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.

The presence of cuprous oxide results in band bending at the interface between cuprous phosphide and cuprous oxide, forming carrier traps, which improves the fluorescence properties of cuprous phosphide.

No abstract

No abstract

Two-dimensional (2D) layered transition-metal dichalcogenides (TMDCs), for example, MoS2 and WS2, are gaining widespread attention at present because of their distinct physical properties. Developing the deeper potential of 2D TMDCs demands fine spatial modulation of chemical compositions and electrical performance to produce desired heterostructures. In this study, we report a one-step chemical vapor deposition synthesis of compositionally tunable WS2–Mo1–x W x S2 vertical heterostructures by adjusting the stacking sequence of Mo/W films as the precursors. Detailed Raman and photoluminescence analyses confirm that as-grown samples present clear structural and optical modulations. The evolution of these heterostructures with different composition ranges is discussed on the basis of the tunable vapor pressure. The present study provides an alternative strategy to facilitate the development of 2D semiconductor heterostructures, which is an essential step toward realizing functional electronics and optoelectronics.

This review summarizes recent advances in the controllable CVD growth of 2D TMDC vertical heterostructures under four different strategies.