Comparison between experimental bulk values (squares and diamonds) and theoretical calculation for the real and imaginary part of copper dielectric function. Experimental values were derived from Johnson and Christy22 while theoretical free and bound electron contributions to the complex dielectric function were carried out using Eqs. (1)–(3). (a) Real component ε′ and (b) imaginary component ε″. Determined parameters are given in Table I.
Real (a) and imaginary (b) parts of the copper complex dielectric function considering free and bound electron contributions for different values of Np radii.
Influence of Eg on the complex dielectric function: (a) real component and (b) imaginary component. The influence of the imaginary part is more noticeable for wavelengths in the range 350–530 nm (region I).
Influence of EF on the complex dielectric function: (a) real part and (b) imaginary part. The influence on the imaginary part is more noticeable between 500 and 750 nm (region II).
Influence of γb on the complex dielectric function: (a) real part and (b) imaginary part. There is a stretching around 570 nm that affects mainly the peak and the valley.
Extinction coefficient for (a) core-shell Cu-Cu2O Np and (b) bare core Cu Np, with and without bound electron size correction. The difference in the spectra is more noticeable for wavelengths smaller that the plasmon peak, where the influence of the bound electron is more important.
Solid line corresponds to normalized experimental spectral extinction of Cu-Cu2O Nps fabricated in water by laser ablation with 500 μJ pulse energy. Dashed line and points shows the best fit calculated theoretically with a bimodal contribution for core-shell Cu-Cu2O Np: (1) R = 0.9 nm and R′-R = 0.36 nm and (2) R = 0.9 and R′-R = 1.35 nm. The abundance for the first contribution is 0.45 and 0.55 for the second.
Solid line corresponds to experimental spectral extinction of Cu-Cu2O Nps fabricated by laser ablation with 500 μJ energy. Squares with full line is calculated extinction spectrum corresponding to R = 0.9 nm and R′-R = 40% R. Circles with dashed line is calculated extinction spectrum corresponding to R = 0.9 nm and R′-R = 150% R.
Experimental spectra and theoretical fit of colloidal suspension in acetone: (a) pulse energy E = 500 μJ. The fit is based on a combination of Cu bare core and Cu-Cu2O structures.
(a) AFM image of the diluted colloidal suspension obtained by laser ablation with 500 μJ pulse energy (upper panel) and height (diameter) of the NPs vs X position for line 1 and line 2 marked on AFM image(lower panel). Notice the single peak in line 1 and two single Np peaks in line 2. (b) AFM image of the mica substrate. (c) Measured roughness profile of the mica substrate shows an average value of 0.07 nm. (d) HRTEM image of core-shell Cu-Cu2O nanoparticles. The external radii observed are in good agreement with the values obtained by the AFM image and extinction spectroscopy.
Optical parameters for bulk copper determined in this work.
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