Abstract
Vertically-oriented two-dimensional (2D) tungsten disulfide (WS2) nanosheets were successfully grown on a Si substrate at a temperature range between and 550 °C via the direct chemical reaction between WCl6 and S in the gas phase. The growth process was carefully optimized by adjusting temperature, the locations of reactants and substrate, and carrier gas flow. Additionally, vertically-oriented 2D WS2 nanosheets with a few layers were tested as a surface-enhanced Raman scattering substrate for detecting rhodamine 6G (R6G) molecules where enhancement occurs from chemical enhancement by charge transfer transition from semiconductor). Raman spectra of R6G molecules adsorbed on vertically-oriented 2D WS2 nanosheets exhibited strong Raman enhancement effects up to 9.2 times greater than that on the exfoliated WS2 monolayer flake sample. From our results, we suggest that the WS2 nanosheets can be an effective surface-enhanced Raman scattering substrate for detecting target molecules.
Highlights
Considerable attention has been devoted to two-dimensional (2D) materials as promising functional materials, in particular to transition metal dichalcogenides (TMDCs) [1,2,3,4], due to rapid advances in synthesis, transfer, spectroscopic detection, and manipulation
The density of vertically-oriented 2D WS2 nanostructures gradually decreased likely because 2D WS2 nanosheets with larger sizes formed due to the faster growth rate at higher temperature
The favorable vertical orientation of the 2D WS2 nanosheets might be attributed to the compression and extrusion between WS2 island layers initially formed on the Si substrate [16]
Summary
Considerable attention has been devoted to two-dimensional (2D) materials as promising functional materials, in particular to transition metal dichalcogenides (TMDCs) [1,2,3,4], due to rapid advances in synthesis, transfer, spectroscopic detection, and manipulation. Among 2D TMDCs, tungsten disulfide (WS2 ), with direct optical band gaps of 1.35 and 2.05 eV for bulk and monolayer structure, is of great interest due to its particular semiconducting behavior, intrinsic electrical conductivity, and electrocatalytic property when the number of layers is lower [9,10,11]. A variety of synthetic methodologies were suggested to grow single and few-layer nanosheets of the high-quality 2D WS2 , the synthesis and characterization of vertically-oriented 2D. We described a novel growth process and its characterizations of vertically-oriented WS2 nanosheets have rarely been reported [13,14,15,16].
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