Preparation of Alq$_{3}$ thin films using a pulsed laser deposition method with cooling target by liquid nitrogen

We have prepared Alq$_{3}$ (tris (8-hydroxyquinoline) aluminum) thin films for organic electroluminescence by a pulsed laser deposition (PLD) method. The bulk Alq$_{3}$ target was not able to produce by sintering above 1,000 $^{\circ}$C, because the glass transition temperature of Alq$_{3}$ was about 160 $^{\circ}$C. Therefore, the density of Alq$_{3}$ target (about 1.3 g/cm$^{3})$ was lower than that of the target used by PLD generally. In order to stabilize the density of the Alq$_{3}$ target, we cooled the target by liquid nitrogen. The temperature of Alq$_{3}$ target cooled by liquid nitrogen was --120 $^{\circ}$C. In this study, we have prepared Alq$_{3}$ thin films by a Nd:YAG laser (532 nm) deposition method with the cooling target by liquid nitrogen. The experimental results suggest that Alq$_{3}$ thin films are deposited at the fluence above 2.3 J/cm$^{2}$. FT-IR spectra of the prepared films are as same as those of the Alq$_{3}$ powder. UV-Vis spectrum shows that the prepared films have an absorption peak around 400 nm, which is distinct absorption peak of Alq$_{3}$. The results suggest that structural and optical properties of the films prepared by cooling target are in agreement with Alq$_{3}$ for organic electroluminescence.