Experimental study on an evaporation process to deposit MoO2 microflakes

Space-Confined One-Step Growth of 2D MoO2 /MoS2 Vertical Heterostructures for Superior Hydrogen Evolution in Alkaline Electrolytes

2D material-based heterostructures are constructed by stacking or spicing individual 2D layers to create an interface between them, which have exotic properties. Here, a new strategy for the in situ growth of large numbers of 2D heterostructures on the centimeter-scale substrate is developed. In the method, large numbers of 2D MoS₂ , MoO₂ , or their heterostructures of MoO₂ /MoS₂ are controllably grown in the same setup by simply tuning the gap distance between metal precursor and growth substrate, which changes the concentration of metal precursors feed. A lateral force microscope is used first to identify the locations of each material in the heterostructures, which have MoO₂ on the top of MoS₂ . Noteworthy, the creation of a clean interface between atomic thin MoO₂ (metallic) and MoS₂ (semiconducting) results in a different electronic structure compared with pure MoO₂ and MoS₂ . Theoretical calculations show that the charge redistribution at such an interface results in an improved HER performance on the MoO₂ /MoS₂ heterostructures, showing an overpotential of 60 mV at 10 mA cm^-2 and a Tafel slope of 47 mV dec^-1 . This work reports a new strategy for the in situ growth of heterostructures on large-scale substrates and provides platforms to exploit their applications.

Photovoltaic effect-driven IR response of heterojunctions obtained by direct CVD synthesis of MoS2 nanolayers on crystalline silicon

The development of technologies of hybrid structures with combined three-dimensional (3D) and two-dimensional (2D) materials is being recognised as a highly attractive opportunity to create new optoelectronic devices with unique properties originating from the atomic thin structures. In the present study, a novel approach in the direct synthesis of MoS2 2D-layers on p-Si was proved to be acceptable for fabricating a photovoltaic effect-driven photodetector based on a hybrid 2D/3D heterojunction that included an atomically thin n-MoS2 film and crystalline p-Si substrate. It was demonstrated experimentally that the heterojunction with the top and bottom contacts was highly sensitive to illumination between 650 and 1200 nm. The experimental study proved that the response to light was originated by the photovoltaic effect in the sample devices without an external power supply. The maximum sensitivity of the 2D/3D heterostructures to the optical power of the illumination was up to 210 V W-1 and was practically independent of the wavelength. The analysis of experimental I-V, C-V characteristics, Raman spectra and AFM surface images allowed us to construct a flat band model of the hybrid 2D/3D n-p-heterojunction that explained the electrical properties of the n-MoS2/p-Si photodetectors. The photovoltaic effect-driven light detectors offer highly promising possibilities in the development of autonomous photonic systems.