Speaker
Description
The novel ASIC Ermine is a photon counting chip specifically designed for laboratory applications. It has an active area of 19.2mm x 14.4mm, organized in a matrix of 256 x 192 pixels with a 75um pitch. The ASIC’s two-side buttable design allows for larger sensitive areas when wider angular coverage is needed. The readout electronics allows for both positive and negative signal polarity, making it compatible with standard silicon sensors (hole collection) and most high-z sensors (electron collection).
One of the advantages of photon counting devices is to provide energy discrimination by means of adjustable energy thresholds [1,2]. The ASIC signal readout is optimized toward low-noise and, while still capable of reaching a high count rate up to 1Mcounts / px /s, achieves an energy resolution of less than 600eV (FWHM at 8keV), which allows it to effectively suppress the undesired fluorescence background coming from the samples that can mask weak diffraction peaks. A typical example would be X-Ray Diffraction (XRD) using a Cu anode (Cu Kα 8.0keV) to investigate iron-containing samples (Fe Kα 6.4keV and Kꞵ 7.1keV).
So far we investigated the performance with a silicon sensor, which is perfect for covering the energy range from 4.5keV to 9.3keV. However, other laboratory applications like PDF (Pair Distribution Function) [3] require radiation with higher energies. Most prominently Mo Kα (17.5keV) and Ag Kα (22.2keV) radiation are used, for which the quantum efficiency of silicon drops down significantly and a high-z sensor material is needed. Another figure of merit is the spatial resolution, which is paramount in wavelength dispersive experiments like von Hamos X-ray spectroscopy to better resolve finely spaced spectral features.
At DECTRIS there is an on-going effort for developing different sensors that will target these experimental needs and the Ermine ASIC is the ideal test platform for them.
In this work we will present the experimental results obtained with sensors developed by the DECTRIS R&D, including different geometries of rectangular pixels for improved spatial resolution, designed with both p-on-n silicon and n-on-p silicon, and GaAs sensor for optimal quantum efficiency at higher energy range.
References:
[1] P. Kraft et al. J. Synchrotron Rad. 2009, 16, 368.
[2] C. Brönnimann C and & Trüb P. In Synchrotron Light Sources and Free-Electron Lasers, 2016, 995.
[3] Sabrina L. J. Thomae et al. Rev. Sci. Instrum. 90, 043905 (2019)