Chlorination of Hydrogenated Silicon Nanosheets Revealed by 1H{35Cl} and 29Si{35Cl} Solid-State NMR 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 an -OH group. Here, we apply 1H{35Cl} and 29Si{35Cl} Reso-nance-Echo Saturation-Pulse DOuble-Resonance (RESPDOR) solid-state NMR experiments to directly confirm the presence of chlorinated Si atoms within Si-NS. Plotting the observed 1H{35Cl} RESPDOR dephasing as a function of the 35Cl saturation pulse offset enables measurement of the 35Cl central-transition (CT) quadrupolar powder pattern and the chlorine quadrupolar coupling constant (CQ). Modelling the 1H{35Cl} RESPDOR dephasing curve shows that the Si-Si interlayer spacing is approximately 6 Å. Plane-wave DFT calculations suggest that the direct band gap transition of Si-NS decreases with increasing chlorination, suggesting that chlorination is a viable pathway to tune the band gap for applications.