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 band gaps and semiconducting properties (e.g., n or p type). The main approaches to deposit few/mono-layers 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.

Using a Lego approach of superposing mono-layers, we can envisage the fabrication of hetero-junctions with original electronic behavior.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) using chemical vapor deposition (CVD) and (b) we exfoliate and deposited (drop-cast or Langmuir Blodgett) 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 nano-materials synthesized slightly differ from the materials with the same stoichiometry synthesized using conventional chemical methods (e.g., solvo-thermal). 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 with a band gap of 2.5 eV but more conductive than silicon. This p-type material is important to fabricate devices such as p-n junctions and hetero-junctions, 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.

Using the same approach, we synthesized high yields of many other bulk 2D layered materials such as silver sulfide, nickel phosphide, silver selenide, and copper selenide. In this talk, we will discuss the synthesis, the very extensive characterizations, the applications tested, and the promise of this technique for the fabrication of bulk 2D layered materials for hetero-junctions based on mono-layers with different properties for future electronic devices.

Now, scroll down and see how our cool materials look like under an electron microscope :)