Near-field Spectroscopic Imaging of Mesoscopic Photophysics: 2D Semiconductors and Lipid Bilayers.

Chi Chen^1*

¹Research Center for Applied Sciences, Academia Sinica, Taipei, Taiwan

* Presenter:Chi Chen, email:chenchi@sinica.edu.tw

Scanning near field optical microscopy (SNOM) is a scanning probe microscopy technique that combines optics with atomic force microscopy (AFM) to achieve sub-diffraction limit optical resolution. We employed near-field photoluminescence (NF-PL) to study the atomically sharp 1D interfaces between WS2 and MoS2. With an optical resolution of 68 nm, a 105 nm-wide region for quenched PL was confirmed using NF-PL imaging, which resolved the narrowest quenching region so far. For low-quantum-yield materials, we developed the near-field broadband transmission (NF-tr) method, which provides abbreviation-free and nanoscale-resolution imaging capabilities of the entire conduction band over a highly lateral inhomogeneity. Both bandgap evolutions with varying compositions and bilayer coupling effects were visualized in real space with 135 nm spatial resolution.
With further instrumentation challenges, we accomplished a water-phase SNOM system for the lateral distribution and phase segregation of the supported lipid bilayers (SLB). Surprisingly, the SNOM tip can manipulate local lipid molecules from the gel phase to the fluid phase and vice versa, which causes the fluorescence contrast to flip the opposite. This demonstrates that there is no particular partition of the fluorescence tag in the fluid or gel phases. Our results reveal the fundamental mechanism and offer a practical guide for interpreting the partitioning of fluorescent tags.

Keywords: Scanning near field optical microscopy (SNOM), Atomic force microscopy (AFM), Transition metal dichalcogenides (TMD), Supported lipid bilayers (SLB)