Studying novel high-pressure phases in laser-shock-affected silicon using poly: an algorithm for spot-wise phase...

Area of Science:

• Materials Science
• Crystallography
• Nanotechnology

Background:

• Laser-induced microexplosions create localized shockwaves, forming novel high-pressure crystalline phases in materials like silicon.
• Previously observed silicon polymorphs (e.g., bt8-Si, st12-Si) show potential for photovoltaic applications.
• Identifying these phases using selected-area electron diffraction (SAED) is challenging due to overlapping diffraction patterns.

Purpose of the Study:

• To develop a novel algorithm for unambiguous identification of crystallographic phases in polymorphic nanomaterials.
• To overcome limitations in analyzing SAED patterns caused by pattern overlap and spot ambiguity.
• To characterize the high-pressure silicon phases formed by laser shock and their subsequent relaxation.

Main Methods:

• Development of a new algorithm, termed 'poly', based on maximizing magnitude and angular correlation between observed and theoretical diffraction spots.
• Application of the 'poly' algorithm to simulated electron diffraction patterns.
• Validation of the algorithm using experimental SAED patterns from laser-shock-affected silicon samples.

Main Results:

• The 'poly' algorithm effectively resolves ambiguities in SAED pattern analysis.
• The most abundant silicon phases identified in laser-shock-affected areas are t32-Si and t32*-Si.
• These high-pressure phases were observed to relax into other silicon phases over a 90-day period post-laser treatment.

Conclusions:

• The 'poly' algorithm provides a robust method for identifying crystallographic phases in complex nanomaterials.
• Laser-induced shock in silicon generates specific high-pressure polymorphs (t32-Si, t32*-Si) with potential photovoltaic properties.
• Understanding the relaxation dynamics of these novel phases is crucial for their practical application.