Simplified Protocol for Analyzing Polarization Properties of Scanning Tunneling Microscope (STM) Light Emission Spectra at an Oblique Angle.

In this work, we present a simple protocol for processing and analyzing multi-peak scanning tunneling microscope light emission (STM-LE) spectra obtained using an all-optical setup integrated into a standard low temperature, ultrahigh-vacuum, scanning tunneling microscope system. The method involves measuring the polarization dependence of the STM-LE spectra and evaluating the localized surface plasmon confinement length to determine the presence and orientation of dipole emitter/s. We apply this technique to the STM-LE from Au-tip/Au(111) surface and Au-tip/Ag(111) surface systems. The observed spectra contain multiple peaks that cannot be described by a single confinement length, indicating the presence of multiple dipole emissions arising from electrical excitation within the tip-surface junction. The polarization of the STM-LE from distinct dipoles reveals that these dipoles have different orientations. Our work demonstrates that a simple and all-optical addition to a standard ultrahigh vacuum STM system can be used to obtain more in-depth information from the STM-LE spectra.