Femtosecond Time-Resolved Vibronic Microscopy

Lead Research Organisation: University of Oxford
Department Name: Oxford Chemistry

Abstract

Traditionally, in order to generate a measurable signal in the presence of measurement noise, transient electronic and vibrational spectroscopy is performed at the ensemble level. However, in nanostructured electronic materials, such as organic semiconductors and metal-halide perovskites, variations in local structure and composition dictate their macroscopic electronic properties. These materials have attracted considerable attention for both their fundamental electronic properties and for their potential applications in next-generation photovoltaics, light emitting diodes and other optoelectronic devices. While the spatial inhomogeneity of thin films of these materials have been extensively studied by electron microscopy, X-ray and photoluminescence techniques, on sub-Mu-m length scales, an understanding of how these structural and chemical properties control and influence exciton and charge dynamics remains unknown. Due to the limited spatial information provided by conventional, ensemble-averaged spectroscopies, there is a clear need for an experimental technique that is able to spatially correlate transient spectroscopic data with local molecular structure and composition, with high temporal and sub-Mu-m spatial resolution.
Previous work has been carried out in the Kukura group in an attempt to design and implement such a technique. Preliminary results present a microscope that is able to record spatially-resolved transient vibronic spectra with shot-noise-limited sensitivity and diffraction-limited spatial resolution, by combining ultrafast spectroscopy with highly efficient optical microscopy. This will be used to investigate the existence, origin and mechanistic underpinning of spatially inhomogeneous electronic dynamics in thin film systems of direct relevance to next generation optoelectronic materials. As well as this, the possibility of expanding this methodology towards super-resolved optical nanospectroscopy on <20 nm length and <10 fs time scales will be explored, for understanding the fundamentals of light matter interaction and energy transport on the nanoscale. The potential of this experimental technique will be further explored with regard to its impulsive Raman capabilities, with the possibility of obtaining otherwise inaccessible excited state structural information.
This research has the potential to provide ground-breaking insights into how structure, chemical composition and spatial inhomogeneity control charge and energy flow in next-generation optoelectronic materials. The results will be of wide interest to a worldwide community working on these materials and will help guide future developments. Furthermore, the experimental methods developed here are likely to find wide application in the study of molecular and optoelectronic materials.
This project falls within the EPSRC Photonic Materials research area.
This work will establish a completely novel but important avenue to study not only the ensemble kinetics of next generation optoelectronic materials, but elucidate both the existence and structural origins any variations therein.

Publications

10 25 50

Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/N509711/1 01/10/2016 30/09/2021
1810912 Studentship EP/N509711/1 01/10/2016 30/09/2019 Lee Priest