Abstract :
Harmonic generation crystals inherently offer the possibility of using multiple wavelengths of light in a single laser pulse. In the present
experiment, the fundamental (1064 nm) and second harmonic (532 nm) wavelengths from an Nd:YAG laser are focused together on GaAs and
GaSb targets for ablation. Incident energy densities up to about 45 J/cm2 at 10 Hz with substrate temperatures between 25 and 600 8C for durations
of about 60 s have been used in an ambient gas pressure of about 10 6 Torr. The ablated material was collected on electron-transparent amorphous
carbon films for TEM analysis. Apart from a high density of isolated nanocrystals, the most common morphology observed consists of a crystalline
GaAs cone-like structure in contact with a sphere of liquid Ga, resembling an ‘‘ice cream cone’’, typically 50–100 nm in length. For all of the
heterostuctures of this type, the liquid/solid/vacuum triple junction is found to correspond to the widest point on the cone. These heterostructures
likely form by preferential evaporation of As from molten GaAs drops ablated from the target. The resulting morphology minimizes the interfacial
and surface energies of the liquid Ga and solid GaAs.
