Additive Nanofabrication with Focused X-rays

Focused soft X-ray beam induced deposition (FXBID) of metallic deposits from metal organic gas-phase precursors is a promising novel technique for additive nanostructure fabrication. It combines the energy-selectivity of X-ray lithography with the idea of deposition of metal nanostructures from suitable precursor gases as known from electron beam based techniques (e.g., EBID). The use of a scanning transmission X-ray microscope (STXM) setup offers the combination of maskless writing by raster-scanning, low minimum feature size defined by the resolution of the applied zone plate optics and in-situ characterization by means of NEXAFS spectroscopy and imaging as well as X-ray magnetic circular dichroism (XMCD) to analyze magnetic properties. We present a comparative study for FXBID deposition of Co (from Co(CO)₃NO) and Mn (from MeCpMn(CO)₃) nanostructures at various incident photons energies at and close to the respective absorption resonances of the precursor molecules. The deposition rates are significantly affected by incident photon energy with respect to the X-ray absorption cross section of the precursors and, therefore, are significantly increased at resonant energies. This effect has been investigated for the L_2,3-edges of the metal centers as well as the N and O K-edges of the ligands of the metal organic precursor complexes. The quality of the nanostructures is comparable those produced by electron beam techniques. Our results point towards a novel fabrication process for complex nanostructures that employs switchable photon energy for selection of deposited metal resulting in hybrid structures with high purity and outstanding magnetic properties.