(Invited) Silicon Nanosheets as Candidates for Silicon-Based Optoelectronics

Abstract

Colloidal Group IV nanomaterials (Si, Ge, Sn and their alloys) are of great interest due to their potential to offer broadly tunable optical properties. By manipulating composition, size, or surface chemistry Group IV nanomaterials have potential to serve as nontoxic, earth abundant phosphors or semiconductors that can be used for optoelectronic applications that span the ultraviolet to the mid-infrared spectral ranges. The synthesis of colloidal Group IV nanostructures is challenging due to the highly covalent character of Si and Ge, and typically require temperatures in excess of 400°C to form crystalline particles. We have recently reported new synthetic methods for Si and Ge nanomaterials derived from precursors synthesized in the solid-state, including suboxides and Zintl phases. In each of these cases, colloidal nanostructures can be accessed by selectively removing unwanted components from the solid-state precursor, liberating nanostructures that are terminated with atomic or molecular species such as hydrogen atoms or methyl groups. We also characterize the structural properties of the Group IV nanostructures that we synthesized using a combination of infrared spectroscopy, solid-state NMR, and pair distribution function analysis to confirm the structure and order. In the case of Si and Ge, single-atom thick nanosheets were synthesized, their stability and decomposition at elevated temperatures were characterized. The optical properties of Group IV nanomaterials have sparked debate over the past few decades. We found that Si nanosheets exhibit fast (nanosecond) photoluminescence lifetime, which is several orders of magnitude greater than Si nanocrystals, and offer potential explanations for the observed difference. Finally we show that Si and Ge nanocrystals and nanosheets can be used for sensing applications, including infrared photodetectors and ionophore-based sensing schemes.