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- ItemLasing by Template-Assisted Self-Assembled Quantum Dots(Weinheim : Wiley-VCH, 2023) Aftenieva, Olha; Sudzius, Markas; Prudnikau, Anatol; Adnan, Mohammad; Sarkar, Swagato; Lesnyak, Vladimir; Leo, Karl; Fery, Andreas; König, Tobias A.F.Miniaturized laser sources with low threshold power are required for integrated photonic devices. Photostable core/shell nanocrystals are well suited as gain material and their laser properties can be exploited by direct patterning as distributed feedback (DFB) lasers. Here, the 2nd-order DFB resonators tuned to the photoluminescence wavelength of the QDs are used. Soft lithography based on template-assisted colloidal self-assembly enables pattern resolution in the subwavelength range. Combined with the directional Langmuir–Blodgett arrangement, control of the waveguide layer thickness is further achieved. It is shown that a lasing threshold of 5.5 mJ cm−2 is reached by a direct printing method, which can be further reduced by a factor of ten (0.6 mJ cm−2) at an optimal waveguide thickness. Moreover, it is discussed how one can adjust the DFB geometries to any working wavelength. This colloidal approach offers prospects for applications in bioimaging, biomedical sensing, anti-counterfeiting, or displays.
- ItemPlasmonic Properties of Colloidal Assemblies(Weinheim : Wiley-VCH, 2021) Rossner, Christian; König, Tobias A.F.; Fery, AndreasThe 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
- ItemMelt-mixed thermoplastic composites containing carbon nanotubes for thermoelectric applications(Springfield, Mo. : AIMS Press, 2016) Luo, Jinji; Krause, Beate; Pötschke, PetraFlexible thermoelectric materials are prepared by melt mixing technique, which can be easily scaled up to industrial level. Hybrid filler systems of carbon nanotubes (CNTs) and copper oxide (CuO), which are environmental friendly materials and contain abundant earth elements, are melt mixed into a thermoplastic matrix, namely polypropylene (PP). With the CNT addition, an electrical network could be built up inside the insulating PP for effective charge transport. The effect of CuO addition is determined by the corresponding CNT concentration. At high CNT concentration, largely above the percolation threshold (φc, ca. 0.1 wt%), the change in the TE properties is small. In contrast, at CNT concentration close to φc, the co-addition of CuO could simultaneously increase the electrical conductivity and Seebeck coefficient. With 5 wt% CuO and 0.8 wt% CNTs where a loose percolated network is formed, the Seebeck coefficient was increased from 34.1 µV/K to 45 µV/K while the electrical conductivity was from 1.6 × 10−3 S/cm to 3.8 × 10−3 S/cm, leading to a power factor of 9.6 × 10−4 µW/mK2 (cf. 1.8 × 10−4 µW/mK2 for the composite with only 0.8 wt% CNTs).
- ItemExploiting 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, AndreasChains 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
- ItemEffects of PNDIT2 end groups on aggregation, thin film structure, alignment and electron transport in field-effect transistors(London [u.a.] : RSC, 2016) Matsidik, Rukiya; Luzio, Alessandro; Hameury, Sophie; Komber, Hartmut; McNeill, Christopher R.; Caironi, Mario; Sommer, MichaelTo develop greener protocols toward the sustainable production of conjugated polymers, we combine the advantages of atom-economic direct arylation polycondensation (DAP) with those of the green solvent 2-methyltetrahydrofuran (MeTHF). The n-type copolymer PNDIT2 is synthesized from unsubstituted bithiophene (T2) and 2,6-dibromonapthalene diimide (NDIBr2) under simple DAP conditions in MeTHF. Extensive optimization is required to suppress nucleophilic substitution of NDIBr end groups, which severely limits molar mass. Different carboxylic acids, bases, palladium precursors and ligands are successfully screened to enable quantitative yield and satisfyingly high molar masses up to Mn,SEC ∼ 20 kDa. In contrast to PNDIT2 made via DAP in toluene with tolyl-chain termini, nucleophilic substitution of NDIBr chain ends in MeTHF finally leads to NDI-OH termination. The influence of different chain termini on the optical, thermal, structural and electronic properties of PNDIT2 is investigated. For samples with identical molecular weight, OH-termination leads to slightly reduced aggregation in solution and bulk crystallinity, a decreased degree of alignment in directionally deposited films, and a consequently reduced, but not compromised, electron mobility with promising values still close to 0.9 cm2 V−1 s−1.
- ItemExperimental and computational analysis of thermoelectric modules based on melt-mixed polypropylene composites(Amsterdam : Elsevier, 2023) Doraghi, Qusay; Żabnieńska-Góra, Alina; Norman, Les; Krause, Beate; Pötschke, Petra; Jouhara, HussamResearchers are constantly looking for new materials that exploit the Seebeck phenomenon to convert heat into electrical energy using thermoelectric generators (TEGs). New lead-free thermoelectric materials are being investigated as part of the EU project InComEss, with one of the anticipated uses being converting wasted heat into electric energy. Such research aims to reduce the production costs as well as the environmental impact of current TEG modules which mostly employ bismuth for their construction. The use of polymers that, despite lower efficiency, achieve increasingly higher values of electrical conductivity and Seebeck coefficients at a low heat transfer coefficient is increasingly discussed in the literature. This article presents two thermoelectric generator (TEG) models based on data previously described in the literature. Two types of designs are presented: consisting of 4- and 49-leg pairs of p- and n-type composites based on polypropylene melt-mixed with single-walled carbon nanotubes. The models being developed using COMSOL Multiphysics software and validated based on measurements carried out in the laboratory. Based on the results of the analysis, conductive polymer composites employing insulating matrices can be considered as a promising material of the future for TEG modules.