Photon Factory Activity Report 2005 #23 Part B (2006)
Electronic Structure of Condensed Matter

2C/2005G101

Photoemission study of TiO2/VO2 interfaces
Koji MAEKAWA1, Masaru TAKIZAWA1, Hiroki WADATI1, Atsushi FUJIMORI1,Hiroshi KUMIGASHIRA2, Masaharu OSHIMA2,Yohei NAGAO3, Yuji MURAOKA3, and Zenji HIROI3
1
Department of Physics and Department of Complexity Science and Engineering,
University of Tokyo, Kashiwa 277-8561, Japan2
Department of Applied Chemistry, University of Tokyo, Tokyo 113-8656, Japan
3
Institute for Solid State Physics, University of Tokyo, Kashiwa 277-8581, JapanExperimentVO2/TiO2 thin films were prepared using pulse laser
deposition (PLD) technique. V2O3 pellet was used as atarget. During the deposition, the substrate temperature
was kept at 733 K and oxygen pressure was maintained at
1.0 Pa. The film thickness was about 10 nm-15 nm. TiO2
capped samples were prepared as follows. The Rutiletype TiO2 (r-TiO2) deposited 673 K on the VO2 thin film,while amorphous TiO2 (a-TiO2) was deposited TiO2 atroom temperature. Photoemission measurements wereperformed at BL-2C of Photon Factory. PES spectra were
measured using a Scienta SES-100 analyzer.
Results and Discussion
PES spectra in the V 3d band region of VO2, aTiO2/VO2, r-TiO2/VO2 are shown in Fig. 1. All the spectra
showed both coherent and incoherent parts. Incoherent
part was observed most strongly in the r-TiO2/VO2 .This
may be caused by the difference in the sample preparation
process. In the r-TiO2/VO2 sample, Ti and V atoms may
be interdiffused at the interface and the interface region
may behave like Ti-doped VO2 which become insulating
as the Ti concentration increases. The temperaturedependence of the V 3d band of a-TiO2/VO2, r-TiO2/VO2
are shown in Fig. 2. In both samples, metallic states were
not observed in the interface between insulating VO2 andinsulating TiO2 at low temperature, in contrast to the caseof SrTiO3-LaTiO3 interface.

96

Users' Reporthν = 518 eV
coherent part
R.T

Intensity (arb. units)

incoherent partVO 2a-TiO 2/VO2
r-TiO 2/VO2
2.0

1.5

1.0

0.5

0-0.5

Binding Energy (eV)Fig. 1: V 3d band of VO2, a-TiO2/VO2, r-TiO2/VO2.

hν = 597 eVa-TiO2/VO2
R.T.
220 K
Intensity (arb. units)

Introduction
Metal-insulator transition has been extensively studied
because of its fundamental interest as well as its close
relationship to remarkable phenomena such as hightemperature superconductivity in cuprates and colossal
magnetoresistance in manganites [1]. Recently, highquality interfaces between transition metal oxides havebecame available due to the development of sample
preparation technique. Particularly, interfaces between theband insulator SrTiO3 (d0) and the Mott insulator
LaSrTiO3 (d1) have attracted interest because of its
metallic behavior [2-5]. In the present work, we have
performed
photoemission
spectroscopy(PES)
measurements of interfaces between another d0 band
insulator TiO2 and d1 Mott insulator VO2.

-2.0

-1.5

-1.0
-0.5
0
Energy relative to EF (eV)0.5

Fig. 2: Temperature-dependent photoemission spectra aTiO2/VO2.
References[1] M. Imada, A. Fujimori, and Y. Tokura, Rev. Mod.
Phys. 70 1039 (1998),[2] A. Ohtomo et al. Nature. 419, 328 (2002).
[3] K. Shibuya et al., Jnp. J. Appl Phys. 43, L1178 (2004).
[4] S. Okamoto and A. J. Millis Nature 428, 630 (2004)[5] M. Takizawa et al., cond-mat/0604201 (2006).
*maekawa@wyvern.phys.s.u-tokyo.ac.jp