An optical microscope, which uses visible light, cannot resolve objects smaller than about 0.2 micrometers (μm) due to the limitations imposed by the wavelength of light. Atoms are on the scale of a few tenths of a nanometer (nm), which is about a thousand times smaller than the resolution limit of an optical microscope. Therefore, an optical microscope cannot be used to see atoms.

To see atoms, one needs to use a microscope that uses a beam of particles with a much shorter wavelength than visible light. One such microscope is the scanning tunneling microscope (STM), which uses a sharp metal tip to scan the surface of a material. The tip is positioned very close to the surface, and a voltage is applied between the tip and the sample. This causes a tunneling current to flow between the tip and the sample, which can be used to create an image of the surface. STM can achieve a resolution of a fraction of a nanometer, allowing it to image individual atoms.

Another type of microscope that can be used to see atoms is the transmission electron microscope (TEM). TEM uses a beam of electrons accelerated to very high energies, which allows it to achieve a resolution of a few picometers (pm), which is about the size of an atom.