Lab exchange grant: Investigating the nanoscale Raman response of Bi2Te3 topological insulator flake

Xinyun was thrilled to see the Neaspec tip enhanced Raman spectroscopy (TERS) system in Prof Rebecca Milot's lab.

Xinyun Liu a PhD student at the University of Manchester was awarded an M4QN laboratory exchange award to visit Dr Edward Butler-Caddle and Prof Rebecca Milot at Warwick University. The visit took place in April 2025.

The purpose of the visit

During the visit, Xinyun had the opportunity to study tip-enhanced Raman spectroscopy (TERS), a nanoscale optical characterisation technique closely aligned with her research in scattering-type scanning near-field optical microscopy (s-SNOM). Prior to this visit, she had already investigated Bi2Te3 topological insulator flakes using the in-house s-SNOM systems in Manchester. To verify the material composition, Xinyun performed complementary Raman measurements at Prof. Rebecca Milot’s laboratory using both the nano-Raman (TERS) system and the Renishaw far-field Raman spectrometer. The far-field Raman data clearly showed the characteristic peaks of Bi2Te3, consistent with literature reports, thereby confirming the quality of the flakes. However, due to technical issues with the nano-Raman system installation, high-quality TERS data could not be obtained.

In addition to these experiments, Xinyun was introduced to a range of other advanced facilities at the University of Warwick, including ultrafast THz spectroscopy, Fourier-transform infrared (FTIR) spectroscopy, and UV-Vis-IR spectrometry. These facilities represent potential avenues for future collaborative projects.

Benefits to the UK materials and quantum community

Topological insulators (TIs) are a type of quantum materials distinguished by their insulating bulk and conducting surface states. These surface states exhibit unique properties such as bandgap-less, high conductivity, spin-momentum locking, and robustness against backscattering, making them attractive for next-generation electronic, optical, and thermal devices. The importance of these states is further amplified in nanoscale structures, where the surface-to-volume ratio increases significantly.

Accurate characterisation of such nanostructures is therefore critical, yet remains challenging due to their minimized geometry. Tip-enhanced techniques such as s-SNOM and TERS offer a powerful solution by combining nanoscale spatial resolution with high surface sensitivity, enabling the non-destructive probing of local optical properties.

By learning and applying these techniques, we gain the capability to extract key material parameters—including conductivity, carrier concentration, chemical composition, and impurity levels—which can directly inform and optimise synthesis processes. This visit to Prof. Milot’s group has therefore strengthened UK capacity in nanoscale characterisation of quantum materials, directly supporting the Materials for Quantum Network’s goal of advancing quantum materials and fostering collaborative research infrastructures.

Visit outcomes

Xinyun writes “The main outcome of this visit was the acquisition of Raman data on Bi2Te3 flakes. While the nano-Raman measurements were limited by technical issues, the far-field Raman spectra provided clear evidence of Bi2Te3 signatures. These results will contribute to a manuscript currently in preparation.

Beyond data collection, this visit allowed me to deepen my understanding of both far-field and tip-enhanced Raman spectroscopy, strengthening my ability to interpret and integrate Raman measurements into my broader research. Importantly, the visit also established a collaborative link with Prof. Milot’s group. Awareness of the complementary capabilities within her laboratory opens the door to future joint projects, enabling access to advanced characterisation tools for the UK quantum materials community.”