ENERGY-EXCHANGE PROCESSES BY TUNNELING ELECTRONS

Resistive heating, emission heating or cooling (e.g., the Nottingham e ffect), and thermal fluctuation radiation are examples of energy excha nge processes which are fundamental in electron field emission and in tunneling junctions of scanning tunneling microscopy. These exchange p rocesses are analyzed for both electronic tunneling processes. We firs t discuss the energy delivered by a monoatomic tip in the field emissi on process. Strong phonon excitation is expected for field emission cu rrents exceeding 1 nA. Secondly we present a theoretical calculation o f the thermal deposition associated with the Nottingham effect in a tu nneling junction. The calculation is based on the free electron model for the electrode materials and the tunneling process across a planar vacuum gap. Our results show that the thermal power is deposited not o nly at the electron receiving electrode but also at the emitting elect rode. This originates from a finite probability for electrons below th e Fermi level to tunnel through the tunneling barrier replaced by elec trons starting from the Fermi level. The comparison between the calcul ations and the recent STM measurements is given. Finally we discuss th e other energy exchange processes in the tunneling junction, and concl ude that the thermal coupling between the tip and the sample of STM is extremely small under UHV conditions. This is important for high temp erature STM.