Photonic crystals in biology

Poster Session, Tuesday, June 15
Theme A1 - B702
CeO x /Al 2 O 3 thin films on Stainless Steel substrate-new understanding of the surface states by
dynamic X-ray Photoelectron spectroscopy
Ivalina Avramova* and Sefik Suzer
Department of Chemistry, Bilkent University, Ankara 06800, Turkey
Abstract— The CeO X /Al 2 O 3 thin films on stainless steel substrate have been a sbject of the investigation under electrical
stimuli by using XPS.
The continuously increasing requirement for the properties
of the materials with possible catalytic or electronic
applications is a motivation for developing of new technique
for their deposition and better understanding of surface state
manners. Cerium dioxide (CeO 2 ) has been of great interest
during the last years due to its multiple applications in several
key areas of thin film technology. Ceria has a potential
application in the area of optoelectronics [1], the high ionic
conductivity has attracted interest for application as gas
sensors [2] and electrolyte or anode materials for intermediate
temperature solid oxide fuel cells [3].
The oxide films of Ce and Al were prepared
electrochemically. The deposition of the films proceeded in a
working electrolyte consisting of saturated absolute univalent
alcohol with different contents of AlCl 3 x 6H 2 O and CeCl 3 x
7H 2 O salts. The cathodic deposition was performed in a
voltostatic regime at different forming voltages in the interval
3–8 V. The deposition time was 60 min. The cathode substrate
used was a stainless steel (20.0% Cr, 5.0% Al, 0.02% C, and
balance Fe) electrode.
XPS measurements were done using a K-Apha electron
spectrometer with Al K X-rays (monochromatic). The close
situated filament make available low-energy electrons for
charge neutralization. Samples were electrically connected
through the sample holder, which have been grounded or
subjected to external, square wave pulses in the range 10 -3 to
100kHz, during record of the X-ray photoelectron spectra.
The electrochemically deposited CeO x /Al 2 O 3 thin films on
stainless steel substrate with different amount of Ce loading
have been subjected to square wave pulses with amplitude of
10V during record of X-ray photoelectron spectra.
As a result of applied ±10V when frequency changes, the
oxygen, aluminium and cerium photoelectron peaks are split
in to a doublet and the resulted Binding Energy (BE)
differences were evaluated.
On Figure 1 are shown the Ce3d photoelectron spectra
recorded at low and high frequency and compared with the
ground one, for the CeOx/Al 2 O 3 thin film having high Ce
loading. The recorded spectra are complex due to the
presence of Ce 4+ and Ce 3+ states on the surface.
The binding energy difference at low frequency region less
than 20eV is well pronounced in case of low Ce loading see
Figure 2. The sample having high Ce loading show less
difference. The BE difference become independent of
frequency changes and reaches 20eV at high frequency region.
The conductivity of the films changes by the Ce loading,
due to the surplus of Ce 4+ or Ce 3+ or a smaller amount of these
states on the surface of the oxides. When Ce 3+ states are
predominant on the surface, the thin films behave as isolator,
while the increase of Ce 4+ states on the oxide surface makes
the film more conductive.
BE difference, eV
20,2
20,0
19,8
19,6
19,4
19,2
19,0
18,8
18,6
18,4
18,2
1E-4 1E-3 0,01 0,1 1 10 100 1000 10000 100000
frequency, Hz
O1s peak
Al2p peak
Ce3d peak
Figure 2. Binding Energy differences versus frequency for the
CeO x /Al 2 O 3 with low Ce loading on stainless steel substrate.
Ce 4+ Ce 4+ Ce3d
Ce 4+
Ce 4+ 100kHz
Ce 3+ Ce 4+
Ce 3+
Ce 4+
ground
0.001Hz
930 920 910 900 890 880 870 860
BE, eV
* iva@fen.bilkent.edu.tr
[1] Petrova N. L., Todrovska R. V. and Todorovsky D. S., 2006.
Spray-Pyrolysis Deposition of CeO 2 Thin Films Using Citric
Complexes as Starting Materials, Solid Stat. Ion., 177: 613-21.
[2] Durrani S. M. A., Al-Kuhaili M. F., and Bakhtiari I. A., 2008.
Carbon Monoxide Gas-Sensing Properties of Electron-Beam
Deposited Cerium Oxide Thin Films, Sens. Actuators B,134: 934-9.
[3] Park J. -Y., Yoon H., and Wachsman E. D., 2005. Fabrication
and Characterization of High-Conductivity Bilayer Electrolytes for
Intermediate-Temperature Solid Oxide Fuel Cells, J. Am. Ceram.
Soc., 88: 2402 -8.
Figure 1. Ce3d spectra at different frequency for the CeO x /Al 2 O 3
with high Ce loading on stainless steel substrate and compared
with the spectrum at ground state.
6th Nanoscience and Nanotechnology Conference, zmir, 2010 271