Bio‐Inspired Nanospiky Metal Particles Enable Thin,Flexible, and Thermo‐Responsive Polymer Nanocomposites for Thermal Regulation

Safety issues remain a major obstacle toward large‐scale applications of high‐energy lithium‐ion batteries. Embedding thermo‐responsive polymer switching materials (TRPS) into batteries is a potential strategy to prevent thermal runaway, which is a major cause of battery failures. Here, thin, flexible, highly responsive polymer nanocomposites enabled by bio‐inspired nanospiky metal (Ni) particles are reported. These unique Ni particles are synthesized by a simple aqueous reaction at gram‐scale with controlled surface morphology and composition to optimize electrical properties of the nanocomposites. The Ni particles provide TRPS films with a high room‐temperature conductivity of up to 300 S cm^?1. Such TRPS composite films also have a high rate (<1 s) of resistance switching within a narrow temperature range, good reversibility upon on/off switching, and a tunable switching temperature (T_s; 75 to 170 °C) that can be achieved by tailing their compositions. The small size (≈500 nm) of Ni particles enables ready fabrication of thin and flexible TPRS films with thickness approaching 5 µm or less. These features suggest the great potential of using this new type of responsive polymer composite for more effective battery thermal regulation without sacrificing cell performance.     

Low‐Dimensional Lead‐Free Inorganic Perovskites for Resistive Switching with Ultralow Bias

3D organic–inorganic and all‐inorganic lead halide perovskites have been intensively pursued for resistive switching memories in recent years. Unfortunately, instability and lead toxicity are two foremost challenges for their large‐scale commercial applications. Dimensional reduction and composition engineering are effective means to overcome these challenges. Herein, low‐dimensional inorganic lead‐free Cs₃Bi₂I₉ and CsBi₃I₁₀ perovskite‐like films are exploited for resistive switching memory applications. Both devices demonstrate stable switching with ultrahigh on/off ratios (≈10⁶), ultralow operation voltages (as low as 0.12 V), and self‐compliance characteristics. 0D Cs₃Bi₂I₉‐based device shows better retention time and larger reset voltage than the 2D CsBi₃I₁₀‐based device. Multilevel resistive switching behavior is also observed by modulating the current compliance, contributing to the device tunability. The resistive switching mechanism is hinged on the formation and rupture of conductive filaments of halide vacancies in the perovskite films, which is correlated with the formation of AgI_x layers at the electrode/perovskite interface. This study enriches the library of switching materials with all‐inorganic lead‐free halide perovskites and offers new insights on tuning the operation of solution‐processed memory devices.     

Multibit Optoelectronic Memory in Top‐Floating‐Gated van der Waals Heterostructures

Nonvolatile memories based on van der Waals heterostructures have been proved to be promising candidates for next‐generation data storage devices. However, little attention has been focused on the structure with separated floating and control gates (the floating gates and control gates distribute at the different side of the channels), which were recently predicted to be capable of further improving device performance. Here, nonvolatile multibit optoelectronic memories are demonstrated using MoS₂, hexagonal boron nitride (h‐BN), and graphene in a top‐floating‐gated structure. With separated top graphene floating gate, the devices show a large memory window (≈95 V) via sweeping gate voltage from 80 to ?80 V, a high on/off ratio (≈10⁶) with an ultralow dark current (≈10^?14 A), as well as excellent retention characteristic (≈10⁴ s) and cyclic endurance. In addition, these devices can also be erased by a laser illumination with broadband spectrum after being electrically programmed. For the multilevel storage property, 7/6 stages controlled by different electrical operations, and 13/6/3 stages by different laser pulse illuminations are gained. The obtained results show a promising performance for nonvolatile optoelectronic memory using a top‐floating‐gated structure.     

High‐Performance Phototransistors Based on Single‐Crystalline n‐Channel Organic Nanowires and Photogenerated Charge‐Carrier Behaviors

The photoelectronic characteristics of single‐crystalline nanowire organic phototransistors (NW‐OPTs) are studied using a high‐performance n‐channel organic semiconductor, N,N′‐bis(2‐phenylethyl)‐perylene‐3,4:9,10‐tetracarboxylic diimide (BPE‐PTCDI), as the photoactive layer. The optoelectronic performances of the NW‐OPTs are analyzed by way of their current–voltage (I–V) characteristics on irradiation at different wavelengths, and comparison with corresponding thin‐film organic phototransistors (OPTs). Significant enhancement in the charge‐carrier mobility of NW‐OPTs is observed upon light irradiation as compared with when performed in the dark. A mobility enhancement is observed when the incident optical power density increases and the wavelength of the light source matches the light‐absorption range of the photoactive material. The photoswitching ratio is strongly dependent upon the incident optical power density, whereas the photoresponsivity is more dependent on matching the light‐source wavelength with the maximum absorption range of the photoactive material. BPE‐PTCDI NW‐OPTs exhibit much higher external quantum efficiency (EQE) values (≈7900 times larger) than thin‐film OPTs, with a maximum EQE of 263 000%. This is attributed to the intrinsically defect‐free single‐crystalline nature of the BPE‐PTCDI NWs. In addition, an approach is devised to analyze the charge‐transport behaviors using charge accumulation/release rates from deep traps under on/off switching of external light sources.     

All‐Polymer Bistable Resistive Memory Device Based on Nanoscale Phase‐Separated PCBM‐Ferroelectric Blends

All polymer nonvolatile bistable memory devices are fabricated from blends of ferroelectric poly(vinylidenefluoride–trifluoroethylene (P(VDF‐TrFE)) and n‐type semiconducting [6,6]‐phenyl‐C61‐butyric acid methyl ester (PCBM). The nanoscale phase separated films consist of PCBM domains that extend from bottom to top electrode, surrounded by a ferroelectric P(VDF‐TrFE) matrix. Highly conducting poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) polymer electrodes are used to engineer band offsets at the interfaces. The devices display resistive switching behavior due to modulation of this injection barrier. With careful optimization of the solvent and processing conditions, it is possible to spin cast very smooth blend films (R_rms ≈ 7.94 nm) and with good reproducibility. The devices exhibit high I_on/I_off ratios (≈3 × 10³), low read voltages (≈5 V), excellent dielectric response at high frequencies (?_r ≈ 8.3 at 1 MHz), and excellent retention characteristics up to 10 000 s.     

High‐Performance PM0.3 Air Filters Using Self‐Polarized Electret Nanofiber/Nets

Particulate matter (PM) pollution in air is thought to be an important mortality risk factor globally. Most existing air filters face the extreme challenge of effectively removing PM_0.3, which has the most penetration particle size (MPPS) of ≈0.3 µm yet is particularly harmful. Here, an innovative in situ electret electrospinning/netting technique that can manipulate both solution phase separation and crystal phase transition is reported to develop self‐polarized polyvinylidene fluoride nanofiber/net membranes with 2D networks and superior surface adhesion. By combining the true nanoscale diameter (≈21 nm), small pore size (≈0.26 µm), and highly electret surface (6.8 kV potential) of the 2D nanonets, the synergistic effect of sieving and adhesion for MPPS PM_0.3 is achieved. Such double capture characteristic enables the high‐efficiency (≈99.998%) capture of PM_0.3 while maintaining low air resistance (≈0.1% atmosphere pressure). Moreover, the nanofiber/net filters show integrated properties of superhydrophobicity, desirable transparency (91%), and long‐term stability. The synthesis of such attractive nanomaterials presents a promising attempt toward the development of high‐performance filtration/separation materials for numerous applications.     

Flexible Solid‐State Supercapacitor Based on Graphene‐based Hybrid Films

A flexible solid‐state asymmetric supercapacitor based on bendable film electrodes with 3D expressway‐like architecture of graphenes and “hard nano‐spacer” is fabricated via an extended filtration assisted method. In the designed structure of the positive electrode, graphene sheets are densely packed, and Ni(OH)₂ nanoplates are intercalated in between the densely stacked graphenes. The 3D expressway‐like electrodes exhibit superior supercapacitive performance including high gravimetric capacitance (≈573 F g^‐1), high volumetric capacitance (≈655 F cm^‐3), excellent rate capability, and superior cycling stability. In addition, another hybrid film of graphene and carbon nanotubes (CNT) is fabricated as the negative electrodes for the designed asymmetric device. In the obtained graphene@CNT films, CNTs served as the hard spacer to prevent restacking of graphene sheets but also as a conductive and robust network to facilitate the electrons collection/transport in order to fulfill the demand of high‐rate performance of the asymmetric supercapacitor. Based on these two hybrid electrode films, a solid‐state flexible asymmetric supercapacitor device is assembled, which is able to deliver competitive volumetric capacitance of 58.5 F cm^‐3 and good rate capacity. There is no obvious degradation of the supercapacitor performance when the device is in bending configuration, suggesting the excellent flexibility of the device.     

Solution‐Processable,High‐Performance Flexible Electroluminescent Devices Based on High‐k Nanodielectrics

Flexible alternating‐current electroluminescent (ACEL) devices have attracted considerable attention for their ability to produce uniform light emission under bent conditions and have enormous potential for applications in back lighting panels, decorative lighting in automobiles, and panel displays. Nevertheless, flexible ACEL devices generally require a high operating bias, which precludes their implementation in low power devices. Herein, solution‐processed La‐doped barium titanate (BTO:La) nanocuboids (≈150 nm) are presented as high dielectric constant (high‐k) nanodielectrics, which can enhance the dielectric constant of an ACEL device from 2.6 to 21 (at 1 kHz), enabling the fabrication of high‐performance flexible ACEL devices with a lower operating voltage as well as higher brightness (≈57.54 cd m^?2 at 240 V, 1 kHz) than devices using undoped BTO nanodielectrics (≈14.3 cd m^?2 at 240 V, 1 kHz). Furthermore, a uniform brightness across the whole panel surface of the flexible ACEL devices and excellent device reliability are achieved via the use of uniform networks of crossaligned silver nanowires as highly conductive and flexible electrodes. The results offer experimental validation of high‐brightness flexible ACELs using solution‐processed BTO:La nanodielectrics, which constitutes an important milestone toward the implementation of high‐k nanodielectrics in flexible displays.     

High‐Energy Asymmetric Supercapacitor Yarns for Self‐Charging Power Textiles

Rapid growth of electronic textile increases the demand for textile‐based power sources, which should have comparable lightweight, flexibility, and comfort. In this work, a self‐charging power textile interwoven by all‐yarn‐based energy‐harvesting triboelectric nanogenerators (TENG) and energy‐storing yarn‐type asymmetric supercapacitors (Y‐ASC) is reported. Common polyester yarns with conformal Ni/Cu coating are utilized as 1D current collectors in Y‐ASCs and electrodes in TENGs. The solid‐state Y‐ASC achieves high areal energy density (≈78.1 µWh cm^?2), high power density (14 mW cm^?2), stable cycling performance (82.7% for 5000 cycles), and excellent flexibility (1000 cycles bending for 180°). The TENG yarn can be woven into common fabrics with desired stylish designs to harvest energy from human daily motions at high output (≈60 V open‐circuit voltage and ≈3 µA short‐circuit current). The integrated self‐charging power textile is demonstrated to power an electronic watch without extra recharging by other power sources, suggesting its promising applications in electronic textiles and wearable electronics.     

Graphene Oxide‐Template Controlled Cuboid‐Shaped High‐Capacity VS4 Nanoparticles as Anode for Sodium‐Ion Batteries

Room‐temperature sodium‐ion batteries have attracted great attentions for large‐scale energy storage applications in renewable energy. However, exploring suitable anode materials with high reversible capacity and cyclic stability is still a challenge. The VS₄, with parallel quasi‐1D chains structure of V⁴⁺(S₂^2?)₂, which provides large interchain distance of 5.83 Å and high capacity, has showed great potential for sodium storage. Here, the uniform cuboid‐shaped VS₄ nanoparticles are prepared as anode for sodium‐ion batteries by the controllable of graphene oxide (GO)‐template contents. It exhibits superb electrochemical performances of high‐specific charge capacity (≈580 mAh·g^?1 at 0.1 A·g^?1), long‐cycle‐life (≈98% retain at 0.5 A·g?¹ after 300 cycles), and high rates (up to 20 A·g^?1). In addition, electrolytes are optimized to understand the sodium storage mechanism. It is thus demonstrated that the findings have great potentials for the applications in high‐performance sodium‐ion batteries.     

High‐Speed,Low‐Voltage,and Environmentally Stable Operation of Electrochemically Gated Zinc Oxide Nanowire Field‐Effect Transistors

Single‐crystal, 1D nanostructures are well known for their high mobility electronic transport properties. Oxide‐nanowire field‐effect transistors (FETs) offer both high optical transparency and large mechanical conformability which are essential for flexible and transparent display applications. Whereas the “on‐currents” achieved with nanowire channel transistors are already sufficient to drive active matrix organic light emitting diode (AMOLED) displays; it is shown here that incorporation of electrochemical‐gating (EG) to nanowire electronics reduces the operation voltage to ≤2 V. This opens up new possibilities of realizing flexible, portable, transparent displays that are powered by thin film batteries. A composite solid polymer electrolyte (CSPE) is used to obtain all‐solid‐state FETs with outstanding performance; the field‐effect mobility, on/off current ratio, transconductance, and subthreshold slope of a typical ZnO single‐nanowire transistor are 62 cm²/Vs, 10⁷, 155 μS/μm and 115 mV/dec, respectively. Practical use of such electrochemically‐gated field‐effect transistor (EG FET) devices is supported by their long‐term stability in air. Moreover, due to the good conductivity (≈10^?2 S/cm) of the CSPE, sufficiently high switching speed of such EG FETs is attainable; a cut‐off frequency in excess of 100 kHz is measured for in‐plane FETs with large gate‐channel distance of >10 μm. Consequently, operation speeds above MHz can be envisaged for top‐gate transistor geometries with insulator thicknesses of a few hundreds of nanometers. The solid polymer electrolyte developed in this study has great potential in future device fabrication using all‐solution processed and high throughput techniques.     

Nano‐Imprinted Ferroelectric Polymer Nanodot Arrays for High Density Data Storage

Ferroelectric vinylidene fluoride‐trifluoroethylene copolymer [P(VDF‐TrFE)] free‐standing ultrahigh density (≈75 Gb inch^?2) nanodot arrays are successfully fabricated through a facile, high‐throughput, and cost‐effective nano‐imprinting method using disposable anodic aluminum oxide with orderly arranged nanometer‐scale pores as molds. The nanodots show a large‐area smooth surface morphology, and the piezoresponse in each nanodot is strong and uniform. The preferred orientation of the copolymer chains in the nanodot arrays is favorable for polarization switching of single nanodots. The ferroelectric polymer memory prototype can be operated by a few volts with high writing/erasing speed, which comply with the requirements of integrated circuit. This approach provides a way of directly writing nanometer electronic features in two dimensions by piezoresponse force microscopy probe based technology, which is attractive for high density data storage.     

An On‐Chip Break Junction System for Combined Single‐Molecule Conductance and Raman Spectroscopies

Systems that are capable of robustly reproducing single‐molecule junctions are an essential prerequisite for enabling the wide‐spread testing of molecular electronic properties, the eventual application of molecular electronic devices, and the development of single‐molecule based electrical and optical diagnostics. Here, a new approach is proposed for achieving a reliable single‐molecule break junction system by using a microelectromechanical system device on a chip. It is demonstrated that the platform can (i) provide subnanometer mechanical resolution over a wide temperature range (≈77–300 K), (ii) provide mechanical stability on par with scanning tunneling microscopy and mechanically controllable break junction systems, and (iii) operate in a variety of environmental conditions. Given these fundamental device performance properties, the electrical characteristics of two standard molecules (hexane‐dithiol and biphenyl‐dithiol) at the single‐molecule level, and their stability in the junction at both room and cryogenic temperatures (≈77 K) are studied. One of the possible distinctive applications of the system is demonstrated, i.e., observing real‐time Raman scattering in a single‐molecule junction. This approach may pave a way to achieving high‐throughput electrical characterization of single‐molecule devices and provide a reliable platform for the convenient characterization and practical application of single‐molecule electronic systems in the future.     

Approaching the Downsizing Limit of Maricite NaFePO4 toward High‐Performance Cathode for Sodium‐Ion Batteries

Maricite NaFePO₄ nanodots with minimized sizes (≈1.6 nm) uniformly embedded in porous N‐doped carbon nanofibers (designated as NaFePO₄@C) are first prepared by electrospinning for maximized Na‐storage performance. The obtained flexible NaFePO₄@C fiber membrane adherent on aluminum foil is directly used as binder‐free cathode for sodium‐ion batteries, revealing that the ultrasmall nanosize effect as well as a high‐potential desodiation process can transform the generally perceived electrochemically inactive maricite NaFePO₄ into a highly active amorphous phase; meanwhile, remarkable electrochemical performance in terms of high reversible capacity (145 mA h g^?1 at 0.2 C), high rate capability (61 mA h g^?1 at 50 C), and unprecedentedly high cyclic stability (≈89% capacity retention over 6300 cycles) is achieved. Furthermore, the soft package Na‐ion full battery constructed by the NaFePO₄@C nanofibers cathode and the pure carbon nanofibers anode displays a promising energy density of 168.1 Wh kg^?1 and a notable capacity retention of 87% after 200 cycles. The distinctive 3D network structure of very fine NaFePO₄ nanoparticles homogeneously encapsulated in interconnected porous N‐doped carbon nanofibers, can effectively improve the active materials' utilization rate, facilitate the electrons/Na⁺ ions transport, and strengthen the electrode stability upon prolonged cycling, leading to the fascinating Na‐storage performance.     

Pulse‐Mode Dynamic Ron Measurement of Large‐Scale High‐Power AlGaN/GaN HFET

We propose pulse‐mode dynamic R_on measurement as a method for analyzing the effect of stress on large‐scale high‐power AlGaN/GaN HFETs. The measurements were carried out under the soft‐switching condition (zero‐voltage switching) and aimed to minimize the self‐heating problem that exists with the conventional hard‐switching measurement. The dynamic R_on of the fabricated AlGaN/GaN MIS‐HFETs was measured under different stabilization time conditions. To do so, the drain‐gate bias is set to zero after applying the off‐state stress. As the stabilization time increased from 0.1 μs to 100 ms, the dynamic R_on decreased from 160 Ω to 2 Ω. This method will be useful in developing high‐performance GaN power FETs suitable for use in high‐efficiency converter/inverter topology design.     

Human HSP70 Promoter‐Based Prussian Blue Nanotheranostics for Thermo‐Controlled Gene Therapy and Synergistic Photothermal Ablation

Realizing precise control of the therapeutic process is crucial for maximizing efficacy and minimizing side effects, especially for strategies involving gene therapy (GT). Herein, a multifunctional Prussian blue (PB) nanotheranostic platform is first designed and then loaded with therapeutic plasmid DNA (HSP70‐p53‐GFP) for near‐infrared (NIR) light‐triggered thermo‐controlled synergistic GT/photothermal therapy (PTT). Due to the unique structure of the PB nanocubes, the resulting PB@PEI/HSP70‐p53‐GFP nanoparticles (NPs) exhibit excellent photothermal properties and pronounced tumor‐contrast performance in T₁/T₂‐weighted magnetic resonance imaging. Both in vitro and in vivo studies demonstrate that mild NIR‐laser irradiation (≈41 °C) activates the HSP70 promoter for tumor suppressor p53‐dependent apoptosis, while strong NIR‐laser irradiation (≈50 °C) induces photothermal ablation for cellular dysregulation and necrosis. Significant synergistic efficacy can be achieved by adjusting the NIR‐laser irradiation (from ≈41 to ≈50 °C), compared to using GT or PTT alone. In addition, in vitro and in vivo toxicity studies demonstrate that PB@PEI/HSP70‐p53‐GFP NPs have good biocompatibility. Therefore, this work provides a promising theranostic approach for controlling combined GT and PTT via the heat‐shock response.     

A Strain‐Mediated Magnetoelectric‐Spin‐Torque Hybrid Structure

Magnetization dynamics induced by spin–orbit torques in a heavy‐metal/ferromagnet can potentially be used to design low‐power spintronics and logic devices. Recent computations have suggested that a strain‐mediated spin–orbit torque (SOT) switching in magnetoelectric (ME) heterostructures is fast, energy‐efficient, and permits a deterministic 180° magnetization switching. However, its experimental realization has remained elusive. Here, the coexistence of the strain‐mediated ME coupling and the SOT in a CoFeB/Pt/ferroelectric hybrid structure is shown experimentally. The voltage‐induced strain only slightly modifies the efficiency of SOT generation, but it gives rise to an effective magnetic anisotropy and rotates the magnetic easy axis which eliminates the incubation delay in current‐induced magnetization switching. The phase field simulations show that the electric‐field‐induced effective magnetic anisotropy field can reduce the switching time approximately by a factor of three for SOT in‐plane magnetization switching. It is anticipated that such strain‐mediated ME‐SOT hybrid structures may enable field‐free, ultrafast magnetization switching.     

Nitrogen‐Doped Mesoporous Carbon Promoted Chemical Adsorption of Sulfur and Fabrication of High‐Areal‐Capacity Sulfur Cathode with Exceptional Cycling Stability for Lithium‐Sulfur Batteries

As one important component of sulfur cathodes, the carbon host plays a key role in the electrochemical performance of lithium‐sulfur (Li‐S) batteries. In this paper, a mesoporous nitrogen‐doped carbon (MPNC)‐sulfur nanocomposite is reported as a novel cathode for advanced Li‐S batteries. The nitrogen doping in the MPNC material can effectively promote chemical adsorption between sulfur atoms and oxygen functional groups on the carbon, as verified by X‐ray absorption near edge structure spectroscopy, and the mechanism by which nitrogen enables the behavior is further revealed by density functional theory calculations. Based on the advantages of the porous structure and nitrogen doping, the MPNC‐sulfur cathodes show excellent cycling stability (95% retention within 100 cycles) at a high current density of 0.7 mAh cm^‐2 with a high sulfur loading (4.2 mg S cm^‐2) and a sulfur content (70 wt%). A high areal capacity (≈3.3 mAh cm^‐2) is demonstrated by using the novel cathode, which is crucial for the practical application of Li‐S batteries. It is believed that the important role of nitrogen doping promoted chemical adsorption can be extended for development of other high performance carbon‐sulfur composite cathodes for Li‐S batteries.     

Single‐Atomic‐Co Electrocatalysts with Self‐Supported Architecture toward Oxygen‐Involved Reaction

Single‐atomic electrocatalysts (SACs) have shown great promise in electrocatalysis fields owing to their theoretical maximum atom utilization (100%). Yet still, it is far from expectation in practical applications due to entrapping within supports and blocking by aggregation. Herein, self‐supported carbon nanosheet arrays consisting of single‐atomic Co electrocatalyst (SS‐Co‐SAC) toward oxygen‐involved reaction and zinc–air batteries are reported. Impressively, the as‐synthesized SS‐Co‐SAC gives a markedly enhanced utilization of active sites (≈22.3%@2.3 wt%) as a result of single‐atomic dispersion of Co within a unique nanosheet arrays architecture, which is the largest value among other reported results. Benefiting from the high utilization of active sites, the SS‐Co‐SAC electrode exhibits outstanding electrocatalytic performance for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Notably, the turnover frequency value for ORR is determined to be ≈9.26 s^?1, which stands for the highest level among noble metal‐free electrocatalysts reported previously. Moreover, as an air‐cathode for zinc–air batteries with SS‐Co‐SAC, a power density of 195.1 mW cm^?2 and a robust durability are achieved. It is believed that this study would guide the future design of highly active and durable single‐atom catalysts for both fundamental research and practical applications.     

Fabrication of a Cu‐Cone‐Shaped Cation Source Inserted Conductive Bridge Random Access Memory and Its Improved Switching Reliability

Conductive bridge random access memory (CBRAM) has been regarded as a promising candidate for the next‐generation nonvolatile memory technology. Even with the great performance of CBRAM, the global generation and overinjection of cations after much repetitive switching cannot be prevented. The overinjection of cations into an electrolyte layer causes high‐resistance‐state resistance (R_HRS) degradation, on/off ratio reduction, and eventual switching failure. It also degrades the switching uniformity. In this work, a Cu‐cone‐structure‐embedded TiN/TiO₂/Cu cone/TiN device is fabricated to alleviate the problems of Cu‐based CBRAM, mentioned above. The fabrication method of the device, which is useful for laboratory scale experiment, is developed, and its superior switching performance and reliability compared with the conventional planar device. The insertion of the Cu cone structure allows the placement of only a limited amount of cation source in each cell, and the embedded conical structure also concentrates the applied electric field, which enables filament growth control. Furthermore, the concentrated field localizes the resistive switching on the tip area of the cone structure, which makes the effective switching area about tens of nanometers even for the much larger area of the entire electrode (several µm²).