Atomic Force Microscopy Probe Research Articles

Local intracellular stiffening of ascidian embryo in cleavage developmental stage observed by atomic force microscopy

During the cleavage stage in ascidian embryos, cells undergo repeated and regular cell division in the animal hemisphere. We investigated how the intracellular stiffness, that is, the apparent Young’s modulus of cells in the animal hemisphere changes in the cleavage stages from the 16-cell to 76-cell stages using atomic force microscopy (AFM). The AFM force mapping experiments showed that a pair of dot-like stiffening clearly appeared in the intracellular region, which involves the cortical and cytoplasmic regions indented by the AFM probe, in a period of the interphase after cell division. The dot-like structures disappeared before beginning to increase the whole cell stiffening towards the proceeding mitotic phase. We found that the positioning of a pair of dots was located so as to intersect the daughter cells formed in the proceeding cell division. These results suggest that the local intracellular stiffening observed in the interphase may play an important role in controlling the orientation of the mitotic spindle that determines the direction of cell division.

Carbon nanocone mechanical behavior and their use as AFM tips for the characterization of polymers in Peak Force mode

Compared to carbon nanotube-based Atomic Force Microscopy probes, carbon nanocone-based probes appear as promising candidates for investigating topography and mechanical properties thanks to the reduced number of artefacts. In this paper, we intend to investigate some of the mechanical features of carbon nanocone (CnC) tips and to evaluate their performances as probes for investigating the mechanical properties of polymer films and composites. Using their force distance curve, the cantilever/CnC spring constant of several CnC probes is determined and the related bending force for each cone is extracted. The results demonstrate CnC bending forces ranging from 100 nN up to 3 μN, which is up to 2 orders of magnitude higher than values reported in the literature for carbon nanotubes. Moreover, the bending phenomenon occurred only when the CnC axis was not strictly perpendicular to the substrate surface. Using Peak-Force Quantitative NanoMechanical (PF-QNM) mode, we demonstrate that CnC probes are suitable to accurately probe polymer mechanical properties, provided the same targeted deformation is used for both the calibration and PF-QNM measurements.

Photoswitchable optoelectronic properties of 2D MoSe2/diarylethene hybrid structures

The ability to modulate optical and electrical properties of two-dimensional (2D) semiconductors has sparked considerable interest in transition metal dichalcogenides (TMDs). Herein, we introduce a facile strategy for modulating optoelectronic properties of monolayer MoSe2 with external light. Photochromic diarylethene (DAE) molecules formed a 2-nm-thick uniform layer on MoSe2, switching between its closed- and open-form isomers under UV and visible irradiation, respectively. We have discovered that the closed DAE conformation under UV has its lowest unoccupied molecular orbital energy level lower than the conduction band minimum of MoSe2, which facilitates photoinduced charge separation at the hybrid interface and quenches photoluminescence (PL) from monolayer flakes. In contrast, open isomers under visible light prevent photoexcited electron transfer from MoSe2 to DAE, thus retaining PL emission properties. Alternating UV and visible light repeatedly show a dynamic modulation of optoelectronic signatures of MoSe2. Conductive atomic force microscopy and Kelvin probe force microscopy also reveal an increase in conductivity and work function of MoSe2/DAE with photoswitched closed-form DAE. These results may open new opportunities for designing new phototransistors and other 2D optoelectronic devices.

Nanoscale Structure of Lipid-Gemini Surfactant Mixed Monolayers Resolved with AFM and KPFM Microscopy.

Drug delivery vehicles composed of lipids and gemini surfactants (GS) are promising in gene therapy. Tuning the composition and properties of the delivery vehicle is important for the efficient load and delivery of DNA fragments (genes). In this paper, we studied novel gene delivery systems composed of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), 1,2-dipalmitoyl-sn-3-phosphocholine (DPPC), and GS of the type N,N-bis(dimethylalkyl)-α,ω-alkanediammonium dibromide at different ratios. The nanoscale properties of the mixed DOPC-DPPC-GS monolayers on the surface of the gene delivery system were studied using atomic force microscopy (AFM) and Kelvin probe force microscopy (KPFM). We demonstrate that lipid-GS mixed monolayers result in the formation of nanoscale domains that vary in size, height, and electrical surface potential. We show that the presence of GS can impart significant changes to the domain topography and electrical surface potential compared to monolayers composed of lipids alone.

Visualizing thickness-dependent magnetic textures in few-layer Cr2Ge2Te6

Magnetic ordering in two-dimensional (2D) materials has recently emerged as a promising platform for data storage, computing, and sensing. To advance these developments, it is vital to gain a detailed understanding of how the magnetic order evolves on the nanometer-scale as a function of the number of atomic layers and applied magnetic field. Here, we image few-layer Cr2Ge2Te6 using a combined scanning superconducting quantum interference device and atomic force microscopy probe. Maps of the material’s stray magnetic field as a function of applied magnetic field reveal its magnetization per layer as well as the thickness-dependent magnetic texture. Using a micromagnetic model, we correlate measured stray-field patterns with the underlying magnetization configurations, including labyrinth domains and skyrmionic bubbles. Comparison between real-space images and simulations demonstrates that the layer dependence of the material’s magnetic texture is a result of the thickness-dependent balance between crystalline and shape anisotropy. These findings represent an important step towards 2D spintronic devices with engineered spin configurations and controlled dependence on external magnetic fields.

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.

AFM-NSOM Nano-Polarimeter: Wide-ranging sensing device for synchronized scanning

This paper explores the use of an enhanced AFM-NSOM system tip as a nanoscale polarimeter. The tip consists of a tungsten-silicon conical photodetector modified with four differently-shaped subwavelength apertures, which enable the determination of incident light's four Stokes parameters and in turn its polarization state on the Poincaré sphere. The system is mounted on a standard Atomic Force Microscope (AFM) cantilever and can serve as a triple-mode scanning system, with complementary topography scanning, optical data analysis, and polarization state detection. The device was designed and simulated using the Comsol Multi-Physics software package, and initial steps toward fabrication were taken using the application of advanced nanotechnology tools to a commercial AFM probe. After a discussion of the advantages and drawbacks of drilled scanning tips vis-a-vis standard ones, the article presents the simulation and fabrication results of the nano-polarimeter tip.

Pt-Black-Modified (Hemi)spherical AFM Sensors: In Situ Imaging of Light-Driven Hydrogen Peroxide Evolution.

In this work, we present (hemi)spherical atomic force microscopy (AFM) sensors for the detection of hydrogen peroxide. Platinum-black (Pt-B) was electrodeposited onto conductive colloidal AFM probes or directly at recessed microelectrodes located at the end of a tipless cantilever, resulting in electrocatalytically active cantilever-based sensors that have a small geometric area but, due to the porosity of the films, exhibit a large electroactive surface area. Focused ion beam-scanning electron microscopy tomography revealed the porous 3D structure of the deposited Pt-B. Given the accurate positioning capability of AFM, these probes are suitable for local in situ sensing of hydrogen peroxide and at the same time can be used for (electrochemical) force spectroscopy measurements. Detection limits for hydrogen peroxide in the nanomolar range (LOD = 68 ± 7 nM) were obtained. Stability test and first in situ proof-of-principle experiments to achieve the electrochemical imaging of hydrogen peroxide generated at a microelectrode and at photocatalytically active structured poly(heptazine imide) films are demonstrated. Force spectroscopic data of the photocatalyst films were recorded in ambient conditions, in solution, and by applying a potential, which demonstrates the versatility of these novel Pt-B-modified spherical AFM probes.

AFM probe with the U-shaped cross-sectional cantilever for measuring the ultra-low coefficient of friction of 10−6

Accurately measuring the coefficient of friction (COF) is the fundamental prerequisite of superlubricity research. This study aimed to reduce the COF measurement resolution Δμ of atomic force microscopy (AFM). Based on the theoretical model, a distinctive strategy was adopted to reduce Δμ by optimizing the cantilever’s cross-section of the AFM probe, inspired by civil engineering. Δμ can be reduced by decreasing the width of the horizontal side wR and the wall thickness t and increasing the width of the vertical side wH. Moreover, the I-shape demonstrates the highest reduction in Δμ, followed by the U-shape. Considering the processability, the AFM probe with the U-shaped cross-sectional cantilever was investigated further, and the dimensions are 35 µm wR, 3.5 µm wH, 0.5 µm t, 50 µm l (cantilever length), and 23 µm htip (tip height). The finite element analysis results confirm its reliability. After being fabricated and calibrated, the AFM probe achieves the minimal Δμ of 1.9×10−6 under the maximum normal force so far. Additionally, the friction detection capability of the fabricated AFM probe improves by 78 times compared to the commercial tipless-force modulation mode (TL-FM) AFM probe with the conventional solid rectangular cross-sectional cantilever. This study provides a powerful tool for measuring 10−6 COF.

Microfabricated double-tilt apparatus for transmission electron microscope imaging of atomic force microscope probe.

Atomic force microscopy (AFM) uses a scanning stylus to directly measure the surface characteristics of a sample. Since AFM relies on nanoscale interaction between the probe and the sample, the resolution of AFM-based measurement is critically dependent on the geometry of the scanning probe tip. This geometry, therefore, can limit the development of related applications. However, AFM itself cannot be effectively used to characterize AFM probe geometry, leading researchers to rely on indirect estimates based on force measurement results. Previous reports have described sample jigs that enable the observation of AFM probe tips using Transmission Electron Microscopy (TEM). However, such setups are too tall to allow sample tilting within more modern high-resolution TEM systems, which can only tilt samples less than a few millimeters in thickness. This makes it impossible to observe atomic-scale crystallographic lattice fringes by aligning the imaging angle perfectly or to view a flat probe tip profile exactly from the side. We have developed an apparatus that can hold an AFM tip for TEM observation while remaining thin enough for tilting, thereby enabling atomic-scale tip characterization. Using this technique, we demonstrated consistent observation of AFM tip crystal structures using tilting in TEM and found that the radii of curvature of nominally identical probes taken from a single box varied widely from 1.4nm for the sharpest to 50nm for the most blunt.

К вопросу определения точки контакта в силовых измерениях методами атомно-силовой микроскопии

Atomic force microscopy (AFM) is a widely used technique for obtaining information about the three-dimensional structure and physical and mechanical properties of surfaces. In nanoindentation methods, an AFM probe is brought to the sample from a distance and then interacts with the surface. Accurate determination of the point of contact of the probe tip with the surface in these measurements is necessary for reliable calculation of both the non-contact interaction constants and the structural and mechanical properties of the material. The tip-surface contact is preceded by a rapid jump of the probe to the surface due to attractive forces in experiments conducted in ambient conditions. If the stiffness of the probe beam or the sample does not allow the probe to deform the surface, then the end of the probe jump (minimum deflection of the beam as the probe approaches the material) is usually taken as the start of the contact. If the surface is soft enough, contact may occur earlier than the end of the rapid jump, i.e., the tip will begin to penetrate into the surface before the jump is complete. In this work it is shown that the contact of the tip with a deformable polymer surface occurs before the completion of the jump of the tip to the surface. It is reasonable to take the point corresponding to the maximum change in the beam deflection as the beginning of the contact between the probe and the material. The significant speed of the approach of the tip to the surface under the action of attractive forces leads to a loss of experimental data in the section of the curve near the transition from non-contact to contact interaction. Insufficient rate of data capture and high approach velocity can cause significant points of the force curve to be missed, i.e., lead to errors in determining the beginning of the contact both for soft and hard surfaces.

Multifunctional chemical anchors achieve a boosted fill factor and mitigate ion migration of high-stability perovskite solar cells.

To date, it is urgent to produce perovskite films with comparative or even better morphologies in an open-air environment. Unfortunately, a substantial number of trap states on the grain surface, especially the grain boundaries (GBs) of a perovskite layer, can bring about significant deterioration in the performance of PSCs. Trap-induced carrier recombination directly exerts a detrimental influence on the carrier collection efficiency and electronic properties of a perovskite active film. Herein, 4(5)-iodoimidazole (4II), a small organic molecule agent, was introduced to passivate the surface and bulk traps of the active film, which resulted in a controlled morphology, improved carrier extraction and suppressed ion migration for the devices fabricated in a relatively humid and O2-containing environment. Conductive atomic force microscopy (C-AFM) and Kelvin probe force microscopy (KPFM) measurements were applied to study trap passivation and suppression of ion migration across the GBs of perovskite films. The results manifest that the -CN group preferably bonds with the less-coordinated Pb2+ and the -NH- group favorably forms hydrogen bonds with the uncoordinated I-. As a result, the champion device delivered a significantly boosted power conversion efficiency from 17.22% to 20.95%, with an improved fill factor (FF) from 70.54% to 80.40%, and improved ambient stability of the unencapsulated device. This study may probe research insight into the design of passivators with synergistic effects for morphology control and reduction of carrier recombination loss for equally efficient perovskite photovoltaics fabricated in ambient air.

Unravelling the non-classical nucleation mechanism of an amyloid nanosheet through atomic force microscopy and an infrared probe technique.

Understanding the amyloid nucleation mechanism is fundamentally important for the development of diagnostics and therapeutics of amyloid-related diseases and for the design and application of amyloid-based materials. To this end, we here explore the use of atomic force microscopy (AFM) and a side-chain-based infrared (IR) probe technique to investigate the amyloid nanosheet formation mechanism of an Aβ16-22 variant, KLVFXAK, where X is p-cyanophenylalanine with its side-chain cyano group being an infrared probe. Using AFM, we reveal that the formation of KLVFXAK amyloid nanosheets follows a two-step non-classical nucleation mechanism. The first step is the rapid formation of a metastable fibrillar intermediate and the second step is slow transformation to the final nanosheet. Using the side-chain-based IR probe technique, we obtain spectroscopic evidence for the proposed nucleation mechanism of the amyloid nanosheet as well as the structural details for the intermediate and amyloid nanosheet. By using the structural constraints set by the two techniques, we propose the structural models for both the fibrillar intermediate and the amyloid nanosheet. In addition, we further investigated the amyloid nanosheet formation mechanism of a similar Aβ16-22 variant, KLVFXAE, and showed the impact of mutation on the amyloid nucleation mechanism. Our work also provides a nice example of how to use the combined approach of AFM and a side-chain-based IR probe technique to unravel the complex nucleation mechanism of amyloid formation.

Evaluation for water stability of bitumen mixture with multi-scale method

The interaction forces were investigated between matrix bitumen and four kinds of aggregates, including basalt, granite, limestone A, and limestone B in various pH solutions. The aim was to accurately evaluate the water damage resistance of bitumen mixtures at macroscopic and microscopic levels with a conjunctive method of boiling water tests, atomic force microscopy (AFM) colloidal probe technique, zeta potential measurements, and molecular dynamics simulation. Macroscopic evaluation was conducted through indoor water-boiled flaking rate tests to analyze the flaking rate and adhesion class of bitumen and aggregate. The microscopic forces were measured by AFM probe technique between bitumen and aggregate, zeta potential measurements were carried out and the extended Derjaguin-Landau-Verwey-Overbeek (DLVO) theory was employed to interpret the bitumen–aggregate interaction behaviors. Molecular dynamics simulations were considered to explain the interface binding tendency between bitumen and aggregate. The AFM force measurements showed that the long-range repulsion forces changed to attractive forces and high adhesive forces with the pH change from 4 to 6. However, the strong long-range repulsive forces were decreased, compounded with a relative low adhesion in the alkaline solution. The long-range force between granite and bitumen was a strong attraction, and adhesion was strong when the solution pH was 4, which is a more special phenomenon. It may be due to the electrostatic attraction between the positive charge on the granite surface and the negative charge on the bitumen surface. Zeta potential values of bitumen droplets and aggregate particles exhibited an overall decreasing trend with increasing solution pH, and the variation of surface potential value is consistent with the variation trend of long-range force between aggregate and bitumen. The microscopic forces between bitumen and aggregate measured by AFM were validated by molecular dynamics simulations, revealing a strong correlation between debonding work and interfacial forces. The results indicate that the adhesion between aggregates and bitumen in aqueous solution followed the order: limestone A > limestone B > basalt > granite, and alkaline conditions are not conducive to preventing water damage in bitumen mixtures. It provides insights into the water stability mechanism of bitumen-aggregate at macroscopic and microscopic scales, offering theoretical support for preventing water damage in bitumen pavements.

Large area arrays of discrete single-molecule junctions derived from host-guest complexes.

The desire to continually reduce the lower limits of semiconductor integrated circuit (IC) fabrication methods continues to inspire interest in unimolecular electronics as a platform technology for the realization of future (opto)electronic devices. However, despite successes in developing methods for the construction and measurement of single-molecule and large-area molecular junctions, exercising control over the precise junction geometry remains a significant challenge. Here, host-guest complexes of the wire-like viologen derivative 1,1'-bis(4-(methylthio)-phenyl)-[4,4'-bipyridine]-1,1'-diium chloride ([1][Cl]2) and cucurbit[7]uril (CB[7]) have been self-assembled in a regular pattern over a gold substrate. Subsequently, ligandless gold nanoparticles (AuNPs) synthesized in situ are deposited over the host-guest array. The agreement between the conductance of individual mono-molecular junctions, appropriately chosen as a function of the AuNP diameter, within this array determined by conductive probe atomic force microscope (c-AFM) and true single-molecule measurements for a closely similar host-guest complex within a scanning tunneling microscope break-junction (STM-BJ) indicates the formation of molecular junctions derived from these host-guest complexes without deleterious intermolecular coupling effects.

Atomic force microscopy and ellipsometry investigations of rare earth oxide Dy2O3 nano-layer processed by electron beam evaporation on n-GaAs substrate

Atomic force microscopy and ellipsometry investigations of rare earth oxide Dy2O3 nano-layer processed by electron beam evaporation on n-GaAs substrate

Deep Learning Image Recognition-Assisted Atomic Force Microscopy for Single-Cell Efficient Mechanics in Co-culture Environments.

Atomic force microscopy (AFM)-based force spectroscopy assay has become an important method for characterizing the mechanical properties of single living cells under aqueous conditions, but a disadvantage is its reliance on manual operation and experience as well as the resulting low throughput. Particularly, providing a capacity to accurately identify the type of the cell grown in co-culture environments without the need of fluorescent labeling will further facilitate the applications of AFM in life sciences. Here, we present a study of deep learning image recognition-assisted AFM, which not only enables fluorescence-independent recognition of the identity of single co-cultured cells but also allows efficient downstream AFM force measurements of the identified cells. With the use of the deep learning-based image recognition model, the viability and type of individual cells grown in co-culture environments were identified directly from the optical bright-field images, which were confirmed by the following cell growth and fluorescent labeling results. Based on the image recognition results, the positional relationship between the AFM probe and the targeted cell was automatically determined, allowing the precise movement of the AFM probe to the target cell to perform force measurements. The experimental results show that the presented method was applicable not only to the conventional (microsphere-modified) AFM probe used in AFM indentation assay for measuring the Young's modulus of single co-cultured cells but also to the single-cell probe used in AFM-based single-cell force spectroscopy (SCFS) assay for measuring the adhesion forces of single co-cultured cells. The study illustrates deep learning imaging recognition-assisted AFM as a promising approach for label-free and high-throughput detection of single-cell mechanics under co-culture conditions, which will facilitate unraveling the mechanical cues involved in cell-cell interactions in their native states at the single-cell level and will benefit the field of mechanobiology.

Plasmonic Nanocone Scanning Antenna: Fabrication and Optical Properties

Optical antennas are nanostructures that introduce unprecedented possibilities for light–matter interaction at the nanoscale. An appropriately tailored plasmonic antenna can enhance the total radiative decay rate and modify the angular radiation pattern of a single‐quantum emitter through controlled near‐field coupling. Despite their ability to surpass the fundamental diffraction limit and confine the electromagnetic field to a tiny mode volume, fabricating 3D sharp scanning nanoscale plasmonic structures with desired aspect ratio is yet an ambitious goal. The fabrication of nanocones by gold evaporation on commercial atomic force microscopy probes followed by a focused ion beam milling technique is presented. The method is versatile and allows the fabrication of nanocones with desired dimensions around 100 nm along with an aspect ratio of ≈1. Their optical properties are studied and it is shown how the variation in the refractive index of the dielectric substrate affects the localized surface plasmon resonance of the nanocones, the decay rate enhancement, and the quantum yield of an emitter relevant for fluorescence/Raman scanning experiments. Theoretical studies using finite‐difference time‐domain calculations have guided the fabrication process and are consistent with experimental results.

Boosting the hydrophobicity of eco‐friendly polyaniline coating using TiO2 and ZnO nanoparticles

This article clarifies the thin layer deposition of superhydrophobic coating using eco‐friendly polymer (polyaniline [PANI]) incorporated with TiO2 and ZnO nanoparticles on indium tin oxide substrate. Using the cyclic voltammetry method, in situ polymerization of PANI incorporated with hybrid (TiO2–ZnO) was accomplished. The morphology and hydrophobicity of electro‐deposited films were examined; the impact of deposition cycles was also investigated. The morphological structure was studied using field‐emission scanning electron microscopy and high‐resolution transmission electron microscopy. X‐ray photoelectron spectroscopy and Fourier transform infrared spectroscopy analysis proved the incorporation of nanoparticles into the composite matrix. Additionally, the water contact angle of the PANI composite was found to be 150.4°, and the findings reflected that (TiO2–ZnO) nanoparticles were significantly implicated in enhancing this superhydrophobicity. The surface roughness of the PANI matrix was increased when TiO2 and ZnO are added, as was shown by atomic force microscope investigation.

The Interplay of Anodic Passivation and Oxygen Evolution of Medium Entropy Alloys in Artificial Seawater

Medium entropy alloys (MEA) have gained increased interest in both academic and industrial sectors due to their favorable mechanical and anti-corrosion properties, rendering them ideal candidates for engineering and potentially catalytic applications. Although previous studies have shown high current densities at high anodic potentials for MEAs, a lack of understanding on the underlying transpassive dissolution and local corrosion behavior remains.This project aimed to investigate and compare the passivation behavior of MEAs CrCoNi and FeCrNi (equimolar) under high anodic potentials, focusing on the mechanisms of transpassive dissolution and the oxygen evolution reaction in artificial seawater. The study utilized various techniques such as scanning electrochemical microscopy (SECM) to instantaneously detect evolving metal species and oxygen, and inductively coupled plasma mass spectrocmetry (ICP-MS) to quantify the dissolved metal species. For these investigations, the alloys were subjected to precisely controlled corrosion loads employing potentiodynamic, potentiostatic, and chronoamperometric methods during the SECM experiments and subsequent ICP-MS analysis.Macroscopic corrosion and passive film properties were studied via potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), and X-Ray Photoelectron Spectroscopy (XPS). Finally, in-situ atomic force microscopy (AFM) and scanning Kelvin probe force microscopy (SKPFM) were used to analyze the corrosion morphology and surface potentials before, during, and after passivity breakdown. Overall, this study aimed to provide a comprehensive understanding of the interplay between passivation, anodic dissolution and oxygen evolution of the MEAs in artificial seawater.