I know, I did a benchtop STM lab for my Nuclear Physics course some years ago. Most of the day was spent trying to make single atom needles by a wrist-flick technique for cutting platinum wire with some sharp pliers.
Surprisingly easy.
For really cool stuff, check out the CO functionalized tip AFM coming out of IBM in Zürich: https://www.zurich.ibm.com/st/atomic_manipulation/pentacene....
The AFM I used was mainly for teaching the concepts, so they wanted simple, cheap, low risk => strong NaOH was out.
The technique back then was, somehow, cutting at about 45° angle and twisting the pliers to make this angle go to zero while cutting/pulling. Then you had to put the tip in the machine and do test images to see whether the tip was good. Usually it wasn't, so you tried again. Finally you got a perfect tip, and maybe got two or three good images before you messed up the tip (from being a noob).
Getting pictures of atoms is nice, but sometimes you want to image molecules, especially organic ones (tricky to do in a STM).
Also, what would the shape of the tip look like if you drew it? I'm wondering what kind of general angles the surface has. Is it like a cone with a single atom at the tip? What kind of slope?
A good tip could be just about anything, from a nice cone to really jagged. One problem was any of the methods one has to view the tip can't actually resolve the single atom that is doing the imaging.
Dumb question .. I get that the needle scans a surface and you get the quantum tunneling effect between the atom you are "looking at" and the tip of the needle. What I don't get is how one figures out depth. For each X,Y position, do you just keep going down until you touch something, and then move up, and go to the next position? If so, apart from the issue with 1 atom tip, I imagine the next problem would how to increment X and Y by 1 atom.
P.S. I think some of the marketing put out on these things really confuses the issue. Sure .. it gets people excited about science but it gives people the wrong intuition. As a non-physics person, I got a lot out of this article.
This means that you're getting a "pseudo-height" map - if you had a surface with 2 types of atoms, both the same size, but with different tunneling barriers, you would see them appear to be different sizes.