Direct ray tracing for low energy electron microscopy

This thesis is concerned with the accurate simulation of electron trajectory paths in electron optics. In particular, it investigates the use of a direct ray tracing method that employs the Cash-Karp 5th order Runge-Kutta technique in combination with a Fourier series fit to axial magnetic/electric field distributions. The direct ray tracing method was used successively to improve the design of several electron optical systems. It was used to calculate the aberration probe size of a low voltage scanning electron microscope mixed field objective lens, for which conventional methods of paraxial-perturbation breakdown. It was also used to plot through-the-lens scattered secondary electrons in such systems, simulating their radial current distribution at a rotationally symmetric detector plane. Lastly, the direct ray tracing method was used to redesign the drift-tube in a dynamic chromatic correction scheme for Photoemission Electron Microscopy (PEEM). The performance of this system was simulated in detail, and compared with the alternative aberration correction method based upon the use of a tetrode mirror.

Author dc:creator

• DING YU

• Direct ray tracing; Low voltage SEM; Electron spectroscopy; Time-of-flight emission microscope; Dynamic chromatic aberration correction; Drift tube