Gold nanoparticle-decorated graphene as a nonlinear optical material in the visible and near-infrared spectral range

AgScP2S6 van der Waals Layered Crystal: A Material with a Unique Combination of Extreme Nonlinear Optical Properties

Research in two-dimensional layered materials (2DLMs) has exploded over the past several years for a variety of applications in photonics and optoelectronics. The 2D nature of these materials allows for a very local electronic probe of material as well as flexible integration with other functional components. Herein, using the femtosecond Z-scan technique, we report a giant two photon absorption (TPA) process and its saturation in the van der Waals gapped silver scandium thiophosphate (AgScP₂S₆) crystal. We have found a TPA coefficient of the order of 10⁴ cm/GW which is orders of magnitude larger compared to many existing semiconductors and nonlinear crystals. Furthermore, we found a TPA cross-section of 10³ GM and characterized the optical limiting (OL) response (0.2 mJ/cm²) and the multipulse laser damage threshold (1.09 ± 0.19 J/cm²). The combination of giant TPA, extremely low OL, and very high damage threshold suggests that this material could be extremely useful in applications like optical limiters or switches.

Ultrafast Nonlinear Absorption and Second Harmonic Generation in Cu0.33In1.30P2S6 van der Waals Layered Crystals

The advancement of ultrafast photonics and optoelectronic devices necessitates the exploration of new materials with optical and chemical stability to implement practical applications. Layered quaternary metal-thio/selenophosphate has attracted much interest over the past few years. Ferroelectric CuInP₂S₆ (CIPS) is an emerging material that belongs to this family. When synthesized with Cu deficiencies, CIPS forms self-assembled in-plane heterostructures, which in turn exhibit properties that are both compositionally and thermally dependent. These characteristics can be explored for applications in nonlinear optoelectronic and photonic devices. Herein, we study the second and third order nonlinear optical behavior of Cu_0.33In_1.30P₂S₆ bulk heterostructure. We observed large two photon induced nonlinear absorptions and self-defocusing at 1032 nm pulsed laser excitation using the Z-scan technique. Furthermore, we identified a polarization-dependent second harmonic signal and determined the laser-induced optical damage threshold. Our observations allow for the designing of optoelectronic and ultrafast photonic devices based on these materials.

Unusually high flexibility of graphene-Cu nanolayered composites under bending

The mechanical properties of graphene-Cu nanolayered (GCuNL) composites under bend loading are investigated via an energy-based analytical model and molecular dynamics (MD) simulations. For an anisotropic material, if it has a weak strength in a certain direction, improving the mechanical properties along this direction is normally difficult for its composites. Here, we find that the flexibility of GCuNL composites can be improved considerably by graphene interfaces, despite graphene's small bending stiffness. The graphene interfaces can delocalize slip bands in the inner Cu layers of GCuNL composites, and impede local nucleation of dislocations, thus greatly increasing the yield and failure bend angles. As the thickness decreases, the flexibility of GCuNL nanofilms increases. However, the GCuNL nanofilms are thermodynamically unstable due to interface instability when the repeat layer spacing is less than 2 nm. The energy-based analytical model for large deformation can accurately characterize the bending response of GCuNL nanofilms.

Nanoscale fracture of defective popgraphene monolayers

A new carbon allotrope, namely popgraphene, has been recently demonstrated to possess high potentials for nanodevice applications. Herein, the fracture of defective popgraphene was studied using molecular dynamics simulations and continuum modeling. Three scenarios of defects were considered, including an individual point defect, distributed point defects, and nanocracks. It was found that the fracture stress of popgraphene with an individual point defect was governed by both the geometry of the defect and the critical bond where fracture initiates. Moreover, the fracture stress of popgraphene with distributed point defects was discovered to be inversely proportional to the defect density, showing a nice linear trend. Furthermore, for popgraphene with a nanocrack, it failed in a brittle fashion and exhibited a negligible lattice trapping effect. The Griffith criterion was subsequently employed with the consideration of crack deflection to accurately predict the dependence of fracture stress on crack size. The present study lays a mechanistic foundation for nanoscale applications of popgraphene and offers a better understanding of the roles of defects in fracture of low-dimensional materials.