Time- and space-resolved optical emission spectroscopy and fast imaging were used for the investigation of the plasma dynamics of high-power impulse magnetron sputtering discharges. 200 μs pulses with a 50 Hz repetition frequency were applied to a Cr target in Ar, N2, and N2/Ar mixtures and in a pressure range from 0.7 to 2.66 Pa. The power density peaked at 2.2–6 kW cm−2. Evidence of dominating self-sputtering was found for all investigated conditions. Up to four different discharge phases within each pulse were identified: (i) the ignition phase, (ii) the high-current metal-dominated phase, (iii) the transient phase, and (iv) the low-current gas-dominated phase. The emission of working gas excited by fast electrons penetrating the space in-between the electrodes during the ignition phase spread far outwards from the target at a speed of 24 km s−1 in 1.3 Pa of Ar and at 7.5 km s−1 in 1.3 Pa of N2. The dense metal plasma created next to the target propagated in the reactor at a speed ranging from 0.7 to 3.5 km s−1, depending on the working gas composition and the pressure. In fact, it increased with higher N2 concentration and lower pressure. The form of the propagating plasma wave changed from a hemispherical shape in Ar, to a droplike shape extending far from the target in N2. An important N2 emission rise in the latter case was detected during the transition at the end of the metal-dominated phase.

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We systematically investigate the reactive behaviour of two types of high-power pulsed magnetron discharges above a Nb target using either square voltage pulses (denoted as HiPIMS) or custom-shaped pulses (denoted as MPPMS), and compare it with that of a dc magnetron sputtering (DCMS) discharge. We demonstrate that the surface metal oxides can be effectively sputter-eroded from the target during both HiPIMS and MPPMS pulses operated in reactive O2/Ar gas mixtures, and that sputtering from a partially oxide-free target is possible even at high oxygen concentrations. This results in a hysteresis-free deposition process which allows one to prepare optically transparent high refractive index Nb2O5 coatings exhibiting an elevated deposition rate without the need for feedback control commonly used in reactive DCMS. The cathode voltage was identified as the principal parameter that affects the reactive discharge behaviour.

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Biomimetic hydrogel made of poly(ethylene glycol) and soy protein with a water content of 96% has been developed for moist wound dressing applications. In this study, such hybrid hydrogels were investigated by both tensile and unconfined compression measurements in order to understand the relationships between structural parameters of the network, its mechanical properties and protein absorption in vitro. Elastic moduli were found to vary from 1 to 17 kPa depending on the composition, while the Poisson's ratio (approximately 0.18) and deformation at break (approximately 300%) showed no dependence on this parameter. Further calculations yielded the crosslinking concentration, the average molecular weight between crosslinks (M(C)) and the mesh size. The results show that reactions between PEG and protein create polymeric chains comprising molecules of PEG and protein fragments between crosslinks. M(C) is three times higher than that expected for a "theoretical network." On the basis of this data, we propose a model for the 3D network of the hydrogel, which is found to be useful for understanding drug release properties and biomedical potential of the studied material.

We systematically investigate and quantify different physical phenomena influencing the deposition rate, a D , of Nb coatings prepared by high power impulse magnetron sputtering (HiPIMS), and propose a straightforward approach for deposition rate enhancement through the control of the magnetron's magnetic field. The magnetic field strength at the target surface, B, of a 50 mm diameter magnetron was controlled by the application of paramagnetic spacers with different thicknesses in between the magnetron surface and the target. We found that lowering B achieved by the application of a 2.8 mm thick spacer led to an increase in a D by a factor of ∼4.5 (from 10.6 to 45.2 nm min −1) when the discharge was operated at a fixed average pulse target power density (2.5 kW cm −2). However, the ionized fraction of the deposition flux onto the substrate was found to be comparable, despite a large difference in B-dependent discharge characteristics (magnetron voltage and discharge current). We show that the decrease in a D commonly observed in HiPIMS (ranging from 33% to 84% in comparison with dc magnetron sputtering in the presented experiments) is governed by different physical processes, depending on the value of B: for high B, the back-attraction of the target ions towards the target is the dominant effect, while for low B the ion back-attraction, the sub-linear dependence of the sputtering yield on the ion energy, and the variation in material transport effects are all important. Finally, we offer a theoretical background for the observed results, demonstrating that the here-presented conclusions may be applicable to HiPIMS discharges using different metal targets and different inert gases.

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Advanced optical filter applications require an appropriate control of the optical constants, as well as of other suitable film properties such as mechanical performance, thermal and environmental stability, absence of refractive index inhomogeneities, and others. In the present work we studied the characteristics of two high index optical materials, namely amorphous tantalum pentoxide (Ta2O5) and niobium pentoxide (Nb2O5) prepared by plasma enhanced chemical vapor deposition, using penta-ethoxy tantalum Ta(OC2H5)5 and penta-ethoxy niobium, Nb(OC2H5)5, precursors. We particularly investigated the effect of energetic conditions on the film growth by using different modes of plasma excitation, namely rf, microwave, and dual-mode microwave/radio frequency discharges. Under sufficient ion bombardment, controlled by the rf-induced negative substrate bias, the dense Ta2O5 and Nb2O5 films exhibited a refractive index of 2.16 and 2.26 (at 550nm), respectively, while the extinction coefficient was below 10−5, as determined by spectroscopic ellipsometry, and spectrophotometry. We found that increasing ion bombardment during the film growth leads to an appreciable increase of carbon concentration, as indicated by a strong double peak at 1400 and 1500cm−1 in the Fourier transform infrared spectra. Elastic recoil detection measurements revealed an atomic concentration of 2.5% and 5.5% of carbon in the bulk of the Ta2O5 and Nb2O5 films. The presence of carbon did not appear to negatively affect the film optical and mechanical performance and stability. We discuss the relationship between the optical properties and microstructure, and the possible mechanism of carbon bonding in the form of chelate and bridging groups.