BUILDING ONE-DIMENSIONAL AND 2-DIMENSIONAL NANOSTRUCTURES BY DIFFUSION-CONTROLLED AGGREGATION AT SURFACES

THE formation of nanometre-scale surface structures by atomic manipula tion with the scanning tunneling microscope has opened up opportunitie s for creating new metastable states of matter atom by atom1. The tech nique allows the fabrication of arbitrary structures, but its applicat ion may be limited by considerations of speed, as only one nanostructu re can be built at a time. Here we describe the simultaneous formation of many densely packed nanostructures of various morphologies using d iffusion-controlled aggregation on surfaces. By exploiting the depende nce of the mobility of adsorbed atoms on substrate crystal face and te mperature, we are able to grow linear, two-dimensional or tenuous frac tal aggregates of nanometre dimensions. The high number density (10(11 )-10(14) cm-2) of these structures means that their physical and chemi cal properties can be easily measured with conventional surface spectr oscopies.