BASICS of ELLIPSOMETRY:
This technique is based on the POLARIZING PROPERTIES of reflection:
Reflection of light from a surface. The plane of incidence contains both incoming and outgoing beams, and the normal to the surface.
Top: reflected amplitude for p-polarized light rp and s-polarized light rs as a function of the angle of incidenceF, note the zero crossing for rp around F=63o.
Bottom: reflected intensities (e.g. reflectance) R=2 for p- and s- light respectively
Scheme of the null-ellipsometer
In practice one measures P and A, from which one obtains the ellipsometric anglesD and Y defined by:
Rp / Rs= tanY exp(iD)
Best precision is achieved by averaging over 2 different configurations differing in polarizer and analyzer setting by known angles, e.g.
The instrument we have in our laboratory is a null-ellipsometer operating atl=632.8 nm:.
Sample environment includes a windowless temperature stabilized cell, and a filtered Hg lamp (l range=3625nm)
The ellipsometric technique (also in imaging mode) can be successfully applied to Langmuir monolayers at the air-water interface:
Based on a physical model for the index of refraction
(Kramers Kronig relations).
Eg. for a 2 component system:
accounting for cis and trans absorption frequencies (w0,j) strengths (fj) and damping (gj) or for a birefringent material
Anisotropy is found along z (i.e. perpendicular to multilayer plane), possibly due to the LS deposition process.