Defect creation in tracks produced by high energy carbon clusters in LiF

doi:10.1016/0168-583X(94)96213-8

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms

Volume 91, Issues 1–4, 1 June 1994, Pages 187-191

https://doi.org/10.1016/0168-583X(94)96213-8 Get rights and content

Abstract

LiF single crystals have been bombarded at room temperature with ₃ and C₅ clusters with energies of 1.74 MeV/carbon atom and fluences ranging from 10¹² to 10¹⁴ carbon atoms/cm². Point defects (color centers: F, F₂ etc.) resulting from electronic excitation processes were measured by optical absorption spectroscopy. The defect concentrations were compared to those produced by irradiations with single ¹²C ions with the respective energy and dose. Also using a differential optical absorption technique, it was possible to determine the defect concentrations close to the sample surface, when the tracks associated to each carbon atom of the cluster overlap. In this zone where the “cluster effect” is maximum due to the very high density of electronic excitations, enhanced defect production is observed. Defect concentrations as large as those obtained previously by Kr and Xe irradiations at GANIL have been measured. In addition to the high production rates of defects observed, aggregation laws (i.e. F → F₂) characteristic of cluster irradiations are also deduced.

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Structural, iono (IL) and thermoluminescence (TL) studies of Zn₂SiO₄:Sm³⁺ (1–5 mol%) nanophosphor bombarded with swift heavy ions in the fluence range 3.91×10¹²–21.48×10¹² cm⁻² have been carried out. The average crystallite sizes for pristine and ion irradiated for 3.91×10¹² ions cm⁻² and 21.48×10¹² ions cm⁻² were found to be 34, 26 and 20 nm. With increase of ion fluence, the intensity of XRD peaks decreases and FWHM increases. The peak broadening indicates the stress induced point/clusters defects produced due to heavy ion irradiation. IL studies were carried out for different Sm³⁺ concentrations in Zn₂SiO₄ by irradiating with ion fluence of 15.62×10¹² ions cm⁻². The characteristic emission peaks at ∼562, 599, 646 and 701 nm were recorded by exciting Si⁷⁺ ions in the fluence range 3.91×10¹²–21.48×10¹² ions cm⁻². These peaks were attributed to ⁴G_5/2→⁶H_5/2 (562 nm), ⁴G_5/2→⁶H_7/2 (599 nm), ⁴G_5/2→⁶H_9/2 (646 nm), and ⁴G_5/2→⁶H_5/2 (701 nm) transitions of Sm³⁺ . The highest emission was recorded at 3 mol% of Sm³⁺ doped Zn₂SiO₄. TL studies were carried out for 3 mol% Sm³⁺ concentration in the fluence range 3.91×10¹²–21.48×10¹² ions cm⁻². Two TL glow peaks at 152 and 223 °C were recorded. The kinetic parameters (E, b, and s), were estimated using Chen's peak shape method. Simple glow curve structure (223 °C), highly resistive, increase in TL intensity up to 19.53×10¹² ions cm⁻², simple trap distribution makes Zn₂SiO₄:Sm³⁺ (3 mol%) phosphor highly useful in radiation dosimetry.
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In some materials, this heat diffusion may increase the volume as a result of which the swelling is observed in the materials [17], sudden explosion of ionized matter leads to the fragmentation of the grains [18,19] as a result of which crystalline structures loose their crystallinity [20]. In case of insulators/phosphors, this energy deposition may lead to the production of new colour centres [21], point defects [22] and in some cases the rearrangement of the trapping centres/luminescent centres is observed which may modify their luminescence properties [23]. This has prompted us to explore the response of SHI irradiation in CaS:Bi nanocrystalline phosphors.
Luminescence studies of CaS:Bi nanocrystalline phosphors synthesized by wet chemical co-precipitation method and irradiated with swift heavy ions (i.e. O⁷⁺-ion with 100 MeV and Ag¹⁵⁺-ion with 200 MeV) have been carried out. The samples have been irradiated at different ion fluences in the range 1 × 10¹²–1 × 10¹³ions/cm². The average grain size of the samples before irradiation was estimated as 35 nm using line broadening of XRD (X-ray diffraction) peaks and TEM (transmission electron microscope) studies. Our results suggest a good structural stability of CaS:Bi against swift heavy ion irradiation. The blue emission band of CaS:Bi³⁺ nanophosphor at 401 nm is from the transition ³P₁→ ¹S₀ of the Bi³⁺. We have observed a decrease in lattice constant (a) and increase of optical energy band gap after ion irradiation. We presume this change due to grain fragmentation by dense electronic excitation induced by swift heavy ion. We have studied the optical and luminescent behavior of the samples by changing the ion energy and also by changing dopant concentration from 0.01 mol% to 0.10 mol%. It has been examined that ion irradiation enhanced the luminescence of the samples.
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Molecular dynamics simulations of various sizes of carbon molecule as clusters impacting a carbon substrate are performed in order to examine the size-dependence of the cluster ion on the impact process. Highly Oriented Pyrolitic Graphite (HOPG) was irradiated with C₁, C₄, C₈, C₁₉ and C₆₀ clusters carrying the same energy-per-atom of 2 keV/atom. When the cluster size is less than eight, interspersed damage is formed by the cascade-collision mechanism, whereas C₁₉ and C₆₀ impacts show homogeneously damaged regions in the surface of the substrate. In the case of large cluster ion impacts, all the incident energy of a cluster is deposited with high density in narrow region on the surface. These results show good agreement with experimental STM observations of single traces induced by the impact of C₆₀ and small carbon molecules.
A comparison between tracks created by high energy mono-atomic and cluster ions in Y<inf>3</inf>Fe<inf>5</inf>O<inf>12</inf>
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Samples of yttrium iron garnet (Y₃Fe₅O₁₂ or YIG) were irradiated with Au₄, C_n (2⩽n⩽20), C₆₀ ions in the MeV energy range. Using transmission electron microscopy (TEM) and Rutherford backscattering spectrometry (RBS), the induced latent tracks are compared with those generated with GeV mono-atomic ions. The cluster ions create amorphous and continuous tracks as in the mono-atomic case. Irradiation at grazing incidence allows to visualise the dissociation of cluster ions inside a solid. Some of the tracks induced by high energy C₆₀ ions contain a “bubble-like” structure inside the amorphous part of the tracks, which is in contrast to the tracks induced by smaller cluster and GeV mono-atomic ions for which no structure is seen. The diameters of the tracks induced by MeV cluster ions and by the low velocity mono-atomic ions are seen to follow the same curve as a function of the linear rate of energy deposition (dE/dx)_e.

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Defect creation in tracks produced by high energy carbon clusters in LiF

Abstract

Nucl. Instr. and Meth.

Appl. Phys. Lett.

J. Mater. Res.

Radiat. Res.