Chlorination of Hydrogenated Silicon Nanosheets Revealed by Solid-State Nuclear Magnetic Resonance Spectroscopy

Two-dimensional silicon nanosheets (Si-NS) synthesized by topotactic deintercalation of CaSi2 are hypothesized to consist of buckled layers of sp3-hybridized silicon atoms that are bonded to three other framework Si atoms and a terminal atom or functional group such as H, Cl, or OH. Here, we apply 1H­{35Cl} and 29Si­{35Cl} Resonance-Echo Saturation-Pulse DOuble-Resonance (RESPDOR) solid-state NMR experiments to directly confirm the presence of chlorinated Si atoms within Si-NS. Plotting the 1H­{35Cl} RESPDOR dephasing as a function of the 35Cl saturation pulse offset reveals that the 35Cl quadrupolar coupling constant (C Q) is 38 MHz, consistent with Cl atoms that are covalently bonded to silicon. Modeling the 1H­{35Cl} RESPDOR dephasing curve shows that the Si–Si interlayer spacing is approximately 6 Å. Plane-wave density functional theory (DFT) calculations show that the direct band gap transition of the Si-NS decreases with increasing chlorination and hydroxylation, suggesting that the band gap of Si-NS can be tuned by modifying the terminal atoms or functional groups.