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We demonstrate the functionality of a new active thermal microchip dedicated to the temperature calibration of scanning thermal microscopy (SThM) probes. The silicon micromachined device consists in a suspended thin dielectric membrane in which a heating resistor with a circular area of 50µm in diameter was embedded. A circular calibration target of 10µm in diameter was patterned at the center and on top of the membrane on which the SThM probe can land. This target is a resistive temperature detector (RTD) that measures the surface temperature of the sample at the level of the contact area. This allows evaluating the ability of any SThM probe to measure a surface temperature in ambient air conditions. Furthermore, by looking at the thermal balance of the device, the heat dissipated through the probe and the different thermal resistances involved at the contact can be estimated. A comparison of the results obtained for two different SThM probes, microthermocouples and probes with a fluorescent particle is presented to validate the functionality of the micromachined device. Based on experiments and simulations, an analysis of the behavior of probes allows pointing out their performances and limits depending on the sample characteristics whose role is always preponderant. Finally, we also show that a smaller area of the temperature sensor would be required to assess the local disturbance at the contact point. [ABSTRACT FROM AUTHOR]

This paper presents the parametrically excited lateral instabilities of an asymmetrical spherical parallel manipulator (SPM) by means of monodromy matrix method. The linearized equation of motion for the lateral vibrations is developed to analyze the stability problem, resorting to the Floquet theory, which is numerically illustrated. To this end, the parametrically excited unstable regions of the manipulator are visualized to reveal the effect of the system parameters on the stability. Critical parameters, such as rotating speeds of the driving shaft, are identified from the constructed parametric stability chart for the manipulator. [ABSTRACT FROM AUTHOR]

The naturally occurring structure of articular cartilage has proven to be an effective means for the facilitation of motion and load support in equine and other animal joints. For this reason, cartilage has been extensively studied for many years. Although the roughness of cartilage has been determined from atomic force microscopy (AFM) and other methods in multiple studies, a comparison of roughness to joint function has not be completed. It is hypothesized that various joint types with different motions and regimes of lubrication have altered demands on the articular surface that may affect cartilage surface properties. Micro- and nanoscale stylus profilometry was performed on the carpal cartilage harvested from 16 equine forelimbs. Eighty cartilage surface samples taken from three different functioning joint types (radiocarpal, midcarpal, and carpometacarpal) were measured by a Veeco Dektak 150 Stylus Surface Profilometer. The average surface roughness measurements were statistically different for each joint. This indicates that the structure of cartilage is adapted to, or worn by, its operating environment. Knowledge of cartilage micro- and nanoscale roughness will assist the future development and design of treatments for intra- articular substances or surfaces to preserve joint integrity and reduce limitations or loss of joint performance. [ABSTRACT FROM AUTHOR]

Displacement measurement in atomic force microscopy (AFM) is most commonly obtained indirectly by measuring the slope of the AFM probe and applying a calibration factor. Static calibration techniques operate on the assumption that the probe response approximates single mode behavior. For off-resonance excitation or different operating conditions the contribution of higher modes may become significant. In this paper, changes to the calibrated slope-displacement relationship and the corresponding implications on measurement accuracy are investigated. A model is developed and numerical simulations are performed to examine the effect of laser spot position, tip mass, quality factor and excitation frequency on measurement accuracy. Free response conditions and operation under nonlinear tip-sample forces are considered. Results are verified experimentally using a representative macroscale system. A laser spot positioned at a nominal position between x = 0.5 and 0.6 is determined to minimize optical lever measurement error under conditions where the response is dominated by contributions from the first two modes, due to excitation as well as other factors. [ABSTRACT FROM AUTHOR]

We present an overview of four types of imaging artifacts that can occur during characterization of sharp sample topographies with intermittent contact atomic force microscopy (AFM) when using short nanotube probes (<100 nm in length). We discuss the causes behind these artifacts, as well as their implications in the context of nanomanufacturing, and explore theoretically their mitigation using AFM techniques that can perform simultaneous imaging and spectroscopy. In particular, we focus on the experimentally validated spectral inversion method [Stark et al., 2002, "Inverting Dynamic Force Microscopy: From Signals to Time-Resolved Interaction Forces," Proc. Natl. Acad. Sci. U.S.A., 99, pp. 8473-8478; Sahin et al., 2007, "An Atomic Force Microscope Tip Designed to Measure Time-Varying Nanomechanical Forces," Nat. Nanotechnol., 2, pp. 507-514] and on a recently proposed dual-frequency-modulation method [Chawla and Solares, 2009, "Single-Cantilever Dual-Frequency-Modulation Atomic Force Microscopy," Meas. Sci. Technol., 20, p. 015501], which has been demonstrated within computational simulations and is under experimental implementation in our laboratory. We discuss the capabilities and limitations of each of these approaches as well as possible areas of future development. [ABSTRACT FROM AUTHOR]

The extreme sensitivity of a scanning probe microscope demands an exceptional noise cancellation device that could effectively cut off a wide range of vibration noise. Existing commercial devices, although excellent in canceling high frequency noise, commonly leave low frequency vibration unattenuated. We design an add-on active stage that can function together with a standalone existing active stage. The objective is to provide a higher level of noise cancellation by lowering the overall system cut-off frequency. This study is concerned with the theoretical aspects of the coupling characteristics involved in stacking independently designed stages together to form a two-stage isolator Whether an add-on stage would pose a stability threat to the existing stage needs to be addressed. In addition, we explore the use of coupling effects to optimize the performance of the overall system. [ABSTRACT FROM AUTHOR]

In the first of this two-part discourse on the extraction of elastic properties from atomic force microscopy (AFM) data, a scheme for automating the analysis of force-distance curves was introduced and experimentally validated for the Hertzian (i.e., linearly elastic and noninteractive probe-sample pairs) indentation of soft, inhomogeneous materials. In the presence of probe-sample adhesive interactions, which are common especially during retraction of the rigid tip from soft materials, the Hertzian models are no longer adequate. A number of theories (e.g., Johnson-Kendall-Roberts and Derjaguin-Muller-Toporov), covering the full range of sample compliance relative to adhesive force and tip radius, are available for analysis of such data. We incorporated Pietrement and Troyon's approximation (2000, "General Equations Describing Elastic Indentation Depth and Normal Contact Stiffness Versus Load," J. Colloid Interface Sci., 226(1), pp. 166-171) of the Maugis-Dugdale model into the automated procedure. The scheme developed for the processing of Hertzian data was extended to allow for adhesive contact by applying the Pietrement-Troyon equation. Retraction force-displacement data from the indentation of polyvinyl alcohol gels were processed using the customized software. Many of the retraction curves exhibited strong adhesive interactions that were absent in extension. We compared the values of Young's modulus extracted from the retraction data to the values obtained from the extension data and from macroscopic uniaxial compression tests. Application of adhesive contact models and the automated scheme to the retraction curves yielded average values of Young's modulus close to those obtained with Hertzian models for the extension curves. The Pietrement-Troyon equation provided a good fit to the data as indicated by small values of the mean-square error. The Maugis-Dugdale theory is capable of accurately modeling adhesive contact between a rigid spherical indenter and a soft, elastic sample. Pietrement and Troyon's empirical equation greatly simplifies the theory and renders it compatible with the general automation strategies that we developed for Hertzian analysis. Our comprehensive algorithm for automated extraction of Young's moduli from AFM indentation data has been expanded to recognize the presence of either adhesive or Hertzian behavior and apply the appropriate contact model. [ABSTRACT FROM AUTHOR]

This paper investigates nanomachining of single-crystal silicon using an atomic force microscope with a diamond-tip cantilever. To enable nanomachining of silicon, a nanomachining cantilever with a pyramidal diamond tip was developed using a combination of photolithography and hot-filament chemical vapor deposition. Nanomachining experiments on silicon using the cantilever are demonstrated under various machining parameters. The silicon surface can be removed with a rate of several tens to hundreds of nanometers in ductile mode, and the cantilever shows superior wear resistance. The experiments demonstrate successful nanomachining of single-crystal silicon. [ABSTRACT FROM AUTHOR]

Atomic force microscopy (AFM) has been widely used for measuring mechanical properties of biological specimens such as cells, DNA, and proteins. This is usually done by monitoring deformations in response to controlled applied forces, which have to be at ultralow levels due to the extreme softness of the specimens. Consequently, such experiments may be susceptible to thermal excitations, manifested as force and displacement fluctuations that could reduce the measurement accuracy. To take advantage of, rather than to be limited by, such fluctuations, we have characterized the thermomechanical responses of an arbitrarily shaped AFM cantilever with the tip coupled to an elastic spring. Our analysis shows that the cantilever and the specimen behave as springs in parallel. This provides a method for determining the elasticity of the specimen by measuring the change in the tip fluctuations in the presence and absence of coupling. For rectangular and V-shaped cantilevers, we have derived a relationship between the mean-square deflection and the mean-square inclination and an approximate expression for the specimen spring constant in terms of contributions to the mean-square inclination from the first few vibration modes. [ABSTRACT FROM AUTHOR]

Presents the evolution of atomic force microscope (AFM) system into a useful tool for direct measurements of intermolecular forces with atomic-resolution characterization that can be employed in a broad spectrum of applications. Unique advantages of non-contact AFM over contemporary scanning probe techniques; Basis of the current AFM imaging techniques on lumped-parameters model and ordinary differential equation representation of the micro-cantilevers; Design of the interaction force identification scheme.

Studies ultra-high-precision positioning with piezoactuators and illustrates the results with an example Scanning Probe Microscopy (SPM) application. High speed scanning probe microscopy; Model-based inversion; Creep and hysteresis effects.

Presents a paper on scanning Joule expansion microscopy (SJEM), a thermal imaging technique. Lateral resolution range of this technique; Description of the scanning Joule expansion microscope; Experimental results of SJEM; Reference to the measurement of surface temperature distribution; Other capabilities of SJEM; Conclusions drawn from results of experiments.

Focuses on the use of scanning probe microscopy (SPM) to test frictional characteristics of several types of boundary lubricants. Definition of the micro-miniaturization; Anchorage of ultrathin organic films; Analysis of frictional behavior of different monolayers.

This paper proposes and demonstrates an estimation scheme for Li-ion concentrations in both electrodes of a Li-ion battery cell. The well-known observability deficiencies in the two-electrode electrochemical models of Li-ion battery cells are first overcome by extending them with a thermal evolution model. Essentially, coupling of electrochemical-thermal dynamics emerging from the fact that the lithium concentrations contribute to the entropic heat generation is utilized to overcome the observability issue. Then, an estimation scheme comprised of a cascade of a sliding-mode observer and an unscented Kalman filter (UKF) is constructed that exploits the resulting structure of the coupled model. The approach gives new real-time estimation capabilities for two often-sought pieces of information about a battery cell: (1) estimation of cell-capacity and (2) tracking the capacity loss due to degradation mechanisms such as lithium plating. These capabilities are possible since the two-electrode model needs not be reduced further to a single-electrode model by adding Li conservation assumptions, which do not hold with long-term operation. Simulation studies are included for the validation of the proposed scheme. Effect of measurement noise and parametric uncertainties is also included in the simulation results to evaluate the performance of the proposed scheme. [ABSTRACT FROM AUTHOR]

New developments in MEMS (microelectromechanical systems) fabrication allowed the development of new types of atomic force microscopy (AFM) sensor with integrated readout circuit and actuator built in on the cantilever. Such a fully instrumented cantilever allows a much more direct measurement and actuation of the cantilever motion and interaction with the sample. This technology is expected to not only allow for high speed imaging but also the miniaturization of AFMs. Based on the complexity of these integrated MEMS devices, a thorough understanding of their behavior and a specialized controls approach is needed to make the most use out of this new technology. In this paper we investigate the intrinsic properties of such MEMS cantilevers and develop a combined approach for sensing and control, optimized for high speed detection and actuation. Further developments based on the results presented in this paper will help to expand the use of atomic force microscopy to a broad range of everyday applications in industrial process control and clinical diagnostics. [ABSTRACT FROM AUTHOR]

While the atomic force microscope (AFM) was mainly developed to image the topography of a sample, it has been discovered as a powerful tool also for nanomanipulation applications within the last decade. A variety of different manipulation types exists, ranging from dip-pen and mechanical lithography to assembly of nano-objects such as carbon nanotubes (CNTs), deoxyribonucleic acid (DNA) strains, or nanospheres. The latter, the assembly of nano-objects, is a very promising technique for prototyping nanoelectronical devices that are composed of DNA-based nanowires, CNTs, etc. But, pushing nano-objects in the order of a few nanometers nowadays remains a very challenging, labor-intensive task that requires frequent human intervention. To increase throughput of AFM-based nanomanipulation, automation can be considered as a long-term goal. However, automation is impeded by spatial uncertainties existing in every AFM system. This article focuses on thermal drift, which is a crucial error source for automating AFM-based nanoassembly, since it implies a varying, spatial displacement between AFM probe and sample. A novel, versatile drift estimation method based on Monte Carlo localization is presented and experimental results obtained on different AFM systems illustrate that the developed algorithm is able to estimate thermal drift inside an AFM reliably even with highly unstructured samples and inside inhomogeneous environments. [ABSTRACT FROM AUTHOR]

Control can enable high-bandwidth nanopositioning needed to increase the operating speed of scanning probe microscopes (SPMs). High-speed SPMs can substantially impact the throughput of a wide range of emerging nanosciences and nanotechnologies. In particular, inversion-based control can find the feedforward input needed to account for the positioning dynamics and, thus, achieve the required precision and bandwidth. This article reviews inversion-based feedforward approaches used for high-speed SPMs such as optimal inversion that accounts for model uncertainty and inversion-based iterative control for repetitive applications. The article establishes connections to other existing methods such as zero-phase-error-tracking feedforward and robust feedforward. Additionally, the article reviews the use of feedforward in emerging applications such as SPM-based nanoscale combinatorial-science studies, image-based control for subnanometer-scale studies, and imaging of large soft biosamples with SPMs. [ABSTRACT FROM AUTHOR]

Piezoresponse force microscopy (PFM) is an atomic force microscopy-based approach utilized for measuring local properties of piezoelectric materials. The objective of this study is to propose a practical framework for simultaneous estimation of the local stiffness and piezoelectric properties of materials. For this, the governing equation of motion of a vertical PFM is derived at a given point on the sample. Using the expansion theorem, the governing ordinary differential equations of the system and their state-space representation are derived under applied external voltage. For the proof of the concept, the results obtained from both frequency and step responses of a PFM experiment are utilized to simultaneously identify the microcantilever parameters along with local spring constant and piezoelectric coefficient of a periodically poled lithium niobate sample. In this regard, a new parameter estimation strategy is developed for modal identification of system parameters under general frequency response. Results indicate good agreements between the identified model and the experimental data using the proposed modeling and identification framework. This method can be particularly applied for accurate characterization of mechanical and piezoelectric properties of biological species and cells. [ABSTRACT FROM AUTHOR]

This article presents an iterative-based feedforward-feedback control approach to achieve high-speed atomic force microscope (AFM) imaging. AFM-imaging requires precision positioning of the probe relative to the sample in all x-y-z axes directions. Particularly, this article is focused on the vertical z-axis positioning. Recently, a current-cycle-feedback iterative-learning-control (CCF-ILC) approach has been developed for precision tracking of a given desired trajectory (even when the desired trajectory is unknown), which can be applied to achieve precision tracking of sample profile on one scanline. In this article, we extend this CCF-ILC approach to imaging of entire sample area. The main contribution of this article is the convergence analysis and the use of the CCF-ILC approach for output tracking in the presence of desired trajectory varation between iterations—the sample topography variations between adjacent scanlines. For general case where the desired trajectory variation occurs between any two successive iterations, the convergence (stability) of the CCF-ILC system is addressed and the allowable size of desired trajectory variation is quantified. The performance improvement achieved by using the CCF-ILC approach is discussed by comparing the tracking error of using the CCF-ILC technique to that of using feedback control alone. The efficacy of the proposed CCF-ILC control approach is illustrated by implementing it to the z-axis control during AFM-imaging. Experimental results are presented to show that the AFM-imaging speed can be substantially increased. [ABSTRACT FROM AUTHOR]

A number of recent studies have demonstrated the effectiveness of atomic force microscopy (AFM) for characterization of cellular stress-relaxation behavior. However, this technique's recent development creates considerable need for exploration of appropriate mechanical models for analysis of the resultant data and of the roles of various cytoskeletal components responsible for governing stress-relaxation behavior. The viscoelastic properties of vascular smooth muscle cells (VSMCs) are of particular interest due to their role in the development of vascular diseases, including atherosclerosis and restenosis. Various cytoskeletal agents, including cytochalasin D, jasplakinolide, paclitaxel, and nocodazole, were used to alter the cytoskeletal architecture of the VSMCs. Stress-relaxation experiments were performed on the VSMCs using AFM. The quasilinear viscoelastic (QLV) reduced-relaxation function, as well as a simple power-law model, and the standard linear solid (SLS) model, were fitted to the resultant stress-relaxation data. Actin depolymerization via cytochalasin D resulted in significant increases in both rate of relaxation and percentage of relaxation; actin stabilization via jasplakinolide did not affect stress-relaxation behavior. Microtubule depolymerization via nocodazole resulted in nonsignificant increases in rate and percentage of relaxation, while microtubule stabilization via paclitaxel caused significant decreases in both rate and percentage of relaxation. Both the QLV reduced-relaxation function and the power-law model provided excellent fits to the data (R²=0.98), while the SLS model was less adequate (R²=0.91). Data from the current study indicate the important role of not only actin, but also microtubules, in governing VSMC viscoelastic behavior. Excellent fits to the data show potential for future use of both the QLV reduced-relaxation function and power-law models in conjunction with AFM stress-relaxation experiments. [ABSTRACT FROM AUTHOR]

The basic unit in microtubules is αβ-tubulin, a heterodimer consisting of an α- and a β-tubulin monomer. The mechanical characteristics of the dimer as well as of the individual monomers may be used to obtain new insight into the microtubule tensile properties. In the present work, we evaluate the elastic constants of each monomer and the interaction force between them by means of molecular dynamics simulations. Molecular models of α-, β-, and αβ-tubulins were developed starting from the 1TUB.pdb structure from the RCSB database. Simulations were carried out in a solvated environment by using explicit water molecules. In order to measure the monomers' elastic constants, simulations were performed by mimicking experiments carried out with atomic force microscopy. A different approach was used to determine the interaction force between the α- and β-monomers by using 16 different monomer configurations based on different intermonomer distances. The obtained results show an elastic constant value for α-tubulin of 3.8-3.9 N/m, while for the β-tubulin, the elastic constant was measured to be 3.3-3.6 N/m. The maximum interaction force between the monomers was estimated to be 11.9 nN. A mechanical model of the tubulin dimer was then constructed and, using the results from MD simulations, Young's modulus was estimated to be 0.6 GPa. A fine agreement with Young's modulus values from literature (0.1-2.5 GPa) is found, thus validating this approach for obtaining molecular scale mechanical characteristics. In perspective, these outcomes will allow exchanging atomic level description with key mechanical features enabling microtubule characterization by continuum mechanics approach. [ABSTRACT FROM AUTHOR]

A set of memory-based properties is employed in this paper for modeling multiple-path hysteresis response of piezoelectric actuators. These properties, namely, targeting turning points, curve alignment, and wiping-out effect, are applied in a linear mapping strategy to develop a mathematical framework for modeling the hysteresis phenomenon. More specifically, the locations of turning points are detected and recorded for the prediction of future hysteresis trajectory. An internal trajectory is assumed to follow a multiple-segmented path via a continuous connection of several curves passing through every two consequent turning points. These curves adopt their shapes via a linear mapping strategy from the reference hysteresis curves with polynomial configurations. Experimental implementation of the proposed method demonstrates slight improvement over the widely used Prandtl-Ishlinskii hysteresis operator. However, to maintain the level of precision during the operation, a sufficient number of memory units must be included to record the turning points. Otherwise, in the event of memory saturation, two memory-allocation modes, namely, "open" and "closed" strategies, can be implemented. It is shown that the closed memory-allocation strategy demonstrates better performance by keeping the most important target points. The proposed modeling framework is adopted in an inverse model-based control scheme for feedforward compensation of hysteresis nonlinearity. The controller is experimentally implemented on a three-dimensional nanopositioning stage for surface topography tracking, a problem typically encountered in scanning probe microscopy applications. [ABSTRACT FROM AUTHOR]