Preparation of nickel-containing conductive amorphous carbon films by magnetron sputtering with negative high-voltage pulsed substrate bias

Highlights: • a-C-Ni films were deposited by magnetron sputtering with substrate biasing. • Influence of pulse duration of bias voltage on a-C film properties was shown. • Effect of Ni content on microstructure and resistivity of a-C-Ni films was evaluated. - Abstract: Nickel-containing amorphous carbon (a-C-Ni) films were deposited by magnetron sputtering of graphite and nickel. Graphite magnetron sputtering power was 1500 W. Nickel magnetron sputtering power changed from 0 W to 1000 W, allowing control of the Ni concentration in the films from 0 to 58 at.%. Growth rates of a-C-Ni films were 1.4–2.5 μm/h. High-voltage negative pulsed bias voltage of ‐3 kV amplitude, frequency of 1 kHz, and pulse duration of 50–250 μs was applied to a substrate. The chemical composition of the films was determined using Auger electron spectroscopy. The surface morphology was observed by atomic force microscopy (AFM). The film structure was characterized by Raman spectroscopy and X-ray diffractometry (XRD). The resistivity of the films was measured by a four-point probe method. Film properties that are changed by the added metal, such as structure, electrical resistivity, and hardness, were evaluated and compared with those of pure a-C films as well as with literature values for a-C-Ni films. It is shown that the resistivity of a-C films depends on the duration of the bias voltage pulses and varies from 3.4 to 7.6·10⁻² Ohm·cm at pulse duration 50 and 250 μs, respectively. In the case of Ni doping, the a-C-Ni film resistivity can be reduced to 6.7·10⁻⁴ Ohm·cm. Where Ni is included in the film in the form of Ni₃C carbide, which has hexagonal (hcp) modification, the crystallite size averages 12 nm. The film has a columnar structure and carbon is also present as a graphite-like interlayer 3 nm thick between the Ni₃C crystallites. At sputtering power of 600 W of nickel magnetron, a-C-Ni film with resistivity of 5.3·10⁻³ Ohm·cm is obtained, which can be used as a barrier layer in thermoelements based on bismuth telluride.