Wüest M. 51 Wykes M. 82 Yamaguchi M. 17 Ybarra G. 129 Yubero F ...

JUNE 26 MONDAY AFTERNOON
RIVA-TF-MoA-OR.11 ADSORPTION PROPERTIES, MICROSTRUCTURE AND OP-
TICAL BEHAVIOUR OF TIO 2 THIN FILMS PREPARED BY PECVD. A.Borrás, A. Barranco,
J. Cotrino, A.R. González-Elipe. Instituto de Ciencia de Materiales de Sevilla (CSIC-Univ.
Sevilla). Avda. Américo Vespucio s/n. 41092 Sevilla (Spain)
It is a common place that the type of microstructure of thin films is critical for an effective control of
their optical properties. Usually, the microstructure is monitored by direct observation by SEM and
related microscopies. Recently, the use of spectroscopic ellipsometry under controlled ambient conditions
to measure adsorption isotherms has become an interesting technique to asses the type of porosity
in the films. In the present paper we discuss the possibilities of the adsorption isotherm technique
measured by means of a quartz crystal monitor (QCM) to asses the porosity of TiO 2 thin films
prepared by PECVD under different conditions. The microstructure and optical properties of the
films have been also characterized by SEM and optical methods. A large variety of TiO 2 thin films
with different microstructures and optical constants (n ranging from 1.8 to 2.2) have been obtained.
SEM gives information about the type of microstructure developed in the films (columnar, globular,
homogeneous, etc.). In addition, the water isotherms measured with the QCM provides important information
about the type of pores present in the films (i.e., micro, meso or macro pores) and the pore
size distribution. The analysis of the reversibility of the adsorption processes, as well as the dependence
of the adsorption characteristics as a function of the thin film thickness, have furnished important
clues to explain the optical properties of the films and their dependence on thickness. Small
variations of the optical constant of thin films exposed to the atmosphere can be also explained by
realising the irreversibility of some of the adsorption processes under ambient conditions.
The use of adsorption isotherms of vapours to characterize the porous structure of thin films can be
considered as an universal tool for the porous characterization of these materials providing complementary
information on the microstructure of the films
43