Ultrahard bulk amorphous carbon from collapsed fullerene.

Area of Science:

• Materials Science
• Solid-State Physics
• Nanotechnology

Background:

• Amorphous materials retain crystalline order, offering unique properties.
• Amorphous carbon with sp² or mixed sp²-sp³ hybridization is technologically relevant.
• Synthesizing bulk amorphous carbon with high sp³ concentration is challenging.

Purpose of the Study:

• To synthesize transparent, nearly pure sp³ amorphous carbon in millimetre-sized samples.
• To investigate the properties of this novel amorphous carbon material.
• To explore potential applications of bulk sp³ amorphous carbon.

Main Methods:

• Heating fullerenes at pressures near the cage collapse boundary.
• Characterization of the synthesized material's structure and properties.
• High-pressure and high-temperature synthesis techniques.

Main Results:

• Successfully synthesized millimetre-sized transparent, nearly pure sp³ amorphous carbon.
• Material exhibits diamond-like short-/medium-range order.
• Achieved highest hardness (101.9 GPa), elastic modulus (1,182 GPa), and thermal conductivity (26.0 W m⁻¹ K⁻¹) for amorphous materials.
• Tunable optical bandgaps from 1.85 eV to 2.79 eV.

Conclusions:

• This study advances the understanding and synthesis of bulk amorphous materials.
• The novel sp³ amorphous carbon possesses superior mechanical and thermal properties.
• Potential for new technological applications of advanced amorphous solids.