> femtometer resolution

The diameter of a carbon atom is 154 picometers. Nobody's going down into the femtos. And you're not going to get atomic resolution, either, because humans move around too much and things like scanning electron microscopes need very stationary samples. Even microscopic vibrations can blur the final image.

Which isn't to say that you couldn't get very good resolution...

Just for illustration: Gravitational wave detection is on the femtometer scale. The proton is about that size. We can measure these things, but the machines are, let's say, "big".