Pure Ellipsometry

SIMON J. HIGGINS, PAULA. CHRISTENSEN, AND ANDREW HAMNETT 

A poiymer it caiuiot be taken as proof, since some other untested growth mechanism may also fit the observed A— evolution. 

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Thus, ellipsometry gives direct evidence for a model of the initial stages of polythiophene growth, disproving the conclusions based purely on coulo-metry. In the same paper, Hamnett and Hillman were able to obtain valuable and complementary information not just on the initial stages of the polymerisation but also on the mechanism of the subsequent nucleation and growth. The unique piece of information that the ellipsometer was able to extract, the changes in film thickness (in real time), when combined with coulometric data allowed a wealth of information to be deduced, e.g. with respect to the film composition, and ably showed the power of the technique. 

The STG was cast from alx 10 3 M solution into which the mirror had been immersed for from 10 to 20 min (see Appendix 1). The presence of a monolayer was confirmed by ellipsometry (18 A). The spectral data agreed with data gathered on a similar system in a powder form. In this case, CuzO powder was immersed in a 0.01 M solution of isooctyl thioglycolate (OTG) in isopropanol for from 1 to 10 min, washed with pure isopropanol, dried in air, and analyzed via infrared transmission in a KBr dispersion pellet (see Appendix 2). A similar spectral shift of approximately 15 cm 1 (1739— 1724 cm-1) was observed and the lack of two distinct carbonyl absorbances suggested the formation of a monolayer. In both cases, the formation of a copper-mercaptoester salt may be responsible... 

SAIE by low-pressure plasma polymerization of TMS was extended to pure iron [8]. Polished pure iron samples (3x3 cm) were plasma pretreated before deposition of TMS plasma polymer. Two to six samples of pure iron were placed on a CRS plate (15 X 10 cm) maintaining the electrical contact so that each pure iron sample acts as the cathode of DC discharge. A few small pieces of silicon water were also placed on the CRS plate to maintain the electrical contact and were used for the estimation of the thickness of TMS plasma polymer by ellipsometry. 

This is [1.7.10.17] after replacing e by n and h by t. We also discussed how t can be experimentally measured. Ellipsometry is usually applied to adsorbed layers that have good optical contrast, but it can of course also be obtained to find for pure liquid-vapour or liquid-liquid interfaces. The problem of (2.8.1) is that to learn what kind of thickness is obtained n (z) must be known and this is determined by p (z). Hence, this is not an independent experiment. 

In SPR and ellipsometry it is usually impossible to determine unambiguously both thickness and refractive index of monolayers. In most studies the latter parameter is therefore arbitrarily assumed to be 1.45-1.5020. This, however, is only true for dense non-absorbing films. For incomplete monolayers, the response is usually assumed to be proportional to the coverage of monolayer, showing zero effective thickness for pure metal support and reaching the theoretical thickness at 100% coverage18. 

Next, we examine the possibilities of determining the dielectric constant of nanometer films by using the pure ellipsometric method or the combination of ellipsometric and reflectivity measurements. In the case of ellipsometry a convenient quantity is ratio SV Sh (or vice versa). On condition that JA and are measured at the same angle of incidence from Eqs. (1) and (2) we obtain... 

The polydimethylsiloxane oils used for antifoams usually spread on the air-water surfaces of surfactant solutions (see Section 3.6.2). At equilibrium, this process produces either complete wetting and duplex films for which 5 = 0 or pseudo-partial wetting and oil films in contact with lenses of bulk oil for which 5 0 (see Section 3.6.2.1). It has been shown by Racz et al. [3], and later confirmed by Denkov et al. [6, 7, 21], that deactivation of hydrophobed silica-polydimethylsiloxane antifoams correlates with the disappearance of this spread oil film. These studies used solutions of both anionic (SDS [3] and AOT [6,7]) and non-ionic surfactants (alkyl glu-copyranoside) [21]. Loss of the spread layer during deactivation is accompanied by an increase in surface tension to that of the pure surfactant solution [6]. It has also been directly observed using ellipsometry [21]. This finding is key to the understanding of deactivation because the presence of a spread layer of polydimethylsiloxane at the air-water surface is a clear indicator that oil has emerged into that surface. 

This modified ellipsometry is the combined reflectance-ellipso-metry technique, also known as the three-parameter ellipsometry (TPE) in contrast to the conventional two-parameter ellipsometry. Since it was first introduced in 1971 by Paik and Bockris to study passivation film formed anodically on cobalt, TPE has proven to be a powerful technique for determining all three unknowns from purely optical measurements alone. The measurements for A, and R are made with the same experimental setup as for the conventional ellipsometer, with minor modifications of the measurement routine if necessary. Here, R is the reflectance at the same angle of incidence as for the A and if/ measurements. Therefore, no alignment change is necessary for additional measurement of R. With some automatic ellipsometers (see Section III.5), all three measurements can be recorded simultaneously. It should be emphasized once more that A, ij/, and R are mutually independent functions, despite the fact that both il/ and R are defined by combinations of and r. ... 

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