Direct transition of a HfGeTe4 ternary transition-metal chalcogenide monolayer with a zigzag van der Waals gap

The ternary transition-metal chalcogenide HfGeTe4 is found to have a direct band gap of around 1.3 eV in its monolayer form, while it has an indirect band gap of about a half of that value in the bulk form. In contrast to the two-dimensional flat layers seen in most van der Waals solids, HfGeTe4 has zigzag shaped layers. The zigzag shape can allow a higher inter-layer cohesive energy and thus lead to better adhesion properties. The discovery of this novel transition metal ternary chalcogenide will open new avenue of materials exploration for future ultrathin electronics applications