Study On Surface-Enhanced Raman Substrates Formed Via Femtosecond Laser Ablation On Silicon Surface

More and more metallic nanostructures have been fabricated out due to the increasing advances in micro-fabrication techniques. Those metallic nanostructures possess unique functional properties, which have presented great potential for application in the research fields of surface-enhanced Raman scattering (SERS), integrated circuits (IC), biosensors, data storage and optical antennas. Meanwhile, it has merged into a new rapidly growing discipline, called surface plasmonics, which covers the research area of physics, chemistry, material science, information science, biology, and their inter-disciplines.We will focus on the application in SERS in this thesis. SERS is a powerful vibrational spectroscopy technique that allows for highly sensitive structural detection of low concentration analytes through the amplification of electromagnetic fields generated by the excitation of localized surface plasmons. Owing to the characteristics of high sensitivity, unique spectroscopic fingerprint, noninvasive to samples, SERS technique has been widely used in biological studies.In this thesis, a nanostructured surface was formed on the Si wafer after femtosecond laser (fs-laser) ablation. Followed by gold film coating we will get SERS-active substrates. The SERS performance of such substrates is probed by rhodamine6G (R6G). The thesis is mainly composed of three sections that are arranged as following:1. We build a femtosecond laser micromachining system by using high precision three-dimensional floating motor. The system sets automatic control, laser ablation and observation as a whole.2. We obtain a series of surface-roughened silicon wafers under different fs-laser powers. Then we will explain the morphology’s dependency on fs-laser power.3. Followed by a typical thickness of50nm gold film coating, the nanostructured silicon wafers become to the SERS-active substrates. The influence of the fs-laser power in laser ablation of Si wafer on the SERS activity is studied experimentally. The best ablation parameters are found through a set of control experiments. To demonstrate the excellent performance of the SERS substrates prepared using a fs-laser ablation approach, we will also measure the sensitivity limit of the substrates by further decreasing the concentration of R6G aqueous solution from10-6M to10’9M. The maximum enhancement factor (EF) is measured up to3×10ˊ.