Optical Property Gradients at Substrate-Layer Interface Effect on Band Intensities in IRRAS

OPTICAL PROPERTY GRADIENTS AT SUBSTRATE-LAYER INTERFACE EFFECT ON BAND INTENSITIES IN IRRAS 

When calculating band intensities in IR spectra of layers measured by either transmission or IRRAS, the models most often nsed to describe the reflection, refraction, and absorption assume an abrupt change in the optical properties at the layer-substrate interface. An exception is microscopic models that take into account the existence of a transition layer, but the relationships derived based on these model are too cumbersome to find wide application in the analysis of optical layers [41, 74, 75]. 

Nevertheless, a comparison of the band intensities calculated on the basis of the typical model (assuming a sharp interface) and experimental results [76] show that in the experimental spectra of layers, the band intensities are several times lower than predicted. Therefore, absorption indices of layers determined fi om experimental spectra using the relationships derived with the sharp interface model (Sections 1.4-1.7) include a systematic error. The root of this problem hes not only in the difference between the optical properties of the thin-fihn materials and solid materials and the error introduced by an uncertainty in the 

The fact that the optical constant gradients of the layer and of the substrate have different effects on the band intensities can be used to determine the gradient 

One might suggest that this technique is limited because of the necessity to determine dependencies on gradient depth not only for each layer-substrate system but also for layers synthesized by different methods optical constants of 

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