Pulsed laser-induced oxygen deficiency at TiO2 surface: Anomalous structure and electrical transport properties |
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Authors: | Tomohiko Nakajima Tetsuo Tsuchiya Toshiya Kumagai |
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Affiliation: | aNational Institute of Advanced Industrial Science and Technology, Tsukuba Central 5, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565, Japan |
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Abstract: | We have studied pulsed laser-induced oxygen deficiencies at rutile TiO2 surfaces. The crystal surface was successfully reduced by excimer laser irradiation, and an oxygen-deficient TiO2−δ layer with 160 nm thickness was formed by means of ArF laser irradiation at 140 mJ/cm2 for 2000 pulses. The TiO2−δ layer fundamentally maintained a rutile structure, though this structure was distorted by many stacking faults caused by the large oxygen deficiency. The electrical resistivity of the obtained TiO2−δ layer exhibited unconventional metallic behavior with hysteresis. A metal–insulator transition occurred at 42 K, and the electrical resistivity exceeded 104 Ω cm below 42 K. This metal–insulator transition could be caused by bipolaronic ordering derived from Ti–Ti pairings that formed along the stacking faults. The constant magnetization behavior observed below 42 K is consistent with the bipolaronic scenario that has been observed previously for Ti4O7. These peculiar electrical properties are strongly linked to the oxygen-deficient crystal structure, which contains many stacking faults formed by instantaneous heating during excimer laser irradiation. |
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Keywords: | Rutile TiO2− δ Oxygen deficiency Laser reduction Metal– insulator transition Stacking faults |
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