Ultra Cleaning And Not Permeable Films To Organic Contamination

Tight films:

There is not existing an organic film that is not permeable to many organics or gas and water vapor molecules, nor will it be ever existing.

Look into a book on vacuum technologies, there are compiled lists of permeability.
Among the best are - naturally - the fluorinated plastics: viton and teflon.
Parylene is quite good as with this a conformal coating can be done.

Metallic and glass and oxidic and nitridic films can be totally tight and will not been permeable if there are no pinholes - a condition that is not reality.

There are some anodic oxidation films that are totally tight - most are porous down to a very thin tight layer (10 to 100 nm thick).

But be cautious: I had an example when a fatty substance came out of aluminum plates after the surface (0.5mm deep) had been removed totally by milling. This is thought to be stored at the grain boundaries but nobody seems to know.

Thats why many plastic shielding foils (also used for food packaging) uses minimum 1 aluminum film inbetween many different plastic films (up to 5 or 7) bonded together to one integral film.

And there are some unexpected data: the ring-structured molecules (benzene,xylene, toluene) will pass easily through polyethylene and similar plastics while linear structured molecules (paraffins) pass only slowly.

Look for PSG or phosphor-silica-glass used in passivation of semiconductors or Si3N4 for the same purpose: these are really tight coatings.

Measurement is mostly done by helium permeability.

The other question about "perfect" cleaning is a really complicated one.

There is no "perfect" surface neither on earth nor in space, everywhere are condensable molecules that will be absorbed onto surfaces, that will remain there, react there (aided bei ultraviolet radiation and catalytic surface activity) and sit there until some process needs a better surface. May be this better surface is contaminated with a different but suitable material.

So if you specify the cleanliness that is attainable for you I can comment how to proceed.

RHABE