The Experts below are selected from a list of 261 Experts worldwide ranked by ideXlab platform
Eduardo Alves - One of the best experts on this subject based on the ideXlab platform.
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Lattice Site location and luminescence studies of AlxGa1−xN alloys doped with thulium ions
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2013Co-Authors: M. Fialho, Katharina Lorenz, Sérgio Ricardo Magalhães, Joana Rodrigues, N. F. Santos, Teresa Monteiro, Eduardo AlvesAbstract:Abstract Rare earth doped AlGaN is being considered for the development of new optoelectronic devices. This wide band gap compound provides lower thermal quenching of rare earth intra-4 f n transitions making room temperature operation possible. In this work a detailed study of Al x Ga 1− x N ( x = 0.15, 0.77) samples grown by halide vapor phase epitaxy on (0 0 0 1) sapphire implanted with Tm is presented. The samples were implanted at room temperature with 300 keV Tm ions to fluences of 1 × 10 14 cm −2 and 1 × 10 15 cm −2 . The damage accumulation and the rare earth Lattice Site location are investigated by Rutherford Backscattering/Channeling Spectrometry. The structural measurements show a higher resistance of the Lattice to irradiation damage with the increase of the AlN content. The analysis of angular scans along different axes using the Monte Carlo code FLUX allows the determination of the rare earth Lattice Sites. Results for Al 0.15 Ga 0.85 N show that Tm ions occupy two preferential Sites: the high symmetry substitutional Ga/Al Site and a Site displaced by ∼0.3 A along the c -axis from this regular Site. Rapid thermal annealing treatments at 1200 °C under N 2 ambient were performed to remove implantation damage and promote the optical activation of rare earth intra-4 f n transitions. Photoluminescence measurements were performed to characterize the thulium ions spectroscopic transitions. The effects of thermal annealing and fluence on the fraction of rare earth optically active ions are exploited and discussed.
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Lattice Site and stability of implanted ag in zno
Physica B-condensed Matter, 2003Co-Authors: E Rita, Eduardo Alves, Ulrich Wahl, J. G. Correia, A. M. L. Lopes, João P. Araújo, J.c. SoaresAbstract:Abstract In this work we report on the Lattice location of implanted Ag in ZnO single crystals, evaluated by means of the emission channeling technique. Following 60 keV low-dose (2×1013 cm−2) ion implantation, the β− emission patterns from 111Ag were monitored with a position-sensitive detector as a function of annealing temperature up to 800°C in vacuum. Our experiments revealed that in the as-implanted state around 30% of the Ag atoms are substitutional at the Zn Site with root mean square displacements around 0.17–0.28 A. Though this fraction did not change with increasing annealing temperature, upon annealing at 600°C the root mean square displacement of Ag from the Zn Site increased considerably, followed by partial outdiffusion during 800°C annealing.
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Lattice Site location and optical activity of er implanted zno
Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, 2003Co-Authors: Eduardo Alves, J.c. Soares, Ulrich Wahl, J. G. Correia, E Rita, T Monteiro, C BoemareAbstract:Abstract ZnO (O face) single crystals were implanted with 150 keV Er + ions to fluences of 5 × 10 14 and 5 × 10 15 Er + /cm 2 at room temperature. For fluences of 5 × 10 15 Er + /cm 2 the implantation damage raises the minimum yield from 2% to 22%. Despite the large amount of damage a fraction of 90% of the implanted Er ions are incorporated in substitutional Sites along the [0 0 0 1] axis. Photoluminescence (PL) studies reveal the presence of a weak emission near 1.54 μm at 77 K due to the 4 I 13/2 → 4 I 15/2 transition of the Er 3+ ions. Annealing in oxidizing atmosphere at 800 °C leads to a reduction of the implantation damage, which is fully recovered after annealing at 1050 °C for 30 min. The annealing at 1050 °C leads to the outdiffusion of Er, with a 50% loss from the implanted region after the annealing. Only a fraction of 25% of the remaining Er is still in regular Sites after the annealing and the Er 3+ PL vanishes.
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Lattice Site Location Studies of Rare-Earths Implanted in ZnO Single-Crystals
MRS Proceedings, 2002Co-Authors: E Rita, Eduardo Alves, Ulrich Wahl, J. G. Correia, A. M. L. Lopes, João P. Araújo, Jose Carvalho SoaresAbstract:In this work we report on the Lattice Site location of rare earths in single-crystalline ZnO by means of the emission channeling (EC) technique. Following low dose (3×10 13 at/cm 2 ) 60 keV ion implantation of the precursor isotope 169 Yb, a position-sensitive electron detector was used to monitor the angular distribution of the conversion electrons emitted from 169 Tm * as a function of the annealing temperature up to 600oC in vacuum. An additional annealing at 800oC in flowing O2 was performed. The EC measurements revealed that around 95-100% of the rare earth atoms occupy substitutional Zn Sites up to an annealing temperature of 600oC/vacuum. After the 800oC/O2 annealing, the emission channeling effects decreased considerably.
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Fe ion implantation in GaN: Damage, annealing, and Lattice Site location
Journal of Applied Physics, 2001Co-Authors: Chang Liu, M F Silva, Eduardo Alves, A.d. Sequeira, N. Franco, J.c. SoaresAbstract:In this article we report the damage and annealing behavior as well as Lattice Site location of Fe atoms in GaN. The Fe ions were homogeneously implanted in GaN films with an energy of 150 keV at room temperature. A two-step annealing (650 °C 15 min and then 1000 °C 2 min) was performed to remove the implantation-induced damage and to drive the dopants into the Lattice Site. The structure of GaN films before and after the implantation as well as at each stage of the annealing was characterized by Rutherford backscattering/channeling combined with particle induced x-ray emission and high resolution x-ray diffraction. The Fe+ implanted GaN films exhibits an expanded Lattice. After the two-step annealing, the Lattice distortion does not fully recover. Angular scans along both [0001] and [1011] directions show that the Fe atoms occupy the Lattice Site of Ga atoms in the case of low dose implantation after annealing. However, for the high dose implanted GaN, about 75% of the implanted Fe atoms substitutes Ga ...
Krzysztof Malarz - One of the best experts on this subject based on the ideXlab platform.
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Square Lattice Site percolation thresholds for complex neighbourhoods
arXiv: Statistical Mechanics, 2006Co-Authors: Mariusz Majewski, Krzysztof MalarzAbstract:In this paper we compute the square Lattice random Sites percolation thresholds in case when Sites from the 4th and the 5th coordination shells are included for neighbourhood. The obtained results support earlier claims, that (a) the coordination number and the space dimension are insufficient for building universal formulae for percolation thresholds and (b) that percolation threshold may not decrease monotonically with Lattice Site coordination number.
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square Lattice Site percolation at increasing ranges of neighbor bonds
Physical Review E, 2005Co-Authors: Krzysztof Malarz, Serge GalamAbstract:We report Site percolation thresholds for square Lattice with neighbor bonds at various increasing ranges. Using Monte Carlo techniques we found that nearest neighbors (NN), next-nearest neighbors (NNN), next-next-nearest neighbors (4N), and fifth-nearest neighbors (6N) yield the same ${p}_{c}=0.592\dots{}$. The fourth-nearest neighbors (5N) give ${p}_{c}=0.298\dots{}$. This equality is proved to be mathematically exact using symmetry argument. We then consider combinations of various kinds of neighborhoods with $(\mathrm{NN}+\mathrm{NNN})$, $(\mathrm{NN}+4\mathrm{N})$, $(\mathrm{NN}+\mathrm{NNN}+4\mathrm{N})$, and $(\mathrm{NN}+5\mathrm{N})$. The calculated associated thresholds are respectively ${p}_{c}=0.407\dots{}$, 0.337\dots{}, 0.288\dots{}, and 0.234\dots{}. The existing Galam-Mauger universal formula for percolation thresholds does not reproduce the data showing dimension and coordination number are not sufficient to build a universal law which extends to complex Lattices.
J.c. Soares - One of the best experts on this subject based on the ideXlab platform.
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Lattice Site and stability of implanted ag in zno
Physica B-condensed Matter, 2003Co-Authors: E Rita, Eduardo Alves, Ulrich Wahl, J. G. Correia, A. M. L. Lopes, João P. Araújo, J.c. SoaresAbstract:Abstract In this work we report on the Lattice location of implanted Ag in ZnO single crystals, evaluated by means of the emission channeling technique. Following 60 keV low-dose (2×1013 cm−2) ion implantation, the β− emission patterns from 111Ag were monitored with a position-sensitive detector as a function of annealing temperature up to 800°C in vacuum. Our experiments revealed that in the as-implanted state around 30% of the Ag atoms are substitutional at the Zn Site with root mean square displacements around 0.17–0.28 A. Though this fraction did not change with increasing annealing temperature, upon annealing at 600°C the root mean square displacement of Ag from the Zn Site increased considerably, followed by partial outdiffusion during 800°C annealing.
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Lattice Site location and optical activity of er implanted zno
Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, 2003Co-Authors: Eduardo Alves, J.c. Soares, Ulrich Wahl, J. G. Correia, E Rita, T Monteiro, C BoemareAbstract:Abstract ZnO (O face) single crystals were implanted with 150 keV Er + ions to fluences of 5 × 10 14 and 5 × 10 15 Er + /cm 2 at room temperature. For fluences of 5 × 10 15 Er + /cm 2 the implantation damage raises the minimum yield from 2% to 22%. Despite the large amount of damage a fraction of 90% of the implanted Er ions are incorporated in substitutional Sites along the [0 0 0 1] axis. Photoluminescence (PL) studies reveal the presence of a weak emission near 1.54 μm at 77 K due to the 4 I 13/2 → 4 I 15/2 transition of the Er 3+ ions. Annealing in oxidizing atmosphere at 800 °C leads to a reduction of the implantation damage, which is fully recovered after annealing at 1050 °C for 30 min. The annealing at 1050 °C leads to the outdiffusion of Er, with a 50% loss from the implanted region after the annealing. Only a fraction of 25% of the remaining Er is still in regular Sites after the annealing and the Er 3+ PL vanishes.
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Change of uranium Lattice Site in LiNbO3 induced by thermal reduction treatment
Radiation Effects and Defects in Solids, 2001Co-Authors: A. Kling, M F Silva, J.c. Soares, J.a. Sanz-garcía, J. García-soléAbstract:Abstract The doping of lithium niobate (LiNbO3) with uranium is of high interest due to the possible infrared laser action of U3+. On the other hand LiNbO3:U crystals grown from melt contain uranium only as U6+. It has been recently shown that by thermal reduction the valence state can be altered to U3+/U4+. Studies on the Lattice Site of uranium show that U occupies exclusively the Nb Site in as-grown material, while after thermal reduction at 1000°C for 16 h under high vacuum ca. 20% of the U atoms have been transferred to the Li Site. These findings confirm the assumption that the dopant valence state is the determining factor for the impurity Lattice Site: dopants with valence states + 1 to + 4 are located on the Li Site, those with valence states + 5 or + 6 on Nb Sites.
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Fe ion implantation in GaN: Damage, annealing, and Lattice Site location
Journal of Applied Physics, 2001Co-Authors: Chang Liu, M F Silva, Eduardo Alves, A.d. Sequeira, N. Franco, J.c. SoaresAbstract:In this article we report the damage and annealing behavior as well as Lattice Site location of Fe atoms in GaN. The Fe ions were homogeneously implanted in GaN films with an energy of 150 keV at room temperature. A two-step annealing (650 °C 15 min and then 1000 °C 2 min) was performed to remove the implantation-induced damage and to drive the dopants into the Lattice Site. The structure of GaN films before and after the implantation as well as at each stage of the annealing was characterized by Rutherford backscattering/channeling combined with particle induced x-ray emission and high resolution x-ray diffraction. The Fe+ implanted GaN films exhibits an expanded Lattice. After the two-step annealing, the Lattice distortion does not fully recover. Angular scans along both [0001] and [1011] directions show that the Fe atoms occupy the Lattice Site of Ga atoms in the case of low dose implantation after annealing. However, for the high dose implanted GaN, about 75% of the implanted Fe atoms substitutes Ga ...
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Annealing behavior and Lattice Site location of Hf implanted GaN
Materials Science and Engineering B-advanced Functional Solid-state Materials, 1999Co-Authors: Eduardo Alves, M F Silva, J.c. Soares, José G. Marques, Kristian FreitagAbstract:Abstract The defect recovery and Lattice Site location of Hf implanted into GaN single crystalline epilayers were studied combining RBS/channelling and hyperfine interactions measurements. The RBS/channelling measurements performed after implantation of 5×1014 Hf+ cm−2 at 100 keV show that nearly all the implanted ions were incorporated into substitutional Sites of the GaN Lattice. The damage produced by the implantation recovers almost completely after one hour annealing at 900°C and all the Hf ions then occupy substitutional Sites. The hyperfine interaction measurements were performed with the radioactive 181Hf/181Ta probe, after implantation of 181Hf to a fluence of 5×1012 Hf+ cm−2 with 80 keV. These measurements show that the defect recovery occurs in the 600–800°C annealing temperature range.
Minn-tsong Lin - One of the best experts on this subject based on the ideXlab platform.
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Quasiparticle interference in ZrSiS: Strongly band-selective scattering depending on impurity Lattice Site
Physical Review B, 2017Co-Authors: Christopher J. Butler, Cheng-rong Hsing, Yi Tseng, Raman Sankar, Ching-ming Wei, Fangcheng Chou, Minn-tsong LinAbstract:Scanning tunneling microscopy visualizations of quasiparticle interference (QPI) enable powerful insights into the k-space properties of superconducting, topological, Rashba and other exotic electronic phases, but their reliance on impurities acting as scattering centers is rarely scrutinized. Here we investigate QPI at the vacuum-cleaved (001) surface of the Dirac semimetal ZrSiS. We find that interference patterns around impurities located on the Zr and S Lattice Sites appear very different, and can be ascribed to selective scattering of different sub-sets of the predominantly Zr 4d-derived band structure, namely the m = 0 and m = +/-1 components. We show that the selectivity of scattering channels requires an explanation beyond the different bands' orbital characteristics and their respective charge density distributions over Zr and S Lattices Sites. Importantly, this result shows that the usual assumption of generic scattering centers allowing observations of quasiparticle interference to shed light indiscriminately and isotropically upon the \textit{q}-space of scattering events does not hold, and that the scope and interpretation of QPI observations can therefore be be strongly contingent on the material defect chemistry. This finding promises to spur new investigations into the quasiparticle scattering process itself, to inform future interpretations of quasiparticle interference observations, and ultimately to aid the understanding and engineering of quantum electronic transport properties.
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Quasiparticle Scattering in the Rashba Semiconductor BiTeBr: The Roles of Spin and Defect Lattice Site.
ACS nano, 2016Co-Authors: Christopher J. Butler, Raman Sankar, Ching-ming Wei, Fangcheng Chou, Po-ya Yang, Yen-neng Lien, Luo-yueh Chang, Chia-hao Chen, Minn-tsong LinAbstract:Observations of quasiparticle interference have been used in recent years to examine exotic carrier behavior at the surfaces of emergent materials, connecting carrier dispersion and scattering dynamics to real-space features with atomic resolution. We observe quasiparticle interference in the strongly Rashba split 2DEG-like surface band found at the tellurium termination of BiTeBr and examine two mechanisms governing quasiparticle scattering: We confirm the suppression of spin-flip scattering by comparing measured quasiparticle interference with a spin-dependent elastic scattering model applied to the calculated spectral function. We also use atomically resolved STM maps to identify point defect Lattice Sites and spectro-microscopy imaging to discern their varying scattering strengths, which we understand in terms of the calculated orbital characteristics of the surface band. Defects on the Bi subLattice cause the strongest scattering of the predominantly Bi 6p derived surface band, with other defects causing nearly no scattering near the conduction band minimum.
O Meyer - One of the best experts on this subject based on the ideXlab platform.
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Implantation of group IVA elements in TiO2: Lattice Site location and diffusion
Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, 2000Co-Authors: R. Fromknecht, I. Khubeis, O MeyerAbstract:Abstract Ge-, Sn- and Pb-ions with oxidation state +4, similar to that of Ti, were implanted into rutile single crystals. Ion profiles and Lattice Site location were determined by Rutherford-backscattering and channeling. Previously it was noted that the widths of the angular dip curves for Ge and Sn were wider and deeper than those of Ti, indicating the formation of coherent precipitates, while Pb atoms were displaced along the c -axis. Annealing at high temperatures caused the impurities to move to regular substitutional Ti Lattice Sites. The influence of diffusion effects on the Lattice Site occupation and on the formation of precipitates has been studied here in more detail for aligned and randomly oriented implants. For aligned implants Sn-diffusion occurred between 850 and 950 K, about 200 K below the temperature region where diffusion is observed for random implants. The steep decrease of the Sn peak area without broadening indicates that the diffusion is governed by trap release. The local damage density near the impurity at the end of the ion track seems to play a big role: for aligned implants the diffusion occurs in the temperature region where the damage anneals, while for random implants ion diffusion is not connected to damage annealing and occurs due to a substitutional process via cation Lattice Sites.
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Oxidation state and Lattice Site occupation of ions implanted into rutile
Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, 1999Co-Authors: O Meyer, R. Fromknecht, I. KhubeisAbstract:Abstract Ions with different oxidation states Ga(+3), Ge(+4) and As(±3,5) were implanted in TiO2 and their Lattice Site location was determined using Rutherford Backscattering and Channeling (RBS-C). Angular scan measurements were performed through the 〈0 0 1〉 and 〈1 0 0〉 crystal directions. Ga was substitutional with a fraction of 1 for concentrations up to 0.2 at %. Arsenic was displaced perpendicular to both directions by an average displacement amplitude of about 0.007 nm, indicating an interaction with oxygen point defects. The Ge dip curve was slightly broader and deeper as that of Ti which may indicate that Ge formed coherent precipitations after implantation at 296 K. Ge became substitutional after annealing at 900 K.
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Ion implantation in TiO2: damage production and recovery, Lattice Site location and electrical conductivity
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 1999Co-Authors: R. Fromknecht, I. Khubeis, S. Massing, O MeyerAbstract:Abstract Ions with different oxidation states were implanted in TiO 2 (rutile). The Lattice disorder as well as the Lattice Site location of the implanted ions were determined using Rutherford Backscattering and Channeling (RBS-C) spectrometry. The production of disorder as a function of dose and temperature, and its recovery was studied in detail. Important results are the observation of dynamic recovery at 293 K and above, and one isothermal at 77 K and two thermal recovery stages between 170 and 210 K and between 260 and 293 K. The recovery at 77 K is proportional to ln t , indicating that the activation energy increases with decreasing disorder density. The results concerning the Lattice Site location of 14 ion species reveal that 13 ions occupy Ti Lattice Site. With increasing netcharge, the maximum soluble concentration decreases by the formation of impurity–defect complexes probably enforced by charge compensation. Directed displacements from the substitutional Lattice Site provide some hints on the structures of these complexes. The electrical conductivity of the implanted samples increased by about 12 orders of magnitude irrespective of the oxidation state of the implanted species. From the temperature and dose dependence of the electrical conductivity as well as from its similar behaviour for noble-gas ions and other species it is concluded, that the carrier transport occurs by single energy states excitation at low doses and by variable range hopping between localized states at high doses.
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Lattice Site location and annealing behavior of W implanted TiO2
Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, 1998Co-Authors: R.c. Da Silva, Eduardo Alves, R. Fromknecht, Luis Redondo, O MeyerAbstract:Abstract The implantation damage and Lattice Site location of W in TiO2 (rutile) was studied using the Rutherford backscattering technique in the channeling mode (RBS-C). The W ions were implanted at room temperature with fluences in the range of 1015 to 1017/cm2 into both 〈1 0 0〉 and 〈0 0 1〉 oriented single crystals. The implanted region becomes completely disordered for W doses higher than 1016/cm2. After annealing experiments at temperatures up to 1100 K the results suggest that Lattice recovery depends on the type of TiO2 single crystal used. While in 〈0 0 1〉 oriented single crystals partial epitaxial solid phase regrowth of the damaged region is seen, for 〈1 0 0〉 oriented single crystals a recrystallization process occurs almost to completion. During damage recovery the high dose samples lose more than 80% of the W from the implanted region. Detailed angular scans for the main axial directions show that in the case of full recovery about 82% of the W remaining in the implanted region are incorporated on Ti Lattice Sites. These observations suggest that there is a strong anisotropy of the Lattice recovery and diffusion properties in W implanted TiO2.
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Ions implanted into TiO2 rutile single crystals: Lattice disorder, Lattice Site occupation and conductivity
Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, 1997Co-Authors: O Meyer, R. Fromknecht, I. Khubeis, S. MassingAbstract:Ions (Au, W, Sb, Hg, Sn, In, Hf, La) with different size mismatch-energies have been implanted at 77 K and 293 K into TiO2. The Lattice disorder and Lattice Site occupation were measured by RBS-C in the 〈001〉 and 〈100〉 crystalline directions. The conductivity was measured as a function of temperature. For the partially damaged rutile phase recovery was observed below room temperature, in contrast to the amorphous phase. The Lattice Site occupation is discussed within the solubility rules for equilibrium solid solutions using the electronegativity and the atomic size as coordinates. A large increase of the conductivity σ was observed with increasing Sb and Sn dose, indicating a saturation behaviour at about 30 Ω−1 cm−1. Between 40 K and 293 K ln σ was proportional to −12 for low doses, and proportional to T−14 for doses of about 1 × 1016 / cm2 and above, indicating that the transport mechanism is due to variable range hopping.
