3 ms·

The only real way to know if you had a single atom tip was to image a known surface. If the image was junk you probably had some funky tip states going on. HOPG

by quanics 10y ago

The only real way to know if you had a single atom tip was to image a known surface. If the image was junk you probably had some funky tip states going on. HOPG (graphite) was the standard we typically used. 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.

tostitos1979 10y ago
Man .. I know what my next hobby project is going to be :) 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.
- maybecorrect 10y ago
  In the simplest configuration have a X-Y stage that you raster, along with Z axis control - generally these are all piezo controlled. Your signal is then acquired by maintaining a constant tunneling current while you raster, so you track the Z axis position as you raster. 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.
joncrocks 10y ago
Yeah, we used to use graphite (as flat as we could get it, tried to ensure we had a single surface) to see how good it was. You could tell how good it was from how much noise you got and therefore how good your image was.

by quanics 10y ago

tostitos1979 10y ago

Man .. I know what my next hobby project is going to be :) 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.

maybecorrect 10y ago
In the simplest configuration have a X-Y stage that you raster, along with Z axis control - generally these are all piezo controlled. Your signal is then acquired by maintaining a constant tunneling current while you raster, so you track the Z axis position as you raster. 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.

joncrocks 10y ago

Yeah, we used to use graphite (as flat as we could get it, tried to ensure we had a single surface) to see how good it was. You could tell how good it was from how much noise you got and therefore how good your image was.