The nominal value of the effective camera length of an EM operating in the selected area mode is not sufficiently accurate for calculations of lattice spacing. The actual value of camera length must be calibrated at the same accelerating voltage and objective lens setting by reference to a known substance with well defined diffraction spacings. A normal specimen is evaporated film of aluminum with a thickness of around 31nm. Very small crystallite size yields ring patterns suitable for calibration. The specimen is supplied with a list of the principal lattice spacings. Made on a G400, 400 square mesh copper Gilder grid.
PELCO® Technical Notes, Diffraction Standard Evaporated Aluminum, Product No. 619 (417KB PDF)
619 - Evaporated Aluminum on 3mm grid, each