A1 Journal article (refereed)
Controlled synthesis and characterization of porous silicon nanoparticles for dynamic nuclear polarization (2024)

von Witte, G., Himmler, A., Hyppönen, V., Jäntti, J., Albannay, M. M., Moilanen, J. O., Ernst, M., Lehto, V.-P., Riikonen, J., Kozerke, S., Kettunen, M. I., & Tamarov, K. (2024). Controlled synthesis and characterization of porous silicon nanoparticles for dynamic nuclear polarization. Nanoscale, 16(41), 19385-19399. https://doi.org/10.1039/d4nr02603a(external link)

JYU authors or editors

Moilanen, Jani

Publication details

All authors or editors: von Witte, Gevin; Himmler, Aaron; Hyppönen, Viivi; Jäntti, Jiri; Albannay, Mohammed M.; Moilanen, Jani O.; Ernst, Matthias; Lehto, Vesa-Pekka; Riikonen, Joakim; Kozerke, Sebastian; et al.

Journal or series: Nanoscale

ISSN: 2040-3364

eISSN: 2040-3372

Publication year: 2024

Publication date: 18/09/2024

Volume: 16

Issue number: 41

Pages range: 19385-19399

Publisher: Royal Society of Chemistry

Publication country: United Kingdom

Publication language: English

DOI: https://doi.org/10.1039/d4nr02603a(external link)

Research data link: https://doi.org/10.3929/ethz-b-000679152(external link)

Publication open access: Openly available

Publication channel open access: Partially open access channel

Publication is parallel published (JYX): https://jyx.jyu.fi/handle/123456789/97603(external link)

Web address of parallel published publication (pre-print): https://doi.org/10.48550/arXiv.2401.08320

Abstract

Si nanoparticles (NPs) have been actively developed as a hyperpolarized magnetic resonance imaging (MRI) contrast agent with an imaging window close to one hour. However, the progress in the development of NPs has been hampered by the incomplete understanding of their structural properties that correspond to efficient hyperpolarization buildup and long polarization decays. In this work we study dynamic nuclear polarization (DNP) of single crystal porous Si (PSi) NPs with defined doping densities ranging from nominally undoped to highly doped with boron or phosphorus. To develop such PSi NPs we perform low-load metal-assisted catalytic etching for electronic grade Si powder followed by thermal oxidation to form the dangling bonds in the Si/SiO2 interface, the Pb centers. Pb centers are the endogenous source of the unpaired electron spins necessary for DNP. The controlled fabrication and oxidation procedures allow us to thoroughly investigate the impact of the magnetic field, temperature and doping on the DNP process. We argue that the buildup and decay rate constants are independent of size of Si crystals between approximately 10 and 60 nm. Instead, the rates are limited by the polarization transfer across the nuclear spin diffusion barrier determined by the large hyperfine shift of the central 29Si nuclei of the Pb centers. The size-independent rates are then weakly affected by the doping degree for low and moderately doped Si although slight doping is required to achieve the highest polarization. Thus, we find the room temperature relaxation of low boron doped PSi NPs reaching 75 ± 3 minutes and nuclear polarization levels exceeding ∼6% when polarized at 6.7 T and 1.4 K. Our study thus establishes solid grounds for further development of Si NPs as hyperpolarized contrast agents.

Keywords: nanoparticleschemical synthesis; ; silicon; magnetic resonance imagingpolarisation; ; nanosciences