Electrodeposition of Microfabricated Rhenium-Filaments

Abstract

Metallic filaments comprised of refractory materials are a necessary part of mass spectrometers used to measure isotopes. The current state-of-the-art material, rhenium, is formed into filaments using a mechanical crimper, limiting the accuracy, speed, and quantity of filaments that can be fabricated. The current work describes the development of wafer-scale, microfabricated Re filaments using silicon molds followed by electrodeposition of Re. The goal is to develop filaments with tight dimensional tolerances, high purity, and mechanical rigidity for the desired application and offer the ability to create 100’s-1000’s of filaments on a single silicon wafer.Electrodeposition of Re is notoriously difficult as the reduction potential of rhenium is close to the hydrogen evolution reaction in aqueous solutions.1 While rhenium has been successfully deposited from alkaline, acid, and concentrated lithium chemistries,2 the films are often thin, porous, and contain many impurities such as hydrogen and oxygen. Rhenium oxide is susceptible to reaction with moisture in the air, resulting in poor quality films with short functional lifetimes. To electroform precise, pure rhenium structures, hardier chemistries must be developed.The current work seeks to address this challenge using a water-in-salt chemistry (WISE) comprised of up to 4M lithium salts, complexing agents, reducing agents, and oxygen scavengers. Numerous physical agitation techniques were utilized to improve the quality of the film. Solutions were analyzed using various electrochemical techniques, UV-VIS, and Raman spectroscopy. The optimized chemistry was used to electrodeposit bulk batches of microfabricated 2mm x 300 um x 300 um filaments. The filaments were analyzed using microscopy, XRF, XRD, SEM, and EDS with a goal of use in high temperature mass spectrometry experiments. References (1) Naor, A.; Eliaz, N.; Burstein, L.; Gileadi, E. Direct Experimental Support for the Catalytic Effect of Iron-Group Metals on Electrodeposition of Rhenium. Electrochemical and Solid-State Letters 2010, 13 (12), D91. DOI: 10.1149/1.3489532.(2) Pappas, D. P.; David, D. E.; Lake, R. E.; Bal, M.; Goldfarb, R. B.; Hite, D. A.; Kim, E.; Ku, H.-S.; Long, J.; McRae, C. Enhanced superconducting transition temperature in electroplated rhenium. Applied Physics Letters 2018, 112 (18), 182601. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525. SAND2022-*****