How to improve the spatial resolution of Raman measurements?
Raman spectroscopy is an essential technique for the chemical and physical analysis of materials. However, when it comes to nanostructures, Raman’s diffraction-limited spatial resolution makes it difficult to unveil their unique molecular- or even atomic-scale properties. To overcome this limitation, Tip-Enhanced Raman Spectroscopy (TERS) uses special metallized probes to both enhance the signal intensity and improve the lateral resolution. In this article, we explain how this technique works and what the role of the probes is.
The principle of TERS spectroscopy
TERS is based on the coupling of a scanning probe microscopy technique, such as atomic force microscopy (AFM) or scanning tunneling microscopy (STM), with a Raman spectrometer. The probe used to scan the sample is coated with a plasmonic metal (like gold or silver), which has the role of amplifying locally the electromagnetic fields of both the incoming laser excitation and the Raman signal scattered from the sample surface. This phenomenon, known as Localized Surface Plasmon Resonance (LSPR), decreases abruptly when getting further from the tip: this means that the TERS effect is spatially confined and dependent only on the tip size (usually in the nanometer range). In conclusion, TERS can successfully enhance the Raman signal and improve its lateral resolution down to the molecular and/or atomic scale.
TERS applications
TERS is particularly useful in various fields of research and industry, including:
- Carbon-based materials: mapping defects in graphene and carbon nanotubes.
- 2D Semiconductors suc as graphene and transition metal dichalcogenides: analysis of interfaces, dopant distribution and opto-electronic properties.
- Life science and polymers: study of their chemical and morphological properties at the nanoscale.
- Nanocatalysis and chemical reactions: real-time monitoring of chemical cahnges at the nanoscale.
Advantages of HORIBA’s TERS probes
HORIBA's TERS probes are designed for optimum performance in nanoscale Raman spectroscopy. Here are their key benefits:
- Increased spatial resolution: TERS probes reach resolutions down to few nanometers, well beyond the diffraction limit of conventional Raman techniques.
- Significant signal enhancement: thanks to theur optimized metal coating, they deliver a signal amplification factor up to 106 with respect to standard micro-Raman.
- Compatibility with different configurations: they adapt to top-, side- or bottom- illuminations setups, guaranteeing flexibility of use.
- Enhanced precision and reproducibility: their design ensures excellent stability for reliable, reproducible measurements.
Conclusion
TERS is a powerful method to gain nanoscale resolution and extreme sensitivity on a broad range of samples. HORIBA’s TERS probes are specifically designed for boosting the TERS performance and reaching results unattainable with conventional Raman techniques. If you want to optimize your nano-spectroscopic analyses, HORIBA’s TERS probes are the ideal solution.
Alice FIOCCO, Product Applications Specialist AFM/AFM-Raman and Agnès TEMPEZ, Market Applications Specialist at HORIBA France.
