Stand-alone diamond binary phase transmission gratings for the EUV band

We report on the development of true free-standing phase transmission gratings for the extreme ultraviolet band. An ultra-nanocrystalline, 300 nm thin diamond film on a backside etched silicon wafer is structured by electron-beam lithography to periods of 1 µm. In this way, flat and stable gratings of 400 µm in diameter are fabricated. First-order net efficiencies up to 28% are obtained from measurements at a synchrotron beamline within a wavelength range from 5.0 nm to 8.3 nm, whereas the 0th order is suppressed to 1% near 6.8 nm. Higher diffraction orders up to the 3rd one contribute less than 7% in sum to the far-field pattern.