**4. Enhancement of Raman signals due to halogen overlayertemplated crystal growth**

This section describes particular surface chemistry leading to the growth of metal-organic surface crystals in the presence of halogen overlayer. The crystals were grown on an Au surface from ethanolic solutions of 4,4′-BiPy, in the presence of HCl. STM-TERS and ordinary Raman spectroscopy were used to reveal details of a crystal growth [55].
