Volume and surface photoemission processes from plasmon resonance fields

Photo yield was measured as a function of incident angle for polarized light incident through a Mg${\mathrm{F}}_2$ semicylinder onto thin (∼ 200-Å) films of Al. Photon energies from threshold at 4.8 up to 10.2 eV were used. For $p$-polarized light near threshold, a surface-plasmon resonance peak was observed at about 50° from normal incidence with yields more than 100 times those at normal incidence. If the yield at normal incidence is assumed to result from pure volume photoemission, the angular yield ratio $\frac{Y\left(\theta \right)}{Y\left(0\right)\mathrm{}}$ can be calculated for the volume process. Only (35 ± 10)% of the yield observed at the plasmon peak could be accounted for by the volume process. The remaining yield was attributed to the surface emission process. The ratios of yields from Al with light normally incident from vacuum and through the Mg${\mathrm{F}}_2$ substrate were analyzed to obtain values of the escape depths for the volume process. Escape lengths were determined ranging from 45 ± 15 Å for 5-eV electrons to 20 ± 10 Å for 8.2-eV electrons.