In sito Ion Beam Analysis of Radiation Damage Kinetics in MgTiO 3 Single Crystals at 170-470 K
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Mat. Res. Soc. Symp. Proc. Vol. 396 © 1996 Materials Research Society
keV Xe 2+
2 MeV
Figure 1 Schematic representation of the geikielite sample orientation with respect to the irradiation beam and analysis beam during in situ ion beam experiments. the radiation damage kinetics in single crystal materials. This system also plays a complementary role to the HVEM-tandem facility at Argonne National Laboratory for radiation effects studies. The sample for ion irradiation was mounted onto a sample stage with silver paint. The orientation and translational motions of the sample were controlled by a multi-axis goniometer in a surface modification target chamber. The chamber was interconnected with both an ion irradiation beamline form a 200 kV implanter and an analysis beamline from a 3 MV tandem accelerator. The sample orientation geometry with respect to the two ion beams is shown schematically in Figure 1. Prior to ion irradiation, the unirradiated sample was first aligned with its axis along the 2 MeV He ion beam using Rutherford backscattering and ion channeling (RBS/C) measurements. The axis has a 350 angle to the c-axis that is close to the sample normal. The sample was then either cooled or heated to temperatures of 170, 300, and 470 K for sequential ion beam irradiation and analysis. Radiation induced lattice disorder was monitored through RBS/C measurements following each irradiation of 400 keV Xe 2+ ions. The irradiation and analysis beam spots were co-centered on the sample surface with beam sizes of about 7 and 2 mm in diameter. The incident angle of the irradiation beam was 25' with respect to the sample normal. The irradiation doses varied from 4x1012 to 2.5x]016 Xe/cm 2 with the irradiation beam flux maintained at -1x10 13 Xe/cm 2-s. The irradiation experiment at a given temperature proceeded until the lattice disorder in the irradiated sample reached a certain saturation level. Following each irradiation experiment at a chosen temperature, the sample was translated to set an unirradiated area for the next irradiation experiment at a different temperature. The sample orientation was maintained throughout the entire experiment, which lasted about eight hours. The LANL in situ capability enhanced the experimental efficiency by a factor of ten and improved the experimental accuracy as compared to those of conventional ex situ measurements. The projected range of 400 keV Xe ions at a 250 incident angle was estimated to be 75 nm, as determined by the TRIM code [12] using a mass density of 4.05 g/cm3 for geikielite. The damage level in the peak damage region was estimated to be 25 displacements per atom (dpa) for a dose of lxl016 Xe/cm 2 if a displacement energy of 40 eV was assumed for all elements. The peak concentration of implanted Xe in geikielite was about 2 at.% for lx1016 Xe/cm2 .
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Energy (MeV) 30
0.6
1.0
1.2
25 a)
20
N 15
Co 10 0
5 0 300
400
500
600
700
Channel Figure 2 In situ RBS/C spectra obtained from a MgTiO 3 crystal when the 2 MeV He incident ion beam was aligned along the
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