Distinct electronic and transport properties between 1T-HfSe₂ and 1T-PtSe₂

In this study, we employed the first-principles calculation to investigate the structural, electronic and transport properties of 1T-HfSe₂ and 1T-PtSe₂ transition metal dichalcogenides, and further explain why they share the same 1T (octahedral) layered structure but exhibit very different electronic and transport properties. There are two underlying concepts: the degree of interlayer bond ionicity and the number of 5d valence electrons of transition metal. The high degree of Hf-Se bond ionicity not only gives rise to the indirect energy gap of HfSe₂ bulk and thin films, but also results in the weak Se-Se vdW interlayer coupling to further restrict the electron transport only within a HfSe₂ layer. On the other hand, the modulation of metallic/semiconducting property of PtSe₂ bulk and thin films can be understood by the significant vdW interlayer coupling, which induces charge redistribution of Se atom and allows electrons to transport within a PtSe₂ layer as well as cross neighboring layers. Finally, our transport calculation for 1T-HfSe₂/1T-PtSe₂ bulks and monolayers suggests the great electron transport within Hf-Se/Pt-Se layer but suppresses/allows electron from neighboring layers. The robust two-dimensional characteristic of 1T-HfSe₂ and the metal-to-semiconductor transition of 1T-PtSe₂ may provide more knowledge for future application in nanoelectronic and optoelectronic devices.