70s of last century, the introduction of surface enhanced Raman spectroscopy (SERS), the introduction of precious metal substrate Raman detection sensitivity increased by a million times, to overcome the inherent weakness of the traditional Raman spectroscopy and other shortcomings, Raman detection It has been widely used in food safety, environmental monitoring, life science and other fields and has rapidly grown to be one of the most sensitive on-site profiling techniques for surface species.However, people are delighted but find it regrettable that SERS is only available in gold, silver, Copper and other precious metals only have a rough surface with high activity, which need to rely on the precious metal surface electromagnetic enhancement 'hot' effect, the choice of substrate is very limited; and practical application of this finely modulated material structure susceptible to environmental factors, the stability is unsatisfactory In fact, exploring new, high performance nonmetallic substrates is one of the most important research directions in SERS technology.Especially in recent years, semiconductor compounds have been proved to have SERS activity, and their rich variety and chemical composition have aroused great interest. However, such compounds as a generally lower SERS basal enhancement factor seems to be difficult to break through the research bottleneck. The performance of SERS is derived from the interaction between the probe molecule and its surface, including EM and CM. It is generally believed that the enhancement of SERS in the metal material is mainly due to the enhancement of the surface chemistry of the semiconductor compound It is precisely because of the different mechanisms that the design of semiconductor materials for SERS substrates should follow a completely different philosophy from the existing noble metal materials.
Recently, a research team led by Zhao Zhigang, a researcher at Suzhou Institute of Nanotechnology and Nanostructure Biology, Chinese Academy of Sciences, discovered that oxygen molecules can be used as the key to unlocking the treasures of SERS in semiconductor compounds. By utilizing the chemical composition of the compound, The stoichiometric composition of the metal compound or the surface lattice oxygen concentration to enhance the signal of the surface species of the non-(weak) SERS active material.
Under the guidance of this academic thought, the research team first selected its own oxygen-deficient W18O49 sea urchin-like nanoparticles as the SERS substrate and obtained excellent SERS performance with high sensitivity and low detection limit. This semiconductor material, first used as a SERS substrate, The detection limit of the molecule can be as low as 10-7M, and the surface oxygen deficiency concentration of W18O49 is further changed by reducing atmosphere (H2, Ar) to increase the SERS enhancement factor of the material to 3.4 × 105, which is the most reported performance In contrast, the stoichiometry has almost no SERS activity than WO3, indicating that oxygen defects have an important effect on the SERS performance of the semiconductor oxide.
With this being the case, Zhao Zhigang's team chose molybdenum sulfide (MoS2), a weakly chalcogenide that has weak SERS properties, since the removal of oxygen from the lattice is so important for the material SERS Semiconductor materials, the insertion of oxygen into their crystal lattices can be easily achieved by both substitution and oxidation.The results show that an appropriate amount of oxygen insertion can increase the SERS activity of molybdenum sulfide by 100,000 times, but excessive oxygen doping leads to large SERS activity In addition, the SERS performance of various compounds such as tungsten selenide, tungsten sulfide, molybdenum selenide and the like can be greatly enhanced by the oxygen insertion method, that is to say, the means of lattice oxygen regulation can improve the SERS performance of the semiconductor SERS Performance quite universal potential.
At this point, the enhancement effect of 'oxygen defect' and 'insertion oxygen' on the semiconductor SERS has been unified and the theoretical calculation results point to the same conclusion.The team of researchers applied the chemically amplified theoretical model to the semiconductor- Organic molecular system, it is found that the increase or decrease of lattice oxygen in semiconductor material can be used as an effective means to control its energy level structure. The 'oxygen defect' introduces deep energy level as 'bouncing plate' of electron transition, Increasing the electronic states near the band edge and narrowing the forbidden band; all these will significantly increase the possibility of electron transition in the semiconductor under laser excitation and further through the Vibronic Coupling effect on the charge transition between semiconductor-organic molecules (Charge Transfer), affecting the polarization of the organic molecules adsorbed on the substrate surface tension, thereby enhancing its Raman spectral response.
The above work proves that properly modulating the lattice oxygen in the semiconductor compound can be used as an effective means for significantly improving the SERS performance, breaking the limitation of the noble metal substrate in the conventional SERS technology and further widening the semiconductor compound as the base material in the SERS detection The results of a series of studies were published online at Nature Communications on Noble metal-comparable SERS enhancement from semiconducting metal oxides by making oxygen vacancies and Semiconductor SERS enhancement enabled by oxygen incorporation, respectively.
Research work by the National Natural Science Foundation of Jiangsu Province outstanding youth fund,
Oxygen Defective W18O49 Nanoparticles as SERS Substrates Excellent Performance
Insert oxygen into MoS2 material