The pertinent discovery dates to February 1990. To pick up a
xenon atom, one holds the tip close to it and applies a pulse of
+1 volts. That causes the atom to jump from the surface and
attach itself to the tip. The tip then moves to a new location,
and one applies a pulse of −1 volts. The atom then jumps back to
the surface.  Having discovered how to do this, Eigler's group
has gone on to use this arrangement as a switch of ultimately
small size in which the active element consists of no more than
a single atom. When the atom lies on the surface, beneath the
tip, the arrangement is in a low-conductance mode. When the atom
jumps to the tip, the system switches into high conductance. In
a representative experiment these two states, respectively,
passed a current of 1.2 × 10−8 and 9 × 10−8 amperes, repeatedly
turning the high current on and off as the single xenon atom
jumped back and forth between tip and surface in response to the
voltage pulses (see Figure 2.6).  Eigler regards this as a proof
of concept for