Instrumentation for Energy-Loss Spectroscopy

Abstract

To characterize a specimen completely in terms of its inelastic scattering, it would be necessary to record the scattered intensity J(x, y, θ _x , θ _y , E) as a function of position (specified by coordinates x and y) on the specimen, as a function of the coordinates of angular deflection θ _x and θ _y , and as a function of energy loss E. Even if such a procedure were technically feasible, it would involve storing a very large amount of data, so in practice an energy-loss experiment records one of the following:

• (a) The intensity J(x, y) or J(θ _x , θ _y ), for a given value of E or a specified range of energy loss. These data correspond to an energy-filtered image or diffraction pattern, and can be obtained using either scanning-beam (STEM) or fixed-beam (CTEM) techniques, as discussed in Section 2.4.

• (b) The intensity J(E) at a given point on the specimen or, more precisely, ∫ J(E) dx dy, where the limits of integration are defined by x² + y² = d²/4, d being the diameter of the incident beam. Here were are referring to energy-loss spectroscopy (or energy analysis) carried out using a double-focusing spectrometer such as the magnetic prism (Sections 2.1.1 and 2.2).

• (c) The intensity J(y, E) for a fixed value of the spatial coordinate x, or J(θ _y , E) for a given θ _x . This involves energy analysis along a line drawn through the specimen or its diffraction pattern and requires a spectrometer which focuses only in the direction of dispersion, such as the Möllenstedt analyzer (Section 2.1.4) or the Wien filter (Section 2.1.3).