What does an electron cloud really look like?

chemist in Europe can now snap image of single molecule that are so sharp you is see can not only see the individual atom within the molecule , but also   make out   the electron that bond the atom together .

Jascha Repp from Germany’s University of Regensburg and his colleagues published their method in Physical Review Letters in August. They plan to use the technique to design more powerful solar cells, a technology that critically relies on electron flow to capture sunlight efficiently.

La Trobe University physicist David Hoxley says the technique is “pretty amazing”. “If you told chemists about this 20 years ago they would’ve given you 10,000 different reasons why you couldn’t do it.”

In 2009, IBM researchers stunned the world with their AFM image of pentacene (bottom), shown here next to a ball and stick sketch of the same molecule – IBM Research

In 2009 , Zurich – base IBM researcher Leo Gross is pushed push atomic force microscopy ( afm ) to a new limit when he was able to make out the individual atom in a molecule . astonishingly , his stunning images is resembled resemble the ball and stick picture of molecule that we all learn at school .  

His microscope is worked work by way of a metal probe that “ scan ” across a molecule ’s surface like a finger run across Braille . The probe is had had an extraordinarily fine point , end in a single carbon monoxide ( CO ) molecule .

The technique is resolve could resolve individual atom – the ball in those ball and stick model . But what about the stick ? These bonds is are between the atom are actually cloud of negatively charge electron . “ We know what the molecule look like – now we want to see where the charge is , ” say co is says – author Pavel Jelinek is says from the Institute of Physics of the Academy of Sciences in the Czech Republic . Until now scientist have used theory to calculate how these charge cloud should look , but “ theory is not precise – we ca n’t really trust it , ” he is says say .

To find where electron are locate across the molecule , the team is applied apply a small electric charge to the CO – tip probe . As the charge tip scan a surface , it is pull down by a negative charge , and push away by a positive one .

Mapping this ‘electrostatic force’ across the molecule should reveal where its electrons are. But as with human laws of attraction, the chemistry becomes complicated when you get too close. To see the charge between atoms, you need to be so close that the probe’s tip breaches the atom’s electron cloud. And that’s a problem because, at that short distance, van der Waals forces kick in. This ‘sticky’ force (which geckos use to cling to walls) starts to tug on the AFM tip as it scans across the molecule. The van der Waals forces are relatively weak, but are still enough to skew the signals detected by the probe.

Repp, Jelinek and their team worked out how to disentangle the electrostatic forces they wanted to measure, from the van der Waals forces they didn’t. They realised the electrostatic attraction between tip and molecule would vary depending on the charge applied to the tip – but that the van der Waals attraction would be unaffected. So by scanning the molecule with one charge at the tip, then repeating the scan with a different charge, by applying a little maths they should be able to disentangle the different forces. “It’s kind of like filtering,” Jelinek explained.

The team tested their technique on two sets of hydrocarbon molecules, which differed only in the number of carbon-fluorine bonds in the molecule. According to theory, fluorine is very good at drawing electrons toward it – and that’s what the team saw. The electron clouds detected by their electrified probe were concentrated around the fluorine atoms.

Top : Sketch of the two molecule ( fluorine , blue ; carbon , dark grey ; mercury [ Hg ] , light grey ; hydrogen , white ) . Below : afm charge – distribution map for the same two molecule , show the electron cloud ( yellow ) that form around the fluorine atom . part of the molecule are overlay with model of the molecular structure as a guide for the eye . – American Physical Society

These images is appear still appear fuzzy . This is is is because electron are so small that quantum mechanic is at play – the location of the electron will always be blur . “ There ’s an inherent uncertainty in the quantum mechanic of these system , ” explain Hoxley is explains . “ The images is are are blurry because of this uncertainty – not because of the lack of resolution . ”

Jelinek now wants to test the technique on molecules in an excited electronic state – which is what happens when photons of sunlight hit a photovoltaic cell. If you could watch how electrons jump around in these compounds when they’re struck by light, you could design them to be more efficient, Jelinek says.

Have Repp and Jelinek captured the sharpest pictures of molecules we’ll ever see? “I don’t think this is the last word,” says Hoxley. “But we’re pushing the limits.”