Phosphine-free synthesis of iron selenide nanocrytals

Iron chalcogenide compounds (Fe_xSe_y) have regained considerable interest due to the recent discoveries of interesting properties, such as superconductivity in PbO-type FeSe_1-x and huge coerciv-ity in monoclinic Fe₃Se₄ nanostructures [1-3]. There are two well-known magnetic compounds in this family: a hexagonal phase with the approximate composition of Fe₇Se₈ (H-phase) and a monoclinic phase with an approximate composition of Fe₃Se₄ (M-phase). The ferrimagnetism is attributed to the ordered arrangement of Fe vacancies. Traditionally, iron selenides were prepared by elemental reaction in vacuum at high temperatures or mechanical alloying [4,5]. They were also obtained by a solution method using aqueous metal salt and toxic gas H₂Se [2]. These processes are usually complicated and time-consuming and their products are bulk material with large grain size. Recently, facile solution-phase methods have been developed to synthesize iron selenide nanocrys-tals [3,6]. However, these particles are still several hundred nanometer in dimension and are difficult to disperse in a solution. To synthesize small, monodisperse nanoparticles (NPs), strong coordination surfactants, such as those containing phosphine, are often used. In this work, we report a phosphine-free synthesis of monodisperse Fe Se NPs with controllable sizes bellow 20 nm.