Dispersion of the Volume Plasmon of Silicon (16.7 eV) at Large Wave Vectors

The dispersion of the volume plasmon of silicon at 16.7 eV has been measured with 50-keV electrons in the directions $〈100〉$ and $〈111〉$ up to the critical wave vector qc1.1 ^-1. It shows a strong anisotropy. Along the $〈100〉$ direction the q dependence could be measured up to large q vectors of {~}2.4 ^-1. At qqc the slope of the dispersion curve decreases strongly in a manner similar to what has been found earlier for Al and Be.