However, the spectrum of the coated paper sample shows a marked difference (see red
curve in figure 2). The peak around 1044 cm-1 from figure 1 is split in two peaks
around 1075 cm-1 and 1000 cm-1 , with the peak at lower wavenumbers pointing down
instead of up. The IR peak pointing in the “wrong” direction is a clear indication that
this peak is not a chemical peak, but an optical phenomenon. Such a behaviour is
known as the Berreman effect [7]. This effect is basically a thin film phenomenon
that leads to a peak in the mid infrared region. This peak is not due to the
chemistry of the thin film, but due to the optical properties of the film and the film
thickness.