Absolute cross sections for beam-surface reactions: N2+ on Ti from 0.25 to 3.0 keV kinetic energy

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Abstract
Analytical expressions for the absolute cross sections of beam‐surface reactions are derived and applied to the N2++Ti→TiN reaction over the kinetic energy range 0.25–3.0 keV. The model assumes that the amount of reaction product P formed near the surface is a function of the collisional dissociation probability of the primary molecules Pd, the reaction cross section σr, and the cross section for product sputtering by the impingent reactant beam σsp. For a dosage R0 of reactant molecules impingent on M0 target atoms, P/M0?rPd/A) R0 in the limit R0→0 (initial reaction), and P/M0=[α+(β/Pd)(σsp/σr)]−1 in the limit R0→∞ (saturation dose), where A is the surface area bombarded and α and β are stoichiometric factors for the product MαRβ. The techniques of x‐ray and UV photoelectron spectroscopy (XPS and UPS), secondary ion mass spectrometry (SIMS), thermal desorption spectrometry (TDS), and depth‐concentration profiling are used to characterize the reaction product and measure the product film thickness and composition for the reaction of N2+ with the (101̄1) face of a titanium single crystal. The measurements yield a film composition of Ti0.89N and show that the properties of the film, including its extremely high stability, are identical to those of commercial TiN. The reaction cross section is determined as σr,0.5=2.1×10−16 cm2 and σr,2.0=1.0×10−16 cm2 at primary N2+ kinetic energies of 0.5 and 2.0 keV, respectively. The formation and profile of the film near the surface, the interpretation of and uncertainties in the cross sections obtained, and comparison of this system to other N2+ metal systems are discussed.