The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.
Aalto

Characterization of Materials and Components Using Accurate Spectrophotometric Measurements and Mathematical Modeling

Saulius Nevas

Dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Department of Electrical and Communications Engineering for public examination and debate in Auditorium S4 at Helsinki University of Technology (Espoo, Finland) on the 15th of October, 2004, at 12 o'clock noon.

Overview in PDF format (ISBN 951-22-7357-8)   [308 KB]
Dissertation is also available in print (ISBN 951-22-7333-0)

Abstract

This thesis considers metrological application of spectrophotometric measurements in characterization of optical thin-film coatings, diffuse reflectance standards, and filter-radiometer components.

For the optical metrology of thin films, various systematic errors in the measurements were studied in order to understand their effect on the determined optical parameters of thin films. The analysis was done based on computer simulations. Experimental results for several coated samples are also presented. The results demonstrate the importance of accurate spectrophotometric measurements for reliable characterization of thin films. It is shown that when the characterization is done based on measurements at oblique angles of incidence, significant errors may be introduced due to certain systematic effects. Thus the use of ordinary commercial spectrophotometers may restrict the accuracy of the characterization. The experimental data obtained with the high-accuracy spectrophotometer at HUT demonstrates consistency among the derived thin-film parameters at both normal and oblique angles of incidence.

For the calibration of diffuse reflectance standards, a gonioreflectometer-based absolute scale of spectral diffuse reflectance has been established at HUT and is presented in the thesis. The newly established absolute scale of spectral diffuse reflectance is at the present moment the second in the world, where the hemispherical reflectance factors are derived without the use of integrating spheres. The gonioreflectometer setup, measurement and characterization procedures, as well as uncertainty analysis and results of test measurements are summarized in the thesis.

For the characterization of filter radiometers (FRs), which is needed for the realization of the primary spectral irradiance scale at HUT, the thesis includes a comprehensive overview of the developed measurement methods, modeling and rigorous uncertainty-analysis procedures. An intercomparison of the characterization techniques in the UV spectral region adopted at HUT and at several other National Metrology Institutes is also presented. For the first time, effects of correlations in the FR signals originating through the characterization of the FRs were studied. This has led to a method of optimizing the selection of FR wavelengths and a practical range of uncertainties in the case of correlations in input parameters.

This thesis consists of an overview and of the following 7 publications:

  1. Nevas S., Manoocheri F., and Ikonen E., 2003. Determination of thin-film parameters from high accuracy measurements of spectral regular transmittance. Metrologia 40, number 1, pages S200-S203.
  2. Nevas S., Manoocheri F., Ikonen E., Tikhonravov A., Kokarev M., and Trubetskov M., 2004. Optical metrology of thin films using high-accuracy spectrophotometric measurements with oblique angles of incidence. In: Amra C., Kaiser N., and Macleod H. A. (editors), Advances in Optical Thin Films. Proceedings of SPIE 5250, pages 234-242.
  3. Haapalinna A., Nevas S., Manoocheri F., and Ikonen E., 2002. Precision spectrometer for measurement of specular reflectance. Review of Scientific Instruments 73, number 6, pages 2237-2241.
  4. Nevas S., Manoocheri F., and Ikonen E., Gonioreflectometer for measuring spectral diffuse reflectance. Applied Optics, accepted for publication.
  5. Kübarsepp T., Kärhä P., Manoocheri F., Nevas S., Ylianttila L., and Ikonen E., 2000. Spectral irradiance measurements of tungsten lamps with filter radiometers in the spectral range 290 nm to 900 nm. Metrologia 37, number 4, pages 305-312.
  6. Kärhä P., Harrison N. J., Nevas S., Hartree W. S., and Abu-Kassem I., 2003. Intercomparison of characterization techniques of filter radiometers in the ultraviolet region. Metrologia 40, number 1, pages S50-S54.
  7. Nevas S., Ikonen E., Kärhä P., and Kübarsepp T., 2004. Effect of correlations in fitting spectral irradiance data. Metrologia 41, number 4, pages 246-250.

Keywords: metrology, spectrophotometric measurements, thin films, filter radiometers

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© 2004 Helsinki University of Technology

Last update 2011-05-26