Simone Altendorf, Dr.
    Phone: +49 351 4646-4205
    Fax: +49 351 4646-4902
    Liu Hao Tjeng, Prof. Dr.
    Phone: +49 351 4646-4900
    Fax: +49 351 4646-4902

    All in-situ/ultra-high vacuum ionic liquid gating study on oxide thin films

    Electrostatic gating is a common approach to alter the properties of a material in thin film form. It is utilized in field effect transistors in which controlled and reversible changes in the carrier concentration of the channel material are induced by applied electric fields. The magnitude of the electric fields supported by conventional gate dielectrics, however, is limited by their dielectric properties; and the maximum possible field strength is often not sufficient to tune the charge carrier concentrations over a wide range to, for instance, induce phase transitions. This motivated gating experiments involving ionic liquids (IL). By replacing the insulating solid-state gates with an IL, much higher electric fields can be implemented due to the formation of an electric double layer at the IL–channel interface that supports higher fields. Consequently, field effect transistor devices that are based on ILs can, in principle, electrostatically induce much higher charge carrier densities in the transistor channel. These high carrier densities, in turn, can lead to the formation of novel phases with interesting properties.

    It has been long assumed that a purely electrostatic charge accumulation is responsible for the IL gate-induced changes. However, many recent studies show that the observed gating effects in various oxide materials are not in agreement with a purely electrostatic picture, but rather related to electrochemical processes. The exact mechanisms are still being discussed and many contradictory results are being published. One important reason underlying these controversies might be a lack of purity in the experiments. Most ILs are known to be very hygroscopic - they easily absorb water from the atmosphere which can considerably change their properties and significantly shrink the electrochemical window of the ILs. Thus, an extremely careful handling of the ILs is required. In most studies, however, at least the critical IL device preparation is done ex-situ.

    The Department Physics of Correlated Matter at the Max Planck Institute for Chemical Physics of Solids has vast expertise in the growth (molecular beam epitaxy (MBE)) and characterization of high quality thin films all under ultra-high vacuum (UHV) conditions. The goal of this project is to upgrade the existing UHV thin film facility for IL gating studies which include in-situ sample and IL device preparation to conduct all in-situ/UHV IL gating experiments on oxide thin films.

    <p>Ultra-high vacuum system for the preparation and characterization of thin films.</p> Zoom Image

    Ultra-high vacuum system for the preparation and characterization of thin films.

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