Nanocrystal Research

Nanocrystals are small crystals that are typically less than 20nm in size. The small size gives them properties that are different from their bulk form, such as enhanced photoluminescence, increased absorption cross-section, improved catalytic performance and discrete energy states similar to an artificial atom. When the nanocrystals are made from semiconducting material, the electrons and holes feel quantum confinement effects and can thus be termed quantum dots. Nanocrystals have wide ranging applications such as solar cells, light emitting diodes, biomedical imaging tags, catalysts and sensors.

We are interested in semiconducting nanocrystals in the form of colloidal quantum dots and their opto-electronic properties. Our recent work has expanded into catalytic nanoparticles such as Pt and understanding their detailed structural forms.

Professor Warner began his nanocrystal research during his PhD in 2001 with photoluminescent PbS and CdS quantum dots synthesized in both aqueous and organic solvent environments. He subsequently broadened his area of experience by working on Si and Ge quantum dots for biomedical imaging, TiO2 nanoparticles for photocatalytic degradation of polymers, and photoluminescent dilute magnetic semiconductor nanocrystals of Mn doped ZnSe.

The current research interests of the group in the nanocrystal area is the interfacing with 2D materials. We aim to develop processing methods that can control how nanocrystals are attached to the surface of graphene, BN or MoS2/WS2 2D crystals. This area is important as it extends the functionality of 2D materials for applications in solar cells, chemical sensors, photodetectors and light emitting diodes. We primarily use transmission electron microscopy to characterize the structure at the atomic level and develop new treatments that improve the interface between the 2D and 0D structures.

The TEM images below show Cobalt Chloride nanocrystals formed on the surface of few layer graphene by direct deposition from a solution precursor. The images are taken using an aberration-corrected transmission electron microscope operated at an accelerating voltage of 80 kV.

In our recent work, illustrated below, we examined PbTe nanocrystals on the surface of suspended monolayer graphene. We were able to see how a ligand exchange process modified the closed-packed array of PbTe nanocrystals into an interconnected aggregation. This helps understand how this chemical treatment influences solar cell performance.