What are “actual pictures” of atoms actually pictures of?

Post by semi-extrinsic » Sun, Jun 26, 2016, 7:13 AM UTC

James001 wrote: post #36

semi-extrinsic wrote: post #2

Well, as the article points out, the things being imaged are most definitely actual atoms. The only thing TFA is nitpicking about is that light isn't used to image those atoms. This is about as interesting as pointing out the fact that an ultrasound picture of a baby isn't an "actual picture", since we use sound instead of light to make the image.

No I disagree. An ultrasound picture of a baby accurately reflects the actual form of the baby. A Scanning Tunneling Electron Microscope does not accurately reflect the form of an atom because it simply uses an artificial dot to represent the presence or absence of an atom. In short, the "map" that STM's give us is abstracted from reality and does not accurately portray an atom (in large part because STM's still simp…

Post by Asooka » Sun, Jun 26, 2016, 8:51 AM UTC

Animats wrote: post #5

semi-extrinsic wrote: post #2

Well, as the article points out, the things being imaged are most definitely actual atoms. The only thing TFA is nitpicking about is that light isn't used to image those atoms. This is about as interesting as pointing out the fact that an ultrasound picture of a baby isn't an "actual picture", since we use sound instead of light to make the image.

The concept of the scanning tunneling microscope is so simple and ridiculous that it was probably thought of and dismissed long before someone built one. "You're going to image atoms by dragging a tiny needle across them"? Yet that's pretty much how it works. The first one was built in 1981, but one could have been built in the 1950s. Piezoelectric crystals were known. Raster scanning circuits were known. Feedback ci…

Post by joncrocks » Sun, Jun 26, 2016, 10:46 AM UTC

quanics wrote: post #28

Pyxl101 wrote: post #25

Earlier quoted context omitted.

How do you know if your tip is one atom wide or not? 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?

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.

Post by dekhn » Sun, Jun 26, 2016, 1:50 PM UTC

Aelinsaar wrote: post #6

I love that offhanded comment about how the helical structure of DNA is not at all obvious from that crystallography. All the more impressive then, the history of that discovery.

Post by ci5er » Sun, Jun 26, 2016, 3:26 PM UTC

kens wrote: post #11

lisper wrote: post #7

One of my first jobs out of college was doing manual chip layouts (which will give you some idea of how old I am). Once the layout was done, the design was sent to a "mask house" which would print the layout onto a series of glass plates (the "masks") which were then used in the chip fabrication process. When the masks for my first chip came back I popped one of them into a bench microscope to see what it looked like…

What era of chip layout was this? I'm surprised that manual chip layout was still being done when chip features were that small. I look at 1970s chips a lot, and the features are easily visible under a microscope, as they are much larger than wavelength-sized.