The amorphous-crystalline transition in SiH₂ nanoclusters

Area of Science:

• Materials Science
• Nanotechnology
• Computational Chemistry

Background:

• Silicon nanocrystals (NCs) are vital for optoelectronics, photovoltaics, and biomedicine.
• Their photo-physical properties critically depend on crystalline or amorphous structure.
• Synthesis conditions significantly impact the structural order of silicon NCs.

Purpose of the Study:

• To investigate the morphology of hydrogen-passivated silicon clusters.
• To determine how structural order depends on the degree of hydrogen passivation.
• To elucidate the formation mechanism of crystalline silicon NCs.

Main Methods:

• Computational calculation of optimal structures for Si_nH_2m clusters (n ≤ 21, 2m ≤ 30).
• Analysis of cluster morphology as a function of hydrogen passivation.
• Construction of the phase P-T diagram for Si-H clusters.

Main Results:

• Silicon clusters transition through three structural types with increasing hydrogen: amorphous with dangling bonds, amorphous without dangling bonds, and crystalline.
• A mechanism for dangling bond removal in amorphous clusters was identified, crucial for structure formation.
• Crystalline structures (diamond or lonsdaleite) emerge upon complete surface bond passivation.

Conclusions:

• Hydrogen passivation dictates the structural transition from amorphous to crystalline silicon clusters.
• The findings provide insights into the formation of silicon NCs and their properties.
• Results are relevant for understanding and synthesizing larger silicon nanoparticles.