Fig. 1. A sample of 50 nm-thin freestanding Si filter: a flat surface without folding

Fig. 2. Measurement results of thickness. (a) XRR measurement and fitting curves of Si thin film; (b) cross-section SEM image of Si filter

Fig. 3. Measured transmission values and theoretical calculation values ("cal.1") for 50 nm-thin freestanding Si filter in 10-20 nm band, where a transmission value as high as 86.02% was measured at 13.5 nm

Fig. 4. XPS measurement results of Si filter. (a) XPS full spectra on surface of filter; (b) distribution of atomic percentage during deep etching

Fig. 5. Measured transmission values and theoretical calculation values for 50 nm-thin freestanding Si filter in 10-20 nm band after optimization of calculation model ("cal.2")