What Is Surface Enhanced Raman Scattering?

Surface enhancement of Raman scattering (SERS). It is a technology developed on the basis of ordinary Raman scattering. In 1974, M. Fleishmann et al. Measured the Raman scattering line of pyridine molecules adsorbed on the silver surface after several redox reactions in the electrochemical cell. In 1976, RPVandyne and others confirmed the above experiment and calculated that the Raman scattering cross section of pyridine adsorbed on the silver surface was 1,000,000 times larger than that of pure pyridine. ^[1]

Surface enhanced Raman scattering

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Surface enhancement of Raman scattering (SERS). It is a technology developed on the basis of ordinary Raman scattering. In 1974, M. Fleishmann et al. Measured the Raman scattering line of pyridine molecules adsorbed on the silver surface after several redox reactions in the electrochemical cell. 1976 RPVandyne and others

Studies show that different molecules or ions such as pyridine, cyanide, benzene, Co, N, ... (currently there are one hundred or two hundred organic and inorganic molecules and ions) are found on the surfaces of metals such as Ag, Cu, and Au. The Mann scattering cross section is enhanced to varying degrees. The enhancement effect is related to the sub-microscopic roughness of the surface. Electron microscope analysis showed that for Ag, the unevenness around 100 nm had the most significant enhancement effect. In addition to the enhancement of the molecular vibrational spectrum, a wide-band continuous background was found. There is no consistent result on the relationship between the enhancement effect and the frequency of the excitation laser.

Because this effect occurs in the metal-adsorption molecular system, many important processes such as heterogeneous catalysis, electrochemical and single-layer molecular detection, and surface research are related to this. In addition, according to theoretical estimates, the nonlinear optical process should also be enhanced, which has been confirmed by experiments by Shen Yuanyang et al.

There are many theoretical models proposed. For example, the image field model believes that the light field induces electric dipoles on the adsorbed molecules, which greatly enhances the dipole radiation intensity under certain conditions. Modulation reflection theory believes that the vibration of adsorbed molecules changes the density of electrons on the surface of the metal through the interaction between the adsorbed molecules and the metal, thereby modulating the reflectivity of the metal, resulting in "frequency-shifted reflection" and thus showing a greatly enhanced scattering intensity . In addition, there are resonance enhancement models, electron-hole pair excitation models, stimulated scattering models, and the like. None of these models currently explain all experiments perfectly. Therefore, many people think that the surface enhancement effect is a complex process, and the enhancement effect may be a combination of several factors.

Theories and experiments are still developing rapidly. In addition to the electrochemical cell system, enhanced Raman scattering effects have been observed in experiments such as ultra-high vacuum metal surfaces, metal particle surfaces in colloids, and rough metal surfaces caused by mechanical polishing. In addition to physical enhancement factors, There may also be chemically enhanced contributions. See the scattering of light.