Pulsed laser deposition of photoresponsive two-dimensional gase nanosheet networks

Synthesis of functional metal chalcogenide (GaSe) nanosheet networks by stoichiometric transfer of laser-vaporized material from bulk GaSe targets is presented. Uniform coverage of interconnected, crystalline, and photore-sponsive GaSe nanosheets in both in-plane and out-of-plane orientations are achieved under different ablation conditions. The propagation of the laser-vaporized material is characterized by in situ ICCD-imaging. High (1 Torr) Ar background gas pressure is found to be crucial for the stoichiometric growth of GaSe nanosheet networks. Individual 1-3 layer GaSe triangular nanosheets of α200 nm domain size are formed within 30 laser pulses, coalescing to form nanosheet networks in as few as 100 laser pulses. The thickness of the deposited networks increases linearly with pulse number, adding layers in a two-dimensional (2D) growth mode. GaSe nanosheet networks show p-type semiconducting characteristics with mobilities reaching as high as 0.1 cm ²V^-1s^-1. Spectrally-resolved photoresponsivities and external quantum efficiencies range from 0.4 AW^-1 and 100% at 700 nm, to 1.4 AW^-1 and 600% at 240 nm, respectively. Pulsed laser deposition under these conditions appears to provide a versatile and rapid approach to stoichiometrically transfer and deposit functional networks of 2D nanosheets with digital thickness control and uniformity for a variety of applications.