TAILORING NANO-STRUCTURES AND EXCITATION WAVELENGTHS TO INCREASE SURFACE ENHANCED RAMAN SCATTERING

Understanding the mechanism of Surface Enhanced Raman Scattering (SERS) phenomena is essential for advancing next generation SERS based chemical sensors. Conventional SERS studies investigate the excitation wavelength dependence for one particular nanostructure morphology at a time. However, more comprehension of SERS mechanisms can be gained when combining excitation wavelength and morphology dependences in a single study. Here, we report combinatorial SERS detection of Fullerene C₆₀ thermally evaporated onto a tapered gold thin film. The gold film slopes from 40 nm down to the glass substrate. The sloped borders provide a range of film morphologies from dense nano-island to nanoparticle structures, as revealed by HR-SEM. SERS spectra were measured with two excitation wavelengths: 532 nm and 784 nm. Excitation of 532 nm generated similar SERS spectra across the border surfaces, with the most enhanced spectra being detected from the Au thin film region. In addition, the SERS spectra fully correlated with normal Raman spectra, strongly indicating a resonant Raman mechanism. In contrast, excitation with a wavelength of 784 nm caused different SERS spectra across the border region of the Au film, in which the SERS intensity measured from the sloped Au surface was 10 times higher than the SERS signal from the Au thin film region. This spectral diversity implies an electromagnetic mechanism controlled by near field interactions of local surface plasmon resonances. When probing SERS with different excitation wavelengths, the most enhancing surface is determined by the molecule’s identity. The ability to optimize the metallic nanostructure and excitation wavelength for a given molecule using combinatorial SERS substrates opens new possibilities for chemical sensing.