Composition- and Phase-Engineered Nanoscale WS2(1− x )Te2 x Alloyed Films for Broadband Photodetection and Surface-Enhanced Raman Sensing toward Molecular Recognition

Abstract Two-dimensional transition metal dichalcogenides (TMDs) offer strong light−matter interactions and tunable electronic properties, but the fixed bandgap of binary WS2 limits its optical response to the visible region. Alloy engineering provides an effective pathway to overcome this constraint by enabling continuous modulation of the band structure and controlled 2H−1T′ phase transitions. In particular, Te alloying in WS2 introduces substantial lattice distortion, narrows the bandgap, and enhances charge-transfer interactions, making WS2(1−x)Te2x promising for broadband photodetection and SERS sensing. However, achieving uniform and composition-controlled alloys is challenging using conventional chemical vapor deposition (CVD) methods. Here, we develop a chemical vapor reaction (CVR) strategy for composition and phase engineering of nanoscale WS2(1−x)Te2x alloy films through controlled S-to-Te chalcogen exchange. Using this approach, we obtain WS2(1−x)Te2x films spanning 2H- to 1T′-dominant regimes, with optimized photodetector performance in 2H-WS1.14Te0.86 and strong SERS enhancement in 1T′-WS0.41Te1.59. The alloys further demonstrate effective detection of melamine and Pseudomonas aeruginosa with excellent chemical stability. These results establish CVR-grown WS2(1−x)Te2x alloys as a versatile platform for broadband optoelectronics and molecular sensing.