The Surface-enhanced Raman Scattering (SERS) is about the amplification of Raman signals by several orders of magnitude mainly through the electromagnetic interaction of light with nano- or meso-structured plasmonic materials such as group 11 metals, which produce large amplification of the laser field through excitation generally known as the localized surface plasmon resonance polariton (LSPR). Developing SERS substrates with relatively low cost, high throughput, large and uniform enhancement factor has been always at the heart of the research on SERS. The materials for SERS substrates have been dominated by silver (Ag) and gold (Au) largely because of their relative chemical stability under ambient condition and strong LSPR in visible wavelengths. Copper (Cu), the cheapest and the m...[ Read more ]

The Surface-enhanced Raman Scattering (SERS) is about the amplification of Raman signals by several orders of magnitude mainly through the electromagnetic interaction of light with nano- or meso-structured plasmonic materials such as group 11 metals, which produce large amplification of the laser field through excitation generally known as the localized surface plasmon resonance polariton (LSPR). Developing SERS substrates with relatively low cost, high throughput, large and uniform enhancement factor has been always at the heart of the research on SERS. The materials for SERS substrates have been dominated by silver (Ag) and gold (Au) largely because of their relative chemical stability under ambient condition and strong LSPR in visible wavelengths. Copper (Cu), the cheapest and the most abundant group 11 metal, has been seldom used as the SERS substrate mainly because of its surface autoxidation under ambient condition.

The main goal of this thesis is to explore the feasibility of developing Cu-based nano- and meso-structures for applications as SERS substrates. Specifically, this thesis tried to achieve three objectives : (i) to develop a facile solution-based electrochemical method for the fabrication of arrayed, pattern-controlled and size-tunable hierarchical Cu mesostructures with good uniformity and reproducibility; (ii) to systematically study the performance of the as-fabricated Cu mesostructures as the SERS substrates, to estimate the corresponding enhancement factors, and to optimize the experiment conditions for achieving the maximum enhancement factor; (iii) to explore viable methods for effectively preventing the autoxidation of the surface of the as-fabricated hierarchical Cu mesostructures.

To achieve the first objective, we developed a method by combining the conventional photolithography with controlled electrochemical deposition, realized the pattern-controlled and size-tunable growth of arrayed hierarchical Cu mesostructures, including facet, split facet, fractal and dense branched morphology. By adjusting the deposition time, we also achieved the size-tuning of the hierarchical Cu mesostructures.

To achieve the second objectives, we carried out a systematic SERS study from a monolayer of 4-mercaptobenzoic acid (4-MBA) molecules self-assembled on the as-fabricated Cu mesostructures. The enhancement factor was estimated to be as high as ~ 10⁷ on the Cu fractal and DBM mesostructures, which is the highest for Cu-based SERS substrate to the best of our knowledge.

To achieve the third objective, we explored three different methods: (i) By applying sacrificial galvanic replacement reaction, the surface of the Cu fractal mesostructure was alloyed with more inert Ag or Au; (ii) By employing the Cu mesostructure as the non-sacrificial working electrode, the surface of Cu mesofractals was protected by a thin film of Ag or Au electrochemically deposited; (iii) By coating a thin layer of Al by metal evaporation followed by its autoxidation, a nanometer-thin layer of alumina was formed on the surface of Cu fractal mesostructure. The third method proved to be a quite effective way for the antioxidative surface protection of the Cu mesostructures.

Finally, the main achievements was summarized, based on which the future perspectives were outlined. To the best of our knowledge, this thesis represents the first systematic study of Cu mesostructure in SERS application.