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 im aging in the voltage range of 20-400 keV. Several markedly different p roperties of this device distinguish it from the charge coupled device (CCD) detectors: (1) the ASIC detector can be used directly under ele ctron bombardment in the voltage range stated above, therefore requiri ng no scintillator screen; (2) each active pixel of the device is an e lectron counter and generates digital output independently; (3) the re adout 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 ap pears that an imaging system based on this type of device would be ide al for low-dose TEM imaging and online diffraction observation and rec ording, as well as more conventional imaging, providing the many advan tages of direct digital readout for almost all applications. (C) 1998 Elsevier Science B.V. All rights reserved.