Nanomaterials Design

We design nanomaterials with advanced functionality.

Controlling nanocrystal shape and composition

The application of nanocrystals as heterogeneous catalysts and plasmonic nanoparticles requires fine control of their shape and chemical composition. A promising idea to achieve synergistic effects is to combine two distinct chemical and/or physical functionalities in bimetallic core@shell nanocrystals. Although techniques for the synthesis of single-component nanocrystals with spherical or anisotropic shape are well-established, new methods are sought to tailor multicomponent nanocrystals. We probed etching in a controlled redox environment as a synthesis technique for multicomponent nanocrystals. We also proposed a route towards nanocatalysts with high durability by depositing an alloyed phase on top of intermetallic seeds and analyzed the etching of core-shell particles using in-situ liquid cell transmission electron microscopy.

Nanocrystal Shape Composition
(Left) Control of the shape of core-shell nanocrystals by choice of materials and geometry. (Right) Im-provement of catalytic activity by alloying the nanoparticle core.

Directional entropic and enthalpic forces

Directional binding is the foundation of organic chemistry, molecular biology, and can lead to liquid crystalline order. More recently directionality was studied in the context of colloidal and nanoscale building blocks, which are called patchy particles if they exhibit preferential geometric attachment. We introduced the concept of directional entropic forces and entropically patchy particles, in which the particle shape itself is the cause of the geometric attachment. Entropic patchiness is a means to rationalize the phase behavior of many anisotropic particles.

Directional Forces
(Left) Control of directional entropic interaction by truncating spheres. (Right) Patchy particles align directionally by depletion interaction.

Amorphous photonic band gap materials

Photonic materials create fascinating structural color effects in plants, insects, and mammals. An important characteristic is the appearance of a photonic band gap, a frequency band where the propagation of light is strictly prohibited. We study photonic band gap formation in amorphous dielectric materials. We used numerical calculations of the photonic density of states in materials where the dielectric structure is derived from hard and hyperuniform disk patterns. A central goal is to better understand the role of short-range order for tailoring Bragg scattering at the isotropic Brillouin zone.

Photonic Band-Gap
(Left) Comparison of disk packings and hyperuniform arrangements. (Right) Emergence of photonic band gaps