Ivan V. Afanasyev-Charkin
Los Alamos National Laboratory
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Featured researches published by Ivan V. Afanasyev-Charkin.
Applied Physics Letters | 2000
Manabu Ishimaru; Ivan V. Afanasyev-Charkin; Kurt E. Sickafus
An ion-beam-induced metastable phase in magnesium aluminate spinel (MgAl2O4) has been examined in detail using transmission electron microscopy. Single crystals of MgAl2O4 with (111) orientation were irradiated with 180-keV Ne+ ions at 120 K to fluences of 1016 and 1017/cm2. Selected-area electron diffraction patterns obtained from the irradiation-induced damaged layer revealed that all even hkl reflections (e.g., 222) possess strong intensity, while all odd hkl reflections (e.g., 111) are weak. The features of these diffraction patterns corresponded to those of the rocksalt (NaCl) structure, suggesting that an ordered spinel to disordered rocksalt structural phase transformation in MgAl2O4 was induced by ion beam irradiation.
Journal of Physics: Condensed Matter | 2002
Manabu Ishimaru; Yoshihiko Hirotsu; Ivan V. Afanasyev-Charkin; Kurt E. Sickafus
Ion-beam-induced microstructures in magnesium aluminate (MgAl2O4) spinel have been examined using transmission electron microscopy (TEM). Irradiations were performed at cryogenic temperature (~120 K) on MgAl2O4 spinel single-crystal surfaces with (111) orientation, using 180 keV neon (Ne+) ions to ion fluences ranging from 1016 to 1017 Ne+ cm-2. Cross-sectional TEM observations indicated that the MgAl2O4 spinel transforms first into a metastable crystalline phase and then into an amorphous phase under these irradiation conditions. On the basis of selected-area electron diffraction and high-resolution TEM, we concluded that Ne-ion-beam irradiation induces an ordered spinel-to-disordered rock-salt-like structural phase transformation. Atomistic structures of amorphous MgAl2O4 were also examined on the basis of atomic pair distribution functions. We compared the experimentally obtained results with previous theoretically calculated results for the metastable and amorphous phases of MgAl2O4, and discussed the validity of the proposed ion-beam-induced structural changes in MgAl2O4 spinel.
Journal of Nuclear Materials | 2002
Ivan V. Afanasyev-Charkin; Kurt E. Sickafus
Abstract Fully stabilized zirconia is known as a radiation resistant material. The objective of many experiments on zirconia has been to test the susceptibility of this material to amorphization. Because zirconia exhibits high radiation tolerance, this has made very high fluence ion irradiation experiments a necessity and so, additional irradiation-induced effects such as surface sputtering become important. In this paper, we present results from 340 keV Xe ++ irradiations of yttria-stabilized zirconia (YSZ) to fluences ranging from 1×10 15 to 1.5×10 21 ions/m 2 . No amorphization of YSZ was observed after irradiation to even the highest ion fluence. To assess sputtering effects at high fluence, an analytical model was developed, using ion range and damage distributions calculated using Monte Carlo simulations for ion–solid interactions. Analysis results and experimental data revealed that at high fluences, the implanted ion and damage distribution profiles are significantly modified by sputtering.
Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms | 1999
Ivan V. Afanasyev-Charkin; V.T Gritsyna; D. W. Cooke; Bryan L. Bennett; Caleb R. Evans; Mark G. Hollander; Kurt E. Sickafus
Abstract We have studied changes in optical absorption of MgAl 2 O 4 spinel crystals implanted with 340 keV Xe ++ ions at about 120 K, to fluences ranging from 10 15 –10 21 ions/m 2 . With increasing ion fluence, we observe an increase in optical absorption, especially in the vicinity of two absorption bands: one centered at 5.3 eV, the other at 6.9 eV. The absorption band at 5.3 eV, caused by F-centers, saturates at a fluence between 1·10 18 and 1·10 19 ions/m 2 . This is the same dose range in which formation of a metastable phase of spinel has been reported previously. The band at 6.9 eV grows with increasing dose and saturates at 1·10 20 –3·10 20 ions/m 2 . Previous studies have shown that spinel is amorphized by Xe ion irradiation in this dose range. Annealing studies were also conducted on the Xe ion implanted spinel crystals. By optical absorption, F-centers were found to anneal at 500°C. Thermoluminescence measurements revealed a temperature dependence of luminescence that correlates well with the optical absorption.
Journal of Nuclear Materials | 2001
Ivan V. Afanasyev-Charkin; Robert M. Dickerson; D. Wayne Cooke; Bryan L. Bennett; V.T. Gritsyna; Kurt E. Sickafus
Abstract Single crystals of magnesium-aluminate spinel MgAl 2 O 4 were irradiated with 340 keV Xe ++ ions at −173°C (∼100 K). A fluence of 1×10 20 Xe/m 2 created an amorphous layer at the surface of the samples. The samples were annealed for 1 h at different temperatures ranging from 130°C to 880°C. Recrystallization took place in the temperature interval between 610°C and 855°C. Transmission electron microscopy (TEM) images show two distinct layers near the surface: (1) a polycrystalline layer with columnar grain structure; and (2) a buried damaged layer epitaxial with the substrate. After annealing at 1100°C for 52 days, the profile of implanted Xe ions did not change, which means that Xe ions are not mobile in the spinel structure up to 1100°C. The thickness of the buried damaged layer decreased significantly in the 1100°C annealed sample comparing to the sample annealed for 1 h at 855°C.
Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms | 2003
Ivan V. Afanasyev-Charkin; M. Nastasi
Abstract Materials with Si–C–N composition are of great interest due to their remarkable properties such as high hardness and oxidation resistance. In this study amorphous silicon nitride and silicon carbonitride films were deposited on glass, fused silica, and carbon substrates by the plasma immersion ion processing technique. Gas pressure during the deposition was kept around 0.13 Pa (1 mTorr) and SiH4, N2, Ar and C2H2 gas mixtures were used. Film hardness, composition and UV–visible optical absorption were characterized using nanoindentation, ion beam analysis techniques, and UV–visible spectroscopy, respectively. The films exhibit high transparency in the visible and near UV regions. Addition of the carbon to the films causes decrease in the density of the films, as well as decrease in hardness and transparency. These results suggest that in the low energy regime of PIIP the deposition of hard carbon composites with nitrogen and silicon does not take place.
Applied Physics Letters | 2004
Ivan V. Afanasyev-Charkin; M. Nastasi
Diamond-like carbon films were deposited using pulsed glow discharge deposition at 4kV. The duty factor was varied and all other parameters were kept constant. It was shown that the contribution of neutral particles to the total number of deposition atoms is much larger than that of energetic ions. At the same time, there is a relationship between the deposition of neutral particles and ion bombardment. The sticking coefficient of the neutral particles in proportional to the flux of energetic ions and does not exceed 5×10−4 for the deposition parameters used in our experiment.
Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms | 2000
V.T. Gritsyna; Ivan V. Afanasyev-Charkin; V.A. Kobyakov; T.I Voitsenya; Kurt E. Sickafus
Abstract The results of an investigation of thermoluminescence (TL) in nominally pure MgAl 2 O 4 spinel single crystals in the temperature range between 80–670 K are presented. For a heating rate of 0.21 K/s, TL spectra exhibit glow peaks in three distinct temperature ranges: 100–160, 270–370 and 470–670 K. The most prominent peaks are at 115, 140, 305, 335, 525, 570 and 605 K. The locations of the temperature maxima, as well as the intensity of the peaks, vary depending on the treatment of the crystals, the type of irradiation and the temperature of irradiation. Measurements of the glow peaks at different emission wavelengths and the use of partial bleaching and isothermal decay techniques for TL, allowed us to propose mechanisms for charge carrier rearrangement at lattice defects and impurity ions, during irradiation and subsequent heating.
Optical Materials | 2001
Ivan V. Afanasyev-Charkin; D. W. Cooke; M. Ishimaru; Bryan L. Bennett; V.T. Gritsyna; J.R. Williams; Kurt E. Sickafus
Abstract Single-crystal MgAl2O4 was subjected to 180 keV Ne+-ion irradiation to fluences of (1, 5, and 10)×10 20 ions/m 2 . The metastable and amorphous phases induced by irradiation were studied using transmission electron microscopy (TEM) and optical transmission spectroscopy. The thicknesses of implantation-induced layer structures were obtained from TEM observations. This information was then used in conjunction with optical transmission results to deduce the refractive indices of individual structures. It was found that the lowest ion fluence produces a metastable layer with a reduced index of refraction (n=1.70±0.005) relative to the pristine substrate (n=1.72), whereas the intermediate fluence induces an amorphous region (n=1.61±0.01) bounded by metastable regions. The effect of the highest fluence is to increase the thickness of the amorphous layer (n=1.60±0.01) at the expense of the metastable regions.
Journal of the American Ceramic Society | 2004
V.T. Gritsyna; Ivan V. Afanasyev-Charkin; Vladimir A. Kobyakov; Kurt E. Sickafus