Energy level shift due to the co evaporated LiF in Alq$_{3}$

Recently, one of us (FS) observed strong improvement in conductivity of LiF-doped tris (8-hydroxyquinoline) aluminum (Alq$_{3}$). We have investigated the p n-doping of the organic material. The doping induces energy level shift in frontier orbital for about 0.25 eV when the doping ratio by weight is 10 \%. Small amount of metal deposition (0.5 $\AA$ of Al, Ag, Au) on LiF-doped Alq$_{3}$ causes further shift, with Al the most ($\sim$1 eV) and Au the least (0.3 eV). Further metal depositions reverse the shift for about 0.5 eV. These results suggest that the metal induced enhancement of n-doping in LiF:Alq$_{3}$ contributes to the improvement in conductivity. After 1$\sim$2 $\AA$, the properties of metals show up and the Energy levels converge.