Electronic properties of small platinum particles as seen by NMR

Abstract

No doubt partially because of their catalytic activity, small platinum particles on mineral supports have been extensively studied by NMR during recent years. Here we will discuss these data in relation to the expected electronic properties of small metal particles. Experimentally, no quantum size effects are found, but the local densities of state at the Fermi energy show considerable site-dependence when going from the surface to the interior of the particle. Such effects have been theoretically predicted for an infinite film. PACS: 76.60.Cg; 36.40. + d This paper focuses on magnetism-related NMR effects that arise through the hyperfine coupling between the electronic and nuclear spins: in bulk metals, the static part of the hyperfine coupling results in the Knight shift K and the dynamic part in the Korringa relation T~-loeT (the spin-lattice relaxation rate is proportional to the temperature). We will restrict the discussion mainly to the case of 195pt NMR for which detailed data have become available since the first studies by C.P. Slichter's group, reported at the Lausanne edition of this conference [1].In theoretical descriptions of the magnetic quantum size effect (QSE) one imagines a collection of particles all containing the same number of atoms; the size-parameter is expressed as = 4 EF/3N