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Stable operations as resistive switching memory were demonstrated in amorphous TaOx (a-TaOx) thin films with very flat surfaces by conductive atomic force microscopy (c-AFM). The a-TaOx thin films fabricated on glass and Nb-doped SrTiO3 substrates by pulsed laser deposition showed high surface flatness with root-mean-square roughness of less than 0.2 nm. The c-AFM observations on the surfaces revealed that the resistive switching in a-TaOx causes almost no change in the topographic structures, and the significant structural deformation appears after the electrical breakdown by longer-range migration of the constituent ions. The possible mechanisms of the resistive switching phenomena were discussed based on the changes in the topographic structures and conduction states.

The open-loop (OL) variant of Kelvin probe force microscopy (KPFM) provides access to the voltage response of the electrostatic interaction between a conductive atomic force microscopy (AFM) probe and the investigated sample. The measured response can be analyzed a posteriori, modeled, and interpreted to include various contributions from the probe geometry and imaged features of the sample. In contrast to this, the currently implemented closed-loop (CL) variants of KPFM, either amplitude-modulation (AM) or frequency-modulation (FM), solely report on their final product in terms of the tip–sample contact potential difference. In ambient atmosphere, both CL AM-KPFM and CL FM-KPFM work at their best during the lift part of a two-pass scanning mode to avoid the direct contact with the surface of the sample. In this work, a new OL AM-KPFM mode was implemented in the single-pass scan of the PeakForce Tapping (PFT) mode. The topographical and electrical components were combined in a single pass by applying the electrical modulation only in between the PFT tip–sample contacts, when the AFM probe separates from the sample. In this way, any contact and tunneling discharges are avoided and, yet, the location of the measured electrical tip–sample interaction is directly affixed to the topography rendered by the mechanical PFT modulation at each tap. Furthermore, because the detailed response of the cantilever to the bias stimulation was recorded, it was possible to analyze and separate an average contribution of the cantilever to the determined local contact potential difference between the AFM probe and the imaged sample. The removal of this unwanted contribution greatly improved the accuracy of the AM-KPFM measurements to the level of the FM-KPFM counterpart.

Conductive atomic force microscopy (C-AFM) was employed to perform conductivity measurements on a facet-specific Cu2O cube, octahedron, and rhombic dodecahedron and intrinsic Si {100}, {111}, and {110} wafers. Similar I–V curves to those recorded previously using a nanomanipulator were obtained with the exception of high conductivity for the Si {110} wafer. Next, I–V curves of different Cu2O–Si heterostructures were evaluated. Among the nine possible arrangements, Cu2O octahedron/Si {100} wafer and Cu2O octahedron/Si {110} wafer combinations show good current rectification behaviors. Under white light illumination, Cu2O cube/Si {110} wafer and Cu2O rhombic dodecahedron/Si {111} wafer combinations exhibit the largest degrees of photocurrent, so such interfacial plane-controlled semiconductor heterojunctions with light sensitivity can be applied to make photodetectors. Adjusted band diagrams are presented highlighting different interfacial band bending situations to facilitate or inhibit current flow for different Cu2O–Si junctions. More importantly, the observation of clear current-rectifying effects produced at the semiconductor heterojunctions with properly selected contacting faces or planes implies that novel field-effect transistors (FETs) can be fabricated using this design strategy, which should integrate well with current chip manufacturing processes., The Cu2O octahedron/Si {100} wafer combination gives a large current-rectifying effect. The Cu2O rhombic dodecahedron/Si {111} wafer combination shows a notable photocurrent response.

Chiral Pb(Sn)-I hybrid organic-inorganic perovskites exhibit outstanding chiral-induced spin selectivity (CISS) performance, but the nontoxic lead-free hybrid materials with high stability are still greatly desired for spin filtering in spintronic applications. We synthesize chiral hybrid copper halides (R/S-MBA)2 CuX4 (MBA=methylbenzylammonium; X=Cl, Br) with characteristic 0D CuX4 tetrahedral structural motifs, combining the low toxicity of Cu2+ and air stability of halide ions (Cl- and Br- ). Despite similar structural and electronic features, (R/S-MBA)2 CuBr4 shows much smaller chiroptical activity than the chloride counterpart. Magnetically conductive atomic force microscopy measurements display a typical spin-polarized charge-transport property with high efficiency up to 90 % for both copper halides. Our work expands the CISS effect into eco-friendly and stable metal-organic halides, which is promising for applications in spintronics based on transition-metal hybrid systems.

Atomic force microscopy techniques (conductive-AFM, I-V spectroscopy and PFM) were used for characterisation of the local electrical properties of bilayer polyaniline-polystyrene/P(VDF-TrFE) polymer nanocomposite. Observed hysteresis of current-voltage characteristics confirms its memristive properties. It was caused by the influence of the ferroelectric polarization of P(VDF-TrFE) layer, the domain structure of which was visualised by piezoelectric force microscopy on the transport of charge carriers at the interface.

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.

One of the most challenging issues facing the organic photovoltaic community is to realize a high fill factor (FF) even with thick active layers. This is because the thick active layer is beneficial for photon absorption but makes charge collection difficult, which is primarily restricted by nongeminate recombination in solar cells. In this work, we have studied nongeminate recombination in four kinds of polymer solar cells based on blends of donor-conjugated polymers with different crystallinities and acceptor-conjugated polymers with a naphthalene diimide unit by using transient photovoltage and photocurrent techniques. As a result, we find that nongeminate recombination is considerably suppressed with an increasing degree of crystallinity of donor polymers, leading to a high FF of more than 0.6 even with an active layer thickness of 300 nm. The origin of such a phenomenon is further discussed in terms of variations in the states of mixed phases with a cascaded energy structure between crystalline domains and amorphous domains evaluated by conductive atomic force microscopy.

A combination of conductive atomic force microscopy (AFM) and confocal fluorescence microscopy was used to measure photocurrents passing through single trimeric photosytem I (PSI) complexes located in the vicinity of single gold nanorods (AuNRs). Simultaneous excitation of PSI and of the AuNR longitudinal plasmon mode and detection of photocurrents from individual PSI in relation to the position of single AuNRs enable insight into plasmon-induced phenomena that are otherwise inaccessible in ensemble experiments. We have observed photocurrent enhancement by the localized plasmons by a factor of 2.9 on average, with maximum enhancement values of up to 8. Selective excitation of the longitudinal plasmon modes by the polarization of the excitation laser enables controllable switch-on of the photocurrent enhancement. The dependence of the extent of enhancement on the distance between PSI and AuNRs indicates that, apart from the enhancement of absorption, there is an additional enhancement mechanism affecting directly the electron transport process. The present study provides deeper insight into the molecular mechanisms of plasmon-enhanced photocurrents, not only in PSI but also potentially in other systems as well.

Composite solid electrolytes (CSEs) which formed a flexible interface with electrodes are considered as promising electrolytes candidates for all-solid-state batteries (ASSBs). However, the role of inorganic particles and migration of Li-ions still need to be investigated. Herein, LLZO-PEO composite electrolyte is prepared with different weight ratios (0, 50, 75 wt. %) of LLZO and in-situ conductive atomic force microscopy (c-AFM) is employed to observe the changes in electrolyte topography and mechanical properties at different temperatures. Furthermore, c-AFM provides novel insights into the inhomogeneous migration of ions and electrons within the electrolyte. At high temperatures, Li-ions migrate along the amorphous PEO interphase of 0 and 50 wt. % LLZO-PEO electrolytes. With the increase of LLZO content (75 wt. %), LLZO particles form a continuous ionic network and Li-ions migrate through the LLZO particles. At low temperatures, Li-ions can only migrate along the amorphous PEO. Also, the addition of LLZO inhibits the migration of electrons and improves the insulative properties of the composite electrolyte. The current work provides novel insights into the design and development of composite electrolytes for next-generation ASSBs.

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.

Dislocations often exhibit unique physical properties distinct from those of the bulk material. However, functional applications of dislocations are challenging due to difficulties in the construction of high-performance devices of dislocations. Here we demonstrate unidirectional single-dislocation Schottky diode arrays in a Fe2O3 thin film on Nb-doped SrTiO3 substrates. Conductivity measurements using conductive atomic force microscopy indicate that a net current will flow through individual dislocation Schottky diodes under forward bias and disappear under reverse bias. Under cyclic bias voltages, the single-dislocation Schottky diodes exhibit a distinct resistive switching behavior containing low-resistance and high-resistance states with a high resistance ratio of ∼103. A combined study of transmission electron microscopy and first-principles calculations reveals that the Fe2O3 dislocations comprise mixed Fe2+ and Fe3+ ions due to O deficiency and exhibit a one-dimensional electrical conductivity. The single-dislocation Schottky diodes may find applications for developing ultrahigh-density electronic and memory devices.

When scaling the lateral size of a ferroelectric random access memory (FeRAM) device down to the nanometer range, the polarization switching-induced displacement current becomes small and challenging to detect, which greatly limits the storage density of FeRAM. Here, we report the observation of significantly enhanced injection currents, much larger than typical switching currents, induced by polarization switching in BiFeO3 thin films via conductive atomic force microscopy. Interestingly, this injected current can be effectively modulated by applying mechanical force. As the loading force increases from ∼50 to ∼750 nN, the magnitude of the injected current increases and the critical voltage to trigger the current injection decreases. Notably, changing the loading force by an order of magnitude increases the peak current by 2-3 orders of magnitude. The mechanically boosted injected current could be useful for the development of high-density FeRAM devices. The mechanical modulation of the injected current may be attributed to the mechanical force-induced changes in the barrier height and interfacial layer width.

Moire superlattices (MSLs) formed in van der Waals materials have become a promising platform to realize novel two-dimensional electronic states. Angle-aligned trilayer structures can form two sets of MSLs which could potentially interfere. In this work, we directly image the moire patterns in both monolayer and twisted bilayer graphene aligned on hexagonal boron nitride (hBN), using combined scanning microwave impedance microscopy and conductive atomic force microscopy. Correlation of the two techniques reveals the contrast mechanism for the achieved ultrahigh spatial resolution (

Electron transport through iron porphyrin (FeP) molecules self-assembled on a gold (Au) substrate was investigated using conductive atomic force microscopy (AFM) to measure current–voltage (I–V) ch...

Protein-based electronic biomaterials represent an attractive alternative to traditional metallic and semiconductor materials due to their environmentally benign production and purification. However, major challenges hindering further development of these materials include (1) limitations associated with processing proteins in organic solvents and (2) difficulties in forming higher-order structures or scaffolds with multilength scale control. This paper addresses both challenges, resulting in the formation of one-dimensional bundles composed of electrically conductive protein nanowires harvested from the microbes Geobacter sulfurreducens and Escherichia coli. Processing these bionanowires from common organic solvents, such as hexane, cyclohexane, and DMF, enabled the production of multilength scale structures composed of distinctly visible pili. Transmission electron microscopy revealed striking images of bundled protein nanowires up to 10 μm in length and with widths ranging from 50-500 nm (representing assembly of tens to hundreds of nanowires). Conductive atomic force microscopy confirmed the presence of an appreciable nanowire conductivity in their bundled state. These results greatly expand the possibilities for fabricating a diverse array of protein nanowire-based electronic device architectures.

We investigate hole-selective passivating contacts that consist of an interfacial layer of silicon oxide (SiOx) and a layer of boron-doped SiCx(p). The fabrication process of these contacts involves an annealing step at temperatures above 750 degrees C which crystallizes the initially amorphous layer and diffuses dopants across the interfacial oxide into the wafer to facilitate charge transport, but it can also disrupt the SiOx layer necessary for wafer-surface passivation. To investigate the transport mechanism of the charge carriers through the selective contact and its changes during the annealing process, we utilize various characterization methods, such as transmission electron microscopy, micro Raman spectroscopy, and conductive atomic force microscopy. Combining the latter with a sequential removal of material, we assemble a tomographic reconstruction of the crystallized layer that reveals the presence of preferential vertical transport channels.

Atomic layer deposition (ALD) derived ultrathin conformal Al2O3 coating has been identified as an effective strategy for enhancing the electrochemical performance of Ni-rich LiNixCoyMnzO2 (NCM; 0 ≤ x, y, z < 1) based cathode active materials (CAM) in Li-ion batteries. However, there is still a need to better understand the beneficial effect of ALD derived surface coatings on the performance of NCM based composite cathodes. In this work, we applied and optimized a low-temperature ALD derived Al2O3 coating on a series of Ni-rich NCM-based (NCM622, NCM71.51.5 and NCM811) ready-to-use composite cathodes and investigated the effect of coating on the surface conductivity of the electrode as well as its electrochemical performance. A highly uniform and conformal coating was successfully achieved on all three different cathode compositions under the same ALD deposition conditions. All the coated cathodes were found to exhibit an improved electrochemical performance during long-term cycling under moderate cycling conditions. The improvement in the electrochemical performance after Al2O3 coating is attributed to the suppression of parasitic side reactions between the electrode and the electrolyte during cycling. Furthermore, conductive atomic force microscopy (C-AFM) was performed on the electrode surface as a non-destructive technique to determine the difference in surface morphology and conductivity between uncoated and coated electrodes before and after cycling. C-AFM measurements on pristine cathodes before cycling allow clear separation between the conductive carbon additives and the embedded NCM secondary particles, which show an electrically insulating behavior. More importantly, the measurements reveal that the ALD-derived Al2O3 coating with an optimized thickness is thin enough to retain the original conduction properties of the coated electrodes, while thicker coating layers are insulating resulting in a worse cycling performance. After cycling, the surface conductivity of the coated electrodes is maintained, while in the case of uncoated electrodes the surface conductivity is completely suppressed confirming the formation of an insulating cathode electrolyte interface due to the parasitic side reactions. The results not only show the possibilities of C-AFM as a non-destructive evaluation of the surface properties, but also reveal that an optimized coating, which preserves the conductive properties of the electrode surface, is a crucial factor for stabilising the long-term battery performance.

The nanofriction properties of hexagonal boron nitride (h-BN) are vital for its application as a substrate for graphene devices and solid lubricants in micro- and nano-electromechanical devices. In this work, the nanofriction characteristics of h-BN on Si/SiO2 substrates with a bias voltage are explored using a conductive atomic force microscopy (AFM) tip sliding on the h-BN surface under different substrate bias voltages. The results show that the nanofriction on h-BN increases with an increase in the applied bias difference (Vt−s) between the conductive tip and the substrate. The nanofriction under negative Vt−s is larger than that under positive Vt−s. The variation in nanofriction is relevant to the electrostatic interaction caused by the charging effect. The electrostatic force between opposite charges localized on the conductive tip and at the SiO2/Si interface increases with an increase in Vt−s. Owing to the characteristics of p-type silicon, a positive Vt−s will first cause depletion of majority carriers, which results in a difference of nanofriction under positive and negative Vt−s. Our findings provide an approach for manipulating the nanofriction of 2D insulating material surfaces through an applied electric field, and are helpful for designing a substrate for graphene devices.

Resistive switching (RS) device behavior is highly dependent on both insulator and electrode material properties. In particular, the bottom electrode (BE) surface morphology can strongly affect RS characteristics. In this work, Ru films with different thicknesses grown on a TiN layer by radical-enhanced atomic layer deposition (REALD) are used as an inert BE in TaOx-based RS structures. The REALD Ru surface roughness is found to increase by more than 1 order of magnitude with the increase in the reaction cycle number. Simultaneously, a wide range of RS parameters, such as switching voltage, resistance both in low and high resistance states, endurance, and so forth, monotonically change. A simplified model is proposed to explain the linkage between RS properties and roughness of the Ru surface. The field distribution was simulated based on the observed surface morphologies, and the resulting conducting filament formation was anticipated based on the local field enhancement. Conductive atomic force microscopy confirmed the theoretical expectations.

We demonstrate the influence of surface terminated V-pits in tuning dark current and spectral responsivity of Al0.25Ga0.75N-based UV-B photodetectors with metal–semiconductor–metal geometry on Si (111) substrate. We show that the V-pit morphological defects contribute to a large internal gain in these photodetectors, thereby leading to a substantial enhancement in external quantum efficiency (EQE) at relatively low applied biases. For photodetectors fabricated on metal organic chemical vapor deposition grown Al0.25Ga0.75N epilayers with a surface pit density of $2 \times 10^{8}$ cm−2, an EQE of 100% was measured at a meager bias of 1.7 V, which increased significantly with bias. The EQE, photo-to-dark current ratio, and UV-to-visible rejection ratio measured $5 \times 10^{4}$ %, $1.2 \times 10^{4}$ , and $2 \times 10^{3}$ , respectively, at 5 V. The evidence of localized enhancement of photoresponse at the surface terminations of V-pits is exemplified by UV-assisted conductive atomic force microscopy. Temperature-dependent carrier transport analysis under dark and UV illumination revealed cumulative contributions of pit-induced thermionic field emission and hole-trapping-induced gain to the observed large EQE. This work presents the highest value of responsivity for III-nitride UV-B detectors at a given bias.

In this work, the local current-voltage characteristics of nanocomposite phase boundaries in the form of a poly(vinylidene fluoride-trifluoroethylene) (PVDF-TrFE) (70/30) matrix filled with conductive polyaniline (PANI) particles are studied by conductive atomic force microscopy. At negative external bias voltages, these dependencies are shown to have an interval with a negative differential resistance. This fact is caused by the switching of ferroelectric polarization of individual nanocrystallites PVDF-TrFE located near the phase boundaries in the amorphous matrix volume. The obtained results confirm assumptions about the memristive properties of the investigated nanocomposites.

Splats are the most fundamental and paramount unit of any plasma sprayed coating and splats are having the potential to manipulate the overall property of the same. Current study shows the insulator-conductor transition of alumina (Al2O3) splat by the hybrid addition of carbonaceous nanofillers, namely carbon nanotubes (CNTs) and Graphene nanoplatelets (GNPs) into it. Reinforcement of CNTs and GNPs changed the splat shape from fragmented to nearly disk shaped as well as from porous splat to densified one upon the reinforcement. Further, Current mapping over the splats were carried out using conductive atomic force microscopy (cAFM). Current map for Al2O3 splat showed fully black region, evincing its insulating nature; whereas hybrid addition of CNTs and GNPs into the splat dramatically improved the electrical conductivity of Al2O3 splat, coining its non-conductive map to conductive one. This transition was attributed to electron tunneling mechanism, which is a function of electron hopping distance of these conductive nanofillers. The electron hopping distance of the matrix got minimized when CNTs and GNPs were simultaneously added to Al2O3 splat, due to their higher aspect ratio. This led to the formation of a 3-dimensional conductive channels for the electron transport in the matrix, converting the whole splat as conductive.

Using conductive atomic force microscopy, current images and I – V characteristics of tin oxide thin films deposited at various substrate temperatures were obtained. When analyzing current images and I – V characteristics, it was found that tin oxide films formed at a higher substrate temperature consist of the SnO2 phase, however, they include local areas with increased resistance that contain the SnO phase.