Irradiation with Ion Beams

Ion Beams. Several investigations have been made on the effects of ion beam irradiation on simple chemical systems. Polymers have also been irradiated with ion beams as an extension of studies on the ion implantation of other materials. To date, most of these studies have been concerned with gross effects, sometimes through to carbonisation (70) but here is a field which could have an industrial potential. 

Recently spin-coated PMMA thin films with a thickness of 0.45 pm on silicon wafer were irradiated with various ion beams (H+, He+, N+, Ni3+). Ion beam energy regions are from 300 keV to 4 MeV. Irradiated PMMA films were developed by isopropyl alcohol in these experiments. After the irradiation by ion beams on PMMA in a vacuum, the thickness of the films were measured both before and after development. Various radiation effects on PMMA films such as ablation (sputtering), main chain scission, and positive-negative inversion were observed as shown in Fig. 11. These phenomena are very different from those in 60 Co gamma-ray or electron beam irradiation. Large LET effects are considered to be due to high density excitation by ion beams. 

In a LEISS experiment, a target surface is irradiated with a beam of inert-gas ions (He, Ne or Ar ) of energy between 20 eV to 500 eV, and the backscattered primary ions are energy-analyzed (Fig. 1). The backscattering can be modeled as a classical two-body inelastic collision between the incident ion and a topmost surface atom governed by the conservation laws of energy and momentum. 

A comparison of the nature of the DNA-radicals produced with y-radiation relative to those produced by ion-beams shows that some radical species which are found in low amounts using /-radiation (low LET) increase by an order of magnitude in absolute yield with ion-beam (high LET) irradiation. For example, work using oxygen ion-beams found evidence for a phosphoryl radical (R0P02 , Scheme 1) in DNA. This radical, formed by dissociative electron attachment (Sec. 3), is clear evidence for a prompt strand break.In addition, formation of sugar radicals via exited states was proposed (Sec. 2.7). 

The electron- and ion-beam irradiation of crossing single-waUed CNTs induces structural defects, which lead to the formation of stable junctions of various geometries between their surfaces (Krasheninnikov et al. 2003, Terrones et al. 2002). The selective EB irradiation of individual CNTs can be used for welding of tubes to a metal surface that improves electric contact between the tube and the surface (Ando et al. 2004, Krasheninnikov et al. 2002). The influence of electron and ion beams on bundles of single-layer and multilayer CNTs modifies their structure with formation of molecular junctions between the tubes and between individual layers in the multilayer tubes (Krasheninnikov and Nordlund 2004). This prcxtess is acccmpanied, as a rule, by the distortion of the tube surface due to the formation of numerous defects in the carbon lattice (see Figure 18.11). The irradiation of multilayer CNTs with ion beams cmi lead to their transformation to amorphous carbon nanowires and diamond nanorods (Sun et al. 2005, Wang et al. 2004). 

ION IMPLANTATION The process of embedding atoms into the surface of a solid by irradiation with a beam of energetic ions used to create the p-1- contacts fa- semiconductor detectors. 

If a surface, typically a metal surface, is irradiated with a probe beam of photons, electrons, or ions (usually positive ions), one generally finds that photons, electrons, and ions are produced in various combinations. A particular method consists of using a particular type of probe beam and detecting a particular type of produced species. The method becomes a spectroscopic one if the intensity or efficiency of the phenomenon is studied as a function of the energy of the produced species at constant probe beam energy, or vice versa. Quite a few combinations are possible, as is evident from the listing in Table VIII-1, and only a few are considered here. 

A promising alternative is provided by Laser isotope separation . Because the ionization energies of and differ slightly, it is possible to ionize the former selectively by irradiating U vapour with laser beams precisely tuned to the appropriate wavelength. The ions can then be collected at a negative electrode. 

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