RHEED-ISS STUDY ON THE ZR-O W(100) SURFACE AT HIGH-TEMPERATURE/

The surface structures of Zr-O/W(100) (oxygen processing at similar to 1700 K in an oxygen partial pressure of similar to 3 x 10(-4) Pa foll owed by subsequent evacuation to similar to 10(-5) Pa at similar to 17 00 K) have been studied by ISS and RHEED. The results have revealed: ( i) oxygen processing induces complete diffusion of 3D islands of an an omalous fee-phase Zr into the W substrate. (ii) Subsequent evacuation after the oxygen processing results in surface segregation of Zr atoms onto the surface, which aligns Zr atoms to form a p(1 x 1) structure at similar to 1700 K on the topmost atomic layer of the Zr-O/W(100) su rface. (iii) This atomic overlayer shows the reversible phase transiti on of the surface structure, i.e. the p(1 x 1) structure at similar to 1700 K changes to the c(2 x 4) + c(4 x 2) structure below similar to 1000 K, and vice versa.