Enhanced-tip Raman spectroscopy used to unravel the structure of nanodiamond-carbon films

Coaxial arc plasma deposition (CAPD) is seen as a promising alternative to more conventional methods, such as sputtering and thermal evaporation, for fabricating nanodiamond composite films. This method has the capability of creating grain sizes at 10 nanometers or smaller on substrates at room temperature.

But accurately measuring the parameters of such advanced nanomaterials by incorporating Raman spectroscopy (RS) as the gold standard has been challenging. RS is generally used to collect average information on the chemical composition of bulk materials. However, measuring the structural and chemical parameters of heterogeneous particles in nanomaterials has remained elusive.

To overcome this limitation, researchers have increased the RS spatial resolution by adding a metalized scanning probe tip, which is illuminated to amplify the local electromagnetic field. Ali et al. have now used this advanced form of RS, called tip-enhanced Raman spectroscopy (TERS), to directly and nondestructively measure parameters of their nanodiamond-carbon composite films containing 10 nanometer diamond crystallites.

They fabricated their films using CAPD to coat amorphous carbon (a-C) powder with diamond nanoparticles on silicon wafers. When they incorporated conventional RS to study the particles, they found that the scattering of the diamond grains competed with the strong signal of the a-C matrix.

Turning to TERS, they were then able to detect the diamond nanocrystallites embedded in the a-C matrix. This demonstrated that the high spatial resolution of TERS enables the identification of different carbon modifications separated by only a few nanometers.

“This work demonstrates that TERS is a powerful, nondestructive method for investigating advanced nanodiamond composite films,” author Ali M. Ali said. “The method allows direct access to parameters that were previously only available as average data.”

Source: “Near- and far-field Raman spectroscopic studies of nanodiamond composite films deposited by coaxial arc plasma,” by Ali M. Ali, Tanja Deckert-Gaudig, Mohamed Egiza, Volker Deckert, and Tsuyoshi Yoshitake, Applied Physics Letters (2020). The article can be accessed at https://doi.org/10.1063/1.5142198 .