John W. Keto,^1,4 William Nichols,¹ Dan O'Brien,2 Michael F. Becker,^2,4 and Desiderio Kovar^3,4

¹Physics Department, ²Department of Computer Engineering, ³Department of Mechanical Engineering, ⁴Texas Materials Institute and the Center for Molecular and Nano Science, The University of Texas at Austin, Austin, TX

ABSTRACT We experimentally demonstrate production and controlled collection of metal and semiconductor nanocrystals by laser ablation of microparticles entrained in a flowing aerosol. Mean particle sizes are controlled from 3-16 nm by varying the type and pressure of the carrier gas. For CdSe nanoparticles, the measured size distributions have a dispersion σ/dia = ±22%. High resolution TEM demonstrates that these particles are nanocrystals without bulk defects. For collection, a micronozzle orifice (d = 200 mm) accelerates nanocrystals through a sonic jet into a vacuum chamber for deposition onto a substrate. We describe two regimes of deposition that depend on the nanocrystal's energy per atom on impact. Soft landings ( E << 0.05 eV/ atom) are achieved using a low pressure argon gas and preserve the individual particle properties. For low energy impaction, CdSe nanoparticles remain crystalline upon deposition and display visible photoluminescence without blinking. 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 films and lines are formed from deposited silver nanocrystals. Line widths of 33mm FWHM are directly written onto substrates using a 200 mm diameter nozzle. We propose to narrow linewidths for written semiconductor particles to less than 100 nm using laser dipole forces. Various techniques for the production of nanocomposite nanostructures are described.