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 considerableattention owing to their unique combination of chemical and physicalproperties, which makes them an exciting candidate for next-generationon-chip light sources and lasers. Despite over 150 years of researchon SiNSs, the effects of the CaSi2 precursor quality onSiNSs have not been studied. Here, we report a comparison of CaSi2 (and SiNSs derived therefrom) synthesized from two reactionpathways: (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 demonstratethat both reaction pathways lead to CaSi2, but the HS-CaSi2 pathway requires only a single step without the need to meltthe CaSi2 product and at a temperature below the peritecticdecomposition of CaSi2. We find that the EM-CaSi2 exhibits grains that lay flat against the substrate, whereas theHS-CaSi2 has little preferred orientation. We deintercalatedboth EM- and HS-CaSi2 with HCl at -35 degrees C toyield hydrogen-terminated SiNSs. We characterized the SiNSs and foundthat the HS-SiNSs and EM-SiNSs exhibit properties that are nearlyidentical, with the exception that the morphology of the precursoris imparted to the SiNSs. These results provide the community witha one-step method to synthesize CaSi2 and demonstrate thatthe morphology of CaSi2 and SiNSs can be controlled withdifferent synthetic techniques.

Automated summary

The effects of CaSi2 precursor quality on SiNSs were studied, and it was found that SiNSs synthesized from different reaction pathways exhibit nearly identical properties, except for the morphology of the precursor.