The objective of this project is to use surface/interface sensitive x-ray diffraction/scattering techniques, e.g., grazing incidence diffraction/scattering/fluorescence, specular reflectivity, standing and evanescent wave experiments, and truncation-rod experiments (all of which require the use of the synchrotron radiation) to examine various materials systems of scientific and technological importance. Some specific areas of investigation are: studies of the reconstructed structure, stress fields, relaxations, roughness, and phase transitions of single-crystal surfaces and interfaces such as Ag/Si(111), Ge/Si, C;i6;i0/Si, Cu/Al;i2O;i3, SnO;i2/Al;i2O;i3, GaN/Al;i2O;i3; the dynamical structural and compositional evolution associated with melting, solidification, passivation, and corrosion.

This program focuses on transmission electron microscopy of interfaces and surfaces. Systems of interest include oxide/semiconductor, metal/semiconductor, and semiconductor/semiconductor interfaces. In one set of experiments, these interfaces are fabricated in situ in an ultrahigh vacuum transmission electron microscope. In another set, atomic resolution images are taken after growth. Quantitative image interpretation is used to elucidate structure/property relationships and to understand the origin of microstructure during growth.

Fatigue behavior of a single-lap joint is examined as a function of joint-end condition, adhesive thickness, and testing conditions. The purpose of our research is to develop a fatigue life prediction methodology that is based on a thorough understanding of the fatigue damage process in the adhesive joint. A backface strain technique is developed and used to pinpoint the precise moment of the fatigue crack initiation in the adhesive joint. Theoretical analyses are performed to relate the crack initiation point with joint geometry and material properties.

The fatigue behavior of mullite fiber reinforced Al-Mg alloy matrix composites is examined as a function of Mg concentration and fiber volume fraction. The primary objective is to understand the role of the interface in the fatigue crack initiation and growth processes. Several reaction products are found at the fiber/matrix interface in the as-received composite. Research is in progress to evaluate the effect of the interfacial reaction on the fatigue properties of the composite.

Experimental and theoretical studies are carried out to understand the relationship between microstructure and mechanical properties of bi-materials interfaces. We have developed new experimental techniques to measure mechanical properties of interfaces and applied these techniques to metal-ceramic, metal-polymer, glass-ceramic, and bi-metals interfaces. We are developing model interfacial microstructures at graphite-epoxy, alumina-aluminum, polyimide-copper, epoxy-metal, and solder-copper interfaces by chemical, physical, electrochemical, and metallurgical surface-modification techniques. We are modeling several salient mechanisms of crack growth, such as crack sliding, crack interlocking, and crack tip plasticity, along model interfaces.