Date of Award
Doctor of Philosophy
Materials Science and Engineering
David C. Joy
Philip D. Rack, Joseph E. Spruiell, Anthony J. Pedraza, Harry M. Meyer
Slow secondary electrons (SEs) (E<50 eV) are those emitted from a sample as the result of bombardment by energetic particles. They are the most important signal source for SEM and for other advanced microanalysis techniques. SE yield δ and spectrum N(E) are the two important parameters evaluating the capability of a sample on producing SEs and the energy distribution of SEs generated from the sample respectively. Measuring δ and N(E) is not easy since SEs are easily affected by sample surface condition and by experimental configuration. Though SE has been studied since its first find in 1902, experimental date of it are inconsistent and unsystematic. Theoretical models on the SE production are not well established.
To better understand the secondary electrons, an optimization of a scattered experimental SE yield database was carried out by fitting the data to a semi-empirical universal curve and by a Monte Carlo simulation. The profiles of SE yield versus beam energy and the values of SE excitation energyε and mean SE escape depthλ were generated for 44 elements. An atomic shell filling effect was found on the maximum SE yields and the corresponding beam energies.
To obtain more accurate and systematic SE yield data, a novel experimental method by collecting electron spectra on an AES instrument (PHI 680 SAN) equipped with a cylindrical mirror analyzer (CMA) was developed. The principles of the CMA and the micro channel plate (MCP) in analyzing and multiplying electron signal were studied. The efficiency of the PHI 680 SAN in response to the electron energy in the range of 0~3200 eV was deduced to calibrate intensity of any as received spectrum.
Measurement on elements and the Cr-W and Cu-Au binary alloys were conducted. The measured SE yields were 50% lower than the optimized values but showed the atomic shell filling effect as expected. Both the SE and BSE yields of the binary alloys showed linear relationship with atomic percent of specimen constituents. Linear synthesis of the elemental SE spectra of the Cr-W alloys agreed well with the measured.
Lin, Yinghong, "A Study of the Secondary Electrons. " PhD diss., University of Tennessee, 2007.