Atomic Force Microscopy Probe Research Articles

A Simple Method for Fabrication of Self‐sharpened Silicon Tips for Atomic Force Microscopy Applications (Crystal Research and Technology 6/2022)

Crystal Research and TechnologyVolume 57, Issue 6 2270011 Cover PictureFree Access A Simple Method for Fabrication of Self-sharpened Silicon Tips for Atomic Force Microscopy Applications (Crystal Research and Technology 6/2022) First published: 09 June 2022 https://doi.org/10.1002/crat.202270011AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Abstract In article number 2100217, Savitha Purakkat, Basavaraju Yeriyur Basavaiah, and co-workers present a simple and high yield method to bulk produce self-sharpened silicon tips using cost-effective chemicals. The generated silicon tips are successfully adopted to fabricate atomic force microscopy probes. After installing in a commercial atomic force microscope, the developed probes produce the images of quality and accuracy of those obtained with commercially available probes. Volume57, Issue6June 20222270011 RelatedInformation

Unveiling the Native Morphology of Extracellular Vesicles from Human Cerebrospinal Fluid by Atomic Force and Cryogenic Electron Microscopy.

Extracellular vesicles (EVs) are membranous structures in biofluids with enormous diagnostic/prognostic potential for application in liquid biopsies. Any such downstream application requires a detailed characterization of EV concentration, size and morphology. This study aimed to observe the native morphology of EVs in human cerebrospinal fluid after traumatic brain injury. Therefore, they were separated by gravity-driven size-exclusion chromatography (SEC) and investigated by atomic force microscopy (AFM) in liquid and cryogenic transmission electron microscopy (cryo-TEM). The enrichment of EVs in early SEC fractions was confirmed by immunoblot for transmembrane proteins CD9 and CD81. These fractions were then pooled, and the concentration and particle size distribution were determined by Tunable Resistive Pulse Sensing (around 1010 particles/mL, mode 100 nm) and Nanoparticle Tracking Analysis (around 109 particles/mL, mode 150 nm). Liquid AFM and cryo-TEM investigations showed mode sizes of about 60 and 90 nm, respectively, and various morphology features. AFM revealed round, concave, multilobed EV structures; and cryo-TEM identified single, double and multi-membrane EVs. By combining AFM for the surface morphology investigation and cryo-TEM for internal structure differentiation, EV morphological subpopulations in cerebrospinal fluid could be identified. These subpopulations should be further investigated because they could have different biological functions.

Diselenide as a Dual Functional Mechanophore Capable of Stress Self-Reporting and Self-Strengthening in Polyurethane Elastomers

Diselenide as a Dual Functional Mechanophore Capable of Stress Self-Reporting and Self-Strengthening in Polyurethane Elastomers

Force Mapping Reveals the Spatial Distribution of Individual Proteins in a Neuron

Conventional methods for studying the spatial distribution and expression level of proteins within neurons have primarily relied on immunolabeling and/or signal amplification. Here, we present an atomic force microscopy (AFM)-based nanoscale force mapping method, where Anti-LIMK1-tethered AFM probes were used to visualize individual LIMK1 proteins in cultured neurons directly through force measurements. We observed that the number density of LIMK1 decreased in neuronal somas after the cells were depolarized. We also elucidated the spatial distribution of LIMK1 in single spine areas and found that the protein predominantly locates at heads of spines rather than dendritic shafts. The study demonstrates that our method enables unveiling of the abundance and spatial distribution of a protein of interest in neurons without signal amplification or labeling. We expected that this approach should facilitate the studies of protein expression phenomena in depth in a wide range of biological systems.

Friction between MXenes and other two-dimensional materials at the nanoscale

Two-dimensional (2D) materials have unique friction properties that are different from their 3D counterparts. MXenes, a large family of 2D transition metal carbides, carbonitrides, and nitrides, have recently attracted attention as solid lubricants on the macroscale. Here we experimentally investigate the friction of Ti3C2Tx and Ti2CTx MXenes against Ti3C2Tx and Ti2CTx MXenes, graphene, and MoSe2 at the nanoscale, using atomic force microscopy (AFM). Ti3C2Tx and Ti2CTx MXene coated SiO2 spherical AFM probes were used to slide against films of these materials with varying number of monolayers deposited on the substrate. We have found that over the 15 nm sliding distance the measured nanoscale coefficients of friction (COFs) for all the investigated 2D interfaces are below 0.01. At the same time, hydrogen bonding involving -O- and –OH surface terminating groups on MXenes induced higher friction forces for the MXene/MXene contacts compared to other contacts. Moreover, a less significant number-of-monolayers effect on the friction was observed for MXenes due to their thicker monolayers compared with other 2D materials in this study. These results further contribute to our understanding of the mechanisms of friction of MXenes and reveal the potential of MXenes as tunable lubricants at the nanoscale.

Band Bending and Ratcheting Explain Triboelectricity in a Flexoelectric Contact Diode.

Triboelectricity was recognized millennia ago, but the fundamental mechanism of charge transfer is still not understood. We have recently proposed a model where flexoelectric band bending due to local asperity contacts drives triboelectric charge transfer in non-metals. While this ab initio model is consistent with a wide range of observed phenomena, to date there have been no quantitative analyses of the proposed band bending. In this work we use a Pt0.8Ir0.2 conductive atomic force microscope probe to simultaneously deform a Nb-doped SrTiO3 sample and collect current-bias data. The current that one expects based upon an analysis including the relevant flexoelectric band bending for a deformed semiconductor quantitively agrees with the experiments. The analysis indicates a general ratcheting mechanism for triboelectric transfer and strong experimental evidence that flexoelectric band bending is of fundamental importance for triboelectric contacts.

Evaluation of performance properties of poly(styrene‐co‐butadiene) rubber reinforced with N,N‐Dimethylacetamide/lithium chloride treated precipitated silica

AbstractPrecipitated silica, treated with N,N‐Dimethylacetamide (DMAc)/Lithium Chloride (LiCl) at different LiCl concentrations, is used as reinforcing filler for poly(styrene‐co‐butadiene) rubber (SBR). DMAc/LiCl treatment of silica reduces hydrogen bonding within silica particles and improve its dispersion in rubber. Fourier transform‐infrared spectroscopy (FTIR) and X‐ray diffraction (XRD) data of treated DMAc/LiCl silica have indicated increased free hydroxyl groups as LiCl concentration in DMAc increases. Scanning electron microscopy (SEM) and Atomic force microscopy (AFM) investigations revealed smaller silica agglomerates, reduced scan height distribution and surface roughness. Better dispersion and reduced storage hardening of DMAc/LiCl treated silica‐filled SBR masterbatches, in the presence of bis‐(triethoxy silylpropyl)‐tetrasulphide (TESPT), are indications of easier processing of these compounds as observed from Mooney viscosity data. Mooney scorch time values at 125°C for compounds containing treated silica have indicated increased cure rates. Moving die rheometer data at 150°C have shown that combination of TESPT and DMAc/LiCl enhanced the processing safety of SBR compounds. Optimum concentration of LiCl combined with TESPT has resulted in enhanced crosslink density, physical properties, reduced swelling and heat build‐up in SBR vulcanizates.

Mechanical Properties of Embryonic Mouse Cartilage and Bone

Differences in material characteristics of cartilage and bone are primarily known through investigation of postnatal specimens but the mechanical properties of these tissue during embryogenesis are less well studied. Importantly, embryonic cartilage and bone have not been tested extensively in aqueous environments, limiting the validity of previous investigations. The purpose of this project is to characterize the stiffness and strength of embryonic cranial bone and cartilage using atomic force microscopy (AFM). We test the hypothesis that embryonic cartilage is stronger than embryonic bone against the null hypothesis that embryonic tissue response will be comparable to adult tissue in which bone is the stronger of the two tissues. In vivo conditions are simulated by immersing tissues in room‐temperature phosphate‐buffered saline before and during testing. Data are acquired using calibrated AFM probes which yield quantitative and qualitative data. Force‐distance curves include data on topography, adhesion, and DMTModulus, the latter of which can be transformed into Young’s Modulus through models which approximate the shape of the AFM probe, including the Sneddon model. Calcified tissue intended for testing is verified on the micro scale using AFM topography and on the macro scale using calcein dye. Each 2 square micron topographical image is accompanied by 16,384 force versus distance curves which yield a value for modulus of elasticity. Data show DMTModulus values ranging from approximately 200 kPa to 7.7 MPa for embryonic cartilage and 120 kPa to 3.0 MPa for embryonic bone providing preliminary data indicating that cartilage varies more than bone and may be significantly stronger than bone in mouse embryos.

Surface Properties and Architectures of Male Moth Trichoid Sensilla Investigated Using Atomic Force Microscopy

The surfaces of trichoid sensilla on male moth antennae have been sculpted over evolutionary time to capture pheromone odorant molecules emitted by the females of their species and transport the molecules in milliseconds into the binding protein milieu of the sensillum lumen. The capture of pheromone molecules likely has been optimized by the topographies and spacings of the numerous ridges and pores on these sensilla. A monolayer of free lipids in the outer epicuticle covers the sensillar surfaces and must also be involved in optimal pheromone odorant capture and transport. Using electro-conductive atomic force microscopy probes, we found that electrical surface potentials of the pores, ridges and flat planar areas between ridges varied in consistent ways, suggesting that there is a heterogeneity in the distribution of surface lipid mixtures amongst these structures that could help facilitate the capture and transport of pheromone molecules down through the pores. We also performed experiments using peak force atomic force microscopy in which we heated the sensilla to determine whether there is a temperature-related change of state of some of the surface lipid exudates such as the prominent domes covering many of the pores. We found that these exudates were unaffected by heating and did not melt or change shape significantly under high heat. Additionally, we measured and compared the topographies of the trichoid sensilla of five species of moths, including the distributions, spacings, heights and diameters of ridges, pores and pore exudates.

In situ strain electrical atomic force microscopy study on two‐dimensional ternary transition metal dichalcogenides

AbstractAtomically thin two‐dimensional (2D) alloys have attracted wide interests of study recently due to their potential in flexible electronic and optoelectronic applications. In particular, monolayer transition metal dichalcogenide (TMD) alloys have emerged as unique 2D semiconductors with tunable bandgaps, by means of alloying. However, response of surface electrical potential and barrier height to strain for 2D TMD alloys–electrode interface is rarely explored. Apparently, revealing such strain‐dependent evolution of electrical properties is crucial for developing advanced 2D TMD based flexible electronics and optoelectronics. Here we performed in situ strain Kelvin probe force microscopy (KPFM) and conductive atomic force microscopy (C‐AFM) investigations of monolayer Mo0.4W0.6Se2 on Au coated flexible substrate, where controlled uniaxial tensile strain is applied. Both contact potential difference (CPD) and Schottky barrier heights (SBH) of monolayer Mo0.4W0.6Se2 show obvious decreases with the increase of strain, which is mainly due to the strain‐induced increment of TMD electron affinity. Our in situ strain photoluminescence (PL) measurements also indicate the changes of electronic band structures under strain. We further exploit the substrate effects on CPD by study the monolayer alloy on the mostly used substrates of SiO2/Si and indium tin oxide (ITO)/glass. Our findings could strengthen the foundation for the potential applications of 2D TMD and their alloys in the fields of strain sensors, flexible photodetectors, and other wearable electronic devices.image

Variations in the Effective Work Function of Graphene in a Sliding Electrical Contact Interface under Ambient Conditions.

Control of work function (WF) in graphene is crucial for graphene application in electrode material replacement and electrode surface protection in optoelectronic devices. Although efforts have been made to manipulate the effective WF of graphene to optimize its application, most studies have focused on graphene employed in static electrical contact interfaces. In this work, we investigated WF variations of supported single-layer graphene (SLG) in sliding electrical contact under ambient conditions, which was achieved by sliding an electrically biased conductive atomic force microscopy (cAFM) probe on the SLG surface. The effective WF, structural properties, and chemical compositions of rubbed SLG were subsequently measured by Kelvin probe force microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy, respectively. We found that the effective WF of the rubbed SLG was governed by both the tunneling triboelectric effect (TTE) and tribochemical-induced surface functionalization. The TTE charges generated by the sliding cAFM probe tunneled through the structural defects of the SLG and were trapped underneath the SLG. The SLG will be either p-doped or n-doped depending on the type of TTE charges and the polarity of electric bias applied to the cAFM probe during the rubbing process. However, the applied electric bias also led to the electrolysis of a water meniscus formed at the cAFM probe-SLG contact, resulting in surface oxidation and the increase of SLG WF. Further absorption of ambient water molecules on the oxygenated functional groups gradually reduced the SLG WF. The influence of TTE and surface functionalization on the SLG WF depends on the magnitude and polarity of applied electric biases, relative humidity, and physical properties of the supporting substrates. Our results demonstrate that the effective WF of SLG in a sliding electrical contact interface will vary with time and might need to be considered for related applications.

The Effect of Incubation near an Inversely Oriented Square Pyramidal Structure on Adsorption Properties of Horseradish Peroxidase

The incubation of a solution of horseradish peroxidase (HRP) enzyme either below the apex or near the base of an inversely oriented square pyramid (inverted square pyramid; ISP) has been found to influence the enzyme’s aggregation and adsorption properties. The HRP enzyme is used herein as a model object due to its importance in analytical chemistry applications. Atomic force microscopy (AFM) is employed to investigate the HRP’s adsorption on mica substrates at the single-molecule level. Conventional spectrophotometry is used in parallel as a reference method for the determination of the HRP’s enzymatic activity. Using AFM, we reveal a significant change in the adsorption properties of HRP on mica substrates after the incubation of the HRP solutions either above the base or below the apex of the ISP in comparison with the control HRP solution. The same situation is observed after the incubation of the enzyme solution above the center of the ISP’s base. Here, the enzymatic activity of HRP remained unaffected in both cases. Since pyramidal structures of positive and inverted orientation are employed in biosensor devices, it is important to take into account the results obtained herein in the development of highly sensitive biosensor systems, in which pyramidal structures are employed as sensor (such as AFM probes) or construction elements.

Membrane Repairing Capability of Non-Small Cell Lung Cancer Cells Is Regulated by Drug Resistance and Epithelial-Mesenchymal-Transition.

The plasma membrane separates the interior of the cells from the extracellular fluid and protects the cell from disruptive external factors. Therefore, the self-repairing capability of the membrane is crucial for cells to maintain homeostasis and survive in a hostile environment. Here, we found that micron-sized membrane pores induced by cylindrical atomic force microscope probe puncture resealed significantly (~1.3–1.5 times) faster in drug-resistant non-small cell lung cancer (NSCLC) cell lines than in their drug-sensitive counterparts. Interestingly, we found that such enhanced membrane repairing ability was due to the overexpression of annexin in drug-resistant NSCLC cells. In addition, a further ~50% reduction in membrane resealing time (i.e., from ~23 s to ~13 s) was observed through the epithelial-mesenchymal-transition, highlighting the superior viability and potential of highly aggressive tumor cells using membrane resealing as an indicator for assessing the drug-resistivity and pathological state of cancer.

Anodization of medical grade stainless steel for improved corrosion resistance and nanostructure formation targeting biomedical applications

Stainless steel is extensively used in various biomedical engineering and hospital applications, including surgical equipment and furniture. Strong adhesion of bacteria and viruses on metal surfaces can restrict long-term utilization for biomedical applications. This study aims to develop an improved electrochemical etching protocol for the anodization of 316 L grade stainless steel (10 × 15 mm) to fabricate nanostructures for biomedical and hospital applications. Anodizing conditions were optimized using two different electrolyte solutions; HNO3: H2SO4 (1:1) and HNO3, by varying applied potential, electrolyte concentration and anodizing time. Morphology and topography of the anodized surfaces were characterized using scanning electron microscopy (SEM), atomic force microscopy (AFM) and scanning Kelvin probe force microscopy (SKPFM). AC and DC electrochemical techniques were used to further characterize the corrosion behaviour of the nanostructured surfaces. Electrochemical optimization produced two different nanostructured surfaces with the anodizing conditions of (1) 50% HNO3 at 0.465 A/cm2 for 1 min (surface 1), and (2) 0.5 M HNO3 + H2SO4 (1:1) at 0.366 A/cm2 for 5 min (surface 2). Both processes produced nanoscale surface roughness with varying corrosion susceptibility. Surfaces anodized using 50% HNO3 comprised of ‘hierarchical roughness’ with dense spikes (10 – 20 nm in diameter), covering rock candy-like protrusion (10 - 15 µm diameter). Whereas the second set of conditions produced single scale roughness with a terrace-like topography with nanoscale ridges of 34.8 ± 1.2 nm in width atop microscale hills. Surface 2 possessed improved corrosion resistance through the formation an oxide film, while the surface 1 was more susceptible to corrosion. Overall, this study demonstrates the importance of the careful optimization of electrochemical surface treatment for medical grade stainless steel in terms of roughness of nanostructures and corrosion susceptibility.

Very-high-frequency probes for atomic force microscopy with silicon optomechanics

Atomic force microscopy (AFM) has been consistently supporting nanosciences and nanotechnologies for over 30 years and is used in many fields from condensed matter physics to biology. It enables the measurement of very weak forces at the nanoscale, thus elucidating the interactions at play in fundamental processes. Here, we leverage the combined benefits of micro/nanoelectromechanical systems and cavity optomechanics to fabricate a sensor for dynamic mode AFM at a frequency above 100 MHz. This frequency is two decades above the fastest commercial AFM probes, suggesting an opportunity for measuring forces at timescales unexplored thus far. The fabrication is achieved using very-large-scale integration technologies derived from photonic silicon circuits. The probe’s optomechanical ring cavity is coupled to a 1.55 μm laser light and features a 130 MHz mechanical resonance mode with a quality factor of 900 in air. A limit of detection in the displacement of 3 × 10−16 m/√Hz is obtained, enabling the detection of the Brownian motion of the probe and paving the way for force sensing experiments in the dynamic mode with a working vibration amplitude in the picometer range. When inserted in a custom AFM instrument embodiment, this optomechanical sensor demonstrates the capacity to perform force-distance measurements and to maintain a constant interaction strength between the tip and sample, an essential requirement for AFM applications. Experiments indeed show a stable closed-loop operation with a setpoint of 4 nN/nm for an unprecedented subpicometer vibration amplitude, where the tip–sample interaction is mediated by a stretched water meniscus.

Ultrafast Growth of Highly Conductive Graphene Films by a Single Subsecond Pulse of Microwave.

Currently, graphene films are expected to achieve real applications in various fields. However, the conventional synthesis methods still have intrinsic limitations, especially not being applicable on a surface with high curvature. Herein, an ultrafast synthesis method was developed for graphene and turbostratic graphite growth by a single subsecond pulse of microwaves generated by a household magnetron. We succeeded in growing high-quality around 10-layered turbostratic graphite in 0.16 s directly on the surface of an atomic force microscope probe and maintaining a tip curvature radius of less than 30 nm. The thus-produced probes showed high conductivity and tip durability. Moreover, turbostratic graphite film was also demonstrated to grow on the surface of dielectric Si flat substrates in a full coverage. Graphene can also grow on metallic Ni tips by this method. Our microwave ultrafast method can be used to grow high-quality graphene in a facile, efficient, and economical way.

Unrecovered ion-irradiated damage after thermal annealing in graphene field effect transistors

Irradiation effects in graphene-based devices are crucial for applications of carbon-based devices utilized in aerospace and other radiation harsh environments. In this work, the deteriorated electrical properties of graphene field effect transistors (GFETs) induced by swift heavy ions (SHIs, 1.8 GeV Ta) and evolution of the defects in device materials after irradiation and thermal annealing have been investigated. The SHIs induced defects in graphene result in the increase of resistance and decrease in carrier mobilities. Thermal annealing at 110 °C could improve the carrier mobility at smaller scale that can be ascribed to the degassing effect. The defects in graphene were unrepairable after annealing at 110 °C. At higher temperature (e.g., 500 °C), the graphene structure was further damaged as a result of the compressive strain induced by thermal contraction of the SiO2 layer. The evolutions of graphene and SiO2 surface morphologies with increasing annealing temperature were studied by Atomic Force Microscopy investigations. After irradiation, the weakened lattice structure order of the Si layer and change of the SiO2/Si interface morphology were confirmed. It was also shown that the damage in SiO2/Si interface did not recover even after the high temperature (e.g., 1100 °C) annealing.

The Story behind the First Automatic Atomic Force Microscope

Abstract:Over the past three decades, atomic force microscopy (AFM) has undergone a series of design changes to attain a flat XY scan and stable non-contact mode in ambient atmosphere. AFM has evolved into an ideal method for non-destructive scanning of samples with longer probe tip life, high accuracy, repeatability, and automation. Together with self-optimizing algorithms for scan parameters in the non-contact mode, AFM can become as widely adopted as other microscopies such as optical or scanning electron microscopy (SEM). Even full automation of AFM probe tip exchange is now possible with probe type recognition software and laser beam alignment on the cantilever and position-sensitive photo diode (PSPD). By separating the optics stage from the Z stage, an AFM system can be made with low mechanical noise and improved optical vision.

Experimental analysis of tip vibrations at higher eigenmodes of QPlus sensors for atomic force microscopy

QPlus sensors are non-contact atomic force microscope probes constructed from a quartz tuning fork and a tungsten wire with an electrochemically etched tip. These probes are self-sensing and offer an atomic-scale spatial resolution. Therefore, qPlus sensors are routinely used to visualize the chemical structure of adsorbed organic molecules via the so-called bond imaging technique. This is achieved by functionalizing the AFM tip with a single CO molecule and exciting the sensor at the first vertical cantilever resonance mode. Recent work using higher-order resonance modes has also resolved the chemical structure of single organic molecules. However, in these experiments, the image contrast can differ significantly from the conventional bond imaging contrast, which was suspected to be caused by unknown vibrations of the tip. This work investigates the source of these artefacts by using a combination of mechanical simulation and laser vibrometry to characterize a range of sensors with different tip wire geometries. The results show that increased tip mass and length cause increased torsional rotation of the tuning fork beam due to the off-center mounting of the tip wire, and increased flexural vibration of the tip. These undesirable motions cause lateral deflection of the probe tip as it approaches the sample, which is rationalized to be the cause of the different image contrast. The results also provide a guide for future probe development to reduce these issues.

Peridynamic Model for Single-Layer Graphene Obtained from Coarse-Grained Bond Forces

An ordinary state-based peridynamic material model is proposed for single-sheet graphene. The model is calibrated using coarse-grained molecular dynamics simulations. The coarse-graining method allows the dependence of bond force on bond length to be determined, including the horizon. The peridynamic model allows the horizon to be rescaled, providing a multiscale capability and allowing for substantial reductions in computational cost compared with molecular dynamics. The calibrated peridynamic model is compared to experimental data on the deflection and perforation of a graphene sheet by an atomic force microscope probe.