomas E; Hulicova-Jurcakova, Denisa; Wang, Lianzhou

    2016-03-01

    The co-doping of heteroatoms has been regarded as a promising approach to improve the energy-storage performance of graphene-based materials because of the synergetic effect of the heteroatom dopants. In this work, a single precursor melamine phosphate was used for the first time to synthesise nitrogen/phosphorus co-doped graphene (N/P-G) monoliths by a facile hydrothermal method. The nitrogen contents of 4.27-6.58 at% and phosphorus levels of 1.03-3.00 at% could be controlled by tuning the mass ratio of melamine phosphate to graphene oxide in the precursors. The N/P-G monoliths exhibited excellent electrochemical performances as electrodes for supercapacitors with a high specific capacitance of 183 F g(-1) at a current density of 0.05 A g(-1), good rate performance and excellent cycling performance. Additionally, the N/P-G electrode was stable at 1.6 V in 1 m H2 SO4 aqueous electrolyte and delivered a high energy density of 11.33 Wh kg(-1) at 1.6 V. PMID:26834002

  16. Nitrogen-fluorine co-doped titania inverse opals for enhanced solar light driven photocatalysis.

    PubMed

    Rahul, T K; Sandhyarani, N

    2015-11-21

    Three dimensionally ordered nitrogen-fluorine (N-F) co-doped TiO2 inverse opals (IOs) were fabricated by templating with polystyrene (PS) colloidal photonic crystals (CPCs) by infiltration. During preparation, the TiO2 precursor was treated with a mixture of nitric acid and trifluoroacetic acid to facilitate N-F co-doping into the TiO2 lattice. Enhanced solar light absorption was observed in the samples as a consequence of the red shift in the electronic band gap of TiO2 due to N-F co-doping. The photonic band gap (PBG) of these TiO2 IO films was tuned by varying the sphere size of the PS CPC templates. The as-prepared N-F co-doped TiO2 IO films were used as photocatalysts for the degradation of Rhodamine B (RhB) dye under solar light irradiation. A significant enhancement in the photocatalytic activity was observed in N-F co-doped TiO2 IO films prepared using PS spheres of 215 nm as a template, with the red edge of the PBG closer to the electronic band gap (EBG) of TiO2. 100% of the dye molecules were degraded within 2 minutes under direct solar irradiation, which is one of the fastest reaction times ever reported for RhB degradation in the presence of TiO2 photocatalysts. The N-F co-doped TiO2 IO film prepared using PS of 460 nm with its PBG centered at 695 nm also showed good photocatalytic activity. It was found that the IO films displayed improved photocatalytic activity in comparison to ordinary nanocrystalline (nc)-TiO2 films. The enhancement could be attributed to the bandgap scattering effect and the slow photon effect, leading to a significant improvement in solar light harvesting. PMID:26487369

  17. Nitrogen-fluorine co-doped titania inverse opals for enhanced solar light driven photocatalysis

    NASA Astrophysics Data System (ADS)

    Rahul, T. K.; Sandhyarani, N.

    2015-10-01

    Three dimensionally ordered nitrogen-fluorine (N-F) co-doped TiO2 inverse opals (IOs) were fabricated by templating with polystyrene (PS) colloidal photonic crystals (CPCs) by infiltration. During preparation, the TiO2 precursor was treated with a mixture of nitric acid and trifluoroacetic acid to facilitate N-F co-doping into the TiO2 lattice. Enhanced solar light absorption was observed in the samples as a consequence of the red shift in the electronic band gap of TiO2 due to N-F co-doping. The photonic band gap (PBG) of these TiO2 IO films was tuned by varying the sphere size of the PS CPC templates. The as-prepared N-F co-doped TiO2 IO films were used as photocatalysts for the degradation of Rhodamine B (RhB) dye under solar light irradiation. A significant enhancement in the photocatalytic activity was observed in N-F co-doped TiO2 IO films prepared using PS spheres of 215 nm as a template, with the red edge of the PBG closer to the electronic band gap (EBG) of TiO2. 100% of the dye molecules were degraded within 2 minutes under direct solar irradiation, which is one of the fastest reaction times ever reported for RhB degradation in the presence of TiO2 photocatalysts. The N-F co-doped TiO2 IO film prepared using PS of 460 nm with its PBG centered at 695 nm also showed good photocatalytic activity. It was found that the IO films displayed improved photocatalytic activity in comparison to ordinary nanocrystalline (nc)-TiO2 films. The enhancement could be attributed to the bandgap scattering effect and the slow photon effect, leading to a significant improvement in solar light harvesting.

  18. Nitrogen-fluorine co-doped titania inverse opals for enhanced solar light driven photocatalysis.

    PubMed

    Rahul, T K; Sandhyarani, N

    2015-11-21

    Three dimensionally ordered nitrogen-fluorine (N-F) co-doped TiO2 inverse opals (IOs) were fabricated by templating with polystyrene (PS) colloidal photonic crystals (CPCs) by infiltration. During preparation, the TiO2 precursor was treated with a mixture of nitric acid and trifluoroacetic acid to facilitate N-F co-doping into the TiO2 lattice. Enhanced solar light absorption was observed in the samples as a consequence of the red shift in the electronic band gap of TiO2 due to N-F co-doping. The photonic band gap (PBG) of these TiO2 IO films was tuned by varying the sphere size of the PS CPC templates. The as-prepared N-F co-doped TiO2 IO films were used as photocatalysts for the degradation of Rhodamine B (RhB) dye under solar light irradiation. A significant enhancement in the photocatalytic activity was observed in N-F co-doped TiO2 IO films prepared using PS spheres of 215 nm as a template, with the red edge of the PBG closer to the electronic band gap (EBG) of TiO2. 100% of the dye molecules were degraded within 2 minutes under direct solar irradiation, which is one of the fastest reaction times ever reported for RhB degradation in the presence of TiO2 photocatalysts. The N-F co-doped TiO2 IO film prepared using PS of 460 nm with its PBG centered at 695 nm also showed good photocatalytic activity. It was found that the IO films displayed improved photocatalytic activity in comparison to ordinary nanocrystalline (nc)-TiO2 films. The enhancement could be attributed to the bandgap scattering effect and the slow photon effect, leading to a significant improvement in solar light harvesting.

  19. Study of new states in visible light active W, N co-doped TiO{sub 2} photo catalyst

    SciTech Connect

    Sajjad, Ahmed Khan Leghari; Shamaila, Sajjad; Zhang, Jinlong

    2012-11-15

    Highlights: ► Visible light efficient W, N co-doped TiO{sub 2} photo catalysts are prepared by sol–gel. ► Oxygen vacancies are detected in the form of new linkages as N-Ti-O, N-W-O, Ti-O-N and W-O-N. ► W, N co-doped titania has new energy states which narrows the band gap effectively. ► Oxygen vacancies are proved to be the cause for high photo catalytic activity. ► W and N co-doping plays the major role to make the composite thermally stable. -- Abstract: The visible light efficient W, N co-doped TiO{sub 2} photo catalysts are prepared by sol–gel method. New linkages of N, W and O are formed as N-Ti-O, N-W-O, Ti-O-N and W-O-N. Electron paramagnetic resonance illustrates the presence of oxygen vacancies in W, N co-doped TiO{sub 2} acting as trapping agencies for electrons to produce active species. X-ray photoelectron spectroscopy confirms the presence of new energy states. New linkages and oxygen vacancies are proved to be the main cause for the improved photo catalytic performances. W, N co-doped TiO{sub 2} has new energy states which narrow the band gap effectively. W, N co-doped TiO{sub 2} is thermally stable and retains its anatase phase up to 900 °C. 4.5% W, N co-doped TiO{sub 2} showed superior activity for the degradation of Rhodamine B and 2,4-dichlorophenol as compared to pure titania, Degussa P-25, traditional N-doped TiO{sub 2} and pure WO{sub 3}.

  20. Role of Gd3+ ion on downshifting and upconversion emission properties of Pr3+, Yb3+ co-doped YNbO4 phosphor and sensitization effect of Bi3+ ion

    NASA Astrophysics Data System (ADS)

    Dwivedi, A.; Mishra, Kavita; Rai, S. B.

    2016-07-01

    Dual-mode luminescence (downshifting-DS and upconversion-UC) properties of Pr3+/Yb3+ co-doped Y1-xGdxNbO4 (x = 0.0, 0.5, and 1.0) phosphors synthesized by solid state reaction technique have been explored with and without Gd3+ ion. The structural characterizations (XRD, SEM, and FTIR) confirm the pure phase of YNbO4 phosphor. Further, with the Gd3+ ion co-doping, the YNbO4 phosphors having a random shape and the large particle size are found to be transformed into nearly spherical shape particles with the reduced particle size. The optical band gaps (Eg) of Y1-xGdxNbO4 (x = 0.00, 0.25, 0.50, and 1.00) calculated from UV-Vis-NIR measurements are ˜3.69, 4.00, 4.38, and 4.44 eV, respectively. Moreover, YNbO4 phosphor is a promising blue emitting material, whereas Y1-x-y-zPryYbzGdxNbO4 phosphor gives intense green, blue, and red emissions via dual-mode optical processes. The broad blue emission arises due to (NbO4)3- group of the host with λex = 264 nm, whereas Pr3+ doped YNbO4 phosphor gives dominant red and blue emissions along with comparatively weak green emission on excitation with λex = 300 nm and 491 nm. The concentration dependent variation in emission intensity at 491 nm (3P0→3H4 transition) and 612 nm (1D2→3H4 transition); at 612 nm (1D2→3H4 transition) and 658 nm (3P0→3F2 transition) of Pr3+ ion in YNbO4 phosphor with λex = 300 nm and 491 nm excitations, respectively, has been thoroughly explored and explained by the cross-relaxation process through different channels. The sensitization effect of Bi3+ ion co-doping on DS properties of the phosphor has also been studied. The observed DS results have been optimized by varying the concentration of Pr3+ and Bi3+ ions, and the results are explained by the well-known simple band structure model. The study of Gd3+ co-doping reveals noticeable differences in DS characteristics of Y1-xPrxNbO4 phosphors: the overall decrement and increment (except for 612 nm emission) in intensity of DS emission on

  1. The electronic structure and optical properties of Mn and B, C, N co-doped MoS2 monolayers

    PubMed Central

    2014-01-01

    The electronic structure and optical properties of Mn and B, C, N co-doped molybdenum disulfide (MoS2) monolayers have been investigated through first-principles calculations. It is shown that the MoS2 monolayer reflects magnetism with a magnetic moment of 0.87 μB when co-doped with Mn-C. However, the systems co-doped with Mn-B and Mn-N atoms exhibit semiconducting behavior and their energy bandgaps are 1.03 and 0.81 eV, respectively. The bandgaps of the co-doped systems are smaller than those of the corresponding pristine forms, due to effective charge compensation between Mn and B (N) atoms. The optical properties of Mn-B (C, N) co-doped systems all reflect the redshift phenomenon. The absorption edge of the pure molybdenum disulfide monolayer is 0.8 eV, while the absorption edges of the Mn-B, Mn-C, and Mn-N co-doped systems become 0.45, 0.5, and 0 eV, respectively. As a potential material, MoS2 is widely used in many fields such as the production of optoelectronic devices, military devices, and civil devices. PMID:25317103

  2. The electronic structure and optical properties of Mn and B, C, N co-doped MoS2 monolayers.

    PubMed

    Xu, Wei-Bin; Huang, Bao-Jun; Li, Ping; Li, Feng; Zhang, Chang-Wen; Wang, Pei-Ji

    2014-01-01

    The electronic structure and optical properties of Mn and B, C, N co-doped molybdenum disulfide (MoS2) monolayers have been investigated through first-principles calculations. It is shown that the MoS2 monolayer reflects magnetism with a magnetic moment of 0.87 μB when co-doped with Mn-C. However, the systems co-doped with Mn-B and Mn-N atoms exhibit semiconducting behavior and their energy bandgaps are 1.03 and 0.81 eV, respectively. The bandgaps of the co-doped systems are smaller than those of the corresponding pristine forms, due to effective charge compensation between Mn and B (N) atoms. The optical properties of Mn-B (C, N) co-doped systems all reflect the redshift phenomenon. The absorption edge of the pure molybdenum disulfide monolayer is 0.8 eV, while the absorption edges of the Mn-B, Mn-C, and Mn-N co-doped systems become 0.45, 0.5, and 0 eV, respectively. As a potential material, MoS2 is widely used in many fields such as the production of optoelectronic devices, military devices, and civil devices.

  3. Effect of Ce and Cu co-doping on the structural, morphological, and optical properties of ZnO nanocrystals and first principle investigation of their stability and magnetic properties

    NASA Astrophysics Data System (ADS)

    Mary, J. Arul; Vijaya, J. Judith; Bououdina, M.; Kennedy, L. John; Dai, J. H.; Song, Y.

    2015-02-01

    Ce, Cu co-doped ZnO (Zn1-2xCexCuxO: x=0.00, 0.01, 0.02, 0.03, 0.04 and 0.05) nanocrystals were synthesized by a microwave combustion method. These nanocrystals were investigated by using X-ray diffraction (XRD), UV-visible diffuse reflectance spectroscopy (DRS), scanning electron microscopy (SEM), and vibrating sample magnetometer (VSM). The stability and magnetic properties of Ce and Cu co-doped ZnO were probed by first principle calculations. XRD results revealed that all the compositions are single crystalline. hexagonal wurtzite structure. The optical band gap of pure ZnO was found to be 3.22 eV, and it decreased from 3.15 to 3.10 eV with an increase in the concentration of Cu and Ce content. The morphologies of Ce and Cu co-doped ZnO samples confirmed the formation of nanocrystals with an average grain size ranging from 70 to 150 nm. The magnetization measurement results affirmed the antiferro and ferromagnetic state for Ce and Cu co-doped ZnO samples and this is in agreement with the first principles theoretical calculations.

  4. Co-doped mesoporous titania photocatalysts prepared from a peroxo-titanium complex solution

    SciTech Connect

    El Saliby, Ibrahim; Erdei, Laszlo; McDonagh, Andrew; Kim, Jong-Beom; Kim, Jong-Ho; Shon, Ho Kyong

    2014-01-01

    Graphical abstract: - Highlights: • Peroxotitanium complex for the synthesis of doped photocatalysts. • Fabrication of N doped and N/Ag co-doped photocatalysts. • Characterization of photocatalysts by SEM, XRD, BET, DRS and XPS. • Bench scale photocatalysis under simulated solar light using crystal violet pollutant. - Abstract: In this study, nitrogen doped and nitrogen/silver co-doped TiO{sub 2} photocatalsysts were fabricated using a sol–gel method at room temperature. The obtained gels were neutralized, washed with pure water, and calcined at 400 °C for 4 h. The photocatalysts were characterized by scanning and transmission electron microscopy, X-ray diffraction, diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy, and BET specific surface area. The results showed that spherical particles with anatase structure were produced after annealing at 400 °C. N 1s (400 eV) and Ag 3d (367.3 eV) states indicated that nitrogen doping and silver co-doping were in the form of NO bonds and AgO, respectively. The photocatalytic activity of photocatalysts was investigated using a batch reactor system exposed to artificial solar irradiation. Both nitrogen and silver/nitrogen co-doped materials were effective in the photocatalytic degradation of hexamethyl pararosaniline chloride.

  5. Microstructure and dielectric properties of (Nb + In) co-doped rutile TiO2 ceramics

    NASA Astrophysics Data System (ADS)

    Li, Jinglei; Li, Fei; Zhuang, Yongyong; Jin, Li; Wang, Linghang; Wei, Xiaoyong; Xu, Zhuo; Zhang, Shujun

    2014-08-01

    The (Nb + In) co-doped TiO2 ceramics recently attracted considerable attention due to their colossal dielectric permittivity (CP) (˜100,000) and low dielectric loss (˜0.05). In this research, the 0.5 mol. % In-only, 0.5 mol. % Nb-only, and 0.5-7 mol. % (Nb + In) co-doped TiO2 ceramics were synthesized by standard conventional solid-state reaction method. Microstructure studies showed that all samples were in pure rutile phase. The Nb and In ions were homogeneously distributed in the grain and grain boundary. Impedance spectroscopy and I-V behavior analysis demonstrated that the ceramics may compose of semiconducting grains and insulating grain boundaries. The high conductivity of grain was associated with the reduction of Ti4+ ions to Ti3+ ions, while the migration of oxygen vacancy may account for the conductivity of grain boundary. The effects of annealing treatment and bias filed on electrical properties were investigated for co-doped TiO2 ceramics, where the electric behaviors of samples were found to be susceptible to the annealing treatment and bias field. The internal-barrier-layer-capacitance mechanism was used to explain the CP phenomenon, the effect of annealing treatment and nonlinear I-V behavior for co-doped rutile TiO2 ceramics. Compared with CaCu3Ti4O12 ceramics, the high activation energy of co-doped rutile TiO2 (3.05 eV for grain boundary) was thought to be responsible for the low dielectric loss.

  6. Proton and Gamma Radiation Effects in Undoped, Single-doped and co-doped YLiF4 and LuLiF4

    NASA Technical Reports Server (NTRS)

    Lee, Hyung; Bai, Yingxin; Yu, Kirong; Singh, U.

    2009-01-01

    Proton and gamma radiation effects in various YLiF4 and LuLiF4 crystals have been investigated. The radiation induced color centers compared with six different kinds of crystal samples in ranges up to 200 krads and 200 MeV. The radiation induced absorption coefficients are strongly dependent on polarization and concentration of rare-earth ions.

  7. A comparative investigation on structure and multiferroic properties of bismuth ferrite thin films by multielement co-doping

    SciTech Connect

    Dong, Guohua; Tan, Guoqiang Luo, Yangyang; Liu, Wenlong; Xia, Ao; Ren, Huijun

    2014-12-15

    Highlights: • Multielement (Tb, Cr and Mn) co-doped BiFeO{sub 3} films were fabricated by CSD method. • Multielement co-doping induces a structural transition. • It is found effective to stabilize the valence of Fe ions at +3 by the strategy. • The co-doping at A/B-sites gives rise to the superior multiferroic properties. - Abstract: (Tb, Cr and Mn) multielement co-doped BiFeO{sub 3} (BTFCMO) thin films were prepared by the chemical solution deposition method on fluorine doped tin oxide (FTO) substrates. X-ray diffraction, Rietveld refinement and Raman analyses revealed that a phase transition from rhombohedral to triclinic structure occurs in the multielement co-doped BiFeO{sub 3} films. It is found that the doping is conducive to stabilizing the valence of Fe ions and reducing leakage current. In addition, the highly enhanced ferroelectric properties with a huge remanent polarization (2P{sub r}) of 239.6 μC/cm{sup 2} and a low coercive field (2E{sub c}) of 615.6 kV/cm are ascribed to the well film texture, the structure transition and the reduced leakage current by the co-doping. Moreover, the structure transition is the dominant factor resulting in the significant enhancement observed in magnetization (M{sub s} ∼ 10.5 emu/cm{sup 3}), owing to the collapse of the space-modulated spin structure. In this contribution, these results demonstrate that the multielement co-doping is in favor of the enhanced multiferroic properties of the BFO films for possible multifunctional applications.

  8. Intense upconversion luminescence and effect of local environment for Tm 3+/Yb 3+ co-doped novel TeO 2-BiCl 3 glass system

    NASA Astrophysics Data System (ADS)

    Wang, Guonian; Dai, Shixun; Zhang, Junjie; Wen, Lei; Yang, Jianhu; Jiang, Zhonghong

    2006-05-01

    We present the results of a study that uses theoretical and experimental methods to investigate the characteristics of the upconversion luminescence of Tm 3+/Yb 3+ codoped TeO 2-BiCl 3 glass system as a function of the BiCl 3 fraction. These glasses are potentially important in the design of upconversion fiber lasers. Effect of local environment around Tm 3+ on upconversion fluorescence intensity was analyzed by theoretical calculations. The structure and spectroscopic properties were investigated in the experiments by measuring the Raman spectra, IR transmission spectra, and absorption and fluorescence intensities at room temperature. The results indicate that blue luminescence quantum efficiency increases with increasing BiCl 3 content from 10 to 60 mol%, which were interpreted by the increase of asymmetry of glass structure, decrease of phonon energy and removing of OH - groups.

  9. Influence of praseodymium and nitrogen co-doping on the photocatalytic activity of TiO{sub 2}

    SciTech Connect

    Wu, Jing; Liu, Qingju; Gao, Pan; Zhu, Zhongqi

    2011-11-15

    Highlights: {yields} The praseodymium and nitrogen co-doped TiO{sub 2} (Pr-N-TiO{sub 2}) powders were prepared and characterized. {yields} The effects on the photocatalytic activity were studied. {yields} The results exhibit that the spectrum absorption region of the co-doped sample is red-shifted to visible light and the recombination of the photo-generated pairs is inhibited. {yields} The photocatalytic activity is greatly improved. -- Abstract: TiO{sub 2} nanoparticles co-doped with different doping concentration of Pr and N were prepared by sol-gel method combined with microwave chemical method. The samples were characterized by XRD, FT-IR, UV-vis, TEM, XPS, PL, and the photocatalytic activity were investigated by photocatalytic degradation of methylene blue (MB). The results indicate that Pr and N ions incorporate into the lattice of TiO{sub 2}, co-doping restrains the increase of grain size, broadens the absorption region to visible light, and inhibits the recombination of the photo-generated electrons and holes. Moreover, the photocatalytic activity of Pr-N-TiO{sub 2} is remarkable improved due to the synergistic effect of the co-doped ions. The degradation rate of MB in 6 h is 92.81%, which is much higher than that of Degussa P25 (45.01%).

  10. Cumulative effect of transition metals on nitrogen and fluorine co-doped graphite nanofibers: an efficient and highly durable non-precious metal catalyst for the oxygen reduction reaction.

    PubMed

    Peera, S Gouse; Arunchander, A; Sahu, A K

    2016-08-14

    Nitrogen and fluorine co-doped graphite nanofibers (N/F-GNF) and their cumulative effect with Fe and Co have been developed as an alternative non-precious metal catalyst for efficient oxygen reduction reaction (ORR) in acidic media. The synergistic effect between the doped hetero atoms and the co-ordinated Fe and Co towards ORR activity and durability of the catalyst is deeply investigated. A high ORR onset potential comparable with commercial Pt/C catalyst is observed with the Fe-Co/NF-GNF catalyst, which indicates that this catalyst is a potential alternative to Pt/C. A fivefold increase in mass activity is achieved by the Fe-Co/NF-GNF catalyst compared to the simple N/F-GNF catalyst, which endorses the significant role of transition metal atoms in enhancing ORR activity. The advanced Fe-Co/NF-GNF catalyst also exhibits complete tolerance to CH3OH and CO. The Fe-Co/NF-GNF catalyst also exhibits excellent durability towards the ORR with only a 10 mV negative shift in its half wave potential after a 10 000 repeated potential cycling test, whereas in the case of a commercial Pt/C catalyst there was an ∼110 mV negative shift under similar environmental conditions. More stringent corrosive test cycles were also performed by maintaining the cell as high as 1.4 V with a later decrease to 0.6 V vs. RHE for 300 cycles, which showed the excellent durability of the Fe-Co/NF-GNF catalyst in comparison with the Pt/C catalyst. XPS analysis of the Fe-Co/NF-GNF catalyst presents the ORR active chemical states of N (pyridinic-N and graphitic-N) and F (semi-ionic-F) and the co-ordinated sites of Fe and Co species with the dopants. The excellent performance and durability of the Fe-Co/NF-GNF catalyst is due to the synergistic effect between the hetero atoms dopants (N and F) and strong co-ordinating bonds of M-N-C, which protect the graphene layers around the metallic species and greatly mitigates the leaching of Co and Fe during the long term cycling test. The high activity

  11. Cumulative effect of transition metals on nitrogen and fluorine co-doped graphite nanofibers: an efficient and highly durable non-precious metal catalyst for the oxygen reduction reaction.

    PubMed

    Peera, S Gouse; Arunchander, A; Sahu, A K

    2016-08-14

    Nitrogen and fluorine co-doped graphite nanofibers (N/F-GNF) and their cumulative effect with Fe and Co have been developed as an alternative non-precious metal catalyst for efficient oxygen reduction reaction (ORR) in acidic media. The synergistic effect between the doped hetero atoms and the co-ordinated Fe and Co towards ORR activity and durability of the catalyst is deeply investigated. A high ORR onset potential comparable with commercial Pt/C catalyst is observed with the Fe-Co/NF-GNF catalyst, which indicates that this catalyst is a potential alternative to Pt/C. A fivefold increase in mass activity is achieved by the Fe-Co/NF-GNF catalyst compared to the simple N/F-GNF catalyst, which endorses the significant role of transition metal atoms in enhancing ORR activity. The advanced Fe-Co/NF-GNF catalyst also exhibits complete tolerance to CH3OH and CO. The Fe-Co/NF-GNF catalyst also exhibits excellent durability towards the ORR with only a 10 mV negative shift in its half wave potential after a 10 000 repeated potential cycling test, whereas in the case of a commercial Pt/C catalyst there was an ∼110 mV negative shift under similar environmental conditions. More stringent corrosive test cycles were also performed by maintaining the cell as high as 1.4 V with a later decrease to 0.6 V vs. RHE for 300 cycles, which showed the excellent durability of the Fe-Co/NF-GNF catalyst in comparison with the Pt/C catalyst. XPS analysis of the Fe-Co/NF-GNF catalyst presents the ORR active chemical states of N (pyridinic-N and graphitic-N) and F (semi-ionic-F) and the co-ordinated sites of Fe and Co species with the dopants. The excellent performance and durability of the Fe-Co/NF-GNF catalyst is due to the synergistic effect between the hetero atoms dopants (N and F) and strong co-ordinating bonds of M-N-C, which protect the graphene layers around the metallic species and greatly mitigates the leaching of Co and Fe during the long term cycling test. The high activity

  12. W/Mo co-doped BiVO4 for photocatalytic treatment of polymer-containing wastewater in oilfield

    NASA Astrophysics Data System (ADS)

    Zhou, Ying; Li, Wei; Wan, Wenchao; Zhang, Ruiyang; Lin, Yuanhua

    2015-06-01

    Polymer flooding is an effective way to enhance oil recovery (EOR). However, the treatment of the oily wastewater becomes an urgent issue. Photocatalysis is a promising approach for this purpose. In this report, W/Mo co-doped BiVO4 particles are synthesized by hydrothermal method. W/Mo co-doping could promote an effective separation of photogenerated carriers reflecting from the 6 times higher photocurrent density compared to pure BiVO4. The photodegradation of partially hydrolyzed polyacrylamide (HPAM) over 0.5 at.% W and 1.5 at.% Mo co-doped BiVO4 is 43% under UV-vis light irradiation for 3 h, which is much higher than that of pure BiVO4 (18%).

  13. Fabrication and photoelectric properties of Er3+ and Yb3+ co-doped ZnO films

    NASA Astrophysics Data System (ADS)

    Feng, Wei; Wang, Xiangfu; Meng, Lan; Yan, Xiaohong

    2016-01-01

    In this paper, the Er3+ and Yb3+ co-doped ZnO films deposited by a novel thermal decomposition method under different annealing temperature process have been reported. The effects of annealing temperature on the morphology and properties of the films are systematically studied. The resulting spectra demonstrate that the Er3+ and Yb3+ co-doped ZnO films possessed the property of up-conversion, converting IR light into visible light that can be absorbed by amorphous silicon solar cell. After all, inner photoelectric effect of the Er3+ and Yb3+ co-doped ZnO films in the amorphous as a light scattering layer are also found with an infrared 980 nm laser as excitation source.

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

    SciTech Connect

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

    2012-01-01

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

  15. Cumulative effect of transition metals on nitrogen and fluorine co-doped graphite nanofibers: an efficient and highly durable non-precious metal catalyst for the oxygen reduction reaction

    NASA Astrophysics Data System (ADS)

    Peera, S. Gouse; Arunchander, A.; Sahu, A. K.

    2016-07-01

    Nitrogen and fluorine co-doped graphite nanofibers (N/F-GNF) and their cumulative effect with Fe and Co have been developed as an alternative non-precious metal catalyst for efficient oxygen reduction reaction (ORR) in acidic media. The synergistic effect between the doped hetero atoms and the co-ordinated Fe and Co towards ORR activity and durability of the catalyst is deeply investigated. A high ORR onset potential comparable with commercial Pt/C catalyst is observed with the Fe-Co/NF-GNF catalyst, which indicates that this catalyst is a potential alternative to Pt/C. A fivefold increase in mass activity is achieved by the Fe-Co/NF-GNF catalyst compared to the simple N/F-GNF catalyst, which endorses the significant role of transition metal atoms in enhancing ORR activity. The advanced Fe-Co/NF-GNF catalyst also exhibits complete tolerance to CH3OH and CO. The Fe-Co/NF-GNF catalyst also exhibits excellent durability towards the ORR with only a 10 mV negative shift in its half wave potential after a 10 000 repeated potential cycling test, whereas in the case of a commercial Pt/C catalyst there was an ~110 mV negative shift under similar environmental conditions. More stringent corrosive test cycles were also performed by maintaining the cell as high as 1.4 V with a later decrease to 0.6 V vs. RHE for 300 cycles, which showed the excellent durability of the Fe-Co/NF-GNF catalyst in comparison with the Pt/C catalyst. XPS analysis of the Fe-Co/NF-GNF catalyst presents the ORR active chemical states of N (pyridinic-N and graphitic-N) and F (semi-ionic-F) and the co-ordinated sites of Fe and Co species with the dopants. The excellent performance and durability of the Fe-Co/NF-GNF catalyst is due to the synergistic effect between the hetero atoms dopants (N and F) and strong co-ordinating bonds of M-N-C, which protect the graphene layers around the metallic species and greatly mitigates the leaching of Co and Fe during the long term cycling test. The high activity and

  16. Cumulative effect of transition metals on nitrogen and fluorine co-doped graphite nanofibers: an efficient and highly durable non-precious metal catalyst for the oxygen reduction reaction

    NASA Astrophysics Data System (ADS)

    Peera, S. Gouse; Arunchander, A.; Sahu, A. K.

    2016-07-01

    Nitrogen and fluorine co-doped graphite nanofibers (N/F-GNF) and their cumulative effect with Fe and Co have been developed as an alternative non-precious metal catalyst for efficient oxygen reduction reaction (ORR) in acidic media. The synergistic effect between the doped hetero atoms and the co-ordinated Fe and Co towards ORR activity and durability of the catalyst is deeply investigated. A high ORR onset potential comparable with commercial Pt/C catalyst is observed with the Fe-Co/NF-GNF catalyst, which indicates that this catalyst is a potential alternative to Pt/C. A fivefold increase in mass activity is achieved by the Fe-Co/NF-GNF catalyst compared to the simple N/F-GNF catalyst, which endorses the significant role of transition metal atoms in enhancing ORR activity. The advanced Fe-Co/NF-GNF catalyst also exhibits complete tolerance to CH3OH and CO. The Fe-Co/NF-GNF catalyst also exhibits excellent durability towards the ORR with only a 10 mV negative shift in its half wave potential after a 10 000 repeated potential cycling test, whereas in the case of a commercial Pt/C catalyst there was an ~110 mV negative shift under similar environmental conditions. More stringent corrosive test cycles were also performed by maintaining the cell as high as 1.4 V with a later decrease to 0.6 V vs. RHE for 300 cycles, which showed the excellent durability of the Fe-Co/NF-GNF catalyst in comparison with the Pt/C catalyst. XPS analysis of the Fe-Co/NF-GNF catalyst presents the ORR active chemical states of N (pyridinic-N and graphitic-N) and F (semi-ionic-F) and the co-ordinated sites of Fe and Co species with the dopants. The excellent performance and durability of the Fe-Co/NF-GNF catalyst is due to the synergistic effect between the hetero atoms dopants (N and F) and strong co-ordinating bonds of M-N-C, which protect the graphene layers around the metallic species and greatly mitigates the leaching of Co and Fe during the long term cycling test. The high activity and

  17. Local structure investigation of (Co, Cu) co-doped ZnO nanocrystals and its correlation with magnetic properties

    NASA Astrophysics Data System (ADS)

    Tiwari, N.; Doke, S.; Lohar, A.; Mahamuni, Shailaja; Kamal, C.; Chakrabarti, Aparna; Choudhary, R. J.; Mondal, P.; Jha, S. N.; Bhattacharyya, D.

    2016-03-01

    Pure, Co doped and (Co, Cu) co-doped ZnO nanocrystals have been prepared by wet chemical route at room temperature to investigate the effect of Cu doping in Co doped ZnO nanocrystals . The nanocrystals have initially been characterized by X-ray diffraction, FTIR, Raman, optical absorption and EPR spectroscopy and the results were corroborated with DFT based electronic structure calculations. Magnetic properties of the samples have been investigated by studying their magnetic hysteresis behavior and temperature dependence of susceptibilities. Finally the local structure at the host and dopant sites of the nanocrystals have been investigated by Zn, Co and Cu K edges EXAFS measurements with synchrotron radiation to explain their experimentally observed magnetic properties.

  18. Structural and electronic properties of Mg and Mg-Nb co-doped TiO2 (101) anatase surface

    NASA Astrophysics Data System (ADS)

    Sasani, Alireza; Baktash, Ardeshir; Mirabbaszadeh, Kavoos; Khoshnevisan, Bahram

    2016-10-01

    In this paper, by using density functional theory, Mg and Nb-Mg co-doping of TiO2 anatase (101) surfaces are studied. By studying the formation energy of the defects and the bond length distribution of the surface, it is shown that Mg defects tend to stay as far as possible to induce least possible lattice distortion while Nb and Mg defects stay close to each other to cause less stress to the surface. By investigating band structure of the surface and changes stemmed from the defects, potential effects of Mg and Mg-Nb co-doping of TiO2 surface on dye-sensitized solar cells are investigated. In this study, it is shown that the Nb-Mg co-doping could increase JSC of the surface while slightly decreasing VOC compared to Mg doped surface, which might result in an increase in efficiency of the DSSCs compared to Nb or Mg doped surfaces.

  19. Hydrophilic Nitrogen and Sulfur Co-doped Molybdenum Carbide Nanosheets for Electrochemical Hydrogen Evolution.

    PubMed

    Ang, Huixiang; Tan, Hui Teng; Luo, Zhi Min; Zhang, Yu; Guo, Yuan Yuan; Guo, Guilue; Zhang, Hua; Yan, Qingyu

    2015-12-16

    Nitrogen and sulfur dual-doped Mo2 C nanosheets provide low operating potential (-86 mV for driving 10 mA cm(-2) of current density). Co-doping of N and S heteroatoms can improve the wetting property of the Mo2C electrocatalyst in aqueous solution and induce synergistic effects via σ-donation and π-back donation with hydronium cation.

  20. Rapid synthesis of Co, Ni co-doped ZnO nanoparticles: Optical and electrochemical properties

    NASA Astrophysics Data System (ADS)

    Romeiro, Fernanda C.; Marinho, Juliane Z.; Lemos, Samantha C. S.; de Moura, Ana P.; Freire, Poliana G.; da Silva, Luis F.; Longo, Elson; Munoz, Rodrigo A. A.; Lima, Renata C.

    2015-10-01

    We report for the first time a rapid preparation of Zn1-2xCoxNixO nanoparticles via a versatile and environmentally friendly route, microwave-assisted hydrothermal (MAH) method. The Co, Ni co-doped ZnO nanoparticles present an effect on photoluminescence and electrochemical properties, exhibiting excellent electrocatalytic performance compared to undoped ZnO sample. Photoluminescence spectroscopy measurements indicated the reduction of the green-orange-red visible emission region after adding Co and Ni ions, revealing the formation of alternative pathways for the generated recombination. The presence of these metallic ions into ZnO creates different defects, contributing to a local structural disorder, as revealed by Raman spectra. Electrochemical experiments revealed that the electrocatalytic oxidation of dopamine on ZnO attached to multi-walled carbon nanotubes improved significantly in the Co, Ni co-doped ZnO samples when compared to pure ZnO.

  1. Synthesis of N, F and S co-doped graphene quantum dots

    NASA Astrophysics Data System (ADS)

    Kundu, Sumana; Yadav, Ram Manohar; Narayanan, T. N.; Shelke, Manjusha V.; Vajtai, Robert; Ajayan, P. M.; Pillai, Vijayamohanan K.

    2015-07-01

    Graphene quantum dots (GQDs) are a promising category of materials with remarkable size dependent properties like tunable bandgap and photoluminescence along with the possibility of effective chemical functionalization. Doping of GQDs with heteroatoms is an interesting way of regulating their properties. Herein, we report a facile and scalable one-step synthesis of luminescent GQDs, substitutionally co-doped with N, F and S, of ~2 nm average size by a microwave treatment of multi-walled carbon nanotubes in a customized ionic liquid medium. The use of an ionic liquid coupled with the use of a microwave technique enables not only an ultrafast process for the synthesis of co-doped GQDs, but also provides excellent photoluminescence quantum yield (70%), perhaps due to the interaction of defect clusters and dopants.Graphene quantum dots (GQDs) are a promising category of materials with remarkable size dependent properties like tunable bandgap and photoluminescence along with the possibility of effective chemical functionalization. Doping of GQDs with heteroatoms is an interesting way of regulating their properties. Herein, we report a facile and scalable one-step synthesis of luminescent GQDs, substitutionally co-doped with N, F and S, of ~2 nm average size by a microwave treatment of multi-walled carbon nanotubes in a customized ionic liquid medium. The use of an ionic liquid coupled with the use of a microwave technique enables not only an ultrafast process for the synthesis of co-doped GQDs, but also provides excellent photoluminescence quantum yield (70%), perhaps due to the interaction of defect clusters and dopants. Electronic supplementary information (ESI) available: PLQY calculation, MWCNT synthetic details, TGA analysis and tabular format of GQD synthesis processes. See DOI: 10.1039/c5nr02427g

  2. Growth study and photocatalytic properties of Co-doped tungsten oxide mesocrystals

    SciTech Connect

    Sun, Shibin; Chang, Xueting; Li, Zhenjiang

    2012-11-15

    Cobalt-doped tungsten oxide mesocrystals with different morphologies have been successfully generated using a solvothermal method with tungsten hexachloride and cobalt chloride salts as precursors. The resulting mesocrystals were characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, Brunauer-Emmet-Teller analysis of nitrogen sorptometer, and UV-vis diffuse reflectance spectroscopy. The photocatalytic properties of the cobalt-doped tungsten oxide mesocrystals were evaluated on the basis of their ability to degrade methyl orange in an aqueous solution under simulated sunlight irradiation. Results showed that the cobalt doping had obvious effect on the morphologies of the final products, and lenticular and blocky cobalt-doped tungsten oxide mesocrystals could be obtained with 1.0 wt.% and 2.0 wt.% cobalt doping, respectively. The cobalt-doped tungsten oxides exhibited superior photocatalytic activities to that of the undoped tungsten oxide. - Graphical abstract: Schematic illustrations of the growth of the bundled nanowires, lenticular mesocrystals, and blocky mesocrystals. Highlights: Black-Right-Pointing-Pointer Co-doped W{sub 18}O{sub 49} mesocrystals were synthesized using a solvothermal method. Black-Right-Pointing-Pointer The Co doping has obvious effect on the morphology of the final mesocrystals. Black-Right-Pointing-Pointer The Co-doped W{sub 18}O{sub 49} exhibited superior photocatalytic activity to the undoped W{sub 18}O{sub 49}.

  3. Rapid synthesis of Co, Ni co-doped ZnO nanoparticles: Optical and electrochemical properties

    SciTech Connect

    Romeiro, Fernanda C.; Marinho, Juliane Z.; Lemos, Samantha C.S.; Moura, Ana P. de; Freire, Poliana G.; Silva, Luis F. da; Longo, Elson; Munoz, Rodrigo A.A.; Lima, Renata C.

    2015-10-15

    We report for the first time a rapid preparation of Zn{sub 1−2x}Co{sub x}Ni{sub x}O nanoparticles via a versatile and environmentally friendly route, microwave-assisted hydrothermal (MAH) method. The Co, Ni co-doped ZnO nanoparticles present an effect on photoluminescence and electrochemical properties, exhibiting excellent electrocatalytic performance compared to undoped ZnO sample. Photoluminescence spectroscopy measurements indicated the reduction of the green–orange–red visible emission region after adding Co and Ni ions, revealing the formation of alternative pathways for the generated recombination. The presence of these metallic ions into ZnO creates different defects, contributing to a local structural disorder, as revealed by Raman spectra. Electrochemical experiments revealed that the electrocatalytic oxidation of dopamine on ZnO attached to multi-walled carbon nanotubes improved significantly in the Co, Ni co-doped ZnO samples when compared to pure ZnO. - Graphical abstract: Rapid synthesis of Co, Ni co-doped ZnO nanoparticles: optical and electrochemical properties. Co, Ni co-doped ZnO hexagonal nanoparticles with optical and electrocatalytic properties were successfully prepared for the first time using a microwave hydrothermal method at mild conditions. - Highlights: • Co{sup 2+} and Ni{sup 2+} into ZnO lattice obtained a mild and environmentally friendly process. • The heating method strongly influences in the growth and shape of the particles. • Short-range defects generated by the ions insertion affects the photoluminescence. • Doped ZnO nanoparticles improve the electrocatalytic properties of pure oxide.

  4. Preparation and photocatalytic activity of nonmetal Co-doped titanium dioxide photocatalyst

    NASA Astrophysics Data System (ADS)

    Sun, Xiaogang; Xing, Jun; Qiu, Jingping

    2016-06-01

    A series of boron and sulfur co-doped titanium dioxide (TiO2) photocatalysts were prepared by a sol-gel method using boric acid, thiourea and tetrabutyl titanate [Ti(OC4H9)4] as precursors. The photoabsorbance of as-prepared photocatalysts was measured by UV-Vis diffuse reflectance spectroscopy (DRS), and its microstructure was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and N2 adsorption-desorption measurements. The prepared photocatalysts consisted of the anatase phase mainly in the form of spherical particles. The photocatalytic performance was studied by photodegradation of methyl blue (MB) in water under UV and visible light irradiation. The calcination temperature and the codoping content influenced the photoactivity. The synergistic effect of boron and sulfur co-doping played an important role in improving the photocatalytic activity. In addition, the possibility of cyclic usage of codoped TiO2 was also confirmed, the photocatalytic activity of TiO2 remained above 91% of that of the fresh sample after being used four times. It was shown that the co-doped TiO2 could be activated by visible light and could thus be potentially applied for the treatment of water contaminated by organic pollutants.

  5. Effective field theory and Ab-initio calculation of p-type (Ga, Fe)N within LDA and SIC approximation

    NASA Astrophysics Data System (ADS)

    Salmani, E.; Mounkachi, O.; Ez-Zahraouy, H.; El Kenz, A.; Hamedoun, M.; Benyoussef, A.

    2013-03-01

    Based on first-principles spin-density functional calculations, using the Korringa-Kohn-Rostoker method combined with the coherent potential approximation, we investigated the half-metallic ferromagnetic behavior of (Ga, Fe)N co-doped with carbon within the self-interaction-corrected local density approximation. Mechanism of hybridization and interaction between magnetic ions in p-type (Ga, Fe)N is investigated. Stability energy of ferromagnetic and disorder local moment states was calculated for different carbon concentration. The local density and the self-interaction-corrected approximations have been used to explain the strong ferromagnetic interaction observed and the mechanism that stabilizes this state. The transition temperature to the ferromagnetic state has been calculated within the effective field theory, with a Honmura-Kaneyoshi differential operator technique.

  6. Co-Doped Polypyrrole Coatings for Stainless Steel Protection

    NASA Astrophysics Data System (ADS)

    Prissanaroon, W.; Brack, N.; Pigram, P. J.; Liesegang, J.

    Polypyrrole (PPy) films have been successfully electrodeposited on stainless steel substrates in aqueous solution. In this work, three systems of electrolytes were studied: oxalic acid, dodecylbenzenesulfonic acid (DBSA) and a mixture of oxalic acid and DBSA. A combination of XPS and TOF-SIMS revealed the formation of an iron oxalate layer at the interface between the oxalic acid-doped PPy (PPy(Ox)) and stainless steel and a thin layer of DBSA was observed at the interface between DBSA-doped PPy (PPy(DBSA)) and stainless steel. Similar to the PPy(Ox) system, an iron oxalate was also present at the co-doped PPy/stainless steel interface. Cyclic voltammetry indicated that an iron oxalate layer initially formed at the surface of the stainless steel when the co-doping system was used. The adhesion strength and corrosion performance of the PPy coating on stainless steel were evaluated by lap shear tests and an anodic potentiodynamic polarization technique, respectively. The co-doped PPy-coated stainless steel exhibited the best adhesion and a significant shift of corrosion potential to the positive direction. This finding opens the possibility for the co-doped PPy coating to be deployed as a strongly adherent corrosion inhibitor by using a simple one-step electropolymerization process.

  7. Near infrared luminescence in Yb3+/Ho3+: co-doped germanate glass

    NASA Astrophysics Data System (ADS)

    Kochanowicz, Marcin; Żmojda, Jacek; Miluski, Piotr; Ragin, Tomasz; Jeleń, Piotr; Sitarz, Maciej; Dorosz, Dominik

    2015-12-01

    The near-infrared emission of low phonon (805 cm-1) germanate glasses from GeO2-Ga2O3-BaO system co-doped with 0.7Yb2O3/(0.07-0.7)Ho2O3 ions has been investigated. Luminescence at 2.1 μm corresponding to 5I7 → 5I8 transition in holmium was obtained by energy transfer between Yb3+ and Ho3+ ions. The optimization of the activator content and the concentration ratio were conducted with the purpose of maximizing the efficiency of energy transfer and as a consequence luminescence intensity at 2mm. The highest value of the luminescence intensity was obtained in glass codoped with 0.7Yb2O3/0.15 Ho2O3.

  8. Er{sup 3+}/Yb{sup 3+}co-doped bismuth molybdate nanosheets upconversion photocatalyst with enhanced photocatalytic activity

    SciTech Connect

    Adhikari, Rajesh; Gyawali, Gobinda; Cho, Sung Hun; Narro-García, R.; Sekino, Tohru; Lee, Soo Wohn

    2014-01-15

    In this paper, we report the microwave hydrothermal synthesis of Er{sup 3+}/Yb{sup 3+} co-doped Bi{sub 2}MoO{sub 6} upconversion photocatalyst. Crystal structure, morphology, elemental composition, optical properties and BET surface area were analyzed in detail. Infrared to visible upconversion luminescence at 532 nm and 546 nm of the co-doped samples was investigated under excitation at 980 nm. The results revealed that the co-doping of Er{sup 3+}/Yb{sup 3+} into Bi{sub 2}MoO{sub 6} exhibited enhanced photocatalytic activity for the decomposition of rhodamine B under simulated solar light irradiation. Enhanced photocatalytic activity can be attributed to the energy transfer between Er{sup 3+}/Yb{sup 3+} and Bi{sub 2}MoO{sub 6} via infrared to visible upconversion from Er{sup 3+}/Yb{sup 3+} ion and higher surface area of the Bi{sub 2}MoO{sub 6} nanosheets. Therefore, this synthetic approach may exhibit a better alternative to fabricate upconversion photocatalyst for integral solar light absorption. - Graphical abstract: Schematic illustration of the upconversion photocatalysis. Display Omitted - Highlights: • Er{sup 3+}/Yb{sup 3+} co-doped Bi{sub 2}MoO{sub 6} upconversion photocatalyst is successfully synthesized. • We obtained the nanosheets having high surface area. • Upconversion of IR to visible light was confirmed. • Upconversion phenomena can be utilized for effective photocatalysis.

  9. Magnetic and optical properties of Co-doped and Mn-doped ZnO nanocrystalline particles

    NASA Astrophysics Data System (ADS)

    Alsmadi, Abdel; Salameh, B.; Shatnawi, M.; Alnawashi, G.; Bsoul, I.

    We carried out a systematic study on the effect of Co doping and Mn doping on the structural, magnetic and optical properties of ZnO nanocrystalline particles, using x-ray diffraction, x-ray photoelectron spectroscopy (XPS), Quantum Design PPMS-9 magnetometry, and Ultra Violet-Visible spectroscopy. The Zn1- x CoxO and Zn1- x MnxO nanoparticles with 0 <= x <= 0 . 1 were successfully prepared by the formal solid-state reaction method. The XPS results and the XRD analysis with full structural Rietveld refinement reveal that both structures have hexagonal wurtzite structure. For all Co-doped ZnO nanoparticles under investigation, the field dependence of the magnetization curves exhibits ferromagnetic behavior with relatively small coercive fields at room temperature. In addition, we found a signature for antiferromagnetic ordering between the Co ions. For the Mn-doped ZnO nanoparticles, we observed ferromagnetic behavior only below 50 K. We also observed a strong correlation between the magnetic and optical behavior of the Co-doped ZnO nanoparticles. Optical diffuse reflectance and absorption spectra exhibit a red shift at room temperature in the absorption band edge with increasing Co-doping. The red shift is attributed to the sp-d exchange interaction between free charge carriers in ZnO band and the localized magnetic moments.

  10. Piezoelectric Franz-Keldysh effect in a GaN/InGaN/AlGaN multilayer structure

    NASA Astrophysics Data System (ADS)

    Hou, Yong T.; Teo, Kie L.; Li, Ming Fu; Uchida, Kazuo; Tokunaga, Hiroki; Akutsu, Nakao; Matsumoto, Koh

    1999-11-01

    Contactless electroreflectance (CER) of a GaN/InGaN/AlGaN multilayer structure grown on sapphire has been measured in the temperature range of 15K and 450K. Except for the GaN exciton structures, well-defined Franz-Keldysh Oscillations are observed above the AlGaN band gap. An electomodulational model based on complex Airy functions is used to analyze the FKOs line shape. The temperature dependence of transition energies is obtained both for GaN and AlGaN. The magnitude of the built in electric field in AlGaN layer is also determined. The temperature dependence of the electric field is found to be consistent with the variation of thermal strain in the epilayer. It is demonstrated that the built-in electric field can be identified to be due to the piezoelectric effect.

  11. Effects of Li+ ions on the enhancement of up-conversion emission in Ho3+-Yb3+ co-doped transparent glass-ceramics containing Ba2LaF7 nanocrystals

    NASA Astrophysics Data System (ADS)

    Li, Zhencai; Zhou, Dacheng; Yang, Yong; Gao, Yuan; Ren, Peng; Qiu, Jianbei

    2016-10-01

    The up-conversion (UC) emission of Ho3+-Yb3+ and Li+ co-doped transparent glass ceramics 45SiO2-15Al2O3-12Na2CO3-21BaF2-7LaF3-0.2HoF3-1YbF3-xLi2CO3 (x = 0, 0.5, 1, 2, 4 and 6 mol%) containing Ba2LaF7 nanocrystals were investigated. These glass ceramics samples were prepared using the conventional quenching techniques. The Ba2LaF7 nanocrystals precipitated from the glass matrix was confirmed by X-ray diffraction (XRD). Compared with the glass ceramics sample without Li+, the UC emission intensity of glass ceramics samples with Li+ were enhanced. It can be proved that the Li+ can affect the enhancement up-conversion (UC) emission. Particularly, the green UC emission intensity band centered at 546 nm was strongly increased twice with the concentration of Li+ increasing up to 4 mol%. Through the comparison and analysis of the energy graph, it was shown that the 5F4/5S2→5I8 transition of Ho3+ ion obtained the green (546 nm) light. There are two weak fluorescences in the red (657 nm) region and near infrared (753 nm) region of spectrum, which is the 5F4/5S2→5I7 and 5F5→5I8 transition of Ho3+. Therefore, the emission results showed that the incorporation of Li+ ions into the Ba2LaF7:Eu3+ lattice could induce a remarkable change of the emission intensity in red region (R = IED/IMD) with 393 nm excitation wavelength. It was indicated that the symmetry of the lattice was destroyed by Li+ in glass ceramics. The possible mechanism responsible for the enhancement of UC emission in Ho-Yb co-doped was discussed.

  12. Photocatalytic performance of nitrogen, osmium co-doped TiO2 for removal of eosin yellow in water under simulated solar radiation.

    PubMed

    Kuvarega, Alex T; Krause, Rui W M; Mamba, Bhekie B

    2013-07-01

    Nitrogen, osmium co-doped TiO2 photocatalysts were prepared by a modified sol-gel method using ammonia as the nitrogen source and osmium tetroxide as the source of osmium. The role of rutile phase OsO2 in enhancing the photocatalytic activity of rutile TiO2 towards the degradation of Eosin Yellow was investigated. The materials were characterised by various techniques that include FTIR, Raman, XRD, SEM, EDS, TEM, TGA and DRUV-Vis. The amorphous, oven dried sample was transformed to the anatase and then the rutile phase with increasing calcination temperature. DRUV-Vis analysis revealed a red shift in absorption with increasing calcination temperature, confirmed by a decrease in the band gap of the material. The photocatalytic activity of N, Os co-doped TiO2 was evaluated using eosin yellow degradation and activity increased with increase in calcination temperature under simulated solar irradiation. The rutile phase of the co-doped TiO2 was found to be more effective in degrading the dye (k(a) = 1.84 x 10(-2) min(-1)) compared to the anatase co-doped phase (k(a) = 9.90 x 10(-3) min(-1)). The enhanced photocatalytic activity was ascribed to the synergistic effects of rutile TiO2 and rutile OsO2 in the N, Os co-doped TiO2. PMID:23901525

  13. Photocatalytic performance of nitrogen, osmium co-doped TiO2 for removal of eosin yellow in water under simulated solar radiation.

    PubMed

    Kuvarega, Alex T; Krause, Rui W M; Mamba, Bhekie B

    2013-07-01

    Nitrogen, osmium co-doped TiO2 photocatalysts were prepared by a modified sol-gel method using ammonia as the nitrogen source and osmium tetroxide as the source of osmium. The role of rutile phase OsO2 in enhancing the photocatalytic activity of rutile TiO2 towards the degradation of Eosin Yellow was investigated. The materials were characterised by various techniques that include FTIR, Raman, XRD, SEM, EDS, TEM, TGA and DRUV-Vis. The amorphous, oven dried sample was transformed to the anatase and then the rutile phase with increasing calcination temperature. DRUV-Vis analysis revealed a red shift in absorption with increasing calcination temperature, confirmed by a decrease in the band gap of the material. The photocatalytic activity of N, Os co-doped TiO2 was evaluated using eosin yellow degradation and activity increased with increase in calcination temperature under simulated solar irradiation. The rutile phase of the co-doped TiO2 was found to be more effective in degrading the dye (k(a) = 1.84 x 10(-2) min(-1)) compared to the anatase co-doped phase (k(a) = 9.90 x 10(-3) min(-1)). The enhanced photocatalytic activity was ascribed to the synergistic effects of rutile TiO2 and rutile OsO2 in the N, Os co-doped TiO2.

  14. Highly piezoelectric co-doped AlN thin films for wideband FBAR applications.

    PubMed

    Yokoyama, Tsuyoshi; Iwazaki, Yoshiki; Onda, Yosuke; Nishihara, Tokihiro; Sasajima, Yuichi; Ueda, Masanori

    2015-06-01

    We report piezoelectric materials composed of charge-compensated co-doped (Mg, β)(x)Al(1-x)N (β = Zr or Hf) thin films. The effect of the dopant element into AlN on the crystal structure, and piezoelectric properties of co-doped AlN was determined on the basis of a first-principles calculation, and the theoretical piezoelectric properties were confirmed by experimentally depositing thin films of magnesium (Mg) and zirconium (Zr) co-doped AlN (Mg-Zr-doped AlN). The Mg-Zrdoped AlN thin films were prepared on Si (100) substrates by using a triple-radio-frequency magnetron reactive co-sputtering system. The crystal structures and piezoelectric coefficients (d33) were investigated as a function of the concentrations, which were measured by X-ray diffraction and a piezometer. The results show that the d33 of Mg-Zr-doped AlN at total Mg and Zr concentrations (both expressed as β) of 0.35 was 280% larger than that of pure AlN. The experimentally measured parameter of the crystal structure and d33 of Mg-Zr-doped AlN (plotted as functions of total Mg and Zr concentrations) were in very close agreement with the corresponding values obtained by the first-principle calculations. Thin film bulk acoustic wave resonators (FBAR) employing (Mg,Zr)0.13Al0.87N and (Mg, Hf)0.13 Al0.87N as a piezoelectric thin film were fabricated, and their resonant characteristics were evaluated. The measured electromechanical coupling coefficient increased from 7.1% for pure AlN to 8.5% for Mg-Zr-doped AlN and 10.0% for Mg- Hf-doped AlN. These results indicate that co-doped (Mg, β)(x)Al(1-x)N (β = Zr or Hf) films have potential as piezoelectric thin films for wideband RF applications.

  15. Effect of Ga on the Wettability of CuGa10 on 304L Steel

    NASA Astrophysics Data System (ADS)

    Silze, Frank; Wiehl, Gunther; Kaban, Ivan; Kühn, Uta; Eckert, Jürgen; Pauly, Simon

    2015-08-01

    In the present work, the effect of Ga on the wetting behavior of the Cu-rich braze filler CuGa10 (wt pct, Cu90.8Ga9.2 at. pct) on the steel 304L was investigated. For this, the macroscopic and microscopic effects governing the wetting of pure Ga, pure Cu, and CuGa10 alloy (wt pct) on the austenitic steel were analyzed and compared. Contact angle and surface tension measurements were carried out by means of the sessile drop technique, and, in addition, the phase formation at the interface was determined. Pure liquid Ga spreads on 304L, which supposedly is related to the formation of intermetallic Fe-Ga phases growing into the liquid Ga. Depending on the annealing time, FeGa3 and Fe14.5Ga12 were identified. In contrast, CuGa10 as well as pure Cu shows secondary wetting on the steel surface. Especially, liquid Cu prefers spreading laterally and vertically along the grain boundaries of the steel substrate. In spite of rather similar mechanisms, CuGa10 wets 304L steel at lower rate than pure Cu above the liquidus temperature.

  16. Enhanced Luminescence in Tb/Ce co-doped Zinc- and Tin-Oxide quantum dots

    NASA Astrophysics Data System (ADS)

    Larochelle, Christie; Xu, Jingjing; McCutcheon, Kelly

    2013-03-01

    SnO2 and ZnO quantum dots doped with Tb3+ exhibit strong luminescence from the Tb3+ dopants due to efficient energy transfer from the semiconductor donors to the Tb3+ acceptor ions. We report results from a study of the effect of co-doping the SnO2 and ZnO dots with both Tb3+ and Ce3+ on the photoluminescence properties of the samples. The dots were synthesized using a sol-gel technique and the Ce3+/Tb3+ ratio was varied while keeping the total doping level at 1wt %. X-ray diffraction and TEM results confirm the presence of nanocrystals of less than 10 nm in diameter. Photoluminescence results indicate that the Tb3+ ions are incorporated in a crystalline environment and that co-doping with Ce3+ enhances the energy transfer efficiency and therefore the intensity of the Tb3+ luminescence. The effect of heat treatment on the size of the dots and the impact of size on luminescence properties was also investigated.

  17. High efficiency Schottky junction solar cells by co-doping of graphene with gold nanoparticles and nitric acid

    NASA Astrophysics Data System (ADS)

    Liu, X.; Zhang, X. W.; Meng, J. H.; Yin, Z. G.; Zhang, L. Q.; Wang, H. L.; Wu, J. L.

    2015-06-01

    We have reported an effective method to enhance the efficiency of graphene-on-Si (Gr/Si) Schottky junction solar cells by co-doping of graphene with Au nanoparticles (NPs) and HNO3. Both Au NPs decoration and HNO3 treatment lead to p-type doping of graphene, and their combination is confirmed to be a more effective approach for achieving the higher work function and enhanced electrical conductivity of graphene. Consequently, the power conversion efficiency of Gr/Si solar cells is increased by 2.6 times, with a maximum value of 10.20%. This work suggests that the co-doping might be a promising way to realize high performance Gr/Si solar cells.

  18. Toward an ultra-broadband emission source based on the bismuth and erbium co-doped optical fiber and a single 830nm laser diode pump.

    PubMed

    Zhang, Jianzhong; Sathi, Zinat M; Luo, Yanhua; Canning, John; Peng, Gang-Ding

    2013-03-25

    We demonstrate a broadband optical emission from Bi/Er co-doped fiber and a single 830nm laser diode pump. The ultra-broadband mechanism is studied and discussed in details based on a combination of experimental measurements, including luminescence, differential luminescence and ESA, on fiber samples of different Bi and Er concentrations. The Er co-doping in Bi doped fiber is found to be effective for broadband emission, by enhancing not only luminescence at C and L bands but also that at O and shorter wavelength bands. The luminescence intensity between 1100 and 1570nm is over -45dBm/5nm in single mode fiber using a few meters of Bi/Er co-doped fiber and offers a modest ~40dB dynamic range and a broad bandwidth of ~470nm for an OSA based spectral measurement.

  19. Effect of GaAs native oxide upon the surface morphology during GaAs MBE growth

    NASA Astrophysics Data System (ADS)

    Ageev, O. A.; Solodovnik, M. S.; Balakirev, S. V.; Mikhaylin, I. A.; Eremenko, M. M.

    2016-08-01

    The GaAs native oxide effect upon the surface morphology of the GaAs epitaxial layer was studied with taking into account the main growth parameters of MBE technology: substrate temperature, effective As4/Ga flux ratio and growth rate. The MBE modes of atomically smooth and rough surfaces and surfaces with Ga droplet array formation were determined. The possibility of the obtaining of GaAs nanowires via GaAs native oxide layer was shown.

  20. Photocatalytic decomposition of perfluorooctanoic acid by iron and niobium co-doped titanium dioxide.

    PubMed

    Estrellan, Carl Renan; Salim, Chris; Hinode, Hirofumi

    2010-07-15

    The photocatalytic decomposition of perfluorooctanoic acid (PFOA) in aqueous solution using Fe and Nb co-doped TiO(2) (Fe:Nb-TiO(2)) prepared by sol-gel method was investigated. The photocatalytic activity of Fe:Nb-TiO(2) towards PFOA degradation was compared to that of pure TiO(2) synthesized using the same method, and that of the commercially available TiO(2) photocatalyst, Aeroxide TiO(2) P25 (AO-TiO(2) P25). The photocatalysts were characterized by XRD, DRS, BET-N(2) adsorption isotherm, and SEM-EDX techniques and the data were correlated to the photocatalytic activity. Fe:Nb-TiO(2) showed the highest activity compared to the undoped TiO(2) and the commercially available TiO(2). Such activity was attributable to the effects of co-doping both on the physico-chemical properties and surface interfacial charge transfer mechanisms. Perfluorocarboxylic acids (PFCAs) with shorter carbon chain length and fluoride ions were identified as photocatalytic reaction intermediates and products.

  1. Thermoelectric performance of co-doped SnTe with resonant levels

    NASA Astrophysics Data System (ADS)

    Zhou, Min; Gibbs, Zachary M.; Wang, Heng; Han, Yemao; Li, Laifeng; Snyder, G. Jeffrey

    2016-07-01

    Some group III elements such as Indium are known to produce the resonant impurity states in IV-VI compounds. The discovery of these impurity states has opened up new ways for engineering the thermoelectric properties of IV-VI compounds. In this work, resonant states in SnTe were studied by co-doping with both resonant (In) and extrinsic (Ag, I) dopants. A characteristic nonlinear relationship was observed between the Hall carrier concentration (nH) and extrinsic dopant concentration (NI, NAg) in the stabilization region, where a linear increase of dopant concentration does not lead to linear response in the measured nH. Upon substituting extrinsic dopants beyond a certain amount, the nH changed proportionally with additional dopants (Ag, I) (the doping region). The Seebeck coefficients are enhanced as the resonant impurity is introduced, whereas the use of extrinsic doping only induces minor changes. Modest zT enhancements are observed at lower temperatures, which lead to an increase in the average zT values over a broad range of temperatures (300-773 K). The improved average zT obtained through co-doping indicates the promise of fine carrier density control in maximizing the favorable effect of resonant levels for thermoelectric materials.

  2. Optical and spectroscopic characterization of Er3+-Yb3+co-doped tellurite glasses and fibers

    NASA Astrophysics Data System (ADS)

    Narro-García, R.; Desirena, H.; Chillcce, E. F.; Barbosa, L. C.; Rodriguez, E.; De la Rosa, E.

    2014-04-01

    Optical and spectroscopic properties of Er3+-Yb3+ co-doped TeO2-WO3-Nb2O5-Na2O-Al2O3 glasses and fibers were investigated. Emission spectra and fluorescence lifetimes of 4I13/2 level of Er3+ion as a function of rare earth concentration and fiber length were measured in glasses. Results show that the self-absorption effect broadens the spectral bandwidth of 4I13/2→4I15/2 transition and lengthens the lifetime significantly from 3.5 to 4.6 ms. Fibers were fabricated by the rod-in-tube technique using a Heathway drawing tower. The emission power of these Er3+-Yb3+ co-doped Step Index Tellurite Fibers (SITFs; lengths varying from 2 to 60 cm) were generated by a 980 nm diode laser pump and then the emission power spectra were acquired with an OSA. The maximum emission power spectra, within the 1530-1560 nm region, were observed for fiber lengths ranging from 3 to 6 cm. The highest bandwidth obtained was 108 nm for 8 cm fiber length around 1.53 µm.

  3. Direct view at colossal permittivity in donor-acceptor (Nb, In) co-doped rutile TiO2

    NASA Astrophysics Data System (ADS)

    Mandal, Suman; Pal, Somnath; Kundu, Asish K.; Menon, Krishnakumar S. R.; Hazarika, Abhijit; Rioult, Maxime; Belkhou, Rachid

    2016-08-01

    Topical observations of colossal permittivity (CP) with low dielectric loss in donor-acceptor cations co-doped rutile TiO2 have opened up several possibilities in microelectronics and energy-storage devices. Yet, the precise origin of the CP behavior, knowledge of which is essential to empower the device integration suitably, is highly disputed in the literature. From spectromicroscopic approach besides dielectric measurements, we explore that microscopic electronic inhomogeneities along with the nano-scale phase boundaries and the low temperature polaronic relaxation are mostly responsible for such a dielectric behavior, rather than electron-pinned defect-dipoles/grain-boundary effects as usually proposed. Donor-acceptor co-doping results in a controlled carrier-hopping inevitably influencing the dielectric loss while invariably upholding the CP value.

  4. Corrosion of soda lime silicate glasses co-doped with Gd2O3 and Y2O3

    NASA Astrophysics Data System (ADS)

    Wang, Mitang; Li, Mei; Cheng, Jinshu; He, Feng; Liu, Zhaogang; Hu, Yanhong

    2014-01-01

    Corrosion behaviors of Gd2O3 and Y2O3 co-doped silicate glasses have been carried out at low reaction progress. The better enhance effect of co-doping with Gd2O3 and Y2O3 on the silicate glass resistance against attacking of neutral and acid media is observed, while the alkaline resistance is Y2O3 > Gd2O3 + Y2O3 > Gd2O3. Moreover, extreme value is also observed in variation of released ions concentration, pH value and mass loss of glass when substituting Y2O3 for Gd2O3.

  5. Bioinspired synthesis of nitrogen/sulfur co-doped graphene as an efficient electrocatalyst for oxygen reduction reaction

    NASA Astrophysics Data System (ADS)

    Zhang, Huanhuan; Liu, Xiangqian; He, Guangli; Zhang, Xiaoxing; Bao, Shujuan; Hu, Weihua

    2015-04-01

    Efficient electrocatalyst of oxygen reduction reaction (ORR) is crucial for a variety of renewable energy applications and heteroatom-doped carbon materials have demonstrated promising catalytic performance towards ORR. In this paper we report a bioinspired method to synthesize nitrogen/sulfur (N/S) co-doped graphene as an efficient ORR electrocatalyst via self-polymerization of polydopamine (PDA) thin layer on graphene oxide sheets, followed by reacting with cysteine and finally thermal annealing in Argon (Ar) atmosphere. As-prepared N/S co-doped graphene exhibits significantly enhanced ORR catalytic activity in alkaline solution compared with pristine graphene or N-doped graphene. It also displays long-term operation stability and strong tolerance to methanol poison effect, indicating it a promising ORR electrocatalyst.

  6. Preparation and characterization of zinc and copper co-doped WO3 nanoparticles: Application in photocatalysis and photobiology.

    PubMed

    Mohammadi, Sanaz; Sohrabi, Maryam; Golikand, Ahmad Nozad; Fakhri, Ali

    2016-08-01

    In this study, pure, Zn, Cu, Zn,Cu co-doped WO3 nanoparticles samples were prepared by precipitation and co-precipitation methods. These nanoparticles were characterized by field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), energy dispersive X-ray spectrometer (EDX), Dynamic light scattering (DLS), UV-visible and photoluminescence (PL) spectroscopy. The synthesized pure, Zn, Cu, Zn,Cu co-doped WO3 nanoparticles have smart optical properties and average sizes with 3.2, 3.12, 3.08 and 2.97eV of band-gap, 18.1, 23.2, 25.7 and 30.2nm, respectively. Photocatalytic activity of four nanoparticles was studying towards degradation of gentamicin antibiotic under ultraviolet and visible light irradiation. The result showed that Zn,Cu co-doped WO3 possessed high photocatalytic activity. The photocatalytic activity of WO3 nanoparticles could be remarkably increased by doping the Zn and Cu impurity. This can be attributed to the fact that the red shift of absorption edge and the trapping effect of the mono and co-doped WO3 nanoparticles. The research result presents a general and effective way to prepare different photocatalysts with enhanced visible and UV light-driven photocatalytic performance. Antibacterial activity of four different WO3 nanoparticles against Escherichia coli bacterium has been assessed by the agar disc method under light irradiation and dark medium. It is concluded from the present findings that WO3 nanoparticles can be used as an efficient antibacterial agent. PMID:27262854

  7. Preparation and characterization of zinc and copper co-doped WO3 nanoparticles: Application in photocatalysis and photobiology.

    PubMed

    Mohammadi, Sanaz; Sohrabi, Maryam; Golikand, Ahmad Nozad; Fakhri, Ali

    2016-08-01

    In this study, pure, Zn, Cu, Zn,Cu co-doped WO3 nanoparticles samples were prepared by precipitation and co-precipitation methods. These nanoparticles were characterized by field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), energy dispersive X-ray spectrometer (EDX), Dynamic light scattering (DLS), UV-visible and photoluminescence (PL) spectroscopy. The synthesized pure, Zn, Cu, Zn,Cu co-doped WO3 nanoparticles have smart optical properties and average sizes with 3.2, 3.12, 3.08 and 2.97eV of band-gap, 18.1, 23.2, 25.7 and 30.2nm, respectively. Photocatalytic activity of four nanoparticles was studying towards degradation of gentamicin antibiotic under ultraviolet and visible light irradiation. The result showed that Zn,Cu co-doped WO3 possessed high photocatalytic activity. The photocatalytic activity of WO3 nanoparticles could be remarkably increased by doping the Zn and Cu impurity. This can be attributed to the fact that the red shift of absorption edge and the trapping effect of the mono and co-doped WO3 nanoparticles. The research result presents a general and effective way to prepare different photocatalysts with enhanced visible and UV light-driven photocatalytic performance. Antibacterial activity of four different WO3 nanoparticles against Escherichia coli bacterium has been assessed by the agar disc method under light irradiation and dark medium. It is concluded from the present findings that WO3 nanoparticles can be used as an efficient antibacterial agent.

  8. AlGaN/GaN field effect transistors for power electronics—Effect of finite GaN layer thickness on thermal characteristics

    SciTech Connect

    Hodges, C. Anaya Calvo, J.; Kuball, M.; Stoffels, S.; Marcon, D.

    2013-11-11

    AlGaN/GaN heterostructure field effect transistors with a 150 nm thick GaN channel within stacked Al{sub x}Ga{sub 1−x}N layers were investigated using Raman thermography. By fitting a thermal simulation to the measured temperatures, the thermal conductivity of the GaN channel was determined to be 60 W m{sup −1} K{sup −1}, over 50% less than typical GaN epilayers, causing an increased peak channel temperature. This agrees with a nanoscale model. A low thermal conductivity AlGaN buffer means the GaN spreads heat; its properties are important for device thermal characteristics. When designing power devices with thin GaN layers, as well as electrical considerations, the reduced channel thermal conductivity must be considered.

  9. Nitrogen and cobalt co-doped zinc oxide nanowires - Viable photoanodes for hydrogen generation via photoelectrochemical water splitting

    NASA Astrophysics Data System (ADS)

    Patel, Prasad Prakash; Hanumantha, Prashanth Jampani; Velikokhatnyi, Oleg I.; Datta, Moni Kanchan; Hong, Daeho; Gattu, Bharat; Poston, James A.; Manivannan, Ayyakkannu; Kumta, Prashant N.

    2015-12-01

    Photoelectrochemical (PEC) water splitting has been considered as a promising and environmentally benign approach for efficient and economic hydrogen generation by utilization of solar energy. Development of semiconductor materials with low band gap, high photoelectrochemical activity and stability has been of particular interest for a viable PEC water splitting system. In this study, Co doped ZnO, .i.e., (Zn0.95Co0.05)O nanowires (NWs) was selected as the composition for further co-doping with nitrogen by comparing solar to hydrogen efficiency (SHE) of ZnO NWs with that of various compositions of (Zn1-xCox)O NWs (x = 0, 0.05, 0.1). Furthermore, nanostructured vertically aligned Co and N-doped ZnO, .i.e., (Zn1-xCox)O:N NWs (x = 0.05) have been studied as photoanodes for PEC water splitting. An optimal SHE of 1.39% the highest reported so far to the best of our knowledge for ZnO based photoanodes was obtained for the co-doped NWs, (Zn0.95Co0.05)O:N - 600 NWs generated at 600 °C in ammonia atmosphere. Further, (Zn0.95Co0.05)O:N-600 NWs exhibited excellent photoelectrochemical stability under illumination compared to pure ZnO NWs. These promising results suggest the potential of (Zn0.95Co0.05)O:N-600 NWs as a viable photoanode in PEC water splitting cell. Additionally, theoretical first principles study conducted explains the beneficial effects of Co and N co-doping on both, the electronic structure and the band gap of ZnO.

  10. Structural, Optical, and Magnetic Properties of Solution-Processed Co-Doped ZnS Thin Films

    NASA Astrophysics Data System (ADS)

    Goktas, A.; Mutlu, İ. H.

    2016-11-01

    Co-doped ZnS thin films have been grown on glass substrates using solution-processing and dip-coating techniques, and the impact of the Co doping level (0% to 5%) and film thickness on certain characteristics examined. X-ray diffraction study revealed that all the films possessed hexagonal crystal structure. Energy-dispersive x-ray analysis confirmed presence of Zn, Co, and S in the samples. Scanning electron microscopy showed that the film surface was homogeneous and dense with some cracks and spots. X-ray photoelectron spectroscopy confirmed introduction and integration of Co2+ ions into the ZnS thin films. Compared with undoped ZnS, optical studies indicated a reduction in optical bandgap energy ( E g) while the refractive index ( n), extinction coefficient ( k), and dielectric constants ( ɛ 1, ɛ 2) increased with film thickness ( t) and Co doping level (except for 5%). Photoluminescence spectra showed enhanced luminescence intensity as the Co concentration was increased, while the dependence on t showed an initial increase followed by a decrease. The origin of the observed low-temperature (5 K and 100 K) ferromagnetic order may be related to point defects such as zinc vacancies, zinc interstitials, and sulfide vacancies or to the grain-boundary effect.

  11. RETRACTED: Investigation of structural, optical and electronic properties in Al-Sn co-doped ZnO thin films

    NASA Astrophysics Data System (ADS)

    Pan, Zhanchang; Tian, Xinlong; Wu, Shoukun; Yu, Xia; Li, Zhuliang; Deng, Jianfeng; Xiao, Chumin; Hu, Guanghui; Wei, Zhigang

    2013-01-01

    This article has been retracted: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy). This article has been retracted at the request of the Editor-in-Chief. Figures 3 and 4 of this paper have also been presented as belonging to other materials in other publications. This observation is evidence of fraud and therefore it is not certain that the described research and conclusions of this paper belong to the presented images. Figures 3 and 4 of this paper can also be found in: Effect of annealing on the structures and properties of Al and F co-doped ZnO nanostructures, Materials Science in Semiconductor Processing, 2014, 17, 162-167, http://dx.doi.org/10.1016/j.mssp.2013.09.023 Highly transparent and conductive Sn/F and Al co-doped ZnO thin films prepared by sol-gel method, Journal of Alloys and Compounds, 2014,583, 32-38, http://dx.doi.org/10.1016/j.jallcom.2013.06.192 Properties of fluorine and tin co-doped ZnO thin films deposited by sol-gel method, Journal of Alloys and Compounds, 2013,576, 31-37, http://dx.doi.org/10.1016/j.jallcom.2013.04.132

  12. Structural, Optical, and Magnetic Properties of Solution-Processed Co-Doped ZnS Thin Films

    NASA Astrophysics Data System (ADS)

    Goktas, A.; Mutlu, İ. H.

    2016-07-01

    Co-doped ZnS thin films have been grown on glass substrates using solution-processing and dip-coating techniques, and the impact of the Co doping level (0% to 5%) and film thickness on certain characteristics examined. X-ray diffraction study revealed that all the films possessed hexagonal crystal structure. Energy-dispersive x-ray analysis confirmed presence of Zn, Co, and S in the samples. Scanning electron microscopy showed that the film surface was homogeneous and dense with some cracks and spots. X-ray photoelectron spectroscopy confirmed introduction and integration of Co2+ ions into the ZnS thin films. Compared with undoped ZnS, optical studies indicated a reduction in optical bandgap energy (E g) while the refractive index (n), extinction coefficient (k), and dielectric constants (ɛ 1, ɛ 2) increased with film thickness (t) and Co doping level (except for 5%). Photoluminescence spectra showed enhanced luminescence intensity as the Co concentration was increased, while the dependence on t showed an initial increase followed by a decrease. The origin of the observed low-temperature (5 K and 100 K) ferromagnetic order may be related to point defects such as zinc vacancies, zinc interstitials, and sulfide vacancies or to the grain-boundary effect.

  13. Improving the ethanol gas-sensing properties of porous ZnO microspheres by Co doping

    SciTech Connect

    Xiao, Qi Wang, Tao

    2013-08-01

    Graphical abstract: - Highlights: • Co-doped porous ZnO microspheres were synthesized. • 3 mol% Co-doped ZnO sensor showed the highest response to ethanol. • 3 mol% Co-doped ZnO sensor exhibited fast recovery property. • 3 mol% Co-doped ZnO sensor exhibited good selectivity and long-term stability. - Abstract: Porous Co-doped ZnO microspheres were prepared by a simple hydrothermal method combined with post-annealing. Co species existed as a form of divalent state in the sample and substituted Zn{sup 2+} sites in ZnO crystal lattice, which was affirmed by X-ray diffraction, UV–vis diffuse reflectance spectroscopy and X-ray photoelectron spectroscopy. The gas-sensing measurements demonstrated that the 3 mol% Co-doped ZnO sample showed the highest response value to 100 ppm ethanol at 350 °C, which were 5 folds higher than that of the pure ZnO sample. In addition, the 3 mol% Co-doped ZnO sensor exhibited fast recovery property, good quantitative determination, good selectivity and long-term stability. The superior sensing properties were contributed to high specific surface area combined with the large amount of oxygen vacancies originating from Co doping.

  14. Piezotronic Effect in Polarity-Controlled GaN Nanowires.

    PubMed

    Zhao, Zhenfu; Pu, Xiong; Han, Changbao; Du, Chunhua; Li, Linxuan; Jiang, Chunyan; Hu, Weiguo; Wang, Zhong Lin

    2015-08-25

    Using high-quality and polarity-controlled GaN nanowires (NWs), we studied the piezotronic effect in crystal orientation defined wurtzite structures. By applying a normal compressive force on c-plane GaN NWs with an atomic force microscopy tip, the Schottky barrier between the Pt tip and GaN can be effectively tuned by the piezotronic effect. In contrast, the normal compressive force cannot change the electron transport characteristics in m-plane GaN NWs whose piezoelectric polarization axis is turned in the transverse direction. This observation provided solid evidence for clarifying the difference between the piezotronic effect and the piezoresistive effect. We further demonstrated a high sensitivity of the m-plane GaN piezotronic transistor to collect the transverse force. The integration of c-plane GaN and m-plane GaN indicates an overall response to an external force in any direction.

  15. Ga content and thickness inhomogeneity effects on Cu(In, Ga)Se2 solar modules

    NASA Astrophysics Data System (ADS)

    Zhu, Xiaobo; Cheng, Tzu-Huan; Liu, Chee Wee

    2016-07-01

    The fluctuation of Ga content and absorption layer thickness of Cu(In, Ga)Se2 (CIGS) solar modules is investigated by 3-dimensional numerical simulation. The band gap of CIGS is increased by the increasing Ga content, and the residual compressive strain. Strain effect worsens the degradation of the power conversion efficiency of CIGS module in addition to Ga fluctuation. The intracell Ga fluctuation degrades the open circuit voltage due to the minimum open circuit voltage in the parallel configuration, and also affects the short circuit current due to the Ga-dependent light absorption. The intercell Ga fluctuation leads to a more significant degradation for CIGS solar module efficiency than the intracell Ga fluctuation due to the additional degradation of the fill factor. The thickness fluctuation has a small effect on open circuit voltage, but causes strong degradation of short circuit current and fill factor, which leads to a more significant degradation on power conversion efficiency than Ga fluctuation to the same fluctuation percentage. In reality, the thickness can be tightly controlled within the fluctuation of 5% or less. [Figure not available: see fulltext.

  16. Enhanced photocatalytic degradation of humic acids using Al and Fe co-doped TiO2 nanotubes under UV/ozonation for drinking water purification.

    PubMed

    Yuan, Rongfang; Zhou, Beihai; Hua, Duo; Shi, Chunhong

    2013-11-15

    O3/UV/TiO2 was used to effectively decompose humic acids (HAs) in drinking water. To obtain a large specific surface area and low band gap energy, Al and Fe co-doped TiO2 nanotubes were successfully synthesized using the hydrothermal method. The effect of the optimal co-doped TiO2 nanotubes catalyst on the HAs removal efficiency through O3/UV/co-doped TiO2 process was investigated. The highest HAs removal efficiency (79.4%) that exhibited a pseudo-first-order rate constant of 0.172 min(-1) was achieved, in the presence of 550 °C calcined 1.0% co-doped TiO2 nanotubes with an Al:Fe ratio of 0.25:0.75. The effects of calcination temperature and doping concentration on anatase phase weight fractions, average crystallite sizes, Brunauer-Emmett-Teller surface area, catalyst band gap energy, and catalyst photocatalytic activity were also discussed. The inorganic anions also affected the catalyst photocatalytic ability. In a neutral solution, SO4(2-) slightly promoted HAs removal. However, HCO3(-) was found to significantly inhibit the catalyst activity, whereas Cl(-) had negligible effect on photocatalytic ability.

  17. Effect of Temperature on GaGdO/GaN Metal Oxide Semiconductor Field Effect Transistors

    SciTech Connect

    Abernathy, C.R.; Baca, A.; Chu, S.N.G.; Hong, M.; Lothian, J.R.; Marcus, M.A.; Pearton, S.J.; Ren, F.; Schurman, M.J.

    1998-10-14

    GaGdO was deposited on GaN for use as a gate dielectric in order to fabricate a depletion metal oxide semiconductor field effect transistor (MOSFET). This is the fmt demonstration of such a device in the III-Nitride system. Analysis of the effect of temperature on the device shows that gate leakage is significantly reduced at elevated temperature relative to a conventional metal semiconductor field effeet transistor (MESFET) fabricated on the same GaN layer. MOSFET device operation in fact improved upon heating to 400 C. Modeling of the effeet of temperature on contact resistance suggests that the improvement is due to a reduction in the parasitic resistances present in the device.

  18. Room temperature ferromagnetism in Co-doped amorphous carbon composites from the spin polarized semiconductor band

    NASA Astrophysics Data System (ADS)

    Hsu, H. S.; Chien, P. C.; Sun, S. J.; Chang, Y. Y.; Lee, C. H.

    2014-08-01

    This study provides conclusive evidence of room temperature ferromagnetism in Co-doped amorphous carbon (a-C) composites from the spin polarized semiconductor band. These composites are constructed from discontinuous [Co(3 nm)/a-C(dc nm)]5 multilayers with dc = 3 nm and dc = 6 nm. Only remnant circular dichroism (CD) was observed from the dc = 3 nm sample but not when dc = 6 nm. In addition, the remnant CD peaks at 5.5 eV, which is comparable with the absorption peak associated with the C σ-σ* gap transition. We suggest that the possible mechanism for this coupling can be considered as a magnetic proximity effect in which a ferromagnetic moment in the C medium is induced by Co/C interfaces.

  19. Deposition of Co-doped TiO2 Thin Films by sol-gel method

    NASA Astrophysics Data System (ADS)

    Boutlala, A.; Bourfaa, F.; Mahtili, M.; Bouaballou, A.

    2016-03-01

    Cobalt doped TiO2 thin films have been prepared by sol-gel method onto glass substrate at room temperature. in this present work, we are interesting to study the effect of Cobalt doped TiO2 thin films.the concentration of Co was varied from 0 to 6%at .The obtained films have been annealed at 500°C for 2 hours. X-ray diffraction patterns showed that Co: TiO2 films are polycrystalline with a tetragonal anatase and orthorhombic brookite types structures. The surface morphologies of the TiO2 doped with cobalt thin films were evaluated by Atomic Force Microscopy (AFM). The optical properties were studied by mean of UV-visible and near infrared spectroscopy.The calculated optical band gap decreases from 3.30 to 2.96 eV with increasing Co doping.

  20. Hydrothermal synthesis and characterization of fluorine & manganese co-doped PZT based cuboidal shaped powder

    NASA Astrophysics Data System (ADS)

    Nawaz, H.; Shuaib, M.; Saleem, M.; Rauf, A.; Aleem, A.

    2016-08-01

    Cuboidal shaped PZT powder particles based composition Pb0.89(Ba, Sr)0.11(Zr0.52Ti0.48)O3 co- doped with 1 mol% manganese and 2 mol% fluorine was prepared through hydrothermal route. 200-250nm size cuboidal particles were observed under FE-SEM. XRD technique revealed that the perovskite type ceramic structure has a dominant rhombohedral phase. The resultant powder particles were then spray dried, uniaxially pressed and sintered at different temperatures to achieve maximum theoretical density. 98% density was obtained in the pellets at a sintering temperature of 1190°C with an average grain size of 1-3um. The electrical properties of sintered samples were also measured before and after poling to evaluate the effect of dopants on piezoelectric properties.

  1. Dynamics of iron-acceptor-pair formation in co-doped silicon

    SciTech Connect

    Bartel, T.; Gibaja, F.; Graf, O.; Gross, D.; Kaes, M.; Heuer, M.; Kirscht, F.; Möller, C.; Lauer, K.

    2013-11-11

    The pairing dynamics of interstitial iron and dopants in silicon co-doped with phosphorous and several acceptor types are presented. The classical picture of iron-acceptor pairing dynamics is expanded to include the thermalization of iron between different dopants. The thermalization is quantitatively described using Boltzmann statistics and different iron-acceptor binding energies. The proper understanding of the pairing dynamics of iron in co-doped silicon will provide additional information on the electronic properties of iron-acceptor pairs and may become an analytical method to quantify and differentiate acceptors in co-doped silicon.

  2. All-inorganic colloidal silicon nanocrystals—surface modification by boron and phosphorus co-doping

    NASA Astrophysics Data System (ADS)

    Fujii, Minoru; Sugimoto, Hiroshi; Imakita, Kenji

    2016-07-01

    Si nanocrystals (Si-NCs) with extremely heavily B- and P-doped shells are developed and their structural and optical properties are studied. Unlike conventional Si-NCs without doping, B and P co-doped Si-NCs are dispersible in alcohol and water perfectly without any surface functionalization processes. The colloidal solution of co-doped Si-NCs is very stable and no precipitates are observed for more than 5 years. The co-doped colloidal Si-NCs exhibit size-controllable photoluminescence (PL) in a very wide energy range covering 0.85 to 1.85 eV. In this paper, we summarize the structural and optical properties of co-doped Si-NCs and demonstrate that they are a new type of environmentally-friendly nano-light emitter working in aqueous environments in the visible and near infrared (NIR) ranges.

  3. The effect of seeds on GA metabolism in pea pericarp

    SciTech Connect

    Ozga, J.A.; Brenner, M.L. )

    1990-05-01

    To determine the effect of seeds on GA metabolism in pea (Pisum sativum) pericarp tissue, a method was developed that allowed access to the seeds while maintaining pericarp growth. Pericarp tissue of ovaries (3 DAA) was split down the across from the seeds, and seeds were removed. After 24 h. ({sup 14}C)-GA{sub 12} was applied to the inside surface of the pericarp of opened ovaries with or without seeds and to intact ovaries (control). Pericarp tissue was harvested 24 h after ({sup 14}C)-GA{sub 12} application, extracted and chromatographed on C18 HPLC. Wounding (opening ovaries) reduced accumulation of ({sup 14}C)-GA{sub 20}. Notably, removal of seeds significantly decreased ({sup 14}C)-GA{sub 20} accumulation when compared to the wounded controls. ({sup 14}C)-GA{sub 53} was present int he highest amount in the control ovaries attached to the plant, 1.5 {plus minus} 1.0% was found in opened ovaries with seeds and none was detected in ovaries without seeds. Metabolism of ({sup 14}C)-GA{sub 12} was similar in ovaries attached or removed from the plant. Application of GA{sub 3} (2.5 {mu}g/ml) to the ovaries in each treatment did not affect ({sup 14}C)-GA{sub 12} metabolism. These results suggest that the presence of seeds may stimulate GA metabolism in the pericarp.

  4. Effect of Fe and Co doping on electrical and thermal properties of La{sub 0.5}Ce{sub 0.5}Mn{sub 1−x}(Fe, Co){sub x}O{sub 3} manganites

    SciTech Connect

    Varshney, Dinesh; Mansuri, Irfan; Shaikh, M.W.; Kuo, Y.K.

    2013-11-15

    Graphical abstract: - Highlights: • Low temperature resistivity minimum contributes to Coulomb and Kondo scattering. • Metallic resistivity shows electron, magnon and phonon scattering are significant. • At high temperatures small polaron conduction mechanism is viable. • Susceptibility measurements show ferromagnetic–paramagnetic transition. - Abstract: The effect of Fe and Co doping on structural, electrical and thermal properties of half doped La{sub 0.5}Ce{sub 0.5}Mn{sub 1−x}(Fe, Co){sub x}O{sub 3} is investigated. The structure of these crystallizes in to orthorhombically distorted perovskite structure. The electrical resistivity of La{sub 0.5}Ce{sub 0.5}MnO{sub 3} exhibits metal-semiconductor transition (T{sub MS} at ∼225 K). However, La{sub 0.5}Ce{sub 0.5}Mn{sub 1−x}TM{sub x}O{sub 3} (TM = Fe, Co; 0.0 ≤ x ≤ 0.1) manganites show semiconducting behavior. The thermopower measurements infer hole as charge carriers and electron–magnon as well spin wave fluctuation mechanism are effective at low temperature domain and SPC model fits the observed data at high temperature. The magnetic susceptibility measurement confirms a transition from paramagnetic to ferromagnetic phase. The observed peaks in the specific heat measurements, shifts to lower temperatures and becomes progressively broader with doping of transition metals on Mn-site. The thermal conductivity is measured in the temperature range of 10–350 K with a magnitude in between 10 and 80 mW/cm K.

  5. Structural, magnetic and electronic structure properties of Co doped ZnO nanoparticles

    SciTech Connect

    Kumar, Shalendra; Song, T.K.; Gautam, Sanjeev; Chae, K.H.; Kim, S.S.; Jang, K.W.

    2015-06-15

    Highlights: • XRD and HR-TEM results show the single phase nature of Co doped ZnO nanoparticles. • XMCD and dc magnetization results indicate the RT-FM in Co doped ZnO nanoparticles. • Co L{sub 3,2} NEXAFS spectra infer that Co ions are in 2+ valence state. • O K edge NEXAFS spectra show that O vacancy increases with Co doping in ZnO. - Abstract: We reported structural, magnetic and electronic structure studies of Co doped ZnO nanoparticles. Doping of Co ions in ZnO host matrix has been studied and confirmed using various methods; such as X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy dispersed X-ray (EDX), high resolution transmission electron microscopy (HR-TEM), Fourier transform infrared spectroscopy (FT-IR), near edge X-ray absorption fine structure (NEXAFS) spectroscopy, magnetic hysteresis loop measurements and X-ray magnetic circular dichroism (XMCD). From the XRD and HR-TEM results, it is observed that Co doped ZnO nanoparticles have single phase nature with wurtzite structure and exclude the possibility of secondary phase formation. FE-SEM and TEM micrographs show that pure and Co doped nanoparticles are nearly spherical in shape. O K edge NEXAFS spectra indicate that O vacancies increase with Co doping. The Co L{sub 3,2} edge NEXAFS spectra revealed that Co ions are in 2+ valence state. DC magnetization hysteresis loops and XMCD results clearly showed the intrinsic origin of temperature ferromagnetism in Co doped ZnO nanoparticles.

  6. InGaAs/GaAs Quantum Dots: Effects of Ensemble Interactions, Interdiffusion, Segregation and Proton Irradiation

    NASA Technical Reports Server (NTRS)

    Leon, R.

    2000-01-01

    A sumary or recent experimental findings on the effects of interdiffusion, segregation, strained ensemble interactions and proton irradiation on the optical properties of InGaAs/GaAs quantum dots (QDs) are presented.

  7. On the AlGaInP-bulk and AlGaInP/GaAs-superlattice confinement effects for heterostructure-emitter bipolar transistors

    SciTech Connect

    Tsai, Jung-Hui

    2015-02-09

    The confinement effect and electrical characteristics of heterostructure-emitter bipolar transistors with an AlGaInP bulk-confinement layer and an AlGaInP/GaAs superlattice-confinement layer are first demonstrated and compared by experimentally results. In the two devices, the relatively large valence band discontinuity at AlGaInP/GaAs heterojunction provides excellent confinement effect for holes to enhance current gain. As to the AlGaInP/GaAs superlattice-confinement device, part of thermionic-emission electrons will be trapped in the GaAs quantum wells of the superlattice. This will result in lower collector current and current gain as compared with the bulk-confinement device. Nevertheless, the superlattice-confinement device exhibits a larger current-gain cutoff frequency, which can be attributed that the tunneling behavior is included in the carrier transportation and transporting time across the emitter region could be substantially reduced.

  8. Investigation of InGaP/GaAs/InGaAs camel-like gate delta-doped p-channel field-effect transistor

    NASA Astrophysics Data System (ADS)

    Tsai, Jung-Hui; Lour, Wen-Shiung; Huang, Chia-Hong; Dale, Ning-Feng; Lee, Yuan-Hong; Sheng, Jhih-Syuan; Liu, Wen-Chau

    2010-03-01

    In this paper, high device linearity and characteristics of an InGaP/GaAs/InGaAs camel-like gate delta-doped p-channel field-effect transistor is demonstrated. The energy band and hole distribution are depicted with respect to the device performance. Due to the npn depletion of the camel-like gate structure, the considerable conduction band discontinuities at n +-InGaP/p-GaAs and p-GaAs/i-In 0.15Ga 0.85As heterojunctions, and the good confinement effect for holes in InGaAs quantum well, a large gate turn-on voltage is achieved. The drain saturation current linearly increases with the gate voltage and the high device linearity is illustrated by fitting the drain current versus the gate voltage. The excellent performance of the studied device is promise for linear amplifiers and high-frequency circuit applications.

  9. Inverse spin Hall effect in Pt/(Ga,Mn)As

    SciTech Connect

    Nakayama, H.; Chen, L.; Chang, H. W.; Ohno, H.; Matsukura, F.

    2015-06-01

    We investigate dc voltages under ferromagnetic resonance in a Pt/(Ga,Mn)As bilayer structure. A part of the observed dc voltage is shown to originate from the inverse spin Hall effect. The sign of the inverse spin Hall voltage is the same as that in Py/Pt bilayer structure, even though the stacking order of ferromagnetic and nonmagnetic layers is opposite to each other. The spin mixing conductance at the Pt/(Ga,Mn)As interface is determined to be of the order of 10{sup 19 }m{sup −2}, which is about ten times greater than that of (Ga,Mn)As/p-GaAs.

  10. Scaling in the quantum Hall effect regime in n-InGaAs/GaAs nanostructures

    SciTech Connect

    Arapov, Yu. G.; Gudina, S. V.; Klepikova, A. S.; Neverov, V. N. Novokshonov, S. G.; Kharus, G. I.; Shelushinina, N. G.; Yakunin, M. V.

    2013-07-15

    The longitudinal {rho}{sub xx}(B) and Hall {rho}{sub xy}(B) magnetoresistances are investigated experimentally in the integer quantum Hall effect (QHE) regime in n-InGaAs/GaAs double quantum well nanostructures in the range of magnetic fields B = (0-16) T and temperatures T = (0.05-70) K before and after IR illumination. The results are evaluated within the scaling hypothesis with regard to electron-electron interaction.

  11. HgNO3 sensitivity of AlGaN/GaN field effect transistors functionalized with phytochelating peptides

    NASA Astrophysics Data System (ADS)

    Rohrbaugh, Nathaniel; Hernandez-Balderrama, Luis; Kaess, Felix; Kirste, Ronny; Collazo, Ramon; Ivanisevic, Albena

    2016-06-01

    This study examined the conductance sensitivity of AlGaN/GaN field effect transistors in response to varying Hg/HNO3 solutions. FET surfaces were covalently functionalized with phytochelatin-5 peptides in order to detect Hg in solution. Results showed a resilience of peptide-AlGaN/GaN bonds in the presence of strong HNO3 aliquots, with significant degradation in FET ID signal. However, devices showed strong and varied response to Hg concentrations of 1, 10, 100, and 1000 ppm. The gathered statistically significant results indicate that peptide terminated AlGaN/GaN devices are capable of differentiating between Hg solutions and demonstrate device sensitivity.

  12. Rutile-type Co doped SnO2 diluted magnetic semiconductor nanoparticles: Structural, dielectric and ferromagnetic behavior

    NASA Astrophysics Data System (ADS)

    Mehraj, Sumaira; Shahnawaze Ansari, M.; Alimuddin

    2013-12-01

    Nanoparticles of basic composition Sn1-xCoxO2 (x=0.00, 0.01, 0.03, 0.05 and 0.1) were synthesized through the citrate-gel method and were characterized for structural properties using X-ray diffraction (XRD), Scanning electron microscopy (SEM), Energy dispersive X-ray spectroscopy (EDS) and Fourier transform infrared spectroscopy (FT-IR). XRD analysis of the powder samples sintered at 500 °C for 12 h showed single phase rutile type tetragonal structure and the crystallite size decreased as the cobalt content was increased. FT-IR spectrum displayed various bands that came due to fundamental overtones and combination of O-H, Sn-O and Sn-O-Sn entities. The effect of Co doping on the electrical and magnetic properties was studied using dielectric spectroscopy and vibrating sample magnetometer (VSM) at room temperature. The dielectric parameters (ε, tan δ and σac) show their maximum value for 10% Co doping. The dielectric loss shows anomalous behavior with frequency where it exhibits the Debye relaxation. The variation of dielectric properties and ac conductivity with frequency reveals that the dispersion is due to the Maxwell-Wagner type of interfacial polarization in general and hopping of charge between Sn2+ and Sn4+ as well as between Co2+ and Co3+ ions. The complex impedance analysis was used to separate the grain and grain boundary contributions in the system which shows that the conduction process in grown nanoparticles takes place predominantly through grain boundary volume. Hysteresis loops were observed clearly in M-H curves from 0.01 to 0.1% Co doped SnO2 samples. The saturation magnetization of the doped samples increased slightly with increase of Co concentration. However pure SnO2 displayed paramagnetism which vanished at higher values of magnetic field.

  13. Auger effect in yellow light emitters based on InGaN-AlGaN-GaN quantum wells

    NASA Astrophysics Data System (ADS)

    Huong Ngo, Thi; Gil, Bernard; Valvin, Pierre; Damilano, Benjamin; Lekhal, Kaddour; De Mierry, Philippe

    2016-05-01

    The Auger effect and its impact on the internal quantum efficiency (IQE) of yellow light emitters based on silicon-doped InGaN-AlGaN-GaN quantum wells are investigated by power dependence measurement and using an ABC model. Photoluminescence intensity recorded as a function of excitation power density follows a linear dependence up to a threshold P T that depends on the design of the sample. Above this threshold, the variation of the intensity becomes sublinear, which is characteristic of the onset of Auger recombination processes. After extracting the evolution of IQE with pump power from the experimental data, we use a modified ABC modeling that includes the residual n-type doping to estimate the contribution of different recombination channels. We find that the Auger effect dominates in the high-excitation regime. In addition, we find that intercalating an AlGaN-strain-compensating layer reduces not only the coefficient of nonradiative recombination rates but also reduces the onset of Auger recombination.

  14. Resistive switching: An investigation of the bipolar–unipolar transition in Co-doped ZnO thin films

    SciTech Connect

    Santos, Daniel A.A.; Zeng, Hao; Macêdo, Marcelo A.

    2015-06-15

    Highlights: • A purely bipolar behavior on a Co-doped ZnO thin film has been demonstrated. • We have shown what can happen if a unipolar test is performed in a purely bipolar device. • An explanation for how a sample can show a purely bipolar switching behavior was suggested. • An important open issue about resistive switching effect was put in debate. - Abstract: In order to investigate the resistive switching effect we built devices in a planar structure in which two Al contacts were deposited on the top of the film and separated by a small gap using a shadow mask. Therefore, two samples of 10% Co-doped ZnO thin films were sputtered on glass substrate. High resolution X-ray diffraction (HRXRD) revealed a highly c-axis oriented crystalline structure, without secondary phase. The high resolution scanning electron microscopy (HRSEM) showed a flat surface with good coverage and thickness about 300 nm. A Keithley 2425 semiconductor characterization system was used to perform the resistive switching tests in the bipolar and unipolar modes. Considering only the effect of compliance current (CC), the devices showed a purely bipolar behavior since an increase in CC did not induce a transition to unipolar behavior.

  15. Ce(3+) /Tb(3+) non-/single-/co-doped K-Lu-F materials: synthesis, optical properties, and energy transfer.

    PubMed

    Cao, Chunyan; Xie, An; Noh, Hyeon Mi; Jeong, Jung Hyun

    2016-08-01

    Using a hydrothermal method, Ce(3+) /Tb(3+) non-/single-/co-doped K-Lu-F materials have been synthesized. The X-ray diffraction (XRD) results suggest that the Ce(3+) and/or Tb(3+) doping had great effects on the crystalline phases of the final samples. The field emission scanning electron microscopy (FE-SEM) images indicated that the samples were in hexagonal disk or polyhedron morphologies in addition to some nanoparticles, which also indicated that the doping also had great effects on the sizes and the morphologies of the samples. The energy-dispersive spectroscopy (EDS) patterns illustrated the constituents of different samples. The enhanced emissions of Tb(3+) were observed in the Ce(3+) /Tb(3+) co-doped K-Lu-F materials. The energy transfer (ET) efficiency ηT were calculated based on the fluorescence yield. The ET mechanism from Ce(3+) to Tb(3+) was confirmed to be the dipole-quadrupole interaction inferred from the theoretical analysis and the experimental data. Copyright © 2015 John Wiley & Sons, Ltd.

  16. Size and grain morphology dependent magnetic behaviour of Co-doped ZnO

    SciTech Connect

    Vagadia, Megha; Ravalia, Ashish; Khachar, Uma; Solanki, P.S.; Doshi, R.R.; Rayaprol, S.; Kuberkar, D.G.

    2011-11-15

    Highlights: {yields} Structure and magnetic studies on Co-doped ZnO. {yields} Synthesis method dependent comparison of magnetic properties. {yields} Grain size and morphology affect the magnetic properties of Co-doped ZnO. -- Abstract: We have carried out a comparative study of structural, microstructural and magnetic properties of the two sets of Co-doped ZnO samples synthesized using solid state reaction and sol-gel method. Rietveld refinement of the X-ray diffraction data reveals single phase hexagonal wurtzite structure for all the samples, while the tunnelling electron microscopy measurements show the presence of nano-phase in the sol-gel grown Co-doped ZnO samples. It is found that, the microstructure strongly depends on the synthesis method adopted. Samples with higher Co-concentration synthesized by SSR route exhibit antiferromagnetism while SG grown Co-doped ZnO samples exhibit weak ferromagnetic behaviour. Improved magnetic phase in the SG grown samples has been attributed to the grain morphology.

  17. Structural, optical, magnetic and photocatalytic properties of Co doped CuS diluted magnetic semiconductor nanoparticles

    NASA Astrophysics Data System (ADS)

    Sreelekha, N.; Subramanyam, K.; Amaranatha Reddy, D.; Murali, G.; Ramu, S.; Rahul Varma, K.; Vijayalakshmi, R. P.

    2016-08-01

    Pristine and Co doped covellite CuS nanoparticles were synthesized in aqueous solution by facile chemical co-precipitation method with Ethylene Diamine Tetra Acetic Acid (EDTA) as a stabilizing agent. EDAX measurements confirmed the presence of Co in the CuS host lattice. Hexagonal crystal structure of pure and Co doped CuS nanoparticles were authenticated by XRD patterns. TEM images indicated that sphere-shape of nanoparticles through a size ranging from 5 to 8 nm. The optical absorption edge moved to higher energies with increase in Co concentration as indicated by UV-vis spectroscopy. Magnetic measurements revealed that bare CuS sample show sign of diamagnetic character where as in Co doped nanoparticles augmentation of room temperature ferromagnetism was observed with increasing doping precursor concentrations. Photocatalytic performance of the pure and Co doped CuS nanoparticles were assessed by evaluating the degradation rate of rhodamine B solution under sun light irradiation. The 5% Co doped CuS nanoparticles provide evidence for high-quality photocatalytic activity.

  18. Effects of Ga ion-beam irradiation on monolayer graphene

    SciTech Connect

    Wang, Quan; Mao, Wei; Zhang, Yanmin; Shao, Ying; Ren, Naifei; Ge, Daohan

    2013-08-12

    The effects of Ga ion on the single layer graphene (SLG) have been studied by Raman spectroscopy (RS), SEM, and field-effect characterization. Under vacuum conditions, Ga ion-irradiation can induce disorders and cause red shift of 2D band of RS, rather than lattice damage in high quality SLG. The compressive strain induced by Ga ion decreases the crystalline size in SLG, which is responsible for the variation of Raman scattering and electrical properties. Nonlinear out-put characteristic and resistance increased are also found in the I-V measurement. The results have important implications during CVD graphene characterization and related device fabrication.

  19. Quantum well intermixing and radiation effects in InGaN/GaN multi quantum wells

    NASA Astrophysics Data System (ADS)

    Lorenz, K.; Redondo-Cubero, A.; Lourenço, M. B.; Sequeira, M. C.; Peres, M.; Freitas, A.; Alves, L. C.; Alves, E.; Leitão, M. P.; Rodrigues, J.; Ben Sedrine, N.; Correia, M. R.; Monteiro, T.

    2016-02-01

    Compositional grading of InGaN/GaN multi quantum wells (QWs) was proposed to mitigate polarization effects and Auger losses in InGaN-based light emitting diodes [K. P. O'Donnell et al., Phys. Status Solidi RRL 6 (2012) 49]. In this paper we are reviewing our recent attempts on achieving such gradient via quantum well intermixing. Annealing up to 1250 °C resulted in negligible interdiffusion of QWs and barriers revealing a surprising thermal stability well above the typical MOCVD growth temperatures. For annealing at 1400 °C results suggest a decomposition of the QWs in regions with high and low InN content. The defect formation upon nitrogen implantation was studied in detail. Despite strong dynamic annealing effects, which keep structural damage low, the created defects strongly quench the QW luminescence even for low implantation fluences. This degradation could not be reversed during thermal annealing and is hampering the use of implantation induced quantum well intermixing in InGaN/GaN structures.

  20. Arsenic implantation-induced intermixing effects on AlGaAs/GaAs single QW structures

    NASA Astrophysics Data System (ADS)

    Liu, X. Q.; Li, Z. F.; Chen, X. S.; Lu, W.; Shen, S. C.; Tan, H. H.; Yuan, S.; Jagadish, C.

    2000-06-01

    The effects of intermixing Al 0.54Ga 0.46As/GaAs/Al 0.54Ga 0.46As quantum well (QW) enhanced by arsenic ion implantation and subsequent annealing have been investigated by photoluminescence and photo-modulated reflectance measurements. Comparing with as-grown QW, obvious blueshifts of all the transitions were observed. The H 22 transition was found to be much less sensitive to the implantation doses than that of H 11. The experimental results are different from the theoretical results calculated by using the model of error function profile of Al composition. The results are fruitful for understanding the potential profile after intermixing enhanced by arsenic ion implantation, and also for the application of implantation enhanced intermixing effects on devices, such as QW lasers and photodetectors, opto-nonlinear devices, etc..

  1. Annealing in tellurium-nitrogen co-doped ZnO films: The roles of intrinsic zinc defects

    SciTech Connect

    Tang, Kun Gu, Ran; Gu, Shulin Ye, Jiandong; Zhu, Shunming; Yao, Zhengrong; Xu, Zhonghua; Zheng, Youdou

    2015-04-07

    In this article, the authors have conducted an extensive investigation on the roles of intrinsic zinc defects by annealing of a batch of Te-N co-doped ZnO films. The formation and annihilation of Zn interstitial (Zn{sub i}) clusters have been found in samples with different annealing temperatures. Electrical and Raman measurements have shown that the Zn{sub i} clusters are a significant compensation source to holes, and the Te co-doping has a notable effect on suppressing the Zn{sub i} clusters. Meanwhile, shallow acceptors have been identified in photoluminescence spectra. The N{sub O}-Zn-Te complex, zinc vacancy (V{sub Zn})-N{sub O} complex, and V{sub Zn} clusters are thought to be the candidates as the shallow acceptors. The evolution of shallow acceptors upon annealing temperature have been also studied. The clustering of V{sub Zn} at high annealing temperature is proposed to be a possible candidate as a stable acceptor in ZnO.

  2. Synergistic enhancement of nitrogen and sulfur co-doped graphene with carbon nanospheres insertion for electrocatalytic oxygen reduction reaction

    DOE PAGES

    Wu, Min; Xin, Huolin L.; Wang, Jie; Wu, Zexing; Wang, Deli

    2015-03-13

    A nitrogen and sulfur co-doped graphene/carbon black (NSGCB) nanocomposite for the oxygen reduction reaction (ORR) was synthesized through a one-pot annealing of a precursor mixture containing graphene oxide, thiourea, and acidized carbon black (CB). The NSGCB showed excellent performance for the ORR with the onset and half-way potentials at 0.96 V and 0.81 V (vs. RHE), respectively. It is significantly improved over that of the catalysts derived from only graphene (0.90 V and 0.76 V) or carbon nanosphere (0.82 V and 0.74 V). The enhanced catalytic activity on the NSGCB electrode could be attributed to the synergistic effect of N/Smore » co-doping and the enlarged interlayer space resulted from the insertion of carbon nanosphere into the graphene sheets. The four-electron selectivity and the limiting current density of the NSGCB nanocomposite are comparable to that of the commercially Pt/C catalyst. Furthermore, the NSGCB nanocomposite was superior to Pt/C in terms of long-term durability and tolerance to methanol poisoning.« less

  3. A sensitive and label-free photoelectrochemical aptasensor using Co-doped ZnO diluted magnetic semiconductor nanoparticles.

    PubMed

    Li, Hongbo; Qiao, Yunfei; Li, Jing; Fang, Hailin; Fan, Dahe; Wang, Wei

    2016-03-15

    Co-doped ZnO diluted magnetic semiconductor as a novel photoelectric beacon was first constructed for photoelectrochemical (PEC) aptasensor of acetamiprid. The fabricated PEC sensing is based on the specific binding of acetamiprid and its aptamer, which induces the decreasement of enhanced photocurrent produced by the electron donor of quercetin. Co(2+) doping has a beneficial effect in extending the band width of light absorption of ZnO into the visible region and to promote the separation of the photoinduced carriers due to the sp-d exchange interactions existing between the band electrons and the localized d electrons of Co(2+). The fabricated aptasensor was linear with the concentration of acetamiprid in the range of 0.5-800 nmolL(-1) with the detection limit of 0.18 nmolL(-1). The presence of same concentration of other conventional pesticides did not interfere in the detection of acetamiprid and the recovery is between 96.2% and 103.7%. This novel PEC aptasensor has good performances with high sensitivity, good selectivity, low cost and portable features. The strategy of Co-doped ZnO diluted magnetic semiconductor paves a new way to improve the performances of PEC aptasensor.

  4. Structural and optical properties of highly crystalline Ce, Eu and co-doped ZnO nanorods

    NASA Astrophysics Data System (ADS)

    Murugadoss, G.; Jayavel, R.; Rajesh Kumar, M.

    2015-06-01

    Different concentrations of europium (Eu), cerium (Ce) doped and co-doped ZnO:Eu (1%), Ce (1%) nanorods were successfully synthesized by chemical method using Polyvinylpyrrolidone as a surfactant. Crystalline phase, morphology, functional groups, optical absorption, emission and thermal properties of prepared samples were investigated by X-ray diffraction (XRD), X-ray photoelectron spectrometer (XPS), Scanning electron microscopy (SEM), High-resolution transmission electron microscopy (HR-TEM), Fourier transform infra-red (FT-IR), UV-visible, Photoluminescence (PL) spectrophotometer and thermogravimetry (TG) and differential thermal analysis (DTA) analysis. The XRD study showed high crystalline nature of the products with nanoscale regime. Optical study showed shifting the absorption and emission spectra toward higher wavelength side when increasing the doping concentrations. Mainly, this is first time observed a red emission peak at 660 nm for Ce (3%) doped ZnO. Additionally, co-doped ZnO:Eu (1%), Ce (1%) nanorods were synthesized and studied their optical properties. This work demonstrates that simply modified their optical absorption and emission of ZnO by introducing rare earth ions can be used as an effective electrode material in solar cell applications, optoelectronic devices and photocatalysis analysis.

  5. A sensitive and label-free photoelectrochemical aptasensor using Co-doped ZnO diluted magnetic semiconductor nanoparticles.

    PubMed

    Li, Hongbo; Qiao, Yunfei; Li, Jing; Fang, Hailin; Fan, Dahe; Wang, Wei

    2016-03-15

    Co-doped ZnO diluted magnetic semiconductor as a novel photoelectric beacon was first constructed for photoelectrochemical (PEC) aptasensor of acetamiprid. The fabricated PEC sensing is based on the specific binding of acetamiprid and its aptamer, which induces the decreasement of enhanced photocurrent produced by the electron donor of quercetin. Co(2+) doping has a beneficial effect in extending the band width of light absorption of ZnO into the visible region and to promote the separation of the photoinduced carriers due to the sp-d exchange interactions existing between the band electrons and the localized d electrons of Co(2+). The fabricated aptasensor was linear with the concentration of acetamiprid in the range of 0.5-800 nmolL(-1) with the detection limit of 0.18 nmolL(-1). The presence of same concentration of other conventional pesticides did not interfere in the detection of acetamiprid and the recovery is between 96.2% and 103.7%. This novel PEC aptasensor has good performances with high sensitivity, good selectivity, low cost and portable features. The strategy of Co-doped ZnO diluted magnetic semiconductor paves a new way to improve the performances of PEC aptasensor. PMID:26436325

  6. Enhanced electrical properties in multiferroic BiFeO3 ceramics co-doped by La3+ and V5+

    NASA Astrophysics Data System (ADS)

    Yu, Benfang; Li, Meiya; Wang, Jing; Pei, Ling; Guo, Dongyun; Zhao, Xingzhong

    2008-09-01

    La3+ and V5+ co-doped Bi0.85La0.15Fe1-xVxO3 (BLFVx, x = 0-0.1) ceramics were prepared by a rapid liquid sintering technique. The effects of the V5+-doping content on the structure and electrical properties of BLFVx ceramics were investigated. In the range of the V5+ content x from 0 to 0.03, BLFVx ceramics had a polycrystalline perovskite structure with tiny residual Bi2O3, while an impurity phase appeared for x > 0.03. As the x increased from 0 to 0.1, both the leakage current density and the dielectric loss (tan δ) for BLFVx ceramics decreased gradually, while the dielectric constant (ɛr) first increased and then decreased gradually in this process, reaching a maximum value of 273 for x = 0.03. Among the BLFVx ceramics, the BLFVx=0.01 ceramic showed a well-saturated hysteresis loop with large remanent polarization (Pr) of 39.4 µC cm-2 and a low coercive electric field (Ec) of ±43.1 kV cm-1 under an applied electric field of ±75 kV cm-1. In addition, these ceramics exhibited good anti-fatigue characteristics after 2 × 1010 read/write polarization cycles. These suggested that La3+ and V5+ co-doping was beneficial for enhancing the dielectric, ferroelectric and anti-fatigue properties of the BLFVx ceramics.

  7. Er 3+ - Yb 3+ co-doped phosphate glass optical fiber for application at 1.54 microns

    NASA Astrophysics Data System (ADS)

    Lafond, Christophe; Osouf, Jocelyne; Laperle, Pierre; Soucy, Jean-Luc; Desrosiers, Cynthia; Morency, Steeve; Croteau, André; Parent, André

    2006-09-01

    We present current work developed at INO on phosphate glass optical fiber for laser and amplifier applications at 1.54 microns. Core and cladding glasses were fabricated by a multi-components melting process which gave an uniform refractive index core profile. Rod-in-tube method under Argon atmosphere was used to fabricate optical fibers. The effect of nitrogen atmosphere on hydroxyl groups OH - during glass melting was studied. The absorption coefficient calculated at 3.42 μm was found to be lower than 0.5 cm -1 which corresponds to less than 70 ppm OH -. Absorption and emission cross sections were calculated at 1534 nm. Fabrication process allowed us to decrease background losses of core Er 3+ - Yb 3+ co-doped fiber between 0.02 and 0.04 dB/cm. Laser power was measured at 1563 nm and a 26% slope efficiency was achieved with a 22 cm-long single-clad fiber co-doped with 1.1 wt% in Er 3+ and 11.1 wt% in Yb 3+. For the same fiber, an internal gain was found to be 20 dB at 1536 nm for a 5-cm-long fiber.

  8. Synergistic enhancement of nitrogen and sulfur co-doped graphene with carbon nanospheres insertion for electrocatalytic oxygen reduction reaction

    SciTech Connect

    Wu, Min; Xin, Huolin L.; Wang, Jie; Wu, Zexing; Wang, Deli

    2015-03-13

    A nitrogen and sulfur co-doped graphene/carbon black (NSGCB) nanocomposite for the oxygen reduction reaction (ORR) was synthesized through a one-pot annealing of a precursor mixture containing graphene oxide, thiourea, and acidized carbon black (CB). The NSGCB showed excellent performance for the ORR with the onset and half-way potentials at 0.96 V and 0.81 V (vs. RHE), respectively. It is significantly improved over that of the catalysts derived from only graphene (0.90 V and 0.76 V) or carbon nanosphere (0.82 V and 0.74 V). The enhanced catalytic activity on the NSGCB electrode could be attributed to the synergistic effect of N/S co-doping and the enlarged interlayer space resulted from the insertion of carbon nanosphere into the graphene sheets. The four-electron selectivity and the limiting current density of the NSGCB nanocomposite are comparable to that of the commercially Pt/C catalyst. Furthermore, the NSGCB nanocomposite was superior to Pt/C in terms of long-term durability and tolerance to methanol poisoning.

  9. Effects of Annealing on GaAs/GaAsSbN/GaAs Core-Multi-shell Nanowires.

    PubMed

    Kasanaboina, Pavan; Sharma, Manish; Deshmukh, Prithviraj; Reynolds, C Lewis; Liu, Yang; Iyer, Shanthi

    2016-12-01

    The effects of ex-situ annealing in a N2 ambient on the properties of GaAs/GaAsSbN/GaAs core-multi-shell nanowires on Si (111) substrate grown by self-catalyzed molecular beam epitaxy (MBE) are reported. As-grown nanowires exhibit band edge emission at ~0.99 eV with a shoulder peak at ~0.85 eV, identified to arise from band tail states. A large red shift of 7 cm(-1) and broadened Raman spectra of as-grown nanowires compared to that of non-nitride nanowires confirmed phonon localization at N-induced localized defects. On annealing nanowires to 750 °C, there was no change in the planar defects in the nanowire with respect to the as-grown nanowire; however, vanishing of the photoluminescence (PL) peak corresponding to band tail states along with enhanced band edge PL intensity, recovery of the Raman shift and increase in the Schottky barrier height from 0.1 to 0.4 eV clearly point to the efficient annihilation of point defects in these GaAsSbN nanowires. A significant reduction in the temperature-induced energy shift in the annealed nanowires is attributed to annihilation of band tail states and weak temperature dependence of N-related localized states. The observation of room temperature PL signal in the 1.3 μm region shows that the strategy of adding small amounts of N to GaAsSb is a promising route to realization of efficient nanoscale light emitters with reduced temperature sensitivity in the telecommunication wavelength region.

  10. Effects of Annealing on GaAs/GaAsSbN/GaAs Core-Multi-shell Nanowires

    NASA Astrophysics Data System (ADS)

    Kasanaboina, Pavan; Sharma, Manish; Deshmukh, Prithviraj; Reynolds, C. Lewis; Liu, Yang; Iyer, Shanthi

    2016-02-01

    The effects of ex-situ annealing in a N2 ambient on the properties of GaAs/GaAsSbN/GaAs core-multi-shell nanowires on Si (111) substrate grown by self-catalyzed molecular beam epitaxy (MBE) are reported. As-grown nanowires exhibit band edge emission at ~0.99 eV with a shoulder peak at ~0.85 eV, identified to arise from band tail states. A large red shift of 7 cm-1 and broadened Raman spectra of as-grown nanowires compared to that of non-nitride nanowires confirmed phonon localization at N-induced localized defects. On annealing nanowires to 750 °C, there was no change in the planar defects in the nanowire with respect to the as-grown nanowire; however, vanishing of the photoluminescence (PL) peak corresponding to band tail states along with enhanced band edge PL intensity, recovery of the Raman shift and increase in the Schottky barrier height from 0.1 to 0.4 eV clearly point to the efficient annihilation of point defects in these GaAsSbN nanowires. A significant reduction in the temperature-induced energy shift in the annealed nanowires is attributed to annihilation of band tail states and weak temperature dependence of N-related localized states. The observation of room temperature PL signal in the 1.3 μm region shows that the strategy of adding small amounts of N to GaAsSb is a promising route to realization of efficient nanoscale light emitters with reduced temperature sensitivity in the telecommunication wavelength region.

  11. Vertically Aligned Carbon Nanotube Arrays Co-doped with Phosphorus and Nitrogen as Efficient Metal-Free Electrocatalysts for Oxygen Reduction.

    PubMed

    Yu, Dingshan; Xue, Yuhua; Dai, Liming

    2012-10-01

    Using a mixture of ferrocene, pyridine, and triphenylphosphine as precursors for injection-assisted chemical vapor deposition (CVD), we prepared the first vertically aligned multiwalled carbon nanotube array co-doped with phosphorus (P) and nitrogen (N) with a relatively high P-doping level (designated as PN-ACNT). We have also demonstrated the potential applications of the resultant PN-ACNTs as high-performance electrocatalysts for the oxygen reduction reaction (ORR). PN-ACNT arrays were shown to exhibit a high ORR electrocatalytic activity, superb long-term durability, and good tolerance to methanol and carbon monoxide, significantly outperforming their counterparts doped with P (P-ACNT) or N (N-ACNT) only and even comparable to the commercially available Pt-C catalyst (45 wt % Pt on Vulcan XC-72R; E-TEK) due to a demonstrated synergetic effect arising from the co-doping of CNTs with both P and N.

  12. Sulfur and nitrogen co-doped, few-layered graphene oxide as a highly efficient electrocatalyst for the oxygen-reduction reaction.

    PubMed

    Xu, Jiaoxing; Dong, Guofa; Jin, Chuanhong; Huang, Meihua; Guan, Lunhui

    2013-03-01

    S and N co-doped, few-layered graphene oxide is synthesized by using pyrimidine and thiophene as precursors for the application of the oxygen reduction reaction (ORR). The dual-doped catalyst with pyrrolic/graphitic N-dominant structures exhibits competitive catalytic activity (10.0 mA cm(-2) kinetic-limiting current density at -0.25 V) that is superior to that for mono N-doped carbon nanomaterials. This is because of a synergetic effect of N and S co-doping. Furthermore, the dual-doped catalyst also shows an efficient four-electron-dominant ORR process, which has excellent methanol tolerance and improved durability in comparison to commercial Pt/C catalysts. PMID:23404829

  13. Magnetic and magnetocaloric properties of Ba and Ti co-doped SrRuO3

    NASA Astrophysics Data System (ADS)

    Sarkar, Babusona; Dalal, Biswajit; Dev Ashok, Vishal; De, S. K.

    2014-12-01

    Temperature evolution of magnetic properties in Ba and Ti doped SrRuO3 has been investigated to observe the effects of larger ionic radius Ba at Sr site and isovalent nonmagnetic impurity Ti at Ru site. Ionic radius mismatch and different electronic configuration in comparison with Ru modify Sr(Ba)-O and Ru(Ti)-O bond lengths and Ru-O-Ru bond angle. The apical and basal Ru-O-Ru bond angles vary significantly with Ti doping. Ferromagnetic Curie temperature decreases from 161 K to 149 K monotonically with Ba (10%) and Ti (10%) substitutions at Sr and Ru sites. The zero field cooled (ZFC) magnetization reveals a prominent peak which shifts towards lower temperature with application of magnetic field. The substitution of tetravalent Ti with localized 3d0 orbitals for Ru with more delocalized 4d4 orbitals leads to a broad peak in ZFC magnetization. A spontaneous ZFC magnetization becomes negative below 160 K for all the compositions. The occurrence of both normal and inverse magnetocaloric effects in Ba and Ti co-doped SrRuO3 makes the system more interesting.

  14. Structural and photoluminescence properties of Cd and Cu co-doped zinc oxide nanoparticles

    NASA Astrophysics Data System (ADS)

    Samuel, T.; Sujatha, K.; Rao, K. Ramachandra; Rao, M. C.

    2016-05-01

    Cd and Cu co-doped ZnO nanoparticles were synthesized by Polyol method and subsequently have been characterized by their structure, optical and photoluminescence studies. XRD and PSA results revealed the formation of Cd and Cu co-doped ZnO nanoparticles with an average crystallite size of 50 nm and average particle size of 246 nm. From Zeta Potential measurements the Zeta Potential was found to be - 29.2 eV indicating the stability of prepared nanoparticles. From Uv-Vis studies, it is found that the absorption of undoped ZnO is less compared with Cd and Cu co-doped ZnO and the absorbance increases with increase in dopant concentration. Photoluminescence studies revealed that the samples are with high structural and optical quality.

  15. Charge Compensated (Al, N) Co-Doped Zinc Oxide (ZnO) Films for Photlelectrochemical Application

    SciTech Connect

    Shet, S.

    2012-01-01

    ZnO thin films with significantly reduced bandgaps were synthesized by doping N and co-doping Al and N at 100oC. All the films were synthesized by radio-frequency magnetron sputtering on F-doped tin-oxide-coated glass. We found that co-doped ZnO:(Al,N) thin films exhibited significantly enhanced crystallinity as compared to ZnO doped solely with N, ZnO:N, at the same growth conditions. Furthermore, annealed ZnO:(Al,N) thin films exhibited enhanced N incorporation over ZnO:N films. As a result, ZnO:(Al,N) films exhibited improved photocurrents than ZnO:N films grown with pure N doping, suggesting that charge-compensated donor-acceptor co-doping could be a potential method for bandgap reduction of wide-bandgap oxide materials to improve their photoelectrochemical performance.

  16. Phosphorus/sulfur Co-doped porous carbon with enhanced specific capacitance for supercapacitor and improved catalytic activity for oxygen reduction reaction

    NASA Astrophysics Data System (ADS)

    Zhou, Yao; Ma, Ruguang; Candelaria, Stephanie L.; Wang, Jiacheng; Liu, Qian; Uchaker, Evan; Li, Pengxi; Chen, Yongfang; Cao, Guozhong

    2016-05-01

    Phosphorus (P)/sulfur (S) co-doped porous carbon derived from resorcinol and furaldehyde are synthesized through one-step sol-gel processing with the addition of phosphorus pentasulfide as P and S source followed with freeze-drying and pyrolysis in nitrogen. The P/S co-doping strategy facilitates the pore size widening both in micropore and mesopore regions, together with the positive effect on the degree of graphitization of porous carbon through elimination of amorphous carbon through the formation and evaporation of carbon disulfide. As an electrode for supercapacitor application, P/S co-doped porous carbon demonstrates 43.5% improvement on specific capacitance of the single electrode compared to pristine porous carbon in organic electrolyte at a current of 0.5 mA due to the P-induced pseudocapacitive reactions. As for electrocatalytic use, promoted electrocatalytic activity and high resistance to crossover effects of oxygen reduction reaction (ORR) in alkaline media are observed after the introduction of P and S into porous carbon. After air activation, the specific capacitance of the single electrode of sample PS-pC reaches up to 103.5 F g-1 and an improved oxygen reduction current density.

  17. Origin of resolution enhancement by co-doping of scintillators: Insight from electronic structure calculations

    SciTech Connect

    Åberg, Daniel Sadigh, Babak; Schleife, André; Erhart, Paul

    2014-05-26

    It was recently shown that the energy resolution of Ce-doped LaBr{sub 3} scintillator radiation detectors can be crucially improved by co-doping with Sr, Ca, or Ba. Here, we outline a mechanism for this enhancement on the basis of electronic structure calculations. We show that (i) Br vacancies are the primary electron traps during the initial stage of thermalization of hot carriers, prior to hole capture by Ce dopants; (ii) isolated Br vacancies are associated with deep levels; (iii) Sr doping increases the Br vacancy concentration by several orders of magnitude; (iv) Sr{sub La} binds to V{sub Br} resulting in a stable neutral complex; and (v) association with Sr causes the deep vacancy level to move toward the conduction band edge. The latter is essential for reducing the effective carrier density available for Auger quenching during thermalization of hot carriers. Subsequent de-trapping of electrons from Sr{sub La}–V{sub Br} complexes can activate Ce dopants that have previously captured a hole leading to luminescence. This mechanism implies an overall reduction of Auger quenching of free carriers, which is expected to improve the linearity of the photon light yield with respect to the energy of incident electron or photon.

  18. Aluminum- and boron-co-doped ZnO ceramics: structural, morphological and electrical characterization

    NASA Astrophysics Data System (ADS)

    Liu, Shimin; Liu, Jindong; Jiang, Weiwei; Liu, Chaoqian; Ding, Wanyu; Wang, Hualin; Wang, Nan

    2016-10-01

    Highly dense and electrically conductive aluminum- and boron-co-doped ZnO (ABZO) ceramics were prepared by traditional pressureless sintering process. Single aluminum-doped ZnO (AZO) ceramics were synthesized with similar process and characterized for comparison. The densification behavior, crystal structure, morphology, composition and electrical properties of the ceramics were studied. Results indicated that AZO ceramics with the maximum relative density of 99.01 % were obtained only at 1350 °C for 4 h, which, however, was accompanied by electrical conductivity deterioration because of the increased insulated ZnAl2O4 phase formed in ceramics. Interestingly, the ABZO ceramics reached the maximum relative density of 98.84 % at 1100 °C, which was 250 °C lower compared with that of AZO ceramics. Moreover, the electrical conductivity of ABZO ceramics improved significantly with the increased sintering temperature and increased insulated ZnAl2O4 phase, which should be ascribed to the decreased grain boundaries and the resultant reduced carrier scattering in ceramics overcoming the influence of increased ZnAl2O4 phase due to boron doping effect.

  19. Combinatorial optimization of La, Ce-co-doped pyrosilicate phosphors as potential scintillator materials.

    PubMed

    Wei, Qinhua; Wan, Jieqiong; Liu, Guanghui; Zhou, Zhenzhen; Yang, Hua; Wang, Jiacheng; Liu, Qian

    2015-04-13

    A combinatorial method was employed to rapidly screen the effects of La, Ce-co-doping on the luminescent properties of Gd2Si2O7 pyrosilicate using an 8 × 8 library. The candidate formulations (Gd1-x-yLax)2Si2O7:Ce2y were evaluated by luminescence pictures under ultraviolet excitation. The optimal composition was found to be (Gd0.89La0.1)2Si2O7:Ce0.02 after scaled-up preparation and detailed characterization of powder samples, which shows an excellent light output under both ultraviolet and X-ray excitation (about 5.43 times of commercial YAG:Ce powders). The XRD results indicate that the phase structure sequence is tetragonal-orthorhombic-triclinic for different calcination temperatures and doping ions. The (Gd0.89La0.1)2Si2O7:Ce0.02 powder sample also demonstrated excellent temperature stability of luminescence up to 200 °C and a short decay time of several tens of nanoseconds, suggesting that this may represent a new kind of scintillation material, such as single crystals, ceramics, glass, or phosphors.

  20. Spectroscopic properties in Er3+/Yb3+ Co-doped fluorophosphate glass

    NASA Astrophysics Data System (ADS)

    Zheng, Tao; Qin, Jie-Ming; Jiang, Da-Yong; Lü, Jing-Wen; Xiao, Sheng-Chun

    2012-04-01

    Using the technique of high-temperature melting, a new Er3+/Yb3+ co-doped fluorophosphate glass was prepared. The absorption and fluorescence spectra were investigated in depth. The effect of Er3+ and Yb3+ concentration on the spectroscopic properties of the glass sample was also discussed. According to the Judd—Ofelt theory, the oscillator strength was computed. The lifetime of 4I13/2 level (τm) of Er3+ ions was 8.23 ms, and the full width at half maximum of the dominating emission peak was 68 nm at 1.53 μm. The large stimulated emission cross section of the Er3+ was calculated by the McCumber theory. The spectroscopic properties of Er3+ ion were compared with those in different glasses. The full width at half maximum and σe are larger than those of other glass hosts, indicating this studied glass may be a potentially useful candidate for high-gain erbium-doped fiber amplifier.

  1. Visible-Light-Induced Bactericidal Activity of Titanium Dioxide Co-doped with Nitrogen and Silver

    PubMed Central

    Wu, Pinggui; Xie, Rongcai; Imlay, Kari; Shang, Jian-Ku

    2011-01-01

    Titanium dioxide nanoparticles co-doped with nitrogen and silver (Ag2O/TiON) were synthesized by the sol-gel process and found to be an effective visible light driven photocatalyst. The catalyst showed strong bactericidal activity against Escherichia coli (E. coli) under visible light irradiation (λ> 400 nm). In x-ray photoelectron spectroscopy and x-ray diffraction characterization of the samples, the as-added Ag species mainly exist as Ag2O. Spin trapping EPR study showed Ag addition greatly enhanced the production of hydroxyl radicals (•OH) under visible light irradiation. The results indicate that the Ag2O species trapped eCB− in the process of Ag2O/TiON photocatalytic reaction, thus inhibiting the recombination of eCB− and hVB+ in agreement with the stronger photocatalytic bactericidal activity of Ag2O/TiON. The killing mechanism of Ag2O/TiON under visible light irradiation is shown to be related to oxidative damages in the forms of cell wall thinning and cell disconfiguration. PMID:20726520

  2. Ni, Fe Co-doped ZnO nanoparticles synthesized by solution combustion method

    SciTech Connect

    Dhiman, Pooja Chand, Jagdish Verma, S. Sarveena, Singh, M.

    2014-04-24

    This paper outlines the synthesis and characterization of Ni-Fe co-doped ZnO nanoparticles by facile solution combustion method. The structural characterization by XRD confirmed the phase purity of the samples. Surface morphology studied by scanning electron microscope revealed cubic type shape of grains. EDS analysis conformed the elemental composition. Higher value of DC electrical conductivity and less band gap for co-doped ZnO from UV-Vis studies confirmed the change in defect chemistry of ZnO Matrix.

  3. Ferromagnetism in (Mn,Li) co-doped CdSe

    NASA Astrophysics Data System (ADS)

    Nabi, Z.; Ahuja, R.

    2008-12-01

    Ab initio calculations based on the density functional theory are reported for the Mn-doped CdSe for 5.5% and 12.5% Mn on a Cd sublattice. It is found that Mn-doped CdSe is antiferromagnetic. An essential ingredient to stabilize the ferromagnetism in bulk Cd1-xMnxSe can be realized by the co-doping of Li. We demonstrate that CdSe co-doped with Mn and Li has a stable ferromagnetic ground state and we show that the electronic structure of Cd1-2xMnxLixSe has a nearly metallic character.

  4. Reversible ferromagnetic spin ordering governed by hydrogen in Co-doped ZnO semiconductor

    SciTech Connect

    Cho, Yong Chan; Kim, Sung-Jin; Lee, Seunghun; Kim, Su Jae; Cho, Chae Ryong; Nahm, Ho-Hyun; Park, Chul Hong; Jeong, Il Kyoung; Park, Sungkyun; Hong, Tae Eun; Kuroda, Shinji; Jeong, Se-Young

    2009-10-26

    We report a reversible manipulation of short-range spin ordering in Co-doped ZnO through hydrogenation and dehydrogenation processes. In both magnetic-circular dichroism and superconducting quantum interference device measurements, the ferromagnetism was clearly induced and removed by the injection and ejection of hydrogen, respectively. The x-ray photoelectron spectroscopy results and the first-principles electronic structure calculations consistently support the dependence of the ferromagnetism on the hydrogen position and the contribution of transition metal ions. The results suggest the ferromagnetic interaction between Co ions can be reversibly controlled by the hydrogen-mediated intrinsic spin ordering in Co doped ZnO.

  5. Effect of impurity trapping on the capacitance-voltage characteristics of n-GaAs/N-AlGaAs heterojunctions

    SciTech Connect

    Tan, K.L.; Lundstrom, M.S.; Melloch, M.R.

    1986-02-10

    We have studied the capacitance-voltage (C-V) characteristics of Schottky barriers on inverted n-GaAs/N-AlGaAs and normal N-AlGaAs/n-GaAs heterojunctions. Impurities introduced during film growth produced a negative sheet charge of 6.0 x 10 cm S at the interface of the inverted n-GaAs/N-AlGaAs heterojunction. The effectiveness of GaAs quantum wells in trapping these impurities was investigated. GaAs quantum wells 20 A wide were placed in intervals of 2500 A for the first 0.75 m of the AlGaAs layer; in the last 0.25 m, the periodicity of the quantum wells was progressively decreased by half with the last quantum well placed at about 160 A from the GaAs/AlGaAs interface. The resulting measured interface charge concentration of 4.4 x 10 cm S is more than a magnitude lower than measured before the use of the quantum wells and is essentially at the limit of the accuracy of the C-V technique for this structure.

  6. Fabrication of the C-N co-doped rod-like TiO{sub 2} photocatalyst with visible-light responsive photocatalytic activity

    SciTech Connect

    Li, Liang-Hai; Lu, Juan; Wang, Zuo-Shan; Yang, Lu; Zhou, Xiu-Feng; Han, Lu

    2012-06-15

    Highlights: ► Novel synthesis of C-N co-doped TiO{sub 2}. ► Self-assembly of C-N co-doped TiO{sub 2} nanorods by nanoparticles. ► Excellent photocatalytic efficiency. -- Abstract: The C-N co-doped TiO{sub 2} nanorods were synthesized by the vapor transport method of water molecules, and urea was used as the carbon and nitrogen source. The samples were characterized by X-ray diffraction and photoelectron spectroscopy analysis. The scanning electron microscope images showed that as-prepared TiO{sub 2} powders were nanorods, which were formed by the stacking of nanoparticles with a uniform size around 40 nm. The degradation of methylene blue with the prepared nanorods demonstrated the photocatalytic activities of TiO{sub 2} under visible light are improved by doping with C and N elements. The main reasons were discussed: doping with C and N elements could enhance the corresponding visible-light absorption of TiO{sub 2}. On the other hand, doping C and N could create more oxygen vacancies in the TiO{sub 2} crystals, which could capture the photogenerated electrons more effectively. Thus, more photogenerated holes could be left to improve the photocatalytic activity of TiO{sub 2}.

  7. Interplay of dopant, defects and electronic structure in driving ferromagnetism in Co-doped oxides: TiO(2), CeO(2) and ZnO.

    PubMed

    Ali, Bakhtyar; Shah, Lubna R; Ni, C; Xiao, J Q; Shah, S Ismat

    2009-11-11

    A comprehensive study of the defects and impurity (Co)-driven ferromagnetism is undertaken in the oxide semiconductors: TiO(2), ZnO and CeO(2). The effect of magnetic (Co(2+)) and non-magnetic (Cu(2+)) impurities in conjunction with defects, such as oxygen vacancies (V(o)), have been thoroughly investigated. Analyses of the x-ray diffraction (XRD) and x-ray photoelectron spectroscopy (XPS) data reveal the incorporation of cobalt in the lattice, with no signature of cobalt segregation. It is shown that oxygen vacancies are necessary for the ferromagnetic coupling in the Co-doped oxides mentioned above. The possible exchange mechanisms responsible for the ferromagnetism are discussed in light of the energy levels of dopants in the host oxides. In addition, Co and Cu co-doped TiO(2) samples are studied in order to understand the role of point defects in establishing room temperature ferromagnetism. The parameters calculated from the bound magnetic polaron (BMP) and Jorgensen's optical electronegativity models offer a satisfactory explanation of the defect-driven ferromagnetism in the doped/co-doped samples.

  8. Synthesis, characterization and degradation of Bisphenol A using Pr, N co-doped TiO 2 with highly visible light activity

    NASA Astrophysics Data System (ADS)

    Yang, Juan; Dai, Jun; Li, Jiantong

    2011-08-01

    Praseodymium and nitrogen co-doped titania (Pr/N-TiO 2) photocatalysts, which could degrade Bisphenol A (BPA) under visible light irradiation, were prepared by the modified sol-gel process. Tetrabutyl titanate, urea and praseodymium nitrate were used as the sources of titanium, nitrogen and praseodymium, respectively. The resulting materials were investigated by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), UV-vis absorbance spectroscopy, X-ray photoelectron spectroscopy (XPS), N 2 adsorption-desorption isotherm and Fourier transform infrared spectra (FTIR). It was found that Pr doping inhibited the growth of crystalline size and the transformation from anatase to rutile. The degradation of BPA under visible light illumination was taken as probe reaction to evaluate the photo-activity of the co-doped photocatalyst. In our experiments, the optimal dopant amount of Pr was 1.2 mol% and the calcination temperature was 500 °C for the best photocatalytic activity. Pr/N-TiO 2 samples exhibited enhanced visible-light photocatalytic activity compared to N-TiO 2, undoped TiO 2 and commercial P25. The nitrogen atoms were incorporated into the crystal of titania and could narrow the band gap energy. Pr doping could slow the radiative recombination of photogenerated electrons and holes in TiO 2. The improvement of photocatalytic activity was ascribed to the synergistic effects of nitrogen and Pr co-doping.

  9. Ultrasonic-assisted sol-gel synthesis of samarium, cerium co-doped TiO2 nanoparticles with enhanced sonocatalytic efficiency.

    PubMed

    Eskandarloo, Hamed; Badiei, Alireza; Behnajady, Mohammad A; Ziarani, Ghodsi Mohammadi

    2015-09-01

    In this work, pure TiO2 and samarium, cerium mono-doped and co-doped TiO2 catalysts were synthesized by an ultrasonic-assisted sol-gel method and their sonocatalytic efficiency studied toward removal of Methyl Orange as a model organic pollutant from the textile industry. The relationship of structure and sonocatalytic performance of catalysts was established by using various techniques, such as XRD, TEM, SEM, EDX, DRS, and PL. A comparison on the removal efficiency of sonolysis alone and sonocatalytic processes was performed. The results showed that the samarium, cerium co-doped TiO2 catalyst with narrower band gap energy and smaller particle size leads to a rapid removal of pollutant. It was believed that Sm(3+) and Ce(4+) ions can serve as superficial trapping for electrons at conduction band of TiO2 and prolonged the lifetime of electron-hole pairs. Finally, the effect of synthesis and operational variables on the sonocatalytic activity of co-doped TiO2 catalyst was studied and optimized using response surface methodology as a statistical technique. The results showed that the maximum removal efficiency (96.33%) was achieved at the optimum conditions: samarium content of 0.6 wt%, cerium content of 0.82 wt%, initial pollutant concentration of 4.31 mg L(-1), catalyst dosage of 0.84 mg L(-1), ultrasonic irradiation power of 700 W, and irradiation time of 50 min.

  10. Strain-dependent electronic and magnetic of Co-doped monolayer of WSe2

    NASA Astrophysics Data System (ADS)

    Wu, Ninghua; Zhao, Xu; Wang, Tianxing

    2016-10-01

    We perform first-principles calculation to investigate electronic and magnetic properties of Co-doped WSe2 monolayer with strains from -10% to 10%. We find that Co can induce magnetic moment about 0.894 μB, the Co-doped WSe2 monolayer is a magnetic semiconductor material without strain. The doped system shows half-metallic properties under tensile strain, and the largest half-metal gap is 0.147 eV at 8% strain. The magnetic moment (0.894 μB) increases slightly from 0% to 6%, and jumps into about 3 μB at 8% and 10%, which presents high-spin state configurations. When we applied compressive strain, the doped system shows a half-metallic feature at -2% strain, and the magnetic moment jumps into 1.623 μB at -4% strain, almost two times as the original moment 0.894 μB at 0% strain. The magnetic moment vanishes at -7% strain. The Co-doped WSe2 can endure strain from -6% to 10%. Strain changes the redistribution of charges and magnetic moment. Our calculation results show that the Co-doped WSe2 monolayer can transform from magnetic semiconductor to half-metallic material under strain.

  11. Study on the characteristics of an Er/Yb co-doped double cladding fiber laser

    NASA Astrophysics Data System (ADS)

    Qu, Zhou; Li, Qiushi; Yan, Mingliang

    2009-07-01

    An Er/Yb co-doped double cladding fiber laser pumped at 980 nm was optimized. The double-cladding fiber laser with whole fiber was obtained by end-pumping and utilizing fiber bragg grating as a resonator. The output power of laser was analyzed along the changes of output grating reflectance (L=10m) as well as the fiber length (R2=4%). Consequently, a fiber with 4 m Er / Yb co-doped double cladding was employed as gain medium while a fiber of which the reflectance was approximately 15% was used as output resonator mirror. Thereafter the technical indexes of EYDF(Er / Yb Double cladding Fiber) were measured. The absorption maximum of fiber core Er3+ was higher than 30dB/m and material gain maximum was observed at 1535nm. Moreover, the diameters of fiber core and inner cladding of double-cladding fiber grating were 6μm and 125μm respectively however the diameters of fiber core and inner cladding of Er/Yb co-doped double cladding fiber were 7μm and 130μm separately.According to the experimental data, a fiber laser with 4 m Er / Yb co-doped double cladding and launched maximum pump power of 3.4 W was set up. Proposed laser shows the maximum output power of 1.25 W and slope efficiency of 40%.

  12. (Al, Er) co-doped ZnO nanoparticles for photodegradation of rhodamine blue

    NASA Astrophysics Data System (ADS)

    Ghomri, R.; Shaikh, M. Nasiruzzaman; Ahmed, M. I.; Bououdina, M.; Ghers, M.

    2016-10-01

    Pure and co-doped (Al, Er) ZnO nanoparticles (NPs) have been synthesized by hydrothermal method using (Zn, Er and Al) nitrates. X-ray diffraction patterns reveal the formation of single phase of ZnO würtzite-type structure. The crystallite size for pure ZnO is in the order of 26.5 nm which decreases up to the range 14.2-22.0 nm after (Al, Er) co-doping. SEM micrographs show that the specimen is composed of regular spherical particles in the nanoscale regime with homogeneous size distribution and high tendency to agglomeration. FTIR spectra exhibit absorption lines located at wavenumbers corresponding to vibration modes between the constituent atoms. Raman spectra recorded under excitation ( λ exc = 632.8 nm) reveal peaks related to modes of transverse and longitudinal optical phonons of the würtzite ZnO structure. The energy band gap E g of ZnO:(Al, Er) NPs ranges in 3.264-3.251 eV. The photocatalytic activity of pure and co-doped (Al, Er) ZnO NPs was evaluated by the photodegradation of rhodamine blue under an irradiation of wavelength 554 nm. It is found that a photodegradation rate above 90 % could be achieved for a period of time of 40 min for pure ZnO and 120 min for (Al, Er) co-doped ZnO. A photodegradation mechanism is proposed.

  13. Effect of photocatalytic oxidation technology on GaN CMP

    NASA Astrophysics Data System (ADS)

    Wang, Jie; Wang, Tongqing; Pan, Guoshun; Lu, Xinchun

    2016-01-01

    GaN is so hard and so chemically inert that it is difficult to obtain a high material removal rate (MRR) in the chemical mechanical polishing (CMP) process. This paper discusses the application of photocatalytic oxidation technology in GaN planarization. Three N-type semiconductor particles (TiO2, SnO2, and Fe2O3) are used as catalysts and added to the H2O2-SiO2-based slurry. By optical excitation, highly reactive photoinduced holes are produced on the surface of the particles, which can oxidize OH- and H2O absorbed on the surface of the catalysts; therefore, more OH* will be generated. As a result, GaN MRRs in an H2O2-SiO2-based polishing system combined with catalysts are improved significantly, especially when using TiO2, the MRR of which is 122 nm/h. The X-ray photoelectron spectroscopy (XPS) analysis shows the variation trend of chemical composition on the GaN surface after polishing, revealing the planarization process. Besides, the effect of pH on photocatalytic oxidation combined with TiO2 is analyzed deeply. Furthermore, the physical model of GaN CMP combined with photocatalytic oxidation technology is proposed to describe the removal mechanism of GaN.

  14. High field effects of GaN HEMTs.

    SciTech Connect

    Barker, Joy; Shul, Randy John

    2004-09-01

    This report represents the completion of a Laboratory-Directed Research and Development (LDRD) program to develop and fabricate geometric test structures for the measurement of transport properties in bulk GaN and AlGaN/GaN heterostructures. A large part of this study was spent examining fabrication issues related to the test structures used in these measurements, due to the fact that GaN processing is still in its infancy. One such issue had to do with surface passivation. Test samples without a surface passivation, often failed at electric fields below 50 kV/cm, due to surface breakdown. A silicon nitride passivation layer of approximately 200 nm was used to reduce the effects of surface states and premature surface breakdown. Another issue was finding quality contacts for the material, especially in the case of the AlGaN/GaN heterostructure samples. Poor contact performance in the heterostructures plagued the test structures with lower than expected velocities due to carrier injection from the contacts themselves. Using a titanium-rich ohmic contact reduced the contact resistance and stopped the carrier injection. The final test structures had an etch constriction with varying lengths and widths (8x2, 10x3, 12x3, 12x4, 15x5, and 16x4 {micro}m) and massive contacts. A pulsed voltage input and a four-point measurement in a 50 {Omega} environment was used to determine the current through and the voltage dropped across the constriction. From these measurements, the drift velocity as a function of the applied electric field was calculated and thus, the velocity-field characteristics in n-type bulk GaN and AlGaN/GaN test structures were determined. These measurements show an apparent saturation velocity near to 2.5x10{sup 7} cm/s at 180 kV/cm and 3.1x10{sup 7} cm/s, at a field of 140 kV/cm, for the bulk GaN and AlGaN heterostructure samples, respectively. These experimental drift velocities mark the highest velocities measured in these materials to date and confirm

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

    SciTech Connect

    Ahn, Shihyun; Zhu, Weidi; Dong, Chen; Le, Lingcong; Hwang, Ya-Hsi; Kim, Byung-Jae; Ren, Fan; Pearton, Stephen J.; Lind, Aaron G.; Jones, Kevin S.; Kravchenko, I. I.; Zhang, Ming-Lan

    2015-04-21

    Here we studied the effect of buffer layer quality on dc characteristics of AlGaN/GaN high electron mobility (HEMTs). AlGaN/GaN HEMT structures with 2 and 5 μm GaN buffer layers on sapphire substrates from two different vendors with the same Al concentration of AlGaN were used. The defect densities of HEMT structures with 2 and 5 μm GaN buffer layer were 7 × 109 and 5 × 108 cm₋2, respectively, as measured by transmission electron microscopy. There was little difference in drain saturation current or in transfer characteristics in HEMTs on these two types of buffer. However, there was no dispersion observed on the nonpassivated HEMTs with 5 μm GaN buffer layer for gate-lag pulsed measurement at 100 kHz, which was in sharp contrast to the 71% drain current reduction for the HEMT with 2 μm GaN buffer layer.

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

    DOE PAGES

    Ahn, Shihyun; Zhu, Weidi; Dong, Chen; Le, Lingcong; Hwang, Ya-Hsi; Kim, Byung-Jae; Ren, Fan; Pearton, Stephen J.; Lind, Aaron G.; Jones, Kevin S.; et al

    2015-04-21

    Here we studied the effect of buffer layer quality on dc characteristics of AlGaN/GaN high electron mobility (HEMTs). AlGaN/GaN HEMT structures with 2 and 5 μm GaN buffer layers on sapphire substrates from two different vendors with the same Al concentration of AlGaN were used. The defect densities of HEMT structures with 2 and 5 μm GaN buffer layer were 7 × 109 and 5 × 108 cm₋2, respectively, as measured by transmission electron microscopy. There was little difference in drain saturation current or in transfer characteristics in HEMTs on these two types of buffer. However, there was no dispersionmore » observed on the nonpassivated HEMTs with 5 μm GaN buffer layer for gate-lag pulsed measurement at 100 kHz, which was in sharp contrast to the 71% drain current reduction for the HEMT with 2 μm GaN buffer layer.« less

  17. Surface passivation of tellurium-doped GaAs nanowires by GaP: Effect on electrical conduction

    SciTech Connect

    Darbandi, A.; Salehzadeh, O.; Watkins, S. P.; Kuyanov, P.; LaPierre, R. R.

    2014-06-21

    We report on the surface passivation of Au-assisted Te-doped GaAs nanowires (NWs) grown by metalorganic vapor phase epitaxy. The electrical properties of individual free standing NWs were assessed using a tungsten nano-probe inside a scanning electron microscope. The diameter independent apparent resistivity of both strained and relaxed passivated NWs suggests the unpinning of the Fermi level and reduction of sidewalls surface states density. Similar current-voltage properties were observed for partially axially relaxed GaAs/GaP NWs. This indicates a negligible contribution of misfit dislocations in the charge transport properties of the NWs. Low temperature micro-photoluminescence (μ-PL) measurements were also carried out for both uncapped and passivated GaAs NWs. The improvement of the integrated (μ-PL) intensity for GaAs/GaP NWs further confirms the effect of passivation.

  18. Oxygen in GaAs - Direct and indirect effects

    NASA Technical Reports Server (NTRS)

    Gatos, H. C.; Skowronski, M.; Pawlowicz, L.; Lagowski, J.

    1984-01-01

    Oxygen has profound effects on the key electronic properties and point defects of GaAs crystals. Thus, when added in the growth system, it decreases the free electron concentration and enhances the concentration of deep donors in the resulting crystals. Both of these effects are highly beneficial for achieving semi-insulating material and have been utilized for that purpose. They have been attributed to the tendency of oxygen to getter silicon impurities during crystal growth. Only recently, it has been found that oxygen in GaAs introduces also a midgap level, ELO, with essentially the same activation energy as EL2 but with four times greater electron capture cross section. The present report reassesses the electrical and optical properties of the midgap levels in GaAs crystals grown by the horizontal Bridgman (HB) and the Czochralski-LEC techniques. Emphasis is placed on the identification of the specific effects of ELO.

  19. Effect of wet oxidized AlxGa1-xAs layer on the interdiffusion of InGaAs/GaAs quantum wells

    NASA Astrophysics Data System (ADS)

    Choe, Joong-Seon; Ryu, Sang-Wan; Choe, Byung-Doo; Lim, H.

    1998-06-01

    The effect of wet oxidized AlAs cap layer and AlGaAs interlayer on the thermal stability of In0.2Ga0.8As/GaAs quantum well (QW) is studied. The QW interdiffusion rate is observed to increase with the Al composition of the AlxGa1-xAs interlayer until x reaches about 0.5 and then saturate for x⩾0.5. When the oxidation is performed at 380 °C for 15 min, the threshold value of x for the enhancement of QW interdiffusion is found to be 0.3. It is also confirmed that the QW interdiffusion can only be explained when the strain effect in InGaAs is taken into account.

  20. Improved visible light photocatalytic activity of fluorine and nitrogen co-doped TiO2 with tunable nanoparticle size

    NASA Astrophysics Data System (ADS)

    Cheng, Junyang; Chen, Jin; Lin, Wei; Liu, Yandong; Kong, Yan

    2015-03-01

    Fluorine and nitrogen co-doped TiO2 (F-N-TiO2) photocatalysts with enhanced photocatalytic activities were facilely synthesized by a simple one-step hydrothermal method using Ti(SO4)2 as an economical precursor, and hydrofluoric acid and ammonia as F and N source, respectively. The structure, morphology, and optical properties of produced nanoparticles were characterized by X-ray diffraction (XRD), N2 adsorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectra (FT-IR) methods. The synergistic effects of F and N doping were systematically examined by changing the molar ratio of F/N. Compared with the un-doped F or N mono-doped TiO2, the co-doped samples exhibited significantly improved photocatalytic performance due to their synergistic effects under visible light. It was shown that F dopant promoted the crystal growth and crystallinity of samples, while N dopant hindered it to some extent, which resulted in the tunable particle size of obtained F-N-TiO2 materials. The effects of F and N dopants on the enhanced photocatalytic activity of modified TiO2 materials were also discussed. The degradation rate of methylene blue (MB) was achieved at 97.31% after 5 h reaction under visible light over the optimized sample of FN3.5T. The materials also showed excellent stability according to the recycling tests of the photodegradation of MB.

  1. Sustained phase separation and spin glass in Co-doped KxFe2 -ySe2 single crystals

    NASA Astrophysics Data System (ADS)

    Ryu, Hyejin; Wang, Kefeng; Opacic, M.; Lazarevic, N.; Warren, J. B.; Popovic, Z. V.; Bozin, Emil S.; Petrovic, C.

    2015-11-01

    We present Co substitution effects in KxFe2 -y -zCozSe2 (0.06 ≤z ≤1.73 ) single-crystal alloys. By 3.5% of Co doping superconductivity is suppressed, whereas phase separation of semiconducting K2Fe4Se5 and superconducting/metallic KxFe2Se2 is still present. We show that the arrangement and distribution of the superconducting phase (stripe phase) are connected with the arrangement of K, Fe, and Co atoms. Semiconducting spin glass is found in proximity to the superconducting state, persisting for large Co concentrations. At high Co concentrations a ferromagnetic metallic state emerges above the spin glass. This is coincident with changes of the unit cell and arrangement and connectivity of the stripe conducting phase.

  2. Sustained phase separation and spin glass in Co-doped KxFe2-ySe2 single crystals

    DOE PAGES

    Ryu, Hyejin; Wang, Kefeng; Opacic, M.; Lazarevic, N.; Warren, J. B.; Popovic, Z. V.; Bozin, Emil S.; Petrovic, C.

    2015-11-19

    We describe Co substitution effects in KxFe2-y-zCozSe2 (0.06 ≤ z ≤ 1.73) single crystal alloys. By 3.5% of Co doping superconductivity is suppressed whereas phase separation of semiconducting K2Fe4Se5 and superconducting/metallic KxFe2Se2 is still present. We show that the arrangement and distribution of superconducting phase (stripe phase) is connected with the arrangement of K, Fe and Co atoms. Semiconducting spin glass is found in proximity to superconducting state, persisting for large Co concentrations. At high Co concentrations ferromagnetic metallic state emerges above the spin glass. This is coincident with changes of the unit cell, arrangement and connectivity of stripemore » conducting phase.« less

  3. Effect of buffer structures on AlGaN/GaN high electron mobility transistor reliability

    SciTech Connect

    Liu, L.; Xi, Y. Y.; Ren, F.; Pearton, S. J.; Laboutin, O.; Cao, Yu; Johnson, Wayne J.; Kravchenko, Ivan I

    2012-01-01

    AlGaN/GaN high electron mobility transistors (HEMTs) with three different types of buffer layers, including a GaN/AlGaN composite layer, or 1 or 2 lm GaN thick layers, were fabricated and their reliability compared. The HEMTs with the thick GaN buffer layer showed the lowest critical voltage (Vcri) during off-state drain step-stress, but this was increased by around 50% and 100% for devices with the composite AlGaN/GaN buffer layers or thinner GaN buffers, respectively. The Voff - state for HEMTs with thin GaN and composite buffers were 100 V, however, this degraded to 50 60V for devices with thick GaN buffers due to the difference in peak electric field near the gate edge. A similar trend was observed in the isolation breakdown voltage measurements, with the highest Viso achieved based on thin GaN or composite buffer designs (600 700 V), while a much smaller Viso of 200V was measured on HEMTs with the thick GaN buffer layers. These results demonstrate the strong influence of buffer structure and defect density on AlGaN/GaN HEMT performance and reliability.

  4. Humidity effects on tribochemical removal of GaAs surfaces

    NASA Astrophysics Data System (ADS)

    Yu, Bingjun; Gao, Jian; Jin, Chenning; Xiao, Chen; Wu, Jiang; Liu, Huiyun; Jiang, Shulan; Chen, Lei; Qian, Linmao

    2016-06-01

    Defect-free tribochemical removal of gallium arsenide (GaAs) was demonstrated in vacuum, dry air, and various humidity environments by scratching with a SiO2 tip. The removal depth increases with increasing relative humidity (1-90%), and reaches its maximum value in water. A perfect crystal matrix without defects was observed in the cross section of the scratched groove using a transmission electron microscope. A model based on reactive tip scratching-induced oxidation, water solubility of debris, and adhesion effect was proposed to interpret tribochemical removal of GaAs surface. This study provides new insights into defect-free and site-controlled nanofabrication of GaAs.

  5. Electrical effects of plasma damage in p-GaN

    SciTech Connect

    Cao, X.A.; Pearton, S.J.; Zhang, A.P.; Dang, G.T.; Ren, F.; Shul, R.J.; Zhang, L.; Hickman, R.; Van Hove, J.M.

    1999-10-01

    The reverse breakdown voltage of p-GaN Schottky diodes was used to measure the electrical effects of high density Ar or H{sub 2} plasma exposure. The near surface of the p-GaN became more compensated through introduction of shallow donor states whose concentration depended on ion flux, ion energy, and ion mass. At high fluxes or energies, the donor concentration exceeded 10{sup 19}&hthinsp;cm{sup {minus}3} and produced {ital p}-to-{ital n} surface conversion. The damage depth was established as {approximately}400 {Angstrom} based on electrical and wet etch rate measurements. Rapid thermal annealing at 900&hthinsp;{degree}C under a N{sub 2} ambient restored the initial electrical properties of the p-GaN. {copyright} {ital 1999 American Institute of Physics.}

  6. Effect of high density H 2 plasmas on InGaP/GaAs and AlGaAs/GaAs HEMTs

    NASA Astrophysics Data System (ADS)

    Ren, F.; Kopf, R. F.; Kuo, J. M.; Lothian, J. R.; Lee, J. W.; Pearton, S. J.; Shul, R. J.; Constantine, C.; Johnson, D.

    1998-05-01

    InGaP/GaAs and AlGaAs/GaAs high electron mobility transistors have been exposed to inductively coupled plasma or electron cyclotron resonance H 2 plasmas as a function of pressure, source power and rf chuck power. The transconductance, gate ideality factor and saturated drain-source current are all degraded by the plasma treatment. Two mechanisms are identified: passivation of Si dopants in the InGaP or AlGaAs donor layers by H 0 and lattice disorder created by H + and H 2+ ion bombardment. HEMTs are found to be more susceptible to plasma-induced degradation than heterojunction bipolar transistors.

  7. Synthesis, structural, optical, and magnetic properties of Co doped, Sm doped and Co+Sm co-doped ZnS nanoparticles

    NASA Astrophysics Data System (ADS)

    Poornaprakash, B.; Poojitha, P. T.; Chalapathi, U.; Subramanyam, K.; Park, Si-Hyun

    2016-09-01

    The compositional, structural, optical and magnetic properties of ZnS, Zn0.98Co0.02S, Zn0.98Sm0.02S and Zn0.96Co0.02Sm0.02S nanoparticles synthesized by a hydrothermal method are presented and discussed. X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) studies revealed that all the samples exhibited cubic structure without any impurity phases. X-ray photoelectron spectroscopy (XPS) results revealed that the Co and Sm ions existed in +2 and +3 states in these samples. The photoluminescence (PL) spectra of all the samples exhibited a broad emission in the visible region. The room temperature magnetization versus applied magnetic field (M-H) curves demonstrated that the Sm+Co doped nanoparticles exhibited enhanced ferromagnetic behavior compare to Co and Sm individually doped ZnS nanoparticles, which is probably due to the exchange interaction between conductive electrons with local spin polarized electrons on the Co2+ or Sm3+ ions. This study intensifies the understanding of the novel performances of co-doped ZnS nanoparticles and also provides possibilities to fabricate future spintronic devices.

  8. Piezoelectric Effects on the Optical Properties of GaN/Al(x)Ga(1-x)N Multiple Quantum Wells

    SciTech Connect

    Botchkarev, A.; Chow, W.W.; Jiang, H.X.; Kim, H.S.; Lin, J.Y.; Morkoc, H.

    1998-11-10

    Piezoelectric effects on the optical properties of GaN/AlGaN multiple quantum wells (MQWS) have been investigated by picosecond time-resolved photoluminescence (PL) measurements. For MQWS with well thickness 30 and 40 the excitonic transition peak positions at 10 K in continuous wave (CW) spectra are red-shifted with respect to the GaN epilayer by 17 meV and 57 meV, respectively. The time-resolved PL spectra of the 30 and 40 well MQWS reveal that the excitonic transition is in fact blue-shifted at early delay times due to quantum confinement of carriers. The spectral peak position shifts toward lower energies as the delay time increases and becomes red-shifted at longer delay times. We have demonstrated that the results described above is due to the presence of the piezoelectric field in the GaN wells of GaN/AlGaN MQWS subject to elastic strain together with screening of the photoexcited carriers. By comparing experimental and calculation results, we conclude that the piezoelectric field strength in GaN/Al.15G~.85N MQWS has a lower limit value of about 560 kV/cm: The electron and hole wave function distributions have also been obtained. The implication of our findings on the practical applications of GaN based optoelectronic devices is also discussed.

  9. Polarization Effects of GaN and AlGaN: Polarization Bound Charge, Band Bending, and Electronic Surface States

    NASA Astrophysics Data System (ADS)

    Eller, Brianna S.; Yang, Jialing; Nemanich, Robert J.

    2014-12-01

    GaN-based devices are currently limited by reliability issues such as gate leakage and current collapse, where the mechanisms responsible for degradation are closely related to the electronic surface state configuration. Therefore, understanding the electronic surface state configuration of GaN-based materials will help improve device performance. Since GaN has an inherent polarization, these materials are also subject to a bound polarization charge, which influences the electronic state configuration. In this study, the surface band bending of N-face GaN, Ga-face GaN, and Ga-face AlGaN was measured with x-ray photoemission spectroscopy after various cleaning steps to investigate the effects of the polarization. Despite the different surface bound charge on these materials, similar band bending was observed regardless of the magnitude or direction of the charge. Specifically, the band bending varied from -0.1 eV to 0.9 eV on these samples, which supported the models of a Fermi level pinning state at ˜0.4 eV to 0.8 eV below the conduction band. Based on available literature, we suggest this pinning state is indirectly evident of a nitrogen vacancy or gallium-dangling bond.

  10. Enhancement of carrier mobility in thin Ge layer by Sn co-doping

    NASA Astrophysics Data System (ADS)

    Prucnal, S.; Liu, F.; Berencén, Y.; Vines, L.; Bischoff, L.; Grenzer, J.; Andric, S.; Tiagulskyi, S.; Pyszniak, K.; Turek, M.; Drozdziel, A.; Helm, M.; Zhou, S.; Skorupa, W.

    2016-10-01

    We present the development, optimization and fabrication of high carrier mobility materials based on GeOI wafers co-doped with Sn and P. The Ge thin films were fabricated using plasma-enhanced chemical vapour deposition followed by ion implantation and explosive solid phase epitaxy, which is induced by millisecond flash lamp annealing. The influence of the recrystallization mechanism and co-doping of Sn on the carrier distribution and carrier mobility both in n-type and p-type GeOI wafers is discussed in detail. This finding significantly contributes to the state-of-the-art of high carrier mobility-GeOI wafers since the results are comparable with GeOI commercial wafers fabricated by epitaxial layer transfer or SmartCut technology.

  11. Preparation of superior lubricious amorphous carbon films co-doped by silicon and aluminum

    NASA Astrophysics Data System (ADS)

    Liu, Xiaoqiang; Hao, Junying; Yang, Jun; Zheng, Jianyun; Liang, Yongmin; Liu, Weimin

    2011-09-01

    Silicon (Si) and aluminum (Al) co-doped amorphous carbon films ((Si, Al)-C:H) were deposited on Si and stainless steel substrates by radio frequency (13.56 MHz) magnetron sputtering. The Al and Si were found to jointly regulate the hybridized carbon bonds. Mechanical properties of the films were detected by nano-indention and scratch tests. The nano-indention results revealed that all the samples exhibited good elastic recovery rate, among which the highest one was beyond 84%. Besides co-regulating the hybridizations of carbon, the co-doped Si and Al also had a common regulation on the mechanical and tribological properties. Especially, the film containing 1.6 at. % of Si and 0.9 at. % of Al showed a super-low friction (< 0.01) and a superior wear resistance in ambient air.

  12. Low-temperature ferromagnetic properties in Co-doped Ag{sub 2}Se nanoparticles

    SciTech Connect

    Yang, Fengxia E-mail: xia9020@hust.edu.cn; Yu, Gen; Han, Chong; Liu, Tingting; Zhang, Duanming; Xia, Zhengcai E-mail: xia9020@hust.edu.cn

    2014-01-06

    β-Ag{sub 2}Se is a topologically nontrivial insulator. The magnetic properties of Co-doped Ag{sub 2}Se nanoparticles with Co concentrations up to 40% were investigated. The cusp of zero-field-cooling magnetization curves and the low-temperature hysteresis loops were observed. With increasing concentration of Co{sup 2+} ions mainly substituting Ag{sub I} sites in the Ag{sub 2}Se structure, the resistivity, Curie temperature T{sub c}, and magnetization increased. At 10 T, a sharp drop of resistance near T{sub c} was detected due to Co dopants. The ferromagnetic behavior in Co-doped Ag{sub 2}Se might result from the intra-layer ferromagnetic coupling and surface spin. This magnetic semiconductor is a promising candidate in electronics and spintronics.

  13. Fe/Co doped molybdenum diselenide: a promising two-dimensional intermediate-band photovoltaic material.

    PubMed

    Zhang, Jiajia; He, Haiyan; Pan, Bicai

    2015-05-15

    An intermediate-band (IB) photovoltaic material is an important candidate in developing the new-generation solar cell. In this paper, we propose that the Fe-doped or the Co-doped MoSe2 just meets the required features in IB photovoltaic materials. Our calculations demonstrate that when the concentration of the doped element reaches 11.11%, the doped MoSe2 shows a high absorptivity for both infrared and visible light, where the photovoltaic efficiency of the doped MoSe2 is as high as 56%, approaching the upper limit of photovoltaic efficiency of IB materials. So, the Fe- or Co-doped MoSe2 is a promising two-dimensional photovoltaic material.

  14. Enhanced electrical activation in In-implanted Ge by C co-doping

    SciTech Connect

    Feng, R. Kremer, F.; Mirzaei, S.; Medling, S. A.; Ridgway, M. C.; Sprouster, D. J.; Decoster, S.; Pereira, L. M. C.; Glover, C. J.; Russo, S. P.

    2015-11-23

    At high dopant concentrations in Ge, electrically activating all implanted dopants is a major obstacle in the fulfillment of high-performance Ge-channel complementary metal oxide semiconductor devices. In this letter, we demonstrate a significant increase in the electrically-active dopant fraction in In-implanted Ge by co-doping with the isovalent element C. Electrical measurements have been correlated with x-ray absorption spectroscopy and transmission electron microscopy results in addition to density functional theory simulations. With C + In co-doping, the electrically active fraction was doubled and tripled at In concentrations of 0.2 and 0.7 at. %, respectively. This marked improvement was the result of C-In pair formation such that In-induced strain in the Ge lattice was reduced while the precipitation of In and the formation of In-V clusters were both suppressed.

  15. First-principles calculation on electronic properties of B and N co-doping carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Jianhao, Shi; Tong, Zhao; Xuechao, Li; Meng, Huo; Rundong, Wan

    2016-03-01

    We apply the Heyd-Scuseria-Ernzerhof hybrid functional calculation to study the (2, 3) nanotube co-doped with various compositions of nitrogen and boron atoms. We find that the bandgaps and other properties of doped nanotubes oscillate with the doped compositions. Our study should shed light on the understanding of the properties of doped small nanotubes. This might have potential in designing new nano electronic-devices.

  16. Yb/Er co-doped phosphate all-solid single-mode photonic crystal fiber.

    PubMed

    Wang, Longfei; He, Dongbing; Feng, Suya; Yu, Chunlei; Hu, Lili; Qiu, Jianrong; Chen, Danping

    2014-01-01

    An all-solid Yb(3+)/Er(3+) co-doped single-mode phosphate photonic crystal fiber (PCF) with Watt-level output power and 20 μm core diameter is demonstrated for the first time. A PCF whose refractivity of the active core is lower than that of the background glass is suggested and theoretically confirmed to be in single-mode operation at 40 μm core diameter.

  17. Structural, optical and dielectric property of Co doped Bi{sub 2}Fe{sub 4}O{sub 9}

    SciTech Connect

    Swain, Smita Mohapatra, S. R. Sahoo, B. Singh, A. K.

    2014-04-24

    Multiferroic Bi{sub 2}Fe{sub 4}O{sub 9} and Co doped Bi{sub 2}Fe{sub 4}O{sub 9} are prepared by solid state route reaction method using bismuth oxide(Bi{sub 2}O{sub 3}), iron oxide(Fe{sub 2}O{sub 3}) and cobalt oxide (Co{sub 3}O{sub 4}). Their structural optical and dielectric properties are studied and compared. X-ray diffraction (XRD) results confirm that there is no change in crystal structure due to Co doping. From dielectric constant measurement we conclude that dielectric constant increases due to Co doping. UV-Visible plot shows due to Co doping bang gap energy increases.

  18. Microstructural analysis and thermoelectric properties of Sn-Al co-doped ZnO ceramics

    NASA Astrophysics Data System (ADS)

    Hoemke, Joshua; Khan, Atta Ullah; Yoshida, Hidehiro; Mori, Takao; Tochigi, Eita; Shibata, Naoya; Ikuhara, Yuichi; Sakka, Yoshio

    2016-08-01

    Sn-Al co-doped polycrystalline ZnO ceramics were prepared by sintering in air. Phase and microstructure analysis was performed by X-ray diffraction and SEM-EDS and thermoelectric properties were measured. XRD analysis showed a ZnO primary phase as well as secondary phase peaks due to the formation of a Zn2SnO4 spinel phase or SnO2(ZnO:Sn-Al)m intergrowth phase. SEM analysis revealed a dense microstructure with a small number of nanometric pores, consistent with the measured density of 5.48 g/cm3. An activated electrical conductivity characteristic of a semiconducting material was observed as well as a negative Seebeck coefficient with both values increasing in absolute value from RT to 730 °C. The power factor had a maximum value of 3.73×10-4 W m-1 K-2 at 730 °C. Thermal conductivity measurements showed a significant reduction over the measured temperature range compared to undoped ZnO. This could be attributed to grain size reduction, the formation of a nanoscale secondary phase or a reduction in crystallinity caused by Sn-Al co-doping. A maximum ZT of 0.06 was obtained at 750 °C for the Sn-Al co-doped ZnO ceramics.

  19. Observation of low field microwave absorption in co-doped ZnO system

    NASA Astrophysics Data System (ADS)

    Mahule, Tebogo S.; Srinivasu, Vijaya V.; Das, Jayashree

    2016-10-01

    Room temperature low field microwave absorption (LFMA) in magnetic materials find application in microwave absorbers and low field sensors. However not all the magnetic materials show LFMA and the phenomenon is not fully understood. We report on the observation of low field microwave absorption (LFMA) or the non-resonant microwave absorption (NRMA) in the transition metal (TM) co-doped ZnO samples of the composition Zn1-x(TM:TM)xO synthesized by solid state reaction technique. LFMA peaks and hysteresis matches very well with that of the magnetization hysteresis loop and the anisotropy fields at room temperature similar to the reports in the literature for other magnetic systems. However we show through our careful experiments that such a correlation between LFMA and the magnetization does not survive at low temperatures and particularly at 10 K the LFMA hysteresis collapses in our TM co-doped ZnO system; whereas the magnetization hysteresis loop becomes very big and anisotropy field becomes bigger in the range of kOe. We interpret the LFMA as field dependent surface impedance or eddy current losses, in terms of a possible role of anomalous hall resistivity that follows magnetization and the ordinary hall resistivity that only follows the applied field. We then argue that LFMA accordingly follows magnetization or applied field when AHE or OHE dominates respectively. Also we confirm the absence of LFMA signals in the rare earth co-doped ZnO system.

  20. Luminescence Properties of Sm3+/Eu3+ Co-Doped ZnO Quantum Dots.

    PubMed

    Liu, Fengyi; Li, Hong; Hu, Yajing; Na, Jin; Mou, Yun; Yang, Kun; Ye, Zuhu; Li, Mingyue; Xie, Ya-Hong

    2016-04-01

    In order to improve luminescence properties of semiconductor ZnO quantum dots (QDs), Sm3+/Eu3+ co-doped ZnO QDs have been controllably synthesized by sol-gel method in this paper. ZnO QDs have a spherical shape with mean diameter at about 5-6 nm, which was characterized by high-resolution transmission electron microscopy (HRTEM). ZnO QDs have hexagonal wurtzite structure with parts of Sm3+ and Eu3+ incorporated into the lattice, which was demonstrated by X-ray Diffraction (XRD). Luminescence properties at room temperature (RT) of different amount of Sm3+ and 2 mol% Eu3+ doped ZnO QDs were examined in-depth by optical spectra. In contrast to the Pr3+/Eu3+ co-doped fluorescent performance researched in our previous study, the photoluminescence (PL) spectra indicates the unique luminescence properties of Sm3+/Eu3+ co-doped ZnO QDs. In addition, fluorescence lifetimes were obtained to illustrate the luminous mechanism. PMID:27451672

  1. Gain dynamics in Er(3+):Yb(+) co-doped fiber amplifiers.

    PubMed

    Steinke, M; Neumann, J; Kracht, D; Wessels, P

    2015-06-01

    Understanding the gain dynamics of fiber amplifiers is essential for the implementation and active stabilization of low noise amplifiers or for coherent beam combining schemes. The gain dynamics of purely Er3+ or Yb3+ doped fiber amplifiers are well studied, whereas no analysis for co-doped systems, especially for Er3+:Yb3+ co-doped fiber amplifiers has been performed, so far. Here, we analyze for the first time the gain dynamics of Er3+:Yb3+ co-doped fiber amplifiers theoretically and experimentally. It is shown that due to the energy transfer between the Yb3+ and Er3+ ions a full analytical solution is not possible. Thus, we used numerical simulations to gain further insights. Comparison of experimental and numerical results shows good qualitative agreement. In addition, we were able to determine the Yb3+-Er3+ transfer function of the energy transfer experimentally.

  2. The effects of the porous buffer layer and doping with dysprosium on internal stresses in the GaInP:Dy/por-GaAs/GaAs(100) heterostructures

    SciTech Connect

    Seredin, P. V.; Gordienko, N. N.; Glotov, A. V.; Zhurbina, I. A.; Domashevskaya, E. P.; Arsent'ev, I. N. Shishkov, M. V.

    2009-08-15

    In structures with a porous buffer layer, residual internal stresses caused by a mismatch between the crystal-lattice parameters of the epitaxial GaInP alloy and the GaAs substrate are redistributed to the porous layer that acts as a buffer and is conducive to disappearance of internal stresses. Doping of the epitaxial layer with dysprosium exerts a similar effect on the internal stresses in the film-substrate structure.

  3. Cubic AlGaN/GaN Hetero-Junction Field-Effect Transistors with Normally-on and Normally-off Characteristics

    SciTech Connect

    Tschumak, E.

    2010-11-01

    The growth of cubic group III-nitrides is a direct way to eliminate polarization effects, which inherently limit the fabrication of normally-off hetero-junction field-effect transistors (HFETs) in GaN technology. HFET structures were fabricated of non-polar cubic AlGaN/GaN hetero layers grown by plasma assisted molecular beam epitaxy on free standing 3C-SiC (001). The electrical insulation of 3C-SiC was realized by Ar{sup +} implantation before c-AlGaN/GaN growth. HFETs with normally-off and normally-on characteristics were fabricated of cubic AlGaN/GaN. Capacitance-voltage characteristics of the gate contact were performed to detect the electron channel at the c-AlGaN/GaN hetero-interface.

  4. Valence band structure and magnetic properties of Co-doped Fe3O4(100) films

    NASA Astrophysics Data System (ADS)

    Ran, F. Y.; Tsunemaru, Y.; Hasegawa, T.; Takeichi, Y.; Harasawa, A.; Yaji, K.; Kim, S.; Kakizaki, A.

    2011-06-01

    Structural and magnetic properties, and the valence band structure of pure and Co-doped (up to 33%) Fe3O4(100) films were investigated. Reconstruction of the Fe3O4(100) surface is found to be blocked by Co doping. Doped Co ions in Fe3O4 are in a charge state of 2 + and substitute the Fe2+ in the B site of Fe3O4. All the films exhibit room temperature ferromagnetism. Co doping changes the coercivity and reduces saturation magnetization. The density of states near the Fermi level is reduced by Co doping due to the decrease of Fe2+ in the B site, which might responsible for the decrease in conductivity and magnetoresistance of Co-doped Fe3O4. The Verwey transition in the range of 100-120 K is observed for the pure Fe3O4 film, while no transition could be detected for Co-doped Fe3O4 films.

  5. Preparation and upconversion emission modification of Yb, Er co-doped Y2SiO5 inverse opal photonic crystals.

    PubMed

    Yan, Dong; Zhu, Jialun; Yang, Zhengwen; Wu, Hangjun; Wang, Rongfei; Qiu, Jianbei; Song, Zhiguo; Zhou, Dacheng; Yang, Yong; Yin, Zhaoyi

    2014-05-01

    Yb, Er co-doped Y2SiO5 inverse opal photonic crystals with three-dimensionally ordered macroporous were fabricated using polystyrene colloidal crystals as the template. Under 980 nm excitation, the effect of the photonic stopband on the upconversion luminescence of Er3+ ions has been investigated in the Y2SiO5:Yb, Er inverse opals. Significant suppression of the green or red UC emissions was detected if the photonic band-gap overlaps with the Er3+ ions emission band. PMID:24734639

  6. Co-doping induced coexistence of superconductivity and ferromagnetism in Bi3.9Co0.1O4S3

    NASA Astrophysics Data System (ADS)

    Yu, Chuan; Feng, Zhenjie; Yin, Xunqing; Li, Qing; Kang, Baojuan; Lu, Bo; Jing, Chao; Cao, Shixun; Zhang, Jincang

    2016-09-01

    The effects of Co doping on the physical properties of the Bi4O4S3 system was studied. We discovered that stable Bi3.9Co0.1O4S3 compound exhibits both long-range ferromagnetism and enhanced superconductivity with thermodynamic evidences for Tc ∼ 5.5 K. We found that there is an anomalous feature which represents superconducting transition in the hysteretic M-vs.-H loops for Bi3.9Co0.1O4S3 at T = 3 K.

  7. Mg doping and its effect on the semipolar GaN(1122) growth kinetics

    SciTech Connect

    Lahourcade, L.; Wirthmueller, A.; Monroy, E.; Chauvat, M. P.; Ruterana, P.; Laufer, A.; Eickhoff, M.

    2009-10-26

    We report the effect of Mg doping on the growth kinetics of semipolar GaN(1122) synthesized by plasma-assisted molecular-beam epitaxy. Mg tends to segregate on the surface, inhibiting the formation of the self-regulated Ga film which is used as a surfactant for the growth of undoped and Si-doped GaN(1122). We observe an enhancement of Mg incorporation in GaN(1122) compared to GaN(0001). Typical structural defects or polarity inversion domains found in Mg-doped GaN(0001) were not observed for the semipolar films investigated in the present study.

  8. Waveguide effect of GaAsSb quantum wells in a laser structure based on GaAs

    SciTech Connect

    Aleshkin, V. Ya.; Afonenko, A. A.; Dikareva, N. V.; Dubinov, A. A. Kudryavtsev, K. E.; Morozov, S. V.; Nekorkin, S. M.

    2013-11-15

    The waveguide effect of GaAsSb quantum wells in a semiconductor-laser structure based on GaAs is studied theoretically and experimentally. It is shown that quantum wells themselves can be used as waveguide layers in the laser structure. As the excitation-power density attains a value of 2 kW/cm{sup 2} at liquid-nitrogen temperature, superluminescence at the wavelength corresponding to the optical transition in bulk GaAs (at 835 nm) is observed.

  9. Effect of InGaAs interlayer on the properties of GaAs grown on Si (111) substrate by molecular beam epitaxy

    SciTech Connect

    Wen, Lei; Gao, Fangliang; Li, Jingling; Guan, Yunfang; Wang, Wenliang; Zhou, Shizhong; Lin, Zhiting; Zhang, Xiaona; Zhang, Shuguang E-mail: mssgzhang@scut.edu.cn; Li, Guoqiang E-mail: mssgzhang@scut.edu.cn

    2014-11-21

    High-quality GaAs films have been epitaxially grown on Si (111) substrates by inserting an In{sub x}Ga{sub 1−x}As interlayer with proper In composition by molecular beam epitaxy (MBE). The effect of In{sub x}Ga{sub 1−x}As (0 < x < 0.2) interlayers on the properties of GaAs films grown on Si (111) substrates by MBE has been studied in detailed. Due to the high compressive strain between InGaAs and Si, InGaAs undergoes partial strain relaxation. Unstrained InGaAs has a larger lattice constant than GaAs. Therefore, a thin InGaAs layer with proper In composition may adopt a close lattice constant with that of GaAs, which is beneficial to the growth of high-quality GaAs epilayer on top. It is found that the proper In composition in In{sub x}Ga{sub 1−x}As interlayer of 10% is beneficial to obtaining high-quality GaAs films, which, on the one hand, greatly compensates the misfit stress between GaAs film and Si substrate, and on the other hand, suppresses the formation of multiple twin during the heteroepitaxial growth of GaAs film. However, when the In composition does not reach the proper value (∼10%), the In{sub x}Ga{sub 1−x}As adopts a lower strain relaxation and undergoes a lattice constant smaller than unstrained GaAs, and therefore introduces compressive stress to GaAs grown on top. When In composition exceeds the proper value, the In{sub x}Ga{sub 1−x}As will adopt a higher strain relaxation and undergoes a lattice constant larger than unstrained GaAs, and therefore introduces tensile stress to GaAs grown on top. As a result, In{sub x}Ga{sub 1−x}As interlayers with improper In composition introduces enlarged misfit stress to GaAs epilayers grown on top, and deteriorates the quality of GaAs epilayers. This work demonstrates a simple but effective method to grow high-quality GaAs epilayers and brings up a broad prospect for the application of GaAs-based optoelectronic devices on Si substrates.

  10. Thermodynamically stable p-channel strained-layer AlGaAs/InGaAs/GaAs heterostructure field effect transistor

    NASA Astrophysics Data System (ADS)

    Baca, A. G.; Zipperian, T. E.; Howard, A. J.; Klem, J. F.; Tigges, C. P.

    1994-08-01

    Device characteristics of a thermodynamically stable p-channel, strained quantum-well heterostructure field effect transistor (HFET) are reported. The AlGaAs/InGaAs/GaAs material system was used to fabricate the p-channel HFETs with Al and In mole fractions of 0.20 and 0.18, respectively. Transconductances of 32 and 94 mS/mm were achieved at 300 and 77 K, respectively, for devices with 1.2 μm recessed gates. These numbers are comparable to InGaAs quantum-well, recessed gate pHFETs whose quantum-well thicknesses exceed the thermodynamic stability limit. These results have important implications for high performance self-aligned devices which require high-temperature processing.

  11. Thermodynamically stable [ital p]-channel strained-layer AlGaAs/InGaAs/GaAs heterostructure field effect transistor

    SciTech Connect

    Baca, A.G.; Zipperian, T.E.; Howard, A.J.; Klem, J.F.; Tigges, C.P. )

    1994-08-08

    Device characteristics of a thermodynamically stable [ital p]-channel, strained quantum-well heterostructure field effect transistor (HFET) are reported. The AlGaAs/InGaAs/GaAs material system was used to fabricate the [ital p]-channel HFETs with Al and In mole fractions of 0.20 and 0.18, respectively. Transconductances of 32 and 94 mS/mm were achieved at 300 and 77 K, respectively, for devices with 1.2 [mu]m recessed gates. These numbers are comparable to InGaAs quantum-well, recessed gate [ital p]HFETs whose quantum-well thicknesses exceed the thermodynamic stability limit. These results have important implications for high performance self-aligned devices which require high-temperature processing.

  12. TlGaInNAs/GaAs double quantum well structures: Effect of barrier layers and substrate orientation

    NASA Astrophysics Data System (ADS)

    Krishnamurthy, D.; Matsumoto, T.; Fujiwara, A.; Hasegawa, S.; Asahi, H.

    2007-04-01

    The quinary TlGaInNAs-based double quantum well (DQW) structures were grown on GaAs substrates by electron cyclotron resonance (ECR)-MBE and the samples were probed by secondary ion mass spectroscopy (SIMS). Light emitting diodes (LEDs) were fabricated using these DQW wafers and their electroluminescence (EL) behaviors were studied at different temperatures. The effects of different barrier layers and substrate orientations on the amount of Tl incorporation and on the temperature dependency of the EL peak wavelengths of the LEDs were studied. Higher incorporation of Tl into the quantum well (QW) region and the ensuing change in the temperature dependency of the peak wavelengths owing to the TlGaAs barrier layer are reported. GaAs substrates having (3 1 1)B orientation were found to allow more Tl incorporation as compared to (1 0 0) and (3 1 1)A oriented substrates. The LEDs fabricated out of the TlGaInNAs/TlGaAs/(3 1 1)B GaAs DQW structures showed the least temperature dependency of the EL peak wavelengths exemplifying the usefulness of Tl in the QW as well as barrier region.

  13. Effect of Light Absorption in InGaN/GaN Vertical Light-Emitting Diodes.

    PubMed

    Sung, Junho; Jeon, Ki-Seong; Lee, Min Woo; Lee, Eun Ah; Kim, Seon Ock; Song, Hooyoung; Choi, Hwanjoon; Kang, Mingu; Choi, Yoon-Ho; Ryu, Han-Youl; O, Beom-Hoan; Lee, Jeong Soo

    2015-07-01

    For evaluating the effect of light absorption in vertically structured thin film light-emitting diodes (VLEDs), we investigate the dependence of the efficiencies on the several specific parameters including thickness and doping concentration (N(D)) of the n-GaN layer, a design of hetero-structures of the n-GaN layer, and a number of pairs of multi-quantum wells (MQWs). Generally, there is a complementary relation between internal quantum efficiency (IQE) and light extraction efficiency (LEE). However, we confirmed that LEE determined by light absorption is more dominant than IQE in VLED structures with a textured surface, from numerical simulation and experimental results. Effect of light absorption is more prominent in the vertical chip with a textured surface than in that with a flat surface, because a travel length of light extracted from the textured surface is longer. Minimizing light absorption in VLEDs is a key technology for improving light output, and light absorption speaks for the index of enhancement by the general technologies for improving LEE.

  14. Effect of dislocation density on thermal boundary conductance across GaSb/GaAs interfaces

    SciTech Connect

    Hopkins, Patrick E.; Duda, John C.; Clark, Stephen P.; Hains, Christopher P.; Rotter, Thomas J.; Balakrishnan, Ganesh; Phinney, Leslie M.

    2011-04-18

    We report on the thermal boundary conductance across structurally-variant GaSb/GaAs interfaces characterized by different dislocations densities, as well as variably-rough Al/GaSb interfaces. The GaSb/GaAs structures are epitaxially grown using both interfacial misfit (IMF) and non-IMF techniques. We measure the thermal boundary conductance from 100 to 450 K with time-domain thermoreflectance. The thermal boundary conductance across the GaSb/GaAs interfaces decreases with increasing strain dislocation density. We develop a model for interfacial transport at structurally-variant interfaces in which phonon propagation and scattering parallels photon attenuation. We find that this model describes the measured thermal boundary conductances well.

  15. DRAM concept based on the hole gas transient effect in a AlGaN/GaN HEMT

    NASA Astrophysics Data System (ADS)

    Bawedin, M.; Uren, M. J.; Udrea, F.

    2010-06-01

    In this paper, a concept for a 1T-DRAM in AlGaN/GaN based HEMTs is presented for the first time - the Hetero-RAM (HRAM). This memory takes advantage of the natural coexistence of both hole and electron gases and uses hole gas transient and dynamic capacitive coupling effects. It is interesting to note that up to now the hole gas has been considered as parasitic, since it was seen to trigger hysteresis and transient effects within the HEMT output characteristics. We discuss an implementation of the memory concept in a GaN/AlN/AlGaN HEMT structure with a Schottky gate, separated from the source and drain contacts via spacers which are used as storage nodes. The HRAM uses only one transistor and offers non-destructive read, relatively long retention time and fast programming while it is amenable to integration with conventional HEMT based technology.

  16. Exciton properties in zincblende InGaN-GaN quantum wells under the effects of intense laser fields.

    PubMed

    Duque, Carlos M; Mora-Ramos, Miguel E; Duque, Carlos A

    2012-01-01

    : In this work, we study the exciton states in a zincblende InGaN/GaN quantum well using a variational technique. The system is considered under the action of intense laser fields with the incorporation of a direct current electric field as an additional external probe. The effects of these external influences as well as of the changes in the geometry of the heterostructure on the exciton binding energy are discussed in detail. PMID:22937963

  17. Effects of misfit dislocations and AlN buffer layer on the GaInN/GaN phase diagram of the growth mode

    NASA Astrophysics Data System (ADS)

    Nakajima, Kazuo; Ujihara, Toru; Miyashita, Satoru; Sazaki, Gen

    2001-01-01

    The thickness-composition phase diagrams of the growth modes were determined for the GaInN-on-GaN (GaInN/GaN) and the GaInN-on-AlN-on-GaN (GaInN/AlN/GaN) structures. For this determination, the strain energy was calculated by considering the stress relaxation due to introduction of misfit dislocations, the surface energy was estimated from bonding enthalpy of the nearest-neighbor bonds on the surface, and the interface energy was estimated by considering both effects of the dangling bonds due to lattice misfit and the abrupt transition of bonding species at the heterointerface. From these phase diagrams, it was found that the layer-by-layer growth such as the Frank-van der Merwe mode was very difficult to obtain for the epitaxial growth of GaInN on GaN when the InN fraction is large. The Volmer-Weber mode is dominant in the phase diagram of the GaInN/GaN structures. The influence of an AlN buffer layer with a larger surface energy was studied by introducing an AlN layer between the GaInN layer and the GaN substrate. It was known that the layer-by-layer growth could be more easily obtained if misfit dislocations were introduced and an AlN layer was used as a buffer.

  18. On the effect of N-GaN/P-GaN/N-GaN/P-GaN/N-GaN built-in junctions in the n-GaN layer for InGaN/GaN light-emitting diodes.

    PubMed

    Kyaw, Zabu; Zhang, Zi-Hui; Liu, Wei; Tan, Swee Tiam; Ju, Zhen Gang; Zhang, Xue Liang; Ji, Yun; Hasanov, Namig; Zhu, Binbin; Lu, Shunpeng; Zhang, Yiping; Sun, Xiao Wei; Demir, Hilmi Volkan

    2014-01-13

    N-GaN/P-GaN/N-GaN/P-GaN/N-GaN (NPNPN-GaN) junctions embedded between the n-GaN region and multiple quantum wells (MQWs) are systematically studied both experimentally and theoretically to increase the performance of InGaN/GaN light emitting diodes (LEDs) in this work. In the proposed architecture, each thin P-GaN layer sandwiched in the NPNPN-GaN structure is completely depleted due to the built-in electric field in the NPNPN-GaN junctions, and the ionized acceptors in these P-GaN layers serve as the energy barriers for electrons from the n-GaN region, resulting in a reduced electron over flow and enhanced the current spreading horizontally in the n- GaN region. These lead to increased optical output power and external quantum efficiency (EQE) from the proposed device.

  19. Effect of GaN template layer strain on the growth of InxGa1-xN/GaN MQW light emitting diodes

    SciTech Connect

    Johnson, M.C.; Bourret-Courchesne, E.D.; Wu, J.; Liliental-Weber, Z.; Zakharov, D.N.; Jorgenson, R.J.; Ng, T.B.; McCready, D.E.; Williams, J.R.

    2004-01-15

    GaN template layer strain effects were investigated on the growth of InGaN/GaN LED devices. Seven period InGaN/GaN multiple quantum well structures were deposited on 5{micro}m and 15{micro}m GaN template layers. It was found that the electroluminescence emission of the 15{micro}m device was red-shifted by approximately 132meV. Triple-axis X-Ray Diffraction and Cross-Sectional Transmission Electron Microscopy show that the 15{micro}m templay layer device was virtually unstrained while the 5{micro}m layer experienced tensile strain. Dynamic Secondary Ion Mass Spectrometry depth profiles show that the 15{micro}m template layer device had an average indium concentration of 11% higher than that of the 5{micro}m template layer device even though the structures were deposited during the same growth run. It was also found that the 15{micro}m layer device had a higher growth rate than the 5{micro}m template layer device. This difference in indium concentration and growth rate was due to changes in thermodynamic limitations caused by strain differences in the template layers.

  20. Synthesis and properties of ZnTe and Eu3+ ion co-doped glass nanocomposites

    NASA Astrophysics Data System (ADS)

    Rahaman Molla, Atiar; Tarafder, Anal; Dey, Chirantan; Karmakar, Basudeb

    2014-10-01

    In this study, ZnTe (II-VI) semiconductor and Eu+3-ion co-doped borosilicate glass has been prepared in the SiO2-K2O-CaO-BaO-B2O3 glass system followed by controlled heat-treatment to produce glass nanocomposites. Glass transition temperature and crystallization peak temperature have been evaluated using DSC analysis. Dilatometric studies were carried out to evaluate thermal expansion co-efficient, glass transition temperature, and dilatometric softening temperature and found to be 10.7 × 10-6/K, 580° C and 628° C, respectively. TEM micrographs demonstrate formation of nano sized crystallites of less than 50 nm. The ZnTe crystal formation also established through selected area electron diffraction (SAED) analysis and high resolution images obtained through TEM studies. With increasing heat treatment time, optical transmission cut-off wavelength (λcut-off) shifted towards higher wavelength. Excitation spectra were recorded by monitoring emission at 613 nm corresponding to the 5D0 → 7F2 transition. An intense 394 nm excitation band corresponding to the 7F0 → 5L6 transition was observed. Emission spectra were then recorded by exciting the glass samples at 394 nm. When the glass is heat-treated for 30 min at 610° C, a 6-fold increase in the intensity of the red emission at 612 nm has been observed, which is attributed to the segregation of Eu3+ ions into the low phonon energy ZnTe crystallites and as the size of the nanocrystals is smaller than the size of the exciton, quantum confinement effect is visible. Further increase in heat-treatment duration led to decrease in luminescence intensity due to the growth of larger size crystals. 5D1 → 7F0 transition is visible only in the samples heat-treated for 30 min and 1 h, which is a characteristic of presence of Eu3+ ions in the low phonon energy ZnTe crystal sites. The micro hardness of the precursor glass and glass nanocomposites was evaluated; base glass shows hardness of 6.7 GPa and hardness of heat

  1. Understanding the infrared to visible upconversion luminescence properties of Er{sup 3+}/Yb{sup 3+} co-doped BaMoO{sub 4} nanocrystals

    SciTech Connect

    Adhikari, Rajesh; Choi, Jinhyuk; Narro-García, R.; De la Rosa, E.; Sekino, Tohru; Lee, Soo Wohn

    2014-08-15

    In this paper we report the infrared to visible upconversion luminescence properties of Er{sup 3+}/Yb{sup 3+} co-doped BaMoO{sub 4} nanocrystals synthesized via microwave assisted sol–gel processing route. Structural, morphological and upconversion luminescence properties were investigated by X-ray diffraction (XRD), Transmission Electron Microscopy (TEM), UV–vis diffuse reflectance spectroscopy (UV–vis DRS) and Upconversion Photoluminescence spectra analysis. Results revealed that the oval shaped BaMoO{sub 4} nanocrystals ranging in size from 40 to 60 nm having tetragonal scheelite crystal structure were obtained by sol–gel route. The infrared to visible upconversion luminescence has been investigated in Er{sup 3+}/Yb{sup 3+} co-doped in BaMoO{sub 4}with different Yb{sup 3+} concentrations. Intense green upconversion emissions around 528, 550 nm, and red emission at 657 nm corresponding to the {sup 2}H{sub 11/2}, {sup 4}S{sub 3/2}, and {sup 4}F{sub 9/2} transitions, respectively to the {sup 4}I{sub 15/2} ground state were observed when excited by CW laser radiation at 980 nm. The green emissions were greatly enhanced after the addition of sensitizer (Yb{sup 3+} ions). The effect of Yb{sup 3+} on the upconversion luminescence intensity was analyzed and explained in terms of the energy transfer process based. The reported work establishes the understanding of molybdates as an alternative host material for upconversion luminescence. - Graphical abstract: Infrared to visible upconversion luminescence of Er{sup 3+}/Yb{sup 3+} co-doped BaMoO{sub 4} nanocrystals. - Highlights: • Nanocrystals were synthesized by microwave assisted sol–gel processing route. • Strong green emissions were observed in Er{sup 3+}/Yb{sup 3+} co-doped BaMoO{sub 4} nanocrystals. • Provides an insight on Upconversion luminescence properties of oxides host materials.

  2. GaN metal-oxide-semiconductor field-effect transistors on AlGaN/GaN heterostructure with recessed gate

    NASA Astrophysics Data System (ADS)

    Wang, Qingpeng; Ao, Jin-Ping; Wang, Pangpang; Jiang, Ying; Li, Liuan; Kawaharada, Kazuya; Liu, Yang

    2015-04-01

    GaN metal-oxide-semiconductor field-effect transistors (MOSFETs) on AlGaN/GaN heterostructure with a recess gate were fabricated and characterized. The device showed good pinch-off characteristics and a maximum field-effect mobility of 145.2 cm2·V-1·s-1. The effects of etching gas of Cl2 and SiCl4 were investigated in the gate recess process. SiCl4-etched devices showed higher channel mobility and lower threshold voltage. Atomic force microscope measurement was done to investigate the etching profile with different etching protection mask. Compared with photoresist, SiO2-masked sample showed lower surface roughness and better profile with stepper sidewall and weaker trenching effect resulting in higher channel mobility in the MOSFET.

  3. Effect of the Yb3+ Concentration in Up-Conversion and Electrical Properties of Ho3+/Yb3+ Co-doped (0.94Na0.5Bi0.5TiO3-0.06BaTiO3) Ceramics

    NASA Astrophysics Data System (ADS)

    Liu, Qian; Li, Yanxia; Li, Jun; Chai, Xiaona; Zhao, Haifeng; Wang, Xusheng; Yao, Xi

    2016-07-01

    Ho3+/Yb3+ co-doped 0.94Na0.5Bi0.5TiO3-0.06BaTiO3 (NBT-BT:Ho3+/Yb3+) ceramics were synthesized by solid-state reaction and characterized by x-ray diffraction (XRD), luminescent, dielectric, ferroelectric and piezoelectric measurements. The XRD diffraction data showed that all the ceramics were single phase with a perovskite structure. Bright green up-conversion (UC) emission bands (545 nm) and weak red UC emission bands (660 nm) corresponded to the transitions from (5F4, 5S2) → 5I8 and 4I5 → 5I8, respectively. Furthermore, optimized UC emission intensity was observed in the NBT-BT:0.005Ho3+/0.03Yb3+ samples. The thermal behavior of UC emission in the ceramics was also investigated and the maximum sensitivity based on fluorescence intensity ratio (FIR) technology was approximately 0.0042 K-1 at 100 K. Moreover, relatively good dielectric properties ( ɛ = 4475) and ferroelectric properties ( P r = 32 μ/cm2 and E c = 37 kV) were obtained in NBT-BT:0.005Ho3+/0.005Yb3+. As a multi-functional material, NBT-BT:Ho3+/Yb3+ ceramics may be useful in electro-optical devices.

  4. Effects of low-temperature capping on the optical properties of GaAs/AlGaAs quantum wells

    PubMed Central

    2011-01-01

    We study the effects of low-temperature capping (200-450°C) on the optical properties of GaAs/AlGaAs quantum wells. Photoluminescence measurements clearly show the formation of abundant nonradiative recombination centers in an AlGaAs capping layer grown at 200°C, while there is a slight degradation of the optical quality in AlGaAs capping layers grown at temperatures above 350°C compared to that of a high-temperature capping layer. In addition, the optical quality can be restored by post-growth annealing without any structural change, except for the 200°C-capped sample. PMID:21711596

  5. Enhance ferromagnetism by stabilizing the cation vacancies in GaN

    NASA Astrophysics Data System (ADS)

    Tang, Zhen-kun; Zhang, Deng-Yu; Tang, Li-Ming; Wang, Ling-Ling; Chen, Ke-Qiu

    2013-06-01

    The magnetic properties related to cation vacancies in GaN are investigated by first-principles calculations. The results show that a neutral Ga-vacancy induces 3 μ B magnetic moment in GaN, but is difficult to form due to the high formation energy. It is found that the Ga-vacancy formation energy can be reduced by adding electrons with uniform compensating positive background charge, by nano-structure engineering, or by co-doping donor-like defects. The Ga-vacancy induced colossal magnetic moment in Gd-doped GaN can be modulated by co-doping the donor like defects. It is suggested that ferromagnetism enhanced by stabilizing the cation vacancies may be applied to other wide band-gap semiconductors as well.

  6. Characterization of Bi and Fe co-doped PZT capacitors for FeRAM

    NASA Astrophysics Data System (ADS)

    Cross, Jeffrey S.; Kim, Seung-Hyun; Wada, Satoshi; Chatterjee, Abhijit

    2010-08-01

    Ferroelectric random access memory (FeRAM) has been in mass production for over 15 years. Higher polarization ferroelectric materials are needed for future devices which can operate above about 100 °C. With this goal in mind, co-doping of thin Pb(Zr40,Ti60)O3 (PZT) films with 1 at.% Bi and 1 at.% Fe was examined in order to enhance the ferroelectric properties as well as characterize the doped material. The XRD patterns of PZT-5% BiFeO3 (BF) and PZT 140-nm thick films showed (111) orientation on (111) platinized Si wafers and a 30 °C increase in the tetragonal to cubic phase transition temperature, often called the Curie temperature, from 350 to 380 °C with co-doping, indicating that Bi and Fe are substituting into the PZT lattice. Raman spectra revealed decreased band intensity with Bi and Fe co-doping of PZT compared to PZT. Polarization hysteresis loops show similar values of remanent polarization, but square-shaped voltage pulse-measured net polarization values of PZT-BF were higher and showed higher endurance to repeated cycling up to 1010 cycles. It is proposed that Bi and Fe are both in the +3 oxidation state and substituting into the perovskite A and B sites, respectively. Substitution of Bi and Fe into the PZT lattice likely creates defect dipoles, which increase the net polarization when measured by the short voltage pulse positive-up-negative-down (PUND) method.

  7. Preparation and properties of sliver and nitrogen co-doped TiO{sub 2} photocatalyst

    SciTech Connect

    Zhang, Ying; Zhang, Jin; Zhu, Zhongqi; Yan, Ningning; Liu, Qingju

    2013-11-15

    Graphical abstract: - Highlights: • The silver and nitrogen co-doped TiO{sub 2} photocatalysts were prepared and characterized. • The light absorption threshold wavelength of Ag–N–TiO{sub 2} is red-shifted to visible light. • The recombination of the photo-generated electrons and holes of Ag–N–TiO{sub 2} is inhibited. • The photocatalytic activity of Ag–N–TiO{sub 2} is remarkable improved. - Abstract: TiO{sub 2} photocatalysts co-doped with different content of Ag and N were prepared by sol–gel method combined with microwave chemical method. The samples were analyzed by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscope (TEM), ultraviolet–visible diffuse reflectance spectrum (UV–vis) and photo-luminescence emission spectrum (PL). The photocatalytic activity was investigated by photocatalytic degradation of methylene blue (MB) under irradiation of fluorescent lamp. The results indicate that Ag and N co-doping can restrain the increase of grain size, broaden the absorption spectrum to visible light region, and inhibit the recombination of the photo-generated electron–hole pairs. Moreover, the photocatalytic activity of Ag–N–TiO{sub 2} in MB degradation is remarkable improved. The degradation rate of the sample with Ag:TiO{sub 2} = 0.05 at%, N:TiO{sub 2} = 18.50 wt% in 5 h is 93.44%, which is much higher than that of Degussa P25 (39.40%)

  8. Leakage effects in n-GaAs MESFET with n-GaAs buffer layer

    NASA Technical Reports Server (NTRS)

    Wang, Y. C.; Bahrami, M.

    1983-01-01

    Whereas improvement of the interface between the active layer and the buffer layer has been demonstrated, the leakage effects can be important if the buffer layer resistivity is not sufficiently high and/or the buffer layer thickness is not sufficiently small. It was found that two buffer leakage currents exist from the channel under the gate to the source and from drain to the channel in addition to the buffer leakage resistance between drain and source. It is shown that for a 1 micron gate-length n-GaAs MESFET, if the buffer layer resistivity is 12 OHM-CM and the buffer layer thickness h is 2 microns, the performance of the device degrades drastically. It is suggested that h should be below 2 microns.

  9. Effects of high-temperature AIN buffer on the microstructure of AlGaN/GaN HEMTs

    SciTech Connect

    Coerekci, S.; Oeztuerk, M. K.; Yu, Hongbo; Cakmak, M.; Oezcelik, S.; Oezbay, E.

    2013-06-15

    Effects on AlGaN/GaN high-electron-mobility transistor structure of a high-temperature AlN buffer on sapphire substrate have been studied by high-resolution x-ray diffraction and atomic force microscopy techniques. The buffer improves the microstructural quality of GaN epilayer and reduces approximately one order of magnitude the edge-type threading dislocation density. As expected, the buffer also leads an atomically flat surface with a low root-mean-square of 0.25 nm and a step termination density in the range of 10{sup 8} cm{sup -2}. Due to the high-temperature buffer layer, no change on the strain character of the GaN and AlGaN epitaxial layers has been observed. Both epilayers exhibit compressive strain in parallel to the growth direction and tensile strain in perpendicular to the growth direction. However, an high-temperature AlN buffer layer on sapphire substrate in the HEMT structure reduces the tensile stress in the AlGaN layer.

  10. Magnetic and dielectric studies of Li-Cu co-doped ZnO nanoparticles

    NASA Astrophysics Data System (ADS)

    Vivek, S.; Ajith, S. K.; Chitralekha, C. S.; Nair, Swapna S.

    2016-05-01

    Room temperature ferromagnetism has been observed in Li-Cu co-doped ZnO nanoparticles prepared by sol-gel route. Our studies indicated that the observed ferromagnetism is a surface phenomenon which depends on oxygen vacancy and the nature of the dopants. Dependence of ferromagnetism on the annealing temperature indicated the role of oxygen vacancy, and the decrease in coercivity as the particle size increases indicates the surface dependence of ferromagnetism. It is found that the addition of dopants also enhanced ferromagnetism. Dielectric studies indicated an increase in dielectric constant as the doping concentration is increased.

  11. Ferromagnetism in Co-doped (La,Sr)TiO3

    SciTech Connect

    Fix, T.; Liberati, M.; Aubriet, H.; Sahonta, S.-L.; Bali, R.; Becker, C.; Ruch, D.; MacManus-Driscoll, J.L.; Arenholz, E.; Blamire, M.G.

    2009-04-21

    The origin of ferromagnetism in Co-doped (La,Sr)TiO{sub 3} epitaxial thin films is discussed. While the as-grown samples are not ferromagnetic at room temperature or at 10 K, ferromagnetism at room temperature appears after annealing the films in reducing conditions and disappears after annealing in oxidizing conditions. Magnetic measurements, x-ray absorption spectroscopy, x-ray photoemission spectroscopy and transmission electron microscopy experiments indicate that within the resolution of the instruments the activation of the ferromagnetism is not due to the presence of pure Co.

  12. Nitrogen and sulfur co-doped carbon dots with strong blue luminescence

    NASA Astrophysics Data System (ADS)

    Ding, Hui; Wei, Ji-Shi; Xiong, Huan-Ming

    2014-10-01

    Sulfur-doped carbon dots (S-CDs) with a quantum yield (QY) of 5.5% and nitrogen, sulfur co-doped carbon dots (N,S-CDs) with a QY of 54.4% were synthesized, respectively, via the same hydrothermal route using α-lipoic acid as the carbon source. The obtained S-CDs and N,S-CDs had similar sizes but different optical features. The QY of N,S-CDs was gradually enhanced when extending the reaction time to increase the nitrogen content. After careful characterization of these CDs, the doped nitrogen element was believed to be in the form of C&z.dbd;N and C-N bonds which enhanced the fluorescence efficiency significantly. Meanwhile, the co-doped sulfur element was found to be synergistic for nitrogen doping in N,S-CDs. The optimal N,S-CDs were successfully employed as good multicolor cell imaging probes due to their fine dispersion in water, excitation-dependent emission, excellent fluorescence stability and low toxicity. Besides, such N,S-CDs showed a wide detection range and excellent accuracy as fluorescent sensors for Fe3+ ions.Sulfur-doped carbon dots (S-CDs) with a quantum yield (QY) of 5.5% and nitrogen, sulfur co-doped carbon dots (N,S-CDs) with a QY of 54.4% were synthesized, respectively, via the same hydrothermal route using α-lipoic acid as the carbon source. The obtained S-CDs and N,S-CDs had similar sizes but different optical features. The QY of N,S-CDs was gradually enhanced when extending the reaction time to increase the nitrogen content. After careful characterization of these CDs, the doped nitrogen element was believed to be in the form of C&z.dbd;N and C-N bonds which enhanced the fluorescence efficiency significantly. Meanwhile, the co-doped sulfur element was found to be synergistic for nitrogen doping in N,S-CDs. The optimal N,S-CDs were successfully employed as good multicolor cell imaging probes due to their fine dispersion in water, excitation-dependent emission, excellent fluorescence stability and low toxicity. Besides, such N,S-CDs showed a

  13. Colossal dielectric permittivity in (Al + Nb) co-doped rutile SnO2 ceramics with low loss at room temperature

    NASA Astrophysics Data System (ADS)

    Song, Yongli; Wang, Xianjie; Zhang, Xingquan; Qi, Xudong; Liu, Zhiguo; Zhang, Lingli; Zhang, Yu; Wang, Yang; Sui, Yu; Song, Bo

    2016-10-01

    The exploration of colossal dielectric permittivity (CP) materials with low dielectric loss in a wide range of frequencies/temperatures continues to attract considerable interest. In this paper, we report CP in (Al + Nb) co-doped rutile SnO2 ceramics with a low dielectric loss at room temperature. Al0.02Nb0.05Sn0.93O2 and Al0.03Nb0.05Sn0.92O2 ceramics exhibit high relative dielectric permittivities (above 103) and low dielectric losses (0.015 < tan δ < 0.1) in a wide range of frequencies and at temperatures from 140 to 400 K. Al doping can effectively modulate the dielectric behavior by increasing the grain and grain boundary resistances. The large differences in the resistance and conductive activation energy of the grains and grain boundaries suggest that the CP in co-doped SnO2 ceramics can be attributed to the internal barrier layer capacitor effect.

  14. Substrate misorientation effects on epitaxial GaInAsSb

    SciTech Connect

    Wang, C.A.; Choi, H.K.; Oakley, D.C.; Charache, G.W.

    1997-12-01

    The effect of substrate misorientation on the growth of GaInAsSb was studied for epilayers grown lattice-matched to GaSb substrates by low-pressure organometallic vapor phase epitaxy. The substrates were (100) misoriented 2 or 6{degree} toward (110), (111)A, or (111)B. The surface is mirror-like and featureless for layers grown with a 6{degree} toward (111)B misorientation, while, a slight texture was observed for layers grown on all other misorientations. The optical quality of layers, as determined by the full width at half-maximum of photoluminescence spectra measured at 4K, is significantly better for layers grown on substrates with a 6{degree} toward (111)B misorientation. The incorporation of Zn as a p-type dopant in GaInAsSb is about 1.5 times more efficient on substrates with 6{degree} toward (111)B misorientation compared to 2{degree} toward (110) misorientation. The external quantum efficiency of thermophotovoltaic devices is not, however, significantly affected by substrate misorientation.

  15. Epitaxially-Grown GaN Junction Field Effect Transistors

    SciTech Connect

    Baca, A.G.; Chang, P.C.; Denbaars, S.P.; Lester, L.F.; Mishra, U.K.; Shul, R.J.; Willison, C.G.; Zhang, L.; Zolper, J.C.

    1999-05-19

    Junction field effect transistors (JFET) are fabricated on a GaN epitaxial structure grown by metal organic chemical vapor deposition (MOCVD). The DC and microwave characteristics of the device are presented. A junction breakdown voltage of 56 V is obtained corresponding to the theoretical limit of the breakdown field in GaN for the doping levels used. A maximum extrinsic transconductance (gm) of 48 mS/mm and a maximum source-drain current of 270 mA/mm are achieved on a 0.8 µ m gate JFET device at VGS= 1 V and VDS=15 V. The intrinsic transconductance, calculated from the measured gm and the source series resistance, is 81 mS/mm. The fT and fmax for these devices are 6 GHz and 12 GHz, respectively. These JFETs exhibit a significant current reduction after a high drain bias is applied, which is attributed to a partially depleted channel caused by trapped hot-electrons in the semi-insulating GaN buffer layer. A theoretical model describing the current collapse is described, and an estimate for the length of the trapped electron region is given.

  16. Magnetism and associated exchange bias in Ni2-xCoxMn1.4Ga0.6

    NASA Astrophysics Data System (ADS)

    Chapai, Ramakanta; Khan, Mahmud

    2016-04-01

    A series of Ni2-xCoxMn1.4Ga0.6 Heusler alloys have been systematically investigated by x-ray diffraction, dc magnetization, and ac susceptibility measurements. For all Co concentration, the alloys exhibit the L10 martensitic structure at room temperature. Interestingly, Co doping simultaneously causes a reduction in the ferromagnetic exchange interaction and enhancement of magnetic anisotropy in Ni2-xCoxMn1.4Ga0.6. Exchange bias effects under both zero field cooled and field cooled condition have been observed in all alloys for x<0.3. The ac susceptibility data show frequency dependence that changes with increasing Co concentration, indicating a change of ground state from spin glass to super spin glass. The experimental results are explained considering the atomic radii of Ni and Co and the fundamental magnetic interactions in Heusler alloys.

  17. Quantum effects in electron beam pumped GaAs

    SciTech Connect

    Yahia, M. E.; Azzouz, I. M.; Moslem, W. M.

    2013-08-19

    Propagation of waves in nano-sized GaAs semiconductor induced by electron beam are investigated. A dispersion relation is derived by using quantum hydrodynamics equations including the electrons and holes quantum recoil effects, exchange-correlation potentials, and degenerate pressures. It is found that the propagating modes are instable and strongly depend on the electron beam parameters, as well as the quantum recoil effects and degenerate pressures. The instability region shrinks with the increase of the semiconductor number density. The instability arises because of the energetic electron beam produces electron-hole pairs, which do not keep in phase with the electrostatic potential arising from the pair plasma.

  18. 3D coral-like nitrogen-sulfur co-doped carbon-sulfur composite for high performance lithium-sulfur batteries

    NASA Astrophysics Data System (ADS)

    Wu, Feng; Li, Jian; Tian, Yafen; Su, Yuefeng; Wang, Jing; Yang, Wen; Li, Ning; Chen, Shi; Bao, Liying

    2015-08-01

    3D coral-like, nitrogen and sulfur co-doped mesoporous carbon has been synthesized by a facile hydrothermal-nanocasting method to house sulfur for Li-S batteries. The primary doped species (pyridinic-N, pyrrolic-N, thiophenic-S and sulfonic-S) enable this carbon matrix to suppress the diffusion of polysulfides, while the interconnected mesoporous carbon network is favourable for rapid transport of both electrons and lithium ions. Based on the synergistic effect of N, S co-doping and the mesoporous conductive pathway, the as-fabricated C/S cathodes yield excellent cycling stability at a current rate of 4 C (1 C = 1675 mA g-1) with only 0.085% capacity decay per cycle for over 250 cycles and ultra-high rate capability (693 mAh g-1 at 10 C rate). These capabilities have rarely been reported before for Li-S batteries.

  19. Role of glass structure in defining the chemical dissolution behavior, bioactivity and antioxidant properties of zinc and strontium co-doped alkali-free phosphosilicate glasses.

    PubMed

    Kapoor, Saurabh; Goel, Ashutosh; Tilocca, Antonio; Dhuna, Vikram; Bhatia, Gaurav; Dhuna, Kshitija; Ferreira, José M F

    2014-07-01

    We investigated the structure-property relationships in a series of alkali-free phosphosilicate glass compositions co-doped with Zn(2+) and Sr(2+). The emphasis was laid on understanding the structural role of Sr(2+) and Zn(2+) co-doping on the chemical dissolution behavior of glasses and its impact on their in vitro bioactivity. The structure of glasses was studied using molecular dynamics simulations in combination with solid state nuclear magnetic resonance spectroscopy. The relevant structural properties are then linked to the observed degradation behavior, in vitro bioactivity, osteoblast proliferation and oxidative stress levels. The apatite-forming ability of glasses has been investigated by X-ray diffraction, infrared spectroscopy and scanning electron microscopy-energy-dispersive spectroscopy after immersion of glass powders/bulk in simulated body fluid (SBF) for time durations varying between 1h and 14 days, while their chemical degradation has been studied in Tris-HCl in accordance with ISO 10993-14. All the glasses exhibit hydroxyapatite formation on their surface within 1-3h of their immersion in SBF. The cellular responses were observed in vitro on bulk glass samples using human osteosarcoma MG63 cell line. The dose-dependent cytoprotective effect of glasses with respect to the concentration of zinc and strontium released from the glasses is also discussed. PMID:24709542

  20. 3D coral-like nitrogen-sulfur co-doped carbon-sulfur composite for high performance lithium-sulfur batteries

    PubMed Central

    Wu, Feng; Li, Jian; Tian, Yafen; Su, Yuefeng; Wang, Jing; Yang, Wen; Li, Ning; Chen, Shi; Bao, Liying

    2015-01-01

    3D coral-like, nitrogen and sulfur co-doped mesoporous carbon has been synthesized by a facile hydrothermal-nanocasting method to house sulfur for Li–S batteries. The primary doped species (pyridinic-N, pyrrolic-N, thiophenic-S and sulfonic-S) enable this carbon matrix to suppress the diffusion of polysulfides, while the interconnected mesoporous carbon network is favourable for rapid transport of both electrons and lithium ions. Based on the synergistic effect of N, S co-doping and the mesoporous conductive pathway, the as-fabricated C/S cathodes yield excellent cycling stability at a current rate of 4 C (1 C = 1675 mA g−1) with only 0.085% capacity decay per cycle for over 250 cycles and ultra-high rate capability (693 mAh g−1 at 10 C rate). These capabilities have rarely been reported before for Li-S batteries. PMID:26288961

  1. Role of glass structure in defining the chemical dissolution behavior, bioactivity and antioxidant properties of zinc and strontium co-doped alkali-free phosphosilicate glasses.

    PubMed

    Kapoor, Saurabh; Goel, Ashutosh; Tilocca, Antonio; Dhuna, Vikram; Bhatia, Gaurav; Dhuna, Kshitija; Ferreira, José M F

    2014-07-01

    We investigated the structure-property relationships in a series of alkali-free phosphosilicate glass compositions co-doped with Zn(2+) and Sr(2+). The emphasis was laid on understanding the structural role of Sr(2+) and Zn(2+) co-doping on the chemical dissolution behavior of glasses and its impact on their in vitro bioactivity. The structure of glasses was studied using molecular dynamics simulations in combination with solid state nuclear magnetic resonance spectroscopy. The relevant structural properties are then linked to the observed degradation behavior, in vitro bioactivity, osteoblast proliferation and oxidative stress levels. The apatite-forming ability of glasses has been investigated by X-ray diffraction, infrared spectroscopy and scanning electron microscopy-energy-dispersive spectroscopy after immersion of glass powders/bulk in simulated body fluid (SBF) for time durations varying between 1h and 14 days, while their chemical degradation has been studied in Tris-HCl in accordance with ISO 10993-14. All the glasses exhibit hydroxyapatite formation on their surface within 1-3h of their immersion in SBF. The cellular responses were observed in vitro on bulk glass samples using human osteosarcoma MG63 cell line. The dose-dependent cytoprotective effect of glasses with respect to the concentration of zinc and strontium released from the glasses is also discussed.

  2. Copper and cerium co-doped titanium dioxide on catalytic photo reduction of carbon dioxide with water: Experimental and theoretical studies

    NASA Astrophysics Data System (ADS)

    Luo, Dongmei; Bi, Ye; Kan, Wei; Zhang, Ning; Hong, Sanguo

    2011-05-01

    The catalytic activities of copper and cerium co-doped titanium dioxide were studied experimentally and theoretically in the synthesis of methanol by the photo reduction of carbon dioxide with water firstly. Photo catalysts copper and cerium co-doped titanium dioxide were prepared via the equivalent-volume incipient wetness impregnation method. The catalysts were characterized by XRD, Raman, BET, and electrochemistry analyses. The catalytic properties were determined in the synthesis of methanol from CO 2 in the aqueous solution. The experimental results suggested that Cu/Ce-TiO 2 catalysts obviously enhanced the efficiency of the photocatalytic reduction of CO 2. The methanol yield could reach up to 180.3 μmol/g-cat rapidly. The different effects of copper and cerium on the surface of titanium dioxide have been calculated at the Becke's three-parameter hybrid exchange functional together with the Lee-Yang-Parr correlation functional (B3LYP) level. Our results revealed that Ce atoms affect the reaction more profoundly than Cu atoms do. Ce atoms activated H 2O and CO 2 molecules, while Cu atoms act as the channel of photoelectrons in real time and prevent the recombination of electrons and holes.

  3. Investigation on broadband near-infrared emission in Yb3+/Ho3+ co-doped antimony-silicate glass and optical fiber

    NASA Astrophysics Data System (ADS)

    Dorosz, D.; Zmojda, J.; Kochanowicz, M.

    2013-10-01

    In the paper antimony-silicate glass and double-clad optical fiber co-doped with ytterbium and holmium ions were investigated. Absorption spectra in infrared (FT-IR) showed characteristic bands: 445, 605, 1037, 1168 cm-1 coming from the vibration of chemical bonds of SbO3 and SiO4, respectively. The combination of relatively low phonon energy with a capability for greater separation (avoiding clustering) of optically active centers in the fabricated glasses should allow an effective expansion of spontaneous emission band. The highest intensity of emission at the wavelength of λe = 1950 nm resulting from energy transfer between Yb3+ → Ho3+ ions was observed in the glass co-doped with 1 mol% Yb2O3:0.5 mol% Ho2O3. As a result of the optical pumping at the wavelength of 976 nm in the produced optical fiber, strong and narrow band of amplified spontaneous emission (ASE) around 2.1 μm, corresponds to the 5I7 → 5I8 transition, were obtained.

  4. Thermoluminescence responses of photon- and electron-irradiated lithium potassium borate co-doped with Cu+Mg or Ti+Mg.

    PubMed

    Alajerami, Y S M; Hashim, S; Ramli, A T; Saleh, M A; Saripan, M I; Alzimami, K; Min Ung, Ngie

    2013-08-01

    New glasses Li2CO3-K2CO3-H3BO3 (LKB) co-doped with CuO and MgO, or with TiO2 and MgO, were synthesized by the chemical quenching technique. The thermoluminescence (TL) responses of LKB:Cu,Mg and LKB:Ti,Mg irradiated with 6 MV photons or 6 MeV electrons were compared in the dose range 0.5-4.0 Gy. The standard commercial dosimeter LiF:Mg,Ti (TLD-100) was used to calibrate the TL reader and as a reference in comparison of the TL properties of the new materials. The dependence of the responses of the new materials on (60)Co dose is linear in the range of 1-1000 Gy. The TL yields of both of the co-doped glasses and TLD-100 are greater for electron irradiation than for photon irradiation. The TL sensitivity of LKB:Ti,Mg is 1.3 times higher than the sensitivity of LKB:Cu,Mg and 12 times less than the sensitivity of TLD-100. The new TL dosimetric materials have low effective atomic numbers, good linearity of the dose responses, excellent signal reproducibility, and a simple glow curve structure. This combination of properties makes them suitable for radiation dosimetry.

  5. Droop-multimode trade-off in GaN-InGaN LEDs: Effect of polarization-matched AlInGaN blocking layers

    NASA Astrophysics Data System (ADS)

    Pendem, Vikas; Adhikari, Sonachand; Mathew, Manish; Singh, Sumitra; Pal, Suchandan

    2015-12-01

    Polarization-matched graded AlInGaN electron blocking layer (EBL) and hole blocking layer (HBL) are proposed to reduce efficiency droop in GaN-InGaN light-emitting diodes (LEDs). Five different structures have been simulated to study the effect of different blocking layers and a significant reduction in the efficiency droop has been noticed, from 52% in conventional structure to 2% in polarization-matched graded AlInGaN EBL and HBL structure at a current density of 1000 A cm-2. This has been achieved at the cost of multimode emission from such polarization-matched blocking layers which sets a trade-off between efficiency droop and multimode emission. The AlInGaN layer can therefore be characterized by droop cut-off condition (DCC) and multimode cut-off condition (MCC). For the best structure proposed in this paper, simulations indicate a DCC having Al and In composition of 0.10 and 0.15 respectively; and an MCC having Al and In composition of 0.08 and 0.23 respectively.

  6. Substantial enhancement in intrinsic coercivity on M-type strontium hexaferrite through the increase in magneto-crystalline anisotropy by co-doping of group-V and alkali elements

    SciTech Connect

    Ahn, Kyunghan Ryu, Byungki; Korolev, Dmitry; Jae Kang, Young

    2013-12-09

    The effect of d{sup 1} impurity doping in Sr-hexaferrite (SrM) on the magnetic anisotropy is investigated. First-principles calculations revealed that group-V elements (V, Nb) are stabilized with co-doping of alkali elements. Na{sup 1+}/K{sup 1+} doping at Sr{sup 2+}-site is found to be critical to form the d{sup 1} impurities at Fe-site. Experimentally, Na–V doped SrM shows the intrinsic coercivity of ∼5.4 kOe, which is ∼300% enhancement compared to undoped SrM and comparable value to La–Co co-doped SrM. Finally, the spin-orbit coupling from non-vanishing angular momentum of d{sup 1} impurity in SrM should be a main factor for such a substantial improvement of intrinsic coercivity.

  7. Upconversion and pump saturation mechanisms in Er{sup 3+}/Yb{sup 3+} co-doped Y{sub 2}Ti{sub 2}O{sub 7} nanocrystals

    SciTech Connect

    Wang, Fengxiao; Song, Feng Zhang, Gong; Han, Yingdong; Li, Qiong; Tian, Jianguo; Ming, Chengguo

    2014-04-07

    The Er{sup 3+}/Yb{sup 3+} co-doped Y{sub 2}Ti{sub 2}O{sub 7} nanocrystals were synthesized by the sol–gel method. X-ray diffraction, transmission electronic microscopy, and photoluminescence spectra were measured to verify the Y{sub 2}Ti{sub 2}O{sub 7} nanocrystalline produced in the sample annealed at 800 °C. The anomalous slopes of the fitted line in the log-log plots for upconversion emissions and the pump-saturation effect of near-infrared emission were observed in the nanocrystalline samples. A theoretical model of practical Er{sup 3+}/Yb{sup 3+} co-doped system based on the rate equations were put forward and explained the experimental phenomena well.

  8. Enhanced photo-catalytic activity of Sr and Ag co-doped TiO2 nanoparticles for the degradation of Direct Green-6 and Reactive Blue-160 under UV & visible light.

    PubMed

    Naraginti, Saraschandra; Thejaswini, T V L; Prabhakaran, D; Sivakumar, A; Satyanarayana, V S V; Arun Prasad, A S

    2015-10-01

    This work is focused on sol-gel synthesis of silver and strontium co-doped TiO2 nanoparticles and their utilization as photo-catalysts in degradation of two textile dyes. Effect of pH, intensity of light, amount of photo-catalyst, concentration of dye, sensitizers, etc., were studied to optimize conditions for obtaining enhanced photo-catalytic activity of synthesized nanoparticles. XRD, BET, HR-TEM, EDAX and UV-Vis (diffused reflectance mode) techniques were used to characterize the nanoparticles. Interestingly, band gap of Sr and Ag co-doped TiO2 nanoparticles showed considerable narrowing (2.6 eV) when compared to Ag doped TiO2 (2.7 eV) and undoped TiO2 (3.17 eV) nanoparticles. Incorporation of Ag and Sr in the lattice of TiO2 could bring isolated energy levels near conduction and valence bands thus narrowing band gap. The XRD analysis shows that both Ag and Sr nanoparticles are finely dispersed on the surface of titania framework, without disturbing its crystalline structure. TEM images indicate that representative grain sizes of Ag-doped TiO2 & Sr and Ag co-doped TiO2 nanoparticles are in the range of 8-20 nm and 11-25 nm, respectively. Effective degradation of Direct Green-6 (DG-6) and Reactive Blue-160 (RB-160) under UV and visible light has been achieved using the photo-catalysts. Sr and Ag co-doped TiO2 photo-catalysts showed higher catalytic activity during degradation process in visible region when compared to Ag-doped and undoped TiO2 nanoparticles which could be attributed to the interactive effect caused by band gap narrowing and enhancement in charge separation. For confirming degradation of the dyes, total organic carbon (TOC) content was monitored periodically.

  9. Crossover between weak anti-localization and weak localization by Co doping and annealing in gapless PbPdO{sub 2} and spin gapless Co-doped PbPdO{sub 2}

    SciTech Connect

    Choo, S. M.; Lee, K. J.; Park, S. M.; Park, G. S.; Jung, M. H.; Yoon, J. B.; You, C.-Y.

    2015-04-27

    The magnetotransport properties of Pb(Pd,Co)O{sub 2} and PbPdO{sub 2} thin films were investigated. In magnetoconductance curves, we observed a crossover between weak anti-localization (WAL) and weak localization (WL) depending on the annealing and Co doping in PbPdO{sub 2} thin films. For the Pb(Pd,Co)O{sub 2} case showing WAL signals, the ex-situ annealing weakens the Pd-O hybridization by stabilizing Co{sup 3+} states and generating Pd{sup 1+} states, instead of Pd{sup 2+}, so that the spin-orbit coupling (SOC) strength is significantly reduced. It causes the dominant magnetotransport mechanism change from WAL to WL. This annealing effect is compared with the PbPdO{sub 2} case, which possesses WL signals. The annealing process stabilizes the oxygen states and enhances the Pd-O hybridization, and consequently the SOC strength is enhanced. Our experimental results are well explained by the Hikami-Larkin-Nagaoka theory in terms of two important physical parameters; SOC strength-related α and inelastic scattering length l{sub ϕ}.

  10. Enrichment of Pyrrolic Nitrogen by Hole Defects in Nitrogen and Sulfur Co-Doped Graphene Hydrogel for Flexible Supercapacitors.

    PubMed

    Tran, Ngoc Quang; Kang, Bong Kyun; Woo, Moo Hyun; Yoon, Dae Ho

    2016-08-23

    The effect of the doping configuration and concentration of nitrogen (N) and sulfur (S) on the electrochemical performance of 3 D N and S co-doped hole defect graphene hydrogel (NS-HGH) electrodes is investigated. Surprisingly, by introducing a hole defect on the graphene surface, the difference in the doping concentrations of N and S can be used to effectively modulate the electrochemical behavior of the NS-HGH. The hole defects provide a rapid ion diffusion path. Finally, we showed that the intriguing specific capacitance (536 F g(-1) ) of the NS-HGH could enhance the overall performance of the pseudocapacitance and electric double layer capacitance. The rational design of the NS-HGH-based flexible solid state supercapacitor results in not only outstanding electrochemical performance with a maximum energy density of 14.8 Wh kg(-1) and power density of 5.2 KW kg(-1) but also in extraordinary mechanical flexibility and excellent cycle stability. PMID:27460556

  11. Hydrothermal growth and conductivity enhancement of (Al, Cu) co-doped ZnO nanorods thin films

    NASA Astrophysics Data System (ADS)

    Chakraborty, Mohua; Mahapatra, Preetilata; Thangavel, R.

    2016-05-01

    The incorporation of Al, Cu co-doping in ZnO host lattice plays an important role in modification of structural, optical and electrical properties in optoelectronic devices. In the present work, we were grown one dimensional ZnO nanorods (NRs) doped with different concentration of Al (0%~5%) and Cu was kept 20 M% on ITO glass substrates using a facile hydrothermal method, and investigated the effect of the codoping on the surface morphology and the electrical and optical performances of the doped ZnO NRs as photo anodes for solar water splitting applications. The crystallite size of NRs shows tuning in the band gap between 3.194 (Zn0.79Al0.01Cu0.2O) to 3.212 eV (Zn0.75Al0.05Cu0.2O) with Aluminium doping concentration and a remarkable improvement in current density (J) from 0.05 mA/cm2 to 4.98 mA/cm2 was achieved by incorporating Al and Cu has a critical effect of ZnO nanorods.

  12. Magnetic and magnetocaloric properties of Ba and Ti co-doped SrRuO{sub 3}

    SciTech Connect

    Sarkar, Babusona; Dalal, Biswajit; Dev Ashok, Vishal; De, S. K.

    2014-12-28

    Temperature evolution of magnetic properties in Ba and Ti doped SrRuO{sub 3} has been investigated to observe the effects of larger ionic radius Ba at Sr site and isovalent nonmagnetic impurity Ti at Ru site. Ionic radius mismatch and different electronic configuration in comparison with Ru modify Sr(Ba)-O and Ru(Ti)-O bond lengths and Ru-O-Ru bond angle. The apical and basal Ru-O-Ru bond angles vary significantly with Ti doping. Ferromagnetic Curie temperature decreases from 161 K to 149 K monotonically with Ba (10%) and Ti (10%) substitutions at Sr and Ru sites. The zero field cooled (ZFC) magnetization reveals a prominent peak which shifts towards lower temperature with application of magnetic field. The substitution of tetravalent Ti with localized 3d{sup 0} orbitals for Ru with more delocalized 4d{sup 4} orbitals leads to a broad peak in ZFC magnetization. A spontaneous ZFC magnetization becomes negative below 160 K for all the compositions. The occurrence of both normal and inverse magnetocaloric effects in Ba and Ti co-doped SrRuO{sub 3} makes the system more interesting.

  13. Indium segregation effects in (111)B-grown (In,Ga)As/GaAs piezoelectric quantum wells

    NASA Astrophysics Data System (ADS)

    Ballet, Philippe; Disseix, Pierre; Leymarie, Joël; Vasson, Aimé; Vasson, Anne-Marie; Grey, Robert

    1999-02-01

    The effect of indium surface segregation on electronic states and excitonic properties is investigated experimentally and theoretically in (111)B-grown (In,Ga)As/GaAs strained piezoelectric quantum wells. Thermally detected optical absorption and electroreflectance experiments are performed on two samples grown by molecular beam epitaxy and containing 7 and 14 wells. Excitonic energies and oscillator strengths are calculated by a variational method within the effective mass approximation. The influence of indium segregation on the piezoelectric field strength and the oscillator strength of excitonic transitions is analyzed.

  14. A theoretical investigation of effective surface recombination velocity in AlGaAs/GaAs heteroface solar cells

    SciTech Connect

    Gee, J.M.; Drummond, T.J.

    1990-01-01

    An AlGaAs window layer is used in high-efficiency GaAs solar cells to reduce carrier recombination at the front surface. Free surfaces of III-V semiconductors have a high density of surface states that serve as recombination sites and create a depletion region at the front surface. We have performed a theoretical investigation of front-surface recombination that includes the effect of a surface space-charge layer. It was found that the surface space-charge layer can have a profound effect on front-surface recombination for thin or lightly doped window layers. 15 refs., 5 figs., 1 tab.

  15. Barrier lowering effect and dark current characteristics in asymmetric GaAs/AlGaAs multi quantum well structure

    NASA Astrophysics Data System (ADS)

    Altin, E.; Hostut, M.; Ergun, Y.

    2011-12-01

    In this study, we investigate dark current voltage characteristics of GaAs/AlGaAs staircase-like asymmetric multiquantum well structure at various temperatures experimentally. The activation energy is calculated by using Arrhenius plots at different voltages. It is found that the activation energy decreased with increasing electric field. This result is evaluated using a barrier lowering effect which is a combination of geometrical and Poole-Frenkel effects. Measured dark current density-voltage ( J- V) characteristics compared with the Levine model, 3D carrier drift model and the emission capture model. The best agreement with the experimental results of dark current densities is obtained by the Levine model.

  16. Size effect in parabolic GaAs/Al sub x Ga sub 1 minus x As quantum wells

    SciTech Connect

    Walukiewicz, W. ); Hopkins, P.F.; Sundaram, M.; Gossard, A.C. )

    1991-11-15

    We report the results of experimental and theoretical studies of the electron mobility in remotely doped, quasi-three-dimensional GaAs/Al{sub {ital x}}Ga{sub 1{minus}{ital x}}As parabolic wells. We show that the electron mobility in such structures is strongly reduced by a size effect due to nonspecular scattering of electrons from rough walls confining the electron gas. The roughness of the walls results from random fluctuations of the remote-ionized-impurity concentration and/or the alloy composition. Incorporation of the size effect allows for a quantitative description of the electron mobility in these parabolic wells.

  17. Preparation and characterization of Mn and (Mn, Cu) co-doped ZnO nanostructures.

    PubMed

    Wang, H B; Wang, H; Zhang, C; Yang, F J; Duan, J X; Yang, C P; Gu, H S; Zhou, M J; Li, Q; Jiang, Y

    2009-05-01

    We report on the ferromagnetic characteristics of Zn(1-x)Mn(x)O nanorods synthesized by a seed-mediated solution method. The as-doped ZnO nanorods had a length about 200 nm and a diameter ranging from 20 to 30 nm. Magnetic property measurements revealed that the Zn(1-x)Mn(x)O nanorods exhibited weak ferromagnetism at 305 K. Similar solution method were also employed to fabricate the (Mn, Cu) co-doped nanostructures. The presence of Cu2+ was found to change the nanorod morphology (in the case of pure ZnO) to nanoparticle. On the other hand, not only the hysteresis curve saturated at lower magnetic field, but also the saturation magnetization was increased with the Cu doping. Transmission electron microscopy, X-ray photoelectron spectroscopy and Photoluminescence analysis suggested that the room temperature (RT) ferromagnetism could be originated from the Mn2+ doped into the ZnO lattice, and additional carriers due to the Cu co-doping may enhance the room temperature ferromagnetism in the Mn:ZnO system.

  18. Electronic and optical properties study on Fesbnd B co-doped anatase TiO2

    NASA Astrophysics Data System (ADS)

    Li, Xuechao; Shi, Jianhao; Chen, Hao; Wan, Rundong; Leng, Chongyan; Lei, Ying

    2016-09-01

    We investigate the density of states and optical properties for Fe, 2B and (Fe, 2B) doped TiO2 with DFT calculations. The calculated results reveal mono-doping introduces midgap states which are half-occupied and easy to become the recombination centers of charge carriers, thus inhibiting the enhancement of photocatalystic activity. The coupling of 2p-3d states in the (Fe, 2B) compensated co-doped TiO2 makes gap states couple with the valence bands edge, thus greatly causing the band gap narrowing and higher visible light absorption. Moreover, the gap states cannot become recombination centers of the photoexcited carriers, thus promoting the separation of electron-hole pairs, prolonging the lifetime of carriers. The analysis of electron density indicates more electrons from Fe transfer to adjacent B, realizing the charge compensation and forming a stronger Fesbnd B bond. Therefore, the (Fe, 2B) compensated co-doped TiO2 exhibits the higher visible-light photocatalystic activity than those of pure and solely doped TiO2.

  19. Tm/Ho co-doped pulsed fiber laser with low spectral and temporal noise

    NASA Astrophysics Data System (ADS)

    Akosman, Ahmet E.; Sander, Michelle Y.

    2016-05-01

    A Tm/Ho co-doped mode-locked soliton fiber laser design is presented with stable and low noise single-pulsing operation at a repetition rate of 135.2 MHz and a transform limited pulse duration of 375 fs. The fiber laser is directly core pumped at a wavelength of 790 nm. In single-pulsing operation, the fiber laser is centered at a wavelength of 1983 nm and can be continuously tuned over an 8 nm bandwidth. The fiber laser consists of a linear cavity which allows scaling of the repetition rate further by reducing the cavity length and utilizing the high pump absorption at 790 nm and efficient absorption/emission dynamics without photodarkening. In addition, co-doping with Tm/Ho increases the efficiency of the lasing with enhanced cross-relaxation rates. Stable mode-locked operation with reduced ripples in the optical spectrum and high signal-to-background ratios in the RF spectrum is observed. A low relative intensity noise with an rms fluctuation level of 0.13 % (frequency interval of 10 Hz to 1 MHz) and a low phase noise with a timing jitter of 20 fs (frequency range of 100 Hz to 1 MHz) characterizes the mode-locked laser.

  20. Synthesis of boron, nitrogen co-doped porous carbon from asphaltene for high-performance supercapacitors

    NASA Astrophysics Data System (ADS)

    Zhou, Ying; Wang, Dao-Long; Wang, Chun-Lei; Jin, Xin-Xin; Qiu, Jie-Shan

    2014-08-01

    Oxidized asphaltene (OA), a thermosetting material with plenty of functional groups, is synthesized from asphaltene (A) using HNO3/H2SO4 as the oxidizing agent. Boron, nitrogen co-doped porous carbon (BNC—OA) is prepared by carbonization of the mixture of boric acid and OA at 1173 K in an argon atmosphere. X-ray photoelectron spectroscopy (XPS) characterization reveals that the BNC—OA has a nitrogen content of 3.26 at.% and a boron content of 1.31 at.%, while its oxidation-free counterpart (BNC—SA) has a nitrogen content of 1.61 at.% and a boron content of 3.02 at.%. The specific surface area and total pore volume of BNC—OA are 1103 m2·g-1 and 0.921 cm3·g-1, respectively. At a current density of 0.1 A·g-1, the specific capacitance of BNC-OA is 335 F·g-1 and the capacitance retention can still reach 83% at 1 A·g-1. The analysis shows that the superior electrochemical performance of the BNC—OA is attributed to the pseudocapacitance behavior of surface heteroatom functional groups and an abundant pore-structure. Boron, nitrogen co-doped porous carbon is a promising electrode material for supercapacitors.

  1. Optical and physical properties of Er3+-Yb3+ co-doped tellurite fibers

    NASA Astrophysics Data System (ADS)

    Narro-García, R.; Chillcce, E. F.; Miranda, A. R.; Giehl, J. M.; Barbosa, L. C.; Rodriguez, E.; Arronte, M.

    2011-10-01

    In this work we present results of physical and optical properties of Er3+-Yb3+ co-doped tellurite glasses and fibers. The Double Clad Tellurite Fibers (DCTFs) are based on glasses with the composition: TeO2-WO3-Nb2O5-Na2O-Al2O3-Er2O3-Yb2O3. The DCTFs were fabricated by using the rod-in-tube technique and a Heathway drawing tower. The optical absorption spectra (ranging from 350 to 1750 nm) of these fibers were measured using an Optical Spectrum Analyzer (OSA). The emission spectra, around 1550 nm band, of these fibers (lengths varying from 1 to 60 cm) were obtained by using a 980nm diode laser pump. The optimal Amplified Spontaneous Emission (ASE) spectra were observed for fiber lengths ranging from 2 to 6 cm. The Er 3+/Yb3+ co-doped DCTFs show an efficient up-conversion process in comparison with the Er3+-doped DCTF.

  2. Thermochromic properties of Sn, W co-doped VO2 nanostructured thin film deposited by pulsed laser deposition.

    PubMed

    Hur, M G; Masaki, T; Yoon, D H

    2014-12-01

    Tin (Sn) and tungsten (W) co-doped vanadium dioxide (VO2) nanostructured thin films with 50-nm thickness were deposited by pulsed laser deposition (PLD) to reduce the transition temperature and improve the IR transmittance. The crystal structure of the nanostructured thin films and the presence of elements were evaluated by XRD and XPS analysis. The transition temperature (T(c)) of 1 at% Sn-1 at% W co-doped VO2 nanostructured thin film was decreased to about 22 degrees C (from 70.3 to 48.5 degrees C) compared with the undoped VO2 nanostructured thin film. The transmittance width in the IR range of the co-doped nanostructured thin film decreased from 37.5% to 27% compared with the undoped VO2 nanostructured thin film. Also, the width of hysteresis was narrowed by Sn doping. PMID:25970986

  3. Thermochromic properties of Sn, W co-doped VO2 nanostructured thin film deposited by pulsed laser deposition.

    PubMed

    Hur, M G; Masaki, T; Yoon, D H

    2014-12-01

    Tin (Sn) and tungsten (W) co-doped vanadium dioxide (VO2) nanostructured thin films with 50-nm thickness were deposited by pulsed laser deposition (PLD) to reduce the transition temperature and improve the IR transmittance. The crystal structure of the nanostructured thin films and the presence of elements were evaluated by XRD and XPS analysis. The transition temperature (T(c)) of 1 at% Sn-1 at% W co-doped VO2 nanostructured thin film was decreased to about 22 degrees C (from 70.3 to 48.5 degrees C) compared with the undoped VO2 nanostructured thin film. The transmittance width in the IR range of the co-doped nanostructured thin film decreased from 37.5% to 27% compared with the undoped VO2 nanostructured thin film. Also, the width of hysteresis was narrowed by Sn doping.

  4. Effect of temperature on Ga2O3(Gd2O3)/GaN metal-oxide-semiconductor field-effect transistors

    NASA Astrophysics Data System (ADS)

    Ren, F.; Hong, M.; Chu, S. N. G.; Marcus, M. A.; Schurman, M. J.; Baca, A.; Pearton, S. J.; Abernathy, C. R.

    1998-12-01

    Ga2O3(Gd2O3) was deposited on GaN for use as a gate dielectric in order to fabricate a depletion metal-oxide-semiconductor field-effect transistor (MOSFET). Analysis of the effect of temperature on the device shows that gate leakage is significantly reduced at elevated temperature relative to a conventional metal-semiconductor field-effect transistor fabricated on the same GaN layer. MOSFET device operation in fact improved upon heating to 400 °C. Modeling of the effect of temperature on contact resistance suggests that the improvement is due to a reduction in the parasitic resistances present in the device.

  5. Catalytic activity of enzymes immobilized on AlGaN /GaN solution gate field-effect transistors

    NASA Astrophysics Data System (ADS)

    Baur, B.; Howgate, J.; von Ribbeck, H.-G.; Gawlina, Y.; Bandalo, V.; Steinhoff, G.; Stutzmann, M.; Eickhoff, M.

    2006-10-01

    Enzyme-modified field-effect transistors (EnFETs) were prepared by immobilization of penicillinase on AlGaN /GaN solution gate field-effect transistors. The influence of the immobilization process on enzyme functionality was analyzed by comparing covalent immobilization and physisorption. Covalent immobilization by Schiff base formation on GaN surfaces modified with an aminopropyltriethoxysilane monolayer exhibits high reproducibility with respect to the enzyme/substrate affinity. Reductive amination of the Schiff base bonds to secondary amines significantly increases the stability of the enzyme layer. Electronic characterization of the EnFET response to penicillin G indicates that covalent immobilization leads to the formation of an enzyme (sub)monolayer.

  6. An analysis of temperature dependent piezoelectric Franz-Keldysh effect in AlGaN

    NASA Astrophysics Data System (ADS)

    Hou, Y. T.; Teo, K. L.; Li, M. F.; Uchida, Kazuo; Tokunaga, Hiroki; Akutsu, Nakao; Matsumoto, Koh

    2000-02-01

    Strong Franz-Keldysh oscillations near the band gap of AlGaN are observed in the contactless electroreflectance (CER) studies of a GaN/InGaN/AlGaN multilayer structure. The line shape analysis of the CER spectra at different temperatures provides an accurate determination of the AlGaN band gap energies and the built-in electric fields. Using the existing data of the thermal expansion coefficients of GaN and sapphire, and the piezoelectric constants of AlGaN, the temperature dependence of the electric field is estimated and is in good agreement with the experimental results between 15 and 300 K. We attribute such electric field to the piezoelectric strain effect.

  7. Structural, optical and magnetic properties of Co-doped ZnO nanorods with hidden secondary phases

    NASA Astrophysics Data System (ADS)

    Wang, Xuefeng; Zheng, Rongkun; Liu, Zongwen; Ho, Ho-pui; Xu, Jianbin; Ringer, Simon P.

    2008-11-01

    Co-doped ZnO nanorods (composition: Zn0.955Co0.045O) were grown by a simple surfactant-assisted hydrothermal technique. The morphological, structural, optical and magnetic properties of the as-prepared nanorods were investigated by means of scanning electron microscopy, high-resolution transmission electron microscopy, x-ray diffraction, x-ray photoelectron spectroscopy, micro-Raman spectroscopy, micro-cathodoluminescence, and vibrating sample magnetometry (VSM). The results showed that the sample had rod-like morphology and that the preferential growth direction was along the c axis. While Co was successfully doped into the ZnO wurtzite lattice structure as revealed by several characterization techniques, hidden secondary phases of ZnyCo3-yO4 (0<=y<=1) were also clearly detected by the micro-Raman spectroscopic technique. We propose that the predominant diffusion-limited Ostwald ripening crystal growth mechanism under the hydrothermal coarsening yielded such phase segregation. VSM results showed that the nanorods displayed relatively weak room-temperature ferromagnetism. We suggest that the origin of the ferromagnetism is probably due to the presence of the mixed cation valence of Co via a d-d double-exchange mechanism rather than the real doping effect. It is essential to control the crystal growth mechanism and defect states associated with the ferromagnetism in order to realize the intrinsic diluted magnetic semiconductors.

  8. Enhanced room temperature ferromagnetism and photoluminescence behavior of Cu-doped ZnO co-doped with Mn

    NASA Astrophysics Data System (ADS)

    Ashokkumar, M.; Muthukumaran, S.

    2015-05-01

    Cu, Mn co-doped ZnO nanoparticles were successfully synthesized by the sol-gel technique. XRD pattern described that Mn-doping did not affect the hexagonal wurtzite structure of the samples and no secondary phases were found. The reduced crystallite size at Mn=2% is due to the suppression of grain surface growth by foreign impurity. The enhancement of crystal size after Mn=2% is due to the expansion of lattice volume produced by the distortion around the dopant ion. The better dielectric constant and conductivity noticed at Mn=2% are explained by charge carrier density and crystallite size. The suppression of broad UV band by Mn-doping is discussed based on the generation of non-radiative recombination centers. Hysteresis loop showed the clear room temperature ferromagnetism in all the samples and the magnetization increased with Mn-doping. Better electrical and magnetic behavior of Zn0.94Cu0.04Mn0.02O sample is suggested for effective opto-magnetic devices.

  9. Enhancement of magnetic and ferroelectric behaviour in (Ca, Co) co-doped HoMnO3 multiferroics

    NASA Astrophysics Data System (ADS)

    Rout, P. P.; Pradhan, S. K.; Das, S. K.; Samantaray, S.; Roul, B. K.

    2013-11-01

    The effect of sintering temperature on structural, electrical and magnetic behaviours of polycrystalline samples of Ho0.9Ca0.1Mn0.9Co0.1O3 prepared by the solid state reaction route sintered at three different temperature 1250 °C, 1350 °C, 1450 °C for 10 h are investigated. XRD, SEM, magnetization, dielectric and ferroelectric measurements were carried out. Experimental results showed the nucleation of orthorhombic phase as the sintering temperature increases from 1250 °C to 1450 °C. Ferroelectric (Tc) and antiferromagnetic transition temperature (TN) increases with increase in sintering temperature. Strong bifurcation of FC and ZFC curve in sample sintered at 1450 °C showed a clear onset of ferromagnetic state around 165 °K, which is confirmed from M to H graph at 165 °K. All the sample showed ferroelectric behaviour at room temperature which are leaky in nature. Sintering temperature along with Ca and Co doping in HoMnO3 ceramics plays an important role in phase transformation along with enhancement in multiferroic properties.

  10. Hydrothermal synthesis of Yb3+, Tm3+ co-doped Gd6MoO12 and its upconversion properties

    NASA Astrophysics Data System (ADS)

    Di, Qiu-Mei; Sun, Yu-Mei; Xu, Qi-Guang; Han, Liu; Xue, Bing; Sun, Jia-Yue

    2015-06-01

    Yb3+, Tm3+ co-doped Gd6MoO12 phosphors with different morphologies are prepared by the hydrothermal method. The dendrites present different morphologies (including hexagonal prisms, spindles, and spheres) after changing the pH value and edetate disodium (EDTA) usage. It is found that each of the two factors plays a crucial role in forming different morphologies. The up-conversion (UC) luminescence is studied. Under 980-nm semiconductor laser excitation, relatively strong blue emission and weak red emission are observed. Finally, the effect of pumping power on the UC luminescence properties and the level diagram mechanism of Gd6MoO12:Yb3+/Tm3+ phosphor are also discussed. Project supported by the National Natural Science Foundation of China (Grant No. 20976002), the Beijing Natural Science Foundation, China (Grant No. 2122012), the Key Projects for Science and Technology of Beijing Education Commission, China (Grant No. KZ201310011013), and the Education and Research Fund of Guangdong Province, China (Grant No. 2011B090400100).

  11. Er 3+-Yb 3+ co-doped glass waveguide amplifiers using ion exchange and field-assisted annealing

    NASA Astrophysics Data System (ADS)

    Zhang, X. Z.; Liu, K.; Mu, S. K.; Tan, C. Z.; Zhang, D.; Pun, E. Y. B.; Zhang, D. M.

    2006-12-01

    Er 3+-Yb 3+ co-doped waveguide amplifiers fabricated using thermal two-step ion-exchange are demonstrated. K +-Na + ion-exchange process was first carried out in pure KNO 3 molten bath, and then field-assisted annealing (FAA) was used to make the buried waveguides. The effective buried depth is estimated to be ˜3.4 μm for the buried FAA waveguides. With the use of cut-back method, the fiber-to-guide coupling loss of ˜4.38 dB, the waveguide loss of ˜2.27 dB/cm, and Er 3+ absorption loss ˜5.7 dB were measured for a ˜1.24-cm-long waveguide. Peak relative gain of ˜7.0 dB is obtained for a ˜1.24-cm-long waveguide. The potential for the fabrication of compact optical amplifiers operating in the range of 1520-1580 nm is also demonstrated.

  12. NIR luminescence studies on Er3+:Yb3+ co-doped sodium telluroborate glasses for lasers and optical amplifer applications

    NASA Astrophysics Data System (ADS)

    Annapoorani, K.; Murthy, N. Suriya; Marimuthu, K.

    2016-05-01

    Er3+:Yb3+ co-doped Sodium telluroborate glasses were prepared with the chemical composition (49.5-x)B2O3+25TeO2+5Li2CO3+10ZnO+10NaF+0.5Er2O3+xYb2O3 (where x= 0.1, 0.5, 1.0 and 2.0 in mol %) following the melt quenching technique. With the addition of Yb3+ ions into Er3+ ions in the prepared glasses, the absorption cross-section values were found to increase due to the effective energy transfer from 2F5/2 level of Yb3+ ions to the 4I11/2 level of Er3+ ions. The fluorescence around 1550 nm correspond to the 4I13/2→4I15/2 transition was observed under 980 nm pumping. Among the present glasses, integrated intensity was found to be higher for 1.0 mol% Yb3+ ion glass. The parameters such as stimulated emission cross- section, Gain bandwidth and quantum efficiency of the 4I13/2→4I15/2 transition was found to be higher for the NTBE1.0Y glass and the same is suggested for potential NIR lasers and optical amplifier applications.

  13. Comparative x-ray absorption spectroscopy study of Co-doped SnO2 and TiO2

    NASA Astrophysics Data System (ADS)

    Lussier, A.; Dvorak, J.; Idzerda, Y. U.; Ogale, S. B.; Shinde, S. R.; Choudary, R. J.; Venkatesan, T.

    2004-06-01

    We performed x-ray absorption spectroscopy measurements at the cobalt L2,3 edge and the oxygen K edge of Co-doped SnO2 and Co-doped TiO2. Our measurements confirm that doped cobalt atoms are in the same local environment in both compounds. Furthermore, the results support the idea that cobalt atoms occupy substitutional cation sites. Additionally, the oxygen spectral shapes offer insight into a possible cause for the observed giant magnetic moment of cobalt atoms present in SnO2, but not in TiO2.

  14. Highly luminescent S, N co-doped graphene quantum dots with broad visible absorption bands for visible light photocatalysts

    NASA Astrophysics Data System (ADS)

    Qu, Dan; Zheng, Min; Du, Peng; Zhou, Yue; Zhang, Ligong; Li, Di; Tan, Huaqiao; Zhao, Zhao; Xie, Zhigang; Sun, Zaicheng

    2013-11-01

    A facile hydrothermal synthesis route to N and S, N co-doped graphene quantum dots (GQDs) was developed by using citric acid as the C source and urea or thiourea as N and S sources. Both N and S, N doped GQDs showed high quantum yield (78% and 71%), excitation independent under excitation of 340-400 nm and single exponential decay under UV excitation. A broad absorption band in the visible region appeared in S, N co-doped GQDs due to doping with sulfur, which alters the surface state of GQDs. However, S, N co-doped GQDs show different color emission under excitation of 420-520 nm due to their absorption in the visible region. The excellent photocatalytic performance of the S, N co-doped GQD/TiO2 composites was demonstrated by degradation of rhodamine B under visible light. The apparent rate of S, N:GQD/TiO2 is 3 and 10 times higher than that of N:GQD/TiO2 and P25 TiO2 under visible light irradiation, respectively.A facile hydrothermal synthesis route to N and S, N co-doped graphene quantum dots (GQDs) was developed by using citric acid as the C source and urea or thiourea as N and S sources. Both N and S, N doped GQDs showed high quantum yield (78% and 71%), excitation independent under excitation of 340-400 nm and single exponential decay under UV excitation. A broad absorption band in the visible region appeared in S, N co-doped GQDs due to doping with sulfur, which alters the surface state of GQDs. However, S, N co-doped GQDs show different color emission under excitation of 420-520 nm due to their absorption in the visible region. The excellent photocatalytic performance of the S, N co-doped GQD/TiO2 composites was demonstrated by degradation of rhodamine B under visible light. The apparent rate of S, N:GQD/TiO2 is 3 and 10 times higher than that of N:GQD/TiO2 and P25 TiO2 under visible light irradiation, respectively. Electronic supplementary information (ESI) available: More XPS and UV-Vis spectra. See DOI: 10.1039/c3nr04402e

  15. Er/Yb co-doped oxy-fluoride glass-ceramics core/polymer cladding optical fibers

    NASA Astrophysics Data System (ADS)

    Czerska, E.; Świderska, M.

    2014-11-01

    Erbium/ytterbium co-doped glasses can be applied as NIR laser sources (1.55 μm) or optical amplifiers in this range. About hundred meters of Er/Yb co-doped oxy-fluoride glass-ceramics fibers have been drawn from a glass preform followed by controlled annealing. Processing temperatures (drawing and annealing) were selected upon thermal analysis results (DTA/DSC plots). Glass-ceramic structure was confirmed by the XRD measurements. Obtained fibers show good optical properties. As a cladding material polymer material (acrylic resin) is considered due to its low deposition temperature and suitable value of refractive index.

  16. Effects of Ga Addition on Interfacial Reactions Between Sn-Based Solders and Ni

    NASA Astrophysics Data System (ADS)

    Wang, Chao-Hong; Li, Kuan-Ting

    2016-07-01

    The use of Ga as a micro-alloying element in Sn-based solders can change the microstructure of solder joints to improve the mechanical properties, and even suppress the interfacial intermetallic compound (IMC) growth. This research investigated the effects of Ga addition (0.2-1 wt.%Ga) on the IMC formation and morphological evolution in the Sn-based solder joints with Ni substrate. In the soldering reaction at 250°C and with less than 0.2 wt.%Ga addition, the formed phase was Ni3Sn4. When the Ga addition increased to 0.5 wt.%, it changed to a thin Ni2Ga3 layer of ˜1 μm thick, which stably existed at the interface in the initial 1-h reaction. Subsequently, the whole Ni2Ga3 layer detached from the Ni substrate and drifted into the molten solder. The Ni3Sn4 phase became dominant in the later stage. Notably, the Ga addition significantly reduced the grain size of Ni3Sn4, resulting in the massive spalling of Ni3Sn4 grains. With 1 wt.%Ga addition, the Ni2Ga3 layer remained very thin with no significant growth, and it stably existed at the interface for more than 10 h. In addition, the solid-state reactions were examined at temperatures of 160°C to 200°C. With addition of 0.5 wt.%Ga, the Ni3Sn4 phase dominated the whole reaction. By contrast, with increasing to 1 wt.%Ga, only a thin Ni2Ga3 layer was found even after aging at 160°C for more than 1200 h. The 1 wt.%Ga addition in solder can effectively inhibit the Ni3Sn4 formation in soldering and the long-term aging process.

  17. Analysis of Photoluminescence Thermal Quenching: Guidance for the Design of Highly Effective p-type Doping of Nitrides

    NASA Astrophysics Data System (ADS)

    Liu, Zhiqiang; Huang, Yang; Yi, Xiaoyan; Fu, Binglei; Yuan, Guodong; Wang, Junxi; Li, Jinmin; Zhang, Yong

    2016-08-01

    A contact-free diagnostic technique for examining position of the impurity energy level of p-type dopants in nitride semiconductors was proposed based on photoluminescence thermal quenching. The Mg ionization energy was extracted by the phenomenological rate-equation model we developed. The diagnostic technique and analysis model reported here are priorities for the design of highly effective p-doping of nitrides and could also be used to explain the abnormal and seldom analyzed low characteristic temperature T0 (about 100 K) of thermal quenching in p-type nitrides systems. An In-Mg co-doped GaN system is given as an example to prove the validity of our methods. Furthermore, a hole concentration as high as 1.94 × 1018 cm-3 was achieved through In-Mg co-doping, which is nearly one order of magnitude higher than typically obtained in our lab.

  18. Analysis of Photoluminescence Thermal Quenching: Guidance for the Design of Highly Effective p-type Doping of Nitrides

    PubMed Central

    Liu, Zhiqiang; Huang, Yang; Yi, Xiaoyan; Fu, Binglei; Yuan, Guodong; Wang, Junxi; Li, Jinmin; Zhang, Yong

    2016-01-01

    A contact-free diagnostic technique for examining position of the impurity energy level of p-type dopants in nitride semiconductors was proposed based on photoluminescence thermal quenching. The Mg ionization energy was extracted by the phenomenological rate-equation model we developed. The diagnostic technique and analysis model reported here are priorities for the design of highly effective p-doping of nitrides and could also be used to explain the abnormal and seldom analyzed low characteristic temperature T0 (about 100 K) of thermal quenching in p-type nitrides systems. An In-Mg co-doped GaN system is given as an example to prove the validity of our methods. Furthermore, a hole concentration as high as 1.94 × 1018 cm−3 was achieved through In-Mg co-doping, which is nearly one order of magnitude higher than typically obtained in our lab. PMID:27550805

  19. Inversion-mode GaAs wave-shaped field-effect transistor on GaAs (100) substrate

    SciTech Connect

    Zhang, Jingyun; Si, Mengwei; Wu, Heng; Ye, Peide D.; Lou, Xiabing; Gordon, Roy G.; Shao, Jiayi; Manfra, Michael J.

    2015-02-16

    Inversion-mode GaAs wave-shaped metal-oxide-semiconductor field-effect transistors (WaveFETs) are demonstrated using atomic-layer epitaxy of La{sub 2}O{sub 3} as gate dielectric on (111)A nano-facets formed on a GaAs (100) substrate. The wave-shaped nano-facets, which are desirable for the device on-state and off-state performance, are realized by lithographic patterning and anisotropic wet etching with optimized geometry. A well-behaved 1 μm gate length GaAs WaveFET shows a maximum drain current of 64 mA/mm, a subthreshold swing of 135 mV/dec, and an I{sub ON}/I{sub OFF} ratio of greater than 10{sup 7}.

  20. Characterization and mechanistic analysis of the visible light response of cerium and nitrogen co-doped TiO2 nano-photocatalyst synthesized using a one-step technique.

    PubMed

    Yu, Tao; Tan, Xin; Zhao, Lin

    2010-04-15

    Cerium and nitrogen co-doped anatase TiO(2) nanoparticles were synthesized using a one-step technique via a modified sol-gel process and characterized by XRD, BET, DRS, Raman and XPS. The photocatalytic mechanism of the degradation of methylene blue (MB) under fluorescent light and visible light irradiation was studied. Co-doping cerium and nitrogen in the crystal lattice of TiO(2) narrowed the band gap from 2.40 eV (Ce-doped TiO(2)) to 2.21 eV (Ce/N co-doped TiO(2)). Ce(4+)/Ce(3+) pairs, oxynitride species and Ti-O-N and Ti-O-Ce bonds were determined by XPS. The recombination of photogenerated electron-hole pairs was inhibited due to the synergistic effect of doping with Ce(4+)/Ce(3+) ions and N atoms. The optimal doping ratio was 0.70% Ce and 0.70% N using MB photocatalytic degradation under fluorescent light and visible light irradiation (lambda>420 nm). The enhanced photocatalytic degradation under visible light irradiation was attributed to the increasing number of photogenerated OH radicals. The recombination of photogenerated e(-)-h(+) was attributed to be the key factor for the decrease in the photocatalytic degradation efficiency of MB.

  1. Enhanced sheet carrier densities in polarization controlled AlInN/AlN/GaN/InGaN field-effect transistor on Si (111)

    SciTech Connect

    Hennig, J. Dadgar, A.; Witte, H.; Bläsing, J.; Lesnik, A.; Strittmatter, A.; Krost, A.

    2015-07-15

    We report on GaN based field-effect transistor (FET) structures exhibiting sheet carrier densities of n = 2.9 10{sup 13} cm{sup −2} for high-power transistor applications. By grading the indium-content of InGaN layers grown prior to a conventional GaN/AlN/AlInN FET structure control of the channel width at the GaN/AlN interface is obtained. The composition of the InGaN layer was graded from nominally x{sub In} = 30 % to pure GaN just below the AlN/AlInN interface. Simulations reveal the impact of the additional InGaN layer on the potential well width which controls the sheet carrier density within the channel region of the devices. Benchmarking the In{sub x}Ga{sub 1−x}N/GaN/AlN/Al{sub 0.87}In{sub 0.13}N based FETs against GaN/AlN/AlInN FET reference structures we found increased maximum current densities of I{sub SD} = 1300 mA/mm (560 mA/mm). In addition, the InGaN layer helps to achieve broader transconductance profiles as well as reduced leakage currents.

  2. Comparative investigation of GaAsSb/InGaAs type-II and InP/InGaAs type-I doped-channel field-effect transistors

    SciTech Connect

    Wu, Yi-Chen; Tsai, Jung-Hui; Chiang, Te-Kuang; Chiang, Chung-Cheng; Wang, Fu-Min

    2015-02-15

    DC performance of GaAsSb/InGaAs type-II and InP/InGaAs type-I doped-channel field-effect transistors (DCFETs) is demonstrated and compared by two-dimensional simulated analysis. As compared with the traditional InP/InGaAs DCFET, the GaAsSb/InGaAs DCFET exhibits a higher drain current of 8.05 mA, a higher transconductance of 216.24 mS/mm, and a lower gate turn-on voltage of 0.25 V for the presence of a relatively large conduction band discontinuity (ΔE{sub c} ≈ 0.4 eV) at GaAsSb/InGaAs heterostructure and the formation of two-dimensional electron gas in the n{sup +}-InGaAs doping channel. However, due to the tunneling effect under large gate-to-source bias, it results in considerably large gate leakage current in the GaAsSb/InGaAs DCFET.

  3. The effect of free-standing GaN substrate on carrier localization in ultraviolet InGaN light-emitting diodes.

    PubMed

    Tsai, Ming-Ta; Chu, Chung-Ming; Huang, Che-Hsuan; Wu, Yin-Hao; Chiu, Ching-Hsueh; Li, Zhen-Yu; Tu, Po-Min; Lee, Wei-I; Kuo, Hao-Chung

    2014-12-01

    In this study, we have grown 380-nm ultraviolet light-emitting diodes (UV-LEDs) based on InGaN/AlInGaN multiple quantum well (MQW) structures on free-standing GaN (FS-GaN) substrate by atmospheric pressure metal-organic chemical vapor deposition (AP-MOCVD), and investigated the relationship between carrier localization degree and FS-GaN. The micro-Raman shift peak mapping image shows low standard deviation (STD), indicating that the UV-LED epi-wafer of low curvature and MQWs of weak quantum-confined Stark effect (QCSE) were grown. High-resolution X-ray diffraction (HRXRD) analyses demonstrated high-order satellite peaks and clear fringes between them for the UV-LEDs grown on the FS-GaN substrate, from which the interface roughness (IRN) was estimated. The temperature-dependent photoluminescence (PL) measurement confirmed that the UV-LEDs grown on the FS-GaN substrate exhibited better carrier confinement. Besides, the high-resolution transmission electron microscopy (HRTEM) and energy-dispersive spectrometer (EDS) mapping images verified that the UV-LEDs on FS-GaN have fairly uniform distribution of indium and more ordered InGaN/AlInGaN MQW structure. Clearly, the FS-GaN can not only improve the light output power but also reduce the efficiency droop phenomenon at high injection current. Based on the results mentioned above, the FS-GaN can offer UV-LEDs based on InGaN/AlInGaN MQW structures with benefits, such as high crystal quality and small carrier localization degree, compared with the UV-LEDs on sapphire.

  4. The effect of free-standing GaN substrate on carrier localization in ultraviolet InGaN light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Tsai, Ming-Ta; Chu, Chung-Ming; Huang, Che-Hsuan; Wu, Yin-Hao; Chiu, Ching-Hsueh; Li, Zhen-Yu; Tu, Po-Min; Lee, Wei-I.; Kuo, Hao-Chung

    2014-12-01

    In this study, we have grown 380-nm ultraviolet light-emitting diodes (UV-LEDs) based on InGaN/AlInGaN multiple quantum well (MQW) structures on free-standing GaN (FS-GaN) substrate by atmospheric pressure metal-organic chemical vapor deposition (AP-MOCVD), and investigated the relationship between carrier localization degree and FS-GaN. The micro-Raman shift peak mapping image shows low standard deviation (STD), indicating that the UV-LED epi-wafer of low curvature and MQWs of weak quantum-confined Stark effect (QCSE) were grown. High-resolution X-ray diffraction (HRXRD) analyses demonstrated high-order satellite peaks and clear fringes between them for the UV-LEDs grown on the FS-GaN substrate, from which the interface roughness (IRN) was estimated. The temperature-dependent photoluminescence (PL) measurement confirmed that the UV-LEDs grown on the FS-GaN substrate exhibited better carrier confinement. Besides, the high-resolution transmission electron microscopy (HRTEM) and energy-dispersive spectrometer (EDS) mapping images verified that the UV-LEDs on FS-GaN have fairly uniform distribution of indium and more ordered InGaN/AlInGaN MQW structure. Clearly, the FS-GaN can not only improve the light output power but also reduce the efficiency droop phenomenon at high injection current. Based on the results mentioned above, the FS-GaN can offer UV-LEDs based on InGaN/AlInGaN MQW structures with benefits, such as high crystal quality and small carrier localization degree, compared with the UV-LEDs on sapphire.

  5. The effect of free-standing GaN substrate on carrier localization in ultraviolet InGaN light-emitting diodes.

    PubMed

    Tsai, Ming-Ta; Chu, Chung-Ming; Huang, Che-Hsuan; Wu, Yin-Hao; Chiu, Ching-Hsueh; Li, Zhen-Yu; Tu, Po-Min; Lee, Wei-I; Kuo, Hao-Chung

    2014-12-01

    In this study, we have grown 380-nm ultraviolet light-emitting diodes (UV-LEDs) based on InGaN/AlInGaN multiple quantum well (MQW) structures on free-standing GaN (FS-GaN) substrate by atmospheric pressure metal-organic chemical vapor deposition (AP-MOCVD), and investigated the relationship between carrier localization degree and FS-GaN. The micro-Raman shift peak mapping image shows low standard deviation (STD), indicating that the UV-LED epi-wafer of low curvature and MQWs of weak quantum-confined Stark effect (QCSE) were grown. High-resolution X-ray diffraction (HRXRD) analyses demonstrated high-order satellite peaks and clear fringes between them for the UV-LEDs grown on the FS-GaN substrate, from which the interface roughness (IRN) was estimated. The temperature-dependent photoluminescence (PL) measurement confirmed that the UV-LEDs grown on the FS-GaN substrate exhibited better carrier confinement. Besides, the high-resolution transmission electron microscopy (HRTEM) and energy-dispersive spectrometer (EDS) mapping images verified that the UV-LEDs on FS-GaN have fairly uniform distribution of indium and more ordered InGaN/AlInGaN MQW structure. Clearly, the FS-GaN can not only improve the light output power but also reduce the efficiency droop phenomenon at high injection current. Based on the results mentioned above, the FS-GaN can offer UV-LEDs based on InGaN/AlInGaN MQW structures with benefits, such as high crystal quality and small carrier localization degree, compared with the UV-LEDs on sapphire. PMID:26088993

  6. Theoretical study on erbium ytterbium co-doped super-fluorescent fiber source

    NASA Astrophysics Data System (ADS)

    Wentao, Guo; Feng, Du; Manqing, Tan; Jian, Jiao; Xiaofeng, Guo

    2016-01-01

    Erbium ytterbium co-doped super-fluorescent fiber source (EYD-SFS) has been simulated by a theoretical model based on rate equations and power transfer equations. The output performances of four basic structures of EYD-SFS have been expressed, and it indicated that the DPF structure is a preferable structure. The dependence of output power, mean wavelength and bandwidth stability on the pump fiber length and the concentration of Er3+ and Yb3+ have also been studied. The results indicated with a proper doping concentration of Er3+ and Yb3+ of 6.0 × 1026 ions/m3 and 1.0 × 1027 ions/m3, the optimal gain fiber length is 3.6 cm. In this condition, good performances of DPF structure of EYD-SFS have been achieved.

  7. Ultrahigh volumetric capacitance and cyclic stability of fluorine and nitrogen co-doped carbon microspheres

    PubMed Central

    Zhou, Junshuang; Lian, Jie; Hou, Li; Zhang, Junchuan; Gou, Huiyang; Xia, Meirong; Zhao, Yufeng; Strobel, Timothy A.; Tao, Lu; Gao, Faming

    2015-01-01

    Highly porous nanostructures with large surface areas are typically employed for electrical double-layer capacitors to improve gravimetric energy storage capacity; however, high surface area carbon-based electrodes result in poor volumetric capacitance because of the low packing density of porous materials. Here, we demonstrate ultrahigh volumetric capacitance of 521 F cm−3 in aqueous electrolytes for non-porous carbon microsphere electrodes co-doped with fluorine and nitrogen synthesized by low-temperature solvothermal route, rivaling expensive RuO2 or MnO2 pseudo-capacitors. The new electrodes also exhibit excellent cyclic stability without capacitance loss after 10,000 cycles in both acidic and basic electrolytes at a high charge current of 5 A g−1. This work provides a new approach for designing high-performance electrodes with exceptional volumetric capacitance with high mass loadings and charge rates for long-lived electrochemical energy storage systems. PMID:26415838

  8. Co-doped sodium chloride crystals exposed to different irradiation temperature

    NASA Astrophysics Data System (ADS)

    Ortiz-Morales, A.; Cruz-Zaragoza, E.; Furetta, C.; Kitis, G.; Flores J., C.; Hernández A., J.; Murrieta S., H.

    2013-07-01

    Monocrystals of NaCl:XCl2:MnCl2(X = Ca,Cd) at four different concentrations have been analyzed. The crystals were exposed to different irradiation temperature, such as at room temperature (RT), solid water (SW), dry ice (DI) and liquid nitrogen (LN). The samples were irradiated with photon from 60Co irradiators. The co-doped sodium chloride crystals show a complex structure of glow curves that can be related to different distribution of traps. The linearity response was analyzed with the F(D) index. The F(D) value was less than unity indicating a sub-linear response was obtained from the TL response on the function of the dose. The glow curves were deconvoluted by using the CGCD program based on the first, second and general order kinetics.

  9. Electronic and magnetic properties of Co doped MoS2 monolayer

    PubMed Central

    Wang, Yiren; Li, Sean; Yi, Jiabao

    2016-01-01

    First principle calculations are employed to calculate the electronic and magnetic properties of Co doped MoS2 by considering a variety of defects including all the possible defect complexes. The results indicate that pristine MoS2 is nonmagnetic. The materials with the existence of S vacancy or Mo vacancy alone are non-magnetic either. Further calculation demonstrates that Co substitution at Mo site leads to spin polarized state. Two substitutional CoMo defects tend to cluster and result in the non-magnetic behaviour. However, the existence of Mo vacancies leads to uniform distribution of Co dopants and it is energy favourable with ferromagnetic coupling, resulting in an intrinsic diluted magnetic semiconductor. PMID:27052641

  10. Magnetic property and possible half-metal behavior in Co-doped graphene

    SciTech Connect

    Li, Zhongyao Xie, Wenze; Liu, Xingen; Wu, Yong

    2015-02-28

    The magnetic property and band structures of Co-monolayer doped graphene were examined on the basis of density-functional theory. The magnetic moment of the system is closely related to the interfacial spacing. Magnetic-nonmagnetic transition would be produced by decreasing the layer distance. Although the magnetic moment can also be reduced by increasing the lattice constant, the ground states are magnetic states under tension. Besides, the increase of lattice constant greatly enlarges the direct and indirect gaps of spin-down bands near the Fermi level. With a little increase of the Fermi level or the electron density, half-metal behavior would be expectable in the Co-doped graphene under tension.

  11. Impacts of Co doping on ZnO transparent switching memory device characteristics

    NASA Astrophysics Data System (ADS)

    Simanjuntak, Firman Mangasa; Prasad, Om Kumar; Panda, Debashis; Lin, Chun-An; Tsai, Tsung-Ling; Wei, Kung-Hwa; Tseng, Tseung-Yuen

    2016-05-01

    The resistive switching characteristics of indium tin oxide (ITO)/Zn1-xCoxO/ITO transparent resistive memory devices were investigated. An appropriate amount of cobalt dopant in ZnO resistive layer demonstrated sufficient memory window and switching stability. In contrast, pure ZnO devices demonstrated a poor memory window, and using an excessive dopant concentration led to switching instability. To achieve suitable memory performance, relying only on controlling defect concentrations is insufficient; the grain growth orientation of the resistive layer must also be considered. Stable endurance with an ON/OFF ratio of more than one order of magnitude during 5000 cycles confirmed that the Co-doped ZnO device is a suitable candidate for resistive random access memory application. Additionally, fully transparent devices with a high transmittance of up to 90% at wavelength of 550 nm have been fabricated.

  12. Highly piezoelectric MgZr co-doped aluminum nitride-based vibrational energy harvesters.

    PubMed

    Minh, Le Van; Hara, Motoaki; Yokoyama, Tsuyoshi; Nishihara, Tokihiro; Ueda, Masanori; Kuwano, Hiroki

    2015-11-01

    The first MgZr co-doped AlN-based vibrational energy harvester (VEH) is presented. (MgZr)AlN, which is a new class of doped AlN, provides high piezoelectricity and cost advantage. Using 13%-(MgZr)-doped AlN for micromachined VEHs, maximum output power of 1.3 μW was achieved with a Q-factor of 400 when resonant frequency, vibration acceleration, load resistance were 792 Hz, 8 m/s(2), and 1.1 MΩ, respectively. Normalized power density was 8.1 kW·g(-2)·m(-3). This was one of the highest values among the currently available piezoelectric VEHs. PMID:26559628

  13. Highly piezoelectric MgZr co-doped aluminum nitride-based vibrational energy harvesters.

    PubMed

    Minh, Le Van; Hara, Motoaki; Yokoyama, Tsuyoshi; Nishihara, Tokihiro; Ueda, Masanori; Kuwano, Hiroki

    2015-11-01

    The first MgZr co-doped AlN-based vibrational energy harvester (VEH) is presented. (MgZr)AlN, which is a new class of doped AlN, provides high piezoelectricity and cost advantage. Using 13%-(MgZr)-doped AlN for micromachined VEHs, maximum output power of 1.3 μW was achieved with a Q-factor of 400 when resonant frequency, vibration acceleration, load resistance were 792 Hz, 8 m/s(2), and 1.1 MΩ, respectively. Normalized power density was 8.1 kW·g(-2)·m(-3). This was one of the highest values among the currently available piezoelectric VEHs.

  14. Co-doped sodium chloride crystals exposed to different irradiation temperature

    SciTech Connect

    Ortiz-Morales, A.; Cruz-Zaragoza, E.; Furetta, C.; Kitis, G.; Flores J, C.; Hernandez A, J.; Murrieta S, H.

    2013-07-03

    Monocrystals of NaCl:XCl{sub 2}:MnCl{sub 2}(X = Ca,Cd) at four different concentrations have been analyzed. The crystals were exposed to different irradiation temperature, such as at room temperature (RT), solid water (SW), dry ice (DI) and liquid nitrogen (LN). The samples were irradiated with photon from {sup 60}Co irradiators. The co-doped sodium chloride crystals show a complex structure of glow curves that can be related to different distribution of traps. The linearity response was analyzed with the F(D) index. The F(D) value was less than unity indicating a sub-linear response was obtained from the TL response on the function of the dose. The glow curves were deconvoluted by using the CGCD program based on the first, second and general order kinetics.

  15. Encapsulation of Fe3O4 Nanoparticles into N, S co-Doped Graphene Sheets with Greatly Enhanced Electrochemical Performance

    PubMed Central

    Yang, Zunxian; Qian, Kun; Lv, Jun; Yan, Wenhuan; Liu, Jiahui; Ai, Jingwei; Zhang, Yuxiang; Guo, Tailiang; Zhou, Xiongtu; Xu, Sheng; Guo, Zaiping

    2016-01-01

    Particular N, S co-doped graphene/Fe3O4 hybrids have been successfully synthesized by the combination of a simple hydrothermal process and a subsequent carbonization heat treatment. The nanostructures exhibit a unique composite architecture, with uniformly dispersed Fe3O4 nanoparticles and N, S co-doped graphene encapsulant. The particular porous characteristics with many meso/micro holes/pores, the highly conductive N, S co-doped graphene, as well as the encapsulating N, S co-doped graphene with the high-level nitrogen and sulfur doping, lead to excellent electrochemical performance of the electrode. The N-S-G/Fe3O4 composite electrode exhibits a high initial reversible capacity of 1362.2 mAhg−1, a high reversible specific capacity of 1055.20 mAhg−1 after 100 cycles, and excellent cycling stability and rate capability, with specific capacity of 556.69 mAhg−1 when cycled at the current density of 1000 mAg−1, indicating that the N-S-G/Fe3O4 composite is a promising anode candidate for Li-ion batteries. PMID:27296103

  16. Encapsulation of Fe3O4 Nanoparticles into N, S co-Doped Graphene Sheets with Greatly Enhanced Electrochemical Performance.

    PubMed

    Yang, Zunxian; Qian, Kun; Lv, Jun; Yan, Wenhuan; Liu, Jiahui; Ai, Jingwei; Zhang, Yuxiang; Guo, Tailiang; Zhou, Xiongtu; Xu, Sheng; Guo, Zaiping

    2016-01-01

    Particular N, S co-doped graphene/Fe3O4 hybrids have been successfully synthesized by the combination of a simple hydrothermal process and a subsequent carbonization heat treatment. The nanostructures exhibit a unique composite architecture, with uniformly dispersed Fe3O4 nanoparticles and N, S co-doped graphene encapsulant. The particular porous characteristics with many meso/micro holes/pores, the highly conductive N, S co-doped graphene, as well as the encapsulating N, S co-doped graphene with the high-level nitrogen and sulfur doping, lead to excellent electrochemical performance of the electrode. The N-S-G/Fe3O4 composite electrode exhibits a high initial reversible capacity of 1362.2 mAhg(-1), a high reversible specific capacity of 1055.20 mAhg(-1) after 100 cycles, and excellent cycling stability and rate capability, with specific capacity of 556.69 mAhg(-1) when cycled at the current density of 1000 mAg(-1), indicating that the N-S-G/Fe3O4 composite is a promising anode candidate for Li-ion batteries. PMID:27296103

  17. Quantitative analysis of immobilized penicillinase using enzyme-modified AlGaN/GaN field-effect transistors.

    PubMed

    Müntze, Gesche Mareike; Baur, Barbara; Schäfer, Wladimir; Sasse, Alexander; Howgate, John; Röth, Kai; Eickhoff, Martin

    2015-02-15

    Penicillinase-modified AlGaN/GaN field-effect transistors (PenFETs) are utilized to systematically investigate the covalently immobilized enzyme penicillinase under different experimental conditions. We demonstrate quantitative evaluation of covalently immobilized penicillinase layers on pH-sensitive field-effect transistors (FETs) using an analytical kinetic PenFET model. This kinetic model is explicitly suited for devices with thin enzyme layers that are not diffusion-limited, as it is the case for the PenFETs discussed here. By means of the kinetic model it was possible to extract the Michaelis constant of covalently immobilized penicillinase as well as relative transport coefficients of the different species associated with the enzymatic reaction which, exempli gratia, give information about the permeability of the enzymatic layer. Based on this analysis we quantify the reproducibility and the stability of the analyzed PenFETs over the course of 33 days as well as the influence of pH and buffer concentration on the properties of the enzymatic layer. Thereby the stability measurements reveal a Michalis constant KM of (67 ± 13)μM while the chronological development of the relative transport coefficients suggests a detachment of physisorbed penicillinase during the first two weeks since production. Our results show that AlGaN/GaN PenFETs prepared by covalent immobilization of a penicillinase enzyme layer present a powerful tool for quantitative analysis of enzyme functionality.

  18. Investigations on luminescence behavior of Er3+/Yb3+ co-doped boro-tellurite glasses

    NASA Astrophysics Data System (ADS)

    Maheshvaran, K.; Arunkumar, S.; Venkata Krishnaiah, K.; Marimuthu, K.

    2015-01-01

    Er3+/Yb3+ co-doped boro-tellurite glasses with the chemical composition 30TeO2+(24 - x)B2O3 + 15SrO + 10BaO + 10Li2O + 10LiF + 1Er2O3 + xYb2O3 (where x = 0, 0.1, 0.5, 1 and 2 in wt%) have been prepared and their luminescence behavior were studied and reported. Absorption spectral measurements have been used to derive the Judd-Ofelt (JO) intensity parameters from the experimental and calculated oscillator strength values following the JO theory. The various lasing parameters such as stimulated emission cross-section (σEp), experimental and calculated branching ratios (βR) and radiative lifetime (τcal) for the 2H9/2 → 4I15/2, 4S3/2 → 4I15/2 and 4I13/2 → 4I15/2 emission transitions were determined using the JO intensity parameters. The absorption and emission cross-section values for the 4I13/2 → 4I15/2 emission band have been calculated using McCumbar theory and the Gain cross-section for the 4I13/2 → 4I15/2 emission transition also obtained. The upconversion emission mechanism have been studied through various energy transfer processes and the intensity of the upconversion emission transitions are found to increase with the increase in Yb3+ ion concentration. The luminescence decay curves corresponding to the 4I13/2 → 4I15/2 transition of the Er3+/Yb3+ co-doped boro-tellurite glasses under 980 nm excitation wavelength have also been studied and reported in the present work.

  19. Temperature dependence anomalous dielectric relaxation in Co doped ZnO nanoparticles

    SciTech Connect

    Ansari, Sajid Ali; Nisar, Ambreen; Fatma, Bushara; Khan, Wasi; Chaman, M.; Azam, Ameer; Naqvi, A.H.

    2012-12-15

    Graphical abstract: Display Omitted Highlights: ► We prepared Co doped ZnO by facile gel-combustion method. ► Studied temperature dependent dielectric properties in detail. ► Relaxation time shifts toward the higher temperature as increase in Co content. ► SEM analysis shows formation and agglomeration of nanoparticles. ► Dielectric constants, loss and ac conductivity increases with rise in temperature. ► The dielectric constant, loss and ac conductivity decreases as Co ion increases. -- Abstract: We have reported temperature and frequency dependence of dielectric behavior of nanocrystalline Zn{sub 1−x}Co{sub x}O (x = 0.0, 0.01, 0.05 and 0.1) samples prepared by gel-combustion method. The synthesized samples were examined by X-ray diffraction (XRD), scanning electron microscopy (SEM) and LCR-meter, respectively. The XRD analysis reveals that ZnO has a hexagonal (wurtzite) crystal structure. The morphology and size of the nanoparticles (∼10–25 nm) were observed by SEM for 5% Co doped ZnO sample. In dielectric properties, complex permittivity (ε{sup *} = ε′ − jε″), loss tangent (tan δ) and ac conductivity (σ{sub ac}) in the frequency range 75 kHz to 5 MHz were analyzed with temperature range 150–400 °C. The experimental results indicate that ε′, ε″, tan δ and σ{sub ac} decreases with increase in frequency and temperature. The transition temperature as obtained in dispersion curve of dielectric constant shifts toward higher temperature with increase Co content.

  20. Tm3+/Yb3+ co-doped tellurite glass with silver nanoparticles for 1.85 μm band laser material

    NASA Astrophysics Data System (ADS)

    Huang, Bo; Zhou, Yaxun; Cheng, Pan; Zhou, Zizhong; Li, Jun; Jin, Wei

    2016-10-01

    Tm3+/Yb3+ co-doped tellurite glasses with different silver nanoparticles (Ag NPs) concentrations were prepared using the conventional melt-quenching technique and characterized by the UV/Vis/NIR absorption spectra, 1.85 μm band fluorescence emission spectra, transmission electron microscopy (TEM) images, differential scanning calorimeter (DSC) curves and X-ray diffraction (XRD) patterns to investigate the effects of Ag NPs on the 1.85 μm band spectroscopic properties of Tm3+ ions, thermal stability and structural nature of glass hosts. Under the excitation of 980 nm laser diode (LD), the 1.85 μm band fluorescence emission of Tm3+ ions enhances significantly in the presence of Ag NPs with average diameter of ∼8 nm and local surface Plasmon resonance (LSPR) band of ∼590 nm, which is mainly attributed to the increased local electric field induced by Ag NPs at the proximity of doped rare-earth ions on the basis of energy transfer from Yb3+ to Tm3+ ions. An improvement by about 110% of fluorescence intensity is observed in the Tm3+/Yb3+ co-doped tellurite glass containing 0.5 mol% amount of AgNO3 while the prepared glass samples possess good thermal stability and amorphous structural nature. Meanwhile, the Judd-Ofelt intensity parameters Ωt (t = 2,4,6), spontaneous radiative transition probabilities, fluorescence branching ratios and radiative lifetimes of relevant excited levels of Tm3+ ions were determined based on the Judd-Ofelt theory to reveal the enhanced effects of Ag NPs on the 1.85 μm band spectroscopic properties, and the energy transfer micro-parameters and phonon contribution ratios were calculated based on the non-resonant energy transfer theory to elucidate the energy transfer mechanism between Yb3+ and Tm3+ ions. The present results indicate that the prepared Tm3+/Yb3+ co-doped tellurite glass with an appropriate amount of Ag NPs is a promising lasing media applied for 1.85 μm band solid-state lasers and amplifiers.

  1. Spin Effects in the n-InxGa1-xAs/GaAs Double Quantum Well Magnetoresistance Under Tilted Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Yakunin, M. V.; Arapov, Yu. G.; Neverov, V. N.; Podgornyh, S. M.; Shelushinina, N. G.; Harus, G. I.; Zvonkov, B. N.; Uskova, E. A.

    2007-04-01

    Precise scanning of the (B⊥,B∥) plane while measuring magnetoresistance of the n-InGaAs/GaAs double quantum well (DQW) reveals a number of peculiarities connected with intricate DQW energy spectrum, which are analyzed on the basis of quasiclassical calculations. Magnetic breakdown effects are also considered. Peaks due to the latter mechanism reveal spin-splittings (in spite of lower mobilities as compared with the traditional n-GaAs/AlGaAs DQWs) corresponding to an enhanced effective Lande g-factor.

  2. Tunnel magnetoresistance effect using perpendicularly magnetized tetragonal and cubic Mn-Co-Ga Heusler alloy electrode

    NASA Astrophysics Data System (ADS)

    Kubota, T.; Mizukami, S.; Ma, Q. L.; Naganuma, H.; Oogane, M.; Ando, Y.; Miyazaki, T.

    2014-05-01

    Epitaxially grown tetragonal and cubic Mn-Co-Ga thin films were fabricated onto single crystalline Cr (001) under a layer. High perpendicular magnetic anisotropy is achieved in the tetragonal Mn2.3Co0.4Ga1.3 film, and a small, unexpected perpendicular magnetic anisotropy was induced in the cubic Mn1.8Co1.2Ga1.0 film as well. The tunnel magnetoresistance (TMR) effect of the Mn-Co-Ga/MgO/CoFeB magnetic tunnel junctions (MTJs) were investigated. TMR ratios of 5% and 11% were observed at room temperature for the MTJs using tetragonal Mn2.3Co0.4Ga1.3 and cubic Mn1.8Co1.2Ga1.0 electrodes, respectively. The composition dependence is discussed briefly.

  3. Optical properties of Bi 12TiO 20 doped with Al, P, Ag, Cu, Co and co-doped with Al+P single crystals

    NASA Astrophysics Data System (ADS)

    Marinova, V.

    2000-11-01

    Large optically homogeneous photorefractive Bi 12TiO 20 (BTO) single crystals doped with Al, P, Ag, Cu, Co and Al+P-co-doping were obtained by the Top Seeded Solution Growth Method (TSSG) in a Bi 2O 3 solution. A strong bleaching effect was observed for the Al, P, Ag and Al+P-doped crystals, whereas doping with Cu and Co induced a strong photochromic effect and increased the absorption coefficients in the red spectral region. Al, P, Al+P-doped crystals increased the values of optical rotator power, while Cu and Ag-doped crystals exhibited a strong decrease in optical activity in comparison with non-doped BTO. The influences of doping elements on the optical rotation power are discussed on the basis of two structural elementary cell units - MO 4 tetrahedra and BiO n polyhedra.

  4. Theory of Spin Hall Effect in GaAs

    NASA Astrophysics Data System (ADS)

    Engel, Hans-Andreas

    2006-03-01

    In the spin Hall effect, an electric current in a system with spin-orbit coupling induces a transverse spin current which leads to non-equilibrium spin accumulation near sample boundaries. Generating and manipulating non-equilibrium spin magnetization by electric fields is one of the most desirable goals of semiconductor spintronics, because electric fields have potentialities for accessing individual spins at nanometer scales. In this talk, I review the different spin-orbit coupling mechanisms in direct gap semiconductors and the implications of these mechanisms for the spin Hall effect. In particular, we recently developed a theory that accounts for spin-orbit coupling at charged impurities. This coupling leads to extrinsic spin currents that contain skew scattering and side jump contribution [1]. Applying our theory to bulk n-GaAs, without any free parameters, we find spin currents that are in reasonable agreement with recent experiments by Kato et al. [2]. Also, such contributions are important for p-doped GaAs. Furthermore, we analyzed the effect of intrinsic spin-orbit coupling in the presence of anisotropic impurity scattering, and found that, somewhat surprisingly, an electrical field can lead to a bulk magnetization component perpendicular to both the spin-orbit field and an external magnetic field. These works have been done in collaboration with B.I. Halperin, E.I. Rashba, and A.A. Burkov. [1] H.-A. Engel, B.I. Halperin, and E.I. Rashba, Phys. Rev.Lett. 95, 166605 (2005). [2] Y.K. Kato, R.C. Myers, A.C. Gossard, and D.D. Awschalom, Science 306, 1910 (2004).

  5. Effect of the V{sub As}V{sub Ga} complex defect doping on properties of the semi-insulating GaAs

    SciTech Connect

    Ma, Deming Qiao, Hongbo; Shi, Wei; Li, Enling

    2014-04-21

    The different position V{sub As}V{sub Ga} cluster defect doping in semi-insulating (SI) GaAs has been studied by first-principles calculation based on hybrid density functional theory. Our calculated results show that EL6 level is formed due to the V{sub As}V{sub Ga} complex defect, which is very close to the experimental result. It provides the explanation of the absorption of laser with the wavelength beyond in semi-insulating GaAs. The formation energy of V{sub As}V{sub Ga} complex defect is found to decrease from surface to interior gradually. The conduction band minima and valence band maxima of GaAs (001) surface with the V{sub As}V{sub Ga} complex defect are all located at Γ point, and some defect levels are produced in the forbidden band. In contrast, the conduction band minima and valence band maxima of GaAs with the interior V{sub As}V{sub Ga} complex defect are not located at the same k-point, so it might involve the change of momentum in the electron transition process. The research will help strengthen the understanding of photoelectronic properties and effectively guide the preparation of the SI-GaAs materials.

  6. Low energy electron beam irradiation effect on optical properties of nanopillar MQW InGaN/GaN structures

    SciTech Connect

    Yakimov, E. B.; Vergeles, P. S.; Polyakov, A. Y.; Jeon, Dae-Woo; Lee, In-Hwan

    2014-02-21

    The low energy electron beam irradiation (LEEBI) effect on optical properties of planar and nanopillar InGaN/GaN muliple quantum well light emitting structures was studied by the cathodoluminescence (CL) method. On the planar structures LEEBI leads to a formation of new InGaN-related emission bands red shifted in comparison with initial one at small irradiation doses and blue shifted at doses higher than 0.5 C/cm{sup 2}. It was observed that after dry etching used for the nanopillar formation the main InGaN-related emission line moves from 2.92 to 2.98 eV that can be explained by a strain relaxation in the quantum wells. The optical properties of nanopilars start to change under LEEBI at a dose of about one order of magnitude lower than that for planar structures. At high irradiation doses the behavior of both structures under LEEBI is similar. The results obtained were explained by the formation and reconstruction of quantum dots inside the quantum wells due to a point defect generation and redistribution stimulated by the electron beam irradiation.

  7. Effect on Sb on the Properties of GaInP Top Cells: Preprint

    SciTech Connect

    Olson, J. M.; McMahon, W. E.; Kurtz, S.

    2006-05-01

    It is well known that the efficiency of GaInP/GaAs tandem solar cells is limited by the band gap of the GaInP top cell, which, in turn, is determined by the degree of compositional ordering in GaInP base layer. Attempts to raise the band gap by the addition of Al to the top cell have met with limited success due to the strong affinity between Al and oxygen. Here we investigate a different approach. It has been shown that the presence of antimony on the surface of GaInP during its growth suppresses the ordering process and increases the band gap. In this paper, we study the effects of Sb on the properties of GaInP top cells. We show that, in addition to raising the band gap of GaInP, it also increases the incorporation of Zn and changes the relative incorporation of Ga and In. These effects depend strongly on the substrate orientation, growth temperature and rate, and the Sb/P ratio in the gas phase. We show that the band gap of the GaInP top cell (and the Voc) can be increased without reducing the minority carrier collection efficiency. The implications of these results are presented and discussed.

  8. Annealing effects on polycrystalline GaN using nitrogen and ammonia ambients

    NASA Astrophysics Data System (ADS)

    Ariff, A.; Zainal, N.; Hassan, Z.

    2016-09-01

    This paper describes effects of using post-annealing treatment in different conditions on the properties of polycrystalline GaN layer grown on m-plane sapphire substrate by electron beam (e-beam) evaporator. Without annealing, GaN surface was found to have a low RMS roughness with agglomeration of GaN grains in a specific direction and the sample consisted of gallium oxide (Ga2O3) material. When the post-annealing treatment was carried out in N2 ambient at 650 °C, initial re-crystallization of the GaN grains was observed while the evidence of Ga2O3 almost disappeared. As the NH3 annealing was conducted at 950 °C, more effect of re-crystallization occurred but with less grains coalescence. Three dominant XRD peaks of GaN in (10 1 bar 0) , (0002) and (10 1 bar 1) orientations were evident. Near band edge (NBE) related emission in GaN was also observed. The significant improvement was attributed to simultaneous recrystallization and effective reduction of N deficiency density. The post-annealing in a mixture of N2 and NH3 ambient at 950 °C was also conducted, but has limited the effectiveness of the N atoms to incorporate on the GaN layer due to 'clouding' effect by the inert N2 gas. Further increase in the annealing temperature at 980 °C and 1100 °C, respectively caused severe deteriorations of the structural and optical properties of the GaN layer. Overall, this work demonstrated initial potential in improving polycrystalline GaN material in simple and inexpensive manner.

  9. Enhanced room temperature ferromagnetism in electrodeposited Co-doped ZnO nanostructured thin films by controlling the oxygen vacancy defects

    SciTech Connect

    Simimol, A.; Anappara, Aji A.; Greulich-Weber, S.; Chowdhury, Prasanta; Barshilia, Harish C.

    2015-06-07

    We report the growth of un-doped and cobalt doped ZnO nanostructures fabricated on FTO coated glass substrates using electrodeposition method. A detailed study on the effects of dopant concentration on morphology, structural, optical, and magnetic properties of the ZnO nanostructures has been carried out systematically by varying the Co concentration (c.{sub Co}) from 0.01 to 1 mM. For c.{sub Co }≤ 0.2 mM, h-wurtzite phase with no secondary phases of Co were present in the ZnO nanostructures. For c.{sub Co} ≤ 0.2 mM, the photoluminescence spectra exhibited a decrease in the intensity of ultraviolet emission as well as band-gap narrowing with an increase in dopant concentration. All the doped samples displayed a broad emission in the visible range and its intensity increased with an increase in Co concentration. It was found that the defect centers such as oxygen vacancies and zinc interstitials were the source of the visible emission. The X-ray photoelectron spectroscopy studies revealed, Co was primarily in the divalent state, replacing the Zn ion inside the tetrahedral crystal site of ZnO without forming any cluster or secondary phases of Co. The un-doped ZnO nanorods exhibited diamagnetic behavior and it remained up to a c.{sub Co} of 0.05 mM, while for c.{sub Co }> 0.05 mM, the ZnO nanostructures exhibited ferromagnetic behavior at room temperature. The coercivity increased to 695 G for 0.2 mM Co-doped sample and then it decreased for c.{sub Co }> 0.2 mM. Our results illustrate that up to a threshold concentration of 0.2 mM, the strong ferromagnetism is due to the oxygen vacancy defects centers, which exist in the Co-doped ZnO nanostructures. The origin of strong ferromagnetism at room temperature in Co-doped ZnO nanostructures is attributed to the s-d exchange interaction between the localized spin moments resulting from the oxygen vacancies and d electrons of Co{sup 2+} ions. Our findings provide a new insight for tuning the

  10. Structural phase analysis, band gap tuning and fluorescence properties of Co doped TiO2 nanoparticles

    NASA Astrophysics Data System (ADS)

    Alamgir; Khan, Wasi; Ahmad, Shabbir; Mehedi Hassan, M.; Naqvi, A. H.

    2014-12-01

    This paper reports on structural and optical properties of Co (0, 3, 5 & 7 mol%) doped TiO2 (titania) nanoparticles (NPs) synthesized by employing acid modified sol-gel method. The crystalline phase of the pure and doped NPs was observed with X-ray diffraction (XRD) followed by Raman scattering technique. Field emission scanning electron microscope and transmission electron microscopy give the morphological details. Fourier transform infrared spectra indicate the bonding interactions of Co ions with the titania lattice framework. Optical studies were attained with UV-visible absorption and fluorescence emission spectroscopy. XRD analysis reveals that all prepared samples have pure anatase phase with tetragonal symmetry devoid of any other secondary phase. The average crystallite size of all samples was calculated using Scherrer's formula and was found to vary from 8 to 10 nm with doping concentration of Co. The Raman spectroscopy further confirmed the formation of TiO2 in anatase structure in both pure and Co doped TiO2 NPs. The most intense Raman active Eg peak of TiO2 NPs shifted to higher energy on doping. Both UV-visible and fluorescence spectra show a blue shift in their absorption and band edge emission subsequently on increasing with Co percentage in titania host matrix, wherever there is an indication of quantum confinement effect with widening of band gap on decreasing in NPs size. There is also a possibility of strong Coulomb interaction effect on the optical processes involving the Co ions. However, the intensities of different emission spectra are not the same but decrease profoundly for doping samples due to concentration quenching effect.

  11. Synergy of metal and nonmetal dopants for visible-light photocatalysis: a case-study of Sn and N co-doped TiO2.

    PubMed

    Zhuang, Huaqiang; Zhang, Yingguang; Chu, Zhenwei; Long, Jinlin; An, Xiaohan; Zhang, Hongwen; Lin, Huaxiang; Zhang, Zizhong; Wang, Xuxu

    2016-04-14

    This paper mainly focuses on the synergistic effect of Sn and N dopants to enhance the photocatalytic performance of anatase TiO2 under visible light or simulated solar light irradiation. The Sn and N co-doped TiO2 (SNT-x) photocatalysts were successfully prepared by the facile sol-gel method and the post-nitridation route in the temperature range of 400-550 °C. All the as-prepared samples were characterized in detail by X-ray diffraction, UV-vis diffuse reflectance spectroscopy, transmission electron microscopy, X-ray photoelectron and electron spin resonance spectroscopy and photoelectrochemical measurements. The characterization results reveal that the co-incorporation of Sn and N atoms remarkably modifies the electronic structure of TiO2, which gives rise to a prominent separation of photogenerated charge carriers and more efficient interfacial charge-transfer reactions in a photocatalytic process. The enhanced photocatalytic activity is attributed to the intensified active oxygen species including hydroxyl radicals (˙OH) and superoxide anion radicals (O2˙(-)) for degradation of organic pollutants. And the result of photocatalytic hydrogen production further confirms the existence of the synergistic effect in the SNT-x samples, because they exhibit higher photocatalytic activity than the sum of N/TiO2 and Sn/TiO2. This work provides a paradigm to consolidate the understanding of the synergistic effect of metal and non-metal co-doped TiO2 in domains of photocatalysis and photoelectrochemistry.

  12. Annealing effects on InGaAsN/GaAs quantum wells analyzed using thermally detected optical absorption and ten band k -p calculations

    NASA Astrophysics Data System (ADS)

    Bouragba, T.; Mihailovic, M.; Reveret, F.; Disseix, P.; Leymarie, J.; Vasson, A.; Damilano, B.; Hugues, M.; Massies, J.; Duboz, J. Y.

    2007-04-01

    The effects of thermal annealing for In0.25Ga0.75As1-yNy/GaAs multiquantum wells (MQWs) have been investigated through thermally detected optical absorption. The QW transition energies have been calculated by using a ten-band k -p model including the band anticrossing model for the description of the InGaAsN band gap variation. The modification of the In concentration profile due to In-Ga interdiffusion during thermal annealing is taken into account through the Fick law. A good agreement is obtained between calculated and experimental energies of optical transitions. Our results show that the In-Ga interdiffusion phenomenon observed in a nitrogen free sample is moderately enhanced by the introduction of nitrogen. The blueshift of optical transitions induced by the annealing process is the result of both In-Ga interdiffusion and rearrangement of local nitrogen environment.

  13. Pr and F co-doped SnO₂ transparent conductive films with high work function deposited by ion-assisted electron beam evaporation.

    PubMed

    Wu, Shaohang; Li, Yantao; Luo, Jinsong; Lin, Jie; Fan, Yi; Gan, Zhihong; Liu, Xingyuan

    2014-02-24

    A transparent conductive oxide (TCO) Pr and F co-doped SnO2 (PFTO) film is prepared by ion-assisted electron beam deposition. An optimized PFTO film shows a high average visible optical transmittance of 83.6% and a minimum electrical resistivity of 3.7 × 10(-3) Ω·cm corresponding to a carrier density of 1.298 × 10(20) cm(-3) and Hall mobility of 12.99 cm(2)/V⋅s. This PFTO film shows a high work function of 5.147 eV and favorable surface morphology with an average roughness of 1.45 nm. Praseodymium fluoride is found to be an effective material to dope F into SnO2 that can simplify the fabrication process of SnO2-based TCO films. PMID:24663792

  14. Effect of buffer layer and external stress on magnetic properties of flexible FeGa films

    NASA Astrophysics Data System (ADS)

    Zhang, Xiaoshan; Zhan, Qingfeng; Dai, Guohong; Liu, Yiwei; Zuo, Zhenghu; Yang, Huali; Chen, Bin; Li, Run-Wei

    2013-05-01

    We systematically investigated the effect of a Ta buffer layer and external stress on the magnetic properties of magnetostrictive Fe81Ga19 films deposited on flexible polyethylene terephthalate (PET) substrates. The Ta buffer layers could effectively smoothen the rough surface of PET. As a result, the FeGa films grown on Ta buffer layers exhibit a weaker uniaxial magnetic anisotropy and lower coercivity, as compared to those films directly grown on PET substrates. By inward and outward bending the FeGa/Ta/PET samples, external in-plane compressive and tensile stresses were applied to the magnetic films. Due to the inverse magnetostrictive effect of FeGa, both the coercivity and squareness of hysteresis loops for FeGa/Ta films could be well tuned under various strains.

  15. Comparison for the carrier mobility between the III-V nitrides and AlGaAs/GaAs heterostructure field-effect transistors

    NASA Astrophysics Data System (ADS)

    Chongbiao, Luan; Zhaojun, Lin; Yuanjie, Lü; Zhihong, Feng; Jingtao, Zhao; Yang, Zhou; Ming, Yang

    2014-09-01

    Using the measured capacitance-voltage curves of Ni/Au Schottky contacts with different areas and the current-voltage characteristics for the AlGaAs/GaAs, AlGaN/AlN/GaN and In0.18 Al0.82N/AlN/GaN heterostructure field-effect transistors (HFETs) at low drain-source voltage, the two-dimensional electron gas (2DEG) electron mobility for the prepared HFETs was calculated and analyzed. It was found that there is an obvious difference for the variation trend of the mobility curves between the III-V nitride HFETs and the AlGaAs/GaAs HFETs. In the III-V nitride HFETs, the variation trend for the curves of the 2DEG electron mobility with the gate bias is closely related to the ratio of the gate length to the drain-to-source distance. While the ratio of the gate length to the drain-to-source distance has no effect on the variation trend for the curves of the 2DEG electron mobility with the gate bias in the AlGaAs/GaAs HFETs. The reason is attributed to the polarization Coulomb field scattering in the III-V nitride HFETs.

  16. Strain effects in low-dimensional silicon MOS and AlGaN/GaN HEMT devices

    NASA Astrophysics Data System (ADS)

    Baykan, Mehmet Onur

    Strained silicon technology is a well established method to enhance sub-100nm MOSFET performance. With the scalability of process-induced strain, strained silicon channels have been used in every advanced CMOS technology since the 90nm node. At the 22nm node, due to the detrimental short channel effects, non-planar silicon CMOS has emerged as a viable solution to sustain transistor scaling without compromising the device performance. Therefore, it is necessary to conduct a physics based investigation of the effects of mechanical strain in silicon MOS device performance enhancement, as the transverse and longitudinal device dimensions scale down for future technology nodes. While silicon is widely used as the material basis for logic transistors, AlGaN/GaN HEMTs promise a superior device platform over silicon based power MOSFETs for high-frequency and high-power applications. In contrast to the mature Si crystal growth technology, the abundance of defects in the GaN material system creates obstacles for the realization of a reliable AlGaN/GaN HEMT device technology. Due to the high levels of internal mechanical strain present in AlGaN/GaN HEMTs, it is of utmost importance to understand the impact of mechanical stress on AlGaN/GaN trap generation. First, we have investigated the underlying physics of the comparable electron mobility observed in (100) and (110) sidewall silicon double-gate FinFETs, which is different from the observed planar (100) and (110) electron mobility. By conducting a systematic experimental study, it is shown that the undoped body, metal gate induced stress, and volume-inversion effects do not explain the comparable electron mobility. Using a self-consistent double-gate FinFET simulator, we have showed that for (110) FinFETs, an increased population of electrons is obtained for the Delta2 valley due to the heavy nonparabolic confinement mass, leading to a comparable average electron transport effective mass for both orientations. The width

  17. Carrier leakage effect on efficiency droop in InGaN/GaN light-emitting diodes

    NASA Astrophysics Data System (ADS)

    Huang, Yang; Liu, Zhiqiang; Yi, Xiaoyan; Guo, Yao; Wu, Shaoteng; Yuan, Guodong; Wang, Junxi; Wang, Guohong; Li, Jinmin

    2016-07-01

    A new model for efficiency droop in InGaN/GaN light-emitting diodes (LEDs) is proposed, where the primary nonradiative recombination mechanisms, including Shockley-Read-Hall (SRH), Auger and carrier leakage, are considered. A room-temperature external quantum efficiency (EQE) measurement was performed on our designed samples and analyzed by the new model. Owing to advantages over the common “ABC + f(n) model”, the “new model” is able to effectively extract recombination coefficients and calculate the leakage currents of the hole and electron. From this new model, we also found that hole leakage is distinct at low injection, while it disappears at high injection, which is contributed to the weak blocking effect of electron in quantum wells (QWs) at low injection.

  18. Self-organized vanadium and nitrogen co-doped titania nanotube arrays with enhanced photocatalytic reduction of CO2 into CH4

    PubMed Central

    2014-01-01

    Self-organized V-N co-doped TiO2 nanotube arrays (TNAs) with various doping amount were synthesized by anodizing in association with hydrothermal treatment. Impacts of V-N co-doping on the morphologies, phase structures, and photoelectrochemical properties of the TNAs films were thoroughly investigated. The co-doped TiO2 photocatalysts show remarkably enhanced photocatalytic activity for the CO2 photoreduction to methane under ultraviolet illumination. The mechanism of the enhanced photocatalytic activity is discussed in detail. PMID:24948893

  19. Strain- and temperature-induced effects in AlGaN/GaN high electron mobility transistors

    NASA Astrophysics Data System (ADS)

    Saran Yalamarthy, Ananth; Senesky, Debbie G.

    2016-03-01

    This paper presents a physics-based model for computing the combined effect of applied strain and temperature on the device characteristics of aluminium gallium nitride (AlGaN/GaN) high electron mobility transistors (HEMTs). More specifically, the electrical response of the HEMT is predicted under applied biaxial strain from ±1% over a wide range of temperatures (300-500 K). In addition, the interface state densities at the Schottky-AlGaN interface are introduced in the model. This physics-based model calculates the charge due to applied, thermal and lattice mismatch strain and temperature effects at the two-dimensional electron gas (2DEG) interface of the HEMT. Coupled with a model for the 2DEG mobility that includes strain and temperature effects, current-voltage characteristics for the HEMT are derived above the threshold voltage. Regimes with large strain sensitivity and temperature compensation are identified and vice-versa. The analysis from the model clarifies the large range of strain response variations observed in the experimentally measured characteristics of HEMTs in literature. Furthermore, the developed model is a useful tool for predicting the response of HEMTs used in sensing and under the influence of packaging in extreme environments, especially when temperature fluctuation and strain coupling is of concern.

  20. Microwave-Assisted Synthesis of Boron and Nitrogen co-doped Reduced Graphene Oxide for the Protection of Electromagnetic Radiation in Ku-Band.

    PubMed

    Umrao, Sima; Gupta, Tejendra K; Kumar, Shiv; Singh, Vijay K; Sultania, Manish K; Jung, Jung Hwan; Oh, Il-Kwon; Srivastava, Anchal

    2015-09-01

    The electromagnetic interference (EMI) shielding of reduced graphene oxide (MRG), B-doped MRG (B-MRG), N-doped MRG (N-MRG), and B-N co-doped MRG (B-N-MRG) have been studied in the Ku-band frequency range (12.8-18 GHz). We have developed a green, fast, and cost-effective microwave assisted route for synthesis of doped MRG. B-N-MRG shows high electrical conductivity in comparison to MRG, B-MRG and N-MRG, which results better electromagnetic interference (EMI) shielding ability. The co-doping of B and N significantly enhances the electrical conductivity of MRG from 21.4 to 124.4 Sm(-1) because N introduces electrons and B provides holes in the system and may form a nanojunction inside the material. Their temperature-dependent electrical conductivity follows 2D-variable range hopping (2D-VRH) and Efros-Shklovskii-VRH (ES-VRH) conduction model in a low temperature range (T<50 K). The spatial configuration of MRG after doping of B and N enhances the space charge polarization, natural resonance, dielectric polarization, and trapping of EM waves by internal reflection leading to a high EMI shielding of -42 dB (∼99.99% attenuation) compared to undoped MRG (-28 dB) at a critical thickness of 1.2 mm. Results suggest that the B-N-MRG has great potential as a candidate for a new type of EMI shielding material useful in aircraft, defense industries, communication systems, and stealth technology. PMID:26287816

  1. Microstructure and property of diamond-like carbon films with Al and Cr co-doping deposited using a hybrid beams system

    NASA Astrophysics Data System (ADS)

    Dai, Wei; Liu, Jingmao; Geng, Dongsen; Guo, Peng; Zheng, Jun; Wang, Qimin

    2016-12-01

    DLC films with weak carbide former Al and carbide former Cr co-doping (Al:Cr-DLC) were deposited by a hybrid beams system comprising an anode-layer linear ion beam source (LIS) and high power impulse magnetron sputtering using a gas mixture of C2H2 and Ar as the precursor. The doped Al and Cr contents were controlled via adjusting the C2H2 fraction in the gas mixture. The composition, microstructure, compressive stress, mechanical properties and tribological behaviors of the Al:Cr-DLC films were researched carefully using X-ray photoelectron spectroscopy, transmission electron microscopy, Raman spectroscopy, stress-tester, nanoindentation and ball-on-plate tribometer as function of the C2H2 fraction. The results show that the Al and Cr contents in the films increased continuously as the C2H2 fraction decreased. The doped Cr atoms preferred to bond with the carbon while the Al atoms mainly existed in metallic state. Structure modulation with alternate multilayer consisted of Al-poor DLC layer and Al-rich DLC layer was found in the films. Those periodic Al-rich DLC layers can effectively release the residual stress of the films. On the other hand, the formation of the carbide component due to Cr incorporation can help to increase the film hardness. Accordingly, the residual stress of the DLC films can be reduced without sacrificing the film hardness though co-doping Al and Cr atoms. Furthermore, it was found that the periodic Al-rich layer can greatly improve the elastic resilience of the DLC films and thus decreases the film friction coefficient and wear rate significantly. However, the existence of the carbide component would cause abrasive wear and thus deteriorate the wear performance of the films.

  2. Microwave-Assisted Synthesis of Boron and Nitrogen co-doped Reduced Graphene Oxide for the Protection of Electromagnetic Radiation in Ku-Band.

    PubMed

    Umrao, Sima; Gupta, Tejendra K; Kumar, Shiv; Singh, Vijay K; Sultania, Manish K; Jung, Jung Hwan; Oh, Il-Kwon; Srivastava, Anchal

    2015-09-01

    The electromagnetic interference (EMI) shielding of reduced graphene oxide (MRG), B-doped MRG (B-MRG), N-doped MRG (N-MRG), and B-N co-doped MRG (B-N-MRG) have been studied in the Ku-band frequency range (12.8-18 GHz). We have developed a green, fast, and cost-effective microwave assisted route for synthesis of doped MRG. B-N-MRG shows high electrical conductivity in comparison to MRG, B-MRG and N-MRG, which results better electromagnetic interference (EMI) shielding ability. The co-doping of B and N significantly enhances the electrical conductivity of MRG from 21.4 to 124.4 Sm(-1) because N introduces electrons and B provides holes in the system and may form a nanojunction inside the material. Their temperature-dependent electrical conductivity follows 2D-variable range hopping (2D-VRH) and Efros-Shklovskii-VRH (ES-VRH) conduction model in a low temperature range (T<50 K). The spatial configuration of MRG after doping of B and N enhances the space charge polarization, natural resonance, dielectric polarization, and trapping of EM waves by internal reflection leading to a high EMI shielding of -42 dB (∼99.99% attenuation) compared to undoped MRG (-28 dB) at a critical thickness of 1.2 mm. Results suggest that the B-N-MRG has great potential as a candidate for a new type of EMI shielding material useful in aircraft, defense industries, communication systems, and stealth technology.

  3. Effect of nitrogen fraction on the temperature dependence of GaNAs/GaAs quantum-well emission

    NASA Astrophysics Data System (ADS)

    Potter, R. J.; Balkan, N.; Carrère, H.; Arnoult, A.; Bedel, E.; Marie, X.

    2003-05-01

    The effects of nitrogen fraction on the temperature dependence of GaNxAs1-x/GaAs (x<2.8%) quantum-well emission was investigated using steady-state photoluminescence between 2 and 300 K. At low temperatures, a characteristic S-shape behavior indicative of carrier localization was observed for each of the samples. This is believed to result from the large miscibility gap induced by the nitrogen, which results in structural/compositional fluctuations in the well. In the high temperature regime (T>150 K) where the emission has a linear dependence, a strong reduction in emission temperature dependence was observed with increasing nitrogen. The temperature dependence was modeled using the band anticrossing approach, with the interaction matrix element parameter CNM (VMN=-CMN√x ) and the nitrogen level parameter γ (EN=EN0-γx) used as fitting parameters.

  4. Effect of Auger recombination and leakage on the droop in InGaN/GaN quantum well LEDs.

    PubMed

    Römer, Friedhard; Witzigmann, Bernd

    2014-10-20

    We investigate the effect of the epitaxial structure and the acceptor doping profile on the efficiency droop in InGaN/GaN LEDs by the physics based simulation of experimental internal quantum efficiency (IQE) characteristics. The device geometry is an integral part of our simulation approach. We demonstrate that even for single quantum well LEDs the droop depends critically on the acceptor doping profile. The Auger recombination was found to increase stronger than with the third power of the carrier density and has been found to dominate the droop in the roll over zone of the IQE. The fitted Auger coefficients are in the range of the values predicted by atomistic simulations.

  5. The effects of nanocavity and photonic crystal in InGaN/GaN nanorod LED arrays

    NASA Astrophysics Data System (ADS)

    Jiao, Qianqian; Chen, Zhizhong; Feng, Yulong; Li, Shunfeng; Jiang, Shengxiang; Li, Junze; Chen, Yifan; Yu, Tongjun; Kang, Xiangning; Shen, Bo; Zhang, Guoyi

    2016-07-01

    InGaN/GaN nanorod light-emitting diode (LED) arrays were fabricated using nanoimprint and reactive ion etching. The diameters of the nanorods range from 120 to 300 nm. The integral photoluminescence (PL) intensity for 120 nm nanorod LED array is enhanced as 13 times compared to that of the planar one. In angular-resolved PL (ARPL) measurements, there are some strong lobes as resonant regime appeared in the far-field radiation patterns of small size nanorod array, in which the PL spectra are sharp and intense. The PL lifetime for resonant regime is 0.088 ns, which is 40 % lower than that of non-resonant regime for 120 nm nanorod LED array. At last, three dimension finite difference time domain (FDTD) simulation is performed. The effects of guided modes coupling in nanocavity and extraction by photonic crystals are explored.

  6. The effect of gate length variation on InAlGaN/GaN HFET device characteristics

    NASA Astrophysics Data System (ADS)

    Ketteniss, N.; Behmenburg, H.; Lecourt, F.; Defrance, N.; Hoel, V.; De Jaeger, J. C.; Heuken, M.; Kalisch, H.; Vescan, A.

    2012-03-01

    InAlGaN/GaN heterostructure field effect transistors (HFETs) with a nearly lattice-matched barrier layer (thickness tbar = 8.3 nm) are investigated. The focus is set on resolving the systematic dependence of device characteristics on the gate length LG. Therefore, five different gate length devices with LG ranging from 75 nm to 2 µm have been realized. Peak values of 460 mS mm-1 and 100 GHz for transconductance gm and unity current gain cut-off frequency fT are obtained for the 75 nm device. DC characteristics as well as the cut-off frequency fT show systematic scaling with the gate length LG. Nevertheless, short-channel effects appear for the short gate length devices in both DC and RF operation, and a critical minimum aspect ratio LG/tbar of 27 is identified for the investigated barrier composition of xIn = 0.11; yAl = 0.63 and zGa = 0.26.

  7. Influence of steering effects on strain detection in AlGaInN/GaN heterostructures by ion channelling

    NASA Astrophysics Data System (ADS)

    Redondo-Cubero, A.; Lorenz, K.; Franco, N.; Fernández-Garrido, S.; Gago, R.; Smulders, P. J. M.; Muñoz, E.; Calleja, E.; Alves, E.

    2009-03-01

    Ion steering effects in the interface of heterostructures can strongly influence the shape and position of angular channelling scans leading to considerable error in the determination of strain by ion channelling. As an example, this paper presents channelling measurements on a near-lattice-matched AlGaInN/GaN heterostructure which show no shift between the angular scans from the quaternary layer and the underlying GaN substrate although high resolution x-ray diffraction data confirm the presence of strain in the layer. Such 'anomalous' behaviour was studied by means of Monte Carlo simulations for nitride ternary and quaternary films in the whole composition range. The simulations show that the thickness, magnitude of the distortion of the strained lattice and energy of the probing beam are critical parameters controlling the impact of steering. Three composition/strain regions were established for a typical beam of 2 MeV alpha particles corresponding to different intensities of the steering potential and in which strain measurements by ion channelling are (a) correct, (b) possible but require corrections and (c) not possible due to steering effects.

  8. Formation of hydroxyl radicals and kinetic study of 2-chlorophenol photocatalytic oxidation using C-doped TiO2, N-doped TiO2, and C,N Co-doped TiO2 under visible light.

    PubMed

    Ananpattarachai, Jirapat; Seraphin, Supapan; Kajitvichyanukul, Puangrat

    2016-02-01

    This work reports on synthesis, characterization, adsorption ability, formation rate of hydroxyl radicals (OH(•)), photocatalytic oxidation kinetics, and mineralization ability of C-doped titanium dioxide (TiO2), N-doped TiO2, and C,N co-doped TiO2 prepared by the sol-gel method. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and UV-visible spectroscopy were used to analyze the titania. The rate of formation of OH(•) for each type of titania was determined, and the OH-index was calculated. The kinetics of as-synthesized TiO2 catalysts in photocatalytic oxidation of 2-chlorophenol (2-CP) under visible light irradiation were evaluated. Results revealed that nitrogen was incorporated into the lattice of titania with the structure of O-Ti-N linkages in N-doped TiO2 and C,N co-doped TiO2. Carbon was joined to the Ti-O-C bond in the C-doped TiO2 and C,N co-doped TiO2. The 2-CP adsorption ability of C,N co-doped TiO2 and C-doped TiO2 originated from a layer composed of a complex carbonaceous mixture at the surface of TiO2. C,N co-doped TiO2 had highest formation rate of OH(•) and photocatalytic activity due to a synergistic effect of carbon and nitrogen co-doping. The order of photocatalytic activity per unit surface area was the same as that of the formation rate of OH(•) unit surface area in the following order: C,N co-doped TiO2 > C-doped TiO2 > N-doped TiO2 > undoped TiO2.

  9. Characteristics of cylindrical surrounding-gate GaAs x Sb1-x /In y Ga1-y As heterojunction tunneling field-effect transistors

    NASA Astrophysics Data System (ADS)

    Guan, Yun-He; Li, Zun-Chao; Luo, Dong-Xu; Meng, Qing-Zhi; Zhang, Ye-Fei

    2016-10-01

    A III-V heterojunction tunneling field-effect transistor (TFET) can enhance the on-state current effectively, and GaAs x Sb1-x /In y Ga1-y As heterojunction exhibits better performance with the adjustable band alignment by modulating the alloy composition. In this paper, the performance of the cylindrical surrounding-gate GaAs x Sb1-x /In y Ga1-y As heterojunction TFET with gate-drain underlap is investigated by numerical simulation. We validate that reducing drain doping concentration and increasing gate-drain underlap could be effective ways to reduce the off-state current and subthreshold swing (SS), while increasing source doping concentration and adjusting the composition of GaAs x Sb1-x /In y Ga1-y As can improve the on-state current. In addition, the resonant TFET based on GaAs x Sb1-x /In y Ga1-y As is also studied, and the result shows that the minimum and average of SS reach 11 mV/decade and 20 mV/decade for five decades of drain current, respectively, and is much superior to the conventional TFET. Project supported by the National Natural Science Foundation of China (Grant Nos. 61176038 and 61474093), the Science and Technology Planning Project of Guangdong Province, China (Grant No. 2015A010103002), and the Technology Development Program of Shaanxi Province, China (Grant No. 2016GY-075).

  10. First principles study of bismuth alloying effects in GaAs saturable absorber.

    PubMed

    Li, Dechun; Yang, Ming; Zhao, Shengzhi; Cai, Yongqing; Feng, Yuanping

    2012-05-01

    First principles hybrid functional calculations have been carried out to study electronic properties of GaAs with Bi alloying effects. It is found that the doping of Bi into GaAs reduces the bandgap due to the intraband level repulsions between Bi induced states and host states, and the Bi-related impurity states originate from the hybridization of Bi-6p and its nearest As-4p orbitals. With the increase of Bi concentration in GaAs, the bandgap decreases monotonously. The calculated optical properties of the undoped and Bi-doped GaAs are similar except the shift toward lower energy of absorption edge and main absorption peaks with Bi doping. These results suggest a promising application of GaBi(x)As(1-x) alloy as semiconductor saturable absorber in Q-switched or mode-locked laser.

  11. Temperature Dependence of the Piezotronic and Piezophototronic Effects in a-axis GaN Nanobelts.

    PubMed

    Wang, Xingfu; Yu, Ruomeng; Peng, Wenbo; Wu, Wenzhuo; Li, Shuti; Wang, Zhong Lin

    2015-12-22

    The temperature dependence of the piezotronic and piezophototronic effects in a-axis GaN nanobelts from 77 to 300 K is investigated. The piezotronic effect is enhanced by over 440% under lower temp-eratures. Two independent processes are discovered to form a competing mechanism through the investigation of the temperature dependence of the piezophototronic effect in a-axis GaN nanobelts.

  12. High-fluence Ga-implanted silicon—The effect of annealing and cover layers

    SciTech Connect

    Fiedler, J. Heera, V.; Hübner, R.; Voelskow, M.; Germer, S.; Schmidt, B.; Skorupa, W.

    2014-07-14

    The influence of SiO{sub 2} and SiN{sub x} cover layers on the dopant distribution as well as microstructure of high fluence Ga implanted Si after thermal processing is investigated. The annealing temperature determines the layer microstructure and the cover layers influence the obtained Ga profile. Rapid thermal annealing at temperatures up to 750 °C leads to a polycrystalline layer structure containing amorphous Ga-rich precipitates. Already after a short 20 ms flash lamp annealing, a Ga-rich interface layer is observed for implantation through the cover layers. This effect can partly be suppressed by annealing temperatures of at least 900 °C. However, in this case, Ga accumulates in larger, cone-like precipitates without disturbing the surrounding Si lattice parameters. Such a Ga-rich crystalline Si phase does not exist in the equilibrium phase diagram according to which the Ga solubility in Si is less than 0.1 at. %. The Ga-rich areas are capped with SiO{sub x} grown during annealing which only can be avoided by the usage of SiN{sub x} cover layers.

  13. Effects of Titanium Layer Oxygen Scavenging on the High-k/InGaAs Interface.

    PubMed

    Winter, Roy; Shekhter, Pini; Tang, Kechao; Floreano, Luca; Verdini, Alberto; McIntyre, Paul C; Eizenberg, Moshe

    2016-07-01

    One of the main challenges in the path to incorporating InGaAs based metal-oxide-semiconductor structures in nanoelectronics is the passivation of high-k/InGaAs interfaces. Here, the oxygen scavenging effect of thin Ti layers on high-k/InGaAs gate stacks was studied. Electrical measurements and synchrotron X-ray photoelectron spectroscopy measurements, with in situ metal deposition, were used. Oxygen removal from the InGaAs native oxide surface layer remotely through interposed Al2O3 and HfO2 layers observed. Synchrotron X-ray photoelectron spectroscopy has revealed a decrease in the intensity of InOx features relative to In in InGaAs after Ti deposition. The signal ratio decreases further after annealing. In addition, Ti 2p spectra clearly show oxidation of the thin Ti layer in the ultrahigh vacuum XPS environment. Using capacitance-voltage and conductance-voltage measurements, Pt/Ti/Al2O3/InGaAs and Pt/Al2O3/InGaAs capacitors were characterized both before and after annealing. It was found that the remote oxygen scavenging from the oxide/semiconductor interface using a thin Ti layer can influence the density of interface traps in the high-k/InGaAs interface. PMID:27282201

  14. First principles study on B/N pairs co-doping zigzag single-walled carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Yao, Xinhua; Li, Kejing; Ye, Jinqian; Shao, Qing Yi

    2016-06-01

    The B/N pairs co-doping (5, 0) single-walled carbon nanotubes (SWCNTs) have been investigated by using density functional theory. We gradually increase B/N doping concentration to simulate the growth of B/N pairs doping. We find that B/N pairs prefer to form a B/N hexagonal ring and then B/N rings successively grow around the axis until they are end to end. All B/N pairs doped tubes are turned to semiconducting and the five BN rings co-doped (5, 0) tube shows the occurrence of magnetism. Moreover, the increase of the doping concentration in a particular law may not change electrical properties obviously.

  15. Enhanced visible light photocatalytic performance of g-C3N4 photocatalysts co-doped with iron and phosphorus

    NASA Astrophysics Data System (ADS)

    Hu, Shaozheng; Ma, Lin; You, Jiguang; Li, Fayun; Fan, Zhiping; Lu, Guang; Liu, Dan; Gui, Jianzhou

    2014-08-01

    Preparation of Fe and P co-doped g-C3N4 was described, using dicyandiamide monomer, ferric nitrate, and diammonium hydrogen phosphate as precursor. X-ray diffraction (XRD), N2 adsorption, UV-vis spectroscopy, Fourier transform infrared spectra (FT-IR), photoluminescence (PL), X-ray photoelectron spectroscopy (XPS), and photocurrent measurement were used to characterize the prepared catalysts. The results indicated that the addition of dopants inhibited the crystal growth of graphitic carbon nitride, enhanced the surface area, decreased the band gap energy, and restrained the recombination of photogenerated electrons and holes. Fe and P co-doped g-C3N4 exhibited much higher Rhodamine B (RhB) photodegradation rate and H2 production ability than that of single doped and neat g-C3N4 catalysts. The possible mechanism and doping sites of P and Fe were proposed.

  16. Re-dispersible Li+ and Eu3+ co-doped nanocrystalline ZnO: luminescence and EPR studies.

    PubMed

    Ningthoujam, R S; Gajbhiye, N S; Ahmed, Asar; Umre, S S; Sharma, S J

    2008-06-01

    Nano-crystals of ZnO, Eu3+ doped ZnO, and Li+, Eu3+ co-doped ZnO have been prepared by urea hydrolysis in ethylene glycol medium at 150 degrees C. Ethylene glycol acts as capping agent for nanoparticles. Three colors 437 (blue), 540 (green) and 615 nm (red) from 2 at.% Li+ and 5 at.% Eu3+ co-doped ZnO have been observed from luminescence studies compared to that from 5 at.%. Eu3+ doped ZnO, which shows emission at 437 and 615 nm. It is established that green light is originated from the oxygen vacancy brought by Li+ incorporation into ZnO. Particles are redispersible in organic solvent such as ethanol, and are able to incorporate into polymer-based material such as SiO2 matrix.

  17. Bipolar charge storage characteristics in copper and cobalt co-doped zinc oxide (ZnO) thin film.

    PubMed

    Kumar, Amit; Herng, Tun Seng; Zeng, Kaiyang; Ding, Jun

    2012-10-24

    The bipolar charge phenomenon in Cu and Co co-doped zinc oxide (ZnO) film samples has been studied using scanning probe microscopy (SPM) techniques. Those ZnO samples are made using a pulsed laser deposition (PLD) technique. It is found that the addition of Cu and Co dopants suppresses the electron density in ZnO and causes a significant change in the work function (Fermi level) value of the ZnO film; this results in the ohmic nature of the contact between the electrode (probe tip) and codoped sample, whereas this contact exhibits a Schottky nature in the undoped and single-element-doped samples. These results are verified by Kelvin probe force microscopy (KPFM) and ultraviolet photoelectron spectroscopy (UPS) measurements. It is also found that the co-doping (Cu and Co) can stabilize the bipolar charge, whereas Cu doping only stabilizes the positive charge in ZnO thin films.

  18. Co and Cu co-doped ZnO epitaxial films—A magnetically soft nano-composite

    NASA Astrophysics Data System (ADS)

    Ney, V.; Venkataraman, V.; Henne, B.; Ollefs, K.; Wilhelm, F.; Rogalev, A.; Ney, A.

    2016-04-01

    A series of Co/Cu co-doped ZnO epitaxial films has been grown on sapphire substrates to investigate the possibilities of tailoring the magnetic properties in functional ZnO-Co/Cu nano-composites. The growth was performed using reactive magnetron sputtering varying the oxygen partial pressure to tune the incorporation of the dopants and the resulting valence state. At high oxygen pressures, Co2+ is formed and the resulting magnetic properties are very similar to phase pure paramagnetic Co-doped ZnO samples. However, the formation of a secondary CuO phase reduces the overall structural quality of the layers and virtually no substitutional incorporation of Cu2+ in ZnO could be evidenced. At low oxygen pressures, a significant fraction of metallic Co and Cu forming nanometer-sized superparamagnetic precipitates of a Co/Cu alloy can be evidenced which are embedded in a ZnO host matrix.

  19. Novel band gap-tunable K-Na co-doped graphitic carbon nitride prepared by molten salt method

    NASA Astrophysics Data System (ADS)

    Zhao, Jiannan; Ma, Lin; Wang, Haoying; Zhao, Yanfeng; Zhang, Jian; Hu, Shaozheng

    2015-03-01

    Novel band gap-tunable K-Na co-doped graphitic carbon nitride was prepared by molten salt method using melamine, KCl, and NaCl as precursor. X-ray diffraction (XRD), N2 adsorption, Scanning electron microscope (SEM), UV-vis spectroscopy, Photoluminescence (PL), and X-ray photoelectron spectroscopy (XPS) were used to characterize the prepared catalysts. The CB and VB potentials of graphitic carbon nitride could be tuned from -1.09 and +1.55 eV to -0.29 and +2.25 eV by controlling the weight ratio of eutectic salts to melamine. Besides, ions doping inhibited the crystal growth of graphitic carbon nitride, enhanced the surface area, and increased the separation rate of photogenerated electrons and holes. The visible-light-driven Rhodamine B (RhB) photodegradation and mineralization performances were significantly improved after K-Na co-doping.

  20. Observation of room temperature ferromagnetic behavior in cluster-free, Co doped HfO2 films

    NASA Astrophysics Data System (ADS)

    Chang, Y. H.; Soo, Y. L.; Lee, W. C.; Huang, M. L.; Lee, Y. J.; Weng, S. C.; Sun, W. H.; Hong, M.; Kwo, J.; Lee, S. F.; Ablett, J. M.; Kao, C.-C.

    2007-08-01

    Extensive structural and magnetic analyses of Hf1-xCoxO2 thin films grown by molecular beam epitaxy are reported. Nearly cobalt cluster-free film with x =0.04-0.1 was obtained via 100°C growth, and Co ions are inferred to be located at interstitial site. Ferromagnetic behavior was observed up to 300K in both magnetization curves and temperature dependence of the moment. Via post-oxygen-annealing studies, a qualitative correlation between saturation magnetization and oxygen vacancy concentration is established, consistent with the impurity-band exchange model, and that the occurrence of ferromagnetic insulator behavior in the Co doped HfO2 is more probable than Co doped ZnO, TiO2, and SnO2 systems for doping concentrations under cation percolation threshold.

  1. Evolution of spin wave excitations with Co-doping in the spinel MnV2O4

    NASA Astrophysics Data System (ADS)

    Hahn, Steven; Ma, Jie; Lee, Jun Hee; Hong, Tao; Cao, Huibo; Aczel, Adam; Dun, Zhiling; Stone, Matthew; Tian, Wei; Qiu, Yiming; Copley, John; Zhou, Haidong; Fishman, Randy; Matsuda, Masaaki

    2015-03-01

    Spin waves were measured at several levels of Co-doping in the spinel system MnV2O4 by inelastic neutron scattering and analyzed with first-principles-guided spin models. Co-doping creates a rich phase diagram encompassing the transition from localized- to itinerant-electron regimes. Increasing Co concentration weakens the single-ion anisotropy and increases both the magnitude and isotropy of the nearest-neighbor exchange interactions. First principles calculations emphasize the the distinctly different microscopic origins of the two-in-two-out magnetic structure at the Mn-rich and Co-rich limits. Research at HFIR and SNS, ORNL, were sponsored by the Scientific User Facilities Division and Materials Science and Engineering Division, Office of Basic Energy Sciences, US Department of Energy.

  2. Photocatalytic enhancement of TiO2 by B and Zr co-doping and modulation of microstructure

    NASA Astrophysics Data System (ADS)

    Fu, Chengxin; Gong, Yinyan; Wu, Yitao; Liu, Jiaqi; Zhang, Zhen; Li, Can; Niu, Lengyuan

    2016-08-01

    Visible-light photodegradation test revealed that B and Zr co-doping can raise the photocatalytic ability of the undoped TiO2 by a fold. XRD crystallography and Raman phonon spectroscopy measurements suggest that the Zr4+ ions replace the Ti4+ ions while the B3+ ions occupy the interstitial sites, expanding the unit-cell volume and reducing crystallite size. The incorporation of interstitial boron dopants creates oxygen vacancies (Ovrad rad) and reduce Ti4+ to Ti3+ to form [Ovrad rad -Ti3+]+, which traps the carriers and prolongs carrier lifetime. Moreover, Zr4+ ions replace Ti4+ ions and form impurity levels, which could improve visible light response. The co-doped samples are benefited from both B interstitials and Zr substitutes.

  3. Electronic, optical and photocatalytic behavior of Mn, N doped and co-doped TiO2: Experiment and simulation

    NASA Astrophysics Data System (ADS)

    Zhao, Ya Fei; Li, Can; Lu, Song; Liu, Ru Xi; Hu, Ji Yuan; Gong, Yin Yan; Niu, Leng Yuan

    2016-03-01

    The crystal phase structure, surface morphology, chemical states and optical properties of Mn, N mono-doped and co-doped TiO2 nanoparticles were investigated by X-ray powder diffractometry, Raman spectra, scanning electron microscopy, X-ray photoelectron spectroscopy and UV-vis diffuse reflectance spectroscopy. Meanwhile, geometry structures, formation energies, electronic and optical properties of all systems have been also analyzed by density functional theory. The results showed that the band gap values and the carrier mobility in the valence band, conduction band and impurity levels have a synergetic influence on the visible-light absorption and photocatalytic activity of the doped TiO2. The number and the carrier mobility of impurity level jointly influence the photocatalytic activity of catalyst under visible-light. Especially, the photocatalytic activity of Mn-2N co-doped TiO2 beyond three-fold than that of pure TiO2 under visible-light.

  4. Green up-converted luminescence in (Er3+-Yb3+) co-doped LiNbO3 crystals

    NASA Astrophysics Data System (ADS)

    Stoffel, M.; Rinnert, H.; Kokanyan, E.; Demirkhanyan, G.; Demirkhanyan, H.; Aillerie, M.

    2016-07-01

    Er3+ doped and (Er3+-Yb3+) co-doped LiNbO3 (LN) crystals grown by the Czochralski method are investigated by photoluminescence spectroscopy. Green up-converted luminescence is observed in Er3+ doped LN crystals under 980 nm excitation. This is explained by an energy transfer between two neighboring Er3+ ions. In (Er3+, Yb3+) co-doped LN crystals, the intensity of the green up-converted luminescence can be further enhanced suggesting that Yb3+ ions also contribute to the up-conversion process. Time resolved photoluminescence measurements clearly demonstrate that an efficient energy transfer occurs between Yb3+ and Er3+ ions. A theoretical model taking into account the contribution of both Er3+-Er3+ pairs and Yb3+-Er3+ pairs is able to describe correctly the decay of the up-converted luminescence.

  5. Effects of N Incorporation on the Structural and Photoluminescence Characteristics of GaSbN/GaSb Single Quantum Wells

    SciTech Connect

    Iyer, Prof Shanthi

    2007-01-01

    The structural and optical properties of GaSbN single quantum wells grown on GaSb substrates by solid source molecular beam epitaxy have been investigated for N concentrations up to 1.5%. The presence of well resolved and pronounced Pendellosung fringes, dynamical diffraction rods seen in the corresponding reciprocal space map, and triple axis full width at half maximum of 10-11 arcsec of the substrate and epilayer peak indicates epilayers of excellent quality with smooth interfaces. Low temperature photoluminescence (PL) exhibited sharp and discrete N related PL line features below the GaSb band edge. Their dependence on N concentration as well as measurement temperature and excitation intensity of the PL strongly suggests that these lines correspond to highly localized N pair/cluster states. No significant effect of in-situ annealing in Sb ambient on the PL features was observed, while ex-situ annealing in N ambient led to the annihilation of these features.

  6. Synthesis and Characterization of Co-doped ZnO Dilute Magnetic Semiconducting Nanorods

    NASA Astrophysics Data System (ADS)

    Das, N.; Khanra, S.; Bhamidipati, S.; Manivannan, K.; Kahol, P.; Ghosh, K.

    2012-02-01

    Transition-metal doped ZnO dilute magnetic semiconducting nanomaterials are considered as ideal systems for carrying out research in the field of spintronics as they can successfully combine magnetism and electronics in a single substance. ZnO is a wurtzite-type wide-bandgap semiconductor of the II-VI semiconductor group with band gap energy of 3.37 eV. Hydrothermal synthesis of undoped ZnO and Co-doped ZnO nanorods is carried out using aqueous solutions of Zn(NO3)2.6H2O, Co(C2H3OO)2.4 H2O, and using NH4OH as hydrolytic catalyst. Nanomaterials of different sizes and shapes were synthesized by varying the process parameters such as molarity (0.15M, 0.3M, 0.5M) and pH (8-11) of the precursors, growth temperature (130^oC), and annealing time during the hydrothermal Process. Structural, morphological, optical and magnetic properties are studied using various techniques such as XRD, SEM, UV-vis spectroscopy, and SQUID magnetometer. XRD and SEM studies reveal nanorods with hexagonal wurtzite structure with length in the range of 200 to 500 nm, and cross section in the range of 30 to 60 nm. Detailed structural, optical, and magnetic properties will be discussed in this presentation.

  7. Significant Enhancement of Water Splitting Activity of N-Carbon Electrocatalyst by Trace Level Co Doping.

    PubMed

    Bayatsarmadi, Bita; Zheng, Yao; Tang, Youhong; Jaroniec, Mietek; Qiao, Shi-Zhang

    2016-07-01

    Replacement of precious metal electrocatalysts with highly active and cost efficient alternatives for complete water splitting at low voltage has attracted a growing attention in recent years. Here, this study reports a carbon-based composite co-doped with nitrogen and trace amount of metallic cobalt (1 at%) as a bifunctional electrocatalyst for water splitting at low overpotential and high current density. An excellent electrochemical activity of the newly developed electrocatalyst originates from its graphitic nanostructure and highly active Co-Nx sites. In the case of carefully optimized sample of this electrocatalyst, 10 mA cm(-2) current density can be achieved for two half reactions in alkaline solutions-hydrogen evolution reaction and oxygen evolution reaction-at low overpotentials of 220 and 350 mV, respectively, which are smaller than those previously reported for nonprecious metal and metal-free counterparts. Based on the spectroscopic and electrochemical investigations, the newly identified Co-Nx sites in the carbon framework are responsible for high electrocatalytic activity of the Co,N-doped carbon. This study indicates that a trace level of the introduced Co into N-doped carbon can significantly enhance its electrocatalytic activity toward water splitting. PMID:27246288

  8. Paramagnetic behavior of Co doped TiO2 nanocrystals controlled by self-purification mechanism

    NASA Astrophysics Data System (ADS)

    Anitha, B.; Khadar, M. Abdul; Banerjee, Alok

    2016-07-01

    Doping in nanocrystals is a challenging process because of the self- purification mechanism which tends to segregate out the dopants resulting in a greater dopant concentration near the surface than at the interior of nanocrystals. In the present work nanocrystals of TiO2 doped with different atom % of Co were synthesized by peroxide gel method. XRD analysis confirmed the tetragonal anatase structure and HRTEM images showed the rod-like morphology of the samples. Raman modes of anatase phase of TiO2 along with weak intensity peaks of Co3O4 for higher Co dopant concentrations were observed for the samples. EPR measurements revealed the presence of cobalt in +2 oxidation state in the TiO2 matrix. SQUID measurements indicated paramagnetic behavior of the Co doped TiO2 nanocrystals. The paramagnetic behavior is attributed to an increased concentration of Co2+ ions and an increased presence of Co3O4 phase near the surface of the TiO2 nanocrystals due to self-purification mechanism.

  9. Structural, linear and nonlinear optical properties of co-doped ZnO thin films

    NASA Astrophysics Data System (ADS)

    Shaaban, E. R.; El-Hagary, M.; Moustafa, El Sayed; Hassan, H. Shokry; Ismail, Yasser A. M.; Emam-Ismail, M.; Ali, A. S.

    2016-01-01

    Different compositions of Co-doped zinc oxide [(Zn(1- x)Co x O) ( x = 0, 0.02, 0.04, 0.06, 0.08 and 0.10)] thin films were evaporated onto highly clean glass substrates by thermal evaporation technique using a modified source. The structural properties investigated by X-ray diffraction revealed hexagonal wurtzite ZnO-type structure. The crystallite size of the films was found to decrease with increasing Co content. The optical characterization of the films has been carried out using spectral transmittance and reflectance obtained in the wavelength range from 300 to 2500 nm. The refractive index has been found to increase with increasing Co content. It was further found that optical energy gap decreases from 3.28 to 3.03 eV with increasing Co content from x = 0 to x = 0.10, respectively. The dispersion of refractive index has been analyzed in terms of Wemple-DiDomenico (WDD) single-oscillator model. The oscillator parameters, the single-oscillator energy ( E o), the dispersion energy ( E d), and the static refractive index ( n 0), were determined. The nonlinear refractive index of the Zn(1- x)Co x O thin films was calculated and revealed well correlation with the linear refractive index and WDD parameters which in turn depend on the density and molar volume of the system.

  10. Boron and nitrogen co-doped porous carbon and its enhanced properties as supercapacitor

    NASA Astrophysics Data System (ADS)

    Guo, Hongliang; Gao, Qiuming

    Boron and nitrogen co-doped porous carbons (BNCs) were prepared through a facile procedure using citric acid, boric acid and nitrogen as C, B and N precursors, respectively. The BNC samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and nitrogen sorption at 77 K. Cyclic voltammetry and galvanostatic charge/discharge experiments were adopted to investigate their electrochemical behaviors. The BNC-9 and BNC-15 samples with high specific surface areas of 894 and 726 m 2 g -1 showed the large specific capacitance up to 268 and 173 F g -1, respectively, with the current of 0.1 A g -1. When the current was set as 1 A g -1, the energy densities were 3.8 and 3.0 Wh kg -1 and the power densities were 165 and 201 W kg -1 for BNC-9 and BNC-15, respectively. Thus, BNC-15 is more suitable to apply in high-power-demanded occasion, while BNC-9 tends to store more energy.

  11. Microstructure of Co-doped TiO{sub 2}(110) rutile by ion implantation

    SciTech Connect

    Wang, C.M.; Shutthanandan, V.; Thevuthasan, S.; Droubay, T.; Chambers, S.A.

    2005-04-01

    Co-doped rutile TiO{sub 2} was synthesized by injecting Co ions into single crystal rutile TiO{sub 2} using high energy ion implantation. Microstructures of the implanted specimens were studied in detail using high-resolution transmission electron microscopy (HRTEM), energy dispersive x-ray spectroscopy, electron diffraction, and HRTEM image simulations. The spatial distribution and conglomeration behavior of the implanted Co ions, as well as the point defect distributions induced by ion implantation, show strong dependences on implantation conditions. Uniform distribution of Co ions in the rutile TiO{sub 2} lattice was obtained by implanting at 1075 K with a Co ion fluence of 1.25x10{sup 16} Co/cm{sup 2}. Implanting at 875 K leads to the formation of Co metal clusters. The precipitated Co metal clusters and surrounding TiO{sub 2} matrix exhibit the orientation relationships Co<110> parallel TiO{sub 2}[001] and Co{l_brace}111{r_brace} parallel TiO{sub 2}(110). A structural model representing the interface between Co metal clusters and TiO{sub 2} is developed based on HRTEM imaging and image simulations.

  12. Microstructure of Co-doped TiO₂ (110) Rutile by Ion Implantation

    SciTech Connect

    Wang, Chong M.; Shutthanandan, V.; Thevuthasan, Suntharampillai; Droubay, Timothy C.; Chambers, Scott A.

    2005-04-01

    Co-doped rutile TiO₂ was synthesized by injecting Co ions into single crystal rutile TiO₂ using high energy ion implantation. Microstructures of the implanted specimens were studied in detail using high-resolution transmission electron microscopy (HRTEM), energy dispersive x-ray spectroscopy (EDS), electron diffraction, and HRTEM image simulations. The spatial distribution and conglomeration behavior of the implanted Co ions, as well as the point defect distributions induced by ion implantation, show strong dependences on implantation conditions. Uniform distribution of Co ions in the rutile TiO₂ lattice was obtained by implanting at 1075 K with a Co ion fluence of 1.25x10¹⁶ Co/cm². Implanting at 875 K leads to the formation of Co metal clusters. The precipitated Co metal clusters and surrounding TiO₂ matrix exhibit the orientation relationships Co<110>//TiO₂[001] and Co{111}//TiO₂(110). A structural model representing the interface between Co metal clusters and TiO₂ is developed based on HRTEM imaging and image simulations.

  13. Visible light carrier generation in co-doped epitaxial titanate films

    SciTech Connect

    Comes, Ryan B. Kaspar, Tiffany C.; Chambers, Scott A.; Smolin, Sergey Y.; Baxter, Jason B.; Gao, Ran; Apgar, Brent A.; Martin, Lane W.; Bowden, Mark E.

    2015-03-02

    Perovskite titanates such as SrTiO{sub 3} (STO) exhibit a wide range of important functional properties, including ferroelectricity and excellent photocatalytic performance. The wide optical band gap of titanates limits their use in these applications; however, making them ill-suited for integration into solar energy harvesting technologies. Our recent work has shown that by doping STO with equal concentrations of La and Cr, we can enhance visible light absorption in epitaxial thin films while avoiding any compensating defects. In this work, we explore the optical properties of photoexcited carriers in these films. Using spectroscopic ellipsometry, we show that the Cr{sup 3+} dopants, which produce electronic states immediately above the top of the O 2p valence band in STO reduce the direct band gap of the material from 3.75 eV to 2.4–2.7 eV depending on doping levels. Transient reflectance spectroscopy measurements are in agreement with the observations from ellipsometry and confirm that optically generated carriers are present for longer than 2 ns. Finally, through photoelectrochemical methylene blue degradation measurements, we show that these co-doped films exhibit enhanced visible light photocatalysis when compared to pure STO.

  14. Study on the Photorefractive Properties of Sc, in Co-Doped Lithium Niobate Crystals

    NASA Astrophysics Data System (ADS)

    Xu, Zhaopeng; Xu, Shiwen; Xu, Yuheng; Wang, Rui

    The Sc:In:LiNbO3 crystals co-doped with 0.5 mol% Sc2O3 and 0, 0.5, 0.75 and 1 mol% In2O3 were grown by the Czochralski method. The structure of the crystals was measured by infrared spectra. The mechanism of the shift of OH- absorption peak was investigated. The photo-damage resistance ability of Sc:In:LiNbO3 crystals was observed by the straightly observing transmission facula distortion method. The Sc:In:LiNbO3 waveguide substrates were fabricated by the proton exchange technique using benzoic acid as the proton source. The photo-damage thresholds of these y-cut waveguide substrates were measured by the m-line method. The results measured by the two methods above all show that the photo-damage resistance ability of Sc:In:LiNbO3 crystals increases two orders of magnitude in comparison with that of pure LiNbO3 crystals. The mechanism of the enhancement of the photo-damage resistance ability of Sc:In:LiNbO3 crystals is discussed by Li-vacancy model.

  15. Significant Enhancement of Water Splitting Activity of N-Carbon Electrocatalyst by Trace Level Co Doping.

    PubMed

    Bayatsarmadi, Bita; Zheng, Yao; Tang, Youhong; Jaroniec, Mietek; Qiao, Shi-Zhang

    2016-07-01

    Replacement of precious metal electrocatalysts with highly active and cost efficient alternatives for complete water splitting at low voltage has attracted a growing attention in recent years. Here, this study reports a carbon-based composite co-doped with nitrogen and trace amount of metallic cobalt (1 at%) as a bifunctional electrocatalyst for water splitting at low overpotential and high current density. An excellent electrochemical activity of the newly developed electrocatalyst originates from its graphitic nanostructure and highly active Co-Nx sites. In the case of carefully optimized sample of this electrocatalyst, 10 mA cm(-2) current density can be achieved for two half reactions in alkaline solutions-hydrogen evolution reaction and oxygen evolution reaction-at low overpotentials of 220 and 350 mV, respectively, which are smaller than those previously reported for nonprecious metal and metal-free counterparts. Based on the spectroscopic and electrochemical investigations, the newly identified Co-Nx sites in the carbon framework are responsible for high electrocatalytic activity of the Co,N-doped carbon. This study indicates that a trace level of the introduced Co into N-doped carbon can significantly enhance its electrocatalytic activity toward water splitting.

  16. Visible light carrier generation in co-doped epitaxial titanate films

    SciTech Connect

    Comes, Ryan B.; Smolin, Sergey Y.; Kaspar, Tiffany C.; Gao, Ran; Apgar, Brent A.; Martin, Lane W.; Bowden, Mark E.; Baxter, Jason; Chambers, Scott A.

    2015-03-02

    Perovskite titanates such as SrTiO3 (STO) exhibit a wide range of important functional properties, including high electron mobility, ferroelectricity—which may be valuable in photovoltaic applications—and excellent photocatalytic performance. The wide optical band gap of titanates limits their use in these applications, however, making them ill-suited for integration into solar energy harvesting technologies. Our recent work has shown that by doping STO with equal concentrations of La and Cr we can enhance visible light absorption in epitaxial thin films while avoiding any compensating defects. In this work, we explore the optical properties of photoexcited carriers in these films. Using spectroscopic ellipsometry, we show that the Cr3+ dopants, which produce electronic states immediately above the top of the O 2p valence band in STO reduce the direct band gap of the material from 3.75 eV to between 2.4 and 2.7 eV depending on doping levels. Transient reflectance measurements confirm that optically generated carriers have a recombination lifetime comparable to that of STO and are in agreement with the observations from ellipsometry. Finally, through photoelectrochemical yield measurements, we show that these co-doped films exhibit enhanced visible light photocatalysis when compared to pure STO.

  17. Dependence of GaAs-AlxGa1 - xAs heterostructures on Al composition for metal-semiconductor field-effect transistor operation

    NASA Astrophysics Data System (ADS)

    Hiruma, Kenji; Mori, Mitsuhiro; Kakibayashi, Hiroji; Ihara, Ayako; Takahashi, Susumu; Yanokura, Eiji

    1989-08-01

    High-quality GaAs-AlxGa1-xAs heterostructures for metal-semiconductor field-effect transistor (MESFET) applications have been grown by metalorganic vapor-phase epitaxy. High electron Hall mobility of up to 4000 cm2/(V s) for a carrier concentration of 3.5×1017 cm-3 was obtained for Si-doped GaAs grown on AlxGa1-xAs. It was learned that the electron Hall mobility of GaAs is not dependent on the Al composition of the AlxGa1-xAs buffer layer for 0≤x≤0.8. Good drain current-voltage saturation characteristics were observed for GaAs MESFETs with a 0.3-μm gate length and AlxGa1-xAs buffer layers. At drain voltages below 3 V, the drain conductance was at its lowest for Al composition around x=0.6. However, an anomalous peak in the drain conductance was observed at drain voltages of 3-6 V and at Al compositions of x=0.6 and 0.8. Drain conductance also increased as x did for x≥0.45 when measured at a microwave frequency. These phenomena can be understood by considering electron injection into the buffer/substrate region from the GaAs channel. The amount of this injection coincided well with the reduction in the conduction-band energy barrier at the GaAs-AlxGa1-xAs heterointerface for x>0.45 for electron transport.

  18. Computational discovery of lanthanide doped and Co-doped Y{sub 3}Al{sub 5}O{sub 12} for optoelectronic applications

    SciTech Connect

    Choudhary, Kamal; Chernatynskiy, Aleksandr; Phillpot, Simon R.; Sinnott, Susan B.; Mathew, Kiran; Bucholz, Eric W.; Hennig, Richard G.

    2015-09-14

    We systematically elucidate the optoelectronic properties of rare-earth doped and Ce co-doped yttrium aluminum garnet (YAG) using hybrid exchange-correlation functional based density functional theory. The predicted optical transitions agree with the experimental observations for single doped Ce:YAG, Pr:YAG, and co-doped Er,Ce:YAG. We find that co-doping of Ce-doped YAG with any lanthanide except Eu and Lu lowers the transition energies; we attribute this behavior to the lanthanide-induced change in bonding environment of the dopant atoms. Furthermore, we find infrared transitions only in case of the Er, Tb, and Tm co-doped Ce:YAG and suggest Tm,Ce:YAG and Tb,Ce:YAG as possible functional materials for efficient spectral up-conversion devices.

  19. Dependences on RE of superconducting properties of transition metal co-doped (Ca, RE)FeAs2 with RE = La-Gd

    NASA Astrophysics Data System (ADS)

    Yakita, H.; Ogino, H.; Sala, A.; Okada, T.; Yamamoto, A.; Kishio, K.; Iyo, A.; Eisaki, H.; Shimoyama, J.

    2015-11-01

    Dependence of superconducting properties of (Ca, RE)(Fe, TM)As2 [(Ca, RE)112, TM: Co, Ni)] on RE elements (RE = La-Gd) was systematically investigated. Improvement of superconducting properties by Co or Ni co-doping was observed for all (Ca, RE)112, which is similar to Co-co-doped (Ca, La)112 or (Ca, Pr)112. Tc of Co-co-doped samples decreased from 38 K for RE = La to 29 K for RE = Gd with decreasing ionic radii of RE3+. However, Co-co-doped (Ca, Eu)112 showed exceptionally low Tc = 21 K probably due to the co-existence of Eu3+ and Eu2+ suggested by longer interlayer distance dFe-Fe of (Ca, Eu)112 than other (Ca, RE)112.

  20. The effect of neutron radiation on the photoelectric parameters of ITO-GaSe structures

    SciTech Connect

    Kovalyuk, Z. D. Litovchenko, P. G.; Politanska, O. A.; Sydor, O. N.; Katerynchuk, V. N.; Lastovetsky, V. F.; Litovchenko, O. P.; Dubovoy, V. K.; Polivtsev, L. A.

    2007-05-15

    The effect of 1-MeV neutrons on the photoelectric parameters of ITO-GaSe heterostructures was studied. It is shown that the observed variations in the current-voltage characteristics are caused by the effect of penetrating radiation on both components of the structure, which brings about an increase in the resistance of the heterostructures. The presence of exciton fine structure in the photosensitivity spectra after irradiation indicates that GaSe retains high structural quality notwithstanding the introduced radiation defects. The results obtained are accounted for by spatial redistribution of doping impurity in GaSe and structural changes in the ITO films.

  1. Preparation and photocatalytic activity of B, Ce Co-doped TiO2 hollow fibers photocatalyst

    NASA Astrophysics Data System (ADS)

    Qiu, Jingping; Sun, Xiaogang; Xing, Jun; Liu, Xiaobo

    2014-07-01

    A series of B, Ce co-doped TiO2 (B, Ce-TiO2) photocatalytic materials with a hollow fiber structure were successfully prepared by template method using boric acid, ammonium ceric nitrate and tetrabutyltitanate as precursors and cotton fibers as template, followed by calcination at 500°C in an N2 atmosphere for 2 h. Scanning electron microscopy (SEM), X-ray diffraction (XRD), nitrogen adsorption-desorption measurements, and UV-visible spectroscopy (UV-Vis) were employed to characterize the morphology, crystal structure, surface structure, and optical absorption properties of the samples. The photocatalytic performance of the samples was studied by photodegradation phenol in water under UV light irradiation. The results showed that the TiO2 fiber materials have hollow structures, and the fiber structure materials showed better photocatalytic properties for the degradation of phenol than pure TiO2 under UV light. In the experiment condition, the photocatalytic activity of B, Ce co-doped TiO2 fibers was optimal of all the prepared samples. In addition, the possibility of cyclic usage of B, Ce co-doped TiO2 fiber photocatalyst was also confirmed, the photocatalytic activity of TiO2 fibers remained above 90% of that of the fresh sample after being used four times. The material was easily removed by centrifugal separation from the medium. It can therefore be potentially applied for the treatment of water contaminated by organic pollutants.

  2. Optical and magnetic properties of Co-doped CuO flower/plates/particles-like nanostructures.

    PubMed

    Basith, N Mohamed; Vijaya, J Judith; Kennedy, L John; Bououdina, M; Hussain, Shamima

    2014-03-01

    In this study, pure and Co-doped CuO nanostructures (0.5, 1.0, 1.5, and 2.0 at wt% of Co) were synthesized by microwave combustion method. The prepared samples were characterized by X-ray diffraction (XRD), high resolution scanning electron microscopy (HR-SEM), energy dispersive X-ray analysis (EDX), diffuse reflectance spectroscopy (DRS), photoluminescence (PL) spectroscopy and vibrating sample magnetometry (VSM). Powder X-ray diffraction patterns refined by the Rietveld method indicated the formation of single-phase monoclinic structure. The surface morphology and elemental analysis of Co-doped CuO nanostructures were studied by using HR-SEM and EDX. Interestingly, the morphology was found to change considerably from nanoflowers to nanoplates then to nanoparticles with the variation of Co concentration. The optical band gap calculated using DRS was found to be 2.1 eV for pure CuO and increases up to 3.4 eV with increasing cobalt content. Photoluminescence measurements also confirm these results. The magnetic measurements indicated that the obtained nanostructures were ferromagnetic at room temperature with an optimum value of saturation magnetization at 1.0 wt.% of Co-doped CuO, i.e., 970 micro emu/g.

  3. AlGaAs/GaAs quasi-bulk effect mixers: Analysis and experiments

    NASA Technical Reports Server (NTRS)

    Yngvesson, K. S.; Yang, J.-X.; Agahi, F.; Dai, D.; Musante, C.; Grammer, W.; Lau, K. M.

    1992-01-01

    The lowest noise temperature for any receiver in the 0.5 to 1 THz range has been achieved with the bulk InSb hot electron mixer, which unfortunately suffers from the problem of having a very narrow bandwidth (1-2 MHz). We have demonstrated a three order of magnitude improvement in the bandwidth of hot electron mixers, by using the two-dimensional electron gas (2DEG) medium at the hetero-interface between AlGaAs and GaAs. We have tested both inhouse MOCVD-grown material, and MBE materials, with similar results. The conversion loss (L(sub c)) at 94 GHz is presently 18 dB for a mixer operating at 20 K, and calculations indicate that L(sub c) can be decreased to about 10 dB in future devices. Calculated and measured curves of L(sub c), versus PLO and IDC, respectively, agree well. We argue that there are several different configurations of hot electron mixers, which will also show wide bandwidth, and that these devices are likely to become important as low-noise THz receivers in the future.

  4. A novel anode comprised of C&N co-doped Co3O4 hollow nanofibres with excellent performance for lithium-ion batteries.

    PubMed

    Yan, Chunshuang; Chen, Gang; Sun, Jingxue; Zhou, Xin; Lv, Chade

    2016-07-20

    C&N co-doped Co3O4 hollow nanofibres are prepared by combining the electrospinning technique and the hydrothermal method, which show a high reversible capacity and excellent cycling stability as anode materials for Li-ion batteries. DFT calculations give a good explanation for the experimentally enhanced conductivity in C&N co-doped Co3O4 hollow nanofibres. PMID:27389924

  5. Self-heating study of an AlGaN/GaN-based heterostructure field effect transistor using ultraviolet micro-Raman scattering.

    SciTech Connect

    Kasisomayajula, V.; Baca, Albert G.; AHMAD, I.; Berg, Jeremy Mark; Holtz, M; Allerman, Andrew Alan; Tigges, Christopher P.; Kurtz, Steven Ross

    2005-01-01

    We report micro-Raman studies of self-heating in an AlGaN/GaN heterostructure field-effect transistor using below (visible 488.0 nm) and near (UV 363.8 nm) GaN band-gap excitation. The shallow penetration depth of the UV light allows us to measure temperature rise ({Delta}T) in the two-dimensional electron gas (2DEG) region of the device between drain and source. Visible light gives the average {Delta}T in the GaN layer, and that of the SiC substrate, at the same lateral position. Combined, we depth profile the self-heating. Measured {Delta}T in the 2DEG is consistently over twice the average GaN-layer value. Electrical and thermal transport properties are simulated. We identify a hotspot, located at the gate edge in the 2DEG, as the prevailing factor in the self-heating.

  6. Effects of GaN interlayer on the transport properties of lattice-matched AlInN/AlN/GaN heterostructures

    SciTech Connect

    Wu, F.; Gao, K. H. Li, Z. Q.; Lin, T.; Zhou, W. Z.

    2015-04-21

    We study the effects of GaN interlayer on the transport properties of two-dimensional electron gases confined in lattice-matched AlInN/AlN/GaN heterostructures. It is found that the Hall mobility is evidently enhanced when an additional ultrathin GaN interlayer is introduced between AlInN and AlN layers. The enhancement of the Hall mobility is especially remarkable at low temperature. The high Hall mobility results in a low sheet resistance of 23 Ω/◻ at 2 K. Meanwhile, Shubnikov-de Haas oscillations (SdH) are also remarkably enhanced due to the existence of GaN interlayer. The enhancement of the SdH oscillations is related to the larger quantum mobility μ{sub q} owing to the suppression of the interface roughness, alloy disorder, and ionized impurity scatterings by the GaN interlayer.

  7. Effect of GA3 Treatment on Seed Development and Seed-Related Gene Expression in Grape

    PubMed Central

    Cheng, Chenxia; Xu, Xiaozhao; Singer, Stacy D.; Li, Jun; Zhang, Hongjing; Gao, Min; Wang, Li; Song, Junyang; Wang, Xiping

    2013-01-01

    Background The phytohormone gibberellic acid (GA3) is widely used in the table grape industry to induce seedlessness in seeded varieties. However, there is a paucity of information concerning the mechanisms by which GAs induce seedlessness in grapes. Methodology/Principal Findings In an effort to systematically analyze the cause of this GA3-induced seed abortion, we conducted an in depth characterization of two seeded grape cultivars (‘Kyoho’ and ‘Red Globe’), along with a seedless cultivar (‘Thompson Seedless’), following treatment with GA3. In a similar fashion to the seedless control, which exhibited GA3-induced abortion of the seeds 9 days after full bloom (DAF), both ‘Kyoho’ and ‘Red Globe’ seeded varieties exhibited complete abortion of the seeds 15 DAF when treated with GA3. Morphological analyses indicated that while fertilization appeared to occur normally following GA3 treatment, as well as in the untreated seedless control cultivar, seed growth eventually ceased. In addition, we found that GA3 application had an effect on redox homeostasis, which could potentially cause cell damage and subsequent seed abortion. Furthermore, we carried out an analysis of antioxidant enzyme activities, as well as transcript levels from various genes believed to be involved in seed development, and found several differences between GA3-treated and untreated controls. Conclusion Therefore, it seems that the mechanisms driving GA3-induced seedlessness are similar in both seeded and seedless cultivars, and that the observed abortion of seeds may result at least in part from a GA3-induced increase in cell damage caused by reactive oxygen species, a decrease in antioxidant enzymatic activities, and an alteration of the expression of genes related to seed development. PMID:24224035

  8. Surfactant effect of gallium during molecular-beam epitaxy of GaN on AlN (0001)

    NASA Astrophysics Data System (ADS)

    Mula, Guido; Adelmann, C.; Moehl, S.; Oullier, J.; Daudin, B.

    2001-11-01

    We study the adsorption of Ga on (0001) GaN surfaces by reflection high-energy electron diffraction. It is shown that a dynamically stable Ga bilayer can be formed on the GaN surface for appropriate Ga fluxes and substrate temperatures. The influence of the presence of this Ga film on the growth mode of GaN on AlN(0001) by plasma-assisted molecular-beam epitaxy is studied. It is demonstrated that under nearly stoichiometric and N-rich conditions, the GaN layer relaxes elastically during the first stages of epitaxy. At high temperatures the growth follows a Stranski-Krastanov mode, whereas at lower temperatures kinetically formed flat platelets are observed. Under Ga-rich conditions-where a Ga bilayer is rapidly formed due to excess Ga accumulating on the surface-the growth follows a Frank-van der Merwe layer-by-layer mode at any growth temperature and no initial elastic relaxation occurs. Hence, it is concluded that excess Ga acts as a surfactant, effectively suppressing both Stranski-Krastanov islanding and platelet formation. It is further demonstrated that the Stranski-Krastanov transition is in competition with elastic relaxation by platelets, and it is only observed when relaxation by platelets is inefficient. As a result, a growth mode phase diagram is outlined for the growth of GaN on AlN(0001).

  9. Effect of gallium concentrations on the morphologies, structural and optical properties of Ga-doped ZnO nanostructures.

    PubMed

    Algarni, H; El-Gomati, M M; Al-Assiri, M S

    2014-07-01

    The effect of gallium ion concentrations (0.5 and 2%) on the morphologies, structural and optical properties of Ga-doped ZnO nanostructures are presented. Ga-doped ZnO nanostructures were synthesized on silicon substrates by simple thermal evaporation process using metallic zinc and Ga powders in the presence of oxygen. Interestingly, it was observed that Ga-ions incorporation in ZnO nanomaterials play an important role on the growth kinetics and hence on the morphologies of as-grown Ga-doped ZnO nanostructures. It was seen that at low Ga-concentration, needle-shaped Ga-doped ZnO nanostructures are formed, presumably by subsequent stacking of hexagonal plates. However, when increasing the Ga-concentration, multipods of Ga-doped ZnO were grown. In addition to the morphologies, incorporating Ga-ions into ZnO also affect the room-temperature photoluminescence properties. Therefore, at lower Ga-ion concentration, an intense UV emission was observed while at high Ga-concentration a deep level emission was seen in the room-temperature photoluminescence spectra. This research demonstrates that by controlling the Ga-ion concentration the morphologies and optical properties of ZnO nanomaterials can be tailored.

  10. Role of sp-d exchange interactions in room-temperature photoluminescence and ferromagnetism of CuCo Co-doped ZnO nanorods.

    PubMed

    Iqbal, Javed; Wang, Baiqi; Liu, Xiaofang; Zhu, Huichao; Yu, Dapeng; Yu, Ronghai

    2009-12-01

    CuCo co-doped ZnO nanorods have been synthesized via a soft chemistry route without using any surfactant, seed and catalyst. Structural analyses reveal that the samples of nominal compositions Cu0.01Co0.02Zn0.97O and Cu0.02Co0.01Zn0.97O have single hexagonal wurtzite structure without forming any extra secondary phase. Photoluminescence (PL) measurements show that the Cu co-doping in Co doped ZnO nanorods strongly influences the optical band structure and gives significant red shifts in the PL spectra. Furthermore, magnetic measurements of CuCo co-doped ZnO nanorods exhibit obvious room temperature ferromagnetism at low concentrations of Cu (< 1%) co-doping, while at higher concentrations of Cu co-doping, magnetization drops off sharply. An experimental relationship has been found to explain the redshift of E(g) edge in PL and the origin of observed ferromagnetism as function of Cu co-dopant concentration due to the spin exchange interactions between the sp band and localized spins of d electrons of dopants, which is useful for future semiconductor based spintronic devices.

  11. Modeling and Characterization of the Magnetocaloric Effect in Ni2MnGa Materials

    SciTech Connect

    Nicholson, Don M; Odbadrakh, Khorgolkhuu; Rios, Orlando; Hodges, Jason P; Ludtka, Gerard Michael; Porter, Wallace D; Sefat, A. S.; Rusanu, Aurelian; Evans III, Boyd Mccutchen

    2012-01-01

    Magnetic shape memory alloys have great promise as magneto-caloric effect refrigerant materials due to their combined magnetic and structural transitions. Computational and experimental research is reported on the Ni2MnGa material system. The magnetic states of this system have been explored using the Wang-Landau statistical approach in conjunction with the Locally Self-consistent Multiple-Scattering (LSMS) method to explore the magnetic states responsible for the magnet-caloric effect in this material. The effects of alloying agents on the transition temperatures of the Ni2MnGa alloy were investigated using differential scanning calorimetry (DSC) and superconducting quantum interference device (SQUID). Neutron scattering experiments were performed to observe the structural and magnetic phase transformations at the Spallation Neutron Source (SNS) at Oak Ridge National Laboratory (ORNL) on alloys of Ni-Mn-Ga and Ni-Mn-Ga-Cu-Fe. Data from the observations are discussed in comparison with the computational studies.

  12. Many-body effects on optical gain in GaAsPN/GaPN quantum well lasers for silicon integration

    SciTech Connect

    Park, Seoung-Hwan

    2014-02-14

    Many-body effects on the optical gain in GaAsPN/GaP QW structures were investigated by using the multiband effective-mass theory and the non-Markovian gain model with many-body effects. The free-carrier model shows that the optical gain peak slightly increases with increasing N composition. In addition, the QW structure with a larger As composition shows a larger optical gain than that with a smaller As composition. On the other hand, in the case of the many-body model, the optical gain peak decreases with increasing N composition. Also, the QW structure with a smaller As composition is observed to have a larger optical gain than that with a larger As composition. This can be explained by the fact that the QW structure with a smaller As or N composition shows a larger Coulomb enhancement effect than that with a larger As or N composition. This means that it is important to consider the many-body effect in obtaining guidelines for device design issues.

  13. Gate length scaling effect on high-electron mobility transistors devices using AlGaN/GaN and AlInN/AlN/GaN heterostructures.

    PubMed

    Liao, S Y; Lu, C C; Chang, T; Huang, C F; Cheng, C H; Chang, L B

    2014-08-01

    Compared to AlGaN/GaN HEMT with 0.15 μm T-gate length, the AlInN/AlN/GaN one exhibits much higher current density and transconductance of 1558 mA/mm at Vd = 2 V and 330 mS/mm, respectively. The high extrinsic ft and fmax of 82 GHz and 70 GHz are extracted from AlInN/AlN/GaN HEMT. Besides, we find that the transconductance roll-off is significant in AlGaN/GaN, but largely improved in AlInN/AlN/GaN HEMT, suggesting that the high carrier density and lattice-matched epitaxial heterostructure is important to reach both large RF output power and high operation frequency, especially for an aggressively gate length scaling.

  14. (Indium, Aluminum) co-doped Zinc Oxide as a Novel Material System for Quantum-Well Multilayer Thermoelectrics

    NASA Astrophysics Data System (ADS)

    Teehan, Sean

    Waste heat recovery from low efficiency industrial processes requires high performance thermoelectric materials to meet challenging requirements. The efficiency such a device is quantified by the dimensionless figure of merit ZT=S2sigmaT/kappa, where S is the Seebeck coefficient, sigma is the electrical conductivity, T is the absolute temperature and kappa is the thermal conductivity. For practical applications these devices are only cost-effective if the ZT is higher than 2. Theoretically it has been proven that by engineering nanostructures with lower dimensionality one can significantly increase ZT. A superlattice, or a system of 2-dimensional multilayer quantum wells has previously shown the potential to be used for thermoelectric structures. However, the use of conventional materials within these structures has only allowed this at low temperatures and has utilized cross-plane transport. This study focuses on both high temperature range operation and the in-plane transport properties of such structures, which benefit from both quantum confinement and an enhancement in density of states near EF. The n-type structures are fabricated by alternately sputtering barrier and well materials of Al-doped ZnO (AZO) and indium co-doped AZO, respectively. Samples investigated consist of 50 periods with targeted layer thicknesses of 10nm, which results in sufficient sampling material as well as quantum well effects. The indium doping level within the quantum well was controlled by varying the target power, and ultimately results in a 3x improvement in power factor (S 2sigma) over the parent bulk materials. The film characterization was determined by X-ray reflectometry, transmission electron microscopy, X-ray diffraction, auger electron spectroscopy, as well as other relevant techniques. In addition, process optimization was performed on material parameters such as layer thickness, interface roughness, and band-gap offset which all play a major role in determining the

  15. Effect of annealing on proton irradiated AlGaN/GaN based micro-Hall sensors

    SciTech Connect

    Abderrahmane, A.; Takahashi, H.; Tashiro, T.; Ko, P. J.; Okada, H.; Sandhu, A.; Sato, S.; Ohshima, T.

    2014-02-20

    The effect of annealing at 673 K on irradiated micro-Hall sensors irradiated with protons at 380keV and fluences of 10{sup 14}, 10{sup 15} and 10{sup 16} protons/cm{sup 2} is reported. Cathodoluminescence measurements were carried out at room temperature before and after annealing and showed improvement in the band edge band emission of the GaN layer. After annealing a sensor irradiated by 10{sup 15} protons/cm{sup 2} the device became operational with improvements in its magnetic sensitivity. All irradiated sensors showed improvement in their electrical characteristics after annealing.

  16. Built-in-polarization field effect on lattice thermal conductivity of AlxGa1-xN/GaN heterostructure

    NASA Astrophysics Data System (ADS)

    Pansari, Anju; Gedam, Vikas; Kumar Sahoo, Bijaya

    2015-12-01

    The built-in-polarization field at the interface of AlxGa1-xN/GaN heterostructure enhances elastic constant, phonon velocity, Debye temperature and their bowing constants of barrier material AlxGa1-xN. The combined phonon relaxation time of acoustics phonons has been computed for with and without built-in-polarization field at room temperature for different aluminum (Al) content (x). Our result shows that the built-in-polarization field suppresses the scattering mechanisms and enhances the combined relaxation time. The thermal conductivity of AlxGa1-xN has been estimated as a function of temperature for x=0, 0.1, 0.5 and 1 for with and without polarization field. Minimum thermal conductivity has been observed for x=0.1 and 0.5. Analysis shows that up to a certain temperature (different for different x) the polarization field acts as negative effect and reduces the thermal conductivity and after this temperature thermal conductivity is significantly contributed by polarization field. This signifies pyroelectric character of AlxGa1-xN. The pyroelectric transition temperature of AlxGa1-xN alloy has been predicted for different x. Our study reports that room temperature thermal conductivity of AlxGa1-xN/GaN heterostructure is enhanced by built-in-polarization field. The temperature dependence of thermal conductivity for x=0.1 and 0.5 are in line with prior experimental studies. The method we have developed can be used for the simulation of heat transport in nitride devices to minimize the self heating processes and in polarization engineering strategies to optimize the thermoelectric performance of AlxGa1-xN/GaN heterostructures.

  17. Effects of phase transformation on the microstructures and magnetostriction of Fe-Ga and Fe-Ga-Zn ferromagnetic shape memory alloys

    NASA Astrophysics Data System (ADS)

    Lin, Yin-Chih; Lin, Chien-Feng

    2015-05-01

    The phase transformation and magnetostriction of bulk Fe73Ga27 and Fe73Ga18Zn9 (at. %) ferromagnetic shape memory alloys (FSMs) were investigated by transmission electron microscopy (TEM), x-ray diffraction (XRD), and a magnetostrictive-meter setup. For the Fe73Ga27 FSM alloy solution treated at 1100 °C for 4 h and quenched in ice brine, the antiphase boundary segments of the D03 domain were observed in the A2 (disordered) matrix, and the Fe73Ga27 FSM alloy had an optimal magnetostriction (λ‖s = 71 × 10-6 and λ⊥s = -31 × 10-6). In Fe73Ga27 FSM alloy as-quenched, aged at 700 °C for 24 h, and furnace cooled, D03 nanoclusters underwent phase transformation to an intermediate tetragonal phase (i.e., L10-like martensite) via Bain distortion, and finally L12 (Fe3Ga) structures precipitated, as observed by TEM and XRD. The L10-like martensite and L12 phases in the aged Fe73Ga27 FSM alloy drastically decreased the magnetostriction from positive to negative (λ‖s = -20 × 10-6 and λ⊥s = -8 × 10-6). However, in Fe73Ga18Zn9 FSM alloy as-quenched and aged, the phase transformation of D03 to an intermediate tetragonal martensite phase and precipitation of L12 structures were not found. The results indicate that the aged Fe73Ga18Zn9 FSM alloy maintained stable magnetostriction (λ‖s = 36 × 10-6 and λ⊥s = -31 × 10-6). Adding Zn can improve the ferromagnetic shape memory effect of aged Fe73Ga18Zn9 alloy, which may be useful in application of the alloy in high temperature environments.

  18. [Effects of GA, and CPPU on grape fruit adjacent leaf photosynthesis and fruit quality].

    PubMed

    Xin, Shou-peng; Liu, Shuai; Yu, Yang; Nie, Song-qing; Gao, Zhi-hong; Tao, Jian-min

    2015-06-01

    Taken the grape cultivar 'Shine Muscat' as the material, the effect of the combination of GA3 and CPPU on the light-response curves in the fruit adjacent leaves and fruit quality were investigated two weeks after blossoming. The results showed that non-rectangular hyperbolic model was more suitable for grape fruit adjacent leaf light response curve-fitting. Pn and g(s) of fruit adjacent leaves among all treatments increased with the increasing light intensity under the combination treat-ments of 25 mg · L(-1) GA3 and 5, 10, 15, 20 mg · L(-1) CPPU, respectively, but Ci decreased. Fruit quality increased with the increasing CPPU concentration under the combination treatments of 25 mg · L(-1) GA3 and 5, 10, 15 mg · L(-1) CPPU, respectively. Grape fruit adjacent leaf photosynthesis under the 25 mg · L(-1) GA3 + 20 mg · L(-1) CPPU treatment was higher than the other treatments. The fruit quality under the 25 mg · L(-1) GA3 + 20 mg · L(-1) CPPU treatment was lower than the 25 mg · L(-1) GA3 + 15 mg · L(-1) CPPU treatment. It indicated that reasonable CPPU treatment concentration could improve fruit adjacent leaf photosynthetic ability and fruit quality. Too high concentration made the fruit quality lower instead. The 25 mg · L(-1) GA3 + 15 mg · L(-1) CPPU treatment was most appropriate in two weeks after blossoming. PMID:26572037

  19. Computational study of the Effect of Sulfur Passivation on GaAs Heterojunction Solar Cells

    NASA Astrophysics Data System (ADS)

    Yu, Ted; Laghuvamarapu, Ramesh; Yan, Liang; You, Wei; Huffaker, Diana; Ratsch, Christian

    2013-03-01

    We report DFT calculations that study the effect of sulfur passivation ((NH4)2 S and octanethiol) on GaAs surfaces. Sulfur passivation of GaAs solar cells is an area of interest, as it improves the I-V characteristics of heterojunctions by decreasing the density of surface states. We elucidate the fundamental mechanism of sulfur passivation on GaAs by showing how the sulfur species react with different reconstructed GaAs (100) and (111B) surfaces. Using state of the art hybrid functionals to calculate band structures and density of states, we find that a reconstructed GaAs surface does not have mid-gap surface states. Therefore, we show that sulfur passivation does not reduce surface states on reconstructed surfaces. We also study arsenic vacancies and adatoms on these surfaces to determine the energies of creating these imperfections. They lead to mid-gap surface states that are shown to be energetically plausible in certain GaAs surface reconstruction. We study the most energetically favorable surface reconstructions with As vacancies and show how sulfur passivation plays a role in removing surface states. These results will guide in the selection of passivating agents for GaAs solar cells and lead to a better understanding of such systems. We appreciate the support of the NSF, Grant Number: DMR-1125931

  20. [Effects of GA, and CPPU on grape fruit adjacent leaf photosynthesis and fruit quality].

    PubMed

    Xin, Shou-peng; Liu, Shuai; Yu, Yang; Nie, Song-qing; Gao, Zhi-hong; Tao, Jian-min

    2015-06-01

    Taken the grape cultivar 'Shine Muscat' as the material, the effect of the combination of GA3 and CPPU on the light-response curves in the fruit adjacent leaves and fruit quality were investigated two weeks after blossoming. The results showed that non-rectangular hyperbolic model was more suitable for grape fruit adjacent leaf light response curve-fitting. Pn and g(s) of fruit adjacent leaves among all treatments increased with the increasing light intensity under the combination treat-ments of 25 mg · L(-1) GA3 and 5, 10, 15, 20 mg · L(-1) CPPU, respectively, but Ci decreased. Fruit quality increased with the increasing CPPU concentration under the combination treatments of 25 mg · L(-1) GA3 and 5, 10, 15 mg · L(-1) CPPU, respectively. Grape fruit adjacent leaf photosynthesis under the 25 mg · L(-1) GA3 + 20 mg · L(-1) CPPU treatment was higher than the other treatments. The fruit quality under the 25 mg · L(-1) GA3 + 20 mg · L(-1) CPPU treatment was lower than the 25 mg · L(-1) GA3 + 15 mg · L(-1) CPPU treatment. It indicated that reasonable CPPU treatment concentration could improve fruit adjacent leaf photosynthetic ability and fruit quality. Too high concentration made the fruit quality lower instead. The 25 mg · L(-1) GA3 + 15 mg · L(-1) CPPU treatment was most appropriate in two weeks after blossoming.

  1. Effect of device geometry on static and dynamic performance of AlGaN/GaN-on-Si high electron mobility transistor

    NASA Astrophysics Data System (ADS)

    Shi, Jin-Shan; Huang, Hong-Fan; Liu, Xiao-Yong; Zhao, Sheng-Xun; Zhang, Lin-Qing; Wang, Peng-Fei

    2016-08-01

    This paper discusses the effects of several geometric parameters in DC and RF performances of AlGaN/GaN high electron mobility transistors (HEMTs) grown on high-resistivity silicon substrates. Those parameters include the dependency of gate length (L g), gate cap length (L cap) and gate-to-source distance (L gs). It is shown that decreasing L g and L gs can both improve maximum drain current and transconductance behaviors. The fabricated 50 μm wide GaN-HEMT exhibits the maximum drain current of 1 A mm‑1 at V g = 2 V and maximum extrinsic transconductance G mmax of 240 mS mm‑1. Besides, decreasing L g and L cap also provides the improvement on current gain frequency (fT ) and maximum oscillation cut off frequency (f MAX). The fT of 40 GHz and f MAX of 55 GHz at V ds = 5 V are demonstrated by GaN-HEMT device featuring L g of 200 nm, L cap of 300 nm and L gs of 1.2 μm, which can realize the compact solid-state power amplifier used in S and C band. However, gate-to-source distance has little effect on RF performance of AlGaN/GaN HEMTs. Those results compared in our study are not only very essential for accurate GaN-based HEMT device modeling and fabrication, but are also vital to better understanding of their device physics.

  2. Effect of device geometry on static and dynamic performance of AlGaN/GaN-on-Si high electron mobility transistor

    NASA Astrophysics Data System (ADS)

    Shi, Jin-Shan; Huang, Hong-Fan; Liu, Xiao-Yong; Zhao, Sheng-Xun; Zhang, Lin-Qing; Wang, Peng-Fei

    2016-08-01

    This paper discusses the effects of several geometric parameters in DC and RF performances of AlGaN/GaN high electron mobility transistors (HEMTs) grown on high-resistivity silicon substrates. Those parameters include the dependency of gate length (L g), gate cap length (L cap) and gate-to-source distance (L gs). It is shown that decreasing L g and L gs can both improve maximum drain current and transconductance behaviors. The fabricated 50 μm wide GaN-HEMT exhibits the maximum drain current of 1 A mm-1 at V g = 2 V and maximum extrinsic transconductance G mmax of 240 mS mm-1. Besides, decreasing L g and L cap also provides the improvement on current gain frequency (fT ) and maximum oscillation cut off frequency (f MAX). The fT of 40 GHz and f MAX of 55 GHz at V ds = 5 V are demonstrated by GaN-HEMT device featuring L g of 200 nm, L cap of 300 nm and L gs of 1.2 μm, which can realize the compact solid-state power amplifier used in S and C band. However, gate-to-source distance has little effect on RF performance of AlGaN/GaN HEMTs. Those results compared in our study are not only very essential for accurate GaN-based HEMT device modeling and fabrication, but are also vital to better understanding of their device physics.

  3. High-κ insulating materials for AlGaN/GaN metal insulator semiconductor heterojunction field effect transistors

    NASA Astrophysics Data System (ADS)

    Colón, Albert; Shi, Junxia

    2014-09-01

    High-κ insulating materials (HfO2, HfO2/Al2O3, HfAlOx, and HfSiOx) were deposited by atomic layer deposition (ALD) on AlGaN/GaN to form Metal-Insulator-Semiconductor Heterostructure Field Effect Transistors (MISHFETs) and were electrically and structurally characterized. The objective of this study is to characterize the interface quality and correlate the results with electrical phenomena for each insulating material. Although there are many studies using HfO2 and Al2O3 on AlGaN, there is limited experimental data using ternary compounds such as HfAlOx or HfSiOx, compared to their binary counterparts. In this work, interface trap density, Dit, was extracted by the conductance method using on-chip metal-insulator-semiconductor heterostructure capacitors (MISHCAPs). HfO2 was measured to have the lowest trap density at low energies on the order of 1012 cm-2 eV-1 and quickly reduced about one order of magnitude less than the others at higher trap energies. HfO2/Al2O3, HfAlOx, and HfSiOx all had similar trap densities on the order of 1012 cm-2 eV-1. Ultra-low gate leakage levels were achieved, especially for HfAlOx on the orders of 10-12 A/mm. Our studies indicate that HfAlOx provides the best electrical characteristics such as lowest gate leakage current, largest channel carrier density and resistance to self-heating effects without the vulnerability to low crystallization temperatures.

  4. Novel tannin-based Si, P co-doped carbon for supercapacitor applications

    NASA Astrophysics Data System (ADS)

    Ramasahayam, Sunil Kumar; Nasini, Udaya B.; Shaikh, Ali U.; Viswanathan, Tito

    2015-02-01

    Increasing environmental pollution and population compounded by a decrease in the availability of non-renewable resources and fossil fuels has propelled the need for sustainable alternate energy storage technologies particularly in the last two decades. An attempt to meet this crisis was carried out by a unique, microwave-assisted method which has enabled the generation of a novel Si, P co-doped carbon (SiPDC) for supercapacitor applications. The microwave-assisted method is useful in developing SiPDC at a rapid and economical fashion that does not employ any inert or reducing gases, but is high yielding. Varying proportions of precursor materials were utilized to generate four SiPDCs (SiPDC-1, SiPDC-2, SiPDC-3 and SiPDC-4) with varying contents of dopants as evidenced by X-ray photoelectron spectroscopic (XPS) results. Surface area and pore size analysis revealed that SiPDC-2 has a surface area of 641.51 m2 g-1, abundant micropores, mesopores and macropores which are critical for electrical double layer capacitance (EDLC). Of all the SiPDCs, SiPDC-2 exhibited highest capacitance of 276 F g-1 in 1 M H2SO4 and 244 F g-1 in 6 M KOH at a scan rate of 5 mV s-1. Galvanostatic charge-discharge studies performed in 6 M KOH establish the high capacitance of SiPDC-2. SiPDC-2 also exhibited excellent electrochemical stability in 1 M H2SO4 and 6 M KOH.

  5. Magnetic nanoparticles formed in glasses co-doped with iron and larger radius elements

    SciTech Connect

    Edelman, I.; Ivanova, O.; Ivantsov, R.; Velikanov, D.; Zabluda, V.; Zubavichus, Y.; Veligzhanin, A.; Zaikovskiy, V.; Stepanov, S.; Artemenko, A.; Curely, J.; Kliava, J.

    2012-10-15

    A new type of nanoparticle-containing glasses based on borate glasses co-doped with low contents of iron and larger radius elements, Dy, Tb, Gd, Ho, Er, Y, and Bi, is studied. Heat treatment of these glasses results in formation of magnetic nanoparticles, radically changing their physical properties. Transmission electron microscopy and synchrotron radiation-based techniques: x-ray diffraction, extended x-ray absorption fine structure, x-ray absorption near-edge structure, and small-angle x-ray scattering, show a broad distribution of nanoparticle sizes with characteristics depending on the treatment regime; a crystalline structure of these nanoparticles is detected in heat treated samples. Magnetic circular dichroism (MCD) studies of samples subjected to heat treatment as well as of maghemite, magnetite, and iron garnet allow to unambiguously assign the nanoparticle structure to maghemite, independently of co-dopant nature and of heat treatment regime used. Different features observed in the MCD spectra are related to different electron transitions in Fe{sup 3+} ions gathered in the nanoparticles. The static magnetization in heat treated samples has non-linear dependence on the magnetizing field with hysteresis. Zero-field cooled magnetization curves show that at higher temperatures the nanoparticles occur in superparamagnetic state with blocking temperatures above 100 K. Below ca. 20 K, a considerable contribution to both zero field-cooled and field-cooled magnetizations occurs from diluted paramagnetic ions. Variable-temperature electron magnetic resonance (EMR) studies unambiguously show that in as-prepared glasses paramagnetic ions are in diluted state and confirm the formation of magnetic nanoparticles already at earlier stages of heat treatment. Computer simulations of the EMR spectra corroborate the broad distribution of nanoparticle sizes found by 'direct' techniques as well as superparamagnetic nanoparticle behaviour demonstrated in the magnetization

  6. Structural and spectroscopic behavior of Er3+:Yb3+ co-doped lithium telluroborate glasses

    NASA Astrophysics Data System (ADS)

    Annapoorani, K.; Maheshvaran, K.; ArunKumar, S.; Suriya Murthy, N.; Soukka, Tero; Marimuthu, K.

    2015-01-01

    A new series of Er3+:Yb3+ co-doped Lithium telluroborate glasses were prepared following the melt quenching technique. The structural analyzes were made through XRD, Raman, FTIR spectra to explore the different vibrations of borate and tellurite network. The absorption spectra have been used to determine the nature of the metal-ligand and further Band gap and Urbach's analysis have also been carried out. The oscillator strength value of the 2H11/2→4I15/2 hypersensitive transition is found to be higher and increases as the concentration of the RE ion increases which emphasis the asymmetry nature of the glasses. The magnitude of the JO intensity parameters follow the trend as Ω2>Ω4>Ω6 uniformly for all the prepared glasses. A bright green emission corresponding to the 2H11/2+4S3/2→ 4I15/2 transition and luminescence from 4I13/2→4I15/2 in eye safe region have also been observed. The radiative parameters such as radiative transition probability, stimulated emission cross-section, branching ratios, radiative lifetime, gain bandwidth and gain linewidth for the 4S3/2 and 4I13/2 level of the title glasses have also been determined. The absorption and emission cross-section corresponding to the 4I13/2 level has been calculated using McCumber theory. Lifetime measurements were made under 980 nm excitation and the quantum efficiency were also calculated to evaluate the appropriateness of the host matrix for the fabrication of laser materials and broad band amplifiers.

  7. Magnetic nanoparticles formed in glasses co-doped with iron and larger radius elements

    NASA Astrophysics Data System (ADS)

    Edelman, I.; Ivanova, O.; Ivantsov, R.; Velikanov, D.; Zabluda, V.; Zubavichus, Y.; Veligzhanin, A.; Zaikovskiy, V.; Stepanov, S.; Artemenko, A.; Curély, J.; Kliava, J.

    2012-10-01

    A new type of nanoparticle-containing glasses based on borate glasses co-doped with low contents of iron and larger radius elements, Dy, Tb, Gd, Ho, Er, Y, and Bi, is studied. Heat treatment of these glasses results in formation of magnetic nanoparticles, radically changing their physical properties. Transmission electron microscopy and synchrotron radiation-based techniques: x-ray diffraction, extended x-ray absorption fine structure, x-ray absorption near-edge structure, and small-angle x-ray scattering, show a broad distribution of nanoparticle sizes with characteristics depending on the treatment regime; a crystalline structure of these nanoparticles is detected in heat treated samples. Magnetic circular dichroism (MCD) studies of samples subjected to heat treatment as well as of maghemite, magnetite, and iron garnet allow to unambiguously assign the nanoparticle structure to maghemite, independently of co-dopant nature and of heat treatment regime used. Different features observed in the MCD spectra are related to different electron transitions in Fe3+ ions gathered in the nanoparticles. The static magnetization in heat treated samples has non-linear dependence on the magnetizing field with hysteresis. Zero-field cooled magnetization curves show that at higher temperatures the nanoparticles occur in superparamagnetic state with blocking temperatures above 100 K. Below ca. 20 K, a considerable contribution to both zero field-cooled and field-cooled magnetizations occurs from diluted paramagnetic ions. Variable-temperature electron magnetic resonance (EMR) studies unambiguously show that in as-prepared glasses paramagnetic ions are in diluted state and confirm the formation of magnetic nanoparticles already at earlier stages of heat treatment. Computer simulations of the EMR spectra corroborate the broad distribution of nanoparticle sizes found by "direct" techniques as well as superparamagnetic nanoparticle behaviour demonstrated in the magnetization studies.

  8. P-Channel InGaN/GaN heterostructure metal-oxide-semiconductor field effect transistor based on polarization-induced two-dimensional hole gas.

    PubMed

    Zhang, Kexiong; Sumiya, Masatomo; Liao, Meiyong; Koide, Yasuo; Sang, Liwen

    2016-01-01

    The concept of p-channel InGaN/GaN heterostructure field effect transistor (FET) using a two-dimensional hole gas (2DHG) induced by polarization effect is demonstrated. The existence of 2DHG near the lower interface of InGaN/GaN heterostructure is verified by theoretical simulation and capacitance-voltage profiling. The metal-oxide-semiconductor FET (MOSFET) with Al2O3 gate dielectric shows a drain-source current density of 0.51 mA/mm at the gate voltage of -2 V and drain bias of -15 V, an ON/OFF ratio of two orders of magnitude and effective hole mobility of 10 cm(2)/Vs at room temperature. The normal operation of MOSFET without freeze-out at 8 K further proves that the p-channel behavior is originated from the polarization-induced 2DHG. PMID:27021054

  9. P-Channel InGaN/GaN heterostructure metal-oxide-semiconductor field effect transistor based on polarization-induced two-dimensional hole gas

    NASA Astrophysics Data System (ADS)

    Zhang, Kexiong; Sumiya, Masatomo; Liao, Meiyong; Koide, Yasuo; Sang, Liwen

    2016-03-01

    The concept of p-channel InGaN/GaN heterostructure field effect transistor (FET) using a two-dimensional hole gas (2DHG) induced by polarization effect is demonstrated. The existence of 2DHG near the lower interface of InGaN/GaN heterostructure is verified by theoretical simulation and capacitance-voltage profiling. The metal-oxide-semiconductor FET (MOSFET) with Al2O3 gate dielectric shows a drain-source current density of 0.51 mA/mm at the gate voltage of ‑2 V and drain bias of ‑15 V, an ON/OFF ratio of two orders of magnitude and effective hole mobility of 10 cm2/Vs at room temperature. The normal operation of MOSFET without freeze-out at 8 K further proves that the p-channel behavior is originated from the polarization-induced 2DHG.

  10. Suppression of self-heating effect in AlGaN/GaN high electron mobility transistors by substrate-transfer technology using h-BN

    SciTech Connect

    Hiroki, Masanobu Kumakura, Kazuhide; Kobayashi, Yasuyuki; Akasaka, Tetsuya; Makimoto, Toshiki; Yamamoto, Hideki

    2014-11-10

    We fabricated AlGaN/GaN high electron mobility transistors (HEMTs) on h-BN/sapphire substrates and transferred them from the host substrates to copper plates using h-BN as a release layer. In current–voltage characteristics, the saturation drain current decreased by about 30% under a high-bias condition before release by self-heating effect. In contrast, after transfer, the current decrement was as small as 8% owing to improved heat dissipation: the device temperature increased to 50 °C in the as-prepared HEMT, but only by several degrees in the transferred HEMT. An effective way to improve AlGaN/GaN HEMT performance by a suppression of self-heating effect has been demonstrated.

  11. Theoretical model of the polarization Coulomb field scattering in strained AlGaN/AlN/GaN heterostructure field-effect transistors

    SciTech Connect

    Luan, Chongbiao; Lin, Zhaojun Zhao, Jingtao; Wang, Yutang; Lv, Yuanjie; Chen, Hong; Wang, Zhanguo

    2014-07-28

    The theoretical model of the polarization Coulomb field scattering (PCF) caused by the polarization charge density variation at the AlGaN/AlN interface in strained AlGaN/AlN/GaN heterostructure field-effect transistors has been developed. And the theoretical values for the electron drift mobility, which were calculated using the Matthiessen's rule that includes PCF, piezoelectric scattering, polar optical-phonon scattering, and interface roughness scattering, are in good agreement with our experimental values. Therefore, the theoretical model for PCF has been confirmed.

  12. Synthesis and properties of ZnTe and Eu{sup 3+} ion co-doped glass nanocomposites

    SciTech Connect

    Rahaman Molla, Atiar; Tarafder, Anal; Dey, Chirantan; Karmakar, Basudeb

    2014-10-28

    In this study, ZnTe (II-VI) semiconductor and Eu{sup +3}-ion co-doped borosilicate glass has been prepared in the SiO{sub 2}-K{sub 2}O-CaO-BaO-B{sub 2}O{sub 3} glass system followed by controlled heat-treatment to produce glass nanocomposites. Glass transition temperature and crystallization peak temperature have been evaluated using DSC analysis. Dilatometric studies were carried out to evaluate thermal expansion co-efficient, glass transition temperature, and dilatometric softening temperature and found to be 10.7 × 10{sup −6}/K, 580° C and 628° C, respectively. TEM micrographs demonstrate formation of nano sized crystallites of less than 50 nm. The ZnTe crystal formation also established through selected area electron diffraction (SAED) analysis and high resolution images obtained through TEM studies. With increasing heat treatment time, optical transmission cut-off wavelength (λ{sub cut-off}) shifted towards higher wavelength. Excitation spectra were recorded by monitoring emission at 613 nm corresponding to the {sup 5}D{sub 0} → {sup 7}F{sub 2} transition. An intense 394 nm excitation band corresponding to the {sup 7}F{sub 0} → {sup 5}L{sub 6} transition was observed. Emission spectra were then recorded by exciting the glass samples at 394 nm. When the glass is heat-treated for 30 min at 610° C, a 6-fold increase in the intensity of the red emission at 612 nm has been observed, which is attributed to the segregation of Eu{sup 3+} ions into the low phonon energy ZnTe crystallites and as the size of the nanocrystals is smaller than the size of the exciton, quantum confinement effect is visible. Further increase in heat-treatment duration led to decrease in luminescence intensity due to the growth of larger size crystals. {sup 5}D{sub 1} → {sup 7}F{sub 0} transition is visible only in the samples heat-treated for 30 min and 1 h, which is a characteristic of presence of Eu{sup 3+} ions in the low phonon energy ZnTe crystal sites. The

  13. Upconversion luminescence and blackbody radiation in tetragonal YSZ co-doped with Tm(3+) and Yb(3+).

    PubMed

    Soares, M R N; Ferro, M; Costa, F M; Monteiro, T

    2015-12-21

    Lanthanide doped inorganic nanoparticles with upconversion luminescence are of utmost importance for biomedical applications, solid state lighting and photovoltaics. In this work we studied the downshifted luminescence, upconversion luminescence (UCL) and blackbody radiation of tetragonal yttrium stabilized zirconia co-doped with Tm(3+) and Yb(3+) single crystals and nanoparticles produced by laser floating zone and laser ablation in liquids, respectively. The photoluminescence (PL) and PL excitation (PLE) were investigated at room temperature (RT). PL spectra exhibit the characteristic lines in UV, blue/green, red and NIR regions of the Tm(3+) (4f(12)) under resonant excitation into the high energy (2S+1)LJ multiplets. Under NIR excitation (980 nm), the samples placed in air display an intense NIR at ∼800 nm due to the (1)G4→(3)H5/(3)H4→(3)H6 transitions. Additionally, red, blue/green and ultraviolet UCL is observed arising from higher excited (1)G4 and (1)D2 multiplets. The power excitation dependence of the UCL intensity indicated that 2-3 low energy absorbed photons are involved in the UCL for low power levels, while for high powers, the identified saturation is dependent on the material size with a enhanced effect on the NPs. The temperature dependence of the UCL was investigated for single crystals and targets used in the ablation. An overall increase of the integrated intensity was found to occur between 12 K and the RT. The thermally activated process is described by activation energies of 10 meV and 30 meV for single crystals and targets, respectively. For the NPs, the UCL was found to be strongly sensitive to pressure conditions. Under vacuum conditions, instead of the narrow lines of the Tm(3+), a wide blackbody radiation was detected, responsible for the change in the emission colour from blue to orange. This phenomenon is totally reversible when the NPs are placed at ambient pressure. The UCL/blackbody radiation in the nanosized material exhibits

  14. Upconversion luminescence and blackbody radiation in tetragonal YSZ co-doped with Tm3+ and Yb3+

    NASA Astrophysics Data System (ADS)

    Soares, M. R. N.; Ferro, M.; Costa, F. M.; Monteiro, T.

    2015-11-01

    Lanthanide doped inorganic nanoparticles with upconversion luminescence are of utmost importance for biomedical applications, solid state lighting and photovoltaics. In this work we studied the downshifted luminescence, upconversion luminescence (UCL) and blackbody radiation of tetragonal yttrium stabilized zirconia co-doped with Tm3+ and Yb3+ single crystals and nanoparticles produced by laser floating zone and laser ablation in liquids, respectively. The photoluminescence (PL) and PL excitation (PLE) were investigated at room temperature (RT). PL spectra exhibit the characteristic lines in UV, blue/green, red and NIR regions of the Tm3+ (4f12) under resonant excitation into the high energy 2S+1LJ multiplets. Under NIR excitation (980 nm), the samples placed in air display an intense NIR at ~800 nm due to the 1G4 --> 3H5/3H4 --> 3H6 transitions. Additionally, red, blue/green and ultraviolet UCL is observed arising from higher excited 1G4 and 1D2 multiplets. The power excitation dependence of the UCL intensity indicated that 2-3 low energy absorbed photons are involved in the UCL for low power levels, while for high powers, the identified saturation is dependent on the material size with a enhanced effect on the NPs. The temperature dependence of the UCL was investigated for single crystals and targets used in the ablation. An overall increase of the integrated intensity was found to occur between 12 K and the RT. The thermally activated process is described by activation energies of 10 meV and 30 meV for single crystals and targets, respectively. For the NPs, the UCL was found to be strongly sensitive to pressure conditions. Under vacuum conditions, instead of the narrow lines of the Tm3+, a wide blackbody radiation was detected, responsible for the change in the emission colour from blue to orange. This phenomenon is totally reversible when the NPs are placed at ambient pressure. The UCL/blackbody radiation in the nanosized material exhibits non-contact pressure

  15. Al xIn 1-xN/GaN heterostructure field effect transistors

    NASA Astrophysics Data System (ADS)

    Xie, J.; Ni, X.; Wu, M.; Leach, J. H.; Özgür, Ü.; Morkoç, H.

    2008-02-01

    In AlGaN/GaN heterostructure field effect transistors (HFETs), two-dimensional-electron-gas (2DEG), induced by strong piezoelectric and spontaneous polarization field, has high sheet density, and can be tuned up to 5 ×10 13 cm -2 with pure AlN barrier.[Appl. Phys. Lett. 90, 182112 (2007)].For Al compositions larger than 40%, due to the large lattice mismatch between GaN and AlGaN, strain-related issues significantly reduce the mobility for these high sheet carrier densities. Recently, using nearly lattice-matched AlInN/GaN to improve the performance of HFETs has been studied theoretically and experimentally. A high sheet density (2.42 ×10 13 cm2) with >1000 cm2/Vs mobility has been reported by inserting an AlN spacer layer between the AlGaN barrier and GaN channel. However, low-temperature mobilities for AlInN/GaN HFETs are much lower than those for AlGaN/GaN HFETs. In this paper, we study the Al 1-xIn xN/AlN/GaN (x=0.20 - 0.12) (HFETs) grown by metalorganic chemical vapor deposition. Reduction of In composition from 20% to 12% increased the room temperature equivalent two-dimensional-electron-gas (2DEG) density from 0.90×10 13 cm -2 to 1.64 ×10 13 cm -2 with corresponding electron mobilities of 1600 cm2/Vs and 1410 cm2/Vs. Furthermore, at 10 K, the mobility reached 17,600 cm2/Vs with a sheet density 9.6 ×10 12 cm -2 for the nearly lattice-matched Al 0.82In 0.18N /AlN/GaN heterostructure. The HFETs having 1 μm gate length exhibited a maximum transconductance of ~ 250 mS/mm with good pinch-off characteristics.

  16. Effects of an intense, high-frequency laser field on bound states in Ga1 - xInxNyAs1 - y/GaAs double quantum well.

    PubMed

    Ungan, Fatih; Yesilgul, Unal; Sakiroğlu, Serpil; Kasapoglu, Esin; Erol, Ayse; Arikan, Mehmet Cetin; Sarı, Huseyin; Sökmen, Ismail

    2012-10-31

    Within the envelope function approach and the effective-mass approximation, we have investigated theoretically the effect of an intense, high-frequency laser field on the bound states in a GaxIn1 - xNyAs1 - y/GaAs double quantum well for different nitrogen and indium mole concentrations. The laser-dressed potential, bound states, and squared wave functions related to these bound states in Ga1 - xInxNyAs1 - y/GaAs double quantum well are investigated as a function of the position and laser-dressing parameter. Our numerical results show that both intense laser field and nitrogen (indium) incorporation into the GaInNAs have strong influences on carrier localization.

  17. Effect of gate length on breakdown voltage in AlGaN/GaN high-electron-mobility transistor

    NASA Astrophysics Data System (ADS)

    Jun, Luo; Sheng-Lei, Zhao; Min-Han, Mi; Wei-Wei, Chen; Bin, Hou; Jin-Cheng, Zhang; Xiao-Hua, Ma; Yue, Hao

    2016-02-01

    The effects of gate length LG on breakdown voltage VBR are investigated in AlGaN/GaN high-electron-mobility transistors (HEMTs) with LG = 1 μm˜ 20 μm. With the increase of LG, VBR is first increased, and then saturated at LG = 3 μm. For the HEMT with LG = 1 μm, breakdown voltage VBR is 117 V, and it can be enhanced to 148 V for the HEMT with LG = 3 μm. The gate length of 3 μm can alleviate the buffer-leakage-induced impact ionization compared with the gate length of 1 μm, and the suppression of the impact ionization is the reason for improving the breakdown voltage. A similar suppression of the impact ionization exists in the HEMTs with LG > 3 μm. As a result, there is no obvious difference in breakdown voltage among the HEMTs with LG = 3 μm˜20 μm, and their breakdown voltages are in a range of 140 V-156 V. Project supported by the National Natural Science Foundation of China (Grant Nos. 61334002, 61106106, and 61204085).

  18. Origin of radiative recombination and manifestations of localization effects in GaAs/GaNAs core/shell nanowires

    SciTech Connect

    Chen, S. L.; Filippov, S.; Chen, W. M.; Buyanova, I. A.; Ishikawa, Fumitaro

    2014-12-22

    Radiative carrier recombination processes in GaAs/GaNAs core/shell nanowires grown by molecular beam epitaxy on a Si substrate are systematically investigated by employing micro-photoluminescence (μ-PL) and μ-PL excitation (μ-PLE) measurements complemented by time-resolved PL spectroscopy. At low temperatures, alloy disorder is found to cause localization of photo-excited carriers leading to predominance of optical transitions from localized excitons (LE). Some of the local fluctuations in N composition are suggested to lead to strongly localized three-dimensional confining potential equivalent to that for quantum dots, based on the observation of sharp and discrete PL lines within the LE contour. The localization effects are found to have minor influence on PL spectra at room temperature due to thermal activation of the localized excitons to extended states. Under these conditions, photo-excited carrier lifetime is found to be governed by non-radiative recombination via surface states which is somewhat suppressed upon N incorporation.

  19. Effect of GaAs substrate orientation on the growth kinetic of GaN layer grown by MOVPE

    NASA Astrophysics Data System (ADS)

    Laifi, J.; Chaaben, N.; Bouazizi, H.; Fourati, N.; Zerrouki, C.; El Gmili, Y.; Bchetnia, A.; Salvestrini, J. P.; El Jani, B.

    2016-06-01

    We have investigated the kinetic growth of low temperature GaN nucleation layers (LT-GaN) grown on GaAs substrates with different crystalline orientations. GaN nucleation layers were grown by metal organic vapor phase epitaxy (MOVPE) in a temperature range of 500-600 °C on oriented (001), (113), (112) and (111) GaAs substrates. The growth was in-situ monitored by laser reflectometry (LR). Using an optical model, including time-dependent surface roughness and growth rate profiles, simulations were performed to best approach the experimental reflectivity curves. Results are discussed and correlated with ex-situ analyses, such as atomic force microscopy (AFM) and UV-visible reflectance (SR). We show that the GaN nucleation layers growth results the formation of GaN islands whose density and size vary greatly with both growth temperature and substrate orientation. Arrhenius plots of the growth rate for each substrate give values of activation energy varying from 0.20 eV for the (001) orientation to 0.35 eV for the (113) orientation. Using cathodoluminescence (CL), we also show that high temperature (800-900 °C) GaN layers grown on top of the low temperature (550 °C) GaN nucleation layers, grown themselves on the GaAs substrates with different orientations, exhibit cubic or hexagonal phase depending on both growth temperature and substrate orientation.

  20. H irradiation effects on the GaAs-like Raman modes in GaAs{sub 1-x}N{sub x}/GaAs{sub 1-x}N{sub x}:H planar heterostructures

    SciTech Connect

    Giulotto, E. Geddo, M.; Patrini, M.; Guizzetti, G.; Felici, M.; Capizzi, M.; Polimeni, A.; Martelli, F.; Rubini, S.

    2014-12-28

    The GaAs-like longitudinal optical phonon frequency in two hydrogenated GaAs{sub 1-x}N{sub x}/GaAs{sub 1-x}N{sub x}:H microwire heterostructures—with similar N concentration, but different H dose and implantation conditions—has been investigated by micro-Raman mapping. In the case of GaAs{sub 0.991}N{sub 0.009} wires embedded in barriers where GaAs-like properties are recovered through H irradiation, the phonon frequency in the barriers undergoes a blue shift with respect to the wires. In GaAs{sub 0.992}N{sub 0.008} wires embedded in less hydrogenated barriers, the phonon frequency exhibits an opposite behavior (red shift). Strain, disorder, phonon localization effects induced by H-irradiation on the GaAs-like phonon frequency are discussed and related to different types of N-H complexes formed in the hydrogenated barriers. It is shown that the red (blue) character of the frequency shift is related to the dominant N-2H (N-3H) type of complexes. Moreover, for specific experimental conditions, an all-optical determination of the uniaxial strain field is obtained. This may improve the design of recently presented devices that exploit the correlation between uniaxial stress and the degree of polarization of photoluminescence.

  1. Theoretical Study of the Effect of an AlGaAs Double Heterostructure on Metal-Semiconductor-Metal Photodetector Performance

    NASA Technical Reports Server (NTRS)

    Salem, Ali F.; Smith, Arlynn W.; Brennan, Kevin F.

    1994-01-01

    The impulse and square-wave input response of different GaAs metal-semiconductor-metal photodetector (MSM) designs are theoretically examined using a two dimensional drift- diffusion numerical calculation with a thermionic-field emission boundary condition model for the heterojunctions. The rise time and the fall time of the output signal current are calculated for a simple GaAs, epitaxially grown, MSM device as well as for various double-heterostructure barrier devices. The double heterostructure devices consist of an AlGaAs layer sandwiched between the top GaAs active, absorption layer and the bottom GaAs substrate. The effect of the depth of the AlGaAs layer on the speed and responsivity of the MSM devices is examined. It is found that there is an optimal depth, at fixed applied bias, of the AlGaAs layer within the structure that provides maximum responsivity at minimal compromise in speed.

  2. Long-term stability assessment of AlGaN/GaN field effect transistors modified with peptides: Device characteristics vs. surface properties

    NASA Astrophysics Data System (ADS)

    Rohrbaugh, Nathaniel; Bryan, Isaac; Bryan, Zachary; Collazo, Ramon; Ivanisevic, Albena

    2015-09-01

    AlGaN/GaN Field Effect Transistors (FETs) are promising biosensing devices. Functionalization of these devices is explored in this study using an in situ approach with phosphoric acid etchant and a phosphonic acid derivative. Devices are terminated on peptides and soaked in water for up to 168 hrs to examine FETs for both device responses and surface chemistry changes. Measurements demonstrated threshold voltage shifting after the functionalization and soaking processes, but demonstrated stable FET behavior throughout. X-ray photoelectron spectroscopy and atomic force microscopy confirmed peptides attachment to device surfaces before and after water soaking. Results of this work point to the stability of peptide coated functionalized AlGaN/GaN devices in solution and support further research of these devices as disposable, long term, in situ biosensors.

  3. Long-term stability assessment of AlGaN/GaN field effect transistors modified with peptides: Device characteristics vs. surface properties

    SciTech Connect

    Rohrbaugh, Nathaniel; Bryan, Isaac; Bryan, Zachary; Collazo, Ramon; Ivanisevic, Albena

    2015-09-15

    AlGaN/GaN Field Effect Transistors (FETs) are promising biosensing devices. Functionalization of these devices is explored in this study using an in situ approach with phosphoric acid etchant and a phosphonic acid derivative. Devices are terminated on peptides and soaked in water for up to 168 hrs to examine FETs for both device responses and surface chemistry changes. Measurements demonstrated threshold voltage shifting after the functionalization and soaking processes, but demonstrated stable FET behavior throughout. X-ray photoelectron spectroscopy and atomic force microscopy confirmed peptides attachment to device surfaces before and after water soaking. Results of this work point to the stability of peptide coated functionalized AlGaN/GaN devices in solution and support further research of these devices as disposable, long term, in situ biosensors.

  4. Evaluation of a gate-first process for AlGaN/GaN metal-oxide-semiconductor heterostructure field-effect transistors with low ohmic annealing temperature

    NASA Astrophysics Data System (ADS)

    Liuan, Li; Jiaqi, Zhang; Yang, Liu; Jin-Ping, Ao

    2016-03-01

    In this paper, TiN/AlOx gated AlGaN/GaN metal-oxide-semiconductor heterostructure field-effect transistors (MOS-HFETs) were fabricated for gate-first process evaluation. By employing a low temperature ohmic process, ohmic contact can be obtained by annealing at 600 °C with the contact resistance approximately 1.6 Ω·mm. The ohmic annealing process also acts as a post-deposition annealing on the oxide film, resulting in good device performance. Those results demonstrated that the TiN/AlOx gated MOS-HFETs with low temperature ohmic process can be applied for self-aligned gate AlGaN/GaN MOS-HFETs. Project supported by the International Science and Technology Collaboration Program of China (Grant No. 2012DFG52260).

  5. Excellent low-field magnetoresistance effect in Ga-doped MnZn ferrites

    SciTech Connect

    Kim, Hyo-Jin; Yoo, Sang-Im

    2014-12-15

    An excellent low field magnetoresistance (LFMR) property was achieved from the Ga-doped (Mn{sub 0.8}Zn{sub 0.2})Fe{sub 2}O{sub 4} (MnZn) ferrites at room temperature (RT). For this study, undoped and Ga-doped MnZn ferrites with the nominal compositions of (Mn{sub 0.8}Zn{sub 0.2}){sub 1−x}Ga{sub x}Fe{sub 2}O{sub 4} (x = 0 ∼ 0.1) were prepared by the conventional solid state reaction at 1400°C for 2 h in air. From the magneto-transport measurements, Ga-doped MnZn ferrites were found to have not only much lower resistivity values but also greatly improved LFMR ratios in comparison with undoped sample. The highest maximum LFMR ratio of 2.5% at 290 K in 0.5 kOe was achievable from 2 mol% Ga-doped MnZn ferrite. This large LFMR effect is attributable to an increase in spin electrons by Ga{sup 3+} ion substitution for the (Mn, Zn){sup 2+} site.

  6. The microstructure of erbium-ytterbium co-doped oxyfluoride glass-ceramic optical fibers

    NASA Astrophysics Data System (ADS)

    Augustyn, Elżbieta; Żelechower, Michał; Stróż, Danuta; Chrapoński, Jacek

    2012-04-01

    Oxyfluoride transparent glass-ceramics combine some features of glasses (easier shaping or lower than single crystals cost of fabrication) and some advantages of rare-earth doped single crystals (narrow absorption/emission lines and longer lifetimes of luminescent levels). Since the material seems to be promising candidate for efficient fiber amplifiers, the manufacturing as well as structural and optical examination of the oxyfluoride glass-ceramic fibers doped with rare-earth ions seems to be a serious challenge. In the first stage oxyfluoride glasses of the following compositions 48SiO2-11Al2O3-7Na2CO3-10CaO-10PbO-11PbF2-3ErF3 and 48SiO2-11Al2O3-7Na2CO3-10CaO-10PbO-10PbF2-3YbF3-1ErF3 (in molar%) were fabricated from high purity commercial chemicals (Sigma-Aldrich). The fabricated glass preforms were drawn into glass fibers using the mini-tower. Finally, the transparent Er3+ doped and Er3+/Yb3+ co-doped oxyfluoride glass-ceramic fibers were obtained by controlled heat treatment of glass fibers. The preceding differential thermal analysis (DTA) studies allowed estimating both the fiber drawing temperature and the controlled crystallization temperature of glass fibers. X-ray diffraction examination (XRD) at each stage of the glass-ceramic fibers fabrication confirmed the undesirable crystallization of preforms and glass fibers has been avoided. The fibers shown their mixed amorphous-crystalline microstructure with nano-crystals of size even below 10 nm distributed in the glassy host. The crystal structure of the grown nano-crystals has been determined by XRD and confirmed by electron diffraction (SAED). Results obtained by both techniques seem to be compatible: Er3FO10Si3 (monoclinic; ICSD 92512), Pb5Al3F19 (triclinic; ICSD 91325) and Er4F2O11Si3 (triclinic; ICSD 51510) against to initially expected PbF2 crystals.

  7. Investigation of the stability of Co-doped apatite ionic conductors in NH{sub 3}

    SciTech Connect

    Headspith, D.A.; Orera, A.; Young, N.A.; Francesconi, M.G.

    2010-12-15

    Hydrogen powered solid oxide fuel cells (SOFCs) are of enormous interest as devices for the efficient and clean production of electrical energy. However, a number of problems linked to hydrogen production, storage and transportation are slowing down the larger scale use of SOFCs. Identifying alternative fuel sources to act as intermediate during the transition to the full use of hydrogen is, therefore, of importance. One excellent alternative is ammonia, which is produced on a large scale, is relatively cheap and has the infrastructure for storage and transportation already in place. However, considering that SOFCs operate at temperatures higher than 500 {sup o}C, a potential problem is the interaction of gaseous ammonia with the materials in the cathode, anode and solid electrolyte. In this paper, we extend earlier work on high temperature reactions of apatite electrolytes with NH{sub 3} to the transition metal (Co) doped systems, La{sub 9.67}Si{sub 5}CoO{sub 26} and La{sub 10}(Si/Ge){sub 5}CoO{sub 26.5}. A combination of PXRD, TGA and XAFS spectroscopy data showed a better structural stability for the silicate systems. Apatite silicates and germanates not containing transition metals tend to substitute nitride anions for their interstitial oxide anions, when reacted with NH{sub 3} at high temperature and, consequentially, lower the interstitial oxide content. In La{sub 9.67}Si{sub 5}CoO{sub 26} and La{sub 10}(Si/Ge){sub 5}CoO{sub 26.5} reduction of Co occurs as a competing process, favouring lower levels of nitride-oxide substitution. -- Graphical Abstract: In reactions between the apatites La{sub 9.67}Si{sub 5}CoO{sub 26} and La{sub 10}(Si/Ge){sub 5}CoO{sub 26.5} and NH{sub 3} (g) at temperatures T>500 {sup o}C, the partial substitution of the Si and Ge by Co seems to discourage O{sup 2-}/N{sup 3-} substitution in favour of the reduction of the metal. Display Omitted

  8. Performance comparison of bismuth/erbium co-doped optical fibre by 830 nm and 980 nm pumping

    NASA Astrophysics Data System (ADS)

    Yan, Binbin; Luo, Yanhua; Zareanborji, Amirhassan; Xiao, Gui; Peng, Gang-Ding; Wen, Jianxiang

    2016-10-01

    The performance of bismuth/erbium co-doped fibre (BEDF) by 830 nm and 980 nm pumping has been studied in detail, including the small signal absorption, pump absorption, emission, gain and excited state absorption (ESA). Based on the study, energy transition diagrams of BEDF under 830 nm or 980 nm pumping are proposed to clarify the spectroscopic properties. The results demonstrate the advantages of 830 nm pumping for BEDF over 980 nm pumping when considering the absorption, pumping efficiency, excited state absorption and optical amplification.

  9. Doping concentration dependence of microstructure and magnetic behaviours in Co-doped TiO2 nanorods

    PubMed Central

    2014-01-01

    Co-doped titanium dioxide (TiO2) nanorods with different doping concentrations were fabricated by a molten salt method. It is found that the morphology of TiO2 changes from nanorods to nanoparticles with increasing doping concentration. The mechanism for the structure and phase evolution is investigated in detail. Undoped TiO2 nanorods show strong ferromagnetism at room temperature, whereas incorporating of Co deteriorates the ferromagnetic ordering. X-ray photoelectron spectroscopy (XPS) and electron spin resonance (ESR) results demonstrate that the ferromagnetism is associated with Ti vacancy. PMID:25593558

  10. Effect of potential barrier height on the carrier transport in InGaAs/GaAsP multi-quantum wells and photoelectric properties of laser diode.

    PubMed

    Dong, Hailiang; Sun, Jing; Ma, Shufang; Liang, Jian; Lu, Taiping; Jia, Zhigang; Liu, Xuguang; Xu, Bingshe

    2016-03-01

    The growth and strain-compensation behaviour of InGaAs/GaAsP multi-quantum wells, which were fabricated by metal-organic chemical vapor deposition, have been studied towards the application of these quantum wells in high-power laser diodes. The effect of the height of the potential barrier on the confined level of carrier transport was studied by incorporating different levels of phosphorus content into the GaAsP barrier. The crystal quality and interface roughness of the InGaAs/GaAsP multi-quantum wells with different phosphorus contents were evaluated by high resolution X-ray diffraction and in situ optical surface reflectivity measurements during the growth. The surface morphology and roughness were characterized by atomic force microscopy, which indicates the variation law of surface roughness, terrace width and uniformity with increasing phosphorus content, owing to strain accumulation. Moreover, the defect generation and structural disorder of the multi-quantum wells were investigated by Raman spectroscopy. The optical properties of the multi-quantum wells were characterized by photoluminescence, which shows that the spectral intensity increases as the phosphorus content increases. The results suggest that more electrons are well bound in InGaAs because of the high potential barrier. Finally, the mechanism of the effect of the height of the potential barrier on laser performance was proposed on the basis of simulation calculations and experimental results. PMID:26879291

  11. Effect of potential barrier height on the carrier transport in InGaAs/GaAsP multi-quantum wells and photoelectric properties of laser diode.

    PubMed

    Dong, Hailiang; Sun, Jing; Ma, Shufang; Liang, Jian; Lu, Taiping; Jia, Zhigang; Liu, Xuguang; Xu, Bingshe

    2016-03-01

    The growth and strain-compensation behaviour of InGaAs/GaAsP multi-quantum wells, which were fabricated by metal-organic chemical vapor deposition, have been studied towards the application of these quantum wells in high-power laser diodes. The effect of the height of the potential barrier on the confined level of carrier transport was studied by incorporating different levels of phosphorus content into the GaAsP barrier. The crystal quality and interface roughness of the InGaAs/GaAsP multi-quantum wells with different phosphorus contents were evaluated by high resolution X-ray diffraction and in situ optical surface reflectivity measurements during the growth. The surface morphology and roughness were characterized by atomic force microscopy, which indicates the variation law of surface roughness, terrace width and uniformity with increasing phosphorus content, owing to strain accumulation. Moreover, the defect generation and structural disorder of the multi-quantum wells were investigated by Raman spectroscopy. The optical properties of the multi-quantum wells were characterized by photoluminescence, which shows that the spectral intensity increases as the phosphorus content increases. The results suggest that more electrons are well bound in InGaAs because of the high potential barrier. Finally, the mechanism of the effect of the height of the potential barrier on laser performance was proposed on the basis of simulation calculations and experimental results.

  12. Effects of threading dislocations on drain current dispersion and slow transients in unpassivated AlGaN/GaN/Si heterostructure field-effect transistors

    SciTech Connect

    Ghosh, Saptarsi Dinara, Syed Mukulika; Mukhopadhyay, Partha; Jana, Sanjay K.; Bag, Ankush; Kabi, Sanjib; Chakraborty, Apurba; Chang, Edward Yi; Biswas, Dhrubes

    2014-08-18

    Current transient analysis combined with response to pulsed bias drives have been used to explore the possibilities of threading dislocations affecting the current dispersion characteristics of AlGaN/GaN heterostructure field-effect transistors (HFETs). A growth strategy is developed to modulate the dislocation density among the heterostructures grown on silicon by plasma-assisted molecular-beam epitaxy. Slow pulsed I-V measurements show severe compressions and appear to be significantly dependent on the threading dislocation density. By analyzing the corresponding slow detrapping process, a deep-level trap with emission time constant in the order of seconds was identified as the cause. Among the specimens, both in the epilayers and at the surface, the number of dislocations was found to have a notable influence on the spatial distribution of deep-level trap density. The observations confirm that the commonly observed degraded frequency performance among AlGaN/GaN HFETs in the form of DC-radio frequency dispersions can at least partly be correlated with threading dislocation density.

  13. Properties of transparent (Gd,Lu)3(Al,Ga)5O12:Ce ceramic with Mg, Ca and Ce co-dopants

    NASA Astrophysics Data System (ADS)

    Wang, Yimin; Baldoni, Gary; Brecher, Charles; Rhodes, William H.; Shirwadkar, Urmila; Glodo, Jarek; Shah, Ishaan; Ji, Chuncheng

    2015-08-01

    Cerium activated mixed lutetium/gadolinium- and aluminum/gallium-based garnets have great potential as host scintillators for medical imaging applications. (Gd,Lu)3(Al,Ga)5O12:Ce and denoted as GLuGAG feature high effective atomic number and good light yield, which make it particularly attractive for Positron Emission Tomography (PET) and other γ-ray detection applications. For PET application, rapid decay and good timing resolution are extremely important. Most Ce-doped mixed garnet materials such as GLuGAG:Ce, have their main decay component at around 80 ns. However, it has been reported that the decays of some single crystal scintillators (e.g., LSO and GGAG) can be effectively accelerated by codoping with selected additives such as Ca, Mg and B. In this study, transparent polycrystalline (Gd,Lu)3(Al,Ga)5O12:Ce ceramics codoped with Ca or Mg or additional Ce, were fabricated by the sinter-HIP approach. It was found the transmission of the ceramics are closely related to the microstructure of the ceramics. As the co-dopant levels increase, 2nd phase occurs in the ceramic and thus transparency of the ceramic decreases. Ca and Mg co-doping in GLuGAG:Ce ceramic effectively accelerate decays of GLuGAG:Ce ceramics at a cost of light output. However, additional Ce doping in the GLuGAG:Ce has no benefit on improving decay time but, on the other hand, reduces transmission, light output. The mechanism under the different scintillation behaviors with Mg, Ca and Ce dopants are discussed. The results suggest that decay time of GLuGAG:Ce ceramics can be effectively tailored by co-doping GLuGAG:Ce ceramic with Mg and Ca for applications with optimal timing resolution.

  14. Synthesis and Photoluminescence Characteristics of CaIn2O4:Dy3+ Phosphors Co-Doped with Gd3+, Zn2+ or AI3+ Ions.

    PubMed

    Gou, Jing; Wang, Jing; Yu, Binxun; Zhang, Dongyang

    2016-04-01

    Novel warm-white emitting phosphors CaIn2O4:Dy3+ co-doped with Gd3+, Zn2+, or Al3+ ions were prepared by solid state reaction. In this paper, a strategy of co-doping with different ions was used with the aim of affecting the luminescence properties of CaIn204:0.6%Dy3+ under NUV excitation. The luminescence intensities of CaIn2O4:0.6%Dy3+ were enhanced by 0.2% Gd3+ or 0.2% Zn2+ ions co-doping under 367 nm excitation, but lowered by co-doping with 0.2% Al3+ ions. Furthermore, the chromaticity coordinates of CaIn2O4:0.6%Dy3+ can be tuned from the cold-white region to warm-white region with Gd3+ or Zn2+ ions co-doping. These findings show that CaIn2O4:0.6%Dy3+,0.2% Gd3+, and CaIn2O4:0.6%Dy3+,0.2% Zn2+ have potential application value as new warm-white LED phosphors. PMID:27451749

  15. Spectroscopic characterization and energy transfer process in cobalt and cobalt-iron co-doped ZnSe/ZnS crystals

    NASA Astrophysics Data System (ADS)

    Peppers, J.; Martyshkin, D. V.; Fedorov, V. V.; Mirov, S. B.

    2014-02-01

    Cobalt doped II-VI wide band semiconductors (e.g. ZnSe, ZnS, CdSe) are promising media for infrared (IR) laser applications. They could be utilized as effective passive Q-switches for cavities of Alexandrite as well as Nd and Er lasers operating over 0.7-0.8, 1.3-1.6, and ~2.8 μm spectral ranges. We report spectroscopic characterization of Co:ZnSe and Co:ZnS crystals. Absorption cross-sections were measured for 4A2(F) → 4T1(P), 4A2(F) → 4T1(F), and 4A2(F) → 4T2(F) transitions with maximum absorption at 768(726), 1615(1500), 2690(2740) nm for ZnSe(ZnS) crystals, respectively. The calculated absorption cross-sections of the above transitions were estimated to be 64(56)×1019, 7.5(7.8)×1019, and 0.52(0.49)×1019 cm2 for ZnSe(ZnS) crystal hosts. In addition to the above applications the cobalt ions could be utilized for excitation of Fe2+ ions via resonance energy transfer process. Tunable room temperature lasing of Fe 2+ doped binary and ternary chalcogenides has been successfully demonstrated over 3.5-6 μm spectral range. However, II-VI lasers based on Fe2+ active ions don't feature convenient commercially available pump sources (e.g. some Fe doped crystal hosts require pump wavelengths longer than 3 μm). Therefore, the process of energy transfer from Co2+ to Fe2+ ions could enable utilization of commercially available visible and near-infrared pump sources. We report a spectroscopic characterization of iron-cobalt co-doped ZnS and ZnSe crystals over 14-300K temperature range. Mid-IR laser oscillation at 3.9 μm(3.6 μm) via energy transfer in the Co:Fe:ZnSe (Co:Fe:ZnS) co-doped crystals was demonstrated under cobalt excitation at 4A2(F) → 4T1(P) (~0.7μm) and 4A2(F) → 4T1(F) (~1.56 μm) transitions.

  16. The effects of GA and ABA treatments on metabolite profile of germinating barley.

    PubMed

    Huang, Yuqing; Cai, Shengguan; Ye, Lingzhen; Hu, Hongliang; Li, Chengdao; Zhang, Guoping

    2016-02-01

    Sugar degradation during grain germination is important for malt quality. In malting industry, gibberellin (GA) is frequently used for improvement of malting quality. In this study, the changes of metabolite profiles and starch-degrading enzymes during grain germination, and as affected by GA and abscisic acid (ABA) were investigated using two wild barley accessions XZ72 and XZ95. Totally fifty-two metabolites with known structures were detected and the change of metabolite during germination was time- and genotype dependent. Sugars and amino acids were the most dramatically changed compounds. Addition of GA enhanced the activities of starch-degrading enzymes, and increased most metabolites, especially sugars and amino acids, whereas ABA had the opposite effect. The effect varied with the barley accessions. The current study is the first attempt in investigating the effect of hormones on metabolite profiles in germinating barley grain, being helpful for identifying the factors affecting barley germination or malt quality. PMID:26304431

  17. Gd-Al co-doped mesoporous silica nanoparticles loaded with Ru(bpy)₃²⁺ as a dual-modality probe for fluorescence and magnetic resonance imaging.

    PubMed

    Zhang, Dan; Gao, Ai; Xu, Yang; Yin, Xue-Bo; He, Xi-Wen; Zhang, Yu-Kui

    2014-09-21

    Mesoporous silica nanoparticles (MSNs) were co-doped with Gd(3+) and Al(3+) and then loaded with Ru(bpy)3(2+) by ion-exchange to prepare Ru/Gd-Al@MSNs. The as-prepared Ru/Gd-Al@MSNs were applied as contrast agents for in vivo fluorescence and magnetic resonance (MR) dual-modality imaging with a mouse as a model. The effects of Al(3+) and MSNs on longitudinal relaxivity (r1) and fluorescence were investigated using a series of Gd-containing silica nanoparticles, including Gd@MSNs, Gd-Al@MSNs, and Ru/Gd-Al@nonporous silica nanoparticles. Co-doping with Al(3+) improved the loading of Gd(3+); the mesoporous structure improved the water exchange rate. The improvement enhanced the MR imaging efficiency of the Ru/Gd-Al@MSN probe. A higher relaxivity (19.2 mM(-1) s(-1)) was observed compared to that from a commercial contrast agent, Gd-diethylene triamine pentaacetic acid (Gd-DTPA). Importantly, the mesoporous structure provided a large specific surface area for the loading of Ru(bpy)3(2+) by a simple ion-exchange procedure. Intense red fluorescence was observed from Ru/Gd-Al@MSN probes. The versatility of Ru/Gd-Al@MSNs for dual-modality imaging was demonstrated using in vivo fluorescence imaging and T1-weighted MR imaging with a mouse model. The nanoparticles are biocompatible and may be attractive for clinical applications.

  18. Effects of catalyst concentration and ultraviolet intensity on chemical mechanical polishing of GaN

    NASA Astrophysics Data System (ADS)

    Wang, Jie; Wang, Tongqing; Pan, Guoshun; Lu, Xinchun

    2016-08-01

    Effects of catalyst concentration and ultraviolet intensity on chemical mechanical polishing (CMP) of GaN were deeply investigated in this paper. Working as an ideal homogeneous substrate material in LED industry, GaN ought to be equipped with a smooth and flat surface. Taking the strong chemical stability of GaN into account, photocatalytic oxidation technology was adopted in GaN CMP process to realize efficient removal. It was found that, because of the improved reaction rate of photocatalytic oxidation, GaN material removal rate (MRR) increases by a certain extent with catalyst concentration increasing. Cross single line analysis on the surface after polishing by Phase Shift MicroXAM-3D was carried out to prove the better removal effect with higher catalyst concentration. Ultraviolet intensity field in H2O2-SiO2-based polishing system was established and simulated, revealing the variation trend of ultraviolet intensity around the outlet of the slurry. It could be concluded that, owing to the higher planarization efficiency and lower energy damage, the UV lamp of 125 W is the most appropriate lamp in this system. Based on the analysis, defects removal model of this work was proposed to describe the effects of higher catalyst concentration and higher power of UV lamp.

  19. High-performance AlGaN /GaN lateral field-effect rectifiers compatible with high electron mobility transistors

    NASA Astrophysics Data System (ADS)

    Chen, Wanjun; Wong, King-Yuen; Huang, Wei; Chen, Kevin J.

    2008-06-01

    A high electron mobility transistor (HEMT)-compatible power lateral field-effect rectifier (L-FER) with low turn-on voltage is demonstrated using the same fabrication process as that for normally off AlGaN /GaN HEMT, providing a low-cost solution for GaN power integrated circuits. The power rectifier features a Schottky-gate-controlled two-dimensional electron gas channel between the cathode and anode. By tying up the Schottky gate and anode together, the forward turn-on voltage of the rectifier is determined by the threshold voltage of the channel instead of the Schottky barrier. The L-FER with a drift length of 10μm features a forward turn-on voltage of 0.63V at a current density of 100A/cm2. This device also exhibits a reverse breakdown voltage (BV) of 390V at a current level of 1mA/mm and a specific on resistance (RON,sp) of 1.4mΩcm2, yielding a figure of merit (BV2/RON,sp) of 108MW/cm2. The excellent device performance, coupled with the lateral device structure and process compatibility with AlGaN /GaN HEMT, make the proposed L-FER a promising candidate for GaN power integrated circuits.

  20. Impact of residual carbon impurities and gallium vacancies on trapping effects in AlGaN/GaN metal insulator semiconductor high electron mobility transistors

    SciTech Connect

    Huber, Martin; Silvestri, Marco; Knuuttila, Lauri; Pozzovivo, Gianmauro; Andreev, Andrei; Lundskog, Anders; Kadashchuk, Andrey; Bonanni, Alberta

    2015-07-20

    Effects of residual C impurities and Ga vacancies on the dynamic instabilities of AlN/AlGaN/GaN metal insulator semiconductor high electron mobility transistors are investigated. Secondary ion mass spectroscopy, positron annihilation spectroscopy, and steady state and time-resolved photoluminescence (PL) measurements have been performed in conjunction with electrical characterization and current transient analyses. The correlation between yellow luminescence (YL), C- and Ga vacancy concentrations is investigated. Time-resolved PL indicating the C{sub N} O{sub N} complex as the main source of the YL, while Ga vacancies or related complexes with C seem not to play a major role. The device dynamic performance is found to be significantly dependent on the C concentration close to the channel of the transistor. Additionally, the magnitude of the YL is found to be in agreement with the threshold voltage shift and with the on-resistance degradation. Trap analysis of the GaN buffer shows an apparent activation energy of ∼0.8 eV for all samples, pointing to a common dominating trapping process and that the growth parameters affect solely the density of trap centres. It is inferred that the trapping process is likely to be directly related to C based defects.

  1. Revealing the effects of nitrogen on threshold current density in GaNxAsyP1-x-y/GaP/AlzGa1-zP type I QW laser structures by hydrostatic pressure

    NASA Astrophysics Data System (ADS)

    Ünsal, Ömer L.; Gönül, Beşire

    2016-06-01

    We present a comprehensive theoretical analysis of threshold current in dilute nitride direct bandgap Ga(NAsP)/GaP/AlGaP quantum wells (QW) on silicon substrates using model calculations. The pressure dependence of band structure, radiative and non-radiative recombination rates, optical confinement factor, transparency- and threshold-carrier densities are calculated in a range of 0-1 GPa at room temperature. The effect of aluminium incorporation into cladding-layer Gallium Phosphide (GaP) with the employed five-layer slab waveguide model is considered and we have shown that incorporation of Aluminium (Al) into cladding-layer GaP increases the photon confinement in well layer. It is found that incorporation of Nitrogen (N) into GaAsP reduces the non-radiative Auger recombination rates which brings an improvement in threshold current. The comparison of our calculated results with that of the experimental data indicates that the Auger effect involving CHCC process can be considered as the dominant non-radiative loss mechanism at 300 K.

  2. Hydrogen Effects on GaAs Device Reliability

    NASA Technical Reports Server (NTRS)

    Kayali, Sammy A.

    1996-01-01

    GaAs and InP devices in hermetically sealed packages have been observed to exhibit unacceptable degradation in both RF and DC characteristics. This degradation has been observed to occur at temperatures as low as 125oC. The source of the degradation has been linked to hydrogen gas that has been absorbed in the package's metals (Kovar, plating, etc.) and converted into atomic hydrogen within the Pt or Pd metallization of the gate structure. Subsequently, atomic hydrogen diffuses into the channel region of the FET structure and neutralizes the Si donors, resulting in a degradation of the device characteristics.

  3. Synthesis, characterization, and photocatalytic activity of porous La-N-co-doped TiO2 nanotubes for gaseous chlorobenzene oxidation.

    PubMed

    Cheng, Zhuowei; Gu, Zhiqi; Chen, Jianmeng; Yu, Jianming; Zhou, Lingjun

    2016-08-01

    The photocatalytic oxidation of gaseous chlorobenzene (CB) by the 365nm-induced photocatalyst La/N-TiO2, synthesized via a sol-gel and hydrothermal method, was evaluated. Response surface methodology (RSM) was used to model and optimize the conditions for synthesis of the photocatalyst. The optimal photocatalyst was 1.2La/0.5N-TiO2 (0.5) and the effects of La/N on crystalline structure, particle morphology, surface element content, and other structural characteristics were investigated by XRD (X-ray diffraction), TEM (Transmission Electron Microscopy), FTIR (Fourier transform infrared spectroscopy), UV-vis (Ultraviolet-visible spectroscopy), and BET (Brunauer Emmett Teller). Greater surface area and smaller particle size were produced with the co-doped TiO2 nanotubes than with reference TiO2. The removal of CB was effective when performed using the synthesized photocatalyst, though it was less efficient at higher initial CB concentrations. Various modified Langmuir-Hinshelwood kinetic models involving the adsorption of chlorobenzene and water on different active sites were evaluated. Fitting results suggested that competitive adsorption caused by water molecules could not be neglected, especially for environments with high relative humidity. The reaction intermediates found after GC-MS (Gas chromatography-mass spectrometry) analysis indicated that most were soluble, low-toxicity, or both. The results demonstrated that the prepared photocatalyst had high activity for VOC (volatile organic compounds) conversion and may be used as a pretreatment prior to biopurification. PMID:27521952

  4. Investigation of temperature influence on output performances of high-power cladding-pumped Er,Yb co-doped fiber laser

    NASA Astrophysics Data System (ADS)

    Chen, Wenting; Sha, Jianjian; Wang, Yong; Shen, Deyuan

    2013-03-01

    Effect of the fiber's temperature on lasing performance is investigated in high-power, cladding-pumped Er, Yb co-doped fiber laser system. A three-layer symmetric cylindrical model is applied to describe the temperature distribution of the fiber under natural air convection. Radial temperature distribution of the fiber is calculated with consideration of the quantum defect heat, the heat from the absorption of spontaneous emission, and the convection and radiation at the heat transfer boundaries. The steady-state theoretical model based on rate equations takes into account of the energy transfers between Er3+-ions and Yb3+-ions and a fraction of nonparticipatory Yb3+-ions. Shooting method and Newton iteration method are used to solve the boundary-value problems under different environmental temperatures, pump powers and reflectivities at the fiber ends. Numerical simulations are consistent with experimental results and show that increasing the fiber's temperature is an effective strategy to suppress the 1 μm parasitic lasing and improve the lasing performance at 1.5 μm, a similar phenomenon is found with enhancing doping concentrations of the two ions and decreasing the reflectivities at the fiber ends. Our numerical results present a theoretical guideline for further improving the laser performance in terms of output power of ~1.5 μm in high-power Er,Yb-doped fiber laser systems.

  5. Enhanced visible-light absorption of mesoporous TiO2 by co-doping with transition-metal/nitrogen ions

    SciTech Connect

    Mathis, John; Bi, Zhonghe; Bridges, Craig A; Kidder, Michelle; Paranthaman, Mariappan Parans

    2013-01-01

    Titanium (IV) oxide, TiO2, has been the object of intense scrutiny for energy applications. TiO2 is inexpensive, non-toxic, and has excellent corrosion resistance when exposed to electrolytes. A major drawback preventing the widespread use TiO2 for photolysis is its relatively large band gap of ~3eV. Only light with wavelengths shorter than 400 nm, which is in the ultraviolet portion of the spectrum, has sufficient energy to be absorbed. Less than 14 percent of the solar irradiation reaching the earth s surface has energy exceeding this band gap. Adding dopants such as transition metals has long been used to reduce the gap and increase photocatalytic activity by accessing the visible part of the solar spectrum. The degree to which the band gap is reduced using transition metals depends in part on the overlap of the d-orbitals of the transition metals with the oxygen p-orbitals. Therefore, doping with anions such as nitrogen to modify the cation-anion orbital overlap is another approach to reduce the gap. Recent studies suggest that using a combination of transition metals and nitrogen as dopants is more effective at introducing intermediate states within the band gap, effectively narrowing it. Here we report the synthesis of mesoporous TiO2 spheres, co-doped with transition metals and nitrogen that exhibit a nearly flat absorbance response across the visible spectrum extending into the near infrared.

  6. Effective mass of two-dimensional electrons in InGaAsN/GaAsSb type II quantum well by Shubnikov-de Haas oscillations

    NASA Astrophysics Data System (ADS)

    Kawamata, Shuichi; Hibino, Akira; Tanaka, Sho; Kawamura, Yuichi

    2016-10-01

    In order to develop optical devices for 2-3 μm wavelength regions, the InP-based InGaAs/GaAsSb type II multiple quantum well system has been investigated. By doping nitrogen into InGaAs layers, the system becomes effective in creating the optical devices with a longer wavelength. In this report, electrical transport properties are reported on the InGaAsN/GaAsSb type II system. The epitaxial layers with the single hetero or multiple quantum well structure on InP substrates are grown by the molecular beam epitaxy. The electrical resistance of samples with different nitrogen concentrations has been measured as a function of the magnetic field up to 9 Tesla at several temperatures between 2 and 6 K. The oscillation of the resistance due to the Shubnikov-de Haas (SdH) effect has been observed at each temperature. The effective mass is obtained from the temperature dependence of the amplitude of the SdH oscillations. The value of the effective mass increases from 0.048 for N = 0.0% to 0.062 for N = 1.2 and 1.5% as the nitrogen concentration increases. The mass enhancement occurs with corresponding to the reduction of the bandgap energy. These results are consistent with the band anticrossing model.

  7. Nonlinear-optical effects in semiconductor lasers based on InGaAs/GaAs/AlGaAs quantum-confinement heterostructures

    SciTech Connect

    Averkiev, N. S.; Slipchenko, S. O. Sokolova, Z. N.; Pikhtin, N. A.; Tarasov, I. S.

    2007-03-15

    Generation of a difference-frequency wave by two electromagnetic waves propagating in a heterolaser is analyzed theoretically. Calculations are carried out for InGaAs/GaAs/AlGaAs heterostructures of design optimized to attain maximum lasing power. It is shown that phase matching between the primary waves and the difference-frequency wave may persist over a distance of {approx}1 mm, comparable to the cavity length (2-3 mm), and the conversion coefficient can be as large as several percent.

  8. Modeling and Characterization of the Magnetocaloric Effect in Ni2MnGa Materials

    SciTech Connect

    Nicholson, Don M; Odbadrakh, Khorgolkhuu; Shassere, Benjamin; Rios, Orlando; Hodges, Jason P; Ludtka, Gerard Michael; Porter, Wallace D; Safa-Sefat, Athena; Rusanu, Aurelian; Brown, Greg; Evans III, Boyd Mccutchen

    2014-01-01

    Magnetic shape memory alloys have great promise as magneto-caloric effect refrigerant materials due to their combined magnetic and structural transitions. Computational and experimental research is reported on the Ni2MnGa material system. The magnetic states of this system are explored using the Wang-Landau statistical approach in conjunction with the Locally Self-consistent Multiple-Scattering method. The effects of alloying agents on the transition temperatures of the Ni2MnGa alloy are investigated using differential scanning calorimetry and superconducting quantum interference device. Experiments are performed at the Spallation Neutron Source at Oak Ridge National Laboratory to observe the structural and magnetic phase transformations.

  9. Effectiveness of spoilers on the GA(W)-1 airfoil with a high performance Fowler flap

    NASA Technical Reports Server (NTRS)

    Wentz, W. H., Jr.

    1975-01-01

    Two-dimensional wind-tunnel tests were conducted to determine effectiveness of spoilers applied to the GA(W)-1 airfoil. Tests of several spoiler configurations show adequate control effectiveness with flap nested. It is found that providing a vent path allowing lower surface air to escape to the upper surface as the spoiler opens alleviates control reversal and hysteresis tendencies. Spoiler cross-sectional shape variations generally have a modest influence on control characteristics. A series of comparative tests of vortex generators applied to the (GA-W)-1 airfoil show that triangular planform vortex generators are superior to square planform vortex generators of the same span.

  10. High-power graphene mode-locked Tm/Ho co-doped fiber laser with evanescent field interaction.

    PubMed

    Li, Xiaohui; Yu, Xuechao; Sun, Zhipei; Yan, Zhiyu; Sun, Biao; Cheng, Yuanbing; Yu, Xia; Zhang, Ying; Wang, Qi Jie

    2015-01-01

    Mid-infrared ultrafast fiber lasers are valuable for various applications, including chemical and biomedical sensing, material processing and military applications. Here, we report all-fiber high-power graphene mode-locked Tm/Ho co-doped fiber laser at long wavelength with evanescent field interaction. Ultrafast pulses up to 7.8 MHz are generated at a center wavelength of 1879.4 nm, with a pulse width of 4.7 ps. A graphene absorber integrated with a side-polished fiber can increase the damage threshold significantly. Harmonics mode-locking can be obtained till to the 21(th) harmonics at a pump power of above 500 mW. By using one stage amplifier in the anomalous dispersion regime, the laser can be amplified up to 450 mW and the narrowest pulse duration of 1.4 ps can be obtained simultaneously. Our work paves the way to graphene Tm/Ho co-doped mode-locked all-fiber master oscillator power amplifiers as potentially efficient and economic laser sources for high-power laser applications, such as special material processing and nonlinear optical studies. PMID:26567536

  11. High-power graphene mode-locked Tm/Ho co-doped fiber laser with evanescent field interaction

    PubMed Central

    Li, Xiaohui; Yu, Xuechao; Sun, Zhipei; Yan, Zhiyu; Sun, Biao; Cheng, Yuanbing; Yu, Xia; Zhang, Ying; Wang, Qi Jie

    2015-01-01

    Mid-infrared ultrafast fiber lasers are valuable for various applications, including chemical and biomedical sensing, material processing and military applications. Here, we report all-fiber high-power graphene mode-locked Tm/Ho co-doped fiber laser at long wavelength with evanescent field interaction. Ultrafast pulses up to 7.8 MHz are generated at a center wavelength of 1879.4 nm, with a pulse width of 4.7 ps. A graphene absorber integrated with a side-polished fiber can increase the damage threshold significantly. Harmonics mode-locking can be obtained till to the 21th harmonics at a pump power of above 500 mW. By using one stage amplifier in the anomalous dispersion regime, the laser can be amplified up to 450 mW and the narrowest pulse duration of 1.4 ps can be obtained simultaneously. Our work paves the way to graphene Tm/Ho co-doped mode-locked all-fiber master oscillator power amplifiers as potentially efficient and economic laser sources for high-power laser applications, such as special material processing and nonlinear optical studies. PMID:26567536

  12. Color-tunable nanophosphors by co-doping flame-made Y2O3 with Tb and Eu.

    PubMed

    Sotiriou, Georgios A; Schneider, Melanie; Pratsinis, Sotiris E

    2011-02-01

    Rare-earth phosphors with tunable optical properties are used in display panels and fluorescent lamps and have potential applications in lasers and bio-imaging. Here, non-aggregated Y2O3 nanocrystals either doped with Tb(3+) (1-5 at%) or co-doped with Tb(3+) (2 at%) and Eu(3+) (0.1-2 at%) ions are made in one-step by scalable flame spray pyrolysis. The morphology of these nanophosphors is investigated by X-ray diffraction, electron microscopy and N2 adsorption while their optical properties are monitored by photoluminescent spectroscopy. When yttria nanocrystals are doped with terbium, a bright green emission is obtained at an optimum Tb-content of 2 at%. When, however, europium is added, the emission color of these Tb-doped yttria nanophosphors can be tuned precisely from green to red depending on the Tb/Eu ratio. Furthermore, energy-transfer from Tb(3+) to Eu(3+) is observed, thus allowing the control of the excitation spectra of the co-doped nanophosphors. PMID:23730401

  13. Laser oscillation of Yb³⁺:Er³⁺ co-doped phosphosilicate microsphere [invited].

    PubMed

    Wu, Tianjiao; Huang, Yantang; Huang, Jing; Huang, Yu; Zhang, Peijin; Ma, Jing

    2014-07-20

    A fiber-taper-microsphere-coupled system was used to research the characteristics of laser oscillation and upconversion luminescence of Yb3+:Er3+ co-doped phosphosilicate (YECP) microspheres. The YECP microspheres were fabricated by melting the end of phosphosilicate filaments. Single- and multimode laser oscillation at 1535-1565 nm within the C-band were obtained. In addition, the output power of the single-mode laser at 1545.5 nm can be as high as 48.98 μW, which was achieved under pump power of 9.63 mW, and the side-mode suppression ratio was 51.49 dB. Upconversion fluorescence of Er3+ at 521, 532, and 544 nm also were measured, and the pump power dependence was studied. The fluorescence intensity was lower than that of Yb3+:Er3+ co-doped silica and oxyfluoride glass ceramic microspheres. Moreover, the physical mechanism of upconversion suppression and laser oscillation enhancement observed in our experiment was presented, which is beneficial to the preparation of rare-earth-doped microcavity lasers. PMID:25090213

  14. Colour emission tunability in Ho3+-Tm3+-Yb3+ co-doped Y2O3 upconverted phosphor

    NASA Astrophysics Data System (ADS)

    Pandey, Anurag; Rai, Vineet Kumar

    2012-12-01

    The frequency upconversion (UC) emission throughout the visible region from the Y2O3:Ho3+-Tm3+-Yb3+ co-doped phosphors synthesized by using low temperature combustion process upon excitation with a diode laser operating at 980 nm have been presented. The colour emission tunability in co-doped phosphor has been observed on increasing the pump power and seen by the naked eyes. The tunability in colour emission has also been visualized by CIE chromaticity diagram. The variation in UC emission intensity of the 1G4 → 3H6 (Tm3+) and 5F3 → 5I8 (Ho3+) transitions lying in the blue region has been monitored with increase in the pump power and marked that their ratio can be used to determine the temperature. The developed phosphor has been used to record fingerprints. The observed most intense visible colour emission from the developed material may be used for photodynamic therapy and as an alternative of traditional fluorescent biolabels.

  15. Electrical, dielectric, photoluminescence and magnetic properties of ZnO nanoparticles co-doped with Co and Cu

    NASA Astrophysics Data System (ADS)

    Ashokkumar, M.; Muthukumaran, S.

    2015-01-01

    X-ray diffraction spectra of Zn0.96-xCu0.04CoxO (0≤x≤0.04) nanoparticles synthesized by co-precipitation method confirmed the hexagonal wurtzite structure without any secondary phase formation. The dielectric dispersion was high at lower frequencies and almost frequency independent at higher frequencies. The observed higher dielectric constant, dielectric loss and ac conductivity in Co=2% doped Zn0.96Cu0.04O samples was explained in terms of average crystalline size and number of nano-dipoles. Photoluminescence spectra of undoped and Co-doped Zn0.96Cu0.04O samples showed four distinct bands, (i) ultra violet emission bands around 382-391 nm, (ii) violet emission band centered at 417 nm, (iii) blue emission bands centered at 478 nm and (iv) green emission bands centered at 523 nm. The observed minimum of Igreen/Iblue revealed that Co=1% doped Zn0.96Cu0.04O sample had minimum defects sites and vacancies and it saturated after Co=3% doping. Undoped Zn0.96Cu0.04O sample had higher magnetization and it was suppressed by Co-doping due to the enhanced antiferromagnetic interaction between neighbouring Cu-Cu ion.

  16. On the Luminescence Enhancement of Mn2+ By Co-doping of Eu2+ in ZnS:Mn,Eu

    SciTech Connect

    Hossu, Marius; Schaeffer, Roger O.; Ma, Lun; Chen, Wei; Zhu, Yongbin; Sammynaiken, Ramaswami; Joly, Alan G.

    2013-06-01

    The photoluminescence and X-ray luminescence of ZnS:Mn, ZnS:Mn,Eu and ZnS:Eu were investigated and it was found that the luminescence intensity of Mn2+ in ZnS:Mn,Eu co-doped phosphors is highly dependent on the doping concentration of Eu2+. At the optimized Eu2+concentration (0.2%), the photoluminescence of Mn2+ shows about a 5.5 times enhancement and its X-ray luminescence is enhanced by a factor of 2.5. Both wurtzite and zinc blend phases are present in the samples with wurtzite phase dominant. Co-doping of Eu2+ into ZnS:Mn does not change appreciably the ratio of the two phases or the Mn2+ emission luminescence lifetime; however, the doping of Eu2+ into ZnS:Mn does change the phonon activity. Furthermore, it was found that the defect-related blue emission of ZnS:Eu overlaps with the excitation bands of Mn2+ in ZnS:Mn and there is likely energy transfer from these defect states to Mn2+ in ZnS:Mn,Eu. This energy transfer and the phonon modification are considered to be the two main reasons for the luminescence enhancement and the intensity dependence of Mn2+ emission on Eu2+ doping concentration in ZnS:Mn,Eu.

  17. Broadband near-infrared emission from Tm{sup 3+}/Er{sup 3+} co-doped nanostructured glass ceramics

    SciTech Connect

    Chen Daqin; Wang Yuansheng; Bao Feng; Yu Yunlong

    2007-06-01

    Transparent SiO{sub 2}-Al{sub 2}O{sub 3}-NaF-YF{sub 3} glass ceramics co-doped with Er{sup 3+} and Tm{sup 3+} were prepared by melt quenching and subsequent heating. X-ray diffraction and transmission electron microscopy experiments revealed that {beta}-YF{sub 3} nanocrystals incorporated with Er{sup 3+} and Tm{sup 3+} were precipitated homogeneously among the oxide glass matrix. An integrated broad near-infrared emission band in the wavelength region of 1300-1700 nm, consisting of Tm{sup 3+} emissions around 1472 nm ({sup 3}H{sub 4}{yields}{sup 3}F{sub 4}) and 1626 nm ({sup 3}F{sub 4}{yields}{sup 3}H{sub 6}), and Er{sup 3+} emission around 1543 nm ({sup 4}I{sub 13/2}{yields}{sup 4}I{sub 15/2}), was obtained under 792 nm laser excitation. The full width at half maximum of this integrated band increased with the increasing of [Tm]/[Er] ratio, and it reached as large as 175 nm for the 0.1 mol% Er{sup 3+} and 0.8 mol% Tm{sup 3+} co-doped sample. The energy transfers between Er{sup 3+} and Tm{sup 3+} were proposed to play an important role in tailoring the emission bandwidth of the sample.

  18. High-power graphene mode-locked Tm/Ho co-doped fiber laser with evanescent field interaction.

    PubMed

    Li, Xiaohui; Yu, Xuechao; Sun, Zhipei; Yan, Zhiyu; Sun, Biao; Cheng, Yuanbing; Yu, Xia; Zhang, Ying; Wang, Qi Jie

    2015-11-16

    Mid-infrared ultrafast fiber lasers are valuable for various applications, including chemical and biomedical sensing, material processing and military applications. Here, we report all-fiber high-power graphene mode-locked Tm/Ho co-doped fiber laser at long wavelength with evanescent field interaction. Ultrafast pulses up to 7.8 MHz are generated at a center wavelength of 1879.4 nm, with a pulse width of 4.7 ps. A graphene absorber integrated with a side-polished fiber can increase the damage threshold significantly. Harmonics mode-locking can be obtained till to the 21(th) harmonics at a pump power of above 500 mW. By using one stage amplifier in the anomalous dispersion regime, the laser can be amplified up to 450 mW and the narrowest pulse duration of 1.4 ps can be obtained simultaneously. Our work paves the way to graphene Tm/Ho co-doped mode-locked all-fiber master oscillator power amplifiers as potentially efficient and economic laser sources for high-power laser applications, such as special material processing and nonlinear optical studies.

  19. N, S co-doped-TiO2/fly ash beads composite material and visible light photocatalytic activity

    NASA Astrophysics Data System (ADS)

    Lv, Jun; Sheng, Tong; Su, Lili; Xu, Guangqing; Wang, Dongmei; Zheng, Zhixiang; Wu, Yucheng

    2013-11-01

    Using TiCl4 as the titanium source, urea as the precipitating agent, nano-TiO2/fly ash beads composite materials were prepared by hydrolysis-precipitation method. Using (NH2)2CO and (NH2)2SC as the N and S source respectively, N and S co-doped TiO2/fly ash beads composite materials were prepared by grinding them together according to a certain proportion and calcined at 500 °C for 2 h. The composite materials were characterized by SEM, EDS, XPS, and UV-vis spectrophotometer methods. The UV-vis absorption spectra results show that the absorption edge of un-doped composites is 390 nm while that of doped composites red-shifts to 500 nm. The photocatalytic activity of composite materials was evaluated by degradation of methyl orange under visible light irradiation (halogen lamp, 250 W). The results showed that after irradiation for 1 h, degradation rate of N, S co-doped-TiO2/fly ash beads composite material can reach 65%, while the degradation rate of un-doped sample and P25 were just 10% and 6%, respectively. The composite material also showed excellent recycling properties.

  20. Luminescence studies on Dy3+ and Dy3+:Eu3+ co-doped boro-phosphate glasses for WLED applications

    NASA Astrophysics Data System (ADS)

    Vijayakumar, M.; Uma, V.; Arunkumar, S.; Marimuthu, K.

    2015-06-01

    Dy3+ and Dy3+:Eu3+ co-doped boro-phosphate glasses have been prepared and optically characterized using absorption, luminescence and decay measurements. The Nephelauxetic ratios (β), Bonding parameters (δ) and Judd-Ofelt (JO) intensity parameters Ωλ (λ = 2, 4 and 6) were calculated to study the nature of the environment around the RE3+ ions in the prepared glasses. The yellow to blue (Y/B) intensity ratio and the chromaticity color coordinates were calculated from the luminescence measurements. The lifetimes of the 4F9/2 excited level were measured using decay curves and is found to decrease in the Dy3+:Eu3+ co-doped glass due to the occurrence of resonant energy transfer between Dy3+-Eu3+ ions and the non-exponential decay rates have been fitted with Inokuti-Hirayama (IH) model. The decay curves are well fitted for S= 6 suggesting that the interaction between active ions for the energy transfer is of dipole-dipole nature.

  1. Upconversion emission in antimony-germanate double-clad optical fiber co-doped with Yb3+/Tm3+ ions

    NASA Astrophysics Data System (ADS)

    Kochanowicz, M.; Dorosz, D.; Zmojda, J.; Miluski, P.; Dorosz, J.; Pisarska, J.; Pisarski, W. A.

    2015-03-01

    In the paper upconversion luminescence properties in Yb3+/Tm3+ co-doped antimony-germanate glass and double-clad optical fiber were studied. The concentration of lanthanides, which has shown the highest upconversion emission intensity at 478 nm (1G4 → 3H6) and 650 nm (1G4 → 3F4), is 1Yb2O3/0.1Tm2O3 (mol%) as a result of exciting with a laser diode (976 nm). The lifetime of 2F5/2 (Yb3+) level decreases from 781 μs to 71 μs in the presence of Tm3+ 0.1-0.75 mol% respectively. Luminescence decay curve of glass co-doped with 1Yb2O3/0.75Tm2O3 suggests donor-donor fast migration followed by Tm3+ → Yb3+ energy transfer. Glass characterized by highest intensity of upconversion luminescence (1Yb2O3/0.1Tm2O3 mol%) was used as core of double-clad optical fiber made by modified rod-in-tube method. Mechanisms influencing differences in upconversion amplified spontaneous emission of the fabricated optical fiber and bulk glass were discussed. Reabsorption of the amplified spontaneous emission signal along the fibre resulting from Tm3+:3H6 → 1G4, transition was observed.

  2. Double Rare-Earth Oxides Co-doped Strontium Zirconate as a New Thermal Barrier Coating Material

    NASA Astrophysics Data System (ADS)

    Ma, Wen; Wang, Dongxing; Dong, Hongying; Lun, Wenshan; He, Weiyan; Zheng, Xuebin

    2013-03-01

    Y2O3 and Yb2O3 co-doped strontium zirconate with chemistry of Sr(Zr0.9Y0.05Yb0.05)O2.95 (SZYY) was synthesized and had a minor second phase of Yb2O3. The SZYY showed good phase stability not only from room temperature to 1400 °C but also at high temperature of 1450 °C for a long period, analyzed by thermogravimetry-differential scanning calorimetry and x-ray diffraction, respectively. The coefficients of thermal expansion (CTEs) of the sintered bulk SZYY were recorded by a high-temperature dilatometer and revealed a positive influence on phase transitions of SrZrO3 by co-doping with Y2O3 and Yb2O3. The thermal conductivities of SZYY were at least ~30% lower in contrast to that of SrZrO3 and 8YSZ in the whole tested temperature range. Good chemical compatibility was observed for SZYY with 8YSZ or Al2O3 powders after a 24 h heat treatment at 1250 °C. The phase stability and the microstructure evolution of the as-sprayed SZYY coating during annealing at 1400 °C were also investigated.

  3. Thickness dependence of structural and transport properties of Co-doped BaFe2As2 on Fe buffered MgO substrates

    NASA Astrophysics Data System (ADS)

    Iida, Kazumasa; Hänisch, Jens; Trommler, Sascha; Haindl, Silvia; Kurth, Fritz; Hühne, Ruben; Schultz, Ludwig; Holzapfel, Bernhard

    2011-12-01

    We have investigated the influence of the superconducting layer thickness, d, on the structural and transport properties of Co-doped BaFe2As2 films deposited on Fe buffered MgO substrates by pulsed laser deposition. The superconducting transition temperature and the texture quality of Co-doped BaFe2As2 films improve with increasing d due to a gradual relief of the tensile strain. For d >= 90 nm an additional 110 textured component of Co-doped BaFe2As2 was observed, which leads to an upward shift in the angle-dependent critical current density at H \\parallel c . These results indicate that the grain boundaries created by the 110 textured component may contribute to the c-axis pinning.

  4. Magnetic field-modulated photo-thermo-electric effect in Fe/GaAs film

    SciTech Connect

    Qiao, Shuang; Liu, Jihong; Yan, Guoying; Wang, Shufang E-mail: sfwang@hbu.edu.cn; Fu, Guangsheng; Zhao, Jianhua; Zhang, Xinhui E-mail: sfwang@hbu.edu.cn

    2015-11-02

    Ferromagnet/semiconductor heterostructure, such as Fe/GaAs, is always one of the key issues in spintronics due to its prerequisite for the realization of spin sensitive devices. In this letter, a lateral photoelectric effect (LPE) was observed in Fe/GaAs. Our results show that the sensitivity was not related to laser wavelength, but only proportional to laser power, suggesting that the lateral photovoltage was induced by photo-thermo-electric effect. Moreover, we also observe that the voltage signal increases with the increase in applied field due to decreasing scattering probability for spin-polarized electrons. Our finding of LPE adds another functionality to the Fe/GaAs system and will be useful in development of spin-polarized voltage devices.

  5. Surface antireflection properties of GaN nanostructures with various effective refractive index profiles.

    PubMed

    Han, Lu; Zhao, Hongping

    2014-12-29

    GaN nanostructures with various effective refractive index profiles (Linear, Cubic, and Quintic functions) were numerically studied as broadband omnidirectional antireflection structures for concentrator photovoltaics by using three-dimensional finite difference time domain (3D-FDTD) method. Effective medium theory was used to design the surface structures corresponding to different refractive index profiles. Surface antireflection properties were calculated and analyzed for incident light with wavelength, polarization and angle dependences. The surface antireflection properties of GaN nanostructures based on six-sided pyramid with both uniform and non-uniform patterns were also investigated. Results indicate a significant dependence of the surface antireflection on the refractive index profiles of surface nanostructures as well as their pattern uniformity. The GaN nanostructures with linear refractive index profile show the best performance to be used as broadband omnidirectional antireflection structures.

  6. Magnetic field-modulated photo-thermo-electric effect in Fe/GaAs film

    NASA Astrophysics Data System (ADS)

    Qiao, Shuang; Liu, Jihong; Yan, Guoying; Zhao, Jianhua; Zhang, Xinhui; Wang, Shufang; Fu, Guangsheng

    2015-11-01

    Ferromagnet/semiconductor heterostructure, such as Fe/GaAs, is always one of the key issues in spintronics due to its prerequisite for the realization of spin sensitive devices. In this letter, a lateral photoelectric effect (LPE) was observed in Fe/GaAs. Our results show that the sensitivity was not related to laser wavelength, but only proportional to laser power, suggesting that the lateral photovoltage was induced by photo-thermo-electric effect. Moreover, we also observe that the voltage signal increases with the increase in applied field due to decreasing scattering probability for spin-polarized electrons. Our finding of LPE adds another functionality to the Fe/GaAs system and will be useful in development of spin-polarized voltage devices.

  7. Sulfuric acid and hydrogen peroxide surface passivation effects on AlGaN/GaN high electron mobility transistors

    SciTech Connect

    Zaidi, Z. H. Lee, K. B.; Qian, H.; Jiang, S.; Houston, P. A.; Guiney, I.; Wallis, D. J.; Humphreys, C. J.

    2014-12-28

    In this work, we have compared SiN{sub x} passivation, hydrogen peroxide, and sulfuric acid treatment on AlGaN/GaN HEMTs surface after full device fabrication on Si substrate. Both the chemical treatments resulted in the suppression of device pinch-off gate leakage current below 1 μA/mm, which is much lower than that for SiN{sub x} passivation. The greatest suppression over the range of devices is observed with the sulfuric acid treatment. The device on/off current ratio is improved (from 10{sup 4}–10{sup 5} to 10{sup 7}) and a reduction in the device sub-threshold (S.S.) slope (from ∼215 to 90 mV/decade) is achieved. The sulfuric acid is believed to work by oxidizing the surface which has a strong passivating effect on the gate leakage current. The interface trap charge density (D{sub it}) is reduced (from 4.86 to 0.90 × 10{sup 12 }cm{sup −2} eV{sup −1}), calculated from the change in the device S.S. The gate surface leakage current mechanism is explained by combined Mott hopping conduction and Poole Frenkel models for both untreated and sulfuric acid treated devices. Combining the sulfuric acid treatment underneath the gate with the SiN{sub x} passivation after full device fabrication results in the reduction of D{sub it} and improves the surface related current collapse.

  8. Erbium and nitrogen co-doped SrTiO{sub 3} with highly visible light photocatalytic activity and stability by solvothermal synthesis

    SciTech Connect

    Xu, Jing; Wei, Yuelin; Huang, Yunfang; Wang, Jing; Zheng, Xuanqing; Sun, Zhixian; Wu, Ying; Tao, Xinling; Fan, Leqing; Wu, Jihuai

    2015-10-15

    Highlights: • Er/N co-doped SrTiO{sub 3} was prepared by a solvothermal process at low temperature. • The co-doping induces the band gap narrowing and prominent absorbance in visible light region. • The samples show excellent catalytic activity and stability under visible light irradiation. - Abstract: Erbium–nitrogen co-doped SrTiO{sub 3} photocatalysts have been synthesized by a facile solvothermal method. The resulting samples were analyzed by FE-SEM, XRD, BET-surface area and UV–vis. The UV–vis absorption spectra of these powders indicated that erbium–nitrogen co-doped SrTiO{sub 3} possessed stronger absorption bands in the visible light region in comparison with that of pure SrTiO{sub 3}. The occurrence of the erbium–nitrogen co-doped cubic SrTiO{sub 3} induced the higher photocatalytic activities for the degradation of methyl orange (MO) under irradiation by ultraviolet light and visible light, respectively, being superior to that of pure SrTiO{sub 3} and commercial TiO{sub 2} (P-25) powders. In addition, the Er–N co-doped SrTiO{sub 3} (initial molar ratios of Sr/Er/N = 1:0.015:0.1, designated as S5) sample showed the best photocatalytic activity with the degradation rate as high as 98% after 30 min under the visible light irradiation. After five cycles, the photocatalytic activity of the S5 catalyst showed no significant decrease, which indicated that the photocatalysts were stable under visible light irradiation.

  9. Effect of thermal annealing on the emission properties of heterostructures containing a quantum-confined GaAsSb layer

    SciTech Connect

    Dikareva, N. V. Vikhrova, O. V.; Zvonkov, B. N.; Malekhonova, N. V.; Nekorkin, S. M.; Pirogov, A. V.; Pavlov, D. A.

    2015-01-15

    Heterostructures containing single GaAsSb/GaAs quantum wells and bilayer GaAsSb/InGaAs quantum wells are produced by metal-organic vapor-phase epitaxy at atmospheric pressure. The growth temperature of the quantum-confined layers is 500–570°C. The structural quality of the samples and the quality of heterointerfaces of the quantum wells are studied by the high-resolution transmission electron microscopy of cross sections. The emission properties of the heterostructures are studied by photoluminescence measurements. The structures are subjected to thermal annealing under conditions chosen in accordance with the temperature and time of growth of the upper cladding p-InGaP layer during the formation of GaAs/InGaP laser structures with an active region containing quantum-confined GaAsSb layers. It is found that such heat treatment can have a profound effect on the emission properties of the active region, only if a bilayer GaAsSb/InGaAs quantum well is formed.

  10. Chromium-niobium co-doped vanadium dioxide films: Large temperature coefficient of resistance and practically no thermal hysteresis of the metal-insulator transition

    NASA Astrophysics Data System (ADS)

    Miyazaki, Kenichi; Shibuya, Keisuke; Suzuki, Megumi; Sakai, Kenichi; Fujita, Jun-ichi; Sawa, Akihito

    2016-05-01

    We investigated the effects of chromium (Cr) and niobium (Nb) co-doping on the temperature coefficient of resistance (TCR) and the thermal hysteresis of the metal-insulator transition of vanadium dioxide (VO2) films. We determined the TCR and thermal-hysteresis-width diagram of the V1-x-yCrxNbyO2 films by electrical-transport measurements and we found that the doping conditions x ≳ y and x + y ≥ 0.1 are appropriate for simultaneously realizing a large TCR value and an absence of thermal hysteresis in the films. By using these findings, we developed a V0.90Cr0.06Nb0.04O2 film grown on a TiO2-buffered SiO2/Si substrate that showed practically no thermal hysteresis while retaining a large TCR of 11.9%/K. This study has potential applications in the development of VO2-based uncooled bolometers.

  11. Microstructure, optical and structural characterization of Cd0.98Fe0.02S thin films co-doped with Zn by chemical bath deposition method

    NASA Astrophysics Data System (ADS)

    Pitchaimani, K.; Amalraj, L.; Muthukumaran, S.

    2016-04-01

    Fe-doped CdS (Cd0.98Fe0.02S) and Fe, Zn co-doped CdS (Cd0.98-xZnxFe0.02S (x=0.02, 0.04, and 0.06)) thin films have been successfully deposited on glass substrate by chemical bath deposition technique using aqueous ammonia solution at pH = 9.5. Phase purity of the samples having cubic structure with (111) as the preferential orientation was confirmed by X-ray diffraction technique. Shift of X-ray diffraction peak position towards higher angle side and decrease of lattice parameters, volume and crystallite size confirmed the proper incorporation of Zn into Cd-Fe-S except Zn=6%. The compositional analysis (EDX) showed that Cd, Fe, Zn and S are present in the films. The enhanced band gap and higher transmittance observed in Cd0.94Zn0.04Fe0.02S films are the effective way to use solar energy and enhance its photocatalytic activity under visible light. The enhanced green band emission than blue band by Zn-doping evidenced the existence of higher defect states.

  12. One-pot hydrothermal synthesis of CuBi co-doped mesoporous zeolite Beta for the removal of NOx by selective catalytic reduction with ammonia.

    PubMed

    Xie, Zhiguo; Zhou, Xiaoxia; Wu, Huixia; Chen, Lisong; Zhao, Han; Liu, Yan; Pan, Linyu; Chen, Hangrong

    2016-01-01

    A series of CuBi co-doped mesoporous zeolite Beta (CuxBiy-mBeta) were prepared by a facile one-pot hydrothermal treatment approach and were characterized by XRD, N2 adsorption-desorption, TEM/SEM, XPS, H2-TPR, NH3-TPD and in situ DRIFTS. The catalysts CuxBiy-mBeta were applied to the removal of NOx by selective catalytic reduction with ammonia (NH3-SCR), especially the optimized Cu1Bi1-mBeta achieved the high efficiency for the removal of NOx and N2 selectivity, superior water and sulfur resistance as well as good durability. The excellent catalytic performance could be attributed to the acid sites of the support and the synergistic effect between copper and bismuth species. Moreover, in situ DRIFTS results showed that amides NH2 and NH4(+) generated from NH3 adsorption could be responsible for the high selective catalytic reduction of NOx to N2. In addition, a possible catalytic reaction mechanism on Cu1Bi1-mBeta for the removal of NOx by NH3-SCR was proposed for explaining this catalytic process. PMID:27445009

  13. Thermoluminescence properties of Li2CO3-K2CO3-H3BO3glass system co-doped with CuO and MgO.

    PubMed

    Alajerami, Yasser Saleh Mustafa; Hashim, Suhairul; Ramli, Ahmad Termizi; Saleh, Muneer Aziz; Kadni, Taiman

    2013-06-01

    The thermoluminescent properties of boric glass modified with lithium and potassium carbonates (LKB) and co-doped with CuO and MgO are reported for the first time. Two techniques are applied to investigate the effect of dopants and co-dopants on the thermal stimulation properties of LKB. The induced TL glow curves of a CuO-doped sample are found to be at 220°C with a single peak. An enhancement of about three times is shown with the increment of 0.1 mol % MgO as a co-dopant impurity. This enhancement may contribute to the ability of magnesium to create extra electron traps and consequently the energy transfer to monovalent Cu(+) ions. LKB:Cu,Mg is low Z material (Zeff=8.55), and observed 15 times less sensitive than LiF: Mg, Ti (TLD-100). The proposed dosemeter showed good linearity in TL dose-response, low fading and excellent reproducibility with a simple glow curve, and thus, can be used in the radiation dosimetry. PMID:23193136

  14. One-pot hydrothermal synthesis of CuBi co-doped mesoporous zeolite Beta for the removal of NOx by selective catalytic reduction with ammonia.

    PubMed

    Xie, Zhiguo; Zhou, Xiaoxia; Wu, Huixia; Chen, Lisong; Zhao, Han; Liu, Yan; Pan, Linyu; Chen, Hangrong

    2016-07-22

    A series of CuBi co-doped mesoporous zeolite Beta (CuxBiy-mBeta) were prepared by a facile one-pot hydrothermal treatment approach and were characterized by XRD, N2 adsorption-desorption, TEM/SEM, XPS, H2-TPR, NH3-TPD and in situ DRIFTS. The catalysts CuxBiy-mBeta were applied to the removal of NOx by selective catalytic reduction with ammonia (NH3-SCR), especially the optimized Cu1Bi1-mBeta achieved the high efficiency for the removal of NOx and N2 selectivity, superior water and sulfur resistance as well as good durability. The excellent catalytic performance could be attributed to the acid sites of the support and the synergistic effect between copper and bismuth species. Moreover, in situ DRIFTS results showed that amides NH2 and NH4(+) generated from NH3 adsorption could be responsible for the high selective catalytic reduction of NOx to N2. In addition, a possible catalytic reaction mechanism on Cu1Bi1-mBeta for the removal of NOx by NH3-SCR was proposed for explaining this catalytic process.

  15. Thermoluminescence properties of Li2CO3-K2CO3-H3BO3glass system co-doped with CuO and MgO.

    PubMed

    Alajerami, Yasser Saleh Mustafa; Hashim, Suhairul; Ramli, Ahmad Termizi; Saleh, Muneer Aziz; Kadni, Taiman

    2013-06-01

    The thermoluminescent properties of boric glass modified with lithium and potassium carbonates (LKB) and co-doped with CuO and MgO are reported for the first time. Two techniques are applied to investigate the effect of dopants and co-dopants on the thermal stimulation properties of LKB. The induced TL glow curves of a CuO-doped sample are found to be at 220°C with a single peak. An enhancement of about three times is shown with the increment of 0.1 mol % MgO as a co-dopant impurity. This enhancement may contribute to the ability of magnesium to create extra electron traps and consequently the energy transfer to monovalent Cu(+) ions. LKB:Cu,Mg is low Z material (Zeff=8.55), and observed 15 times less sensitive than LiF: Mg, Ti (TLD-100). The proposed dosemeter showed good linearity in TL dose-response, low fading and excellent reproducibility with a simple glow curve, and thus, can be used in the radiation dosimetry.

  16. The contribution of vanadium and titanium on improving methylene blue decolorization through heterogeneous UV-Fenton reaction catalyzed by their co-doped magnetite.

    PubMed

    Liang, Xiaoliang; Zhong, Yuanhong; Zhu, Sanyuan; Ma, Lingya; Yuan, Peng; Zhu, Jianxi; He, Hongping; Jiang, Zheng

    2012-01-15

    This study investigated the methylene blue (MB) decolorization through heterogeneous UV-Fenton reaction catalyzed by V-Ti co-doped magnetites, with emphasis on comparing the contribution of V and Ti cations on improving the adsorption and catalytic activity of magnetite. In the well crystallized spinel structure, both Ti(4+) and V(3+) occupied the octahedral sites. Ti(4+) showed a more obvious effect on increasing specific surface area and superficial hydroxyl amount than V(3+) did, resulting in a significant improvement of the adsorption ability of magnetite to MB. The UV introduction greatly accelerated MB degradation. And magnetite with more Ti and less V displayed better catalytic activity in MB degradation through heterogeneous UV-Fenton reaction. The transformation of degradation products and individual contribution from vanadium and titanium on improving adsorption and catalytic activity of magnetite were also investigated. These new insights are of high importance for well understanding the interface interaction between contaminants and metal doped magnetites, and the environmental application of natural and synthetic magnetites.

  17. One-pot hydrothermal synthesis of CuBi co-doped mesoporous zeolite Beta for the removal of NOx by selective catalytic reduction with ammonia

    NASA Astrophysics Data System (ADS)

    Xie, Zhiguo; Zhou, Xiaoxia; Wu, Huixia; Chen, Lisong; Zhao, Han; Liu, Yan; Pan, Linyu; Chen, Hangrong

    2016-07-01

    A series of CuBi co-doped mesoporous zeolite Beta (CuxBiy-mBeta) were prepared by a facile one-pot hydrothermal treatment approach and were characterized by XRD, N2 adsorption-desorption, TEM/SEM, XPS, H2-TPR, NH3-TPD and in situ DRIFTS. The catalysts CuxBiy-mBeta were applied to the removal of NOx by selective catalytic reduction with ammonia (NH3-SCR), especially the optimized Cu1Bi1-mBeta achieved the high efficiency for the removal of NOx and N2 selectivity, superior water and sulfur resistance as well as good durability. The excellent catalytic performance could be attributed to the acid sites of the support and the synergistic effect between copper and bismuth species. Moreover, in situ DRIFTS results showed that amides NH2 and NH4+ generated from NH3 adsorption could be responsible for the high selective catalytic reduction of NOx to N2. In addition, a possible catalytic reaction mechanism on Cu1Bi1-mBeta for the removal of NOx by NH3-SCR was proposed for explaining this catalytic process.

  18. One-pot hydrothermal synthesis of CuBi co-doped mesoporous zeolite Beta for the removal of NOx by selective catalytic reduction with ammonia

    PubMed Central

    Xie, Zhiguo; Zhou, Xiaoxia; Wu, Huixia; Chen, Lisong; Zhao, Han; Liu, Yan; Pan, Linyu; Chen, Hangrong

    2016-01-01

    A series of CuBi co-doped mesoporous zeolite Beta (CuxBiy-mBeta) were prepared by a facile one-pot hydrothermal treatment approach and were characterized by XRD, N2 adsorption-desorption, TEM/SEM, XPS, H2-TPR, NH3-TPD and in situ DRIFTS. The catalysts CuxBiy-mBeta were applied to the removal of NOx by selective catalytic reduction with ammonia (NH3-SCR), especially the optimized Cu1Bi1-mBeta achieved the high efficiency for the removal of NOx and N2 selectivity, superior water and sulfur resistance as well as good durability. The excellent catalytic performance could be attributed to the acid sites of the support and the synergistic effect between copper and bismuth species. Moreover, in situ DRIFTS results showed that amides NH2 and NH4+ generated from NH3 adsorption could be responsible for the high selective catalytic reduction of NOx to N2. In addition, a possible catalytic reaction mechanism on Cu1Bi1-mBeta for the removal of NOx by NH3-SCR was proposed for explaining this catalytic process. PMID:27445009

  19. Facile synthesis and enhanced visible light photocatalytic activity of N and Zr co-doped TiO2 nanostructures from nanotubular titanic acid precursors.

    PubMed

    Zhang, Min; Yu, Xinluan; Lu, Dandan; Yang, Jianjun

    2013-01-01

    Zr/N co-doped TiO2 nanostructures were successfully synthesized using nanotubular titanic acid (NTA) as precursors by a facile wet chemical route and subsequent calcination. These Zr/N-doped TiO2 nanostructures made by NTA precursors show significantly enhanced visible light absorption and much higher photocatalytic performance than the Zr/N-doped P25 TiO2 nanoparticles. Impacts of Zr/N co-doping on the morphologies, optical properties, and photocatalytic activities of the NTA precursor-based TiO2 were thoroughly investigated. The origin of the enhanced visible light photocatalytic activity is discussed in detail.

  20. Facile synthesis and enhanced visible light photocatalytic activity of N and Zr co-doped TiO2 nanostructures from nanotubular titanic acid precursors

    NASA Astrophysics Data System (ADS)

    Zhang, Min; Yu, Xinluan; Lu, Dandan; Yang, Jianjun

    2013-12-01

    Zr/N co-doped TiO2 nanostructures were successfully synthesized using nanotubular titanic acid (NTA) as precursors by a facile wet chemical route and subsequent calcination. These Zr/N-doped TiO2 nanostructures made by NTA precursors show significantly enhanced visible light absorption and much higher photocatalytic performance than the Zr/N-doped P25 TiO2 nanoparticles. Impacts of Zr/N co-doping on the morphologies, optical properties, and photocatalytic activities of the NTA precursor-based TiO2 were thoroughly investigated. The origin of the enhanced visible light photocatalytic activity is discussed in detail.

  1. Effects of phase transformation on the microstructures and magnetostriction of Fe-Ga and Fe-Ga-Zn ferromagnetic shape memory alloys

    SciTech Connect

    Lin, Yin-Chih Lin, Chien-Feng

    2015-05-07

    The phase transformation and magnetostriction of bulk Fe{sub 73}Ga{sub 27} and Fe{sub 73}Ga{sub 18}Zn{sub 9} (at. %) ferromagnetic shape memory alloys (FSMs) were investigated by transmission electron microscopy (TEM), x-ray diffraction (XRD), and a magnetostrictive-meter setup. For the Fe{sub 73}Ga{sub 27} FSM alloy solution treated at 1100 °C for 4 h and quenched in ice brine, the antiphase boundary segments of the D0{sub 3} domain were observed in the A2 (disordered) matrix, and the Fe{sub 73}Ga{sub 27} FSM alloy had an optimal magnetostriction (λ{sub ‖}{sup s }= 71 × 10{sup −6} and λ{sub ⊥}{sup s }= −31 × 10{sup −6}). In Fe{sub 73}Ga{sub 27} FSM alloy as-quenched, aged at 700 °C for 24 h, and furnace cooled, D0{sub 3} nanoclusters underwent phase transformation to an intermediate tetragonal phase (i.e., L1{sub 0}-like martensite) via Bain distortion, and finally L1{sub 2} (Fe{sub 3}Ga) structures precipitated, as observed by TEM and XRD. The L1{sub 0}-like martensite and L1{sub 2} phases in the aged Fe{sub 73}Ga{sub 27} FSM alloy drastically decreased the magnetostriction from positive to negative (λ{sub ‖}{sup s }= −20 × 10{sup −6} and λ{sub ⊥}{sup s }= −8 × 10{sup −6}). However, in Fe{sub 73}Ga{sub 18}Zn{sub 9} FSM alloy as-quenched and aged, the phase transformation of D0{sub 3} to an intermediate tetragonal martensite phase and precipitation of L1{sub 2} structures were not found. The results indicate that the aged Fe{sub 73}Ga{sub 18}Zn{sub 9} FSM alloy maintained stable magnetostriction (λ{sub ‖}{sup s }= 36 × 10{sup −6} and λ{sub ⊥}{sup s }= −31 × 10{sup −6}). Adding Zn can improve the ferromagnetic shape memory effect of aged Fe{sub 73}Ga{sub 18}Zn{sub 9} alloy, which may be useful in application of the alloy in high temperature environments.

  2. AlGaN channel field effect transistors with graded heterostructure ohmic contacts

    NASA Astrophysics Data System (ADS)

    Bajaj, Sanyam; Akyol, Fatih; Krishnamoorthy, Sriram; Zhang, Yuewei; Rajan, Siddharth

    2016-09-01

    We report on ultra-wide bandgap (UWBG) Al0.75Ga0.25N channel metal-insulator-semiconductor field-effect transistors (MISFETs) with heterostructure engineered low-resistance ohmic contacts. The low intrinsic electron affinity of AlN (0.6 eV) leads to large Schottky barriers at the metal-AlGaN interface, resulting in highly resistive ohmic contacts. In this work, we use a reverse compositional graded n++ AlGaN contact layer to achieve upward electron affinity grading, leading to a low specific contact resistance (ρsp) of 1.9 × 10-6 Ω cm2 to n-Al0.75Ga0.25N channels (bandgap ˜5.3 eV) with non-alloyed contacts. We also demonstrate UWBG Al0.75Ga0.25N channel MISFET device operation employing the compositional graded n++ ohmic contact layer and 20 nm atomic layer deposited Al2O3 as the gate-dielectric.

  3. Effect of different EBL structures on deep violet InGaN laser diodes performance

    NASA Astrophysics Data System (ADS)

    Alahyarizadeh, Gh.; Amirhoseiny, M.; Hassan, Z.

    2016-01-01

    Some specific designs on band structure near the active region, including the modifications of the material and thickness of the electron blocking layer (EBL), in the deep violet InGaN laser diodes (LDs) are investigated numerically with the ISE TCAD software. The analyses focus on electron and hole carrier injection efficiency, carrier distributions, electron leakage, and radiative recombination, subsequently, optical material gain, and optical intensity. The results indicate that for the ternary AlGaN EBL, the lowest threshold current and the highest output power, slope efficiency, and DQE have been obtained for the 15 nm EBL thickness with 0.22 Al mole fraction. In addition, a comparative study has been conducted on the performance characteristics of the LD structures with a ternary AlGaN EBL and a quaternary AlInGaN EBL with an output emission wavelength at 390 nm. The simulation results showed that the using quaternary AlInGaN EBL effectively improves the LD performance characteristics.

  4. Effect of V/III ratio on the structural and optical properties of self-catalysed GaAs nanowires

    NASA Astrophysics Data System (ADS)

    Ahtapodov, L.; Munshi, A. M.; Nilsen, J. S.; Reinertsen, J. F.; Dheeraj, D. L.; Fimland, B. O.; van Helvoort, A. T. J.; Weman, H.

    2016-11-01

    The performance of GaAs nanowire (NW) devices depends critically on the presence of crystallographic defects in the NWs such as twinning planes and stacking faults, and considerable effort has been devoted to understanding and preventing the occurrence of these. For self-catalysed GaAs NWs grown by molecular beam epitaxy (MBE) in particular, there are in addition other types of defects that may be just as important for NW-based optoelectronic devices. These are the point defects such as the As vacancy and the Ga antisite occurring due to the inherently Ga-rich conditions of the self-catalysed growth. Here we demonstrate experimentally the effects of these point defects on the optical properties of GaAs/AlGaAs core–shell NWs grown by self-catalysed MBE. The present results enable insight into the role of the point defects both on their own and in conjunction with crystallographic planar defects.

  5. Performance of AlGaN/GaN Nanowire Omega-Shaped-Gate Fin-Shaped Field-Effect Transistor.

    PubMed

    Lee, Dong-Gi; Sindhuri, V; Jo, Young-Woo; Son, Dong-Hyeok; Kang, Hee-Sung; Lee, Jae-Hong; Lee, Jae-Hoon; Cristoloveanu, Sorin; Im, Ki-Sik; Lee, Jung-Hee

    2016-05-01

    The AlGaN/GaN nanowire omega-shaped-gate FinFET have been successfully fabricated demonstrating much improved performance compared to conventional AlGaN/GaN MISHFET. The AlGaN/GaN omega-shaped-gate FinFET exhibited the remarkable on-state performances, such as maximum drain current of 1.1 A/mm, low on-resistance, and low current collapse compared to that of the conventional device structure. In addition, the excellent off-state performances were measured: low off-state leakage current as low as -10(-10) mA, the theoretical SS value of -62 mV/dec, and high I(ON)/I(OFF) ratio (-10(9)). Improved dc performances were obtained for omega-shaped-gate structure due to the fully depletion of the active fin body and perfectly separation of the depleted fin from the underlying thick GaN buffer layer. Furthermore, the additional reason for the enhanced device performance of the proposed device is the improved gate controllability compared to the conventional MISHFET. The proposed nano-structure device is very promising candidate for the steep switching device applications.

  6. Performance of AlGaN/GaN Nanowire Omega-Shaped-Gate Fin-Shaped Field-Effect Transistor.

    PubMed

    Lee, Dong-Gi; Sindhuri, V; Jo, Young-Woo; Son, Dong-Hyeok; Kang, Hee-Sung; Lee, Jae-Hong; Lee, Jae-Hoon; Cristoloveanu, Sorin; Im, Ki-Sik; Lee, Jung-Hee

    2016-05-01

    The AlGaN/GaN nanowire omega-shaped-gate FinFET have been successfully fabricated demonstrating much improved performance compared to conventional AlGaN/GaN MISHFET. The AlGaN/GaN omega-shaped-gate FinFET exhibited the remarkable on-state performances, such as maximum drain current of 1.1 A/mm, low on-resistance, and low current collapse compared to that of the conventional device structure. In addition, the excellent off-state performances were measured: low off-state leakage current as low as -10(-10) mA, the theoretical SS value of -62 mV/dec, and high I(ON)/I(OFF) ratio (-10(9)). Improved dc performances were obtained for omega-shaped-gate structure due to the fully depletion of the active fin body and perfectly separation of the depleted fin from the underlying thick GaN buffer layer. Furthermore, the additional reason for the enhanced device performance of the proposed device is the improved gate controllability compared to the conventional MISHFET. The proposed nano-structure device is very promising candidate for the steep switching device applications. PMID:27483869

  7. Si doping effects on (In,Ga)N nanowires

    SciTech Connect

    Kamimura, J. Ramsteiner, M.; Geelhaar, L.; Riechert, H.

    2014-12-28

    Si doped (In,Ga)N nanowires (In content up to 0.4) are grown on Si(111) substrates by plasma-assisted molecular beam epitaxy. By increasing the Si doping level, coalescence between nanowires is reduced and a more uniform morphology is obtained. The Raman spectra from highly doped samples show a characteristic broad band in the optical phonon frequency range, which became more prominent at higher doping levels. This Raman band can be explained by plasmon-phonon scattering from a free electron gas with strong wave-vector nonconservation, providing evidence for successful n-type doping. The measured plasmon-phonon modes are explained by lineshape simulations taking into account the simultaneous contribution of both the charge-density fluctuation and the impurity induced Fröhlich scattering mechanisms. The according lineshape analysis allows for an estimate of the carrier concentration.

  8. Effect of illumination uniformity on GaAs photoconductive switches

    SciTech Connect

    Donaldson, W.R.; Mu, L. . Lab. for Laser Energetics)

    1994-12-01

    The dynamic behavior of a GaAs photoconductive switch was studied with an electro-optic imaging system during the first 2 ns after optical illumination. The switch behavior changed as a function of the spatial distribution of the optical illumination. Symmetric and asymmetric illumination schemes were investigated experimentally with their electro-optic imaging system. The electric fields were significantly enhanced in the regions of low photo-carrier density. Approximately 1 ns after illumination the simple longitudinal variation of the electric field gave way to nonuniform transverse structure. The experimental results were modeled by treating the switch as an integral part of a transmission line consisting of discrete elements. The experimental results matched the predictions of the transmission-line model in terms of the electric-field enhancements and efficiency.

  9. Segregation and temperature effect on the atomic structure of Bi30Ga70 liquid alloy

    NASA Astrophysics Data System (ADS)

    Sbihi, D. Es; Grosdidier, B.; Kaban, I.; Gruner, S.; Hoyer, W.; Gasser, J.-G.

    2009-06-01

    We investigate the structure of liquid monotectic alloy Bi30Ga70 above and below the critical point. The three-dimensional structure at 265 °C is modelled by means of the reverse Monte Carlo simulation technique using neutron and x-ray diffraction experimental data. It is shown that atomic segregation on the short-range scale exists in the liquid Bi30Ga70 slightly above the critical temperature (TC = 262 °C). We present also the structure factors of Bi30Ga70 liquid alloy under the critical point at 240 and 230 °C obtained with neutron diffraction to highlight the temperature effect in the atomic structure.

  10. Segregation and temperature effect on the atomic structure of Bi(30)Ga(70) liquid alloy.

    PubMed

    Sbihi, D Es; Grosdidier, B; Kaban, I; Gruner, S; Hoyer, W; Gasser, J-G

    2009-06-17

    We investigate the structure of liquid monotectic alloy Bi(30)Ga(70) above and below the critical point. The three-dimensional structure at 265 °C is modelled by means of the reverse Monte Carlo simulation technique using neutron and x-ray diffraction experimental data. It is shown that atomic segregation on the short-range scale exists in the liquid Bi(30)Ga(70) slightly above the critical temperature (T(C) = 262 °C). We present also the structure factors of Bi(30)Ga(70) liquid alloy under the critical point at 240 and 230 °C obtained with neutron diffraction to highlight the temperature effect in the atomic structure. PMID:21693940

  11. Measurement of the electrostatic edge effect in wurtzite GaN nanowires

    SciTech Connect

    Henning, Alex; Rosenwaks, Yossi; Klein, Benjamin; Bertness, Kris A.; Blanchard, Paul T.; Sanford, Norman A.

    2014-11-24

    The electrostatic effect of the hexagonal corner on the electronic structure in wurtzite GaN nanowires (NWs) was directly measured using Kelvin probe force microscopy (KPFM). By correlating electrostatic simulations with the measured potential difference between the nanowire face and the hexagonal vertices, the surface state concentration and band bending of GaN NWs were estimated. The surface band bending is important for an efficient design of high electron mobility transistors and for opto-electronic devices based on GaN NWs. This methodology provides a way to extract NW parameters without making assumptions concerning the electron affinity. We are taking advantage of electrostatic modeling and the high precision that KPFM offers to circumvent a major source of uncertainty in determining the surface band bending.

  12. Investigation of the thickness effect to impedance analysis results AlGaN acoustic sensor

    NASA Astrophysics Data System (ADS)

    Özen, Soner; Bilgiç, Eyüp; Gülmez, Gülay; Şenay, Volkan; Pat, Suat; Korkmaz, Şadan; Mohammadigharehbagh, Reza

    2016-03-01

    In this study, AlGaN acoustic sensors were deposited on aluminum metal substrate by thermionic vacuum arc (TVA) method, for the first time. Impedance analyses of the fabricated acoustic sensors were investigated for the determining of effect of the nano layer thickness. Thickness values are very close to each others. Fabricated sensors have been fabricated from AlGaN deposited on aluminum substrates. Gallium materials are used in many applications for optoelectronic device and semiconductor technology. Thermionic vacuum arc is the deposition technology for the variously materials and applications field. TVA production parameters and some properties of the deposited layers were investigated. TVA is the fast deposition technology for the gallium compounds and doped gallium compounds. Obtained results that AlGaN layer are very promising material for an acoustic sensor but also TVA is proper fast technology for the production.

  13. Surface-Effect-Induced Optical Bandgap Shrinkage in GaN Nanotubes.

    PubMed

    Park, Young S; Lee, Geunsik; Holmes, Mark J; Chan, Christopher C S; Reid, Benjamin P L; Alexander-Webber, Jack A; Nicholas, Robin J; Taylor, Robert A; Kim, Kwang S; Han, Sang W; Yang, Woochul; Jo, Y; Kim, J; Im, Hyunsik

    2015-07-01

    We investigate nontrivial surface effects on the optical properties of self-assembled crystalline GaN nanotubes grown on Si substrates. The excitonic emission is observed to redshift by ∼100 meV with respect to that of bulk GaN. We find that the conduction band edge is mainly dominated by surface atoms, and that a larger number of surface atoms for the tube is likely to increase the bandwidth, thus reducing the optical bandgap. The experimental findings can have important impacts in the understanding of the role of surfaces in nanostructured semiconductors with an enhanced surface/volume ratio.

  14. Improved modeling of GaN HEMTs for predicting thermal and trapping-induced-kink effects

    NASA Astrophysics Data System (ADS)

    Jarndal, Anwar; Ghannouchi, Fadhel M.

    2016-09-01

    In this paper, an improved modeling approach has been developed and validated for GaN high electron mobility transistors (HEMTs). The proposed analytical model accurately simulates the drain current and its inherent trapping and thermal effects. Genetic-algorithm-based procedure is developed to automatically find the fitting parameters of the model. The developed modeling technique is implemented on a packaged GaN-on-Si HEMT and validated by DC and small-/large-signal RF measurements. The model is also employed for designing and realizing a switch-mode inverse class-F power amplifier. The amplifier simulations showed a very good agreement with RF large-signal measurements.

  15. The effect of optical intensity on the photoresponse of the GaAs MESFET

    NASA Astrophysics Data System (ADS)

    Paolella, Arthur; Herczfeld, Peter R.; Madjar, Asher

    1993-01-01

    Results of measurements of the optical response of a GaAs MESFET as a function of the incident optical intensity are reported. It is found that the photoresponse gain of the MESFET can be increased by 10 dB as the optical intensity is decreased; the bandwidth of the MESFET can be increased by an order of magnitude with an increase in optical power. It is concluded that the MESFET can be effectively used as an optical detector in GaAS-based MMICs.

  16. Modeling the effect of deep impurity ionization on GaAs photoconductive switches

    SciTech Connect

    Yee, J.H.; Khanaka, G.H.; Druce, R.L.; Pocha, M.D.

    1992-01-01

    The ionization coefficient of deep traps in GaAs is determined from a gas breakdown model together with the recent experimental data obtained at LLNL (Lawrence Livermore National Laboratory) and Boeing. Using this coefficient in our nonlinear device transport code, we have investigated theoretically the nonlinear switching phenomena in GaAs devices. The results obtained from our investigations show that if we take into consideration the effect of the field ionization of the deep traps, we can show how the Lock-On'' phenomena could occur in the device.

  17. Exciton kinetics and few particle effects in self-assembled GaAs-based quantum dashes

    SciTech Connect

    SePk, G.; Musial, A.; Podemski, P.; Syperek, M.; Misiewicz, J.; Loeffler, A.; Hoefling, S.; Worschech, L.; Forchel, A.

    2010-05-15

    We report on the emission properties of single molecular-beam-epitaxially grown InGaAs/GaAs quantum dashes. Supported by a few level rate equation model it has been revealed a decreased exciton to biexciton radiative lifetimes ratio being a fingerprint of a weak carrier confinement. Furthermore, a biexciton sideband, connected with the Coulomb interaction of quantum dash biexciton with excitons confined in the wetting layer (WL), has been observed in photoluminescence (PL). Both the effects have found a confirmation in direct measurements of PL decay times, including long radiative lifetimes of the WL states which appeared to have a localized character.

  18. Long-term temperature effects on GaAs solar cells

    NASA Technical Reports Server (NTRS)

    Heinbockel, J. H.; Hong, K. H.

    1979-01-01

    The thermal degradation of AlGaAs solar cells resulting from a long-term operation in a space environment is investigated. The solar cell degradation effects caused by zinc and aluminum diffusion as well as deterioration by arsenic evaporation are presented. Also, the results are presented of experimental testing and measurements of various GaAs solar cell properties while the solar cell was operating in the temperature range of 27 C to 350 C. In particular, the properties of light current voltage curves, dark current voltage curves, and spectral response characteristics are given. Finally, some theoretical models for the annealing of radiation damage over various times and temperatures are included.

  19. Effects of trigger laser pulse width on the jitter time of GaAs photoconductive semiconductor switch.

    PubMed

    Shi, Wei; Gui, Huaimeng; Zhang, Lin; Ma, Cheng; Li, Mengxia; Xu, Ming; Wang, Luyi

    2013-07-01

    The effects of trigger laser pulse width on the jitter time of a GaAs photoconductive semiconductor switch (PCSS) is investigated in the experiment. The laser is split into two optical beams by a cross grating to excite two 3 mm gap GaAs PCSSs in parallel at the same time. This work reveals that the jitter time of the GaAs PCSS is reduced as the trigger laser pulse width decreases. Our results overcome a significant obstacle that hinders the testing and theory of GaAs PCSSs in high-time-precision synchronous control.

  20. Gate frequency sweep: An effective method to evaluate the dynamic performance of AlGaN/GaN power heterojunction field effect transistors

    SciTech Connect

    Santi, C. de; Meneghini, M. Meneghesso, G.; Zanoni, E.

    2014-08-18

    With this paper we propose a test method for evaluating the dynamic performance of GaN-based transistors, namely, gate-frequency sweep measurements: the effectiveness of the method is verified by characterizing the dynamic performance of Gate Injection Transistors. We demonstrate that this method can provide an effective description of the impact of traps on the transient performance of Heterojunction Field Effect Transistors, and information on the properties (activation energy and cross section) of the related defects. Moreover, we discuss the relation between the results obtained by gate-frequency sweep measurements and those collected by conventional drain current transients and double pulse characterization.