Analysis of elements close to the surface of a solid - by directing pure molecular beam over the surface, and observing the light spectrum

摘要

A pure molecular beam, pref. of helium atoms, is directed onto the surface of a solid and the light spectrum emitted by the varying elements is analysed on a monochrometer by comparison with spectra of known elements. The energy of the molecular beam varies from 0.1 to 1 electron-volt for elements on the surface, 1 to 25 electron-volts for elements near to the surface and over 25 electron-volts for heavier solids. It is possible to direct several beams onto the surface so that the elements at various points can be simultaneously and continuously analysed. By filtering the light emitted so that only that of a certain element is allowed through it is possible to obt. the concn. of that element over a swept area, and by bombarding one spot of the surface with the molecular beam a graph of concn. of element with depth from surface can be made. A thin transparent layer of a body can be observed from the side opposite that of impact of the beam. Used for surface analysis of metals and alloys and partic. for biological analysis e.g. cells and tissues. Pure molecular beams with neutral atoms is not repelled so closer beam can be maintained over longer distance. Neutral atoms of pure molecular beam are less harmful hence sample can be under higher pressures approx 10-3 torr, giving also longer analysing time as degassing occurs more slowly. The intensity of the light emission does not depend on the form of the surface.