Optical microscopes can help us see the microscopic world, but to use them to examine individual atoms is like measuring an ant with a measuring tape. An atom is way too smaller as compared to the wavelength of any visible light, which's the key mechanism to form optical images.
Thanks to physicists and inventors Gerd Binnig and Heinrich Rohrer, we now have Scanning Tunneling Microscopy (STM), an imaging method that can reveal the structural detail of certain materials at the atomic level. The duo has been working for IBM since the early 1970s, where they dedicated their efforts to interrogate the surface characteristics of electronic components. Using no light rays or other kind of electromagnetic radiation, an STM examines its objects in a way close to a turntable: it applies a tiny metal probe to arrays of atoms on a surface.
To achieve atom-scale resolution, Binnig and Rohrer experimented with some of the most advanced techniques and frontier knowledge during the development of STM.
For instance, they applied electrochemical etching, an erosive microfabrication method, to make the tip of a tungsten probe as fine as the size of an atom. The finished tip, which matches the size of the STM object, allows the microscope to scan one atom at a time.
They also took advantage of tunneling, a quantum mechanics principle that describes a bizarre behavior of subatomic particles. Take an electron for example, its existence (which appears at locations of specific probabilities within an atom) can be transferred from one side of a potential barrier (say a vacuum) to the other, which's what happens as the STM scans the atoms of its objects.
Besides allowing us to investigate electronic materials, the STM has also found a diversity of applications in many other fields such as nanotechnology, material science, semiconductor science, and even structural biology. That's why Binnig and Rohrer were honored with the Physics Nobel in 1986 for making zooming in on atoms possible.
Source: SciShow via Youtube