173 CHARACTERIZATION OF TI ALLOYS BOMBARDED BY KEV DEUTERIUM IONS G.P. Chambers , G. K. Hubler, J.A. Sprague and K.S. Grabowski Naval Research Laboratory, Washington D.C. 20375 D. Simons, NIST, Gaithersburg MD 20899 ABSTRACT Thin Ti films have been bombarded at room temperature with 350-500 eV deuterium ions at current densities up to 0.5 mA/cm 2 . Analysis using scanning electron microscopy, x-ray diffraction, transmission electron microscopy, and secondary ion mass spectroscopy were carried out before and after bombardment. It was determined that deuterium diffuses rapidly throughout the Ti film, that the films were in a state of high compressive stress, and that the TiD2 phase was formed. No evidence of deuterium gas bubbles was found. I. Introduction There have been several studies of the formation of TiD2 by means of ion implantation of deuterium into Ti at keV energies where the alloy is formed by direct ion implantation. In the present study, low energy deuterium beams were used which differs in two respects from previous results: 1) the energy of the deuterium is below the threshold for atomic displacements, and 2) any formation of the TiD2 phase must result from the buildup of deuterium concentration in the bulk from in-diffusion from the surface, and a concomitant concentration-driven phase transformation. The process is similar to the formation of TiD2 in high pressure, high temperature deuterium gas environments. In our case, however, diffusion is driven at room temperature by extremely high concentration gradients very near the surface. During bombardment of these films, a silicon particle detector placed directly behind the thin fidm samples registered counts of MeV particles [I]. The analysis reported here was done to determine a mechanism for the charged particle emission. il. Thin Film Deposition and Ion Beam Irradiation Thin films were prepared by electron beam evaporation in a typical base pressure of 6.6 x10" 5 Pa. A high purity charge was used to deposit -1~gm thick Ti films onto 3.8 pmr-thick nickel foils at an average rate of 5 nm/s. After deposition, foils were mounted onto an aluminum washer and were then moved immediately to the bombardhnent chamber. Some films had 0.5 pm Au deposited prior to deposition of Ti to provide a barrier to deuterium diffusion into the nickel. Sample #3 consisted of an as-received 25-pin-thick Ti foil backed with 0.5 pm of Au. Low energy deuterium ions (350 - 500 eV) produced by an electron cyclotron resonance (ECR) microwave plasma source were directed onto the Ti side of the films, while a Si particle detector placed directly behind the film searched for charged particle emission. Details of the ECR ion source and particle detection experiment can be found elsewhere [I]. The source operating conditions typically produced a beam of 80% D+ and 20% D2+, and a flux of -5x1015 deuterium atoms/cm 2 /sec at the sample. The ion beam current was monitored by an electrostatically suppressed Faraday cup attached to a water-cooled Cu block which surrounded the sample and detector. The base pressure was 6.6x 10-6 Pa and the operating pressure was 2.7- 5.3 x10- 2 Pa of 99.5% purity D2 gas. The projected range (straggling) of 175 and 350 eV deuterium in Ti are 4.7 nm (2.6 nm) and 7.8 nm (3.9 nm), respectively, from TRIM [2] calculations. Two independent measurements of room temperature diffusion coefficients for D in Ti (- l.5x10-11 cm 2 /s) [31 and (~5x10"1 3 cm 2 /sec) [41 indicate that there is sufficient mobility for deuteriun implanted into the surface to diffuse through the I-pm thick films in -300 to 10,000 sec. Mat. Res. Soc. Symp. Proc. Vol. 268. 01992 Materials Research Society