Nanoscale Chemical Characterization of Novel Semiconductor Materials using Tip-Enhanced Optical Spectroscopy

In this webinar, I will discuss the application of Tip-Enhanced Optical Spectroscopy (TEOS) for the nanoscale investigation of two classes of semiconductor materials: two-dimensional (2D) transition metal dichalcogenides (TMDs) and organic photovoltaic (OPV) devices.

In the case of 2D TMDs, I will demonstrate how TEOS can be applied to study excitonic processes in single-layer MoS2 and WSe2. Through hyperspectral tip-enhanced photoluminescence (TEPL) imaging, the heterogeneity of excitons and trions in single layer MoS2 can be successfully mapped with a spatial resolution of 20 nm ^[1]. Furthermore, the combination of TEOS with Kelvin probe force microscopy can reveal the optoelectronic behavior of grain boundaries in single layer WSe2 with a resolution of 50 nm, providing insights into the distinct electronic and excitonic properties governed by the orientation of the merged WSe2 sheets ^[2].
In the case of OPV devices, I will introduce a novel methodology called simultaneous topographical, electrical, and optical microscopy (STEOM) where TEOS is combined with photoconductive-AFM ^[3]. This approach enables the simultaneous characterization of topography, chemical composition, and photoelectrical properties with sub-20 nm resolution. I will demonstrate how STEOM can be applied to study the nanoscale morphology and local chemical composition of an operational OPV device, revealing correlations between surface and subsurface molecular distribution and local photocurrent generation.

^{References
[1] Nanoscale, 2016, 8, 10564-10569
[2] The Journal of Physical Chemistry C, 2021, 125, 26883-2689
[3] Nanoscale, 2017, 9, 2723-2731}