7 ms·
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 im
by semi-extrinsic 10y ago
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.
- Animats 10y agoThe 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 circuits for controlling the height were known. The tricks for making one-atom sharp points were not known, but the earliest STMs just stretched out a tiny platinum wire until it broke, and sometimes you got a one-atom point. Hobbyists have built STMs.[1] It's simpler than building a 3D printer. [1] https://dberard.com/home-built-stm/ https://dberard.com/home-built-stm/
- semi-extrinsic 10y agoI 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.
- joncrocks 10y agoI worked in the lab at the Nation Physical Lab in the UK that had the low pressure + low temperature STM, we used to make the tips by dipping the ends in a very strong solution of NaOH. You relied on the surface tension as it dissolved to produce you a very sharp tip. Surprisingly easy.
- semi-extrinsic 10y agoCool. I know people also buy tips, but they're expensive. 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.html 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).
- joncrocks 10y agoTBH, more people were using AFMs than STMs, because they're cheaper (I think) and the fact that the STM is based on conductivity limits what can be imaged. Getting pictures of atoms is nice, but sometimes you want to image molecules, especially organic ones (tricky to do in a STM).
- Pyxl101 10y agoHow 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?
- quanics 10y agoThe 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.
- 10y ago
- pizza 10y agoCould you post a quick summary describing the technique? Sounds like my definition of esoteric fun, haha.
- tlmde 10y agodan's work is awesome I wish teensy was around in 1996 http://www.phys.ttu.edu/~tlmde/thesis/INTRODUCTION.html http://www.phys.ttu.edu/~tlmde/thesis/INTRODUCTION.html
- xyzzy123 10y agoI 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.
- Animats 10y agoThat'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 http://www.tubebooks.org/Books/rider_VTVM.pdf
- Asooka 10y agoHow do you verify that the tip is indeed one atom sharp without already having something like an STM?
- Stratoscope 10y agoI found the article really interesting and learned a few things from it. I do know how an ultrasound image works, and I had some basic knowledge about scanning tunneling microscopes, but this article - and the many links in it - were definitely worth my time reading.
- lanna 10y agoIt is the distinction between pictures and photographs: they definitively are pictures of atoms, but they aren't nor could ever be photographs. Ultrasounds also are pictures, but not photographs.
- amelius 10y agoIsn'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?
- cfallin 10y agoIsn'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...
- amelius 10y agoYes, so my question is if we can do it also on individual targets.
- cfallin 10y agoAh, yes, sorry, I missed your "of a single non-repeating atom" :-) I'm also curious -- but I wonder, would this allow for imaging anything that a scanning electron microscope can't?
- sukilot 10y agoXrays are human-invisible light, part of the EM spectrum. No liberty needed.
- James001 10y agoNo 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).
- semi-extrinsic 10y agoWell, we can image molecular orbitals using STM [1], which I'd say is one of the best ways to represent the shapes of atoms. [1] https://physics.aps.org/featured-article-pdf/10.1103/PhysRevLett.107.086101 https://physics.aps.org/featured-article-pdf/10.1103/PhysRev... (open access)