T. Suzuki, R. Souda / Surface Science 445 (2000) 506–511
511
by X-ray diffraction ( XRD) when Ti and O were
and RHEED. The surface structure of the TiO
film was investigated, no notable surface relaxation
being found on the TiO(001), while the O vacan-
cies exist on the outermost surface whose concen-
tration was estimated to be 28%. A TiO-2×2-O
superstructure was found to be formed when the
2
supplied alternately. The partial pressure of O in
2
their conditions was on the order of 10−5 Torr.
They interpreted the feature of XRD showing only
the periodicity of the MgO substrate at the film
formed by the alternative supply of Ti and O as
2
due to the amorphous formation of the deposited
TiO film was exposed to O atmosphere of
2
film. However, we propose that their results indi-
cate the formation of TiO. The structure of TiO
is rock-salt, and the lattice mismatch between TiO
and MgO is only 0.71%, so that it is difficult to
distinguish between TiO and MgO by the diffrac-
tion technique. If our interpretation is correct, the
results of Aoki et al. may indicate that the structure
of the deposited Ti oxide is able to be controlled
1×10−8 Torr partial pressure whilst maintaining
the substrate temperature at 1070 K. In the 2×2-O
structure, O adsorbed on the top sites of Ti of the
outermost TiO surface, where the distance between
˚
O and Ti was 2.09 A.
References
between TiO (anatase and rutile) and TiO by
2
changing the partial pressure of O gas.
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2
As mentioned in the Introduction, the electronic
structure of TiO has attracted attention, and many
theoretical efforts have been devoted to its study.
Significant differences in the calculated band struc-
ture have been found between Hartree–Fock and
statistical exchange (Xa) [8]. The experimental
determination of the electronic structure of TiO,
which was found to be available as the epitaxial
film on MgO in the present study, is expected.
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4. Conclusions
[14] T. Suzuki, R. Souda, W. Maus-Friedrichs, V. Kempter,
Phys. Rev. B (1999) submitted.
[15] T. Aoki, K. Maki, Q. Tang, Y. Kumagai, S. Matsumoto,
J. Vac. Sci. Technol. A 15 (1997) 2485.
The TiO epitaxial film was found to be available
by the simultaneous supply of Ti vapor and O
2
gas on MgO for the first time using Li+ ICISS