Progress of Proximity Sensors for Potential Applications in Electronic Skins

Recently,electronic skins and fl exible wearable devices have been developed for widespread applications in medical monitoring,artifi cial intelligence,human–machine interaction,and artifi cial prosthetics.Flexible proximity sensors can accurately perceive external objects without contact,introducing a new way to achieve an ultrasensitive perception of objects.This article reviews the progress of fl exible capacitive proximity sensors,fl exible triboelectric proximity sensors,and fl exible gate-enhanced proximity sensors,focusing on their applications in the electronic skin fi eld.Herein,their working mechanism,materials,preparation methods,and research progress are discussed in detail.Finally,we summarize the future challenges in developing fl exible proximity sensors.

A Pore-Forming Strategy Toward Porous Carbon-Based Substrates for High Performance Flexible Lithium Metal Full Batteries

Self-standing carbon-based substrates with satisfied structural stability and property adjustability have promising applications in flexible lithium(Li)metal batteries(FLMBs).Current strategies for modifying carbon materials are normally carried out on powder carbon,and very few of them are suitable for self-standing carbon substrates.Herein,a pore-forming strategy based on the redox chemistry of metallic oxide nanodots is developed to prepare two porous carbon substrates for anode and cathode.Starting with cotton cloth,the resulting hollow carbon fibers substrate with nanopores effectively prevents from Li dendrites formation and large volume change in lithium metal anode(LMA).Simulations indicate that the porous structure leads to homogeneous ion flux,Li-ion concentration,and electric field during Li deposition.Li symmetrical cell based on this substrate remains stable for 8300 h with an ultralow voltage hysteresis of 9 mV.Via a similar route,porous carbon cloth substrate is obtained for subsequently seeding V_(2)O_(5)nanowires to prepare the cathode.The assembled FLMBs pouch cell delivers a capacity of 8.2 mAh with a high capacity retention of~100%even under dramatic deformation.The demonstrated strategy has far-reaching potential in preparing free-standing porous carbon-based materials for flexible energy storage devices.

Emerging of Ag particles on ZnO nanowire arrays for blue-ray hologram storage

Noble-metal/metal-oxide-semiconductor nanostructures as an important material platform have been applied in massive data storage. ZnO exhibits excellent optical modulation ability. However, plasmon induced charge separation effect in Ag/ZnO systems is very weak due to the low chemical activity on surface of the oxide. Herein, we prepare ZnO nanowire arrays via the hydrothermal method, and measure their absorption spectra, photoluminescence spectra and electron paramagnetic resonance, proving the existence of oxygen defects in ZnO. Accordingly, an idea of “electron reverse transfer” is proposed such that blue-ray(403.4 nm) induces reduction of Ag^(+) ions through the excitation of ZnO. Rod-like and spherical silver nanoparticles emerge on the surface and in the gap of ZnO nanowire arrays, respectively, after the visible light stimulus. It is found that nanowire density, oxygen defects and surface roughness are dependent on hydrothermal time. The optimized diffraction efficiency of 0.08% is obtained for reconstructing hologram in the nanocomposite film. This work provides a bright way for construction of ZnO-based optoelectronic integrated devices.

Performance enhancement of ZnO nanowires/PbS quantum dot depleted bulk heterojunction solar cells with an ultrathin Al_2O_3 interlayer

Depleted bulk heterojunction （DBH） PbS quantum dot solar cells （QDSCs）, appearing with boosted short-circuit current density （Jsc）, represent the great potential of solar radiation utilization, but suffer from the problem of increased interfacial charge recombination and reduced open-circuit voltage （Voc）. Herein, we report that an insertion of ultrathin A1203 layer （ca. 1.2 A thickness） at the interface of ZnO nanowires （NWs） and PbS quantum dots （QDs） could remarkably improve the performance of DBH-QDSCs fabricated from them, i.e., an increase of Voc from 449 mV to 572 mV, J^c from 21.90 mA/cm2 to 23.98 mA/cm2, and power conversion efficiency （PCE） from 4.29% to 6.11%. Such an improvement of device performance is ascribed to the significant reduction of the interfacial charge recombination rate, as evidenced by the light intensity dependence on Jsc and Voc, the prolonged electron lifetime, the lowered trap density, and the enlarged recombination activation energy. The present research therefore provides an effective interfacial engineering means to improving the overall performance of DBH-QDSCs, which might also be effective to other types of optoelectronic devices with large interface area.

Novel two-step CdS deposition strategy to improve the performance of Cu2ZnSn(S,Se)4 solar cell

Kesterite Cu2ZnSn(S,Se)4(CZTSSe)solar cells have drawn worldwide attention for their promising photovoltaics performance and earth-abundant element composition,yet the record efficiency of this type of device is still far lower than its theoretical conversion efficiency.Undesirable band alignment and severe non-radiative recombination at CZTSSe/CdS heterojunction interfaces are the major causes limiting the current/voltage output and overall device performance.Herein,we propose a novel two-step CdS deposition strategy to improve the quality of CZTSSe/CdS heterojunction interface and thereby improve the performance of CZTSSe solar cell.The two-step strategy includes firstly pre-deposits CdS thin layer on CZTSSe absorber layer by chemical bath deposition(CBD),followed with a mild heat treatment to facilitate element inter-diffusion,and secondly deposits an appropriate thickness of CdS layer by CBD to cover the whole surface of pre-deposited CdS and CZTSSe layers.The solar energy conversion efficiency of CZTSSe solar cells with two-step deposited CdS layer approaches to 8.76%(with an active area of about 0.19 cm2),which shows an encouraging improvement of over 87.98%or 30.16%compared to the devices with traditional CBD-deposited CdS layer without and with the mild annealing process,respectively.The performance enhancement by the two-step CdS deposition is attributed to the formation of more favorable band alignment at CZTSSe/CdS interface as well as the effective decrease in interfacial recombination paths on the basis of material and device characterizations.The two-step CdS deposition strategy is simple but effective,and should have large room to improve the quality of CZTSSe/CdS heterojunction interface and further lift up the conversion efficiency of CZTSSe solar cells.

TiO_2 nanoparticle-based electron transport layer with improved wettability for efficient planar-heterojunction perovskite solar cell

The electron transport layer （ETL） plays an important role in planar heterojunction perovskite solar cell （PSCs）, by affecting the light-harvesting, electron injection and transportation processes, and especially the crystal- lization of perovskite absorber. In this work, we utilized a commercial TKD-TiO2 nanoparticle with a small diameter of 6 nm for the first time to prepare a compact ETL by spin coating. The packing of small-size particles endowed TKD-TiO2 ETL an appropriate surface-wettability, which is beneficial to the crystallization of perovskite deposited via solution-processed method. The uniform and high-transmittance TKD-TiO2 films were successfully incorporated into PSCs as ETLs. Further careful optimization of ETL thickness gave birth to a highest power conversion efficiency of 11.0%, which was much higher than that of PSC using an ETL with the same thickness made by spray pyrolysis. This TKD-TiO2 provided a universal solar material suitable for the further large-scale production of PSCs. The excellent morphology and the convenient preparation method of TKD-TiO2 film gave it an extensive application in photovoltaic devices.

Hall conductance of a non-Hermitian two-band system with k-dependent decay rates

Two-band model works well for Hall effect in topological insulators. It turns out to be non-Hermitian when the system is subjected to environments, and its topology characterized by Chern numbers has received extensive studies in the past decades. However, how a non-Hermitian system responses to an electric field and what is the connection of the response to the Chern number defined via the non-Hermitian Hamiltonian remains barely explored. In this paper, focusing on a k-dependent decay rate, we address this issue by studying the response of such a non-Hermitian Chern insulator to an external electric field. To this aim, we first derive an effective non-Hermitian Hamiltonian to describe the system and give a specific form of k-dependent decay rate. Then we calculate the response of the non-Hermitian system to a constant electric field.We observe that the environment leads the Hall conductance to be a weighted integration of curvature of the ground band and hence the conductance is no longer quantized in general. And the environment induces a delay in the response of the system to the electric field. A discussion on the validity of the non-Hermitian model compared with the master equation description is also presented.

Electrospun nanofibers of poly(vinyl pyrrolidone)/Eu^(3+) and its photoluminescence properties

Nanofibers of poly（vinyl pyrrolidone） （PVP）/Eu^3＋ with diameters of 300-900 nm were prepared by using sol-gel processing and electrospinning technique. The products were characterized by scanning electron microscope （SEM）, Fourier transform infrared spectroscopy （FT-IR）, and photoluminescence （PL）. The results indicated that, Eu^3＋ was successfully embedded in the onedimensional hybrid nanofibers, and the PVP/Eu^3＋ hybrid nanofibers had favorable photoluminescence properties.

Electrical Conductivity of Alkaline-reduced Graphene Oxide

A green route using a very simple and straightforward ultrasonic process under alkaline conditions, rather than a general chemical reduction process using hydrazine, was utilized to obtain the hydrophilic reduced graphene oxide（RGO） sheets, via removing oxygen functional groups from graphene oxide（GO） and repairing the aromatic structure. It is found that the conductivity of the obtained RGO could be tuned by changing pH value in alkaline solution, and the current-voltage（I-V） curves of both GO and RGO are nonlinear and slightly asymmetric. Under the same applied voltage, the current of RGO is much larger than that of GO, indicating a pronounced increase in the electrical conductivity of RGO, compared to that of GO.

Preparation of CdSe/ZnSe Core-shell Nanocrystal in One-step Reaction

High-quality Zn-doped CdSe core-shell nanocrystals were successfully prepared by incorporating a stoichiometric amount of Zn precursor into the CdSe reaction system, in which the Se precursor was excess and an Se-rich surface was formed. By injecting different amounts of Zn precursor, the core-shell nanocrystals demonstrated by the emission spectra were formed. The obtained Zn-doped CdSe nanocrystals exhibit a photoluminescence efficiency from 30% to 85%, which is comparable to those for the reported CdSe/ZnS, CdSe/CdS in the literature. In particular, a shell ZnSe layer with different thicknesses of ZnSe can be formed in this experiment by only changing the amount of Zn precursor added, which is simple and effective.

Preparation and Photocatalysis of Mesoporous TiO_2 Nanofibers via an Electrospinning Technique

Mesoporous TiO2 nanofibers have been synthesized by a new method that combines sol-gel chemistry and electrospinning technique.The obtained mesoporous TiO2 nanofibers were characterized with scanning electron microscopy（SEM）,X-ray diffraction（XRD）,transmission electron microscopy（TEM） and nitrogen adsorptiondesorption isotherms.The photocatalytic performance was evaluated by the photocatalytic degradation of Rhodamine B under UV light irradiation.The results show that mesoporous TiO2 nanofibers exhibit higher photocatalytic activity compared with nonporous TiO2 nanofibers.

Voltage-dependent plasticity and image Boolean operations realized in a WOx-based memristive synapse

The development of electronic devices that possess the functionality of biological synapses is a crucial step towards neuromorphic computing.In this work,we present a WOx-based memristive device that can emulate voltage-dependent synaptic plasticity.By adjusting the amplitude of the applied voltage,we were able to reproduce short-term plasticity(STP)and the transition from STP to long-term potentiation.The stimulation with high intensity induced long-term enhancement of conductance without any decay process,thus representing a permanent memory behavior.Moreover,the image Boolean operations(including intersection,subtraction,and union)were also demonstrated in the memristive synapse array based on the above voltage-dependent plasticity.The experimental achievements of this study provide a new insight into the successful mimicry of essential characteristics of synaptic behaviors.

InfoMat:A cross-field exploration of information technology and materials science

As our modern society continuously embraces the captivating concepts of automation,artificial intelligence,virtual/augmented reality,and machine learning,information technology has extensively influenced all aspects of our personal,professional,and social lives.Information technology will continue to transform the world for decades to come.However,the innovation of information technology not only relies on the development of sophisticated algorithms and programming but also requires novel materials and high-performance devices to achieve interactions between humans and machines.With microprocessors and other key components shrinking down to nanoscale,electronic devices have fundamentally altered our communication and working patterns,ushering in a new era of the“Internet of Things.”However,current microelectronic technologies still need to overcome the physical limitations of traditional semiconductor materials to keep“Moore's law”alive.Researchers from different fields have realized that developing novel and reliable materials is essential to improving computing capability and device portability and functionality while reducing energy consumption.The unremitting efforts of cross-field research works have broadened the academic horizon and brought together materials scientists,chemists,applied and theoretical physicists,and electrical engineers,designing new material paradigms and state-of-the-art manufacturing methods or reviving present materials for brand-new applications for next-generation information technology.

Coexistence of unipolar and bipolar modes in Ag/ZnO/Pt resistive switching memory with oxygen-vacancy and metal-Ag filaments

In this study, the unipolar resistive switching （URS） and bipolar resistive switching （BRS） are demonstrated to be coexistent in the Ag/ZnO/Pt memory device, and both modes are observed to strongly depend on the polarity of forming voltage. The mechanisms of the URS and BRS behaviors could be attributed to the electric-field-induced migration of oxygen vacancies （Vo） and metal-Ag conducting filaments （CFs） respectively, which are confirmed by investigating the temperature dependences of low resistance states in both modes. Furthermore, we compare the resistive switching （RS） characteristics （e.g., forming and switching voltages, reset current and resistance states） between these two modes based on Vo- and Ag-CFs. The BRS mode shows better switching uniformity and lower power than the URS mode. Both of these modes exhibit good RS performances, including good retention, reliable cycling and high-speed switching. The result indicates that the coexistence of URS and BRS behaviors in a single device has great potential applications in future nonvolatile multi-level memory.

Dissipative preparation of multipartite Greenberger-Horne-Zeilinger states of Rydberg atoms

The multipartite Greenberger-Horne-Zeilinger(GHZ)states play an important role in large-scale quantum information processing.We utilize the polychromatic driving fields and the engineered spontaneous emissions of Rydberg states to dissipatively drive three-and four-partite neutral atom systems into the steady GHZ states,at the presence of the nextnearest neighbor interaction of excited Rydberg states.Furthermore,the introduction of quantum Lyapunov control can help us optimize the dissipative dynamics of the system so as to shorten the convergence time of the target state,improve the robustness against the spontaneous radiations of the excited Rydberg states,and release the limiting condition for the strengths of the polychromatic driving fields.Under the feasible experimental conditions,the fidelities of three-and four-partite GHZ states can be stabilized at 99.24%and 98.76%,respectively.

A single Eu^(2+)-activated high-color-rendering oxychloride white-light phosphor for white-light-emitting diodes

Single-phased,high-color-rendering index(CRI)white-light phosphors are emerging as potential phosphor-converted white-light-emitting diodes(WLEDs)and as an alternative to blends of tricolor phosphors.However,it is a challenge to create a high CRI white light from a single-doped activator.Here,we present a high CRI(Ra 591)white-light phosphor,Sr_(5)(PO_(4))_(3-x)(BO_(3))_(x)Cl:Eu^(2+),composed of Sr5(PO4)3Cl as the beginning member and Sr_(5)(BO_(3))_(3)Cl as the end member.This work utilized the solid-solution method,and tunable Eu^(2+) emission was achieved.Color-tunable Eu^(2+) emissions in response to structural variation were observed in Sr_(5)(PO_(4))_(3-x)(BO_(3))_(x)Cl solid solutions.This was further confirmed using X-ray Rietveld refinement,electron paramagnetic resonance spectroscopy,and in the photoluminescence spectra.The color-tunable emissions included the white light that originated from the combination of the blue emission of Sr_(5)(PO_(4))_(3)Cl:Eu^(2+) and an induced Eu^(2+) yellow emission at approximately 550 nm in the solid solution.Importantly,the white-light phosphors showed a greater R9590.2 under excitation at 365 nm.This result has rarely been reported in the literature and is greater than that of(R9514.3)commercial Y_(3)A_(l5)O_(12):Ce^(3+)-based WLEDs.These findings demonstrate the great potential of Sr_(5)(PO_(4))_(3-x)(BO_(3))_(x)Cl:0.04Eu^(2+) as a white-light phosphor for near-UV phosphor-converted WLEDs.These results also provide a shortcut for developing a high CRI white-light phosphor from a single Eu^(2+)-doped compound.

Polymer Electron Acceptors Based on Fluorinated Isoindigo Unit for Polymer Solar Cells

Most of efficient polymer electron acceptors for polymer solar cells （PSCs） are based on naphthalene diimide or perylene diimide as the electron deficient building block. In this paper, for the first time, we report polymer electron acceptors based on fluorinated isoindigo IF-lID） as the electron deficient building block. We synthesized two polymer electron acceptors consisting of alternating F-lID unit and thiophene/selenophen unit, They show low-lying LUMo/HOMO energy levels of-3.69/-5.69 eV, high electron mobilities of 1.31 ×10-5 cm2.V-1s-1 and broad absorption spectra with the optical bandgap of 1.61 eV. PSC devices using the two F-liD-based polymers as polymer electron acceptors show encouraging power conversion efficiencies （PCEs） of up to 1.50% with an open-circuit voltage （Voc） of 0.97V, a short-circuit current density （Jsc） of 2.91 mA.cm2, and a fill factor （FF） of 53.2%. This work suggests a new kind of polymer electron acceptors based on F-IID unit.

Breakthroughs in projection-enabled additive manufacturing:From novel strategies to cutting-edge applications

As one of the crucial technologies of additive manufacturing(AM),projection technology,which features fast printing speed,high molding accuracy,and low cost,exhibits great potential in cutting-edge applications.The basic principle of projection-enabled AM(PAM)is the stacking of layer-wise structures,in which the dynamic mask pattern is projected onto the surface of the liquid photosensitive resin,triggering polymerization in a specific area to accomplish single-layer printing.This facilitates the layer-wise manufacture of complex three-dimensional(3D)structures.Currently,the projection technologies of PAM can be mainly classified into liquid crystal displays,digital light processing(DLP),and silicon-based light crystal spatial light modulators.Among these,DLP is distinguished by its programmable two-dimensional(2D)projection ability.

Ultra-broadband metamaterial absorbers from long to very long infrared regime

Broadband metamaterials absorbers with high absorption,ultrathin thickness and easy configurations are in great demand for many potential applications.In this paper,we first analyse the coupling resonances in a Ti/Ge/Ti three-layer absorber,which can realise broadband absorption from 8 to 12 pm.Then we experimentally demonstrate two types of absorbers based on the Ti/Ge/Si_(3)N_(4)/Ti configuration.By taking advantage of coupling surface plasmon resonances and intrinsic absorption of lossy material Si_(3)N_(4),the average absorptions of two types of absorbers achieve almost 95%from 8 to 14μm(experiment result:78%from 6.5 to 13.5μm).In order to expand the absorption bandwidth,we further propose two Ti/Si/SiO_(2)/Ti absorbers which can absorb 92%and 87%of ultra-broadband light in the 14-30μm and 8-30μm spectral range,respectively.Our findings establish general and systematic strategies for guiding the design of metamaterial absorbers with excellent broadband absorption and pave the way for enhancing the optical performance in applications of infrared thermal emitters,imaging and photodetectors.

Dissipative preparation of Bell states with parallel quantum Zeno dynamics

We propose a new mechanism, parallel quantum Zeno dynamics, to dissipatively prepare all Bell entangled states of the twoqubit system in the context of cavity quantum electrodynamics. This mechanism can provide two transition channels between ground states and two different dark states simultaneously, which efficiently speeds up the stabilization of the entanglement and suppresses the adverse influence of surrounding environments. In addition, there is no need for the initialization of quantum states and the Clauser-Horne-Shimony-Holt inequality can be violated in a finite temperature bath. The experimental feasibility is also studied by the state-of-the-art technique and a high fidelity about 99% can be achieved.