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

askamathematician.com

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

#31

Post by NegativeLatency »

lisper wrote: post #16
kens wrote: post #11

Earlier quoted context omitted.

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.

This was in 1984, and it was for experimental chips, not production chips. The layout was done using CAD tools, but the placement was all manual. Also, I think they were analog chips, not digital. I'm not sure. This was a co-op job in my first year at college at the IBM plant on Cottle Road, and I was never fully in touch with the big picture. I think they were making big-ass hard drives, and the chips I was working…

How many features were on the chip?

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

#32

Post by tlmde »

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…

dan's work is awesome I wish teensy was around in 1996 http://www.phys.ttu.edu/~tlmde/thesis/INTRODUCTION.html

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

#33

Post by xyzzy123 »

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…

I think actually the hard part in the 50s might be the current amplifier but I'm not au fait enough with the tech of the time to know if nanoamp amplifiers were easy. I think it's not so different from radio but would be interested in an educated opinion.

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

#34

Post by tostitos1979 »

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.

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.

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

#35

Post by lisper »

NegativeLatency wrote: post #31
lisper wrote: post #16

Earlier quoted context omitted.

This was in 1984, and it was for experimental chips, not production chips. The layout was done using CAD tools, but the placement was all manual. Also, I think they were analog chips, not digital. I'm not sure. This was a co-op job in my first year at college at the IBM plant on Cottle Road, and I was never fully in touch with the big picture. I think they were making big-ass hard drives, and the chips I was working…

How many features were on the chip?

I have no idea. This was more than 30 years ago. But the number of transistors was in the hundreds or maybe low thousands. (I can't recall if I was laying out individual transistors or functional modules.)

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

#36

Post by James001 »

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 simply due not measure at the scale of an atom).

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

#37

Post by maybecorrect »

tostitos1979 wrote: post #34
quanics wrote: post #28

Earlier quoted context omitted.

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.

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…

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.

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

#38

Post by cfallin »

amelius wrote: post #24
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.

Isn't it possible to make an image using light, but by computing the "real" image from the interference pattern (of a single non-repeating atom/structure)? And if there is more than one solution, then perhaps by using images from multiple angles, or with different wavelengths?

Isn't that basically what X-ray crystallography is (taking the liberty to include X-rays as "light")? Though with the (significant) restriction that it only works for repeating crystal structures, not unique individual targets...

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

#39

Post by Animats »

xyzzy123 wrote: post #33
Animats wrote: post #5

Earlier quoted context omitted.

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…

I think actually the hard part in the 50s might be the current amplifier but I'm not au fait enough with the tech of the time to know if nanoamp amplifiers were easy. I think it's not so different from radio but would be interested in an educated opinion.

That's a good point. A very high gain DC amplifier with low noise would have been hard then. A STM needs to sense about 1na at 0.1V, which means a series resistance of about 100 megohms. Vacuum tube voltmeters of the 1940s and 1950s era were getting close, with about 10 megohms input resistance.[1] Sensing 0.1V through 100 megohms with tubes doesn't seem out of reach.

High RF gains are easier to get than DC gains; you can filter out everything but the frequency of interest and reduce noise. That's basically how radios amplify weak signals. But I don't think you can run an STM on RF.

[1] http://www.tubebooks.org/Books/rider_VTVM.pdf

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

#40

Post by moptar »

There's a philosophy idea that in order to say we can "see" something, we have to be able to collect consistent information by several different methods. For example if all we have is a STM, then we don't know which parts of the image are artifacts and which are real so we haven't seen anything. But if we have an STM and crystallography, we can have more faith in the features that are common to both images - such as interatomic distances and the geometry of crystal structure. But we still couldn't say that we've seen the shape of an atom since that would look different in each instrument's image.

A great example is people who "discovered" lost cities under the sea. They saw regular patterns of lines on the seafloor in Google Earth and interpreted them as ancient roads or walls. But they were only seeing artifacts from ships that had sailed back and forth in straight lines collecting data. If they had looked both at those sonar scans and some other data for the same location, they would have only seen the lines on one image and been able to conclude that they were either an artifact of the sonar or below the level of sensitivity of the other instrument.

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