Interactions of ion beams with surfaces: Dynamics of the reaction of N2+with rhenium

摘要

Reactions of N2+ion beams with the surface of polycrystalline rhenium foil over the range 150ndash;3thinsp;000 eV have been studied by the techniques of xhyphen;ray photoelectron spectroscopy (XPS) and thermal desorption spectrometry (TDS). The reactions produce a nitride layer of the type ReNx, 0.21les;xles;0.40, withxvarying as a function of ion kinetic energy and depth into the surface. The nitride layer extends from the surface down to the penetration depth of the atoms, which varies from sim;15 Aring; at 0.3 keV to sim;76 Aring; at 2.5 keV ion energy. The product nitride and chemisorbed nitrogen on Re are distinctly different, exhibiting N1sbinding energies of 397.9 and 396.8 eV, respectively, and TDS maxima near 425 and 600thinsp;deg;C, respectively. The value ofxin ReNxincreases linearly with the nitrogen ion flux and reaches a steady state condition at a dose of 9.5 times;1016ions/cm2which is determined by the opposing rate of nitride formation and the sputtering rate by impinging N2+ions. An expression describing the rate of nitration as a function of the reaction cross section sgr;rand the sputtering cross section sgr;sis derived. The simplified expressions for the limiting cases of initial rates (trarr;0) and the steady state (trarr;infin;) product concentration, which are used to interpret the experimental results, yield sgr;rsime;3times;10minus;18cm2for the N2++Re(metal)rarr;ReNxreaction at an ion impact energy of 500 eV.