Layered two-dimensional (2D) materials display great potential for a range of applications, particularly in electronics. We report the large-scale synthesis of thin films of platinum diselenide (PtSe), a thus far scarcely investigated transition metal dichalcogenide. Importantly, the synthesis by thermally assisted conversion is performed at 400 °C, representing a breakthrough for the direct integration of this material with silicon (Si) technology. Besides the thorough characterization of this 2D material, we demonstrate its promise for applications in high-performance gas sensing with extremely short response and recovery times observed due to the 2D nature of the films. Furthermore, we realized vertically stacked heterostructures of PtSe on Si which act as both photodiodes and photovoltaic cells. Thus, this study establishes PtSe as a potential candidate for next-generation sensors and (opto-)electronic devices, using fabrication protocols compatible with established Si technologies.

and duesberg@tcd.ie Platinum diselenide (PtSe 2 ) is a newly discovered 2D material which is of great interest for applications in electronics and catalysis. PtSe 2 films were synthesized by thermally-assisted selenization of predeposited platinum films and scanning transmission electron microscopy revealed the crystal structure of these films to be 1T. Raman scattering of these films was studied as a function of film thickness, laser wavelength and laser polarization. E g and A 1gRaman active modes were identified using polarization measurements in the Raman setup.These modes were found to display a clear position and intensity dependence with film thickness, for multiple excitation wavelengths, and their peak positions agree with simulated phonon dispersion curves for PtSe 2 . These results highlight the practicality of using Raman spectroscopy as a prime characterization technique for newly-synthesized 2D materials.

The optical nonlinearity of WS2 and MoS2 monolayer and few-layer films was investigated using the Z-scan technique with femtosecond pulses from the visible to the near-infrared range. The nonlinear absorption of few- and multilayer WS2 and MoS2 films and their dependences on excitation wavelength were studied. WS2 films with 1-3 layers exhibited a giant two-photon absorption (TPA) coefficient as high as (1.0 ± 0.8) × 10(4) cm/GW. TPA saturation was observed for the WS2 film with 1-3 layers and for the MoS2 film with 25-27 layers. The giant nonlinearity of WS2 and MoS2 films is attributed to a two-dimensional confinement, a giant exciton effect, and the band edge resonance of TPA.