Abstract
The possibility to directly write electrically conducting channels in a desired position in rutile TiO2 devices equipped with asymmetric electrodes—like in memristive devices—by means of the X‐ray nanopatterning (XNP) technique (i.e., intense, localized irradiation exploiting an X‐ray nanobeam) is investigated. Device characterization is carried out by means of a multitechnique approach involving X‐ray fluorescence (XRF), X‐ray excited optical luminescence (XEOL), electrical transport, and atomic force microscopy (AFM) techniques. It is shown that the device conductivity increases and the rectifying effect of the Pt/TiO2 Schottky barrier decreases after irradiation with doses of the order of 1011 Gy and fluences of the order of 1012 J m−2. Irradiated regions also show the ability to pin and guide the electroforming process between the electrodes. Indications are that XNP should be able to promote the local formation of oxygen vacancies. This effect could lead to a more deterministic implementation of electroforming, being of interest for production of memristive devices.
Highlights
The possibility to directly write electrically conducting channels in a desired scenario, alternative approaches and novel position in rutile TiO2 devices equipped with asymmetric electrodes—like in memristive devices—by means of the X-ray nanopatterning (XNP) technique is investigated
Keeping in mind that at 17.5 keV the attenuation length in TiO2 is over 160 μm, this result can be ascribed to a shadow effect of the metal electrodes partially absorbing the X-ray fluorescence (XRF) signal coming from the bulk of the substrate underneath
The C-atomic force microscopy (AFM) image reported in Figure 4b clearly shows at the same position an electrically conducting path induced by the X-ray irradiation, which extends up to the surface of the sample and testifies that TiO2 has been locally turned into a conducting material
Summary
The devices were fabricated by depositing two metal electrodes on a (110)-oriented TiO2 rutile single crystal. The nonannealed samples with a 6.7 μm gap were irradiated during the first campaign with a 55 Â 52 nm nanobeam, with an energy of 17.8 keV in pink beam mode (ΔE/E % 10À2) and the 16-bunch filling mode of the storage ring, corresponding to a maximum current of 90 mA. A single line connecting the two electrodes was irradiated multiple times with a 50 nm step at increasing exposure times and photon fluxes by progressively removing Si filters from the beam, up to a maximum time-averaged photon flux Φ0 1⁄4 1 Â 1011 ph sÀ1 In this 16-bunch filling mode, such a maximum value of Φ0 corresponds to about 1.76 Â 104 photons per pulse and to a fluence of. At the end of each campaign, samples were analyzed by means of conducting atomic force microscopy (C-AFM) with a Cypher S system by Asylum Research available at the Partnership for Soft Condensed Matter (PSCM) of ESRF
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