Edda Rädlein

Research and development in the field of glass-based laser additive manufacturing continues to receive significant interest within scientific and industrial contexts. In particular, powder bed fusion by laser radiation (PBF-LB) enables the additive manufacturing of porous and vitrified, complex three-dimensional components. The present study investigates the glass morphology that can be achieved using PBF-LB for components made from alkali borosilicate glass. The investigations focus on the comprehensive analysis of the entire process window, including the characterisation of porous and molten glass morphology. In particular, the influence of different laser-beam diameters, which are achieved through defocusing, and the variation in volume energy density are examined in detail and compared with conventional shaping. It was determined that the process of mechanically stable shaping is constrained to temperatures above the softening temperature and relative component densities within the range of ρrel = 37.8…94.2%. Furthermore, it has been demonstrated that the process-related line-like energy input results in the formation of characteristic vitrification strands. This research contributes to the overall understanding of the producible glass morphology and the process limitations of the PBF-LB process. In addition, the entire range of glass morphologies, ranging from open-pored to closed-melt configurations, could be analysed for the first time.

Kurzfassung: Lithium ist das zentrale Element moderner Batterietechnologien, und die Herstellung von lithiumhaltigen Materialien mittels Atomlagenabscheidung (engl. Atomic Layer Deposition, ALD) bietet erhebliche Vorteile bei der Kontrolle der Schichtdicke und ‐zusammensetzung. In dieser Studie wird ein neuer mononuklearer, durch ein N‐heterocyclisches Carben (NHC) stabilisierter Lithiumkomplex, [Li( ^tBu NHC)(hmds)], als vielversprechender Präkursor für die ALD von lithiumhaltigen Dünnschichten vorgestellt. Die strukturelle Charakterisierung erfolgt durch den Vergleich von Dichtefunktionaltheorie (DFT) und Einkristall‐Röntgenbeugung (engl. Single‐Crystal X‐ray Diffraction, SC‐XRD), wobei die seltene mononukleare Struktur bestätigt wird. Thermogravimetrische Analysen (TGA) zeigen vorteilhafte thermische Eigenschaften für ALD‐Anwendungen. Die Verbindung weist einen niedrigen Schmelzpunkt, saubere Verdampfung und ermutigende Volatilitätsparameter im Vergleich zu anderen Lithium‐Präkursoren auf. ALD‐Experimente mit [Li( ^tBu NHC)(hmds)] und Ozon zeigen dessen Effektivität bei der Abscheidung von LiSi _x O _y ‐Filmen. Der ALD‐Prozess zeigt ein gesättigtes Wachstum pro Zyklus (engl. Growth per Cycle, GPC) von 0,95 Å. Die Zusammensetzung, analysiert mittels Rutherford‐Rückstreu‐Spektrometrie/Kernreaktionsanalyse (engl. Rutherford Backscattering Spectrometry/Nuclear Reaction Analysis, RBS/NRA), Röntgenphotoelektronenspektroskopie (engl. X‐ray Photoelectron Spectroscopy, XPS) und Glimmentladungsspektroskopie (engl. Glow Discharge Optical Emission Spectrometry, GD‐OES), bestätigt das Vorhandensein von Lithium und Silizium in den erwarteten Verhältnissen. Diese Arbeit stellt nicht nur einen neuen ALD‐Präkursor vor, sondern trägt auch zum Verständnis der Lithiumchemie bei und bietet Einblicke in die faszinierende Koordinationschemie und das thermische Verhalten von durch NHC‐Liganden stabilisierten Lithiumkomplexen.

Lithium is the core material of modern battery technologies and fabricating the lithium‐containing materials with atomic layer deposition (ALD) confers significant benefits in control of film composition and thickness. In this work, a new mononuclear N‐heterocyclic carbene (NHC) stabilized lithium complex, [Li( ^tBu NHC)(hmds)], is introduced as a promising precursor for ALD of lithium‐containing thin films. Structural characterization is performed, comparing density functional theory (DFT) and single‐crystal X‐ray diffraction (SC‐XRD), confirming a rare mononuclear structure. Favorable thermal properties for ALD applications are evidenced by thermogravimetric analysis (TGA). The compound exhibits a low melting point, clean evaporation, and its volatility parameters are encouraging compared to other lithium precursors. ALD trials using [Li( ^tBu NHC)(hmds)] with ozone demonstrate its effectiveness in depositing LiSi _x O _y films. The ALD process exhibits a saturated growth per cycle (GPC) of 0.95 Å. Compositional analysis using Rutherford backscattering spectrometry/nuclear reaction analysis (RBS/NRA), X‐ray photoelectron spectrometry (XPS), and glow discharge optical emission spectrometry (GD‐OES), confirms the presence of lithium and silicon in the expected ratios. This work not only presents a new ALD precursor but also contributes to the understanding of lithium chemistry, offering insights into the intriguing coordination chemistry and thermal behavior of lithium complexes stabilized by NHC ligands.

Photosensitive glasses for radiation-induced 3D microstructuring, due to their optical transparency and thermal, mechanical, and chemical resistance, enable the use of new strategies for numerous microscale applications, ranging from optics to biomedical systems. In this context, we investigated the plasma etching of photosensitive glasses after their exposure and compared it to the established wet chemical etching method, which offers new degrees of freedom in microstructuring control and microsystem fabrication. A CF₄/H₂ etching gas mixture with a constant volumetric flow of 30 sccm and a variable H₂ concentration from 0% to 40% was utilized for plasma-based etching, while for wet chemical etching, diluted hydrofluoric acid (1% ≤ c_HF ≤ 20%) was used. Therefore, both etching processes are based on a chemical etching attack involving fluorine ions. A key result is the observed reversion of the etch selectivity between the initial glassy and partially crystallized parts that evolve after UV exposure and thermal treatment. The crystallized parts were found to be 27 times more soluble than the unexposed glass parts during wet chemical etching. During the plasma etching process, the glassy components dissolve approximately 2.5 times faster than the partially crystalline components. Unlike wet chemical etching, the surfaces of plasma etched photostructured samples showed cone- and truncated-cone-shaped topographies, which supposedly resulted from self-masking effects during plasma etching, as well as a distinct physical contribution from the plasma etching process. The influences of various water species on the etching behaviors of the homogeneous glass and partially crystallized material are discussed based on FTIR-ATR and in relation to the respective etch rates and SNMS measurements.