DR G.K.L. CRANSTOUN / SCIENCE PHOTO LIBRARY DR G.K.L. CRANSTOUN / SCIENCE PHOTO LIBRARY
Field ion micrograph of tungsten. The coloured dots are the locations of individual atoms; the ring-like patterns are facets of a single crystal of the metal. The image was made by superimposing successive micrographs, taken with different col- our filters, to show small changes on the surface. Field-ion microscopy involves placing a tiny needle of a substance, such as tungsten, in a gas- filled chamber & passing a high voltage through it. The drifting gas ions hit the charged atoms & are repelled at right angles to form this pattern on a screen.
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