Scientific Research

Research Interests

HIV Vaccine

About AIDS Vaccines (IAVI)

Outcome of clinical trial of the Merck HIV adenovirus vector vaccine 

Inorganic-Organic Hybrid Nanocomposites

Nanostructural control at the near-atomic scale of organic as well as inorganic materials is an essential feature of growth phenomena in living organisms. In biological systems it has been achieved through long evolutionary optimization processes and is often the result of a complex interplay between a large number of constituents.

Such nanostructural control in the synthetic approach to polymer-inorganic nanocomposite materials is still a challenge. Here the effect of block copolymers as structure directing agents will be discussed. Unprecedented morphology control is achieved by changing from conventional silicon precursors to organically modified ceramic (ormocer) precursors in the block copolymer directed synthesis. The resulting polymer-inorganic nanocomposite materials show a unique type of interface between organic and inorganic components in which one of the blocks is entirely embedded into the inorganic phase. This leads to a two phase system which shows very similar phase behavior as observed in phase diagrams of block copolymers and mixtures with their respective homopolymers. With the help of transmission electron microscopy (TEM) and two-dimensional small angle x-ray scattering (SAXS) we show the existence of a whole range of block copolymer microstructures for the polymer-inorganic nanocomposites. Particular emphasis will be on the analysis of bicontinuous cubic structures in which the polymer phase is the minority component. Calcination leads to mesoporous materials which have potential applications in the fields of catalysis, separation technology and microelectronics.

Electrochemical Deposition of Single Atomic Monolayers

Simultaneous time-resolved measurements of the charge transfer and x-ray scattering during the phase transition. This is a transition between a phase with a single layer of copper atoms adsorbed on a surface and a phase where some of those atoms has been desorbed. We examined the desorption and subsequent nucleation of islands of the new phase.

Sample paper: Nucleation and Ordering of an Electrodeposited Two-Dimensional Crystal: Real-time X-ray Scattering and Electronic Measurements (PDF)

Charge-Density Waves

Kinetic X-ray measurements of charge-density waves (CDWs). A CDW is a low temperature phenomenon which creates a standing longitudinal wave in the crystal. Once, CDWs were believed to be good models for superconductivity.  While that is no longer true today, they are still ideal systems for understanding certain types of physical problems, and interesting systems in their own right.

Good introduction by Rob Thorne (PDF) in the Physics Today magazine. Or, some introductory slides (powerpoint).

Sample paper: X-ray Scattering Measurements of the Transient Structure of a Driven Charge-Density-Wave

Electronic states at semiconductor-metal interfaces Surfaces

Schottky Band-bending at the interface of gallium-arsenide (a common semiconductor) and aluminum.

See the very nicely done tutorial at CUNY by Professor Tung.

Explanation of Band Bending and Metal-induced gap states on Wikipedia.