A narrow zero-intensity spot arising from an x-ray vortex has huge potential for future applications such as nanoscopy and nanofabrication. We here present an X-ray Free Electron Laser (XFEL) experiment with a focused vortex wavefront which generated high aspect ratio nanoneedles on a Cr/Au multi-layer (ML) specimen. A sharp needle with a typical width and height of 310 and 600 nm was formed with a high occurrence rate at the center of a 7.71 keV x-ray vortex on this ML specimen, respectively. The observed width exceeds the diffraction limit, and the smallest structures ever reported using an intense-XFEL ablation were fabricated. We found that the elemental composition of the nanoneedles shows a significant difference from that of the unaffected area of Cr/Au ML. All these results are well explained by the molecular dynamics simulations, leading to the elucidation of the needle formation mechanism on an ultra-fast timescale.
References
The electron ranges of 15 keV probes in the EDX are 1.1 and 0.5 μm on Cr and Au layers, respectively, according to the formula in Goldstein et al.19 The attenuation lengths of Cr Kα and Au Lα fluorescent lines are 0.9 and 4 μm, respectively, for Au layers, and are significantly larger for Cr layers.20
