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The conversion efficiency of energy-harvesting devices can be increased by utilizing hot-carriers (HCs). However, due to ultrafast carrier-carrier scattering and the lack of carrier injection dynamics, HC-based devices have low efficiencies. In the present work, we report the effective utilization of HCs at the nanoscale and their transfer dynamics from a non-noble metal to a metal oxide interface by means of real-space photocurrent mapping by using local probe techniques and conducting femtosecond transient absorption (TA) measurements. The photocurrent maps obtained under white light unambiguously show that the HCs are injected into the metal oxide layer from the TiN layer, as also confirmed by conductive atomic force microscopy. In addition, the increased photocurrent in the bilayer structure indicates the injection of HCs from both layers due to the broadband absorption efficiency of TiN layer, passivation of the surface states by the top TiN layer, and smaller barrier height of the interfaces. Furthermore, electrostatic force microscopy and Kelvin probe force microscopy provide direct evidence of charge injection from TiN to the MoOx film at the nanoscale. The TA absorption spectra show a strong photo-bleaching signal over wide spectral range and ultrafast decaying behavior at the picosecond time scale, which indicate efficient electron transfer from TiN to MoOx. Thus, our simple and effective approach can facilitate HC collection under white light, thereby achieving high conversion efficiency for optoelectronic devices.

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.

Defect states in a semiconductor are known to affect its optoelectronic properties and control its chemical composition. In this paper, based on conductive atomic force microscopy (cAFM) and electrostatic force microscopy (EFM) measurements, we demonstrate charge trapping at grain boundaries of ZnO:SnO2 (ZTO: zinc tin oxide) films, indicating the existence of local band-bending. Electrostatic force microscopy measurements reveal that charge trapping is more at grain boundaries in comparison to grains. On the other hand, cAFM and Kelvin probe force microscopy (KPFM) measurements provide an experimental existence of local band-bending at grain boundaries of ZTO films. In addition, compositional analysis of the films confirms the presence of oxygen vacancies, resulting in the formation of defect states within the band gap which further control the charge transport. The present observations are explained in the basis of defect-dependent potential barrier formation due to oxygen vacancies in the film. The present findings help to understand nanoscale charge transport in ZTO thin films using a combination of local probe techniques which should be useful in fabricating ZTO-based transparent optoelectronic devices.

International audience; Understanding the surface properties of hybrid perovskite materials is a key aspect to improve not only the interface properties in photovoltaic cells but also the stability against moisture degradation. In this work, we study the local electronic properties of two series of CH 3 NH 3 PbI 3 perovskite films by atomic force microscopybased methods. We correlate nanoscale features such as the local surface potential (as measured by Kelvin probe force microscopy) to the current response (as measured by conductive atomic force microscopy). CH 3 NH 3 PbI 3 perovskites made using lead acetate as a precursor result in films with high purity and crystallinity and also result in heterogeneous local electrical properties, attributed to variations in the density of surface states. In contrast, when using lead iodide as a precursor, the perovskite surface exhibits a uniform distribution of surface states. This work also aims to understand the early stages of water-induced degradation at the surface of those films. Through high-precision exposure to small amounts of water vapor, we observe a higher stability for surfaces prepared with lead iodide precursors. More importantly, each precursor-based fabrication route is associated with either nor p-type behavior of the films. These characteristics are determined by the type of surface states, which also and eventually preside over stability. This work should help discriminate between perovskite synthesis routes and improve their stability in photovoltaic cell applications.

CZTS is a compound semiconductor made from elements which are plainly available and nonpoisonous having favorable optoelectronic properties for thin film solar cell (TFSC) applications. In this study, Cu-poor CZTS thin film was fabricated on soda lime glass (SLG)/Mo-deposited substrate using cosputtering followed by post sulfurization in H2S atmosphere. Local electrical transport study was carried out by using conductive atomic force microscopy (C-AFM) for small bias voltage (100 mV). Here we observed that most of the dark current (Idark) flow through grain boundaries (GBs) than grain interiors. The positive high current about 3.4 nA and sharp C-AFM signal at the GBs, dips to the zero (0) value at the grain interior. Local surface potential (Vsurface) study was carried out using kelvin probe force microscopy (KPFM), which showed that the positive Vsurface potential about 175 mV in the vicinity of GBs in a Cu-poor CZTS sample. On the basis of these results we inferred a potential landscape (VL) around the GBs. All result shows that due to variation in elemental composition which creates Cu-deficit or CuZn anti site defects at GBs, leads reduced effective band gap (Eeff) than the bulk towards grain inner to GBs.[-2pt]

The correlation between threading dislocations and leakage current in a CdZnTe(001)/GaAs epilayer grown by close-spaced sublimation was studied using scanning electron microscopy, Kelvin probe force microscopy, conductive atomic force microscopy (C-AFM) and current–voltage (I–V) systems. The electrostatic potential differences between the charged dislocations and the CZT epitaxial film were found to be lower than those in bulk CZT crystal. C-AFM tests in the CZT epitaxial film under forward bias demonstrated that dislocations guided the high current leakage paths. The leakage current at dislocation sites was found to be two orders higher than that at dislocation-free areas with an applied bias of 5 V. The rapid increase in leakage current under applied bias in the range of 3.5–7.5 V was associated with the Poole–Frenkel effect, where high leakage current arises from the high density of trapped carriers escaping from the traps segregated around dislocations.

Integration of yttrium iron garnet (YIG) with Si can bring new avenues for garnet-based complementary metal-oxide semiconductor compatible devices. Herein, investigations on the morphological, electrical, and magnetic properties of postgrowth annealed YIG thin films grown on Si substrate were systematically performed at nanoscale lateral resolution, employing the variants of atomic force microscopy (AFM) viz., conductive AFM (C-AFM), kelvin probe force microscopy, and magnetic force microscopy (MFM). Scanning electron microscopy analysis has revealed the formation of three different regions with varied crystallinity defined as center, dark, and surrounding matrix. Interestingly, AFM topography has not shown any surface variation of the obtained three different regions. Despite no variation in their surface topography, notable changes occur in their local conductivity, surface potential, and microstructure of their magnetic domains. C-AFM studies have shown the formation of conducting channels with three different resistivity regions. The tunneling current was enhanced nearly 50 times from the dark region (~1 pA) to the center region (~50 pA). MFM image analysis reveals the formation of two different magnetically active domains in the form of circles (-0.3°) distributed in a surrounding matrix (+0.3°) with a steep change in their magnetic phase degree. The formation of circular magnetic domains with highly distinguishable regions has suggested the potential of YIG/Si films for magnetic memory application. This work has shed light on the prospective of YIG/Si films for resistive and magnetic memory applications and fundamental aspects of growth of YIG on nongarnet substrates.

This paper presents multiple-modes Scanning Probe Microscopy (SPM) studies on characterize the correlation of resistance switching (RS) and polarization rotation (PR) in copper doped ZnO (ZnO:Cu) thin films. Firstly, the bipolar RS behavior is confirmed by conductive Atomic Force Microscopy (c-AFM). The PR with almost 180° phase angle is confirmed by using the Piezoresponse Force Microscopy (PFM) on the same location. In addition, it elucidates that obvious PR behavior can be observed in the sample with increasing Cu concentration by combining Kelvin Probe Force Microscopy (KPFM). Furthermore, it is found that the region with downward polarization has low resistance state (LRS), whereas the region with upward polarization has high resistance state (HRS). Moreover, the Piezoresponse Force Spectroscopy (PFS) and Switching Spectroscopy PFM (SS-PFM) measurements further confirm that the existence of the built-in voltage, Vbuilt-in is largest in the ZnO:Cu (8 at.%) film deposited at the oxygen partial pressure of 2 × 10−4 Torr. The schematic diagrams of energy band diagram with varied built-in field, Ebuilt-in, polarization directions and redistributed charges are presented to explain the correlation between RS and PR behavior. Keywords: Resistive switching, Polarization rotation, Built-in voltage, ZnO:Cu thin film, Next generation memory

Conductive atomic force microscopy (C-AFM) and Kelvin probe force microscopy (KPFM) are applied to investigate the nanoscale current imaging of the Cu-dopped NiO thin film on fluorine tin oxide (FTO) substrate. The results show that the Cu doping has a significant impact on the nanoscale current and work function of NiO film. The higher nanoscale current and work function is probably attributed to the presence of Cu+ and nickel vacancy defects. The nanoscale current is consistent to Richardson-Schottky (RS) thermionic emission model.

Conductive atomic force microscopy (C-AFM) and Kelvin probe force microscopy (KPFM) are applied to visualize the nanoscale current imaging and potential imaging of the NiO thin film on fluorine tin oxide (FTO) substrate. The results show that the grain boundary (GB) has a significant impact on the nanoscale current and potential of NiO film . The electronic conductivity and work function of NiO in grain face is higher than that of the NiO film on GB. The width of the conductive zone in the NiO film over GBs is ∼60 nm. The higher nanoscale current and work function in grain face is probably attributed to the presence of nickel vacancy (V Ni) defects and excess oxygen (O2− ) defects. The GB barrier in single-layer and bilayer NiO film was ∼0.0169 eV and ∼0.0226 eV, respectively. The nanoscale current is consistent to Schottky thermionic emission model.

Organic-inorganic halide perovskite materials are emerging as a new class of photoelectric materials for its low cost, easy preparation, and, especially, outstanding optoelectronic properties. Although tremendous efforts have been made on the regulation and optimization of perovskite materials and their microscopic electrical properties for high-efficiency solar cells, few reports focus on the evolution of electrical properties with temperature changes, especially at the microscopic scale, which will directly affect the device performances at varying temperatures. Here, we map the contact potential difference and photocurrent distribution of MAPbI3 at different temperatures in situ by Kelvin probe force microscopy and conductive atomic force microscopy, emphasizing the different influences of variable temperature and phase transition on the photoelectric properties of grains and grain boundaries (GBs). It is discovered that both the Fermi level and photocurrent decrease as the sample is heated from 30 to 80 °C gradually because of the variation of effective carrier concentration and the degradation of carrier mobility implicated by lattice vibration scattering. The difference between the Fermi level at GBs and that on the grains ascends first and then descends, peaking at 50 °C, near which MAPbI3 transforms from a tetragonal phase to a cubic phase. This peak is speculated as a comprehensive consequence of the increasing difference of the Fermi level of semiconductors with different doping concentrations and the converging properties of grains and GBs with the temperature rising because the lower ion activation energy of the cubic phase at higher temperatures facilitates greatly the ions' movement between grains and GB. The variation trend of the difference of the photocurrent is the same. These findings advance the knowledge on the temperature-induced variations of microscopic photoelectrical properties of organic-inorganic hybrid perovskite materials, which may guide the development of strategies for improving their thermal stability.

Neuromorphic systems require integrated structures with high-density memory and selector devices to avoid interference and recognition errors between neighboring memory cells. To improve the performance of a selector device, it is important to understand the characteristics of the switching process. As changes by switching cycle occur at local nanoscale areas, a high-resolution analysis method is needed to investigate this phenomenon. Atomic force microscopy (AFM) is used to analyze the local changes because it offers nanoscale detection with high-resolution capabilities. This review introduces various types of AFM such as conductive AFM (C-AFM), electrostatic force microscopy (EFM), and Kelvin probe force microscopy (KPFM) to study switching behaviors.

Three carbo-mer derivatives based on a C18Ph4 core decorated with two identical electro-active groups X, i.e. two aromatic carbo-benzenes (1 and 2, X = 4-anilinyl) and one pro-aromatic carbo-quinoid (the carbo-TTF 3, X = 1,3-dithiol-2-ylidene) were studied through Scanning Probe Microscopies (SPMs). Self-Assembled Monolayers (SAMs) were fabricated (thickness ~160 pm), for the two centrosymmetric representatives 1 and 3, the organization of which on the HOPG substrate was found to be structure-specific. Electrical/electronic properties of the three carbo-mers were determined by using Atomic Force Microscopy (AFM) and its electrical modes: Kelvin Probe Force Microscopy (KPFM) and conductive Atomic Force Microscopy (c-AFM). Measurements of the work function (∅) through KPFM result in a ∅ = 5.60 eV value for 1, 4.97 eV for 2 and 4.82 eV for 3. Hole mobility (µ) values extracted from local I-V plots by using c-AFM are 15 × 10 − 8 cm 2 V − 1 s − 1 for 1, 3 × 10 − 6 cm 2 V − 1 s − 1 for 2 and 87 × 10 − 8 cm 2 V − 1 s − 1 for 3. A concept test of the possible application of carbo-mers in self-assembled hole transporting monolayer (SA-HTM), with the view to replacing the most common p-type contact used in organic solar cells (OSCs), PEDOT:PSS, is also reported.

Charge injection and retention in thin dielectric layers remain critical issues due to the great number of failure mechanisms they inflict. Achieving a better understanding and control of charge injection, trapping and transport phenomena in thin dielectric films is of high priority aiming at increasing lifetime and improving reliability of dielectric parts in electronic and electrical devices. Thermal silica is an excellent dielectric but for many of the current technological developments more flexible processes are required for synthesizing high quality dielectric materials such as amorphous silicon oxynitride layers using plasma methods. In this article, the studied dielectric layers are plasma deposited SiO x N y . Independently on the layer thickness, they are structurally identical: optically transparent, having the same refractive index, equal to the one of thermal silica. Influence of the dielectric film thickness on charging phenomena in such layers is investigated at nanoscale using Kelvin probe force microscopy (KPFM) and conductive atomic force microscopy. The main effect of the dielectric film thickness variation concerns the charge flow in the layer during the charge injection step. According to the SiO x N y layer thickness two distinct trends of the measured surface potential and current are found, thus defining ultrathin (up to 15 nm thickness) and thin (15–150 nm thickness) layers. Nevertheless, analyses of KPFM surface potential measurements associated with results from finite element modeling of the structures show that the dielectric layer thickness has weak influence on the amount of injected charge and on the decay dynamics, meaning that pretty homogeneous layers can be processed. The charge penetration depth in such dielectric layers is evaluated to 10 nm regardless the dielectric thickness.

The bottom-up DNA-templated nanoelectronics exploits the unparalleled self-assembly properties of DNA molecules and their amenability with various types of nanomaterials. In principle, nanoelectronic devices can be bottom-up assembled with near-atomic precision, which compares favorably with well-established top-down fabrication process with nanometer precision. Over the past decade, intensive effort has been made to develop DNA-based nanoassemblies including DNA-metal, DNA-polymer, and DNA-carbon nanotube complexes. This review introduces the history of DNA-based fabrication for nanoelectronics briefly and summarizes the state-of-art advances of DNA-based nanoelectronics. In particular, the most widely applied characterization techniques to explore their unique electronic properties at the nanoscale are described and discussed, including scanning tunneling microscopy, conductive atomic force microscopy, and Kelvin probe force microscopy. We also provide a perspective on potential applications of DNA-based nanoelectronics.

A more inclusive and detailed measurement of various physical interactions is enabled by the advance of high-speed data digitization. For surface potential characterization, this was demonstrated recently in terms of open-loop amplitude modulation Kelvin probe force microscopy (OL AM-KPFM). Its counterpart, namely open-loop frequency modulation Kelvin probe force microscopy (OL FM-KPFM), is examined here across different materials and under various bias voltages in the form of OL sideband FM-KPFM. In this implementation the changes in the amplitude and resonance frequency of the cantilever were continuously tracked as a conductive AFM probe was modulated by a 2 kHz AC bias voltage around the first eigenmode frequency of the cantilever. The contact potential difference (CPD) between the AFM probe and sample was determined from the time series analysis of the high-speed 4 MHz digitized amplitude and frequency signals of the OL sideband FM-KPFM mode. This interpretation is demonstrated to be superior to the analysis of the parabolic bias dependent response, which is more commonly used to extract the CPD in OL KPFM modes. The measured OL sideband FM-KPFM amplitude and frequency responses are directly related to the electrostatic force and force-gradient between the AFM probe and sample, respectively. As a result, clear distinction was observed for the determined CPD in each of these cases across materials of different surface potentials, with far superior spatial resolution when the force-gradient detection was used. In addition, the CPD values obtained from OL sideband FM-KPFM amplitude and frequency measurements perfectly matched those determined from their closed-loop AM-KPFM and FM-KPFM counterparts, respectively.

MXenes have drawn considerable attention in both academia and industry due to their attractive properties, such as a combination of metallic conductivity and surface hydrophilicity. However, to the best of our knowledge, the potential use of MXenes in non-volatile resistive random access memories (RRAMs) has rarely been reported. In this paper, we first demonstrated a RRAM device with MXene (Ti3C2) as the active component. The Ti3C2-based RRAM exhibited typical bipolar switching behavior, long retention characteristics, low SET voltage, good mechanical stability and excellent reliability. By adjusting different compliance currents in the SET process, multi-state information storage was achieved. The charge trapping assisting hopping process is considered to be the main mechanism of resistive switching for this fabricated Ti3C2-based RRAM, which was verified by conductive atomic force microscopy (C-AFM) and Kelvin probe force microscopy (KPFM). Moreover, this flexible Ti3C2-based RRAM, with good mechanical stability and long retention properties, was successfully fabricated on a plastic substrate. Ti3C2-based RRAMs may open the door to additional applications and functionalities, with high potential for application in flexible electronics.

Mimicking biological synapses with resistive random switching memory (RRAM) can lay a concrete foundation for the future of artificial intelligence. RRAMs based on low-cost and solution-processed organic materials provide a competitive approach. Here, we report an artificial synaptic device with a solution-processed small molecule (bis-4-(N-carbazolyl)phenyl)phenylphosphine oxide (BCPO) based RRAM. The BCPO-based RRAM exhibits reproducible resistive switching behavior, a long retention time as well as good thermal tolerance with a sufficient on/off current ratio. In situ Kelvin probe force microscopy (KPFM), conductive atomic force microscopy (C-AFM) and density function theory (DFT) calculations demonstrate that both the redox state and the trap-filled space charge limited current (SCLC) determine the resistive switching of a BCPO-based RRAM. Furthermore, the fabricated device was employed to emulate a biological synapse in which several synaptic functions, including spike-rate-dependent plasticity (SRDP), a transition from short-term plasticity (STP) to long-term plasticity (LTP) and spike-time-dependent plasticity (STDP), were realized. To the best of our knowledge, this is the first successful demonstration of solution-processed small molecules in artificial synaptic devices. The BCPO layer is solution-processed at low temperature which is compatible with a flexible substrate and printable electronics. We believe this electronic synapse will have a wide range of applications in future neuromorphic computing.

Understanding the mobility and electrochemical process of ion species at the nanoscale is the key step to obtain high performance non-volatile data storage devices. Here, we present a systematic study on the resistive switching mechanism of an assembled metal–oxo cluster [Bi6O4(OH)4](NO3)6 (BiON) to build reliable non-volatile memory devices. The bipolar resistive-switching with low operation voltage is observed and is attributed to the migration of ion species (mainly OH−) with low activation energy (∼0.20 eV) along the polar electric field and simultaneous valence change of the bismuth of the [Bi6O4(OH)4] clusters in the BiON film. The X-ray photoelectron spectroscopy (XPS), conductive atomic force microscopy (CAFM) and Kelvin probe force microscopy (KPFM) characterization confirms that OH− with low activation energy is expected to facilitate the formation and rupture of anion vacancy filaments. Moreover, intermediate oxide layers formed at the Al/BiON interfaces could help to stabilize and assist the resistive switching. The control of the clusters and counter-ion species in the metal–oxo cluster-assembled materials represents a step toward next generation multi-level, high-speed and low energy consumption non-volatile memory devices for in-memory computing and artificial intelligence.

Current-voltage (I-V) characteristics well reveal the resistive switching performance of materials promising for the next-generation memory-resistance random access memory (ReRAM). It has been observed that the atmospheric environment can affect the resistive switching performance, but the origin of this effect is still under debate. Conductive Atomic Force Microscopy (c-AFM) is widely used to study the resistive switching performance because of its capability to realize the resistive switching at the nanoscale that is becoming attractive as the miniaturization of memory devices. This study therefore aims to understand the effects of oxygen and moisture on the I-V characteristics of the TiO2 thin film by performing c-AFM measurements in ambient air, synthetic air, and argon gas. It is found that the oxygen in the environment can reduce the set and the reset voltages for the resistive switching, and it can also reduce the resistance at the low resistance state (LRS). Where the moisture in the environment can increase the set and reset voltages, and increase the resistance at LRS. These effects of oxygen and moisture in the environment can be attributed to the modification of the effective electric field during the resistive switching processes, which have been further confirmed by Kelvin Probe Force Microscopy (KPFM) measurements. In addition, it is found that the local ionic dynamics of TiO2 during the resistive switching are strongly dependent of the environments by performing the FORC-IV (First Order Reversal Curve-Current-Voltage) measurements in the three gas environments. Results in this work can provide a new perspective on the effect of environments on the resistive switching of materials, that is, the modulation of the effective electric field due to the adsorption of oxygen and moisture under the c-AFM tip. Keywords: Resistive switching, Environmental control, c-AFM, KPFM, FORC-IV

Cu2ZnSn(S,Se)4 (CZTSSe) thin-film solar cells have been fabricated by various methods. Sputtering is one of the vacuum processes that can be used for the growth of the precursors. In this study, CZTSSe thin-films that were fabricated using metal-precursors and with a high efficiency of 12.3% were examined in a comparison with CZTSSe thin-films that were fabricated using compound-precursors, whose efficiency is 9.1%. Especially, the Kelvin probe force microscopy (KPFM) analysis and local current measurement by conductive atomic force microscopy (c-AFM) show that their local electrical properties indicate completely opposite results. The grain boundaries (GBs) has a downward surface potential bending, and this repelled the minority carriers into the intragrains (IGs) in the sample from the metal-precursors. Therefore, we originally verified the differences between the carrier behaviors and the current flows on the surface.

The effect of grain boundaries (GBs) especially twin boundaries (TBs) on the performance of polycrystalline CdTe thin film (1–2 μm in thickness) solar cells remains largely controversial. Understanding the GB’s microstructure and physical property and their impact on the photovoltaic efficiency is critically important to the optimization of the solar cell performance. In this work, we present a systematic study of GBs in CdTe thin film solar cells of different efficiencies in the range of 1.97–9.68%, aiming to elucidate a quantitative correlation of GBs especially TBs with the solar cell charge transport by integrating several advanced approaches including electron backscattering diffraction, transmission electron microscopy, conductive atomic force microscopy, and scanning Kelvin probe force microscopy. Importantly, we have confirmed {111} Σ3 TBs form in the PLD CdTe solar cells and are beneficial by providing an efficient channel for charge transport. The percentage of {111} Σ3 TBs was found to be corre...

The semicontinuous gold film, enabling various electronic applications including development of surface-enhanced Raman scattering (SERS) substrate, is investigated using conductive atomic force microscopy (CAFM) and Kelvin probe force microscopy (KPFM) to reveal and investigate local electronic characteristics potentially associated with SERS generation of the film material. Although the gold film fully covers the underlying silicon surface, CAFM results reveal that local conductivity of the film is not continuous with insulating nanoislands appearing throughout the surface due to incomplete film percolation. Our analysis also suggests the two-step photo-induced charge transfer (CT) play the dominant role in the enhancement of SERS intensity with strong contribution from free electrons of the silicon support. Silicon-to-gold charge transport is illustrated by KPFM results showing that Fermi level of the gold film is slightly inhomogeneous and far below the silicon conduction band. We propose that inhomogeneity of the film workfunction affecting chemical charge transfer between gold and Raman probe molecule is associated with the SERS intensity varying across the surface. These findings provide deeper understanding of charge transfer mechanism for SERS which can help in design and development of the semicontinuous gold film-based SERS substrate and other electronic applications.

The initial formation process of nanobubbles at solid–water interfaces remains unclear because of the limitations of current imaging techniques. To directly observe the formation process, an astigmatic high-speed atomic force microscope (AFM) was modified to enable imaging in the liquid environment. By using a customized cantilever holder, the resonance of small cantilevers was effectively enhanced in water. The proposed high-speed imaging technique yielded highly dynamic quasi-two-dimensional (2D) gas structures (thickness: 20–30 nm) initially at the graphite–water interface. The 2D structures were laterally mobile mainly within certain areas, but occasionally a gas structure might extensively migrate and settle in a new area. The 2D structures were often confined by substrate step edges in one lateral dimension. Eventually, all quasi-2D gas structures were transformed into cap-shaped nanobubbles of higher heights and reduced lateral dimensions. These nanobubbles were immobile and remained stable under continuous AFM imaging. This study demonstrated that nanobubbles could be stably imaged at a scan rate of 100 lines per second (640 μm/s).

Efficient and controlled charge transport in networks of semiconducting single-walled carbon nanotubes is the basis for their application in electronic devices, especially in field-effect transistors and thermoelectrics. The recent advances in selective growth, purification, and sorting of semiconducting and even monochiral carbon nanotubes have enabled field-effect transistors with high carrier mobilities and on/off current ratios that were impossible a few years ago. They have also allowed researchers to examine the microscopic interplay of parameters such as nanotube length, density, diameter distribution, carrier density, intentional and unintentional defects, dielectric environment, etc., and their impact on the macroscopic charge transport properties in a rational and reproducible manner. This review discusses various models that are considered for charge transport in nanotube networks and the experimental methods to characterize and investigate transport beyond simple conductivity or transistor measurements. Static and dynamic absorption, photoluminescence and electroluminescence spectroscopy, as well as scanning probe techniques (e.g., conductive atomic force microscopy, Kelvin probe force microscopy), and their unique insights in the distribution of charge carriers in a given nanotube network and the resulting current pathways will be introduced. Finally, recommendations for further optimization of nanotube network devices and a list of remaining challenges are provided.

We experimentally demonstrate that the conductivity of graded AlxGa1–xN increases as a function of the magnitude of the Al concentration gradient (%Al/nm) due to polarization doping effects, without the use of impurity dopants. Using three up/down-graded AlxGa1–xN nanolayers with Al gradients ranging from ∼0.16 to ∼0.28%Al/nm combined in one structure, the effects of polarization engineering for localized electric fields and current transport were investigated. Cross-sectional Kelvin probe force microscopy and conductive atomic force microscopy were used to directly probe the electrical properties of the films with spatial resolution along the thickness of the growth. The experimental profiles of the built-in electric fields and the spreading current found in the graded layers are shown to be consistent with simulations of the field distribution as well as of the electron and hole densities. Finally, it was directly observed that for gradients less than 0.28%Al/nm the native n-type donors still limit pola...

Nondestructive scanning probe microscopy of fragile nanoscale objects is currently in increasing need. In this paper, we report a novel atomic force microscopy mode, HybriD Piezoresponse Force Microscopy (HD-PFM), for simultaneous nondestructive analysis of piezoresponse as well as of mechanical and dielectric properties of nanoscale objects. We demonstrate this mode in application to self-assembled diphenylalanine peptide micro- and nanotubes formed on a gold-covered substrate. Nondestructive in- and out-of-plane piezoresponse measurements of tubes of less than 100 nm in diameter are demonstrated for the first time. High-resolution maps of tube elastic properties were obtained simultaneously with HD-PFM. Analysis of the measurement data combined with the finite-elements simulations allowed quantification of tube Young's modulus. The obtained value of 29 ± 1 GPa agrees well with the data obtained with other methods and reported in the literature.

Ferroelectricity has been reported in organic–inorganic perovskites, and it can enhance the power conversion efficiencies (PCEs) of perovskite solar cells (PSCs) because ferroelectricity can facilitate charge carrier separation and charge transport through the perovskite layer. However, the existence of ferroelectricity in perovskites has been in hot debate, particularly at room temperature. Here, we report the ferroelectric polarization switching of MAPb(I1−xBrx)3 which showed a high dependence on its composition. The ferroelectric behavior of MAPbI3-50% PbBr2 is confirmed with domain switching by Piezoelectric Force Microscopy (PFM) imaging and bias-off “butterfly-like” amplitude loops and piezoresponse hysteresis loops at room temperature. The possible factors, such as film electrical properties attributed to the enhanced room-temperature ferroelectricity in MAPb(I1−xBrx)3 films are clarified by using conductive atomic force microscopy (C-AFM). In addition, the charge separation and charge transport in the perovskite MAPb(I1−xBrx)3 films are further investigated by Kelvin probe force microscopy (KPFM). Finally, the possible influences of polarization orientations, trapping effects and ion migrations within the MAPb(I1−xBrx)3 films on the J–V characteristics of PSC devices are discussed in detail. It discovers that the polarization switching under the positive tip biased condition in the PSCs with 50% PbBr2, which could hinder the photovoltaic performance. These findings help better understand the electronic structure of hybrid organic–inorganic perovskites and provide guidance for the improvement of the PSC performance and other electronic applications of perovskites.

In this work, CuO ( 1 ¯ 1 1 ) preferred orientation thin films with nano wheatear array have been prepared by using reactive magnetron sputtering. Their structures, physical properties were measured, and the surface energies of CuO films were calculated by first-principle calculations. Especially, single nanowire electronic measuring method based on conductive atomic force microscopy (C-AFM) and Kelvin probe force microscopy (KPFM) were developed. The prepared CuO films with nano wheatear array have good crystallinity. Here, wheatear is an ear of wheat, and the morphology of nanowire is similar to that of the wheatear. It is found that the band gaps of CuO films can be modulated from 1.54 to 1.25 eV by changing length of nano wheatear. Moreover, the measured results by KPFM show the existence of the p-type carrier, the decrease of the band gap with increasing length of nano wheatear. At the same time, the applied electric field (E) dependence of the current density (J) for single nano CuO wheatear was measured by C-AFM. The experimental results in the injection and direct tunnel regimes indicate that, with increasing length of nano CuO wheatear, the work function is enhanced and the band gap is decreased. The measured results on work function and band gap by C-AFM are consistent with those by KPFM. At last, it is suggested that KPFM and C-AFM can provide both effective methods in measuring the band gap of the semiconductor.

Motivated by the biological neuromorphic system with a high degree of connectivity to process huge amounts of information, light-triggered electronic synapses are expected to pave the way for overcoming the von Neumann bottleneck for non-conventional computing. Here, a light-triggered electronic synapse based on solution-processed ZnO–phosphorene nanoparticles (ZP NPs) with an in situ fabricated heterojunction is demonstrated. In situ Kelvin probe force microscopy (KPFM) and conductive atomic force microscopy (CAFM) have been employed to investigate the operation principle of the memristor. The essential synaptic functions of learning and memory of the bio-synapse have been emulated, including potentiation and depression under positive and negative pulse trains, paired-pulse facilitation (PPF), spike-rate-dependent plasticity (SRDP), spike-timing-dependent plasticity (STDP) and short-term potentiation (STP) to long-term potentiation transition (LTP). The well-arranged pn junction inside the ZP NPs arouses the multiple wavelength response and fast separation of photogenerated excitons, which serves as the basis for broadband optically-mediated plasticity. The experimental results confirm that ZP nanoparticles could be promising key components for mimicking biological synaptic behaviors with light stimulation, which is of great importance for the further development of artificial light triggered neural systems.

Organic semiconducting/ferroelectric blend films integrate both resistive and rectifying properties and thus well solve the cross-talk problem usually suffered in resistive memories. Till now several kinds of semiconducting/ferroelectric blend systems have been developed with good retention and ON/OFF properties. However, seldom work concerns air stability of their electrical properties. Here we report one kind of blend resistive films with air-stable Poly[(9,9-dioctylfluorenyl-2,7-diyl) -alt-co-(bithiophene)] (F8T2) as semiconducting material and the copolymer of vinylidene fluoride and trifluoroethylene (P(VDF-TrFE)) as ferroelectric material. We introduce AFM based nanoscale electrical measurements into the observation of phase separation in F8T2/P(VDF-TrFE) blend films. Conductive AFM measurements present discrete high-conductivity circular domains embedded in continuous low-conductivity matrix. Surface Potential Microscopy results further indicate that these discrete circular domains show lower surface potential than those from their surrounding matrix, implying the difference in chemical structures. It is reasonable to attribute those continuous surrounding matrix to ferroelectric P(VDF-TrFE) phase and those discrete circular domains to semiconducting F8T2 phase who penetrates the whole film resulting in large electrical conductivity. F8T2/P(VDF-TrFE) resistive blend films present good restive performance with high ON/OFF ratio up to 3.5×103. Such blend films show excellent electrical stability in air even after aging of 200 days.

Machining or patterning ultra-thin films with specified structures are critical challenges. In this work, a novel mode of atomic force microscopy nanomachining is proposed. The phase response of the cantilever is used as the input of feedback control to modulate the machining force to achieve the desired machined depth. The proposed phase mode, overcoming the disadvantages of force mode, is not affected by the debris piled-up and has the ability to sense the interface of an ultra-thin film and predict the machining depth without post-imaging. The effectiveness of the phase mode has been proven by experiments.

We demonstrate a polarization-mediated tunable nanoscale charge transport in Al-doped ZnO (AZO) thin film using conductive atomic force microscopy. In fact, we show that charge transport across an AZO film can be tuned by applying an external nano-Newton force, which confirms the presence of polarization in the film. In addition, we also demonstrate the role of polarization on the inhomogeneous work function using Kelvin probe force microscopy. The observed experimental result is attributed to defect-induced polarization in AZO film and will be a step forward to fabricate mechanical force tunable diode.

Dimensional measurements on nano-objects by atomic force microscopy (AFM) require samples of safely fixed and well individualized particles with a suitable surface-specific particle number on flat and clean substrates. Several known and proven particle preparation methods, i.e., membrane filtration, drying, rinsing, dip coating as well as electrostatic and thermal precipitation, were performed by means of scanning electron microscopy to examine their suitability for preparing samples for dimensional AFM measurements. Different suspensions of nano-objects (with varying material, size and shape) stabilized in aqueous solutions were prepared therefore on different flat substrates. The drop-drying method was found to be the most suitable one for the analysed suspensions, because it does not require expensive dedicated equipment and led to a uniform local distribution of individualized nano-objects. Traceable AFM measurements based on Si and SiO2 coated substrates confirmed the suitability of this technique.

Atomic force microscopy (AFM) offers unparalleled insight into structure and material functionality across nanometer length scales. However, the spatial resolution afforded by the AFM tip is counterpoised by slow detection speeds compared to other common microscopy techniques (e.g., optical, scanning electron microscopy, etc.). In this work, we develop an ultrafast AFM imaging approach allowing direct reconstruction of the tip-sample forces with ∼3 order of magnitude higher time resolution than is achievable using standard AFM detection methods. Fast free force recovery (F3R) overcomes the widely viewed temporal bottleneck in AFM, that is, the mechanical bandwidth of the cantilever, enabling time-resolved imaging at sub-bandwidth speeds. We demonstrate quantitative recovery of electrostatic forces with ∼10 μs temporal resolution, free from influences of the cantilever ring-down. We further apply the F3R method to Kelvin probe force microscopy (KPFM) measurements. F3R-KPFM is an open loop imaging approach ...

Adaptive multiloop-mode (AMLM) imaging to substantially increase (over an order of magnitude) the speed of tapping-mode (TM) imaging is tested and evaluated through imaging three largely different heterogeneous polymer samples in experiments. It has been demonstrated that AMLM imaging, through the combination of a suite of advanced control techniques, is promising to achieve high-speed dynamic-mode atomic force microscopy imaging. The performance, usability, and robustness of the AMLM in various imaging applications, however, is yet to be assessed. In this work, three benchmark polymer samples, including a PS–LDPE sample, an SBS sample, and a Celgard sample, differing in feature size and stiffness of two orders of magnitude, are imaged using the AMLM technique at high-speeds of 25 Hz and 20 Hz, respectively. The comparison of the images obtained to those obtained by using TM imaging at scan rates of 1 Hz and 2 Hz showed that the quality of the 25 Hz and 20 Hz AMLM imaging is at the same level of that of the 1 Hz TM imaging, while the tip–sample interaction force is substantially smaller than that of the 2 Hz TM imaging.

Effect of silicon atomic force microscope probe position and particle spacing on the local absorption of an array of gold nanoparticles placed over a dielectric borosilicate glass surface are evaluated. An improved, vectorized version of discrete dipole approximation coupled with surface interactions is employed throughout the study. It is shown that surface evanescent waves interacting with the system of nanoparticles and atomic force microscope probe result in a near-field coupling between them. This coupling can enhance or reduce the local absorption by the nanoparticles depending on the position of atomic force microscope tip in three-dimensional space and direction of propagation of the surface evanescent wave. The position of the atomic force microscope's tip and spacing that maximize the absorption are identified. This concept can be used for selective heating of nanoparticles placed over a surface that enables precision manufacturing at nanometer scales.

The topography of a surface consists of structures of different length scales. The surface roughness caused by these structures plays a decisive role in interfacial properties. Atomic Force Microscopy (AFM) can be applied to measure the surface topography with great accuracy and thus facilitates roughness quantification. Here, however, the data reduction poses a challenge. In a conventional approach, surface roughness parameters are evaluated based on averaging height differences, which leads to values dominated by the largest height differences of the surface topography. To quantify contributions of smaller structures to the roughness, a previous study presented a tunable local background correction, which eliminates structures on a larger than selected scale. Therefore, this method only considers surface structures smaller than the chosen scale. A different approach to quantify surface roughness on all length scales covered by AFM measurements uses Fourier transformation of the surface topography to calculate the power spectral density, which describes the amplitudes of different contributing spatial frequencies.In the current study, a new approach based on power spectral density is used to quantify surface roughness parameters as a function of the length scale of contributions to the surface topography. This procedure allows a comprehensive characterization of surface roughness and an intuitive comparison of different surfaces.The usefulness of this method and its compatibility to local background correction is demonstrated by analyzing several commercially available carbon fibers with and without different fiber surface treatments.

It is fundamentally important to understand the nanoscale electronic properties of a single quantum dot (QD) contrary to an ensemble of QDs. Kelvin probe force microscopy (KPFM) and conductive atomic force microscopy (CAFM) are two important tools, which could be employed to probe surface potential, charging phenomena, and current transport mechanism of individual QD. We demonstrate the aforementioned characteristics of self-assembled Ge QDs, which was grown on Si substrates by solid source molecular beam epitaxy driven by the Stranski-Krastanov method. Study reveals that each Ge QD acts as charge storage node even at zero applied bias. The shape, size and density of QDs could be well probed by CAFM and KPFM, whereas QD facets could be better resolved by the conductive tip. The CAFM investigation further reveals that there exists a composition gradient within the QDs and Ge core can be charged more efficiently than the Si-Ge periphery at low level of bias. Schematic energy band diagram at the tip-sample contact is presented to explain the current transport mechanism, charging/discharging characteristics and the threshold voltages of I–V characteristics of the individual Ge QDs.

The electrons and holes were injected into the blend electrets of polystyrene and C60 (PS/C60) by adjusting the biases of conductive atomic force microscopy probe. We visualized the charges trapping, release, diffusion, and retention processes of the PS/C60 electrets by utilizing the Kelvin Probe Force Microscopy (KPFM), and found that the localization and retention abilities of the ambipolar charges are enhanced with the increase of C60 content, indicating that blending C60 in PS matrix is a promising method for the charge trapping layer in transistor memory devices. Furthermore, we discussed the storage and diffusion mechanisms, and speculated that the interface of C60 and PS in the blend electrets and repulsive force between charge clusters around C60 are the important factors for the novel storage effect of the blend electret.

Measuring vector quantities in nanoscale systems is challenging — often only scalar magnitudes can be experimentally obtained. Now, a multi-frequency atomic force microscopy method for probing the 3D force response of a Ge(001) surface is reported. Probing physical quantities on the nanoscale that have directionality, such as magnetic moments, electric dipoles, or the force response of a surface, is essential for characterizing functionalized materials for nanotechnological device applications1,2,3. Currently, such physical quantities are usually experimentally obtained as scalars. To investigate the physical properties of a surface on the nanoscale in depth, these properties must be measured as vectors. Here we demonstrate a three-force-component detection method, based on multi-frequency atomic force microscopy on the subatomic scale4,5,6,7,8,9 and apply it to a Ge(001)-c(4 × 2) surface. We probed the surface-normal and surface-parallel force components above the surface and their direction-dependent anisotropy and expressed them as a three-dimensional force vector distribution. Access to the atomic-scale force distribution on the surface will enable better understanding of nanoscale surface morphologies, chemical composition and reactions10,11, probing nanostructures via atomic or molecular manipulation12,13, and provide insights into the behaviour of nano-machines on substrates14,15.

We present a procedure to perform and interpret pull-off force measurements during the jump-off-contact process between a liquid drop and rough surfaces using a conventional atomic force microscope. In this method, a micrometric liquid mercury drop is attached to an AFM tipless cantilever to measure the force required to pull this drop off a rough surface. We test the method with two surfaces: a square array of nanometer-sized peaks commonly used for the determination of AFM tip sharpness and a multi-scaled rough diamond surface containing sub-micrometer protrusions. Measurements are carried out in a nitrogen atmosphere to avoid water capillary interactions. We obtain information about the average force of adhesion between a single peak or protrusion and the liquid drop. This procedure could provide useful microscopic information to improve our understanding of wetting phenomena on rough surfaces.

Quartz tuning forks that have a probe tip attached to the end of one of its prongs while the other prong is arrested to a holder (“qPlus” configuration) have gained considerable popularity in recent years for high-resolution atomic force microscopy imaging. The small size of the tuning forks and the complexity of the sensor architecture, however, often impede predictions on how variations in the execution of the individual assembly steps affect the performance of the completed sensor. Extending an earlier study that provided numerical analysis of qPlus-style setups without tips, this work quantifies the influence of tip attachment on the operational characteristics of the sensor. The results using finite element modeling show in particular that for setups that include a metallic tip that is connected via a separate wire to enable the simultaneous collection of local forces and tunneling currents, the exact realization of this wire connection has a major effect on sensor properties such as spring constant, quality factor, resonance frequency, and its deviation from an ideal vertical oscillation.

Organic photovoltaic systems comprising donor polymers and acceptor fullerene derivatives are attractive for inexpensive energy harvesting. Extensive research on polymer solar cells has provided insight into the factors governing device-level efficiency and stability. However, the detailed investigation of nanoscale structures is still challenging. Here we demonstrate the analysis and modification of unidentified surface aggregates. The aggregates are characterized electrically by Kelvin probe force microscopy and conductive atomic force microscopy (C-AFM), whereby the correlation between local electrical potential and current confirms a defective charge transport. Bimodal AFM modification confirms that the aggregates exist on top of the solar cell structure, and is used to remove them and to reveal the underlying active layer. The systematic analysis of the surface aggregates suggests that the structure consists of PCBM molecules.

Chemical vapour deposition (CVD) is a promising method for producing large-scale graphene (Gr). Nevertheless, microscopic inhomogeneity of Gr grown on traditional metal substrates such as copper or nickel results in a spatial variation of Gr properties due to long wrinkles formed when the metal substrate shrinks during the cooling part of the production cycle. Recently, molybdenum (Mo) has emerged as an alternative substrate for CVD growth of Gr, mainly due to a better matching of the thermal expansion coefficient of the substrate and Gr. We investigate the quality of multilayer Gr grown on Mo and the relation between Gr morphology and nanoscale mechanical and electrical properties, and spatial homogeneity of these parameters. With atomic force microscopy (AFM) based scratching, Kelvin probe force microscopy, and conductive AFM, we measure friction and wear, surface potential, and local conductivity, respectively. We find that Gr grown on Mo is free of large wrinkles that are common with growth on other metals, although it contains a dense network of small wrinkles. We demonstrate that as a result of this unique and favorable morphology, the Gr studied here has low friction, high wear resistance, and excellent homogeneity of electrical surface potential and conductivity., Accepted for publication in Applied Surface Science, 31 pages, 10 figures

It has been reported that the output performance of a triboelectric nanogenerator (TENG) can be enhanced by applying light; however, the coupling mechanism between photogenerated carriers and triboelectric charges is still not well explained. Here, we propose a light-enhanced TENG based on a P3HT:PC61BM active blend layer, which processes dual functions of the photoelectric effect and the triboelectric effect. The open-circuit voltage, short circuit current, and amount of transferred charges for the TENG were enhanced by 63%, 76%, and 127%, respectively, after illumination under the white light condition. Moreover, we have investigated the interaction between the triboelectric charges and the photogenerated carriers to further explore the coupling mechanism between the triboelectric and photoelectric effects. Both Kelvin probe force microscopy and conductive atomic force microscopy demonstrate that the photogenerated carriers produced by the P3HT:PC61BM active blend layer can improve the surface triboelectric charge density. More interestingly, the transient absorption spectrum indicates that the electrostatic field induced by triboelectric charges contributes to the dissociation of excitons. In other words, there exists a beneficial promoting effect between the triboelectric charges and the photogenerated carriers during the operation of the light-enhanced TENG. This work provides an important guideline for the design and performance improvement of the hybrid TENG that captures both mechanical energy and light energy simultaneously.

Carrier injection in wide-band-gap materials is attracting a considerable research interest due to its potential applications in hot carrier solar cells, photocatalysis, next generation of ultrafast nanophotonics, etc. Herein, we fabricate a ZnO/Al2O3/silver-nanowires heterostructure using sputtering and atomic layer deposition techniques and report the tunneling dynamics of hot carriers via Al2O3 layer, revealed by nanoscale current maps and bulk current-voltage measurements. Atomic force microscopic and scanning electron microscopic studies reveal the uniform distribution of granular nanostructures (of ZnO thin films) and random distribution of Ag-NWs. The absorption measurements of the heterostructure show light absorption in wide wavelength range. In addition, the thickness of tunneling layer (Al2O3 films) was varied and 2 nm-thick Al2O3 layer provides the relatively easy charge transport due to resonant tunneling effect, as is confirmed using electrostatic force microscopy, Kelvin probe force microscopy, and conductive atomic force microscopy measurements. Further, current-voltage characteristics reveal the photocurrent under different wavelength illumination for 2 nm-thick Al2O3 layer heterostructure. Interestingly, the ZnO/Al2O3 (2 nm)/Ag-NWs device demonstrates fast decay and hot carriers transfer from Ag-NWs to ZnO, as is evident from the femtosecond pump-probe transient absorption measurements. Our finding paves an effective approach for improving the hot carrier injection efficiency in the wide band gap materials for use in photovoltaics and photocatalysis applications.

Controlling the resistive switching parameters by using external fields is of great importance in the application of the resistive memory devices. In this work, we investigate the effect of light illumination and oxygen atmosphere on the resistive switching of the anatase phase polycrystalline TiO2 thin film using the in-situ conductive atomic force microscopy and Kelvin probe force microscopy. A forming free bipolar resistive switching effect with ON/OFF ratio over 104 was achieved in nanoscale uniformly on the film. The conduction characteristics can be changed from the non-rectifying behavior in vacuum to the Schottky rectifying behavior in oxygen gas with nearly the same ON/OFF ratio. The reversible surface potential shift accompanied by the resistance switching was also observed. Furthermore, the resistance states and the surface potential contrast can be erased by 395 nm near-UV illumination, demonstrating a good optical erasing performance of the device. Combining the surface potential shift and the response to the illumination and oxygen gas, a charge trapping/detrapping mechanism was confirmed to account for the observed switching behavior. These results provide a new way to fabricate the controllable and optical erasable resistive switching devices in nanoscale.

All-inorganic halide perovskites (AIHPs) have become one of the most promising materials for commercial perovskite photovoltaics owing to their enhanced efficiency and thermodynamic stability. Output instability, such as current hysteresis, is stressed in organic-inorganic hybrid perovskite photovoltaics but is neglected in AIHP solar cells. Here, the origin and suppression of current hysteresis in AIHP solar cells are addressed from a microscopic viewpoint. The incorporation of fullerene into AIHP films efficiently suppresses ion migration, which alleviates the macroscopic current hysteresis in solar cells. This result is confirmed by both Kelvin probe force microscopy and conductive atomic force microscopy measurements. Our results provide an advanced understanding of the microscopic properties of AIHPs but also clearly clarify how to suppress the macroscopic current hysteresis, which further inspires the optimization of solar cells up to the levels of organic–inorganic hybrid counterparts.

Local defects in water layers growing on metal surfaces have a key influence on the wetting process at the surfaces; however, such minor structures are undetectable by macroscopic methods. Here, we demonstrate ultrahigh-resolution imaging of single water layers on a copper(110) surface by using non-contact atomic force microscopy (AFM) with molecular functionalized tips at 4.8 K. AFM with a probe tip terminated by carbon monoxide predominantly images oxygen atoms, whereas the contribution of hydrogen atoms is modest. Oxygen skeletons in the AFM images reveal that the water networks containing local defects and edges are composed of pentagonal and hexagonal rings. The results reinforce the applicability of AFM to characterize atomic structures of weakly bonded molecular assemblies., The structure of water in the first layer on surfaces is essential to our understanding of various phenomena, such as surface wettability and heterogeneous catalysis. Here, the authors use atomic force microscopy with a CO-functionalized tip to image water defects on copper surface at atomic resolution.