Colloquium: Monique van der Veen

09/19/2013

16:00

VU niversity Amsterdam, Science Building, S6.31, De Boelelaan 1081, 1081 HV Amsterdam

Unravelling the structure, growth and function of nanoporous materials with nonlinear and ultrafast optical spectroscopy.

Monique van der Veen

LaserLaB

Sciences

Seminar

Unravelling the structure, growth and function of nanoporous materials with nonlinear and ultrafast optical spectroscopy.

Nanoporous materials that are crystalline and have pore diameters up to 2 nm have extraordinary properties. Most notable materials type in this class are zeolites and metal-organic frameworks. Due to their uniform pores with widths close to molecular sizes, they can be used to separate different molecules as molecular sieves, or as carriers for controlled drug delivery in the human body. Their structure can moreover be explored for applications such as ferroelectricity, where the combination with the defined pores can lead to multifunctional materials.

To understand structure-activity relationships of these materials it is of paramount importance to have a clear understanding of the structure. Therefore we will show in this talk how the second-order nonlinear optical effect second-harmonic generation (SHG) can be used for structural determination. More specifically paradigms will be shown how SHG microscopy can unravel the intergrown structure of crystals, their point group symmetry and phase transitions. A new second-harmonic generation based technique will be introduced, namely time-resolved angle-dependent second-harmonic scattering. This technique is capable of  structure sensitive dynamic measurements. This makes it ideally suited to study the crystal growth of materials. Although these paradigms and techniques will be applied in this lecture on nanoporous materials, they are universally applicable to a wide class of materials, including biological materials.

Nanoporous materials, most notably metal-organic frameworks, have attracted significant attention the last few years as photocatalysts. Yet, very little is known on the charge separation and photocatalytic mechanism. This hampers the development of photocatalysts capable of highly efficient conversion of carbon dioxide into chemical fuels. Ultrafast pump-probe spectroscopy is capable of providing this information as it can follow the pathway of photo-excited charges leading to bond breaking and making. The first results and conclusions of ultrafast spectroscopy on metal-organic frameworksempty will be given to end the talk.