ELECTRON-ENERGY LOSSES IN HEMISPHERICAL TARGETS

In the framework of classical dielectric theory, the hemispherical geo metry is studied. Calculations on surface modes are carried out for is olated Drude-like hemispheres. The convergence of the results with res pect to the number of coupled terms in the expressions of the potentia l is discussed. The electron-energy-loss probability is studied for Al and Ag particles involving this geometry. The surface modes and hence the energy-loss probability are given by coupled expressions, the phy sical meaning of which is the coupling among multipolar terms, because of the particular geometry. The results obtained here present a good quantitative agreement with experiments in the case of clear surfaces (Ag) and provide a qualitative understanding for the experiments in Al , in terms of the position and impact parameter of the beam. This allo ws us to set the validity of the dielectric theory for cases that seem ed to question it.