Conference papers from 2018 to 2021

Anzahl der Treffer: 649
Erstellt: Thu, 02 Feb 2023 23:02:26 +0100 in 0.0664 sec

Tan, Xinu; Liu, Yushun; Li, Feitao; Qiu, Risheng; Liu, Qing
Formation of nanocrystalline γ-ZrH in Zr-Nb alloy: crystal structure and twinning. - In: Micron, ISSN 1878-4291, (2023), 103414

In the present work, the lattice parameter and the twins of γ-ZrH hydride in Zr-2.5Nb-1Si were characterized using high resolution electron microscopy. The lattice parameters of γ-ZrH (P42/mmc, Zr2H2 unit cell) is determined to be a= 0.336nm, c=0.508nm. Twinning γ-ZrH hydride ({011}<0̅11> type) is for the first time reported in zirconium alloys, whose orientation relationship with α-Zr is [100]γ-twins // [1̅210]α and (011)γ-twins // (0002)α. The formation process of γ-ZrH twins is also discussed based on a ‘grow-in’ mechanism during the transformation from α-Zr to γ-ZrH hydride.
Glaser, Marcus; Matthes, Sebastian; Hildebrand, Jörg; Bergmann, Jean Pierre; Schaaf, Peter
Hybrid thermoplastic-metal joining based on Al/Ni multilayer foils - analysis of the joining zone. - In: Materials and design, ISSN 1873-4197, Bd. 226 (2023), 111561, insges. 16 S.

Multi material pairings like metal-plastic hybrid compounds are becoming increasingly important across all industrial sectors. However, the substitution of metals by plastics leads to a multitude of challenges based on the combination of dissimilar materials. The variations in the chemical and physical properties of the used materials require innovative joining processes. The application of reactive multilayers represents an advanced joining method for flexible and low-distortion joining of dissimilar joining partners by means of a short-term and localized application of thermal energy. In the context of this publication, the joining process between semi-crystalline polyamide 6 and austenitic stainless steel X5CrNi18-10(EN 1.4301 / AlSI304) based on reactive Al/Ni multilayers is investigated. In addition to evaluation of resulting joint strength, the focus of the work is in particular the characterization of the resulting failure behavior at the fracture interface under tensile load and the deriving binding mechanisms in the joint. From the results obtained, it is estimated that a direct bond can be generated between plastic and metal despite the presence of a residual reacted foil in the joining area. The structures present in the metal surface have a particularly positive influence on crack initiation and the resulting increased bond strength.
Li, Feitao; Tan, Xinu; Flock, Dominik; Qiu, Risheng; Wang, Dong; Schaaf, Peter
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.
Gunnlaugsson, Haraldur P.; Mokhles Gerami, Adeleh; Masenda, Hilary; Ólafsson, Sveinn; Adhikari, Rajdeep; Johnston, Karl; Naicker, Kimara; Peters, Gerrard; Schell, Juliana; Zyabkin, Dmitry; Bharuth-Ram, Krish; Krastev, Petko; Mantovan, Roberto; Naidoo, Deena; Unzueta, Iraultza
Charge and spin state of dilute Fe in NaCl and LiF. - In: Physical review, ISSN 2469-9969, Bd. 106 (2022), 17, 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.
Liang, Zhengchen; Wang, Dong; Ziegler, Mario; Hübner, Uwe; Xie, Peng; Ding, Qi; Zhang, Hong; Wang, Wei
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.
Große-Knetter, Jörn; Schaaf, Peter
Das physikalische Praktikum : Handbuch 2022/2023 für Studentinnen und Studenten der Physik. - Göttingen : Universitätsverlag Göttingen, 2022. - (Universitätsdrucke)
Jaekel, Konrad; Bartsch, Heike; Müller, Jens; Sauni Camposano, Yesenia Haydee; Matthes, Sebastian; Schaaf, Peter
Effect of line structures on the self-propagating reaction of Al/Ni multilayer. - In: IEEE Xplore digital library, ISSN 2473-2001, (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 &ring;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.
Kurtash, Vladislav; Mathew, Sobin; Thiele, Sebastian; Scheler, Theresa; Reiprich, Johannes; Hähnlein, Bernd; Stauffenberg, Jaqueline; Manske, Eberhard; Narasimha, Shilpashree; Abedin, Saadman; Jacobs, Heiko O.; Pezoldt, Jörg
Hysteresis associated with intrinsic-oxide traps in gate-tunable tetrahedral CVD-MoS2 memristor. - In: IEEE Xplore digital library, ISSN 2473-2001, (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.
Quispe, Roger; Torres, Carlos; Eggert, Lara; Ccama, Gianella A.; Kurniawan, Mario; Hopfeld, Marcus; Zárate Moya, José Luis; Camargo, Magali K.; Rosenkranz, Andreas; Acosta, Julio A.; Bund, Andreas; Schaaf, Peter; Grieseler, Rolf
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.
Mathew, Sobin; Narasimha, Shilpashree; Reiprich, Johannes; Scheler, Theresa; Hähnlein, Bernd; Thiele, Sebastian; Stauffenberg, Jaqueline; Kurtash, Vladislav; Abedin, Saadman; Manske, Eberhard; Jacobs, Heiko O.; Pezoldt, Jörg
Formation and characterization of three-dimensional tetrahedral MoS2 thin films by chemical vapor deposition. - In: Crystal growth & design, ISSN 1528-7505, Bd. 22 (2022), 9, S. 5229-5238

A method to synthesize the three-dimensional arrangement of bulk tetrahedral MoS2 thin films by solid source chemical vapor deposition of MoO3 and S is presented. The developed synthesizing recipe uses a temperature ramping with a constant N2 gas flow in the deposition process to grow tetrahedral MoS2 thin film layers. The study analyses the time-dependent growth morphologies, and the results are combined and presented in a growth model. A combination of optical, electron, atomic force microscopy, Raman spectroscopy, and X-ray diffraction are used to study the morphological and structural features of the tetrahedral MoS2 thin layers. The grown MoS2 is c-axis oriented 2H-MoS2. Additionally, the synthesized material is further used to fabricate back-gated field-effect transistors (FETs). The fabricated FET devices on the tetrahedral MoS2 show on/off current ratios of 10^6 and mobility up to ∼56 cm^2 V^-1 s^-1 with an estimated carrier concentration of 4 × 10^16 cm-3 for VGS = 0 V.