Depth profiles of ion-induced structural changes in diamond from X-ray photoelectron spectroscopy

Abstract

Angle-resolved X-ray photoelectron spectroscopy (X.p.s.) has been used to monitor the bombardment of (110) faces of diamond by 600 V argon ions at both room temperature and 350 °C, and the subsequent removal of the structurally damaged surface regions by oxidative erosion with microwave-excited nitric oxide at 350 °C. Ion bombardment drastically increased the width of the C Is peak (initially symmetrical and almost as sharp as that from graphite) producing a well defined two-component signal, more clearly resolved following bombardment at the higher temperature. The angular variation of the intensities of these two components, and the behaviour of the C Is signal during erosion, suggest that ion bombardment displaces many carbon atoms to sites of lower coordination, the fraction of atoms so displaced decreasing approximately exponentially with depth from a value of ca . 0.8 at the surface to ca . 0.4 at about 17 Åf depth. After erosion of all the damaged carbon, the angular variation of the signal from the underlying diamond showed pronounced structure arising from diffraction of the outgoing photoelectrons. Monitoring the Ar 2p peaks as a function of erosion time enabled experimental depth profiles to be obtained for the implanted argon. The depth scale was quantified, independently, by considerations relating to the initial rate of uptake of oxygen and from studies of the angular variations in the intensities of the X.p.s. signals. The argon concentration at adepth, z Å ,below the surface followed the function 1/(1 + 0.3 z ) quite closely down to z = 40Å (from a value of ca . 4 atomic % of the surface), regardless of the temperature of the initial bombardment; but whereas after bombardment at room temperature, argon could not be detected below ca . 60 Å, pronounced tailing of the argon distribution occurred during bombardment at 350 °C, resulting in penetration of detectable quantities of argon as deep as 150 Å. Possible explanations of this phenomenon are briefly discussed.