Core and surface engineering in binary, ternary and quaternary semiconductor nanocrystals—A critical review

Abstract

In the past two decades significant research efforts of chemists, physicists, materials scientists and electronic engineers have been devoted to the elaboration of semiconductor nanocrystals with controlled optoelectronic properties and dispersable in various media, including aqueous ones. This review discusses problems of the inorganic nanocrystals synthesis with special emphasis on the role of initial ligands i.e. ligands originating from the reaction mixture in this process. Chemical nature of initial ligands and their topology have a profound effect on the nanocrystals’ shape and size, as well as on their physical properties. Also methods for identification of initial ligands are outlined. Classification of these ligands is presented and their interactions with nanocrystal surface is discussed in the frame of HSAB (hard and soft (Lewis) acid and bases) theory. Since exchange of initial ligands for functional ones, which could tune electrical transport and other properties of the resulting nanomaterials, is crucial for nanocrystals engineering, effective ligands exchange procedures are also described, including exchange for organic ligands of semiconductor nature. Not neglecting initially developed nanocrystals (CdSe and PbS), frequently considered as “model” systems, in this review special interest is focused on heavy metal-free nanocrystals, attracting increasing scientific interests in recent years, namely binary InP NCs, ternary stoichiometric (CuInS2) and nonstoichiometric (Cu-In-S) NCs, and quaternary Cu-In-Zn-S ones. To enhance practical utility of this review, recommended nanocrystals preparation methods, resulting in different initial ligands, as well as ligands exchange procedures are presented for each group of the discussed nanocrystals.