0
$\begingroup$

"Using a state-of-the-art atomic force microscope, the scientists have taken the first atom-by-atom pictures, including images of the chemical bonds between atoms, clearly depicting how a molecule's structure changed during a reaction. Until now, scientists have only been able to infer this type of information from spectroscopic analysis."

http://www.sciencedaily.com/releases/2013/05/130530142007.htm

Are there any papers how this thing actually works?

$\endgroup$
1
$\begingroup$

The seminal paper you're looking for is:

Binnig, G., & Quate, C. F. (1986). Atomic force microscope. Physical Review Letters, 56(9), 930-933.

Here's the short version, along with some speculation since I don't have their manuscript.

Atomic force microscopy (AFM) is a scanning probe microscopy technique, meaning a sharp probe is scanned in a raster pattern over/in contact with the sample. A probe my look like this.

AFM probe

I will refer to the point as the tip, and that is where the carbon monoxide molecule mentioned in the article resides. The substrate the tip is attached to will be referred to as the cantilever.

A laser is bounced off the top of the cantilever, onto a dicrotic mirror, and finally into a photodetector, as shown below.

AFM beam bounce diagram

The researcher has control of the laser and mirror alignment. Alignment procedure is to place the laser centered, and as close to the end of the cantilever as possible, for the maximum deflection signal. The mirror is then adjusted to put the reflected laser on the most sensitive part of the photodetector.

The article mentions using non-contact AFM. That is about as meaningful as saying "we can the signal through a digital filter." There are multiple non-contact modes, but my guess (without having access to the manuscript) is they used a form of tapping mode.

The cantilever has a self resonant frequency, typically around 300 kHz. The cantilever is driven to resonance, and scanned over the sample. The deflection signal generated is an amplitude modulated version of the topography. It is also possible to obtain information about material properties this way.

That is the short version. If I get access to the manuscript or someone asks questions, I would be happy to add more information about how this system works.

$\endgroup$
  • $\begingroup$ 1986?? Why do they still talk about the first image of molecules in 2013? $\endgroup$ – user8005 May 31 '13 at 6:08
  • $\begingroup$ That's a good question. I remember seeing another article back around 2009 stating researchers had "taken the first pictures of a molecule" and their images were very similar. Taking images of a single atom is nothing new. I think what these guys were so excited about was the visibility of the bonds. $\endgroup$ – Matt Young May 31 '13 at 11:03
  • 1
    $\begingroup$ @user8005 It's because they saw before and after pictures of a chemical reaction - this is quite hard as many reactions require molecules to move and are otherwise "rare events". To scan with AFM, have it react, then scan the exact same molecule again is quite a chore. $\endgroup$ – Lucas Jun 2 '13 at 14:19

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.