Multi-band reprogrammable phase-change metasurface spectral filters for on-chip spectrometers.

Active optical metasurfaces provide a platform for dynamic and real-time manipulation of light at subwavelength scales. However, most active metasurfaces are unable to simultaneously possess a wide wavelength tuning range and narrow resonance peaks, thereby limiting further advancements in the field of high-precision sensing or detection. In the paper, we proposed a reprogrammable active metasurface that employs the non-volatile phase change material Ge2Sb2Te5 and demonstrated its excellent performance in on-chip spectrometer. The active metasurfaces support magnetic modes and feature Friedrich-Wintgen quasi bound states in the continuum, capable of achieving multi-resonant near-perfect absorption, a multilevel tuning range, and narrowband performance in the infrared band. Meanwhile, we numerically investigated the coupling phenomenon and the intrinsic relationship between different resonance modes under various structural parameters. Furthermore, using the active metasurfaces as tunable filters and combined with compressive sensing algorithms, we successfully reconstructed various types of spectral signals with an average fidelity rate exceeding 0.99, utilizing only 51 measurements with a single nanostructure. A spectral resolution of 0.5 nm at a center wavelength 2.538 µm is predicted when the crystallization fractions of GST change from 0 to 20%. This work has promising potential in on-site matter inspection and point-of-care (POC) testing.

Improving liming mode for remediation of Cd-contaminated acidic paddy soils: Identifying the optimal soil pH, model and efficacies.

Liming has been widely taken to remediate Cd-contaminated acidic paddy soils, whereas liming mode involving in the relevant optimal soil pH, model and efficacies remain unclear. Both soil and field liming experiments were conducted to improve liming mode for precise remediation of Cd-contaminated acidic paddy soils. Soil batch liming experiments indicated soil DTPA-Cd and CaCl2-Cd were piecewise linearly correlated to soil pH with nodes of 6.8-8.0, and decreased respectively by 15.3%37.7% and 80.7%93.8% (P < 0.05) when soil pH raised over the nodes, indicating an appropriate target soil pH 7.0 for liming. Stepwise linear regression revealed that liming ratio (LR, kg ha-1) could be estimated from soil basal pH (pH0) and the interval to the target soil pH (ΔpH), as [LR=exp(1.10 ×ΔpH+0.61 ×pH0-4.98), R2 = 0.97, n = 42, P < 0.01]. The model exhibited high prediction accuracy (95.2%), low mean estimation error (-0.02) and root mean square error (0.20). Field liming experiment indicated liming to target pH decreased respectively soil CaCl2-Cd by 95.2-98.0% and rice grain Cd by 59.8-80.6% (P < 0.01), whereas uninfluenced rice grain yield. Correlation analysis and structural equation models (SEM) demonstrated that great reduction in Cd phytoavailability was mainly attributed to the transformation of soil water-soluble and exchangeable Cd to carbonate-bound Cd and Fe/Mn oxides-bound Cd and reduced Cd in iron plaque as increasing soil pH. However, rice grain Cd of 50% samples met national food safety standards limit of China (0.2 mg kg-1) due to the high soil Cd level (0.8 mg kg-1). In conclusion, liming to target soil pH 7.0 could be considered as a precise and effective remediation mode for Cd-contaminated acidic paddy soils and complementary practices should be implemented for severe pollution. Our results could provide novel insights on precise liming remediation of Cd-contaminated acidic paddy soils.

Multistep optimization for the electrodeposited mixed perovskite FA1-yCsyPbBrxI3-xsolar cells.

The electrodeposition method has recently been developed for the fabrication of perovskite solar cells due to its potential advantages in commercial preparation. However, there is few studies on the preparation of perovskite solar cells by the electrodeposition method, especially on the perovskite FAPbI3-based solar cells. Herein, we fabricated the mixed perovskite FA1-yCsyPbBrxI3-xsolar cells by an optimized electrodeposition method, in which the electrodeposited PbO2reacts directly with FAI and an appropriate amount of CsBr dopants. The corresponding solar cells display the best PCE of 4.97%. By regulating the growth temperature in the reaction between PbO2and FAI/CsBr, the efficiency of the mixed perovskite solar cells can be promoted to 10.18%. These results illustrate that the element doping and growth environment regulation can optimize the quality of the perovskite films, thus promoting the efficiency of the perovskite solar cells. With further optimizing the growth process in the electrodeposition method, it is expected to open up a new commercial preparation route for the perovskite solar cells in the near future.

Interface Optimization and Performance Enhancement of Er2O3-Based MOS Devices by ALD-Derived Al2O3 Passivation Layers and Annealing Treatment.

In this paper, the effect of atomic layer deposition (ALD)-derived Al2O3 passivation layers and annealing temperatures on the interfacial chemistry and transport properties of sputtering-deposited Er2O3 high-k gate dielectrics on Si substrate has been investigated. X-ray photoelectron spectroscopy (XPS) analyses have showed that the ALD-derived Al2O3 passivation layer remarkably prevents the formation of the low-k hydroxides generated by moisture absorption of the gate oxide and greatly optimizes the gate dielectric properties. Electrical performance measurements of metal oxide semiconductor (MOS) capacitors with different gate stack order have revealed that the lowest leakage current density of 4.57 × 10-9 A/cm2 and the smallest interfacial density of states (Dit) of 2.38 × 1012 cm-2 eV-1 have been achieved in the Al2O3/Er2O3/Si MOS capacitor, which can be attributed to the optimized interface chemistry. Further electrical measurements of annealed Al2O3/Er2O3/Si gate stacks at 450 °C have demonstrated superior dielectric properties with a leakage current density of 1.38 × 10-9 A/cm2. At the same, the leakage current conduction mechanism of MOS devices under various stack structures is systematically investigated.

Construction of WO3 quantum dots/TiO2 nanowire arrays type II heterojunction via electrostatic self-assembly for efficient solar-driven photoelectrochemical water splitting.

Construction of a heterojunction between quantum dots and TiO2 nanowire arrays via electrostatic self-assembly is rarely reported. In this work, mercury lamp irradiation was used to change the surface potential of WO3 quantum dots and TiO2 nanowire arrays, resulting in WO3 quantum dots tightly attached on the surface of TiO2 nanowire through electrostatic self-assembly. Photoelectrochemical measurements showed that the WO3 quantum dots formed a type II heterojunction with the TiO2 nanowire arrays rather than serving as carrier-trapping sites. In the self-assembly system, the TiO2 nanowire arrays provide a charge-transfer channel for the WO3 quantum dots, greatly improving the contribution of the WO3 quantum dots to the photocurrent. Quantitative calculations showed that the improvement of the bulk carrier-separation efficiency was the reason for the enhanced photoelectrochemical performance of the self-assembled system. The photocurrent density of the optical self-assembled system at 1.23 V (vs. RHE) was ∼5.5 times as high as that of the TiO2 nanowire arrays. More importantly, the self-assembled system exhibited excellent photoelectrochemical stability.

Synergistic effects of the Rh-S bond and spatially separated dual cocatalysts on photocatalytic overall water splitting activity of ZnIn2S4 nanosheets under visible light irradiation.

Photodeposition of dual-cocatalysts Pt-Cr or Rh-Cr on the surface of ZnIn2S4 is used to achieve overall water splitting. Compared with the hybrid loading of the Pt element and Cr element, the formation of the Rh-S bond results in space separation of the Rh element and Cr element. The Rh-S bond and space separation of cocatalysts promote the transfer of bulk carriers to the surface and inhibit self-corrosion.

Constructing a Surface Multi-cationic Heterojunction for CsPbI1.5Br1.5 Perovskite Solar Cells with Efficiency beyond 14.

All-inorganic CsPbI1.5Br1.5 perovskite solar cells are considered as top cell candidates for tandem cells as a result of their excellent thermal stability and photoelectric performance. However, their power conversion efficiencies (PCEs) are still low and far below the theoretical limit mainly as a result of the severe non-radiative recombination and optical loss. Herein, we introduce an versatile method to construct a surface multi-cationic heterojunction to achieve an efficient and stable CsPbI1.5Br1.5 perovskite solar cell. By precisely controlling the content of FA+ and MA+ on PbBr2-rich perovskite films, a high-quality heterojunction layer is formed to help effectively passivate the surface defects and reduce the optical loss of the CsPbI1.5Br1.5 perovskite. In addition, the incorporation of a heterojunction layer can also improve energy-level alignment and reduce interfacial charge recombination loss. As a result, the champion device with the incorporation of SMH exhibits a PCE of 14.11%, which presents the highest reported efficiency for inorganic CsPbI1.5Br1.5 solar cells thus far while retaining 85% of the initial efficiency after 1000 h of storage without encapsulation.

Three-dimensional graphene encapsulated hollow CoSe2-SnSe2nanoboxes for high performance asymmetric supercapacitors.

Construction of metal selenides with a large specific surface area and a hollow structure is one of the effective methods to improve the electrochemical performance of supercapacitors. However, the nano-material easily agglomerates due to the lack of support, resulting in the loss of electrochemical performance. Herein, we successfully design a three-dimensional graphene (3DG) encapsulation-protected hollow nanoboxes (CoSe2-SnSe2) composite aerogel (3DG/CoSe2-SnSe2) via a co-precipitation method coupled with self-assembly route, followed by a high temperature selenidation strategy. The obtained aerogel possesses porous 3DG conductive network, large specific surface area and plenty of reactive active sites. It could be used as a flexible and binder-free electrode after a facile mechanical compression process, which provided a high specific capacitance of 460 F g-1at 0.5 A g-1, good rate capability of 212.7 F g-1at 10 A g-1The capacitance retention rate is 80% at 2 A g-1after 5000 cycles due to the fast electron/ion transfer and electrolyte diffusion. With the as-prepared 3DG/CoSe2-SnSe2as positive electrodes and the AC (activated carbon) as negative electrodes, an asymmetric supercapacitor (3DG/CoSe2-SnSe2//AC) was fabricated, which delivered a high specific capacity of 38 F g-1at 1 A g-1and an energy density of 11.89 Wh kg-1at 749.9 W kg-1, as well as excellent cycle stability. This work provides a new method for preparing electrode material.

Interface Optimization and Transport Modulation of Sm2O3/InP Metal Oxide Semiconductor Capacitors with Atomic Layer Deposition-Derived Laminated Interlayer.

In this paper, the effect of atomic layer deposition-derived laminated interlayer on the interface chemistry and transport characteristics of sputtering-deposited Sm2O3/InP gate stacks have been investigated systematically. Based on X-ray photoelectron spectroscopy (XPS) measurements, it can be noted that ALD-derived Al2O3 interface passivation layer significantly prevents the appearance of substrate diffusion oxides and substantially optimizes gate dielectric performance. The leakage current experimental results confirm that the Sm2O3/Al2O3/InP stacked gate dielectric structure exhibits a lower leakage current density than the other samples, reaching a value of 2.87 × 10-6 A/cm2. In addition, conductivity analysis shows that high-quality metal oxide semiconductor capacitors based on Sm2O3/Al2O3/InP gate stacks have the lowest interfacial density of states (Dit) value of 1.05 × 1013 cm-2 eV-1. The conduction mechanisms of the InP-based MOS capacitors at low temperatures are not yet known, and to further explore the electron transport in InP-based MOS capacitors with different stacked gate dielectric structures, we placed samples for leakage current measurements at low varying temperatures (77-227 K). Based on the measurement results, Sm2O3/Al2O3/InP stacked gate dielectric is a promising candidate for InP-based metal oxide semiconductor field-effect-transistor devices (MOSFET) in the future.

Superlithiation Performance of Covalent Triazine Frameworks as Anodes in Lithium-Ion Batteries.

Organics with the merit of renewability have been viewed as the promising alternative of inorganic electrode materials in lithium-ion batteries, but most of them display inferior performance due to the sluggish ion/electron diffusion and the potential dissolution in aprotic electrolytes. Here, covalent triazine frameworks (CTFs-1), full of vertical pores and layered spaces for Li+ transfer, have been synthesized with p-dicyanobenzene as the monomer by a facile two-step method including a prepolymerization with CF3SO3H as the catalyst and deep polymerization in molten ZnCl2. CTFs-1-400, obtained at the deep polymerization temperature of 400 °C, exhibits the superlithiation property with the specific capacities of 1626 mA h g-1 at 25 °C and 1913 mA h g-1 at 45 °C at 100 mA g-1, indicating the formation of Li6C6/Li6C3N3 in the reduction process. Electrochemical analysis and density functional theory calculation indicate that the ultrahigh capacity is mainly contributed by the capacitance of micropores and the redox capacity of benzene and triazine rings. Moreover, CTFs-1-400 displays the specific capacity of 740 mA h g-1 for 1000 cycles at 1 A g-1 with almost no capacity fading.

Interface Chemistry and Dielectric Optimization of TMA-Passivated high-k/Ge Gate Stacks by ALD-Driven Laminated Interlayers.

In the present study, a comparative study on the influence of different laminated stacks driven by aomic layer deposition (ALD) on the interfacial and electrcial properties of high-k/Ge gate stacks passivated by trimethylaluminum (TMA) has been performed in detail via X-ray photoelectron spectroscopy (XPS) and electrical measurements. XPS measurements indicate that HfO2/Al2O3/Ge gate stacks can effectively inhibit the formation of Ge suboxides and a low-k germanate layer. Compared to Al2O3/HfO2 and HfO2/Al2O3/HfO2 gate stacks, the HfO2/Al2O3/Ge metal oxide semiconductor (MOS) capacitors exhibited improved electrical performance, including a maximum permittivity of 18.15, disappearing hysteresis, an almost neglected flat band voltage of 0.01 V, and a minimum leakage current density of 3.82 × 10-8 A/cm2 at room temperature. Especially, the leakage current mechanisms of Ge-MOS capacitors based on different laminated stacks measured at room temperature and low temperature (77-327 K) have been comprehensively analyzed. By comparing three different laminated gate stacks, it can be inferred that HfO2/Al2O3/Ge gate stacks have a potential application prospect in Ge-based microelectronic devices.

Polypyrrole encapsulation-protected porous multishelled Co3O4 hollow microspheres for advanced all-solid-state asymmetric supercapacitors with boosted reaction kinetics and stability.

Transition metal oxides (TMOs) have shown great potential in high-performance supercapacitors (SCs) because of their high theoretical capacities, low cost and simple preparation process. However, considerable challenges still remain in simultaneously improving their electrical conductivity, reaction kinetics and stability. Herein, we deliberately designed a polypyrrole encapsulation-protected porous multishelled Co3O4 hollow microspheres (pMS-Co3O4/PPy) composite via a modified carbon self-templating method and in situ oxidative polymerization route. The unique porous multishelled structure of the pMS-Co3O4 hollow microspheres assembled by interconnected Co3O4 nanoparticles can provide sufficient active sites, shorted ion diffusion paths and efficiently alleviate the structural strain. Meanwhile, the PPy encapsulation-protected nanolayers significantly improve their electrical conductivity, contribute pseudocapacitance and protect Co3O4 nanoparticles from structural pulverization-chemical dissolution into electrolyte. The prepared pMS-Co3O4/PPy electrodes exhibited a high specific capacitance (1292.2 F g-1 at 1 A g-1), excellent rate capability (1205.8 F g-1 at 10 A g-1) and cycle stability (ultrahigh capacitance retention of 91.5% for 5000 cycles), which has rarely been achieved in previously reported Co3O4-based electrodes. Furthermore, the assembled all-solid-state asymmetric supercapacitors (pMS-Co3O4/PPy//AC) delivered a high energy density of 40.2 Wh kg-1 at a power density of 761.7 W kg-1 and superior stability with a capacitance retention of 90.6% for 5000 cycles. This study offers an effective nanostructure design strategy to solve the issues of TMOs and develop high-performance energy storage systems.

Interface chemistry modulation and dielectric optimization of TMA-passivated HfDyO x /Ge gate stacks using doping concentration and thermal treatment.

In this work, the effects of different Dy-doping concentrations and annealing temperatures on the interfacial chemistry and electrical properties of TMA-passivated HfDyO x /Ge gate stacks have been investigated systematically. The microstructural, optical, interfacial chemistry, and electrical characteristics of sputtering-driven HfDyO x gate dielectrics have been characterized by means of X-ray diffraction (XRD), UV-Vis transmission spectroscopy, X-ray photoelectron spectroscopy (XPS), and electrical measurements. This work reveals that the interfacial chemistry evolution takes place via two competing processes, including oxide growth and oxide desorption. XPS analyses have confirmed that the 10 W-deposited targeted gate dielectrics display optimized interface characteristics, which can be attributed to the suppressed unstable Ge oxides and inhibition effects on inter-diffusion at the interface. Electrical observations show that the 10 W-driven HfDyO x /Ge MOS device without annealing treatment exhibits optimized electrical performance, including a larger permittivity of 22.4, a smaller flat band voltage of 0.07 V, vanishing hysteresis, a lowest oxide charge density of ∼1011 cm-2, and a lowest leakage current density of 2.31 × 10-8 A cm-2. Furthermore, the influences of doping and annealing conditions on the leakage current conduction mechanisms (CCMs) of HfDyO x /Ge MOS capacitors have also been investigated systematically. All of the experimental results indicate that TMA-passivated HfDyO x /Ge gate stacks with appropriate doping concentrations demonstrate potential application prospects for Ge-based MOSFET devices.

A facile method to fabricate a porous Si/C composite with excellent cycling stability for use as the anode in a lithium ion battery.

Porous Si/C has been fabricated by dehydrating Si/sucrose mixed powder with concentrated H2SO4. The obtained Si/C presents excellent cycling stability with a capacity retention of 85.6% in the 920th cycle at 100 mA g-1, compared with only 13.2% for pure Si in the 100th cycle.

Porous multishelled NiO hollow microspheres encapsulated within three-dimensional graphene as flexible free-standing electrodes for high-performance supercapacitors.

Exploration of electrode materials with well-defined nanostructures and good flexibility is an efficient approach for achieving high-performance and flexible energy storage systems. However, it is still challenging to well integrate active materials into flexible electrodes and simultaneously maintain satisfactory electrochemical performance. Herein, we successfully synthesize novel three-dimensional graphene (3DG)-encapsulated porous multishelled NiO hollow microsphere (3DG/pMS-NiO) composite aerogels via a modified self-templating method and a dopamine (DA)-assisted self-assembly route. The well-designed highly interconnected porous 3DG network and the close contact NiO-graphene structure of the 3DG/pMS-NiO composite aerogels offer multiple advantages such as high porosity and accessible area, improved conductivity, enhanced electrolyte diffusion and a simple electrode preparation process. Thus, the as-prepared flexible 3DG/pMS-NiO electrodes showed significantly improved specific capacitance of 710.4 F g-1 at 0.5 A g-1 and excellent rate capability with an ultrahigh capacitance retention of 92.5% at 10 A g-1. In addition, the fabricated asymmetric supercapacitors (3DG/pMS-NiO//AC) showed a high specific capacitance of 34.4 F g-1 at 1 A g-1 with a voltage window of 0-1.6 V, a large energy density of 12.3 W h kg-1 at a power density of 815.3 W kg-1, and a decent cycling stability. This work profoundly enlightens the material design and electrode preparation, and even opens up an avenue for the development of high-performance and flexible energy storage systems.

Efficient Fractionation of Graphene Oxide Based on Reversible Adsorption of Polymer and Size-Dependent Sodium Ion Storage.

Graphene oxide (GO) is not only a unique class of two-dimensional (2D) materials but also an important precursor for scalable preparation of graphene. The efficient size fractionation of GO is of great importance to the fundamental and applied studies of chemically modified graphene, but remains a great challenge. Herein, we report an efficient and scalable fractionation method of GO employing reversible adsorption/desorption of temperature-responsive poly( N-isopropylacrylamide) on GO to amplify its mass difference and significantly improve the fractionation efficiency. Furthermore, size-dependent sodium ion storage of the resulting fractionated reduced GO (RGO) is revealed for the first time with high sodium storage performance achieved for the smallest RGO because of its largest d-spacing and most defect sites. This work provides valuable insights into the size fractionation and size-dependent electrochemical performance of graphene, which can be potentially extended to other 2D materials.

On the Effect of Native SiO2 on Si over the SPR-mediated Photocatalytic Activities of Au and Ag Nanoparticles.

In hybrid materials containing plasmonic nanoparticles such as Au and Ag, charge-transfer processes from and to Au or Ag can affect both activities and selectivity in plasmonic catalysis. Inspired by the widespread utilization of commercial Si wafers in surface-enhanced Raman spectroscopy (SERS) studies, we investigated herein the effect of the native SiO2 layer on Si wafers over the surface plasmon resonance (SPR)-mediated activities of the Au and Ag nanoparticles (NPs). We prepared SERS-active plasmonic comprised of Au and Ag NPs deposited onto a Si wafer. Here, two kinds of Si wafers were employed: Si with a native oxide surface layer (Si/SiO2 ) and Si without a native oxide surface layer (Si). This led to Si/SiO2 /Au, Si/SiO2 /Ag, Si/Au, and Si/Ag NPs. The SPR-mediated oxidation of p-aminothiophenol (PATP) to p,p'-dimercaptoazobenzene (DMAB) was employed as a model transformation. By comparing the performances and band structures for the Si/Au and Si/Ag relative to Si/SiO2 /Au and Si/SiO2 /Ag NPs, it was found that the presence of a SiO2 layer was crucial to enable higher SPR-mediated PATP to DMAB conversions. The SiO2 layer acts to prevent the charge transfer of SPR-excited hot electrons from Au or Ag nanoparticles to the Si substrate. This enabled SPR-excited hot electrons to be transferred to adsorbed O2 molecules, which then participate in the selective oxidation of PATP to DMAB. In the absence of a SiO2 layer, SPR-excited hot electrons are preferentially transferred to Si instead of adsorbed O2 molecules, leading to much lower PATP oxidation.

Preparation and Rate Capability of Carbon Coated LiNi1/3Co1/3Mn1/3O2 as Cathode Material in Lithium Ion Batteries.

LiNi1/3Co1/3Mn1/3O2 (NCM) is regarded as a promising material for next-generation lithium ion batteries due to the high capacity, but its practical applications are limited by the poor electronic conductivity. Here, a one-step method is used to prepare carbon coated LiNi1/3Co1/3Mn1/3O2 (NCM/C) by applying active carbon as reaction matrix. TEM shows LiNi1/3Co1/3Mn1/3O2 particles are homogeneously coated by carbon with a thickness about 10 nm. NCM/C delivers the discharge capacity of 191.2 mAh g-1 at 0.5 C (85 mA g-1) with a columbic efficiency of 91.1%. At 40 C (6800 mA g-1), the discharge capacity of NCM/C is 54.6 mAh g-1, whereas NCM prepared through sol-gel route only delivers 13.2 mAh g-1. After 100 charge and discharge cycles at 1 C (170 mA g-1) the capacity retention is 90.3% for NCM/C, whereas it is only 72.4% for NCM. The superior charge/discharge performance of NCM/C owes much to the carbon coating layer, which is not only helpful to increase the electronic conductivity but also contributive to inhibit the side reactions between LiNi1/3Co1/3Mn1/3O2 and the liquid electrolyte.

Optoelectronic Evaluation and Loss Analysis of PEDOT:PSS/Si Hybrid Heterojunction Solar Cells.

The organic/silicon (Si) hybrid heterojunction solar cells (HHSCs) have attracted considerable attention due to their potential advantages in high efficiency and low cost. However, as a newly arisen photovoltaic device, its current efficiency is still much worse than commercially available Si solar cells. Therefore, a comprehensive and systematical optoelectronic evaluation and loss analysis on this HHSC is therefore highly necessary to fully explore its efficiency potential. Here, a thoroughly optoelectronic simulation is provided on a typical planar polymer poly (3,4-ethylenedioxy thiophene):polystyrenesulfonate (PEDOT:PSS)/Si HHSC. The calculated spectra of reflection and external quantum efficiency (EQE) match well with the experimental results in a full-wavelength range. The losses in current density, which are contributed by both optical losses (i.e., reflection, electrode shield, and parasitic absorption) and electrical recombination (i.e., the bulk and surface recombination), are predicted via carefully addressing the electromagnetic and carrier-transport processes. In addition, the effects of Si doping concentrations and rear surface recombination velocities on the device performance are fully investigated. The results drawn in this study are beneficial to the guidance of designing high-performance PEDOT:PSS/Si HHSCs.