Bar Ilan University,
Keywords: metal chalcogenides, sulfide, phosphide, selenide, chemical vapor deposition
Summary:Since the excitement about graphene, a monolayer of graphite, with its 2010 Nobel Prize, there has been extensive research in the synthesis of other non-carbon few/mono-layers exhibiting a variety of bandgaps and semiconducting properties (e.g., n or p type). The main approaches to deposit few/monolayers on a substrate are: (a) bottom-up synthesis from precursors using chemical vapor deposition (CVD) or (b) top-down exfoliation (liquid or mechanical) of bulk layered material. Here we show a combined bottom-up and top-down approach where (a) we synthesize in one step high yields of bulk layered materials by annealing a metal in the presence of a gas precursor (sulfur, phosphorous, or selenium) and (b) we exfoliate and dropcast few/mono-layers on a substrate from a sonicated mixture of our material in a specific solvent. It is interesting to note that, besides the structure being 2D layered, the properties of the nanomaterials synthesized slightly differ from the materials with the same stoichiometry synthesized using conventional chemical methods. For instance, we synthesized Cu9S5 and characterized it using multiple spectroscopy, X-ray techniques, and electrical AFM . We found that is a highly doped, p-type material. This is critical to fabricate devices such as p-n junctions and heterojunctions, since most of the recently discovered and studied layered materials such as MoS2, or MoSe2 are n-type, while few materials, such as phosphorene, which suffers from rapid oxidation, are p-type. We tested the synthesized Cu9S5 as an electrode for Li-ion battery. Using the same approach, we synthesized high yields of bulk layered silver sulfide (Ag2S), which exhibits very high performance for hydrogen evolution reaction (HER) and copper phosphide (Cu3P), which shows a promising application in supercapacitors. We will share also unpublished initial results on the synthesis of selenides. In this talk, we will discuss the synthesis, the extensive characterizations, the applications tested, and the promise of this technique for the fabrication of bulk materials for energy application and of heterojunctions based on monolayers for future electronic devices.