New One‐Dimensional Material Nb₂Se₉: Theoretical Prediction of Indirect to Direct Band Gap Transition due to Dimensional Reduction

Abstract

Layered two‐dimensional (2D) transition metal dichalcogenides (TMDCs) often form 2D sheets and some of these show an indirect to direct band gap transition as the number of layers decreases from that of the bulk structure. Recently, a new one‐dimensional (1D) material of Nb2Se9 is successfully prepared by solid state reaction. This material is semiconducting and composed of periodically stacked single‐chain atomic crystals (SCAC) where the SCACs form inorganic bulk crystals due to strong bonds within the chain but with weak inter‐chain interactions. To determine the potential applications of our newly developed 1D nanowire, theoretical prediction of its material properties is performed. As a first step, the band structures of bundles of Nb2Se9 SCACs, which are composed of 1–7 single chains, are calculated by using density functional theory. Unlike the bulk structure of Nb2Se9, the chain bundles composed of up to 21 single SCACs would have a direct band gap. Accordingly, it is expected that an Nb2Se9 bundle SCAC with a diameter of 3.6 nm can cause the electronic transition without being disturbed by the phononic environment due to the direct band gap, and can therefore be used in photoluminescence applications.

Indirect-To-Direct Band Gap Transition of One-Dimensional V2Se9: Theoretical Study with Dispersion Energy Correction

“…35 These phenomena are mainly caused by vdW interchain interactions. Previous studies of metal chalcogenides used only the generalized gradient approximation method, 35,47,48 which cannot properly describe vdW effects; therefore, further calculations were performed to incorporate vdW interactions. 36,49 We chose the DFT-D3 method, which introduces the dispersion energy correction proportional to 1/ r 6 .…”

Ta2Ni3Se8: 1D van der Waals Material with Ambipolar Behavior

“…[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. Therefore, it is necessary to discover new types of 1D materials, verify their electronic properties, and expand the potential candidates for future electronic device applications.…”

The effect of the metal and selenium precursors on the properties of NbSe2and Nb2Se9nanostructures and their application in dye-sensitized solar cells

“… 23 The weak van der Waals forces are responsible for the easy sliding of the layers relative to one another, thus providing a favourable matrix for intercalation reactions and exfoliation. 24 The coordination around the Nb atom can either be a distorted octahedral or trigonal prismatic. 23 On the other hand, Nb 2 Se 9 is a new 1D material made up of periodically stacked single-chain atomic crystals, which form the inorganic bulk of the crystals due to strong covalent bonds within the chain and weak van der Waals interaction between the chains, as shown in Fig.…”