How scientists photograph atoms


Can you make atoms visible?


In order to answer this question, it is important to first understand what the difficulties are. The reason humans cannot easily see atoms with the naked eye is because of their size. Atoms are tiny. Expressed in numbers, an atom has a diameter of 0.1 nanometers, i.e. 0.0000000001 meters. For comparison, one would have to tear a DIN A4 sheet of paper 32 times in half widthwise in order to generate individual atoms. Doesn't sound like a lot, but have fun trying it out.

For this reason, humans need tools to be able to look at these tiny atoms. Unfortunately, it is not enough to put a “few atoms” under an optical microscope and turn on maximum magnification. This is due to certain properties of light. With the help of visible light, only structures that have a size of around 380 nanometers can be resolved. However, that is 3000 times too big. So you need other instruments.

Nowadays there are several technical methods that make atomic resolution possible. A very elegant and easy to explain method is the examination with the help of an atomic force microscope (AFM).

How it works can be derived from its name. What is measured with the help of this microscope is the force that an atom exerts on the tip of a thin needle. The easiest way to explain the way this microscope works is to make a comparison. Imagine that you are blind. Although you cannot see what you are reading, there are books you can read. These books are written in Braille. The writing does not consist of drawn characters, but of small bumps that are printed into the paper. As a blind person, you use your finger to feel these small bumps and so you can read scriptures. An AFM works according to the same principle. With this examination method, however, the braille is replaced by the sample to be examined and the finger is replaced by a very sharp needle point. Ideally, this tip is so thin that there is only a single atom at the very end.

The tip is then moved towards the sample and experiences a repulsive force. This is comparable to two magnets that are brought closer and closer to each other. When the two negative poles point towards each other, at some point you feel a repulsive force between them. The same is also the case with the atoms between the sample and the measuring tip - only at the atomic level. So you use another atom, so to speak, to make an atom visible. The very sharp tip is located on a very small and thin metal strip (called 'cantilever' in technical jargon). The metal strip bends due to the repulsion between the atoms in the sample and the measuring tip. This bending is detected with a laser and provides information about the height of the sample. By scanning the sample point by point with the measuring tip, a three-dimensional image of the surface can be created.

In conclusion you can say: No, you can't see atoms nowadays, but over time humans have developed methods with which you can make atoms visible. However, only the outer areas of the electron shell that surrounds the atomic nucleus are shown. A real image of an atom with its internal structure of protons, electrons and neutrons is currently not possible with technical methods. The current state of research can be compared with an aerial photo of a housing estate. The individual houses can be seen and differentiated, but the interior of the houses is still closed to the scientists.