“…The most obvious advantage of LFAD is the self-traceability of nano-grating pitch to a natural constant, which produces a series of characteristics, such as uniformity, homogeneity, and consistency. [2] Since the invention of Cr atom lithography in 1992, [3,4] a series of different working elements have been demonstrated successfully, such as Cr, [5,6] Al, [7] Yb, [8] and Fe. [9] Nowadays, the LFAD technology has even shown the ability of inventing natural square rulers at nanoscale, [10] which opens a new way for fabricating angle standards precisely.…”