Luminescent Properties of Multilayered Eu2O3 and TiO2 Grown by Atomic Layer Deposition

Atomic layer deposition (ALD) is used to control the interatomic interactions of Eu and Ti in multilayered structures, as measured by characterizing the luminescent properties of the deposited material. Luminescent multilayer structures of Eu2O3 and TiO2 are deposited as thin films by ALD at 300 degrees C using Eu(thd)(3)/O-3 and TiCl4/H2O (thd=2,2,6,6-tetramethyl-3,5-heptanedione) as precursor systems. The individual layer thickness of the multilayered structure is produced from first N ALD cycles Eu2O3 and then N ALD cycles TiO2 (N=1 to 50), while the total film thickness is kept constant. The thinnest distinct layers are detected for N=10, where each layer is measured to be less than 0.4nm thick. The as-deposited films are smooth (root mean square (rms) roughness<0.4nm) and amorphous, independent of the layer thickness, N. The refractive index and extinction coefficient are also independent of N, while the luminescence efficiency is constant for N up to 10 cycles, and decreases for thicker superlayers. Annealing deteriorates the layered structures, causing a decrease in luminescence efficiency for thin superlayers, while thick superlayers increase in efficiency upon annealing. The films are characterized by spectroscopic ellipsometry (SE), photoluminescence (PL), X-ray diffraction (XRD), X-ray fluorescence (XRF), X-ray reflectivity (XRR), and atomic force microscopy (AFM).