Nanoindentations were made on a (100) single crystal Si wafer at room temperature with a series of triangular pyramidal indenters having centerline-to-face angles ranging from 35° to 85°. Indentations produced at high (80 mN) and low (10 mN) loads were examined in plan-view by scanning electron microscopy and in cross-section by transmission electron microscopy. Microstructural observations were correlated with the indentation load-displacement behavior. Cracking and extrusion are more prevalent for sharp indenters with small centerline-to-face angles, regardless of the load. At low loads, the transformed material is amorphous silicon for all indenter angles. For Berkovich indentations made at high-load, the transformed material is a nanocrystalline mix of Si-I and Si-III/Si-XII, as confirmed by selected area diffraction. Extrusion of material at high loads for the cube-corner indenter reduces the volume of transformed material remaining underneath the indenter, thereby eliminating the pop-out in the unloading curve.

Strength, friction, and wear are dominant factors in the performance and reliability of materials and devices fabricated using nickel based LIGA and silicon based MEMS technologies. However, the effects of frictional contacts and wear on the mechanical performance of microdevices are not well-defined. To address these effects on performance of LIGA nickel, we have begun a program employing nanoscratch and nanoindentation. Nanoscratch techniques were used to generate wear patterns using loads of 100, 200, 500, and 990 μN with each load applied for 1, 2, 5, and 10 passes. Nanoindentation was then used to measure properties in each wear pattern correcting for surface roughness. The results showed a systematic increase in hardness with applied load and number of nanoscratch passes. The results also showed that the work hardening coefficient determined from indentation tests within wear patterns follows the work hardening behavior established from tensile tests, supporting use of a nanomechanics-based approach for studying mechanical properties of wear tested material.

The risk of dental caries increases with the use of orthodontic appliances, and it does not only depend on a patient's oral hygiene. Caries cause teeth enamel demineralization close to the orthodontic bracket. The hardness of the teeth consequently decreases, and they become brittle and loose. The type of adhesive used to fix brackets may or may not reduce enamel demineralization. Previous studies have shown that a resin-modified glass ionomer (RMGI) inhibits demineralization. The purpose of this work is to evaluate the effect of a fluoride-releasing bracket on mechanical properties of dentin and enamel on regions adjacent to orthodontic brackets bonded with RMGI and composite resin cements. The remineralization effect due to fluoride on teeth was assessed by measuring hardness and reduced elastic modulus on dentin, enamel and dentin-enamel junction (DEJ) around the bracket area by nanoindentation methods. Nanoindentation was performed using a TriboScope from Hysitron. For this purpose two sets of polished samples were prepared: one sample was a cut along a longitudinal section and the other one along a cross-section of a tooth with orthodontic treatment using RMGI. Anisotropy in the mechanical properties of the teeth is observed along each direction.

This paper demonstrates a new displacement modulation technique for using a depth sensing nanoindentation instrument to measure the dynamic mechanical properties of viscoelastic materials. For testing low modulus, high damping polymeric materials, dynamic nanoindentation offers several advantages over quasi-static testing. In this research, a model for the dynamic response of the system is proposed and shown to match well with experimental observations. A new calibration procedure, which involves the use of a variable cantilever spring, is employed to determine the damping characteristics of the testing frame as a function of excitation frequency. Using the proposed procedure dynamic nanoindentation tests are carried out on a viscoelastic material to determine the storage and loss moduli as functions of excitation frequency. Finally, a comparison with results from conventional testing (DMA) is provided.

The nano single scratch experiment has been proven to be a suitable method to evaluate the scratch resistance of a coating. Single scratch damage and its recovery have been studied for a variety of clear coats under dry as well as wet conditions; these investigations were complemented by multi-scratch tests. Bulk mechanical materials properties of free standing films of the clear coats were determined by tensile tests and dynamic mechanical analysis (DMA). It was found that the recovery of the scratch groove is inversely related to the maximum value of the loss tangent (tan δ) as obtained from DMA analysis. The results of our comparative experiments and implications for the evaluation of the scratch resistance of organic coatings will be discussed.

A hybrid simulation method is used to study non-adhesive contact between two-dimensional self-affine rough surfaces. We find strong scale dependence as the contact dimensions decrease to the atomic scale. Both purely elastic and plastic materials are considered, and show different trends with system size. In all cases the contact area rises linearly with applied load, but the slope is substantially different from continuum predictions. We also examine the effect of commensurability between contacting surfaces. Contact area and frictional forces can be very different for commensurate and incommensurate surfaces, particularly for plastic materials.

Monitoring of acoustic emission (AE) activity was employed to characterize the initiation and progression of local failure processes during nanoindentation-induced fracture. Specimens of various brittle materials were loaded with a cube-corner indenter and AE activity was monitored during the entire loading and unloading event using an AE transducer mounted inside the specimen holder. As observed from the nanoindentation and AE response, there were fundamental differences in the fracture behavior of the various materials. Post-failure observations were used to identify particular features in the AE signal (amplitude, frequency, rise-time) that correspond to specific types of fracture events. Furthermore, analysis of the parametric and transient AE data was used to establish the crack-initiation threshold, crack-arrest threshold, and energy dissipation during failure. It was demonstrated that the monitoring of AE signals yields both qualitative and quantitative information regarding highly local failure events in brittle materials.

Dynamic nanoindentation was performed on a poly(methyl methacrylate, PMMA), and two different poly(dimethyl siloxane, PDMS) samples having different crosslink densities. Comparison was made between dynamic nanoindentation and rheological instrumentation measurements in the glassy and rubbery plateau regions of polymeric materials. Excellent agreement between bulk rheological data and dynamic nanoindentation data was observed for the two glassy materials and the less compliant of the two PDMS samples. Results were divergent for the more compliant PDMS sample.

Implants, tissue engineering scaffold materials, drug delivery and bio-micro electromechanical systems (BioMEMs) all use polymer or hydrogel materials. These applications require both mechanical performance and successful integration of the material into a biological environment. Mechanical strength, storage and loss moduli, wear resistance and surface adhesion properties are all critical in biomedical device design and can be determined using nanoindentation. The difficulty of obtaining large samples of specialized materials, and the complexity of testing soft materials in traditional materials testing apparatus, make nanoindentation an attractive alternative. Our previous research using nanoindentation to measure the surface mechanical properties of non-hydrated polymers led to improvement in nanoindentation testing protocols. One of the major challenges in using this technique for hydrogels and tissues is maintaining and controlling hydration of the materials during the test. Here we describe the design of a microfluidic platform for nanoindentation that facilitates continuous hydration of hydrogel samples and high throughput nanomechanical testing. Data from creep experiments on synthetic, hydrated poly-2-hydroxyethyl methacrylate (poly-HEMA) are presented. In addition, we show data to validate the materials properties determined from nanomechanical testing by complementary testing. Finally, the data is fitted to a phenomenological model for viscoelastic materials, specifically the three-element standard linear solid model used by Cheng et al. [1].

Nanomechanical properties of mineralized tissues are determined by microstructural tissue organization and relative composition of organic, mineral, and water phases. We combine nanoindentation and quantitative backscattered electron (qBSE) imaging to understand how these factors influence material properties at the ultrastructural and tissue level. Developmental stages of equine tooth enamel provide a good situation for studying the effects of enamel prism orientation and mineralization. Equine cheek teeth continue to form new enamel whilst mature tissue is being worn away. Hence we can study graded mineral content that increases with enamel maturity. Hunter-Schreger bands (HSBs) containing enamel prisms of contrasting orientations allow investigation of the effect of orientation on modulus. An equine second mandibular molar (2-year-old) was embedded in poly-methylmethacrylate, sectioned longitudinally, polished, carbon coated, imaged in qBSE, and subjected to nanoindentation testing. Elastic modulus increases significantly during maturation as enamel protein matrix degradation makes space for increased mineral content with closer proximity of enamel crystals, finally reaching values exceeding 80 GPa for little further increase in mineral content. Indentations spanning HSBs in immature, poorly mineralized enamel yielded modulus values that varied with prism orientation in a sinusoidal pattern where modulus varies by as much as a factor of three. Nanoindentation helps to elucidate how the composition and ultrastructural organization of enamel contribute to mechanical properties.

Our recent progress in elevated temperature nanoindentation is reviewed, with an emphasis on the study of discrete events (i.e., pop-in phenomena) observed during nanoindentation. For crystalline materials the incipient plasticity problem is associated with the nucleation of dislocations, an effect which we show to be significantly temperature dependent. For metallic glasses it is the operation of individual shear bands beneath the indenter that gives rise to pop-in events; here we also show this to be a temperature dependent phenomenon. Approaches to extract the activation volume and energy of defects involved in plastic flow beneath the indenter are also briefly described.

Instrumented indentation and micro-Raman spectroscopy were used to investigate the mechanical and structural properties of Bombyx mori silk films. Twelve different films were prepared from B. mori silk fibroin protein using a variety of post-deposition processing treatments (e.g. soaking in methanol, soaking in water, stretching, and/or enzymatic etching). The results show that different treatments lead to changes in both the conformation of the silk fibroin protein and the mechanical properties of the films.

A new generation of sensors based on biologically inspired whisking action will help determine the presence and location of solid objects and fluid vortices similar to mechanisms used by whisker bearing animals such as rats and seals. By using nanoindentation, we demonstrate that mechanical properties are essentially uniform by cross section, but vary longitudinally from the whisker base (a 3.9 GPa elastic modulus) to the tip (a 3.1 GPa elastic modulus). Several recent studies show propagation of high frequency information through whiskers that are tuned by their physical properties. In order to fully understand and model these properties, this study demonstrates a more complex whisker structure than previously assumed.

We recently developed an integrated imaging platform that combines single molecule evanescent wave fluorescence imaging (and spectroscopy) with in situ scanning probe microscopy. The advantages, challenges, and potential represented by this coupled tool will be described in the context of the structure-function characteristics of nanostructured biomaterials and thin lipid films.

We explore the effect of the substrate on mechanical behavior of thin films using a depth-sensing indentation. For this purpose, nanoindentation has been performed on thermally grown silicon oxide films on the silicon substrate. One primary goal of this study is to extract ‘film-only’ mechanical properties from the nanoindentation data by subtracting the substrate effect. It is also shown that elastic modulus of the film is more influenced by the substrate than hardness due to a larger elastic extension beyond a plastically deformed region, as well as a larger elastic mismatch between the SiO2 film and the Si substrate. Further, an inverse analysis of indentation data is proposed to estimate a thickness of thin films. Consequently, this study provides a fundamental understanding in mechanical phenomena of thin films occurring at nanoscales.

Based on the effects of residual surface stress on the unloading curves of indentation load-depth responses, an experimental scheme for determination of the residual stress by depth-sensing indentation is proposed. From the point that the elastic unloading portion of the load-depth curves can be expected to be unaffected by the residual stresses, the formula for evaluating surface stress by indentation is derived based on energy method. The proposed formula is verified by using FEM simulated indentation load-depth responses for different surface stress levels. The levels of surface stress evaluated by the proposed formula show a good agreement with the ones used as input parameters in FEM simulation.

Nanoindentation is used to provide a measurement of coating plain strain modulus. The coating properties are then measured by surface acoustic wave spectroscopy (SAWS). It is shown that, by exploiting the relative insensitivity of the SAWS acoustical model to Poisson's ratio, it is possible to measure either the thickness or the density of a thin coating given the input of the other. Furthermore, the indentation and acoustical tests are non-destructive and the resulting value of thickness or density is of high precision. A case study is presented for the measurement of density for a 250 nm thick nano-crystalline Niobium coating on a Si (001) substrate. The density is found to be ρ = 8.4 ± 0.3 g cm−3, about 2 % below bulk values but the modulus is found to be only 85 GPa (for a Poisson's ratio of 0.4), which is 18 % below bulk.

This paper describes a new method of dynamic nanoindentation testing whereby, instead of the imposition of a single sinusoidal modulation onto the driving force signal, a multiple-frequency modulation is applied and a Fourier analysis used to extract frequency-dependent mechanical properties. The instrument response is cancelled by the use of a reference transfer function using an equalization process. The present work gives details of the method and presents some example measurements.

In this study, the microstructural change of the surface of Si single crystal (Si(100)) after the scratching tests under very small loading forces was investigated. At first, line-scratching tests and scanning-scratching tests were carried out using an atomic force/friction force microscope (AFM/FFM). Next, cross-sectional TEM observations of the wear marks which were generated by the scratching tests were carried out. As a result of the TEM observations after the line-scratching tests, it was found that dislocations were observed in the area of less than 100nm thickness from the surface of the wear marks which were formed under the loading forces of more than 5μN. In the case of the loading forces of more than 20μN, an amorphous region was also observed just under the wear marks. As a result of the TEM observations after the scanning-scratching tests, it was found that the introduction of dislocations took place and no amorphous region appeared. It was also found that the several atomic layers at the top surface of the wear marks shifted in parallel to (100).

The deformation behavior of both ion-implanted and deposited amorphous Si (a-Si) films has been studied using spherical nanoindentation, followed by analysis using Raman spectroscopy and cross-sectional transmission electron microscopy (XTEM). Indentation was carried out on both unannealed a-Si films (the so-called unrelaxed state) and in ion implanted films that were annealed to 450°C to fully relax the amorphous film. The dominant mode of deformation in unrelaxed films was via plastic flow of the amorphous phase rather than phase transformation, with measured hardness being typically 75–85% of that of crystalline Si. In contrast, deformation via phase transformation was clearly observed in the relaxed state of ion implanted a-Si, with the load-unload curves displaying characteristic discontinuities and Raman and XTEM indicating the presence of high-pressure crystalline phases Si-III and Si-XII following pressure release. In such cases the measured hardness was within 5% of that of the crystalline phase.