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Combined ellipsometry and refractometry technique for characterisation of liquid crystal based nanocomposites

Combined ellipsometry and refractometry technique for characterisation of liquid crystal based nanocomposites
Combined ellipsometry and refractometry technique for characterisation of liquid crystal based nanocomposites
Spectroscopic ellipsometry is a technique especially well suited to measure the effective optical properties of a composite material. However, as the sample is optically thick and anisotropic, this technique loses its accuracy for two reasons: anisotropy means that two parameters have to be determined (ordinary and extraordinary indices) and optically thick means a large order of interference. In that case, several dielectric functions can emerge out of the fitting procedure with a similar mean square error and no criterion to discriminate the right solution. In this paper, we develop a methodology to overcome that drawback. It combines ellipsometry with refractometry. The same sample is used in a total internal reflection (TIR) setup and in a spectroscopic ellipsometer. The number of parameters to be determined by the fitting procedure is reduced in analysing two spectra, the correct final solution is found by using the TIR results both as initial values for the parameters and as check for the final dielectric function. A prefitting routine is developed to enter the right initial values in the fitting procedure and so to approach the right solution. As an example, this methodology is used to analyse the optical properties of BaTiO3 nanoparticles embedded in a nematic liquid crystal. Such a methodology can also be used to analyse experimentally the validity of the mixing laws, since ellipsometry gives the effective dielectric function and thus, can be compared to the dielectric function of the components of the mixture, as it is shown on the example of BaTiO3/nematic composite.
0034-6748
1-7
Warenghem, Marc
3bcded9d-7f89-4556-9b9b-6b74fab65cff
Henninot, Jean François
8d2588b5-c0ad-4591-9a18-c3c536e48d09
Blach, Jean-François
b3bcbb72-789c-49b1-91bd-4166299bf76e
Buchnev, Oleksandr
60cdb0d2-3388-47be-a066-61b3b396f69d
Kaczmarek, Malgosia
408ec59b-8dba-41c1-89d0-af846d1bf327
Stchakovsky, Michel
66c7918f-9d9b-4562-80d2-7d7cc99c7a9a
Warenghem, Marc
3bcded9d-7f89-4556-9b9b-6b74fab65cff
Henninot, Jean François
8d2588b5-c0ad-4591-9a18-c3c536e48d09
Blach, Jean-François
b3bcbb72-789c-49b1-91bd-4166299bf76e
Buchnev, Oleksandr
60cdb0d2-3388-47be-a066-61b3b396f69d
Kaczmarek, Malgosia
408ec59b-8dba-41c1-89d0-af846d1bf327
Stchakovsky, Michel
66c7918f-9d9b-4562-80d2-7d7cc99c7a9a

Warenghem, Marc, Henninot, Jean François, Blach, Jean-François, Buchnev, Oleksandr, Kaczmarek, Malgosia and Stchakovsky, Michel (2012) Combined ellipsometry and refractometry technique for characterisation of liquid crystal based nanocomposites. Review of Scientific Instruments, 83 (3), 1-7. (doi:10.1063/1.3690382).

Record type: Article

Abstract

Spectroscopic ellipsometry is a technique especially well suited to measure the effective optical properties of a composite material. However, as the sample is optically thick and anisotropic, this technique loses its accuracy for two reasons: anisotropy means that two parameters have to be determined (ordinary and extraordinary indices) and optically thick means a large order of interference. In that case, several dielectric functions can emerge out of the fitting procedure with a similar mean square error and no criterion to discriminate the right solution. In this paper, we develop a methodology to overcome that drawback. It combines ellipsometry with refractometry. The same sample is used in a total internal reflection (TIR) setup and in a spectroscopic ellipsometer. The number of parameters to be determined by the fitting procedure is reduced in analysing two spectra, the correct final solution is found by using the TIR results both as initial values for the parameters and as check for the final dielectric function. A prefitting routine is developed to enter the right initial values in the fitting procedure and so to approach the right solution. As an example, this methodology is used to analyse the optical properties of BaTiO3 nanoparticles embedded in a nematic liquid crystal. Such a methodology can also be used to analyse experimentally the validity of the mixing laws, since ellipsometry gives the effective dielectric function and thus, can be compared to the dielectric function of the components of the mixture, as it is shown on the example of BaTiO3/nematic composite.

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More information

Published date: 2012
Organisations: Optoelectronics Research Centre, Quantum, Light & Matter Group

Identifiers

Local EPrints ID: 378370
URI: https://eprints.soton.ac.uk/id/eprint/378370
ISSN: 0034-6748
PURE UUID: 6fa50f2c-18c0-4087-ad68-acae7509b084

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Date deposited: 30 Jun 2015 14:23
Last modified: 17 Jul 2017 20:52

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Contributors

Author: Marc Warenghem
Author: Jean François Henninot
Author: Jean-François Blach
Author: Oleksandr Buchnev
Author: Michel Stchakovsky

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