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Nuclear Science and Engineering

IVEM: In situ Dual-Ion Beams

In Situ Helium Ion Implantation

A low-energy ion source provides helium ions with an energy of 5-20 keV and a flux up to about 2x1012 ions/cm2/s for helium implantation in situ. The helium beam merges with the NEC implanter ion beam before entering the microscope with an incident angle of 30° from the electron optical axis, permitting real time TEM observations. Similar to the ion beam, the helium beam is weakly rastered to produce a uniform beam 1.5 mm in diameter. The helium flux is measured by the annular Faraday cup to an accuracy of ±10%.

In Situ Helium Ion Implantation and Heavy Ion Irradiation

In situ dual-ion beam implantation and irradiation is performed by simultaneously running the heavy ion beam (NEC ion implanter) and helium beam (low-energy ion source). A range of appm helium to displacement per atom (appmHe/dpa) ratio can be performed by choosing the desired combination of energy and flux of heavy ions and helium ions using SRIM program to estimate the damage and implantation of helium and heavy ions. For example, dual-beam implantation/irradiation with an implantation/damage ratio from 5 to 10000 appmHe/dpa in a stainless steel thin foil can be achieved with appropriate choice of fluxes for 12 keV helium ions and 1 MeV Kr ions.

Irradiation Defect Dynamics in Fe

In situ movie of defect formation, motion, and coalescence to form extended dislocation structures in Fe under ion irradiation. These structures lead to degradation of the mechanical properties in irradiated metals.

M. Hernandez-Mayoral, Z. Yao, M. Jenkins, M. Kirk, Heavy-ion irradiations of Fe and Fe-Cr model alloys Part 2: Damage evolution in thin-foils at higher doses,” Phil Mag 88(21), 2881 (2008).