COLLECTIVE AND SINGLE-PARTICLE EXCITATIONS IN THE PHOTOYIELD SPECTRUMOF AL

Using angle- and energy-resolved photoyield spectroscopy, we investiga te the properties of the multipole plasmon excitation. At higher energ ies, a systematic dependence of the photoyield on the photon angle of incidence is observed and explained on the basis of classical Fresnel theory, indicating the possibility of obtaining information about opti cal constants from such measurements. A feature above the multipole pl asmon is assigned to the excitation of a bulk plasmon by the photon he ld.