Abnormal reflections in electron-diffraction patterns from tin condensed in low-pressure air or oxygen

Additional arcs in electron-diffraction reflection patterns from tin films condensed in air or oxygen at pressures of between 100 and 1 ?torr are shown to be due to normally forbidden diffractions arising from secondary scattering, and not to the presence of crystalline SnO. These diffractions are evidently associated with the presence of oxygen, but this is only because they are prominent when the tin develops a preferred (110) orientation, as happens when it is condensed in oxygen at pressures above 10 ?torr.