Muller, Erwin W. (1911-1977), a German-born American physicist, in 1955 became the first person to see an atom, using a microscope he invented.

Erwin Wilhelm Muller (also spelled Mueller) was born June 13, 1911, in Berlin, Germany. As a student at the Technical University of Berlin, Muller studied physics under Gustav Hertz, who had shared the 1925 Nobel Prize in physics with James Franck for confirming the quantum theory of Max Karl Ernst Ludwig Planck by experiments on the effects produced by bombarding atoms with electrons. In 1936, during a decade of research for a variety of German firms, Muller invented the field-emission microscope. In this instrument, a high negative voltage is applied to a metal needle, and electrons ejected from the needle are attracted to a positively charged screen. Although the images displayed on the screen are too fuzzy to reveal individual atoms, they can indicate how the electrons stream from different metals.

Following World War II (1939–1945), Muller began an academic career with appointments at the Kaiser Wilhelm Institute for Physical Chemistry in Göttingen and later at the Free University of West Berlin. In 1951, building upon his field-emission microscope, he developed the ion microscope, which could produce pictures of molecules as small as 1/25,000,000th of an inch in diameter. In 1951, Muller used an ion microscope to take the first picture of the arrangement of atoms on a metal's surface. Also in 1951, Muller emigrated to the United States, where the following year he joined the faculty of Pennsylvania State University. In 1954, he developed a modified version of the ion microscope, the atom-probe field-ion microscope, which can analyze a single atom on a specimen's surface. In August 1955, Muller, using his new microscope, became the first person to see an atom. The atom-probe fieldion microscope can also remove atoms from a metal surface and send them to an instrument called a mass spectrometer. This technique is called field ionization mass spectrometry.

Muller was elected to the National Academy of Sciences and the National Academy of Engineering in 1975.