Fig. 4.

Alternative scan geometries tested to overcome the limit of fly-scan pixel size s in fly-scan ptychography with a beam diameter d = 100 nm, indicated by s/d. In the doubled scan approach (a), two ptychographic fly scans are acquired with a horizontal displacement of s/2 between them. The probe intensity is halved in these two scans to yield equivalent intensity on the sample as in other fly scans. Images with high fidelity are obtained with s/d = 2.50, while scans with s/d = 3.00 also show good contrast and visibility though some light stripes appear on the image. In the offset scan approach (b), a single scan is acquired with a displacement between odd and even scan lines. In this case, scans with s/d = 2.50 show fairly good results, while some artifacts begin to appear when using s/d = 3.00. In all cases the vertical step size is 50 nm, the same as in aforementioned fly scans. The insets show the expected (green box) and recovered (magenta box) footprints of the beam on the sample. The scale bar for the footprints (lower right magenta box) is 200 nm.