Exfoliable Transition Metal Chalcogenide Semiconductor NbSe₂I₂

As the field of exfoliated van der Waals electronics grows to include complex heterostructures, the variety of available in-plane symmetries and geometries becomes increasingly valuable. In this work, we present an efficient chemical vapor transport synthesis of NbSe₂I₂ with the triclinic space group P1̅. This material contains Nb-Nb dimers and an in-plane crystallographic angle γ = 61.3°. We show that NbSe₂I₂ can be exfoliated down to few-layer and monolayer structures and use Raman spectroscopy to test the preservation of the crystal structure of exfoliated thin films. The crystal structure was verified by single-crystal and powder X-ray diffraction methods. Density functional theory calculations show triclinic NbSe₂I₂ to be a semiconductor with a band gap of around 1 eV, with similar band structure features for bulk and monolayer crystals. The physical properties of NbSe₂I₂ have been characterized by transport, thermal, optical, and magnetic measurements, demonstrating triclinic NbSe₂I₂ to be a diamagnetic semiconductor that does not exhibit any phase transformation below room temperature.