Tuning Surface Potential Polarization to Enhance N2 Affinity for Ammonia Electrosynthesis.

Electrocatalytic N2 reduction reaction (NRR) to synthesize ammonia is a sustainable reaction that is expected to replace Haber Bosch process. Laminated Bi2 WO6 has great potential as an NRR electrocatalyst, however, the effective activity requires that the inert substrate is fully activated. Here, for the first time, success is achieved in activating the Bi2 WO6 basal planes with NRR activity through Ti doping. The introduction of Ti successfully tunes the surface potential distribution and enhances the N2 adsorption. The subsequently strong hybrid coupling of d(Ti)-p(N) orbitals fills the electronic state of N2 antibonding molecular orbital, which greatly weakens the bonding strength of N≡N bonds. Further, in situ synchrotron radiation-based Fourier transform infrared (SR-FTIR) spectrum and theoretical calculations show that surface potential polarization enhances the adsorption of HNN* by Bi-Ti dual-metal sites, which is beneficial for the subsequent activation hydrogenation process. The Ti-Bi2 WO6 nanosheets achieve 11.44% Faradaic efficiency (-0.2 V vs. RHE), a NH3 yield rate of 23.14 µg mg-1  h-1 (15 N calibration), and satisfactory stability in 0.1 M HCl environment. The mutual assistance of theory and experiment can help understand and develop of excellent two-dimensional (2D) materials for the NRR.

Recent Progress in the Application of Ion Beam Technology in the Modification and Fabrication of Nanostructured Energy Materials.

The development of green, renewable energy conversion and storage systems is an urgent task to address the energy crisis and environmental issues in the future. To achieve high performance, stable, and safe operation of energy conversion and storage systems, energy materials need to be modified and fabricated through rationalization. Among various modification and fabrication strategies, ion beam technology has been widely used to introduce various defects/dopants into energy materials and fabricate various nanostructures, where the structure, composition, and property of prefabricated materials can be further accurately tailored to achieve better performance. In this paper, we review the recent progress in the application of ion beam technology in material modification and fabrication, focusing on nanostructured energy materials for energy conversion and storage including photo- (electro-) water splitting, batteries (solar cells, fuel cells, and metal-ion batteries), supercapacitors, thermoelectrics, and hydrogen storage. This review first provides a brief basic overview of ion beam technology and describes the classification and technological advantages of ion beam technology in the modification and fabrication of materials. Then, modification of energy materials by ion beams is reviewed mainly concerning doping and defect introduction. Fabrication of energy materials is also discussed mainly in terms of heterojunctions, nanoparticles, nanocavities, and other nanostructures. In particular, we emphasize the advantages of ion beam technology in improving the performance of energy materials. Finally, we point out our understanding of challenges and future perspectives in applying ion beam technology for the modification and fabrication of energy materials.

Insights into electronic properties of strained two-dimensional semiconductors by out-of-plane bending.

Strain engineering is an important strategy to modulate the electronic and optical properties of two-dimensional (2D) semiconductors. In experiments, an effective and feasible method to induce strains on 2D semiconductors is the out-of-plane bending. However, in contrast to the in-plane methods, it will generate a combined strain effect on 2D semiconductors, which deserves further explorations. In this work, we theoretically investigate the carrier transport-related electronic properties of arsenene, antimonene, phosphorene, and MoS2under the out-of-plane bending. The bending effect can be disassembled into the in-plane and out-of-plane rolling strains. We find that the rolling always degrades the transport performance, while the in-plane strain could boost carrier mobilities by restraining the intervalley scattering. In other words, pursuing the maximum in-plane strain at the expense of minimum rolling should be the primary strategy to promote transports in 2D semiconductors through bending. Electrons in 2D semiconductors usually suffer from the serious intervalley scattering caused by optical phonons. The in-plane strain can break the crystal symmetry and separate nonequivalent energy valleys at band edges energetically, confining carrier transports at the Brillouin zone Γ point and eliminating the intervalley scattering. Investigation results show that the arsenene and antimonene are suitable for the bending technology, because of their small layer thicknesses which can relieve the rolling burden. Their electron and hole mobilities can be doubled simultaneously, compared with their unstrained 2D structures. From this study, the rules for the out-of-plane bending technology towards promoting transport abilities in 2D semiconductors are obtained.

Enhanced performance of p-type SnOxthin film transistors through defect compensation.

Due to the unique outermost orbitals of Sn, hole carriers in tin monoxide (SnO) possess small effective mass and high mobility among oxide semiconductors, making it a promising p-channel material for thin film field-effect transistors (TFTs). However, the Sn vacancy induced field-effect mobility deterioration and threshold voltage (Vth) shift in experiments greatly limit its application in complementary metal-oxide-semiconductor (CMOS) transistors. In this study, the internal mechanism of vacancy defect compensation by aluminum (Al) doping in SnOxfilm is studied combining experiments with the density functional theory (DFT). The doping is achieved by an argon (Ar) plasma treatment of Al2O3deposited onto the SnOxfilm, in which the Al2O3provides both the surface passivation and Al doping source. Experimental results show a wideVthmodulation range (6.08 to -19.77 V) and notable mobility enhancement (11.56 cm2V-1s-1) in the SnOxTFTs after the Al doping by Ar plasma. DFT results reveal that the most possible positions of Al in SnO and SnO2segments are the compensation to Sn vacancy and interstitial. The compensation will create an n-type doping effect and improve the hole carrier transport by reducing the hole effective mass (mh*), which is responsible for the device performance variation, while the interstitial in the SnO2segment can hardly affect the valence transport of the film. The defect compensation is suitable for the electronic property modulation of SnO towards the high-performance CMOS application.

High Transient-Thermal-Shock Resistant Nanochannel Tungsten Films.

Developing high-performance tungsten plasma-facing materials for fusion reactors is an urgent task. In this paper, novel nanochannel structural W films prepared by magnetron sputtering deposition were irradiated using a high-power pulsed electron beam or ion beam to study their edge-localized modes, such as transient thermal shock resistance. Under electron beam irradiation, a 1 µm thick nanochannel W film with 150 watt power showed a higher absorbed power density related cracking threshold (0.28-0.43 GW/m2) than the commercial bulk W (0.16-0.28 GW/m2) at room temperature. With ion beam irradiation with an energy density of 1 J/cm2 for different pulses, the bulk W displayed many large cracks with the increase of pulse number, while only micro-crack networks with a width of tens of nanometers were found in the nanochannel W film. For the mechanism of the high resistance of nanochannel W films to transient thermal shock, a residual stress analysis was made by Grazing-incidence X-ray diffraction (GIXRD), and the results showed that the irradiated nanochannel W films had a much lower stress than that of the irradiated bulk W, which indicates that the nanochannel structure can release more stress, due to its special nanochannel structure and ability for the annihilation of irradiation induced defects.

Ion Irradiation Inducing Oxygen Vacancy-Rich NiO/NiFe2 O4 Heterostructure for Enhanced Electrocatalytic Water Splitting.

Oxygen evolution reaction (OER) is an obstacle to the electrocatalytic water splitting due to its unique four-proton-and-electron-transfer reaction process. Many methods, such as engineering heterostructure and introducing oxygen vacancy, have been used to improve the catalytic performance of electrocatalysts for OER. Herein, the above two kinds of regulation are simultaneously realized in a catalyst by using unique ion irradiation technology. A nanosheet structured NiO/NiFe2 O4 heterostructure with rich oxygen vacancies converted from nickel-iron layered double hydroxides by Ar+ ions irradiation shows significant enhancement in both OER and hydrogen evolution reaction performance. Density functional theory (DFT) calculations reveal that the construction of NiO/NiFe2 O4 can optimize the free energy of O* to OOH* process during OER reaction. The oxygen vacancy-rich NiO/NiFe2 O4 nanosheets have an overpotential of 279 mV at 10 mA cm-2 and a low Tafel slope of 42 mV dec-1 . Moreover, this NiO/NiFe2 O4 electrode shows an excellent long-term stability at 100 mA cm-2 for 450 h. The synergetic effects between NiO and NiFe2 O4 make NiO/NiFe2 O4 heterostructure have high conductivity and fast charge transfer, abundant active sites, and high catalytic reactivity, contributing to its excellent performance.

Springtail-Inspired Superamphiphobic Ordered Nanohoodoo Arrays with Quasi-Doubly Reentrant Structures.

The skin of springtails is well-known for being able to repel water and organic liquids using their hexagonally arranged protrusions with reentrant structures. Here, a method to prepare 100 nm-sized nanohoodoo arrays with quasi-doubly reentrant structures over square centimeters through combining the nanosphere lithography and the template-protected selective reactive ion etching technique is demonstrated. The top size of the nanohoodoos, the intra-nanohoodoo distance, and the height of the nanohoodoos can be readily controlled by the plasma-etching time of the polystyrene (PS) spheres, the size of the PS spheres used, and the reactive ion etching time of silicon. The strong structural control capability allows for the study of the relationship between the nanohoodoo structure and the wetting property. Superamphiphobic nanohoodoo arrays with outstanding water/organic liquid repellent properties are finally obtained. The superamphiphobic and liquid repellent properties endow the nanohoodoo arrays with remarkable self-cleaning performance even using hot water droplets, anti-fogging performance, and the surface-enhanced Raman scattering sensitivity improvement by enriching the analyte molecules on the nanohoodoo arrays. Overall, the simple and massive production of the superamphiphobic nanohoodoo structures will push their practical application processes in diverse fields where wettability and liquid repellency need to be carefully engineered.

Active Electron Density Modulation of Co3 O4 -Based Catalysts Enhances their Oxygen Evolution Performance.

Despite the fact that many strategies have been developed to improve the efficiency of the oxygen evolution reaction (OER), the precise modulation of the surface electronic properties of catalysts to improve their catalytic activity is still challenging. Herein, we demonstrate that the surface active electron density of Co3 O4 can be effectively regulated by an argon-ion irradiation method. X-ray photoelectron and synchrotron x-ray absorption spectroscopy, UV photoelectron spectrometry, and DFT calculations show that the surface active electron density band center of Co3 O4 has been upshifted, leading to a significantly enhanced absorption capability of the oxo group. The optimized Co3 O4 -based catalysts exhibit an excellent overpotential of 260 mV at 10 mA cm-2 and Tafel slope of 54 mV dec-1 , superior to the capability of the benchmark RuO2 , representing one of the best Co-based OER catalysts. This approach could guide the future rational design and discovery of ideal electrocatalysts.

Thermal Conductivity, Electrical Resistivity, and Microstructure of Cu/W Multilayered Nanofilms.

Metallic multilayered nanofilms have been extensively studied owing to their unique physical properties and applications. However, studies on the thermal conductivity and electrical resistivity of metallic multilayered nanofilms, as their important physical properties, are seldom reported. In this work, Cu/W multilayered nanofilms with periodic thickness varying from 6 to 150 nm were deposited by magnetron sputtering. The resistivities of the Cu/W multilayered nanofilms increase with the decrease of periodic thickness, especially when the periodic thickness is smaller than 37 nm. The resistivities of the multilayered nanofilms fit well with the Fuchs-Sondheimer and Mayadas-Shatzkes (FS-MS) model, which considers both interface scattering and grain boundary scattering. The thermal conductivities of the Cu/W multilayered nanofilms were measured by the three-omega (3ω) method, which decrease with a decrease of periodic thickness initially and increase at the smallest periodic thickness of 6 nm. The Boltzmann transport equation (BTE)-based model was used, to explain the periodic thickness-dependent thermal conductivity of metallic multilayered nanofilms by considering the contributions from both phonon and electron heat transport processes, where the calculated thermal conductivities agree well with the measured ones. The electrical resistivity and thermal conductivity strongly depend on the microstructures of the multilayered nanofilms.

Substantially Improving Device Performance of All-Inorganic Perovskite-Based Phototransistors via Indium Tin Oxide Nanowire Incorporation.

All-inorganic halide perovskites (IHPs) have attracted enormous attention due to their intrinsically high optical absorption coefficient and superior ambient stabilities. However, the photosensitivity of IHP-based photodetectors is still restricted by their poor conductivities. Here, a facile design of hybrid phototransistors based on the CsPbBr3 thin film and indium tin oxide (ITO) nanowires (NWs) integrated into a InGaZnO channel in order to achieve both high photoresponsivity and fast response is reported. The metallic ITO NWs are employed as electron pumps and expressways to efficiently extract photocarriers from CsPbBr3 and inject electrons into InGaZnO. The obtained device exhibits the outstanding responsivity of 4.9 × 106 A W-1 , which is about 100-fold better than the previous best results of CsPbBr3 -based photodetectors, together with the fast response (0.45/0.55 s), long-term stability (200 h in ambient), and excellent mechanical flexibility. By operating the phototransistor in the depletion regime, an ultrahigh specific detectivity up to 7.6 × 1013 Jones is achieved. More importantly, the optimized spin-coating manufacturing process is highly beneficial for achieving uniform InGaZnO-ITO/perovskite hybrid films for high-performance flexible detector arrays. All these results can not only indicate the potential of these hybrid phototransistors but also provide a valuable insight into the design of hybrid material systems for high-performance photodetection.

Beehive-Inspired Macroporous SERS Probe for Cancer Detection through Capturing and Analyzing Exosomes in Plasma.

The protein phosphorylation status of exosomes can regulate the activity and function of proteins related to cancer development, and it is highly possible to diagnose cancers through analyzing the protein phosphorylation status. However, monitoring the protein phosphorylation status with a simple and label-free method is still clinically challenging. Here, inspired by beehives, we developed an Au-coated TiO2 macroporous inverse opal (MIO) structure with an engineered "slow light effect" and thus with outstanding surface-enhanced Raman scattering (SERS) performance. The MIO structure can capture and analyze the exosomes from plasma of cancer patients without any labeling processes. It was found that the SERS intensity of exosomes at 1087 cm-1 arising from the P-O bond within the phosphoproteins can be used as a criterion for tumor liquid biopsies. The intensity of the 1087 cm-1 SERS peak from exosomes extracted from the plasma of cancer patients (prostate, lung, liver, and colon) is at least two times of that from healthy people. This indicates the simplicity and versatility of this method in cancer diagnostics. Our method has obvious advantages (noninvasive and time-saving) over currently clinically used tumor liquid biopsy techniques (such as western blot), which has great potentials to make vitro cancer diagnostics/monitoring as simple as diagnostics/monitoring of common diseases.

Modulating the filament rupture degree of threshold switching device for self-selective and low-current nonvolatile memory application.

Resistive switching devices have tremendous potential for memory, logic, and neuromorphic computing applications. Cation-based resistive switching devices intrinsically show nonvolatile memory characteristics under high compliance current (I CC), while show volatile threshold switching (TS) selector characteristics under low I CC. However, separate researches about cation-based memory or selector are hard to evade the typical current-retention dilemma, which results in the hardship to obtain low-current memory and high-current selector. Here, we propose a novel strategy to realize nonvolatile storage characteristics in a volatile TS device by modulating the rupture degree of conductive filament (CF). Enlarging the rupture degree of the CF with a certain RESET process, as confirmed by transmission electron microscope and energy dispersive spectrometry results, the threshold voltage of the Ag/HfO2/Pt TS devices can be enlarged from 0.9 to 2.8 V. Generation of the voltage difference enables the volatile TS devices the ability of self-selective nonvolatile storage. Increasing the RESET magnitude and shrinking the device size have been proved effective ways to increase the read window of the TS memory (TSM) devices. Evading the limit of the current-retention dilemma, ultra-low energy dissipation can be obtained by decreasing I CC to nA level. With self-selective, low-energy, and potential high-density integration characteristics, the proposed TSM device can act as a potential supplement of novel storage class memories.

Anionic Dopant Delocalization through p-Band Modulation to Endow Metal Oxides with Enhanced Visible-Light Photoactivity.

An N-doped TiO2 model reveals a conceptually different mechanism for activating the N dopant based on delocalized orbital hybridization through O vacancy incorporation. Synchrotron-based X-ray absorption spectroscopy, time-resolved fluorescence, and DFT studies revealed that O vacancy incorporation can effectively stimulate the delocalization of N impurity states through p-band orbital modulation, which leads to a significant enhancement in photocarrier lifetime. Consequently, this effect also results in a remarkable increase in the incident photon-to-electron conversion efficiency in the range of 400-550 nm compared to that of conventional N-incorporated TiO2 (15 % versus 1 % at 450 nm). This work reveals the fundamental necessity of orbital modulation in the band engineering of metal oxides for driving solar water splitting and beyond.

Different Radiation Tolerances of Ultrafine-Grained Zirconia-Magnesia Composite Ceramics with Different Grain Sizes.

Developing high-radiation-tolerant inert matrix fuel (IMF) with a long lifetime is important for advanced fission nuclear systems. In this work, we combined zirconia (ZrO2) with magnesia (MgO) to form ultrafine-grained ZrO2-MgO composite ceramics. On the one hand, the formation of phase interfaces can stabilize the structure of ZrO2 as well as inhibiting excessive coarsening of grains. On the other hand, the grain refinement of the composite ceramics can increase the defect sinks. Two kinds of composite ceramics with different grain sizes were prepared by spark plasma sintering (SPS), and their radiation damage behaviors were evaluated by helium (He) and xenon (Xe) ion irradiation. It was found that these dual-phase composite ceramics had better radiation tolerance than the pure yttria-stabilized ZrO2 (YSZ) and MgO. Regarding He+ ion irradiation with low displacement damage, the ZrO2-MgO composite ceramic with smaller grain size had a better ability to manage He bubbles than the composite ceramic with larger grain size. However, the ZrO2-MgO composite ceramic with a larger grain size could withstand higher displacement damage in the phase transformation under heavy ion irradiation. Therefore, the balance in managing He bubbles and phase stability should be considered in choosing suitable grain sizes.

Toward fiber-, paper-, and foam-based flexible solid-state supercapacitors: electrode materials and device designs.

Flexible solid-state supercapacitors possess promising safety performance and intrinsic fast charging-discharging properties, enabling them to accomplish the requirements of lightweight and multifunctional wearable electronics that have recently become fairly popular. Because electrode materials are the core component of flexible solid-state supercapacitors, we exhaustively review the recent investigations involving electrode materials that have used carbons, metal oxides, and conductive polymers. The principles and methods of optimizing and fabricating electrodes for use in flexible supercapacitors are discussed through a comprehensive analysis of the literature. In addition, we focused on three types of flexible solid-state supercapacitors (fiber-, paper-, and porous foam-based structures) to satisfy the requirements of flexible electronic devices. Further, we summarize the practical applications of flexible solid-state supercapacitors, including energy conversion/collection devices and energy storage/detection devices. Finally, we provide the developmental direction for flexible solid-state supercapacitors in the future.

Volume-Enhanced Raman Scattering Detection of Viruses.

Virus detection and analysis are of critical importance in biological fields and medicine. Surface-enhanced Raman scattering (SERS) has shown great promise in small molecule and even single molecule detection, and can provide fingerprint signals of molecules. Despite the powerful detection capabilities of SERS, the size discrepancy between the SERS "hot spots" (generally, <10 nm) and viruses (usually, sub-100 nm) yields poor detection reliability of viruses. Inspired by the concept of molecular imprinting, a volume-enhanced Raman scattering (VERS) substrate composed of hollow nanocones at the bottom of microbowls (HNCMB) is developed. The hollow nanocones of the resulting VERS substrates serve a twofold purpose: 1) extending the region of Raman signal enhancement from the nanocone surface (e.g., surface "hot spots") to the hollow area within the cone (e.g., volume "hot spots")-a novel method of Raman signal enhancement, and 2) directing analyte such as viruses of a wide range of sizes to those VERS "hot spots" while simultaneously increasing the surface area contributing to SERS. Using HNCMB VERS substrates, greatly improved Raman signals of single viruses are demonstrated, an achievement with important implications in disease diagnostics and monitoring, biomedical fields, as well as in clinical treatment.

Catalytic Application and Mechanism Studies of Argentic Chloride Coupled Ag/Au Hollow Heterostructures: Considering the Interface Between Ag/Au Bimetals.

For an economical use of solar energy, photocatalysts that are sufficiently efficient, stable, and capable of harvesting light are required. Composite heterostructures composed of noble metals and semiconductors exhibited the excellent in catalytic application. Here, 1D Ag/Au/AgCl hollow heterostructures are synthesized by galvanic replacement reaction (GRR) from Ag nanowires (NWs). The catalytic properties of these as-obtained Ag/Au/AgCl hollow heterostructures with different ratios are investigated by reducing 4-nitrophenol (Nip) into 4-aminophenol (Amp) in the presence of NaBH4, and the influence of AgCl semiconductor to the catalytic performances of Ag/Au bimetals is also investigated. These hollow heterostructures show the higher catalytic properties than pure Ag NWs, and the AgCl not only act as supporting materials, but the excess AgCl is also the obstacle for contact of Ag/Au bimetals with reactive species. Moreover, the photocatalytic performances of these hollow heterostructures are carried out by degradation of acid orange 7 (AO7) under UV and visible light. These Ag/Au/AgCl hollow heterostructures present the higher photocatalytic activities than pure Ag NWs and commercial TiO2 (P25), and the Ag/Au bimetals enhance the photocatalytic activity of AgCl semiconductor via the localized surface plasmon resonance (LSPR) and plasmon resonance energy transfer (PRET) mechanisms. The as-synthesized 1D Ag/Au/AgCl hollow heterostructures with multifunction could apply in practical environmental remedy by catalytic manners.

NIR light-activated upconversion semiconductor photocatalysts.

Harvesting of near infrared (NIR) light in the abundant and environmentally friendly solar spectrum is particularly significant to enhance the utilization rate of the cleanest energy on earth. Appreciating the unique nonlinear optical properties of upconversion materials for converting low-energy incident light into high-energy radiation, they become the most promising candidates for fabricating NIR light-active photocatalytic systems by integrating with semiconductors. The present review summarizes recent NIR light-active photocatalytic systems based on a sequence of NaYF4-based, fluoride-based, oxide-based and Ln3+ ion-doped semiconductor-based photocatalysts for degradation of organic molecules. In addition, we provide an in-depth analysis of various photocatalytic mechanisms and enhancement effects for efficient photo-redox performance of different upconversion semiconductor photocatalysts. We envision that this review can inspire multidisciplinary research interest in rational design and fabrication of efficient full-spectrum active (UV-visible-NIR) photocatalytic systems and their wider applications in solar energy conversion.

Co2P Nanoparticles Wrapped in Amorphous Porous Carbon as an Efficient and Stable Catalyst for Water Oxidation.

Exploring highly active, enduringly stable, and low-cost oxygen evolution reaction catalysts continues to be a dominant challenge to commercialize renewable electrochemical water-splitting technology. High-active and earth-abundant cobalt phosphides are recently considered as promising candidates. However, the poor inherent electron transfer efficiency and instability hinder its further development. In this work, a novel approach was demonstrated to effectively synthesize Co2P nanoparticles wrapped in amorphous porous carbon framework (Co2P/C). Benefiting from extremely high specific surface area of porous carbon, plenty of active sites were adequately exposed. Meanwhile, unique anchoring structure between Co2P nanoparticles and amorphous carbon outerwear insured high charge transfer efficiency and superior stability of Co2P/C. Due to these favorable properties, low overpotential of 281 mV at 10 mA cm-2 and Tafel slope of 69 mV dec-1 were achieved in resultant Co2P/C catalyst. More significantly, it only exhibited a negligible overpotential increase after 30 h stability test, and these performances entirely preceded commercial RuO2 benchmark. In summary, we proposed a simple and feasible strategy to prepare metal phosphides wrapped with amorphous porous carbon outerwear for efficient and durable electrochemical water oxidation.

Ultrasensitive Au Nanooctahedron Micropinball Sensor for Mercury Ions.

Mercury ion (Hg2+) is one of the most toxic heavy metals that has severe adverse effects on the environment and human organs even at very low concentrations. Therefore, highly sensitive and selective detection of Hg2+ is desirable. Here, we introduce plasmonic micropinball constructed from Au nanooctahedron as a three-dimensional surface-enhanced Raman spectroscopy (SERS) platform, enabling ultrasensitive detection of trace Hg2+ ions. Typically, strong SERS signals could be obtained when the single-stranded DNA structure converts to the hairpin structure in the presence of Hg2+ ions, due to the formation of thymine (T)-Hg2+-T. As a result, the detection limit of Hg2+ ions is as low as 1 × 10-16 M, which is far below compared to that reported for conventional analytical strategies. Moreover, to achieve rapid multiple detection, we combine the micropinball sensors with microflow tube online detection. Our platform prevents cross-talk and tube contamination, allowing multiassay analysis, rapid identification, and quantification of different analytes and concentrations across separate phases.