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Recently, in electric mobilities and stationary energy storage device applications, the development of long‐lasting, low‐cost, and high‐safety lithium‐ion batteries (LIBs) is widely studied. LiFePO4 (LFP) is a core cathode material for LIBs owing to its cost‐effectiveness and high safety. However, it exhibits low electronic conductivity and sluggish Li+ diffusion, hindering the application of LFP cathodes in high‐power battery industries. Herein, a triazole‐motivated electrolyte additive, 1‐(trimethylsilyl)−1H‐benzotriazole (TMSBTA) is presented, for mitigating iron dissolution via HF scavenging, reinforcing the robustness of the solid electrolyte interphase and constructing a cathode–electrolyte interface (CEI) to balance the ion and electron conduction of the CEI on the LFP cathode. Scanning probe microscopy performed in the conductive atomic force microscopy mode indicates that the electronically conductive CEI created by the oxidative decomposition of TMSBTA enables rapid and homogeneous lithiation and delithiation during cycling without morphological changes in the LFP particles. This study elucidates the design principles of the CEI on the LFP cathode and is expected to guide integrated electrolyte additive engineering for LFP‐containing LIBs. [ABSTRACT FROM AUTHOR]

The dielectric gap between the scanning probe microscopy (SPM) tip and the surface of a ferroelectric using conductive atomic force microscopy and piezoresponse force microscopy (PFM) is investigated. While the gap functions as a dielectric layer, it also allows tunneling current to inject charges into the ferroelectric when a critical loading force between 10–20 µN is applied to a tip with a radius of 25 nm under a bias voltage of 0.5 V. It is observed that the permittivity of the dielectric gap determines the coercive voltage measured by the piezoresponse hysteresis loop. While such studies done in air often produce coercive voltages much larger than those studied for the same materials in capacitor‐based studies, the use of high permittivity media such as water (ɛr = 79) or silicone oil (ɛr = 2.1‐2.8) produces coercive fields that more closely match those measured in conventional capacitor‐based polarization hysteresis loop measurements. Furthermore, using water as a dielectric medium in PFM imaging enhances the accuracy in extracting the amplitude and phase data from periodically poled lithium niobate crystals. These findings provide insight into the nanoscale phenomena of polarization switching instigated by the SPM tip and provide a pathway to improved quantitative studies. [ABSTRACT FROM AUTHOR]

One of the most advanced and versatile nanoscale diagnostic tools is atomic force microscopy. By enabling advanced imaging techniques, it allows us to determine various assets of a surface, including morphological, electrical, mechanical, magnetic, and thermal properties. Measuring local current flow is one of the very important methods of evaluation for, for instance, photovoltaic materials or semiconductor structures and other nanodevices. Due to contact areas, the current densities can easily reach above 1 kA/m2; therefore, special detection/measurement setups are required. They meet the required measurement range, sensitivity, noise level, and bandwidth at the measurement scale. Also, they prevent the sample from becoming damaged and prevent unwanted tip–sample issues. In this paper, we present three different nanoscale current measurement solutions, supported with test results, proving their performance. [ABSTRACT FROM AUTHOR]

The results of the research on the resistive switching in Pt/HfO2/HfOxNy/TiN, Pt/HfO2/TaOxNy/TiN and Pt/Al2O3/HfO2/TaOxNy/TiN structures are presented. Active layers of the structures were deposited by atomic layer deposition. The formation of conductive filaments in all three structures was demonstrated using conductive atomic force microscopy. A full cycle of resistive switching with a microscope probe in these structures was also demonstrated. The properties of filaments formed at different voltages were studied, and the distributions of the filament density by conductivity and size were presented. The characteristics of the studied structures were compared. It appears that the Pt/Al2O3/HfO2/TaOxNy/TiN structure has the greatest potential for resistive random-access memory application. [ABSTRACT FROM AUTHOR]

The topography and electrical properties are two crucial characteristics that determine the roles and functionalities of materials. Conductive atomic force microscopy (CAFM) is widely recognized for its ability to independently measure the topography and conductivity. The increasing trend towards miniaturization in electrical devices and sensors has encouraged an urgent demand for enhancing the accuracy of CAFM characterization. However, when performing CAFM tests on Bi0.5Na0.5TiO3 bulk ceramic, it is interesting to observe significant currents related to the topography. Why do insulators exhibit "conductivity" in CAFM testing? Herein, we thoroughly investigated the topography-dependent current during CAFM testing for the first time. Based on the linear dependence between the current and the first derivative of topography, the calibration method has been proposed to eliminate the topographic crosstalk. This method is evaluated on Bi0.5Na0.5TiO3 bulk ceramic, one-dimensional (1D) ZnO nanowire, two-dimensional (2D) NbOI2 flake, and biological lotus leaf. The corresponding results of negligible topography-interference current affirm the feasibility and universality of this calibration method. This work effectively addresses the challenge of topographic crosstalk in CAFM characterization, thereby preventing the erroneous estimation of the conductivity of any unknown sample. [ABSTRACT FROM AUTHOR]

Extraordinary physical properties arise at polar interfaces in oxide materials, including the emergence of 2D electron gases, sheet‐superconductivity, and multiferroicity. A special type of polar interface is ferroelectric domain walls, where electronic reconstruction phenomena can be driven by bound charges. Great progress has been achieved in the characterization of such domain walls and, over the last decade, their potential for next‐generation nanotechnology has become clear. Established tomography techniques, however, are either destructive or offer insufficient spatial resolution, creating a pressing demand for 3D imaging compatible with future fabrication processes. Here, non‐destructive tomographic imaging of ferroelectric domain walls is demonstrated using secondary electrons. Utilizing conventional scanning electron microscopy (SEM), the position, orientation, and charge state of hidden domain walls are reconstructed at distances up to several hundreds of nanometers away from the surface. A mathematical model is derived that links the SEM intensity variations at the surface to the local domain wall properties, enabling non‐destructive tomography with good noise tolerance on the timescale of seconds. The SEM‐based approach facilitates high‐throughput screening of materials with functional domain walls and domain‐wall‐based devices, which is essential for monitoring during the production of device architectures and quality control in real‐time. [ABSTRACT FROM AUTHOR]

Determining the conductivity of molecular layers is a crucial step in advancing towards applications in molecular electronics. A common test bed for fundamental investigations on how to acquire this conductivity are alkanethiol layers on gold substrates. A widely used approach in measuring the conductivity of a molecular layer is conductive atomic force microscopy. Using this method, we investigate the influence of a rougher and a flatter gold substrate on the lateral variation of the conductivity. We find that the roughness of the substrate crucially defines this variation. We conclude that it is paramount to adequately choose a gold substrate for investigations on molecular layer conductivity.

We report on investigating the structural and electronic properties of semiconducting and insulating layers produced in a process resembling percolation in a unique cold plasma fabrication method (plasma-enhanced chemical vapor deposition—PECVD). Amorphous carbon–tin films (Sn–C) produced from tetramethyl tin (TMT) with an acoustic-frequency glow discharge in a three-electrode reactor were investigated. The layers, after air exposure, oxidized to SnO2/Sn–C. Depending on the coupling capacitance applied to the plasma reactor, the films could be obtained in the form of an amorphous semiconductor or an amorphous insulator. We assume that the semiconductor consists of an internal network of channels auto-organized during deposition. The insulator does not demonstrate any internal structure features. An investigation on conductive filaments creating low-dimensional (LD) nanojunctions in the semiconductor and the location of energetic levels in the insulator was performed. The main parameters of the electronic band structure of the insulating film, such as the transport gap EG (5.2 eV), optical gap Eopt (3.1 eV), electron affinity Χ (2.1 eV), and ionization potential J (7.3 eV), were determined. We have demonstrated a simple approach for developing a catalyst candidate consisting of amorphous semiconductor–insulator nanojunctions for (photo)catalytic hydrogen evolution or CO2 reduction. [ABSTRACT FROM AUTHOR]

1D organic semiconductor nanostructures have attracted considerable attention; however, only a few studies are conducted on p–n junction organic semiconductor 1D nanostructures. Herein, p‐ and n‐type and p–n junction phthalocyanine (Pc) nanorods are grown in the out‐of‐plane direction of a substrate via vacuum deposition using typical organic semiconductors with copper phthalocyanine (CuPc) as the p‐type semiconductor and copper octafluorophthalocyanine (F8CuPc) and copper hexadecafluorophthalocyanine (F16CuPc) as the n‐type semiconductors. p–n junction Pc nanorods are fabricated via the continuous deposition of F8CuPc and F16CuPc onto CuPc nanorods. Fourier‐transform infrared spectroscopy reveals that the Pc molecules in the nanorods are perpendicularly aligned, with their molecular planes oriented toward the longitudinal direction of the nanorods. The local current–voltage properties of the nanorods are measured using conductive atomic force microscopy. The hole mobility in the CuPc nanorods is 10 times higher than that in the CuPc thin films. The p–n junction properties of F8CuPc/CuPc nanorods are evaluated. [ABSTRACT FROM AUTHOR]

One of the most advanced and versatile nanoscale diagnostic tools is atomic force microscopy. By enabling advanced imaging techniques, it allows us to determine various assets of a surface, including morphological, electrical, mechanical, magnetic, and thermal properties. Measuring local current flow is one of the very important methods of evaluation for, for instance, photovoltaic materials or semiconductor structures and other nanodevices. Due to contact areas, the current densities can easily reach above 1 kA/m2; therefore, special detection/measurement setups are required. They meet the required measurement range, sensitivity, noise level, and bandwidth at the measurement scale. Also, they prevent the sample from becoming damaged and prevent unwanted tip–sample issues. In this paper, we present three different nanoscale current measurement solutions, supported with test results, proving their performance.

Triboelectric nanogenerators (TENGs) based on sliding metal–semiconductor junctions are an emerging technology that can efficiently convert mechanical into electrical energy. These miniature autonomous power sources can output large direct current (DC) densities, but often suffer from limited durability; hence, their practical scope remains uncertain. Herein, through a combination of conductive atomic force microscopy (C-AFM) and photocurrent decay (PCM) experiments, we explored the underlying cause of surface wear during the operation of DC-TENGs. Using monolayer-functionalized Si(211) surfaces as the model system, we demonstrate the extent to which surface damage develops during TENG operation. We reveal that the introduction of surface defects (oxide growth) during TENG operation is not caused by the passage of the rather large current densities (average output of ~2 × 106 A/m2); it is instead mainly caused by the large pressure (~GPa) required for the sliding Schottky diode to output a measurable zero-bias current. We also discovered that the drop in output during operation occurs with a delay in the friction/pressure event, which partially explains why such deterioration of DC-TENG performance is often underestimated or not reported.

Solar cells incorporating perovskite films with a blend of A-site cations have gained significant attention due to their enhanced stability and high-power conversion efficiencies. However, the relationship between the microstructure, electrical properties of perovskite films, compositions of A-site cations, and their correlation with the charge carrier dynamics of perovskite solar cells remains unknown. In this study, we investigated the electrical properties of APbI3 perovskite films with varying A-site cations (A = Cs, CsFA, CsFAMA) at the grain boundaries (GBs) and grain interiors (GIs) using advanced probing microscopies. Measurements conducted with voltage-controlled Kelvin probe force microscopy (KPFM) confirmed the presence of ion motion within the perovskite films. By altering the illumination conditions, both KPFM and conductive atomic force microscopy measurements reveal that the hysteresis of CsFA perovskite thin film was significantly greater than that of CsPbI3 and CsFAMA. Moreover, the variation in potential between the three thin films in the GB region and adjacent GI indicates the existence of band bending in the GB region of all three thin films. These findings are crucial for identifying the role of A-site cations in determining the electrical properties of perovskite films in relation to GIs and GBs, thereby facilitating further enhancements in photovoltaic devices through compositional engineering. [ABSTRACT FROM AUTHOR]

Boron-doped diamond (BDD) films grown by chemical vapor deposition (CVD) exhibit unique electrical and optical properties owing to the non-uniform uptake of boron dopants across grains. This study utilizes scanning probe microscopy and confocal microspectroscopy techniques to elucidate the influence of grain-dependent boron incorporation on the nano-electrical and local optical characteristics of polycrystalline BDD. The CVDgrown BDD film contained crystallites up to tens of microns, while the surface comprised 200…800 nm grains. Scanning spreading resistance microscopy (SSRM) revealed significant nanoscale resistance variations among individual grains, attributable to differential boron distributions. No distinct grain boundary features were discernible in SSRM data, likely due to the high boron doping of ~ 3·1019 cm–3 . SSRM of the Au surface of a BDD/Ti/Pd/Au contact indicated a comparable granular morphology but three orders lower resistance. A network of more resistive grain boundaries was evident, modulated by underlying BDD grain clusters. Photoluminescence spectroscopy showed characteristic bands of nitrogen-vacancy centers and donor-acceptor pairs. Confocal Raman and photoluminescence mapping elucidated substantial spatial heterogeneity in micrometerscale grains regarding crystal quality, boron and nitrogen concentrations, related to preferential incorporation. The observed peculiarities in BDD’s structural and nanoelectrical characteristics stem from inherent growth inhomogeneities and grain-dependent boron uptake influenced by defects and strain fields modifying local chemical potentials. This multifaceted nanoscale examination provides critical insights into optimizing electrical and optical properties of BDD films by controlling synthesis conditions and minimizing defects for tailored performance in electronic, electrochemical, and quantum applications. [ABSTRACT FROM AUTHOR]

Triboelectric nanogenerators (TENGs) based on sliding metal–semiconductor junctions are an emerging technology that can efficiently convert mechanical into electrical energy. These miniature autonomous power sources can output large direct current (DC) densities, but often suffer from limited durability; hence, their practical scope remains uncertain. Herein, through a combination of conductive atomic force microscopy (C-AFM) and photocurrent decay (PCM) experiments, we explored the underlying cause of surface wear during the operation of DC-TENGs. Using monolayer-functionalized Si(211) surfaces as the model system, we demonstrate the extent to which surface damage develops during TENG operation. We reveal that the introduction of surface defects (oxide growth) during TENG operation is not caused by the passage of the rather large current densities (average output of ~2 × 106 A/m2); it is instead mainly caused by the large pressure (~GPa) required for the sliding Schottky diode to output a measurable zero-bias current. We also discovered that the drop in output during operation occurs with a delay in the friction/pressure event, which partially explains why such deterioration of DC-TENG performance is often underestimated or not reported. [ABSTRACT FROM AUTHOR]

Abstract: Electrical contact resistance (ECR) measurements performed via conductive atomic force microscopy (C-AFM) suffer from poor reliability and reproducibility. These issues are due to a number of factors, including sample roughness, contamination via adsorbates, changes in environmental conditions such as humidity and temperature, as well as deformation of the tip apex caused by contact pressures and/or Joule heating. Consequently, ECR may vary dramatically from measurement to measurement even on a single sample tested with the same instrument. Here we present an approach aimed at improving the reliability of such measurements by addressing multiple sources of variability. In particular, we perform current-voltage spectroscopy on atomically flat terraces of highly oriented pyrolytic graphite (HOPG) under an inert nitrogen atmosphere and at controlled temperatures. The sample is annealed before the measurements to desorb adsorbates, and conductive diamond tips are used to limit tip apex deformation. These precautions lead to measured ECR values that follow a Gaussian distribution with significantly smaller standard deviation than those obtained under conventional measurement conditions. The key factor leading to this improvement is identified as the switch from ambient conditions to a dry nitrogen atmosphere. Despite these improvements, spontaneous changes in ECR are observed during measurements performed over several minutes. However, it is shown that such variations can be suppressed by applying a higher normal load.

Molybdenum trioxide shows many attractive properties, such as a wide electronic band gap and a high relative permittivity. Monolayers of this material are particularly important, as they offer new avenues in optoelectronic devices, e.g., to alter the properties of graphene electrodes. Nanoscale electrical characterization is essential for potential applications of monolayer molybdenum trioxide. We present a conductive atomic force microscopy study of an epitaxially grown 2D molybdenum oxide layer on a graphene-like substrate, such as highly oriented pyrolytic graphite (HOPG). Monolayers were also investigated using X-ray photoelectron spectroscopy, atomic force microscopy (semi-contact and contact mode), Kelvin probe force microscopy, and lateral force microscopy. We demonstrate mobility of the unpinned island under slight mechanical stress as well as shaping and detachment of the material with applied electrical stimulation. Non-stoichiometric MoO3-x monolayers show heterogeneous behavior in terms of electrical conductivity, which can be related to the crystalline domains and defects in the structure. Different regions show various I–V characteristics, which are correlated with their susceptibility to electrodegradation. In this work, we cover the existing gap regarding nanomanipulation and electrical nanocharacterization of the MoO3 monolayer. [ABSTRACT FROM AUTHOR]

Neuromorphic computing seeks functional materials capable of emulating brain‐like dynamics to solve computational problems with time and energy efficiency, outclassing current transistor‐based hardware architectures. Major efforts are focused on integrating memristive devices into highly regular circuits (i.e., crossbar arrays), where the information representation in individual memristive devices is closely oriented toward the behavior of artificial neurons. However, artificial neurons are rather rigid mathematical concepts than realistic projections of complex neuronal dynamics. Neuroscience suggests that highly efficient information representation on the level of individual neurons relies on dynamical features such as excitatory and inhibitory contributions, irregularity of firing patterns, and temporal correlations. Here, a conductive atomic force microscopy approach is applied to probe the memristive dynamics of nanoscale assemblies of AgPt‐nanoparticles at the stability border of the conducting state, where physical forces causing the formation and decay of filamentary structures appear to be balanced. This unveils a dynamic regime, where the memristive response is governed by irregular firing patterns. The significance of such a dynamical regime is motivated by close similarities to excitation and inhibition‐governed behavior in biological neuronal systems, which is crucial to tune biological neuronal systems into a state most suitable for information representation and computation. [ABSTRACT FROM AUTHOR]

We report on investigating the structural and electronic properties of semiconducting and insulating layers produced in a process resembling percolation in a unique cold plasma fabrication method (plasma-enhanced chemical vapor deposition—PECVD). Amorphous carbon–tin films (Sn–C) produced from tetramethyl tin (TMT) with an acoustic-frequency glow discharge in a three-electrode reactor were investigated. The layers, after air exposure, oxidized to SnO2/Sn–C. Depending on the coupling capacitance applied to the plasma reactor, the films could be obtained in the form of an amorphous semiconductor or an amorphous insulator. We assume that the semiconductor consists of an internal network of channels auto-organized during deposition. The insulator does not demonstrate any internal structure features. An investigation on conductive filaments creating low-dimensional (LD) nanojunctions in the semiconductor and the location of energetic levels in the insulator was performed. The main parameters of the electronic band structure of the insulating film, such as the transport gap EG (5.2 eV), optical gap Eopt (3.1 eV), electron affinity Χ (2.1 eV), and ionization potential J (7.3 eV), were determined. We have demonstrated a simple approach for developing a catalyst candidate consisting of amorphous semiconductor–insulator nanojunctions for (photo)catalytic hydrogen evolution or CO2 reduction.

In this paper, 2D/3D heterojunction diodes have been fabricated by pulsed laser deposition (PLD) of MoS2 on 4H‐SiC(0001) surfaces with different doping levels, i.e., n− epitaxial doping (≈1016 cm−3) and n+ ion implantation doping (>1019 cm−3). After assessing the excellent thickness uniformity (≈3L‐MoS2) and conformal coverage of the PLD‐grown films by Raman mapping and transmission electron microscopy, the current injection across the heterojunctions is investigated by temperature‐dependent current–voltage characterization of the diodes and by nanoscale current mapping with conductive atomic force microscopy. A wide tunability of the transport properties is shown by the SiC surface doping, with highly rectifying behavior for the MoS2/n− SiC junction and a strongly enhanced current injection for MoS2/n+ SiC one. Thermionic emission is found the dominant mechanism ruling forward current in MoS2/n− SiC diodes, with an effective barrier ΦB = (1.04 ± 0.09) eV. Instead, the significantly lower effective barrier ΦB = (0.31 ± 0.01) eV and a temperature‐dependent ideality factor for MoS2/n+ SiC junctions is explained by thermionic‐field‐emission through the thin depletion region of n+ doped SiC. The scalability of PLD MoS2 deposition and the electronic transport tunability by implantation doping of SiC represents key steps for industrial development of MoS2/SiC devices. [ABSTRACT FROM AUTHOR]

3D nanoprinting via focused electron beam induced deposition (FEBID) is applied for fabrication of all-metal nanoprobes for atomic force microscopy (AFM)-based electrical operation modes. The 3D tip concept is based on a hollow-cone (HC) design, with all-metal material properties and apex radii in the sub-10 nm regime to allow for high-resolution imaging during morphological imaging, conductive AFM (CAFM) and electrostatic force microscopy (EFM). The study starts with design aspects to motivate the proposed HC architecture, followed by detailed fabrication characterization to identify and optimize FEBID process parameters. To arrive at desired material properties, e-beam assisted purification in low-pressure water atmospheres was applied at room temperature, which enabled the removal of carbon impurities from as-deposited structures. The microstructure of final HCs was analyzed via scanning transmission electron microscopy—high-angle annular dark field (STEM-HAADF), whereas electrical and mechanical properties were investigated in situ using micromanipulators. Finally, AFM/EFM/CAFM measurements were performed in comparison to non-functional, high-resolution tips and commercially available electric probes. In essence, we demonstrate that the proposed all-metal HCs provide the resolution capabilities of the former, with the electric conductivity of the latter onboard, combining both assets in one design. [ABSTRACT FROM AUTHOR]

Abstract In this paper, 2D/3D heterojunction diodes have been fabricated by pulsed laser deposition (PLD) of MoS2 on 4H‐SiC(0001) surfaces with different doping levels, i.e., n− epitaxial doping (≈1016 cm−3) and n+ ion implantation doping (>1019 cm−3). After assessing the excellent thickness uniformity (≈3L‐MoS2) and conformal coverage of the PLD‐grown films by Raman mapping and transmission electron microscopy, the current injection across the heterojunctions is investigated by temperature‐dependent current–voltage characterization of the diodes and by nanoscale current mapping with conductive atomic force microscopy. A wide tunability of the transport properties is shown by the SiC surface doping, with highly rectifying behavior for the MoS2/n− SiC junction and a strongly enhanced current injection for MoS2/n+ SiC one. Thermionic emission is found the dominant mechanism ruling forward current in MoS2/n− SiC diodes, with an effective barrier ΦB = (1.04 ± 0.09) eV. Instead, the significantly lower effective barrier ΦB = (0.31 ± 0.01) eV and a temperature‐dependent ideality factor for MoS2/n+ SiC junctions is explained by thermionic‐field‐emission through the thin depletion region of n+ doped SiC. The scalability of PLD MoS2 deposition and the electronic transport tunability by implantation doping of SiC represents key steps for industrial development of MoS2/SiC devices.

Electrochemical exfoliation of graphite is a method for synthesizing graphene oxide (GO) with fewer structural defects than GO synthesized by conventional chemical oxidation. Photoreduction of GO has been focused on due to their facile procedures, and environmental friendliness. In this report, electrochemically-exfoliated graphene oxide (EGO) was irradiated by vacuum ultraviolet (VUV) light at 140 °C under a high vacuum environment, named thermal-assisted VUV light treatment. Conductive atomic force microscopy was used to investigate the electrical characteristics of individual sheets on the nanometer scale. The electrical conductivity of the treated sheet (1.4 × 105 S m−1) was higher than the pristine EGO by an order of magnitude. The chemical and structural analysis showed that the EGO was reduced and their π -conjugated domains were restored through a hybrid of photochemical and thermal treatment. These results indicate that our hybrid approach has the potential for reducing the EGO. [ABSTRACT FROM AUTHOR]

Semiconductor single-walled carbon nanotube (s-SWNT) networks have gained prominence in electronic devices due to their cost-effectiveness, relatively production-naturality, and satisfactory performance. Configuration, density, and resistance of SWNT-SWNT junctions are considered crucial factors influencing the overall conductivity of s-SWNT networks. In this study, we present a method for inferring the lower bounds of the SWNT-SWNT junction resistance in s-SWNT networks based on conductive atomic force microscopy TUNA images. This method further enables the proposal of a classification for SWNT-SWNT junctions based on the current behavior relative to their surroundings. The three types of SWNT-SWNT junctions are denoted as (i) true contact (T), (ii) poor contact (P), and (iii) false contact (F). Of them, the true and poor contacts, respectively, represent good and poor electrical contact for the subject SWNT-SWNT junctions whose electrical conductivity hardly improves under external tip pressure, while that of the false contact can be further improved by external pressure. Statistical analysis demonstrates that while T-type junctions make a significant contribution to network conductivity, their proportion accounts for only approximately 40%. The P-type and F-type junctions, which constitute over 60% of the total, may be a contributing factor that constrains the overall conductivity of the s-SWNT networks. The height ratio of the junction to the sum of two SWNTs was also observed to exhibit variations among the three types. Finally, we propose a three-dimensional model to elucidate the formation mechanism underlying each type of junction. The present study provides insights into the performance of spontaneous contacts between s-SWNTs in the networks, and the systematic image acquisition and junction classification processes may provide support for future advancements in these networks.

Conductive atomic force microscopy (CAFM) analyzes electronic phenomena in materials and devices with nanoscale lateral resolution, and it is widely used by companies, research institutions, and universities. Most data published in the field of CAFM is collected in air at a relative humidity (RH) of 30-60%. However, the effect of RH in CAFM remains unclear because previous studies often made contradictory claims, plus the number of samples and locations tested is scarce. Moreover, previous studies on this topic did not apply current limitations, which can degrade the CAFM tips and generate false data. This article systematically analyzes the effect of RH in CAFM by applying ramped voltage stresses at over 17,000 locations on ten different samples (insulating, semiconducting, and conducting) under seven different RH. An ultra-reliable setup with a 110-pA current limitation during electrical stresses is employed, and excellent CAFM tip integrity after thousands of tests is demonstrated. It is found that higher RH results in increased currents due to the presence of a conductive water meniscus at the tip/sample junction, which increases the effective area for electron flow. This trend is observed in insulators and ultra-thin semiconductors; however, in thicker semiconductors the electron mean free path is high enough to mask this effect. Metallic samples show no dependence on RH. This study clarifies the effect of relative humidity in CAFM, enhances understanding of the technique, and teaches researchers how to improve the reliability of their studies in this field., (© 2024 The Author(s). Advanced Materials published by Wiley‐VCH GmbH.)

Molybdenum (Mo) is considered as a promising plasma-facing material, which is expected to be used in the manufacture of critical components for the neutral beam injection (NBI) inductively coupled plasma (ICP) source. Hydrogen isotope retention and bubble formation are regarded as the unavoidable issues that degrade the metal properties in the ion source. In this work, the evolution of hydrogen bubbles in Mo pre-irradiated by 35 eV hydrogen ion energy during different annealing processes is studied through conductive atomic force microscopy (CAFM) observation. Meanwhile, the corresponding numerical simulation is applied to analyze the mechanisms of hydrogen bubble growth. It is found that the average size and density of hydrogen bubbles are enhanced with the increase of hydrogen ion fluence at 400 K in experiments and simulations. In the subsequent annealing process, it is demonstrated that annealing temperature has a certain effect on bubble growth and evolution. No obvious changes in bubbles are observed at the annealing temperature below 573 K. The average radius of hydrogen bubbles is increased by ∼1.0–2.5 nm in Mo annealed at 673–873 K. The bubble size increases with the rise of annealing temperature, indicating that the thermal annealing promotes the growth of bubbles. When the temperature rises above 873 K, the change in bubble size is not obvious. The simulation results indicate that temperature-induced changes in the internal pressure of hydrogen bubbles leads to the growth of bubbles, but this mechanism is not significant under high annealing temperatures due to the release of hydrogen from the surface.

Molybdenum trioxide shows many attractive properties, such as a wide electronic band gap and a high relative permittivity. Monolayers of this material are particularly important, as they offer new avenues in optoelectronic devices, e.g., to alter the properties of graphene electrodes. Nanoscale electrical characterization is essential for potential applications of monolayer molybdenum trioxide. We present a conductive atomic force microscopy study of an epitaxially grown 2D molybdenum oxide layer on a graphene-like substrate, such as highly oriented pyrolytic graphite (HOPG). Monolayers were also investigated using X-ray photoelectron spectroscopy, atomic force microscopy (semi-contact and contact mode), Kelvin probe force microscopy, and lateral force microscopy. We demonstrate mobility of the unpinned island under slight mechanical stress as well as shaping and detachment of the material with applied electrical stimulation. Non-stoichiometric MoO3-x monolayers show heterogeneous behavior in terms of electrical conductivity, which can be related to the crystalline domains and defects in the structure. Different regions show various I–V characteristics, which are correlated with their susceptibility to electrodegradation. In this work, we cover the existing gap regarding nanomanipulation and electrical nanocharacterization of the MoO3 monolayer.

The physical properties of tumor-derived exosomes have gained much attention because they are helpful to better understand the exosomes in biomedicine. In this study, the conductive atomic force microscopy (C-AFM) was employed to perform the electrical characterizations of exosomes, and it obtained the topography and current images of samples simultaneously. The exosomes were absorbed onto the mica substrates coated with a gold film of 20 nm thick for obtaining the current images of samples by C-AFM in air. The results showed that the single exosomes had the weak conductivity. Furthermore, the currents on exosomes were measured at different bias voltages and pH conditions. It illustrated that the conductivity of exosomes was affected by external factors such as bias voltages and solutions with different pH values. In addition, the electrical responses of low and high metastatic potential cell-derived exosomes were also compared under different voltages and pH conditions. This work is important for better understanding the physical properties of tumor-derived exosomes and promoting the clinical applications of tumor-derived exosomes. [ABSTRACT FROM AUTHOR]

Atomically thin two‐dimensional (2D) alloys have attracted wide interests of study recently due to their potential in flexible electronic and optoelectronic applications. In particular, monolayer transition metal dichalcogenide (TMD) alloys have emerged as unique 2D semiconductors with tunable bandgaps, by means of alloying. However, response of surface electrical potential and barrier height to strain for 2D TMD alloys–electrode interface is rarely explored. Apparently, revealing such strain‐dependent evolution of electrical properties is crucial for developing advanced 2D TMD based flexible electronics and optoelectronics. Here we performed in situ strain Kelvin probe force microscopy (KPFM) and conductive atomic force microscopy (C‐AFM) investigations of monolayer Mo0.4W0.6Se2 on Au coated flexible substrate, where controlled uniaxial tensile strain is applied. Both contact potential difference (CPD) and Schottky barrier heights (SBH) of monolayer Mo0.4W0.6Se2 show obvious decreases with the increase of strain, which is mainly due to the strain‐induced increment of TMD electron affinity. Our in situ strain photoluminescence (PL) measurements also indicate the changes of electronic band structures under strain. We further exploit the substrate effects on CPD by study the monolayer alloy on the mostly used substrates of SiO2/Si and indium tin oxide (ITO)/glass. Our findings could strengthen the foundation for the potential applications of 2D TMD and their alloys in the fields of strain sensors, flexible photodetectors, and other wearable electronic devices. [ABSTRACT FROM AUTHOR]

Two-terminal memristive devices are considering as a potential candidate to mimic human brain functionality to enable artificial intelligence. Particularly, two-terminal nanoscale devices are regarded as a promising solution for implementing bio-synapses due to their small dimensions, extremely compact, and low power to operate neuromorphic functions. Here, we demonstrate that the nanoscale charge transport and resistive switching behavior of VOx thin film can be tuned by modulating the substrate morphology. Particularly, the device prepared with flat-Si shows totally distinguished behavior in comprising of reactive ion-etched-Si substrates. Interestingly, conductive atomic force microscopy current maps revealed the electric field inhomogeneity due to a change in substrate morphology. A reliable bipolar resistive switching behavior of the corresponding etched devices have been demonstrated. Due to an increase in the etching time of substrate, an increase in active area and decrease in work function was observed. Further, nanoscale synaptic functions were generated from the corresponding devices, showing a strong conduction path at preferential bright spots of the particular devices. Moreover, finite element simulations confirm the modulation in generation of localized current conduction in particular etched devices by applying tip voltages. These findings represent a new way to generate nanoscale artificial synaptic functions.

Abstract Atomically thin two‐dimensional (2D) alloys have attracted wide interests of study recently due to their potential in flexible electronic and optoelectronic applications. In particular, monolayer transition metal dichalcogenide (TMD) alloys have emerged as unique 2D semiconductors with tunable bandgaps, by means of alloying. However, response of surface electrical potential and barrier height to strain for 2D TMD alloys–electrode interface is rarely explored. Apparently, revealing such strain‐dependent evolution of electrical properties is crucial for developing advanced 2D TMD based flexible electronics and optoelectronics. Here we performed in situ strain Kelvin probe force microscopy (KPFM) and conductive atomic force microscopy (C‐AFM) investigations of monolayer Mo0.4W0.6Se2 on Au coated flexible substrate, where controlled uniaxial tensile strain is applied. Both contact potential difference (CPD) and Schottky barrier heights (SBH) of monolayer Mo0.4W0.6Se2 show obvious decreases with the increase of strain, which is mainly due to the strain‐induced increment of TMD electron affinity. Our in situ strain photoluminescence (PL) measurements also indicate the changes of electronic band structures under strain. We further exploit the substrate effects on CPD by study the monolayer alloy on the mostly used substrates of SiO2/Si and indium tin oxide (ITO)/glass. Our findings could strengthen the foundation for the potential applications of 2D TMD and their alloys in the fields of strain sensors, flexible photodetectors, and other wearable electronic devices.

All‐inorganic metal halide perovskites are highly attractive materials for optoelectronics and are typically implemented as thin films, nanocrystals, and single crystals with macroscopic and millimeter‐size dimensions. Single crystals with regular shapes in the micrometer range are less explored and present an interesting alternative when a well‐defined and spatially localized response is desired. Here, CsPbBr3 microcrystals are fabricated by simple and fast drop‐casting of a precursor solution on several substrates that for the growth process are heated to temperatures in the range from 80 to 150 °C. The microcrystals have a cubic shape and feature a pyramidal cavity on their top surface that forms due to faster growth at the edges once the growing crystal is attached to the substrate. Distinct heterogeneity in the photoluminescence (PL) and conductivity of the different facets are measured by µ‐PL and conductive atomic force microscopy experiments. Toward device applications, the authors contact single microcrystals on conductive substrates mechanically with a micromanipulator tip. They observe diode‐like current–voltage curves and good photodetector functionality, obtaining a high responsivity of 150–300 A W−1 in the blue–green spectral region under forward bias, and a sharp detection band centered around 540 nm with peak responsivity close to 0.7 A W−1 under reverse bias. [ABSTRACT FROM AUTHOR]

Melanopsin is an essential element in the human eye, sensing optical light, indeed beyond the function of rods and cones, and contributing largely to non‐image‐forming functions like learning behavior, emotions, and maintaining sun cycle. Mimicking melanopsin behavior using an optoelectronic device could be an essential step toward the advancement of future technologies, including data storage applications and artificial vision. This research proposes and illustrates the mimicking of the primitive functions of melanopsin in a manner very similar to the human eye retina by using an integrated Schottky photodetector and an HfO2‐based memory device. Particularly, current–voltage curves show nominal hysteresis loop opening under dark conditions, whereas stable analog hysteresis loops form with light illumination, which is regulated progressively by increasing the intensity. Based on photoconductive atomic force microscopy and charge transport measurements, the charge trapping/detrapping is estimated to be associated with the light‐regulated hysteresis loop opening. Specifically, versatile synaptic functions are stimulated artificially with an optical pulse, which is sustained over a long period of time even after removing the light, indeed very similar to melanopsin behavior. The optically regulated properties described herein pave the way for the development of artificial optoelectronic melanopsin, artificial biological electronics, soft robotics, and data storage applications. [ABSTRACT FROM AUTHOR]

As a model of neurodegenerative disease, the study on SH-SY5Y cells is of great significance due to the complexity of cause and difficulty in cure. Based on this reality, we studied the influence of culture duration on the morphology and mechanical properties of living SH-SY5Y cells by atomic force microscopy (AFM). A comparative analysis was made to characterize the cell size and tip-cell adhesion, and their increased trends with the increase of cell culture duration were obtained, providing a guideline for the physiological characteristics of the cells. As the culture time increased from 24 h to 48 h, the measured average height and width of cells were increased by 0.59 μ m and 1.38 μ m, respectively. As for cell elasticity, statistical analysis showed that the difference between different parts of the cell was obvious. Additionally, the electrophysiological characteristic as an important indicator for measuring the functional activities of SH-SY5Y cells was investigated. Here, a homemade conductive atomic force microscope (C-AFM) provided an effective way for membrane potential recordings. It was successfully used to study the real-time responses of living SH-SY5Y cells to mechanical insertions, and a membrane potential with an amplitude of − 0. 1 0 1 V was obtained without losing cell viability. The conductive probe equipped on a homemade C-AFM was isolated with dielectric material except for the tip apex, which enabled it to act as a nanoelectrode. As the sharp tip moves towards the target cell, the noise caused by liquid disturbance about 2 mV amplitude was captured. Right after the tip was inserted into the cell surface, a membrane potential spike with an amplitude of −0.101 V was successfully recorded. [ABSTRACT FROM AUTHOR]

Thin layers of polyaniline on the surface of highly oriented pyrolytic graphite are obtained by in-situ chemical oxidative polymerization of aniline. The current-voltage characteristics of the tip/polyaniline/graphite contact, which have a form characteristic of tunnel contacts, have been measured by the method of conducting atomic force microscopy. By modeling the current-voltage characteristics using the Simmons model, the width of the potential barrier is determined, which for the investigated heterojunction is 0,5 nm.

Abstract Periodically ordered arrays of vertically aligned Si nanowires (Si NWs) are successfully fabricated by nanosphere lithography combined with metal-assisted chemical etching. By adjusting the etching time, both the nanowires’ diameter and length can be well controlled. The conductive properties of such Si NWs and particularly their size dependence are investigated by conductive atomic force microscopy (CAFM) on individual nanowires. The results indicate that the conductance of Si NWs is greatly relevant to their diameter and length. Si NWs with smaller diameters and shorter lengths exhibit better conductive properties. Together with the I–V curve characterization, a possible mechanism is supposed with the viewpoint of size-dependent Schottky barrier height, which is further verified by the electrostatic force microscopy (EFM) measurements. This study also suggests that CAFM can act as an effective means to explore the size (or other parameters) dependence of conductive properties on individual nanostructures, which should be essential for both fabrication optimization and potential applications of nanostructures.

Resistive random-access memories, also known as memristors, whose resistance can be modulated by the electrically driven formation and disruption of conductive filaments within an insulator, are promising candidates for neuromorphic applications due to their scalability, low-power operation and diverse functional behaviors. However, understanding the dynamics of individual filaments, and the surrounding material, is challenging, owing to the typically very large cross-sectional areas of test devices relative to the nanometer scale of individual filaments. In the present work, conductive atomic force microscopy is used to study the evolution of conductivity at the nanoscale in a fully CMOS-compatible silicon suboxide thin film. Distinct filamentary plasticity and background conductivity enhancement are reported, suggesting that device behavior might be best described by composite core (filament) and shell (background conductivity) dynamics. Furthermore, constant current measurements demonstrate an interplay between filament formation and rupture, resulting in current-controlled voltage spiking in nanoscale regions, with an estimated optimal energy consumption of 25 attojoules per spike. This is very promising for extremely low-power neuromorphic computation and suggests that the dynamic behavior observed in larger devices should persist and improve as dimensions are scaled down.

Light emission from ultracompact electrically driven optical antennas (EDOAs) has garnered significant attention due to its terahertz modulation bandwidth. Typically, the EDOAs are fixed and nonadjustable once fabricated, thus hindering the attempts to investigate the influence of structural geometry on light emission properties. Here, we propose and demonstrate that the EDOAs can be constructed by carefully manipulating the gold-coated tips of atomic force microscopy operated in conductive mode into contact with the optical antennas covered by insulating film, where the position of the tunnel junction on the antenna surface can be controlled with high accuracy and flexibility. Taking gold nanorod antennas covered by HfO 2 film as an example, we found that the highest light generation efficiency is obtained when the tunnel junction is located at the shoulder edge of the nanorod antenna, where the bonding dipolar surface plasmon mode in the junction is spectrally and spatially coupled with the longitudinal radiation mode of the EDOAs. Besides, position variation of the tunnel junction on the nanorod surface also strongly influences the far-field radiation angular distribution and emission spectrum. Numerical simulations are in good agreement with the experimental results. Our findings offer fundamental insights into the influence of structural parameters on the light emission performance of EDOAs, thus leading to better design of EDOAs with high light generation efficiency and powerful functionality.

Achieving high power conversion efficiency in perovskite solar cells (PSCs) heavily relies on fabricating homogeneous perovskite films. However, understanding microscopic-scale properties such as current generation and open-circuit voltage within perovskite crystals has been challenging due to difficulties in quantifying intragrain behavior. In this study, the local current intensity within state-of-the-art perovskite films mapped by conductive atomic force microscopy reveals a distinct heterogeneity, which exhibits a strong anticorrelation to the external biases. Particularly under different external bias polarities, specific regions in the current mapping show contrasting conductivity. Moreover, grains oriented differently exhibit varied surface potentials and currents, leading us to associate this local current heterogeneity with the grain orientation. It was found that the films treated with isopropanol exhibit ordered grain orientation, demonstrating minimized lattice heterogeneity, fewer microstructure defects, and reduced electronic disorder. Importantly, devices exhibiting an ordered orientation showcase elevated macroscopic optoelectronic properties and boosted device performance. These observations underscore the critical importance of fine-tuning the grain homogenization of perovskite films, offering a promising avenue for further enhancing the efficiency of PSCs.

Ionically mediated phenomena underpin the functioning of various devices, including batteries, solid oxide fuel cells, memristors, and neuromorphic devices. The ionic behavior corresponding to ionically mediated phenomena causes not only variations in the electrical properties but also mechanical deformation, which is crucial for device reliability. However, the interrelation between ionically mediated electrical properties and mechanical deformation has not been elucidated yet. This study investigates ionically mediated mechanical deformation accompanied by memristive switching in a TiO2 single crystal through simultaneous conductive atomic force microscopy and electrochemical strain microscopy. A comprehensive analysis indicates the existence of a relationship between mechanical deformation and memristive switching based on the ionic behavior. Furthermore, an ionic state variable is used to simplify the interrelation between the electrochemical strain hysteresis and memristive switching associated with applied voltage. This study provides insights on the ionic behavior and can be extended to other systems for the general analysis of the relationship between mechanical deformation and electrical properties. [ABSTRACT FROM AUTHOR]

In this paper, the authors demonstrate the atomic layer deposition (ALD) of highly homogeneous and ultrathin (≈3.6 nm) Al2O3 films with very good insulating properties (breakdown field of ≈10–12 MV cm−1) directly onto monolayer (1L) MoS2 exfoliated on gold. Differently than in the case of 1L MoS2 supported by a common insulating substrate (Al2O3/Si), a better nucleation process of the high‐k film is observed on the 1L MoS2/Au system since the ALD early stages. Atomic force microscopy analyses show a ≈50% Al2O3 surface coverage just after 10 ALD cycles, its increase to >90% (after 40 cycles), and a uniform ≈3.6 nm film (after 80 cycles). The Al2O3 density on bilayer MoS2 is found to be significantly reduced with respect to 1L MoS2/Au, suggesting a role of screened interface charges with the metal substrate on the adsorption of ALD precursors. Finally, Raman and photoluminescence spectroscopy show a p‐type doping and tensile strain of 1L MoS2 induced by the Au substrate, providing an insight on the evolution of vibrational and optical properties after the Al2O3 deposition. The direct ALD growth of Al2O3 on large‐area 1L MoS2 induced by the Au underlayer can be of wide interest for electronic applications. [ABSTRACT FROM AUTHOR]

Intelligent touch sensing is now becoming an essential part of various human‐machine interactions and communication, including in touchpads, autonomous vehicles, and smart robotics. Usually, sensing of physical objects is enabled by applied force/pressure sensors; however, reported conventional tactile devices are not able to differentiate sharp and blunt objects, although sharp objects can cause unavoidable damage. Therefore, it is central issue to implement electronic devices that can classify sense of touch and simultaneously generate pain signals to avoid further potential damage from sharp objects. Here, concept of force‐enabled nociceptive behavior is proposed and demonstrated using vanadium oxide‐based artificial receptors. Specifically, versatile criteria of bio‐nociceptor like threshold, relaxation, no adaptation, allodynia, and hyperalgesia behaviors are triggered by pointed force, but the device does not mimic any of these by the force applied by blunt objects; thus, the proposed device classifies the intent of touch. Further, supported by finite element simulation, the nanoscale dynamic is unambiguously revealed by conductive atomic force microscopy and results are attributed to the point force‐triggered Mott transition, as also confirmed by temperature‐dependent measurements. The reported features open a new avenue for developing mechano‐nociceptors, which enable a high‐level of artificial intelligence within the device to classify physical touch. [ABSTRACT FROM AUTHOR]

Nonvolatile memory devices based on resistive switching with fast switching speed and high density have driven extensive research that is potentially ideal for data‐centric applications such as neuromorphic computing. However, due to uncontrolled filament formation, resistive random access memories (RRAM) still suffer from instability and reproducibility. In this study, NiO layer is added to the WO3‐based RRAM layer to confine the conducting path for multilevel resistive switching. The current‐voltage characteristics show the multilevel resistive switching, which is further confirmed by conductive atomic force microscopy measurements at nanoscale. At low voltages, few localized conducting channels are formed (in small area) within the oxide film while at the higher voltages they are distributed throughout the film and the active surface area increases from 4.5 to 75%. Kelvin probe force microscopy was employed to confirm nanoscale variations in surface potential, which are responsible for spatial current variation. Furthermore, it is found that the charge trapping/detrapping is the main governing mechanism and the conducting paths are formed gradually with increasing applied bias. We propose a strategy to achieve stable and reproducible electric field‐induced multilevel memory storage which will be utilized for the development of ultrahigh density multilevel nonvolatile storage and neuromorphic computing. [ABSTRACT FROM AUTHOR]

Two-terminal memristive devices are considering as a potential candidate to mimic human brain functionality to enable artificial intelligence. Particularly, two-terminal nanoscale devices are regarded as a promising solution for implementing bio-synapses due to their small dimensions, extremely compact, and low power to operate neuromorphic functions. Here, we demonstrate that the nanoscale charge transport and resistive switching behavior of VOx thin film can be tuned by modulating the substrate morphology. Particularly, the device prepared with flat-Si shows totally distinguished behavior in comprising of reactive ion-etched-Si substrates. Interestingly, conductive atomic force microscopy current maps revealed the electric field inhomogeneity due to a change in substrate morphology. A reliable bipolar resistive switching behavior of the corresponding etched devices have been demonstrated. Due to an increase in the etching time of substrate, an increase in active area and decrease in work function was observed. Further, nanoscale synaptic functions were generated from the corresponding devices, showing a strong conduction path at preferential bright spots of the particular devices. Moreover, finite element simulations confirm the modulation in generation of localized current conduction in particular etched devices by applying tip voltages. These findings represent a new way to generate nanoscale artificial synaptic functions. [ABSTRACT FROM AUTHOR]

Abstract Piezoelectric and ferroelectric materials have garnered significant interest owing to their excellent physical properties and multiple potential applications. Accordingly, the need for evaluating piezoelectric and ferroelectric properties has also increased. The piezoelectric and ferroelectric properties are evaluated macroscopically using laser interferometers and polarization–electric field loop measurements. However, as the research focus is shifted from bulk to nanosized materials, scanning probe microscopy (SPM) techniques have been suggested as an alternative approach for evaluating piezoelectric and ferroelectric properties. In this Progress Report, the recent progress on the nanoscale evaluation of piezoelectric and ferroelectric properties of diverse materials using SPM‐based methods is summarized. Among the SPM techniques, the focus is on recent studies that are related to piezoresponse force microscopy and conductive atomic force microscopy; further, the utilization of these two modes to understand piezoelectric and ferroelectric properties at the nanoscale level is discussed. This work can provide guidelines for evaluating the piezoelectric and ferroelectric properties of materials based on SPM techniques.

The process of electron transfer through an individual hemoglobin molecule (Hb) has been studied by conductive atomic force microscopy. It is shown that the current through the Hb molecule arises at applied force equal 45 nN. According to estimates, the height of the deformed molecule is 4,5 nm. Based on the analysis of the experimental I-V characteristic of the probe/Hb/substrate contact using of the non-resonant tunneling transport model, the parameters of tunnel electron transport through the individual Hb molecule are determined.