When I was still in grad school, there was a lot of interest in charged-particle beams (electrons or ions) for high-resolution lithography, since the diffraction limit was much better than for photons.
Instead of physical masks, they would use beam deflection, as in a CRT, to expose the pattern on a resist layer, or deposit metal ions directly.
(There are lots of other practical problems with charged-particle optics, especially aberrations, but electron microscopes had achieved spatial resolution better than 1 nm more than 50 years ago.)
The shorter and shorter wavelength UV clearly won out since then, but I wonder when massive particles will re-appear?
Most likely never: e-beam has too poor imaging after all (the deposited charge ends up in an explosion of scattering ionization, i.e. the exposure spot is much larger than the incident beam, also secondary emission that rains back down as a halo around the spot), and similar effects play with ions (plus physical damage to the resist, sputtering and whatnot); it would be great if a beam could be imaged but there's probably no way to do that. Even e-beams are difficult to project an image with; an example being a patterned cathode*, but imagine trying to maintain optical precision on a
heated thermionic cathode, plus contamination due to ion bombardment, plus smearing/divergence due to space charge?! There's just no such thing for ions, and you can't like mask or reflect them. I guess it would be
really interesting to have, like, a huge drift chamber where ions could move towards an oversized electrostatic or magnetic image of the mask, and kinda make an electromagnetic DLP, and
somehow manage to refocus the beam into some meaningful image, but....... right? And I don't think it'd be something you can really reduce all that much, to get any kind of resolution out of naturally-blurry EM fields you're going to need a huge area, even if intimately patterned.
*Supposedly, the pattern you see, say on an analog scope with deflection stopped (NORM mode pre-trigger, or X-Y mode) and the focus cranked way out, is characteristic of the cathode, i.e. imaging the emission itself, give or take the optical path of the gun. So if it's rough, flakey, salt-and-pepper, whatever, that's indication of a poor or failing cathode. I'm not actually sure how true all of this is; I'm far from an expert on electron optics...
Do you know something about this effect and what it means for photograhpy?
I'm guessing it's to say the PSF varies with coordinate, and not in a way that's easy to compensate for (and for all the compensation they're already doing, that must be saying something), but I'd also like to know more

Tim