Radiative Decay of Electron Induced Surface Waves in Evaporated Sodium Films

Abstract

Experimental results about radiative decay of surface plasmons induced by 1 8 keV-electrons at sodium surfaces are discussed. The metal-films were evaporated in UHV on substrates cooled down to 77 K. The peak wavelength of an evaporated film (thickness about 0.7 µm) on sapphire is 300 nm (4.13 eV) with a half-width of 80 nm. When using a stainless steel substrate the spectrum is strongly broadened up to a half-width of 135 nm due to a greater surface roughness of the sodium film. The measurements are compared with the theoretical results about the surface roughness coupling between electron induced surface waves and the electromagnetic field. The spectrum calculated with the optically measured optical constants of sodium has a half-width of only 15 nm.