Figure 5.

TEM images of gold nanoparticles formed by citrate reduction as function of elapsed time. TEM images of gold nanoparticles formed by citrate reduction as function of elapsed time when using a conventional ultrasonic bath (40 kHz, 300 W): (a) after 10 sec, (b) after 30 sec, (c) after 70 sec, (d) after 140 sec, (e) after 15 min; and (f) after 45 min. Initial HAuCl₄ concentration was 0.25 mM, and molar ratio between HAuCl₄ and sodium citrate was set at 1:3.5.