Modification and Characterisation of Materials by Swift Heavy Ions

Abstract

Swift heavy ions (SHI) available with 15 million Volt Pelletron accelerator at Inter University Accelerator Centre (IUAC) Delhi, formerly known as Nuclear Science Centre, (NSC), provide a unique opportunity to researchers for accelerator based materials science research. The major research areas can be broadly categorised as electronic sputtering, interface modifications, synthesis and modification of nanostructures, phase transitions and ion beam-induced epitaxial crystallisation. In, general, SHI irradiation based-materials may not be economically feasible, still it could be of interest for very specific cases in defence and space research. The paper gives a glimpse of the current research activities in materials science with SHIs, at IUAC.Keywords: Swift heavy ions, SHI, materials science, materials research systhesis of materials, characterisation of materials, nuclear energy loss, ion energy loss, electronic energy-loss-defects in materials, defect engineering INTRODUCTIONThe ions with energy ranging from a fraction of keV to GeV are useful in synthesis, modification and characterization of materials. The energetic ions during their passage through a material loose energy via two processes. These are nuclear energy loss S n and electronic energy loss S e . In the former process, the energy is lost by elastic collisions of incident ions with the atoms in the material, which is dominant at low energies. In the electronic energy loss process, dominant at high energies (>1 MeV/nucleon), the energy is lost by inelastic collisions of the ion with the atoms, leading to excitation or ionisation of the atoms. At these energies of heavy ions, the velocity of the ion is comparable to or higher than the velocity of Bohr electron. The ions with such high energies are also referred to as Swift Heavy Ions (SHI). The electronic energy loss for SHI is, generally, about two orders of magnitude higher than the nuclear energy loss1 . An interesting characteristic of the SHI is that it creates a columnar type of defect along its path (called as ion track), specially, in insulators. SHI during its passage through material can cause defect annealing, cluster of point defects and columnar type of defects depending on the mass and energy of the ion and the material. Therefore the SHI can be used for engineering the defects in the materials. The parameters of ion beam, which play crucial role in defect engineering, are the energy deposited per unit length and the fluence.The ion mass and its energy, decide the magnitudes of the electronic as well as nuclear energy losses. Especially for heavy ions at high energies (i.e., for SHI), the electronic energy loss decides the type of defects as the nuclear energy loss. The other ion beam parameter, fluence, dictates the number of defects (produced). The number of ion

High electronic excitation induced modifications by 100MeV O7+ and 150MeV Ni11+ ions in Makrofol KG polycarbonate film

“…An interesting characteristic of the ion insulator interaction is that it produces a columnar type of defect along its path (called as latent ion track) [26]. The final highest density of defects is observed at depths close to the ion range, which is a characteristic of heavy ion irradiation.…”

Modified structural, surface morphological and optical studies of Li3+ swift heavy ion irradiation on zinc oxide nanoparticles

“…[21][22][23][24][25][26] D. Avasthi et al 27 reported that when an energetic ion penetrates into any material, it loses energy mainly by two independent processes: (i) elastic collisions with the nuclei, known as nuclear energy loss (dE/dx)n, which dominates at an energy of about 1 keV per amu, and (ii) inelastic collisions of the highly charged projectile ion with the atomic electrons of the matter, known as electronic energy loss (dE/dx)e, which dominates at an energy of about 1 MeV per amu or more. Swi heavy ion irradiation (SHII) of nanostructures has induced changes in size and shape.…”

Modification of magnetic anisotropy induced by swift heavy ion irradiation in cobalt ferrite thin films

“…SHI during their passage through material result in excitation and ionization of the atoms by inelastic collisions (called as electronic energy loss, S e ) or displace them by elastic collisions (nuclear energy loss, S n ). These are known to result in production of defects in the target [26]. The shape of the defects introduced by SHI irradiation depends on the S e of the impinging ions.…”

“…In complex system like ferrites; where cations reside in two different sublattices, the defects can disturb the arrangement of cations which may result in significant effects on magnetic properties including the magnetic anisotropy. The advantage of SHI irradiation is that the properties can be locally and controllably changed depending upon the electronic energy loss and fluence values in the target materials [26]. The present study focuses on the modification of magnetic anisotropy in CoFe 2 O 4 thin films by SHI irradiation using 200 MeV Ag +17 ions at different fluences.…”