Films were sputtered on glass from circular tin cathodes. These films, when produced in air or oxygen and viewed with monochromatic light, show alternately light and dark rings; in white light they show several cycles of the colors of the visible continuous spectrum, similar in appearance to Newton’s rings. In the formation of a set of rings the center gradually passes through a cycle of colors of increasing wave-length to the red. The red center then merges into blue and the cycle is repeated. With the appearance of each new center color, all preceding colors move outward and form surrounding rings. The rate of growth of a set of rings depends on the sputtering conditions. Under proper conditions, the change of color of the center and the addition of another set of color rings takes place with definite regularity. These colors are believed to be due to an interference effect produced by the variation in thickness of the film layer. This layer is probably stannic oxide. Films produced in nitrogen are opaque brown deposits. Tests indicate the material of these films to be a tin-nitrogen compound. Heating such a film in oxygen produced a nearly transparent color film similar to those sputtered in oxygen or air. Films produced in hydrogen have mirror surfaces of high reflecting power.
CLARENCE J. OVERBECK, "Color in Films of Sputtered Tin," J. Opt. Soc. Am. 23, 109-113 (1933)