A low energy electron diffraction (LEED) instrument incorporating a delay line detector has been constructed to rapidly collect high-quality digital LEED images with low total electron exposures. The system uses a position-sensitive pulse-counting detector with high bias current microchannel plates. This delay-line detector combined with a femtoampere electron gun offers a wide range of flexibility, with electron dosing currents ranging from . Using the highest current setting and collecting counts per image, individual LEED images can be completed in with an acquisition rate of and a total electron exposure of electrons. Under the latter conditions, images can be collected in with an acquisition rate of with a total electron exposure of electrons. An angular width of 0.13° at is demonstrated, which means that domain sizes as large as can be resolved, depending on the surface quality of the crystal. The system electronics collect images with a spatial resolution of about . The dynamic range of this system is (limited only by physical memory). The construction of the detector results in a “plus”-shaped artifact, which requires that, for a given sample orientation, two images be taken at a relative angle of 45°. Identical current-voltage curves from an terminated sample, taken during several hours of exposure to the low current electron beam, demonstrate minimal electron induced H desorption.
Available from Burle Electro-Optics, Sturbridge, Mass., USA.
If the timing of the particles with respect to an external trigger signal is of interest can used as a third (time) coordinate. In this case the trigger signal is used as the common start signal.