The ultimate spatial resolution D x  of a Fresnel zone plate (first order) is determined by the width wmin of the outermost zone:

 D x ~ wmin

For a photon sieve the diameter d of the pinholes can be larger than the width of the corresponding zone. This allows pinholes to be positioned on Fresnel zones that are narrower than the fabrication limit (20 - 40 nm) and the resolution

 D x ~ wmin= dmin / (d/w)max  

could be increased to better than 10 nm



Comparison of calculated intensity distributions of photon sieves and zone plates with smallest structure sizes dmin = wmin = 30 nm.Transverse intensity distribution in focal plane (left axis shows a linear scale, right axis shows a log scale) for a zone plate (red dotted lines) with a rectangular transmission window and two different photon sieves: (d/w)max = 2.4 (green solid lines) and (d/w)max = 7.5 (green dashed line), l = 2.4 nm.