ATOMIC-SCALE SCANNING TUNNELING MICROSCOPY OF AMORPHOUS SURFACES

Surfaces of amorphous metals are studied by scanning tunneling microscopy (STM). In situ prepared surfaces of amorphous ribbons and splats as well as thin $(l5 \mathrm{nm})$ films show a characteristic morphology that is attributed to the amorphous state. STM images allow us to clearly distinguish the amorphous and crystalline state as evidenced by experiments where the same sample is imaged in both states of order. True atomic resolution in the sense that the positions of all surface atoms can be derived from the data is not obtained, although the images contain regions where atom-sized features appear. Two reasons for this laterally nonuniform resolution capability are discussed: (i) the geometrical hiding of lower-lying atoms and (ii) lateral variations of the electronic structure. Both are intrinsic for amorphous surfaces. Hence, STM images do not allow a straightforward real-space structure determination of amorphous surfaces. Thick vapor-quenched amorphous films look significantly different due to kinetic roughening occurring during the growth.