A gallium arsenide hybrid-pixel counting detector for 100 keV cryo-electron microscopy.

The recent interest in 100 keV cryo-electron microscopy has created a demand for specialized detectors that maximize information per unit dose while remaining cost-effective. We present a hybrid-pixel electron counting detector system tailored for cryo-electron microscopy applications using 100 keV electron energy. The demonstrator uses a 500 μm-thick, chromium-compensated gallium arsenide (high-Z) sensor with a 36 μm pixel pitch arranged in a seamless 1266 × 1057 matrix. Its low-noise front-end electronics achieve a threshold energy as low as 2.5 keV and include an in-pixel hit digitization mechanism. The matrix is read out at a speed of 7.2 kfps and has a counter depth of 1 bit, allowing for an incoming rate of 28 e/s/pix at 5% coincidence loss. The imaging performance is evaluated in standard counting and super-resolution acquisition modes. Thanks to a custom-developed super-resolution algorithm, the detective quantum efficiency at zero-frequency amounts to 0.96 and at the physical Nyquist frequency to 0.56, resulting in an effective pixel size of 27.5 μm. Experimental data are complemented and critically compared with Monte Carlo simulations and analytical models.