In this novel version of Raman spectroscopy, tin oxide SNCs are loaded onto the thin silica shell layers of plasmonic amplifiers, which enhance the Raman signals of the SNCs to a detectable level. Image: Science Advances.
In this novel version of Raman spectroscopy, tin oxide SNCs are loaded onto the thin silica shell layers of plasmonic amplifiers, which enhance the Raman signals of the SNCs to a detectable level. Image: Science Advances.

Scientists at the Tokyo Institute of Technology (Tokyo Tech) in Japan have developed a new methodology that allows researchers to assess the chemical composition and structure of metallic particles with a diameter of just 0.5nm to 2nm. This breakthrough in analytical techniques, reported in a paper in Science Advances, will spur the development and application of minuscule materials in the fields of electronics, biomedicine, chemistry and more.

The study and development of novel materials have led to countless technological breakthroughs in many fields of science, from medicine and bioengineering to cutting-edge electronics. The rational design and analysis of innovative materials at nanoscopic scales allows scientists to push through the limits of previous devices and methodologies to reach unprecedented levels of efficiency and capability.

This is the case for metal nanoparticles, which are currently in the spotlight because of their myriad potential applications. A recently developed synthesis method using dendrimer molecules as a template is now allowing researchers to create metallic nanocrystals with diameters of 0.5nm to 2nm. These incredibly small particles, termed ‘subnano clusters’ (SNCs), have very distinctive properties. For example, they are excellent catalyzers for (electro)chemical reactions and also exhibit peculiar quantum phenomena that are very sensitive to changes in the number of atoms in the particles.

Unfortunately, existing analytic methods for studying the structure of nanoscale materials and particles are not suitable for analyzing SNCs. One such method, called Raman spectroscopy, works by irradiating a sample with a laser and analyzing the resulting scattered light to obtain a molecular fingerprint or profile of the possible components of the material. Although traditional Raman spectroscopy and its variants have proved invaluable tools for researchers, they are not sensitive enough for detecting and studying SNCs. But now Kimihisa Yamamoto and his colleagues at Tokyo Tech have found a way to enhance Raman spectroscopy so that it can be used for SNC analysis.

One particular type of Raman spectroscopy is known as surface-enhanced Raman spectroscopy, which involves adding gold and/or silver nanoparticles enclosed in an inert thin silica shell to a sample to amplify optical signals and thus increase the sensitivity of the technique. The research team first focused on theoretically determining the optimal size and composition of these nanoparticles, finding that 100nm silver optical amplifiers (almost twice the size commonly used) can greatly amplify the signals produced by SNCs that adhere to the porous silica shell.

"This spectroscopic technique selectively generates Raman signals of substances that are in close proximity to the surface of the optical amplifiers," explains Yamamoto.

To put the technique to the test, the team measured the Raman spectra of tin oxide SNCs to see if their structural or chemical composition could help to explain their surprisingly high catalytic activity for certain chemical reactions. By comparing their Raman measurements with structural simulations and theoretical analyses, the team gained new insights into the structure of the tin oxide SNCs that explained the origin of their atomicity-dependent catalytic activity.

The methodology employed in this research could have a major influence on the development of better analytic techniques and subnanoscale science. "Detailed understanding of the physical and chemical nature of substances facilitates the rational design of subnanomaterials for practical applications. Highly sensitive spectroscopic methods will accelerate material innovation and promote subnanoscience as an interdisciplinary research field," concludes Yamamoto.

This story is adapted from material from the Tokyo Institute of Technology, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.