Event-based hyperspectral EELS: towards nanosecond temporal resolution

Abstract

The acquisition of a hyperspectral image is nowadays a standard technique used in the Scanning Transmission Electron Microscope (STEM). It relates a spatial position of the electron probe with the spectral data associated to 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 (ASIC) detector with two supplementary time-to-digital (TDC) lines embedded. In such a system, electron events are characterized by their positional and temporal coordinates, while 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 arbitrary scanning pixel dwell time and thus perform, with no additional cost, a hyperspectral image at ADF rate. To demonstrate our event-based hyperspectral EELS, we have studied the decomposition of calcite (CaCO 3 ) into calcium oxide (CaO) under the electron beam irradiation.

Cavity-mediated electron-photon pairs

“…Hereby, an external synchronization of the electron arrival time and photon counts at the SPAD becomes possible using the joint global time stamp of the detector and TDC channels. Technologically, event-based imaging in electron microscopy enables new experimental concept, including background suppression in X-ray spectroscopy [66], continuous illumination picosecond imaging [72] and dose-optimized high-speed STEM [73,74].…”