Multilayer Langmuir Film of Monodisperse Au Nanoclusters: Unusual Growth via Bilayers

Abstract

The assembly of nanomaterials into thin films is an important area in the nanofabrication of novel devices. The monodispersity of nanoparticles plays an essential role in the resulting quality of the assembled mono-and multilayers. Larger polydispersity leads to smaller lateral correlation lengths and smaller domains of aligned nanoparticles, thus resulting in more point and line defects. Perfectly monodisperse nanoparticles should therefore minimize the number of defects in the assembled films. Despite tremendous progress in reducing the polydispersity of nanoparticles, there has been limited research on the assembly of thin films out of perfectly monodisperse nanoclusters. Here, we show a formation of Langmuir films using perfectly monodisperse gold nanoclusters with composition Au 32 ( n Bu 3 P) 12 Cl 8 exhibiting a diameter of 1.8 nm. Using both in situ and ex situ small-angle X-ray scattering, we show that the monolayer formed on a Langmuir− Blodgett trough exhibits long-range order. Moreover, after compressing the monolayer, we found that the stress accumulated prior to the monolayer collapse triggers a transition to a short-range order not previously reported. If such monolayer is compressed further, the second layer is not formed as in the case of standard nanoparticles. Instead, a growth of islands by an odd number of layers is observed, leading to a thin film with a structure consisting of two different orientations of the hexagonal lattice. Such anomalous behavior may have implications for the possibilities of thin-film formation.

Tunable Subnanometer Gaps in Self-Assembled Monolayer Gold Nanoparticle Superlattices Enabling Strong Plasmonic Field Confinement

“…We conducted in situ grazing-incidence small-angle X-ray scattering (GISAXS) measurements to investigate a real-time change in the nanoscopic arrangement of GNP films. GISAXS measurements provide high accuracy in determining interparticle gap distances with robust statistics thanks to the large-area sampling nature. ,,− Figure c shows a GISAXS pattern of a free-floating GNP film on acetonitrile before and after the ligand exchange with C2DT, respectively. Due to the low absorption of the X-ray in acetonitrile, we could observe the scattering pattern of both the reflected and transmitted beams .…”

Nanocrystal Assemblies: Current Advances and Open Problems

“…Microstructural analysis of monolayers prepared via fluid interface-assisted assembly typically relies on microscopy (atomic force and electron microscopy) and scattering (X-ray and light scattering). , The application of such techniques assumes the microstructure is conserved during transfer to a solid interface and subsequent drying, which might be untrue. Combining ex situ (i.e., after the deposition of the monolayer on the solid substrate) with in situ analysis – revealed significant changes in the microstructure . This study covers only micron-sized core-shell NCs.…”

Photofunctional Gold Nanocluster Composites for Bioapplications

“…For Au 32 ( n Bu 3 P) 12 Cl 8 nanoclusters, uniform chlorine ligands may induce anisotropic interactions. Together with the dipolar interaction between chlorine ligands and water molecules, the AuNCs can assemble into a multilayer Langmuir film . Flat films serve as substrates, facilitating their effective integration of structures and functions.…”