ИСТИНА

onic liquid (IL) gating has become a powerful technique to manipulate the electronic and magnetic structure of correlated thin oxide films, which may open new perspectives for new electronic devices. The basic mechanism of IL gating relies on the high electric fields created by the gated controlled polarization of the liquid, which is sufficiently strong to extract oxygen atoms out of the crystal structure involving a reversible insulator to metal transition (IMT). In this context, VO2 and -MoO3 are intensely studied materials. For instance, it has been shown, that in the case of VO2 the metallic (rutile-type structure) phase can be stabilized down to low temperatures and that it involves the entire thickness (10 nm) of the film. The IL gating effect is fully reversible by reversing the gate voltage. The IMT goes in parallel with giant structural changes. For instance, the c-lattice parameter of (001) oriented VO2 increases by up to 3% while for -MoO3 about 1.5% is found. This goes in parallel with a drop of the resistivity by up to several orders of magnitude. Although it is generally accepted that the formation of oxygen vacancies within the crystal structure of the films plays the decisive role for the observed IMT, no details of the atomic structure are known so far. We have carried out highly precise x-ray structure determinations of the VO2 and the -MoO3 films, which in combination with first principle calculations provide direct evidence for the presence of oxygen interstitial atoms within large channels of the crystal structure of rutile-type VO2 and -MoO3 while a corresponding concentration of vacancies is found in the host lattice. The importance of these findings in the context of the electronic film properties is discussed.