Laser physical vapor deposition of nanocrystalline dots using nanopore filters

Abstract

Nanocrystalline dots of n-type Bi₂Te_2.7Se_0.3 thermoelectric compound and of silicon were deposited by laser physical vapor deposition using polycarbonate or alumina nanopore filters as templates. The films were characterized by scanning electron microscopy and transmission electron microscopy. Using a pore size of 0.2 μm in the nanopore filters, a uniform distribution of crystallites with size 3 to 4 nm and separated from each other was observed by high-resolution transmission electron microscopy. The dots were all single crystals, as seen by the resolved crystal lattice planes. The compositions of the crystallites, of both the thermoelectric compound and silicon, were analyzed by energy dispersive X-ray analysis. The composition of the thermoelectric compound nanocrystals differed significantly from that of the bulk target, likely due to vapor pressure differences of the constituent elements. The results are promising for synthesis of nanocrystalline dots with controlled size but compositional control is a different task that is not carried out. The observations illustrate that nonstoichiometry is a result of difference in the vapor pressure of different elements in the compound. The method of synthesis is found to be suitable for deposition of quantum dots below certain size determined by the size of the pores in the porous filter.