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Details of Grant 

EPSRC Reference: EP/C009509/1
Title: The Development of a Novel Direct Electron Detector for TEM
Principal Investigator: Kirkland, Professor A
Other Investigators:
Wilshaw, Professor P
Researcher Co-Investigators:
Dr RR Meyer
Project Partners:
E.A. Fischione Instruments Inc
Department: Materials
Organisation: University of Oxford
Scheme: Standard Research (Pre-FEC)
Starts: 01 December 2005 Ends: 30 April 2010 Value (£): 524,993
EPSRC Research Topic Classifications:
Electronic Devices & Subsys.
EPSRC Industrial Sector Classifications:
Related Grants:
Panel History:  
Summary on Grant Application Form
The development of Transmission Electron Microscopes (TEM's) has made tremendous progress in the last few years and these instruments are now rouitinely used to obtain structural data from many materials. However the cameras and other detectors used for digital recording of images and spectra are still based on relatively old technology which in many cases limits the performance of these instruments (the detector gap ). The purpose of this project is to develop an entirely new type of detector that can be used to record images and spectra formed in medium voltage (up to 400kV) TEM's to overcome this detector gap. The basic problem lies in the construction and operation of current detectors used on these instruments which are based on Charge Coupled Devices (CCD's) similar to those used for optical imaging. However these CCD's cannot be directly exposed to the electron beam and must be coupled to a scintillator which converts the imaging electrons into photons and which is located between the detector and the incident electron beam. These photons are then recorded by the CCD. This indirect coupling leads to spreading of the electrons before they are detected which severely limits the resolution and sensitivity of these detectors in TEM's such that they have a detection efficiency for the smallest resolvable spacings (which are limited by the pixel size) of only 10% or worse. The active portion of the new detector that we propose to construct is related to silicon strip detectors used in nuclear physics experiments, with the important difference that it is fabricated on a thin (30-50?m) membrane of silicon with a pitch between the strips of only 10-20?m. In the active area each pixel is based on a directly fabricated diode structure which will directly detect the incident electrons and will allow much greater sensitivity and resolution. This will enable a much greater detection efficiency which we estimate will exceed 80% for the smallest resolvable spacings and this will be sufficient for single electron detection. We believe that it will be possible to construct detectors with large pixel arrays (initially 1024 x 1024 pixels are planned) at least equal to the array sizes available for CCD's using the same fabrication technology. In order to optimize the performance of this new device the readout amplifiers will be specifically designed and fabricated and will be directly bonded to the active sensor in order to reduce noise. The signal output from these will then be read directly to memory on a host computer to enable fast data transfer and this will allow high frame rates without the need for any mechanical shutter in the TEM. Overall these improved characteristics will greatly improve the performance of TEM's by providing less noisy digital images and spectra and in this way enabling materials to be studied with less radiation exposure. This is vitally important when the TEM is used to study many modern materials, such as semiconductors, catalysts and carbon based nanostructures which are often damaged in the electron beam. It will also be extremely useful for imaging biological materials which are extremely electron sensitive. For these samples the resolution of the images that can be obtained with conventional coupled CCD's is limited by the need to use very low electron doses to avoid radiation damage to the materials consequently leading to extremely noisy images. Finally, because the detector will be able to operate at higher frame rates than CCD's (we estimate that 50 full frames / s or more will be possible) due to the optimized electronics and direct memory connection it can also be used to directly observe, in situ, dynamic events that occur in many samples on these timescales.
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