Near-Field Nanospectroscopy and Tip- Enhanced Raman Spectroscopy (TERS)

This chapter covers state-of-the-art development and results in tip-enhanced Raman spectroscopy (TERS) as a significant configuration of near-field nanospectroscopy. The chapter develops by drawing attention to the importance of TERS with a background motivation of the specific research area. Subsequently, the development of TERS instrumentation is discussed in detail, stretching its limit in terms of spatial resolution using atomic force microscopy (AFM) and scanning tunneling microscopy (STM) to circumvent the diffraction limit. To understand various chemical processes precisely, TERS studies in high- and ultrahigh-vacuum (UHV) for AFM- and STM-assisted measurements are elaborated with up-to-date information, including the study of a single molecule. Finally, low-temperature UHV-STM is described for molecular as well as submolecular level measurements using TERS. In describing various applications of TERS, the chapter elaborates on studies of inorganic materials of strategic importance, e.g., strained Si and quantum dots, along with other layered MXenes and Van der Waal bonded materials. An important area of molecular switching is also reported for the chemical identification at the nanoscale using TERS. The study of biomolecules is the most challenging yet most fascinating application of TERS, which is used for both DNA and RNA sequencing, including the study of bacteria and viruses. TERS being chemically sensitive, is also used for the understanding catalytic properties of plasmonic, bimetallic, and organometallic phthalocyanine materials. Tip-enhanced fluorescence microscopy is specifically reported for studying fluid cracking catalysts. The nano-spectroscopic study is further extended to imaging 2D transition metal dichalcogenide stacking as near-field second-harmonic generation efficiency is greatly enhanced by excitons. Finally, the chapter concludes with its important application of tip-enhanced photoluminescence measurements for understanding excitonic properties of semiconductors as luminescence characteristics are essentially confined to a few nm or sub-nm region owing to compositional variation, presence of defects or impurities, and strain.