Characterization and luminescence properties of Alq3 films grown by ionized-cluster-beam deposition, neutral-cluster-beam deposition and thermal evaporation

Tris-(8-hydroxyquinoline) aluminum (Alq3) films have been grown on silicon substrates by several techniques: neutral-cluster-beam deposition; thermal evaporation; and ionized-cluster-beam deposition technique. The films were characterized by low angle X-ray reflectivity, atomic force microscopy, Fourier transformed infrared (FTIR) spectroscopy and photoluminescence. According to the FTIR spectroscopy measurement, the spectra of all the Alq3 samples show almost the same signals of atomic binding regardless of the process conditions. However, the photoluminescence intensities of the films are different. When all the films are adjusted to the same thickness, neutral-cluster-beam deposition films show more intense photoluminescence than the thermal-evaporated ones, while ionized-cluster-beam deposition samples are found to be inferior in intensity. Since the photoluminescence intensity of the 8-hydroxyquinoline aluminum layers is one of the important factors for the performance of organic light emitting devices, the neutral-cluster-beam deposition seems to be a promising method for the film deposition of organic electroluminescence materials.