In FTIR spectroscopy, a typical spectrometer output is a transmittance spectrum (kT). In order to match the spectrum data against a table of absorbance peaks, the original data set is converted to an absorption spectrum (kα):

$$\alpha(k) = - \frac{1}{2 w \sqrt{2}} \log\left(\frac{T(k)}{1 - r^2}\right).$$

The width of the sample film w is a result of direct measurement, i.e. microscopy. The reflectance r is deduced from the mean maximum transmittance level Tₒ (dashed line) disregarding signal oscillations as r = 1 − Tₒ. Much of this data processing can be entrusted to a machine.

The default demo spectrum was taken from a porous 53-micron thin silicon film previously exposed to electrochemical etching in a fluoric acid solution.

Edit and submit a transmittance spectrum (kT) or an absorption spectrum (kα) data set.
Units: wavenumber, k in cm⁻¹, transmittance, T in %.

For a transmittance spectrum (kT), take the following steps to convert it to an absorbance spectrum (kα) first. In case of an absorption spectrum (kα), skip the following conversion and proceed directly to the peak detection.

Thickness of the film, μm:

Reflectance of the film (autodetect):

Convert (kT) to (kα).

There is a default built-in reference data set of absorption peaks for Si films. If it is applicable, proceed directly to the peak identification. To apply a different reference data set, edit it.

Identify absorbance peaks.