Nanocrystal Synthesis

Oriented Attachment of PbSe Nanostructures

Crystalline PbSe nanowires and nanorings can be created through oriented attachment of nanocrystals that fuse along identical crystal faces [PbSe Nanowires and Nanorings through Oriented Attachment].  A mixture of surfactants mediates the growth of unique nanostructures at elevated temperatures.  This approach produces large quantities of high-quality, catalyst-free semiconductor nanowires which form stable colloidal dispersions.

Nanowire synthesis through oriented attachment produces nanowires with control of wire dimensions and morphology. In addition to straight nanowires, zigzag, helical, branched, and tapered nanowires as well as single-crystal nanorings could all be prepared by adjustment of the reaction conditions. 

Straight nanowires with minimal surface roughness may provide the high carrier mobilities necessary for high-performance field effect transistors.  On the other hand, the performance of nanowire-based sensors and photovoltaic devices should improve by increasing the wire surface area, that is, highly branched nanowires may best match these applications. The performance of nanowire-based thermoelectric devices may benefit from the multiple scattering of acoustic phonons in zigzag and helical nanowires.


Bismuth Nanocrystals and Self-Assembled Superlattices

We developed a novel organometallic synthesis of bismuth nanocrystals passivated with hexadecylamine and oleic acid ligand molecules showing controllable size and size uniformity [Monodisperse Bi Nanocrystals and Their Assembly into Superlattices]. These materials can be used in the solution-based catalytic growth of nanowires and as precursors for other Bi-based nanostructures.

Highly ordered two-dimensional and three-dimensional superlattice structures were obtained from Bi NCs, which may be of interest for thermoelectric and magnetoresistance studies.


Alkyl Chains of Suface Ligands and CdSe Polytypism

We show that not only the functional groups of the ligand molecules but also the length of their alkyl chains can have a strong impact on the equilibrium between the wurzite (W) and zinc blende (ZB) CdSe polytypes [Alkyl Chains of Surface Ligands Affect Polytypism of CdSe Nanocrystals].

In situ WAXS studies show that ZB-CdSe NCs in the ligand mixture containing short-chain propylphosphonic acid (PPA) preserve their phase, while W-CdSe NCs in the presence of PPA partially converted to the ZB phase.  In contrast, long-chain octadecylphosphonic acid (ODPA) induces both W-CdSe and ZB-CdSe to evolve towards a structure intermediate between W and ZB phases.

It was concluded that morphological selectivity during seeded growth of CdSe/CdS heterostructures primarily has a thermodynamic rather than a kinetic origin. The addition of shortchain phosphonic acids stabilizes the ZB-CdSe phase and thus promotes the formation of nanotetrapods.