Defect engineering is a promising means to create patterns on two-dimensional (2D) materials to enable unconventional properties. However, defects usually exist abundantly and randomly on 2D materials, which makes it difficult to tune the properties in a controllable manner. Therefore, it is highly desirable to find out the formation mechanism and controllable fabrication method of defects on 2D materials. In this report, we systematically investigated the line defects on monolayer MoS2 formed by introducing oxygen during the CVD growth. The line defects were formed due to the overoxidation of the MoS2 flake along crystal boundaries, which bulged out of the surface and had the same surface potential as the basal plane. Therefore, the MoS2 flake with line defects maintained the optical and electrical integrity but exhibited distinct properties as compared to the pristine one. By controlling the oxygen concentration during CVD growth, the density of the line defects can be precisely controlled to implement controllable property tuning. Moreover, during the transfer process, the MoS2 flake was easily broken along the line defects, which increased the active sites to achieve enhanced hydrogen evolution reaction performance. This work is expected to inspire the development of patterned functional 2D materials by defect engineering.
Beta-phase gallium sesquioxide ( β -Ga 2 O 3 ), possessing an ultrawide bandgap and high breakdown voltage, exhibits strong potential for deep-ultraviolet photodetection and high-power electronics. However, nanometer-scale line defects, prevalent in β -Ga 2 O 3 growth, degrade device performance by increasing leakage currents and reducing breakdown voltages, thus termed “killer defects”. Critically, the impact of these defects at the atomic scale remains unclear due to limited characterization and a lack of detailed understanding. Here, the observation of novel conductive atomic line defects is reported within β -Ga 2 O 3 nanoflakes using near-field infrared imaging. Combining atomic-resolution imaging with density functional theory calculations, these defects are identified as interstitial Ga atoms migrating along the c -axis. These atomic line defects exhibit a broadband infrared response and quenched cathodoluminescence, indicative of significantly enhanced local conductivity. This elevated conductivity enables subsurface near-field detection of the defects and remote excitation of phonon polaritons in a hexagonal boron nitride ( h BN) capping layer. These findings underscore the distinct conductivity of atomic-scale line defects, emphasizing the need for their controlled management during material synthesis and device fabrication, while simultaneously suggesting opportunities for their exploitation in nanophotonic applications.
Yuyu Bu,Jun Ren,Huawei Zhang,Dongjiang Yang,Zhuoyuan Chen,Jin-Ping Ao
Point defects, such as oxygen vacancies in semiconductors, have been widely proven to influence the separation and transfer processes of the photogenerated hot charges. Besides point defects, to date, scarcely any study has focused on expounding the functions of line defects (such as dislocations) in the crystal of semiconductor photoanodes and influencing the photogenerated hot charge separation process. Herein, a nanoflower (NF)-like WO3 single-crystal thin film photoanode with edge dislocations is reported. The dislocation induces mismatch of the (002) and (020) facets. Further photoelectrochemical (PEC) performance and DOS calculation results indicate that a heterojunction system could be formed along the edge dislocations due to the energy difference between the mismatched (002) and (020) facets. Therefore, this present study provides an understanding of the line defect in the photogenerated hot carrier separation process and a novel method to improve the properties of photoelectrodes and photocatalytic materials in the near future.
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