Scanning Probe Microscopy Images Research Articles

МЕТОДИ ПІДВИЩЕННЯ ТОЧНОСТІ ВИМІРЮВАННЯ СКАНУЮЧИМ ЗОНДОВИМ МІКРОСКОПОМ В ЗАЛЕЖНОСТІ ВІД ГЕОМЕТРІЇ ЗОНДУ

The article analyzes the influence of different types of probe geometry of a scanning probe microscope (SPM) on the features of measuring the surface topography of a nano-object. Based on the analysis, it was determined that the main drawback inherent in all modes of scanning probe microscopy is the finite size of the measuring probe tip, which cannot reach certain areas of the measuring surface during scanning, which is caused by the geometric characteristics of the probe shape. This leads to a significant deterioration of the spatial resolution and significant distortions in the SPM images when scanning surfaces with large unevenness of the ratio between the typical vertical and horizontal dimensions. Based on the conducted research, the methods of restoration of SPM images are proposed, which are built on mathematical and computer processing of SPM data, which takes into account the specific shape of the probe tip and allows improving the metrological characteristics of the measurement information. It is proved that the SPM image and the experimentally obtained shape of the tip are two-dimensional arrays of discrete values, for which the derivative is an incorrectly determined value. It is recommended that instead of deriving discrete functions during the numerical deconvolution of SPM images, during scanning with a constant average height, use the requirement for the minimum distance of the tip to the surface. It has been proven that the most effective way of digital correction of the surface topography is numerical deconvolution using the tip image obtained experimentally by scanning test structures with a well-known topography and subsequent computer processing of the data. A method of partial restoration of the topography is proposed, which is characterized by flexibility to the set metrological tasks and is aimed at increasing the speed of computing operations while ensuring the necessary accuracy of measurement information.

Machine Vision Automated Chiral Molecule Detection and Classification in Molecular Imaging.

Scanning probe microscopy (SPM) is recognized as an essential characterization tool in a broad range of applications, allowing for real-space atomic imaging of solid surfaces, nanomaterials, and molecular systems. Recently, the imaging of chiral molecular nanostructures via SPM has become a matter of increased scientific and technological interest due to their imminent use as functional platforms in a wide scope of applications, including nonlinear chiroptics, enantioselective catalysis, and enantiospecific sensing. Due to the time-consuming and error-prone image analysis process, a highly efficient analytic framework capable of identifying complex chiral patterns in SPM images is needed. Here, we adopted a state-of-the-art machine vision algorithm to develop a one-image-one-system deep learning framework for the analysis of SPM images. To demonstrate its accuracy and versatility, we employed it to determine the chirality of the molecules comprising two supramolecular self-assemblies with two distinct chiral organization patterns. Our framework accurately detected the position and labeled the chirality of each molecule. This framework underpins the tremendous potential of machine learning algorithms for the automated recognition of complex SPM image patterns in a wide range of research disciplines.

Measurement of the Length of Objects on Scanning Probe Microscope Images Using Curvature Detectors

Measurement of the Length of Objects on Scanning Probe Microscope Images Using Curvature Detectors

Removing background and estimating a unit height of atomic steps from a scanning probe microscopy image using a statistical model.

We present a statistical method to remove background and estimate a unit height of atomic steps of an image obtained using a scanning probe microscope. We adopt a mixture model consisting of multiple statistical distributions to describe an image. This statistical approach provides a comprehensive way to subtract a background surface even in the presence of atomic steps as well as to evaluate terrace heights in a single framework. Moreover, it also enables us to extract further quantitative information by introducing additional prior knowledge about the image. An example of this extension is estimating a unit height of atomic steps together with the terrace heights. We demonstrate the capability of our method for a topographic image of a Cu(111) surface taken using a scanning tunneling microscope. The background subtraction corrects all terraces to be parallel to a horizontal plane, and the precision of the estimated unit height reaches the order of a picometer. An open-source implementation of our method is available on the web.

Development of Environmentally Safe Biodegradable, Antibacterial Surgical Sutures Using Nanosilver Particles

Bacterial infection from medical devices is a significant problem and accounts for an increasing number of deaths and high medical costs. Surgical sutures are a major source of nosocomial infection through surgical wound contamination and the rates of which are increasing globally. One efficient way to prevent this is by modifying the surface of the sutures in such a way that no bacterial adhesion can occur. In this investigation, biodegradable polymer sutures with excellent antibacterial properties were developed. Antibacterial properties were achieved by coating nanosilver incorporated biopolymer polycaprolactone material on the surface of the sutures. Biocompatible polyethylene glycol was selected as the solvent for the dispersion of nanosilver particles, which improved the mechanical properties of the sutures. The nanoparticle coating was found to be uniform and more effective with the electrospinning method. The mechanical property of the coated suture was analysed using the Universal Test Method, and the results were in agreement with the standard results. The surface morphology of coated sutures becomes uniform on adding nanosilver particles, confirmed by scanning electron microscope studies. A comparative study of force–displacement, hardness, and reduced modulus as a function of contact depth indentation tests were performed on coated and uncoated suture samples using a Nanoindentation Test Machine. In-situ Scanning Probe Microscopy images were captured for coated and uncoated suture materials. These studies confirmed a new strategy in developing antibacterial sutures suitable for wound closure following surgery.

Measuring the length of objects on scanning probe microscope images using curvature detectors

The article is devoted to the automatic measurement of objects longitudinal dimensions on images obtained by probe microscopy. The solution of this problem can be relevant for quality control of microelectronics, nanotechnics products and materials. Existing tools for objects length measuring are compared by means of test image containing geometric figures with known dimensions. The advantages of software surface curvature detectors, intended for objects lengths measuring directly on a halftone image by forming the skeleton of an object with a surface curvature detector, are shown. A two-dimensional “Circle” detector, based on the curvature analysis of raster images line and column profilograms, was used for the measuring. The curvature was estimated based on the area of the figure bounded by the profilogram at a predefined interval. Features of measuring the length of objects using curvature maxima are considered. It is shown that the curvature detector allows to more accurately determine the lengths of objects with overlapping contours and a significant brightness range. Algorithms of the detector operation, formation of the object skeleton and determination of its length are described. The results of investigation confirming the performance of the presented algorithms are presented. Comparative analysis with existing length measurement tools, performed on magnetic disk domains and nanopolymer fibers images, showed a more correct detector operation in sceletonization of object and measuring its length.

Study of the dental zirconium implant surface in a nano-scale using an atomic-force microscope

The influence of various surface treatments of zirconium implants on the adhesion strength in the connection “individual milled transdental implant – cement – hard tooth tissues” was investigated. As analogs of such implants, we used pins made of zirconium dioxide, individually made for prepared previously extracted teeth, in combination with the most effective Fuji-1 and Multilink-N cements. To assess the quality of the formed "cleanliness" of the surface, the experiments were carried out in two stages. At the first stage, the specimens were processed by a sandblasting machine under a pressure of 2 atmospheres by aluminum oxide powder with a grain size of 50, 100 and 250 μm. The treatment was carried out once in one direction, longitudinally to the axis of the implant. At the second stage, the same specimens were processed again in the same mode, but in two directions. The processed specimens were studied in a probe nanolaboratory (Troitsk, Russia) using an atomic force microscope (AFM). Roughness parameters were measured in nanometers on each sample from three images of a scanning probe microscope (SPM). Analysis of the SPM images revealed that the roughness of the specimens is higher when processed with larger grains. The results of the study showed that a single sandblasting by zirconium dioxide is quite enough to improve the adhesive properties of the implants both to the fixing cements and to the patient's bone tissue.

Improving the segmentation of scanning probe microscope images using convolutional neural networks

A wide range of techniques can be considered for segmentation of images of nanostructured surfaces. Manually segmenting these images is time-consuming and results in a user-dependent segmentation bias, while there is currently no consensus on the best automated segmentation methods for particular techniques, image classes, and samples. Any image segmentation approach must minimise the noise in the images to ensure accurate and meaningful statistical analysis can be carried out. Here we develop protocols for the segmentation of images of 2D assemblies of gold nanoparticles formed on silicon surfaces via deposition from an organic solvent. The evaporation of the solvent drives far-from-equilibrium self-organisation of the particles, producing a wide variety of nano- and micro-structured patterns. We show that a segmentation strategy using the U-Net convolutional neural network has some benefits over traditional automated approaches and has particular potential in the processing of images of nanostructured systems.

Scanning Electrochemical Cell Microscopy; Measurement Process Optimization to the Electrochemical Response Based on Experimental Parameters

As the development of scanning probe microscopy (SPM) continues, the spatial resolution and sensitivity for various material properties steadily improve. Therefore, SPM images morphological features as well as electrical, mechanical, magnetic, and chemical properties with a nanoscale resolution. Among the various SPM techniques, pipette-based SPM offers new possibilities and insights into the sample’s electrochemical properties. Since the invention of scanning electrochemical microscopy (SECM), the first-generation pipette-based SPM for electrochemical measurement, it has been extensively used in many research fields, e.g. for visualizing chemical reactions at surfaces and interfaces. However, the difficult distance control between the pipette probe and the sample surface limits the application of SECM.Here, we introduce scanning electrochemical cell microscopy (SECCM): a latest pipette-based SPM method, which investigates electrochemical responses on target materials in a point-by-point approach using the ionic current for distance control. We present experimental and theoretical data on contributing factors to the electrochemical response, including pipette configuration, redox species, scan rate and choice of substrate. A variety of pipette inner diameters (range from ~150 nm to ~ 1 μm), buffer concentrations, and voltammetric sweep rates are reviewed using well-defined conductive substrates and electrodes. Based on our results, we propose optimized experimental parameters for various measurement conditions. We believe that SECCM has great potential in providing new insights to electrochemical properties of surfaces and interfaces required for research on chemical energy storage, among others. Figure 1

Defect identification and statistics toolbox: automated defect analysis for scanning probe microscopy images

Identifying and classifying defects in scanning probe microscopy (SPM) images is an important task that is tedious to perform by hand. In this paper we present the defect identification and statistics toolbox (DIST), an image processing toolbox for identifying and analyzing atomic defects in SPM images. DIST combines automation with user input to accurately and efficiently identify defects and automatically compute critical statistics. We describe using DIST for interactive image processing, generating contour plots for isolating extrema from an image background, and processes for identifying defects.

Effects of discharging vibration conditions and coating structures on improving discharge particle flowability in a smaller particle admixing system

Particle flowability can be improved by admixing particles smaller than the original particles (main particles). However, the effects of coating structures on the improvement of flowability are not yet fully understood. In this study, we focused on vibrating discharge particle flowability and investigated the effect of discharging vibration conditions and coating structures on improving the flowability. Main and admixed particles of 60.8 μm and 8 nm in diameter, respectively, were mixed in various mass ratios, and the discharge particle flow rates of the mixed particles were measured. Scanning electron microscopy and scanning probe microscopy images were used to analyze the coverage diameter, surface coverage ratio, and coverage height of the admixed particles on the main particle surfaces. As a result, the admixing mass ratio that gave maximum flowability was found to depend on the maximum value of the vibration acceleration. This could be explained by the relationship between the coating structures of admixed particles and the coated average surface distances due to the vibration acceleration.

Effect of reduced graphene oxide overcoating on scratch resistance of Ag nanowire electrodes

In this study, the effect of reduced graphene oxide (rGO) overcoating on the scratch resistance of Ag nanowire electrodes was explored for the first time. By performing nanoscratch tests on the nanowire electrodes with and without the rGO overcoating, the lateral forces imposed on the samples were measured when the nanoscale tip was moved laterally; these forces were correlated to the scratch resistance. The lateral forces of the Ag nanowire electrode with an rGO overcoating were significantly higher than those of the uncoated electrode, indicating an increased resistance to the lateral movement of the tip and thus an enhanced scratch resistance. Furthermore, scanning probe microscope images showed that the Ag nanowire electrode without an rGO overcoating exhibited wider scratches after testing than those observed at the coated electrode. These results confirmed that rGO overcoating is effective for enhancing the scratch resistance of Ag nanowire electrodes.

Imaging the flow of holes from a collimating contact in graphene

A beam of holes formed in graphene by a collimating contact is imaged using a liquid-He cooled scanning probe microscope (SPM). The mean free path of holes is greater than the device dimensions. A zigzag shaped pattern on both sides of the collimating contact absorbs holes that enter at large angles. The image charge beneath the SPM tip defects holes, and the pattern of flow is imaged by displaying the change in conductance between contacts on opposite sides, as the tip is raster scanned across the sample. Collimation is confirmed by bending hole trajectories away from the receiving contact with an applied magnetic field. The SPM images agree well with ray-tracing simulations.

Scanning probe microscopy cantilevers improvement for advanced research and manipulation at nano scale.

Scanning probe microscopy (SPM) is a widely used method for the different kind of objects investigation. It allows to obtain information about the surface topography including its mechanical and electromagnetic characteristics at nano scale. SPM also could be used for manipulation of nanoobjects. The most popular and widely used SPM methods are atomic force (AFM) and magnetic force microscopy (MFM). Both of them based on measuring interaction between sample and cantilever (probe). Type of cantilever its curvature radius, coating, resonant frequency, hardness and other parameters significantly influence on the SPM images. Scientist constantly improving process of probes producing to fit the current demands. It is important to keep in mind that collected AFM data could contain not only direct information about the sample but also it might be a convolution of the sample and cantilever in case then the tip size comparable with the studied object. Convolution effect limits the AFM resolution [1]. Thus one of the most important task for researchers is to minimize this effect by reducing tip size both for AFM and MFM methods.

Tailoring molecular island shapes: influence of microscopic interaction on mesostructure

Controlling the structure formation of molecules on surfaces is fundamental for creating molecular nanostructures with tailored properties and functionalities and relies on tuning the subtle balance between intermolecular and molecule-surface interactions. So far, however, reliable rules of design are largely lacking, preventing the controlled fabrication of self-assembled functional structures on surfaces. In addition, while so far many studies focused on varying the molecular building blocks, the impact of systematically adjusting the underlying substrate has been less frequently addressed. Here, we elucidate the potential of tailoring the mesoscopic island shape by tuning the interactions at the molecular level. As a model system, we have selected the molecule dimolybdenum tetraacetate on three prototypical surfaces, Cu(111), Au(111) and CaF2(111). While providing the same hexagonal geometry, compared to Cu(111), the lattice constants of Au(111) and CaF2(111) differ by a factor of 1.1 and 1.5, respectively. Our high-resolution scanning probe microscopy images reveal molecular-level information on the resulting islands and elucidate the molecular-level design principles for the observed mesoscopic island shapes. Our study demonstrates the capability to tailor the mesoscopic island shape by exclusively tuning the substrate lattice constant, in spite of the very different electronic structure of the substrates involved. This work provides insights for developing general design strategies for controlling molecular mesostructures on surfaces.

Nanomechanical and nanotribological properties of self-lubricating Ti/MoS<SUB align="right">2 nanocoating at nanoscale level

Ti/MoS2 coating of thickness 99.79 nm was prepared by pulse laser deposition method on Al-Si substrate. Mechanical and nanotribological properties of Ti/MoS2 coating were obtained by carrying out nanoindentation, nanoscratch and nanowear tests at low loads. It was observed that Young's modulus and nanohardness of Ti/MoS2 coating decrease with increasing load. The coefficient of friction also decreases with the increase in sliding distance, which proves that Ti/MoS2 coating have self-lubricating property. The wear rate of Ti/MoS2 coating increases from 5.7 × 10−10 mm3/Nm to 2.1 × 10−9 mm3/Nm with the increase in load. Scanning probe microscope images of Ti/MoS2 coating shows the plastic flow of coating with no debris and cracks on the surface. It indicates that the abrasive wear is the main wear mechanism.

Adhesion Property of Self-lubricating Si/MoS2 Nanocoating at Nano-scale Level

Nanoscratch test was performed on self-lubricating Si/MoS2 nanocoating of 115 nm thickness prepared by pulse laser deposited technique on Al-13Si substrate. The surface morphology and surface elemental analysis of Si/MoS2nanocoated sample were studied using Scanning electron microscope integrated with Energy dispersive X-ray spectroscopy. The structural analysis of Si/MoS2 nanocoating was conducted using X-ray diffraction and Raman spectroscopy. Nanoscratch tests were conducted at low load of 250-1250 µN to examine the adhesion, deformation and failure behaviour of the coating/substrate system. The results indicate that Si/MoS2 nanocoating show better adhesion strength at low loads. Also, in-situ scanning probe microscope images of Si/MoS2nanocoating shows plastic flow of coating with no debris and cracks on the surface. Therefore, the wear mechanism is mostly ductile and abrasive.

Atomistic Simulations in Surface Chemistry to Interpret Scanning Probe Microscopy Images: A Short Review.

Atomistic simulations are a powerful tool to explain and guide experimental investigations, but there are cases where a clear correspondence is difficult to obtain. While the theoretical framework to get the static picture of the equilibrium structures in vacuum is well-established, it is challenging to correctly model them in operando conditions (at the right experimental temperature, pH and pressure). In this short review the main theoretical approaches are briefly presented, supported by selected case studies where the structural and dynamical properties of different systems are investigated. A successful match with the experimental data is accomplished by choosing the proper level of theory in order to describe the structure under study in the most accurate and realistic way.

Fast mechanical model for probe–sample elastic deformation estimation in scanning probe microscopy

We present a numerical approach for estimation of the probe–sample elastic deformation for higher contact forces and/or smaller probe apex radii in Scanning Probe Microscopy (SPM) measurements. It is based on a mass-spring model implemented on a graphics card in order to perform very high numbers of individual force–distance curves calculations in reasonable time, forming virtual profiles or virtual SPM images. The model is suitable for predicting the mechanical response of the probe and sample in SPM mechanical properties mapping regimes and for estimating the uncertainty sources related to probe-sample elastic deformation in dimensional nanometrology. As the model is based on using regular orthogonal mesh formed from the scanned surface topography, it can be also used as preprocessor for various pixel by pixel physical quantities calculations using Finite Difference Method, namely for the energy transfer between probe and sample, where a realistic probe–sample contact formation needs to be taken into account. Model performance is demonstrated via comparison to analytical solutions for simple contact mechanics tasks and its possibilities for SPM data interpretation are illustrated on measurements on simple reference structures, such as step edges or quantum dots.

A method to correct hysteresis of scanning probe microscope images based on a sinusoidal model.

Piezoelectric actuators are widely used in scanning platforms of scanning probe microscopes (SPMs). However, the hysteresis of piezoelectric actuators reduces positioning accuracy and results in distorted SPM images. When regular raster scanning of SPM starts, the piezoelectric actuators move repeatedly at the same scanning range and frequency once the scanning parameters are set. In this study, a practical and simple mathematical model derived from experimental phenomenon, which is the combination of sinusoidal and linear functions, was proposed to describe the hysteresis behavior of piezoelectric actuators with repeated scanning. The model parameter was calculated from the coordinates of matched feature points in the trace and retrace images of ordinary sample obtained with an atomic force microscope (AFM). Experimental results show that the hysteresis of the scanned images is decreased from 107.46 pixels to 2.50 pixels after correction, with a width of 800 pixels. Hysteresis in other scanned images with different scanning frequencies and ranges was also corrected effectively using this model. The proposed model can be used to correct the hysteresis of AFM images without using any expensive displacement sensors or standard samples. The model is suitable and easy to be integrated into the scanning program of AFM without requiring hardware modifications.