Metal-to-semiconductor transition and enhanced photoconductivity in PtSe2 nanoflakes

The electronic transport properties of two-dimensional (2D) platinum diselenide (PtSe2) were systematically investigated. X-ray diffractometry, Raman spectroscopy, high-resolution transmission electron microscopy, and selected-area electron diffractometry were utilized to confirm the PtSe2 with the single crystalline 1T-phase structure. The mechanically exfoliated PtSe2 nanosheets exhibit semiconducting transport characteristic, which are different from their bulk counterparts with metallic nature. The room temperature conductivity at the range of 60–90 Ω−1 cm−1 is much lower than the values (2600 Ω−1 cm−1) of the metallic bulks. The exceptional photocurrent responses were also observed under different excitation wavelengths from 405 to 808 nm in the semiconducting PtSe2 nanoflakes. The highest photocurrent responsivity of 1100 A/W and photoconductive gain of 3300 were achieved at the excitation wavelength of 405 nm. The presence of acceptor-like surface states resulting in metal-to-semiconductor transition and enhanced photoconduction in the 1T-PtSe2 2D nanostructures were proposed and discussed.