Ion tracks

Ion tracks are damage-trails created by swift heavy ions penetrating through solids, which may be sufficiently-contiguous for chemical etching in a variety of crystalline, glassy, and/or polymeric solids. They are associated with cylindrical damage-regions several nanometers in diameter and can be studied by Rutherford backscattering spectrometry (RBS), transmission electron microscopy (TEM), small-angle neutron scattering (SANS), small-angle X-ray scattering (SAXS) or gas permeation.

Ion track technology deals with the production and application of ion tracks in microtechnology and nanotechnology. Ion tracks can be selectively etched in many insulating solids, leading to cones or cylinders, down to 8 nanometers in diameter. Etched track cylinders can be used as filters,Coulter counter microchannels, be modified with monolayers, or be filled by electroplating.

Ion track technology has been developed to fill certain niche areas where conventional nanolithography fails, including:

The class of ion track recording materials is characterized by the following properties:

Several types of swift heavy ion generators and irradiation schemes are currently used:

When a swift heavy ion penetrates through a solid, it leaves behind a trace of irregular and modified material confined to a cylinder of few nanometers in diameter. The energy transfer between the heavy projectile ion and the light target electrons occurs in binary collisions. The knocked-off primary electrons leave a charged region behind, inducing a secondary electron collision cascade involving an increasing number of electrons of decreasing energy. This electron collision cascade stops when ionization is no longer possible. The remaining energy leads to atomic excitation and vibration, producing (heat). Due to the large proton-to-electron mass ratio, the energy of the projectile decreases gradually and the projectile path is straight. A small fraction of the transferred energy remains as an ion track in the solid. The diameter of the ion track increases with increasing radiation sensitivity of the material. Several models are used to describe ion track formation.

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