Commercial Atomic Force Microscope Research Articles

Shortened and simplified traceability chain for dimensional metrology based on self-traceable standards

Abstract Nanoscale measurement is an essential task of nanomanufacturing, and measurement traceability is a fundamental aspect of nanoscale measurement. High-precision nanoscale measurement instruments (e.g. atomic force microscopes (AFM) and scanning electron microscopes (SEM)) need to be calibrated by traceable standards to ensure their accuracy and reliability. However, due to the suboptimal accuracy, uniformity, and consistency of existing standards, they need to be calibrated by metrological instruments traceable to primary length standards (e.g. physical wavelength standards) before use. This results in a long traceability chain that leads to error accumulation and significantly reduces calibration efficiency. This paper proposes a novel shortened and simplified traceability chain, where the physical wavelength standard corresponding to the 7S3 → 7P4° transition frequency of chromium atoms is materialized into self-traceable gratings using the atom lithography technology. The self-traceable gratings can then be directly applied for calibrating measurement instruments. To verify this approach, the self-traceable gratings are calibrated using a metrological AFM of the Physikalisch-Technische Bundesanstalt. Measurement results confirmed the feasibility of the approach. Particularly, our results show that the self-traceable gratings have excellent uniformity over different measurement areas and consistency over different samples, both at 0.001 nm level. Finally, the application of the self-traceable gratings for the calibrations of a commercial AFM and SEM is demonstrated. The new traceability chain significantly simplifies the calibration process, providing a more reliable and higher efficient calibration approach for advanced nanomanufacturing than that of the state-of-the-art.

Step height measurement of monoatomic silicon crystal lattice steps with a commercial atomic force microscope

Abstract Precise control of advanced materials relies on accurate dimensional metrology at the sub-nanometre scale. At this scale, the accuracy of scanning probe microscopy (SPM) has been limited by the lack of traceable transfer standard artefacts with calibration structures of suitable dimensions. With the adoption in 2019 of the silicon crystal lattice spacing as a secondary realization of the metre in the International System of Units (SI), SPM users have direct access to a realization of the SI metre at the sub-nanometre level by means of the step height of self-assembled monatomic lattice steps that can form on the surface of silicon crystals. A key challenge of successfully adopting this pathway is establishing the need for established protocols to minimize measurement errors and artifacts in routine laboratory use.
In this study, step height measurements of monoatomic lattice steps in an ordinal/staircase structure on a Si(111) crystal surface have been derived from images acquired with a commercially available, research-level atomic force microscope (AFM). Measurement results derived from AFM images using three different SPM image processing and analysis software packages are compared. Significant sources of measurement uncertainty are identified; principally the contribution from the dependence on scan direction. The calibration of the
AFM derived from this measurment was used to traceably measure the sub-nanometre lattice steps on a silicon carbide crystal surface to demonstrate the viability of this calibration pathway.

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.

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.

Design and realization of scanning probe microscope based on a T-shaped high-aspect-ratio probe

With the growing importance of three-dimensional (3D) nanomaterials and devices, the use of high-aspect-ratio (HAR) probes in atomic force microscopy (AFM) imaging enables full-profile topography characterization. However, HAR-AFM probes are difficult to manufacture due to the expensive materials and complex processes. Inspired by the Wollaston scanning probe, we successfully fabricated a T-shaped tungsten probe and installed in a home-made scanning probe microscope system. Compared with commercial AFM, the home-made platform utilizes a set of LabVIEW control programs based on field programmable gate array hardware feedback, which improves the scanning speed and makes the control program more flexible. The reliability of the system was verified by comparing with the scanning results of commercial AFM. The T-shaped probe exhibits better fidelity in HAR-hole imaging compared to AFM standard pyramidal probes. This approach will likely find a convenient and material-saving fabrication route, especially for custom functional nanoprobes.

Simultaneous quantification of Young’s modulus and dispersion forces with nanoscale spatial resolution

Many advances in polymers and layered materials rely on a precise understanding of the local interactions between adjacent molecular or atomic layers. Quantifying dispersion forces at the nanoscale is particularly challenging with existing methods often time consuming, destructive, relying on surface averaging or requiring bespoke equipment. Here, we present a non-invasive method able to quantify the local mechanical and dispersion properties of a given sample with nanometer lateral precision. The method, based on atomic force microscopy (AFM), uses the frequency shift of a vibrating AFM cantilever in combination with established contact mechanics models to simultaneously derive the Hamaker constant and the effective Young’s modulus at a given sample location. The derived Hamaker constant and Young’s modulus represent an average over a small (typically <100) number of molecules or atoms. The oscillation amplitude of the vibrating AFM probe is used to select the length-scale of the features to analyse, with small vibrations able to resolve the contribution of sub-nanometric defects and large ones exploring effectively homogeneous areas. The accuracy of the method is validated on a range of 2D materials in air and water as well as on polymer thin films. We also provide the first experimental measurements of the Hamaker constant of HBN, MoT2, WSe2 and polymer films, verifying theoretical predictions and computer simulations. The simplicity and robustness of the method, implemented with a commercial AFM, may support a broad range of technological applications in the growing field of polymers and nanostructured materials where a fine control of the van der Waals interactions is crucial to tune their properties.

Calibrate the non-orthogonal error of AFM with two-dimensional self-traceable grating

The calibration of the non-orthogonal error in nanoscale measurements is of paramount importance for analytical measuring instruments. Particularly, the calibration of non-orthogonal errors in atomic force microscopy (AFM) is essential for the traceable measurements of novel materials and two-dimensional (2D) crystals. The 2D self-traceable grating with a theoretical non-orthogonal angle of less than 0.0027° and an expanded uncertainty of 0.003° (k = 2) are measured by the Metrological Large Range Scanning Probe Microscope (Met. LR-SPM). In this study, we characterized the local and overall non-orthogonal error in AFM scans and proposed a protocol to tune the optimal scanning parameters of AFM minimizing the non-orthogonal error. We presented the method for accurately calibrating a commercial AFM system for non-orthogonal by establishing a detailed uncertainty budget and errors analysis. Our results verified the important advantages of the 2D self-traceable grating in calibrating precision instruments.

A Measurement System with High Precision and Large Range for Structured Surface Metrology Based on Atomic Force Microscope

With the rapid and continuous development of nanomanufacturing technology, the demands for both large range and high precision metrology of structured surfaces are becoming increasingly urgent. This paper proposes a metrological measurement system based on a commercial atomic force microscope. By using the nano-positioning platform from SIOS, the measurement range of the system expands from 110 μm × 110 μm × 20 μm to 25 mm × 25 mm × 5 mm. A signal amplifier with low noise and a high common mode rejection ratio that decreases the noise level of the measurement system to 2 nm is designed. Integration of the metrological system, signal processing, and calibration of the whole system is introduced. Three experimental studies are carried out on an ultrahigh step, an atomic deposition grating, and a cutting tool. The experimental results demonstrate high measurement repeatability and reproducibility in both vertical and lateral directions. By repeating 10 times of measurement, the expended uncertainties of the step and the grating measurement are 36.24 nm and 0.60 nm, respectively. Additionally, measurement of a cutting tool tip is conducted to illustrate the performance of the system. The Ra and Rz values of the tool tip arc ripple are 29.8 nm and 189 nm, respectively.

3D printed fiber-optic nanomechanical bioprobe

Ultrasensitive nanomechanical instruments, e.g. atomic force microscopy (AFM), can be used to perform delicate biomechanical measurements and reveal the complex mechanical environment of biological processes. However, these instruments are limited because of their size and complex feedback system. In this study, we demonstrate a miniature fiber optical nanomechanical probe (FONP) that can be used to detect the mechanical properties of single cells and in vivo tissue measurements. A FONP that can operate in air and in liquids was developed by programming a microcantilever probe on the end face of a single-mode fiber using femtosecond laser two-photon polymerization nanolithography. To realize stiffness matching of the FONP and sample, a strategy of customizing the microcantilever’s spring constant according to the sample was proposed based on structure-correlated mechanics. As a proof-of concept, three FONPs with spring constants varying from 0.421 N m−1 to 52.6 N m−1 by more than two orders of magnitude were prepared. The highest microforce sensitivity was 54.5 nm μN−1 and the detection limit was 2.1 nN. The Young’s modulus of heterogeneous soft materials, such as polydimethylsiloxane, muscle tissue of living mice, onion cells, and MCF-7 cells, were successfully measured, which validating the broad applicability of this method. Our strategy provides a universal protocol for directly programming fiber-optic AFMs. Moreover, this method has no special requirements for the size and shape of living biological samples, which is infeasible when using commercial AFMs. FONP has made substantial progress in realizing basic biological discoveries, which may create new biomedical applications that cannot be realized by current AFMs.

A probe-based nanometric morphology measurement system using intermittent-contact mode.

In the present study, a homemade probe-based nanometric morphology measurement system is proposed, which can be easily integrated with other probes, such as a diamond probe and an electrochemical electrode. In this system, an intermittent-contact mode is adopted, which is based on a set of micro-force servo modules. The micro-force serve module is mainly composed of a piezoelectric ceramic transducer, a capacitive displacement sensor, an excitation piezoelectric ceramic ring, and a four-beam spring. The four-beam spring integrated with a diamond probe is driven by the excitation piezoelectric ceramic ring. The mechanical structure and the control system of the measurement system are also designed. The vibration amplitude and the resolution of a normal load are calibrated during the engagement process under open-loop control. Moreover, the optimal values for parameters P, I, and D are obtained for the closed-loop measurement. The performance of the developed system is verified by measuring a standard sample. The measured depths agree well with the results obtained by commercial atomic force microscopy. The developed system can be used to measure nanostructures with high precision.

Spectroscopic imaging ellipsometry for two-dimensional thin film thickness measurement using a digital light processing projector

An improved version of spectroscopic imaging ellipsometry is described for accurate reconstruction of two-dimensional thin film thickness. A digital light processing projector enables a selected area of the back focal plane of the objective lens to be illuminated so that the angle of incidence and the polarization state of the light source vary depending on the area of the back focal plane being illuminated. By combining multiple images of the object plane obtained at different polarization states, every pixel in the field of view has its own ellipsometric parameters; therefore a reconstruction of two-dimensional thin film thickness is possible. Because the proposed ellipsometry system has a co-axial optical structure in which the objective lens is arranged in the normal direction to the measurement target, the spatial resolution is improved due to the application of a high-magnitude objective lens. In addition, spectroscopic analysis can be conducted using a number of band-pass filters which each have a central wavelength. The effect of the proposed method on thin film thickness measurement was evaluated by comparing the experimental results with a topographic profile obtained using a commercial atomic force microscope.

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

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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.

Fabrication of probe tips via the FIB method for nanodiagnostics of the surface of solids by atomic force microscopy

In this work, we carried out an investigation of commercial atomic force microscope (AFM) probes for contact and semi-contact modes, which were modified by focused ion beam (FIB). This method was used to modify the original tip shape of silicon AFM probes, by ion-etching and ion-enhance gas deposition. we show a better performance of the FIB-modified probes in contrast with the non-modified commercial probes. These results were obtained after using both probes in semi-contact mode in a calibration grating sample.

Development of a force measurement system with a large punctual measurement range

Atomic force microscopes (AFMs) are precise force measurement instruments that can be used to measure multiple surface properties, such as adhesion force, surface potential, and elasticity at the nanoscale. AFM is increasingly used in diverse fields, especially in industrial applications. However, most existing commercial AFMs provide a scanning range of less than a few 100 μm. Moreover, the size of the sample must usually be less than a few centimeters to fit the mechanical constraints of the device. In this paper, we propose a gantry-type force measurement system that can perform force curve measurements over a large range. The measurement range of the proposed device is 240 mm minus the sample width in air environments. In liquid environments, the measurement range is mainly limited by the size of the Petri dish. For instance, a measurement range of 41.5 mm can be achieved by using a Petri dish having a diameter of 85.5 mm. In the experiments, (a) surface adhesion measurements on the ultraviolet/ozone (UV/O3) treated glass slides in air and (b) surface potential measurements on a mica surface in water were performed. The experimental results were consistent with the values obtained by the commercial AFMs, which demonstrated the accuracy of the proposed system.

Demonstration of atomic force microscopy imaging using an integrated opto-electro-mechanical transducer

The low throughput of atomic force microscopy (AFM) is the main drawback in its large-scale deployment in industrial metrology. A promising solution would be based on the parallelization of the scanning probe system, allowing acquisition of the image by an array of probes operating simultaneously. A key step for reaching this goal relies on the miniaturization and integration of the sensing mechanism. Here, we demonstrate AFM imaging employing an on-chip displacement sensor, based on a photonic crystal cavity, combined with an integrated photodetector and coupled to an on-chip waveguide. This fully-integrated sensor allows high-sensitivity and high-resolution in a very small footprint and its readout is compatible with current commercial AFM systems.

High-resolution measurement of atomic force microscope cantilever resonance frequency

The atomic force microscope (AFM) is widely used in a wide range of applications due to its high scanning resolution and diverse scanning modes. In many applications, there is a need for accurate and precise measurement of the vibrational resonance frequency of a cantilever. These frequency shifts can be related to changes in mass of the cantilever arising from, e.g., loss of fluid due to a nanolithography operation. A common method of measuring resonance frequency examines the power spectral density of the free random motion of the cantilever, commonly known as a thermal. While the thermal is capable of reasonable measurement resolution and speed, some applications are sensitive to changes in the resonance frequency of the cantilever, which are small, rapid, or both, and the performance of the thermal does not offer sufficient resolution in frequency or in time. In this work, we describe a method based on a narrow-range frequency sweep to measure the resonance frequency of a vibrational mode of an AFM cantilever and demonstrate it by monitoring the evaporation of glycerol from a cantilever. It can be seamlessly integrated into many commercial AFMs without additional hardware modifications and adapts to cantilevers with a wide range of resonance frequencies. Furthermore, this method can rapidly detect small changes in resonance frequency (with our experiments showing a resolution of ∼0.1 Hz for cantilever resonances ranging from 70 kHz to 300 kHz) at a rate far faster than with a thermal. These attributes are particularly beneficial for techniques such as dip-pen nanolithography.

The nano-scale viscoelasticity using atomic force microscopy in liquid environment

We measured viscoelasticity of two nanoscale systems, single protein molecules and molecular layers of water confined between solid walls. In order to quantify the viscoelastic response of these nanoscale systems in liquid environment, the measurements are performed using two types of atomic force microscopes (AFMs), which employ different detection schemes to measure the cantilever response. We used a deflection detection scheme, available in commercial AFMs, that measures cantilever bending and a fibre-interferometer based detection which measures cantilever displacement. The hydrodynamics of the cantilever is modelled using Euler–Bernoulli equation with appropriate boundary conditions which accommodate both detection schemes. In a direct contradiction with many reports in the literature, the dissipation coefficient of a single octomer of titin I278 is found to be immeasurably low. The upper bound on the dissipation coefficient is 5 × 10−7 kg s−1, which is much lower than the reported values. The entropic stiffness of single unfolded domains of protein measured using both methods is in the range of 10 mN m−1. We show that in a conventional deflection detection measurement, the phase of the bending signal can be a primary source of artefacts in the dissipation estimates. It is recognized that the measurement of cantilever displacement, which has negligibly small phase lag due to hydrodynamics of the cantilever at low excitation frequencies, is better suited for ensuring artefact-free measurement of viscoelasticity compared to the measurement of the cantilever bending. Further, it was possible to measure dissipation in molecular layers of water confined between the tip and the substrate using fibre interferometer based AFM with similar experimental parameters. It confirms that the dissipation coefficient of a single I278 is below the detection limit of AFM. The results shed light on the discrepancy observed in the measured diffusional dynamics of protein collapse measured using Force spectroscopic techniques and single-molecule optical techniques.

Multiparametric analytical quantification of materials at nanoscale in tapping force microscopy

Atomic force microscopy (AFM) is a powerful technique for accurate, reliable and non-destructive imaging and characterization of materials at the nanoscale. Among the numerous AFM methods, amplitude modulation or tapping mode AFM (AM-AFM) is an established method for imaging and characterization for most commercial AFM systems. Despite its high spatial resolution and sensitivity, quantitative characterization by AM-AFM lag behind other advanced AFM methods as far as quantification of materials properties is concerned. In this paper a fully analytical multiparametric approach for AM-AFM is proposed which simultaneously quantifies the Hamaker constant and viscoelastic properties of materials. The main advantage of the proposed method lies in the inclusion of adhesion to calculate viscoelasticity, which makes it superior to the current equations used in the AFM community. The accuracy of the proposed method is validated by several simulations and experiments and comparison with nanoindentation results, which strongly support its candidacy as a method of choice for material properties quantification by dynamic AFM.