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Daniel Franta, David Nečas, Lenka Zajíčková, Vilma Buršíková

Proc: Modeling of DLC Optical Properties Based on Parameterization of Density of States

Proceedings of International Workshop on the Application of Nanocrystalline Diamond and Diamond Like Carbon Materials (2006) pp.39-50

Published by Saha Institute of Nuclear Physics, Kolkata, India

The optical properties of materials in visible and UV range reflect the band structure of valence electrons. Therefore, in evaluation of optical measurements, it is useful to use dispersion formulae of the optical constants employing parameters that have some relations with the electronic structure. The present work describes a model based on the parameterization of density of states (PDOS). The efficiency and usefulness of this model for a study of diamond-like carbon (DLC) films and their structural changes caused by annealing or addition of SiOx groups is demonstrated. Since DLC is composed of carbon in two different bonding configurations, i.e. sp3 and sp2, and hydrogen, π and σ bands are distinguished in the model and parameterized individually by three parameters each. These three parameters have clear physical meaning. One describes a minimum energy needed for band transitions, i.e. band gap, the second is a maximum energy of transitions and the third is proportional to total density of electronic states. It is shown that some other structural parameters such as sp3-to-sp2 ratio can be calculated. If the set of the DLC films annealed to different temperatures is optically studied and the concentration of hydrogen in as deposited and annealed DLC films is obtained by some other method the probability ratio of π→π* and σ→σ* interband transitions can be determined too.

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