Investigation of Nonbiological Samples with TERS

In the last one and a half decade, the broad scope of application of TERS was demonstrated on many different samples. In this chapter, selected TERS investigations of nonbiological samples are shown followed by biological specimen. For a quick overview, representative samples and the associated references are listed in Table 11.1. 

In particular, carbon nanotubes (CNTs) are frequently investigated by TERS. The enhancement of the characteristic G band (around 1580 cm ) and D band (around 1330 cm ) is a major objective of TERS investigations. A nice example for the suitability of TERS in this field is the intensity ratio of G/D. This value can be considered as a quality indicator of CNTs (high quality CNT G/D 100), which can be nicely visualized with TERS. In case of defects, the D band intensity increases so that the G/D ratio gets smaller allowing conclusions on the CNT quality. The lateral resolution in these experiments was at least around 15 nm [20]. 

Another very prominent molecule for TERS measurements is malachite green isothiocyanate (MGITC). In a comparative study on CN ions and MGITC, it was demonstrated that enhancement factors of around 10 could be achieved [16]. 

In this context, different refractive indices of underlying substrates were tested in TERS experiments and differences in the enhancement of the Raman signal 

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