Information Technology Reference
In-Depth Information
Fig. 1.9 Images obtained on a scanning electron microscope (see text for explanations)
Prize for Physics, jointly (and that is remarkable), with Ernst Ruska, who was
awarded “for his fundamental work in electron optics and for the design of the first
electron microscope.”
The design of Binnig and Rohrer is based on the principle of quantum-
mechanical tunneling of electrons through a nonconductive barrier.
The quantum-mechanical tunneling effect is a process whereupon particles leak
through a potential barrier and penetrate the areas that in classical mechanics would
have been inaccessible to them. Suppose there is a particle held in a potential well
by a barrier of finite height and width. Suppose that the energy of the particle is such
that, based on the laws of classical mechanics, it is not sufficient for the particle to
escape the well, passing over the potential barrier. A quantum-mechanical treat-
ment of this problem shows that there is some chance of the particle tunneling
through the barrier and exiting the well. The possibility of tunneling arises from the
requirement of continuity of the wave function on the walls of the well. If the
amplitude of the wave function is not equal to zero at the inner edge of the barrier
(which is permissible, provided that the potential at this point does not become
infinite), it cannot just disappear inside the barrier. Instead, it begins to approach
zero more or less quickly (Fig.
1.10
). If the drop of the amplitude happens not too
fast, it may not reach zero at the outer edge of the barrier. At this point, the wave
function should make a smooth transition to the function characteristic for free
