Femtosecond Laser Synthesis of Multi-Element Nanocrystals
We studied the conditions under which short-pulsed laser deposited (PLD) stoichiometric multi-element nanocrystals of GaAs,InP,CoPt and Inconel (an alloy of Cr, Fe and Ni) are formed. The properties of the PLD nanoclusters and the irradiated targets were investigated as a function of the laser pulse-length (150 fs-500 ps) and the inert background gas pressure in the synthesis chamber (microTorr to hundreds of Torr). Our results reveal that the formation of stoichiometric GaAs nanocrystals required ablating a GaAs target with a shorter than 25 ps laser in a {ge} 50 miliTorr of inert background pressure. For InP, a mixture of stoichiometric InP and In nanocrystals with an InP/In ratio of {approx} 1 resulted upon ablating an InP target in Ar at 1 Torr. This InP/In ratio increased to {approx} 5 when ablating the InP target in an Ar pressure of 750 Torr. In case of CoPt alloy, the stoichiometry in the target was not reflected in the collected nanocluster films, independent of the background gas pressure. Interestingly, the stoichiometry of the target was found in the collected nanocluster films when an Inconel target was ablated by a femtosecond laser even in vacuum. It is noted that the constituents of Inconel (Cr, Fe and Ni) have similar vapor pressures while Co and Pt do not. Our experimental results suggest that the stoichiometries of the PLD multi-element nanoclusters are closer with those of the targets when shorter than 25 ps lasers are used. However, this does not imply that simply irradiating a multi-element target in vacuum with a shorter than 25 ps pulse-length laser would automatically result in the formation of stoichiometric nanocrystals. The preservation of the stoichiometry of the irradiated target and the formation of stoichiometric semiconductor nanocrystals require ablating the targets with a shorter than 25 ps laser in a background gas. The minimum background gas pressure is materials dependent. And for metal alloys, the stoichiometry of the ablated target cannot be found in the collected nanocluster films if the constituent elements have widely different vapor pressures. We have also successfully used density-functional based tight-binding potentials to study the femtosecond laser/GaAs target interaction. This code work can be extended to other multi-element compounds/alloys as well.
- Research Organization:
- Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
- Sponsoring Organization:
- US Department of Energy (US)
- DOE Contract Number:
- W-7405-ENG-48
- OSTI ID:
- 15006361
- Report Number(s):
- UCRL-ID-150296; TRN: US200409%%43
- Resource Relation:
- Other Information: PBD: 8 Jan 2003
- Country of Publication:
- United States
- Language:
- English
Similar Records
GaAs nanostructures and films deposited by a Cu-vapor laser
Pulsed laser deposition to synthesize the bridge structure of artificial nacre: Comparison of nano- and femtosecond lasers