A scanning-tunnelling microscope image of a silver surface, showing individual iron atoms. Image: Andreas Riemann/Western Washington University
With high-powered microscopes. Most of our early knowledge of atomic structure was based on indirect experimental observations, but in 1955, Erwin Muller and Kanwar Bahadur of Penn State University in the US imaged individual atoms using field-ion microscopy.
Fifteen years later, scanning-transmission electron microscopy produced atomic-resolution images from a stream of electrons scanning across an object’s surface. Since the 1980s, scanning-tunnelling microscopes have been used to image individual atoms. These microscopes detect electrons as they tunnel across the distance between the microscope’s probe and a surface. By observing this process, scientists can see the surface with atomic resolution.
