Energy transport and conversion in nanostructured materials.

The phononic and electronic density of states in quantum structures leads to transport characteristics that are distinctly different than those of bulk materials.

For instance, much like a blackbody radiation spectrum, the phononic spectrum of bulk materials is broadband and continuous.

In contrast, the phononic spectrum of a self-assembled monolayer (SAM) is a discrete spectrum of narrow bands.

Experiments demonstrate that thermal transport through solid-SAM-solid junction is markedly different than thermal transport in a solid-solid junction.

In particular, the thermal conductance of a solid-SAM-solid junction (∼10 1 MW/m2K) is much lower than the typical solid-solid junction (∼102 MW/m2K).

In effect the discrete spectrum of the SAM creates a phonon filtering that reduces the overall heat transfer through it.

This is analogous to how a blue filter can reduce the overall light intensity through it.

Next, charge transport in thin films made of colloidal PbSe nanocrystals is discussed.

These PbSe nanocrystals exhibit strong three-dimensional quantum confinement which results in an electronic structure similar to that of an atom.

This electronic structure can be exploited to create a substantial Seebeck coefficient enhancement of several hundred muV/K relative to bulk PbSe.

In addition, the carrier concentration of the nanocrystal thin films can be tuned by adjusting nanocrystal size and/or adjusting the nanocrystal chemical environment.

For the last topic, an inexpensive and scalable technique to solution-process metal chalcogenides is presented.

This technique uses hydrazine to create soluble precursors of solid metal chalcogenides.

For example, a liquid-phase precursor for Bi2S3 can be made by mixing together solid-phase Bi2S3 with sulfur and hydrazine.

This liquid precursor can then be spin-coated, printed, and/or stamped and then converted back into Bi2S3 by heating.

Not only does this technique have promise for solution-processing of bulk materials, but with continued work, it has promise for solution-processing of nanostructured materials.

For example, nanoparticles embedded in a matrix of Bi2S3 could be made by suspending nanoparticles in the liquid Bi2S3 precursor and then heating the mixture.