Scale used: the information bar at the bottom of the image (rows ~962-1023) shows magnification x5,000 (15.0 kV, WD 10.0 mm) and a scale bar labelled 1 um. The bar is 53 px long (x = 1202-1254), so 1 px = 18.9 nm (about 53 px/um); the 1280 px width is about 24 um. The image area used for analysis was rows 0-959 (information bar excluded).

Method: background-subtracted, Hann-windowed 2D FFT (zero-padded) of the image area. There is one dominant peak pair at spatial frequency about 1/47.4 px^-1, with the wave vector almost exactly along the image x-axis (about 2 degrees from horizontal). Sub-windows (quadrants) give 46-47 px, and the x-profile autocorrelation gives 46 px, consistent with the FFT.

Result: dominant period is about 47 px, which is about 47 x 18.9 nm = about 890 nm (range about 860-895 nm between regions).

Orientation: the periodic structures are line-like ripples/stripes running nearly vertically in the image (long axis about 88-90 degrees from the horizontal, i.e. tilted about 2 degrees from vertical). The periodicity is across the image, along the horizontal x-direction.

RESULT: period = 890 nm
