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High-fluence femtosecond laser pulses can induce physical and chemical changes in materials that are unrealizable under standard laboratory conditions. The exact nature of these changes can depend strongly on the gaseous environment in which the material is irradiated since near-surface chemical reactions can occur between the two materials. Surface modifications of silicon are of particular interest due to its significance in semiconductor-based applications. Specifically, the formation of silicon nitride (Si3N4) structures is desirable for multiple applications due to its high stability and low dielectric constant. Herein, we report on femtosecond laser-induced morphological and chemical modifications of silicon in a nitrogen atmosphere. We observed an extremely fast chemical reaction in the silicon-nitrogen system. The presence of crystalline Si3N4 was confirmed using high-resolution transmission electron microscopy, representing the first reported synthesis of Si3N4 nanocrystals through femtosecond laser-based methods. In addition, the surface was found to contain alternating layers of amorphous and crystalline silicon. Provided are plausible mechanisms for the formation of each of these structures. Taken together, these findings on surface modification of silicon using femtosecond laser irradiation may provide new pathways for manufacturing of nanoscale devices. 

Gold cores functionalized with dithiol linkers are densely populated with Turkevich-synthesized satellite nanoparticles in under thirty minutes at 100% yield using procedures that promote rapid assembly while avoiding potential pitfalls.