Dissertation

Characterization of 7Be-Implanted Superconducting Quantum Sensors Using Atom Probe Tomography and Transmission Electron Microscopy

Harris, Cameron N

2024

Overview

When atoms are subjected to different environments in molecules or solid-state materials, the electronic energy levels and general structure of the mutual system are altered away from the pure atomic state. For metals that are bombarded with ion beams, this structure can be complicated and an interplay between theory and materials imaging is required to evaluate these complex materials effects. The Beryllium Electron capture in Superconducting Tunnel junctions (BeEST) experiment currently uses 7Be embedded in superconducting tunnel junction (STJ) sensors to search for physics beyond the Standard Model in the neutrino sector by measuring the eV-scale radiation from 7Li that is emitted in the electron capture (EC) decay of 7Be. Understanding the spatial distribution of the final state 7Li in these superconductors at the eV-scale is thus important for characterizing material effects in these precision experiments, and to-date, represents the first attempt at performing so-called “atomic scale sensor characterization” for subatomic physics detectors.The chemical shifts resulting from the location and distribution of these implanted species in the final state have been estimated to contribute to broadening in the STJ spectrum during Li core-hole relaxation by recent theoretical calculations. In this thesis, atom probe tomography (APT) and transmission electron microscopy (TEM) were used to explore the Li distribution in the Al and Ta columnar polycrystalline layers. The Li concentration and clustering were compared in both purpose-fabricated thin film wafers and STJs for this imaging. The maximum separation method was used to classify clusters at the unit cell scale, as Li-Li interactions at this distance cause shifts in the 1s binding energy. Li clustering was seen in the ultra-high-dose (UHD) thin film wafers. The low concentration of Li in the STJs suggests no clustering within the unit cell. The Li clustering and concentration profiles provide future implantation dose limits. These limits are greater than the projected total implantation dose for future phases of the BeEST experiment. The Li distribution along the grain boundary (GB) was also explored. Li appeared to segregate at GBs in the Al and Ta thin film wafers. Due to low Li concentrations, GB segregation determinations in the Al and Ta STJs were inconclusive. These insights are critical in understanding the specific environment for the Li core-hole and subsequent relaxation.

• Publisher: ProQuest Dissertations & Theses
• Subject: Inorganic chemistry / Materials science / Nanoscience / Nuclear physics
• ISBN: 9798310301061