A technique is described which allows the scanning transmission electron microscope to be operated either in its usual mode to give a transmission image from a thin film, or with a tilted sample to give a low-loss image of the surface. The low-loss image obtained from one surface of a thin-film gold sample is compared with the bright field image of the same area. Microtwins in this film display strong topographic contrast on the single surface studied. From this, it appears that the microtwins are formed by deformation, rather than as growth accidents during the preparation of the sample. It is found advantageous in the low-loss mode to operate with a less steeply tilted sample than heretofore.