39 results on '"L. B. Bayu Aji"'
Search Results
2. Radio-frequency magnetron sputter deposition of ultrathick boron carbide films
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L. B. Bayu Aji, S. J. Shin, J. H. Bae, A. M. Engwall, J. A. Hammons, S. T. Sen-Britain, P. B. Mirkarimi, and S. O. Kucheyev
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Surfaces and Interfaces ,Condensed Matter Physics ,Surfaces, Coatings and Films - Abstract
The deposition of thick B[Formula: see text]C films with low residual stress by conventional direct-current magnetron sputtering is accompanied by the formation of dust particulates contaminating the target, chamber, and substrates and leading to the formation of nodular defects in films. Here, we demonstrate that the formation of particulates is greatly reduced during radio-frequency magnetron sputtering (RFMS). We systematically study properties of B[Formula: see text]C films deposited by RFMS with a substrate temperature of 330 [Formula: see text]C, a target-to-substrate distance of 10 cm, Ar working gas pressure in the range of 4.5–12.0 mTorr (0.6–1.6 Pa), and substrate tilt angles of 0[Formula: see text]–80[Formula: see text]. All films are x-ray amorphous. A columnar structure develops with increasing either Ar pressure or substrate tilt. For columnar films, the column tilt angle decreases with increasing Ar pressure, which we attribute to a corresponding increase in the width of the distribution of impact angles of deposition flux. In contrast to the Keller–Simmons rule, the deposition rate increases with increasing Ar pressure, which suggests a better coupling of the RF energy to the plasma processes that lead to target sputtering at higher pressures. There is a critical substrate tilt angle above which the total residual stress is close to zero. This critical substrate tilt angle is [Formula: see text] for an Ar pressure of 12 mTorr (1.6 Pa). The lower residual stress state, necessary for depositing ultrathick films, is characterized by a larger concentration of nanoscale inhomogeneities and decreased mechanical properties. Based on these results, RFMS deposition of 60-[Formula: see text]m-thick B[Formula: see text]C films is demonstrated.
- Published
- 2023
3. Combinatorial sputter deposition of ultrathick Au-Bi alloy films
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L B Bayu Aji, A M Engwall, S J Shin, J H Bae, A A Baker, D J Strozzi, S K McCall, J D Moody, and S O Kucheyev
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Acoustics and Ultrasonics ,Condensed Matter Physics ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials - Abstract
Gold-bismuth alloys are of interest as catalysts and catalytic sensing systems, electrochemical sensors, superconductors, and hohlraums for magnetically assisted inertial confinement fusion implosions. Radiation-hydrodynamics simulations with the Lasnex code of laser-driven hohlraums predict higher x-ray drive from Au-Bi alloys compared with cases of Au-Ta or pure Au and Bi hohlraums. Here, we use direct current magnetron sputtering in Ar gas, with co-sputtering from two elemental targets, to deposit Au-Bi alloys with Bi content of 9–77 at.% and thicknesses up to ∼20 µm. Films are characterized by a combination of x-ray diffraction, Rutherford backscattering, scanning electron microscopy, substrate-curvature-based residual stress, and electronic transport measurements. Experiments are complemented by Monte Carlo simulations of ballistic sputtering and gas phase transport of depositing species and Ar gas atoms. Results show that all films are polycrystalline, with three distinct compositional regimes dominated by Au, Au2Bi, and Bi crystallographic phases. A metallic behavior of the temperature dependence of electrical resistivity is observed for all the films. Films with Bi content above ∼30 at.% exhibit porosity, which is tolerable to hohlraum x-ray drive based on Lasnex simulations.
- Published
- 2022
4. Reactive co-sputtering of ternary Au–Ta–O films with tunable electrical resistivity
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S. J. Shin, L. B. Bayu Aji, A. M. Engwall, J. H. Bae, A. A. Baker, J. D. Moody, and S. O. Kucheyev
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Physics and Astronomy (miscellaneous) - Abstract
Heavy-metal-based films with high electrical resistivity are needed for hohlraums for magnetically assisted inertial confinement fusion. Here, we study ternary Au–Ta–O films deposited by reactive direct-current magnetron co-sputtering from elemental Au and Ta targets in an oxygen containing atmosphere. By varying the O content, the electrical resistivity of films can be tuned in a wide range of [Formula: see text] [Formula: see text] cm. With increasing O content, a drastic increase in resistivity occurs at [Formula: see text] at. % of O, separating regimes with two different dominant conduction mechanisms attributed to metallic conduction through the Au–Ta alloy matrix (for [Formula: see text] at. % of O) and tunneling across insulating Ta2O5 layers separating conducting islands (for [Formula: see text] at. % of O). Post-deposition annealing at 300 °C leads to the segregation of Au into [Formula: see text]-nm islands, sharply decreasing the resistivity for films with [Formula: see text] at. % of O but not for the metal-like films with lower O content.
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- 2022
5. Impact of pre-existing disorder on radiation defect dynamics in Si
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J. B. Wallace, Sergei O. Kucheyev, Lin Shao, and L. B. Bayu Aji
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0301 basic medicine ,Multidisciplinary ,Materials science ,Condensed matter physics ,lcsh:R ,Time constant ,Defect engineering ,lcsh:Medicine ,Radiation ,Ion bombardment ,Article ,03 medical and health sciences ,Surfaces, interfaces and thin films ,030104 developmental biology ,0302 clinical medicine ,Lattice defects ,Lattice (order) ,Electronic devices ,Interaction dynamics ,lcsh:Q ,lcsh:Science ,030217 neurology & neurosurgery - Abstract
The effect of pre-existing lattice defects on radiation defect dynamics in solids remains unexplored. Here, we use a pulsed beam method to measure the time constant of defect relaxation for 500 keV Ar ion bombardment of Si at 100 °C with the following two representative types of pre- existing lattice disorder: (i) point defect clusters and (ii) so-called “clamshell” defects consisting of a high density of dislocations. Results show that point defect clusters slow down defect relaxation processes, while regions with dislocations exhibit faster defect interaction dynamics. These experimental observations demonstrate that the dynamic aspects of damage buildup, attributed to defect trapping-detrapping processes, can be controlled by defect engineering.
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- 2019
6. Sculpting Non-Machinable Porous Materials
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Tyler M. Fears, Sergei O. Kucheyev, I. Winter, and L. B. Bayu Aji
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Materials science ,Composite material ,Porous medium - Published
- 2020
7. Effect of substrate temperature on sputter-deposited boron carbide films
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L. B. Bayu Aji, S. J. Shin, J. H. Bae, A. M. Engwall, J. A. Hammons, X. Lepró, N. Catarineu, P. B. Mirkarimi, and S. O. Kucheyev
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General Physics and Astronomy - Published
- 2022
8. Radiation defect dynamics in 3C-, 4H-, and 6H-SiC studied by pulsed ion beams
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Sergei O. Kucheyev, J. B. Wallace, and L. B. Bayu Aji
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010302 applied physics ,Nuclear and High Energy Physics ,Materials science ,Relaxation (NMR) ,Dynamics (mechanics) ,02 engineering and technology ,Crystal structure ,Radiation ,021001 nanoscience & nanotechnology ,01 natural sciences ,Molecular physics ,Ion ,0103 physical sciences ,Radiation damage ,Interaction dynamics ,Irradiation ,0210 nano-technology ,Instrumentation - Abstract
Radiation damage behavior of SiC depends on its lattice structure. Here, we use a pulsed-ion-beam method to study defect interaction dynamics in 6 H -SiC and damage buildup in 4 H - and 6 H -SiC irradiated at 100 ° C with 500 keV Ar ions. These results are compared with previously reported data for Ar-ion-irradiated 3 C - and 4 H -SiC. We find that, for these irradiation conditions, damage buildup in 3 C - and 6 H -SiC is statistically indistinguishable and is significantly more efficient than in 4 H -SiC. Within a stimulated amorphization model, 4 H -SiC is described by a reduced amorphization cross-section constant, while the point defect cluster production cross-section is the same (within experimental errors) for the three polytypes studied. Moreover, 4 H -SiC exhibits slower defect relaxation dynamics than 3 C - and 6 H -SiC. These results clearly demonstrate the importance of the lattice structure in damage buildup and defect interaction dynamics in SiC.
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- 2018
9. Degradation of ultra-thin boron films in air
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Scott K. McCall, Anna M. Hiszpanski, J. H. Bae, Elissaios Stavrou, L. B. Bayu Aji, Sergei O. Kucheyev, and Alexander A. Baker
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010302 applied physics ,Materials science ,Annealing (metallurgy) ,Analytical chemistry ,Time constant ,General Physics and Astronomy ,chemistry.chemical_element ,02 engineering and technology ,Surfaces and Interfaces ,General Chemistry ,Glassy carbon ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Surfaces, Coatings and Films ,Amorphous solid ,Corrosion ,chemistry ,0103 physical sciences ,Thin film ,0210 nano-technology ,Boron ,Inert gas - Abstract
Corrosion of B films in air can limit their practical applications. Here, we study the evolution of the elemental composition, thickness, and morphology of 10 – 100 -nm-thick amorphous B films sputter-deposited onto glassy carbon substrates and stored under different conditions. Results show that films with thicknesses of ≳ 55 nm have expected excellent corrosion resistance during storage in laboratory air at room temperature over several months. In contrast, ≲ 45 -nm-thick films exhibit pronounced degradation upon air exposure, starting with a change in the composition to ∼ 30 and ∼ 50 at.% of O and H, respectively. After such an O and H uptake, the degradation proceeds via mass loss with a characteristic time constant of ∼ 5 days in air at room temperature. A post-deposition annealing at 1000 ° C in an inert atmosphere makes all the films corrosion resistant.
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- 2018
10. Gold-tantalum alloy films deposited by high-density-plasma magnetron sputtering
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Sergei O. Kucheyev, A. M. Engwall, Scott K. McCall, J. D. Moody, Michael H. Nielsen, Alexander A. Baker, J. H. Bae, S. J. Shin, and L. B. Bayu Aji
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Materials science ,Alloy ,Tantalum ,General Physics and Astronomy ,chemistry.chemical_element ,Substrate (electronics) ,Sputter deposition ,engineering.material ,Condensed Matter::Materials Science ,chemistry ,Electrical resistivity and conductivity ,Residual stress ,Phase (matter) ,engineering ,Composite material ,High-power impulse magnetron sputtering - Abstract
Gold-tantalum alloy films are of interest for biomedical and magnetically-assisted inertial confinement fusion applications. Here, we systematically study the effects of substrate tilt ( 0°–80°) and negative substrate bias (0–100 V) on properties of ≲3- μm-thick films deposited by high-power impulse magnetron sputtering (HiPIMS) from a Au–Ta alloy target (with 80 at. % of Ta). Results reveal that, for all the substrate bias values studied, an increase in substrate tilt leads to a monotonic decrease in film thickness, density, residual compressive stress, and electrical conductivity. Larger substrate bias favors the formation of a body-centered cubic phase, with films exhibiting lower column tilt and higher density, electrical conductivity, and residual compressive stress. These changes are attributed to metal atom ionization effects, based on the lack of correlation with distributions of landing energies and incident angles of depositing species as calculated by Monte Carlo simulations of ballistic collisions and gas phase atomic transport. By varying substrate tilt and bias in HiPIMS deposition, properties of Au–Ta alloy films can be controlled in a very wide range, including residual stress from −2 to +0.5 GPa, density from 12 to 17 g/ cm3, and the electrical resistivity from 50 to 4500 μΩ cm, enabling optimum deposition conditions to be selected for specific applications.
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- 2021
11. Oblique angle deposition of boron carbide films by magnetron sputtering
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Michael H. Nielsen, J. H. Bae, A. M. Engwall, Sergei O. Kucheyev, Byeongdu Lee, X. Lepro, X. B. Zuo, S. J. Shin, Joshua A. Hammons, P. B. Mirkarimi, and L. B. Bayu Aji
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Materials science ,General Physics and Astronomy ,Substrate (electronics) ,Boron carbide ,Sputter deposition ,Amorphous solid ,Condensed Matter::Materials Science ,chemistry.chemical_compound ,Tilt (optics) ,chemistry ,Residual stress ,Condensed Matter::Superconductivity ,Deposition (phase transition) ,Composite material ,Refractive index - Abstract
Many applications of boron carbide ( B4C) films entail deposition on non-planar substrates, necessitating a better understanding of oblique angle deposition phenomena. Here, we systematically study the effect of substrate tilt on properties of B4C films with thicknesses up to 10 μm deposited by direct current magnetron sputtering. Results show that all films are amorphous and columnar with an average column width of ∼100 nm, independent of substrate tilt. Column tilt angles are limited to ∼20° even for substrate tilt of 80°. Film density, residual stress, and the refractive index weakly (within ≲20%) depend on substrate tilt. Oxygen impurities bond preferentially with carbon atoms in inter-columnar regions. Substrate tilt has a major effect on mechanical properties that decrease by ∼50%, suggesting weak interconnection between nano-columns. Implications of these observations for the deposition onto non-planar substrates are discussed.
- Published
- 2021
12. Comparative study of radiation defect dynamics in 3C-SiC by X-ray diffraction, Raman scattering, and ion channeling
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L. B. Bayu Aji, Elissaios Stavrou, Alexandre Boulle, Aurélien Debelle, Sergei O. Kucheyev, J. B. Wallace, Max-Planck-Institut für Festkörperforschung, Max-Planck-Gesellschaft, Speed Laboratory, University of Galasgow, IRCER - Axe 3 : organisation structurale multiéchelle des matériaux (IRCER-AXE3), Institut de Recherche sur les CERamiques (IRCER), Institut des Procédés Appliqués aux Matériaux (IPAM), Université de Limoges (UNILIM)-Université de Limoges (UNILIM)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS)-Institut des Procédés Appliqués aux Matériaux (IPAM), Université de Limoges (UNILIM)-Université de Limoges (UNILIM)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS), Centre de Sciences Nucléaires et de Sciences de la Matière (CSNSM), and Université Paris-Sud - Paris 11 (UP11)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS)
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010302 applied physics ,Diffraction ,Materials science ,Relaxation (NMR) ,[CHIM.MATE]Chemical Sciences/Material chemistry ,02 engineering and technology ,General Chemistry ,Radiation ,021001 nanoscience & nanotechnology ,01 natural sciences ,Molecular physics ,Ion ,Characterization (materials science) ,symbols.namesake ,0103 physical sciences ,X-ray crystallography ,symbols ,Radiation damage ,General Materials Science ,0210 nano-technology ,ComputingMilieux_MISCELLANEOUS ,Raman scattering - Abstract
At moderately elevated temperatures, radiation defects in SiC exhibit pronounced dynamic annealing, which remains poorly understood. Here, we study 3C-SiC bombarded at 100 $$^{\circ }$$ C with pulsed beams of 500 keV Ar ions. Radiation damage is monitored by a combination of X-ray diffraction, Raman scattering, and ion channeling. Similar damage buildup behavior but with different defect relaxation time constants, ranging from $$\sim 1$$ to $$\sim 6$$ ms, is observed for the different types of lattice defects probed by these techniques. A correlation between relaxation times and the nature of the defects is proposed. These results reveal additional complexity of radiation defect dynamics in SiC and demonstrate that results of different defect characterization techniques are needed for a better understanding of dynamic annealing processes in solids.
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- 2018
13. Effect of substrate tilt on sputter-deposited AuTa films
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A. M. Engwall, Alexander A. Baker, Scott K. McCall, J. D. Moody, S. J. Shin, L. B. Bayu Aji, J. H. Bae, and Sergei O. Kucheyev
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Materials science ,Condensed matter physics ,General Physics and Astronomy ,02 engineering and technology ,Surfaces and Interfaces ,General Chemistry ,Substrate (electronics) ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,0104 chemical sciences ,Surfaces, Coatings and Films ,Amorphous solid ,Stress (mechanics) ,Condensed Matter::Materials Science ,Tilt (optics) ,Sputtering ,Electrical resistivity and conductivity ,Thin film ,0210 nano-technology ,Inertial confinement fusion - Abstract
Gold-tantalum alloy films are of interest for biomedical and magnetically-assisted inertial confinement fusion applications. However, growth mechanisms of such Au-Ta alloy films are not well understood. Here, we systematically study the effect of substrate tilt on properties of films deposited by direct current magnetron sputtering from a AuTa alloy target. Experimental data is correlated with distributions of landing energies and incident angles of sputtered and backscattered species calculated by Monte Carlo simulations of ballistic collisions and gas phase atomic transport. Results reveal that the deposition rate and film density monotonically decrease with increasing substrate tilt. Properties are similar for films with a tilt of 40 ° and below: films are amorphous, with an average compressive stress of 0.5 GPa, a density of 16 g/cm3, and electrical resistivity of 200 μ Ω cm. The critical substrate tilt angle for the onset of porosity, a transition to a reduced stress state, and an increase in electrical resistivity lies between 40 and 60 ° . Based on Monte Carlo simulations, these changes in film properties are correlated with an increase in the average impact angle of the ballistic component of atomic flux. Implications of these results to deposition onto non-planar substrates are discussed.
- Published
- 2021
14. Sputtered Au–Ta films with tunable electrical resistivity
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J. H. Bae, Jacob L. Beckham, S. J. Shin, Scott K. McCall, Sergei O. Kucheyev, J. D. Moody, A. M. Engwall, Alexander A. Baker, X. Lepro Chavez, and L. B. Bayu Aji
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Materials science ,Acoustics and Ultrasonics ,business.industry ,Electrical resistivity and conductivity ,Optoelectronics ,Thin film ,Sputter deposition ,Condensed Matter Physics ,business ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials - Abstract
Gold–tantalum alloy films are attractive for hohlraums used in indirect drive magnetized inertial confinement fusion. A high electrical resistivity of over ∼100 µΩ cm at cryogenic temperatures is an essential requirement for allowing an externally imposed pulsed magnetic field to soak through a hohlraum and magnetize the fusion fuel. Here, we systematically study properties of Au–Ta alloy films in the entire compositional range from pure Au to pure Ta with thicknesses up to 30 µm. These films are made by direct current magnetron co-sputtering on planar substrates. Films are characterized by a combination of high-energy ion scattering, x-ray diffraction, electron microscopy, nanoindentation, and electrical transport measurements. Results show that an alloy with ∼80 at.% of Ta forms a metallic glass exhibiting a maximum electrical resistivity of ∼300 µΩ cm with a weak temperature dependence in the range of 5–400 K. The deposition of a film with ∼80 at.% of Ta onto a sphero-cylindrical substrate for hohlraum fabrication is also demonstrated.
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- 2020
15. Sputter-deposited low-stress boron carbide films
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J. H. Bae, A. M. Engwall, Sergei O. Kucheyev, P. B. Mirkarimi, L. B. Bayu Aji, and S. J. Shin
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010302 applied physics ,Materials science ,General Physics and Astronomy ,02 engineering and technology ,Substrate (electronics) ,Boron carbide ,Sputter deposition ,021001 nanoscience & nanotechnology ,01 natural sciences ,Molecular physics ,Amorphous solid ,Stress (mechanics) ,Condensed Matter::Materials Science ,chemistry.chemical_compound ,chemistry ,Sputtering ,Residual stress ,0103 physical sciences ,Deposition (phase transition) ,0210 nano-technology - Abstract
Significant challenges have been faced in the manufacturing of low-stress B 4C films. Here, we demonstrate a set of process parameters for direct-current magnetron sputter deposition of smooth, high-purity, amorphous B 4C films with near-zero total residual stress and with thicknesses up to 10 μm. Films are characterized by a combination of high-energy ion scattering, x-ray diffraction, electron microscopy, and stress measurements based on substrate curvature. In order to facilitate the process transfer to other sputtering geometries, the favorable deposition conditions are correlated with distributions of landing energies and incident angles of depositing species estimated by Monte Carlo simulations of ballistic collisions and gas phase atomic transport. Based on such simulations, a decrease in compressive stress with increasing Ar working gas pressure is attributed to the corresponding broadening of the angular distribution of depositing species and associated atomic shadowing effects.
- Published
- 2020
16. Hollow-cathode chemical vapor deposition of thick, low-stress diamond-like carbon films
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Sergei O. Kucheyev, C. Wasz, Selim Elhadj, A. Moore, S. Falabella, Alejandro Ceballos, L. B. Bayu Aji, and J S Miller
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Materials science ,Diamond-like carbon ,Analytical chemistry ,chemistry.chemical_element ,02 engineering and technology ,Chemical vapor deposition ,01 natural sciences ,Condensed Matter::Materials Science ,symbols.namesake ,Physics::Plasma Physics ,0103 physical sciences ,Materials Chemistry ,010302 applied physics ,Metals and Alloys ,Surfaces and Interfaces ,Plasma ,021001 nanoscience & nanotechnology ,Rutherford backscattering spectrometry ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Amorphous solid ,Elastic recoil detection ,chemistry ,symbols ,0210 nano-technology ,Raman spectroscopy ,Carbon - Abstract
A radio-frequency (RF), hollow-cathode plasma source with confining magnetic field is described for the chemical vapor deposition of thick ( > 10 µm), amorphous diamond-like carbon ablator films for inertial confinement fusion applications. Plasma is characterized by optical emission spectroscopy, while properties of the resultant films are measured by a combination of profilometry, Rutherford backscattering spectrometry, elastic recoil detection analysis, X-ray diffraction, Raman spectroscopy, and atomic force microscopy. The dependence of the deposition rate, film density, elemental composition, self-bias and residual stress is reported as a function of RF power. Higher density films were found when using Ar plasma, than N2 or H2 plasma. The coatings produced are x-ray amorphous, exhibit low compressive stress ( ~ 100 MPa), high density (
- Published
- 2020
17. Superconducting magnesium diboride films for levitation of laser targets
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Alexander A. Baker, S. J. Shin, Scott K. McCall, R. E. Jacob, J. H. Bae, Jacob L. Beckham, Sergei O. Kucheyev, and L. B. Bayu Aji
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010302 applied physics ,Materials science ,Metals and Alloys ,02 engineering and technology ,Surfaces and Interfaces ,Chemical vapor deposition ,Sputter deposition ,engineering.material ,Glassy carbon ,021001 nanoscience & nanotechnology ,01 natural sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,chemistry.chemical_compound ,Coating ,chemistry ,0103 physical sciences ,Materials Chemistry ,engineering ,Magnesium diboride ,Levitation ,Graphite ,Composite material ,Thin film ,0210 nano-technology - Abstract
Inertial confinement fusion targets would benefit from being levitated inside hohlraums to avoid capsule support-related implosion perturbations. Levitation inside a magnetic trap requires coating the capsule with a thin film that is superconducting at 20 K. Such non-epitaxial film growth on non-planar substrates is challenging. Here, we study Mg vapor annealing and solid-phase reactive inter-diffusion methods to form superconducting magnesium diboride (MgB2) films on different planar and spherical carbon substrates, evaluating glassy carbon, polycrystalline diamond made by chemical vapor deposition, and carbon deposited by magnetron sputtering of graphite targets. Thin films of B and Mg are produced by magnetron sputtering onto stationary planar or rolling spherical substrates and annealed at either 600 or 850 ∘C in Mg vapor. The films are characterized by a combination of high-energy ion scattering, electron microscopy, and magnetometry. Results show that the critical superconducting temperature of resultant films depends on film microstructure and oxygen impurity content. The formation of MgB2 films is also strongly substrate dependent, even in this case of non-epitaxial growth. Important factors to consider are oxygen outgassing of the substrate during thermal processing, substrate surface roughness, and the matching of thermal expansion coefficients of different layers in the multilayer structure.
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- 2020
18. Superconducting films of MgB2 via ion beam mixing of Mg/B multilayers
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R. E. Jacob, Jacob L. Beckham, Sergei O. Kucheyev, Scott K. McCall, Elissaios Stavrou, Alexander A. Baker, L. B. Bayu Aji, and J. H. Bae
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Materials science ,Acoustics and Ultrasonics ,Ion beam mixing ,Condensed matter physics ,Annealing (metallurgy) ,Transition temperature ,Condensed Matter Physics ,Epitaxy ,Crystallographic defect ,Charged particle ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Ion ,chemistry.chemical_compound ,chemistry ,Magnesium diboride - Published
- 2020
19. Deterministic Role of Collision Cascade Density in Radiation Defect Dynamics in Si
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Sergei O. Kucheyev, J. B. Wallace, L. B. Bayu Aji, and Lin Shao
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Arrhenius equation ,Range (particle radiation) ,Materials science ,Ion beam ,General Physics and Astronomy ,02 engineering and technology ,Activation energy ,021001 nanoscience & nanotechnology ,01 natural sciences ,Molecular physics ,Ion ,symbols.namesake ,Cascade ,0103 physical sciences ,symbols ,Collision cascade ,Irradiation ,010306 general physics ,0210 nano-technology - Abstract
The formation of stable radiation damage in solids often proceeds via complex dynamic annealing (DA) processes, involving point defect migration and interaction. The dependence of DA on irradiation conditions remains poorly understood even for Si. Here, we use a pulsed ion beam method to study defect interaction dynamics in Si bombarded in the temperature range from ∼-30 °C to 210 °C with ions in a wide range of masses, from Ne to Xe, creating collision cascades with different densities. We demonstrate that the complexity of the influence of irradiation conditions on defect dynamics can be reduced to a deterministic effect of a single parameter, the average cascade density, calculated by taking into account the fractal nature of collision cascades. For each ion species, the DA rate exhibits two well-defined Arrhenius regions where different DA mechanisms dominate. These two regions intersect at a critical temperature, which depends linearly on the cascade density. The low-temperature DA regime is characterized by an activation energy of ∼0.1 eV, independent of the cascade density. The high-temperature regime, however, exhibits a change in the dominant DA process for cascade densities above ∼0.04 at.%, evidenced by an increase in the activation energy. These results clearly demonstrate a crucial role of the collision cascade density and can be used to predict radiation defect dynamics in Si.
- Published
- 2018
20. The amorphization of 3C-SiC irradiated at moderately elevated temperatures as revealed by X-ray diffraction
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J. B. Wallace, Alexandre Boulle, L. B. Bayu Aji, Sergei O. Kucheyev, Aurélien Debelle, IRCER - Axe 3 : organisation structurale multiéchelle des matériaux (IRCER-AXE3), Institut de Recherche sur les CERamiques (IRCER), Institut des Procédés Appliqués aux Matériaux (IPAM), Université de Limoges (UNILIM)-Université de Limoges (UNILIM)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS)-Institut des Procédés Appliqués aux Matériaux (IPAM), Université de Limoges (UNILIM)-Université de Limoges (UNILIM)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS), Centre de Spectrométrie Nucléaire et de Spectrométrie de Masse (CSNSM), Centre National de la Recherche Scientifique (CNRS)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Université Paris-Sud - Paris 11 (UP11), Speed Laboratory, University of Galasgow, Axe 3 : organisation structurale multiéchelle des matériaux (SPCTS-AXE3), Science des Procédés Céramiques et de Traitements de Surface (SPCTS), Université de Limoges (UNILIM)-Ecole Nationale Supérieure de Céramique Industrielle (ENSCI)-Institut des Procédés Appliqués aux Matériaux (IPAM), Université de Limoges (UNILIM)-Université de Limoges (UNILIM)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS)-Université de Limoges (UNILIM)-Ecole Nationale Supérieure de Céramique Industrielle (ENSCI)-Institut des Procédés Appliqués aux Matériaux (IPAM), and Université Paris-Sud - Paris 11 (UP11)-Institut National de Physique Nucléaire et de Physique des Particules du CNRS (IN2P3)-Centre National de la Recherche Scientifique (CNRS)
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010302 applied physics ,Diffraction ,Materials science ,Polymers and Plastics ,Metals and Alloys ,Analytical chemistry ,02 engineering and technology ,[CHIM.MATE]Chemical Sciences/Material chemistry ,Atmospheric temperature range ,021001 nanoscience & nanotechnology ,01 natural sciences ,Fluence ,[SPI.MAT]Engineering Sciences [physics]/Materials ,Electronic, Optical and Magnetic Materials ,Ion ,Crystal ,Crystallography ,0103 physical sciences ,X-ray crystallography ,Ceramics and Composites ,Radiation damage ,Irradiation ,0210 nano-technology ,ComputingMilieux_MISCELLANEOUS - Abstract
International audience; Mechanisms of radiation damage buildup in 3C-SiC remain poorly understood. Here, we use X-ray diffraction in combination with numerical simulations to study depth profiles of radiation-produced strain and lattice damage in 3C-SiC bombarded in the temperature range of 25-200 °C with 500 keV Ar ions. Results reveal increased defect recombination with increasing temperature, with a critical amorphization fluence increasing from 0.17 to 0.44 displacements per atom. The amorphization process is found to be correlated with the evolution of lattice strain. We find that, at fluences corresponding to the onset of amorphization, lattice strain is ~2% and is independent of temperature. With continuing bombardment above the onset of amorphization, the strain in the crystal bulk increases and reaches a saturation value that decreases from 7% to 5% with increasing temperature. Based on strain profiles, we compute depth profiles of the effective concentration of point defect clusters in the crystalline phase. Bombardment at higher temperatures results in lower maximum defect concentrations pointing to enhanced defect mobility. 1
- Published
- 2017
21. Fractal analysis of collision cascades in pulsed-ion-beam-irradiated solids
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J. B. Wallace, Sergei O. Kucheyev, L. B. Bayu Aji, and Lin Shao
- Subjects
Multidisciplinary ,Materials science ,Ion beam ,lcsh:R ,lcsh:Medicine ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Fractal dimension ,Molecular physics ,Fractal analysis ,Article ,Ion ,Fractal ,Cascade ,0103 physical sciences ,Radiation damage ,lcsh:Q ,Diffusion (business) ,lcsh:Science ,010306 general physics ,0210 nano-technology - Abstract
The buildup of radiation damage in ion-irradiated crystals often depends on the spatial distribution of atomic displacements within collision cascades. Although collision cascades have previously been described as fractals, the correlation of their fractal parameters with experimental observations of radiation damage buildup remains elusive. Here, we use a pulsed-ion-beam method to study defect interaction dynamics in 3C-SiC irradiated at 100 °C with ions of different masses. These data, together with results of previous studies of SiC and Si, are analyzed with a model of radiation damage formation which accounts for the fractal nature of collision cascades. Our emphasis is on the extraction of the effective defect diffusion length from pulsed beam measurements. Results show that, for both Si and SiC, collision cascades are mass fractals with fractal dimensions in the range of ~1–2, depending on ion mass, energy, and the depth from the sample surface. Within our fractal model, the effective defect diffusion length is ~10 nm for SiC and ~20 nm for Si, and it decreases with increasing cascade density. These results demonstrate a general method by which the fractal nature of collision cascades can be used to explain experimental observations and predict material’s response to radiation.
- Published
- 2017
22. Effects of collision cascade density on radiation defect dynamics in 3C-SiC
- Author
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L. B. Bayu Aji, Sergei O. Kucheyev, and J. B. Wallace
- Subjects
010302 applied physics ,Multidisciplinary ,Materials science ,Dynamics (mechanics) ,Time constant ,02 engineering and technology ,Radiation ,021001 nanoscience & nanotechnology ,Collision ,01 natural sciences ,Molecular physics ,Article ,Ion ,Condensed Matter::Materials Science ,Cascade ,0103 physical sciences ,Radiation damage ,Collision cascade ,0210 nano-technology ,Nuclear Experiment - Abstract
Effects of the collision cascade density on radiation damage in SiC remain poorly understood. Here, we study damage buildup and defect interaction dynamics in 3C-SiC bombarded at 100 °C with either continuous or pulsed beams of 500 keV Ne, Ar, Kr, or Xe ions. We find that bombardment with heavier ions, which create denser collision cascades, results in a decrease in the dynamic annealing efficiency and an increase in both the amorphization cross-section constant and the time constant of dynamic annealing. The cascade density behavior of these parameters is non-linear and appears to be uncorrelated. These results demonstrate clearly (and quantitatively) an important role of the collision cascade density in dynamic radiation defect processes in 3C-SiC.
- Published
- 2017
23. The role of Frenkel defect diffusion in dynamic annealing in ion-irradiated Si
- Author
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Lin Shao, J. B. Wallace, L. B. Bayu Aji, S. J. Shin, Sergei O. Kucheyev, and Aiden A. Martin
- Subjects
Arrhenius equation ,Multidisciplinary ,Materials science ,Ion beam ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Crystallographic defect ,Article ,Ion ,symbols.namesake ,Condensed Matter::Materials Science ,Chemical physics ,Vacancy defect ,Kröger–Vink notation ,0103 physical sciences ,symbols ,Frenkel defect ,Diffusion (business) ,010306 general physics ,0210 nano-technology - Abstract
The formation of stable radiation damage in crystalline solids often proceeds via complex dynamic annealing processes, involving migration and interaction of ballistically-generated point defects. The dominant dynamic annealing processes, however, remain unknown even for crystalline Si. Here, we use a pulsed ion beam method to study defect dynamics in Si bombarded in the temperature range from −20 to 140 °C with 500 keV Ar ions. Results reveal a defect relaxation time constant of ~10–0.2 ms, which decreases monotonically with increasing temperature. The dynamic annealing rate shows an Arrhenius dependence with two well-defined activation energies of 73 ± 5 meV and 420 ± 10 meV, below and above 60 °C, respectively. Rate theory modeling, bench-marked against this data, suggests a crucial role of both vacancy and interstitial diffusion, with the dynamic annealing rate limited by the migration and interaction of vacancies.
- Published
- 2017
- Full Text
- View/download PDF
24. Radiation defect dynamics in SiC with pre-existing defects
- Author
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L. B. Bayu Aji, Sergei O. Kucheyev, and J. B. Wallace
- Subjects
010302 applied physics ,Materials science ,Ion beam ,Condensed matter physics ,Time constant ,General Physics and Astronomy ,Defect engineering ,02 engineering and technology ,Radiation ,021001 nanoscience & nanotechnology ,Relaxation time constant ,01 natural sciences ,Dynamic annealing ,stomatognathic system ,Lattice (order) ,0103 physical sciences ,0210 nano-technology - Abstract
The influence of pre-existing lattice disorder on radiation defect dynamics in SiC remains unexplored. Here, we use a pulsed ion beam method to study dynamic annealing in Ar-ion-bombarded 3C-SiC at 200 °C with different levels of pre-existing lattice disorder. Results reveal a nonmonotonic dependence of the defect relaxation time constant on the level of pre-existing disorder, exhibiting a maximum of ∼4 ms at a level of relative initial disorder of ∼0.4, while crystals without pre-existing damage are characterized by a time constant of ∼1.4 ms. These observations demonstrate that radiation defect dynamics in SiC can be controlled by defect engineering.
- Published
- 2019
25. Control of superconductivity in MgB2 by ion bombardment
- Author
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J. H. Bae, Jacob L. Beckham, Scott K. McCall, Elissaios Stavrou, Sergei O. Kucheyev, L. B. Bayu Aji, and Alexander A. Baker
- Subjects
Superconductivity ,chemistry.chemical_compound ,Materials science ,Acoustics and Ultrasonics ,chemistry ,Condensed matter physics ,Magnesium diboride ,Levitation ,Condensed Matter Physics ,Ion bombardment ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials - Published
- 2019
26. Solid-phase reactive inter-diffusion of Mg/B multilayers
- Author
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A. A. Maich, Scott K. McCall, Sergei O. Kucheyev, L. B. Bayu Aji, J. H. Bae, J. A. Rodriguez, Alexander A. Baker, and R. E. Jacob
- Subjects
010302 applied physics ,Materials science ,Diffusion ,Kinetics ,Nucleation ,General Physics and Astronomy ,Thermodynamics ,02 engineering and technology ,Activation energy ,Glassy carbon ,Atmospheric temperature range ,021001 nanoscience & nanotechnology ,01 natural sciences ,Chemical kinetics ,Condensed Matter::Superconductivity ,Phase (matter) ,0103 physical sciences ,0210 nano-technology - Abstract
A better understanding of the reaction of Mg and B in the solid-phase regime is needed for the low-temperature synthesis of MgB2 films. Here, we study the kinetics of reactive inter-diffusion of Mg and B multilayers on glassy carbon substrates in the temperature range of 400−650°C. Results show that, at these temperatures, inter-diffusion is characterized by a single activation energy of ∼0.45eV. The formation of the superconducting MgB2 phase with critical temperatures of 25–31 K occurs at reaction temperatures of 450°C and above, with the rate of inter-diffusion obeying a power law with a kinetic exponent of ∼0.3. This suggests that rate-limiting processes are the nucleation and growth of MgB2 grains rather than diffusion and interfacial reactions. Implications of these results to the low-temperature synthesis of MgB2 films are discussed.
- Published
- 2019
27. Non-monotonic temperature dependence of radiation defect dynamics in silicon carbide
- Author
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J. B. Wallace, Sergei O. Kucheyev, Lin Shao, and L. B. Bayu Aji
- Subjects
010302 applied physics ,Multidisciplinary ,Materials science ,Condensed matter physics ,Dynamics (mechanics) ,Particle irradiation ,Monotonic function ,02 engineering and technology ,Radiation ,Atmospheric temperature range ,021001 nanoscience & nanotechnology ,01 natural sciences ,Article ,chemistry.chemical_compound ,Dynamic annealing ,chemistry ,visual_art ,0103 physical sciences ,Silicon carbide ,visual_art.visual_art_medium ,Ceramic ,0210 nano-technology - Abstract
Understanding response of solids to particle irradiation remains a major materials physics challenge. This applies even to SiC, which is a prototypical nuclear ceramic and wide-band-gap semiconductor material. The lack of predictability is largely related to the complex, dynamic nature of radiation defect formation. Here, we use a novel pulsed-ion-beam method to study dynamic annealing in 4H-SiC ion-bombarded in the temperature range of 25–250 °C. We find that, while the defect recombination efficiency shows an expected monotonic increase with increasing temperature, the defect lifetime exhibits a non-monotonic temperature dependence with a maximum at ~100 °C. This finding indicates a change in the dominant defect interaction mechanism at ~100 °C. The understanding of radiation defect dynamics may suggest new paths to designing radiation-resistant materials.
- Published
- 2016
- Full Text
- View/download PDF
28. Radiation defect dynamics in GaAs studied by pulsed ion beams
- Author
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L. B. Bayu Aji, Sergei O. Kucheyev, and J. B. Wallace
- Subjects
0301 basic medicine ,Materials science ,Annealing (metallurgy) ,General Physics and Astronomy ,Activation energy ,Atmospheric temperature range ,Molecular physics ,Ion ,Arsenide ,Gallium arsenide ,Condensed Matter::Materials Science ,03 medical and health sciences ,chemistry.chemical_compound ,030104 developmental biology ,chemistry ,Melting point ,Irradiation - Abstract
Gallium arsenide under ion bombardment at room temperature and above exhibits pronounced dynamic annealing that remains poorly understood. Here, we use a pulsed beam method to study radiation defect dynamics in GaAs in the temperature range of 20–100 °C irradiated with 500 keV Xe ions. Results show that, with increasing temperature, the defect relaxation time constant monotonically decreases from ∼5.2 to ∼0.4 ms. A change in the dominant dynamic annealing process occurs at a critical temperature of ∼60 °C, as evidenced by a change in the activation energy. A comparison with the other semiconductors studied by the pulsed beam method (Si, Ge, and 4H-SiC) reveals that both the high-temperature activation energy and the temperature below which dynamic annealing becomes negligible scale with the melting point.Gallium arsenide under ion bombardment at room temperature and above exhibits pronounced dynamic annealing that remains poorly understood. Here, we use a pulsed beam method to study radiation defect dynamics in GaAs in the temperature range of 20–100 °C irradiated with 500 keV Xe ions. Results show that, with increasing temperature, the defect relaxation time constant monotonically decreases from ∼5.2 to ∼0.4 ms. A change in the dominant dynamic annealing process occurs at a critical temperature of ∼60 °C, as evidenced by a change in the activation energy. A comparison with the other semiconductors studied by the pulsed beam method (Si, Ge, and 4H-SiC) reveals that both the high-temperature activation energy and the temperature below which dynamic annealing becomes negligible scale with the melting point.
- Published
- 2018
29. Vapor annealing synthesis of non-epitaxial MgB2films on glassy carbon
- Author
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J. H. Bae, D. J. Steich, Alexander A. Baker, Scott K. McCall, L. B. Bayu Aji, Sergei O. Kucheyev, and Elissaios Stavrou
- Subjects
Materials science ,Annealing (metallurgy) ,Metals and Alloys ,02 engineering and technology ,Glassy carbon ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Epitaxy ,01 natural sciences ,Chemical engineering ,0103 physical sciences ,Materials Chemistry ,Ceramics and Composites ,Electrical and Electronic Engineering ,010306 general physics ,0210 nano-technology - Published
- 2018
30. Dose-rate dependence of damage buildup in 3C-SiC
- Author
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J. B. Wallace, L. B. Bayu Aji, Sergei O. Kucheyev, and Tian T. Li
- Subjects
010302 applied physics ,Materials science ,Wide-bandgap semiconductor ,General Physics and Astronomy ,02 engineering and technology ,Atmospheric temperature range ,021001 nanoscience & nanotechnology ,Channelling ,01 natural sciences ,Molecular physics ,Ion ,law.invention ,Transmission electron microscopy ,law ,0103 physical sciences ,Radiation damage ,Electron microscope ,Atomic physics ,0210 nano-technology ,Saturation (chemistry) - Abstract
The influence of the defect generation rate on radiation damage processes in SiC remains poorly understood. Here, we use a combination of ion channeling and transmission electron microscopy to systematically study the dose-rate dependence of damage buildup in 3C-SiC bombarded in the temperature range of 25–200 °C with 500 keV Ar ions. The results reveal a pronounced dose-rate effect, whose magnitude increases close-to-linearly with temperature. When ion dose and temperature are held constant, the dose-rate dependence of the damage level is nonlinear, with saturation at high dose rates. Electron microscopy reveals that the average size of stable defect clusters increases with increasing dose rate. These findings have important implications for understanding and predicting radiation damage in SiC.
- Published
- 2017
31. Effect of medium range order on pulsed laser crystallization of amorphous germanium thin films
- Author
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Melissa K. Santala, L. B. Bayu Aji, Sergei O. Kucheyev, G. H. Campbell, Tae Wook Heo, and Tian T. Li
- Subjects
010302 applied physics ,Materials science ,Physics and Astronomy (miscellaneous) ,Analytical chemistry ,Crystal growth ,02 engineering and technology ,Sputter deposition ,021001 nanoscience & nanotechnology ,01 natural sciences ,Amorphous solid ,law.invention ,Pulsed laser deposition ,Crystallography ,law ,Sputtering ,Transmission electron microscopy ,0103 physical sciences ,sense organs ,Thin film ,Crystallization ,0210 nano-technology - Abstract
Sputter deposited amorphous Ge thin films had their nanostructure altered by irradiation with high-energy Ar+ ions. The change in the structure resulted in a reduction in medium range order (MRO) characterized using fluctuation electron microscopy. The pulsed laser crystallization kinetics of the as-deposited versus irradiated materials were investigated using the dynamic transmission electron microscope operated in the multi-frame movie mode. The propagation rate of the crystallization front for the irradiated material was lower; the changes were correlated to the MRO difference and formation of a thin liquid layer during crystallization.
- Published
- 2016
32. Effective defect diffusion lengths in Ar-ion bombarded 3C-SiC
- Author
-
J. B. Wallace, Sergei O. Kucheyev, L. B. Bayu Aji, and Lin Shao
- Subjects
Materials science ,Acoustics and Ultrasonics ,Ion beam ,02 engineering and technology ,Atmospheric temperature range ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Crystallographic defect ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Ion ,stomatognathic system ,0103 physical sciences ,Radiation damage ,Atomic physics ,Diffusion (business) ,010306 general physics ,0210 nano-technology - Abstract
Above room temperature, SiC exhibits pronounced processes of diffusion and interaction of radiation-generated point defects. Here, we use the recently developed pulsed ion beam method to measure effective defect diffusion lengths in 3C-SiC bombarded in the temperature range of 25–200 °C with 500 keV Ar ions. Results reveal a diffusion length of ~10 nm, which exhibits a weak temperature dependence, changing from 9 to 13 nm with increasing temperature. Lastly, these results have important implications for understanding and predicting radiation damage in SiC and for the development of radiation-resistant materials via interface-mediated defect reactions.
- Published
- 2016
33. Radiation defect dynamics in Si at room temperature studied by pulsed ion beams
- Author
-
M.T. Myers, J. B. Wallace, L. B. Bayu Aji, Supakit Charnvanichborikarn, Sergei O. Kucheyev, and Lin Shao
- Subjects
Thermalisation ,Dopant ,Annealing (metallurgy) ,Chemistry ,Time constant ,General Physics and Astronomy ,Radiation ,Atomic physics ,Channelling ,Kinetic energy ,Ion - Abstract
The evolution of radiation defects after the thermalization of collision cascades often plays the dominant role in the formation of stable radiation disorder in crystalline solids of interest to electronics and nuclear materials applications. Here, we explore a pulsed-ion-beam method to study defect interaction dynamics in Si crystals bombarded at room temperature with 500 keV Ne, Ar, Kr, and Xe ions. The effective time constant of defect interaction is measured directly by studying the dependence of lattice disorder, monitored by ion channeling, on the passive part of the beam duty cycle. The effective defect diffusion length is revealed by the dependence of damage on the active part of the beam duty cycle. Results show that the defect relaxation behavior obeys a second order kinetic process for all the cases studied, with a time constant in the range of ∼4–13 ms and a diffusion length of ∼15–50 nm. Both radiation dynamics parameters (the time constant and diffusion length) are essentially independent of the maximum instantaneous dose rate, total ion dose, and dopant concentration within the ranges studied. However, both the time constant and diffusion length increase with increasing ion mass. This demonstrates that the density of collision cascades influences not only defect production and annealing efficiencies but also the defect interaction dynamics.
- Published
- 2015
34. Damage buildup in Ar-ion-irradiated 3C-SiC at elevated temperatures
- Author
-
Tian T. Li, J. B. Wallace, Sergei O. Kucheyev, L. B. Bayu Aji, and Lin Shao
- Subjects
Materials science ,Transmission electron microscopy ,Ion channeling ,Radiation damage ,General Physics and Astronomy ,Irradiation ,Atomic physics ,Atmospheric temperature range ,Channelling ,Molecular physics ,Ion - Abstract
Above room temperature, the accumulation of radiation damage in 3C-SiC is strongly influenced by dynamic defect interaction processes and remains poorly understood. Here, we use a combination of ion channeling and transmission electron microscopy to study lattice disorder in 3C-SiC irradiated with 500 keV Ar ions in the temperature range of 25–250 °C. Results reveal sigmoidal damage buildup for all the temperatures studied. For 150 °C and below, the damage level monotonically increases with ion dose up to amorphization. Starting at 200 °C, the shape of damage–depth profiles becomes anomalous, with the damage peak narrowing and moving to larger depths and an additional shoulder forming close to the ion end of range. As a result, damage buildup curves for 200 and 250 °C exhibit an anomalous two-step shape, with a damage saturation stage followed by rapid amorphization above a critical ion dose, suggesting a nucleation-limited amorphization behavior. Despite their complexity, all damage buildup curves are we...
- Published
- 2015
35. Time constant of defect relaxation in ion-irradiated 3C-SiC
- Author
-
J. B. Wallace, Lin Shao, L. B. Bayu Aji, and Sergei O. Kucheyev
- Subjects
Condensed Matter::Materials Science ,Materials science ,Physics and Astronomy (miscellaneous) ,Annealing (metallurgy) ,Relaxation (NMR) ,Radiation damage ,Time constant ,Irradiation ,Atomic physics ,Channelling ,Crystallographic defect ,Ion - Abstract
Above room temperature, the buildup of radiation damage in SiC is a dynamic process governed by the mobility and interaction of ballistically generated point defects. Here, we study the dynamics of radiation defects in 3C-SiC bombarded at 100 °C with 500 keV Ar ions, with the total ion dose split into a train of equal pulses. Damage–depth profiles are measured by ion channeling for a series of samples irradiated under identical conditions except for different durations of the passive part of the beam cycle. Results reveal an effective defect relaxation time constant of ∼3 ms (for second order kinetics) and a dynamic annealing efficiency of ∼40% for defects in both Si and C sublattices. This demonstrates a crucial role of dynamic annealing at elevated temperatures and provides evidence of the strong coupling of defect accumulation processes in the two sublattices of 3C-SiC.
- Published
- 2015
36. Superconducting films of MgB2 via ion beam mixing of Mg/B multilayers.
- Author
-
J L Beckham, L B Bayu Aji, A A Baker, J H Bae, E Stavrou, R E Jacob, S K McCall, and S O Kucheyev
- Subjects
- *
SUPERCONDUCTING films , *ION beams , *ION bombardment , *ANNEALING of metals , *MULTILAYERS , *SUPERCONDUCTING transition temperature , *MULTILAYERED thin films - Abstract
The growth of smooth superconducting MgB2 films in a non-epitaxial regime is challenging. Here, we study the formation of superconducting MgB2 films by solid-phase reactive inter-diffusion of sputter-deposited Mg/B multilayers, employing ion beam mixing to disperse the multilayers prior to thermal annealing. The multilayers are intermixed by room-temperature bombardment with 500 keV Xe ions to doses up to 4 × 1016 cm−2, followed by thermal annealing to form MgB2. Results show that such an intermixing step leads to a dramatic reduction in surface roughness of superconducting films. However, lattice defects produced by ion bombardment reduce the critical superconducting transition temperature, an effect which scales monotonically with ion dose. The critical temperature can be recovered by an additional defect annealing step at . [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
37. Control of superconductivity in MgB2 by ion bombardment.
- Author
-
A A Baker, L B Bayu Aji, J H Bae, E Stavrou, J L Beckham, S K McCall, and S O Kucheyev
- Subjects
- *
ION bombardment , *CURRENT density (Electromagnetism) , *SUPERCONDUCTING transition temperature , *SUPERCONDUCTIVITY , *SUPERCONDUCTING transitions , *ATOMIC displacements - Abstract
The superconducting properties of MgB2 can be modified via controlled introduction of lattice defects by ion bombardment. Here, magnetometry and Raman spectroscopy are used to study ∼160 nm-thick MgB2 films bombarded at room temperature with megaelectronvolt-energy He, Ar, or Xe ions. Ion bombardment leads to a monotonic reduction in the critical superconducting transition temperature, transition width, and critical current density. There is a clear collision cascade density effect, whereby radiation-induced changes, once normalized to the number of atomic displacements generated, are greater for heavier ions. The sharpening of the superconducting transition with increasing ion dose suggests improved homogeneity of irradiated films. The suppression of superconducting properties correlates with the growth of defect signatures revealed by Raman spectroscopy. Superconducting properties can be recovered by annealing at relatively low temperatures of 500 °C, even for films exposed to high doses of heavy ions. These results have direct implications for the performance of MgB2 in radiation environments and understanding its defect-mediated superconductivity. [ABSTRACT FROM AUTHOR]
- Published
- 2019
- Full Text
- View/download PDF
38. Vapor annealing synthesis of non-epitaxial MgB2 films on glassy carbon.
- Author
-
A A Baker, L B Bayu Aji, J H Bae, E Stavrou, D J Steich, S K McCall, and S O Kucheyev
- Subjects
- *
EPITAXY , *THICK films , *MAGNESIUM diboride - Abstract
We describe the fabrication and characterization of 25–800 nm thick MgB2 films on glassy carbon substrates by Mg vapor annealing of sputter-deposited amorphous B films. Results demonstrate a critical role of both the initial B film thickness and the temperature–time profile on the microstructure, elemental composition, and superconducting properties of the resultant MgB2 films. Films with thicknesses of 55 nm and below exhibit a smooth surface, with a roughness of 1.1 nm, while thicker films have surface morphology consisting of elongated nano-crystallites. The suppression of the superconducting transition temperature for thin films scales linearly with the oxygen impurity concentration and also correlates with the amount of lattice disorder probed by Raman scattering. The best results are obtained by a rapid (12 min) anneal at 850 °C with large temperature ramp and cooling rates of ∼540 °C min−1. Such fast processing suppresses the deleterious oxygen uptake. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
39. Effective defect diffusion lengths in Ar-ion bombarded 3C-SiC.
- Author
-
L B Bayu Aji, J B Wallace, L Shao, and S O Kucheyev
- Subjects
- *
SILICON carbide , *DIFFUSION , *ARGON , *IONS , *ION bombardment - Abstract
Above room temperature, SiC exhibits pronounced processes of diffusion and interaction of radiation-generated point defects. Here, we use the recently developed pulsed ion beam method to measure effective defect diffusion lengths in 3C-SiC bombarded in the temperature range of 25–200 °C with 500 keV Ar ions. Results reveal a diffusion length of ∼10 nm, which exhibits a weak temperature dependence, changing from 9 to 13 nm with increasing temperature. These results have important implications for understanding and predicting radiation damage in SiC and for the development of radiation-resistant materials via interface-mediated defect reactions. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
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