Pd nanoclusters grown by plasma sputtering deposition on amorphous substrates

In this work, we study the deposition of palladium by a non-conventional plasma sputtering technique. The metal atom sower is a biased wire which is sputtered by argon ions present in an HF-excited plasma. Two energetic plasma species (ions and metastable atoms) impinge onto the substrate surface during deposition and thus, may influence the growth. The flux of metastable atoms can be evaluated to 10(14) atoms/cm(2) with a potential energy of 12 eV. Electrical measurements of the plasma performed by the Langmuir probe allow the evaluation of the ion flux. It is of the order of 10(14) ions/cm(2) s for a kinetic energy of 50 eV. The respective effect of both species cannot be separated but, since ions carry higher energy, they are expected to play the major role. Thus, comparison is made with conventional ion beam-assisted deposition techniques, for which the ion flux vs, metal atom flux ratio is low (values less than or equal to 0.1 against 10 in plasma sputtering technique) and the incoming ion energy is high: of the order of hundreds or thousands of electron volts. Information on the film growth in these particular conditions are obtained by transmission electron microscopy (TEM) analysis of deposits performed on carbon membrane (coating copper grids) and by grazing incidence small angle X-ray scattering (GISAXS) characterization of Pd/amorphous SiO2 deposits. In the present plasma conditions (100 mTorr argon pressure and -100 V wire bias), 3D clusters are found to be formed which grow in size and coalesce to form meandering islands. After the coalescence step, when the fractional covered area is sufficiently high, it is evidenced that the simultaneous energetic species flux causes a reorganization of the meandering aggregates, and further, the formation of more compact islands composed of bigger elementary clusters. This is attributed to a rise of the mobility of metal atoms and small clusters under bombardment. (C) 2000 Elsevier Science B.V. All rights reserved.