Czech scientists first to look inside atom, open new window into understanding quantum physics
A team of Czech scientists has developed a new microscopic method that made it possible to look inside the atom for the first time ever. The new method was tested on the theory of so-called “sigma holes” - asymmetric electron density distributions on single atoms of halogen elements. To find out more about how the discovery works and what it could lead to I spoke to one of the scientists that took part in the project - Dr Pavel Jelínek from the Institute of Physics at the Czech Academy of Sciences.
“As far as we know this really is the first time that features inside the single atom have been observed. Importantly, these features can also be somehow related to some chemical or physical properties of the given atom.
“In our work we use the Kelvin probe force microscopy technique, which can basically routinely image single atoms that typically appear as spheres. What happens sometimes is that you can of course see that the atoms are not perfectly spherical. This could either be down to the measurement, or it could be related to something else that is important.
“Kelvin probe microscopy technique works kind of like a gramophone. On a gramophone, you have a needle which is just scanning over a desk. In our microscopic method we have a needle which is ideally terminated by a single atom.”
“Thus far, these asymmetric measurements were not directly related to any physical meaning. In our case, we decided to look at the sigma hole, because we know that this feature has been theoretically predicted for a long time, but no one was able to resolve it. From this perspective we can see this anisotropic charge distribution on a single atom, which has a direct physical or chemical interpretation.
“It’s basically the first time that we can see some physical or chemical quantity within the single atom, which can be interpreted in a very direct way.”
Gramophone needle the size of an atom
To test their new method, the team searched specifically for molecules where halogen atoms host a sigma hole pointing out of the surface. The reason for this was due to the way that the measurement device itself works, says the physicist, likening the Kelvin probe microscopy technique to a gramophone scanning a vinyl record.
“On a gramophone, you have a needle which is just scanning over a desk. In our microscopic method we have a needle which is ideally terminated by a single atom. The base of it is microscopic, about 1mm. It is a wire which you have to shape so that its tip is just a single atom. It is quite a challenge to do that.
“When we scan with the needle we want to detect some sort of quantity. For example, the force that is acting between the anisotropic electron density that is on the sigma hole and our atom that is on the tip [of the measurement needle].
“We wanted to optimise this [measurement] technique to make it extremely sensitive to this electric field.”
“In our case, because we knew that we wanted to resolve some anisotropic electron distribution, we needed to tune our sensor to be extremely sensitive only to electrostatic interaction. That’s because these electrons create an electric field which is anisotropic. We wanted to optimise this [measurement] technique to make it extremely sensitive to this electric field.
“That was basically our contribution and the reason why we were able to resolve this anisotropic charge with such sub-atomic resolution.”
A useful tool for medicine, nano-electronics – and understanding quantum physics at large
Dr Jelínek says that the significance of the discovery is very broad, because chemical and physical processes on an atomic scale are driven by the distribution of such electron clouds.
“For example, if you have a molecule and you know that there is a part of it which is positively charged, then you know that some kind of chemical interaction will happen. You know that that this molecule will be attracted by another molecule that has a rich electron cloud.
“Being able to know the detailed distribution of these electron densities inside molecules or on atoms themselves is the key quantity that we need to understand the behaviour of these objects.
“Once you know this, you can start to scale up. You can say: ‘Ok, if I know the electron density, I am able to say something about its reactivity, its interaction with other objects to form molecular assemblies.’ You can basically start generalising and then apply these finding.”
“For example, you can use it in developing new drugs…You can also use this knowledge in nano-electronics, where we want to organise self-assembled molecular structures.“
“For example, you can use it in developing new drugs. This is because we know that the halogen bond, which originates from this sigma hole, is very important in the functional design of drugs. You can also use this knowledge in nano-electronics, where we want to organise self-assembled molecular structures. These self-assemblies are driven by intermolecular interactions which, again, are dictated by these electron densities.”
Aside from these practical applications of the new microscopic method, Dr Jelínek says that the discovery is aiming for a more fundamental level of understanding, one that will expand our knowledge of the strange world of quantum physics.
“We have a limited access to this quantum world – how we can investigate atoms and electron densities that are not observable through the eye. We need a technique that will help us understand how the quantum world behaves and what its rules are. For that we need tools that will make us able to understand these kinds of objects better.”
The new microscopic method was developed by scientists and researchers from the Czech Advanced Technology and Research Institute at Palacký University in Olomouc, the Institute of Organic Chemistry and Biochemistry and the Institute of Physics at the Czech Academy of Sciences and the IT4Inovations Supercomputing Center at the Technical University of Ostrava.
