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Light-induced conversion of an insulating refractory oxide into a persistent electronic conductor


Materials that are good electrical conductors are not in general optically transparent, yet a combination of high conductivity and transparency is desirable for many emerging opto-electronic applications1,2,3,4,5,6. To this end, various transparent oxides composed of transition or post-transition metals (such as indium tin oxide) are rendered electrically conducting by ion doping1,2,3,4,5,6. But such an approach does not work for the abundant transparent oxides of the main-group metals. Here we demonstrate a process by which the transparent insulating oxide 12CaO·7Al2O3 (refs 7–13) can be converted into an electrical conductor. H- ions are incorporated into the subnanometre-sized cages of the oxide by a thermal treatment in a hydrogen atmosphere; subsequent irradiation of the material with ultraviolet light results in a conductive state that persists after irradiation ceases. The photo-activated material exhibits moderate electrical conductivity (0.3 S cm-1) at room temperature, with visible light absorption losses of only one per cent for 200-nm-thick films. We suggest that this concept can be applied to other main-group metal oxides, for the direct optical writing of conducting wires in insulating transparent media and the formation of a high-density optical memory.

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Figure 1: Incorporation of H- ions in C12A7.
Figure 2: Insulator–conductor conversion of C12A7:H.
Figure 3: Electronic conduction in C12A7:H.
Figure 4: F+ centre in C12A7:H.


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We thank I. Tanaka and S. Watauchi for growing the single crystals, S. Takeda for NMR measurements, and M. Sadakata, Q.-X. Li and T. Nishioka for TOF-MS measurements.

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Correspondence to Katsuro Hayashi.

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Hayashi, K., Matsuishi, S., Kamiya, T. et al. Light-induced conversion of an insulating refractory oxide into a persistent electronic conductor. Nature 419, 462–465 (2002).

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