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~ ) Solid State Communications, Vol. 77, No. 5, pp. 341-343, 1991. Printed in Great Britain.
0038-1098/9153.00+ .00 Pergamon Press plc
a
b
X-RAY PHOTOELECTRON SPECTROSCOPIC STUDIES OF THE O Is STATE ON THE
SURFACE OF DUAL ION BEAM DEPOSITED ZrOx FILMS
Y.S.Tang • and N.K.Huang b
Department of Electronics and Electrical Engineering, University of Glasgow, Glasgow G12
8QQ, Scotland
Institute of Nuclear Science and Technology, Sichuan University, Chengdu, People's Republic of
China
(Received by D. Van Dyck - October 15, 1990)
The 0 Is state on the surface of dual ion beam deposited ZrOx films were studied
by using x-ray photoelectron spectroscopy. Different from the bulk of the films, it
was found that a new O Is peak exists on the surface, which is assigned to be due
to the existence of carbon contamination.
X-ray photoelectron spectroscopy (XPS) has
widely been used in analyzing the bonding and
composition properties of materials including pre-
cision optical films, such as TiO v SiO v Ta20 ~,
ZrO 2 films etc., especially on surface and interface
studies. As one of the most important optical films,
ZrO 2 has been studied by several groups.tl-~l The
deposition methods applied were vacuum evapora-
tion, ion beam assisted evaporation and dual ion
beam deposition techniques. For the characteriza-
tion, various techniques, such as x-ray diffraction,
electron transmission spectroscopy, ellipsometry,
Rutherford backscattering, XPS etc. have been
employed. In the previous studies,t3.4~ we reported
the dual ion beam deposition process dependent
refractive index, atomic composition and Zr bond-
ing properties of the ZrOx (0 < x _< 2) films. Here
we concentrate on the O Is state on the natural
surface of the dual ion beam deposited ZrOx films.
Except for the state same as in the bulk of the
films, a new O Is state was observed, which will
be discussed in detail in this communication.
As reported before,m the samples were prepared
by a dual ion beam deposition technique. The
341
composition of the ZrOx films, depending on the
deposition parameters, is 0 _< x _< 2. The XPS
measurements were carried out on a VG ESCAL-
AB MkII system using monochromatic AI Kcz
radiation (hv = 1486.6 eV) as the x-ray source,
which has a pass energy of 20 eV and a typical
sampling depth of about 3 nm. During the experi-
ments, an ultrahigh vacuum (better than 0.4x10 -'°
Torr) was maintained in the analyzer chamber. The
sputtering beam was from a cold cathode A r ion
gun run at 4 kV, which gives an estimated etching
rate of about 3 nm/min.
Figure la shows a wide scan spectrum in the
0-1000 eV kinetic energy range of a sample on the
natural surface. The major components are Zr 3s,
Zr 3p, Zr 3d, Zr 4s, Zr 4p, 0 Is, 0 2s, C Is, C
(KLL), Ar 2,o and Si 2p lines. After 10 min of ion
etching, the approximate composition becomes
stoichiometric ZrOvm which is considered as the
bulk of the films. It can be seen in figure lb that no
apparent carbon related lines appear again. De-
tailed depth profile studies were reported else-
where.m
What is interesting is that the O l s line on the
342 X-RAY PHOTOELECTRON SPECTROSCOPIC STUDIES Vol. 77, No. 5
Io J ~ N I ~
(a)
200 400 600 800 1000
BINDING ENERGY (eV)
Fig.1 XPS surveys of a sample both on the
surface and in the bulk.
D 0
natural surface of the samples has a shoulder on
the higher energy side, as shown in figure 2a. A
number of experiments indicate that the double
peaks always exist despite the different values of x
in the films, but the energy separation of this two
peaks varies with x and is typically within a range
of 1.8-2.3 eV. This is similar to the previous
observed results on the real surface of glasses,
such as alkali silicate glasses, where two O ls
peaks were observed, which were assigned to be
.4
[.., z
o L)
0 Is A B (b)
527 529 531 533 535 537 539
BINDING ENERGY (eV)
Comparison of the O I s states on the
surface and in the bulk of a sample.
Fig.2
due to the -Si-O-Si- bridging (high energy peak)
and -=Si-O non-bridging (low energy peak) oxygen
configurations.[5-?l In our case, the situation is
slightly different from the above. Comparing fig-
ures 2a and 2b, it is obvious that the lower energy
peak A locating at 531.2 eV is resulting from the -
Zr-O-Z~ bridging oxygen configuration (shown in
figure 3a), but is the higher energy peak B locating
at 533.3 eV due to the -~Zr-O- oxygen configura-
tion? As we know, usually, the more ionic the
oxygen ions, the lower kinetic energy the XPS
peak locates at. So that the new O l s peak B
(533.3 eV) is more likely to be resolving a ---
Zr-O-Si= or a =Zr-O-C= bonding oxygen configu-
ration. From the composition and depth profile
analyses2) it seems likely to be the -Zr-O-C-
bonding oxygen configuration (see figure 3b) due
to the carbon contamination on the sample surface.
To confirm the above idea, we first clean a
sample surface by using the Ar* ion beam to etch
the sample for 5 min until XPS showing the
existence of only one O Is peak, and then intro-
duce it into a carbon contaminated chamber for
one hour. Further XPS measurements on the
surface of this sample indicate the reappearance of
the double O l s peaks, similar to that shown in
figure 2a, which gives a strong evidence of the
above discussion.
In conclusion, we have studied the O Is state on
the surface of the dual ion beam deposited ZrOx
films. Two O l s peaks were observed, which are
Zr Zr N \
0 0 N N
Z r - - O - - Z r - - O - - Z r Z r - - O - - Z r - - O - - C / /
O O / /
Zr Zr
(a) (b)
Fig.3 Bonding models of oxygen on the natural
surface of the samples.
Vol. 77, No. 5 X-RAY PHOTOELECTRON SPECTROSCOPIC STUDIES 343
common for all the samples with different values Acknowledgement - The authors are grateful to
of x, and are respectively assigned to -=Zr-O-Z~ Mr.H.Liu of the University of Surrey for his help
and ----Zr-O-C-- bonding oxygen configurations, with the XPS experiments.
REFERENCES
[1] P.J.Martin, J. Mater. Sci. 21, 1(1986) and
references therein.
[2] K-H.Muller, J. Vac. Sci. & Technol. A4,
184(1986).
[3] Y.S.Tang, B.J.Sealy and N.K.Huang, 7th Int.
Conf. on Ion Beam Modification of Materials,
Knoxville, USA, Sept. 1990.
[4] Y.S.Tang, J.E.Castle, H.Liu, J.F.Watts and
N.K.Huang, Phys. St. Sol. (a) 121, K61(1990).
[5] O.Puglisi, A.Torrisi and G.Marletta, J.
Non-Cryst. Solids 68, 219(1984).
[6] J.G.Clabes, R.E.Fem and G.H.Frischat, J. Vac.
Sci. & Technol. A4, 1580(1986).
[7] J.S.Jen and M.R.Kalinowski, J. Non-Cryst.
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