Bi nanocrystals embedded in an amorphous Ge matrix grown by pulsed laser deposition

Bi nanoclusters embedded in an amorphous Ge matrix have been produced by alternate pulsed laser deposition in a vacuum. The resulting thin films have been analyzed by high resolution electron microscopy, and the images show that the Ge matrix is amorphous and that Bi nanocrystals are formed. The size of the nanoclusters was easily changed within the range 2 nm to 25 nm by varying the number of pulses on the Bi target. Both the dependence of the nanocrystal size on the number of laser pulses on the Bi target and the results of tilting experiments in the electron microscope show that the nanocrystals have an oblate ellipsoidal shape with a much shorter axis in the direction of the film normal. This particular shape is related to their growth mechanism after nucleation at the substrate.