Scalable colloidal synthesis of Bi2Te2.7Se0.3 plate-like particles give access to a high-performing n-type thermoelectric material for low temperature application.

Colloidal synthesis is harnessed for the gram-scale preparation of hexagonal-shaped plate-like Bi2Te2.7Se0.3 particles, yielding nearly 5 g of the product in one experiment. The resultant textured particles are highly crystalline, phase-pure, chemically uniform, and can serve as a starting material for the preparation of bulk thermoelectrics for room temperature applications. The consolidation occurs via spark plasma sintering, which affords nanostructured n-type Bi2Te2.7Se0.3 material exhibiting a high figure of merit ZT ≈ 1 at 373 K with an average ZT ≈ 0.93 (300-473 K). Our experimental and theoretical studies indicate that the high thermoelectric performance is attributed to a favorable combination of the resultant transport properties. Specifically, bottom-up formation of the plate-like particles results in the substantial reduction of thermal conductivity by nanostructuring as observed experimentally and can be ascribed to phonon scattering at grain boundaries and suppressed bipolar conduction. When coupled with high electrical conductivity, which is preserved at the bulk scale as confirmed by ab initio calculations, these factors boost the thermoelectric performance of the as-synthesized n-type Bi2Te2.7Se0.3 bulk nanostructured alloy to the state-of-the-art level. The combination of a newly developed scalable colloidal synthesis with optimized spark plasma sintering constitutes a convenient route to nanostructured bulk thermoelectrics, which is an interesting pathway for the preparation of simple and complex thermoelectric chalcogenides.

Self-assembly of bis-salphen compounds: from semiflexible chains to webs of nanorings.

The recently-observed self-assembly of certain salphen-based compounds into neuron-like networks of microrings interconnected with nano-thin strings may suggest a new highly-potent tool for nanoscale patterning. However, the mechanism behind such phenomena needs to be clarified before they can be applied in materials design. Here we show that, in contrast with what was initially presumed, the emergence of a "rings-and-rods" pattern is unlikely to be explained by merging, collapse and piercing of vesicles as in previously reported cases of nanorings self-assembly via non-bonding interactions. We propose an alternative explanation: the compounds under study form a 1D coordination polymer, the fibres of which are elastic enough to fold into toroidal globules upon solvent evaporation, while being able to link separate chains into extended networks. This becomes possible because the structure of the compound's scaffold is found to adopt a very different conformation from that inferred in the original work. Based on ab initio and molecular dynamics calculations we propose a step-by-step description of self-assembly process of a supramolecular structure which explains all the observed phenomena in a simple and clear way. The individual roles of the compound' s scaffold structure, coordination centres, functional groups and solvent effects are also explained, opening a route to control the morphology of self-assembled networks and to synthesize new compounds exhibiting similar behaviour.

Nanorings and rods interconnected by self-assembly mimicking an artificial network of neurons.

Molecular electronics based on structures ordered as neural networks emerges as the next evolutionary milestone in the construction of nanodevices with unprecedented applications. However, the straightforward formation of geometrically defined and interconnected nanostructures is crucial for the production of electronic circuitry nanoequivalents. Here we report on the molecularly fine-tuned self-assembly of tetrakis-Schiff base compounds into nanosized rings interconnected by unusually large nanorods providing a set of connections that mimic a biological network of neurons. The networks are produced through self-assembly resulting from the molecular conformation and noncovalent intermolecular interactions. These features can be easily generated on flat surfaces and in a polymeric matrix by casting from solution under ambient conditions. The structures can be used to guide the position of electron-transporting agents such as carbon nanotubes on a surface or in a polymer matrix to create electrically conducting networks that can find direct use in constructing nanoelectronic circuits.