Structure evolution of epitaxial Pd grown on MgO(001): a comparison between sputtering and electron-beam evaporation

Abstract

Thin films grown by sputtering and electron-beam evaporation typically show differences in structure and morphology, and thus in physical properties. In this paper we report on morphology and crystallographic structure of thin palladium films grown on MgO(001), both by electron-beam evaporation and sputtering, in order to compare the two growth methods for fabrication of model catalysts. The depositions were made under high-vacuum conditions. The grown films were studied as a function of nominal film thickness (from 0.5 to 20 nm) and deposition temperature (300 and 600°C), using grazing incidence X-ray diffraction, transmission electron microscopy and atomic force microscopy. For the used deposition temperatures, no large differences were seen between the evaporated and the sputtered samples with nominal film thickness ≥2.5 nm. The Pd nucleated and grew as three-dimensional particles, showing a strong epitaxial tendency with Pd 〈100〉//MgO 〈100〉. In a few cases, four 111-oriented Pd domains rotated 90 degrees with respect to each other were detected using X-ray diffraction. For the films of 0.5 nm nominal thickness, differences between the evaporated and the sputtered films were found. The Pd particles were larger and less strained in the case of sputtering, suggesting that the energetic species present during sputtering increases the apparent surface diffusivity of the Pd adatoms during growth.