Growth of large-area, uniform, and high-quality monolayer transition-metal dichalcogenides (TMDs) for practical and industrial applications remains a long-standing challenge. The present study demonstrates a modified predeposited chemical vapor deposition (CVD) process by employing an annealing procedure before sulfurization, which helps in achieving large-area, highly uniform, and high-quality TMDs on various substrates. The annealing procedure resulted in a molten liquid state of the precursors in the CVD process, which not only facilitated a uniform redistribution of the precursor on the substrate (avoid the aggregation) because of the uniform redistribution of the liquid precursor on the substrate but more importantly avoided the undesired multilayer growth via the selflimited lateral supply precursors mechanism. A 2 in. uniform and continuous monolayer WS 2 film has been synthesized on the SiO 2 /Si substrate. Moreover, uniform monolayer WS 2 single crystals can be prepared on more general and various substrates including sapphire, mica, quartz, and Si 3 N 4 using the same growth procedure. Besides, this growth mechanism can be generalized to synthesize other monolayer TMDs such as MoS 2 and MoS 2 /WS 2 heterostructures. Hence, the present method provides a generalized attractive strategy to grow large-area, uniform, single-layer two-dimensional (2D) materials. This study has significant implications in the advancement of batch production of various 2D-material-based devices for industrial and commercial applications.

Two-dimensional (2D) magnetic materials can be used to construct multifunctional electronic and spintronic devices attributed to their unique 2D restricted magnetic properties. However, some magnetic materials are non-van der Waals materials, and the substrate used in chemical vapor deposition (CVD) is usually a van der Waals substrate like mica. This kind of substrate can cause transfer problems and increase the complexity of equipment fabrication or magnetic measurement. It is meaningful to further optimize the current production process for realizing good repeatability and simple fabrication. Growing materials on SiO2/Si can directly make electronic devices and measure magnetic properties. Herein, we use potassium hydroxide to modify a SiO2/Si substrate and succeed in growing Cr2X3 (X = S, Se, and Te) directly on the SiO2/Si surface by a CVD method. OH– is attached to the surface of SiO2/Si, thereby inhibiting the growth of thin layered Cr2X3 along the [001] zone axis. Through density function theory calculation, it is verified that the formation energy of Cr2S3 and SiO2/Si heterojunction can be enlarged by introducing OH–, which is beneficial to the growth of Cr2X3 on the SiO2/Si surface. At the same time, we have also achieved Cr2S3 and Cr2Se3 with controlled size and thickness. The thinnest thickness of the three materials on SiO2/Si can be close to 1 unit cell. Cr2S3, Cr2Se3, and Cr2Te3 nanosheets exhibit ferrimagnetic, spin glass, and ferromagnetic behavior, respectively. This work can provide a new method for the growth of non-van der Waals 2D materials on SiO2/Si, and it is of great significance to the fabrication of spintronic devices.

Trivalent lanthanides are commonly incorporated into sodium yttrium fluoride nanocrystals to enhance their optical properties. Lanthanides are expected to randomly replace trivalent yttrium cations due to their isovalent nature, and the dopant−dopant distance decreases with increasing dopant concentration. Combining spectroscopy with quantum mechanical calculations, we find that large lanthanides exhibit an anisotropic distribution in the hexagonal yttrium sublattice at low dopant concentrations. This counterintuitive substitution suggests the formation of one-dimensional dimers or chains with short dopant−dopant distances. Our study of the distance-sensitive cross-relaxation between Nd 3+ dopants in β-NaYF 4 nanocrystals confirms that the concentration quenching threshold is lower than that of their cubic counterparts, consistent with the proposed chain-like model. Moreover, we demonstrate modulation of the anisotropic distribution by microstrain management via alkali metal codoping. Research into dopant distribution in inorganic crystals may enable the development of new materials and properties for future challenges.