Applied Surface Science 256 (2010) 7496–7503
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Applied Surface Science
journal homepage: www.elsevier.com/locate/apsusc
Influence of preparation conditions on the dispersion parameters of sprayed
iron oxide thin films
Alaa A. Akl
∗
Physics Department, Faculty of Science, El-Minia University, El-Minia 111955, Egypt
article info
Article history:
Received 29 January 2010
Received in revised form 27 May 2010
Accepted 27 May 2010
Available online 4 June 2010
Keywords:
Optical dispersion
Iron oxide
Spray pyrolysis
Thin films
abstract
Iron oxide thin films were prepared by spray pyrolysis technique (SPT) at various substrate temperatures
(T
sub
) and different deposition time. X-ray diffraction (XRD) analysis showed that, at T
sub
≥ 350
◦
C, a single
phase of -Fe
2
O
3
film is formed which has the rhombohedral structure. Moreover, the crystallinity was
improved by increasing T
sub
. The effect of T
sub
as well as deposition time on the optical dispersion of these
films has been investigated. The optical transmittance and reflectance measurements were performed by
using spectrophotometer in the wavelength range from 300 to 2500 nm. The refractive index was deter-
mined by using Murmann’s exact equation. It was observed that, the refractive index increased with
increasing in both the T
sub
and film thickness. The optical dispersion parameters have been evaluated
and analyzed by using Wemple–Didomenico equation. The obtained results showed that, the dielectric
properties have weak dependencies of growth temperature and film thickness. At T
sub
≥ 350
◦
C, the aver-
age values of oscillator energy, E
o
and dispersion energy, E
d
were found to be 5.96 and 34.08 eV. While at
different thickness, the average values of dispersion energies were found to be 3.93 and 17.08 eV. Also, the
average values of oscillator strength S
o
and single resonant frequency ω
o
were estimated 10.78 × 10
13
m
-2
and 5.99 × 10
15
Hz, while at different thickness were evaluating 4.81 × 10
13
m
-2
and 6.11 × 10
15
Hz. Fur-
thermore, the optical parameters such as wavelength of single oscillator
o
, plasma frequency ω
p
, and
dielectric constant ε have been evaluated. The carrier concentration N
opt
by using Drud’s theory was
obtained the range of 5.07 × 10
25
m
-3
to 1.04 × 10
26
m
-3
.
© 2010 Elsevier B.V. All rights reserved.
1. Introduction
Iron oxides thin films can be used for the production of catalysts,
sensors, non-linear optical, magnetic devices, anode in lithium-
ion batteries, and various technological devices [1]. However, the
device performance is related to the morphology, optical properties
and structural order of the film, which in turn depend on the deposi-
tion technique and the growth parameters. Furthermore, the ferrite
thin films exhibit an excellent magneto-optical property and also a
strong chemical stability. Therefore, those films are suitable materi-
als for magneto-optical memory and their recording applications.
On the other hand, -Fe
2
O
3
particles with various morphologies
have been used widely as a raw material for the preparation of
-Fe
2
O
3
, a useful magnetic recording material. Optical dispersion
of iron oxide thin films was extensively studied because of their
importance in magnetic recording technology. An important opti-
cal dispersion parameters such as optical dispersion energies E
o
and E
d
, dielectric constant ε, ratio between number of charge car-
riers and effective mass N/m*, wavelength of single oscillator
o
,
∗
Tel.: +2 086 2348681; fax: +2 086 2363011.
E-mail addresses: alaaakl@link.net, alia 2010@windowslive.com.
plasma frequency ω
p
, single resonant frequency ω
o
and the aver-
age of oscillator strength S
o
, have been evaluated. Various physical
methods like chemical vapor deposition [2], pulsed laser evapo-
ration [3], reactive sputtering [4], electro deposition [5], and spray
pyrolysis [6–8] have been used for the growth of -Fe
2
O
3
thin films.
Most of these techniques are either not feasible or too expensive
for industrial applications. The spray pyrolysis technique’s (SPT),
simplicity, low cost and feasibility for mass production process are
the added advantages of this technique. High deposition rate and
possibility to coat large areas with non-planer geometries make
this technique attractive.
In the previous two papers: the first paper [7]; iron oxide thin
films have been prepared onto heated glass substrate using spray
pyrolysis from iron chloride (FeCl
3
·3H
2
O) to get films with dif-
ferent degrees of crystallinity. XRD and SEM characterized the
nanostructure of the films. The XRD study revealed rhombohedral
structural modification for films deposited onto heated substrates
350 ≤ T
sub
≤ 500
◦
C. XRD data analysis showed that a single phase
of polycrystalline -Fe
2
O
3
is present Single order Voigt profile
method had been used to determine the nanostructure parame-
ters (crystallite size and macrostrain). The obtained values of the
crystallite size and macrostrain were found to be increase with
increasing both of the T
sub
and deposition time (film thickness). The
0169-4332/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.apsusc.2010.05.096