Atomic absportion spectroscopy for monitoring evaporation processes

摘要

Atomic Absorption Spectroscopy (AAS) was investigated as a technique for monitoring the rate of deposition in vacuum evaporation processes using a commercially available AAS unit. The absorption was measured as a function of the rate of deposition on a quartz crystal monitor for several materials (Al, Si, and Ge). Each absorption-vs.-rate curve can be fitted by an equation with two adjustable parameters. This equation is drived by assuming that the absorpton and emission line shapes are both Gaussian, that the absorption line shape does not vary with depositiioon rate, and that the deposition rate is proportional to the vapor density. The two adjustable parameters for the equation represent (1) the ratio of the widths of the absoprtion and emission lines, and (2) a proportionality constant related to the deposition rate. Similar equations de-scribing absorption-vs.-rate curves are obtained for an idealized evaporation process with a cosine source distribution. These equations have the advantage of explociityly including all gemometric factors so that a fit to absorption-vs.-rate data for one case may be used to predict the corresponding curves for alternate depostion geometries.