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.

We report on a reference-free Raman spectroscopy method for a precise thickness determination of the multilayered graphene oxide flakes. The method is based on the normalization of the total integral intensity of D and G Raman bands to the integral intensity of the second-order optical phonon peak of the silicon substrate in the Raman spectrum. The normalization provides discrete ratio values corresponding to the number of graphene oxide layers in the respective flakes with the intensity linearly increasing with the number of layers. This provides a fast and robust determination of the thickness of graphene oxide flakes in terms of the layer number up to high values. A comparison with conventional spectrally resolved reflectivity mapping shows similar sensitivity, while selectivity to particular functional chemical groups is a bonus of the Raman-based method. Copyright

An in situ small-angle x-ray scattering study of the nanoparticle displacement in a self-assembled monolayer as a function of a supporting membrane strain is presented. The average nanoparticle spacing is 6.7 nm in the unstrained state and increases in the applied force direction, following linearly the membrane strain which reaches the maximum value of 11%. The experimental results suggest a continuous mutual shift of the nanoparticles and their gradual separation with the growing stress rather than nanoparticle islands formation. No measurable shift of the nanoparticles was observed in the direction perpendicular to the applied stress.