Field gradient imaging of nanoparticle systems: analysis of geometry and surface coatingeffects

Abstract

In this work we compare the standard imaging of various types of nanoparticlesdeposited on surfaces by atomic force microscopy (AFM) with a complementaryanalysis of the same samples by either electrostatic force microscopy (EFM) ormagnetic force microscopy (MFM). Experiments were carried out on goldnanoparticles (decahedrons and stars) and two different iron oxide systems: goethite(α-FeOOH)and hematite (α-Fe2O3). Regardless of the particular geometry, the EFM signal appears to be stronger on edges ortips of pure gold nanoparticles. Both EFM and MFM experiments were also carried out oniron oxide particles. Apart from the structural analysis, we analyzed the influence of a shelllayer deposited on the gold and iron oxide particles, the shell being amorphousSiO2. Although the silica layer was found to have an insulating effect around the particles, in allcases EFM/MFM measurements could still be performed by the proper choice of the scanlift height (with an eventual slight increase of the sample bias, where applicable).