Nanoparticle Superlattices: The Roles of Soft Ligands

Abstract

Nanoparticle superlattices are periodic arrays of nanoscale inorganic building blocks including metal nanoparticles, quantum dots and magnetic nanoparticles. Such assemblies can exhibit exciting new collective properties different from those of individual nanoparticle or corresponding bulk materials. However, fabrication of nanoparticle superlattices is nontrivial because nanoparticles are notoriously difficult to manipulate due to complex nanoscale forces among them. An effective way to manipulate these nanoscale forces is to use soft ligands, which can prevent nanoparticles from disordered aggregation, fine‐tune the interparticle potential as well as program lattice structures and interparticle distances – the two key parameters governing superlattice properties. This article aims to review the up‐to‐date advances of superlattices from the viewpoint of soft ligands. We first describe the theories and design principles of soft‐ligand‐based approach and then thoroughly cover experimental techniques developed from soft ligands such as molecules, polymer and DNA. Finally, we discuss the remaining challenges and future perspectives in nanoparticle superlattices.

Metal Nanoclusters: New Paradigm in Catalysis for Water Splitting, Solar and Chemical Energy Conversion

“…[132] After the earlier reports of Au 102 ,A u 38 ,a nd Au 25 NCs with different geometry,i tw as thought that NCs with fcc geometry are not stable at this small size, but Au 36 (SPh-tBu) 24 with af cctype Au core could be successfully crystalized for the first time. [63] Zeng et al [133] studied the synthesis of Au 28 ,A u 36 ,A u 44 , and Au 52 NCs and their detailed electronic properties. Recently, Higaki et al synthesized Au 103 S 2 (S-Nap) 41 (S-Nap = 2-naphtalenethiolate) using also the ligand-exchange methoda nd determined itsstructure by means of crystallography.…”

“…After the earlier reports of Au 102 , Au 38 , and Au 25 NCs with different geometry, it was thought that NCs with fcc geometry are not stable at this small size, but Au 36 (SPh‐ t Bu) 24 with a fcc‐type Au core could be successfully crystalized for the first time . Zeng et al .…”

“…Out of all these ligands, thiols are state-of-art because of their strong affinity to metal centers, particularly in the case of noble metalss uch as Au, Pt, Ag. Various theories including the soft and hard acid base (SHAB)c oncept [63] have been proposed for the selectiveg rowth of the metal/metal oxide NPs/NCs in the presence of different ligands under controlled conditions. It is suggested that metal centers act as ap ositive charge (Lewis acid) whereas ligands with different donora toms (N, O, S, Se, etc.)…”

Ordered Networks of Gold Nanoparticles Crosslinked by Dithiol‐Oligomers

“…Assembling nanoparticles (NPs) into superlattices with specific symmetries is crucial for applications such as catalysis, optical devices, sensors, and energy storage . Although there has been considerable progress in assembling 2D and 3D superlattices of metallic and semiconductor NPs, the challenge of up‐scaling and stabilizing these crystals still remains . In this regard, self‐assembly of NPs driven by interparticle and thermodynamic forces has proven to be a promising approach for the formation of macroscale ordered assemblies …”

“…In solution based methods of NP assembly a surface ligand, covalently bound to a NP, interacts with neighboring ligands via noncovalent interactions such as hydrogen bonding . While there is a plethora of studies reporting structural properties of NPs by DNA‐mediated assembly, there is a relative dearth of studies on the structure of NP networks obtained by covalent crosslinkers, such as dithiol molecules, which are an obvious choice for linking gold nanoparticles (AuNPs).…”