Swift heavy ion induced modification of C60 thin films

Abstract

Modification induced by 110 MeV Ni ion irradiated thin film samples of C 60 on Si and quartz substrates were studied at various fluences. The pristine and irradiated samples were investigated using Raman spectroscopy, electrical conductivity and optical absorption spectroscopy. The Raman data and band gap measurements indicate that swift ions at low fluences result in formations that involve multiple molecular units like dimer or polymer. High fluence irradiation resulted in sub-molecular formations and amorphous semiconducting carbon, indicating overall damage of the fullerene molecules. These sub-molecular units have been identified with nanocrystalline diamond and nanocrystalline graphite like formations. INTRODUCTIONEver since its synthesization in the laboratory 1 , the fullerene solid has been a subject of significant interest as target for ion-beam irradiation. The interest was stimulated by the potential of fullerene material towards superconductivity by implanting foreign ions in the fullerene cage and other applications like optical limiters, electrical storage devices, C 60 based diodes and transistors etc. Irradiation effects of keV and some MeV energies has been investigated [2][3][4][5][6][7][8][9][10][11][12][13][14] . In general, it has been observed by various research groups that the C 60 materials undergo heavy damage by low energy ion irradiation in the energy range 30 -300 keV of various ions [2][3][4][5][6] . There has also been study on irradiation effects of MeV energies on fullerene films [7][8][9][12][13][14] . Itoh et al 7 have reported fragmentation of C 60 induced by impacts of 2 MeV Si 4+ ions. T.Le.Brun et al 8 have reported ionization and fragmentation in C 60 molecules by impacts of Xe ions in the energy range of 420 -625 MeV. Subsequently 9 , there has been some interest in studying the phase transformations of the C 60 solids using MeV energies. It has been reported that under suitable conditions of temperature and pressure, the C 60 undergoes a dimer or a polymeric phase transformation 10,11 . Ion beam irradiation could provide similar conditions so that the formation of aggregates (of molecules of C 60 ) is favoured. This could further result in the formation of solids of these aggregates. The energy of the ions and their fluence play a key role in the end product of the target.Energetic ions loose energy during their passage in a material. The strength of interaction of the incident ion in a material i.e., with the electrons of the atoms in the target material (including the core electrons of the constituent atoms or molecules) as well as with the nuclei 2 (which happen to be the mass centers) depends on the mass, charge and energy of the incident ion. Therefore, it is of interest to study the interaction of ion beams with fullerene solids using swift ions at various fluences. The interaction of the incident ion with the atomic radii (or molecular mass center) is an elastic collision process and is prominent at low energy (eV to few hundred keV). On the other hand the intera...

Formation and characterization of carbon nanowires

“…19,21 The improved field emission arises due to the structural transformation along the ion paths. Some of us have shown previ- ously that the conductivity of the SHI irradiated fullerene thin film increases significantly, 12,22 which is attributed to the fact that the swift heavy ions create track in fullerene thin film, breaking the fullerene cages within the track to form nanocrystalline graphite embedded in a-C carbon, 14 which is electrically more conducting than the parent fullerene molecule.…”

“…1͑a͔͒ is known to break the fullerene cages and within the nanosized track to form nanocrystalline graphite. 13,14 From a technological viewpoint, one of the more important aspects is the development of large scale and controllable production methods, especially for aligned nanowire production. Although electron beam lithography 15 allows the formation of catalyst sites for aligned growth of nanowires, this serial technique is too slow for scalable mass production.…”

Swift heavy ion induced modifications of single walled carbon nanotube thin films

“…Due to their radiation stability, CNTs can also be used as radiation shields in nuclear reactors [6]. Irradiation causes defects on the surface of CNTs which give rise to various types of structural modifications such as welding and bending [7,8], formation of nanocompartments [9], transformation of single walled nanotubes to multi-walled carbon nanotubes [10], reordering, healing of the system [10][11][12][13][14].…”

Swift heavy ion induced modifications of optical and microstructural properties of silver–fullerene C60 nanocomposite

“…Transformation from one allotrope into another can be promoted locally by swift heavy ion irradiation due to its unique feature of depositing large electronic energy density localized in a narrow cylindrical region [1,2]. The properties of metal nanoparticles embedded in insulating matrices are attractive for their tunability as a function of the particles size, shape, matrix physical constants and mutual polarization.…”