Tip-enhanced Raman spectroscopy

By using the techniques discussed in the previous sections of this chapter, it can be seen that the spatial resolution achievable by infrared or Raman microspectroscopy is governed by the diffraction limit shown in Equation 1.3. It is possible to 

It has been shown that localized plasmon polaritons inthe region of sharp metal tips act in an analogous fashion, giving rise to TERS. In the usual mode of operation, TERS employs a sharp metal tip, which is illuminated from the outside to create a localized light source [42]. Alternatively, silver nanoparticles have been deposited on silica or titania surfaces and a silicon tip is used [43, 44]. TERS is rapidly becoming an important technique for microspectroscopy and is described in some detail in Chapter 11 of this book. 

SSV surfaces are ideally suited for electrochemical SE(R)RS studies because of their low surface roughness, high surface enhancement, and good stability. They have been used for electrochemical SE(R)RS studies of pyridine [175], flavin [183, 

adenine [184], jj-thioglucose [189], and an osmium redox hydrogel [188], and for discrimination of DNA mutations [190, 191]. Recent work by Jose et al. has also demonstrated enhanced fluorescence on SSV surfaces [192]. 

The idea of TERS is to have a localized probe that, ideally, stimulates SERS but without perturbing the chemical system under study. This concept has been taken forward by Tian s group in recent work on silica- or alumina-coated Au nanoparticles in so-called shell-isolated nanoparticle-enhanced Raman spectroscopy, or SHINERS [208], The idea is that the thin (a few nanometers) silica or alumina coating renders the particles inert so that they can be scattered over the surface of interest to generate SERS signals without perturbing the surface chemistry, rather like a large random array of TERS tips. 

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Pettinger, B., Picardi, G., Schuster, R. and Ertl, G. (2002) Surface-enhanced and STM-Tip-enhanced Raman spectroscopy at metal surfaces. Single Mol., 5-6, 285—294. 

Ren, B., Picardi, G. and Pettinger, B. (2004) Preparation of gold tips suitable for tip-enhanced Raman spectroscopy and light emission by electrochemical etching. Rev. Sci. Instrum., 75, 837-841. 

Picardi, G., Nguyen, Q., Schreiber, J. and Ossikovski, R. (2007) Comparative study of atomic force mode and tunneling mode tip-enhanced Raman spectroscopy. Eur. Phys. J. Appl. Phys., 40, 197-201. 

Steidtner, J. and Pettinger, B. (2008) Tip-enhanced Raman spectroscopy and microscopy on single dye molecules with 15 nm resolution. Phys. Rev. Lett., 100, 236101-1-236101-4. 

Stockle, R. M., Suh, Y. D., Deckert, V. and Zenobi, R. (2000) Nanoscale chemical analysis by tip-enhanced Raman spectroscopy. Chem. Phys. Lett., 318, 131-136. 

Hayazawa, N., Saito, Y., and Kawata, S. 2004b. Detection and characterization of longitudinal field for tip-enhanced Raman spectroscopy. Appl. Phys. Lett. 85 6239 1. 

Watanabe, H., Hayazawa, N., Inouye, Y, and Kawata, S. 2005. DFT vibrational calculations of rhodamine 6G adsorbed on silver Analysis of tip-enhanced Raman spectroscopy. J. Phys. Chem. B 109 5012-20. 

Zhang, W., Yeo, B. S., Schmid, T. and Zenobi, R., (2007). Single molecule tip-enhanced Raman spectroscopy with silver tips. J. Phys. Chem. C. Ill 1733-1738. 

For overcoming the limit of light microscopy and further improvement in spatial resolution, the implementation of scaiuiing near-held microscopy (SNOM) by means of a local illumination probe is an interesting approach [33-35]. The method is based on the held enhancement in the cavity between a sharp metal dp and the sample. In combination with Raman spectroscopy, this scanning probe technique is called tip-enhanced Raman spectroscopy (TERS) and enables high-resolution spatial microscopy with a lateral resolution of 50 nm [35]. Bouhelier [36] has reviewed advances in this held. 

Results will be split into various sections the first of which will be fundamentals of hot spots. This will include a summary of the most important developments in the theory of SERS hot spots for both the EM and CT enhancement mechanisms. The second section will cover developments in tip-enhanced Raman spectroscopy (TERS) which represents the idealized hot spot. Then some issues regarding hot spots and the single molecule will be tackled such as the magnitude of enhancement required for single-molecule detection, the effects of molecular orientation with respect to the hot spot as well as the possible influence of optical forces. Sections 4.4 and 4.5 will cover developments in the imaging and fabrication of SERS hot spots, respectively, which have important implications for theoretical modeling as well control of SERS hot spots. The chapter will conclude by summarizing some of the applications of SERS hot spots that have been recently reported. 

Idealized Hot Spot Control Tip-Enhanced Raman Spectroscopy (TERS)... 

Domke KF, Pettinger B (2009) Tip-enhanced Raman spectroscopy of 6 H-SiC with graphene adlayers selective suppression of El modes. J Raman Spectrosc 40(10) 1427-1433... 

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