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Due to the limited variety of natural atoms and the preparation of nanoparticles with low size polydispersity, it is still a challenge to adjust the interesting properties of graphene at the atomic level by changing its interlayer spacing. Here, we demonstrate that superatoms can fill the deficiency by providing adjustable and stable intercalation units between graphene layers, offering effective control of the interlayer distance. Our calculations show that for Au20superatoms intercalating between graphene interlayers, as their density increases from 2.1 × 10–3to 4.0 × 10–3superatom/Å2, the graphene interlayer spacing increases from 9.3 to 11.4 Å. The Au20maintains to be in a dispersion interaction-dominated physical adsorption state with the graphene layer till the density is decreased to 1.6 × 10–3superatom/Å2, after which the graphene can crush Au20, resulting in a graphene structure with chemical adsorption of the deformed Au20. This work suggests that superatoms can have an important prospect in membrane separation applications.

The functional structures at the nanoscale containing high-angular-momentum (HAM) electrons possess wide potential applications. However, HAM electrons generally exist in high-Zelements, while the related materials are difficult to obtain through either mining or synthesis. Therefore, it is significant to design new materials building blocks to mimic the electronic properties of high-Zelements. In this study, a series of cage structures formed by light elements of boron and nitrogen (BN) have been proven to present superatomic properties. Especially, the superatomic molecular orbitals of the BN cage are found, all containing orbitals occupied by HAM electrons, for example, f, g, and h. Their electronic configurations can be represented as 1S21P61D101F142S22P61G182D101H102F6, 1S21P61D101F141G182S22P61H222D102F14, and 1S21P61D101F141G181H222S22P62D102F14for B12N12, B16N16, and B28N28structures, respectively. These findings open up a prospect of using abundant light elements to form superatomic structures with HAM electronic characteristics and are of significance for the development of functional materials and devices.

This paper reports the possible reaction paths of small silicon clusters Sin(n= 1−4) with the oxygen molecule based on density functional theoretical calculations. It is shown that their potential energy surfaces are very complex, involving spin conserving and inversion. There are no net barriers on any of the proposed reaction paths for the oxidation of Si, Si2, and Si3clusters, but their reverse reactions are endothermic with high energy barriers. The Si4cluster cannot react with the ground-state, spin-triplet oxygen molecule because of the potential barrier of its spin inversion. The most favorable and accessible reaction path for Si/Si2/Si3+ O2may be the one with a high exothermic value since there are no net barriers on the potential energy surfaces. The reactions of silicon clusters with the oxygen molecule are easier than the oxidations of their corresponding suboxides. Our findings are expected to provide valuable information to help understand the growth mechanism of silicon nanowires.

Recently, an n → π* weak interaction has been found to be ubiquitous and significant in proteins, functional materials, medicines, and biological processes. To reveal the mechanism underlying the n → π* interaction, we performed density functional theory calculations for single-walled carbon nanotubes (SWNTs) covalently or noncovalently functionalized by the 4-(1-pyrenyl)phenyl (PP) group. The n → π* interaction can be formed between the nonbonding (n) radical electron of the PP group and the π-conjugation antibonding orbitals (π*) of SWNTs facilitated by the π–π stacking between them. The n → π* interaction is found to be dominantly responsible for a distinguishable optical response, leading to visible light absorption at ∼450 nm. Specifically, the photo-induced charge carriers are separated effectively through n → π* electron transition with the hole “locked” on the PP group. Our result is useful for the rational design of novel SWNT modification by aromatic groups in applications of (photo)electrochemical reactions, functional devices, or sensors.

In research on molecular machines, the flexibility of the molecules has been shown to significantly affect the performance of such “soft” machines and thus lead to unexpected phenomena that differ from rigid machines in the macroscopic world. Taking several typical rotational molecules as examples, we examine how the deformation of the molecule (commonly caused by curving parts of a molecule due to its interaction with other molecules) affects the effectiveness of a molecular machine system, such as a chain of molecular gears. From the viewpoint of quantum chemistry and classical mechanics, we introduce a torque analysis strategy to quantitatively analyze the strength of the repulsion/attraction force induced by the deformation of such molecules. By comparing different types of chemical bonds, we show that a bond connecting to an aromatic ring exhibits a larger stiffness than bonds that do not directly connect to an aromatic ring. We thereby highlight that the inclusion of aromatic rings in a molecular machine can considerably increase the stiffness of the machine, which is an important factor in designing effective molecular machines.

TiO2nanorods arrays (NRAs) have been considered as very promising photoanode materials in photoelectrochemical (PEC) cells. However, the performance of TiO2NRAs still requires substantial improvement in order to reach the goal of practical applications. Annealing treatment of TiO2NRAs can help to improve the PEC performance, but the mechanism is still not yet fully understood. In this work, we systematically investigated the optical and electronic properties, as well as the PEC performance of the thermally treated rutile single-crystalline TiO2NRAs. Surprisingly, we recorded a maximum photocurrent density of 1.38 mA/cm2at 1.3 V versus reversible hydrogen electrode for TiO2NRAs annealed in O2, which is about 28 times higher than that of the pristine TiO2NRAs. We further revealed that the surface adsorbed Cl ions largely suppress the photoresponse of the TiO2NRAs as they serve as recombination centers and block the adsorption of water molecules to the surface of TiO2NRAs. The enhancement in photocurrent after annealing in O2is due to the desorption of the Cl ions, filling of the surface Vo, expansion of the depletion layer, and increase of the grain size. Our results shed light on the effect of annealing on the PEC performance of TiO2NRAs and offer guidance for annealing of other semiconductor materials.

On the basis of calculations using time-dependent density functional theory, we conducted detailed analyses of the surface-enhanced Raman scattering (SERS) of pyridine adsorbed on 13-atom icosahedral M@Au12and M@Ag12(M = Mo, W) clusters in this article. Surprisingly, we find that, although the SERS enhancements for all complexes can reach the order of 104, the signals of pyridine on M@Ag12at charge transfer (CT) transition excitations are twice as much as that of pyridine on M@Au12, and the corresponding energies used for SERS excitations are significantly different in the low-energy region of 1.63–2.10 eV. The interactive modulation between the core and shell can produce varying strong CT transitions from metal clusters to pyridine, which tunes the SERS enhancements with altered optical properties. The complexes of pyridine on silver-caged clusters are more easily influenced by the tunability of the core than that of pyridine on gold-caged clusters. Our analyses are expected to provide a theoretical basis for experimentally synthesizing multicomponent SERS substrates and exploring the dependence of SERS enhancement on the synergies between the different components in core@shell binary metal clusters.

The size-dependent optical properties of silicon nanosheets (SiNSs) are investigated using the time-dependent density functional based tight-binding method (TD-DFTB). Evidence for the formation of self-trapped exciton states in SiNSs is provided by examining the localization properties in terms of the characteristic size of the electronic excitations. We show that the frontier molecular orbitals in the first excited state are highly localized in the central stretched Si–Si bond of the NSs due to structural relaxation, which leads to a significant red-shift of the optical gaps. For SiNSs, the boundary length and local structure of the central section in SiNSs influence the spatial extent of self-trapped excitons in the first excited state. The first excited states are observed to be spatially less localized for SiNSs with a longer boundary length. The distribution of electronic density perturbation is diverse in the case of central Si6or a single Si–Si bond, thereby leading to different spatial confinement of structural relaxation. In contrast with zero- and one-dimensional Si nanomaterials, the two-dimensional SiNSs show a highly localized exciton when the width is less than 2 nm, which suggests it as a candidate for exploring the characteristics of exciton self-trapping.

As surface-enhanced Raman scattering (SERS) substrates, coinage bimetallic clusters offer high SERS enhancement and potential for applications in precision molecule detection. Here, we elucidate the chemical mechanism and reveal the tunability of the SERS of a pyridine molecule (Py) on coinage bimetallic substrate by investigating various possible heteronuclear coinage metal diatomic clusters (HCMDCs) interacting with the pyridine molecule. We obtain the Raman spectra, molecular orbital, and binding property of each HCMDC–Py system using density functional theory. We find that the Raman characteristic peaks, adsorption energy, charge transfer, geometry parameters, and molecular orbital distribution are all closely related to the compositions and binding sites of the HCMDC. The results show that the synergistic effect of different coinage metal atoms in the HCMDC plays an important role in SERS enhancement, which varies with the component and adsorption site of the HCMDC, thus providing the possibility of optimizing the SERS substrate by tuning the bimetallic cluster composition and adsorption site.

The adsorption of pentacene, perfluoropentacene, other acenes, and biphenyl on a Cu(111) single-crystal surface was studied by a modified version of a van der Waals density functional. Accurate and consistent interface geometries and adsorption energies were obtained for the first time. All studied interactions between the organics and the metal are in the sensitive intermediate regime between chemisorption and physisorption, in which regime both geometric and electronic structures of the adsorbates are strongly modified by the metal surface. Adsorption induced gentle curving of flat acenes is demonstrated and explained (the ends of the acenes curving away from the metal relative to their center); in contrast, biphenyl, which is twisted when free, becomes coplanar after adsorption. More importantly, perfluoropentacene is “pinned” to Cu(111) by a sharp bend that creates a localized strong bond, which explains earlier puzzling experimental observations reported for perfluoropentacene relative to pentacene. Electronic structures of these two adsorbates are compared to further probe their different interface mechanisms.

The electronic properties of strained hydrogen-passivated Si nanosheets are investigated using the first-principles density functional theory. Asymmetrical strain has been found to cause a direct-to-indirect transition in the (100) Si nanosheet, while symmetrical strain retains its direct band gap characteristic. Under asymmetrical strain along the ⟨100⟩ direction, the direct band gap of the (110) Si nanosheet exhibits unique characteristics, with the direct band gap varying linearly with strain. Similar band gap variation behaviors are observed for the (110) Si nanosheet subject to symmetrical and asymmetrical strains along the ⟨110⟩ direction. The various strain dependences are attributed to the changes in its charge density. Our results can be used to guide the strain engineering of the electronic properties of low-dimensional silicon materials.

We have identified a class of metal oxide surfaces that are very effective in dissociating water. These oxide surfaces are characterized by having their surface O 2p level lying significantly above the valence band maximum (VBM) and within the band gap. Density functional theory is used to determine the adsorption energy per water molecule and finds that water dissociates completely at all coverages on these surfaces. Fourier transform infrared (FTIR) spectroscopy is used to verify that there is little or no molecular water present on the surface. Besides splitting water, this class of metal oxide surfaces should also be effective in splitting other kinds of hydrogen compounds. By contrast, oxides whose surface O 2p level lies buried inside the valence band are much less reactive, and water adsorbs on these surfaces in molecular form.

The pressure-induced metallization of alkaline earth hydrides was systematically investigated using ab initio methods. While BeH2and MgH2present different semimetallic phases, CaH2, SrH2, and BaH2share the same metallic phase (P6/mmm). The metallization pressure shows an attractive decrease with each increment of metal radius, and this trend is well correlated with both the electronegativity of alkaline earth metals and the band gap of alkaline earth hydrides at ambient pressure. Our results are consistent with current experimental data, and the obtained trend has significant implications for designing and engineering metallic hydrides for energy applications.

By performing density functional theoretical calculations, we evaluate the thermal and chemical stabilities of two isomer series of silicon monoxide clusters, namely, silicon segregated clusters and silicon cored clusters, which may act as precursors to silicon nanowire synthesis. The results show that the former favor dissociation at the growth temperature of the silicon nanowire, as revealed in dissociation path searches and molecular dynamic simulations, with reactivity with oxygen that is greater in the former than in the latter. We expect our results to provide some insight into the nucleation and growth mechanism of silicon nanostructures.

A facile fabricating method has been established for large-area uniform silicon nanowires arrays. All silicon nanowires obtained were single crystals and epitaxial on the substrate. Six kinds of silicon wafers with different types, surface orientations, and doping levels were utilized as starting materials. With the catalysis of silver nanoparticles, room-temperature mild chemical etching was conducted in aqueous solution of hydrofluoric acid (HF) and hydrogen peroxide (H2O2). The corresponding silicon nanowires arrays with different morphologies were obtained. The silicon nanowires possess the same type and same doping level of the starting wafer. All nanowires on the substrate have the same orientation. For instance, both (100)- and (111)-oriented p-type wafers produced silicon nanowires in the (100) direction. For every kind of silicon wafer, the effect of etching conditions, such as components of etchant, temperature, and time, were systemically investigated. This is an appropriate method to produce a large amount of silicon nanowires with defined type, doping level, and growth direction for industrial applications.

The role of hydrogen bonding in forming self-assembled monolayers of two BF2-substituted -dicarbonyl derivatives has been studied by scanning tunneling microscopy (STM). Both molecules spontaneously adsorb on HOPG surface and self-organize into well-ordered two-dimensional (2D) lamellae. The hydrogen bonding at different positions is found to have a significant impact on the self-assembled structures. On one hand, the C−H···F hydrogen bonding between the ortho carbon of the phenyl ring and the fluorine of the BF2group dominates the formation of the lamellae. On the other hand, the O−H···O hydrogen bonding between the neighboring carboxyl groups doubles the width of the lamellae. The present results provide significant information in understanding the noncovalent effect on molecular self-organization.

The photoelectrochemical (PEC) performance of g-CN can be enhanced by modifying its photocatalytic properties, which has been considered as a typical challenging agent for water splitting. Here, we present a study of metal-free surface charge transfer doping (SCTD) of g-CN films by means of surface alteration treatment and accordingly demonstrated its influence on the PEC performance by combining experiments and theoretical calculations. The as-prepared doped films using a boron dopant boost the photocurrent density by a factor of 3 versus RHE with no sacrificial reagents as compared to pristine g-CN films. The boron dopant can readily substitute the nitrogen atom when the film is coated five times and, consequently, reduce the band gap by raising the valence band edge. We conjecture that such improvement is due to the effective SCTD and enhanced charge carrier separation, which are beneficial for improving charge migration, charge mobility, space charge region, and recombination rate.