Evaporation of colloidal nanoparticle solutions is known to produce ordered monolayers of nanoparticles, self-assembled arrays of magnetic nanoparticles being of special importance for applications. The in situ time-resolved grazing-incidence small-angle x-ray scattering with the temporal resolution down to 100 ms was employed to study the self-assembling process of iron oxide nanoparticles after a colloidal drop was applied on a silicon substrate. The x-ray scattering contributions from the evaporating drop volume, drop surface, and substrate surface were monitored and separated. The x-ray scattering from the drop for the distances from the substrate surface larger than Ϸ80 m shows the absence of self-assembled clusters in the drop volume or self-assembled domains on the drop surface. These results indicate that the nanoparticle self-assembling occurs in the vicinity of the three-phase drop contact line. The ordered nanoparticle monolayer exhibits hexagonal close-packed arrangement.
Fe3O4/γ-Fe2O3 nanoparticles (NPs) based thin films were used as active layers in solid state resistive chemical sensors. NPs were synthesized by high temperature solution phase reaction. Sensing NP monolayers (ML) were deposited by Langmuir-Blodgett (LB) techniques onto chemoresistive transduction platforms. The sensing ML were UV treated to remove NP insulating capping. Sensors surface was characterized by scanning electron microscopy (SEM). Systematic gas sensing tests in controlled atmosphere were carried out toward NO2, CO, and acetone at different concentrations and working temperatures of the sensing layers. The best sensing performance results were obtained for sensors with higher NPs coverage (10 ML), mainly for NO2 gas showing interesting selectivity toward nitrogen oxides. Electrical properties and conduction mechanisms are discussed.
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