Journal of Applied Physics

MAPb x Sn 1 − x I 3 alloys are highly promising for photovoltaic, optoelectronic, and spintronics applications. Using k.p calculations, we derived the fundamental band parameters of these tetragonal hybrid halide perovskites as a function of Pb content ( x ). Our study focuses on the experimentally confirmed C 4 v point group structures: P4mm for Sn-rich alloys and I4cm for Pb-rich alloys. Our theoretical model successfully reproduces the non-monotonic behavior of the bandgap and provides detailed insights into the electron, hole, and reduced exciton masses ( m e, m h, and μ). We find that hole masses are slightly larger than electron masses, with both increasing linearly as x rises. At the structural transition ( x = 0.5) between P4mm and I4cm, we observe a discontinuity in hole masses and a steeper linear increase in Pb-rich structures. The calculated exciton masses show excellent agreement with experimental data across a wide range of alloy compositions. Additionally, we predict the Landé g-factors for charge carriers ( g e, g h) and excitons ( g X). For Pb-rich alloys, g e increases with decreasing bandgap energy, while for Sn-rich alloys, g e decreases. Exciton g-factors g X are predominantly governed by the large positive g e values, as the smaller negative g h values provide minimal compensation. Consequently, g X is not constant but varies with the bandgap, ranging from 2.4 and 4.8 for Pb-rich alloys and from 4.8 and 3.7 for Sn-rich alloys. These results highlight the tunable electronic and spin properties of MAPb x Sn 1 − x I 3 alloys, positioning them as versatile candidates for next-generation device applications.

Sulfur hexafluoride (SF6), a widely used arc quenching medium in the power industry, has been designated as a greenhouse gas, necessitating its reduction and replacement. Identifying eco-friendly alternatives to SF6 is a complex and expensive process, particularly since these alternatives often consist of gas mixtures that may function at varying pressures. In this work, we propose an efficient method for evaluating the arc quenching performance of gases or gas mixtures using the time-dependent Elenbaas–Heller and Boltzmann equations, which circumvents the computational costs associated with traditional 2D or 3D magnetohydrodynamic arc models. We segment the arc quenching process into four distinct stages: the thermal recovery stage, pre-dielectric recovery stage, post-dielectric recovery stage, and residual-gas cooling stage. To quantitatively assess arc quenching performance, we introduce two key parameters: recovery rate and recovery strength. The recovery rate is defined as the harmonic mean of thermal, pre-dielectric, and post-dielectric recovery rates. The recovery strength is characterized by the harmonic mean of the average recovery voltage, maximum critical electric field strength, and room-temperature dielectric strength. Our method is validated using several SF6 alternatives, including SF6 mixtures, C4F8, C4F7N, C5F10O, and their mixtures with CO2, N2, and O2. The results demonstrate that the coupling of the time-dependent Elenbaas–Heller and Boltzmann equations well describes the arc decaying process. Moreover, the proposed recovery rate and recovery strength metrics effectively quantify the arc quenching ability, enabling a systematic and efficient evaluation of various gas mixtures for arc interruption performance.

This article provides an overview of the latest results in the field of improving the properties of multiatomic inorganic oxide compounds for scintillators. A possibility to control the spatial distribution of nonequilibrium carriers in the ionization track by creating a compositional disorder in the crystalline matrix is in focus. Managing the disorder at the nanoscale level creates an opportunity for the efficient energy loss by carriers during thermalization, smaller spatial dispersion, and, consequently, more efficient binding into excitons and, further, an increase in the scintillation yield. The methods to produce multicationic crystalline scintillation materials have been discussed. The effectiveness of the approach is confirmed for both activated and self-activated scintillation materials.

Since the photoconversion efficiency η of the silicon-based solar cells (SCs) under laboratory conditions is approaching the theoretical fundamental limit, further improvement of their performance requires theoretical modeling and/or numerical simulation to optimize the SCs parameters and design. The existing numerical approaches to modeling and optimizing the key parameters of high-efficiency solar cells based on monocrystalline silicon, the dominant material in photovoltaics, are described. It is shown that, in addition to the four usually considered recombination processes, namely, Shockley–Read-Hall, surface, radiative, and band-to-band Auger recombination mechanisms, the non-radiative exciton Auger recombination and recombination in the space charge region (SCR) have to be included. To develop the analytical SC characterization formalism, we proposed a simple expression to model the wavelength-dependent external quantum efficiency of the photocurrent near the absorption edge. Based on this parameterization, the theory developed allows for calculating and optimizing the base thickness-dependent short-circuit current, the open-circuit voltage, and the SC photoconversion efficiency. The accuracy of the approach to optimizing solar cell parameters, particularly thickness and base doping level, is demonstrated by its application to three Si solar cells reported in the literature: one with an efficiency of 26.63%, another with 26.81%, and a third with a record efficiency of 27.3%. The results show that the developed formalism enables further optimization of solar cell thickness and doping levels, leading to potential increases in efficiency.

Two-dimensional (2D) magnetic materials offer promising prospects for applications in magnetic storage and spin field-effect transistors. However, the inherently low Curie temperatures of intrinsic 2D ferromagnetic semiconductor materials pose significant limitations on their practical device applications. An effective approach to achieving room-temperature ferromagnetism involves doping non-magnetic semiconductors with specific magnetic atoms. Here, we present the room-temperature ferromagnetism of chromium (Cr)-doped molybdenum disulfide (MoS2) nanosheets synthesized through chemical vapor deposition. The magnetic hysteresis loops, recorded across a temperature span of 10–300 K, underscore the remarkable stability of their magnetic attributes. To gain deeper microscopic insights into the magnetic properties of Cr-doped MoS2, we conducted first-principles calculations, which further validated our experimental findings. This research underscores a promising pathway for the development of 2D ferromagnetic materials with broad application potential in magnetic storage and spin field-effect transistors.

The continuous technological development of electronic devices and the introduction of new materials lead to ever greater demands on the fabrication of semiconductor heterostructures and their characterization. This work focuses on optimizing Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) depth profiles of semiconductor heterostructures aiming at a minimization of measurement-induced profile broadening. As a model system, a state-of-the-art Molecular Beam Epitaxy (MBE) grown multilayer homostructure consisting of n a tSi/ 28Si bilayers with only 2 nm in thickness is investigated while varying the most relevant sputter parameters. Atomic concentration-depth profiles are determined and an error function based description model is used to quantify layer thicknesses as well as profile broadening. The optimization process leads to an excellent resolution of the multilayer homostructure. The results of this optimization guide to a ToF-SIMS analysis of another MBE grown heterostructure consisting of a strained and highly purified 28Si layer sandwiched between two Si 0.7Ge 0.3 layers. The sandwiched 28Si layer represents a quantum well that has proven to be an excellent host for the implementation of electron-spin qubits.

Silicon (Si) acts as an amphoteric impurity in gallium arsenide (GaAs), occupying various sites and exhibiting different coordination structures within the material. In this study, we employed electron microscopy, x-ray absorption spectroscopy, and theoretical simulations to analyze the Si-occupied sites and local coordination structures at concentrations ranging from 2 to 4 × 10¹⁹ atoms/cm³ in heavily doped GaAs. High angular resolution electron channeling x-ray spectroscopy was employed to analyze the Si-occupied sites. This method quantitatively estimates site occupancies through statistical analysis of atom site-dependent spectra. It was observed that Si substitutes for both Ga and As sites with nearly equal occupancies. Si K-edge x-ray absorption fine structure (XAFS) measurements and density functional theory calculations were used to explore the local coordination structures of Si. The peak positions of experimental XAFS spectra aligned closely with those of the calculated XAFS spectra for neutral SiGa–SiAs dumbbells, particularly when Si atoms were in close proximity. Considering the effect of vacancies, the experimental XAFS peak position corresponded well with that of the calculated Si dumbbell–VAs pair. In addition, the observed pre-peak was attributed to neutral Si, likely originating from Si clusters. These findings enhance our understanding of Si-related defect structures and their influence on the properties of heavily Si-doped GaAs.

We present PyLRO, an open-source Python calculator designed to detect, quantify, and display long-range order in periodic structures. The program’s design methodology, workflow, and approach to order quantification are described and demonstrated using a simple toy model. Additionally, we apply PyLRO to a series of metastable AlPO 4 structural intermediates from a prior high-pressure study, demonstrating how to compute and visualize structural order in all directions on a Miller sphere. We further highlight the program’s capabilities through a high-throughput analysis of structural patterns in the pressure-induced amorphization of AlPO 4, revealing atomistic insights into specific energy regions of massive amorphous structures. These results suggest that PyLRO can be a valuable tool for investigating crystal–amorphous transition in materials research.

The integration of metal–semiconductor nanostructures is of significant interest to the advanced technology development. However, the synthesis methods for metal–semiconductor nanostructures are complicated and require multi-stage processing, which includes the separate synthesis of metallic and semiconductor nanostructures, controlling pH, and dedicated equipments. Herein, we report a one-step in situ synthesis and simultaneous embedding of Ru nanostructures on g-C3N4 nanosheets using the synchrotron x-ray irradiation method. The results indicate that Ru nanostructures were uniformly embedded within the g-C3N4 nanosheets, leading to the formation of Ru—O, RuO2, and Ru—O—Ru chemical bonds. Moreover, three distinct types of Ru nanostructures could be achieved by adjusting the x-ray dose. High-performance triboelectric nanogenerators (TENGs) were fabricated using these three types of Ru-embedded g-C3N4 nanosheets within a PDMS matrix. The output performance of these TENG devices was compared with that of PDMS and g-C3N4/PDMS TENGs. The improved dielectric constant contributes to the high performance of the TENG. The synthesized Ru/g-C3N4 nanostructures are notably significant due to increased contact surface area, charge distribution density, and the formation of a metal–semiconductor heterostructure system. These characteristics lead to high charge transfer rates, improved charge transport, and a higher density of charge trapping centers within the insulating matrix. Thus, we achieved a high TENG peak power density of 4.86 W/m² during the contact separation process. The practical applicability of the TENG is also demonstrated. Furthermore, a 47 μF capacitor could be charged to 7.8 V in ∼400 s and can be used to continuously drive low power electronic gadgets.

Piezoelectric semiconductors (PSCs) are crucial in micro-electromechanical systems, but analyzing their size effects and accurately determining flexoelectric parameters is challenging due to the complexity of multi-scale and multi-field coupling. Physics-informed neural networks (PINNs), which merge physical laws with machine learning, provide a promising approach for solving partial differential equations and parameter inversion. In this paper, we develop a PINN model to solve a system of fourth-order partial differential equations for PSC nanowires, accounting for strain gradient and flexoelectric effects. Predictions by the model closely match results from traditional numerical methods. Additionally, with minimal labeled data, the PINN model can predict both physical solutions and material parameters, such as the flexoelectric coefficient. It is expected that PINNs offer an effective method for analyzing PSC nanowires and inverting key material properties.

For nearly 60 years, cold field emitters have been the source of choice for electron microscopy due to their high brightness and relatively low energy spread. In this paper, we have examined an alternative: nanoscale electron sources based on near-threshold photoemission. While these sources have not yet been realized, they hold the potential to produce significantly brighter beams than cold field emitters. We model electron–electron Coulomb interactions in beams emitted from such sources to calculate the impact of these interactions on the brightness and the energy spread. Our results show that these sources can theoretically deliver more than an order of magnitude brighter electron beams compared to cold field emitters along with more than an order of magnitude smaller energy spread, before being limited by the Coulomb interactions. Electron sources with such high brightness and low energy spread would be transformational for electron microscopy, enabling electron energy loss-based vibrational spectroscopy at the sub-nanometer scale.

We develop the theoretical foundation to determine the thermal conductivity of a single nanowire by using the optical contrast of the metallic and insulating domains of a VO 2 nanowire excited with either a temperature difference or a laser beam. Considering the temperature dependence of the VO 2 thermal conductivity, the heat flux and the temperature profile along a VO 2 nanowire are obtained and used to derive explicit expressions for the position of the metal/insulator domain interface as a function of the thermal excitation. This relation determines the variations of the metallic and insulating domains’ lengths, which can be employed to retrieve the thermal conductivity of a single nanowire bonded to a VO 2 one. Furthermore, the advantages and disadvantages of each thermal excitation are discussed along with the appearance of invariants driving the one-dimensional nonlinear heat conduction along VO 2 nanowires.

Electron transport measurements on 60-nm-thick multilayers containing N = 2–58 individual Ru and Co layers are employed to quantify the specific resistance of Ru/Co interfaces. Sputter deposition on Al2O3(0001) at Ts = 400 °C leads to a 0001 preferred orientation with x-ray diffraction (XRD) Ru and Co 0002 peaks that shift closer to each other with increasing N, suggesting interfacial intermixing. The intermixing is quantified by x-ray reflectivity (XRR) and confirmed by an XRD Ru/Co alloy peak that develops during in situ synchrotron annealing as well as for deposition at a higher Ts = 600 °C. The room-temperature resistivity increases from 15.0 to 47.5 μΩ cm with decreasing superlattice period Λ = 60–2 nm. This is attributed to increasing electron scattering at the intermixed metal interfaces. The transport data are well described by a parallel conductor model that treats metal layers and the intermixed alloy as parallel resistors, where the resistivity of the intermixed alloy of 60.4 μΩ cm is determined from a co-deposited Ru/Co sample. Data fitting provides values for the effective thickness of the intermixed interface of 16.8 nm, in good agreement with the XRR value, yielding a Ru/Co contact resistance of 8.5 × 10⁻¹⁵ Ω m² for interfaces deposited at 400 °C. The overall results show that the Ru/Co contact resistance is dominated by a high-resistivity interfacial alloy and, therefore, is a strong function of the deposition process, particularly the processing temperature.

In this letter, we evaluate temperature quenching of photoluminescence in ultra-high quality epitaxial InN films to assess the internal quantum efficiency (IQE) of band-to-band light emission. Measured room-temperature carrier lifetimes of ∼10 ns in the samples with record-low dislocation density of Nd ∼ 5 × 10⁸ cm⁻² appear consistent with the diffusion-limited Shockley–Reed–Hall recombination model and lead to a maximum emission IQE of ∼1.5% at T = 300 K. For the stimulated emission (SE) regime, dislocation densities in excess of 10¹⁰ cm⁻² can be actually tolerated without seriously affecting the SE threshold, and its temperature dependence is determined by a competition between radiative and Auger processes, with a crossover point around liquid-nitrogen temperature.

The early stage of the impact-initiated reaction of supersonic cylindrical reactive metal projectiles (magnesium, aluminum, titanium, and zirconium) with an inert aluminum oxide target is investigated experimentally with impact velocities from 1.1 to 1.3 km/s. A three-color imaging pyrometer is used to obtain temperature maps of the condensed fragments generated during the first few microseconds following contact between the projectile and the target. Experiments conducted in inert and oxidizing atmospheres confirm that chemical reactions initiate readily upon contact between the projectile and the target. In oxidizing atmospheres, the fragment temperatures measured for each metal are, on average, below but near the respective adiabatic temperature in air, except for Zr which produced temperatures significantly below expectations. Only the particles shed at the interface between the projectile and the target visibly react with the oxygen in the ambient atmosphere. At the impact velocities under study, only a small fraction, on the order of a few percent, of the mass of the projectile is finely fragmented during the initial impact event.

The influence of laser polarization on the laser-induced damage threshold of fused silica is presented. Measurements were performed using femtosecond and nanosecond laser pulse durations. The impact of laser polarization on the laser damage varies with laser wavelength. While no difference in UV laser damage was observed between linear and circular polarizations, circular polarization improved the damage resistance of fused silica to infrared and visible laser radiation in comparison with linear polarization. By measuring the femtosecond laser damage of a SiO 2 thin film deposited onto a substrate, we show that the ratio between the bandgap of the sample and the photon energy causes the polarization dependent laser damage to change. These experimental findings are explained by considering the photoionization theory for solids.

Despite the many advantages afforded to the investigation of complex compositional systems by combinatorial sputtering, the application of this synthesis technique is hindered by high-throughput characterization bottlenecks. The recent application of translatable compositional and magnetic characterization techniques, such as precision Wavelength Dispersive X-ray Fluorescence (WDXRF) and Magneto-Optic Kerr Effect (MOKE), are enabling for full wafer mapping of film chemistry, magnetic moment, and coercivity, although under-applied. An example system that stands to benefit from the application of combinatorial sputtering and high-throughput characterization is lightly nitrided FexVyNz, which, among other doped FeN materials, is a candidate rare earth-free permanent magnet for electric motor and read/write head applications. Within this report, a combinatorial sputtering and characterization procedure, which leverages high-throughput WDXRF and MOKE mapping, is utilized to investigate the effects of V composition on the room temperature ferromagnetic properties of FexVyNz. Observations made using WDXRF and MOKE mapping are shown to closely agree with vibrating sample magnetometry and x-ray photoelectron spectroscopy measurements made on cleaved regions of interest from the parent wafer. It is observed that the inclusion of V deleteriously affects the saturated moment of FeN, resulting in complete macroscopic reduction at 18 at. %. A maximum film coercivity of 165 Oe is observed at 10 at. % V, likely contributed to by crystallographic texture due to processing, followed by a complete reduction along with the saturated moment. These observations support the high-throughput characterization approaches of WDXRF and MOKE to combinatorial synthesis workflows.

Fiber Bragg gratings (FBGs) are widely used in high-radiation environments owing to their high sensitivity, stability, and resistance to electromagnetic interference. In this study, pure and Ge-doped silica core fibers were fabricated using chemical vapor deposition. Based on these fibers, two temperature sensors, FBG-Si and FBG-Ge, were developed using femtosecond laser direct writing combined with metalized armoring. The fibers and sensors were exposed to gamma radiation, and their stability, temperature accuracy, and refractive index were systematically evaluated. Electron paramagnetic resonance and radiation-induced loss were used to investigate the effects of gamma radiation on the fiber materials and temperature sensors at the atomic micro-scale. The results showed that the Bragg center wavelength (λB) of the FBGs linearly redshifted with increasing temperature under non-stressed conditions. After gamma irradiation, at a temperature, λB, redshifted further with increasing radiation dose. The FBG-Si sensor exhibited higher stability and smaller temperature errors than FBG-Ge. Both sensors exhibited a decrease in output power after irradiation. The performance degradation of the FBGs after irradiation is attributed to an increase in the number of color centers and defects within the grating, leading to higher transmission losses. As the radiation dose increased, the concentration of the color centers increased, leading to changes in the refractive index of the gratings. This ultimately resulted in a redshift in λB and caused temperature measurement errors.

Environment-friendly, low power-consuming magnetoelectric composites possess the interesting coupling between various ferro-order parameters and find applications in magnetic sensors, waveguides, transducers, spintronics, four-state memory devices, etc. The particulate composites (x)NiFe2O4–(1 − x)Ba0.9Sr0.1TiO3 were prepared using the hybrid sol-gel method using the conventional ceramic double-sintering method. The ferromagnetic nickel ferrite crystallized into a cubic crystal structure whose x-ray diffraction (XRD) peaks could be indexed to F d 3 ¯ m space group. The ferroelectric strontium-substituted barium titanate crystallized to a tetragonal crystal structure with P 4 m m space group. Presence of both crystal symmetries and elemental compositions as per the proposed stoichimetry were observed from experimental results (XRD and electron microscopy techniques). Koop's phenomenological theory could be employed to explain the impedance spectra in the range of 1 kHz to 1 MHz. The effect of Maxwell–Wagner polarization and space charge polarization on the dielectric properties of composites have been observed. The Arrott plot technique successfully explains the suitability of composites for high-energy storage applications. The coupling between both ferro-orderings has been revealed from the magneto-dielectric curves and its dependency on the microstructure has been observed. The magnetocapacitance increased with the increase in NiFe2O4 composition in the (x)NiFe2O4–(1 − x)Ba0.9Sr0.1TiO3 composite. The 30% NiFe2O4 in (x)NiFe2O4–(1 − x)Ba0.9Sr0.1TiO3 composite exhibited overall better energy harvesting (η = 62.9%) and magnetodielectric properties (MC = 1.4%, MI = 20% at 1 kHz).

The formation of AlN/AlGaN short period superlattices (SPSLs) was investigated though the introduction of a constant Ga overpressure during the metal modulated epitaxy (MME) growth of AlN. A combination of x-ray diffraction (XRD) and scanning transmission electron microscopy (STEM) analyses found that control over the Al composition in the AlGaN layer was achieved through modulating the Ga beam equivalent pressure (BEP), with a minimum partial pressure of 3 × 10⁻⁷ Torr needed for Ga to incorporate at a growth temperature of 825 °C. A minimum Al composition in the AlGaN layer of 72% was achieved for a Ga BEP of 1 × 10⁻⁶ Torr using this method. An apparent limit of the AlGaN layer thickness of 3–4 ML indicated that the incorporation of Ga was confined to the consumption region of the MME growth process. Determination of this behavior made clear the requirements of having both XRD and STEM in order to be able to fully characterize the SPSL layer structure. Finally, AFM imaging highlighted that the presence of Ga on the surface behaved as a surfactant, with a minimum RMS roughness of 0.46 nm achieved at the maximum Ga BEP of 1 × 10⁻⁶ Torr.

The medium- or high-entropy strategy has emerged as a new paradigm for designing high-performance piezoelectric ceramics. However, the effectiveness of this approach remains unclear to the development of high Curie temperature (TC) piezo-/ferroelectric materials with outstanding performance. To develop high-performance piezo-/ferroelectric materials suitable for high-temperature environments, in this work, we design a novel ceramic system based on a medium-entropy morphotropic phase boundary (ME-MPB) strategy. Piezo-/ferroelectric ceramics of the formula, Pb(Yb1/2Nb1/2)O3–Pb(In1/2Nb1/2)O3–PbTiO3, meeting the medium entropy criteria, were successfully synthesized using the conventional solid-state reaction method. The crystal structure, microstructure, dielectric, piezoelectric, and ferroelectric properties of the ceramics of the ME-MPB compositions were systematically investigated. X-ray diffraction and scanning electron microscopy analyses revealed that these ceramics possess a pure perovskite phase and dense microstructure. Notably, the prepared ceramics exhibited exceptional piezoelectric performance, with a high d33 up to 603 pC/N, a large strain of 0.20%, a high remanent polarization of 44.0 μC/cm², and a high Curie temperature of 362 °C. This study demonstrates an effective design approach based on the ME-MPB strategy and points out a new pathway for developing high-performance materials for high-temperature applications as sensors, thereby expanding the research perspective on the design of medium-entropy piezo-/ferroelectric ceramics.

Zinc single crystals have been shocked by planar impact along the [ 10 1 ¯ 0 ] axis as well as in the off-axis direction. The evolution of compression waves has been analyzed from the free surface velocity profiles of zinc single crystal samples. A slip on the primary system is activated by impact loading in directions making angles of θ = 17°–64° with respect to the [ 10 1 ¯ 0 ] axis. The phenomenon of the formation of two plastic compression waves propagating at different velocities is observed in samples oriented at angles of 53° and 64°. The spall fracture of single crystal zinc samples oriented in different directions has been measured. It is shown that the highest value of spall strength is recorded along the highly symmetric axis of the crystal. The experimental results presented are consistent with the data published in the scientific literature on beryllium and magnesium and confirm the important role of crystalline anisotropy in the process of inelastic deformation of single crystals.

The performance of neuromorphic computing (NC) in executing data-intensive artificial intelligence tasks relies on hardware network structure and information processing behavior mimicking neural networks in the human brain. The functionalities of synapses and neurons, the key components in neural networks, have been widely pursued in memristor systems. Nevertheless, the realization of neuronal functionalities in a single memristor remains challenging. By theoretical modeling, here we propose asymmetric ferroelectric tunneling junction (AFTJ) as a potential platform to realize neuronal functionalities. The volatility, a necessary property for a memristor to implement a neuron device, is enhanced by the co-effect of polarization asymmetry and Joule heating. The simulated polarization reversal dynamics of the AFTJ memristor under trains of electric pulses reproduces the leaky integrate-and-fire functionality of spiking neurons. Interestingly, multiple spiking behaviors are found by modulating the pulse width and interval of trains of electric pulses, which has not yet been reported in ferroelectric neuron. The influences of several key factors on the neuronal functionalities of AFTJ are further discussed. Our study provides a novel design scheme for ferroelectric neuron devices and inspires further explorations of ferroelectric devices in neuromorphic computing.

Multilevel resistance states with respect to the volume of the reversed domains in ferroelectric tunneling junctions and erasable conducting domain walls in an insulating ferroelectric matrix enable high-speed and energy-efficient ferroelectric synapses, memories, and transistors. According to the domain nucleation model, the operation speeds of these devices are assumedly limited by domain nucleation time while the subsequent domain growth time is neglected. Unfortunately, these two times cannot be separated from the experiment yet. Here, we observed independent switching behaviors of domain nucleation and growth at two discrete coercive fields for a mesa-like memory cell formed at the surface of a LiNbO3 single crystal. After the application of an in-plane electric field to two side electrodes, we observed the on currents upon antiparallel domain reversals via the creation of conducting domain walls between them. Once the applied electric field is removed, the domains within the interfacial layers between the two side electrodes and the cell are volatile and switch back into their initial orientations automatically, unlike the nonvolatile bulk domain encoding digital information. In consideration of volatile and nonvolatile natures of the two domains, we separately observed their switching behaviors from the measurements of frequency-dependent domain switching hysteresis loops after programing various write and read pulses. It is found that all coercive fields with the involvement of domain nucleation at the interfaces are always frequency-dependent, unlike domain forward growth within the bulk layer that is frequency-independent. This provides the direct evidence that the operation speed of the low-dimensional ferroelectric device is limited by the domain nucleation rate at the interface.

The typical nanoscale vacuum field emission triode with a controllable gate distance, created via focused ion beam etching and photolithography, is presented in this study. The field emission performance under coplanar gate control is distinguished from the gate distance (dg) in a low vacuum environment. It is, therefore, necessary to highlight a vital parameter dg defined by the nanogap between the center of the nanoscale channel and the edge of the coplanar gate, to methodically illustrate the working mechanism. For the case of a device with large dg, the F–N tunneling current was positively increased by up to one order of magnitude when high bias conditions on the anode and coplanar gate were applied. In contrast, the device with short dg displayed a negative drop in F–N tunneling current under the same measurement condition. As the gate bias increased continuously to a critical value, this device became cut off in this situation with an insignificant gate leakage current. This opposite trend of F–N emission current is eventually verified to have a relationship with dg and it is suggested to play a crucial role in the device. This work clarified the role of the coplanar gate when device operated in the F–N tunneling mechanism and conducted a thorough analysis of the charge transport mechanism related to dg. This work will aid coplanar nanoscale vacuum electron field emission device design in the future.