RESEARCH PROJECTS
We use light as a versatile tool to trigger, characterize and control electronic behavior in advanced materials on extreme spatiotemporal scales.
Questions we explore include:
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How can we sensitively characterize energy transport while tracking relevant parameters including transfer rate, energy, momentum, etc ?
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How can we investigate the role of molecular/lattice vibrations in energy transport and exploit them in modern device design?
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How can we use light or structure design to direct energy transport or chemical reactions?
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The current explosion of nanomaterials, metamaterials and quantum computing materials presents us a fantastic opportunity. Below are the approaches we use.
Spatiotemporally resolving energy transport
stroboSCAT is a method of integrating pump-probe spectroscopy into a microscope setup. Upon pulsed photoexcitation, a nanoscale distribution of energy carriers (free electrons, excitons, etc.) are generated. After a controllable time delay, interferometric scattering microscopy (iSCAT) is used to track the expanding of spatial distribution of these energy carriers. The rate at which this distribution expand indicates the transport rate, and provide an important criteria of determining a mechanism.
Additional parameters can be resolved, such as energy relaxation and photon momentum directions, so that exotic phenomena, for example polaritons, can be explored.
Ultrafast infrared and UV/Vis spectroscopies
We employ ultrafast infrared methods, for example, two dimensional infrared (2D IR) spectroscopy, which is akin to 2D NMR but operates on time scales eight to ten orders of magnitude faster than NMR.
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The vibrational frequency of a chemical bond is usually sensitive to the intra/inter-molecular interactions. In an inhomogeneously broadened IR absorption spectrum below, each tiny frequency under the envelope corresponds to a particular intra/inter-molecular configuration. If we can track the fluctuation of the vibrational frequency, then we can track the ultrafast dynamics such intra/inter-molecular configurations.
2D IR is able to measure frequencies at two time points with a controlled delay time Tw. Thus, the frequency correlation function can be obtained and the Tw-dependent decorrelation depicts the frequency randomization process. Thus, 2D IR is a powerful tool for examining molecular dynamics in real time.
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We are also developing strategies to characterize molecular dynamics in the electronic excited states as well as to determine if vibrational excitation can direct energy transfer or a chemical reaction.
