Spectroscopic ellipsometry studies of nanocrystalline carbon thin films deposited by HFCVD

Nanocrystalline carbon thin films were grown by hot-filament chemical vapor deposition (HFCVD) using a relatively high concentration of methane in hyd rogen. The films were deposited on molybdenum substrates at 900 degreesC, a nd under various substrate-biasing conditions. The optical properties were examined ex situ using spectroscopic phase-modulated ellipsometry (SPME) fr om the near IR to the near UV region (1.5-5.0 eV). The ellipsometry data [p si(lambda (i)), Delta(lambda (i))] were modeled using Bruggeman effective-m edium approximation (EMA) and the dispersion relation for the amorphous sem iconductor (Forouhi and Bloomer Model Phys. Rev. B 34, 7018, 1986). We perf ormed these simulations by least-square regression analysis (LRA) and obtai ned the true dielectric function of our nanocrystalline carbon material and the energy band-gap (E-g), along with the film thickness, bulk void fracti on and roughness layer. We discuss the possible physical meaning of the fiv e parameters in the amorphous dispersion model applied to the case of nanoc rystalline carbon. Micro-Raman spectroscopy and profilometry were used to g uide and validate the simulations. (C) 2001 Elsevier Science B.V. All right s reserved.