Development of Neutron Polarizers and Analyzers via Polarizing Supermirrors by Atomic Layer Deposition

The Department of Energy's support for neutron facilities, such as the Spallation Neutron Source (SNS) and the Los Alamos Neutron Science Center (LANSCE), has been instrumental in advancing scientific knowledge and innovation. Polarized neutron scattering experiments which require polarizer and analyzer devices allow for the separation of magnetic scattering, enabling unique insights into magnetic order in magnetic materials, and are also used in soft-matter investigations. Today, polarized neutron supermirrors which are crucial components of polarizers and analyzers are manufactured in Europe using physical vapor deposition (PVD) techniques. However, this approach has challenges, including supply-chain vulnerability posed by a non-US manufacturer and issues with warpage of the thin substrates due to stress from the supermirror coating. RMD proposes to address these challenges and enable US manufacturing of polarizers and analyzers by leveraging Atomic Layer Deposition (ALD). Due to its conformal nature, supermirrors deposited by ALD can coat complex geometries needed for easier manufacturing of polarizer and analyzer devices, as well as simultaneously coating both sides of substrates to prevent warpage. RMD's expertise in thin films and ongoing work in conformal neutron supermirrors via ALD and neutron guides using a hybrid ALD-PVD technique further empowers the project. In Phase I, RMD will identify and develop ALD processes for suitable magnetic and non-magnetic materials for neutron polarizing supermirrors. Initial simulations suggest Fe3N and TiN as promising candidates due to their high contrast of neutrons spin direction to discriminate whether neutrons are reflected or transmitted. We will collaborate with Dr. Boris Khaykovich at MIT Nuclear Reactor Laboratory (NRL) for supermirror designs and evaluate ALD-grown magnetic materials. The goal is to design a mirror with m=4 reflectivity and polarization efficiency > 90%, and ultimately to deposit a simple supermirror coating on both sides of a substrate by the end of Phase I as proof of concept. There are five neutron facilities in the U.S., Oak Ridge National Laboratory (ORNL) plans within the next several years, to replace all of the neutron guides at the High Flux Isotope Reactor (HFIR), to build additional instruments at the First Target Station (FTS) of the SNS, and to begin construction on the Second Target Station (STS) at the SNS. STS at ORNL has plans to use a wide variety of polarizers and analyzers which will require polarizing neutron supermirrors. There is no present US producer of supermirrors; the current suppliers for ORNL are European small businesses. Development of a domestic supplier would be useful to ORNL for both competition and capacity reasons. Additionally, aperiodic multilayer interference coatings are of particular interest for a variety of hard x-ray applications, including target diagnostics, astrophysics, high energy physics and free-electron lasers.