Design and implementation of a device based on an off-axis parabolic mirror to perform luminescence experiments in a scanning tunneling microscope

TL;DR

This paper introduces a novel off-axis parabolic mirror device for efficient light collection and injection in low-temperature STM, enabling multiple spectroscopic techniques with high efficiency and resolution.

Contribution

The paper presents a new off-axis parabolic mirror system that enhances light collection efficiency and allows simultaneous STM-induced luminescence, photoluminescence, and Raman spectroscopy in a low-temperature STM.

Findings

Achieved 72% light collection efficiency considering the hemisphere above the sample surface.

Successfully performed STM-LE, PL, and Raman spectroscopy on various nanostructures.

Obtained atomically resolved images and spectroscopy confirming system performance.

Abstract

We present the design, implementation, and illustrative results of a light collection/injection strategy based on an off-axis parabolic mirror collector for a low-temperature Scanning Tunneling Microscope (STM). This device allows us to perform STM induced Light Emission (STM-LE) and Cathodoluminescence (STM-CL) experiments and in situ Photoluminescence (PL) and Raman spectroscopy as complementary techniques. Considering the \'Etendue conservation and using an off-axis parabolic mirror, it is possible to design a light collection and injection system that displays 72% of collection efficiency (considering the hemisphere above the sample surface) while maintaining high spectral resolution and minimizing signal loss. The performance of the STM is tested by atomically resolved images and scanning tunneling spectroscopy results on standard sample surfaces. The capabilities of our system are demonstrated by performing STM-LE on metallic surfaces and two-dimensional semiconducting samples, observing both plasmonic and excitonic emissions. In addition, we carried out in situ PL measurements on semiconducting monolayers and quantum dots and in situ Raman on graphite and hexagonal boron nitride (h-BN) samples. Additionally, STM-CL and PL were obtained on monolayer h-BN gathering luminescence spectra that are typically associated with intragap states related to carbon defects. The results show that the flexible and efficient light injection and collection device based on an off-axis parabolic mirror is a powerful tool to study several types of nanostructures with multiple spectroscopic techniques in correlation with their morphology at the atomic scale and electronic structure.