Secondary electron emission from MgO protective layer by Auger neutralization of ions

Abstract

A theoretical model of the secondary electron emission yield (γ) from a MgO layer is developed based on the Auger neutralization of ions, resulting in an analytical expression of γ in terms of the ionization energy Ei for the density of states in the valence band, being an exponentially decaying function of the energy deviation from the band characteristic energy of 7.88 eV. The analytical expression recovers the previously known empirical formulation of γ∼(Ei−2φ) for the work function φ. Results of the theoretical model agree well with the measured data in terms of the data trend.

Measurement of valence band structure in arbitrary dielectric films

“…The stimulated electron labeled as 2 in Fig. 2 gains kinetic energy of E k = E i À a À b, and thus escapes the dielectric surface [18] if E k > 0, becoming an electron emitted from the film. For convenience in the subsequent analysis, the dimensionless energy variables x and x 0 are correspondingly defined as x = (a À e 0 )/x and x 0 ¼ ðb À e 0 Þ=x, where x is the characteristic energy spread of the electrons in the valence band.…”

“…Fig. 1 shows the current signal, represented by the solid squared curve and captured by a picoammeter connected to the grounded copper pad in FIB [18] in which the collector voltage varies from À6 V to +9 V. Neon ions with E i = 21.56 eV are used in Fig. 1 and the dielectric film is an MgO layer that is 7000 Å in thickness.…”

“…The profile of the distribution in energy of the emitted electrons can be measured and rescaled so that Auger self-convolution arises, revealing the detail structure of the valence band, including all of the necessary band information. A focused ion-beam (FIB) system [18] was constructed. The electrons are emitted from the dielectric films due to the Auger neutralization mechanism, if a noble gas ion with ionization energy E i approaches the surface of a dielectric film in FIB system.…”

Scanning transmission imaging in the helium ion microscope using a microchannel plate with a delay line detector

“…In the present form of the detector, we use two MCPs, each with a 50 mm by 50 mm square active area, stacked and rotated by 90° to each other with a gap of 100 μm between them. The first MCP has a magnesium oxide coating to increase the SE yield [ 37 ]. The MCP pores have a diameter of 25 μm and a center-to-center spacing of 32 μm.…”

Auger neutralization and ionization processes for charge exchange between slow noble gas atoms and solid surfaces

“…With suitable modifications these methods can be applied to the characterization of oxidized surfaces, a problem of renewed interest nowadays [171,172,173,174]. Further progress in this field requires, first, realistic "ab initio" calculations for the interaction energies of different atomic terms in the proximity of the surface and, second, a detailed evaluation of the surface response function by improving on the simple jellium model with the inclusion of the band structure of the surface.…”