INFLUENCE OF RADIATION INTERFERENCE ON THE SHAPE OF RAMAN-SPECTRA FORAMORPHOUS HYDROGEN-FREE DIAMOND-LIKE CARBON-FILMS

The influence of interference on the shape of Raman spectra from thin films is considered. High refractive index, low absorption and suffici ent film thickness combined with high reflection from a substrate surf ace are the conditions to enhance the interference distortion of the R aman spectra. In the case of an amorphous hydrogen-free diamondlike ca rbon film deposited onto a highly reflecting aluminum layer, the inter ference dramatically distorts the ratio of Raman intensities at 500 an d 1550 cm(-1), by about a factor of four when the spectra are register ed by using a conventional backscattering geometry. The effect is smal ler but clearly noticeable for ordinary silicon-substrate samples as w ell. The magnitude of the interference modification is strongly influe nced by geometrical factors such as the direction and polarization of the detected Raman scattered light. (C) 1996 American Institute of Phy sics.