Lewis acid-doped transition metal dichalcogenides for ultraviolet–visible photodetectors

Ultraviolet photodetectors(UV PDs)are widely used in civilian,scientific,and military fields due to their high sensitivity and low false alarm rates.We present a temperature-dependent Lewis acid p-type doping method for transition metal dichalcogenides(TMDs),which can effectively be used to extend the optical response range.The p-type doping based on surface charge transfer involves the chemical adsorption of the Lewis acid SnCl_(4)as a light absorption layer on the surface of WS_(2),significantly enhancing its UV photodetection performance.Under 365 nm laser irradiation,WS_(2)PDs exhibit response speed of 24 ms/20 ms,responsivity of 660 mA/W,detectivity of 3.3×10^(11)Jones,and external quantum efficiency of 226%.Moreover,we successfully apply this doping method to other TMDs materials(such as MoS_(2),MoSe_(2),and WSe_(2))and fabricate WS_(2) lateral p–n heterojunction PDs.

Oxygen vacancies enable the visible light photoactivity of chromium-implanted TiO2 nanowires

Although computational studies have demonstrated that metal ion doping can effectively narrow the bandgap of TiO_(2),the visible-light photoactivity of metal-doped TiO_(2) photoanodes is still far from satisfactory.Herein,we report an effective strategy to activate the visible-light photoactivity of chromiumimplanted TiO_(2) via the incorporation of oxygen vacancies.The chromium-doped TiO_(2) activated by oxygen vacancies(Cr-TiO_(2)-vac)exhibited an incident photon-to-electron conversion efficiency(IPCE)of~6.8%at450 nm,which is one of the best values reported for metal-doped TiO_(2).Moreover,Cr-TiO_(2)-vac showed no obvious photocurrent decay after 100 h under visible-light illumination.

Oxygen Vacancy-induced Electron Density Tuning of Fe_(3)O_(4) for Enhanced Oxygen Evolution Catalysis

Despite the tremendous efforts devoted to enhancing the activity of oxygen evolution reaction(OER)catalysts,there is still a huge challenge to deeply understand the electronic structure characteristics of transition metal oxide to guide the design of more active catalysts.Herein,Fe_(3)O_(4)with oxygen vacancies(Fe_(3)O_(4)-Vac)was synthesized via Ar ion irradiation method and its OER activity was greatly improved by properly modulating the electron density around Fe atoms.The electron density of Fe_(3)O_(4)-Vac around Fe atoms increased compared to that of Fe_(3)O_(4)according to the characterization of synchrotron-based X-ray absorption near-edge structure(XANES),extended X-ray absorption fine structure(EXAFS)spectra,and density functional theory(DFT)calculation.Moreover,the DFT results indicate the enhancement of the desorption of HOO^(*)groups which significantly reduced the OER reaction barrier.Fe_(3)O_(4)-Vac catalyst shows an overpotential of 353 m V,lower than that of Fe OOH(853 m V)and Fe_(3)O_(4)(415 m V)at 10 m A cm^(-2),and a low Tafel slope of 50 m V dec^(-1)in 1 M KOH,which was even better than commercial RuO_(2)at high potential.This modulation approach provides us with valuable insights for exploring efficient and robust water-splitting electrocatalysts.

In-situ structural evolution of Bi_(2)O_(3) nanoparticle catalysts for CO_(2) electroreduction

Under the complex external reaction conditions,uncovering the true structural evolution of the catalyst is of profound significance for the establishment of relevant structure–activity relationships and the rational design of electrocatalysts.Here,the surface reconstruction of the catalyst was characterized by ex-situ methods and in-situ Raman spectroscopy in CO_(2)electroreduction.The final results showed that the Bi_(2)O_(3) nanoparticles were transformed into Bi/Bi_(2)O_(3) two-dimensional thin-layer nanosheets(NSs).It is considered to be the active phase in the electrocatalytic process.The Bi/Bi_(2)O_(3) NSs showed good catalytic performance with a Faraday efficiency(FE)of 94.8%for formate and a current density of 26 mA cm^(−2) at−1.01 V.While the catalyst maintained a 90%FE in a wide potential range(−0.91 V to−1.21 V)and long-term stability(24 h).Theoretical calculations support the theory that the excellent performance originates from the enhanced bonding state of surface Bi-Bi,which stabilized the adsorption of the key intermediate OCHO^(∗) and thus promoted the production of formate.

Oxygen vacancies and V co-doped Co_(3)O_(4) prepared by ion implantation boosts oxygen evolution catalysis

Introducing heteroatoms and defects is a significant strategy to improve oxygen evolution reaction(OER)performance of electrocatalysts.However,the synergistic interaction of the heteroatom and defect still needs further investigations.Herein,we demonstrated an oxygen vacancy-rich vanadium-doped Co_(3)O_(4)(V-Ov-Co_(3)O_(4)),fabricated by V-ion implantation,could be used for high-efficient OER catalysis.X-ray photoelectron spectra(XPS)and density functional theory(DFT)calculations show that the charge density of Co atom increased,and the reaction barrier of reaction pathway from O∗to HOO∗decreased.V-Ov-Co_(3)O_(4) catalyst shows a low overpotential of 329 mV to maintain current density of 10 mA·cm^(−2),and a small Tafel slope of 74.5 mV·dec^(−1).This modification provides us with valuable perception for future design of heteroatom-doped and defect-based electrocatalysts.

Electronic Coupling of Single Atom and FePS_3 Boosts Water Electrolysis

Engineering the electronic structure of surface active sites at the atomic level can be an efficient way to modulate the reactivity of catalysts.Herein,we report the rational tuning of surface electronic structure of FePS_(3) nanosheets(NSs)by anchoring atomically dispersed metal atom.Theoretical calculations predict that the strong electronic coupling effect in single-atom Ni-FePS_(3) facilitates electron aggregation from Fe atom to the nearby Ni-S bond and enhances the electron-transfer of Ni and S sites,which balances the oxygen species adsorption capacity,reinforces water adsorption and dissociation process to accelerate corresponding oxygen evolution reaction(OER)and hydrogen evolution reaction(HER).The optimal Ni-FePS_(3)NSs/C exhibits outstanding electrochemical water-splitting activities,delivering an overpotential of 287 mV at the current density of 10 mA cm^(-2) and a Tafel slope of 41.1 mV dec^(-1) for OER;as well as an overpotential decrease of 219 mV for HER compared with pure FePS_(3)NSs/C.The concept of electronic coupling interaction between the substrate and implanted single active species offers an additional method for catalyst design and beyond.

Unraveling the modulation essence of p bands in Co-based oxide stability on acidic oxygen evolution reaction

The oxygen evolution reaction(OER)electrocatalysts,which can keep active for a long time in acidic media,are of great significance to proton exchange membrane water electrolyzers.Here,Ru-Co_(3)O_(4)electrocatalysts with transition metal oxide Co_(3)O_(4)as matrix and the noble metal Ru as doping element have been prepared through an ion exchange–pyrolysis process mediated by metal-organic framework,in which Ru atoms occupy the octahedral sites of Co_(3)O_(4).Experimental and theoretical studies show that introduced Ru atoms have a passivation effect on lattice oxygen.The strong coupling between Ru and O causes a negative shift in the energy position of the O p-band centers.Therefore,the bonding activity of oxygen in the adsorbed state to the lattice oxygen is greatly passivated during the OER process,thus improving the stability of matrix material.In addition,benefiting from the modulating effect of the introduced Ru atoms on the metal active sites,the thermodynamic and kinetic barriers have been significantly reduced,which greatly enhances both the catalytic stability and reaction efficiency of Co_(3)O_(4).

Spatially selective p-type doping for constructing lateral WS_(2) p-n homojunction via low-energy nitrogen ion implantation

The construction of lateral p-n junctions is very important and challenging in two-dimensional(2D)semiconductor manufacturing process.Previous researches have demonstrated that vertical p-n junction can be prepared simply by vertical stacking of 2D materials.However,interface pollution and large area scalability are challenges that are difficult to overcome with vertical stacking technology.Constructing 2D lateral p-n homojunction is an effective strategy to address these issues.Spatially selective p-type doping of 2D semiconductors is expected to construct lateral p-n homojunction.In this work,we have developed a low-energy ion implantation system that reduces the implanted energy to 300 eV.Low-energy implantation can form a shallow implantation depth,which is more suitable for modulating the electrical and optical properties of 2D materials.Hence,we utilize low-energy ion implantation to directly dope nitrogen ions into few-layer WS_(2) and successfully realize a precise regulation for WS_(2) with its conductivity type transforming from n-type to bipolar or even p-type conduction.Furthermore,the universality of this method is demonstrated by extending it to other 2D semiconductors,including WSe_(2),SnS_(2) and MoS_(2).Based on this method,a lateral WS_(2) p-n homojunction is fabricated,which exhibits significant rectification characteristics.A photodetector based on p-n junction with photovoltaic effect is also prepared,and the open circuit voltage can reach to 0.39 V.This work provides an effective way for controllable doping of 2D semiconductors.

Early cancer detection by serum biomolecular fingerprinting spectroscopy with machine learning

Label-free surface-enhanced Raman scattering(SERS)technique with ultra-sensitivity becomes more and more desirable in biomedical analysis,which is yet hindered by inefficient follow-up data analysis.Here we report an integrative method based on SERS and Artificial Intelligence for Cancer Screening(SERS-AICS)for liquid biopsy such as serum via silver nanowires,combining molecular vibrational signals processing with large-scale data mining algorithm.According to 382 healthy controls and 1582 patients from two independent cohorts,SERS-AICS not only distinguishes pan-cancer patients from health controls with 95.81% overall accuracy and 95.87% sensitivity at 95.40% specificity,but also screens out those samples at early cancer stage.The supereminent efficiency potentiates SERS-AICS a promising tool for detecting cancer with broader types at earlier stage,accompanying with the establishment of a data platform for further deep analysis.

Low operating voltage memtransistors based on ion bombarded p-type GeSe nanosheets for artificial synapse applications

Two-dimensional(2D)layered materials have many potential applications in memristors owing to their unique atomic structures and electronic properties.Memristors can overcome the in-memory bottleneck for use in brain-like neuromorphic computing.However,exploiting additional lateral memtransistors based on 2D layered materials remains challenging.There are few studies on p-type semiconductors that have not been theoretically analyzed.In this study,a lateral memtransistor based on p-type GeSe nanosheets is investigated.A threeterminal GeSe memtransistor that modulated the interfacial barrier height was fabricated using low-energy ion irradiation;the memtransistor exhibited a low operating voltage.The memtransistor successfully mimics biological synapse,including neuroplasticity functions,such as short-term plasticity,long-term plasticity,paired-pulse facilitation,and spike-timing-dependent plasticity.The mechanism of interfacial modulation was verified by experimental results and theoretical calculations.The results show that it is feasible to modulate the interface of 2D GeSe nanosheets using low-energy ion irradiation to realize a lateral memtransistor.This may provide promising opportunities for artificial neuromorphic system applications based on 2D layered materials.

The d-orbital coupling modulation of CuNi alloy for acetonitrile electrochemical reduction and in-situ hydrogenation behavior characterization

Electrochemical reduction of acetonitrile to ethylamine with a high selectivity is a novel approach to manufacture valuable primary amines which are important raw material in organic chemical industry. However, the poor ethylamine Faradic efficiency(FE_(ethylamine)) and catalyst stability at the high current density prohibit this method from being practically used. Herein, CuNi alloy ultrafine-nano-particles based on the d-orbital coupling modulation were synthesized through the electrodeposition and their catalytic performance towards acetonitrile reduction reaction(ACNRR) has been systematically studied. The highest FE_(ethylamine)(97%) is achieved with the current density of-114 mA cm^(-2). For practical application, the current density can reach-602.8 mA cm^(-2) with 82.8% FE_(ethylamine)maintained. With the appearance of other organics which co-exist with acetonitrile in the SOHIO process, CuNi can also hydrogenate acetonitrile in it with more than 80% FE_(ethylamine). Our in-situ spectroscopy analysis and DFT calculations towards the acetonitrile hydrogenation behavior reveal that the evenly dispersed Ni in Cu modulates the dband so as to endow CuNi with the better acetonitrile adsorption, milder binding energy with the reaction intermediates, smaller barrier for *CH_3CH_2NH_2 desorption and higher ability for H_2O dissociation to provide *H.

Recent progress about 2D metal dichalcogenides: Synthesis and application in photodetectors

In recent years, two-dimensional (2D) layered metal dichalcogenides (MDCs) have received enormous attention on account of their excellent optoelectronic properties. Especially, various MDCs can be constructed into vertical/lateral heterostructures with many novel optical and electrical properties, exhibiting great potential for the application in photodetectors. Therefore, the batch production of 2D MDCs and their heterostructures is crucial for the practical application. Recently, the vapour phase methods have been proved to be dependable for growing large-scale MDCs and related heterostructures with high quality. In this paper, we summarize the latest progress about the synthesis of 2D MDCs and their heterostructures by vapour phase methods. Particular focus is paid to the control of influence factors during the vapour phase growth process. Furthermore, the application of MDCs and their heterostructures in photodetectors with outstanding performance is also outlined. Finally, the challenges and prospects for the future application are presented.

Recent progress in periodic patterning fabricated by self-assembly of colloidal spheres for optical applications

Colloidal crystals are periodically ordered arrays of monodisperse colloidal particles which represent a new class of self-assembled materials showing potential applications in many fields.Two-dimensional graphic nanostructures based on colloidal crystals have inherent periodicity from tens of nanometers to several micrometers,which gives them rich and interesting optical properties.This article presents a comprehensive review about the current research activities on the self-assembly of colloidal spheres which is an effective strategy for fabrication of various hierarchical and ordered nanostructures,with particular attention paid to the unique properties and applications of the colloidal crystal-based nanostructures.Three main aspects are elaborated:a)controllable self-assembly of colloidal crystals;b)the functions of the obtained colloidal spheres acting as the patterned mask for successive construction of numerous nanostructures;c)the novel properties and promising optical applications of the patterned nanostructures in various domains,such as plasmonic-related fields,antireflection,photonic crystals,photocatalysis and electronic devices.After that,the current challenges and future perspectives in this area are provided.This review aims to inspire more ingenious designs and exciting research for manufacturing nanostructures utilizing colloidal self-assembly.

Recent progress in the fabrication of SERS substrates based on the arrays of polystyrene nanospheres

Micro/nanostructures have broad applications in diverse application fields, such as surface enhanced Raman spectroscopy (SERS), photocatalysis, field emission, photonic crystals, microfluidic devices, electrochemical devices, etc. Using polystyrene (PS) spheres formed monolayer colloidal crystal templates as masks, scaffolds, or molds with different materials growth techniques, many different periodic nanostructured arrays can be obtained with the building units varied from nanoparticles, nanopores, nanorings, nanorods, to nanoshells. Significant progresses have been made on the synthesis of micro/nanostructures with efficient SERS response. In this review, we mainly focus on the various PS template-based fabrication techniques in realizing micro/nanostructured arrays and the SERS applications.

The effect of Laves phase on heavy-ion radiation response of Nb-containing FeCrAl alloy for accident-tolerant fuel cladding

As a promising candidate material for the accident tolerant fuel cladding in light water reactors,the Nb-containing FeCrAl alloy has shown outstanding out-of-pile service performance due to the Laves phase precipitation.In this work,the radiation response in FeCrAl alloys with gradient Nb content under heavy ion radiation has been investigated.The focus is on the effect of the Laves phase on irradiation-induced defects and hardening.We found that the phase boundary between the matrix and Laves phase can play a critical role in capturing radiation defects,as verified by in-situ heavy-ion radiation experiments and molecular dynamic simulations.Additionally,the evolution of Laves phase under radiation is analyzed.Radiation-induced amorphization and segregations observed at high radiation doses will deepen the fundamental understanding of the stability of Laves phases in the radiation environment.

Structure and Growth Mechanism of V/Ag Multilayers with Different Periodic Thickness Fabricated by Magnetron Sputtering Deposition

V/Ag multilayers with different periodic thicknesses were fabricated by magnetron sputtering deposition. The columnar structure and the orientation relationship of the multilayers were investigated by transmission electron microscopy, high resolution transmission electron microscopy, selected-area electron diffraction and X-ray diffraction. It was found that the multilayered structure became flatter as increasing individual layer thickness from 2 to 6 nm, and then became waved as the individual layer thickness increases to 8 nm. At the beginning of the growth, the morphology of the multilayers with small periodic thickness was influenced mainly by thermodynamic instabilities, and the morphology of the multilayers with larger periodic thickness was mainly influenced mainly by the columnar growth of V. When the waved interfaces were formed, the continuum growth of the multilayers was also influenced by the shadowing effect and the finite atomic size effect. All of these factors resulted in the columnar structure of the multilayers. Multilayers with small periodic thickness presented strong orientation relationship. Nano-hardness tests indicated that multilayers with flat sublayer morphology and clear interfaces exhibited larger hardness.

Construct Fe^(2+) species and Au particles for significantly enhanced photoelectrochemical performance of α-Fe_2O_3 by ion implantation

Photoelectrochemical（PEC） water splitting is a promising approach to producing H2 and O2. Hematite（α-Fe2O3） is considered one of the most promising photoelectrodes for PEC water splitting, due to its good photochemical stability, non-toxicity, abundance in earth, and suitable bandgap（Eg2.1 eV）. However, the PEC water splitting efficiency of hematite is severely hampered by its short hole diffusion length（2–4 nm）, poor conductivity, and ultrafast recombination of photogenerated carriers（about 10 ps）. Here,we show a novel and effective method for significantly improving the PEC water splitting performance of hematite by Au ion implantation and the following high-temperature annealing process. Based on a series of characterizations and analyses, we have found Fe2＋ species and tightly attached Au particles were produced at Au-implanted hematite. As a result,the charge separation and charge injection efficiency of Auimplanted Fe2O3 are markedly increased. The photocurrent density of optimized Au-implanted Fe2O3 could reach1.16 m A cm-2 at 1.5 V vs. RHE which was nearly 300 times higher than that of the pristine Fe2O3（4 μA cm-2）. Furthermore, the Au-implanted Fe2O3 photoelectrode exhibited great stability for the 8-hour PEC water splitting test without photocurrent decay.

Flammable gases produced by TiO_(2) nanoparticles under magnetic stirring in water

The friction between nanomaterials and Teflon magnetic stirring rods has recently drawn much attention for its role in dye degradation by magnetic stirring in dark.Presently the friction between TiO_(2) nanoparticles and magnetic stirring rods in water has been deliberately enhanced and explored.As much as 1.00 g TiO_(2) nanoparticles were dispersed in 50 mL water in 100 mL quartz glass reactor,which got gas-closed with about 50 mL air and a Teflon magnetic stirring rod in it.The suspension in the reactor was magnetically stirred in dark.Flammable gases of 22.00 ppm CO,2.45 ppm CH_(4),and 0.75 ppm H_(2) were surprisingly observed after 50 h of magnetic stirring.For reference,only 1.78 ppm CO,2.17 ppm CH_(4),and 0.33 ppm H_(2) were obtained after the same time of magnetic stirring without TiO_(2) nanoparticles.Four magnetic stirring rods were simultaneously employed to further enhance the stirring,and as much as 30.04 ppm CO,2.61 ppm CH_(4),and 8.98 ppm H_(2) were produced after 50 h of magnetic stirring.A mechanism for the catalytic role of TiO_(2) nanoparticles in producing the flammable gases is established,in which mechanical energy is absorbed through friction by TiO_(2) nanoparticles and converted into chemical energy for the reduction of CO_(2) and H_(2)O.This finding clearly demonstrates a great potential for nanostructured semiconductors to utilize mechanical energy through friction for the production of flammable gases.

Two-dimensional PtPb-PbS heterostructure enables improved kinetics and highlighted bifunctional antipoisoning for methanol electrooxidation

Two-dimensional(2 D) platinum(Pt)-based nanomaterials are considered as the ideal fuel cell catalysts, while their rational synthesis associated with phase control remains a formidable challenge. Herein, we firstly design the novel 2 D Pt-lead-sulphur heterophased nanosheets(Pt Pb S HPNSs) as efficient high-toleration electrocatalysts for methanol oxidation reaction(MOR).They exhibit much higher activity and more highlighted bifunctional antipoisoning abilities than Pt Pb NSs and commercial Pt/C.Further density functional theory(DFT) simulation verifies that the decreased electron density of Pt sites worked by Pb and S makes CO intermediate favorable to desorb, avoiding the formation of CO*-polluted Pt sites. Simultaneously, this heterophased interface effectively weakens the adsorption of S^(2-)-species and improves the S-poisoning tolerance, showing a route to realize nearly innoxious catalysis. The present work highlights the importance of heterophase control in tuning antipoisoning property for 2 D Pt-based nanomaterials, which is key for the rational design of efficient fuel cell anodic catalysts.

Intrinsic defects of nonprecious metal electrocatalysts for energy conversion: Synthesis, advanced characterization, and fundamentals

With the depletion of fossil fuels and environmental pollution, energy storage and conversion have become the focus of current research. Water splitting and fuel cell technologies have made outstanding contributions to energy conversion. However, the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) have slow kinetics, which limit the capacity of fuel cells. It is of great significance to develop catalysts for the OER and ORR and continuously improve their catalytic performance. Many studies have shown that intrinsic defects, especially vacancies (anion and cation vacancies), can effectively improve the efficiency of electrochemical energy storage and conversion. The introduction of intrinsic defects can generally expose more active sites, enhance conductivity, adjust the electronic state, and promote ion diffusion, thereby enhancing the catalytic performance. This review comprehensively summarizes the latest developments regarding the effects of intrinsic defects on the performance of non-noble metal electrocatalysts. According to the type of intrinsic defect, this article reviews in detail the regulation mechanism, preparation methods and advanced characterization techniques of intrinsic defects in different materials (oxides, non-oxides, etc.). Then, the current difficulties and future development of intrinsic defect regulation are analyzed and discussed thoroughly. Finally, the prospect of intrinsic defects in the field of electrochemical energy storage is further explored.