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Carbon is a versatile element that has allotropes with both sp2 (graphene) and sp3 (diamond) bonding. However, none of the allotropes can be used as light-absorber materials in solar cells due to either too large or too small band gap. Here, we propose a novel concept that enables a tunable band gap of carbon phases with sp2 carbon atoms within a sp3 carbon structure. The tunability is due to the quantum confinement effect. By embedding the sp2 atoms within the sp3 structure, we can design new carbon allotropes with ideal optical properties for optoelectronic applications. Five carbon allotropes incorporated this structural feature were identified by combining this new concept with our freshly developed multi-objective inverse band structure design approach. They all have proper band gaps for optical absorption, and the simulated photovoltaic efficiency of C10-C is even higher than conventional absorber materials such as GaAs, which indicates that C10-C with mixed sp2 sp3 hybridization may have potential application as light-absorber material in electronic and optoelectronic devices.

We use inverse design of materials by multi-objective differential evolution (IM2ODE) method to globally search the most stable configurations of Au n , Au n - 1 Pt, Au n - 2 Pt 2 (n = 2–9) clusters. Combining with first-principles calculations, based on the density functional theory (DFT), we find that all of the ground state structures of clusters prefer to keep low spin multiplicity and form planar structures. Pt atom tends to occupy the most highly coordinated position. Especially Au 6 Pt and Au 4 Pt 2 clusters exhibit highly relative stability and have a closed electronic shell based on the spherial jellium model, so we conclude that Au 6 Pt and Au 4 Pt 2 should be magic number clusters. Mulliken occupation analysis of Pt and Au atoms indicate that a competition exits between electronegativity of atoms and valence electron configuration of atoms in small Au n Pt m clusters.

Despite the recent progress of developing graphitic carbon nitride (g-C3N4) as a metal-free photocatalyst, the synthesis of nanostructured g-C3N4 has still remained a complicated and time-consuming approach from its bulk powder, which substantially limits its photoelectrochemical (PEC) applications as well as the potential to form composites with other semiconductors. Different from the labor-intensive methods used before, such as exfoliation or assistant templates, herein, we developed a facile method to synthesize graphitic C3N4 quantum dots (g-CNQDs) directly grown on TiO2 nanowire arrays via a one-step quasi-chemical vapor deposition (CVD) process in a homemade system. The as-synthesized g-CNQDs uniformly covered over the surface of TiO2 nanowires and exhibited attractive photoluminescence (PL) properties. In addition, compared to pristine TiO2, the heterojunction of g-CNQD-decorated TiO2 nanowires showed a substantially enhanced PEC photocurrent density of 3.40 mA/cm2 at 0 V of applied potential vs Ag/AgCl under simulated solar light (300 mW/cm2) and excellent stability with ?82% of the photocurrent retained after over 10 h of continuous testing, attributed to the quantum and sensitization effects of g-CNQDs. Density functional theory calculations were further carried out to illustrate the synergistic effect of TiO2 and g-CNQD. Our method suggests that a variety of g-CNQD-based composites with other semiconductor nanowires can be synthesized for energy applications. 2016 American Chemical Society. We thank the following funding agencies for supporting this work: the National Key Basic Research Program of China (2013CB934104), the Natural Science Foundation of China (21322311, 21473038, 21471034), the Science and Technology Commission of Shanghai Municipality (14JC1490500), the Program for Professor of Special Appointment (Eastern Scholar) at Shanghai Institutions of Higher Learning, and the Collaborative Innovation Center of Chemistry for Energy Materials (2011-iChem). The authors extend their sincere appreciation to the Deanship of Scientific Research at King Saud University for funding the Prolific Research group (PRG-1436-14). Scopus

Two-dimensional (2D) magnetic materials have been experimentally recognized recently, however, the Curie temperatures (T C) of known 2D systems are quite low. Generally, magnetic systems can be seen as constituent magnetic elements providing spins and the non-magnetic elements providing frameworks to host the magnetic elements. Short bond lengths between the magnetic and non-magnetic elements would be beneficial for strong magnetic interactions and thus high T C. Based on this, we propose to combine the magnetic element Cr and the non-magnetic element boron to design novel 2D magnetic systems. Using our self-developed software package IM2ODE, we design a series of chromium-boride based 2D magnetic materials. Nine stable magnetic systems are identified. Among them, we find that CrB4-I, CrB4-II and CrB5-I with common structural units [CrB8] are ferromagnetic metals with estimated T C of 270 K, 120 K and 110 K, respectively. On the other hand, five CrB3 phases with structural units [Cr2B12] are antiferromagnetic metals. Additionally, we also find one antiferromagnetic semiconductor CrB2-I. Our work may open new directions for identifying 2D magnetic systems with high T C.

A three-dimensional (3D) mesoporous Fe2O3-CdS nanopyramid heterostructure is developed for solar-driven, real-time, and selective photoelectrochemical sensing of Cu(2+) in the living cells. Fabrication of the mesoporous Fe2O3 nanopyramids is realized by an interfacial aligned growth and self-assembly process, based on the van der drift model and subsequent selective in situ growth of CdS nanocrystals. The as-prepared mesoporous Fe2O3-CdS heterostructures achieve significant enhancement (∼3-fold) in the photocurrent density compared to pristine mesoporous Fe2O3, which is attributed to the unique mesoporous heterostructures with multiple features including excellent flexibility, high surface area (∼87 m(2)/g), and large pore size (∼20 nm), enabling the PEC performance enhancement by facilitating ion transport and providing more active electrochemical reaction sites. In addition, the introduction of Cu(2+) enables the activation of quenching the charge transfer efficiency, thus leading to sensitive photoelectrochemical recording of Cu(2+) level in buffer and cellular environments. Furthermore, real-time monitoring (∼0.5 nM) of Cu(2+) released from apoptotic HeLa cell is performed using the as-prepared 3D mesoporous Fe2O3-CdS sensor, suggesting the capability of studying the nanomaterial-cell interfaces and illuminating the role of Cu(2+) as trace element.

The direct production of branched semiconductor arrays with highly ordered orientation has proven to be a considerable challenge over the last two decades. Here we report a mesoporous interfacial atomic rearrangement (MIAR) method to directly produce highly crystalline, finger-like branched iron oxide nanoarrays from the mesoporous nanopyramids. This method has excellent versatility and flexibility for heteroatom doping of metallic elements, including Sn, Bi, Mn, Fe, Co, Ni, Cu, Zn, and W, in which the mesoporous nanopyramids first absorb guest-doping molecules into the mesoporous channels and then convert the mesoporous pyramids into branching artificial nanofingers. The crystalline structure can provide more optoelectronic active sites of the nanofingers by interfacial atomic rearrangements of doping molecules and mesopore channels at the porous solid-solid interface. As a proof-of-concept, the Sn-doped Fe2O3 artificial nanofingers (ANFs) exhibit a high photocurrent density of ∼1.26 mA/cm(2), ∼5.25-fold of the pristine mesoporous Fe2O3 nanopyramid arrays. Furthermore, with surface chemical functionalization, the Sn-doped ANF biointerfaces allow nanomolar level recognition of metabolism-related biomolecules (∼5 nm for glutathione). This MIAR method suggests a new growth means of branched mesostructures, with enhanced optoelectronic applications.

We developed a postgrowth modification method of two-dimensional WO3 nanoflakes by a simultaneous solution etching and reducing process in a weakly acidic condition. The obtained dual etched and reduced WO3 nanoflakes have a much rougher surface, in which oxygen vacancies are created during the simultaneous etching/reducing process for optimized photoelectrochemical performance. The obtained photoanodes show an enhanced photocurrent density of ∼1.10 mA/cm2 at 1.0 V vs Ag/AgCl (∼1.23 V vs reversible hydrogen electrode), compared to 0.62 mA/cm2 of pristine WO3 nanoflakes. The electrochemical impedance spectroscopy measurement and the density functional theory calculation demonstrate that this improved performance of dual etched and reduced WO3 nanoflakes is attributed to the increase of charge carrier density as a result of the synergetic effect of etching and reducing.

The electronic structure and orbital characters of iron-pnictide NaFeAs have been studied by polarization dependent angle-resolved photoemission spectroscopy. Some of the bands are mixed with the orbitals of opposite symmetries, which could be interpreted by the hybridization among the bands. According to the photon energy dependent experiment, the k z dispersions of the bands that cross the Fermi energy are weak in both paramagnetic and spin density wave states. However, a band well below the Fermi level shows a k z dispersion of 41 meV, which mainly contains the d z 2 orbital.

The ability to release, as electrical energy, potential energy stored at the water:carbon interface is attractive, since water is abundant and available. However, many previous reports of such energy converters rely on either flowing water or specially designed ionic aqueous solutions. These requirements restrict practical application, particularly in environments with quiescent water. Here, a carbon-based chemical-to-electricity device that transfers the chemical energy to electrical form when coming into contact with quiescent deionized water is reported. The device is built using carbon nanotube yarns, oxygen content of which is modulated using oxygen plasma-treatment. When immersed in water, the device discharges electricity with a power density that exceeds 700 mW m-2 , one order of magnitude higher than the best previously published result. X-ray absorption and density functional theory studies support a mechanism of operation that relies on the polarization of sp2 hybridized carbon atoms. The devices are incorporated into a flexible fabric for powering personal electronic devices.

We report a nitrogen-doped carbon nanodot (N-Cdot)/TiO2 nanowire photoanode for solar-driven, real-time, and sensitive photoelectrochemical probing of the cellular generation of H2S, an important endogenous gasotransmitter based on a tunable interfacial charge carrier transfer mechanism. Synthesized by a microwave-assisted solvothermal method and subsequent surface chemical conjugation, the obtained N-Cdot/TiO2 nanowire photoanode shows much enhanced photoelectrochemical photocurrent compared with pristine TiO2 nanowires. This photocurrent increase is attributed to the injection of photogenerated electrons from N-Cdots to TiO2 nanowires, confirmed by density functional theory simulation. In addition, the charge transfer efficiency is quenched by Cu(2+), whereas the introduction of H2S or S(2-) ions resets the charge transfer and subsequently the photocurrent, thus leading to sensitive photoelectrochemical recording of the H2S level in buffer and cellular environments. Moreover, this N-Cdot-TiO2 nanowire photoanode has been demonstrated for direct growth and interfacing of H9c2 cardiac myoblasts, with the capability of interrogating H2S cellular generation pathways by vascular endothelial growth factor stimulation as well as inhibition.

The electronic structure of ${\text{BaTi}}_{2}$${\text{As}}_{2}O$, a parent compound of the newly discovered titanium-based oxypnictide superconductors, is studied by angle-resolved photoemission spectroscopy and first-principles calculation. The experimental electronic structure shows a multiorbital nature and three-dimensional character, which is consistent with the calculated results. An anomalous temperature-dependent spectral weight redistribution and broad line shape indicate the incoherent nature of the spectral function. At the density-wave-like transition temperature around 200 K, a partial gap opens at the Fermi patches. These findings suggest that ${\text{BaTi}}_{2}$${\text{As}}_{2}O$ is likely a charge density wave material in the strong-interaction regime.

Eu(Fe(0.79)Ru(0.21))2As2 is suggested to be a nodeless superconductor based on the empirical correlation between pnictogen height (hPn) and superconducting gap behavior, in contrast to BaFe2(As(0.7)P(0.3))2 and Ba(Fe(0.65)Ru(0.35))2As2. We studied the low-lying electronic structure of Eu(Fe(0.79)Ru(0.21))2As2 with angle-resolved photoemission spectroscopy (ARPES). By photon energy dependence and polarization dependence measurements, we resolved the band structure in the three-dimensional momentum space and determined the orbital character of each band. In particular, we found that the dz2 -originated ζ band does not contribute spectral weight to the Fermi surface around Z, unlike BaFe2(As(0.7)P(0.3))2 and Ba(Fe(0.65)Ru(0.35))2As2. Since BaFe2(As(0.7)P(0.3))2 and Ba(Fe(0.65)Ru(0.35))2As2 are nodal superconductors and their hPn's are less than 1.33 Å, while the hPn of Eu(Fe(0.79)Ru(0.21))2As2 is larger than 1.33 Å, our results provide more evidence for a direct relationship between nodes, dz2 orbital character and hPn. Our results help to provide an understanding of the nodal superconductivity in iron-based superconductors.