SUPPRESSIVE INFLUENCE OF STEPS ON A PHASE-TRANSITION OF THE SI(001) SURFACE

We have studied an order-disorder phase transition of a vicinal Si(001 ) surface from a 2 X 1 to a c(4 X 2) structure using low-temperature s canning tunneling microscopy (STM). The order parameter for the c(4 X 2) structure is derived from the Fourier transform of the atomically r esolved STM images in the 65-300 K temperature range, The order parame ter on the A terrace bounded with an S-A step is found to reach only 0 .7, even at 65 K, while the c(4 X 2) structure is almost complete on t he B terrace bounded with an S-B step. In the STM images at 65 K, dime rs at the lower side of the S-A step still appear symmetric, resulting in an order-parameter reduction of the B terrace. [S0163-1829(98)5130 8-2].