Nanometric chemical clocks.

Field ion microscopy combined with video techniques and chemical probing reveals the existence of catalytic oscillatory patterns at the nanoscale. This is the case when a rhodium nanosized crystal--conditioned as a field emitter tip--is exposed to hydrogen and oxygen. Here, we show that these nonequilibrium oscillatory patterns find their origin in the different catalytic properties of all of the nanofacets that are simultaneously exposed at the tip's surface. These results suggest that the underlying surface anisotropy, rather than a standard reaction-diffusion mechanism, plays a major role in determining the self-organizational behavior of multifaceted nanostructured surfaces. Surprisingly, this nanoreactor, composed of the tip crystal and a constant molecular flow of reactants, is large enough for the emergence of regular oscillations from the molecular fluctuations.

Early stages in the nucleation process of carbon nanotubes.

The early stages of carbon nanotube nucleation are investigated using field ion/electron microscopy along with in situ local chemical probing of a single nanosized nickel crystal. To go beyond experiments, tight-binding Monte Carlo simulations are performed on oriented Ni slabs. Real-time field electron imaging demonstrates a carbon-induced increase of the number density of steps in the truncated vertices of a polyhedral Ni nanoparticle. The necessary diffusion and step-site trapping of adsorbed carbon atoms are observed in the simulations and precede the nucleation of graphene-based sheets in these steps. Chemical probing of selected nanofacets of the Ni crystal reveals the occurrence of Cn (n=1-4) surface species. Kinetic studies prove C2+ species are formed from C1 with a delay time of several milliseconds at 623 K. Carbon dimers, C2, must not necessarily be formed on the Ni surface. Tight-binding Monte Carlo simulations reveal the high stability of such dimers in the first layer beneath the surface.