Ultrafast Rate Research Articles

Zwitterionic surface charge regulation in ionic covalent organic nanosheets: Synergistic adsorption of fluoroquinolone antibiotics

The effective removal of zwitterionic fluoroquinolone (FQ) antibiotics with high water solubility in wastewater is a key environmental challenge due to the inefficacy of conventional methods of wastewater treatment. In this work, zwitterionic covalent organic frameworks (Tp-MTABs) were synthesized through a solvothermal route using 5,5′,5″-methanetriyltris(2-aminobenzenesulfonic acid) (MTABs) as a zwitterionic linker and 1,3,5-triformylphloroglucinol (Tp) as neutral knots for efficient uptake of FQ antibiotics. Tp-MTABs compose of regular distributions of sulfonic acids and amines that produce zwitterionic binding sites, which produce complementary ion-pair interactions with zwitterionic FQ antibiotics. The charge on Tp-MTABs facilitates its initial self-exfoliation to few-layered ionic covalent organic nanosheets (iCONs) with controlled surface charge, which exposes more surface ionic sites and phenyl groups toward FQ antibiotics, improving ion-pair and π–π interactions between iCONs and FQ antibiotics. These iCONs with multiple active sites highly facilitated the process of antibiotics adsorption, boosting the adsorption kinetics and improving the selectivity towards FQ antibiotics. Tp-MTABs endows ultrafast adsorption rate (<30 s) of FQ antibiotics (average over 99%). In addition, Tp-MTABs exhibit high selectivity to the removal of FQs in complex systems containing multiple competing organic compounds and high-salinity natural seawater. This work explored the structural and functional design of iCONs for the removal of organic molecules in environmental remediation.

Diffusion Along Dislocations Mitigates Self-Limiting Na Diffusion in Crystalline Sn.

The diffusion of carrier ions in alloying anodes often develops compressive stresses in front of the propagating interface, suppressing the carrier-ion diffusion and limiting their full penetration into alloying anodes during battery cycles. This phenomenon, termed "self-limiting diffusion (SLD)", reduces the rate performance of batteries and hinders the full usage of anode materials. However, SLD is mitigated in some systems where tensile residual stresses develop at the interface, causing them to manifest significantly improved rate performance and energy capacity. Here, a comparative study of LiSi and NaSn systems to elucidate how the differing diffusion kinetics displayed by the two systems can influence SLD behaviors and the rate performance of batteries is performed. Experiments show that the Na diffusion into soft Sn crystals induces tensile stresses near the interface, promoting the nucleation of high-density dislocations. Thus-formed dislocations facilitate Na diffusion at ultrafast rates by providing pathways for dislocation pipe diffusion and alleviate SLD, making crystalline Sn suitable for fast-charging anode material. The outcomes of this study, while filling the knowledge gaps on the reasons for SLD, offer some guidelines for the appropriate choice of potential anode materials with superior rate performance and energy capacity suitable for future applications.

Nanoarchitectonics of Lotus Seed Derived Nanoporous Carbon Materials for Supercapacitor Applications.

Of the available environmentally friendly energy storage devices, supercapacitors are the most promising because of their high energy density, ultra-fast charging-discharging rate, outstanding cycle life, cost-effectiveness, and safety. In this work, nanoporous carbon materials were prepared by applying zinc chloride activation of lotus seed powder from 600 °C to 1000 °C and the electrochemical energy storage (supercapacitance) of the resulting materials in aqueous electrolyte (1M H2SO4) are reported. Lotus seed-derived activated carbon materials display hierarchically porous structures comprised of micropore and mesopore architectures, and exhibited excellent supercapacitance performances. The specific surface areas and pore volumes were found in the ranges 1103.0–1316.7 m2 g−1 and 0.741–0.887 cm3 g−1, respectively. The specific capacitance of the optimum sample was ca. 317.5 F g−1 at 5 mV s−1 and 272.9 F g−1 at 1 A g−1 accompanied by high capacitance retention of 70.49% at a high potential sweep rate of 500 mV s−1. The electrode also showed good rate capability of 52.1% upon increasing current density from 1 to 50 A g−1 with exceptional cyclic stability of 99.2% after 10,000 cycles demonstrating the excellent prospects for agricultural waste stuffs, such as lotus seed, in the production of the high performance porous carbon materials required for supercapacitor applications.

Multi-functional polyethersulfone nanofibrous membranes with ultra-high adsorption capacity and ultra-fast removal rates for dyes and bacteria

The adsorption technology has been widely applied in water remediation for contamination removal of dyes and bacteria, by virtue of the advantages of adsorption technology including high efficiency, energy conservation and ease of operation. Simultaneous removal of dyes and bacteria has been realized by some reported materials, but to achieve satisfactory adsorption amounts and rates remain an unmet goal for decades. Herein, a poly(methacrylatoethyl trimethyl ammonium chloride-co-methyl methacrylate) copolymer was synthesized, and then blended with polyethersulfone for the fabrication of nanofibrous membranes via electrospinning for the use of fast and massive removal of dyes and bacteria. Owing to the introduction of abundant quaternary ammonium groups, the maximum adsorption amount for methyl orange was up to 909.8 mg g−1. In addition, the modified nanofibrous membranes showed good recyclability, broad applications in severe environments, selective adsorption ability, and excellent dynamic removal performance. Especially, thanks to the abundant functional groups, the membranes showed fast adsorption ability for bacteria through electrostatic interaction. It should be noted that the clearance ratio for Staphylococcus aureus or Escherichia coli by 6 min of static adsorption could reach 93 % or 90 % for each. Additionally, dynamic removal ratio via filtration with the nanofibrous membranes could reach 99.7 % for Staphylococcus aureus or 98.7 % for Escherichia coli in 90 s. Therefore, the proposed approach towards the quaternary ammonium modified polyethersulfone nanofibrous membranes creates a new route for ultra-high adsorption capacity and ultra-fast removal rates for dyes and bacteria in water remediation.

Excited State Proton Transfer of Quinone Cyanine 9: Implications on the Origin of Super‐Photoacidity

AbstractQuinone cyanine 9 (QCy9) is one of the strongest photoacids known to date. The origin of “super”‐photoacidity was investigated via time‐resolved fluorescence (TF) with high time resolution to accurately resolve the ultrafast dynamics of the excited‐state proton transfer (ESPT) to solvent. The ESPT of QCy9 in water is found to proceed fully by two ultrafast time constants of 40 fs (65 %) and 200 fs (35 %). More importantly, the initially created base form of QCy9 in the excited state undergoes a significant dynamic red shift of over 2700 cm−1 by solvation. We suggest that the entirely ultrafast reaction rate and the massive solvation of the conjugate base could make QCy9 a particularly strong photoacid. Quantum chemical calculations show that structural diversity leads to the nonexponential behavior of the ESPT dynamics.

Biocompatible porous boron nitride nano/microrods with ultrafast selective adsorption for dyes

Wastewater treatment and separation technologies are critical to meet global challenges of insufficient water supply and inadequate resources. However, simple adsorption can no longer satisfy these demands, and thus more and more water recovery technologies have attracted attention. Here, we report a novel kind of porous BN nano/microrods with excellent features including high surface area of 1109.11 m²/g, large pore volume of 0.454 cm³/g and small pore size of 2.60 nm. These unique properties make the as-obtained porous BN nano/microrods show an ultrafast adsorption rate for the cationic dye methylene blue (MB+), and they can also be able to selectively adsorb cationic dyes from the mixtures of anionic and cationic dyes. The corresponding selective adsorption mechanism is also proposed based on the microstructure and surface property of the as-obtained porous BN nano/microrods. Furthermore, the cytotoxicity test was performed and the results show that the as-obtained porous BN nano/microrods have good biocompatibility with the cell survival rate of 80 % after a test period of 5 days, and this result is much higher than that of commercial BN. This finding provides a new application field for BN nanomaterials to selectively adsorb/separate anionic and cationic dyes in organic dye-containing wastewater treatment.

Noble-metal-free ultrathin MXene coupled with In2S3 nanoflakes for ultrafast photocatalytic reduction of hexavalent chromium

The conversion of highly toxic heavy metal hexavalent chromium (Cr(VI)) in the natural environment into low-toxic trivalent chromium (Cr(III)) is one of the research topics of great concern. Herein, a binary noble-metal-free photocatalyst consisting of ultrathin MXene (Ti3C2) and indium sulfide (In2S3) is prepared for ultrafast photocatalytic reduction of Cr(VI) to Cr(III) under visible light. A simple electrostatic assembly and reflow method uniformly coats the In2S3 nanoflakes on the surface of hollow Ti3C2 nanospheres, which effectively boost the separation of charges and thus enhance the photocatalytic performance. Thus, the prepared heterojunction can reduce Cr(VI) to Cr(III) completely within 6 min with an ultrafast rate constant of k = 0.739 min−1. More importantly, the appropriate band structure ensures the stable existence of Cr(III). Therefore, it provides a new insight for economic MXene-based binary photocatalysts for efficient environmental remediation.

Novel synthesis of tailored Li4SiO4-based microspheres for ultrafast CO2 adsorption

It has been widely acknowledged that the Li4SiO4-based adsorbents with smaller particle size and tailored structure will certainly exhibit superior CO2 capture performance. In this work, a novel two-phase synthesis method was proposed to produce tailored micro-scale Li4SiO4-based adsorbents with ultrafast CO2 capture rate. The effects of synthetic temperature on the phase compositions, the chemical bonds, the pore structure, the surface morphology and the CO2 capture performance of obtained adsorbents were systematically investigated. It is found that the increase of temperature during synthesis process could promote the Li4SiO4 content of obtained adsorbents. Nevertheless, higher temperature also leads to the aggravation and sintering of particles, thus hindering the capacity of adsorbents. Examining the pros and cons, the adsorbent calcined at 600 °C shows the greatest morphology consisted of hollow-structured microspheres with a uniform diameter of 1–2 μm and exhibits the fastest adsorption rate as well as the highest adsorption capacity (~ 0.184 g CO2/g adsorbent within only 5 min's adsorption under 15 vol% CO2), leading to a superior Li4SiO4 conversion as high as ~80%. In a word, this two-phase method is promising in the future production of Li4SiO4-based microspheres for high-efficient and ultrafast CO2 capture.

Halloysite nanotubes stabilized polyurethane foam carbon coupled with iron oxide for high-efficient and fast treatment of arsenic(III/V) wastewater

Adsorbent with high efficiency, fast removal rate and good reusability is very important for arsenic remediation. Herein, a novel porous magnetic nanocomposite was prepared for efficient arsenic removal by simple one-pot coprecipitation of Fe3O4 NPs on porous halloysite nanotubes/C (HNTs/C) preformed using abandoned polyurethane foam as a template. HNTs were inserted into the pore of polyurethane foam and formed the skeleton of the nanocomposites after sticking by the carbonized phenolic resin. Fe3O4 NPs were well dispersed on the skeleton and finally formed the porous stable HNTs/C/Fe3O4 nanocomposites. The optimized HNTs/C/Fe3O4 showed ultrafast removal rate (>98% arsenic was removed within 10 min), high removal efficiency and good regeneration capacity. It is worth noting that the adsorption efficiency of As (V) by HNTs/C/Fe3O4 was still above 99% after 5 times reuse, indicating the sustainable application. In addition, the application of HNTs/C/Fe3O4 for arsenic adsorption is almost not limited by pH. The chemical adsorption process was confirmed by adsorption kinetics, XPS and isothermal adsorption. The qm of As(III) and As(V) is 34.54 mg/g and 1491.72 mg/g, respectively, which is the highest capacity of As (V) known at present. This study demonstrates an ultrafast, high-efficient and sustainable adsorbent for arsenic treatment in contaminated water, which might also give light on other heavy metals remediation.

Fabrication of ultrafast temperature‐responsive nanofibrous hydrogel with superelasticity and its 'on–off' switchable drug releasing capacity

AbstractThe temperature‐responsive bulky hydrogel with fast response rate and satisfactory mechanical property has fascinating application potential in many aspects, such as the implantable macroscale controlled drug release carrier for post‐surgical therapy; however, creating such a smart hydrogel was proven extremely challenging. Here a novel type of temperature‐responsive bulky hydrogel with ultrafast response rate and super compressible elasticity was fabricated by the fibrous freeze‐shaping technique using shortened temperature‐responsive polymer based electrospun hollow nanofibers as building blocks, followed by heat treatment for endowing the hydrogel with high stability in water. Because the hydrogel has hierarchical porous structure and its constituent nanofibers have hollow structure, which are beneficial to diffusion of its embodied water during temperature‐induced volume phase transition, its temperature‐response time is less than 30 s. In addition, the hierarchical porous structure benefits dissipation of the compression stress exerted on the hydrogel. Fluorescein isothiocyanate (FITC)‐dextran as a model biomacromolecular drug, was loaded into the shells of the hollow nanofibers during coaxial electrospinning, and the ultimately obtained nanofibrous hydrogel can release its loaded FITC‐dextran in a 'on–off' switchable fashion in response to temperature alternation between 15 and 47°C. Cell cytotoxicity test results demonstrate that the temperature‐responsive nanofibrous hydrogel is biocompatible.

Coaxial Aperture Arrays Produced by Ultrafast Direct Femtosecond Laser Processing with Spatially Multiplexed Cylindrical Vector Beams

Direct femtosecond laser printing was used to fabricate circular-and coaxial-shaped hole arrays at ultrafast printing rate up to 106 elements per second. To achieve such fast printing rate, we implemented a spatial multiplexing of either a single Gaussian or cylindrical vector beams into linear array of identical laser spots. Being compared to ordinary microholes, the coaxial openings arranged at the same periodicity demonstrate enhanced transmission in the mid-IR spectral range resulted from coupling between localized electromagnetic mode supported by coaxial unit cell and the lattice-type surface plasmon resonance. At optimized geometry of the coaxial openings and their arrangement we demonstrated resonant transmission as high as 92% at wavelengths ranging from 7.5 to 9 μm. This makes the coaxial microhole arrays with tailored spectral properties produced with ultrafast and inexpensive direct laser printing promising for sensing applications based on surface enhanced infrared absorption.

Confinement of Quantum Dots in between Monolayered Graphene Nanosheets for Arousing Boosted Multifarious Photoredox Selective Organic Transformation.

Transition metal chalcogenide quantum dots (TMC QDs) represent promising light-harvesting antennas because of their fascinating physicochemical properties including quantum confinement effect and suitable energy band structures. However, TMC QDs generally suffer from poor photoactivities and photostability due to deficiency of active sites and ultrafast recombination rate of photoinduced charge carriers. Here, we demonstrate how to rationally arouse the charge transfer kinetic of TMC QDs by close monolayered graphene (GR) encapsulation via a ligand-dominated layer-by-layer (LbL) assembly utilizing oppositely charged TMC QDs and GR nanosheets as the building blocks. The assembly units were spontaneously and intimately integrated in an alternate integration mode, thereby resulting in the multilayered three-dimensional (3D) TMC QDs/GR ensembles. It was unveiled that multifarious photoactivities of TMC QDs/GR nanocomposites toward versatile photoredox organic catalysis including photocatalytic aromatic alcohols oxidation to aldehydes and nitroaromatics reduction to amino derivatives under visible light irradiation are conspicuously boosted because of spatially multilayered monolayered GR encapsulation which are superior to those of TMC QDs counterparts. The substantially enhanced photoactivities of TMC QDs/GR nanocomposites arise from reasons including improved light absorption and enhanced charge separation efficacy because of GR encapsulation together with unique stacking mode between TMC QDs and GR endowed by LbL assembly. Our work would provide a promising and efficacious route to smartly accelerate the charge transfer kinetic of TMC QDs for solar energy conversion.

Mamyshev Oscillator With a Widely Tunable Repetition Rate

Controlling an ultrafast laser oscillator repetition rate is crucial for the emerging laser burst micromachining. The efficiency of a material surface treatment process as well as the quality of live tissue ablation depends, to a considerable extent, on the number of laser pulses in a burst window. In the following article, we present an all-PM fiber harmonically mode-locked Mamyshev ring oscillator capable of producing laser pulses with a tunable period. The oscillator can be operated at any frequency, being a multiple of the fundamental repetition rate up to 305 MHz at 19th harmonic. We found that the operation frequency is limited by the available pump power only. What is worth noting is that the energy of the emitted pulses is independent of the operating frequency. The essential laser parameters are excellent: an amplitude noise of 0.1% and fundamental frequency suppression levels of 70 dB at every repetition rate. Additionally, the mechanism of harmonic mode-locking is discussed in detail and is found to be caused by gain depletion and recovery effect.

Development of electrochemical high-speed atomic force microscopy for visualizing dynamic processes of battery electrode materials.

Development of lithium ion batteries with ultrafast charging rate as well as high energy/power densities and long cycle-life is one of the imperative works in the field of batteries. To achieve this goal, it requires not only to develop new electrode materials but also to develop nano-characterization techniques that are capable of investigating the dynamic evolution of the surface/interface morphology and property of fast charging electrode materials during battery operation. Although electrochemical atomic force microscopy (EC-AFM) holds high spatial resolution, its imaging speed is too slow to visualize dynamics occurring on the timescale of minutes. In this article, we present an electrochemical high-speed AFM (EC-HS-AFM), developed by addressing key technologies involving optical detection of small cantilever deflection, dual scanner capable of high-speed and wide-range imaging, and electrochemical cell with three electrodes. EC-HS-AFM imaging from 1 fpm to ∼1 fps with a maximum scan range of 40 × 40 µm2 has been stably and reliably realized. Dynamic morphological changes in the LiMn2O4 nanoparticles during cyclic voltammetry measurements in the 0.5 mol/l Li2SO4 solution were successfully visualized. This technique will provide the possibility of tracking dynamic processes of fast charging battery materials and other surface/interface processes such as the formation of the solid electrolyte interphase layer.

Enhanced photocatalytic performance of electrospun hollow titanium dioxide nanofibers decorated with graphene quantum dots

Titanium dioxide (TiO2) is an outstanding photocatalytic semiconductor, but wide band gap of TiO2 significantly restricts its photocatalytic performance. Graphene possesses promising mechanical, optical and electrical properties. Relying on the excellent gain effect of graphene quantum dots (GQDs) on conductivity, unique up-conversion photoluminescence property and remarkable dye adsorption, the photoelectric properties of TiO2 can be significantly improved. In this study, a novel structure of GQDs-decorated TiO2 nanofibers was successfully prepared by electrospinning and hydrothermal synthesis procedures. The synthesized GQDs/TiO2 nanofibers composite exhibited a one-dimensional structure. The results show that introduction of GQDs prohibits the adverse recombination between photoinduced charges and prolongs the existence time. The photocatalytic properties characterization results show that 10% mass fraction of GQDs in composite nanofibers has the best degradation activity with its ultrafast electron transport rate and low electron–hole pair recombination rate.

Vacancy‐Driven High Rate Capabilities in Calcium‐Doped Na0.4MnO2 Cathodes for Aqueous Sodium‐Ion Batteries

AbstractAqueous sodium‐ion batteries are expected to be low‐cost, safe, and environmentally friendly systems for large scale energy storage due to the abundance and low cost of sodium. However, only a few candidates have been reported for cathodes and there is a need to develop new practical host materials with improved electrochemical performance. Here, tunnel‐type, calcium‐doped, sodium manganese oxide is demonstrated as a novel cathode material, ultrafast rate capabilities and superior high‐rate cycling stability—98.8% capacity retention at the 1000th cycle—for aqueous sodium‐ion batteries. Advanced structural analysis of the Ca0.07Na0.26MnO2 material using X‐ray diffraction and ab initio calculations identify the calcium sites and indicate a plausible sodium diffusion mechanism. Calcium preferentially substitutes at the Na(1) sites among the three different types of Na sites. This substitution creates vacancies at the Na(2) and Na(3) sites. Calculations of the energy barrier for Na ion diffusion indicate that diffusion along the Na(2)‐to‐Na(2) and Na(2)‐to‐Na(3) pathways is the most feasible. These vacancies provide improved diffusion kinetics and show 43% capacity enhancement at 50 C‐rate. The results suggest that Ca0.07Na0.26MnO2 is a promising cathode material for aqueous sodium‐ion batteries, and provide an improved fundamental understanding of sodium storage mechanisms.

High-temperature-resistant silicon-polymer hybrid modulator operating at up to 200\u2009Gbit\u2009s\u22121 for energy-efficient datacentres and harsh-environment applications

To reduce the ever-increasing energy consumption in datacenters, one of the effective approaches is to increase the ambient temperature, thus lowering the energy consumed in the cooling systems. However, this entails more stringent requirements for the reliability and durability of the optoelectronic components. Herein, we fabricate and demonstrate silicon-polymer hybrid modulators which support ultra-fast single-lane data rates up to 200 gigabits per second, and meanwhile feature excellent reliability with an exceptional signal fidelity retained at extremely-high ambient temperatures up to 110 °C and even after long-term exposure to high temperatures. This is achieved by taking advantage of the high electro-optic (EO) activities (in-device n3r33 = 1021 pm V−1), low dielectric constant, low propagation loss (α, 0.22 dB mm−1), and ultra-high glass transition temperature (Tg, 172 °C) of the developed side-chain EO polymers. The presented modulator simultaneously fulfils the requirements of bandwidth, EO efficiency, and thermal stability for EO modulators. It could provide ultra-fast and reliable interconnects for energy-hungry and harsh-environment applications such as datacentres, 5G/B5G, autonomous driving, and aviation systems, effectively addressing the energy consumption issue for the next-generation optical communication.

Nitrogen-doped TiO2(B) nanobelts enabling enhancement of electronic conductivity and efficiency of lithium-ion storage

To enhance the intrinsic electrical conductivities of TiO2(B) nanobelts, nitrogen(N)-doped TiO2(B) nanobelts (N-TNB) were prepared in this study by a facile and cost-effective hydrothermal method using urea as the nitrogen source with TiO2 (P25) nanoparticles. x-ray photoelectron spectroscopy confirmed that the N-atoms preferentially occupied up to ∼0.516 atom% in the interstitial sites of the N-TNB and the maximum concentration of substituted-N bonds in the N-TNB was ∼0.154 atom%, thereby the total concentration of doped nitrogen elements of ∼0.67 atom% improved the high intrinsic electrical conductivity and ionic diffusivity of the TiO2(B) nanobelts. The as-prepared N-TNB electrode delivered the highest specific capacity of 133.9 mAh g−1 in the first cycle, with an exceptional cyclic capacity retention at an ultrafast current rate of 1000 mA g−1; this is not less than 51% after 500 cycles and represents an excellent rate capability of ∼37 mAh g−1 at an ultra-high rate of 40 C. These values are among the best ever reported on comparison of the delivered highest discharge capacity of N-TNB at 1000 mA g−1 and high-rate capabilities of its Li+ ion storage with the literature data for N-TNB (∼231.5 mAh g−1 at a very low current density of 16.75 mA g−1, ∼0.1 C) of similar materials used in sodium-ion batteries. This implies the potential feasibility of these N-TNB as high-capacity anode materials for next-generation, high-energy-density, electrochemical energy-storage devices.

Recycling waste epoxy resin as hydrophobic coating of melamine foam for high-efficiency oil absorption

The preparation of oil absorption materials with both low-cost and high efficiency remains a great challenge. In this work, a waste epoxy resins (EPs) derived hydrophobic modifier was developed to fabricate high-efficient oil absorbents by simple dip-coating on melamine foam (MF). EPs were effectively degraded by acid digestion in mild condition to obtain the degradation products (DEPs) with a large molecular weight. DEPs can be directly used as a hydrophobic agent due to excellent hydrophobicity and processability. The resulting DEPs@MF exhibited excellent absorption performance for various oils or organic solvents with an ultrafast adsorption rate of 2 s and high oil absorption capacity of 116 g g−1. Moreover, the absorbed oils can be recovered by simple mechanical extrusion, and the adsorption capacity of the DEPs@MF did not deteriorate even after it was reused for 10 times. Besides, an oil recovery unit was successfully designed to achieve continuous oil–water separation. This research not only provides a new approach to the preparation of highly efficient and reusable oil-absorbing materials, but also provides new insight into solving the increasingly serious problem of waste thermosetting polymers.

Plasmonic-enhanced light emission from a waveguide-integrated tunnel junction

Light emission from inelastic electron tunneling has been demonstrated for 40 years. The ultrafast response rate and the ultracompact footprint make it promising for high-speed miniaturized light sources. But the application of the tunnel junction is limited by extremely low external quantum efficiency due to the low proportion of inelastic tunneling electron and wave vector mismatch between surface plasmons and photon emission. Here, we present a plasmonic-enhanced metal-insulator-semiconductor (MIS) junction coupled to a silicon waveguide with a coplanar electrode connected to a nanoantenna. The proposed tunnel junction can be fabricated using existing semiconductor planar processes to achieve controllable barrier thickness and quality for vertical current injection. Finally, an electrically driven light source with a radiation power nearly 8000 times higher than the spontaneous emission power in free space is shown to be achievable with the new structure at an operating wavelength of 1.31 µm. It is 510-fold higher than that of typical planar MIS junctions.