Size-dependent angular distributions of low-energy photoelectrons emitted from NaCl nanoparticles

Angle-resolved threshold photoelectron spectra are recorded for size-selected beams of sodium chloride nanoparticles (radius = 25-250 nm). The photoelectron angular distributions exhibit a size-dependent asymmetry that is inversely proportional to particle radius. A model of the internal electric field amplitude and the photoelectron escape probability inside the particles reveals that the asymmetry in photoemission arises because the finite dimensions of the particle are comparable to both the photon penetration depth (14-22 nm) and electron escape length (10 nm).