Cu 2−x S nanocrystal synthesis: a chemical toolbox for controlling nanocrystal geometry, phase and plasmonic behavior

Cu2xS nanocrystals (NCs) have been recently exploited in several fields, ranging from energy conversion tobiomedical applications, due to their intriguing geometry and phase-dependent semiconductor and near-infrared plasmonic properties. Although advances have been made in their synthesis by hot-injection at thepresent stage of research, the unexpected sizes and shapes of the Cu2xS NCs and broad polydispersity stillrepresentcriticalissuesthatmustbeavoided,astheyareresponsiblefortheunpredictableopticalresponseand undesirable broadening of the spectroscopic feature. This study intends to explore the influence that thereactantsusedintheCu2xS NC synthesis have in the modulation of size, shape and phase. Furthermore, weaim to provide an effective toolbox for a judicious choice of synthetic conditions towards the production ofmonodispersed and uniform NCs. The way how, the precursor nature, tied up with the composition ofamphiphilic molecules, controls the final NC geometry (e.g., size, shape and size/shape distribution), phase andplasmonic properties, is discussed on the basis of the Hard-Soft Acid-Base theory. In this regard, Cu2xSNCsprepared by means of various typically used reactants (CuCl, CuCl2, Cu(acetylacetonate)2,Cu(acetate)2,S8,tert-dodecanthiol (tDT) or dibuthyldisulfide (DBDS)) and amphiphilic molecules (oleic acid and oleylamine) are,in this work, extensively investigated. The valence of copper ions, copper counterion, molar ratio of copper tosulphur precursors, and coordinating agents demonstrate the essential factors to achieve a qualitativeestimation of the nucleation and growth rate, and aneffective elucidation of the NC growth mode and henceof the final NC plasmonic behavior.