Laser-induced manipulation of the size and shape of small metal particles:: Towards monodisperse clusters on surfaces

A novel experimental technique is presented for post growth narrowing of the size distribution of metal nanoparticles on dielectric substrates. In order to demonstrate the potential of the method, oblate Ag clusters with mean radii of (R) = 6 nm and broad size distributions were prepared under ultrahigh vacuum conditions on quartz substrates. Narrowing of the width of their size distribution was accomplished by irradiation with short laser pulses. The laser light excites plasmons in the particles, the frequency of which depends on the size and shape of the clusters. By choosing the light frequency such that only the smallest and the largest particles selectively absorb light, evaporate atoms and shrink in size, the size distribution was narrowed by 40%. A scenario for producing monodisperse particles is discussed.