The ultrafast quantitative analysis during chemical reactions in nanocrystals became possible in a novel approach that was developed at the IPCMS. A technique of analytical electron microscopy with nanosecond resolution was applied and gives access to the quantitative elemental composition of nanomaterials with combined spatio-temporal resolution. An ultrafast transmission electron microscope (UTEM) that has been designed within an EQUIPEX project is used to study irreversible chemical reactions with nanometer and nanosecond precision. In a pump-probe approach, chemical reactions are induced thermally by an intense laser pulse and studied after an adjustable delay with a nanosecond electron pulse in the UTEM.
Many solid-state reactions in nanomaterials are irreversible by nature. At high temperatures, the reactions can be very fast due to the small size of the reactants. The microscopic investigation of such reactions and their kinetics has always been difficult due to the lack of suitable techniques combining high spatial with high temporal resolution. Now, for the first time, this task became possible due to the availability of analytical tools in the UTEM such as electron energy-loss spectroscopy (EELS) in the single-shot approach. This technique is now demonstrated in a study of the fast reduction of nickel oxide nanocrystals at high temperature. The combination of imaging, electron diffraction and EELS gives unprecedented insight into the dynamics of the reaction. The kinetics of the reaction, in particular the reaction order and rate constant as well as the presence of liquid nickel as a short-lived transition state, allows the detailed understanding of the reaction mechanisms.