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search.filters.applied.f.access: openAccess × End date: 2022 × Start date: 2022 × End date: 2022 × Start date: 2020 × DDC: 670 × Type: Article ×

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Now showing 1 - 10 of 30
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    Plasmonic Properties of Colloidal Assemblies
    (Weinheim : Wiley-VCH, 2021) Rossner, Christian; König, Tobias A.F.; Fery, Andreas
    The assembly of metal nanoparticles into supracolloidal structures unlocks optical features, which can go beyond synergistic combinations of the properties of their primary building units. This is due to inter-particle plasmonic coupling effects, which give rise to emergent properties. The motivation for this progress report is twofold: First, it is described how simulation approaches can be used to predict and understand the optical properties of supracolloidal metal clusters. These simulations may form the basis for the rational design of plasmonic assembly architectures, based on the desired functional cluster properties, and they may also spark novel material designs. Second, selected scalable state-of-the-art preparative strategies based on synthetic polymers to guide the supracolloidal assembly are discussed. These routes also allow for equipping the assembly structures with adaptive properties, which in turn enables (inter-)active control over the cluster optical properties. © 2021 The Authors. Advanced Optical Materials published by Wiley-VCH GmbH
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    Spectrometer‐free Optical Hydrogen Sensing Based on Fano‐like Spatial Distribution of Transmission in a Metal−Insulator−Metal Plasmonic Doppler Grating
    (Weinheim : Wiley-VCH, 2021) Chen, Yi‐Ju; Lin, Fan‐Cheng; Singh, Ankit Kumar; Ouyang, Lei; Huang, Jer‐Shing
    Optical nanosensors are promising for hydrogen sensing because they are small, free from spark generation, and feasible for remote optical readout. Conventional optical nanosensors require broadband excitation and spectrometers, rendering the devices bulky and complex. An alternative is spatial intensity-based optical sensing, which only requires an imaging system and a smartly designed platform to report the spatial distribution of analytical optical signals. Here, a spatial intensity-based hydrogen sensing platform is presented based on Fano-like spatial distribution of the transmission in a Pd-Al2O3-Au metal-insulator-metal plasmonic Doppler grating (MIM-PDG). The MIM-PDG manifests the Fano resonance as an asymmetric spatial transmission intensity profile. The absorption of hydrogen changes the spatial Fano-like transmission profiles, which can be analyzed with a “spatial” Fano resonance model and the extracted Fano resonance parameters can be used to establish analytical calibration lines. While gratings sensitive to hydrogen absorption are suitable for hydrogen sensing, hydrogen insensitive gratings are also found, which provide an unperturbed reference signal and may find applications in nanophotonic devices that require a stable optical response under fluctuating hydrogen atmosphere. The MIM-PDG platform is a spectrometer-free and intensity-based optical sensor that requires only an imaging system, making it promising for cellphone-based optical sensing applications. © 2021 The Authors. Advanced Optical Materials published by Wiley-VCH GmbH.
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    Tailored Disorder in Photonics: Learning from Nature
    (Weinheim : Wiley-VCH, 2021) Rothammer, Maximilian; Zollfrank, Cordt; Busch, Kurt; Freymann, Georg von
    Disorder and photonics have long been seen as natural adversaries and designers of optical systems have often driven systems to perfection by minimizing deviations from the ideal design. Especially in the field of photonic crystals and metamaterials but also for optical circuits, disorder has been avoided as a nuisance for many years. However, starting from the very robust structural colors found in nature, scientists learn to analyze and tailor disorder to achieve functionalities beyond what is possible with perfectly ordered or ideal systems alone. This review article covers theoretical and materials aspects of tailored disorder as well as experimental results. Furthermore selected examples are highlighted in greater detail, for which the intentional use of disorder adds additional functionality or provides novel functionality impossible without disorder. © 2021 The Authors. Advanced Optical Materials published by Wiley-VCH GmbH
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    An AI-based open recommender system for personalized labor market driven education
    (Amsterdam [u.a.] : Elsevier Science, 2022) Tavakoli, Mohammadreza; Faraji, Abdolali; Vrolijk, Jarno; Molavi, Mohammadreza; Mol, Stefan T.; Kismihók, Gábor
    Attaining those skills that match labor market demand is getting increasingly complicated, not in the last place in engineering education, as prerequisite knowledge, skills, and abilities are evolving dynamically through an uncontrollable and seemingly unpredictable process. Anticipating and addressing such dynamism is a fundamental challenge to twenty-first century education. The burgeoning availability of data, not only on the demand side but also on the supply side (in the form of open educational resources) coupled with smart technologies, may provide a fertile ground for addressing this challenge. In this paper, we propose a novel, Artificial Intelligence (AI) driven approach to the development of an open, personalized, and labor market oriented learning recommender system, called eDoer. We discuss the complete system development cycle starting with a systematic user requirements gathering, and followed by system design, implementation, and validation. Our recommender prototype (1) derives the skill requirements for particular occupations through an analysis of online job vacancy announcements
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    Emission Manipulation by DNA Origami‐Assisted Plasmonic Nanoantennas
    (Weinheim : Wiley-VCH, 2021) Yeşilyurt, Ayşe Tuğça Mina; Huang, Jer‐Shing
    Plasmonic nanoantennas mediate far and near optical fields and confine the light to subwavelength dimensions. The spatial organization of nanoantenna elements is critical as it affects the interelement coupling and determines the resultant antenna mode. To couple quantum emitters to optical antennas, high precision on the order of a few nm with respect to the antenna is necessary. As an emerging nanofabrication technique, DNA origami has proven itself to be a robust nanobreadboard to obtain sub-5 nm positioning precision for a diverse range of materials. Eliminating the need for expensive state-of-the-art top-down fabrication facilities, DNA origami enables cost-efficient implementation of nanoscale architectures, including novel nanoantennas. The ability of DNA origami to deterministically position single quantum emitters into nanoscale hotspots further boosts the efficiency of light–matter interaction controlled via optical antennas. This review recapitulates the recent progress in plasmonic nanoantennas assisted by DNA origami and focuses on their various configurations. How those nanoantennas act on the emission and absorption properties of quantum emitters positioned in the hotspots is explicitly discussed. In the end, open challenges are outlined and future possibilities lying ahead are pointed out for this powerful triad of biotechnology, nanooptics, and photophysics. © 2021 The Authors. Advanced Optical Materials published by Wiley-VCH GmbH
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    Exploiting Combinatorics to Investigate Plasmonic Properties in Heterogeneous Ag-Au Nanosphere Chain Assemblies
    (Weinheim : Wiley-VCH, 2021) Schletz, Daniel; Schultz, Johannes; Potapov, Pavel L.; Steiner, Anja Maria; Krehl, Jonas; König, Tobias A.F.; Mayer, Martin; Lubk, Axel; Fery, Andreas
    Chains of coupled metallic nanoparticles are of special interest for plasmonic applications because they can sustain highly dispersive plasmon bands, allowing strong ballistic plasmon wave transport. Whereas early studies focused on homogeneous particle chains exhibiting only one dominant band, heterogeneous assemblies consisting of different nanoparticle species came into the spotlight recently. Their increased configuration space principally allows engineering multiple bands, bandgaps, or topological states. Simultaneously, the challenge of the precise arrangement of nanoparticles, including their distances and geometric patterns, as well as the precise characterization of the plasmonics in these systems, persists. Here, the surface plasmon resonances in heterogeneous Ag-Au nanoparticle chains are reported. Wrinkled templates are used for directed self-assembly of monodisperse gold and silver nanospheres as chains, which allows assembling statistical combinations of more than 109 particles. To reveal the spatial and spectral distribution of the plasmonic response, state-of-the-art scanning transmission electron microscopy coupled with electron energy loss spectroscopy accompanied by boundary element simulations is used. A variety of modes in the heterogeneous chains are found, ranging from localized surface plasmon modes occurring in single gold or silver spheres, respectively, to modes that result from the hybridization of the single particles. This approach opens a novel avenue toward combinatorial studies of plasmonic properties in heterosystems. © 2021 The Authors. Advanced Optical Materials published by Wiley-VCH GmbH
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    Tailoring Plasmonics of Au@Ag Nanoparticles by Silica Encapsulation
    (Weinheim : Wiley-VCH, 2021) Schultz, Johannes; Kirner, Felizitas; Potapov, Pavel; Büchner, Bernd; Lubk, Axel; Sturm, Elena V.
    Hybrid metallic nanoparticles (NPs) encapsulated in oxide shells are currently intensely studied for plasmonic applications in sensing, medicine, catalysis, and photovoltaics. Here, a method for the synthesis of Au@Ag@SiO2 cubes with a uniform silica shell of variable and adjustable thickness in the nanometer range is introduced and their excellent, highly reproducible, and tunable optical response is demonstrated. Varying the silica shell thickness, the excitation energies of the single NP plasmon modes can be tuned in a broad spectral range between 2.55 and 3.25 eV. Most importantly, a strong coherent coupling of the surface plasmons is revealed at the silver–silica interface with Mie resonances at the silica–vacuum interface leading to a significant field enhancement at the encapsulated NP surface in the range of 100% at shell thicknesses t ≃ 20 nm. Consequently, the synthesis method and the field enhancement open pathways to a widespread use of silver NPs in plasmonic applications including photonic crystals and may be transferred to other non-precious metals. © 2021 The Authors. Advanced Optical Materials published by Wiley-VCH GmbH
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    Fabrication of four-level hierarchical topographies through the combination of LIPSS and direct laser interference pattering on near-beta titanium alloy
    (New York, NY [u.a.] : Elsevier, 2022) Schell, Frederic; Alamri, Sabri; Hariharan, Avinash; Gebert, Annett; Lasagni, Andrés Fabián; Kunze, Tim
    Complex repetitive periodic surface patterns were produced on a near-beta Ti-13Nb-13Zr alloy, using two-beam Direct Laser Interference Patterning (DLIP) employing a picosecond-pulsed laser source with wavelengths of 355 nm, 532 nm and 1064 nm. Different types of Laser-induced periodic surface structures (LIPSS) are produced, including low and high spatial frequency LIPSS, which are observed frequently on top of the line-like DLIP microstructures, as well as quasi-periodic microstructures with periods greater than the laser wavelength. The feature size of the fabricated LIPSS features could be tuned as function of the utilized laser process parameters.
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    Failure mechanism analysis based on laser-based surface treatments for aluminum-polyamide laser joining
    (Amsterdam [u.a.] : Elsevier, 2021) Elahi, Amne; Koch, Marcus; Bardon, Julien; Addiego, Frédéric; Plapper, Peter
    The development of strong metal to polymer assemblies is currently an important research subject thanks to its prominence to develop lightweight structures. Furthermore, laser welding is known to be a fast, reliable, and versatile joining process, and it was demonstrated recently that it can be applied to such metal to polymer systems. To enhance the mechanical properties of the laser-joined aluminum-polyamide (Al-PA) specimens, laser polishing and laser ablation processes have been implemented on the aluminum surface before joining. The polyamide surface was also treated with the laser beam, separately. The surfaces were tested by several characterization techniques before and after each surface treatment. Then aluminum and polyamide samples with different surface treatments have been joined with an identical laser joining process. The mechanical properties of the joints in single lap shear configuration are reported and the failure mechanisms are discussed based on micro-computed x-ray tomography imaging of joined specimens and microscopic analysis before failure. Results show that both surface treatments of aluminum significantly improve the shear load of the joint; however, with different failure mechanisms. Polyamide surface treatment and increasing degree of crystallinity are effective when combined with the laser polishing of the Al surface. This combination is responsible for further enhancement of the shear load of the joint to the limit of base metal strength which is approximately 60 % improvement compared to the untreated samples. Finally, energy dispersive X-ray mapping shows the physicochemical bonding between aluminum oxide and polyamide at the interface.
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    Dissolution and precipitation of copper-rich phases during heating and cooling of precipitation-hardening steel X5CrNiCuNb16-4 (17-4 PH)
    (Dordrecht [u.a.] : Springer Science + Business Media B.V, 2020) Rowolt, Christian; Milkereit, Benjamin; Springer, Armin; Kreyenschulte, Carsten; Kessler, Olaf
    Continuous heating transformation (CHT) diagrams and continuous cooling transformation (CCT) diagrams of precipitation-hardening steels have the drawback that important information on the dissolution and precipitation of Cu-rich phases during continuous heating and cooling are missing. This work uses a comparison of different techniques, namely dilatometry and differential scanning calorimetry for the in situ analysis of the so far neglected dissolution and precipitation of Cu-rich phases during continuous heating and cooling to overcome these drawbacks. Compared to dilatometry, DSC is much more sensitive to phase transformation affecting small volume fractions, like precipitation. Thus, the important solvus temperature for the dissolution of Cu-rich phases was revealed from DSC and integrated into the CHT diagram. Moreover, DSC reveals that during continuous cooling from solution treatment, premature Cu-rich phases may form depending on cooling rate. Those quench-induced precipitates were analysed for a broad range of cooling rates and imaged for microstructural analysis using optical microscopy, scanning electron microscopy and transmission electron microscopy. This information substantially improves the CCT diagram.