Pressure-Induced Enhancement and Retainability of Optoelectronic Properties in Layered Zirconium Disulfide.

Transition metal dichalcogenides (TMDs) exhibit excellent electronic and photoelectric properties under pressure, prompting researchers to investigate their structural phase transitions, electrical transport, and photoelectric response upon compression. Herein, the structural and photoelectric properties of layered ZrS2 under pressure using in situ high-pressure photocurrent, Raman scattering spectroscopy, alternating current impedance spectroscopy, absorption spectroscopy, and theoretical calculations are studied. The experimental results show that the photocurrent of ZrS2 continuously increases with increasing pressure. At 24.6 GPa, the photocurrent of high-pressure phase P21/m is three orders of magnitude greater than that of the initial phase P 3 ¯ m 1 $P\bar{3}m1$ at ambient pressure. The minimum synthesis pressure for pure high-pressure phase P21/m of ZrS2 is 18.8 GPa, which exhibits a photocurrent that is two orders of magnitude higher than that of the initial phase P 3 ¯ m 1 $P\bar{3}m1$ and displays excellent stability. Additionally, it is discovered that the crystal structure, electrical transport properties and bandgap of layered ZrS2 can also be regulated by pressure. This work offers researchers a new direction for synthesizing high-performance TMDs photoelectric materials using high pressure, which is crucial for enhancing the performance of photoelectric devices in the future.

The metal atomic substitution induced half-metallic properties, metallic properties and semiconducting properties in X-N4 nanoribbons.

Armchair X-N4 nanoribbons (X-AN4NRs) and zigzag X-N4 nanoribbons (X-ZN4NRs) were calculated using first-principles calculations. Ferromagnets (FM) were found to be the most stable among the initial magnetic structures. Furthermore, nanoribbons were found to be thermodynamically stable through molecular dynamics simulations. It can be found that when the temperature and total energy of X-AN4NRs and X-ZN4NRs change with time, they have a small oscillation range, which confirms the dynamic stability of X-AN4NRs and X-ZN4NRs under realistic experimental conditions. Subsequently, the magnetic moment analysis of the X-AN4NRs and X-ZN4NRs revealed that the magnetic moment of the X-AN4NRs is significantly smaller than that of X-ZN4NRs. The band structure and density of states (DOS) of the X-AN4NRs and X-ZN4NRs were also computed, which indicate different properties for different transition metal nanoribbons. The results suggest that different edge structures and transition metals can influence the electronic structure of the nanoribbons. Moreover, based on the band structure and DOS, it was found that Mn-AN4NRs and Fe-ZN4NRs exhibit half-metallic properties. They can generate 100% polarized currents at the Fermi level, providing valuable information for developing spintronic devices. Our study has a positive value for regulating the properties of the nanoribbons by metal atom substitution.

High-pressure magnetic properties and electrical transport behaviors of half-metallic ferromagnet CrO2.

The magnetic properties and electrical transport behaviors of half-metallic ferromagnet chromium dioxide (CrO2) powders under high pressure have been investigated by in situ electrical resistivity, magneto-resistivity, and Hall-effect measurements. Our results reveal that the Hall coefficient, carrier concentration, and mobility all present discontinuous changes from 11.7 GPa to 14.9 GPa which can be attributed to the second-order structural transition from the rutile-type to CaCl2-type. However, the resistivity decreases monotonically from ambient pressure to 16.5 GPa. This is due to, first, the decreased carrier concentration and the increased carrier mobility canceling the effects of each other on the resistivity; second, according to the calculation results, the bandgap of CrO2 decreased gradually with the pressure, and the bandgaps of the rutile-type phase and the CaCl2-type phase are extremely similar. CrO2 exhibits a linear and negative magnetoresistance under the applied magnetic field (0∼ ± 15 kOe). As the pressure increases, the magnetoresistance remains negative, but it becomes nonlinear and less symmetric, suggesting that pressure has an appreciable impact on the double-exchange mechanism leading to ferromagnetism in CrO2.

Tailored modifications of the electronic properties of g-C3N4/C2N-h2D nanoribbons by first-principles calculations.

The electronic structure of g-C3N4/C2N-h2D nanoribbons was investigated by first-principles calculations. As a splice structure, we first computed the three magnetic coupled states of g-C3N4/C2N-h2D nanoribbons. After self-consistent calculations, both the antiferromagnetic and paramagnetic coupling states become ferromagnetic coupling states. It was proved that the ferromagnetic coupling state is the most stable state. Thermodynamic stability was subsequently verified based on the ferromagnetic coupling state. It had a steady electron spin polarization, with a magnetic moment of 1 µB for each primitive cell. It changed from a direct band-gap semiconductor to an indirect band-gap semiconductor and exhibited the properties of a narrow band gap semiconductor through the analysis of the energy band and charge density. To transform the electronic structure, we adsorbed different transition metals in g-C3N4/C2N-h2D nanoribbons. We investigated the electronic structure of g-C3N4/C2N-h2D nanoribbons adsorbed by different transition metals. It was shown that the electronic structure of g-C3N4/C2N-h2D nanoribbons could be regulated by the adsorption of different transition metal atoms. Moreover, the adsorption of Fe and Ni can generate a 100% polarized current in the Fermi surface, which will provide more application potential for spintronics devices.

Doping atom improves photocatalytic performance in a new metal-free organic photocatalyst for water splitting.

Photocatalytic water splitting, using solar energy to obtain hydrogen, is an ideal technology for producing new energy. In the process of photocatalysis, the improvement of the catalytic performance of the catalysts used is a matter of great concern to scientists. So far, there are many problems preventing improvements in photocatalytic performance. In this paper, we propose an atom-doping method, which is an effective method to improve the catalytic performance. We present a type of graphene-like carbon nitride material, whose primitive cell is composed of 12 carbon atoms and 14 nitrogen atoms, so it is denoted as g-C12N14. The energy band, density of states, and optical absorption spectrum of g-C12N14 have been studied using first-principles calculations. From the characteristics of these properties, it is concluded that g-C12N14 can be used as a photocatalyst, but its catalytic performance is low. To improve the catalytic performance, atom doping has been used, which can change the electronic state of the surface to enhance the activity of the photocatalyst. It was calculated that the doped phosphorus and boron system improved the optical absorption range, thus improving the photocatalytic efficiency. To make the results more accurate, all the calculations used the computationally-large HSE06 hybrid functional method.

HvGST4 enhances tolerance to multiple abiotic stresses in barley: Evidence from integrated meta-analysis to functional verification.

Extreme weather events have become more frequent, increasing crop yield fluctuations in many regions and thus the risk to global food security. Breeding crop cultivars with improved tolerance to a combination of abiotic stresses is an effective solution to counter the adverse impact of climate change. The ever-increasing genomic data and analytical tools provide unprecedented opportunities to mine genes with tolerance to multiple abiotic stresses through bioinformatics analysis. We undertook an integrated meta-analysis using 260 transcriptome data of barley related to drought, salt, heat, cold, and waterlogging stresses. A total of 223 shared differentially expressed genes (DEGs) were identified in response to five abiotic stresses, and significantly enriched in 'glutathione metabolism' and 'monoterpenoid biosynthesis' pathways. Using weighted gene co-expression network analysis (WGCNA), we further identified 15 hub genes (e.g., MYB, WRKY, NADH, and GST4) and selected the GST4 gene for functional validation. HvGST4 overexpression in Arabidopsis thaliana enhanced the tolerance to multiple abiotic stresses, likely through increasing the content of glutathione to scavenge reactive oxygen species and alleviate cell membrane peroxidation. Furthermore, we showed that virus-induced gene silencing (VIGS) of HvGST4 in barley leaves exacerbated cell membrane peroxidation under five abiotic stresses, reducing tolerance to multiple abiotic stress. Our study provides a new solution for identifying genes with tolerance to multiple abiotic stresses based on meta-analysis, which could contribute to breeding new varieties adapted genetically to adverse environmental conditions.

HvbZIP21, a Novel Transcription Factor From Wild Barley Confers Drought Tolerance by Modulating ROS Scavenging.

Drought stress is a common environmental stress, which adversely affects the yield and quality of crops. Due to its excellent drought tolerance, wild barley from the Middle East region is considered a valuable source for barley improvement. Here, we compared the growth rate, stomatal regulation and capacity to metabolize reactive oxygen species (ROS) of two barley cultivars and one wild barley accession. The results indicated the wild barley EC_S1 showed a more significant decline in stomatal aperture and less ROS production. Transcriptomic analysis revealed that EC_S1 has slower transcriptional regulation (5,050 DEGs) in the early stage of drought stress (14 days) than Baudin (7,022 DEGs) and Tadmor (6,090 DEGs). In addition, 30 hub genes, including nine known drought-related genes were identified by WGCNA analysis. Then, we cloned a novel bZIP transcription factor, HvbZIP21, from EC_S1. HvbZIP21 was subcellularly targeted to the nucleus. Overexpression of HvbZIP21 in Arabidopsis enhanced drought tolerance due to increasing activities of superoxide dismutase, peroxidase, and catalase activities as well as glutathione content. Silencing of HvbZIP21 in EC_S1 suppressed drought tolerance in BSMV:HvbZIP21-inoculated plants. Taken together, our findings suggest that HvbZIP21 play a critical role in drought tolerance by manipulating ROS scavenging.

Electron momentum density of boron-doped carbon nano-onions studied by electron energy-loss spectroscopy.

Valence Compton profiles (CPs) (electron momentum density projections) of B-doped carbon nano-onions (CNOs) as a function of the boron doping content were obtained by recording electron energy-loss spectra at large scattering angles using a transmission electron microscope, a technique known as electron Compton scattering from solids (ECOSS). The amplitude of the CPs at zero momentum increases with increasing doping content, while the shape of the CPs becomes narrower with increasing doping content. The differences between the profiles of B-doped CNOs and that of pristine CNOs have been clearly observed. These experimental results indicate substantially greater delocalization of the ground-state charge density in B-doped CNOs than in pristine CNOs. The results clearly demonstrate that the ECOSS technique is an efficient and reliable experimental method for studying electron density distributions in solids as a function of the heteroatom doping content.

Two-component gas quartz-enhanced photoacoustic spectroscopy sensor based on time-division multiplexing of distributed-feedback laser driver current.

A two-component gas sensor in quartz-enhanced photoacoustic spectroscopy based on time-division multiplexing (TDM) technology of a distributed-feedback (DFB) laser driver current was proposed and experimentally demonstrated. The quartz tuning-fork-based photoacoustic spectroscopy (PAS) cell configuration with two optical collimators and two acoustic microresonators was designed to detect the second-harmonic (${2}f$2f) PAS signal. The two optical collimators guaranteed that the two laser beams would inject the PAS cell conveniently, providing higher power input than a 3 dB optical fiber coupler. Two-component gas sensing was achieved by the TDM of the DFB laser driver current. We used this two-component gas sensing technique to detect acetylene (${{\rm C}_2}{{\rm H}_2}$C2H2) at 1532.83 nm and methane (${{\rm CH}_4}$CH4) at 1653.722 nm. The ${{\rm C}_2}{{\rm H}_2}$C2H2 and ${{\rm CH}_4}$CH4 detection was achieved at a 2.4 s interval. The minimum detection limits of 1 ppmv for ${{\rm C}_2}{{\rm H}_2}$C2H2 and 13.14 ppmv for ${{\rm CH}_4}$CH4 were obtained, and the linear responses reached were 0.99968 and 0.99652 for ${{\rm C}_2}{{\rm H}_2}$C2H2 and ${{\rm CH}_4}$CH4, respectively. Moreover, the continuous monitoring of ${{\rm CH}_4}$CH4 and ${{\rm C}_2}{{\rm H}_2}$C2H2 for 40 min showed a good stability. The TDM technology of the DFB laser driver current would play an important role on the multi-component detection.

Compton profile of few-layer graphene investigated by electron energy-loss spectroscopy.

In this paper, acquisition of the valence Compton profile of few-layer graphene using electron energy-loss spectroscopy at large scattering angle is reported. The experimental Compton profile is compared with the corresponding theoretical profile, calculated using the full-potential linearized augmented plane wave method based on the local-density approximation. Good agreement exists between the theoretical calculation and experiment. The graphene profile indicates a substantially greater delocalization of the ground state charge density compared to that of graphite.

3D aluminum/silver hierarchical nanostructure with large areas of dense hot spots for surface-enhanced raman scattering.

Plasmonic nanomaterials possessing large-volume, high-density hot spots with high field enhancement are highly desirable for ultrasensitive surface-enhanced Raman scattering (SERS) sensing. However, many as-prepared plasmonic nanomaterials are limited in available dense hot spots and in sample size, which greatly hinder their wide applications in SERS devices. Here, we develop a two-step physical deposition protocol and successfully fabricate 3D hierarchical nanostructures with highly dense hot spots across a large scale (6 × 6 cm2 ). The nanopatterned aluminum film was first prepared by thermal evaporation process, which can provide 3D quasi-periodic cloud-like nanostructure arrays suitable for noble metal deposition; then a large number of silver nanoparticles with controllable shape and size were decorated onto the alumina layer surfaces by laser molecular beam epitaxy, which can realize large-area accessible dense hot spots. The optimized 3D-structured SERS substrate exhibits high-quality detection performance with excellent reproducibility (13.1 and 17.1%), whose LOD of rhodamine 6G molecules was 10-9 M. Furthermore, the as-prepared 3D aluminum/silver SERS substrate was applied in detection of melamine with the concentration down to 10-7 M and direct detection of melamine in infant formula solution with the concentration as low 10 mg/L. Such method to realize large-area hierarchical nanostructures can greatly simplify the fabrication procedure for 3D SERS platforms, and should be of technological significance in mass production of SERS-based sensors.

Investigation of Electron Momentum Density in Carbon Nanotubes Using Transmission Electron Microscopy.

Valence Compton profiles (CPs) of multiwall (MWCNTs) and single-wall carbon nanotubes (SWCNTs) were obtained by recording electron energy-loss spectra at large momentum transfer in the transmission electron microscope, a technique known as electron Compton scattering from solids (ECOSS). The experimental MWCNT/SWCNT results were compared with that of graphite. Differences between the valence CPs of MWCNTs and SWCNTs were observed, and the SWCNT CPs indicate a greater delocalization of the ground-state charge density compared to graphite. The results clearly demonstrate the feasibility and potential of the ECOSS technique as a complementary tool for studying the electronic structure of materials with nanoscale spatial resolution.

Combined study of the ground and excited states in the transformation of nanodiamonds into carbon onions by electron energy-loss spectroscopy.

The electron momentum density and sp2/sp3 ratio of carbon materials in the thermal transformation of detonation nanodiamonds (ND) into carbon nano-onions are systematically studied by electron energy-loss spectroscopy (EELS). Electron energy-loss near-edge structures of the carbon K-ionization in the electron energy-loss spectroscopy are measured to determine the sp2 content of the ND-derived samples. We use the method developed by Titantah and Lamoen, which is based on the ability to isolate the π* spectrum and has been shown to give reliable and accurate results. Compton profiles (CPs) of the ND-derived carbon materials are obtained by performing EELS on the electron Compton scattering region. The amplitude of the CPs at zero momentum increases with increasing annealing temperature above 500 °C. The dramatic changes occur in the temperature range of 900-1300 °C, which indicates that the graphitization process mainly occurs in this annealing temperature region. Our results complement the previous work on the thermal transformation of ND-derived carbon onions and provide deeper insight into the evolution of the electronic properties in the graphitization process.

Bioscaffold arrays decorated with Ag nanoparticles as a SERS substrate for direct detection of melamine in infant formula.

Three-dimensional (3D) plasmonic structures have been intensively investigated as high performance surface enhanced Raman scattering (SERS) substrates. Here, we demonstrate a 3D biomimetic SERS substrate prepared by deposition of silver nanoparticles (Ag NPs) on the bioscaffold arrays of cicada wings using laser molecular beam epitaxy. This deposition method can offer a large number of nanoparticles with average diameter of ∼10 nm and nanogaps of sub-10 nm on the surface of chitin nanopillars to generate a high density of hotspots. The prepared 3D Ag/cicada SERS substrate shows a limit of detection (LOD) for Rhodamine 6G as low as 10-7 M, high enhancement factor of 1.09 × 105, and excellent signal uniformity of 6.8%. Moreover, the molecular fingerprints of melamine in infant formula can be directly extracted with an LOD as low as 10 mg L-1, without the need for functional modification. The prepared SERS-active substrate, due to its low cost, high-throughput, and good detection performance, can be widely used in applications such as food safety and environmental monitoring.

The charge regulation of electronic structure and optical properties of graphitic carbon nitride under strain.

The electronic structure of the graphitic carbon nitride (g-C6N6) under strain was obtained using the hybrid density functional HSE06 with a larger computational workload. The g-C6N6 could withstand 12% of the applied tensile strain. The electronic structure of g-C6N6 could be changed effectively under the tensile force. The band gap changed from direct to indirect under the strain and could be tuned in the range of 3.16 eV to 3.75 eV. At approximately 4% of the applied strain, there was a transition of the valence band maximum (VBM). A wider range of light absorption could be obtained under the strain. Our results provide a prospect for the future applications of two-dimensional materials in electronic and optoelectronic devices.

Insights into the surface chemistry and electronic properties of sp2 and sp3-hybridized nanocarbon materials for catalysis.

Ultra-dispersed nanodiamond and its derivatives (UNDDs), including bucky nanodiamond and onion-like carbon, offer superior catalytic behavior relative to other nanocarbons. However, a systematic study of their unique properties has been rarely achieved. Their surface chemistry and electronic properties are therefore studied to reveal the essential differences of UNDDs compared to other nanocarbons for catalysis.

The influence of carbon surface chemistry on supported palladium nanoparticles in heterogeneous reactions.

The surface chemistry of nanocarbon support can tailor chemical properties of precious metal nanoparticle/nanocarbon hybrid catalyst in heterogeneous reactions. We report on modified reduced graphene oxide (rGO) support with ionic liquid-derived carbonaceous surface for palladium nanoparticle (Pd NPs) decoration and their actions in different heterogeneous reactions. The surface chemistry of support materials was characterized in detail, and the influence of which on the formation and distribution of metal particles was further investigated. Three different types of reactions including Suzuki-Miyaura coupling reaction, CO oxidation and phenol reduction were examined in terms of reactivity and selectivity. The roles of substituted nitrogen in graphitic lattice and grafted groups on the carbon surface were exploited. Nitrogen-doping can give rise to changes in electronic properties of supported metals, and the Lewis basicity of the doped nitrogen atoms can favor the adsorption of acidic reactants in phenol reduction. The grafted groups derived a negative impact to the Suzuki-Miyaura coupling reaction, due to the involvement of larger reactant molecules, despite that they could prevent significant sintering of Pd NPs in the CO oxidation.

Multi-Walled Carbon Nanotubes as a Catalyst for Gas-Phase Oxidation of Ethanol to Acetaldehyde.

Multi-walled carbon nanotubes (CNTs) were directly used as a sustainable and green catalyst to convert ethanol into acetaldehyde in the presence of molecular oxygen. The C=O groups generated on the nanocarbon surface were demonstrated as active sites for the selective oxidation of ethanol to acetaldehyde. The transformation of disordered carbon debris on the CNT surface to ordered graphitic structures induced by thermal-treatment significantly enhanced the stability of the active C=O groups, and thus the catalytic performance. A high reactivity with approximately 60 % ethanol conversion and 93 % acetaldehyde selectivity was obtained over the optimized CNT catalyst at 270 °C. More importantly, the catalytic performance was quite stable even after 500 h, which is comparable with a supported gold catalyst. The robust catalytic performance displayed the potential application of CNTs in the industrial catalysis field.

Selective and Stable Ethylbenzene Dehydrogenation to Styrene over Nanodiamonds under Oxygen-lean Conditions.

For the first time, significant improvement of the catalytic performance of nanodiamonds was achieved for the dehydrogenation of ethylbenzene to styrene under oxygen-lean conditions. We demonstrated that the combination of direct dehydrogenation and oxidative dehydrogenation indeed occurred on the nanodiamond surface throughout the reaction system. It was found that the active sp(2)-sp(3) hybridized nanostructure was well maintained after the long-term test and the active ketonic carbonyl groups could be generated in situ. A high reactivity with 40% ethylbenzene conversion and 92% styrene selectivity was obtained over the nanodiamond catalyst under oxygen-lean conditions even after a 240 h test, demonstrating the potential of this procedure for application as a promising industrial process for the ethylbenzene dehydrogenation to styrene without steam protection.

Communication: Investigation of the electron momentum density distribution of nanodiamonds by electron energy-loss spectroscopy.

The electron momentum distribution of detonation nanodiamonds (DND) was investigated by recording electron energy-loss spectra at large momentum transfer in the transmission electron microscope (TEM), which is known as electron Compton scattering from solid (ECOSS). Compton profile of diamond film obtained by ECOSS was found in good agreement with prior photon experimental measurement and theoretical calculation that for bulk diamond. Compared to the diamond film, the valence Compton profile of DND was found to be narrower, which indicates a more delocalization of the ground-state charge density for the latter. Combining with other TEM characterizations such as high-resolution transmission electron spectroscopy, diffraction, and energy dispersive X-ray spectroscopy measurements, ECOSS was shown to be a great potential technique to study ground-state electronic properties of nanomaterials.