The Surface of Nanoparticle Silicon as Studied by Solid-State NMR

Area of Science:

• Materials Science
• Solid-State Chemistry
• Nanotechnology

Background:

• Commercially available silicon nanopowder (np-Si) is a crucial nanomaterial with applications in various fields.
• Understanding the surface structure of np-Si is essential for controlling its reactivity and performance.
• Previous studies have indicated a complex surface chemistry, but detailed characterization remains challenging.

Purpose of the Study:

• To comprehensively investigate the surface structure and adjacent interior of silicon nanopowder (np-Si).
• To identify and quantify various silicon chemical structures present on the np-Si surface.
• To explore the effects of chemical treatments, such as oxidation, on the surface composition.

Main Methods:

• Multinuclear, solid-state Nuclear Magnetic Resonance (NMR) spectroscopy, including ¹H, ²⁹Si, and ²H magic-angle-spinning (MAS) NMR.
• Quantum mechanical ²⁹Si chemical shift calculations.
• Extension of the DEPTH background suppression method for T₂ relaxation parameter measurement.

Main Results:

• The interior of np-Si consists of highly ordered, crystalline silicon atoms with tetrahedral bonding.
• Surface silicon atoms exhibit diverse chemical structures, dominated by Si-H and silanol (Si-OH) moieties.
• Chemical treatments, particularly oxidation, significantly alter the population of surface structures, enhancing Si-OH groups.

Conclusions:

• Silicon nanopowder possesses a crystalline core and a heterogeneous, chemically active surface.
• The surface chemistry, characterized by Si-H and Si-OH groups, can be tailored through controlled chemical modifications.
• The developed NMR techniques provide valuable insights into the surface structure and dynamics of nanomaterials.