A 2-dimensional detection system for Electron Energy Loss Spectroscopy

Abstract

A UHV-compatible parallel and serial detection system for electron energy-loss spectroscopy (EELS) has been developed for the VG HB501 field-emission scanning transmission electron microscope (STEM) using a 2-dimensional detector. As pointed out previously the charge coupled devices (CCD) available commercially are vastly superior, in terms of read-out noise, to linear photodiode arrays which are currently used for parallel EELS detection. This feature, together with the ability of operating as an imaging and storage device, makes the 2-dimensional CCD array an attractive choice for parallel EELS and low light-level imaging applications.The system reported here (Fig. 1) is an extension of the VG ELS501 sector magnetspectrometer used for serial EELS with many STEMS. It uses one quadrupole lens to magnify the energy-loss spectrum over a range of 2 to 0.1 eV per detector element. An electromagnetic deflector steers the spectrum to one of three YAG scintillators. Two of these scintillators with suitable masks are used for parallel EELS detection; the third is used for serial EELS and energy filtered STEM imaging via a lightguide and photomultiplier system by scanning the beam across a variable slit as in ELS 501 systems.