Self-Assembled\nPlasmonic Nanoparticles on Vertically\nAligned Carbon Nanotube Electrodes via Thermal Evaporation

Abstract

This\nstudy details the development of a large-area, three-dimensional\n(3D), plasmonic integrated electrode (PIE) system. Vertically aligned\nmultiwalled carbon nanotube (VA-MWNT) electrodes are grown and populated\nwith self-assembling silver nanoparticles via thermal evaporation.\nDue to the geometric and surface characteristics of VA-MWNTs, evaporated\nsilver atoms form nanoparticles approximately 15–20 nm in diameter.\nThe nanoparticles are well distributed on VA-MWNTs, with a 5–10\nnm gap between particles. The size and gap of the self-assembled plasmonic\nnanoparticles is dependent upon both the length of the MWNT and the\nthickness of the evaporated silver. The wetting properties of water\nof the VA-MWNT electrodes change from hydrophilic (∼70°)\nto hydrophobic (∼120°) as a result of the evaporated silver.\nThis effect is particularly pronounced on the VA-MWNT electrodes with\na length of 1 μm, where the contact angle is altered from an\ninitial 8° to 124°. Based on UV–visible spectroscopic\nanalysis, plasmonic resonance of the PIE systems occurs at a wavelength\nof approximately 400 nm. The optical behavior was found to vary as\na function of MWNT length, with the exception of MWNT with a length\nof 1 μm. Using our PIE systems, we were able to obtain clear\nsurface-enhanced Raman scattering (SERS) spectra with a detection\nlimit of ∼10 nM and an enhancement factor of ∼10⁶. This PIE system shows promise for use as a novel electrode\nsystem in next-generation optoelectronics such as photovoltaics, light-emitting\ndiodes, and solar water splitting.