The most prominent consequence of irradiating HAuCl4-solutions is the reduction of goldcontaining species to elementary Au, which agglomerates and forms crystalline structures easily detectable in TEM. For this mechanism, an electron flux density exceeding an estimated threshold between 2 • 10³ and 3 • 10³ e -(nm²s) -1 was concluded previously. However, our simulation results (Figure ) do not indicate a threshold existing for irradiation of a 20 mM HAuCl4 solution, the same specimen investigated by Park et al.. A respective experiment, demonstrated in Figure , displays a growth event of a gold nanostructure at 540 e -(nm²s) -1 . The growth rate decreased over time, suggesting the convergence against a steady-state condition. This observation indicates the existence of "sub-threshold" gold reduction.