Low-dimensional phases engineering for improving the emission efficiency and stability of quasi-2D perovskite films

The two-dimensional(2 D) Ruddlesden–Popper-type perovskites, possessing tunable bandgap, narrow light emission,strong quantum confinement effect, as well as a simple preparation method, are identified as a new generation of candidate materials for efficient light-emitting diodes. However, the preparation of high-quality quasi-2 D perovskite films is still a challenge currently, such as the severe mixing of phases and a high density of defects within the films, impeding the further promotion of device performance. Here, we prepared the quasi-2 D PEA_(2) MA_(n-1) Pbn Br_(3 n+1) perovskite films by a modified spin-coating method, and the phases with large bandgap were effectively suppressed by the vacuum evaporation treatment. We systematically investigated the optical properties and stability of the optimized films, and the photoluminescence(PL) quantum yield of the treated films was enhanced from 23% to 45%. We also studied the emission mechanisms by temperature-dependent PL spectra. Moreover, the stability of films against moisture, ultraviolet light, and heat was also greatly improved.

Self-assembly 2D plasmonic nanorice film for surface-enhanced Raman spectroscopy

As an ultrasensitive sensing technology,the application of surface enhanced Raman spectroscopy(SERS)is one interesting topic of nano-optics,which has huge application prospectives in plenty of research fields.In recent years,the bottleneck in SERS application could be the fabrication of SERS substrate with excellent enhancement.In this work,a two-dimensional(2D)Ag nanorice film is fabricated by self-assembly method as a SERS substrate.The collected SERS spectra of various molecules on this 2D plasmonic film demonstrate quantitative detection could be performed on this SERS substrate.The experiment data also demonstrate this 2D plasmonic film consisted of anisotropic nanostructures has no obvious SERS polarization dependence.The simulated electric field distribution points out the SERS enhancement comes from the surface plasmon coupling between nanorices.And the SERS signals is dominated by molecules adsorbed at different regions of nanorice surface at various wavelengths,which could be a good near IR SERS substrate for bioanalysis.Our work not only enlarges the surface plasmon properties of metal nanostructure,but also exhibits the good application prospect in SERS related fields.

Graphene as a Strictly 2D Sheet or as a Film of Small but Finite Thickness

We study an interface between two media separated by a strictly 2D sheet. We show how the amplitude reflection coef- ficient can be modeled by that for an interface where the 2D sheet has been replaced by a film of small but finite thick- ness. We give the relationship between the 3D dielectric function of the thin film and the 2D dielectric function of the sheet. We apply this to graphene and show how the van der Waals interaction between two graphene sheets is modified when going from the 2D sheet description to the thin film description. We also show the wrong result from keeping the 2D dielectric function to represent the film medium.

3d过渡金属掺杂TiO_2纳米晶膜电极的光电化学研究

应用原子力显微镜和X射线粉末法对 3d过渡金属离子Cr(Ⅲ ) ,Fe(Ⅲ ) ,Mn(Ⅱ ) ,Co(Ⅱ ) ,Ni(Ⅱ ) ,Cu(Ⅱ )和Zn(Ⅱ )掺杂TiO2 纳米晶粒 (简写为M3d TiO2 )作了表征 ,并用光电化学方法研究了M3d TiO2 纳米结构多孔膜电极 .实验结果表明 ,M3d TiO2 纳米粒子的颗粒较均匀 ,粒径约为 1 5nm ,其晶型为锐钛矿和板钛矿的混晶 .在所研究的M3d TiO2 中 ,只有Zn2 + TiO2 电极的光电流大于未掺杂的TiO2 纳米结构多孔膜电极 .3d金属离子的掺杂引起各电极的光电流信号在一定波长范围内出现 p

1,1,2,2-四(5-三甲基硅-二噻吩并[2,3-b:3′,2′-d]噻吩-2-)乙烯的发光现象研究

通过对典型AIE分子,即四噻吩乙烯(TTE)分子结构的拓展,本文研究了一种聚集诱导发光(AIE)分子,即1,1,2,2-四(5-三甲基硅-二噻吩并[2,3-b:3′,2′-d]噻吩-2-)乙烯(TFTE)在溶液态、AIE态与冻结态下的发光行为,考察了介质的极性、粘度与温度等条件下的分子发光现象。研究发现,TFTE分子在有机溶剂中发较弱的荧光,发光峰约在480 nm,而在THF-H_(2)O二元溶剂体系中表现出显著的AIE态的发光特性,聚集态发光峰位于569 nm。在甲醇-甘油的二元溶剂体系中,单分子发光红移至595 nm,体现出显著的分子内单键旋转受阻与强的溶剂化作用。在分子运动完全受限(冻结态)条件下,TFTE分子展现出独特的长波长单分子发光,发光峰位于565 nm,并与TFTE分子的AIE发光峰非常接近,说明了AIE态与冻结态下TFTE分子的构象是相近的。TFTE分子在薄膜态下的发光峰位位于607 nm,比AIE态发光红移了38 nm,说明了薄膜中TFTE分子间存在显著的轨道相互作用,而在AIE态下分子间的相互作用微弱。

Layered Foam/Film Polymer Nanocomposites with Highly Efficient EMI Shielding Properties and Ultralow Reflection

Lightweight,high-efficiency and low reflection electromagnetic interference(EMI)shielding polymer composites are greatly desired for addressing the challenge of ever-increasing electromagnetic pollution.Lightweight layered foam/film PVDF nanocomposites with efficient EMI shielding effectiveness and ultralow reflection power were fabricated by physical foaming.The unique layered foam/film structure was composed of PVDF/SiCnw/MXene(Ti_(3)C_(2)Tx)composite foam as absorption layer and highly conductive PVDF/MWCNT/GnPs composite film as a reflection layer.The foam layer with numerous heterogeneous interfaces developed between the SiC nanowires(SiCnw)and 2D MXene nanosheets imparted superior EM wave attenuation capability.Furthermore,the microcellular structure effectively tuned the impedance matching and prolonged the wave propagating path by internal scattering and multiple reflections.Meanwhile,the highly conductive PVDF/MWCNT/GnPs composite(~220 S m^(−1))exhibited superior reflectivity(R)of 0.95.The tailored structure in the layered foam/film PVDF nanocomposite exhibited an EMI SE of 32.6 dB and a low reflection bandwidth of 4 GHz(R<0.1)over the Kuband(12.4-18.0 GHz)at a thickness of 1.95 mm.A peak SER of 3.1×10^(-4) dB was obtained which corresponds to only 0.0022% reflection efficiency.In consequence,this study introduces a feasible approach to develop lightweight,high-efficiency EMI shielding materials with ultralow reflection for emerging applications.

Protective behavior of an SO_2/CO_2 gas mixture for molten AZ91D alloy

The protective behavior for a molten AZ91D alloy in an open melting furnace was investigated under a protective gas mixture containing 3% SO2 and 97% CO2, and the protection mechanism was discussed. Experimental results show that the gas mixture provides effective protection for AZ91D melt in the temperature range from 680 ℃ to 730 ℃. The microstructure, chemical composition and phase composition of the surface film formed on the molten AZ91D alloy were analyzed using scanning electron microscopy （SEM） with energy dispersive spectrometer （EDS） and X-ray diffraction （XRD）. The SEM results demonstrate that the surface films with an average thickness between 0.5 pm and 2 pm are dense and coherent in the protected temperature range. The EDS results reveal that the surface film mainly contains elements S, C, O, AI and Mg. The XRD results show that the surface film consists of MgO, MgS and a small amount of C phase.

The Gas Nucleation Process Study of Anatase TiO_2 in Atmospheric Non-Thermal Plasma Enhanced Chemical Vapor Deposition

Abstract The gas phase nucleation process of anatase TiO2 in atmospheric non-thermal plasma enhanced chemical vapor deposition is studied. The particles synthesized in the plasma gas phase at different power density were collected outside of the reactor. The structure of the collected particles has been investigated by field scanning electron microscope （FESEM）, X-ray diffraction （XRD）, high resolution transmission electron microscopy （HRTEM） and selected area electron diffraction （SAED）. The analysis shows that uniform crystalline nuclei with average size of several nanometers have been formed in the scale of micro second through this reactive atmo- spheric plasma gas process. The crystallinity of the nanoparticles increases with power density. The high density of crystalline nanonuclei in the plasma gas phase and the low gas temperature are beneficial to the fast deposition of the 3D porous anatase TiO2 film.

Synthesis of Flower-Like Bi2Te3 Nano Structure and Studying Its Structural and Thermo-electric Properties

Flower-like Bi2Te3 nanostructures were successfully synthesised for the first time by a simple magnetron technique or D.C. sputtering method. The phase and morphology of the products were characterized by X-ray diffraction （XRD）, manning electron microscope （SEM） and atomic force microscope （AFM）. It was found that the as-deposited Bi2Te3 has a well re-crystallized Rhombohedral phase and consisted of a wealth of flower-like structure, also the thermo-electric properties of Bi2Te3 were examined and we find that the Seebeck coefficient is 136.6μ volt/K.

Allying interfacial engineering of 2D carbon nanosheet-,graphene-,and graphdiyne-based heterostructured electrocatalysts toward hydrogen evolution and overall water splitting

Electrochemical hydrogen evolution reaction(HER)and overall water splitting(OWS)for renewable energy generation have recently become a highly promising and sustainable strategy to tackle energy crisis and global warming arising from our overreliance on fossil fuels.Previously,tremendous research breakthroughs have been made in 2D carbon-based heterostructured electrocatalysts in this field.Such heterostructures are distinguished by their remarkable electrical conductivity,exposed active sites,and mechanical stability.Herein,with fundamental mechanisms of electrocatalytic OWS summarized,our review critically emphasized on state-of-the-art 2D carbon nanosheet-,graphene-,and graphdiyne-based heterostructured electrocatalysts in HER and OWS since 2018.Particularly,the three emerging carbonaceous substrates tend to be incorporated with metal carbides,phosphides,dichalcogenides,nitrides,oxides,nanoparticles,single atom catalysts,or layered double hydroxides.Meanwhile,fascinating structural engineering and facile synthesis strategies were also unraveled to establish the structure-activity relationship,which will enlighten future electrocatalyst developments toward ameliorated HER and OWS activities.Additionally,computational results from density functional theory simulations were highlighted as well to better comprehend the synergistic effects within the heterostructures.Finally,current stages and future recommendations of this brand-new electrocatalyst type were concluded and discussed for advanced catalyst designs and future practical applications.

Ferroelectric perovskite-type films with robust in-plane polarization toward efficient room-temperature chemiresistive sensing

Ferroelectric materials have become key components for versatile device applications,and their thin films are highly desirable for integrating the miniaturized devices.Despite substantial endeavors,it is still challenging to achieve effective chemiresistive sensing in the ferroelectric films.Here,for the first time,we have exploited ferroelectric thin films of 2D hybrid perovskite BA_(2)EA_(2)Pb_(3)I_(10)(1),to fabricate the high-performance chemiresistor gas sensors.The spin-coated films of 1 exhibit high orientation and good crystallinity,thus preserving robust in-plane spontaneous polarization(P_(s)~2.0μC/cm^(2))and low electric coercivity.Notably,such ferroelectric filmbased sensors after electric poling enable the dramatic room-temperature sensing responses to NO_(2) gas,including high sensitivity(0.05 ppm^(-1)),extremely low detection limit(1 ppm)and fast responding rate(~6 s).Besides,the chemiresistive responses are remarkably enhanced by threefold(up to 320%)through electric poling.It is proposed that this behavior closely involves with strong in-plane ferroelectric polarization of 1 that generates a built-in electric field inhibiting the recombination of charge carriers.As far as we know,this ferroelectric-based film chemiresisor is one of the best room-temperature sensors for NO_(2) gas among all the existing candidate materials.These findings highlight great potential of ferroelectrics toward effective chemiresistive performances,and also establish a bright direction to explore their future device applications.

Low-temperature crystalline lead-free piezoelectric thin films grown on 2D perovskite nanosheet for flexible electronic device applications

A monolayer of Sr2Nb3Oio(SNO)is deposited on the Pt/Ti/SiCWSi(Pt?Si)or Pt/Ti/polyimide(Pt-Pl)substrate by using the Langmuir-Blodgett method and employed as a seed-layer for the growth of a crystalline(Nai_xKx)NbO3(NKN)film at 350℃.The crystalline NKN film is grown along the[001]direction on the SNO/Pt-Si(or SNO/Pt-PI)substrate.Due to the presence of oxygen vacancies in the SNO seed-layer,the NKN film exhibits low ferroelectric properties and large leakage current.To ameliorate these properties,the SNO/Pt-Si substrate is annealed in a 50 Torr oxygen atmosphere at 300℃,which removes the oxygen vacancies.Consequently,the NKN film deposited on this substrate exhibits promising electrical properties,namely a dielectric constant of 278,dissipation factor of 1.7%,a piezoelectric 8nstant of 175 pm`V^-1,and a leakage current density of 6.47 x 10^-7 A cm^-2 at-0.2 MV crrT1.Similar electrical properties are obtained from the NKN film grown on the flexible SNO/Pt-PI substrate at 350°C.Hence,the NKN films grown on the SNO seed-layer at 350°C can be applied to electronic devices with flexible polymer substrates.

Superconductivity in two-dimensionalη-Mo3C2 films

Two-dimensional(2D)superconductors have intriguing physical properties and abundant potential applications.Recently,2D superconductingα-Mo2C and facecentered cubic Mo2C have been controllably prepared and they bring new viewpoints to carbon-based superconductivity.Although molybdenum carbides(Mo-Cs)have multiple crystalline stacking orders,there are still few structures reported for the lack of higher energy supply during growth.In this study,we report a two-step vapor deposition method to grow superconducting η-Mo3C2 films with different thicknesses,with the assistance of controllable plasma power.The grownη-Mo3C2 films show polycrystalline characteristics,but they still present superior superconductivity.The 3.0-nm-thick film has the superconducting transition temperature of 5.38 K,and its electrical performances follow truly 2D superconducting transitions.This study will not only exhibit a robust superconductingη-Mo3C2 ultrathin film,but also provides a convenient growth way to realize more carbide-based heterostructures for future device applications.

Extensive study of optical contrast between bulk and nanoscale transition metal dichalcogenide semiconductors

A remarkable refinement in the optical behavior of two-dimensional transition metal dichalcogenides(TMDs)has been brought to light when cleaved from their respective bulks.These atomically thin direct bandgap semiconductors are highly responsive to optical energy which proposes the route for futuristic photonic devices.In this manuscript,we have substantially focused on the optical study of MoS_(2)and WS_(2)nanosheets and comparative analysis with their bulk counterparts.The synthesis of nanosheets has been accomplished with liquid exfoliation followed by fabrication of thin films with drop-casting technique.X-ray diffraction and field emission scanning electron microscopy affirmed the morphology,whereas,UV-visible spectroscopy served as the primary tool for optical analysis.It was observed that several parameters,like optical conductivity,optical band-gap energy etc.have enhanced statistics in the case of exfoliated nanosheets as compared to their respective bulks.Some researchers have touched upon this analysis for MoS_(2),but it is completely novel for WS_(2).We expect our work to clearly distinguish between the optical behaviors of nanoscale and bulk TMDs so as to intensify and strengthen the research related to 2D-layered materials for optoelectronic and photovoltaic applications.

Organophosphine ligand derived sandwich-structural electrocatalyst for oxygen evolution reaction

The synchronous construction of metal phosphate and phosphorus-doped carbon structures is of great significance to innovate the design,synthesis,and application of catalysts,as these phosphoruscontaining composite materials have shown a remarkable contribution to electrocatalysts.However,their preparation procedure generally involves using large amounts of excess phosphorus sources for phosphorization,which inevitably release poisonous PH_(3) or dangerous phosphorus vapor.Here,a strategy for in-situ formation of FePO_(4) embedded in P-doped carbon 2D nano film(FePO_(4)/PdC)is developed using a highly integrated precursor,which is a small molecular organophosphine ligand,1,1’bis(diphenylphosphine)ferrocene(DPPF).The multi-source precursor DPPF that contains Fe,P,and C is molecular-vapor-deposited on the nickel foam(NF)supported ZIF-67 nanosheets to obtain the composite catalyst,namely DPPF-500/ZIF-67/NF.FePO_(4)/PdC encapsulated the ZIF-67 derived Co/N-doped carbon matrix(Co NC)to form a sandwich structure FePO_(4)/PdC@CoNC.The constructed catalyst shows good performance for OER,requiring an overpotential of only 297 m V to deliver 600 m A/cm^(2) with a Tafel slope of 42.7 m V dec^(-1).DFT calculations demonstrate that the synergistic effects between the metal active center and P-doped carbon film reduce the energy barriers and improve electron transport.This method of constructing P-containing catalysts overcomes the demand for additional P sources to realize eco-friendly fabrication and yields a unique structure with good catalytic activity.

Al_(2)O_(3)对Ti膜离子注入表面损伤及D滞留量的影响研究

为提高中子管Ti膜的储氢及抗溅射损伤性能,该研究通过在Ti膜表面沉积一层Al_(2)O_(3)保护层,研究了该保护层对Ti膜在D离子注入过程中表面损伤及D滞留量的影响。采用射频磁控溅射技术完成了Ti膜和表面有Al_(2)O_(3)保护层的Ti膜(Al_(2)O_(3)/Ti膜)样品的制备,开展了D离子注入实验,利用扫描电子显微镜(SEM)对D离子注入前后的表面形貌进行分析,并通过热脱附谱(TDS)实验研究保护层对Ti膜中D滞留量的影响。SEM结果表明,注入5×10^(17)个D离子后,Ti膜表面出现开裂和剥离现象,而Al_(2)O_(3)/Ti膜表面无开裂和剥离现象,Al_(2)O_(3)保护层抑制了Ti膜的开裂和剥离,可提高Ti膜使用寿命。TDS实验结果表明,增加Al_(2)O_(3)保护层后,D脱附峰值温度提升4.9%,膜内D滞留量提升10.3%,在D离子注入过程中Al_(2)O_(3)保护层可阻止膜内D原子的释放进而提升Ti膜内D滞留量。该文初步验证了Al_(2)O_(3)有作为中子管Ti膜保护层材料的潜力。

Layer-by-layer assembly of long-afterglow self-supporting thin films with dual-stimuli-responsive phosphorescence and antiforgery applications

The assembly of thin films （TFs） having long-lasting luminescence can be expected to play an important role in the development of new-generation smart sensors, anti-counterfeiting materials, and information-encryption systems. However, such films are limited compared with their powder and solution counterparts. In this study, by exploiting the self-organization of phosphors in the two-dimensional （2D） galleries between clay nanosheets, we developed a method for the ordered assembly of long-afterglow TFs by utilizing a hydrogen-bonding layer-by-layer （LBL） process. Compared with the pristine powder, the TFs exhibit high polarization and up-conversion room-temperature phosphorescence （RTP）, as well as enhanced quantum yields and luminescence lifetimes, allowing them to be used as room-temperature phosphorescent sensors for humidity and oxygen. Moreover, modified clay-based hybrids with multicolor RTP can serve as anti-counterfeiting marks and triple-mode 2D barcode displays. We anticipate that the LBL assembly process can be extended to the fabrication of other inorganic--organic room-temperature phosphorescent hybrids with smart luminescent sensor and antiforgery applications.

Centimeter-scale growth of two-dimensional layered high-mobility bismuth films by pulsed laser deposition

Ever since discovery of graphene,two-dimensional(2D)materials become a new tool box for information technology.Among the 2D family,ultrathin bismuth(Bi)has attracted a great deal of attention in recent years due to its unique topological insulating properties and large magnetoresistance.However,the scalable synthesis of layered Bi ultrathin films is rarely been reported,which would greatly restrict further fundamental investigation and practical device development.Here,we demonstrate the direct growth of homogeneous and centimeter-scale layered Bi films by pulsed laser deposition(PLD)technique.The as-grown Bi film exhibits high-purity phase and good crystallinity.In addition,both(111)and(110)-oriented Bi films can be synthesized by precisely controlling the processing temperature.The characterization of optical properties shows a thickness dependent band gaps(0.075-0.2 eV).Moreover,Bi thin-film-based field-effect transistors have been demonstrated,exhibiting a large carrier mobility of 220 cm2 V−1 s−1.Our work suggests that the PLD-grown Bi films would hold the potential to develop spintronic applications,electronic and optoelectronic devices used for information science and technology.

Energy-band engineering by 2D MXene doping for high-performance homojunction transistors and logic circuits

The homojunction based on Ti_(3)C_(2)T_(x) MXene-doped In_(2)O_(3) and indium oxide as the channel layer is real-ized in high-performance metal oxide thin film transistors(TFTs).Doping of MXene into In_(2)O_(3) results in n-type semiconductor behavior,realizing tunable work function of In_(2)O_(3) from 5.11 to 4.79 eV as MXene content increases from 0 to 2 wt.%.MXene-doped In_(2)O_(3)-based homojunction TFT presents optimal per-formance with electron mobilities of greater than 27.10 cm^(2)/(V s)at 240°C,far exceeding the maximum mobility of 3.91 cm^(2)/(V s)for single-layer In_(2)O_(3)TFTs.The improved performance originates from boosting of a two-dimensional electron gas(2DEG)formed at carefully engineered In_(2)O_(3)/MXene-doped In_(2)O_(3)ox-ide homojunction interface.Besides,the transformation in conduction mechanism leads to better stability of MXene-doped In_(2)O_(3) homojunction devices compared to undoped bilayer In_(2)O_(3).Low-frequency noise further illustrates that doping MXene into In_(2)O_(3) helps to reduce the device trap density,demonstrating excellent electrical performance.A resistor-loaded unipolar inverter based on In_(2)O_(3)/0.5%MXene-In_(2)O_(3)TFT has demonstrated full swing characteristics and a high gain of 13.The effective doping of MXene into constructed homojunction TFTs not only contributes to improved stability,but also provides an ef-fective strategy for designing novel homojunction TFTs for low-cost oxide-based electronics.

Graphene oxide film for efficient solar desalination under one sun with a confined 2D water path

Subject Code:A04With the support by the National Natural Science Foundation of China and the State Key Program for Basic Research of China,the research team led by Prof.Zhu Jia(朱嘉)at the National Laboratory of Solid State Microstructures,College of Engineering and Applied Sciences,Nanjing University,improved the efficiency of solar desalination using graphene oxide film through suppressing the conduction loss。