Tip-induced surface plasmons

Second Figure 9.1(b), is a mechanism that occurs on metal samples and highly doped semiconductors, carriers are injected hot from the tip (or from the sample if the polarity is reversed) and excite tip-induced surface plasmons (TISP). These states can decay radiatively in the tip/sample plasmonically active gap. The efficiency of this process is generally around 10 " photons/ electron. Third, a direct transition between surface states on the tip and band edge states on a semiconductor substrate can be radiative with an efficiency of... 

Figure 9.1 Four major mechanisms for light emission in a scanning tunneling microscope. (a) Injection of minority carriers from the tip into an unoccupied band of a doped semiconductor leading to carrier diffusion and radiative recombination, (b) Surface plasmon mediated emission. Hot carrier injection into a metal leads to radiative decay of a tip-induced surface plasmon. (c) Direct dipole radiation. The transition from tip to substrate results in a direct dipole that can emit light, (d) An absorbed molecule or nanostructure accepts opposite carriers into its states leading to radiative recombination on the molecule.

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