A research team led by Prof. HUANG Zhulin from the Hefei Institutes of Physical Science of the Chinese Academy of Sciences, together with researchers from the University of Massachusetts Amherst, has synthesized three different crystalline phases of molybdenum boride with a strong Raman signal enhancement performance.

These findings were published in Small.

Surface-enhanced Raman scattering (SERS) is a rapid and non-destructive detection method widely used in various fields, including trace contaminant monitoring, food safety, chemical catalysis, and molecular fingerprinting. However, most noble metal SERS materials are costly and exhibit poor physical and chemical stability, especially under extreme conditions such as high temperatures and highly corrosive environments, where the SERS enhancement effect rapidly decreases.

In this study, the researchers leveraged the properties of transition metal borides, which can withstand extreme conditions like high temperatures, strong acids, and strong bases, to synthesize three molybdenum boride ceramic powders (β-MoB, MoB₂, and Mo₂B₅) based on liquid-phase precursor and carbo/borothermal reduction.

The SERS performance of these molybdenum borides was evaluated using Rhodamine 6G (R6G) probes, and the results showed that β-MoB exhibits SERS enhancement of five orders of magnitude, which is comparable to Au nanoparticles. The excellent SERS enhancement performance of β-MoB can be attributed to its higher adsorption energy for R6G molecules and significant charge interactions between them.

In addition, the researchers investigated the effects of strong acid and strong base solutions as well as high-temperature oxidation on the SERS activity of molybdenum borides, and the test results indicated that the SERS effect of molybdenum borides could be well maintained even when exposed to such corrosive environments and high temperatures.

This work elucidates the phase control methodology and SERS enhancement mechanism of molybdenum boride ceramics, expanding the selection range of SERS active materials from noble metals and semiconductors to ultra-high temperature ceramics, which are expected to be used for optical sensing and detection in extreme environments.

Preparation process and microstructure of molybdenum boride ceramics. (Image by HU Mengen)