Free-standing nanolayers based on Ru silicide formation on Si(100)
Free-standing layers of nanoscale thickness are essential in numerous applications but challenging to fabricate for all but a small selection of materials. We report a versatile, chemical-free pathway of exfoliating centimeter-sized free-standing nanolayers from Si(100) with native oxide based on the spontaneous delamination of thin Ru and Ru-based films upon annealing at temperatures as low as 400 °C. Combining results from x-ray photoelectron spectroscopy (XPS), and transmission and scanning electron microscopy (TEM, SEM), we identify that the element Ru, a thin SiO2 layer, and the Si(100) substrate are essential ingredients for the delamination and propose a stress-based mechanism to explain the effect. The diffusion of Si into the layer upon annealing leads to the formation of a Ru-Si compound at the thin-film side of the Ru/Si(100) interface and pyramidal cavities in the Si(100) substrate. Moreover, the uptake of Si results in an increase in layer thickness and the buildup of in-plane compressive stress, which is reduced by local buckling and finally by the separation of the full layer from the substrate at the SiO2-Si(100) interface. The use of a thin Ru-buffer layer allows us to apply this delamination process to produce free-standing nanolayers of Mo and HfMoNbTiZr in this simple, chemical-free, and vacuum-compatible manner. These results indicate the potential of the reported effect for the fabrication of free-standing layers using a wide range of compositions, deposition techniques, and growth conditions below the onset temperature of delamination.