S. Link et al., Alloy formation of gold-silver nanoparticles and the dependence of the plasmon absorption on their composition, J PHYS CH B, 103(18), 1999, pp. 3529-3533
Gold-silver alloy nanoparticles with varying mole fractions are prepared in
aqueous solution by the co-reduction of chlorauric acid HAuCl4 and silver
nitrate AgNO3 with sodium citrate. As the optical absorption spectra of the
ir solutions show only one plasmon absorption it is concluded that mixing o
f gold and silver leads to a homogeneous formation of alloy nanoparticles.
The maximum of the plasmon band blue-shifts linearly with increasing silver
content. This fact cannot be explained by a simple linear combination of t
he dielectric constants of gold and silver within the Mie theory. On the ot
her hand, the extinction coefficient is found to decrease exponentially rat
her than linearly with increasing gold mole fraction x(Au). Furthermore, th
e size distribution of the alloy nanoparticles is examined using transmissi
on electron microscopy (TEM). High-resolution TEM (HRTEM) also confirms the
formation of homogeneous gold-silver alloy nanocrystals.