Development of an in situ ultra-high-vacuum scanning tunneling microscope in the beamline of the 15 MV tandem accelerator for studies of surface modification by a swift heavy ion beam

We report the installation and testing of an ultra-high-vacuum (UHV) scanning tunneling microscope (STM) in the beamline for materials science studies of the 15 MV Pelletron accelerator at the Nuclear Science Center (NSC), New Delhi. This is a new facility for in situ irradiation-induced surface modification studies, available in an accelerator laboratory. The article describes its vibration isolation, in-vacuum sample transfer and other salient features for integrating the STM to the beamline. The UHV STM is tested by obtaining atomically resolved images of highly oriented pyrolytic graphite (HOPG). In situtopographic and spectroscopic studies of defect structures produced by impact of 200 MeV Au ions on HOPG, p-type Si, and 200 MeV Ag-irradiated $Y_1Ba_2Cu_3O_{7+\delta}$ are studied