Jochen M. Schneider

Ionized sputter deposition using an extremely high plasma density pulsed magnetron discharge

Time resolved plasma probe measurements of a novel high power density pulsed plasma discharge are presented. Extreme peak power densities in the pulse (on the order of several kW cm−2) result in a very dense plasma with substrate ionic flux densities of up to 1 A cm−2 at source-to-substrate distances of several cm and at a pressure of 0.13 Pa (1 mTorr). The pulse duration was ∼100 μs with a pulse repetition frequency of 50 Hz. The plasma consists of metallic and inert gas ions, as determined from time resolved Langmuir probe measurements and in situ optical emission spectroscopy data. It was found that the plasma composition at the beginning of the pulse was dominated by Ar ions. As time elapsed metal ions were detected and finally dominated the ion composition. The effect of the process parameters on the temporal development of the ionic fluxes is discussed. The ionized portion of the sputtered metal flux was found to have an average velocity of 2500 m s−1 at 6 cm distance from the source, which conforms...

Structure and bulk modulus of M2AlC (M=Ti, V, and Cr)

We have performed theoretical studies of the bulk modulus of M2AlC, where M=Ti, V, Cr by means of ab initio total energy calculations using the projector augmented wave methods. Our estimated equilibrium volume and the lattice parameters (c/a) agree well (within ±2% and ±0.06%, respectively) with experimental data. The bulk modulus of M2AlC increases as Ti is substituted with V and Cr by 19% and 36%, respectively. This can be understood since the substitution of Ti by V and Cr is associated with an extensive increase in the M–Al and M–C bond energy.

Influence of the Al distribution on the structure, elastic properties, and phase stability of supersaturated Ti1−xAlxN

Ti1−xAlxN films and/or their alloys are employed in many industrial applications due to their excellent mechanical and thermal properties. Synthesized by plasma-assisted vapor deposition, Ti1−xAlxN is reported to crystallize in the cubic NaCl (c) structure for AlN mole fractions below 0.4–0.91, whereas at larger Al contents the hexagonal ZnS-wurtzite (w) structure is observed. Here we use ab initio calculations to analyze the effect of composition and Al distribution on the metal sublattice on phase stability, structure, and elastic properties of c-Ti1−xAlxN and w-Ti1−xAlxN. We show that the phase stability of supersaturated c-Ti1−xAlxN not only depends on the chemical composition but also on the Al distribution of the metal sublattice. An increase of the metastable solubility limit of AlN in c-Ti1−xAlxN from 0.64 to 0.74 is obtained by decreasing the number of Ti–Al bonds. This can be understood by considering the Al distribution induced changes of the electronic structure, bond energy, and configuration...

Crystalline alumina deposited at low temperatures by ionized magnetron sputtering

Ionized magnetron sputtering based on the work of Rossnagel and Hopwood [J. Vac. Sci. Technol. B 12, 449 (1994)] has been used to deposit alumina films containing orthorhombic κ alumina and monoclinic θ alumina at substrate temperatures of 370 to 430 °C. An inductively coupled rf Ar/O2/Al discharge between the sputter source and the heated substrate table was used to effectively ionize not only Ar but more importantly Al and O2. Both ion energy as well as the ion flux to the substrate influence the structure and properties of the coatings. The ion energy was controlled by the substrate bias potential, and the ion flux by means of the rf power supplied to the coil. The effect of the degree of ionization and therefore the ion flux to the substrate was studied at a constant substrate bias potential of −70 V. It was found that as the ion flux to the substrate was increased, the film crystallinity increased (i.e. the Bragg diffraction peaks were sharper and had higher intensity). It was shown that the formatio...

Multilayer composite ceramicmetal-DLC coatings for sliding wear applications

Abstract The design of anti-friction coatings able to perform well in different wear conditions without lubricants requires a combination of adequate hardness and toughness, good adhesion, a low friction coefficient and a low wear rate. Recently introduced metaldiamond like carbon (DLC) coatings produced by magnetron sputtering of metals from targets, which are to a controlled extent covered with carbon from the chamber atmosphere, can be a step towards the achievement of such a combination. These coatings consist of an amorphous a:CH matrix with the possible incorporation of metal (Ta, W, Nb, Ti), metal carbide and/or graphite grains. Previous studies of Ti x% -DLC coatings showed their good protective properties against abrasive, impact and single scratch wear, as well as a requirement for supporting interlayers to successfully apply such coatings to low-cost steels. In the present work an example of the selection of metal-ceramic Ti-TiN-TiCN supporting interlayers is given based on studies of their morphology, structure and mechanical properties. This resulted in the development of Ti-TiN-TiCN-[TiC-(Ti x% -DLC)] multilayer composite coatings. Several coatings were prepared with the same supporting interlayer and a variation in the preparation of the Ti x% -DLC layer. Ball-on-disc experiments were carried out to investigate these coatings in conditions of sliding wear against steel and cemented tungsten carbide balls. CrN, TiN and TiCN coatings were also deposited and tested in the same conditions to provide a reference. Low friction coefficients (below 0.2 at an air humidity of 50% RH) in combination with low normalized wear rates were found for multilayer coatings with upper Ti 20% -DLC and Ti 35% -DLC layers.

Ab initio calculated binodal and spinodal of cubic Ti1−xAlxN

During annealing, metastable NaCl-structured (c) Ti1−xAlxN films initially exhibit spinodal decomposition which results in age hardening. Based on ab initio calculations, we show that the chemical requirement for spinodal decomposition in the quasibinary c‐TiN–c‐AlN system is fulfilled over a wide composition and temperature range. The enthalpy change for the decomposition of c‐Ti0.34Al0.66N is ∼26.4kJmol−1, which is in good agreement with previously reported experiments. The obtained results enable materials design of Ti1−xAlxN-based coating systems for high-temperature applications.

Influence of the negative oxygen ions on the structure evolution of transition metal oxide thin films

The energy distributions of O− ions of magnetron sputtered Nb, Ta, Zr, and Hf in an Ar∕O2 atmosphere were measured as a function of the oxygen partial pressure. Three ion populations were detected in the plasma: high, medium, and low energy ions, with energies corresponding to the target potential, half of the target potential, and <150eV, respectively. The ion energy distribution functions were compared to distributions obtained based on Sigmund’s linear collision cascade sputtering theory. If the surface binding energy is assumed to be equal to the heat of formation, good agreement between the experiment and theory was achieved. From correlating the measured ion energy distributions with previously published phase stability data [Ngaruiya et al., Appl. Phys. Lett. 85, 748 (2004)], it can be deduced that large fluxes of medium and high energy O− ions comparable to the fluxes of the low energy O− ions enable formation of crystalline transition metal oxide thin films during low temperature growth. The pres...

Recent developments in plasma assisted physical vapour deposition

Recent developments in plasma assisted physical vapour deposition (PAPVD) processes are reviewed. A short section on milestones in advances in PAPVD covering the time period from 1938 when the first PAPVD system was patented to the end of the 1980s is followed by a more detailed discussion of some more recent advances, most of which have been related to increases in plasma density. It has been demonstrated that the state of the art PAPVD processes operate in a plasma density range of 1011 to 1013 cm-3. In this range a substantial fraction of the plasma consists of ionized film forming species. Hence, the energy of the condensing film forming species can be directly controlled, as opposed to utilizing indirect energy control with, for example, ionized inert gas bombardment. For a large variety of applications ranging from ceramic film synthesis at conditions far from thermodynamic equilibrium to state of the art metallization technology, such direct energy control of the condensing film forming species is of critical importance, and offers the possibility to engineer the coating microstructure and hence the coating properties.

Wear resistant composite coatings deposited by electron enhanced closed field unbalanced magnetron sputtering

There is presently considerable interest in wear resistant coatings produced using closed field unbalanced magnetron sputtering technology. For example, layered films of diamond-like carbon (DLC) with tungsten or titanium additions have been widely reported. The benefit is that the mechanical properties are enhanced (e.g. giving greater toughness); also it is possible to control the stress state and enhance adhesion. Here we report the further development of this concept by the addition of TiN, TiCN and TiC layers in DLC-based composites, utilizing an additional source of electrons in the vicinity of substrate to enhance ionisation of the plasma and increase coating density. Composite coatings of ceramics TiN, TiCxNy, TiC, CrN, TiCrN, TiCrCN, TiCrC, metal doped Tix%-DLC and their combinations were deposited on 316 stainless steel substrates. The mass flow of reactive gases into the chamber was controlled using plasma optical emission monitoring to achieve the desired coating composition. The morphology of the coatings was investigated and correlated with Knoop microhardness, scratch adhesion, pin-on-disc and wet abrasive wheel tests. Dense T-type structures were found for most of the coatings and a high toughness of Ti30%-DLC coating with a TiC interlayer was observed. Low friction coefficients of 0.15–0.18 for coatings with Tix%-DLC layers confirmed their benefit in sliding wear applications, while TiCN coatings were found to be the best in abrasive wear conditions.

Energy distribution of O- ions during reactive magnetron sputtering

Low, medium, and high energy O− ion populations were experimentally detected during magnetron sputtering of Al in an Ar∕O2 atmosphere. Based on calculations, the authors propose that nonsputtered O− ions originating from the target surface are accelerated in the cathode fall, while sputtered O− ions may be excluded as a significant contribution to the high energy ion population. Furthermore, the formation of medium energy O− ions is consistent with the notion of sputtered, in the cathode fall accelerated, and subsequently dissociated AlO− and AlO2− clusters. These findings may be of importance for understanding plasma energetics and growth involving electronegative species.