The focus of this program is to provide an understanding of the basic processes of damage formation by heavy-ion irradiation of metal systems. Transmission electron microscopy is used extensively to characterize the damage structure as a function of ion dose and irradiation temperature. The experimental information obtained is used to evaluate current damage models and to provide a better understanding of how material properties are affected in a nuclear reactor and how irradiation with energetic heavy-ions modifies the surface properties of a material.

The implantation of energetic heavy ions into both elemental (Si) and compound semiconductors (GaAs, GaP) causes considerable damage and at high doses leads to the formation of surface or subsurface amorphous layers. The mechanisms of formation of amorphous zones from displacement cascades and the development of the amorphous layer are not well understood. The crystalline to amorphous transition and the stability of the amorphous material are being investigated by performing heavy-ion irradiations at temperatures between 30 K and 300 K in situ in the high-voltage electron microscope at Argonne National Laboratory.

The embrittlement of pressure vessel steels is one of the most serious problems facing the nuclear industry. Embrittlement is due partly to changes in the chemistry of the grain boundary, to the formation of Cu precipitates, and to the underlying neutron damage. To assess how these changes influence the properties, deformation experiments will be performed in situ in a transmission electron microscope. This will allow direct assessment of the dynamics of the interaction of the dislocations with the Cu precipitates, with the neutron damage component, and with the grain boundaries. This type of information will allow assessment of the different mechanisms of embrittlement and testing of current hardening theories.

Fundamental aspects of ion-beam-induced amorphization and layer intermixing in III-V semiconductor heterostructures are being studied by using a combination of low-temperature ion channeling and transmission electron microscopy techniques. Specifically, we are interested in understanding the effect of increasing the Al content on the ion dose needed to cause amorphization in the AlGaAs system and the mechanisms of mixing in AlGaAs-GaAs heterostructures.

Ion implantation is used extensively in the semiconductor industry to introduce dopants. The accompanying damage must be removed before devices can be activated. The focus of this effort is on understanding the mechanisms of solid-phase epitaxial crystallization of amorphous material in simple and compound semiconductors. The regrowth process can be stimulated by means of an energetic electron beam, which allows, through variation of the electron energy, the role of defects created in the crystalline material (interstitials and vacancies) or interface defects (dangling bonds or charged kinks) to be directly assessed.