Effect
of Thickness Reduction in UV Absorption Spectrum for a-C:H Thin Films
G. LAZĂR, I. LAZĂR, M. STAMATE
Abstract. Some peculiarities in ultraviolet (UV) absorption spectra
for amorphous hydrogenated carbon thin films are presented. The films were
deposited by the rf magnetron sputtering method, with a gas pressure
between 0.1 and 0.3 Torr. The most significant result found was that the
films deposited at high pressures (greater than 0.2 Torr) and small
thickness (bellow 400 nm) presents some peculiarities in the UV absorption
spectrum. The Tauc plot for these films, compared with the films with
thickness greater than 1000 nm, presents two different regions
corresponding to two different optical transitions. Films deposited under
similar conditions, with a thickness greater than 1 μm, present an optical
band gap around 2.5 eV and a large sp3 ratio (greater than 85%). The
results suggest a dimensional effect indicating optical absorption
behaviour closer to diamond. |