  Diagnostics of the beam transverse profile with ever more demanding spatial
resolution is required by the progress on novel particle accelerators - such as
laser and plasma driven accelerators - and by the stringent beam specifications
of the new generation of X-ray facilities. In a linac driven
Free-Electron-Laser (FEL), the spatial resolution constraint joins with the
further requirement for the diagnostics to be minimally invasive in order to
protect radiation sensitive components - such as the undulators - and to
preserve the lasing mechanism. As for high resolution measurements of the beam
transverse profile in a FEL, wire-scanners (WS) are the top-ranked diagnostics.
Nevertheless, conventional WS consisting of a metallic wire (beam-probe)
stretched onto a frame (fork) can provide at best a rms spatial resolution at
the micrometer scale along with an equivalent surface of impact on the electron
beam. In order to improve the spatial resolution of a WS beyond the micrometer
scale along with the transparency to the lasing, PSI and FERMI are
independently pursuing the technique of the nano-lithography to fabricate a
free-standing and sub-micrometer wide WS beam-probe fully integrated into a
fork. Free-standing WS with a geometrical resolution of about 250 nm have been
successfully tested at SwissFEL where low charge electron beams with a vertical
size of 400-500 nm have been characterized. Further experimental tests carried
out at SwissFEL at the nominal beam charge of 200 pC confirmed the resilience
to the heat-loading of the nano-fabricated WS. In this work, details on the
nano-fabrication of free-standing WS as well as results of the electron-beam
characterization are presented.
