Impact of Microstructure of Nanoscale Magnetron Sputtered Ru/Al Multilayers on Thermally Induced Phase Formation

In this study, we report on phase formation and microstructure evolution in multiscale magnetron sputtered Ru/Al multilayers upon thermal annealing in vacuum at slow heating rates of 10 K/min. By specifically adjusting the microstructure and design of the as-deposited multilayers, the formation of certain desired phases can be tuned. We demonstrate that the synthesis of single phase RuAl thin films is possible in a very controlled manner in a solid state only via thermal activation without initiating the self-propagating exothermic reactions of Ru/Al multilayers. To investigate phase formation sequences and the resulting microstructures, Ru/Al multilayers were designed via magnetron sputtering with systematic variation of bilayer modulation periods and subsequent vacuum annealing. Thin films samples were characterized by in situ high-temperature XRD, TEM imaging and diffraction. It is shown that different phase sequences appear in strong correlation with the modulation length. Depending on the multilayer design, the phase formation toward single-phase RuAl thin films happens as either a multi-step or single-step event. In particular, below a critical threshold of the modulation period, the multi-step phase formation can be suppressed, and only the desired RuAl target phase is obtained with a pronounced growth in a preferred orientation. This finding may be versatile for the targeted synthesis of intermetallic phases, contributing to further understanding of phase formation in such nanoscale multilayer systems

Impact of Microstructure of Nanoscale Magnetron Sputtered Ru/Al Multilayers on Thermally Induced Phase Formation

In this study, we report on phase formation and microstructure evolution in multiscale magnetron sputtered Ru/Al multilayers upon thermal annealing in vacuum at slow heating rates of 10 K/min. By specifically adjusting the microstructure and design of the as-deposited multilayers, the formation of certain desired phases can be tuned. We demonstrate that the synthesis of single phase RuAl thin films is possible in a very controlled manner in a solid state only via thermal activation without initiating the self-propagating exothermic reactions of Ru/Al multilayers. To investigate phase formation sequences and the resulting microstructures, Ru/Al multilayers were designed via magnetron sputtering with systematic variation of bilayer modulation periods and subsequent vacuum annealing. Thin films samples were characterized by in situ high-temperature XRD, TEM imaging and diffraction. It is shown that different phase sequences appear in strong correlation with the modulation length. Depending on the multilayer design, the phase formation toward single-phase RuAl thin films happens as either a multi-step or single-step event. In particular, below a critical threshold of the modulation period, the multi-step phase formation can be suppressed, and only the desired RuAl target phase is obtained with a pronounced growth in a preferred orientation. This finding may be versatile for the targeted synthesis of intermetallic phases, contributing to further understanding of phase formation in such nanoscale multilayer systems

In situ transmission electron microscopy investigation of the interfacial reaction between Ni and Al during rapid heating in a nanocalorimeter

The Al/Ni formation reaction is highly exothermic and of both scientific and technological significance. In this report, we study the evolution of intermetallic phases in this reaction at a heating rate of 830 K/s. 100-nm-thick Al/Ni bilayers were deposited onto nanocalorimeter sensors that enable the measurement of temperature and heat flow during rapid heating. Time-resolved transmission electron diffraction patterns captured simultaneously with thermal measurements allow us to identify the intermetallic phases present and reconstruct the phase transformation sequence as a function of time and temperature. The results show a mostly unaltered phase transformation sequence compared to lower heating rates

Solid state and self-propagating reactions in multilayers to synthesize RuAl thin films

Die Kombination aus guten Hochtemperatureigenschaften, hoher Raumtemperaturduktilität, stark exothermer Synthesereaktion und Existenz bei Nicht-Stöchiometrie positioniert die intermetallische Phase RuAl im Anwendungsfeld von thermischen Schutzschichten und des Reaktivfügens. Die einphasige RuAl-Dünnschichtsynthese ist bislang noch nicht erforscht. Festkörperphasenumwandlungen und selbstfortschreitende Reaktionen in äquiatomaren Ru/Al-Multischichten werden daher erstmals grundlegend charakterisiert. Möglichkeiten der Umwandlungs- und Reaktionskontrolle durch die Doppelschichtdicke (Periode) werden aufgezeigt. Die Festkörperreaktion beginnt bei 150 °C mit einer Al-dominierten Interdiffusion an den Grenzflächen. Oberhalb von 300 °C werden periodenabhängig maximal vier Umwandlungen durchlaufen. Optimal ist die RuAl-Dünnschichtsynthese für Perioden < 22 nm. Zum ersten Mal wird diese abgeleitet, sowie die Umwandlungskinetik und der Mikrostruktureinfluss quantifiziert. Die selbstfortschreitenden Reaktionen erlauben ebenfalls die einphasige Dünnschichtsynthese. Periodenunabhängig liegt eine einstufige Umwandlung an fest(Ru)/flüssig(Al)-Grenzflächen vor. Eine maximale Reaktionsgeschwindigkeit und -temperatur von 10,9 m/s beziehungsweise 1946 °C zeigen erstmalig die höhere Energiedichte gegenüber kommerziellen Ni/Al-Schichten. Das reaktive Bonden mit Ru/Al-Multischichten verspricht dadurch einen technologischen Fortschritt bei der stetigen Miniaturisierung in der Mikrosystemtechnik.The combination of good high temperature properties, unusual room temperature ductility, a highly exothermic synthesis reaction and non-stoichiometry positions the intermetallic phase RuAl in the application fields of thermal protection layers and reactive bonding. Since the single-phase thin-film synthesis of RuAl has yet to be explored, the solid-state phase transformations and self-propagating reactions in equiatomic Ru/Al multilayers are fundamentally characterized for the first time. The different options to control the transformations and reaction throughout the bilayer thickness (period) are shown. The solid-state transformation begins at 150 °C with an Al-dominated interdiffusion at the interfaces. Above 300 °C a maximum of four transformations are active depending on the period. The RuAl thin film synthesis is optimal for periods < 22 nm. This parameter as well as the transformation kinetics and the microstructure influence have been quantified for the first time. The self-propagating reactions also allow the single-phase thin-film synthesis where one-stage transformations at solid Ru/liquid Al interfaces occur regardless of the period. First ever maximum reaction rates and temperatures of 10.9 m/s and 1946 °C, respectively, reveal the superior energy density compared to commercial Ni/Al layers. Ru/Al multilayer reactive bonding is thus a promising technological advance in the context of an ongoing miniaturization in microsystems technology

Rapid thermal characterization of graphene oxide-nanocalorimetry as a pathway for novel insights in tribology

The use of solid lubricants such as graphene, graphene oxide, and other nanoparticles have gained notable attention in the tribological community to reduce friction and wear thus aiming at improved energy efficiency and sustainability. Tribological experiments unify rather extreme conditions such as high contact pressures, small contact areas, relative sliding motion, and rapid heating. This combination leads to mechanically- and/or thermally induced chemical, structural and microstructural modifications of the lubricating nanoparticles during rubbing thus altering their material’s properties. Due to the high sensitivity, we propose nanocalorimetry as the method of choice to shed more light on the thermally-induced processes and changes. As a model material for solid lubricants, we explore the transitions of graphene oxide under heating with 1000 °C/s up to 600 °C using quasi-adiabatic nanocalorimetry. We identify a strong exothermic runaway reaction at 317 °C. This runaway is preceded by exothermic reactions between 75–125 °C, which are correlated with the release of intercalated species and the formation of CO and CO$_{2}$

Rapid Thermal Characterization of Graphene Oxide—Nanocalorimetry as a Pathway for Novel Insights in Tribology

The use of solid lubricants such as graphene, graphene oxide, and other nanoparticles have gained notable attention in the tribological community to reduce friction and wear thus aiming at improved energy efficiency and sustainability. Tribological experiments unify rather extreme conditions such as high contact pressures, small contact areas, relative sliding motion, and rapid heating. This combination leads to mechanically- and/or thermally induced chemical, structural and microstructural modifications of the lubricating nanoparticles during rubbing thus altering their material&rsquo;s properties. Due to the high sensitivity, we propose nanocalorimetry as the method of choice to shed more light on the thermally-induced processes and changes. As a model material for solid lubricants, we explore the transitions of graphene oxide under heating with 1000 &deg;C/s up to 600 &deg;C using quasi-adiabatic nanocalorimetry. We identify a strong exothermic runaway reaction at 317 &deg;C. This runaway is preceded by exothermic reactions between 75&ndash;125 &deg;C, which are correlated with the release of intercalated species and the formation of CO and CO2

Impact of Microstructure of Nanoscale Magnetron Sputtered Ru/Al Multilayers on Thermally Induced Phase Formation

In this study, we report on phase formation and microstructure evolution in multiscale magnetron sputtered Ru/Al multilayers upon thermal annealing in vacuum at slow heating rates of 10 K/min. By specifically adjusting the microstructure and design of the as-deposited multilayers, the formation of certain desired phases can be tuned. We demonstrate that the synthesis of single phase RuAl thin films is possible in a very controlled manner in a solid state only via thermal activation without initiating the self-propagating exothermic reactions of Ru/Al multilayers. To investigate phase formation sequences and the resulting microstructures, Ru/Al multilayers were designed via magnetron sputtering with systematic variation of bilayer modulation periods and subsequent vacuum annealing. Thin films samples were characterized by in situ high-temperature XRD, TEM imaging and diffraction. It is shown that different phase sequences appear in strong correlation with the modulation length. Depending on the multilayer design, the phase formation toward single-phase RuAl thin films happens as either a multi-step or single-step event. In particular, below a critical threshold of the modulation period, the multi-step phase formation can be suppressed, and only the desired RuAl target phase is obtained with a pronounced growth in a preferred orientation. This finding may be versatile for the targeted synthesis of intermetallic phases, contributing to further understanding of phase formation in such nanoscale multilayer systems

Leptospira spp. in Rodents and Shrews in Germany

Leptospirosis is an acute, febrile disease occurring in humans and animals worldwide. Leptospira spp. are usually transmitted through direct or indirect contact with the urine of infected reservoir animals. Among wildlife species, rodents act as the most important reservoir for both human and animal infection. To gain a better understanding of the occurrence and distribution of pathogenic leptospires in rodent and shrew populations in Germany, kidney specimens of 2973 animals from 11 of the 16 federal states were examined by PCR. Rodent species captured included five murine species (family Muridae), six vole species (family Cricetidae) and six shrew species (family Soricidae). The most abundantly trapped animals were representatives of the rodent species Apodemus flavicollis, Clethrionomys glareolus and Microtus agrestis. Leptospiral DNA was amplified in 10% of all animals originating from eight of the 11 federal states. The highest carrier rate was found in Microtus spp. (13%), followed by Apodemus spp. (11%) and Clethrionomys spp. (6%). The most common Leptospira genomospecies determined by duplex PCR was L. kirschneri, followed by L. interrogans and L. borgpetersenii; all identified by single locus sequence typing (SLST). Representatives of the shrew species were also carriers of Leptospira spp. In 20% of Crocidura spp. and 6% of the Sorex spp. leptospiral DNA was detected. Here, only the pathogenic genomospecies L. kirschneri was identified