The discussion above about formation of a cluster of Au atoms implies that some atomic motion is visible. This is indeed the case for beam currents above about 100 picoAmp. The example to the right is a display of several frames at approximately real time. (5 fps) The Au atoms can be seen to move about each other and to form what look like three dimensional structures. The power spectrum of the image is displayed in the upper right. From time to time it shows lattice periodicities which are characteristic of a Au crystal. Since atoms sometimes remain unmoved, sometimes move a small amount, and sometimes move large distances, it appears that the distance which is moved is probably controlled by available binding sites, while the rate of movement is controlled by the beam excitation. In the upper middle, two atom images appear to coalesce, possibly implying that this is really only one atom which rapidly explores two binding sites, so that it appears twice in the same image.