  Well-separated mercury sulfide (HgS) nanocrystals are synthesized by a wet
chemical route. Transmission electron microscopy studies show that nanocrystals
are nearly spherical in shape with average size of 9 nm. Grazing angle X-ray
diffraction confirms that HgS nanocrystals are in cinnabar phase. Particle
induced X-ray emission and Rutherford back scattering spectrometry analysis
reveal HgS nanocrystals are stoichiometric and free from foreign impurities.
The optical absorption measurements show two excitonic peaks corresponding to
electron-heavy hole and electron-light hole transitions, which are blue shifted
by 0.1 and 0.2 eV, respectively, from its bulk value, due to quantum size
effect. The experimental data obtained by optical absorption measurement is
simulated with a theoretical model considering the particle size distribution
as Gaussian.
