Ion Implantation Penetration and Atomic Radius

Try reading up on reverse osmosis. It's not exactly what you have in mind, but at least the analogy is there. http://en.wikipedia.org/wiki/Reverse_Osmosis

Here is a thought: Every material arranges itself in some form of lattice structure. The larger the atom (ion) for implantation the harder it gets because of the force required to push it through the lattice faces or to even dislodge the material atoms at the lattice edges: In general as soon as the diameter of the atom for implantation becomes equals the diameter of the inscribed circle of the lattice face spacing, the implantation gets harder and the difficulty increases from that diameter with increasing diameter.

This is based on drawing from Material Science concepts.

Does this work for you? This is one of those concepts that are easier explained with drawings, but ...

A naked ion, with zero orbital electrons is very tiny. What prevents deep travel is the large field on a positive ion that interacts with the matrix to produce drag. Usually they determine the best ion speed and the number of electrons stripped to reach the depth needed by test and measure, and then leave it like that. the ions tend to deposit at he same depth if they arrived at the same speed, so you need to determine the speed. You can use a charged plate to curve the ion beam to produce a spectrum of speeds and after trials you find the proper settings. This is much like the plates in oscilloscopes moving electons. Ions are heavier, so it takes more work to change them.

I thionk this is a mature discipline and there must be texts in any major library.

If you take a look at ion implantation charts, the energies go up as the depth desired increases but they vary quite a bit based on a whole variety of process parameters. Experimentation is often the means of determining the optimal energy for a particular ion, a particular semiconductor material, a preferred depth of implantation, implantation equipment and implantation geometry.

As far as the size of the ion, remember that the nucleus is a miniscule dot in the middle of the atom and the atoms size is actually determined by the electron cloud surrounding it. The ion is not stripped of all of its electrons. It still has most of them, and once you pass a certain number of electrons the physical dimensions of the atoms change very little. The arguement about size making it more difficult works well for molecules - not so for atoms.

The more mass the ion has, the more energy is required to accelerate it to a given speed. However, the larger the mass, the greater the momentum and the harder it is for the substrate material to stop it, thus deeper penetration despite any miniscule difference in physical size.

When the accelerated ions strike the material, the energy of impact is sufficient to break lattice bonds and the ion passes right through and actually becomes part of the lattice structure when it stops. If implanting into a metal instead of a semiconductor (they do this to change surface properties such as hardness etc) the ions become part of the metal lattice, changing it to an alloy.

Bottom line, the physical size differences between ions is very small and can be ignored in ion implantation. Mass of the ion, depth of penetration, material to be penetrated, angle of impact, substrate temperature and other factors all play a large part in the required acceleration energy. Sorry to say you will not be able to find any support for your assertion/view.