Measurement Of Nanomechanical Properties Research Articles

Scanning Probe Microscopy Techniques for Studying the Cell Glycocalyx.

The glycocalyx is a brush-like layer that covers the surfaces of the membranes of most cell types. It consists of a mixture of carbohydrates, mainly glycoproteins and proteoglycans. Due to its structure and sensitivity to environmental conditions, it represents a complicated object to investigate. Here, we review studies of the glycocalyx conducted using scanning probe microscopy approaches. This includes imaging techniques as well as the measurement of nanomechanical properties. The nanomechanics of the glycocalyx is particularly important since it is widely present on the surfaces of mechanosensitive cells such as endothelial cells. An overview of problems with the interpretation of indirect data via the use of analytical models is presented. Special insight is given into changes in glycocalyx properties during pathological processes. The biological background and alternative research methods are briefly covered.

Observation of defect density dependent elastic modulus of graphene

The recent decade has witnessed a tremendous development of graphene applications in many fields; however, as one of the key considerations, the mechanical properties of graphene still remain largely unexplored. Herein, by employing focused ion beam irradiation, graphene with various defect levels is obtained and further investigated by using Raman spectroscopy and scanning tunneling microscopy. Specially, our atomic force microscopy based nanomechanical property measurement demonstrates a clear defect density dependent behavior in the elastic modulus of graphene on a substrate as the defect density is higher than a threshold value of 1012 cm−2, where a clear decay is observed in the stiffness of graphene. This defect density dependence is mainly attributed to the appearance of amorphous graphene, which is further confirmed with our molecular dynamics calculations. Therefore, our reported result provides an essential guidance to enable the rational design of graphene materials in nanodevices, especially from the perspective of mechanical properties.

Investigation and Measurement of Nanomechanical Properties of the HSS Powder Metallurgy ASP2017 and ASP2055 Steels

The intention of the team of authors in the presented scientific article was experimental measurement with subsequent evaluation of nanomechanical properties of selected microstructural components of the investigated high-speed steels type ASP2017 and ASP2055 produced by powder metallurgy. The whole experiment was performed under laboratory conditions on an experimental apparatus called Hysitron TI 950 Triboindeneter. The used device is a part of the laboratory equipment of the Center for Diagnostics and Quality Testing of Materials. The proposed process of experimental research of the mentioned properties of PM steels was carried out precisely because of the relatively high require-ments for the use of this type of steel for the needs of special applications in the engineering industry. Therefore, the research of nanomechanical properties such as nanohardness H and the reduced and real Young's modulus Er and the Young's modulus of elasticity Es were therefore the subject of the authors' research. The authors proposed the use of a Berkovich geometry tip as a test or indentation body, respectively. In terms of the proposed structure of the article, the authors describe the current state of research from the assigned problem using database sources. The experimental part of their research already solves the obtained nanomechanical properties of individual components of the struc-ture of the tested PM steels, as well as the distribution of individual positions of indents. These were designed using so-called SPM scans (Scanning Probe Microscopy). Nanoindentation curves were generated from them using the Triboscan evaluation software. Based on the performed measurements and the Er obtained from them, and the Es was also calculated using mathematical relations. The authors graphically expressed the final values of nanomechanical quantities and described them in a discussion of the experiments.

Effects of aging on nanomechanical properties of mice bone marrow derived adherent cells using atomic force microscopy (AFM).

Aging is a complicated process leading to variation in biological and physical traits of living organisms. In this study, we investigate how the nanomechanical properties of live cells such as Young's modulus, and deformation are affected by aging using Atomic Force Microscopy (AFM) at single molecule level. AFM is an outstanding platform to perform high resolution imaging and nanomechanical property characterization of the biomolecules, and live cells. For mice bone marrow-derived cells (BMDC), there weren’t significant effects of aging on the costimulatory molecule expression of the cells or the cytokine secretion for the non-adherent cell population whereas spleen derived dendritic cells were affected by aging. In our study, mice bone marrow-derived adherent cells were used as a model system for the measurement of nanomechanical properties using AFM. The same PFQNM-LC-CAL-A probe with calibrated spring constant of 0.101 N/m and uniform scanning parameters was used for all the experiments on both aged and younger cells in this study in Peak Force QNM mode. Our results showed that average Young's modulus values of older mice cells (48.13± 6.73 kPa) are higher than younger mice cells (35.37±2.34 kPa) and deformation values of older mice cells are lower compared to younger cells. So, unlike non-adherent BMDCs, nanomechanical properties of adherent BMDCs are affected by aging. We intend to perform similar measurements with AFM on cells derived from older and younger population of reptiles like snake and turtles to improve the understanding of aging process.

Atomic force microscopy for nanoscale mechanical property characterization

Over the past several decades, atomic force microscopy (AFM) has advanced from a technique used primarily for surface topography imaging to one capable of characterizing a range of chemical, mechanical, electrical, and magnetic material properties with subnanometer resolution. In this review, we focus on AFM as a nanoscale mechanical property characterization tool and examine various AFM contact and intermittent contact modes that add mechanical contrast to an imaged surface. Through detailed analysis of the tip-sample contact mechanics, this contrast can be converted into quantitative measurements of various nanomechanical properties including elastic modulus, shear modulus, wear rate, adhesion, and viscoelasticity. Different AFM modes that provide such measurements are compared and contrasted in this work on a wide range of materials including ceramics, metals, semiconductors, polymers, and biomaterials. In the last few years, considerable improvements have been made in terms of fast imaging capabilities, tip preservation, and quantitative mechanics for multifrequency measurements as well as well-known AFM modes like amplitude modulation and peak-force tapping. In line with these developments, a major highlight of this review is the discussion of the operation and capabilities of one such mode, namely, intermittent contact resonance AFM (ICR-AFM). The applications of ICR-AFM to nanoscale surface and subsurface quantitative mechanical characterizations are reviewed with specific examples provided for thin polymeric films and patterned nanostructures of organosilicate dielectric materials. The combination of AFM-based mechanical characterization with AFM-based chemical spectroscopy to allow nanoscale structure-property characterization is also discussed and demonstrated for the analysis of low-k dielectric/copper nanoelectronic interconnect structures and further highlights synergistic advances in the AFM field.

Microstructural analysis of examined 33NiCrMoV15 steel and investigation of its nanome-chanical properties after machining

The authors presented paper deals with experimental measurement and evaluation of nanomechanical properties of hard turned and grinded surfaces on the cross section specimens made of the 33NiCrMoV15 steel. 33NiCrMoV15 steel was selected to perform for all realized investigations. Even before the start of the experi-ments that investigated the effect of hard finish turning against grinding, it was necessary to subject the investi-gated 33NiCrMoV15 steel to basic research with regard to its chemical composition, fundamental microstructure and basic mechanical properties. The microstructure was performed on Neophot 32 optical microscope. Chemical composition was realized on the spectral analyzer Spectrolab Jr CCD. Mechanical properties, like nanohardness H and reduced Young modulus Er were subsequently performed on the Hysitron TI950 Triboindenter with a Cube Corner measuring tip, and evaluated by software Triboscan. Based on the acquired values, a 2D nanostructure of the distribution map of s H and Er was then evaluated in Matlab. This scientific research, together with all measured and calculated values, is the fundamental that will help to optimizing the quality and used all these results to optimize presented material and technological processes in term of surface integrity.

Measurement of nanomechanical properties of DNA molecules by PeakForce atomic force microscopy based on DNA origami.

Characterization of the stiffness of thin DNA strands remains difficult. By constructing bilayer DNA molecules, we investigated their mechanical properties using AFM. Increased DNA thickness through DNA origami greatly reduced the substrate effect when measuring Young's modulus, thus providing a more accurate picture of the inherent nanomechanical properties of DNA.

AFM/TIRF force clamp measurements of neurosecretory vesicle tethers reveal characteristic unfolding steps.

Although several proteins have been implicated in secretory vesicle tethering, the identity and mechanical properties of the components forming the physical vesicle-plasma membrane link remain unknown. Here we present the first experimental measurements of nanomechanical properties of secretory vesicle-plasma membrane tethers using combined AFM force clamp and TIRF microscopy on membrane sheets from PC12 cells expressing the vesicle marker ANF-eGFP. Application of pulling forces generated tether extensions composed of multiple steps with variable length. The frequency of short (<10 nm) tether extension events was markedly higher when a fluorescent vesicle was present at the cantilever tip and increased in the presence of GTPγS, indicating that these events reflect specifically the properties of vesicle-plasma membrane tethers. The magnitude of the short tether extension events is consistent with extension lengths expected from progressive unfolding of individual helices of the exocyst complex, supporting its direct role in forming the physical vesicle-plasma membrane link.

Measurement of Thin-film Coating Hardness in the Presence of Contamination and Roughness: Implications for Tribology

Standard nanoindentation measurements on commercially available TiAlN, CrN, metal-containing diamond-like carbon, and TiN coatings, deposited on steel substrates were performed to determine coating hardness and elastic modulus. It was found that the coating surface roughness/morphology present after deposition can significantly affect the measurements of nanomechanical properties so that measurements of these properties on the as-deposited coating surface may be significantly different from the bulk. In addition, a surface measurement may produce a lower nanohardness due to the existence of a soft surface contamination layer. A simple method was developed to enable accurate measurement of the nanomechanical properties of coatings, while avoiding errors introduced by surface topography and the presence of superficial contamination layers on thin films. Friction and wear behavior, as well as the wear mechanisms in dry reciprocating sliding contact of the various coatings with a steel ball can be correlated to the surface attributes of each coating in terms of roughness and the presence of contamination layers, both of which are shown to also affect the nanohardness measurements.

Photothermally excited force modulation microscopy for broadband nanomechanical property measurements.

We demonstrate photothermally excited force modulation microscopy (PTE FMM) for mechanical property characterization across a broad frequency range with an atomic force microscope (AFM). Photothermal excitation allows for an AFM cantilever driving force that varies smoothly as a function of drive frequency, thus avoiding the problem of spurious resonant vibrations that hinder piezoelectric excitation schemes. A complication of PTE FMM is that the sub-resonance cantilever vibration shape is fundamentally different compared to piezoelectric excitation. By directly measuring the vibrational shape of the cantilever, we show that PTE FMM is an accurate nanomechanical characterization method. PTE FMM is a pathway towards the characterization of frequency sensitive specimens such as polymers and biomaterials with frequency range limited only by the resonance frequency of the cantilever and the low frequency limit of the AFM.

Studying biological membranes with extended range high-speed atomic force microscopy.

High—speed atomic force microscopy has proven to be a valuable tool for the study of biomolecular systems at the nanoscale. Expanding its application to larger biological specimens such as membranes or cells has, however, proven difficult, often requiring fundamental changes in the AFM instrument. Here we show a way to utilize conventional AFM instrumentation with minor alterations to perform high-speed AFM imaging with a large scan range. Using a two—actuator design with adapted control systems, a 130 × 130 × 5 μm scanner with nearly 100 kHz open—loop small-signal Z—bandwidth is implemented. This allows for high-speed imaging of biologically relevant samples as well as high-speed measurements of nanomechanical surface properties. We demonstrate the system performance by real-time imaging of the effect of charged polymer nanoparticles on the integrity of lipid membranes at high imaging speeds and peak force tapping measurements at 32 kHz peak force rate.

Effects of sputtering pressure on nanostructure and nanomechanical properties of AlN films prepared by RF reactive sputtering

Wurtzite aluminum nitride (AlN) films were deposited on Si(100) wafers under various sputtering pressures by radio-frequency (RF) reactive magnetron sputtering. The film properties were investigated by XRD, SEM, AFM, XPS and nanoindenter techniques. It is suggested from the XRD patterns that highly c-axis oriented films grow preferentially at low pressures and the growth of (100) planes are preferred at higher pressures. The SEM and AFM images both reveal that the deposition rate and the surface roughness decrease while the average grain size increases with increasing the sputtering pressure. XPS results show that lowering the sputtering pressure is a useful way to minimize the incorporation of oxygen atoms into the AlN films and hence a film with closer stoichiometric composition is obtained. From the measurement of nanomechanical properties of AlN thin films, the largest hardness and elastic modulus are obtained at 0.30 Pa.

Characterizing the free and surface-coupled vibrations of heated-tip atomic force microscope cantilevers**Publication of NIST, an agency of the US government, not subject to copyright.

Combining heated-tip atomic force microscopy (HT-AFM) with quantitative methods for determining surface mechanical properties, such as contact resonance force microscopy, creates an avenue for nanoscale thermomechanical property characterization. For nanomechanical methods that employ an atomic force microscope cantilever’s vibrational modes, it is essential to understand how the vibrations of the U-shaped HT-AFM cantilever differ from those of a more traditional rectangular lever, for which analytical techniques are better developed. Here we show, with a combination of finite element analysis (FEA) and experiments, that the HT-AFM cantilever exhibits many more readily-excited vibrational modes over typical AFM frequencies compared to a rectangular cantilever. The arms of U-shaped HT-AFM cantilevers exhibit two distinct forms of flexural vibrations that differ depending on whether the two arms are vibrating in-phase or out-of-phase with one another. The in-phase vibrations are qualitatively similar to flexural vibrations in rectangular cantilevers and generally show larger sensitivity to surface stiffness changes than the out-of-phase vibrations. Vibration types can be identified from their frequency and by considering vibration amplitudes in the horizontal and vertical channels of the AFM at different laser spot positions on the cantilever. For identifying contact resonance vibrational modes, we also consider the sensitivity of the resonant frequencies to a change in applied force and hence to tip–sample contact stiffness. Finally, we assess how existing analytical models can be used to accurately predict contact stiffness from contact-resonance HT-AFM results. A simple two-parameter Euler–Bernoulli beam model provided good agreement with FEA for in-phase modes up to a contact stiffness 500 times the cantilever spring constant. By providing insight into cantilever vibrations and exploring the potential of current analysis techniques, our results lay the groundwork for future use of HT-AFM cantilevers for accurate nanomechanical property measurements.

Quantitative imaging of diatoms by PeakForce atomic force microscopy

A novel approach to study nanomechanical properties such as deformation, adhesion or Young's modulus is presented for freshwater diatoms having sizes ranging from tens to hundreds of micrometers. Changes occurring in the environment, such as water acidity or temperature variations, have an impact on the diatoms population, as they can cause the death of certain species favoring simultaneously the growth of another. The nanomechanical properties were measured by means of atomic force microscopy (AFM) in a unique PeakForce tapping (PFT) mode. The observed changes of the Young's modulus measured in the frustule of Cyclotella meneghini diatom were in the range of 7–25 GPa, clearly confirming that, in this part of the diatom, degeneration occurs. The use of the PFT mode in the AFM allowed also for measuring the surface of diatoms exhibiting a very developed topography. This is a new methodology for quantitative measurements of nanomechanical properties allowing to monitor environmental changes. Copyright © 2014 John Wiley &amp; Sons, Ltd.

Imaging and Measurement of Nanomechanical Properties within Primary Xylem Cell Walls of Broadleaves

A technique of atomic force microscopy (AFM) called PeakForce quantitative nanomechanical mapping (PeakForce QNM) is an efficient tool for the quantitative mechanobiological imaging of fibrillar aggregate, human epidermal cell and woody plant cell wall topography (Sweers et al., 2011; Heu et al., 2012; Ďurkovič et al., 2012; Ďurkovič et al., 2013). Here, we describe a detailed protocol for the measurement of nanomechanical properties of primary xylem cell walls in woody plants, for the determination of reduced Young’s modulus of elasticity (MOE), adhesion, deformation, and energy dissipation (Figure 1). This new technique provides direct control of the maximum loading force and the deformation depth in cell wall samples keeping indentations small, while at the same time eliminating damaging lateral forces in order to preserve both the AFM tip and plant sample. High-resolution and non-destructive imaging shed new quantitative mechanistic insights into the structural biology of woody plant cell walls. This procedure can also be adapted for other biological samples with a varying range of stiffness.

A Control-Based Approach to Accurate Nanoindentation Quantification in Broadband Nanomechanical Measurement Using Scanning Probe Microscope

This paper presents a control-based approach to accurately quantify the indentation in broadband nanomechanical property measurements using scanning probe microscope (SPM). Accurate indentation measurement is essential to probe-based material property characterization as the force exerted and the indentation generated are the two most important physical variables measured in the process. Large measurement errors, however, occur when the measurement frequency range becomes large (i.e., broadband). Such errors result from the inability of the conventional method to account for the difference between the SPM z-axis piezo actuator displacement and the vertical displacement of the cantilever at its fixed end, and the lateral-vertical coupling-caused cantilever motion when the measurement frequency range increases. A control-based approach is presented to address these limits of the conventional method. The proposed approach is demonstrated through experiments to measure the viscoelastic properties of a Polydimethylsiloxane (PDMS) sample over a broad-frequency range.

Indentation quantification for in-liquid nanomechanical measurement of soft material using an atomic force microscope: Rate-dependent elastic modulus of live cells

In this paper, a control-based approach to replace the conventional method to achieve accurate indentation quantification is proposed for nanomechanical measurement of live cells using atomic force microscope. Accurate indentation quantification is central to probe-based nanomechanical property measurement. The conventional method for in-liquid nanomechanical measurement of live cells, however, fails to accurately quantify the indentation as effects of the relative probe acceleration and the hydrodynamic force are not addressed. As a result, significant errors and uncertainties are induced in the nanomechanical properties measured. In this paper, a control-based approach is proposed to account for these adverse effects by tracking the same excitation force profile on both a live cell and a hard reference sample through the use of an advanced control technique, and by quantifying the indentation from the difference of the cantilever base displacement in these two measurements. The proposed control-based approach not only eliminates the relative probe acceleration effect with no need to calibrate the parameters involved, but it also reduces the hydrodynamic force effect significantly when the force load rate becomes high. We further hypothesize that, by using the proposed control-based approach, the rate-dependent elastic modulus of live human epithelial cells under different stress conditions can be reliably quantified to predict the elasticity evolution of cell membranes, and hence can be used to predict cellular behaviors. By implementing the proposed approach, the elastic modulus of HeLa cells before and after the stress process were quantified as the force load rate was changed over three orders of magnitude from 0.1 to 100 Hz, where the amplitude of the applied force and the indentation were at 0.4-2 nN and 250-450 nm, respectively. The measured elastic modulus of HeLa cells showed a clear power-law dependence on the load rate, both before and after the stress process. Moreover, the elastic modulus of HeLa cells was substantially reduced by two to five times due to the stress process. Thus, our measurements demonstrate that the control-based protocol is effective in quantifying and characterizing the evolution of nanomechanical properties during the stress process of live cells.

Optimal Excitation Force Design in Indentation-Based Rapid Broadband Nanomechanical Spectroscopy: Poly(dimethylsiloxane) Example

This paper presents an optimal input design approach to achieve rapid broadband nanomechanical measurements of soft materials using indentation-based method. The indentation-based nanomechanical measurement provides unique quantification of material properties at specified locations. The measurement, however, is currently too slow and too narrow in frequency (range) to characterize time-elapsing material properties during dynamic evolutions (e.g., the rapid-stage of the crystallization process of polymers). These limitations exist because the excitation input force used in current methods cannot rapidly excite broadband nanomechanical properties of materials. The challenges arise as a result of the instrumental hardware dynamics being excited and convoluted with the material properties during the measurement when the frequencies in the excitation force increase, resulting in large measurement errors. Moreover, measurement takes a long time when the frequency range is large, which, in turn, leads to large temporal measurement errors upon dynamic evolution of the sample. In this paper, we develop an optimal-input design approach to tackle these challenges. Particularly, an input force profile with discrete spectrum is optimized to maximize the Fisher information matrix of the linear compliance model of the soft material. Both simulation and experiments on a Poly(dimethylsiloxane) (PDMS) sample are presented to illustrate the need for optimal input design and the efficacy of the proposed approach in probe-based nanomechanical property measurements.

Accurate and precise calibration of AFM cantilever spring constants using laser Doppler vibrometry

Accurate cantilever spring constants are important in atomic force microscopy both in control of sensitive imaging and to provide correct nanomechanical property measurements. Conventional atomic force microscope (AFM) spring constant calibration techniques are usually performed in an AFM. They rely on significant handling and often require touching the cantilever probe tip to a surface to calibrate the optical lever sensitivity of the configuration. This can damage the tip. The thermal calibration technique developed for laser Doppler vibrometry (LDV) can be used to calibrate cantilevers without handling or touching the tip to a surface. Both flexural and torsional spring constants can be measured. Using both Euler–Bernoulli modeling and an SI traceable electrostatic force balance technique as a comparison we demonstrate that the LDV thermal technique is capable of providing rapid calibrations with a combination of ease, accuracy and precision beyond anything previously available.

Tunable glass reference materials for quantitative backscattered electron imaging of mineralized tissues

Abstract