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.

Recently, we synthesized a one-dimensional (1D) structure of V2Se9. The 1D V2Se9 resembles another 1D material, Nb2Se9, which is expected to have a direct band gap. To determine the potential applications of this material, we calculated the band structures of 1D and bulk V2Se9 using density functional theory by varying the number of chains and comparing their band structures and electronic properties with those of Nb2Se9. The results showed that a small number of V2Se9 chains have a direct band gap, whereas bulk V2Se9 possesses an indirect band gap, like Nb2Se9. We expect that V2Se9 nanowires with diameters less than ∼20 Å would have direct band gaps. This indirect-to-direct band gap transition could lead to potential optoelectronic applications for this 1D material because materials with direct band gaps can absorb photons without being disturbed by phonons.

Comparison of density functionals for energy and structural differences between the high-[ 5 T 2g :(t 2g) 4 (e g) 2 ] and low-[ 1 A 1g :(t 2g) 6 (e g) 0 ] spin states of iron(II) coordination compounds. II. More functionals and the hexaminoferrous cation, [ Fe (NH 3) 6 ] 2+ We analyze the low-energy electronic structure of a series of symmetric cationic diarylmethanes, which are bridge-substituted derivatives of Michler's Hydrol Blue. We use a four-electron, three-orbital complete active space self-consistent field and multi-state multi-reference perturbation theory model to calculate a three-state diabatic effective Hamiltonian for each dye in the series. We exploit an isolobal analogy between the active spaces of the self-consistent field solutions for each dye to represent the electronic structure in a set of analogous diabatic states. The diabatic states can be identified with the bonding structures in classical resonance-theoretic models of cyanine dyes. We identify diabatic states with opposing charge and bond-order localization, analogous to the classical resonance structures, and a third state with charge on the bridge. While the left-and right-charged structures are similar for all dyes, the structure of the bridge-charged diabatic state, and the Hamiltonian matrix elements connected to it, change significantly across the series. The change is correlated with an inversion of the sign of the charge carrier on the bridge, which changes from an electron pair to a hole as the series is traversed.

In this work, high-quality 1D van der Waals (vdW) Nb 2 Pd 3 Se 8 is synthesized, showing an excellent scalability from bulk to single-ribbon due to weakly bonded repeating unit ribbons. The calculation of electronic band structures confirmed that this novel Nb 2 Pd 3 Se 8 is a semiconducting material, displaying indirect-to-direct bandgap transition with decreasing the number of unit-ribbons from bulk to single. Field effect transistors (FETs) fabricated on the mechanically exfoliated Nb 2 Pd 3 Se 8 nanowires exhibit n-type transport characteristics at room temperature, resulting in the values for the electron mobility and I on /I off ratio of 31 cm 2 V −1 s −1 and ≈10 4 , respectively. Through transport measurements at various temperatures from room temperature down to 90 K, it is confirmed that Nb 2 Pd 3 Se 8 FETs can achieve negligible Schottky barrier height (SBH) for the Au contacts at the temperature range, displaying clear ohmic contact characteristics. Furthermore, top-gated FETs fabricated with the Al 2 O 3 dielectric layer are studied simultaneously with back-gated FETs.

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.

In this study, high‐purity and centimeter‐scale bulk Ta2Ni3Se8 crystals are obtained by controlling the growth temperature and stoichiometric ratio between tantalum, nickel, and selenium. It is demonstrated that the bulk Ta2Ni3Se8 crystals could be effectively exfoliated into a few chain‐scale nanowires through simple mechanical exfoliation and liquid‐phase exfoliation. Also, the calculation of electronic band structures confirms that Ta2Ni3Se8 is a semiconducting material with a small bandgap. A field‐effect transistor is successfully fabricated on the mechanically exfoliated Ta2Ni3Se8 nanowires. Transport measurements at room temperature reveal that Ta2Ni3Se8 nanowires exhibit ambipolar semiconducting behavior with maximum mobilities of 20.3 and 3.52 cm2 V−1 s−1 for electrons and holes, respectively. The temperature‐dependent transport measurement (from 90 to 295 K) confirms the carrier transport mechanism of Ta2Ni3Se8 nanowires. Based on these characteristics, the obtained 1D vdW material is expected to be a potential candidate for additional 1D materials as channel materials.

In the present study, the experimental Raman spectrum of niobium‐selenide nanowires (Nb2Se9) is reported for the first time followed by an analysis of the Raman spectrum using the density functional theory (DFT). According to the group‐theoretical analysis, 33 Ag modes were identified as Raman active modes. In the experimental spectrum, 19 well‐resolved Raman modes were observed: 13 modes in the low‐wavenumber range (50–200 cm−1) and six modes in the high‐wavenumber range (220–340 cm−1). The DFT calculations were performed using the local‐density approximation (LDA) functional and generalized gradient approximation (GGA) functional of Perdew–Burke–Ernzerhof (PBE) with van der Waals corrections (PBE‐D3). PBE‐D3 showed better compatibility with the experimental data for the high‐wavenumber range. Our results provide an essential reference for the Raman scattering of newly synthesized Nb2Se9 nanowires and nanodevices in the future.

Due to their unique properties and potential applications, van der Waals (vdW) crystals with covalently bonded building blocks through vdW interactions have sparked widespread interest. In this article, we introduce a Ta2Ni3Se8 material as an example of an emerging one-dimensional (1D)-vdW-based material. Recently, it was demonstrated that bulk Ta2Ni3Se8 crystals may be effectively exfoliated into a few-chain-scale nanowires using simple mechanical and liquid-phase exfoliation. We performed density-functional theory calculations to get a better understanding of its electrical, magnetic, and transport properties. Theoretically, we expect that this Ta2Ni3Se8 is a semiconducting material, displaying the indirect-to-direct bandgap transition from bulk to single, as well as the band splitting and bandgap opening with the inclusion of Coulomb interaction. Based on deformation potential theory, the carrier mobility of bulk Ta2Ni3Se8 along the axis direction (a-axis) is as high as 264.00 cm2 V−1 s−1 for electrons and 119.62 cm2 V−1 s−1 for holes. The calculated carrier mobility of Ta2Ni3Se8, a 1D single nanowire, is 59.60 cm2 V−1 s−1 for electrons and 42.90 cm2 V−1 s−1 for holes, which is comparable to that of other 1D materials. This confirms that a recently developed field-effect transistor based on Ta2Ni3Se8 nanowires exhibits maximum experimental mobilities of 20.3 and 3.52 cm2 V−1 s−1 for electrons and holes, respectively. On the basis of the obtained intriguing properties of 1D vdW Ta2Ni3Se8 material, it is expected to be a potential candidate for additional 1D materials as channel materials.