Position-sensitive detector performance and relevance to time-resolved electron energy loss spectroscopy

Abstract

The use of position-sensitive detectors (PSDs) has become common in many spectroscopies. The increased signal provided by the parallel detection of many spectral elements affords increases in sensitivity and/or time resolution. Recently, the use of a PSD to increase the temporal resolution of an electron energy loss (EEL) spectrometer has been demonstrated in our laboratory. This article summarizes the present development of EEL spectrometers and then presents a detailed review of four classes of PSDs in the context of their potential application to EEL spectroscopy (EELS). The four classes considered are (a) discrete channel detectors, (b) coincidence array detectors, (c) charge division detectors, and (d) optical detectors imaging phosphor screens. All four designs, as typically implemented, utilize microchannel plates (MCPs) as spatially imaging electron multipliers. The performance of MCPs is reviewed and the constraints that MCP behavior at the high count rates achievable in EELS places on acceptable PSD performance are outlined. The inability of present MCPs to maintain saturation gain at count rates above 1 MHz mm−2 implies that the PSD must tolerate significant gain reduction in the electron multiplier. The possibility of eliminating the MCP and using an electron-bombarded silicon gain mechanism is proposed. Such a device could, in principle, support count rates in excess of 100 MHz/channel, providing an order of magnitude increase in performance over the best existing detectors.