IR/ERS

External Reflection Spectroscopy (ERS)

Unlike transmission spectroscopy, for External Reflection Spectroscopy the irradiated beam does not go through the sample but reflects on its surface. This means that the preparation of the sample requires less complexity and a nondestructive technique. On the other hand, for the acquired intensity spectra to be consistent and reproducible, a smooth (specular) surface is needed and a reference background for Io recording, required.

External reflection spectroscopy

This technique is a noncontact spectroscopy method and is particularly useful for film thickness and refractive index measurements in applications such as recording the spectra of thin films or coatings on metal surfaces.

Particularly, the targeted samples for this spectroscopy method are metal, semiconductor, dielectric or liquid materials and it is principally used to measure the dielectric function of solids or to characterize thin films of materials located at interfaces. The chemical specificity of infrared spectroscopy is used for the molecular level characterization of thin polymer films or organic monolayer structures.

External reflection spectroscopy

ERS spectra are dependent on the reflection angle and may follow the dispersion in refractive index and spectral contrast could not depend linearly on the sample thickness. This can lead to differences when compared to TS by a shift of spectral bands to higher wave numbers.

When using this technique to characterize film on metal surfaces, other terms such as “Double Transmission” or “Reflection Absorption” are frequently used since the metal is largely non-interacting resulting on an absorption spectrum of the coating film.