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 incidence F, 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 angles D 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 at l=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.