Metal-doped diamond-like carbon (Me-DLC) is a typical industrial solution for wear resistant coating due to their tribological properties. DLC doping with metal is used to reduce internal stress of ...the DLC coating, improve its thermal stability, hardness, coating-substrate adhesion, and wear resistance. Furthermore, application of the High Power Impulse Magnetron Sputtering (HiPIMS) for Me-DLC deposition allows improvement of coating adhesion and densification of the coating. To improve the properties of the DLC coatings doping with tungsten and molybdenum from a mixed W-Mo-C target can be used. This study concerns the plasma chemistry and composition for a W-Mo-C target operated with HIPIMS in argon atmosphere. For a HIPIMS discharge with a fixed pulse length of 150μs a linear dependence of the average power and current are observed. The optical emission spectroscopy experiments reveal a temporal dependence of the plasma composition as the current pulse develops. First plasma is dominated by argon neutrals and ions followed by molybdenum and tungsten. Significant separation between the two metal species is observed in terms of the times of onset and peak of the emission. As a consequence of the change of the neutral gas to metal ratio the estimated effective electron temperature, Te, changes from ~2eV as estimated from Ar I emission to ~0.3–0.6eV as indicated by W I emission. A change of Te is also observed with the change of HIPIMS frequency: the Te estimated from metal excitations increases most probably as a result of the processes taking place in the afterglow phase between HIPIMS pulses. The transition from argon plasma at the beginning of the pulse to metal-rich plasma in the second phase of the pulse is discussed in comparison with the ion current measurements performed with a planar probe.
•Optical emission spectroscopy study of a multicomponent target (Mo-W-C) in argon atmosphere•Time-resolved OES measurements demonstrated a temporal separation of Ar, W and Mo emission•Temporal dependence of the saturation ion current was proposed to be a result of Ar, Mo and W dynamics in the discharge•An increase in ion saturation current has been demonstrated to occur in conjunction with an increase in the metal content in the plasma with HIPIMS frequency
We studied the transport properties of highly boron-doped nanocrystalline diamond thin films at temperatures down to 50 mK. The system undergoes a doping-induced metal-insulator transition with an ...interplay between intergranular conductance g and intragranular conductance g0, as expected for a granular system. The conduction mechanism in the case of the low-conductivity films close to the metal-insulator transition has a temperature dependence similar to Efros-Shklovskii type of hopping. On the metallic side of the transition, in the normal state, a logarithmic temperature dependence of the conductivity is observed, as expected for a metallic granular system. Metallic samples far away from the transition show similarities to heavily borondoped single-crystal diamond. Close to the transition, the behavior is richer. Global phase coherence leads in both cases to superconductivity also checked by ac susceptibility , but a peak in the low-temperature magnetoresistance measurements occurs for samples close to the transition. Corrections to the conductance according to superconducting fluctuations account for this negative magnetoresistance.
We report on the electronic and optical properties of boron-doped nanocrystalline diamond NCD thin films grown on quartz substrates by CH4 /H2 plasma chemical vapor deposition. Diamond thin films ...with a thickness below 350 nm and with boron concentration ranging from 1017 to 1021 cm−3 have been investigated. UV Raman spectroscopy and atomic force microscopy have been used to assess the quality and morphology of the diamond films. Hall-effect measurements confirmed the expected p-type conductivity. At room temperature, the conductivity varies from 1.5 10−8 −1 cm−1 for a nonintentionally doped film up to 76 −1 cm−1 for a heavily B-doped film. Increasing the doping level results in a higher carrier concentration while the mobility decreases from 1.8 down to 0.2 cm2 V−1 s−1. For NCD films with low boron concentration, the conductivity strongly depends on temperature. However, the conductivity and the carrier concentration are no longer temperature dependent for films with the highest boron doping and the NCD films exhibit metallic properties. Highly doped films show superconducting properties with critical temperatures up to 2 K. The critical boron concentration for the metal-insulator transition is in the range from 2 1020 up to 3 1020 cm−3. We discuss different transport mechanisms to explain the influence of the grain boundaries and boron doping on the electronic properties of NCD films. Valence-band transport dominates at low boron concentration and high temperatures, whereas hopping between boron acceptors is the dominant transport mechanism for borondoping concentration close to the Mott transition. Grain boundaries strongly reduce the mobility for low and very high doping levels. However, at intermediate doping levels where hopping transport is important, grain boundaries have a less pronounced effect on the mobility. The influence of boron and the effect of grain boundaries on the optoelectronic properties of the NCD films are examined using spectrally resolved photocurrent measurements and photothermal deflection spectroscopy. Major differences occur in the low energy range, between 0.5 and 1.0 eV, where both boron impurities and the sp2 carbon phase in the grain boundaries govern the optical absorption.
The low temperature electronic transport of highly boron‐doped nanocrystalline diamond films is studied down to 300 mK. The films show superconducting properties with critical temperatures Tc up to ...2.1 K. The metal–insulator and superconducting transitions are driven by the dopant concentration and greatly influenced by the granularity in this system, as compared to highly boron‐doped single crystal diamond. The critical boron concentration for the metal–insulator transition lies in the range from 2.3 × 1020 up to 2.9 × 1020 cm−3, as determined from transport measurements at low temperatures. Insulating nanocrystalline samples follow an Efros–Shklovskii (ES) type of temperature dependence for the conductivity up to room temperature, in contrast to Mott variable range hopping (VRH) in the case of insulating single crystal diamond close to the metal–insulator transition. The electronic transport in the metallic samples not only depends on the properties of the grains (highly boron‐doped single crystal diamond), but also on the intergranular coupling between the grains. The Josephson coupling between the grains plays an important role for the superconductivity in this system, leading to a superconducting transition with global phase coherence at sufficiently low temperatures. Metallic nanocrystalline samples show similarities to highly boron‐doped single crystal diamond. However, metallic samples close to the metal–insulator transition show a richer behavior. In particular, a peak was observed in the low‐temperature magnetoresistance measurements for samples close to the transition, which can be explained by corrections to the conductance arising from superconducting fluctuations.
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