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Planar 2D materials are possibly the ideal channel candidates for future field effect transistors (FETs), due to their unique electronic properties. However, the performance of FETs based on 2D materials is yet to exceed those of conventional silicon based devices. Here, a 2D channel thin film made from liquid phase exfoliated molybdenum oxide nanoflake inks with highly controllable substoichiometric levels is presented. The ability to induce oxygen vacancies by solar light irradiation in an aqueous environment allows the tuning of electronic properties in 2D substoichiometric molybdenum oxides (MoO3−x). The highest mobility is found to be ≈600 cm2 V−1 s−1 with an estimated free electron concentration of ≈1.6 × 1021 cm−3 and an optimal IOn/IOff ratio of >105 for the FETs made of 2D flakes irradiated for 30 min (x = 0.042). These values are significant and represent a real opportunity to realize the next generation of tunable electronic devices using electronic inks.

Heterostructures assembled from atomically thin materials have led to a new paradigm in the development of the next-generation high-performing functional devices. However, the construction of the ultrathin van der Waals (vdW) heterostructures is challenging and/or limited to materials with layered crystal structures. Herein, liquid metal vdW transfer method is used to construct large area heterostructures of atomically thin metal oxides of p-SnO/n-In2O3 with ease. The heterostructure exhibits both outstanding photodetectivity of 5 x 10(9) Jones and photoresponsivity of 1047 A W-1 with fast response time of 1 ms under illumination of the 280 nm light. Such excellent performances are due to the formation of the narrow bandgap of the staggered gap at the p-n junction produced by the high-quality SnO/In2O3 heterostructure. The facile production of high-quality vdW heterostructures using the liquid metal-based method therefore provides a promising pathway for realizing future optoelectronic devices.

Few-layer two-dimensional (2D) molybdenum oxide nanoflakes are exfoliated using a grinding assisted liquid phase sonication exfoliation method. The sonication process is carried out in five different mixtures of water with both aprotic and protic solvents. We found that surface energy and solubility of mixtures play important roles in changing the thickness, lateral dimension, and synthetic yield of the nanoflakes. We demonstrate an increase in proton intercalation in 2D nanoflakes upon simulated solar light exposure. This results in substoichiometric flakes and a subsequent enhancement in free electron concentrations, producing plasmon resonances. Two plasmon resonance peaks associated with the thickness and the lateral dimension axes are observable in the samples, in which the plasmonic peak positions could be tuned by the choice of the solvent in exfoliating 2D molybdenum oxide. The extinction coefficients of the plasmonic absorption bands of 2D molybdenum oxide nanoflakes in all samples are found to be high (ε10(9) L mol(-1) cm(-1)). It is expected that the tunable plasmon resonances of 2D molybdenum oxide nanoflakes presented in this work can be used in future electronic, optical, and sensing devices.