In the first half of the project, we have successfully setup the THz-STM lab featuring a commercial low-temperature scanning probe microscope and a custom optical setup. The latter features a femtosecond fiber laser with high repetition rate, various home-built modules for THz pulse generation, THz waveform shaping and detection, and an optical spectrometer. The development of this state-of-the-art ultrafast STM marks a significant achievement in this project. Our experiments demonstrated THz-driven tunnelling currents in bulk metals and semiconducting 2D materials as a function of THz field amplitude and THz phase. Through near-field waveform sampling and precise amplitude calibration, we gained the capability to selectively access specific defect orbitals and dispersive band states in 2D semiconductors.
In collaboration with experts from the Center for 2D Layered Materials at Pennsylvania State University, we developed strategies to introduce dopants into semiconducting 2D transition metal dichalcogenides (TMDs), such as MoS2, WS2, and WSe2, during synthetic growth. Through detailed characterization, we gained insights into the structural, electronic, and magnetic properties of these single dopants, including carbon-hydrogen complexes, vanadium, and rhenium. Notably, we discovered the stabilization of spin states in vanadium dimers and the atomically-precise activation of carbon radical ions in certain TMDs. Currently, we are developing THz pump-THz probe schemes to probe ultrafast charge, spin, and exciton dynamics on these TMD defect systems.
The project team has actively disseminated their research findings through various channels. The PI delivered seven invited conference talks and research seminars, while group members presented 18 contributed talks and posters at international conferences and workshops. Additionally, the PI co-organized a four-day symposium at the MRS Spring Meeting 2022, along with a one-day satellite workshop of the MRS Quantum Staging Group. These events facilitated collaboration and knowledge exchange among experts in solid-state spin defects and 2D materials science.
