Scanning Probe Techniques Research Articles

Electrochemical Intercalation in Atomically Thin van der Waals Materials for Structural Phase Transition and Device Applications.

In van der Waals (vdWs) materials and heterostructures, the interlayers are bonded by weak vdWs interactions due to the lack of dangling bonds. The vdWs gap at the homo- or heterointerface provides great freedom to enrich the tunability of electronic structures by external intercalation of foreign ions or atoms at the interface, leading to the discovery of new physics and functionalities. Herein, the recent progress on electrochemical intercalation of foreign species into atomically thin vdWs materials for structural phase transition and device applications is reviewed and future opportunities are discussed. First, several kinds of electrochemical intercalation platforms to achieve the intercalation in vdWs materials and heterostructures are introduced. Next, the in situ characterization of electrochemical intercalation dynamics by state-of-the-art techniques is summarized, including optical techniques, scanning probe techniques, and electrical transport. Moreover, particular attention is paid on the experimentally reported phase transition and multifunctional applications of intercalated devices. Finally, future applications and challenges of intercalation in vdWs materials and heterostructures are proposed, including the intrinsic intercalation mechanism of solid ion conductors, exact identification of intercalated foreign species by near-field optical techniques, and the tunability of intercalation kinetics for ultrafast switching.

Control of magnetic interactions between surface adatoms via orbital repopulation

We propose a reversible mechanism for switching Heisenberg-type exchange interactions between deposited transition metal adatoms from ferromagnetic to antiferromagnetic. Using first-principles calculations, we show that this mechanism can be realized for cobalt atoms on the surface of black phosphorus by making use of electrically-controlled orbital repopulation, as recently demonstrated by scanning probe techniques [Nat. Commun. 9, 3904 (2018)]. We find that field-induced repopulation not only affects the spin state, but also causes considerable modification of exchange interaction between adatoms, including its sign. Our model analysis demonstrates that variable adatom-substrate hybridization is a key factor responsible for this modification. We perform quantum simulations of inelastic tunneling characteristics and discuss possible ways to verify the proposed mechanism experimentally.

Atomic force microscopy: Emerging illuminated and operando techniques for solar fuel research.

Integrated photoelectrochemical devices rely on the synergy between components to efficiently generate sustainable fuels from sunlight. The micro- and/or nanoscale characteristics of the components and their interfaces often control critical processes of the device, such as charge-carrier generation, electron and ion transport, surface potentials, and electrocatalysis. Understanding the spatial properties and structure-property relationships of these components can provide insight into designing scalable and efficient solar fuel components and systems. These processes can be probed ex situ or in situ with nanometer-scale spatial resolution using emerging scanning-probe techniques based on atomic force microscopy (AFM). In this Perspective, we summarize recent developments of AFM-based techniques relevant to solar fuel research. We review recent progress in AFM for (1) steady-state and dynamic light-induced surface photovoltage measurements; (2) nanoelectrical conductive measurements to resolve charge-carrier heterogeneity and junction energetics; (3) operando investigations of morphological changes, as well as surface electrochemical potentials, currents, and photovoltages in liquids. Opportunities for research include: (1) control of ambient conditions for performing AFM measurements; (2) in situ visualization of corrosion and morphological evolution of electrodes; (3) operando AFM techniques to allow nanoscale mapping of local catalytic activities and photo-induced currents and potentials.

Measurement of electrostatic tip-sample interactions by time-domain Kelvin probe force microscopy.

Kelvin probe force microscopy is a scanning probe technique used to quantify the local electrostatic potential of a surface. In common implementations, the bias voltage between the tip and the sample is modulated. The resulting electrostatic force or force gradient is detected via lock-in techniques and canceled by adjusting the dc component of the tip–sample bias. This allows for an electrostatic characterization and simultaneously minimizes the electrostatic influence onto the topography measurement. However, a static contribution due to the bias modulation itself remains uncompensated, which can induce topographic height errors. Here, we demonstrate an alternative approach to find the surface potential without lock-in detection. Our method operates directly on the frequency-shift signal measured in frequency-modulated atomic force microscopy and continuously estimates the electrostatic influence due to the applied voltage modulation. This results in a continuous measurement of the local surface potential, the capacitance gradient, and the frequency shift induced by surface topography. In contrast to conventional techniques, the detection of the topography-induced frequency shift enables the compensation of all electrostatic influences, including the component arising from the bias modulation. This constitutes an important improvement over conventional techniques and paves the way for more reliable and accurate measurements of electrostatics and topography.

Methods of Composite Electrode Imaging

Lithium intercalation electrodes are composite devices that consist of typically at least four different constituents that provide separately charge storage, electronic conduction, ionic conduction and mechanical integrity. Consequently, the microstructure of these composites has an important role to play in intercalation electrode performance. An inhomogeneous electrode microstructure affects battery performance by increasing peak local current densities and resistances during the operation. This reduces accessible capacity, compromises safety, as it facilitates localized overcharging, and impacts ion transport and consequently power performance.1 Origins for inhomogeneity in electrode microstructure can lie in the casting procedure, slow carbon agglomeration over cycling as well as in binder adhesive failure due to active material volume changes, which causes a connectivity loss between active material and the matrix.Given this impact of the electrode microstructure, an improved understanding of microstructure and microscopic performance variations is of great importance to optimizing overall battery performance. As such, we need tools that allow us to measure microscopic performance, and correlate to microstructure, interfaces and their development over cycling. Thus a variety of spatial imaging techniques can be used to characterize the processes ex situ, in situ, and operando. Each technique gives a unique and specific information about certain process.2 , 1 We are highlighting herein X-ray tomography and scanning electrochemical microscopy (SECM) as tools for the investigation of disconnection mechanisms.X-ray Tomography (XRT) is a 3D imaging technique used to visualize complex mechanical interactions in batteries during operation. This nondestructive technique can provide a spatial resolution down to the nanometer scale. X-ray tomography can provide information of the material porosity and tortuosity, chemical composition and crystals and the reactions inside the battery.4 , 2 We are using this technique in the imaging, analysis and tracking of electrode microstructure with cycling.Scanning electrochemical microscopy (SECM) is a scanning probe technique that uses a microscopic electrochemical electrode as probe. This allows the measurement of local electrochemical activity on a substrate surface. It has previously been used to investigate the properties of solid electrolyte interphase (SEI) of the negative electrode as well as exploring the lithium ion activity at micro and nano scales resolution.3 We are employing this method to correlate microstructure and performance inhomogeneity.This presentation summarizes first results from both techniques and contrasts structural with performance inhomogeneity. We will be using these tools as we are developing new binders and microstructures for intercalation electrodes to improve the synergy between electrode constituents and optimize overall electrode performance.References(1) Müller, S.; Eller, J.; Ebner, M.; Burns, C.; Dahn, J.; Wood, V. Quantifying Inhomogeneity of Lithium Ion Battery Electrodes and Its Influence on Electrochemical Performance. J. Electrochem. Soc. 2018, 165 (2), A339–A344. https://doi.org/10.1149/2.0311802jes.(2) Schröder, D.; Bender, C. L.; Arlt, T.; Osenberg, M.; Hilger, A.; Risse, S.; Ballauff, M.; Manke, I.; Janek, J. In Operando X-Ray Tomography for next-Generation Batteries: A Systematic Approach to Monitor Reaction Product Distribution and Transport Processes. J. Phys. D. Appl. Phys. 2016, 49 (40), 404001. https://doi.org/10.1088/0022-3727/49/40/404001.(3) Ventosa, E.; Schuhmann, W. Scanning Electrochemical Microscopy of Li-Ion Batteries. Phys. Chem. Chem. Phys. 2015, 17 (43), 28441–28450. https://doi.org/10.1039/c5cp02268a.(4) Pietsch, P.; Wood, V. X-Ray Tomography for Lithium Ion Battery Research: A Practical Guide. Annu. Rev. Mater. Res. 2017, 47 (1), 451–479. https://doi.org/10.1146/annurev-matsci-070616-123957.

(Invited) Backside Absorbing Layer Microscopy: A New Tool to Study the Optical, Chemical and Electrochemical Properties of 2D Materials

Optical microscopy based on anti-reflective coatings is a simple yet powerful characterization tool which notably allowed the first observation of graphene in 2004 and of other single-layered materials in the following years. Since then, the field of two-dimensional materials has developed rapidly both at the fundamental and applied levels. Yet, these ultrathin materials present inhomogeneities (edges, grain boundaries, defects, multilayers...) which strongly impact their intrinsic (physical, chemical) properties and the performances of the electronic, optoelectronic and energy-conversion devices. The use of local characterization techniques (spectroscopy mapping, scanning probe techniques...) is thus essential. Recently, D. Ausserré et al. introduced a new enhanced-contrast optical microscopy technique, named BALM (Backside Absorbing Layer Microscopy), based on ultrathin (2-5 nm) and strongly light-absorbing (metallic) anti-reflective layers. This talk aims at presenting the remarkable assets of this technique for the study of 2D materials. BALM notably allows observing mono-layered materials with very strong contrast even in the case of transparent ones such as graphene oxide [1]. The inverted microscope geometry allows imaging in solvents so that it is possible to investigate molecular adsorption dynamics on 2D materials in real-time and with extreme sensitivity.[1-2] With its wavelength sensitivity, it can also be used as a precise technique to determine the refractive index and extinction coefficient of TMDCs (MoS2, WS2). But one of the main benefits of BALM comes from its combination to other techniques. We particularly considered the coupling between optical measurements and electrochemistry for which the anti-reflective substrate serves as working electrode. We investigated optically the dynamic of the electrochemical reduction of Graphene Oxide (GO), the electro-grafting of organic layers by diazonium salts reduction on GO and its reduced form (rGO),[3] as well as the intercalation of metallic ions within stacked GO sheets. By combining versatility and high-contrast, BALM is established as a promising tool for the study of 2D materials, especially for the local and in situ characterization of their optical, chemical and electrochemical properties.[1] S. Campidelli, R. Abou Khachfe, K. Jaouen, J. Monteiller, C. Amra, M. Zerrad, R. Cornut, V. Derycke, D. Ausserré, Backside absorbing layer microscopy: Watching graphene chemistry, Science Advances 3, e1601724 (2017).[2] K. Jaouen, R. Cornut, D. Ausserré, S. Campidelli, V. Derycke, Ideal optical contrast for 2D materials observation using bi-layer antireflection absorbing substrates, Nanoscale 11, 6129 (2019).[3] K. Jaouen, F. Lebon, B. Jousselme, S. Campidelli, R. Cornut, V. Derycke, Optical monitoring of diazonium electrografting on gold and graphene oxide using Backside Absorbing Layer Microscopy, submitted.

(Invited) Nanoscale Optics of 2D Materials for Multi-Dimensional Sensing

Starting with thorough nanoscale characterization of 2D materials (2DM) with a scattering-type scanning near-field optical microscope (sSNOM), further sensing applications of the surface modified 2DMs are discussed. sSNOM imaging and spectroscopy reveals subwavelength features and correlate optical properties of 2DMs to the surface structure. When supplemented by other scanning probe techniques (KPFM/EFM), correlation of the sSNOM maps of the same surface area in MIR and visible range allows an additional information to be extracted. Surface polariton waves are discussed in relation to the surface optical impedance of the structures. Far-field measurements are finally matched to the near-field data.SVR acknowledges help of Ms. X. Li (PSU) and samples provided by NSF 2DCC MIP (Dr. J. Redwing and Dr. J. Robinson). Research of TI was partially supported by the UNCG Faculty First Award. sSNOM facility is partially funded by Penn State Quantum Characterization Infrastructure initiative.

(Invited) Characterizing Defects in Semiconductors for Solar Cells and Understanding Their Impact on Device Performance

Solar cells are intrinsically sensitive to minority carrier properties and therefore to intrinsic and extrinsic defects. This talk presents an overview of the application of microchemical, microstructural, and optoelectronic characterization techniques to observe these defects and connect their optoelectronic effects to the defect chemistry. This is particularly important in highly ionic materials and in materials that are applied as polycrystals where self-compensation, defect complexes, impurities segregated at grain boundaries, and second phases are critical. Therefore the talk will concentrate on those types of semiconductors. Scanning probe techniques and capacitance-based methods are particularly useful as they can probe within an individual grain even when that grain is small. Modeling to connect the individual defects to device performances is also described.

(Invited) Detection of Cancer Biomarkers By Scanning Electrochemical Microscopy

Scanning electrochemical microscopy (SECM) is a scanning probe technique that is composed of a micro- or nanoelectrode that can be scanned in close proximity to an interface. Faradaic current signals can be recorded due to the flux of redox active species between the sample and an amperometric SECM probe. SECM can be used to image the topography and reactivity of biological specimens for mapping localized biochemical activity. Although SECM has been applied to different biological systems, SECM studies of tissues are still under exploration. The reason is due to the shape and high roughness of such real samples and requires overcoming major drawbacks in conventional SECM instrumentation when scanning large, i.e. square centimeter sized, areas with irregular surface keeping a constant working distance.My research aims to develop various reliable SECM bioimaging techniques for the study of the distribution of biomarkers in tape-stripping cancer samples and human melanoma tumor samples. Melanoma is the most lethal form of skin cancer striking thousands of people around the world. The survival rate depends on the stage of the cancer when it is diagnosed. SECM could improve the diagnosis and understanding of different melanoma stages based on highly resolved maps of the tyrosinase distribution in tumor sections. [1]Furthermore, the increasing levels of tyrosinase were recorded in cells that were collected from the skin of melanoma mouse models representing three different stages of tumor growth. [2] Additionally, SECM results of tape-stripped different human melanoma cell lines were confirmed by previous studies based on traditionally fixed and permeabilized cells. The presented electrochemical tyrosinase detection approach can potentially be integrated into point of-care testing (POCT) devices. SECM scanning parameters, such as microelectrode size and step size can be used to determine experimentally the best design before fabricating microelectrode array prototypes. [1] 1. Lin TE, Lu YJ, Sun CL, Pick H, Chen JP, Lesch A, Girault H. Soft electrochemical probes for mapping the distribution of biomarkers and injected nanomaterials in animal and human tissues Angew. Chem. Int. Ed. 2017;56:16498–16502.2. Darvishi S, Pick H, Lin TE, Zhu Y, Li X, Ho PC, Girault HG, Lesch A. Tape-Stripping Electrochemical Detection of Melanoma Anal. Chem. 2019, 91, 12900–12908

Electrochemical Imaging of Biomarkers for Oral Cancer Staging

Each year, approximately 450,000 new cases are reported with oral or oropharyngeal cancer worldwide. Despite their high incidence, oral cancers are often neglected at the first stage, resulting in cancer metastasis with high mortality rate, especially for men. Conventional methods for diagnosis of oral cancer rely on the visual inspection and biopsy. However, it may lead to misdiagnosis or delayed diagnosis because of insufficient information. Therefore, it is important to develop a novel tool for the detection of oral cancer at an initial stage itself.Electrochemical screening methods have shown to be very promising for the rapid, sensitive, and cost-effective detection of oral cancer biomarkers.1 To enhance the resolution of the electrochemical imaging, we employ the concept of image fusion, with the image obtained by scanning electrochemical microscopy (SECM) and optical microscopy. Through the prediction of the presence of biomarkers in tissue area, the fused image can provide a more accurate description of the biomarker distribution of the oral cancer slices. For the purpose of investigating the distribution of IL-6 protein, a biomarker of oral cancer, in different cancer stages, we use SECM to image tissue sections and fused it with H&E stain images obtained by optical microscope. SECM is a scanning probe technique that is composed of three electrode system and soft probe can scan closely over a sample surface. The primary antibody and secondary antibody labeled with horse radish peroxidase (HRP) were applied to reveal the locations of IL-6 on the samples. Then, the cancer sections were immersed in electrolytes containing FcMeOH and H2O2. The FcMeOH+ ions were generated from the catalytic reaction of HRP, and hence, the Faradaic current signals from the reduction of FcMeOH+ can be recorded through the scanning of SECM probe. Due to the fusion of SECM with H&E stain, IL-6 distribution patterns in cancers with different stages can be analyzed precisely. We discovered that in stage III of oral cancer, the IL-6 expression level is the highest as compared to the normal tissue and cancer tissue at earlier stages. 1. T.-E. Lin, Y.-J. Lu, C.-L. Sun, H. Pick, J. P. Chen, A. Lesch, H. H. Girault, Angew. Chem. Int. Ed. 2017, 56, 16498-162. T.-E. Lin, C.-L. Chen, Y.-C. Huang, H.-H. Chung, C.-W. Lin, K.-C. Chen, Y.-J. Peng, S.-T. Ding, M.-Y. Wang, T.-L. Shen, C.-C. Hsu Anal. Chim. Acta. 2019.

The true corrugation of a h-BN nanomesh layer

Hexagonal boron nitride (h-BN) nanomesh, a two-dimensional insulating monolayer, grown on the (111) surface of rhodium exhibits an intriguing hexagonal corrugation pattern with a lattice constant of 3.2 nm. Despite numerous experimental and theoretical studies no quantitative agreement has been found on some details of the adsorption geometry such as the corrugation amplitude. The issue highlights the differences in chemical and electronic environment in the strongly bound pore regions and the weakly bound wire regions of the corrugated structure. For reliable results it is important to probe the structure with a method that is intrinsically sensitive to the position of the atomic cores rather than the electron density of states.In this work, we determine the corrugation of h-BN nanomesh from angle- and energy-resolved photoelectron diffraction measurements with chemical state resolution. By combining the results from angle and energy scans and comparing them to multiple-scattering simulations true adsorbate-substrate distance can be measured with high precision, avoiding pitfalls of apparent topography observed in scanning probe techniques. Our experimental results give accurate values for the peak-to-peak corrugation amplitude (0.80 Å), the bonding distance to the substrate (2.20 Å) and the buckling of the boron and nitrogen atoms in the strongly bound pore regions (0.07 Å).These results are important for the development of theoretical methods that involve a quantitative description of van der Waals systems as required for the understanding of the physics of two-dimensional sp2 layers.

Surface Evolution of Lithium Titanate upon Electrochemical Cycling Using a Combination of Surface Specific Characterization Techniques

AbstractAmong the electrodes for Li‐ion batteries, Li4Ti5O12 (LTO) stands out as anode owing to its stability and safety, in part ascribed to its low surface reactivity. However, the overlayer formation on the LTO surface upon electrochemical cycling is reported in recent years; a rough surface layer of electrochemically inactive α‐Li2TiO3 on top of the LTO (111) surface is suggested on the grounds of scanning probe techniques and theoretical ab initio calculations which would negatively strike on the battery performance. Hence the investigation of the LTO surface evolution is key to achieve more stable and safer Li‐ion batteries. LTO (111) thin film electrodes are used as model system where a variety of surface specific characterization techniques are applied to unveil the surface behavior of LTO in Li‐ion batteries. In contrast with previous studies, with the help of high‐resolution transmission electron microscopy and synchrotron‐based surface X‐ray diffraction, α‐Li2TiO3 is found to be a surface preparation product. Of special importance is the use of high‐resolution electron backscatter diffraction to report an increase on the LTO surface strain upon electrochemical cycling which can have a critical effect in long cycling performance of LTO that is always considered a zero‐strain material.

Non-Invasive Nanoscale Potentiometry and Ballistic Transport in Epigraphene Nanoribbons.

The recent observation of non-classical electron transport regimes in two-dimensional materials has called for new high-resolution non-invasive techniques to locally probe electronic properties. We introduce a novel hybrid scanning probe technique to map the local resistance and electrochemical potential with nm- and μV resolution, and we apply it to study epigraphene nanoribbons grown on the sidewalls of SiC substrate steps. Remarkably, the potential drop is non-uniform along the ribbons, and μm-long segments show no potential variation with distance. The potential maps are in excellent agreement with measurements of the local resistance. This reveals ballistic transport, compatible with μm-long room-temperature electronic mean-free paths.

Metal-Conductive Polymer Core-Shell Nanowires: Electroless Reduction of Pd and Cu On Polypyrrole/DNA Templates Bearing 2-2'-Bipyridyl Groups

A method for the preparation of conductive polymer nanowires bearing metal ion chelating 2,2’-bipyridyl groups is described. N-(3-pyrrol-1-yl-propyl)-2,2'-bipyridinium hexafluorophosphate (NP2PBH) was templated on λ-DNA in aqueous solution using FeCl3 as oxidant to initiate polymerization. The polyNP2PBH/DNA nanowires were then decorated with metals (Cu or Pd) by electroless deposition [Cu(NO3)2/ascorbate or PdCl42-/NaBH4]. UV-vis absorption spectra of the hybrid materials show the absorption peak due to the plasmon resonance of Cu at about 550 nm and a broad continuous band consistent with metallic Pd in the range 300−700 nm. The morphology, size and electrical properties of the hybrid nanostructures have been characterized using scanning probe techniques (atomic force microscopy (AFM), scanning conductance microscopy (SCM) and conductive atomic force microscopy (cAFM)). The polyNP2PBH/DNA nanowires show a continuous, smooth and uniform appearance (mean diameter 5.0 nm). Cu deposits on polyNP2PBH/DNA nanowires by a nucleation and growth process that leads eventually to smooth, conductive Cu nanowires. In contrast, Pd deposits in a non-uniform manner on polyNP2PBH/DNA and has inconsistent electrical conductivity. The electrical conductivity of single Cu/polyNP2PBH/DNA nanowires was estimated to be 1.6 ± 0.27 S cm-1 which we suggest is limited by electron transfer between Cu grains.

Measurement of sub-nanonewton forces inside a scanning electron microscope.

van der Waals forces, electrostatic interactions, and capillary forces are the dominant force interactions at the micro- and nanoscale. This complex ensemble of surface forces is oftentimes summarized as adhesion and is important for various applications and research fields. So far, numerous measurement techniques have evolved in this field. However, there is still a lack of experimental insight into the complex interplay of van der Waals, electrostatic, and capillary forces for small force ranges below 10 nN, as this is the order of magnitude of the latter, which can shadow other interactions in ambient and even inert gas environments. To exclude capillary forces and thus to turn the van der Waals and electrostatic forces into the most significant interactions, we develop an interferometric force spectroscopy setup based on a scanning probe technique, featuring a sub-nanonewton resolution, and integrate it into the vacuum chamber of a scanning electron microscope. In this work, we describe the setup integration, show the long-term drift behavior and resolution capabilities, and conduct first measurements of adhesion energies between a silica colloidal probe and a silicon substrate. The presented setup shows its capability to reliably measure adhesive interactions in vacuum and an ambient environment with a sub-nanonewton resolution proving its potential to allow for the investigation of the separate contribution of capillary, van der Waals, and electrostatic interactions to adhesion and for a systematic experimental validation of the established adhesion theories and approximations on the micro- and nanoscale.

Embedding human heuristics in machine-learning-enabled probe microscopy

Scanning probe microscopists generally do not rely on complete images to assess the quality of data acquired during a scan. Instead, assessments of the state of the tip apex, which not only determines the resolution in any scanning probe technique, but can also generate a wide array of frustrating artefacts, are carried out in real time on the basis of a few lines of an image (and, typically, their associated line profiles.) The very small number of machine learning approaches to probe microscopy published to date, however, involve classifications based on full images. Given that data acquisition is the most time-consuming task during routine tip conditioning, automated methods are thus currently extremely slow in comparison to the tried-and-trusted strategies and heuristics used routinely by probe microscopists. Here, we explore various strategies by which different STM image classes (arising from changes in the tip state) can be correctly identified from partial scans. By employing a secondary temporal network and a rolling window of a small group of individual scanlines, we find that tip assessment is possible with a small fraction of a complete image. We achieve this with little-to-no performance penalty—or, indeed, markedly improved performance in some cases—and introduce a protocol to detect the state of the tip apex in real time.

A versatile and robust surface-poison-resisting Scanning Amperometric Proton Microscopy

Abstract A sensitive and accurate measurement of localized pH with improving spatial resolution is highly desirable to the scientific understanding of many processes ranging from clean energy production to biological cellular mechanisms. In this study, we report the observation that the diffusion-limited current (DLC) of hydrogen evolution reaction (HER) on Pt surface is largely surface poison-resisting to carbon monoxide and thiol, two well-known Pt surface poisons. Building upon this observation, we proposed and tested a technique for amperometrically measuring localized proton concentration with a sub-μm spatial resolution through the utilization of a linear pH dependence of HER DLC on a Pt ultramicroelectrode, hereby referred to as Scanning Amperometric Proton Microscopy (SAPM). By bringing the Pt ultramicroelectrode close to a proton generating/consuming substrate through resonance feedback on an atomic force microscopy (AFM) tuning fork, SAPM can be used to measure and image localized proton concentrations and changes in pH caused by an active catalytic surface during reactions, largely free of concerns about the presence of surface-poisoning species. This was demonstrated through three proof-of-concept cases: methanol oxidation reaction (MOR) on a Pt thin film substrate, active proton-coupled electron transfer by a membrane-tethered protein (cytochrome c oxidase) in biological compatible electrolyte, and SAPM imaging of PtRu islands electrodeposited onto a Pt film substrate during MOR. The development of this surface-poison-resisting scanning probe technique through this study shows the potential of a broadly applicable way to study proton-generating or -consuming reactions for catalytically-active substrates with a sub-μm spatial resolution, including biological processes involving localized pH changes in a variety of salts, buffers or broth-type reaction media at near-neutral pH values.

Three dimensional resistance mapping of self-organized Sr3V2O8 nanorods on metallic perovskite SrVO3 matrix

Self-organized epitaxial nanorods, obtained by an adapted annealing process after deposition of metallic strontium vanadate perovskite (SrVO3) thin films, are analyzed to determine their structural, chemical and electrical properties. After the identification of the Sr3V2O8 phase of the nanorods by electron diffraction; Electron Energy Loss Spectroscopy investigations show the vanadium oxidation state (V5+) for the nanorods. Two scanning probe techniques are deployed to determine the specific local electrical properties of these Sr3V2O8 nanorods. In ambient conditions, local electrical properties are studied by Scanning Spreading Resistance Microscopy based on an Atomic Force Microscope and multiple probe scanning tunneling microscopy is used for the study in ultrahigh vacuum. Both techniques reveal that local electrical resistances of the nanorods are five order of magnitude higher than the resistance of the perovskite SrVO3 matrix. Futhermore, the nanorods are found to be etched by repeating scanning of the conductive Atomic Force Microcopy probe, enabling a three-dimensional depth profile of the nanorods resistance with 3D-Spreading Resistance Microscopy mode. A partial embedding of the nanorods in the underlying SrVO3 film is proved and the impact of the water meniscus at the origin of the selective etching observed during Scanning Spreading Resistance Microscopy, in ambient conditions, is discussed.

A combined SECM and electrochemical AFM approach to probe interfacial processes affecting molecular reactivity at redox flow battery electrodes

Understanding interfacial reaction mechanisms of redoxmers at redox flow battery model carbon electrodes using insightful electrochemical scanning probe techniques enables new strategies for high-performance energy storage.

Operando Surface Characterization of InP Nanowire p-n Junctions.

We present an in-depth analysis of the surface band alignment and local potential distribution of InP nanowires containing a p–n junction using scanning probe and photoelectron microscopy techniques. The depletion region is localized to a 15 nm thin surface region by scanning tunneling spectroscopy and an electronic shift of up to 0.5 eV between the n- and p-doped nanowire segments was observed and confirmed by Kelvin probe force microscopy. Scanning photoelectron microscopy then allowed us to measure the intrinsic chemical shift of the In 3d, In 4d, and P 2p core level spectra along the nanowire and the effect of operating the nanowire diode in forward and reverse bias on these shifts. Thanks to the high-resolution techniques utilized, we observe fluctuations in the potential and chemical energy of the surface along the nanowire in great detail, exposing the sensitive nature of nanodevices to small scale structural variations.