Spectral Characterization of Solid-State Photocathode Emission
thesisposted on 01.12.2020, 00:00 by Gowri D Adhikari
The goal of this thesis work is to connect the electronic properties of a crystal (i.e. its band structure) to its photoemission properties and thereby provide a roadmap for the discovery (or development) of photocathode materials with low intrinsic emittance. I have introduced a new photoemission formalism that includes the triangular barrier generated by an applied surface acceleration field Eacc of the electron gun, transverse momentum conservation, and the properties of the bulk band and vacuum states involved in the photoemission process. The direct connection between the electronic band structure of a solid-state photocathode material and it’s experimentally determined spectral photoemission properties (the mean transverse energy (MTE) and quantum efficiency (QE)) is shown for a Rh(110) photocathode at 300K. In accordance with theoretical expectations, a low effective mass (i.e. high dispersion) of the bulk emission bands is shown to be the cause of the significant reduction in the MTE of photoemission from single-crystal Hf(0001) photocathode. Further, modification of the one-step photoemission formalism allowed for an explanation of the observed spectral dependence of the MTE from a Hf(0001)/HfO2 photocathode through the inclusion of defect state emission from the native oxide layer. In addition, a record low MTE value of 6meV was observed for Cu(001) at 35K and an excess photoemission energy E of 0.11eV.