Dongil Lee, Ph.D.

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Research Focus

NanosCALE Materials and Their Applications

1. Synthesis and Characterization of Metal Quantum Dots

Our main interests lie in the development of novel nanomaterials and their assemblies for applications in catalysis, sensors, optoelectronics, and solar energy conversion. Scaling behavior, size and shape dependence, and quantum confinement phenomena are all areas of interest in which these materials provide a powerful and often unique environment for manipulation and investigation. Metal nanoparticles containing hundreds down to a few tens of atoms are particularly interesting because they appear, from a variety of synthetic, spectral, and electrochemical observations, to represent the bulk-to-molecule transition region where electronic band energetics yield to quantum confinement effects and discrete electronic states emerge. The barest outline of electronic properties of metal quantum dots has begun to emerge from these studies. The principal analytical tools employed in the characterization of these materials are electrochemistry, spectroscopy, and scanning probe and electron microscopy.

2. Rationally Assembled Nanoparticle Photocatalysts

Metal-coated semiconductor nanoparticles have been the focus of numerous investigations in recent years in photocatalysis relevant to the solar energy conversion and environmental cleanup. A noble metal such as Pt or Au acts as a sinker for photo-induced charge carriers, promoting charge separation and catalytic activity. A significant challenge in developing these catalysts is controlling the charge separation and transfer to carry out a selective catalytic reaction. There has been notable progress made recently in molecular catalysts capable of controlled charge transfer. However, significantly less progress has been made in nanoparticle catalysts which often exhibit unusual catalytic activities due to quantum size effects. We are developing structurally and energetically well-defined nanoparticle assemblies as model systems for systematic study of the interfacial electron and energy transfer processes, and applying the results to the development of nanoparticle photocatalysts.

3. Electron Transfer Dynamics in Metal Nanoparticle Monolayers

A major challenge for nanotechnology is the rational assembly of individual nanoscale elements into well-defined architectures with controlled physical and chemical properties. We are exploring new methodologies for constructing nanoscale objects based on the Langmuir-Blodgett technique. The nanoparticle Langmuir monolayer offers particular virtues for the investigation of electron transfer dynamics where two most critical parameters—the site charging energy dictated by the nanoparticle core size and the site-site coupling by core-core distance—of an assembly can be independently varied. We use electrochemical, SECM and in-situ optical techniques to conduct a detailed interrogation of the assembly structure and interesting properties that this assembly uniquely exhibits (e.g., single electron transfer, capacitance modulation, and surface plasmonics). We are also pursuing the use of this technique as a tool for constructing composite nanomaterials with functional polymers or biomaterials.