SPHALERITE-WURTZITE INTERMEDIATES IN NANOCRYSTALLINE CDS

Cadmium sulfide nanoparticles have been synthesized using mercaptoetha nol as a capping agent. A refined analysis of the powder X-ray diffrac tion by Debye function analysis shows that the as synthesized material consists of both similar to 50 wt % hexagonal wurtzite-type nanoparti cles of about 2 nn and larger cubic sphalerite-type particles of about 2.6 nm, respectively. Both species have also been identified by high resolution electron microscopy, some of them show multiply twinning wi th Ei-fold decahedral symmetry. The thermal stability of these nanopar ticles is surprisingly high under He. The total mass-averaged size. in creases from 2.3 nn (as synthesized) to 3.2 nm after exposure to 315 d egrees C in helium for 12 min. However, both polymorphs are still pres ent. Heavy sintering occurs only above similar to 380 degrees C, leadi ng to wurtzite particles of 41 nn on average. These particles are stro ngly faulted by hexagonal (001) stacking faults (faulting probability = 1.1%)but show negligible twin defects. After synthesis, the particle s show the optical absorption peaks at similar to 400 nm. The related optical band gap of 3.1 eV is in excellent agreement with the theoreti cal tight-binding approximation of Lippens and Lannoo for CdS particle s of this size.