By the beginning of the 19th century, most scientists were convinced that the natural world was composed of elementary particles called atoms but no one could provide tangible proof because no one could see an atom. The typical size of a single atom ranges from 30 to 300 picometers. With the wavelength of visible light coming in at a whopping 400 – 700 nanometers, it is simply not possible to “see” an atom. Not possible with visible light, that is. So the debate on whether atoms really exist continued for centuries. Albert Einstein put the nail in the coffin of the anti-atom crowd in his 1905 paper on Brownian motion. In a spectacular triumph of pure thought, Einstein’s theory proved that the behavior of tiny particles suspended in a liquid cannot be due to any other thing except the movement of atoms. But the first direct ‘proof’ that atoms exist arrived only in 1982, when two researchers at IBM’s Zurich Research Laboratory, Gerd Binnig and Heinrich Rohrer unveiled an image of the atoms on silicon surface, the world’s first.

This seminal result was made possible by the scanning tunneling microscope (STM) technique invented by Binnig and Rohrer. STM works by scanning a very sharp metal wire tip over a surface. By bringing the tip very close to the surface, and by applying an electrical voltage to the tip or sample, an image of the surface at an extremely small scale – down to resolving individual atoms – can be captured. STM exploits a weird quantum mechanical effect known as quantum tunneling (see my previous post). It is this effect that allows us to “see” the surface by allowing electrons move through a barrier that they classically shouldn’t be able to move through. For their groundbreaking work, Binnig and Rohrer received the Nobel Prize in Physics in 1986.