Interfacial charge transfer is critical for the photocatalytic activities of compositional photocatalysts. In this work, we have developed a strategy of growing single-layer MoS2 sheets on the rutile TiO2(110) single-crystal surface using a chemical vapor deposition method. Both on-site and off-site characterizations confirmed the monolayer thickness and single crystallinity of the MoS2 adlayer as well as the atomic flatness of the composite surface. Without the presence of contamination, the charge flow across the interface of MoS2 and TiO2 is greatly enhanced, which hence favors the charge separation under excitations and boots up the catalytic activity of the composite system. Moreover, we found the luminescing property of MoS2 is significantly tailored upon coupling with the TiO2 surface. Our work has established a method for revealing the interface properties of the transition-metal dichalcogenides and oxide semiconductors at the atomic level.
The elaborate interface interactions can be critical in determining the achievable functionality of a semiconductor heterojunction (SH), particularly when two-dimensional material is enclosed in the system and its thickness is at an atomic extreme. In this work, we have successfully constructed a SH model system composed of typical transition-metal chalcogenide (TMDs) and transition metal oxides (TMO) by directly growing molybdenum sulfide (MoS2) nanosheets on atomically flat strontium titanate (SrTiO3) single crystal substrates through a conventional chemical vapor deposition (CVD) synthetic method. Multiple measurements have demonstrated the uniform monolayer thickness and single crystallinity of the MoS2 nanosheets as well as the atomic flatness of the heterojunction surface, both characterizing an extremely high quality of the interface. Clear evidence have been obtained for the electron transfer from the MoS2 adlayer to the SrTiO3 substrate which varies against the interface conditions. More importantly, the photoluminescence of MoS2 is significantly tailored, which is correlated with both the cleanness of the interface and the crystal orientation of the SrTiO3 substrate. These results not only shed fresh lights on the structure–property relationship of the TMDs/TMO heterostructures but also manifest the importance of the ideal interface structure for a hybridized system.
Molybdenum disulfide (MoS 2 ) has attracted considerable interest due to its superior electronic and optical properties, which have seen promising applications in optoelectronics and catalysis. Chemical vapor deposition (CVD) has been successfully applied in synthesizing MoS 2 on various substrates. However, it remains a great challenge to fabricate high-quality MoS 2 sheets with well-controlled micro/nano size and homogeneous distribution over the functional substrates such as active metal oxides. Herein, we have developed a two-step synthetic strategy via depositing MoO 3 first followed by subsequent vulcanization, to grow single-layer MoS 2 on an atomically flat rutile TiO 2 (110) (r-TiO 2 (110)) substrate. This method not only very well controls the size as well as the spatial distribution of MoS 2 nanosheets over the TiO 2 surface but also averts the formation of contaminative species at the heterojunction while maintaining the atomic structure of the substrate surface. The extensive characterizations reveal that the formation of MoS 2 derives from the sulfurization of the singly dispersed Mo 6+ and Mo 5+ species in the surface/subsurface region instead of the aggregated MoO 3 patches on top of the TiO 2 surface. Such a mechanism may dictate a general way for synthesizing high-quality transition-metal dichalcogenides (TMDs) over a variety of functional substrates.
Hybridization with oxide semiconductors provides a versatile strategy for tailoring physicochemical properties of two-dimensional materials (2DMs). However, the direct impacts of specific interface interactions have not yet been very well categorized, in particular at an atomic level. In the present work, through a chemical vapor deposition (CVD) method, we successfully grew monolayer MoS2 flakes on an atomically smooth rutile TiO2 single crystal with (100), (110), and (001) terminations. We found that the fabrication of comparable high-quality MoS2 on all of the TiO2 substrates can only be achieved via finely varying the growth parameters. Moreover, the photoluminescence of MoS2 also changes against the substrate terminations, showing a gradually reduced A 0/A – exciton ratio following the sequence of (100) > (110) > (001). Detailed X-ray photoelectron spectroscopy measurements showed the same tendency for the binding energy shifts of both Ti and O in the MoS2/TiO2 samples, which were attributed to the varied dipole fields established at the MoS2/TiO2 interfaces. Our work not only reinforces the important role of interface charge redistribution in tailoring the properties of hybridized systems but also emphasizes that the facet effect may be applied as an efficient strategy for optimizing the photocatalytic activities of compositional systems.
Distinguishing between normal, inflammatory, and progressing tumor cells plays a vital role in early diagnoses and clinical studies. The simultaneous quantification of multiple biomarkers in cells can reveal cellular heterogeneity, which contributes to the discrimination of different types of cells. Herein, a dual-channel fluorescent probe has been developed for monitoring peroxynitrite (ONOO–) and glutathione (GSH) to accurately discriminate normal cells, inflammatory cells, and progressing cancer cells. The probe can monitor exogenous and endogenous mitochondrial GSH and ONOO– in living cells and zebrafish by green (530 nm, G530) and red (630 nm, R630) emission based on its good selectivity and low biotoxicity. GSH and ONOO– are visualized via fluorescence imaging, and the corresponding output signals can be employed to differentiate nontumorigenic, malignant, and metastatic breast cells in cocultured cells. Furthermore, the accurate discrimination among normal, inflammatory, and cancerous cells is achieved through the changes in the dual-channel fluorescence signal, which shows great potential for the diagnosis of inflammation and cancer diseases.
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