Scanning Probe Microscopy Techniques Research Articles

Characterization of heterogeneity of CVD graphene on copper foil by scanning probe microscopy and Raman spectroscopy

The comparative analysis of the structural, morphological, and local electrical properties of CVD graphene films synthesized at atmospheric and low pressure CVD growth conditions was carried out. The use of electrical techniques of scanning probe microscopy, such as Kelvin probe force microscopy, scanning capacitance microscopy, electrostatic force microscopy, and conductive atomic-force microscopy for investigation of heterogeneous graphene coverage was discussed. A significant change in the surface potential values was observed indicating the formation of p-type multilayered graphene domains on single layer graphene at low pressure and n-type multilayered graphene films at atmospheric pressure CVD. The effect of Ar flow rate increasing during cooling stage in the temperature range of 700–200 °C causing graphite formation was described. The employment of surface potential spectroscopy allows to indicate the presence of nonlinear phenomena in heterogeneous graphene.

Scanning probe microscopy and microwave phenomena in composite containing iron nanoparticles and carbon nanotubes

Epoxyamine matrix-based composites containing 15 wt% of Fe nanoparticles and 1.5 or 2 wt% of carbon nanotubes, as well as composites containing only Fe particles, have been studied using microwave methods and various scanning probe microscopy techniques, such as scanning capacitance microscopy and scanning Kelvin probe force microscopy. The composites were prepared using technological methods that improve their homogeneity. Probe current dependences investigated by applying different voltages to the probe in the Kelvin probe force microscopy mode have shown that the falling regions of the dependences at both positive and negative values of the bias voltage are found only for the sample containing both the Fe particles and the CNT in the “soft epoxy” matrix. Microwave measurements of the transmission and reflection coefficients were performed in the frequency range from 26 to 38 GHz. The field dependences of the microwave power dissipation have been plotted. The ferromagnetic resonance in the composites has been investigated. Frequency dependences of the complex dielectric permittivity of the composites have been determined. Microwave properties of the CNT-containing and CNT-free composites have been compared.

The parabasal filaments of Trichomonas vaginalis: A new filament and observations using 0.8 nm-resolution scanning electron microscopy

Trichomonas vaginalis is the etiologic agent of trichomoniasis, the most common nonviral sexually transmitted infection worldwide, with an estimated 260 million new cases annually. T. vaginalis contains organelles common to all eukaryotic cells, uncommon cell structures such as hydrogenosomes, and a complex and elaborate cytoskeleton constituting the mastigont system. The mastigont system is mainly formed by several proteinaceous structures associated with basal bodies, the pelta-axostylar complex made of microtubules, and striated filaments named the costa and the parabasal filaments (PFs). Although the structural organization of trichomonad cytoskeletons has been analyzed using several techniques, observation using a new generation of scanning electron microscopes with a resolution exceeding 1 nm has allowed more detailed visualization of the three-dimensional organization of the mastigont system. In this study, we have investigated the cytoskeleton of T. vaginalis using a diverse range of scanning probe microscopy techniques, which were complemented by electron tomography and Fast-Fourier methods. This multi-modal approach has allowed us to characterize an unknown parabasal filament and reveal the ultrastructure of other striated fibers that have not been published before. Here, we show the differences in origin, striation pattern, size, localization, and additional details of the PFs, thus improving the knowledge of the cell biology of this parasite.

Evaluating the optoelectronic properties of individual CsPbBr3 microcrystals by electric AFM techniques

All-inorganic perovskite materials are attracting the attention of researchers owing to the good performance that they exhibit in optoelectronic device applications. In particular, cesium lead halide single crystals are of interest for their electric conductivity. However, the conductive properties of these materials are still far from being fully understood. In this work, we used several scanning probe microscopy techniques to investigate different properties of CsPbBr3 single crystals, namely their topography, electric conductivity, electric surface potential and ferroelectricity. We observed heterogeneity in conductance and work function of the different facets by using conductive atomic force microscopy and Kelvin probe force microscopy measurements. Additionally, piezo-response force microscopy was carried out to gain insight on the origin of the hysteresis in our microcrystals. Our results show the absence of ferroelectric domains and we attribute the I–V hysteresis to ionic migration within the crystal.

Atomic Force Microscopy Applied to the Study of Tauopathies.

Atomic force microscopy (AFM) is a scanning probe microscopy technique which has a physical principle, the measurement of interatomic forces between a very thin tip and the surface of a sample, allowing the obtaining of quantitative data at the nanoscale, contributing to the surface study and mechanical characterization. Due to its great versatility, AFM has been used to investigate the structural and nanomechanical properties of several inorganic and biological materials, including neurons affected by tauopathies. Tauopathies are neurodegenerative diseases featured by aggregation of phosphorylated tau protein inside neurons, leading to functional loss and progressive neurotoxicity. In the broad universe of neurodegenerative diseases, tauopathies comprise the most prevalent, with Alzheimer's disease as its main representative. This review highlights the use of AFM as a suitable research technique for the study of cellular damages in tauopathies, even in early stages, allowing elucidation of pathogenic mechanisms of these diseases.

Simultaneous Scanning Ion Conductance and Electrochemical Microscopy in Lithium‐Ion Battery Research

AbstractDeeper understanding of processes involved in operation of lithium‐ion batteries (LIBs) is necessary to further optimize them for future applications. Extensive research was conducted on the formation of a solid electrolyte interphase (SEI) on negative battery electrodes, still leaving several questions unanswered. Scanning probe microscopies (SPMs) enable in situ and operando investigations and have the potential to explain some phenomena. Scanning electrochemical microscopy (SECM) and scanning ion conductance microscopy (SICM) could be employed in LIB studies. A novel SICM method based on the redox couple ferrocene/ferrocenium is introduced for applications in carbonate solvents widely used in LIBs. Proof of concept measurements were conducted with a micro milled copper circuit board as model substrate. Furthermore, the proposed SICM approach was hyphenated with feedback mode SECM resulting in the simultaneous mapping of morphology and electrochemical activity. A flexible dual‐probe arrangement was developed enabling usage of both SPM techniques at the same time, and furthermore, an easy replacement of both individual probes if needed. The setup was applied in the characterisation of commercial graphite electrodes for LIBs before and after conducting a pre‐charging protocol. Changes in electrochemical activity and topography of the graphite electrode were resolved in simultaneously generated SECM/SICM recordings.

UnDrift: A versatile software for fast offline SPM image drift correction.

Scanning probe microscopy (SPM) techniques are widely used to study the structure and properties of surfaces and interfaces across a variety of disciplines in chemistry and physics. One of the major artifacts in SPM is (thermal) drift, an unintended movement between sample and probe, which causes a distortion of the recorded SPM data. Literature holds a multitude of strategies to compensate for drift during the measurement (online drift correction) or afterwards (offline drift correction). With the currently available software tools, however, offline drift correction of SPM data is often a tedious and time-consuming task. This is particularly disadvantageous when analyzing long image series. Here, we present unDrift, an easy-to-use scientific software for fast and reliable drift correction of SPM images. unDrift provides three different algorithms to determine the drift velocity based on two consecutive SPM images. All algorithms can drift-correct the input data without any additional reference. The first semi-automatic drift correction algorithm analyzes the different distortion of periodic structures in two consecutive up and down (down and up) images, which enables unDrift to correct SPM images without stationary features or overlapping scan areas. The other two algorithms determine the drift velocity from the apparent movement of stationary features either by automatic evaluation of the cross-correlation image or based on positions identified manually by the user. We demonstrate the performance and reliability of unDrift using three challenging examples, namely images distorted by a very high drift velocity, only partly usable images, and images exhibiting an overall weak contrast. Moreover, we show that the semi-automatic analysis of periodic images can be applied to a long series containing hundreds of images measured at the calcite-water interface.

(Invited) Advanced Scanning Probe Microscopy for Studying Biofilm Formation and Single Cell Entities at Electrified Interfaces

Advanced scanning probe microscopy techniques such as atomic force – scanning electrochemical microscopy (AFM-SECM) und scanning electrochemical microscopy (SECM) are highly attractive hybrid techniques for studying biomedically relevant samples down to the single entity level. Our group introduced a new type of AFM-SECM probe having a conductive colloid instead of a sharp AFM tip. As this spherical microelectrode, which is located at the end of an electrically insulated AFM cantilever can be easily modified by electrodeposition with e.g., conductive polymers and electrocatalytic layers, single cell force spectroscopy under potential control allows studying adhesion properties [1,2]. Cell adhesion is a crucial parameter not only for developing new materials serving as substrates for neural scaffolds, electrodes, and biomedical devices but also in biofilm formation. Biofilms are well-organized aggregates of bacteria able to attach to and proliferate at almost every type of solid surface resulting in increased resistance to conventional antimicrobial and antibiofouling agents [3].The first attachment of bacterials is a process highly influenced by the nature of the surface, such as hydrophobicity, chemical structure, surface charge, and presence of antimicrobials [4].In this contribution, we present the potential of various scanning probe microscopy techniques, as suitable tools to locally investigate the early stages of biofilm formation and the effects of various antibiofouling and antimicrobial systems against Escherichia coli and Pseudomonas fluorescens. For example, the properties of polydopamine, a bio-compatible polymer, are studied in respect to early stages of bacterial adhesion in dependence of surface charge density and applied potential [5]. Colloidal conductive AFM probes can also be modified electrocatalytic layers, suitable for detecting signaling molecules and at the same time allow electrochemical force spectroscopy at soft samples like biomedically relevant single entities.

(Invited) Transparent Conductive Films of PEDOT:PSS-Amino Acid Composite

Transparent conductive electrode is an important component of optoelectronic devices such as light emitting diodes, photodiodes, and photovoltaic cells as well touchscreen technology. Growing demand for these technologies, as well as need for functionalities such as cost-effectiveness and flexibility, has resulted in various research on developing organic polymer-based transparent electrodes as an alternative to indium tin oxide (ITO) which is the current industry standard. One of the organic conducting polymers most commonly studied for their potential to be used as ITO-free transparent electrodes is PEDOT:PSS due to its high transmittance as a thin film, solution processability, flexibility, environmental stability, and commercial availability. There have been various works carried out to improve the conductivity of the PEDOT:PSS-based thin films by introducing dopants to improve the charge transport. We present our results demonstrating that not only the conductivity but also the transmittance of PEDOT-PSS-based films can be significantly improved by the introduction of amino acids such as phenylalanine in the film. We have observed that this enhancement in conductivity and optical transmittance of PEDOT:PSS-phenylalanine composite film is retained even when the amount of amino acid in the composite films is larger than the amount of PEDOT:PSS. We will present our study on the charge transport mechanism on these films based on electrochemical impedance spectroscopy (EIS) measurements. We will also further present our studies based on Scanning Electron Microscopy (SEM) as well as Scanning Probe Microscopy techniques such as topography imaging and conducting probe atomic force microscopy (CP-AFM) to elucidate the relationship between film morphology and charge transport in these composite films. The use of bioderived materials such as amino acids to create transparent composite films could open up avenues for developing and integrating bio-based materials in future electronics, help improve the environmental footprint of the electronics, and potentially also allow for the development of materials with a higher degree of biocompatibility for their application in bioelectronics.

(Invited) Insights into Processes at the Electrode/Electrolyte Interface of Battery Electrodes Via Scanning (Electrochemical) Probe Microscopy

Scanning (electrochemical) probe microscopy (SEPM) techniques such as atomic force microscopy (AFM), scanning electrochemical microscopy (SECM), nano-pipette derived scanning probe methods like scanning electrochemical cell microscopy (SECCM) and hybrid methods have recently been used to study interfacial processes occurring at solid/electrolyte interfaces of battery electrodes [1]. So far, mainly Lithium-ion battery (LIB) electrodes have been studied, such as the solid-electrolyte interphase formation at graphite anodes [2,3]. Next generation battery chemistries, using earth abundant elements like sodium (Na), potassium (K), aluminum (Al) improving sustainability still suffer from insufficient knowledge of processes occurring during cycling at the electrode/electrolyte interface such as interphase formation, as gained insights from Li batteries cannot simply be transferred to post-Li chemistries.In this contribution, an overview of the potential of SEPM techniques to gain insight in interfacial process of post-Li battery chemistries will be given, focusing mainly on the SEI formation on hard carbon composite anodes for Na-ion batteries (SIBs) [4]. The influence of the electrolyte composition along with the effects of additives on the SEI formation and the nanomechanical properties of the electrode will be presented. In addition, given the abundance of Al and the high theoretical volumetric capacity, makes Al a highly attractive battery chemistry [5]. Despite these advantages, there are several challenges like the Al2O3 passivating layer and the mostly used acidic ionic liquid (IL)-based electrolyte AlCl3/1-ethyl-3-methylimidazolium chloride [EMIm]Cl that leads to corrosion, which determines the plating and stripping efficiency and therefore the overall performance. First correlative SECCM/EDX/EBSD studies on Al anodes will be presented. Acknowledgement This work contributes to the research performed at CELEST (Center for Electrochemical Energy Storage Ulm - Karlsruhe) and was funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany's Excellence Strategy – EXC 2154 – Project number 390874152 (POLiS Cluster of Excellence).

Scanning Probe Microscopy Techniques for Studying the Cell Glycocalyx.

The glycocalyx is a brush-like layer that covers the surfaces of the membranes of most cell types. It consists of a mixture of carbohydrates, mainly glycoproteins and proteoglycans. Due to its structure and sensitivity to environmental conditions, it represents a complicated object to investigate. Here, we review studies of the glycocalyx conducted using scanning probe microscopy approaches. This includes imaging techniques as well as the measurement of nanomechanical properties. The nanomechanics of the glycocalyx is particularly important since it is widely present on the surfaces of mechanosensitive cells such as endothelial cells. An overview of problems with the interpretation of indirect data via the use of analytical models is presented. Special insight is given into changes in glycocalyx properties during pathological processes. The biological background and alternative research methods are briefly covered.

Scanning probe microscopy in the age of machine learning

Scanning probe microscopy (SPM) has revolutionized our ability to explore the nanoscale world, enabling the imaging, manipulation, and characterization of materials at the atomic and molecular level. However, conventional SPM techniques suffer from limitations, such as slow data acquisition, low signal-to-noise ratio, and complex data analysis. In recent years, the field of machine learning (ML) has emerged as a powerful tool for analyzing complex datasets and extracting meaningful patterns and features in multiple fields. The combination of ML with SPM techniques has the potential to overcome many of the limitations of conventional SPM methods and unlock new opportunities for nanoscale research. In this review article, we will provide an overview of the recent developments in ML-based SPM, including its applications in topography imaging, surface characterization, and secondary imaging modes, such as electrical, spectroscopic, and mechanical datasets. We will also discuss the challenges and opportunities of integrating ML with SPM techniques and highlight the potential impact of this interdisciplinary field on various fields of science and engineering.

Nano-scale wear: A critical review on its measuring methods and parameters affecting nano-tribology

This paper presents a critical review on the measuring methods and parameters affecting nano-tribology in the context of nano-scale wear. Nano-scale wear phenomena play a crucial role in various industries, including micro/nano-systems, electronics, and biotechnology. The review begins by discussing the significance of nano-scale wear and its impact on device performance, lifespan, durability, energy efficiency, cost savings, and environmental sustainability. It then delves into the measuring methods employed to assess nano-scale wear, including scanning probe microscopy (SPM) techniques such as atomic force microscopy (AFM) and friction force microscopy (FFM). The capabilities of AFM and FFM in studying the roughness of surface, adhesion, friction, scratch, abrasion, and nano-scale material transfer are highlighted. Additionally, the review explores the parameters affecting nano-wear, such as lubrication strategies, stress levels, sliding velocity, and atomic-scale reactions. The article concludes by emphasizing the importance of advanced microscopy techniques in understanding tribological mechanisms at different scales, bridging the gap between macro and nano-tribology studies.

Piezoelectricity of Bi2Se3 Nanosheet.

Bi2Se3, one of the most extensively studied topological insulators, has received significant attention, and abundant research has been dedicated to exploring its surface electronic properties. However, little attention has been given to its piezoelectric properties. Herein, we investigate the piezoelectric response in a five-layer Bi2Se3 nanosheet using scanning probe microscopy (SPM) techniques. The piezoelectricity of Bi2Se3 is characterized using both conventional piezoresponse force microscopy (PFM) and a sequential excitation scanning probe microscopy (SE-SPM) technique. To confirm the linear piezoelectricity of Bi2Se3 two-dimensional materials, measurements of point-wise linear and quadratic electromechanical responses are carried out. Furthermore, the presence of polarization and relaxation is confirmed through hysteresis loops. As expected, the Bi2Se3 nanosheet exhibits an electromechanical solid response. Due to the inevitable loss of translational symmetry at the crystal edge, the lattice of the odd-layer Bi2Se3 nanosheet is noncentrosymmetric, indicating its potential for linear piezoelectricity. This research holds promise for nanoelectromechanical systems (NEMS) applications and future nanogenerators.

Robust Switchable Polarization and Coupled Electronic Characteristics of Magnesium-Doped Zinc Oxide.

Ferroelectrics possess a spontaneous polarization that is switchable by an electric field and is critical for the development of low-energy nanoelectronics and neuromorphic applications. However, apart from a few recent developments, the realization of switchable polarization in metal oxides with simpler structures has been a major challenge. Here, we demonstrate the presence of robust switchable polarization at the level of a single nanocrystallite in magnesium-doped zinc oxide thin films with polar wurtzite crystal structures. Using a combination of high-resolution scanning probe microscopy and spectroscopic techniques, voltage control of the polarization and the coupled electronic transport behavior revealing a giant resistance change of approximately 10000% is unveiled. Time- and frequency-resolved nanoscale measurements provide key insights into the polarization phenomenon and a 9-fold increase in the effective longitudinal piezoelectric coefficient. Our work thus constitutes a crucial step toward validating nanoscale ferroelectricity in polar wurtzites for use in advanced nanoelectronics and memory applications.

Localized Tortuosity Determination of Li-Ion Battery Electrode Using SECM and SICM

Li-ion batteries’ limited power represents a barrier to their application in the domain of renewable energy. To examine the origin of this limitation, the effect of microstructural parameters such as porosity and tortuosity on ionic transport, especially through the electrolyte within the electrode pores needs to be studied. In this work, we tried to determine the local tortuosity in Li4Ti5O12 (LTO) electrodes with various porosities using two scanning probe microscopic techniques: Scanning Ion Conductance Microscopy (SICM) and Scanning Electrochemical Microscopy (SECM). SICM measures the effective ionic conductivity of Li+ ions whereas SECM probes the diffusion of electroactive species like anthracene.1,2 We observed that in both cases, the normalized current increases with porosity as more ions reach the tip through the pores of the electrode. The MacMullin number calculated from SICM and SECM measurements for the LTO electrodes having porosities from 50% to 63% shows that these techniques are complementary. Improved transport through these porous electrodes is indicated by the lower tortuosity values obtained compared to those anticipated by the mass transport models like the Bruggeman relationship. Hence, the tortuosity values determined from these microscopic techniques can be used as a strong tool to improve the modeling of electrolyte transport within electrodes. In turn, this should be highly valuable in the design of batteries with high power density.

Quantitative Mapping of Chemical Defects at Charged Grain Boundaries in a Ferroelectric Oxide.

Polar discontinuities, as well as compositional and structural changes at oxide interfaces can give rise to a large variety of electronic and ionic phenomena. In contrast to earlier work focused on domain walls and epitaxial systems, here, w e investigate the potential relation between polar discontinuities and the local chemistry at grain boundaries in polycrystalline ferroelectric ErMnO3 . Using orientation mapping and different scanning probe microscopy techniques, w e demonstrate that the polycrystalline material develops charged grain boundaries with enhanced electronic conductance. By performing atom probe tomography measurements, w e find an enrichment of erbium and a depletion of oxygen at all grain boundaries. The observed compositional changes translate into a charge that exceeds possible polarization-driven effects, demonstrating that structural phenomena rather than electrostatics determine the local chemical composition and related changes in the electronic transport behavior. The study shows that the charged grain boundaries behave distinctly different from charged domain walls, giving additional opportunities for property engineering at polar oxide interfaces. This article is protected by copyright. All rights reserved.

In situ characterization of Ni-rich NMC811 thin films prepared by sol-gel method using different scanning probe microscopy techniques

In this paper, LiNi0.8Co0.1Mn0.1O2 (NMC811) thin films were prepared by the sol-gel method based on different parameter conditions, and the microstructure and electrochemical properties of the films were compared to obtain the film sample under the best preparation parameters. In order to explain the formation mechanism of cell battery performance based on the NMC811 cathode at the nano scale, electrochemical strain microscopy, conductive atomic force microscopy and Kelvin probe force microscopy are specifically utilized to study the changes of NMC811 thin film in electrochemical deformation, conductivity, and potential distribution under different electrical and thermal fields. The results indicate that the local amplitude, conductivity, and electrical potential of thin film in the scanning region increases with the voltage from 0 V to 3 V and the temperature from 25 °C to 150 °C. However, the electrochemical deformation, conductivity, and potential of the film decrease significantly when the voltage is applied to 4 V or the temperature rises to 200 °C.These results provide visual evidence for the influence of external field on the phase structure change and lithium-ion diffusion behavior of NMC811 thin film.

Imaging beyond the surface region: Probing hidden materials via atomic force microscopy.

Probing material properties at surfaces down to the single-particle scale of atoms and molecules has been achieved, but high-resolution subsurface imaging remains a nanometrology challenge due to electromagnetic and acoustic dispersion and diffraction. The atomically sharp probe used in scanning probe microscopy (SPM) has broken these limits at surfaces. Subsurface imaging is possible under certain physical, chemical, electrical, and thermal gradients present in the material. Of all the SPM techniques, atomic force microscopy has entertained unique opportunities for nondestructive and label-free measurements. Here, we explore the physics of the subsurface imaging problem and the emerging solutions that offer exceptional potential for visualization. We discuss materials science, electronics, biology, polymer and composite sciences, and emerging quantum sensing and quantum bio-imaging applications. The perspectives and prospects of subsurface techniques are presented to stimulate further work toward enabling noninvasive high spatial and spectral resolution investigation of materials including meta- and quantum materials.

Advances in probing single biomolecules: From DNA bases to glycans

AbstractImaging biomolecules in real space is crucial for gaining a comprehensive understanding of the properties and functions of biological systems at the most fundamental level. Among the various imaging techniques available for biomolecules and their assembled nanostructures, scanning probe microscopy (SPM) provides a powerful and nondestructive imaging option. SPM is unique in visualizing intrinsically disordered biomolecules at the nanometer scale (e.g., glycans). This review highlights recent achievements in studying biomolecules using SPM technique, focusing on DNA bases, amino acids, proteins, and glycans. The atomic‐level analysis of biomolecules made possible by SPM allows for a more accurate definition of the local structure–property relationship. High‐resolution SPM imaging of single biomolecules offers a new way to study basic processes of life at the molecular level.