Localisation of the electron distribution in small nickel particles embedded in metallic or insulating matrices

The d spectral electron distribution is reported for 2-3 nm nickel particles vacuum deposited and embedded in MgF2. The study is performed by soft X-ray emission (XES) and absorption (XAS) spectroscopies. Results are discussed in comparison with previous ones obtained for nickel embedded in aluminium. Two kinds of modification are observed: first, those which are independent of the matrix and are ascribed to a partal localisation of the occupied d states due to the size decrease and to the loss of long-range order, and, second, those which depend on the existence of an overlap between the orbitals of the nickel particles and the embedding matrix. When such an overlap occurs, as in the case of an aluminium matrix, the localisation of the empty nickel d states is not observed; such a localisation is observed for the MgF2 insulating matrix.