Anisotropic Disorder and Thermal Stability of Silicane

Abstract

Atomically thin silicon nanosheets (SiNSs), such as silicane, have potential for next-generation computing paradigms, such as integrated photonics, owing to their efficient photoluminescence emission and complementary-metal-oxidesemiconductor (CMOS) compatibility. To be considered as a viable material for next-generation photonics, the SiNSs must retain their structural and optical properties at operating temperatures. However, the intersheet disorder of SiNSs and their nanoscale structure makes structural characterization difficult. Here, we use synchrotron X-ray diffraction and atomic pair distribution function (PDF) analysis to characterize the anisotropic disorder within SiNSs, demonstrating they exhibit disorder within the intersheet spacing, but have little translational or rotational disorder among adjacent SiNSs. Furthermore, we identify changes in their structural, chemical, and optical properties after being heated in an inert atmosphere up to 475 °C. We characterized changes of the annealed SiNSs using synchrotron-based total X-ray scattering, infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, electron paramagnetic resonance, absorbance, photoluminescence, and excited-state lifetime. We find that the silicon framework is robust, with an onset of amorphization at ∼300 °C, which is well above the required operating temperatures of photonic devices. Above ∼300 °C, we demonstrate that the SiNSs begin to coalesce while keeping their translational alignment to yield amorphous silicon nanosheets. In addition, our DFT results provide information on the structure, energetics, band structures, and vibrational properties of 11 distinct oxygen-containing SiNSs. Overall, these results provide critical information for the implementation of atomically thin silicon nanosheets in next-generation CMOScompatible integrated photonic devices.

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

“…6 Å gives best agreement with the experiments. This result is in excellent agreement with the spacing we determined in our previous synchrotron X-ray diffraction study . Finally, we used plane-wave DFT calculations to construct geometry-optimized models of Si-NS containing 0%, 20%, 50%, or 100% Cl termination and a model with 20% Cl termination and 10% OH termination (Figures and S9).…”

“…This result is in excellent agreement with the spacing we determined in our previous synchrotron X-ray diffraction study. 12 Finally, we used plane-wave DFT calculations to construct geometry-optimized models of Si-NS containing 0%, 20%, 50%, or 100% Cl termination and a model with 20% Cl termination and 10% OH termination (Figures 5 and S9). The calculations predict that the Si−Si interlayer distance increases with increasing chlorination to accommodate the longer Si−Cl bond length.…”

“…Si-NS were synthesized via the topotactic deintercalation of CaSi 2 in aqueous HCl at ca. −30 °C; CaSi 2 was prepared via the melting of elemental Ca and Si. , Note that the CaSi 2 used here was of very high purity and did not contain iron or bulk silicon impurities typically found in commercial CaSi 2 . , Scanning electron microscopy energy-dispersive X-ray spectroscopy (SEM EDS) analysis indicates that the material studied here has a Si:Cl atomic ratio between 5.7 and 6.3 (Figures S1 and S2, Table S1, see the Supporting Information for more discussion). Consistent with these results, our prior SEM EDS analysis of a different sample of Si-NS gave Si:Cl atomic ratios between 8 and 5.3, depending upon the portion of the sample that was imaged .…”

“…Si-NS were synthesized via our previously reported procedure. , In summary, CaSi 2 was prepared by melting Si and Ca (1:2 molar ratio of Ca to Si) in a sealed Ta tube inside an Ar-filled glovebox for ca. 1 min.…”

Green and facile method for valorization of lignin to high-performance degradable thermosets

“…In the FTIR spectrum of KL-70, the peaks between 1300 cm −1 and 1000 cm −1 belong to C-O-C in the lignin structure, newly formed Si-O-C from lignin and KH560, and Si-O-Si from the self-condensation of silanol groups. Specifically, the peaks at 1180-1060 cm −1 and 956 cm −1 correspond to Si-O-C (-CH 2 ) and Si-O-Ph generated by the dehydration condensation of lignin and KH560, respectively, [37][38][39] which indicates that the silanol groups produced by the hydrolysis of KH560 reacted with the lignin hydroxyl groups. The newly generated peak at 1018 cm −1 corresponds to Si-O-Si produced by the self-con-densation of silanol groups.…”