A simple route to synthesize size-controlled Ag₂S core-shell nanocrystals, and their self-assembly

Silver sulfide (Ag₂S) nanocrystals were successfully synthesized by the thermal treatment of the single source precursors, silver dialkyldithiophosphates (Ag[S₂P(OC_nH_2n+1) ₂]), under mild reaction conditions. The size of Ag₂S nanocrystals with regular shape can be controlled in the range of tens of nanometers by adjusting critical parameters, such as the carbon number of the substitute alkyl, the solvent and the reaction temperature. Electron diffraction and x-ray powder diffraction confirmed the orthorhombic phase of the Ag ₂S nanocrystals. The as-prepared Ag₂S nanocrystals have an inorganic-organic core-shell structure, in which Ag₂S nanocrystals are the inorganic core and the organic modifiers, consisting of oleylamine and dialkyldithiophosphate, are the shell. The organic modifiers were anchored to the surface of Ag₂S nanocores by their active groups of -NH ₂ and -SPS- , respectively, and their direct-alkyl chains spread to the outside. So, these as-prepared Ag₂S nanocrystals can self-assemble to form orderly two-dimensional arrays easily, and they disperse in some non-polar solvents stably.