COSEGREGATION-INDUCED PHASE-TRANSITION ON FE-3-PERCENT-V-N(110) - THEFORMATION OF A VN SURFACE COMPOUND

We report a cosegregation-induced phase transition of first order on ( 110) oriented Fe-3%V-N single crystals. Cosegregation has been investi gated in detail applying Auger electron spectroscopy (AES) and low ene rgy electron diffraction (LEED). The formation of a two-dimensional VN surface compound has been studied in the temperature range from 570 d egrees C to 740 degrees C. The stoichiometry of the VN surface compoun d corresponds to VN1.0+/-0.1 as is determined by quantitative evaluati on of Auger peak height ratios. After short annealing times streaking LEED pattern are observed indicating partial disorder in one direction of the direct space. Upon sufficient annihilation of surface defects sharp (4 x 1) pattern appear. We propose a missing and added row model for the VN surface compound on the Fe-3%V-N(110) substrate surface. T he findings of the present work indicate the cosegregation-induced mor phological instability of the Fe-3%V-N (110) surface.