Nuclear Instruments and Methodi in Physics Research B7/8 (3985) 147-150 North-Holland, Amsterdam 147 zyxwvut XPS S’Il.JDiES AT VARIOUS ~MPE~~~ OF NITROGEN 1~~~ COPPER P.D. PRABHAWALKAR ‘I, D.C. KOTHARI ‘I, M.R. NAIR ‘) and P.M. RAOLE ‘) I) Regionuf Sophisticated Instnrmentrrtion Centre, Indian Institute of Technoiogy, Pow& Bombay 400 076, India fj Departmen? of Physics, U~~~ers~ty of Eombay, Vidyanagarl Bombay 400 098, India Metastable nitride formation by nitrogen implantation in copper is studied using the te&nique of X-ray photoelectron spectroscopy (XPS). XPS spectra were recorded at various temperatures to study the thermal stability of nitrides formed by implantation. It is observed that Cu,N phases for x greater than 0.5 are- formed. These phases start decomposing above 250°C. The nitrogen gas released mainly from the bulk of the metal is seen on the surface even at high temperatures up to zyxwvutsrqponmlkjihgfe SOOT. I. In~~on Ion implantation is envisaged as a new technique to form new metastable phases in the near surface region. In this paper we report the formation of metastable copper nitride phases. Nitrogen is known to be insolu- ble in copper by conventional techniques. However it forms metastable compounds with copper [l]. It is al- ways interesting to study the fo~ation of such therm- ally unstable nitrides of copper. Earlier, the studies of the reduction of the atmospheric tarnishing of copper was done, by using boron ions [2,3]. Similarly the study of oxidation of single crystal of copper, by using im- planted Al+ ions was reported, by using ion back- scattering techniques [4]. Study of oxidation of single crystal copper at elevated temperature was done after implanting 220 keV Al+ ions [S]. Naguil et al. [6] studied the oxidation procedure of polycrystalline sam- ple by implanting B+ , C+ , N+ . They observed a strange behaviour for nitrogen in particular where the oxidation increased at low doses (< l0l6 ions/cm2) and decreased at high doses. It was therefore decided to study the formation of metastable compounds of copper with nitrogen at higher doses and at various temperatures, which may be responsible for the inhibition of oxida- tion. One of the most powerful tools to study the phenom- enon occurring in the near surface region is electron spectroscopy. Here we have used X-ray photoelectron spectroscopy (XPS) to study the NC implanted poly- crystalline copper. The prelude for such work was sug- gested in a number of works [7-g]. 2. Experimental Polycrystalline Cu foils were thoroughly cleaned and used as target material. The material was mounted in a 0168-583X/85/$03.30 8 Elsevier Science publishers B.V. (North-Holland Physics Publishing Division) conventional target chember in which a heat sink was provided for the target. Implantation was carried out at a pressure of 5 x 10e6 Torr, at room temperature, using N$ ions of 30 keV through a mask of area 1 cm2. The current maintained was 20 PA/cm’ which amounted to a dose rate of 124 x 1Or2 ions crnB2 s-r. The total dose given was 5 x 10” ions cm-‘. Liquid nitrogen traps were used at various places to avoid contamination and backstreaming. The nitrogen gas used was ~.~8~ pure. In order to ensure uniform implantation an ion beam sweeping mechanism was employed. XPS studies were carried out with the help of VG Scientific Mark II machine with a twin anode X-ray source. For our experiments Al K, (1486.6 eV) anode was used. The sample holder was in the form of a flat stainless steel strip. Samples were mounted by using a temperature withstanding highly conducting silver epoxy. The experiments were carried out at a vacuum better than 5 x lo- ” Torr. The samples were heated by resistive heating and the temperatures measured by a Cr-Al thermocouple. At the time of heating there was degasing probably due to bursts of nitrogen. Hence the sample was kept at the same temperature for at least half an hour so that the original vacuum was restored and the sample conditions reached steady state. C 1s line from the sample holder and the sample was used for possible charge correction. 3. Results and discussion The total scan of the implanted sample from a binding energy of 0 eV to a binding energy of 1000 eV is shown in fig. 1. In the figure the elements seen are copper, nitrogen, oxygen, carbon , silver (from epoxy), however the carbon and the oxygen lines are relatively weak and did not show any shift indicating that they are only adsorbed species. Thus the implanted sample was III. METALS Lattice sites, Defects, Theory