Optimum
concentration of FeCl
3: I don't quite remember, but it was close to the usual concentration to etch copper for printed circuit boards. For such small amounts of aluminium, you can try directly in an etch bath used commonly for printed circuits, it won't deteriorate the bath. Your aluminium is probably very pure and will resist etching better than my Al-Cu4, but for 100nm it won't last long.
My solution
boiled only because etching was so fast with aluminium. At the beginning it had the outside air temperature. And since the aluminium was a long tube and the FeCl
3 was inside, in 50kg amount, this experiment was the dirtiest I made.
0.9µm, that's damn thin! I feel 12.7µm Mylar already weak enough. Hey, as soon as you can manufacture and handle 1km
2 foils (preferibly of Kapton or any PI), I want them for
solar sails! I have already a pleasant concept for lightweight booms there
http://www.scienceforums.net/topic/78265-solar-sails-bits-and-pieces/#entry857978but presently 12.7µm or 6.3µm (the thinnest laminated by the chemical industry) is the minimum.
I propose in message #1 there a method to
thin an existing polymer foil. In case this is possible and fits your needs, you could:
- Evaporate the aluminium on a thicker polymer film. Good adhesion. Or better, buy the aluminised mylar film.
- Etch the well adhering metal as you need.
- Thin the polymer film as needed.
The thinning machine would resemble an aluminium evaporation machine that passes the film from one big roll to and other and processes it in vacuum in between. In fact, I suggest to modify such an existing machine. Instead of evaporating aluminium there, it would etch the polymer film, for instance by plasma and possibly in several passes, controlling the remaining thickness for instance optically in a feedback loop.
I ignore the nature of the
varnish on space blankets.
Laser ablation works for very thin materials. The trick is to use very short pulses (like fs from Ti:sapphire) so the heat has no time to diffuse to the depth, and then it evaporate the nearest surface without damage deeper. My concern is that Mylar may absorb more light than aluminium.
When I worked with semiconductors (during the paleomonolithic era) we had made
stencils of milled metal to deposit aluminium through them by evaporation. This spared us etching the aluminium and sufficed for mm-sized patterns. Adherence was good thanks to evaporation. Stencils of silicon could be eched much finer; put them in contact with your film to limit blurring.