In this thesis I present my research on the physics of some important processes in the production of thin films. I studied physical vapour deposition (PVD) and thin film modification through ion... Show moreIn this thesis I present my research on the physics of some important processes in the production of thin films. I studied physical vapour deposition (PVD) and thin film modification through ion bombardment using a newly developed, high-speed scanning tunneling microscope (STM). The instrument has the special property that it can be tilted and azimuthally rotated to allow atom or ion beams a direct line-of-sight access to the region of the surface that is being imaged by the STM tip. With the microscope I have recorded STM movies (available as supplementary material) that offer a unique insight into the atomic surface processes that occur during thin film growth and ion beam sputtering. The __real-time STM__ was applied to the study of some key steps in the fabrication of Mo-Si multilayer optical coatings. I have investigated the non-idealities of these optics, i.e. the alloying of Mo and Si during deposition and the surface roughness formation of a deposited layer. Furthermore, I successfully used the STM to find a possibility to smooth a rough Mo layer after its deposition by means of ion bombardment. Show less