for absorbing thin films using
J. M. Siqueiros, Luis E. Regalado and R. Machorro
We propose a method for determination
of the complex refractive index of absorbing materials either in bulk
or film geometry by measuring its reflectivity when coated with a well-characterized
transparent dielectric at
two specific optical thicknesses: ndj =
and njdj = X
/2. The complex refractive index of the sample
is calculated for the monitoring wavelength X0. The selected optical thicknesses of the coating allow the
calculation of its geometrical thickness, therefore the variation of h with wavelength in the region where the
reflectivity is measured can be determined.
There are many methods for determination of the
of thin films; several reviews were
published before computers were developed and acces-
sible to everybody.1-
Since then, many other meth-
ods have been proposed
using the advantages
accurate commercial apparatus for both, measure-
ments and calculations. However, a comparison of
several techniques and methods used in different lab-
oratories for characterizing
the same samples1
considerable discrepancies among their results.
We present here our method for determining the
complex refractive index of thin metal film samples.
It is based on reflectance measurements that can be
obtained in a conventional spectrophotometer or with
a monitoring attachment in the evaporation chamber;
the convenience of this method is the small effect that
the experimental errors have on the determination of
the thickness and
of the dielectric and that it
provides comparable results with those obtained by
more elaborate techniques.
A discussion is given for an absorbing thin film char-
acterized in the visible spectral region and a compari-
son is made with results reported in the literature.
Luis Regalado is with Universidad de Sonora, Centro de Investiga-
cion en Fisica, Apdo. Postal H-88, Hermosillo, Sonora, Mexico; the
other authors are with Universidad Nacional Autonoma de Mexico,
de Fisica, Lab. Ensenada,
Apdo. Postal 2681, Ensenada,
Received 23 March 1988.
© 1988 Optical Society of America.
Since we wish to determine
a complex refractive
index we must know at least two relevant experimental
values; our choice is the reflectance (R), because it
allows the study of opaque films as well as bulk materi-
als, measured at two different conditions, which are
defined as follows.
One part of the sample is coated with a transparent
dielectric of optical thickness h, defined as the film
thickness times the refractive index, equal to X
the other part with the same dielectric but optical
thickness of Xo/2 for a given wavelength X0, as shown in
Fig. 1. In practice, this can be done in a single run of
the evaporating plant, overcoating the absorbing layer
with the selected dielectric of real index n, until the