Theoretical optical extinction spectra of copper bare core Nps compared with a core-shell Cu-Cu2O Nps with the same core and 50% of shell thickness: (a) subnanometric and (b) nanometric. The shell produces a measurable redshift of the plasmon peak. Inset in panel (a) shows the dielectric function of Cu2O taken from Palik.
Experimental extinction spectra of copper Nps fabricated by fs pulse laser ablation at different pulse energies in different surrounding media: (a) in water and (b) in acetone
(a) Experimental spectrum of colloidal suspensions fabricated in water with 500 μJ pulse energy and a theoretical fit considering a core-shell structure of the Cu-Cu2O type. (b) Comparison between the fits of the same experimental spectrum using Cu-Cu2O and Cu-CuO core-shell structures.
Raman spectrum corresponding to copper in water with E = 500 μJ pulse energy. Peaks correspond to resonant transitions of Γ12 (108 cm−1), Γ12 (1) (165 cm−1) and 2 Γ12 (−) (232 cm−1) of Cu2O.
Experimental spectra of colloidal suspensions fabricated in water with 100 μJ pulse energy. Theoretical fit was obtained with Cu2O-Cu and Cu2O Nps. The inset shows the optimal size distribution of core radii and shell thickness that best fits the experimental spectrum.
(a) AFM image of copper Nps in water obtained with 100 μJ pulse energy, (b) height profiles of the six horizontal lines shown in panel (a), (c) AFM image of free area of the mica substrate used in the image, (d) height profile of image in panel (c), (e) HRTEM image of the same colloidal suspension.
Experimental spectra and theoretical fit of colloidal suspension in acetone: (a) pulse energy E = 500 μJ, (b) pulse energy E = 100 μJ, and (c) pulse energy E = 50 μJ. In each panel, the inset shows the optimal size distribution of core radii and shell thickness that fits the whole experimental spectrum. The fit in panel (a) is based on a combination of Cu bare core and Cu-Cu2O structures. The fit in panel (b) is based on Cu-Cu2O structure, while the fit in panel (c) is based on a combination of Cu-Cu2O and Cu2O-Cu configurations.
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