Abstract
The ongoing miniaturization of electronic devices has boosted the development of new post-silicon two-dimensional (2D) semiconductors, such as transition metal dichalcogenides, one of the most prominent materials being molybdenum disulfide (MoS2). A major obstacle for the industrial production of MoS2-based devices lies in the growth techniques. These must ensure the reliable fabrication of MoS2 with tailored 2D properties to allow for the typical direct bandgap of 1.9 eV, while maintaining large-area growth and device compatibility. In this work, we used a versatile and industrially scalable MoS2 growth method based on ionized jet deposition and annealing at 250 °C, through which a 3D stable and scalable material exhibiting excellent electronic and optical properties of 2D MoS2 is synthesized. The thickness-related limit, i.e., the desired optical and electronic properties being limited to 2D single/few-layered MoS2, was overcome in the thin film through the formation of encapsulated highly crystalline 2D MoS2 nanosheets exhibiting a bandgap of 1.9 eV and sharp optical emission. The newly synthesized 2D-in-3D MoS2 structure will facilitate device compatibility of 2D materials and confer superior optoelectronic device function.
Highlights
Two-dimensional (2D) transition metal dichalcogenides (TMDCs) such as MoS2 hold great potential for applications in nextgeneration optoelectronic devices, e.g., by overcoming the intrinsic limitation of graphene-related to its semi-metal character[1]
MoS2 are typically observed as a broad peak centred at ~650 nm (1.9 eV), commonly ascribed to A exciton complexes, i.e., a convolution of neutral (X0) and red-shifted charged excitons with linewidths around 50−100 meV2,40–43, whereas the X0 and T excitons are resolved in low-temperature PL spectra of encapsulated 2D-MoS2 reaching linewidths around 10 meV44–46
Whereas before annealing no PL signal is detected, after annealing the MoS2 remarkably displays a PL emission spectrum consisting of a minor X0 peak centred at 1902 meV (652 nm) and a sharp peak stemming from charged excitons located 47 meV below X0 with a linewidth of less than 10 meV
Summary
Two-dimensional (2D) transition metal dichalcogenides (TMDCs) such as MoS2 hold great potential for applications in nextgeneration optoelectronic devices, e.g., by overcoming the intrinsic limitation of graphene-related to its semi-metal character (i.e., zero bandgap)[1]. If 2D materials are used as electrodes (usually in form of a single or few-layered flake), the devices can fail due to disruption of the layer integrity These problems call for a synthesis method able to provide 2D materials possessing the desired properties, but with the strength of the bulk material. A competitive approach for low-cost and industrially scalable growth of materials is the ionized jet deposition (IJD), which is a pulsed electron deposition method developed by Noivion S.r.l. (Italy)[27,28,29] and optimized for MoS2 deposition in collaboration with the IMEM-CNR institute (Italy)[30] It is based on an ionized gas jet, which acts as source and carrier gas of pulsed electrons and in a later step as carrier gas (plasma) for the material to be deposited.
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