A formalism of the quasicontinuum method suitable for atomistic-continuum modeling of oxide crystals is presented. Multiple interacting quasicontinua, one per sublattice, which overlap in the physical crystal space, are used to model the oxide crystals. The method is implemented with the shell model for atomic interactions in ionic crystals, along with the Wolf's method for treating the long-range forces. Results are presented for the structural relaxation of strained and unstrained Fe2O3 crystal under periodic boundary conditions.

To quantify the mechanical properties and deformation behaviour of sub-micron wires, an in-situ nanoindenter system is being developed for a TEM. The miniaturized displacement controlled nanoindenter fits inside a side entry specimen holder. For coarse positioning, a novel 3-axis inertial positioner has been developed. This positioner has a range of 5mm with a 300 nm resolution. The fine displacements are generated by means of a tube piezo and the force is measured using a fibre optic interferometer.

The mechanism by which deformation is transferred across grain boundaries and ways in which boundaries of different misorientations impact this process has been studied using indentation testing. This information could be useful in designing texture of nanocrystalline materials to maximize their mechanical properties for specific applications. Atomic force microscopy (AFM) and orientation imaging microscopy (OIM) has been combined to identify slip systems activated around indentations. When indentations are placed near grain boundaries, slip steps can be imaged on both sides of the boundary and the associated slip systems of each grain can be determined. Dislocation pile ups have been observed around indentations near boundaries which do not share a common slip direction with the active slip planes of either grain, and slip steps have been seen to traverse boundaries when these shared slip directions are present.

A series of InxGa1-xAs superlattices grown on InP substrates with differing coherency strains have been deformed by bending at 500°C and by nanoindentation at room temperature. The deformation was characterised by transmission electron microscopy through examination of thin sections machined in a focused ion beam microscope. The bent samples sheared along {111} planes, and the most highly strained samples partially relaxed through the formation of misfit dislocations. Under indentation the majority of the plastic strain in the multilayers is accommodated by twinning whereas no twins were observed under indents in the InP substrate. The overall dimensions of the plastic zone increased linearly with indent load.

Microcontact printing is a straightforward and effective method for generating surface patterns of micron or submicron lateral dimensions. The fidelity of the ultimate pattern is a complex interplay of mechanical behavior of the elastomeric stamp, fluid transfer between surfaces and the ability of the ink to self-assemble on the new surface. We present here experimental observations and modeling of stamp deformation during precise external loads and visualization of inked surfaces by high contrast analytical methods. Stamp behavior was observed visually in an inverted microscope and load-displacement relationships used to determine onset of failure modes such as roof collapse and buckling of slender relief features as a function of stamp geometry. The load was applied with a glass sphere so as to obviate problems with alignment and to precisely determine contact areas.

A “robotic stamper” fabricated from an AFM instrument can deliver ink under conditions of precise load. Surfaces inked with varying densities or combinations of SAMs can be imaged with excellent contrast by scanning surface potential microscopy (SSPM). The same area of the sample can then be examined using time-of-flight SIMS or other surface analytical technique with no additional etching or sample preparation. In this way the fidelity and density of the patterned monolayers can be evaluated. The effect of load on ink pattern quality can also be established.

Dislocation nucleation under an idealized nanoindenter is analyzed based on the Peierls-Nabarro dislocation model. The variational boundary integral method is used to obtain the dislocation profiles that correspond to the shear displacements between the adjacent atomic layers along the slip plane. The critical condition for dislocation nucleation at absolute zero and the activation energies required to thermally activate dislocations from their stable to unstable saddle point configurations are determined. By treating the surface as part of an infinite crack embedded in the infinite medium, a rather straightforward approach is adopted to account for the surface effect. The emission of multiple dislocations from the surface of a film-substrate system is also studied. The size effects of the indenter width and film thickness are characterized by the typical load-displacement relation.

Bone is a complex natural composite with a lamellar structure on the micro scale. In this study, scanning nanoindentation was used to assess the mechanical properties of individual lamellar and inter-lamellar components of trabecular bone under static and dynamic loading conditions. The combination of careful sample preparation, good topographical characterization of the sample surface, and a scanning nanoindenter provided insight into the mechanical properties of the individual lamellar structures. The results of quasi-static, as well as dynamic nanoindentation tests of bone are reported and discussed.

A surface roughness of only 18-20 nm RMS was achieved. Nonetheless, indentation depths in the range of 100 nm and above were required in order to minimize the effect of topography on the measurement. This requirement conflicts with the need to keep the probed volume small enough to sample only one component at a time. A simple volume-averaging model was developed and used as a tool to determine when individual lamellar bone structures were being probed and to help determine the properties of the lamellar and inter-lamellar materials.

A functionally graded nanocrystalline metalloceramic coating on cobalt-chrome alloy was investigated using thin film x-ray diffraction (XRD), cross-sectional transmission electron microscopy (TEM), nanoindentation, and scratch adhesion testing. The gradual transition in bonding from metallic (Cr/CrTi) near the interface to predominantly covalent (CrTiN) near the surface provides a combination of high toughness and high surface hardness. XRD analysis of the (CrTiN) coating suggests a cubic sodium chloride type phase structure with lattice parameter a = 4.2169±0.0035 Å. The surface layer structure is described as a tertiary Ti-N-Cr disordered solid solution that is predominantly cubic TiN, but with some Cr atoms substituted for Ti. TEM shows a transition from equiaxed 20-40 nm-sized grains at the surface to larger, elongated columnar grains below the surface. Nanoindentation measurements of the coating result in a hardness of 27 GPa and Young's modulus of 320 GPa. In addition, the high plasticity of 55% observed for this coating represents an increase in toughness over other ceramic coatings having similar hardness. The unique, functionally graded, smooth nanocrystalline metalloceramic coating structure provides an opportunity to reduce wear and increase longevity of total hip joint replacements.

An analysis of the fluctuations of a {100} FCC interface has been used to locate the surface roughening transition in kinetic Monte Carlo simulations. These simulations were conducted using a spin 1/2 Ising model treatment of the solid-liquid interface. A temperature gradient was imposed on the simulation cell providing a restoring force to the interface. Fluctuations in the number of solid atoms in the system were measured using time correlations. The fluctuation dissipation theorem was employed to relate the characteristic times retrieved from the time correlation to the kinetic coeffcients of the system. A dramatic change was found in these characteristic times, which locates the surface roughening transition.

A modification of the jogged-screw model has been adopted recently by the authors to explain observations of 1/2[110]-type jogged-screw dislocations in equiaxed Ti-48Al under creep conditions. The aim of this study has been to verify and validate the parameters and functional dependencies that have been assumed in this previous work. The original solution has been reformulated to take into account the finite length of the moving jog. This is a better approximation of the tall jog. The substructural model parameters have been further investigated in light of the Finite Length Moving Line (FLML) source approximation. The original model assumes that the critical jog height (beyond which the jog is not dragged) is inversely proportional to the applied stress. By accounting for the fact that there are three competing mechanisms (jog dragging, dipole dragging, dipole bypass) possible, we can arrive at a modified critical jog height. The critical jog height was found to be more strongly stress dependent than assumed previously. The original model assumes the jog spacing to be invariant over the stress range. However, dynamic simulation using a line tension model has shown that the jog spacing is inversely proportional to the applied stress. This has also been confirmed by TEM measurements of jog spacings over a range of stresses. Taylor's expression assumed previously to provide the dependence of dislocation density on the applied stress, has now been confirmed by actual dislocation density measurements. Combining all of these parameters and dependencies, derived both from experiment and theory, leads to an excellent prediction of creep rates and stress exponents. The further application of this model to other materials, and the important role of atomistic and dislocation dynamics simulations in its continued development is also discussed.