Research

The Science Resonates Group focuses on a variety of nanoparticles and nanomaterials. More specific themes include:

• Novel nanoparticle synthesis, for example new alloys, Janus particles and core-shell particles
• Low-temperature crystallization
• Nanoparticle processing via dip-coating to form a material
• Nanoparticle and nanomaterial characterization
• Metamaterials
• Silicon particles

To expand on selected projects:

Nanoparticle synthesis

Silicon. Optics and photonics has motivated research into the synthesis of silicon nano-objects with applications in plasmonics, telecommunications, solar and photovoltaic cells, and biomedicine. The bottom-up synthesis of well-defined silicon particles is frustrated by the difficulty controlling silicon particle nucleation and growth, and by its oxidation to silica. Ideally, silicon nano-objects should be crystalline, giving a high refractive index, and with dimensions between 75 and 200 nm, in order to scatter visible light. Today, such a synthesis does not exist in the literature. We have discovered a supercritical synthesis method to produce silicon particles with resonance at visible frequencies. The synthesis consists of a reaction betweeen trisilane and a silicon coordination complex that we have developed in house. As a function of the ratio between these two silicon precursors, the size of the particles can be tuned. These particles in fact exist as core-shell particles, with a silicon core and a silica-like shell. The core varies between 150 and 175 nm in diameter. These particles are partially crystalline, with an effective refractive index of about 4 and low light absorption, making them efficient at scattering light. Unlike other spherical silicon particles, the electric field and the magnetic field of light are scattered at the same frequency, making these particles efficient Huygens sources.

Particle organization on a substrate

Alignment of helices. Via dip-coating we are able to organize particles on a substrate. Without using chemical or physical substrate patterning, we are able control particle placement. An example of this in the deposition of highly anisotropic silica nanohelices, having diameters of 20 nm and a form factor between 50 et 150. By optimizing the solution properties (choice of solvent and concentration of helices and polyelectrolytes) and the deposition conditions (withdrawal rate, temperature and relative humidity), a horizontal or vertical alignment could be obtained. Exploiting the stick-slip phenomenon yielded periodic dense bands of nanohelices. Polymer additives and physicochemical forces at higher withdrawal rates formed vertical bands of controllable spacing and density.