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.
Gold atoms readily move under the beam, sometimes forming a 3-d structure.