RBS Study of a Dilute Alloy of Ga(99.8% at.):Bi(0.2% at.)

Dilute alloys of bismuth in gallium (98-99% at.) are known from theoretical calculations and x-ray scattering to display a strong segregation of bismuth atoms at the surface, a monatomic layer of bismuth appearing because of the lower surface tension of the Bi compared to the Ga. Rutherford backscattering (RBS) spectra from 2 MeV He+ and 2 MeV C+ on a dilute alloy of Ga(99.8% at.):Bi(0.2% at.) have been measured. A distinct peak in the RBS spectra, corresponding to scattering from the surface of the alloy, is consistent with a monatomic layer of bismuth on the alloy over a range of temperatures for which the alloy is a liquid to room temperature where it is a solid. The peak is not observed when the alloy is cooled to a solid state and this observation is thought to be due to the irregular surface structure of the alloy. Bismuth is also observed to be uniformly distributed throughout the gallium host for the depths studied at these beam energies. Some oxide may be present due to the 10-7 Torr vacuum and the long spectral integration times.