Acta Physico-Chimica Sinica ›› 2020, Vol. 36 ›› Issue (9): 1908041.doi: 10.3866/PKU.WHXB201908041

Special Issue: Precise Nanosynthesis

• Article • Previous Articles     Next Articles

Self-Assembly and Structural Characterization of Au Binary Nanocrystal Superlattices

Yanan Zhao, Min He, Xiaofang Liu, Bin Liu, Jianhui Yang()   

  • Received:2019-08-30 Accepted:2019-09-24 Published:2019-09-27
  • Contact: Jianhui Yang
  • Supported by:
    the National Natural Science Foundation of China(21501141);the Cyrus Tang Foundation for Tang Scholar and the "Top-rated Discipline" construction scheme of Shaanxi higher education


The assembly of two-component nanocrystals (NCs) such as metals, magnets, and semiconductors into binary nanocrystal superlattices (BNSLs) provides a fabrication route to novel classes of materials. BNSLs with certain structures can exhibit the combined and collective properties of their building blocks and are widespread in the fields of electronics and magnetic devices. As most studies have focused on combined two-component NCs of different sizes for self-assembling BNSLs, there are a few studies on single-component NCs of different sizes for the construction of BNSLs; this is especially true for Au NCs. Noble metallic Au NCs are an excellent candidate material because of their exceptional chemical stability, catalytic activity, process ability, and metallic nature; these characteristics provide them unique size-dependent optical and electronic properties as well as a wide variety of applications in sensing, imaging, electronic devices, medical diagnostics, and cancer therapeutics owing to their strong interactions with external electromagnetic fields. Therefore, it is important to develop a simple and efficient procedure to build BNSLs with different sizes of Au NCs. In our study, we synthesized monodispersed (size distribution < 10%) 6.0, 7.3, and 9.6 nm Au NCs using dodecanethiol-stabilized 3.7 nm Au NCs as seeds through a seed-growth method in oleylamine. The obtained Au NCs exhibited morphology and nanocrystallinity (single-domain and polycrystalline) similar to those of Au seeds. As the size of Au NCs increased from 3.7 to 6.0, 7.3, and 9.6 nm, the surface plasmon resonance peaks narrowed and indicated a red shift. The oleylamine-functionalized 6.0, 7.3, and 9.6 nm Au NCs were mixed with 3.7 nm Au NCs at certain concentration ratios. Au BNSLs with AB2 (hexagonal AlB2 structure), AB13 (NaZn13 structure), and AB (cubic NaCl structure) type were obtained through the solvent evaporation method. The (001) plane of the AlB2-type structure, (001) plane of the NaZn13-type structure, and (100) plane of NaCl-type structure superlattices were observed through transmission electron microscopy (TEM). The effective particle size ratios (γ= Dsmall/Dlarge) serve as the critical determining factor in the formation of the BNSLs. The effective particle size of NCs is equal to the sum of the metal core diameter and twice the thicknesses of the surface ligand. In our study, the effective particle size Dsmall (Au seed) is 5.7 nm; the effective particle sizes Dlarge (6.0, 7.3, and 9.6 nm Au NCs) are 9.0, 10.3, and 12.6 nm, respectively. The effective particle size ratios γ were therefore calculated to be 0.63, 0.55, and 0.45, respectively. The relevant space filling principle predicted the stability of the AlB2, NaZn13, and NaCl-type structures in the range of 0.482 < γ < 0.624, 0.54 < γ < 0.625, and γ < 0.458, respectively; the experimental results adequately matched the relevant space filling principle. The investigation of such a single nanocomponent as a building block is noteworthy with regard to the structures and properties of BNSLs as well as the potential development of novel meta-materials.

Key words: Seed growth method, Au nanocrystal, Self-assembly, Binary nanocrystal superlattice, Structure