The effect of surface roughness on infrared external reflection spectroscopy

The effect of surface roughness of the back-side of a film-supporting material on Fourier transform infrared (FTIR) external reflection (ER) spectra was studied by using 9-monolayer cadmium stearate Langmuir-Blodgett (LB) films. The LB films are prepared on two infrared-transparent ZnSe substrates whose top surfaces are optically polished and bottom surfaces have controlled surface roughness with 1.2 and 0.1 mu m of protrusions, Although the roughness of 0.1 mu m is smaller than the wave-length of the infrared ray, both LB films show typical ER spectra qualitatively. On closer inspection, however, the LB film on the substrate with 0.1 mu m protrusions is irregular and the LB film on 1.2 mu m protrusions is better. These results indicate that the surface roughness of the backside of substrate is necessary for ER analyses. (C) 1999 Elsevier Science B.V. All rights reserved.