Novel comparison of microscopy and diffraction techniques on the structure of iron oxide nanoparticle monolayers...

Iron oxide nanoparticles undergo self-assembly into well-ordered monolayer films of macroscopic size at the air-water interface. This self-assembly process is the result of the van der Waals forces between the constituent particles. For roughly spherical particles, this monolayer is a 2D hexagonal close packed lattice. With Grazing Incidence X-Ray Diffraction (GID), one can obtain global statistical information about the film's spacing and correlation length. Herein, we demonstrate that comparable structural information can be obtained by a novel Fourier transform analysis method applied to Scanning Electron Microscopy (SEM) images taken of the film after it has been transferred to a silicon substrate. This consists of using numerical methods to isolate the lattice structure of the monolayer in the SEM image to which a 2D discrete Fourier Transform is applied and the result integrated. This results in Bragg peak information akin to that obtained from GID, whose structure shows the same hexagonal close packed lattice with similar spacing and of greater peak contrast. This analysis technique may prove to be a suitable alternative or compliment to GID for many applications.