Edge Defect-Free Anisotropic Two-Dimensional Sheets with Nearly Direct Band Gaps from a True One-Dimensional Van der Waals Nb₂Se₉ Material

Abstract

Dangling-bond-free two-dimensional (2D) materials can be isolated from the bulk structures of one-dimensional (1D) van der Waals materials to produce edge-defect-free 2D materials. Conventional 2D materials have dangling bonds on their edges, which act as scattering centers that deteriorate the transport properties of carriers. Highly anisotropic 2D sheets, made of 1D van der Waals Nb2Se9 material, have three planar structures depending on the cutting direction of the bulk Nb2Se9 crystal. To investigate the applications of these 2D Nb2Se9 sheets, we calculated the band structures of the three planar sheets and observed that two sheets had nearly direct band gaps, which were only slightly greater (0.01 eV) than the indirect band gaps. These energy differences were smaller than the thermal energy at room temperature. The 2D Nb2Se9 plane with an indirect band gap had the shortest interchain distance for selenium ions among the three planes and exhibited significant interchain interactions on the conduction band. The interchain strain induced an indirect-to-direct band gap transition in the 2D Nb2Se9 sheets. These 2D sheets of Nb2Se9 with direct band gaps also had different band structures because of different interactions between chains, implying that they can have different charge mobilities. We expect these dangling-bond-free 2D Nb2Se9 sheets to be applied in optoelectronic devices because they allow for nearly direct band gaps. They can also be used in mechanical sensors because the band gaps can be controlled by varying the interchain strain.

Tunable Layer Orientation and Morphology in Vapor–Liquid–Solid Growth of One-Dimensional GeS van der Waals Nanostructures

“…Recently a particular class of semiconductor nanostructures has emerged1D nanowires of 2D van der Waals crystals, which combine the distinct structure of layered materials, i.e., covalent bonding within the layers and weak van der Waals bonding between them, and 1D confinement achieved in nanowires. This is distinct from efforts of separating quasi-1D nanostructures by exfoliation from bulk materials made possible by the presence of anisotropy in the crystal structure of transition-metal trichalcogenides such as TiS 3 , , TaSe 3 , , ZrSe 3 , NbS 3 , Sb 2 Se 3 , , Ta 2 Pd 3 Se 8 , as well as 1D nanostructures in which the van der Waals units represent true 1D chains (V 2 Se 9 , Nb 2 Se 9 , etc.). It is well established that nanowires of conventional 3D semiconductors grow with a preferred crystal orientation, e.g., with the symmetry axis along the [111] direction for Si and Ge nanowires .…”

Ternary Transition Metal Chalcogenide Nb2Pd3Se8: A New Candidate of 1D Van der Waals Materials for Field‐Effect Transistors

“…[20,21] Besides TMTCs, other 1D-vdW materials such as Te, Nb 2 Se 9 , and Sb 2 X 3 (X = S or Se) have the structural advantage of dangling bond-free on their edges as well as surfaces, which act as charge carrier scattering sites that deteriorate the transport property. [22][23][24][25] In addition, it was theoretically proved that some of the 1D-vdW materials exhibit thickness-dependent bandgap properties with indirectto-direct transition. [26][27][28] Based on these aspects, 1D nanowire materials are expected to promote development in the electronic application, but there are still many things to be explored in terms of material diversity.…”

Ta2Ni3Se8: 1D van der Waals Material with Ambipolar Behavior

“…[14][15][16][17] Especially, 1D vdW materials possessing strong covalent intrachain bonds and weak interchain vdW interactions have the structural advantage of dangling bonds-free on their edges, which act as charge carrier scattering sites that deteriorate the transport property. [18][19][20][21] Moreover, it was theoretically confirmed that some of the 1D vdW materials exhibit thickness-dependent properties, such as the bandgap expansion with the indirect-to-direct transition as the number of unit chains decrease from their bulk crystal, similar to well-studied transition metal dichalcogenides (TMDs). [22][23][24][25] Based on this aspect, numerous studies have been conducted to utilize 1D nanowires in functional electronic devices such as FET [26][27][28][29] and photodetectors, [30][31][32][33] but diversity among promising materials is still limited.…”