C. Eisenmenger-Sittner

Zirconium and hafnium oxoclusters as molecular building blocks for highly dispersed ZrO2 or HfO2 nanoparticles in silica thin films

A novel synthetic route for the preparation of ZrO2 or HfO2 nanoparticles homogeneously dispersed in SiO2 thin films was developed. This route is based on the copolymerisation of organically modified crystalline oxozirconium or oxohafnium clusters (M4O2(OMc)12, M = Zr, Hf; OMc = OC(O)–C(CH3)CH2) with (methacryloxymethyl)triethoxysilane (MAMTES, CH2C(CH3)C(O)O–CH2Si(OCH2CH3)3). These crystalline clusters, which are the precursors for the corresponding metal oxides (MO2), were prepared via the sol–gel route by reaction of zirconium or hafnium butoxide (M(OBu)4) with methacrylic acid. The copolymerisation of the clusters with the methacrylate-functionalised siloxane was photoinitaited by Irgacure 184 and allowed the anchoring of the cluster to the forming silica network. The solution was cast into films by dip-coating and UV cured (10 min, 125 W) to promote the copolymerisation of the methacrylate groups of the cluster with those of the silane. Transparent and homogeneous films 200–450 nm thick were obtained after calcination at 800 °C in air. This route allowed the production of a very homogeneous dispersion of the MO2 precursors inside the silica matrix. The surface and in-depth composition of the thin films was investigated through IR, X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS). SIMS and XPS depth profiles evidenced a very homogenous distribution of both zirconium or hafnium throughout the silica films and sharp film–substrate interfaces. The surface morphology of the coatings was investigated through atomic force microscopy (AFM), which showed smooth, homogeneous and crack-free surfaces. Through X-ray diffraction (XRD) the crystallisation of hafnium and zirconium oxides was revealed, while the presence of isolated crystalline nanoparticles having a diameter of 5–10 nm was evidenced by transmission electron microscopy (TEM). A pull-off test indicated a very good adhesion of the films to the substrate.

The influence of mechanical adhesion of copper coatings on carbon surfaces on the interfacial thermal contact resistance

The weak mechanical and thermal interface in Copper based Metal Matrix Composites (MMCs) reinforced by carbon fibers is the background of this research study. In order to investigate the mechanical adhesion strength and the thermal contact resistance between copper and carbon, a simplified model system based on coated flat carbon substrates has been used. Cu coatings of approximately 1 μm thickness on intermediate Ti bond layers have been deposited on carbon substrates by a sputter deposition process. The resulting different adhesion strengths between coating and substrate have been measured by means of a pull-off method, and non-destructive photothermal method, giving information on the depth-resolved thermal properties of the samples has been used to determine the Thermal Contact Resistance (TCR). By combining the results of mechanical adhesion tests and of photothermal IR radiometry, the correlation of the mechanical adhesion of Cu coatings on Carbon surfaces with the interfacial thermal contact resistance has been analysed.

Angular distribution of sputtered neutrals in a post magnetron geometry: Measurement and Monte Carlo simulation

The angular distributions of Cu particles sputtered from a cylindrical (post) magnetron were measured in a pinhole arrangement at various working gas pressures. The differentially pumped pinhole camera—described in a previous article—allows measurements in a pressure range up to 10 Pa and samples the three‐dimensional distributions in planar sections. Two different planes, namely, parallel and perpendicular to the magnetron axis, were selected for the investigation. Cu was sputtered by Ar ions with an energy of about 0.5 keV from a post magnetron with a very uniform erosion zone. The orifice of the pinhole camera was located at a distance of 50 mm from the cathode surface and in the middle of the erosion zone. The working gas pressure was varied from 0.1 to 1 Pa. The angular distribution of particles was deduced from thickness measurements of films deposited on a semicircular substrate with a 21 mm radius centered around the pinhole. The pressure‐dependent amount of scattering was studied by comparing the...

Deposition and structural properties of two-component metal coatings for tribological applications

Abstract Advanced vacuum deposition processes are gaining increasing importance in material manufacturing. This paper describes the deposition of immiscible metal-metal systems by magnetron sputtering. Two basic deposition modes, codeposition from a multicomponent target and sequential deposition from two separate targets, are discussed. We show that it is possible to obtain a film structure of soft metal particles homogeneously dispersed in a tough metal matrix. In practical, e.g. tribological, applications, the tough matrix takes high mechanical loads, while the soft particles act as a solid lubricant. The dependence of the film structure on the process parameters and film composition is discussed with respect to the different deposition modes. A thermodynamic model, which describes the roughness evolution and phase distribution of a system consisting of a layer-forming matrix and an island-forming inclusion component, is presented for the sequential deposition mode. The results are compared with quantitative atomic force microscopy (AFM) measurements of the surface roughness. For the codeposition mode, the phase distribution in the film can be described by a dynamic model of structural evolution based on the far-from-equilibrium process of diffusion-limited aggregation (DLA). The complex morphological properties of the soft phase are qualitatively well matched with the structures obtained from the model. In conclusion, we discuss a practical application of metallic two-component films as coatings for plain bearings in high performance diesel engines. These bearings are always oil lubricated during the operation of the engine to prevent metal-metal contact. Nevertheless, they are exposed to severe pressures and pressure gradients. Therefore the coating has to resist extremely high and time-dependent mechanical loads. The wear properties of aluminum-tin films, which are currently manufactured by high rate post magnetron sputtering in an industrial process, are compared with conventional bearing designs and are found to be superior to all alternative surface modified designs.

Stranski-Krastanov growth of Sn on a polycrystalline Al film surface initiated by the wetting of Al by Sn

Abstract The deposition of tin (Sn) layers on polycrystalline aluminum surfaces exhibits pronounced islanding. The island formation slightly depends on the deposition rate, substrate temperature and on the surface topography of the Al underlayer. The present study clarifies this islanding mechanism by combined SEM, atomic force microscopy and scanning Auger microscopic (SAM) investigations. The detection of a continuous Sn coverage (“wetting layer”) between the islands indicates a Stranski–Krastanov growth mode of the Sn islands despite the polycrystallinity of the underlying Al surface. The wetting of the Al surface by Sn was proved by in situ sputter cleaning of the sample surface in the SAM chamber. It was possible to completely remove the wetting layer by the sputter cleaning process. Surprisingly, the clean Al surface was covered again by Sn after several minutes as observed by a re-appearance of the Sn-AES signal. The Sn coverage of the surface developed at room temperature within some minutes after removing the wetting layer. Spatially resolved SAM measurements proved that the Sn emerged from the Sn islands (and not from the Al bulk by surface segregation) and spread over the Al surface uniformly. This process led to the complete wetting of the Al surface by Sn despite the thermodynamic immiscibility of this binary system.

Angular distribution of surface excitations for electrons backscattered from Al and Si surfaces

Abstract Spectra of electrons reflected from non crystalline Aluminum and Silicon surfaces have been measured for energies between 300 and 3400 eV. Angular distributions of the elastic peak as well as multiple surface and bulk excitations were recorded for two geometrical arrangements, being each others mirror image with respect to the trajectory of each detected electron. These geometries allow to distinguish between incoming and outgoing electrons in the case such a difference depends on the direction of the electrons with respect to the surface normal. Theoretical calculations [Surf. Interf. Anal. 26 (1998) 682] suggest that such a difference exists in the ratio of the elastic peak and the intensity of the first surface plasmon. The present paper compares experimental results on this quantity that is closely related to the so-called surface excitation parameter for Aluminum and Silicon with theory. The angular distribution of the elastic peak was found to closely follow the single deflection model. Within the experimental accuracy of ∼5% no difference regarding the surface excitation parameter for incoming and outgoing electron trajectories was observed.

Intrinsic resputtering during film deposition investigated by Monte Carlo simulation

In sputter deposition intrinsic resputtering is caused by energetic neutral particles which result from the primary sputter events at the target. These energetic particles are target material atoms, known to have energies up to tens of electron volts and sputter gas neutrals backscattered from the target with energies of up to hundreds of electron volts. The yield for each kind of sputter event depends on the mass of the impinging particle and the mass and surface binding energy of the sputtered atom. Therefore, the composition of a binary alloy film with strongly different surface binding energies and masses of the atoms involved in the deposition process varies due to their individual amount of resputter events. To explore the intrinsic resputtering we chose the Cu–Pb system. The gas phase transport of energetic particles from a Cu 2.05 at. % Pb target to a cylindrical substrate and the resputtering effects from the chamber walls as well as the substrate were calculated using the Monte Carlo technique. ...

Measurement of the angular distribution of sputtered neutrals in a planar magnetron geometry

In the low temperature regime (T<0.3Tm), the microstructure of sputtered films is determined predominantly by the mechanisms of self‐shadowing. Shadowing effects are directly related to the angular distribution of incoming sputtered particles. The angular distributions of copper and lead particles sputtered by Ar+ ions in a planar magnetron geometry were measured using a differentially pumped pinhole camera. The pressure in the pinhole camera was lower by a factor of 10 compared to the ambient working gas. Thus it was possible to monitor the angular distribution of the incoming sputter particles for working gas pressures up to 4 Pa. Transparent films of the impinging particles were deposited on semicircular transparent substrates. Their relative thicknesses were measured by optical densitometry, giving a direct representation of the angular distribution at an arbitrarily chosen point of the sputter chamber. A comparison of the measured angular distributions with distributions calculated for the particular...

AFM and AUGER investigations of as-deposited and heat treated copper coatings on glassy carbon surfaces with titanium intermediate layers

Copper carbon composites are a prospective material for application as heat sink material in thermal management applications. One of the main drawbacks of this material combination is the lack of adhesion between copper and carbon. In order to improve the interfacial properties in this system a basic investigation on carbon substrates was done, where the influence of an adhesion promoting intermediate layer was investigated. Besides the study of the influence of a Ti intermediate layer on the growth mode and surface topography of a copper coating, the diffusion of Ti after a heat treatment was analysed by using Auger electron spectroscopy.

Interface Design in Copper-Diamond Composite by Using PVD and CVD Coated Diamonds

One of the key problems in copper-diamond composites is the interface between the metal matrix and the diamond reinforcement. In order to take advantage of the high thermal conductive diamond filler in a composite the design of the interface is crucial. One approach to minimize the thermal contact resistance between metal and diamond reinforcement is to coat the diamonds with functional layers, e.g. Mo or W. For coating of diamonds PVD and CVD have been used followed by characterization of coating thickness by different methods. The coated diamonds were used for composite manufacturing and the thermal diffusivity of the compacted materials was measured.