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Tip enhanced Raman Scattering (TERS) imaging is gaining more and more popularity for the nanoscale spectroscopic characterization of novel 2D semiconductors and their vertical and lateral heterostructures. Gap mode TERS imaging when a thin sample is sandwiched between the TERS active SPM probe and plasmonic substrate like silver or gold, is the most popular and advantageous option due to strong enhancement of optical electric field in the tip-substrate cavity. Despite multiple examples of successful application of the gap-mode TERS imaging of nanoscale heterogeneities in 2D semiconductors such as transition metal dichalcogenides (TMD), the exact physics of complex interaction between the plasmons in the tip-substrate junction and excitons in TMDs remains poorly understood. One of the possible approaches towards probing complex resonant phenomena occurring in gap-mode TERS experimental conditions is performing TERS imaging with varied excitation wavelength [1]. I’ll demonstrate that the TERS spectra of WS2-WSe2 vertical heterostructures obtained with 785 nm, 632.8 nm, 671 nm and 593.8 nm excitation may differ significantly, the intensity of characteristic Raman bands of WSe2 at around 250-260 cm-1 being extremely low in case of 632.8 nm excitation but rising as we move to shorter or longer excitation wavelengths. I’ll discuss the advantages of concurrent two-color excitation TERS imaging as well as interesting counterintuitive variations of the intensity of TERS bands of the monolayer WS2 as the function of the excitation wavelength. Finally, I’ll demonstrate that the ratio of the intensity of the in-plane E2g and the out-of-plane A1g modes in the above- and below- the-band-gap non resonant TERS spectra of bilayer WS2 on silver inverses as we move from 532 nm to 785 nm excitation.
Références
[1] Andrey Krayev, Peng Chen, Humberto Terrones, Xidong Duan, Zhengwei Zhang, and Xiangfeng Duan The Journal of Physical Chemistry C 2022, 126, 11, 5218-522
DOI: 10.1021/acs.jpcc.1c10469
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