High power impulse magnetron sputtering (HiPIMS) of diamond-like carbon coatings is reviewed. Three variations of HiPIMS were used to deposit diamond-like carbon coatings: use of neon as compared to argon for sputtering, very high discharge peak current density in an Ar atmosphere, and the use of bursts of short sputtering pulses. All three variations were able to provide sufficient ion-to-neutral ratios to effectively control the coating quality using substrate bias. The resulting coatings are typically smooth, amorphous, hard (up to 25 GPa), and dense but have low stress (below 2.5 GPa). The coatings exhibit an increased stability at higher temperature (up to 500 °C) compared to the coatings prepared using standard magnetron sputtering. The resulting coatings also exhibited low wear rates in ambient ball-on-disc tests (2.1 × 10−8 mm3 N−1 m−1). These improvements are explained in terms of the rate of sputtered carbon atom ionization in the plasma and material transport to the substrate. However, the chemical bonding in the films is not yet well understood as relatively low sp3 bond content has been observed.

In this work, we investigate the use of high power impulse magnetron sputtering (HiPIMS) for the deposition of micrometer thick diamond like carbon (DLC) coatings on Si and steel substrates. The adhesion on both types of substrates is ensured with a simple Ti interlayer, while the energy of impinging ions is adjusted by using RF (Radio Frequency) biasing on the substrate at −100 V DC self-bias. Addition of acetylene to the working Ar+Ne atmosphere is investigated as an alternative to Ar sputtering, to improve process stability and coatings quality. Peak current is maintained constant, providing reliable comparison between different deposition conditions used in this study. The main advantages of adding acetylene to the Ar+Ne gas mixture are an increase of deposition rate by a factor of 2, when comparing to the Ar+Ne process. Moreover, a decrease of the number of surface defects, from ~40% surface defects coverage to ~1% is obtained, due to reduced arcing. The mechanical and tribological properties of the deposited DLC films remain comparable for all investigated gas compositions. Nanoindentation hardness of all coatings is in the range of 25 to 30 GPa, friction coefficient is between 0.05 and 0.1 and wear rate is in the range of 0.47 to 0.77 × 10⁻⁶ mm³ N⁻¹m⁻¹.

Pressure and target voltage driven discharge runaway from low to high discharge current density regimes in high power impulse magnetron sputtering of carbon is investigated. The main purpose is to provide a meaningful insight of the discharge dynamics, with the ultimate goal to establish a correlation between discharge properties and process parameters to control the film growth. This is achieved by examining a wide range of pressures (2–20 mTorr) and target voltages (700–850 V) and measuring ion saturation current density at the substrate position. We show that the minimum plasma impedance is an important parameter identifying the discharge transition as well as establishing a stable operating condition. Using the formalism of generalized recycling model, we introduce a new parameter, ‘recycling ratio’, to quantify the process gas recycling for specific process conditions. The model takes into account the ion flux to the target, the amount of gas available, and the amount of gas required for sustaining the discharge. We show that this parameter describes the relation between the gas recycling and the discharge current density. As a test case, we discuss the pressure and voltage driven transitions by changing the gas composition when adding Ne into the discharge. We propose that standard Ar HiPIMS discharges operated with significant gas recycling do not require Ne to increase the carbon ionization.

In this work, (Ba_0.75Sr_0.25) (Ti_0.95Co_0.05) O₃ perovskite nanostructured material, denoted subsequently as Co-doped BaSrTiO₃, was synthesized in a one-step process in hydrothermal conditions. The obtained powder was heat-treated at 800 °C and 1000 °C, respectively, in order to study nanostructured powder behavior during thermal treatment. The Co-doped BaSrTiO₃ powder was pressed into pellets of 5.08 cm (2 inches) then used for thin film deposition onto commercial Al₂O₃ substrates by RF sputtering method. The microstructural, thermal, and gas sensing properties were investigated. The electrical and thermodynamic characterization allowed the evaluation of thermodynamic stability and the correlation of structural features with the sensing properties revealed under real operating conditions. The sensing behavior with respect to the temperature range between 23 and 400 °C, for a fixed CO₂ concentration of 3000 ppm, highlighted specific differences between Co-doped BaSrTiO₃ treated at 800 °C compared to that treated at 1000 °C. The influence of the relative humidity level on the CO₂ concentrations and the other potential interfering gases was also analyzed. Two possible mechanisms for CO₂ interaction were then proposed. The simple and low-cost technology, together with the high sensitivity when operating at room temperature corresponding to low power consumption, suggests that Co-doped BaSrTiO₃ has a good potential for use in developing portable CO₂ detectors.