Low energy ion implantation is a technique used to discover the structure of crystals, and the structures of the surfaces of substances. The electrical and magnetic properties of substances can be studied in the same way.
The basic principle is that a low energy-emitting isotope of some sort is introduced onto or into the substance, and a study is made of how much and in which directions these energies are then emitted. The physics are complex, and measurements are fractional. Low energy ion implantation is a direct development of Rutherford’s early work on x-ray crystallography.
In the past such studies have been done by using heat and high-energy radiation. The problem with this was that by their very nature these processes changed the properties of the substance being studied. These higher energy methods also tended to go further into the surface of a material being studied. Low energy implantation studies the very surface layer of a substance. Low energy scanning is one of the few techniques available for the study of hydrogen atoms
Low energy implantation allows for small controlled amounts of isotopes to be introduced to the surface of the study materiel. It involves the production of ions. To produce these ions a gas is treated to produce its positive ion and an electron, the ions then being “fired” in a controlled manner at the target substance. The actual equipment for all this is very complicated. Studies have to be carried out in a vacuum and measurement equipment has to be very finely calibrated to detect changes.
On hitting the surface ions may bounce off unchanged, or bounce off changed in charge or velocity, or be absorbed onto the surface of the substance. To get accurate results the original “dose” of ions must be known, and the final position and energy of all those ions, as far as possible, must be placed.
Typically the source of these ions is one of the inert noble gases, such as neon. These are used because of their inherent lack of reactivity. The ions are relatively easy to produce, and they are unlikely to react with the target substance. The ions do not last very long however, and they commonly extract electrons from the target material to attain stability. For this reason the alkali metals are often used in place of neon, and the other noble gases, as the ions themselves are more stable.
Work in this field may lead to the development of even faster and smaller microchips following from a greater understanding of the electrical properties and the structure of crystals.
