Measurement Of Nanomechanical Properties Research Articles

The Measurements of Nanomechanical Properties and Vibration Modal Analysis of Dragonfly Wing

The Measurements of Nanomechanical Properties and Vibration Modal Analysis of Dragonfly Wing

Direct Tip Shape Determination of a Berkovich Indenter: Effect on Nanomechanical Property Measurement and Description of a Worn Indenter

The minimization of sources of uncertainty in nanoindentation experiments is crucial for accurate determination of nanomechanical properties. A common source of uncertainty in these measurements is the estimation of tip shape and size. Besides the experimental determination of the indenter's real geometry, determination of the instrument's compliance is also necessary. We use an atomic-force-microscope-based procedure for the determination of nanoindentation tip parameters needed to account for errors induced by tip shape nonideality and to permit the evaluation of the relative contributions of the instrumental errors associated with the experimentally determined values of hardness and modulus. We compare the definitions of the currently used tip shape area function based on physically relevant parameters with the scan and propose a hyperbolic definition that meets all physically relevant criteria while being simple enough to yield good results with numerical nonlinear fitting routines.

A model-based approach to compensate for the dynamics convolution effect on nanomechanical property measurement

A model-based approach to compensate for the dynamics convolution effect on the measurement of nanomechanical properties is proposed. In indentation-based approach to measure nanomechanical properties of soft materials, an excitation force consisting of multiple frequencies needs to be accurately exerted (from the probe) to the sample material, and the indentation generated in the sample needs to be accurately measured. However, when the measurement frequency range becomes close to the bandwidth of the instrument hardware, the instrument dynamics along with the probe-sample interaction can be convoluted with the mechanical behavior of the soft material, resulting in distortions in both the applied force and the measured indentation, which, in turn, directly lead to errors in the measured nanomechanical properties of the material (e.g., the creep compliance). In this article, the dynamics involved in indentation-based nanomechanical property measurement is investigated to reveal that the convoluted dynamics effect can be described as the difference between the lightly damped probe-sample interaction and the overdamped nanomechanical behavior of the soft sample. Thus, these two different dynamics effects can be decoupled via numerical fitting based on the viscoelastic model of the soft material. The proposed approach is illustrated by implementing it to compensate for the dynamics convolution effect on a broadband viscoelasticity measurement of a polydimethylsiloxane sample using a scanning probe microscope.

Nanostructured CrN thin films prepared by reactive pulsed DC magnetron sputtering

High quality chromium nitride (CrN) films have been deposited onto silicon (1 0 0) substrates using pulsed DC magnetron sputtering of pure Cr target at different gas mixtures of argon and nitrogen and in the substrate temperature range 303–973 K. At low N 2 flow rates (<2 sccm), only pure Cr is detected, while at the intermediate flow rates (5 sccm), the hexagonal and cubic phases of Cr–N (Cr 2N and CrN) are obtained. At higher flow rates, in the range of 10–25 sccm, only cubic CrN phase is obtained. The films prepared at different substrate temperatures and at 10 sccm of nitrogen flow rate indicated the formation of cubic CrN phase at room temperature and the phase formed is found to be stable up to 973 K. The deposition of the films as a function of nitrogen flow rate and substrate temperatures indicated that the good quality crystalline films could be formed at 773 K, 10 sccm of nitrogen flow rate. The Cr 2p 3/2 and N 1s of XPS spectra also confirmed the formation of CrN phase. Determination of the texture coefficients of the CrN films as a function of substrate temperature showed that the preferred orientation changes from [1 1 1] to [1 0 0]. Deposition as a function of nitrogen flow rates and substrate temperatures showed significant changes in the morphology and RMS surface roughness, which could be related to the difference in the growth mechanism of the CrN films. Measurement of nanomechanical properties on typical films deposited on titanium modified stainless steel substrates at optimum conditions show hardness of 12 ± 1.81 GPa, Young's modulus of about (250 ± 51.28 GPa) and coefficient of friction of 0.16.

Microstructural Studies of Nanocomposite Thin Films of Ni/CrN Prepared by Reactive Magnetron Sputtering

Synthesis and characterization of nanocomposites of Ni/CrN thin films prepared by DC magnetron sputtering from a target of 50 wt.%Ni-50 wt.%Cr is investigated. The films prepared as a function of nitrogen flow rate and substrate temperature showed that the films contained Ni and CrN phases with crystallite sizes in the nanometer range. Measurement of nanomechanical properties of the composite films exhibited a significant decrease in the values of hardness and Young's modulus than those of pure CrN films.

Mechanical Interferometry of Nanoscale Motion and Local Mechanical Properties of Living Zebrafish Embryos

We present an interferometric imaging technique that permits local measurement of mechanical properties and nanomechanical motion in small living animals. Measurements of nanomechanical properties and spatially resolved pulsations of <60 nm were recorded for the developing eye of a living zebrafish (Danio rerio) embryo, an important model organism. We also used magnetic microreflectors to conduct contact nanomechanical indentation measurements of the stiffness of the embryonic eye.

Atomic force microscopy tip torsion contribution to the measurement of nanomechanical properties

The nanomechanical properties of polymethyl methacrylate and indium phosphide were measured with an atomic force microscope and a nanoindentation system. The elastic moduli measured with the atomic force microscope are in good agreement with the values obtained with the nanoindentation system. The hardness is shown to be affected by the tip radius used in our experiments. The cantilever vertical and lateral movements were independently analyzed during nanoindentation, and the tip torsion can be attributed to a change from elastic to plastic deformation regimes of materials during force microscopy nanoindentation. An analysis of the lateral movement of the laser beam associated with the cantilever torsion was used to determine the material yield stress.

Recent Development of Nanomechanical Property Measurement

Nanomechanical mapping by atomic force microscopy (AFM) has been developed as the useful application to measure the physical properties of soft materials at nano-meter scale. To date, the Hertz theory was used for analyzing force-distance curves as the simplest model of contact mechanics between elastic bodies. However, the preexisting methods based on Hertz theory do not consider the adhesive interaction in principle, which cannot be neglected in the ambient condition. First, we introduce a new analysis to estimate the elasticity and adhesive energy simultaneously by means of the JKR theory, describing adhesive contact between elastic materials. Secondly, poly(dimethylsiloxane), PDMS, and butyl rubber, isobutene-co-isoprene rubber (IIR), were analyzed to verify the validity of the JKR analysis, the method mentioned above. For elastic samples such as PDMS, the force-deformation (F-δ) plots obtained experimentally were consistent with JKR theoretical curves. Meanwhile, for viscoelastic samples, especially for IIR, the F-δplots revealed deviations from JKR curves depending on scan velocity and indentation depth. To elucidate the limit of the JKR method, we compared the characteristic behaviors of elastic and viscoelastic materials observed from contact measurement at nano-meter scale.

Mechanical characterization device for in situ measurement of nanomechanical properties of micro/nanostructures

A characterization device was developed for nanomechanical testing on one-dimensional micro/nanostructures. The tool consists of a nanomanipulator, a three-plate capacitive transducer, and associated probes, and is operated inside a scanning electron microscope. The transducer independently measures force and displacement with micronewton and nanometer sale resolutions, respectively. Tensile testing of a polyaniline microfiber (diameter ∼1μm) demonstrated the capabilities of the system. Engineering stress versus strain curves exhibited two distinct regions with different Young’s moduli. Failure at the probe-sample weld occurred at ∼67MPa, suggesting that polyaniline microfibers exhibit a yield stress that is higher than most comparable bulk polymers.

Using Atomic Force Microscopy to Retrieve Nanomechanical Surface Properties of Materials

When atomic force microscopy is used to retrieve nanomechanical surface properties of materials, unsuspected measurement and instrumentation errors may occur. In this work, some error sources are investigated and operating and correction procedures are proposed in order to maximize the accuracy of the measurements. Experiments were performed on sapphire, Ni, Co and Ni-30%Co samples. A triangular pyramidal diamond tip was used to perform indentation and scratch tests, as well as for surface visualization. It was found that nonlinearities of the z-piezo scanner, in particular the creep of the z-piezo, and errors in the determination of the real dimensions of tested areas, are critical parameters to be considered. However, it was observed that there is a critical load application rate, above which the influence of the creep of the z-piezo can be neglected. Also, it was observed that deconvolution of the tip geometry from the image of the tested area is essential to obtain accurate values of the dimensions of indentations and scratches. The application of these procedures enables minimizing the errors in nanomechanical property measurements using atomic force microscopy techniques.

Nanomechanical properties of nacre

Nacre, the inner iridescent layer of seashells is a model biomimetic system composed of 95% of inorganic (aragonite) phase and 5% of organic phase. Nacre exhibits an interlocked layered “brick and mortar” structure where the bricks are made up of aragonitic calcium carbonate and mortar is an organic phase. Here, we report the role of indentation load and penetration depth on measurement of nanomechanical properties of nacre. A range of loads from 10 μN to 10,000 μN were applied to obtain the response from different depths of nacre. The values of hardness and elastic modulus decrease with increasing load (i.e., increase in penetration depth). The variation in these values is significant at lower loads and decreases with increase in indentation load. From our results, it appears that the nanoindentation tests done at lower loads are highly influenced by micro and nanostructure in nacre. The indentation experiments performed at low loads indicate an elastic modulus of about 15 GPa for the organic phase. The low load, low penetration experiments appear to be better indicators of nanomechanical behavior. Also, we have observed a step-like behavior in the load-displacement curves at high load indentations on nacre. These features are attributed to the organic layer between the aragonite platelets. The indentation tests with penetration depths more than ∼250-300 nm often disrupt the organic layer and the behavior is not recovered in the unloading part of the curve. The microarchitecture and the composition of nacre contribute to the decrease in hardness values with increasing depth along with the indentation size effects.

Influence of surface energy and relative humidity on AFM nanomechanical contact stiffness

The effects of surface functionality and relative humidity (RH) on nanomechanical contact stiffness were investigated using atomic force acoustic microscopy (AFAM), a contact scanned-probe microscopy (SPM) technique. Self-assembled monolayers (SAMs) with controlled surface energy were studied systematically in a controlled-humidity chamber. AFAM amplitude images of a micropatterned, graded-surface-energy SAM sample revealed that image contrast depended on both ambient humidity and surface energy. Quantitative AFAM point measurements indicated that the contact stiffness remained roughly constant for the hydrophobic SAM but increased monotonically for the hydrophilic SAM. To correct for this unphysical behavior, a viscoelastic damping term representing capillary forces between the tip and the SAM was added to the data analysis model. The contact stiffness calculated with this revised model remained constant with RH, while the damping term increased strongly with RH for the hydrophilic SAM. The observed behavior is consistent with previous studies of surface energy and RH behavior using AFM pull-off forces. Our results show that surface and environmental conditions can influence accurate measurements of nanomechanical properties with SPM methods such as AFAM.

A highly sensitive atomic force microscope for linear measurements of molecular forces in liquids

We describe a highly improved atomic force microscope for quantitative nanomechanical measurements in liquids. The main feature of this microscope is a modified fiber interferometer mounted on a five axis inertial slider which provides a deflection sensitivity that is significantly better than conventional laser deflection based systems. The measured low noise floor of 572.0fm∕Hz provides excellent cantilever amplitude resolution. This allows us to operate the instrument far below resonance at extremely small cantilever amplitudes of less than 1 Å. Thus linear measurements of nanomechanical properties of liquid systems can be performed. In particular, we present measurements of solvation forces in confined octamethylcyclotetrasiloxane and water with amplitudes smaller than the size of the respective molecules. In general, the development of the instrument is important in the context of quantitative nanomechanical measurements in liquid environments.

Surface and sub-micron sub-surface evolution of Al390-T6 undergoing tribological testing under submerged lubrication conditions in the presence of CO2 refrigerant

Carbon dioxide (CO2) with its environmental benefits is considered a good replacement for commonly used synthetic refrigerants. In this study, the surface and sub-surface changes in simulated CO2 environment during the initial or transient stages of a sliding contacting interface were investigated. Pin-on-disk configurations involving Al390-T6 disks in contact with 52100 steel pins were used in controlled tribological experiments using a High Pressure Tribometer. In order to evaluate the effectiveness of CO2 refrigerant, comparative tribological experiments involving a conventional refrigerant and different commonly used lubricants were initially performed in a step-increasing load manner under submerged lubricated conditions. Subsequent detailed experiments for investigating the surface and sub-surface changes were performed in the presence of CO2 refrigerant and the best performing lubricant, polyalkyline glycol. Burnishing was observed on the surfaces during the transient (evolutionary) stage, which indicated asperity contacts due to the breaking of the elasto-hydrodynamic lubrication film. In order to quantify the surface and sub-micron sub-surface changes that occurred during this transient stage of tribological operation, several analytical tasks were performed, which involved the measurements of nanomechanical properties, chemical compositions of the topmost 200 nm surface layer, and surface roughness. Such studies of detailed evolutionary changes that occurred during the transient stage of a tribopair shed light on the complex interactions between surface and sub-surface changes that determine whether successful tribological conditions will eventually be achieved. Based on the analyses presented in this work, it is concluded that CO2 is a viable refrigerant from a tribology point of view.

Nanomechanics Using an Ultra-Small Amplitude AFM

ABSTRACTA new type of AFM is presented which allows for direct measurements of nanomechanical properties in ultra-high vacuum and liquid environments. The AFM is also capable of atomic-scale imaging of force gradients. This is achieved by vibrating a stiff lever at very small amplitudes of less than 1 Å (peak-to-peak) at a sub-resonance amplitude. This linearizes the measurement and makes the interpretation of the data straight-forward. At the atomic scale, interaction force gradients are measured which are consistent with the observation of single atomic bonds. Also, atomic scale damping is observed which rapidly rises with the tip-sample separation. A mechanism is proposed to explain this damping in terms of atomic relaxation in the tip. We also present recent results in water where we were able to measure the mechanical response due to the molecular ordering of water close to an atomically flat surface.

Confined Flow in Polymer Films at Interfaces

Measurements of nanomechanical properties of unannealed homopolymers show that the spin coating process in the presence of an interactive interface can be the source for molecular constraints in the interfacial boundary regime of elastomeric films. The surface mechanical response of poly(ethylenepropylene) (PEP) films of various thicknesses spin cast on hydrogen passivated silicon surfaces was studied using scanning force microscopy (SFM). At least two distinct rheological regimes can be observed in thicker films: high-entropy viscous plug flow at low load and low-entropy shear sliding at high load. The transition point from high-entropy to low-entropy shear has been found to shift to lower loads for decreasing film thickness. The transition point was found to disappear, and only shear sliding was observed at a critical film thickness, which was comparable to the radius of gyration of the sample polymer. These results were interpreted in a model wherein a highly distorted anisotropic layer induced by high-speed spinning and solvent evaporation is formed near the silicon interface. Pinning interactions prevent the layer from annealing, and a two-fluid-type response occurs. The surface free energy, determined by SFM lateral

Nanoindentation and contact stiffness measurement using force modulation with a capacitive load-displacement transducer

We have implemented a force modulation technique for nanoindentation using a three-plate capacitive load-displacement transducer. The stiffness sensitivity of the instrument is ∼0.1 N/m. We show that the sensitivity of this instrument is sufficient to detect long-range surface forces and to locate the surface of a specimen. The low spring mass (236 mg), spring constant (116 N/m), and damping coefficient (0.008 Ns/m) of the transducer allows measurement of the damping losses for nanoscale contacts. We present the experimental technique, important specimen mounting information, and system calibration for nanomechanical property measurement.

The Strength and Fracture of Passive Oxide Films on Metals

AbstractPassive films have been grown electrochemically on a polycrystalline titanium alloy. By varying the applied voltages, the film thickness is varied. A testing apparatus has been constructed to allow measurements of nanomechanical properties during electrochemical testing using a Ag/AgCl reference electrode in a traditional three-electrode potentiostatic scan. The stress at which oxide film fracture occurs is correlated to the applied potential. Observations of in situ film fracture measurements on single grains during immersion show the strength of the film remains constant in environments in which the film is inert, but decreases by approximately 20% in solutions which lead to corrosion. The fracture mode of the oxide has been observed using atomic force microscopy, and is shown to qualitatively match the largest tensile stresses which develop using elastic contact mechanics. A simplified model for determining the maximum tensile stress around an indentation is presented, and is used to show the stress required for fracture increases approximately linearly with increasing applied anodic polarization, from 850 MiPa to approximately 3 GPa for applied potentials between 1 and 9 V.

Macro and microtribological studies of CrO 2 video tapes

Atomic force microscopy (AFM) and its modification-friction force microscopy (FFM) are becoming increasingly important in the understanding of friction, wear, lubrication and nanomechanical property measurements. We describe modified AFM and FFM techniques and present data on microtribological studies of two CrO 2 video tapes. Macro-scale friction measurements were also made on the two tapes. We have observed that macro-scale friction is higher than that on micro-scale. Lower values of micro-scale friction as compared to macro-scale friction may be because of less ploughing contribution in micro-scale friction measurements. The directionality effects observed in micro-scale friction may come from the asymmetrical transfer of wipe material or from the calendering. Differences in the macro-scale friction in the two tapes appear to correlate with the changes in scratch resistance, wear resistance and the hardness of the tape surface on a micro-scale to nano-scales. It is demonstrated that AFM/FFM techniques are valuable in the fundamental understanding of tribology of magnetic tapes.