A parallel acquisition charged particle energy analyser using a magnetic field

Abstract

A new form of charged particle energy analyser is proposed. It is broadly based on the 180°magnetic spectrograph, but is intended to detect charged particles moving out of the dispersion plane with a helical motion. The analyser has the capability to acquire charged particle energy spectra over a large energy range, similar to those acquired in Auger electron spectroscopy, ca. 2500 eV and large angular range, up to 90°, in parallel. These conditions are more favourable for surface analysis by electron spectroscopy at high vacuum, where for example an electron energy resolution of 0.2% to 0.5% is typical. Expressions showing how the landing positions of the charged particles on the detector vary as a function of energy and polar take off angle are determined as well as the conditions for optimum energy resolution at a range of polar take off angles. The equations reveal that in general, the device obtains the highest resolution at angles of revolution greater than 180°. The design is simple and could be easily put into practice using available material and technologies and be used to analyse the energies of electrons emitted from a sample placed in a scanning electron microscope. It can be made to function with a primary electron beam of any desired energy and could fit in to the small space between the sample and the end of an electron column. However, the device is difficult to retrofit into existing SEMs and ideally an SEM column needs to be designed to work in association with the analyser. The direction of the magnetic field of the analyser is coincident with the axis of the electron gun so that the primary beam is little influenced by the magnetic field and symmetry can be maintained in the primary beam electron column. Because the device is intended to acquire electron spectra in parallel, any movement of the primary beam on the sample because of a ramping field in the analyser is avoided. The field of view and the effect of the analyser upon the operation of the SEM are discussed. Spectra including elastic and Auger peaks reveal an energy resolution of~4 eV at 900-eV electron energy. Copyright © 2016 John Wiley & Sons, Ltd.Keywords: auger; parallel; analyser; spectrometer; magnetic; electron energy spectrum IntroductionThe idea of letting charged particles fly in a semicircle in a uniform magnetic field in order to study them as a function of energy first originated from Danycz [1] working in Mme Curies laboratory (see [2] for an overview of the early history of nuclear physics). The idea was put into practice shortly after by Rutherford and Robinson [3] . Sadly Danycz was unable to fulfil his early work as he died on the battlefields of France whilst serving in the French Army in 1914. The spectrometer had only single focussing of first order but high resolving powers could be obtained easily and a wide energy range could be recorded simultaneously. However, this advantage is lost when a detector capable of detecting only a narrow energy range (e.g. a Geiger-Muller (G-M) tube) is used [4] . The aperture h...

Diagnostic Techniques for Electrical Discharge Plasma Used in PVD Coating Processes

“…To determine the parameters of the ionic component, a charged particle energy analyzer (multigrid probe) was used [60][61][62][63][64][65]. Figure 1 exhibits the method for measuring the energy of charged particles using a retarding potential energy analyzer [66].…”