Unraveling Anomalous Dielectric Phase Transition in Few-Layered 2H/1T MoS<sub>2</sub> Nanosheets
Charu Sharma, Simadri Badatya, Avanish Kumar Srivastava, Manoj Kumar Gupta
Abstract
In the present work, highly crystalline molybdenum disulfide (MoS2) nanosheets were grown by a simple and cost-effective hydrothermal route. An anomalous structural phase transition in MoS2 nanosheets was observed in dielectric investigation. X-ray diffraction confirmed the formation of a hexagonal crystal phase in few-layer MoS2 nanosheets. High-resolution transmission electron microscopy and atomic force microscopy results also confirmed the formation of few-layer MoS2 nanosheets. Raman investigation reveals the formation of few-layer MoS2 nanosheets with the coexistence of dual semiconducting (2H) and metallic (1T) phases. In dielectric studies, a very high dielectric constant (ε′) of 2612 and an unusual dissipation factor of 250 were observed at 1 kHz frequency at room temperature compared to bulk MoS2 (ε′ ∼ 19). The unusual high dielectric constant and high dissipation factor from MoS2 nanosheets may be due to the nanoscale-driven large polarization density and coexistence of the metallic phase in MoS2, respectively. An anomalous phase transition at 62 and 102 °C was also observed in the temperature-dependent dielectric analysis. Such phase transition in MoS2 nanosheets may be associated with the crystal structure (2H-1T′) and the presence of sulfur vacancy in MoS2. AC conductivity and activation energy of few-layer MoS2 nanosheets were calculated in various temperature and frequency ranges. Charge conduction behavior is analyzed in terms of metallic and semiconducting behavior of MoS2 nanosheets. The present experimental study sheds light on the phase transition mechanism not only for dual-phase nanoscale MoS2 but also for other two-dimensional transition metal dichalcogenide materials for their application in next-generation electronic devices.