Nucleation of a <111> screw dislocation at a step from a {112} surface of tantalum has been studied by a multiscale approach. The profile of the dislocation, represented by the relative displacement between two adjacent atomic layers along the slip plane, is solved based on the variational boundary integral formulation of the Peierls-Nabarro dislocation model, in which the interatomic potential is incorporated based on atomic calculations of generalized stacking fault energies. The results show that the atomic scale step significantly facilitates dislocation nucleation from the surface. The results from all atom calculations are also presented to corroborate the results obtained by this multiscale approach.

The aim of this paper is to investigate the deformation behaviour of an AlN/CrN multilayer with wavelengths varying from 6–400 nm, deposited on M42 tool steel and how this varies as the temperature is increased to 500 °C. These measurements have been correlated with changes in deformation patterns using cross-sectional transmission electron microscopy, where sections have been prepared directly through the indents.

A novel method of in-situ detection of the high pressure phase transformation of silicon during dead-load scratching is described. The method is based on the simple fact that single crystal silicon is transparent to Infrared light while metallic materials are not. Infrared heating during scratching has been performed to thermally soften and deform the transformed metallic material and some promising results were obtained. The sample material used here is silicon, but the same approach can be applied to germanium and other materials, such as ceramics (SiC), which have appropriate optical properties.

Elastic modulus values of the thin films utilized in three different hard film- soft substrate systems were measured using a combination of traditional and continuous stiffness indentation. These systems were chosen to represent typical systems currently utilized in MEMS and included Si/SU8/W, Si/SiO2/Ti/Pt/PZT, and Si/SiO2/Ti/Pt. The last system was coated with either a compressive or nonstressed Cr film. By taking into account ratio between the creep due to the polymer substrate, SU8, to the unloading rate, the modulus of W was measured to be 400 GPa. The modulus of the SU8 was also determined to be 6 GPa. Comparing both the CSM and traditional indentation for the Si/SiO2/Ti/Pt/PZT system showed that the dynamic motion of the indenter caused pile-up in the PZT and resulting in the overestimation of the PZT modulus. This pile-up is a function of the sinusoidal loading frequency. Instead, the modulus of the PZT was measured by shallow depths of traditional indentation that resulted in the PZT modulus of 100 GPa. The hard film-soft substrate systems were show to follow the same trend as stressed soft-film hard-substrate systems with residual stress. The modulus was over estimated for compressively stressed Cr films.

Cyclic indentation was performed on standard fused quartz, single crystal Ni3Al (111) and nanocrystalline Ni-25at. %Al alloy thin film with average grain size of a few nanometers. For the thin film sample, it is found the scattering of the effective Young's modulus at small depths goes far beyond the expectation from effects due to surface roughness alone. Three representative deformation mechanisms during initial contact stage were identified to be responsible for the scattering with the assistance of immediate pre and post indentation atomic force microscopy imaging. Furthermore, repeated loading was found to stiffen the thin film sample, but not the bulk ones.

Specialized large-scale computational finite-element and molecular dynamic models have been used to understand and predict how dislocation density emission and contact stress fields due to nanoindentation affect inelastic deformation evolution at scales that span the molecular to the continuum level in ductile crystalline systems. Dislocation density distributions and local stress fields have been obtained for different crystalline slip-system and grain-boundary orientations. The interrelated effects of grain-boundary interfaces and orientations, dislocation density evolution and crystalline structure on indentation inelastic regions have been investigated.

Nanoimprint and a number of other related techniques are a collection of surface patterning technologies that involve direct contact of a master template with the target surface. As such, they are governed by the laws of contacting bodies, and the mechanics involved can readily be investigated by existing indentation methods or close variants thereof. Among the many demonstrated applications of nanoimprint, lithographic resist processing has generated considerable interest due to its combination of high resolution with rapid throughput over wide areas. Pattern transfer can be achieved by the application of heat and pressure to the stamp (hot embossing), or solely by the generation of shear stress at the contact (cold forming.) In both cases we have found that elastic and viscoplastic strains are present during the forming process, the former of which can considerably alter the characteristics of the pattern transfer. The use of depth sensing instrumented indentation in conjunction with specially designed stamps and a variety of microscopy techniques has allowed us to isolate, control, and measure many of the stresses and strains directly during the imprint process. Further, in a more standard role, the indenter can be used to characterize the mechanical properties of imprinted structures. In this paper we summarize our experimental findings and conclusions on the role of important factors influencing the fidelity of the imprint process including elastic stresses, plastic deformation mechanisms, complexities in the confined deformation rheology, and choices in the form of applied stress. These are illustrated by a series of idealized experiments ranging from the squeeze flow of prepared coupons to the flat punch indentation of thin films and back extrusion into isolated cavities. A connection between these more localized experiments and the established findings and requirements of applications such as wide area lithography and functional polymer patterning will be made to establish the concept of “instrumented imprint”.

Nanoindentation is a promising tool for obtaining the elastic properties of thin films. However, no means exists to predict or extrapolate the elastic modulus of the top layer in multilayer systems from experimental data. The mechanical properties of PZT multilayer systems have become increasingly important in applications for MEMS devices. The indentation modulus vs. a/t behaviour of PZT on Pt/SiO2/Si wafer substrate was investigated and compared with a new analytical solution for Herztian indentation of multilayers. Five different PZT film thicknesses were indented (70, 140, 400, 700, 1500 nm), using a 10 μm radius indenter. Good agreement was found between analytical equations and experimental data. However the behaviour of the multilayer system was complex. This makes the deconvolution of film properties difficult for thicknesses less than about 1000 nm.

A technique is described to measure the rotations of the crystal lattice in the deformed region around a nanoindent from volumes smaller than 3 × 10−5 μm3. To demonstrate this method, a copper crystal has been indented on its (001) face to depths of 500 and 1300 nm. Cross-sections of nanoindents were prepared for transmission electron microscopy by focused ion beam milling, and rotations were measured about the [001], [010] and [100] axes using convergent beam electron diffraction.

Previous studies of how material creep parameters can be measured by nanoindentation testing have focused mostly on measurement of the stress exponent for creep, n, and the activation energy, Qc. However, a more complete characterization requires that the material constant A in the uniaxial creep equation εu =Aσn (where εu is the uniaxial strain rate and σ is the uniaxial stress) also be evaluated. Here, we begin to address this issue by performing simple nanoindentation creep experiments in amorphous selenium at temperatures above and below the glass transition. At 35°C and above, the material exhibits a simple linear viscous creep behavior that is load history independent. This allows the parameter A to be determined from the indentation load-displacement-time data by means of an analytical solution. To examine the validity of the approach, values of the parameter A measured in nanoindentation tests are compared to independent measurements obtained in uniaxial tension creep experiments.

Using analytical and finite element modeling, we study conical indentation in linear viscoelastic solids and examine the relationship between initial unloading slope, contact depth, and viscoelastic properties. We will then discuss whether the Oliver-Pharr method for determining contact depth, originally proposed for indentation in elastic and elastic-plastic solids, is applicable to indentation in viscoelastic solids.

Cortical bone is an anisotropic material, and its mechanical properties are determined by its composition as well as its microstructure. Mechanical properties of bone are a consequence of the proportions of, and the interactions between, mineral, collagen and water. Mid-shaft palmar cortical tissue from the equine third metacarpal bone is relatively dense and uniform with low porosity. The mainly primary osteons are aligned to within a few degrees of the long axis of the bone. Beams of compact cortical bone were prepared to examine effects of dehydration and embedding and to study contribution of collagen and mineral to nano-scale material properties. Five beams were tested: untreated (hydrated); 100% ethanol (dehydrated); or embedded in poly-methylmethacrylate (PMMA) for one normal, one decalcified, and one deproteinated bone sample. Elastic modulus was obtained by nanoindentation using spherical indenters, with the loading direction transverse [1] and longitudinal to the bone axis. By selectively removing water, mineral and organic components from the composite, insights into the ultrastructure of the tissue can be gained from the corresponding changes in the experimentally determined elastic moduli.

The application of nanoindentation methods to compliant materials, such as polymeric and biological materials, often requires the use of instrumentation designed with enhanced force sensitivity, which limits its maximum force level. Because tip geometry is normally characterized using indentation of fused silica, the maximum contact depths achieved by low-force instruments during this calibration are often less than 300 nm. However, penetration into more compliant materials can be several micrometers or more. Extrapolation of tip shape data from fused silica indentation can lead to significant uncertainties in the indentation measurements for compliant materials. In this paper, atomic force microscopy (AFM) is used to provide tip shape information for a Berkovich tip and a series of conical tips. Use of AFM allows a larger range of depth to be calibrated and provides three-dimensional tip information.

Measurement of material creep parameters by means of nanoindentation using continuous stiffness techniques avoids the problems associated with thermal drift that often plague creep measurements based on the time dependence of the indentation depth alone [1, 2]. Problems with thermal drift are negligible from a practical point of view during continuous stiffness measurements because the contact stiffness can be measured over a short time period, typically less than one second, during which time the displacements due to thermal drift are minimal. Determination of the time dependence of the indentation depth from the stiffness data relies on the well-known relation between contact stiffness and the square root of the contact area. For pyramidal indenters, the true indentation contact depth must be proportional to the contact stiffness, leading to the assumption that indentation depth is also proportional to the contact stiffness. In this study, we critically examine this assumption using data obtained from experiments on a relatively soft material, epoxy, and a relatively hard material, fused quartz. The results show that just after initial load application, the change in contact area may be different than that expected from the change in indentation depth. One possible explanation for the observed behavior is examined by finite element modeling.

Depth-sensing indentation testing is a common way to characterize the mechanical behavior of stiff, time-independent materials but presents both experimental and analytical challenges for compliant, time-dependent materials. Many of these experimental challenges can be overcome by using a spherical indenter tip with a radius substantially larger than the indentation depth, thus restricting deformation to viscoelastic (and not plastic) modes in glassy polymers and permitting large loads and contact stiffness to be generated in compliant elastomers. Elastic-viscoelastic correspondence was used to generate spherical indenter solutions for a number of indentation testing protocols including creep following loading at a constant rate and a multiple ramp-and-hold protocol to measure creep response at several loads (and depths) within the same test. The ramp-creep solution was recast as a modification to a step-load creep solution with a finite loading rate correction factor that is a dimensionless function of the ratio of experimental ramp time to the material time constant. Creep tests were performed with different loading rates and different peak load levels on glassy and rubbery polymeric materials. Experimental data are fit to the spherical indentation solutions to obtain elastic modulus and time-constants, and good agreement is found between the results and known modulus values. Emphasis is given to the use of multiple experiments (or multiple levels within a single experiment) to test the a priori assumption of linear viscoelastic material behavior used in the modeling.

Many modern and future technological applications involve ultrathin polymer films with a thickness below the 100-nanometer scale, where statistical bulk averaging is jeopardized and interfacial constraints dictate transport properties. In such confined polymeric systems, transport properties strongly depend on molecular relaxation and structural phases that deviate from the bulk. This is particularly relevant in applications involving nano-electromechanical systems (NEMS). In this paper, we address the correspondence between bulk deviating local glass transition values with the non-monotonic plastic deformation properties in ultrathin polystyrene films. Polystyrene serves as a model material in a NEMS application designed to circumvent the superparamagnetic limit associated with magnetic data storage. The application involves data bit writing via an ultrahigh density thermomechanical indentation process. An elaborate friction-velocity analysis is introduced as a material characterization tool. It provides fundamental insight into the glass forming process, and consequently, the glass transition value in ultrathin spin coated polymer films. The glass transition value is thereby discussed as a phenomenological limit, not unlike an asymptote, to a diverging size of cooperative rearranging regions upon cooling. Unexpected large cooperative clusters up to 40 nm were observed – a dimension that is noticeable at the 100-nanometer length scale. In the light of MD simulations and their good correspondence with the presented intrinsic friction analysis, the importance of angular and torsional intramolecular motions are particularly emphasized for nanotechnological applications.

Mechanical characterization of polymeric thin films and small volume structures is critical to device development in industrial applications ranging from low-k dielectric microelectronic packaging films to engineered and natural biological substrata. Although nanoindentation has the potential to quantify mechanical properties of polymeric systems, the established analyses developed for metals and ceramics (eg, calculation of hardness and Young's modulus) do not capture key aspects of viscoelastoplastic deformation and are therefore not quantitatively applicable. Here, we present a set of complementary, nanoscale contact-based experimental approaches that together characterize specific energy absorption as a unique mechanical characteristic of polymers, and provide examples for a set of amorphous polymers.

Instrumented indentation was used to characterize the mechanical response of polymeric materials. A model based on contact between a rigid probe and a linear viscoelastic material was used to calculate values for creep compliance and stress relaxation modulus for epoxy, poly(methyl methacrylate) (PMMA), and two poly(dimethyl siloxane) (PDMS) elastomers. Results from bulk rheometry studies were used for comparison to the indentation creep and stress relaxation results. For the two glassy polymers, the use of sharp pyramidal tips produced responses that were considerably more compliant (less stiff) than rheometry values. Additional study of the deformation remaining in epoxy after creep testing revealed that a large portion of the creep displacement measured was due to post-yield flow. Indentation creep measurements of the epoxy using a rounded conical tip also produced nonlinear responses, but the creep compliance values appeared to approach linear viscoelastic values with decreasing creep force. Responses measured for the PDMS were mainly linear elastic, but the filled PDMS exhibited some time-dependence and nonlinearity in both rheometry and indentation measurements.

Model epoxy nanocomposite thin films containing one of three types of titanium dioxide (TiO2) particles were degraded using an integrating sphere-based ultraviolet weathering chamber. Instrumental Indentation Testing (IIT) was used to measure nanomechanical changes in the surface region of thin films resulting from UV exposure. Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR) and Differential Scanning Calorimetry (DSC) were used to support the mechanical results with chemical and thermal data. The unfilled epoxy was the most photosensitive sample tested, exhibiting the highest rates of chemical oxidation, the largest decrease in the glass transition (Tg), and the greatest increase in elastic modulus with increased exposure. Similar trends were observed in the nanocomposite films, but the rates of change were much lower than the unfilled epoxy and decreased with increasing volume fraction of nanoparticles.