HCI potential energy sputtering measured with magnetic tunnel junctions

In this paper, the use of tunnel junctions as sensors for estimating the potential energy sputtering yield of highly charged ions (HCIs) incident on ultra-thin insulating films is experimentally explored. HCIs are known to strongly ablate insulating materials upon collision by destabilizing the solid's chemical structure in the region of impact and producing a mass loss, referred to as potential energy sputtering. In previous work, increased conductance of tunnel junctions due to highly charged ion irradiation was shown while demonstrating that tunnelling remains the dominant transport mechanism. These studies indicate that the conductance increases linearly with the number of HCIs and so, for any given tunnel barrier recipe and HCI charge state, the conductance per HCI can be found. Since the conductance of a tunnel junction is exponentially sensitive to its thickness, the increase in conductance can be used to evaluate an effective tunnel junction thickness reduction, which, in turn, can be explored as a metric for the potential energy sputtering of the tunnel barrier. These tunnel junction measurements provide new information about the nano-features formed on insulators by HCIs, and this paper considers the possibility of using these data to estimate potential energy sputtering. A method for relating the increased conductance to a mass loss is considered and compared against other potential energy sputtering measurements.