Formation of CuO whiskers and facet-controlled oxidation during the oxidation of Au-Cu nanoparticles fabricated by solid-state dewetting. - In: Applied surface science, Bd. 610 (2023), 155547
The fabrication of cupric oxide (CuO) nanowires from Cu particles via thermal oxidation provides a simple and scalable method to produce hierarchical structures. A stress-induced growth mechanism is believed to account for the nanowire formation while a slow oxidation rate is favored to sustain the driving force. Here, CuO whiskers are grown from Au-Cu nanoparticles because the formation of Au-Cu phases decreases the Cu diffusion rate and in turn slows down the oxidation rate. The driving force for the whisker growth is attributed to the compressive stress imposed by the CuO shell on the Au-Cu core, which is induced by the significantdifference in their linear thermal expansion coefficients. The contribution of the compressive stress is proved by the calculation. Moreover, preferred oxidation is observed and it is related to the crystalline structures of different facets existing on the surface of Au-Cu nanoparticles. The more compact the plane, the slower the diffusion rate through the plane, resulting in the formation of thinner CuO on the relevant facet. The results open a cost-effect way to fabricate hybrid nanostructures consisting of Cu-based core-shell nanoparticles attached with CuO whiskers and bring new insights into the oxidation behaviors of Cu on different crystal planes.
https://doi.org/10.1016/j.apsusc.2022.155547
Photon-induced near-field interaction in ultrafast low energy electron microscopy. - [Washington, D.C., USA] : Optica Publishing Group. - 1 Online-Ressource (Paper Tu3A.5)
We report the first observation of optical near-field coupling to an ultrafast wavepacket of free, low-energy electrons. Transient optical near-fields, highly spatially confined around a nanometer-sized Yagi-Uda-antenna are probed in a point-projection-microscope with 30-fs resolution.
https://doi.org/10.1364/UP.2022.Tu3A.5
Entwicklung und Anwendung eines neuen in situ Emissions/online/offline Mössbauer Magnet Analysators an ISOLDE (CERN) für das Hysteresedesign in innovativen Magnetwerkstoffen für die Energiewende - eMMA : Schlussbericht : 01.07.2019-30.06.2022. - Ilmenau : TU Ilmenau. - 1 Online-Ressource (21 Seiten, 1.014,81 KB)Förderkennzeichen BMBF 05K19SI1
https://edocs.tib.eu/files/e01fb24/1882590457.pdf
Mössbauer spectroscopy. - In: Reference module in materials science and materials engineering, (2022), insges. 14 S.
The current chapter provides the reader with a general introduction of Mössbauer effect following by its unique utilization, which became known as Mössbauer spectroscopy. Mössbauer spectroscopy is based on the recoilless emission and following resonant absorption of gamma radiation by atomic nuclei and has been at the scientific forefront of physics, chemistry, biology, mineralogy for more than 60 years. Soon after the discovery of the Mössbauer effect, it became obvious that this effect can be used to study various properties of materials on a microscopic scale via hyperfine interactions with an unprecedented resolution. This was the beginning of a new analytical tool - Mössbauer spectroscopy. Today, it has developed into a standard analytical technique used in many laboratories and big research facilities. The current chapter provides the reader with a general introduction, explains the underlying hyperfine interactions and gives examples of the possible application of the method.
https://doi.org/10.1016/B978-0-323-90800-9.00137-2
Charge and spin state of dilute Fe in NaCl and LiF. - In: Physical review, ISSN 2469-9969, Bd. 106 (2022), 17, 174108, S. 174108-1-174108-10
There is an apparent mismatch between electron paramagnetic resonance and Mössbauer spectroscopy results on the charge and spin states of dilute Fe impurities in NaCl; Mössbauer spectroscopy data have been interpreted in terms of high-spin Fe2+, while electron paramagnetic resonance studies suggest low-spin Fe1+. In the present study, the charge and spin states of dilute substitutional Fe impurities in NaCl and LiF have been investigated with 57Mn&flech;57Fe emission Mössbauer spectroscopy. A scheme is proposed which takes into account the effects of nearest-neighbor distances and electronegativity difference of the host atoms on the Mössbauer isomer shift and allows for the unequivocal differentiation between high-spin Fe2+ and high/low-spin Fe1+ in Mössbauer spectroscopy. From these considerations, the Mössbauer results are found to be consistent with dilute Fe impurities in NaCl and LiF in a low-spin Fe1+ state. These conclusions are supported by theoretical calculations of isomer shifts and formation energies based on the density-functional theory. The experimental results furthermore suggest that charge compensation of dilute Mn2+ dopants in NaCl and LiF is achieved by Na vacancies and F− interstitials, respectively.
https://doi.org/10.1103/PhysRevB.106.174108
Coupling-induced tunable broadband superradiance in 2D metal-dielectric-metal nanocavity arrays. - In: Laser & photonics reviews, ISSN 1863-8899, Bd. 16 (2022), 11, 2200393, S. 1-8
Subradiance/superradiance, cooperative effects causing suppressed/enhanced radiative decay, are of particular interest in plasmonic systems as they play a very important role in modulating dampings and optical properties of resonant systems. However, subradiance/superradiance are generally limited in narrow spectral range with inaccessible tunability. Realizing broadband subradiant and superradiant plasmon modes with flexible tuning is still challenging. Here, a 2D periodic multilayer metal-dielectric-metal (MDM) nanostructure is rationally designed and fabricated to realize a tunable superradiant mode over a broad visible range. Angle-resolved spectroscopy combined with full quantum calculations reveal a sufficient hybridization of delocalized guided plasmons with localized plasmons and a plasmonic cavity mode, leading to an emissive superradiant hybrid mode over a broadband visible range, which can be readily tuned by controlling the spectral three-mode overlap. Greatly shortened polariton lifetimes down to 4 fs are achieved as direct consequence of the Rabi phases and considerable incoherent coupling strengths between interacting subsystems. Such a control of plasmon damping by cooperative mode interactions paves the way toward efficient manipulation of light emission for applications requiring bright, fast-emitting photon sources.
https://doi.org/10.1002/lpor.202200393
Das physikalische Praktikum : Handbuch 2022/2023 für Studentinnen und Studenten der Physik. - Göttingen : Universitätsverlag Göttingen, 2022. - (Universitätsdrucke)
Effect of line structures on the self-propagating reaction of Al/Ni multilayer. - In: 2022 IEEE 9th Electronics System-Integration Technology Conference (ESTC), (2022), S. 379-382
This work investigates the influence of a structured chip surface on the propagation of a self-sustaining reaction that is aimed to be used as heat source for chip assembly. A silicon (100) surface was structured by a combination of thermal oxidation and dry and wet etching to obtain line structures with height lesser than 1 µm. To ensure reaction of 5 µm thick Al/Ni multilayers, 1 µm of SiO2 is used as thermal insulator. Different widths of lines and valleys, with a ratio of 1:1, were processed. Width values were chosen to be 30 µm, 50 µm and 80 µm. Bilayer thickness of 50 nm with a 50/50 at% of Al/Ni were deposited using magnetron sputtering. By using focused ion beam with integrated scanning electron microscope and X-ray diffractometer the samples were analyzed prior to reaction. Velocity and temperature were measured with high-speed camera and high-speed pyrometer. Variations in reaction speed depending on the structure width were recorded and analyzed in perspective of the influence of the additional inclined reaction path. Calculation of the extended reaction paths and their influence on the reaction speed between the structures was performed. The results show that the additional distance has only a low influence on the velocity. Different reasons were identified, but it was not possible to determine the main cause. It was possible to slow down the reaction and keeping the temperature over 350 ˚C for over 500 ms, which provides enough energy to melt solders. The influence of smaller structures can be applied to bonding applications with reactive multilayers.
https://doi.org/10.1109/ESTC55720.2022.9939472
Hysteresis associated with intrinsic-oxide traps in gate-tunable tetrahedral CVD-MoS2 memristor. - In: IEEE 22nd International Conference on Nanotechnology (NANO), (2022), S. 527-530
We introduce back gated memristor based on CVD-grown 30-40 nm thick MoS2 channel. The device demonstrates bipolar behaviour and the measurements are consistent with the simulations performed within the intrinsic-oxide traps model. This confirms the theory that the source of hysteresis in thin-film MoS2 memristors is charge trapping on MoS2/SiO2 interface and the grain boundaries. The impact of back gate voltage bias, voltage sweep range and channel area on memristive effect was studied and quantified using hysteresis area. Hysteresis in bipolar memristors can be tuned by back gate voltage, which makes these devices promising for neuromorphic computing.
https://doi.org/10.1109/NANO54668.2022.9928717
Tribological and mechanical performance of Ti2AlC and Ti3AlC2 thin films. - In: Advanced engineering materials, ISSN 1527-2648, Bd. 24 (2022), 10, 2200188, S. 1-11
Mn+1AXn (MAX) phases are novel structural and functional materials with a layered crystal structure. Their unique properties such as good machinability, high electrical conductivity, low friction, and corrosion resistance are appealing for many engineering applications. Herein, Ti2AlC and Ti3AlC2 MAX thin films are synthesized by magnetron sputtering and subsequent thermal annealing. A multilayer approach is used to deposit single-element nanolayers of titanium, aluminum, and carbon onto silicon substrates with a double-layer-diffusion barrier of SiO2 and SixNy. Ti2AlC and Ti3AlC2 thin films (thickness ≈500 nm) are formed via rapid thermal annealing and verified by X-Ray diffraction. Nanoindentation tests show hardness values of about 11.6 and 5.3 GPa for Ti2AlC and Ti3AlC2, respectively. The tribological behavior of the Ti2AlC and Ti3AlC2 thin films against AISI 52100 steel balls under dry sliding conditions is studied using ball-on-flat tribometry. The resulting coefficient of friction (CoF) for Ti2AlC and Ti3AlC2 ranges between 0.21-0.42 and 0.64-0.91, respectively. The better tribological behavior observed for Ti2AlC thin films is ascribed to its smaller grain size, reduced surface roughness, and higher hardness.
https://doi.org/10.1002/adem.202200188