Localized compositional depth profiles in near surface of Cu-50 wt% Ag alloy

Abstract

The segregation-induced depth profiles of the constituent in a binary alloy system under irradiation with energetic particles are interesting phenomena and have been extensively studied by many authors in the last two decades [1-3], because of their importance for various technological applications and many areas of material science. In general, segregation-induced or bombardment-induced depth profiles are often studied by use of ion sputtering in combination with surface analytical methods such as secondary ion mass spectrometer (SIMS) and auger electron spectrometer (AES). However, these analytical results for depth profile, i.e. the composition distribution in the near-surface region, are average values since the beam spot of the probe in SIMS or AES apparatus is very large (>/50/lm), one to two orders of magnitude beyond the size of a micro-phase region on the surface of the two-phase binary alloy as in previous studies [4, 5]. Therefore, a rational hypothesis is that research on the depth-profile of near-surface composition must involve a study of the depth profile changes combined with micro-phase region changes. Recently, depth-profile measurements for Ar ÷ ion bombarded A170Sn30 alloy have shown significant variation between two different micro-phase regions [6]. At present, in order to investigate further the composition distribution in the near-surface region of a two-phase binary alloy, we chose a Cu-50 wt % Ag alloy as sample. This is a typical two-phase system with which to study the depth profile of elements in the near surface. We shall see that differences in the composition depth profile for different micro-phase regions are observed. The Cu-50 wt % Ag alloy sample was in the form of a disc of 15 mm diameter and i mm thickness. The sample surface was mechanically polished, and in the final step, 0.05/~m alumina was used to give an optically smooth surface with no protrusions observable by scanning electron microscopy (SEM) (x5000). The sample was bombarded in the electromagnetic isotope separator with normally incident Ar ÷ ions (27 keV). During the bombardmental experiment the vacuum was kept below 1.33 × 10 .4 Pa, and the Ar ÷ ion beam current density was kept below 3 #A/cm 2. In addition, the sample was mounted on a LN2 indirectly cooled copper backer, so the temperature within the beam spot (3 mm diameter) was estimated not to exceed 300 K. After ion bombardment the irradiated surface was exmained in a S-570 model SEM. A typical surface region is shown in Fig. 1.