[A Summary by D.K. Avasthi]
A brief survey of the research performed on ion beam synthesis and modification of carbon nanostructures is given here.
1. Modifications of the fullerene molecules (C60 and C70)
Studies of ion irradiation of C60 films show the formation of dimmer of fullerene (polymerization) [1-4] at low fluences and destruction of fullerene molecules at high fluences. The damage cross section of fullerene films under different Se has been studied [1,3,4].
The irradiation of fullerene thin film at low fluence by 90 MeV Si results in enhancement of PL emission. Most of the optical molecular transitions could be observed in PL in irradiated fullerene film . The UV-Vis spectrum of the irradiated sample also revealed the molecular transitions, which were not so clear in the pristine sample.
Modifications of properties of C70 thin films following ion beam irradiation with 120 MeV Au ions have been investigated. The energetic ion impacts lead to the destruction of the C70 molecules. The radius of damaged cylindrical zone is about 2.9 nm . A study on the comparision of behavior of C60 and C70 under the SHI impingement indicates that C60 fullerenes form dimmer whereas C70 fullerenes do not form dimmer under SHI bombardment .
2. Ion beam synthesis of conducting nanowires
SHI irradiation of fullerene thin films at low fluence (1010 ions/cm2 ) results in the formation of conducting C nano wires embedded in fullerene matrix [1-3]. The conductivity of ion beam synthesized carbon nano wire is about 7 orders of magnitude more than the conductivity of virgin C60 film. The nanowires are parallel to each other and their length can be controlled by the thickness of fullerene film. The orientation of nanowires can be changed by simply changing the incidence angle of ion beam. As expected these nanowires like structure exhibits the field emission properties . The formation of conducting C nanowires also occurs in SHI irradiation of DLC films [4-10].
The carbon nano-dot and nano-wires have also been synthesized using SHI irradiation of inorganic polymers/gels [6-10].
3. Ordering of Carbon Nanoubes by SHI irradiation
The experiments on SHI irradiation of CNT’s reveal that low fluence irradiation of carbon nanotubes results in the ordering of CNTs and destruction occurs at higher fluence . The single-wall CNTs (SWCNTs) and multiwalled CNTs (MWCNTs) under irradiation of 55 MeV carbon ions show healing of CNTs under ion beam irradiation. The annealing process appears to begin at the lowest value of fluences and continues till the irradiation fluence of ~ 1x1014 ions/cm2 when the MWCNTs begin to amorphize whereas the SWCNTs continue to heal . At low values of Se the defect annealing occurs till high fluences whereas the defect annealing at high Se values begins to vanish at lower fluence. Similar effects are observed for 120 MeV Au ion irradiation of multiwalled CNTs (MWCNTs). It is speculated that a narrow cylindrical region gets defects due to large energy density whereas in larger annular region surrounding it, the defect annealing takes place. The SHI irradiation results in Improvement in field emission properties of carbon nanotubes, diamond like carbon (DLC) films and nanocrystalline diamond film [3-8].
4. SHI induced Reorientation of Ni planes in Ni encapsulated by CNT
Reorientation of the crystalline planes occurs in nickel nanorods confined in CNT under SHI irradiation [1,2]. The effect of irradiation is dependent on the numbers of tube walls. The irradiation experiments show that the multi walled carbon nanotubes can be effectively used as radiation resistant coatings.
5. Defect mediated magnetism in Carbon Based Materials
The experimental findings based on SHI irradiation of fullerene films by Amit et al. [1-3] show that the magnetism in carbon based materials is mainly defect mediated. It was proposed the ferromagnetism in irradiated fullerene is due to some ordering of sp2 and sp3 bonded atoms having the correlation between unpaired spins and/or it could be related to the defects due to increase of O in the irradiated film.
6. SHI induced modification of diamond thin films and
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