Surface segregation of zirconium in oxygen-processed [formula omitted] system at high temperatures

Abstract

The behavior of Zr-atoms on W(111) surface associated with oxygen adsorption at different sample temperatures has been studied by Auger electron spectroscopy (AES), ion scattering spectroscopy (ISS) and measurement of relative change of the workfunction which was assessed from the shift of the onset of secondary electron energy distribution (Δф). The results have revealed: (1) adsorption of Zr onto the W(111) surface followed by the elevation of sample temperature up to 1750 K in an oxygen partial pressure of 2.7 × 10−4 Pa induces drastic diffusion of Zr-atoms into the W(111) substrate, resulting in a high work function of ∼ 4.9 eV; (2) keeping the sample temperature at 1750 K, simple evacuation of the system to 2.7 × 10−6 Pa has resulted in the segregation of Zr-atoms onto the surface. However, the W- and oxygen-atoms were also observed by ISS, indicating that the surface was not fully covered with Zr-atoms in contrast with the previous results for ZrW(100) system, resulting in a work function of ∼4.8 eV; (3) the ISS studies under different incident angles have indicated clearly that the W intensity increases with increasing incident angle, suggesting that the segregated Zr-atoms are slightly embedded in the outermost atomic layer of tungsten.