Abstract
This study successfully demonstrated the tailoring properties of hafnium nitride (HfN) thin films via reactive gas-timing (RGT) RF magnetron sputtering for surface-enhanced Raman spectroscopy (SERS) substrate applications. The optimal RGT sputtering condition was investigated by varying the duration time of the argon and nitrogen gas sequence. The RGT technique formed thin films with a grain size of approximately 15 nm. Additionally, the atomic ratios of nitrogen and hafnium can be controlled between 0.24 and 0.28, which is greater than the conventional technique, resulting in a high absorbance in the long wavelength region. Moreover, the HfN thin film exhibited a high Raman signal intensity with an EF of 8.5 × 104 to methylene blue molecules and was capable of being reused five times. A superior performance of HfN as a SERS substrate can be attributed to its tailored grain size and chemical composition, which results in an increase in the hot spot effect. These results demonstrate that the RGT technique is a viable method for fabricating HfN thin films with controlled properties at room temperature, which makes them an attractive material for SERS and other plasmonic applications.
Highlights
The additional peak at 2θ = 57.774 corresponding to an hafnium nitride (HfN)(220) plane was found in the samples RGT5, RGT7, and MIX
The total energy of sputtered atoms directly correlates with RF power and working pressure, which could be attributed to the energy transferred by Ar+ to an atom on a target surface
0.28, when gas-timing N2 turn-on time increased from 1 to 7 s, while the MIX film showed the lowest Hf ratio of approximately 0.49. These results show that reactive gas-timing (RGT) is a promising technique to control the chemical composition of an HfN film
Summary
Surface-enhanced Raman spectroscopy (SERS) is a powerful vibrational spectroscopy technique that is characterized by its rapid, nondestructive, ultrasensitive, and fingerprint creativecommons.org/licenses/by/. SERS substrates are made of noble metal, such as gold, silver, and copper, due to localized surface plasmon resonance (LSPR) inducing highly electromagnetic fields in the nanostructures. TMNs (e.g., titanium nitride (TiN), zirconium nitride (ZrN), and hafnium nitride (HfN)) are interesting due to their high melting point, strong mechanical properties, intrinsic chemical stability in harsh environments, and localized plasmon resonances that are extremely comparable to gold [9,10,11,12]. We demonstrate the tailored properties of HfN thin films through RGT RF magnetron sputtering. The HfN thin film prepared by the RGT technique can be utilized as a reusable SERS substrate
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