CRITICAL PROPERTIES IN 2-DIMENSIONAL ORDER-DISORDER PHASE-TRANSITIONS- EXPERIMENTAL-DETERMINATION OF THE EXPONENT-ALPHA AND EXPONENT-ETA BY INTEGRATING METHODS

Integrating methods in low-energy electron diffraction (LEED) -turning the instrument to low resolution in k(parallel to)- can reliably be u sed to study critical properties of continuous two-dimensional phase t ransitions and to determine critical exponents alpha and eta. We perfo rmed systematic tests of the conditions under which an energy-like pow er dependence of the diffracted intensity of superstructure beams can be observed in order-disorder phase transitions of adsorbed atomic lay ers belonging to 3- and 4-state Potts universality classes. We further show that in the limit k xi much greater than 1 the exponent eta can be determined reliably both below and above T-c using integrated inten sities.