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A “perfectly clean” surface… This sample looked clean and shiny when I held it up to the light - I had cleaned it several times in harsh solvents like acetone, and even blasted it with high-energy plasma for a good ten minutes.  Under the electron microscope, I learned the real truth - a persistent coating of photoresist residue still lingered.  It’s a thin coating, maybe a thousandth the thickness of a single sheet of paper.  Here you see it draped languidly over the edge of the sample, as if daring me to try to remove it.  Maybe it’s time to introduce the nanogunk to a little thing we like to call “Piranha etch”…