Polymers capable of thermally controlled reversible bonding reactions are promising candidates for stimuli responsive materials, as required for self-healing or drug delivery materials. In order to investigate how the dynamic reactions can be controlled, effective analytical tools are demanded that are capable of analyzing not only the polymers but can also monitor the respective bonding reactions. Herein, we employ size exclusion chromatography in a newly developed temperature dependent mode (TD SEC) for the in situ characterization of polymers that undergo retro Diels-Alder (rDA) reaction at temperatures higher than 60 °C. Monitoring the evolution of the molar mass distribution of the polymers during the rDA reaction and evaluating the data quantitatively gives detailed information about the extent of the reaction and allows elucidating structural parameters that can be used for controlling the polymers debonding behavior. In contrast to spectroscopic techniques, TD SEC analyzes only the size of the polymers, hence the polymers do not need to fulfill any particular requirements (e.g. presence of detectable functional groups) but only need to be soluble in the TD SEC, which makes the method universally applicable. Side effects that might bias the results are minimized by using a high temperature chromatograph that allows performing the analysis in a broad temperature range (60 – 200 °C) and in different solvents. Thus, the analysis can be performed under the exact conditions that are required for the bonding reactions and an in situ image is provided.

Die Mechanochemie wird als Alternative zu konventionellen Syntheserouten mittlerweile vielfältig eingesetzt. In dieser Arbeit wurden verschiedene Ansätze genutzt, um die mechanochemischen Mechanismen systematisch aufzuklären. Anhand von Modellsystemen (Cokristalle) wurden die mechanochemischen Synthesewege durch in situ-Verfolgung aufgeklärt, die kinetischen sowie thermodynamischen Stabilitäten der Edukte und Produkte ermittelt sowie die Aktivierungsenergie quantitativ abgeschätzt. Die Ergebnisse führten zur Hypothese, dass die mechanochemische Cokristallisation über einen nicht-kristallinen – wahrscheinlich amorphen – Übergangszustand abläuft und ähnlich der Kristallisation aus Lösung ist. / Mechanochemistry is a widely used alternative for conventional synthesis methods. In this work, different approaches were considered to evaluate the mechanochemical formation pathways. Based on model systems (cocrystals) the synthesis pathways were elucidated using in situ monitoring techniques and thermodynamic and kinetic aspects were investigated. The activation energy of a mechanochemical reaction was quantitavely estimated. The results lead to the assumption that the mechanochemical cocrystallisation proceeds via a non-crystalline phase and that it is similar to the crystallisation from solution.

Polymers capable of thermally controlled reversible bonding reactions are promising candidates for stimuli responsive materials, as required for self-healing or drug delivery materials. In order to investigate how the dynamic reactions can be controlled, effective analytical tools are demanded that are capable of analyzing not only the polymers but can also monitor the respective bonding reactions. Herein, we employ size exclusion chromatography in a newly developed temperature dependent mode (TD SEC) for the in situ characterization of polymers that undergo retro Diels-Alder (rDA) reaction at temperatures higher than 60 °C. Monitoring the evolution of the molar mass distribution of the polymers during the rDA reaction and evaluating the data quantitatively gives detailed information about the extent of the reaction and allows elucidating structural parameters that can be used for controlling the polymers debonding behavior. In contrast to spectroscopic techniques, TD SEC analyzes only the size of the polymers, hence the polymers do not need to fulfill any particular requirements (e.g. presence of detectable functional groups) but only need to be soluble in the TD SEC, which makes the method universally applicable. Side effects that might bias the results are minimized by using a high temperature chromatograph that allows performing the analysis in a broad temperature range (60 – 200 °C) and in different solvents. Thus, the analysis can be performed under the exact conditions that are required for the bonding reactions and an in situ image is provided.

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.