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The control of domain sizes provides a powerful means to engineer the characteristics of monolayer (ML) MoS2 films for specific applications including catalysts for hydrogen evolution and thin-film transistors. Here, we report an efficient way to control domain structures of MoS2 by substrate-dependent growth mode control. Deterministic control of growth modes, associated with catalytic intermediates, is introduced by utilizing different growth substrates in metal-organic chemical vapor deposition (MOCVD) of ML MoS2. Na-Mo-O eutectic alloys formed by a soda lime (SL) substrate dominate the growth based on a vapor-liquid-solid (VLS) process, resulting in large-crystalline domains of MoS2 with a reduced density of liquid nuclei. On the other hand, MoO3-x seeds formed from an alkali aluminosilicate (AA) substrate accelerate nucleation via a vapor-solid-solid (VSS) process for nanocrystalline domains. ML MoS2 of nanocrystalline domains resulted in efficient hydrogen evolution reactions (HERs), while large-domain films showed better electron conductivity. [ABSTRACT FROM AUTHOR]

Atomic-scaledefects strongly influence the electrical and optical properties ofmaterials, and their impact can be more pronounced in localized dimensions.Here, we directly demonstrate that strain triggers the formation ofoxygen vacancies in complex oxides by examining the tilt boundaryof SrTiO3bicrystals. Through transmission electron microscopyand electron energy loss spectroscopy, we identify strains along thetilt boundary and oxygen vacancies in the strain-imposed regions betweendislocation cores. First-principles calculations support that strains,irrespective of their type or sign, lower the formation energy ofoxygen vacancies, thereby enhancing vacancy formation. Finally, current–voltagemeasurements confirm that such oxygen vacancies at the strained boundaryresult in a decrease of the nonlinearity of the I–Vcurve as well as the resistivity. Ourresults strongly indicate that oxygen vacancies are preferentiallyformed and are segregated at the regions where strains accumulate,such as heterogeneous interfaces and grain boundaries. [ABSTRACT FROM AUTHOR]