A combined experimental and theoretical study of the energy loss of protons in fluorides and organic films is presented. The measurements were performed in fresh ${\mathrm{AlF}}_3$, LiF, and $N$,$N^{\prime }$-bis(1-ethylpropyl)-perylene-3,4,9,10-tetracarboxdiimide (EP-PTCDI) evaporated in situ on self-supported C or Ag foils, covering the very low energy range from $25$ keV down to $0.7$ keV. The transmission method is used in combination with time-of-flight (TOF) spectrometry. In the case of fluorides with large band gap energies (${\mathrm{AlF}}_3$ and LiF), the experimental stopping power increases almost linearly with the mean projectile velocity showing a velocity threshold at about $0.1$ a.u. These features are well reproduced by a model based on quantum scattering theory that takes into account the velocity distribution and the excitation of the active 2$p$ electrons in the $F^{-}$ anions, and the properties of the electronic bands of the insulators. In the case of the semiconductor organic film with a lower gap, the experimental stopping power increases linearly with the mean projectile velocity without presenting a clear threshold. This trend is also reproduced by the proposed model.

• Received 16 November 2009

DOI:https://doi.org/10.1103/PhysRevA.81.022902