Interference phenomena in thin films

In Subsection 5.6.a we review the theory of multilayer thin films. In Subsection 5.6.b this theory is applied to the design of antireflection coatings for infrared windows, lenses, and other components. The same theory is used again in Section 5.6.C to find suitable beam dividers of the free-standing, self-supporting type as well as of the type requiring a transparent substrate. Subsection 5.6.d deals with interference filters and Fabry-Perot interferometers. 

---

Various methods have been developed for Raman characterization of very thin films and amorphous phase films that exploit the optical properties of the film to enhance the intensity of the Raman scattered radiation. Such techniques involve the lateral transmission of light in thin films, interference phenomena upon reflection at interfaces, or direct absorption of the probe radiation by the thin film. Raman scattering experiments based on these phenomena exhibit an increase in sensitivity from one to several orders of magnitude and allow molecular characterization of very thin films. 

This variation in thickness, over the surface of the film, as a function of time enables information concerning the draining and thinning mechanisms to be deduced. We shall now analyse the interference phenomena in some detail. 

Clear-bright and blue-bright chromium conversion colors are thin films (qv) and may be obtained from both Cr(III) and Cr(VI) conversion baths. The perceived colors are actually the result of interference phenomena. Iridescent yellows, browns, bron2es, oHve drabs, and blacks are only obtained from hexavalent conversion baths, and the colors are Hsted in the order of increasing film thickness. Generally, the thicker the film, the better the corrosion protection (see Eilmdepositiontechniques). 

In the past decade, effects of an EEF on the properties of lubrication and wear have attracted significant attention. Many experimental results indicate that the friction coefficient changes with the intensity of the EEF on tribo-pairs. These phenomena are thought to be that the EEF can enhance the electrochemical reaction between lubricants and the surfaces of tribo-pairs, change the tropism of polar lubricant molecules, or help the formation of ordered lubricant molecular layers [51,73-77]. An instrument for measuring lubricant film thickness with a technique of the relative optical interference intensity (ROII) has been developed by Luo et al. [4,48,51,78] to capture such real-time interference fringes and to study the phenomenon when an EEF is applied, which is helpful to the understanding of the mechanism of thin film lubrication under the action of the EEF. 

The recollless fraction, that Is, the relative number of events In which no exchange of momentum occurs between the nucleus and Its environment. Is determined primarily by the quantum mechanical and physical structure of the surrounding media. It Is thus not possible to observe a Mossbauer effect of an active nucleus In a liquid, such as an Ion or a molecule In solution. This represents a serious limitation to the study of certain phenomena It allows, however, the Investigation of films or adsorbed molecules on solid surfaces without Interference from other species In solution. This factor In conjunction with the low attenuation of Y-rays by thin layers of liquids, metals or other materials makes Mossbauer spectroscopy particularly attractive for situ studies of a variety of electrochemical systems. These advantages, however, have not apparently been fully realized, as evidenced by the relatively small number of reports In the literature (17). 

---