Anisotropic buckling of few-layer black phosphorus.

When a two-dimensional material, adhered onto a compliant substrate, is subjected to compression it can undergo a buckling instability yielding to a periodic rippling. Interestingly, when black phosphorus (bP) flakes are compressed along the zig-zag crystal direction, the flake buckles forming ripples with a 40% longer period than that obtained when the compression is applied along the armchair direction. This anisotropic buckling stems from the puckered honeycomb crystal structure of bP and a quantitative analysis of the ripple period allows the determination of the Youngs's modulus of few-layer bP along the armchair direction (EbP_AC = 35.1 ± 6.3 GPa) and the zig-zag direction (EbP_ZZ = 93.3 ± 21.8 GPa).

Engineering the optoelectronic properties of MoS2 photodetectors through reversible noncovalent functionalization.

We present an easy noncovalent functionalization of MoS2-based photodetectors that results in an enhancement of the photoresponse by about four orders of magnitude, reaching responsivities up to 100 A W-1. The functionalization is technologically trivial, air-stable, fully reversible and reproducible, and opens the door to the combination of 2D-materials with molecular dyes for the development of high performance photodetectors.

Strong Modulation of Optical Properties in Black Phosphorus through Strain-Engineered Rippling.

Controlling the bandgap through local-strain engineering is an exciting avenue for tailoring optoelectronic materials. Two-dimensional crystals are particularly suited for this purpose because they can withstand unprecedented nonhomogeneous deformations before rupture; one can literally bend them and fold them up almost like a piece of paper. Here, we study multilayer black phosphorus sheets subjected to periodic stress to modulate their optoelectronic properties. We find a remarkable shift of the optical absorption band-edge of up to ∼0.7 eV between the regions under tensile and compressive stress, greatly exceeding the strain tunability reported for transition metal dichalcogenides. This observation is supported by theoretical models that also predict that this periodic stress modulation can yield to quantum confinement of carriers at low temperatures. The possibility of generating large strain-induced variations in the local density of charge carriers opens the door for a variety of applications including photovoltaics, quantum optics, and two-dimensional optoelectronic devices.