Asymmetric microparticles and heterogeneous microshells via angled colloidal lithography

Controlling the Interaction and Non-Close-Packed Arrangement of Nanoparticles on Large Areas

In light of the importance of nanostructured surfaces for a variety of technological applications, the quest for simple and reliable preparation methods of ordered, nanometer ranged structures is ongoing. Herein, a versatile method to prepare ordered, non-close-packed arrangements of nanoparticles on centimeter sized surfaces by self-assembly is described using monodisperse (118-162 nm Ø), amino-functionalized silica nanoparticles as an exploratory example. It is shown that the arrangement of the particles is governed by the interplay between the electrostatic repulsion between the particles and the interaction between particles and surfaces. The latter is tuned by the properties of the particles such as their surface roughness as well as the chemistry of the linkage. Weak dispersive interactions between amino groups and gold surfaces are compared to a covalent amide linkage of the amino groups with carboxylic acid functionalized self-assembled monolayers. It was shown that the order of the former systems may suffer from capillary forces between particles during the drying process, while the covalently bonded systems do not. In turn, covalently bonded systems can be dried quickly, while the van der Waals bonded systems require a slow drying process to minimize aggregation. These highly ordered structures can be used as templates for the formation of a second, ordered, non-close-packed layer of nanoparticles exemplified for larger polystyrene particles (Ø 368 ± 14 nm), which highlights the prospect of this approach as a simple preparation method for ordered arrays of nanoparticles with tunable properties.

Template-assisted GLAD: approach to single and multipatch patchy particles with controlled patch shape

Template-assisted glancing angle deposition (GLAD) is explored for the fabrication of single and multipatch patchy particles with one or more patches of controlled but asymmetric shape. The template is used to ensure the formation of uniform patchy particles, whereas rotation of the template gives access to a large number of asymmetric patch shapes caused by the shadowing effect of the templating groove and/or the neighboring particle. Careful analysis with a straightforward geometric model reveals the effect of the angle of incidence, rotational angle, groove size, and particle size on the patch shape. Initial magnetic field assembly results are presented to illustrate the removal of patchy particles from their template and accessibility to a large number of patchy particles. Two-patch particles with overlapping patches are also accessible by means of secondary metal vapor deposition. The connectivity of these two patches on each particle and the predictable size of the overlapping section provide access to functional patchy particles. The combination of the template-assisted GLAD method with rotation of the template and secondary evaporation is demonstrated to be a good method for fabricating patchy particles with a variety of asymmetric patch shapes, sizes, and multipatches where every particle of a batch carries exactly the same patch pattern and thereby provides valuable input on experimentally accessible patch shapes for future experimental and computational studies of patchy particles.

Tunable plasmon resonances and two-dimensional anisotropy of angular optical response of overlapped nanoshells

Symmetry breaking of metallic nanoparticles results in many unique optical properties. We use the discrete dipole approximation method to study the optical properties of overlapped nanoshells which further break the rotational symmetry compared with the semishells. The optical properties of the nanoparticles can be tuned from the visible to near infrared regime by varying the geometry parameters and the hybrid components of nanoparticles. The calculated extinction spectra show the two-dimensional anisotropy of the angular optical response of the nanoparticles. The plasmon hybridization model provides a way to interpret the resonance modes of the nanoparticles. The tunable plasmon resonances, the enhanced local fields and the anisotropic optical properties suggest that the overlapped nanoshells have potential applications in surface-enhanced spectroscopy and "smart" coating in windows or display devices.