Techn. University, Diss., 2004--Dresden.

In dieser Arbeit wurden die mechanischen Eigenschaften der Magnesiumsandgusslegierung AZ91 in Abhängigkeit von den Prozessparametern untersucht. Es wurde gezeigt, dass durch die Anwendung von Filtration, Kornfeinung und Wärmebehandlung das Niveau der mechanischen Eigenschaften des Sandgusses dem des Druckgusses angepasst werden kann. In dieser Arbeit wurde außerdem der Einfluss der Prozessparameter auf die Spannungsrelaxations- und Dämpfungseigenschaften untersucht.

Techn. Universiẗat, Diss., 2005--Darmstadt.

The aim of the presented work was to deposit cubic boron nitride thin films by magnetron sputtering under simultaneous stress relaxation by ion implantation. An in situ instrument based on laser deflectometry on cantilever structures and in situ ellipsometry, was used for in situ stress measurements. The characteristic evolution of the instantaneous stress during the layered growth of cBN films observed in IBAD experiments, could be reproduced for magnetron sputter deposition. To achieve simultaneous stress relaxation by ion implantation, a complex bipolar pulsed substrate bias source was constructed. This power supply enables the growth of cBN thin films under low energy ion irradiation (up to 200 eV) and, for the first time, the simultaneous implantation of ions with an energy of up to 8 keV during high voltage pulses. It was demonstrated that the instantaneous stress in cBN thin films can be released down to -1.1 GPa by simultaneous ion bombardment during the high voltage pulses. A simultaneous stress relaxation during growth is possible in the total investigated ion energy range between 2.5 and 8 keV. These are the lowest ion energies reported for the stress relaxation in cBN. Since such a substrate bias power supply is easy to integrate in existing process lines, this result is important for industrial deposition of thin films, not only for cubic boron nitride films. It was found that the amount of stress relaxation depends on the number of atomic displacements (displacements per atom: dpa) that are induced by the high energy ion bombardment and is therefore dependent on the ion energy and the high energy ion flux. In practise, this means that the stress relaxation is controlled by the product of the pulse voltage and the pulse duty cycle or frequency. The cantilever bending measurements were complemented on microscopic scale by x-ray diffraction (XRD). The analysis of the cBN (111) lattice distances revealed a pronounced biaxial compressive state of stress in a non-relaxed cBN film with d(111) being larger in out-of-plane than in in-plane direction. Post deposition annealing at 900 ° C of a sample with an ion induced damage of 1.2 dpa, resulted in a complete relaxation of the lattice with equal in-plane and out-of-plane lattice parameters. In the case of medium-energy ion bombardment, the in-plane and out-of-plane lattice parameters approach the value of the annealed sample with increasing ion damage. This is a clear evidence for stress relaxation within the cBN lattice. The stability of cBN under ion bombardment was investigated by IR spectroscopy and XRD. The crystalline cBN was found to be very stable against ion irradiation. However a short-range ordered, sp3/sp2 - mixed phase may exist in the films, which could be preferably converted to a sp2 -phase at high damage values. From the analysis of the near surface region by XANES, it can be concluded the stress relaxation by the energetic ion bombardment is less at the surface than in the bulk film. This is explained with the dynamic profile of the ion induced damage, that reaches the stationary bulk value in 15-20 nm depth, whereas it is decreasing towards the surface. This fits with the results that the stress relaxation is dependent on the amount of ion induced damage. Comparing the results from substrate curvature measurement, XRD, XANES, and IR spectroscopy possible mechanisms of stress relaxation are discussed. Concluding the results, it can be stated that using simultaneous ion implantation for stress relaxation during the deposition it is possible to produce BN films with a high amount of the cubic phase and with very low residual stress.

The aim of the presented work was to deposit cubic boron nitride thin films by magnetron sputtering under simultaneous stress relaxation by ion implantation. An in situ instrument based on laser deflectometry on cantilever structures and in situ ellipsometry, was used for in situ stress measurements. The characteristic evolution of the instantaneous stress during the layered growth of cBN films observed in IBAD experiments, could be reproduced for magnetron sputter deposition. To achieve simultaneous stress relaxation by ion implantation, a complex bipolar pulsed substrate bias source was constructed. This power supply enables the growth of cBN thin films under low energy ion irradiation (up to 200 eV) and, for the first time, the simultaneous implantation of ions with an energy of up to 8 keV during high voltage pulses. It was demonstrated that the instantaneous stress in cBN thin films can be released down to -1.1 GPa by simultaneous ion bombardment during the high voltage pulses. A simultaneous stress relaxation during growth is possible in the total investigated ion energy range between 2.5 and 8 keV. These are the lowest ion energies reported for the stress relaxation in cBN. Since such a substrate bias power supply is easy to integrate in existing process lines, this result is important for industrial deposition of thin films, not only for cubic boron nitride films. It was found that the amount of stress relaxation depends on the number of atomic displacements (displacements per atom: dpa) that are induced by the high energy ion bombardment and is therefore dependent on the ion energy and the high energy ion flux. In practise, this means that the stress relaxation is controlled by the product of the pulse voltage and the pulse duty cycle or frequency. The cantilever bending measurements were complemented on microscopic scale by x-ray diffraction (XRD). The analysis of the cBN (111) lattice distances revealed a pronounced biaxial compressive state of stress in a non-relaxed cBN film with d(111) being larger in out-of-plane than in in-plane direction. Post deposition annealing at 900 ° C of a sample with an ion induced damage of 1.2 dpa, resulted in a complete relaxation of the lattice with equal in-plane and out-of-plane lattice parameters. In the case of medium-energy ion bombardment, the in-plane and out-of-plane lattice parameters approach the value of the annealed sample with increasing ion damage. This is a clear evidence for stress relaxation within the cBN lattice. The stability of cBN under ion bombardment was investigated by IR spectroscopy and XRD. The crystalline cBN was found to be very stable against ion irradiation. However a short-range ordered, sp3/sp2 - mixed phase may exist in the films, which could be preferably converted to a sp2 -phase at high damage values. From the analysis of the near surface region by XANES, it can be concluded the stress relaxation by the energetic ion bombardment is less at the surface than in the bulk film. This is explained with the dynamic profile of the ion induced damage, that reaches the stationary bulk value in 15-20 nm depth, whereas it is decreasing towards the surface. This fits with the results that the stress relaxation is dependent on the amount of ion induced damage. Comparing the results from substrate curvature measurement, XRD, XANES, and IR spectroscopy possible mechanisms of stress relaxation are discussed. Concluding the results, it can be stated that using simultaneous ion implantation for stress relaxation during the deposition it is possible to produce BN films with a high amount of the cubic phase and with very low residual stress.

Techn. Universiẗat, Diss., 2005--Darmstadt.

In dieser Arbeit wurden die mechanischen Eigenschaften der Magnesiumsandgusslegierung AZ91 in Abhängigkeit von den Prozessparametern untersucht. Es wurde gezeigt, dass durch die Anwendung von Filtration, Kornfeinung und Wärmebehandlung das Niveau der mechanischen Eigenschaften des Sandgusses dem des Druckgusses angepasst werden kann. In dieser Arbeit wurde außerdem der Einfluss der Prozessparameter auf die Spannungsrelaxations- und Dämpfungseigenschaften untersucht.

Nanotubular structures from a new family of misfit compounds LnS–TaS₂ with (Ln = La, Ce, Nd, Ho, Er) and LaSe–TaSe₂ (some of them not known hitherto) are reported. Stress relaxation originating from the lattice mismatch between the alternating LnS(Se) and TaS₂(Se) layers, combined with seaming of the dangling bonds in the rim, leads to the formation of a variety of nanotubular structures. Their structures are studied via scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), scanning transmission electron microscopy (STEM) and selected area electron diffraction (SAED). Tubules exhibiting a single folding vector for the LnS(Se) as well as TaS₂(Se) layers were often found. The small values of the c-axis periodicities are indicative of a strong interaction between the two constituent layers which was also supported by Raman spectroscopy and theoretical calculations.