Experimental Evidence for Surface Quenching of the Surface Plasmon on InSb(110)

In high-resolution electron-energy-loss spectroscopy on clean cleaved InSb(100) surfaces, coupled surface plasmon-phonon losses are studied as a function of primary energy $E_0$. The $E_0$ dependence of the relative intensities of the phononlike and plasmonlike losses shows the existence of a dead layer for surface plasmons of free electrons. Comparison of the spacecharge electron density with the bulk concentration indicates that the dead layer arises from a dynamical quenching of the plasmon amplitude rather than from a depletion of carriers due to band bending.