Phase diagram of chemisorbed oxygen layer on the tungsten (112) surface

The adsorption of oxygen on the W(112) surface results in an ordered $p(2\mathrm{}\times 1)$ structure which exists over a wide range of temperature and submonolayer coverage. By analyzing the low-energy electron diffraction angular profile and peak intensity of the half-order beams as a function of coverage ($\ominus$) and temperature ($T$), the growth and disordering of the overlayer were studied. The order-disorder transition temperature ($T_c$) depends on the coverage with the highest $T_c$ obtained at a coverage of 0.5 monolayer (ML). From the coverage-dependent transition temperatures the phase diagram ($T-\ominus$) was obtained. Oxygen atoms are only partially mobile at the dissolution temperature of the first-order phase boundary. Adatom-adatom interactions were estimated from the phase diagram. The measured angular width at room temperature also depends on coverage. With the use of an island-size-broadening model, the smallest islands are estimated to be less than 20 Å in length, and the largest islands occur at 0.5-ML coverage.