FLEXIBLE CONSTRUCTION OF ERROR FUNCTIONS AND THEIR MINIMIZATION - APPLICATION TO THE CALCULATION OF OPTICAL-CONSTANTS OF ABSORBING OR SCATTERING THIN-FILM MATERIALS FROM SPECTROPHOTOMETRIC DATA

A flexible numerical procedure for the calculation of thin-film optica l constants from specular transmittance and reflectance data is presen ted. The method is based on the minimization of a quadratic error func tion, which may be adapted to the specifics of the optical behaviour o f the given sample (or set of samples), and the given wavenumber regio n. The flexibility in choosing an appropriate form of the minimized er ror function, in combination with the powerful minimization method of conjugated gradients, allowed us to investigate the optical constants of very different types of novel thin-film material with a complicated optical loss behaviour. In particular, the results concerning the inv estigation of single- and two-layer systems based on the following tec hnologically interesting optical thin film materials are presented: (1 ) amorphous silicon as an example of an anorganic solar cell material; (2) as-deposited (rough) CVD diamond layers as an example of a polycr ystalline protective material; (3) hydrogenated amorphous carbon, appl icable as a protective long-wavelength IR antireflection coating as we ll as a spectrally selective solar absorber; (4) copper phthalocyanine layers as an example of a molecular solid, potentially applicable as an organic solar cell material; (5) rare-earth diphthalocyanine layers , interesting because of their electrochromic behaviour.