Event-based hyperspectral EELS: towards nanosecond temporal resolution

TL;DR

This paper introduces an event-based hyperspectral EELS technique using a Timepix3 detector, enabling rapid spectral imaging at the same rate as single-channel detectors, reducing sample damage and improving temporal resolution.

Contribution

The work presents a novel event-based hyperspectral EELS method utilizing a Timepix3 detector with TDC lines, allowing high-speed spectral imaging without additional cost.

Findings

Achieved hyperspectral imaging at the same rate as single-channel detectors.

Demonstrated decomposition of calcite into CaO and CO₂ under electron irradiation.

Reduced sample damage by faster spectral acquisition.

Abstract

The acquisition of a hyperspectral image is nowadays a standard technique used in the scanning transmission electron microscope. It relates the spatial position of the electron probe to the spectral data associated with it. In the case of electron energy loss spectroscopy (EELS), frame-based hyperspectral acquisition is much slower than the achievable rastering time of the scan unit (SU), which sometimes leads to undesirable effects in the sample, such as electron irradiation damage, that goes unperceived during frame acquisition. In this work, we have developed an event-based hyperspectral EELS by using a Timepix3 application-specific integrated circuit detector with two supplementary time-to-digital (TDC) lines embedded. In such a system, electron events are characterized by their positional and temporal coordinates, but TDC events only by temporal ones. By sending reference signals from the SU to the TDC line, it is possible to reconstruct the entire spectral image with SU-limited scanning pixel dwell time and thus acquire, with no additional cost, a hyperspectral image at the same rate as that of a single channel detector, such as annular dark-field. To exemplify the possibilities behind event-based hyperspectral EELS, we have studied the decomposition of calcite (CaCO$_3$) into calcium oxide (CaO) and carbon dioxide (CO$_2$) under the electron beam irradiation.