Comparison of detection limits of direct-counting CMOS and CCD cameras in EELS experiments

Mitsutaka Haruta; Jun Kikkawa; Koji Kimoto; Hiroki Kurata

doi:10.1016/j.ultramic.2022.113577

Comparison of detection limits of direct-counting CMOS and CCD cameras in EELS experiments

Ultramicroscopy. 2022 Oct:240:113577. doi: 10.1016/j.ultramic.2022.113577. Epub 2022 Jun 14.

Authors

Mitsutaka Haruta¹, Jun Kikkawa², Koji Kimoto², Hiroki Kurata³

Affiliations

¹ Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan. Electronic address: haruta@eels.kuicr.kyoto-u.ac.jp.
² Research Center for Advanced Measurement and Characterization, National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan.
³ Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan.

PMID: 35728341
DOI: 10.1016/j.ultramic.2022.113577

Abstract

The noise performance and the detection limits of a direct-counting complementary metal-oxide semiconductor (CMOS) K2 camera and a charge-coupled device (CCD) camera in electron energy loss spectroscopy (EELS) experiments were evaluated. In the case of a single spectrum acquired at the shortest dwell times (2.5 ms for K2 and 1 μs for CCD), the detection limit, defined as three times the standard deviation of the spectral noise (3σ), was very low (1 e^-/channel) in the counting-mode spectrum acquired with the K2 camera compared with that acquired with the CCD camera (5 e^-/channel). By contrast, the spectral noise of the K2 camera changed depending on the dwell time because of the multiple read-outs related to its fixed frame rate (400 fps). The spectral noise of the K2 camera was greater than that of the CCD camera when the dwell time was longer than ∼30 ms. Thus, the CCD camera was found to still be useful when detecting a very small number of electrons using a long acquisition time. In the case of an accumulated spectrum obtained by acquiring 10,000 spectra after subtracting the ultra-high-quality dark reference signal, the detection limits per read-out were ∼0.016 and ∼0.025 e^-/channel/read-out for the K2 and CCD cameras, respectively. Because both cameras have advantages and disadvantages with respect to their detection limit, speed, and dynamic range, their proper use is important.

Keywords: CCD; Direct detector; EELS.