Electrically conductive properties of tungsten-containing diamond-like carbon films

Tungsten-containing diamond-like carbon films with different metal concentrations were investigated. The films of several hundred nanometers in thickness were deposited on the silicon wafer using RF-PECVD (radio frequency plasma enhanced chemical vapor deposition) method. During deposition, metal component was co-sputtered using DC magnetron of tungsten target. The six samples with the concentration of 3.8, 6.1, 8.0, 16.3, 24.3 and 41.4 at.% of tungsten were made. The structural analyses were performed by TEM (transmission electron microscope) and Raman spectroscopy. These results indicated that tungsten clusters were well dispersed in amorphous carbon host matrix in the case of tungsten concentration from 3.8 to 24.2 at.%. However, no such a structure can be observed in the sample with 41.4 at.%. The AC electrical resistance was measured in the temperature range of 2–300 K using four-probe method in vacuum condition. The observed temperature dependence of electrical conductivity can be expressed by σ=σ0exp⁡⌊−2(C0/k⁢T)1/2⌋σ=σ0exp⁡⌊−2(C0/k⁢T)1/2⌋ and tungsten concentration from 3.8 at.% to 24.2 at.%. In addition, the sample with 41.4 at.% showed the resistive superconducting transition at Tc of around ∼ 5.5 K.