Trying to observe an atom directly through a traditional microscope is a physically impossible task. No matter how many millions of euros the most advanced optical instrument on the planet costs, its lenses will never be able to focus an elementary particle. The reason does not lie in a technical manufacturing limitation, but in a border imposed by the wave nature of electromagnetic radiation itself.
The wavelength of visible light ranges between four hundred and seven hundred nanometers, dimensions thousands of times larger than the diameter of a typical atom, which is only around a tenth of a nanometer. Due to this phenomenon, the light wave cannot bounce off the atom or interact with it to project a clear image to our eyes; the particle is simply too small to be resolved by light.
To overcome this insurmountable limit, quantum physics opened a completely different path in the 1980s with the development of the scanning tunneling microscope (STM). Instead of using lenses or photons, this device uses an extraordinarily sharp metal needle whose end ends in a single atom. By bringing the probe close to the surface of the sample at atomic distances and applying a tiny electrical voltage, the electrons jump through the vacuum taking advantage of the quantum tunneling effect.
By recording the variations of this infinitesimal electrical current as the needle sweeps across the surface, a computer reconstructs with topographical precision the exact location of each atom. We no longer look at fundamental matter with light: we touch it through quantum laws, making it possible even to manipulate atoms individually.
Santiago Campillo (@Scruzcampillo) is a biologist and scientific communicator specialized in health, nutrition and nature.
