Prospective scintillation electron detectors for S(T)EM based on garnet film scintillators

Abstract

The performance of a scintillation electron detector for a scanning electron microscope and/or a scanning transmission electron microscope (S(T)EM) based on new epitaxial garnet film scintillators was explored. The LuGAGG:Ce and LuGAGG:Ce,Mg film scintillators with chemical formula (Ce0.01Lu0.27Gd0.74)3–wMgw(Ga2.48Al2.46)O12 were prepared and their cathodoluminescence (CL) and optical properties were studied and compared with the properties of current standard bulk single crystal YAG:Ce and YAP:Ce scintillators. More specifically, CL decay characteristics, CL emission spectra, CL intensities, optical absorption coefficients, and the refractive indices of the mentioned scintillators were measured. Furthermore, electron interaction volumes with absorbed energy distributions, photomultiplier (PMT) photocathode matchings, modulation transfer functions (MTF), and the photon transport efficiencies of scintillation detectors with the mentioned scintillators were calculated. A CL decay time for the LuGAGG:Ce,Mg film scintillator as low as 28 ns with an afterglow of only 0.02% at 1 μs after the e‐beam excitation was observed. As determined from calculated MTFs, the scintillation detectors with the new film scintillators lose contrast transfer ability above 0.6 lp/pixel, while the currently commonly used YAG:Ce single crystal scintillators already do so above 0.1 lp/pixel. It was also calculated that the new studied film scintillators have an 8% higher photon transfer efficiency, even for a simple disk shape compared with the standard bulk single crystal YAG:Ce scintillator. The studied LuGAGG:Ce,Mg epitaxial garnet film scintillators were evaluated as prospective fast scintillators for electron detectors, not only in S(T)EM but also in other e‐beam devices.

Overview of S(T)EMelectron detectors with garnet scintillators: Some potentials and limits

“…Other results can also be found in our previous papers (Schauer et al, 2017;Schauer et al, 2019). A comparison of the garnet CL intensities and maximum CL emission wavelengths is shown in Table 2.…”

“…One standard Ce 3+ activated yttrium aluminum garnet (YAG:Ce-Y 3 Al 5 O 12 :Ce 3+ ) single crystal scintillator and five Ce 3+ activated epitaxial garnet film scintillators were included for investigation in this paper. The YAG:Ce scintillator, which is often used as a reference crystal in our laboratory (Schauer et al, 2019), was grown with the Czochralski method and subsequently cut and polished into a disc with a diameter of 10 mm and a thickness of 1 mm in Crytur Ltd. The electron impact side of this scintillator was perfectly polished, while the light exit side was matted.…”

“…The sample, hereinafter referred to as "LuGdGaAG:Ce, high Ce" is a highly Ce 3+ activated lutetium gadolinium gallium aluminum garnet film. This film scintillator is also presented as LuGAGG:Ce in other papers (Chewpraditkul et al, 2020;Schauer et al, 2019;Schauer, Lalinsky, Kucera, Lucenicova, & Hanus, 2017).…”

“…The thicknesses of both films were about 16 μm. More detailed information about both samples is in our previous paper (Schauer et al, 2019).…”

“…However, the electron trajectories have little predictive value for the energy distribution of absorbed electrons, and they are unusable to determine losses due to electron passages through the solid. Nevertheless, simulating the longitudinal distribution of absorbed electrons towards the depth of the material is very useful for assessing the efficiency of a scintillation detector (Schauer et al, 2019). Therefore, the longitudinal distribution simulations were performed for all three components of the scintillator, that is, for the conductive coatings, the scintillators, and their substrates, if necessary.…”