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Mueller, Erwin Wilhelm

tip field microscope conditions

[mü ler] (1911–77) German–US physicist: invented the field-ion microscope.

A graduate in engineering from Berlin, Mueller worked for industrial laboratories in Berlin and for the Fritz Haber Institute until 1952 when he joined Pennsylvania State University. In 1936 he invented the field-emission microscope, in which a high negative voltage is applied to a fine metal tip held in a vacuum near a phosphorescent screen. Electrons emitted from the tip travel to the screen and form a highly magnified image of the tip’s surface, allowing study of conditions at that point of atoms and molecules provided they are stable enough to survive the conditions at the tip. In 1951 he devised a field-ion microscope, in which the metal tip is held positive in gas at a low pressure. Gas adsorbed on the tip becomes ionized, and the resulting positive ions are repelled from the tip and form the image. The resolution is improved by cooling the tip with liquid helium, and in this way in 1956 Mueller was able to obtain well-resolved images from atoms for the first time.

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