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 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.

P1=90+P3

A1=180-A3

 

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:

 

SPECTROSCOPIC ELLIPSOMETRY

 

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.