Gunnar Sorensen

Electrostatic spraying: a novel technique for preparation of polymer coatings on electrodes.

A liquid flow emerging from a tip or a thin tube under the influence of a strong electric field will, due to charging of the dielectric liquid, break up into small droplets. Thus, if a polymer material is dissolved in the liquid, this electrodeposition technique can be utilized for producing polymer coatings on electrodes. The method was applied for in situ formation of ultrathin (∼3000 Å) cellulose acetate (CA) phase inversion membranes on glassy carbon electrodes. The purpose of the membrane was to protect the electrode surface from fouling by macromolecular species. The spraying liquid consisted of CA, acetone, and aqueous magnesium perchlorate as pore former, and the spraying voltage was 14 kV. Profilometric measurements showed that the thickness of the spray-cast membranes was much more uniform than that of similar membranes formed by solvent casting. By using cadmium and lead as test analytes and differential pulse anodic stripping voltammetry as detection method, it was found that the membranes prepared by spray casting offered better protection against interference from poly(ethylene glycol) (PEG) 6000 than those prepared by solvent casting. Also, the interference from PEG 2000 was significantly reduced. Experimental details of the electrostatic spraying technique are given.

Effect of reactive gas mass flow on the composition and structure of AIN films deposited by reactive sputtering

Abstract The mass flow of the reactive gas during sputtering of AIN has been studied in order to control film stoichiometry as well as film structure and morphology. It has been observed that the film composition and sputtering rate depend strongly on the deposition conditions and, in particular, on the mass flow and the sputtering pressure. It has been possible to deposit transparent, almost stoichiometric as well as non-transparent, metal-rich AIN films. The metal-rich films had a sputtering rate which was a factor of six higher than that for the stoichiometric films. The crystalline texture and the morphology have been studied as a function of the total sputtering pressure for both film types. For the transparent films, this novel deposition procedure may be applied in surface acoustic wave devices. The non-transparent AIN films exhibit some similarities to films obtained by ion vapour deposition or ion-beam-enhanced deposition methods, and the films exhibit interesting tribological properties.

Multilayer film deposition of TiN/AlN on a rotating substrate holder from reactive sputtering of elemental targets of titanium and aluminum

(Ti,Al)Nx coatings have previously been deposited by reactive sputtering from (TiAl) targets. This article will report on a multilayer approach, where a substrate is rotating successively through sputter zones with targets of elemental Ti and Al. In reactive sputtering of these elements the well-known hysteresis curves of total pressure versus reactive gas flow for constant Ar flow were observed. It was then possible to select certain flow values of nitrogen and to maintain a constant sputtering pressure by using a PC process control. By variation of the substrate holder velocity a multilayer TiNx/AlNx system, with bilayer thicknesses from 1 to 8 nm, was studied. The multilayer film was characterized by the acoustic-emission scratch technique used in adhesion studies. Consistency between the various critical load values were achieved, and adhesion values between 40 and 80 N were measured; wear was also found to depend on the number of multilayers.

Reactively sputtered Cr nitride coatings studied using the acoustic emission scratch test technique

Abstract This paper reports the application of the acoustic scratch test technique, developed for adhesion measurements, in a prenormative study related to the cyclic fatigue performance of motor valve springs. The scratch test technique has been considered reliable for adhesion measurements; however, few systematic studies exist, and studies of coatings on contoured shapes are rare. The present study can be considered as a novel mechanical testing methodology based on a comprehensive compilation of results obtained in a surface engineering project for the improvement of the fatigue properties of coated springs. The critical load for chromium nitride coatings, deposited using well-specified plasma conditions on steel substrates, has been measured by optical inspection and derived by studying horizontal force and acoustic emission as a function of load. An Alcatel 650 r.f./d.c. sputtering equipment, with two sputtering cathodes in a sandwich configuration and a computer-controlled reactive gas dosage system defining controllable sputter deposition points, was used. Thus it was possible to measure the sputter rates from both targets and to compare the properties of coatings deposited from lower (L) and upper (U) sputtering targets. To facilitate the establishment of correlations between the plasma conditions and coating characteristics, the paradox database system was used for sorting the data. The data presented show a need for more prenormative research in areas related to scratch testing, such as the initiation and propagation of cracks, in order to obtain more basic information on coating performance.

Solid lubricating films produced by ion bombardment of sputter deposited MoSx films

Abstract Several attempts to enhance the wear resistance (the “sliding life”) of sputter deposited MoS x films have previously been made. However, sputter deposition of MoS x films is often difficult to control owing to changes in substrate temperature and presence of water vapour in the plasma during deposition. In the present study MoS x films were deposited under extremely well controlled conditions with respect to both the deposition temperature and the water vapour pressure. 400 keV Ar + bombardment, performed after film deposition at doses varying from 3 × 10 13 Ar + cm -2 is shown to have a minor influence on film composition, and a marked influence on film structure. The ion bombarded films were subjected to tribological investigations and the sliding life of the various ion bombarded MoS x layers was related to film structure. Using this approach it was possible to gain valuable information on the relation between MoS x film structure and tribological behaviour. Thus, it was shown that the characteristic columnar plate-like MoS x structure is only obtained when H 2 O is present in the plasma, and high fluence (around 1 × 10 16 Ar + cm -2 ) ion beam enhanced sliding life is only found when bombarding these plate-like films. Furthermore, it is shown that the presence of substantial amounts of oxygen in the films (about 25 at.%) is not detrimental to the tribological behaviour, unless the oxygen induces inferior plate-like structures.

Deposition of boron‐nitride films by nitrogen sputtering from a boron‐metal target

This contribution deals with reactive growth of boron‐nitride films by a rf nitrogen‐sputtering process from a boron‐metal target; thus nitrogen is functioning both as sputter and reactive gas. Only few and superficial reports of reactive sputter depositions from a metallic boron target in various argon/nitrogen mixtures exist, compared to the number of reports on rf sputtering from a BN target. Nitrogen sputtering of boron‐metal has previously not been reported. It was shown by Fourier‐transform infrared (FTIR) spectroscopy that the hexagonal structure of BN exclusively was deposited. Sputter rates were measured and showed no dependence on the reactive‐gas flow and only a marginal dependence on sputter‐gas mixtures containing 20% of krypton, argon, or helium. The reported nitrogen‐sputtering process appears to be appropriate for exploration of the key parameters for phase control in BN growth and for additional surface engineering processes such as substrate bias and post‐ion bombardment.

Film growth of nanostructured C–N/TiNx multilayers reactively sputtered in pure nitrogen

The present communication reports on reactive sputtered nanostructured C–N/TiNx multilayers deposited in pure nitrogen. Carbon and titanium sputtering cathodes are operating concurrently in the side by side configuration. Experimental parameters of relevance for the pseudomorphic growth of the carbon nitride multilayer system, for instance, nitrogen flow and the rotation speed of the substrate holder, varying the bilayer thickness, are discussed. Nanostructured composite coatings, typically 2–3 μm thick, were deposited at a pressure ranging from 0.2 to 1 Pa, and seeding with TiN sputtered in pure nitrogen is reported for the C–N/TiNx system. The acoustic emission scratch test was used, both for measurement of coating adhesion and for tribological characterization. Relevant friction parameters, such as friction coefficient and film transfer, when a WC or a Si3N4 ball is reciprocating on the nanostructured multilayer were studied. Further the dynamic impact method was used for testing the coating system, an...

A study of film growth and tribological characterization of nanostructured C-N/TiNX multilayer coatings

Abstract Coatings of C-N/TiN X composite multilayers, where X ≤ 1 in the nanometer range, have been deposited in a reactive sputtering system with side-by-side cathodes of titanium and carbon. Coatings were deposited on samples of tungsten carbide, and high-speed steel on a substrate holder rotating with variable speed from 2 to 28 rpm. Sputtering was performed in nitrogen/argon with a constant Ar flow of 25 sccm. The individual bilayer thicknesses were derived from the deposition rate and the rotation speed. Power for the Ti and C cathodes was kept constant at 1200 W. Deposition parameters were selected from curves showing total sputtering pressure and the voltages of the Ti and C sputtering cathodes versus the nitrogen gas flow. The acoustic emission scratch test developed for coating-adhesion measurements was used as a coarse test for coating evaluation. Particularly, the acoustic emission signal will be discussed and the friction coefficient for sliding against a Si 3 N 4 ball in a ball-on-disk tribometer was measured, and showed a strong dependence on the deposition parameters.

Ion bombardment of AlN films deposited in a reactive sputtering process with accurate control of the mass flow of the reactive gas

Abstract Aluminum nitride (AlN) films can be used as tribological coatings in aggressive media to reduce wear and corrosion owing to its remarkable chemical stability and high decomposition temperature. In the present investigations AlN films were produced by r.f. sputtering under different conditions and then post bombarded by light ions to tailor the surface properties for low coefficient of friction and long wear life. AlN films deposited with varying sputtering conditions differ considerably in deposition rates, crystallinity, and stoichiometry. As-deposited and ion bombarded metal-rich AlN films exhibit a much lower coefficient of friction (less than 0.2) than stoichiometric AlN films (around 0.6). Metal-rich and stoichiometric AlN films exhibit an enormous improvement in wear life when bombarded with B + ions or a mixture of B + and C + ions. The improvement factor due to ion bombardment is higher for metal-rich AlN films. Ionic bombardment of metal-rich AlN film results in improved crystallinity and increased grain size as a function of ion dose.

The formation of conductive films on polyimide by ion-beam-induced decomposition of metal compounds

Thin films of palladium diacetate, palladium dichloride, and palladium dibromide on polyimide substrates have been irradiated with H+, H+2, 3He+,4He+, Ne+, ar+, Kr+ and Xe+ ion beams in the energy range from 35 keV to 2 MeV. Gas evolution was seen during bombardment, after which the films to various degrees appeared metal-like. Conductivity has been induced by heavy-ion bombardment, giving sheet-resistance values between 105 and 13 Ω/□ and resistivity values down to 50 μΩ cm for ion doses between 5 × 1013 and 2.5 × 1015ionscm2. The mechanism of the ion-decomposition process has been investigated by high-energy, light-ion irradiations, and it was found to be related to both nuclear- and electronic-stopping processes, ruling out any beam-heating effects. The selectivity of the decomposition has been demonstrated, producing 5–6 μm features.