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A high power impulse magnetron sputtering (HiPIMS) discharge assisted by a dc pre-ionizer operating at low pressure has been investigated using the Langmuir probe technique as well as energy-resolved mass spectrometry. It was found that the background plasma with densities of about 1 × 109 cm-3 provided by the dc pre-ionizer can reduce the ignition delay time of the HiPIMS plasma from more than 50 μs to less than 5 μs at a working pressure of about 0.1 Pa. Furthermore, the technique of super-imposing HiPIMS with the dc discharge can be readily employed with a low self-sputtering yield target (Ti) at a working pressure of 0.08 Pa, with a pulse width and a repetition frequency of 100 μs and 100 Hz, respectively. This leads to a power density of 450 Won 2 at the target. At these operating conditions, the probe measurements showed a high-density plasma 6 cm in front of the target. The maximum electron density was found to be 8 × 1011 cm-3, with an effective electron temperature of about 3-4 eV. A study of the ion mass distribution revealed that the intensity of Ti2+ ions is larger than the peak of Ti+ in low-pressure operation. Moreover, the number of metal ions in the high-energy tail of the ion energy distribution function increased with a decreasing pressure from 0.5 to 0.08 Pa.

6 pags, 7 figs, 3 tabs, A dielectric barrier discharge (DBD) technique has been employed to produce uniform atmospheric plasmas of He and N2 gas mixtures in open air in order to functionalize the surface of filtered-arc deposited hydrogen-free diamond-like carbon (DLC) films. XPS measurements were carried out on both untreated and He/N2 DBD plasma-treated DLC surfaces. Chemical states of the C 1s and N 1s peaks were collected and used to characterize the surface bonds. Contact angle measurements were also used to record the short- and long-term variations in wettability of treated and untreated DLC. In addition, cell viability tests were performed to determine the influence of various He/N2 atmospheric plasma treatments on the attachment of osteoblast MC3T3 cells. Current evidence shows the feasibility of atmospheric plasmas in producing long-lasting variations in the surface bonding and surface energy of hydrogen-free DLC and consequently the potential for this technique in the functionalization of DLC-coated devices. © 2008 Elsevier B.V. All rights reserved., Financial support from the Marie Curie Outgoing Fellowship Grant MOIF-CT-2005-02195 is gratefully acknowledged. Work at Lawrence Berkeley National Laboratory was supported by the U.S. Department of Energy under Contract No. DE-AC02-05CH11231. Financial support from the Spanish Ministry of Education under project MAT2004-01451 is also gratefully acknowledged

By using a time-resolved Langmuir probe, the temporal evolution of plasma parameters (including the electron energy distribution function) in a preionised HiPIMS discharge were investigated for a number of discharge conditions. Assistance from a DC preioniser circuit providing the remnant and ‘active’ charge particles for the subsequence pulse with the delay time of plasma build-up being decreased dramatically to T de

Optical emission spectroscopy in the range 200-800 nm was applied for investigation of the copper plasma produced by a metal vapour vacuum arc plasma source. The experiments were conducted for the cases when the plasma was guided by straight and Ω-shaped curved solenoids as well as without solenoids, and also for different vacuum conditions. It was found that, besides singly- and doubly-charged ions, a relatively high concentration of excited neutral copper atoms was present in the plasma. The relative fraction of excited atoms was much higher in the region close to the cathode surface than in the plasma column inside the solenoid. The concentration of excited neutral, singly- and doubly-ionized atoms increased proportionally when the arc current was increased to 400 A. Some weak lines were attributed to more highly ionized copper species and impurities in the cathode material.

Energy-resolved mass spectrometry has been used to measure the time-averaged energy and mass distributions of negative ion species in high power impulse magnetron sputtering (HiPIMS) of titanium in an argon/oxygen gas mixture for a number of different discharge conditions. The discharges were found to contain O−, , TiO−, and ions and their respective energy spectra are presented. The oxygen negative ion (O− and ) energy distributions exhibit three broad energy populations (low, medium and high energy) and their origin is discussed. The high-energy peak is found to coincide with a value corresponding to the absolute target potential during the stable on-phase of the HiPIMS pulse. The shape of the high-energy population of O− ions is compared with both a theoretical Thompson energy distribution of sputtered particles and a current-weighted target potential distribution function.A study of the attenuation of high-energy O− ions as a function of the pressure–distance product has been performed. An exponential decrease in intensity of the high-energy O− ions with an increasing pressure–distance product in the substrate region is observed, yielding an effective total cross section of 2.2 × 10−19 m2 for O− interacting with the background gas mixture.

Using a biased quartz crystal microbalance in combination with a gridded electrode, the ionized metal flux fraction in a high power impulse magnetron sputtering (HiPIMS) discharge operated with a titanium target has been investigated. The average discharge power was controlled by varying three different parameters; initial target voltage, pulse width and pulse frequency. The average discharge power was varied from 0.3 to 1.3 kW and irrespective of the power control method used an associated decrease in the flux fraction (from 50% to 30%) was observed. The mechanisms responsible for this decrease in the time-averaged flux fraction of metal ions are discussed.

The velocity and energy distribution functions of ions escaping radially from the magnetic trap region of a HiPIMS discharge have been measured using a retarding field analyzer (RFA). Spatially and angularly resolved measurements recorded at a representative time show more energetic ions detected along a line-of-sight coincident with an oncoming rotating ion fluid, which circulates above the racetrack in the same direction as the electron E ? B drift. The difference in the mean ion energies between measurements made into and against the direction of rotation is ~5?eV. Numerical solutions of the equation of motion for the ions accounting for azimuthal acceleration (modified two-stream instability model used by Lundin et al) have been found. The centripetal force caused by the radial electric field and a drag force term accounting for ion collisions revealed that only a small fraction (typically

Using a time-resolved Langmuir probe the temporal evolution of the bulk plasma parameters in a high-power impulse magnetron sputtering (HiPIMS) discharge was investigated for a number of different discharge conditions. The magnetron was operated in argon between 0.5 and 1.6 Pa with a titanium target and with peak target power densities up to 1000 W cm−2. The pulse width and repetition rate were held constant at 100 µs and 100 Hz, respectively. Using an OML analysis as well as a Druyvesteyn formulation, the electron densities, effective temperatures and energy distribution functions were obtained throughout the pulse period (0–9 ms), including a detailed study of the first 10 µs, which was achieved with a temporal resolution better than 0.5 µs. In the initial phase of the voltage pulse (t ~ 1–4 µs), three distinct groups of electrons (indistinguishable from Maxwellian electrons) were observed, namely 'super-thermal', 'hot' and 'cold' populations with effective temperatures of 70–100 eV, 5–7 eV and 0.8–1 eV, respectively. After 4 µs these groups become energetically indistinguishable from each other to form a single distribution with an electron temperature that decays from about 5 to 3 eV during the rest of the pulse on-time. The presence of the 'super-thermal' electron group pushes the probe floating potential to a very negative value (significantly deeper than −95 V) during the initial period of the pulse. In the off-time, the electron density decays with two-fold characteristic times, revealing initially short-term (30–40 µs) and ultimately long-term (3–4 ms) decay rates. These long decay times lead to a relative high density remnant plasma (2 × 109 cm−3) at the end of the off-time, which serves to seed the next voltage pulse. The electron temperature and plasma potential also exhibit two-fold decay in the off-time, but with typically somewhat faster decays, particularly for the long-term decay (100–500 µs) up to the end of the off-time. The time evolution of the plasma potential shows that for a considerable fraction of the on-time the plasma potential remains negative (down to −12 V) only becoming positive after t ~ 60 µs which corresponds to a time of maximum plasma density (typical values of 2 × 1012 cm−3). The generation of super-thermal electrons in the initial phase of the discharge is argued through the development of a simple magnetized-electron bounce model of the expanding sheath.