Van der Waals heterostructures (vdWH) formed of two-dimensional (2D) materials offer means to obtain materials by design with unique electronic properties. Research on 2D vdWH has so far been focused on fabricating such heterostructures by stacking individual 2D crystals, which leads to stacks with the presence of fabrication defects. Franckeite (Fr) is a naturally occurring vdWH comprised of two different alternately stacked semiconducting layers, that enables the study of a complex layered system where the crystal orientation between layers has been preserved. Unlike other layered sulfide-based materials, Fr is a grainedtextured rock composed of few-millimeter flakes in random orientation. In consequence, exfoliation of uniform thin flakes is especially challenging. By precise manipulation of the starting flake in combination with different substrates, we were able to increase the quality of exfoliation and obtain few-layer Franckeite flakes with uniform surface areas of approximately 5 microns. Here we present results on the developed exfoliation technique and the evolution of Raman peaks of Franckeite with increasing temperature.

Viviane Z. Costa

San Francisco State University