Dimensionality-Dependent Hot Electrons Diffusion in Gold Nanoplates Visualized by Transient Absorption Microscopy^†

The gold nano- plates (Au NPLs) have been extensively studied for their high quality factor as mechanical resonators. But it remains still unclear how the thickness and morphology of Au NPLs affect the hot electron diffusion. Here we have employed transient absorption microscopy to gain spatiotemporal imaging of the hot electron diffusion in Au NPLs. Au NPLs of varying thickness over 200 nm were synthesized. It was found that the hot electron diffusion of Au NPL excited at the boundary is obviously faster than that excited at the internal surface. And thinner Au NPLs exhibit a faster hot electron diffusion rate compared to thicker Au NPLs. Because the time constant of hot electron cooling (electron−phonon coupling) is independent of the excited position and thickness of Au NPLs, the effect of electron−phonon coupling on hot electron diffusion should be ruled out. So the hot electron diffusion rate is highly dimensionality-dependent. The quasi-one-dimensional diffusion along the boundary of nanoplate has the fastest rate of 50 cm²/s, and the three dimensional diffusion has the slowest rate of 22 cm²/s. The fundamental investigation on the hot electrons transport property of Au NPLs offers a new insight for designing metal-based optoelectronic devices.