Defect-Dependent Surface Phase Transformation on 1T-TiS₂ Assisted by Water

The phase transformation from the TiS2 to TiS on the surface of bulk 1T-TiS2 crystals is achieved by thermal vacuum annealing. This is demonstrated by a combination of photoemission spectroscopy, electron paramagnetic resonance spectroscopy, and Raman spectroscopy. The chemical interaction between TiS2 and surface-adsorbed H2O molecules is expected to assist this transformation. Especially, the transformation temperature is found to depend on the natural defects present in the TiS2 crystals. Ti interstitial (Tii) and S vacancy (Sv) defects hinder TiS2 to TiS transformation, whereas Ti-OH species facilitate the phase transformation. These results not only provide a valuable insight into the water-assisted phase transformation modulated by defects but also highlight a potential strategy for designing an unusual TiS2-TiS heterostructure through a combination of phase and defect engineering.