The well directed organization of nanoparticles is of increasing technical and scientific interest. One approach is the organization of nanoparticles at the air/water interface for applications, like producing 2D colloidal crystals or nanowires.
For example, Gil et al. (2007) monitored the formation of 2D colloidal crystals by Langmuir–Blodgett technique. They used Brewster angle microscopy to observe the film quality. Zang et al. (2009) have also studied silica nanoparticle layers at the air/water interface by multiple angle of incidence ellipsometry. For data interpretation, they introduce a two-layer model which enables them to evaluate the radius of interfacial aggregates and the contact angle of the nanoparticle surface at the air/water interface
Volinsky and Jalinek (2009) worked with gold nanoparticles. They demonstrate the formation of a network of elongated Au “wires”. The laser-induced structured films exhibited high stability and could be transferred from water onto solid substrates without disrupting the Au organization. To follow the formation at the liquid/solid interface, Brewster angle microscopy was used.
In this work focus on aggregations of nanoparticles in line shaped pattern . Two pattern of SiO2 nanoparticles on a glass substrate were characterized with a spectroscopic imaging ellipsometry and AFM.
Photonic crystals are periodic structures of alternating high/low refractive index domains made of transparent materials. Those crystals can be non-transparent for a particular wavelength range due to multiple reflections and interference in the crystal. Theoretical calculations demonstrate that for fcc (face cubic centred) crystals the ratio between the refractive indices of the different domains must be higher than 2.8 to form a photonic crystal with bandgap. These crystals are used as filters for electro-magnetic radiation, e.g. infrared filters. The filter wavelength depends on the domain size and the refractive index difference between the domains.
Application Note Nanoparticles