Contact Resonance Atomic Force Microscopy Research Articles

Local vibrational and mechanical characterization of Ag conducting chalcogenide glasses

Macroscopic and local studies of vibrational and mechanical properties of bulk Agx(Ge0.25Se0.75)100-x glasses were conducted using Raman (mapping) spectroscopy, Vickers microhardness Hv and Contact Resonance Atomic Force Microscopy (CR-AFM). For the glass containing 10 at% in Ag, Raman mapping gave evidence of a phase separation through continuous interpenetrating phases (Ag-rich and Ag-poor phases) in the spinodal decomposition process. Combined mechanical characterizations (Hv and CR-AFM) indicated that the microhardness and rigidity modulus decrease with the silver content in the glass. At nanoscale level, CR-AFM measurements highlighted a modulation of the rigidity with Ag content. The structural origin of these changes was confirmed using Raman mapping evidencing modifications in the tetrahedral network between two phases. The results could suggest a different Ge/Se ratio in Ag-poor and Ag-rich phases.To further investigate the liquid-liquid phase separation morphology, small angle neutron scattering was performed at different temperatures in the liquid state. Whereas liquids with 15 and 25 at% in Ag showed a nucleation/growth morphology for all studied liquid temperatures, a spinodal decomposition with fractal dimension D from 2.6 to 3.4 was found for 5 at% in Ag when the temperature increases from 600 °C to 700 °C.

Identification of nanoparticles and nanosystems in biological matrices with scanning probe microscopy.

Identification of nanoparticles and nanosystems into cells and biological matrices is a hot research topic in nanobiotechnologies. Because of their capability to map physical properties (mechanical, electric, magnetic, chemical, or optical), several scanning probe microscopy based techniques have been proposed for the subsurface detection of nanomaterials in biological systems. In particular, atomic force microscopy (AFM) can be used to reveal stiff nanoparticles in cells and other soft biomaterials by probing the sample mechanical properties through the acquisition of local indentation curves or through the combination of ultrasound-based methods, like contact resonance AFM (CR-AFM) or scanning near field ultrasound holography. Magnetic force microscopy can detect magnetic nanoparticles and other magnetic (bio)materials in nonmagnetic biological samples, while electric force microscopy, conductive AFM, and Kelvin probe force microscopy can reveal buried nanomaterials on the basis of the differences between their electric properties and those of the surrounding matrices. Finally, scanning near field optical microscopy and tip-enhanced Raman spectroscopy can visualize buried nanostructures on the basis of their optical and chemical properties. Despite at a still early stage, these methods are promising for detection of nanomaterials in biological systems as they could be truly noninvasive, would not require destructive and time-consuming specific sample preparation, could be performed in vitro, on alive samples and in water or physiological environment, and by continuously imaging the same sample could be used to dynamically monitor the diffusion paths and interaction mechanisms of nanomaterials into cells and biological systems. This article is categorized under: Diagnostic Tools > In Vivo Nanodiagnostics and Imaging Nanotechnology Approaches to Biology > Nanoscale Systems in Biology.

Scanning speed phenomenon in contact-resonance atomic force microscopy.

This work presents data confirming the existence of a scan speed related phenomenon in contact-mode atomic force microscopy (AFM). Specifically, contact-resonance spectroscopy is used to interrogate this phenomenon. Above a critical scan speed, a monotonic decrease in the recorded contact-resonance frequency is observed with increasing scan speed. Proper characterization and understanding of this phenomenon is necessary to conduct accurate quantitative imaging using contact-resonance AFM, and other contact-mode AFM techniques, at higher scan speeds. A squeeze film hydrodynamic theory is proposed to explain this phenomenon, and model predictions are compared against the experimental data.

Sounding out buried nanostructures using subsurface ultrasonic resonance force microscopy

ABSTRACTImaging of nanoscale structures buried in a covering material is an extremely challenging task, but is also considered extremely important in a wide variety of fields. From fundamental research into the way living cells are built up to process control in semiconductor manufacturing would all benefit from the capability to image nanoscale structures through arbitrary covering layers. Combining Atomic Force Microscopy (AFM) with ultrasound has been shown a promising technology to enable such imaging in various configurations. Here we report the development of an alternative method of combining AFM with ultrasound which we call SubSurface Ultrasonic Resonance Force Microscopy (SSURFM) and which is based on a combination of the two most common variants described in literature, which each have their specific strong points: Ultrasonic Force Microscopy (UFM) and Contact Resonance AFM (CR-AFM). We show the excellent performance of this combination on a number of samples designed specifically to mimic relevant conditions for the application as a metrology technique in the semiconductor manufacturing process. We also discuss the physics of the image contrast mechanism which is based on sensing local changes in visco-elastic properties of the sample bygenerating large indentations in the surface.

Piezoresponse force and electrochemical strain microscopy in dual AC resonance tracking mode: Analysis of tracking errors

Contact-resonance atomic force microscopy allows the quantitative mapping of local viscoelastic and electromechanical properties. Excitation and amplification are generally described by the damped harmonic oscillator (DHO) model. The dual AC resonance tracking technique measures the amplitude and phase at two probing frequencies close to the resonance frequency and calculates the parameters of the DHO model from the amplitudes and phases. However, real systems show contact-resonance curves with slight deviations from the DHO model. In this work, we analyze how these deviations influence the obtained DHO parameters. We show that for a piezoelectric sample and for a mixed ion-electron conducting sample, the drive amplitude increases with increasing tracking error, while the opposite is observed for the amplification factor. Thus, in electrochemical strain microscopy experiments, the influence of the tracking error on the DHO parameters can be analyzed by calculating a tracking error image and studying correlations with the DHO parameter images.

Tracking Ion Intercalation into Layered Materials on the Nanoscale

In the past decades, electrochemical capacitors (supercapacitors) have drawn considerable attention for applications in portable electronics, grid and transportation systems due to their rapid power delivery and an almost unlimited cycle life. In search for new materials with higher electrochemical performance, two dimensional (2D) transition metal carbides – MXenes, are of particular interest owing to their excellent electrical conductivity and high volumetric capacitance[1] [2] . A variety of aqueous cations can be electrochemically intercalated into Ti3C2, the most studied MXene to date, resulting in very high volumetric capacitance outperforming a variety of carbons[1] . The mechanism for high capacitance was essentially described as intercalation pseudo-capacitance arising from redox reactions of the Ti atoms. On the other hand, Ti3C2shows intercalation capacitive behavior even at quite high rates, while normally a slow intercalation takes place in layered battery materials. Similar to graphite or other electrode materials in various electrolytes, MXene electrodes also show a significant change in volume when ions are intercalated. This electro-chemo-mechanical coupling can be used to get unprecedented insight into ion intercalation pathways with lateral resolution of 10’s of nm using Scanning Probe Microscopy (SPM) techniques. In this communication, we introduce contact resonance SPM which allows to extract mechanical properties and its changes under electrochemical control when ions are intercalated into MXene[3] [4] . Of special interest to boost energy storage is the intercalation of multivalent ions such as Mg2+ which suffers from sluggish intercalation and transport kinetics due to its ion size. By combining traditional electrochemical characterization techniques with electrochemical dilatometry and contact resonance atomic force microscopy, the synergetic effects of pre-intercalation of K+ ions are demonstrated to improve charge storage of multivalent ions, as well as tune mechanical and actuation properties of Ti3C2 MXene[4] [5] .Our results have important implications for quantitatively understanding the charge storage processes in intercalation compounds and provide a new path for studying the mechanical evolution of energy storage materials. The experiments and sample preparation in this work were supported as part of the Fluid Interface Reactions, Structures and Transport (FIRST) Center, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences. The facilities to perform the experiments were provided by the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility.

Multiscale mechanical characterization of hybrid Ti/PMMA layered materials

Metal surfaces coated with organic layers are innovative materials with high potential for many industrial applications. To overcome the limitations due to the generally poor adhesion between these two components, polymers covalently anchored onto the substrate (‘grafted’ polymers) have been proposed as adhesives interlayers. Their mechanical properties, however, strongly affect their performances and thus have to be characterized at different scales. In this paper we report the mechanical characterization of thick poly(methyl methacrylate) (PMMA) layers grafted on titanium substrates using standard nanoindentation as well as different AFM-based techniques, namely AFM-based nanoindentation, contact resonance AFM (CR-AFM), HarmoniX™, and PeakForce quantitative nanomechanical mapping (PF-QNM™). The specific results obtained with each technique reflect the mechanical properties at different scales for these multiscale systems. Thus, these methods constitute a unique set of techniques for the complete analysis of the mechanical response of advanced materials from the macro- down to the nanoscale.

Microstructural evidence for seismic and aseismic slips along clay‐bearing, carbonate faults

AbstractIn this multimethodological study, microstructural observations of fault rocks are combined with micromechanical property analyses (contact resonance atomic force microscopy (CR‐AFM)) and with rotary friction experiments (Slow‐ to High‐Velocity rotary‐shear friction Apparatus apparatus) to find evidence of seismic to aseismic slip and understand the nanoscale rheology of clay‐bearing, carbonate‐hosted faults. Fluidized structures, truncated clasts, pores and vesicles, and phyllosilicate nanosized spherules and tubes suggest fast deformation events occurred during seismic slip, whereas clay‐assisted pressure‐solution processes, clumped clasts, foliation surfaces, and mantled clasts indicate slow deformation events occurred during postseismic/interseismic periods. CR‐AFM measurements show that the occurrence of ~5 wt % of clay within the carbonate‐hosted gouges can significantly reduce the fault core stiffness at nanoscale. In addition, during high‐velocity friction experiments simulating seismic slip conditions, the presence of ultrathin phyllosilicate‐bearing (≤3 wt %) layers within calcite gouges, as those observed in the natural fault, show faster dynamic weakening than that of pure calcite gouges. The weak behavior of such layers could facilitate the upward propagation of seismic slip during earthquakes, thus possibly enhancing surface faulting. Microstructural observations and experimental evidence fit some well‐known geophysical and geodetic observations on the short‐ to long‐term mechanical behavior of faults such as postseismic/interseismic aseismic creep, interseismic fault locking, and seismic slip propagation up to the Earth's surface.

Detection of subsurface cavity structures using contact-resonance atomic force microscopy

To meet the surging demands for quantitative and nondestructive testing at the nanoscale in various fields, ultrasonic-based scanning probe microscopy techniques, such as contact-resonance atomic force microscopy (CR-AFM), have attracted increased attention. Despite considerable success in subsurface nanostructure or defect imaging, the detecting capabilities of CR-AFM have not been fully explored yet. In this paper, we present an analytical model of CR-AFM for detecting subsurface cavities by adopting a circular freestanding membrane structure as an equivalent cavity. The parameters describing the detection limits of CR-AFM for such structures include the detecting depth and the detectable area. These parameters are systematically studied for different cantilever eigenmodes for structures of different sizes and depths. The results show that the detecting depth depends on the structure size. The higher eigenmodes generally provide better detecting capabilities than the lower ones. For an experimental verification, samples were prepared by covering a polymethylmethacrylate (PMMA) substrate with open pores at its surface with HOPG flakes. CR-AFM imaging on the HOPG-covered area was carried out using different eigenmodes in order to detect the pores in the PMMA. In addition, the influence of the applied tip load is also discussed.

Relationships between chemical structure, mechanical properties and materials processing in nanopatterned organosilicate fins.

The exploitation of nanoscale size effects to create new nanostructured materials necessitates the development of an understanding of relationships between molecular structure, physical properties and material processing at the nanoscale. Numerous metrologies capable of thermal, mechanical, and electrical characterization at the nanoscale have been demonstrated over the past two decades. However, the ability to perform nanoscale molecular/chemical structure characterization has only been recently demonstrated with the advent of atomic-force-microscopy-based infrared spectroscopy (AFM-IR) and related techniques. Therefore, we have combined measurements of chemical structures with AFM-IR and of mechanical properties with contact resonance AFM (CR-AFM) to investigate the fabrication of 20–500 nm wide fin structures in a nanoporous organosilicate material. We show that by combining these two techniques, one can clearly observe variations of chemical structure and mechanical properties that correlate with the fabrication process and the feature size of the organosilicate fins. Specifically, we have observed an inverse correlation between the concentration of terminal organic groups and the stiffness of nanopatterned organosilicate fins. The selective removal of the organic component during etching results in a stiffness increase and reinsertion via chemical silylation results in a stiffness decrease. Examination of this effect as a function of fin width indicates that the loss of terminal organic groups and stiffness increase occur primarily at the exposed surfaces of the fins over a length scale of 10–20 nm. While the observed structure–property relationships are specific to organosilicates, we believe the combined demonstration of AFM-IR with CR-AFM should pave the way for a similar nanoscale characterization of other materials where the understanding of such relationships is essential.

Sub-surface AFM imaging using tip generated stress and electric fields

It is well known that sub-surface nano-objects can be detected by Atomic Force Microscopy (AFM) with either sub-surface stress or electric fields, by using dynamic AFM methods such as Contact Resonance AFM (CR-AFM) or 2nd-harmonic Kelvin Probe Force Microscopy (KPFM), respectively. However, little is understood regarding the relative differences between the two methods. We present a head-to-head comparison between the sub-surface imaging capabilities of these two methods through experiments and computational models based on finite element analysis (FEA). High resolution subsurface images are obtained using both techniques, from the same area of a polymer composite film containing single-walled carbon nanotube networks embedded in a polyimide matrix. The results are used to interpret quantitatively the observables from CR-AFM and KPFM, with a particular focus on the depth sensitivity and lateral resolution. The depth of the buried carbon nanotube bundles estimated by combining experiments and FEA is found to be in good agreement between the two methods.

Contact resonance AFM to quantify the in-plane and out-of-plane loss tangents of polymers simultaneously

Contact resonance atomic force microscope (AFM) methods are used to quantify the elastic and viscoelastic properties of numerous materials including polymers. More recently, U-shaped AFM thermalevers have been developed to allow the local heating of samples, and the resonances of these probes are much more complex. These probes also allow the in-plane and out-of-plane tip-sample motion to be excited independently at the same location using a Lorentz force excitation. Here, such a probe is used to determine the in-plane and out-of-plane viscoelastic properties at the same location. The approach is demonstrated with respect to the indentation and shear loss tangents on high-density polyethylene and polystyrene.

Role of geometry on the frequency spectra of U-shaped atomic force microscope probes

Contact resonance atomic force microscopy (CR-AFM) is a specific technique that is used to determine elastic or viscoelastic properties of materials. The success of this technique is highly dependent on the accuracy of frequency spectra that must be measured for both noncontact and the case in which the tip is in contact with the sample of interest. Thus, choosing the right probe is crucial for accurate experiments. U-shaped probes also offer new opportunities for CR-AFM measurements because of certain specific modes that have tip motion parallel to the sample surface such that these resonances can access in-plane sample properties. However, analysis of the spectra from U-shaped probes is much more challenging due to these modes. The geometry of these probes is the main driver for the spectral response. Here, this influence on the resonance frequencies of the commercially fabricated U-shaped probe AN2-300 is evaluated with respect to geometry in terms of leg width, crossbeam width, and crossbeam length. Both noncontact and contact cases are examined with respect to variations of the nominal geometry. An energy distribution approach is also presented to assist with the identification of modes that have close resonances. Finally, this analysis allows recommendations to be made in order to minimize the convergence of multiple resonances for a specific range of measurement parameters.

Conduction electrons as dissipation channel in friction experiments at the metal-metal transition of LSMO measured by contact-resonance atomic force microscopy

We report on friction measurements on a La0.6Sr0.4MnO3 (LSMO) thin film using atomic force microscopy cantilever contact-resonances. There is a contribution to the damping of the cantilever oscillations, which is caused by micro-sliding of the cantilever tip on the surface of the thin film. This frictional part decreases with temperature parallel to the increase in the resistivity of the thin film. The LSMO is well-known for a ferromagnetic to paramagnetic phase transition that occurs without changes in the rhombohedral (R-3c) crystalline structure. The magnetic transition at the Curie temperature TC ∼ 360 K is accompanied by a metal-to-metal transition with a large increase in electrical resistivity. The behavior of the cantilever damping constant demonstrates that there is a direct coupling between mechanical friction and the mobility of the electrons in the LSMO film.

Beyond the concepts of nanocomposite and 3D printing: PVA and nanodiamonds for layer-by-layer additive manufacturing

The use of dispersions of poly(vinyl alcohol) PVA and detonation nanodiamond (DND) as novel inks for 3D printing of variously shaped objects using a layer-by-layer additive manufacturing method is reported. In parallel with the nanocomposites preparation, we designed a 3D printing apparatus and settled protocols for the shaping of hybrid materials, choosing PVA-DND inks as a model system to test the performances of the 3D apparatus. Along with material design and preparation, we discuss the main factors influencing the quality of the final printed objects and enlighten the importance of the matching between the chemical/physical properties of the materials to be extruded and the characteristics of the 3D printer. The thermal and mechanical properties of the printed systems have been tested by Differential Scanning Calorimetry and Contact Resonance Atomic Force Microscopy. The analysis of the mechanical properties of the 3D printed objects evidenced, for 0.5%w/w, 1%w and 5%w DND-loaded nanocomposites, values of mean indentation modulus that are 22%, 44% and 200% higher, respectively, than that of the unloaded PVA. The results of the present research, indicate that an appropriate methodology is able to print PVA-DND nanocomposites in well-defined and shaped structures, suitable for a variety of possible applications.

Detection of stiff nanoparticles within cellular structures by contact resonance atomic force microscopy subsurface nanomechanical imaging.

Detecting stiff nanoparticles buried in soft biological matrices by atomic force microscopy (AFM) based techniques represents a new frontier in the field of scanning probe microscopies, originally developed as surface characterization methods. Here we report the detection of stiff (magnetic) nanoparticles (NPs) internalized in cells by using contact resonance AFM (CR-AFM) employed as a potentially non-destructive subsurface characterization tool. Magnetite (Fe3O4) NPs were internalized in microglial cells from cerebral cortices of mouse embryos of 18 days by phagocytosis. Nanomechanical imaging of cells was performed by detecting the contact resonance frequencies (CRFs) of an AFM cantilever held in contact with the sample. Agglomerates of NPs internalized in cells were visualized on the basis of the local increase in the contact stiffness with respect to the surrounding biological matrix. A second AFM-based technique for nanomechanical imaging, i.e., HarmoniX™, as well as magnetic force microscopy and light microscopy were used to confirm the CR-AFM results. Thus, CR-AFM was demonstrated as a promising technique for subsurface imaging of nanomaterials in biological samples.

Synergetic effects of K+ and Mg2+ ion intercalation on the electrochemical and actuation properties of the two-dimensional Ti3C2 MXene.

Two-dimensional materials, such as MXenes, are attractive candidates for energy storage and electrochemical actuators due to their high volume changes upon ion intercalation. Of special interest for boosting energy storage is the intercalation of multivalent ions such as Mg2+, which suffers from sluggish intercalation and transport kinetics due to its ion size. By combining traditional electrochemical characterization techniques with electrochemical dilatometry and contact resonance atomic force microscopy, the synergetic effects of the pre-intercalation of K+ ions are demonstrated to improve the charge storage of multivalent ions, as well as tune the mechanical and actuation properties of the Ti3C2 MXene. Our results have important implications for quantitatively understanding the charge storage processes in intercalation compounds and provide a new path for studying the mechanical evolution of energy storage materials.

Micromechanical contact stiffness devices and application for calibrating contact resonance atomic force microscopy

This paper reports the design, fabrication, and characterization of micromechanical devices that can present an engineered contact stiffness to an atomic force microscope (AFM) cantilever tip. These devices allow the contact stiffness between the AFM tip and a substrate to be easily and accurately measured, and can be used to calibrate the cantilever for subsequent mechanical property measurements. The contact stiffness devices are rigid copper disks of diameters 2–18 μm integrated onto a soft silicone substrate. Analytical modeling and finite element simulations predict the elastic response of the devices. Measurements of tip–sample interactions during quasi-static force measurements compare well with modeling simulation, confirming the expected elastic response of the devices, which are shown to have contact stiffness 32–156 N m−1. To demonstrate one application, we use the disk sample to calibrate three resonant modes of a U-shaped AFM cantilever actuated via Lorentz force, at approximately 220, 450, and 1200 kHz. We then use the calibrated cantilever to determine the contact stiffness and elastic modulus of three polymer samples at these modes. The overall approach allows cantilever calibration without prior knowledge of the cantilever geometry or its resonance modes, and could be broadly applied to both static and dynamic measurements that require AFM calibration against a known contact stiffness.

Nanoscale tomographic reconstruction of the subsurface mechanical properties of low-k high-aspect ratio patterns

In this work, intermittent contact resonance atomic force microscopy (ICR-AFM) was performed on high-aspect ratio a-SiOC:H patterned fins (100 nm in height and width from 20 to 90 nm) to map the depth and width dependencies of the material stiffness. The spatial resolution and depth sensitivity of the measurements were assessed from tomographic cross-sections over various regions of interest within the 3D space of the measurements. Furthermore, the depth-dependence of the measured contact stiffness over the scanned area was used to determine the sub-surface variation of the elastic modulus at each point in the scan. This was achieved by iteratively adjusting the local elastic profile until the depth dependence of the resulted contact stiffness matched the depth dependence of the contact stiffness measured by ICR-AFM at that location. The results of this analysis were assembled into nanoscale sub-surface tomographic images of the elastic modulus of the investigated SiOC:H patterns. A new 3D structure-property representation emerged from these tomographic images with direct evidence for the alterations sustained by the structures during processing.

A theoretical model for the cantilever motion in contact-resonance atomic force microscopy and its application to phase calibration in piezoresponse force and electrochemical strain microscopy

Contact-resonance scanning probe techniques are frequently used for characterizing the mechanical sample properties via atomic force acoustic/ultrasonic microscopy as well as for detecting sample displacement via piezoresponse force microscopy (PFM) and via electrochemical strain microscopy (ESM). For a better understanding of the measurement principle and for a quantification of the signals, a theoretical description of the cantilever motion is necessary. Here, we present a comprehensive model from which the cantilever motion can be calculated numerically. Compared to previous models, our model takes into account a sample tilt and a position-dependent electrostatic load acting on the cantilever. We demonstrate a phase calibration technique for PFM and ESM measurements, which allows us to determine the absolute excitation phase of the signal with an uncertainty of only 2° for an amplification factor of 100.