Cross-correlated SPM and TERS/TEPL imaging: unique tool for nanoscale structural characterization of 2D semiconductors and the vertical / lateral heterostructures thereof.

A. Krayev
HORIBA Scientific,
United States

Keywords: SPM, Raman, TMD, TERS


In this presentation we’ll discuss the unique advantages that proper integration of a scanning probe microscope (SPM) and a Raman spectrometer can provide for the nanoscale (5-20 nm) characterization of the structural peculiarities and defects in 2D semiconductors like transition metal dichalcogenides (TMDs) and their vertical and lateral heterostructures. It will be showed that the use of special plasmonic probes that enable the tip enhanced Raman scattering (TERS) and the tip enhanced photoluminescence (TEPL) imaging can greatly improve the spatial resolution of spectroscopic imaging down to 5 nm level in ambient conditions. We’ll also discuss how the possibility of conducting the SPM measurements in true dark conditions and under well controlled illumination (power, polarization, wavelength) can be extremely helpful for characterization of photovoltaic materials. Unique advantages of the TERS imaging cross-correlated with various SPM channels like topography and the surface potential will be demonstrated for the nanoscale structural characterization of the junction line in MoS2-WS2 lateral heteromonolayers [1], where TERS imaging revealed that the width of the alloyed area at the junction of the MoS2 core and WS2 shell can vary by more than order of magnitude within the same crystal. In addition, it will be showed how TERS imaging reveals decoupling of the layers at the crown of the nanobubbles of twisted WS2-WSe2 heterobilayers [2]. With 785nm excitation we observed an ultra-low frequency band at about 23 cm-1 all over the nanobubble except for the very top. The disappearance of this band was spatially correlated with the appearance of A1g mode of WS2 that was not visible over the main body of the nanobubbles. In addition it will be demonstrated that the photocurrent generated by WS2-WSe2 twisted heterobilayer can be used for direct imaging of the lattice-like Moire pattern in this vertical heterostructure. Brief description of application of the SPM and correlated TERS imaging for characterization of structural defects in other class of scientifically relevant 2D semiconductors, namely- Janus TMDs MoSSe and MoSeS derived from MoS2 and MoSe2 correspondingly, will be given at the end of the talk.