It is generally accepted that the hardness of silicon and germanium is limited by a phase transformation. Observations of the deformation under indents using transmission electron microscopy indicate that, in addition to the phase transformation, there is also plastic flow both in the transformed and in the untransformed material. These observations are consistent with those made elsewhere and with predictions based on the spherical cavity model for indentation, modified to quantify the effect of a phase transformation on the measured hardness. The analysis predicts that the hardness can only be approximately equal to the transformation pressure provided the yield strength of the transformed material is low, and that there is a region where plastic deformation in the untransformed material can occur in addition to the phase transformation. These predictions are consistent with the experimental observations of substantial plastic deformation of the transformed phase, as well as with estimates of its Peierls stress.

The growth of thin gold films on highly crystalline TiO2 and amorphous Al2O3 substrates and its dependence on substrate temperature was investigated under UHV-conditions by in situ internal stress measurements. Deposition of gold on amorphous Al2O3 at substrate temperatures between 27°C and 300°C shows a stress vs. thickness curve which indicates island growth at first and the formation of a polycrystalline film at higher thickness. A comparable stress vs. thickness curve is found for the growth of gold on the highly crystalline TiO2 substrate at substrate temperatures below 200°C, again indicating island growth. At higher temperatures, however, a new tensile stress feature at low gold coverage is interpreted to indicate the formation of a strained interface layer. This strain in the gold film is eliminated after deposition of a few monolayers most likely through incorporation of dislocations and defects. The growth stress at higher film thickness is indicative of island film growth.

A comprehensive indentation fracture mechanics framework is established that allows the fracture properties of thin films to be determined. The framework is composed of four stress-intensity factors characterizing the stress fields arising from (i) elastic contact, (ii) wedging, (iii) residual elastic-plastic mismatch and (iv) pre-existing film stress. The amplitudes of the stress-intensity factors depend on the deformation properties of the film and vary throughout the indentation cycle. The toughness values of a PVD alumina, for which (iii) and (iv) are dominant, and a low-k film, for which (i), (ii) and (iv) are dominant, are evaluated.

While there are many stress relief mechanisms observed in thin films, excessive residual and externally applied stresses cause film fracture. In the case of tensile stress a network of through-thickness cracks forms in the film. In the case of compressive stress thin film buckling is observed in the form of blisters. Thin film delamination is an inseparable phenomenon of buckling. The buckling delamination blisters can be either circular, straight, or form periodic buckling patterns commonly known as telephone cord delamination morphology.

While excessive biaxial residual stress is the key for causing thin film fracture, either in tension, or compression, it is the influence of the external stress that can control the final fracture pattern. In this paper we consider phone cord buckling delamination observed in compressed W/Si and TiWN/GaAs thin film systems, as well as spiral and sinusoidal though-thickness cracks observed in Mo/Si multilayers under 3-point high-temperature bending in tension.

Hardness and elastic modulus can be derived from instrumented sharp indentation curves by considering the effects of materials pile-up and sink-in and tip blunting. In particular, this study quantifies pile-up or sink-in effects in determining contact area based on indentation-curve analysis. Two approaches, finite-element simulation and theoretical modeling, were used to describe the detailed contact morphologies. The ratio of contact depth to maximum indentation depth was proposed as a key indentation parameter and was found to be a material constant independent of indentation load. In addition, this parameter can be determined strictly in terms of indentation-curve parameters, such as loading and unloading slopes at maximum depth and indentation energy ratio. This curve-analysis method was verified by finite-element simulations and nanoindentation experiments.

Studies of orthopaedic implant failures have shown that mechanical failure of an implant almost exclusively occurs at the biomaterial-tissue interface. Hydroxyapatite (HA) mimics the behavior of natural bone, and provides a strong, long-lasting adhesive interface between a bone replacement implant and the surrounding tissue. Currently, thin film HA is not commonly used because it contains defects, porosity, and cracks. Delamination of the hydroxyapatite film and formation of hydroxyapatite particles may lead to implant wear and loosening. Furthermore, the coating also acts only as a temporary barrier to ion release from the bulk biomaterial. One method to improve the tribological properties of a bioactive coating is to strengthen the microstructure of the coating through the placement of a DLC (hydrogen-free diamondlike carbon) interlayer. DLC coatings possess properties close to diamond in terms of hardness, atomic smoothness, and chemical inertness. We have developed a diamondlike carbon/HA bilayer, in which the bilayer surface (HA) is bioactive and the interlayer (diamondlike carbon) is biocompatible, wear resistant, and corrosion resistant. We have successfully deposited nanocrystalline hydroxyapatite and DLC films by ablating a hydroxyapatite target and a graphite target using a KrF laser. A novel target design was adopted to incorporate alloying atoms into the films during pulsed laser deposition. These alloying elements possess unique biological properties. Surface morphology was studied using SEM, interfacial structure was studied using TEM, and HA phase microstructure was studied using XRD. The DLC/nanocrystalline HA bilayer material is potentially useful for several orthopedic implant designs.

Synchrotron x-ray diffraction experiments were used to study the thermomechanical behavior of individual texture components in passivated Cu thin films. Films were deposited to a thickness of 500 nm on SiNx barrier layers on Si substrates and then passivated with SiNx. The films were highly textured with grains having (111) or (100) planes parallel to the plane of the film. In-plane film stresses were determined separately in the two texture components as a function of temperature during thermal cycles and also during isothermal holds at 140°C. The results are compared to models of yield behavior and anelastic recovery.

In this work, we developed a phase field model describing surface evolution dynamics of a strained solid in contact with gas phase. Elastic solutions are solved with an iteration method for the system in which a solid film, strained by the mismatch strain between the film and substrate, has anisotropic elastic constants and the vapor phase has zero elastic constants. Elastic solutions are incorporated into the phase field evolution equation. The model predicts stable morphology at a given mismatch strain and perturbation wavelength.

Nanoindentation is one of the few available methods and the most commercially widespread technique for investigating the elastic and plastic properties of small volumes such as thin films. Quantitative methods for obtaining the indentation (plane strain) modulus and hardness of a coating have been published and finite element models (FEM) of the elastic-plastic response of indentation have been developed. Comparison of the FEM output with actual indentation data has shown that, as the indentation size reduces, the apparent yield stress of the material increases. We have shown that the increase in yield stress is predictable and falls on a master curve (MRS Symp. Proc., Vol 788, p123, 2003). Predictions have been tested and agree for a range of metals (Cu, Al, W, Ir). This points to there being a fundamental length scale for dislocation-based deformation and raises the question as to whether the yield stress of thin films may be altered by reducing thickness. This study therefore investigates the indentation response of Al coatings on Borosilicate glass as a function of coating thickness and indentation depth. FEM of the indentation contact will be compared with indentation data and AFM measurements of the surface profile to investigate the relative contributions of the indentation size effect and the effect of hardening due to the additional constraint of substrate proximity to the plastic zone.

The effect of oxygen on adhesion and chemistry at interfaces between Cu thin films and SiNx barrier layers on Si substrates was investigated. Films were deposited in an ultra-high-vacuum sputter deposition chamber with good control of oxygen content. Adhesion was measured using a high throughput driver film method. Microstructure and bonding were investigated using transmission electron microscopy and electron energy loss spectroscopy, respectively, on sample cross sections. For films to which a small amount of oxygen was added during deposition, oxygen segregated to Cu/SiNx interfaces during thermal cycling, where it induced charge transfer and the presence of Cu+ interfacial states, and significantly reduced the work of adhesion.

Free-standing Al thin films were loaded statically and dynamically through the use of a custom-built microtensile system. The system is capable of performing monotonic loading/unloading up to 50 μm/s (10-1/s) and tension-tension fatigue experiments at 100 Hz on 600 μm long, 100 μm wide, and 1 μm thick free-standing Al microtensile beams. Monotonic loading/unloading and stress relaxation experiments have been performed. The microtensile beams show plasticity as well as a relaxation dependence on strain rate and stress level. Displacement controlled tension-tension fatigue experiments have also been performed. A trend of decreasing cycles to failure with increasing displacement amplitude and increasing mean displacement has been noted but requires further experimental exploration.