Fig. 4

Wet-chemical oxidation of nanogratings. a A schematic illustration of the nanogratings characterizing the 100 nm pitch with sub-50 nm line patterns; and an SEM image of the side view of a piece of the nanogratings showing the 40 nm features. b TEM images showing a cross section of one pattern of the nanogratings after oxidation for 5 min (left) and the corresponding magnification of peaks and valley area (right)