Monolayer MoS 2 is an emerging two-dimensional semiconductor with wide-ranging potential applications in the next generation electronic and optoelectronic devices. Understanding the influences of the supporting substrates on the physical properties of grown MoS 2 is an important step toward its applications. Here we synthesized two typical rhomboid shaped MoS 2 on MoO 2 and triangle shaped MoS 2 on SiO 2 /Si substrates and characterized them by multiple means of X-Ray Photoemission Spectroscopy, Atomic Force Microscopy , Electrostatic Force Microscopy, Raman and Photoluminescence techniques. We found that triangle shaped MoS 2 exhibits different core level spectra compared with rhomboid shaped MoS 2 , attributed to dissimilar charge transfer with the underlying SiO 2 substrate. Interestingly, the triangle shaped MoS 2 single crystals exhibit distinct electrostatic and photoluminescence properties at center and edges. The underlying mechanism is proposed that partial decoupling of MoS 2 at edges from SiO 2 substrate induces different doping level and strain effects, resulting in anomalous physical properties at edges. The results reported here demonstrate that doping and strain effects induced by substrates have a significant influence on physical properties of monolayer triangle shaped MoS 2 ，which can be generally applicable to other transition metal dichalcogenides materials.
The friction influence of 2-D molybdenum disulfide (MoS 2 ) films deposited on different substrates (Si, SiO 2 and Al 2 O 3 ) by atomic layer deposition (ALD) has been investigated. All of the three substrates showed a trend of decreasing friction with increasing number of layers of MoS 2 , but the friction leveled off for more than 6 layers samples. Comparing these 2-D MoS 2 films with each other, MoS 2 on the Al 2 O 3 possesses the lowest friction, while MoS 2 on the Si possesses the highest one, owing to effect of substrate on the specific self-limiting reaction in ALD process. At the same time, the friction of the monolayer MoS 2 is strongest affected by sulfur deficient. As the number of layers increases, the influence of the substrate on the friction of MoS 2 can be approximately characterized by the work of adhesion. Greater work of adhesion corresponds to a higher friction force. When the thickness is more than 6 layers, the substrate effect disappears gradually. Moreover, the friction of 2-D MoS 2 could be controlled near linearly by changing plasma treatment time within the range from 1 to 20 s, which suggests a possible way for the friction control of 2-D MoS 2 on different substrate quasi-qualitatively or even qualitatively.
Chemical vapor deposition (CVD)-grown 2D materials like MoS 2 and WS 2 have been widely used for research and application. Here, we study substrates’ effects on CVD-grown MoS 2 and WS 2 . The morphology, crystalline quality and optical properties have been modified while changing substrates, which can be derived from lattice matching between 2D materials and substrate, defect/impurities on the interface and conductance/transparency of different substrates. The results provide suggestion for further study in CVD growth of 2D materials and device fabrications.
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