Controllable synthesis of 2D layered 3‐rhombohedral phase WS2 and WSe2 atomic layers with full‐covered top layers is realized by physical vapor deposition. Compared to the 2‐hexagonal phase, 3‐rhombohedral phase layers show unique photoluminescence and Raman spectra, and more importantly quadratically increasing second harmonic generation intensity with respect to layer numbers, which is promising for nonlinear optics. Abstract 2D layered 3‐rhombohedral (3R) phase transition metal dichalcogenides (TMDs) have received significantly increased research interest in nonlinear optical applications due to their unique crystal structures and broken inversion symmetry. However, controlled growth of 2D 3R phase TMDs still remains a great challenge. In this work, a direct growth of large‐area WS2 and WSe2 atomic layers with controllable crystal phases via a developed temperature selective physical vapor deposition route is reported. Large‐area triangular 3R phase layers are synthesized at a lower deposition temperature. Steady state and time‐resolved photoluminescence spectroscopy and Raman spectroscopy are used to study the unique properties of 3R phase layers due to different layer stacking and interlayer coupling. More importantly, with broken inversion symmetry, 3R phase layers show a quadratically increased second harmonic generation (SHG) intensity with respect to layer numbers. Furthermore, by polarization‐resolved SHG, a uniform polarization preference is observed in bilayer and trilayer 3R phase WS2, which could be a benefit for practical applications. The results not only contribute to the controlled growth of 2D TMDs layers with different phases but also pave the way to promising nonlinear optical devices.
Published in: "Advanced Functional Materials".