Ph. D. THESIS 2009

Figure 11. Evolution of the UV absorption spectra of an aqueous solution
containing 1 mMol Au(III), 1 mMol Fe(III)-citrate and 1 mL PSS upon irradiation:
a) in solution, at every 20 minutes; b) in thin film, at every 15 minutes.
Upon irradiation a plasmon band clearly appears (Figure 11a) indicating the
generation of gold nanoparticles. The gradual increase of this band and the red
shifted plasmon peak position represent the growth of the gold particles in
solution. As expected, this phenomenon is coupled with the decrease of the
Au(III) band located at around 310 nm, assuming that the Au(III) ions are
reduced upon irradiation. In the solid state, similar spectra can be observed.
Nevertheless as diffusion of active species is much slower than in solution,
after similar time of irradiation (an hour), the plasmon band is less broad and
located at lower wavelenght around 550 nm.
Figure 12. UV spectrum recorded for the mixture containing 1 mMol
Au(III), Fe(III)-citrate and 1 mL PSS upon irradiation at the same irradiation
times in thin film, at 1:2 ammonium ferric citrate:gold salt ratio.
4.3. The gold structures fabrication process
8