Amorphous silicon: new insights into an old material

Area of Science:

• Materials Science
• Inorganic Chemistry
• Chemical Engineering

Background:

• Amorphous silicon (a-Si) is a key material in various technologies.
• Synthesis methods for a-Si often involve harsh conditions and limited control over reactivity.
• Exploring alternative synthetic routes is crucial for developing novel silicon-based materials and processes.

Purpose of the Study:

• To synthesize amorphous silicon (a-Si) via a novel method using tetrahalosilanes and molten sodium.
• To investigate the reactivity and stability of the synthesized a-Si towards common reagents like oxygen, air, moisture, and alcohols.
• To explore the potential of methanolysis reactions for producing valuable methoxysilanes and hydrogen gas.

Main Methods:

• Synthesis of a-Si by reacting tetrahalosilanes (SiX4, X=Cl, F) with molten sodium in high-boiling solvents (diglyme, nonane).
• Characterization of the synthesized a-Si's reactivity and stability under various conditions (oxygen, air, moisture, RCl, alcohols).
• Investigation of methanolysis reactions to determine product yields and reaction pathways, including thermolysis of tetramethoxysilane.

Main Results:

• Amorphous silicon was successfully synthesized as brown or black solids with varying reactivities.
• The synthesized a-Si exhibited different stability profiles towards oxygen, air, moisture, and chlorine-containing compounds.
• Methanolysis reactions yielded tetramethoxysilane and hydrogen gas under ambient conditions, demonstrating potential for decentralized hydrogen production.
• Competitive insertion into MeO-H and Me-OH bonds resulted in H- and/or methyl-substituted methoxy functional silanes.
• Compounds like Men Si(OMe)4-n (n=0-3) were obtained in high yields (up to 100% for n=0) via thermolysis of tetramethoxysilane over molten sodium.
• Specific yields for methoxysilanes were reported: n=0 (100%), n=1 (51%), n=2 (27%), and HSi(OMe)3 (85%).

Conclusions:

• The molten sodium route provides a viable method for synthesizing amorphous silicon with tunable reactivity.
• Methanolysis of silicon presents a promising pathway for producing valuable methoxysilanes and for decentralized hydrogen generation.
• The synthesized methoxysilanes could serve as precursors for future silicon-based products, opening new avenues in materials science and chemical synthesis.