Ellipsometric technique

A paper that demonstrates the power of the ellipsometric technique is that of Hamnett and Hillman (1988) which investigated the nucleation and growth of polythiophene on an electrode in situ. The ellipsometer employed by the... 

Ellipsometric techniques in which amplitude ratios and phase shifts for reflected light are directly measured as opposed to the previous technique in which the phase shift is indirectly obtained. This is difficult to do over large wavelength regions because of requirements on optical elements such as polarizers and retarders. 

A good review article on optical constants and their measurement is that by Bell (1967). Determination of optical constants from reflectance measurements is treated by Wendlandt and Hecht (1966) and from internal reflection spectroscopy by Harrick (1967). Ellipsometric techniques are discussed at length by Azzam and Bashara (1977). 

The ellipsometric technique described earlier has the unique feature that the index of refraction can be determined independently of the film thickness. Then, knowledge of this index can be used to infer the chemical composition of a film. For example, thin silicon dioxide films have an index of 1.46, while silicon nitride films have a value of 2.0 typically. Now, when either of these films are deposited by PECVD techniques, their stoichiometry can vary depending on deposition conditions. It turns out that this variation in stoichiometry can be related to the measured refractive index. Accordingly, measurements of the refractive index can be used as an approximate guide to film stoichiometry. 

A. Hamnett, Ellipsometric Techniques for the Characterization of Electrode Surfaces, J. Chem. Soc. Faraday Trat s. 89 (1993) 1593. (Review-type paper.)... 

The molecular structure of the film adsorbed on a substrate such as germanium, silicon, or various common IR-transmitting salts [either before or after their surfaces were modified by standard techniques such as monolayer formation (I, 2)], is readily deduced by the internal reflection technique which has been described (3). When the substrate is a material of high reflectivity and high intrinsic refractive index such as germanium (which is used in most of our experiments), film thickness and refractive index may be determined nondestructively by ellipsometric techniques (4). A third nondestructive and noncontacting technique, which is easily applied to thin film samples on germanium or any con-... 

So there you are. I find it difficult to chose between my projects. Since you are an electron diffractionist what you probably think of first is my early treatment of the effects of anharmonicity of molecular vibrations on analyses of molecular structures. This was reviewed in detail in the prefatory chapter you and your husband solicited. Surface chemists might think my invention of an ellipsometric technique to measure absorption spectra of films as thin as monomolecular might qualify as the most important. Since I was too poor to do electron diffraction work, I constructed some ellipsometers during my early years at Iowa State and discovered their unique capabilities. 

Characterization of Materials, Thin Films, and Interfaces by Optical Reflectance and Ellipsometric Techniques... 

For example, the ellipsometric technique was used to determine the interfacial thickness in SAN/PA blends, compatibilized by addition of SMA [Yukioka and Inoue, 1991, 1993]. A thin bi-layer film of SMA/SAN was prepared then mounted on a thick PA substrate. The interfacial thickness varied with the compatibilization time from A1 = 2 to 30 nm. The method was also used to study the interphasial thickness variation in PCL blends with CTBN or CTBR. Without a reactive modifier (aminopropyltriethoxysilane, APS), the measured thickness was A1 = 3 nm, upon addition increasing to 6 nm [Okamoto and Inoue, 1993]. 

Figure 2 is a good illustration of the power of the ellipsometric technique. Curve (a) on the figure shows the specific attachment of antibody to a preadsorbed BSA layer. Curve (b) is a repeat of the experiment, except roughly 90 sec. after the start of the run, additional BSA was added to the solution thus effectively neutralizing the specific antibodies. 

In Figure 3 the film thickness of a polymer is presented as a function of deposition time O). It can be seen from the data of Figure 3 that polymer films of thicknesses of the order of 30 to 40 angstroms can be readily detected by ellipsometric techniques. 

The ellipsometric technique has been used for the estimation of thickness, refractive index and optical dielectric constants of a conducting polymer film [89]. These conducting polymer films have been used for the fabrication of electrochromic and glucose biosensing... 

For example, the ellipsometric technique was used to determine the interfacial thickness in SAN/PA blends, compatibUized by the addition of SMA... 

The generally accepted criterion of polymer misdbility is the detection of a single glass transition temperature (T, the value of which is intermediate between those corresponding to two-component polymers. The variable temperature ellipsometric technique has been used widely to determine Tg in thin polymer films by... 

A number of methods have been used to measure the EO coefficients and ni of the poled polymer samples. These EO measurements are made by detecting the change in refractive index of the poled polymer sample when a modulating electric field is applied to the sample. Mach-Zehnder [42,43]. Fabry-Perot [44,45], and Mich-elson [46] interferometric techniques have been used to evaluate the EO coefficients. Other techniques, such as an attenuated total reflection technique [47,48] and an ellipsometric technique [49-51], have also been employed to determine the r coefficients. 

Fig. 26.5 The experimental arrangement for measurement of the EO coefficient using the ellipsometric technique.

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