Did you ever get the low temp vantablack working as expected? I’m guessing oxygen is passivating the aluminum surface somewhere in the process, and the paper doesn’t document how careful they were. I’d personally want to do this under a nitrogen atmosphere, but I’ve never sonicated under a controlled atmosphere.
I’d bet the reason you can sort of get aluminum to blacken over the heated beaker has something to do either with the fact that the beaker is effectively positive pressure and pushing out everything but water vapor, or that the condensed watervapor on the surface of the aluminum is consistently oxygen free.
I find the former somewhat less believable than the latter, but it’s been a while since I’ve worked on things like this.
I’d bet the reason you can sort of get aluminum to blacken over the heated beaker has something to do either with the fact that the beaker is effectively positive pressure and pushing out everything but water vapor, or that the condensed watervapor on the surface of the aluminum is consistently oxygen free.
I find the former somewhat less believable than the latter, but it’s been a while since I’ve worked on things like this.