TEMPERATURE-DEPENDENCE OF W(100) LEED INTENSITIES

The temperature dependence of W(100) LEED intensities has been measured by a very fast television method with automatic thermal diffuse background subtraction for both the (1 × 1) and c(2 × 2) surface structure phases. In contrast to the usual kinematic interpretation the dynamical theory is used to evaluate the surface Debye temperature θs which leads for the high temperature (1 × 1) phase to a value of θs = 210 ± 40 K and for the low temperature c(2 × 2) phase to a value of θs = 400 ± 100 K. The considerable difference is possibly a consequence of a soft phonon. Experimental I(E) curves measured with the same fast method were compared with theoretical spectra calculated with the RFS method. The application of the R-factor formalism leads to 10 ± 2% surface layer contraction in case of the (1 × 1) structure phase. (This value also holds for the c(2 × 2) structure.) The 1 2 1 2 beam half width decreases continuously during the structure phase transition between 350 and 150 K. It indicates a growth of c(2 × 2) domains with decreasing temperature. The average domain size is about 60 Å at 250 K. The corresponding total work function change amounts to 50± 5 meV. © 1979.