Ellipsometry
Thin film analysis using a spectroscopic imaging ellipsometer
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 either as a discrete regional analysis or in a mapping mode.
Applications of Ellipsometry
- Thin film thickness measurement
- Thin film thickness mapping
- Sample composition
- Optical constant determination
- Sample crystallinity assessment
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 sample 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 therefore achieve Ångström resolution. It is an ideal technique for thin films with thicknesses in the nanometre range.
Our Ellipsometry Facilities
Accurion Nanofilm_EP4 Imaging Ellipsometer
- Hosted within the Nanoscale and Microscale Research Centre's Nanofabrication Nottingham (NaNo) Suite
- Imaging ellipsometer for visualisation of samples with ellipsometic contrast e.g. thickness mapping
- Spectral Range of between 190nm-1000nm
- Can measure at a range of angles
- Lateral resolution of down to 1 micron for high resolution mapping
- 5x, 10x, 20x, 50x and Nanochromat (UV/IR) objective lenses for a range of field of views and light sources
- Fully automated measurements for autonomous data collection
- Full data processing and modelling software
- Located within a class 4 cleanroom to prevent sample contamination
Alpha-SE Ellipsometer (J. A. Woolan)
- Non-imaging ellipsometer
- 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
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Redox-active hierarchical assemblies of hybrid polyoxometalate nanostructures at carbon surfaces, Amin, S. S., Cameron, J. M., Cousins, R. B., Wrigley, J., Liirò-Peluso, L., Sans, V., Walsh, D. A. & Newton, G. N., Inorganic Chemistry Frontiers (2022). doi:10.1039/D2QI00174H