Functionalization of the oxides properties by means of high-intensity X-ray nanobeams

The technological development of synchrotron sources is opening new scientific opportunities and challenges, widening the exploration level of matter. Among the new strategies adopted, the X-ray nanopatterning (XNP) is a novel direct-writing resist–free technique, which exploits the modification capabilities of intense hard X-ray nanobeams to functionalize locally the properties of oxide materials. Indeed, by changing their stoichiometry, oxides can change phase and have a variety of electric properties from superconducting to insulating. By exploring XNP of oxides, new functional devices have been fabricated in different systems[1-3].

XNP has been successfully applied in TiO2 bulk crystals, inducing the formation of electrically conductive channels embedded in their insulating matrix. [3] Exploiting these changes, a resistive switching behavior and IV characteristics typical of memristor devices have been obtained. In superconducting microsized systems, such as Bi₂Sr₂CaCu₂O_8+δ superconductor in form of whiskers, hard X-ray irradiation have resulted in an increase of the crystal mosaicity and in a modification of the electrical properties[1, 2]. Some devices based on the Josephson junctions, which are naturally present in their crystal structure, have been successfully fabricated by means of XNP. By coupling radiation and thermal transport problems, the thermal heating induced by XNP in Bi₂Sr₂CaCu₂O_8+δ has been simulated, highlighting that, even if the maximum temperature increase is not enough to justify a thermal melting, the crystal response is modulated in time by the pulsed structure of the synchrotron radiation.

These findings represent a breakthrough in the field of XNP, whose approach allows exploiting the full X-ray potential both for device fabrication and for their diagnostics, thanks to the use of in-situ analytical tools such as fluorescence and diffraction detectors, and of real-time electrical monitoring of the process.

References
[1] V. Bonino et al., Crystengcomm, 20, 6667-6676 (2018).
[2] V. Bonino et al., paper presented at the SPIE Optics + Optoelectronics, 110350I (2019).
[3] L. Mino et al., Adv. Electron. Mater., 5, 1900129 (2019).