Electron Energy Loss Spectrometry

Abstract

Experiment 26.1a: Serial Collection Conditions. There are many more variables related to spectrum acquisition in EELS than in EDS. These variables can greatly affect the nature and quality of the data. Often when a satisfactory EELS setup is obtained for a particular application, the same settings will be used for a similar application in future experiments so that the data can be compared. Because of the large dynamic range of the EELS spectrum (very high intensities and very low intensities), some method of scaling the two regions is required This scaling may be obtained in three ways in serial EELS: by switching the PMT from analog current measurement to single electron pulse counting, by changing the gain of the PMT, or by changing the dwell time per channel of the MCA. Generally, data taken using a specific gain change are preferred; however, to reduce scintillator exposure and to speed data collection we used only the dwell time change in this experiment. The slit width adjustment is performed while observing the video monitor. For moderate energy resolution the slit is closed down until a small flat top remains on the zero loss peak. The three features in the spectrum are: the zero loss E ₀ peak at 0 eV, the carbon plasmon loss at 24 eV, and the carbon K edge at 284 eV. See Figure A26.1a.