Effects of Outer Shell Layer on the Electronic Transport Behaviors of Sn@SnOx Nanoparticles

Tin oxide-encapsulated tin nanoparticles (Sn@SnOx NCs) are in situ prepared by a modified DC arc-discharge plasma process. The as-prepared Sn@SnOx NCs are typically 50-70 nm in diameter with 6 nm of the SnOx shell. The diameter of Sn@SnOx NCs is 50-80 nm and the thickness of the SnOx shell increases to approximate to 25 nm after heat treatment in a vacuum tube furnace. The effect of SnOx shell thickness on the electrical properties of Sn@SnOx NCs is measured by the four-probe technique. The results show that the resistivity is described using Bloch-Gruneisen's equation with SnOx shell thickness-dependent resistivity and SnOx shell thickness-dependent Debye temperature above the superconducting transition temperature T-c. Superconductivity occurs in both Sn@SnOx NCs with different shell thicknesses when the temperature is lower than T-c. The T-c of the two NCs (3.98 K, 4.15 K) is slightly higher than that of the metal block (3.73 K) due to the electron-scattering effect of the particles' surface shell. The resistances of the two samples below T-c show an exponential decay mode, which is the result of the thermally activated phase slip (TAPS) and quantum phase slip (QPS).