The LEED Instrument Response Function

Abstract

The effect of the measurement system is usually ignored in the interpretation of LEED patterns. This effect can, however, be treated analytically through the use of the instrument response function, which represents the intensity function the instrument would record for a perfect surface. We have measured the response function for a particular LEED system using a double aperture Faraday collector and have identified the various experimental factors which determine its detailed functional form. The Fourier transform of the response function defines the range over which the instrument behaves as an interference detector. The effect of long range correlations on the pattern is suppressed by this finite range, with the result that fairly untidy surfaces may not be easily distinguished from those which are nearly perfect.