Leveraging Hierarchical Self-Assembly Pathways for Realizing Colloidal Photonic Crystals

Area of Science:

• Materials Science
• Nanotechnology
• Crystallography

Background:

• Colloidal open crystals are promising for photonic applications.
• Fabricating these structures via self-assembly is challenging due to mechanical instability and polymorph control.
• Achieving thermodynamically favored and kinetically accessible structures is crucial.

Purpose of the Study:

• To devise hierarchical self-assembly pathways for fabricating stable colloidal open crystals.
• To control the formation of specific crystal polymorphs (cubic and hexagonal).
• To investigate the photonic properties of the resulting crystals.

Main Methods:

• Utilizing designer triblock patchy particles for hierarchical self-assembly.
• Employing a two-stage self-assembly process via tetrahedral clusters.
• Analyzing crystallization pathways by suppressing ring formations.
• Implementing slow annealing to influence polymorph selection.
• Calculating photonic band structures for different polymorphs.

Main Results:

• Successful hierarchical self-assembly yielding tetrahedral clusters and tetrastack crystals.
• Suppression of unfavorable ring structures, promoting ordered crystallization.
• Slow annealing biases self-assembly towards the cubic polymorph.
• The cubic polymorph exhibits a complete photonic band gap at a realizable filling fraction.
• The hexagonal polymorph also shows a complete photonic band gap with post-assembly processing.

Conclusions:

• Hierarchical self-assembly offers a viable route to mechanically stable colloidal open crystals.
• The devised pathways effectively control polymorph selection and crystallization.
• Both cubic and hexagonal polymorphs demonstrate potential for photonic applications, with different fabrication requirements.