Franckeite as a naturally occurring van der Waals heterostructure

Abstract

The fabrication of van der Waals heterostructures, artificial materials assembled by individual stacking of 2D layers, is among the most promising directions in 2D materials research. Until now, the most widespread approach to stack 2D layers relies on deterministic placement methods, which are cumbersome and tend to suffer from poor control over the lattice orientations and the presence of unwanted interlayer adsorbates. Here, we present a different approach to fabricate ultrathin heterostructures by exfoliation of bulk franckeite which is a naturally occurring and air stable van der Waals heterostructure (composed of alternating SnS2-like and PbS-like layers stacked on top of each other). Presenting both an attractive narrow bandgap (<0.7 eV) and p-type doping, we find that the material can be exfoliated both mechanically and chemically down to few-layer thicknesses. We present extensive theoretical and experimental characterizations of the material's electronic properties and crystal structure, and explore applications for near-infrared photodetectors.

Symmetry Breakdown in Franckeite: Spontaneous Strain, Rippling, and Interlayer Moiré

“…We point the reader to Ref. (13) for a detailed characterization of the franckeite bulk crystal. Figure 1a shows an optical microscopy image of a franckeite flake that has been transferred onto a holey Si3N4 transmission electron microscopy (TEM) grid.…”

“…Several peaks observed in our spectra are in agreement with previously reported data. (13,14,18) Peaks at 195 and 328 cm -1 correspond to vibrational modes of the hexagonal layer of SnS2. (27,28) The two peaks at 259 and 284 cm -1 were previously assigned to the vibrations of Sb2S3, however the energies of these modes are lower than in isolated stibnite.…”

2D Metal Chalcogenides for IR Photodetection

“…2D group IVA metal chalcogenides are a growing interest in IR photodetection, including GeSe, SnS, SnS 2 , SnSe 2 , and PbS due to their unique crystal structures and electronic structures. GeSe possesses a high anisotropic crystal structure, thus inducing anisotropic optical absorption .…”

Putting Rings around Carbon Nanotubes

“…Seriously,they still are. After graphene made its flamboyant entrance, [1] Nobel Prize included, [2,3] followedb ya cohort of other bidimensional materials [4,5] and their mixtures, [6][7][8] it would seem like CNTsa re shying away from the research spotlight, but CNTss till have all the amazing properties that made them candidates to build anything and everything, including as pace elevator! Their extraordinary mechanical properties are still there.…”