ASIC-based event-driven 2D digital electron counter for TEM imaging.

A two-dimensional application specific integrated circuit (ASIC) based detector, designed for X-ray protein crystallography, has been tested to determine its suitability as a direct electron detector for TEM imaging in the voltage range of 20-400 keV. Several markedly different properties of this device distinguish it from the charge coupled device (CCD) detectors: (1) the ASIC detector can be used directly under electron bombardment in the voltage range stated above, therefore requiring no scintillator screen; (2) each active pixel of the device is an electron counter and generates digital output independently; (3) the readout of the device is frameless and event driven; (4) the device can be operated at the room temperature and is nearly noise free; and (5) the counting dynamic range of the device is virtually unlimited. It appears that an imaging system based on this type of device would be ideal for low-dose TEM imaging and online diffraction observation and recording, as well as more conventional imaging, providing the many advantages of direct digital readout for almost all applications.