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Speeding Up STM Imaging
Roland Piquepaille writes "Probably not many of you have used a scanning tunneling microscope (STM), the essential tool of nanoscience. And you might think that it's as easy to take a picture of an atom with an STM as it is to take a shot with your digital camera. In fact, the imaging of individual atoms with an STM is quite slow. Now researchers at Cornell University have shown how to accelerate this process — by adding a radio transmitter, they are able to speed up atomic-level microscopy by a factor of at least 100. A typical STM currently has a sampling rate of about one KHz. This new radio-frequency STM can operate a thousand times faster."
Probably not many of you have used a scanning tunneling microscope (STM), the essential tool of nanoscience
You might be surprised.
Suddenly, the hairy finger of a familiar monkey tapped me on the shoulder. It was time.--G. T.
so now when i go around my physicist friends house not only do i get to see the photos now i have to sit through the movie?
Do it yourself, because no one else will do it yourself. [beta blockade 10-17 Feb]
Don't buy one now though, because a model with double the features will be out in 6 months for less $$$ ;)
It's only paranoia if your wrong...
you mean like... one megahertz?
I thought the limiting factor of SPMs (including STMs) is the feedback loop: one has to keep the probe tip from crashing into the surface as it's dragged back and forth, which means that the scan has to be slow enough that the piezo stack that's moving the probe tip up and down can do its job (limited by speed of sound through the material), as well as the electronics that have to decide how to move the thing in the first place. This might help with the electronics, but 1000x speedup in sampling rate doesn't mean 1000x speedup in imaging speed.
So.. is the speedup 100 or 1000?
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If you want to see photos of atoms taken by an STM, there's a great gallery here:
STM Image Gallery
http://www.almaden.ibm.com/vis/stm/gallery.html
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Essential? Bah! I work in a nanotech lab, and we don't have a STM!
We do have a brand new AFM, though, and it is kinda sluggish. I wonder if this technique would speed up that.
sub f{($f)=@_;print"$f(q{$f});";}f(q{sub f{($f)=@_;print"$f(q{$f});";}f});
When I was in high school in the Soviet Union around 1992 a friend of mine built one. He used a regular broken sewing needle for the tip, the idea was that when you break a needle the resulting surface is not smooth and there are bumps with a single atom on top.
US-UK-Israel: The real Axis of Evil
I'm working on a project using an AFM and STM, and there is really no problem with the scan rate. There is a monitor which is used for aligning the sample and lowering the cantilever onto the surface. . . but the monitor happens to be a TV, so we have the joy of daytime terrestrial television to pass the time. . .
New readers may not understand why such vitriol would be addressed to someone who submits interesting science stories to Slashdot. After all, while there is a link to his blog if you click on his name, this is standard practice with story submissions. So what's the big deal?
Well, there was a time back when Roland first started submitting stories where he would put a link to his blog in the summary content, blatantly suggesting that said blog might be a good place to discuss the story. Since there are ad links on his blog, that makes it horrible, evil and self-serving; readers were in an uproar.
Since then the blog link has been restricted to the submitter name at the beginning of the summary (again, standard practice). But some people really cannot ever let go, and we have to put up with silly tags and dumb trolls on every single one of his submissions. Kinda makes you long for the days when almost everyone on Slashdot was more interested in science than name-calling.
I have seen the future, and it is inconvenient.
So will this device allow us to observe viruses in real time? so instead of finding cures for specific viruses that do not work on the next mutation, we could find how viruses operate on atom level and find a cure for that level...much like doing debugging in assembly language.
STMs can be used to push together atoms into molecules. If they can get the access time down, and the seek time, put it into a cheap USB enclosure, then I'll take one.
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make install -not war
Because in the mean time this all seems about as useful to us as the scientific research that was ostensibly to figure out why some men get belly button fuzz and some don't. [slight pot belly, body hair in the navel region, and cotton shirts]. Would someone please explain why a STM is important as the rest of the story?
...Open Source isn't the only answer -- but it's almost always a better value than the alternatives...
Your question is similar to "What's the use of a telescope? All it does is make things look bigger! It doesn't have any effect on real life."
Galileo used one of the first telescopes to see that Jupiter is a planet with it's own orbiting moons. Again, that was just a bit of trivia to the common man in his day. But a few centuries later we're using that knowledge to send spacecraft around the solar system.
A new scientific measurement technique is first used to explore fundamental physics and acquire basic knowledge. It could take decades at least before you can point to some everyday object and say "that specific instrument made this possible".
Sometimes the instruments themselves get adapted into everyday tools, like telescope technology being adapted for cameras or Earth-sensing satellites. As somebody else mentioned, maybe high speed ATM could be used as an ultra-high density information storage device. But it's very hard to predict what the everyday impact will be from a bit of fundamental science.
This news is more interesting to those of us who are scientists but didn't know that STM could be done so much faster. Besides saving time to get static scans, high enough speeds would make dynamic scans possible. We could learn a lot about physics, chemistry, and biology if we could watch atoms moving, bonding, and rearranging in real time.
STMs and AFMs are important because they let us see things much smaller than conventional optical microscopes can. Increasing the scan rate by a factor of 1000 might yield new applications, taking better STM movies, and elucidating mechanisms that run that much faster.
The only public data released on the RF STM stuff seems to be this one lonely chart. The gamma variable (on the Y axis) has to do with electrical reflections that come about because of impedance mismatches on transmission lines. For more information, take a look at these lecture notes (2.5MB PDF) which start from voltage and current, and end with the gamma plane.
In conventional (non-RF) STM, the tunneling current is exponentially related to the distance above the surface. This is a part of why control systems for STMs, which are supposed to keep the tip hovering a few nanometers or less above the surface, are challenging to get right. In general, the surface and scanning tip are kept at a constant bias voltage of a few volts, and there is a feedback loop which attempts to maintain a constant current (and thus constant height over the sample) by adjusting the displacement of the tip.
In this system, it appears that they've found that the small-signal impedance of the tunneling junction varies significantly enough to make a large impact on the reflection coefficient, and (more importantly) that that's a good way to go.
Considering they've released so little technical data, there's only one really obvious savings here to me: noise. If you're an electrical engineer, you'll know that most devices (and thus most circuits) have noise at all frequencies, but that things get particularly bad for low frequencies around DC. This is often called 1/f noise, and if you take f to zero (DC), you've clearly got a problem! Additionally, you get other nasty effects at DC, like drift related to temperature, etc, which tend to be much worse than at high frequencies. By designing their system to work with small signals at high frequencies, they're able to avoid 1/f noise yet still make the height measurement they want. Pretty smart.
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It has been 20+ years since I worked on EMs at Colorado State U. I was thinking of SEMs.
I prefer the "u" in honour as it seems to be missing these days.
I happen to be a student at Cornell, and we have used mini, portable desktop STM's.