3D nanoprinting of metals by spatiotemporally confined hot electrons via multiple-electron excitations in nanocrystals.

For decades, multi-photon polymerization has been a key technology for fabricating complex 3D micro- and nanoscale structures from polymer materials. However, extending this capability beyond polymers remains a significant challenge. In particular, nanoscale metal printing is challenging because solid metal formation typically requires energy-driven reactions or thermally activated processes that are difficult to spatially localize, resulting in compromised feature resolution. Here, we demonstrate 3D nanoprinting of metals with depth and lateral resolution <250 nm. The method employs femtosecond laser-induced hot electrons spatiotemporally confined in nanocrystals to facilitate nonlinear multi-electron absorption, ligand desorption, and nanocrystal fusion. This approach operates at a pulse energy about 100× lower than simultaneous multi-photon processes, avoids organic additives, and is compatible with free-space or layer-by-layer printing. Printing of multiple metals is demonstrated, achieving mechanical strength comparable to pure metals, along with functional mechanical and optical metamaterials. This technology enables customizable 3D metal nanoprinting for advanced applications in metamaterials, biotechnology, nanorobotics, sensors, and semiconductor manufacturing.