Electron transport in amorphous carbon-silicon nanocomposites containing Nb

The evolution of the electron transport in Nb-containing hydrogenated amorphous carbon-silicon nanocomposite films with an increase in niobium concentration in the range of 13-33 at.% was studied in the wide temperature range of 80-400 K. The films were deposited onto ceramics substrates by the combination of DC magnetron sputtering of a Nb target and decomposition of siloxane vapors in a stimulated DC discharge. The model of inelastic tunneling of electrons in amorphous dielectrics was applied to analysis of the experimental conductivity-temperature dependences. It was shown that the average number of localized states in the potential barriers between metal clusters is not greater than 2 and nonmonotonically depends on Nb concentration in the investigated films. This dependence can be explained in terms of the modifications both of metal and carbon phase structures by increasing metal concentration. The Raman spectroscopy data demonstrate that these structural transformations take place in the carbon phase of the host matrix as the Nb concentration exceeds 23-25 at.%. An increase in the average size of sp ² clusters from 0.7-0.9 up to 1.1-1.3 nm is observed.