Spatial and electronic characterization of nano-features created by highly charged ions

Abstract

Scanning tunneling microscope (STM) images of highly charged ion (HCI) synthesized nano-features formed on the Au(111) surface are presented as well as transport studies of HCI modified magnetic tunnel junctions (MTJs). HCIs can carry a significant amount of neutralization energy (51 keV per ion for Xe44+, used in most of the results presented) in addition to their kinetic energy. This potential energy amplifies the violence of the HCI's interaction with the surface by generating massive secondary electron and sputtered atom yields and can displace thousands of substrate atoms. This paper presents STM images of surface features observed on the Au(111) surface with emphasis on the characteristics of the physical structure and formation mechanisms. In separate experiments, the HCIs are used to ablate small portions of the oxide barrier in MTJs to allow nano-scale metal shunts to be created through the barrier. Electronic measurements of HCI irradiated MTJs demonstrate that the MTJ total conductance increases linearly with the HCI dose for thin barriers and quadratically for thicker barriers. Initial results from a second generation of MTJs demonstrate that magnetoresistance is diminished but not destroyed when HCIs are used to modify MTJ barrier layer.