Laser fluorescence spectroscopy of sputtered zirconium atoms

Doppler shift laser induced fluorescence spectroscopy was used to determine the relative sputtering yields and number density velocity distribution of sputtered neutral ground state zirconium atoms. Neither change in primary ion energy over the range 1–3 keV nor change in primary ion mass (Ar+, Kr+) affected the velocity distribution despite large changes in the sputtering yield. The measured number density velocity distributions n(v) are well explained by standard linear collision cascade theory and follow the expression n(v)dv α [v2/(v2+v2b)3]dv, where vb is the velocity corresponding to a surface binding energy, Eb = 1/2mZrv2b, with Eb = 6.305 eV, the bulk zirconium sublimation energy. Surprisingly, the number density velocity distributions of zirconium atoms sputtered in two excited states (a 3F3,4) are indistinquishable from that measured for ground state zirconium atoms. Further, the sputtering yield dependence on primary ion energy for the 3F3,4 was also, within experimental error, the same as for the 3F2 ground state zirconium. The sputtering yield for the two excited states represents almot 40% of the total yield of zirconium. Evaluation of the results incorporates for the first time the effects of power broadening, transit time broadening, and velocity dependent fluorescent detection efficiencies.