Supersonic Nanocrystal Deposition for Nanostructured Materials

We experimentally demonstrate the large scale production and controlled collection of metal and semiconductor nanocrystals by laser ablation of microparticles entrained at high density in a flowing aerosol. For silver, produced nanocrystals exhibit bimodal, log-normal size distributions. Mean particle sizes are controlled from 3-16 nm by varying the type and pressure of carrier gas as well as laser fluence. For collection, a micronozzle orifice (d = 200 [.mu]m) accelerates nanocrystals through a sonic jet into a vacuum chamber for deposition onto a room temperature substrate. We describe two regimes of deposition that depend on the nanocrystal’s energy per atom on impact. Soft landings ( E << 1 eV/ atom) preserve the individual particle properties such as size and shape. Low energy impaction is demonstrated for CdSe in an argon carrier gas. The CdSe nanoclusters remain crystalline upon deposition and display visible photoluminescence. At higher particle impaction velocities (E ∼ 0.3 eV/atom) nanocrystals exhibit the onset of self sintering upon impact. At high number densities, adherent, conductive lines are formed from deposited silver nanocrystals. Line widths of 33 [.mu]m FWHM are directly written onto substrates using a 200 [.mu]m diameter nozzle.