Electrical Resistivity and Morphology of Sn_1&minus;<i>_x</i>/Si<i>_x</i> Core&ndash;Shell Cluster Network Prepared by a Plasma-Gas-Condensation Cluster Source

Abstract

Sn 1¹x /Si x cluster assembled films have been prepared by a plasma-gas-condensation cluster beam deposition apparatus. Transmission electron microscope images indicate that individual clusters have coreshell morphology, where Sn cores are covered by Si shells. Temperature dependence of electrical resistivity exhibits a metallic behavior and a superconducting transition at low temperature for 0 < x < 0.20, while a semiconductor-type behavior and no superconductivity down to 2 K for x > 0.29. These results indicate that the cluster network and/or coreshell morphology Sn 1¹x /Si x cluster assembled films changes with x.

Electric Evolution in Sputter-Deposited Sn_{<i>c</i>_Sn}Si_{1−<i>c</i>_Sn} Alloy Films

“…4 is much larger than v p = 0.16 for the 3 dimensional site percolation theory (a random and/or homogenous mixture) 8,9) . It is also larger than v p = 0.21 ∼ 0.25 which correspond to the threshold values of v Sn = 0.7 ∼ 0.8 in Sn/Si coreshell cluster assemblies, provided that the packing density of such cluster assemblies is about 30% of its bulk state 1,2,10) . The present result of v p ≅ 0.4 is still larger than v p = 0.33 for the effective medium theory (a heterogeneous binary mixture, i.e., a patchwork pattern) 11) .…”

“…In Sn c Sn Si 1−c Sn composite system prepared by a plasma-gascondensation method, Sn/Si core-shell clusters are formed via collision of Sn and Si atoms in a high Ar gas atmosphere, where Sn cores are protected against oxidation by thin Si shells consisting of 2 nm Si nanoparticles. With increasing c Sn in Sn/Si core-shell cluster assemblies, Sn cores partially contact with each other, agglomerate and attain a semiconductor to metal transition at around c Sn = 0.7 ∼ 0.8, Then, a superconductivity of Sn core is a little enhanced by exiton-mediation at their core-shell interfaces 1,2) .…”