Pseudo-γ aluminum oxide: A new transparent conductive oxide with outstanding structural properties

Wolframcarbid (WC) ist aufgrund seiner hohen Härte und Reibungsfestigkeit ein weit ver- breitetes Material für Schneidwerkzeuge. Bei hohen Temperaturen (z.B. durch Reibung beim Schnittprozess) tritt Oxidation auf und die stabile Phase von Wolframcarbid wird in eine pul- vrige Phase umgewandelt. Um Oxidation zu vermeiden und die Lebensdauer des Werkzeugs zu erhöhen, werden einzelne oder mehrere Schutzschichten aus verschiedenen Oxiden und Nitriden auf WC-Substrate aufgebracht. Bei Abscheidung mittels physical vapor deposition (PVD) Prozessen (bspw. Magnetron- Sputtern) wird ein Vorspannungspotential an das Substrat angelegt, um die für den Wachstumsprozess erforderliche Oberflächenenergie zu erreichen. Beim Aufwachsen von isolierenden Schichten (wie den meisten Metalloxiden) wird das effektive Vorspannungspoten- tial während des Wachstums verringert, was zu einer schlechteren Kristallinität führt. Die Entwicklung eines halbleitenden Oxids mit herausragenden mechanischen Eigenschaften für Beschichtungsanwendungen ist daher von großem Interesse. In dieser Arbeit wurde Aluminiumoxid auf Wolframcarbidsubstrat abgeschieden, wobei Dual- Magnetron-Sputtern (DMS) mit Argon als Sputtergas verwendet wurde. Die Abscheidungs- bedingungen während des Wachstumsprozesses werden durch viele verschiedene Parameter definiert. Es wurde eine Kombination aus Argon- und Sauerstoffdruck während des Sputterns zusammen mit dem Vorspannungspotential und der Substrattemperatur identifiziert, die zu einer elektrisch leitfähigen Aluminiumoxidphase führt. Ziel dieser Arbeit war es, die leitfähige Aluminiumoxidphase hinsichtlich der strukturellen und elektrischen Eigenschaften zu analysieren. Neben der verbesserten Qualität verschleißfester Beschichtungen für Schneidanwendungen ist leitfähiges Aluminiumoxid ein interessantes neues Mitglied der transparenten leitfähigen Oxide (TCO). Große Forschungsanstrengungen werden unternommen, um einen Ersatz für Indiumzinnoxid (ITO) zu finden, da es aus teuren und seltenen Materialien besteht. Ein leitfähiges Aluminiumoxid benötigt hingegen nur leicht verfügbare Materialien und ist daher ein hervorragender Kandidat, um bei zukünftigen TCO- Entwicklungen eine wichtige Rolle zu spielen. Die in dieser Arbeit analysierte Proben wurden von der Walter AG in Tübingen zur Verfügung gestellt. Die Proben bestehen aus WC-Substrat mit Verschleissschutzschichten aus Aluminiu- moxid, abgeschieden mittels DMS. Eine Teil der Proben wurde mittels Hochleistungsimpuls- Magnetron-Sputtern (HIPIMS) mit einer zusätzlichen Ti 0.33 Al 0.67 N-Schicht beschichtet. Die Struktur der leitfähigen Phase wurde als ungeordnete kubische Struktur identifiziert aus Aluminium und Sauerstoff, sowie Argon mit Molanteilen bis zu 2.5 at%. Bisher bekannte un- geordnete kubische Aluminiumoxidphasen sind als γ Aluminiumoxid bekannt und sind alle elektrisch isolierend. Um daher die elektrische leitfähige Phase abzugrenzen, wurde der Begriff pseudo-γ Aluminiumoxid eingeführt. Aufgrund seiner einzigartigen Struktur (bekannt als ungeordneter Spinell) ist es möglich, große Mengen an Edelgasatomen in die Struktur einzubauen. Doch nur beim Wachstum mittels DMS führt der Einbau von Argon zur Bildung der leitfähigen Phase. Die Ar- Atome scheinen die pseudo-γ Phase zu stabilisieren. Um die Rolle des Argon innerhalb der leitfähigen Phase zu verstehen, wurden die strukturellen Merkmale sowie die elektrischen Eigenschaften der pseudo-γ Phase in dieser Arbeit detailliert untersucht. Die Charakterisierung der Proben wurde sowohl an Draufsicht- als auch an Querschnittsproben durchgeführt. Die Proben wurden so ausgewählt, dass sie einen breiten Bereich an Probeneigenschaften abdecken, bspw. Probendicke, Vorspannungspotential, aber auch unter- schiedliche Härtewerte. Quantitative energiedispersive Röntgen-Spektroskopie (EDX) wurde im Rasterelektronenmikroskop (REM) durchgeführt, um die Ar-Molanteile zu bestimmen und eine Korrelation der Probenhärte mit der Ar-Molfraktion aufzustellen. Durch genaue Bestimmung des Ar- Anteils in Draufsicht sowie im Querschnitt konnte der Ar- Anteil erfolgreich mit der Probenhärte korreliert werden. Dies zeigt, dass die Ar- Atome für die Bildung der stabilen Struktur wesentlich sind. Zudem konnte mittels Röntgendiffraktometrie (XRD) beobachtet werden, dass die Gitterkonstante der Struktur umso größer wird, je mehr Ar in die pseudo-γ Phase eingebaut wurde. In REM-EDX Linescans an Querschnittproben wurde eine inhomogene Ar-Verteilung fest- gestellt. Der höchste Ar-Anteil wurde immer an der Grenzfläche zum WC-Substrat gemessen. Für den Rest der Probe wurden unterschiedliche Argonprofile gefunden, die von einem linearen Abfall im gesamten Film bis zu einem zweiten, kleineren Maximum des Ar-Anteils reichen. Untersuchungen im Transmissionselektronenmikroskop (TEM) ergaben, dass die Unterschiede im Ar-Molanteil tatsächlich mit den Strukturmerkmalen der pseudo-γAluminiumoxidphase zusammenhängen. Für die im TEM untersuchten Proben wurde eine Mehrschichtstruktur an der Grenzfläche zum Substrat mit hohen Ar-Molanteilen bis zu 10 at% gefunden. Für den Rest der Probe wurden unterschiedliche Merkmale für die Probe mit höherer und niedrigerer Härte gefunden. Die Probe mit hoher Härte zeigte säulenförmige Körner mit einem konstanten Ar- Molanteil bei ≈ 2 at%, während die Probe mit geringer Härte kleinere Körner mit abnehmen- dem Ar-Molanteil zur Oberseite des Films zeigte. Im Hinblick auf die elektrische Charakterisierung wurden zwei verschiedene Kontak- tierungsmethoden erfolgreich angewendet, sowohl DC-gesputterte Au-Kontakte als auch mit HIPIMS abgeschiedene Ti 0.33 Al 0.67 N-Kontakte. DC-Au-Kontakte zeigten niedrige ohmsche Widerstandswerte bei Raumtemperatur und halbleitendes Verhalten bei temperaturabhängi- gen Messungen. An denselben Proben wurde auch das Verhältnis der Thermokraft zur Wärmeleitfähigkeit von pseudo-γ Aluminiumoxid bestimmt, wobei ein positives Vorzeichen der Thermokraft festgestellt wurde. Temperaturabhängige Messungen des elektrischen Widerstandes wurden auch an Proben mit Ti 0.33 Al 0.67 N auf pseudo-γ Aluminiumoxid durchgeführt. Alle Proben zeigten in Arrhenius- Diagrammen gekrümmte Linien der elektrischen Leitfähigkeit, wie sie für einen polykristalli- nen Halbleiter erwartet werden. Durch die sorgfältige Auswahl des richtigen Modells zur Erk- lärung der Krümmung können Einblicke in die für das angewandte Modell wesentlichen Struk- turmerkmale wie Kornstruktur und Homogenität der Filme gewonnen werden. Für die weitere Verwendung von pseudo-γ Aluminiumoxid als TCO wurde die Möglichkeit un- tersucht, die Struktur auf verschiedene Substrate zu übertragen. Dünne Aluminiumoxid Filme wurden auf WC-Substrat (als Referenz) und auf elektrisch isolierendem SiO 2 abgeschieden, was in beiden Fällen zur gleichen pseudo-γ Aluminiumoxidphase führte. Alle angewandten Charakterisierungsmethoden wie XRD, REM und REM EDX zeigten, dass die abgeschiedenen Aluminiumoxidfilme identisch sind und nicht vom Substratmaterial abhängen. Die Optimierung des Kontaktierungsverfahrens für pseudo-γ Aluminiumoxid Schichten gilt es weiterhin zu optimieren. Insbesondere die Abscheidung strukturierter Kontakte auf Proben mit isolierenden SiO 2 -Substraten ist wichtig, um den spezfischen elektrischen Widerstand und die absoluten Thermokraftwerte zu bestimmen. Aufgrund seiner günstigen Ausgangsmaterialien ist pseudo-γ Aluminiumoxid ein hervorragender Kandidat für den zukünftigen Einsatz als transparentes leitfähiges Oxid.Tungsten carbide (WC) is a widely used material for cutting tools due to its high mechanical hardness and friction toughness. When exposed to high temperature (e.g. due to friction), oxidation occurs and transforms the stable phase of tungsten carbide to a powdery phase. To avoid oxidation and enhance the tool lifetime, protective layers are deposited on top of WC substrates consisting of various oxides or nitrides, either as single layers or as multilayer structures. For physical vapor deposition (PVD) processes (e.g. magnetron sputtering), a bias potential is applied to the substrate to achieve the surface energy necessary for the growth process. When growing insulating layers (such as most of the metal oxides), the bias potential is reduced during growth, leading to poorer crystallinity as the layer thickness increases. Therefore, the development of a semi conductive oxide with advantageous mechanical properties for coating applications is of great interest. In this thesis, aluminum oxide (Al 2 O 3 ) was deposited on tungsten carbide substrates using dual magnetron sputtering (DSM) with argon as the sputtering gas. The deposition conditions during the growth process provide many different parameters that influence the crystal growth. A combination of argon and oxygen pressure during sputtering, together with the bias potential and substrate temperature was identified as necessary to achieve an electrically conductive aluminum oxide phase. The goal of this thesis was to analyze the conductive aluminum oxide phase with respect to the structural and electrical features. In addition to the enhanced quality of wear resistant coatings for cutting applications, conductive aluminum oxide is an interesting new member of the transparent conductive oxide (TCO) family. Strong efforts are made to find a replacement for the most widely used material indium tin oxide (ITO), since it relies on expensive and rare materials. A conductive aluminum oxide only requires easily available materials and is therefore an excellent candidate to play an important role in future TCO developments. Samples analyzed in this thesis were provided by Walter AG in Tübingen. The samples consist of WC substrates (for cutting applications) and wear resistive coatings of aluminum oxide were deposited using DMS. A subset of the samples was coated with an additional Ti 0.33 Al 0.67 N layer using high power impulse magnetron sputtering (HIPIMS). The structure of the conductive phase was identified as a disordered cubic structure, containing aluminum, oxygen and argon up to mole fractions of 2.5 at%. To make a distinction to insulating disordered cubic aluminum oxide phases known as γ aluminum oxide, the conductive phase is called pseudo-γ aluminum oxide. Due to its unique structure (known as disordered spinel) of γ aluminum oxide, it is possible to incorporate rather large amounts of noble gas atoms into the structure. But only when argon is incorporated in the growth using DMS, the conductive phase is formed. The Ar atoms seem to stabilize the pseudo-γ phase. To get a grasp on the role of argon in the formation of the conductive phase, the structural feasen to cover a wide range of samples properties such as film thickness, deposition bias, but also different hardness values. Quantitative energy-dispersive x-ray spectroscopy (EDX) in a scanning electron microscope (SEM) was carried out to trace the Ar mole fraction and to establish a correlation thereof to the sample hardness. By precisely determining the Ar mole fraction in plan-view as well as cross-section in SEM EDX point scans, the argon mole fraction was successfully correlated to the sample hardness, showing that the Ar atoms are essential to the forming of the stable structure. In addition, a shift in the lattice spacing towards a larger unit cell was observed when more Ar was incorporated into the pseudo-γ aluminum oxide phase. By performing SEM EDX linescans in cross-section, the Ar distribution was found to be nonuniform. The highest Ar amount was always found at the interface to the WC substrate, but different content profiles were found for the rest of the sample, ranging from a linear decay throughout the film to a second, smaller maximum in the Ar content. TEM investigation revealed that the differences in the Ar mole fraction are in fact linked to structures features of the pseudo-γ aluminum oxide phase. For both samples under investigation in the TEM, a multilayer structure was found at the interface to the substrate with high argon mole fractions up to 10 at%. For the rest of the sample, different structures were found for the sample with higher and lower hardness. The high hardness sample showed columnar grains with a constant Ar mole fraction at ≈ 2 at%, whereas the low hardness sample showed much smaller grains with decreasing Ar mole fraction towards the top of the film. In terms of electrical characterization, two different contacting methods were successfully applied, using DC sputtered Au contacts and Ti 0.33 Al 0.67 N contacts deposited using HIPIMS. Such contacts showed low ohmic electrical resistance values at room temperature and semiconducting behavior in temperature dependent measurements. The same samples were also used to determine the ratio of the thermopower of pseudo-γ aluminum oxide to its heat conductivity, revealing a positive sign of the thermopower. Temperature dependent measurements of the electrical resistance were also performed on samples with Ti 0.33 Al 0.67 N on top of pseudo-γ aluminum oxide. All samples showed curved lines in Arrhenius plots of the electrical conductivity as is expected for a polycrystalline semiconductor. By carefully choosing the right model to explain the curvature of the reference samples, it is possible to gain insight on the structural features that are essential for the applied model, such as grain structure and homogeneity of the films. For further use of pseudo-γ aluminum oxide as a transparent conductive oxide, the possibility to transfer the structure to different substrates was successfully investigated. Films were deposited on WC substrate as a reference and on electrically insulating SiO 2 , leading to the same pseudo-γ aluminum oxide phase in both cases. All applied methods of characterization such as x-ray diffraction (XRD), SEM and SEM EDX showed that the pseudo-γ aluminum oxide layers are identical and do not depend on the substrate material. Future work still needs to be done on the optimization of the contacting procedure of the pseudo-γ films. Especially the deposition of structured contacts on samples with insulating SiO 2 substrates is important to determine electrical resistivity and absolute thermopower values that can lead to a deeper understanding of the pseudo-γ aluminum oxide phase. Due to its cheap materials, pseudo-γ aluminum oxide is an excellent candidate for future use as a transparent conductive oxide. tures as well as the electrical properties were investigated in detail in this thesis. Investigations were performed both in plan-view and in cross-section. The samples were chosen to cover a wide range of samples properties such as film thickness, deposition bias, but also different hardness values. Quantitative energy-dispersive x-ray spectroscopy (EDX) in a scan- ning electron microscope (SEM) was carried out to trace the Ar mole fraction and to establish a correlation thereof to the sample hardness. By precisely determining the Ar mole fraction in plan-view as well as cross-section in SEM EDX point scans, the argon mole fraction was successfully correlated to the sample hardness, showing that the Ar atoms are essential to the forming of the stable structure. In addition, a shift in the lattice spacing towards a larger unit cell was observed when more Ar was incorporated into the pseudo-γ aluminum oxide phase. By performing SEM EDX linescans in cross-section, the Ar distribution was found to be non- uniform. The highest Ar amount was always found at the interface to the WC substrate, but different content profiles were found for the rest of the sample, ranging from a linear decay throughout the film to a second, smaller maximum in the Ar content. TEM investigation revealed that the differences in the Ar mole fraction are in fact linked to structures features of the pseudo-γ aluminum oxide phase. For both samples under investiga- tion in the TEM, a multilayer structure was found at the interface to the substrate with high argon mole fractions up to 10 at%. For the rest of the sample, different structures were found for the sample with higher and lower hardness. The high hardness sample showed columnar grains with a constant Ar mole fraction at ≈ 2 at%, whereas the low hardness sample showed much smaller grains with decreasing Ar mole fraction towards the top of the film. In terms of electrical characterization, two different contacting methods were successfully ap- plied, using DC sputtered Au contacts and Ti 0.33 Al 0.67 N contacts deposited using HIPIMS. Such contacts showed low ohmic electrical resistance values at room temperature and semiconduct- ing behavior in temperature dependent measurements. The same samples were also used to determine the ratio of the thermopower of pseudo-γ aluminum oxide to its heat conductivity, revealing a positive sign of the thermopower. Temperature dependent measurements of the electrical resistance were also performed on sam- ples with Ti 0.33 Al 0.67 N on top of pseudo-γ aluminum oxide. All samples showed curved lines in Arrhenius plots of the electrical conductivity as is expected for a polycrystalline semiconductor. By carefully choosing the right model to explain the curvature of the reference samples, it is possible to gain insight on the structural features that are essential for the applied model, such as grain structure and homogeneity of the films. For further use of pseudo-γ aluminum oxide as a transparent conductive oxide, the possibility to transfer the structure to different substrates was successfully investigated. Films were de- posited on WC substrate as a reference and on electrically insulating SiO 2 , leading to the same pseudo-γ aluminum oxide phase in both cases. All applied methods of characterization such as x-ray diffraction (XRD), SEM and SEM EDX showed that the pseudo-γ aluminum oxide layers are identical and do not depend on the substrate material. Future work still needs to be done on the optimization of the contacting procedure of the pseudo-γ films. Especially the deposition of structured contacts on samples with insulating SiO 2 substrates is important to determine electrical resistivity and absolute thermopower values that can lead to a deeper understanding of the pseudo-γ aluminum oxide phase. Due to its cheap materials, pseudo-γ aluminum oxide is an excellent candidate for future use as a transparent conductive oxide

Secondary Somatic Mutations in G-Protein-Related Pathways and Mutation Signatures in Uveal Melanoma

Background: Uveal melanoma (UM), a rare cancer of the eye, is characterized by initiating mutations in the genes G-protein subunit alpha Q (GNAQ), G-protein subunit alpha 11 (GNA11), cysteinyl leukotriene receptor 2 (CYSLTR2), and phospholipase C beta 4 (PLCB4) and by metastasis-promoting mutations in the genes splicing factor 3B1 (SF3B1), serine and arginine rich splicing factor 2 (SRSF2), and BRCA1-associated protein 1 (BAP1). Here, we tested the hypothesis that additional mutations, though occurring in only a few cases (\u201csecondary drivers\u201d), might influence tumor development. Methods: We analyzed all the 4125 mutations detected in exome sequencing datasets, comprising a total of 139 Ums, and tested the enrichment of secondary drivers in Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways that also contained the initiating mutations. We searched for additional mutations in the putative secondary driver gene protein tyrosine kinase 2 beta (PTK2B) and we developed new mutational signatures that explain the mutational pattern observed in UM. Results: Secondary drivers were significantly enriched in KEGG pathways that also contained GNAQ and GNA11, such as the calcium-signaling pathway. Many of the secondary drivers were known cancer driver genes and were strongly associated with metastasis and survival. We identified additional mutations in PTK2B. Sparse dictionary learning allowed for the identification of mutational signatures specific for UM. Conclusions: A considerable part of rare mutations that occur in addition to known driver mutations are likely to affect tumor development and progression

Bringing 'place' back in: regional clusters, project governance, and new product outcomes

We examine new product outcomes in the context of regional clusters. Based on past research on marketing relationships, clusters, and social networks, we propose that the overall configuration of a cluster helps promote particular governance practices among its members. These practices have distinct value-creating properties, and when they are brought to bear on a specific new product development project within a cluster, they promote performance outcomes like product novelty and speed to market. Ultimately, these performance effects are reinforced by the configuration of the cluster itself. In general, we propose that new product outcomes follow from complex interactions between a cluster's macro-level configuration and its micro-level governance processes. More broadly, our framework points to the importance of geographical variables and to the role of “place” in marketing decision-making

Post-Operative Functional Outcomes in Early Age Onset Rectal Cancer

Background: Impairment of bowel, urogenital and fertility-related function in patients treated for rectal cancer is common. While the rate of rectal cancer in the young (<50 years) is rising, there is little data on functional outcomes in this group. Methods: The REACCT international collaborative database was reviewed and data on eligible patients analysed. Inclusion criteria comprised patients with a histologically confirmed rectal cancer, <50 years of age at time of diagnosis and with documented follow-up including functional outcomes. Results: A total of 1428 (n=1428) patients met the eligibility criteria and were included in the final analysis. Metastatic disease was present at diagnosis in 13%. Of these, 40% received neoadjuvant therapy and 50% adjuvant chemotherapy. The incidence of post-operative major morbidity was 10%. A defunctioning stoma was placed for 621 patients (43%); 534 of these proceeded to elective restoration of bowel continuity. The median follow-up time was 42 months. Of this cohort, a total of 415 (29%) reported persistent impairment of functional outcomes, the most frequent of which was bowel dysfunction (16%), followed by bladder dysfunction (7%), sexual dysfunction (4.5%) and infertility (1%). Conclusion: A substantial proportion of patients with early-onset rectal cancer who undergo surgery report persistent impairment of functional status. Patients should be involved in the discussion regarding their treatment options and potential impact on quality of life. Functional outcomes should be routinely recorded as part of follow up alongside oncological parameters

Measuring the return on investment in international assignments: an action research approach

This paper progresses the debate on the underresearched topic of return on investment (ROI) in international assignments by complementing and extending recent research streams on the conceptual understanding and challenging nature of measuring ROI. The study reported in this paper applies an action research methodology. Working in close collaboration with nine multinational companies, a set of metrics were developed to explore and gauge the ROI of international assignments. An in-depth exploration of the assignment purpose and individual and organizational otucomes over time highlights the importance of context and the dynamic nature of the task of assessing ROI. These themes have significant implications for international assignment strategy policy and practice. Insights from an action research perspective are discussed

White-Toothed Shrews (Genus <i>Crocidura</i>): Potential Reservoirs for Zoonotic <i>Leptospira</i> spp. and Arthropod-Borne Pathogens?

Three species of white-toothed shrews of the order Eulipotyphla are present in central Europe: the bicolored (Crocidura leucodon), greater (Crocidura russula) and lesser (Crocidura suaveolens) white-toothed shrews. Their precise distribution in Germany is ill-defined and little is known about them as reservoirs for zoonotic pathogens (Leptospira spp., Coxiella burnetii, Brucella spp., Anaplasma phagocytophilum, Babesia spp., Neoehrlichia mikurensis and Bartonella spp.). We investigated 372 Crocidura spp. from Germany (n = 341), Austria (n = 18), Luxembourg (n = 2) and Slovakia (n = 11). West European hedgehogs (Erinaceus europaeus) were added to compare the presence of pathogens in co-occurring insectivores. Crocidura russula were distributed mainly in western and C. suaveolens mainly in north-eastern Germany. Crocidura leucodon occurred in overlapping ranges with the other shrews. Leptospira spp. DNA was detected in 28/227 C. russula and 2/78 C. leucodon samples. Further characterization revealed that Leptospira kirschneri had a sequence type (ST) 100. Neoehrlichia mikurensis DNA was detected in spleen tissue from 2/213 C. russula samples. Hedgehogs carried DNA from L. kirschneri (ST 100), L. interrogans (ST 24), A. phagocytophilum and two Bartonella species. This study improves the knowledge of the current distribution of Crocidura shrews and identifies C. russula as carrier of Leptospira kirschneri. However, shrews seem to play little-to-no role in the circulation of the arthropod-borne pathogens investigated