Self-assembled simple hexagonal AB(2) binary nanocrystal superlattices: SEM, GISAXS, and defects

Area of Science:

• Materials Science
• Nanotechnology
• Crystallography

Background:

• Binary superlattices (BSLs) offer tunable properties through controlled arrangement of different-sized nanoparticles.
• Self-assembly of nanocrystals is a key strategy for creating ordered nanomaterials.
• Understanding the structural nuances of BSLs is crucial for their application.

Purpose of the Study:

• To assemble and characterize binary superlattices (BSLs) of iron oxide and gold nanocrystals.
• To elucidate the structural ordering and symmetry of the assembled BSLs.
• To investigate the effects of substrate interaction and drying on BSL structure.

Main Methods:

• Slow evaporation of colloidal dispersions onto tilted substrates.
• Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) for structural analysis.
• Grazing incidence small-angle X-ray scattering (GISAXS) for long-range order and structural parameters.

Main Results:

• Assembly of simple hexagonal (sh) AB(2) binary superlattices (isostructural with AlB(2)).
• Confirmation of long-range order and identification of nanocrystal arrangement (large Fe(2)O(3) in lattice, small Au in interstitial sites).
• Observation of superlattice contraction (8-12%) perpendicular to the substrate due to solvent drying, leading to centered orthorhombic symmetry on (100) planes.
• Identification of superlattice dislocations composed of inserted gold nanocrystal half-planes.

Conclusions:

• Fe(2)O(3) and Au nanocrystal BSLs can be assembled into ordered sh-AB(2) structures.
• Solvent drying induces significant structural contraction and symmetry changes.
• The study provides insights into the self-assembly mechanisms and structural stability of nanocrystal superlattices.