Electronic Structure Engineering via On-Plane Chemical Functionalization: A Comparison Study on Two-Dimensional Polysilane and Graphane

Two-dimensional materials are important for electronics applications. A natural way of electronic structure engineering for two-dimensional systems is on-plane chemical functionalization. On the basis of density functional theory, we study the electronic structures of fluorine-substituted planar polysilane and graphane. We find that carbon and silicon present very different surface chemistries. The indirect energy gap of planar polysilane becomes direct upon fluorine decoration, and its gap width is mainly determined by fluorine coverage regardless of its distribution on the surface. However, the electronic structure of fluorine doped graphane is very sensitive to the doping configuration, due to the competition between antibonding states and nearly free electron (NFE) states. With specific fluorine distribution patterns, zero-dimensional and one-dimensional NFE states can be obtained. Our results demonstrate the advantages of two-dimensional silicon based materials compared with carbon based materials, in the viewpoint of practical electronic structure engineering by surface chemical functionalization

Surface Structure of Zigzag SnO₂ Nanobelts

SnO₂ nanobelts are attracting much attention for their promising applications in gas-sensing nanodevices. However, at present, too little is known on the surface structure and charge of these as-grown nanostructures. Herein, the surfaces of zigzag rutile SnO₂ nanobelts are investigated at atomic scale using the recently developed negative spherical-aberration imaging technique in an aberration-corrected transmission electron microscope. It is found that most of the {101} surfaces of zigzag SnO₂ nanobelts, synthesized by a solid−vapor process, are reduced surfaces terminated by Sn atoms, and the Sn-terminated surface is a nonpolar surface, i.e., electrostatically stable termination

Strain Relaxation-Induced Twin Interface Migration and Morphology Evolution of Silver Nanoparticles

The twinned structure of nanoscale metal particles is considered to be an important factor in the formation of novel morphologies. Nevertheless, most studies are focused on the growth of nanoparticles with stable twinned structures and little is known about the intrinsic relationship between the morphological evolution and the strain relaxation induced by twin boundary migration. In this study, we elucidated the mechanisms of symmetry breaking induced by strain relaxation in Ag nanoparticles by employing transmission electron microscopy, electron tomography, and strain analysis. The experimental results reveal that decahedral nanoparticles larger than ∼50 nm evolve into asymmetrical rhomboid pyramids to relax the lattice strain energy in the 5-fold twin through twin pole migration. This migration is achieved by coordinating slip and dissociation of partial and perfect dislocations. In addition, we found that the rhomboid pyramid further evolves into a rhomboid bar during growth in a specific way to avoid increasing the strain energy in the crystal

CRISPR-Cas9 Facilitated Multiple-Chromosome Fusion in Saccharomyces cerevisiae

Eukaryotic cells usually contain multiple linear chromosomes. Recently, we artificially created a functional single-chromosome yeast via sequential two-chromosome fusion utilizing the high performance of the CRISPR-Cas9 system and homologous recombination in Saccharomyces cerevisiae. In this paper, we adapted this method for the simultaneous fusion of multiple chromosomes. We demonstrated the fusion of two, two-chromosome sets with a 75% positive rate and three-chromosome fusions with a 50% positive rate. We also found that by using an additional selection marker, the positive rate of two-chromosome fusions reached 100%. Due to the simplicity, efficiency, and portability of this method, we expect that it can be easily adapted for multiple-chromosome fusions in other organisms

Unravelling Structure and Formation Mechanisms of Ruddlesden–Popper-Phase-like Nanodomains in Inorganic Lead Halide Perovskites

Ultrastable CsPbBr3 nanoplates against electron beam irradiations are fabricated and nanodomains with anomalous high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) contrasts are observed within CsPbBr3 nanoplates. Atomic resolution energy dispersive X-ray spectroscopy (EDS) mapping, which requires even higher beam currents and may cause significant damages on electron beam sensitive materials, are obtained without any detectable damages or decomposition. Combining HAADF-STEM images, atomic resolution EDS mapping, and image simulations has revealed detailed structure and chemistry of the nanodomains to be induced by Ruddlesden–Popper faults (RP faults) rather than any chemical intermixing or formation of new phases. A formation mechanism is also proposed on the basis of the atomic structure of the nanodomains. This result promotes an atomic-level understanding of inorganic lead halide perovskites and may help to reveal their structure–property relationship

Tuning Electronic and Magnetic Properties of Early Transition-Metal Dichalcogenides via Tensile Strain

We have performed a systematic first-principles study of the effect of tensile strains on the electronic properties of early transition-metal dichalcogenide (TMDC) monolayers MX₂ (M = Sc, Ti, Zr, Hf, Ta, Cr; X = S, Se, Te). Our density functional theory calculations suggest that the tensile strain can significantly affect the electronic properties of many early TMDCs in general and the electronic bandgap in particular. For group IVB TMDCs (TiX₂, ZrX₂, HfX₂), the bandgap increases with the tensile strain, but for ZrX₂ and HfX₂ (X = S, Se), the bandgap starts to decrease at strain 6–8%. For the group VB TMDCs (TaX₂), the tensile strain can either induce the ferromagnetism or enhance the existing ferromagnetism. For the group VIB TMDCs (CrX₂), the direct-to-indirect bandgap transition is seen upon application of the tensile strain, except CrTe₂ whose bandgap decreases with the tensile strain even though the direct character of its bandgap is retained. Lastly, for the group IIIB TMDCs (ScX₂) in the T metallic phase, we find that the tensile strain has little effect on their electronic and magnetic properties. Our study suggests that strain engineering is an effective approach to modify electronic and magnetic properties of most early TMDC monolayers, thereby opening an alternative way for future optoelectronic and spintronic applications

Additional file 1 of Yeasts from Chinese strong flavour Daqu samples: isolation and evaluation of their potential for fortified Daqu production

Additional file 1: Table S1. Sugar fermentation profiles of different yeasts. Table S2. The volatile aroma compounds detected and measured in fortified Daqu obtained by using various yeast strains. Table S3. The volatile aroma compounds detected and measured in fortified Daqu obtained by using different inoculum sizes of strain YE006 and YE010

Photothermionic Effect-Assisted Ultrafast Charge Transfer in NbS₂/MoS₂ Heterostructure

Two-dimensional (2D) van der Waals heterostructures (vdW HSs) composed of transition metal dichalcogenides (TMDCs) have emerged as frontrunners in the optoelectronics field, owing to their exceptional optical and electrical properties. Recent research on the intrinsic interlayer charge transfer mechanism has been primarily focused on the Type II HSs, while metal–semiconductor (MS) vertical HSs, promising for advancing photodetector technology, have received comparatively less attention. Here, we reveal the first experimental observation of photothermionic effect-assisted ultrafast interlayer charge transfer in the NbS2/MoS2 heterostructure using femtosecond transient absorption technology and first-principles calculations, effectively ignoring the Schottky barrier height. We demonstrate that within 500 fs, charge transfer occurs from NbS2 to MoS2 in the heterostructure, resulting in supplementary carrier generation in the visible spectrum when excited with infrared light below the MoS2 bandgap, at wavelengths of 1030 and 1500 nm. Such promising characteristics of 2D NbS2-semiconductor heterostructures offer a potential platform for synergistically combining low contact resistance with broadband photocarrier generation, marking a significant advancement in optoelectronics and light harvesting

Two-Dimensional Biphenylene-Based Carbon Allotrope Family with High Potassium Storage Ability

The development of new carbon materials with novel properties and excellent applications is essential and urgent in many fields, such as potassium-ion batteries (PIBs). In this study, a family of 30 two-dimensional biphenylene carbon allotropes (2D-BCAs) have been systematically extended in theory. The energies of these allotropes are slightly higher than that of graphene, which can be well described by a quantitative energy equation. The 2D-BCAs show high synthesizability consistent with the experimental biphenylene network via “HF-zipping” reactions. The 2D-BCAs are metallic or semimetallic. Six representative 2D-BCAs exhibit good lattice dynamical and thermal stability, excellent anisotropic mechanical properties, and ORR catalytic activity. Moreover, the selected 2D-BCAs demonstrate ultrahigh theoretical potassium-storage capacities of 1116–1489 mAh·g–1, low migration barriers of 0.03–0.22 eV, and low open-circuit voltages of 1.10–0.02 V. The remarkable properties render 2D-BCAs as promising anode materials in PIBs, electrocatalysts, and conductors in electronics and iontronics

Phosphorene Nanoribbons, Phosphorus Nanotubes, and van der Waals Multilayers

We perform a comprehensive first-principles study of the electronic properties of phosphorene nanoribbons, phosphorus nanotubes, multilayer phosphorene sheets, and heterobilayers of phosphorene and two-dimensional (2D) transition-metal dichalcogenide (TMDC) monolayer. The tensile strain and electric-field effects on electronic properties of low-dimensional phosphorene nanostructures are also investigated. Our calculations show that the bare zigzag phosphorene nanoribbons (z-PNRs) are metals regardless of the ribbon width, whereas the bare armchair phosphorene nanoribbons (a-PNRs) are semiconductors with indirect bandgaps and the bandgaps decrease with increasing ribbon width. We find that compressive (or tensile) strains can reduce (or enlarge) the bandgap of the bare a-PNRs while an in-plane electric field can significantly reduce the bandgap of the bare a-PNRs, leading to the semiconductor-to-metal transition beyond certain electric field. For edge-passivated PNR by hydrogen, z-PNRs become semiconductor with nearly direct bandgaps and a-PNRs are still semiconductor but with direct bandgaps. The response to tensile strain and electric field for the edge-passivated PNRs is similar to that for the edge-unpassivated (bare) a-PNRs. For single-walled phosphorus nanotubes, both armchair and zigzag nanotubes are semiconductors with direct bandgaps. With either tensile strains or transverse electric field, behavior of bandgap modulation similar to that for a-PNRs can arise. It is known that multilayer phosphorene sheets are semiconductors whose bandgaps decrease with an increase in the number of multilayers. In the presence of a vertical electric field, the bandgaps of multilayer phosphorene sheets decrease with increasing electric field and the bandgap modulation is more significant with more layers. Lastly, heterobilayers of phosphorene (p-type) with an n-type TMDC (MoS₂ or WS₂) monolayer are still semiconductors while their bandgaps can be reduced by applying a vertical electric field as well. We also show that the combined phosphorene/MoS₂ heterolayers can be an effective solar cell material. Our estimated power conversion efficiency for the phosphorene/MoS₂ heterobilayer has a theoretical maximum value of 17.5%