Luminescent Silicon Nanosheet Paracrystals from Elemental- and Hydride-Based Syntheses of CaSi₂ Precursors: Implications for Photonic and Optoelectronic Applications

Layered silicon nanosheets (SiNSs) have attracted considerable attention owing to their unique combination of chemical and physical properties, which makes them an exciting candidate for next-generation on-chip light sources and lasers. Despite over 150 years of research on SiNSs, the effects of the CaSi 2 precursor quality on SiNSs have not been studied. Here, we report a comparison of CaSi 2 (and SiNSs derived therefrom) synthesized from two reaction pathways: (1) melting Ca and Si (elemental melting, or EM-CaSi 2 ) and (2) the less-explored reaction between CaH 2 and Si (hydride synthesis, or HS-CaSi 2 ). We demonstrate that both reaction pathways lead to CaSi 2, but the HS-CaSi 2 pathway requires only a single step without the need to melt the CaSi 2 product and at a temperature below the peritectic decomposition of CaSi 2 . We find that the EM-CaSi 2 exhibits grains that lay flat against the substrate, whereas the HS-CaSi 2 has little preferred orientation. We deintercalated both EM- and HS-CaSi 2 with HCl at −35 °C to yield hydrogen-terminated SiNSs. We characterized the SiNSs and found that the HS-SiNSs and EM-SiNSs exhibit properties that are nearly identical, with the exception that the morphology of the precursor is imparted to the SiNSs. These results provide the community with a one-step method to synthesize CaSi 2 and demonstrate that the morphology of CaSi 2 and SiNSs can be controlled with different synthetic techniques.