Multiple-wavelength ellipsometry in thin uniaxial nonabsorbing films

Explosives detection with electron‐rich polymers

“…Experiments at different wavelengths were proposed to obtain sufficient data . However, it turned out that unique characterization of uniaxial thin films by multiple wavelength ellipsometry is only possible if both the substrate and the incident medium are highly dispersive …”

“…Figure (c) showed a different behavior, whereas the value of Δ n was fluctuating by increasing or decreasing over the applied spectral range. Such kind of optical behavior indicates that the PVK polymer film is not optically uniaxial, and hence, the net result for the differences in the refractive indices Δ n was either increasing or decreasing upon absorption of PNT vapor molecules . The existence of more than one unique optical axis in the polymer film led to the interference between the transmitted lights from the sample, resulting in either inphase constructive interaction, and hence the value of Δ n increased or out of phase destructive interaction, and hence the value of Δ n decreased.…”

“…[60] However, it turned out that unique characterization of uniaxial thin films by multiple wavelength ellipsometry is only possible if both the substrate and the incident medium are highly dispersive. [61] This experimental part represents a continuation of our earlier investigation on some functional copolymer films that can be used for detecting trace amounts of nitroaromatics with adequate changes in their refractive index (Δn > 0.003). [62] Ellipsometric measurement data were reported in the form of changes in the refractive indices of the copolymer films (Δn) because of the exposure to PNT vapors as measured by A. Woollem Co. variable angle spectroscopic ellipsometer.…”

“…Such kind of optical behavior indicates that the PVK polymer film is not optically uniaxial, and hence, the net result for the differences in the refractive indices Δn was either increasing or decreasing upon absorption of PNT vapor molecules. [59][60][61] The existence of more than one unique optical axis in the polymer film led to the interference between the transmitted lights from the sample, resulting in either inphase constructive interaction, and hence the value of Δn increased or out of phase destructive interaction, and hence the value of Δn decreased. Both samples of PS-co-PVDAT and PMMA-co-PVDAT showed only unique variation of Δn with the applied wavelength (λ) because of the exposure to PNT vapors, and this indicate that these copolymers are optically uniaxial.…”

Monolayer properties of mixed chlorophyll a-digalactosyldiacylglycerol at the nitrogen–water interface

“…5A, 6A decreases again. At first glance, this is rather surprising since the ellipsometric 6A is known to be more sensitive to refractive index than to film thickness (19). Since the length of the hydrophobic moieties of both components Chl a and DGDG are comparable, it can be assumed that the film thickness is constant at a given surface pressure, and independent of the species in excess.…”