Improvement of experimental data via consistency conditions
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Applied Physics A Materials Science & Processing
Surface Ostwald ripening of Pd nanoparticles on the MgO (100) surface ´ Imre1,∗ , D.L. Beke1 , E. Gontier-Moya2 , I.A. Szab´o1 , E. Gillet2 A. 1 Department 2 Laboratoire
of Solid State Physics, University of Debrecen, 4010 Debrecen, P.O. Box 2, Hungary SERMEC, B61, Facult´e des Sciences et Techniques de St. Jerôme, 13397-Marseille Cedex 20, France
Received: 28 November 1999/Accepted: 28 March 2000/Published online: 7 June 2000 – Springer-Verlag 2000
Abstract. Morphological changes of Pd nanoparticles on the (100) surface of MgO single crystal were investigated by Auger electron spectroscopy in the temperature range of 873–983 K. The size and distribution of clusters were also examined by means of atomic force microscopy. It was shown that there was practically no decrease of the effective thickness of deposited Pd during heat treatments under 6 × 10−9 mbar. Assuming that the observed change in the Auger intensities is due to the surface Ostwald ripening the temperature dependence of the surface mass transport diffusion coefficients can be given as −(136 ± 15) kJ mol−1 +8.2 0 −8 Ds = 1.6−1.34 × 10 exp m2 s−1 . RT
PACS: 82.80.Pv; 61.46.+w; 66.30.-h The knowledge of the surface diffusion parameters is important in the understanding of different surface-related phenomena, such as thin film growth, sintering, surface chemical reactions and stability of new-type thin film catalysts. At moderate temperatures, when there is no significant evaporation and/or dissolution into the substrate, and if the surface diffusion fields around the isolated particles are overlapping, surface Ostwald ripening process can be observed [1–4]. During this process the size of large particles increases at the expense of small ones while the mass of the discontinuous film is conserved. The particles on the surface can be treated as spherical caps and, thus, their ensemble can be characterized by the average radius, R, the number of particles per unit surface, Ns , and the contact angle θ. From the investigation of morphological changes of such discontinuous films, the surface mass transport parameters can be determined [1–4]. In our previous paper [5] we have shown that by measuring the Auger intensity the time dependence of the average ∗ Corresponding
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radius can be obtained. Furthermore – assuming that the surface Ostwald ripening is controlled by surface diffusion – the surface diffusion coefficients of Pd on the (1012) surface of sapphire were determined. In this paper the results of the investigation of surface Ostwald ripening of beaded Pd films (with average radius of 19.8 nm) on the (100) surface of MgO single crystal, obtained by means of Auger electron spectroscopy (AES) and atomic force microscopy (AFM), are described. The Pd/MgO system is well known in catalysis [6] but until now there are no data on the surface diffusion [7] in this system.
1 Theoretical relations The time evolution of the average radius of p
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