Growth mechanism of liquid Hg/solid β-HgS metal-semiconductor heterostructures

Density functional theory （DFT） was utilized to simulate the reactions occurred in the mixture solution of cysteine and Hg（II） ions with the ratio 〈 2. Simulation result shows that Hg ions will coordinate to cysteine by the thiol groups with the form of S-Hg2 and S-Hg3; and moreover, the content of free Hg ions can only be reduced by these two forms. OH- plays an important role in the growth of β-HgS, because its nucleophilic substitution reaction supplies plenty of Hg-S-Hg radicals, which will be adsorbed onto the surface of liquid mercury ball and form the precursor of 13-HgS（111） plane. Three valent bonds adsorption of Hg-S-Hg radicals onto the surface of Hg ball has more adsorption energy （-32.768 kcal mol-1） than that of two valent bond adsorption （-20.882 kcal - mol-1）. Hg balls will stop growing after completely covered with Hg-S-Hg radicals and their size will be limited. The growth direction of β-HgS is parallel to the ＂repel- ling＂ force, that is [111] direction in β-HgS lattice. The calculated results are in good agreement with the experimental observations, demonstrating that the DFT method can be taken as a very useful tool to interpret the solution reactions that cannot be solved by conventional methods.