Electron tunnelling energy level scheme

Electron tunneling is the elementary process which accounts for the operation of STM/STS. It will be described in accord with the approach adopted by Ter-soff and Hamann [9]. Additional material can be found in the review literature [6,10,11 ]. The energy level scheme of a tunnel barrier is shown in Fig. 4, as are the shapes of the wavefunctions outside and inside the barrier the exponential dependence inside the barrier is particularly relevant to the problem at hand. The tunnel current is... 

Fig. 17. Scheme of the tunneling reaction B" + A( -> B + A. dn and bn are the energy levels of the united system of B and A particles which correspond to the localization of the transferred electron on the atomic cores B (the initial particle B ) and A 1 (the final particle A), respectively. a is the isoenergetic electron tunneling b is the electron tunneling accompanied by light emission. 

Fig. 19. The scheme of bands explaining the voltage-current curve of a tunnel diode, a. The p-region b, the n-region c, the forbidden energy gap. Arrows show the directions of electron transfer. 0, The case of the zero shift of the Fermi levels 1, 2, tunneling through the forbidden energy gap 3, the position of bands corresponding to the minimum of the voltage current curve for a diode 4, thermal currents.

For some spectroscopic problems it is necessary to use three lasers in order to populate molecular or atomic states that cannot be reached by two-step excitation. One example is the investigation of high-lying vibrational levels in excited electronic states, which give information about the interaction potential between excited atoms at large internuclear separations. This potential V R) may exhibit a barrier or hump, and the molecules in levels above the true dissociation energy V(R = 00) may tunnel through the potential barrier. Such a triple resonance scheme is illustrated in Fig. 5.42a for the Na2 molecule. A dye laser Li excites the selected level (v J )... 

---