Large Crystallographic Orientation Difference Contacts Induce Phase Transformation of WS2 Nanosheets from 2H to 1T
The synthesis of phase-pure 1T-WS2 remains a persistent challenge due to the thermodynamic metastability of the octahedral phase and the absence of a mechanistic understanding of the 2H-to-1T transformation at the atomic scale. This study demonstrates that when two 2H-WS2 grains with crystallographic orientation differences exceeding 10° are brought into contact at 1000 °C, they coalesce and transform into a single, pure 1T-WS2 grain devoid of orientation mismatch. First-principles calculations reveal a thermodynamic crossover at 280 K: below this temperature, 2H-WS2 is the stable phase, whereas above 280 K, 1T-WS2 becomes energetically favored. Kinetic analysis of nucleation shows that homogeneous nucleation of the 1T phase requires overcoming an energy barrier of 2.314 eV, while heterogeneous nucleation at the contact interface of two nanosheets necessitates only 0.005 eV, a reduction of nearly three orders of magnitude. This dramatic barrier lowering is attributed to the synergistic effect of elevated temperature and lattice mismatch-induced interfacial restructuring, which promotes atomic rearrangement and the formation of 1T-WS2 at the contact boundary. The 1T phase region subsequently expands, consuming the surrounding 2H nanosheets and yielding large-area, phase-pure 1T-WS2 films. This work establishes a straightforward, clean synthesis route for 1T-TMDs and provides a mechanistic framework for interface-driven phase engineering in two-dimensional materials.