The background is a copper plate.

"Copper plate: The scientists used copper 111 as the surface of the animation — the same material they used 10 years ago when they built the first computer that performed digital computation operations. Carbon monoxide (CO): ok The scientists chose carbon monoxide molecules to move around the plate. Carbon monoxide has one carbon atom and one oxygen atom, stacked on top of each other."

http://www.research.ibm.com/articles/madewithatoms.shtml#fbi...

I assume focus / depth of field is why the surface looks smooth. Or whatever the equivalent of that is for a scanning/tunnelling microscope.

One thing I don't understand with that quote: it seems to imply this video was made only ten years after "first computer that performed digital computation operations". Is this a typo in the original or are they referring to something else?

Probably something like logic gates assembled by moving atoms around?

Smoothness is likely due to the grounding of the backplate.

If anything I would posture that they’ve filmed the backplate and the A atoms are the shadow from the scattering of the electrons that didn’t hit the backplate.

Atoms aren't the smallest thing, but that's sort of irrelevant, because this was "filmed" with a scanning tunneling microscope: https://en.wikipedia.org/wiki/Scanning_tunneling_microscope

It's not like normal photography, it's more of a visualization of an electrical current sensor. The background is just the area of the plane they were scanning that didn't have any atoms.

> didn't have any atoms

That sounds a bit weird...

Didn't have any atoms sitting on it.

Well what was 'it' if it wasn't made of atoms?

A slice of quantum foam.

Not quite.

Just empty space. There's a smooth plane of atoms, then a few atoms that make up your frame on top of that, and everything else is vacuum.

Other atoms, but further away. Effectively the background is blurred because it's out of focus. The depth of field is thin enough that this works. (These are analogies. It's not strictly correct.)

It's so far from correct as to be not a useful analogy.

The real question is, how is the microscope's output converted into a visual picture? Hint, it isn't by lensing light. Thus there is no "focus" to be out of.

An atomic force microscope produces images by sensing atoms with a probe. It scans in a planar layer, analogous to a very narrow depth of field for a film camera. The background atoms do exert force on the probe, but much more weakly.

I presume it's sitting on a flat layer of other atoms, but they are picturing only the top layer, kind of how a focused photo has a blurry background.