Kinetics of Interfaces in Materials under Irradiation
P. Bellon,* D. Lefloc'h, J. Turek
U.S. Department of Energy, DE-FG02-96ER45439 (In cooperation with the Materials Research Laboratory)

The goals of this study are (1) to develop the basic understanding of the behavior of interfaces in materials submitted to radiation field and (2) to investigate the consequences for the microstructure-properties relationship in these materials. Two types of behavior are currently being investigated by atomistic computer simulations and irradiation experiments: the coarsening of ordered domains and the shape of precipitates in two-phase materials. In these two cases, the evolution of the alloy is mostly controlled by dynamical processes taking place at interfaces, such as atomic mixing and interface roughening. We have determined that irradiation can induce a nonequilibrium roughening as well as a nonequilibrium faceting of precipitates at steady-state.

Radiation Damage in Borosilicate Glasses
J. Kieffer,* E. Guilbert
CEA (French Atomic Energy Agency)

Large-scale molecular dynamic simulations are carried out to investigate the structural damage in borosilicate glasses, created by recoil nuclei upon radioactive decay. Simulated systems contain five or more oxides in order to adequately model the actual materials that are used for radioactive waste storage. Because of the size of these systems, semiempirical potentials have to be designed that accurately describe the interactions between the various components. Furthermore, novel analysis methods need to be developed to assess the damage within a structure, which is already disordered in the relaxed state.

Radiation Damage in Metals
I. M. Robertson*
U.S. Department of Energy, DE-FG02-96ER45439 (In cooperation with the Materials Research Laboratory)

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.

Amorphization and Intermixing Mechanisms in III-V Semiconductor Heterostructure Systems
I. M. Robertson,* B. Lagow
U.S. Department of Energy, DE-FG02-96ER45439 (In cooperation with the Materials Research Laboratory)

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.

Epitaxial Regrowth of Amorphous Material in Semiconductor Systems
I. M. Robertson,* I. Jencic, E. Hollar
U.S. Department of Energy, DE-FG02-96ER45439 (In cooperation with the Materials Research Laboratory)

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.