Browsing by Author "Nancarrow, M"

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    Application of an SOI microdosimeter for monitoring of neutrons in various mixed radiation field environments
    (Institute of Electrical and Electronics Engineers (IEEE), 2022-03-01) Pan, VA; Vohradsky, J; James, B; Pagani, F; Chartier, L; Debrot, E; Pastuovic, Z; Cutajar, D; Poder, J; Nancarrow, M; Pereloma, E; Bolst, D; Lee, SH; Inaniwa, T; Safavi-Naeini, M; Prokopovich, DA; Guatelli, S; Petasecca, M; Lerch, MLF; Povoli, M; Kok, A; Tran, LT; Rosenfeld, AB
    Radiation monitoring in space radiation is complex due to galactic cosmic rays (GCRs), solar particle events (SPEs), and albedo particles. Thermal neutrons are an important component in the Moon radiation albedo field which can cause single event upset (SEU) in electronics when they interact with the 10 B present in electronic components. In this work, we studied an application of silicon on insulator (SOI) microdosimeters for neutron monitoring in various mixed radiation field environments. A 10- μm SOI microdosimeter was utilized in conjunction with a 10 B 4 C thin-film converter to successfully measure the thermal neutron contribution out of field of a therapeutic proton beam as well as an 18-MV X-ray linear accelerator (LINAC). The microdosimeter was placed downstream of the Bragg peak (BP) as well as laterally out of field of the proton beam and at two positions along the treatment couch of the 18-MV LINAC. It was demonstrated that the 10- μm SOI microdosimeter with 10 B 4 C converter is suitable for detection of thermal neutrons with excellent discrimination of gamma, fast and thermal neutron components in the presence of a gamma-neutron pulsed field of an 18-MV LINAC. To reduce the gamma contribution and further improve detection of neutrons in mixed radiation fields, a new 2 μm Mushroom-planar microdosimeter was fabricated and characterized in detail using an ion beam induced charge collection (IBIC) technique with 1.78 MeV He2+ ions. It was demonstrated that this 2 μm SOI microdosimeter can be operated in a passive mode. The SOI microdosimeter with the 10 B 4 C converter can be recommended for the detection of thermal neutrons for SEU prediction in the mixed gamma-neutron fields during space missions, especially for the Moon mission.© Copyright 2025 IEEE
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    Creating thin magnetic layers at the surface of Sb2Te3 topological insulators using a low-energy chromium ion beam
    (AIP Publishing, 2020-05-11) Cortie, DL; Zhao, WY; Yue, Z; Li, Z; Bake, A; Marenych, O; Pastuovic, Z; Nancarrow, M; Zhang, ZM; Qi, DC; Evans, PJ; Mitchell, DRG; Wang, XL
    The surfaces of Sb2Te3 topological insulator crystals were implanted using a 40 keV chromium ion beam. To facilitate uniform doping, the Sb2Te3 was passivated with a thin TiO2 film before the implantation step. The resulting chemical structure was studied using atomic-resolution transmission electron microscopy. A fluence of 7 × 1015 ions/cm2 at 40 keV lead to amorphization of the Sb2Te3 surface, with chromium predominantly incorporated in the amorphous layer. Heating to 200 °C caused the amorphous region to recrystallize and led to the formation of a thin chromium-rich interfacial layer. Near-edge x-ray absorption spectroscopy indicates a uniform valence state of Cr3+ throughout, with no evidence of metallic clustering. High-temperature superparamagnetic behavior was detected up to 300 K, with an increased magnetic moment below 50 K. © 2020 Author(s).
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    Lamellae preparation for atomic-resolution STEM imaging from ion-beam-sensitive topological insulator crystals
    (AIP Publishing, 2022-04-06) Bake, A; Zhao, WY; Mitchell, DRG; Wang, XL; Nancarrow, M; Cortie, DL
    Good specimen quality is a key factor in achieving successful scanning transmission electron microscope analysis. Thin and damage-free specimens are prerequisites for obtaining atomic-resolution imaging. Topological insulator single crystals and thin films in the chalcogenide family such as Sb2Te3 are sensitive to electron and ion beams. It is, therefore, challenging to prepare a lamella suitable for high-resolution imaging from these topological insulator materials using standard focused ion-beam instruments. We have developed a modified method to fabricate thin focused ion-beam (FIB) lamellae with minimal ion-beam damage and artefacts. The technique described in the current study enables the reliable preparation of high-quality transmission electron microscope (TEM) specimens necessary for studying ultra-thin surface regions. We have successfully demonstrated that the careful selection of FIB milling parameters at each stage minimizes the damage layer without the need for post-treatment. © 2022 Author(s). Published under an exclusive license by the AVS.
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    Structure and magnetism of ultra-small cobalt particles assembled at titania surfaces by ion beam synthesis
    (Elsevier, 2021-12) Bake, A; Rezoanur Rahman, M; Evans, PJ; Cortie, MB; Nancarrow, M; Abrudan, R; Radu, F; Khaydukov, Y; Causer, GL; Callori, SJ; Livesey, KL; Mitchell, DRG; Pastuovic, Z; Wang, XL; Cortie, DL
    Metallic cobalt nanoparticles offer attractive magnetic properties but are vulnerable to oxidation, which suppresses their magnetization. In this article, we report the use of ion beam synthesis to produce ultra-small, oxidation-resistant, cobalt nanoparticles embedded within substoichiometric TiO2-δ thin films. Using high fluence implantation of cobalt at 20–60 keV, the particles were assembled with an average size of 1.5 ± 1 nm. The geometry and structure of the nanoparticles were studied using scanning transmission electron microscopy. Near-edge X-ray fluorescence spectroscopy on the L2,3 Co edges confirms that the majority of the particles beneath the surface are metallic, unoxidised cobalt. Further evidence of the metallic nature of the small particles is provided via their high magnetization and superparamagnetic response between 3 and 300 K with a low blocking temperature of 4.5 K. The magnetic properties were studied using a combination of vibrating sample magnetometry, element-resolved X-ray magnetic circular dichroism, and depth-resolved polarised neutron reflectometry. These techniques provide a unified picture of the magnetic metallic Co particles. We argue, based on these experimental observations and thermodynamic calculations, that the cobalt is protected against oxidation beneath the surface of titania owing to the enthalpic stability of TiO2 over CoO which inhibits solid state reactions. Crown Copyright © 2021 Published by Elsevier B.V.
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    Top-down patterning of topological surface and edge states using a focused ion beam
    (Springer Nature, 2023-03-27) Bake, A; Zhang, Q; Ho, CS; Causer, GL; Zhao, WY; Yue, ZJ; Nguyen, A; Akhgar, G; Karel, J; Mitchell, DRG; Pastuovic, Z; Lewis, RA; Cole, JH; Nancarrow, M; Wang, XL; Cortie, DL
    The conducting boundary states of topological insulators appear at an interface where the characteristic invariant ℤ2 switches from 1 to 0. These states offer prospects for quantum electronics; however, a method is needed to spatially-control ℤ2 to pattern conducting channels. It is shown that modifying Sb2Te3 single-crystal surfaces with an ion beam switches the topological insulator into an amorphous state exhibiting negligible bulk and surface conductivity. This is attributed to a transition from ℤ2 = 1 → ℤ2 = 0 at a threshold disorder strength. This observation is supported by density functional theory and model Hamiltonian calculations. Here we show that this ion-beam treatment allows for inverse lithography to pattern arrays of topological surfaces, edges and corners which are the building blocks of topological electronics. Open Access This article is licensed under a Creative Commons Attribution 4.0 © Crown Copyright 2023
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    Ultra-small cobalt particles embedded in titania by ion beam synthesis: additional datasets including electron microscopy, neutron reflectometry, modelling outputs and particle size analysis
    (Elsevier, 2022-02) Bake, A; Rahman, R; Evans, PJ; Cortie, MB; Nancarrow, M; Abrudan, R; Radu, F; Khaydukov, Y; Causer, GL; Livesey, KL; Callori, SJ; Mitchell, DRG; Pastuovic, Z; Wang, XL; Cortie, DL
    This Data-in-brief article includes datasets of electron microscopy, polarised neutron reflectometry and magnetometry for ultra-small cobalt particles formed in titania thin films via ion beam synthesis. Raw data for polarised neutron reflectometry, magnetometry and the particle size distribution are included and made available on a public repository. Additional elemental maps from scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) are also presented. Data were obtained using the following types of equipment: the NREX and PLATYPUS polarised neutron reflectometers; a Quantum Design Physical Property Measurement System (14 T); a JEOL JSM-6490LV SEM, and a JEOL ARM-200F scanning transmission electron microscope (STEM). The data is provided as supporting evidence for the article in Applied Surface Science (A. Bake et al., Appl. Surf. Sci., vol. 570, p. 151068, 2021, DOI 10.1016/j.apsusc.2021.151068), where a full discussion is given. The additional supplementary reflectometry and modelling datasets are intended to assist future scientific software development of advanced fitting algorithms for magnetization gradients in thin films. Crown Copyright © 2021 - Open Access CC BY-NC-ND