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

• Published in: Physica status solidi. PSS-RRL. Rapid research letters 2019-02, Vol.13 (2), p.n/a
• Main Authors: Lee, Weon‐Gyu, Chae, Sudong, Chung, You Kyoung, Oh, Seungbae, Choi, Jae‐Young, Huh, Joonsuk
• Format: Article
• Language: English
• Subjects: Bonding strength; Bulk density; Bundles; Bundling; Chains; Density functional theory; direct band gap transition; Energy gap; Material properties; Nanowires; Nb2Se9; one‐dimensional materials; Photoluminescence; Transition metal compounds
• ISSN: 1862-6254; 1862-6270
• DOI: 10.1002/pssr.201800517

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. One‐dimensional (1D) Nb2Se9 is successfully synthesized recently. The theoretical study by density functional theory indicates that the 1D nanowire of Nb2Se9 is a direct band gap semiconductor, while the bulk structure has an indirect band gap. This implies that the 1D Nb2Se9 single‐chain atomic crystal can interact with light without vibrational motion.