Unusual behavior in magnesium-copper cluster matter produced by helium droplet mediated deposition.
We demonstrate the ability to produce core-shell nanoclusters of materials that typically undergo intermetallic reactions using helium droplet mediated deposition. Composite structures of magnesium and copper were produced by sequential condensation of metal vapors inside the 0.4 K helium droplet baths and then gently deposited onto a substrate for analysis. Upon deposition, the individual clusters, with diameters ∼5 nm, form a cluster material which was subsequently characterized using scanning and transmission electron microscopies. Results of this analysis reveal the following about the deposited cluster material: it is in the un-alloyed chemical state, it maintains a stable core-shell 5 nm structure at sub-monolayer quantities, and it aggregates into unreacted structures of ∼75 nm during further deposition. Surprisingly, high angle annular dark field scanning transmission electron microscopy images revealed that the copper appears to displace the magnesium at the core of the composite cluster despite magnesium being the initially condensed species within the droplet. This phenomenon was studied further using preliminary density functional theory which revealed that copper atoms, when added sequentially to magnesium clusters, penetrate into the magnesium cores.
University of Dayton Research Institute, 300 College Park, Dayton, Ohio 45469, USA; Air Force Research Laboratory, Munitions Directorate, 2306 Perimeter Rd., Eglin AFB, Florida 32542, USA.
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Emery
National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310, USA.
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Xin
Air Force Research Laboratory, Munitions Directorate, 2306 Perimeter Rd., Eglin AFB, Florida 32542, USA.
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CJ
Ridge
ERC Inc., Edwards AFB, California 93524, USA.
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RJ
Buszek
Air Force Research Laboratory, Aerospace System Directorate, Edwards AFB, California 93524, USA.
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JA
Boatz
Naval Surface Warfare Center Indian Head Explosive Ordnance Technology Division, Indian Head, Maryland 20640, USA.
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JM
Boyle
University of Dayton Research Institute, 300 College Park, Dayton, Ohio 45469, USA; Air Force Research Laboratory, Munitions Directorate, 2306 Perimeter Rd., Eglin AFB, Florida 32542, USA.
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Little
Air Force Research Laboratory, Munitions Directorate, 2306 Perimeter Rd., Eglin AFB, Florida 32542, USA.
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Lindsay