Superconductivity of Mg-B layers prepared by a multi-energy implantation of boron into magnesium and magnesium into boron bulk substrates followed by the furnace and pulsed plasma annealing

摘要

B ions into Mg and Mg ions into B substrates were implanted in triple mode, i.e. each sample was sequentially implanted at three different energies starting from the highest one (80-150 keV range) to the lowest one (40-70 keV range). The energies and fluencies in each particular batch were simulated to yield a possibly large region in which the Mg:B ratio corresponds to stoichiometric MgB2 compound. These structures were next annealed using high intensity hydrogen plasma pulses of energy densities between 1.5 and 4.0 J/cm(2), or furnace annealed at 350-600 degrees C in a stream of flowing Ar-4%H-2 mixture. The simulated profiles were in fair agreement with those derived from the RBS measurements. Magnetically modulated microwave absorption (MMMA), magnetization and resistance measurements showed that the superconducting transition onset temperature T-c(onset) shifted from about 13 K in the best magnesium sample implanted with single-energy B ions, to 22-28 K for multi-energy implantation treatments. Respective shift in Mg-implanted boron samples was from about 33.3 K to 36.5 K. However, broadening of the transition to the superconducting state is observed for the multi-energy treatment in both cases. Possible reasons for these effects and proposed means to improve the method are discussed.