Properties of NbC/C nanocomposite films and sculpted films via reactive sputtering and oblique angle deposition

We have demonstrated the growth of NbC-Amorphous C films and nanorod films that manifest a nanocomposite structure. The films were deposited using reactive DC sputtering in a CH₄/Ar atmosphere at normal incidence for the film and at 85° for nanorod samples. A metallic Nb sputtering target was sputtered in an argon/CH₄ atmosphere with a pressure range of 5.9 to 8.5 mTorr as the CH₄ flow was varied. Crystalline NbC films and nanorod films were deposited at room temperature at the lowest CH₄ flow rate, 1 SCCM and 0.3 SCCM, respectively. The films exhibited ohmic electrical response at room temperature. The DC electrical resistivity scaled almost 4 orders of magnitude from 4.39 × 10⁻⁴ Ω-cm to 1.08 × 10⁻¹ Ω-cm through changes in CH₄ flow rates and the resultant C content of the films. The large variation in resistivity cannot be attributed to the changes in sample composition, e.g. volumetric mixing. It is postulated from XRD and TEM results that the large change in resistivity is due to the decreasing NbC crystallite size with increasing CH₄. This leads to additional three-dimensional nanoscale intragranular interfaces and results in increased resistivity. X-ray reflectivity measurements were conducted, and the modelled film density was found to match the expected density for the film compositions as measured using X-ray photoelectron spectroscopy. Elastic recoil detection analysis (ERDA) was used to quantify H content of the films. The H content increased from 5.5 to 22 atomic percent with corresponding increase in CH₄ flow. Transmission electron microscopy, precession electron diffraction (PED), and selected area diffraction was conducted and showed a strong dependence of crystallinity on CH₄ flow in both the films and nanorod films. A multilayer layer sample with varying CH₄ flowrates was examined with TEM and showed that films were amorphous in nature for flow rates above 10 SCCM CH₄; in agreement with XRD results.