Silver Nanoparticle Monolayer-to-Bilayer Transition at the Air/Water Interface as Studied by the GISAXS Technique: Application of a New Paracrystal Model

Abstract

An original diffraction model for the analysis of grazing-incidence small-angle X-ray scattering (GISAXS) from the nanoparticle Langmuir films was developed. This model relies on the concept of the 2D hexagonal paracrystal and employs the distorted-wave Born approximation that is relevant for GISAXS measurements at the air/water interface when the angle of incidence is close to the critical value. The model comprises the cases of the close-packed nanoparticle monolayer and bilayer with the AB-type layer stacking. In this way, both the lateral (along the interface) and vertical (normal to the interface) correlations of the nanoparticle positions can be analyzed. The model was applied to an in situ GISAXS study of the formation of a silver nanoparticle Langmuir film during compression at the air/water interface in the Langmuir-Blodgett trough. Spherical nanoparticles of 5.8 ± 0.6 nm diameter were employed. Different compression stages starting from the submonolayer up to the monolayer collapse via bilayer formation were analyzed in terms of the mean lateral interparticle distance, degree of paracrystal disorder, interlayer distance, vertical disorder, and layer-stacking type in the bilayer as well as the ratio between the monolayer and bilayer coverage in the final film. The model developed is applicable to any nanoparticle Langmuir film formed at the air/liquid interface to extract structural parameters on the nanoscale. The particular results obtained have direct implications on the preparation of silver plasmonic templates with "hot spots" for surface-enhanced Raman scattering.

Subnanometre ligand-shell asymmetry leads to Janus-like nanoparticle membranes

“…pMA on air-facing side pMA on water-facing side * * For a more quantitative measurement of the asymmetry of the ligand shell, we used grazing incidence small-angle X-ray scattering (GISAXS), a highly sensitive and quantitative probe for studying kinetics and structures in low-dimensional systems, including nanoparticle assembly on substrates and on liquid-air interfaces [14][15][16][17][18] . Recent developments in GISAXS analysis based on multilayer distorted-wave Born approximations is capable of 3D structural determination with subnanometre resolution 19 .…”

Real-time tracking of the self-assembled growth of a 3D Ge quantum dot lattice in an alumina matrix

“…the long acquisition time which precludes an acceptable temporal resolution, compatibility with the deposition conditions etc.). Therefore, various strategies of real-time and in situ X-ray scattering experiments have been developed in the past (Vegso et al, 2012;Gibaud et al, 2004;Sharma et al, 2015;Renaud et al, 2009;Siffalovic et al, 2007;Hodas et al, 2017).…”

A model of compression isotherms for analyzing particle layers

“…Formation of bilayer structures was reported as well for gold [23] and silver [24] nanoparticles. A study on the formation of Ag nanoparticle film using X-ray grazing incidence small angle scattering, Brewster angle microscopy and imaging ellipsometry was published recently [25,26]. It was observed that a nanoparticle monolayer is formed via coalescence of free self-assembled nanoparticle islands with a hexagonal closepacked order at the early stage of compression.…”