N. Takubo

Photoinduced conductivity in tin dioxide thin films

The effects of ultraviolet light irradiation on the conducting properties of SnO2−x thin films grown epitaxially on TiO2 or Al2O3 single-crystal substrates are studied at room temperature. A large increase in conductivity by two to four orders of magnitude is observed with light irradiation in an inert atmosphere and remains after the light is removed. The high-conducting state reverts to the original low-conducting state by exposing it to oxygen gas. These reversible phenomena are ascribed to the desorption and adsorption of negatively charged oxygen species at the grain boundaries, which critically change the mobility of electron carriers already present inside grains by changing the potential barrier height at the grain boundary. The UV light irradiation provides us with an easy and useful route to achieve a high-conducting state even at low carrier density in transparent conducting oxides and also to draw an invisible conducting wire or a specific pattern on an insulating film.

Photoinduced metallic state in VO2 proved by the terahertz pump-probe spectroscopy

We investigated the ultrafast terahertz response to the photoexcitation for vanadium dioxide single crystals and thin films using the optical-pump terahertz-probe technique at room temperature. The optical excitation induced an ultrafast decrease of the transmittance of the terahertz radiation within 0.7ps. Since we expect only the free carrier response in the terahertz range, the decrease of the transmittance is unambiguously assigned to the appearance of the high electronic conductivity due to free carriers. The conductivity increases more than ten times in the picosecond time range after photoexcitation and it is concluded that the electronic states are metallic.

Pseudomorphic strain effect on the charge-orbital ordering pattern in Pr0.5Sr0.5MnO3 epitaxial thin films

We accomplished coherent epitaxial growth of a Pr0.5Sr0.5MnO3 thin film on (LaAlO3)0.3–(SrAl0.5Ta0.5O3)0.7 (110) substrate, which demonstrates a robust charge-orbital ordering (COO) phase transition. In addition to the isotropic transport properties, a drastic recovery of high-resistivity state (>20Ωcm) from a field-cooled metallic state (∼0.5mΩcm) was observed at 5K with a release of a magnetic field. These results indicate a possible modification of COO pattern into CE-type COO state [d(3x2−r2∕3y2−r2)] in the film from A-type stripe COO state [d(x2−y2)] observed in bulk samples by a substrate-induced strain.

Conductivity Switching by Ultraviolet Light in Tin Dioxide Thin Films

The effects of ultraviolet (UV) light irradiation on the conducting properties of SnO2-x films are studied at room temperature (RT). Large enhancements in conductivity up to 4 orders of magnitude are observed in vacuum for almost insulating films containing small amounts of oxygen vacancies. It is ascribed to the desorption of negatively-charged oxygen species from the grain boundary, which dramatically enhances the mobility of electron carriers already present in the grains through the reduction of potential barriers at the boundary. The low-resistive state induced by light irradiation recovers to the original insulating state by exposing oxygen gas at RT.

Observation of photoinduced phase transition in phase-separated Pr0.55 (Ca1-y Sry) 0.45 Mn O3 thin films via x-ray photoemission spectroscopy

Perovskite manganite thin films,

Effect of UV light irradiation in SnO2 thin film

{\mathrm{Pr}}_{0.55}{({\mathrm{Ca}}_{1\ensuremath{-}y}{\mathrm{Sr}}_{y})}_{0.45}\mathrm{Mn}{\mathrm{O}}_{3}

Inhomogeneous transport properties in phase-separated manganite thin films

, have been studied using x-ray photoemission spectroscopy in order to clarify the consequence of the competition between ferromagnetic metal (FM) and charge-orbital-ordered insulator (COOI). Films with

Little volume change in orbital ordering transition in manganite thin films

y=0.40

Photo-induced charge-orbital switching in transition-metal compounds probed by photoemission spectroscopy

undergo a uniform paramagnetic insulator to FM transition. On the other hand, in films with

Structural study on \mbox{\sffamily\bfseries Pr}_{\hbox{\sffamily\bfseries\fontsize{10}{12}\selectfont 0.55}}\mbox{\sffamily\bfseries (Ca}_{\hbox{\sffamily\bfseries\fontsize{10}{12}\selectfont 1 thin films on perovskite (011) substrate

y=0.25