Comparison of ion beam mixing at room temperature and 40 K

Ion beam mixing in Ni amorphous Si has been compared at room temperature and 40 K by monitoring the spreading of thin embedded impurity layers in samples mounted on a stage that could be cryo-cooled. The markers were ∽ 10 Å layers of Ge and Sn in an amorphous Si matrix and a ∽30 Å layer of Si in a Ni matrix, and the mixing was induced by 100 keV Ar+ ions. The marker distribution was monitored in situ by helium ion backscattering spectrometry before after the Ar+ irradiation. Gaussian curves were fitted to the marker profiles and the magnitude of the mixing was deduced from the increases in the variances of the curves. The results indicate no variation of the mixing as the Ar+ irradiation temperature is varied from 300 K to 40 K in either system, with upper limits for the activation energies of any thermally activated mixing all less than 4 × 10−3 eV. The results for the Ge and Sn markers in Si are in excellent agreement with the results of earlier work with similar targets in the overlapping temperature ranges (∽80–300 K). Additional backscattering analyses conducted on the samples after they had been irradiated at 40 K and subsequently warmed to room temperature indicate that no further diffusion of either marker occurs during this warming process.