  We report on the characterization of the response of windowless silicon
avalanche photo-diodes to electrons in the 90-900 eV energy range. The
electrons were provided by a monoenergetic electron gun present in the LASEC
laboratories of University of Roma Tre. We find that the avalanche photo-diode
generates a current proportional to the current of electrons hitting its active
surface. The gain is found to depend on the electron energy $E_e$, and varies
from $2.147 \pm 0.027$ (for $E_e = 90$ eV) to $385.8 \pm 3.3$ (for $E_e = 900$
eV), when operating the diode at a bias of $V_{apd} = 350$ V.} This is the
first time silicon avalanche photo-diodes are employed to measure electrons
with $E_e < 1$ keV.
