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 CaSi2 precursor quality on SiNSs have not been studied. Here, we report a comparison of CaSi2 (and SiNSs derived therefrom) synthesized from two reaction pathways: (1) melting Ca and Si (elemental melting, or EM-CaSi2) and (2) the less-explored reaction between CaH2 and Si (hydride synthesis, or HS-CaSi2). We demonstrate that both reaction pathways lead to CaSi2, but the HS-CaSi2 pathway requires only a single step without the need to melt the CaSi2 product and at a temperature below the peritectic decomposition of CaSi2. We find that the EM-CaSi2 exhibits grains that lay flat against the substrate, whereas the HS-CaSi2 has little preferred orientation. We deintercalated both EM- and HS-CaSi2 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 CaSi2 and demonstrate that the morphology of CaSi2 and SiNSs can be controlled with different synthetic techniques.