Atomic Force Microscopy Probe Research Articles

Magnetic Domains and Their Power Spectral Densities in Non-Oriented Electrical Steel after Thermal Compression at Different Rates.

The magnetic domains of non-oriented electrical steel bearing cumulative thermal compressions made by a Gleeble 3500 Thermal System were observed using an atomic force microscope (AFM). The component forces, comprising the magnetic forces between the AFM probe and magnetic domains of the samples, along the freedom direction of the probe, were measured, and they formed the value fluctuation of the magnetic domains. The fluctuations of the magnetic domains were analyzed by examining the power spectral density (PSD) curves. The hysteresis curves of the samples were measured using a highly sensitive magnetic measurement system. An analysis of the magnetic force microscope (MFM) maps suggested that some magnetic domains were compressed into crushed and fragmented shapes, similar to the microstructure of deformed grains. Meanwhile, some were reconstructed within the thermal compressions, like dynamic recrystallization microstructures. Meaningfully, the MFM probe moved and deformed the proximal magnetic domains of tested samples within the region of its weak magnetic field. The peak positions of the magnetic domains with a high deformation rate were shifted and moved during the measuring processes by the weakly polarized probe. Both windward and leeward sides simultaneously expressed a slope towards each co-adjacent valley in the MFM maps and induced a statistical throbbing within a narrow band in the PSD curves. Thus, the MFM scanning mode was also analyzed and improved to obtain accurate MFM maps with low disturbances from the weak magnetic field of the probe. Swapping the order positions of the middle processes in the MFM scanning and adding a gliding step between them could offset the peak skewing of magnetic domains caused by the weakly polarized probe during MFM measurement process without incurring excessive replacement costs. Accumulative compression at a high rate (10 s-1) would crush magnetic domains into irregularly decreasing sizes with messy boundaries. This investigation provides an example of the complete relationships among deformations, magnetic domains, and magnetic properties.

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.

Effect of structural defects on the physiochemical properties of supportive single-layer graphene in a sliding electrical contact interface under ambient conditions

We investigated the physiochemical properties of single-layer graphene (SLG) with controlled structural defects that were used in sliding electrical contact. Conductive atomic force microscopy (cAFM) probes applied with electric biases were used to rub the SLG surface under ambient conditions. Structural and chemical properties of rubbed SLG were investigated using Raman spectroscopy, photothermal infrared atomic force microscopy (AFM), and X-ray photoelectron spectroscopy. The work function (WF) and conductivity were determined using Kelvin probe force microscopy and cAFM. Adhesive properties were examined using AFM in the force-volume mode. Biases applied to the cAFM probe resulted in the tunneling triboelectric effect (TTE), which modulated the WF of SLG. The formation of water menisci around the cAFM probe–SLG contact will be electrolyzed, leading to the surface oxidation of SLG, which also impacts the WF of SLG. Compared with pristine SLG with minimum defects, more-defective SLG enhanced the TTE and surface functionalization during the rubbing process, substantially affecting the morphological, electronic, chemical, and adhesive properties of rubbed defective SLG. Our results demonstrated that the physiochemical properties of SLG in a sliding contact are considerably affected by the presence of structural defects in SLG, which should be considered when SLG is used for electrode applications.

Preparation of Al2O3 /PVA Nanocomposite Thin Films by a Plasma Jet Method

Alumina thin films have significant applications in the areas of optoelectronics, optics, electrical insulators, sensors and tribology. The novel aspect of this work is that the homogeneous alumina thin films were prepared in several stages to generate a plasma jet. In this paper, aluminium nanoparticles suspended in vinyl alcohol were prepared using exploding wire plasma. TEM analysis was used to determine the size and shape of particles in aluminium and vinyl alcohol suspensions; the TEM images showed that the particle size is 17.2 nm. Aluminium/poly vinyl alcohol (Al/PVA) thin films were prepared using this suspension on quartz substrate by plasma jet technique at room temperature with an argon gas flow rate of 1 L/min. The Al/PVA thin films were thermally converted to alumina films, where they were annealed at different temperatures (700, 800, or 900°C). X-ray diffraction (XRD), atomic force microscopy (AFM), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR) techniques were used to characterise these thin films before and after annealing process. The diffraction patterns of the prepared thin films before subjecting them to the annealing process indicated the presence of peaks belonging to aluminium and PVA; however, the diffraction patterns and FTIR spectra obtained for these films after the annealing process showed peaks indicating the formation of alumina films of different phases. AFM and SEM investigations proved that the formed particles for all prepared films before and after the annealing process were similar in size and almost spherical; the diameter of the particles was on the order of a few nanometres. To control the properties of prepared thin films, the plasma which was used to produce thin films is diagnosed spectrophotometrically. The generated plasma was diagnosed using optical emission spectroscopy to estimate the electron temperature Te; the electron temperature was 1.925 eV.

Electrospun Poly-L-Lactic Acid Scaffolds Surface-Modified via Reactive Magnetron Sputtering Using Different Mixing Ratios of Nitrogen and Xenon.

Controlled regeneration processes involving tissue growth using the surface and structure of scaffolds, are actively used in tissue engineering. Reactive magnetron sputtering is a versatile surface modification method of both metal and polymer substrates, as the properties of the formed coatings can be modified in a wide range by changing the process parameters. In magnetron sputtering, the working gas and its composition have an influence on the chemical composition and physical characteristics of the obtained coatings. However, there are no studies addressing the influence of the nitrogen/xenon gas mixture ratio in direct current magnetron sputtering on the deposition rate, physicochemical and in vitro properties of surface-modified biocompatible poly-L-lactic acid scaffolds. In this study, the application of mixtures of nitrogen and xenon in various ratios is demonstrated to modify the surface of non-woven poly-L-lactic acid scaffolds by direct current magnetron sputtering of a titanium target. It has been found that the magnetron sputtering parameters chosen do not negatively influence the morphology of the prepared scaffolds, but increase the hydrophilicity. Moreover, quantitative spectroscopic analysis results indicate that the formed coatings are primarily composed of titanium oxide and titanium oxynitride compounds and is dependent on the gas mixture ratio only to a certain extent. Atomic force microscopy investigations of the roughness of the fibers of the electrospun scaffolds and the thickness of the coatings formed on them show that the considerable variations observed in the intrinsic fiber reliefs are due to the formation of a fine layer on the fiber surfaces. The observed decrease in roughness after plasma modification is due to temperature and radiation effects of the plasma. In vitro experiments with human osteosarcoma cells show that the scaffolds investigated here have no cytotoxic effect on these cells. The cells adhere and proliferate well on each of the surface-modified electrospun scaffolds, with stimulation of cell differentiation in the osteogenic direction.

Influence of structural disorder on the elastic, frictional, and electrical properties in functionalized polyaniline thin films at the nanoscale investigated by atomic force microscopy

We investigated the influence of structural order on the elastic, frictional, and electrical properties of butylthio-functionalized PANI (PANI-SBu) films by atomic force microscopy (AFM)-based techniques, including PeakForce quantitative nanomechanical mapping, friction force microscopy, and conductive AFM. The PANI-SBu films were prepared by the drop-cast method from the solution of PANI-SBu in N-methyl-2-pyrrolidone that was continuously stirred. The PANI-SBu films were fabricated after different solution stirring times. The shear force during the mechanical stir will disentangle the highly-coiled PANI-SBu polymer chains in the solution. Therefore, the polymer chains in solution cast on the substrates will progressively self-assemble into a more organized structure when solvents evaporate, leading to PANI-SBu films with improved structural order. Our AFM studies discovered that more structurally-ordered PANI-SBu films have substantially larger out-of-plane elastic moduli and charge mobility but smaller kinetic friction coefficients. The denser packing of polymer molecules increases film elasticities and promotes chain-to-chain charge transport. In addition, stiffer PANI-SBu film surfaces are more difficult to deform when sheared by the sliding AFM probe, resulting in less energy dissipation during AFM friction measurements. Thus, smaller kinetic friction coefficients were found. Conversely, more structurally-disordered PANI-SBu films have smaller elasticity and charge mobility but larger kinetic friction coefficients. Our results demonstrate that it is possible to manipulate the elastic, frictional, and electrical properties of PANI-SBu films by controlling their structural order, which can be essential for developing polymer-based composite materials and flexible electronic devices.

Flake-Like WO3-Based Thin Films for Enhanced Ethanol Sensing Applications

Undoped and vanadium-doped tungsten trioxide (V–WO3) nanocrystalline thin films were prepared on glass substrates with spray pyrolysis. The synthesized films were characterized using XRD, Raman spectroscopy, AFM, FESEM, UV-visible spectroscopy, and XPS for micro-structural, topographical, optical and chemical properties. The results showed that XRD analysis confirmed that WO3-based thin films were hexagonal phases. The FESEM images showed the interconnected nanoflake-like morphology of the undoped and V–WO3 thin films. Atomic Force Microscopy (AFM) investigations confirmed that the average surface roughness of the thin films ranged from 3.36 nm to 14.2 nm. The optical energy bandgap of the films was estimated from the optical spectrum of absorption. The static liquid distribution method was utilized to examine the gas-sensing characteristics of deposited films. The results show that the 4 wt% vanadium-doped WO3 sensor responds to ethanol vapour at room temperature. The response and recovery times towards 50 ppm of ethanol gas were determined as 32 and 21 s, respectively. The 4 wt% V-WO3 film has shown a response of 2.8, which is 2.15 times more than the undoped WO3.

Study of CO molecules on Pd/Al2O3/NiAl(110) surface by atomic force microscopy and Kelvin probe force microscopy

Study of CO molecules on Pd/Al2O3/NiAl(110) surface by atomic force microscopy and Kelvin probe force microscopy

Quantitative nanopatterning of fg-scale liquids with dip-pen nanolithography

The ability to precisely pattern nanoscale amounts of liquids is essential for biotechnology and high-throughput chemistry, but controlling fluid flow on these scales is very challenging. Scanning probe lithography methods such as dip-pen nanolithography (DPN) provide a mechanism to write fluids at the nanoscale, but this is an open loop process as methods to provide feedback while patterning sub-pg features have yet to be reported. Here, we demonstrate a novel method for programmably nanopatterning liquid features at the fg-scale through a combination of ultrafast atomic force microscopy probes, the use of spherical tips, and inertial mass sensing. We begin by investigating the required probe properties that would provide sufficient mass responsivity to detect fg-scale mass changes and find ultrafast probes to be capable of this resolution. Further, we attach a spherical bead to the tip of an ultrafast probe as we hypothesize that the spherical tip could hold a drop at its apex which both facilitates interpretation of inertial sensing and maintains a consistent fluid environment for reliable patterning. We experimentally find that sphere-tipped ultrafast probes are capable of reliably patterning hundreds of features in a single experiment. Analyzing the changes in the vibrational resonance frequency during the patterning process, we find that drift in the resonance frequency complicates analysis, but that it can be removed through a systematic correction. Subsequently, we quantitatively study patterning using sphere-tipped ultrafast probes as a function of retraction speed and dwell time to find that the mass of fluid transferred can be modulated by greater than an order of magnitude and that liquid features as small as 6 fg can be patterned and resolved. Taken together, this work addresses a persistent concern in DPN by enabling quantitative feedback for nanopatterning of aL-scale features and lays the foundation for programmably nanopatterning fluids.

The nucleation, growth, and adhesion of water bridges in sliding nano-contacts.

We provide experimental observations of the nucleation and growth of water capillary bridges in nanometer gaps between a laterally moving atomic force microscope probe and a smooth silicon wafer. We find rising nucleation rates with increasing lateral velocity and a smaller separation gap. The interplay between nucleation rate and lateral velocity is attributed to the entrainment of water molecules into the gap by the combination of lateral motion and collisions of the water molecules with the surfaces of the interface. The capillary volume of the full-grown water bridge increases with the distance between the two surfaces and can be limited by lateral shearing at high velocities. Our experimental results demonstrate a novel method to study in situ how water diffusion and transport impact dynamic interfaces at the nanoscale, ultimately leading to friction and adhesion forces at the macroscale.

Integrated Photonic Optomechanical Atomic Force Microscopy Probes Batch Fabricated Using Deep UV Photolithography

Chip-scale planar nanofabricated optomechanical devices that optically couple a mechanical moving nanostructure to an on-chip photonic cavity of high quality factor can be used for sensing motion with high precision and bandwidth. Motion in nanoscale mechanical structures can be measured optically on-chip with unprecedented precision and bandwidth. Wider scientific and commercial adoption of such sensors required the ability to mass fabricate, flexibility of design, and permanent fiber attachment for robustness and ease of use. In this paper, we demonstrated this by fabricating an atomic force microscopy probe using a commercial foundry process employing deep UV photolithography on 200 mm wafers. The batch fabricated devices with 150 nm minimum features perform similarly to the research prototypes previously fabricated using sequential electron beam lithography. This demonstration eliminates a key technical barrier to the wider adoption of high-performance integrated optomechanical sensing in nanomechanical transducers. 2022-0186

Interfacial Behavior of Cubosomes: Combined Langmuir-Blodgett/Langmuir-Schaefer and AFM Investigations.

The Langmuir technique was applied for the first time to compare the layers obtained by spreading lipid liquid-crystalline nanoparticles monoolein 1-oleoyl-rac-glycerol (GMO)/Pluronic F108 cubosomes with the monolayers obtained by mixing the same components in chloroform at the air-water interface. The differences in the monolayer behavior and in the acting intermolecular forces were examined. The similarity of the isotherms obtained for the mixed components system and the cubosome-derived layer proved the disintegration of cubosomes into a single monolayer upon contact with the air-water interface. Despite the low Pluronic F108 content in both types of layers, a strong structural role of this stabilizer was also demonstrated. Cubosome-derived systems supported on hydrophilic mica substrates were prepared either using the combined Langmuir-Blodgett and Langmuir-Schaefer technique or via direct adsorption from the solution. The topographies of the obtained layers were studied by atomic force microscopy (AFM). Images obtained in the air mode revealed the disintegration of cubosomes and the formation of large crystallized structures of the polymer, while AFM imaging performed in water confirmed the presence of intact cubosomes on the surface of mica. We proved that the original structure of cubosomes remains on one condition: the films must not dry out; therefore, the aqueous environment must be preserved. This new approach provides an explanation in the ongoing discussion of what happens to lipid nanoparticles with or without cargo when they come into contact with an interface.

Lateral Bending of Ag Nanowires toward Controllable Manipulation

Nanowires (NWs) provide opportunities for building high-performance sensors and devices at micro-/nanoscales. Directional movement and assembly of NWs have attracted extensive attention; however, controllable manipulation remains challenging partly due to the lack of understanding on interfacial interactions between NWs and substrates (or contacting probes). In the present study, lateral bending of Ag NWs was investigated under various bending angles and pushing velocities, and the mechanical performance corresponding to microstructures was clarified based on high-resolution transmission electron microscope (HRTRM) detections. The bending-angle-dependent fractures of Ag NWs were detected by an atomic force microscope (AFM) and a scanning electron microscope (SEM), and the fractures occurred when the bending angle was larger than 80°. Compared with an Ag substrate, Ag NWs exhibited a lower system stiffness according to the nanoindentation with an AFM probe. HRTRM observations indicated that there were grain boundaries inside Ag NWs, which would be contributors to the generation of fractures and cracks on Ag NWs during lateral bending and nanoindentation. This study provides a guide to controllably manipulate NWs and fabricate high-performance micro-/nanodevices.

Disentangling Electronic Transport and Hysteresis at Individual Grain Boundaries in Hybrid Perovskites via Automated Scanning Probe Microscopy

Underlying the rapidly increasing photovoltaic efficiency and stability of metal halide perovskites (MHPs) is the advancement in the understanding of the microstructure of polycrystalline MHP thin film. Over the past decade, intense efforts have been aimed at understanding the effect of microstructures on MHP properties, including chemical heterogeneity, strain disorder, phase impurity, etc. It has been found that grain and grain boundary (GB) are tightly related to lots of microscale and nanoscale behavior in MHP thin films. Atomic force microscopy (AFM) is widely used to observe grain and boundary structures in topography and subsequently to study the correlative surface potential and conductivity of these structures. For now, most AFM measurements have been performed in imaging mode to study the static behavior; in contrast, AFM spectroscopy mode allows us to investigate the dynamic behavior of materials, e.g., conductivity under sweeping voltage. However, a major limitation of AFM spectroscopy measurements is that they require manual operation by human operators, and as such only limited data can be obtained, hindering systematic investigations of these microstructures. In this work, we designed a workflow combining the conductive AFM measurement with a machine learning (ML) algorithm to systematically investigate grain boundaries in MHPs. The trained ML model can extract GBs locations from the topography image, and the workflow drives the AFM probe to each GB location to perform a current-voltage (IV) curve automatically. Then, we are able to have IV curves at all GB locations, allowing us to systematically understand the property of GBs. Using this method, we discovered that the GB junction points are less conductive, potentially more photoactive, and can play critical roles in MHP stability, while most previous works only focused on the difference between GB and grains.

Probing carrier trapping and hysteresis at perovskite grain boundaries via in situ characterization

Plenty of trap states in the photo-active layer of perovskite solar cells (PSCs) have ineradicable impacts on device performance and long-term stability. Varied chemical agents have been applied as capping layer or precursor additives in order to enhance film quality and reduce trap state. However, there are still debates about whether these strategies exert the comparable effect on improvement of device performance and ambient stability. In addition, it is essential to clarify whether the agents would diffuse into the crystal lattice or aggregate at the grain boundaries to suppress ion migration. Herein, β-phenylethylammoniumiodide (β-PAI) was applied both as buffer layer and additive for perovskite materials and their underlying distinct roles in hysteresis reduction as well as trap deactivation were elucidated via in situ conductive atomic force microscopy (C-AFM) and Kelvin probe force microscopy (KPFM). For the fully open-air fabricated cells, β-PAI as additive can boost the maximum power conversion efficiency (PCE) of 20.24%, while as interlayer can maintain 96% of the initial PCE after 35 d under 35 ± 5%RH in ambient air. In the end, some mechanistic guidelines were proposed to clarify the distinct roles of additives and interlayer, which is beneficial for further chemical design in order to promote the performance and stability for perovskite devices.

Influence of the Mn Content on the Corrosion Behaviour of HEA CoCrFeN-iMnX (X=5, 20, 35 at.%) Prepared via MA+SPS

The high entropy alloys with intended chemical compositions of CoCrFeNiMnX (X=5, 20 and 35 at.%) were prepared by the means of mechanical alloying. Prepared powders were then compacted using the progressive spark plasma sintering, which minimizes the deleterious microstructural coarsening. The compacts were, regardless of the actual chemical composition, composed of a solid solution with FCC crystallographic lattice and a small amount of carbides identified as Cr7C3. The dimensions of those carbides increased with the content of Mn, which was confirmed also by atomic force microscopy (AFM) and scanning kelvin probe microscopy (SKPM). The surface topography measured by AFM confirmed its presence as they emerged from the surface, perfectly matching the positive potential measured by the SKPM. It was found, that the HEAs are showing rather worse corrosion resistance in the aqueous environment containing 9 g/l NaCl compared to the reference 316L stainless steel. Moreover, the higher the content of Mn, the worse the corrosion resistance increasing the corrosion current density and shifting open circuit potential towards more negative values. When exposed to the elevated temperature of 600 °C, the alloys formed a poor protective oxidic layer that tended to chip off due to thermal stresses.

Large Range Atomic Force Microscopy with High Aspect Ratio Micropipette Probe for Deep Trench Imaging.

Atomic force microscopy (AFM) has been adopted in both industry and academia for high-fidelity, full-profile topographic characterization. Typically, the tiny tip of the cantilever and the limited traveling range of the scanner restrict AFM measurement to relatively flat samples (recommend 1µm). The primary objective of this work is to address these limitations using a large-range AFM (measuring height >10µm) system consisting of a novel repairable high aspect ratio probe (HARP) with a nested-proportional-integral-derivative (nested-PID) AFM system. The HARP is fabricated using a reliable, cost-efficient bench-top process. The tip is then fused by pulling the end of the micropipette cantilever with a length up to hundreds of micrometers and a tip diameter of 30nm. The design, simulation, fabrication, and performance of the HARP are described herein. This instrument is then tested using polymer trenches which reveals superior image fidelity compared to standard silicon tips. Finally, a nested-PID system is developed and employed to facilitate 3D characterization of 50-µm-step samples. The results demonstrate the efficacy of the proposed bench-top technique for the fabrication of low-cost, simple HAR AFM probes that facilitate the imaging of samples with deep trenches.

Recent advances in the application of atomic force microscopy to structural biology

The application of atomic force microscopy (AFM) for functional imaging and manipulating biomolecules at all levels of organization has enabled great progress in the structural biology field over the last decades, contributing to the discovery of novel structural entities of biological significance across many disciplines ranging from biochemistry, biomedicine and biophysics to molecular and cell biology, up to food systems and beyond. AFM has the capability to generate high-resolution topographic images spanning from the submolecular to the (sub)cellular range and can probe biochemical and biophysical sample properties in close to native conditions with excellent temporal resolution. Instrumental developments in the past decade enable dynamical structural and conformational studies of single biomolecules and new techniques for structural and chemical modification of the AFM probe have converted the cantilever into a versatile tool to study different biological phenomena, such as the mechanical stability of biomolecular complexes or the force induced dynamic changes of mechanically stressed proteins at the nanoscopic level. To improve the functionality of AFM and approach dynamic processes of complex biological systems ex vivo, AFM is combined with complementary microscopy, nanoscopy and spectroscopy tools. These multimethodological approaches provide unprecedented possibilities of probing physical, chemical and biological properties of complex cellular systems with high spatio-temporal resolution, leading to novel applications that correlate structural results with functional biochemical, biophysical, immunological, or genetic data of the system under study.

AFM probe for measuring ∼10−5 ultra-low friction coefficient: Design and application

Superlubricity provides a novel approach to addressing friction and wear issues in mechanical systems. However, little is known regarding improving the atomic force microscope (AFM) friction coefficient measurement resolution. Accordingly, this study established the theoretical formula for the AFM friction coefficient measurement and deduced the measurement resolution. Then, the formula was applied to the AFM probe with a rectangular cross-section cantilever. The measurement resolution is associated with the dimensional properties of the AFM probe, the mechanical properties of the cantilever material, the properties of the position-sensitive detector (PSD), and probably the anti-vibration performance of the AFM. It is feasible to make the cantilever as short as possible and the tip as high as possible to improve the measurement resolution. An AFM probe for measuring an ultra-low friction coefficient was designed and fabricated. The cantilever’s length, width, and thickness are 50, 35, and 0.6 µm, respectively. The tip height is 23 µm. The measurement resolution can reach 7.1×10−6 under the maximum normal force. Moreover, the AFM probe was applied to measure the superlubricity between graphene layers. The friction coefficient is 0.00139 under 853.08 nN. This work provides a promising method for measuring a ∼10−5 friction coefficient of superlubricity.

The Formation of Au Nanoparticles in SiO2–TiO2 Films by Local Electrochemical Reduction Using an Atomic Force Microscope Probe

The Formation of Au Nanoparticles in SiO2–TiO2 Films by Local Electrochemical Reduction Using an Atomic Force Microscope Probe