Anisotropic Disorder and Thermal Stability of Silicane

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-oxide-semiconductor (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
CMOS-compatible integrated photonic devices.