With the rapid development of portable electronics, such as e-paper and other flexible devices, practical power sources with ultrathin geometries become an important prerequisite, in which supercapacitors with in-plane configurations are recently emerging as a favorable and competitive candidate. As is known, electrode materials with two-dimensional (2D) permeable channels, high-conductivity structural scaffolds, and high specific surface areas are the indispensible requirements for the development of in-plane supercapacitors with superior performance, while it is difficult for the presently available inorganic materials to make the best in all aspects. In this sense, vanadium disulfide (VS(2)) presents an ideal material platform due to its synergic properties of metallic nature and exfoliative characteristic brought by the conducting S-V-S layers stacked up by weak van der Waals interlayer interactions, offering great potential as high-performance in-plane supercapacitor electrodes. Herein, we developed a unique ammonia-assisted strategy to exfoliate bulk VS(2) flakes into ultrathin VS(2) nanosheets stacked with less than five S-V-S single layers, representing a brand new two-dimensional material having metallic behavior aside from graphene. Moreover, highly conductive VS(2) thin films were successfully assembled for constructing the electrodes of in-plane supercapacitors. As is expected, a specific capacitance of 4760 μF/cm(2) was realized here in a 150 nm in-plane configuration, of which no obvious degradation was observed even after 1000 charge/discharge cycles, offering as a new in-plane supercapacitor with high performance based on quasi-two-dimensional materials.

Inorganic graphene analogues (IGAs) are a conceptually new class of materials with attractive applications in next-generation flexible and transparent nanodevices. However, their species are only limited to layered compounds, and the difficulty in extension to nonlayered compounds hampers their widespread applicability. Here we report the fabrication of large-area freestanding single layers of non-layered Znse with four-atomic thickness, using a strategy involving a lamellar hybrid intermediate. Their surface distortion, revealed by means of synchrotron radiation X-ray absorption fine structure spectroscopy, is shown to give rise to a unique electronic structure and an excellent structural stability, thus determining an enhanced solar water splitting efficiency and photostability. The Znse single layers exhibit a photocurrent density of 2.14 mA cm − 2 at 0.72 V versus Ag/AgCl under 300 W Xe lamp irradiation, 195 times higher than that of bulk counterpart. This work opens the door for extending atomically thick IGAs to non-layered compounds and holds promise for a wealth of innovative applications.

Utilizing a thin film of VS(2) ultrathin nanosheets with giant and fast moisture responsiveness, a brand-new model of moisture-based positioning interface is put forward here, by which not only the 2D position information of finger tips can be acquired, but also the relative height can be detected as the third dimensionality, representing a promising platform for advanced man-machine interactive systems.

As a conceptually new class of two-dimensional (2D) materials, the ultrathin nanosheets as inorganic graphene analogues (IGAs) play an increasingly vital role in the new-generation electronics. However, the relatively low electrical conductivity of inorganic ultrathin nanosheets in current stage significantly hampered their conducting electrode applications in constructing nanodevices. We developed the unprecedentedly high electrical conductivity in inorganic ultrathin nanosheets. The hydric titanium disulfide (HTS) ultrathin nanosheets, as a new IGAs, exhibit the exclusively high electrical conductivity of 6.76 × 10(4) S/m at room temperature, which is superior to indium tin oxide (1.9 × 10(4) S/m), recording the best value in the solution assembled 2D thin films of both graphene (5.5 × 10(4) S/m) and inorganic graphene analogues (5.0 × 10(2) S/m). The modified hydrogen on S-Ti-S layers contributes additional electrons to the TiS2 layered frameworks, rendering the controllable electrical conductivity as well as the electron concentrations. Together with synergic advantages of the excellent mechanical flexibility, high stability, and stamp-transferrable properties, the HTS thin films show promising capability for being the next generation conducting electrode material in the nanodevice fields.

Recently, novel two-dimensional materials for solar water splitting have drawn enormous research attention for the interesting tunable electronic and optical properties. We investigate the geometry, electronic, and optical properties of the monolayer (ML) and multilayer Janus MoSSe with the first-principles calculations. We find that the ML Janus MoSSe is a semiconductor with a direct band gap of 2.14 eV, which is suitable for absorbing visual light efficiently. It also holds an appropriate band edge alignment with the water redox potentials. The biaxial strain could effectively modulate the electronic and optical properties of the ML MoSSe, from a direct semiconductor to the indirect one, even to be metal. As for the bilayer (BL) MoSSe, the stacking order could effectively affect the electronic, optical, and redox properties. The most stable stacking order is the A′B type, followed by the AA′, AA-SeSe, AA-SS, and AA-SSe stacking faults. For the BL MoSSe, they are all indirect semiconductors. The indirect band gap of the multilayer MoSSe decreases monotonously as the number of layers increases, maybe due to the quantum confinement effect and interaction between the layers. The appropriate optical and band alignment with the water redox potentials together with the rich modulation methods imply that MoSSe could be used as an efficient photocatalysist for the water splitting.

The nitrogenated porous two-dimensional (2D) material C 2 N has been successfully synthesized using a simple wet-chemical reaction, which provides a high-performance way to produce such 2D materials with novel electronic and optical properties. In this work, density functional theory (DFT) calculations were performed to investigate the structural, electronic, and optical properties of the layered C 2 N/MoS 2 van der Waals (vdW) heterojunction. The C 2 N/MoS 2 heterojunction was found to have a direct band gap of 1.30 eV and to present the typical type-II heterojunction feature, facilitating the effective separation of photogenerated electrons and holes. The calculated band alignment and enhanced optical absorption suggest that the C 2 N/MoS 2 heterojunction should exhibit good light-harvesting properties. The vertical strain can effectively tune the electronic properties and optical absorption of the C 2 N/MoS 2 heterojunction by changing the interaction between the p z orbital of C 2 N and the d z 2 orbital of MoS 2 . The moderate band gap, well-separated photogenerated electrons and holes, and enhanced visible-light absorption indicate that the C 2 N/MoS 2 heterojunction is a potential photovoltaic structure for solar energy.

Adsorption of formic acid on rutile TiO2 (110) revisited: An infrared reflection-absorption spectroscopy and density functional theory study. Journal of Chemical Physics AbstractFormic acid (HCOOH) adsorption on rutile TiO 2 (110) has been studied by s-and p-polarized infrared reflection-absorption spectroscopy (IRRAS) and spin-polarized density functional theory together with Hubbard U contributions (DFT+U) calculations. To compare with IRRAS spectra, the results from the DFT+U calculations were used to simulate IR spectra by employing a three-layer model, where the adsorbate layer was modelled using Lorentz oscillators with calculated dielectric constants. To account for the experimental observations, four possible formate adsorption geometries were calculated, describing both the perfect (110) surface, and surfaces with defects; either O vacancies or hydroxyls. The binding energy was found to be E bind = 1.84 eV for the bridging bidentate formate species, which bonds with its IRRAS spectra measured on surfaces prepared to be either reduced, stoichiometric, or to contain surplus O adatoms, were found to be very similar. By comparisons with computed spectra, it is concluded that formate binds to in-plane Ti 5c atoms rather than to O vacancy sites. The results emphasize the importance of protonation and reactive surface hydroxylseven under UHV conditions -as reactive sites in e.g. catalytic applications.

By first-principles theory we study the nearly free electron (NFE) states of carbon and boron nitride nanotubes. In addition to the well-known π bands, we found a series of one-dimensional (1D) NFE bands with on-axis spatial distributions, which resemble atomic orbitals projected onto a plane. These bands are 1D counterparts of the recently discovered superatom orbitals of 0D fullerenes. In addition to the previously reported lowest energy NFE state with the angular quantum number l = 0 corresponding to s atomic orbital character, we find higher energy NFE bands with l > 0 corresponding to the p, d, etc., orbitals. We show that these atom-like states of nanotubes originate from the many-body screening, which is responsible for the image potential of the parent two-dimensional (2D) graphene or BN sheets. With a model potential that combines the short-range exchange-correlation and the long-range Coulomb interactions, we reproduce the energies and radial wave function profiles of the NFE states from the density functional theory calculations. When the nanotube radius exceeds the radial extent on NFE states, the NFE state energies converge to those of image potential states of the parent 2D molecular sheets. To explore possible applications in molecular electronics that take advantage of the NFE properties of nanotube building blocks, we investigate the modification of NFE states by transverse electric fields, alkali metal encapsulation, and lateral and concentric nanotube dimerization.