User:Reimarspohr/Temp/Ion Track Technology/Track Etching

When a fast ion penetrates through a polymer an ion track is obtained. The technique uses etching as a chemical amplifier. In this way the effect is magnified by orders of magnitude. The etching process accentuates the invisible defect raising it to a useful level. Due to the high energy density of ions many homogeneous dielectric materials are susceptible to selective etching.

In comparison with photons and electrons: accelerated ions provide a much higher energy density. The acceleration energy of heavy ions exceeds classical techniques by orders of magnitude. The ion energy is released in a narrow channel along the ion path. Classical lithography requires radiation sensitive resists for scribing. Ion tracks are not restricted to resists. They cover a much wider range of materials. Even radiation resistant materials can be treated. They are usually non-conducting and homogeneous down to the molecular scale. Quartz is one example of such a radiation resistant material that can be treated. Many technical polymers are susceptible to selective ion track etching. Sodium hydroxide solutions are most commonly used for polymers. After short etching, small etch troughs are formed. After long etching, penetrating channels are formed. At high energy deposition density cylindrical perforations are possible.

For applications in micro and nano-technology, one has to master the fabrication of nearly identical nano-channels. In many cases cylindrical geometry is preferred.

Soap bubbles consist of self organized mono-layers of tenside molecules forming a flexible membrane. Similar to biological membranes the membrane is impermeable for hydrated ions. Tenside molecules have a water-loving (hydrophilic) and a water repellent (hydrophobic) end. They fill a larger volume than the hydrated ions of the etching medium (Na+ and OH-). A flexible, but impenetrable mono layer of tenside molecules forms between the etching medium and the channel wall. Its thickness corresponds to the length of the tenside molecule. As soon as the channel diameter suffices for the tenside molecules to penetrate into it, a protective mono-layer forms on the channel wall. However, the tenside molecules are too large to penetrate into the tip, where selective etching occurs as usual. The result is a cylindrical channel.