Surface-plasmon excitation in small spherical graphite particles by x rays

X-ray scattering experiments have been carried out on dried colloidal graphite, for scattering angles φ=0° and φ=10°, using CrKβ₁ line as a primary radiation. The spectrum for φ=0° shows a faint new component shifted by 13±1 eV from the primary line; the same line was also found for a scattering angle φ=10°. If the dried colloidal graphite was replaced by dried colloidal graphite embedded in gelatine, the new component moved to a position shifted by 10 ± 1 eV from the primary line. The corresponding experiments with polycrystalline graphite did not show such components. These new components can be attributed to a plasmon excitation on the spherical surface of each particle of colloidal graphite. This experiment shows that surface plasmons can be excited in small spherical particles independently of the scattering angle.