Functional Modifications Induced via X‐ray Nanopatterning in TiO₂ Rutile Single Crystals

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.

Improving the control of the electroforming process in oxide-based memristive devices by X-ray nanopatterning

“…5B) an increase in the surface conductivity of the TiO 2 crystal, which is more evident in the borders of the bump. A previous study 10 using space-resolved X-ray excited optical luminescence (XEOL) showed that these higher conductivity regions are associated with a lower intensity of a XEOL signal centered at 830 nm, which is attributed to the radiative recombination of electrons trapped in intra-band gap states with free holes in the valence band. 36 These states have been ascribed to the presence of lattice defects like V O or Ti interstitials.…”

“…[6][7][8] Then, the process was extended to oxides with tightly bound oxygen atoms, like TiO 2 , where the creation of X-ray-induced V O led to a local increase of the material electrical conductivity. 9,10 The possibility to manipulate the oxygen content at the nanoscale by XNP could be extremely interesting for the fabrication of oxide-based electronic devices, such as memristors. Memristive devices, which can retain a state of internal resistance based on the history of applied voltage and current, are attracting increasing interest for several applications ranging from nonvolatile memories to neuromorphic computing.…”

“…6–8 Then, the process was extended to oxides with tightly bound oxygen atoms, like TiO 2 , where the creation of X-ray-induced V O led to a local increase of the material electrical conductivity. 9,10…”