An international research team led by Project Prof. Yousoo Kim has developed a groundbreaking method to control and study charge transfer in single molecules. Charge transfer between molecules and electrodes is a fundamental process that plays a key role in organic devices and chemical reactions on catalyst surfaces. However, these charge transfers occur extremely fast, on the scale of picoseconds, making them difficult to observe.
By combining terahertz (THz) light pulses with a custom-built optical scanning tunneling microscope (optical STM), the researchers achieved ultrafast control of charge injection at the nanoscale. In their experiments, they used a molecule called Pd-phthalocyanine, which contains a palladium atom, on a silver substrate covered with an insulating layer. When THz pulses were applied, the molecule emitted light at about 660 nm, signaling that charges were being injected into its orbitals and an exciton was forming. A tiny amount of current was detected during the luminescence measurement, indicating that the charge transfer occurred between the STM tip and the molecule.
In addition, the team was able to tune the light emission efficiency by changing the THz pulse waveform. This novel approach provides new insights into ultrafast molecular dynamics and holds promise for improving organic light-emitting diodes, solar cells and other devices.
Papers
Journal: Science
Title: Ultrafast on-demand exciton formation in a single-molecule junction by tailored terahertz pulses
Authors: Kensuke Kimura, Ryo Tamaki, Minhui Lee, Xingmei Ouyang, Satoshi Kusaba, Rafael B. Jaculbia, Yoichi Kawada, Jaehoon Jung, Atsuya Muranaka, Hiroshi Imada, Ikufumi Katayama, Jun Takeda, Yousoo Kim