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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 1 - THz Photochemistry (THz Photochemistry: Biased Proton Transfer by Ultrafast Electric Fields)

Teaser

Summary

The main objective of the project is to drive chemical reactions by intense THz pulses and monitor the dynamics. As the photon energy of THz is way lower than activation energy of chemical reaction, this approach is rather counter-intuitive and novel. In order to realize this concept, the main practical goal is building a new spectroscopic setup including strong THz pulse and broad visible pulse generation, control over the relative delay time between two pulses with sub-ps time scale, and sensitive detection scheme.

Work performed

(1) THz pump â€“ visible probe experimental setup - High field THz pulse generation and characterization - Visible continuum pulse generation and CMOS detection - Constructing software
: We were able to obtain the field strength of ~ 120 kV/cm and the sensitivity of ~ 10-4 OD level, Characterization of broad visible pulse temporal dispersion by ZnTe
(2) The validation of the new setup
: We were able to validate the performance of the setup by using various solid state samples: ZnTe, single-layered graphene, and methylammonium lead iodide perovskite
(3) Theoretical description of response of the chemical system (BPB solution) as a function of time, field strength, and initial concentration of BPB
: We estimated the signal level of ~ 10-4 OD with 100 kV/cm of the field strength.
(4) Systematic THz pump â€“ visible probe studies on BPB solutions
: We couldnâ€™t detect the signal from BPB solution yet despite of the well validated performance.
: We developed our strategy to apply external electric voltage by using nm scale spectro-electrochemical cell. Currently we are preparing the cell and holder.
(5) Study on Carrier dynamics
: We were able to obtain the time- and energy- resolved signal from graphene and perovskite samples. Currently we are developing the suitable model to understand carrier dynamics induced by strong electric field.
* List of major deliverables
- The validated fs THz pump â€“ visible probe spectrometer, Technical diagram of the instrument, Data acquisition software
- The time- and frequency- resolved pump probe spectra in controlled environments

Final results

One of the expected implications is understanding carrier dynamics in environmentally friendly energy sources including hydrogen fuel cell and solar cell materials. By employing the new setup, we observed the nonlinear behavior of carrier dynamics in perovskite materials as a function of the electric field strength and currently we are working on modeling to understanding the effect of the external voltage in the solar cell device. In addition, from the preliminary result of graphene, we demonstrated the noble time- and energy- resolved approach which is very beneficial to study carrier multiplication and thermalization effect of electric field in this solid state research society.