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DDC: 620 × Type: article × search.filters.applied.f.series: Scientific Reports 9 (2019), Nr. 1 × WGL Institute: IPHT ×

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    Superlattice in collapsed graphene wrinkles
    (Berlin : Nature Publishing, 2019) Verhagen, Timotheus; Pacakova, Barbara; Bousa, Milan; Hübner, Uwe; Kalbac, Martin; Vejpravova, Jana; Frank, Otakar
    Topographic corrugations, such as wrinkles, are known to introduce diverse physical phenomena that can significantly modify the electrical, optical and chemical properties of two-dimensional materials. This range of assets can be expanded even further when the crystal lattices of the walls of the wrinkle are aligned and form a superlattice, thereby creating a high aspect ratio analogue of a twisted bilayer or multilayer – the so-called twisted wrinkle. Here we present an experimental proof that such twisted wrinkles exist in graphene monolayers on the scale of several micrometres. Combining atomic force microscopy and Raman spectral mapping using a wide range of visible excitation energies, we show that the wrinkles are extremely narrow and their Raman spectra exhibit all the characteristic features of twisted bilayer or multilayer graphene. In light of a recent breakthrough – the superconductivity of a magic-angle graphene bilayer, the collapsed wrinkles represent naturally occurring systems with tuneable collective regimes.
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    Biomimetic light dilution using side-emitting optical fiber for enhancing the productivity of microalgae reactors
    (Berlin : Nature Publishing, 2019) Wondraczek, Lothar; Gründler, Alexander; Reupert, Aaron; Wondraczek, Katrin; Schmidt, Markus A.; Pohnert, Georg; Nolte, Stephan
    Photoautotrophic microbes present vast opportunities for sustainable lipid production, CO2 storage and green chemistry, for example, using microalgae beds to generate biofuels. A major challenge of microalgae cultivation and other photochemical reactors is the efficiency of light delivery. In order to break even on large scale, dedicated photon management will be required across all levels of reactor hierarchy – from the harvesting of light and its efficient injection and distribution inside of the reactor to the design of optical antenna and pathways of energy transfer on molecular scale. Here, we discuss a biomimetic approach for light dilution which enables homogeneous illumination of large reactor volumes with high optical density. We show that the immersion of side-emitting optical fiber within the reactor can enhance the fraction of illuminated volume by more than two orders of magnitude already at cell densities as low as ~5 104ml−1. Using the green algae Haematococcus pluvialis as a model system, we demonstrate an increase in the rate of reproduction by up to 93%. Beyond micoralgae, the versatile properties of side-emitting fiber enable the injection and dilution of light with tailored spectral and temporal characteristics into virtually any reactor containment.