|M.Sc Student||Shentcis Michael|
|Subject||Radiation Emission Effects from Periodic Interactions|
of Free Electrons
|Department||Department of Electrical Engineering||Supervisor||Dr. Ido Kaminer|
|Full Thesis text|
The wealth of unique properties of van der Waals (vdW) materials in either bulk or single-atomic-layer form have constituted the basis of many novel physical phenomena and fundamental advances in recent years. Here, we present a new type of applications for vdW materials, showing that their layered structures make them promising candidates for the realization of tunable and monochromatic X-ray radiation sources. We present the first observation of tunable X-ray generation using free electrons passing through vdW materials. The process by which the X-ray is generated combines two different mechanisms: parametric X-ray radiation and coherent bremsstrahlung. The output photon energy is controlled by changing the incident electron energy, as well as through a new method, based on adjusting the composition and stacking of the vdW material structure.
The energy tunability of X-ray sources is a key factor in many applications such as core level spectroscopy and various X-ray imaging techniques. In terms of tunability, state-of-the-art sources include synchrotron radiation and free-electron lasers, which are based on periodic undulation of relativistic charged particles. Their operation necessitates immense resources of space, energy and safety measures, which limits their accessibility and potential for widespread use. Our study explores free-electron undulation at the ultimate small periodicity: that of the atomic crystal lattice, enabling generation of tunable, monochromatic X-ray radiation by modest electron energies that are available in relatively simple systems such as a transmission electron microscope.
The wide range of compositions and flexibility in the stacking of vdW materials provide extra versatility to the design of compact X-ray sources, allowing us to shape the output radiation through the control of the atomic lattice geometry. Specifically, we present a comparative study demonstrating the accurate dependence of the X-ray energy spectrum on different options for one of the main elements in the vdW material.
The presented results constitute a proof-of-principle for our proposal of a wider novel designer approach to precisely tailor the radiation energy spectrum and angular distribution of X-ray emission by means of designed superlattice atomic structures to realize tunable, versatile sources of X-ray radiation with a table-top footprint.