Invited Paper SS2-WeA1
Real Time Monitoring of the Structure and Morphology of Growing Nanoparticles by Grazing Incidence Small and Wide Angle X-ray Scattering, in situ, in UHV
Islands of nanometer size grown on substrates display a set of fascinating properties, which are of interest for both basic and applied research. They include model catalysts made of supported metallic particles whose reactivity and selectivity can be adapted to given needs, single-domain magnetic particles which show original spin-dependent transport properties and coherently strained semiconductor aggregates, the so-called "quantum dots", which exhibit remarkable opto-electronic properties. A strong promise of novel device applications merges up provided that nanoparticles could be purposely tailored to specific uses. The properties of these particles depend to a great extent on their internal atomic structure, their strain, their shape, size, size distribution and ordering, which in turn rely on the growth mechanisms. In this context, a challenging issue is to control the growth of large collections of particles by monitoring the relevant parameters in situ and in real time. A unique technique to probe collections of very small objects is Grazing Incidence Small Angle X-ray Scattering (GISAXS). However, to date, due to technical limitations, GISAXS has never been used during growth. In this report, we demonstrate this possibility using two prototypical cases. The first is the growth of metals (Ag, Pd, Pt) on MgO(001) at different temperatures, which are models of Volmer-Weber 3D growth of metal on oxide surfaces, and is thoroughly studied to investigate the elementary processes of heterogeneous catalysis. The second is the growth of cobalt on the herringbone reconstructed Au(111) surface, which is a model of self-organized cluster growth. We show that a complete description of the islands can be obtained by supplementing GISAXS measurements by grazing incidence wide angle x-ray scattering measurements performed in situ during growth, at the same time.