H. Bangert

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.

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.

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...

Structure related optical and mechanical properties of oxygen doped Al films

The present results clearly show that the structure of oxygen doped Al films varies from columnar polycrystalline to nanocrystalline and amorphous structure with increasing oxygen concentration. Through the whole scale of oxygen content the structural changes are accompanied by remarkable changes of optical and mechanical properties. The reflectance varies from pure metallic to pure dielectric behaviour. The hardness increases rapidly with increasing oxygen content in agreement with the Hall-Petch relation. The polarization resistance, however, is better for pure Al films.

Solid state diffusion of Sn in polycyrstalline Al films

Abstract The formation of a wetting layer of Sn and the Stranski–Krastanov growth of Sn on a polycrystalline Al film surface has been proved recently. In the present experiments the influence of Sn on the structure evolution of Al films has been analyzed in detail. The films were prepared in HV by magnetron sputtering at 180 °C substrate temperature on Si wafers covered by the native oxide. Al and Sn were sequentially sputtered from a 100-mm diameter DC magnetron target. The samples consisted of an Al-base layer (400 nm), a Sn interlayer (10 nm) and an Al-capping layer (400 nm) and were investigated by analytical and high resolution X-TEM, AFM and scanning AES. If the Sn-interlayer is oxidized, no effect on the growth of the Al-capping layer is observable. If, on the other hand, the Sn-interlayer is prevented from oxidation grain growth is promoted in the Al-capping layer as confirmed by X-TEM and AFM. The capping layer contains intragranular line-like features roughly parallel to the substrate plane. Microanalysis shows the presence of Sn in the capping layer and indicates that Sn is associated with these linear features. The promotion of grain growth in the capping layer can be attributed to the permanent transport of Sn to the growth front via grain boundaries which was confirmed by dynamic scanning AES-measurements. The linear intragranular feature formation is explained by the oxidation of Sn on the free surface due to the residual oxygen present in the background gas.

Monte Carlo simulation of the variation of a binary alloy film composition due to intrinsic resputtering using different working gases

Abstract Intrinsic resputtering is inherently associated with the sputtering process. It is caused by energetic neutral particles resulting from primary sputtering events at the target. These energetic particles are target material atoms with energies up to tens of electronvolts and sputter gas neutrals backscattered from the target with energies exceeding 100 eV. To calculate the gas phase transport of energetic particles and the resputtering effects from the vacuum chamber walls and the substrate, we employed the Monte Carlo technique. The yield for each kind of sputtering event (and also the resputtering process) depends on the mass of the impinging particle and the mass and surface binding energy of the sputtered atom. To study the effect of various working gas atoms on the intrinsic resputtering processes, we simulated the deposition of a Cu-Pb film. Cu and Pb atoms have very different surface binding energies and masses. The variation of the working gas influences the energy of the primary sputtered target atoms and the reflected neutrals. Hence the composition of the deposited binary alloy film due to intrinsic resputtering varies with the pressure due to the different energy transfer from the target to the substrate and the surrounding chamber walls. To check the validity of the simulation results, we also performed experiments with an identical geometry with sputtering from a Cu-2.05at.%Pb target using He, Ne, Ar and Xe as the sputter gases.