**3. Enhancement of Raman signals due to chemisorption**

This section summarizes our studies on molecular adsorption and orientation of 4,4′-bipyridine (4,4′-BiPy) and 4,4′-bipyridine *N,N′*-dioxide (4,4′-BiPyO2 ) in monolayers formed on gold thin films deposited on muscovite mica substrates using STM-TERS supported by calculated Raman tensor polarizability components. The enhancement of the Raman signals is attributed to the formation of a chemisorbed overlayer with a standing up molecular configuration [52].
