Looking at the smallest is the passion of physics professor Sara Bals (UAntwerp). In this episode of the University of Flanders she explains how you can determine the stacking of individual atoms in materials, and how this knowledge can then be used to make new materials.
Everything around us is made up of atoms: the chair we sit on, the screen we look at, and even the glass we drink from. In recent decades, scientists have succeeded in creating new materials with new properties by stacking individual atoms in a lattice. You can imagine it as tinkering with atoms. Those new materials are usually very small and have dimensions in the nanometer scale, which is only a billionth of a meter. We therefore call these mini-materials “nanomaterials”.
Nanomaterials are very interesting because their properties are often very different from those of the same material on a larger scale. For example, gold is known as a material that shows little reactivity, but in the form of nanoparticles gold is actually used to speed up chemical reactions. Without us perhaps realizing it, nanotechnology has already played an important role in our daily lives: transparent sun creams contain zinc oxide nanoparticles, and the antibacterial properties of silver nanoparticles are used, for example, in wound dressings or in coatings for medical instruments. In principle, many more applications can be developed, but tinkering at the nanoscale is quite difficult because you cannot see the atoms.
Looking at atoms
The research group Electron Microscopy for Materials Science (EMAT) of the University of Antwerp specializes in studying nanomaterials down to the scale of individual atoms. The researchers in our group work with very powerful electron microscopes. Electrons are accelerated and then fired at a (nano) material. The result is an image that corresponds to a two-dimensional projection of the atomic structure. These images already provide an enormous amount of information, but the properties of the nanoparticles usually depend very much on their three-dimensional shape. By choosing their shape and size correctly, gold nanoparticles, for example, could be used in the future to detect cancer or even to destroy cancer cells.
This example indicates that it is crucial to investigate what these nanoparticles look like in three dimensions. We therefore use the electron microscopes to apply “electron tomography”, a technique whose concept can be compared to the idea behind a medical scanner: two-dimensional images are recorded in different directions and through a computer program we can form a three-dimensional image.
The special thing about the three-dimensional images created within EMAT is that they show atomic resolution. So we can map the material atom by atom. In addition, we can determine not only where an atom is, but also what type of atom it is: gold, silver, zinc, etc.
These very precise measurements are very important because small deviations from the perfect lattice of the atoms can indeed cause important changes during the applications of the nanomaterials. Moreover, a theoretical physicist can use the results of atomic electron tomography as a starting point for calculating the properties of the nanomaterials. In this way, we now also have a better understanding of the relationship between the structure and the properties at the nanoscale. The aim within nanoscience is that in the future this knowledge will result in an ‘on demand’ production of nanomaterials with specific properties.
This possibility sounds very promising, but it is also important to realize that a lot of fundamental research goes into developing new and accurate characterization techniques. Scientists should therefore have the freedom to invest sufficient time and resources in basic research. For example, in order to achieve atomic resolution with electron tomography it was necessary to invest in better electron microscopes and furthermore it was necessary to develop better mathematical three-dimensional reconstruction algorithms. New breakthroughs can only be created if there is room for groundbreaking research.
Looking at the smallest has a big impact
Finally, it is important to note that the characterization of nanomaterials is only one small piece of a much larger puzzle. Nanomaterials are sent to EMAT from all over the world for a thorough characterization of structure and composition. For example, there is a close collaboration with the CIC Biomagune laboratory in San Sebastian. Within this research group, nanoparticles are being developed for medical applications such as controlled drug release or biosensing. In turn, CIC Biomagune has a collaboration with a medical group. We are collaborating with Utrecht University on a better understanding of catalysis. These insights and new characterization techniques can later be used in collaborations with industrial partners. Our fundamental research is therefore only a small, but important, link in a larger chain. In any case, it is clear that looking at the smallest can lead to major changes.