UM Chemistry/Research/Li Research Group

• Metal-Solution Interfaces
• Identification of surface adsorbed species
• Applications of Raman Spectroscopy

Publications

Description:
One of our research interests is to couple surface Raman and Infrared spectroscopic methods with conventional electrochemical techniques for the study of metal-solution interfaces. The approach is to enhance the attenuated total reflectance (ATR) infrared (IR) adsorption and Raman scattering signals by making use of a uniform sub-monolayer deposition of noble metal such as silver or gold onto the metal electrode. The major advantages of this method for obtaining in situ interface information are high sensitivity and good specificity with negligible interference from solutions. This research should help to promote the development and the evaluation of new material films in a wide variety of applications. It would be very useful for in situ identification and characterization of metal or alloy passivated films under a specific solution condition.

Another research is to develop surface-enhanced Raman scattering-active substrates for in situ identifying surface adsorption species and monitoring reaction products generated in solutions. Both the sol gel process and the impregnation techniques are applied in the development. It is expected that the research will help to study the adsorption behavior of species at molecular level, shed light on in situ spectroelectrochemical studies of passivated films and redox chemical process in solution, and explore surface-enhanced Raman spectroscopic method for sensitive identification. Our recent research has demonstrated that the silver oxide sols and the silver solutions are surface-enhanced Raman - active. This should provide an excellent potential for investigating metal oxide and metal oxide/metal catalyst by surface Raman spectroscopy. We have also shown that the catalyst techniques are very useful in preparing surface-enhanced Raman substrates.

We are also interested in applying the self-assembled monomolecular films (SAM) in the material chemistry projects. Spectroscopic methods would be applied to identify the films and to study the adsorption behavior of surface species. It would be our interest to answer the question how the surface properties of the films are related to the film material and the characteristics of absorbed molecules.

Another goal of our research is to develop a new optical fiber probe by using laser Raman scattering method. The success of this research will make it possible the in situ remote monitoring of drugs in biomedical applications, chemical processes in industry, and pollutants in environments. One major problem with the probe is the background interference. For this reason, we have engaged in some basic experimental and theoretical studies on the spatial distribution of the Raman background from optical fibers and the dependence of the background intensity upon the fiber parameters including the cladding and core materials, diameter, and numerical aperture. It is our current effort to fabricate optical sensors, which are sensitive, durable and convenient.

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• J. Ma and Y. S. Li, An Optical Fiber Raman Probe with Tilted-End Fibers", Appl. Spectrosc., 51, 277-79 (1997).
• K. Wang, Y. S. Li and P. He, "In-Situ Identification of Surface Species on Molybddenum in Different Media," Electrochim. Acta, 43, 2459-67 (1998).
• Y. S. Li, J. C. Cheng and L. B. Coons, "A Silver Solution for Surface-Enhanced Raman Scattering", Spectrochim. Acta, 55A, 1197-1207 (1999).
• J. Ma and Y. S. Li, "Low Background SERS Measurements Using Unfiltered Optical Fiber Probes", Int. J. Vib. Spectrosc. 2-1, 42-49 (1998).
• B. X. Huang, K. Wang, J. S. Church, and Y. S. Li, "Characterization of Oxides on Niobium by Raman and Infrared spectroscopy", Electrochim. Acta, 44, 2571-2577 (1999).
• Y. S. Li, K. Wang, P. He, B. X. Huang, and P. Kovacs, "Surface-Enhanced Raman electrochemical Studies of Corrosion Films on Implant Co-Cr-Mo Alloy Biosimulating Solutions", J. Raman Spectrosc., 30, 97-103 (1999).
• Y. Cao and Y. S. Li, "Coupling Self Assembled Monolayers with Selective Etching Process to Construct Surface Roughness of Silver for Surface Enhanced Raman Scattering", Appl. Spectrosc., 53, 540-546 (1999).
• Y. S. Li, X. Lin, and Y. Cao, "An Application of Sol-Gel Process for the Fabrication of Surface-Enhanced Raman Scattering Active Substrates", Vibr. Spectrosc. 20, 95-101 (1999).