Spectroscopic evidence of the formation of (V,Ti)O{sub 2} solid solution in VO{sub 2} thinner films grown on TiO{sub 2}(001) substrates

Journal Article · Tue Feb 15 00:00:00 EST 2011 · Journal of Applied Physics

DOI:https://doi.org/10.1063/1.3549835· OSTI ID:21538100

Muraoka, Y; Wakita, T; Hirai, M; Yokoya, T ^[1]; Saeki, K ^[1]; Eguchi, R ^[1]; Shin, S ^[2]

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1. Graduate School of Natural Science and Technology, Okayama University, 3-1-1 Tsushimanaka, Kita-ku, Okayama 700-8530 (Japan)
2. RIKEN/SPring-8, 1-1-1 Kouto, Sayo, Hyogo, 679-5148 (Japan)

We have prepared VO{sub 2} thin films epitaxially grown on TiO{sub 2}(001) substrates with thickness systematically varied from 2.5 to 13 nm using a pulsed laser deposition method, and studied the transport property and electronic states of the films by means of resistivity and in situ synchrotron photoemission spectroscopy (SRPES). In resistivity measurements, the 13-nm-thick film exhibits a metal-insulator transition at around 290 K on cooling with change of three orders of magnitudes in resistivity. As the film thickness decreases, the metal-insulator transition broadens and the transition temperature increases. Below 4 nm, the films do not show the transition and become insulators. In situ SRPES measurements of near the Fermi level valence band find that the electronic state of the 2.5-nm-thick film is different than that of the temperature-induced insulator phase of VO{sub 2} itself although these two states are insulating. Ti 2p core-level photoemission measurements reveal that Ti ions exist near the interface between the films and TiO{sub 2} substrates, with a chemical state similar to that in (V,Ti)O{sub 2} solid solution. These results indicate that insulating (V,Ti)O{sub 2} solid solution is formed in the thinner films. We propose a simple growth model of a VO{sub 2} thin film on a TiO{sub 2}(001) substrate. Near the interface, insulating (V,Ti)O{sub 2} solid solution is formed due to the diffusion of Ti ions from the TiO{sub 2} substrate into the VO{sub 2} film. The concentration of Ti in (V,Ti)O{sub 2} is relatively high near the interface and decreases toward the surface of the film. Beyond a certain film thickness (about 7 nm in the case of the present 13-nm-thick film), the VO{sub 2} thin film without any Ti ions starts to grow. Our work suggests that developing a technique for preparing the sharp interface between the VO{sub 2} thin films and TiO{sub 2} substrates is a key issue to study the physical property of an ultrathin film of ''pure'' VO{sub 2}, especially to examine the presence of the novel electronic state called a semi-Dirac point phase predicted by calculations.

• OSTI ID: 21538100
• Journal Information: Journal of Applied Physics, Vol. 109, Issue 4; Other Information: DOI: 10.1063/1.3549835; (c) 2011 American Institute of Physics; ISSN 0021-8979
• Country of Publication: United States
• Language: English

Related Subjects

75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
36 MATERIALS SCIENCE
ABSORPTION SPECTROSCOPY
DIFFUSION
ELECTRIC CONDUCTIVITY
ENERGY BEAM DEPOSITION
EPITAXY
EQUILIBRIUM
FERMI LEVEL
INFRARED SPECTRA
INTERFACES
LASER RADIATION
LEAST SQUARE FIT
PHOTOEMISSION
SOLID SOLUTIONS
SURFACES
THIN FILMS
TITANIUM IONS
TITANIUM OXIDES
TRANSITION TEMPERATURE
VANADIUM OXIDES
X-RAY PHOTOELECTRON SPECTROSCOPY
CHALCOGENIDES
CHARGED PARTICLES
CRYSTAL GROWTH METHODS
DEPOSITION
DISPERSIONS
ELECTRICAL PROPERTIES
ELECTROMAGNETIC RADIATION
ELECTRON SPECTROSCOPY
EMISSION
ENERGY LEVELS
FILMS
HOMOGENEOUS MIXTURES
IONS
MATHEMATICAL SOLUTIONS
MAXIMUM-LIKELIHOOD FIT
MIXTURES
NUMERICAL SOLUTION
OXIDES
OXYGEN COMPOUNDS
PHOTOELECTRON SPECTROSCOPY
PHYSICAL PROPERTIES
RADIATIONS
SECONDARY EMISSION
SOLUTIONS
SPECTRA
SPECTROSCOPY
SURFACE COATING
THERMODYNAMIC PROPERTIES
TITANIUM COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
VANADIUM COMPOUNDS