Reflection single thin films

The behaviour of a single thin film on a substrate is similar to that discussed for the case of a single thin film in air. Now, however, it is necessary to take into account any change of phase that might occur on reflection at the back surface of the film. If the substrate has a lower refractive index than the film on the surface then the treatment will be identical to that for a thin film in air. In this case, the reflected colours observed when the film is viewed at normal incidence in white light will be the same as those listed in the colour reflected column of Table S4.1, Section S4.ll. 

Fig. 5.33). Upon 408 nm light irradiation, the reflection bands of BP II red-shifted from the UV to 520 nm. Once the BP II transformed into the BP I, the corresponding reflection bands discontinuously jumped to 560 nm, which was further red-shifted from 560 to 710 mn within BP I state. The reflection spectra shown in Fig. 5.33 clearly indicate that red, green and blue reflections were achieved in this self-organized 3D cubic nanostructured single thin film. 

For single crystal substrates which are not in the form of thin films, the techniques of transmission microscopy and nanodiffraction can not be used. For such cases, the techniques of reflection electron microscopy (REM) or its scanning variant (SREM) and reflection high energy electron diffraction (RHEED), in the selected area or convergent beam modes, may be applied (18). 

At this point it is important to realize that from single crystals the full crystallographic information is usually obtained by XRD methods (space group, lattice parameters and atomic coordinates) but that for thin films this is hardly the case, because of the physical limitation imposed by the substrate, in particular when the microcrystals are oriented, in which case only a reduced number of reflections are available. Hence only partial information is obtained with conventional diffraction methods. Removing the microcrystals, e.g., by scratching, in order to perform XRD measurements from the powder is not always possible and handling such small and fragile microcrystals with the usual tools is almost impossible. 

Absorption of infrared radiation by characteristic vibrations of a surface can be used to obtain information about that surface, by comparison with known absorption frequencies in molecules of known structure. Surface sensitivity is obtained by using small particles ) and thin films or, better, a multiple-reflection arrangement with optimized angles of incidence and reflection in particular making work on single-... 

The extent of the interaction between the evanescent field and the absorbing medium is formally described by the effective thickness, effective thickness is the thickness of the absorbing phase that would have to be passed through by the incident beam in a transmission experiment to give the same energy loss as in the attenuated total reflection experiment. The exact expressions for effective thickness can be very complex. However, for a single attenuated total reflection of an incident beam of radiation of electric field E that occurs at an interface between two bulk phases (ie, phase 2 is not a thin film), d is given by... 

The excitation of an SEW using a single prism is seen as a dip in the reflectivity from the prism base (see Fig. 8) when the angle of incidence satisfies Eq. (8). The location in angle of the minimum in reflectivity, the depth of the minimum and its width are very sensitive to the presence of an overlayer on the metal substrate. Pockrand, et al.— have pointed out that this technique is considerably more sensitive than ellipsometry for measuring the optical properties of thin films. They also discuss the problems due to the fact that the dye films are really anistropic. 

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