The Use of Correlation Techniques in EELS

Abstract

The signal rate which is attainable in analyzing small volumes of material in the electron microscope is essentially proportional to the cross-section of the process and the number of atoms probed. When analyzing nanometer scale volumes, small concentrations of material or processes of low probability, the experimenter is always faced with spectra of low signal-to-noise (i.e., poor statistics). Provided that the signal rate is larger than the background counting rate due to the detection system, the main approach to increasing statistics (if the probe current density has been maximized) is just to effectively count for a longer period of time.There are, however, several problems with implementing long counting times on nanovolumes. One is the stability of the incident beam position which effectively limits the analyzed volume. The other is the energy stability of the incident electron beam. For systems with cold field emission sources which are capable of <0.3eV natural energy spreads, the energy stability of the beam is as stringent for EELS as for imaging if one wishes to take full advantage of the narrow energy distribution of the source.