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Sample records for trapping implantation-induced vacancies

  1. Correlated lifetimes of free paraexcitons and excitons trapped at oxygen vacancies in cuprous oxide

    International Nuclear Information System (INIS)

    Koirala, Sandhaya; Naka, Nobuko; Tanaka, Koichiro

    2013-01-01

    We have studied transients of luminescence due to free excitons and excitons trapped at oxygen vacancies in cuprous oxide. We find that both trapped and free paraexcitons have lifetime dependent on temperature and on the oxygen concentration. By using samples containing much less copper vacancies relative to oxygen vacancies, we find out the direct correlation between the free paraexciton lifetime and trapped exciton lifetime. - Highlights: ► We have investigated trapping of free excitons at oxygen vacancies in cuprous oxide. ► Lifetimes of free and trapped excitons exhibit correlative temperature dependence. ► Four-level model with the activation energy of 33 meV well explains the observation. ► Comparison is made using the four samples with different vacancy concentrations. ► We clarified the crucial role of the oxygen vacancy in shortening the lifetimes.

  2. Trapping of positron in gallium arsenide: evidencing of vacancies and of ions with a negative charge

    International Nuclear Information System (INIS)

    Pierre, F.

    1989-12-01

    Vacancy type defects in Ga As as grown and irradiated by electrons are characterized by lifetime of positrons. Positron lifetime increases from 230 ps to 258 and 295 ps in presence of native vacancies in n type Ga As. Configuration of native vacancies changes when Fermi level crosses energy levels localized in the forbidden zone at 0.035eV and at 0.10eV from the bottom of the conduction band. Native vacancies are identified to arsenic vacancies with or without other point defects. Positron lifetime increases from 230 to 260 ps in presence of vacancies produced by low temperature irradiation negative ions are also produced. In irradiated Ga As, these ions trap positrons in competition with vacancies produced by irradiation, showing they have a negative charge. Two annealing zones between 180-300K and 300-600K are presented by vacancies. Ions do not anneal below ambient temperature. Vacancies and negative ions are identified respectively to gallium vacancies and gallium antisite [fr

  3. Positronium bloch function, and trapping of positronium in vacancies, in ice

    International Nuclear Information System (INIS)

    Mogensen, O.E.; Eldrup, M.

    1977-08-01

    Positron annihilation techniques were used to study the behaviour of positronium (Ps) in pure light and heavy ice in the temperature interval -185 2 was extracted by very detailed computer analyses. A nearly-free-Ps theory, including phonon influence, could not explain the temperature dependence of /Asub(g vector)/ 2 . The Ps trapping in vacancies could not be explained in detail in terms of several models, including the simple 'trapping model'. A main difficulty was the fact that para-Ps and ortho-Ps are trapped at roughly the same amount at a certain vacancy concentration. Our results imply a high (several ppm) vacancy concentration at the melting point in ice in agreement with other independent estimates. This fact might introduce pronounced changes in currently accepted theories of the electrical properties of ice. (author)

  4. Loading an Optical Trap with Diamond Nanocrystals Containing Nitrogen-Vacancy Centers from a Surface

    Science.gov (United States)

    Hsu, Jen-Feng; Ji, Peng; Dutt, M. V. Gurudev; D'Urso, Brian R.

    2015-03-01

    We present a simple and effective method of loading particles into an optical trap. Our primary application of this method is loading photoluminescent material, such as diamond nanocrystals containing nitrogen-vacancy (NV) centers, for coupling the mechanical motion of the trapped crystal with the spin of the NV centers. Highly absorptive material at the trapping laser frequency, such as tartrazine dye, is used as media to attach nanodiamonds and burn into a cloud of air-borne particles as the material is swept near the trapping laser focus on a glass slide. Particles are then trapped with the laser used for burning or transferred to a second laser trap at a different wavelength. Evidence of successful loading diamond nanocrystals into the trap presented includes high sensitivity of the photoluminecscence (PL) to the excitation laser and the PL spectra of the optically trapped particles

  5. On the positron-trapping states of metal mono-vacancies

    International Nuclear Information System (INIS)

    Sankar, S.; Iyakutti, K.

    1987-07-01

    A model calculation based on the static dielectric screening theory has been performed to estimate the probable number of positron-trapping levels in metal mono-vacancies and it is shown that there cannot be more than one. (author). 8 refs, 1 tab

  6. Hydrogen isotope in erbium oxide: Adsorption, penetration, diffusion, and vacancy trapping

    International Nuclear Information System (INIS)

    Mao, Wei; Chikada, Takumi; Suzuki, Akihiro; Terai, Takayuki; Matsuzaki, Hiroyuki

    2015-01-01

    Highlights: • H adsorption on cubic Er 2 O 3 surface results in electron transfer from H to the surface. • The H penetration energy of at least 1.6 eV is required for cubic Er 2 O 3 surface. • The dominated mechanisms of H diffusion in bulk Er 2 O 3 are elucidated. • H diffusion near or at vacancies in Er 2 O 3 is an exothermic reaction. - Abstract: In this study, we report results using first-principles density functional theory calculations for four critical aspects of the interaction: H adsorption on Er 2 O 3 surface, surface-to-subsurface penetration of H into Er 2 O 3 , bulk diffusion of H in Er 2 O 3 , and trapping of H at vacancies. We identify surface stable adsorption positions and find that H prefers to transfer electrons to the surfaces and form covalent bonds with the nearest neighboring four oxygen atoms. For low surface coverage of H as in our case (0.89 × 10 14 H/cm 2 ), a penetration energy of at least 1.60 eV is required for cubic Er 2 O 3 surfaces. Further, the H diffusion barrier between the planes defined by Er 2 O 3 units along the favorable <1 1 1> direction is found to be very small – 0.16 eV – whereas higher barriers of 0.41 eV and 1.64 eV are required for diffusion across the planes, somewhat higher than the diffusion energy barrier of 0.20 eV observed experimentally at 873 K. In addition, we predict that interstitial H is exothermically trapped when it approaches a vacancy with the vacancy defect behaving as an electron trap since the H-vacancy defect is found to be more stable than the intrinsic defect

  7. Deuterium trapping at vacancy clusters in electron/neutron-irradiated tungsten studied by positron annihilation spectroscopy

    Science.gov (United States)

    Toyama, T.; Ami, K.; Inoue, K.; Nagai, Y.; Sato, K.; Xu, Q.; Hatano, Y.

    2018-02-01

    Deuterium trapping at irradiation-induced defects in tungsten, a candidate material for plasma facing components in fusion reactors, was revealed by positron annihilation spectroscopy. Pure tungsten was electron-irradiated (8.5 MeV at ∼373 K and to a dose of ∼1 × 10-3 dpa) or neutron-irradiated (at 573 K to a dose of ∼0.3 dpa), followed by post-irradiation annealing at 573 K for 100 h in deuterium gas of ∼0.1 MPa. In both cases of electron- or neutron-irradiation, vacancy clusters were found by positron lifetime measurements. In addition, positron annihilation with deuterium electrons was demonstrated by coincidence Doppler broadening measurements, directly indicating deuterium trapping at vacancy-type defects. This is expected to cause significant increase in deuterium retention in irradiated-tungsten.

  8. Annihilation momentum density of positrons trapped at vacancy-type defects in metals and alloys

    International Nuclear Information System (INIS)

    Bansil, A.; Prasad, R.; Benedek, R.

    1988-01-01

    Positron annihilation, especially the angular correlation of annihilation radiation, is a powerful tool for investigating the electronic spectra of ordered as well as defected materials. The tendency of positrons to trap at vacancy-type defects should enable this technique to study the local environment of such defects. However, we need to develop a theoretical basis for calculating the two-photon annihilation momentum density rho/sub 2gamma/(p-vector). We have recently formulated and implemented a theory of rho/sub 2gamma/(p-vector) from vacancy-type defects in metals and alloys. This article gives an outline of our approach together with a few of our results. Section 2 summarizes the basic equations for evaluating rho/sub 2gamma/(p-vector). Our Green's function-based approach is nonperturbative and employs a realistic (one-particle) muffin-tin Hamiltonian for treating electrons and positrons. Section 3 presents and discusses rho/sub 2gamma/(p-vector) results for a mono-vacancy in Cu. We have neglected the effects of electron-positron correlations and of lattice distortion around the vacancy. Section 4 comments briefly on the question of treating defects such as divacancies and metal-impurity complexes in metals and alloys. Finally, in Section 5, we remark on the form of rho/sub 2gamma/(p-vector) for a mono-vacancy in jellium. 2 figs

  9. Double vacancy on BN layer: A natural trap for Hydrogen Molecule

    International Nuclear Information System (INIS)

    Arellano, J S

    2015-01-01

    A pair of vacancies, one of boron and other of nitrogen atom at a flat layer becomes a natural trap to capture a hydrogen molecule at the center of the cavity defined by the empty space left by the lack of a nitrogen and a boron atom at the perfect BN layer formed by 16 N atoms and 16 B atoms. The adsorption of the hydrogen molecule is compared with the equivalent graphene layer with a pair of carbon vacancies. The little increase in the BN cell parameter respect to the graphene cell parameter, besides the differences between N, B and C atoms helps to explain the easier adsorption on the defective BN layer

  10. Electron spin resonance of nitrogen-vacancy centers in optically trapped nanodiamonds

    Science.gov (United States)

    Horowitz, Viva R.; Alemán, Benjamín J.; Christle, David J.; Cleland, Andrew N.; Awschalom, David D.

    2012-01-01

    Using an optical tweezers apparatus, we demonstrate three-dimensional control of nanodiamonds in solution with simultaneous readout of ground-state electron-spin resonance (ESR) transitions in an ensemble of diamond nitrogen-vacancy color centers. Despite the motion and random orientation of nitrogen-vacancy centers suspended in the optical trap, we observe distinct peaks in the measured ESR spectra qualitatively similar to the same measurement in bulk. Accounting for the random dynamics, we model the ESR spectra observed in an externally applied magnetic field to enable dc magnetometry in solution. We estimate the dc magnetic field sensitivity based on variations in ESR line shapes to be approximately . This technique may provide a pathway for spin-based magnetic, electric, and thermal sensing in fluidic environments and biophysical systems inaccessible to existing scanning probe techniques. PMID:22869706

  11. Hydrogen isotope in erbium oxide: Adsorption, penetration, diffusion, and vacancy trapping

    Energy Technology Data Exchange (ETDEWEB)

    Mao, Wei, E-mail: mao@nuclear.jp [Department of Nuclear Engineering and Management, School of Engineering, The University of Tokyo, 2-11-16 Yayoi, Bunkyo-ku, Tokyo 113-8656 (Japan); The University Museum, The University of Tokyo, 2-11-16 Yayoi, Bunkyo-ku, Tokyo 113-0032 (Japan); Chikada, Takumi [Department of Chemistry, Graduate School of Science, Shizuoka University, 836 Ohya, Suruga-ku, Shizuoka 422-8529 (Japan); Suzuki, Akihiro [Nuclear Professional School, School of Engineering, The University of Tokyo, 2-22, Shirakata-shirane, Tokai, Naka 319-1188, Ibaraki (Japan); Terai, Takayuki [Department of Nuclear Engineering and Management, School of Engineering, The University of Tokyo, 2-11-16 Yayoi, Bunkyo-ku, Tokyo 113-8656 (Japan); Matsuzaki, Hiroyuki [The University Museum, The University of Tokyo, 2-11-16 Yayoi, Bunkyo-ku, Tokyo 113-0032 (Japan)

    2015-03-15

    Highlights: • H adsorption on cubic Er{sub 2}O{sub 3} surface results in electron transfer from H to the surface. • The H penetration energy of at least 1.6 eV is required for cubic Er{sub 2}O{sub 3} surface. • The dominated mechanisms of H diffusion in bulk Er{sub 2}O{sub 3} are elucidated. • H diffusion near or at vacancies in Er{sub 2}O{sub 3} is an exothermic reaction. - Abstract: In this study, we report results using first-principles density functional theory calculations for four critical aspects of the interaction: H adsorption on Er{sub 2}O{sub 3} surface, surface-to-subsurface penetration of H into Er{sub 2}O{sub 3}, bulk diffusion of H in Er{sub 2}O{sub 3}, and trapping of H at vacancies. We identify surface stable adsorption positions and find that H prefers to transfer electrons to the surfaces and form covalent bonds with the nearest neighboring four oxygen atoms. For low surface coverage of H as in our case (0.89 × 10{sup 14} H/cm{sup 2}), a penetration energy of at least 1.60 eV is required for cubic Er{sub 2}O{sub 3} surfaces. Further, the H diffusion barrier between the planes defined by Er{sub 2}O{sub 3} units along the favorable <1 1 1> direction is found to be very small – 0.16 eV – whereas higher barriers of 0.41 eV and 1.64 eV are required for diffusion across the planes, somewhat higher than the diffusion energy barrier of 0.20 eV observed experimentally at 873 K. In addition, we predict that interstitial H is exothermically trapped when it approaches a vacancy with the vacancy defect behaving as an electron trap since the H-vacancy defect is found to be more stable than the intrinsic defect.

  12. The influence of positron trapping at vacancies on a pattern of the Fermi surface of #betta#-brass studied by positron annihilation

    International Nuclear Information System (INIS)

    Rozenfeld, B.; Chabik, S.; Pajak, J.

    1982-01-01

    Angular correlations of positron annihilation quanta (ACPAQ) have been measured for differently oriented monocrystalline samples of the ordered #betta#-brass under conditions permitting the neglecting of the trapping of positrons at vacancies as well as in the case when almost all the positrons annihilate being trapped at vacancies. It has been shown that trapping of positrons at vacancies can make the observation of the directional anisotropy in electron momentum distribution impossible. (Auth.)

  13. Observation of Diamond Nitrogen-Vacancy Center Photoluminescence under High Vacuum in a Magneto-Gravitational Trap

    Science.gov (United States)

    Ji, Peng; Hsu, Jen-Feng; Lewandowski, Charles W.; Dutt, M. V. Gurudev; D'Urso, Brian

    2016-05-01

    We report the observation of photoluminescence from nitrogen-vacancy (NV) centers in diamond nanocrystals levitated in a magneto-gravitational trap. The trap utilizes a combination of strong magnetic field gradients and gravity to confine diamagnetic particles in three dimensions. The well-characterized NV centers in trapped diamond nanocrystals provide an ideal built-in sensor to measure the trap magnetic field and the temperature of the trapped diamond nanocrystal. In the future, the NV center spin state could be coupled to the mechanical motion through magnetic field gradients, enabling in an ideal quantum interface between NV center spin and the mechanical motion. National Science Foundation, Grant No. 1540879.

  14. Strong coupling between a single nitrogen-vacancy spin and the rotational mode of diamonds levitating in an ion trap

    Science.gov (United States)

    Delord, T.; Nicolas, L.; Chassagneux, Y.; Hétet, G.

    2017-12-01

    A scheme for strong coupling between a single atomic spin and the rotational mode of levitating nanoparticles is proposed. The idea is based on spin readout of nitrogen-vacancy centers embedded in aspherical nanodiamonds levitating in an ion trap. We show that the asymmetry of the diamond induces a rotational confinement in the ion trap. Using a weak homogeneous magnetic field and a strong microwave driving we then demonstrate that the spin of the nitrogen-vacancy center can be strongly coupled to the rotational mode of the diamond.

  15. Temperature dependence of positron trapping by vacancies, loops and voids in molybdenum

    International Nuclear Information System (INIS)

    Bentzon, M.D.; Linderoth, S.; Petersen, K.

    1985-01-01

    The temperature dependence of positron trapping by defects in molybdenum has been studied. By resolving positron lifetime spectra into three components, it has been possible to distinguish the temperature dependence of positron trapping into loops and voids. The results show that the positron trapping rate into voids depends linearly on temperature. The temperature dependence of positron trapping by loops can be interpreted as positrons being trapped by jogs, directly or via the dislocation line. The temperature dependence of positrons trapped by loops is argued mainly to be due to the trapping at the dislocation line, and not to detrapping. The observed temperature dependence of positron annihilation parameters in an electron irradiated sample (below stage III), is explained by competitive positron trapping in interstitial loops at low temperatures

  16. Passivation of interstitial and vacancy mediated trap-states for efficient and stable triple-cation perovskite solar cells

    Science.gov (United States)

    Mahmud, Md Arafat; Elumalai, Naveen Kumar; Upama, Mushfika Baishakhi; Wang, Dian; Gonçales, Vinicius R.; Wright, Matthew; Xu, Cheng; Haque, Faiazul; Uddin, Ashraf

    2018-04-01

    The current work reports the concurrent passivation of interstitial and oxygen vacancy mediated defect states in low temperature processed ZnO electron transport layer (ETL) via Ultraviolet-Ozone (UVO) treatment for fabricating highly efficient (maximum efficiency: 16.70%), triple cation based MA0.57FA0.38Rb0.05PbI3 (MA: methyl ammonium, FA: formamidinium, Rb: rubidium) perovskite solar cell (PSC). Under UV exposure, ozone decomposes to free atomic oxygen and intercalates into the interstitial and oxygen vacancy induced defect sites in the ZnO lattice matrix, which contributes to suppressed trap-assisted recombination phenomena in perovskite device. UVO treatment also reduces the content of functional hydroxyl group on ZnO surface, that increases the inter-particle connectivity and grain size of perovskite film on UVO treated ZnO ETL. Owing to this, the perovskite film atop UVO treated ZnO film exhibits reduced micro-strain and dislocation density values, which contribute to the enhanced photovoltaic performance of PSC with modified ZnO ETL. The modified PSCs exhibit higher recombination resistance (RRec) ∼40% compared to pristine ZnO ETL based control devices. Adding to the merit, the UVO treated ZnO PSC also demonstrates superior device stability, retaining about 88% of its initial PCE in the course of a month-long, systematic degradation study.

  17. Energy of charged states in the acetanilide crystal: Trapping of charge-transfer states at vacancies as a possible mechanism for optical damage

    Science.gov (United States)

    Tsiaousis, D.; Munn, R. W.

    2004-04-01

    Calculations for the acetanilide crystal yield the effective polarizability (16.6 Å3), local electric field tensor, effective dipole moment (5.41 D), and dipole-dipole energy (-12.8 kJ/mol). Fourier-transform techniques are used to calculate the polarization energy P for a single charge in the perfect crystal (-1.16 eV); the charge-dipole energy WD is zero if the crystal carries no bulk dipole moment. Polarization energies for charge-transfer (CT) pairs combine with the Coulomb energy EC to give the screened Coulomb energy Escr; screening is nearly isotropic, with Escr≈EC/2.7. For CT pairs WD reduces to a term δWD arising from the interaction of the charge on each ion with the change in dipole moment on the other ion relative to the neutral molecule. The dipole moments calculated by density-functional theory methods with the B3LYP functional at the 6-311++G** level are 3.62 D for the neutral molecule, changing to 7.13 D and 4.38 D for the anion and cation, relative to the center of mass. Because of the large change in the anion, δWD reaches -0.9 eV and modifies the sequence of CT energies markedly from that of Escr, giving the lowest two CT pairs at -1.98 eV and -1.41 eV. The changes in P and WD near a vacancy are calculated; WD changes for the individual charges because the vacancy removes a dipole moment and modifies the crystal dielectric response, but δWD and EC do not change. A vacancy yields a positive change ΔP that scatters a charge or CT pair, but the change ΔWD can be negative and large enough to outweigh ΔP, yielding traps with depths that can exceed 150 meV for single charges and for CT pairs. Divacancies yield traps with depths nearly equal to the sum of those produced by the separate vacancies and so they can exceed 300 meV. These results are consistent with a mechanism of optical damage in which vacancies trap optically generated CT pairs that recombine and release energy; this can disrupt the lattice around the vacancy, thereby favoring

  18. N+ ion-implantation-induced defects in ZnO studied with a slow positron beam

    International Nuclear Information System (INIS)

    Chen, Z Q; Sekiguchi, T; Yuan, X L; Maekawa, M; Kawasuso, A

    2004-01-01

    Undoped ZnO single crystals were implanted with multiple-energy N + ions ranging from 50 to 380 keV with doses from 10 12 to 10 14 cm -2 . Positron annihilation measurements show that vacancy defects are introduced in the implanted layers. The concentration of the vacancy defects increases with increasing ion dose. The annealing behaviour of the defects can be divided into four stages, which correspond to the formation and recovery of large vacancy clusters and the formation and disappearance of vacancy-impurity complexes, respectively. All the implantation-induced defects are removed by annealing at 1200 deg. C. Cathodoluminescence measurements show that the ion-implantation-induced defects act as nonradiative recombination centres to suppress the ultraviolet (UV) emission. After annealing, these defects disappear gradually and the UV emission reappears, which coincides with positron annihilation measurements. Hall measurements reveal that after N + implantation, the ZnO layer still shows n-type conductivity

  19. Radiation-induced defects in LiAlO{sub 2} crystals: Holes trapped by lithium vacancies and their role in thermoluminescence

    Energy Technology Data Exchange (ETDEWEB)

    Holston, M.S.; McClory, J.W.; Giles, N.C. [Department of Engineering Physics, Air Force Institute of Technology, Wright-Patterson Air Force Base, OH 45433 (United States); Halliburton, L.E., E-mail: Larry.Halliburton@mail.wvu.edu [Department of Physics and Astronomy, West Virginia University, Morgantown, WV 26506 (United States)

    2015-04-15

    Electron paramagnetic resonance (EPR) is used to identify the primary hole trap in undoped lithium aluminate (LiAlO{sub 2}) crystals. Our interest in this material arises because it is a candidate for radiation detection applications involving either optically stimulated luminescence (OSL) or thermoluminescence (TL). During an x-ray irradiation at room temperature, holes are trapped at oxygen ions adjacent to lithium vacancies. Large concentrations of these lithium vacancies are introduced into the crystal during growth. With the magnetic field along the [001] direction, the EPR spectrum from these trapped-hole centers consists of eleven lines, evenly spaced but with varying intensities, caused by nearly equal hyperfine interactions with two {sup 27}Al nuclei (I=5/2, 100% abundant). The g matrix is determined from the angular dependence of the EPR spectrum and has principal values of 2.0130, 2.0675, and 2.0015. These g shifts strongly support the model of a hole in a p orbital on an oxygen ion. The adjacent lithium vacancy stabilizes the hole on the oxygen ion. A sequence of pulsed thermal anneals above room temperature shows that the EPR spectrum from the holes trapped adjacent to the lithium vacancies disappears in the 90–120 °C range. The thermal decay of these hole centers directly correlates with an intense TL peak near 105 °C. Signals at lower magnetic field in the 9.4 GHz EPR spectra suggest that the electron trap associated with this TL peak at 105 °C may be a transition-metal-ion impurity, most likely Fe, located at a cation site. Additional less intense TL peaks are observed near 138, 176, and 278 °C. - Highlights: • Undoped LiAlO{sub 2} crystals are irradiated at room temperature with x-rays. • EPR is used to identify holes trapped at oxygen ions adjacent to lithium vacancies. • Thermal decay of the EPR spectrum correlates with an intense TL peak at 105 °C.

  20. Trapping of oxygen vacancies on twin walls of CaTiO3: a computer simulation study

    International Nuclear Information System (INIS)

    Calleja, Mark; Dove, Martin T; Salje, Ekhard K H

    2003-01-01

    We have studied the atomic structure of [001] 90 deg. rotation twin walls in orthorhombic CaTiO 3 (symmetry Pbnm) at low temperature (10 K) and their effects on oxygen vacancies. The wall thickness was found to be 2.3 nm at T || T c and it was found that it is energetically favourable for such vacancies to reside in the wall, particularly when bridging titania ions in the (001) plane. The binding energy of an oxygen vacancy in the wall with respect to the bulk is calculated to be ≤ 1.2 eV

  1. He implantation induced nanovoids in crystalline Si

    International Nuclear Information System (INIS)

    Kilpelaeinen, S.; Kuitunen, K.; Slotte, J.; Tuomisto, F.; Bruno, E.; Mirabella, S.; Priolo, F.

    2009-01-01

    Positron annihilation spectroscopy (PAS) in Doppler broadening mode was used to study the vacancy profile of crystalline Si after He and B implantation and subsequent annealing. In the He-implanted samples two different void layers were observed, one consisting of large voids at the projected range of He and another containing 'nanovoids' slightly larger than divacancies at roughly halfway between R p of He and the surface. The nanovoid layer was shown to be absent from samples co-implanted with B, implying that interstitials created during B implantation get trapped in the nanovoids and fill them, thus hindering interstitial-mediated B diffusion.

  2. HYDROGEN VACANCY INTERACTION IN TUNGSTEN

    NARCIS (Netherlands)

    FRANSENS, [No Value; ELKERIEM, MSA; PLEITER, F

    1991-01-01

    Hydrogen-vacancy interaction in tungsten was investigated by means of the perturbed angular correlation technique, using the isotope In-111 as a probe. Hydrogen trapping at an In-111-vacancy cluster manifests itself as a change of the local electric field gradient, which gives rise to an observable

  3. Synergistic effect of single-electron-trapped oxygen vacancies and carbon species on the visible light photocatalytic activity of carbon-modified TiO2

    International Nuclear Information System (INIS)

    Wang, Xiaodong; Xue, Xiaoxiao; Liu, Xiaogang; Xing, Xing; Li, Qiuye; Yang, Jianjun

    2015-01-01

    Carbon-modified TiO 2 (CT) nanoparticles were prepared via a two-step method of heat treatment without the resorcinol-formaldehyde (RF) polymer. As-prepared CT nanoparticles were characterized by means of X-ray diffraction (XRD), UV–Vis diffuse reflectance spectroscopy (UV–Vis/DRS), transmission electron microscopy (TEM), N 2 adsorption–desorption isotherms, thermal analysis (TA), electron spin resonance (ESR), and X-ray photoelectron spectroscopy (XPS). The visible light photocatalytic activities were evaluated on the basis of the degradation of methyl orange (MO). The synergistic effect of single-electron-trapped oxygen vacancies (SETOVs) and the carbon species on the visible light photocatalytic activities of the CT nanoparticles were discussed. It was found that the crystalline phase, the morphology, and particle size of the CT nanoparticles depended on the second heat-treatment temperature instead of the first heat-treatment temperature. The visible light photocatalytic activities were attributed to the synergistic effect of SETOVs and the carbon species, and also depended on the specific surface area of the photocatalysts. - Highlights: • Carbon-modified TiO 2 particles have been prepared without RF polymer. • The visible light photocatalytic activities of the particles have been evaluated. • The band gap energy structure of the carbon-modified TiO 2 has been proposed. • Synergistic effect of SETOVs and carbon species has been discussed. • The activities also depend on the specific surface area of the catalysts

  4. HYDROGEN VACANCY INTERACTION IN MOLYBDENUM

    NARCIS (Netherlands)

    Abd El Keriem, M.S.; van der Werf, D.P.; Pleiter, F

    1993-01-01

    Vacancy-hydrogen interaction in molybdenum was investigated by means of the perturbed angular correlation technique, using the isotope In-111 as a probe. The complex InV2 turned out to trap up to two hydrogen atoms: trapping of a single hydrogen atom gives rise to a decrease of the quadrupole

  5. Ion species dependence of the implantation-induced defects in ZnO studied by a slow positron beam

    International Nuclear Information System (INIS)

    Chen, Z.Q.; Maekawa, M.; Kawasuso, A.; Naramoto, H.

    2007-01-01

    In this work, we implanted B + , O + , Al + , and P + ions into ZnO with energy of 50-380 keV and total doses of 4 x 10 15 cm -2 for each ion. The implantation-induced defects and their thermal recovery were studied using a slow positron beam. Vacancy clusters are produced in all the implanted samples. It is found that the thermal recovery of these vacancies induced by different ions shows much difference. In case of B + and Al + -implantation, the vacancy clusters agglomerate to much larger size and might evolve to microvoids during annealing. However, for O + and P + ions, which are heavier than B + and Al + , the vacancies show a much weaker agglomeration process. The mechanism of such difference is discussed. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  6. N{sup +} ion-implantation-induced defects in ZnO studied with a slow positron beam

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Z Q [Japan Atomic Energy Research Institute, 1233 Watanuki, Takasaki, Gunma 370-1292, Japan (Japan); Sekiguchi, T [Nanomaterials Laboratory, National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047 (Japan); Yuan, X L [Nanomaterials Laboratory, National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047 (Japan); Maekawa, M [Japan Atomic Energy Research Institute, 1233 Watanuki, Takasaki, Gunma 370-1292, Japan (Japan); Kawasuso, A [Japan Atomic Energy Research Institute, 1233 Watanuki, Takasaki, Gunma 370-1292, Japan (Japan)

    2004-01-21

    Undoped ZnO single crystals were implanted with multiple-energy N{sup +} ions ranging from 50 to 380 keV with doses from 10{sup 12} to 10{sup 14} cm{sup -2}. Positron annihilation measurements show that vacancy defects are introduced in the implanted layers. The concentration of the vacancy defects increases with increasing ion dose. The annealing behaviour of the defects can be divided into four stages, which correspond to the formation and recovery of large vacancy clusters and the formation and disappearance of vacancy-impurity complexes, respectively. All the implantation-induced defects are removed by annealing at 1200 deg. C. Cathodoluminescence measurements show that the ion-implantation-induced defects act as nonradiative recombination centres to suppress the ultraviolet (UV) emission. After annealing, these defects disappear gradually and the UV emission reappears, which coincides with positron annihilation measurements. Hall measurements reveal that after N{sup +} implantation, the ZnO layer still shows n-type conductivity.

  7. Vacancies in thermal equilibrium in Nb

    International Nuclear Information System (INIS)

    Nielsen, B.; Lynn, K.G.; Hurst, J.; Vehanen, A.; Schultz, P.J.

    1985-06-01

    We have measured the diffusion of positrons in Nb(110) in the temperature range from 300K to 2450K utilizing a variable energy positron beam. The purpose was to study the vacancy formation. However, no significant sign of vacancy trapping was observed. This could be due to a high detrapping rate caused by a low positron binding energy or due to a high vacancy formation enthalpy H/sub IV//sup F/. The last possibility is consistent with recent studies of the vacancy migration and with calculation of the positron binding energy. In this case we find the H/sub IV//sup F/ > 3 eV

  8. Ion species dependence of the implantation-induced defects in ZnO studied by a slow positron beam

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Z.Q. [Department of Physics, Wuhan University (China); Maekawa, M.; Kawasuso, A.; Naramoto, H. [Advanced Science Research Center, Japan Atomic Energy Agency, Takasaki, Gunma (Japan)

    2007-07-01

    In this work, we implanted B{sup +}, O{sup +}, Al{sup +}, and P{sup +} ions into ZnO with energy of 50-380 keV and total doses of 4 x 10{sup 15} cm{sup -2} for each ion. The implantation-induced defects and their thermal recovery were studied using a slow positron beam. Vacancy clusters are produced in all the implanted samples. It is found that the thermal recovery of these vacancies induced by different ions shows much difference. In case of B{sup +} and Al{sup +}-implantation, the vacancy clusters agglomerate to much larger size and might evolve to microvoids during annealing. However, for O{sup +} and P{sup +} ions, which are heavier than B{sup +} and Al{sup +}, the vacancies show a much weaker agglomeration process. The mechanism of such difference is discussed. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  9. Vacancy-acceptor complexes in germanium produced by ion implantation

    Energy Technology Data Exchange (ETDEWEB)

    Feuser, U.; Vianden, R. (Inst. fuer Strahlen- und Kernphysik, Univ. Bonn (Germany)); Alves, E.; Silva, M.F. da (Dept. de Fisica, ICEN/LNETI, Sacavem (Portugal)); Szilagyi, E.; Paszti, F. (Central Research Inst. for Physics, Hungarian Academy of Sciences, Budapest (Hungary)); Soares, J.C. (Centro de Fisica Nuclear, Univ. Lisbon (Portugal))

    1991-07-01

    Combining results obtained by the {gamma}-{gamma} perturbed angular correlation method, Rutherford backscattering and elastic recoil detection of hydrogen, a defect complex formed in germanium by indium implantation is identified as a vacancy trapped by the indium probe. (orig.).

  10. Ion implantation induced blistering of rutile single crystals

    Energy Technology Data Exchange (ETDEWEB)

    Xiang, Bing-Xi [School of Physics, Shandong University, Jinan, Shandong 250100 (China); Jiao, Yang [College of Physics and Electronics, Shandong Normal University, Jinan, Shandong 250100 (China); Guan, Jing [School of Physics, Shandong University, Jinan, Shandong 250100 (China); Wang, Lei [School of Physics, Shandong University, Jinan, Shandong 250100 (China); Key Laboratory of Nanodevices and Applications, Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences (China)

    2015-07-01

    The rutile single crystals were implanted by 200 keV He{sup +} ions with a series fluence and annealed at different temperatures to investigate the blistering behavior. The Rutherford backscattering spectrometry, optical microscope and X-ray diffraction were employed to characterize the implantation induced lattice damage and blistering. It was found that the blistering on rutile surface region can be realized by He{sup +} ion implantation with appropriate fluence and the following thermal annealing.

  11. Vacancy supersaturations produced by high-energy ion implantation

    International Nuclear Information System (INIS)

    Venezia, V.C.; Eaglesham, D.J.; Jacobson, D.C.; Gossmann, H.J.

    1998-01-01

    A new technique for detecting the vacancy clusters produced by high-energy ion implantation into silicon is proposed and tested. This technique takes advantage of the fact that metal impurities, such as Au, are gettered near one-half of the projected range (1/2 R p ) of MeV implants. The vacancy clustered region produced by a 2 MeV Si + implant into silicon has been labeled with Au diffused in from the front surface. The trapped Au was detected by Rutherford backscattering spectrometry (RBS) to profile the vacancy clusters. Cross section transmission electron microscopy (XTEM) analysis shows that the Au in the region of vacancy clusters is in the form of precipitates. By annealing MeV implanted samples prior to introduction of the Au, changes in the defect concentration within the vacancy clustered region were monitored as a function of annealing conditions

  12. Vacancies and negative ions in GaAs

    International Nuclear Information System (INIS)

    Corbel, C.

    1991-01-01

    We use positron lifetime studies performed in GaAs materials to show the defect properties which can be investigated by implanting positive positrons in semiconductors. The studies concern native and electron irradiation induced defects. These studies show that vacancy charge state and vacancy ionization levels can be determined from positron annihilation. They show also that positrons are trapped by negative ions and give information on their concentration

  13. First-principles study of intrinsic vacancy defects in Sr2MgSi2O7 phosphorescent host material

    Science.gov (United States)

    Duan, H.; Dong, Y. Z.; Huang, Y.; Hu, Y. H.; Chen, X. S.

    2016-01-01

    Electronic structures of intrinsic vacancy defects in Sr2MgSi2O7 phosphorescent host material are investigated using first-principles calculations. Si vacancies are too high in energy to play any role in the persistent luminescence of Sr2MgSi2O7 phosphor. Mg vacancies form easier than Sr vacancies as a result of strain relief. Among all the vacancies, O1 vacancies stand out as a likely candidate because they are the most favorable in energy and introduce an empty triply degenerate state just below the CBM and a fully-occupied singlet state at ~1 eV above the VBM, constituting in this case effective hole trap level and electron trap levels, respectively. Mg vacancies are unlikely to explain the persistent luminescence because of its too shallow electron trap level but they may compensate the hole trap associated with O1 vacancies. We yield consistent evidence for the defect physics of these vacancy defects on the basis of the equilibrium properties of Sr2MgSi2O7, total-energy calculations, and electronic structures. The persistent luminescence mechanism of Sr2MgSi2O7:Eu2+, Dy3+ phosphor is also discussed based on our results for O1 vacancies trap center. Our results provide a guide to more refined experiments to control intrinsic traps, whereby probing synthetic strategies toward new improved phosphors.

  14. Deuterium trapping in tungsten

    Science.gov (United States)

    Poon, Michael

    Tungsten is one of the primary material candidates being investigated for use in the first-wall of a magnetic confinement fusion reactor. An ion accelerator was used to simulate the type of ion interaction that may occur at a plasma-facing material. Thermal desorption spectroscopy (TDS) was the primary tool used to analyze the effects of the irradiation. Secondary ion mass spectroscopy (SIMS) was used to determine the distribution of trapped D in the tungsten specimen. The tritium migration analysis program (TMAP) was used to simulate thermal desorption profiles from the D depth distributions. Fitting of the simulated thermal desorption profiles with the measured TDS results provided values of the D trap energies. Deuterium trapping in single crystal tungsten was studied as a function of the incident ion fluence, ion flux, irradiation temperature, irradiation history, and surface impurity levels during irradiation. The results show that deuterium was trapped at vacancies and voids. Two deuterium atoms could be trapped at a tungsten vacancy, with trapping energies of 1.4 eV and 1.2 eV for the first and second D atoms, respectively. In a tungsten void, D is trapped as atoms adsorbed on the inner walls of the void with a trap energy of 2.1 eV, or as D2 molecules inside the void with a trap energy of 1.2 eV. Deuterium trapping in polycrystalline tungsten was also studied as a function of the incident fluence, irradiation temperature, and irradiation history. Deuterium trapping in polycrystalline tungsten also occurs primarily at vacancies and voids with the same trap energies as in single crystal tungsten; however, the presence of grain boundaries promotes the formation of large surface blisters with high fluence irradiations at 500 K. In general, D trapping is greater in polycrystalline tungsten than in single crystal tungsten. To simulate mixed materials comprising of carbon (C) and tungsten, tungsten specimens were pre-irradiated with carbon ions prior to D

  15. Deuterium trapping in tungsten

    International Nuclear Information System (INIS)

    Poon, M.

    2004-01-01

    Tungsten is one of the primary material candidates being investigated for use in the first-wall of a magnetic confinement fusion reactor. An ion accelerator was used to simulate the type of ion interaction that may occur at a plasma-facing material. Thermal desorption spectroscopy (TDS) was the primary tool used to analyze the effects of the irradiation Secondary ion mass spectroscopy (SIMS) was used to determine the distribution of trapped D in the tungsten specimen. The tritium migration analysis program (TMAP) was used to simulate thermal desorption profiles from the D depth distributions. Fitting of the simulated thermal desorption profiles with the measured TDS results provided values of the D trap energies. . Deuterium trapping in single crystal tungsten was studied as a function of the incident ion fluence, ion flux, irradiation temperature, irradiation history, and surface impurity levels during irradiation The results show that deuterium was trapped at vacancies and voids. Two deuterium atoms could be trapped at a tungsten vacancy, with trapping energies of 1.4 eV and 1.2 eV for the first and second D atoms, respectively. In a tungsten void, D is trapped as atoms adsorbed on the inner walls of the void with a trap energy of 2.1 eV, or as D 2 molecules inside the void with a trap energy of 1.2 eV. . Deuterium trapping in polycrystalline tungsten was also studied as a function of the incident fluence, irradiation temperature, and irradiation history. Deuterium trapping in polycrystalline tungsten also occurs primarily at vacancies and voids with the same trap energies as in single crystal tungsten; however, the presence of grain boundaries promotes the formation of large surface blisters with high fluence irradiations at 500 K. In general, D trapping is greater in polycrystalline tungsten than in single crystal tungsten. To simulate mixed materials comprising of carbon (C) and tungsten, tungsten specimens were pre-irradiated with carbon ions prior to D

  16. Deuterium trapping in tungsten

    Energy Technology Data Exchange (ETDEWEB)

    Poon, M

    2004-07-01

    Tungsten is one of the primary material candidates being investigated for use in the first-wall of a magnetic confinement fusion reactor. An ion accelerator was used to simulate the type of ion interaction that may occur at a plasma-facing material. Thermal desorption spectroscopy (TDS) was the primary tool used to analyze the effects of the irradiation Secondary ion mass spectroscopy (SIMS) was used to determine the distribution of trapped D in the tungsten specimen. The tritium migration analysis program (TMAP) was used to simulate thermal desorption profiles from the D depth distributions. Fitting of the simulated thermal desorption profiles with the measured TDS results provided values of the D trap energies. . Deuterium trapping in single crystal tungsten was studied as a function of the incident ion fluence, ion flux, irradiation temperature, irradiation history, and surface impurity levels during irradiation The results show that deuterium was trapped at vacancies and voids. Two deuterium atoms could be trapped at a tungsten vacancy, with trapping energies of 1.4 eV and 1.2 eV for the first and second D atoms, respectively. In a tungsten void, D is trapped as atoms adsorbed on the inner walls of the void with a trap energy of 2.1 eV, or as D{sub 2} molecules inside the void with a trap energy of 1.2 eV. . Deuterium trapping in polycrystalline tungsten was also studied as a function of the incident fluence, irradiation temperature, and irradiation history. Deuterium trapping in polycrystalline tungsten also occurs primarily at vacancies and voids with the same trap energies as in single crystal tungsten; however, the presence of grain boundaries promotes the formation of large surface blisters with high fluence irradiations at 500 K. In general, D trapping is greater in polycrystalline tungsten than in single crystal tungsten. To simulate mixed materials comprising of carbon (C) and tungsten, tungsten specimens were pre-irradiated with carbon ions prior to D

  17. Ion implantation induced martensite nucleation in SUS301 steel

    International Nuclear Information System (INIS)

    Kinoshita, Hiroshi; Takahashi, Heishichiro; Gustiono, Dwi; Sakaguchi, Norihito; Shibayama, Tamaki; Watanabe, Seiichi

    2007-01-01

    Phase transformation behaviors of the austenitic 301 stainless steel was studied under Fe + , Ti + and Ar + ions implantation at room temperature with 100, 200 and 300 keV up to fluence of 1x10 21 ions/m 2 and the microstructures were observed by means of transmission electron microscopy (TEM). The plane and cross-sectional observations of the implanted specimen showed that the induced-phases due to implantation from the γ matrix phase were identified as α' martensite phases with the orientation relationship of (11-bar0) α parallel (111-bar) γ and [111] α parallel [011] γ close to the Kurdjumov-Sachs (K-S). The ion implantation induced phases nucleated near the surface region and the depth position of the nucleation changed depending on the ion accelerating energy and ion species. It was also found that the induced marten sites phases nucleate under the influence of the stress distribution, which is introduced due to the concentration of implanted ions, especially due to the stress gradient caused by the corresponding concentration gradient. (author)

  18. Vacancy defects in electron-irradiated ZnO studied by Doppler broadening of annihilation radiation

    Science.gov (United States)

    Chen, Z. Q.; Betsuyaku, K.; Kawasuso, A.

    2008-03-01

    Vacancy defects in ZnO induced by electron irradiation were characterized by the Doppler broadening of annihilation radiation measurements together with the local density approximation calculations. Zinc vacancies (VZn) are responsible for positron trapping in the as-irradiated state. These are annealed out below 200°C . The further annealing at 400°C results in the formation of secondary defects attributed to the complexes composed of zinc vacancies and zinc antisites (VZn-ZnO) .

  19. Ion implantation induced nanotopography on titanium and bone cell adhesion

    Energy Technology Data Exchange (ETDEWEB)

    Braceras, Iñigo, E-mail: inigo.braceras@tecnalia.com [Tecnalia, Mikeletegi Pasealekua 2, 20009 Donostia-San Sebastian (Spain); CIBER de Bioingeniería, Biomateriales y Nanomedicina (Ciber-BBN) (Spain); Vera, Carolina; Ayerdi-Izquierdo, Ana [Tecnalia, Mikeletegi Pasealekua 2, 20009 Donostia-San Sebastian (Spain); CIBER de Bioingeniería, Biomateriales y Nanomedicina (Ciber-BBN) (Spain); Muñoz, Roberto [Tecnalia, Mikeletegi Pasealekua 2, 20009 Donostia-San Sebastian (Spain); Lorenzo, Jaione; Alvarez, Noelia [Tecnalia, Mikeletegi Pasealekua 2, 20009 Donostia-San Sebastian (Spain); CIBER de Bioingeniería, Biomateriales y Nanomedicina (Ciber-BBN) (Spain); Maeztu, Miguel Ángel de [Private Practice, P° San Francisco, 43 A-1°, 20400 Tolosa (Spain)

    2014-08-15

    Graphical abstract: Titanium surfaces modified by inert ion implantation affect cell adhesion through modification of the nanotopography in the same dimensional range of that of human bone inorganic phases. - Highlights: • Inert ion implantation on Ti modifies surface nanotopography and bone cell adhesion. • Ion implantation can produce nanostructured surfaces on titanium in the very same range as of those of the mineral phase of the human bone. • Appropriate tool for studying the relevance of nanostructured surfaces on bone mineralization and implant osseointegration. • Ion implantation induced nanotopography have a statistically significant influence on bone cell adhesion. - Abstract: Permanent endo-osseous implants require a fast, reliable and consistent osseointegration, i.e. intimate bonding between bone and implant, so biomechanical loads can be safely transferred. Among the parameters that affect this process, it is widely admitted that implant surface topography, surface energy and composition play an important role. Most surface treatments to improve osseointegration focus on micro-scale features, as few can effectively control the effects of the treatment at nanoscale. On the other hand, ion implantation allows controlling such nanofeatures. This study has investigated the nanotopography of titanium, as induced by different ion implantation surface treatments, its similarity with human bone tissue structure and its effect on human bone cell adhesion, as a first step in the process of osseointegration. The effect of ion implantation treatment parameters such as energy (40–80 keV), fluence (1–2 e17 ion/cm{sup 2}) and ion species (Kr, Ar, Ne and Xe) on the nanotopography of medical grade titanium has been measured and assessed by AFM and contact angle. Then, in vitro tests have been performed to assess the effect of these nanotopographies on osteoblast adhesion. The results have shown that the nanostructure of bone and the studied ion implanted

  20. Ion implantation induced nanotopography on titanium and bone cell adhesion

    International Nuclear Information System (INIS)

    Braceras, Iñigo; Vera, Carolina; Ayerdi-Izquierdo, Ana; Muñoz, Roberto; Lorenzo, Jaione; Alvarez, Noelia; Maeztu, Miguel Ángel de

    2014-01-01

    Graphical abstract: Titanium surfaces modified by inert ion implantation affect cell adhesion through modification of the nanotopography in the same dimensional range of that of human bone inorganic phases. - Highlights: • Inert ion implantation on Ti modifies surface nanotopography and bone cell adhesion. • Ion implantation can produce nanostructured surfaces on titanium in the very same range as of those of the mineral phase of the human bone. • Appropriate tool for studying the relevance of nanostructured surfaces on bone mineralization and implant osseointegration. • Ion implantation induced nanotopography have a statistically significant influence on bone cell adhesion. - Abstract: Permanent endo-osseous implants require a fast, reliable and consistent osseointegration, i.e. intimate bonding between bone and implant, so biomechanical loads can be safely transferred. Among the parameters that affect this process, it is widely admitted that implant surface topography, surface energy and composition play an important role. Most surface treatments to improve osseointegration focus on micro-scale features, as few can effectively control the effects of the treatment at nanoscale. On the other hand, ion implantation allows controlling such nanofeatures. This study has investigated the nanotopography of titanium, as induced by different ion implantation surface treatments, its similarity with human bone tissue structure and its effect on human bone cell adhesion, as a first step in the process of osseointegration. The effect of ion implantation treatment parameters such as energy (40–80 keV), fluence (1–2 e17 ion/cm 2 ) and ion species (Kr, Ar, Ne and Xe) on the nanotopography of medical grade titanium has been measured and assessed by AFM and contact angle. Then, in vitro tests have been performed to assess the effect of these nanotopographies on osteoblast adhesion. The results have shown that the nanostructure of bone and the studied ion implanted

  1. Formation of vacancy clusters in tungsten crystals under hydrogen-rich condition

    International Nuclear Information System (INIS)

    Kato, Daiji; Iwakiri, Hirotomo; Morishita, Kazunori

    2011-01-01

    Di-vacancy formation assisted by hydrogen trapping is studied in terms of nucleation free-energies evaluated with density functional theory. Calculations give binding energies for single hydrogen atom as first- and second-nearest-neighbor of di-vacancies of 1.80 and 2.15 eV, respectively, which are significantly larger than that for mono-vacancies. At elevated atomic concentrations of interstitial hydrogen atoms, evaluated nucleation free-energies indicate that the hydrogen assisted di-vacancy formation becomes more favorable. It is suggested that the formation would be preceded by VH cluster formation.

  2. Formation of vacancy clusters in tungsten crystals under hydrogen-rich condition

    Energy Technology Data Exchange (ETDEWEB)

    Kato, Daiji, E-mail: kato.daiji@nifs.ac.jp [National Institute for Fusion Science, 322-6 Oroshi-cho, Toki, Gifu 509-5292 (Japan); Iwakiri, Hirotomo, E-mail: iwakiri@edu.u-ryukyu.ac.jp [University of the Ryukyus, Okinawa 903-0213 (Japan); Morishita, Kazunori, E-mail: morishita@iae.kyoto-u.ac.jp [Institute of Advanced Energy, Kyoto University, Kyoto 611-0011 (Japan)

    2011-10-01

    Di-vacancy formation assisted by hydrogen trapping is studied in terms of nucleation free-energies evaluated with density functional theory. Calculations give binding energies for single hydrogen atom as first- and second-nearest-neighbor of di-vacancies of 1.80 and 2.15 eV, respectively, which are significantly larger than that for mono-vacancies. At elevated atomic concentrations of interstitial hydrogen atoms, evaluated nucleation free-energies indicate that the hydrogen assisted di-vacancy formation becomes more favorable. It is suggested that the formation would be preceded by VH cluster formation.

  3. Vacancies in transition metals

    International Nuclear Information System (INIS)

    Allan, G.; Lannoo, M.

    1976-01-01

    A calculation of the formation energy and volume for a vacancy in transition metals is described. A tight-binding scheme is used for the d band and a Born-Mayer type potential to account for the repulsive part of the energy at small distances. The results show that the relaxation energy is small in all cases, less than 0.1 eV. This seems to be coherent with the good agreement obtained for the theoretical and experimental values of the formation energy Esub(F)sup(V) of the vacancy, without including relaxation. The center of the transitional series is found to give a contraction (Formation volume of order -0.4 at.vol.) whereas the edges are found to produce dilations. (author)

  4. Positron annihilation studies on nasicon analogues containing cation vacancies

    International Nuclear Information System (INIS)

    Sreeramalu, V.; Sreepad, H.R.; Chandrashekara, A.; Ravindrachary, V.; Gopal, S.

    1990-01-01

    Positron annihilation studies were carried out on the Nasicon analogue Na 2 (La, Al)Zr(PO 4 ) 3 compound for three different concentrations (2.2, 2.8 and 5.2 by wt.%) of ZrO 2 in the nutrient. Angular correlation study of annihilated photons reveals that the defect concentration is maximum for 2.8(wt.%) of ZrO 2 . Further, positron lifetime studies indicate that the positrons are trapped at cation vacancies. Application of a two state trapping model to this system made it possible to evaluate the lifetime of positrons in the Bloch state and of positrons trapped at cation vacancies. (author). 16 refs., 4 figs

  5. Cellular structure formed by ion-implantation-induced point defect

    International Nuclear Information System (INIS)

    Nitta, N.; Taniwaki, M.; Hayashi, Y.; Yoshiie, T.

    2006-01-01

    The authors have found that a cellular defect structure is formed on the surface of Sn + ion implanted GaSb at a low temperature and proposed its formation mechanism based on the movement of the induced point defects. This research was carried out in order to examine the validity of the mechanism by clarifying the effect of the mobility of the point defects on the defect formation. The defect structure on the GaSb surfaces implanted at cryogenic temperature and room temperature was investigated by scanning electron microscopy (SEM) and cross-sectional transmission electron microscopy (TEM) observation. In the sample implanted at room temperature, the sponge-like structure (a pileup of voids) was formed and the cellular structure, as observed at a low temperature, did not develop. This behavior was explained by the high mobility of the vacancies during implantation at room temperature, and the proposed idea that the defect formation process is dominated by the induced point defects was confirmed

  6. Clustering and segregation of small vacancy clusters near tungsten (0 0 1) surface

    Science.gov (United States)

    Duan, Guohua; Li, Xiangyan; Xu, Yichun; Zhang, Yange; Jiang, Yan; Hao, Congyu; Liu, C. S.; Fang, Q. F.; Chen, Jun-Ling; Luo, G.-N.; Wang, Zhiguang

    2018-01-01

    Nanoporous metals have been shown to exhibit radiation-tolerance due to the trapping of the defects by the surface. However, the behavior of vacancy clusters near the surface is not clear which involves the competition between the self-trapping and segregation of small vacancy clusters (Vn) nearby the surface. In this study, we investigated the energetic and kinetic properties of small vacancy clusters near tungsten (0 0 1) surface by combining molecular statics (MS) calculations and object Kinetic Monte Carlo (OKMC) simulations. Results show that vacancies could be clustered with the reduced formation energy and migration energy of the single vacancy around a cluster as the respective energetic and kinetic driving forces. The small cluster has a migration energy barrier comparable to that for the single vacancy; the migration energy barriers for V1-5 and V7 are 1.80, 1.94, 2.17, 2.78, 3.12 and 3.11 eV, respectively. Clusters and become unstable near surface (0 0 1) and tend to dissociate into the surface. At the operation temperature of 1000 K, the single vacancy, V2, 2 V 3 V3 and V4 were observed to segregate to the surface within a time of one hour. Meanwhile, larger clusters survived near the surface, which could serve as nucleating center for voids near the surface. Our results suggest that under a low radiation dose, surface (0 0 1) could act as a sink for small vacancy clusters, alleviating defect accumulation in the material under a low radiation dose. We also obtained several empirical expressions for the vacancy cluster formation energy, binding energy, and trapping radius as a function of the number of vacancies in the cluster.

  7. Determination of the vacancy formation enthalpy for high purity Ni

    International Nuclear Information System (INIS)

    Lynn, K.G.; Snead, C.L. Jr.; Hurst, J.J.; Farrell, K.

    1979-01-01

    Positron-annihilation lifetime measurements have been made on Ni over a temperature range of 4.2 to 1700 K. We find a small change in the lifetime from 4.2 - 900 K indicating a very small thermal-expansion effect. A small precursor effect is observed before the onset of significant vacancy trapping. A monovacancy formation enthalpy of 1.54sub(+0.2)sup(-0.1) eV is extracted without taking divacancies into consideration in the analysis. No detrapping from mono-vacancies is observed even at the higher temperatures. The vacancy formation enthalpy extracted from the lifetime data is compared to values obtained by Doppler-broadening and angular-correlation techniques. (author)

  8. Determination of the vacancy formation enthalpy for high purity Ni

    International Nuclear Information System (INIS)

    Lynn, K.G.; Snead, C.L. Jr.; Hurst, J.J.; Farrell, K.

    1979-01-01

    Positron-annihilation lifetime measurements have been made on Ni over a temperature range of 4.2 to 1700 K. We find a small change in the lifetime from 4.2 to 900 K indicating a very small thermal-expansion effect. A small precursor effect is observed before the onset of significant vacancy trapping. A monovacancy formation enthalpy of 1.54/sub +0.2//sup -0.1/ eV is extracted without taking divacancies into consideration in the analysis. No detrapping from mono-vacancies is observed even at the higher temperatures. The vacancy formation enthalpy extracted from the lifetime data is compared to values obtained by Doppler-broadening and angular-correlation techniques

  9. Electronic structure of vacancies and vacancy clusters in simple metals

    International Nuclear Information System (INIS)

    Manninen, M.; Nieminen, R.M.

    1978-05-01

    The self-consistent density functional approach has been applied in a study of electronic properties of vacancies and vacancy clusters in simple metals. The electron density profiles and potentials have been obtained for spherical voids of varying size. The formation energies and residual resistivities have been calculated for vacancies using both perturbational and variational inclusion of discrete lattice effects. The relation of the void properties to the plane surface ones is studied, and the inadequacy of the jellium-based methods to high-index faces is demonstrated. (author)

  10. Ordering of vacancies on Si(001)

    NARCIS (Netherlands)

    Zandvliet, Henricus J.W.

    1997-01-01

    Missing dimer vacancies are always present on the clean Si(001) surface. The vacancy density can be increased by ion bombardment (Xe+, Ar+), etching (O2, Br2, I2, etc.) or Ni contamination. The equilibrium shape at low vacancy concentrations (<0.2¿0.3 monolayers) of these vacancy islands is

  11. Vacancy clusters at nanoparticle surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Xu, J.; Moxom, J.; Somieski, B.; White, C.W. [Oak Ridge National Lab., TN (United States); Mills, A.P. Jr. [Bell Labs., Lucent Technologies, Murray Hill, NJ (United States); Suzuki, R.; Ishibashi, S. [Electrotechnical Lab., Tsukuba, Ibaraki (Japan); Ueda, A.; Henderson, D. [Physics Dept., Fisk Univ., Nashville, TN (United States)

    2001-07-01

    We detect vacancy clusters at Au nanoparticle surfaces using a combination of positron lifetime spectroscopy, 1- detector, and 2-detector measurements of Doppler broadening of annihilation radiation. Gold nanoparticles are formed by MeV implantation of gold ions into MgO (100) followed by annealing. Clusters of two Mg and two O vacancies (v{sub 4}) are attached to the gold nanoparticle surfaces within the projected range (R{sub p}). (orig.)

  12. Vacancy clusters at nanoparticle surfaces

    International Nuclear Information System (INIS)

    Xu, J.; Moxom, J.; Somieski, B.; White, C.W.; Mills, A.P. Jr.; Suzuki, R.; Ishibashi, S.; Ueda, A.; Henderson, D.

    2001-01-01

    We detect vacancy clusters at Au nanoparticle surfaces using a combination of positron lifetime spectroscopy, 1- detector, and 2-detector measurements of Doppler broadening of annihilation radiation. Gold nanoparticles are formed by MeV implantation of gold ions into MgO (100) followed by annealing. Clusters of two Mg and two O vacancies (v 4 ) are attached to the gold nanoparticle surfaces within the projected range (R p ). (orig.)

  13. Cation vacancies in ferroelectric PbTiO3 and Pb(Zr,Ti)O3 : A positron annihilation lifetime spectroscopy study

    Science.gov (United States)

    Keeble, D. J.; Singh, S.; Mackie, R. A.; Morozov, M.; McGuire, S.; Damjanovic, D.

    2007-10-01

    Positron annihilation lifetime spectroscopy measurements identify A - and B -site cation vacancies in ferroelectric perovskite oxides (ABO3) . Crystal PbTiO3 and ceramic lead zirconium titanate (PZT) were studied and gave consistent values for the lifetime resulting from positron localization at lead vacancies VPb . Positron trapping to B -site vacancies was inferred in PZT. Temperature dependent studies showed that the defect specific trapping rate was higher for VB compared to VPb , consistent with the larger negative charge. Doping PZT with Fe increased the fraction positron trapping to VB compared to VPb -type defects.

  14. Moessbauer effect and vacancy diffusion

    International Nuclear Information System (INIS)

    Gunther, L.

    1976-01-01

    A dynamical theory of vacancy diffusion which was motivated by the need to explain recent experimental results for the Moessbauer spectra of Fe in Cu, Fe in Au and Fe in Al is presented. Diffusion in these systems is dominated by the vacancy mechanism, which involves strong correlations between successive jumps. The theory developed by Singwi and Sjoelander for the Moessbauer spectrum of a diffusing nucleus is therefore not applicable. The inverse of the normalized Moessbauer spectrum evaluated at zero frequency is introduced as a useful means of comparing experimental with theoretical spectral widths

  15. Positron annihilation studies of vacancies in Ag-Zn alloys

    International Nuclear Information System (INIS)

    Chabik, S.

    1982-01-01

    The temperature dependence of annihilation rate, F(T), at the peak of angular correlation curve has been measured for Ag-29.2%at Zn and Ag-50%at Zn alloys. By applying the trapping model the vacancy formation energy for Ag-29.2%at Zn alloy has been found to be equal to 0.94+-0.06 eV. It has been found that the course of the F(T) curve for Ag-50%at Zn depends on the phase composition and thermal history of the investigated sample. For alloys containing not more than 50%at Zn, the concentration dependence of the vacancy formation energy for Ag-Zn alloys is very similar to that for Cu-Zn alloys. (Auth.)

  16. Metastable self-trapping of positrons in MgO

    Science.gov (United States)

    Monge, M. A.; Pareja, R.; González, R.; Chen, Y.

    1997-01-01

    Low-temperature positron annihilation measurements have been performed on MgO single crystals containing either cation or anion vacancies. The temperature dependence of the S parameter is explained in terms of metastable self-trapped positrons which thermally hop through the crystal lattice. The experimental results are analyzed using a three-state trapping model assuming transitions from both delocalized and self-trapped states to deep trapped states at vacancies. The energy level of the self-trapped state was determined to be (62+/-5) meV above the delocalized state. The activation enthalpy for the hopping process of self-trapped positrons appears to depend on the kind of defect present in the crystals.

  17. Dynamics of ordering processes in annealed dilute systems: Island formation, vacancies at domain boundaries, and compactification

    DEFF Research Database (Denmark)

    Shah, Peter Jivan; Mouritsen, Ole G.

    1990-01-01

    The dynamics of the ordering processes in two-dimensional lattice models with annealed vacancies and nonconserved order parameter is studied as a function of temperature and vacancy concentration by means of Monte Carlo temperature-quenching simulations. The models are Ising antiferromagnets...... with couplings leading to twofold-degenerate as well as fourfold-degenerate ordering. The models are quenched into a phase-separation region, which makes it possible for both types of ordering to observe the following scenario of ordering processes: (i) early-time nucleation and growth of ordered domains, (ii......) intermediate-time trapping of the mobile vacancies at the domain boundaries, and (iii) late-time diffusion of vacancies along the domain-boundary network towards the surface. In the case of high dilution, the ordering processes correspond to early-time island formation and late-time coarsening...

  18. Vacancy decay in endohedral atoms

    International Nuclear Information System (INIS)

    Amusia, M. Ya.; Baltenkov, A. S.

    2006-01-01

    It is demonstrated that the fullerene shell dramatically affects the radiative and Auger vacancy decay of an endohedral atom A-C 60 . The collectivized electrons of the C 60 shell add new possibilities for radiative and nonradiative decays similar to that in ordinary atoms where the vacancies in the initial and final state almost always belong to different subshells. It is shown that the smallness of the atomic shell radii as compared to that of the fullerene shell provides an opportunity to derive the simple formulas for the probabilities of the electron transitions. It is shown that the radiative and Auger (or Koster-Kronig) widths of the vacancy decay due to electron transition in the atom A in A-C 60 acquire an additional factor that can be expressed via the polarizability of the C 60 at transition energy. It is demonstrated that due to an opening of the nonradiative decay channel for vacancies in subvalent subshells the decay probability increases by five to six orders of magnitude

  19. Low-temperature positron lifetime and Doppler-broadening measurements for single-crystal nickel oxide containing cation vacancies

    International Nuclear Information System (INIS)

    Waber, J.T.; Snead, C.L. Jr.; Lynn, K.G.

    1985-01-01

    Lifetime and Doppler-broadening measurements for positron annihilation in substoichiometric nickelous oxide have been made concomitantly from liquid-helium to room temperature. The concentration of cation vacancies is readily controlled by altering the ambient oxygen pressure while annealing the crystals at 1673 0 K. It was found that neither of the three lifetimes observed or their relative intensities varied significantly with the oxygen pressure, and the bulk rate only increased slightly when the specimen was cooled from room to liquid-helium temperatures. These results are interpreted as indicating that some of the positrons are trapped by the existing cation vacancies and a smaller fraction by vacancy clusters

  20. Photoconversion and dynamic hole recycling process in anion vacancies in neutron-irradiated MgO crystals

    International Nuclear Information System (INIS)

    Monge, M.A.; Gonzalez, R.; Munoz Santiuste, J.E.; Pareja, R.; Chen, Y.; Kotomin, E.A.; Popov, A.I.

    1999-01-01

    Optical spectroscopy and theory demonstrate that photon excitation of the positively charged anion vacancies (F + centers) at 5.0 eV in neutron-irradiated MgO crystals releases holes that are subsequently trapped at V-type centers, which are cation vacancies charge compensated by impurities, such as Al 3+ , F - , and OH - ions. The concentration of trapped-hole centers was found to exceed that of available anion vacancies. The disproportionately large amount of holes produced is attributed to a dynamic recycling process, by which the F + center serves to release a hole to the V-type centers and subsequently trap a hole from an Fe 3+ ion. The net effect was the increase of V-type centers mostly at the expense of Fe 3+ ions. It was also shown that concurrently there was a component which distributed holes directly from Fe 3+ to the V-type centers. copyright 1999 The American Physical Society

  1. Hard-to-fill vacancies.

    Science.gov (United States)

    Williams, Ruth

    2010-09-29

    Skills for Health has launched a set of resources to help healthcare employers tackle hard-to-fill entry-level vacancies and provide sustainable employment for local unemployed people. The Sector Employability Toolkit aims to reduce recruitment and retention costs for entry-level posts and repare people for employment through pre-job training programmes, and support employers to develop local partnerships to gain access to wider pools of candidates and funding streams.

  2. Effect of annealing ambience on the formation of surface/bulk oxygen vacancies in TiO2 for photocatalytic hydrogen evolution

    Science.gov (United States)

    Hou, Lili; Zhang, Min; Guan, Zhongjie; Li, Qiuye; Yang, Jianjun

    2018-01-01

    The surface and bulk oxygen vacancy have a prominent effect on the photocatalytic performance of TiO2. In this study, TiO2 possessing different types and concentration of oxygen vacancies were prepared by annealing nanotube titanic acid (NTA) at various temperatures in air or vacuum atmosphere. TiO2 with the unitary bulk single-electron-trapped oxygen vacancies (SETOVs) formed when NTA were calcined in air. Whereas, TiO2 with both bulk and surface oxygen vacancies were obtained when NTA were annealed in vacuum. The series of TiO2 with different oxygen vacancies were systematically characterized by TEM, XRD, PL, XPS, ESR, and TGA. The PL and ESR analysis verified that surface oxygen vacancies and more bulk oxygen vacancies could form in vacuum atmosphere. Surface oxygen vacancies can trap electron and hinder the recombination of photo-generated charges, while bulk SETOVs act as the recombination center. The surface or bulk oxygen vacancies attributed different roles on the photo-absorbance and activity, leading that the sample of NTA-A400 displayed higher hydrogen evolution rate under UV light, whereas NTA-V400 displayed higher hydrogen evolution rate under visible light because bulk SETOVs can improve visible light absorption because sub-band formed by bulk SETOVs prompted the secondary transition of electron excited.

  3. Effect of impurities on vacancy migration energy in Fe-based alloys

    International Nuclear Information System (INIS)

    Hashimoto, N.; Sakuraya, S.; Tanimoto, J.; Ohnuki, S.

    2014-01-01

    Effects of impurities, such as carbon, nitrogen, helium and hydrogen, on microstructural evolution in pure iron were investigated by means of a multi-beam electron microscope. Growth rate of dislocation loops were measured to calculate vacancy migration energies. In all irradiation temperature conditions, both the size and the number density of dislocation loops were increased as a function of dose. Irradiation with more impurities showed an increase in the temperature dependence of the dislocation loop growth rate compared to irradiation with little impurities. The in situ experiment indicated that the net migration energy of vacancies could be increased due to trapping by impurities, and the effect of C and N on the migration energy of vacancy would be larger than that of W, V, Ta. Furthermore, H and He would increase vacancy migration energy greater than C and N, as well as W, V, Ta. The density functional theory (DFT), applied to the atomic models of BCC iron, indicated an increase in vacancy migration energy by the trapping of impurity atoms, that is a good agreement with this in situ experiment

  4. High-temperature equilibrium vacancy formation in ceramic materials studied by positron annihilation

    International Nuclear Information System (INIS)

    Forster, M.; Claudy, W.; Hermes, H.; Major, J.; Schaefer, H.E.; Koch, M.; Maier, K.; Stoll, H.

    1992-01-01

    Positron lifetime measurements were used in order to study thermal vacancy formation in NiO, YBa 2 Cu 3 O 7-δ , α-Al 2 O 3 , MgO and 6H-SiC at high temperatures. In NiO two increases of the positron trapping rate at 450K and 1200K (po 2 =10 5 Pa) are attributed to the change of charge of neutral extrinsic Ni-vacancies (c ≅ 10 -4 ) into a negative charge state and to the nonstochiometric formation of charged Ni-vacancies at high temperatures. In YBa 2 Cu 3 O 7-δ the oxygen loss or uptake at T > 680K with an activation enthalpy of 1.03eV can be studied by the variation of the positron lifetime with temperature and oxygen partial pressure. In α-Al 2 O 3 the positrons are annihilated from the delocalized free state between 1000K and 2250K and no positron trapping of thermally formed vacancies was detected which may be understood in terms of the theoretically predicted low concentrations of thermal vacancies. In MgO and 6H-SiC positron lifetime measurements were performed up to temperatures of about 2000K

  5. Micro- and macro-structure of implantation-induced disorder in Ge

    CERN Document Server

    Glover, C J; Byrne, A P; Yu, K M; Foran, G J; Clerc, C; Hansen, J L; Nylandsted-Larsen, A

    2000-01-01

    The structure of ion implantation-induced damage in Ge substrates has been investigated with a combination of ion- and photon-based techniques including Rutherford backscattering spectrometry (RBS), perturbed angular correlation (PAC) and extended X-ray absorption fine structure (EXAFS) spectroscopy. For MeV Ge ion implantation at -196 degrees C, the dose dependence of the decrease in local atomic order, determined from EXAFS and PAC, was compared to the number of displaced atoms determined from RBS measurements. An EXAFS determined damage fraction was shown to be a better estimate of amorphous fraction than the number of displaced atoms. PAC was used to elucidate the evolution of defective configurations, and was compared to the RBS and EXAFS results. A fit to the overlap model with the overlap of two ion cascades for complete amorphization best described the experimental results. (16 refs).

  6. Comparison of proton and phosphorous ion implantation-induced intermixing of InAs/InP quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Barik, S; Tan, H H; Jagadish, C [Department of Electronic Materials Engineering, Research School of Physical Sciences and Engineering, Australian National University, Canberra, Australian Capital Territory 0200 (Australia)

    2007-05-02

    We report and compare proton and phosphorous ion implantation-induced intermixing of InAs/InP quantum dots (QDs). After ion implantation at 20-300 deg. C, the QDs are rapid thermally annealed at 850 deg. C for 30 s. Proton implantation induces less energy shift than P ion implantation for a given concentration of atomic displacements due to the more efficient dynamic annealing of the defects created by protons. The implantation-induced energy shift reaches a maximum value of about 260 meV for a dose of 5 x 10{sup 12} ions cm{sup -2} in the P ion implanted QDs, which also show narrower PL linewidths compared to the proton implanted QDs. We also report the effects of an InGaAs top cap layer on the ion implantation-induced QD intermixing and show that defect production and annihilation processes evolve differently in InGaAs and InP layers and vary with the implantation temperature. When the implantation is performed at higher temperatures, the energy shift of the P ion implanted QDs capped with an InP layer increases due to the reduction in larger defect cluster formation at higher temperatures, while the energy shift of the proton implanted QDs decreases due to increased dynamic annealing irrespective of their cap layers.

  7. Comparative study of 150 keV Ar+ and O+ ion implantation induced structural modification on electrical conductivity in Bakelite polymer

    Science.gov (United States)

    Aneesh Kumar, K. V.; Krishnaveni, S.; Asokan, K.; Ranganathaiah, C.; Ravikumar, H. B.

    2018-02-01

    A comparative study of 150 keV argon (Ar+) and oxygen (O+) ion implantation induced microstructural modifications in Bakelite Resistive Plate Chamber (RPC) detector material at different implantation fluences have been studied using Positron Annihilation Lifetime Spectroscopy (PALS). Positron lifetime parameters viz., o-Ps lifetime (τ3) and its intensity (I3) upon lower implantation fluences can be interpreted as the cross-linking and the increased local temperature induced diffusion followed by trapping of ions in the interior polymer voids. The increased o-Ps lifetime (τ3) at higher O+ ion implantation fluences indicates chain scission owing to the oxidation and track formation. This is also justified by the X-Ray Diffraction (XRD) and Fourier Transform Infrared (FTIR) results. The modification in the microstructure and electrical conductivity of Bakelite materials are more upon implantation of O+ ions than Ar+ ions of same energy and fluences. The reduced electrical conductivity of Bakelite polymer material upon ion implantation of both the ions is correlated to the conducting pathways and cross-links in the polymer matrix. The appropriate energy and fluence of implanting ions might reduce the leakage current and hence improve the performance of Bakelite RPC detectors.

  8. Trapping, self-trapping and the polaron family

    International Nuclear Information System (INIS)

    Stoneham, A M; Gavartin, J; Shluger, A L; Kimmel, A V; Ramo, D Munoz; Roennow, H M; Aeppli, G; Renner, C

    2007-01-01

    The earliest ideas of the polaron recognized that the coupling of an electron to ionic vibrations would affect its apparent mass and could effectively immobilize the carrier (self-trapping). We discuss how these basic ideas have been generalized to recognize new materials and new phenomena. First, there is an interplay between self-trapping and trapping associated with defects or with fluctuations in an amorphous solid. In high dielectric constant oxides, like HfO 2 , this leads to oxygen vacancies having as many as five charge states. In colossal magnetoresistance manganites, this interplay makes possible the scanning tunnelling microscopy (STM) observation of polarons. Second, excitons can self-trap and, by doing so, localize energy in ways that can modify the material properties. Third, new materials introduce new features, with polaron-related ideas emerging for uranium dioxide, gate dielectric oxides, Jahn-Teller systems, semiconducting polymers and biological systems. The phonon modes that initiate self-trapping can be quite different from the longitudinal optic modes usually assumed to dominate. Fourth, there are new phenomena, like possible magnetism in simple oxides, or with the evolution of short-lived polarons, like muons or excitons. The central idea remains that of a particle whose properties are modified by polarizing or deforming its host solid, sometimes profoundly. However, some of the simpler standard assumptions can give a limited, indeed misleading, description of real systems, with qualitative inconsistencies. We discuss representative cases for which theory and experiment can be compared in detail

  9. Stability, magnetic and electronic properties of cobalt–vacancy defect pairs in graphene: A first-principles study

    International Nuclear Information System (INIS)

    Raji, Abdulrafiu T.; Lombardi, Enrico B.

    2015-01-01

    We report a first-principles investigation of the structural, electronic and magnetic properties of cobalt–vacancy defect complexes in graphene, within the framework of density-functional theory (DFT), incorporating DFT+U. Specifically, we consider the interactions of cobalt and vacancies in graphene, at varying separations and sub-lattices. We show that it is energetically favorable for substitutional Co in graphene to trap an additional vacancy in graphene, forming a Co–vacancy complex. In all the configurations considered, the most stable configuration is when the Co atom is embedded in a divacancy. The magnetic moment induced on the cobalt atom varies as the vacancy–cobalt separation changes, depending not only on the separation, but also on the sub-lattice of the vacancy relative to cobalt. Furthermore, for each separation and sub-lattice considered, the linear density of states of graphene is modified such that Dirac point is either not discernible or has shifted above the Fermi energy. Since individual vacancies or transition metal (TM) atoms, such as cobalt in graphene, have mostly been studied in isolation up to now, ignoring possible transition metal–vacancy interactions, these results have important implications to the fundamental understanding of TM–vacancy defect interactions in graphene

  10. The Effect of Acceptor and Donor Doping on Oxygen Vacancy Concentrations in Lead Zirconate Titanate (PZT).

    Science.gov (United States)

    Slouka, Christoph; Kainz, Theresa; Navickas, Edvinas; Walch, Gregor; Hutter, Herbert; Reichmann, Klaus; Fleig, Jürgen

    2016-11-22

    The different properties of acceptor-doped (hard) and donor-doped (soft) lead zirconate titanate (PZT) ceramics are often attributed to different amounts of oxygen vacancies introduced by the dopant. Acceptor doping is believed to cause high oxygen vacancy concentrations, while donors are expected to strongly suppress their amount. In this study, La 3+ donor-doped, Fe 3+ acceptor-doped and La 3+ /Fe 3+ -co-doped PZT samples were investigated by oxygen tracer exchange and electrochemical impedance spectroscopy in order to analyse the effect of doping on oxygen vacancy concentrations. Relative changes in the tracer diffusion coefficients for different doping and quantitative relations between defect concentrations allowed estimates of oxygen vacancy concentrations. Donor doping does not completely suppress the formation of oxygen vacancies; rather, it concentrates them in the grain boundary region. Acceptor doping enhances the amount of oxygen vacancies but estimates suggest that bulk concentrations are still in the ppm range, even for 1% acceptor doping. Trapped holes might thus considerably contribute to the charge balancing of the acceptor dopants. This could also be of relevance in understanding the properties of hard and soft PZT.

  11. The Effect of Acceptor and Donor Doping on Oxygen Vacancy Concentrations in Lead Zirconate Titanate (PZT

    Directory of Open Access Journals (Sweden)

    Christoph Slouka

    2016-11-01

    Full Text Available The different properties of acceptor-doped (hard and donor-doped (soft lead zirconate titanate (PZT ceramics are often attributed to different amounts of oxygen vacancies introduced by the dopant. Acceptor doping is believed to cause high oxygen vacancy concentrations, while donors are expected to strongly suppress their amount. In this study, La3+ donor-doped, Fe3+ acceptor-doped and La3+/Fe3+-co-doped PZT samples were investigated by oxygen tracer exchange and electrochemical impedance spectroscopy in order to analyse the effect of doping on oxygen vacancy concentrations. Relative changes in the tracer diffusion coefficients for different doping and quantitative relations between defect concentrations allowed estimates of oxygen vacancy concentrations. Donor doping does not completely suppress the formation of oxygen vacancies; rather, it concentrates them in the grain boundary region. Acceptor doping enhances the amount of oxygen vacancies but estimates suggest that bulk concentrations are still in the ppm range, even for 1% acceptor doping. Trapped holes might thus considerably contribute to the charge balancing of the acceptor dopants. This could also be of relevance in understanding the properties of hard and soft PZT.

  12. Superabundant vacancies in fcc metals: A combination of ab-initio, thermodynamic and kinetics approaches

    Energy Technology Data Exchange (ETDEWEB)

    Nazarov, Roman; Hickel, Tilmann; Neugebauer, Joerg [Max-Planck-Institut fuer Eisenforschung, Duesseldorf (Germany)

    2011-07-01

    A dramatic increase of the vacancy concentration in a H-rich atmosphere, the so called superabundant vacancy formation, has been experimentally observed in several metals and alloys. In order to study this phenomenon we systematically applied density functional theory to a large set of fcc metals. We found that a large amount of H can be trapped by a monovacancy with, e.g., up to 15 H atoms in an Al vacancy, up to 12 H atoms in the case of Pd and more than 17 H atoms for Pb. Based on the defect formation energies from DFT calculations, we have constructed a thermodynamic model that determines the equilibrium concentration of point defects as a function of temperature and H chemical potential. By applying this approach we revealed that the vacancy concentration can indeed strongly increase if H is added. To understand the phenomenon of accelerated self-diffusion in a H-rich atmosphere we coupled the information on the number of vacancies from the thermodynamic treatment with self-diffusion barriers obtained from DFT calculations. Using this approach we found that the self-diffusion coefficient is reduced not only due to the increased vacancy concentration, but also as a result of a H-induced lubricant effect.

  13. First-principles study on migration of vacancy in tungsten

    International Nuclear Information System (INIS)

    Oda, Yasuhiro; Ito, Atsushi M.; Takayama, Arimichi; Nakamura, Hiroaki

    2014-03-01

    We calculated di-vacancy binding energies and migration energies of mono-vacancy and di-vacancy in tungsten material using DFT calculation. The mono-vacancy diffuses in [111] direction easily rather than in [001] direction. The migration energies of di-vacancies are almost the same value of the mono-vacancy. The migration of di-vacancy is approximately the same as the migration of mono-vacancy. The di-vacancy binding energies are almost zero or negative. The interactions between two vacancies in tungsten material are repulsive from the second to fifth nearest-neighbor. The vacancies are difficult to aggregate since di-vacancy is less stable than mono-vacancy. (author)

  14. Electronic properties of hafnium oxide: A contribution from defects and traps

    Energy Technology Data Exchange (ETDEWEB)

    Gritsenko, Vladimir A., E-mail: grits@isp.nsc.ru; Perevalov, Timofey V.; Islamov, Damir R., E-mail: damir@isp.nsc.ru

    2016-02-15

    In the present article, we give a review of modern data and latest achievements pertaining to the study of electronic properties of oxygen vacancies in hafnium oxide. Hafnium oxide is a key dielectric for use in many advanced silicon devices. Oxygen vacancies in hafnium oxide largely determine the electronic properties of the material. We show that the electronic transitions between the states due to oxygen vacancies largely determine the optical absorption and luminescent properties of hafnium oxide. We discuss the role of oxygen vacancies as traps that facilitate charge transport in hafnium oxide films. Also, we demonstrate the fact that the electrical conductivity in hafnium oxide is controlled by the phonon-assisted tunnelling of charge carriers between traps that were identified as oxygen vacancies.

  15. Effects of impurity trapping on irradiation-induced swelling and creep

    Energy Technology Data Exchange (ETDEWEB)

    Mansur, L. K.; Yoo, M. H.

    1977-12-01

    A general theory of the effects of point defect trapping on radiation-induced swelling and creep deformation rates is developed. The effects on the fraction of defects recombining, and on void nucleation, void growth and creep due to the separate processes of dislocation climb-glide and dislocation climb (the so-called SIPA mechanism) are studied. Trapping of vacancies or interstitials increases total recombination and decreases the rates of deformation processes. For fixed trapping parameters, the reduction is largest for void nucleation, less for void growth and creep due to dislocation climb-glide, and least for creep due to dislocation climb. With this formation, the effects of trapping at multiple vacancy and interstitial traps and of spatial and temporal variation in trap concentrations may be determined. Alternative pictures for viewing point defect trapping in terms of effective recombination and diffusion coefficients are derived. It is shown that previous derivations of these coefficients are incorrect. A rigorous explanation is given of the well-known numerical result that interstitial trapping is significant only if the binding energy exceeds the difference between the vacancy and interstitial migration energies, while vacancy trapping is significant even at small binding energies. Corrections which become necessary at solute concentrations above about 0.1% are described. Numerical results for a wide range of material and irradiation parameters are presented.

  16. Vibrational and electronic spectroscopy of ion-implantation-induced defects in fused silica and crystalline quartz

    International Nuclear Information System (INIS)

    Arnold, G.W.

    1978-01-01

    Defects produced by implantation of various atomic species in fused and crystalline SiO 2 were studied using infrared reflection spectroscopy (IRS) with UV-visible spectroscopy. We observe a new vibrational band at 830 cm -1 which is tentatively associated with the creation of two nonbridging O atoms in SiO 4 units. Numerous chemical effects were also observed, including evidence for chemical incorporation of Li and anomalously large O-vacancy production for Al + , B + and Si + implantation

  17. Determination of the vacancy formation enthalpy in chromium by positron annihilation

    International Nuclear Information System (INIS)

    Loper, G.D.; Smedskjaer, L.C.; Chason, M.K.; Siegel, R.W.

    1985-01-01

    Doppler broadening of the positron annihilation lineshape in 99.99 at. % pure chromium was measured over the temperature range 296 to 2049 0 K. The chromium sample was encapsulated in sapphire owing to its high vapor pressure near melting. Saturation-like behavior of the lineshape was observed near the melting temperature (2130 0 K). A two-state trapping model fit to the data yielded a vacancy formation enthalpy of 2.0 +- 0.2 eV. This result is discussed in relation to extant empirical relations for vacancy migration and self-diffusion in metals and to data from previous self-diffusion and annealing experiments in chromium. It is concluded that the observed vacancy ensemble is unlikely to be responsible for the measured self-diffusion behavior. The implications of the present results in terms of our understanding of mechanisms for self-diffusion in chromium and other refractory bcc metals are discussed

  18. Oxygen-vacancy defects on BaTiO3 (001) surface: a quantum chemical study

    International Nuclear Information System (INIS)

    Duque, Carlos; Stashans, Arvids

    2003-01-01

    A quantum-chemical study of technologically important BaTiO 3 crystal and oxygen-vacancy defects on its (001) surface is reported in the present work. The computations are made using a quantum-chemical method developed for periodic systems (crystals), which is based on the Hartree-Fock theory. The atomic rearrangement due to the surface creation is obtained for a pure BaTiO 3 by means of the periodic large unit cell (LUC) model and using an automated geometry optimisation procedure. The same technique is employed to study the electronic and structural properties of the material due to the presence of an O vacancy and F centre (two electrons trapped in an oxygen vacancy). The computations are carried out for both cubic and tetragonal lattices

  19. Trapped antihydrogen

    Energy Technology Data Exchange (ETDEWEB)

    Butler, E., E-mail: eoin.butler@cern.ch [CERN, Physics Department (Switzerland); Andresen, G. B. [Aarhus University, Department of Physics and Astronomy (Denmark); Ashkezari, M. D. [Simon Fraser University, Department of Physics (Canada); Baquero-Ruiz, M. [University of California, Department of Physics (United States); Bertsche, W. [Swansea University, Department of Physics (United Kingdom); Bowe, P. D. [Aarhus University, Department of Physics and Astronomy (Denmark); Cesar, C. L. [Universidade Federal do Rio de Janeiro, Instituto de Fisica (Brazil); Chapman, S. [University of California, Department of Physics (United States); Charlton, M.; Deller, A.; Eriksson, S. [Swansea University, Department of Physics (United Kingdom); Fajans, J. [University of California, Department of Physics (United States); Friesen, T.; Fujiwara, M. C. [University of Calgary, Department of Physics and Astronomy (Canada); Gill, D. R. [TRIUMF (Canada); Gutierrez, A. [University of British Columbia, Department of Physics and Astronomy (Canada); Hangst, J. S. [Aarhus University, Department of Physics and Astronomy (Denmark); Hardy, W. N. [University of British Columbia, Department of Physics and Astronomy (Canada); Hayden, M. E. [Simon Fraser University, Department of Physics (Canada); Humphries, A. J. [Swansea University, Department of Physics (United Kingdom); Collaboration: ALPHA Collaboration; and others

    2012-12-15

    Precision spectroscopic comparison of hydrogen and antihydrogen holds the promise of a sensitive test of the Charge-Parity-Time theorem and matter-antimatter equivalence. The clearest path towards realising this goal is to hold a sample of antihydrogen in an atomic trap for interrogation by electromagnetic radiation. Achieving this poses a huge experimental challenge, as state-of-the-art magnetic-minimum atom traps have well depths of only {approx}1 T ({approx}0.5 K for ground state antihydrogen atoms). The atoms annihilate on contact with matter and must be 'born' inside the magnetic trap with low kinetic energies. At the ALPHA experiment, antihydrogen atoms are produced from antiprotons and positrons stored in the form of non-neutral plasmas, where the typical electrostatic potential energy per particle is on the order of electronvolts, more than 10{sup 4} times the maximum trappable kinetic energy. In November 2010, ALPHA published the observation of 38 antiproton annihilations due to antihydrogen atoms that had been trapped for at least 172 ms and then released-the first instance of a purely antimatter atomic system confined for any length of time (Andresen et al., Nature 468:673, 2010). We present a description of the main components of the ALPHA traps and detectors that were key to realising this result. We discuss how the antihydrogen atoms were identified and how they were discriminated from the background processes. Since the results published in Andresen et al. (Nature 468:673, 2010), refinements in the antihydrogen production technique have allowed many more antihydrogen atoms to be trapped, and held for much longer times. We have identified antihydrogen atoms that have been trapped for at least 1,000 s in the apparatus (Andresen et al., Nature Physics 7:558, 2011). This is more than sufficient time to interrogate the atoms spectroscopically, as well as to ensure that they have relaxed to their ground state.

  20. Fast and slow border traps in MOS devices

    International Nuclear Information System (INIS)

    Fleetwood, D.M.

    1996-01-01

    Convergent lines of evidence are reviewed which show that near-interfacial oxide traps (border traps) that exchange charge with the Si can strongly affect the performance, radiation response, and long-term reliability of MOS devices. Observable effects of border traps include capacitance-voltage (C-V) hysteresis, enhanced l/f noise, compensation of trapped holes, and increased thermally stimulated current in MOS capacitors. Effects of faster (switching times between ∼10 -6 s and ∼1 s) and slower (switching times greater than ∼1 s) border traps have been resolved via a dual-transistor technique. In conjunction with studies of MOS electrical response, electron paramagnetic resonance and spin dependent recombination studies suggest that E' defects (trivalent Si centers in SiO 2 associated with O vacancies) can function as border traps in MOS devices exposed to ionizing radiation or high-field stress. Hydrogen-related centers may also be border traps

  1. 7 CFR 1221.105 - Vacancies.

    Science.gov (United States)

    2010-01-01

    ... Regulations of the Department of Agriculture (Continued) AGRICULTURAL MARKETING SERVICE (MARKETING AGREEMENTS... INFORMATION ORDER Sorghum Promotion, Research, and Information Order Sorghum Promotion, Research, and Information Board § 1221.105 Vacancies. To fill any vacancy occasioned by the death, removal, resignation, or...

  2. 24 CFR 983.352 - Vacancy payment.

    Science.gov (United States)

    2010-04-01

    ... PROJECT-BASED VOUCHER (PBV) PROGRAM Payment to Owner § 983.352 Vacancy payment. (a) Payment for move-out month. If an assisted family moves out of the unit, the owner may keep the housing assistance payment... 24 Housing and Urban Development 4 2010-04-01 2010-04-01 false Vacancy payment. 983.352 Section...

  3. VACANCIES AND THE RECRUITMENT OF NEW EMPLOYEES

    NARCIS (Netherlands)

    VANOURS, J; RIDDER, G

    Little is known about the search strategy that employers use in their efforts to fill job vacancies. In this article, we analyze unique micro data to study this search strategy. We conclude that almost all vacancies are filled from a pool of applicants that is formed shortly after the posting of the

  4. Defining and Measuring Job Vacancies in a Dynamic Perspective

    NARCIS (Netherlands)

    P.A. Donker van Heel (Peter)

    2015-01-01

    textabstractWhat is the best definition for job vacancies, what is the best method to measure job vacancies, and what further research is needed to gain a better insight into job vacancies in a dynamic perspective?

  5. Evaluation of structural vacancies for 1/1-Al-Re-Si approximant crystals by positron annihilation spectroscopy

    Science.gov (United States)

    Yamada, K.; Suzuki, H.; Kitahata, H.; Matsushita, Y.; Nozawa, K.; Komori, F.; Yu, R. S.; Kobayashi, Y.; Ohdaira, T.; Oshima, N.; Suzuki, R.; Takagiwa, Y.; Kimura, K.; Kanazawa, I.

    2018-01-01

    The size of structural vacancies and structural vacancy density of 1/1-Al-Re-Si approximant crystals with different Re compositions were evaluated by positron annihilation lifetime and Doppler broadening measurements. Incident positrons were found to be trapped at the monovacancy-size open space surrounded by Al atoms. From a previous analysis using the maximum entropy method and Rietveld method, such an open space is shown to correspond to the centre of Al icosahedral clusters, which locates at the vertex and body centre. The structural vacancy density of non-metallic Al73Re17Si10 was larger than that of metallic Al73Re15Si12. The observed difference in the structural vacancy density reflects that in bonding nature and may explain that in the physical properties of the two samples.

  6. Vacancy enhanced formation and phase transition of Cu-rich precipitates in α - iron under neutron irradiation

    Energy Technology Data Exchange (ETDEWEB)

    Lv, G. C. [Basic Experimental Center of Natural Science, University of Science and Technology Beijing, Beijing, 100083 (China); Corrosion and Protection Center, Key Laboratory of Environmental Fracture (MOE), University of Science and Technology Beijing, Beijing, 100083 (China); Zhang, H. [Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Canada, T6G2V4 (Canada); He, X. F.; Yang, W. [China Institute of Atomic Energy, Beijing, 102413 (China); Su, Y. J., E-mail: yjsu@ustb.edu.cn [Corrosion and Protection Center, Key Laboratory of Environmental Fracture (MOE), University of Science and Technology Beijing, Beijing, 100083 (China)

    2016-04-15

    In this paper, we employed both molecular statics and molecular dynamics simulation methods to investigate the role of vacancies in the formation and phase transition of Cu-rich precipitates in α-iron. The results indicated that vacancies promoted the diffusion of Cu atoms to form Cu-rich precipitates. After Cu-rich precipitates formed, they further trapped vacancies. The supersaturated vacancy concentration in the Cu-rich precipitate induced a shear strain, which triggered the phase transition from bcc to fcc structure by transforming the initial bcc (110) plane into fcc (111) plane. In addition, the formation of the fcc-twin structure and the stacking fault structure in the Cu-rich precipitates was observed in dynamics simulations.

  7. Simulation of the Atomic and Electronic Structure of Oxygen Vacancies and Polyvacancies in ZrO2

    Science.gov (United States)

    Perevalov, T. V.

    2018-03-01

    Cubic, tetragonal, and monoclinic phases of zirconium oxide with oxygen vacancies and polyvacancies are studied by quantum chemical modeling of the atomic and electronic structure. It is demonstrated that an oxygen vacancy in ZrO2 may act as both an electron trap and a hole one. An electron added to the ZrO2 structure with an oxygen vacancy is distributed between two neighboring Zr atoms and is a bonding orbital by nature. It is advantageous for each subsequent O vacancy to form close to the already existing ones; notably, one Zr atom has no more than two removed O atoms related to it. Defect levels from oxygen polyvacancies are distributed in the bandgap with preferential localization in the vicinity of the oxygen monovacancy level.

  8. Ion implantation-induced defects in Oxide Dispersion Strengthened (ODS) steel probed by positron annihilation spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Anwand, Wolfgang; Butterling, Maik; Brauer, Gerhard; Wagner, Andreas [HZDR, Institut fuer Strahlenphysik (Germany); Richter, Astrid [Technische Hochschule Wildau (Germany); Koegler, Reinhard [HZDR, Institut fuer Ionenstrahlphysik und Materialforschung (Germany); Chen, C.L. [I-Shou University, Kaohsiung (China)

    2012-07-01

    ODS steel is a promising candidate for an application in fission and fusion power plants of a new generation because of its advantageous properties as stability and temperature resistance. A microscopic understanding of the physical reasons of the mechanical and thermal properties as well as the behaviour of the material under irradiation is an important pre-condition for such applications. The investigated ODS FeCrAl alloy *PM2000* has been produced in a powder metallurgical way. Neutron-induced damage at ODS steel was simulated by He{sup +} and Fe{sup 2+} co-implantation with energies of 2.5 MeV and 400 keV, respectively, and different fluences. The implantation has been carried out with a dual ion beam which enables a simultaneous implantation of both ion types. Thereby the Fe{sup 2+} implantation was used for the creation of radiation defects, and He{sup +} was implanted in order to reproduce He bubbles as they are expected to appear by neutron irradiation. The implantation-induced damage was investigated by depth dependent Doppler broadening measurements using a variable energy slow positron beam.

  9. Oxygen ion implantation induced microstructural changes and electrical conductivity in Bakelite RPC detector material

    Energy Technology Data Exchange (ETDEWEB)

    Kumar, K. V. Aneesh, E-mail: aneesh1098@gmail.com; Ravikumar, H. B., E-mail: hbr@physics.uni-mysore.ac.in [Department of Studies in Physics, University of Mysore, Mysore-570006 (India); Ranganathaiah, C., E-mail: cr@physics.uni-mysore.ac.in [Govt. Research Centre, Sahyadri Educational Institutions, Mangalore-575007 (India); Kumarswamy, G. N., E-mail: kumy79@gmail.com [Department of Studies in Physics, Amrita Vishwa Vidyapeetham, Bangalore-560035 (India)

    2016-05-06

    In order to explore the structural modification induced electrical conductivity, samples of Bakelite Resistive Plate Chamber (RPC) detector materials were exposed to 100 keV Oxygen ion in the fluences of 10{sup 12}, 10{sup 13}, 10{sup 14} and 10{sup 15} ions/cm{sup 2}. Ion implantation induced microstructural changes have been studied using Positron Annihilation Lifetime Spectroscopy (PALS) and X-Ray Diffraction (XRD) techniques. Positron lifetime parameters viz., o-Ps lifetime and its intensity shows the deposition of high energy interior track and chain scission leads to the formation of radicals, secondary ions and electrons at lower ion implantation fluences (10{sup 12} to10{sup 14} ions/cm{sup 2}) followed by cross-linking at 10{sup 15} ions/cm{sup 2} fluence due to the radical reactions. The reduction in electrical conductivity of Bakelite detector material is correlated to the conducting pathways and cross-links in the polymer matrix. The appropriate implantation energy and fluence of Oxygen ion on polymer based Bakelite RPC detector material may reduce the leakage current, improves the efficiency, time resolution and thereby rectify the aging crisis of the RPC detectors.

  10. Characterization of carbon ion implantation induced graded microstructure and phase transformation in stainless steel

    Energy Technology Data Exchange (ETDEWEB)

    Feng, Kai; Wang, Yibo [Shanghai Key laboratory of Materials Laser Processing and Modification, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240 (China); Li, Zhuguo, E-mail: lizg@sjtu.edu.cn [Shanghai Key laboratory of Materials Laser Processing and Modification, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240 (China); Chu, Paul K. [Department of Physics and Materials Science, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong (China)

    2015-08-15

    Austenitic stainless steel 316L is ion implanted by carbon with implantation fluences of 1.2 × 10{sup 17} ions-cm{sup −} {sup 2}, 2.4 × 10{sup 17} ions-cm{sup −} {sup 2}, and 4.8 × 10{sup 17} ions-cm{sup −} {sup 2}. The ion implantation induced graded microstructure and phase transformation in stainless steel is investigated by X-ray diffraction, X-ray photoelectron spectroscopy and high resolution transmission electron microscopy. The corrosion resistance is evaluated by potentiodynamic test. It is found that the initial phase is austenite with a small amount of ferrite. After low fluence carbon ion implantation, an amorphous layer and ferrite phase enriched region underneath are formed. Nanophase particles precipitate from the amorphous layer due to energy minimization and irradiation at larger ion implantation fluence. The morphology of the precipitated nanophase particles changes from circular to dumbbell-like with increasing implantation fluence. The corrosion resistance of stainless steel is enhanced by the formation of amorphous layer and graphitic solid state carbon after carbon ion implantation. - Highlights: • Carbon implantation leads to phase transformation from austenite to ferrite. • The passive film on SS316L becomes thinner after carbon ion implantation. • An amorphous layer is formed by carbon ion implantation. • Nanophase precipitate from amorphous layer at higher ion implantation fluence. • Corrosion resistance of SS316L is improved by carbon implantation.

  11. A Study of the Vacancy-Impurity Interaction in Dilute Nickel Alloys by Core Electron Annihilation

    Science.gov (United States)

    Arbuzov, V. L.; Danilov, S. E.; Druzhkov, A. P.

    1997-08-01

    It is shown that the angular correlation of annihilation radiation can be used to identify vacancy-impurity complexes in dilute alloys. Annihilation of trapped positrons with core electrons bears information about the chemical environment of a vacancy defect. The method is especially effective for d-matrices doped with sp-impurities since annihilation parameters of positrons with d- and sp-shell electrons differ considerably. The potentialities of the method of core-electron annihilation of positrons are demonstrated taking electron-irradiated dilute Ni-P and Ni-Si alloys as an example. It is shown that the interaction between the vacancies, which migrate at the III stage of annealing, and P atoms in Ni-P causes a considerable change in the annihilation parameters of positrons with core electrons compared to pure Ni. In Ni-Si alloys the annihilation parameters of trapped positrons with core electrons do not differ from those in Ni. This fact is an evidence that Si atoms do not interact with vacancies in Ni.

  12. Positron annihilation spectroscopy of vacancy aggregates in neutron-irradiated MgO crystals

    International Nuclear Information System (INIS)

    Pareja, R.; De La Cruz, R.M.; Gonzalez, R.; Chen, Y.; Department of Energy, Washington, DC

    1992-01-01

    Positron annihilation measurements in neutron-irradiated MgO crystals show that the positron lifetime is shorter than in as-grown crystals, suggesting that most of the defects produced by neutron irradiations are positively charged. The concentration of the neutral anion vacancy (possibly also the neutral anion divacancy) is estimated to be no more than ∼ 10 16 cm -3 for samples irradiated to a dose of 10 17 to 10 19 n cm -2 . Annealing experiments on the neutron-irradiated crystals show a significant increase in the positron lifetime after anneals at 900 K. The increase is attributed to positron trapping by anion-vacancy aggregates. A lifetime of (284±15)ps is tentatively assigned to positrons trapped in these aggregates. (Author)

  13. Characterization of vacancy defects in Cu(In,GaSe2 by positron annihilation spectroscopy

    Directory of Open Access Journals (Sweden)

    M. R. M. Elsharkawy

    2016-12-01

    Full Text Available The photovoltaic performance of Cu(In1-x,GaxSe2 (CIGS materials is commonly assumed to be degraded by the presence of vacancy-related defects. However, experimental identification of specific vacancy defects remains challenging. In this work we report positron lifetime measurements on CIGS crystals with x = 0, and x = 0.05, saturation trapping to two dominant vacancy defect types, in both types of crystal, is observed and found to be independent of temperature between 15–300 K. Atomic superposition method calculations of the positron lifetimes for a range of vacancy defects in CIS and CGS are reported. The calculated lifetimes support the assignment of the first experimental lifetime component to monovacancy or divacancy defects, and the second to trivacancies, or possibly the large In-Se divacancy. Further, the calculated positron parameters obtained here provide evidence that positron annihilation spectroscopy has the capability to identify specific vacancy-related defects in the Cu(In1-x,GaxSe2 chalcogenides.

  14. Role of oxygen vacancies in anodic TiO2 thin films

    International Nuclear Information System (INIS)

    Tit, N.; Halley, J.W.

    1992-05-01

    Defects play an important role in the electronic and optical properties of amorphous solids in general. Here we present both experimental and theoretical investigations on the nature and origin of defect states in anodic rutile TiO 2 thin films (of thickness 5nm to 20nm). There is experimental evidence that the observed gap state at 0.7eV below the edge of conduction-band is due to an oxygen vacancy. For this reason, oxygen vacancies are used in our model. A comparison of the calculated bulk-photoconductivity to photospectroscopy experiment reveals that the films have bulk-like transport properties. On the other hand a fit of the surface density of states to the scanning tunneling microscopy (STM) on the (001) surfaces has suggested a surface defect density of 5% of oxygen vacancies. To resolve this discrepancy, we calculated the dc-conductivity where localization effects are included. Our results show an impurity band formation at about p c =9% of oxygen vacancies. We concluded that the gap states seen in STM are localized and the oxygen vacancies are playing the role of trapping centers (deep levels) in the studied films. (author). 15 refs, 5 figs

  15. Effects of internal hydrogen on the vacancy loop formation probability in Al

    International Nuclear Information System (INIS)

    Bui, T.X.; Sirois, E.; Robertson, I.M.

    1990-04-01

    The effect of internal hydrogen on the formation of vacancy dislocation loops from heavy-ion generated displacement cascades in Al has been investigated. Samples of high-purity aluminum and aluminum containing 900 and 1300 appM of hydrogen were irradiated at room temperature with 50 keV Kr+ ions. The ion dose rate was typically 2 x 10 10 ions cm -2 sec -1 and the ion dose was between 10 11 and 10 13 ion cm -2 . Under these irradiation conditions, dislocation loops were observed in all compositions, although the formation probability was relatively low (less than 10 percent of the displacement cascades produced a vacancy loop). The loop formation probability was further reduced by the presence of hydrogen. No difference in the geometry or the size of the loops created in the hydrogen free and hydrogen charged samples was found. These results are difficult to interpret, and the explanation may lie in the distribution and form of the hydrogen. To account for the large hydrogen concentrations and from calculations of the energy associated with hydrogen entry into aluminum, it has been suggested that the hydrogen enters the aluminum lattice with an accompanying vacancy. This will create hydrogen-vacancy complexes in the material; two dimensional complexes have been detected in the hydrogen-charged, but unirradiated, samples by the small-angle x-ray scattering technique. The possibility of these complexes trapping the vacancies produced by the cascade process exists thus lowering the formation probability. However, such a mechanism must occur within the lifetime of the cascade. Alternatively, if a displacement cascade overlaps with the hydrogen-vacancy complexes, the lower atomic density of the region will result in an increase in the cascade volume (decrease in the local vacancy concentration) which will also reduce the loop formation probability

  16. Electrical properties of the regrown implantation-induced amorphous layer on (1 1-bar 0 0)- and (1 1 2-bar 0)-oriented 6H-SiC

    International Nuclear Information System (INIS)

    Nakamura, Tomonori; Tanabe, Hitoshi; Hitomi, Takeshi; Satoh, Masataka

    2003-01-01

    In the (1 1-bar 0 0) and (1 1 2-bar 0)-oriented 6H-SiC, the electrical properties and activation process of the implanted phosphorus in the layer regrown from the implantation-induced amorphous layer are investigated by means of Hall effect measurement and Rutherford backscattering spectrometry. The samples are implanted by 60 keV phosphorus ions at room temperature with doses of 3 x 10 15 and 1 x 10 15 cm -2 to form implantation-induced amorphous layer and the partially disordered implant-layer, respectively. The implanted phosphorus in the implantation-induced amorphous layer can be electrically activated by annealing at 1000 deg. C. The electrical activity for the case of the implantation-induced amorphous layer (ratio of sheet carrier concentration to ion dose) is 2-3 times larger than that for the case of the partially disordered implant-layer for the annealing temperature of 1500 deg. C

  17. Ion-implantation induced defects in ZnO studied by a slow positron beam

    International Nuclear Information System (INIS)

    Chen, Z.Q.; Maekawa, M.; Kawasuso, A.; Sekiguchi, T.; Suzuki, R.

    2004-01-01

    Introduction and annealing behavior of defects in Al + -implanted ZnO have been studied using an energy variable slow positron beam. Vacancy clusters are produced after Al + -implantation. With increasing ion dose above 10 14 Al + /cm 2 the implanted layer is amorphized. Heat treatment up to 600 C enhances the creation of large voids that allow the positronium formation. The large voids disappear accompanying the recrystallization process by further heat treatment above 600 C. Afterwards, implanted Al impurities are completely activated to contribute to the n-type conduction. The ZnO crystal quality is also improved after recrystallization. (orig.)

  18. Ion-implantation induced defects in ZnO studied by a slow positron beam

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Z.Q.; Maekawa, M.; Kawasuso, A. [Japan Atomic Energy Research Institute, Gunma (Japan); Sekiguchi, T. [National Inst. for Materials Science, Tsukuba, Ibaraki (Japan); Suzuki, R. [National Inst. of Advanced Industrial Science and Technology, Tsukuba, Ibaraki (Japan)

    2004-07-01

    Introduction and annealing behavior of defects in Al{sup +}-implanted ZnO have been studied using an energy variable slow positron beam. Vacancy clusters are produced after Al{sup +}-implantation. With increasing ion dose above 10{sup 14} Al{sup +}/cm{sup 2} the implanted layer is amorphized. Heat treatment up to 600 C enhances the creation of large voids that allow the positronium formation. The large voids disappear accompanying the recrystallization process by further heat treatment above 600 C. Afterwards, implanted Al impurities are completely activated to contribute to the n-type conduction. The ZnO crystal quality is also improved after recrystallization. (orig.)

  19. Solute-vacancy binding in aluminum

    International Nuclear Information System (INIS)

    Wolverton, C.

    2007-01-01

    Previous efforts to understand solute-vacancy binding in aluminum alloys have been hampered by a scarcity of reliable, quantitative experimental measurements. Here, we report a large database of solute-vacancy binding energies determined from first-principles density functional calculations. The calculated binding energies agree well with accurate measurements where available, and provide an accurate predictor of solute-vacancy binding in other systems. We find: (i) some common solutes in commercial Al alloys (e.g., Cu and Mg) possess either very weak (Cu), or even repulsive (Mg), binding energies. Hence, we assert that some previously reported large binding energies for these solutes are erroneous. (ii) Large binding energies are found for Sn, Cd and In, confirming the proposed mechanism for the reduced natural aging in Al-Cu alloys containing microalloying additions of these solutes. (iii) In addition, we predict that similar reduction in natural aging should occur with additions of Si, Ge and Au. (iv) Even larger binding energies are found for other solutes (e.g., Pb, Bi, Sr, Ba), but these solutes possess essentially no solubility in Al. (v) We have explored the physical effects controlling solute-vacancy binding in Al. We find that there is a strong correlation between binding energy and solute size, with larger solute atoms possessing a stronger binding with vacancies. (vi) Most transition-metal 3d solutes do not bind strongly with vacancies, and some are even energetically strongly repelled from vacancies, particularly for the early 3d solutes, Ti and V

  20. Identification of vacancy defect complexes in transparent semiconducting oxides ZnO, In2O3 and SnO2

    International Nuclear Information System (INIS)

    Makkonen, Ilja; Korhonen, Esa; Prozheeva, Vera; Tuomisto, Filip

    2016-01-01

    Positron annihilation spectroscopy, when combined with supporting high-quality modeling of positron states and annihilation in matter, is a powerful tool for detailed defect identification of vacancy-type defects in semiconductors and oxides. Here we demonstrate that the Doppler broadening of the positron annihilation radiation is a very sensitive means for observing the oxygen environment around cation vacancies, the main open-volume defects trapping positrons in measurements made for transparent semiconducting oxides. Changes in the positron annihilation signal due to external manipulation such as irradiation and annealing can be correlated with the associated changes in the sizes of the detected vacancy clusters. Our examples for ZnO, In 2 O 3 and SnO 2 demonstrate that oxygen vacancies in oxides can be detected directly using positron annihilation spectroscopy when they are complexed with cation vacancies. (paper)

  1. Identification of vacancy defect complexes in transparent semiconducting oxides ZnO, In2O3 and SnO2

    Science.gov (United States)

    Makkonen, Ilja; Korhonen, Esa; Prozheeva, Vera; Tuomisto, Filip

    2016-06-01

    Positron annihilation spectroscopy, when combined with supporting high-quality modeling of positron states and annihilation in matter, is a powerful tool for detailed defect identification of vacancy-type defects in semiconductors and oxides. Here we demonstrate that the Doppler broadening of the positron annihilation radiation is a very sensitive means for observing the oxygen environment around cation vacancies, the main open-volume defects trapping positrons in measurements made for transparent semiconducting oxides. Changes in the positron annihilation signal due to external manipulation such as irradiation and annealing can be correlated with the associated changes in the sizes of the detected vacancy clusters. Our examples for ZnO, In2O3 and SnO2 demonstrate that oxygen vacancies in oxides can be detected directly using positron annihilation spectroscopy when they are complexed with cation vacancies.

  2. Ripple Trap

    Science.gov (United States)

    2006-01-01

    3 April 2006 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows the margin of a lava flow on a cratered plain in the Athabasca Vallis region of Mars. Remarkably, the cratered plain in this scene is essentially free of bright, windblown ripples. Conversely, the lava flow apparently acted as a trap for windblown materials, illustrated by the presence of the light-toned, wave-like texture over much of the flow. That the lava flow surface trapped windblown sand and granules better than the cratered plain indicates that the flow surface has a rougher texture at a scale too small to resolve in this image. Location near: 10.7oN, 204.5oW Image width: 3 km (1.9 mi) Illumination from: lower left Season: Northern Winter

  3. 7 CFR 1210.324 - Vacancies.

    Science.gov (United States)

    2010-01-01

    ... Regulations of the Department of Agriculture (Continued) AGRICULTURAL MARKETING SERVICE (MARKETING AGREEMENTS AND ORDERS; MISCELLANEOUS COMMODITIES), DEPARTMENT OF AGRICULTURE WATERMELON RESEARCH AND PROMOTION PLAN Watermelon Research and Promotion Plan National Watermelon Promotion Board § 1210.324 Vacancies...

  4. 7 CFR 920.26 - Vacancies.

    Science.gov (United States)

    2010-01-01

    ... member or as an alternate member of the committee to qualify, or in the event of the death, removal... vacancy without regard to nominations, which selection shall be made on the basis of representation...

  5. 7 CFR 924.26 - Vacancies.

    Science.gov (United States)

    2010-01-01

    ... an alternate member of the committee to qualify, or in the event of the death, removal, resignation... vacancy without regard to nominations, which selection shall be made on the basis of representation...

  6. Trapped antihydrogen

    CERN Document Server

    Butler, E; Ashkezari, M D; Baquero-Ruiz, M; Bertsche, W; Bowe, P D; Cesar, C L; Chapman, S; Charlton, M; Deller, A; Eriksson, S; Fajans, J; Friesen, T; Fujiwara, M C; Gill, D R; Gutierrez, A; Hangst, J S; Hardy, W N; Hayden, M E; Humphries, A J; Hydomako, R; Jenkins, M J; Jonsell, S; Jørgensen, L V; Kemp, S L; Kurchaninov, L; Madsen, N; Menary, S; Nolan, P; Olchanski, K; Olin, A; Povilus, A; Pusa, P; Rasmussen, C Ø; Robicheaux, F; Sarid, E; Seif el Nasr, S; Silveira, D M; So, C; Storey, J W; Thompson, R I; van der Werf, D P; Wurtele, J S; Yamazaki,Y

    2012-01-01

    Precision spectroscopic comparison of hydrogen and antihydrogen holds the promise of a sensitive test of the Charge-Parity-Time theorem and matter-antimatter equivalence. The clearest path towards realising this goal is to hold a sample of antihydrogen in an atomic trap for interrogation by electromagnetic radiation. Achieving this poses a huge experimental challenge, as state-of-the-art magnetic-minimum atom traps have well depths of only ∼1 T (∼0.5 K for ground state antihydrogen atoms). The atoms annihilate on contact with matter and must be ‘born’ inside the magnetic trap with low kinetic energies. At the ALPHA experiment, antihydrogen atoms are produced from antiprotons and positrons stored in the form of non-neutral plasmas, where the typical electrostatic potential energy per particle is on the order of electronvolts, more than 104 times the maximum trappable kinetic energy. In November 2010, ALPHA published the observation of 38 antiproton annihilations due to antihydrogen atoms that had been ...

  7. Vacancies in quantal Wigner crystals near melting

    International Nuclear Information System (INIS)

    Barraza, N.; Colletti, L.; Tosi, M.P.

    1999-04-01

    We estimate the formation energy of lattice vacancies in quantal Wigner crystals of charged particles near their melting point at zero temperature, in terms of the crystalline Lindemann parameter and of the static dielectric function of the fluid phase near freezing. For both 3D and 2D crystals of electrons our results suggest the presence of vacancies in the ground state at the melting density. (author)

  8. Effect of vacancy loops on swelling of metals under irradiation

    International Nuclear Information System (INIS)

    Golubov, S.I.

    1981-01-01

    Subsequent analysis of vacancy loops formation in metals under irradiation is carried out and effect of vacancy loops on vacancy porosity is studied. Expression for quasistationary function of vacancy loops distribution according to sizes taking into consideration two mechanisms of their initiation-cascade and fluctuational ones - is obtained. It is shown that rate of vacancy absorption and interstitials by vacancy loops in quasiequilibrium state is similar and depends only on summary length of loops, for its calculations the self-coordinated procedure is formulated. For the rate of metal swelling under irradiation obtained is the expression taking into consideration the presence of vacancy loops [ru

  9. Atomic adsorption on graphene with a single vacancy: systematic DFT study through the periodic table of elements

    Science.gov (United States)

    Pašti, Igor A.; Jovanović, Aleksandar; Dobrota, Ana S.; Mentus, Slavko V.; Johansson, Börje; Skorodumova, Natalia V.

    Vacancies in graphene present sites of altered chemical reactivity and open possibilities to tune graphene properties by defect engineering. The understanding of chemical reactivity of such defects is essential for successful implementation of carbon materials in advanced technologies. We report the results of a systematic DFT study of atomic adsorption on graphene with a single vacancy for the elements of rows 1 to 6 of the Periodic Table of Elements (PTE), excluding lanthanides. The calculations have been performed using PBE, long-range dispersion interaction-corrected PBE (PBE+D2 and PBE+D3) and non-local vdW-DF2 functional. We find that most elements strongly bind to the vacancy, except for the elements of groups 11 and 12, and noble gases, for which the contribution of dispersion interaction to bonding is most significant. The strength of the interaction with the vacancy correlates with the cohesive energy of the elements in their stable phases: the higher the cohesive energy is the stronger bonding to the vacancy can be expected. As most atoms can be trapped at the SV site we have calculated the potentials of dissolution and found that in most cases the metals adsorbed at the vacancy are more "noble" than they are in their corresponding stable phases.

  10. The Correlation Between Dislocations and Vacancy Defects Using Positron Annihilation Spectroscopy

    Science.gov (United States)

    Pang, Jinbiao; Li, Hui; Zhou, Kai; Wang, Zhu

    2012-07-01

    An analysis program for positron annihilation lifetime spectra is only applicable to isolated defects, but is of no use in the presence of defective correlations. Such limitations have long caused problems for positron researchers in their studies of complicated defective systems. In order to solve this problem, we aim to take a semiconductor material, for example, to achieve a credible average lifetime of single crystal silicon under plastic deformation at different temperatures using positron life time spectroscopy. By establishing reasonable positron trapping models with defective correlations and sorting out four lifetime components with multiple parameters, as well as their respective intensities, information is obtained on the positron trapping centers, such as the positron trapping rates of defects, the density of the dislocation lines and correlation between the dislocation lines, and the vacancy defects, by fitting with the average lifetime with the aid of Matlab software. These results give strong grounds for the existence of dislocation-vacancy correlation in plastically deformed silicon, and lay a theoretical foundation for the analysis of positron lifetime spectra when the positron trapping model involves dislocation-related defects.

  11. Formation of hydrogen-related traps in electron-irradiated n-type silicon by wet chemical etching

    International Nuclear Information System (INIS)

    Tokuda, Yutaka; Shimada, Hitoshi

    1998-01-01

    Interaction of hydrogen atoms and vacancy-related defects in 10 MeV electron-irradiated n-type silicon has been studied by deep-level transient spectroscopy. Hydrogen has been incorporated into electron-irradiated n-type silicon by wet chemical etching. The reduction of the concentration of the vacancy-oxygen pair and divacancy occurs by the incorporation of hydrogen, while the formation of the NH1 electron trap (E c - 0.31 eV) is observed. Further decrease of the concentration of the vacancy-oxygen pair and further increase of the concentration of the NH1 trap are observed upon subsequent below-band-gap light illumination. It is suggested that the trap NH1 is tentatively ascribed to the vacancy-oxygen pair which is partly saturated with hydrogen

  12. Spin properties of dense near-surface ensembles of nitrogen-vacancy centers in diamond

    Science.gov (United States)

    Tetienne, J.-P.; de Gille, R. W.; Broadway, D. A.; Teraji, T.; Lillie, S. E.; McCoey, J. M.; Dontschuk, N.; Hall, L. T.; Stacey, A.; Simpson, D. A.; Hollenberg, L. C. L.

    2018-02-01

    We present a study of the spin properties of dense layers of near-surface nitrogen-vacancy (NV) centers in diamond created by nitrogen ion implantation. The optically detected magnetic resonance contrast and linewidth, spin coherence time, and spin relaxation time, are measured as a function of implantation energy, dose, annealing temperature, and surface treatment. To track the presence of damage and surface-related spin defects, we perform in situ electron spin resonance spectroscopy through both double electron-electron resonance and cross-relaxation spectroscopy on the NV centers. We find that, for the energy (4 -30 keV) and dose (5 ×1011-1013ions/cm 2 ) ranges considered, the NV spin properties are mainly governed by the dose via residual implantation-induced paramagnetic defects, but that the resulting magnetic sensitivity is essentially independent of both dose and energy. We then show that the magnetic sensitivity is significantly improved by high-temperature annealing at ≥1100 ∘C . Moreover, the spin properties are not significantly affected by oxygen annealing, apart from the spin relaxation time, which is dramatically decreased. Finally, the average NV depth is determined by nuclear magnetic resonance measurements, giving ≈10 -17 nm at 4-6 keV implantation energy. This study sheds light on the optimal conditions to create dense layers of near-surface NV centers for high-sensitivity sensing and imaging applications.

  13. Positron annihilation study of formation of Mg vacancy in MgO

    International Nuclear Information System (INIS)

    Mizuno, M.; Araki, H.; Shirai, Y.; Inoue, Y.; Sugita, K.; Mizoguchi, T.; Tanaka, I.; Adachi, H.

    2004-01-01

    We have investigated the formation of Mg vacancy induced by ultra-dilute trivalent impurities in MgO by a combination of positron annihilation measurement and theoretical calculations of positron lifetimes. The undoped MgO yields the shortest positron lifetime of 130 ps that is shorter than that of 166 ps previously reported using a single crystal sample. The positron lifetime of the doped samples increases with the increase of the Al or Ga dopant concentration and is saturated at around 170 ps. This result indicates that the previously reported value of 166 ps is ascribed to not the bulk but the vacancy state induced by impurities. The experimental bulk lifetime of 130 ps, which is obtained by employing trapping model, is well reproduced by the theoretical calculation using the semiconductor model. The calculated defect lifetime is about 20 ps longer than the experimental value. This may be due to the lattice relaxation around Mg vacancy associated with the trapping of positrons. (orig.)

  14. Positron annihilation study of formation of Mg vacancy in MgO

    Energy Technology Data Exchange (ETDEWEB)

    Mizuno, M.; Araki, H.; Shirai, Y. [Science and Technology Center for Atoms, Molecules and Ions Control, Osaka Univ., Osaka (Japan); Inoue, Y.; Sugita, K. [Dept. of Materials Science and Engineering, Osaka Univ., Osaka (Japan); Mizoguchi, T.; Tanaka, I.; Adachi, H. [Dept. of Materials Science and Engineering, Kyoto Univ., Kyoto (Japan)

    2004-07-01

    We have investigated the formation of Mg vacancy induced by ultra-dilute trivalent impurities in MgO by a combination of positron annihilation measurement and theoretical calculations of positron lifetimes. The undoped MgO yields the shortest positron lifetime of 130 ps that is shorter than that of 166 ps previously reported using a single crystal sample. The positron lifetime of the doped samples increases with the increase of the Al or Ga dopant concentration and is saturated at around 170 ps. This result indicates that the previously reported value of 166 ps is ascribed to not the bulk but the vacancy state induced by impurities. The experimental bulk lifetime of 130 ps, which is obtained by employing trapping model, is well reproduced by the theoretical calculation using the semiconductor model. The calculated defect lifetime is about 20 ps longer than the experimental value. This may be due to the lattice relaxation around Mg vacancy associated with the trapping of positrons. (orig.)

  15. A detailed physical model for ion implant induced damage in silicon

    International Nuclear Information System (INIS)

    Tian, S.; Morris, M.F.; Morris, S.J.; Obradovic, B.; Wang, G.; Tasch, A.F.

    1998-01-01

    A unified physically based ion implantation damage model has been developed which successfully predicts both the impurity profiles and the damage profiles for a wide range of implant conditions for arsenic, phosphorus, BF 2 , and boron implants into single-crystal silicon. In addition, the amorphous layer thicknesses predicted by this new damage model are also in excellent agreement with experimental measurements. This damage model is based on the physics of point defects in silicon, and explicitly simulates the defect production, diffusion, and their interactions which include interstitial-vacancy recombination, clustering of same type of defects, defect-impurity complex formation, emission of mobile defects from clusters, and surface effects for the first time. New computationally efficient algorithms have been developed to overcome the barrier of the excessive computational requirements. In addition, the new model has been incorporated in the UT-MARLOWE ion implantation simulator, and has been developed primarily for use in engineering workstations. This damage model is the most physical model in the literature to date within the framework of the binary collision approximation (BCA), and provides the required, accurate as-implanted impurity profiles and damage profiles for transient enhanced diffusion (TED) simulation

  16. Photoluminescence related to Gd3+:N-vacancy complex in GaN:Gd multi-quantum wells

    International Nuclear Information System (INIS)

    Almokhtar, Mohamed; Emura, Shuichi; Koide, Akihiro; Fujikawa, Takashi; Asahi, Hajime

    2015-01-01

    Highlights: • We grew Gd-doped GaN multi-quantum wells (MQWs) with quantum layer thickness of one nm by MBE. • The X-ray absorption near edge structure spectra observed at Gd LIII-edge indicate a nitrogen vacancy adjacent to Gd substituting the Ga ion in Gd-doped GaN MQW. • The photoluminescence of the samples is discussed considering the formation of a Gd 3+ :Nitrogen-vacancy complex. • A model is presented considering exciton-polaron formation trapped in defect sites around the Gd 3+ :N-vacancy complex in Gd-doped GaN MQWs. - Abstract: The photoluminescence of Gd-doped GaN multi-quantum wells (MQWs) is presented and discussed considering the formation of a Gd 3+ :Nitrogen-vacancy (N-vacancy) complex. A lower energy photoluminescence peak was observed for the Gd-doped GaN MQW sample with respect to the main peak assigned to a neutral donor bound exciton (D 0 X) of the undoped GaN MQW sample. The X-ray absorption near edge structure spectrum observed at Gd L III -edge indicates a nitrogen vacancy adjacent to the Gd substituting the Ga ion in Gd-doped GaN MQW sample. Local stresses around the Gd dopants in Gd-doped GaN matrix generated due to the larger diameter of the Gd 3+ ion with respect to the Ga 3+ ion can be relieved by the creation of vacancies. The lower formation energy of N-vacancies in GaN matrix introduce them as a preferred candidate to relieve the generated stresses. A Gd 3+ :N-vacancy complex consisting of a Gd 3+ ion and the created nitrogen vacancy adjacent to the Gd 3+ dopant is likely to form in GaN:Gd matrix. The lower photoluminescence peak energy observed in the Gd-doped GaN MQW sample is assigned to the recombination of an exciton captured at the Gd 3+ :N-vacancy complex forming a small polaron-like state. A model is presented considering the small exciton-polaron population in defect sites captured around the Gd 3+ ions in the Gd-doped GaN

  17. Vacancy formation enthalpies in bcc and fcc FeCo by positron annihilation

    International Nuclear Information System (INIS)

    Jackman, J.A.; Kim, S.M.; Buyers, W.J.L.

    1982-01-01

    A long slit angular correlation apparatus was used to measure the peak coincidence count rate in stoichiometric FeCo from 290 K to 1510 K. The count rate did not change significantly at the order-disorder phase transition (1008 K), but decreased sharply by 3.2% at the bcc-fcc phase transition at 1258 K. The threshold temperatures for the trapping of positrons in vacancies are measured to be 1125 K for the bcc phase and 1260 K for the fcc phase. The vacancy formation enthalpies in the bcc and fcc phases are determined to be 1.45 +- 0.05 eV and 1.63 +- 0.05 eV. The activation energies for self-diffusion have been estimated from the threshold temperatures, and are found to be 2.45 eV and 2.74 eV for the bcc and fcc phases respectively. (Auth.)

  18. Trapping of deuterium in argon-implanted nickel

    International Nuclear Information System (INIS)

    Frank, R.C.; Rehn, L.E.; Baldo, P.

    1985-01-01

    Argon ions with energy 250 keV were implanted at fluences of 2 x 10 16 cm -2 at temperatures of 500, 250, and 21 0 C, in the specimen of relatively pure polycrystalline nickel. Deuterium was introduced into the surface and implanted regions by making the specimen the negative electrode of an electrolytic cell containing 1-N pure deuterated sulfuric acid. Deuterium trapped in the vacancy complexes of the implanted regions was analyzed as a function of temperature using the vacancy complexes of the implanted regions was analyzed as a function of temperature using the 2 H( 3 He, 1 H) 4 He nuclear reaction during an isochronal annealing process. The results indicate that the types of traps and trap densities found in the regions implanted at 21 and 250 0 C were essentially identical while the trap density found in the region implanted at 500 0 C was approximately 40% of that found in the other regions. Math model comparison with the experimental results suggests the existence of at least two types of traps in each region. Trap binding enthalpies used in the math model to fit the experimental data were slightly higher for the region implanted with argon at 500 0 C than for the regions implanted at the lower temperatures. TEM studies revealed the presence of small voids in the region implanted at 500 0 as well as dislocation loops similar to those found in the regions implanted at the lower temperatures. 20 references, 2 figures

  19. Globalisation Trapped

    Directory of Open Access Journals (Sweden)

    João Caraça

    2017-05-01

    Full Text Available The promise of making society progress through the direct applications of science was finally fulfilled in the mid-20th century. Science progressed immensely, propelled by the effects of the two world wars. The first science-based technologies saw the daylight during the 1940s and their transformative power was such that neither the military, nor subsequently the markets, allowed science to return intact to its curiosity-driven nest. Technoscience was born then and (being progressively pulled away from curiosity-driven science was able to grow enormously, erecting a formidable structure of networks of institutions that impacted decisively on the economy. It is a paradox, or maybe a trap, that the fulfillment of science’s solemn promise of ‘transforming nature’ means seeing ourselves and our Western societies entangled in crises after crises with no clear outcome in view. A redistribution of geopolitical power is under way, along with the deployment of information and communication technologies, forcing dominant structures to oscillate, as knowledge about organization and methods, marketing, design, and software begins to challenge the role of technoscience as the main vector of economic growth and wealth accumulation. What ought to be done?

  20. 7 CFR 1260.146 - Vacancies.

    Science.gov (United States)

    2010-01-01

    ... Regulations of the Department of Agriculture (Continued) AGRICULTURAL MARKETING SERVICE (MARKETING AGREEMENTS AND ORDERS; MISCELLANEOUS COMMODITIES), DEPARTMENT OF AGRICULTURE BEEF PROMOTION AND RESEARCH Beef Promotion and Research Order Cattlemen's Beef Promotion and Research Board § 1260.146 Vacancies. To fill any...

  1. 7 CFR 1207.324 - Vacancies.

    Science.gov (United States)

    2010-01-01

    ... Regulations of the Department of Agriculture (Continued) AGRICULTURAL MARKETING SERVICE (MARKETING AGREEMENTS AND ORDERS; MISCELLANEOUS COMMODITIES), DEPARTMENT OF AGRICULTURE POTATO RESEARCH AND PROMOTION PLAN Potato Research and Promotion Plan National Potato Promotion Board § 1207.324 Vacancies. To fill any...

  2. 7 CFR 1280.205 - Vacancies.

    Science.gov (United States)

    2010-01-01

    ... 7 Agriculture 10 2010-01-01 2010-01-01 false Vacancies. 1280.205 Section 1280.205 Agriculture Regulations of the Department of Agriculture (Continued) AGRICULTURAL MARKETING SERVICE (MARKETING AGREEMENTS... INFORMATION ORDER Lamb Promotion, Research, and Information Order Lamb Promotion, Research, and Information...

  3. 7 CFR 1215.25 - Vacancies.

    Science.gov (United States)

    2010-01-01

    ... 7 Agriculture 10 2010-01-01 2010-01-01 false Vacancies. 1215.25 Section 1215.25 Agriculture Regulations of the Department of Agriculture (Continued) AGRICULTURAL MARKETING SERVICE (MARKETING AGREEMENTS... CONSUMER INFORMATION Popcorn Promotion, Research, and Consumer Information Order Popcorn Board § 1215.25...

  4. Inflammasome components ASC and AIM2 modulate the acute phase of biomaterial implant-induced foreign body responses

    Science.gov (United States)

    Christo, Susan N.; Diener, Kerrilyn R.; Manavis, Jim; Grimbaldeston, Michele A.; Bachhuka, Akash; Vasilev, Krasimir; Hayball, John D.

    2016-01-01

    Detailing the inflammatory mechanisms of biomaterial-implant induced foreign body responses (FBR) has implications for revealing targetable pathways that may reduce leukocyte activation and fibrotic encapsulation of the implant. We have adapted a model of poly(methylmethacrylate) (PMMA) bead injection to perform an assessment of the mechanistic role of the ASC-dependent inflammasome in this process. We first demonstrate that ASC−/− mice subjected to PMMA bead injections had reduced cell infiltration and altered collagen deposition, suggesting a role for the inflammasome in the FBR. We next investigated the NLRP3 and AIM2 sensors because of their known contributions in recognising damaged and apoptotic cells. We found that NLRP3 was dispensable for the fibrotic encapsulation; however AIM2 expression influenced leukocyte infiltration and controlled collagen deposition, suggesting a previously unexplored link between AIM2 and biomaterial-induced FBR. PMID:26860464

  5. Self-trapping of helium in metals

    International Nuclear Information System (INIS)

    Wilson, W.D.; Bisson, C.L.; Baskes, M.I.

    1981-01-01

    Atomistic calculations are presented which demonstrate that helium atoms in a metal lattice are able to cluster with each other, producing vacancies and nearby self-interstitial defects. Even a small number of helium atoms is found to be sufficient to create these large distortions. As few as five interstitial helium can spontaneously produce a lattice vacancy and nearby self-interstitial. An eight-helium-atom cluster gives rise to two such defects, and 16 helium atoms to more than five self-interstitial vacancy pairs. It was noted that the self-interstitials prefer to agglomerate on the same ''side'' of the helium cluster rather than to spread themselves out uniformly. The binding energy of each additional helium atom to these clusters increases with helium concentration and the trap is apparently unsaturable. A rate theory using these atomistic binding energies has been used to calculate the kinetics of helium-bubble nucleation and growth. The results are consistent with measurements of the properties of helium resulting from tritium decay

  6. Cryogenic surface ion traps

    International Nuclear Information System (INIS)

    Niedermayr, M.

    2015-01-01

    Microfabricated surface traps are a promising architecture to realize a scalable quantum computer based on trapped ions. In principle, hundreds or thousands of surface traps can be located on a single substrate in order to provide large arrays of interacting ions. To this end, trap designs and fabrication methods are required that provide scalable, stable and reproducible ion traps. This work presents a novel surface-trap design developed for cryogenic applications. Intrinsic silicon is used as the substrate material of the traps. The well-developed microfabrication and structuring methods of silicon are utilized to create simple and reproducible traps. The traps were tested and characterized in a cryogenic setup. Ions could be trapped and their life time and motional heating were investigated. Long ion lifetimes of several hours were observed and the measured heating rates were reproducibly low at around 1 phonon per second at a trap frequency of 1 MHz. (author) [de

  7. Electron spin resonance from NV centers in diamonds levitating in an ion trap

    International Nuclear Information System (INIS)

    Delord, T; Nicolas, L; Schwab, L; Hétet, G

    2017-01-01

    We report observations of the electron spin resonance (ESR) of nitrogen vacancy centers in diamonds that are levitating in an ion trap. Using a needle Paul trap operating under ambient conditions, we demonstrate efficient microwave driving of the electronic spin and show that the spin properties of deposited diamond particles measured by the ESR are retained in the Paul trap. We also exploit the ESR signal to show angle stability of single trapped mono-crystals, a necessary step towards spin-controlled levitating macroscopic objects. (paper)

  8. A trap activation model for hydrogen retention and isotope exchange in some refractory materials

    International Nuclear Information System (INIS)

    Brice, D.K.; Doyle, B.L.

    1982-01-01

    Our recently-developed Local Mixing Model (LMM) has been successful in describing and predicting the properties of hydrogen retention and isotope exchange for a variety of refractory materials. For some materials, however, the detailed predictions of the LMM are not observed. A Trap Activation Model (TAM) is proposed here to account for the observed departures from the LMM. Comparison of experimental room temperature saturation depth profiles for H + →Si with the predictions of TAM suggests that the hydrogen traps are multiple-vacancy complexes in this system. The observed profiles result from a beam-induced competition between trap creation/annihilation and H-trapping/detrapping. (orig.)

  9. Influence of impurities on the evolution of vacancy-type defects in neutron-irradiated nickel

    International Nuclear Information System (INIS)

    Druzhkov, A.P.; Perminov, D.A.; Arbuzov, V.L.

    2012-01-01

    Highlights: ► We study, by means of PAS, the effects of purity on damage evolution in neutron-irradiated Ni at 330 K. ► Impurity carbon atoms in solution decrease the cascade efficiency during irradiation. ► C–V complexes are formed on the recovery stage III in impure Ni irradiated with 10 −4 dpa. ► The formation of V-loops and SFTs dominate on stage III with increasing dose level. ► The thermal stability of SFTs in impure Ni is similar to that in pure Ni. - Abstract: In order to investigate the effect of impurities on vacancy defect evolution in nickel, specimens with high (5N) and technical (3N) purity were neutron-irradiated at ∼330 K in the IVV-2M reactor (Russia) to fluencies in the range of 1 × 10 21 –1 × 10 23 n/m 2 (E > 0.1 MeV) corresponding to displacement dose levels in the range of about 0.0001–0.01 dpa and subsequently stepwise annealed to about 900 K. The specimens of Ni with different purities were characterized both in as-irradiated state as well as after post-irradiation annealing by positron annihilation spectroscopy. The formation of three-dimensional vacancy clusters (3D-VCs) in cascades was observed under neutron irradiation. The density and size of 3D-VCs depended not only on dose level, but also on purity. The population of 3D-VCs in the technical Ni is lower than that in the high-purity Ni. 3D-VCs collapse into secondary-type clusters (stacking fault tetrahedra (SFTs) and vacancy loops) during stepwise annealing at 350–450 K (stage III in Ni). The suppression of secondary cluster formation in 3N Ni is attributed to an effective vacancy interaction with impurity carbon atoms, which based on a relatively large vacancy–carbon atom binding energy (0.32–0.35 eV). The trapping of vacancies released at the collapse of 3D-VCs by the interstitial impurity atoms dominates at low irradiation dose level (10 −4 dpa). Thus, we found that carbon impurity atoms have strong effects both on the primary vacancy-type defect

  10. Extraction of sub-gap density of states via capacitance-voltage measurement for the erasing process in a TFT charge-trapping memory

    Science.gov (United States)

    Chiang, Yen-Chang; Hsiao, Yang-Hsuan; Li, Jeng-Ting; Chen, Jen-Sue

    2018-02-01

    Charge-trapping memories (CTMs) based on zinc tin oxide (ZTO) semiconductor thin-film transistors (TFTs) can be programmed by a positive gate voltage and erased by a negative gate voltage in conjunction with light illumination. To understand the mechanism involved, the sub-gap density of states associated with ionized oxygen vacancies in the ZTO active layer is extracted from optical response capacitance-voltage (C-V) measurements. The corresponding energy states of ionized oxygen vacancies are observed below the conduction band minimum at approximately 0.5-1.0 eV. From a comparison of the fitted oxygen vacancy concentration in the CTM-TFT after the light-bias erasing operation, it is found that the pristine-erased device contains more oxygen vacancies than the program-erased device because the trapped electrons in the programmed device are pulled into the active layer and neutralized by the oxygen vacancies that are present there.

  11. Involvement of hydrogen-vacancy complexes in the baking effect of niobium cavities

    Directory of Open Access Journals (Sweden)

    B. Visentin

    2010-05-01

    Full Text Available Baking is necessary to improve high accelerating gradient performances of superconducting niobium cavities. Ten years after this discovery in 1998, the understanding of this effect still resists a lot of theoretical explanations. For the first time, positron annihilation spectroscopy performed on niobium samples reveals the increase after baking of positrons trapped under the Nb surface. Presence of hydrogen-vacancy complexes and their dissociation by baking could both explain rf losses observed at high fields (Q drop and its cure (baking effect.

  12. Simulation of vacancy migration energy in Cu under high strain

    International Nuclear Information System (INIS)

    Sato, K.; Yoshiie, T.; Satoh, Y.; Xu, Q.; Kiritani, M.

    2003-01-01

    The activation energy for the migration of vacancies in Cu under high strain was calculated by computer simulation using static methods. The migration energy of vacancies was 0.98 eV in the absence of deformation. It varied with the migration direction and stress direction because the distance between a vacancy and its neighboring atoms changes by deformation. For example, the migration energy for the shortest migration distance was reduced to 9.6 and 39.4% of its initial value by 10% compression and 20% elongation, respectively, while that for the longest migration distance was raised to 171.7 by 20% elongation. If many vacancies are created during high-speed deformation, the lowering of migration energy enables vacancies to escape to sinks such as surfaces, even during the shorter deformation period. The critical strain rate above which the strain rate dependence of vacancy accumulation ceases to exist increases with the lowering of vacancy migration energy

  13. Diffusion in a pure, high-vacancy-content crystal

    International Nuclear Information System (INIS)

    McKee, R.A.

    1981-01-01

    The idea that vacancies can follow a nonrandom walk in a solid has been developed and put into a quantitative form for diffusion in a pure, high-vacancy-content crystal. Intrinsic and tracer diffusion in a metal have been analyzed, and the electrical mobility in an ionic solid has been expressed in terms of the tracer diffusion coefficient and the separate correlation factors for atoms and vacancies. The description uses classical methods of diffusion theory, and generalized results that account for nonrandom vacancy walk have been shown to reduce to those obtained by Howard and Lidiard in a system where the vacancy moves randomly as an isolated point defect. Experimental data for carbon diffusion in fcc iron have been examined to illustrate an interstitial-vacancy analogy that was used in this analysis, and the general result has been applied specifically to discuss vacancy diffusion in Fe/sub 1-x/S

  14. Probing vacancy-type free-volume defects in Li2B4O7 single crystal by positron annihilation lifetime spectroscopy

    Science.gov (United States)

    Shpotyuk, O.; Adamiv, V.; Teslyuk, I.; Ingram, A.; Demchenko, P.

    2018-01-01

    Vacancy-type free-volume defects in lithium tetraborate Li2B4O7 single crystal, grown by the Czochralski technique, are probed with positron annihilation spectroscopy in the lifetime measuring mode. The experimental positron lifetime spectrum is reconstructed within the three-component fitting, involving channels of positron and positronium Ps trapping, as well as within the two-component fitting with a positronium-compensating source input. Structural configurations of the most efficient positron traps are considered using the crystallographic specificity of lithium tetraborate with the main accent on cation-type vacancies. Possible channels of positron trapping are visualized using the electronic structure calculations with density functional theory at the basis of structural parameters proper to Li2B4O7. Spatially-extended positron-trapping complexes involving singly-ionized lithium vacancies, with character lifetime close to 0.32 ns, are responsible for positron trapping in the nominally undoped lithium tetraborate Li2B4O7 crystal.

  15. Vacancy-indium clusters in implanted germanium

    KAUST Repository

    Chroneos, Alexander I.

    2010-04-01

    Secondary ion mass spectroscopy measurements of heavily indium doped germanium samples revealed that a significant proportion of the indium dose is immobile. Using electronic structure calculations we address the possibility of indium clustering with point defects by predicting the stability of indium-vacancy clusters, InnVm. We find that the formation of large clusters is energetically favorable, which can explain the immobility of the indium ions. © 2010 Elsevier B.V. All rights reserved.

  16. Vacancy-indium clusters in implanted germanium

    KAUST Repository

    Chroneos, Alexander I.; Kube, R.; Bracht, Hartmut A.; Grimes, Robin W.; Schwingenschlö gl, Udo

    2010-01-01

    Secondary ion mass spectroscopy measurements of heavily indium doped germanium samples revealed that a significant proportion of the indium dose is immobile. Using electronic structure calculations we address the possibility of indium clustering with point defects by predicting the stability of indium-vacancy clusters, InnVm. We find that the formation of large clusters is energetically favorable, which can explain the immobility of the indium ions. © 2010 Elsevier B.V. All rights reserved.

  17. Photoionization and vacancy decay of endohedral atoms

    International Nuclear Information System (INIS)

    Amusia, M. Ya.

    2007-01-01

    We demonstrate the role played by the fullerenes shell in the photoionization and vacancy decay of endohedral atoms A-C 60 . It is shown, partly in the frame of a rather simple model that describes the fullerene shell, partly using only the assumption on the smallness of the atom A in comparison to the size of C 60 that it affects photoionization and the vacancy decay of A-C 60 profoundly. Namely, it leads to a number of new resonances in photoionization cross-section and other photoionization characteristics as well as strong modifications of the vacancy decay probabilities and to opening of new decay channels. We will discuss the problem of photon propagation through the C 60 shell and conclude that at any considered frequency ω, 0 ≤ ω ≤ 60 eV the C 60 enhances the incoming radiation. This shows non-metallic dielectric behavior of the 240 collectivized electrons in C 60 . We also discuss the effects of C 60 upon the fast electron inelastic scattering. The results obtained are valid qualitatively also for other than C 60 molecules, e.g. for C 70 or C 76

  18. Photoionization and vacancy decay of endohedral atoms

    Energy Technology Data Exchange (ETDEWEB)

    Amusia, M. Ya. [Racah Institute of Physics, Hebrew University, Jerusalem 91904 (Israel); A.F. Ioffe Physical-Technical Institute, St. Petersburg 194021 (Russian Federation)], E-mail: amusia@vms.huji.ac.il

    2007-10-15

    We demonstrate the role played by the fullerenes shell in the photoionization and vacancy decay of endohedral atoms A-C{sub 60}. It is shown, partly in the frame of a rather simple model that describes the fullerene shell, partly using only the assumption on the smallness of the atom A in comparison to the size of C{sub 60} that it affects photoionization and the vacancy decay of A-C{sub 60} profoundly. Namely, it leads to a number of new resonances in photoionization cross-section and other photoionization characteristics as well as strong modifications of the vacancy decay probabilities and to opening of new decay channels. We will discuss the problem of photon propagation through the C{sub 60} shell and conclude that at any considered frequency {omega}, 0 {<=} {omega} {<=} 60 eV the C{sub 60} enhances the incoming radiation. This shows non-metallic dielectric behavior of the 240 collectivized electrons in C{sub 60}. We also discuss the effects of C{sub 60} upon the fast electron inelastic scattering. The results obtained are valid qualitatively also for other than C{sub 60} molecules, e.g. for C{sub 70} or C{sub 76}.

  19. Atomic origin of high-temperature electron trapping in metal-oxide-semiconductor devices

    Energy Technology Data Exchange (ETDEWEB)

    Shen, Xiao, E-mail: xiao.shen@vanderbilt.edu [Department of Physics and Astronomy, Vanderbilt University, Nashville, Tennessee 37235 (United States); Dhar, Sarit [Department of Physics, Auburn University, Auburn, Alabama 36849 (United States); Pantelides, Sokrates T. [Department of Physics and Astronomy, Vanderbilt University, Nashville, Tennessee 37235 (United States); Department of Electrical Engineering and Computer Science, Vanderbilt University, Nashville, Tennessee 37235 (United States); Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States)

    2015-04-06

    MOSFETs based on wide-band-gap semiconductors are suitable for operation at high temperature, at which additional atomic-scale processes that are benign at lower temperatures can get activated, resulting in device degradation. Recently, significant enhancement of electron trapping was observed under positive bias in SiC MOSFETs at temperatures higher than 150 °C. Here, we report first-principles calculations showing that the enhanced electron trapping is associated with thermally activated capturing of a second electron by an oxygen vacancy in SiO{sub 2} by which the vacancy transforms into a structure that comprises one Si dangling bond and a bond between a five-fold and a four-fold Si atoms. The results suggest a key role of oxygen vacancies and their structural reconfigurations in the reliability of high-temperature MOS devices.

  20. Dissolving, trapping and detrapping mechanisms of hydrogen in bcc and fcc transition metals

    Directory of Open Access Journals (Sweden)

    Yu-Wei You

    2013-01-01

    Full Text Available First-principles calculations are performed to investigate the dissolving, trapping and detrapping of H in six bcc (V, Nb, Ta, Cr, Mo, W and six fcc (Ni, Pd, Pt, Cu, Ag, Au metals. We find that the zero-point vibrations do not change the site-preference order of H at interstitial sites in these metals except Pt. One vacancy could trap a maximum of 4 H atoms in Au and Pt, 6 H atoms in V, Nb, Ta, Cr, Ni, Pd, Cu and Ag, and 12 H atoms in Mo and W. The zero-point vibrations never change the maximum number of H atoms trapped in a single vacancy in these metals. By calculating the formation energy of vacancy-H (Vac-Hn complex, the superabundant vacancy in V, Nb, Ta, Pd and Ni is demonstrated to be much more easily formed than in the other metals, which has been found in many metals including Pd, Ni and Nb experimentally. Besides, we find that it is most energetically favorable to form Vac-H1 complex in Pt, Cu, Ag and Au, Vac-H4 in Cr, Mo and W, and Vac-H6 in V, Nb, Ta, Pd and Ni. At last, we examine the detrapping behaviors of H atoms in a single vacancy and find that with the heating rate of 10 K/min a vacancy could accommodate 4, 5 and 6 H atoms in Cr, Mo and W at room temperature, respectively. The detrapping temperatures of all H atoms in a single vacancy in V, Nb, Ta, Ni, Pd, Cu and Ag are below room temperature.

  1. Oxygen vacancy chain and conductive filament formation in hafnia

    Science.gov (United States)

    Xue, Kan-Hao; Miao, Xiang-Shui

    2018-04-01

    The stability and aggregation mechanisms of oxygen vacancy chains are studied for hafnia using self-energy corrected density functional theory. While oxygen vacancies tend not to align along the c-axis of monoclinic HfO2, oxygen vacancy chains along a-axis and b-axis are energetically favorable, with cohesive energies of 0.05 eV and 0.03 eV per vacancy, respectively. Nevertheless, with an increase of the cross section area, intensive oxygen vacancy chains become much more stable in hafnia, which yields phase separation into Hf-clusters and HfO2. Compared with disperse single vacancy chains, intensive oxygen vacancy chains made of 4, 6, and 8 single vacancy chains are energetically more favorable by 0.17, 0.20, and 0.30 eV per oxygen vacancy, respectively. On the other hand, while a single oxygen vacancy chain exhibits a tiny electronic energy gap of around 0.5 eV, metallic conduction emerges for the intensive vacancy chain made of 8 single vacancy chains, which possesses a filament cross section area of ˜0.4 nm2. This sets a lower area limit for Hf-cluster filaments from metallic conduction point of view, but in real hafnia resistive RAM devices the cross section area of the filaments can generally be much larger (>5 nm2) for the sake of energy minimization. Our work sets up a bridge between oxygen vacancy ordering and phase separation in hafnia, and shows a clear trend of filament stabilization with larger dimensions. The results could explain the threshold switching phenomenon in hafnia when a small AFM tip was used as the top electrode, as well as the undesired multimode operation in resistive RAM cells with 3 nm-thick hafnia.

  2. Vacancy defects and defect clusters in alkali metal ion-doped MgO nanocrystallites studied by positron annihilation and photoluminescence spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Sellaiyan, S.; Uedono, A. [University of Tsukuba, Division of Applied Physics, Tsukuba, Ibaraki (Japan); Sivaji, K.; Janet Priscilla, S. [University of Madras, Department of Nuclear Physics, Chennai (India); Sivasankari, J. [Anna University, Department of Physics, Chennai (India); Selvalakshmi, T. [National Institute of Technology, Nanomaterials Laboratory, Department of Physics, Tiruchirappalli (India)

    2016-10-15

    Pure and alkali metal ion (Li, Na, and K)-doped MgO nanocrystallites synthesized by solution combustion technique have been studied by positron lifetime and Doppler broadening spectroscopy methods. Positron lifetime analysis exhibits four characteristic lifetime components for all the samples. Doping reduces the Mg vacancy after annealing to 800 C. It was observed that Li ion migrates to the vacancy site to recover Mg vacancy-type defects, reducing cluster vacancies and micropores. For Na- and K-doped MgO, the aforementioned defects are reduced and immobile at 800 C. Coincidence Doppler broadening studies show the positron trapping sites as vacancy clusters. The decrease in the S parameter is due to the particle growth and reduction in the defect concentration at 800 C. Photoluminescence study shows an emission peak at 445 nm and 498 nm, associated with F{sub 2} {sup 2+} and recombination of higher-order vacancy complexes. Further, annealing process is likely to dissociate F{sub 2} {sup 2+} to F{sup +} and this F{sup +} is converted into F centers at 416 nm. (orig.)

  3. Vacancy defects and defect clusters in alkali metal ion-doped MgO nanocrystallites studied by positron annihilation and photoluminescence spectroscopy

    Science.gov (United States)

    Sellaiyan, S.; Uedono, A.; Sivaji, K.; Janet Priscilla, S.; Sivasankari, J.; Selvalakshmi, T.

    2016-10-01

    Pure and alkali metal ion (Li, Na, and K)-doped MgO nanocrystallites synthesized by solution combustion technique have been studied by positron lifetime and Doppler broadening spectroscopy methods. Positron lifetime analysis exhibits four characteristic lifetime components for all the samples. Doping reduces the Mg vacancy after annealing to 800 °C. It was observed that Li ion migrates to the vacancy site to recover Mg vacancy-type defects, reducing cluster vacancies and micropores. For Na- and K-doped MgO, the aforementioned defects are reduced and immobile at 800 °C. Coincidence Doppler broadening studies show the positron trapping sites as vacancy clusters. The decrease in the S parameter is due to the particle growth and reduction in the defect concentration at 800 °C. Photoluminescence study shows an emission peak at 445 nm and 498 nm, associated with F2 2+ and recombination of higher-order vacancy complexes. Further, annealing process is likely to dissociate F2 2+ to F+ and this F+ is converted into F centers at 416 nm.

  4. Vacancy defects and defect clusters in alkali metal ion-doped MgO nanocrystallites studied by positron annihilation and photoluminescence spectroscopy

    International Nuclear Information System (INIS)

    Sellaiyan, S.; Uedono, A.; Sivaji, K.; Janet Priscilla, S.; Sivasankari, J.; Selvalakshmi, T.

    2016-01-01

    Pure and alkali metal ion (Li, Na, and K)-doped MgO nanocrystallites synthesized by solution combustion technique have been studied by positron lifetime and Doppler broadening spectroscopy methods. Positron lifetime analysis exhibits four characteristic lifetime components for all the samples. Doping reduces the Mg vacancy after annealing to 800 C. It was observed that Li ion migrates to the vacancy site to recover Mg vacancy-type defects, reducing cluster vacancies and micropores. For Na- and K-doped MgO, the aforementioned defects are reduced and immobile at 800 C. Coincidence Doppler broadening studies show the positron trapping sites as vacancy clusters. The decrease in the S parameter is due to the particle growth and reduction in the defect concentration at 800 C. Photoluminescence study shows an emission peak at 445 nm and 498 nm, associated with F_2 "2"+ and recombination of higher-order vacancy complexes. Further, annealing process is likely to dissociate F_2 "2"+ to F"+ and this F"+ is converted into F centers at 416 nm. (orig.)

  5. Shrew trap efficiency

    DEFF Research Database (Denmark)

    Gambalemoke, Mbalitini; Mukinzi, Itoka; Amundala, Drazo

    2008-01-01

    We investigated the efficiency of four trap types (pitfall, Sherman LFA, Victor snap and Museum Special snap traps) to capture shrews. This experiment was conducted in five inter-riverine forest blocks in the region of Kisangani. The total trapping effort was 6,300, 9,240, 5,280 and 5,460 trap......, our results indicate that pitfall traps are the most efficient for capturing shrews: not only do they have a higher efficiency (yield), but the taxonomic diversity of shrews is also higher when pitfall traps are used....

  6. Positron lifetime in vacancy clusters. Application to the study of vacancy-impurity interactions

    International Nuclear Information System (INIS)

    Corbel, C.

    1986-02-01

    Positron lifetime measurements are used to study the vacancy recovery (77-650 K) in 20 K electron irradiated dilute gold or iron alloys in stainless steels. Positron lifetimes in clusters of various shapes and structures are calculated to precise the information obtained by measuring the positron lifetime in a vacancy cluster of unknown size and configuration. From the calculations, we have drawn the following conclusions: - the minimal size of an unknown cluster can be deduced from the measurement of the positron lifetime in the cluster; - a decrease of the positron lifetime when the structure of the cluster evolves, means either a decrease of the size of the cluster, or, the appearance of a relaxed configuration. - The positron lifetime is very useful to discriminate between a spatial planar or relaxed configuration and a tri-dimensional one. In AuGe, AuSb, AuTn alloys, vacancy clusters decorated by solute atoms appear at 250 K. Their configurations are different from those in pure Au. Mobile vacancy-solutes complexes are involved in the clustering process in AuGe, AuSb. The clusters are probably decorated by several solute atoms in AuGe and AuSb where the resistivity evidences a clustering of solute atoms. In AuFe, vacancy-single or multi-complexes stable up to 670 K prevent cluster formation. In FeTi, FeSb, FeAu, vacancy migration is hindered by the formation of vacancy-solute complexes up to 315 K (Ti), up to 670 K (Sb), up to 700 K (Au). In FeSi, FeCu, FeAg, tri-dimensional clusters grow less easily than Fe. This is likely due to the formation of several kinds of small decorated clusters with relaxed or planar configurations. They are peculiarly stable, surviving up to 700 K at least. In Si (resp. Ti) doped 59Fe25Ni16Cr, solute atoms retain the vacancies up to 300 K (resp. 320 K) [fr

  7. St. Croix trap study

    Data.gov (United States)

    National Oceanic and Atmospheric Administration, Department of Commerce — The data set contains detailed information about the catch from 600 trap stations around St. Croix. Data fields include species caught, size data, trap location...

  8. Defects spectroscopy by means of the simple trapping model of the Fe78Si9B13 alloy

    International Nuclear Information System (INIS)

    Lopez M, A.; Cabral P, A.; Garcia S, S.F.

    2007-01-01

    In this work it is analyzed quantitatively the results of the positron annihilation in the Fe 78 Si 9 B 13 alloy by means of the simple trapping model. From this analysis its are derived: a reason of positron trapping in the defects (K), the defects concentration (C d ) and the electronic density associated to the defect (n d ); both first parameters, (K, C d ) its increase and n d diminishes when increasing the alloy temperature. From this analysis it is also inferred that the defect consists of a multi vacancy of between 15 and 20 mono vacancies. (Author)

  9. Energetics of charged metal clusters containing vacancies

    Science.gov (United States)

    Pogosov, Valentin V.; Reva, Vitalii I.

    2018-01-01

    We study theoretically large metal clusters containing vacancies. We propose an approach, which combines the Kohn-Sham results for monovacancy in a bulk of metal and analytical expansions in small parameters cv (relative concentration of vacancies) and RN,v -1, RN ,v being cluster radii. We obtain expressions of the ionization potential and electron affinity in the form of corrections to electron work function, which require only the characteristics of 3D defect-free metal. The Kohn-Sham method is used to calculate the electron profiles, ionization potential, electron affinity, electrical capacitance; dissociation, cohesion, and monovacancy-formation energies of the small perfect clusters NaN, MgN, AlN (N ≤ 270) and the clusters containing a monovacancy (N ≥ 12) in the stabilized-jellium model. The quantum-sized dependences for monovacancy-formation energies are calculated for the Schottky scenario and the "bubble blowing" scenario, and their asymptotic behavior is also determined. It is shown that the asymptotical behaviors of size dependences for these two mechanisms differ from each other and weakly depend on the number of atoms in the cluster. The contribution of monovacancy to energetics of charged clusters and the size dependences of their characteristics and asymptotics are discussed. It is shown that the difference between the characteristics for the neutral and charged clusters is entirely determined by size dependences of ionization potential and electron affinity. Obtained analytical dependences may be useful for the analysis of the results of photoionization experiments and for the estimation of the size dependences of the vacancy concentration including the vicinity of the melting point.

  10. Motion Control and Optical Interrogation of a Levitating Single Nitrogen Vacancy in Vacuum.

    Science.gov (United States)

    Conangla, Gerard P; Schell, Andreas W; Rica, Raúl A; Quidant, Romain

    2018-05-24

    Levitation optomechanics exploits the unique mechanical properties of trapped nano-objects in vacuum to address some of the limitations of clamped nanomechanical resonators. In particular, its performance is foreseen to contribute to a better understanding of quantum decoherence at the mesoscopic scale as well as to lead to novel ultrasensitive sensing schemes. While most efforts have focused so far on the optical trapping of low-absorption silica particles, further opportunities arise from levitating objects with internal degrees of freedom, such as color centers. Nevertheless, inefficient heat dissipation at low pressures poses a challenge because most nano-objects, even with low-absorption materials, experience photodamage in an optical trap. Here, by using a Paul trap, we demonstrate levitation in vacuum and center-of-mass feedback cooling of a nanodiamond hosting a single nitrogen-vacancy center. The achieved level of motion control enables us to optically interrogate and characterize the emitter response. The developed platform is applicable to a wide range of other nano-objects and represents a promising step toward coupling internal and external degrees of freedom.

  11. Angular trap for macroparticles

    International Nuclear Information System (INIS)

    Aksyonov, D.S.

    2013-01-01

    Properties of angular macroparticle traps were investigated in this work. These properties are required to design vacuum arc plasma filters. The correlation between trap geometry parameters and its ability to absorb macroparticles were found. Calculations allow one to predict the behaviour of filtering abilities of separators which contain such traps in their design. Recommendations regarding the use of angular traps in filters of different builds are given.

  12. Wide-Field Imaging Using Nitrogen Vacancies

    Science.gov (United States)

    Englund, Dirk Robert (Inventor); Trusheim, Matthew Edwin (Inventor)

    2017-01-01

    Nitrogen vacancies in bulk diamonds and nanodiamonds can be used to sense temperature, pressure, electromagnetic fields, and pH. Unfortunately, conventional sensing techniques use gated detection and confocal imaging, limiting the measurement sensitivity and precluding wide-field imaging. Conversely, the present sensing techniques do not require gated detection or confocal imaging and can therefore be used to image temperature, pressure, electromagnetic fields, and pH over wide fields of view. In some cases, wide-field imaging supports spatial localization of the NVs to precisions at or below the diffraction limit. Moreover, the measurement range can extend over extremely wide dynamic range at very high sensitivity.

  13. Strain Relaxation and Vacancy Creation in Thin Platinum Films

    International Nuclear Information System (INIS)

    Gruber, W.; Chakravarty, S.; Schmidt, H.; Baehtz, C.; Leitenberger, W.; Bruns, M.; Kobler, A.; Kuebel, C.

    2011-01-01

    Synchrotron based combined in situ x-ray diffractometry and reflectometry is used to investigate the role of vacancies for the relaxation of residual stress in thin metallic Pt films. From the experimentally determined relative changes of the lattice parameter a and of the film thickness L the modification of vacancy concentration and residual strain was derived as a function of annealing time at 130 deg. C. The results indicate that relaxation of strain resulting from compressive stress is accompanied by the creation of vacancies at the free film surface. This proves experimentally the postulated dominant role of vacancies for stress relaxation in thin metal films close to room temperature.

  14. Electronic structure and formation energy of a vacancy in aluminum

    International Nuclear Information System (INIS)

    Chakraborty, B.; Siegel, R.W.

    1981-11-01

    The electronic structure of a vacancy in Al was calculated self-consistently using norm-conserving ionic pseudopotentials obtained from ab initio atomic calculations. A 27-atom-site supercell containing 1 vacancy and 26 atoms was used to simulate the environment of the vacancy. A vacancy formation energy of 1.5 eV was also calculated (cf. the experimental value of 0.66 eV). The effects of the supercell and the nature of the ionic potential on the resulting electronic structure and formation energy are discussed. Results for the electronic structure of a divacancy are also presented. 3 figures

  15. Interaction of oxygen vacancies in yttrium germanates

    KAUST Repository

    Wang, Hao

    2012-01-01

    Forming a good Ge/dielectric interface is important to improve the electron mobility of a Ge metal oxide semiconductor field-effect transistor. A thin yttrium germanate capping layer can improve the properties of the Ge/GeO 2 system. We employ electronic structure calculations to investigate the effect of oxygen vacancies in yttrium-doped GeO 2 and the yttrium germanates Y 2Ge 2O 7 and Y 2GeO 5. The calculated densities of states indicate that dangling bonds from oxygen vacancies introduce in-gap states, but the system remains insulating. However, yttrium-doped GeO 2 becomes metallic under oxygen deficiency. Y-doped GeO 2, Y 2Ge 2O 7 and Y 2GeO 5 are calculated to be oxygen substoichiometric under low Fermi energy conditions. The use of yttrium germanates is proposed as a way to effectively passivate the Ge/dielectric interface. This journal is © 2012 the Owner Societies.

  16. Irreversible traps, their influence on the embrittlement of high strength steel

    International Nuclear Information System (INIS)

    Mariano, I; Mansilla, G

    2012-01-01

    Hydrogen (H) can be trapped in lattice defects such as vacancies, dislocations, grain boundaries and interfaces between the matrix and precipitates. The effect on the mechanical properties depends on factors inherent in materials such as the activation energy of irreversible traps (H trapped in Network Places) and its sensitivity to embrittlement. Differential scanning calorimetry (DSC) allows the study of those processes in which enthalpy variation occurs. The purpose is to record the difference in enthalpy change that occurs in the sample as a function of temperature or time. This work represents a study of H embrittlement of high strength steel resulfurized

  17. Effects of point defect trapping and solute segregation on irradiation-induced swelling and creep

    International Nuclear Information System (INIS)

    Mansur, L.K.

    1978-01-01

    The theory of irradiation swelling and creep, generalized to include impurity trapping of point defects and impurity-induced changes in sink efficiencies for point defects, is reviewed. The mathematical framework is developed and significant results are described. These include the relation between vacancy and interstitial trapping and the effectiveness of trapping as compared to segregation-induced changes in sink efficiencies in modifying void nucleation, void growth, and creep. Current understanding is critically assessed. Several areas requiring further development are identified. In particular those given special attention are the treatment of nondilute solutions and the consequences of current uncertainties in fundamental materials properties whose importance has been identified using the theory

  18. A Facile Approach to Prepare Black TiO2 with Oxygen Vacancy for Enhancing Photocatalytic Activity

    Science.gov (United States)

    Chen, Shihao; Xiao, Yang; Hu, Zhengfa; Zhao, Hui; Xie, Wei

    2018-01-01

    Black TiO2 has triggered worldwide research interest due to its excellent photocatalytic properties. However, the understanding of its structure–property relationships and a more effective, facile and versatile method to produce it remain great challenges. We have developed a facile approach to synthesize black TiO2 nanoparticles with significantly improved light absorption in the visible and infrared regions. The experimental results show that oxygen vacancies are the major factors responsible for black coloration. More importantly, our black TiO2 nanoparticles have no Ti3+ ions. These oxygen vacancies could introduce localized states in the bandgap and act as trap centers, significantly decreasing the electron–hole recombination. The photocatalytic decomposition of both rhodamine B and methylene blue demonstrated that, under ultraviolet light irradiation, better photocatalytic performance is achieved with our black TiO2 nanoparticles than with commercial TiO2 nanoparticles. PMID:29659500

  19. Ahmed glaucoma valve in uveitic patients with fluocinolone acetonide implant-induced glaucoma: 3-year follow-up.

    Science.gov (United States)

    Kubaisi, Buraa; Maleki, Arash; Ahmed, Aseef; Lamba, Neel; Sahawneh, Haitham; Stephenson, Andrew; Montieth, Alyssa; Topgi, Shobha; Foster, C Stephen

    2018-01-01

    To evaluate the efficacy and safety of Ahmed glaucoma valve (AGV) in eyes with noninfectious uveitis that had fluocinolone acetonide intravitreal implant (Retisert™)-induced glaucoma. This retrospective study reviewed the safety and efficacy of AGV implantation in patients with persistently elevated intraocular pressure (IOP) after implantation of a fluocinolone acetonide intravitreal implant at the Massachusetts Eye Research and Surgery Institution between August 2006 and November 2015. Nine patients with 10 uveitic eyes were included in this study, none of which had preexisting glaucoma in the study eye. Mean patient age was 42 years; 6 patients were female and 3 were male. Baseline mean IOP was 30.6 mmHg prior to AGV placement while mean IOP-lowering medications were 2.9. In the treatment groups, there was a statistically significant reduction in post-AGV IOP. IOP was lowest at 1-week after AGV implantation (9.0 mmHg). Nine out of 10 eyes achieved an IOP below target value of 22 mmHg and/or a 20% reduction in IOP from baseline 1 month and 1 year following AGV placement. All other postoperative time points showed all 10 eyes reaching this goal. A statistically significant decrease in IOP-lowering medication was seen at the 1-week, 1-month, and 3-year time points compared to baseline, while a statistically significant increase was seen at the 3-month, 6-month, and 2-year post-AGV time points. No significant change in retinal nerve thickness or visual field analysis was found. AGV is an effective and safe method of treatment in fluocinolone acetonide intravitreal implant-induced glaucoma. High survival rate is expected for at least 3 years.

  20. Hydrogen vacancies facilitate hydrogen transport kinetics in sodium hydride nanocrystallites

    NARCIS (Netherlands)

    Singh, S.; Eijt, S.W.H.

    2008-01-01

    We report ab initio calculations based on density-functional theory, of the vacancy-mediated hydrogen migration energy in bulk NaH and near the NaH(001) surface. The estimated rate of the vacancy mediated hydrogen transport, obtained within a hopping diffusion model, is consistent with the reaction

  1. 24 CFR 990.145 - Dwelling units with approved vacancies.

    Science.gov (United States)

    2010-04-01

    ... 24 Housing and Urban Development 4 2010-04-01 2010-04-01 false Dwelling units with approved vacancies. 990.145 Section 990.145 Housing and Urban Development Regulations Relating to Housing and Urban...; Computation of Eligible Unit Months § 990.145 Dwelling units with approved vacancies. (a) A PHA is eligible to...

  2. Photoluminescence study of trap-state defect on TiO2 thin films at different substrate temperature via RF magnetron sputtering

    Science.gov (United States)

    Abdullah, S. A.; Sahdan, M. Z.; Nafarizal, N.; Saim, H.; Bakri, A. S.; Cik Rohaida, C. H.; Adriyanto, F.; Sari, Y.

    2018-04-01

    This paper highlights the defect levels using photoluminescence spectroscopy of TiO2 thin films. The TiO2 were deposited by Magnetron Sputtering system with 200, 300, 400, and 500 °C substrate temperature on microscope glass substrate. The PL result shows profound effect of various substrate temperatures to defect levels of oxygen vacancies and Ti3+ at titanium interstitial site. Increasing temperature would minimize the oxygen vacancy defect, however Ti3+ shows otherwise. Green region of PL consist of trapped hole for oxygen vacancy, while red region of PL is trapped electron associated to structural defect Ti3+. Green PL is dominant peak at temperature 200 °C, indicating that oxygen vacancy is the main defect at this temperature. However, PL peak shows slightly same value for others samples indicating that the temperature did not give high influence to other level of defect after 200 °C.

  3. Controlled manipulation of oxygen vacancies using nanoscale flexoelectricity

    Energy Technology Data Exchange (ETDEWEB)

    Das, Saikat [Inst. for Basic Science (IBS), Seoul (Republic of Korea). Center for Correlated Electron Systems; Seoul National University (SNU), Seoul (Republic of Korea). Dept. of Physics and Astronomy; Wang, Bo [Pennsylvania State Univ., University Park, PA (United States).Dept. of Materials Science and Engineering; Cao, Ye [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Center for Nanophase Materials Science (CNMS); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Inst. for; Rae Cho, Myung [Inst. for Basic Science (IBS), Seoul (Republic of Korea). Center for Correlated Electron Systems; Seoul National University (SNU), Seoul (Republic of Korea). Dept. of Physics and Astronomy; Jae Shin, Yeong [Inst. for Basic Science (IBS), Seoul (Republic of Korea). Center for Correlated Electron Systems; Seoul National University (SNU), Seoul (Republic of Korea). Dept. of Physics and Astronomy; Mo Yang, Sang [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Center for Nanophase Materials Science (CNMS); Sookmyung Women' s Univ., Seoul (Republic of Korea). Dept. of Physics; Wang, Lingfei [Inst. for Basic Science (IBS), Seoul (Republic of Korea). Center for Correlated Electron Systems; Seoul National University (SNU), Seoul (Republic of Korea). Dept. of Physics and Astronomy; Kim, Minu [Inst. for Basic Science (IBS), Seoul (Republic of Korea). Center for Correlated Electron Systems; Seoul National University (SNU), Seoul (Republic of Korea). Dept. of Physics and Astronomy; Kalinin, Sergei V. [Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Center for Nanophase Materials Science (CNMS); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Inst. for Functional Imaging of Materials; Chen, Long-Qing [Pennsylvania State Univ., University Park, PA (United States).Dept. of Materials Science and Engineering; Noh, Tae Won [Inst. for Basic Science (IBS), Seoul (Republic of Korea). Center for Correlated Electron Systems; Seoul National University (SNU), Seoul (Republic of Korea). Dept. of Physics and Astronomy

    2017-09-20

    Oxygen vacancies, especially their distribution, are directly coupled to the electromagnetic properties of oxides and related emergent functionalities that have implications for device applications. Here using a homoepitaxial strontium titanate thin film, we demonstrate a controlled manipulation of the oxygen vacancy distribution using the mechanical force from a scanning probe microscope tip. By combining Kelvin probe force microscopy imaging and phase-field simulations, we show that oxygen vacancies can move under a stress-gradient-induced depolarisation field. When tailored, this nanoscale flexoelectric effect enables a controlled spatial modulation. In motion, the scanning probe tip thereby deterministically reconfigures the spatial distribution of vacancies. Finally, the ability to locally manipulate oxygen vacancies on-demand provides a tool for the exploration of mesoscale quantum phenomena and engineering multifunctional oxide devices.

  4. Cooperatively enhanced dipole forces from artificial atoms in trapped nanodiamonds

    Science.gov (United States)

    Juan, Mathieu L.; Bradac, Carlo; Besga, Benjamin; Johnsson, Mattias; Brennen, Gavin; Molina-Terriza, Gabriel; Volz, Thomas

    2017-03-01

    Optical trapping is a powerful tool to manipulate small particles, from micrometre-size beads in liquid environments to single atoms in vacuum. The trapping mechanism relies on the interaction between a dipole and the electric field of laser light. In atom trapping, the dominant contribution to the associated force typically comes from the allowed optical transition closest to the laser wavelength, whereas for mesoscopic particles it is given by the polarizability of the bulk material. Here, we show that for nanoscale diamond crystals containing a large number of artificial atoms, nitrogen-vacancy colour centres, the contributions from both the nanodiamond and the colour centres to the optical trapping strength can be simultaneously observed in a noisy liquid environment. For wavelengths around the zero-phonon line transition of the colour centres, we observe a 10% increase of overall trapping strength. The magnitude of this effect suggests that due to the large density of centres, cooperative effects between the artificial atoms contribute to the observed modification of the trapping strength. Our approach may enable the study of cooperativity in nanoscale solid-state systems and the use of atomic physics techniques in the field of nano-manipulation.

  5. EPR study of electron traps in x-ray-irradiated yttria-stabilized zirconia

    International Nuclear Information System (INIS)

    Azzoni, C.B.; Paleari, A.

    1989-01-01

    Single crystals of yttria-stabilized zirconia (12 mol % of Y 2 O 3 ) have been x-ray irradiated at room temperature. The electron paramagnetic resonance spectrum of the filled electron traps is analyzed in terms of a single oxygen vacancy type of defect with its symmetry axis along the left-angle 111 right-angle direction. The angular dependence of the linewidth and the asymmetry of the line shape are attributed to the disordered rearrangements of the anion sublattice surrounding the oxygen vacancy. This affects the local crystal fields and the directions of the symmetry axis of the defects

  6. EPR study of electron traps in x-ray-irradiated yttria-stabilized zirconia

    Energy Technology Data Exchange (ETDEWEB)

    Azzoni, C.B.; Paleari, A. (Dipartimento di Fisica, Alessandro Volta dell' Universita di Pavia, via Bassi 6, 27100 Pavia, Italy (IT))

    1989-10-01

    Single crystals of yttria-stabilized zirconia (12 mol % of Y{sub 2}O{sub 3}) have been x-ray irradiated at room temperature. The electron paramagnetic resonance spectrum of the filled electron traps is analyzed in terms of a single oxygen vacancy type of defect with its symmetry axis along the {l angle}111{r angle} direction. The angular dependence of the linewidth and the asymmetry of the line shape are attributed to the disordered rearrangements of the anion sublattice surrounding the oxygen vacancy. This affects the local crystal fields and the directions of the symmetry axis of the defects.

  7. Photonics and electronics for nitrogen vacancy control

    International Nuclear Information System (INIS)

    Shaun Ho

    2014-01-01

    Deterministic indistinguishable single photon sources are one of the key requirements for the realisation of Optical Quantum Computing. Recent low temperature experiments have shown the potential of the negatively charged nitrogen vacancy (NV-) centre as a source of indistinguishable photons. Furthermore its ground state spin structure with extensional decoherence time and spin dependent transitions means it can be harnessed as a spin-photon interface. However, development of these potential applications requires exquisite control of te electronic and spin states via Stark and Zeeman shifting, as well as enhanced photon collection through photonic structures. Here we present the integration of micro-fabricated solid immersion lenses with lithographically defined gold electrodes for control and spin manipulation. (author)

  8. Ion Trap Quantum Computing

    Science.gov (United States)

    2011-12-01

    variations of ion traps, including (1) the cylindrically symmetric 3D ring trap; (2) the linear trap with a combination of cavity QED; (#) the symmetric...concepts of quantum information. The major demonstration has been the test of a Bell inequality as demonstrated by Rowe et al. [50] and a decoherence...famous physics experiment [62]. Wolfgang Paul demonstrated a similar apparatus during his Nobel Prize speech [63]. This device is hyperbolic- parabolic

  9. Towards trapped antihydrogen

    CERN Document Server

    Jorgensen, L V; Bertsche, W; Boston, A; Bowe, P D; Cesar, C L; Chapman, S; Charlton, M; Fajans, J; Fujiwara, M C; Funakoshi, R; Gill, D R; Hangst, J S; Hayano, R S; Hydomako, R; Jenkins, M J; Kurchaninov, L; Madsen, N; Nolan, P; Olchanski, K; Olin, A; Page, R D; Povilus, A; Robicheaux, F; Sarid, E; Silveira, D M; Storey, J W; Thompson, R I; van der Werf, D P; Wurtele, J S; Yamazaki, Y

    2008-01-01

    Substantial progress has been made in the last few years in the nascent field of antihydrogen physics. The next big step forward is expected to be the trapping of the formed antihydrogen atoms using a magnetic multipole trap. ALPHA is a new international project that started to take data in 2006 at CERN’s Antiproton Decelerator facility. The primary goal of ALPHA is stable trapping of cold antihydrogen atoms to facilitate measurements of its properties. We discuss the status of the ALPHA project and the prospects for antihydrogen trapping.

  10. Positron spectroscopy analysis of vacancy-solute nanoaggregates in Al-Cu

    International Nuclear Information System (INIS)

    Ferragut, R.; Ferro, G.; Biasini, M.; Dupasquier, A.; Somoza, A.

    2004-01-01

    This work addresses the process of ageing in Al-4wt.% Cu at two temperatures (150 C, 180 C) and in conditions of secondary ageing at temperatures up to 60 C, after artificial ageing treatment at 150 C, Positron lifetime and coincidence Doppler broadening measurements are reported. The analysis shows an initial association of positron trapping sites with Cu (about 9 at.% Cu at the annihilation site) that decreases to 7/6% in the initial stages of ageing, but then increases sharply (up to 25 at.% Cu after 300 hours at 180 C). The positron lifetime also displays an initial decrease followed by a final increase. The results confirm the hypothesis that positrons are not trapped in GP[1] zones, but show that trapping occurs in GP[2] zones formed at 150 C. During secondary ageing, the vacancy-Cu association as well as the positron lifetime decrease with the ageing time. This is attributed to the formation of GP[1] zones due to residual supersaturation. (orig.)

  11. Molecular dynamics simulations of ferroelectric domain formation by oxygen vacancy

    Science.gov (United States)

    Zhu, Lin; You, Jeong Ho; Chen, Jinghong; Yeo, Changdong

    2018-05-01

    An oxygen vacancy, known to be detrimental to ferroelectric properties, has been investigated numerically for the potential uses to control ferroelectric domains in films using molecular dynamics simulations based on the first-principles effective Hamiltonian. As an electron donor, an oxygen vacancy generates inhomogeneous electrostatic and displacement fields which impose preferred polarization directions near the oxygen vacancy. When the oxygen vacancies are placed at the top and bottom interfaces, the out-of-plane polarizations are locally developed near the interfaces in the directions away from the interfaces. These polarizations from the interfaces are in opposite directions so that the overall out-of-plane polarization becomes significantly reduced. In the middle of the films, the in-plane domains are formed with containing 90° a 1/a 2 domain walls and the films are polarized along the [1 1 0] direction even when no electric field is applied. With oxygen vacancies placed at the top interface only, the films exhibit asymmetric hysteresis loops, confirming that the oxygen vacancies are one of the possible sources of ferroelectric imprint. It has been qualitatively demonstrated that the domain structures in the imprint films can be turned on and off by controlling an external field along the thickness direction. This study shows qualitatively that the oxygen vacancies can be utilized for tuning ferroelectric domain structures in films.

  12. Ahmed glaucoma valve in uveitic patients with fluocinolone acetonide implant-induced glaucoma: 3-year follow-up

    Directory of Open Access Journals (Sweden)

    Kubaisi B

    2018-05-01

    treatment in fluocinolone acetonide intravitreal implant-induced glaucoma. High survival rate is expected for at least 3 years. Keywords: uveitis, glaucoma, Ahmed glaucoma valve, fluocinolone acetonide intravitreal implant, ocular inflammation

  13. Theoretical examination of the trapping of ion-implanted hydrogen in metals

    International Nuclear Information System (INIS)

    Myers, S.M.; Nordlander, P.; Besenbacher, F.; Norskov, J.K.

    1986-01-01

    Theoretical analysis of the defect trapping of ion-implanted hydrogen in metals has been extended in two respects. A new transport formalism has been developed which takes account not only of the diffusion, trapping, and surface release of the hydrogen, which were included in earlier treatments, but also the diffusion, recombination, agglomeration, and surface annihilation of the vacancy and interstitial traps. In addition, effective-medium theory has been used to examine multiple hydrogen occupancy of the vacancy, and, for the fcc structure, appreciable binding enthalpies relative to the solution site have been found for occupancies of up to six. These extensions have been employed to model the depth distribution of ion-implanted hydrogen in Ni and Al during linear ramping of temperature, and the results have been used to interpret previously published data from these metals. The agreement between theory and experiment is good for both systems. In the case of Ni, the two experimentally observed hydrogen-release stages are both accounted for in terms of trapping at vacancies with a binding enthalpy that depends upon occupancy in accord with effective-medium theory

  14. Identification of electron and hole traps in KH2PO4 crystals

    International Nuclear Information System (INIS)

    Garces, N. Y.; Stevens, K. T.; Halliburton, L. E.; Demos, S. G.; Radousky, H. B.; Zaitseva, N. P.

    2001-01-01

    Electron paramagnetic resonance (EPR) has been used to characterize a hole trap and several electron traps in single crystals of potassium dihydrogen phosphate (KH 2 PO 4 or KDP). The paramagnetic charge states of these centers are produced by ionizing radiation (e.g., x rays or a 266 nm beam from a pulsed Nd:YAG laser) and are stable for days and even weeks at room temperature. One center consists of a hole trapped on an oxygen ion adjacent to a silicon impurity located on a phosphorus site. This defect has a small, but easily observed, hyperfine interaction with the adjacent substitutional proton. The other centers are formed when an electron is trapped at an oxygen vacancy. These latter defects are best described as (PO 3 ) 2- molecular ions, where the primary phosphorus nucleus is responsible for a large hyperfine splitting (500--800 G in magnitude). Five EPR spectra representing variations of these oxygen vacancy centers are observed, with the differences being attributed to the relative position of a nearby cation vacancy, either a missing proton or potassium. An angular study of the EPR spectra, conducted at room temperature, provided principal values and principal directions for the g matrices and hyperfine matrices for the hole center and two of the electron centers

  15. Versatile electrostatic trap

    NARCIS (Netherlands)

    van Veldhoven, J.; Bethlem, H.L.; Schnell, M.; Meijer, G.

    2006-01-01

    A four electrode electrostatic trap geometry is demonstrated that can be used to combine a dipole, quadrupole, and hexapole field. A cold packet of ND315 molecules is confined in both a purely quadrupolar and hexapolar trapping field and additionally, a dipole field is added to a hexapole field to

  16. Liquid metal cold trap

    International Nuclear Information System (INIS)

    Hundal, R.

    1976-01-01

    A cold trap assembly for removing impurities from a liquid metal is described. A hole between the incoming impure liquid metal and purified outgoing liquid metal acts as a continuous bleed means and thus prevents the accumulation of cover gases within the cold trap assembly

  17. Photocatalytic Conversion of Nitrogen to Ammonia with Water on Surface Oxygen Vacancies of Titanium Dioxide.

    Science.gov (United States)

    Hirakawa, Hiroaki; Hashimoto, Masaki; Shiraishi, Yasuhiro; Hirai, Takayuki

    2017-08-09

    Ammonia (NH 3 ) is an essential chemical in modern society. It is currently manufactured by the Haber-Bosch process using H 2 and N 2 under extremely high-pressure (>200 bar) and high-temperature (>673 K) conditions. Photocatalytic NH 3 production from water and N 2 at atmospheric pressure and room temperature is ideal. Several semiconductor photocatalysts have been proposed, but all suffer from low efficiency. Here we report that a commercially available TiO 2 with a large number of surface oxygen vacancies, when photoirradiated by UV light in pure water with N 2 , successfully produces NH 3 . The active sites for N 2 reduction are the Ti 3+ species on the oxygen vacancies. These species act as adsorption sites for N 2 and trapping sites for the photoformed conduction band electrons. These properties therefore promote efficient reduction of N 2 to NH 3 . The solar-to-chemical energy conversion efficiency is 0.02%, which is the highest efficiency among the early reported photocatalytic systems. This noble-metal-free TiO 2 system therefore shows a potential as a new artificial photosynthesis for green NH 3 production.

  18. Realizing nanographene activated by a vacancy to solve hydrogen storage problem

    Science.gov (United States)

    Sunnardianto, Gagus Ketut; Maruyama, Isao; Kusakabe, Koichi

    We found a triply hydrogenated vacancy (V111) in nanographene reduces an activation barrier of adsorption-desorption process in both ways in an equal manner from the known values for pristine graphene as well as those of other hydrogenated vacancies of graphene. This finding may give a key to overcome existing problems in the hydrogen uptake and release processes in known hydrogen storage materials, e.g. graphene and organic hydrides (OHs) in near ambient operation temperature. In this study, we used DFT-NEB simulation to estimate the barrier height, which is supported by realized real experiments. We consider a nanographene molecule (VANG) which contains V111 with armchair structure at the periphery. We found interesting feature in comparable values of energy barriers for both hydrogen uptake and release, where hydrogenation process is even a little bit endothermic and dehydrogenation is a little but exothermic nature. Thus, this material structure acts as ``self-catalytic properties'', which has an important role in reducing an energy barrier and as a trapping site for hydrogen serving a new material prevailing other hopeful candidates. The work is supported by JSPS KAKENHI in Science of Atomic Layers\\x9D.

  19. Temperature dependence of helium-implantation-induced lattice swelling in polycrystalline tungsten: X-ray micro-diffraction and Eigenstrain modelling

    International Nuclear Information System (INIS)

    Broglie, I. de; Beck, C.E.; Liu, W.; Hofmann, F.

    2015-01-01

    Using synchrotron X-ray micro-diffraction and Eigenstrain analysis the distribution of lattice swelling near grain boundaries in helium-implanted polycrystalline tungsten is quantified. Samples heat-treated at up to 1473 K after implantation show less uniform lattice swelling that varies significantly from grain to grain compared to as-implanted samples. An increase in lattice swelling is found in the vicinity of some grain boundaries, even at depths beyond the implanted layer. These findings are discussed in terms of the evolution of helium-ion-implantation-induced defects

  20. Trapping radioactive ions

    CERN Document Server

    Kluge, Heinz-Jürgen

    2004-01-01

    Trapping devices for atomic and nuclear physics experiments with radioactive ions are becoming more and more important at accelerator facilities. While about ten years ago only one online Penning trap experiment existed, namely ISOLTRAP at ISOLDE/CERN, meanwhile almost every radioactive beam facility has installed or plans an ion trap setup. This article gives an overview on ion traps in the operation, construction or planing phase which will be used for fundamental studies with short-lived radioactive nuclides such as mass spectrometry, laser spectroscopy and nuclear decay spectroscopy. In addition, this article summarizes the use of gas cells and radiofrequency quadrupole (Paul) traps at different facilities as a versatile tool for ion beam manipulation like retardation, cooling, bunching, and cleaning.

  1. Trapping radioactive ions

    International Nuclear Information System (INIS)

    Kluge, H.-J.; Blaum, K.

    2004-01-01

    Trapping devices for atomic and nuclear physics experiments with radioactive ions are becoming more and more important at accelerator facilities. While about ten years ago only one online Penning trap experiment existed, namely ISOLTRAP at ISOLDE/CERN, meanwhile almost every radioactive beam facility has installed or plans an ion trap setup. This article gives an overview on ion traps in the operation, construction or planing phase which will be used for fundamental studies with short-lived radioactive nuclides such as mass spectrometry, laser spectroscopy and nuclear decay spectroscopy. In addition, this article summarizes the use of gas cells and radiofrequency quadrupole (Paul) traps at different facilities as a versatile tool for ion beam manipulation like retardation, cooling, bunching, and cleaning

  2. Vacancy distribution in nonstoichiometric vanadium monoxide

    International Nuclear Information System (INIS)

    Gusev, A.I.; Davydov, D.A.; Valeeva, A.A.

    2011-01-01

    Graphical abstract: Display Omitted Research highlights: → A certain fraction of vanadium atoms in disordered cubic vanadium monoxide VO y and ordered tetragonal phase V 52 O 64 is located in tetrahedral positions of a basic cubic lattice. → These positions are never occupied by any atoms in other strongly nonstoichiometric carbides, nitrides and oxides. → Both disordered and ordered structures of vanadium monoxide are characterized by the presence of short-range order of displacements in the oxygen sublattice and short-range order of substitution in the metal sublattice. → The short-range order of displacement is caused by the local displacements of O atoms from V (t) atoms occupying tetrahedral positions. The short-range order of substitution appears because V (t) atoms in the tetrahedral positions are always in the environment of four vacancies □ of the vanadium sublattice. - Abstract: Structural vacancy distribution in the crystal lattice of the tetragonal V 52 O 64 superstructure which is formed on the basis of disordered superstoichiometric cubic vanadium monoxide VO y ≡V x O z is experimentally determined and the presence of significant local atomic displacements and large local microstrains in a crystal lattice of real ordered phase is established. It is shown that the relaxation of local microstrains takes place owing to the basic disordered cubic phase grain refinement and a formation of ordered phase domains. The ordered phase domains grow in the direction from the boundaries to the centre of grains of the disordered basic cubic phase. Isothermal evolution at 970 K of the average domain size in ordered VO 1.29 vanadium monoxide is established. It is shown that the short-range order presents in a metal sublattice of disordered cubic VO y vanadium monoxide. The character of the short-range order is such that vanadium atoms occupying tetrahedral positions are in the environment of four vacant sites of the vanadium sublattice. This means that the

  3. Phosphorous vacancy nearest neighbor hopping induced instabilities in InP capacitors II. Computer simulation

    International Nuclear Information System (INIS)

    Juang, M.T.; Wager, J.F.; Van Vechten, J.A.

    1988-01-01

    Drain current drift in InP metal insulator semiconductor devices display distinct activation energies and pre-exponential factors. The authors have given evidence that these result from two physical mechanisms: thermionic tunneling of electrons into native oxide traps and phosphorous vacancy nearest neighbor hopping (PVNNH). They here present a computer simulation of the effect of the PVNHH mechanism on flatband voltage shift vs. bias stress time measurements. The simulation is based on an analysis of the kinetics of the PVNNH defect reaction sequence in which the electron concentration in the channel is related to the applied bias by a solution of the Poisson equation. The simulation demonstrates quantitatively that the temperature dependence of the flatband shift is associated with PVNNH for temperatures above room temperature

  4. Evaluation of vacancy-type defects in ZnO by the positron annihilation lifetime spectroscopy

    International Nuclear Information System (INIS)

    Ono, R.; Togimitsu, T.; Sato, W.

    2015-01-01

    Thermal behavior of vacancy-type defects in polycrystalline ZnO was studied by the positron annihilation lifetime spectroscopy. Two-component analysis of the PALS spectra revealed that the defect-related longer-lifetime component decreases as the annealing temperature is raised, and almost disappears within 15 min when annealed at 1,273 K. We also found that the intensity of this component decreases with increasing density of the annealed ZnO pellets; however, little density dependence was seen in its lifetime. These observations evidently suggest that this component having long lifetime of about 400 ps corresponds to the positrons trapped in grain boundaries in the polycrystalline ZnO. (author)

  5. Controlling vacancies in chalcogenides as energy harvesting materials

    NARCIS (Netherlands)

    Li, Guowei

    2016-01-01

    Recent years witnessed fruitful results on tailoring properties and application performance, especially in the field of clean energy storage and harvesting materials. Defects, especially elemental vacancies, exist universally and are inevitable in materials. Due to the difficulties to precisely map

  6. 78 FR 42945 - Health Information Technology Policy Committee Vacancy

    Science.gov (United States)

    2013-07-18

    ... GOVERNMENT ACCOUNTABILITY OFFICE Health Information Technology Policy Committee Vacancy AGENCY... American Recovery and Reinvestment Act of 2009 (ARRA) established the Health Information Technology Policy... its 20 members. ARRA requires that one member have expertise in health information privacy and...

  7. Double K-vacancy production by x-ray photoionization

    International Nuclear Information System (INIS)

    Southworth, S. H.; Dunford, R. W.; Kanter, E. P.; Krassig, B.; Young, L.; Armen, G. B.; Levin, J. C.; Chen, M. H.; Ederer, D. L.

    2002-01-01

    We have studied double K-shell photoionization of Ne and Mo (Z = 10 and 42) at the Advanced Photon Source. Double K-vacancy production in Ne was observed by recording the KK-KLL Auger hypersatellite spectrum. Comparison is made with calculations using the multiconfiguration Dirac-Fock method. For Mo, double K-vacancy production was observed by recording the Kα, β fluorescence hypersatellite and satellite x rays in coincidence. From the intensities of the Auger or x-ray hypersatellites relative to diagram lines, the probabilities for double K-vacancy production relative to single K-vacancies were determined. These results, along with reported measurements on other atoms, are compared with Z-scaling calculations of the high-energy limits of the double-to-single K-shell photoionization ratio

  8. 5 CFR 330.707 - Reporting vacancies to OPM.

    Science.gov (United States)

    2010-01-01

    ... RECRUITMENT, SELECTION, AND PLACEMENT (GENERAL) Interagency Career Transition Assistance Plan for Displaced Employees § 330.707 Reporting vacancies to OPM. (a) Agencies are required to report all competitive service...

  9. Nematode-Trapping Fungi.

    Science.gov (United States)

    Jiang, Xiangzhi; Xiang, Meichun; Liu, Xingzhong

    2017-01-01

    Nematode-trapping fungi are a unique and intriguing group of carnivorous microorganisms that can trap and digest nematodes by means of specialized trapping structures. They can develop diverse trapping devices, such as adhesive hyphae, adhesive knobs, adhesive networks, constricting rings, and nonconstricting rings. Nematode-trapping fungi have been found in all regions of the world, from the tropics to Antarctica, from terrestrial to aquatic ecosystems. They play an important ecological role in regulating nematode dynamics in soil. Molecular phylogenetic studies have shown that the majority of nematode-trapping fungi belong to a monophyletic group in the order Orbiliales (Ascomycota). Nematode-trapping fungi serve as an excellent model system for understanding fungal evolution and interaction between fungi and nematodes. With the development of molecular techniques and genome sequencing, their evolutionary origins and divergence, and the mechanisms underlying fungus-nematode interactions have been well studied. In recent decades, an increasing concern about the environmental hazards of using chemical nematicides has led to the application of these biological control agents as a rapidly developing component of crop protection.

  10. Evidence for vacancy migration in stage III for copper

    International Nuclear Information System (INIS)

    Antesberger, G.; Sonnenberg, K.; Wienhold, P.; Coltman, R.R.; Klabunde, C.E.; Williams, J.M.

    1975-01-01

    Specimens doped with interstitial clusters and single vacancies have been annealed isochronally through the temperature range of stage III. Combining this annealing with a test irradiation after each annealing step reactions of mobile single test interstitials with the doping defects were studied. These reactions provide information about the variation of the doping defect structure during annealing. The experimental results suggest that vacancy clusters are formed in stage III

  11. Chemical analysis using coincidence Doppler broadening and supporting first-principles theory: Applications to vacancy defects in compound semiconductors

    International Nuclear Information System (INIS)

    Makkonen, I.; Rauch, C.; Mäki, J.-M.; Tuomisto, F.

    2012-01-01

    The Doppler broadening of the positron annihilation radiation contains information on the chemical environment of vacancy defects trapping positrons in solids. The measured signal can, for instance, reveal impurity atoms situated next to vacancies. As compared to integrated quantities such as the positron annihilation rate or the annihilation line shape parameters, the full Doppler spectrum measured in the coincidence mode contains much more useful information for defect identification. This information, however, is indirect and complementary understanding is needed to fully interpret the results. First-principles calculations are a valuable tool in the analysis of measured spectra. One can construct an atomic-scale model for a given candidate defect, calculate from first principles the corresponding Doppler spectrum, and directly compare results between experiment and theory. In this paper we discuss recent examples of successful combinations of coincidence Doppler broadening measurements and supporting first-principles calculations. These demonstrate the predictive power of state-of-the-art calculations and the usefulness of such an approach in the chemical analysis of vacancy defects.

  12. Quantum transport in defective phosphorene nanoribbons: Effects of atomic vacancies

    Science.gov (United States)

    Li, L. L.; Peeters, F. M.

    2018-02-01

    Defects are almost inevitably present in realistic materials and defective materials are expected to exhibit very different properties than their nondefective (perfect) counterparts. Here, using a combination of the tight-binding approach and the scattering matrix formalism, we investigate the electronic transport properties of defective phosphorene nanoribbons (PNRs) containing atomic vacancies. We find that for both armchair PNRs (APNRs) and zigzag PNRs (ZPNRs), single vacancies can create quasilocalized states, which can affect their conductance. With increasing vacancy concentration, three different transport regimes are identified: ballistic, diffusive, and Anderson localized ones. In particular, ZPNRs that are known to be metallic due to the presence of edge states become semiconducting: edge conductance vanishes and transport gap appears due to Anderson localization. Moreover, we find that for a fixed vacancy concentration, both APNRs and ZPNRs of narrower width and/or longer length are more sensitive to vacancy disorder than their wider and/or shorter counterparts, and that for the same ribbon length and width, ZPNRs are more sensitive to vacancy disorder than APNRs.

  13. Effect of vacancies on the mechanical properties of phosphorene nanotubes

    Science.gov (United States)

    Sorkin, V.; Zhang, Y. W.

    2018-06-01

    Using density functional tight-binding method, we studied the mechanical properties, deformation and failure of armchair (AC) and zigzag (ZZ) phosphorene nanotubes (PNTs) with monovacancies and divacancies subjected to uniaxial tensile strain. We found that divacancies in AC PNTs and monovacancies in ZZ PNTs possess the lowest vacancy formation energy, which decreases with the tube diameter in AC PNTs and increases in ZZ PNTs. The Young’s modulus is reduced, while the radial and thickness Poisson’s ratios are increased by hosted vacancies. In defective AC PNTs, deformation involves fracture of the intra-pucker bonds and formation of the new inter-pucker bonds at a critical strain, and the most stretched bonds around the vacancy rupture first, triggering a sequence of the structural transformations terminated by the ultimate failure. The critical strain of AC PNTs is reduced significantly by hosted vacancies, whereas their effect on the critical stress is relatively weaker. Defective ZZ PNTs fail in a brittle-like manner once the most stretched bonds around a vacancy rupture, and vacancies are able to significantly reduce the failure strain but only moderately reduce the failure stress of ZZ PNTs. The understandings revealed here on the mechanical properties and the deformation and failure mechanisms of PNTs provide useful guidelines for their design and fabrication as building blocks in nanodevices.

  14. Concerning the trapping of positrons in ionic solids

    International Nuclear Information System (INIS)

    Kunz, A.B.; Waber, J.T.

    1982-01-01

    The total energy of several ionic crystals which contain lattice defects plus a positron were studied in the Hartree-Fock limit. Large uncontracted basis sets of GTO's were used to ensure binding if it would occur. Specifically, the attraction of a positron to a cation vacancy was sought for alkali halides as well as for nickel oxide. While the binding energy to nickel oxide was 8.1 eV, there was very little tendency for the positron to be trapped in the alkali halides. The trapping at a Vsub(k) site was also investigated using similar restricted HF approximation with large sets of GTO's. This defect in LiF was shown to be stable by 0.73 eV, by itself but was unable to bind a positron. These two results are not compatible with qPs being localized in such crystals. (Auth.)

  15. Vacancy defect and defect cluster energetics in ion-implanted ZnO

    Science.gov (United States)

    Dong, Yufeng; Tuomisto, F.; Svensson, B. G.; Kuznetsov, A. Yu.; Brillson, Leonard J.

    2010-02-01

    We have used depth-resolved cathodoluminescence, positron annihilation, and surface photovoltage spectroscopies to determine the energy levels of Zn vacancies and vacancy clusters in bulk ZnO crystals. Doppler broadening-measured transformation of Zn vacancies to vacancy clusters with annealing shifts defect energies significantly lower in the ZnO band gap. Zn and corresponding O vacancy-related depth distributions provide a consistent explanation of depth-dependent resistivity and carrier-concentration changes induced by ion implantation.

  16. Computation of transverse muon-spin relaxation functions including trapping-detrapping reactions, with application to electron-irradiated tantalum

    International Nuclear Information System (INIS)

    Doering, K.P.; Aurenz, T.; Herlach, D.; Schaefer, H.E.; Arnold, K.P.; Jacobs, W.; Orth, H.; Haas, N.; Seeger, A.; Max-Planck-Institut fuer Metallforschung, Stuttgart

    1986-01-01

    A new technique for the economical evaluation of transverse muon spin relaxation functions in situations involving μ + trapping at and detrapping from crystal defects is applied to electron-irradiated Ta exhibiting relaxation maxima at about 35 K, 100 K, and 250 K. The long-range μ + diffusion is shown to be limted by traps over the entire temperature range investigated. The (static) relaxation rates for several possible configurations of trapped muons are discussed, including the effect of the simultaneous presence of a proton in a vacancy. (orig.)

  17. Trapping and Probing Antihydrogen

    Energy Technology Data Exchange (ETDEWEB)

    Wurtele, Jonathan [UC Berkeley and LBNL

    2013-03-27

    Precision spectroscopy of antihydrogen is a promising path to sensitive tests of CPT symmetry. The most direct route to achieve this goal is to create and probe antihydrogen in a magnetic minimum trap. Antihydrogen has been synthesized and trapped for 1000s at CERN by the ALPHA Collaboration. Some of the challenges associated with achieving these milestones will be discussed, including mixing cryogenic positron and antiproton plasmas to synthesize antihydrogen with kinetic energy less than the trap potential of .5K. Recent experiments in which hyperfine transitions were resonantly induced with microwaves will be presented. The opportunity for gravitational measurements in traps based on detailed studies of antihydrogen dynamics will be described. The talk will conclude with a discussion future antihydrogen research that will use a new experimental apparatus, ALPHA-I.

  18. EBIT trapping program

    International Nuclear Information System (INIS)

    Elliott, S.R.; Beck, B.; Beiersdorfer, P.; Church, D.; DeWitt, D.; Knapp, D.K.; Marrs, R.E.; Schneider, D.; Schweikhard, L.

    1993-01-01

    The LLNL electron beam ion trap provides the world's only source of stationary highly charged ions up to bare U. This unique capability makes many new atomic and nuclear physics experiments possible. (orig.)

  19. Microfabricated Waveguide Atom Traps.

    Energy Technology Data Exchange (ETDEWEB)

    Jau, Yuan-Yu [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)

    2017-09-01

    A nanoscale , microfabricated waveguide structure can in - principle be used to trap atoms in well - defined locations and enable strong photon-atom interactions . A neutral - atom platform based on this microfabrication technology will be prealigned , which is especially important for quantum - control applications. At present, there is still no reported demonstration of evanescent - field atom trapping using a microfabricated waveguide structure. We described the capabilities established by our team for future development of the waveguide atom - trapping technology at SNL and report our studies to overcome the technical challenges of loading cold atoms into the waveguide atom traps, efficient and broadband optical coupling to a waveguide, and the waveguide material for high - power optical transmission. From the atomic - physics and the waveguide modeling, w e have shown that a square nano-waveguide can be utilized t o achieve better atomic spin squeezing than using a nanofiber for first time.

  20. Pressure response of vacancy ordered maghemite (γ-Fe2O3) and high pressure transformed hematite (α-Fe2O3)

    International Nuclear Information System (INIS)

    Hearne, Giovanni; Pischedda, Vittoria

    2012-01-01

    Combined XRD and Mössbauer effect spectroscopy studies to high pressures of ∼30 GPa of vacancy ordered maghemite are presented. The vacancy ordered superstructure is robust and remains intact up to the pressure-induced onset transition to hematite at 13–16 GPa. The pressure transformed hematite is shown to be crystallographically textured, unlike the randomised low pressure maghemite phase. This arises out of a pressure or stress instigated topotactic transformation of the cubic-spinel to hexagonal-corundum structure. The textured sample permits us to obtain information on the spin reorientation behavior of the pressure transformed hematite in compression and decompression sequences. Spin reorientation is restricted to ∼15° over wide pressure ranges, attributable to the effect of entrapped vacancies in the high pressure structure. Thus there are structural and magnetic peculiarities specific to pressure transformed hematite not evident in pressurized hematite starting material. These are triggered by the maghemite→hematite transformation. - Graphical abstract: Pressure instigated topotactic transformation of vacancy ordered γ-Fe 2 O 3 →α-Fe 2 O 3 . There is restricted spin (B hf ) reorientation in the new pressure transformed hematite due to entrapped vacancies. The change in direction of V zz signifies a distortion of the FeO 6 octahedral local environment. Highlights: ► Robust vacancy ordered superstructure in maghemite to high pressures. ► Pressure instigated topotactic transformation to hematite and subsequent texture. ► Defect trapping in the pressure transformed hematite. ► Entrapped defects restricts spin reorientation in pressure transformed hematite. ► Contrasting behavior with pressurized hematite starting material.

  1. Search For Trapped Antihydrogen

    CERN Document Server

    Andresen, Gorm B.; Baquero-Ruiz, Marcelo; Bertsche, William; Bowe, Paul D.; Bray, Crystal C.; Butler, Eoin; Cesar, Claudio L.; Chapman, Steven; Charlton, Michael; Fajans, Joel; Friesen, Tim; Fujiwara, Makoto C.; Gill, David R.; Hangst, Jeffrey S.; Hardy, Walter N.; Hayano, Ryugo S.; Hayden, Michael E.; Humphries, Andrew J.; Hydomako, Richard; Jonsell, Svante; Jorgensen, Lars V.; Kurchaninov, Lenoid; Lambo, Ricardo; Madsen, Niels; Menary, Scott; Nolan, Paul; Olchanski, Konstantin; Olin, Art; Povilus, Alexander; Pusa, Petteri; Robicheaux, Francis; Sarid, Eli; Nasr, Sarah Seif El; Silveira, Daniel M.; So, Chukman; Storey, James W.; Thompson, Robert I.; van der Werf, Dirk P.; Wilding, Dean; Wurtele, Jonathan S.; Yamazaki, Yasunori

    2011-01-01

    We present the results of an experiment to search for trapped antihydrogen atoms with the ALPHA antihydrogen trap at the CERN Antiproton Decelerator. Sensitive diagnostics of the temperatures, sizes, and densities of the trapped antiproton and positron plasmas have been developed, which in turn permitted development of techniques to precisely and reproducibly control the initial experimental parameters. The use of a position-sensitive annihilation vertex detector, together with the capability of controllably quenching the superconducting magnetic minimum trap, enabled us to carry out a high-sensitivity and low-background search for trapped synthesised antihydrogen atoms. We aim to identify the annihilations of antihydrogen atoms held for at least 130 ms in the trap before being released over ~30 ms. After a three-week experimental run in 2009 involving mixing of 10^7 antiprotons with 1.3 10^9 positrons to produce 6 10^5 antihydrogen atoms, we have identified six antiproton annihilation events that are consist...

  2. DFT study of anisotropy effects on the electronic properties of diamond nanowires with nitrogen-vacancy center.

    Science.gov (United States)

    Solano, Jesús Ramírez; Baños, Alejandro Trejo; Durán, Álvaro Miranda; Quiroz, Eliel Carvajal; Irisson, Miguel Cruz

    2017-09-26

    In the development of quantum computing and communications, improvements in materials capable of single photon emission are of great importance. Advances in single photon emission have been achieved experimentally by introducing nitrogen-vacancy (N-V) centers on diamond nanostructures. However, theoretical modeling of the anisotropic effects on the electronic properties of these materials is almost nonexistent. In this study, the electronic band structure and density of states of diamond nanowires with N-V defects were analyzed through first principles approach using the density functional theory and the supercell scheme. The nanowires were modeled on two growth directions [001] and [111]. All surface dangling bonds were passivated with hydrogen (H) atoms. The results show that the N-V introduces multiple trap states within the energy band gap of the diamond nanowire. The energy difference between these states is influenced by the growth direction of the nanowires, which could contribute to the emission of photons with different wavelengths. The presence of these trap states could reduce the recombination rate between the conduction and the valence band, thus favoring the single photon emission. Graphical abstract Diamond nanowires with nitrogen-vacancy centerᅟ.

  3. Vacancy-type defects in Al2O3/GaN structure probed by monoenergetic positron beams

    Science.gov (United States)

    Uedono, Akira; Nabatame, Toshihide; Egger, Werner; Koschine, Tönjes; Hugenschmidt, Christoph; Dickmann, Marcel; Sumiya, Masatomo; Ishibashi, Shoji

    2018-04-01

    Defects in the Al2O3(25 nm)/GaN structure were probed by using monoenergetic positron beams. Al2O3 films were deposited on GaN by atomic layer deposition at 300 °C. Temperature treatment above 800 °C leads to the introduction of vacancy-type defects in GaN due to outdiffusion of atoms from GaN into Al2O3. The width of the damaged region was determined to be 40-50 nm from the Al2O3/GaN interface, and some of the vacancies were identified to act as electron trapping centers. In the Al2O3 film before and after annealing treatment at 300-900 °C, open spaces with three different sizes were found to coexist. The density of medium-sized open spaces started to decrease above 800 °C, which was associated with the interaction between GaN and Al2O3. Effects of the electron trapping/detrapping processes of interface states on the flat band voltage and the defects in GaN were also discussed.

  4. Intrinsic electron traps in atomic-layer deposited HfO{sub 2} insulators

    Energy Technology Data Exchange (ETDEWEB)

    Cerbu, F.; Madia, O.; Afanas' ev, V. V.; Houssa, M.; Stesmans, A. [Laboratory of Semiconductor Physics, Department of Physics and Astronomy, University of Leuven, 3001 Leuven (Belgium); Andreev, D. V. [Laboratory of Semiconductor Physics, Department of Physics and Astronomy, University of Leuven, 3001 Leuven (Belgium); Bauman Moscow State Technical University—Kaluga Branch, 248000 Kaluga, Moscow obl. (Russian Federation); Fadida, S.; Eizenberg, M. [Department of Materials Science and Engineering, Technion-Israel Institute of Technology, 32000 Haifa (Israel); Breuil, L. [imec, 3001 Leuven (Belgium); Lisoni, J. G. [imec, 3001 Leuven (Belgium); Institute of Physics and Mathematics, Faculty of Science, Universidad Austral de Chile, Valdivia (Chile); Kittl, J. A. [Laboratory of Semiconductor Physics, Department of Physics and Astronomy, University of Leuven, 3001 Leuven (Belgium); Advanced Logic Lab, Samsung Semiconductor, Inc., Austin, 78754 Texas (United States); Strand, J.; Shluger, A. L. [Department of Physics and Astronomy, University College London, London WC1E 6BT (United Kingdom)

    2016-05-30

    Analysis of photodepopulation of electron traps in HfO{sub 2} films grown by atomic layer deposition is shown to provide the trap energy distribution across the entire oxide bandgap. The presence is revealed of two kinds of deep electron traps energetically distributed at around E{sub t} ≈ 2.0 eV and E{sub t} ≈ 3.0 eV below the oxide conduction band. Comparison of the trapped electron energy distributions in HfO{sub 2} layers prepared using different precursors or subjected to thermal treatment suggests that these centers are intrinsic in origin. However, the common assumption that these would implicate O vacancies cannot explain the charging behavior of HfO{sub 2}, suggesting that alternative defect models should be considered.

  5. Strong trapping and slow diffusion of helium in a tungsten grain boundary

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Xin-Xin [Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016 (China); School of Materials Science and Engineering, University of Science and Technology of China, Hefei 230026 (China); Niu, Liang-Liang, E-mail: nliangli@umich.edu [Department of Physics, Beihang University, Beijing 100191 (China); Department of Nuclear Engineering and Radiological Science, University of Michigan, Ann Arbor, MI 48109 (United States); Wang, Shaoqing [Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016 (China)

    2017-04-15

    We have investigated the segregation, trapping and diffusion of He in a ∑3<110>{111} W grain boundary (GB) using combined techniques of ab initio and classical atomistic simulations. We show that, with an average segregation energy of −3.20 eV, the strong He trapping can be attributed to a GB interstitial trapping or a vacancy trapping mechanism, while an average energy barrier of 1.97 eV leads to a slow diffusion of He in the GB plane. We further reveal by molecular dynamics simulations that the He diffusion will be dictated by GB migration through the motion of GB disconnections. Interestingly, we also observe a He-induced GB structural transition in classical simulations. The present work suggests that the GB does not provide fast transport channel for He, providing useful reference for the possible application of polycrystalline W under He irradiation in advanced nuclear fusion reactors.

  6. Vacancies and defect levels in III–V semiconductors

    KAUST Repository

    Tahini, H. A.

    2013-08-13

    Using electronic structure calculations, we systematically investigate the formation of vacancies in III-V semiconductors (III = Al, Ga, and In and V = P, As, and Sb), for a range of charges ( −3≤q≤3 ) as a function of the Fermi level and under different growth conditions. The formation energies were corrected using the scheme due to Freysoldt et al. [Phys. Rev. Lett. 102, 016402 (2009)] to account for finite size effects. Vacancy formation energies were found to decrease as the size of the group V atom increased. This trend was maintained for Al-V, Ga-V, and In-V compounds. The negative-U effect was only observed for the arsenic vacancy in GaAs, which makes a charge state transition from +1 to –1. It is also found that even under group III rich conditions, group III vacancies dominate in AlSb and GaSb. For InSb, group V vacancies are favoured even under group V rich conditions.

  7. Strain engineering of magnetic state in vacancy-doped phosphorene

    Energy Technology Data Exchange (ETDEWEB)

    Ren, Jie [Hunan Provincial Key Laboratory of Micro–Nano Energy Materials and Devices, Xiangtan University, Xiangtan 411105, Hunan (China); Zhang, Chunxiao, E-mail: zhangchunxiao@xtu.edu.cn [Hunan Provincial Key Laboratory of Micro–Nano Energy Materials and Devices, Xiangtan University, Xiangtan 411105, Hunan (China); Li, Jin [Hunan Provincial Key Laboratory of Micro–Nano Energy Materials and Devices, Xiangtan University, Xiangtan 411105, Hunan (China); Guo, Zhixin [Department of Physics, Xiangtan University, Xiangtan 411105, Hunan (China); Xiao, Huaping, E-mail: hpxiao@xtu.edu.cn [Hunan Provincial Key Laboratory of Micro–Nano Energy Materials and Devices, Xiangtan University, Xiangtan 411105, Hunan (China); Zhong, Jianxin [Hunan Provincial Key Laboratory of Micro–Nano Energy Materials and Devices, Xiangtan University, Xiangtan 411105, Hunan (China)

    2016-09-23

    Inducing and manipulating the magnetism in two-dimensional materials play an important role for the development of the next-generation spintronics. In this letter, the effects of the biaxial strain on magnetic properties of vacancy-doped phosphorene are investigated using first-principles calculation. We find although only SV956 doping induces magnetism for unstrained phosphorene, the biaxial strain induces nonzero magnetic moment for SV5566 and DVa doped phosphorene. The biaxial strain also modulates the magnetic state for SV956, SV5566 and DVa doped phosphorene. The local magnetic moment derives from the spin polarization of the dangling bonds near the vacancy. The biaxial strain influences the local bonding configuration near the vacancy which determines the presence of dangling bonds, and then modulates the magnetic state. Our findings promise the synergistic effect of strain engineering and vacancy decoration is an effective method for the operation of phosphorene-based spintronic devices. - Highlights: • Investigation of the magnetic moment of vacancy-doped phosphorene by DFT calculation. • The modulation of the magnetic moment by the biaxial strain. • The analysis of the bonding configuration with the biaxial strain. • The analysis of the electronic structures to explain the evolution of the magnetic moment. • The effects of the biaxial strain on the band gap and doping levels.

  8. Vacancies and defect levels in III–V semiconductors

    KAUST Repository

    Tahini, H. A.; Chroneos, Alexander; Grimes, R. W.; Murphy, S. T.; Schwingenschlö gl, Udo

    2013-01-01

    Using electronic structure calculations, we systematically investigate the formation of vacancies in III-V semiconductors (III = Al, Ga, and In and V = P, As, and Sb), for a range of charges ( −3≤q≤3 ) as a function of the Fermi level and under different growth conditions. The formation energies were corrected using the scheme due to Freysoldt et al. [Phys. Rev. Lett. 102, 016402 (2009)] to account for finite size effects. Vacancy formation energies were found to decrease as the size of the group V atom increased. This trend was maintained for Al-V, Ga-V, and In-V compounds. The negative-U effect was only observed for the arsenic vacancy in GaAs, which makes a charge state transition from +1 to –1. It is also found that even under group III rich conditions, group III vacancies dominate in AlSb and GaSb. For InSb, group V vacancies are favoured even under group V rich conditions.

  9. Thermodesorption examination of interaction of hydrogen with traps in silver

    International Nuclear Information System (INIS)

    Gabis, I.E.; Kurdyumov, A.A.; Ovsvannikova, T.A.

    1992-01-01

    The authors have previously examined the interaction of hydrogen with silver by the methods of thermal desorption spectrometry (TDS) and hydrogen permeability. The results showed that the TDS spectra contained a high-temperature phase linked with hydrogen which left the volume of the specimen during heating. It was assumed that hydrogen was captured and released by structural defects acting as traps. These traps can be represented by vacancies and their clusters. In this work, the high-temperature desorption of hydrogen from silver was studied. The experimental setup consisted of an all-metal vacuum system, a time-of-flight mass spectrometer, a DVK-2M computing system, and a Camac system. The described model of a local equilibrium should be regarded only as a first approximation. The results provide unambiguous information on the processes of permeability and desorption, and make it possible to assume that the formation of the high-temperature phase in TD spectra was caused by the generation of hydrogen from the traps. The parameters of the interaction of hydrogen with the traps were determined by the concentration wave method. 7 refs., 2 figs

  10. Physics with Trapped Antihydrogen

    Science.gov (United States)

    Charlton, Michael

    2017-04-01

    For more than a decade antihydrogen atoms have been formed by mixing antiprotons and positrons held in arrangements of charged particle (Penning) traps. More recently, magnetic minimum neutral atom traps have been superimposed upon the anti-atom production region, promoting the trapping of a small quantity of the antihydrogen yield. We will review these advances, and describe some of the first physics experiments performed on anrtihydrogen including the observation of the two-photon 1S-2S transition, invesigation of the charge neutrailty of the anti-atom and studies of the ground state hyperfine splitting. We will discuss the physics motivations for undertaking these experiments and describe some near-future initiatives.

  11. Agglomeration Versus Localization Of Hydrogen In BCC Fe Vacancies

    International Nuclear Information System (INIS)

    Simonetti, S.; Juan, A.; Brizuela, G.; Simonetti, S.

    2006-01-01

    Severe embrittlement can be produced in many metals by small amounts of hydrogen. The interactions of hydrogen with lattice imperfections are important and often dominant in determining the influence of this impurity on the properties of solids. The interaction between four-hydrogen atoms and a BCC Fe structure having a vacancy has been studied using a cluster model and a semiempirical method. For a study of sequential absorption, the hydrogen atoms were positioned in their energy minima configurations, near to the tetrahedral sites neighbouring the vacancy. VH 2 and VH 3 complexes are energetically the most stables in BCC Fe. The studies about the stability of the hydrogen agglomeration gave as a result that the accumulation is unfavourable in complex vacancy-hydrogen with more than three atoms of hydrogen. (authors)

  12. Quantum corrections to conductivity in graphene with vacancies

    Science.gov (United States)

    Araujo, E. N. D.; Brant, J. C.; Archanjo, B. S.; Medeiros-Ribeiro, G.; Alves, E. S.

    2018-06-01

    In this work, different regions of a graphene device were exposed to a 30 keV helium ion beam creating a series of alternating strips of vacancy-type defects and pristine graphene. From magnetoconductance measurements as function of temperature, density of carriers and density of strips we show that the electron-electron interaction is important to explain the logarithmic quantum corrections to the Drude conductivity in graphene with vacancies. It is known that vacancies in graphene behave as local magnetic moments that interact with the conduction electrons and leads to a logarithmic correction to the conductance through the Kondo effect. However, our work shows that it is necessary to account for the non-homogeneity of the sample to avoid misinterpretations about the Kondo physics due the difficulties in separating the electron-electron interaction from the Kondo effect.

  13. Role of nitrogen vacancies in cerium doped aluminum nitride

    International Nuclear Information System (INIS)

    Majid, Abdul; Asghar, Farzana; Rana, Usman Ali; Ud-Din Khan, Salah; Yoshiya, Masato; Hussain, Fayyaz; Ahmad, Iftikhar

    2016-01-01

    In this report, a systematic density functional theory based investigation to explain the character of nitrogen vacancies in structural, electronic and magnetic properties of Ce doped wurtzite AlN is presented. The work demonstrates the modification in the properties of the material upon doping thereby addressing dopant concentration and inter-dopant distance. The presence of anionic vacancy reveals spin polarization and introduction of magnetic character in the structure. The doping produced the magnetic character in the material which was of ferromagnetic nature in most cases except the situation when dopants separated by largest distance of 5.873 Å. The calculated values of total energy and exchange energy suggested the configuration including Ce Al –V N complex is more favorable and exhibits ferromagnetic ordering. - Highlights: • Ce doped AlN with and without nitrogen vacancy. • Dopant at nearest neighbor site introduce ferromagnetism. • Ce Al –V N complex is favorable in Ce:AlN.

  14. Vacancy-rearrangement theory in the first Magnus approximation

    International Nuclear Information System (INIS)

    Becker, R.L.

    1984-01-01

    In the present paper we employ the first Magnus approximation (M1A), a unitarized Born approximation, in semiclassical collision theory. We have found previously that the M1A gives a substantial improvement over the first Born approximation (B1A) and can give a good approximation to a full coupled channels calculation of the mean L-shell vacancy probability per electron, p/sub L/, when the L-vacancies are accompanied by a K-shell vacancy (p/sub L/ is obtained experimentally from measurements of K/sub α/-satellite intensities). For sufficiently strong projectile-electron interactions (sufficiently large Z/sub p/ or small v) the M1A ceases to reproduce the coupled channels results, but it is accurate over a much wider range of Z/sub p/ and v than the B1A. 27 references

  15. Mechanism of vacancy formation induced by hydrogen in tungsten

    Directory of Open Access Journals (Sweden)

    Yi-Nan Liu

    2013-12-01

    Full Text Available We report a hydrogen induced vacancy formation mechanism in tungsten based on classical molecular dynamics simulations. We demonstrate the vacancy formation in tungsten due to the presence of hydrogen associated directly with a stable hexagonal self-interstitial cluster as well as a linear crowdion. The stability of different self-interstitial structures has been further studied and it is particularly shown that hydrogen plays a crucial role in determining the configuration of SIAs, in which the hexagonal cluster structure is preferred. Energetic analysis has been carried out to prove that the formation of SIA clusters facilitates the formation of vacancies. Such a mechanism contributes to the understanding of the early stage of the hydrogen blistering in tungsten under a fusion reactor environment.

  16. Origin of Nanobubbles Electrochemically Formed in a Magnetic Field: Ionic Vacancy Production in Electrode Reaction

    Science.gov (United States)

    Aogaki, Ryoichi; Sugiyama, Atsushi; Miura, Makoto; Oshikiri, Yoshinobu; Miura, Miki; Morimoto, Ryoichi; Takagi, Satoshi; Mogi, Iwao; Yamauchi, Yusuke

    2016-07-01

    As a process complementing conventional electrode reactions, ionic vacancy production in electrode reaction was theoretically examined; whether reaction is anodic or cathodic, based on the momentum conservation by Newton’s second law of motion, electron transfer necessarily leads to the emission of original embryo vacancies, and dielectric polarization endows to them the same electric charge as trans- ferred in the reaction. Then, the emitted embryo vacancies immediately receive the thermal relaxation of solution particles to develop steady-state vacancies. After the vacancy production, nanobubbles are created by the collision of the vacancies in a vertical magnetic field.

  17. Ion trap device

    Science.gov (United States)

    Ibrahim, Yehia M.; Smith, Richard D.

    2016-01-26

    An ion trap device is disclosed. The device includes a series of electrodes that define an ion flow path. A radio frequency (RF) field is applied to the series of electrodes such that each electrode is phase shifted approximately 180 degrees from an adjacent electrode. A DC voltage is superimposed with the RF field to create a DC gradient to drive ions in the direction of the gradient. A second RF field or DC voltage is applied to selectively trap and release the ions from the device. Further, the device may be gridless and utilized at high pressure.

  18. Asymmetric ion trap

    Science.gov (United States)

    Barlow, Stephan E.; Alexander, Michael L.; Follansbee, James C.

    1997-01-01

    An ion trap having two end cap electrodes disposed asymmetrically about a center of a ring electrode. The inner surface of the end cap electrodes are conformed to an asymmetric pair of equipotential lines of the harmonic formed by the application of voltages to the electrodes. The asymmetry of the end cap electrodes allows ejection of charged species through the closer of the two electrodes which in turn allows for simultaneously detecting anions and cations expelled from the ion trap through the use of two detectors charged with opposite polarity.

  19. Energy Characteristics of Small Metal Clusters Containing Vacancies

    Science.gov (United States)

    Reva, V. I.; Pogosov, V. V.

    2018-02-01

    Self-consistent calculations of spatial distributions of electrons, potentials, and energies of dissociation, cohesion, vacancy formation, and electron attachment, as well as the ionization potential of solid Al N , Na N clusters ( N ≥ 254), and clusters containing a vacancy ( N ≥ 12) have been performed using a model of stable jellium. The contribution of a monovacancy to the energy of the cluster, the size dependences of the characteristics, and their asymptotic forms have been considered. The calculations have been performed on the SKIT-3 cluster at the Glushkov Institute of Cybernetics, National Academy of Sciences of Ukraine (Rpeak = 7.4 Tflops).

  20. Tunable resonances due to vacancies in graphene nanoribbons

    Science.gov (United States)

    Bahamon, D. A.; Pereira, A. L. C.; Schulz, P. A.

    2010-10-01

    The coherent electron transport along zigzag and metallic armchair graphene nanoribbons in the presence of one or two vacancies is investigated. Having in mind atomic scale tunability of the conductance fingerprints, the primary focus is on the effect of the distance to the edges and intervacancies spacing. An involved interplay of vacancies sublattice location and nanoribbon edge termination, together with the spacing parameters lead to a wide conductance resonance line-shape modification. Turning on a magnetic field introduces a new length scale that unveils counterintuitive aspects of the interplay between purely geometric aspects of the system and the underlying atomic scale nature of graphene.

  1. Electrical compensation by Ga vacancies in Ga2O3

    OpenAIRE

    Korhonen, Esa; Tuomisto, F.; Gogova, D.; Wagner, G.; Baldini, M.; Galazka, Z.; Schewski, R.; Albrecht, M.

    2015-01-01

    The authors have applied positron annihilation spectroscopy to study the vacancy defects in undoped and Si-doped Ga2O3 thin films. The results show that Ga vacancies are formed efficiently during metal-organic vapor phase epitaxy growth of Ga2O3 thin films. Their concentrations are high enough to fully account for the electrical compensation of Si doping. This is in clear contrast to another n-type transparent semiconducting oxide In2O3, where recent results show that n-type conductivity is n...

  2. Oxygen vacancy tuned Ohmic-Schottky conversion for enhanced performance in β-Ga{sub 2}O{sub 3} solar-blind ultraviolet photodetectors

    Energy Technology Data Exchange (ETDEWEB)

    Guo, D. Y.; Wu, Z. P.; An, Y. H.; Guo, X. C.; Chu, X. L.; Sun, C. L.; Tang, W. H., E-mail: whtang@bupt.edu.cn [School of Science, Beijing University of Posts and Telecommunications, Beijing 100876 (China); State Key Laboratory of Information Photonics and Optical Communications, Beijing University of Posts and Telecommunications, Beijing 100876 (China); Li, L. H. [Physics Department, The State University of New York at Potsdam, Potsdam, New York 13676-2294 (United States); Li, P. G., E-mail: pgli@zstu.edu.cn [School of Science, Beijing University of Posts and Telecommunications, Beijing 100876 (China); Center for Optoelectronics Materials and Devices, Department of Physics, Zhejiang Sci-Tech University, Hangzhou, 310018 Zhejiang (China)

    2014-07-14

    β-Ga{sub 2}O{sub 3} epitaxial thin films were deposited using laser molecular beam epitaxy technique and oxygen atmosphere in situ annealed in order to reduce the oxygen vacancy. Metal/semiconductor/metal structured photodetectors were fabricated using as-grown film and annealed film separately. Au/Ti electrodes were Ohmic contact with the as-grown films and Schottky contact with the annealed films. In compare with the Ohmic-type photodetector, the Schottky-type photodetector takes on lower dark current, higher photoresponse, and shorter switching time, which benefit from Schottky barrier controlling electron transport and the quantity of photogenerated carriers trapped by oxygen vacancy significant decreasing.

  3. Effects of alloy composition and Si-doping on vacancy defect formation in (InxGa1-x)2O3 thin films

    Science.gov (United States)

    Prozheeva, V.; Hölldobler, R.; von Wenckstern, H.; Grundmann, M.; Tuomisto, F.

    2018-03-01

    Various nominally undoped and Si-doped (InxGa1-x)2O3 thin films were grown by pulsed laser deposition in a continuous composition spread mode on c-plane α-sapphire and (100)-oriented MgO substrates. Positron annihilation spectroscopy in the Doppler broadening mode was used as the primary characterisation technique in order to investigate the effect of alloy composition and dopant atoms on the formation of vacancy-type defects. In the undoped samples, we observe a Ga2O3-like trend for low indium concentrations changing to In2O3-like behaviour along with the increase in the indium fraction. Increasing indium concentration is found to suppress defect formation in the undoped samples at [In] > 70 at. %. Si doping leads to positron saturation trapping in VIn-like defects, suggesting a vacancy concentration of at least mid-1018 cm-3 independent of the indium content.

  4. WATER-TRAPPED WORLDS

    International Nuclear Information System (INIS)

    Menou, Kristen

    2013-01-01

    Although tidally locked habitable planets orbiting nearby M-dwarf stars are among the best astronomical targets to search for extrasolar life, they may also be deficient in volatiles and water. Climate models for this class of planets show atmospheric transport of water from the dayside to the nightside, where it is precipitated as snow and trapped as ice. Since ice only slowly flows back to the dayside upon accumulation, the resulting hydrological cycle can trap a large amount of water in the form of nightside ice. Using ice sheet dynamical and thermodynamical constraints, I illustrate how planets with less than about a quarter the Earth's oceans could trap most of their surface water on the nightside. This would leave their dayside, where habitable conditions are met, potentially dry. The amount and distribution of residual liquid water on the dayside depend on a variety of geophysical factors, including the efficiency of rock weathering at regulating atmospheric CO 2 as dayside ocean basins dry up. Water-trapped worlds with dry daysides may offer similar advantages as land planets for habitability, by contrast with worlds where more abundant water freely flows around the globe

  5. Redesigning octopus traps

    Directory of Open Access Journals (Sweden)

    Eduarda Gomes

    2014-06-01

    In order to minimise the identified problems in the actual traps, the present work proposes a new design with the aim of reducing the volume and weight during transport, and also during onshore storage. Alternative materials to avoid corrosion and formation of encrustations were also proposed.

  6. WATER-TRAPPED WORLDS

    Energy Technology Data Exchange (ETDEWEB)

    Menou, Kristen [Department of Astronomy, Columbia University, 550 West 120th Street, New York, NY 10027 (United States)

    2013-09-01

    Although tidally locked habitable planets orbiting nearby M-dwarf stars are among the best astronomical targets to search for extrasolar life, they may also be deficient in volatiles and water. Climate models for this class of planets show atmospheric transport of water from the dayside to the nightside, where it is precipitated as snow and trapped as ice. Since ice only slowly flows back to the dayside upon accumulation, the resulting hydrological cycle can trap a large amount of water in the form of nightside ice. Using ice sheet dynamical and thermodynamical constraints, I illustrate how planets with less than about a quarter the Earth's oceans could trap most of their surface water on the nightside. This would leave their dayside, where habitable conditions are met, potentially dry. The amount and distribution of residual liquid water on the dayside depend on a variety of geophysical factors, including the efficiency of rock weathering at regulating atmospheric CO{sub 2} as dayside ocean basins dry up. Water-trapped worlds with dry daysides may offer similar advantages as land planets for habitability, by contrast with worlds where more abundant water freely flows around the globe.

  7. First-principles calculations of the vacancy formation energy in transition and noble metals

    DEFF Research Database (Denmark)

    Korzhavyi, P.A.; Abrikosov, Igor A.; Johansson, Börje

    1999-01-01

    approach and include electrostatic multipole corrections to the atomic sphere approximation. The results are in excellent agreement with available full-potential calculations and with the vacancy formation energies obtained in positron annihilation measurements. The variation of the vacancy formation...

  8. Vacancy induced half-metallicity in half-Heusler semiconductors

    KAUST Repository

    Zhu, Zhiyong; Cheng, Yingchun; Schwingenschlö gl, Udo

    2011-01-01

    First-principles calculations are performed to investigate the effect of vacancies on the electronic structure and magnetic properties of the two prototypical half-Heusler semiconductors NiTiSn and CoTiSb. The spin degeneracy of the host materials

  9. 77 FR 27774 - Health Information Technology Policy Committee Vacancy

    Science.gov (United States)

    2012-05-11

    ... GOVERNMENT ACCOUNTABILITY OFFICE Health Information Technology Policy Committee Vacancy AGENCY... American Recovery and Reinvestment Act of 2009 (ARRA) established the Health Information Technology Policy.... ADDRESSES: GAO: [email protected] . GAO: 441 G Street NW., Washington, DC 20548. FOR FURTHER INFORMATION...

  10. Diffusion of elements and vacancies in multi-component systems

    Czech Academy of Sciences Publication Activity Database

    Fischer, F. D.; Svoboda, Jiří

    2014-01-01

    Roč. 60, MAR (2014), s. 338-367 ISSN 0079-6425 Institutional support: RVO:68081723 Keywords : multi-component diffusion * vacancy activity * manning theory * stress-driven diffusion Subject RIV: BJ - Thermodynamics Impact factor: 27.417, year: 2014

  11. Vector magnetic field microscopy using nitrogen vacancy centers in diamond

    NARCIS (Netherlands)

    Maertz, B.J.; Wijnheijmer, A.P.; Fuchs, G.D.; Nowakowski, M.E.; Awschalom, D.D.

    2010-01-01

    The localized spin triplet ground state of a nitrogen vacancy (NV) center in diamond can be used in atomic-scale detection of local magnetic fields. Here we present a technique using ensembles of these defects in diamond to image fields around magnetic structures. We extract the local magnetic field

  12. Improved thermodynamic treatment of vacancy-mediated diffusion and creep

    Czech Academy of Sciences Publication Activity Database

    Fischer, F. D.; Hackl, K.; Svoboda, Jiří

    2016-01-01

    Roč. 108, APR (2016), s. 347-354 ISSN 1359-6454 R&D Projects: GA ČR(CZ) GA15-06390S Institutional support: RVO:68081723 Keywords : Thermodynamics * Non-equilibrium * Diffusion * Vacancies * Thermodynamic extremal principle Subject RIV: BJ - Thermodynamics Impact factor: 5.301, year: 2016

  13. Triplet states at an O vacancy in alpha-quartz

    DEFF Research Database (Denmark)

    Lægsgaard, Jesper

    2002-01-01

    The energy landscape of an alpha-quartz O vacancy in the lowest triplet state is investigated. Four local minima are identified and geometries, total energies, and electron paramagnetic resonance (EPR) parameters are obtained. On the basis of calculated values for the magnetic dipole interaction...

  14. 75 FR 49508 - Navigation Safety Advisory Council; Vacancies

    Science.gov (United States)

    2010-08-13

    ... Council; Vacancies AGENCY: Coast Guard, DHS. ACTION: Request for applications. SUMMARY: The Coast Guard seeks applications for membership on the Navigation Safety Advisory Council (NAVSAC). This Committee... prevention of collisions, rammings, and groundings. This includes, but is not limited to: Inland and...

  15. 76 FR 33773 - Navigation Safety Advisory Council; Vacancies

    Science.gov (United States)

    2011-06-09

    ... Council; Vacancies AGENCY: Coast Guard, DHS. ACTION: Request for applications. SUMMARY: The Coast Guard seeks applications for membership on the Navigation Safety Advisory Council (NAVSAC). NAVSAC provides... the U.S. Coast Guard, on matters relating to prevention of maritime collisions, rammings, and...

  16. Vibrational properties of vacancy in bcc transition metals using ...

    Indian Academy of Sciences (India)

    The calculated results of the formation entropy of the vacancy compared well with other available ... for Fe, Mo and W transition metals employing a third-neighbour model. ... For the atomic electron density we have chosen a power law: f (r) = fe.

  17. Tracking Oxygen Vacancies in Thin Film SOFC Cathodes

    Science.gov (United States)

    Leonard, Donovan; Kumar, Amit; Jesse, Stephen; Kalinin, Sergei; Shao-Horn, Yang; Crumlin, Ethan; Mutoro, Eva; Biegalski, Michael; Christen, Hans; Pennycook, Stephen; Borisevich, Albina

    2011-03-01

    Oxygen vacancies have been proposed to control the rate of the oxygen reduction reaction and ionic transport in complex oxides used as solid oxide fuel cell (SOFC) cathodes [1,2]. In this study oxygen vacancies were tracked, both dynamically and statically, with the combined use of scanned probe microscopy (SPM) and scanning transmission electron microscopy (STEM). Epitaxial films of La 0.8 Sr 0.2 Co O3 (L SC113) and L SC113 / LaSrCo O4 (L SC214) on a GDC/YSZ substrate were studied, where the latter showed increased electrocatalytic activity at moderate temperature. At atomic resolution, high angle annular dark field STEM micrographs revealed vacancy ordering in L SC113 as evidenced by lattice parameter modulation and EELS studies. The evolution of oxygen vacancy concentration and ordering with applied bias and the effects of bias cycling on the SOFC cathode performance will be discussed. Research is sponsored by the of Materials Sciences and Engineering Division, U.S. DOE.

  18. [Trapping techniques for Solenopsis invicta].

    Science.gov (United States)

    Liang, Xiao-song; Zhang, Qiang; Zhuang, Yiong-lin; Li, Gui-wen; Ji, Lin-peng; Wang, Jian-guo; Dai, Hua-guo

    2007-06-01

    A field study was made to investigate the trapping effects of different attractants, traps, and wind directions on Solenopsis invicta. The results showed that among the test attractants, TB1 (50 g fishmeal, 40 g peptone, 10 ml 10% sucrose water solution and 20 ml soybean oil) had the best effect, followed by TB2 (ham), TB6 (100 g cornmeal and 20 ml soybean oil) and TB4 (10 ml 10% sucrose water solution, 100 g sugarcane powder and 20 ml soybean oil), with a mean capture efficiency being 77.6, 58.7, 29 and 7.7 individuals per trap, respectively. No S. invicta was trapped with TB3 (10 ml 10% sucrose water solution, 100 g cornmeal and 20 ml soybean oil) and TB5 (honey). Tube trap was superior to dish trap, with a trapping efficiency of 75.2 and 35 individuals per trap, respectively. The attractants had better effects in leeward than in windward.

  19. Optical trapping of gold aerosols

    DEFF Research Database (Denmark)

    Schmitt, Regina K.; Pedersen, Liselotte Jauffred; Taheri, S. M.

    2015-01-01

    Aerosol trapping has proven challenging and was only recently demonstrated.1 This was accomplished by utilizing an air chamber designed to have a minimum of turbulence and a laser beam with a minimum of aberration. Individual gold nano-particles with diameters between 80 nm and 200 nm were trapped...... in air using a 1064 nm laser. The positions visited by the trapped gold nano-particle were quantified using a quadrant photo diode placed in the back focal plane. The time traces were analyzed and the trapping stiffness characterizing gold aerosol trapping determined and compared to aerosol trapping...... of nanometer sized silica and polystyrene particles. Based on our analysis, we concluded that gold nano-particles trap more strongly in air than similarly sized polystyrene and silica particles. We found that, in a certain power range, the trapping strength of polystyrene particles is linearly decreasing...

  20. Contribution to the study of vacancies in silver and uranium (1962); Contribution a l'etude des lacunes dans l'argent et l'uranium (1962)

    Energy Technology Data Exchange (ETDEWEB)

    Quere, Y [Commissariat a l' Energie Atomique, Saclay (France). Centre d' Etudes Nucleaires

    1961-12-15

    In metals, high temperature vacancies can be retained by quenching. Results are given for the quenching of uranium (in liquid helium) and of silver (in liquid nitrogen). In this last case the energy of formation (1.06 eV) and the energy of mobility (0.86 eV) of the vacancies have been measured as well as the energy of mobility of the divacancies (0.58 eV). If the quenching is slow, it is shown that it is possible to trap the vacancies on the impurities of the metal. This leads to increases in the electrical resistivity observed by annealing after quenching, the vacancies being released before disappearing into sinks. The vacancy-impurity binding energy (the impurity being probably oxygen which is present in the silver used at a concentration of 20 ppm. atom.) can thus be estimated to be 0.4 eV. (author) [French] Dans un metal, les lacunes de haute temperature peuvent etre retenues par trempe. On presente des experiences de trempe d'uranium (dans l'helium liquide) et d'argent (dans l'azote liquide). Dans ce dernier cas, on mesure l'energie de formation (1,06 eV) et l'energie de mobilite (0,86 eV) des lacunes ainsi que l'energie de mobilite des bilacunes (0,58 eV). Si la trempe est lente, on montre que l'on peut pieger des lacunes sur les impuretes du metal. On interprete de cette facon des augmentations de resistivite electrique observees par recuit apres trempe, les lacunes se depiegeant avant de disparaitre dans des puits. L'energie de liaison lacune-impurete (l'impurete etant probablement l'oxygene dont l'argent utilise contient 20 ppm. atom.) peut alors etre evalue 0,4 eV. (auteur)

  1. Impurity decoration of native vacancies in Ga and N sublattices of gallium nitride

    OpenAIRE

    Hautakangas, Sami

    2005-01-01

    The effects of impurity atoms as well as various growth methods to the formation of vacancy type defects in gallium nitride (GaN) have been studied by positron annihilation spectroscopy. It is shown that vacancy defects are formed in Ga or N sublattices depending on the doping of the material. Vacancies are decorated with impurity atoms leading to the compensation of the free carriers of the samples. In addition, the vacancy clusters are found to be present in significant concentrations in n-...

  2. On the stability and mobility of di-vacancies in tungsten

    Science.gov (United States)

    Heinola, K.; Djurabekova, F.; Ahlgren, T.

    2018-02-01

    Properties of small vacancy clusters in tungsten were studied with first-principles calculations. The binding and formation energies of the vacancy clusters increase with the cluster size. Dynamic characteristics of a di-vacancy were specified between room temperature and 700 K with lattice kinetic Monte Carlo calculations, which were parametrised with the present first-principles results for the dissociation barriers. An Arrhenius fit for the di-vacancy diffusion yielded \

  3. Electron trapping in neutron-irradiated very thin films of Al2O3

    International Nuclear Information System (INIS)

    Srivastava, P.C.; Bardhan, A.R.

    1979-01-01

    Oxide layers of thicknesses less than 100 A have been prepared by thermal-oxidation of a base metal electrode film of aluminium. These films were then neutron-irradiated from a laboratory Ra-Be source to a fluence of approximately 10 11 neutrons cm -2 and the sandwich structure, Al-Al 2 O 3 -Au, was completed by depositing a thin metal film of gold over the irradiated oxide layer. D.C. steady and transient flow through the sandwich structures have been studied. Results obtained in the experiments with irradiated sandwiches have been compared with unirradiated ones to show that traps are introduced because of the damage caused by the incident neutrons. Transient voltage measurement across the junction gives a trap density of approximately 10 18 cm -3 . A capture cross-section of the order 10 -28 cm 2 is estimated for the traps. It is found that the (identified) traps are uniformly distributed within an energy of 0.099 eV below the conduction band edge of aluminium oxide. The physical nature of the traps is discussed by comparing the capture cross-sections of the physically known trapping centres. The possibility of vacancies or F-centres acting as traps (for the identified ones) has been suggested. (author)

  4. Unraveling the oxygen vacancy structures at the reduced Ce O2(111 ) surface

    Science.gov (United States)

    Han, Zhong-Kang; Yang, Yi-Zhou; Zhu, Beien; Ganduglia-Pirovano, M. Verónica; Gao, Yi

    2018-03-01

    Oxygen vacancies at ceria (Ce O2 ) surfaces play an essential role in catalytic applications. However, during the past decade, the near-surface vacancy structures at Ce O2(111 ) have been questioned due to the contradictory results from experiments and theoretical simulations. Whether surface vacancies agglomerate, and which is the most stable vacancy structure for varying vacancy concentration and temperature, are being heatedly debated. By combining density functional theory calculations and Monte Carlo simulations, we proposed a unified model to explain all conflicting experimental observations and theoretical results. We find a novel trimeric vacancy structure which is more stable than any other one previously reported, which perfectly reproduces the characteristics of the double linear surface oxygen vacancy clusters observed by STM. Monte Carlo simulations show that at low temperature and low vacancy concentrations, vacancies prefer subsurface sites with a local (2 × 2) ordering, whereas mostly linear surface vacancy clusters do form with increased temperature and degree of reduction. These results well explain the disputes about the stable vacancy structure and surface vacancy clustering at Ce O2(111 ) , and provide a foundation for the understanding of the redox and catalytic chemistry of metal oxides.

  5. Synthesis and characterization of magnesium oxide nanocrystallites and probing the vacancy-type defects through positron annihilation studies

    Science.gov (United States)

    Das, Anjan; Mandal, Atis Chandra; Roy, Soma; Prashanth, Pendem; Ahamed, Sk Izaz; Kar, Subhrasmita; Prasad, Mithun S.; Nambissan, P. M. G.

    2016-09-01

    Magnesium oxide nanocrystallites exhibit certain abnormal characteristics when compared to those of other wide band gap oxide semiconductors in the sense they are most prone to water absorption and formation of a hydroxide layer on the surface. The problem can be rectified by heating and pure nanocrystallites can be synthesized with controllable sizes. Inevitably the defect properties are distinctly divided between two stages, the one with the hydroxide layer (region I) and the other after the removal of the layer by annealing (region II). The lattice parameters, the optical band gap and even the positron annihilation characteristics are conspicuous by their distinct behavior in the two stages of the surface configurations of nanoparticles. While region I was specific with the formation of positronium-hydrogen complexes that drastically altered the defect-specific positron lifetimes, pick-off annihilation of orthopositronium atoms marked region II. The vacancy clusters within the nanocrystallites also trapped positrons. They agglomerated due to the effect of the higher temperatures and resulted in the growth of the nanocrystallites. The coincidence Doppler broadening spectroscopic measurements supported these findings and all the more indicated the trapping of positrons additionally into the neutral divacancies and negatively charged trivacancies. This is apart from the Mg2+ monovacancies which acted as the dominant trapping centers for positrons.

  6. Mobility and stability of large vacancy and vacancy-copper clusters in iron: An atomistic kinetic Monte Carlo study

    Energy Technology Data Exchange (ETDEWEB)

    Castin, N., E-mail: ncastin@sckcen.be [Studiecentrum voor Kernenergie - Centre d' Etudes de l' energie Nucleaire (SCK-CEN), Nuclear Materials Science Institute, Unit Structural Materials Modelling and Microstructure-Boeretang 200, B2400 Mol (Belgium); Pascuet, M.I., E-mail: pascuet@cnea.gov.ar [Consejo Nacional de Investigaciones Cientificas y Tecnicas (CONICET), Av. Rivadavia 1917, C1033AAJ Buenos Aires (Argentina); Malerba, L. [Studiecentrum voor Kernenergie - Centre d' Etudes de l' energie Nucleaire (SCK-CEN), Nuclear Materials Science Institute, Unit Structural Materials Modelling and Microstructure-Boeretang 200, B2400 Mol (Belgium)

    2012-10-15

    The formation of Cu-rich precipitates under irradiation is a major cause for changes in the mechanical response to load of reactor pressure vessel steels. In previous works, it has been shown that the mechanism under which precipitation occurs is governed by diffusion of vacancy-copper (VCu) complexes, also in the absence of irradiation. Coarse-grained computer models (such as object kinetic Monte Carlo) aimed at simulating irradiation processes in model alloys or steels should therefore explicitly include the mobility of Cu precipitates, as a consequence of vacancy hops at their surface. For this purpose, in this work we calculate diffusion coefficients and lifetimes for a large variety of VCu complexes. We use an innovative atomistic model, where vacancy migration energies are calculated with little approximations, taking into account all effects of static relaxation and long-range chemical interaction as predicted by an interatomic potential. Our results show that, contrary to what intuition might suggest, saturation in vacancies tend to slow down the transport of Cu atoms.

  7. Escaping the tolerance trap

    International Nuclear Information System (INIS)

    Hammoudeh, S.; Madan, V.

    1994-01-01

    In order to examine the implications of the weakening of OPEC's responsiveness in adjusting its production levels, this paper explicitly incorporates rigidity in the quantity adjustment mechanism, thereby extending previous research which assumed smooth quantity adjustments. The rigidity is manifested in a tolerance range for the discrepancy between the declared target price and that of the market. This environment gives rise to a 'tolerance trap' which impedes the convergence process and inevitably brings the market to a standstill before its reaches the targeted price and revenue objectives. OPEC's reaction to the standstill has important implications for the achievement of the target-based equilibrium and for the potential collapse of the market price. This paper examines OPEC's policy options in the tolerance trap and reveals that the optional policy in order to break this impasse and move closer to the equilibrium point is gradually to reduce output and not to flood the market. (Author)

  8. Trapped Ion Qubits

    Energy Technology Data Exchange (ETDEWEB)

    Maunz, Peter Lukas Wilhelm

    2017-04-01

    Qubits can be encoded in clock states of trapped ions. These states are well isolated from the environment resulting in long coherence times [1] while enabling efficient high-fidelity qubit interactions mediated by the Coulomb coupled motion of the ions in the trap. Quantum states can be prepared with high fidelity and measured efficiently using fluorescence detection. State preparation and detection with 99.93% fidelity have been realized in multiple systems [1,2]. Single qubit gates have been demonstrated below rigorous fault-tolerance thresholds [1,3]. Two qubit gates have been realized with more than 99.9% fidelity [4,5]. Quantum algorithms have been demonstrated on systems of 5 to 15 qubits [6–8].

  9. Sediment Trapping in Estuaries

    Science.gov (United States)

    Burchard, Hans; Schuttelaars, Henk M.; Ralston, David K.

    2018-01-01

    Estuarine turbidity maxima (ETMs) are generated by a large suite of hydrodynamic and sediment dynamic processes, leading to longitudinal convergence of cross-sectionally integrated and tidally averaged transport of cohesive and noncohesive suspended particulate matter (SPM). The relative importance of these processes for SPM trapping varies substantially among estuaries depending on topography, fluvial and tidal forcing, and SPM composition. The high-frequency dynamics of ETMs are constrained by interactions with the low-frequency dynamics of the bottom pool of easily erodible sediments. Here, we use a transport decomposition to present processes that lead to convergent SPM transport, and review trapping mechanisms that lead to ETMs at the landward limit of the salt intrusion, in the freshwater zone, at topographic transitions, and by lateral processes within the cross section. We use model simulations of example estuaries to demonstrate the complex concurrence of ETM formation mechanisms. We also discuss how changes in SPM trapping mechanisms, often caused by direct human interference, can lead to the generation of hyperturbid estuaries.

  10. Mobile quantum sensing with spins in optically trapped nanodiamonds

    Science.gov (United States)

    Awschalom, David D.

    2013-03-01

    The nitrogen-vacancy (NV) color center in diamond has emerged as a powerful, optically addressable, spin-based probe of electromagnetic fields and temperature. For nanoscale sensing applications, the NV center's atom-like nature enables the close-range interactions necessary for both high spatial resolution and the detection of fields generated by proximal nuclei, electrons, or molecules. Using a custom-designed optical tweezers apparatus, we demonstrate three-dimensional position control of nanodiamonds in solution with simultaneous optical measurement of electron spin resonance (ESR)[3]. Despite the motion and random orientation of NV centers suspended in the optical trap, we observe distinct peaks in the ESR spectra from the ground-state spin transitions. Accounting for the random dynamics of the trapped nanodiamonds, we model the ESR spectra observed in an applied magnetic field and estimate the dc magnetic sensitivity based on the ESR line shapes to be 50 μT/√{ Hz }. We utilize the optically trapped nanodiamonds to characterize the magnetic field generated by current-carrying wires and ferromagnetic structures in microfluidic circuits. These measurements provide a pathway to spin-based sensing in fluidic environments and biophysical systems that are inaccessible to existing scanning probe techniques, such as the interiors of living cells. This work is supported by AFOSR and DARPA.

  11. Total K-vacancy production in Ne (10 MeV) traversing Al

    International Nuclear Information System (INIS)

    Groeneveld, K.O.; Kolb, B.; Schader, J.; Sevier, K.D.

    1976-01-01

    Deexcitation of projectile inner shell vacancies created while traversing a solid foil may take place via competing processes: a) vacancy sharing with foil atoms in close impacts, b) radiative and non-radiative electron capture, and c) such X-ray and Auger electron transitions are possible in the heavy ion projectile. The change in K-vacancy creation with foil thickness can be investigated by measuring either projectile or target X-rays where the vacancies are created by Coulomb excitation and process a. In the system Ne (10 MeV) on Al, detecting Al K X-rays, the Ne K-vacancy production probability has been determined. (orig.) [de

  12. Ab initio study of He trapping, diffusion and clustering in Y{sub 2}O{sub 3}

    Energy Technology Data Exchange (ETDEWEB)

    Lai, Wensheng, E-mail: wslai@tsinghua.edu.cn [Advanced Material Laboratory, School of Materials Science & Engineering, Tsinghua University, Beijing 100084 (China); Ou, Yidian; Lou, Xiaofeng [Advanced Material Laboratory, School of Materials Science & Engineering, Tsinghua University, Beijing 100084 (China); Wang, Fei [Advanced Material Laboratory, School of Materials Science & Engineering, Tsinghua University, Beijing 100084 (China); Xi’an High Technology Research Center, Xi’an 710025 (China)

    2017-02-15

    Ab initio calculations have been performed to study the formation and migration energies of helium atoms and the stability of helium-vacancy clusters in a Y{sub 2}O{sub 3} crystal. The calculated formation energies show that a helium atom is preferred to occupy an yttrium vacancy site with a large volume and low electron density. The migration energy of the helium atom by an interstitial mechanism is 0.31 eV. Calculations of the binding energies of an extra helium atom to the helium-vacancy clusters vary with the number of helium atoms in the clusters with a typical value of 0.4–0.7 eV. This turns negative when the He atoms reach saturation; that indicates that vacancy clusters can attract a limited number of helium atoms to form small stable helium-vacancy clusters. Our calculations suggest that the use of Y{sub 2}O{sub 3} in oxide dispersion strengthened ferritic steels may reduce He gas bubble formation as it may act as sink for trapping helium atoms.

  13. Ultrathin FeOOH nanolayers with abundant oxygen vacancies on BiVO{sub 4} photoanodes for efficient water oxidation

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Beibei [State Key Laboratory for Oxo Synthesis and Selective Oxidation, National Engineering Research Center for Fine Petrochemical Intermediates, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou (China); State Key Laboratory of Applied Organic Chemistry, Key Laboratory of Nonferrous Metals Chemistry and Resources Utilization of Gansu Province, and College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou (China); Wang, Lei; Zhang, Yajun; Bi, Yingpu [State Key Laboratory for Oxo Synthesis and Selective Oxidation, National Engineering Research Center for Fine Petrochemical Intermediates, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou (China); Ding, Yong [State Key Laboratory of Applied Organic Chemistry, Key Laboratory of Nonferrous Metals Chemistry and Resources Utilization of Gansu Province, and College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou (China)

    2018-02-19

    Photoelectrochemical (PEC) water splitting is a promising method for storing solar energy in the form of hydrogen fuel, but it is greatly hindered by the sluggish kinetics of the oxygen evolution reaction (OER). Herein, a facile solution impregnation method is developed for growing ultrathin (2 nm) highly crystalline β-FeOOH nanolayers with abundant oxygen vacancies on BiVO{sub 4} photoanodes. These exhibited a remarkable photocurrent density of 4.3 mA cm{sup -2} at 1.23 V (vs. reversible hydrogen electrode (RHE), AM 1.5 G), which is approximately two times higher than that of amorphous FeOOH fabricated by electrodeposition. Systematic studies reveal that the excellent PEC activity should be attributed to their ultrathin crystalline structure and abundant oxygen vacancies, which could effectively facilitate the hole transport/trapping and provide more active sites for water oxidation. (copyright 2018 Wiley-VCH Verlag GmbH and Co. KGaA, Weinheim)

  14. Vacancy complexes induce long-range ferromagnetism in GaN

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Zhenkui; Schwingenschlögl, Udo, E-mail: Udo.Schwingenschlogl@kaust.edu.sa, E-mail: Iman.Roqan@kaust.edu.sa; Roqan, Iman S., E-mail: Udo.Schwingenschlogl@kaust.edu.sa, E-mail: Iman.Roqan@kaust.edu.sa [Physical Sciences and Engineering Division, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900 (Saudi Arabia)

    2014-11-14

    By means of density functional theory, we argue that ferromagnetism in GaN can be induced by vacancy complexes. Spin polarization originates from the charge compensation between neutral N and Ga vacancies. Defect formation energy calculations predict that a vacancy complex of two positively charged N vacancies and one doubly negative Ga vacancy is likely to form. This defect complex induces a net moment of 1 μ{sub B}, which is localized around the negative Ga center and exhibits pronounced in-plane ferromagnetic coupling. In contrast to simple Ga vacancy induced ferromagnetism, the proposed picture is in line with the fact that N vacancies have a low formation energy. Formation energies indicate mutual stabilization of the intrinsic defects in GaN.

  15. Vacancy complexes induce long-range ferromagnetism in GaN

    KAUST Repository

    Zhang, Zhenkui; Schwingenschlö gl, Udo; Roqan, Iman S.

    2014-01-01

    By means of density functional theory, we argue that ferromagnetism in GaN can be induced by vacancy complexes. Spin polarization originates from the charge compensation between neutral N and Ga vacancies. Defect formation energy calculations predict that a vacancy complex of two positively charged N vacancies and one doubly negative Ga vacancy is likely to form. This defect complex induces a net moment of 1 μB, which is localized around the negative Ga center and exhibits pronounced in-plane ferromagnetic coupling. In contrast to simple Ga vacancy induced ferromagnetism, the proposed picture is in line with the fact that N vacancies have a low formation energy. Formation energies indicate mutual stabilization of the intrinsic defects in GaN.

  16. Dynamics of vacancies in two-dimensional Lennard-Jones crystals

    Science.gov (United States)

    Yao, Zhenwei; Olvera de La Cruz, Monica

    2015-03-01

    Vacancies represent an important class of crystallographic defects, and their behaviors can be strongly coupled with relevant material properties. We report the rich dynamics of vacancies in two-dimensional Lennard-Jones crystals in several thermodynamic states. Specifically, we numerically observe significantly faster diffusion of the 2-point vacancy with two missing particles in comparison with other types of vacancies; it opens the possibility of doping 2-point vacancies into atomic materials to enhance atomic migration. In addition, the resulting dislocations in the healing of a long vacancy suggest the intimate connection between vacancies and topological defects that may provide an extra dimension in the engineering of defects in extensive crystalline materials for desired properties. We thank the financial support from the U.S. Department of Commerce, National Institute of Standards and Technology, the Office of the Director of Defense Research and Engineering (DDR&E) and the Air Force Office of Scientific Research.

  17. Vacancy complexes induce long-range ferromagnetism in GaN

    KAUST Repository

    Zhang, Zhenkui

    2014-11-14

    By means of density functional theory, we argue that ferromagnetism in GaN can be induced by vacancy complexes. Spin polarization originates from the charge compensation between neutral N and Ga vacancies. Defect formation energy calculations predict that a vacancy complex of two positively charged N vacancies and one doubly negative Ga vacancy is likely to form. This defect complex induces a net moment of 1 μB, which is localized around the negative Ga center and exhibits pronounced in-plane ferromagnetic coupling. In contrast to simple Ga vacancy induced ferromagnetism, the proposed picture is in line with the fact that N vacancies have a low formation energy. Formation energies indicate mutual stabilization of the intrinsic defects in GaN.

  18. Reconstruction of mono-vacancies in carbon nanotubes: Atomic relaxation vs. spin polarization

    Energy Technology Data Exchange (ETDEWEB)

    Berber, S. [Institute of Physics, University of Tsukuba, 1-1-1 Tennodai, Tsukuba 305-8571 (Japan)]. E-mail: berber@comas.frsc.tsukuba.ac.jp; Oshiyama, A. [Institute of Physics, University of Tsukuba, 1-1-1 Tennodai, Tsukuba 305-8571 (Japan)

    2006-04-01

    We have investigated the reconstruction of mono-vacancies in carbon nanotubes using density functional theory (DFT) geometry optimization and electronic structure calculations, employing a numerical basis set. We considered mono-vacancies in achiral nanotubes with diameter range {approx}4-9A. Contrary to previous tight-binding calculations, our results indicate that mono-vacancies could have several metastable geometries, confirming the previous plane-wave DFT results. Formation energy of mono-vacancies is 4.5-5.5eV, increasing with increasing tube diameter. Net magnetic moment decreases from ideal mono-vacancy value after reconstruction, reflecting the reduction of the number of dangling bonds. In spite of the existence of a dangling bond, ground state of mono-vacancies in semiconducting tubes have no spin polarization. Metallic carbon nanotubes show net magnetic moment for most stable structure of mono-vacancy, except for very small diameter tubes.

  19. Reconstruction of mono-vacancies in carbon nanotubes: Atomic relaxation vs. spin polarization

    International Nuclear Information System (INIS)

    Berber, S.; Oshiyama, A.

    2006-01-01

    We have investigated the reconstruction of mono-vacancies in carbon nanotubes using density functional theory (DFT) geometry optimization and electronic structure calculations, employing a numerical basis set. We considered mono-vacancies in achiral nanotubes with diameter range ∼4-9A. Contrary to previous tight-binding calculations, our results indicate that mono-vacancies could have several metastable geometries, confirming the previous plane-wave DFT results. Formation energy of mono-vacancies is 4.5-5.5eV, increasing with increasing tube diameter. Net magnetic moment decreases from ideal mono-vacancy value after reconstruction, reflecting the reduction of the number of dangling bonds. In spite of the existence of a dangling bond, ground state of mono-vacancies in semiconducting tubes have no spin polarization. Metallic carbon nanotubes show net magnetic moment for most stable structure of mono-vacancy, except for very small diameter tubes

  20. Ordered array of CoPc-vacancies filled with single-molecule rotors

    Science.gov (United States)

    Xie, Zheng-Bo; Wang, Ya-Li; Tao, Min-Long; Sun, Kai; Tu, Yu-Bing; Yuan, Hong-Kuan; Wang, Jun-Zhong

    2018-05-01

    We report the highly ordered array of CoPc-vacancies and the single-molecule rotors inside the vacancies. When CoPc molecules are deposited on Cd(0001) at low-temperature, three types of molecular vacancies appeared randomly in the CoPc monolayer. Annealing the sample to higher temperature leads to the spontaneous phase separation and self-organized arrangement of the vacancies. Highly ordered arrays of two-molecule vacancies and single-molecule vacancies have been obtained. In particular, there is a rotating CoPc molecule inside each single-molecule vacancy, which constitutes the array of single-molecule rotors. These results provide a new routine to fabricate the nano-machines on a large scale.

  1. Molecular dynamics simulations of oxygen vacancy diffusion in SrTiO3

    International Nuclear Information System (INIS)

    Schie, Marcel; Marchewka, Astrid; Waser, Rainer; Müller, Thomas; De Souza, Roger A

    2012-01-01

    A classical force-field model with partial ionic charges was applied to study the behaviour of oxygen vacancies in the perovskite oxide strontium titanate (SrTiO 3 ). The dynamical behaviour of these point defects was investigated as a function of temperature and defect concentration by means of molecular dynamics (MD) simulations. The interaction between oxygen vacancies and an extended defect, here a Σ3(111) grain boundary, was also examined by means of MD simulations. Analysis of the vacancy distribution revealed considerable accumulation of vacancies in the envelope of the grain boundary. The possible clustering of oxygen vacancies in bulk SrTiO 3 was studied by means of static lattice calculations within the Mott-Littleton approach. All binary vacancy-vacancy configurations were found to be energetically unfavourable.

  2. Molecular dynamics simulations of oxygen vacancy diffusion in SrTiO3.

    Science.gov (United States)

    Schie, Marcel; Marchewka, Astrid; Müller, Thomas; De Souza, Roger A; Waser, Rainer

    2012-12-05

    A classical force-field model with partial ionic charges was applied to study the behaviour of oxygen vacancies in the perovskite oxide strontium titanate (SrTiO(3)). The dynamical behaviour of these point defects was investigated as a function of temperature and defect concentration by means of molecular dynamics (MD) simulations. The interaction between oxygen vacancies and an extended defect, here a Σ3(111) grain boundary, was also examined by means of MD simulations. Analysis of the vacancy distribution revealed considerable accumulation of vacancies in the envelope of the grain boundary. The possible clustering of oxygen vacancies in bulk SrTiO(3) was studied by means of static lattice calculations within the Mott-Littleton approach. All binary vacancy-vacancy configurations were found to be energetically unfavourable.

  3. Stable Trapping of Multielectron Helium Bubbles in a Paul Trap

    Science.gov (United States)

    Joseph, E. M.; Vadakkumbatt, V.; Pal, A.; Ghosh, A.

    2017-06-01

    In a recent experiment, we have used a linear Paul trap to store and study multielectron bubbles (MEBs) in liquid helium. MEBs have a charge-to-mass ratio (between 10^{-4} and 10^{-2} C/kg) which is several orders of magnitude smaller than ions (between 10^6 and 10^8 C/kg) studied in traditional ion traps. In addition, MEBs experience significant drag force while moving through the liquid. As a result, the experimental parameters for stable trapping of MEBs, such as magnitude and frequency of the applied electric fields, are very different from those used in typical ion trap experiments. The purpose of this paper is to model the motion of MEBs inside a linear Paul trap in liquid helium, determine the range of working parameters of the trap, and compare the results with experiments.

  4. Vacancies and a generalised melting curve of metals

    International Nuclear Information System (INIS)

    Gorecki, T.

    1979-01-01

    The vacancy mechanism of the melting process is used as a starting point for deriving an expression for the pressure dependence of the melting temperature of metals. The results obtained for the initial slope of the melting curve are compared with experimental data for 45 metals and in most cases the agreement is very good. The nonlinearity of the melting curve and the appearance of a maximum on the melting curve at a pressure approximately equal to the bulk modules is also predicted, with qualitative agreement with experimental data. A relation between bonding energy, atomic volume, and bulk modulus of metals is established. On the basis of this relation and the proposed vacancy mechanism, a generalised equation for the pressure dependence of the melting temperature of metals is derived. (author)

  5. The interaction of impurity oxygen in silicon with vacancies

    International Nuclear Information System (INIS)

    Aslanyan, A.A.; Babayan, S.A.; Eritsyan, G.N.; Kholodar, G.A.; Melkonyan, R.A.; Vinetskij, V.L.

    1981-01-01

    Silicon specimens irradiated with 50 MeV electrons, containing along with isolated oxygen atoms more complicated oxy-quasi-molecules of SiOsub(n) (n=1,2,3,...) type are investigated. At isochronal and isothermal annealing in the temperature range 300-350 deg C, besides the reaction of vacancy capturing by oxygen atoms with formation of A-centres, there occur more complicated reactions with participation of vacancies, A-centres, oxygen containing quasi-molecules, and a variety of sinks. The kinetics of the processing taking place at irradiation and annealing was studied with respect to the measurement of IR absorption spectra in the region 1-16 μm. A model is suggested to describe the observed processes that differ qualitatively from those taking place in specimens containing completely dissociated oxygen [ru

  6. Vacancy induced half-metallicity in half-Heusler semiconductors

    KAUST Repository

    Zhu, Zhiyong

    2011-09-28

    First-principles calculations are performed to investigate the effect of vacancies on the electronic structure and magnetic properties of the two prototypical half-Heusler semiconductors NiTiSn and CoTiSb. The spin degeneracy of the host materials is broken for all types of isolated vacancies under consideration, except for Ni-deficient NiTiSn. A half-metallic character is identified in Sn-deficient NiTiSn and Co/Ti/Sb-deficient CoTiSb. We can explain our findings by introducing an extending Slater-Pauling rule for systems with defects. A ferromagnetic ordering of the local moments due to double exchange appears to be likely.

  7. Cooling the center-of-mass motion of a diamond nanocrystal in a magneto-gravitational trap

    Science.gov (United States)

    Hsu, Jen-Feng

    A magneto-gravitational trap for micro/nanometer sized diamagnetic particles, such as diamond nanocrystals, is tested and characterized. After exploring various other systems, such as a suspended graphene beam and an optical trap, this magneto-gravitational nanomechanical trapping system for diamond with nitrogen-vacancy (NV) centers presents unique advantages for experiments in fundamental quantum mechanics. Those include, for example, the generation of large quantum superposition states and tests of quantum gravity. Features are demonstrated for this system, such as stable and passive levitation from atmospheric pressure to high vacuum, low resonant frequencies and damping rates, and cooling of the center-of-mass motions to below 1 K. The construction of the trap, vacuum system, optics, and motion detection electronics are described in detail.

  8. Positron trapping at defects in copper oxide superconductors

    International Nuclear Information System (INIS)

    McMullen, T.; Jena, P.; Khanna, S.N.; Li, Y.; Jensen, K.O.

    1991-01-01

    Positron states and lifetimes at defects in the copper oxide superconductors La 2-x Sr x CuO 4 , YBa 2 Cu 3 O 7-x , and Bi 2 Sr 2 CaCu 2 O 8+x are calculated with use of the superposed-atom model. In the Bi 2 Sr 2 CaCu 2 O 8+x compound, we find that the smaller metal-ion vacancies appear to only bind positrons weakly, while missing oxygens do not trap positrons. In contrast, metal-ion vacancies in La 2-x Sr x CuO 4 and YBa 2 Cu 3 O 7-x bind positrons by ∼1 eV, and oxygen-related defects appear to be the weak-binding sites in these materials. The sites that bind positrons only weakly, by energies ∼k BT , are of particular interest in view of the complex temperature dependences of the annihilation characteristics that are observed in these materials

  9. Helium interaction with vacancy-type defects created in silicon carbide single crystal

    Science.gov (United States)

    Linez, F.; Gilabert, E.; Debelle, A.; Desgardin, P.; Barthe, M.-F.

    2013-05-01

    Generation of He bubbles or cavities in silicon carbide is an important issue for the use of this material in nuclear and electronic applications. To understand the mechanisms prior to the growth of these structures, an atomic-scale study has been conducted. 6H-SiC single crystals have been implanted with 50 keV-He ions at 2 × 1014 and 1015 cm-2 and successively annealed at various temperatures from 150 to 1400 °C. After each annealing, the defect distributions in the samples have been probed by positron annihilation spectroscopy. Four main evolution stages have been evidenced for the two investigated implantation fluences: at (1) 400 °C for both fluences, (2) at 850 °C for the low fluence and 950 °C for the high one, (3) at 950 °C for the low fluence and 1050 °C for the high one and (4) at 1300 °C for both fluences. The perfect correlation between the positron annihilation spectroscopy and the thermodesorption measurements has highlighted the He involvement in the first two stages corresponding respectively to its trapping by irradiation-induced divacancies and the detrapping from various vacancy-type defects generated by agglomeration processes.

  10. Helium interaction with vacancy-type defects created in silicon carbide single crystal

    Energy Technology Data Exchange (ETDEWEB)

    Linez, F., E-mail: florence.linez@aalto.fi [CEMHTI CNRS, 3A rue de la Férollerie, 45071 Orléans (France); Gilabert, E. [CENBG, U.R.A. 451 CNRS, Université de Bordeaux I, BP120, Le Haut Vigneau, 33175 Gradignan Cedex (France); Debelle, A. [CSNSM, Univ. Paris-Sud, CNRS-IN2P3, 91405 Orsay Campus (France); Desgardin, P.; Barthe, M.-F. [CEMHTI CNRS, 3A rue de la Férollerie, 45071 Orléans (France)

    2013-05-15

    Generation of He bubbles or cavities in silicon carbide is an important issue for the use of this material in nuclear and electronic applications. To understand the mechanisms prior to the growth of these structures, an atomic-scale study has been conducted. 6H–SiC single crystals have been implanted with 50 keV-He ions at 2 × 10{sup 14} and 10{sup 15} cm{sup −2} and successively annealed at various temperatures from 150 to 1400 °C. After each annealing, the defect distributions in the samples have been probed by positron annihilation spectroscopy. Four main evolution stages have been evidenced for the two investigated implantation fluences: at (1) 400 °C for both fluences, (2) at 850 °C for the low fluence and 950 °C for the high one, (3) at 950 °C for the low fluence and 1050 °C for the high one and (4) at 1300 °C for both fluences. The perfect correlation between the positron annihilation spectroscopy and the thermodesorption measurements has highlighted the He involvement in the first two stages corresponding respectively to its trapping by irradiation-induced divacancies and the detrapping from various vacancy-type defects generated by agglomeration processes.

  11. All-Optical dc Nanotesla Magnetometry Using Silicon Vacancy Fine Structure in Isotopically Purified Silicon Carbide

    Directory of Open Access Journals (Sweden)

    D. Simin

    2016-07-01

    Full Text Available We uncover the fine structure of a silicon vacancy in isotopically purified silicon carbide (4H-^{28}SiC and reveal not yet considered terms in the spin Hamiltonian, originated from the trigonal pyramidal symmetry of this spin-3/2 color center. These terms give rise to additional spin transitions, which would be otherwise forbidden, and lead to a level anticrossing in an external magnetic field. We observe a sharp variation of the photoluminescence intensity in the vicinity of this level anticrossing, which can be used for a purely all-optical sensing of the magnetic field. We achieve dc magnetic field sensitivity better than 100  nT/sqrt[Hz] within a volume of 3×10^{-7}mm^{3} at room temperature and demonstrate that this contactless method is robust at high temperatures up to at least 500 K. As our approach does not require application of radio-frequency fields, it is scalable to much larger volumes. For an optimized light-trapping waveguide of 3  mm^{3}, the projection noise limit is below 100  fT/sqrt[Hz].

  12. Positron probing of phosphorus-vacancy complexes in silicon irradiated with 15 MeV protons

    Science.gov (United States)

    Arutyunov, N.; Emtsev, V.; Krause-Rehberg, R.; Elsayed, M.; Kessler, C.; Kozlovski, V.; Oganesyan, G.

    2015-06-01

    Defects in phosphorus-doped silicon samples of floating-zone material, n-FZ-Si(P), produced under irradiation with 15 MeV protons at room temperature are studied by positron annihilation lifetime spectroscopy over the temperature range of ∼ 30 K - 300 K and by low- temperature Hall effect measurements. After annealing of E-centersand divacancies, we detected for the first time high concentrations of positron traps which had not been observed earlier. These defects are isochronally annealed over the temperature interval of ∼ 320 °C - 700 °C they manifest themselves as electrically neutral deep donor centersin the material of n-type. A long-lived component of the positron lifetime, τ2(I2 enthalpy and entropy of annealing of these centersare Ea ∼ 1.05(0.21) eV and ΔSm ≈ 3.1(0.6)kB, respectively. It is argued that the microstructure of the defect consists of two vacancies, VV, and one atom of phosphorus, P. The split configuration of the VPV complex is shortly discussed.

  13. Optical and microwave control of germanium-vacancy center spins in diamond

    Science.gov (United States)

    Siyushev, Petr; Metsch, Mathias H.; Ijaz, Aroosa; Binder, Jan M.; Bhaskar, Mihir K.; Sukachev, Denis D.; Sipahigil, Alp; Evans, Ruffin E.; Nguyen, Christian T.; Lukin, Mikhail D.; Hemmer, Philip R.; Palyanov, Yuri N.; Kupriyanov, Igor N.; Borzdov, Yuri M.; Rogers, Lachlan J.; Jelezko, Fedor

    2017-08-01

    A solid-state system combining a stable spin degree of freedom with an efficient optical interface is highly desirable as an element for integrated quantum-optical and quantum-information systems. We demonstrate a bright color center in diamond with excellent optical properties and controllable electronic spin states. Specifically, we carry out detailed optical spectroscopy of a germanium-vacancy (GeV ) color center demonstrating optical spectral stability. Using an external magnetic field to lift the electronic spin degeneracy, we explore the spin degree of freedom as a controllable qubit. Spin polarization is achieved using optical pumping, and a spin relaxation time in excess of 20 μ s is demonstrated. We report resonant microwave control of spin transitions, and use this as a probe to measure the Autler-Townes effect in a microwave-optical double-resonance experiment. Superposition spin states were prepared using coherent population trapping, and a pure dephasing time of about 19 ns was observed at a temperature of 2.0 K.

  14. Atom trap trace analysis

    Energy Technology Data Exchange (ETDEWEB)

    Lu, Z.-T.; Bailey, K.; Chen, C.-Y.; Du, X.; Li, Y.-M.; O' Connor, T. P.; Young, L.

    2000-05-25

    A new method of ultrasensitive trace-isotope analysis has been developed based upon the technique of laser manipulation of neutral atoms. It has been used to count individual {sup 85}Kr and {sup 81}Kr atoms present in a natural krypton sample with isotopic abundances in the range of 10{sup {minus}11} and 10{sup {minus}13}, respectively. The atom counts are free of contamination from other isotopes, elements,or molecules. The method is applicable to other trace-isotopes that can be efficiently captured with a magneto-optical trap, and has a broad range of potential applications.

  15. Atom trap trace analysis

    International Nuclear Information System (INIS)

    Lu, Z.-T.; Bailey, K.; Chen, C.-Y.; Du, X.; Li, Y.-M.; O'Connor, T. P.; Young, L.

    2000-01-01

    A new method of ultrasensitive trace-isotope analysis has been developed based upon the technique of laser manipulation of neutral atoms. It has been used to count individual 85 Kr and 81 Kr atoms present in a natural krypton sample with isotopic abundances in the range of 10 -11 and 10 -13 , respectively. The atom counts are free of contamination from other isotopes, elements,or molecules. The method is applicable to other trace-isotopes that can be efficiently captured with a magneto-optical trap, and has a broad range of potential applications

  16. Pinning by oxygen vacancies in high-Tc superconductors

    International Nuclear Information System (INIS)

    Chudnovsky, E.M.

    1990-01-01

    It is shown that recent data of Murray et al. on spatial correlations in flux lattices of Bi-Sr-Ca-Cu-O (BSCCO) may be explained if one assumes that 1% of oxygen atoms in CuO 2 layers are missing. This estimate, being in remarkable agreement with that deduced by Kes and van der Beek from ac-susceptibility measurements, provides strong confidence that oxygen vacancies are the major source of pinning in BSCCO

  17. Multiple vacancy production by high energy heavy ions

    International Nuclear Information System (INIS)

    Becker, R.L.; Ford, A.L.; Reading, J.F.

    1984-01-01

    The theory of atomic collisions has two ingredients: collision theory and atomic structure theory. The collision theories differ with respect to (A) the collision dynamics and (B) the treatment of the relative motion of the projectile and target nuclei. With regard to the dynamics multiple vacancy production is of fundamental interest because it is a signature for and probe of strong interactions between the projectile and the target electrons. For projectiles of large nuclear charge, Z/sub p/, especially for those which are highly stripped so as to have a large ionic charge, q, the interaction becomes strong enough to give a high probability of multiple vacancy production and a breakdown of perturbation theory. The familiar first and second Born approximations and their off-shoots cease to be adequate. Not even the recent strong-potential Born approximation (see Taulbjerg 1984) is sufficient, because the weaker of the potentials generated by the projectile and the target nuclei, respectively, is treated in first order. One needs a unitary, non-perturbative collision theory. At present this is generally available for multiple vacancy production only in the form of the highly numerical coupled channels theory (Becker et al. 1983, 1984b). For special problems analytically tractable models have been devised. For example, a simple, unitary, geometrical encounter probability model for the calculation of p/sub L/(0), the inclusive L-shell vacancy probability per electron in collisions with impact parameter B = 0, has been introduced by Sulik et al. (1984) and further developed by Sulik and Hock (1984). Along with earlier coupled-channels calculations (Becker et al. 1984ab) and first Magnus calculations (Becker et al. 1984b), this model is able to describe the saturation of p/sub L/(0) with Z/sub p/ at fixed impact speed, v, whereas all the first-order theories predict p/sub L/ proportional to Z/sub p/ 2 , which eventually exceeds unity

  18. Magnetic traps with a sperical separatrix: Tornado traps

    International Nuclear Information System (INIS)

    Peregood, B.P.; Lehnert, B.

    1979-11-01

    A review is given on the features of magnetic traps with a spherical separatrix, with special emphesis on Tornado spiral coil configurations. The confinement and heating of static plasmas in Tornado traps is treated, including the topology of the magnetic field structure, the magneto-mechanical properties of the magnetic coil system, as well as the particle orbits and plasma behaviour in these traps. In additio, the mode of rotating plasma operation by crossed electric and magnetic fields is being described. The results of experiments on static and rotating plasmas are summarized, and conclusions are drawn about future possibilities of Tornado traps for the creation and containment of hot plasmas. (author)

  19. Magnetic traps with a spherical separatrix: Tornado traps

    International Nuclear Information System (INIS)

    Peregood, B.P.; Lehnert, B.

    1981-01-01

    A review is given on the features of magnetic traps with a spherical separatrix, with special emphasis on Tornado spiral coil configurations. The confinement and heating of static plasms in Tornado traps is treated, including the topology of the magnetic field structure, the magneto-mechanical properties of the magnetic coil system, as well as the particle orbits and plasma behaviour in these traps. In addition, the mode of rotating plasma operation by crossed electric and magnetic fields is described. The results of experiments on static and rotating plasmas are summarized, and conclusions are drawn about future possibilities of Tornado traps in the creation and containment of hot plasmas. (orig.)

  20. Characteristics of trapped electrons and electron traps in single crystals

    International Nuclear Information System (INIS)

    Budzinski, E.E.; Potter, W.R.; Potienko, G.; Box, H.C.

    1979-01-01

    Two additional carbohydrates are reported whose crystal structures trap electrons intermolecularly in single crystals x irradiated at low temperature, namely sucrose and rhamnose. Five carbohydrate and polyhydroxy compounds are now known which exhibit this phenomenon. The following characteristics of the phenomenon were investigated: (1) the hyperfine couplings of the electron with protons of the polarized hydroxy groups forming the trap; (2) the distances between these protons and the trapped electron; (3) the spin density of the electron at the protons and (4) the relative stabilities of the electron trapped in various crystal structures

  1. Role of nitrogen vacancies in cerium doped aluminum nitride

    Energy Technology Data Exchange (ETDEWEB)

    Majid, Abdul, E-mail: abdulmajid40@yahoo.com [Department of Physics, University of Gujrat, Gujrat (Pakistan); Department of Adaptive Machine Systems, Osaka University, Osaka (Japan); Asghar, Farzana [Department of Physics, University of Gujrat, Gujrat (Pakistan); Rana, Usman Ali; Ud-Din Khan, Salah [Sustainable Energy Technologies Center, College of Engineering, King Saud University, PO-Box 800, Riyadh 11421 (Saudi Arabia); Yoshiya, Masato [Department of Adaptive Machine Systems, Osaka University, Osaka (Japan); Hussain, Fayyaz [Physics Department, Bahauddin Zakarya University, Multan (Pakistan); Ahmad, Iftikhar [Department of Mathematics, University of Gujrat, Gujrat (Pakistan)

    2016-08-15

    In this report, a systematic density functional theory based investigation to explain the character of nitrogen vacancies in structural, electronic and magnetic properties of Ce doped wurtzite AlN is presented. The work demonstrates the modification in the properties of the material upon doping thereby addressing dopant concentration and inter-dopant distance. The presence of anionic vacancy reveals spin polarization and introduction of magnetic character in the structure. The doping produced the magnetic character in the material which was of ferromagnetic nature in most cases except the situation when dopants separated by largest distance of 5.873 Å. The calculated values of total energy and exchange energy suggested the configuration including Ce{sub Al}–V{sub N} complex is more favorable and exhibits ferromagnetic ordering. - Highlights: • Ce doped AlN with and without nitrogen vacancy. • Dopant at nearest neighbor site introduce ferromagnetism. • Ce{sub Al}–V{sub N} complex is favorable in Ce:AlN.

  2. Size of oxide vacancies in fluorite and perovskite structured oxides

    DEFF Research Database (Denmark)

    Chatzichristodoulou, Christodoulos; Norby, Poul; Hendriksen, Peter Vang

    2015-01-01

    An analysis of the effective radii of vacancies and the stoichiometric expansion coefficient is performed on metal oxides with fluorite and perovskite structures. Using the hard sphere model with Shannon ion radii we find that the effective radius of the oxide vacancy in fluorites increases...... with increasing ion radius of the host cation and that it is significantly smaller than the radius of the oxide ion in all cases, from 37% smaller for HfO2 to 13 % smaller for ThO2. The perovskite structured LaGaO3 doped with Sr or Mg or both is analyzed in some detail. The results show that the effective radius...... of an oxide vacancy in doped LaGaO3 is only about 6 % smaller than the oxide ion. In spite of this the stoichiometric expansion coefficient (a kind of chemical expansion coefficient) of the similar perovskite, LaCrO3, is significantly smaller than the stoichiometric expansion coefficient of the fluorite...

  3. Vacancy behavior in a compressed fcc Lennard-Jones crystal

    International Nuclear Information System (INIS)

    Beeler, J.R. Jr.

    1981-12-01

    This computer experiment study concerns the determination of the stable vacancy configuration in a compressed fcc Lennard-Jones crystal and the migration of this defect in a compressed crystal. Isotropic and uniaxial compression stress conditions were studied. The isotropic and uniaxial compression magnitudes employed were 0.94 less than or equal to eta less than or equal to 1.5, and 1.0 less than or equal to eta less than or equal to 1.5, respectively. The site-centered vacancy (SCV) was the stable vacancy configuration whenever cubic symmetry was present. This includes all of the isotropic compression cases and the particular uniaxial compression case (eta = √2) that give a bcc structure. In addition, the SCV was the stable configuration for uniaxial compression eta 1.20, the SV-OP is an extended defect and, therefore, a saddle point for SV-OP migration could not be determined. The mechanism for the transformation from the SCV to the SV-OP as the stable form at eta = 1.29 appears to be an alternating sign [101] and/or [011] shear process

  4. Simple method to enhance positive bias stress stability of In-Ga-Zn-O thin-film transistors using a vertically graded oxygen-vacancy active layer.

    Science.gov (United States)

    Park, Ji Hoon; Kim, Yeong-Gyu; Yoon, Seokhyun; Hong, Seonghwan; Kim, Hyun Jae

    2014-12-10

    We proposed a simple method to deposit a vertically graded oxygen-vacancy active layer (VGA) to enhance the positive bias stress (PBS) stability of amorphous indium gallium zinc oxide (a-IGZO) thin-film transistors (TFTs). We deposited a-IGZO films by sputtering (target composition; In2O3:Ga2O3:ZnO = 1:1:1 mol %), and the oxygen partial pressure was varied during deposition so that the front channel of the TFTs was fabricated with low oxygen partial pressure and the back channel with high oxygen partial pressure. Using this method, we were able to control the oxygen vacancy concentration of the active layer so that it varied with depth. As a result, the turn-on voltage shift following a 10 000 s PBS of optimized VGA TFT was drastically improved from 12.0 to 5.6 V compared with a conventional a-IGZO TFT, without a significant decrease in the field effect mobility. These results came from the self-passivation effect and decrease in oxygen-vacancy-related trap sites of the VGA TFTs.

  5. ATRAP - Progress Towards Trapped Antihydrogen

    International Nuclear Information System (INIS)

    Grzonka, D.; Goldenbaum, F.; Oelert, W.; Sefzick, T.; Zhang, Z.; Comeau, D.; Hessels, E.A.; Storry, C.H.; Gabrielse, G.; Larochelle, P.; Lesage, D.; Levitt, B.; Speck, A.; Haensch, T.W.; Pittner, H.; Walz, J.

    2005-01-01

    The ATRAP experiment at the CERN antiproton decelerator AD aims for a test of the CPT invariance by a high precision comparison of the 1s-2s transition in the hydrogen and the antihydrogen atom.Antihydrogen production is routinely operated at ATRAP and detailed studies have been performed in order to optimize the production efficiency of useful antihydrogen.For high precision measurements of atomic transitions cold antihydrogen in the ground state is required which must be trapped due to the low number of available antihydrogen atoms compared to the cold hydrogen beam used for hydrogen spectroscopy. To ensure a reasonable antihydrogen trapping efficiency a magnetic trap has to be superposed the nested Penning trap. First trapping tests of charged particles within a combined magnetic/Penning trap have started at ATRAP

  6. ATRAP Progress Towards Trapped Antihydrogen

    CERN Document Server

    Grzonka, D; Gabrielse, G; Goldenbaum, F; Hänsch, T W; Hessels, E A; Larochelle, P; Le Sage, D; Levitt, B; Oelert, W; Pittner, H; Sefzick, T; Speck, A; Storry, C H; Walz, J; Zhang, Z

    2005-01-01

    The ATRAP experiment at the CERN antiproton decelerator AD aims for a test of the CPT invariance by a high precision comparison of the 1s‐2s transition in the hydrogen and the antihydrogen atom. Antihydrogen production is routinely operated at ATRAP and detailed studies have been performed in order to optimize the production efficiency of useful antihydrogen. For high precision measurements of atomic transitions cold antihydrogen in the ground state is required which must be trapped due to the low number of available antihydrogen atoms compared to the cold hydrogen beam used for hydrogen spectroscopy. To ensure a reasonable antihydrogen trapping efficiency a magnetic trap has to be superposed the nested Penning trap. First trapping tests of charged particles within a combined magnetic/Penning trap have started at ATRAP.

  7. Intrinsic charge trapping in amorphous oxide films: status and challenges

    Science.gov (United States)

    Strand, Jack; Kaviani, Moloud; Gao, David; El-Sayed, Al-Moatasem; Afanas’ev, Valeri V.; Shluger, Alexander L.

    2018-06-01

    We review the current understanding of intrinsic electron and hole trapping in insulating amorphous oxide films on semiconductor and metal substrates. The experimental and theoretical evidences are provided for the existence of intrinsic deep electron and hole trap states stemming from the disorder of amorphous metal oxide networks. We start from presenting the results for amorphous (a) HfO2, chosen due to the availability of highest purity amorphous films, which is vital for studying their intrinsic electronic properties. Exhaustive photo-depopulation spectroscopy measurements and theoretical calculations using density functional theory shed light on the atomic nature of electronic gap states responsible for deep electron trapping observed in a-HfO2. We review theoretical methods used for creating models of amorphous structures and electronic structure calculations of amorphous oxides and outline some of the challenges in modeling defects in amorphous materials. We then discuss theoretical models of electron polarons and bi-polarons in a-HfO2 and demonstrate that these intrinsic states originate from low-coordinated ions and elongated metal-oxygen bonds in the amorphous oxide network. Similarly, holes can be captured at under-coordinated O sites. We then discuss electron and hole trapping in other amorphous oxides, such as a-SiO2, a-Al2O3, a-TiO2. We propose that the presence of low-coordinated ions in amorphous oxides with electron states of significant p and d character near the conduction band minimum can lead to electron trapping and that deep hole trapping should be common to all amorphous oxides. Finally, we demonstrate that bi-electron trapping in a-HfO2 and a-SiO2 weakens Hf(Si)–O bonds and significantly reduces barriers for forming Frenkel defects, neutral O vacancies and O2‑ ions in these materials. These results should be useful for better understanding of electronic properties and structural evolution of thin amorphous films under carrier injection

  8. Calibration of optically trapped nanotools

    Energy Technology Data Exchange (ETDEWEB)

    Carberry, D M; Simpson, S H; Grieve, J A; Hanna, S; Miles, M J [H H Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol BS8 1TL (United Kingdom); Wang, Y; Schaefer, H; Steinhart, M [Institute for Chemistry, University of Osnabrueck, Osnabrueck (Germany); Bowman, R; Gibson, G M; Padgett, M J, E-mail: m.j.miles@bristol.ac.uk [SUPA, Department of Physics and Astronomy, University of Glasgow, Science Road, Glasgow G12 8QQ (United Kingdom)

    2010-04-30

    Holographically trapped nanotools can be used in a novel form of force microscopy. By measuring the displacement of the tool in the optical traps, the contact force experienced by the probe can be inferred. In the following paper we experimentally demonstrate the calibration of such a device and show that its behaviour is independent of small changes in the relative position of the optical traps. Furthermore, we explore more general aspects of the thermal motion of the tool.

  9. Optical traps with geometric aberrations

    International Nuclear Information System (INIS)

    Roichman, Yael; Waldron, Alex; Gardel, Emily; Grier, David G.

    2006-01-01

    We assess the influence of geometric aberrations on the in-plane performance of optical traps by studying the dynamics of trapped colloidal spheres in deliberately distorted holographic optical tweezers. The lateral stiffness of the traps turns out to be insensitive to moderate amounts of coma, astigmatism, and spherical aberration. Moreover holographic aberration correction enables us to compensate inherent shortcomings in the optical train, thereby adaptively improving its performance. We also demonstrate the effects of geometric aberrations on the intensity profiles of optical vortices, whose readily measured deformations suggest a method for rapidly estimating and correcting geometric aberrations in holographic trapping systems

  10. Characterisation and modelling of vacancy dynamics in Ni–Mn–Ga ferromagnetic shape memory alloys

    Energy Technology Data Exchange (ETDEWEB)

    Merida, D., E-mail: david.merida@ehu.es [Fisika Aplikatua II Saila, Euskal Herriko Unibertsitatea UPV/EHU, p.k. 644, 48080 Bilbao (Spain); Elektrizitate eta Elektronika Saila, Euskal Herriko Unibertsitatea UPV/EHU, p.k. 644, 48080 Bilbao (Spain); García, J.A. [Fisika Aplikatua II Saila, Euskal Herriko Unibertsitatea UPV/EHU, p.k. 644, 48080 Bilbao (Spain); BC Materials (Basque Centre for Materials, Application and Nanostructures), 48040 Leioa (Spain); Sánchez-Alarcos, V. [Departamento de Física, Universidad Pública de Navarra, Campus de Arrosadia, 31006 Pamplona (Spain); Pérez-Landazábal, J.I.; Recarte, V. [Departamento de Física, Universidad Pública de Navarra, Campus de Arrosadia, 31006 Pamplona (Spain); Institute for Advanced Materials (INAMAT), Universidad Pública de Navarra, Campus de Arrosadía, 31006 Pamplona (Spain); Plazaola, F. [Elektrizitate eta Elektronika Saila, Euskal Herriko Unibertsitatea UPV/EHU, p.k. 644, 48080 Bilbao (Spain)

    2015-08-05

    Highlights: • We study the dynamics of vacancies for three different Ni–Mn–Ga alloy samples. • The formation and migration energies have been obtained experimentally. • The entropic factor and the distance a vacancy has to reach a sink are measured. • We present a theoretical model to explain the dynamics of vacancies. • Results are applicable for any thermal treatment and extensible to other alloys. - Abstract: The dynamics of vacancies in Ni–Mn–Ga shape memory alloys has been studied by positron annihilation lifetime spectroscopy. The temperature evolution of the vacancy concentration for three different Ni–Mn–Ga samples, two polycrystalline and one monocrystalline, have been determined. The formation and migration energies and the entropic factors are quite similar in all cases, but vary slightly according to composition. However, the number of jumps a vacancy has to overtake to reach a sink is five times higher in the single crystal. This is an expected result, due to the role that surfaces and grain boundaries should play in balancing the vacancy concentration. In all cases, the initial vacancy concentration for the samples quenched from 1173 K lies between 1000 ppm and 2000 ppm. A phenomenological model able to explain the dynamics of vacancies has been developed in terms of the previous parameters. The model can reproduce the vacancy dynamics for any different kind of thermal history and can be easily extended to other alloys.

  11. Localized versus itinerant states created by multiple oxygen vacancies in SrTiO3

    Science.gov (United States)

    Jeschke, Harald O.; Shen, Juan; Valentí, Roser

    2015-02-01

    Oxygen vacancies in strontium titanate surfaces (SrTiO3) have been linked to the presence of a two-dimensional electron gas with unique behavior. We perform a detailed density functional theory study of the lattice and electronic structure of SrTiO3 slabs with multiple oxygen vacancies, with a main focus on two vacancies near a titanium dioxide terminated SrTiO3 surface. We conclude based on total energies that the two vacancies preferably inhabit the first two layers, i.e. they cluster vertically, while in the direction parallel to the surface, the vacancies show a weak tendency towards equal spacing. Analysis of the nonmagnetic electronic structure indicates that oxygen defects in the surface TiO2 layer lead to population of Ti {{t}2g} states and thus itinerancy of the electrons donated by the oxygen vacancy. In contrast, electrons from subsurface oxygen vacancies populate Ti eg states and remain localized on the two Ti ions neighboring the vacancy. We find that both the formation of a bound oxygen-vacancy state composed of hybridized Ti 3eg and 4p states neighboring the oxygen vacancy as well as the elastic deformation after extracting oxygen contribute to the stabilization of the in-gap state.

  12. Molecular dynamics simulation on mechanical properties of crystalline CoSb3 with vacancy defect

    International Nuclear Information System (INIS)

    Yang Xuqiu; Zhai Pengcheng; Liu Lisheng; Zhang Qingjie

    2012-01-01

    The present work has investigated the tensile mechanical behavior of the skutterudite CoSb 3 single-crystal in the presence of antimony vacancies, since the antimony atoms in CoSb 3 are active and are usually easy to lose in practice. The molecular dynamics simulation method is employed. The vacancy atoms, whose fraction is limited up to 5%, are chosen randomly. The virtual uniaxial tension is carried out by strain controlling along a principal crystallographic direction at 300 K. The specimens with vacancies show similar stress-strain response features to there of the perfect crystal. However, the effective Young's modulus decreases linearly with the increase of the vacancy content, and the ultimate strength drops substantially from no vacancy to even a small vacancy fraction. Temperature dependence of the simulation results is also considered. Both Young's modulus and the ultimate strength exhibit an approximately linear reduction with increasing temperature for a specific vacancy fraction, and moreover, the reduction rate is comparable for different vacancy fractions. The Vacancy distribution effect is briefly discussed as well. As the vacancy concentration becomes uniform, the ultimate strength of the material would be promoted significantly.

  13. A live-trap and trapping technique for fossorial mammals

    African Journals Online (AJOL)

    mammals. G.C. Hickman. An effective live-trap was designed for Cryptomys hottentotus .... that there is an animal in the burrow system, and to lessen the likelihood of the .... the further testing and modification of existing trap types. Not only is it ...

  14. Electron traps in semiconducting polymers : Exponential versus Gaussian trap distribution

    NARCIS (Netherlands)

    Nicolai, H. T.; Mandoc, M. M.; Blom, P. W. M.

    2011-01-01

    The low electron currents in poly(dialkoxy-p-phenylene vinylene) (PPV) derivatives and their steep voltage dependence are generally explained by trap-limited conduction in the presence of an exponential trap distribution. Here we demonstrate that the electron transport of several PPV derivatives can

  15. Electron traps in semiconducting polymers: exponential versus Gaussian trap distribution

    NARCIS (Netherlands)

    Nicolai, H.T.; Mandoc, M.M.; Blom, P.W.M.

    2011-01-01

    The low electron currents in poly(dialkoxy-p-phenylene vinylene) (PPV) derivatives and their steep voltage dependence are generally explained by trap-limited conduction in the presence of an exponential trap distribution. Here we demonstrate that the electron transport of several PPV derivatives can

  16. Pressure response of vacancy ordered maghemite ({gamma}-Fe{sub 2}O{sub 3}) and high pressure transformed hematite ({alpha}-Fe{sub 2}O{sub 3})

    Energy Technology Data Exchange (ETDEWEB)

    Hearne, Giovanni, E-mail: grhearne@uj.ac.za [Department of Physics, University of Johannesburg, PO Box 524, Auckland Park, 2006 Johannesburg (South Africa); Pischedda, Vittoria, E-mail: Vittoria.Pischedda@univ-lyon1.fr [Laboratoire de Physique de la Matiere Condensee et Nanostructures, University Lyon 1 and CNRS, 69622 Villeurbanne Cedex (France)

    2012-03-15

    Combined XRD and Moessbauer effect spectroscopy studies to high pressures of {approx}30 GPa of vacancy ordered maghemite are presented. The vacancy ordered superstructure is robust and remains intact up to the pressure-induced onset transition to hematite at 13-16 GPa. The pressure transformed hematite is shown to be crystallographically textured, unlike the randomised low pressure maghemite phase. This arises out of a pressure or stress instigated topotactic transformation of the cubic-spinel to hexagonal-corundum structure. The textured sample permits us to obtain information on the spin reorientation behavior of the pressure transformed hematite in compression and decompression sequences. Spin reorientation is restricted to {approx}15 Degree-Sign over wide pressure ranges, attributable to the effect of entrapped vacancies in the high pressure structure. Thus there are structural and magnetic peculiarities specific to pressure transformed hematite not evident in pressurized hematite starting material. These are triggered by the maghemite{yields}hematite transformation. - Graphical abstract: Pressure instigated topotactic transformation of vacancy ordered {gamma}-Fe{sub 2}O{sub 3}{yields}{alpha}-Fe{sub 2}O{sub 3}. There is restricted spin (B{sub hf}) reorientation in the new pressure transformed hematite due to entrapped vacancies. The change in direction of V{sub zz} signifies a distortion of the FeO{sub 6} octahedral local environment. Highlights: Black-Right-Pointing-Pointer Robust vacancy ordered superstructure in maghemite to high pressures. Black-Right-Pointing-Pointer Pressure instigated topotactic transformation to hematite and subsequent texture. Black-Right-Pointing-Pointer Defect trapping in the pressure transformed hematite. Black-Right-Pointing-Pointer Entrapped defects restricts spin reorientation in pressure transformed hematite. Black-Right-Pointing-Pointer Contrasting behavior with pressurized hematite starting material.

  17. Segmented trapped vortex cavity

    Science.gov (United States)

    Grammel, Jr., Leonard Paul (Inventor); Pennekamp, David Lance (Inventor); Winslow, Jr., Ralph Henry (Inventor)

    2010-01-01

    An annular trapped vortex cavity assembly segment comprising includes a cavity forward wall, a cavity aft wall, and a cavity radially outer wall there between defining a cavity segment therein. A cavity opening extends between the forward and aft walls at a radially inner end of the assembly segment. Radially spaced apart pluralities of air injection first and second holes extend through the forward and aft walls respectively. The segment may include first and second expansion joint features at distal first and second ends respectively of the segment. The segment may include a forward subcomponent including the cavity forward wall attached to an aft subcomponent including the cavity aft wall. The forward and aft subcomponents include forward and aft portions of the cavity radially outer wall respectively. A ring of the segments may be circumferentially disposed about an axis to form an annular segmented vortex cavity assembly.

  18. Detection of trapped antihydrogen

    Energy Technology Data Exchange (ETDEWEB)

    Hydomako, Richard [Calgary Univ., AB (Canada). Dept. of Physics and Astronomy

    2013-02-01

    A landmark thesis describing the first ever trapping of antihydrogen atoms in CERN's ALPHA apparatus. Opens the way to crucial tests of fundamental theories. Nominated as an outstanding contribution by the University of Calgary. In 2010, the ALPHA collaboration achieved a first for mankind: the stable, long-term storage of atomic antimatter, a project carried out a the Antiproton Decelerator facility at CERN. A crucial element of this observation was a dedicated silicon vertexing detector used to identify and analyze antihydrogen annihilations. This thesis reports the methods used to reconstruct the annihilation location. Specifically, the methods used to identify and extrapolate charged particle tracks and estimate the originating annihilation location are outlined. Finally, the experimental results demonstrating the first-ever magnetic confinement of antihydrogen atoms are presented. These results rely heavily on the silicon detector, and as such, the role of the annihilation vertex reconstruction is emphasized.

  19. Flux trapping in superconducting cavities

    International Nuclear Information System (INIS)

    Vallet, C.; Bolore, M.; Bonin, B.; Charrier, J.P.; Daillant, B.; Gratadour, J.; Koechlin, F.; Safa, H.

    1992-01-01

    The flux trapped in various field cooled Nb and Pb samples has been measured. For ambient fields smaller than 3 Gauss, 100% of the flux is trapped. The consequences of this result on the behavior of superconducting RF cavities are discussed. (author) 12 refs.; 2 figs

  20. Injection into electron plasma traps

    International Nuclear Information System (INIS)

    Gorgadze, Vladimir; Pasquini, Thomas A.; Fajans, Joel; Wurtele, Jonathan S.

    2003-01-01

    Computational studies and experimental measurements of plasma injection into a Malmberg-Penning trap reveal that the number of trapped particles can be an order of magnitude higher than predicted by a simple estimates based on a ballistic trapping model. Enhanced trapping is associated with a rich nonlinear dynamics generated by the space-charge forces of the evolving trapped electron density. A particle-in-cell simulation is used to identify the physical mechanisms that lead to the increase in trapped electrons. The simulations initially show strong two-stream interactions between the electrons emitted from the cathode and those reflected off the end plug of the trap. This is followed by virtual cathode oscillations near the injection region. As electrons are trapped, the initially hollow longitudinal phase-space is filled, and the transverse radial density profile evolves so that the plasma potential matches that of the cathode. Simple theoretical arguments are given that describe the different dynamical regimes. Good agreement is found between simulation and theory

  1. The ALPHA antihydrogen trapping apparatus

    Energy Technology Data Exchange (ETDEWEB)

    Amole, C. [Department of Physics and Astronomy, York University, Toronto ON Canada, M3J 1P3 (Canada); Andresen, G.B. [Department of Physics and Astronomy, Aarhus University, DK-8000 Aarhus C (Denmark); Ashkezari, M.D. [Department of Physics, Simon Fraser University, Burnaby, BC Canada, V5A 1S6 (Canada); Baquero-Ruiz, M. [Department of Physics, University of California at Berkeley, Berkeley, CA 94720-7300 (United States); Bertsche, W. [Department of Physics, College of Science, Swansea University, Swansea SA2 8PP (United Kingdom); School of Physics and Astronomy, University of Manchester, Manchester M13 9PL (United Kingdom); The Cockcroft Institute, Warrington WA4 4AD (United Kingdom); Bowe, P.D. [Department of Physics and Astronomy, Aarhus University, DK-8000 Aarhus C (Denmark); Butler, E. [Physics Department, CERN, CH-1211 Geneva 23 (Switzerland); Capra, A. [Department of Physics and Astronomy, York University, Toronto ON Canada, M3J 1P3 (Canada); Carpenter, P.T. [Department of Physics, Auburn University, Auburn, AL 36849-5311 (United States); Cesar, C.L. [Instituto de Física, Universidade Federal do Rio de Janeiro, Rio de Janeiro 21941-972 (Brazil); Chapman, S. [Department of Physics, University of California at Berkeley, Berkeley, CA 94720-7300 (United States); Charlton, M.; Deller, A.; Eriksson, S. [Department of Physics, College of Science, Swansea University, Swansea SA2 8PP (United Kingdom); Escallier, J. [Brookhaven National Laboratory, Upton, NY 11973 (United States); Fajans, J. [Department of Physics, University of California at Berkeley, Berkeley, CA 94720-7300 (United States); Friesen, T. [Department of Physics and Astronomy, University of Calgary, Calgary AB, Canada, T2N 1N4 (Canada); Fujiwara, M.C.; Gill, D.R. [TRIUMF, 4004 Wesbrook Mall, Vancouver BC, Canada V6T 2A3 (Canada); Gutierrez, A. [Department of Physics and Astronomy, University of British Columbia, Vancouver BC, Canada V6T 1Z4 (Canada); and others

    2014-01-21

    The ALPHA collaboration, based at CERN, has recently succeeded in confining cold antihydrogen atoms in a magnetic minimum neutral atom trap and has performed the first study of a resonant transition of the anti-atoms. The ALPHA apparatus will be described herein, with emphasis on the structural aspects, diagnostic methods and techniques that have enabled antihydrogen trapping and experimentation to be achieved.

  2. Electromagnetic trapping of neutral atoms

    International Nuclear Information System (INIS)

    Metcalf, H.J.

    1986-01-01

    Cooling and trapping of neutral atoms is a new branch of applied physics that has potential for application in many areas. The authors present an introduction to laser cooling and magnetic trapping. Some basic ideas and fundamental limitations are discussed, and the first successful experiments are reviewed. Trapping a neutral object depends on the interaction between an inhomogeneous electromagnetic field and a multiple moment that results in the exchange of kinetic for potential energy. In neutral atom traps, the potential energy must be stored as internal atomic energy, resulting in two immediate and extremely important consequences. First, the atomic energy levels will necessarily shift as the atoms move in the trap, and, second, practical traps for ground state neutral atoms atr necessarily very shallow compared to thermal energy. This small depth also dictates stringent vacuum requirements because a trapped atom cannot survive a single collision with a thermal energy background gas molecule. Neutral trapping, therefore, depends on substantial cooling of a thermal atomic sample and is inextricably connected with the cooling process

  3. Quantum computing with trapped ions

    Energy Technology Data Exchange (ETDEWEB)

    Hughes, R.J.

    1998-01-01

    The significance of quantum computation for cryptography is discussed. Following a brief survey of the requirements for quantum computational hardware, an overview of the ion trap quantum computation project at Los Alamos is presented. The physical limitations to quantum computation with trapped ions are analyzed and an assessment of the computational potential of the technology is made.

  4. Trapped surfaces in spherical stars

    International Nuclear Information System (INIS)

    Bizon, P.; Malec, E.; O'Murchadha, N.

    1988-01-01

    We give necessary and sufficient conditions for the existence of trapped surfaces in spherically symmetric spacetimes. These conditions show that the formation of trapped surfaces depends on both the degree of concentration and the average flow of the matter. The result can be considered as a partial validation of the cosmic-censorship hypothesis

  5. Vacancy dynamic in Ni-Mn-Ga ferromagnetic shape memory alloys

    Energy Technology Data Exchange (ETDEWEB)

    Merida, D., E-mail: david.merida@ehu.es [Fisika Aplikatua II Saila, Euskal Herriko Unibertsitatea UPV/EHU, p.k. 644, 48080 Bilbao (Spain); Elektrizitate eta Elektronika Saila, Euskal Herriko Unibertsitatea UPV/EHU, p.k. 644, 48080 Bilbao (Spain); García, J. A. [Fisika Aplikatua II Saila, Euskal Herriko Unibertsitatea UPV/EHU, p.k. 644, 48080 Bilbao (Spain); BC Materials (Basque Centre for Materials, Application and Nanostructures), 48040 Leioa (Spain); Sánchez-Alarcos, V.; Pérez-Landazábal, J. I.; Recarte, V. [Departamento de Física, Universidad Pública de Navarra, Campus de Arrosadia, 31006 Pamplona (Spain); Plazaola, F. [Elektrizitate eta Elektronika Saila, Euskal Herriko Unibertsitatea UPV/EHU, p.k. 644, 48080 Bilbao (Spain)

    2014-06-09

    Vacancies control any atomic ordering process and consequently most of the order-dependent properties of the martensitic transformation in ferromagnetic shape memory alloys. Positron annihilation spectroscopy demonstrates to be a powerful technique to study vacancies in NiMnGa alloys quenched from different temperatures and subjected to post-quench isothermal annealing treatments. Considering an effective vacancy type the temperature dependence of the vacancy concentration has been evaluated. Samples quenched from 1173 K show a vacancy concentration of 1100 ± 200 ppm. The vacancy migration and formation energies have been estimated to be 0.55 ± 0.05 eV and 0.90 ± 0.07 eV, respectively.

  6. Vacancies in functional materials for clean energy storage and harvesting: the perfect imperfection.

    Science.gov (United States)

    Li, Guowei; Blake, Graeme R; Palstra, Thomas T M

    2017-03-21

    Vacancies exist throughout nature and determine the physical properties of materials. By manipulating the density and distribution of vacancies, it is possible to influence their physical properties such as band-gap, conductivity, magnetism, etc. This can generate exciting applications in the fields of water treatment, energy storage, and physical devices such as resistance-change memories. In this review, we focus on recent progress in vacancy engineering for the design of materials for energy harvesting applications. A brief discription of the concept of vacancies, the way to create and control them, as well as their fundamental properties, is first provided. Then, emphasis is placed on the strategies used to tailor vacancies for metal-insulator transitions, electronic structures, and introducing magnetism in non-magnetic materials. Finally, we present representative applications of different structures with vacancies as active electrode materials of lithium or sodium ion batteries, catalysts for water splitting, and hydrogen evolution.

  7. Observation of Zn vacancies in ZnO grown by chemical vapor transport

    Energy Technology Data Exchange (ETDEWEB)

    Tuomisto, F.; Saarinen, K. [Laboratory of Physics, Helsinki University of Technology, P.O. Box 1100, 02015 TKK (Finland); Grasza, K.; Mycielski, A. [Institute of Physics, Polish Academy of Sciences, Lotnikow 32/46, 02-668 Warsaw (Poland)

    2006-03-15

    We have used positron annihilation spectroscopy to study the vacancy defects in ZnO crystals grown by both the conventional and contactless chemical vapor transport (CVT and CCVT). Our results show that Zn vacancies or Zn vacancy related defects are present in as-grown ZnO, irrespective of the growth method. Zn vacancies are observed in CVT-grown undoped ZnO and (Zn,Mn)O. The Zn vacancies present in undoped CCVT-ZnO are the dominant negatively charged point defect in the material. Doping the material with As introduces also Zn vacancy-related defect complexes with larger open volume. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  8. Spin resonance with trapped ions

    Energy Technology Data Exchange (ETDEWEB)

    Wunderlich, Ch; Balzer, Ch; Hannemann, T; Mintert, F; Neuhauser, W; Reiss, D; Toschek, P E [Institut fuer Laser-Physik, Universitaet Hamburg, Jungiusstrasse 9, 20355 Hamburg (Germany)

    2003-03-14

    A modified ion trap is described where experiments (in particular related to quantum information processing) that usually require optical radiation can be carried out using microwave or radio frequency electromagnetic fields. Instead of applying the usual methods for coherent manipulation of trapped ions, a string of ions in such a modified trap can be treated like a molecule in nuclear magnetic resonance experiments taking advantage of spin-spin coupling. The collection of trapped ions can be viewed as an N-qubit molecule with adjustable spin-spin coupling constants. Given N identically prepared quantum mechanical two-level systems (qubits), the optimal strategy to estimate their quantum state requires collective measurements. Using the ground state hyperfine levels of electrodynamically trapped {sup 171}Yb{sup +}, we have implemented an adaptive algorithm for state estimation involving sequential measurements on arbitrary qubit states.

  9. Spin resonance with trapped ions

    International Nuclear Information System (INIS)

    Wunderlich, Ch; Balzer, Ch; Hannemann, T; Mintert, F; Neuhauser, W; Reiss, D; Toschek, P E

    2003-01-01

    A modified ion trap is described where experiments (in particular related to quantum information processing) that usually require optical radiation can be carried out using microwave or radio frequency electromagnetic fields. Instead of applying the usual methods for coherent manipulation of trapped ions, a string of ions in such a modified trap can be treated like a molecule in nuclear magnetic resonance experiments taking advantage of spin-spin coupling. The collection of trapped ions can be viewed as an N-qubit molecule with adjustable spin-spin coupling constants. Given N identically prepared quantum mechanical two-level systems (qubits), the optimal strategy to estimate their quantum state requires collective measurements. Using the ground state hyperfine levels of electrodynamically trapped 171 Yb + , we have implemented an adaptive algorithm for state estimation involving sequential measurements on arbitrary qubit states

  10. Chemical effect of Si+ ions on the implantation-induced defects in ZnO studied by a slow positron beam

    Science.gov (United States)

    Jiang, M.; Wang, D. D.; Chen, Z. Q.; Kimura, S.; Yamashita, Y.; Mori, A.; Uedono, A.

    2013-01-01

    Undoped ZnO single crystals were implanted with 300 keV Si+ ions to a dose of 6 × 1016 cm-2. A combination of X-ray diffraction (XRD), positron annihilation, Raman scattering, high resolution transmission electron microscopy (HRTEM), and photoluminescence (PL) was used to study the microstructure evolution after implantation and subsequent annealing. A very large increase of Doppler broadening S parameters in Si+-implanted region was detected by using a slow positron beam, indicating that vacancy clusters or microvoids are induced by implantation. The S parameters increase further after annealing up to 700 °C, suggesting agglomeration of these vacancies or microvoids to larger size. Most of these defects are removed after annealing up to 1100 °C. The other measurements such as XRD, Raman scattering, and PL all indicate severe damage and even disordered structure induced by Si+ implantation. The damage and disordered lattice shows recovery after annealing above 700 °C. Amorphous regions are observed by HRTEM measurement, directly testifies that amorphous phase is induced by Si+ implantation in ZnO. Analysis of the S - W correlation and the coincidence Doppler broadening spectra gives direct evidence of SiO2 precipitates in the sample annealed at 700 °C, which strongly supports the chemical effect of Si ions on the amorphization of ZnO lattice.

  11. Origin of the main deep electron trap in electron irradiated InP

    International Nuclear Information System (INIS)

    Sibille, A.

    1986-01-01

    The electrical activity and annealing behavior of the main electron trap in electron irradiated InP p + n junctions has been investigated. A very marked depth dependence of the annealing rate has been found. Moreover, this center apparently acts as if it were a deep donor, leading to an increase of carrier concentration on the n side. All these results are coherently interpreted with a model in terms of radiation defect D(P) (phosphorus interstitial or vacancy), residual shallow acceptor complexing, the final annealing resulting from a dissociation of the complex followed by a diffusion and either recapture or annihilation of D(P)

  12. Dissociative diffusion mechanism in vacancy-rich materials according to mass action kinetics

    Directory of Open Access Journals (Sweden)

    N. J. Biderman

    2016-05-01

    Full Text Available Two sets of diffusion-reaction numerical simulations using a finite difference method (FDM were conducted to investigate fast impurity diffusion via interstitial sites in vacancy-rich materials such as Cu(In,GaSe2 (CIGS and Cu2ZnSn(S, Se4 (CZTSSe or CZTS via the dissociative diffusion mechanism where the interstitial diffuser ultimately reacts with a vacancy to produce a substitutional. The first set of simulations extends the standard interstitial-limited dissociative diffusion theory to vacancy-rich material conditions where vacancies are annihilated in large amounts, introducing non-equilibrium vacancy concentration profiles. The second simulation set explores the vacancy-limited dissociative diffusion where impurity incorporation increases the equilibrium vacancy concentration. In addition to diffusion profiles of varying concentrations and shapes that were obtained in all simulations, some of the profiles can be fitted with the constant- and limited-source solutions of Fick’s second law despite the non-equilibrium condition induced by the interstitial-vacancy reaction. The first set of simulations reveals that the dissociative diffusion coefficient in vacancy-rich materials is inversely proportional to the initial vacancy concentration. In the second set of numerical simulations, impurity-induced changes in the vacancy concentration lead to distinctive diffusion profile shapes. The simulation results are also compared with published data of impurity diffusion in CIGS. According to the characteristic properties of diffusion profiles from the two set of simulations, experimental detection of the dissociative diffusion mechanism in vacancy-rich materials may be possible.

  13. Valence and atomic size dependent exchange barriers in vacancy-mediated dopant diffusion

    International Nuclear Information System (INIS)

    Nelson, J.S.; Schultz, P.A.; Wright, A.F.

    1998-01-01

    First-principles pseudopotential calculations of dopant-vacancy exchange barriers indicate a strong dependency on dopant valence and atomic size, in contrast to current models of vacancy-mediated dopant diffusion. First-row elements (B, C, N) are found to have exchange barriers which are an order of magnitude larger than the assumed value of 0.3 eV (the Si vacancy migration energy). copyright 1998 American Institute of Physics

  14. Oxygen vacancy and Moessbauer parameters of Fe doped tin oxides

    International Nuclear Information System (INIS)

    Nomura, K.; Mudarra Navarro, A.M.; Errico, L.; Rodriguez Torres, C.E.

    2013-01-01

    It is not clear what the local environment of Fe ions included in rutile structure is. In order to clarify this point, Moessbauer parameters of 57 Fe doped SnO 2 are compared with the results of ab initio calculation taking into account different configurations of iron and oxygen vacancy in the rutile structure of SnO 2 . Calculations were performed using the LAPW+lo method (Wien2k); RMT x Kmax = 7, A mesh of 50 k-points at IBZ, 2x2x2 super cell of SnO 2 . (J.P.N.)

  15. Vacancies und melting curves of metals at high pressure

    International Nuclear Information System (INIS)

    Gorecki, T.

    1977-01-01

    The vacancy mechanism of the melting process is utilized as a starting point in derivation of the pressure dependence of melting temperature for metals. The results obtained for the initial slope of the melting curve are compared with experimental data for 45 metals (including U, Np, Pu, rare earths) and in most cases the agreement is very good. An on-linearity of the fusion curve and appearence of the maximum on the melting curve at a pressure approximately equal to the bulk modulus is also predicted with qualitative agreement with existing experimental data. (orig./GSC) [de

  16. Alignment of the diamond nitrogen vacancy center by strain engineering

    Energy Technology Data Exchange (ETDEWEB)

    Karin, Todd [Department of Physics, University of Washington, Seattle, Washington 98195 (United States); Dunham, Scott [Department of Electrical Engineering, University of Washington, Seattle, Washington 98195 (United States); Fu, Kai-Mei [Department of Physics, University of Washington, Seattle, Washington 98195 (United States); Department of Electrical Engineering, University of Washington, Seattle, Washington 98195 (United States)

    2014-08-04

    The nitrogen vacancy (NV) center in diamond is a sensitive probe of magnetic field and a promising qubit candidate for quantum information processing. The performance of many NV-based devices improves by aligning the NV(s) parallel to a single crystallographic direction. Using ab initio theoretical techniques, we show that NV orientation can be controlled by high-temperature annealing in the presence of strain under currently accessible experimental conditions. We find that (89 ± 7)% of NVs align along the [111] crystallographic direction under 2% compressive biaxial strain (perpendicular to [111]) and an annealing temperature of 970 °C.

  17. Vacancy identification in Co+ doped rutile TiO2 crystal with positron annihilation spectroscopy

    Science.gov (United States)

    Qin, X. B.; Zhang, P.; Liang, L. H.; Zhao, B. Z.; Yu, R. S.; Wang, B. Y.; Wu, W. M.

    2011-01-01

    Co-doped rutile TiO2 films were synthesized by ion implantation. Variable energy positron annihilation Doppler broadening spectroscopy and coincidence Doppler broadening measurements were performed for identification of the vacancies. A newly formed type of vacancy can be concluded by the S-W plot and the CDB results indicated that the oxygen vacancy (VO) complex Ti-Co-VO and/or Ti-VO are formed with Co ions implantation and the vacancy concentration is increased with increase of dopant dose.

  18. Gold fillings unravel the vacancy role in the phase transition of GeTe

    Science.gov (United States)

    Feng, Jinlong; Xu, Meng; Wang, Xiaojie; Lin, Qi; Cheng, Xiaomin; Xu, Ming; Tong, Hao; Miao, Xiangshui

    2018-02-01

    Phase change memory (PCM) is an important candidate for future memory devices. The crystalline phase of PCM materials contains abundant intrinsic vacancies, which plays an important role in the rapid phase transition upon memory switching. However, few experimental efforts have been invested to study these invisible entities. In this work, Au dopants are alloyed into the crystalline GeTe to fill the intrinsic Ge vacancies so that the role of these vacancies in the amorphization of GeTe can be indirectly studied. As a result, the reduction of Ge vacancies induced by Au dopants hampers the amorphization of GeTe as the activation energy of this process becomes higher. This is because the vacancy-interrupted lattice can be "repaired" by Au dopants with the recovery of bond connectivity. Our results demonstrate the importance of vacancies in the phase transition of chalcogenides, and we employ the percolation theory to explain the impact of these intrinsic defects on this vacancy-ridden crystal quantitatively. Specifically, the threshold of amorphization increases with the decrease in vacancies. The understanding of the vacancy effect sheds light on the long-standing puzzle of the mechanism of ultra-fast phase transition in PCMs. It also paves the way for designing low-power-consumption electronic devices by reducing the threshold of amorphization in chalcogenides.

  19. Migration of O vacancies in α-quartz: The effect of excitons and electron holes

    International Nuclear Information System (INIS)

    Song, Jakyoung; Corrales, L. Rene; Kresse, Georg; Jonsson, Hannes

    2001-01-01

    We have used density-functional theory and the nudged elastic-band method to calculate migration pathways and estimated the activation energy for the diffusion of oxygen vacancies in α-quartz. While the energy barrier for the diffusion of a neutral vacancy is very high, 4.1 eV, the binding of a triplet-state exciton to the vacancy lowers the barrier to 1.7 eV and the attachment of a hole lowers the barrier to 1.9 eV, making the vacancy mobile at commonly used annealing temperatures

  20. Defects spectroscopy by means of the simple trapping model of the Fe{sub 78}Si{sub 9}B{sub 13} alloy; Espectroscopia de defectos mediante el modelo de atrapamiento simple de la aleacion Fe{sub 78}Si{sub 9}B{sub 13}

    Energy Technology Data Exchange (ETDEWEB)

    Lopez M, A.; Cabral P, A.; Garcia S, S.F. [Laboratorio de Fisica Avanzada, Facultad de Ciencias, Universidad Autonoma del Estado de Mexico. El Cerillo Piedras Blancas, 50000 Toluca, Estado de Mexico (Mexico)

    2007-07-01

    In this work it is analyzed quantitatively the results of the positron annihilation in the Fe{sub 78}Si{sub 9}B{sub 13} alloy by means of the simple trapping model. From this analysis its are derived: a reason of positron trapping in the defects (K), the defects concentration (C{sub d}) and the electronic density associated to the defect (n{sub d}); both first parameters, (K, C{sub d}) its increase and n{sub d} diminishes when increasing the alloy temperature. From this analysis it is also inferred that the defect consists of a multi vacancy of between 15 and 20 mono vacancies. (Author)

  1. Radiation induced traps of zinc phosphate and phosphide

    International Nuclear Information System (INIS)

    Murali, K.R.; Rao, D.R.

    1980-01-01

    Thermoluminescence (TL) glow curve (TGC) method has been used to study the traps produced by X-irradiation in Zn 3 (PO 4 ) 2 and Zn 3 P 2 . Prominent TL glow peaks were observed at 100 0 and 360 0 C for zinc phosphate while for zinc phosphide only one glow peak at 245 0 C was observed, and in the latter case the TL output was in general quite low compared to zinc phosphate. The TL spectra for both the glow peaks of zinc phosphate indicated emission band in the region around 560 nm, while for zinc phosphide the emission occurred at 575 nm (in the temperature region 200-270 0 C). The low temperature glow peaks below 270 0 C were less stable compared to those above 300 0 C and were completely destroyed when the irradiated samples were stored in darkness for 24 hr at room temperature. Shining by 470 nm light however produced preferential bleaching of the two TL peaks at 100 and 360 0 C with no effect on the 245 0 C glow peak of zinc phosphide. It is concluded that during heat treatment large numbers of Zn-vacancies are formed due to which complexes like Zn-P are produced by irradiation and the TL traps destroyed in a radiative recombination process are related with these complexes. (author)

  2. Optical patterning of trapped charge in nitrogen-doped diamond

    Science.gov (United States)

    Jayakumar, Harishankar; Henshaw, Jacob; Dhomkar, Siddharth; Pagliero, Daniela; Laraoui, Abdelghani; Manson, Neil B.; Albu, Remus; Doherty, Marcus W.; Meriles, Carlos A.

    2016-08-01

    The nitrogen-vacancy (NV) centre in diamond is emerging as a promising platform for solid-state quantum information processing and nanoscale metrology. Of interest in these applications is the manipulation of the NV charge, which can be attained by optical excitation. Here, we use two-colour optical microscopy to investigate the dynamics of NV photo-ionization, charge diffusion and trapping in type-1b diamond. We combine fixed-point laser excitation and scanning fluorescence imaging to locally alter the concentration of negatively charged NVs, and to subsequently probe the corresponding redistribution of charge. We uncover the formation of spatial patterns of trapped charge, which we qualitatively reproduce via a model of the interplay between photo-excited carriers and atomic defects. Further, by using the NV as a probe, we map the relative fraction of positively charged nitrogen on localized optical excitation. These observations may prove important to transporting quantum information between NVs or to developing three-dimensional, charge-based memories.

  3. Electronic relaxation of deep bulk trap and interface state in ZnO ceramics

    International Nuclear Information System (INIS)

    Yang Yan; Li Sheng-Tao; Ding Can; Cheng Peng-Fei

    2011-01-01

    This paper investigates the electronic relaxation of deep bulk trap and interface state in ZnO ceramics based on dielectric spectra measured in a wide range of temperature, frequency and bias, in addition to the steady state response. It discusses the nature of net current flowing over the barrier affected by interface state, and then obtains temperature-dependent barrier height by approximate calculation from steady I—V (current—voltage) characteristics. Additional conductance and capacitance arising from deep bulk trap relaxation are calculated based on the displacement of the cross point between deep bulk trap and Fermi level under small AC signal. From the resonances due to deep bulk trap relaxation on dielectric spectra, the activation energies are obtained as 0.22 eV and 0.35 eV, which are consistent with the electronic levels of the main defect interstitial Zn and vacancy oxygen in the depletion layer. Under moderate bias, another resonance due to interface relaxation is shown on the dielectric spectra. The DC-like conductance is also observed in high temperature region on dielectric spectra, and the activation energy is much smaller than the barrier height in steady state condition, which is attributed to the displacement current coming from the shallow bulk trap relaxation or other factors. (fluids, plasmas and electric discharges)

  4. Trapping tsetse flies on water

    Directory of Open Access Journals (Sweden)

    Laveissière C.

    2011-05-01

    Full Text Available Riverine tsetse flies such as Glossina palpalis gambiensis and G. tachinoides are the vectors of human and animal trypanosomoses in West Africa. Despite intimate links between tsetse and water, to our knowledge there has never been any attempt to design trapping devices that would catch tsetse on water. In mangrove (Guinea one challenging issue is the tide, because height above the ground for a trap is a key factor affecting tsetse catches. The trap was mounted on the remains of an old wooden dugout, and attached with rope to nearby branches, thereby allowing it to rise and fall with the tide. Catches showed a very high density of 93.9 flies/”water-trap”/day, which was significantly higher (p < 0.05 than all the catches from other habitats where the classical trap had been used. In savannah, on the Comoe river of South Burkina Faso, the biconical trap was mounted on a small wooden raft anchored to a stone, and catches were compared with the classical biconical trap put on the shores. G. p. gambiensis and G. tachinoides densities were not significantly different from those from the classical biconical one. The adaptations described here have allowed to efficiently catch tsetse on the water, which to our knowledge is reported here for the first time. This represents a great progress and opens new opportunities to undertake studies on the vectors of trypanosomoses in mangrove areas of Guinea, which are currently the areas showing the highest prevalences of sleeping sickness in West Africa. It also has huge potential for tsetse control using insecticide impregnated traps in savannah areas where traps become less efficient in rainy season. The Guinean National control programme has already expressed its willingness to use such modified traps in its control campaigns in Guinea, as has the national PATTEC programme in Burkina Faso during rainy season.

  5. Status of THe-Trap

    Energy Technology Data Exchange (ETDEWEB)

    Streubel, Sebastian; Eronen, Tommi; Hoecker, Martin; Ketter, Jochen; Blaum, Klaus [Max-Planck-Institut fuer Kernphysik, Heidelberg (Germany); Van Dyck, Robert S. Jr. [Department of Physics, University of Washington, Seattle, WA (United States)

    2013-07-01

    THe-Trap (short for Tritium-{sup 3}He Trap) is a Penning-trap setup dedicated to measure the {sup 3}H to {sup 3}He mass-ratio with a relative uncertainty of better than 10{sup -11}. The ratio is of relevance for the KArlsruhe TRItium Neutrino experiment (KATRIN), which aims to measure the electron anti-neutrino mass, by measuring the shape of the β-decay energy spectrum close to its endpoint. An independent measurement of the {sup 3}H to {sup 3}He mass-ratio pins down this endpoint, and thus will help to determine the systematics of KATRIN. The trap setup consists of two Penning-traps: One trap for precision measurements, the other trap for ion storage. Ideally, the trap content will be periodically switched, which reduces the time between the measurements of the two ions' motional frequencies. In 2012, a mass ratio measurement of {sup 12}C{sup 4+} to {sup 14}N{sup 5+} was performed to characterize systematic effects of the traps. This measurement yielded a accuracy of 10{sup -9}. Further investigations revealed that a major reason for the modest accuracy is the large axial amplitude of ∼100 μm, compared to a ideal case of 3 μm at 4 K. In addition, relative magnetic fluctuations at a 3 x 10{sup -10} level on a 10 h timescale need to be significantly improved. In this contribution, the aforementioned findings and further systematic studies will be presented.

  6. Skills and Vacancy Analysis with Data Mining Techniques

    Directory of Open Access Journals (Sweden)

    Izabela A. Wowczko

    2015-11-01

    Full Text Available Through recognizing the importance of a qualified workforce, skills research has become one of the focal points in economics, sociology, and education. Great effort is dedicated to analyzing labor demand and supply, and actions are taken at many levels to match one with the other. In this work we concentrate on skills needs, a dynamic variable dependent on many aspects such as geography, time, or the type of industry. Historically, skills in demand were easy to evaluate since transitions in that area were fairly slow, gradual, and easy to adjust to. In contrast, current changes are occurring rapidly and might take an unexpected turn. Therefore, we introduce a relatively simple yet effective method of monitoring skills needs straight from the source—as expressed by potential employers in their job advertisements. We employ open source tools such as RapidMiner and R as well as easily accessible online vacancy data. We demonstrate selected techniques, namely classification with k-NN and information extraction from a textual dataset, to determine effective ways of discovering knowledge from a given collection of vacancies.

  7. Silicon-vacancy centre as an artificial atom in diamond

    International Nuclear Information System (INIS)

    Lachlan Rogers

    2014-01-01

    A transition at 738 nm in diamond has been attributed to the silicon vacancy (SiV) colour centre. Much less is known about this defect site than the famous nitrogen-vacancy centre, but it appears to have advantages for some applications It is particularly promising as a single-photon source, due to a bright optical transition which has most of its intensity in the zero-phonon-line and only a small phonon sideband. A number of results will be reported for single SiV sites in bulk diamond, complementing recent activity on SiV in nanodiamonds. Individual SiV sites in the low-strain environment of bulk diamond show almost no variation in photoluminescence spectra. By fabricating a solid-immersion lens in the diamond over a SiV site we have enhanced the photon collection rate by nearly a factor of ten. In order to identify whether the SiV centre could be useful for broader quantum information processing application, it is first necessary to establish its electronic structure. Recent experimental developments in this direction will be discussed. (author)

  8. Magnetism of a relaxed single atom vacancy in graphene

    Science.gov (United States)

    Wu, Yunyi; Hu, Yonghong; Xue, Li; Sun, Tieyu; Wang, Yu

    2018-04-01

    It has been suggested in literature that defects in graphene (e.g. absorbed atoms and vacancies) may induce magnetizations due to unpaired electrons. The nature of magnetism, i.e. ferromagnetic or anti-ferromagnetic, is dependent on a number of structural factors including locations of magnetic moments and lattice symmetry. In the present work we investigated the influence of a relaxed single atom vacancy in garphnene on magnetization which were obtained under different pinning boundary conditions, aiming to achieve a better understanding of the magnetic behaviors of graphene. Through first principles calculations, we found that major spin polarizations occur on atoms that deviate slightly from their original lattice positions, and pinning boundaries could also affect the relaxed positions of atoms and determine which atom(s) would become the main source(s) of total spin polarizations and magnetic moments. When the pinning boundary condition is free, a special non-magnetic and semi-conductive structure may be obtained, suggesting that magnetization should more readily occur under pinning boundary conditions.

  9. A reservoir trap for antiprotons

    CERN Document Server

    Smorra, Christian; Franke, Kurt; Nagahama, Hiroki; Schneider, Georg; Higuchi, Takashi; Van Gorp, Simon; Blaum, Klaus; Matsuda, Yasuyuki; Quint, Wolfgang; Walz, Jochen; Yamazaki, Yasunori; Ulmer, Stefan

    2015-01-01

    We have developed techniques to extract arbitrary fractions of antiprotons from an accumulated reservoir, and to inject them into a Penning-trap system for high-precision measurements. In our trap-system antiproton storage times > 1.08 years are estimated. The device is fail-safe against power-cuts of up to 10 hours. This makes our planned comparisons of the fundamental properties of protons and antiprotons independent from accelerator cycles, and will enable us to perform experiments during long accelerator shutdown periods when background magnetic noise is low. The demonstrated scheme has the potential to be applied in many other precision Penning trap experiments dealing with exotic particles.

  10. Interfacial trapping mechanism of He in Cu–Nb multilayer materials

    Energy Technology Data Exchange (ETDEWEB)

    McPhie, M.G., E-mail: mathieu.mcphie@georgiatech-metz.fr [UMI 2958, Georgia Tech-CNRS, 2-3 rue Marconi, 57070 Metz (France); Capolungo, L. [UMI 2958, Georgia Tech-CNRS, 2-3 rue Marconi, 57070 Metz (France); G.W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0405 (United States); Dunn, A.Y. [UMI 2958, Georgia Tech-CNRS, 2-3 rue Marconi, 57070 Metz (France); Cherkaoui, M. [UMI 2958, Georgia Tech-CNRS, 2-3 rue Marconi, 57070 Metz (France); G.W. Woodruff School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0405 (United States)

    2013-06-15

    He atom trapping in hetero-interphase materials is studied by atomistic simulations, focusing on the KS1 and KSmin interfaces in Cu–Nb. If the bulk crystalline materials are defect free, single He atoms eventually become absorbed into the interfacial region via one of two different processes. In the first process, all He atoms arriving at the interface from the Cu side of the interface and some He atoms arriving from the Nb side, are trapped via the formation of a helium-vacancy (HeV) cluster in the second or third interfacial planes of the copper crystal. The immobile HeV cluster is found to be stable against dissociation and recombination. In the second case the He atoms are absorbed as interstitial atoms in one of the terminal planes. This process is dependent on the interstitial content of the interface and is found to be weak in the case of the KS1 interface.

  11. Towards a Quantum Interface between Diamond Spin Qubits and Phonons in an Optical Trap

    Science.gov (United States)

    Ji, Peng; Momeen, M. Ummal; Hsu, Jen-Feng; D'Urso, Brian; Dutt, Gurudev

    2014-05-01

    We introduce a method to optically levitate a pre-selected nanodiamond crystal in air or vacuum. The nanodiamond containing nitrogen-vacancy (NV) centers is suspended on a monolayer of graphene transferred onto a patterned substrate. Laser light is focused onto the sample, using a home-built confocal microscope with a high numerical aperture (NA = 0.9) objective, simultaneously burning the graphene and creating a 3D optical trap that captures the falling nano-diamond at the beam waist. The trapped diamond is an ultra-high-Q mechanical oscillator, allowing us to engineer strong linear and quadratic coupling between the spin of the NV center and the phonon mode. The system could result in an ideal quantum interface between a spin qubit and vibrational phonon mode, potentially enabling applications in quantum information processing and sensing the development of quantum information storage and processing.

  12. Urban fall traps

    Directory of Open Access Journals (Sweden)

    Vera Lucia de Almeida Valsecchi

    2007-06-01

    Full Text Available Objectives: To evaluate the repercussion of falls in the elderly peoplewho live in the city of São Paulo and address - though synthetically- some questions regarding the city and its relation to aging and thequality of life of the elderly. Methods: This is a qualitative study. As fordata collection, “in-depth individual interviews” were applied. Selectionof subjects was guided by a procedure named as “network”. Results:Ten interviews were performed, nine with elderly individuals who werevictims of falls and one with a public authority representative. Dataresulting from interviews confirmed that significant changes occurin live of the elderly, who are victims of what has been called “urbantraps”, and that, by extrapolating mobility and dependence contexts,invade feelings, emotions and desires. The inappropriate environmentprovided by the city of São Paulo is confirmed by absence of adequateurban planning and lack of commitment of public authorities. It alsorevealed that the particular way of being old and living an elderlylife, in addition to right to citizenship, is reflected by major or lesserdifficulties imposed to the elderly to fight for their rights and have theirpublic space respected. Conclusion: The city of São Paulo is not anideal locus for an older person to live in. To the traps that are found inpublic places one can add those that are found in private places andthat contribute to the hard experience of falls among the elderly, anexperience that is sometimes fatal. In Brazil, the attention is basicallyfocused on the consequences of falls and not on prevention, by meansof urban planning that should meet the needs of the most vulnerablegroups - the physically disabled and the elderly.

  13. Innovation: the classic traps.

    Science.gov (United States)

    Kanter, Rosabeth Moss

    2006-11-01

    these traps.

  14. On the empirical determination of positron trapping coefficient at nano-scale helium bubbles in steels irradiated in spallation target

    Science.gov (United States)

    Krsjak, Vladimir; Kuriplach, Jan; Vieh, Christiane; Peng, Lei; Dai, Yong

    2018-06-01

    In the present work, the specific positron trapping rate of small helium bubbles was empirically derived from positron annihilation lifetime spectroscopy (PALS) and transmission electron microscopy (TEM) studies of Fe9Cr martensitic steels. Both techniques are well known to be sensitive to nanometer-sized helium-filled cavities induced during irradiation in a mixed proton-neutron spectrum of spallation target. Complementary TEM and PALS studies show that positrons are being trapped to these defects at a rate of 1.2 ± 0.8 × 10-14 m3s-1. This suggests that helium bubbles in ferritic/martensitic steels are attractive traps for positrons comparable to mono-vacancies and quantitative analysis of the bubbles by PALS technique is plausible.

  15. Mini ion trap mass spectrometer

    Science.gov (United States)

    Dietrich, D.D.; Keville, R.F.

    1995-09-19

    An ion trap is described which operates in the regime between research ion traps which can detect ions with a mass resolution of better than 1:10{sup 9} and commercial mass spectrometers requiring 10{sup 4} ions with resolutions of a few hundred. The power consumption is kept to a minimum by the use of permanent magnets and a novel electron gun design. By Fourier analyzing the ion cyclotron resonance signals induced in the trap electrodes, a complete mass spectra in a single combined structure can be detected. An attribute of the ion trap mass spectrometer is that overall system size is drastically reduced due to combining a unique electron source and mass analyzer/detector in a single device. This enables portable low power mass spectrometers for the detection of environmental pollutants or illicit substances, as well as sensors for on board diagnostics to monitor engine performance or for active feedback in any process involving exhausting waste products. 10 figs.

  16. Charged particle traps II applications

    CERN Document Server

    Werth, Günther; Major, Fouad G

    2009-01-01

    This, the second volume of Charged Particle Traps, is devoted to applications, complementing the first volume’s comprehensive treatment of the theory and practice of charged particle traps, their many variants and refinements. In recent years, applications of far reaching importance have emerged ranging from the ultra-precise mass determinations of elementary particles and their antiparticles and short-lived isotopes, to high-resolution Zeeman spectroscopy on multiply-charged ions, to microwave and optical spectroscopy, some involving "forbidden" transitions from metastable states of such high resolution that optical frequency standards are realized by locking lasers to them. Further the potential application of trapped ions to quantum computing is explored, based on the extraordinary quantum state coherence made possible by the particle isolation. Consideration is given to the Paul and Penning traps as potential quantum information processors.

  17. Holes in magneto electrostatic traps

    International Nuclear Information System (INIS)

    Jones, R.

    1996-01-01

    We observe that in magneto electrostatic confinement (MEC) devices the magnetic surfaces are not always equipotentials. The lack of symmetry in the equipotential surfaces can result in holes in MEC plasma traps. (author)

  18. Trapping Triatominae in Silvatic Habitats

    Directory of Open Access Journals (Sweden)

    Noireau François

    2002-01-01

    Full Text Available Large-scale trials of a trapping system designed to collect silvatic Triatominae are reported. Live-baited adhesive traps were tested in various ecosystems and different triatomine habitats (arboreal and terrestrial. The trials were always successful, with a rate of positive habitats generally over 20% and reaching 48.4% for palm trees of the Amazon basin. Eleven species of Triatominae belonging to the three genera of public health importance (Triatoma, Rhodnius and Panstrongylus were captured. This trapping system provides an effective way to detect the presence of triatomines in terrestrial and arboreal silvatic habitats and represents a promising tool for ecological studies. Various lines of research are contemplated to improve the performance of this trapping system.

  19. Vacancies in functional materials for clean energy storage and harvesting : the perfect imperfection

    NARCIS (Netherlands)

    Li, Guowei; Blake, Graeme R; Palstra, Thomas T M

    2017-01-01

    Vacancies exist throughout nature and determine the physical properties of materials. By manipulating the density and distribution of vacancies, it is possible to influence their physical properties such as band-gap, conductivity, magnetism, etc. This can generate exciting applications in the fields

  20. 76 FR 75899 - Announcement of Vacancy on the Osage Tribal Education Committee

    Science.gov (United States)

    2011-12-05

    ... DEPARTMENT OF THE INTERIOR Bureau of Indian Affairs Announcement of Vacancy on the Osage Tribal Education Committee AGENCY: Bureau of Indian Education, Interior. ACTION: Notice. SUMMARY: The Bureau of Indian Education is announcing that a vacancy has occurred on the Osage Tribal Education Committee. This...

  1. A critical discussion of the vacancy diffusion model of ion beam induced epitaxial crystallization

    International Nuclear Information System (INIS)

    Heera, V.

    1989-01-01

    A simple vacancy diffusion model of ion beam induced epitaxial crystallization of silicon including divacancy formation is developed. The model reproduces some of the experimental findings, as e.g. the dose rate dependence of the crystallization rate. However, the measured activation energy of the ion beam induced epitaxial crystallization cannot be accounted for by vacancy diffusion alone. (author)

  2. Living on the edge : STM studies of the creation, diffusion and annihilation of surface vacancies

    NARCIS (Netherlands)

    Schoots, Koen

    2007-01-01

    This thesis describes an STM study of the creation, diffusion and annihilation of missing atoms, so-called surface vacancies, in the Cu(100) surface. Because of the extremely high mobility of surface vacancies in combination with their extremely low density, we have been forced to use tracer

  3. Internal positron source production with a cyclotron and vacancy study in silicon

    Energy Technology Data Exchange (ETDEWEB)

    Kawasuso, Atsuo; Masuno, Shin-ichi; Okada, Sohei [Japan Atomic Energy Research Inst., Takasaki, Gunma (Japan). Takasaki Radiation Chemistry Research Establishment; Hasegawa, Masayuki; Suezawa, Masashi

    1997-03-01

    In order to detect thermal vacancies in Si, in situ positron annihilation measurement has been performed using an internal source method. An increase (decrease) in S-parameter (W-parameter) was observed above 1200degC. It was explained in terms of the formation of thermal vacancies. (author)

  4. Science, conservation, and camera traps

    Science.gov (United States)

    Nichols, James D.; Karanth, K. Ullas; O'Connel, Allan F.; O'Connell, Allan F.; Nichols, James D.; Karanth, K. Ullas

    2011-01-01

    Biologists commonly perceive camera traps as a new tool that enables them to enter the hitherto secret world of wild animals. Camera traps are being used in a wide range of studies dealing with animal ecology, behavior, and conservation. Our intention in this volume is not to simply present the various uses of camera traps, but to focus on their use in the conduct of science and conservation. In this chapter, we provide an overview of these two broad classes of endeavor and sketch the manner in which camera traps are likely to be able to contribute to them. Our main point here is that neither photographs of individual animals, nor detection history data, nor parameter estimates generated from detection histories are the ultimate objective of a camera trap study directed at either science or management. Instead, the ultimate objectives are best viewed as either gaining an understanding of how ecological systems work (science) or trying to make wise decisions that move systems from less desirable to more desirable states (conservation, management). Therefore, we briefly describe here basic approaches to science and management, emphasizing the role of field data and associated analyses in these processes. We provide examples of ways in which camera trap data can inform science and management.

  5. Status of THe-trap

    Energy Technology Data Exchange (ETDEWEB)

    Ketter, Jochen; Eronen, Tommi; Hoecker, Martin; Streubel, Sebastian; Blaum, Klaus [Max-Planck-Institut fuer Kernphysik, Heidelberg (Germany); Van Dyck, Robert S. Jr. [Department of Physics, University of Washington, Seattle, WA (United States)

    2012-07-01

    Originally developed at the University of Washington and relocated to the Max-Planck-Institut fuer Kernphysik in 2008, the Penning-trap spectrometer THe-Trap is specially tailored for a {sup 3}H/{sup 3}He mass-ratio measurement, from which the Q-value of the beta-decay of {sup 3}H to {sup 3}He can be derived. Improving the current best value by at least an order of magnitude will provide an important independent test parameter for the determination of the electron-antineutrino's mass by the Karlsruhe Tritium Neutrino Experiment (KATRIN). However, Penning-trap mass spectrometry has to be pushed to its limits in a dedicated experiment for a sufficiently accurate mass-ratio measurement with a relative uncertainty of 10{sup -11}. Unlike the closed-envelope, single-trap predecessor, the new spectrometer features an external ion source, owing to the radioactive nature of tritium, and two traps in order to speed up the measurement cycle. While the double-trap technique holds great promise, it also calls for more intricate procedures, such as ion transfer. Details about the recent progress of the experiment are given.

  6. Amplification at λ ∼ 2.8 A on Xe(L),(2s-bar2p-bar) double-vacancy states produced by 248 nm excitation of Xe clusters in plasma channels

    International Nuclear Information System (INIS)

    Borisov, Alex B; Song Xiangyang; Zhang Ping; Dasgupta, Arati; Davis, Jack; Kepple, Paul C; Dai Yang; Boyer, Keith; Rhodes, Charles K

    2005-01-01

    Xe(L),(2s-bar2p-bar) double-vacancy states undergo strong amplification in relativistic self-trapped plasma channels on 3d → 2p transitions in the λ = 2.78-2.81 A region. The 2 P 3/2 → 2 S 1/2 component at λ ≅ 2.786 A exhibits saturated amplification demonstrated by both (1) the observation of spectral hole-burning in the spontaneous emission profile and (2) the correlated enhancement of 3p → 2s cascade transitions ( 2 S 1/2 → 2 P j ; j = 1/2, 3/2) at λ = 2.558 and λ = 2.600 A. The condition of saturation places a lower limit of ∼10 17 W cm -2 on the intensity of the x-ray beam produced by the amplification in the channel. The anomalous strength of the amplification signalled by the saturation mirrors the equivalently anomalous behaviour observed for all 3d → 2p transitions corresponding to 2p-bar) single-vacancy Xe q+ arrays (q = 31, 32, 34, 35, 36) that exhibit gain. The conspicuous absence of amplification involving states with (2p-bar) 2 double-vacancy configurations suggests the operation of a selective interaction that enhances the production of 2s-bar2p-bar states. Overall, the generation of double-vacancy states of this genre demonstrates that an excitation rate approaching ∼1 W/atom for ionic species is achievable in self-trapped plasma channels

  7. Effect of triangular vacancy defect on thermal conductivity and thermal rectification in graphene nanoribbons

    Energy Technology Data Exchange (ETDEWEB)

    Yang, Ping, E-mail: yangpingdm@ujs.edu.cn [Laboratory of Advanced Manufacturing and Reliability for MEMS/NEMS/OEDS, Jiangsu University, Zhenjiang 212013 (China); Li, Xialong; Zhao, Yanfan [Laboratory of Advanced Manufacturing and Reliability for MEMS/NEMS/OEDS, Jiangsu University, Zhenjiang 212013 (China); Yang, Haiying [School of Materials Science and Engineering, Jiangsu University, Zhenjiang 212013 (China); Wang, Shuting, E-mail: wangst@mail.hust.edu.cn [School of Mechanical Science and Engineering, Huazhong University of Science and Technology, Wuhan, Hubei 430074 (China)

    2013-11-01

    We investigate the thermal transport properties of armchair graphene nanoribbons (AGNRs) possessing various sizes of triangular vacancy defect within a temperature range of 200–600 K by using classical molecular dynamics simulation. The results show that the thermal conductivities of the graphene nanoribbons decrease with increasing sizes of triangular vacancy defects in both directions across the whole temperature range tested, and the presence of the defect can decrease the thermal conductivity by more than 40% as the number of removed cluster atoms is increased to 25 (1.56% for vacancy concentration) owing to the effect of phonon–defect scattering. In the meantime, we find the thermal conductivity of defective graphene nanoribbons is insensitive to the temperature change at higher vacancy concentrations. Furthermore, the dependence of temperatures and various sizes of triangular vacancy defect for the thermal rectification ration are also detected. This work implies a possible route to achieve thermal rectifier for 2D materials by defect engineering.

  8. Dependence of the electrical properties of defective single-walled carbon nanotubes on the vacancy density

    International Nuclear Information System (INIS)

    Luo Yu-Pin; Tien Li-Gan; Tsai Chuen-Horng; Lee Ming-Hsien; Li Feng-Yin

    2011-01-01

    The relationship between the electric properties and the vacancy density in single-walled carbon nanotubes has been investigated from first principles as well as the dependence of the influencing range of a vacancy in the nanotube on the nanotube chirality. Compared with the long-range interaction of the vacancies in a single-walled carbon nanotube with non-zero chiral angle, a much shorter interaction was found between vacancies in a zigzag single-walled carbon nanotube. In this study, we investigated the bandstructure fluctuations caused by the nanotube strain, which depends on both the vacancy density and the tube chirality. These theoretical results provide new insight to understand the relationship between the local deformation of a defective single-walled carbon nanotube and its measurable electronic properties. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

  9. Detection of current-induced vacancies in thin aluminum endash copper lines using positrons

    International Nuclear Information System (INIS)

    Asoka-Kumar, P.; OBrien, K.; Lynn, K.G.; Simpson, P.J.; Rodbell, K.P.

    1996-01-01

    In situ depth-resolved positron annihilation spectroscopy (PAS) is used to show dynamic formation of vacancies in 1 μmx1 μm Al-0.5 wt% Cu lines under current flow. We show that the number of vacancies in these lines increases when a dc current (8x10 4 A/cm 2 ) is applied. This increase in vacancy concentration is substantially greater than that due to thermal vacancy generation alone (4x10 18 cm -3 versus 3x10 17 cm -3 ). Isothermal measurements (with no current flow) yield a vacancy formation energy of 0.60±0.02 eV. These results show that PAS can be used to examine the initial stages of interconnect damage due to electromigration. copyright 1996 American Institute of Physics

  10. Vacancy defects in electron irradiated RPV steels studied by positron lifetime

    Energy Technology Data Exchange (ETDEWEB)

    Moser, P; Li, X H [CEA Centre d` Etudes de Grenoble, 38 (France). Dept. de Recherche Fondamentale sur la Matiere Condensee; Akamatsu, M; Van Duysen, J C [Electricite de France (EDF), 77 - Ecuelles (France)

    1994-12-31

    Specimens of French RPV (reactor pressure vessels) steels at different rates of segregation have been irradiated at 150 and 288 deg C with 3 MeV electrons (irradiation dose: 4*10{sup 19} e-/cm{sup 2}). Vacancy defects are studied by positron lifetime measurements before and after irradiation and at each step of isochronal annealing. After 150 deg C irradiation, a recovery step is observed in both specimens, for annealing treatments in the range 220-370 deg C and is attributed to the dissociation of vacancy-impurity complexes. The size of vacancy clusters never overcome 10 empty atomic volumes. If ``fresh`` dislocations are created just before irradiation, big vacancy clusters could be formed. After 288 deg C irradiation, small vacancy cluster of 4-10 empty atomic volumes are observed. (authors). 3 figs., 7 refs.

  11. Introduction of oxygen vacancies and fluorine into TiO2 nanoparticles by co-milling with PTFE

    International Nuclear Information System (INIS)

    Senna, Mamoru; Šepelák, Vladimir; Shi, Jianmin; Bauer, Benjamin; Feldhoff, Armin; Laporte, Vincent; Becker, Klaus-Dieter

    2012-01-01

    Solid-state processes of introducing oxygen vacancies and transference of fluorine to n-TiO 2 nanoparticles by co-milling with poly(tetrafluoroethylene) (PTFE) powder were examined by diffuse reflectance spectroscopy (DRS) of UV, visual, near- and mid-IR regions, thermal analyses (TG-DTA), energy-dispersive X-ray spectroscopy (EDXS), X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD). The broad absorption peak at around 8800 cm −1 (1140 nm) was attributed to the change in the electronic states, viz. electrons trapped at the oxygen vacancies (Vo) and d–d transitions of titanium ions. Incorporation of fluorine into n-TiO 2 was concentrated at the near surface region and amounted to ca. 40 at% of the total fluorine in PTFE, after co-milling for 3 h, as confirmed by the F1s XPS spectrum. The overall atomic ratio, F/Ti, determined by EDXS was 0.294. By combining these analytical results, a mechanism of the present solid state processes at the boundary between PTFE and n-TiO 2 was proposed. The entire process is triggered by the partial oxidative decomposition of PTFE. This is accompanied by the abstraction of oxygen atoms from the n-TiO 2 lattices. Loss of the oxygen atoms results in the formation of the diverse states of locally distorted coordination units of titania, i.e. TiO 6−n Vo n , located at the near surface region. This leads subsequent partial ligand exchange between F and O, to incorporate fluorine preferentially to the near surface region of n-TiO 2 particles, where local non-crystalline states predominate. - Graphical abstract: Scheme of the reaction processes: (a) pristine mixture, (b) oxygen abstraction from TiO 2 and (c) fluorine migration from PTFE to TiO 2 . Highlights: Transfer of fluorine from PTFE to n-TiO 2 in a dry solid state process was confirmed. ► 40% of F in PTFE was incorporated to the near surface region of n-TiO 2 nanoparticles. ► The transfer process is

  12. Fen (n=1–6) clusters chemisorbed on vacancy defects in graphene: Stability, spin-dipole moment, and magnetic anisotropy

    KAUST Repository

    Haldar, Soumyajyoti; Pujari, Bhalchandra S.; Bhandary, Sumanta; Cossu, Fabrizio; Eriksson, Olle; Kanhere, Dilip G.; Sanyal, Biplab

    2014-01-01

    In this work, we have studied the chemical and magnetic interactions of Fen (n=1–6) clusters with vacancy defects (monovacancy to correlated vacancies with six missing C atoms) in a graphene sheet by ab initio density functional calculations

  13. Energetic, structural and electronic properties of metal vacancies in strained AlN/GaN interfaces.

    Science.gov (United States)

    Kioseoglou, J; Pontikis, V; Komninou, Ph; Pavloudis, Th; Chen, J; Karakostas, Th

    2015-04-01

    AlN/GaN heterostructures have been studied using density-functional pseudopotential calculations yielding the formation energies of metal vacancies under the influence of local interfacial strains, the associated charge distribution and the energies of vacancy-induced electronic states. Interfaces are built normal to the polar direction of the wurtzite structure by joining two single crystals of AlN and GaN that are a few atomic layers thick; thus, periodic boundary conditions generate two distinct heterophase interfaces. We show that the formation energy of vacancies is a function of their distance from the interfaces: the vacancy-interface interaction is found repulsive or attractive, depending on the type of the interface. When the interaction is attractive, the vacancy formation energy decreases with increasing the associated electric charge, and hence the equilibrium vacancy concentration at the interface is greater. This finding can reveal the well-known morphological differences existing between the two types of investigated interfaces. Moreover, we found that the electric charge is strongly localized around the Ga vacancy, while in the case of Al vacancies is almost uniformly distributed throughout the AlN/GaN heterostructure. Crucially, for the applications of heterostructures, metal vacancies introduce deep states in the calculated bandgap at energy levels from 0.5 to 1 eV above the valence band maximum (VBM). It is, therefore, predicted that vacancies could initiate 'green luminescence' i.e. light emission in the energy range of 2.5 eV stemming from electronic transitions between these extra levels, and the conduction band, or energy levels, due to shallow donors.

  14. Vacancies and atomic processes in intermetallics - From crystals to quasicrystals and bulk metallic glasses

    Energy Technology Data Exchange (ETDEWEB)

    Schaefer, Hans-Eckhardt [Institute of Theoretical and Applied Physics, Stuttgart University, Pfaffenwaldring 57, 70569 Stuttgart (Germany); Baier, Falko [Voith Turbo Comp., Alexanderstr. 2, 89552 Heidenheim (Germany); Mueller, Markus A. [GFT Technologies A. G., Filderhauptstr. 142, 70599 Stuttgart (Germany); Reichle, Klaus J. [Philipp-Matthaeus-Hahn School, Jakob-Beutter-Str. 15, 72336 Balingen (Germany); Reimann, Klaus [NXP Semiconductors, Central Research and Development, High Tech Campus 4, 5656 AE Eindhoven (Netherlands); Rempel, Andrey A. [Institute of Solid State Chemistry, Russian Academy of Sciences, Ul. Pervomaiskaya 91, 620041 Ekaterinburg (Russian Federation); Sato, Kiminori [Tokyo Gakugei University, Nukuikita 4-1-1, Koganei, Tokyo 184-8501 (Japan); Ye, Feng [State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, 30 Xue Yuan Road, Beijing 100083 (China); Zhang, Xiangyi [Yanshan University, Qinhuangdao 066004 (China); Sprengel, Wolfgang [Institute of Materials Physics, Graz University of Technology, Petersgasse 16, 8010 Graz (Austria)

    2011-10-15

    A review is given on atomic vacancies in intermetallic compounds. The intermetallic compounds cover crystalline, quasicrystalline, and bulk metallic glass (BMG) structures. Vacancies can be specifically characterized by their positron lifetimes, by the coincident measurement of the Doppler broadening of the two quanta emitted by positron-electron annihilation, or by time-differential dilatometry. By these techniques, high concentrations and low mobilities of thermal vacancies were found in open-structured B2 intermetallics such as FeAl or NiAl, whereas the concentrations of vacancies are low and their mobilities high in close-packed structure as, e.g., L1{sub 2}-Ni{sub 3}Al. The activation volumes of vacancy formation and migration are determined by high-pressure experiments. The favorable sublattice for vacancy formation is found to be the majority sublattice in Fe{sub 61}Al{sub 39} and in MoSi{sub 2}. In the icosahedral quasicrystal Al{sub 70}Pd{sub 21}Mn{sub 9} the thermal vacancy concentration is low, whereas in the BMG Zr{sub 57}Cu{sub 15.4}Ni{sub 12.6}Nb{sub 3}Al{sub 10} thermal vacancies are found in high concentrations with low mobilities. This may determine the basic mechanisms of the glass transition. Making use of the experimentally determined vacancy data, the main features of atomic diffusion studies in crystalline intermetallics, in quasicrystals, and in BMGs can be understood. Manfred Faehnle and his group have substantially contributed to the theoretical understanding of vacancies and diffusion mechanisms in intermetallics. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  15. Effects of oxide traps, interface traps, and ''border traps'' on metal-oxide-semiconductor devices

    International Nuclear Information System (INIS)

    Fleetwood, D.M.; Winokur, P.S.; Reber, R.A. Jr.; Meisenheimer, T.L.; Schwank, J.R.; Shaneyfelt, M.R.; Riewe, L.C.

    1993-01-01

    We have identified several features of the 1/f noise and radiation response of metal-oxide-semiconductor (MOS) devices that are difficult to explain with standard defect models. To address this issue, and in response to ambiguities in the literature, we have developed a revised nomenclature for defects in MOS devices that clearly distinguishes the language used to describe the physical location of defects from that used to describe their electrical response. In this nomenclature, ''oxide traps'' are simply defects in the SiO 2 layer of the MOS structure, and ''interface traps'' are defects at the Si/SiO 2 interface. Nothing is presumed about how either type of defect communicates with the underlying Si. Electrically, ''fixed states'' are defined as trap levels that do not communicate with the Si on the time scale of the measurements, but ''switching states'' can exchange charge with the Si. Fixed states presumably are oxide traps in most types of measurements, but switching states can either be interface traps or near-interfacial oxide traps that can communicate with the Si, i.e., ''border traps'' [D. M. Fleetwood, IEEE Trans. Nucl. Sci. NS-39, 269 (1992)]. The effective density of border traps depends on the time scale and bias conditions of the measurements. We show the revised nomenclature can provide focus to discussions of the buildup and annealing of radiation-induced charge in non-radiation-hardened MOS transistors, and to changes in the 1/f noise of MOS devices through irradiation and elevated-temperature annealing

  16. Live-cell thermometry with nitrogen vacancy centers in nanodiamonds

    Science.gov (United States)

    Jayakumar, Harishankar; Fedder, Helmut; Chen, Andrew; Yang, Liudi; Li, Chenghai; Wrachtrup, Joerg; Wang, Sihong; Meriles, Carlos

    The ability to measure temperature is typically affected by a tradeoff between sensitivity and spatial resolution. Good thermometers tend to be bulky systems and hence are ill-suited for thermal sensing with high spatial localization. Conversely, the signal resulting from nanoscale temperature probes is often impacted by noise to a level where the measurement precision becomes poor. Adding to the microscopist toolbox, the nitrogen vacancy (NV) center in diamond has recently emerged as a promising platform for high-sensitivity nanoscale thermometry. Of particular interest are applications in living cells because diamond nanocrystals are biocompatible and can be chemically functionalized to target specific organelles. Here we report progress on the ability to probe and compare temperature within and between living cells using nanodiamond-hosted NV thermometry. We focus our study on cancerous cells, where atypical metabolic pathways arguably lead to changes in the way a cell generates heat, and thus on its temperature profile.

  17. The vacancy-interstitial model of DX centers

    International Nuclear Information System (INIS)

    Morgan, T.N.

    1989-01-01

    Recent DLTS (deep level transient spectroscopy) studies of 'DX' centers in dilute Al x Ga 1-x As alloys agree with a model of the deep neutral state in which the donor has moved into an adjacent interstitial site leaving behind a vacancy. The enthalpy and entropy of these states, which depend on the number (0 to 3) of Al atoms adjacent to the donors, have been obtained by fitting the data. This model, which also predicts the large potential barriers between the centered and relaxed states, thus accounting for PPC (persistent photoconductivity), is an extension to large displacement of the displaced donor model proposed earlier. It is equivalent to recent model of the EL2 metastable state based on displaced antisite double-donors. (author) 9 refs., 3 figs., 1 tab

  18. Zn vacancy-donor impurity complexes in ZnO

    Science.gov (United States)

    Frodason, Y. K.; Johansen, K. M.; Bjørheim, T. S.; Svensson, B. G.; Alkauskas, A.

    2018-03-01

    Results from hybrid density functional theory calculations on the thermodynamic stability and optical properties of the Zn vacancy (VZn) complexed with common donor impurities in ZnO are reported. Complexing VZn with donors successively removes its charge-state transition levels in the band gap, starting from the most negative one. Interestingly, the presence of a donor leads only to modest shifts in the positions of the VZn charge-state transition levels, the sign and magnitude of which can be interpreted from a polaron energetics model by taking hole-donor repulsion into account. By employing a one-dimensional configuration coordinate model, luminescence lineshapes and positions were calculated. Due to the aforementioned effects, the isolated VZn gradually changes from a mainly nonradiative defect with transitions in the infrared region in n -type material, to a radiative one with broad emission in the visible range when complexed with shallow donors.

  19. Phase and vacancy behaviour of hard "slanted" cubes

    Science.gov (United States)

    van Damme, R.; van der Meer, B.; van den Broeke, J. J.; Smallenburg, F.; Filion, L.

    2017-09-01

    We use computer simulations to study the phase behaviour for hard, right rhombic prisms as a function of the angle of their rhombic face (the "slant" angle). More specifically, using a combination of event-driven molecular dynamics simulations, Monte Carlo simulations, and free-energy calculations, we determine and characterize the equilibrium phases formed by these particles for various slant angles and densities. Surprisingly, we find that the equilibrium crystal structure for a large range of slant angles and densities is the simple cubic crystal—despite the fact that the particles do not have cubic symmetry. Moreover, we find that the equilibrium vacancy concentration in this simple cubic phase is extremely high and depends only on the packing fraction and not the particle shape. At higher densities, a rhombic crystal appears as the equilibrium phase. We summarize the phase behaviour of this system by drawing a phase diagram in the slant angle-packing fraction plane.

  20. Nanophotonic quantum interface for nitrogen vacancy centers in diamond

    International Nuclear Information System (INIS)

    Yiwen Chu

    2014-01-01

    Nitrogen vacancy (NV) centers in diamond have emerged as a promising solid-state platform for quantum communication, quantum information processing and nanoscale sensing with optical read-out. Engineering light-matter interactions is crucial for the practical realization of these systems. I will present our work toward realizing individual NV centers embedded in nanofabricated hybrid photonic crystal cavities consisting of single crystal diamond and PMMA based Bragg structures. Devices with quality factors up to 3,000 coupled to NV centers have been implemented, leading to substantial Purcell enhancement of zero-phonon line. We investigate the optical coherence properties of NV centers inside these nanoscale structures and report on first cavity QED experiments with such systems. Applications of diamond nanophotonic devices for quantum networks and nonlinear optics with single photons will be discussed. (author)

  1. Quantum Properties of Dichroic Silicon Vacancies in Silicon Carbide

    Science.gov (United States)

    Nagy, Roland; Widmann, Matthias; Niethammer, Matthias; Dasari, Durga B. R.; Gerhardt, Ilja; Soykal, Öney O.; Radulaski, Marina; Ohshima, Takeshi; Vučković, Jelena; Son, Nguyen Tien; Ivanov, Ivan G.; Economou, Sophia E.; Bonato, Cristian; Lee, Sang-Yun; Wrachtrup, Jörg

    2018-03-01

    Although various defect centers have displayed promise as either quantum sensors, single photon emitters, or light-matter interfaces, the search for an ideal defect with multifunctional ability remains open. In this spirit, we study the dichroic silicon vacancies in silicon carbide that feature two well-distinguishable zero-phonon lines and analyze the quantum properties in their optical emission and spin control. We demonstrate that this center combines 40% optical emission into the zero-phonon lines showing the contrasting difference in optical properties with varying temperature and polarization, and a 100% increase in the fluorescence intensity upon the spin resonance, and long spin coherence time of their spin-3 /2 ground states up to 0.6 ms. These results single out this defect center as a promising system for spin-based quantum technologies.

  2. Vacancy-Mediated Magnetism in Pure Copper Oxide Nanoparticles

    Science.gov (United States)

    2010-01-01

    Room temperature ferromagnetism (RTF) is observed in pure copper oxide (CuO) nanoparticles which were prepared by precipitation method with the post-annealing in air without any ferromagnetic dopant. X-ray photoelectron spectroscopy (XPS) result indicates that the mixture valence states of Cu1+ and Cu2+ ions exist at the surface of the particles. Vacuum annealing enhances the ferromagnetism (FM) of CuO nanoparticles, while oxygen atmosphere annealing reduces it. The origin of FM is suggested to the oxygen vacancies at the surface/or interface of the particles. Such a ferromagnet without the presence of any transition metal could be a very good option for a class of spintronics. PMID:20671775

  3. Isotopically varying spectral features of silicon-vacancy in diamond

    International Nuclear Information System (INIS)

    Dietrich, Andreas; Jahnke, Kay D; Binder, Jan M; Rogers, Lachlan J; Jelezko, Fedor; Teraji, Tokuyuki; Isoya, Junichi

    2014-01-01

    The silicon-vacancy centre (SiV − ) in diamond has exceptional spectral properties for single-emitter quantum information applications. Most of the fluorescence is concentrated in a strong zero phonon line (ZPL), with a weak phonon sideband extending for 100 nm that contains several clear features. We demonstrate that the ZPL position can be used to reliably identify the silicon isotope present in a single SiV − centre. This is of interest for quantum information applications since only the 29 Si isotope has nuclear spin. In addition, we show that the sharp 64 meV phonon peak is due to a local vibrational mode of the silicon atom. The presence of a local mode suggests a plausible origin of the measured isotopic shift of the ZPL. (paper)

  4. Images d’un camp de vacances en pays socialiste

    Directory of Open Access Journals (Sweden)

    Ania Szczepanska

    2009-12-01

    Full Text Available En 1976, Marcel Lozinski choisit d’aller filmer un camp de vacances organisé par le mouvement de la jeunesse socialiste dans la région des lacs de Mazurie en Pologne. Le cinéaste décide de filmer le quotidien de ces jeunes familles en vacances, entre quiz politiques, leçons de savoir vivre et concours de la famille modèle. Pour cela, il élabore un protocole de travail singulier : aux vacanciers s’ajoutent des personnes complices du cinéaste dont le rôle sera pour certains de participer activement à la vie collective, pour d’autres de s’y opposer.Tourné en 1976, le documentaire Comment vivre attendra cinq années avant d’être diffusé en salle, en tant que fiction. Pourquoi cette diffusion retardée et surtout, que penser de cette requalification a posteriori ? Outre l’analyse du film lui-même, un entretien mené avec Marcel Lozinski ainsi que des archives consultées à la filmothèque de Varsovie apporteront des éléments d’analyse sur la réception de l’œuvre par les autorités cinématographiques de l’époque, mais également sur le sens produit par les dispositifs mis en place par le cinéaste au cours de ce tournage.

  5. A magnetic particle micro-trap for large trapping surfaces

    KAUST Repository

    Gooneratne, Chinthaka P.

    2012-01-08

    Manipulation of micron-size magnetic particles of the superparamagnetic type contributes significantly in many applications like controlling the antibody/antigen binding process in immunoassays. Specifically, more target biomolecules can be attached/tagged and analyzed since the three dimensional structure of the magnetic particles increases the surface to volume ratio. Additionally, such biomolecular-tagged magnetic particles can be easily manipulated by an external magnetic field due to their superparamagnetic behavior. Therefore, magnetic particle- based immunoassays are extensively applied in micro-flow cytometry. The design of a square-loop micro-trap as a magnetic particle manipulator as well as numerical and experimental analysis is presented. Experimental results showed that the micro-trap could successfully trap and concentrate magnetic particles from a large to a small area with a high spatial range.

  6. A magnetic particle micro-trap for large trapping surfaces

    KAUST Repository

    Gooneratne, Chinthaka P.; Liang, Cai; Giouroudi, Ioanna; Kosel, Jü rgen

    2012-01-01

    Manipulation of micron-size magnetic particles of the superparamagnetic type contributes significantly in many applications like controlling the antibody/antigen binding process in immunoassays. Specifically, more target biomolecules can be attached/tagged and analyzed since the three dimensional structure of the magnetic particles increases the surface to volume ratio. Additionally, such biomolecular-tagged magnetic particles can be easily manipulated by an external magnetic field due to their superparamagnetic behavior. Therefore, magnetic particle- based immunoassays are extensively applied in micro-flow cytometry. The design of a square-loop micro-trap as a magnetic particle manipulator as well as numerical and experimental analysis is presented. Experimental results showed that the micro-trap could successfully trap and concentrate magnetic particles from a large to a small area with a high spatial range.

  7. Hydrogen solubility, diffusivity and trapping in a tempered Fe–C–Cr martensitic steel under various mechanical stress states

    International Nuclear Information System (INIS)

    Frappart, S.; Feaugas, X.; Creus, J.; Thebault, F.; Delattre, L.; Marchebois, H.

    2012-01-01

    Highlights: ► Engineering elasticity is divided into three mechanical behaviours. ► Apparent diffusion coefficient is affected in the generalized plasticity domain. ► Plasticity increases irreversibly trapped H related to dislocation creation. ► A local elastic distortion seems to affect hydrogen lattice concentration. ► Elastic field around precipitates seems to be reversible trapping sites. - Abstract: Electrochemical permeation test under stress conditions was carried out to determine the consequences of lattice distortion and defects on hydrogen solubility, diffusivity and trapping in a quenched and tempered martensitic steel. We focused our attention within the “engineering” elastic domain which can be divided into three domains: elasticity, micro-plasticity and generalized plasticity. The local elastic distortion associated with hydrogen atoms in lattice sites and residual vacancies seems to affect hydrogen lattice concentration. The hydrogen trapped in elastic fields shows a complex behaviour as a function of stress related to a possible internal relaxation of stresses around precipitates with the occurrence of plasticity. The plastic deformation caused a substantial increase of irreversible trapping sites in relation with the dislocation multiplication. Apparent diffusion coefficient decreased in this deformation domain in agreement with classical trapping models.

  8. First principle study of structural, electronic and magnetic properties of zigzag boron nitride nanoribbon: Role of vacancies

    Energy Technology Data Exchange (ETDEWEB)

    Kumar, Arun [Department of Physics, Govt. College Banjar, Kullu, Himanchal Pradesh, 175123 India (India); Bahadur, Amar, E-mail: abr.phys@gmail.com [Department of Physics, Kamla Nehru Institute of Physical and Social Sciences, Sultanpur, Uttar Pradesh, 228118 India (India); Mishra, Madhukar [Department of Physics, Birla Institute of Technology and Science, Pilani, Rajasthan, 333031 India (India); Vasudeva, Neena [Department of Physics, S. V. G. College, Ghumarwin, Bilaspur, Himanchal Pradesh, 1714021 India (India)

    2015-05-15

    We study the effect of vacancies on the structural, electronic and magnetic properties of zigzag boron nitride nanoribbon (ZBNNR) by using first principle calculations. We find that the shift of the vacancies with respect to the ribbon edges causes change in the structural geometry, electronic structure and magnetization of ZBNNR. These vacancies also produce band gap modulation and consequently results the magnetization of ZBNNR.

  9. First-principles calculations of vacancy formation in In-free photovoltaic semiconductor Cu2ZnSnSe4

    International Nuclear Information System (INIS)

    Maeda, Tsuyoshi; Nakamura, Satoshi; Wada, Takahiro

    2011-01-01

    To quantitatively evaluate the formation energies of Cu, Zn, Sn, and Se vacancies in kesterite-type Cu 2 ZnSnSe 4 (CZTSe), first-principles pseudopotential calculations using plane-wave basis functions were performed. The formation energies of neutral Cu, Zn, Sn and Se vacancies were calculated as a function of the atomic chemical potentials of constituent elements. The obtained results were as follows: (1) the formation energy of Cu vacancy was generally smaller than those of the other Zn, Sn and Se vacancies, (2) under the Cu-poor and Zn-rich condition, the formation energy of Cu vacancy was particularly low, (3) the formation energy of Zn vacancy greatly depended on the chemical potentials of the constituent elements and under the Zn-poor and Se-rich condition, the formation energy of Zn vacancy was smaller than that of Cu vacancy, and (4) the formation energy of Sn vacancy did not greatly depend on the chemical potentials of the constituent elements and was much larger than those of Cu, Zn, and Se vacancies. These results indicate that Cu vacancy is easily formed under Cu-poor and Zn-rich conditions, but Zn vacancy is easily formed under the Zn-poor and Se-rich conditions.

  10. Particle trapping in stimulated scattering processes

    International Nuclear Information System (INIS)

    Karttunen, S.J.; Heikkinen, J.A.

    1981-01-01

    Particle trapping effects on stimulated Brillouin and Raman scattering are investigated. A time and space dependent model assumes a Maxwellian plasma which is taken to be homogeneous in the interaction region. Ion trapping has a rather weak effect on stimulated Brillouin scattering and large reflectivities are obtained even in strong trapping regime. Stimulated Raman scattering is considerably reduced by electron trapping. Typically 15-20 times larger laser intensities are required to obtain same reflectivity levels than without trapping. (author)

  11. Calcium Atom Trap for Atom Trap Mass Spectrometer

    Energy Technology Data Exchange (ETDEWEB)

    Ko, Kwang Hoon; Park, Hyun Min; Han, Jae Min; Kim, Taek Soo; Cha, Yong Ho; Lim, Gwon; Jeong, Do Young [Korea Atomic Energy Research Institute, Daejeon (Korea, Republic of)

    2012-05-15

    Trace isotope analysis has been an important role in science, archaeological dating, geology, biology and nuclear industry. Artificially produced fission products such as Sr-90, Cs-135 and Kr-85 can be released to the environment when nuclear accident occurs and the reprocessing factory operates. Thus, the analysis of them has been of interest in nuclear industry. But it is difficult to detect them due to low natural abundance less then 10-10. The ultra-trace radio isotopes have been analyzed by the radio-chemical method, accelerator mass spectrometer, and laser based method. The radiochemical method has been used in the nuclear industry. But this method has disadvantages of long measurement time for long lived radioisotopes and toxic chemical process for the purification. The accelerator mass spectrometer has high isotope selectivity, but the system is huge and it has the isobar effects. The laser based method, such as RIMS (Resonance Ionization Mass Spectrometry) is a basically isobar-effect free method. Recently, ATTA (Atom Trap Trace Analysis), one of the laser based method, has been successfully demonstrated sufficient isotope selectivity with small system size. It has been applied for the detection of Kr-81 and Kr-85. However, it is not suitable for real sample detection, because it requires steady atomic beam generation during detection and is not allowed simultaneous detection of other isotopes. Therefore, we proposed the coupled method of Atom Trap and Mass Spectrometer. It consists of three parts, neutral atom trap, ionization and mass spectrometer. In this paper, we present the demonstration of the magneto-optical trap of neutral calcium. We discuss the isotope selective characteristics of the MOT (Magneto Optical Trap) of calcium by the fluorescence measurement. In addition, the frequency stabilization of the trap beam will be presented

  12. Vacancy identification in Co+ doped rutile TiO2 crystal with positron annihilation spectroscopy

    International Nuclear Information System (INIS)

    Ma Minyang; Qin Xiubo; Wang Baoyi; Wu Weiming

    2013-01-01

    Background: Room temperature Diluted Magnetic Semiconductor (DMS) is a critical path in the study of spin-electronic devices, but there are many disputes in the intrinsic properties and origin of the room temperature ferromagnetism. Positron annihilation spectroscopy (PAS) is a powerful technique for evaluating vacancy-type defects. Purpose: We aim to establish the relationship between the defect structure and ferromagnetism of the materials by analyzing the parameters of positron annihilation. Methods: Co-doped rutile TiO 2 films were synthesized by ion implantation and extensively studied by variable energy positron annihilation Doppler broadening spectroscopy (DBS) and coincidence Doppler broadening (CDB) measurements with variable energy slow positron beam for identification of the vacancies. Results: The results of DBS showed that a newly formed type of vacancy could be concluded by the S-W plot and the CDB results indicated that the oxygen vacancy (Vo) complex Ti-Co-Vo and/or Ti-Vo were formed with Co ions implantation and the vacancy concentration increased with increasing dopant dose. Conclusion: We identify that the generation of Ti-Vo and/or Ti-Co-Vo vacancy complex are induced by the existence of excess Ti 3d electrons around the oxygen vacancy. (authors)

  13. Stability enhancement of Cu2S against Cu vacancy formation by Ag alloying

    Science.gov (United States)

    Barman, Sajib K.; Huda, Muhammad N.

    2018-04-01

    As a potential solar absorber material, Cu2S has proved its importance in the field of renewable energy. However, almost all the known minerals of Cu2S suffer from spontaneous Cu vacancy formation in the structure. The Cu vacancy formation causes the structure to possess very high p-type doping that leads the material to behave as a degenerate semiconductor. This vacancy formation tendency is a major obstacle for this material in this regard. A relatively new predicted phase of Cu2S which has an acanthite-like structure was found to be preferable than the well-known low chalcocite Cu2S. However, the Cu-vacancy formation tendency in this phase remained similar. We have found that alloying silver with this structure can help to reduce Cu vacancy formation tendency without altering its electronic property. The band gap of silver alloyed structure is higher than pristine acanthite Cu2S. In addition, Cu diffusion in the structure can be reduced with Ag doped in Cu sites. In this study, a systematic approach is presented within the density functional theory framework to study Cu vacancy formation tendency and diffusion in silver alloyed acanthite Cu2S, and proposed a possible route to stabilize Cu2S against Cu vacancy formations by alloying it with Ag.

  14. Multi-scale modeling of interaction between vacancies and alloying elements in ferritic alloys

    International Nuclear Information System (INIS)

    Barouh, Caroline

    2015-01-01

    This PhD thesis is devoted to the study of interaction between vacancies and alloying elements in Oxide Dispersion Strengthened (ODS) steels, which are promising candidate materials for future nuclear reactors. This work is based on multi-scale modeling of a simplified system composed by oxygen, yttrium and titanium atoms and vacancies in an α-iron lattice. We particularly focused on the role of vacancies which are created in excess during the fabrication of these steels. The stability and mobility of vacancy-solute clusters have been examined using ab initio calculations for oxygen, on one hand, which has been systematically compared to carbon and nitrogen, interstitial solutes frequently present in iron-based materials, and, on the other hand, for substitutional solutes: titanium and yttrium. The three interstitial solutes show very similar energetic and kinetic behaviors. The impact of small mobile vacancy-solute clusters has been verified using a cluster dynamics model based on our ab initio results. It has been thus demonstrated that with over-saturation of vacancies, diffusion of interstitial solutes may be accelerated, while substitutional solutes do not become necessarily faster. These conclusions are consistent with existing experimental observations. All these results have been then used to complete our understanding of nano-clusters formation mechanisms. It appeared that the relative mobility of yttrium and titanium, as well as the number of potential nuclei to form nanoparticles strongly depend on the total vacancy concentration in the system. (author) [fr

  15. Neutral atom traps of radioactives

    International Nuclear Information System (INIS)

    Behr, J.A.

    2003-01-01

    Neutral atoms trapped with modern laser cooling techniques offer the promise of improving several broad classes of experiments with radioactive isotopes. In nuclear β decay, neutrino spectroscopy from beta-recoil coincidences, along with highly polarized samples, enable experiments to search for non-Standard Model interactions, test whether parity symmetry is maximally violated, and search for new sources of time reversal violation. Ongoing efforts at TRIUMF, Los Alamos and Berkeley will be highlighted. The traps also offer bright sources for Doppler-free spectroscopy, particularly in high-Z atoms where precision measurements could measure the strength of weak neutral nucleon-nucleon and electron-nucleon interactions. Physics with francium atoms has been vigorously pursued at Stony Brook. Several facilities plan work with radioactive atom traps; concrete plans and efforts at KVI Groningen and Legnaro will be among those summarized. Contributions to the multidisciplinary field of trace analysis will be left up to other presenters

  16. Neutral atom traps of radioactives

    CERN Document Server

    Behr, J A

    2003-01-01

    Neutral atoms trapped with modern laser cooling techniques offer the promise of improving several broad classes of experiments with radioactive isotopes. In nuclear beta decay, neutrino spectroscopy from beta-recoil coincidences, along with highly polarized samples, enable experiments to search for non-Standard Model interactions, test whether parity symmetry is maximally violated, and search for new sources of time reversal violation. Ongoing efforts at TRIUMF, Los Alamos and Berkeley will be highlighted. The traps also offer bright sources for Doppler-free spectroscopy, particularly in high-Z atoms where precision measurements could measure the strength of weak neutral nucleon-nucleon and electron-nucleon interactions. Physics with francium atoms has been vigorously pursued at Stony Brook. Several facilities plan work with radioactive atom traps; concrete plans and efforts at KVI Groningen and Legnaro will be among those summarized. Contributions to the multidisciplinary field of trace analysis will be left...

  17. Trapped atoms along nanophotonic resonators

    Science.gov (United States)

    Fields, Brian; Kim, May; Chang, Tzu-Han; Hung, Chen-Lung

    2017-04-01

    Many-body systems subject to long-range interactions have remained a very challenging topic experimentally. Ultracold atoms trapped in extreme proximity to the surface of nanophotonic structures provides a dynamic system combining the strong atom-atom interactions mediated by guided mode photons with the exquisite control implemented with trapped atom systems. The hybrid system promises pair-wise tunability of long-range interactions between atomic pseudo spins, allowing studies of quantum magnetism extending far beyond nearest neighbor interactions. In this talk, we will discuss our current status developing high quality nanophotonic ring resonators, engineered on CMOS compatible optical chips with integrated nanostructures that, in combination with a side illuminating beam, can realize stable atom traps approximately 100nm above the surface. We will report on our progress towards loading arrays of cold atoms near the surface of these structures and studying atom-atom interaction mediated by photons with high cooperativity.

  18. Quantized motion of trapped ions

    International Nuclear Information System (INIS)

    Steinbach, J.

    1999-01-01

    This thesis is concerned with a theoretical and numerical study of the preparation and coherent manipulation of quantum states in the external and internal degrees of freedom of trapped ions. In its first part, this thesis proposes and investigates schemes for generating several nonclassical states for the quantized vibrational motion of a trapped ion. Based on dark state preparation specific laser excitation configurations are presented which, given appropriately chosen initial states, realize the desired motional states in the steady-state, indicated by the cessation of the fluorescence emitted by the ion. The focus is on the SU(1,1) intelligent states in both their single- and two-mode realization, corresponding to one- and two-dimensional motion of the ion. The presented schemes are also studied numerically using a Monte-Carlo state-vector method. The second part of the thesis describes how two vibrational degrees of freedom of a single trapped ion can be coupled through the action of suitably chosen laser excitation. Concentrating on a two-dimensional ion trap with dissimilar vibrational frequencies a variety of quantized two-mode couplings are derived. The focus is on a linear coupling that takes excitations from one mode to another. It is demonstrated how this can result in a state rotation, in which it is possible to coherently transfer the motional state of the ion between orthogonal directions without prior knowledge of that motional state. The third part of this thesis presents a new efficient method for generating maximally entangled internal states of a collection of trapped ions. The method is deterministic and independent of the number of ions in the trap. As the essential element of the scheme a mechanism for the realization of a controlled NOT operation that can operate on multiple ions is proposed. The potential application of the scheme for high-precision frequency standards is explored. (author)

  19. Open trap with ambipolar mirrors

    International Nuclear Information System (INIS)

    Dimov, G.I.; Zakajdakov, V.V.; Kishinevskij, M.E.

    1977-01-01

    Results of numerical calculations on the behaviour of a thermonuclear plasma, allowing for α-particles in a trap with longitudinal confinement of the main ions by ambipolar electric fields are presented. This trap is formed by connecting two small-volume ''mirrortrons'' to an ordinary open trap. Into the extreme mirrortrons, approximately 1-MeV ions are introduced continuously by ionization of atomic beams on the plasma, and approximately 10-keV ions are similarly introduced into the main central region of the trap. By a suitable choice of injection currents, the plasma density established in the extreme mirrortrons is higher than in the central region. As a result of the quasi-neutrality condition, a longitudinal ambipolar field forming a potential well not only for electrons but also for the central ions is formed in the plasma. When the depth of the well for the central ions is much greater than their temperature, their life-time considerably exceeds the time of confinement by the magnetic mirrors. As a result, the plasma density is constant over the entire length of the central mirrortron, including the regions near the mirrors, and an ambipolar field is formed only in the extreme mirrortrons. The distribution of central ions and ambipolar potential in the extreme mirrortrons is uniquely determined by the density distribution of fast extreme ions. It is shown in the present study that an amplification coefficient Q as high as desired can, in principle, be reached in the trap under consideration, allowing for α-particles. However, this requires high magnetic fields in the mirrors and a sufficient length of the central mirrotron. It is shown that for moderate values of Q=3-8, it is desirable not to confine the central fast α-particles. To achieve a coefficient of Q=5, it is necessary to create fields of 250 kG in the mirrors, and the length of the trap must not be greater than 100 m. (author)

  20. Ion trap architectures and new directions

    Science.gov (United States)

    Siverns, James D.; Quraishi, Qudsia

    2017-12-01

    Trapped ion technology has seen advances in performance, robustness and versatility over the last decade. With increasing numbers of trapped ion groups worldwide, a myriad of trap architectures are currently in use. Applications of trapped ions include: quantum simulation, computing and networking, time standards and fundamental studies in quantum dynamics. Design of such traps is driven by these various research aims, but some universally desirable properties have lead to the development of ion trap foundries. Additionally, the excellent control achievable with trapped ions and the ability to do photonic readout has allowed progress on quantum networking using entanglement between remotely situated ion-based nodes. Here, we present a selection of trap architectures currently in use by the community and present their most salient characteristics, identifying features particularly suited for quantum networking. We also discuss our own in-house research efforts aimed at long-distance trapped ion networking.

  1. Vacancy formation in MoO3: hybrid density functional theory and photoemission experiments

    KAUST Repository

    Salawu, Omotayo Akande

    2016-09-29

    Molybdenum oxide (MoO3) is an important material that is being considered for numerous technological applications, including catalysis and electrochromism. In the present study, we apply hybrid density functional theory to investigate O and Mo vacancies in the orthorhombic phase. We determine the vacancy formation energies of different defect sites as functions of the electron chemical potential, addressing different charge states. In addition, we investigate the consequences of defects for the material properties. Ultraviolet photoemission spectroscopy is employed to study the valence band of stoichiometric and O defective MoO3. We show that O vacancies result in occupied in-gap states.

  2. Observation and control of blinking nitrogen-vacancy centres in discrete nanodiamonds.

    Science.gov (United States)

    Bradac, C; Gaebel, T; Naidoo, N; Sellars, M J; Twamley, J; Brown, L J; Barnard, A S; Plakhotnik, T; Zvyagin, A V; Rabeau, J R

    2010-05-01

    Nitrogen-vacancy colour centres in diamond can undergo strong, spin-sensitive optical transitions under ambient conditions, which makes them attractive for applications in quantum optics, nanoscale magnetometry and biolabelling. Although nitrogen-vacancy centres have been observed in aggregated detonation nanodiamonds and milled nanodiamonds, they have not been observed in very small isolated nanodiamonds. Here, we report the first direct observation of nitrogen-vacancy centres in discrete 5-nm nanodiamonds at room temperature, including evidence for intermittency in the luminescence (blinking) from the nanodiamonds. We also show that it is possible to control this blinking by modifying the surface of the nanodiamonds.

  3. Ab-initio calculation for cation vacancy formation energy in anti-fluorite structure

    Science.gov (United States)

    Saleel, V. P. Saleel Ahammad; Chitra, D.; Veluraja, K.; Eithiraj, R. D.

    2018-04-01

    Lithium oxide (Li2O) has been suggested as a suitable breeder blanket material for fusion reactors. Li+ vacancies are created by neutron irradiation, forming bulk defect complex whose extra character is experimentally unclear. We present a theoretical study of Li2O using density functional theory (DFT) with a plane-wave basis set. The generalized gradient approximation (GGA) and local-density approximation (LDA) were used for exchange and correlation. Here we address the total energy for defect free, cation defect, cation vacancy and vacancy formation energy in Li2O crystal in anti-fluorite structure.

  4. Ionized zinc vacancy mediated ferromagnetism in copper doped ZnO thin films

    Directory of Open Access Journals (Sweden)

    Shi-Yi Zhuo

    2012-03-01

    Full Text Available This paper reports the origin of ferromagnetism in Cu-doped ZnO thin films. Room-temperature ferromagnetism is obtained in all the thin films when deposited at different oxygen partial pressure. An obviously enhanced peak corresponding to zinc vacancy is observed in the photoluminescence spectra, while the electrical spin resonance measurement implies the zinc vacancy is negative charged. After excluding the possibility of direct exchange mechanisms (via free carriers, we tentatively propose a quasi-indirect exchange model (via ionized zinc vacancy for Cu-doped ZnO system.

  5. Fracture of vacancy-defected carbon nanotubes and their embedded nanocomposites

    International Nuclear Information System (INIS)

    Xiao Shaoping; Hou Wenyi

    2006-01-01

    In this paper, we investigate effects of vacancy defects on fracture of carbon nanotubes and carbon nanotube/aluminum composites. Our studies show that even a one-atom vacancy defect can dramatically reduce the failure stresses and strains of carbon nanotubes. Consequently, nanocomposites, in which vacancy-defected nanotubes are embedded, exhibit different characteristics from those in which pristine nanotubes are embedded. It has been found that defected nanotubes with a small volume fraction cannot reinforce but instead weaken nanocomposite materials. Although a large volume fraction of defected nanotubes can slightly increase the failure stresses of nanocomposites, the failure strains of nanocomposites are always decreased

  6. Vacancy formation in MoO3: hybrid density functional theory and photoemission experiments

    KAUST Repository

    Salawu, Omotayo Akande; Chroneos, Alexander; Vasilopoulou, Maria; Kennou, Stella; Schwingenschlö gl, Udo

    2016-01-01

    Molybdenum oxide (MoO3) is an important material that is being considered for numerous technological applications, including catalysis and electrochromism. In the present study, we apply hybrid density functional theory to investigate O and Mo vacancies in the orthorhombic phase. We determine the vacancy formation energies of different defect sites as functions of the electron chemical potential, addressing different charge states. In addition, we investigate the consequences of defects for the material properties. Ultraviolet photoemission spectroscopy is employed to study the valence band of stoichiometric and O defective MoO3. We show that O vacancies result in occupied in-gap states.

  7. Generation of Nitrogen-Vacancy Centers in Diamond with Ion Implantation

    International Nuclear Information System (INIS)

    Cui Jin-Ming; Chen Xiang-Dong; Gong Zhao-Jun; Sun Fang-Wen; Han Zheng-Fu; Guo Guang-Can; Fan Le-Le; Zou Chong-Wen

    2012-01-01

    Nitrogen-vacancy defect color centers are created in a high purity single crystal diamond by nitrogen-ion implantation. Both optical spectrum and optically detected magnetic resonance are measured for these artificial quantum emitters. Moreover, with a suitable mask, a lattice composed of nitrogen-vacancy centers is fabricated. Rabi oscillation driven by micro-waves is carried out to show the quality of the ion implantation and potential in quantum manipulation. Along with compatible standard lithography, such an implantation technique shows high potential in future to make structures with nitrogen-vacancy centers for diamond photonics and integrated photonic quantum chip

  8. Oxygen vacancies at the spinel/perovskite γ-Al{sub 2}O{sub 3}/SrTiO{sub 3} heterointerface probed by resonant photoelectron spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Schuetz, Philipp; Pfaff, Florian; Zapf, Michael; Gabel, Judith; Dudy, Lenart; Berner, Goetz; Sing, Michael; Claessen, Ralph [Physikalisches Institut and Roentgen Center for Complex Material Systems (RCCM), Universitaet Wuerzburg (Germany); Chen, Yunzhong; Pryds, Nini [Department of Energy Conversion and Storage, Technical University of Denmark, Risoe (Denmark); Schlueter, Christoph; Lee, Tien-Lin [Diamond Light Source Ltd., Harwell Science and Innovation Campus, Didcot (United Kingdom)

    2016-07-01

    The spinel/perovskite heterointerface between the band insulators γ-Al{sub 2}O{sub 3} and SrTiO{sub 3} hosts a two-dimensional electron system (2DES) with exceptionally high electron mobility. Soft x-ray resonant photoelectron spectroscopy at the Ti L absorption edge is used to probe the Ti 3d derived interface states. Marked differences in the resonance behavior are found for the SrTiO{sub 3} valence band and the different interface states, which are observed in the band gap of SrTiO{sub 3}. A comparison to X-ray absorption spectra of Ti 3d{sup 0} and Ti 3d{sup 1} systems reveals the presence of different types of electronic states with Ti 3d character, i.e., oxygen vacancy induced, trapped in-gap states and itinerant states contributing to the 2DES. Exposure to low doses of oxygen during irradiation allows for the reversible manipulation of the oxygen stoichiometry, thus revealing the presence of an oxygen vacancy-induced state, which is characteristic for this spinel/perovskite interface.

  9. Artificial covering on trap nests improves the colonization of trap-nesting wasps

    OpenAIRE

    Taki, Hisatomo; Kevan, Peter G.; Viana, Blandina Felipe; Silva, Fabiana O.; Buck, Matthias

    2008-01-01

    Acesso restrito: Texto completo. p. 225-229 To evaluate the role that a trap-nest cover might have on sampling methodologies, the abundance of each species of trap-nesting Hymenoptera and the parasitism rate in a Canadian forest were compared between artificially covered and uncovered traps. Of trap tubes exposed at eight forest sites in six trap-nest boxes, 531 trap tubes were occupied and 1216 individuals of 12 wasp species of four predatory families, Vespidae (Eumeninae), Crabronidae...

  10. Trapping of He clusters by inert-gas impurities in tungsten: First-principles predictions and experimental validation

    Energy Technology Data Exchange (ETDEWEB)

    Nguyen-Manh, Duc, E-mail: duc.nguyen@ccfe.ac.uk; Dudarev, S.L.

    2015-06-01

    Properties of point defects resulting from the incorporation of inert-gas atoms in bcc tungsten are investigated systematically using first-principles density functional theory (DFT) calculations. The most stable configuration for the interstitial neon, argon, krypton and xenon atoms is the tetrahedral site, similarly to what was found earlier for helium in W. The calculated formation energies for single inert-gas atoms at interstitial sites as well as at substitutional sites are much larger for Ne, Ar, Kr and Xe than for He. While the variation of the energy of insertion of inert-gas defects into interstitial configurations can be explained by a strong effect of their large atomic size, the trend exhibited by their substitutional energies is more likely related to the covalent interaction between the noble gas impurity atoms and the tungsten atoms. There is a remarkable variation exhibited by the energy of interaction between inert-gas impurities and vacancies, where a pronounced size effect is observed when going from He to Ne, Ar, Kr, Xe. The origin of this trend is explained by electronic structure calculations showing that p-orbitals play an important part in the formation of chemical bonds between a vacancy and an atom of any of the four inert-gas elements in comparison with helium, where the latter contains only 1s{sup 2} electrons in the outer shell. The binding energies of a helium atom trapped by five different defects (He-v, Ne-v, Ar-v, Kr-v, Xe-v, where v denotes a vacancy in bcc-W) are all in excellent agreement with experimental data derived from thermal desorption spectroscopy. Attachment of He clusters to inert gas impurity atom traps in tungsten is analysed as a function of the number of successive trapping helium atoms. Variation of the Young modulus due to inert-gas impurities is analysed on the basis of data derived from DFT calculations.

  11. Microfabricated linear Paul-Straubel ion trap

    Science.gov (United States)

    Mangan, Michael A [Albuquerque, NM; Blain, Matthew G [Albuquerque, NM; Tigges, Chris P [Albuquerque, NM; Linker, Kevin L [Albuquerque, NM

    2011-04-19

    An array of microfabricated linear Paul-Straubel ion traps can be used for mass spectrometric applications. Each ion trap comprises two parallel inner RF electrodes and two parallel outer DC control electrodes symmetric about a central trap axis and suspended over an opening in a substrate. Neighboring ion traps in the array can share a common outer DC control electrode. The ions confined transversely by an RF quadrupole electric field potential well on the ion trap axis. The array can trap a wide array of ions.

  12. Interaction of nitrogen with vacancy defects in N+-implanted ZnO studied using a slow positron beam

    International Nuclear Information System (INIS)

    Chen, Z.Q.; Maekawa, M.; Kawasuso, A.; Suzuki, R.; Ohdaira, T.

    2005-01-01

    ZnO crystals were implanted with N + , O + , and Al + , and co-implanted with O + /N + and Al + /N + ions. Positron annihilation measurements indicate introduction of vacancy clusters upon implantation. In the N + -implanted and Al + /N + co-implanted samples, these vacancy clusters are only partially annealed at 800 deg. C, as compared with their entire recovery in the O + - and Al + -implanted samples at 800-900 deg. C, suggesting a strong interaction between nitrogen and vacancy clusters. However, in the O + /N + co-implanted sample, most vacancy clusters disappear at 800 deg. C. Probably oxygen scavenges nitrogen to enhance the annealing of the vacancy clusters. Upon further annealing at 1000-1100 deg. C, nitrogen also forms stable complexes with thermally generated vacancies. These nitrogen-related vacancy complexes need high-temperature annealing at 1200-1250 deg. C to be fully removed

  13. Asymmetric Penning trap coherent states

    International Nuclear Information System (INIS)

    Contreras-Astorga, Alonso; Fernandez, David J.

    2010-01-01

    By using a matrix technique, which allows to identify directly the ladder operators, the coherent states of the asymmetric Penning trap are derived as eigenstates of the appropriate annihilation operators. They are compared with those obtained through the displacement operator method.

  14. Indeterminacy, sunspots, and development traps

    Czech Academy of Sciences Publication Activity Database

    Slobodyan, Sergey

    2005-01-01

    Roč. 29, 1-2 (2005), s. 159-185 ISSN 0165-1889 Institutional research plan: CEZ:AV0Z70850503 Keywords : indeterminacy * development trap * stochastic stability Subject RIV: AH - Economics Impact factor: 0.691, year: 2005 http://dx.doi.org/10.1016/j.jedc.2003.04.011

  15. Efficiency of subaquatic light traps

    Czech Academy of Sciences Publication Activity Database

    Ditrich, Tomáš; Čihák, P.

    2017-01-01

    Roč. 38, č. 3 (2017), s. 171-184 ISSN 0165-0424 R&D Projects: GA ČR(CZ) GA14-29857S Institutional support: RVO:60077344 Keywords : Heteroptera * Diptera * light trap Subject RIV: EH - Ecology, Behaviour OBOR OECD: Ecology Impact factor: 0.524, year: 2016

  16. The rise of trapped populations

    Directory of Open Access Journals (Sweden)

    April T Humble

    2014-02-01

    Full Text Available As border security increases and borders become less permeable, cross-border migration is becoming increasingly difficult, selective and dangerous. Growing numbers of people are becoming trapped in their own countries or in transit countries, or being forced to roam border areas, unable to access legal protection or basic social necessities.

  17. Magnetic trapping of Rydberg atoms

    NARCIS (Netherlands)

    Niestadt, D.; Naber, J.; Kokkelmans, S.J.J.M.F.; Spreeuw, R.J.C.

    2016-01-01

    Magnetic trapping is a well-established technique for ground state atoms. We seek to extend this concept to Rydberg atoms. Rydberg atoms are important for current visions of quantum simulators that will be used in the near future to simulate and analyse quantum problems. Current efforts in Amsterdam

  18. Quantum computing with trapped ions

    International Nuclear Information System (INIS)

    Haeffner, H.; Roos, C.F.; Blatt, R.

    2008-01-01

    Quantum computers hold the promise of solving certain computational tasks much more efficiently than classical computers. We review recent experimental advances towards a quantum computer with trapped ions. In particular, various implementations of qubits, quantum gates and some key experiments are discussed. Furthermore, we review some implementations of quantum algorithms such as a deterministic teleportation of quantum information and an error correction scheme

  19. Effect of single vacancy on the structural, electronic structure and magnetic properties of monolayer graphyne by first-principles

    Energy Technology Data Exchange (ETDEWEB)

    Yun, Jiangni, E-mail: niniyun@nwu.edu.cn; Zhang, Yanni; Xu, Manzhang; Wang, Keyun; Zhang, Zhiyong

    2016-10-01

    The effect of single vacancy on the structural, electronic and magnetic properties of monolayer graphyne is investigated by the first-principles calculations. The calculated results reveal that single vacancy can result in the spin polarization in monolayer graphyne and the spin polarization is sensitive to local geometric structure of the vacancy. In the case of monolayer graphyne with one single vacancy at the sp{sup 2} hybridized C site, the vacancy introduces rather weakly spin-polarized, flat bands in the band gap. Due to the localization nature of the defect-induced bands, the magnetic moment is mainly localized at the vacancy site. As for the monolayer graphyne with one single vacancy at the sp hybridized C site, one defect-induced state which is highly split appears in the band gap. The spin-up band of the defect-induced state is highly dispersive and shows considerable delocalization, suggesting that the magnetic moment is dispersed around the vacancy site. The above magnetization in monolayer graphyne with one single vacancy is possibly explained in terms of the valence-bond theory. - Graphical abstract: Calculated band structure of the monolayer graphyne without (a) and with one single vacancy at Vb site (b) and at Vr site(c), respectively. Blue and red lines represent the spin-up and spin-down bands, respectively. For the sake of clarity, the band structure near the Fermi energy is also presented on the right panel. The Fermi level is set to zero on the energy scale. - Highlights: • A Jahn-Teller distortion occurs in monolayer graphyne with single vacancy. • The spin polarization is sensitive to local geometric structure of the vacancy. • Vacancy lying at sp{sup 2} hybridized C site introduces weakly spin-polarized defect bands. • A strong spin splitting occurs when the vacancy lies at sp hybridized C site. • The magnetization is explained in terms of the valence-bond theory.

  20. Benign Synthesis of Black Microspheres of Anatase TiO2 with Paramagnetic Oxygen Vacancies through NH3 Treatment.

    Science.gov (United States)

    Maqbool, Qysar; Srivastava, Aasheesh

    2017-10-09

    Coloured TiO 2 is coveted for its ability to extract energy from the visible region of electromagnetic spectrum. Here a facile synthesis of black anatase titania microspheres (B-TiO 2 ) through a two-step process is reported. In the first step, amorphous white TiO 2 microspheres (W-TiO 2 ) are obtained by hydrolysing titanium tetraisopropoxide by ammonia vapours in ethanol. In the second step, the W-TiO 2 is thermally annealed at 500 °C to obtain B-TiO 2 . The diffuse reflectance analysis showed that B-TiO 2 absorbs across visible spectrum with absorption extending well into NIR region. Raman scattering together with EPR analysis showed compelling evidence of the existence of oxygen deficiency within the crystal in B-TiO 2 that induces black colouration in the sample. The defects present in the black anatase sample were confirmed to be single-electron-trapped (or paramagnetic) oxygen vacancies (V o ⋅) by XPS and EPR studies. The magnetic susceptibility studies showed existence of antiferromagnetic interactions between these unpaired electron spins. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  1. Charge Dynamics in near-Surface, Variable-Density Ensembles of Nitrogen-Vacancy Centers in Diamond.

    Science.gov (United States)

    Dhomkar, Siddharth; Jayakumar, Harishankar; Zangara, Pablo R; Meriles, Carlos A

    2018-06-13

    Although the spin properties of superficial shallow nitrogen-vacancy (NV) centers have been the subject of extensive scrutiny, considerably less attention has been devoted to studying the dynamics of NV charge conversion near the diamond surface. Using multicolor confocal microscopy, here we show that near-surface point defects arising from high-density ion implantation dramatically increase the ionization and recombination rates of shallow NVs compared to those in bulk diamond. Further, we find that these rates grow linearly, not quadratically, with laser intensity, indicative of single-photon processes enabled by NV state mixing with other defect states. Accompanying these findings, we observe NV ionization and recombination in the dark, likely the result of charge transfer to neighboring traps. Despite the altered charge dynamics, we show that one can imprint rewritable, long-lasting patterns of charged-initialized, near-surface NVs over large areas, an ability that could be exploited for electrochemical biosensing or to optically store digital data sets with subdiffraction resolution.

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

    Science.gov (United States)

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

    2016-05-01

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

  3. Enhanced diffusion of dopants in vacancy supersaturation produced by MeV implantation

    International Nuclear Information System (INIS)

    Venezia, V.C.; Univ. of North Texas, Denton, TX; Haynes, T.E.; Agarwal, A.; Lucent Technologies, Murray Hill, NJ; Gossmann, H.J.; Eaglesham, D.J.

    1997-04-01

    The diffusion of Sb and B markers has been studied in vacancy supersaturations produced by MeV Si implantation in float zone (FZ) silicon and bonded etch-back silicon-on-insulator (BESOI) substrates. MeV Si implantation produces a vacancy supersaturated near-surface region and an interstitial-rich region at the projected ion range. Transient enhanced diffusion (TED) of Sb in the near surface layer was observed as a result of a 2 MeV Si + , 1 x 10 16 /cm 2 , implant. A 4x larger TED of Sb was observed in BESOI than in FZ silicon, demonstrating that the vacancy supersaturation persists longer in BESOI than in FZ. B markers in samples with MeV Si implant showed a factor of 10x smaller diffusion relative to markers without the MeV Si + implant. This data demonstrates that a 2 MeV Si + implant injects vacancies into the near surface region

  4. Evaluation of the energetics of copper-vacancy clusters in Fe

    Energy Technology Data Exchange (ETDEWEB)

    Morishita, Kazunori, E-mail: morishita@iae.kyoto-u.ac.jp; Nakasuji, Toshiki; Ruan, Xiaoyong

    2017-02-15

    Highlights: • Thermodynamics evaluation of the nucleation process of copper-vacancy clusters in Fe is performed. • Nucleation free energy of copper-vacancy clusters in Fe is formulated. • With this energetics, two different nucleation paths of clusters are found as a function of the damage rate. - Abstract: A theoretical study is conducted to evaluate the nucleation free energy of copper-vacancy clusters in Fe as a function of the numbers of copper atoms and of vacancies in a cluster. Using this free energy value, cluster nucleation processes during irradiation are investigated. The results clearly show that there are two different types of cluster nucleation paths on the free energy surface; one is the formation of empty voids by jumping over the ridge of the free energy surface, and the other corresponds to a path for the formation of copper clusters by going around the ridge. The dependence of easy nucleation paths on the damage rate is discussed.

  5. Energy band modulation of graphane by hydrogen-vacancy chains: A first-principles study

    Directory of Open Access Journals (Sweden)

    Bi-Ru Wu

    2014-08-01

    Full Text Available We investigated a variety of configurations of hydrogen-vacancy chains in graphane by first-principles density functional calculation. We found that graphane with two zigzag H-vacancy chains segregated by one or more H chain is generally a nonmagnetic conductor or has a negligible band gap. However, the same structure is turned into a semiconductor and generates a magnetic moment if either one or both of the vacancy chains are blocked by isolated H atoms. If H-vacancy chains are continuously distributed, the structure is similar to a zigzag graphene nanoribbon embedded in graphane. It was also found that the embedded zigzag graphene nanoribbon is antiferromagnetic, and isolated H atoms left in the 2-chain nanoribbon can tune the band gap and generate net magnetic moments. Similar effects are also obtained if bare carbon atoms are present outside the nanoribbon. These results are useful for designing graphene-based nanoelectronic circuits.

  6. EnviroAtlas - Residential vacancy rate by Census Tract for the Conterminous United States

    Data.gov (United States)

    U.S. Environmental Protection Agency — This EnviroAtlas dataset portrays the vacancy rate for residential addresses for each Census Tract for each year from 2010-2014. Vacant buildings are included if...

  7. EnviroAtlas - Business vacancy rate by Census Tract for the Conterminous United States

    Data.gov (United States)

    U.S. Environmental Protection Agency — This EnviroAtlas dataset portrays the vacancy rate for business addresses for each Census Tract for each year from 2010-2014. Vacant buildings are included if they...

  8. A new method for determining the formation energy of a vacancy in concentrated alloys

    International Nuclear Information System (INIS)

    Kinoshita, C.; Kitajima, S.; Eguchi, T.

    1978-01-01

    The disadvantages in the conventional method which determines the formation energy of a vacancy in concentrated alloys from their kinetic behavior during annealing after quenching are pointed out, and an alternative method for overcoming these disadvantages is proposed. (Auth.)

  9. The influence of excess vacancy generation on the diffusion of ion implanted phosphorus into silicon

    International Nuclear Information System (INIS)

    Bakowski, A.

    1985-01-01

    The diffusion of ion implanted phosphorus in silicon has been studied. It was found that the diffusion coefficient is not only dependent on the phosphorus surface concentration (the concentration effect) but also on the conditions at the silicon surface (the surface effect). The phosphorus diffusion coefficient is considerably lower when the silicon surface during annealing is covered with a CVD oxide layer. It is suggested that excess vacancies generated at the surface are reponsible for both the concentration and surface effects. Enhanced phosphorus diffusion is attributed to the disturbance of thermodynamic equilibrium in the crystal through phosphorus-vacancy part formation by vacancies introduced into silicon at the surface. On the basis of the data presented, it can be concluded that two mechanisms for excess vacancy generation are involved. Assuming that phosphorus diffuses via E-centers, calculations of the concentration profiles and the diffusion coefficient were performed for different concentrations and surface conditions. (orig.)

  10. Fast nanoscale addressability of nitrogen-vacancy spins via coupling to a dynamic ferromagnetic vortex

    Science.gov (United States)

    Wolf, M. S.; Badea, R.; Berezovsky, J.

    2016-01-01

    The core of a ferromagnetic vortex domain creates a strong, localized magnetic field, which can be manipulated on nanosecond timescales, providing a platform for addressing and controlling individual nitrogen-vacancy centre spins in diamond at room temperature, with nanometre-scale resolution. Here, we show that the ferromagnetic vortex can be driven into proximity with a nitrogen-vacancy defect using small applied magnetic fields, inducing significant nitrogen-vacancy spin splitting. We also find that the magnetic field gradient produced by the vortex is sufficient to address spins separated by nanometre-length scales. By applying a microwave-frequency magnetic field, we drive both the vortex and the nitrogen-vacancy spins, resulting in enhanced coherent rotation of the spin state. Finally, we demonstrate that by driving the vortex on fast timescales, sequential addressing and coherent manipulation of spins is possible on ∼100 ns timescales. PMID:27296550

  11. New vacancy source in ultrahigh-purity aluminium single crystals with a low dislocation density

    Energy Technology Data Exchange (ETDEWEB)

    Mizuno, Kaoru; Yamamoto, Satoshi [Shimane Univ., Faculty of Science and Engineering, Matsue, Shimane (Japan); Morikawa, Kimihiko [Hokkaido Univ., Institute for Low Temperature Science, Sapporo, Hokkaido (Japan); Kuga, Masanori [Kanazawa Univ., Faculty of Science, Kanazawa, Ishikawa (Japan); Okamoto, Hiroyuki [Kanazawa Univ., Faculty of Medicine, Kanazawa, Ishikawa (Japan); Hashimoto, Eiji [Hiroshima Univ., Hiroshima Synchrotron Radiation Center, Higashi-Hiroshima, Hiroshima (Japan)

    2004-05-01

    The vacancy generation process in ultrahigh-purity aluminum single crystals with a low dislocation density was investigated by synchrotron radiation topography using a white X-ray beam. Some straight lines were observed in the topographys taken after temperature rose to 300degC from room temperature, and they were confirmed to be rows of successive small interstitial-type dislocation loops grown as vacancy sources. It was concluded that the thermal generation mechanism of vacancies in ultrahigh-purity aluminum single crystals with a low dislocation density consists of the following two steps. First, small interstitial loops are heterogeneously formed in the crystal lattice; second, these convert to lengthened loops with the development of screw components and finally grow into rows of dislocation loops emitting vacancies into the lattice. (author)

  12. New vacancy source in ultrahigh-purity aluminium single crystals with a low dislocation density

    International Nuclear Information System (INIS)

    Mizuno, Kaoru; Yamamoto, Satoshi; Morikawa, Kimihiko; Kuga, Masanori; Okamoto, Hiroyuki; Hashimoto, Eiji

    2004-01-01

    The vacancy generation process in ultrahigh-purity aluminum single crystals with a low dislocation density was investigated by synchrotron radiation topography using a white X-ray beam. Some straight lines were observed in the topographys taken after temperature rose to 300degC from room temperature, and they were confirmed to be rows of successive small interstitial-type dislocation loops grown as vacancy sources. It was concluded that the thermal generation mechanism of vacancies in ultrahigh-purity aluminum single crystals with a low dislocation density consists of the following two steps. First, small interstitial loops are heterogeneously formed in the crystal lattice; second, these convert to lengthened loops with the development of screw components and finally grow into rows of dislocation loops emitting vacancies into the lattice. (author)

  13. Beyond the Cahn-Hilliard equation: a vacancy-based kinetic theory

    International Nuclear Information System (INIS)

    Nastar, M.

    2011-01-01

    A Self-Consistent Mean Field (SCMF) kinetic theory including an explicit description of the vacancy diffusion mechanism is developed. The present theory goes beyond the usual local equilibrium hypothesis. It is applied to the study of the early time spinodal decomposition in alloys. The resulting analytical expression of the structure function highlights the contribution of the vacancy diffusion mechanism. Instead of the single amplification rate of the Cahn-Hillard linear theory, the linearized SCMF kinetic equations involve three constant rates, first one describing the vacancy relaxation kinetics, second one related to the kinetic coupling between local concentrations and pair correlations and the third one representing the spinodal amplification rate. Starting from the same vacancy diffusion model, we perform kinetic Monte Carlo simulations of a Body Centered Cubic (BCC) demixting alloy. The resulting spherically averaged structure function is compared to the SCMF predictions. Both qualitative and quantitative agreements are satisfying. (authors)

  14. Optical spectroscopy of vacancy related defects in silicon carbide generated by proton irradiation

    Energy Technology Data Exchange (ETDEWEB)

    Kasper, C.; Sperlich, A.; Simin, D.; Astakhov, G.V. [Experimental Physics VI, Julius Maximilian University of Wuerzburg (Germany); Kraus, H. [Japan Atomic EnergyAgency, Takasaki, Gunma (Japan); Experimental Physics VI, Julius Maximilian University of Wuerzburg (Germany); Makino, T.; Sato, S.I.; Ohshima, T. [Japan Atomic EnergyAgency, Takasaki, Gunma (Japan); Dyakonov, V. [Experimental Physics VI, Julius Maximilian University of Wuerzburg (Germany); ZAE Bayern, Wuerzburg (Germany)

    2016-07-01

    Defects in silicon carbide (SiC) received growing attention in recent years, because they are promising candidates for spin based quantum information processing. In this study we examine silicon vacancies in 4H-SiC crystals generated by proton irradiation. By the use of confocal microscopy the implantation depth of Si vacancies for varying proton energies can be verified. An important issue is to ascertain the nature and distribution of the defects. For this purpose, we use the characteristic photoluminescence spectrum of Si vacancies, whose intensity is proportional to the defect density. Using xyz-scans, where the photoluminescence at each mapping point is recorded, one can thus determine the vacancies nature and their distribution in the SiC crystal. Additionally we verify the nature of the examined defects by measuring their uniquely defined zero-field-splitting by using ODMR associated with defect spins.

  15. Oxygen Vacancy-Mediated ZnO Nanoparticle Photocatalyst for Degradation of Methylene Blue

    Directory of Open Access Journals (Sweden)

    Qiuping Zhang

    2018-02-01

    Full Text Available ZnO nanoparticles (NPs are synthesized by deoxidizing ZnO powder in a vacuum drying process. This process reduces the size of the NPs and increases the concentration of oxygen vacancies on their surfaces. ZnO NPs with sufficient oxygen vacancies are highly effective for the photodecomposition of methylene blue (MB dye in water under ultraviolet irradiation. The MB degradation efficiency exceeds 99 percent after 50 min of light irradiation, and the catalytic property of the NPs remains stable over several complete degradation cycles. It is revealed that the concentration of oxygen vacancies on the surface, and the photocatalytic activity, are both higher for smaller NPs. Oxygen vacancies reduce the recombination rate of photo-generated charge carriers by capturing the electrons and hence, improve the efficiency of redox reactions. In addition, a smaller particle size leads to a larger specific surface area and a higher photonic efficiency for the ZnO NPs.

  16. Zinc Vacancy Formation and its Effect on the Conductivity of ZnO

    Science.gov (United States)

    Khan, Enamul; Weber, Marc; Langford, Steve; Dickinson, Tom

    2010-03-01

    Exposing single crystal ZnO to 193-nm ArF excimer laser radiation can produce metallic zinc nanoparticles along the surface. The particle production mechanism appears to involve interstitial-vacancy pair formation in the near-surface bulk. Conductivity measurements made with one probe inside the laser spot and the other outside show evidence for rectifying behavior. Positron annihilation spectroscopy confirms the presence of Zn vacancies. We suggest that Zn vacancies are a possible source of p-type behavior in irradiated ZnO. Quadrupole mass spectroscopy shows that both oxygen and zinc are emitted during irradiation. Electron-hole pair production has previously been invoked to account for particle desorption from ZnO during UV illumination. Our results suggest that preexisting and laser-generated defects play a critical role in particle desorption and Zn vacancy formation.

  17. Scheduling with Group Dynamics: a Multi-Robot Task Allocation Algorithm based on Vacancy Chains

    National Research Council Canada - National Science Library

    Dahl, Torbjorn S; Mataric, Maja J; Sukhatme, Gaurav S

    2002-01-01

    .... We present a multi-robot task allocation algorithm that is sensitive to group dynamics. Our algorithm is based on vacancy chains, a resource distribution process common in human and animal societies...

  18. Mechanism of dopant-vacancy association in α-quartz GeO2

    KAUST Repository

    Wang, Hao; Chroneos, Alexander; Schwingenschlö gl, Udo

    2013-01-01

    Improving the electron mobility of devices such as Ge metal oxide semiconductor field effect transistors requires good Ge/dielectric interfaces. GeO2 thus is reconsidered as a passivation layer for Ge. However, O-vacancies need to be controlled as they have a deleterious impact on the properties. We employ electronic structure calculations to investigate the introduction of trivalent ions (Al, Y, and La) in α-quartz GeO2. The binding energies of the dopant-vacancy pairs reveal that dopants can be used to control the O-vacancies and reduce the induced dangling bonds. It is proposed that the introduction of Al will limit the concentration of O-vacancies at low Fermi energy.

  19. Mechanism of dopant-vacancy association in α-quartz GeO2

    KAUST Repository

    Wang, Hao

    2013-02-28

    Improving the electron mobility of devices such as Ge metal oxide semiconductor field effect transistors requires good Ge/dielectric interfaces. GeO2 thus is reconsidered as a passivation layer for Ge. However, O-vacancies need to be controlled as they have a deleterious impact on the properties. We employ electronic structure calculations to investigate the introduction of trivalent ions (Al, Y, and La) in α-quartz GeO2. The binding energies of the dopant-vacancy pairs reveal that dopants can be used to control the O-vacancies and reduce the induced dangling bonds. It is proposed that the introduction of Al will limit the concentration of O-vacancies at low Fermi energy.

  20. 50 CFR 697.19 - Trap limits and trap tag requirements for vessels fishing with lobster traps.

    Science.gov (United States)

    2010-10-01

    ... vessels fishing with lobster traps. 697.19 Section 697.19 Wildlife and Fisheries FISHERY CONSERVATION AND... requirements for vessels fishing with lobster traps. (a) Trap limits for vessels fishing or authorized to fish... management area designation certificate or valid limited access American lobster permit specifying one or...

  1. Spin-dependent recombination involving oxygen-vacancy complexes in silicon

    OpenAIRE

    Franke, David P.; Hoehne, Felix; Vlasenko, Leonid S.; Itoh, Kohei M.; Brandt, Martin S.

    2014-01-01

    Spin-dependent relaxation and recombination processes in $\\gamma$-irradiated $n$-type Czochralski-grown silicon are studied using continuous wave (cw) and pulsed electrically detected magnetic resonance (EDMR). Two processes involving the SL1 center, the neutral excited triplet state of the oxygen-vacancy complex, are observed which can be separated by their different dynamics. One of the processes is the relaxation of the excited SL1 state to the ground state of the oxygen-vacancy complex, t...

  2. Vacancy clustering behavior in hydrogen-charged martensitic steel AISI 410 under tensile deformation

    International Nuclear Information System (INIS)

    Sugita, K; Mutou, Y; Shirai, Y

    2016-01-01

    The formation and accumulation of defects under tensile deformation of hydrogen- charged AISI 410 martensitic steels were investigated by using positron lifetime spectroscopy. During the deformation process, dislocations and vacancy-clusters were introduced and increased with increasing strains. Between hydrogen-charged and uncharged samples with the same tensile strains there was no significant difference in the dislocation density and monovacancy equivalent vacancy density. (paper)

  3. Oxygen vacancy-induced ferromagnetism in un-doped ZnO thin films

    Science.gov (United States)

    Zhan, Peng; Wang, Weipeng; Liu, Can; Hu, Yang; Li, Zhengcao; Zhang, Zhengjun; Zhang, Peng; Wang, Baoyi; Cao, Xingzhong

    2012-02-01

    ZnO films became ferromagnetic when defects were introduced by thermal-annealing in flowing argon. This ferromagnetism, as shown by the photoluminescence measurement and positron annihilation analysis, was induced by the singly occupied oxygen vacancy with a saturated magnetization dependent positively on the amount of this vacancy. This study clarified the origin of the ferromagnetism of un-doped ZnO thin films and provides possibly an alternative way to prepare ferromagnetic ZnO films.

  4. Scaling ion traps for quantum computing

    CSIR Research Space (South Africa)

    Uys, H

    2010-09-01

    Full Text Available The design, fabrication and preliminary testing of a chipscale, multi-zone, surface electrode ion trap is reported. The modular design and fabrication techniques used are anticipated to advance scalability of ion trap quantum computing architectures...

  5. Servo control of an optical trap.

    Science.gov (United States)

    Wulff, Kurt D; Cole, Daniel G; Clark, Robert L

    2007-08-01

    A versatile optical trap has been constructed to control the position of trapped objects and ultimately to apply specified forces using feedback control. While the design, development, and use of optical traps has been extensive and feedback control has played a critical role in pushing the state of the art, few comprehensive examinations of feedback control of optical traps have been undertaken. Furthermore, as the requirements are pushed to ever smaller distances and forces, the performance of optical traps reaches limits. It is well understood that feedback control can result in both positive and negative effects in controlled systems. We give an analysis of the trapping limits as well as introducing an optical trap with a feedback control scheme that dramatically improves an optical trap's sensitivity at low frequencies.

  6. Enhanced Photocatalytic Activity of Vacuum-activated TiO2 Induced by Oxygen Vacancies.

    Science.gov (United States)

    Dong, Guoyan; Wang, Xin; Chen, Zhiwu; Lu, Zhenya

    2018-05-01

    TiO 2 (Degussa P25) photocatalysts harboring abundant oxygen vacancies (Vacuum P25) were manufactured using a simple and economic Vacuum deoxidation process. Control experiments showed that temperature and time of vacuum deoxidation had a significant effect on Vacuum P25 photocatalytic activity. After 240 min of visible light illumination, the optimal Vacuum P25 photocatalysts (vacuum deoxidation treated at 330 °C for 3 h) reach as high as 94% and 88% of photodegradation efficiency for rhodamine B (RhB) and tetracycline, respectively, which are around 4.5 and 4.9 times as that of pristine P25. The XPS, PL and EPR analyses indicated that the oxygen vacancies were produced in the Vacuum P25 during the vacuum deoxidation process. The oxygen vacancy states can produce vacancy energy level located below the conduction band minimum, which resulting in the bandgap narrowing, thus extending the photoresponse wavelength range of Vacuum P25. The positron annihilation analysis indicated that the concentrations ratio of bulk and surface oxygen vacancies could be adjusted by changing the vacuum deoxidation temperature and time. Decreasing the ratio of bulk and surface oxygen vacancies was shown to improve photogenerated electron-hole pair separation efficiency, which leads to an obvious enhancement of the visible photocatalytic activities of Vacuum P25. © 2017 The American Society of Photobiology.

  7. Thermodynamic, electronic, and magnetic properties of intrinsic vacancy defects in antiperovskite Ca3SnO

    Science.gov (United States)

    Batool, Javaria; Alay-e-Abbas, Syed Muhammad; Amin, Nasir

    2018-04-01

    The density functional theory based total energy calculations are performed to examine the effect of charge neutral and fully charged intrinsic vacancy defects on the thermodynamic, electronic, and magnetic properties of Ca3SnO antiperovskite. The chemical stability of Ca3SnO is evaluated with respect to binary compounds CaO, CaSn, and Ca2Sn, and the limits of atomic chemical potentials of Ca, Sn, and O atoms for stable synthesis of Ca3SnO are determined within the generalized gradient approximation parametrization scheme. The electronic properties of the pristine and the non-stoichiometric forms of this compound have been explored and the influence of isolated intrinsic vacancy defects (Ca, Sn, and O) on the structural, bonding, and electronic properties of non-stoichiometric Ca3SnO are analyzed. We also predict the possibility of achieving stable ferromagnetism in non-stoichiometric Ca3SnO by means of charge neutral tin vacancies. From the calculated total energies and the valid ranges of atomic chemical potentials, the formation energetics of intrinsic vacancy defects in Ca3SnO are evaluated for various growth conditions. Our results indicate that the fully charged calcium vacancies are thermodynamically stable under the permissible Sn-rich condition of stable synthesis of Ca3SnO, while tin and oxygen vacancies are found to be stable under the extreme Ca-rich condition.

  8. Influence of surface vacancy defects on the carburisation of Fe 110 surface by carbon monoxide

    Energy Technology Data Exchange (ETDEWEB)

    Chakrabarty, Aurab, E-mail: aurab.chakrabarty@qatar.tamu.edu; Bouhali, Othmane [Texas A& M University at Qatar, P.O. Box 23874, Doha (Qatar); Mousseau, Normand [Département de Physique and RQMP, Université de Montréal, Case Postale 6128, Succursale Centre-Ville, Montréal (QC) H3C 3J7 (Canada); Becquart, Charlotte S. [UMET, UMR CNRS 8207, ENSCL, Université Lille I, 59655 Villeneuve d’Ascq cédex (France); El-Mellouhi, Fedwa, E-mail: felmellouhi@qf.org.qa [Qatar Environment and Energy Research Institute, Hamad Bin Khalifa University, P.O. Box 5825 Doha (Qatar)

    2016-07-28

    Adsorption and dissociation of gaseous carbon monoxide (CO) on metal surfaces is one of the most frequently occurring processes of carburisation, known as primary initiator of metal dusting corrosion. Among the various factors that can significantly influence the carburisation process are the intrinsic surface defects such as single surface vacancies occurring at high concentrations due to their low formation energy. Intuitively, adsorption and dissociation barriers of CO are expected to be lowered in the vicinity of a surface vacancy, due to the strong attractive interaction between the vacancy and the C atom. Here the adsorption energies and dissociation pathways of CO on clean and defective Fe 110 surface are explored by means of density functional theory. Interestingly, we find that the O adatom, resulting from the CO dissociation, is unstable in the electron-deficit neighbourhood of the vacancy due to its large electron affinity, and raises the barrier of the carburisation pathway. Still, a full comparative study between the clean surface and the vacancy-defected surface reveals that the complete process of carburisation, starting from adsorption to subsurface diffusion of C, is more favourable in the vicinity of a vacancy defect.

  9. Theoretical study on magnetism induced by H vacancy in isolated Alq3 and Gaq3 molecules

    Science.gov (United States)

    Ju, Lin; Xu, Tongshuai; Zhang, Yongjia; Sun, Li

    2017-10-01

    The magnetism induced by H vacancy in isolated Alq3 and Gaq3 molecules has been studied based on density functional theory. The isolated stoichiometric Alq3 and Gaq3 molecules are non-magnetic. With an H vacancy, both Alq3 and Gaq3 molecules could show magnetism, which are mainly due to the polarization of the C 2p electrons and the magnetic moments are mainly distributed at most nearby C atoms of H vacancies. This is because the unpaired electron on the C atom appears, when the H atom nearby is removed. Six cases of the H vacancy introduced in the Alq3 and Gaq3 molecules are considered, respectively. By comparing the relative defect formation energy, the V H3 vacancy is most likely to appear in the two kinds of molecules. In addition, for the ground state configuration of isolated Alq3 and Gaq3 molecules with two H vacancies, the energy of the ferromagnetic state is lower than that of the antiferromagnetic state, which means that the ferromagnetic state is stable. The ferromagnetic mechanism can be explained by the Heisenberg direct exchange interaction between two the polarized C atoms. Our work opens a new way to synthesize organic magnetic materials and perfects the theory of organic ferromagnetism by introducing the d 0 ferromagnetism.

  10. Inhomogeneous Oxygen Vacancy Distribution in Semiconductor Gas Sensors: Formation, Migration and Determination on Gas Sensing Characteristics

    Directory of Open Access Journals (Sweden)

    Jianqiao Liu

    2017-08-01

    Full Text Available The density of oxygen vacancies in semiconductor gas sensors was often assumed to be identical throughout the grain in the numerical discussion of the gas-sensing mechanism of the devices. In contrast, the actual devices had grains with inhomogeneous distribution of oxygen vacancy under non-ideal conditions. This conflict between reality and discussion drove us to study the formation and migration of the oxygen defects in semiconductor grains. A model of the gradient-distributed oxygen vacancy was proposed based on the effects of cooling rate and re-annealing on semiconductive thin films. The model established the diffusion equations of oxygen vacancy according to the defect kinetics of diffusion and exclusion. We described that the steady-state and transient-state oxygen vacancy distributions, which were used to calculate the gas-sensing characteristics of the sensor resistance and response to reducing gases under two different conditions. The gradient-distributed oxygen vacancy model had the applications in simulating the sensor performances, such as the power law, the grain size effect and the effect of depletion layer width.

  11. Vacancy-type defects induced by grinding of Si wafers studied by monoenergetic positron beams

    Energy Technology Data Exchange (ETDEWEB)

    Uedono, Akira; Yoshihara, Nakaaki [Division of Applied Physics, Faculty of Pure and Applied Science, University of Tsukuba, Tsukuba, Ibaraki 305-8573 (Japan); Mizushima, Yoriko [Devices and Materials Labs Fujitsu Laboratories Ltd., Atsugi, Kanagawa 243-0197 (Japan); ICE Cube Center, Tokyo Institute of Technology, Yokohama 226-8503 (Japan); Kim, Youngsuk [ICE Cube Center, Tokyo Institute of Technology, Yokohama 226-8503 (Japan); Disco Corporation, Ota, Tokyo 143-8580 (Japan); Nakamura, Tomoji [Devices and Materials Labs Fujitsu Laboratories Ltd., Atsugi, Kanagawa 243-0197 (Japan); Ohba, Takayuki [ICE Cube Center, Tokyo Institute of Technology, Yokohama 226-8503 (Japan); Oshima, Nagayasu; Suzuki, Ryoichi [Research Institute of Instrumentation Frontier, National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki 305-8568 (Japan)

    2014-10-07

    Vacancy-type defects introduced by the grinding of Czochralski-grown Si wafers were studied using monoenergetic positron beams. Measurements of Doppler broadening spectra of the annihilation radiation and the lifetime spectra of positrons showed that vacancy-type defects were introduced in the surface region (<98 nm), and the major defect species were identified as (i) relatively small vacancies incorporated in dislocations and (ii) large vacancy clusters. Annealing experiments showed that the defect concentration decreased with increasing annealing temperature in the range between 100 and 500°C. After 600–700°C annealing, the defect-rich region expanded up to about 170 nm, which was attributed to rearrangements of dislocation networks, and a resultant emission of point defects toward the inside of the sample. Above 800°C, the stability limit of those vacancies was reached and they started to disappear. After the vacancies were annealed out (900°C), oxygen-related defects were the major point defects and they were located at <25 nm.

  12. Inhomogeneous Oxygen Vacancy Distribution in Semiconductor Gas Sensors: Formation, Migration and Determination on Gas Sensing Characteristics.

    Science.gov (United States)

    Liu, Jianqiao; Gao, Yinglin; Wu, Xu; Jin, Guohua; Zhai, Zhaoxia; Liu, Huan

    2017-08-10

    The density of oxygen vacancies in semiconductor gas sensors was often assumed to be identical throughout the grain in the numerical discussion of the gas-sensing mechanism of the devices. In contrast, the actual devices had grains with inhomogeneous distribution of oxygen vacancy under non-ideal conditions. This conflict between reality and discussion drove us to study the formation and migration of the oxygen defects in semiconductor grains. A model of the gradient-distributed oxygen vacancy was proposed based on the effects of cooling rate and re-annealing on semiconductive thin films. The model established the diffusion equations of oxygen vacancy according to the defect kinetics of diffusion and exclusion. We described that the steady-state and transient-state oxygen vacancy distributions, which were used to calculate the gas-sensing characteristics of the sensor resistance and response to reducing gases under two different conditions. The gradient-distributed oxygen vacancy model had the applications in simulating the sensor performances, such as the power law, the grain size effect and the effect of depletion layer width.

  13. Understanding the presence of vacancy clusters in ZnO from a kinetic perspective

    Science.gov (United States)

    Bang, Junhyeok; Kim, Youg-Sung; Park, C. H.; Gao, F.; Zhang, S. B.

    2014-06-01

    Vacancy clusters have been observed in ZnO by positron-annihilation spectroscopy (PAS), but detailed mechanisms are unclear. This is because the clustering happens in non-equilibrium conditions, for which theoretical method has not been well established. Combining first-principles calculation and kinetic Monte Carlo simulation, we determine the roles of non-equilibrium kinetics on the vacancies clustering. We find that clustering starts with the formation of Zn and O vacancy pairs (VZn - Vo), which further grow by attracting additional mono-vacancies. At this stage, vacancy diffusivity becomes crucial: due to the larger diffusivity of VZn compared to VO, more VZn-abundant clusters are formed than VO-abundant clusters. The large dissociation energy barriers, e.g., over 2.5 eV for (VZn - Vo), suggest that, once formed, it is difficult for the clusters to dissociate. By promoting mono-vacancy diffusion, thermal annealing will increase the size of the clusters. As the PAS is insensitive to VO donor defects, our results suggest an interpretation of the experimental data that could not have been made without the in-depth calculations.

  14. Understanding the presence of vacancy clusters in ZnO from a kinetic perspective

    International Nuclear Information System (INIS)

    Bang, Junhyeok; Zhang, S. B.; Kim, Youg-Sung; Park, C. H.; Gao, F.

    2014-01-01

    Vacancy clusters have been observed in ZnO by positron-annihilation spectroscopy (PAS), but detailed mechanisms are unclear. This is because the clustering happens in non-equilibrium conditions, for which theoretical method has not been well established. Combining first-principles calculation and kinetic Monte Carlo simulation, we determine the roles of non-equilibrium kinetics on the vacancies clustering. We find that clustering starts with the formation of Zn and O vacancy pairs (V Zn  − Vo), which further grow by attracting additional mono-vacancies. At this stage, vacancy diffusivity becomes crucial: due to the larger diffusivity of V Zn compared to V O , more V Zn -abundant clusters are formed than V O -abundant clusters. The large dissociation energy barriers, e.g., over 2.5 eV for (V Zn  − Vo), suggest that, once formed, it is difficult for the clusters to dissociate. By promoting mono-vacancy diffusion, thermal annealing will increase the size of the clusters. As the PAS is insensitive to V O donor defects, our results suggest an interpretation of the experimental data that could not have been made without the in-depth calculations.

  15. Understanding the presence of vacancy clusters in ZnO from a kinetic perspective

    Energy Technology Data Exchange (ETDEWEB)

    Bang, Junhyeok; Zhang, S. B., E-mail: zhangs9@rpi.edu, E-mail: kimyongsung@gmail.com [Department of Physics, Applied Physics, and Astronomy, Rensselaer Polytechnic Institute, Troy, New York 12180 (United States); Kim, Youg-Sung, E-mail: zhangs9@rpi.edu, E-mail: kimyongsung@gmail.com [Korea Research Institute of Standards and Science, Daejeon 305-340 (Korea, Republic of); Department of Nano Science, University of Science and Technology, Daejeon 305-350 (Korea, Republic of); Park, C. H. [Research Center for Dielectric and Advanced Matter Physics, Pusan National University, Busan 609-735 (Korea, Republic of); Gao, F. [Pacific Northwest National Laboratory, MS K8-93, P.O. Box 999, Richland, Washington 99352 (United States)

    2014-06-23

    Vacancy clusters have been observed in ZnO by positron-annihilation spectroscopy (PAS), but detailed mechanisms are unclear. This is because the clustering happens in non-equilibrium conditions, for which theoretical method has not been well established. Combining first-principles calculation and kinetic Monte Carlo simulation, we determine the roles of non-equilibrium kinetics on the vacancies clustering. We find that clustering starts with the formation of Zn and O vacancy pairs (V{sub Zn} − Vo), which further grow by attracting additional mono-vacancies. At this stage, vacancy diffusivity becomes crucial: due to the larger diffusivity of V{sub Zn} compared to V{sub O}, more V{sub Zn}-abundant clusters are formed than V{sub O}-abundant clusters. The large dissociation energy barriers, e.g., over 2.5 eV for (V{sub Zn} − Vo), suggest that, once formed, it is difficult for the clusters to dissociate. By promoting mono-vacancy diffusion, thermal annealing will increase the size of the clusters. As the PAS is insensitive to V{sub O} donor defects, our results suggest an interpretation of the experimental data that could not have been made without the in-depth calculations.

  16. Migration mechanisms and diffusion barriers of vacancies in Ga2O3

    Science.gov (United States)

    Kyrtsos, Alexandros; Matsubara, Masahiko; Bellotti, Enrico

    2017-06-01

    We employ the nudged elastic band and the dimer methods within the standard density functional theory (DFT) formalism to study the migration of the oxygen and gallium vacancies in the monoclinic structure of β -Ga2O3 . We identify all the first nearest neighbor paths and calculate the migration barriers for the diffusion of the oxygen and gallium vacancies. We also identify the metastable sites of the gallium vacancies which are critical for the diffusion of the gallium atoms. The migration barriers for the diffusion of the gallium vacancies are lower than the migration barriers for oxygen vacancies by 1 eV on average, suggesting that the gallium vacancies are mobile at lower temperatures. Using the calculated migration barriers we estimate the annealing temperature of these defects within the harmonic transition state theory formalism, finding excellent agreement with the observed experimental annealing temperatures. Finally, we suggest the existence of percolation paths which enable the migration of the species without utilizing all the migration paths of the crystal.

  17. Perturbation of the γ angular distribution due to vacancy-induced quadrupole interaction in metals

    International Nuclear Information System (INIS)

    Abromeit, C.

    1976-01-01

    This paper presents an investigation of the influence of diffusing vacancies on the results of PAC/PAD experiments. The fluctuating hyperfine interaction process, caused by thermal hopping of the vacancies, is described by a stochastic model, and the mean value of the density matrix time development operator of the probe nucleus. First, the nuclear perturbation factors, containing all information about the interaction of the nuclear spin system with the environment, are defined. The stochastic process of vacancy diffusion in a discrete lattice is presented, and approximation methods are given leading to a significant simplification and in some cases even make possible an evaluation at all. The problem of vacancy preparation at the initial stage of the PAC/PAD-experiment is studied. For the electric field gradients produced by the vacancies at the position of the probe nucleus, an empirical ansatz is given. For different lattice structures, numerical results for integral and differential measurements with and without an applied external magnetic field are presentd. These results are discussed in view of the approximations made and compared with the experiment. Also, the influence of the initial vacancy distribution on the calculated perturbation factors is investigated. The results show good agreement with experimental data. (orig./HPOE) [de

  18. Two-baffle trap for macroparticles

    International Nuclear Information System (INIS)

    Aksyonov, D.S.

    2014-01-01

    In this work, properties of two-baffle macroparticle traps were investigated. These properties are needed for designing and optimization of vacuum arc plasma filters. The dependencies between trap geometry parameters and its ability to absorb macroparticles were found. Calculations made allow one to predict the behaviour of filtering abilities of separators containing such traps in their design. Recommendations regarding the use of two-baffle traps in filters of different builds are given

  19. Cavity sideband cooling of trapped molecules

    NARCIS (Netherlands)

    Kowalewski, Markus; Morigi, Giovanna; Pinkse, Pepijn Willemszoon Harry; de Vivie-Riedle, Regina

    2011-01-01

    The efficiency of cavity sideband cooling of trapped molecules is theoretically investigated for the case in which the infrared transition between two rovibrational states is used as a cycling transition. The molecules are assumed to be trapped either by a radiofrequency or optical trapping

  20. An Open Standard for Camera Trap Data

    NARCIS (Netherlands)

    Forrester, Tavis; O'Brien, Tim; Fegraus, Eric; Jansen, P.A.; Palmer, Jonathan; Kays, Roland; Ahumada, Jorge; Stern, Beth; McShea, William

    2016-01-01

    Camera traps that capture photos of animals are a valuable tool for monitoring biodiversity. The use of camera traps is rapidly increasing and there is an urgent need for standardization to facilitate data management, reporting and data sharing. Here we offer the Camera Trap Metadata Standard as an

  1. Influence of trap location on the efficiency of trapping in dendrimers and regular hyperbranched polymers.

    Science.gov (United States)

    Lin, Yuan; Zhang, Zhongzhi

    2013-03-07

    The trapping process in polymer systems constitutes a fundamental mechanism for various other dynamical processes taking place in these systems. In this paper, we study the trapping problem in two representative polymer networks, Cayley trees and Vicsek fractals, which separately model dendrimers and regular hyperbranched polymers. Our goal is to explore the impact of trap location on the efficiency of trapping in these two important polymer systems, with the efficiency being measured by the average trapping time (ATT) that is the average of source-to-trap mean first-passage time over every staring point in the whole networks. For Cayley trees, we derive an exact analytic formula for the ATT to an arbitrary trap node, based on which we further obtain the explicit expression of ATT for the case that the trap is uniformly distributed. For Vicsek fractals, we provide the closed-form solution for ATT to a peripheral node farthest from the central node, as well as the numerical solutions for the case when the trap is placed on other nodes. Moreover, we derive the exact formula for the ATT corresponding to the trapping problem when the trap has a uniform distribution over all nodes. Our results show that the influence of trap location on the trapping efficiency is completely different for the two polymer networks. In Cayley trees, the leading scaling of ATT increases with the shortest distance between the trap and the central node, implying that trap's position has an essential impact on the trapping efficiency; while in Vicsek fractals, the effect of location of the trap is negligible, since the dominant behavior of ATT is identical, respective of the location where the trap is placed. We also present that for all cases of trapping problems being studied, the trapping process is more efficient in Cayley trees than in Vicsek fractals. We demonstrate that all differences related to trapping in the two polymer systems are rooted in their underlying topological structures.

  2. First-principles study of vacancy formation and migration in clean and Re-doped γ'-Ni3Al

    International Nuclear Information System (INIS)

    Zhang Xu; Wang Chongyu

    2009-01-01

    Using density functional theory calculations in conjunction with the climbing images nudged elastic band method, we studied the vacancy formation and migration in clean and Re-doped Ni 3 Al. Both the chemical potential of the species and the magnetic effect are considered to determine the vacancy formation energy. We also simulated the vacancy migration in a complete set of migration paths. The evaluated vacancy formation energy and activation energy for the motion of vacancy compared well with the experimental results. Also, the obtained migration ways for the diffusion of Ni and Al atoms are consistent with previous theoretical predictions and experimental observations. Magnetism is found to influence both the vacancy formation and migration. Our results reveal that Re doping can inhibit the formation of Ni vacancies but facilitate the formation of Al vacancies, and can also inhibit the migration of neighboring vacancies. While the doped Re atom on the Al site is stable, the Re atom on the Ni site can diffuse within the Ni-sublattice mediated by Ni vacancies

  3. Fundamental physics in particle traps

    International Nuclear Information System (INIS)

    Quint, Wolfgang; Vogel, Manuel

    2014-01-01

    The individual topics are covered by leading experts in the respective fields of research. Provides readers with present theory and experiments in this field. A useful reference for researchers. This volume provides detailed insight into the field of precision spectroscopy and fundamental physics with particles confined in traps. It comprises experiments with electrons and positrons, protons and antiprotons, antimatter and highly charged ions, together with corresponding theoretical background. Such investigations represent stringent tests of quantum electrodynamics and the Standard model, antiparticle and antimatter research, test of fundamental symmetries, constants, and their possible variations with time and space. They are key to various aspects within metrology such as mass measurements and time standards, as well as promising to further developments in quantum information processing. The reader obtains a valuable source of information suited for beginners and experts with an interest in fundamental studies using particle traps.

  4. Trapping and spectroscopy of hydrogen

    International Nuclear Information System (INIS)

    Cesar, Claudio Lenz

    1997-01-01

    I review the results and techniques used by the MIT H↑ group to achieve a fractional resolution of 2 parts in 10 12 in the 1S-2S transition in hydrogen [Cesar, D. Fried, T. Killian, A. Polcyn, J. Sandberg, I.A. Yu, T. Greytak, D. Kleppner and J. Doyle, Two-photon spectroscopy of trapped atomic hydrogen, Phys. Rev. Lett. 77 (1996) 255.] With some improvements, this system should deliver 100 times higher resolution with an improved signal count rate getting us closer to an old advertised goal of a precision of 1 part in 10 18 . While these developments are very important for the proposed test of the CPT theorem through the comparison with anti-hydrogen, some of the techniques used with hydrogen are not applicable to anti-hydrogen and I discuss some difficulties and alternatives for the trapping and spectroscopy of anti-hydrogen

  5. Centrifugal trapping in the magnetotail

    Directory of Open Access Journals (Sweden)

    D. C. Delcourt

    Full Text Available Particles leaving the neutral sheet in the distant magnetotail at times display adiabatic trajectory sequences characterized by an inflection toward the equator and subsequent mirroring in its vicinity. We demonstrate that this low-latitude mirroring results primarily from a centrifugal deceleration due to the fast direction-changing E×B drift. This effect which we refer to as "centrifugal trapping" appears both in guiding centre and full particle treatments. It thus does not directly relate to nonadiabatic motion. However, pitch angle scattering due to nonadiabatic neutral sheet interaction does play a role in reducing the parallel speed of the particles. We show that centrifugal trapping is an important mechanism for the confinement of the slowest (typically below the equatorial E×B drift speed plasma sheet populations to the midplane vicinity.

  6. Centrifugal trapping in the magnetotail

    Directory of Open Access Journals (Sweden)

    D. C. Delcourt

    1995-03-01

    Full Text Available Particles leaving the neutral sheet in the distant magnetotail at times display adiabatic trajectory sequences characterized by an inflection toward the equator and subsequent mirroring in its vicinity. We demonstrate that this low-latitude mirroring results primarily from a centrifugal deceleration due to the fast direction-changing E×B drift. This effect which we refer to as "centrifugal trapping" appears both in guiding centre and full particle treatments. It thus does not directly relate to nonadiabatic motion. However, pitch angle scattering due to nonadiabatic neutral sheet interaction does play a role in reducing the parallel speed of the particles. We show that centrifugal trapping is an important mechanism for the confinement of the slowest (typically below the equatorial E×B drift speed plasma sheet populations to the midplane vicinity.

  7. Vapor trap for liquid metal

    Energy Technology Data Exchange (ETDEWEB)

    Watanabe, T

    1968-05-22

    In a pipe system which transfers liquid metal, inert gas (cover gas) is packed above the surface of the liquid metal to prevent oxidization of the liquid. If the metal vapor is contained in such cover gas, the circulating system of the cover gas is blocked due to condensation of liquid metal inside the system. The present invention relates to an improvement in vapor trap to remove the metal vapor from the cover gas. The trap consists of a cylindrical outer body, an inlet nozzle which is deeply inserted inside the outer body and has a number of holes to inject the cove gas into the body, metal mesh or steel wool which covers the exterior of the nozzle and on which the condensation of the metal gas takes place, and a heater wire hich is wound around the nozzle to prevent condensation of the metal vapor at the inner peripheral side of the mesh.

  8. Optical trapping for analytical biotechnology.

    Science.gov (United States)

    Ashok, Praveen C; Dholakia, Kishan

    2012-02-01

    We describe the exciting advances of using optical trapping in the field of analytical biotechnology. This technique has opened up opportunities to manipulate biological particles at the single cell or even at subcellular levels which has allowed an insight into the physical and chemical mechanisms of many biological processes. The ability of this technique to manipulate microparticles and measure pico-Newton forces has found several applications such as understanding the dynamics of biological macromolecules, cell-cell interactions and the micro-rheology of both cells and fluids. Furthermore we may probe and analyse the biological world when combining trapping with analytical techniques such as Raman spectroscopy and imaging. Copyright © 2011 Elsevier Ltd. All rights reserved.

  9. Lift enhancement by trapped vortex

    Science.gov (United States)

    Rossow, Vernon J.

    1992-01-01

    The viewgraphs and discussion of lift enhancement by trapped vortex are provided. Efforts are continuously being made to find simple ways to convert wings of aircraft from an efficient cruise configuration to one that develops the high lift needed during landing and takeoff. The high-lift configurations studied here consist of conventional airfoils with a trapped vortex over the upper surface. The vortex is trapped by one or two vertical fences that serve as barriers to the oncoming stream and as reflection planes for the vortex and the sink that form a separation bubble on top of the airfoil. Since the full three-dimensional unsteady flow problem over the wing of an aircraft is so complicated that it is hard to get an understanding of the principles that govern the vortex trapping process, the analysis is restricted here to the flow field illustrated in the first slide. It is assumed that the flow field between the two end plates approximates a streamwise strip of the flow over a wing. The flow between the endplates and about the airfoil consists of a spanwise vortex located between the suction orifices in the endplates. The spanwise fence or spoiler located near the nose of the airfoil serves to form a separated flow region and a shear layer. The vorticity in the shear layer is concentrated into the vortex by withdrawal of fluid at the suction orifices. As the strength of the vortex increases with time, it eventually dominates the flow in the separated region so that a shear or vertical layer is no longer shed from the tip of the fence. At that point, the vortex strength is fixed and its location is such that all of the velocity contributions at its center sum to zero thereby making it an equilibrium point for the vortex. The results of a theoretical analysis of such an idealized flow field are described.

  10. Exchange and Dzyaloshinskii-Moriya interactions in bulk FeGe: Effects of atomic vacancies

    Science.gov (United States)

    Loh, G. C.; Gan, C. K.

    2017-05-01

    We examine the effects of atomic vacancies on the (1) spin interaction, and (2) electronic character in the cubic B20 chiral magnet FeGe. For the former, Heisenberg exchange and Dzyaloshinskii-Moriya (DM) interactions are studied. The latter is done via a particular Wannier flavor of the Hamiltonian in the form of maximally-localized Wannier functions (MLWFs). Using first-principles calculations based on full-potential linearized augmented plane-wave (FLAPW)-based density functional theory (DFT), the spin order of bulk FeGe, in its pristine form, and with a Fe (Fe75%Ge100%) or Ge vacancy (Fe100%Ge75%) is investigated. Despite the presence of vacancies, the ground state of FeGe remains helimagnetic, i.e. spin spirals in FeGe are fairly robust. The energetic stability of FeGe increases in the presence of the vacancies. The spiral size is increased by approximately 40%, suggesting that vacancies can be introduced to manipulate the chiral order. The vacancies lift the band degeneracy in the valence manifold of the Wannier-interpolated band structures. Only the spin-down Fermi surfaces are substantially different between the pristine and defective FeGe; it is electron-like in the pristine case, but largely hole-like in the defective ones. The Ge vacancy splits the Fermi surface more than the Fe vacancy. The Heisenberg exchange between nearest Fe pairs is ferromagnetic in pristine FeGe. This Fe-Fe interaction remains ferromagnetic, albeit a slight decrease in strength, in the presence of a Fe vacancy. In contrast, a Ge vacancy in FeGe induces anti-ferromagnetism between nearest Fe pairs. By including spin-orbit coupling effects, we find that the DM interaction of defective FeGe is reversed in sign, and it is more uniform in strength along the three highly symmetric directions, relative to that in pristine FeGe. All in all, the versatility of FeGe makes it an excellent functional material, especially in data storage and spintronics applications.

  11. Antihydrogen Formation, Dynamics and Trapping

    CERN Document Server

    Butler, Eoin; Charlton, Michael

    2011-01-01

    Antihydrogen, the simplest pure-antimatter atomic system, holds the promise of direct tests of matter-antimatter equivalence and CPT invariance, two of the outstanding unanswered questions in modern physics. Antihydrogen is now routinely produced in charged-particle traps through the combination of plasmas of antiprotons and positrons, but the atoms escape and are destroyed in a minuscule fraction of a second. The focus of this work is the production of a sample of cold antihydrogen atoms in a magnetic atom trap. This poses an extreme challenge, because the state-of-the-art atom traps are only approximately 0.5 K deep for ground-state antihydrogen atoms, much shallower than the energies of particles stored in the plasmas. This thesis will outline the main parts of the ALPHA experiment, with an overview of the important physical processes at work. Antihydrogen production techniques will be described, and an analysis of the spatial annihilation distribution to give indications of the temperature and binding ene...

  12. Nonadiabatic transitions in electrostatically trapped ammonia molecules

    International Nuclear Information System (INIS)

    Kirste, Moritz; Schnell, Melanie; Meijer, Gerard; Sartakov, Boris G.

    2009-01-01

    Nonadiabatic transitions are known to be major loss channels for atoms in magnetic traps but have thus far not been experimentally reported upon for trapped molecules. We have observed and quantified losses due to nonadiabatic transitions for three isotopologues of ammonia in electrostatic traps by comparing the trapping times in traps with a zero and a nonzero electric field at the center. Nonadiabatic transitions are seen to dominate the overall loss rate even for the present samples that are at relatively high temperatures of 30 mK. It is anticipated that losses due to nonadiabatic transitions in electric fields are omnipresent in ongoing experiments on cold molecules.

  13. Sognenavne, Albertslund Kommune (3 artikler). trap.dk

    DEFF Research Database (Denmark)

    Kællerød, Lars-Jakob Harding

    2019-01-01

    Artikler til Trap Danmarks netpublikation trap.dk Sognenavnene Herstedvester, Herstedøster og Opstandelseskirkens Sogn......Artikler til Trap Danmarks netpublikation trap.dk Sognenavnene Herstedvester, Herstedøster og Opstandelseskirkens Sogn...

  14. Cooling the Motion of Diamond Nanocrystals in a Magneto-Gravitational Trap in High Vacuum.

    Science.gov (United States)

    Hsu, Jen-Feng; Ji, Peng; Lewandowski, Charles W; D'Urso, Brian

    2016-07-22

    Levitated diamond nanocrystals with nitrogen-vacancy (NV) centres in high vacuum have been proposed as a unique system for experiments in fundamental quantum mechanics, including the generation of large quantum superposition states and tests of quantum gravity. This system promises extreme isolation from its environment while providing quantum control and sensing through the NV centre spin. While optical trapping has been the most explored method of levitation, recent results indicate that excessive optical heating of the nanodiamonds under vacuum may make the method impractical with currently available materials. Here, we study an alternative magneto-gravitational trap for diamagnetic particles, such as diamond nanocrystals, with stable levitation from atmospheric pressure to high vacuum. Magnetic field gradients from permanent magnets confine the particle in two dimensions, while confinement in the third dimension is gravitational. We demonstrate that feedback cooling of the centre-of-mass motion of a trapped nanodiamond cluster results in cooling of one degree of freedom to less than 1 K.

  15. Algae commensal community in Genlisea traps

    Directory of Open Access Journals (Sweden)

    Konrad Wołowski

    2011-01-01

    Full Text Available The community of algae occurring in Genlisea traps and on the external traps surface in laboratory conditions were studied. A total of 29 taxa were found inside the traps, with abundant diatoms, green algae (Chlamydophyceae and four morphotypes of chrysophytes stomatocysts. One morphotype is described as new for science. There are two ways of algae getting into Genlisea traps. The majority of those recorded inside the traps, are mobile; swimming freely by flagella or moving exuding mucilage like diatoms being ablate to colonize the traps themselves. Another possibility is transport of algae by invertebrates such as mites and crustaceans. In any case algae in the Genlisea traps come from the surrounding environment. Two dominant groups of algae (Chladymonas div. and diatoms in the trap environment, show ability to hydrolyze phosphomonoseters. We suggest that algae in carnivorous plant traps can compete with plant (host for organic phosphate (phosphomonoseters. From the spectrum and ecological requirements of algal species found in the traps, environment inside the traps seems to be acidic. However, further studies are needed to test the relations between algae and carnivorous plants both in laboratory conditions and in the natural environment. All the reported taxa are described briefly and documented with 74 LM and SEM micrographs.

  16. Ion traps fabricated in a CMOS foundry

    Energy Technology Data Exchange (ETDEWEB)

    Mehta, K. K.; Ram, R. J. [Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States); Eltony, A. M.; Chuang, I. L. [Center for Ultracold Atoms, Research Laboratory of Electronics and Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States); Bruzewicz, C. D.; Sage, J. M., E-mail: jsage@ll.mit.edu; Chiaverini, J., E-mail: john.chiaverini@ll.mit.edu [Lincoln Laboratory, Massachusetts Institute of Technology, Lexington, Massachusetts 02420 (United States)

    2014-07-28

    We demonstrate trapping in a surface-electrode ion trap fabricated in a 90-nm CMOS (complementary metal-oxide-semiconductor) foundry process utilizing the top metal layer of the process for the trap electrodes. The process includes doped active regions and metal interconnect layers, allowing for co-fabrication of standard CMOS circuitry as well as devices for optical control and measurement. With one of the interconnect layers defining a ground plane between the trap electrode layer and the p-type doped silicon substrate, ion loading is robust and trapping is stable. We measure a motional heating rate comparable to those seen in surface-electrode traps of similar size. This demonstration of scalable quantum computing hardware utilizing a commercial CMOS process opens the door to integration and co-fabrication of electronics and photonics for large-scale quantum processing in trapped-ion arrays.

  17. Trapping Dust to Form Planets

    Science.gov (United States)

    Kohler, Susanna

    2017-10-01

    Growing a planet from a dust grain is hard work! A new study explores how vortices in protoplanetary disks can assist this process.When Dust Growth FailsTop: ALMA image of the protoplanetary disk of V1247 Orionis, with different emission components labeled. Bottom: Synthetic image constructed from the best-fit model. [Kraus et al. 2017]Gradual accretion onto a seed particle seems like a reasonable way to grow a planet from a grain of dust; after all, planetary embryos orbit within dusty protoplanetary disks, which provides them with plenty of fuel to accrete so they can grow. Theres a challenge to this picture, though: the radial drift problem.The radial drift problem acknowledges that, as growing dust grains orbit within the disk, the drag force on them continues to grow as well. For large enough dust grains perhaps around 1 millimeter the drag force will cause the grains orbits to decay, and the particles drift into the star before they are able to grow into planetesimals and planets.A Close-Up Look with ALMASo how do we overcome the radial drift problem in order to form planets? A commonly proposed mechanism is dust trapping, in which long-lived vortices in the disk trap the dust particles, preventing them from falling inwards. This allows the particles to persist for millions of years long enough to grow beyond the radial drift barrier.Observationally, these dust-trapping vortices should have signatures: we would expect to see, at millimeter wavelengths, specific bright, asymmetric structures where the trapping occurs in protoplanetary disks. Such disk structures have been difficult to spot with past instrumentation, but the Atacama Large Millimeter/submillimeter Array (ALMA) has made some new observations of the disk V1247 Orionis that might be just what were looking for.Schematic of the authors model for the disk of V1247 Orionis. [Kraus et al. 2017]Trapped in a Vortex?ALMAs observations of V1247 Orionis are reported by a team of scientists led by Stefan

  18. Trapped

    OpenAIRE

    Storvik, Pamela

    2012-01-01

    This study explores how the Muslim Sunni Women in the city of Tripoli- Lebanon perceive the the inequity in the rights of women in terms of those of men within the Personal Status codes practiced today in the Sunni Muslim Sharīʻa Courts in the country. Lebanese women and men in general are subject to an imbalanced patronage as a result of the patriarchal conditions dominating the Lebanese society and its various communities. This project further explores the factors that have led to the failu...

  19. In-situ TEM visualization of vacancy injection and chemical partition during oxidation of Ni-Cr nanoparticles.

    Science.gov (United States)

    Wang, Chong-Min; Genc, Arda; Cheng, Huikai; Pullan, Lee; Baer, Donald R; Bruemmer, Stephen M

    2014-01-14

    Oxidation of alloy often involves chemical partition and injection of vacancies. Chemical partition is the consequence of selective oxidation, while injection of vacancies is associated with the differences of diffusivity of cations and anions. It is far from clear as how the injected vacancies behave during oxidation of metal. Using in-situ transmission electron microscopy, we captured unprecedented details on the collective behavior of injected vacancies during oxidation of metal, featuring an initial multi-site oxide nucleation, vacancy supersaturation, nucleation of a single cavity, sinking of vacancies into the cavity and accelerated oxidation of the particle. High sensitive energy dispersive x-ray spectroscopy mapping reveals that Cr is preferentially oxidized even at the initial oxidation, leading to a structure that Cr oxide is sandwiched near the inner wall of the hollow particle. The work provides a general guidance on tailoring of nanostructured materials involving multi-ion exchange such as core-shell structured composite nanoparticles.

  20. The structure and properties of vacancies in Si nano-crystals calculated by real space pseudopotential methods

    International Nuclear Information System (INIS)

    Beckman, S.P.; Chelikowsky, James R.

    2007-01-01

    The structure and properties of vacancies in a 2 nm Si nano-crystal are studied using a real space density functional theory/pseudopotential method. It is observed that a vacancy's electronic properties and energy of formation are directly related to the local symmetry of the vacancy site. The formation energy for vacancies and Frenkel pair are calculated. It is found that both defects have lower energy in smaller crystals. In a 2 nm nano-crystal the energy to form a Frenkel pair is 1.7 eV and the energy to form a vacancy is no larger than 2.3 eV. The energy barrier for vacancy diffusion is examined via a nudged elastic band algorithm

  1. Oxygen vacancy defects in Ta{sub 2}O{sub 5} showing long-range atomic re-arrangements

    Energy Technology Data Exchange (ETDEWEB)

    Guo, Yuzheng; Robertson, John [Engineering Department, Cambridge University, Cambridge CB2 1PZ (United Kingdom)

    2014-03-17

    The structure, formation energy, and energy levels of the various oxygen vacancies in Ta{sub 2}O{sub 5} have been calculated using the λ phase model. The intra-layer vacancies give rise to unusual, long-range bonding rearrangements, which are different for each defect charge state. The 2-fold coordinated intra-layer vacancy is the lowest cost vacancy and forms a deep level 1.5 eV below the conduction band edge. The 3-fold intra-layer vacancy and the 2-fold inter-layer vacancy are higher cost defects, and form shallower levels. The unusual bonding rearrangements lead to low oxygen migration barriers, which are useful for resistive random access memory applications.

  2. Theory of the temperature dependence of positron bulk lifetimes-implications for vacancy formation enthalpy measurements via positron experiments

    International Nuclear Information System (INIS)

    Tam, S.W.; Sinha, S.K.; Siegel, R.W.

    1977-02-01

    Temperature dependent effects, which may have a bearing on determinations of vacancy formation enthalpies in metals by positron annihilation, have been observed in certain metals. These effects have been observed to occur both at temperatures below those at which positron annihilation is most sensitive to equilibrium vacancies and at temperatures well within the vacancy-sensitive region. The effect of thermal lattice displacements on positron lifetimes in metals was investigated to help understand these phenomena

  3. Teaching Vacancies and Difficult-to-Staff Teaching Positions in Public Schools. Stats in Brief. NCES 2015-065

    Science.gov (United States)

    Malkus, Nat; Hoyer, Kathleen Mulvaney; Sparks, Dinah

    2015-01-01

    This brief investigates teaching vacancies and difficult-to-staff teaching positions (i.e., positions for which the principals reported that it was very difficult to fill a vacancy or that they could not fill a vacancy in a specific subject area) in public schools in four school years (1999-2000, 2003-04, 2007-08, and 2011-12). This Statistics in…

  4. Oxygen vacancies dependent phase transition of Y{sub 2}O{sub 3} films

    Energy Technology Data Exchange (ETDEWEB)

    Yu, Pengfei; Zhang, Kan [Department of Materials Science, State Key Laboratory of Superhard Materials, and Key Laboratory of Automobile Materials, MOE, Jilin University, Changchun 130012 (China); Huang, Hao [Titanium Alloys Lab. Beijing Institute of Aeronautical Materials, Beijing 81-15 100095 (China); Wen, Mao, E-mail: Wenmao225@jlu.edu.cn [Department of Materials Science, State Key Laboratory of Superhard Materials, and Key Laboratory of Automobile Materials, MOE, Jilin University, Changchun 130012 (China); Li, Quan; Zhang, Wei; Hu, Chaoquan [Department of Materials Science, State Key Laboratory of Superhard Materials, and Key Laboratory of Automobile Materials, MOE, Jilin University, Changchun 130012 (China); Zheng, Weitao, E-mail: WTZheng@jlu.edu.cn [Department of Materials Science, State Key Laboratory of Automotive Simulation and Control and Key Laboratory of Automobile Materials, MOE, Jilin University, Changchun 130012 (China)

    2017-07-15

    Highlights: • Oxygen vacancies for Y{sub 2}O{sub 3} films increase monotonously with increasing T{sub s}. • Oxygen vacancies can promote the nucleation of monoclinic phase. • That monoclinic phase with oxygen deficiency is not thermodynamic stable at high temperature. • Phase transition from monoclinic to oxygen defective occurs at high concentrations of oxygen vacancies. • High hardness just appears in Y{sub 2}O{sub 3} films with mixed phase configurations. - Abstract: Y{sub 2}O{sub 3} films have great application potential in high-temperature metal matrix composite and nuclear engineering, used as interface diffusion and reaction barrier coating owing to their excellent thermal and chemical stability, high melting point and extremely negative Gibbs formation energy, and thus their structural and mechanical properties at elevated temperature are especially important. Oxygen vacancies exist commonly in yttrium oxide (Y{sub 2}O{sub 3}) thin films and act strongly on the phase structure and properties, but oxygen vacancies dependent phase transition at elevated temperature has not been well explored yet. Y{sub 2}O{sub 3} thin films with different oxygen vacancy concentrations have been achieved by reactive sputtering through varying substrate temperature (T{sub s}), in which oxygen vacancies increase monotonously with increasing T{sub s}. For as-deposited Y{sub 2}O{sub 3} films, oxygen vacancies present at high T{sub s} can promote the nucleation of monoclinic phase, meanwhile, high T{sub s} can induce the instability of monoclinic phase. Thus their competition results in forming mixed phases of cubic and monoclinic at high T{sub s}. During vacuum annealing at 1000 °C, a critical oxygen vacancy concentration is observed, below which phase transition from monoclinic to cubic takes place, and above which phase transfer from monoclinic to the oxygen defective phase (ICDD file no. 39-1063), accompanying by stress reversal from compressive to tensile and

  5. Formation and Migration of Oxygen Vacancies in SrCoO3 and their effect on Oxygen Evolution Reactions

    KAUST Repository

    Tahini, Hassan A.

    2016-07-18

    Perovskite SrCoO3 is a potentially useful material for promoting the electrocatalytic oxygen evolution reaction, with high activities predicted theoretically and observed experimentally for closely related doped perovskite materials. However, complete stoichiometric oxidation is very difficult to realize experimentally – in almost all cases there are significant fractions of oxygen vacancies present. Here, using first principles calculations we study oxygen vacancies in perovskite SrCoO3 from thermodynamic, electronic and kinetic points of view. We find that an oxygen vacancy donates two electrons to neighboring Co sites in the form of localized charge. The formation energy of a single vacancy is very low and estimated to be 1.26 eV in the dilute limit. We find that a vacancy is quite mobile with a migration energy of ~0.5 eV. Moreover, we predict that oxygen vacancies exhibit a tendency towards clustering which is in accordance with the material’s ability to form a variety of oxygen-deficient structures. These vacancies have a profound effect on the material’s ability to facilitate OER, increasing the overpotential from ~0.3 V for the perfect material to ~0.7 for defective surfaces. A moderate compressive biaxial strain (2%) is predicted here to increase the surface oxygen vacancy formation energy by ca. 30%, thus reducing the concentration of surface vacancies and thereby preserving the OER activity of the material.

  6. Formation and Migration of Oxygen Vacancies in SrCoO3 and their effect on Oxygen Evolution Reactions

    KAUST Repository

    Tahini, Hassan A.; Tan, Xin; Schwingenschlö gl, Udo; Smith, Sean C.

    2016-01-01

    Perovskite SrCoO3 is a potentially useful material for promoting the electrocatalytic oxygen evolution reaction, with high activities predicted theoretically and observed experimentally for closely related doped perovskite materials. However, complete stoichiometric oxidation is very difficult to realize experimentally – in almost all cases there are significant fractions of oxygen vacancies present. Here, using first principles calculations we study oxygen vacancies in perovskite SrCoO3 from thermodynamic, electronic and kinetic points of view. We find that an oxygen vacancy donates two electrons to neighboring Co sites in the form of localized charge. The formation energy of a single vacancy is very low and estimated to be 1.26 eV in the dilute limit. We find that a vacancy is quite mobile with a migration energy of ~0.5 eV. Moreover, we predict that oxygen vacancies exhibit a tendency towards clustering which is in accordance with the material’s ability to form a variety of oxygen-deficient structures. These vacancies have a profound effect on the material’s ability to facilitate OER, increasing the overpotential from ~0.3 V for the perfect material to ~0.7 for defective surfaces. A moderate compressive biaxial strain (2%) is predicted here to increase the surface oxygen vacancy formation energy by ca. 30%, thus reducing the concentration of surface vacancies and thereby preserving the OER activity of the material.

  7. Status and outlook of CHIP-TRAP: The Central Michigan University high precision Penning trap

    Science.gov (United States)

    Redshaw, M.; Bryce, R. A.; Hawks, P.; Gamage, N. D.; Hunt, C.; Kandegedara, R. M. E. B.; Ratnayake, I. S.; Sharp, L.

    2016-06-01

    At Central Michigan University we are developing a high-precision Penning trap mass spectrometer (CHIP-TRAP) that will focus on measurements with long-lived radioactive isotopes. CHIP-TRAP will consist of a pair of hyperbolic precision-measurement Penning traps, and a cylindrical capture/filter trap in a 12 T magnetic field. Ions will be produced by external ion sources, including a laser ablation source, and transported to the capture trap at low energies enabling ions of a given m / q ratio to be selected via their time-of-flight. In the capture trap, contaminant ions will be removed with a mass-selective rf dipole excitation and the ion of interest will be transported to the measurement traps. A phase-sensitive image charge detection technique will be used for simultaneous cyclotron frequency measurements on single ions in the two precision traps, resulting in a reduction in statistical uncertainty due to magnetic field fluctuations.

  8. Discriminating between antihydrogen and mirror-trapped antiprotons in a minimum-B trap

    CERN Document Server

    Amole, C; Ashkezari, M D; Baquero-Ruiz, M; Bertsche, W; Butler, E; Cesar, C L; Chapman, S; Charlton, M; Deller, A; Eriksson, S; Fajans, J; Friesen, T; Fujiwara, M C; Gill, D R; Gutierrez, A; Hangst, J S; Hardy, W N; Hayden, M E; Humphries, A J; Hydomako, R; Kurchaninov, L; Jonsell, S; Madsen, N; Menary, S; Nolan, P; Olchanski, K; Olin, A; Povilus, A; Pusa, P; Robicheaux, F; Sarid, E; Silveira, D M; So, C; Storey, J W; Thompson, R I; van der Werf, D P; Wurtele, J S

    2012-01-01

    Recently, antihydrogen atoms were trapped at CERN in a magnetic minimum (minimum-B) trap formed by superconducting octupole and mirror magnet coils. The trapped antiatoms were detected by rapidly turning off these magnets, thereby eliminating the magnetic minimum and releasing any antiatoms contained in the trap. Once released, these antiatoms quickly hit the trap wall, whereupon the positrons and antiprotons in the antiatoms annihilated. The antiproton annihilations produce easily detected signals; we used these signals to prove that we trapped antihydrogen. However, our technique could be confounded by mirror-trapped antiprotons, which would produce seemingly-identical annihilation signals upon hitting the trap wall. In this paper, we discuss possible sources of mirror-trapped antiprotons and show that antihydrogen and antiprotons can be readily distinguished, often with the aid of applied electric fields, by analyzing the annihilation locations and times. We further discuss the general properties of antipr...

  9. Anisotropic chemical strain in cubic ceria due to oxygen-vacancy-induced elastic dipoles.

    Science.gov (United States)

    Das, Tridip; Nicholas, Jason D; Sheldon, Brian W; Qi, Yue

    2018-06-06

    Accurate characterization of chemical strain is required to study a broad range of chemical-mechanical coupling phenomena. One of the most studied mechano-chemically active oxides, nonstoichiometric ceria (CeO2-δ), has only been described by a scalar chemical strain assuming isotropic deformation. However, combined density functional theory (DFT) calculations and elastic dipole tensor theory reveal that both the short-range bond distortions surrounding an oxygen-vacancy and the long-range chemical strain are anisotropic in cubic CeO2-δ. The origin of this anisotropy is the charge disproportionation between the four cerium atoms around each oxygen-vacancy (two become Ce3+ and two become Ce4+) when a neutral oxygen-vacancy is formed. Around the oxygen-vacancy, six of the Ce3+-O bonds elongate, one of the Ce3+-O bond shorten, and all seven of the Ce4+-O bonds shorten. Further, the average and maximum chemical strain values obtained through tensor analysis successfully bound the various experimental data. Lastly, the anisotropic, oxygen-vacancy-elastic-dipole induced chemical strain is polarizable, which provides a physical model for the giant electrostriction recently discovered in doped and non-doped CeO2-δ. Together, this work highlights the need to consider anisotropic tensors when calculating the chemical strain induced by dilute point defects in all materials, regardless of their symmetry.

  10. Significant room-temperature ferromagnetism in porous ZnO films: The role of oxygen vacancies

    Energy Technology Data Exchange (ETDEWEB)

    Hou, Xue; Liu, Huiyuan [College of Physics Science & Information Engineering, Hebei Normal University, Shijiazhuang 050024 (China); Key Laboratory of Advanced Films of Hebei Province, Shijiazhuang 050024 (China); Sun, Huiyuan, E-mail: huiyuansun@126.com [College of Physics Science & Information Engineering, Hebei Normal University, Shijiazhuang 050024 (China); Key Laboratory of Advanced Films of Hebei Province, Shijiazhuang 050024 (China); Liu, Lihu; Jia, Xiaoxuan [College of Physics Science & Information Engineering, Hebei Normal University, Shijiazhuang 050024 (China); Key Laboratory of Advanced Films of Hebei Province, Shijiazhuang 050024 (China)

    2015-10-15

    Graphical abstract: - Highlights: • Porous ZnO films were deposited on porous anodic alumina substrates. • Significant ferromagnetism (FM) has been observed in porous ZnO films (110 emu/cm{sup 3}). • The strong magnetic anisotropy was observed in the porous ZnO films. • The origin of FM is attributed to the oxygen vacancy with a local magnetic moment. - Abstract: Pure porous ZnO films were prepared by direct current reactive magnetron sputtering on porous anodic alumina substrates. Remarkably large room-temperature ferromagnetism was observed in the films. The highest saturation moment along the out-of-plane direction was about 110 emu/cm{sup 3}. Experimental and theoretical results suggested that the oxygen vacancies and the unique porous structure of the films are responsible for the large ferromagnetism. There are two modes of coupling between oxygen vacancies in the porous ZnO films: (i) exchange interactions directly between the oxygen vacancies and (ii) with the mediation of conduction electrons. In addition, it was found that the magnetic moment of ZnO films can be changed by tuning the concentration of oxygen vacancies. These observations may be useful in the development of ZnO-based spintronics devices.

  11. Magnetic properties of ZnO nanowires with Li dopants and Zn vacancies

    Energy Technology Data Exchange (ETDEWEB)

    Guan, Xinhong; Cai, Ningning [Key Laboratory of Information Photonics and Optical Communications (Beijing University of Posts and Telecommunications), Ministry of Education, P.O. Box 72, Beijing 100876 (China); Yang, Chuanghua [School of Physics and Telecommunication Engineering, Shanxi University of Technology (SNUT), Hanzhong 723001, Shanxi (China); Chen, Jun [Beijing Applied Physics and Computational Mathematics, Beijing 100088 (China); Lu, Pengfei, E-mail: photon.bupt@gmail.com [Key Laboratory of Information Photonics and Optical Communications (Beijing University of Posts and Telecommunications), Ministry of Education, P.O. Box 72, Beijing 100876 (China)

    2016-04-30

    The electronic and magnetic properties of ZnO nanowire with Li dopants and vacancies have been investigated using first-principles density functional theory. It is found that the Zn vacancy can induce magnetism while increasing the formation energy of the system. However, the calculated results indicate that the introduction of Li-dopants will reduce the formation energy of system. We also have studied the magnetic couplings with vacancies as well as their corresponding configurations with Li-dopants for four configurations of ZnO nanowires. The results show that ferromagnetic properties can be improved/reversed after the introduction of Li-dopants. Ferromagnetic mechanism is originated from the fierce p–p hybridization of O near the Fermi level. We find that ferromagnetism of Li-doped ZnO nanowires with Zn vacancies can be realized at room temperature and they are promising spintronic materials. - Highlights: • Li-dopants will reduce the formation energy of ZnO nanowires with Zn vacancy. • The fierce p–p hybridization of O near Fermi level is responsible for FM properties. • Li-doped ZnO–V{sub Zn} nanowire is a promising FM semiconductor material.

  12. On the role of Mn(IV) vacancies in the photoreductive dissolution of hexagonal birnessite

    Energy Technology Data Exchange (ETDEWEB)

    Kwon, K.D.; Refson, K.; Sposito, G.

    2009-06-01

    Photoreductive dissolution of layer type Mn(IV) oxides (birnessite) under sunlight illumination to form soluble Mn(II) has been observed in both field and laboratory settings, leading to a consensus that this process is a key driver of the biogeochemical cycling of Mn in the euphotic zones of marine and freshwater ecosystems. However, the underlying mechanisms for the process remain unknown, although they have been linked to the semiconducting characteristics of hexagonal birnessite, the ubiquitous Mn(IV) oxide produced mainly by bacterial oxidation of soluble Mn(II). One of the universal properties of this biogenic mineral is the presence of Mn(IV) vacancies, long-identified as strong adsorption sites for metal cations. In this paper, the possible role of Mn vacancies in photoreductive dissolution is investigated theoretically using quantum mechanical calculations based on spin-polarized density functional theory (DFT). Our DFT study demonstrates unequivocally that Mn vacancies significantly reduce the band-gap energy for hexagonal birnessite relative to a hypothetical vacancy-free MnO{sub 2} and thus would increase the concentration of photo-induced electrons available for Mn(IV) reduction upon illumination of the mineral by sunlight. Calculations of the charge distribution in the presence of vacancies, although not fully conclusive, show a clear separation of photo-induced electrons and holes, implying a slow recombination of these charge-carriers that facilitates the two-electron reduction of Mn(IV) to Mn(II).

  13. A bond-order theory on the phonon scattering by vacancies in two-dimensional materials.

    Science.gov (United States)

    Xie, Guofeng; Shen, Yulu; Wei, Xiaolin; Yang, Liwen; Xiao, Huaping; Zhong, Jianxin; Zhang, Gang

    2014-05-28

    We theoretically investigate the phonon scattering by vacancies, including the impacts of missing mass and linkages (τ(V)(-1)) and the variation of the force constant of bonds associated with vacancies (τ(A)(-1)) by the bond-order-length-strength correlation mechanism. We find that in bulk crystals, the phonon scattering rate due to change of force constant τ(A)(-1) is about three orders of magnitude lower than that due to missing mass and linkages τ(V)(-1). In contrast to the negligible τ(A)(-1) in bulk materials, τ(A)(-1) in two-dimensional materials can be 3-10 folds larger than τ(V)(-1). Incorporating this phonon scattering mechanism to the Boltzmann transport equation derives that the thermal conductivity of vacancy defective graphene is severely reduced even for very low vacancy density. High-frequency phonon contribution to thermal conductivity reduces substantially. Our findings are helpful not only to understand the severe suppression of thermal conductivity by vacancies, but also to manipulate thermal conductivity in two-dimensional materials by phononic engineering.

  14. Effect of random vacancies on the electronic properties of graphene and T graphene: a theoretical approach

    Science.gov (United States)

    Sadhukhan, B.; Nayak, A.; Mookerjee, A.

    2017-12-01

    In this communication we present together four distinct techniques for the study of electronic structure of solids: the tight-binding linear muffin-tin orbitals, the real space and augmented space recursions and the modified exchange-correlation. Using this we investigate the effect of random vacancies on the electronic properties of the carbon hexagonal allotrope, graphene, and the non-hexagonal allotrope, planar T graphene. We have inserted random vacancies at different concentrations, to simulate disorder in pristine graphene and planar T graphene sheets. The resulting disorder, both on-site (diagonal disorder) as well as in the hopping integrals (off-diagonal disorder), introduces sharp peaks in the vicinity of the Dirac point built up from localized states for both hexagonal and non-hexagonal structures. These peaks become resonances with increasing vacancy concentration. We find that in presence of vacancies, graphene-like linear dispersion appears in planar T graphene and the cross points form a loop in the first Brillouin zone similar to buckled T graphene that originates from π and π* bands without regular hexagonal symmetry. We also calculate the single-particle relaxation time, τ (ěc {q}) of ěc {q} labeled quantum electronic states which originates from scattering due to presence of vacancies, causing quantum level broadening.

  15. Vacancy profile in reverse osmosis membranes studied by positron annihilation lifetime measurements and molecular dynamics simulations

    International Nuclear Information System (INIS)

    Shimazu, A; Shintani, T; Hirose, M; Goto, H; Suzuki, R; Kobayashi, Y

    2013-01-01

    The positron annihilation technique using a slow positron beam can be used for the study of the vacancy profiles in typical reverse osmosis (RO) membranes. In this study, the vacancy profile in the polyamide membrane that exhibits a high permselectivity between ions and water was studied using the positron annihilation technique and molecular dynamics simulations. Ortho-positronium (o-Ps) lifetimes in the surface region of the membranes were evaluated by using a slow positron beam. The diffusion behavior of Na + and water in the polyamides was simulated by molecular dynamics (MD) methods using the TSUBAME2 supercomputer at the Tokyo Institute of Technology and discussed with the vacancy profile probed by the o-Ps. The results suggested that the large hydration size of Na + compared to the vacancy size in the polyamides contributes to the increased diffusivity selectivity of water/Na + that is related to the NaCl desalination performance of the membrane. Both the hydration size of the ions and the vacancy size appeared to be significant parameters to discuss the diffusivity selectivity of water/ions in typical polyamide membranes.

  16. Portable Pbars, traps that travel

    International Nuclear Information System (INIS)

    Howe, S.D.; Hynes, M.V.; Picklesimer, A.

    1987-10-01

    The advent of antiproton research utilizing relatively small scale storage devices for very large numbers of these particles opens the possibility of transporting these devices to a research site removed from the accelerator center that produced the antiprotons. Such a portable source of antiprotons could open many new areas of research and make antiprotons available to a new research community. At present antiprotons are available at energies down to 1 MeV. From a portable source these particles can be made available at energies ranging from several tens of kilovolts down to a few millielectron volts. These low energies are in the domain of interest to the atomic and condensed matter physicist. In addition such a source can be used as an injector for an accelerator which could increase the energy domain even further. Moreover, the availability of such a source at a university will open research with antiprotons to a broader range of students than possible at a centralized research facility. This report focuses on the use of ion traps, in particular cylindrical traps, for the antiproton storage device. These devices store the charged antiprotons in a combination of electric and magnet fields. At high enough density and low enough temperature the charged cloud will be susceptible to plasma instabilities. Present day ion trap work is just starting to explore this domain. Our assessment of feasibility is based on what could be done with present day technology and what future technology could achieve. We conclude our report with a radiation safety study that shows that about 10 11 antiprotons can be transported safely, however the federal guidelines for this transport must be reviewed in detail. More antiprotons than this will require special transportation arrangements. 28 refs., 8 figs

  17. Trapping molecules in two and three dimensions

    International Nuclear Information System (INIS)

    Pinkse, PW.H.; Junglen, T.; Rieger, T.; Rangwala, S.A.; Windpassinger, P.; Rempe, G.

    2005-01-01

    Full text: Cold molecules offer a new testing ground for quantum-physical effects in nature. For example, producing slow beams of large molecules could push experiments studying the boundary between quantum interference and classical particles up towards ever heavier particles. Moreover, cold molecules, in particular YbF, seem an attractive way to narrow down the constraints on the value of the electron dipole moment and finally, quantum information processing using chains of cold polar molecules or vibrational states in molecules have been proposed. All these proposals rely on advanced production and trapping techniques, most of which are still under development. Therefore, novel production and trapping techniques for cold molecules could offer new possibilities not found in previous methods. Electric traps hold promise for deep trap potentials for neutral molecules. Recently we have demonstrated two-dimensional trapping of polar molecules in a four-wire guide using electrostatic and electrodynamic trapping techniques. Filled from a thermal effusive source, such a guide will deliver a beam of slow molecules, which is an ideal source for interferometry experiments with large molecules, for instance. Here we report about the extension of this work to three-dimensional trapping. Polar molecules with a positive Stark shift can be trapped in the minimum of an electrostatic field. We have successfully tested a large volume electrostatic trap for ND3 molecules. A special feature of this trap is that it can be loaded continuously from an electrostatic guide, at a temperature of a few hundred mK. (author)

  18. Introduced species as evolutionary traps

    Science.gov (United States)

    Schlaepfer, Martin A.; Sherman, P.W.; Blossey, B.; Runge, M.C.

    2005-01-01

    Invasive species can alter environments in such a way that normal behavioural decision-making rules of native species are no longer adaptive. The evolutionary trap concept provides a useful framework for predicting and managing the impact of harmful invasive species. We discuss how native species can respond to changes in their selective regime via evolution or learning. We also propose novel management strategies to promote the long-term co-existence of native and introduced species in cases where the eradication of the latter is either economically or biologically unrealistic.

  19. Gyrotactic trapping: A numerical study

    Science.gov (United States)

    Ghorai, S.

    2016-04-01

    Gyrotactic trapping is a mechanism proposed by Durham et al. ["Disruption of vertical motility by shear triggers formation of thin Phytoplankton layers," Science 323, 1067-1070 (2009)] to explain the formation of thin phytoplankton layer just below the ocean surface. This mechanism is examined numerically using a rational model based on the generalized Taylor dispersion theory. The crucial role of sedimentation speed in the thin layer formation is demonstrated. The effects of variation in different parameters on the thin layer formation are also investigated.

  20. Telomerase Repeated Amplification Protocol (TRAP).

    Science.gov (United States)

    Mender, Ilgen; Shay, Jerry W

    2015-11-20

    Telomeres are found at the end of eukaryotic linear chromosomes, and proteins that bind to telomeres protect DNA from being recognized as double-strand breaks thus preventing end-to-end fusions (Griffith et al. , 1999). However, due to the end replication problem and other factors such as oxidative damage, the limited life span of cultured cells (Hayflick limit) results in progressive shortening of these protective structures (Hayflick and Moorhead, 1961; Olovnikov, 1973). The ribonucleoprotein enzyme complex telomerase-consisting of a protein catalytic component hTERT and a functional RNA component hTR or hTERC - counteracts telomere shortening by adding telomeric repeats to the end of chromosomes in ~90% of primary human tumors and in some transiently proliferating stem-like cells (Shay and Wright, 1996; Shay and Wright, 2001). This results in continuous proliferation of cells which is a hallmark of cancer. Therefore, telomere biology has a central role in aging, cancer progression/metastasis as well as targeted cancer therapies. There are commonly used methods in telomere biology such as Telomere Restriction Fragment (TRF) (Mender and Shay, 2015b), Telomere Repeat Amplification Protocol (TRAP) and Telomere dysfunction Induced Foci (TIF) analysis (Mender and Shay, 2015a). In this detailed protocol we describe Telomere Repeat Amplification Protocol (TRAP). The TRAP assay is a popular method to determine telomerase activity in mammalian cells and tissue samples (Kim et al. , 1994). The TRAP assay includes three steps: extension, amplification, and detection of telomerase products. In the extension step, telomeric repeats are added to the telomerase substrate (which is actually a non telomeric oligonucleotide, TS) by telomerase. In the amplification step, the extension products are amplified by the polymerase chain reaction (PCR) using specific primers (TS upstream primer and ACX downstream primer) and in the detection step, the presence or absence of telomerase is

  1. Bose condensation in (random traps

    Directory of Open Access Journals (Sweden)

    V.A. Zagrebnov

    2009-01-01

    Full Text Available We study a non-interacting (perfect Bose-gas in random external potentials (traps. It is shown that a generalized Bose-Einstein condensation in the random eigenstates manifests if and only if the same occurs in the one-particle kinetic-energy eigenstates, which corresponds to the generalized condensation of the free Bose-gas. Moreover, we prove that the amounts of both condensate densities are equal. This statement is relevant for justification of the Bogoliubov approximation} in the theory of disordered boson systems.

  2. A coupled model of transport-reaction-mechanics with trapping. Part I - Small strain analysis

    Science.gov (United States)

    Salvadori, A.; McMeeking, R.; Grazioli, D.; Magri, M.

    2018-05-01

    A fully coupled model for mass and heat transport, mechanics, and chemical reactions with trapping is proposed. It is rooted in non-equilibrium rational thermodynamics and assumes that displacements and strains are small. Balance laws for mass, linear and angular momentum, energy, and entropy are stated. Thermodynamic restrictions are identified, based on an additive strain decomposition and on the definition of the Helmholtz free energy. Constitutive theory and chemical kinetics are studied in order to finally write the governing equations for the multi-physics problem. The field equations are solved numerically with the finite element method, stemming from a three-fields variational formulation. Three case-studies on vacancies redistribution in metals, hydrogen embrittlement, and the charge-discharge of active particles in Li-ion batteries demonstrate the features and the potential of the proposed model.

  3. Understanding the ionic conductivity maximum in doped ceria: trapping and blocking.

    Science.gov (United States)

    Koettgen, Julius; Grieshammer, Steffen; Hein, Philipp; Grope, Benjamin O H; Nakayama, Masanobu; Martin, Manfred

    2018-02-26

    Materials with high oxygen ion conductivity and low electronic conductivity are required for electrolytes in solid oxide fuel cells (SOFC) and high-temperature electrolysis (SOEC). A potential candidate for the electrolytes, which separate oxidation and reduction processes, is rare-earth doped ceria. The prediction of the ionic conductivity of the electrolytes and a better understanding of the underlying atomistic mechanisms provide an important contribution to the future of sustainable and efficient energy conversion and storage. The central aim of this paper is the detailed investigation of the relationship between defect interactions at the microscopic level and the macroscopic oxygen ion conductivity in the bulk of doped ceria. By combining ab initio density functional theory (DFT) with Kinetic Monte Carlo (KMC) simulations, the oxygen ion conductivity is predicted as a function of the doping concentration. Migration barriers are analyzed for energy contributions, which are caused by the interactions of dopants and vacancies with the migrating oxygen vacancy. We clearly distinguish between energy contributions that are either uniform for forward and backward jumps or favor one migration direction over the reverse direction. If the presence of a dopant changes the migration energy identically for forward and backward jumps, the resulting energy contribution is referred to as blocking. If the change in migration energy due to doping is different for forward and backward jumps of a specific ionic configuration, the resulting energy contributions are referred to as trapping. The influence of both effects on the ionic conductivity is analyzed: blocking determines the dopant fraction where the ionic conductivity exhibits the maximum. Trapping limits the maximum ionic conductivity value. In this way, a deeper understanding of the underlying mechanisms determining the influence of dopants on the ionic conductivity is obtained and the ionic conductivity is predicted

  4. Progress at THe-trap

    Energy Technology Data Exchange (ETDEWEB)

    Hoecker, Martin; Eronen, Tommi; Ketter, Jochen; Schuh, Marc; Streubel, Sebastian; Blaum, Klaus [Max-Planck-Institut fuer Kernphysik, Heidelberg (Germany); Van Dyck, Robert S. Jr. [Department of Physics, University of Washington, Seattle, WA 98195-1560 (United States)

    2014-07-01

    THe-Trap is a Penning-trap mass spectrometry experiment that is currently being set up to measure the atomic mass ratio of tritium and helium-3 with a relative uncertainty of 10{sup -11}. In 2013, the experiment's first high-precision mass ratio measurement was performed on the ions {sup 12}C{sup 4+} and {sup 16}O{sup 5+}. The carbon-12/oxygen-16 mass ratio is one of the most precisely determined mass ratios and serves as a benchmark for the experiment. This measurement reached a statistical uncertainty of 6.3 . 10{sup -11} and was limited by systematic frequency shifts due to too high motional amplitudes. In the following service cycle, the experiment was modified to address the shortcomings that were discovered in the 2013 ratio measurements. This talk summarizes the results of the 2013 measurements and introduces the upgrades to the experiment, including a new amplifier, a modified ion source, and an improved vacuum system.

  5. Dynamic array of dark optical traps

    DEFF Research Database (Denmark)

    Daria, V.R.; Rodrigo, P.J.; Glückstad, J.

    2004-01-01

    A dynamic array of dark optical traps is generated for simultaneous trapping and arbitrary manipulation of multiple low-index microstructures. The dynamic intensity patterns forming the dark optical trap arrays are generated using a nearly loss-less phase-to-intensity conversion of a phase......-encoded coherent light source. Two-dimensional input phase distributions corresponding to the trapping patterns are encoded using a computer-programmable spatial light modulator, enabling each trap to be shaped and moved arbitrarily within the plane of observation. We demonstrate the generation of multiple dark...... optical traps for simultaneous manipulation of hollow "air-filled" glass microspheres suspended in an aqueous medium. (C) 2004 American Institute of Physics....

  6. High temperature thermoelectric properties of strontium titanate thin films with oxygen vacancy and niobium doping

    KAUST Repository

    Sarath Kumar, S. R.

    2013-08-14

    We report the evolution of high temperature thermoelectric properties of SrTiO3 thin films doped with Nb and oxygen vacancies. Structure-property relations in this important thermoelectric oxide are elucidated and the variation of transport properties with dopant concentrations is discussed. Oxygen vacancies are incorporated during growth or annealing in Ar/H2 above 800 K. An increase in lattice constant due to the inclusion of Nb and oxygen vacancies is found to result in an increase in carrier density and electrical conductivity with simultaneous decrease in carrier effective mass and Seebeck coefficient. The lattice thermal conductivity at 300 K is found to be 2.22 W m-1 K-1, and the estimated figure of merit is 0.29 at 1000 K. © 2013 American Chemical Society.

  7. Experimental identification of nitrogen-vacancy complexes in nitrogen implanted silicon

    Science.gov (United States)

    Adam, Lahir Shaik; Law, Mark E.; Szpala, Stanislaw; Simpson, P. J.; Lawther, Derek; Dokumaci, Omer; Hegde, Suri

    2001-07-01

    Nitrogen implantation is commonly used in multigate oxide thickness processing for mixed signal complementary metal-oxide-semiconductor and System on a Chip technologies. Current experiments and diffusion models indicate that upon annealing, implanted nitrogen diffuses towards the surface. The mechanism proposed for nitrogen diffusion is the formation of nitrogen-vacancy complexes in silicon, as indicated by ab initio studies by J. S. Nelson, P. A. Schultz, and A. F. Wright [Appl. Phys. Lett. 73, 247 (1998)]. However, to date, there does not exist any experimental evidence of nitrogen-vacancy formation in silicon. This letter provides experimental evidence through positron annihilation spectroscopy that nitrogen-vacancy complexes indeed form in nitrogen implanted silicon, and compares the experimental results to the ab initio studies, providing qualitative support for the same.

  8. Formation of vacancies in thermal equilibrium in α-range alloys

    International Nuclear Information System (INIS)

    Hehenkamp, Th.

    1982-01-01

    A model for aggregates (complexes) between vacancies and one or more impurity atoms is described for nearest neighbor interactions. Binding enthalpies in the different complexes have been unambigeously derived therefrom employing a variety of experimental techniques for the determination of vacancy concentrations as function of composition and temperature, (resistivity, positron annihilation, calorimetry, dl/l - da/a techniques), for some noble metals alloys. Solvent diffusion in these alloys has been found to be essentially governed by the increase of vacancy concentrations as function of these variables. Approximation for changes in the migration and correlation permits one to obtain the different binding enthalpies from measurements of solvent diffusion enhancement in an independent fashion and gives comparable results to the former techniques. (author)

  9. Reducing RN Vacancy Rate: A Nursing Recruitment Office Process Improvement Project.

    Science.gov (United States)

    Hisgen, Stephanie A; Page, Nancy E; Thornlow, Deirdre K; Merwin, Elizabeth I

    2018-06-01

    The aim of this study was to reduce the RN vacancy rate at an academic medical center by improving the hiring process in the Nursing Recruitment Office. Inability to fill RN positions can lead to higher vacancy rates and negatively impact staff and patient satisfaction, quality outcomes, and the organization's bottom line. The Model for Improvement was used to design and implement a process improvement project to improve the hiring process from time of interview through the position being filled. Number of days to interview and check references decreased significantly, but no change in overall time to hire and time to fill positions was noted. RN vacancy rate also decreased significantly. Nurse manager satisfaction with the hiring process increased significantly. Redesigning the recruitment process supported operational efficiencies of the organization related to RN recruitment.

  10. Defect production and formation of helium-vacancy clusters due to cascades in α-iron

    International Nuclear Information System (INIS)

    Yang, L.; Zu, X.T.; Xiao, H.Y.; Gao, F.; Heinisch, H.L.; Kurtz, R.J.

    2007-01-01

    Displacement cascades are simulated by molecular dynamics methods in α-Fe containing different concentrations of substitutional He atoms. Primary knock-on atom (PKA) energies, E p , from 0.5 to 5 keV are considered at the irradiation temperature of 100 K. The concentration of He in Fe varies from 1 to 5 at%, and the results are compared with the simulations performed in pure α-Fe. We find that the total number of point defects increases with increasing He concentration. The present studies reveal the formation and the configurations of He-vacancy clusters in the cascades of α-Fe. Furthermore, the production efficiency of He-vacancy clusters increases with increasing He concentration and PKA energy. The nucleation mechanisms of He-vacancy clusters in displacement cascades are discussed in detail

  11. High temperature thermoelectric properties of strontium titanate thin films with oxygen vacancy and niobium doping

    KAUST Repository

    Sarath Kumar, S. R.; Barasheed, Abeer Z.; Alshareef, Husam N.

    2013-01-01

    We report the evolution of high temperature thermoelectric properties of SrTiO3 thin films doped with Nb and oxygen vacancies. Structure-property relations in this important thermoelectric oxide are elucidated and the variation of transport properties with dopant concentrations is discussed. Oxygen vacancies are incorporated during growth or annealing in Ar/H2 above 800 K. An increase in lattice constant due to the inclusion of Nb and oxygen vacancies is found to result in an increase in carrier density and electrical conductivity with simultaneous decrease in carrier effective mass and Seebeck coefficient. The lattice thermal conductivity at 300 K is found to be 2.22 W m-1 K-1, and the estimated figure of merit is 0.29 at 1000 K. © 2013 American Chemical Society.

  12. Detection of the ODMR signal of a nitrogen vacancy centre in nanodiamond in propagating surface plasmons

    Science.gov (United States)

    Al-Baiaty, Zahraa; Cumming, Benjamin P.; Gan, Xiaosong; Gu, Min

    2018-02-01

    We demonstrate that the optically detected magnetic resonance (ODMR) signal of a nitrogen vacancy (NV) centre can be coupled to propagating surface plasmons for the detection of the NV centre spin states, and of external magnetic fields. By coupling the spin dependent luminescence signal of a NV centre in a nanodiamond (ND) to a chemically synthesized silver nanowire, we demonstrate the readout of the ODMR signal as a reduction in the surface plasmon polariton intensity, with improved contrast in comparison to the emission from the NV centre. Furthermore, on the application of a permanent magnetic field from zero to 13 G, we demonstrate that the Zeeman splitting of the magnetic spin states of the nitrogen vacancy centre ground states can also be detected in the coupled surface plasmons. This is an important step in the development of a compact on-chip information processing system utilizing the nitrogen vacancy in nanodiamond as an on-chip source with efficient magnetometry sensing properties.

  13. On the conditions required for vacancy loop growth in irradiated metals and alloys

    International Nuclear Information System (INIS)

    Hayns, M.R.

    1980-07-01

    A simple theoretical model is investigated which allows the conditions under which vacancy dislocation loop growth is possible to be examined. This forms an extension of previous work in that bulk defect recombination is not ignored and the effects of vacancy thermal emission are included. Whilst the present work does not provide a kinetic model for vacancy loop growth it has been possible to examine the criteria required for stable growth in some detail. The effects of network dislocation density, temperature, damage rate, the influence of other critical sinks, notably voids and grain boundaries, and interstitial dislocation loops have been considered. The analogy with the growth conditions for cavities as voids is highlighted. A detailed comparison with experiment is not attempted as this is being considered separately. (author)

  14. Démocratie et vacances, éléments de débat

    Directory of Open Access Journals (Sweden)

    Christophe Terrier

    2002-04-01

    Full Text Available Et si la démocratie avait achoppé sur les vacances ? ou plutôt sur la non-prise en compte des vacances par le politique ? Il y a quelques mois, quand les professionnels du tourisme, inquiets de l'impact négatif prévisible pour leurs entreprises de la coïncidence éventuelle des dates d'élection avec les vacances scolaires, pressaient le gouvernement de questions sur la fixation de ces dates, ils s'étaient entendu répondre –avec suffisance ?- que les dates d'élection n'étaient pas la préoccupa...

  15. Group-III vacancy induced InxGa1-xAs quantum dot interdiffusion

    International Nuclear Information System (INIS)

    Djie, H. S.; Wang, D.-N.; Ooi, B. S.; Hwang, J. C. M.; Gunawan, O.

    2006-01-01

    The impact of group-III vacancy diffusion, generated during dielectric cap induced intermixing, on the energy state transition and the inhomogeneity reduction in the InGaAs/GaAs quantum-dot structure is investigated. We use a three-dimensional quantum-dot diffusion model and photoluminescence data to determine the thermal and the interdiffusion properties of the quantum dot. The band gap energy variation related to the dot uniformity is found to be dominantly affected by the height fluctuation. A group-III vacancies migration energy H m for InGaAs quantum dots of 1.7 eV was deduced. This result is similar to the value obtained from the bulk and GaAs/AlGaAs quantum-well materials confirming the role of SiO 2 capping enhanced group-III vacancy induced interdiffusion in the InGaAs quantum dots

  16. Zinc Vacancy-Induced Room-Temperature Ferromagnetism in Undoped ZnO Thin Films

    Directory of Open Access Journals (Sweden)

    Hongtao Ren

    2012-01-01

    Full Text Available Undoped ZnO thin films are prepared by polymer-assisted deposition (PAD and treated by postannealing at different temperatures in oxygen or forming gases (95%  Ar+5% H2. All the samples exhibit ferromagnetism at room temperature (RT. SQUID and positron annihilation measurements show that post-annealing treatments greatly enhance the magnetizations in undoped ZnO samples, and there is a positive correlation between the magnetization and zinc vacancies in the ZnO thin films. XPS measurements indicate that annealing also induces oxygen vacancies that have no direct relationship with ferromagnetism. Further analysis of the results suggests that the ferromagnetism in undoped ZnO is induced by Zn vacancies.

  17. Case Study: Trap Crop with Pheromone Traps for Suppressing Euschistus servus (Heteroptera: Pentatomidae in Cotton

    Directory of Open Access Journals (Sweden)

    P. G. Tillman

    2012-01-01

    Full Text Available The brown stink bug, Euschistus servus (Say, can disperse from source habitats, including corn, Zea mays L., and peanut, Arachis hypogaea L., into cotton, Gossypium hirsutum L. Therefore, a 2-year on-farm experiment was conducted to determine the effectiveness of a sorghum (Sorghum bicolor (L. Moench spp. bicolor trap crop, with or without Euschistus spp. pheromone traps, to suppress dispersal of this pest to cotton. In 2004, density of E. servus was lower in cotton fields with sorghum trap crops (with or without pheromone traps compared to control cotton fields. Similarly, in 2006, density of E. servus was lower in cotton fields with sorghum trap crops and pheromone traps compared to control cotton fields. Thus, the combination of the sorghum trap crop and pheromone traps effectively suppressed dispersal of E. servus into cotton. Inclusion of pheromone traps with trap crops potentially offers additional benefits, including: (1 reducing the density of E. servus adults in a trap crop, especially females, to possibly decrease the local population over time and reduce the overwintering population, (2 reducing dispersal of E. servus adults from the trap crop into cotton, and (3 potentially attracting more dispersing E. servus adults into a trap crop during a period of time when preferred food is not prevalent in the landscape.

  18. Effect of voids-controlled vacancy supersaturations on B diffusion

    International Nuclear Information System (INIS)

    Marcelot, O.; Claverie, A.; Cristiano, F.; Cayrel, F.; Alquier, D.; Lerch, W.; Paul, S.; Rubin, L.; Jaouen, H.; Armand, C.

    2007-01-01

    We present here preliminary results on boron diffusion in presence of pre-formed voids of different characteristics. The voids were fabricated by helium implantation followed by annealing allowing the desorption of He prior to boron implantation. We show that under such conditions boron diffusion is always largely reduced and can even be suppressed in some cases. Boron diffusion suppression can be observed in samples not containing nanovoids in the boron-rich region. It is suggested that direct trapping of Si(int)s by the voids is not the mechanism responsible for the reduction of boron diffusion in such layers. Alternatively, our experimental results suggest that this reduction of diffusivity is more probably due to the competition between two Ostwald ripening phenomena taking place at the same time: in the boron-rich region, the competitive growth of extrinsic defects at the origin of TED and, in the void region, the Ostwald ripening of the voids which involves large supersaturations of Vs

  19. Effect of voids-controlled vacancy supersaturations on B diffusion

    Energy Technology Data Exchange (ETDEWEB)

    Marcelot, O. [CEMES/CNRS, 29 rue Jeanne Marvig, 31055 Toulouse (France)]. E-mail: marcelot@cemes.fr; Claverie, A. [CEMES/CNRS, 29 rue Jeanne Marvig, 31055 Toulouse (France); Cristiano, F. [LAAS/CNRS, 7 av. du Col. Roche, 31077 Toulouse (France); Cayrel, F. [LMP, Universite de Tours, 16 rue Pierre et Marie Curie, BP 7155, 37071 Tours (France); Alquier, D. [LMP, Universite de Tours, 16 rue Pierre et Marie Curie, BP 7155, 37071 Tours (France); Lerch, W. [Mattson Thermal Products GmbH, Daimlerstr. 10, D-89160 Dornstadt (Germany); Paul, S. [Mattson Thermal Products GmbH, Daimlerstr. 10, D-89160 Dornstadt (Germany); Rubin, L. [Axcelis Technologies, 108 Cherry Hill Drive, Beverly MA 01915 (United States); Jaouen, H. [STMicroelectronics, 850 rue Jean Monnet, 38926 Crolles (France); Armand, C. [LNMO/INSA, Service analyseur ionique, 135 av. de Rangueil, 31077 Toulouse (France)

    2007-04-15

    We present here preliminary results on boron diffusion in presence of pre-formed voids of different characteristics. The voids were fabricated by helium implantation followed by annealing allowing the desorption of He prior to boron implantation. We show that under such conditions boron diffusion is always largely reduced and can even be suppressed in some cases. Boron diffusion suppression can be observed in samples not containing nanovoids in the boron-rich region. It is suggested that direct trapping of Si(int)s by the voids is not the mechanism responsible for the reduction of boron diffusion in such layers. Alternatively, our experimental results suggest that this reduction of diffusivity is more probably due to the competition between two Ostwald ripening phenomena taking place at the same time: in the boron-rich region, the competitive growth of extrinsic defects at the origin of TED and, in the void region, the Ostwald ripening of the voids which involves large supersaturations of Vs.

  20. Diffusion to finite-size traps

    International Nuclear Information System (INIS)

    Richards, P.M.

    1986-01-01

    The survival probability of a random-walking particle is derived for hopping in a random distribution of traps of arbitrary radius and concentration. The single-center approximation is shown to be valid for times of physical interest even when the fraction of volume occupied by traps approaches unity. The theory is based on computation of the number of different potential trap regions sampled in a random walk and is confirmed by simulations on a simple-cubic lattice