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Polymer-assisted deposition of homogeneous metal oxide films to produce nuclear targets

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Abstract

Targets are essential in experimental nuclear sciences as a source of stationary nuclei for nuclear reactions with ion beams. Typically, targets should be chemically pure, uniform, homogeneous and crack-free over the irradiation area, while also being structurally rigid. The polymer-assisted deposition (PAD) method uses a water-soluble multidentate polymer that chelates metal precursors in solution. This polymer-metal solution is then spin coated and annealed to yield a crack-free, homogeneous metal oxide film. In this protocol, nuclear targets are created using PAD on silicon nitride (Si3N4) windows with silicon frames. Silicon wafers ([100], single-side polished) coated with 1 μm of silicon nitride on both sides are patterned and etched to create 1-μm silicon nitride windows. The PAD solution is then spun onto the silicon nitride window and annealed to create a thin, uniform metal oxide film of variable thickness on top of the silicon nitride backing. The production of a target window and the deposition of a thin film ranging from 50 to 150 nm takes ∼13.5 h. Subsequent reapplications to grow thicker films require an additional 5 h per application.

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Figure 1: Banana-shaped target frame for mounting on wheel targets.
Figure 2: Left, back side of the silicon wafer.
Figure 3: Schematic of silicon nitride window fabrication.
Figure 4: Spin-coating apparatus with wheel target shown.
Figure 5: Wheel target stencil held securely onto the backside of a silicon nitride–coated wafer.
Figure 6: Assembled etching apparatus.
Figure 7: A representative SEM cross-sectional image of a single-layer hafnium(IV) oxide (HfO2) film created using a 10% (wt/wt) hafnium solution.
Figure 8: A representative AFM image of a double-layered thulium(III) oxide film, created using a 6% (wt/wt) thulium solution.
Figure 9: Four targets of 500-μm-thick lead oxide on 1-μm-thick silicon nitride.

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Acknowledgements

This work was supported by the National Nuclear Security Administration under the Stewardship Sciences Academic Alliance Program, project NS00075, award Number DE-FG52-06NA27480. Work at the Molecular Foundry was supported by the Director, Office of Science, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering, of the US Department of Energy under contract no. DE-AC02-05CH11231.

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Authors and Affiliations

  1. Department of Chemistry, University of California, Berkeley, California, USA

    Mazhar N Ali, Mitch A Garcia, T Parsons-Moss & Heino Nitsche

  2. Lawrence Berkeley National Laboratory, Berkeley, California, USA

    Mazhar N Ali, Mitch A Garcia, T Parsons-Moss & Heino Nitsche

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  1. Mazhar N Ali
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  2. Mitch A Garcia
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  3. T Parsons-Moss
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  4. Heino Nitsche
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All authors contributed extensively to the work presented in this article.

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Correspondence to Heino Nitsche.

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Ali, M., Garcia, M., Parsons-Moss, T. et al. Polymer-assisted deposition of homogeneous metal oxide films to produce nuclear targets. Nat Protoc 5, 1440–1446 (2010). https://doi.org/10.1038/nprot.2010.105

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