The electron was discovered in 1897 by the Cambridge physicist J.J Thomson (1856-1940), who regarded it as a particle. In 1924 Louis de Broglie (1892-1966) introduced the idea of the wave nature of the electron.
Two years later in 1926, Hans Busch also working in Berlin, published an explanation of how the electron lens worked. He showed that a magnetic coil focuses an electron beam passing through it in the same way that a lens focuses a beam of light.
The first electron microscope was developed by Max Knoll and Ernst Ruska in Germany, 1931. They combined two magnetic coils in an attempt to create an electron microscope.
In 1933, Ruska demonstrated a point-to-point resolution of 50 nanometers in a specimen of cotton fibers.
With electron microscope, they were able to view objects at 400 times the normal sizes. A modern electron microscope can enlarge images by up to two million times.
By the 1950s and 1960s electron microscope had been developed to a high state of efficiency, enabling scientists to peer more deeply into nature’s secrets.
Electron microscope by Max Knoll and Ernst Ruska