Highly enhanced electron injection in organic light-emitting diodes with an n-type semiconducting MnO2 layer

Highly enhanced electron injection is demonstrated with a thin manganese dioxide (MnO₂) electron injection layer (EIL) in Alq₃-based organic light-emitting diodes. Insertion of the MnO₂ EIL between the Al cathode and Alq₃ results in highly improved device characteristics. In situ photoelectron spectroscopy shows remarkable reduction of the electron injection barrier without significant chemical reactions between Alq₃ and MnO₂, which could induce Alq₃ destruction. The reduction of the electron injection barrier is due to the n-type doping effect, and the lack of strong interfacial reaction is advantageous with regards to more efficient electron injection than a conventional LiF EIL. These properties render the MnO₂, a potential EIL.     

Hydrothermal Synthesis of Structure‐ and Shape‐Controlled Manganese Oxide Octahedral Molecular Sieve Nanomaterials

Highly uniform single‐crystal Na‐OMS‐2 (OMS: octahedral molecular sieve), pyrolusite, and γ‐MnO₂ nanostructures with an interesting 3D urchinlike morphology have been successfully prepared using a hydrothermal method based on a mild and direct reaction between sodium dichromate and manganese sulfate. The crystal phases, shapes, and tunnel sizes of the manganese dioxide nanostructures can be tailored. Reaction temperature, concentrations of the reactants, and acidity of the solution play important roles in controlling the synthesis of these manganese dioxides. Field‐emission scanning electron microscopy and transmission electron microscopy (TEM) studies show that the nanomaterials obtained are constructed of self‐assembled nanorods. X‐ray diffraction and TEM results indicate that the constituent manganese dioxide particles are single‐crystalline materials. Energy dispersive X‐ray analysis and magnetic studies imply that chromium cations may be incorporated into the framework and/or tunnels of the manganese dioxides. A mechanism for the growth of manganese dioxides with urchinlike architectures is proposed.     

Revealing the Synergy of Cation and Anion Vacancies on Improving Overall Water Splitting Kinetics

The exact understanding for each promotional role of cation and anion vacancies in bifunctional water splitting activity will assist in the development of an efficient activation strategy of inert catalysts. Herein, systematic first-principles computations demonstrate that the synergy of anion–oxygen and cation–manganese vacancies (V_O and V_Mn) in manganese dioxide (MnO₂) nanosheets results in abnormal local lattice distortion and electronic modulation. Such alterations enrich the accessible active centers, increase conductivity, enhance the water dissociation step, and favor intermediate adsorption–desorption, consequently promoting HER and OER kinetics. As proof of concept, robust electrocatalysts, MnO₂ ultrathin nanosheets doped with dual vacancies (DV–MnO₂) are obtained via a maturely chemical strategy. Detailed characterizations confirm the cation vacancies-V_Mn contribute to enhanced conductivity and anion vacancies-V_O enrich the active centers with optimized local electronic configurations, consistent with the simulative predictions. As expected, DV–MnO₂ exhibits exceptional bifunctionality with the strong assistance of synergetic dual vacancies which act as abundant “hot spots” for active multiple intermediates. Leading to a lower cell voltage (1.55 V) in alkali electrolyte is required to reach 10 mA cm⁻² for the overall water splitting system. These atomic-level insights on synergetic DV can favor the development of activating strategy from inert electrocatalysts.     

Mesoporous Hydrous Manganese Dioxide Nanowall Arrays with Large Lithium Ion Energy Storage Capacities

Novel nanowall arrays of hydrous manganese dioxide MnO₂ · 0.5H₂O are deposited onto cathodic substrates by the potentiostatic method from a mixed aqueous solution of manganese acetate and sodium sulfate. The deposition is induced by a change of local pH resulting from electrolysis of H₂O, and hierarchical mesoporous nanowall arrays are formed as a result of simultaneous precipitation of manganese hydroxide and release of hydrogen gas bubbles from the cathode. The morphology and lithium ion intercalation properties are found to change appreciably with the concentration of the precursor electrolyte, with a significant reduction in specific surface area with an increased precursor concentration. For example, mesoporous nanowall arrays deposited from 0.1 M solution possess a surface area of ～96 m² g^?1 and exhibit a stable high intercalation capacity of 256 mA hg^?1 with a film of 0.5 µm in thickness, far exceeding the theoretical limit of 150 mA hg^?1 for manganese dioxide bulk film. Such mesoporous nanowall arrays offer much greater energy storage capacity (e.g., ～230 mA hg^?1 for films of ～2.5 µm) than that of anodic deposited films of the same thickness (～80 mA hg^?1). Such high lithium ion intercalation capacity and excellent cyclic stability of the mesoporous nanowall arrays, especially for thicker films, are ascribed to the hierarchically structured macro‐ and mesoporosity of the MnO₂ · 0.5H₂O nanowall arrays, which offer large surface to volume ratio favoring interface Faradaic reactions, short solid‐state diffusion paths, and freedom to permit volume change during lithium ion intercalation and de‐intercalation.     

Room Temperature Bolometric Applications Using Manganese Oxide Thin Films

We report the optical responses of magnetic manganese oxide La_2/3Ca_1/3MnO_δ thin films at room temperature. The voltage responses to a He-Ne laser at the wavelength of 0.63 μm and incident infrared (IR) power at the wavelength of 8-14 μm were measured. The measured signals were attributably to a bolometric response due to the heating of the sample by radiation. We report the optical responses in La_2/3Ca_1/3MnO_δ thin films as a function of chopping frequency and bias current. The noise behavior around room temperature was also discussed. It is suggested that perovskite manganese oxide thin films are suitable candidates for uncooled optical detectors.     

Influence of Dopants on Electrical Properties of ZnO-V2O5 Varistors Deduced from AC Impedance and Variable-Temperature Dielectric Spectroscopy

The influence of MnO₂, PbO, and a mixture of MnO₂, PbO, and B₂O₃ on the electrical and dielectric properties of ZnO-V₂O₅ ceramics was studied by alternating-current (AC) impedance and variable-temperature dielectric spectroscopy. The results show that, compared with the resistivity of the intervening layer at the grain boundary, the Schottky barrier present at the grain boundary is much more important for varistor performance, which can be significantly improved by using a mixture of MnO₂, PbO, and B₂O₃. Consequently, better varistor performance is achieved for 94.5?mol.% ZnO?+?0.5?mol.% V₂O₅?+?1.0?mol.% MnO₂?+?2.0?mol.% PbO?+?2.0?mol.% B₂O₃ (ZVMPB), i.e., nonlinear coefficient ???=?35.3 and leakage current density I _l?=?2.72???A/cm². The activation energy for the characteristic dielectric relaxation process is in the range of 0.339?eV to 0.365?eV, indicating that it is only associated with oxygen vacancy V _O ^· .     

Response of Granular La1− xCaxMnO3 Film to 10 GHz and 35 GHz Frequency Electromagnetic Radiation

The nonbolometric response of La_1???xCa_xMnO₃ film to 10 GHz and 35 GHz frequency electromagnetic radiation is investigated in the case when, in addition to the strong electric field of the wave, the film is subjected to a stationary electric bias field. Dependences of responses on the radiation power P at temperature T = 80 K are presented. In the low power region, a linear dependence of the response on P is observed at both frequencies whereas for high powers the dependence behaves as ~P ^1/2. The obtained results are explained taking into account that the nonbolometric response originates from the intergranular junctions that operate in the reverse current regime. There two effects take place: (i) at low powers the detection resistance decreases with increasing power P, and (ii) at higher powers in addition to that the film resistance decreases as P ^1/2 due to the avalanche of charge carriers in the electric field of the electromagnetic wave.     

A Universal Voltage Design for Triggering Manganese Dioxide Defects Construction to Significantly Boost the Pseudocapacitance

Electrochemical activation can be appropriate for constructing tunable/controllable defects within the interior of electrode materials. However, the activation mechanisms under different applied electric fields urgently need to be systematically explored. Herein, the electrochemically activated manganese dioxide (MnO₂) samples are prepared via applying a positive/negative electric field, and two different activation mechanisms are revealed through a series of characterization methods. During the activation process, it is fascinating to discover that MnO₂ mainly generates the O vacancies under positive voltage, whereas the electrolyte cations are embedded in the interlayer under negative voltage. The generated O vacancies and intercalated ions not only act as active sites or participate in the charge-transport process, but also enhance the transmission capability of carriers. In contrast, the specific capacitances of optimized MnO₂ samples are 2.9 and 2.8 times than that of pure-MnO₂ after electrochemical activation under positive and negative voltage, respectively. In addition, the activated samples exhibit excellent cycle stability and resistance to electrochemical corrosion, which can well-maintain the 3D network structure composed of nanosheets after 5000 cycles. This strategy opens up a promising approach for exploring efficient and corrosion-resistant electrode materials.     

Dichroism of (CH3NH3)2CdCl4 in the farinfrared

The dielectric constant of (CH₃NH₃)₂ CdCl₄ has been measured as a function of temperature in the submillimeter range. Freshly grown samples with a wide domain structure at room temperature show a pronounced dichroism in this spectral range which is caused by the orientation of the molecules in the room temperature orthorhombic phase and their response to the electromagnetic wave.     

Effect of thermal annealing on the structural,morphological and super capacitor behavior of MnO2 nanocrystals

Precursors of nanosized manganese dioxide were prepared through a chemical precipitation method. The synthesized precursors of MnO₂ were subjected to thermo gravimetric analysis. The thermal analysis results showed the MnO₂ formation at 500 °C. To study the effect of thermal treatments on the capacitive behavior of MnO₂, the precursors were annealed at different temperatures (300, 400 and 500 °C). The annealed products were characterized by X-ray diffraction (XRD), Fourier transforms infra-red spectroscopy (FT-IR) and cyclic Voltammetry (CV) analysis. Among the annealed products, MnO₂ annealed at 400 °C exhibits high specific capacitance. The morphologies of the products annealed at 400 and 500 °C were analyzed by a scanning electron microscope (SEM) and atomic force microscopy (AFM). The sample annealed at 500 °C shows spherical morphology with the inclusion of nanorods. To confirm the morphology of the annealed products, field emission transmission electron microscope (FE-TEM) measurements were carried out.     

Interdispersed Amorphous MnOx–Carbon Nanocomposites with Superior Electrochemical Performance as Lithium‐Storage Material

The realization of manganese oxide anode materials for lithium‐ion batteries is hindered by inferior cycle stability, rate capability, and high overpotential induced by the agglomeration of manganese metal grains, low conductivity of manganese oxide, and the high stress/strain in the crystalline manganese oxide structure during the repeated lithiation/delithiation process. To overcome these challenges, unique amorphous MnO_x–C nanocomposite particles with interdispersed carbon are synthesized using aerosol spray pyrolysis. The carbon filled in the pores of amorphous MnO_x blocks the penetration of liquid electrolyte to the inside of MnO_x, thus reducing the formation of a solid electrolyte interphase and lowering the irreversible capacity. The high electronic and lithium‐ion conductivity of carbon also enhances the rate capability. Moreover, the interdispersed carbon functions as a barrier structure to prevent manganese grain agglomeration. The amorphous structure of MnO_x brings additional benefits by reducing the stress/strain of the conversion reaction, thus lowering lithiation/delithiation overpotential. As the result, the amorphous MnO_x‐C particles demonstrated the best performance as an anode material for lithium‐ion batteries to date.     

Impedance and dielectric analysis of polycrystalline undoped and Fe doped SnS2

Polycrystalline Sn_1−xFe_xS₂ samples with (x=0, 0.125, 0.250 and 0.375) have been prepared by the molten salt solid state reaction method. The X-ray diffraction (XRD) shows that all the samples crystallize in the hexagonal structure, with P-3m1 space group in preferred orientation of (011). The electrical properties have been studied by complex impedance spectroscopy over the frequency range (20 Hz up to 1 MHz) at room temperature. The Nyquist plot for all samples have been fitted using ZMAN software. The impedance analysis showed that all samples exhibit both bulk and grain boundary contributions and it was found that by increasing the iron content, the resistance increases, but, the dielectric constant and dielectric loss tangent decrease which leads to decrease in conduction. The absorption coefficient (α) has been calculated from the complex dielectric constant. Interestingly, there was a significant correlation between the electromagnetic wave absorption and the reduction in the peak intensity of the XRD patterns indicating that when the iron content increases the sample seems to be a good absorber of electromagnetic waves.     

The effect of the base composition and microstructure of nickel-zinc ferrites on the level of absorption of electromagnetic radiation

Promising absorbing materials include Ni—Zn ferrites, as they quite intensively absorb electromagnetic waves in the frequency range from 50 to 1000 MHz. The electromagnetic properties of Ni—Zn ferrite absorbing materials obtained by different technological methods were studied in this paper. A model making it possible to evaluate the dielectric permeability of the ferrite material, depending on the microstructure parameters and electrophysical properties of grain boundaries, was proposed. The influence of base composition and microstructure on the amount of absorption of electromagnetic radiation by Ni—Zn ferrite absorbing materials was determined. It was stated that the increase of the content of excess Fe₂O₃ to 51.0 mol % leads to the shift of the frequency range of the absorption of electromagnetic radiation towards lower frequencies. It can be explained by the increase of the dielectric and magnetic permeability of ferrite. Moreover, the introduction of an excess of Fe₂O₃ in the grinding stage of the synthesized burden is more efficient. It was revealed that increasing the sintering temperature to 1350°C also shifts the frequency range of absorption of electromagnetic radiation towards lower frequencies. Probably it is caused by the increase of the dielectric and magnetic permeability of ferrite and the shift of the resonance frequency of domain walls as a result of the formation of a coarse-grained structure.     

Modulation of Hypoxia in Solid Tumor Microenvironment with MnO2 Nanoparticles to Enhance Photodynamic Therapy

Hypoxia not only promotes tumor metastasis but also strengthens tumor resistance to therapies that demand the involvement of oxygen, such as radiation therapy and photodynamic therapy (PDT). Herein, taking advantage of the high reactivity of manganese dioxide (MnO₂) nanoparticles toward endogenous hydrogen peroxide (H₂O₂) within the tumor microenvironment to generate O₂, multifunctional chlorine e6 (Ce6) loaded MnO₂ nanoparticles with surface polyethylene glycol (PEG) modification (Ce6@MnO₂‐PEG) are formulated to achieve enhanced tumor‐specific PDT. In vitro studies under an oxygen‐deficient atmosphere uncover that Ce6@MnO₂‐PEG nanoparticles could effectively enhance the efficacy of light‐induced PDT due to the increased intracellular O₂ level benefited from the reaction between MnO₂ and H₂O₂, the latter of which is produced by cancer cells under the hypoxic condition. Owing to the efficient tumor homing of Ce6@MnO₂‐PEG nanoparticles upon intravenous injection as revealed by T1‐weighted magnetic resonance imaging, the intratumoral hypoxia is alleviated to a great extent. Thus, in vivo PDT with Ce6@MnO₂‐PEG nanoparticles even at a largely reduced dose offers remarkably improved therapeutic efficacy in inhibiting tumor growth compared to free Ce6. The results highlight the promise of modulating unfavorable tumor microenvironment with nanotechnology to overcome current limitations of cancer therapies.     

高平坦度可调谐多通道吸收器的优化设计

为了提升多通道吸收器的平坦度和光谱特性的可调性,本文构建了一种硅基底/铝底板/银单缝/石墨烯/二氧化硅(SiO₂)介质层的五层结构多通道吸收器。不但吸收光谱特性易调谐,各通道平坦度也可提升到2.84 dB。基于电磁场时域有限差分法(finite-difference time-domain, FDTD)从理论上分析了结构设计尺寸对吸收光谱的影响规律,同时优化了设计结构。模拟结果证明,吸收器顶层设置SiO₂介质层和单缝内填充Au均可显著增大吸收通道的平坦度,同时通过调节顶层SiO₂或上层石墨烯的宽度,可有效调谐吸收光谱通道数、通道间隔和单通道带宽;尤其可通过改变石墨烯费米能级实施吸收频段和吸收率的需求选择,在生化检测、环境监测和智能传感等领域均具有较好的应用前景。     

Integrated Electromagnetic Device with On-Off Heterointerface for Intelligent Switching Between Wave-Absorption and Wave-Transmission

Intelligent electromagnetic wave absorbers (IEAs) are in high demand due to their dynamic electromagnetic parameters that can adapt to the complex and volatile application environments of the current 5G era. Despite of this, there is currently a lack of research on the convertible electromagnetic wave (EMW) absorption mode (switching between wave-absorption and wave-transmission) and their integrated design with external physical stimulations, so that the electromagnetic device will realize intelligent switching in any conditions. In this work, a V₂C-VO₂(M) heterostructure that exhibits a reversible metal–insulator transition at the temperature of 62 °C is fabricated via oxidation of MXene. The heterostructures demonstrate near wave-transmission characteristics at 25 °C while wave-absorption behavior with wide effective absorption bandwidth (4.04 GHz) at 70 °C. VO₂(M) exhibits stronger intrinsic conductivity after phase transition, and the “on-off” heterostructure between V₂C and VO₂ lead to poor/strong local conductive network and interfacial polarization in 25/70 °C, thus creating “quantized” dielectric loss. Furthermore, a multilayered electromagnetic functional device is developed to facilitate the absorber's phase transition temperature at a voltage of 17.5 V. This work presents promising opportunities of the V₂C-VO₂(M) heterostructure for various applications, including radar stealth, portable stealth suits, signal regulation, and deicing.     

A High‐Energy Aqueous Aluminum‐Manganese Battery

Rechargeable aluminum‐ion batteries have drawn considerable attention as a new energy storage system, but their applications are still significantly impeded by critical issues such as low energy density and the lack of excellent electrolytes. Herein, a high‐energy aluminum‐manganese battery is fabricated by using a Birnessite MnO₂ cathode, which can be greatly optimized by a divalence manganese ions (Mn²⁺) electrolyte pre‐addition strategy. The battery exhibits a remarkable energy density of 620 Wh kg^?1 (based on the Birnessite MnO₂ material) and a capacity retention above 320 mAh g^?1 for over 65 cycles, much superior to that with no Mn²⁺ pre‐addition. The electrochemical reactions of the battery are scrutinized by a series of analysis techniques, indicating that the Birnessite MnO₂ pristine cathode is first reduced as Mn²⁺ to dissolve in the electrolyte upon discharge, and Al_xMn_(1?x)O₂ is then generated upon charge, serving as a reversible cathode active material in following cycles. This work provides new opportunities for the development of high‐performance and low‐cost aqueous aluminum‐ion batteries for prospective applications.     

Porphyrin MOF Dots–Based,Function‐Adaptive Nanoplatform for Enhanced Penetration and Photodynamic Eradication of Bacterial Biofilms

Recently, antimicrobial photodynamic therapy (aPDT) has been considered as an attractive treatment option for biofilms ablation. However, even very efficient photosensitizers (PSs) still need high light doses and PS concentrations to eliminate biofilms due to the limited penetration and diffusion of PSs in biofilms. Moreover, the hypoxic microenvironment and rapid depletion of oxygen during PDT severely limit their therapeutic effects. Herein, for the first time, a porphyrin‐based metal organic framework (pMOF) dots–based nanoplatform with effective biofilm penetration, self‐oxygen generation, and enhanced photodynamic efficiency is synthesized for bacterial biofilms eradication. The function‐adaptive nanoplatform is composed of pMOF dots encapsulated by human serum albumin–coated manganese dioxide (MnO₂). The pH/H₂O₂‐responsive decomposition of MnO₂ in biofilms triggers the release of ultra‐small and positively charged pMOF dots and simultaneously generates O₂ in situ to alleviate hypoxia for biofilms. The released pMOF dots with high reactive oxygen species yield can effectively penetrate into biofilms, strongly bind with bacterial cell surface, and ablate bacterial biofilms. Importantly, such a nanoplatform can realize great therapeutic outcomes for treatment of Staphylococcus aureus–infected subcutaneous abscesses in vivo without damage to healthy tissues, which offers a promising strategy for efficient biofilms eradication.     

Nanostructured Alkaline‐Cation‐Containing δ‐MnO2 for Photocatalytic Water Oxidation

Oxygen evolution from water is one of the key reactions for solar fuel production. Here, two nanostructured K‐containing δ‐MnO₂ are synthesized: K‐δ‐MnO₂ nanosheets and K‐δ‐MnO₂ nanoparticles, both of which exhibit high catalytic activity in visible‐light‐driven water oxidation. The role of alkaline cations in oxygen evolution is first explored by replacing the K⁺ ions in the δ‐MnO₂ structure with H⁺ ions through proton ion exchange. H‐δ‐MnO₂ catalysts with a similar morphology and crystal structure exhibit activities per surface site approximately one order of magnitude lower than that of K‐δ‐MnO₂, although both nanostructured H‐δ‐MnO₂ catalysts have much larger Brunauer–Emmett–Teller (BET) surface areas. Such a low turnover frequency (TOF) per surface Mn atom might be due to the fact that the Ru²⁺(bpy)₃ sensitizer is too large to access the additional surface area created during proton exchange. Also, a prepared Na‐containing δ‐MnO₂ material with an identical crystal structure exhibits a TOF similar to that of the K‐containing δ‐MnO₂, suggesting that the alkaline cations are not directly involved in catalytic water oxidation, but instead stabilize the layered structure of the δ‐MnO₂.     

Band Diagram and Rate Analysis of Thin Film Spinel LiMn2O4 Formed by Electrochemical Conversion of ALD‐Grown MnO

Nanoscale spinel lithium manganese oxide is of interest as a high‐rate cathode material for advanced battery technologies among other electrochemical applications. In this work, the synthesis of ultrathin films of spinel lithium manganese oxide (LiMn₂O₄) between 20 and 200 nm in thickness by room‐temperature electrochemical conversion of MnO grown by atomic layer deposition (ALD) is demonstrated. The charge storage properties of LiMn₂O₄ thin films in electrolytes containing Li⁺, Na⁺, K⁺, and Mg²⁺ are investigated. A unified electrochemical band‐diagram (UEB) analysis of LiMn₂O₄ informed by screened hybrid density functional theory calculations is also employed to expand on existing understanding of the underpinnings of charge storage and stability in LiMn₂O₄. It is shown that the incorporation of Li⁺ or other cations into the host manganese dioxide spinel structure (λ‐MnO₂) stabilizes electronic states from the conduction band which align with the known redox potentials of LiMn₂O₄. Furthermore, the cyclic voltammetry experiments demonstrate that up to 30% of the capacity of LiMn₂O₄ arises from bulk electronic charge‐switching which does not require compensating cation mass transport. The hybrid ALD‐electrochemical synthesis, UEB analysis, and unique charge storage mechanism described here provide a fundamental framework to guide the development of future nanoscale electrode materials for ion‐incorporation charge storage.