Growth and morphology of cobalt nanoparticles on alumina

Cobalt films of different average thickness (t(Co) = 0.15-4.8 nm) have been deposited on amorphous alumina (a-Al2O3) at different temperatures (T-s = 130-600 degreesC), with the aim of forming Co nanoparticles of well-defined size and shape. Two deposition techniques have been used: thermal evaporat ion (TE) of a Co filament at the pressure P = 10(-10) mbar and pulsed laser deposition (PLD) from a Co target at P = 2 x 10(-6) mbar. The structural p roperties of the Co films have been investigated by using transmission elec tron microscopy (TEM), electron diffraction (TED) and high resolution (HREM ). Co nanoparticles are found at high temperature, T-s = 350 degreesC and a bove, in the films prepared by both techniques. In the early stages of grow th, they are nearly spherical and at further stages they become oblate and the height/base-diameter (h/phi) ratio decreases when the diameter increase s. The differences between the films prepared by the two techniques appear principally at low deposition temperature, T-s = 270 degreesC and below: wo rm-like shape of pure Co are found in the films grown in the TE chamber and quasicontinuous layer films containing Co and Co oxide are found in the fi lms grown in the PLD chamber. (C) 2001 Elsevier Science B.V. All rights res erved.