Fabrication and characterization of Periodically Bent Germanium Crystals as innovative gamma-ray sources

Periodically Bent Crystals (PBCr) are single crystals with regularly bent crystallographic planes. With appropriate sinusoidal lattice deformation and high crystal quality, they can potentially be used as Crystalline Undulators (CU) in synchrotrons by harnessing high-energy positron channeling. This process generates crystalline undulator radiation with energies ranging from hundreds of keV up to tens of MeV, representing a potential new gamma-ray source with high brilliance in an energy range not accessible by current magnetic field-based sources. In this thesis, PBCrs were fabricated by creating epitaxial stressor films on the surfaces of a Germanium (Ge) crystal. Specifically, Ge-PBCrs were fabricated through the surface Germanium-Antimony (Ge-Sb) periodic alloying. The fabrication process was comprehensive, covering design, microfabrication, and characterization stages. A starting Ge wafer was chemically-mechanically polished and cut to create the desired substrate. On the surfaces, a lift-off procedure was performed to deposit metallic Sb periodic strips, which were introduced into the Ge bulk using pulsed laser melting, forming the epitaxial Ge-Sb alloy pattern. All these procedures were optimized, and various characterization techniques were employed to verify the success of the processes. In conclusion, Ge-PBCr prototypes were successfully fabricated based on two different designs.