Date of Award

5-2016

Document Type

Honors Thesis

Degree Name

Bachelor of Science

Department

Nanoscale Science

First Advisor

Eric Lifshin

Abstract

The efficiency of secondary electron collection by a scanning electron microscope detector is not generally known, particularly as the electric field on the detector is varied. It is often assumed that the detector collects almost all of the secondary electrons emitted from the sample. This works seeks to better understand the mechanism of secondary electron collection by the detector in order to optimize collection efficiency. The benefit of collecting more secondary electrons is the enhancement of the signal-to-noise ratio, which means better quality images can be obtained, allowing us to better understand the relationship between secondary electron images and the objects they represent. Secondary electron trajectory modeling was done to evaluate the efficiency of the current SEM detector setup. The CASINO modeling program was used to model the trajectories of secondary electrons generated within the sample to determine the initial directions and energies of the emitted secondary electrons. The SIMION modeling program was used to model the trajectories of secondary electrons emitted from the sample using a uniform distribution of initial directions and energies to determine the collection efficiency of the detector. Certain setup and operating parameters, such as the size of the detector and the potential applied to it, were studied for the optimization of secondary electron collection efficiency. A more efficient detector setup was designed using a pusher electrode to collect more secondary electrons emitted from the sample at high elevation angles. Trajectory modeling using SIMION was done to evaluate the efficiency of our improved system design, validating its performance enhancement. Although a bridge between CASINO and SIMION has not yet been made, useful data was obtained from both CASINO and SIMION simulations.

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