NON-ARRHENIUS BEHAVIOR OF SURFACE-DIFFUSION NEAR A PHASE-TRANSITION BOUNDARY

We study the non-Arrhenius behavior of surface diffusion near the seco nd-order phase transition boundary of an adsorbate layer. In contrast to expectations based on macroscopic thermodynamic effects, we show th at this behavior can be related to the average microscopic jump rate, which in turn is determined by the waiting-time distribution W(t) of s ingle-particle jumps at short times. At long times, W(t) yields a barr ier that corresponds to the rate-limiting step in diffusion. The micro scopic information in W(t) should be accessible by scanning tunneling microscopy measurements.