Coating Thickness Calculation and Adhesion

Abstract

Coating thickness measurement over curved surfaces such as ball bearings and circular cross section rods is difficult. One could attempt to measure thickness directly by probing the coating material with a beam of electrons, starting from the coating surface and penetrating by a sputter method through to the surface of the ball. Probe-based methods rely on spectroscopy tools and may require some surface preparation before measurement. Auger electron spectroscopy (AES) for example requires high-vacuum conditions to enable an electron beam to knock-off film atom electrons as the beam penetrates the film surface. The energy emission resulting from the shift in electron shells is characteristic to the film material and may be compared with base standards to confirm the film composition. Once the probe is complete a sputter technique is used to remove a layer of atoms and the process is repeated through the film. The AES method, as well as others that use spectrometry, rely on sputtering-rate curves of a similar material of known thickness and sputtering time. Typically a surface chemistry-sensitive method such as X-ray photoelectron spectroscopy (XPS) is needed to help interpret the AES results.