Synthesis and characterization of WSe2 nanosheets and WS2 quantum dots for electronics and optoelectronics device applications

Abstract

Two-dimensional (2D) transition metal dichalcogenide (2D-TMDC) semiconductors have attracted significant attention because of their unique physical properties which are very important for fundamental and applied research. Due to the variety of properties owing to their layer dependent optical bandgap variation efficient charge transfer and strong light-matter interactions; TMDC materials provides a stand that allows to create of larger range of device for various applications. In recent advances, in the development of nanostructures of 2D materials, the zero-dimensional (0D) quantum dots (QDs) offered new possibilities for the broad range photodetectors, bio imaging, batteries, electrochemical water splitting and optoelectronic applications because of their intriguing optical, electrical, catalytic and electrochemical properties. QDs derived from TMDC, specifically molybdenum disulfide (MoS2), are gaining popularity due to their advantageous properties in optoelectronics, imaging, and sensors. Despite this, little research has been conducted to synthesize and investigate photoluminescent 0D Tungsten disulfide (WS2) QDs, particularly using a bottom-up approach without the use of typical toxic organic solvents. TMDCs nanosheets (NSs) are ultrathin two-dimensional materials that are fundamentally and technologically intriguing. They are more chemically versatile than graphene sheets. Mono- or few-layered TMDCs are direct/indirect-bandgap semiconductors with varying bandgap energy and carrier type (n- or p-type) depending on composition, structure, and dimensionality. In this thesis, we will discuss about the recent research advancement with emphasising on synthesis, optical and structural characterization of WSe2 NSs on n-Si substrate and WS2 QDs on p-Si substrate. Here I present a simple bottom-up strategy for producing high-quality water-soluble tungsten disulfide (WS2) QDs via hydrothermal reaction with sodium tungstate dihydrate and L-cysteine as W and S sources. Along with, we have also synthesised tungsten diselenide (WSe2) nanosheets by using hydrothermal technique using Sodium tungstate dihydrate (Na2WO4·2H2O)) as a precursor, Se-powder and sodium borohydride acts as selenium source as a reducing agent and using DMF (N, N-dimethylformamide) as solvent. Further, the surface morphology, crystal structure and sources. Along with, we have also synthesised tungsten diselenide (WSe2) nanosheets by using hydrothermal technique using Sodium tungstate dihydrate (Na2WO4·2H2O)) as a precursor, Se-powder and sodium borohydride acts as selenium source as a reducing agent and using DMF (N, N-dimethylformamide) as solvent. Further, the surface morphology, crystal structure and optical properties, were investigated using Scanning & Tunnelling electron microscopy, X-ray diffraction, photoluminescence, UV–visible and Raman spectroscopies.