Ion-beam mixing of Ni/Pd layers: I. Cascade mixing regime (low temperature)
- PDF / 563,854 Bytes
- 6 Pages / 593.28 x 841.68 pts Page_size
- 54 Downloads / 215 Views
Ion-beam mixing of Ni/Pd layers: I. Cascade mixing regime (low temperature) U. G. Akano.D.A. Thompson, J. A. Davies, and W. W. Smeltzer Department ofEngineering Physics and Institute/or Materials Research, McMasterUniversity, Hamilton, OntarioL8S4M1, Canada (Received 11 May 1988; accepted 15 August 1988)
Atomic mixing resulting from heavy-ion bombardment of thin-film Ni/Pd bilayers and thin Pd markers sandwiched between Ni layers has been investigated. Mixing experiments were performed over a temperature range 40-473 K, using 120 keV A r + and 145 keV K r + ions at a constantdose rate of5.5X 1012 ions c m " 2 s ~ ' f o r doses up t o 4 x 10 16 cm~ 2 . The resulting interdiffusion was measured, in situ, using Rutherford backscattering with 2-2.8 MeV 4 H e + ions. The results showed that, for both markers and bilayers, the amount of mixing is similar for both configurations and varies linearly with the square root of the ion dose. Comparison of the induced mixing per ion, following irradiation at 40 K, shows that the mixing is dependent on the damage energy FD deposited at the interface region. The mixing is essentially athermal. I. INTRODUCTION Ion-beam mixing has been widely studied as a technique for surface layer alloy formation.' Potential applications of this process include improved corrosion resistance2 and catalytic behavior.3"5 However, a full understanding of the various processes that may contribute to ion-beam mixing is still lacking. At sufficiently low temperatures, where thermally activated processes are suppressed, experimental observations resulting from ion bombardment are usually ascribed to athermal atomic rearrangements occurring within the collision cascade.6 The observed ion-beam mixing at such low temperatures, however, varies from one system to another,7 even in collisionally similar systems, and the magnitude of the mixing generally differs from theoretical predictions.8 Below a cricital temperature Tc, which depends on the particular system, ion-beam mixing shows either a very weak temperature dependence [e.g.,Ni/Si (Ref.9),Ni/Au (Ref. 10)] oratemperature-independent behavior [Si/Ge (Ref. 11)]. Above Tc, ion mixing exhibits a strong temperature dependence that is usually ascribed to radiation-enhanced diffusion (RED). However, the predicted12 dose rate dependence of RED has been observed in only a few cases.13 Hence, it has not yet been established whether the RED model, as presently formulated,12 can adequately describe the temperature dependence of ionbeam mixing. In some systems, alloy phases formed during ion mixing are similar to those normally resulting from thermal processing,14 while in other systems, novel nonequilibrium phases (Pd/Al) have been observed.15 The initial hope that ion mixing would be independent of thermodynamic constraints is now recognized as unrealistic. 16 Indeed, purely collisional mixing fails completely whenever the chemical heat of mixing is signifiJ. Mater. Res. 3(6), Nov/Dec 1988
http://journals.cambridge.org
cantly exothermic. In the Ni/Pd system, this
Data Loading...
