Defects play an indispensable role in tuning the optical properties of twodimensional materials. Herein, we study the influence of defects on the photoluminescence and resonance Raman spectra of as-grown monolayer (1L) WS 2 . Increasing the density of defects significantly lowers the excitonic binding energy by up to 110 meV. These defect-modified excitonic binding energies in 1L-WS 2 strongly mediate the Raman resonance condition, resulting in unexpected Raman intensity variations in the LA(M), 2LA(M), and A 1 ′(Γ) phonon modes. The sample with the highest density of defects exhibits an almost temperature-independent resonance in different Raman modes at low temperature, whereas the samples with low densities of defects exhibit a clear resonance with decreasing temperature. This study will further increase our understanding of the role of defects in resonance Raman spectroscopy and of the phonon−exciton interaction in 1L-WS 2 .

The growth mechanism and optical performance of MoS2 crystals have been systemically studied by manipulating the growth parameters.

Vertical heterostructures of two-dimensional (2D) transition metal dichalcogenides (TMDCs) provide a prospective foreground for practical applications via combining novel physical characteristics that are distinguished from those of traditional counterparts. Here, we report the position-selective growth of 2D WS 2 -based vertical heterostructures, including WS 2 /MoS 2 , WS 2 /MoS 2 -Mo 0.42 W 0.58 S 2 , WS 2 /MoS 2 -Mo 1−x W x S 2 (0.4 ≤ x ≤ 0.85), and WS 2 /Mo 1−x W x S 2 (0 ≤ x ≤ 0.76), with the WS 2 monolayer as the top layer by a one-step chemical vapor deposition (CVD) method. Systematical Raman and photoluminescence (PL) characterizations corroborate that position-dependent vertical heterostructures exhibit a significant relationship between structural/optical characteristics and compositions. A possible growth mechanism of various 2D WS 2 -based heterostructures at different deposition regions is discussed based on the variation of metallic atoms along the gas flow direction. The current work supplies a promising and efficient strategy to fabricate complex heterostructures composed of various TMDCs, which is a crucial step to develop functional optoelectronic applications.