as core materials for future spintronics given their potential for high Curie temperature (T C ) and efficient field-tunable magnetic properties. [1][2][3] Despite half-century-long research efforts, the following three primary issues remain unsolved: i) the uncertain origin of ferromagnetism, called phantom ferromagnetism, owing to a lack of structural analysis of nanodefects; [4,5] ii) solubility limit to only a few percent without forming aggregation; [6] and iii) activation of short-range antiferromagnetic transitions in the high-dopingconcentration regime, [7] which limits the improvement of the magnetic moment and T C .The recent emergence of magnetic order in 2D van der Waals layered materials, which is enabled by strong magnetic anisotropy, [8] has stimulated interest in 2D-DMSs owing to their exotic spindependent physical properties, including long spin-relaxation time, light-controlled magnetism, [9] and spin-valley locking, inherent to their atomically thin nature. [10][11][12] In particular, transition metal dichalcogenide (TMD) semiconductors with magnetic dopants synthesized via chemical vapor deposition (CVD) offer room-temperature T C and gate-tunable magnetism. [13][14][15] Although vanadium dopants in WSe 2 and WS 2 semiconductors have been successfully distributed randomly without aggregation to a relatively high doping concentration of approximately 10%, their saturation magnetization is still limited to approximately 10 −5 emu cm −2 , thus making further analysis and applications difficult. [14,15] While magnetism has been proposed for inducing various defects such as vacancies, [16] anti-sites, [17] and grain boundaries [18] in III-V, oxides, and nitride DMSs, the underlying mechanism of magnetism is little known mainly due to the lack of structural analysis. On the contrary, because of facile monolayer growth, a variety of defects, including transition metal and chalcogen vacancies in 2D-TMDs, can be precisely analyzed using state-of-the-art scanning transmission electron microscopy (STEM) with atomic elemental mapping. [19] This affords the possibility of elucidating the origins of magnetism from defects and further enhancing magnetic order by tailoring intrinsic defects and impurities in 2D-TMD semiconductors. Here, we present a comprehensive atomic analysis of Se-vacancy defects Magnetic order has been proposed to arise from a variety of defects, including vacancies, antisites, and grain boundaries, which are relevant in numerous electronics and spintronics applications. Nevertheless, its magnetism remains controversial due to the lack of structural analysis. The escalation of ferromagnetism in vanadium-doped WSe 2 monolayer is herein demonstrated by tailoring complex configurations of Se vacancies (Se Vac ) via post heat-treatment. Structural analysis of atomic defects is systematically performed using transmission electron microscopy (TEM), enabled by the monolayer nature. Temperature-dependent magnetoresistance hysteresis ensures enhanced magnetic order after high-temperature heat-tre...

Atomic dopants and defects play a crucial role in creating new functionalities in 2D transition metal dichalcogenides (2D TMDs). Therefore, atomic‐scale identification and their quantification warrant precise engineering that widens their application to many fields, ranging from development of optoelectronic devices to magnetic semiconductors. Scanning transmission electron microscopy with a sub‐Å probe has provided a facile way to observe local dopants and defects in 2D TMDs. However, manual data analytics of experimental images is a time‐consuming task, and often requires subjective decisions to interpret observed signals. Therefore, an approach is required to automate the detection and classification of dopants and defects. In this study, based on a deep learning algorithm, fully convolutional neural network that shows a superior ability of image segmentation, an efficient and automated method for reliable quantification of dopants and defects in TMDs is proposed with single‐atom precision. The approach demonstrates that atomic dopants and defects are precisely mapped with a detection limit of ≈1 × 1012 cm−2, and with a measurement accuracy of ≈98% for most atomic sites. Furthermore, this methodology is applicable to large volume of image data to extract atomic site‐specific information, thus providing insights into the formation mechanisms of various defects under stimuli.

Photoinduced generation of mobile charge carriers is the fundamental process underlying many applications, such as solar energy harvesting, solar fuel production, and efficient photodetectors. Monolayer transition-metal dichalcogenides (TMDCs) are an attractive model system for studying photoinduced carrier generation mechanisms in low-dimensional materials because they possess strong direct band gap absorption, large exciton binding energies, and are only a few atoms thick. While a number of studies have observed charge generation in neat TMDCs for photoexcitation at, above, or even below the optical band gap, the role of nonlinear processes (resulting from high photon fluences), defect states, excess charges, and layer interactions remains unclear. In this study, we introduce steady-state microwave conductivity (SSMC) spectroscopy for measuring charge generation action spectra in a model WS2 mono- to few-layer TMDC system at fluences that coincide with the terrestrial solar flux. Despite utilizing photon fluences well below those used in previous pump–probe measurements, the SSMC technique is sensitive enough to easily resolve the photoconductivity spectrum arising in mono- to few-layer WS2. By correlating SSMC with other spectroscopy and microscopy experiments, we find that photoconductivity is observed predominantly for excitation wavelengths resonant with the excitonic transition of the multilayer portions of the sample, the density of which can be controlled by the synthesis conditions. These results highlight the potential of layer engineering as a route toward achieving high yields of photoinduced charge carriers in neat TMDCs, with implications for a broad range of optoelectronic applications.