## 1 Introduction  
The phenomenon of optical scattering has a special effect that is similar to the Compton effect of X-ray scattering. The frequency of light will change after scattering. \"Raman scattering\" implies that the molecules and photons in the substance transfer energy when a certain frequency of laser irradiates the surface of a sample [1]. According to the vibration dynamics (such as the swing and twist of atoms, as well as the swing and vibration of chemical bonds), particles change in various ways and degrees, scattering light of different frequencies. The changes of frequency are dependent on the characteristics of the scattering material. Different types of atomic groupings have different vibration modes. Therefore, the scattering light, with a specific difference from the frequency of the incident light, can be generated. The spectrum is referred to as the \"Fingerprint spectrum\", which can identify the types of molecules that make up the material according to this principle [2, 3]. Some bands with weak absorption or intensity change in the infrared spectrum may be strong bands in the Raman spectrum, which is conducive to the detection of these groups. In addition, the measurement range of the Raman spectrum in the low wavenumber direction is wide, which is conducive to providing the vibration information of heavy atoms. For the change of structure, the Raman spectrum is more sensitive than the infrared spectrum, and the Raman spectrum peak is clear and sharp, which is more suitable for quantitative research. Fixed samples can be determined directly without sample preparation, and can be used for qualitative and quantitative analysis without damage [4]. The surface-enhanced Raman scattering (SERS) mechanism, generally recognised in the academic community, mainly includes physical enhancement mechanisms and chemical enhancement mechanisms [5, 6, 7]. The most significant contribution is thought to be the enhancement of the local electromagnetic field induced by the surface plasmon resonance [8]. The surface plasmon is the collective oscillation effect of the free electrons in the metal under the optical field. Due to the fact that the energy gaps of the d electrons and s electrons of the three group IB metals of Cu, Ag, and Au are larger in comparison to those of the transition metal, they are less prone to inter-band transitions [9; 10]. As long as the appropriate excitation light wavelength is chosen for these three kinds of metal systems, the energy of absorbed light can be prevented from being converted into heat, owing to the occurrence of inter-band transitions, and thereby tending to realise an efficient SPR scattering process [11]. In the Raman process, the chemical interaction mostly manifests the difficulty of the electron density deformation under the optical field. When molecular chemistry is adsorbed on the surface of the substrate, surface, surface-adsorbing atoms, and other co-adsorbed species may have certain chemical interactions with the molecule. These factors have a direct impact on the electron density distribution of the molecule, as well as the system's polarizability, which changes Raman intensity [12; 13]. Chemical enhancements primarily comprise the following three types of mechanisms: non-resonance enhancement due to chemical bonding of the adsorbate to the metal substrate; increased resonance because of the formation of surface complexes (new molecular systems) by adsorbed molecules and surface-adsorbed atoms; enhanced resonance of photoinduced charge transfer of molecular metal systems by excitation light. After decades of debate, the electromagnetic enhancement mechanism is now universally regarded as the main contributor to most SERS processes [14]. Amplified light enhancement results from excitation of localised surface plasmon resonance. This light concentration is preferentially present in gaps, cracks, or sharp features of plasmonic materials that are traditionally aristocratic, and coinage metals (silver, gold, and copper) with nanoscale features [15].