Application of matrix isolation spectroscopy to quantitative sputtering studies. I. Energies and oscillator strengths of the resonance transitions of gold atoms isolated in noble gas matrices

Abstract

Matrix isolation spectroscopy has been applied to quantitative sputtering studies by developing techniques for the codeposition of backsputtered metal atoms with a large excess of noble gas atoms. The electronic spectra of Au atoms, produced by bombardment of an Au target with 50 keV Ar⁺ ions, were studied in Ar, Kr, and Xe matrices. Energy level shifts of the Au resonance doublet due to matrix perturbations have been interpreted in terms of changes in the spin‐orbit coupling interaction of the Au 6p electron. The values in the various matrices were found to be ζ_Xe = 2570 cm⁻¹; ζ_Kr = 2943 cm⁻¹; ζ_Ar = 3215 cm⁻¹ (ζ_gas = 2543 cm⁻¹). The [inverted lazy s] 650 cm⁻¹ splitting of the ²P_3/2 state in the various matrices was interpreted in terms of an axial distortion of a dodecahedral substitutional site. Simultaneous diagonalization of spin‐orbit and ``crystal'' field interactions was employed to obtain ζ and A<sub>2</sub> splitting parameters. Oscillator strengths for the resonance transitions were determined by developing an equation which relates the sputtering yield, integrated current, and a geometric factor based on a cosine law distribution of sputtered atoms to the integrated absorbance over an absorption band and the area sampled by the spectrometer beam. Oscillator strengths for the <sup>2</sup>P<sub>1/2</sub> and <sup>2</sup>P<sub>3/2</sub> transitions were found to be 0.132, 0.293 in Ar; 0.090, 0.200 in Kr; and 0.061, 0.145 in Xe. By comparison the gaseous atom values (``hook'' method) are 0.19, 0.41. It is pointed out that the matrix isolation method can determine Au atom concentrations equivalent to 0.1 monolayer and is therefore among the more sensitive and rapid techniques for measuring sputtering yields.