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Ellipsometry

 

Ellipsometry at a glance


Ellipsometry is an optical technique used to determine substrate layer thickness with Ångström resolution. It analyses a reflected beam of polarised light from a sample of interest to see how the sample structure has influenced the beam. From this it is possible to infer material properties.

 

Applications of Ellipsometry

  • Thin film thickness measurement
  • Sample composition
  • Optical constant determination 
  • Sample crystallinity
 

How does Ellipsometry work?

Ellipsometry is so called due to use of elliptically polarised light (two light beams that are out of phase) to analyse samples. It is an optical, non-invasive and non-destructive technique that identifies the change in polarisation after an incident beam is reflected off a sample. This effect can then be compared with a mathematical model (generally assuming the sample is composed of a small number of discrete, well-defined layers that are optically homogeneous and isotropic) to derive material properties. Predominantly, a change in polarisation is dependent upon samples thickness, complex refractive index or dielectric function tensor. A direct measurement is made of the ratio of the amplitude component (Ψ) and the phase difference (Δ) of a system, which then must undergo model analysis to infer the material properties. Values for Ψ and Δ are therefore always correct, but the material property accuracy depends on the model employed. However, because ellipsometry utilises polarisation information, it is not limited by diffraction in its measurement like primary optical techniques and can achieve Ångström resolution. It is an ideal technique for thin films with thicknesses from nanometres up to micrometres.
 
 

Our Ellipsometry Facilities

Alpha-SE Ellipsometer (J. A. Woolan)

  • Spectral Range: 380nm to 900nm, 180 wavelengths
  • Angle of Incidence: 65°, 70°, 75° or 90° (transmission)
  • Data Acquisition Rate: 3 sec. (Fast mode) 10 sec. (Standard mode) 30 sec. (High-precision mode)
  • Rotating compensator technology with CCD detection
 

 

Publications of Interest

  • Korolkov V.V., Allen S., Roberts C., Tendler S.J.B., (2011). High-Temperature Adsorption of p-Terphenylthiol on Au(111) Surfaces. Journal of Physical Chemistry. 115;14899–14906

Interface and Surface Analysis Centre (ISAC)

Email: isac@nottingham.ac.uk