We investigate the spin-orbit opened energy gap and the band topology in recently synthesized silicene as well as two-dimensional low-buckled honeycomb structures of germanium using first-principles ...calculations. We demonstrate that silicene with topologically nontrivial electronic structures can realize the quantum spin Hall effect (QSHE) by exploiting adiabatic continuity and the direct calculation of the Z(2) topological invariant. We predict that the QSHE can be observed in an experimentally accessible low temperature regime in silicene with the spin-orbit band gap of 1.55 meV, much higher than that of graphene. Furthermore, we find that the gap will increase to 2.9 meV under certain pressure strain. Finally, we also study germanium with a similar low-buckled stable structure, and predict that spin-orbit coupling opens a band gap of 23.9 meV, much higher than the liquid nitrogen temperature.
Topological nodal line semimetals, a novel quantum state of materials, possess topologically nontrivial valence and conduction bands that touch at a line near the Fermi level. The exotic band ...structure can lead to various novel properties, such as long-range Coulomb interaction and flat Landau levels. Recently, topological nodal lines have been observed in several bulk materials, such as PtSn4, ZrSiS, TlTaSe2 and PbTaSe2. However, in two-dimensional materials, experimental research on nodal line fermions is still lacking. Here, we report the discovery of two-dimensional Dirac nodal line fermions in monolayer Cu2Si based on combined theoretical calculations and angle-resolved photoemission spectroscopy measurements. The Dirac nodal lines in Cu2Si form two concentric loops centred around the Γ point and are protected by mirror reflection symmetry. Our results establish Cu2Si as a platform to study the novel physical properties in two-dimensional Dirac materials and provide opportunities to realize high-speed low-dissipation devices.
Majorana bound states often occur at the end of a 1D topological superconductor. Validated by a new bulk invariant and an intuitive edge argument, we show the emergence of one Majorana Kramers pair ...at each corner of a square-shaped 2D topological insulator proximitized by an s_{±}-wave (e.g., Fe-based) superconductor. We obtain a phase diagram that addresses the relaxation of crystal symmetry and edge orientation. We propose two experimental realizations in candidate materials. Our scheme offers a higher-order and higher-temperature route for exploring non-Abelian quasiparticles.
Silicene, a sheet of silicon atoms in a honeycomb lattice, was proposed to be a new Dirac-type electron system similar to graphene. We performed scanning tunneling microscopy and spectroscopy studies ...on the atomic and electronic properties of silicene on Ag(111). An unexpected √3 × √3 reconstruction was found, which is explained by an extra-buckling model. Pronounced quasiparticle interferences (QPI) patterns, originating from both the intervalley and intravalley scatter, were observed. From the QPI patterns we derived a linear energy-momentum dispersion and a large Fermi velocity, which prove the existence of Dirac fermions in silicene.
Organic light‐emitting transistors (OLETs), as novel and attractive kinds of organic electronic devices, have gained extensive attention from both academia and industry. The unique device ...architectures can simultaneously combine the electrical switching functionality of organic field‐effect transistors and the light generation capability of organic light‐emitting diodes in a single device, thereby holding great promise for reducing the complicated processes of next‐generation pixel circuitry. This review involves the design, fabrication, and applications of OLETs with a comprehensive coverage of this field with the aim to give a deep insight into the intrinsic mechanisms of devices. Challenges and future prospects of OLETs are also discussed.
Organic light‐emitting transistors (OLETs) represent a novel class of organic optoelectronic devices that combine the current modulating function of a transistor with light emission. Unipolar OLETs, ambipolar OLETs, and new device structures, most of which intend to elaborate their working principles and the construction of high‐quality optoelectronic devices, are spotlighted in terms of the representative paradigms.
It is highly profitable to transform glycerol - the main by-product from biodiesel production to high value-added chemicals. In this work, we develop a photoelectrochemical system based on nanoporous ...BiVO
for selective oxidation of glycerol to 1,3-dihydroxyacetone - one of the most valuable derivatives of glycerol. Under AM 1.5G front illumination (100 mW cm
) in an acidic medium (pH = 2) without adscititious oxidant, the nanoporous BiVO
photoanode achieves a glycerol oxidation photocurrent density of 3.7 mA cm
at a potential of 1.2 V versus RHE with 51% 1,3-dihydroxyacetone selectivity, equivalent to a production rate of 200 mmol of 1,3-dihydroxyacetone per m
of illumination area in one hour.
Hexagonal boron nitride (h-BN) has recently emerged as an excellent substrate for graphene nanodevices, owing to its atomically flat surface and its potential to engineer graphene's electronic ...structure. Thus far, graphene/h-BN heterostructures have been obtained only through a transfer process, which introduces structural uncertainties due to the random stacking between graphene and h-BN substrate. Here we report the epitaxial growth of single-domain graphene on h-BN by a plasma-assisted deposition method. Large-area graphene single crystals were successfully grown for the first time on h-BN with a fixed stacking orientation. A two-dimensional (2D) superlattice of trigonal moiré pattern was observed on graphene by atomic force microscopy. Extra sets of Dirac points are produced as a result of the trigonal superlattice potential and the quantum Hall effect is observed with the 2D-superlattice-related feature developed in the fan diagram of longitudinal and Hall resistance, and the Dirac fermion physics near the original Dirac point is unperturbed. The macroscopic epitaxial graphene is in principle limited only by the size of the h-BN substrate and our synthesis method is potentially applicable on other flat surfaces. Our growth approach could thus open new ways of graphene band engineering through epitaxy on different substrates.
•CO2-effect on microalgal-bacterial granular sludge (MBGS) process was evaluated.•CO2 could maintain the compact structure and the stable performance of MBGS.•CO2 could enhance the organics and ...phosphorus removal of MBGS process.•CO2 could promote the growth of algae and phosphorus accumulating organisms.•CO2 supply for MBGS process could achieve a carbon-negative objective.
As a promising wastewater treatment technology, little is known about whether the greenhouse gas CO2 can be applied for microalgal-bacterial granular sludge (MBGS) process. This article applied CO2 for improving MBGS process. It was found that the physical structure of MBGS with no CO2 addition appeared to have a trend to be loose and disintegrated, with a sludge volume index at 5 min (SVI5) of over 150 mL/g and an average pore size of 35 nm in 60 d operation. However, CO2 could maintain the compact and integrated structure of MBGS with a SVI5 lower than 50 mL/g and an average pore size ranging from 10 to 13 nm. CO2 could enhance the production of extracellular polysaccharides and aromatic protein, thus favoring the granular stability of MBGS. CO2 could change the aqueous environment, e.g. lowering the pH values, which resulted in different microbial communities as well as metabolic potentials of MBGS. As for the reactor performance, CO2 could significantly improve the removals of organics and phosphorus, evidenced by the enhancement of genes encoding acetate-CoA ligase and ATPase, respectively. Although the mass ratio of algae to bacteria was elevated by CO2 addition, the ammonia removal related enzymes of glutamate dehydrogenase and glutamine synthetase could be negatively and positively impacted by CO2, respectively. Mass balance analysis of carbon indicated that CO2 could provide additional carbon source as well as enhance the buffering capacity for the MBGS system. Further estimations suggested that the MBGS process could achieve a carbon-negative objective for municipal wastewater treatment by supplying CO2 as additional carbon source. Hence, CO2 supply for MBGS process in municipal wastewater treatment can be deemed as a two-birds-one-stone strategy, i.e. maintaining the granular stability and eliminating the carbon emission. This article can advance our basic knowledge on MBGS process towards environment-sustainable wastewater treatment.
Display omitted
We find theoretically a new quantum state of matter-the valley-polarized quantum anomalous Hall state in silicene. In the presence of Rashba spin-orbit coupling and an exchange field, silicene hosts ...a quantum anomalous Hall state with Chern number C=2. We show that through tuning the Rashba spin-orbit coupling, a topological phase transition results in a valley-polarized quantum anomalous Hall state, i.e., a quantum state that exhibits the electronic properties of both the quantum valley Hall state (valley Chern number Cv=3) and quantum anomalous Hall state with C=-1. This finding provides a platform for designing dissipationless valleytronics in a more robust manner.
PDF
